Solid-State Double-Network Hydrogel Redox Electrolytes for High-Performance Flexible Supercapacitors

Abstract

Flexible supercapacitors have great potential applications in wearable and portable electronics, but their practical applications were limited due to the low energy density and mechanical flexibility of solid-state electrolytes used for the construction of flexible supercapacitors. In this study, we first report the solid-state double-network (DN) hydrogel electrolytes (HEs) incorporated with Na2MoO4 redox additives. It is found that the solid-state DN HEs with Na2MoO4 redox additives exhibit high electrochemical performance, excellent mechanical properties, and fast self-recovery features. We then demonstrate novel symmetric supercapacitors (SSCs) incorporated with the solid-state Na2MoO4 DN HEs and the active carbon cloths as the electrodes. The SSCs exhibit a specific capacitance of 84 mF/cm2 at a current density of 1 mA/cm2 and an energy density of 70 μWh/cm2 at a power density of 3800 μWh/cm2. Moreover, the SSCs retain approximately 80% capacitance retention after 7000 charge/discharge cycles, which indicates that the SSCs possess excellent flexibility and stability. All of these results demonstrate that the SSCs incorporated with the solid-state Na2MoO4 DN HEs as energy-storage devices have great practical applications in wearable and portable electronics.

Recent progress in the all‐solid‐state flexible supercapacitors

“…In the aqueous gel electrolytes, the plasticizer is water. The electrolytic salts in the aqueous gel electrolytes contain strong acids (like H 2 SO 4 , 222–224 HCl, 225,226 H 3 PO 4 104,227,228 ), strong bases (KOH 229–231 ), or some neutral salts (like Na 2 SO 4 232,233 and LiCl 234–236 ). Compared to commercial organic electrolytes, these aqueous gel electrolytes are much cheaper and less toxic.…”

“…Recently, we introduced Na 2 MoO 4 , a kind of pseudocapacitive redox additive into DN HEs 226 . The schematic illustration of the solid‐state gelatin pHEAA chitosan Na 2 MoO 4 DN HEs was shown in Figure 18A.…”

“…SSC, symtrical supercapacitors. Reproduced with permission: Copyright 2021, American Chemical Society 226 …”

“…In the aqueous gel electrolytes, the plasticizer is water. The electrolytic salts in the aqueous gel electrolytes contain strong acids (like H 2 SO 4 , [222][223][224] HCl, 225,226 H 3 PO 4 104,227,228 ), strong bases (KOH [229][230][231] ), or some neutral salts (like Na 2 SO 4 232,233…”

“…Recently, we introduced Na 2 MoO 4 , a kind of pseudocapacitive redox additive into DN HEs. 226 The schematic illustration of the solid-state gelatin pHEAA chitosan Na 2 MoO 4 DN HEs was shown in Figure 18A. Figure 18B presents the CV curves of the symtrical supercapacitors (SSCs) incorporated with the solid-state gelatin pHEAA chitosan Na 2 MoO 4 DN HEs absorbed H 2 SO 4 solution under different scan rates.…”