ABSTRACT The commercialization of solid polymer electrolytes is hindered by low lithium‐ion (Li + ) conductivity and transference number. Here, we demonstrate tautomerization‐switched anion‐ π interactions effectively improve the ionic conduction of polyethylene oxide (PEO)‐based solid‐state electrolytes (PEO‐SSEs). Cyanuric acid (CA) with a unique tautomerization behavior between enol‐ and keto‐ tautomers is employed as a small‐molecule accelerator. The tautomerization from enol‐ to keto‐ configuration stimulated by Li salts switches the intensive anion‐ π interactions between CA and anions of Li salts to release more free Li + . The hydrogen‐bond (H‐bond) interactions between CA and PEO reduce the Li + coordination with ether oxygen atoms in PEO (EO(O)), accelerating the Li + transport. PEO‐SSE with the introduction of CA (CA‐PEO‐SSE) thus exhibits a high ionic conductivity of 2.14 × 10 −4 S cm −1 at 35°C and a high Li + transference number of 0.65, enabling a long lifespan over 2000 h of Li||Li symmetric cells at 0.1 mA cm −2 (0.1 mAh cm −2 ). Li metal batteries (LMBs) assembled by LiFePO 4 cathodes deliver a high specific capacity of 115.3 mAh g −1 and an excellent stability with a capacity retention of 99.9% over 922 cycles at 0.2 C and 35°C, demonstrating the efficient engineering strategy of tautomerization‐switched anion‐ π interactions to construct high‐performance polymer‐based SSEs.
Gao et al. (2026) studied this question.