Study On Preparation And Modification Of Cobalt Nickel Manganese Ternary Material As Cathode For Lithium Ion Batteries

LNCM ternary material has the advantages of high energy density,good rate capacity,cycle capacity and safety performance as the positive electrode material for lithium ion battery.However,the cation mixing in the lithium layer of LNCM material affects the stability of the material,and the first charge and discharge efficiency and discharge voltage platform are lower.At present,it has become the researching hotspots that improve the tap density,the rate performance,the cycle stability under high/low temperature and high voltage of the type ternary material.Metal-organic framework materials have been widely used in the field of energy storage due to their high porosity,interpenetrating pores,large specific surface area and good chemical stability.In this paper,the metal organic framework NiCoMn-NDC material was synthesized by hydrothermal method.Next,the precursor was fully mixed with the lithium salt and ground,and then the LNCM ternary cathode material was prepared by high temperature calcining above-mentioned mixture.On this basis,LNCM was modified by Li₂ZrO₃ and Al₂O₃,respectively.1.The precursor NiCoMn-NDC was prepared by solvothermal method and characterized by XRD and SEM.It was found that NiCoMn-NDC materials exhibited characteristic diffraction peaks of Co-NDC,Mn-NDC and Ni-NDC materials.The shape was blocky,the size was about several tens of micrometers and the distribution was not uniform.2.The precursor of NiCoMn-NDC material and LiOH·H₂O were sufficient grounded.LNCM materials were obtained through calcining at different temperatures?750°C,850°C and 900°C?.Through a series of tests and characterization,it was found that the too low or too high calcining temperature was not conducive to the electrochemical performance of the material.At lower temperature,the material will be incompletely crystallized and the purity will be low,resulting in poor electrochemical performance.Too high calcining temperature will increase the grain size,hindering the transportation of lithium ions and the diffusion of the electrolyte.Meanwhile,it was also not beneficial to the electrochemical properties of the material.The obtained LNCM ternary material under 850?which had the best electrochemical performance.Therefore,850?was the optimum calcination temperature.The first cycle discharge specific capacity of LNCM-850 was 126.2 mAh/g,and the discharge specific capacity was 103.7 mAh/g after cycling100 cycles.The capacity retention rate was82.1%.3.In this paper,different amounts of Li₂ZrO₃ were used to modify the performence of LNCM cathode material,and the cathode material Li₂ZrO₃@LNCM was synthesized.The test results showed that the original layered structure of the material was not changed after coating,and the Li₂ZrO₃ were attached to the surface of the LNCM material in the form of small particles.After coating Li₂ZrO₃,the first circle discharge specific capacity and rate performance of the LNCM material was improved.When the coating amount was 3%,the first discharge specific capacity was 169.1 mAh/g,the material still possessed a specific capacity of 86 mAh/g under current density of 1800 mA/g.Furthermore,the material of discharge capacity and voltage platform was improved during the cycling.After cycling for100 cycles at the current density of 900 mA/g,the capacity retention ratio of the materials that0%Li₂ZrO₃@LNCM and 3%Li₂ZrO₃@LNCM were 75.18%and 91.89%,respectively.Because the proper amount of Li₂ZrO₃ improved the material's structural stability.Therfore,we found that the cyclic stability of the coated material was significantly improved,The dissolution of the material in the electrolyte was prohibited,therefore 3%Li₂ZrO₃ was determined to be the optimum coating amount.4.LNCM also was modified with different amounts of Al₂O₃ as coating material.The test results showed that after coating Al₂O₃,small particles appear on the surface of the material,and the amount of small particles increased with the increasing of coating amount.Al₂O₃adhered to the surface of LNCM material as small particles.Compared with other coating ammounts,the material 5%Al₂O₃@LNCM had better electrochemical performance than the pure sample in terms of specific capacity and voltage platform.After a large current charging and discharging,the 5%Al₂O₃@LNCM material could still maintain an initial specific capacity of 92.7%when the current density returned to 18 mA/g.Moreover,at the high current density of 1800 mA/g,the material still had a specific capacity of 78.0 mAh/g and a relatively obvious discharge platform.On the other hand,the cycle performance of was also greatly improved.At the current density of 900 mA/g,the capacity retention ratio of0%Al₂O₃@LNCM and 5%Al₂O₃@LNCM materials were 75.18%and 99.7%after cycling100 cycles,respectively.It was shown that the Al₂O₃ coating layer prohibited the side reaction of the electrode material in direct contact with the electrolyte,significantly improved the interface stability and charge transfer ability between LNCM cathode and electrolyte.