Abstract
Sodium-ion batteries (SIBs), remains today as the most economically viable and practically achievable of all post-lithium ion batteries (LIBs) technology. The wide availability and abundances of sodium resources and the related commodities directly implied that its development and process manufacturing are inherently inexpensive. It is therefore highly suggestive that SIBs is largely favourable to the popularization of renewable and sustainable energy generation which are extremely transient and crucially requires practically scalable and economical storage solution. Fundamentally, SIBs is electrochemically very similar to LIBs which implies that the advent of SIBs could leveraged on the years of knowledge of LIBs development. However in reality, sodiumions are much larger and heavier and therefore lacking the fast-kinetic advantage of lithium-ions. Thus to realise its fullest potential, developing a suitable storage platform, i.e. electrode materials, that promises large capacity (high energy storage density), fast kinetics (high power utilization) and stable performance (long lifetime) remains more challenging, persisting and urgent in stark contrast to lithium-ion technologies. In the first two chapters of this dissertation, the recent research conclusions of SIBs and the experimental details on this research is introduced in an informative yet concise manner. In recent years, the materials research community are especially upbeat by the emergence of two-dimensional based materials. Their novel properties have introduced new physics/chemistry and paved new opportunities in realising outstanding performance in the field of electronics and electrocatalysts materials. As one of the 2D materials, transition metal sulfides (TMS) have transformed and benefitted the energy research community in similar fashion. In this dissertation, we are motivated, relentless and highlyconverged on: (i) stimulating and realizing the sodium storage potentials of TMS-based electrode materials through nanostructure and surface engineering methods, and (ii) elucidating the sodium storage mechanisms and capabilities of novel but potentially functional TMS-based materials/nanostructures. In Chapter 3, a novel yet effective method in enhancing the sodium storage performance of WS2 by a novel metal-organic framework materials derivation technology. In Chapter 4, we discussed a rarely reviewed but highly capable TMS (ReS2) by introducing a newly developed synthesis methods to achieve high yield output and quality and revealing its sodiation/desodiation redox mechanism and ionkinetics capabilities. In Chapter 5, we focused our effort on revealing the intrinsic surfacebased capacitive and redox mechanism of bimetallic-based TMS (BMS) and vastly improved the stability performance by containment of the bimetallic structure within graphene scaffold. In Chapter 6, a novel nanostructure engineering methodology were developed as an effective capacitive and performance stimuli technology to further elicit the extrinsic pseudocapacitive behaviour of intrinsically pseudocapacitive materials (MnCo2S4), and demonstrating particularly high rate performance. To elaborate and to clarify the materials choices/strategies before Chapter 3 & 4 (as Part I of the thesis), and Chapter 5 & 6 (as Part II), a short discussion is included to clarify our intentions/purposes. In Chapter 7, we reiterate the contributions and conclusions of these stated works and introduced the possible future works and outlook for the development of high-performance SIBs. To date, delicately formulated and designed nanostructures is instrumental in realising the storage potential via alleviating the inherent Na-ions feature disadvantages. Understanding the Na-ions kinetics (capability and adsorption simulation) and the electronic transfer dynamics (density of states and sodiation working mechanism) provides profound insights in further refining the performance of TMS from the perspective of systematic and materials design methodologies. The work introduced in this dissertation provides a valid and highly-potential strategy in developing functional electrode materials serving and targeting as fast, and electrochemically stable energy storage solutions.