Influence of Pitch with Different Softening Points on the Coating Properties of Natural Graphite
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摘要: 采用3款不同软化点的石油基沥青，以液相包覆法处理天然石墨，对所得样品的粒度、结构、形貌和电化学性能等进行分析。结果表明，采用250 ℃软化点的沥青包覆天然石墨表现出最佳的电化学性能，其首次库伦效率由84.7%提高到88.04%，250次循环的容量保持率由63.14%提高到81.19%。低软化点沥青由于炭化时轻组分释放，包覆层形成大量微孔导致不可逆容量损失较多，高软化点沥青有利于形成完整包覆层，其对天然石墨的循环性能和倍率性能改善最佳。Abstract: Three petroleum-based pitches with different softening points were used to treat natural graphite by liquid phase coating method. The particle size, structure, morphology and electrochemical properties of the samples were analyzed. The results show that the high softening point pitch can form a thicker coating layer on the natural graphite surface, and the graphite surface becomes more rounded and the defects are reduced. The pitch coated natural graphite with softening point 250 ℃ shows the best electrochemical performance, the first Coulomb efficiency increases from 84.7% to 88.04%, and the capacity retention rate increases from 63.14% to 81.19% after 250 cycles. The low softening point pitch has a large irreversible capacity loss due to the large number of micropores formed by the light component release coating during carbonization, while the high softening point pitch is beneficial to the formation of complete coating, which can improve the cycling and rate performance of natural graphite best.
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Key words:
- coating pitch /
- natural graphite /
- cycle performance /
- anode materials
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图 1 包覆天然石墨负极材料的粒度分布曲线
Figure 1. Particle size distribution curve of pitch coated natural graphite anode materials
图 2 包覆天然石墨负极材料的氮气吸脱附等温线（a）和DFT孔径分布图（b）
Figure 2. Nitrogen adsorption and desorption isotherms (a) and DFT pore size distribution (b) of pitch coated natural graphite anode material
图 3 包覆天然石墨负极材料的XRD图谱
Figure 3. XRD pattern of pitch coated natural graphite anode materials
图 4 包覆天然石墨负极材料的Raman光谱图
Figure 4. Raman spectra of pitch coated natural graphite anode materials
图 5 包覆天然石墨负极材料的SEM图片
Figure 5. SEM image of pitch coated natural graphite anode materials
a, b−NG; c, d−P170@NG; e, f−P2200@NG; g, h−P250@NG
图 6 包覆天然石墨负极材料的循环性能（a）和倍率性能（b）
Figure 6. Cyclic properties (a) and rate properties (b) of pitch coated natural graphite anode materials
图 7 包覆天然石墨负极材料的电化学阻抗谱拟合曲线
Figure 7. Fitting curve of electrochemical impedance spectrum of pitch coated natural graphite anode materials
表 1 包覆沥青的基本性质
Table 1. Basic properties of coating pitches
Samples Softening
Point/℃Coking
Value/%Toluene Insoluble
Content/%Quinoline Insoluble
Content/%C/% H/% N/% S/% O/% H/C P170
P220
P250174
218
25140.1
49.8
57.826.2
47.7
53.70
0.75
1.0793.63
94.07
94.355.76
5.31
5.060.10
0.12
0.110.00
0.00
0.000.51
0.50
0.480.74
0.68
0.64
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表 2 包覆天然石墨负极材料的氮气吸附数据
Table 2. Nitrogen adsorption data of pitch coated natural graphite anode materials
Samples SBET/(m2·g−1) Smicro/(m2·g−1) Vtotal/(cm3·g−1) NG 9.65 0 0.0316 P170@NG 10.77 4.507 0.0101 P220@NG 5.88 0.076 0.009 P250@NG 4.11 0 0.0058
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表 3 包覆天然石墨负极材料的晶体结构参数
Table 3. Crystal structure parameters of pitch coated natural graphite anode materials
Samples 2θ/(°) d002/nm β/° Lc/nm g/% NG 26.481 0.33631 0.182 44.34 89.42 P170@NG 26.44 0.33682 0.23 35.09 83.47 P220@NG 26.44 0.33682 0.227 35.55 83.47 P250@NG 26.459 0.33658 0.225 35.87 86.23
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表 4 包覆天然石墨负极材料的恒流充放电性能
Table 4. Constant current charge-discharge performance of pitch coated natural graphite anode materials
Samples Initial discharge
capacity/
(mAh·g−1)Initial charge
capacity /
(mAh·g−1)Irreversible
capacity/
(mAh·g−1)Initial Coulomb
efficiency/(%)NG 401.0 339.7 61.3 84.70 P170@NG 393.2 316.4 76.8 80.46 P220@NG 404.7 348.6 56.1 86.15 P250@NG 384.6 338.6 46.0 88.04
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表 5 包覆天然石墨负极材料在0.5C电流密度下的循环性能
Table 5. Cycling properties of pitch coated natural graphite anode material at 0.5C current density
Samples Initial discharge capacity/(mAh·g−1) 250th discharge capacity/(mAh·g−1) Capacity retention/(%) NG 371.4 234.5 63.14 P170@NG 364.2 248.6 68.26 P220@NG 374.8 275.5 73.51 P250@NG 366.8 297.8 81.19
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表 6 包覆天然石墨负极材料的电化学阻抗谱参数
Table 6. Parameters of electrochemical impedance spectrum of pitch coated natural graphite anode materials
Samples Rs/Ω Rf/Ω Rct/Ω NG 5.8 19.6 37.6 P170@NG 3.9 26.4 35.8 P220@NG 3.4 14.7 21.0 P250@NG 3.8 5.8 23.0
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