Abstract:

The high-nickel ternary cathode material LiNi_0.65Co_0.15Mn_0.2O₂（NCM） is widely used because of its high specific capacity，low cost，and environmental friendliness，but its high nickel content leads to severe cation mixing and poor cycling and rate performance.In order to improve the above mentioned deficiencies，elemental doping is an effective strategy to reduce the degree of cation mixing and enhance the structural stability.Na⁺-doped LiNi_0.65Co_0.15Mn_0.2O₂（NCM-x%Na） anode materials were prepared by co-precipitation method（where x% was the fraction of substance）.The NCM-x%Na material was characterized morphologically and structurally by means of X-ray diffraction（XRD） and scanning electron microscopy（SEM），and its electrochemical properties were tested by means of a charge-discharge test system.The results showed that Na⁺ doping could effectively reduce the particle size and inhibit the degree of cation mixing，and enlarge the lithium layer spacing，which could help to improve the diffusion rate of lithium ions.The Na⁺-doped LiNi_0.65Co_0.15Mn_0.2O₂ sample（NCM-2%Na） had the best electrochemical performance when x=2.The discharge specific capacity after 100 cycles at 2.7~4.4 V，0.1C was 139.0 mA·h/g（capacity retention of 86%），which was 17% higher than that of NCM.The discharge specific capacity of NCM-2%Na material at 2.0C was 82.2 mA·h/g，which was much higher than that of unmodified LiNi_0.65Co_0.15Mn_0.2O₂（39.4 mA·h/g）.The multiplication performance was tested at 0.1C，0.2C，0.5C，1.0C，and 2.0C.The capacity retention of NCM-2%Na was 90% after 25 cycles at 0.1C，which was 9% higher than that of NCM.The reaction kinetics showed that NCM-2%Na had a smaller charge transfer resistance and a higher lithium ion diffusion coefficient than NCM，resulting in enhanced charge transfer kinetics.

Key words: high-nickel, cathode material, LiNi_0.65Co_0.15Mn_0.2O₂, Na⁺-doped, rate performance