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Page 18 of 23 Yang et al. Energy Mater 2024;4:400061 https://dx.doi.org/10.20517/energymater.2023.144

CONCLUSION AND OUTLOOK
To ensure the safety of LMBs, the strategy of introducing flame retardants into LEs or replacing
conventional solvents with flame retardants has been proposed. However, this measure did not solve the
inherent problem of LEs being prone to leakage. Subsequently, SSEs with non-leakage susceptibility and
high mechanical strength have been proposed; nevertheless, their poor interfacial compatibility and low ion
transport efficiency pose challenges in practical applications. In an attempt to compensate for these
shortcomings, GPEs, which combine the advantages of both LEs and SSEs, have emerged. Figure 7
summarizes the key properties of the various electrolytes. GPEs offer non-leakage properties that reduce
safety risks, while internal plasticizers address the interfacial compatibility issues of SSEs. However, the
highly flammable LE in GPEs still presents a potential safety hazard. Efforts have been made to improve the
safety of GPEs by developing nonflammable GPEs. The approaches include incorporating flame retardants
into plasticizers or using flame retardants and grafting flame-retardant groups onto the polymer backbone.
Combining these two approaches can lead to safer and more reliable GPEs. This review first provides a brief
analysis of the mechanism of thermal runaway in LMBs and then introduces the characterization methods
for assessing the thermal safety of batteries. Finally, it presents a categorization of various GPEs and their
synthesis methods and provides suggestions for improving the safety of LMBs by combining different
moieties. Despite the innovative results in secure GPEs and LMBs, comprehensive research is still needed to
address the following aspects and realize truly secure and reliable GPEs and LMBs.

(1) The first prerequisite for solving the thermal runaway problem of LMBs is a thorough understanding of
the evolution of this phenomenon. However, the existing research on the thermal runaway process of LMBs
has yet to achieve the necessary depth. This deficiency can be attributed to the unique anode structure of
LMBs, which results in a thermal runaway process different from that of LIBs. Therefore, it is essential to
emphasize the need for thoroughly examining the thermal runaway process of LMBs, with a specific focus
on the potential impact of dead Li generated by the anode during the cycling process. This aspect requires
more detailed exploration and elucidation. Only by gaining a comprehensive understanding of these crucial
processes can we effectively address the thermal runaway problem and furnish robust support for
enhancing the reliability and performance of LMBs.

(2) Improving the temperature adaptability of GPEs is crucial for ensuring consistent and reliable
performance across a wide temperature range. GPEs face challenges under extreme conditions as specific
components may volatilize at high temperatures, leading to electrolyte failure, while at low temperatures,
they may solidify, impeding effective ion transport. Currently, there is a lack of comprehensive studies on
GPEs that operate optimally in varying temperatures. Therefore, research focused on enhancing the
temperature adaptability of GPEs is of utmost importance for their viability in LMBs under diverse
environmental conditions. It is essential to address this issue to ensure the efficient and reliable
performance of LMBs, even under extreme temperatures.

(3) At present, safe GPEs still exhibit certain disadvantages in terms of ionic conductivity when compared to
LEs. Despite significant advancements in research, most results remain comparable to those of LEs or show
only marginal differences in ionic conductivity. Therefore, there is a pressing need for future research to
overcome the current limitations in ionic conductivity and develop GPEs that significantly surpass the
performance of LEs. Simultaneously, it is imperative for such innovations to prioritize safety considerations
and maintain the overall reliability of the battery system.

(4) To comprehensively explore the performance and thermal runaway mechanism of LMBs, advanced
characterization techniques need to be introduced to enable nondestructive observation of the internal