QING Da, WANG Yilong, YANG Liandi, WANG Jingfu, YANG Ning, LI Hong,

WANG Jian, ZHANG Huifang, SUN Xiuwei

(Tangshan Guoliang New Energy Research Institute, Tangshan 036000, Hebei, China)

Extended Abstract:[Significance] In the current context of the global push for sustainable development, the "double carbon" policy has emerged as a crucial strategy. As the new energy industry, including electric vehicles and energy storage systems, experiences rapid expansion, while the demand for lithium-ion batteries has been skyrocketing. The cathode in these batteries is a linchpin in determining their overall performance, dictating factors such as energy density, charge-discharge efficiency and cycle life. During the manufacturing process of cathode materials, high-temperature sintering is an essential step, where the sagger plays a vital role. Acting as a container for loading and safeguarding cathode materials during this high-temperature operation, the saggers' properties have a profound influence on the quality of the final cathode materials. Commonly used sagger materials like alumina do possess certain advantages. They exhibit remarkable high-temperature resistance and chemical stability, which are fundamental requirements for withstanding the harsh sintering environment. However, they still have flaws. One of the prominent issues is their relatively poor corrosion resistance. In the high-temperature and chemically active sintering atmosphere, alumina saggers can gradually be corroded, which not only affects their service life but also has the potential to contaminate the cathode materials. Additionally, the mismatch of the thermal expansion coefficient between the sagger and the cathode material can lead to mechanical stress during heating and cooling cycles, potentially causing cracks in the sagger or affecting the structural integrity of the cathode materials.[Progress] To address these challenges, two main strategies have been proposed to enhance the performance of saggers. The first approach is to introduce anti-corrosion materials. By incorporating substances with excellent corrosion-resistant properties, such as certain rare-earth-doped compounds or high-performance ceramics, thermal shock stability of the saggers could be enhanced, so that they can better withstand the rapid temperature changes during sintering without cracking. Moreover, the mechanical strength of the saggers can also be improved, thus ensuring structural integrity over multiple sintering cycles. The second strategy is to apply surface coatings. These coatings, such as ceramic-based or polymer - based thin films, can effectively isolate the cathode materials from the sagger matrix. This isolation not only prolongs the life of the saggers by preventing direct contact-induced corrosion, but also significantly ensures purity of the cathode materials. A purer cathode material, in turn, can enhance the electrochemical performance of the lithium-ion battery, leading to higher energy efficiency and longer cycle life.[Conclusions and Prospects] Firstly, the damage mechanism of saggers under thermal stress and chemical erosion is summarized. The interrelationships between temperature gradients, chemical reactants in the sintering atmosphere and the sagger materials are analyzed. Then, the raw material composition, preparation method and performance improvement methods of cordierite-mullite saggers are comprehensively presented. Cordierite-mullite saggers have attracted increasing attention due to their unique combination of properties. Their raw material composition, which includes appropriate ratios of cordierite and mullite precursors, can be optimized to achieve high performance. Different preparation methods, such as traditional powder sintering, sol-gel processes and additive manufacturing techniques, are compared in terms of their influence on microstructure and properties of the saggers. Finally, based on the current research status, the future development direction of saggers for cathode material synthesis is prospected, including exploring novel materials, developing more advanced preparation techniques, and achieving more precise control over the sagger-cathode material interface to meet the ever- increasing demands of the new energy industry.

Key words: cathode material; cordierite-mullite; sagger; preparation method