Title page for ETD etd-12082010-161626


Type of Document Master's Thesis
Author Cai, Chuan
Author's Email Address ccai1@tigers.lsu.edu
URN etd-12082010-161626
Title V2O5-WO3 Composite Films and Surface-Coated LiCoO2 for Enhanced Li-Ion Intercalation Properties
Degree Master of Science in Mechanical Engineering (M.S.M.E.)
Department Mechanical Engineering
Advisory Committee
Advisor Name Title
Wang,Ying Committee Chair
Guo,Shengmin Committee Member
Meng,Wen Jin Committee Member
Moldovan,Dorel Committee Member
Keywords
  • LiCoO2
  • WO3
  • V2O5
  • ALD
  • solution processing
  • Li-ion battery
Date of Defense 2010-11-08
Availability unrestricted
Abstract
We have investigated the enhanced Li-ion intercalation properties of two different materials, which are V2O5-WO3 composite and surface-coated LiCoO2. A simple and novel solution processing method is employed to prepare V2O5-WO3 composite films that demonstrate enhanced Li-ion intercalation properties for applications in Li-ion batteries or electrochromic displays. This solution processing method employs precursors that only contain the elements of V, W, O and H, which avoids impurity elements such as Na that has been commonly used in other solution methods (e.g. using precursors of sodium metavanadate and sodium tungstate solution). The V2O5-WO3 composite films show enhanced Li-ion intercalation properties compared to pure V2O5 and WO3 films. For example, at a high current density of 1.33 A/g, the V2O5-WO3 film with a V2O5/WO3 molar ratio of 10/1 exhibits the highest discharge capacities of 200 mAh/g at the first cycle and 132 mAh/g after 50 cycles, while pure V2O5 film delivers discharge capacities of 108 mAh/g at the first cycle and 122 mAh/g after 50 cycles. The enhanced capacity of the composite films is ascribed to the reduced crystallinity, increased porosity and thus the enhanced surface area. Both cyclic voltammogram and chronopotentiometric curves of the V2O5-WO3 film with a molar ratio of 10:1 are distinctively different from those of pure oxide films, suggesting a different Li-ion intercalation process in the V2O5-WO3 film with the molar ratio of 10:1.

For surface-coated LiCoO2, a molten salt synthesis method is employed to prepare LiCoO2 powders with submicron size, and ultrathin conformal Al2O3 or ZnO layers are coated on LiCoO2 electrodes by utilizing atomic layer deposition. The Al2O3-coated LiCoO2 electrode exhibits improve cycling stability during the electrochemical measurements, while the ZnO-coated LiCoO2 electrode does not show an improved cycling performance. The Al2O3 coating can prevent the direct contact between LiCoO2 and the electrolyte, and thus suppress the cobalt dissolution and side reaction. Therefore, LiCoO2 with nanosized thin Al2O3 coating exhibits improved cycling performance. In contrast, the ZnO coating is not electrochemically stable, so the ZnO-coated LiCoO2 electrode exhibits a similar cycling performance with the bare LiCoO2 electrode.

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