Achieving Insertion‐Like Capacity at Ultrahigh Rate via Tunable Surface Pseudocapacitance

Abstract

The insertion/deinsertion mechanism enables plenty of charge-storage sites in the bulk phase to be accessible to intercalated ions, giving rise to at least one more order of magnitude higher energy density than the adsorption/desorption mechanism. However, the sluggish ion diffusion in the bulk phase leads to several orders of magnitude slower charge-transport kinetics. An ideal energy-storage device should possess high power density and large energy density simultaneously. Herein, surface-modified Fe O quantum dots anchored on graphene nanosheets are developed and exhibit greatly enhanced pseudocapacitance via fast dual-ion-involved redox reactions with both large specific capacity and fast charge/discharge capability. By using an aqueous Na SO electrolyte, the oxygen-vacancy-tuned Fe O surface greatly enhances the absorption of SO anions that majorly increase the surface pseudocapacitance. Significantly, the Fe O -based electrode delivers a high specific capacity of 749 C g at 5 mV s and retains 290 C g at an ultrahigh scan rate of 3.2 V s . With a novel dual-electrolyte design, a 2 V Fe O /Na SO //MnO /Na SO asymmetric supercapacitor is constructed, delivering a high energy density of 75 W h kg at a power density of 3125 W kg .

Surface Engineering for Advanced Aqueous Supercapacitors: A Review

“…Notably, the surface of electrode is critical as the interface between electrode and electrolytes. Hence, future researches should attempt to engineer the surface from both electrode and electrolyte sides, i. e ., increasing extra active sites around surface via redox additives and achieving outstanding electrochemical performance by building a relationship between redox additives and electrode surface High energy density, as well as high power density, is the fundamental goal for aqueous SCs.…”

“…), demand higher power than batteries can deliver . Therefore, considerable attention has been focused on the supercapacitors (SCs) due to their large power density and excellent cycling stability, which makes it more suitable for high‐power applications . Aqueous electrolyte based SCs are attractive because of their excellent power output, much longer cycle life, superior safety, low‐cost, and environmental friendliness .…”

“…[9][10][11] Therefore, considerable attention has been focused on the supercapacitors (SCs) due to their large power density and excellent cycling stability, which makes it more suitable for high-power applications. [12][13][14] Aqueous electrolyte based SCs are attractive because of their excellent power output, much longer cycle life, superior safety, low-cost, and environmental friendliness. [15][16][17] Nevertheless, the lower energy densities (E) of aqueous SCs as compared to batteries have impeded their range of commercial applications.…”

Redox‐Mediator‐Enhanced Electrochemical Capacitors: Recent Advances and Future Perspectives

“…However, their widespread application is hindered by their low energy density resulting from charge storage occurring on the surface only . Pseudocapacitive behavior, introduced to increase the energy density, is based on fast faradaic reactions occurring on the surface/near‐surface of active materials (Figure c) . Various pseudocapacitive materials, mainly metal oxides and polymers, have been developed .…”

Electrochemical Double‐Layer Capacitor Energized by Adding an Ambipolar Organic Redox Radical into the Electrolyte

“…[1] However, their energy density is still much lower than rechargeable batteries. [3][4][5][6][7][8][9][10][11][12] One typical approach is to increase the efficient surface area of carbon materials for ions adsorption, [13][14][15][16][17][18] but which generally results in the reduction of tap density of electrodes.A nother is to modify the carbon materials with pseudo-capacitive materials (such as metal oxides and conductive polymers) to combine the adsorption capacitance and pseudo-capacitance, [19][20][21][22] but with the sacrifice of conductivity and stability of electrodes. [3][4][5][6][7][8][9][10][11][12] One typical approach is to increase the efficient surface area of carbon materials for ions adsorption, [13][14][15][16][17][18] but which generally results in the reduction of tap density of electrodes.A nother is to modify the carbon materials with pseudo-capacitive materials (such as metal oxides and conductive polymers) to combine the adsorption capacitance and pseudo-capacitance, [19][20][21][22] but with the sacrifice of conductivity and stability of electrodes.…”