| The floatation concentrate of anthracite(ANT) was heat-treated with different maximum heat treatment temperature(HTTmax). The microstructures of the samples heat-treated with different HTTmax were characterized by their densities and XRD spectra. The charging-discharging performances of these samples used as the negative electrodes in lithium ion batteries(LIB) were investigated by galvanostatic charging-discharging experiments and powder microelectrode cyclic voltammetry experiments. The relations between their charging-discharging performances and their microstructures were discussed. The compatibilities of sample A3000 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 charging-discharging current density, the granularity of A3000, the content of acetylene black and the content of PTFE) on the charging- discharging performance of sample A3000 were also investigated by the orthogonal method through galvanostatic charging-discharging experiments. The experimental results are as follows:l.The microstructures and the charging-discharging performances of ANT samples relate to HTTmax. When HTTmax <2100℃, the microstructure of the ANT sample is turbostratic, the graphite crystallites have not appeared. The mechanism of storing lithium-ions is to insert lithium ions into 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. Increasing the HTTmax, the micropores in ANT samples become fewer and smaller, therefore the charging-discharging capacities decrease. When HTTmax = 2100℃, the charging-discharging capacity reaches the minimum since the number of the micropores reaches the minimum and the size of them become very small, the number of graphite crystallite in ANT samples is still few and the size of them is also small. When HTTmax>2100℃, the graphite crystallites 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 intothe layers of graphite crystallites. The charging-discharging curves of the samples look like the letter "U" and have low potential flat plateaus. Comparing with the other soft carbonaceous materials, the HTTmax of ANT sample is higher(the optimum HTTmax is 3000℃) and the time of heating in the high temperature range is long, it means that the ANT samples are more difficult to be graphitized.2.The compositions of electrolytes make great influences on the charging-discharging performances of ANT sample. The chemical compositions of SEI films formed on the interfaces of A3000 samples in different electrolytes during the first charging process are mainly Li2CO3 and LiOCO2R, but their textures are different. The SEI films formed in EC-based electrolytes are thin and compact, which can prevent the solvated lithium ions from cointercalating between two graphene layers of the graphite crystallites effectively, therefore samples A3000 have small irreversible capacities and good compatibilities with this kinds of electrolytes. However, the SEI films formed in PC-based electrolytes are thick but defective, which could not effectively prevent solvated lithium ions from intercalation, therefore sample A3000 shows large irreversible capacities in PC-based electrolytes and bad compatibilities with this kind of electrolytes. For EC-based system, the charging-discharging efficiencies using the solute LiClO4 are a little higher than using the solute LiPF6.3. Other factors such as the charging-discharging current density (A), the granularity of A30000 (B), the content of acetylene black(C) and the content of PTFE (D) also make influences on the charging-discharging performance of sample A300... |
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