Rare-Earth-Free Chloride Solid Electrolytes with High Ionic Conductivity for All-Solid-State Lithium Batteries

The commercialization of all-solid-state lithium batteries (ASSLBs) depends on solid electrolytes (SEs) that simultaneously offer high ionic conductivity (>1 mS cm^-1) and low cost (<$20 kg^-1). However, existing SEs face performance-cost trade-off: highly conductive materials rely on expensive precursors, whereas low-cost alternatives fail to meet conductivity benchmarks. Herein, we report a rare-earth-free chloride SE, Li_2.03Zr_0.98P_0.02Cl_5.95S_0.05 (LZC-1PS), which combines ultralow cost ($15.21 kg^-1) with a room-temperature ionic conductivity of 1.02 mS cm^-1. The fast ionic migration behavior arises from a reduced diffusion barrier (particularly along the a-b lattice plane), achieved via a dual-site substitution strategy where Cl^- is partially replaced by more polarizable S^2- to ease electrostatic constraints, and Zr⁴⁺ is substituted with more electronegative P⁵⁺ to weaken Li⁺-anion interactions through inductive effects. As proof of concept, the LZC-1PS is tested in combination with a Li₆PS₅Cl-coated Li-In anode and LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) or LiCoO₂ (LCO) cathode in lab-scale cell configuration. Those ASSLBs show outstanding cycling stability, retaining 75.2% capacity after 1200 cycles for LCO cathodes and 76.6% after 1000 cycles for NCM811 cathodes at 1C.