Coupling Tetraalkylammonium and Ethylene Glycol Ether Side Chain To Enable Highly Soluble Anthraquinone-Based Ionic Species for Nonaqueous Redox Flow Battery

Nonaqueous redox flow batteries (NARFBs) have promise for large-scale energy storage with high energy density. Developing advanced active materials is of paramount importance to achieve high stability and energy density. Herein, we adopt the molecular engineering strategy by coupling tetraalkylammonium and an ethylene glycol ether side chain to design anthraquinone-based ionic active species. By adjusting the length of the ethylene glycol ether chain, an ionic active species 2-((9,10-dioxo-9,10-dihydroanthracen-I -yl)amino) -N- (2- (2-methoxyethoxy)ethyl) - (N,N-dimethyle-than-l-aminium)-bis(trifluoromethylsulfonyl)imide (AQEG2TFSI) with high solubility and stability is obtained. Paired with a FcNTFSI cathode, the full battery provides an impressive cycling performance with discharge capacity retentions of 99.96% and 99.74% per cycle over 100 cycles with 0.1 and 0.4 M AQEG2TFSI, respectively.

Automated summary

Nonaqueous redox flow batteries (NARFBs) have great potential for large-scale energy storage due to their high energy density. This study focuses on molecular engineering strategy to design anthraquinone-based ionic active species with improved solubility and stability. The experimental results demonstrate that the designed ionic active species, in combination with a specific cathode, achieves high discharge capacity retention over multiple cycles.