| Recent years, lithium ion battery cathode material LiMN1/3Co1/3Ni1/3O2 has became one of the most promising cathode materials for lithium batteries and the hot research topic in the field of new energy duo to its characteristics of high tap density, good cycle performance, low manufacturing cost and little environment pollution.In this paper, LiMn1/3Co1/3Ni1/3O2 cathode materials were synthesized by co-precipitation and hydrothermal method. XRD, SEM, EDS and some electrochemical methods were used to characterize the structure, morphology and electrochemical properties. The optimum conditions of LiMn1/3Co1/3Ni1/3O2 prepared by different preparation methods were discussed and its modification research was also investigated by doping Pd2+ and Zn2+.In co-precipitation synthesis, we systemically studied the effects of pH value, reaction temperature, lithium ratio and calcining temperature on the structure and electrochemical performance of LiMn1/3Co1/3Ni1/3O2 prepared by different precipitating agents Na2CO3/NaHCO3/NH4HCO3(Na2CO3+NH4HCO3). The results showed that: when Na2CO3 was used as the precipitating agent, pH value was 8.5, reaction temperature was 50 ℃, calcining temperature was 850℃, the sample had the most uniform particle size and the first discharge capacity of 168.75 mAh·g-1 at 0.1 C rate within 2.5-4.3 V, maintained the rate of 95.76% after 20 cycles; Among the four carbonate precipitation agents, NH4HCO3 showed better performance, and the material LiMn1/3Co1/3Ni1/3O2 prepared by all of these agents had the α-NaFeO2 layer structure. When NaOH was used as the precipitating agent, pH value was 11, lithium ratio was 1.05:1, calcining temperature was 850 ℃, the sample had the better structure, electrochemical properties and the first discharge capacity of 174.66 mAh·g-1 at 0.1 C rate within 2.5～4.3 V, maintained the rate of 97.30% after 20 cycles. The material LiMn1/3Co1/3Ni1/3O2 also had the α-NaFeO2 structure and uniform particle size.In hydrothermal method, we systemically studied the effects of lithium ratio, reaction temperature, reaction time and other factors on the properties of LiMn1/3Co1/3Ni1/3O2 material, the results indicated that when the lithium ratio was 30:1, reaction temperature was 200℃ and reaction time was 10h, the sample had the α-NaFeO2 structure and showed better electrochemical performance, it had the first discharge capacity of 167.68 mAh·g-1 at 0.1 C rate within 2.5～4.3 V, maintained the rate of 94.64% after 20 cycles.By Pd2+ hydrothermal doping and Zn2+ co-precipitation doping, the materials were modified. The results exhibited that Pd2+ doping did not change the α-NaFeO2 layered structure of LiMn1/3Co1/3Ni1/3O2 but increase the stability. The material had the best electrochemical performance when the amount of Pd2+ doping was 3%, it showed the first discharge capacity of 169.24 mAh·g-1 at 0.1 C rate within 2.5～4.3 V under room temperature and the capacity of 137.86 mAh·g-1 at 0.5 C after 50 cycles, maintained the rate of 78.82%; Both cyclic voltammetry and AC impedance showed 3% Pd2+ doping can reduce the charge transfer resistance during Li+ intercalation reaction, increase the rate of Li+ diffusion and improve the electrochemical performance. Zn2+ doping improved the material discharge capacity, rate capability, the rate of Li+ diffusion and reversibility, the optimal amount of 1% Zn2+ doping showed the first discharge capacity of 184.39 mAh·g-1 at 0.1 C rate within 2.5～4.3 V under room temperature and the capacity of 104.66 mAh·g-1 at 2.0 C after 100 cycles, maintained the rate of 56.76%. |
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