| Recent severe fluctuations in crude-oil prices and global environmental concernshave accelerated efforts to develop lithium ion batteries for hybrid electric vehicles(HEVs). With the expanding demand of hybrid vehicles and a variety of portableconsumer electronics, lithium ion batteries are developing towards the direction ofhigh energy density, high capacity, high security, more environmentally friendly, andlow-cost. Cathode material is an important component of lithium ion battery, so it’sessential to develop the high rate and high capacity cathode materials to meet theincreasing requirement of electronic applications. Although commercializedLi[Ni1/3Co1/3Mn1/3]O2and Li[Ni0.5Co0.2Mn0.3]O2are cheap, high capacity, and highstability, their rate capability, cycle stability, their high voltage or high rate cycliabilityremain to be improved.In this paper, Li[Ni0.48Co0.24Mn0.28]O2has been synthesized via coprecipitationmethod, and then is coated with Li3VO4, etc. The results show that the optimumammonia concentration and PH for synthesis of [Ni0.48Co0.24Mn0.28](OH)2precursorare separately0.4mol/L and11, and the synthesized precursor exhibits uniformprimary particles, low agglomeration, and integrity crystal structure. ThenLi[Ni0.48Co0.24Mn0.28]O2is prepared with synthesized [Ni0.48Co0.24Mn0.28](OH)2asstarting material. It is found that Li[Ni0.48Co0.24Mn0.28]O2exhibits superiorelectrochemical performance when synthesized [Ni0.48Co0.24Mn0.28](OH)2is mixedwith Li2CO3and then is calcined under850°C for10h. Furthermore, the synthesizedLi[Ni0.48Co0.24Mn0.28]O2is coated with Li3VO4,etc. Electrochemical performanceresults show that Li3VO4-coated Li[Ni0.48Co0.24Mn0.28]O2shows improved ratecapability and high rate cycliability and Li[Ni0.48Co0.24Mn0.28]O2coated with3wt.%Li3VO4delivers a highest capacity of144.1mAh/g at1C after100cycles in thevoltage range2.8-4.4V. Moreover, it delivers a highest capacity of45.0mAh/g evenat20C.Among the coating materials of Li3PO4, LiCoPO4, LiNiPO4, MnPO4, and Li3VO4,Li3PO4can significantly improve the rate capability of Li[Ni1/3Co1/3Mn1/3]O2; what’smore, only Li3VO4can significantly improve high voltage capability ofLi[Ni1/3Co1/3Mn1/3]O2.Further study on Li3VO4-coated Li[Ni0.5Co0.2Mn0.3]O2indicates that high voltage or high rate cycliability of Li[Ni0.5Co0.2Mn0.3]O2have been improved by coating withLi3VO4. The sample coated with3wt.%Li3VO4shows the optimum electrochemicalperformance. It delivers a capacity of61.5mAh/g at10C after100cycles. Thecapacity retention at1C is63.5%at cut-off voltage4.6V, and63.0%at a highercut-off voltage4.8V. |
