Synthesis of Li2Si2O5-coated LiNi0.6Co0.2Mn0.2O2 cathode materials with enhanced high-voltage electrochemical properties for lithium-ion batteries

Abstract

Ni-rich ternary layered oxides, (LiNix [M]1−xO2, x ≥ 0.5, M = Co and Mn), have become one of the mainstream cathode materials for next-generation lithium-ion batteries due to their high capacity and cost efficiency compared with LiCoO2. However, the high-voltage operation of the Ni-rich oxides (>4.3 V) required for high capacity is inevitably accompanied with a rapid capacity decay over numerous cycles. In this work, we reported a surface coating of LiNi0.6Co0.2Mn0.2O2 with Li2Si2O5via a facile and efficient synthetic approach, which involves the employment of silicic acid (H2SiO3) as remover to react with the surface residual lithium compounds (e.g. Li2CO3 and LiOH) of LiNi0.6Co0.2Mn0.2O2 and consequent formation of a robust and complete Li+-conductive Li2Si2O5 protective coating layer. The structure and morphology of the coated cathode materials are fully characterized by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Compared with the pristine LiNi0.6Co0.2Mn0.2O2, coating with the Li+-conductive Li2Si2O5 is found to be very effective for improving the rate capability of the LiNi0.6Co0.2Mn0.2O2 when evaluated at a high cut-off voltage up to 4.5 V. Specifically, 1 wt. % H2SiO3-treated LiNi0.6Co0.2Mn0.2O2 electrode exhibits high discharge specific capacities of 213.9 and 121.6 mAh g−1 at 0.1 and 10 C, respectively, whereas the pristine electrode only shows 196.8 and 92.1 mAh g−1. Besides, the surface-modified LiNi0.6Co0.2Mn0.2O2 electrode also manifests an enhanced long-term cycling stability (67% capacity retention after 200 cycles at 5 C), much better than the pristine electrode (52% retention) due to the robust protective effect of the Li2Si2O5 coating layer. All these results indicate that the Li2Si2O5-coated LiNi0.6Co0.2Mn0.2O2 will be a promising cathode material for lithium-ion batteries with fascinating electrochemical energy storage capabilities.