Zinc-Sponge Battery Electrodes that Suppress Dendrites

Summary

The goal of the reported protocols is to create rechargeable zinc-sponge electrodes that suppress dendrites and shape change in zinc batteries, such as nickel–zinc or zinc–air.

Abstract

We report two methods to create zinc-sponge electrodes that suppress dendrite formation and shape change for rechargeable zinc batteries. Both methods are characterized by creating a paste made of zinc particles, organic porogen, and viscosity-enhancing agent that is heated under an inert gas and then air. During heating under the inert gas, the zinc particles anneal together, and the porogen decomposes; under air, the zinc fuses and residual organic burns out, yielding an open-cell metal foam or sponge. We tune the mechanical and electrochemical properties of the zinc sponges by varying zinc-to-porogen mass ratio, heating time under inert gas and air, and size and shape of the zinc and porogen particles. An advantage of the reported methods is their ability to finely tune zinc-sponge architecture. The selected size and shape of the zinc and porogen particles influence the morphology of the pore structure. A limitation is that resulting sponges have disordered pore structures that result in low mechanical strength at low volume fractions of zinc (<30%). Applications for these zinc-sponge electrodes include batteries for grid-storage, personal electronics, electric vehicles, and electric aviation. Users can expect zinc-sponge electrodes to cycle up to 40% depth of discharge at technologically relevant rates and areal capacities without the formation of separator-piercing dendrites.

Introduction

The purpose of the reported fabrication methods is to create zinc (Zn) sponge electrodes that suppress dendrite formation and shape change. Historically, these problems have limited the cycle life of Zn batteries. Zinc-sponge electrodes have resolved these issues, enabling Zn batteries with longer cycle lives^1,2,3,4,5,6. The sponge structure suppresses dendrite formation and shape change because (1) the fused Zn framework electrically wires the entire volume of the sponge;....

Protocol

1. An emulsion-based method to create Zn-sponge electrodes

1. Add 2.054 mL of deionized water to a 100 mL glass beaker.
2. Add 4.565 mL of decane to the beaker.
3. Stir in 0.1000 ± 0.0003 g of sodium dodecyl sulfate (SDS) until dissolved.
4. Stir in 0.0050 ± 0.0003 g of water-soluble medium viscosity carboxymethyl cellulose (CMC) sodium salt by hand for 5 min or until the CMC is fully dissolved.
   NOTE: Use plastic or plastic-coated stirring tools. Stirring with tools with a metallic surface can adversely affect resulting Zn sponges.
5. Stir in 0.844 ± 0.002 g of water-insoluble preswollen carb....

Results

Resulting, fully heat-treated, emulsion-based Zn sponges have densities of 2.8 g∙cm^–3 while aqueous-based sponges approach 3.3 g∙cm^–3. During heating under air, a layer of ZnO forms on the Zn surfaces, which should have a thickness of 0.5–1.0 µm (observed using scanning electron microscopy)⁵. The solid in the resulting sponges should be 72% Zn (emulsion version) or 78% Zn (aqueous version) with the remainder being ZnO (measured by X-ray diffraction)⁶. .......

Discussion

Modifications and troubleshooting associated with these protocols include filling the freshly mixed Zn paste into a mold cavity. Care should be taken to avoid air pockets. Unwanted voids can be decreased by tapping the mold after filling or while filling. Because the aqueous Zn paste is dry, pressure can be applied directly to the Zn paste to push out air pockets while filling up the mold cavity.

A limitation of the methods is that Zn-sponge pore structure is disordered, but the Zn and porogen.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Corn starch	Argo	Not applicable	This acts as a porogen and viscosity-enhancing agent.
Decane	MilliporeSigma	D901
Medium viscosity water-soluble carboxymethyl cellulose (CMC) sodium salt	MilliporeSigma	C4888-500G	This CMC acts primarily as a viscosity-enhancing agent.
Overhead stirrer	Caframo Lab Solutions	BDC3030
Small cylindrical models for Zn sponges	VWR	66014-358	The caps of the vials can be used as molds.
Sodium dodecyl sulfate	MilliporeSigma	436143
Water-insoluble IonSep CMC 52 preswollen carboxymethyl cellulose resin	BIOpHORETICS	B45019.01	This CMC acts as a porogen and viscosity-enhancing agent.
Zn powder	EverZinc	Custom order