炭包覆LiFePO4纳米片的制备及电化学性能研究

doi:10.15541/jim20180120

摘要/Abstract

摘要：

为改善磷酸铁锂正极材料的倍率性能, 以乙二醇为溶剂, 采用一步溶剂热法制备磷酸铁锂纳米片。再以葡萄糖为碳前驱体, 对磷酸铁锂纳米片进行炭包覆。通过X射线衍射, N₂吸脱附曲线、扫描电子显微镜、透射电子显微镜和循环伏安法等测试方法考察了炭包覆量对磷酸铁锂纳米片结构与电化学性能的影响。结果表明, 制备的磷酸铁锂为具有较短b轴的纳米片状结构, 尺寸约为150 nm×100 nm×60 nm。磷酸铁锂纳米片的倍率性能随炭包覆量的增加而增强, 当炭包覆量为6.4wt%时具有最佳的倍率性能, 在0.2C和10C的电流密度下放电容量分别为157.3和132.6 mAh/g。同时循环稳定性良好, 在5C电流密度下循环500次后容量保持率达到了80.2%。

关键词: 磷酸铁锂, 纳米片状结构, 溶剂热, 倍率性能, 循环性能

Abstract:

To improve the rate performance of LiFePO₄ cathode material, LiFePO₄nanoplates were synthesized via one-step glycol-based solvothermal process. Additionally, carbon was employed to coat LiFePO₄ with glucose served as carbon source. The morphologies and electrochemical properties of the as-prepared materials were characterized by XRD, BET, SEM, TEM, cyclic voltammetry, etc. Results showed that LiFePO₄nanoplates had the size of approximately 150 nm×100 nm×60 nm, displaying a short b-axis. The rate performance of LiFePO₄ nanoplates was enhanced with the increment of carbon content, and the sample containing 6.4wt% carbon (LF0.2) exhibited the most outstanding electrochemical performance, which delivered discharge capacities of 157.3 mAh/g and 132.6 mAh/g at 0.2C and 10C rates, respectively. Meanwhile, excellent cycling stability of LF0.2, 80.2% capacity retention after 500 cycles at 5C rate, was observed.

Key words: LiFePO₄, nanoplate structure, solvothermal, rate performance, cycling performance

中图分类号:

O646

王琦, 彭大春, 马倩, 何月德, 刘洪波. 炭包覆LiFePO₄纳米片的制备及电化学性能研究[J]. 无机材料学报, 2018, 33(12): 1349-1354.

WANG Qi, PENG Da-Chun, MA Qian, HE Yue-De, LIU Hong-Bo. Synthesis and Electrochemical Property of Carbon Coated LiFePO₄ Nanoplates[J]. Journal of Inorganic Materials, 2018, 33(12): 1349-1354.

图/表 9

图1 LiFePO4/C样品的XRD图谱

Fig. 1 XRD patterns of LiFePO4/C samples

图2 LiFePO4/C样品的氮气吸脱附曲线

Fig. 2 N2 adsorption-desorption isotherms of LiFePO4/C samples

图3 样品的SEM照片

Fig. 3 SEM images of LiFePO4/C samples(a) LF0; (b)LF0.05; (c)LF0.1; (d)LF0.2

图4 LF0.2的TEM照片(a)、HRTEM 照片(b)和选区电子衍射照片(c)

Fig. 4 TEM(a), HRTEM(b) and SEAD (c) images of LF0.2 sample

图5 LiFePO4/C样品的循环伏安曲线

Fig. 5 CV curves of all LiFePO4/C samples

图6 (a)LiFePO4/C样品的倍率性能; (b)LiFePO4/C样品在0.2C倍率下的第三次充放电曲线; (c)LiFePO4/C样品在5C倍率下的第三次充放电曲线; (d)在不同倍率下的中值电压性能图

Fig. 6 (a) Specific capacities of all samples at various rates; Comparison of the third charging and discharging profiles of the all samples at (b) 0.2C rate and (c) 5C rate; (d) The dependency of the middle discharge voltage on current rate in the range of 0.2C to 10C

图7 LiFePO4/C样品的循环性能图

Fig. 7 Cycling performances of LiFePO4/C samples(a) 1C; (b) 5C

图8 (a) LiFePO4/C样品的交流阻抗图谱以及对应的等效电路; (b) Z°-ω-1/2的直线拟合

Fig. 8 (a) The EIS curves and the corresponding equivalent circuit model of LiFePO4/C samples; (b) Linear fitting of Z°-ω-1/2

表1 等效电路中各个电阻的拟合值以及对应的锂离子扩散系数

Table 1 The fitting values of the resistance components in the simplified equivalent circuit and the Li+ diffusion coefficients.

Samples	R_S/Ω	R_F/Ω	R_ct/Ω	D⁺_Li/(×10^-13, cm²∙s^-1)
LF0	8.1	241.8	235.2	0.067
LF0.05	3.8	35.7	95.7	5.300
LF0.1	3.5	17.6	74.1	12.000
LF0.2	2.2	9.3	62.9	41.500

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炭包覆LiFePO₄纳米片的制备及电化学性能研究

Synthesis and Electrochemical Property of Carbon Coated LiFePO₄ Nanoplates

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