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

Ni-rich ternary layered oxides , (LiNi x [M] 1−x O 2 , 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 LiCoO 2 . 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 LiNi 0.6 Co 0.2 Mn 0.2 O 2 with Li 2 Si 2 O 5 via a facile and efficient synthetic approach, which involves the employment of silicic acid (H 2 SiO 3 ) as remover to react with the surface residual lithium compounds ( e.g. Li 2 CO 3 and LiOH) of LiNi 0.6 Co 0.2 Mn 0.2 O 2 and consequent formation of a robust and complete Li + -conductive Li 2 Si 2 O 5 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 LiNi 0.6 Co 0.2 Mn 0.2 O 2 , coating with the Li + -conductive Li 2 Si 2 O 5 is found to be very effective for improving the rate capability of the LiNi 0.6 Co 0.2 Mn 0.2 O 2 when evaluated at a high cut-off voltage up to 4.5 V. Specifically, 1 wt. % H 2 SiO 3 -treated LiNi 0.6 Co 0.2 Mn 0.2 O 2 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 LiNi 0.6 Co 0.2 Mn 0.2 O 2 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 Li 2 Si 2 O 5 coating layer. All these results indicate that the Li 2 Si 2 O 5 -coated LiNi 0.6 Co 0.2 Mn 0.2 O 2 will be a promising cathode material for lithium-ion batteries with fascinating electrochemical energy storage capabilities.