Anion-exchange fluorinated ion conductors for stable high-voltage lithium battery

The development of high-energy all-solid-state batteries is critically hindered by the electrochemical instability of solid electrolytes against high-voltage oxide positive electrodes. While fluorination is a promising strategy to enhance electrolyte stability, conventional methods are ineffective, resulting in insufficient fluorine content and a debilitating trade-off with ionic conductivity. Here, we report a solid-state anion-exchange strategy that overcomes these limitations by producing core-shell Li-fluoride/LiCl nanocomposite precursors. These precursors enable the synthesis of heavily fluorinated lithium-halide and lithium-sulfide electrolytes that combine high ionic conductivity with good oxidative stability. This stability originates from the formation of a robust, self-limiting LiF-rich interphase at the positive electrode. Consequently, an all-solid-state battery using a Li-rich oxide positive electrode achieves high performance, retaining over 77.5% capacity after 2000 cycles at a high rate of 3 C (1 C = 275 mA/g) and a 5.0 V cutoff. This anion-exchange approach is broadly applicable to other systems and establishes a versatile platform for designing advanced fluorinated materials for next-generation batteries.