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We have synthesized a series of Li1+x(Ni0.5Mn0.5)1–xO2(LNMO) materials to study the influence of excess lithium ions on the structure and electrochemical behaviors of nickel–manganese-based layered compounds. The increasing content of Li+ions in the transition-metal (TM) layer leads to the departure of the follower-like clusters to Ni-rich and Mn-rich clusters. The Ni2+ions in the Li layer couple with adjacent transition-metal ions via strong 180° exchange interactions and moderate the local structure, which leads to magnetic clusters with finite size. Electrochemical performance shows that appropriate Ni2+ions could improve the cycle stability without decreasing the rate capability. Among them, Li1.1Ni0.45Mn0.45O2shows a rate capability of 76 mAh g–1at 1000 mA g–1and a lifespan of 300 cycles at 200 mA g–1. This work shows that structure moderation has an essential impact on its electrochemical performance. Besides this, the crystal and magnetic combined methods we use could offer a better way of studying cathode materials.

The Li(Li0.18Ni0.15Co0.15Mn0.52)O2cathode material is modified by a Li4M5O12-like heterostructure and a BiOF surface layer. The interfacial heterostructure triggers the layered-to-Li4M5O12transformation of the material which is different from the layered-to-LiMn2O4transformation of the pristine Li(Li0.18Ni0.15Co0.15Mn0.52)O2. This Li4M5O12-like transformation helps the material to keep high working voltage, long cycle life and excellent rate capability. Mass spectrometry, in situ X-ray diffraction and transmission electron microscope show that the Li4M5O12-like phase prohibits oxygen release from the material bulk at elevated temperatures. In addition, the BiOF coating layer protects the material from harmful side reactions with the electrolyte. These advantages significantly improve the electrochemical performance of Li(Li0.18Ni0.15Co0.15Mn0.52)O2. The material shows a discharge capacity of 292 mAh g–1at 0.2 C with capacity retention of 92% after 100 cycles. Moreover, a high discharge capacity of 78 mAh g–1could be obtained at 25 C. The exothermic temperature of the fully charged electrode is elevated from 203 to 261 °C with 50% reduction of the total thermal release, highlighting excellent thermal safety of the material.