Impact of Binder Functional Groups on Controlling Chemical Reactions to Improve Stability of Rechargeable Zinc-Ion Batteries

Rechargeable zinc-ion batteries (ZIBs) are promising alternatives for large-scale energy storage systems. However, instability of the cathode during operation leads to rapid capacity fading and poor stability. Binders play a crucial role in keeping all components in the cathode intact during cycling. However, the impact of the binders' chemical structure on the electrochemical reaction in ZIBs is not well understood. Herein, the effect of the chemical structure of a conventional polyvinylidene fluoride (PVDF) and green binders, that is, sodium carboxymethyl cellulose (CMC) and cellulose acetate (CA), on the performance, cyclability, and reaction of Zn/α-MnO2 aqueous batteries is investigated. Results show that a cathode having a PVDF binder yields the highest specific capacity in a full battery. Besides, the CMC-based ZIB is seen to attain superior cycling stability through 500 galvanostatic charge–discharge (GCD) cycles having no irreversible products confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). It is found that the Na+ ion in the CMC structure plays a critical role in promoting prominent battery reactions. The CMC-based ZIB, therefore, is able to maintain its high ionic diffusivity obtained from the galvanostatic intermittent titration technique (GITT) during prolonged operation. Moreover, the interaction between binders and α-MnO2 has been investigated via density-functional theory (DFT) to affirm the high stability of the ZIB/α-MnO2 with the CMC binder. This work highlights the importance of the selection of functional groups on the binder not only to enhance stability but also to control the preferential reactions of batteries. Such findings are ultimate keys for the development of low-cost, stable, and eco-friendly energy storage devices.