Investigation On Lithium-rich Ternary Cathode Materials Synthesized By Hydrothermal Method

Nowadays,rapid development of portable equipment and new energy vehicles pose a new challenge to Lithium ion batteries.The commercialized materials like LiCoO2 are very expensive and have poor safety performance which restrict them from further application,LiFePO4 have low capacity density and poor rate performance which can not satisfy the current demand for high-energy batteries.Lithium-rich ternary cathode materials have promising perspective for their relatively higher energy density compared to traditional cathode materials.However,their practical applications are hindered by their low coulombic efficiency,poor cycle performance and limited rate performance.In this paper,Li1.45Ni0.15Co0.15Mn0.7O2 materials were prepared by solvthermal route and characterized by means of XRD,SEM,TG and XPS techniques.Further,galvanostatic charge-discharge,cyclic voltammetry and electrochemical impedance spectroscopy tests,effects of composing system,synthetic process and aluminum doping on material performance were also studied.?1?In the synthesis of precursor,solvent composition,pH value for reaction,metal concentration of the solution,the lithium source and loading amount of lithium were investigated.The optimal synthetic conditions were as follows:solvent composed of V glycol:V deionized water=6:4,pH value of 8.0,metal concentration of 0.08 M,LiOH as lithium source and with lithium loading amount of Li/M=1.45.The battery made under optimal synthetic conditions achieved the best discharge capacity of 301.4 mAh g^-1 at 0.5 C and 271.4 mAh g^-1at 1 C.?2?In the course of optimizing the synthetic conditions,the temperature of solvethermal reaction,the sequence of adding lithium,the calcination temperature and electrochemical activation were explored.The best synthetic process was determined as:with solvethermal temperature of 160?,lithium salt being mixed with precursor,calcining at 450? for 6hours then 750? for 12 hours,charging and discharging between 2.0 V to 4.5 V,2.0 V to 4.6V and 2.0 V to 4.7 V for 2 circles respectively before circling between 2.0 V to 4.8 V.Compared with the normal calcination temperature of 850?,the temperature of 750? can promote discharge capacity and coulombic efficiency for the first circle.The electrochemical test procedure for batteries would have significant influence on performance,the exactly 6circle of activation could facilitate circle performance?3?By adding aluminum nitrate during solvethermal reaction,Li_1.45Ni_0.15Co_0.125Al_0.025Mn_0.7O₂ Li-rich quaternary material was synthesized successful.Al³⁺doping could enhance layered characteristic and reduce degree of cationic mixing.At the same time,it could restrict phase transformation from layered to spinel-like structure as well as voltage decay of the materials during cycle.At 0.5 C,the obtained material with doping of Al=0.025 showed the best discharge capacity of 278.4 mAh g^-1 and 235.1 mAh g^-1 for the100^th circle,with capacity retention of 84.4%.