Electrodes with Electrodeposited Water-excluding Polymer Coating Enable High-Voltage Aqueous Supercapacitors.

Wujie Dong,Zhichao Zhang,Xin Wang,Yuan Wang,Xiaotao Yuan,Fuqiang Huang,Jian Huang,Tianquan Lin,I-Wei Chen,Jie Lin

doi:10.34133/2020/4178179

Abstract

Aqueous supercapacitors are powerful energy sources, but they are limited by energy density that is much lower than lithium-ion batteries. Since raising the voltage beyond the thermodynamic potential for water splitting (1.23 V) can boost the energy density, there has been much effort on water-stabilizing salvation additives such as Li2SO4 that can provide an aqueous electrolyte capable of withstanding ~1.8 V. Guided by the first-principles calculations that reveal water can promote hydrogen and oxygen evolution reactions, here, we pursue a new strategy of covering the electrode with a dense electroplated polymerized polyacrylic acid, which is an electron insulator but a proton conductor and proton reservoir. The combined effect of salvation and coating expands the electrochemical window throughout pH 3 to pH 10 to 2.4 V for both fast and slow proton-mediated redox reactions. This allows activated carbon to quadruple the energy density, a kilogram of nitrogen-doped graphene to provide 127 Watt-hour, and both to have improved endurance because of suppression of water-mediated corrosion. Therefore, aqueous supercapacitors can now achieve energy densities quite comparable to that of a lithium-ion battery, but at 100 times the charging/discharging speed and cycle durability.

Highlights

The energy of an electrochemical cell of a linear capacitance C operating at a voltage V is 1⁄2CV2
After the preliminary screening (Fig. S4), we focused on polyacrylic acid (PAA, (C3H4O2)n), a weak acid with pKa = 4:7
PAA is compatible with electrochemical operations and is already used as an electrode binder [20,21,22,23] and a solid/quasisolid electrolyte [21, 24,25,26,27,28,29,30]

Summary

Introduction

The energy of an electrochemical cell of a linear capacitance C operating at a voltage V is 1⁄2CV2. The voltage is limited by the stability of the electrolyte, and aqueous electrolytes decompose into hydrogen and oxygen at 1.23 V. The disadvantage of a small electrochemical window (ECW) is partially mitigated by advanced carbon electrodes, such as N-doped few-layer graphene that reaches a specific capacity of 855 F g-1, or three times the value of activated carbon in commercial supercapacitors [2]. The aim of this work is to demonstrate a waterexcluding polymer-coated advanced carbon electrode that can reproducibly operate (over 105 cycles) at 2.4 V in a Li2SO4 aqueous electrolyte at both high and low rates over a pH window from 3 to 10. The resulting aqueous (symmetric) supercapacitor is capable of an energy density quite comparable to that of a lithium-ion battery, but at 100 times the charging/discharging speed and cycle durability

Objectives

Methods

Results

Conclusion