Lithium-ion batteries (LIBs) have been widely used in new energy technologies. However, external factors such as pressure, vibration, temperature, overcharging, and discharging can significantly affect the internal electrochemical behavior of LIBs, which may lead to serious accidents such as flames, explosions, and the release of large amounts of toxic gases. In order to reduce safety risks and economic losses, it is necessary to implement early screening and warning strategies for abnormal faults in lithium-ion batteries.
The global electric vehicle safety regulations require electric vehicles to issue a warning to passengers at least five minutes before a serious accident occurs. Trace amounts of electrolyte vapor leakage is considered as early symptoms of lithium battery damage, and therefore can be monitored through volatile organic compounds (VOCs) sensors. Compared with temperature, voltage, and current measurement devices, they can issue battery failure alarms earlier, achieving "rapid warning". However, early gas leaks in lithium batteries usually only reach the ppm (parts per million) level, making trace VOCs detection difficult.
In a new paper published in Light: Advanced Manufacturing, a team of scientists, led by Professor Qizhen Sun and Dr. Hao Li from School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei, China, have proposed a micro-nano fiber (MNF) sensor with a "gas sensitive coating" (MNFs*ZIF). They modified the MNF with ZIF-8 (zeolitic imidazolate framework-8) film as a "coating" to enhance the absorption performance of VOCs in the electrolyte. Combined with the high evanescent, efficient coupling conversion of gas-light was achieved, and then high-sensitivity detection of electrolyte vapor leakage in LIB was achieved through refractive index sensing. Compared to gas sensors such as quartz crystal microbalances, electrochemistry, thermal conductivity, and metal oxide semiconductors, the MNFs*ZIF proposed has unique advantages such as high sensitivity, anti-electromagnetic interference, and extreme environmental resistance, making it more suitable for safe in-situ online monitoring of LIBs.
They designed and tested MNFS * ZIF in three steps:
(1) Comprehensively analyzed the regulation mechanism of gas sensitivity by the diameter of MNFs and the thickness of ZIF-8 films, studied the modulation effect of film thickness on transmission spectra, selected 7 μm diameter MNFs that are close to the maximum sensitivity and have good robustness as the substrate, and modified a 500nm thick ZIF-8 film that has both high sensitivity and high extinction ratio spectral modulation effects.
(2) Established a CCD assisted tapering system with improved flame stability to prepare MNFs. Designed a four period in-situ self-assembly scheme for ZIF-8 in methanol solvent. Through hydrogen bonding molecular interactions and optimized crystallization process, ZIF-8 in-situ crystals were grown on the surface of MNFs to form a "gas sensitive coating".
(3) Verified the ability of the sensor for common volatile gases in lithium batteries, such as diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), and propylene carbonate (PC). Through wavelength demodulation, the MNFs*ZIF has a high sensitivity of 43.6 pm/ppm in the ppm range. The theoretical detection limit for DMC gas detection is 2.65 ppm, and its excellent reversibility and repeatability have been experimentally verified.
"When MNF*ZIF detects the concentration of organic gases leaked from LIBs, the wavelength of the transmission interference peak immediately shows a rapid wavelength red shift in the leakage, and the wavelength of the interference peak shows an exponential growth trend. Meanwhile, it achieves early warning 35 hours before battery load stop. MNF * ZIF shows quick response to organic vapors in the electrolyte, enabling it to quickly measure battery damage and failure events, providing protection for the safety of LIBs." they added.
"The presented technique can find applications in various energy health monitoring fields, such as in the comprehensive management system of electric vehicle batteries. Through trace gas detection, it can provide early warning of hazardous factors such as battery leakage, avoid serious accidents such as battery explosions and fires, and has promising application prospects." the scientists forecast.
