Recent Advances on Boosting the Cell Voltage of Aqueous Supercapacitors

Abstract

• High-voltage aqueous supercapacitors hold promise for commercial energy storage devices due to the excellent electrochemical performance. • This review summarizes the efficacious measures on boosting the cell voltage of aqueous supercapacitors from the aspects of electrode, electrolyte, and asymmetric design. ABSTRACT Due to its ultra-fast charge/discharge rate, long cyclic life span, and environmental benignity, aqueous supercapacitor (SC) is considered as a proper nextgeneration energy storage device. Unfortunately, limited by undesirable water electrolysis and unreasonable electrode potential range, aqueous SC normally generates a narrow cell voltage, resulting in a low energy density. To address such challenge, enormous efforts have been made to construct high-voltage aqueous SCs. Despite these achievements, the systematic reviews about this field are still rare. To fill this knowledge gap, this review summarizes the recent advances about boosting the cell voltage of aqueous SCs. From the viewpoint of electrode, doping alkali cations, modulating the electrode mass ratio, and optimizing the surface charge density are regarded as three effective pathways to achieve this goal. However, adjusting the appropriate pH level, introducing redox mediators, and constructing "water-in-salt" electrolyte are other three universal routes from the electrolyte aspect. Furthermore, it is also effective to obtain the high-voltage aqueous SCs through asymmetric design, such as designing asymmetric SCs. The confronting challenges and future development tendency towards the high-voltage aqueous SCs are further discussed.

Electrochemical Zinc Ion Capacitors: Fundamentals, Materials, and Systems

“…[55][56][57] Another effective strategy is to introduce pseudocapacitance. [58,59] High pseudocapacitance can be obtained by introducing heteroatom dopants [60][61][62] and redox-active materials such as conductive redox polymers, [63] redox organic materials, [64,65] and redox metal oxides. [66,67] Additionally, special pseudocapacitance such as oxygen reduction reaction and hydrogen adsorption can be adopted in aqueous ZICs.…”

Recent Development of Mn‐based Oxides as Zinc‐Ion Battery Cathode

“…Tao and co‐workers demonstrated the dissolution of zinc acetate concurrently with exceptionally high salt concentrated potassium acetate aqueous solution [1 m Zn(CH 3 COO) 2 +31 m KCH 3 COO] to form “water in bisalt” electrolyte [119] . “Water in salt” electrolyte is also an important type of electrolyte in other devices [120] . Based on these inexpensive and less toxic salts, a wide electrochemical stability window of 3.4 V is achieved for aqueous ZIB applications in contrast to conventional electrochemical window range from 1.0 to 1.8 V.…”

Enabling 2.4-V aqueous supercapacitors through the rational design of an integrated electrode of hollow vanadium trioxide/carbon nanospheres

“…In contrast to the specific capacitance, the energy density is proportional to the square of the cell voltage. Therefore, increasing the voltage window of the devices is an extremely effective strategy to enhance their energy density [10,11]. Due to the low decomposition voltage of water (~1.23 V), organic electrolytes are usually used in SCs to increase the voltage window [12][13][14][15].…”