Zn-Ion hybrid capacitors utilizing redox electrolytes derived from naphthoquinone molecules

Advanced redox electrolytes are essential for boosting the electrochemical performance of hybrid capacitors, which merge the high-power density of supercapacitors with the energy density of metal-ion batteries. This work focuses on the development of redox electrolytes using naphthoquinone compounds. A series of naphthoquinone derivatives with diverse structures were investigated for their application in zinc-ion hybrid capacitors (ZICs). The results reveal that naphthoquinone molecules featuring adjacent bonding ligands exhibit enhanced stability of zinc anodes due to their bidentate behavior, which facilitates strong chelating interactions with metal atoms. The redox electrolyte, prepared by 2-Hydroxy-1,4-naphthoquinone (HNQ), improves the durability of Zn//Zn cells from 24 to 972 cycles at 1 mAh cm−2 and 2 mA cm−2. Moreover, the ZIC based on the HNQ-containing electrolyte demonstrates an increased capacity of 82.2 mAh g−1, compared to 64.4 mAh g−1 for the pristine ZnSO4 electrolyte. The findings underscore the dual role of redox electrolytes in improving the electrochemical stability of zinc anodes while simultaneously enhancing the capacity of ZICs.