New 'water battery' design achieves 220 cycles with no capacity loss

Researchers at Xi’an Jiaotong University, led by Professor Gang He, have developed a novel aqueous organic redox flow battery (AORFB) featuring a zwitterion-modified naphthalene diimide (NDI) derivative as the anolyte. This new electrolyte design addresses key challenges in AORFBs related to molecular stability and cost. Traditional NDI-based electrolytes suffer from degradation due to hydroxide ion attacks and radical-induced aggregation, which reduce battery lifespan and performance. By introducing zwitterions that create electrostatic repulsion among NDI molecules, the team achieved a parallel-staggered molecular stacking that enhances solubility (up to 1.49 M) and stabilizes the molecule during electron transfer, preventing decomposition. The modified electrolyte, paired with a potassium ferrocyanide catholyte, demonstrated stable cycling over 220 charge-discharge cycles with no significant capacity loss at a high electron concentration of 2 M. The total electrolyte cost is estimated at