Study On Preparation And Modification Of Ni-rich Cathode Material LiNi_0.8Mn_0.2O₂

With the support of national policy and the demand of the market,electrical vehicles?EVs?develop rapidly,as a significant part of the EVs,lithium ion batteries are paid more attention.Nowadays,Ni-rich cathode materials are popular in power Li-ion battery since its high energy density and low cost,while thier cycle performance are poor as well as the thermal stability.In this paper,Ni-rich compound LiNi_0.8Mn_0.2O₂ was synthesized and the influence of synthesis conditions on material properties were investigated.Furthermore,oxides adding and cobalt doping were carried out to improve the electrochemical performance,in order to reach the better method of modification,a lot of chemical,physical and electrochemical properties were tested between the modified materials.? Spherical LiNi_0.8Mn_0.2O₂ compound was synthesized by sintering 10% excess amount of LiOH�H₂O and Ni_0.8Mn_0.2?OH?₂ precursor which prepared by co-precipitation method.The results showed that the optimal preparation condition of the LiNi_0.8Mn_0.2O₂ was 800? for 12 hours under 0.6L�min-1 oxygen flowing.The materials can be identified by a typical structure of hexagonal ?-NaFeO₂ type,the particle size was about 10?m.The electrochemical measurements at 25? showed that it delivered an initial discharge capacity of 173.6mAh�g-1 with the voltage range of 2.75-4.2V at 0.2C rate and the capacity faded 9.3% after 95 cycles;the 100 cycles capacity fading rate was 10.4% when increased the voltage cutoff to 4.3V.? Adding oxides can enhance the cycle performance and improve discharge capacity at 55? and-20?.After adding 0.5% Al₂O₃,the capacity attenuation of 25? after 100 cycled at 0.2C rate between 2.75 and 4.3V was 5.9%.In addition,it can obtain 69.3% discharge efficiency at 55? and 71.7% at-20?.The modified material which adding 1% ZrO₂ also exhibited good electrochemical performances,at the same test condition,the initial discharge capacity was 182.6mAh�g-1 and the capacity attenuation was only 5.2%.When discharged at 55? and-20?,it can reach 71.3%,72.9% discharge efficiency,respectively.? Cobalt doping was an effective method to improve the cation ordering,the cycle stability of LiNi_0.8Co_xMn_0.2-xO₂?x=0.05,0.1,0.15?was better than LiNi_0.8Mn_0.2O₂.When cycled between 2.75 and 4.2V at 1C rate,the LiNi_0.8Co_0.15Mn_0.05O₂ can deliver an initial discharge capacity of 180.0mAh�g-1 and a capacity fading rate of 4.2% after 300 cycles;when cycled between 2.75 and 4.3V at 0.2C rate,the initial discharge capacity increased to 192.3mAh�g-1 and the capacity fading rate was 2.5% after 100 cycles.The discharge efficiency at 55? and-20? was 71.2%,77.1%,respectively.What was more,XPS was performed to confirm the oxidation states of Ni,Co and Mn in LiNi_0.8Mn_0.05Co_0.15O₂ powder and TEM tests were applied to investigate the structural and morphological changes of the LiNi_0.8Mn_0.05Co_0.15O₂ electrode after cycled.