Page 197 - Read Online

Page 8 of 23 Yang et al. Energy Mater 2024;4:400061 https://dx.doi.org/10.20517/energymater.2023.144

(2) Overdischarge test

The thermal effect of overdischarge, when compared with overcharge, is relatively less severe; however, it
can lead to catastrophic outcomes for the battery, especially in cases of high-current or repeated
overdischarge, which can significantly affect the battery. To assess the battery’s response, it was fully
charged at a rate of 1 C, followed by a 1 C discharge for 90 min per GB 38031-2020. The battery was then
observed for an additional hour, during which there were no incidents of explosion, fire, or leakage,
indicating the successful passing of the test.

Thermal abuse
During use, batteries are often subjected to elevated temperatures due to factors such as high contact
resistance, inadequate heat dissipation, accidental heating, or extreme climatic conditions. As the external
temperature increases, the internal temperature of the battery also rises. If the internal temperature reaches
a critical threshold, the battery’s diaphragm may melt and rupture, or exothermic reactions inside the
battery may further elevate the temperature, potentially leading to safety hazards. This chain of events
underscores the critical importance of managing heat within battery systems to ensure safe and reliable
[65]
operation .

(1) Heating test

To evaluate the safety performance of a battery under high-temperature conditions, a heating test is
conducted. According to the national standard GB 38031-2020, this process involves placing a fully charged
battery in a temperature chamber and gradually heating it from room temperature to 130 °C at a fixed rate.
Subsequently, the battery is maintained at this temperature for 30 min to assess its reaction - whether it
explodes or catches fire. This test aims to simulate the high-temperature situation that the battery may
encounter during usage and ascertain its safety under such conditions.

Experience is the teacher of action, and understanding the thermal runaway mechanism of LMBs can help
people deepen their understanding of thermal runaway. At the same time, understanding the safety
characteristics of LMBs is an important part of leading research into electrolytes to prevent thermal
runaway. Through in-depth study of these mechanisms and characteristics, people have begun to actively
explore flame-retardant GPEs with excellent thermal safety, and these new GPEs will be introduced one by
one below.

FLAME-RETARDANT GPES
The core components of GPEs typically include a polymer backbone, a liquid phase plasticizer, and a
lithium salt. The polymer backbone, serving as the foundation, features a molecular structure characterized
by a cross-linked network design. This structure plays a crucial role in enabling the full absorption of the
plasticizer, resulting in the GPEs adopting a gel state with exceptional mechanical properties. Plasticizers
and lithium salts are integral to GPEs, often referred to as the vital components that partially address the
weaknesses of solid polymer electrolytes by enhancing ionic conductivity and overall battery performance.
To enhance the safety features of GPEs, a common approach involves incorporating flame retardants into
plasticizers or directly integrating flame-retardant groups into the polymer backbone. This modification
aims to bolster the thermal stability of GPEs. Subsequently, we will expound on the various types of these
flame-retardant groups and their respective functions.