Surface stabilized LiNi0.5Mn1.5O4 cathode materials with high-rate capability and long cycle life for lithium ion batteries

Li4P2O7-stabilized LiNi0.5Mn1.5O4 was prepared by solid-state synthesis. The material was characterized by X-ray diffraction and high-resolution transition electron microscopy, which showed a coating layer (<10 nm) of Li4P2O7 crystallite co-existing with a little Li3PO4 on the LiNi0.5Mn1.5O4/Li4P2O7 primary particles. LiNi0.5Mn1.5O4/Li4P2O7 synthesized at 760 degrees C for 200 h had a cubic spinet structure with a space group of Fd<(3)over bar> m; its estimated crystallite size was 527 nm. LiNi0.5Mn1.5O4/Li4P2O7 possessed better rate capability and cycling capability. The introduced Li4P2O7 coating layer acted as a solid electrolyte or artificial SEI layer: by separating the active material from the electrolyte, the coating layer prevented the Ni2+ /Ni3+ or Ni3+/Ni4+ redox couple from decomposing the electrolyte. Stress/strain from the Ni2+ reversible arrow Ni-3 reversible arrow Ni4+ spinet phase change caused fractures and pulverization of the cycled stoichiometric LiNi0.5Mn1.5O4 crystal surface, especially noticeable for this well-developed micro-sized crystal. The ordered stoichiometric LiNi0.5Mn1.5O4 had more side reactions, led to a quick fading of the material's capacity. Both the Li4P2O7 coating layer and the disordered Fd (3) over bar m space group LiNi0.5Mn1.5O4 structure bring benefit to the LiNi0.5Mn1.5O4/Li4P2O7 performance. Thus, the introduced Li4P2O7 coating layer can build an effective solid electrolyte or artificial SEI layer to protect the interface between LiNi0.5Mn1.5O4 and electrolyte. (C) 2012 Elsevier Ltd. All rights reserved.