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New approach to high power energy storage devices: graphene surface-enabled Li ion-exchanging cells

Jang2
The Ragone plots of graphene surface-enabled Li ion-exchanging cells with different electrode thicknesses. Credit: ACS, Jang et al. Click to enlarge.

A team from Nanotek Instruments and Angstrom Materials reports on a new strategy for the design of high-power and high energy-density devices based on the massive exchange of lithium ions between surfaces (not the bulk) of two nanostructured electrodes. This approach obviates the need for lithium intercalation or deintercalation—the basic process used in Li-ion batteries.

In a paper published in the ACS journal Nano Letters, the team reports that such surface-enabled, lithium ion-exchanging cells—based on unoptimized materials and configuration—are already capable of storing an energy density of 160 Wh/kgcell, which is some 30 times higher than that (5 Wh/kgcell) of conventional symmetric supercapacitors and comparable to that of Li-ion batteries. They are also capable of delivering a power density of 100 kW/kgcell, which is 10 times higher than that (10 kW/kgcell) of supercapacitors and 100 times higher than that (1 kW/kgcell) of Li-ion batteries.

In both electrodes, massive graphene surfaces in direct contact with liquid electrolyte are capable of rapidly and reversibly capturing lithium ions through surface adsorption and/or surface redox reaction.

Both the cathode and the anode are porous, having large amounts of graphene surfaces in direct contact with liquid electrolyte, thereby enabling fast and direct surface adsorption of lithium ions and/or surface functional group-lithium interaction, and obviating the need for intercalation. When the cell is made, particles or foil of lithium metal are implemented at the anode [upper portion of figure below] which are ionized during the first discharge cycle, supplying a large amount of lithium ions.

These ions migrate to the nanostructured cathode through liquid electrolyte, entering the pores and reaching the surfaces in the interior of the cathode without having to undergo solid-state intercalation. [lower left in diagram below] When the cell is recharged, a massive flux of lithium ions are quickly released from the large amount of cathode surface, migrating into the anode zone. The large surface area of the nanostructured anode enable concurrent and high-rate deposition of lithium ions [lower right in diagram below] re-establishing an electrochemical potential difference between the lithium-decorated anode and the cathode.

—Jang et al.

Jang1
Top shows the structure of a fully surface-enabled, Li ion-exchanging cell containing an anode current collector and a nanostructured material at the anode; a Li ion source (e.g., pieces of Li foil or surface-stabilized Li powder); a porous separator; liquid electrolyte; and a nanostructured functional material at the cathode. The lower left portion shows the structure of this cell after its first discharge (Li is ionized with the Li ions diffusing through liquid electrolyte to reach surface-borne functional groups in the nanostructured cathode and rapidly reacting with these groups). Lower right portion shows the structure of this cell after being recharged (Li ions are rapidly released from the massive cathode surface, diffusing through liquid electrolyte to reach the anode side, where the huge surface areas can serve as a supporting substrate onto which massive amounts of Li ions can electrodeposit concurrently.
Credit: ACS, Jang et al. Click diagram to enlarge.

The team prepared both oxidized and reduced single-layer and multilayer graphene from natural graphite (N), petroleum pitch-derived artificial graphite (M), micrometer-scaled graphite fibers (C), exfoliated graphite (G or EG), AC, carbon black (CB), and chemically treated carbon black (t-CB). They then constructed coin-size cells to test these nanostructured carbon materials. Electrodes were prepared with 85% active material, 5% conductive additive, and 10% binder.

Among their observations were:

  • For the fully surface-mediated cells, the electrode thickness is a dominating factor. In the case of using functionalized NGP as the electrodes, the total migration time of Li ions in liquid electrolyte is 1.27 s if the cathode and anode are each 200 μm thick and separator is 100 μm thick. The migration time is reduced to 0.318 s if the anode = cathode thickness = 100 μm and separator thickness = 50 μm.

  • The surface-enabled cells should have an extraordinary power density, particularly when the electrodes are ultrathin. The power densities observed with graphene-enabled, fully surface-mediated cells are comparable or slightly superior to those of LBL f-CNT-based batteries (thickness of 3 μm) at comparable current densities.

...the surface-enabled cells are a class of energy storage cells by itself, distinct from both supercapacitors and lithium-ion batteries. More work is needed to more clearly differentiate the dominant lithium-storage mechanism(s) between surface redox, surface adsorption, and surface defect trapping.

—Jang et al.

Resources

  • Bor Z. Jang, Chenguang Liu, David Neff, Zhenning Yu, Ming C. Wang, Wei Xiong, Aruna Zhamu (2011) Graphene Surface-Enabled Lithium Ion-Exchanging Cells: Next-Generation High-Power Energy Storage Devices. Nano Letters Article ASAP doi: 10.1021/nl201849

Comments

HarveyD

If this can ever be turned into a long lasting affordable battery, it could be charged/discharged almost as quickly as the energy conductor can manage. It could also be ideal as a grid voltage regulator.

Engineer-Poet

This is what EEstor promised and failed to deliver.

The batacitor lives!

HarveyD

Yes....the line is getting thinner between super caps and very quick charge/discharge batteries.

However, this on may be as far away from the market place as ESStor.

It wouldn't be the first time that a wonder product failed to materialize all the way to mass market.

HarveyD

correction......(should read) However, this ONE may......

Treehugger

in contrast with EESTOR, their claims are supported by facts that can be reviewed by the scientific community , not by mystery...all this is brilliant but very very futuristic

clett

This is soooo what Formula 1 is going to use.

Zhukova

The high power Titanium Li-Ion batteries from Altairnano only have about 50 Wh/kg.

DaveD

This is based on very practical principals. This is the first time I've seen a true breakthrough that screams: REALITY.

soltesza

Sorry guys, but as far as I understand, this is not even similar to the thing EESTOR is/was developing.

They never had to do anything with lithium particles.

They claimed to have found a solution for an extremely energy dense capacitor by allegedly finding material which avoids voltage breakdown at extreme energy capacities/voltage.

DaveD

This is NOTHING like the EESTOR crap. EESTOR was claiming to have a magic way to get around the phyics of voltage breakdown at the granular level of barium titanate at high voltage and current. In other words, the current couldn't flow across the boundary of the different grains of the powder. So if you were willing to live with a battery the size of a grain of pollen...you'd have one hell of a capacitor. :-)

People have known of this problem in reality vs. the theory for decades. EESTOR claimed to have a magic way to get around this problem but they couldn't tell you how...or they'd have to kill you. And they couldn't demonstrate it or even provide a sample device to show investors....because then they'd have to kill them too LOL

What these guys at Nanotek are talking about is disclosed for others to duplicate and it very similar to say using lead foam to increase the surface area and hence the power and energy density compared to traditional lead-acid batteries.

Now that you see it, it's one of those things where you slap yourself in the forehead and go: "duh, why didn't I think of that".

Engineer-Poet

Forget the mechanism. If you treat the two things as black boxes, the similarity in energy density and charge rate is eerie.

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