Soft-switching vector control for resonant snubber based inverters

This paper gives a new classification of soft-switching inverters according to the principle of operation. After discussing the soft-switching phenomena in hard-switching inverters, the concept of soft-switching vector (SSV) is introduced. The proposed SSV is not only helpful in analyzing the changes of switching states, but also easily realized in control scheme. Theoretical analyses are conducted step by step for both with and without SSV control applied to resonant snubber based inverters (RSI). The experimental results closely agree with theoretical analyses and show the significant reduction in power loss after using SSV. Moreover, a modified version of SSV is also presented to achieve the better working condition at low load current with current ripple.published_or_final_versio

Characterisation of the lithium-solid electrolyte interface in solid state batteries

All-solid-state batteries (ASSBs) with a Li-metal negative electrode have the potential to drastically improve on state-of-the-art energy densities. Improved understanding failure mechanisms is needed to reach commercialisation, but physical characterisation is challenging. In this thesis, I will investigate the use of electron microscopy as a tool to better understand degradation mechanisms at the interfaces between solid-state electrolytes (SSEs) and Li. First, plasma focused-ion beam (PFIB) and scanning electron microscopy (SEM) are used to access and image the interface between Li-based electrodes and a Li6PS5Cl electrolyte with minimal artifact introduction. Li alloys are found to be more stable to ion milling than pure Li, allowing Li-Mg to be used as a characterisation proxy for Li metal, and the microstructure of the Li-In reference electrode to be interpreted. Cryo-PFIB is then used to investigate the Li deposition structure with more complex SSEs; a composite, thin SSE and a SSE combined with a C-Ag interlayer. To investigate the morphology of the thin (approx. 10 - 100s nm), air- and electron-beam- sensitive solid electrolyte interphase (SEI) layer, a sample preparation technique is developed to reliably produce electron-transparent samples incorporating the SSE-SEI-Li interface. This is combined with low-dose 4D-scanning transmission electron microscopy, which enables spatio-compositional mapping of the interface without beam damage. Analysis reveals information on the crystallite size and distribution across the SEI. Statistical analysis of the SEI component spatial relationships demonstrates a complex structure with component intermixing. This is also shown to be the case with Li5.5PS4.5Cl0.75Br0.75, despite the differing morphology leading to smaller SEI component domain sizes. This information helps better understand the degradation processes at ASSB interfaces and, in particular, enables improved characterisation of the SEI