New Approach for High-Voltage Electrical Double-Layer Capacitors Using Vertical Graphene Nanowalls with and without Nitrogen Doping

Abstract

Integrating various devices to achieve high-performance energy storage systems to satisfy various demands in modern societies become more and more important. Electrical double-layer capacitors (EDLCs), one kind of the electrochemical capacitors, generally provide the merits of high charge-discharge rates, extremely long cycle life, and high efficiency in electricity capture/storage, leading to a desirable device of electricity management from portable electronics to hybrid vehicles or even smart grid application. However, the low cell voltage (2.5-2.7 V in organic liquid electrolytes) of EDLCs lacks the direct combination of Li-ion batteries (LIBs) and EDLCs for creating new functions in future applications without considering the issue of a relatively low energy density. Here we propose a guideline, "choosing a matching pair of electrode materials and electrolytes", to effectively extend the cell voltage of EDLCs according to three general strategies. Based on the new strategy proposed in this work, materials with an inert surface enable to tolerate a wider potential window in commercially available organic electrolytes in comparison with activated carbons (ACs). The binder-free, vertically grown graphene nanowalls (GNW) and nitrogen-doped GNW (NGNW) electrodes respectively provide good examples for extending the upper potential limit of a positive electrode of EDLCs from 0.1 to 1.5 V (vs Ag/AgNO3) as well as the lower potential limit of a negative electrode of EDLCs from -2.0 V to ca. -2.5 V in 1 M TEABF4/PC (propylene carbonate) compared to ACs. This newly designed asymmetric EDLC exhibits a cell voltage of 4 V, specific energy of 52 Wh kg(-1) (ca. a device energy density of 13 Wh kg(-1)), and specific power of 8 kW kg(-1) and ca. 100% retention after 10,000 cycles charge-discharge, reducing the series number of EDLCs to enlarge the module voltage and opening the possibility for directly combining EDLCs and LIBs in advanced applications.

Heteroatom‐Doped and Oxygen‐Functionalized Nanocarbons for High‐Performance Supercapacitors

“…[177] The highest potential window of 4 V has been achieved with asymmetric EDLC device with vertical graphene and N-doped vertical graphene nanostructures in TEABF 4 /PC electrolyte. [272] The redox reactions in an organic electrolyte (TEABF 4 /PC) are proposed as follows [273] C PH :…”

Vertically Aligned Graphene Nanosheet Arrays: Synthesis, Properties and Applications in Electrochemical Energy Conversion and Storage

“…100% retention after 10 000 cycles' operation. [87] This is very remarkable performance for EDLC electrodes, making it a promising candidate for electrochemical energy storage in flexible devices.…”

Optimization of Electrode Potential Ranges for Constructing 4.0 V Carbon‐Based Supercapacitors

“…Therefore, great efforts have been devoted to increase the energy density of SCs. [6][7][8][9][10][11][12]44,45] The calculation formula of energy density is E = 0.5 CV 2 , where E stands for energy density, C stands for specific capacitance and V stands for operating potential window (OPW). From this formula, we know that the energy density can be significantly increased by enlarging the OPW.…”