Year

2018

Degree Name

Doctor of Philosophy

Abstract

With the spotlight on renewable energy generation and electric vehicles, the demand for power supplies, mainly based on batteries, is rapidly increasing. Nevertheless, the energy density limitations of current batteries are compelling researchers to develop new structured materials and explore new battery systems. The research works in this thesis on all-integrated silicon anode and the fabrication of few-layered antimony sulphide/carbon sheets (SBS/C) relate to the design of materials, and the potassium-selenium battery and potassium antimony sulphide battery relate to the exploration of new types of energy storage.

The concept of all-integrated design with multi-functionalization has been widely employed in optoelectronic devices, sensors, resonator systems, and microfluidic devices, resulting in benefits for many ongoing research projects. Maintaining structural/electrode stability against large volume change by means of an all-integrated design is realized for silicon anode in this work. The all-integrated silicon anode has been achieved via multicomponent interlinking among carbon@void@silica@silicon (CVSS) nanospheres and cross-linked carboxymethyl cellulose and citric acid polymer binder (c-CMC-CA). Due to the additional protection from the silica layer, CVSS is superior to carbon@void@silicon (CVS) electrode in terms of longterm cyclability. The as-prepared all-integrated CVSS electrode exhibits high mechanical strength, which can be ascribed to the high adhesivity and ductility of c-CMC-CA binder and the strong binding energy between CVSS and c-CMC-CA, as calculated based on density functional theory. This electrode exhibits a high reversible capacity of 1640 mAh g-1 after 100 cycles at a current density of 1 A g-1, high rate performance, and long-term cycling stability with 84.6 % capacity retention after 1000 cycles at 5 A g-1.

Due to the energy limitations and high cost of lithium ion batteries, the potassium ion battery been investigated in recent years as an alternative and promising energy storage device. A new reversible and high-performance potassium-selenium (K-Se) battery, using confinedselenium/ carbonized-polyacrylonitrile (PAN) composite (c-PAN-Se) as cathode and metallic potassium as anode, is reported in my work. The PAN-derived carbon matrix could effectively confine the small Se molecules and provide a sufficient buffer for the volume changes. The reversible formation of small-molecule trigonal Se (Se1, P3121) phase could essentially inhibit the formation of polyselenides and accounts for the outstanding electrochemical performance of this material. The carbonate-based electrolyte further synergistically diminishes the shuttle effect by simultaneously inhibiting the formation of polyselenides. The as-prepared K-Se battery shows a reversible capacity of 1904 mAh cm-3 after 100 cycles at 0.2 C and rate retention of 89% from 0.1 C to 2 C. In addition, the chargedischarge mechanism was also investigated via the combination of in-situ and ex-situ synchrotron X-ray diffraction, and Raman spectroscopy analysis. The results reveal that the introduction of K+ ions leads to the cleavage of C-Se bonds, the rearrangement of selenium atoms, and the final formation of the main product K2Se. Moreover, the reversible formation of trigonal Se (Se1, P3121) phase was detected in the reaction with K+. These findings not only can advance our understanding of this family of batteries, but also provide insight into chemically-bonded selenium composite electrodes, which could give guidance for scientific research and the optimization of Se and S electrodes for K-S, Na-S, Li-S, Na-Se, and Li-Se batteries.

Earth-abundant potassium is a promising alternative to lithium in rechargeable batteries, but a pivotal limitation of potassium ion batteries is their relatively low capacity and poor cycling stability. Here, a high-performance potassium ion battery is achieved by employing few layered antimony sulphide/carbon sheet composite anode fabricated via one-step high-shear exfoliation in ethanol/water solvent. Antimony sulphide with few-layered structure minimizes the volume expansion during potassiation and shortens the ion transport pathways, thus enhancing the rate capability; while carbon sheets in the composite provide electrical conductivity and maintain the electrode cycling stability by trapping the inevitable byproduct, elemental sulphur. Meanwhile, the effect of the exfoliation solvent on the fabrication of two-dimensional antimony sulphide/carbon is also investigated. It is found that water facilitates the exfoliation by lower diffusion barrier along the [010] direction of antimony sulphide, while ethanol in the solvent acts as the carbon source for in-situ carbonization.

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