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Berkeley Lab team develops high-performance lithium sulfide-carbon composite cathode materials for high-energy batteries targeting EVs

4 December 2012

Cai
Estimated cell specific energy plot (including all components except the cell housing) as a function of the specific capacity based on S and the S content of the electrode. Data reported in prior studies are marked by blue squares for comparison purposes; the data of the Berkeley Lab work are indicated by the red star. Credit: ACS, Cai et al. Click to enlarge.

Researchers from Lawrence Berkeley National Laboratory (Berkeley Lab) have developed nanostructured lithium sulfide/carbon (Li2S–C) composite cathodes that show promise for use in high-energy batteries. The paper on their work, published in the ACS journal Nano Letters, follows shortly after an earlier report from a Stanford team led by Yi Cui on another approach to using lithium-sulfide materials to build rechargeable batteries with specific energies of about 4 times that of current technology and approaching those of lithium-sulfur (LiS) systems, while avoiding some of the issues with those systems. (Earlier post.)

The Berkeley Lab team reported that, with a very high specific capacity of 1144 mA·h·g–1 (98% of the theoretical value) obtained at a high Li2S content (67.5 wt %), the estimated specific energy of a cell using the nanostructured composite was 610 W·h·kg–1—the highest demonstrated so far for lithium-sulfide cells. The cells also maintained good rate capability and improved cycle life.

Newly emerging technologies such as electric vehicles (EV) and advanced portable electronics are placing a strong and urgent demand on the next generation of rechargeable batteries with high specific energy. Current lithium-ion cells with oxide-based cathodes, such as LiCoO2 and LiMn2O4, have theoretical specific energies of approximately 430−570 W·h·kg−1, but their practical (or obtainable) specific energies are only in the range of 120−200 W·h·kg−1, which is insufficient for long EV driving ranges (i.e., >300 km). In this regard, the lithium/sulfur cell is considered to be a potential candidate to replace current lithium-ion cells because its theoretical specific energy and volumetric energy density are estimated to be 2600 W·h·kg−1 and 2800 W·h·L−1, respectively, based on the electrochemical reaction 16Li + S8 = 8Li2S. Additionally, the abundant availability and low price of sulfur offer the opportunity for a significant cost reduction.

However, the insulating nature of sulfur, dissolution and shuttling of lithium polysulfides during cycling, and their high reactivity with the lithium metal anode, together with significant volume change, are currently preventing the use of this promising system in practical applications.

Recently, the lithium sulfide (Li2S) cathode, with a theoretical capacity of 1166 mA·h·g−1, has received much attention due to the potential to use non-lithium anodes; other high-capacity anode materials (e.g., silicon or tin-based compounds which can form alloys with lithium) can be used as negative electrodes with improved safety. To resolve the insulating problem of Li2S that prevents the achievement of high utilization (or high capacity), various efforts have been made to improve the contact between Li2S and electronic conductive additives such as carbon and metals.

...Despite these efforts, a relatively high capacity could only be obtained when the Li2S content is lower than 50 wt %, while higher Li2S contents often resulted in very low discharge capacity (i.e., only ∼200 mA·h·g−1 at 76.8 wt %). To meet the rigorous requirements of high specific energy for EV applications, we need to dramatically increase the loading of Li2S while maintaining good electrochemical utilization and good cycle life.

—Cai et al.

Cai2
Cycling performance of Li2S−C composite electrodes. The capacity is normalized both by the weight of Li2S and sulfur. The average loading of the electrodes is 0.794 mg·cm−2, which corresponds to 0.54 mg·cm−2 of Li2S. Credit; ACS, Cai et al. Click to enlarge.

The Berkeley team devised a cost-effective way of preparing nanostructured Li2S-carbon composite cathodes via the high-energy dry ball milling of commercially available micrometer-sized Li2S powder together with carbon additives. This overcame the difficulties in efficiently converting lithium sulfide to sulfur due to the particle size of commercial Li2S powder (between 10 and 30 μm) and its insulating nature.

After high-energy dry ball milling for 2 h, the size of Li2S particles was reduced to about 200−500 nm with some agglomeration, while carbon black was found to be uniformly dispersed and deposited onto the surface of these smaller Li2S particles. The smaller dimensions can effectively reduce the distance that Li-ions and electrons must travel during cycling in the solid state.

They then used a simple but effective electrochemical activation processto significantly improve the utilization and reversibility of the Li2S–C electrodes, which was confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. They further improved the cycling stability of the Li2S–C electrodes by adding multi-walled carbon nanotubes (MWCNT) to the nanocomposites.

With the highest specific energy (∼610 W·h·kg−1) demonstrated in this report, and with further improvement in capacity retention, this Li2S−C nanocomposite electrode may offer a significant opportunity to go beyond traditional Li-ion cells toward the development of rechargeable batteries with much higher specific energy.

—Cai et al.

Resources

  • Kunpeng Cai, Min-Kyu Song, Elton J. Cairns, and Yuegang Zhang (2012) Nanostructured Li2S–C Composites as Cathode Material for High-Energy Lithium/Sulfur Batteries. Nano Letters doi: 10.1021/nl303965a

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Comments

Pouch it, sell it, let the public if it is high performance.

One more potential improved technology for future higher performance batteries for extended range EVs.

Who is going to be the first to mass produce (660+ Wh/Kg) affordable battery units?

We already have something better then this, it's called hydrogen fuelcell.

Even if they were able to build a 4x battery, there will be still the problem of fast recharging it while travelling. Actually there is few fast chargers, fast chargers cost a lot of money, there is 4 different incompatible fast recharging norms, there is many bev that don't have a fast charging port.

I said many time to begin commercialisation of technology that already work without furtur researchs.

If they get 400-600 Watt hours per kilogram, then EVs can be 150 mile range at $25,000. People will rethink what they use cars for most of the time.

My concern with fuel cells is that it may have a distribution model much closer to that of gasoline, with no opportunities to move to a lower fuel when prices get high. At least the electricity distribution model seems to end up with a more reasonable and consistent price for fuel. Not perfect, but better.

I'm enamored with electric technology and it's capabilities. But, for once I'd like to see fewer promises and more results.

We've been fed this line before...For years and years.

Yet, batteries still have significant and unfortunate limits. Not one of the promises has materialized into results. Not one.

So,how do you produce H2? Answer: By reforming fossil fuels...so,no wonder the Oil Companies would love this fuel...they could move right into the market by installing a pressure gas pump on the island of any gasoline station and continue to control the country's energy supply.

There are too many David/Dave's in the world LOL Now we have a DavidD and a DaveD contributing here on GCC...and we seem to share similar perspectives as well as our names :-)

Cujet, I think there are more advances than we're giving credit for. The batteries that Tesla is using for the Model S are the 255Wh/kg Panasonic modules which are quite a bit better than the modules even being used by Nissan or A123 cells commonly used today. In addition, Bob Wallace pointed out that Envia has a 400Wh/kg cell out now that has been confirmed by 3rd party sources and I believe they are already sampling to people.

We just have to keep in mind that it takes at least 5 years for anything to really make it into production even if it's real. And we here about every false alarm as well as the ones that are going to make it and all together it just *feels* like forever.

But if you consider the progress over the last hundred years and compare it to the progress in the last 5 years....we're moving ahead by leaps and bounds now. It's just starting from small leaps.

Li2S will likely be the right cathode. Low cost and high energy. The cell degradation due to sulfur dissolution in the electrolyte and subsequent contamination of the anode is what typically leads to the fast capacity loss. For LBNL to say they have invented something and that they get "improved cycling" is silly. Do they have a solution to the degradation of capacity due to the sulfur migration to the anode? I'll bet they have a twenty year plan to grow a program to look into it though.

Solve the high cost, long recharge time, short range and low number of cycles for EV car batteries and call me when you have something.

Don't make the polysulfides, make your cathode immune to them and never let them get to your anode.

AD...PEM fuel cells are not (currently) efficient enough due to the very low efficiency (50%) of current electrolyzers and the inherent low efficiency (50%) of the PEM FC. When hydrogen compression, transportation, and other power train losses are considered, fuel cell powered vehicles end to end efficiency would not be much over 15%. That's about what we get with our gas guzzling ICEVs.

On the other hand, BEVs end to end efficiency is close to or slightly over 60% or about 4X FC powered vehicles.

Secondly, FCs are not cheap ($100+/kW), have poor start up in cold weather and have low operation duration (5000 hours or so).

One major advantage over BEVs is their extended range potential, i.e. to the limit of the size of the hydrogen on-board tank. That would favor larger vehicles such as pick-ups, buses and trucks.

One current limitation is the lack of hydrogen making and distribution network in most countries. A domestic electrolyzer + compressor + high pressure hydrogen tank would cost a lot more than a simple 240 VAC charger. Large hydrogen stations would also cost relatively more than EV chargers.

Let me see, I can think of a number of chemistries currently in the research labs that show excellent promise: LiS4, LiAir, NiZn, MgC, etc.

But, as pointed out above, all this research is not going to improve the range of my Leaf any time soon; in fact, the news from the MyLeaf forum is somewhat bleak. Nissan has not indicated they will have an improved battery in their 2013 car.

"We just have to keep in mind that it takes at least 5 years for anything to really make it into production even if it's real."

WHY? many RAV4 EVs allowed on the road have been there running for 15 years.

The DECADES of battery breakthroughs are 'drop-in components' for a three element cell. Suppose batteries needed a billion parts, transistors, like modern microprocessors?

What if other electric systems advanced like batteries?

We would still be stringing manual telegraph.

Kelly,
I think one of the main reasons is that we love to sue the hell out of anything that moves, and most things that don't. There are something like 100,000 car fires in the US every year, but let there be 5 fires for a BEV, and suddenly there are commercials from blood-sucking lawyers to join their class action lawsuit so that all of you can get $5 each while the lawyers pocket $100Million. New tech gets sued for no reason, simply because our society encourages it.

So you have to test for 3 years before you start to put it into production AND the only way to really prove battery life is to actually go for many years. Otherwise, it is just speculating as to whether the curve observed for the first three years of testing will extend through 10 years. What happens if you're predictions are wrong and it "falls off the cliff" after 5 years? See above: Lawyers with class action lawsuits trying to put Nissan out of business to give each of us $5 and make themselves hundreds of millions of dollars.

Just practical reality.

DaveD...a rather direct description of where a corrupted 'Democracy' can go if left unchecked for too long. The 3% (and Hell's Angles) will do just about anything you can imagine (and more) to get their hands on more million $$ (if left unchecked) while the 97% is getting less and less.

One can look at Greece, Spain, Portugal and Italy to see where this type of unchecked 'Democracy' can lead to.

Lad...in the last 10 years or so, LI-ON EV battery energy density has gone up from about 100 Wh/Kg to 400 Wh/Kg. That's faster progress than many posters are willing to admit but it is real facts.

If the next 10 years give us the same progress, we could have 1200 to 1600 Wh/Kg batteries by 2020/2022 or so. That would make extended range BEVs a reality and it could the start of the end of most ICEVs.

The future of high performance batteries and extended range BEVs is very promising, specially by 2020 or shortly thereafter.

What is the point of this article?????????????????

Another sulfur–carbon composite cathode developed by Chinese already archived 1,130 mA·h·g–1 while this one have 1,144 mA·h·g–1

Yeah 1144 is bigger then 1130, a rounding error look at cycle life.

Cathode discussed in this article drops to 700 while Chinese cathode drops to 900 mA·h·g–1 after first five cycles.

And then after 50 cycles this one drops to 400. While Chinese one drops to 800 mA·h·g–1.

http://link.springer.com/article/10.1007/s10008-012-1864-7

Right now it looks like most car makers are aiming at about 20-60 kwh for bevs and 60-200 kwh for fuel cell systems. Same setup is also happening in mopeds and motorcycles where low energy systems will be bevs and higher energy systems are comming up fuel cells.

Good exmple in india they have a tiny fuel cell moped with a 75 km range and a bev moped with a 15 km range.... And the fuel cell and bev motorbikes I have seen also seem to have this 3 to 1 or so total energy difference.

As far as this new battery tech... I dont think it changes this market segmentation at all but insgtead MIGHT make fore sleaker lighter bev mopeds and motorcycles... and maybe cars if its durable enough and I dont think it is yet...

Electrovaya manufactures lithiated manganese oxide-based series of cells that exceed 200 Wh/kg.

Chrysler tested them in the PHEVs they are developing but abandoned them because they heated up too much during rapid charging. With an active cooling system like the Volt employs a 100 mile range EV might become a 160 mile range EV.

Progress, in spite of what some believe, is being made....

If they get 140 mile EV range for under $30,000 we could see a reevaluation of what a car is for. Once people see that most trips are under 50 miles and they can save thousands of dollars per year, interest might develop.

I dont think so sjc. If that were the case sales should have been far higher then they currently are. Something basic is keeping sales low and we are missing it completely.

Not really, people cling to the idea that a car has to go on long trips of 400 miles, when they might a few times per year and they could fly.

Id rather ride behind an explosively flatulent hippo then fly these days.

This is your choice, but judging from the passenger miles per year, not everyone agrees with you. Besides, if you are dead set on driving, rental car rates are great on the weekends.

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