Aqueous batteries have been around for centuries. They are safe and relatively low-cost, but their adoption in new energy storage systems - such as grid storage and electric vehicles - has been limited. One major reason is material compatibility: many electrode materials do not perform well in aqueous electrolytes. For organic redox polymers in particular, hydrophobicity has been a barrier. Like other polymer materials, they also present challenges when it comes to decomposition and recycling.

Now, a research team from Tohoku University, working in collaboration with NITTO BOSEKI CO., LTD., has developed a new organic redox polymer that addresses these long-standing challenges.

To overcome the hurdles, the team introduced p-dihydroxybenzene - an organic molecule with high charge storage capacity - into a polyamine, which is water-soluble due to its positive charge. This was achieved through a simple condensation reaction. The resulting polymer retains high hydrophilicity, can be used as an electrode-active material at room temperature (25°C), and can be broken down into its raw components under mild conditions at temperatures below 100°C.

"This study provides a design strategy for making hydrophobic redox molecules compatible with aqueous systems," said Kouki Oka, associate professor at Institute of Multidisciplinary Research for Advanced Materials, Tohoku University. "By combining high charge storage capacity with recyclability, we can open new directions for sustainable battery research."

The findings highlight two key benefits. First, the use of water-based electrolytes avoids the risk of fire associated with conventional flammable solvents. Second, because the new polymers are made from abundant elements and can be easily decomposed, they may help reduce resource consumption and plastic pollution.

"Our next step is to evaluate durability and other performance factors to understand the full potential of this material for real-world applications," added Oka.

The research was published online in Polymer Journal on August 26, 2025 and was selected for the special issue Rising Stars in Polymer Science 2025.