Electrochemical Properties of Quinone-Based Organic Electrode Materials in Lithium Chloride/Dimethyl Sulfoxide Electrolyte Solutions
Authors: Okubo Sho , Hayashi Masahiko , Taguchi Hiroaki , Aratake Atsushi 
Published: December 2024

Introduction

Fluorinated compounds such as PVdF and PTFE are widely utilized as binding materials for lithium secondary battery electrodes, and those such as LiPF6 and LiTFSA are used as electrolyte salts. However, there has been growing public concern about the impact of hazardous substances on the environment. In particular, there is a movement to tighten regulations, mainly in Europe, on fluorinated compounds represented by PFAS (perfluoroalkyl substances and polyfluoroalkyl substances). In response to this tightening regulation, we have been investigating a fluorine compound-free electrode 1 that uses 2,5-dimethoxy-1,4-benzoquinone (DMBQ), a quinone-based organic electrode material, as the positive electrode material and styrene butadiene rubber (SBR) as the binder. We have also focused on LiCl/dimethyl sulfoxide (DMSO) 2 as an alternative to electrolyte containing fluorine compounds. In the current study, we examine the electrochemical properties of the DMBQ electrode in this electrolyte with the aim of achieving fluorine compound-free batteries.

Experimental

As the working electrode, DMBQ mixed with AB, a conductive material, and binders (SBR and CMC) in a weight ratio of 8.0:1.0:0.8:0.2 was coated on Al foil and allowed to dry. Li metal foil (Φ17 mm) was used as the counter electrode and 1.0 mol dm-3 LiCl/DMSO was used as the electrolyte. A two-electrode cell was prepared using a glass fiber separator. For a comparison, an electrochemical cell with a similar configuration was prepared using 1.0 mol dm-3 LiPF6/DMSO, an electrolyte containing fluorinated compounds. Charge-discharge tests were performed at cell voltages ranging from 1.80 V to 3.10 V at a constant current density of 50 µA cm-2. The DMBQ electrodes were removed from the cell at each potential (discharge voltages of 2.66 V, 2.64 V, and 1.80 V; charge voltages of 2.76 V, 2.78 V, and 3.10 V) and washed with DMC, and then XRD and FTIR were used to analyze the changes in crystallinity and chemical bonding states of DMBQ during charge-discharge.

Results and discussion

Figure 1 (a) shows the first charge-discharge curves of the DMBQ electrode in LiCl/DMSO. The discharge plateau voltage was about 2.70 V. The first discharge capacity was about 230 mAh g-1, which corresponds to about 75% of the theoretical capacity assuming a two-electron redox reaction of DMBQ. Figure 1 (b) and (c) respectively show the XRD patterns and FTIR spectra of the DMBQ electrode at the potentials shown in (a). In Fig. 1 (b), the XRD peaks identified as DMBQ disappeared with discharging and changed to pristine peaks with charging. In Fig. 1 (c), the FTIR peaks originating from DMBQ disappeared with discharge and returned to original peak with charge. A new peak around 1540 cm-1 appeared with discharging and disappeared with charging. These changes were similar to those in the LiPF6/DMSO system. We assume these results are due to the interaction between DMBQ and Li ions during charge-discharge reaction, suggesting that LiCl/DMSO is an effective electrolyte for fluorine compound-free batteries using DMBQ electrodes.

References

Okubo, M. Nohara, M. Hayashi, H. Taguchi, and A. Aratake, 90th Annual Meeting of the Electrochemical Society of Japan, Abstr., 2I04 (2023). [in Japanese]

Wang, J. Wang, G. Li, Z. Guo, J. Chu, X. Ai, and Z. Song, Energy Stor. Mater., 50, 658 (2022).

Fig. 1. (a) Discharge/charge curves, (b) XRD patterns, and (c) FTIR spectra of the DMBQ electrode in different states during the first discharge-charge cycle in 1.0 mol dm-3 LiCl/DMSO electrolyte solution.

Figure 1