PVP-bridged γ-LiAlO2 nanolayer on Li1.2Ni0.182Co0.08Mn0.538O2 cathode materials for improving the rate capability and cycling stability

Abstract

Li-rich layered materials have been considered as promising cathode materials for next-generation lithium-ion batteries due to their high capacity (≥250 mAh g−1). Unfortunately, this type of cathode material still suffers from intrinsic deficiencies of capacity fading and side reactions. Surface coating with a protective layer can resolve the above problems to some extent, whereas normal coating strategies still suffer from process complexity and are difficult to prevent phase separation that leads to the formation of an independent miscellaneous phase. Herein, we report an effective PVP-bridged coating method, in which the PVP molecules can bridge the gap between the coating shell and the electrode material core through hydrogen bonding and functional groups. Utilizing this strategy, a uniform Li-ion conductor γ-LiAlO2 nanolayer with a thickness of 7 nm is successfully formed on the surface of the Li1.2Ni0.182Co0.08Mn0.538O2 cathode material, which leads to an excellent rate capability (177.0 mAh g−1 delivered at 5 C) and superior cycling stability (89.3% capacity retention achieved after 100 cycles at 10 C) for the composite material. Furthermore, the exothermic reaction for the composite material takes place at a higher temperature (234.1 °C) relative to the uncoated sample (220.9 °C), implying its improved thermal stability. Galvanostatic intermittent titration technique and density functional theory calculation demonstrate a higher Li+ diffusion coefficient for the γ-LiAlO2 coated sample and a lower Li+ diffusion energy barrier in γ-LiAlO2. Based on the promising results, the PVP-bridged coating strategy presented in this study provides a new perspective in material design towards high-performance Li-rich cathode materials for lithium-ion batteries.