Electrical Conductivity-Relay between Organic Charge-Transfer and Radical Salts toward Conductive Additive-Free Rechargeable Battery

Abstract

In recent years, organic electrode materials have been strongly considered for use in sustainable batteries. However, most organic electrode materials have low electrical conductivity and require a lot of conductive additives, which decrease effective capacity based on the entire electrode weight/volume. In this study, we propose a novel electrical conductivity-relay system that imparts electrical conductivity to organic small molecular electrodes without any conductive additive throughout the charge/discharge cycles. It consists of the combination of the charge-transfer phenomenon in a pristine state and the formation of organic radical salts in redox states. Herein we demonstrate this electrical conductivity-relay system using a simply mixed molecular crystal couple of tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) as a cathode without any conductive additive and an aqueous sodium bromide as an electrolyte. During charge/discharge, electrical conductivity of the cathode is supported by charge-transfer at the TTF/TCNQ interface and (TTF)Brn and NaTCNQ radical salts, and the cathode exhibits the specific capacity of 112 mAh g^–1 and the retention rate of 80.7% at the 30th cycle. Furthermore, the molecular crystal couple electrode of TTF and TCNQ shows the better charge/discharge performance than the pure charge-transfer complex electrode, indicating that this system expands the candidate for organic electrode materials to various pairs and mixing ratio of small molecules even not forming charge-transfer complexes.