Composite Cathodes for Solid State Lithium Batteries

Abstract

All-solid-state lithium batteries (ASSLBs) have emerged as promising next-generation candidates for electric vehicles. By replacing the flammable liquid electrolyte with a stable solid electrolyte and using lithium-metal anodes, ASSLBs can offer enhanced safety, higher energy density, and increased power density. However, the transition from conventional liquid to solid-state system presents several significant challenges, including low ionic conductivity, mechanical integrity of solid-state electrolytes (SSE), high electrode and electrolyte interfacial resistance, and complexities in manufacturing at scale. In conventional liquid-based Li-ion systems, the electrolyte fills the porous cathode, ensuring effective lithium-ion transport pathways. In contrast, ASSLBs often suffer from incomplete contact between the solid electrolyte materials and the active materials within the cathode, resulting in high tortuosity and leading to inefficient transport of both ions and electrons. This leads to high polarization, limited high-rate performance, and rapid cathode degradation. Hence, in this report we present a study on composite electrode development, which aims to address the above challenges with careful cathode microstructure engineering. This work uses lithium-iron-phosphate (LFP)-based cathodes as a model system, which can be extended to high electrochemical potential lithium-nickel-manganese-cobalt-oxide (NMC) cathodes. By systematically reducing tortuosity, the cathodes present good ion/electron transportation while decreasing internal resistance. Moreover, we integrate high-conductivity composite solid electrolytes to enhance mechanical and electrochemical stability. This comprehensive design strategy is a step towards cost-effective, and high-performance ASSLBs suitable for many battery applications including consumer electronics and electric vehicle batteries.