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Page 16 of 23 Yang et al. Energy Mater 2024;4:400061 https://dx.doi.org/10.20517/energymater.2023.144

compatibility. Taking the v-NBR/TAC/IL-assembled Li||LFP battery as an example, the capacity retention
rate is still close to 89% after 250 cycles at 0.5 C in the cycling test, whereas the battery without TAC showed
significant capacity degradation after about 25 cycles, confirming the superior cycling stability of the v-
NBR/TAC/IL system. Moreover, Li||LFP cells assembled with the v-NBR/TAC/IL system demonstrated
excellent damage resistance under extreme conditions such as bending, pinning, and shearing, highlighting
its reliability in practical applications and emphasizing its high safety.

Amide for GPEs
Similar to nitrile flame retardants, amide flame retardants are also nitrogen-based. When exposed to heat,
they generate inert gases such as N , effectively mitigating the risk of combustion and thermal runaway. Due
2
to their outstanding flame-retardant properties, amide groups are extensively employed in the electrolytes of
LMBs . Zhu et al. developed an innovative gel electrolyte based on an amide-based skeleton, successfully
[83]
synthesizing a GPE during the preparation process by mixing the LE with 3% N,N'-methylene bis
[58]
(acrylamide) and polymerizing it in situ . Through this method, GPEs with nonflammable properties in
ignition tests were produced, attributed to forming a polymer cross-linking network by N,N'-methylene
bis(acrylamide) [Figure 6H]. Furthermore, the GPEs demonstrated a significantly high Young’s modulus,
effectively preventing the overgrowth of Li dendrites, thereby reducing potential safety hazards. To assess
the feasibility of practical applications, the research team conducted pinning experiments on the assembled
Li||lithium-rich layered oxide (LLO) pouch cells. Encouragingly, the experimental results showed that the
pouch battery maintained normal operation without performance failure or burning. These experiments
highlight the excellent safety features of amide-based GPEs in practical applications. Additionally, the
introduction of amide groups not only improved the oxidation window of the electrolyte, but also
maintained a capacity retention of up to 97.6% after 160 cycles for Li||LLO batteries assembled with this gel
electrolyte, further confirming the significant impact of amide-based GPEs on battery performance.
Consequently, these findings demonstrate the multifaceted benefits and potential of amide-based GPEs in
enhancing both the safety and performance of LMBs.

Polyimide for GPEs
Polyimide (PI), as a polymer, shares similarities with other amides in terms of vapor phase flame
retardancy . If it is incorporated into the polymer backbone, it can significantly enhance the thermal safety
[84]
of GPEs. Its excellent heat resistance and flame retardancy play a crucial role in augmenting the thermal
safety of LMBs by effectively preventing thermal runaway. To further improve its performance and reduce
potential safety risks, Zhang et al. have successfully synthesized a unique PI that exhibits the ability to cross-
link and polymerize with solvents in conventional carbonate electrolytes to form a special gel electrolyte
(GPE-PI10), thereby effectively reducing potential hazards arising from carbonate solvent leakage
[Figure 6I] . GPE-PI10 has reportedly demonstrated excellent performance in flammability evaluations by
[85]
conducting flame retardancy tests. Compared to conventional LEs, the gel electrolyte showed nonflammable
properties in ignition tests, effectively reducing the risk of fire. In addition, in TGA tests, the thermal
decomposition temperature of GPE-PI10 is significantly higher than that of LEs, thereby enhancing its
stability in high-temperature environments. Cycling tests of the Li||GPE-PI10||sulfurized polyacrylonitrile
(SPAN) battery demonstrated that the battery maintained high capacity retention after 450 cycles at 0.2 C,
thereby attesting to the excellent cycling stability of GPE-PI10 as an electrolyte. This study has thus
introduced novel materials and synthesis strategies for developing safer, high-performance LMBs.

Silicon-based for GPEs
Silicone-based GPEs typically consist of polysiloxanes and sesquisiloxanes. Silicones, known for their
exceptional thermal stability and nonflammability, are thought to enhance the thermal safety of GPEs.
Zhang et al. conducted the successful synthesis of a novel silicone-doped polyether-type GPEs (PTCDs)