## Photothermally reduced graphene papers as high-rate capable Li-ion anode material

##### 23 August 2012
 Ragone plot showing the energy density and power density of photothermally reduced graphene. For comparison, activated carbon control has also been plotted. Although activated carbon lies well within the Li-ion battery region for lower C rates (1 C), its performance drastically reduces at higher power rates. Credit: ACS, Mukherjee et al. Click to enlarge.

Researchers at Rensselaer Polytechnic Institute led by Nikhil Koratkar reported the use of photoflash- and laser-reduced free-standing graphene papers as high-rate capable anodes for lithium-ion batteries in a paper published in the journal ACS Nano.

Photothermal reduction of graphene oxide—by photoflash or laser—results in an expanded structure with micrometer-scale pores, cracks, and intersheet voids. This open-pore structure enables access to the underlying sheets of graphene for lithium ions and facilitates efficient intercalation kinetics even at ultrafast charge/discharge rates of >100 C, they reported. The photothermally reduced graphene anodes are also structurally robust and display outstanding stability and cycling ability. At charge/discharge rates of 40 C, the anodes delivered a steady capacity of 156 mAh/ganode continuously over 1,000 charge/discharge cycles, providing a stable power density of 10 kW/kganode.

In addition, the team suggests that such electrodes could be mass scalable with relatively simple and low-cost fabrication procedures, thereby providing a clear pathway toward commercialization.

Although standard Li-ion batteries can provide very high energy densities, they are unable to provide high power densities, the authors note. A lithium-ion battery provides capacities through lithium intercalation with an active electrode material; its high-rate performance is thus largely governed by Li+ diffusivity and electron conductivity.

It should be noted that achieving high capacities at elevated C rates is particularly challenging since the time available for lithium ions to diffuse through the anode and intercalate is now significantly shorter. As a result, only a partial lithiation is achieved, if at all, and the capacities are often very low. Another limitation with ultrahigh charge/discharge rates is the electron transfer mechanism. The electron conductivity of the anode material directly influences the charge transfer mechanism and thus largely governs the achievable C rates. Finally, a high surface area is desirable for operating at high rates since it is of prime importance that the lithium ions have sufficient active sites for intercalation to make up for the diffusivity constraints.

...Here we describe the photothermal reduction of free-standing graphene oxide paper to obtain graphene anodes with a unique “open-pore” structure. The energy from a camera flash or laser causes instantaneous and extensive heating of graphene oxide and induces a deoxygenation reaction. We show that this rapid outgassing creates microscale pores, cracks, and voids in graphene paper, which enhances lithium intercalation kinetics at ultrafast charge/discharge rates. We attribute this to better ion diffusivity, greater access to the underlying graphene sheets through the micropores, and improved electrolyte wetting of the electrode.

—Mukherjee et al.

They found a stable capacity at 5 C of of ∼370 mAh/g, which is the highest capacity reported at 5 C for a pure carbon anode (without any additives) in a Li-ion cell. The capacity drops with increasing C rate, but the electrode is still capable of delivering ∼156 mAh/g at 40 C and ∼100 mAh/g at 100 C.

...these are by far the highest capacities reported so far for pure carbon-based anodes (without additives) at 40 and 100 C and are an order of magnitude higher than conventional graphitic anodes. Most importantly, these capacities were highly stable and could be maintained for over a thousand cycles of continuous high-rate charge/discharge. While laser-scribed graphene has recently been demonstrated in an electrochemical capacitor, to our knowledge, this is the first demonstration of photoreduced graphene electrodes in lithium-ion batteries.

—Mukherjee et al.

Along with Koratkar, co-authors of the paper are Rensselaer graduate students Rahul Mukherjee, Abhay Varghese Thomas, and Ajay Krishnamurthy, all of the Department of Mechanical, Aerospace, and Nuclear Engineering (MANE).

The study was funded by the National Science Foundation, and supported by Koratkar’s John A. Clark and Edward T.Crossan Endowed Chair Professorship at Rensselaer.

Koratkar is a professor in MANE and the Department of Materials Science and Engineering at Rensselaer. He is also a faculty member of the university’s Center for Future Energy Systems and the Rensselaer Nanotechnology Center.

Resources

• Rahul Mukherjee, Abhay Varghese Thomas, Ajay Krishnamurthy, and Nikhil Koratkar (2012) Photothermally Reduced Graphene as High-Power Anodes for Lithium-Ion Batteries. ACS Nano doi: 10.1021/nn303145j

"In addition, the team suggests that such electrodes could be mass scalable with relatively simple and low-cost fabrication procedures, thereby providing a clear pathway toward commercialization."

This article implies switching anodes in a battery. How many years should this take? In real time, in battery years?

Kelly,

That depends. How will I, as the researcher, get paid for this. Is everything (IP I create) owned by my employer? If so, supply me, please, with motivation. Oh, you'll let me keep my job. Why, how considerate. How will you know that I am trying to actually solve the problem? I see MBAs as managers that can't make a technical determination. I'll just say the ten magic mumbo jumbo words, nod at the marketing director and say "That's a really good idea, sir", and they'll all get a warm and fuzzy feeling. Thus I stretch out my career and never really give up what has value. If I solve the problem in six months it could be determined that they no longer need me. And what have I done? Made the MBAs successful and gotten myself unemployed. It's not a simple process to change the carbon in a batteries, this will take years of effort and product testing. I think we actually need to step back and try and understand the basics. We don't really have a good fundamental understanding of the phenomena.

Did B4 just confirmed that R & D + mass production will continue to move (at an accelerated rate) to countries with different work ethics, higher morality and better attitude. Those countries may very be China, South Korea, Japan, India, etc?

When developed, this technology may very well produce the improved very quick charge/discharge batteries required for extended range BEVs. Their very quick charge/discharge capabilities will also make them very good candidates for improved HEVs and PHEVs.

More good reasons why R & D and mass production will continue to move to other countries.

BrotherKenny,

This is why a small company needs to be spun off from RPI with the license to do this research and the geeks need to have some share in the company ownership, even if small.
One percent of a small company that grows to a multi-billion doller jackpot still makes the geeks happy.
:-)

" I think we actually need to step back and try and understand the basics. We don't really have a good fundamental understanding of the phenomena."

PLEASE, 150 years since the first 3 component, no moving parts, storage battery and we still don't know how to replace one of the three components - even if it's part of a decades commercialized lithium-ion battery - without years of per-commercialization?

How the h$%l do billion transistor chips get built? B4 nailed it, that is exactly what has and IS now happening. Those engineers will not be able to get the venture capital either, unless the capitalists own it all in the end. The university study was Fed-funded, so we are "the capitalists [who] own it all in the end." I'd be curious as to an estimate of how long it might take to bring this technology to market. A lot of University research ends up in the hands of private parties. This is part of using public funds to leverage private profits. It's a matter of replacing one form of carbon anode with another. Aside from issues with diffusion rates through the separator, it should be close to a drop-in replacement. However, your 100C-capable anode needs a 100C-capable cathode. Maybe carbonized lithium manganese oxide would do. I'll estimate a long time. Pardon the bad link above, here's the correct one. BOTE here: at 100 mAh/g at 100C, the anode is good for about 10 kA/kg or ~36 kW/kg. If you can get about the same out of the cathode, and the cathode and anode comprise 50% of the weight of the cell, you get 9 kW/kg net. 11 kg of battery would yield roughly 100 kW of peak power, though storing just 1 kWh. That's enough for some pretty impressive hybrid performance in dynamic braking and acceleration; it would totally transform the auto industry. "....though storing just 1 kWh" EP, I'd KILL for that spec :-) EP, Oh, sorry...I mis-read your post. You're saying it would store only 1kWh per 11kg, NOT 1kWh/kg? Yeah, that is pretty low and this would be much better suited to a hybrid battery. The capacity rises substantially as the current goes down, but I was looking more for "batacitor" applications because that's where the greatest fuel savings per unit of battery are achieved. Yes, the $B in public money given for R % D often ends up in the hands of the 1% to 3% to further increase their wealth. It is ridiculous to use borrowed $$B or$$$B from the 97% to further enrich the 1% to 3%. There must be better ways to do it and/or to equally enrich the 97%? How can the 97% collectively get a good return on their investments/taxes. Couldn't governments loan seed  at a fair interest rate and get convertible preferred shares instead of giving away$1T/year in subsidies, grants, tax breaks, tax credits, hand outs etc? Why governments could not become investors like pension funds and make money at the same time?

The $1T/year saved could repay the national debt in less than 20 years. It all seems to make so much sense but who would pay (black and/or white ) for elections? A new law would be needed to limit election expenditures to a total of$10 per elector or vote or so. Treasury could pay most of it. Very low (under $100) individual contributions could be tolerated but the$10/voter expenditures limit should be respected/imposed.

Something has to change. Otherwise, our democracy style will keep on deteriorating and inequalities will keep growing. The 1% will have an absolute control on politics, laws, economy, education, health care, justice and the general well and not so well being of the nation. We will be back to the 12th century's Lords and Kings with absolute powers. We are getting there at an accelerated rate.

HarvyD....are you saying that rich people are hijacking democracy?!!! Say it aint so!

So free-market capitalism is fundamentally anti-democratic....I've said that all along.

aser—results in an expanded structure with micrometer-scale pores, cracks, and intersheet voids. This open-pore structure enables access to the underlying sheets of graphene for lithium ions and facilitates efficient user

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