RPI researchers develop safe, long-cycling Li-metal rechargeable battery electrode; demonstrate Li-carbon battery
27 April 2014
Researchers at Rensselaer Polytechnic Institute have developed a safe, extended cycling lithium-metal electrode for rechargeable Li-ion batteries by entrapping lithium metal within a porous graphene network (Li-PGN). The graphene “cage” prevents dendritic growth, enabling extended cycling of the electrode.
In a paper in the journal Nature Communications, the team reported that the plating of lithium metal within the interior of the porous graphene structure results in very high specific capacities in excess of 850 mAh g-1. Extended testing for over 1,000 charge/discharge cycles indicates excellent reversibility and coulombic efficiencies above 99%. The RPI team also demonstrated the use of the PGN material as a high-capacity anode, and demonstrated a full-cell configuration with a PGN anode and a lithium-metal/PGN cathode, thus creating a Li-carbon rechargeable battery.
Background. Lithium metal has a very high theoretical capacity of 3,842 mAh g-1 in rechargeable lithium batteries; however, the use of metallic lithium leads to extensive dendritic growth that short circuits the battery, leading to serious safety hazards as well as truncated battery life.
The first practical lithium (Li) battery was developed as far back as 1976 by Exxon, using TiS2 as the anode and bare lithium metal as the cathode. However, soon after its inception the viability of such a cell composition was questioned owing primarily to the use of the lithium metal–liquid electrolyte combination. In a non-aqueous electrolyte, dendritic projections tend to develop at the lithium–electrolyte interface. The dendritic growth occurs during the charge/discharge cycling process, expanding in diameter and at the same time, extending from the tip.
The tip-wise extension poses a serious challenge as extended cycling can often cause the dendrite tip to pierce through the separator, resulting in an electrical short between the anode and cathode. Moreover, the tip-wise dendritic formation process is accelerated as the current density is increased (typically ≥0.1 C, where a rate of nC is defined as charge or discharge in 1/n hours), which is attributed to a higher localized charge density at the dendrite tip. This in turn significantly limits the rate capability of such batteries.—Mukherjee et al.
To get around that problem, industry replaced lithium metal with layered lithium metal oxide and phospho-olivine cathodes that offer safer performance over extended cycling, although with significantly reduced capacities.
The RPI work. The RPI team thermally shocked graphene oxide (GO) paper, creating pores—defects—in the material measuring between a few nanometers to a few hundred nanometers. When compared with graphitic anodes (commonly LiC6: capacity ~372 mAh g-1, energy density ~180 Wh kg-1), the resulting PGN delivers capacities of ~900 mAh g-1 with an energy density of ~547 Wh kg-1.
The reason why such a porous graphene anode delivers a capacity and energy density that is almost threefold higher than conventional graphitic anodes and stable over 1,000 charge/discharge cycles remains unclear. Some studies with graphene anodes have reported achieving a capacity higher than the theoretical capacity of graphite and have generally attributed it to the formation of Li2C6, corresponding to the intercalation of lithium ions on both sides of the graphene sheets. However, a detailed understanding of this phenomenon is fundamentally lacking at this point.—Mukherjee et al.
They then looked at the interaction of elemental lithium with such defect sites in the graphene. They found that lithium ions are strongly attracted to defect sites, which creates a very high local concentration of lithium near the defects. This initiates the formation, or “plating,” of metallic lithium at the defect sites.
Compared with conventional cathodes, the PGN structure with entrapped lithium metal provides capacities of ~850 mAh g-1, with an energy density of ~637 Wh kg-1. Extended testing for over 1,000 charge/discharge cycles indicates excellent reversibility and coulombic efficiencies above 99%. Even after 1,000 cycles there was no indication of any significant dendritic structures.
So why does this Li plating for PGN not result in the formation of dendrites? … Within the interior of the electrode, Li metal plating occurs within pores that are few tens of nanometres in size … As a consequence, any dendritic structures associated with this plating will tend to remain confined within these pores due to its size constraints. However, it is noteworthy that even the exterior (outer) surface of the PGN electrode did not show any significant dendritic growth even though there is no entrapment mechanism for Li that plates onto the exterior surface of the PGN.
To understand this, we investigated the thickness of the plated Li on the exterior surface of the PGN. Our estimate for the maximum Li film thickness that plates onto the external PGN surface is ~5.8 nm … The reason why this layer is so thin is that the exterior (outer) surface area of the PGN is very small when compared with the total surface area contained within the bulk of the porous PGN electrode.
In other words, the porous PGN serves as a sponge that absorbs the majority of the Li metal into the interior of the electrode structure. The recent study by Harry et al. shows that contrary to conventional wisdom dendrites are formed in the subsurface of Li foils, and not on the exterior surfaces as was previously thought. In fact, they found that the volume of the dendrite within the electrode is of the same order as the volume protruding into the electrolyte. For these reasons, the few-nanometre-thick Li film that plates onto the external surfaces of the PGN electrode will be unable to generate significant volumes of dendrites, which is consistent with our experimental observations.—Mukherjee et al.
To demonstrate the capabilities of PGNs, they assembled a full-cell with PGN anodes and lithiated PGN (Li-PGN) cathodes, stacked to provide an ampere-hour rating of ~20 mAh. Since exclusively carbon based materials are used for the electrode construction, the only active source of lithium in the full-cell is the lithium metal that is entrapped within the pores of the PGN cathode. They used the pouch cell to power an LED device.
It should be noted that the full-cell (with PGN electrodes) … operates on the well-established principle of transfer of Li ions back and forth between the cathode and anode material. In this regard this concept is no different from a conventional Li-ion battery. What is different is that the electrode material that stores the Li is all-carbon for both the anode as well as the cathode. Therefore the electrodes in our Li-ion full-cell configuration are exclusively made from carbon (PGN) materials into which Li ions are reversibly plated and stored.—Mukherjee et al.
Along with Koratkar, co-authors of the paper are: graduate students Rahul Mukherjee, Abhay Thomas, and Eklavya Singh, and visiting scientist Osman Eksik, of the Rensselaer Department of Mechanical, Aerospace, and Nuclear Engineering; graduate student Dibakar Datta of Brown University; and postdoctoral scientist Junwen Li and Professor Vivek Shenoy of the University of Pennsylvania.
Koratkar’s graduate student and first author of the paper, Mukherjee, was a finalist in the 2014 MIT-Lemelson National Collegiate Student Prize Competition in the graduate student category and presented his research at the Massachusetts Institute of Technology earlier this month. With fellow student Eklavya Singh, Mukherjee won the “best of the best” grand prize at the spring 2014 Change the World Challenge competition at Rensselaer.
This research was supported by the National Science Foundation, as well as the John A. Clark and Edward T. Crossan Professorship at Rensselaer, and a Bob Buhrmaster ’69 grant from the Severino Center for Technological Entrepreneurship and Lally School of Management at Rensselaer.
Rahul Mukherjee, Abhay V. Thomas, Dibakar Datta, Eklavya Singh, Junwen Li, Osman Eksik, Vivek B. Shenoy & Nikhil Koratkar (2014) “Defect-induced plating of lithium metal within porous graphene networks,” Nature Communications 5, Article number: 3710 doi: 10.1038/ncomms4710
This is one more demonstration that graphene sheet can be used to improve performance of Li-Carbon and other Lithium rechargeable batteries by about 3X and more.
How long will it take for the process to be mass produced?
Is six years or by 2020 or so enough for a few major battery producers to do it? Will patent legal battles be used to stop mass production?
Posted by: HarveyD | 27 April 2014 at 07:15 AM
I've been one of the early supporters on here for full BEVs and hoping for a breakthrough to make them reality for most of us. But I've also become one of the most cynical skeptics over the years. Not sure why, but this one feels real to me and makes me think it could be a big player in that next step to useful, next gen batteries.
Posted by: DaveD | 27 April 2014 at 09:51 AM
There are just too many applications which need/want improved batteries and too much R&D flowing to them to keep them from being developed. The cells in the Tesla battery aren't the product of automotive development, but for powering laptops.
The patent trick worked to keep prismatic NiMH cells out of electric cars, but I think that was a one-time trick. With peak oil in the rear-view mirror and the oil companies pulling back upstream investment, there's not much reason to try it again anyway; they'll still be able to sell everything they can pump.
Posted by: Engineer-Poet | 27 April 2014 at 10:55 AM
There is no reasons to celebrate, this is full of drawbacks and still problematic. There will never be something like mass adoption of battery electric vehicles whatsoever. Instead I said many time to start nat gas vehicle nationwide for small cars, and also big trucks now. Also for even less pollution and cost start fuelcell vehicles commercialization with the hydrogen been made with water electrolysis at the point of sale. These batteries are a flagrant flop both commercially and technologically, people do not LIKE to plug and with a short range, a fast recharger network is impossible period due to long recharging time with too many different norm like chademo, sae and tesla supercharger. Tesla will go bankrupt one day or another. Stop harassing me with deficient battery breakthrus, there will never be with all the deceiving researchs been done paid by fraudulent tax subsidies.
There is sufficient low polluting natural gas for all the transport vehicles for more than 100 years, this is cheaper and less polluting than liquid gasoline. Wesport innovation engines are ready to be mass produced for all the world. Im following their stock on the stock market and im about to buy as soon as it start. I noticed that the bankrupt government never give subsidies toward nat gas but give ton of subsidies toward limp batteries for researchs and for commercialization, this is a dramatic mistake impeding real progress for cheap efficient low polluting transport.
Posted by: gorr | 27 April 2014 at 11:15 AM
Gor, my friend, I still disagree with you on BEVs. I think they are inevitable....it's just whether it's ten years or fifteen. My opinion.
Posted by: DaveD | 27 April 2014 at 11:28 AM
Gor, aside from the obvious nonsense you are spewing about BEVs:
Why on Earth do you think the natgas is any better as a long-term transportation fuel solution than oil/gas itself?
It burns cleaner but that's about it. It is lower-polluting than gas but it is nowhere compared to batteries charged with renewable generators. Not even in sight.
Here in the EU, you cannot even go into a closed-air garage with a natgas vehicle which in itself is a nonstarter for a lot of people.
Natgas is extremely expensive here in the EU and since it is coming from the Russians it is a big strain on the economies of natgas-dependent countries. Fracking is mostly not possible here, and it already being banned by the most advanced/responsible countries (e.g.: France). Bio-natgas is as expensive as fossil nat-gas and it is not obvious how it will get drastically cheaper as it requires fairly complex machinery and supply chain.
Fossil natgas is a non-starter anyways since it is a greenhouse gas. You have to be some GW-denialist fool to even consider it as anything more than a transitional fuel until batteries, fual-cells and possibly bio-natgas gets cheap enough.
Posted by: sola | 27 April 2014 at 11:52 AM
Wow. Batteries with 3X capacity, very long lasting, made only of carbon and lithium. Game changer if it pans out.
Posted by: Nick Lyons | 27 April 2014 at 12:12 PM
Fossil NG burns about 25% cleaner than coal in large power plants. In ground vehicles it probably does much worse due to other power train and ICE losses.
BEVs and FCEVs are probably the best final solutions for cars and heavy vehicles. Both technologies have pros and cons but are better and cleaner than gas, diesel and NG.
HEVs and PHEVs are good interim solutions but will be obsolete by 2020-2030.
Posted by: HarveyD | 27 April 2014 at 01:01 PM
Posted by: Zhukova | 27 April 2014 at 07:27 PM
I think gor's personal frustration with his situation is coming out. It's no indication of anything in the technology.
Posted by: Engineer-Poet | 27 April 2014 at 08:14 PM
FOR MOST COUNTRIES THERE IS NO OTHER OPTION EXCEPT ELECTRIC AND PLUG IN VEHICLES BASED ON SOLAR CHARGERS. INDIA CAN NEVER HAVE ABOUT 400 MT OF OIL EVERY YEAR.THERE WILL BE TOO MUCH POLLUTION AND WE CAN NEVER AFFORD SUCH LEVEL OF IMPORTS. VEHICLES LIKE TOYOTO I ROADS ARE THE SOLUTION.
Posted by: Nirmalkumar | 28 April 2014 at 12:41 AM
A little late into the forum but quite happy to see our paper being featured in the discussion! Just to clarify a couple of points...
>> How long will it take for the process to be mass produced?
HarveyD (and others who have this question), I am not completely sure of that myself but I can say we have covered at least 60% of the journey. Scaling a nano-material to power an actual device is unimaginably challenging. The electrodes when I first started out had a mass loading of 0.05 mg/cm2 (3 years back), now they are at 3 mg/cm2... The goal here is at least 5 mg/cm2 so yeah, we are getting there slowly but surely. The exact time? Well, some days I wake up and think, "Yeah 2018 it is" and on other days I just go "Well, hopefully by 2020"!
How expensive would it be? We do eliminate cobalt, aluminum, nickel and the whole copper current collector alright but we do use graphite oxide... Today, you don't get graphite oxide in bulk qualities like you get graphite. To make a million batteries with the resources that are there today, I wouldn't be too happy with the pricing of our technology at this stage. But then again, this is true for any new technology and it then depends on economies of scale to bring down the prices.
Gor, I am not sure what makes you think an all-battery EV is not feasible. If you think there are commercial/economic/infrastructure-based challenges to implementation, yes of course there are and no one's denying that. It is still early stage after all (you may want to read about Tesla's coast-to-coast charging stations to get an idea of what the industry is doing to address those gaps). But if you think there is a fundamental flaw in the technology, feel free to ask me and I will try my best to give a non-biased response.
Posted by: Rahul | 29 April 2014 at 11:28 PM
Tks Rahul for the added information.
If graphite oxide is too costly, could another material be used?
Future extended range BEV batteries must be affordable, long lasting, quick charging and capable of 600+ Wh/Kg.
Posted by: HarveyD | 30 April 2014 at 02:01 PM
Out of 8 listed scientists/inventors, judging by names, 6 are from India, one from Turkey (Osman Eksik), one from China (Junwen Li).
It has become more rule than exception that foreign graduates form over 60% of listed scientists, at least in articles here at GCC.
Perhaps this battery could be called "Indian battery".
All licencing fees would probably go to US based Rensselaer Polytechnic Institute. How fair is that?
Posted by: Alex_C | 30 April 2014 at 08:06 PM
HarveyD, graphite oxide is costly because graphite manufacturers/suppliers do not produce graphite oxide in bulk quantities yet (there is not much demand apart from R&D as of now). It's a similar trend that you would see in IC devices for example, starting from 1980s to present day... the price declines as the demand goes up and there are more and more manufacturers moving in to increase through-put. Having said that, to answer your exact question, "could another material be used?", the answer is probably not if we are targeting an all-carbon battery capable of an energy density of 600+ Wh/kg and a power density of 30 kW/kg (by the way, that's the power density we can achieve... didn't find it mentioned in this article... it was actually an earlier study by our group that came out in 2012). Keeping the composition constrained to carbon will possibly be the key to substantially reducing the cost when the tech is finally commercialized.
Posted by: Rahul | 01 May 2014 at 06:32 AM
Hope that this technology can be comercialized by 2020 or even before.
Wish you the very best to finalize development and start mass production as soon as possible.
Tesla (and many others) would certainly be an interested large customers.
Posted by: HarveyD | 01 May 2014 at 08:58 AM
@Rahul, Thanks so much for taking the time to join in and answer a few questions! It's always good to see someone on the inside get involved with real information vs. our fun speculating LOL
I'm glad you mentioned the power density. 30kW/kg is outstanding, but with the cycle life you're achieving I suspected it would be pretty high...just not that great.
Good luck in your work.
Posted by: DaveD | 01 May 2014 at 07:04 PM
30 kW/kg is great! I keep waiting for Li-Air battery to be perfected, but they seem to be plagued by low current density. So you need a 400 kg battery to get 100 hp, but 1,200 mile range.
RPI's 600 wh/kg and 30kw/kg in a 100 kg battery would allow a BEV with about 250 miles range and 4000 hp!
Posted by: Zhukova | 02 May 2014 at 01:35 PM
"The first practical lithium (Li) battery was developed as far back as 1976 by Exxon, using TiS2 as the anode and bare lithium metal as the cathode. "
The original research (http://www.sciencemag.org/content/192/4244/1126.full.pdf , http://authors.library.caltech.edu/5456/1/hrst.mit.edu/hrs/materials/public/Whittingham/Whit_publs/Whit_Science_1974.htm) talked about TiS2 cathode and bare Lithium anode.
Posted by: jumpjack | 07 May 2014 at 02:57 AM