Dual-ion batteries (DIBs) have attracted much attention owing to their low-cost, high-voltage, and environmental friendliness.

As the source of active ions during the charging/discharging process, the electrolyte plays a critical role in the performance of DIBs, including capacity, energy density, and cycling life. However, most used electrolyte systems based on the LiPF₆ salt shows unsatisfied performance in DIBs.  

Researchers from the Shenzhen Institutes of Advanced Technology (SIAT) of the Chinese Academy of Sciences developed a 7.5m lithium bis (fluorosulfonyl) imide (LiFSI) in carbonate electrolyte system, which improved energy density by decreasing the usage of electrolyte. 

The study was published in Angewandte Chemie International Edition.  

After investigated the matching behaviors of different electrolyte solvents and salts, the team found that combining the merits of LiFSI salt with the features of EC: DMC solvent system was possible to realize highly concentrated electrolytes. 

Compared with diluted electrolyte, this concentrated electrolyte showed improved intercalation capacity and reversibility for FSI^- intercalation at graphite cathode due to the improved oxidative stability of concentrated electrolyte.  

Moreover, the proposed electrolyte system enhanced structural stability of Al anode during cycling due to the formation of LiF-rich SEI layer since more LiFSI salts were involved into the SEI formation. 

A proof-of-concept DIB based on this concentrated electrolyte exhibited a discharge capacity of 94.0 mAh g^-1 at 200 mA g^-1 and 96.8% capacity retention after 500 cycles.

The energy density of this pro-type DIB reached up to ~180 Wh kg^-1, which was among the best performance of previously reported DIBs.