*4.2. Material Preparation*

The polymer was prepared at the Department of Materials Engineering at the São Carlos School of Engineering, University of São Paulo, Brazil, according to Dias e Chinelatto (2019) [36]. The material used was Poly(acid lactic) (PLA grade: Ingeo 3251D), manufactured by NatureWorks Co. Ltd. with 80,000 g.mol−1, 1.4% of D-PLA content, 48 MPa tensile strength, 2.5% strain at break, and 16 J.m−1 Izod impact resistance. Polymer implants (1 cm2 and 1 mm thick) were produced via hot pressing at 180 ◦C. Sterilization was performed with ethylene oxide (Acecil Central de Esterilização Comércio e Indústria Ltda, Campinas, São Paulo, Brazil).


**About the Editor**

**Krzysztof Okarma** (Dr Hab., Assoc. Prof.) was born in Szczecin on Mar 22, 1975, graduated from the secondary school no. 4 in Szczecin with honors in 1994 and Szczecin University of Technology (currently West Pomeranian University of Technology in Szczecin—ZUT) in 1999 with honors (electronics and telecommunication) and 2001 (computer science). Since 1999, he has worked with ZUT as an assistant, PhD student, Assistant Professor and Associate Professor. Currently he is the Head of Department of Signal Processing and Multimedia Engineering and Dean of Faculty of Electrical Engineering (since 2016). He defended the PhD thesis in electrical engineering (specialty: signal processing) in 2003 and obtained the habilitation in automation and robotics (specialty: applied computer science) in 2013. The topic of his habilitation was related to image quality assessment methods, particularly applications of combined metrics. He was the auxiliary supervisor of one PhD candidate, reviewer of one habilitation and five PhD theses (including one in Lithuania) and currently is a supervisor in four projects registered for PhD degree conferment procedures. He is an author or co-author of 2 granted patents and over 200 journal and conference papers (including 25 papers in JCR journals, 10 conference papers included in CORE database and over 50 other conference papers indexed in Web of Science or Scopus databases). His papers were cited more than 300 times according to Web of Science (h-Index 10) and more than 500 times according to Scopus (h-Index 13). He was the guest editor in two Special Issues in JCR-indexed journals and a member of scientific boards of two other JCR-indexed journals and several international conferences. Currently he is the chairman of the Board of Control in the Polish chapter of IAPR (Association for Image Processing). He has also been the supervisor of over 50 master's and engineering theses and the reviewer of over 300 papers for international journals and conferences.


**4. Discussion**

Amorphous silicon dioxides are known to confer desirable attributes upon incorporation with active ingredients including enhanced biocompatibility, improved chemical stability, and improved thermal stability [7,9,37–39]. Modified Stöber methodologies employed by Cong et al. afford silica coatings on fluorescent dye-doped polymeric nanoparticles towards obtaining an insulating layer with improved physical stability [37]. Silver-silica core-shell structures, successfully prepared by Xu et al., use a modified Stöber process to confer chemical stability to metallic silver nanoparticles without hindering antimicrobial efficacy [9]. These methods are conducive to conventional organic drugs or weak oxidizing agents such as metallic silver, affording control over polymerization and deposition of silicon dioxide. However, in the presence of strong oxidizing agents such as silver oxynitrate, chemical incompatibilities restrict the successful application of these methodologies. Acid-catalyzed polymerization or deposition of alkali silicates are also known to generate amorphous silica [5,24,25,27]. Similar to the aforementioned silica-shell strategies, conventional acid-precipitated silicate methodologies are reliant upon the use of surfactants and organic precursors as structure-directing agents and therefore pose challenges for use with highly oxidizing materials. In the present work, alternate methods for the in-situ polymerization of silica with higher oxidation state silvers are presented wherein the formation of the silica structure is self-directed through acidic by-products of silver oxynitrate synthetic reactions.

Silicate ions will polymerize to form silica in solutions having pH of less than about 10 (H4SiO4, p*K*a1 = 9.8) [40]. In the preparation of silver oxynitrate, Equation (3), it is known that sulfuric and nitric acids are generated as by-products of the silver oxidation reaction resulting in the reduction of pH of the solution from neutral to pH 1–2 (data not shown). These acids, as shown previously, are suitable to e ffect protonation of silicic acid at room temperature and formation of oligomeric silicic acids resulting in the precipitation of amorphous silica [24,25,40]. In the methodologies presented herein alkali silicates at various concentrations relative to silver are dispersed into an oxidizing solution of potassium persulfate to which a soluble silver solution is added resulting in the oxidation of silver and chemical deposition of silver oxynitrate, as verified by XRD in Figure 1. Finite nucleation locus of silver oxynitrate, a crystalline compound with the cubic space group Fm3m, generate an acid gradient in the immediate vicinity of silver oxynitrate nucleation sites, directing the spatial polymerization or precipitation of silica [41]. As observed in Figures 2 and 3, silver oxynitrate solids are observed to be impregnated in a silica framework. Absence of AgO or other degradation products of silver oxynitrate, as seen in in Figure 1, indicates that the co-deposition process does not impair the formation of silver oxynitrate. Formation of silver sulfate does not occur as a by-product of the reaction, as seen in Equation (3). Rather silver sulfate is an impurity forming due to incomplete conversion of soluble silver to silver oxynitrate. This impurity is a minor component in the silver oxynitrate control and observed at increasing relative quantities as silica ratios rise from 0.1:1 to 0.5:1, SiO2:Ag, as shown by relative peak area in Figure S1.

Increasing the relative concentration of silica during the co-deposition reaction was also shown to be an e ffective method for crystalline size control of silver oxynitrate. Utilizing the FWHM for the four strongest reflections in the di ffraction pattern for silver oxynitrate, observed at 31.2, 36.3, 52.3, 62,2 ◦2Θ, respectively (222), (400), (220) and (622) reflections, the relative size of the silver oxynitrate crystals were calculated as per the Debye-Scherrer equation [41,42]. Based upon the average crystal size determination from these primary reflections, the crystal size of silver oxynitrate decreases from 1032 ± 152 Å to 500 ± 75 Å as the relative ratio of SiO2:Ag increases from 0.0:1 to 0.5:1. This same trend in silver oxynitrate crystalline size reduction upon increasing silica ratio may be observed the SEM and TEM images collected for the co-deposition products as shown in Figures 2 and 3.

As silica is known to confer enhanced stability of active ingredients, the stability of silver oxynitrate and Ag7NO11:SiO2 were compared over the course of four months under ambient and 40 ◦C storage. The thermal degradation pathways for silver oxynitrate are well known [21,23,30]. The first two decomposition processes for silver oxynitrate, Equations (4) and (5) are exothermic with associated enthalpies of Δ H = −244 KJ/mol and −75.8 KJ/mol and initiation temperatures of 80–85 ◦C and 115–120 ◦C respectively [21]. In contrast, the subsequent degradation processes, Equations (6) and (7), are endothermic with associated enthalpies of Δ H = 659 KJ/mol and 338 KJ/mol and initiation temperatures of 350 ◦C and 425–435 ◦C respectively [21]. It is also known that the rate of decomposition of silver oxynitrate is accelerated in the presence of heat and water [30,41]. Under ambient conditions, silver oxynitrate is observed to proceed through the first decomposition process as shown in Figure 4A. The rate of this degradation process is retarded in Ag7NO11:SiO2 as shown in Figure 4B. At elevated temperatures, a more rapid degradation of silver oxynitrate will result in increased thermal energy due to the exothermic nature of the first two degradation processes. In combination with the elevated storage temperature, initiation of subsequent endothermic degradation processes as shown in Equations (6) and (7) are observed to occur for silver oxynitrate as seen in Figure 5A. These advanced degradation processes are not observed in Ag7NO11:SiO2. At elevated temperatures only the first degradation process, Equation (4), is observed for Ag7NO11:SiO2 as seen in Figure 5B.

Silica is a thermal insulator with a very low thermal conductivity; beneficial in aerospace and construction applications [43–45]. As an aerogel, Reim et al. demonstrated silica granulates may a fford a heat transfer coe fficient of less than 0.4 W/(m2 K) [44]. Silica is also well known as a desiccant, capable of sequestering water from organic solvents to less than 100 ppm and significant reductions in water content in solid-state powder samples [46,47]. The results presented here suggest that the presence of an interspersed silica framework with thermally insulating and desiccating properties may obstruct heat transfer and restrict the step-wise degradation of silver oxynitrate. These properties enhance the long term and thermal stability of silver oxynitrate within the silica framework.

Silver oxynitrate has been previously shown to rapidly and effectively eliminate bacterial organisms in both free and biofilm states [16–18]. Silicate drug delivery systems, such as silica core-shell systems, may provide an enhanced stability and biocompatibility however, they are also known to modify drug release profiles [3,4]. Gaining understanding for how the silica co-deposition process may impact solution-phase behavior, a series of investigations were performed to evaluate silver oxynitrate and Ag7NO11:SiO2 antimicrobial activities and degradation profiles in aqueous media. As described above, water is known to accelerate the rate of degradation of silver oxynitrate to silver oxide [30,41]. This effect is observed in Figure 6A where over the course of seven days silver oxynitrate proceeds through the degradation process described in Equation (4) to form argentic oxide: AgO. A similar degradation process is observed for Ag7NO11:SiO2 as shown in Figure 6B. This solid-state transformation is visualized by the change in crystalline morphology by SEM where the cuboctahedra structure of silver oxynitrate observed prior to aqueous exposure, Figure 7A,D is replaced by geometric platelets of monoclinic silver (I, III) oxide over the seven day period [22,41]. Similarly, equivalent antimicrobial and antibiofilm log reduction values (*p* value > 0.05) are observed for silver oxynitrate and Ag7NO11:SiO2 against *P. aeruginosa* and *S. aureus* as shown in Figure 8. These results are in agreement with the silica co-deposition framework providing enhanced thermal stability without hindering aqueous degradation profiles or antimicrobial efficacy.


**6. Conclusions**

CH to BS. It is energy efficient and balances the energy consumption of the network. Further, it minimizes the un-cluster nodes, that is, nodes that are not within the communication range of any CH are minimized. But, load balancing among CHs

that are not reachable to any CH are not considered.

*Wireless Sensor Networks - Design, Deployment and Applications*

gathering and is concentrated on the following issues:

• Duplication of data generation and forwarding

generation increases the energy consumption.

cluster-based routing protocols.

• Selection of multi-hop routing path

• Selection of cluster head

ing new routing techniques:

energy is an issue.

problem.

**96**

• Operations to perform data aggregation

Multi-objective load-balancing clustering technique (MLBC) [64] has been proposed for clustering in WSN by adopting multi-objective PSO (MOPSO) strategy which is used for CH selection. The shortest-path tree (SPT) for loop-free routing is created using Dijkstra's algorithm. It is energy efficient and reliable. But, the nodes

In energy-efficient and delay-less routing [65], CH selection is performed using firefly with cyclic randomization (FCR) algorithm. This approach reduces transmission delay in the network. But, this approach has not considered energy

Overall comparison of above routing protocols are shown in **Table 2** with the

Overall, the above discussed techniques' main objective is energy-efficient data

However, we need to concentrate on the following future directions for propos-

• Almost all protocols require location information for routing. Location finding can be done using localization or GPS techniques, which are dependent on energy consumption. Finding of sensor location with less consumption of

• Most of the multi-hop routing protocols suffer from overheads and delay due to path setup and relay nodes. Also, formation of loops in aggregate tree

• Most of the literature failed in energy calculations at the time of CH selection in

• The size (with respect to area and number of members) inequality among the clusters leads to network coverage problem due to limited communication

• Uneven distribution of cluster heads will generate unequal-sized clusters, unbalanced energy consumption between cluster members, and CH coverage

techniques used, metrics considered, and drawbacks of each solution.

• Congestion or data storm problem nearer to the base station

is not considered.

balancing.

**5. Future directions**

In this chapter, classification of data collection routing protocols in WSN has been thoroughly discussed. Various techniques such as clustering, duty cycling, aggregation, network coding, sink mobility, and cross-layered solutions, and directional antennas have been utilized by data collection routing protocols for attaining long lifetime, energy efficiency, fault tolerance, and low latency. These techniques are reviewed briefly in this chapter. Finally, this chapter demonstrates a paramount comparison among the existing approaches applicable on data collection process in WSN. Future directions of routing protocols are presented at the end of this chapter.

**References**

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*Data Collection Protocols in Wireless Sensor Networks DOI: http://dx.doi.org/10.5772/intechopen.93659*

> [10] Di Francesco M, Das SK, Anastasi G. Data collection in wireless sensor networks with mobile elements: A survey. ACM Transactions on Sensor

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Heinzelman W. A taxonomy of wireless micro-sensor network models. Mobile Computing and Communications

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[16] Sarkar A, Senthil Murugan T. Routing protocols for wireless sensor networks: What the literature says? Alexandria Engineering Journal. 2016;

[17] Singh SK, Kumar P, Singh JP. A survey on successors of leach protocol.

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[18] Aslam M, Javaid N, Rahim A, Nazir U, Bibi A, Khan ZA. Survey of extended leach-based clustering routing protocols for wireless sensor networks.

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[6] Akkaya K, Younis M. A survey on routing protocols for wireless sensor networks. Ad Hoc Networks. 2005;**3**(3):

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**99**


**4. Influence factors and solutions of cucumber fermentation**

Cucumber pickles are most commonly fermented vegetable and widely consumed throughout the world [12]. Good fermentation depends on the proper combinations and interactions of multiple physical, chemical and microbiological factors [13]. Brine storage and process operations are susceptible to oxidation reactions during the fermentation process, and this has adverse influence on the quality property of cucumber pickles. To control the influence factors of cucumber fermentation, researchers have done many efforts on modern and advanced technologies, such as reducing the concentration of brining sodium chloride, developing the brining properties using lactic acid bacteria cultures, developing an anaerobic tank system, preventing cucumber gaseous deterioration by pouring of CO2 from fermentation brines [13]. After storing the brine, excess salt and organic wastes need to be leached to complete the product processing, and these wastes are sources of serious environmental concern. Thus, the waste disposal needs to be solved in the cucumber pickle industry.

#### **5. Performance, structure and constraints of cucumber market**

Marketing is vital for linking production and consumption and facilitating agricultural productivity and employment [14]. Market performance is the ultimate result of various market activities, and market structure is the organization characteristics of the market that influence the nature of competition and pricing [15]. Both male and female participate in cucumber marketing, and the male–female rate has great differences in different regions. The wholesalers are older than the retailers. In Ibadan, most of the retailers were within 31–40 years age, whereas most of the wholesalers were within 41–50 years age. It's gratifying that cucumber marketing is usually profitable for the retailers and wholesalers at both peak and lean seasons of cucumber production. However, the cucumber market is competitive, and inequality exists in the market. Commodity perishability is an important constraint in cucumber market. Thus, it is indispensable to reduce perishable degree and prolong storage time after post-harvest.

**5**

*Introductory Chapter: Studies on Cucumber DOI: http://dx.doi.org/10.5772/intechopen.97360*

**cultivated condition**

biostimulator is applied.

**6. Soil moisture and fertilizer management of cucumber**

Inappropriate farming systems and poor agronomic management are

**7. Biostimulators promote growth of cucumber under soilless**

**8. Pests and diseases during cucumber cultivation and production**

During growth process, cucumber might be affected by multiple insect pests and diseases, resulting in decrease of yield and quality. The major insect pests in cucumber including *Diabrotica undecimpunctata*, *Acalymma vitatum*, *Bactrocera cucurbitae*, *Raphidopalpa foveicollis*, *Epilachna implicate*, *Myzus persicae*, *Aphis gossypii*, *Anasa tristis*, *Trialeurodes vaparariorus*, *Bemisia tabaci* and *B. argentifolii* [22, 23]. Currently, the pest management mainly relies on chemical pesticides

Soilless cultivation in substrate culture is an important cultivation pattern for cucumber in greenhouses. The substrates should have specific physical properties including pore volume, air and water capacity, and density of substrates. Studies indicate that biostimulators can stabilize the production process to enhance plant growth under stress conditions. For instance, humate can increase vitality and growth of plants, improve seed germination, promote nutrient uptake, enhance transport and availability of micronutrients, and increase ion-exchange capacity. Lactates can produce bioregulatory effects to improve nutrient balance and plant vitality [21]. *Bacillus subtilis*, as a microorganism from the rhizosphere, can accelerate plant growth, stimulate the process of formation of plant organs, and enhance the resistance of biotic and abiotic stresses [21]. Application of biostimulators mixture (humate, lactate, and *Bacillus subtilis*) prevent growth reduction of cucumber under pH and temperature stresses through enhancing the root growth, whereas the growth is markedly reduced under stresses if no

responsible for low yield of cucumber. The quality/fertility status of soils is essential for growth and development for cucumber [16]. With good moisture and fertilizer management, optimum yield of cucumber might be attained. The conventional irrigation methods including flooding irrigation, furrow irrigation and drip

irrigation have been widely applied for a long time in cucumber cultivation because of their low cost or simple operation [17, 18]. However, these irrigation methods are surface irrigation and are driven by positive pressure, which may cause low water use efficiency, water wastage and nutrient loss [16, 19]. To solve these problems, new irrigation technique such as negative pressure irrigation that controls automatically water release based on the soil water potential difference should be encouraged [16]. Inadequate fertilizer use causes low soil fertility that cannot provide sufficient nutrients for the normal growth of cucumber. The integration application of inorganic and organic fertilizer is more beneficial than the sole use of inorganic fertilizer or organic manures in cucumber production [20]. Moreover, fertilizer sources need to dissolve or decompose to make nutrients available for cucumber plants, so soil fertility also depends on soil water, temperature and density. Consequently, the soil management strategies such as negative pressure irrigation, seasonable fertilization, application of organic mulches and conservation tillage should be appropriately applied for sustainable production of cucumber.

*Cucumber Economic Values and Its Cultivation and Breeding*

treatments [11].

industry.

**3. Culinary, therapeutic and cosmetic uses of cucumber**

At present, cucumber is the fourth most widely cultivated vegetable after

tomato, cabbage and onion [8]. Cucumber has versatile uses in culinary, therapeutic and cosmetic purposes [5, 6]. Nutritional and epidemiological researches have shown various benefits of cucumber. For example, cucumber contains abundant nutrients and has crunchy texture and unique flavor, so it is a quintessential vegetable used for a variety of dishes, and it is also indispensable for salad, soup and smoothie. Cucumber is rich in superior hydration and phytochemicals, which have diverse health benefits including weight loss, anti-inflammation, remedy for multiple diseases of eczema, constipation, hypertension, atherosclerosis, cancer, etc. [9]. Recent studies found that the presence of kaempferol in cucumber is an important antidiabetic agent [10]. Furthermore, cucumber is popularly used for natural beautification and for skin

**4. Influence factors and solutions of cucumber fermentation**

**5. Performance, structure and constraints of cucumber market**

agricultural productivity and employment [14]. Market performance is the ultimate result of various market activities, and market structure is the

are older than the retailers. In Ibadan, most of the retailers were within

31–40 years age, whereas most of the wholesalers were within 41–50 years age. It's gratifying that cucumber marketing is usually profitable for the retailers and wholesalers at both peak and lean seasons of cucumber production. However, the cucumber market is competitive, and inequality exists in the market. Commodity perishability is an important constraint in cucumber market. Thus, it is indispensable to reduce perishable degree and prolong storage time after

Marketing is vital for linking production and consumption and facilitating

organization characteristics of the market that influence the nature of competition and pricing [15]. Both male and female participate in cucumber marketing, and the male–female rate has great differences in different regions. The wholesalers

Cucumber pickles are most commonly fermented vegetable and widely consumed throughout the world [12]. Good fermentation depends on the proper combinations and interactions of multiple physical, chemical and

microbiological factors [13]. Brine storage and process operations are susceptible to oxidation reactions during the fermentation process, and this has adverse influence on the quality property of cucumber pickles. To control the influence factors of cucumber fermentation, researchers have done many efforts on modern and advanced technologies, such as reducing the concentration of brining sodium chloride, developing the brining properties using lactic acid bacteria cultures, developing an anaerobic tank system, preventing cucumber gaseous deterioration by pouring of CO2 from fermentation brines [13]. After storing the brine, excess salt and organic wastes need to be leached to complete the product processing, and these wastes are sources of serious environmental concern. Thus, the waste disposal needs to be solved in the cucumber pickle

**4**

post-harvest.


**3. Ionic liquid as quasi solid and solid electrolyte**

Liquid electrolytes need additional encapsulation. Thus, SCs applied ILs face difficulty in integration and manufacturing flexible devices. These problems can be addressed by solidifying the ILs because the ILs maintain the conductivity even when solidified, unlike a typical organic electrolyte. Generally, polymers are applied for solid state with various devices, and ILs adopted polymer structure are described in **Figure 10**.

**Figure 10.** Ionic liquid-polymer electrolyte.

#### **3.1. Ionic liquid-blended polymer electrolyte**

ILs blended polymer electrolyte can be referred to ion gel (iongel, ionogel) because most of the ILs blended polymer electrolytes were synthesized in gel polymer type. The initial gel polymer electrolyte consisted of ion conducting salts (ILs), organic solvent, and polymers like gel polymer electrolyte of LIBs. In 1997, Fuller et al. reported iongel that contains ILs, organic solvent, and poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) [74]. The iongel which was composed of [EMI][BF4] and [EMI][CF3 SO3 − ] and PVdF-HFP achieved the highest ionic conductivity of 5.8 mS cm−1. Various carbon materials were adopted from classical AC to nanostructured carbon such as CNT and graphene [75–77]. Pandey et al. also proposed [EMI] [B(CN)4 ] and PVdF-HFP-based iongel electrolyte [77]. SCs applied ion gel was tested with multiwall carbon nanotube (MWCNT) electrode. The SCs adopting [EMI][B(CN)4 ] based iongel shows good thermal stability up to 310°C, a wider electrochemical window of ∼3.8 V, and a high ionic conductivity of ∼9 × 10−3 S cm−1 at room temperature. The SCs also show a specific energy of ∼3.5 W h kg−1 and a specific power of ∼4.2 kW kg−1. Lu et al. also studied ion gel with PVdF-HFP and [EMI][FSI] [78]. They compared different polymer composites. The ion gels were flexible and mechanically strong and show 28 Wh kg−1 of the energy density with 2317 W kg−1 of the power density. The features of iongel and the structure of the SCs using the iongel are shown in **Figure 11**.

specific current of 2.67 A g−1, and energy density and power density of 25.7 Wh kg−1 and 35.2 kW kg−1, respectively. The ion gel stretched up to 150%. Other polymeric matrixes such as poly(acrylonitrile), polyvinylidene fluoride/polyvinyl acetate, poly(ethylene oxide), poly(vinylalcohol), poly(methylmethacrylate), poly(tetrafluoroethylene), and chitosan were

**Figure 11.** (a) Photographs of ILGPEs prepared by different methods: (A) PVdF-HFP/EMIMTf2N by ionic-liquid–

N] by ionic-liquid–polymer membrane method. (b) Photograph of a capacitor before assembly

N]/zeolite ILGPE.

N]/zeolite by ionic-liquid–inorganicpolymer composite method,

Ionic Liquid for High Voltage Supercapacitor http://dx.doi.org/10.5772/intechopen.73053 37

Most of the introduced ILs and iongel operated at 2.0–3.5 V. These operating voltages were not enough to overcome intrinsic limitation of ILs because ILs have low ionic conductivity and high viscosity, such properties cause decrement of specific capacity. To overcome relatively low specific capacity, operating voltage have to be enhanced at 3.5–4.0 V. Additionally, high operating voltage is helpful to manage power supply. SCs are regarded as excellent energy storage devices due to their high power density and permanent life cycles. However, SCs face with critical challenge of low energy density. Therefore, LIBs and SCs are applied together for the complementary purpose. The typical case is a wireless detection system that needs two kinds of power supply units. One is a continuous power supply for operation, and the other is a pulse power to transmit data to the control system. Continuous power systems require

investigated [80–83].

and (C) PTFE/[EMIM][Tf2

polymer gelation method, (B) PVdF-HFP/[EMIM][Tf2

from two carbon electrodes and a PVdF-HFP/[EMIM][Tf2

Each carbon electrode was attached on a polypropylene plate on the aluminum foil side. ([EMIM][Tf2 N]: [EMI][FSI] and PTFE: Poly(tetrafluoroethylene)) [78]. Other type of polymers and ILs has been tried as ion gel electrolyte. Tamilarasan et al. reported ion gel as stretchable electrolyte. The synthesized [BMI][TFSI] incorporated stretchable poly(methyl methacrylate)(PMMA) electrolyte [79]. The device has specific capacitance of 83 F g−1,

**Figure 11.** (a) Photographs of ILGPEs prepared by different methods: (A) PVdF-HFP/EMIMTf2N by ionic-liquid– polymer gelation method, (B) PVdF-HFP/[EMIM][Tf2 N]/zeolite by ionic-liquid–inorganicpolymer composite method, and (C) PTFE/[EMIM][Tf2 N] by ionic-liquid–polymer membrane method. (b) Photograph of a capacitor before assembly from two carbon electrodes and a PVdF-HFP/[EMIM][Tf2 N]/zeolite ILGPE.

**3.1. Ionic liquid-blended polymer electrolyte**

**Figure 10.** Ionic liquid-polymer electrolyte.

36 Supercapacitors - Theoretical and Practical Solutions

which was composed of [EMI][BF4] and [EMI][CF3

[B(CN)4

([EMIM][Tf2

iongel are shown in **Figure 11**.

ILs blended polymer electrolyte can be referred to ion gel (iongel, ionogel) because most of the ILs blended polymer electrolytes were synthesized in gel polymer type. The initial gel polymer electrolyte consisted of ion conducting salts (ILs), organic solvent, and polymers like gel polymer electrolyte of LIBs. In 1997, Fuller et al. reported iongel that contains ILs, organic solvent, and poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) [74]. The iongel

ionic conductivity of 5.8 mS cm−1. Various carbon materials were adopted from classical AC to nanostructured carbon such as CNT and graphene [75–77]. Pandey et al. also proposed [EMI]

gel shows good thermal stability up to 310°C, a wider electrochemical window of ∼3.8 V, and a high ionic conductivity of ∼9 × 10−3 S cm−1 at room temperature. The SCs also show a specific energy of ∼3.5 W h kg−1 and a specific power of ∼4.2 kW kg−1. Lu et al. also studied ion gel with PVdF-HFP and [EMI][FSI] [78]. They compared different polymer composites. The ion gels were flexible and mechanically strong and show 28 Wh kg−1 of the energy density with 2317 W kg−1 of the power density. The features of iongel and the structure of the SCs using the

Each carbon electrode was attached on a polypropylene plate on the aluminum foil side.

mers and ILs has been tried as ion gel electrolyte. Tamilarasan et al. reported ion gel as stretchable electrolyte. The synthesized [BMI][TFSI] incorporated stretchable poly(methyl methacrylate)(PMMA) electrolyte [79]. The device has specific capacitance of 83 F g−1,

N]: [EMI][FSI] and PTFE: Poly(tetrafluoroethylene)) [78]. Other type of poly-

multiwall carbon nanotube (MWCNT) electrode. The SCs adopting [EMI][B(CN)4

SO3 −

] and PVdF-HFP-based iongel electrolyte [77]. SCs applied ion gel was tested with

] and PVdF-HFP achieved the highest

] based ion-

specific current of 2.67 A g−1, and energy density and power density of 25.7 Wh kg−1 and 35.2 kW kg−1, respectively. The ion gel stretched up to 150%. Other polymeric matrixes such as poly(acrylonitrile), polyvinylidene fluoride/polyvinyl acetate, poly(ethylene oxide), poly(vinylalcohol), poly(methylmethacrylate), poly(tetrafluoroethylene), and chitosan were investigated [80–83].

Most of the introduced ILs and iongel operated at 2.0–3.5 V. These operating voltages were not enough to overcome intrinsic limitation of ILs because ILs have low ionic conductivity and high viscosity, such properties cause decrement of specific capacity. To overcome relatively low specific capacity, operating voltage have to be enhanced at 3.5–4.0 V. Additionally, high operating voltage is helpful to manage power supply. SCs are regarded as excellent energy storage devices due to their high power density and permanent life cycles. However, SCs face with critical challenge of low energy density. Therefore, LIBs and SCs are applied together for the complementary purpose. The typical case is a wireless detection system that needs two kinds of power supply units. One is a continuous power supply for operation, and the other is a pulse power to transmit data to the control system. Continuous power systems require high-energy densities, while pulse power systems need high-power densities. Consequently, LIBs are responsible for device operation, while SCs are used for data transmission. A critical issue in this system is voltage leveling between the LIBs and SCs. The operating voltage of LIBs is from 3.5 to 4.0 V. Thus two or more SCs in series are needed for a wireless detection system. If SCs achieve the 3.5–4.0 V rated voltage with high energy densities or LIBs achieve high power densities, then the power supply unit can be minimized and integrated. LIBs have intrinsic limitations in power densities due to their energy storage mechanisms. Hence, SCs that show high energy densities and wide operating voltages have been researched extensively. Thus, new approaches were reported to enhance working voltage of SCs. Pandey et al. adopted zeolite as additives for enhancing operating voltage, and the zeolite added SCs was stable up to 4.1 V [78]. Cross-linked polymer matrix was suggested as solid electrolyte for high-voltage SCs. Choi et al. suggested all printable SCs using UV curable materials. [BMI] [BF4 ] and UV-cured ethoxylated trimethylolpropane triacrylate (ETPTA)-based gel polymer electrolytes are incorporated to produce the solid-state SCs. They showed various shapes of inkjet-printed SCs described in **Figure 12**. Interestingly, proposed UV-cured ion gel was water proof despite of adopting [BMI][BF4 ] [84].

Our team proposed a quasi-solid polymer electrolyte based on a composite cross-linked poly-4-vninyphenol (c-P4 VPh) embedded [EMI][TFSI] [5]. [EMI][TFSI] was selected for its high ionic conductivity, and c-P4 VPh was used for its ability to enhance electrochemical stability by hydrogen bonding between [EMI][TFSI] and c-P4 VPh in addition to maintaining a quasi-solid state. Also, cross-linked polymers can keep a larger amount of ILs than other polymer by swelling. The composite electrolytes are highly ionic conductive solid state due to the rigid framework of c-P4 VPh and high ionic conductivity from large contents of [EMI][TFSI] over 60 wt%. The IL-CPs are thermally stable over 300°C and electrochemically stable over 7.0 V, since there are hydrogen bonds between c-P4 VPh and [EMI][TFSI]. We also introduced all-solid state SCs that operate at 4.0 V and have high energy density without sacrificing power density. SCs showed the best electrochemical performances and had capacitance of 172.5 F g-1 and energy density of 72.3 Wh kg−1. Their structure and electrochemical characteristics are displayed in **Figure 13**.

#### **3.2. Poly ionic liquid as solid electrolyte**

A poly IL (PIL) or polymeric ionic liquid is a polymer electrolyte containing a polymer backbone and an IL species in the monomer repeat unit. Certain characteristics of IL such as negligible vapor pressure, thermal stability, nonflammability, relatively high ionic conductivity, and broad electrochemical stability window are transferred to the polymer chain (from oligomers to high molecular weight polymers) [85]. Various PIL structures and properties are required for various applications of polymer electrolytes, electrochemical devices, smart materials, catalyst supports, porous polymer structures, and antibacterial PILs. The standard synthetic pathway for PILs relies on a basic strategy: (1) direct chain growth polymerization of IL with or without nonionic monomers; (2) step-growth polymerization of IL monomers; and (3) post-modification of polymer chains with IL monomers.

**Figure 12.** Esthetic versatility and IoT applications of the inkjet-printed SCs as object-tailored/monolithically integrated power sources. (a) Photograph of the inkjet-printed Korea map, wherein the inkjet-printed SCs (marked by red boxes) were seamlessly connected to LED lamps (marked by blue boxes) via the inkjet-printed electric circuits. (b) SEM image of the LED lamp connected to the inkjet-printed electric circuits. (c) CV profile (scan rate = 1.0 mV s−1) of the inkjet-printed SC in the map. (d) Photograph of the inkjet-printed, letter ("OR")-shaped SCs that were seamlessly connected to the letter ("HOT" and "COLD")-shaped electric circuits onto A4 paper. (e) Galvanostatic charge/discharge profile (current density = 1.0 mA cm−2) of the inkjet-printed, letter ("OR")-shaped SCs that were composed of 4 cells connected in series. (f) Photograph depicting the operation of the blue LED lamp in the smart cup (for cold water (∼10°C)), wherein the inset is a photograph of a temperature sensor assembled with an Arduino board. (g) Photograph depicting the operation of the red LED lamp in the smart cup (for hot water

Ionic Liquid for High Voltage Supercapacitor http://dx.doi.org/10.5772/intechopen.73053 39

(∼80°C)) [84].

Properties required as solid electrolytes include ionic conductivity, thermal stability, and electrochemical stability. The ionic conductivity of PILs is an important property when applied as

high-energy densities, while pulse power systems need high-power densities. Consequently, LIBs are responsible for device operation, while SCs are used for data transmission. A critical issue in this system is voltage leveling between the LIBs and SCs. The operating voltage of LIBs is from 3.5 to 4.0 V. Thus two or more SCs in series are needed for a wireless detection system. If SCs achieve the 3.5–4.0 V rated voltage with high energy densities or LIBs achieve high power densities, then the power supply unit can be minimized and integrated. LIBs have intrinsic limitations in power densities due to their energy storage mechanisms. Hence, SCs that show high energy densities and wide operating voltages have been researched extensively. Thus, new approaches were reported to enhance working voltage of SCs. Pandey et al. adopted zeolite as additives for enhancing operating voltage, and the zeolite added SCs was stable up to 4.1 V [78]. Cross-linked polymer matrix was suggested as solid electrolyte for high-voltage SCs. Choi et al. suggested all printable SCs using UV curable materials. [BMI]

] and UV-cured ethoxylated trimethylolpropane triacrylate (ETPTA)-based gel polymer electrolytes are incorporated to produce the solid-state SCs. They showed various shapes of inkjet-printed SCs described in **Figure 12**. Interestingly, proposed UV-cured ion gel was water

Our team proposed a quasi-solid polymer electrolyte based on a composite cross-linked poly-

Also, cross-linked polymers can keep a larger amount of ILs than other polymer by swelling. The composite electrolytes are highly ionic conductive solid state due to the rigid framework

operate at 4.0 V and have high energy density without sacrificing power density. SCs showed the best electrochemical performances and had capacitance of 172.5 F g-1 and energy density of 72.3 Wh kg−1. Their structure and electrochemical characteristics are displayed in **Figure 13**.

A poly IL (PIL) or polymeric ionic liquid is a polymer electrolyte containing a polymer backbone and an IL species in the monomer repeat unit. Certain characteristics of IL such as negligible vapor pressure, thermal stability, nonflammability, relatively high ionic conductivity, and broad electrochemical stability window are transferred to the polymer chain (from oligomers to high molecular weight polymers) [85]. Various PIL structures and properties are required for various applications of polymer electrolytes, electrochemical devices, smart materials, catalyst supports, porous polymer structures, and antibacterial PILs. The standard synthetic pathway for PILs relies on a basic strategy: (1) direct chain growth polymerization of IL with or without nonionic monomers; (2) step-growth polymerization of IL monomers;

Properties required as solid electrolytes include ionic conductivity, thermal stability, and electrochemical stability. The ionic conductivity of PILs is an important property when applied as

VPh and high ionic conductivity from large contents of [EMI][TFSI] over 60 wt%. The IL-CPs are thermally stable over 300°C and electrochemically stable over 7.0 V, since there are

VPh) embedded [EMI][TFSI] [5]. [EMI][TFSI] was selected for its high ionic

VPh was used for its ability to enhance electrochemical stability by hydro-

VPh and [EMI][TFSI]. We also introduced all-solid state SCs that

VPh in addition to maintaining a quasi-solid state.

] [84].

[BF4

of c-P4

proof despite of adopting [BMI][BF4

38 Supercapacitors - Theoretical and Practical Solutions

gen bonding between [EMI][TFSI] and c-P4

**3.2. Poly ionic liquid as solid electrolyte**

and (3) post-modification of polymer chains with IL monomers.

4-vninyphenol (c-P4

conductivity, and c-P4

hydrogen bonds between c-P4

**Figure 12.** Esthetic versatility and IoT applications of the inkjet-printed SCs as object-tailored/monolithically integrated power sources. (a) Photograph of the inkjet-printed Korea map, wherein the inkjet-printed SCs (marked by red boxes) were seamlessly connected to LED lamps (marked by blue boxes) via the inkjet-printed electric circuits. (b) SEM image of the LED lamp connected to the inkjet-printed electric circuits. (c) CV profile (scan rate = 1.0 mV s−1) of the inkjet-printed SC in the map. (d) Photograph of the inkjet-printed, letter ("OR")-shaped SCs that were seamlessly connected to the letter ("HOT" and "COLD")-shaped electric circuits onto A4 paper. (e) Galvanostatic charge/discharge profile (current density = 1.0 mA cm−2) of the inkjet-printed, letter ("OR")-shaped SCs that were composed of 4 cells connected in series. (f) Photograph depicting the operation of the blue LED lamp in the smart cup (for cold water (∼10°C)), wherein the inset is a photograph of a temperature sensor assembled with an Arduino board. (g) Photograph depicting the operation of the red LED lamp in the smart cup (for hot water (∼80°C)) [84].

(110°C). Flexible backbones yield lower Tg

resulting PIL exhibits a low Tg

30°C and ~10−3 S cm−1 at 90°C.

on PIL thermal stability [89]. [CF3

[C16H34PO4

− ]. values. Similarly, Hu et al. directly grafted TFSI

Ionic Liquid for High Voltage Supercapacitor http://dx.doi.org/10.5772/intechopen.73053

value (up to −14°C) and an average conductivity of 10−5 S cm−1 at

H4 SO3 − ] > [PF6

] > bromide >

41

anions onto the polyethylene oxide backbone via anionic ring-opening polymerization [88]. The

The thermal stability of the PILs is directly related to the lifetime and stability of the capacitor and chemical and electrochemical stability. In thermogravimetric analysis (TGA) experiments, the decomposition starting temperature (Tonset) is usually controlled through the nature of the PIL backbone chemical structure. Imidazolium-based PILs have improved thermal stability due to conjugate structure and steric hindrance. They have higher Tonset values than pyrrolidinium-based PILs. The thermal stability of PILs increases with the length of the substituent of the cation. The chemical structure of anions also affects the Tonset value of PILs. Poly (1-vinyl-3-ethyl-imazazolium) X-PIL was studied by comparing the effects of counter anions

] > [TFSI] > [C12H25C6

PIL-based polymer electrolytes have high ionic conductivity (up to 10−3 S cm−1 at 25°C), wide electrochemical windows (up to 5 V), and high thermal stability (up to 350°C) [86]. Pyrrolidinium-based PILs have been reported to have better electrochemical stability than imidazolium-based PILs. The pyrrolidinium cations also exhibit a much larger cathodic electrolysis potential than the quaternary ammonium cations of the noncyclic and unsaturated rings [90]. Because of excellent electrochemical stability and reasonable ionic conductivity in solid phase, PIL electrolytes have been considered as an ideal electrolyte for supercapacitors. However, only a few studies have been reported in this area by Marcilla group, and (Diallyldimethylammonium) bis (trifluoromethanesulfonyl) imide dissolved in [PYR14] was prepared and applied as a solid state electrolyte [91, 92]. Impregnating the electrode with the electrolyte before assembling the SCs is an important process for improving the carbonelectrolyte contact. However, these manufactured SCs high ESR values due to poor electrode/ electrolyte interface performance. Further studies using pyrrolidium-based PIL electrolytes with high ionic conductivity have greatly improved relative dielectric constant. **Figure 14**

In conclusion, ILs have tremendous potential in electrochemical systems with combination of cations and anion. However, their applicability has been limited by the general perception that they are ionic electrolytes for replacing conventional electrolytes. However, due to its high viscosity, low ionic conductivity, and high price, it is difficult to replace conventional electrolytes directly. In other words, ILs should not be chosen as an alternative to organic solvents. Therefore, it is considered that the ILs-based liquid electrolyte are used to enhance the energy density by increasing the high operating voltage of the SCs. They are also helpful to secure the stability and safety of SCs. In addition, since IL is stable at high temperatures, it can be applied to SCs that must be used under extreme conditions. In the same way, IL is more attractive as a solid electrolyte instead of a conventional electrolyte. In particular, IL-based solid polymer electrolytes appear to be one of the most promising choices for flexible SCs. However, current research on ILs as electrolytes has focused on several ILs, including imidazolium and pyrrolidinium cation. As mentioned, ILs have design flexibility due to the

SO3 −

shows the PILs structure and electrochemical characteristics.

**Figure 13.** (a) Chemical structure of IL-CPs, (b) LSV for EMITFSI and IL-CPs in the SUS/SUS cell (CR 2032), (c) flexibility of IL-CPs and bending performance of SCs with IL-CPs for 1000 cycles, and (d) photograph of a green light-emittingdiode (LED) powered by a single SC with IL-CP3.5. (IL-CPs: [EMI][TFSI]/c-P4 VPh composite, and IL-CPx: x = weight ratio of [EMI][TFSI]) [5].

a solid electrolyte. Unlike ILs and ion gels in which both anions and cations can move, PILs are typically single-ion conductors. In this case, anions or cations are structurally constrained as part of the polymer skeleton [86]. Therefore, the ionic conductivity of PIL is generally lower than that of monomeric ILs ionic conductivity. This phenomenon is due to the significant increment of glass transition temperature (Tg ) and depletion of mobile ions after covalent or ionic bonding [85]. The ionic conductivity of PIL is affected by polymer architecture, molecular weight, and chemical nature of polymer chains.

Particularly, the ionic conductivity of PIL is related to the glass transition temperature, and the ionic conductivity is usually increased when the Tg is low. PIL has weak binding ions and can exhibit low Tg despite having very high charge densities due to weak electrostatic ion pair interactions. Counter ions affect the Tg of these polymers. Therefore, a method of lowering the Tg using a different kind of anion has been proposed. Tang et al. found that anion tendency with poly 1-(p-Vinylbenzyl)-3-methyl-imidazolium cation, the Tg also changes in order [FSI] (3°C) < o-benzoicsulphimide (40°C) < [BF4 ] (78°C) < [PF6 ] (85°C) [87]. For PILs with the same anion [BF4 ], the Tg varied according to the backbone and Poly[(1-butylimidazolium-3)methylethylene oxide (33°C) < 1-[2-(Methacryloyloxy)ethyl]-3-butyl-imidazolium (54°C) < Poly[1- (p-Vinylbenzyl)-3-butyl-imidazolium (78°C) < poly 1-(p-Vinylbenzyl)-3-methyl-imidazolium (110°C). Flexible backbones yield lower Tg values. Similarly, Hu et al. directly grafted TFSI anions onto the polyethylene oxide backbone via anionic ring-opening polymerization [88]. The resulting PIL exhibits a low Tg value (up to −14°C) and an average conductivity of 10−5 S cm−1 at 30°C and ~10−3 S cm−1 at 90°C.

The thermal stability of the PILs is directly related to the lifetime and stability of the capacitor and chemical and electrochemical stability. In thermogravimetric analysis (TGA) experiments, the decomposition starting temperature (Tonset) is usually controlled through the nature of the PIL backbone chemical structure. Imidazolium-based PILs have improved thermal stability due to conjugate structure and steric hindrance. They have higher Tonset values than pyrrolidinium-based PILs. The thermal stability of PILs increases with the length of the substituent of the cation. The chemical structure of anions also affects the Tonset value of PILs. Poly (1-vinyl-3-ethyl-imazazolium) X-PIL was studied by comparing the effects of counter anions on PIL thermal stability [89]. [CF3 SO3 − ] > [TFSI] > [C12H25C6 H4 SO3 − ] > [PF6 ] > bromide > [C16H34PO4 − ].

PIL-based polymer electrolytes have high ionic conductivity (up to 10−3 S cm−1 at 25°C), wide electrochemical windows (up to 5 V), and high thermal stability (up to 350°C) [86]. Pyrrolidinium-based PILs have been reported to have better electrochemical stability than imidazolium-based PILs. The pyrrolidinium cations also exhibit a much larger cathodic electrolysis potential than the quaternary ammonium cations of the noncyclic and unsaturated rings [90]. Because of excellent electrochemical stability and reasonable ionic conductivity in solid phase, PIL electrolytes have been considered as an ideal electrolyte for supercapacitors. However, only a few studies have been reported in this area by Marcilla group, and (Diallyldimethylammonium) bis (trifluoromethanesulfonyl) imide dissolved in [PYR14] was prepared and applied as a solid state electrolyte [91, 92]. Impregnating the electrode with the electrolyte before assembling the SCs is an important process for improving the carbonelectrolyte contact. However, these manufactured SCs high ESR values due to poor electrode/ electrolyte interface performance. Further studies using pyrrolidium-based PIL electrolytes with high ionic conductivity have greatly improved relative dielectric constant. **Figure 14** shows the PILs structure and electrochemical characteristics.

a solid electrolyte. Unlike ILs and ion gels in which both anions and cations can move, PILs are typically single-ion conductors. In this case, anions or cations are structurally constrained as part of the polymer skeleton [86]. Therefore, the ionic conductivity of PIL is generally lower than that of monomeric ILs ionic conductivity. This phenomenon is due to the significant

**Figure 13.** (a) Chemical structure of IL-CPs, (b) LSV for EMITFSI and IL-CPs in the SUS/SUS cell (CR 2032), (c) flexibility of IL-CPs and bending performance of SCs with IL-CPs for 1000 cycles, and (d) photograph of a green light-emitting-

ionic bonding [85]. The ionic conductivity of PIL is affected by polymer architecture, molecu-

Particularly, the ionic conductivity of PIL is related to the glass transition temperature, and

using a different kind of anion has been proposed. Tang et al. found that anion tendency

] (78°C) < [PF6

ethylene oxide (33°C) < 1-[2-(Methacryloyloxy)ethyl]-3-butyl-imidazolium (54°C) < Poly[1- (p-Vinylbenzyl)-3-butyl-imidazolium (78°C) < poly 1-(p-Vinylbenzyl)-3-methyl-imidazolium

despite having very high charge densities due to weak electrostatic ion pair

varied according to the backbone and Poly[(1-butylimidazolium-3)methyl-

) and depletion of mobile ions after covalent or

of these polymers. Therefore, a method of lowering the

is low. PIL has weak binding ions and

VPh composite, and IL-CPx: x = weight

] (85°C) [87]. For PILs with the same

also changes in order [FSI]

increment of glass transition temperature (Tg

40 Supercapacitors - Theoretical and Practical Solutions

interactions. Counter ions affect the Tg

], the Tg

(3°C) < o-benzoicsulphimide (40°C) < [BF4

can exhibit low Tg

ratio of [EMI][TFSI]) [5].

Tg

anion [BF4

lar weight, and chemical nature of polymer chains.

the ionic conductivity is usually increased when the Tg

diode (LED) powered by a single SC with IL-CP3.5. (IL-CPs: [EMI][TFSI]/c-P4

with poly 1-(p-Vinylbenzyl)-3-methyl-imidazolium cation, the Tg

In conclusion, ILs have tremendous potential in electrochemical systems with combination of cations and anion. However, their applicability has been limited by the general perception that they are ionic electrolytes for replacing conventional electrolytes. However, due to its high viscosity, low ionic conductivity, and high price, it is difficult to replace conventional electrolytes directly. In other words, ILs should not be chosen as an alternative to organic solvents. Therefore, it is considered that the ILs-based liquid electrolyte are used to enhance the energy density by increasing the high operating voltage of the SCs. They are also helpful to secure the stability and safety of SCs. In addition, since IL is stable at high temperatures, it can be applied to SCs that must be used under extreme conditions. In the same way, IL is more attractive as a solid electrolyte instead of a conventional electrolyte. In particular, IL-based solid polymer electrolytes appear to be one of the most promising choices for flexible SCs. However, current research on ILs as electrolytes has focused on several ILs, including imidazolium and pyrrolidinium cation. As mentioned, ILs have design flexibility due to the

numerous possible combinations of anions and cations. We believe this flexibility should be achieved by designing a new type of supercapacitor by thinking outside the box beyond what

Ionic Liquid for High Voltage Supercapacitor http://dx.doi.org/10.5772/intechopen.73053 43

Program in Nano Science and Technology, Graduate School of Convergence Science and

[1] Zhang F, Zhang T, Yang X, Zhang L, Leng K, Huang Y, Chen Y. A high-performance supercapacitor-battery hybrid energy storage device based on graphene-enhanced electrode materials with ultrahigh energy density. Energy & Environmental Science. 2013;

[2] Mahlia TMI, Saktisahdan TJ, Jannifar A, Hasan MH, Matseelar HSC. A review of available methods and development on energy storage; technology update. Renewable and

[3] Hannan MA, Hoque MM, Mohamed A, Ayob A. Review of energy storage systems for electric vehicle applications: Issues and challenges. Renewable and Sustainable Energy

[4] Zhang Z, Zhang X, Chen W, Rasim Y, Salman W, Pan H, Yuan Y, Wang C. A high-efficiency energy regenerative shock absorber using supercapacitors for renewable energy applications in range extended electric vehicle. Applied Energy. 2016;**178**:177-188.  All solid state flexible supercapacitors operating at 4 V with a cross-linked polymer–ionic liquid electrolyte. Journal of Materials Chemistry A. 2016;**4**:4386-4391. DOI: 10.1039/C6TA

[6] Béguin F, Presser V, Balducci A, Frackowiak E. Carbons and electrolytes for advanced supercapacitors. Advanced Materials. 2014;**26**:2219-2251. DOI: 10.1002/adma.201304137

[7] Senthilkumar ST, Selvan RK, Melo JS. Redox additive/active electrolytes: A novel approach to enhance the performance of supercapacitors. Journal of Materials Chemistry

Sustainable Energy Reviews. 2014;**33**:532-545. DOI: 10.1016/j.rser.2014.01.068

is available.

**Author details**

Address all correspondence to<EMAIL_ADDRESS>
**6**:1623-1632. DOI: 10.1039/C3EE40509E

10.1016/j.apenergy.2016.06.054

00643D

Technology, Seoul National University, Seoul, Republic of Korea

Reviews. 2017;**69**:771-789. DOI: 10.1016/j.rser.2016.11.171

A. 2013;**1**:12386-12394. DOI: 10.1039/C3TA11959A

Jeeyoung Yoo

**References**

**Figure 14.** Charge–discharge characterization of all-solid state supercapacitors with different impregnation ratios. (a) Charge–discharge profiles from 0 to 3.5 V at 1 mAcm−2, (b) equivalent series resistance (ESR), (c) specific capacitance (Cam), (d) specific real energy (Ereal) from charge–discharge profiles at different current densities and (e) schematic representation of all-solid state supercapacitors. (IL-b-PE: Ionic liquid based polymer electrolyte).

numerous possible combinations of anions and cations. We believe this flexibility should be achieved by designing a new type of supercapacitor by thinking outside the box beyond what is available.


**3.2. Numerical simulations**

The validation of the digital attitude controller was carried through a scheme of co-simulation, where a computer performs the simulation of the satellite's motion, in MATLAB/Simulink, using models of attitude kinematics and dynamics, and a Blackfin 537 DSP device (installed on ADSP-BF537 kit, Analog Devices) plays the digital LQG controller processing, and also the PWPF modulator [7].

The interface with the computer uses the Real-Time Workshop tool, through the Embedded IDE link, as shown in the Fig. 3.

The validation tests comprise two distinct scenarios. In the first one, the tests consider the same case studied in the precedent sections, i.e. the three axes attitude stabilization. In the second scenario, the attitude control is aimed to perform a maneuver to achieve a new orientation, i.e. a task of attitude tracking.

The co-simulation scheme is based on the computer communication with the DSP (cf. Fig. 4), which is facilitated by Simulink tool, which allows integration of several external processors, including the BF537, by creating a block *Processor-In-the-Loop* (PIL) in the simulation diagram. This communication is made possible through the interaction of the Simulink with the BF537 development environment, the Visual DSP ++ (Fig. 5).

**Figure 4.** Co-simulation scheme: the DSP processes the LQG controller and the PWPF modulator, and computer simu‐

Processor-in-the-Loop Simulations Applied to the Design and Evaluation of a Satellite Attitude Control

http://dx.doi.org/10.5772/57219

167

**Figure 3.** The PIL interface screen of the Real-Time Workshop (MATLAB/Simulink).

lates the motion of the satellite attitude.

Processor-in-the-Loop Simulations Applied to the Design and Evaluation of a Satellite Attitude Control http://dx.doi.org/10.5772/57219 167

**Figure 3.** The PIL interface screen of the Real-Time Workshop (MATLAB/Simulink).

**Figure 2.** Scheme of the discret LQG controller.

The validation of the digital attitude controller was carried through a scheme of co-simulation, where a computer performs the simulation of the satellite's motion, in MATLAB/Simulink, using models of attitude kinematics and dynamics, and a Blackfin 537 DSP device (installed on ADSP-BF537 kit, Analog Devices) plays the digital LQG controller processing, and also the

The interface with the computer uses the Real-Time Workshop tool, through the Embedded

The validation tests comprise two distinct scenarios. In the first one, the tests consider the same case studied in the precedent sections, i.e. the three axes attitude stabilization. In the second scenario, the attitude control is aimed to perform a maneuver to achieve a new orientation, i.e.

The co-simulation scheme is based on the computer communication with the DSP (cf. Fig. 4), which is facilitated by Simulink tool, which allows integration of several external processors, including the BF537, by creating a block *Processor-In-the-Loop* (PIL) in the simulation diagram. This communication is made possible through the interaction of the Simulink with the BF537

**3.2. Numerical simulations**

166 Computational and Numerical Simulations

PWPF modulator [7].

IDE link, as shown in the Fig. 3.

a task of attitude tracking.

development environment, the Visual DSP ++ (Fig. 5).

**Figure 4.** Co-simulation scheme: the DSP processes the LQG controller and the PWPF modulator, and computer simu‐ lates the motion of the satellite attitude.

**Figure 5.** The session opening in Visual DSP++ environment.

The block PIL is inserted in the block diagram developed in the Simulink environment. It is responsible for the communication with the DSP, i.e. in charge of sending the information of the satellite attitude and of receiving the commands related to the control action, i.e. the gas jets driving from the PWPF modulator.

Figure 6 shows the results for the three Euler angles, of the validation tests for the case of threeaxis stabilization scheme using co-simulation. The considered initial deviation is 10 degrees for each one of the three Euler angles, as in the case of the previous simulations.

The differences are smaller than 0.1 degree for the three angles. However, we cannot conclude about the better precision scenario. Both simulations met the accuracy specifications, never‐ theless the simulation of continuous-time system lacks of realism for an experimental appli‐ cation. In fact, the small difference between the two cases shows only that the co-simulation scheme works very similarly to the idealized case, which may suggest an optimistic outcome

Processor-in-the-Loop Simulations Applied to the Design and Evaluation of a Satellite Attitude Control

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169

In a second test case, the satellite is commanded to change its attitude, initially with three angles (roll, pitch, and yaw) at the same value of 10°, for a new attitude defined by the values

in relation to the expectations of an experimental application.

**Figure 6.** Co-simulation results of attitude control using a DSP (for ϕ, θ, ψ, in degrees).

A comparative analysis of the obtained results in the case of continuous LQG controller (in a simulation made only in MATLAB/ Simulink environment), and those obtained in the scheme of co-simulation (Fig. 6), can be made from a plot of the results differences. This differences plot is shown in Fig. 7.

**Figure 6.** Co-simulation results of attitude control using a DSP (for ϕ, θ, ψ, in degrees).

**Figure 5.** The session opening in Visual DSP++ environment.

jets driving from the PWPF modulator.

168 Computational and Numerical Simulations

plot is shown in Fig. 7.

The block PIL is inserted in the block diagram developed in the Simulink environment. It is responsible for the communication with the DSP, i.e. in charge of sending the information of the satellite attitude and of receiving the commands related to the control action, i.e. the gas

Figure 6 shows the results for the three Euler angles, of the validation tests for the case of threeaxis stabilization scheme using co-simulation. The considered initial deviation is 10 degrees

A comparative analysis of the obtained results in the case of continuous LQG controller (in a simulation made only in MATLAB/ Simulink environment), and those obtained in the scheme of co-simulation (Fig. 6), can be made from a plot of the results differences. This differences

for each one of the three Euler angles, as in the case of the previous simulations.

The differences are smaller than 0.1 degree for the three angles. However, we cannot conclude about the better precision scenario. Both simulations met the accuracy specifications, never‐ theless the simulation of continuous-time system lacks of realism for an experimental appli‐ cation. In fact, the small difference between the two cases shows only that the co-simulation scheme works very similarly to the idealized case, which may suggest an optimistic outcome in relation to the expectations of an experimental application.

In a second test case, the satellite is commanded to change its attitude, initially with three angles (roll, pitch, and yaw) at the same value of 10°, for a new attitude defined by the values

angular velocities. It shows that the adopted controller achieves adequate performance even with this difference between models, and it presents interesting features of robustness.

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171

**Figure 8.** Co-simulation results of attitude control for the three Euler's angles, considering a tracking maneuver.

In terms of adopted sampling time, it was observed that the simulation in MATLAB/ Simulink waits the DSP processing to continue the calculations, preventing it from some problem related to the interval between two controller processing and actuation. However, there is a DSP development platform tool that allows the measurement of processing time and data traffic.

**Figure 7.** Difference between the simulation results of the continuous controller and co-simulation of digital control (for ϕ, θ, ψ, in degrees).

50, 60 and 45°, respectively. The results are shown in Fig. 8. It was observed that the controller performs satisfactorily its task, with tracking maneuver time of about 45 seconds. An important remark: the gap angles between initial and final attitudes are relatively large for the considered approximations in the synthesis of LQG control law. In the controller design, we adopted a linearized model for small angle values, whereas in the simulation of the motion of the satellite attitude we used nonlinear models of kinematics and dynamics. These models, in the case of large angles, exhibit very different behaviors of the linearized model, especially for higher

angular velocities. It shows that the adopted controller achieves adequate performance even with this difference between models, and it presents interesting features of robustness.

**Figure 8.** Co-simulation results of attitude control for the three Euler's angles, considering a tracking maneuver.

50, 60 and 45°, respectively. The results are shown in Fig. 8. It was observed that the controller performs satisfactorily its task, with tracking maneuver time of about 45 seconds. An important remark: the gap angles between initial and final attitudes are relatively large for the considered approximations in the synthesis of LQG control law. In the controller design, we adopted a linearized model for small angle values, whereas in the simulation of the motion of the satellite attitude we used nonlinear models of kinematics and dynamics. These models, in the case of large angles, exhibit very different behaviors of the linearized model, especially for higher

**Figure 7.** Difference between the simulation results of the continuous controller and co-simulation of digital control

(for ϕ, θ, ψ, in degrees).

170 Computational and Numerical Simulations

In terms of adopted sampling time, it was observed that the simulation in MATLAB/ Simulink waits the DSP processing to continue the calculations, preventing it from some problem related to the interval between two controller processing and actuation. However, there is a DSP development platform tool that allows the measurement of processing time and data traffic. Consequently, it is possible to verify if the DSP processing time remains inferior to the maximum time period provided for sampling (10ms in this study). This tool is the *Cycle Counter*, which considers the frequency of the DSP core, 500MHz. The obtained result was processing and traffic time, much smaller than the time available due to the sampling period. It's possible to conclude that there are no problems in this application related to the aspect of the controller discretization and the use of a digital processor to perform the function of controlling and modulating the actuators.

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