Study On Modification Of Ternary Cathode Material For Lithium-Ion Batteries

As a typical cathode materials for lithium-ion batteries,Li Ni_0.8Co_0.15Al_0.05O₂ has been attracted increasing attentions in power battery and energy storage battery with the assistance of high energy density and low cost.While during the charging process,the strongly oxidizing Ni⁴⁺generated on the surface of delithiated NCA is tend to react with electrolyte,resulting in severe degradation of material and even causing uncertain risks.Surface coating can effectively address this issue by avoiding the direct contact between bare NCA and electrolyte.Firstly the spherical Ni_0.8Co_0.15Al_0.05?OH?₂ precursor was achieved by coprecipitation method.XRD and HRSEM results shows that NCA has good crystallinity,high sphericity and uniform particle size.The initial charge/discharge capacity is 208.5 m Ah?g^-1 and declines to136.7 m Ah?g^-1 after 50 cycles at room temperature.The capacity retention after 50 cycles at room temperature and 60?are only 71.4%.and 61.09%.So that the surface modification were applied to improve the cycle performance.The NCA was coated with Si O₂ by sol-gel method,using the TEOS as the source of Si.The influence of coating content on the crystal structure and electrochemical performance of NCA materials were investigated.The results show that Si O₂ coating cannot change the NCA bulk structure.The coated material with 1 wt%Si O₂ shows the best cycle performance at room temperature and high temperature.The capacity retention was 67.08%after cycling at1C-rate and 60?for 50 cycles,much higher than that of the pristine NCA.While the Si O₂coating prepared by wet method was not very uniform and conformal,resulting the decline of capacity and rate capability.It is meaningful to further improved the performance of NCA by prepared more conformal and uniform coating.Given that,a low temperature plasma method and hexamethyldisiloxane were used to deposit the Si O_x on the surface of NCA particles.The prepared coating layer is controllable and conformal,dramatically improving its electrochemical performance.This article systematically discusses the effects on the physical and electrochemical properties of NCA materials with Si O_x surface coatings prepared with different oxygen partial pressure,different discharge power and different discharge time.The results show that the coating was very thin,uniform and conformal.The thickness of coating and the bind energy o f Si2p increase first and decrease with increasing O₂/HMDSO flow rate and discharge power.The thickness increases with the time increasing.The coated materials prepared under the condition of O₂/HMDSO=1,150 W and 40 min shows the best electrochemical performance.The rate capacity at 5 C-rate of the coated material was 41 m Ah?g^-1 higher than that of pristine NCA,and its capacity retention increased from 61.09%to 75.3%after cycling at 1C-rate and 60?for 50 cycles.