Research On The Controllable Preparation,Structure Regulation And Electrochemical Performance Of Lithium-rich Layered Oxide Cathode Material

Lithium-ion batteries are widely used in 3C digital,new energy vehicles and electrochemical research fields.In order to improve the performance of mass energy density and cruising range,high discharge specific capacity lithium-ion battery cathode materials are required.Layered lithium-rich manganese-based cathode materials have theoretical energy density greater than 1000 Wh kg^-1,specific capacity greater than 300 m Ah g^-1,etc.advantage.However,during the first charging process,the irreversible reaction of Li₂Mn O₃resulted in low initial Coulombic efficiency,and during the long cycle,the layered structure changed to the rock salt phase,which caused the average discharge voltage to decay.However,the current experiments ignore the detailed characterization and control of the structure during the synthesis process.In this paper,by adjusting the stoichiometric ratio of manganese/nickel,lithium-rich manganese layered oxide(LLMO)cathode materials with different local structures were synthesized.The local structure was designed to accelerate the deintercalation rate of lithium ions,and Na ion doping was adopted.Miscellaneous means introduce more oxygen vacancies to inhibit the release of oxygen and improve its first coulombic efficiency.By introducing Al₂O₃coating,the interface of the cathode material is improved,and its cycle performance is improved.The main contents are as follows:In order to reduce the average discharge voltage attenuation of Li_1.2Mn_0.56Ni_0.16Co_0.08O₂material,improve the discharge capacity and cycle performance.By adjusting the stoichiometric ratio of manganese/nickel,Li_1.3Mn_0.6+xNi_0.3-xCo_0.1O_2.3+x(x=0,0.1 and 0.2)cathode materials with different local structures were prepared.The electrochemical test of Li_1.3Mn_0.7Ni_0.2Co_0.1O_2.4cathode material showed that its initial discharge capacity reached261.1 m A hg^-1.After 100 cycles at 0.5 C,the capacity retention rate increased from 70.4%to89.1.%.In addition,the voltage retention rate of Li_1.3Mn_0.7Ni_0.2Co_0.1O_2.4cathode material at0.5C after 100 cycles was 93.8%.The enhancement of electrochemical performance is mainly due to the proper amount of Li/transition metal(TM)mixing in the Li layer.TM ions act as pillars and at the same time weaken the repulsive force between adjacent oxygen layers,stabilize the layered structure,and delay voltage attenuation.Secondly,in order to improve the initial coulombic efficiency of Li_1.2Mn_0.56Ni_0.16C o_0.08O₂and obtain excellent rate performance,Li_1.2-2xNa_xMn_0.56Ni_0.16Co_0.08O₂(x=0,0.05,0.1 and 0.2)Cathode material.Experimental data shows that the first coulombic effici ency of Li_1.0Na_0.1Mn_0.56Ni_0.16Co_0.08O₂cathode material reaches 84.2%.The increase in t he initial coulombic efficiency is attributed to the introduction of oxygen vacancies(V _o)on the surface of the material to inhibit the release of oxygen.At 0.5 C,after 100 cycles,the capacity retention rate reached 93.5%.After 100 cycles,the voltage deca y rate is only 4.1%,and the discharge capacity reaches 151.5 m Ah g^-1at 5 C.The i ncrease in rate performance is mainly due to the increase in the Li layer spacing due to Na doping,which increases the Li diffusion rate and enhances the structural stabil ity.In order to enhance the cycle performance of Li_1.2Mn_0.56Ni_0.16Co_0.08O₂cathode material,alumina-coated Li_1.2Mn_0.56Ni_0.16Co_0.08Mg_0.01O₂cathode material was synthesized.SEM and TEM analysis of the morphology and microstructure confirmed that alumina was completely coated on the surface of the magnesium-doped Li_1.2Mn_0.56Ni_0.16Co_0.08Mg_0.01O₂material.Electrochemical test data showed that after 100 cycles at 0.5C,the capacity retention rate increased from 87.3%to 95.4%.At 0.5 C,after 100 cycles,the average discharge voltage attenuation is only 0.177 V.Its excellent cycle life and low voltage attenuation are attributed to the formation of a stable SEI film by the Al₂O₃coating,which reduces interface side reactions.At the same time,Mg is introduced into the supporting layered structure to inhibit structural transformation.