Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Mechanical and Materials Engineering

Supervisor

Prof. Xueliang Sun

2nd Supervisor

Prof. Tsun-Kong Sham

Co-Supervisor

Abstract

Lithium ion batteries (LIBs) have been the dominant candidate in the field of energy storage. The ever-growing demand of high energy and power density, longer battery life, and more assured safety level has geared the development of LIBs towards all-solid-state batteries (ASSBs). The solid-state nature allows more flexibility in battery design and higher area capacity to be obtained within limited space. Moreover, replacing liquid electrolytes with solid-state electrolytes (SSEs) is a most effective approach to achieve safer battery system. In addition, ASSBs hold great promise in the actual fabrication of microbatteries for microelectronics. Therefore, a technique which can synthesize materials in a precisely controlled manner is extremely critical. Atomic layer deposition (ALD) strikes as a thin film deposition technique which is capable of depositing ultrathin, uniform, conformal and pinhole-free thin films over various complex structures.

In this thesis, we reported the fabrication of nanomaterials by ALD as electrodes and SSEs for next-generation batteries. More focus has been put on the development of SSEs. Amorphous lithium phosphate (LPO) was deposited by a simplified route of reaction. The composition of the as-prepared thin films was analyzed and an acceptable ionic conductivity was obtained.

Based on the first SSE developed, a nanocomposite as anode material for LIBs was rationally designed combining ALD procedures of TiO2 and LPO. Carbon nanotubes were utilized as an electronically conductive scaffold. The detailed structure of the nanocomposite was investigated. Excellent electrochemical performance was obtained.

Furthermore, another SSE, lithium silicate, was developed by ALD. The composition of the as-deposited thin films can be adjusted by changing the lithium to silicon subcycle ratio. The relation of composition and deposition temperature was studied. And a stoichiometry close to lithium orthosilicate demonstrated the best ionic conductivity.

The third system explored by ALD as SSEs was lithium niobium oxide. Similarly, the atomic ratio between Li and Nb was tuned by the subcycle number. The local structure was studied. The ionic conductivity was also assessed, exceeding 10-8 S cm at room temperature.

In summary, ALD has been proven to be a promising technique to develop electrode and SSE materials for the next-generation ASSBs.

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