Fabrication and characterization of mullite whisker-reinforced refractory saggars for Li-ion battery cathode calcination

초록

The rapid growth of electric vehicles and energy storage systems has led to increased production of lithium-ion batteries (LIBs), driving the demand for high-energy-density Ni-rich cathode materials (LiNixCoᵧMn1-x-ᵧO2, x ≥ 0.6). However, their calcination at high temperatures (700–1000 °C) involves highly reactive lithium compounds (LiOH, Li2O), which cause severe corrosion and structural damage to saggars. In this study, a mullite-whisker-reinforced saggar was developed to enhance chemical and thermal durability under such conditions. Using a kaolin–Al2O3-based composition with MoO3 as a catalyst, a three-dimensional whisker network was formed through in-situ reaction sintering at 1400 °C. The fabricated saggar exhibited improved mechanical strength (44.3 MPa) and retained 62.3% of its strength after five thermal shock cycles, outperforming conventional mullite particulate and cordierite–spinel–corundum (CSC) compositions. Corrosion tests revealed that the whisker network effectively suppressed lithium diffusion and mitigated the growth of Li–Al–Si reaction layers, resulting in reduced erosion depth and minimized strength degradation. In addition, simulated lithium corrosion by-products (LiAlSiO4, LiAlSi2O6, and Li2SiO3) were intentionally introduced into NCM811 cathodes to evaluate their impact on electrochemical performance, confirming that such impurities significantly deteriorated battery characteristics. Overall, the mullite whisker architecture provides a viable microstructural design strategy for extending saggar lifetime and ensuring contamination-free calcination of Ni-rich LIB cathodes.

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