Mechanistic trade-offs in dense cathode architectures for high-energy-density solid-state batteries

Abstract

As solid-state batteries (SSBs) employing Li metal anodes emerge as a promising technology for next-generation energy storage, cathodes remain a critical bottleneck, hindering further improvements in energy densities. In current state-of-the-art composite cathodes, transport constraints within the solid electrolyte (SE) network impose significant limitations on the achievable cathode active material (CAM) loading and electrode thickness. In this work, we investigate cathode design featuring densely packed, crystallographically oriented cathode crystals, free of SE and secondary phases, utilizing LiCoO₂ (LCO) as our model system. By examining the complex interplay between cathode microstructure, reaction-transport interactions, and chemo-mechanical phenomena underlying such dense cathodes, we evaluate their performance and identify key limiting mechanisms. We show that dense cathodes yield substantial improvements in energy density, outperforming composite cathodes by 98.7% in volumetric and 32.9% in gravimetric density at 1C. However, our findings also reveal critical interfacial, microstructural, and chemo-mechanical challenges that presently hinder the realization of their full potential. Microstructural heterogeneities in dense cathodes lead to the formation of electrochemical and mechanical hotspots during cell operation, which are identified as mechanistic pain points, impacting their rate capability, structural integrity, and cycle life. This work offers foundational insights and mechanistic guidelines for the development of high-energy-density cathodes for the next-generation SSBs.