Organic Ionic Plastic Crystal Composite Solid Electrolytes with Efficient Interfacial Lithium-Ion Percolation for Solid-State Lithium Metal Batteries

Solid-state lithium metal batteries (SSLMBs) are hindered by the intrinsic limitations of conventional solid-state electrolytes (SSEs), including low ionic conductivity and interfacial instability. To address these challenges, we developed an innovative ternary composite electrolyte (TCE) by incorporating an organic ionic plastic crystal (OIPC), P12TFSI, along with a LiTFSI lithium salt, into a lithiophilic poly(ethylene oxide) polymer matrix. The synergistic coordination and defect engineering of the high-plasticity OIPC with the Li-rich polymer electrolyte create a low-tortuosity (τ = 0.3) ion-transfer pathway in the target TCE, resulting in superior interfacial lithium-ion percolation capability and high ionic conductivity of 6.3 × 10–4 S cm–1 (at 30 °C). The assembled Li||Li symmetric cell can be cycled for 250 h (at 0.3 mA cm–2) without short-circuiting, thereby demonstrating its remarkable stability against lithium metal. The Li||LiFePO4 SSLMB employing this state-of-the-art TCE exhibits a reversible capacity of 145 mAh g–1 (versus LiFePO4), with 91% capacity retention over 200 cycles at 0.5 C. This work not only presents a viable strategy for designing high-performance OIPC-based SSEs but also underscores their potential for practical SSLMB applications.