The Study Of Lithium Ion Battery Cathode Material And Its Charging Mode

At present, lithium ion battery has been extensively studied, because of its high working potential and excellent cycle performance advantages. Since 1997, Goodendugh reported that Li MPO4 is one of the main cathode materials for the lithium ion battery, olivine structure Li MPO4 has been a focus for researchers. But because Li Fe PO4 cathode material has low working potential and Li Mn PO4 is very difficult to synthesized, its advantages of low electronic conductivity and low ionic conductivity lead to its poor rate capability and cuticles characteristic, researchers have modified it by methods of doping, carbon coated and refining particles, however, the results are unsatisfactory. To solve this problem, this study modifies Li MnzFe1-zPO4/C by doping fast ion conductor Li3V2(PO4), combined with the methods of carbon coated and nano to improve the electrochemical property of the composites. The researchers are as below:The research prepared a series of different proportion of the cathode material Li MnzFe1-zPO4/C(z=0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) by solid phase method. The samples were roasted under the 650 ℃ calcinations temperature for ten hours, because the electrochemical performances of the samples under this conditions is excellent. The experiment results show that Li MnzFe1-zPO4/C cathode material is olivine structure has no impurity peak, and the sample has not been found of the diffraction peaks of the carbon, that is to say the carbon in the samples is amorphous. The initial discharging capacities of the samples(z=0.3, 0.5, 0.7, 0.9) at 0.05 C are 125.0, 125.0, 103.1 and 93.1 m Ah·g-1. And at 0.05 C for 10 cycles,the capacity retentions are 97.5%, 98.9%, 96.4% and 98.2%.On the basis of the above research, the research went on the study of x Li Mn0.9Fe0.1PO4·y Li3V2(PO4)3/C cathode material by solid phase method, the samples were roasted under the 650℃ calcinations temperature for ten hours. The performance of the cathode material was studied. Composite samples contain Li Mn0.9Fe0.1PO4 and Li3V2(PO4)3 sample, samples are not found that the diffraction peaks of the carbon in the sample, so residual carbon is amorphous. Although under different proportion samples capacity are not the same, but compared with before, capacity has been improved greatly. Compared with Li Mn0.9Fe0.1PO4, x Li Mn0.9Fe0.1PO4·y Li3V2(PO4)3/C composite material shows smaller polarization, and has more excellent electrochemical performance. The initial discharge capacities of the x Li Mn0.9Fe0.1PO4·y Li3V2(PO4)3/C samples(x:y=1:0, 9:1, 5:1, 3:1, 1:1, 0:1) at 0.05 C are 72.2, 120.1, 158.0 and 145.2 m Ah·g-1. And the capacity retentions of x Li Mn0.9Fe0.1PO4·y Li2V3(PO4)3/C samples(x:y=5:1, 3:1, 1:1, 0:1) are 97.7%, 97.9%, 94.8% and 95.9% after 80 cycles.Not only that, the research also prepared Li Mn0.9Fe0.1PO4 composite cathode material coated by Li3V2(PO4)3, the research mainly discusses the change of morphology, structure and electrochemical performance, when fast ion conductor Li3V2(PO4)3 coated Li Mn0.9Fe0.1PO4 before and after. The coated cathode material 5Li Mn0.9Fe0.1PO4@Li2V3(PO4)3/C are consisted of Li Mn0.9Fe0.1PO4 and Li3V2(PO4)3 samples. And samples are not found the diffraction peaks of the carbon, so residual carbon is amorphous structure. The initial discharge capacities of the 5Li Mn0.9Fe0.1PO4@Li3V2(PO4)3/C sample at 0.05 C are 145.0 m Ah·g-1. And after 80 cycles, the capacity retention of the sample is 95.9%.In addition, paper also studied the charging and discharging mode for the lithium ion battery cathode material. This paper mainly studies the principle of test system and its hardware circuit. The experiments show that the mode of constant current and voltage is best mode to charge the battery.