Ultrathin All‐Inorganic Halide Solid‐State Electrolyte Membranes for All‐Solid‐State Li‐Ion Batteries

Reducing the thickness of inorganic solid‐state electrolytes (SSEs) can improve both the gravimetric/volumetric energy density due to the decreased weight/thickness of the cells. Unfortunately, the thickness of inorganic SSEs by the powder‐pressing method is 500–1000 µm, which brings large internal resistance. In this work, an ultrathin SSE membrane is prepared via a simple solution‐infusion method using a ZrO2 nanowire as the skeleton and Li3InCl6 as the Li‐ion conductor. This membrane can be self‐standing with a minimum thickness of 25 µm, less than 1/20 in thickness of that electrolyte by the powder‐pressing method. Attributed to a high Li3InCl6 loading, the membrane remains a high conductivity. When used as the electrolyte in solid cells, such the membrane can enable a much‐reduced resistance compared to the traditional SSE layer. Due to the fact that the electrolyte membrane does not contain any organic components, it exhibits good thermal stability. Benefiting from the soft nature of the halide SSEs, the membrane, without any modification, can close contact with the composite cathode. The LiNi0.8Co0.1Mn0.1O2/LiIn cell exhibits a high reversible capacity and the capacity retention is above 80% after 200 cycles. All‐inorganic, free‐standing, ultra‐thin halide solid electrolyte membranes with a thickness of 25 µm can be obtained by the solution infusion method. The reduction in thickness results in a corresponding reduction in the mass and internal resistance of the battery, which contributes to an increase in the energy density and rate performance of the battery.