Improving the electrochemical properties of high-voltage lithium nickel manganese oxide by surface coating with vanadium oxides for lithium ion batteries

Abstract

The V2O5-coated LiNi0.5Mn1.5O4 (LNMO) cathode materials are synthesized via a wet-coating method. V2O5 is capable of lithium intercalating, so the surface of materials is purified. Furthermore lithium ion conductor V2O5 is not only a barrier between electrolyte and LNMO surface to prevent electrolyte decomposition especially at high voltage, but also a HF scavenger thus the spinel structural integrity of LNMO can be preserved for a better cycling reversibility, especially at high temperatures under which conditions the dissolution of Mn3+ ions into electrolyte via reacting with HF is severely problematic for pristine LNMO as cathode materials. The amount of V2O5 coating affects the electrochemical properties of these samples. We discover that the optimal amount of V2O5 on LNMO surface is about 5 wt%. Compared with pristine LNMO, the coating amount with 5 wt% exhibits an excellent rate capability and better reversibility. The discharge capacity is increased by 15.8%, 17.9%, 16.2%, 16.3%, 19.1% and 21.0% in comparison with pure LNMO, presenting a discharge specific capacity of 123.9, 119.1, 120.8, 117.5, 111.9 and 105.3 mAh g−1 at the rates of 0.2, 0.5, 1, 2, 5 and 10C respectively. In addition, the sample presents a discharge capacity of 131.5 mAh g−1 at 1C, with a retention of 92.2% after 100 cycles. Even cycling at 5C rate and 55 °C, the cell with 5% V2O5-coated LNMO cathode can has a capacity of 126.3 mAh g−1, with 92% capacity retention after 100 cycles, implying that V2O5-coating of LNMO is an effective modified method for lithium ion batteries.