Structural Modification And Surface Modification Of Ternary Cathode Materials For Lithium Ion Batteries

Rechargeable lithium ion batteries?LIBs?have attracted a great deal of attention as power sources for portable electronic devices,electric vehicles?EVs?or hybrid electric vehicles?HEVs?,due to their high energydensity,highpower density and long cycling life.Cathode layered ternary material Li(Ni_xCo_y Mn_1-x-y)O₂ are among the most promising cathode materials because of their relatively low cost,low toxicity,high rate capability and excellent reversible capacity,especially for EV and HEV applications.However,highly delithiated Cathode layered ternary material Li(Ni_xCo_yMn_1-x-y)O₂ materials become unstable due to the appearance of abundant Nickel ion during charge/discharge,which react with organic electrolyte,increasing the impedance and lowering the cyclability of LIBs,These problems hinder the use of ternary materials on a large scale.In this paper,two kinds of positive electrode layered Li(Ni_0.5Co_0.2Mn_0.3)O₂?hereinafter referred to as NCM523?and Li(Ni_0.8Co_0.1Mn_0.1)O₂?hereinafter referred to as NCM811?were selected.The structure and surface modification were used to solve the above problems.The materials were characterized by XRD,SEM,TEM,Fourier infrared spectroscopy,ICP,charge and discharge test and AC impedance test.First,the precursor of NCM523 precursor was prepared by coprecipitation method.The results showed that when the concentration of ammonia was 2.2mon / L,the pH value was 10.5 and the stirring speed was 800 r / min,the precursor had good spherical shape and smooth surface,The concentration gradient varies uniformly from the core to the housing.Secondly,the effect of temperature and time on the structure,morphology and electrochemical properties of the mixed electrode of NCM523 was investigated by high temperature solid-state method.The results showed that when the lithium content was 1.05,The sintering temperature is 920 ?,the sintering time is 8h,the concentration gradient NCM523 material has the best morphology and the layered structure,the first discharge capacity is up to 176 mAh / g,the Coulomb efficiency of 1C cycle is 96.2%.commercialized NCM523 material first discharge specific capacity of 170 mAh / g,1C cycle 200 cycles Coulomb efficiency of 82.8%,with better electrochemical performance.Finally,the high nickel material NCM811 because of its surface pH is too high,easy to absorb and react with the electrolyte side effects to increase the resistance and cycle performance.In this experiment,the residual lithium was removed from the surface of the high-nickel material by protonic acid phosphoric acid and coated with the organic silane coupling agent kh-560.The results showed that there were two layers of uniform and dense coating on the surface of the material,The cladding material did not change the lamellar structure of the original material.After the electrochemical performance test,the first discharge capacity of the coated material was 193.4 mAh / g,and the capacity retention rate was 93.1% after 200 cycles of 1C cycle.For the first time Discharge capacity of 185 mAh / g,1C cycle 200 laps after the capacity retention rate of 84.5%,coated material solution after the resistance value is reduced and has better cycle performance.