China University of Science and Technology has made progress in in-situ monitoring of thermal runaway in lithium-ion batteries with optical fibers

Recently, the team of Professor Sun Jinhua and researcher Wang Qingsong of the University of Science and Technology of China and the team of Professor Guo Tuan of Jinan University have made important achievements in the field of early warning of thermal runaway optical fiber detection of lithium-ion batteries. 

A high-precision, multi-mode integrated fiber optic device that can be implanted inside the battery has been successfully developed, and it has taken the lead in realizing accurate analysis and early warning of the whole process of thermal runaway of commercial lithium batteries. The relevant research results are entitled "Operando monitoring of thermal runaway in commercial lithium-ion cells via advanced lab-on-fiber. technologies, "was published online August 29 in the journal Nature Communications

With the emergence of the global energy crisis, and driven by the "double carbon" goal, lithium-ion batteries have been booming, but the battery thermal runaway has been hailed as a "cancer" that threatens battery safety, and is the core bottleneck that restricts the large-scale development of electric vehicles and new energy storage. 

Therefore, it is urgent to deeply understand the evolution mechanism of thermal runaway of lithium-ion batteries, and put forward early warning strategies to prevent fire and explosion accidents. The root cause of the thermal runaway of the battery is a series of complex and interrelated "chain side reactions" inside the battery. 

The most representative chain reactions include: external electrical, thermal, and mechanical abuse → internal heat production →SEI film decomposition → negative reaction with electrolyte, gas production → diaphragm melting → internal short circuit → safety valve opening → positive reaction with electrolyte, gas production → electrolyte decomposition, gas production → electrolyte, gas combustion → fire explosion! From local short circuit to large area short circuit, the internal temperature of the battery increases rapidly, which can be as high as 800 ° C or more, causing the battery to burst into flames.

It can be seen that "tracing the internal inducement of the occurrence of battery thermal runaway, clarifying the coupling relationship between each step reaction, revealing the leading mechanism and dynamic law of thermal runaway, and advancing the warning time window of thermal runaway" is the core of fundamentally solving the energy storage safety problem. 

However, due to the closed structure of the battery and the complex reaction mechanism inside, the accuracy and real-time detection of the core state parameters inside the battery cannot be guaranteed. The recently reported scientific instruments with "perspective" detection capabilities (such as neutron diffraction, X-ray diffraction, cryopreservation electron microscopy, etc.) cannot be applied to battery terminals due to their large volume and high price. How to predict battery safety hazards scientifically, timely and accurately has become an international scientific problem in the field of battery safety.

In order to overcome this problem, the team proposed a multi-mode integrated optical fiber in-situ monitoring technology that can be implanted inside the battery, and took the lead in the world to achieve accurate analysis and early warning of the entire process of thermal runaway of commercial lithium batteries. 

The joint team designed and successfully developed a multi-mode integrated fiber optic sensor that can work normally under high temperature and high pressure environment of 1000℃, realized synchronous and accurate measurement of internal temperature and pressure in the whole process of battery thermal runaway, overcome the problem of mutual crosstalk between temperature and pressure signals in extreme thermal runaway environment, and proposed a new method to decouple battery heat production and pressure change rate. 

For the first time, the characteristic inflection points and common rules that trigger the thermal runaway chain reaction of the battery were found, which realized the accurate identification of the microscopic "irreversible reaction" inside the battery, and provided an important means for quickly cutting off the thermal runaway chain reaction of the battery and ensuring the operation of the battery in the safe range.

FIG. Internal characteristics of in-situ optical fiber monitoring battery thermal runaway and establishment of early warning interval

In the future, fiber optic sensors, due to their small size, flexible shape, resistance to electrical interference and remote operation, are suitable for standard manufacturing techniques for mass production, and can enable a single fiber to simultaneously monitor several key parameters such as temperature, pressure, refractive index, gas composition and ion concentration in multiple locations of the battery. The combination of optical fiber sensing technology and batteries will play an important role in the fields of new energy vehicles and energy storage power station safety detection.

Wang Qingsong, a researcher at the University of Science and Technology of China, and Guo Tuan, a professor at Jinan University, are co-corresponding authors of the paper. Mei Wenxin, a postdoctoral fellow at the University of Science and Technology of China, and Liu Zhi, a master's candidate at Jinan University, are co-first authors of the paper. The work was carried out in collaboration with the University of Science and Technology of China, Jinan University, the National Research Council of Canada, the Hong Kong Polytechnic University and Carleton University.

This research work has been supported by the National Natural Science Foundation of China, the Youth Innovation Promotion Association of the Chinese Academy of Sciences, the Leading Talents of Science and Technology Innovation under the Special Support Program of Guangdong Province, and the National Bo Xin Program.

Source: Chinese Optical Journal Network