Effect of particle size and purity on the low temperature electrochemical performance of LiFePO4/C cathode material
Effect of particle size and purity on the low temperature electrochemical performance of LiFePO4/C cathode material
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DOI：
10.1016/j.jallcom.2016.04.070
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发表时间：
2016-10
影响因子：
6.2
通讯作者：
Nannan Zhao;Yongsheng Li;Xinxin Zhao;Xiaoke Zhi;Guangchuan Liang
中科院分区：
文献类型：
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作者：
Nannan Zhao;Yongsheng Li;Xinxin Zhao;Xiaoke Zhi;Guangchuan Liang
系统研究了LiFePO 4/C材料的粒度和纯度对以FePO 4. 2 H2O为前驱体制备的LiFePO 4/C材料低温性能的影响。研究发现，减小LiFePO 4/C材料的粒径可以提高材料的低温性能，而LiFePO 4/C材料的纯度对材料的低温性能有着更为重要的影响。与高纯度LiFePO 4/C材料相比，低纯度LiFePO 4/C材料表现出较差的低温性能。在0.2C下的-20 °C下，低纯度LiFePO 4/C材料的比容量为52.4 mAh g− 1，低于高纯度LiFePO 4/C材料的105.6 mAh g−1。18650-1400 mAh圆柱形电池证实了这一观点。在0.2C下0、−20和−40 °C的工作温度下，低纯度LiFePO 4/C材料的容量保持率分别为40.9%、30.3%和10.9%，远低于高纯LiFePO 4/C材料的容量保持率，高纯LiFePO 4/C材料的容量保持率分别为81.5%、70.2%和46.6%。机理研究表明，低纯度LiFePO 4/C材料中含有杂质，这些杂质通过高温扩散过程进入LiFePO 4晶格，导致晶格畸变，阻碍Li+离子的扩散。计算表明，低纯度LiFePO 4/C材料的扩散动力学常数为8.28 × 10− 15 cm 2 s − 1，比高纯LiFePO 4/C材料的扩散动力学常数2.73 × 10− 13 cm 2 s −1低两个数量级，导致低温下Li+离子扩散动力学的滞后。因此，LiFePO 4/C材料的粒径和纯度是影响LiFePO 4/C材料低温性能的主要因素，其中去除原料中的杂质，提高铁源纯度合成FePO 4·2 H2O材料是提高LiFePO 4/C材料低温性能的确定性途径。
The effect of particle size and purity of LiFePO4/C material on the low temperature performance of LiFePO4/C material prepared with FePO4·2H2O as precursor are systematically investigated. It is found that reducing particle size of LiFePO4/C material can improve the low temperature performance, and the purity of LiFePO4/C material has more important influence on the low temperature performance. Compared to the high purity LiFePO4/C material, the low purity LiFePO4/C material exhibits poor low temperature performance. At −20 °C under 0.2C, the specific capacity of low purity LiFePO4/C material is 52.4 mAh g−1lower than that of high purity LiFePO4/C material which is 105.6 mAh g−1. The 18650-1400 mAh cylindrical batteries confirm the opinion. At the operation temperature of 0, −20 and −40 °C under 0.2C, the capacity retentions of low purity LiFePO4/C material are 40.9%, 30.3% and 10.9% much lower than those of high purity LiFePO4/C material which are 81.5%, 70.2% and 46.6% compared with those of at 25 °C, respectively. The studies on the mechanism indicate that low purity LiFePO4/C material contains impurities which could incorporated into LiFePO4lattice by high-temperature diffusion process and cause the lattice distortion, blocking the Li+ions diffusion. It have calculated that the DLivalue of low purity LiFePO4/C material is 8.28 × 10−15cm2s−1lower two orders than that of high purity LiFePO4/C material which is 2.73 × 10−13cm2s−1, leading to the sluggish Li+ions diffusion kinetics at low temperature. Therefore, the particle size and purity of LiFePO4/C material are the mainly factors influencing the low temperature performance of LiFePO4/C material, of which removing the impurities in the raw materials and improving the purity of the iron source to synthesize FePO4·2H2O material is a deterministic way to improve the low temperature performance of LiFePO4/C material.