*Edited by Gisela Montero and Margarita Stoytcheva*

This book entitled "Biodiesel: Quality, Emissions and By-products" covers topics related to biodiesel quality, performance of combustion engines that use biodiesel and the emissions they generate. New routes to determinate biodiesel properties are proposed and the process how the raw material source, impurities and production practices can affect the quality of the biodiesel is analyzed. In relation to the utilization of biofuel, the performance of combustion engines fuelled by biodiesel and biodiesels blends are evaluated. The applications of glycerol, a byproduct of the biodiesel production process as a feedstock for biotechnological processes, and a key compound of the biorefinery of the future is also emphasized.

ISBN 978-953-307-784-0

Biodiesel - Quality, Emissions and By-Products

Photo by PRImageFactory / iStock

## Biodiesel Quality, Emissions and By-Products

*Edited by Gisela Montero and Margarita Stoytcheva*

**BIODIESEL –**

**QUALITY, EMISSIONS**

**AND BY-PRODUCTS**

Edited by **Gisela Montero**  and **Margarita Stoytcheva**

**INTECHOPEN.COM**


**3. Results**

#### *3.1. Cannabinoid Treatments Reduce Nitric Oxide and Cytokine Production of LPS-Activated Peritoneal Macrophages*

Upon activation, macrophages produce large amounts of nitric oxide (NO•). To test the effect of cannabinoid treatments on macrophage activation, NO• secretion was determined. Macrophages from previously thioglycollate (tg)-injected C57BL/6 mice were collected by peritoneal lavage, and then activated for 24 h with lipopolysaccharide (LPS), in the presence of cannabinoid treatments; 1400W dihydrochloride, a specific iNOS inhibitor, served as control. All treatments show dose dependent effect on NO• secretion (Figure S1). For our further experiments, we used 5 μg/mL of each treatment (THC, CBD, or cannabis extracts). Our results demonstrate 42–72% inhibition of activation-induced NO• secretion from peritoneal macrophages from female (Figure 1a) and male (Figure 1b) mice in the presence of cannabinoid treatments. The reduced NO• secretion was not caused by decreasing cell number, since the treatments showed no toxic effect on the cells in MTT viability assay (Figure S2). The differences between THC and CBD treatments were significant only in the female mice. Importantly, both extracts were significantly more efficient (*p* < 0.0001) than the pure cannabinoids in female and male mice. A treatment with the combination of THC and CBD (2.5 μg/mL of each) was less effective than the pure cannabinoids (Figure S3).

Next, we examined the influence of aging on the responsiveness of macrophages to cannabinoid treatments. For this aim, we obtained peritoneal macrophages from aged (18 months old) mice and compared their NO• secretion with macrophages from young (2 months old) mice. Figure 1c (left) shows elevated secretion of NO• from non-activated cells and reduced secretion upon activation of old peritoneal macrophages. The effect of cannabinoid treatments on NO• secretion was significantly reduced as compared with cells from young mice (Figure 1c, right). In addition, peritoneal macrophages from aged mice demonstrate alleviated expression of the cannabinoid receptors (Figure 1d).

**Figure 1.** The influence of pure CBD/THC and cannabis extracts on nitric oxide production of LPS-activated peritoneal macrophages. Peritoneal macrophages from C57BL/6 female (**a**) and male (**b**) mice were activated for 24 h with LPS, in the presence of cannabinoid treatments (5 μg/mL). 1400W (1400), a specific iNOS inhibitor, served as control. NO• levels in the supernatant were analyzed. (**a**)—*n* = 10 mice, from 3 independent experiments; (**b**)—*n* = 7 mice, from 3 independent experiments. The differences of all treatments as compare with LPS-activated control (indicated on the graphs) are highly significant. The differences of THCE and THC between CBDE and CBD are significant in (**a**,**b**); (**c**) NO• levels in the supernatant of activated peritoneal macrophages from young (2 months old) and aged (18 months old) C57BL/6 female and male mice. *n* = 7 mice per group, from 3 independent experiments. The differences between aged and young mice in each treatment, are indicated on the graph; (**d**) the expression levels of CB1 and CB2 in peritoneal macrophages from young and aged C57BL/6 female mice (*n* = 3/group) were assessed by real-time PCR analysis. The results are expressed as mean + SEM. *p*-value \*, <0.05; \*\*, <0.01; \*\*\*, <0.001. NA—non-activated; LPS— lipopolysaccharide-activated macrophages; THC—D9 tetrahydrocannabino; CBD—cannabidiol; THCE—high THC cannabis extract; CBDE—high CBD cannabis extract; n.s.—not significant.

To examine the effect of the treatments on inflammatory cytokine/chemokine secretion from peritoneal macrophages, we collected the supernatant of 24 h LPS-activated cells and analyzed the levels of different cytokines using a LEGENDplex™ MU Macrophage/Microglia Panel cytokine array assay. IL6, TNF-alpha, CXCL2, and G-CSF levels in the culture media increased upon activation (Figure 2a–d). Our results demonstrate 40–74% inhibition of activation-induced IL6 secretion from peritoneal macrophages (Figure 2a), 22–66% inhibition of TNF-alpha secretion (Figure 2b), 4–44% inhibition of CXCL2 secretion (Figure 2c), and 0–58% inhibition of GM-CSF secretion (Figure 2d). CBD and CBDE had more significant inhibitory effect on cytokine/chemokine secretion as compared with THC and THCE. The differences between CBD and THC are significant in TNF-alpha, CXCL2, and G-CSF. IL12p40, CCL22, and IL18 were also elevated following activation, however, the cannabinoid-based treatments did not have clear effects on their levels (Figure S4).

**Figure 2.** The influence of pure CBD/THC and cannabis extracts on cytokine/chemokine production of LPS-activated peritoneal macrophages. Peritoneal macrophages were activated for 24 h with LPS, in the presence of cannabinoid treatments (5 μg/mL), as in Figure 1. *n* = 3 mice. IL6 (**a**), TNF-alpha (**b**), CXCL2 (**c**), and G-CSF (**d**) levels in the culture supernatant were detected. The results are expressed as mean + SEM. *p*-value as compare with LPS-activated control cells \*, <0.05; \*\*, <0.01; \*\*\*, <0.001. NA— non-activated; LPS—lipopolysaccharide-activated macrophages; THC—D9 tetrahydrocannabinol; CBD—cannabidiol; THCE—high THC cannabis extract; CBDE—high CBD cannabis extract.

#### *3.2. Cannabinoid Treatments Affect the Phenotype of Activated Peritoneal Macrophages*

To learn more about CBD and THC molecular effects in macrophages, we tested cell surface expression of several molecules in the activated macrophages. Class II molecules of the major histocompatibility complex (MHCII) is upregulated on some polarized macrophage populations upon activation. We found that both THC and CBD treatments induce small, but significant, further elevation in MHCII expression (Figure 3a). R. A. Ezekowitz and S. Gordon have demonstrated that expression levels of the F4/80 glycoprotein and the Fc

receptor CD16/32 on peritoneal macrophages are dependent on the activator [17]. In our study, in tg-induced macrophages activated with LPS, F4/80 was elevated by THC (15%), but reduced by CBD treatment (32%) (Figure 3b). CD16/32 cell surface expression was elevated on LPS-activated cells, but the cannabinoid treatments had no significant effect on its expression (Figure 3c).

**Figure 3.** The effect of CBD and THC on the phenotype of LPS-activated peritoneal macrophages. Peritoneal macrophages from C57BL/6 female mice were activated for 24 h with LPS, in the presence of cannabinoid treatments (5 μg/mL). Cell surface expression levels of MHCII ((**a**), *n* = 5), F4/80 ((**b**), *n* = 6), and CD16/32 ((**c**), *n* = 7) were determined by flow cytometry. The results are expressed as mean + SEM. *p*-value as compare with LPS-activated control cells \*, <0.05; \*\*, <0.01; \*\*\*, <0.001. NA— non-activated; LPS—lipopolysaccharide-activated macrophages; THC—D9 tetrahydrocannabinol; CBD—cannabidiol; n.s.—not significant.

#### *3.3. Cannabis Extracts Have Improved Effect in Murine Colitis DSS Model Mice as Compared with Pure Cannabinoids*

We chose the murine colitis dextran sodium sulfate (DSS) model to compare the efficacy of the different cannabinoid treatments in macrophage-related inflammation in vivo. DSS is a chemical colitogen with anticoagulant properties. In the acute intestinal inflammation model, DSS causes disruption of the intestinal epithelial monolayer lining, leading to the entry of luminal bacteria and associated antigens into the mucosa and activation of the innate immunity [18].

Acute colitis was induced by adding DSS to the mice drinking water at 2% (*w*/*v*) ad libitum for 7 days, and then replaced with plain water. Cannabinoid treatments, 5 mg/kg, were administered intraperitoneal, every other day, from Day 1 to Day 10 (Figure 4a). All treatments, but particularly the CBD extract (CBDE), significantly inhibited weight loss in the DSS mice (Figure 4b). THC and CBD extracts both had better effect on the disease clinical score as compared with the pure cannabinoids (Figure 4c). This improved effect was also evident in the measurement of colon length (Figure 4d); the average length of the colon in the CBDE-treated mice was 4.8 cm, significantly higher than the average length of the colon in the CBD-treated mice 3.9 cm (*p* < 0.0001). In THCE-treated mice, the average length of the colon was 4.8 cm vs. 4.1 cm in the THC-treated mice (*p* < 0.0001). All treatment significantly improved the clinical condition of the mice as compared with the vehicle DSS group. The difference between the CBD and THC groups was not significant.

**Figure 4.** Cannabis/cannabinoids administration for treatment of murine colitis in DSS model mice: (**a**) Acute colitis was induced by adding DSS to the mice drinking water at 2% (*w*/*v*) ad libitum for 7 days,

and then replaced with plain water. 5 mg/kg cannabis/cannabinoids were administered IP every other day, starting from Day 1; (**b**) the effect of pure cannabinoids (left) and cannabis extracts (right) on weight loss. Differences between DSS group and THCE- as well as CBDE-treated groups are significant. The difference between the CBD- and CBDE-treated groups is significant *p* < 0.05; (**c**) the effect of pure cannabinoids (left) and cannabis extracts (right) on clinical score. Differences between the DSS group and all cannabinoid-treated groups are significant *p* < 0.005. Differences between cannabis extracts and pure cannabinoids are significant *p* < 0.008. The difference between the CBDand THC-treated groups is significant *p* < 0.05; (**d**) the effect of pure cannabinoids and cannabis extracts on colon length, at the end of the experiment (Day 10). *p*-value as compare with the DSS control group \*\*\*, <0.001. The differences between THCE and THC and between CBDE and CBD are significant. Data are summarized from 5 independent experiments, 5–7 mice/group in each experiment. DSS—dextran sodium sulfate; THC—D9 tetrahydrocannabinol; CBD—cannabidiol; THCE—high THC cannabis extract; CBDE—high CBD cannabis extract.

The improved clinical outcome of all cannabinoid-based treatments is also demonstrated in the histopathology of the colon (Figure 5a,b). Colon sections were stained with haematoxylin/eosin and scored for the infiltration with inflammatory cells, damage in crypt architecture, and thickening of the bowel wall. In this assay, no significant differences between the four cannabinoid-based treatments were found.

**Figure 5.** Histopathology of the colons of DSS model mice. Paraffin sections were stained with H&E and scored for inflammation and tissue damage; (**a**) Summary of average scores. *p*-value as compare

with the DSS control group \*\*, <0.01; \*\*\*, <0.001; (**b**) representative pictures of H&E stained sections. DSS—dextran sodium sulfate; THC—D9 tetrahydrocannabinol; CBD—cannabidiol; THCE—high THC cannabis extract; CBDE—high CBD cannabis extract.

#### *3.4. Cannabinoid Treatments Reduce Intestinal Macrophage Infiltration and the Levels of Inflammatory Cytokines in the Plasma of DSS Mice*

Next, we examined the effects of the treatments on macrophages and inflammation in the DSS model. In IBD patients, an increased number of macrophages in the inflamed mucosa initiate a rapid response to luminal microbial antigens [3]. Immunohistochemistry with F4/80 antibody was performed to detect macrophages in the colon. As demonstrated in Figure 6a,b, the number of macrophages in the colon tissue is highly elevated in the DSS mice. All the cannabinoid-based treatments significantly inhibited colon infiltration of macrophages in the DSS mice (40–60% inhibition). CBDE treatment inhibition of macrophage infiltration was significantly more effective than pure CBD treatment (*p* = 0.03). The THCE and THC treatments were not significantly different.

**Figure 6.** Immunostaining for macrophages in the colons of DSS model mice. Paraffin sections were stained with anti-F4/80 antibodies: (**a**) Average number of positive cells. *p*-value as compare with the

DSS control group \*, <0.05; \*\*, <0.01; \*\*\*, <0.001. The difference between the CBDE and CBD groups is significant; (**b**) representative pictures of F4/80 immunostained sections. DSS—dextran sodium sulfate; THC—D9 tetrahydrocannabinol; CBD—cannabidiol; THCE—high THC cannabis extract; CBDE—high CBD cannabis extract.

Cytokine levels in the blood reflect the inflammatory status in the body. It was also demonstrated that inflammatory cytokines have a crucial role in the pathogenesis of IBD, where they control multiple aspects of the inflammatory response [19]. We, therefore, tested the plasma levels of inflammatory cytokines of treated DSS mice using a mouse inflammation cytokine array assay. Interestingly, we found that the different treatments have unique effects on plasma cytokines (Figure 7). IL6 levels were reduced by all treatments, but particularly by CBDE. The levels of TNF-alpha were significantly reduced only by the cannabis extracts; but pure cannabinoids had stronger effect on IFN-beta levels. The levels of other tested cytokines were not significantly changed in the plasma of DSS mice as compared with healthy controls.

**Figure 7.** The influence of pure CBD/THC and cannabis extracts on inflammatory cytokines in the blood of DSS model mice. Blood samples for cytokine analysis were obtained at Day 10. The levels of TNFa (**a**), IL6 (**b**), and IFNb (**c**) in the plasma were determined using a LEGENDplex ™ Mouse Inflammation Panel cytokine array; *n* = 5–10 mice/group. The results are expressed as mean + SEM. *p*-value as compare with the DSS group \*, <0.05; \*\*, <0.01; \*\*\*, <0.001. DSS—dextran sodium sulfate; THC—D9 tetrahydrocannabinol; CBD—cannabidiol; THCE—high THC cannabis extract; CBDE—high CBD cannabis extract; n.s.—not significant.


**5. Pathogenesis**

The molecular pathogenesis of anesthesia-induced neurotoxicity has also been investigated in experimental studies.

Neonates are born with approximately 100 billion neurons, and the number of neurons does not increase over time. The neonatal brains weigh approximately 300–400 g. Increased myelination, synapse formation, neuron maturation, and proliferation of glial cells increase the weight of the brain to 1100 g at 3 years of age and 1300–1400 g at adulthood. A newborn infant has approximately 50 trillion synapses, increasing to 1000 trillion within the first year of life and decreasing to 500 trillion in adulthood.

Thus, brain maturation is not complete at birth, and there is a heterogeneous maturation process in the brain following birth. Maturation is particularly slow in the cortex and in the limbic system [38–40]. Alteration of neurotransmission in the immature brain due to anesthesia exposure may lead to future impairments.

Synaptogenesis has been defined as the most important period of brain development, also described as the "fragile period" or "critical period." Synaptogenesis consists of five phases. The greatest leap in synapse formation occurs in phase 3, which is sometimes referred to as the "big bang." Phase 3 corresponds to the neonatal period. Following phase 3, synaptogenesis continues with the same speed during phase 4. This phase is referred to as the plateau phase, corresponding to infancy and adolescence. During phase 5, which occurs during adulthood, synaptogenesis continues, but it is limited and localized [41]. The initiation, duration, and end of these critical periods (phase 3 and phase 4) are controlled by multiple genetic and epigenetic mechanisms. The brain's sensitivity to environmental stimuli is at maximum during the neonatal and infancy period when synaptogenesis is also maximized [41].

were under the effect of ketamine for 9 or 24 hours. In cell culture study of Bosnjak et al. [25], they demonstrated that ketamine decreases neuronal viability time and dose dependently, leads to neuronal ultrastructural abnormalities, causes depolarization of mitochondrial membrane potential, induces apoptotic pathway, causes cytochrome c release from mitochondria

Yu et al. examined neuroapoptosis and long-term behavioral changes in PND7 rats that were given single and repetitive doses of propofol. Their findings included reduction in neuron density, morphological changes in pyramidal cells, apoptosis, and suppressed release of excitatory neurotransmitters. Additionally, these effects were more pronounced among the

Benzodiazepines (clonazepam, diazepam, and midazolam), which are intravenous anesthetics, have controversial effects on apoptosis; however, barbiturates (pentobarbital, phenobarbital) clearly increase apoptosis. The few studies that have examined the effects of sodium thiopental reported that exposure did not result in increased apoptosis [27–33]. Thompson [34] has suggested high-dose narcotic anesthetic for neonatal and infant. But, fetal and neonatal chronic exposure to opioids has been associated with neuronal changes. Although opioid-based anesthesia and opioids coadministered with inhalation anesthetics have been shown to reduce apoptosis, safety has not been demonstrated with these preparations [35, 36]. However, these studies are controversial and their safety has been in question. Another study has demonstrated that dexmedetomidine, the current intravenous anesthetic, reduces

The molecular pathogenesis of anesthesia-induced neurotoxicity has also been investigated

Neonates are born with approximately 100 billion neurons, and the number of neurons does not increase over time. The neonatal brains weigh approximately 300–400 g. Increased myelination, synapse formation, neuron maturation, and proliferation of glial cells increase the weight of the brain to 1100 g at 3 years of age and 1300–1400 g at adulthood. A newborn infant has approximately 50 trillion synapses, increasing to 1000 trillion within the first year of life and decreasing to 500 trillion in adulthood.  Maturation is particularly slow in the cortex and in the limbic system [38–40]. Alteration of neurotransmission in the immature brain due to anesthe-

Synaptogenesis has been defined as the most important period of brain development, also described as the "fragile period" or "critical period." Synaptogenesis consists of five phases. The greatest leap in synapse formation occurs in phase 3, which is sometimes referred to as

the intrauterine period, the first 3 years of life and puberty [38–40].

sia exposure may lead to future impairments.

into cytosol, and induces free oxygen radical production.

group that was subject to repeated doses of propofol [26].

prenatal toxicity caused by propofol [37].

**5. Pathogenesis**

106 Current Topics in Anesthesiology

in experimental studies.

Anesthetics elicit their effects by enhancing the activity of major inhibitory neurotransmitters gamma-aminobutyric acid (GABA) and glycine or antagonizing the N-methyl-D-aspartate (NMDA) receptors of the major excitatory neurotransmitter glutamate. During brain development, GABA facilitates cell proliferation, neuroblast migration, and dendritic maturation, and unlike in adults, it acts as an excitatory neurotransmitter during infancy rather than an inhibitory neurotransmitter [42, 43]. This is because these two mediators increase the permeability of the cell membrane to chloride ions through intrinsic chloride-conducting ion pores. After the permeability of the GABA, ligand-gated ion channel to chloride is increased, KCC2 K+/Cl-2 cotransporter aids in influx of chloride ion. Thus, the neuron is hyperpolarized and its activity is suppressed. However, because KCC2 expression is low during the early period of development, the chloride action potential is reversed by GABAA and glycine receptor activity, leading to neuronal depolarization and increased permeability to chloride. Clinical studies have shown that sevoflurane, isoflurane, and propofol cause excitability in electroencephalogram in neonates [44–46]. The major excitatory neurotransmitters glutamate and aspartate are present in the brain at very high concentrations (glutamate 10 mmol/L and aspartate 4 mmol/L). Glutamate and aspartate direct synaptic signaling at nerve terminals and control ion intake to neurons. They have been found to influence synaptogenesis, neuronal plasticity, learning, and memory [47–49]. Although the excitatory neurotransmitters are normally responsible for nerve conduction, they are also potential sources of neurotoxicity. An abnormal decrease in glutamate may disturb normal excitation, and abnormal increases may cause excitotoxicity and cell death by disturbing calcium homeostasis. Glutamate and similar amino acids have been shown to cause acute swelling in the neuron body, dendrites, and glia and also promote neuronal degeneration over extended periods of time. For this reason, there is a delicate mechanism acting in normal conditions to regulate glutamate levels in the synaptic gap involving reuptake of excess glutamate from the synaptic gap through receptors present in presynaptic end of nerve terminal and glial cells. Although glutamate is a strong and rapid-acting toxin under physiological conditions, this mechanism ensures that even direct application to the brain does not cause damage [47]. Nevertheless, pathological conditions that result in insufficiency of this system or cause release of large amounts of glutamate would lead to neuronal loss. For these reasons, anesthesia applications are believed to disrupt the balance between excitatory and inhibitory neurotransmission and thus cause neuronal injury [47–49].

Regarding neuronal viability and development, one of the most studied neurotropins in neonatal subjects is brain-derived neurotrophic factor (BDNF). Mature BDNF is formed by destruction of proBDNF in the synaptic gap by the action of plasmin. Mature BDNF binds to the TrkB receptors present on the postsynaptic membrane and enhances viability of the target cell. However, in conditions where plasmin release is reduced or blocked, such as when anesthesia is applied, proBDNF cannot be converted to the mature form, and it stimulates p75NTR instead of the TrkB receptor. Activation of p75NTR receptor, also called the "death receptor," leads to actin depolymerization and apoptosis. Head et al. [50] demonstrated that isoflurane causes apoptosis in the neonatal mice brain through this pathway.

Apoptosis is a programmed cell death that can occur in both physiological and pathological conditions. Apoptosis is physiologically present in the developing brain, occurring at a rate of approximately 1%. However, apoptosis that occurs following pathological processes like hypoxia and ischemia is typically problematic. Several experimental studies have shown that apoptosis is increased following anesthesia exposure. However, it is not possible to conduct such studies in humans. Therefore, it is difficult to estimate the rate of apoptosis following anesthesia exposure in humans to what extent this apoptosis affects maturation of the developing brain. Experimental studies have shown that anesthesia induces apoptosis via intrinsic and extrinsic pathways. Anesthesia application causes leakage of cytochrome c and translocation of Bax protein to the mitochondria, leading to activation of the apaf-1 and caspase pathways, respectively. This in turn results in lipid peroxidation via release of free oxygen radicals. Apoptosis occurs not only in intrinsic pathway but also in extrinsic pathway which activates Fas protein [51–53].

There are three publications that demonstrate the relationship between microRNA and anesthetic-induced developmental neurotoxicity; according to these publications, while propofol downregulates microRNA-21, ketamine upregulates microRNA-34a, microRNA-34c, and microRNA-124 and downregulates microRNA-137 [54–56].

In cell culture models, it has been demonstrated that neuron development is highly dependent on the actin cytoskeleton, and anesthetics are dangerous for actin regulation [57–59].

Tau protein hyperphosphorylation at serine 404 demonstrates neurodegeneration and is induced by ketamine. Therefore, microtubules are disrupted and damaged [60].

Translocator protein (TSPO, 18 kDa) is a biomarker that could be used for evaluation of reactive gliosis and microglia activity and has the potential for use in noninvasive imaging using positron emission tomography and single photon emission computed tomography [61]. The relationship between anesthesia-associated neurotoxicity and DNA methylation and gene expression has been investigated [62].

Treatment strategies to reduce neurodegeneration induced by anesthetics have also been widely investigated. Lithium, melatonin, estradiol, pilocarpine, dexmedetomidine, xenon, erythropoietin, L-carnitine, hydrogen gas, and pramipexole are among the leading candidates for this emerging therapy [63, 64].


**1. Introduction**

28 Will-be-set-by-IN-TECH

312 Nuclear Reactors

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ANL-FRA-1996-5, Argonne National Laboratory

Nuclear reactor technology is known as an emerging area of study from past to present. It is an implementation of the nuclear sciences including reactions about atomic nucleus and productions. During the construction of a nuclear reactor, the most important issue is nuclear safety. The term of security can be attributed radiation shielding processes. For nuclear reactors, there are several different materials used to radiation shielding. While determining the most appropriate material to shield, the type and energy of radiation is extremely important.

There are two types of nuclear reactions reveals very large energies. These are the disintegration of atomic nuclei (fission) and merging small atomic nuclei (fusion) reactions. Therefore, nuclear reactors can be divided into two groups according to the type of reaction occurred during as fission reactors and fusion reactors. Currently a nuclear reactor working with fusion reactions is not available. Today, there are the hundreds of nuclear reactors based on the fission reactions. For the realization of nuclear fission, a large fissile atomic nucleus such as 235U can absorb a neutron particle. At the end of nuclear fission event, fission products (two or more light nucleus, kinetic energy, gamma radiation and free neutrons) arise. Fission reactions are controls by using neutron attenuators such as heavy water, cadmium, graphite, beryllium and several hydrocarbons. While designing a reactor shield materials against gamma and neutron radiations should be used.

Vermiculite is a monoclinic-prismatic crystal mineral including Al2O3, H2O, MgO, FeO and SiO2. It is used in heat applications, as soil conditioner, as loose-fill insulation, as absorber package material and lightweight aggregate for plaster etc. Its chemical formula is known as (MgFe,Al)3(Al,Si)4O10(OH)2·4H2O and physical density of it about 2.5 g.cm-3. Melting point of vermiculite is above 13500C. This mineral can be used as additive building material in terms of mineral properties.

Vermiculite is a component of the phyllosilicate or sheet silicate group of minerals. It has high-level exfoliation property. So if vermiculite is heated, it expands to many times its

Neutron Shielding Properties of Some Vermiculite-Loaded New Samples 315

done. According to the results of this study, the expanded vermiculite had a greater affinity for oil than hydrophobized vermiculite. XRD characteristics of Poland vermiculites were studied and crystal structure of it was determined. A general study about typical properties and some parameters of different vermiculites was performed. In this study, especially heat conduction coefficients were commented and an evaluation was done about vermiculite based building materials. In another study, flyash-based fibre-reinforced hybrid phenolic composites filled with vermiculite were fabricated and characterized for their physical,

Neutron shielding studies have a wide range of literature. For example, colemanite and epoxy resin mixtures have been prepared for neutron shielding applications by Okuno, 2005. Agosteo et al. have investigated double differential neutron distribution and neutron attenuation in concrete using 100-250 MeV proton accelerator. In another study, neutron transmission measurements were studied through pyrolytic graphite crystals by Adib et al. Neutron attenuation properties of zirconium borohydrite and zirconium hydride were determined by Hayashi et al., 2009. Sato et al. designed a new material evaluation method

In this paper; we investigated usability of vermiculite loaded samples for nuclear reactor shielding processes, because of excellent thermal insulation properties of it. This mineral was doped in cement and new samples including different vermiculite percents were produced. 4.5 MeV neutron dose transmission values were determined. Also 4.5 MeV

Before the mixing procedure, a part of mixing water at the percentage of water absorption capacity of expanded vermiculite aggregate by weight was added to vermiculite to make it fully saturated with water. Fig.1 shows the expanded vermiculite particles saturated with

Then, the rest of the mixing water cement and silica fume or steel fiber were mixed together for 1 minute in a mixer, and finally, expanded vermiculite aggregate saturated with water

thermal, mechanical and tribological performance.

by using a pulsed neutron transmission with pixel type detectors.

neutron attenuation lengths were calculated for each sample.

Fig. 1. Expanded vermiculite fine aggregate saturated with water.

**2. Experiments**

water.

**2.1 Sample preparation**

original volume. This feature is a striking ability for a mineral. Because it looks like *vermicularis*, its name is vermiculite. They molecular structure consists of two tetrahedral layers as silica and alumina and an octahedral layer including O, Mg, Fe and hydroxyl molecules. Water located between layers is an important member in the vermiculite. If mineral heats suddenly, inter-layer water transforms to steam and exfoliation feature occurs.

Vermiculite is clean to handle, odorless and mould durable. It has a wide range of uses as thermal insulation, fire durability, liquid absorption capability, low density and usefulness etc… The main uses of minerals are listed as follows;

In literature, there are several studies about vermiculite and its usage. A comparative study about the effects of grinding and ultrasonic treatment on vermiculite was done. The effect of mechanical treatment and cation type on the clay micro porosity of the Santa Olalla vermiculite untreated and mechanically treated (sonicated and ground) and saturated with different captions was investigated. An experimental study was performed about thermal conductivity of expanded vermiculite based samples. In this paper, measurements were carried out on samples in the temperature range of 300-1100 K. Because of the high heat insulation properties of vermiculite mineral, we frequently encounter studies on thermal properties of it. In another study, researchers produced new materials including vermiculite that can withstand up to 11500C. The cement-vermiculite composition was used to produce new materials to leach 54Mn and 89Sr radionuclide. Researchers have received the best results when using 95% Portland cement and 5% vermiculite composition. The effect on ultrasounds on natural macroscopic vermiculite flakes has been studied and effects of ultrasound treatment on the several parameters (particle sizes, crystal structure, surface area, etc...) were investigated. Finally, micron and submicron-sized vermiculites were prepared. High surface area silica was obtained by selectively leaching vermiculite. In this study, also the characteristics of the porous silica obtained from vermiculite are compared with those from other clay minerals. Studies are performed on the material composition and typical characteristics of micaceous minerals of the vermiculite series in the Tebinbulak deposit. Thermal treatments of nano-layered vermiculite samples were studied up to 9000C. In another thermal effect study was achieved for 15-8000C temperature range vermiculite originated by Tanzania region. Thermal properties of polypropylene-vermiculite composites were investigated using differential scanning calorimetry (DSC) and thermogravimetry (TG) techniques. At the end of this study, new composites with high thermal stability were produced. The effect of sodium ion exchange on the properties of vermiculite was studied by several methodology (scanning electron microscopy, X-ray fluorescence spectroscopy, inductively coupled plasma mass spectroscopy, X-ray diffraction and thermo mechanical analysis) and sodium exchange lowered the exfoliation onset temperature to below 300 °C. A comparative study about oil affinity of expanded and hydrophobized vermiculite was done. According to the results of this study, the expanded vermiculite had a greater affinity for oil than hydrophobized vermiculite. XRD characteristics of Poland vermiculites were studied and crystal structure of it was determined. A general study about typical properties and some parameters of different vermiculites was performed. In this study, especially heat conduction coefficients were commented and an evaluation was done about vermiculite based building materials. In another study, flyash-based fibre-reinforced hybrid phenolic composites filled with vermiculite were fabricated and characterized for their physical, thermal, mechanical and tribological performance.

Neutron shielding studies have a wide range of literature. For example, colemanite and epoxy resin mixtures have been prepared for neutron shielding applications by Okuno, 2005. Agosteo et al. have investigated double differential neutron distribution and neutron attenuation in concrete using 100-250 MeV proton accelerator. In another study, neutron transmission measurements were studied through pyrolytic graphite crystals by Adib et al. Neutron attenuation properties of zirconium borohydrite and zirconium hydride were determined by Hayashi et al., 2009. Sato et al. designed a new material evaluation method by using a pulsed neutron transmission with pixel type detectors.

In this paper; we investigated usability of vermiculite loaded samples for nuclear reactor shielding processes, because of excellent thermal insulation properties of it. This mineral was doped in cement and new samples including different vermiculite percents were produced. 4.5 MeV neutron dose transmission values were determined. Also 4.5 MeV neutron attenuation lengths were calculated for each sample.


**Chapter 3**

*Advances in Extracorporeal Membrane Oxygenation - Volume 3*

[31] Swafford K, Culpepper R, Dunn C. Use of a comprehensive program to reduce the incidence of hospitalacquired pressure ulcers in an intensive care unit. American Journal of Critical

Care. 2016;**25**(2):152-155

2013;**145**:e32-e33

2014;**190**:488-496

2016;**6**:50-60

[34] Villa G, Katz N, Ronco C.

[35] Vincent J, Rello J, Marshall J, Silva E, Anzueto A, Martin C, et al. International study of the prevalence and outcomes of infection in intensive care units. JAMA. 2009;**302**:2323-2329

Extracorporeal membrane oxygenation and the kidney. CardioRenal Medicine.

[36] Wells CL, Forrester J, Vogel J, Rector R, Tabatabai A, Herr D. Safety and feasibility of early physical therapy for patients on extracorporeal membrane oxygenator: University of Maryland Medical Center experience. Critical Care Medicine. 2018;**46**:53-59

[37] Wolf MJ, Chanani NK, Heard ML, Kanter KR, Mahle WT. Early renal replacement therapy during pediatric cardiac extracorporeal support increases mortality. Annals of Thoracic Surgery.

[32] Tang G, Malekan R, Kai M, Lansman S, Spielvogel D. Peripheral venoarterial extracorporeal membrane

oxygenation improves survival in myocardial infarction with cardiogenic shock. The Journal of Thoracic and Cardiovascular Surgery.

[33] The International ECMO Network [ECMONet]. Position paper for the organization of extracorporeal membrane oxygenation programs for acute respiratory failure in adult patients. American Journal of Respiratory and Critical Care Medicine.

**26**

2013;**96**:917-922


Recent Advances on Meta-Heuristics and Their Application to Real Scenarios

*Edited by Javier Del Ser*

**RECENT ADVANCES ON**

**META-HEURISTICS AND**

**THEIR APPLICATION TO**

**REAL SCENARIOS**

Edited by **Javier Del Ser**


An additional reflection is also observed at 2θ ≈ 8.8◦ , see **Figure 5**, resulting from the (1 1 0) plane in Li2Bi. This Li2Bi phase forms in small quantities during conversion from Li3Bi at the discharged state to LiBi during charge. The Li2Bi structure was recently reported in an amendment to the Li-Bi phase diagram (Pavlyuk et al., 2015). Li2Bi adopts a hexagonal unit with space group P−6 2 c, and in our cell was found to have lattice parameters of a = 8.061(5) Å and c = 6.835(3) Å. In **Figure 5** we also observe reflections corresponding to the (1 1 1), (0 0 1) and (0 0 3) planes of Li3Bi, LiBi, and Bi respectively.

Closer inspection of the diffraction data in **Figure 5** shows a slight shift in the position of the LiBi 001 reflection (2θ ≈ 8.37◦ ) at the beginning of the experiment. Beyond this point, the lattice parameters of the lithiated bismuth phases remain constant, see **Figure 6**, and reaction proceeds via a two-phase mechanism as Bi is formed. The a and c lattice parameters of LiBi, see **Figures 6B,C**, behave nearly identically as the insertion of lithium into Lix Bi causes an isotropic expansion of the unit cell.

## CONCLUSIONS

The use of in situ diffraction to study structural evolution in thin film devices is demonstrated. A series of phase transitions from lithiated bismuth to bismuth metal were identified as the device was charged. This preliminary study of a Bi/LiPON/Li all-solid-state cell demonstrates that these thin film devices can be used to explore the phase transformations which occur within the electrodes during cell operation. Further, the ability to resolve these phase transformations highlights that electrochemical insertion could provide a novel way to explore the phase diagrams of binary alloy systems at ambient temperatures.

### AUTHOR CONTRIBUTIONS

DG performed the in-situ experiment, analyzed the data and wrote a significant proportion of the manuscript. NS instigated the research and performed the in-situ experiment. JK experimental design at the Australian Synchrotron. JG made and tested the in-situ cells and designs. BP instigated the research and provided research support throughout the project. FL instigated the research and developed the in-situ cell design.

### ACKNOWLEDGMENTS

This research was undertaken on the Powder Diffraction beamline at the Australian Synchrotron, Victoria, Australia. DG acknowledges the support of the Australian Government Research Training Program Scholarship. NS would like to thank the Australian Research Council for financial support provided via grants DE160100237 and DP170 100269.

#### SUPPLEMENTARY MATERIAL

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fenrg. 2018.00064/full#supplementary-material

#### REFERENCES

**Conflict of Interest Statement:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2018 Goonetilleke, Sharma, Kimpton, Galipaud, Pecquenard and Le Cras. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

# In-situ Studies of High Temperature Thermal Batteries: A Perspective

Julia L. Payne1 \*, Kyriakos Giagloglou1 , George M. Carins 1 , Christina J. Crouch1,2 , Julia D. Percival 2 , Ronald I. Smith3 , Richard K. B. Gover 2 and John T. S. Irvine1

1 School of Chemistry, Faculty of Science, University of St Andrews, St Andrews, United Kingdom, 2 AWE Aldermaston, Reading, United Kingdom, 3 ISIS Facility STFC Rutherford Appleton Laboratory, Didcot, United Kingdom

Here we present a perspective on in-situ studies of high temperature batteries. We focus on a primary battery technology- the thermal battery- which possesses a molten salt electrolyte. We discuss aspects of sample environment design, data collection and will briefly look at some case studies. We aim to highlight the importance of using in-situ techniques in studying electrochemical devices such as high temperature batteries.

Keywords: in-situ, neutron diffraction, thermal battery, transition metal sulfides, high temperature batteries

#### Edited by:

INTRODUCTION

Neeraj Sharma, University of New South Wales, Australia

#### Reviewed by:

Xiangyu Zhao, Nanjing Tech University, China Verónica Palomares, Universidad del País Vasco, Spain Donna Claire Arnold, University of Kent, United Kingdom

> \*Correspondence: Julia L. Payne<EMAIL_ADDRESS>
#### Specialty section:

This article was submitted to Energy Storage, a section of the journal Frontiers in Energy Research

Received: 04 May 2018 Accepted: 25 October 2018 Published: 20 November 2018

#### Citation:

Payne JL, Giagloglou K, Carins GM, Crouch CJ, Percival JD, Smith RI, Gover RKB and Irvine JTS (2018) In-situ Studies of High Temperature Thermal Batteries: A Perspective. Front. Energy Res. 6:121. doi: 10.3389/fenrg.2018.00121 In recent years, the study of battery technologies using in-situ techniques has become increasingly important (Sharma et al., 2015). This has been driven by a desire for the precise understanding of the processes occurring during battery operation, which may be used to optimize batteries or inform the future synthetic targets of new battery materials with improved performance. This has been accompanied by improvements in the design of cells which allow collection of both electrochemical data and the data of interest (Bergstrom et al., 1998; Berg and Thomas, 1999; Sharma and Peterson, 2012; Roberts et al., 2013; Biendicho et al., 2014; Sharma et al., 2015; Brant et al., 2016).  This has been accompanied by improvements in instrumentation at synchrotron and neutron facilities, along with a willingness to accommodate unusual sample environments and set-ups on the beamline.

With the lithium-ion battery revolutionizing the portable electronics market in recent years, it is unsurprising that the majority of these in-situ studies have focused on batteries which operate at room temperature. However, batteries are required for a wide range of applications and there remain several battery technologies that have not been studied using in-situ techniques.

One battery technology which we are currently investigating is the thermal battery. Thermal batteries are primary batteries which are used in emergency power supplies in aircraft, ejector seats, and other military applications (Guidotti and Masset, 2006). Applications which utilize thermal batteries require a constant power to be drawn over a length of time, so as a result, materials that operate via conversion reactions, rather than intercalation reactions are usually preferred. Typically they consist of a cathode, anode, molten salt electrolyte, separator and a pyrotechnic ignition source to heat the battery (Masset and Guidotti, 2007, 2008a,b; Guidotti and Masset, 2008). Due to the use of a molten salt electrolyte, thermal batteries must operate at a temperature above the melting point of the electrolyte, which means that they often operate at temperatures close to 500◦C. The high temperature operation, in addition to the fact that air/moisture-sensitive transition metal sulfides are the most commonly used cathodes, means that structural studies of this battery technology would be best performed using in-situ techniques, and would require a complex cell design. To the best of our knowledge no such studies have been reported.

Our current research interests have focused on the in-situ study of thermal batteries which use transition metal sulfides as the cathode material, Li13Si4 as the anode material, KCl-LiCl eutectic as an electrolyte and MgO as the separator. In particular the transition metal disulfides, MS2 (where M = Fe, Co, and Ni) are the most commonly used cathode materials in thermal batteries and they offer a particularly intriguing study, as the discharge mechanisms are thought to be different depending on the transition metal present in the cathode, with only cells using FeS2 as a cathode forming lithiated compounds upon battery discharge (Preto et al., 1983).

## EXPERIMENTAL CONSIDERATIONS

#### Design of Sample Environment

The purpose of our experiments was to carry out combined battery discharge and powder neutron diffraction studies. A sample environment for combined conductivity and neutron diffraction studies of hydride ion conductors was designed by one of us, so this sample environment was modified to enable it to be used for in-situ thermal battery studies instead (Payne et al., 2017; Carins et al., in preparation). A photograph of the sample environment is shown in **Figure 1A**. This sample environment is able to maintain an inert atmosphere around the sample, which is important when looking at air/moisture sensitive species. During each experiment, Argon gas was continuously flowed through the sample environment.

The sample environment consists of a closed-end quartz tube, which has thinned walls near the sample area to allow for beam entry and exit. There is a gas inlet/outlet on the top of the tube. Wires for electrical connections run from the top of the tube to the sample holder and are sheathed in Al2O3.

By modifying the sample environment using vanadium plates as both current collectors and sample holder (**Figure 1B**) we were able to simplify the data analysis by reducing the number of phases that will be observed in the diffraction pattern [vanadium's very low neutron scattering length (−0.39 fm) compared to those of the atomic species making up the other phases present means that it contributes very little to the neutron diffraction pattern of the battery]. Neutron diffraction is particularly appropriate when studying lithium-containing materials in the presence of much higher Z-number atoms because unlike X-ray scattering (which depends on the number of electrons) neutrons scatter from the atomic nucleus and this results in the scattering power of lithium being comparable to the other species in the battery. Recesses in the vanadium plates hold the sample in position for optimum beam convergence on the sample. A diagram of the vanadium plate sample holder is shown in **Figure 1B**.

The design of an equivalent cell for the equivalent X-ray diffraction experiment would be non-trivial. A suitable current collector is difficult to find and existing sample environments

FIGURE 1 | (A) Photograph of the in-situ sample environment used for studies of thermal batteries which allows the flow of an inert gas during the course of the experiment to maintain an inert atmosphere. (B) Shows a diagram of vanadium plate current collector which doubles as a sample holder. Screws are used to help hold the sample in place. (C) Comparison of powder diffraction data obtained in 5 min on the Polaris diffractometer for two cells using two different cathode materials: CoS2 and CoNi2S4 (D) multi-phase Rietveld fit to data collected in 5 min on the Polaris diffractometer during the discharge of a thermal battery which uses CoNi2S4 as the cathode material. Please note that differences in intensity of the CoNi2S4 data are due to the data being collected at different states of discharge. Broad features in the background of the diffraction pattern are due to the amorphous quartz outer container of the in-situ sample environment and molten salt eutectic.

designed to work at room temperature use beryllium windows which would oxidize at the high temperatures required for this study.

### Choice of Instrument

Our in-situ experiments have been carried out on the Polaris diffractometer at the ISIS facility, Rutherford Appleton Laboratory, UK. Polaris is a high flux, medium resolution diffractometer, which is particularly suited to fast data collection and unusual sample environments, making it the ideal choice for the in-situ experiment. The recent upgrade of Polaris enables the collection of good quality diffraction data, even with very small samples (Lindsay-Scott et al., 2014).

## Data Collection Protocols

With any in-situ experiment, there is balance to be achieved between the electrochemistry and the structural data that will be collected. Neutron powder diffraction requires larger samples than the corresponding X-ray diffraction experiment. In our first experiments we decided to preserve the electrochemistry as much as possible, which resulted in the use of a thinner pellet shaped cell (∼1–2 mm thickness) than would normally be required for neutron diffraction. This led to limitations in the parameters that could be extracted from multi-phase Rietveld refinement, such as meaningful thermal parameters. **Figure 1C** shows the data quality from 5 min neutron powder diffraction data collections on CoS2 and CoNi2S4 based cells. Much better data quality could be obtained for the CoNi2S4 cell which benefitted from both being a slightly thicker sample, along with the higher neutron scattering length of nickel (10.3 fm) in comparison to cobalt (2.49 fm) and sulfur (2.85 fm). Data were analyzed by carrying out multi-phase Rietveld refinements. **Figure 1D** shows a multiphase Rietveld fit to a 5 min data set collected during discharge of a thermal battery which used CoNi2S4 as the cathode material. This indicates that good quality data can often be obtained in times as short as a few minutes when using neutron diffraction, but it is dependent on the sample being studied.

During an in-situ experiment, it is important to minimize the contributions to the diffraction pattern from parts of the sample environment, and we were able to do this by adjusting the dimensions of the incident neutron beam to match the geometry of the thermal battery sample as well as utilizing neutron shielding materials (boron nitride) to cover parts of the sample environment that may scatter (and would contribute to the diffraction pattern). The reliability of a spallation neutron source can also be challenging during such in-situ experiments, where short interruptions to the beam due to minor accelerator faults may result in "gaps" in the data, but fortunately for our experiments carried out to date, this has not been problematic.

In terms of carrying out the battery discharge, two approaches have been used. Firstly, potentiostatic discharge has been used, where data are collected at fixed isopotentials. The isopotentials are determined by an ex-situ battery discharge in our home laboratory before our in-situ experiment, in order to ensure that diffraction data are collected at the key plateaux on the discharge profile. Longer diffraction datasets are collected at the isopotentials, and on switching between isopotentials faster data collection takes place. Alternatively, galvanostatic discharge maybe carried out, during which a large number of diffraction patterns are collected continuously over short periods of time (e.g., 5 mins each), and which subsequently may be summed to obtain higher quality datasets on plateaux in the discharge profile. We have had success with both types of measurement, but we found that it was difficult to get meaningful capacities from our in-situ experiments to date.

### Sample Preparation

The samples for the experiments were prepared by sequentially pressing the powders for the anode, electrolyte/separator and cathode into pellets. The sequential pressing offers the opportunity to make good contacts between each layer. It is then relatively straightforward to handle the pellet and load it into the in-situ sample environment inside the glovebox. The eutectic of choice for the electrolyte is the KCl-LiCl eutectic (melting point = 352◦C). At room temperature, peaks from the electrolyte are present in the neutron powder diffraction pattern, but on heating above the melting point of the electrolyte, the peaks disappear, which again simplifies the data analysis by reducing the number of phases observed in the neutron diffraction pattern.

## CASE STUDIES: THERMAL BATTERIES USING TRANSITION METAL SULFIDES, AS CATHODES

As discussed earlier, transition metal disulfides MS2 (where M = Fe, Co, and Ni) are some of the most commonly used cathode materials for thermal batteries, and indeed it was these materials which have formed the basis of our first in-situ studies on thermal batteries (Payne et al., 2017; Payne et al., in preparation). In addition, our recent synthetic and electrochemical work has looked at some other transition metal sulfides as potential cathodes for thermal batteries (Giagloglou et al., 2016, 2017; Giagloglou et al., in preparation).

Our first in-situ study looked at the discharge of a thermal battery which used NiS2 (a conversion material) as the cathode, Li13Si4 as the anode, KCl-LiCl eutectic as the electrolyte and MgO as the separator (Payne et al., 2017). This experiment was carried out at 520◦C, which to the best of our knowledge, is the highest temperature in-situ battery experiment carried out to date. **Figure 2** shows some of the results from this experiment, including a film plot of the diffraction data collected during battery discharge, a plot of the evolution of phase fraction and discharge profile over the course of the experiment and finally the changes in crystal structure of Ni-containing species during discharge. In our study, we were able to correlate the evolution of crystalline phases with plateaux observed in the battery discharge profile and a total of four nickel containing phases were observed in the diffraction patterns. A film plot of the diffraction data shows evolution of the crystalline phases upon discharge and is shown in **Figure 2A**. Rietveld refinement was used to extract phase fractions from the diffraction data. This allows us to correlate the phase fractions with the electrochemical data, and in particular with the plateau in the voltage discharge profile. **Figure 2B** shows the evolution of phase fraction and cell voltage during discharge. This shows that the plateau in the voltage discharge profile at ∼1.7 V was due to the NiS2 to NiS transformation, whilst the plateau at ∼1.4–1.3 V was due to the NiS to Ni3S2 transformation. We did not observe Ni7S6, which had previously been observed in cells examined at room temperature and this led us to propose a new discharge mechanism for NiS2 when it is used as a cathode (Payne et al., 2017). The structures of the Ni-containing phases that were identified during discharge are shown in **Figure 2C**. We should also point out that we also observed changes in cell parameter of the NiS phase, which provides evidence for a region of solid solution, and although the changes in composition of this phase could not be accurately determined it is possible that this change in cell parameter was due to either a non-stoichiometric Ni1−xS phase or some Li incorporation in NiS. It was particularly useful to collect synchrotron powder X-ray diffraction data on the cathode after our in-situ neutron diffraction data, as this enabled conclusive identification of all cell components present,

as we benefitted from the high intensity and resolution of the synchrotron source. This emphasizes the importance of using complementary techniques (where possible) to enhance the understanding of the system under study.

Co. KGaA and are reproduced from Payne et al. (2017) with permission.

Li13Si4 is an anode commonly used in thermal batteries. However, in our in-situ studies to date, the combination of a large unit cell and low symmetry of the Li13Si4 structure, which is then pressed into a pellet, means that it is particularly difficult to study the changes in the structure of the anode material during discharge. Although the lithium silicides have been well-studied by a variety of techniques, including single crystal diffraction and NMR, much less is known about their high temperature behavior, including the high temperature crystallography (Key et al., 2009, 2011; Zeilinger and Faessler, 2013; Zeilinger et al., 2013a,b). It is also possible that Li13Si4 (and related phases) are largely amorphous during battery discharge, as electrochemically driven amorphisation is known to occur in lithium ion batteries upon lithium uptake when Si is used as an anode (Limthongkul et al., 2003a,b). The challenges in studying the anode material highlights that often questions still remain after an in-situ experiment, meaning that such experiments may often need follow up studies, in order to fully understand the system of interest.

Restricting in-situ studies to diffraction based techniques means that it can be easy to neglect any components which are amorphous. In the case of the thermal battery, the presence of molten salt electrolytes can simplify data analysis, due to the reduction in the number of crystalline phases observed in the diffraction pattern at device operating temperature. However, there may be occasions when we are interested in the amount of amorphous material in the battery. The use of a crystalline ceramic separator in thermal batteries is particularly useful as it can be used as an internal standard to quantify the amorphous content the battery. The importance of gaining an understanding of non-crystalline phases has recently been highlighted in a study of the in-situ synthesis of the Li7La3Zr2O12 Li-ion conductor. This quantified the fraction of molten/amorphous phases present in this system and found that the presence of a carbonate melt assists the synthesis of Li7La3Zr2O12 (Rao et al., 2015).

### OTHER HIGH-TEMPERATURE BATTERY TECHNOLOGIES: SODIUM METAL HALIDE BATTERIES

We should point out that thermal batteries are not the only high temperature battery technology. Sodium-metal halide batteries, which are also often referred to as "ZEBRA" (Zero-Emission Battery Research Activities) cells are another high temperature battery technology which have been studied using in-situ techniques (Zinth et al., 2015, 2016). These cells typically operate at around 300◦C and have also been studied by in-situ neutron diffraction (Zinth et al., 2015). Spatially resolved neutron diffraction data were collected at different points within the cathode of such a cell, enabling reaction fronts to be monitored as they move through the battery (Zinth et al., 2015). In-situ neutron tomography and radiography have been used to probe the changes in morphology of the cell components during battery cycling (Zinth et al., 2016). The phase evolution in sodium metal halide batteries and the presence of intermediates have also been studied using in-situ energy dispersive X-ray diffraction and this has allowed both spatial and kinetic information to be obtained on the battery charge/discharge process (Russenbeek et al., 2011).

### CONCLUSIONS

Although most in-situ studies of batteries have focused on batteries which operate at room temperature, other battery technologies, such as the thermal battery and the sodium metal halide battery, operate at higher temperatures and require insitu studies to be carried out at elevated temperature, in order to gain a better understanding of the processes taking place in them. Our recent in-situ work has successfully probed and shed light on the processes occurring in thermal batteries during discharge at their high operating temperatures of around 500◦C. To the best of our knowledge we believe that these are the highest temperature in-situ battery studies carried out to date. We should also point out that studies using complementary techniques such as synchrotron PXRD post battery testing offer advantages such as high resolution and intensity, which can help to unambiguously identify products formed during battery discharge. Although improvements can be envisioned and there are still many questions to be answered, this work paves the way for future high temperature in-situ studies of batteries.

### AUTHOR CONTRIBUTIONS

JLP co-wrote the article, carried out experiments, and analyzed data. KG prepared samples and carried out experiments. GC

#### REFERENCES

developed the sample environment and carried out experiments. CC carried out experiments. JDP and RS carried out experiments and co-wrote manuscript. RG and JI co-wrote manuscript and oversaw research.

#### FUNDING

We thank AWE and EPSRC (EP/P007821/1) for supporting this programme of research.

### ACKNOWLEDGMENTS

We thank the STFC for provision of neutron diffraction beamtime and Diamond Light Source for the provision of X-ray diffraction beam-time.

silicon electrodes for lithium-ion batteries. J. Am. Chem. Soc. 131, 9239–9249. doi: 10.1021/ja8086278

electrolytes. Chem. Mater. 27, 2903–2910. doi: 10.1021/acs.chemmater. 5b00149

**Conflict of Interest Statement:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Crown Copyright © 2018 Authors: Payne, Giagloglou, Carins, Crouch, Percival, Smith, Gover and Irvine. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

# New Opportunities for Air Cathode Batteries; in-Situ Neutron Diffraction Measurements

Jordi Jacas Biendicho1 \*, Dag Noréus 2 , Colin Offer 3 , Gunnar Svensson2 , Ronald I. Smith3 and Stephen Hull 3

1 Catalonia Institute for Energy Research, Sant Adrià de Besòs, Spain, 2 Department of Material and Environmental Chemistry, Stockholm University, Stockholm, Sweden, 3 ISIS Neutron and Muon Source, STFC Rutherford Appleton Laboratory, Didcot, United Kingdom

Batteries with air electrodes are gaining interest as Energy Storage Systems (ESSs) for Electrical Vehicles (EVs) because of their high specific energy density. The electrochemical performance of these batteries is limited by the metallic electrode, which suffers structural transformations and corrosion during cycling that reduces the cycle life of the battery. In this context, relevant information on the discharge products may be obtained by in-situ neutron diffraction, a suitable technique to study electrodes that contain light elements or near neighbor elements in the periodic table. Case studies of MH-air and Fe-air batteries are highlighted.

#### Edited by:

Verónica Palomares, University of the Basque Country (UPV/EHU), Spain

#### Reviewed by:

Branimir Nikola Grgur, University of Belgrade, Serbia Wei Kong Pang, University of Wollongong, Australia

\*Correspondence:

Jordi Jacas Biendicho<EMAIL_ADDRESS>
#### Specialty section:

This article was submitted to Energy Storage, a section of the journal Frontiers in Energy Research

Received: 19 March 2018 Accepted: 25 June 2018 Published: 12 July 2018

#### Citation:

Jacas Biendicho J, Noréus D, Offer C, Svensson G, Smith RI and Hull S (2018) New Opportunities for Air Cathode Batteries; in-Situ Neutron Diffraction Measurements. Front. Energy Res. 6:69. doi: 10.3389/fenrg.2018.00069 Keywords: metal-air battery, metal hybrid air battery, in-situ neutron diffraction, rechargeable batteries, fuel cells

## INTRODUCTION

Air cathode-based batteries are promising energy storage systems for Electrical Vehicles (EVs) because they are lighter and, theoretically, may store higher electrochemical capacity than Li-ion batteries. This, in turn, maximizes the specific energy density (kWkg−1 ) of the battery and may lead to a substantial increase of the range capability of EVs beyond the present limit of ∼300 Km (Science and Technology, 2017). Tesla has recently obtained patent(s) on this technology (Herman et al., 2017), with the aim of developing new chemistries and optimizing the existing ones which, unfortunately, are not yet competitive enough to replace current technology, especially in terms of cycle life.

An air cathode battery is a hybrid system that falls into two technologies; fuel cells and rechargeable batteries. The positive electrode or cathode is a light electrode that requires a continuous source of fuel or gaseous reactant to release the stored energy, as in Solid Oxide Fuel Cells (SOFCs) (Singhal, 2000). The anode is a metallic electrode which usually contains additives to improve its electrochemical performance and it is immersed in the electrolyte, typically an aqueous one. This hybrid configuration overcomes some of the problems associated with fuel cells and rechargeable batteries, when considered individually. For instance, air cathode batteries do not rely on H2 gas, so safety issues and costs associated with hydrogen storage using highly-pressurized cylinders are not a limitation in Metal-air batteries. Or the electrochemical capacity of a rechargeable Nickel-Metal Hydride battery (NiMH) may be significantly increased by the use of an air-electrode instead of Ni(OH)2 (Dong et al., 2010), hence a MH-air battery.

Half-cell reactions in an aqueous air cathode battery are presented below. For the positive air electrode, oxygen or air is supplied during discharge and the oxygen reduction reaction takes place giving 2 hydroxide molecules. It is difficult to develop air-electrodes able to withstand the electrochemical evolution and reduction of oxygen (OER and ORR) at high current rates (Jörissen, 2006). For our work investigating phase formation and transformations during charge/discharge using in-situ powder diffraction methods, Ni mesh may be used at the anode. The use of nickel mesh is motivated by its relatively simple diffraction pattern, which minimizes the number of Bragg reflections contaminating the neutron diffraction patterns collected in-situ. Concerning half-cell reactions at the metallic electrode, two reactions are presented which generally describe the chemistry at this electrode, which is the limiting one in terms of battery electrochemical capacity. In the case where the metallic electrode is a hydrogen-absorbing metal or metal-hydride as in MH-air batteries, reaction 2, protons diffuse to the particle surface and recombine with OH- at the interface with the electrolyte during discharge, forming H2O and releasing electrons (Young and Nei, 2013; Yartys et al., 2016). Or, alternatively, the metallic electrode oxidizes forming hydroxides and/or oxide compounds, depending on the depth-of-discharge, reaction 3. In this category, Al-air, Mg-air, Zn-air or Fe-air batteries are included (Rahman Md et al., 2013).

Air electrode: 2OH− ↔ 1 /2O2 + H2O + 2e− reaction 1 MH -electrode: 2M + 2H2O + 2e− ↔ 2MH + 2OH− reaction 2 Metallic electrode 2M(OH)x + 2e− ↔ 2M + 2OH−

reaction 3 The cycle life of an air cathode battery is limited by the reactions taking place at the metallic electrode. In MH-air batteries, the stored electrochemical capacity is high (∼300 mAhg−1 for AB5 type alloys) and may be increased if superlattice A2B7-type alloys are used, which also show lower self-discharge (Yartys et al., 2016). However, these materials corrode in alkaline solutions, forming insulating phases such as La(OH)2 at the particle/electrolyte interface, which reduce the diffusivity of protons to the bulk and, as the electrochemical reaction proceeds, capacity rapidly decreases. Corrosion also affects Metal-air batteries. In Li-Air batteries (Aurbach et al., 2016), the chemical interaction between Li metal and the electrolyte is critical to avoid formation of irreversible phases, and aprotic electrolytes have shown better performance than aqueous ones. Critically, the latter one needs passivation of the metallic lithium in order to operate safely. The highly irreversible formation of discharge products at the metallic electrodes in Al-air, Zn-air, Fe-air and Mg-air batteries affect their performance and, in addition, H2 gas evolution occurs at the discharge potentials, which reduces the efficiency of the batteries (Rahman Md et al., 2013). In the case of Fe-air, addition of K2SnO3 to the aqueous electrolyte improves the electrochemical performance of the battery (Chamoun et al., 2017).

Powder diffraction experiments are a fundamental method of determining phase composition and structures in multicomponent systems such as batteries, of which the metallic compounds contained inside, are one example. However, corrosion products in Li and Na-based batteries may be difficult to characterize using X-rays due to the low atomic number elements contained in them. In a similar way there is very little contrast between elements adjacent to each other in the periodic table, e.g., transition metals, when X-ray radiation is used, so limiting the structural information that can be obtained from Rietveld refinement of the crystal structure(s). With neutron diffraction, however, the scattering power of nuclei can vary dramatically between elements of similar atomic number, and also between isotopes of the same element. Furthermore, neutrons are highly penetrating compared to Xrays, meaning that information is gained from the bulk of a sample rather than near-surface regions. Consequently in-situ neutron diffraction is the ideal technique to obtain accurate structural information on the phases commonly found in air cathode batteries in real time as they are charged and discharged in the neutron beam. However, air cathode electrodes have additional requirements compared to rechargeable batteries which need to be implemented into cell design e.g. O2 or H2 evolution.

In this manuscript, the use of in-situ neutron diffraction to characterize Metal-air batteries is highlighted in two case studies, MH-air and Fe-air, using a customized electrochemical cell for air cathode.

#### METHODS

In-situ neutron diffraction data were collected at the Polaris diffractometer (Hull et al., 1992) at ISIS, and diffraction data were analyzed by the Rietveld method using GSAS least-squares refinement software (Larson and Von Dreele, 1990). Neutron diffraction data were collected using the backscattering detector (135◦ ≤ 2θ ≤ 168◦ , dmax = 2.7 Å). Further information of cell design and components may be found in (Biendicho et al., 2014, 2015; Chamoun et al., 2017).

#### RESULTS AND DISCUSSION

The electrochemical cell originally constructed to conduct in-situ studies in a NiMH battery (Biendicho et al., 2014, 2015), may be easily adapted to other energy storage systems due to its modular and flexible configuration. As presented in previous publications, the cell is based in a planar design stacking the components on top of each other, as in coin cells used in a laboratory to characterize electrode materials ex-situ. However, the dimensions of the in-situ cell are significantly larger compared to standard coin cells to maximize the amount of electrode material exposed to the neutron beam; the outer cell diameter of the cell is 84 mm and usually accommodates rectangular-shaped electrodes of 1– 2 g. **Figures 1A,B** show an expanded view of the in-situ cell and a sketch of the cell components and their position with respect to the incident neutron beam, respectively. Further details of the cell components and materials used to collect neutron diffraction patterns with an increased peak-to-background ratio may be found in previous publications (Roberts et al., 2013; Biendicho et al., 2014, 2015).

As discussed above, the positive electrode in a metal-air battery requires a constant source of fuel to release the stored energy. It is necessary, therefore, to take into account this requirement at the cell design stage, especially if long-term stability studies are considered. A special separator module was designed and is presented in **Figure 1C**. The upper part of the

FIGURE 1 | (A) Expanded view of the in-situ cell; 1 and 2 correspond to the alloy clamp rings and PEEK screws used to seal the cell after assembly, 3 and 4 are the two windows which hold the thin Ni metal sheets used as positive and negative electrodes, 5 are inlet/outlet connections for the tubing to pump in gas fuel or electrolyte and 6 is the threaded block used to mount the cell on the diffractometer; (B) sketch of the cell components and their position with respect to the incident neutron beam; (C) close-up detail of the separator module; the two apertures that connect the inner compartment of the battery with the cell exterior (indicated by the black arrows); (D) assembled cell with tubing connections prior in-situ experiment.

separator module has two apertures, indicated by black arrows, which connect the inner compartment of the battery to the cell exterior, allowing either gas fuel or electrolyte to be pumped in and out of the cell during in-situ diffraction measurements. These apertures are also used to avoid cell over-pressure during discharge at the positive electrode (H2 evolution). **Figure 1D** shows the assembled in-situ cell with inlet and outlet connections, which was constructed prior to one of the experiments conducted at the ISIS neutron spallation source. Considering the positive electrode, a nickel mesh is preferred since it is the same material as current collector. Other catalytic materials could be used as electrodes but they would either add extra Bragg peaks to the neutron diffraction patterns or increase the background, potentially masking reflections from the negative electrode.

Two examples are presented in the following paragraphs i.e., MH-air and Fe-air, to show the quality of diffraction patterns obtained by the customized electrochemical cell, and the type of structural information that may be extracted by in-situ measurements, respectively.

**Figure 2A** shows neutron diffraction patterns of the cell assembled with an AB5-type alloy as anode as a function of discharge state using a current of ∼30 mA. Because the incoherent neutron scattering from hydrogen atoms would produce a large background signal, deuterated 6 M KOD electrolyte was used instead during battery construction. The most intense sharp diffraction peaks correspond to nickel from the thin current collectors and Ni mesh used as counter electrode, and the small background contribution is related to a Polypropylene membrane. The cell was loaded with 1.8 gr of alloy with composition MmNi3.6Al0.4Mn0.3Co0.7 where Mm denotes Misch metals. Additional information of cell assembly, cycling conditions and components may be found in Biendicho et al. (2014, 2015).

As discharge proceeds, the intensity of the reflections corresponding to the β-phase with lattice parameters a ∼5.26 Å and c ∼4.17 Å decrease and other reflections appear that can be indexed using a smaller unit cell corresponding to the α-phase, with a ∼5.00 Å and c ∼4.04 Å. Because of the good signal-tonoise ratio of the in-situ neutron diffraction patterns, it is also possible to observe differences in diffraction line widths between the charged phase and the discharged one. Bragg Peaks of βphase are broader than the ones corresponding to the α-phase, demonstrating a substantial disorder of the deuterium atoms in the crystal structure of the charged material. For this alloy composition, an intermediate an intermediate phase (γ-phase) has been detected, in addition to the β- and α- phases, during charge and its appearance has been related to an improved stability of the electrode to corrosion and, in turn, to a better cycle life (Latroche et al., 1999).

**Figure 2B** shows phase fraction (weight %) as a function of cell potential for a Fe-air battery. Blue, red and black markers correspond to Fe, Fe3O4 and a new intermediate hydride phase that was identified during in-situ measurements. The electrolyte composition was deuterated 6 KOD and 0.1 M K2SO3 which was used as additive to reduce H2 evolution and no membrane was used to separate the Fe and Ni mesh electrodes. Instead, physical separation with a 5 mm distance between the electrodes was provided. The total weight of the Fe electrode was 1.25 g. Additional information of cell assembly, cycling conditions and components may be found in Chamoun et al. (2017).

Structural refinements of the new phase observed in the Fe electrode showed a good agreement between observed and calculated data (see Chamoun et al., 2017). The new metastable phase was refined using a tetragonal unit cell and with composition being a solid solution of Fe, Sn, Bi, and C. its weight fraction was then monitored in-situ, as for the other phases. In-situ structural information, which may also involve lattice or atomic displacement parameters, are interesting because they give in-deep understanding of the redox chemistry in the electrode, otherwise inaccessible by ex-situ techniques.

#### CONCLUSIONS

In-situ neutron diffraction is, therefore, a technique that contributes to a better understanding of charge/discharge mechanism in the metallic alloys presently used in many battery systems. Such knowledge is vital in allowing the development of new materials and compositions having improved capacity retention, fewer irreversible side-reaction and better efficiency.

The updated electrochemical cell presented in this paper provides the requirements to characterize the structure of

metallic electrodes in an air cathode battery in-situ. The specially designed separator module, the choice of Ni mesh as cathode and the use of deuterated aqueous electrolyte are key components to obtain neutron diffraction patterns with good signal-to-noise ratio, which may be used to extract relevant structural information such as phase stability or phase fraction as highlighted for an MH-air and a Fe-air battery, respectively.

a function of time using a Fe electrode and Ni mesh as anode and cathode, respectively.

#### REFERENCES

#### AUTHOR CONTRIBUTIONS

Cell design and construction were conducted at ISIS and Stockholm university. For this task, JJ, SH, GS, and CO contributed equally. Material preparation and ex-situ battery testing were conducted at Stockholm University by JJ and DN. In-situ experiments presented in the paper were obtained at ISIS neutron and Muon source by JJ, SH, and RS.

behavior studied by in situ neutron diffraction. J. Alloys Compd. 293–295, 637–642.

**Conflict of Interest Statement:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2018 Jacas Biendicho, Noréus, Offer, Svensson, Smith and Hull. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.