Synthesis And Properties Of Lithium-rich Ternary Cathode Materials Based On Sol-gel Method

Lithium-ion batteries are widely used in the field of energy storage due to their high specific energy,cycle life and environmental friendliness.In recent years,in order to meet the pursuit of higher specific energy and environment friendly of lithium-ion batteries,the research of Li-rich Mn-based layered oxide cathodes are increasing gradually.The Li_1.2Mn_0.54Ni_0.13Co_0.13O₂(LMNCO)own the advantages of high discharge specific capacity,high energy density and environment friendly,which have attracted attention gradually.However,there are also have large irreversible capacity loss at first cycle,poor cycle performance and rate performance.To solve these problems,the sol-gel method has been used to prepare of LMNCO in this paper.By controlling the synthetic conditions,the organic complexing agent,gelatin adjuvant,and Zn,Mg element doping are used to improve the structure,morphology,particles size and electrochemical properties of LMNCO cathode.The LMNCO cathode material is synthesized by the sol-gel method using Lactic acid as complexing agent.The presintering temperature(450?),and the sintering temperature(850?)are determined by TG analysis.The structure,microstructure and electrochemical properties of the materials at p H of 5.5,7.0 and 8.5 are investigated.The LMNCO-7.0 sample shows a sphere-like morphology,and has higher discharge specific capacity and rate capacity.At 0.1C,the first discharge specific capacity of the LMNCO-7.0 sample is 232.31m Ah g^-1,which is higher than that of LMNCO-5.5(224.75 m Ah?g^-1)and LMNCO-8.5(223.68 m Ah?g^-1).LMNCO-7.0 sample also shows the highest discharge specific capacity at 0.2C,while the cycling performance is not as good as that of LMNCO-5.5 sample.Choosing p H=7.0 as the synthesis condition,LMNCO are synthesized using sol-gel method with lactic acid,malic acid and citric acid as complexing agent,respectively.The effects of different organic acids on the structure,microstructure and electrochemical properties of LMNCO cathode materials are studied.Compared with S-L samples prepared by lactic acid and S-M samples prepared by malic acid,the particle sizes of S-C samples prepared by citric acid as the complexing agent are more uniform and smaller.The specific capacities at first cycle of the S-C samples at 0.1C and 0.5C are 246.25 and 147.43 m Ah?g^-1,respectively,which are higher than those of the other two groups of samples and have higher rate capacities.However,the cycle performance indicates that the capacity of the S-C sample decay rapidly.In order to further reduce the particle size of cathode materials and improve particle dispersion to improve the electrochemical properties of LMNCO cathode material.The gelatin adjuvant with different contents(0wt%,5wt%,10wt%and15wt%)is added to study the effects on the structure,microstructure and electrochemical properties of the LMNCO material.It reveals that the addition of gelatin effective reduce the particle size of the material,but has no significant effect on the discharging capacity and rate performance.However,the cyclic stability of the materials has been improved.After 100 cycles,the capacity retention of the gelatin-assisted SG-5,SG-10,and SG-15 were 84.55%,79.65%and 81.55%,respectively,which are all higher than that of the pure samples(73.49%).Divalent metal ions Zn and Mg are doped to stabilize the structure of the material and improve the cyclic stability of the LMNCO.After 100 cycles at 0.5C,the specific discharge capacities of Zn-2 and Zn-4 are 155.12 m Ah?g^-1 and 155.81 m Ah?g^-1,and capacity retention rates are 93.61%and 94.37%,which are better than those of Zn-0sample(148.43 m Ah?g^-1)and 79.48%.However,the particle size of cathode materials prepared by Zn incorporation is larger,which leads to a lower initial discharge specific capacity.By comparing the effects of Mg doping,Zn doping and Zn-Mg co-doping on the structure and properties of the materials.It was found that Zn-Mg co-doping shows better rate performance,and each sample shows a good cycling stability.After 100 cycles at 0.5C,the capacity retention rates of Zn-4,Mg-4 and Zn-Mg-2 samples are 94.37%,92.03%and 83.87%,respectively,which are higher than those of the Zn-0 sample.