Doctor of Philosophy (PhD)
Rechargeable lithium-ion battery is one of the most promising energy conversion and storage systems that offers high energy and powder densities, long service life and assuring safety. Performance of lithium-ion batteries crucially relies on electrochemical characteristics of electrode materials, i.e., anode and cathode materials. This dissertation work aims at developing novel electrode materials with high capacity, excellent cycling stability and remarkable rate capability for next-generation lithium-ion batteries. The effects of surface modifications for LiMn2O4 cathode materials are studied by depositing ultrathin conformal amphoteric oxides via atomic layer deposition (ALD). In the case of ZnO coating, the thickness of ZnO ALD layers can be finely optimized at atomic scale by varying ALD growth cycles. Six ZnO ALD layers demonstrate to have the optimal thickness (~ 1 nm) for the best electrochemical performance of LiMn2O4 cathodes either at room temperature or elevated temperature. Furthermore, the effects of crystalline ZrO2 ALD coating on improving elevated-temperature performance of either micro-sized or nano-sized LiMn2O4 particles are evaluated. Other work concentrates on boosting electrochemical performance of Li-excess layered transition metal oxides, which are emerging lithium-ion battery cathode materials with very high theoretical capacities but suffering from drastic initial capacity loss and poor rate capability. To solve these issues, one strategy involves preparing hierarchical functional surface modifications on Li[Li0.2Mn0.54Ni0.13Co0.13]O2 nanoparticles, which consist of nano-sized LiCoO2 shell and sub-nano-sized ZrO2 ALD coating. The other route is to completely convert Li-excess layered Li[Li0.2Mn0.54Ni0.13Co0.13]O2 to a Li4Mn5O12-type spinel product via ex-situ ion-exchanges and a post-annealing process. The enhanced electrochemical performance of Li-excess layered cathode materials is achieved from the synergetic effects of ALD oxide coating and core-shell structure, ex-situ layered-to-spinel phase transformation, and nanoarchitecture with high surface area. In addition to cathode materials, multi-shell spherical Mn0.54Ni0.13Co0.13(CO3)0.8 carbonate anode material is synthesized by a hydrothermal approach, which is combined with its lithiated yolk-shell-structured Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode for a full battery cell exhibiting excellent electrochemical performance.
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Zhao, Jianqing, "Novel Syntheses and Surface Modifications of Electrode Materials for Superior Lithium-Ion Batteries" (2014). LSU Doctoral Dissertations. 841.