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

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.

Enhanced activated carbon lithium-ion capacitor electrochemical stability through electrolyte dielectric optimisation

“…Zhang et al 19 further investigated the electrochemical behaviour and stability of AC in electrolytes containing different lithium salts. Techniques such as surface treatment, 20–25 defect reduction 15 and atomic layer deposition of ZnO 26 have been utilised to improve the electrochemical stability of AC electrodes, while these modification processes are often intensive and complex. However, to the best of our knowledge, little attention has been paid to optimise the solvent of the electrolytes used in LiC containing AC electrodes to improve their stability.…”

Al Foil-Supported Carbon Nanosheets as Self-Supporting Electrodes for High Areal Capacitance Supercapacitors

“…The Zn, Al, C, N, and O elements can be detected in the full spectrum of XPS ( Figure 4 a), where the contents of C, N, and O are 3.7, 0.21, and 2.56 at.%, respectively ( Table S1 ). Two peaks at a binding energy (BE) of 1021.9 and 1044.9 eV are considered as Zn 2p 3/2 and Zn 2p 1/2 , respectively, indicating that Zn 2+ presents in CNS-120 [ 32 , 48 ]. There are also three peaks located at about 10.9, 89.5, and 140.0 eV, corresponding to Zn 3d, Zn 3p, and Zn 3s, respectively.…”

Atomic Layer Deposition—A Versatile Toolbox for Designing/Engineering Electrodes for Advanced Supercapacitors

“…[303] Generally, AC exhibits instability above a certain threshold potential range, which restricts their use to lower operating voltages. In a recent study, Wu et al [304] deposited ZnO via ALD to enhance the cycling performance of AC-based SC electrodes, as mentioned in Figure 15l. To achieve high electric conductivity and strong capacitance retention among the AC materials, the authors optimized the ZnO coating process by altering the precursor exposure period, number of ALD cycles, and growth temperature.…”

“…The figure displays a schematic of ALD coating and an EDLC cell modified with crystalline ZnO in (l). Reproduced with permission [304]. Copyright 2021, MDPI.…”