Ca-Based Dual-Carbon Batteries in Ternary Ionic Liquid Electrolytes.

Herein, we propose Ca-based dual-carbon batteries (DCBs) that undergo a simultaneous occurrence of reversible accommodations of Ca in a graphite anode (mesocarbon microbeads) and of bis(trifluoromethanesulfonyl)imide (TFSI) in a graphite cathode (KS6L). For this purpose, we precisely tune electrolytes composed of Ca complexed with a single tetraglyme molecule ([Ca:G]) in -butyl--methylpyrrolidinium TFSI (PyrTFSI) ionic liquid (IL). This ternary electrolyte is required for the enhancement of anodic stability that is needed to accomplish maximal TFSI intercalation into KS6L at a high potential. A solution of 0.5 M [Ca:G] in IL ([Ca:G]/IL) is found to be optimal for DCBs. First, the electrochemical properties and the structural evolution of each graphite in a half-cell configuration are described to demonstrate excellent electrochemical performance. Second, the negligible intercalation of Pyr into an MCMB anode is ascertained in 0.5 M [Ca:G]/IL. Finally, DCBs are constructed by coupling two electrodes to show high capacity (54.0 mA h g at 200 mA g) and reasonable cyclability (capacity fading of 0.022 mA h g cycle at 200 mA g during 300 charge/discharge cycles). This work is the first to examine DCBs based on Ca intercalation and helps pave the way for the development of a new type of next-generation batteries.