Preparation of cordierite-mullite saggar used in high-temperature synthesis of Li(Ni_0.5Co_0.2Mn_0.3)O₂ cathode material

抄録

A cordierite-mullite saggar was prepared via high-temperature sintering with cordierite, mullite and alumina (α-Al₂O₃) and yellow dextrin as raw materials. The physical properties (i.e., density/porosity, linear shrinkage, ignition loss, bending strength and residual strength), thermal shock resistance and durability of the saggar in the synthesis of Li(Ni_0.5Co_0.2Mn_0.3)O₂ (LNCM) as a ternary cathode material were investigated. The results show that the cordierite-mullite saggar with 12.50 wt % α-Al₂O₃ addition prepared at 1420 °C has the optimum properties (i.e., the bending strength of 11.3 MPa, the residual strength of 8.6 MPa and the residual strength retention rate of 76 % after three cycles of thermal shocks) and a prolonged service life at 1000 °C and 4 h for 20 times. This is because the saggar is attacked by Li₂O to generate LiAlSiO₄ and LiAlO₂ with higher thermal expansion coefficients, and LiAlSiO₄ and LiAlO₂ fill the pores to compact the structure of the permeable layer in the high-temperature synthesis of LNCM. As a result, a protective layer decreases the likelihood of the reaction with coordinate and mullite to increase the durability of the saggar in the high-temperature synthesis of LNCM. However, as the time of erosion cycle further increases (i.e., >20 times), the thermal expansion mismatch between LiAlO₂/LiAlSiO₄ and cordierite/mullite can produce more cracks, declining the mechanical properties of saggar and thus damaging the saggar.