Preparation And Modification Of Nickel-rich Cathode Materials For Lithium Ion Batteries

With the development of society,lithium-ion batteries are closely related to our lives,which requires the improvement of energy density and safety performance of lithium-ion batteries,and the further development of electrode materials,especially cathode materials.LiNi_0.8Co_0.1Mn_0.1O₂（NCM811）is considered to have the most development potential.However,the thermal and cycling stability of NCM811 ternary cathode material during cycling is poor,limiting its commercial application.Therefore,starting from the synthesis process of cathode materials,this thesis studies the effects of calcination temperature and lithium ratio on the structure and properties of the material,and conducts coating modification and doping modification on the prepared NCM811 cathode material,and studies its structure and morphology.and electrochemical performance.The main research contents and results are as follows:（1）The lithiation reaction process of Ni_0.8Co_0.1Mn_0.1（OH）₂ precursor was deduced by TG/DSC analysis,and the calcination time and temperature were designed.It was found that the cathode material synthesized at 500℃for 4 h,then 750℃for 14 h,the lithium ratio Li/Me value was 1.07,the crystal structure of the cathode material was good,the cation disorder was low,the particle size was uniform,and the primary single crystal particle shape was regular.,the particle size is moderate,the spherical structure of the secondary particles formed by close arrangement and polymerization is stable,the discharge specific capacity is 200.4 m Ah/g,the first charge-discharge efficiency is 86.7%,and it has good electrochemical performance.（2）Al₂O₃-coated LiNi_0.8Co_0.1Mn_0.1O₂ composites were successfully prepared by wet chemical method and high-temperature solid-phase method.The coating layer not only did not destroy the crystal structure of the material,but also effectively alleviated the lithium-nickel mixing effect in the material.The coating material showed better performance when burned back at 700℃.The discharge specific capacity of NCM@Al-700 sample was 213.4 m Ah/g,reducing the loss of lithium during the first cycle,and at the same time,the rate performance is also greatly improved.When reducing the coating material,the water content involved in the hydrolysis reaction should also be reduced at the same time,the thickness of the coating layer formed is small,and the capacity retention rate of the obtained sample after 100 cycles is as high as 95.7%,which has a certain effect on the cycle stability of the material.improve.（3）La³⁺-doped Li(Ni_0.8Co_0.1Mn_0.1)_1-xLa_xO₂ composite cathode materials were synthesized by high-temperature solid-state method,and the relationship between doping content and the structure and electrochemical performance of NCM materials with different lithium ratios was studied,and Effect of calcination time on doped materials.The effects of calcination time and different content of La³⁺doping on the crystal structure and electrochemical properties of the material were found.It is found that La³⁺is doped into the lattice to generate La₂Li_0.5Ni_0.5O₄ crystal phase,but it will not affect the development of the material structure.When the NCM material with Li/M=1.07 is doped,the capacity of La³⁺ion-doped NCM with La/M=0.02 is maintained.The rate was 91.9%.Due to the La³⁺doping into the lattice and the formation of the La₂Li_0.5Ni_0.5O₄ crystal phase,the specific capacity of the material begins to decrease,but the synergistic effect between the formed La₂Li_0.5Ni_0.5O₄ crystal phase and La³⁺doping makes the material have a higher capacity retention.When the NCM material with Li/M=1.05 is doped,the La/M=0.015 sample still has a discharge specific capacity of 161.7 m Ah/g at 5 C,and the rate performance is greatly improved.Further research on the calcination time of the doped material shows that the La³⁺doped material can quickly form a crystal structure during the calcination process.It can be seen that the doped La³⁺can stabilize the crystal structure,and the surface La₂Li_0.5Ni_0.5O₄ crystal has a certain degree of protection against the material.As a result,the capacity retention rate and rate performance of doped materials are improved.