Tailoring electrolyte additives for advanced Mg-based anodes in primary aqueous Mg-air battery
This doctoral work proposes new approaches to boost discharge performance of aqueous Mg-air batteries (AMABs) via tailoring electrolyte additives for newly developed Mg-Ca anodes. Micro-alloyed Mg-Ca anode exhibits negative discharge potential and high utilization efficiency (UE) compared to other commercial Mg alloys. With the addition of suitable Mg2+ complexing agent into electrolyte, the discharge performance of Mg-Ca is able to be further improved. Therefore, the effect of Mg2+ complexing agents on the corrosion and discharge performance of Mg-Ca anode was investigated, indicating the potential of Mg2+ complexing agents to regulate the interfacial condition of the Mg anode/electrolyte and to enhance the specific energy of AMABs. In order to reveal the working mechanism of electrolyte additives, the evolution of interfacial condition between Mg anode and electrolyte was traced by electrochemical impedance spectroscopy. Nevertheless, the interpretation of impedance spectra has been still controversial, which may affect the accurate understanding of the additive working mechanism. Therefore, the physical interpretations of high frequency and middle frequency time constants in Mg impedance spectra were thoroughly investigated, revealing the high frequency time constant is originated form the barrier effect of surface film and the middle frequency time constant is related to charge transfer process and the electric double layer. Based on a better understanding about Mg impedance spectra, EIS measurements during discharge interval were applied to study the working mechanism of selected electrolyte additives. This work proposes two different types of electrolyte additives for AMABs based on a deep understanding of their working mechanisms, which would greatly facilitate the development and widespread applications of high-performance AMAB systems.
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