Indigo Dye as a Positive-electrode Material for Rechargeable Lithium Batteries

Abstract

The performance of indigo carmine (5,5¤-indigodisulfonic acid sodium salt) as a positive-electrode material for rechargeable lithium batteries was investigated. The prepared electrode showed an initial discharge capacity of 110 mA h g ¹1, which corresponds to two-electron-redox behavior. Furthermore, the electrode was shown to have good cycle-life stability.Indigo has been used for dyeing and printing, and its dark blue color has fascinated people all over the world since ancient times. 15 In particular, indigo is widely known as a dye for blue jeans. This dye is an organic compound with a heterocyclic structure and can be obtained from some plants. Several peripherally substituted derivatives are known and these indigo derivatives can be chemically reduced to form leuco-indigo derivatives (Scheme 1). In this reaction, the indigo skeleton undergoes two-electron reduction, and the resulting leuco-indigo can easily return to the original form by air oxidation. This reaction process is particularly important for dyeing since waterinsoluble indigo becomes soluble via this reduction. Furthermore, this two-electron redox reaction has potential as an active material in batteries.6 For rechargeable lithium batteries, which are widely used as power sources due to their high energy densities, inorganic compounds represented by lithium cobalt oxide (LiCoO 2 ) have been used as active materials in positive electrodes; 7 however, alternative low-polluting materials are becoming increasingly desirable owing to the consideration of environmental effects. Among several candidates, organic materials have recently been attracting attention since they do not contain expensive and harmful heavy metals.718 Furthermore, these organic active materials are also noteworthy from the viewpoint of carbon neutrality, since some of them can be extracted from plants. 9,16 As novel low-polluting organic active materials, we focused our attention on indigo derivatives and discovered that the watersoluble derivative indigo carmine (5,5¤-indigodisulfonic acid sodium salt) (Scheme 2), which is used as a blue dye for food and drugs, shows an initial capacity density of above 100 mA h g ¹1 and relatively good cycle-life performance. In the present paper, the primary charge/discharge performance of indigo carmine as a positive-electrode active material will be described.An R2032 coin-type sealed cell composed of a positive electrode incorporating indigo carmine and a negative electrode using a lithium metal sheet was prepared for battery tests. The weight ratio of indigo carmine powder, acetylene black as the conductive additive, and a poly(tetrafluoroethylene) binder was 4:5:1. The typical amount of the active material deposited on an aluminum mesh current collector was 3 mg. A mixed solution of ethylene carbonate and diethyl carbonate containing lithium hexafluorophosphate (1.0 mol L ¹1 LiPF 6 in EC/DEC = 1/1 by vol.) was used as an electrolyte solution. The charge/discharge tests were performed with computer-controlled systems equipped with a ther...

Molecular Engineering with Organic Carbonyl Electrode Materials for Advanced Stationary and Redox Flow Rechargeable Batteries

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5,5′-alkylsubsituted indigo for solution-processed optoelectronic devices

“…2e4 Recently, indigos and functionalized indigos were applied for optoelectronic devices, such as field effect transistors, 5e7 solar cells, 8,9 sensors, 10,11 and electrodes for ion batteries. 12,13 In particular, Pitayatanakul et al, reported on the halogen or phenyl group functionalized indigos for organic semiconductors. In this series of compounds, the indigos showed a herring-bone like structure for the halogen substitution derivatives, whereas a brickwork arrangement of the crystal structure was observed in the case of phenyl-derivatives because of pep interactions arising from the functionalization substitution at 5-position.…”

Indigo carmine: An organic crystal as a positive-electrode material for rechargeable sodium batteries

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