Concentrated Electrolyte for High-Performance Ca-Ion Battery Based on Organic Anode and Graphite Cathode

Due to the large abundance, low redox potential, and multivalent properties of calcium (Ca), Ca-ion batteries (CIBs) show promising prospects for energy storage applications. However, current research on CIBs faces the challenges of unsatisfactory cycling stability and capacity, mainly restricted by the lack of suitable electrolytes and electrode materials. Herein, we firstly developed a 3.5 m concentrated electrolyte with a calcium bis(fluorosulfonyl)imide (Ca(FSI)(2)) salt dissolved in carbonate solvents. This electrolyte significantly improved the intercalation capacity for anions in the graphite cathode and contributed to the reversible insertion of Ca2+ in the organic anode. By combining this concentrated electrolyte with the low-cost and environmentally friendly graphite cathode and organic anode, the assembled Ca-based dual-ion battery (Ca-DIB) exhibits 75.4 mAhg(-1) specific discharge capacity at 100 mAg(-1) and 84.7 % capacity retention over 350 cycles, among the best results known for CIBs.

Automated summary

Calcium-ion batteries (CIBs) have great potential for energy storage applications due to the abundance, low redox potential, and multivalent properties of calcium (Ca). However, the lack of suitable electrolytes and electrode materials has restricted the cycling stability and capacity of CIBs. In this study, a concentrated electrolyte with a calcium bis(fluorosulfonyl)imide (Ca(FSI)(2)) salt dissolved in carbonate solvents was developed, which significantly improved the intercalation capacity for anions in the graphite cathode and the reversible insertion of Ca2+ in the organic anode. By combining this electrolyte with low-cost graphite cathode and organic anode, a Ca-based dual-ion battery (Ca-DIB) with high specific discharge capacity and good capacity retention was achieved.