Scalable fabrication of all-ceramic composite cathodes via controlled lithium compensation for Li-garnet batteries

Developing scalable processing routes for oxide-based solid-state batteries remains a central challenge, particularly in maintaining lithium stoichiometry and interfacial stability during high-temperature sintering. In this work, we develop alternative lithium compensation strategies for the fabrication of fully dense, secondary-phase-free composite cathodes beyond gas-phase lithiation, using LiCoO₂–Li₇La₃Zr₂O₁₂ as a model system. Specifically, two solid-phase approaches were explored: the addition of lithium precursors and the use of an overlithiated garnet catholyte. Both methods effectively suppressed the formation of LaCoO₃-type interphases and yielded highly dense microstructures after sintering at 1050 °C, achieving performance comparable to gas-phase lithium compensation. These results, first verified on pellet samples, were successfully translated into flat, 100 µm-thick free-standing membranes via a tape casting process, demonstrating versatility and scalability. The membranes reduce the area-specific resistance to 4.5 Ω cm² while maintaining high electrochemical activity and delivering a discharge capacity of up to 1.49 mAh cm⁻² at 0.25 mA cm⁻². These advances establish a scalable route toward industrially relevant, all-ceramic composite cathodes for garnet-based solid-state batteries.