Enabling a Co-Free, High-Voltage LiNi0.5Mn1.5O4 Cathode in All-Solid-State Batteries with a Halide Electrolyte

One approach to increase the energy density of all-solid-state batteries (ASSBs) is to use high-voltage cathode materials. The spinel LiNi0.5Mn1.5O4 (LNMO) cathode is one such example, as it offers a high reaction potential (close to 5 V). Moreover, it is a Co-free cathode system, which makes it an environmentally friendly and a low-cost alternative. However, several challenges must be addressed before it can be properly adopted in ASSB technologies. Herein, we reveal that lithium argyrodite (Li6PS5Cl), a sulfide solid-state electrolyte (SSE), possesses intrinsic chemical incompatibility with the LNMO cathode. We demonstrate the necessity of using a halide SSE, Li3YCl6 (LYC), through careful analysis of the LNMO/SSE interface. Moreover, we emphasize the necessity of applying a protective coating layer to LNMO particles, even when halide SSEs are used. Furthermore, the chemical phenomena involving LYC in the oxidative environment of LNMO are analyzed, including a comparison between coated and uncoated LNMO particles.