Advantage of Dimethyl Sulfoxide in the Fabrication of Binder-Free Layered Double Hydroxides Electrodes: Impacts of Physical Parameters on the Crystalline Domain and Electrochemical Performance

Abstract

The electrode fabrication stage is a crucial step in the design of supercapacitors. The latter involves the binder generally for adhesive purposes. The binder is electrochemically dormant and has weak interactions, leading to isolating the active material and conductive additive and then compromising the electrochemical performance. Designing binder-free electrodes is a practical way to improve the electrochemical performance of supercapacitors. However, most of the methods developed for the fabrication of binder-free LDH electrodes do not accommodate LDH materials prepared via the co-precipitation or ions exchange routes. Herein, we developed a novel method to fabricate binder-free LDH electrodes which accommodates LDH materials from other synthesis routes. The induced impacts of various physical parameters such as the temperature and time applied during the fabrication process on the crystalline domain and electrochemical performances of all the binder-free LDH electrodes were studied. The electrochemical analysis showed that the electrode prepared at 200 °C-1 h exhibited the best electrochemical performance compared to its counterparts. A specific capacitance of 3050.95 Fg^-1 at 10 mVs^-1 was achieved by it, while its Rct value was 0.68 Ω. Moreover, it retained 97% of capacitance after 5000 cycles at 120 mVs^-1. The XRD and FTIR studies demonstrated that its excellent electrochemical performance was due to its crystalline domain which had held an important amount of water than other electrodes. The as-developed method proved to be reliable and advantageous due to its simplicity and cost-effectiveness.

Keywords: binder-free LDH electrode; dimethyl sulfoxide; layered double hydroxides; supercapacitor.

Figure 1

XRD patterns of the as-synthesized LDH used as electrode active material.

Figure 2

(a) Schematic illustration of the fabrication process of binder-free LDH electrodes; (b) the image of the as-fabricated binder-free LDH electrode; (c) XRD patterns of the LDH-100-1h, LDH-100-1h30, LDH-100-2h, LDH-150-1h, and LDH-200-1h electrodes; and (d) FTIR spectra of the LDH-100-1h, LDH-100-1h30, LDH-100-2h, LDH-150-1h, and LDH-200-1h electrodes.

Figure 3

FESEM images of (a) the as-synthesized LDH used as electrode active material; (b–f) the LDH-100-1h, LDH-100-1h30, LDH-100-2h, LDH-150-1h, and LDH-200-1h electrodes.

Figure 4

(a–e) FESEM images of the LDH-100-1h, LDH-100-1h30, LDH-100-2h, LDH-150-1h, and LDH-200-1h electrodes at a different magnification.

Figure 5

(a) Comparative CV curves for the LDH-100-1h, LDH-100-1h30, and LDH-100-2h electrodes at a scan rate of 10 mVs⁻¹; (b) comparative CV curves for the LDH-100-2h, LDH-150-1h, and LDH-200-1h electrodes at a scan rate of 10 mVs⁻¹.

Figure 6

CV curves for the (a) LDH-100-1h, (b) LDH-100-1h30, (c) LDH-100-2h, (d) LDH-150-1h, and (e) LDH-200-1h electrodes, respectively at various scan rates.

Figure 7

Dependence of the anodic peak current (ipa) on the square root of the scan rate for the (a) LDH-100-1h, (b) LDH-100-1h30, (c) LDH-100-2h, (d) LDH-150-1h, and (e) LDH-200-1h electrodes, respectively.

Figure 8

Linear relationship related to various potential levels of i/V1/2 against V1/2 for the (a) LDH-100-1h, (b) LDH-100-1h30, (c) LDH-100-2h, (d) LDH-150-1h, and (e) LDH-200-1h electrodes, respectively; (f) contribution fractions of the surface capacitance and diffusion-controlled processes for the LDH-100-1h, LDH-100-1h30, LDH-100-2h, LDH-150-1h, and LDH-200-1h electrodes, respectively, at the scan rate of 10 mVs⁻¹.

Figure 9

(a) Nyquist plots for the LDH-100-1h, LDH-100-1h30, and LDH-100-2h electrodes; and (b) Nyquist plots for the LDH-100-2h, LDH-150-1h, and LDH-200-1h electrodes.

Figure 10

(a) Specific capacitances of the LDH-100-1h, LDH-100-1h30, LDH-100-2h, LDH-150-1h, and LDH-200-1h electrodes at various scan rates; (b) plot of capacitance retention against cycle number (insert: cyclic voltammogram of the LDH-200-1h electrode at 120 mVs⁻¹).