Our present-day rechargeable batteries, like lithium-ion batteries, are not sustainable. An alternative is organic batteries that use redox-organic electrode materials (OEMs) made from eco-friendly materials. A Chinese research group has recently presented a new OEM for aqueous organic high-capacity batteries in the journal Angewandte Chemie, which can be recycled at a low cost with ease.
The use of conventional inorganic electrode materials in commercial batteries poses a plethora of issues, ranging from limited resources, toxic elements, and environmental problems, to unacceptable mining conditions, limited capacity, difficulties in recycling, and high costs. Unfortunately, sustainable batteries cannot be produced on a large scale using these electrodes, even though they are essential for an energy transition.
The application of organic batteries using OEMs is still in its early stages and has a long way to go before practical implementation. However, a team headed by Chengliang Wang from Huazhong University of Science and Technology has made a significant stride towards this goal. The objective is to utilize OEMs in batteries with aqueous electrolytes, which are more eco-friendly, sustainable, and cost-effective compared to the conventional organic electrolytes present in lithium-ion batteries.
To achieve their objective, the team opted to utilize azobenzene, a material that can be produced on a large scale at a low cost and is insoluble in water but highly soluble in organic solvents. Unlike most other functional groups that can only transfer a single electron, the azo group (–N=N–) in this molecule can transfer two electrons reversibly, thereby increasing its capacity. Extensive analyses showed that during the discharge process, the azobenzene transforms into hydroazobenzene after absorbing two electrons – this occurs through the rapid and reversible binding of two protons (H+). The team successfully developed prototype coin cells and laminated pouch cells of varying sizes, containing azobenzene OEMs and zinc
Unlike polymeric OEMs, the small azobenzene molecules can be easily recycled using commercial organic solvents at a low cost. The electrode material is stable in both its charged and discharged states and can be recycled with yields exceeding 90% in every state of charge. The recycled products can be reused as OEMs without any loss of capacity, making them highly sustainable.
