Johanna Timhagen, Materials Physics

Calcium metal batteries (CMBs), a promising next generation battery technology, have gained research interest over the last decade. CMBs are attractive for the prospect of a more sustainable chemistry, given the large abundance of Ca in the Earth's crust, and the high energy density, linked to their anodes' low electrochemical potential and large volumetric capacity. Ca metal anodes, however, are prone to form unwanted passivation layers, a phenomenon heavily influenced by the CMB electrolyte chemistry, making clever electrolyte design choices vital.

This thesis foremost covers two CMB electrolyte concepts. The first is solvent-free electrolytes in the form of molten salt electrolytes (MSEs), i.e. binary and multi-component systems of inorganic cations and anions, for which we explore how degradation can possibly be avoided. The second is dual-salt electrolytes, where the complex interplay between boron and K⁺-ions alters and hopefully enhances electrochemical performance. Furthermore, the large implications of varying purity for commercially sourced Ca-salts are explored, as this can be detrimental to early-stage assessments of battery technologies in their infancy, such as CMBs.

The thermal properties of salts and electrolytes were evaluated by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC), while local structure, particularly the entropic stabilization of MSEs and the ion-ion and ion-solvent interactions in liquid electrolytes, was explored by Raman spectroscopy. Finally, electrochemical performance was evaluated primarily using symmetric Ca||Ca cells, and, taken altogether, we generated data and creative ideas for advancing and expanding knowledge of various CMB electrolyte designs.