Study On Synthesis And Electrochemical Properties Of Ni-rich Cathode Materials

Nickel rich layered oxide cathodes for lithium-ion batteries have been identified as one of the most promising cathode materials with high discharge capacity.However,for their further practical applications,there are still lots of challenges to be resolved,such as the difficulty of synthesis,poor cyclability and rate capability.In this work,nickel rich layered LiNi_1-xMn_x O₂ materials have been synthesized through co-precipitation method.The influence of different Ni-Mn ratio on the electrochemical performance of the material was investigated.And optimized the synthesis process of LiNi_0.9Mn_0.1O₂.In order to improve the performance of LiNi_0.9Mn_0.1O₂,Ti⁴⁺or Co³⁺was doped,The influence of doping modification on the structure and electrochemical performance of the material was discussed,and a relatively optimized modification method was obtained.The main research contents are summarized as follows:The results indicate that the electrochemical properties of LiNi_1-xMn_xO₂（x=0.1,0.2,0.3）cathode materials with different values of x indicates that the material with high Ni content has higher capacity and the material with higher Mn content has higher cycling stability.For example,LiNi_0.9Mn_0.1O₂ had the highest initial discharge capacity,174.2mAh/g.LiNi_0.7Mn_0.3O₂ had the highest capacity retention after 50 cycles was 93.6%.The best synthesis conditions for LiNi_0.9Mn_0.1O₂ can be obtained by calcining the Li/（Ni+Mn）mixtures with a molar ratio of 1.10 at 750℃for 12 hours during high purity oxygen flows.The obtained materials have a typicalα-NaFeO₂ layered structure and homogeneous spherical morphology.The initial discharge specific capacity of the material is 174.2mAh/g at 0.5C in the voltage range of 2.5-4.3 V under 25℃.And it can still maintain 88.7%of the initial discharge capacity after 50 cycles.After doping TiO₂,the cathode materials still have the typicalα-NaFeO₂ type layered structure.The cycle performance and rate performance of the material are significantly improved.When the amount of TiO₂ added was 2.5%,the capacity retention of the material was 92.3%at 0.5C in the voltage of 2.5-4.3V under 25℃after 50 cycles.The discharge capacity was 156.1mAh/g at 1C.And the capacity still maintain 145.9 mAh/g at 2C.Cobalt doping was an effective method to improve the cation ordering,the cycle stability and rate performance of LiNi_0.9Co_xMn_0.1-xO₂（x=0.025、0.05、0.075）was better than LiNi_0.9Mn_0.1O₂.With the increase of the amount for Co,the electrode performance becomes better.When x is 0.075,the initial discharge specific capacity is 184.5 mAh/g at 0.5 C in the voltage range of 2.5-4.3V under 25℃and it can still maintain 95.2%of the initial discharge capacity after 50 cycles.