(Nanowerk News) Our modern rechargeable batteries, like lithium-ion batteries, are not environmentally friendly at all. One alternative is organic batteries with organic-redox electrode materials (OEM), which can be synthesized from natural “green” materials. In the journal Applied chemistry (“Recyclable and Scalable High-Capacity Organic Battery”), the Chinese team has now introduced a new OEM for high-capacity organic aqueous batteries that can be recycled easily and inexpensively.
Traditional inorganic electrode materials in commercial batteries involve the entire spectrum of problems: limited resources, toxic elements, environmental concerns, partially unacceptable mining conditions, limited capacities, difficulties in recycling, and high costs. No sustainable battery has been developed on a large scale based on these electrodes, although they are necessary for the energy transition.
Organic batteries with OEMs are still at the beginning of a long road to practical application. A team led by Chengliang Wang at Huazhong University of Science and Technology has now taken a significant step in this direction. The goal is to use OEMs in batteries with aqueous electrolytes. It is “greener”, more sustainable, and less expensive than the conventional organic electrolyte in lithium-ion batteries.
The team chose to use azobenzene, a material that can be produced cheaply on a large scale and is insoluble in water but highly soluble in organic solvents. While most of the other functional groups can only transfer one electron, the azo groups (–N=N–) in this molecule are capable of reversibly transferring two electrons, which contributes to their high capacities.
Comprehensive analysis shows that, during the removal process, azobenzene is converted to hydroazobenzene after absorbing two electrons—via fast and reversible binding of two protons (H+). Coin cell prototypes and various sizes of coated pocket cells with OEM azobenzene and zinc counter electrodes achieved capacity on the ampere-hour scale, which was maintained for 200 charge/discharge cycles.
In contrast to polymeric OEMs, small azobenzene molecules can be recycled inexpensively by simple extraction using commercial organic solvents. The electrode material is stable in air in both charged and uncharged states and can be recycled at a yield of over 90% in each charged state. Recycled products can be directly reused as OEMs without losing capacity.