Synthesis And Modification Of High-LiNi_0.9Co_0.05Mn_0.05O₂ Cathode Materials

In recent years,as the share of hybrid and electric vehicles in the market grows year by year,the end consumers’requirements for electric vehicle range and price are also rising.In order to better cater to consumers,the development of high-capacity,low-cost and clean cathode materials for lithium-ion battery has become a trend.Among them,Li Ni_0.9Co_0.05Mn_0.05O₂（LNCM90）cathode material not only exhibits high specific capacity,but also has great advantages in cost and environmental protection due to its low cobalt content.The purpose of this work was to synthesize LNCM90 with superior performance.Firstly,the process parameters for the preparation of optimal precursors were explored,then the calcination process of cathode material was determined,finally,the effective modification mean was found by elemental co-doping.Ni_0.9Co_0.05Mn_0.05CO₃ precursors were prepared by hydrothermal method,with using urea as precipitant and transition metal acetates as raw materials.The effects of urea concentration,hydrothermal temperature and time on its crystal structure,chemical composition,morphology,particle size and cycling performance were investigated.When the molar ratio of urea to transition metal was 5:2,hydrothermal temperature was 180℃and time was 12 h,Ni_0.9Co_0.05Mn_0.05CO₃ precursors with good crystallinity,correct chemical composition,homogeneous morphology and excellent cycling performance could be synthesized.On basis of the above best-prepared precursors,Li Ni_0.9Co_0.05Mn_0.05O₂cathode materials were synthesized by solid-phase sintering method,with using lithium hydroxide as the lithium source.The effects of different lithium excess,calcination temperature and calcination time on its crystal structure,morphology and electrochemical properties were explored.When the molar ratio of Li/M（M=Ni,Co,Mn）was 1.05,calcination temperature was 750℃and sintering time was 12 h,Li Ni_0.9Co_0.05Mn_0.05O₂cathode materials with ordered cation arrangement and homogeneous morphology could be prepared.This material delivered an initial discharge specific capacity of 209 m Ah g^-1 between 2.75 and 4.3 V,with the capacity retention of 83.33%after 100 cycles.It also transferred a specific discharge capacity of 110 m Ah g^-1 at 5 C.On basis of the above best-prepared calcination process,Mg-Al,Mg-B and Al-B co-doping LNCM90 cathode materials were synthesized by solid-phase sintering method,with using Mg O,Al（OH）₃ and H₂BO₃ as raw materials.The degree of cation mixing in the structure and the amount of residual lithium on the surface were analyzed by XRD,SEM,EDS,XPS.The kinetic properties in LNCM90 and modified-LNCM90 were analyzed by cyclic voltammetry tests at different scan rates.The experimental results showed that Mg-Al co-doping LNCM90 exhibited an excellent electrochemical performance.This material delivered an initial discharge specific capacity of 208 m Ah g^-1,with capacity retention rate increasing to86.17%.It also exhibited a superior discharge capacity of 135 m Ah g^-1 at5 C.