| The Changling petroleum coke samples were heat-treated with different maximum heat treatment temperatures (HTTmax). The microstructures of these samples were characterized by their densities and XRD spectra. The charging-discharging performances of these samples were examined with galvanostatic charging-discharging experiments and powder microelectrode cyclic voltammetry experiments. According to these results, the relations among HTTmax, the charging-discharging performances and the microstructures were discussed, and the best HTTmax was determined. For saving energy, Sample C3000-2 with the best structure of reserving lithium ion was made at 3000 with the technical condition of high efficiency. The compatibilities of sample C3000-2 with four kinds of electrolytes were investigated. 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 the content of acetylene black in sample C3000-2(A), the granularity of C3000-2(B), the content of PTFE(C) and the charge-discharge current density(D) on the charging- discharging performances of C3000-2 were also investigated by the orthogonal method through galvanostatic charging- discharging experiments. The experimental results are as follows:1.HTTmax has an great influence on the microstructures and the charging-discharging performances of Changling petroleum coke samples. When HTTmax <1800 , there are no graphite crystallites in the sample or there are only very little and a small amount of graphite crystallites in the sample. 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 sizesof the micropores. Increasing the HTTnax, the micropores in these samples become fewer and smaller, therefore the charging-discharging capacities decrease. When HTTmax= 1800 , 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 samples is still few and the size of them is also small. When HTTmax>1800 , 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 into the graphlene layers of graphite crystallites. The charging-discharging curves of the samples look like the letter "U" and have low potential flat plateaus. When HTTmax=3000 , the discharging capacity of C3000-1 in 1mol/L LiC104/EC+DMC ( 1 : 1 ) electrolyte is 289.2mAh/g , the charging-discharging efficiency is 93. 6%, while the discharging capacity of the sample C3000-2 is D3=346. 3mAh/g, the charging-discharging efficiency is 94. 6%. The sample C3000-2 have better charging-discharging performance.2. The chemical compositions of SEI films formed on the interfaces of sample C3000-2 in different electrolytes are mainly Li2CO3 and LiOCO2R. The SEI films formed in EC-based electrolytes are thin and compact, which can prevent the solvated lithium ions from cointercalating into the graphene layers of graphite crystallite effectively, therefore the sample has small irreversible capacities and good compatibilities with the electrolyte. However, the SEI films formed in PC-based electrolytes are thick but defective, which could not effectively prevent solvated lithium ions from intercalation, so the sample shows large irreversible capacities in PC-based electrolytes and bad compatibilities with the electrolytes.3. The content of acetylene black in the carbon membrane of sample C3000-2 (A), the granularity of sample C3000-2(B), the content of PTFE (C) in the carbon membrane and the charging-discharging current density (D)make influences on the charging-discharging performance of sample C3000-2in d... |
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