An All‐Solid‐State Li–Cu Battery via Cuprous/Lithium‐Ion Halide Solid Electrolyte

The Cu cathode has great potential due to its low cost and high capacity. However, the limited ionic conductivity of the electrolyte for Cu ions and poor solubility of Cu species severely hinder the rapid development of Li–Cu batteries. Herein, we synthesized a Cu + halide solid electrolyte (Cu 2 ZrCl 6 , CZC) by mechanochemical method, which exhibited a high room‐temperature Cu + conductivity (about 14 mS cm −1 ) and high solubility of Cu species. The Cu||CZC||Cu symmetric battery demonstrated the ability to maintain stable Cu + plating/stripping over 1000 h at 0.1 mA cm −2 . We further constructed a model of the synergistic migration and ion exchange of Cu + and Li + in CZC and Li 2 ZrCl 6 electrolytes. Based on this, we assembled the first all‐solid‐state lithium–copper battery (ASSLCB), which delivered a high reversible specific capacity of 360 mAh g −1 (1.7–3.8 V versus Li⁺/Li, at 37 mA g −1 ) and exhibited outstanding cycling performance across 50 cycles at a current of 62.5 mA g −1 . Additionally, we designed a cathode‐free ASSLCB, utilizing aluminum foil as the current collector to demonstrate the deposition and dissolution of pure copper metal. This study provides a new design concept for Cu + conductors and lays a foundation for the future research of ASSLCBs.