Batteries play a
critical role in achieving zero-emission
goals
and in the transition toward a more circular economy. Ensuring battery
safety is a top priority for manufacturers and consumers alike, and
hence is an active topic of research. Metal-oxide nanostructures have
unique properties that make them highly promising for gas sensing
in battery safety applications. In this study, we investigate the
gas-sensing capabilities of semiconducting metal oxides for detecting
vapors produced by common battery components, such as solvents, salts,
or their degassing products. Our main objective is to develop sensors
capable of early detection of common vapors produced by malfunctioning
batteries to prevent explosions and further safety hazards. Typical
electrolyte components and degassing products for the Li-ion, Li–S,
or solid-state batteries that were investigated in this study include
1,3-dioxololane (C3H6O2—DOL),
1,2-dimethoxyethane (C4H10O2—DME),
ethylene carbonate (C3H4O3—EC),
dimethyl carbonate (C4H10O2—DMC),
lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium nitrate
(LiNO3) salts in a mixture of DOL and DME, lithium hexafluorophosphate
(LiPF6), nitrogen dioxide (NO2), and phosphorous
pentafluoride (PF5). Our sensing platform was based on
ternary and binary heterostructures consisting of TiO2(111)/CuO(1̅11)/Cu2O(111) and CuO(1̅11)/Cu2O(111), respectively,
with various CuO layer thicknesses (10, 30, and 50 nm). We have analyzed
these structures using scanning electron microscopy (SEM), energy-dispersive
X-ray spectroscopy (EDX), micro-Raman spectroscopy, and ultraviolet–visible
(UV–vis) spectroscopy. We found that the sensors reliably detected
DME C4H10O2vapors up to a concentration
of 1000 ppm with a gas response of 136%, and concentrations as low
as 1, 5, and 10 ppm with response values of approximately 7, 23, and
30%, respectively. Our devices can serve as 2-in-1 sensors, functioning
as a temperature sensor at low operating temperatures and as a gas
sensor at temperatures above 200 °C. Density functional theory
calculations were also employed to study the adsorption of the vapors
produced by battery solvents or their degassing products, as well
as water, to investigate the impact of humidity. PF5and
C4H10O2showed the most exothermic
molecular interactions, which are consistent with our gas response
investigations. Our results indicate that humidity does not impact
the performance of the sensors, which is crucial for the early detection
of thermal runaway under harsh conditions in Li-ion batteries. We
show that our semiconducting metal-oxide sensors can detect the vapors
produced by battery solvents and degassing products with high accuracy
and can serve as high-performance battery safety sensors to prevent
explosions in malfunctioning Li-ion batteries. Despite the fact that
the sensors work independently of the type of battery, the work presented
here is of particular interest for the monitoring of solid-state batteries,
since DOL is a solvent typically used in this type of batteries.