Phase Stability and Electrical Performance of Solid-State Battery Materials

Abstract

The escalating demand for safer, higher-energy-density energy storage solutions has positioned solid-state batteries (SSBs) as a promising successor to conventional lithium-ion batteries, addressing critical limitations such as flammability, limited energy density, and safety risks associated with liquid electrolytes. This review comprehensively examines the phase stability and electrical performance of key solid electrolyte materials, emphasizing thermodynamic principles governing interfacial reactions, ion transport mechanisms, and strategies to overcome solid-solid interface challenges in all-solid-state systems. Thermodynamic stability is evaluated through lithium chemical potential windows and grand potential phase diagrams, revealing that decomposition driving forces dictate compatibility with high-voltage cathodes and lithium-metal anodes. Oxide-based electrolytes (garnet LLZO, NASICON LATP) offer wide electrochemical windows (>5 V) and excellent chemical/thermal stability but suffer from brittleness and high interfacial resistance. Sulfide electrolytes (LGPS, argyrodites) deliver superionic conductivities (up to 25 mS/cm) and mechanical ductility for facile processing, yet face narrow stability windows, air/moisture sensitivity, and H₂S evolution risks. Emerging halide electrolytes and high-entropy materials provide balanced oxidative stability and improved low-temperature performance, while polymer and composite electrolytes enhance flexibility and wettability, albeit with lower room-temperature conductivity. Electrical performance hinges on ionic conduction pathways (Arrhenius behavior, BCC frameworks), grain boundary contributions, electronic insulation to prevent self-discharge, and charge-transfer kinetics at rigid interfaces. Interphase engineering via coatings (e.g., LiNbO₃, Al₂O₃), doping, and artificial interlayers mitigates resistive or mixed-conducting interphases. Electro-chemo-mechanical stresses from volume changes (up to 18% in high-energy cells) are addressed through compliant binders and reduced stack pressures. Advanced operando characterization and machine learning accelerate material discovery and performance prediction. Scalable manufacturing roadmaps project significant cost reductions (<$100/kWh by 2035) and market growth, with pilot production and automotive integration targeted for 2027–2028. Despite persistent hurdles in interfacial stability, mechanical integrity, and low-temperature operation, integrated strategies combining material innovation, interface engineering, and computational design pave the way for commercially viable SSBs with superior safety, energy density (>400–500 Wh/kg), and cycle life.