Synthesis And Modification Of Nickel Rich Concentration Gradient Cathode Materials

Ni-rich ternary materials?abbreviated as NCM?has great commercial application potential due to high specific discharge capacity and low cast.However,its cycle performance is unstable,so the modification research has become a hot spot in recent years.In this paper,the NCM concentration gradient cathode material was prepared by co-precipitation method.The concentration gradient structure of precursor microspheres was realized by separately arranging manganese sulfate into solution and adding it to mixed salt solution.When the ratio of nickel,cobalt and manganese was 80:10:10,the ternary proportion of 10% manganese sulfate was divided into two parts.When the compounding method was prepared 7.5% manganese sulfate separately and the remaining 2.5% was added to the initial salt solution,the battery had the best performance at this time.The first discharge specific capacity was 184 m Ah/g,and the capacity retention rate after 350 charge and discharge cycles was 99%.In order to increase the discharge specific capacity,it increased the proportion of nickel in the ternary material to 83%,a method of separately preparing a portion of the manganese sulfate and uniformly feeding it was still used.When the ratio of nickel,cobalt and manganese was 83:12:5,it was found that the material had relatively high cycle performance when 3% manganese sulfate was prepared separately.The initial discharge specific capacity was 186 m Ah/g,and the capacity retention rate after 300 cycles was 91%.For materials with a ternary ratio of 83:5:12,the initial discharge specific capacity was 186 m Ah/g,but various feed modes were adjusted,and the cycle performance was poor.The capacity retention after 300 cycles was only 63%.Precursors with a nickel ratio of 80% and 83% were selected and doped with Nb₂O₅.To try different doping amounts,it was found that for both precursors with different nickel contents,when the doping amount was 3wt%,the improvement of cycle performance was best.The material with a nickel content of 80% ha d a capacity retention rate of 94% at 1 C after 500 cycles,while the nickel accounted for 83%,the capacity retention rate was 77.5%.The concentration gradient NCM materials with good nickel ratio of 80% and 83% were selected and coated with H₅Nb₃O₁₀.By experimenting with different coating amounts,it was found that when the coating amount of cerium hydroxide was 1wt%,the cycle performance of the material with nickel ratio of 80% was improved,and the capacity retention rate was 93.6% at 1 C after 450 cycles.While nickel accounts for 83%,the effect of coating modification was not obvious.The mechanism of the concentration gradient structure to improve the cycle performance was explored.Through different characterization methods,it was found that during the multiple charging and discharging process,the nickel ions inside the microspheres will gradually migrate to the surface,which will aggravate the side reaction between the material and the electrolyte surface.At the edge of the concentration gradient material,there were fewer initial nickel elements.And even after numerous cycles,nickel content maintains low on the surface,which was beneficial to keep stability of structure and improve the cycle performance.