Abstract: To further enhance the performance of saggars used for calcining lithium-ion battery cathode materials,a spinel-forsterite multiphase aggregate（S-F）was synthesized from coal gangue and Mg（OH）₂ as raw materials for preparing the saggar composite layer. The thermal-shock and corrosion resistances of the specimens were evaluated. The results show that replacing forsterite and spinel aggregates with the S-F aggregate in equal amounts can improve the bonding between the aggregate and the matrix. This promotes a higher proportion of cracks propagating through the aggregate and an increased frequency of crack deflection within the composite layer specimen,thereby consuming more fracture energy. Consequently,the rupture modulus of the composite layer rises from 16.4 MPa to 20.2 MPa,and the residual-strength ratio after three thermal-shock cycles increases from 33.5% to 37.1%. Within the multiphase aggregate,the spinel grains are enveloped by the forsterite phase,preventing direct contact and reaction between the spinel and the cathode material that would otherwise cause excessive volume expansion. As a result,the average thickness of the corrosion layer decreases from 518 μm to 320 μm,significantly enhancing the corrosion resistance of the saggar composite layer against cathode materials.