Ultra-Thin AlPO₄ Layer Coated LiNi_0.7Co_0.15Mn_0.15O₂ Cathodes With Enhanced High-Voltage and High-Temperature...

Side-reactions in LiNi_1-x-yCo Mn O₂ (0≤_- x+y≤1) cathode materials are one kind of the problems that would deteriorate the surface structure and the electrochemical stabilities of the cathodes, especially when they are working at high cut-off voltages and high temperatures. In this study, an ultrathin (~10 nm) AlPO₄ coating layer was fabricated through a two-step "feeding" process on LiNi_0.7Co_0.15Mn_0.15O₂ (NCM) cathode materials. The structure and chemical composition of the AlPO₄ coating were studied by XRD, SEM, TEM, and XPS characterizations. Further electrochemical testing revealed that the AlPO₄-coated LiNi_0.7Co_0.15Mn_0.15O₂ cathode exhibited enhanced electrochemical stabilities in the case of high cut-off voltage at both 25 and 55°C. In detail, the AlPO₄-coated LiNi_0.7Co_0.15Mn_0.15O₂ could deliver 186.50 mAh g^-1 with 81.5% capacity retention after 100 cycles at 1C over 3-4.5 V in coin cell, far higher than the 71.4% capacity retention of the pristine electrode. In prismatic full cell, the coated sample also kept 89.5% capacity retention at 25°C and 81.1% capacity retention at 55°C even after 300 cycles (2.75-4.35 V, 1C), showing better cycling stability than that of the pristine NCM. The ultrathin AlPO₄ coating could not only keep the bulk structure stability from the surface degradation, but also diminishes the electrochemical resistance varies after cycles, thereby supporting the coated cathodes with enhanced electrochemical stability.