Damian Goonetilleke

Electrochemical Modification of Negative Thermal Expansion Materials in the TaxNb1–xVO5 Series

Electrochemical processes transfer charge carriers to and from electrodes, e.g., Li+ ions are inserted into anodes during discharge and extracted during charge in a Li half-cell. Using an electrode that features negative thermal expansion (NTE) properties in an electrochemical cell allows a means to study the interaction of the charge carrier with an NTE material and potentially modify or tune its NTE properties. This work examines the NTE properties of Ta xNb1- xVO5 ( x = 1, 0.9, 0.75, 0.5, 0.25) and the effect of Li+/Na+/K+ electrochemical discharge of TaVO5-based electrodes. Sodium discharge was found to drastically alter NTE properties with 25% Na+ discharged electrodes exhibiting a linear volumetric coefficient of thermal expansion of -5.75 ± 0.20 × 10-5 Å3/°C between 350 and 500 °C, one of the largest reported for any NTE system. Furthermore, at higher temperatures, the Na+- and K+-discharged and heated electrodes generate new phases, suggesting that a combination of electrochemical discharge and thermal treatment can be used to synthesize new compounds. This work lays the foundation for the concept of using electrochemical discharge followed by subsequent thermal treatments to modify the physical properties of a compound.

Insight into the formation of lithium alloys in all-solid-state thin-film lithium batteries

Solid-state thin-film batteries utilise electrode and electrolyte components which are nanometres or micrometres thick, enabling the production of novel devices with new form factors. Here, in situ X-ray diffraction is used to carry out the first study of a solid-state thin-film lithium-ion battery containing a solid-state LiPON electrolyte and Bi negative electrode. The structure-electrochemistry relationships in the Li-Bi system are revealed and details of cell construction, data collection, and data analysis is presented to guide for research.

SmFeO3 and Bi-doped SmFeO3 perovskites as an alternative class of electrodes in lithium-ion batteries

The search for new electrodes in alkali-ion batteries requires the investigation of a variety of classes of materials, each showing subtly different crystal structure motifs or frameworks. The structure–electrochemistry of SmFeO3 and Sm0.92(2)Bi0.08(2)FeO3 electrode materials are characterized by in situ and ex situ X-ray diffraction (XRD), galvanostatic charge/discharge cycling and electrochemical impedance spectroscopy. SmFeO3 and Sm0.92(2)Bi0.08(2)FeO3 electrodes deliver first discharge capacities of 450 and 550 mAh g−1, and their corresponding reversible discharge capacities are 300 and 400 mAh g−1, respectively, following this cycle at a current rate of 5 mA g−1. Interestingly, after the 20th cycle, SmFeO3 retains 98% of its capacity from previous cycles whereas Bi-doped SmFeO3 appears to lose its capacity extremely fast. In situ synchrotron XRD data suggests that discharge results in a partial loss of crystallinity, while charging slightly recovers the crystallinity of SmFeO3 but not of Bi-doped SmFeO3, which is also confirmed by ex situ XRD data. The lack of crystallinity recovery could be related to the poor higher rate performance observed for this doping regime. This work shows the potential of this class of materials as electrode materials, unconventional but possibly reliable.