Interface-driven phase stability enables co-sintered composite anodes for intrinsically safe all-solid-state-batteries

The development of all-solid-state batteries (ASSBs) is hindered by interfacial instability between solid-electrolytes (SEs) and Li metal anodes. In this work, we propose a co-sintered composite anode strategy based on Li₄Ti₅O₁₂ (LTO), a ‘zero-strain’ anode material, to address interfacial challenges in NASICON-type systems. Systematic investigations reveal that LTO undergoes progressive phase decomposition during co-sintering with Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) due to the thermodynamic driving force from Li chemical potential difference and the high reactivity of phosphate groups. In contrast, LTO maintains structural integrity and chemical compatibility up to 900 °C when co-sintered with Li_0.33La_0.56TiO₃ (LLTO). Additionally, thermodynamic instability between LATP and LLTO at high-temperatures is observed, indicating challenges in multi-electrolyte integration. Notably, the preferential Li loss from LLTO within the LTO+LLTO composite anode during co-sintering with LATP pellet exerts a protective effect for LTO, helping to maintain the structural integrity of LTO. Building upon these findings, an integrated (LTO+LLTO)|LATP bilayer structure is successfully fabricated via co-sintering at 600°C. This work offers critical insights into phase evolution and interfacial chemistry for coupling SEs with anode materials, guiding the rational design of co-sintering composite anodes and demonstrating a promising pathway toward intrinsically safe ASSBs.