Reaction and transport mechanism investigation for magnesium metal battery anode

The increasing worlds' energy demands are resulting in an escalation of pressure on the environment as well as a boost in the electrochemical field of science for research and development of new, reliable and high energy sources. Among those, batteries based on metal anodes are a forefront alternative, since they could bring a breakthrough in terms of the available energy density. The most studied metal anode battery systems use lithium metal as an anode, which has issues with availability, sustainability and safety. Alternative, divalent, metal anodes have better sustainability and promise a twofold increase in volumetric energy density. An example of such multivalent metallic battery anode is magnesium, which is abundant, has a low reduction potential and is less prone to dendrite formation than lithium. This makes it promising for the development of future high energy battery cells. The key problem stalling the further development of magnesium rechargeable batteries is low efficiency of plating/stripping of the negative electrode. This is directly related to the understanding of the mass transport of electro-active species in the electrolyte, presence of passivation layers, and the mechanism of charge transfer reactions, all issues, which have not been studied systematically. This project aims to provide crucial information for the important research challenges of understanding passive layer presence, growth, and its kinetics in magnesium metal anode and determination of bottle-neck processes and limiting parameters in the Mg anode operation. This will be achieved through two important steps. First, the passive layer growth will be characterized through symmetrical Mg metal cells impedance spectra measurements at OCV. Cell parameters such as electrolyte type, electrolyte concentration and separator thickness will be varied to determine their influence. The morphology of the passive layer formations will be evaluated with microscopy tools, while spectroscopy measurements will be used to determine its chemical composition. Secondly, operando dynamic impedance measurements applicable to the present electrochemical system will be developed and optimized in order to study the processes taking place during magnesium metal anode operation. Similarly as with electrodes which underwent EIS@OCV measurements, cell parameters will be varied and electrodes analytically evaluated post-mortem. The information will be used to propose a mechanism of operation of the magnesium metal anode, describing the interfacial and transport processes taking place. On the basis of this mechanism, a physics-based impedance spectra model will be built and used to simulate and fit the measured EIS data, validating the model. This type of new approach in the electrochemical scientific field has been developed in our laboratory and allows for determination of bottle-neck processes and limiting parameters in the operation of the electrochemical system in question. Since all parameters in this type of impedance models have a direct connection to physical-chemical properties in the cell, the fitted spectra can be used to extract valuable system parameters (reaction rate, transport properties, etc.), providing relevant trans-disciplinary information.