Year

2014

Degree Name

Degree of Philosophy

Department

Institute for Superconducting and Electronic Materials

Abstract

Prior to being applied in electric vehicles (EVs), lithium-ion batteries (LIBs) have already been widely used in various portable and smart devices, including cell phones, MP3 devices, cameras, and laptop computers. Compared to portable and smart devices, EVs (including hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs)) require significant improvements in many aspects of LIBs performance, such as energy density (> 150 W/kg), safety, and cost. The key to success in the development of advanced LIBs to meet the emerging EVs market demands is the electrode materials. It is thus necessary to develop and employ cost-effective electrode materials for sustainable development. Currently, it is the fact that the working voltage, energy density, and rate capability of a LIB are mainly determined by the limited theoretical capacity and thermodynamics of the cathode material in the present LIB technology. Therefore, it is critical to develop the promising cathode materials for the current LIBs technology. In this doctoral work, the promissing cathode materials for LIBs, including lithium metal oxide LiNi1/3Mn1/3Co1/3O2, lithium metal phosphates LiCoPO4 and Li3V2(PO4)3, and lithium metal pyrophosphate Li2FeP2O7, are well investigated. Futhermore, compared with current advanced state-of-the-art cathode materials, including lithium metal oxides (140 - 200 mAh g-1 and 500 - 700 Wh kg-1) and lithium metal phosphates (140 - 190 mAh g-1 and 560 - 800 Wh kg-1), sulfur as one of the most promising cathode material for lithium-sulfur (Li-S) batteries is also investigated because of its higher theoretical capacity (~ 1675 mAh g-1) and energy density (~ 2600 Wh kg-1).

On the other hand, for LIBs, there has also recently been increasing concern that the increasing cost ($5000/ton for lithium vs. $150/ton for sodium) and the limited terrestrial lithium reserves in the world would be not sufficient to satisfy the demand from large-scale commercial applications. Sodium, the sixth most abundant element in the earth's crust and another member of the alkali family shares many similar chemical properties to lithium. The working mechanisms of sodium-ion batteries (SIBs) and LIBs are very similar. Therefore, SIBs may prove to be a cheaper one to store energy than the commonly used LIBs. In this doctoral work, the advanced materials for SIBs, including sodium metal oxide NaFe1/2Mn1/2O2 as cathode material and three-dimensional nitrogen-doped graphene foams as anode material, are also investigated.

As a result, in order to achieve the goal of pursuing high-performance of LIBs (including Li-S batteries) and SIBs for EVs, the preparation methods, characterization methods, and electrochemical measurements of advanced materials mentioned above were explored and are discussed in this doctoral work. Moreover, the influence of the structure, morphology, and physical and chemical properties of these materials on electrochemical performance are also critically investigated.

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