Lithium-ion Battery Cathode Material Of Lini <sub> 0.8 </ Sub> The Co <sub> 0.2 </ Sub> O <sub> 2 </ Sub> Synthesis And Performance Study

Lithium nickel cobalt oxide is one of the most promising cathode materials forlithium ion batteries. The spherical LiNi_0.8Co_0.2O₂ cathode material has high tapdensity and excellent specific capacity, which contribute to increasing cell's energydensity, meanwhile the spherical materials have much better manufacture property.Interms of these advantages, we prepared the spherical LiNi_0.8Co_0.2O₂ powders via"controlled crystallization" method, which includes co-precipitation process andsintering process at high temperature. The two parts were studied as below.Firstly, spherical Ni_0.8Co_0.2(OH)₂ powders were prepared by co-precipitationmethod. The main factors such as stirring speed, flowing speed of nickel cobalt vitriolsolution, NH₃/(Ni+Co), pH value, temperature, reaction time, etc, were investigated.The experiments were carried in 12 liter agiteted reactor. The effect of various processcondition on Ni_0.8Co_0.2(OH)₂ particle morphology, particle diametric distribution aswell as tap-density were studied systematically, which will offer good reference toindustrial produce.We found that under the optimum conditions, in which metal saltsolution flow rate was 8ml/min,stirring speed was 450rpm, NH₃/(Ni+Co) was 1.5,pH value was 11.5, and reaction time was 56h, the spherical Ni_0.8Co_0.2(OH)₂ powderswith tap-density of 2.02 g/cm³ were obtained. The EDS were used to analysis thecrystal structure and element distribution of Ni, Co on the atomic ratio of 4: 1.The effects of high temperature synthesis conditions, such as pre-treatingtemperature, sintering atmosphere, sintering temperature, sintering time, molar rationof Li to (Ni+Co), on morphology, structure, and electrochemical performance ofLiNi_0.8Co_0.2O₂ were studied. Firstly, the obtained Ni_0.8Co_0.2(OH)₂ was fired at 550℃for 6h,then the product of (Ni_0.8Co_0.2)O_x mixed with LiOH·H₂O with 1.07 Li/(Ni+Co)ratio and followed by sinterring in 800ml/min flowing oxygen and at 750℃for 16h,the LiNi_0.8Co_0.2O₂ was synthesized. The results showed that the initial dischargecapacity of LiNi_0.8Co_0.2O₂ cell was 195.3mAh/g between 3.0-4.3V at 0.2C rate and thecapacity fading was 9.42％after 50 cycles, which indicated the material has highdischarge capacity and good cycling property under these optimum conditions.The Mg-doping experiment was also studied. The electrochemical test indicatedthe the capacity fading after 50 cycles of LiNi_0.75Co_0.2Mg_0.05O₂ cell tested between3.0-4.3V at 0.2C rate is only 3％, which indicated Mg-doping help to improve electrochemical cyclic property. Cyclic voltammogram indicated the sample dopedMg could help to suppress the phase transition in the process of charge/discharge.Electrochemical impedance spectroscopy showed the increasing of charge transferresistance could be limited due to doping Mg.All above proved that Mg doping helpssteady the structure during charge/discharge and improve cycling property.