Solvent-Free Solid-State Lithium Battery Based on LiFePO₄ and MWCNT/PEO/PVDF-HFP for High-Temperature Applications

Rechargeable lithium-ion batteries (LIBs) have a wide range of applications but face challenges in harsh working or operating environments at high temperatures. In this work, a solid polymer electrolyte with MWCNT-COOH as an additive (MWCNT-SPE) was obtained. MWCNT-SPE has a high thermal stability and can be used in high-temperature operating environments. Solid-state lithium batteries based on MWCNT-SPE and LiFePO₄ were assembled. The resulting lithium batteries exhibited excellent electrochemical properties at 70 and 120 °C, demonstrating a wide range of operations suitable for solid-state batteries with extreme demands. The symmetrical Li/MWCNT-SPE/Li cell operated for 1800 h with low polarization voltage and no short circuit, and the LiFePO₄/MWCNT-SPE/Li cell delivered superior cycling performance under both 0.2 and 0.5 C-rates, indicating that the interface compatibility between the lithium metal and MWCNT-SPE membrane was good and could effectively suppress the formation of lithium dendrites. The superior performance of the resulting MWCNT-SPE was due to the weak interaction between PEO, PVDF-HFP, and MWCNT-COOH, which reduced the tendency of PEO's crystallinity and thereby significantly increased the Li⁺ migration ability and improved the cycling life of the batteries.