The Design And Manufacture Of High-Power Lithium Iron Phosphate Power Battery

Currently, the new industrialization, which take the"low-carbon and circular economy"as the subject, is promoting the new energy vehicles industry development. Hybrid electric vehicle(HEV) is the fastest developing new energy vehicle, and high-power lithium-ion power battery with the high-performance can well satisfy the requirements of HEV.Cathode material is one of the most critical materials for the high-power lithium-ion power battery. Among them, LiFePO₄ is the preferred cathode material for high-power lithium-ion power battery due to its long cycle life, high thermal stability, green environmental protection, abundant resources and low cost. However, the low electron conductivity and slow Li-ion diffusion rate of the material lead to poor rate capability, which greatly limit its application on high-power lithium-ion power battery.In this paper, LiFePO₄/C composite was prepared by two-step high temperature solid state reaction. The effects of calcination temperature, carbon source and addition amount of carbon on the structure, morphology and properties of the material were investigated by XRD, SEM and electrochemical testing. The results showed that the LiFePO₄/C composite synthesized at 700℃with 6.4% mass percentage of carbon which using glucose as carbon source had the ordered olivine-type LiFePO₄ structure and displayed best electrochemical performance. The constant charge-discharge tests showed that the special discharge of 126.2mAh/g, 111.8mAh/g and 88.2mAh/g were obtained at 1C, 2C and 4C, respectively.Doping is an effective way to improve the performance of LiFePO₄/C composite. Zr⁴⁺ doped-LiZryFe_1-2yPO₄/C (y = 0, 0.01, 0.03, 0.05) and Y³⁺ doped-LiYyFe_1-1.5yPO₄- /C (y = 0, y = 0.01, y = 0.02, y = 0.03) were obtained by two-step high temperature solid state reaction under the optimum conditions. The effects of the contents of Zr⁴⁺ doped and Y³⁺ doped on the properties of LiFePO₄/C composite were studied by XRD, SEM, constant charge-discharge and cyclic voltammetry tests. The results showed that LiZr0.03Fe0.94PO₄/C had good crystallinity, small uniform particle size and excellent electrochemical reversibility among a series of Zr⁴⁺ doped samples, and the discharge special capacity at 1C, 2C and 4C reached 137.6mAh/g, 128.7mAh/g and 114.1mAh/- g, respectively. In addition, LiY0.02Fe0.97PO₄/C showed the best electrochemical perfo- rmance among a series of Y³⁺ doped samples , and the discharge capacity at 1C, 2C and 4C were 130.0mAh/g,119.9mAh/g and 105.2mAh/g, respectively.The high-power 3095170 size lithium-ion power battery with nominal capacity of 32000mAh was fabricated using LiZr_0.03Fe_0.94PO₄/C as cathode active material and MCMB as anode active material. Charge retention characteristic, power performance and safety property of the battery were systemly studied. The results showed that the 3095170 size lithium-ion power battery exhibited a energy density of 70.58 Wh/kg and a power density of 832.0W/kg at a discharge rate of 10C. The capacity retention was more than 86% after 450 cycles at a charge/discharge rate of 1C. Safety performance test showed that battery reliability and other technology parameters can meet the design requirements.