Temperature‐Responsive Electrodes Enabled by Poly(3‐Alkylthiophene)s with Tailored Branches

Abstract The safety concerns inherent to lithium‐ion batteries constitute a primary technical barrier hindering their large‐scale deployment. Poly(3‐alkylthiophene)s (P3ATs) are promising candidates for thermally responsive electrodes aimed at suppressing thermal runaway owing to their pronounced positive temperature coefficient (PTC) effect. Nevertheless, a comprehensive understanding of how the molecular architecture of p‐type conducting polymers affects their PTC characteristics remains lacking. Herein, P3ATs with varying branched alkyl side‐chains are synthesized, and the influence of different anionic dopants (PF ₆ ⁻ , ClO ₄ ⁻ , and TFSI ⁻ ) on the PTC switching temperature and resistance ratio is systematically investigated. It is found that polymers with branched side chains doped by smaller anions exhibit higher PTC transition temperatures and larger PTC resistance ratios, which is attributed to enhanced segmental mobility and more efficient dopant dissociation. However, the polymer's resistance ratio decreases with increasing thermal cycles, indicating that the reversibility of its PTC effect weakens as thermal cycling proceeds. Moreover, temperature‐sensitive LiFePO ₄ /polymers composite electrodes exhibit an effective current‐interruption capability at 100 °C with reversible PTC effect. These findings establish molecular‐design principles for next‐generation thermally responsive battery materials with intrinsic thermal‐protection functionality.