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Carbon Aerogels Based Composites As Electrode Materials For Lithium Batteries

Posted on:2014-02-08Degree:MasterType:Thesis
Country:ChinaCandidate:F B HaoFull Text:PDF
GTID:2232330398461173Subject:Materials science
Abstract/Summary:PDF Full Text Request
Nowadays, with the development of the major storage demand in miniature electronic devices, lithium ion batteries (LIBs) have a wide application, and play the more and more important role. However, the limited capacity hindered its further development. As we all know, the improvement of LIBs depends on the electrode materials. In this paper, we synthesized CA and its composites with metal oxides and sulfur, and investigated their lithium battery performance. The results show that the lithium storage performance can be improved observably. The main contents are summarized as follows:1. An old gel-ageing method was used to synthesize CA with different structure by using resorcinol and formaldehyde as the precursors. The ratio of R and C of the three different CA were500,1000,1500, and the BET surface area were669,483,398m2g-1respectively. Through the electrochemical testing, it is indicated that the composite electrode showed a first discharge capacity of1753,715,509mAgh"1at the current density of50mAg-1, which are much higher than graphite, and remained stable capacity of470,250,270mAgh-1after50cycles. The good electrochemical performance of CA owe to the high surface area and mesoporous structure.2. Cobalt oxide and CA composites (Co3O4-CA) were synthesized by a facile way of solution immersion. In order to reduce the irreversible capacity of CA and the capacity fading of pure cobalt oxide, we synthesized Co3O4-CA using CA(RC=500) as the matrix, cobalt nitrate hexahydrate as the precursor of cobalt oxide, the contents of Co3O4in the composites were15,25,35wt%respectively, the size of nanoparticle was about5nm. Through the electrochemical testing, it is indicated the composites electrode showed a first discharge capacity of1698,1797,2043mAgh-1at the current density of50mAg-1, and remained stable capacity of770mAgh-1(Co3O4content:25wt%) after50cycles. The significant improvement in electrochemistry of Co3O4-CA composites can be attributed to their synergistic effects and three-dimensional structure of porous CA matrix, which act as a buffer for the volume expansion and contraction of Co3O4during charging and discharging progress. On the other hand, because the Co3O4nanoparticle dispersed homogeneously in the CA, the irreversible active sites of CA were reduced, and the nanoparticle offer more reversible active sites, therefore, the electrochemical performance was improved.3. The ZnMn2O4/CA (with tetragonal spinel structure) were synthesized by a facile solution immersion route. In order to take full advantage of the excellent performance of ZnMn2O4(stabilization, high capacity, non-toxic, low cost, low voltage platform), avoid the disadvantage of volume change and low conductivity. We synthesized four types of ZnMn2O4/CVCA composites, CA acting as the conductive substrate and buffer substance. Through the electrochemical testing, it is indicated that at the current density of100mAg-1, the composite electrode shows a first discharge capacity of1548mAhg-1,1722mAhg-1,1660mAhg-1,1688mAhg-1, and remained stable capacity of700mAhg-1,780mAhg-1,820mAhg-1after50cycles, displaying excellent lithium performance.4. The low temperature melt impregnation method was used to synthesize lithium-sulfur batteries cathode materials:CA/S composite material. The sulfur content of18,27,35wt%composites were prepared through controlling the volatile time. Through the constant current cycle performance and rate performance testing, the reversible capacity of CA/S composite (sulfur content:27wt%) was750mAhg-1after50cycles at the current density of0.2C, even at the current density of3.2C, the capacity was still kept about445mAhg-1, showing excellent electrochemical performance. The micropore structure and high surface area offered more contact opportunity between sulfur and electrolyte, reduced volatilization of polysulphide, and the CA matrix enhanced the conductivity of composites to help to improve the performance of the lithium ion battery.
Keywords/Search Tags:crbon aerogel, cobalt oxide, hetaerolite, lithium ion batteries, sulfur, lithium-sulfur batteries
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