Research On The Electrochemical Performance Modification Of O2-type Lithium-rich Manganese-based Cathode Material

In order to meet the requirements of high energy storage devices and high energy density in modern society,lithium-manganese rich cathode materials have become one of the choices to solve the battery life problem of lithium ion because of their high specific capacity and energy density.Although O2-type lithium-rich manganese materials have a better structure than traditional O3-type materials,However,its cycle performance and voltage stability can not meet the needs of practical applications.In order to improve the electrochemical performance,especially the cycling performance,of traditional O₂-type lithium-rich manganese materials,the relevant research contents and structures are as follows:（1）Firstly,the Ce doped Li_1.25Mn_0.55Co_0.2O₂ cathode material was prepared.The initial specific discharge capacity of the Ce doped Li_1.25Mn_0.55Co_0.2O₂ cathode material with 3%doping content is 305.2.6m Ah/g at the current density of 0.1C,and the specific discharge capacity is 226.79m Ah/g after 40 charging and discharging cycles.The voltage attenuation through the discharge is 0.135V,which is 88.25%lower than that of the original material.（2）Boron doped Li_1.25Mn_0.55Co_0.2O₂ cathode material was prepared by adding sodium borohydride.The cathode material 5%of the doped Li_1.25Mn_0.55Co_0.2O₂ can improve the first coulomb efficiency,and the discharge specific capacity decreases from the initial 287.93 m Ah/g to 227.38m Ah/g after 50 cycles of charge and discharge at 0.1C current density.The specific discharge capacity is 252.67 m Ah/g,227.53 m Ah/g and 201.12 m Ah/g at 0.2C,0.5C,1C and 2C respectively.In addition,the average voltage of the material decreased by only 0.100V.（3）The material was doped with two elements so that Ce and B could play synergistic roles.The results show that the cyclic stability of Li_1.25Mn_0.55Co_0.2O₂materials with mixed doping content of 5%is improved.The specific initial discharge capacity was 287.93 m Ah/g at 0.1C rate,and the capacity retention rate was 83.06%after 75 charge-discharge cycles.And the specific discharge capacities of 269.30m Ah/g,252.81 m Ah/g,223.87 m Ah/g and 205.15 m Ah/g are still available at 0.2C.The median voltage of the initial cycle discharge of the material is 3.251V,which decreases by 0.091V after 50 cycles of charge and discharge,the phase transition rate is effectively delayed.