Fluorinated Alkoxyaluminates As Electrolytes for Calcium-Ion Batteries

Abstract

In the field of multivalent Batteries, the reversibility of stripping and plating of the metal in question will dictate the overall performance of a battery. With recent advances in non-aqueous calcium electrolytes, it is now possible to reversibly strip and plate calcium at room temperature. Several new electrolytes were found since then, which all suffer from short cycle lives, due to the strong tendency of calcium metal surfaces to passivate. An alternative route to achieve longer cycle life is to alloy the Calcium anode. It was shown that Ca-Sn alloy anodes can help, extend the cycle life by preventing the formation of impenetrable passivisation layers. However, this comes with the cost of decreased energy density, since the alloying material is not involved in the Energy storage process. In this work we focused on a new electrolyte that can extend the cycle life of a calcium-ion battery (CIB) and still work with a pure calcium metal anode. Electrolytes based on alkoxy-aluminates in glycol ethers have shown high conductivity and electrochemical stability when used in Mg-Ion batteries. But more importantly, the metal deposits obtained are remarkably pure, even after hundreds of cycles. In this work, we present the Calcium homologue,calcium-tetra-1,1,1,3,3,3-hexaflouroisopropylo-aluminate Ca[Al(HFIP)4]2, in Dimethoxyethane (DME) as a promising candidate for calcium-ion batteries. Besides its high conductivity (8.99 mS/cm2 at 25°C ) and high anodic stability (>3V vs. Ca0/Ca2+), reversible stripping and plating could be sustained for up to 550 cycles.