Wider Voltage Window, High Capacity and Ultra‐Long Life of an Na_0.91MnO₂ Cathode for an Aqueous High‐Performance Supercapacitor

Abstract

The potential window of an aqueous supercapacitor cathode is usually less than 1.3 V, which hinders the enhancement of the energy density and can be conquered by activating the multiple redox reactions of the cathode. Herein, tetragonal phase Na 0.91 MnO 2 nanosheets/nanowires arrays with high cation content are produced in situ on an electrochemically treated carbon cloth by an electrochemical oxidation method. It is observed that the Na 0.91 MnO 2 nanosheet/nanowire array electrode can operate stably within the potential window of À 0.6 V to 1.2 V (vs Ag/AgCl) with an ultrahigh capacity of 856 C g À 1 and an outstanding stability and excellent rate ability. With a carbon fiber fabric with a large surface area as the anode, the Na 0.91 MnO 2 cathode in the two-electrode cell can still operate stably within the voltage range from 0 to 2.07 V (still within the range of the three redox peak couples, demonstrating a high energy density of 138 Wh kg À 1 , an excellent power density of 33 kW kg À 1 as well as 100 % retention even after 120 000 cycles. This work may pave the way for the development of an aqueous supercapacitor cathode with a wider potential window. amount of deionized water and dried at 60°C in an oven overnight. The electrochemical treated carbon cloth is denoted as ECC.

Challenges and prospects of high-voltage aqueous electrolytes for energy storage applications

“…47 According to E ∝ V 2 , the energy density E of EES devices is proportional to the square of the operating voltage V , which is mainly determined by the decomposition of interfacial electrolyte. 48 Therefore, to increase the energy density of supercapacitors, it is very effective to increase the electrochemical stability window of the electrolyte.…”

High‐Voltage Electrolytes for Aqueous Energy Storage Devices

“…However, their energy density is relatively lower compared with batteries. According to the equation: E =1/2 CV 2 (where E , C , and V represent the energy density, capacitance, and operating voltage, respectively), the capacitance and the operating voltage play a key impact on the energy density . Many works are focused on developing electrode materials with high capacitance .…”

Use of Silk Fibroin Material Composites for Green, Flexible Supercapacitors

“…However, current supercapacitors cannot match the energy storage densities of batteries or the charge–discharge speed of traditional capacitors. Supercapacitance is achieved with the use of high-surface-area electrodes bridged by electrolytes to volumetrically store charge. , Supercapacitors as high-power energy storage systems have been employed to power portable medical and electronic devices as well as electric vehicles. , Unfortunately, it is often difficult for conventional supercapacitors to be integrated into emerging technologies due to mechanical/biological performance limitations . Future supercapacitors will need to offer extended functionalities, including flexibility, implantability, biodegradability, and shape freedom to meet the needs of next-generation electronics .…”

“…Supercapacitance is achieved with the use of high-surface-area electrodes bridged by electrolytes to volumetrically store charge. 3,4 Supercapacitors as high-power energy storage systems have been employed to power portable medical and electronic devices as well as electric vehicles. 5,6 Unfortunately, it is often difficult for conventional supercapacitors to be integrated into emerging technologies due to mechanical/biological performance limitations.…”