Synthesis And Modification Of Layered-spinel Composite Cathode For Lithium Ion Batteries

Li-Ni-Mn layered-spinel cathode materials became the hot research topic of the lithium ion battery cathode material for they possess the advantages of both the layered phase and spinel phase.In this paper,we prepared the layered-spinel composite cathode material Li_xMn_0.75Ni_0.25O_1.75+x/2by hydrothermal method,and investigated the influence of process parameters on the composite,in order to find the optimum synthesis condition;based on above work,Co/Cr doping and heterostructure modification were adopted to improve the electrochemical performance.The influence of hydrothermal temperature,hydrothermal time,calcination time,Li contents and the?NH₄?₂S₂O₈ contents on the composite material were systematically investigated.The optimum synthesis condition was obtained as hydrothermal temperature of 160 ?,hydrothermal time of 2 hours,calcination temperature of 800 ?,calcination time of 5 hours.At the same time we found that the hydrothermal time has a great influence on the composition of materials.When prolonging the reaction time,the layered phase content may increased and the spinel phase content decreased.For the hydrothermal time 2 h sample it shows the best electrochemical performance with the highest first discharge capacity of 245 mAhg^-1,and discharge capacity of 156.5,105.3 mAhg^-1 under 2 C and 5 C rates.We also prepared the Co doped materials Li_xMn_0.75Ni_0.225CoyO_1.75+x/2?y=0.025,0.05,0.075,0.1,0.125,0.15?and Cr doped materials Li_xMn_0.75Ni_0.225CryO_1.75+x/2?y=0.025,0.05?.The doping content and hydrothermal time on the performance of Cr doping materials were investigated.Charge/discharge tests revealed that Co/Cr doping may lower the discharge capacity but restrain the formation of impurity phase,and Co doping can improve the first discharge capacity(253 mAhg^-1).Preparing the heterostructure modification materials coated with a layer of spinel phase outside the base material.The discharge capacity at low rates and the cycling stability are improved because the spinel layer can make the structure stable.