All-Solid-State Li Batteries with NCM–Garnet-Based Composite Cathodes: The Impact of NCM Composition on Material Compatibility

Garnet-based all-solid-state batteries (ASBs) with high energy density require composite cathodes with high areal loading and high-capacity cathode active materials. While all ceramic cathodes can typically be manufactured via cosintering, the elevated temperatures necessary for this process pose challenges with respect to material compatibility. High-capacity cathode active materials like Ni-rich LiNixCoyMn1–x–yO2 (NCM) show insufficient material compatibility toward the solid electrolyte Li6.45Al0.05La3Zr1.6Ta0.4O12 (LLZO:Ta) during cosintering, leading to the formation of highly resistive interphases. We investigated this secondary phase formation both experimentally and via density functional theory calculation to get a mechanistic understanding of the cosintering behavior of LLZO:Ta with NCM111 and Ni-rich NCM811. Furthermore, we employed B doping of both NCM materials in order to assess its impact on the cation interchange and subsequent secondary phase formation. While secondary phases were formed for all four NCM materials, their onset temperature, nature, and amount strongly depend on the NCM composition and doping. Surprisingly, Ni-rich NCM811 turned out to be the most promising cathode active material for the combination with garnet-type LLZO:Ta. As proof of concept, fully inorganic, ceramic all-solid-state lithium batteries featuring only a Li-metal anode, an LLZO:Ta separator, and a composite cathode, consisting of LLZO:Ta, Li3BO3, and NCM811, were prepared by conventional sintering. The purely inorganic full cells delivered a high specific areal discharge capacity of 0.7 mA h cm–2 in the initial cycle.