Electrochemical properties of nanostructured copper hydroxysulfate mineral brochantite upon reaction with lithium

Cu-containing conversion electrodes have received much study as high capacity electrodes for lithium-ion batteries, but many suffer from poor reversibility. The electrochemical properties of the copper hydroxysulfate compound, Cu₄(OH)₆SO₄, more commonly known as the mineral brochantite and as a patina constituent on the Statue of Liberty, were investigated. Nanostructured brochantite was synthesized using precipitation and microwave-assisted hydrothermal reactions and evaluated in half-cells with Li metal counter electrodes. Reversible capacities >400 mAh/g corresponding to the 2 electron reduction of Cu²⁺ and discharge potential of 1.8 V versus Li/Li⁺ were observed in brochantite with a nanoplate morphology. Detailed characterization using X-ray diffraction, scanning and transmission electron microscopy, and X-ray photoelectron spectroscopy was performed to better understand the conversion process.