【作者】 范长岭；

【导师】 徐仲榆；

【作者基本信息】 湖南大学 ， 材料学， 2005， 硕士

【摘要】 为了考察某电炭厂石墨制品废料用作锂离子电池（LIB）负极活性材料的可行性，将其原试样进一步进行了不同最高热处理温度(HTT_max)的热处理。用试样的密度、灰分含量和XRD图谱表征了试样的微观结构。用恒电流充、放电实验考察了试样的充、放电性能。据此讨论了试样的微观结构与宏观电化学性能的关系，确定了最佳热处理工艺制度。结合恒电流充、放电实验、粉末微电极循环伏安实验和FTIR分析考察了具有良好贮锂结构的XT-28试样与六种不同电解液的相容性。采用正交法通过恒电流充、放电实验考察了XT-28试样的粒度、炭膜中导电剂乙炔黑和粘结剂PTFE的含量以及充、放电电流密度等因素对其充、放电性能的影响。采用粉末微电极循环伏安实验估测了在最佳实验条件下XT-28试样的循环性能。实验结果表明： 1．采用“从室温升温至2400℃时，边加热边抽真空”的热处理制度有利于除去试样中部分杂质，但要将试样内妨碍锂离子在其中扩散的杂质SiC和铁-渗碳体（Fe₃C）除去，HTT_max必须不低于2800℃。从节能观点出发，最佳HTT_max应为2800℃，XT-28为最佳试样，其第三循环放电容量（D₃）为330.2mAh／g、充、放电效率（η₃）为97.5％。 2．XT-28试样在六种不同电解液中首次充电时，试样颗粒表面形成了固体电解质中间相（SEI）膜，其主要成份均为碳酸锂。EC基电解液在试样颗粒表面发生的还原反应比较缓和，能够形成薄而致密的、只允许锂离子通过的SEI膜；而PC基电解液在试样颗粒表面发生的还原反应比较激烈，形成的SEI膜厚而不均匀、锂离子难以通过。 3．由正交试验结果可知，XT-28试样在1mol／L LiClO₄／EC+DEC（1：1）电解液中进行恒电流充、放电时，试样的粒度（A）、炭膜中导电剂乙炔黑的含量（B）、炭膜中粘结剂PTFE的含量（C）以及充、放电电流密度（D）等因素对第三循环放电容量D₃及充、放电效率η₃影响的大小顺序均为：B＞D＞A＞C。但对D₃的影响（极差R=23.1～37.3mAh／g）远大于对η₃的影响（极差R=0.3～1.2％）。上述四个因素的最佳水平组合为A₂B₃C₂D₂：即试样粒度为水平2（-325目），炭膜中乙炔黑含量为水平3（6％），PTFE含量为水平2（5％），充、放电电流密度为水平2（15mA／g）。采用这一组合时D₃≥338.7mAh／g，η₃≥96.1％。 4．粉末微电极循环伏安实验表明XT-28试样的循环性能很好，当进行到第500循环时，其放电容量为第60循环最大放电容量的72.22％，充、放电效率为93.35％。更多还原

【Abstract】 In order to examine the possibility of using the processing graphite wastes from an electric-carbon factory as the negative electrode materials in lithium ion batteries (LIB), the original samples were heat-treated with different maximum heat treatment temperatures (HTTmax). The microstructures of these heat-treated samples were characterized by their densities, ash contents and XRD spectra. The charging-discharging performances of them were investigated by galvanostatic charging-discharging experiments. The relationship between their charging-discharging performances and microstructures was discussed and the optimized heat treatment technology was determined. Sample XT-28 has a good structure for storing up lithium ions. The compatibility of it with six different kinds of electrolytes was investigated by the galvanostatic charging-discharging experiments, powder microelectrode cyclic voltammetric experiments and FTIR analysis. The influences of some other factors: thegranularity of sample, the content of conductive additive--acetylene black and thecontent of binder--PTFE in the carbon membrane and the charging-dischargingcurrent density etc, on the charging-discharging performances of sample XT-28 were investigated by the orthogonal method through galvanostatic charging-discharging experiments. The cyclic performance of the sample XT-28 under the best experimental conditions was investigated by the powder microelectrode cyclic voltammetric experiments. The experimental results are as follows:1. The heat treatment technology--extracting air during heating from roomtemperature to 2400℃ is helpful to remove part of impurities in the original sample. However, the HTTmax can not be lower than 2800 ℃, if we want to remove the impurities SiC and FesC which hinder the lithium ions from diffusing inside the sample. For saving energy, the best HTTmax of sample should be 2800℃ and sample XT-28 is the best one. In the third cycle, its discharging capacity is 330.2mAh/g and the charging-discharging efficiency is 97.5%.2. Solid electrolyte interphase (SEI) films are formed on the surfaces of the particles of sample in six different electrolytes during the first charging process. The main content of all the SEI films is lithium carbonate. EC-based electrolytes can react with the surfaces of particles moderately and form thin and compact SEI films which only the lithium ions can pass through. On the contrary, the reaction between PC-based electrolytes and the surfaces of particles are intense and the SEI films are thick and nonhomogeneous, which the lithium ions are difficult to pass through.3. According to the results of orthogonal experiments, when sample XT-28 charges and discharges in the electrolyte of 1 mol/L LiC104/EC+DEC(1:1), the factors such as the granularity of sample XT-28 (A), the content of acetylene black (B) and the content of PTFE (C) in the carbon membrane and the charging-discharging current density (D) also make influences on the discharging capacities and the charging-discharging efficiencies of the 3rd cycle (D3 and η3). The influence degree orders of the above four factors on D3 and η3 are the same, that is B>D>A>C. However, the influence on D3 (maximum difference R=23.1~37.3mAh/g) is much greater than that on η3 (R=0.3~1 .2%). The best level combination of the above four factors is A2B3C2D2: the granularity of sample XT-28 is at level 2 (-325 mesh), the content of acetylene black in carbon membrane is at level 3 (6%), the content of PTFE in carbon membrane is at level 2 (5%) and the charging-discharging current density is at level 2 (15mA/g), while D3 is larger than 338.7mAh/g and η3 is greater than 96.1%.4. The powder microelectrode cyclic voltammetric experiments show that sample XT-28 has a good cyclic performance. In the 500th cycle, the discharging capacity keeps 72.22% of the maximum discharging capacity (in the 60th cycle) and the charging-discharging efficiency of the 500th cycle is 93.35%.更多还原