| As global shortage of fossil energy and environmental problem are more serious recently, people pay more attention to the new energy market. Lithium ion battery appeared and was commercialized in 1991, which has character of good safety and easy to carry, and lithium ion battery quickly becomes the focus of new energy market. LiCoO2 is the most part of lithium ion battery cathode materials. Production cost of LiCoO2 is very high since the amount and stocks of Co element is limited and low.LiNi1/3Co1/3Mn1/3O2 cathode material was first reported in 2001. With the advantage of low production cost, high capacity, structure stability and good safety, LiNi1/3Co1/3Mn1/3O2 is considered the substitute of LiCoO2.Indirect coprecipitation is most common method of LiNi1/3Co1/3Mn1/3O2 cathode material preparation. Indirect coprecipitation means that the Nickel(Ni), cobalt(Co), manganese(Mn) are mixed by chemical precipitation, and then lithium salts are blended through physical grind. As the lithium salts are mixed by physical method, the material is not easy to mix uniformly.This paper introduced a new preparation way, namely oxalic direct coprecipitation. The new method could mix Li, Ni, Co and Mn by coprecipitation, and the resultant was mixed well at atomic level. The reaction was always in acid environment, so Mn2+ could exist stably vithout oxidized into Mn4+.This paper researched the optimal reaction condition to prepare LiNi1/3Co1/3Mn1/3O2 cathode material by use the oxalic ion direct co-precipitation, and also made doping to improve the electrochemical performance of the cathode material.1. Prepared the LiNi1/3Co1/3Mn1/3O2 at different calcination temperature, different calcination time and different Li percentage, and made characterization for the resultants’ structure and electrochemical performance. The test results showed that when the Li excess 5% and prepared by calcined 14h at 850℃, the resultant had the most complete layered structure, the minimum cation mixing degree, and best electrochemical character. First discharge capacity of LiNi1/3Co1/3Mn1/3O2 obtained at such conditions could reach 161.5mAh·g-1, and the coulombic efficiency was 83.4%, maintenance rate of capacity was 102.16% after 30 charge-discharge circles.2. Comparing the LiNi1/3Co1/3Mn1/3O2 cathode material prepared by oxalic direct coprecipitation with oxalic indirect coprecipitation, the XRD analysis showed that the lattice parameters and cation mixing degree were similar, and both had the favorable layered structure. Electrochemical test indicated that the first discharge capacity of resultant of two preparation method differed little, but specific capacity at high rate and rate performance of LiNi1/3Co1/3Mn1/3O2 prepared with direct co-precipitation was higher and better. Charge-discharge circle test at 0.2C showed that the retetion rate of capacity of cathode material prepared by two methods decreased rapidly after 160 circles, which was less than 50% after 300 circles, and the circle characters of cathode material need to enhance.3.Li[(Ni1/3Co1/3Mn1/3)1-xMgx]O2(x=0,0.01,0.03,0.05) was synthesized by doping different portions of Mg into cathode material (LiNi1/3Co1/3Mn1/3O2). XRD analysis showed that the doped material with Mg had a layered α-NaFeO2 structure, space group R3m without any impurities. As the Mg doped, the cation mixing degree of material firstly decreased and then increased, and Li[(Ni1/3Co1/3Mn1/3)1-0.01Mg0.01]O2isthe lowest. The electrochemical test result revealed that discharge capacity decreased with increasing of Mg doping percentage, and Li[(Ni1/3Co1/3Mn1/3)1-0.01Mg0.01]O2 had the optimal electrochemical performance.4.Li[(Ni1/3Co1/3Mn1/3)1-x(Mg1/2Zn1/2)x]O2(x=0,0.01,0.03,0.05) was synthesized by doping different portions of Mg、Zn into cathode material (LiNi1/3Co1/3Mn1/3O2). XRD analysis showed that the doped material with Mg and Zn had a layered α-NaFeO2 structure, space group R3m without any impurities. As the Mg and Zn doped, the cation mixing degree of material firstly decreased and then increased. The lowest is Li[(Ni1/3Co1/3Mn1/3)1-0.01(Mg1/2Zn1/2)0.01]O2. The first discharge capacity of Li[(Ni1/3Co1/3Mn1/3)1-0.01(Mg1/2Zn1/2)0.01]O2 was 155 mAh·g-1 at 0.2 C, the coulombic efficiency was 91.5%, and the capacity retention rate was 98.41% after 30 charge-discharge cycles, which was better than the other Mg、Zn doped materials.5. The results compared LiNi1/3Co1/3Mn1/3O2(without doping) with Li[(Ni1/3Co1/3Mn1/3)1-0.01Mg0.01]O2 and Li[(Ni1/3Co1/3Mn1/3)1-0.01(Mg1/2Zn1/2)0.01]O2 demonstrated that Mg doping would not improve the high-rate discharge capacity significantly, whereas its cycling capability was better than that without doping. However, the Mg and Zn doped materials had the best cycling performance at both low and high rate. CV and EIS results showed that Li[(Ni1/3Co1/3Mn1/3)1-0.01(Mg1/2Zn1/2)0.01]O2 had a best eversibility and the highest Li diffusion coefficient among them. |
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