Stabilizing the Halide Solid Electrolyte to Lithium by a β-Li₃N Interfacial Layer

As a new class of solid electrolytes, halide solid electrolytes have the advantages of high ionic conductivity at room temperature, stability to high-voltage cathodes, and good deformability, but they generally show a problem of being unstable to a lithium anode. Here, we report the use of Li3N as an interface modification layer to improve the interfacial stability of Li2ZrCl6 to the Li anode. We found that commercial Li3N can be easily transformed into an α-phase and a β-phase by ball-milling and annealing, respectively, in which β-phase Li3N simultaneously has high room-temperature ionic conductivity and good stability to both Li and Li2ZrCl6, making it a good choice for an artificial interface layer material. After the modification of the β-Li3N interfacial layer, the interfacial impedance between Li2ZrCl6 and the Li anode decreased from 1929 to ∼400 Ω. At a current density of 0.1 mA cm–2, the overpotential of the Li symmetric cell decreased from 250 to ∼50 mV, which did not show an obvious increase for at least 300 h, indicating that the β-Li3N interface layer effectively improves the interfacial stability between Li2ZrCl6 and Li.