Li₂FeCl₄ as a Cost-Effective and Durable Cathode for Solid-State Li-Ion Batteries

Low-cost cathode materials with high energy density and good rate performance are critical for the development of next-generation solid-state Li-ion batteries (SSLIBs). Here, we report Li₂FeCl₄ as a cathode material for SSLIBs with highly reversible Li intercalation and deintercalation, a high operation voltage of 3.7 V vs Li⁺/Li, good rate capability, and good cycling stability with an 86% capacity retention after 6000 cycles. Operando synchrotron XRD reveals that the phase evolution of Li₂FeCl₄ during charge-discharge cycling involves both solid-solution and two-phase reactions, which maintains a very stable framework during Li insertion and extraction.