Study On Fabrication And Electrochemical Properties Of LiNi_1/3Co_1/3Mn_1/3O₂ Lithium Battery Cathode Materials

The key to the development of lithium-ion batteries with high specific energy,high specific power and long lifetime is to develop the low cost fabrication technology of high quality cathode materials.The structure and electrochemical stability of anode materials have important effects on the capacity,charging and discharging platform and cycling performance of lithium-ion batteries.Taking LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials as the research object,by introducing the analytic hierarchy process?AHP?to multiple target decomposition,it is concluded that the index weight ratio products model?capacity:coulomb efficiency:capacity retention ratio:15C/1C ratio=0.0955:0.0955:0.2495:0.5595?.orthogonal test design was carried out to obtain the optimal technological parameters as A1B1C3D1,the technological parameter combination is optimized as precursor particle size of 3 microns,L/M ratio of 1.02,calcining temperature of970^oC and calcining time of 8h.The orthogonal test results showed that the two pairs of X-ray diffraction peaks?006?/?012?and?018?/?110?of LiNi_1/3Co_1/3Mn_1/3O₂ powders are prepared under optimized process parameters,and the characteristic peaks of XRD I_?003?/I_?104?exhibit obvious splitting,and the ratio of I_?003?/I_?104?is 1.88,and the layered structure is very obvious.The electrochemical performance of LiNi_1/3Co_1/3Mn_1/3O₂ is then tested by an electrochemical workstation.It was found that within the voltage range of 4.2V to 3.0V,the initial capacity reached 149.3mAh/g and the initial coulomb efficiency was 90.7%at 0.2C discharge.After 300cycles at room temperature,the capacity retention ratio is 94.20%,and the specific capacity of 15C reaches134.6mAh/g,that is,the ratio of 15C/1C reaches 91.9%.Through the range analysis and variance analysis of the orthogonal test data,it was found that the size of the precursor particle has a significant impact on the comprehensive performance within the 95 confidence interval,and with increasing the size of the precursor particle,the size of single crystal increases horizontally and the specific surface area decreases horizontally,and the comprehensive performances exhibit a downward trend.Through the study of Li(Ni_1/3Co_1/3Mn_1/3)₁-_x Al_x O₂ material doped with Al ions,it was found that with increasing the doping amount of Al ions,the crystal size increases,the XRD characteristic peak I_?006?+I_?012?/I_?101?gradually increases,and the formation of cambium-layer structure particles decreases.When x=0.036,the primary particle size of Li(Ni_1/3Co_1/3Mn_1/3)_1-x-x Al_x O₂ is differentiated from the average particle size of 250nm before Al ion doping to 200nm and 400nm.When x=0.072,the number of crystals in the secondary particles decreases and the specific surface area decreases.Al ion doping can regulate the crystal growth of Li(Ni_1/3Co_1/3Mn_1/3)_1-x-x Al_x O₂.When x=0?pure phase?,the ratio performance is the best.The specfic capacities under conditions of 10C and 15C are 142.6mAh/g and134.6mAh/g,respectively.When x=0.036,the cycling performance at room temperature is the best,and the capacity retention rate after 300cycles is 94.80%.At x=0.072,5C has the largest specific capacity,and the coulombic efficiency reaches the maximum value?91.60%?for the first time.After the coating modification of LiNi_1/3Co_1/3Mn_1/3O₂@x Al₂O₃ material,it was found that the coating treatment could modify the material surface and significantly reduce the CO₃^2-index,i.e.,the residual amount of free Li⁺,which effectively inhibits the decomposition reaction of electrolyte on the surface of electrode material at high temperature and improved the cycling performance at high temperature of 60^oC.In this paper,the influence of Al₂O₃ coating method on the cycling performance was studied.It was found that when the Al₂O₃ amount by dry coating is x=0.018,the capacity retention rate of the material after 300cycles at 60^oC is 93.40%,which is 1.6%higher than that without Al₂O₃ coating.However,when the wet coating is applied and the Al₂O₃ amount is x=0.018,the capacity retention rate of the material after 300cycles at 60^oC is 95.00%,which is 3.2%higher than that without Al₂O₃ coating.The improvement of high temperature cycling performance by Al₂O₃ coating treatment is opposite to the decrease trend of CO₃^2-index,indicating that the coating treatment can effectively reduce surface lithium residue and improve high temperature cycling performance.