[Paper Review] Graphene based Supercapacitors with Improved Specific Capacitance and Fast Charging Time at High Current Density

Santhakumar Kannappan, K. Karthikeyan+6 more|arXiv (Cornell University)|Nov 6, 2013

Supercapacitor Materials and Fabrication32 citations

TL;DR

This study presents a graphene-based supercapacitor with enhanced specific capacitance (195 Fg⁻¹) and energy density (83.4 Whkg⁻¹) at 2.5 A g⁻¹, achieving fast charging in ~25 seconds for 64.18 Whkg⁻¹. The performance stems from a highly porous, non-restacked graphene structure with improved ion accessibility and an optimized current collection method, enabling stable operation at high current densities with 98% capacitance retention after 10,000 cycles.

ABSTRACT

Graphene is a promising material for energy storage, especially for high performance supercapacitors. For real time high power applications, it is critical to have high specific capacitance with fast charging time at high current density. Using a modified Hummer's method and tip sonication for graphene synthesis, here we show graphene-based supercapacitors with high stability and significantly-improved electrical double layer capacitance and energy density with fast charging and discharging time at a high current density, due to enhanced ionic electrolyte accessibility in deeper regions. The discharge capacitance and energy density values, 195 Fg-1 and 83.4 Whkg-1, are achieved at a current density of 2.5 Ag-1. The time required to discharge 64.18 Whkg-1 at 5 A/g is around 25 sec. At 7.5 Ag-1 current density, the cell can deliver a specific capacitance of about 137 Fg-1 and maintain 98 % of its initial value after 10,000 cycles, suggesting that the stable performance of supercapacitors at high current rates is suitable for fast charging-discharging applications. We attribute this superior performance to the highly porous nature of graphene prepared with minimum restacking due to crimple nature wrinkles and the improved current collecting method.

Motivation & Objective

• To develop graphene-based supercapacitors with high specific capacitance and fast charging for high-power applications.
• To address the challenge of capacitance decay and slow kinetics at high current densities in conventional graphene supercapacitors.
• To enhance ionic electrolyte accessibility in graphene electrodes through structural engineering.
• To improve current collection efficiency to support high-rate performance.
• To achieve stable, long-term cycling performance under high current density operation.

Proposed method

• Synthesis of graphene via a modified Hummer’s method followed by tip sonication to reduce restacking and induce wrinkles.
• Creation of a highly porous graphene architecture with intrinsic crumples to enhance ion transport and electrolyte access.
• Use of an optimized current collecting method to minimize resistance and improve electron transfer.
• Electrochemical characterization using cyclic voltammetry, galvanostatic charge-discharge, and cycling stability tests at varying current densities.
• Measurement of specific capacitance, energy density, and charge-discharge time under high current conditions (up to 7.5 A g⁻¹).
• Analysis of structural and electrochemical properties to correlate morphology with performance.

Experimental results

Research questions

• RQ1 Can a modified Hummer’s method combined with tip sonication produce graphene with reduced restacking and enhanced porosity for improved supercapacitor performance?
• RQ2 Does the presence of crumpled, porous graphene structures significantly enhance ionic accessibility and reduce ion diffusion resistance at high current densities?
• RQ3 To what extent does the optimized current collection method improve rate capability and reduce polarization in graphene-based supercapacitors?
• RQ4 Can high specific capacitance and energy density be maintained at high current densities (e.g., 2.5–7.5 A g⁻¹) without significant degradation?
• RQ5 What is the long-term cycling stability of the supercapacitor at high current densities, particularly after 10,000 cycles?

Key findings

• The supercapacitor achieved a specific capacitance of 195 Fg⁻¹ and energy density of 83.4 Whkg⁻¹ at a current density of 2.5 A g⁻¹.
• The time required to discharge 64.18 Whkg⁻¹ of energy was approximately 25 seconds at 5 A g⁻¹.
• At 7.5 A g⁻¹, the device maintained a specific capacitance of about 137 Fg⁻¹ with 98% retention after 10,000 cycles.
• The highly porous, non-restacked graphene structure with crumpled wrinkles enabled enhanced ionic electrolyte accessibility and faster ion transport.
• The optimized current collection method contributed to reduced internal resistance and improved rate performance.
• The combination of structural engineering and interface optimization enabled stable, high-power operation under extreme current conditions.