Preparation And Modification Of Li_1.2Ni_0.2Co_0.08Mn_0.52O₂ Cathode Materials With Ultra-long Life For Lithium-ion Batteries

Nowadays,lithium-ion batteries play an important role in various electronic products.It is necessary to develop long-life and high capacity cathode materials for lithium-ion battery.Lithium-rich cathode materials have higher theoretical discharge capacity and operating voltage,but the obvious shortcomings,such as fast voltage decay,poor cycle life and rate performance,need to be improved.In this paper,the preparation methods of Li1.2Ni0.2Co0.08Mn0.52O2?LNCM?lithium-rich cathode material were explored,and carbonate co-precipitation method was finally selected to synthesize LNCM material.Then the LNCM material was modified by KF and P123 surfactant.The analysis methods of XRD,TEM,SEM and XPS were used to characterize the modified materials.The electrochemical properties of the modified materials were tested by charge-discharge test,cyclic voltammetry test and AC impedance test.The specific research work is as follows:?1?The synthesis method of LNCM material was explored,and co-precipitation method was selected.At the same time,the influence factors on property of LNCM material,such as precipitant adding method,amount of ammonia,reaction temperature and lithium amount were studied.It was found that the most suitable synthesis conditions were dropwise adding precipitant,addition of 3 ml ammonia,35?of reaction temperature and 5 mol%of excess lithium.?2?KF co-doping method was used to improve the electrochemical performance of LNCM material.The co-doping method differing from others was simple and other ions would not be introduced.After modification,Li1.19K0.01Ni0.2Co0.08Mn0.52O1.19F0.01?KF-LNCM?material showed superior electrochemical performance:It had the specific capacity of 131.57 m Ah g^-1 at 10 C,and showed high capacity retention of 93.37%after1500 cycles.At the same time,the electrochemical performance of Li1.19K0.01Ni0.2Co0.08Mn0.52O1.19F0.01?C-LNCM?material co-doped with K and F elements from different sources was also tested.KF-LNCM material was proofed to have longer cycle life according to the testing data.?3?P123 surfactant was used to improve the electrochemical performance of LNCM material during the precursor synthesis process.After modification,P123-LNCM sample had a discharge capacity of 138 m Ah g^-1 at 5 C,the capacity retention was 89.9%after 200 cycles.XRD test proved that P123-LNCM material had larger layer spacing and complete layered structure than LNCM.AC impedance test showed that P123 surfactant could effectively reduce the charge transfer resistance,thus improving the electrochemical performance.