Preparation And Modification Of Ni-Rich LiNi_0.8Co_0.1Mn_0.1O₂ Cathodes For Lithium Ion Batteries

The reduction of fossil energy reserves and the serious environmental pollution have made the demand for the construction of low-carbon society more and more intense.The key to the problem is to develop new energy vehicles,especially electric vehicles(EV),which require a lithium-ion battery with a high specific energy density to meet long-distance requirements after each charging.Then it is extremely important to prepare a cathode electrode material with high discharge capacity and high operating voltage.The cathode material LiNi0.8Co0.1Mn0.1O2 of the layered nickel-rich lithium-ion battery has a good market prospect,and has higher theoretical specific capacity and lower cost compared with the positive materials such as LiNiO2,LiCoO2 and LiMnO2.However,that nickel-rich cathode material still has some shortcomings,such as a high first irreversible capacity,an unfavorable phase change in the high-voltage charge state,and side reactions between the electrode material and the electrolyte during the cycle,which result in an increase in the polarization of the electrode and a decrease in the capacity.In this work,Ni-enriched ternary anode material LiNi0.8Co0.1Mn0.1O2(NCM811)was prepared by co-precipitation method,and the electrochemical performance of Ni-rich material under different firing temperatures was investigated,and the material was modified with the method of Mo-modified and F substitution.The specific contents of the study are as follows:1.Effect of calcination temperature for Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode MaterialsThe precursor of the Ni-rich NCM811 cathode material was prepared by co-precipitation method,and the precursor and the lithium hydroxide were mechanically mixed according to a molar ratio of 1:1.05,the lithium source was uniformly mixed by grinding method and placed in the tube furnace.The NCM811 cathode material was prepared by calcination.The influence of the second stage calcination temperature on the structure and electrochemical properties of the material was investigated.The NCM811 material prepared at different calcination temperatures was tested by XRD,scanning electron microscopy and electrochemical performance test.The result show that the initial discharge capacity of the sample with calcination temperature of 800 ?at 0.1C was 193.8 mAhg-1,and the coulombic efficiency was 86.03%.The initial discharge capacity and capacity retention of the sample under the 1 C cycle test were 169.7.mAh g-1 and 94.7%,respectively.Study have shown that the higher discharge specific capacity and better cycling stability of the sample result from its good crystallization degree,lower cation disorder phenomenon,smaller polarization,smaller resistance and higher lithium ion diffusion coefficient.For the sample to be studied,the best second step calcination temperature was 800?.2.Mo modification to improve the performance of Ni-rich LiNi0.8Co0.1Mn0.iO2 cathode MaterialsMo was successfully doped into NCM811 by simple physical mixing and calcination.The prepared material was electrochemically tested,wherein a material having a doping amount of 0.5%had a discharge specific capacity of 160 mAh/g at a high current of 5 C,44 mAh/g higher than that of the undoped sample,and the sample had a first discharge specific capacity of 182.8 mAh/g at 1 C,and the capacity retention rate was 89.7%after 100 cycles.The experimental results show that proper amount of Mo doping can improve the high rate performance and cycle stability of the material.3.Effect of fluorine substitution on the electrochemical performance of LiNi0.8Co0.1Mn0.1O2 cathode MaterialsLi0.8Co0.1Mn0.1O2-zFz materials were successfully prepared by calcination of NH4HF2 and NCM811 cathode materials.The effects of fluorine substitution on the structure,morphology and electrochemical properties of NCM811 cathode materials were studied.The results show that the initial discharge capacity of F-substituted samples is lower than that of pure samples,mainly because the bonding strength of Li-F(577 kJ mol-1)bond is stronger than the Li-O bond(341 kJ mol-1),which interferes with the intercalation of Li ions,but it is precisely because the strong bonding bond of Li-F improves the structural stability of the material.The F-0.02 sample had a discharge capacity of 168.6 mAh/g after 100 cycles at 1 C,and the capacity retention rate was as high as 92%,and The specific discharge capacity at 0.5C,1C,2C and 5C rates was 188 mAh/g,180 mAh/g,172 mAh/g and 157 mAh/g,the corresponding capacity retention rates were 91.3%,87.9%,84%and 75.7%,respectively.The fluorine substitution is effective to improve the cycle stability and high rate performance of the material.