Molecular Engineering of Poly(3‐Alkylthiophene)s with Enhanced Positive Temperature Coefficient Effects for Intrinsically Safe Lithium‐Ion Batteries

The escalating deployment of high-energy density lithium-ion batteries (LIBs) in electric vehicles and energy storage stations has intensified concerns over their thermal safety. Poly(3-alkylthiophene)s (P3ATs), known for their positive temperature coefficient (PTC) effect, are promising candidates for thermally responsive electrodes to suppress LIBs thermal runaway. However, the structure-property relationships governing their PTC behavior remain poorly elucidated. This study systematically synthesizes P3ATs with tailored alkyl side chains and investigates the impact of anion dopants (PF₆ ^-, TFSI^-, ClO₄ ^-) on their PTC transition temperatures and resistance ratios. It is revealed that polymers with longer alkyl side chains and smaller dopant anions exhibit lower PTC transition temperatures and higher PTC resistance ratios, attributed to enhanced chain mobility and dopant dissociation efficiency. While the PTC effect demonstrates partial reversibility, increased thermal cycling and extended alkyl side chains accelerate performance degradation due to side-chain entanglement and dopant leaching. Moreover, LiFePO₄-based temperature-sensitive electrodes (LFP-P3ATs) effectively shut down the electrode reactions at 110 °C, showing reliable temperature-sensitive characteristics. These findings establish molecular design principles for next-generation smart battery materials with intrinsic thermal protection capabilities.