Synthesis And Properties Of Nickel-rich Ternary Cathode Materials For Lithium-ion Batteries

Lithium-ion batteries are widely used in various consumer electronic equipment due to their high energy density,large output power,small self-discharge,long cycle life and pollution-free,and the market scale in new energy automobile industry is getting larger and larger.Ni-Co-Mn ternary cathode materials,especially rich-nickel materials?nickel content more than 50%?with higher cost performance,have attracted great attention from the industry.However,limited by its own crystal structure,rich-nickel materials have some problems such as poor cycling performance and high temperature storage performance.In this paper,LiNi_0.5Co_0.2Mn_0.3O₂?NCM523?,LiNi_0.6Co_0.1Mn_0.3O₂?NCM613?,LiNi_0.8Co_0.1Mn_0.1O₂?NCM811?,were prepared by solid phase method.The main research results are as follows:1)NCM523,NCM613 and NCM811 cathode materials were prepared by solid phase method using commercial precursor and LiOH·H₂O as raw materials.The effects of sintering temperature,lithium content and sintering time on the crystal structures,morphologies and electrochemical properties of three materials were investigated.Experiments show that three materials obtained under the optimal sintering process have uniform particle size,good crystallinity and complete layered structure.The optimal sintering process of NCM523material is as follows:when lithium content of 1.04 and sintering temperature of 800?for 12h,the synthesized material has a better spherical morphology and the excellent electrochemical performance,and its capacity retention rate under 1C reaches 90.36%.The optimal sintering process of NCM613 material is as follows:when lithium content of 1.04 and sintering temperature of 800?for 15h,and the capacity of the first discharge was 166.7mAh/g at 1C.The NCM811 material synthesized under oxygen atmosphere with lithium content of 1.06,sintering temperature of 850?and holding time of 15h showed a good first discharge capacity up to 183.2mAh/g.2)The electrochemical behaviors of three materials under different cut-off voltages were investigated,and their crystal structure,morphology and electrochemical properties were compared.The results show that three materials have the same?-NaFeO₂ layered structure,and the XRD characteristic peak intensity is decreased obviously after the charge-discharge cycle.Three materials were spherical or quasi-spherical formed by small primary particles,and NCM811 material has a slight agglomeration phenomenon.Electrochemical tests show that the three materials exhibit different electrochemical behaviors.The main structure of NCM523 and NCM613 materials was very stable during the cycle,and the structure does not change after the cut-off voltage is increased to 4.5V.NCM811 material undergoes multiple microstructural phase transitions during charging and discharging at a lower cut-off voltage of 4.2V,which indicates that even at the lower cut-off voltage,the structure of high nickel material?NCM811?was unstable in the process of charge-discharge.