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Light Adv. Manuf. | "Gas-sensitive" micro-nano optical fibers "safeguard" lithium batteries

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I. Lithium Battery Safety

Lithium-ion batteries (LIBs) have been widely used in new energy technologies, especially dominating the portable electronic products and electric vehicle markets. However, in most application scenarios, external factors such as pressure, vibration, temperature, overcharging, and discharging significantly affect the internal electrochemical behavior of lithium-ion batteries, which may lead to potential hazards such as thermal runaway (TR), and even cause serious accidents such as flames, explosions, and the release of a large amount of toxic gases. In order to reduce safety risks and economic losses,early screening and warning strategies for abnormal faults in lithium-ion batteries must be implemented to "protect" lithium batteries.

In order to monitor the safety status of lithium batteries, people detect parameters such as strain, temperature, gas concentration, and electrical characteristics at different stages of the battery. Global electric vehicle safety regulations require electric vehicles to issue warnings to passengers at least five minutes before a serious accident occurs. Lithium battery electrolytes usually use volatile carbonate organic solvents,and trace amounts of electrolyte vapor leakage can be regarded as an early symptom of lithium battery damage, so it can be monitored by volatile organic compound (VOC) sensors.VOC gas sensors can detect signals related to battery faults seven minutes before thermal failure,which can issue battery fault alarms earlier than temperature, voltage, and current measurement devices, achieving "rapid early warning" of lithium battery faults at room temperature.However, early gas leakage from lithium batteries usually only reaches the ppm (parts per million) level,making the detection of trace VOCs a challenge.

II. "Gas-Sensitive" Micro-nano Optical Fiber

Recently, Huazhong University of Science and TechnologyDr. Li HaoandProfessor Sun Qizhenteamproposed a micro-nano optical fiber sensor with a "gas-sensitive coat"，as shown in Figure 1. The team modified micro-nano optical fibers (MNFs*ZIF) with a ZIF-8 (zeolitic imidazolate framework-8) film as a "coat" to enhance the absorption performance of volatile organic gases in the electrolyte, and combined with the high evanescent field optical sensing characteristics of micro-nano optical fibers to achievehigh-efficiency "gas-light" coupling conversion，and then achieve high-sensitivity detection of lithium battery electrolyte vapor leakage through refractive index sensing. Compared with quartz crystal microbalances, electrochemical, thermal conductivity, and metal oxide semiconductor gas sensors, the MNFs*ZIF proposed by the team has unique advantages such as high sensitivity, anti-electromagnetic interference, and resistance to extreme environments, making it more suitable for in-situ online monitoring of lithium-ion battery safety.

The results were published inEarly detection of lithium battery leakage using a highly sensitive in situ ZIF-8 membrane-coated micro-nano optical fibrepublished inLight: Advanced Manufacturingjournal.

Figure 1 (cover image): Working principle of "gas-sensitive" micro-nano optical fiber sensor

Micro-nano optical fibers (MNFs) are a special type of optical waveguide formed by melting and tapering ordinary optical fibers. The waist diameter is only at the micron and nano scale, and it has a very high evanescent field. Compared with other fiber optic sensors, thanks to the high evanescent field characteristics, it is easier to achieve high-sensitivity perception of changes in the refractive index of the external environment.However, the ppm-level VOC concentration produced by lithium batteries has a very weak modulation of the refractive index of the air near the MNFs surface, making it difficult to directly monitor the gas in real time.In this paper, the scholars proposed to modify and sensitize it with a ZIF-8 flexible material film. ZIF-8 has high stability, hydrophobicity, a highly regular pore structure, adjustable pore size and cage size, and excellent adsorption performance for volatile organic compound gases, increasing the VOC concentration on the surface of the micro-nano optical fiber by several orders of magnitude.

In order to obtain the highest possible sensitivity and comprehensively consider the actual preparation control accuracy of the optical fiber, the scholars in this paper, through theoretical modeling,comprehensively analyzed the control mechanism of the micro-nano optical fiber diameter and ZIF-8 film thickness on gas sensitivity, and studied the modulation effect of film thickness on the transmission spectrum.After comprehensively considering factors such as robustness, sensitivity, and accuracy, 7μm diameter MNFs, which are close to the maximum sensitivity and have good robustness, were selected as the substrate, and a 500nm thick ZIF-8 film with both high sensitivity and high extinction ratio spectral modulation was modified. Scholars have builta CCD-assisted tapering system with improved flame stability，mechanically drawn by an electric displacement platform, hydrogen-oxygen flame melting and taperingto realize the preparation of micro-nano optical fibers;designed a four-cycle in-situ self-assembly scheme of ZIF-8 in methanol solvent，through hydrogen bond molecular interaction,the optimized crystallization process enables ZIF-8 to in-situ crystallize and grow on the surface of the micro-nano optical fiber to form a "gas-sensitive coat"，realizing the preparation of the sensor. The detection ability of the sensor for common volatile gases in lithium batteries, diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), and propylene carbonate (PC), was verified. Through wavelength demodulation, the MNFs*ZIF sensor has a high sensitivity of43.6 pm/ppmin the ppm range, and the theoretical detection limit for DMC gas detection is2.65 ppm，and the experiment verified its excellent reversibility and repeatability.

Figure 2: VOCs sensing performance of MNFs*ZIF (a) Repeatability; (b) Sensitivity; (c) Response time; (d) Detection of common electrolyte components

Three, "Safeguarding" Lithium Batteries

Using the above-mentioned "gas-sensitive" micro-nano optical fiber sensor, early online safety monitoring of lithium battery leakage has been further realized. Experiments have shown that the method of judging whether a lithium battery is faulty by observing whether the external load of the lithium battery can work normally needs to wait at least 34 h after the battery is damaged before the existence of a lithium battery fault can be discovered. However, under the method of detecting the concentration of organic gases leaked from the lithium battery by the MNFs*ZIF gas sensor, the transmission interference peak wavelength of the MNFs*ZIF sensor immediately shows a rapid redshift when leakage occurs, and the redshift rate gradually increases. The interference peak wavelength shows an exponential growth trend,This indicates that the rapid response of the MNFs*ZIF sensor to organic vapors of the electrolyte enables the MNFs*ZIF sensor to quickly measure the occurrence of battery damage failure and immediately issue a warning, "safeguarding" the safety of lithium batteries.

Figure 3: Lithium battery leakage safety monitoring (a) Schematic diagram of electrolyte leakage detection; (b) Output voltage vs. time curve; (c) Wavelength drift vs. time curve

Summary and Outlook

With the excellent sensing characteristics of high sensitivity, reversibility and rapid response of this sensor, it can find Applications in many energy health monitoring fields. For example, it can be used in the Battery Management System (BMS) of electric vehicles. Through trace gas detection, it can pre-warn dangerous factors such as battery leakage, preventing serious accidents such as battery explosion and fire, which has promising Applications!

Paper Information

Sheng Shunfeng, Li Hao, Zhang Yi, Li Liangye, Xiao Kai, Huang Xiukang, Liu Yunfei, Xu Wangyang, Li Zhen, Yan Lison, Yan Zhijun, Huang Yunhui, Sun Qizhen. Early detection of lithium battery leakage using a high-sensitivity in-situ ZIF-8 membrane-coated micro-nano fiber [J]. Light: Advanced Manufacturing 6, 14 (2025).

https://doi.org/10.37188/lam.2025.014