A pH-Neutral, Aqueous Redox Flow Battery with a 3600-Cycle Lifetime: Micellization-Enabled High Stability and Crossover Suppression

Redox-flow batteries (RFBs) are a highly promising large-scale energy storage technology for mitigating the intermittent nature of renewable energy sources. Here, the design and implementation of a micellization strategy in an anthraquinone-based, pH-neutral, nontoxic, and metal-free aqueous RFB is reported. The micellization strategy (1) improves stability by protecting the redox-active anthraquinone core with a hydrophilic poly(ethylene glycol) shell and (2) increases the overall size to mitigate the crossover issue through a physical blocking mechanism. Paired with a well-established potassium ferrocyanide catholyte, the micelle-based RFB displayed an excellent capacity retention of 90.7 % after 3600 charge/discharge cycles (28.3 days), corresponding to a capacity retention of 99.67 % per day and 99.998 % per cycle. The mechanistic studies of redox-active materials were also conducted and indicated the absence of side reactions commonly observed in other anthraquinone-based RFBs. The outstanding performance of the RFB demonstrates the effectiveness of the micellization strategy for enhancing the performance of organic material-based aqueous RFBs.