Preparation And Performance Of Single Crystal High Nickel Oxide Cathode Material

High-Ni layered Ni Co Mn（NCM）ternary cathode materials have high spe cific energy and working voltage,and the modification of single crystal as secondary spherical particles can make up for the shortage of secondary particles,which will play an important role in the future lithium ion battery materials.In this paper,high temperature solid phase sintering method was used to explore the synthesis process of single crystal,and the influence of calcination temperature,holding time and sintering atmosphere on the synthesis of single crystal was discussed.On this basis,niobium doping was innovatively used for modification to further improve the electrochemical performance of single crystal materials.The precursors were prepared by co-precipitation method,exploring the calcination temperature,holding time and sintering atmosphere for single crystal structure and properties of the material.The final product is of structure of single crystal,and the optimum sintering temperature is 900℃.By analyzing the performance characterization.The holding time is 12 h,calcining atmosphere is oxygen.The single crystal material synthesized has a complete crystal structure,high purity and better three-dimensional layered structure,which show better electrochemical performance.At 0.1 C ratio,the discharge specific capacity reached195.6 m Ah/g for the first time,and still maintained 80.3%of the initial specific capacity after 100 cycles of 1 C.Based on the temperature of the initial formation of single crystal at 870℃,the optimal holding time of 12 h in the oxygen atmosphere to explore the optimal synthesis process of doped Nb₂O₅ single crystal preparation.The precursor,lithium source and conventional size Nb₂O₅ were uniformly mixed and calcined in a tubular furnace at high temperature,so as to explore the effects of calcination temperature and doping ratio on the synthesis process of Nb₂O₅ modified single crystal materials.The results show that when the calcination temperature is 900℃and the doping amount of Nb₂O₅ is 1%,the electrochemical performance of single crystal is the best.The specific discharge capacity of 0.1C is 199.8 m Ah/g for the first time,and the retention rate of 100 cycles and 200 cycles is 99.3%and 93.7%at 1C ratio,respectively.The formation mechanism of single crystal material was investigated.A variety of means to show that the formation process of single crystal following dissolving-recrystallization mechanism,namely the lithium in precursor calcination process with the increase of temperature,reunited into a secondary spherical particle of a particle,lead to hydroxyl spherical precursor collapse,then a particle dispersed,as the growth of the holding time,the energy of dynamic balance,driven by the nanocrystalline primary grains grow up gradually and form crystalline surfaces to produce single crystal particles.The cyclic failure mechanism of single crystal materials at different cut-off voltages was investigated.The cells were assembled with single crystal materials synthesized under the optimum process and tested at different cut-off voltages.The results show that the monocrystalline cathode material circulates at a voltage of2.7-4.3 V,and reversible interlamellar slip exists within the crystal,but the slip will recover with the charging process,and the monocrystalline particles still maintain the integrity of the crystal structure.However,when the voltage exceeds 4.3 V,with multiple charge-discharge cycles,the interlaminar slip in the crystal cannot be completely recovered during the charging process,but the slip fold layer will be left behind.As the cut-off voltage continues to increase,the slip fold layer will increase,and the plane defect will appear in the single crystal,until the micr o-crack will appear in the single crystal after multiple cycles,which ultimately leads to the degradation of the electrochemical performance of the material.