Prof. Amy Prieto, Colorado State University

Progress Toward a Three-Dimensional Lithium-ion Rechargeable Battery

Inorganic Division Seminar Series

The two main limitations to the rate of charging and discharging in Li-ion batteries are the slow diffusion of Li+ into the anode and the cathode and the slow diffusion between them. A successful method to decreasing the diffusion length of Li+ in intercalation reactions has been to fabricate electrode materials as high surface area nanowire arrays. The fabrication of nanowire arrays of both carbon based anodes and several common cathode materials has been shown to dramatically enhance electrode performance. The problem of decreasing the Li+ diffusion length between the cathode and anode has not yet been solved. We are incorporating nanowire arrays of a novel anode material, Cu2Sb, into a new battery architecture. Each nanowire anode is conformally coated with a polymer electrolyte via reductive electropolymerization, and then surrounded by the cathode electrode synthesized using sol-gel chemistry. The significant advantage to this geometry is that the diffusion length between the electrodes has been dramatically reduced. The ultimate goal is a battery with much faster charge and discharge rates and a longer lifetime.

As a first step toward this proposed architecture we have developed the direct electrodeposition of stoichiometric, crystalline Cu2Sb from aqueous solutions at room temperature. We used citric acid as a binding ligand to shift the reduction potentials of Cu2+ and Sb3+ to within 50 mV of each other. The result is the deposition of the desired compound at a single potential. Nanowires have been fabricated by pulsed electrodeposition into porous alumina templates. The template can then be dissolved, and the exposed Cu2Sb nanowires are used as electrodes for the reductive polymerization of [Zn(4',vinyl-4,methyl-2,2'-bipyridine)3](PF6)2. Redox shut-off (passivation) experiments have shown that the polymer is deposited conformally over high-aspect ratio wires without pinhole defects. Also, DC measurements show that the polymer is electrically insulating up to 5 V. Current work is focused on impedance measurements of the Li+ conductivity into the anode and polymer electrolyte, as well as the integration of LixCo1-xO2 as the cathode material in the battery.

For more information contact Prof. Jake Soper (404-894-4022).