Enhanced Electrochemical Performance of Supercapacitors via Atomic Layer Deposition of ZnO on the Activated Carbon Electrode Material.

Junqi Sun,Daniel Q. Tan,Yair Ein-Eli,Junyan Chen,Xiangshang Xiao,Fuming Zhang,Dayakar Gandla,Chongrui Wu

doi:10.3390/molecules26144188

Abstract

Fabricating electrical double-layer capacitors (EDLCs) with high energy density for various applications has been of great interest in recent years. However, activated carbon (AC) electrodes are restricted to a lower operating voltage because they suffer from instability above a threshold potential window. Thus, they are limited in their energy storage. The deposition of inorganic compounds’ atomic layer deposition (ALD) aiming to enhance cycling performance of supercapacitors and battery electrodes can be applied to the AC electrode materials. Here, we report on the investigation of zinc oxide (ZnO) coating strategy in terms of different pulse times of precursors, ALD cycles, and deposition temperatures to ensure high electrical conductivity and capacitance retention without blocking the micropores of the AC electrode. Crystalline ZnO phase with its optimal forming condition is obtained preferably using a longer precursor pulse time. Supercapacitors comprising AC electrodes coated with 20 cycles of ALD ZnO at 70 °C and operated in TEABF4/acetonitrile organic electrolyte show a specific capacitance of 23.13 F g−1 at 5 mA cm−2 and enhanced capacitance retention at 3.2 V, which well exceeds the normal working voltage of a commercial EDLC product (2.7 V). This work delivers an additional feasible approach of using ZnO ALD modification of AC materials, enhancing and promoting stable EDLC cells under high working voltages.

Highlights

As the conventional and traditional energy resources are depleting, there is an increasing need to develop renewable, low-cost, and efficient power and energy sources.To satisfy the needs of modern society, supercapacitors with fast charging/discharging rates, long cycle life, and high-power density attract worldwide research and commercial attention
Ein-Eli and co-workers have applied different metal-fluorides (MgF2, AlF3, and LiF) atomic layer deposition (ALD) coating on LMNO powder material and reported a massive enhancement in cycling stability [18,19,20]. These results demonstrated that the ALD technique is the most effective tool to cope with the severe cycling deterioration of high operational voltage materials in lithium-ion batteries and supercapacitors
activated carbon (AC) powders used in this work were YP−50F (Kuraray), and PVDF binders and carbon black were purchased from Sigma Aldrich

Summary

Introduction

To satisfy the needs of modern society, supercapacitors with fast charging/discharging rates, long cycle life, and high-power density attract worldwide research and commercial attention. An electrical double-layer capacitor (EDLC) is a common device showing great potential in fast energy discharge applications. The low operating voltages, high leakage current, and low energy density of supercapacitors limit their applications [1,2]. The degradation at the interface of electrodes and electrolytes is of a concern when raising the operation voltages [3,4]. To prolong and extend the cycling life of the EDLC and battery electrodes, researchers are directing their efforts at surface modification of the electrodes as a most effective way to reach the target

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