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Cs137 is generated from fission nuclear reactor operations. It has a half-life time of 30 years, and it is considered to be an excellent source of gamma radiation. Cs137 needs to be separated from nuclear waste before its disposal. Electrically switched ion exchange (ESIX) is one method which can be used for its separation from nuclear waste. ESIX consists of an ion exchange film that is deposited onto a conductive electrode surface. Typically, for Cs+ removal, this film is composed of nickel hexacyanoferrate, which is known for its selectivity for that ion. The ESIX method involves the sequential application of reduction and oxidation potentials to an ion exchange film to induce the respective loading and unloading of Cs+. ESIX can be used to separate Cs137 from nuclear radioactive waste as well as Cs+ from industrial wastewater. The goal of this research was to enhance the capacity of the nickel hexacyanoferrate ion exchange film deposited on nickel electrodes by modulating the applied potential for the ESIX film preparation. This goal was achieved by preparing an ESIX film on a nickel substrate using a two-step process in which voltage is applied to a nickel electrode surface prepared prior to the film deposition using diamond sand paper 2500 grit. The results show the preparation of a film with capacity 63 times higher than that which is previously reported in the literature. Another four ESIX films composed of nickel hexacyanoferrate were deposited on nickel substrates with varying potentials, again in a two-step process and with surface treatment using 800 grit diamond sand paper prior to the film deposition. The surface morphology of the films was studied using scanning electronic microscope (SEM) to note any differences which could have occurred from the changes in deposition procedures. Electrospray ionization-mass spectroscopy was used to quantify the Cs+ loaded and unloaded onto the film. The results show that all of the four prepared ESIX film have a high capacity compared to those reported in the literature and that their performance regarding Cs+ loading was affected by the applied potential used for the ESIX film preparation. Another goal of this research was to enhance the capacity of the nickel hexacyanoferrate ESIX film by changing the substrate from nickel to graphite. This goal was achieved by adsorbing the film into the pores of graphite electrodes. X-ray tomography was used to visualize the nickel hexacyanoferrate film inside the graphite electrodes. Cyclic voltammetry was conducted to detect the response of the prepared film with Cs+. Electrospray ionization-mass spectroscopy was used to quantify the amount of Cs+ adsorbed and desorbed by the electrode. The x-ray tomography results show that the graphite electrode adsorbed nickel hexacyanoferrate material. The cyclic voltammetry figures confirm that the response of each electrode prepared with Cs+ was related to the concentration of nickel hexacyanoferrate in the graphite electrode. Finally, the results obtained from electrospray ionization-mass spectroscopy about how much Cs+ was adsorbed and desorbed confirms that the two prepared electrodes have a higher capacity for Cs+ adsorption based on their interaction with a prepared Cs+ solution as a test solution. Another goal was to observe the performance of a new ESIX film material, namely nickel hexacyanocobaltate. This film was also adsorbed by graphite electrodes. Cyclic voltammetry was conducted to measure the performance of the hexacyanocobaltate film with regard to Cs+, and the results show a significant increase in the nickel hexacyanocobaltate material inside the graphite electrode and Cs+ in the test solution. Electrospray ionization-mass spectroscopy was used to quantify the Cs+ adsorbed and desorbed by the electrode. The Results show that nickel hexacyanocobaltate as an ESIX have high capacity for Cs+ adsorption from test solution. / Thesis / Doctor of Philosophy (PhD)

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In order for battery manufacturers to have a sustainable business, the batteries they produce must be as safe as possible. For lithium-ion batteries, reducing the flammability of the electrolyte is considered to be one way to improve safety, which might be achieved by adding flame retardants to the electrolyte. On the other hand, sodium-ion batteries are attracting attention from academic researchers due to the abundance of sodium reserves compared to lithium reserves. However, there are virtually no studies about the safety of sodium-ion batteries. In this thesis, studies of these two issues will be reported. The reactivity of charged/discharged electrode materials for sodium-ion batteries in different solvents and electrolytes at elevated temperature was studied using Accelerating Rate Calorimetry (ARC). Hard carbon was studied as a negative electrode material for sodium-ion batteries. The reactivity of sodium-inserted hard carbon in solvents and electrolytes was investigated. Then, the reactivity of sodium-inserted hard carbon was compared to lithiated graphite. NaCrO2, NaxCoO2 and NaNi0.5Mn0.5O2 were studied as positive electrode materials for sodium-ion batteries. The electrochemical performance of these materials was investigated. The reactivity of charged NaCrO2, NaxCoO2 and NaNi0.5Mn0.5O2 in solvents and electrolytes was studied using ARC. Sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) was studied as an electrolyte salt for sodium-ion batteries. The electrochemical performance of hard carbon and NaCrO2 in NaTFSI/PC electrolyte was studied. The reactivity of sodium-inserted hard carbon and deintercalated NaCrO2 in NaTFSI/PC electrolyte was also investigated. Triphenyl phosphate (TPP) was studied as a flame retardant additive for lithium-ion batteries. Its impact on electrochemical performance of negative electrode materials (petroleum coke and graphite) and positive electrode materials (LiNi1/3Mn1/3Co1/3O2 (NMC) and LiNi0.8Co0.15Al0.05O2 (NCA)) was studied using an automated storage test, symmetric cells and Electrochemical Impedance Spectroscopy (EIS). The reactivity of lithiated graphite, deintercalated NMC and NCA in electrolyte containing TPP was investigated using ARC. Finally, the flammability of electrolytes containing TPP was studied using a Self-Extinguishing Time (SET) test.

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