Instigation of Low Cost, Non-Toxic and Environmentally Benign Binders for Mild Aqueous Zn/MnO₂ Systems

In recent years, zinc has gained significant attention due to its wide availability (fourth-most mined material on the Earth), low-cost nature and recyclability. Moreover, it allows water-based batteries (i.e. Zn/MnO2) that could compete with LIBs for both transportation and stationary applications without safety issues. However, they are not considered rechargeable in practice yet due to the capacity limitation from the cathode materials and the detrimental zinc dendrite formation. Most of the electrode preparations are currently based on the use of fluorine-containing polymer binders, such as polyvinylidene difluoride (PVDF) and poly-tetrafluoroethylene (PTFE) with N-methyl-2-pyrrolidone (NMP) as a solvent/dispersant due to its good electrochemical stability and high adhesion to the electrode materials and current collectors. However, the fluorinated binders are relatively expensive and NMP is considered to be a hazardous and toxic substance. Therefore, switching to alternate electrode processing routes with non-toxic binders is crucial to providing a fully sustainable and environmentally friendly electrochemical energy storage device. In this study, various water-soluble binders have been evaluated in mild aqueous electrolyte conditions for Zn/MnO2 systems and are compared with the conventional MnO2/PVDF systems. We observed water-soluble binders can be stable and offer desirable adhesion at certain pH levels (3.5~5) without any decomposition. Electrochemical data also indicates that higher capacity utilization and lower cell overpotential is achieved in the cells with aqueous binders versus the cells with PVDF binder. In summary, our work suggests that the implementation of water-soluble binders can lead to substantial improvements for efficient and effective aqueous battery systems.