Nature Communications, Published online: 22 June 2026; doi:10.1038/s41467-026-74773-8 Conventional fluorination cannot resolve the stability/ion-transport trade-off in solid electrolytes. Here, authors report core-shell Li-fluoride/LiCl nanocomposite precursors to synthesize heavily fluorinated Li-halide and Li-sulfide electrolytes with both high ionic conductivity and good oxidative stability.