Modification Research Of Nickel-Rich Ternary Cathode Material Lini_0.83Co_0.11Mn_0.06O₂ For Lithium Ion Batteries

The rapid development of new energy vehicles has greatly stimulated the market demand for high-performance lithium-ion batteries,and it puts forward higher expectations for lithium-ion battery cathode materials.The nickel-rich ternary cathode material LiNi_1-xM_xO₂（x≥0.6,M=Co,Mn,Al）has become a popular cathode material due to its advantages of low cost and high capacity,but its further development is hindered by defects such as poor structural stability and short cycle life.Considering these problems,the prepared LiNi_0.83Co_0.11Mn_0.06O₂ nickel-rich ternary cathode materials were modified by bulk doping and surface coating,and various test results of the materials before and after modification were discussed in detail,as follows:（1）In order to systematically understand the modification effect of phase doping of different lattice strcuture,K⁺,Nb⁵⁺and F^-doped LiNi_0.83Co_0.11Mn_0.06O₂ cathode materials were prepared,in which K⁺,Nb⁵⁺and F^-enter in the Lisite,transition metal site and O site in the crystal lattice,respectively.The results show that the cationic mixing degree of K⁺-doped LiNi_0.83Co_0.11Mn_0.06O₂ material decreas from 3.02%to1.68%,and it has the discharge specific capacity of 160.1 m Ah/g at 5.0 C,which is much higher than that of the pristine LiNi_0.83Co_0.11Mn_0.06O₂ of 104.2 m Ah/g.The Nb⁵⁺-doped LiNi_0.83Co_0.11Mn_0.06O₂ material with a more stable structure delivers a capacity retention of 86.6%after 200 cycles at 1.0 C,while the capacity retention rate of the pristine LiNi_0.83Co_0.11Mn_0.06O₂ is only 61.2%.The F^--doped LiNi_0.83Co_0.11Mn_0.06O₂ material has better interfacial stability,and it has a capacity retention of 78.3%after 200 cycles at 1.0 C.By comparing the improvement of cycle performance and rate performance,it is determined that the electrochemical performance of Nb⁵⁺-doped LiNi_0.83Co_0.11Mn_0.06O₂ cathode material is the best.（2）For exploring the effect of Nb⁵⁺doping content on nickel-rich ternary cathode materials,LiNi_0.83Co_0.11Mn_0.06O₂ cathode materials with different Nb⁵⁺doping content are prepared,and the results show that 1 mol%Nb⁵⁺doping can significantly improve cycle stability with lower capacity sacrifice.Compared with the pristine LiNi0.83Co0.11Mn0.06O2,the c/a of Li（Ni0.83Co0.11Mn0.06）0.99Nb0.01O2 increases from 4.9414 to 4.9421,indicating that Li(Ni_0.83Co_0.11Mn_0.06)_0.99Nb_0.01O₂ obtains a more ordered layered structure.In addition,it has tighter secondary spherical particles and a more stable structure,which is due to the introduction of strong Nb-O bonds.The battery assembled with Li(Ni_0.83Co_0.11Mn_0.06)_0.99Nb_0.01O₂ electrode has a discharge specific capacity of 154.6 m Ah/g at 5.0 C,and the recovery reaches 97.3%after the rate performance test.Moreover,it not only has a capacity retention of 86.6%after 200 cycles at 1.0 C at 25°C,but also has a capacity retention of 71.7%even after 200 cycles at 1.0 C at 60°C,indicating that the performance is significantly improved.（3）To further improve surface side reaction,the surface coating of Li₃PO₄ is carried out on Li(Ni_0.83Co_0.11Mn_0.06)_0.99Nb_0.01O₂ material,and the results show the obvious decrease of residual lithium content on the surface of the prepared Li₃PO₄@Li(Ni_0.83Co_0.11Mn_0.06)_0.99Nb_0.01O₂ cathode material.A uniform coating layer with a thickness of about 12.6 nm is formed on the surface,and the diffusion coefficient of Li⁺increase from 8.4852×10^-11 cm^-2s^-1 to 1.0660×10^-10 cm^-2s^-1.Under the good synergistic effect of Nb⁵⁺doping and Li₃PO₄ coating,the battery assembled with Li₃PO₄@Li(Ni_0.83Co_0.11Mn_0.06)_0.99Nb_0.01O₂ electrode still retains the residual specific capacity of 154.1 m Ah/g with the capacity retention of 88.8%after 200cycles at 1.0 C at 25°C.Even at 1.0 C at 60°C,it also possesses the capacity retention of 72.0%,and it has the discharge specific capacity of 156.7 m Ah/g at 5.0 C.More importantly,the secondary spherical particles and the coating layer of Li₃PO₄@Li(Ni_0.83Co_0.11Mn_0.06)_0.99Nb_0.01O₂ remain intact without obvious agglomeration after cycling test.