Mineral-Inspired, Nanostructured Polyanion Materials for Rechargeable Battery Electrodes

Polyanion materials are promising candidates for new rechargeable battery electrodes due to their good capacity, operation voltage, safety characteristics, as well as low cost. A family of materials based on metal hydroxysulfate or hydroxyphosphate naturally occurring minerals offers the possibility for improved performance as cathode materials due to the following characteristics: (1) open framework or layered structures that can facilitate fast Li+ insertion, (2) flexibility in alkali and transition metal cation incorporation as observed in nature, which can allow for the design of solid-solutions to enhance structural stability, capacity, and reaction potentials, and (3) possibility for multi-electron redox reactions, which can result in capacities >200 mAh/g. This presentation will introduce our investigation into nanostructured brochantite and jarosite minerals for use as electrodes in Li-ion and Na-ion batteries. The electrochemical properties of brochantite, Cu4(OH)6SO4, a natural mineral and 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. The electrochemical properties of the jarosite and V3+ jarosite analogue compounds, MN3(SO4)2(OH)6, where M=K, Na and N=Fe, V, were also investigated. A common industrial mining waste byproduct and naturally occurring mineral on Earth and Mars, the jarosite structure can accommodate many different cations and may serve as a good starting point for developing cathodes for batteries beyond Li-ion. Microstructured jarosites were synthesized using microwave-assisted hydrothermal reaction and the electrochemical characteristic were evaluated in half-cells with Li and Na metal. Detailed characterization using X-ray diffraction, scanning and transmission electron microscopy, and X-ray photoelectron spectroscopy was performed to better understand the structural changes and reaction mechanisms in both brochantite and jarosite systems. Reference: R. Zhao, T. Yang, M.A. Miller, C.K. Chan, Nano Lett., 13, 6055 – 6063 (2013).