Enhanced thermal robustness of NCM-LATP composite cathodes via in situ lithium compensators for co-sintering

Composite cathodes integrating Ni-rich layered oxides and oxide solid electrolytes are essential for high-energy all-solid-state lithium-ion batteries (ASSLBs), yet interfacial degradation during high-temperature co-sintering (>600 °C) remains a critical challenge. While surface passivation strategies mitigate reactions below 400 °C, their effectiveness diminishes at elevated temperatures due to inability to counteract Li⁺ concentration gradients. Here, we introduce in situ lithium compensators, i.e., LiOH/Li₂CO₃, into NCM-LATP composite cathodes to dynamically replenish Li⁺ during co-sintering. These additives melt to form transient Li⁺-rich phases that back-diffuse Li⁺ into NCM lattices, suppressing layered-to-rock salt transitions and stabilizing the interface. Quasi in situ XRD confirms retention of the layered structure at temperature up to 700 °C, while electrochemical tests demonstrate a reversible capacity of 222.2 mA h g⁻¹—comparable to NCM before co-sintering—and an impressive 65.3% capacity retention improvement over 100 cycles. In contrast, uncompensated cathodes exhibit severe degradation to 96.5 mA h g⁻¹ due to Li depletion and resistive Li-Ti-O interphases. This strategy integrates sacrificial chemistry with scalable powder-mixing workflows, achieving a 93.4% reduction in interfacial impedance. By addressing Li⁺ flux homogenization and structural stability, this work provides a practical pathway toward industrial-scale fabrication of high-performance ASSLBs.