| The successful commercialization of LiFePO4 cathode stimulate the enthusiasm of scientific researchers to develop its homologue LiMnPO4 with higher energy density. LiMnP04 cathode has the advantages of wide raw material source, low cost, environmental friendliness and high safety. It is promising to be one of the options of the next generation of lithium ion battery cathode materials. But its characteristics of one-dimensional diffusion direction of Li+, poor electronic conductivity and lithium ion diffusion coefficients and Jahn-Teller effect of Mn3+ result in Mn2+ dissolution and unstable crystal structure. So the rate and cycling performance of LiMnPO4 are still unsatisfactory, which need to be further improved.In this paper, a series of LiMnP04 nano materials with different morphologies were synthesized by solvothermal method by using different manganese sources, lithium sources, adjusting the proportion of raw materials, reaction temperature, solvent species and so on. It was found that the ratio of raw materials in precursor is the key parameter influencing the morphology of LiMnP04. The sizes of pure LiMnP04 materials were in the ranges of 2μm to 30 nm. The results showed that the discharge capacities were about 80 to 100 mAh g-1 of the two kinds of smaller LiMnPO4, which were in the shape of ball-like particles with a size of about 30 nm and sheet about 50 nm in length.Based on the above results, we synthesized pure LiMnPO4 by solvothermal method in the ratio of 2.5～5:1:1 among the raw materials of lithium acetate, phosphoric acid and manganese chloride. The SEM results showed that the spindle like LiMnPO4 was about 100nm in length, and the TEM results showed that the particle surface was composed of a layer of carbon about 2 nm in thickness. Under the ratio of 5-6:1:1, LiMnPO4 showed the best electrochemical performance. The discharge capacity was 157.33,124.06,99.26 and 71.77 g mAh-1 at 0.05,1,5 and 20 C respectively. After 200 cycles, the capacity retention at 1C and 5C rates were 77% and 72% respectively.By using lithium acetate, phosphoric acid and manganese chloride as the raw materials and in the ratio of 5:1:1, amplified experiment was carried out to prepare LiMnPO4 by polyol method. The results showed that the pure LiMnPO4 can be obtained at 160℃, and the discharge capacity at 0.05 C and 10 C were 123.74 and 83.59 mAh g-1. PVP and sucrose were used as the carbon source in the spray drying process to obtain walnut like particles about 5μm. After calcination treatment at high temperature, it can still maintain the spherical morphology, but the surface was of porous structure. Electrochemical performance test results showed that attenuation of rate dependent discharge capacity was little. At 0.05 C,10 C and 20 C, the discharge capacity were 116.06,91.09 and 83.08 mAh g-1. This indicated that the kind of LiMnPO4 cathode material owned promising prospect in the industrial application. |
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