【作者】 谢辉；

【导师】 徐仲榆； 尹笃林；

【作者基本信息】 湖南师范大学 ， 应用化学， 2003， 硕士

【摘要】 将针状焦（NC）进行不同HTT_max（最高热处理温度）的热处理，用密度、XRD图谱和激光Raman图谱来表征热处理后NC试样的微观结构。运用恒电流充、放电实验和粉末微电极循环伏安实验来检测上述NC试样的充、放电性能。在此基础上探讨了NC试样的微观结构与充、放电性能之间的关系。考察了具有最佳贮锂结构的NC₂₇₀₀试样和六种电解液之间的相容性，利用FTIR图谱对NC₂₇₀₀试样在上述六种电解液中首次充电时在炭负极表面所形成的SEI（固体电解质中间相）膜的成分和织构进行了分析，研究了试样与电解液的相容性和SEI膜的关系。结合恒电流充、放电实验，采用正交法分析了NC₂₇₀₀试样的粒度、炭膜中乙炔黑的含量以及PTFE的含量对NC₂₇₀₀负极材料的充放电性能的影响。试验结果表明： 1．HTT_max对NC试样的微观结构和充、放电性能有很大影响。当HTT_max≤1500℃时，由于NC已经过1400℃～1500℃的煅烧，因此其微观结构及充、放电性能没有多大改变；在HTT_max＜2100℃的范围内，NC属于乱层结构，石墨微晶尚未出现或数量很少，贮锂机制为“孔隙贮锂”，由于孔隙的大小不一，插锂时克服阻力所需的电位也不同，因此充、放电曲线呈“V”字形，无充、放电电位平台；随着HTT_max的增大，材料中孔隙逐渐变小、变少，充、放电容量也逐渐变小；HTT_max=2100℃时，微孔几乎消失，而石墨微晶又少又小，因此试样的充、放电容量最低：HTT_max＞2100℃时，石墨微晶迅速成长，充、放电容量迅速增大，充、放电曲线为“U”字形，充、放电平台低而平稳，循环性能良好，表现出典型的“石墨微晶层间嵌锂”机制；当HTT_max=2700℃时，NC₂₇₀₀在1mol/L LiClO₄/EC+DEC（1：1）电解液中第三循环的放电容量D₃=314.3mAh/g，充、放电效率η₃=95.7％，具有最好的充、放电性能；HTT_max＞2700℃时，随着HTT_max的升高，石墨微晶继续增大，但由于能阻止溶剂化锂离子插入到石墨层间的sp³键减少，使NC充、放电性能降低。 2．不论使用LiClO₄还是LiPF₆作锂盐电解质，EC基溶剂体系总是大大优于PC基溶剂体系，当采用EC基溶剂体系时，以LiClO₄作溶质时的充、放电效率比以LiPF₆作溶质时相对要高5％左右。NC₂₇₀₀试样在不同的电解液中，首次充电过程中形成的SEI膜化学组分均为碳酸铿和烷基碳酸铿，但在EC基电解液中形成的sEI膜薄而致密，可以有效地阻止溶剂化铿离子插入石墨层间，不可逆容量少，表现出与NC270(、负极材料有良好的相容性;在PC基电解液中形成的SEI膜虽厚但有缺陷，不能有效地阻止溶剂化铿离子插入石墨层间，不可逆容量大，与NC270。负极材料的相容性极差。 3.NC27(l(，负极材料的粒度（A）、炭膜中导电剂乙炔黑的含量（B）和粘结剂PTFE的含量（C）对NC270。的充、放电性能均有影响，但程度不同。对NC27o.，负极材料在lm。1/L Lie10，/EC+DEC（l:l）电解液中第三循环放电容量的影响顺序为:A>B>C;对第三循环充、放电效率的影响顺序为:A>C>B。当NC270(，负极材料的粒度为一325目，乙炔黑含量为6%，PTFE含量为3%时，NC二。，的第三循环放电容量最大（D:、=318.4 mAh/g）。当NC27《，(，负极材料的粒度为一200「!，乙炔黑含量为O%，PTFE含量为3%时，NC270。的第三循环充、放电效率最大（几3=96.9%）。可以看出:NC270。负极材料的第三循环放电容量达到最大时各因素的水平与第三循环充、放电效率最人时并不致，考虑到第三循环充、放电效率的极差都不大，因此在压制炭膜时上述三因素可以选用第三循环的放电容量为最大时的水平。 4.由方案2制备的NC270。试样既可以保持由方案1所制备的NC270.，试样的贮铿结构和充、放电性能，又能节约石墨化过程「一扫的能耗。 5.当选取组合为AZB:，C.的炭膜时，NC27.川在lmol/L LICIO，/EC+DEC（1:l）电解液中第三循环的放电容量压=3 18.4mAh/g，充、放电效率n厂90.7%，是一种理想的铿离子电池负极材料。更多还原

【Abstract】 NC (Needle coke) was heat-treated with different HTTmax (the maximum heated-treatment temperature). The microstructures of these samples were characterized by their densities, XRD spectra and Raman spectra. Their charging-discharging performances were investigated by galvanostatic charging-discharging experiments and powder microelectrode cyclic voltammetry experiments. The relationship between their charging-discharging performances and the microstructures was discussed. The compatibilities of sample NC2700 with six kinds of electrolytes were investigated too. The compositions of the solid electrolyte interphase(SEI) films formed during the first charging process were analyzed by FTIR spectra. The relationship between the SEI films and the compatibilities of samples with electrolytes was examined. The influences of other factors (the granularity of NC2700, the content of PTFE and the content of acetylene black) on the charging-discharging performances of NC2700 were also investigated by the orthogonal method through galvanostatic charging-discharging experiments. The experimental results are as follows:1.The microstructures and the charging-discharging performances of NC samples relate to HTTmax. When HTTmax<1500 ℃, the microstructures and the charging-discharging performances of NC samples remain unchanged due to the previous calcination under temperature 1400℃-1500℃. When HTTmax <2100℃, the graphite microcrystals have not appeared. The mechanism of storing’ lithium-ions is to insert lithium ions in the micropores of the samples. The charging-discharging curves look like the letter "V" and have no flat plateaus due to the different sizes of the micropores. With the increasing of HTTmax, the micropores in NC samples become smaller and fewer and the charging-discharging capacities decrease. When HTTmax = 2100℃, the charging-discharging capacity reaches the minimum due to the minimum micropores and the small and few graphite microcrystals in NC samples. When HTTmax >2100℃, the graphite microcrystals grow rapidly, and the charging-discharging capacities of the samples increase too. The mechanism of storing lithium-ions converts to the intercalation of the lithium ions between the graphene layers of the graphite microcrystals. The charging-discharging curves of the samples look like the letter "U" and have low potential flat plateaus. When HTT.ax-2700℃, the charging-discharging characteristic of NC sample in 1mol/L LiClO4/EC+DEC (1:1) electrolyte reaches the optimum with discharging capacity 314.3mAh/g and charging-discharging efficiency 95.7% in the 3rd cycle. When HTTmax>2700℃, the charging-discharging performances of NC become worse since the exfoliation of graphene layers in the graphite microcrystals due to the decrease of sp3 bonds which can prevent the solvate-d lithium ions from intercalating into graphene layers.2. Using either LiClO4 or LiPF6 as the lithium salt solute, the charging-discharging performances in EC-based solvent system are always much better than in PC based solvent system. For EC-based system, the charging-discharging efficiency using the solute LiClO4 is about 5% higher than using the solute LiPF6. The chemical compositions of SEI films formed on the interfaces of NC2700 samples in different electrolytes during the first charging process are mainly Li2CO3 and LiOCO2R, but their textures are different. The SEI films formed inEC-based electrolytes are thin and compact, which can prevent the solvated lithium ions from cointercalating into graphene layers; the irreversible capacities are small. The compatibilities with NC2700 are good. However, the SEI films formed in PC-based electrolytes are thick but defective, which could not effectively prevent solvated lithium ions from intercalation; the irreversible capacities in PC-based electrolytes are large. The compatibilities with NC2700 are very bad.3. In the process of the manufacture of the electrode, the granularity of NC2700 (A), the contents of PTFE (B) and acetylene black(C) influence the charging-dischargi更多还原