Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Doctor of Philosophy


Mechanical and Materials Engineering


Xueliang Sun

2nd Supervisor

Tsun-Kong Sham



All-solid-state batteries (ASSBs), in which solid superionic conductors are used as electrolytes to transport ions between cathode and anode, have been regarded as one of the most promising candidates for the next-generation energy storage technologies in electric vehicles (EVs), grid applications, etc. The advances of ASSBs over conventional lithium-ion batteries (LIBs) come from their inherent safety and high energy density, which benefits from the use of nonflammable solid electrolytes (SEs) to potentially enable metal anodes (such as Li metal or Na metal) and high-voltage cathode active materials (CAM) in ASSBs. Since that, the research and design of SEs have been a hot topic to accelerate the development of ASSBs. At the same time, a good compatibility (e.g., chemical stability, electrochemical stability, and mechanical compatibility) between SEs and metal anodes/high-voltage cathodes are essential for achieving high-energy-density ASSBs with long cycle life.

In this dissertation, the research towards SEs development and SE/electrodes interfacial protection have been studied. First, several new superionic conductors (Lix-3YIx, xLi2O-TaCl5, and xLi2O-HfCl4) with considerable Li-ion conductivity over 10‒3 S cm‒1 are developed, some of which are feasible in ASSBs with stable cycling performances. The novel structures those solids behave have been firstly discovered, deepening the fundamental understandings for ionic conductors. Then, by rational modifying an existing SE to possess high practical anodic limit, the stability between SE and high-voltage cathode can be achieved for high-voltage ASSBs. Finally, the concerns associated with active Na anode and SEs are addressed via applying functional molecular layer deposition (MLD) coatings. The results on SE synthesis, interfacial engineering, and mechanism studies in this dissertation shall pave the way to achieve high-performance all-solid-state Li-ion batteries, as well as guide the development for the beyond lithium battery technologies.

Summary for Lay Audience

All-solid-state batteries (ASSBs) are types of advanced batteries which use solid electrolytes (SEs) to replace the conventional liquid electrolytes. The main advantages of ASSBs over conventional batteries are high safety and energy density, which make ASSBs become attractive energy storage devices for portable electronics and electric vehicles (EVs). SE is a core component of ASSB, which is a solid ionic conductor between the cathode and anode. A promising SE should essentially possess good ionic conductivity (over 10−3 S cm−1), anodic stabilities (>4.5 V vs. Li/Li+), and good metal anode compatibility. However, there has been few SEs that can simultaneously show those properties. Besides, driven by the concerns of lithium scarce in the earth, fundamental understandings as well as established technologies should be applied to support the development of the beyond lithium batteries (such as all-solid-state Na-ion batteries).

In this dissertation, the improvements of SEs in terms of good ionic conductivities and anodic stabilities are accessed. Besides, referring to the coating technologies in conventional liquid batteries, the instability between active Na anode and SEs is addressed. In specific, several inorganic ionic conductors are developed with an attractive Li-ion conductivity around 10−3 S cm−1. Some of them also show good cathode compatibility and anodic stability, which enables the use of 4 V class cathode active materials (CAMs) in ASSBs even high-voltage ASSBs with stable cycling. Second, the developed molecular layer deposition (MLD) coating strategy is adopted to solve the instability issues between active Na anode and SEs. The solutions and understandings in this thesis shall provide some guidance for developing high-performance ASSBs

Available for download on Friday, August 09, 2024