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. An aqueous redox flow battery using PEGylated micellar anthraquinone anolyte and potassium ferricyanide catholyte delivered an excellent capacity retention of 90.7 % (99.998 % per cycle) after 3600 cycles (28.3 days) at a current density of 60 mA cm−2.