Weak-Solvation Molecular Ion Gates Enabling Multipath Li + Hopping and Air Stability in Garnet/Poly(ethylene oxide) Electrolytes

Abstract Poly(ethylene oxide) (PEO)-based composite polymer electrolytes facilitate Li+ transport via coordination and decoordination. However, strong coordination impedes ion transport, while weak coordination limits the carrier density. This dilemma is further aggravated by the Li2CO3-passivated garnet surface that blocks ion migration, restricting practical applications. Here, we develop a weak-solvation molecular ion gate (WSMI) strategy by chemically anchoring 4-methoxy-2-(trifluoromethyl)benzoic acid onto Li6.4La3Zr1.4Ta0.6O12 (LLZTO). The carboxyl group eliminates the alkaline Li2CO3 surface layer and forms a robust, chemically anchored WSMI interphase that shields LLZTO from atmospheric moisture, thus significantly enhancing air stability. Additionally, the −CF3 groups enhance LiTFSI dissociation, weaken Li+-EO and Li+-TFSI– interactions, and accelerate coordination exchange and interfacial hopping. Simultaneously, the ether-oxygen moieties provide Li+ -transport sites at the LLZTO/PEO interface, activating polymer, interfacial, and garnet-associated Li+ transport regions. As a result, the composite electrolyte delivers a Li+ transference number of 0.622 and an electrochemical stability window of 5.38 V (vs Li+/Li). Li||Li symmetric cells cycle stably for over 2000 h at 0.2 mA cm–2 and 0.2 mAh cm–2, and LiFePO4||Li full cells retain 87.8% of their initial capacity after 1100 cycles at 1 C. The WSMI strategy proposed in this work provides valuable insights into tailoring interfacial chemical environments for all-solid-state batteries.