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.