Organic Plastic Crystal Composite Electrolytes: A Path to High-Conductivity and Low-Temperature Operation in Solid-State Lithium Batteries

Solid-state batteries are the next generation of electrochemical devices, offering enhanced safety and higher energy density for the energy transition. Among solid electrolytes, composite polymers are appealing candidates due to their balanced ionic conductivity and mechanical flexibility compared to their purely inorganic or polymeric counterparts. In this work, we develop a composite polymer electrolyte incorporating an organic ionic plastic crystal (OIPC) into a poly(ethylene) oxide matrix with a Li_1.3Al_0.3Ti_1.7(PO₄)₃ceramic filler. The addition of the OIPC significantly enhances the ionic conductivity by a factor of 3 at room temperature. Coupled with the mechanical reinforcement from the ceramic phase, the resulting electrolyte enables cycling in full cells at 40 °C, a temperature typically unsuitable for PEO-based systems. Besides elucidating the synergistic effects of the composite electrolyte, its electrochemical assessment is validated in symmetric lithium cells and full LiFePO₄cathodes, validating the potential of this electrolyte system for advanced battery applications.