Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Doctor of Philosophy




Sham, Tsun-Kong

2nd Supervisor

Sun, Xueliang



All-solid-state batteries (ASSBs) are widely recognized as the next frontier in energy storage systems, holding the potential to surpass the capabilities of current lithium-ion batteries (LIBs). Their unique feature of utilizing non-flammable solid-state electrolytes (SSEs) instead of liquid electrolytes (LEs) directly addresses safety concerns in power supply applications, particularly within the electric vehicle and aviation industries. However, the inherent rigidity of solid materials introduces a challenge in the form of sluggish ion diffusion behaviors, observable within SSEs, the cathode active materials (CAMs), and the interfaces between these components. This sluggish diffusion ultimately contributes to a reduction in the operational efficiency of ASSBs.

Within the scope of this thesis, a comprehensive investigation is undertaken into the intricacies influencing ion transport in halide materials. Factors such as bond covalency, long-range and short-range structures, and the amorphous state are meticulously examined. Regarding the bond covalency, the superionic conducting transition of Li3InBr6 was investigated by in situ characterization upon the transition temperature (Tc). It is revealed that this superionic transition correlates with the covalency of the In-Br bond. The superionic conducting transition behaviors can be further tuned through cation (Y and Ga) doping in Li3InBr6 via the modification of metal-ligand covalency. Regarding the crystal structures, a new class of zeolite-like halide frameworks was studied, SmCl3 for example, in which 1-dimensional channels are enclosed by [SmCl9]6- tricapped trigonal prisms to provide a short jumping distance of 2.08 Å between two octahedrons for Li-ion hopping. Similar to zeolites, the SmCl3 framework can be grafted with halide species to obtain mobile ions without altering the base structure, achieving an ionic conductivity over 10-4 S cm-1 at 30 °C with LiCl as the adsorbent. Regarding the design of heterogeneous structure electrolytes (HSEs), the structural variances between high- and low-coordination halide frameworks were exploited to develop a new class of Na+-conducting halide HSEs. The HSEs using UCl3-type high-coordination frameworks achieved the highest Na-ion conductivity (2.7 mS cm-1 at room temperature) among halides so far. The synergistic processes within halide HSEs were unrevealed, providing a comprehensive explanation of the amorphization effect.

Taking advancements a step further, an all-in-one cathode electrode solution is realized through the rational design of a halide cathode material, Li1.3Fe1.2Cl4. All-in-one active materials can transport ions and electrons themselves, thus showing advantages in high active material content (theoretically 100%), low tortuosity for Li+/e- diffusion, and eliminating cathode/SE interface reactions. The identification of halide materials, studies on diffusion mechanisms, and electrode engineering highlighted in this dissertation pave the way for the development of high-performance ASSBs.

Summary for Lay Audience

All-solid-state batteries (ASSBs) represent a class of advanced energy storage devices that employ solid-state electrolytes (SSEs) instead of liquid electrolytes in conventional liquid electrolytes. The primary advantages associated with ASSBs, namely enhanced safety and energy density, render them highly appealing for employment in portable electronics and electric vehicles (EVs) as cutting-edge energy storage solutions. The rate of ion transport within solid materials holds significant importance in the operational mechanism of solid-state batteries. Whether pertaining to the electrolyte material or the electrode material, the velocity of ion movement, be it rapid or sluggish, fundamentally governs the charging and discharging rates as well as the overall efficiency of the battery system. In this context, comprehending the diverse array of factors influencing ionic transport, spanning from materials to electrodes, and subsequently employing this knowledge in the design of efficient ASSBs, becomes paramount. This dissertation evaluates advancements in ion diffusion for halide-based SE design and cathode active material design. Besides, the concern over limited lithium reserves motivates the exploration of sodium-conducting SEs for efficient application in sodium-ion ASSBs. Specifically, variables influencing ion diffusion in halide SEs are systematically investigated, including electronic structure (bond covalency), short- and long-range material structures (amorphous and crystalline), and electrode architecture. Several Li+/Na+ superionic conductors are discovered and integrated into high-performing ASSBs, thereby providing valuable insights for future high-performance ASSB development.

Available for download on Friday, August 22, 2025