Redox-active electrolytes as a viable approach for the one-step assembly of metal-ion capacitors

Abstract

The assembly of metal-ion capacitors is a very challenging task; the use of traditional metallic electrodes or sacrificial materials induces technical problems during cell assembly or affects its normal operation. Here, we report an efficient, one-step method for assembling metal-ion capacitors using redox-active electrolytes with thiocyanate-based salts. The addition of a redox-active salt compensates for the charge on the positive electrode while enabling the insertion of metal ions into the structure of the negative electrode. The proposed approach reduces assembly time and cost and results in increased specific energy compared to that from the traditional two-step assembled hybrid systems. Furthermore, we demonstrate that the proposed approach can be successfully implemented for sodium-ion and potassium-ion hybrid capacitors. Our results are supported by operando techniques and can potentially facilitate further research on metal-ion capacitors and applications of these devices.