Janus Graphene Could 10X the Energy Capacity of Sodium-ion Batteries

Sodium batteries could become much cheaper than lithium-ion batteries but sodium-ion batteries capacity has been too low.

“We have added a molecule spacer on one side of the graphene layer. When the layers are stacked together, the molecule creates larger space between graphene sheets and provides an interaction point, which leads to a significantly higher capacity,” says researcher Jinhua Sun at the Department of Industrial and Materials Science at Chalmers and first author of the scientific paper, published in Science Advances.

Ten times the energy capacity of standard graphite

Typically, the capacity of sodium intercalation in standard graphite is about 35 milliampere hours per gram (mA h g-1). This is less than one tenth of the capacity for lithium-ion intercalation in graphite. With the novel graphene the specific capacity for sodium ions is 332 milliampere hours per gram. the energy capacity boost gets sodium batteries near the capacity of lithium in graphite. The results also showed full reversibility and high cycling stability.

Science Advances, “Real-time imaging of Na+ reversible intercalation in “Janus” graphene stacks for battery applications” written by Jinhua Sun, Matthew Sadd, Philip Edenborg, Henrik Grönbeck, Peter H. Thiesen, Zhenyuan Xia, Vanesa Quintano, Ren Qiu, Aleksandar Matic and Vincenzo Palermo.

Abstract
Sodium, in contrast to other metals, cannot intercalate in graphite, hindering the use of this cheap, abundant element in rechargeable batteries. Here, we report a nanometric graphite-like anode for Na+ storage, formed by stacked graphene sheets functionalized only on one side, termed Janus graphene. The asymmetric functionalization allows reversible intercalation of Na+, as monitored by operando Raman spectroelectrochemistry and visualized by imaging ellipsometry. Our Janus graphene has uniform pore size, controllable functionalization density, and few edges; it can store Na+ differently from graphite and stacked graphene. Density functional theory calculations demonstrate that Na+ preferably rests close to -NH2 group forming synergic ionic bonds to graphene, making the interaction process energetically favorable. The estimated sodium storage up to C6.9Na is comparable to graphite for standard lithium ion batteries. Given such encouraging Na+ reversible intercalation behavior, our approach provides a way to design carbon-based materials for sodium ion batteries.

SOURCES- Science Advances, Chalmers
Written By Brian Wang, Nextbigfuture.com

12 thoughts on “Janus Graphene Could 10X the Energy Capacity of Sodium-ion Batteries”

  1. Of course, I would like graphene to become much cheaper, but it has a long way until it can compete with graphite. Graphite ranges from 1 USD to 20 USD (medium flake to battery grade flake) per kg. So graphene would have to fall by a factor of 8 before it would be on par with the most expensive graphite

    Also, the most common method to make graphene starts with graphite, which makes it unlikely that graphene will ever reach price parity with graphite.

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  2. True, until the cost of producing graphene drops due to the economies of scale.
    Li is sometimes hard to acquire. Graphene is modified C, and Na is abundant. The raw inputs are rather cheap. Today the cost of producing graphene is high but that could change if they produce a winning battery.
    Usually a good start would be using the new formula for space missions, where the need for dependability outweighs the cost of the product. Then go from there.

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  3. The suggested graphene-sodium anode would be much, much, more expensive than todays battery anodes..

    There is about 0.8 kg of graphite in one kWh of lithium battery today. If this sodium anode has the same energy density – roughly claimed above – then you also need about 0.8 kg of graphene per kWh of battery. One kg of graphene – when bought in bulk – costs about 200 USD. So, using graphene in the above suggested anode would contribute a cost of 160 USD per kWh, which is more than the cost of a complete 1 kWh battery today…

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  4. Not the bulk lithium. Lithium costs about 16 USD per kilo, and there is about 370 g of lithium in 1 kWh, i.e. about 6 USD per kWh. Which would be about 6% of the battery price.

    Of course, one does not use bulk lithium, but rather highly purified lithium hydroxide which makes the anode material more expensive. But presumably, one would not use bulk sodium either, but some purified chemical compound of it so you would get the additional cost of purifying the sodium compound as well. I.e. the cost advantage of sodium must be minuscule at today's battery prices…

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  5. Surprisingly high percentage, actually. Over 25%. Might not sound like much changing that, but when a single car might take what, 80 cells per kilowatt hour, and need maybe 70 kWh or 5,000+ cells all told, a few percents is a big deal.

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  6. That’s what is usually comes down to. Which chemistry does the money want to bet on to bring a technology like this to market? Because it always takes a lot.

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  7. They're going to mess with so many chemistries and configurations in the next few years it'll make your head spin. The winning bet is deciding upon which one everyone eventually goes for.

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