Surface Coating Modification of Cathode Material for Long-Term Stable All-Solid-State Batteries

The decomposition of solid electrolytes at the surface of the cathode has become one of the critical bottlenecks in the further widespread of all-solid-state batteries. To this end, we applied a fluidized bed coating method on the cathode and obtained the LiAlO₂-coated NCM622 (LiAlO₂@NCM622) and Al₂O₃-coated NCM622 (Al₂O₃@NCM622). The morphologies, structures, and electrochemical properties of NCM622, LiAlO₂@NCM622, and Al₂O₃@NCM622 were characterized by SEM, EDS, ICP-AES, XRD, laser particle size analyzer, and electrochemical tests. For LiAlO₂@NCM622 and Al₂O₃@NCM622, the coating layers are uniformly distributed on the surface of the cathode active material while the intrinsic structures of NCM622 remain unchanged after coating. Besides, the particle sizes of LiAlO₂@NCM622 and Al₂O₃@NCM622 are larger than NCM622. Furthermore, solid-state batteries were assembled with NCM622, LiAlO₂@NCM622, and Al₂O₃@NCM622 as cathodes, respectively, polyoxyethylene as the solid electrolyte and lithium metal as the anode. The electrochemical tests show that the assembled batteries with LiAlO₂@NCM622 and Al₂O₃@NCM622 exhibit better cycle performance than pristine NCM622. The capacity retention decreases to 80% at the 28th cycle for NCM622, 64th cycle for LiAlO₂@NCM622, and 55th cycle for Al₂O₃@NCM622, respectively, demonstrating that the compatibility between the surface-coated cathode and the solid electrolyte has been significantly improved. This work promotes the application of surface modification technology and paves the way toward next-generation solid-state batteries.