From Copper to Basic Copper Carbonate: A Reversible Conversion Cathode in Aqueous Anion Batteries.

Dual-ion batteries that use anions and cations as charge carriers represent a promising energy-storage technology. However, an uncharted area is to explore transition metals as electrodes to host carbonate in conversion reactions. Here we report the reversible conversion reaction from copper to Cu CO (OH) , where the copper electrode comprising K CO and KOH solid is self-sufficient with anion-charge carriers. This electrode dissociates and associates K ions during battery charge and discharge. The copper active mass and the anion-bearing cathode exhibit a reversible capacity of 664 mAh g and 299 mAh g , respectively, and relatively stable cycling in a saturated mixture electrolyte of K CO and KOH. The results open an avenue to use carbonate as a charge carrier for batteries to serve for the consumption and storage of CO .