| Lithium-ion battery (LIB) is the third generation of the small and high specific energy batteries after Ni-Cdand Ni (H) batteries. It is environment-protective and represents the most advanced level of battery techniques. One of the critical techniques is to study and develop new high specific energy carbon materials used as negative material of LIB.In this dissertation, liquid phase carbonized samples P16(QI=2. 2%), P14 (QI=4. 3%) were selected as the rawmaterials. They were heat-treated with different maximum heat-treatment temperatures (HTT.J. The mirostructures of these samples were characterized by XRD spectra and Raman spectra. The charging-discharging performances of these samples were investigated by the galvanostatic charging-discharging experiments and the powder microelectrode cyclic voltammetry experiments. The relationship between their charging-discharging performances and the microstructures were discussed, the textures ?microstructures and charging-discharging capacities of these two kinds samples were contrasted. The compatibilities of p!6-2800 sample with six kinds of electrolytes were investigated too. The components and the textures of the solid electrolyte interface(SEI) film which formed during the first charging process were analyzed by means of FTIR. The relationship between the SEI film and the compatibilities of samples with electrolytes was examined. The experimental results are as follows:(1): HTTmax made great influence on the microstructures and the charging-discharging performances of P16 and P14 samples . When HTTmax <2000 , the graphite microcrystals didn't appear.The mechanism of storing lithium-ions was to store lithium ionsin the micropores of the samples. Since the micropores which formed in the process of liquid phase carbonization had different sizes , the smaller the micropores , the lower the potential to overcome the resistance for inserting lithium ions . The charging-discharging curves looked like the letter "V" and had no flat plateaus, the charging-discharging capacities were high but faded rapidly. With the increasing of HIT., , the micropores became smaller and fewer, hence the charging-discharging capacity decreased. When HTTmax = 2000 , the micropores nearly disappeared, the graphite microcrystals were few and small, therefore the charging-discharging capacities reached the minimum. When HTTmax > 2000 , the graphite microcrystals grew rapidly, and the charging-discharging capacity of the samples increased rapidly too. The mechanism of storing lithium-ions was to intercalate the lithium ions into the layers of the graphite microcrystals. The charging-discharging curves of the samples looked like the letter "U" and had low potential flat plateaus. The samples behaved for a long cyclic life. When HTTmax = 2800 , the charging-discharging capacities of the P16 and P14 samples reached the maximum. There were no clear difference between P16 and P14 samples , so we concluded that QI content hardly made influence on the textures , the microstructures and the charging-discharging capacities of P16 and P14 samples in the studied QI content range .(2): In the system of same solute, the charging-discharging capacities and efficiencies of the sample p16-2800 depended on the kind of mixed solvents. The order according to their charging-discharging capacities and efficiencies is EC+DEC>EC+DMC>PODME. In the system of same solvent, thecharging-discharging capacities depend on the solute, and LiC104 is generally better than LiPF6. The chemical compositions of SEI films formed on the interfaces of P16-2800 samples in the different electrolytes during the first charging process were Li2C03 and LiOCO2R, but their textures are different. The SEI films formed in EC-based electrolytes was thin and compact. However, the SEI film formed in PC-based electrolytes was thick and loose, which could not effectively prevent solvated lithium ions from intercalation. The irreversible capacities in PC-based electrolytes were large. Therefore, the electrolytes based on... |
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