In Situ Dense Interfacial Barrier via Tailored CA 6 Gradation and Si Doping for Durable Li‐Ion Battery Saggars

Severe saggar corrosion by cathode materials hinders the sustainable production of lithium‐ion batteries. Herein, high‐performance refractory saggars were fabricated via high‐temperature reconstruction using waste high‐voltage porcelain insulators as the main raw material, combined with other solid wastes and mineral additives to form a dense mullite–corundum matrix. A physical–chemical synergistic strategy was adopted by optimizing calcium hexa‐aluminate (CA 6 ) particle‐size gradation and Si powder addition. At an optimal coarse‐to‐fine CA 6 ratio of 5:15, a stable interlocking skeleton was formed, reducing open pores and enhancing matrix packing density. Meanwhile, 2 wt% Si enabled in situ modification through oxidation‐derived liquid SiO 2 filling and mullitization‐induced micro‐expansion, effectively sealing residual micro‐ and nanoscale pores. Consequently, the apparent porosity decreased below 1% while maintaining high mechanical strength and thermal shock resistance. During service, the refined matrix forms a liquid–solid double interfacial barrier: high‐viscosity lithium silicate glass immobilizes Li + , while a compact β‐eucryptite layer blocks Li 2 O inward diffusion. This work offers a low‐cost route for long‐life refractory saggars and high‐value solid‐waste utilization.