Volume 95 Issue 21 | p. 6 | News of The Week
Issue Date: May 22, 2017 | Web Date: May 17, 2017

Electroplated batteries store more energy

A new process for making pure battery electrodes improves performance
Department: Science & Technology
News Channels: Materials SCENE, Materials SCENE, Materials SCENE, Materials SCENE
Keywords: energy storage, batteries, electroplating, flexible batteries, lithium, energy, electronics
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Electroplating can grow films of lithium cobalt oxide on aluminum foil, as seen in this electron micrograph.
Credit: Hailong Ning and Jerome Davis III/Xerion Advanced Battery Corp
A micrograph of an electrode material
 
Electroplating can grow films of lithium cobalt oxide on aluminum foil, as seen in this electron micrograph.
Credit: Hailong Ning and Jerome Davis III/Xerion Advanced Battery Corp

Electroplated battery electrodes can store 30% more energy than today’s best commercial models, according to a new study. The electroplating process is compatible with a range of high-performance cathode materials called lithium transition-metal oxides. And it could help make flexible batteries needed for wearable electronics.

Making electrodes from these oxide materials normally requires high temperatures, which is a constraint on battery designs and performance, says Paul Braun, a materials scientist at the University of Illinois, Urbana-Champaign. The process starts by heating lithium and the transition metal of choice, such as cobalt, to 700–1000 °C to form an oxide powder. The high-temperature process ensures the oxide has good crystallinity, which is necessary for high performance. The resulting powder then gets blended with binders and other additives to make an electrode. These additives don’t store any energy, and they take up space and add weight, both of which are at a premium in portable electronics.

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A flexible electroplated lithium cobalt oxide battery electrode can be rolled up.
Credit: Hailong Ning and Jerome Davis III/Xerion Advanced Battery Corp
A photograph of a flexible battery electrode.
 
A flexible electroplated lithium cobalt oxide battery electrode can be rolled up.
Credit: Hailong Ning and Jerome Davis III/Xerion Advanced Battery Corp

Braun’s group avoided using these space-wasting additives by electroplating the material directly on an electrode support. Because electroplating is driven by electricity, the required temperature can be lower than those usually needed to form the desired oxides.

The researchers placed foam electrodes or aluminum battery foils in a molten salt made of a mixture of lithium hydroxide, potassium hydroxide, and cobalt oxide. This made good quality films of lithium cobalt oxide on the foams and foils at 260 °C. Using this plating method, the group deposited three different cathode materials by switching out the cobalt oxide for manganese oxide and other compounds (Sci. Adv. 2017, DOI: 10.1126/sciadv.1602427). The process works well because this solution has a high ionic conductivity, and the transition-metal salts are highly soluble in it.

“It’s exciting to see a new idea” for making batteries, says Yi Cui, a materials scientist at Stanford University, who was not involved with the work. “They make lithium metal oxides with excellent crystallinity, and that shows up in the battery materials they’ve made.”

Braun says the electroplated materials have higher energy densities than those of state-of-the-art batteries because of the purity—around 90%—of the lithium cobalt oxide or lithium manganese oxide. With no additives, the electroplated cathodes can store more energy in a given volume. And the process is compatible with unconventional electrodes, including flexible mats of carbon nanotubes.

The question is whether electroplating will work at manufacturing scales, says Sehee Lee, a materials scientist at the University of Colorado, Boulder. Typically, battery electrodes are made on large-volume, roll-to-roll systems that run 24 hours a day. “If they can do this electroplating process on a roll-to-roll system that would be interesting,” he says.

Xerion Advanced Battery Corp. is now developing the electroplated cathodes, Braun says. He thinks they will be most useful in portable electronics, possibly flexible ones for future smart watch bands or apparel.


CORRECTION: On May 17, 2017, this story was updated to correct the scale bar in the micrograph.

 
Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society
Comments
John Lithius (Wed May 17 21:08:52 EDT 2017)
There are two technical problems in this otherwise interesting story:

1. "The process starts by heating lithium and the transition metal of choice, such as cobalt, to 700–1000 °C to form an oxide powder. " Well, that might be really dangerous! Typically, lithium carbonate is used as the source of lithium, never lithium metal!

2. That "wasted" pore volume in the standard electrode has a very important function: the liquid electrolyte absorbed in the pores serves as an excellent medium in which lithium and other ions diffuse in and out, determining the power capability of the battery. Energy alone is not enough if you can power only a watch, and all-solid cathodes have had notoriously poor charge and discharge rate capability due to severe diffusion rate limitations in the solid state.
Paul Braun (Wed May 17 23:41:24 EDT 2017)
John,

1. You are correct that various compounds are used as precursors for LCO. What is stated here is simplified to keep the report concise.

2. As we report in the publication, the rate capability is quite good (comparable or better than commercial LCO cathodes). We suspect this is at least in part because the plating process still leaves a small volume fraction pores, and the pores have a low tortuosity.
John Lithius (Fri May 19 16:05:03 EDT 2017)
Re both responses to my comment #2: it would be interesting to see what are the experimentally determined Li diffusion coefficients in the two phases, the liquid and the solid. I believe the difference is more than 3 orders of magnitude. Comparing the density of the electrode by mercury (non-wetting, pores smaller than ~50 um are left unfilled) and helium pycnometry would resolve the issue, let alone GITT etc.

Another practical question: what's the smallest radius that such an electrode can be wrapped around without cracking and delamination? Some porosity would certainly help here.
SVETLANA MITROVSKI (Thu May 18 11:53:41 EDT 2017)
I would agree with the first comment, but not with the second. Yes, diffusion is faster along grain boundaries, so having a polycrystalline material rather than a single crystal would help speed up the diffusion.
The challenge is to make a polycrystalline material with lots of grain boundaries, but one without additives that are otherwise inert.
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