Synthesis And Modification Of Lithium-Rich Manganese Based Layer Oxide Li[Li_0.2Ni_0.2Mn_0.6]O₂as A Cathode Material Of Lithium-Ion Batteries

Lithium-rich manganese based layer oxides, as a kind of high capacity cathode material of lithium-ion batteries, have received widespread concern in recent years. Among them,0.5Li2MnO3·0.5Li [Ni1/2Mn1/2]O2(Li[Li0.2Ni0.2Mn0.6]O2) has good prospects because of high electrochemical capacity, completely excluding cobalt, low cost, good safety and friendliness to environment.Li[Li0.2Ni0.2Mn0.6]02was synthesized by solid state method using LiOH·H2O, Ni(OH)2and Mn3O4as starting materials. The structure and morphology of the products were characterized by XRD and SEM. The electrochemical performance was also investigated. It is found that the layer Li[Li0.2Ni0.2Mn0.6]02material prepared at900℃for10h exhibits uniform fine particle size, high electrochemical capacity and good cycling stability. The discharge capacity reachs about250mAh/g after10cycles, and does not fade in the next40cycles. The first discharge capacity is as high as279.6mAh/g at50℃, and does not fade in the next17cycles. While the battery performance deteriorates at low temperature and high rates.In order to improve the first discharge efficiency of Li[Li0.2Ni0.2Mn0.6]O2as cathode material for rechargeable lithium batteries, Li[Li0.2Ni0.2Mn0.6]O2synthesized by solid state method was preconditioned in acids. It is found that the first discharge efficiency of Li[Li0.2Ni0.2Mn0.6]O2after acid treatment has been greatly improved, the sample treated with0.5mol/L HNO3for5h shows the best result:the efficiency reaches86.7%, meanwhile, the discharge capacity reaches the maximum255.9mAh/g in four cycles, but an obvious3V platform appears in the discharge curve. According to the structure and characteristics of charge-discharge curve of the sample, the reason of acid leaching modification is attributed to the appearance of the spinel structure Li4Mn5O12phase in the Li[Li0.2Ni0.2Mn0.6]O2.Li[Li0.2Ni0.2Mn0.6]O2was also synthesized by carbonate co-precipitation method and sol-gel method. The structure, morphology and electrochemical performance of the products were compared with that synthesized by solid state method.It is found that the layer structure of Li[Li0.2Ni0.2Mn0.6]O2synthesized by carbonate co-precipitation is not so ideal, and the capacity increases more obviously, and the layer structure of Li[Li0.2Ni0.2Mn0.6]O2synthesized by sol-gel methode is completely formed, the first discharge capacity is higher, with less time spent in reaching up to the maximum247.4mAh/g.