3D Zinc Sponge Anodes: Towards Next-Generation Ni-Zn Batteries

Abstract

Zinc-based batteries (e.g., Zn–air, Ag–Zn, Ni–Zn) are endowed with high specific energy (up to 400 Wh kg–1), high specific power, nonflammable alkaline electrolytes, and an earth-abundance of active materials. The advantages of zinc-based batteries make them the ideal energy storage solution to address the pitfalls of its battery-chemistry competitors—from the toxicity and low specific energy of Pb-acid to the flammability of Li-ion. The historical failure of zinc to be recognized as a worthy competitor to other technologies lies in its bedeviled non-rechargeability and modest zinc utilization (typically <60% of theoretical discharge capacity), especially when constructed as an ad-hoc powder composited electrode. Traditionally, when Zn is oxidized to Zn2+ during discharge, it forms zincate complexes (e.g. Zn(OH)4 2– (aq) ) that are soluble in the alkaline electrolyte. These mobile Zn-carriers can diffuse beyond the site of generation but eventually supersaturate and precipitate as poorly conductive ZnO. The reverse step (charging) is initiated by re-dissolution of the ZnO to zincate prior to reduction back to Zn0. Multiple iterations of the above processes eventually lead to electronic isolation of portions of the electrode, hotspots of high-current density, and growth of short-inducing dendrites. To circumvent these problems, we design and fabricate 3D zinc "sponge" anodes that are monolithic and comprise an interpenetrating, co-continuous network of solid and void [1]. The electrode—now wired in 3D—enables low cell resistances throughout discharge that allow access to >90% of the zinc [2]. The morphology of the discharged sponges reveals a uniform deposition of ZnO on the inner walls of the sponge electrode, providing a core–shell 3D structure with an 3D-wired inner Zn metallic core that is ideal for electrochemical recharge with 100% capacity retention. We have identified the Ni–Zn battery system, with its established and rechargeable NiOOH cathode, as a prime candidate to begin implementing 3D-Zn sponge electrodes towards next-generation alternatives to Pb-acid, Ni–Cd, Ni–MH, and Li-ion batteries. We present the design and fabrication of 3D-Zn sponge anodes and their cycling performance in Ni–Zn full cells, with specific emphasis on cell fabrication, electrolyte composition, and post-mortem analysis. The information, data, or work presented herein was funded in part by the Office of Naval Research and by the Advanced Research Projects Agency–Energy (ARPA–E), U.S. Department of Energy, under Award Number DE-AR-0000391; the work has been Approved for Public Release, Distribution Unlimited. [1] J.F. Parker, C.N. Chervin, E.S. Nelson, J.W. Long, D.R. Rolison, Energy Environ. Sci. 7 (2014) 1117–1124. [2] J.F. Parker, E.S. Nelson, M.D. Wattendorf, C.N. Chervin, J.W. Long, D.R. Rolison, ACS Appl. Mater. Interfaces, in the press.