Ion Doping And Surface Modification Of LiNi_0.5Co_0.2Mn_0.3O₂ Ternary Cathode Materials

LiNi_0.5Co_0.2Mn_0.3O₂（NCM 523）,as a kind of layered oxide,has attracted much attention due to its low cost and facile preparation method.However,NCM 523 material has the disadvantages of fast discharge capacity attenuation,poor cycle stability and low discharge capacity at high rates in practical application.For the sake of improving its shortcomings,the effects of different metal ions doping and surface dielectric modification on NCM 523cathode materials were investigated by ball milling spray drying method and solvothermal method respectively.The main research contents are as follows:（1）Li[Ni_0.5Co_0.2Mn_0.3-xAl_x]O₂ layered compounds were successfully synthesized by ball milling spray drying method.The results indicate that:After 150 cycles at 10 C,NCM-25(Li[Ni_0.5Co_0.2Mn_0.275Al_0.025]O₂)loses only 32.9 m Ahg^-1of discharge capacity.Even at higher15 C,NCM-25 still delivers the highest initial discharge capacity of 97.8 m Ahg^-1,and exhibits prominent capacity retention than NCM after 300 cycles.（2）Li_1.05[Ni_0.5Co_0.2-xMn_0.3Ce_x]O₂ layered compounds were successfully synthesized by ball milling spray drying method.The results indicate that:Cycled at 5 C,Ce0.15%-NCM((Li_1.05[Ni_0.5Co_0.1985Mn_0.3Ce_0.0015]O₂)has superior initial discharge capacity of 138.7 m Ahg^-1and capacity retention of 83.99%after 200 cycles.So far as to the full-cells state,Ce0.15%-NCM delivers the initial energy density of 406 Wh kg^-1 and 72.94%retention.（3）The well-distributed smaller sized Graphene-Oxide（GO）modified LiNi_0.5Co_0.2Mn_0.3O₂ layered cathodes are successfully synthesized by using hydrothermal method.The results indicate that:G10-NCM（GO addition:10mg）exhibits the optimal capacity retention as high as 78.8%after 150 cycles at 15 C.At full cell state,GO-modified NCM has better rate performance and displays excellent energy density as high as 310.5 Wh kg^-1 after 200 cycles at 1 C.