Preparation And Modification Of Enriched Lithium Manganese-based Ternary Positive Electrode Material

Lithium-rich manganese-based ternary cathode materials have received widespread attention due to their advantages such as high energy density,wide operating voltage,and low cost.However,along with many advantages,the material has low coulombic efficiency for the first time,low cycle capacity retention rate,and high current density down charge.Poor discharge performance is also the main problem to be solved.First of all,This paper takes the material x Li₂Mn O₃·（1-x）Li[Ni_1/3Mn_1/3Co_1/3]O₂as the research object,and explores the structure,morphology and electrochemical performance of lithium-rich ternary cathode materials prepared by sol-gel method with different components and temperatures.As an electrolyte,solid electrolyte also has conductivity.Mo doping can not only stabilize the cubic phase structure of solid electrolyte,but also increase the structural stability of cathode material.Then,the three modification methods are studied:cationic Mo doping,solid electrolyte Li₇La₃Zr₂O₁₂（LLZO）coating,and different components of Mo⁶⁺doped into LLZO to coat the material.The structure and electrochemistry of the modified lithium-rich manganese-based ternary cathode material are studied.Changes in performance.Mainly include the following:（1）The lithium rich manganese ternary cathode material x Li₂Mn O₃·（1-x）Li[Ni_1/3Mn_1/3Co_1/3]O₂with component coefficients of x=0.4,0.5 and 0.6 was synthesized by sol-gel method,and the optimal components were selected to study the calcination temperature.The effects of different components and calcination temperature on the structure,morphology and properties of the material were discussed.With the change of the components in the material and the increase of the calcination temperature,the discharge specific capacity and the specific capacity retention rate of the material increase first and then decrease.The optimum composition and calcination temperature were determined,that is,the Li_1.2Ni_1.3Co_1.3Mn_0.54O₂material with a component coefficient of x=0.5 was calcined at 900℃.Obtain the discharge specific capacity of the material is 230.5 m Ah/g at the current density of 20m A/g and the voltage range of 2.0～4.8V.After 100 cycles,the specific discharge capacity is 186.5m Ah/g,and the capacity loss is 19.1%compared with the capacity at the first discharge.（2）Li_1.2Ni_1.3Co_1.3Mn_0.54-yMo_yO₂（y=0.03,0.06and0.09）was synthesized by doping Li_1.2Ni_1.3Co_1.3Mn_0.54O₂（LNCMO）with cationic Mo on the basis of sol-gel method.The test results show that with the increase of Mo doping,although the first discharge specific capacity of the sample material gradually decreases,the first cycle coulomb efficiency and cycle performance are better,and the rate performance is also effectively improved.The sample with Mo component coefficient y=0.06 shows the best capacity retention and magnification performance.Under the conditions of 2.0～4.8V and 0.1C,the first cycle coulomb efficiency is73.8%;After 100 cycles,the specific discharge capacity is 183.9mah/g,and the capacity retention rate is 83.2%.It shows a specific capacity of114.0m Ah/g at 2.0C discharge current,showing a high rate performance.After EIS test,it is known that the material with y=0.06 has the minimum charge transfer impedance（RCT）.（3）LNCMO material was also coated with LLZO by sol gel method.The test results show that a small amount of llzo material coated on the surface can not only prevent the reaction between the electrode material and the electrolyte to stabilize the material structure,but also improve the ionic conductivity of the material surface and increase the rate of charge diffusion and transmission.The material coated with 3wt%LLZO has the best morphological characteristics and electrochemical performance.The specific discharge capacity is 250.4m Ah/g in the first cycle,231.5m Ah/g after 100 cycles,it was 211.5m Ah/g,and the capacity retention rate was84.5%.At the current density of 2.0C,the discharge capacity is145.3m Ah/g,which has the optimal cycle stability at high magnification and the minimum charge transfer impedance.Therefore,coating a small amount of LLZO material on the surface can not only prevent the reaction between the electrode material and the electrolyte,so as to stabilize the material structure,but also improve the conductivity of ions on the sample surface and increase the rate of charge diffusion and transmission.（4）In the end,dop LLZO with Mo,and then the surface of LNMCO was coated.The results show that the LNMCO-LLZO-Mo_zmaterial obtained by Mo component doping has better layered properties than the LNMCO-LLZO material without Mo component doping.Under the conditions of 2.0～4.8V and 0.1C,the LNMCO-LLZO-Mo_0.2material with Mo doping component z=0.2 has the best electrochemical performance.The specific discharge capacity is 234.2m Ah/g in the first cycle and 226.3m Ah/g after 100 cycles,it was 194.8m Ah/g,and the capacity retention rate was 85.3%.The material also has the minimum charge transfer impedance.