In Situ Construction of an Ultra‐Stable Conductive Composite Interface for High‐Voltage All‐Solid‐State Lithium Metal Batteries.

The garnet electrolyte presents poor wettability with Li metal, resulting in an extremely large interfacial impedance and drastic growth of Li dendrites. Herein, a novel ultra‐stable conductive composite interface (CCI) consisting of LiySn alloy and Li3N is constructed in situ between Li6.4La3Zr1.4Ta0.6O12 (LLZTO) pellet and Li metal by a conversion reaction of SnNx with Li metal at 300 °C. The LiySn alloy as a continuous and robust bridge between LLZTO and Li metal can effectively reduce the LLZTO/Li interfacial resistance from 4468.0 Ω to 164.8 Ω. Meanwhile, the Li3N as a fast Li‐ion channel can efficiently transfer Li ions and give their uniform distribution at the LLZTO/Li interface. Therefore, the Li/LLZTO@CCI/Li symmetric battery stably cycles for 1200 h without short circuit, and the all‐solid‐state high‐voltage Li/LLZTO@CCI/LiNi0.5Co0.2Mn0.3O2 battery achieves a specific capacity of 161.4 mAh g−1 at 0.25 C with a capacity retention rate of 92.6 % and coulombic efficiency of 100.0 % after 200 cycles at 25 °C. [ABSTRACT FROM AUTHOR]