Endowing Metal Oxychloride Solid Electrolytes with Improved Li Compatibility

Typically, the Li incompatibility of inorganic solid electrolytes (ISEs) arises from the presence of non-Li metal cations, which will be reduced into electronic conductors to promote further reactions. Making such ISEs compatible with Li can significantly expand the candidate pool for ISEs in Li metal batteries, but, to this end, the Li/ISE interphase, which inevitably contains electronic conductors, must become electron-blocking. Here, we propose a nonmetal cation incorporation strategy to achieve such a seemingly paradoxical goal. By populating the ISE with nonmetal cations that would yield electron-blocking reduction products, we can make the electron-blocking species in the Li/ISE interphase predominate over the electronic conductors, thereby blocking electron percolation. This strategy significantly improves the Li compatibility in Zr-based oxychloride ISEs, which possess numerous advantages but have always been Li-incompatible; the 0.8Li₂SO₄-ZrCl₄ ISE we design enables stable cycling of Li symmetric cells (5000 h), Li-LiNi_0.92Co_0.06Mn_0.02O₂ cells (80% capacity retention for 170 cycles), and Li₁₃Si₄-LiNi_0.92Co_0.06Mn_0.02O₂ cells (80% capacity retention for 1312 cycles) at 25 °C. Our strategy opens new avenues for the development of Li-compatible ISEs.