Berkeley Lab team demonstrates high-rate, high-energy, long-life Li/S battery in the lab; looking for industry partners

20 November 2013
 Long-term cycling test results of the Li/S cell with CTAB-modified S−GO composite cathodes. This result represents the longest cycle life (exceeding 1,500 cycles) with an extremely low decay rate (0.039% per cycle) demonstrated so far for a Li/S cell. Credit: ACS, Song et al. Click to enlarge.

Researchers at the US Department of Energy’s Lawrence Berkeley National Laboratory have demonstrated in the laboratory a lithium-sulfur (Li/S) battery that has more than twice the specific energy of lithium-ion batteries, and that lasts for more than 1,500 cycles of charge-discharge with minimal decay of the battery’s capacity.

In a paper in the ACS journal Nano Letters, the team reported that a Li/S cell employing a sulfur-graphene oxide (S–GO) nanocomposite cathode can be discharged at rates as high as 6C (1C = 1.675 A/g of sulfur) and charged at rates as high as 3C while still maintaining high specific capacity (800 mA·h/g of sulfur at 6C), with a long cycle life exceeding 1,500 cycles and an extremely low decay rate (0.039% per cycle)—perhaps the best performance demonstrated so far for a Li/S cell.

The initial estimated cell-level specific energy of the cell was 500 W·h/kg—much higher than that of current Li-ion cells (~200 W·h/kg). Even after 1,500 cycles, the cell exhibited a very high specific capacity (740 mA·h/g of sulfur), which corresponds to 414 mA·h/g of electrode—still higher than state-of-the-art Li-ion cells. These Li/S cells with lithium metal electrodes can be cycled with an excellent Coulombic efficiency of 96.3% after 1,500 cycles, which, the team said, was enabled by its new formulation of the ionic liquid-based electrolyte.

For electric vehicles to have a 300-mile range, the battery should provide a cell-level specific energy of 350 to 400 Watt-hours/kilogram (Wh/kg), they noted. This would require almost double the specific energy (about 200 Wh/kg) of current lithium-ion batteries. The batteries would also need to have at least 1,000, and preferably 1,500 charge-discharge cycles without showing a noticeable power or energy storage capacity loss.

Lithium-sulfur batteries are attractive for electric vehicles and advanced electronic devices due to their much higher theoretical specific energy (∼2600 W·h/kg) than that of current lithium-ion cells (∼600 W·h/kg). This is due to the very high specific capacity of sulfur (1675 mA·h/g), based on a two-electron reaction (S + 2Li+ + 2e ↔ Li2S)—significantly larger than the specific capacities of current cathode materials (130−200 mA·h/g).

Li/S batteries would be cheaper than current Li-ion batteries, and they would be less prone to safety problems that have plagued Li-ion batteries, such as overheating and catching fire.

However, the poor cycle life and rate capability have remained a grand challenge, preventing the practical application of this attractive technology. During discharge lithium polysulfides tend to dissolve from the cathode in the electrolytes and react with the lithium anode forming a barrier layer of Li2S. This chemical degradation is one reason why the cell capacity begins to fade after just a few cycles.

Another problem with Li/S batteries is that the conversion reaction from sulfur to Li2S and back causes the volume of the sulfur electrode to swell and contract up to 76% during cell operation, which leads to mechanical degradation of the electrodes. As the sulfur electrode expands and shrinks during cycling, the sulfur particles can become electrically isolated from the current collector of the electrode.

 A schematic of a lithium-sulfur battery with SEM photo of silicon-graphene oxide material. Source: Berkeley Lab. Click to enlarge.

The prototype cell uses several electrochemical technologies to address this array of problems. For one, the S-GO cathode can accommodate the volume change of the electrode active material as sulfur is converted to Li2S on discharge, and back to elemental sulfur on recharge.

To further reduce mechanical degradation from the volume change during operation, the team used an elastomeric binder. By combining elastomeric styrene butadiene rubber (SBR) binder with a thickening agent, the cycle life and power density of the battery cell increased substantially over batteries using conventional binders.

To address the problem of polysulfide dissolution and the chemical degradation the research team applied a coating of cetyltrimethyl ammonium bromide (CTAB) surfactant that is also used in drug delivery systems, dyes, and other chemical processes. CTAB coating on the sulfur electrode reduces the ability of the electrolyte to penetrate and dissolve the electrode material.

Furthermore, the team developed a novel ionic liquid based electrolyte. The new electrolyte inhibits polysulfides dissolution and helps the battery operate at a high rate, increasing the speed at which the battery can be charged up, and the power it can deliver during discharge. The ionic liquid-based electrolyte also significantly improves the safety of the Li/S battery, as ionic liquids are non-volatile and non-flammable.

In summary, we have developed a long-life, high-rate Li/S cell with a high specific energy through a multifaceted approach by uniquely combining CTAB-modified S−GO nanocomposite with an elastomeric SBR/CMC binder and an ionic liquid-based novel electrolyte containing LiNO3 additive.… With the estimated high specific energy, long cycle life, and excellent rate capability demonstrated in this work, the Li/S cell seems to be a promising candidate to challenge the dominant position of the current Li-ion cells.

—Song et al.

The team is now seeking support for the continuing development of the Li/S cell, including higher sulfur utilization, operation under extreme conditions, and scale-up. Partnerships with industry are being sought. The next steps in the development are to further increase the cell energy density, improve cell performance under extreme conditions, and scale up to larger cells.

The paper was authored by Min-Kyu Song (Molecular Foundry, Berkeley Lab), Yuegang Zhang (Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences) and Elton Cairns (Environmental Energy Technologies Division, Berkeley Lab). The research was funded by the US Department of Energy’s Office of Science and a University of California Proof of Concept Award.

The Molecular Foundry is one of five DOE Nanoscale Science Research Centers (NSRCs), national user facilities for interdisciplinary research at the nanoscale, supported by the DOE Office of Science. Together the NSRCs comprise a suite of complementary facilities that provide researchers with state-of-the-art capabilities to fabricate, process, characterize, and model nanoscale materials, and constitute the largest infrastructure investment of the National Nanotechnology Initiative.

The NSRCs are located at DOE’s Argonne, Brookhaven, Lawrence Berkeley, Oak Ridge and Sandia and Los Alamos national laboratories.

Resources

• Min-Kyu Song, Yuegang Zhang, and Elton J. Cairns (2013) “A Long-Life, High-Rate Lithium/Sulfur Cell: A Multifaceted Approach to Enhancing Cell Performance,” Nano Letters doi: 10.1021/nl402793z

1500 cycles in a 300 mile range vehicle is knocking on towards 500,000 miles of life.
That'll do.

0.039% capacity decay per cycle means it only gets to about 500 cycles, not 1500, before it loses 20% of total capacity. It's much longer than previous Li-S batteries, but still not matching longer life Li-ion.

At 300 miles of range at end-of-life, it is about 165,000 miles per pack. Good, but "only" 10-12 years at 12-15K miles per year. For a sedan this would be about an 90kWh pack. If you wanted to build a 200 mile range pack, you'd have to decrease the state of charge window down to 80% to end up with a 140,000 mile pack.

That said, this battery seems to meet a lot of the requirements for scaling up EVs...
* 500Wh/kg for reduced pack weight
* cheaper cells cost due to materials involved
* high rate capable for fast recharging

And price.  You can't forget price in these things.

Carbon, either as graphene or nanotubes, is the "magic sauce" in these formulations.  Both the sulfur and silicon cathodes rely on carbon to provide the mechanical and electrical support to avoid pulverization and loss of active material.

The question, as always, is "which way forward?"  Laptops, phones and headsets are always going to love a 500 Wh/kg battery.  So long as the makers are cranking them out at a profit, auto companies will be able to get in line for them; just look at Tesla.

Yes, Tesla could eventually reduce the size and weight of their battery pack by 50+%.

After further development and fine tuning, this cell could probably reach high enough energy density, cycles, safety, lower cost etc., to mass produce the battery packs required for future 350+ miles (500+ Km) affordable EVs?

Of course, portable devices such as cell phone, tablets, notebooks, laptops etc., would also benefit.

Forget the 350-mile EV.  At 70 MPH cruise, the battery would be discharging at C/5; this wastes the 6C continuous capability of this chemistry.

The best early option is PHEV.  100 kW driving, 50 kW braking takes 17 kWh of capacity at 6C/3C; at 500 Wh/kg, it's 34 kg of cells.  17 kWh @ 250 Wh/mile is 68 miles AER.  Just leave the car on the charger all the time and most of its mileage will be electric when in normal service.

3C charging is a full charge in 20 minutes.  A full charge in a long-ish bathroom break would eliminate fuel consumption for the next hour on the highway.  If this can be gotten to market as a traction battery at any sort of reasonable price, the oil companies are going to be hurting bad.

Anthony F: "0.039% capacity decay per cycle means it only gets to about 500 cycles, not 1500, before it loses 20% of total capacity. It's much longer than previous Li-S batteries, but still not matching longer life Li-ion."

The question is how much battery life can be improved by not performing full cycles. Most of the time you do not need to fully cycle the cell - after all the typical car is only driven around 30 miles / day with distances farther than that performed rarely.

If the battery is capable of driving the car 100 miles, you might only cycle the battery between 70%-40% normally - 3 of those cycles is a lot easier on the battery than a single 95%-5% cycle for example. The swelling/shrinking during charge/discharge which causes the degradation of the battery is minimized by cycling the battery within a smaller SOC range.

It seems ridiculous when researchers publish results that measure the BEV targeted battery lifetimes in deep discharge cycles, when everybody know that nobody wants a car that only goes 50 miles. The 50 mile range would cover average mileage per day and assumes full discharge and charging each day.

But if people won't buy less than 200 mile range, then the researchers should always report the battery lifetime in terms of partial discharge and recharge cycles.

"Forget the 350-mile EV. At 70 MPH cruise" How many people drive 350 miles per day at constant 70 mph? Very few, so wasting the high output is a minor issue. Much more important is the high energy capacity and cycle lifetime. These Li-S batteries are likely to cost much less than Li-Ion and therefore, may result in a BEV vehicle that costs less than a half-ICE PHEV. With 350 mile range, cost is the bottom line, even if the lifetime is short.

Having enough juice to go 350 miles (500 Km) does not mean that you use it every day. The average is under 50 miles but if you live further up North you will appreciate the 350 miles on cold snowy days with very slow traffic. I used to work 22 - 25 Km from home but on many winter days the return home took well over one hour. The only way to beat it was to work till 19:00+h.

With current low performance (100 to 150 Wh/Kg) batteries, a PHEV is a better solution than 80 to 90 miles EVs.

With future (2020 or so) much higher performance batteries (450 to 600 Wh/Kg), EVs with 270 to 350 miles range will not need an on-board genset and users would always have enough juice left to return home in a snow storm. That's when I'll buy a BEV. I hope to do it in 2020.

How many people drive 350 miles per day at constant 70 mph?

When I am on the road trying to get someplace, 700 miles is a slow day.  350 is nothing.

Such legs are very little of my driving, but if a PHEV with these cells could manage to knock 20-30% off the fuel consumption even on such extreme legs and 100% of daily driving, that would be finito for the oil industry.

Good point, E-P, but don't worry about the oil industry! It will take several decades for full penetration of PHEV, BEV, and FCV into the auto market. By then, either oil will have already run out, and/ or the oil/gas industry (the energy industry) will have plenty of time and money to get into providing RE, H2 supply, PEV-fast-charging facility, and battery-making business. Early research in solar PV's were funded by the oil industry.

I cannot understand why many posters here are still favoring BEV's over PHEV's, when all it takes to make a PHEV from a BEV is a low-cost and simple ICE of 2-cylinder and under 1 liter, while reducing the battery capacity to 1/5 -1/10 that of a BEV. ICE can be produced real fast, while the bottle neck in BEV manufacturing en masse will be the rate at which batteries can be made. Rapid adoption of PEV's to reduce oil consumption and to halt GW can be done much faster by adopting PHEV's instead of BEV's. Perhaps many posters here who are in favor of BEV's over PHEV's have affiliation with BEV-manufacturing companies or battery manufacturers.

LDVs in the USA drive half their lifetime mileage in their first 6 years, give or take.  If a PHEV-70 with adequate charging infrastructure cut fuel demand by 90% and was rolled out tomorrow, LDV fuel demand would fall to 55% of today's by the end of 2019.  You can project where things would go from there, but you'd probably be better advised to incorporate an increasing fraction of BEVs since 3C charging allows "Superchargers" to substitute for gas pumps.

After 120+ years of ICEVs it seems that the world will progressively move to EVs via:

1. 20 years of HEVs (2000 - 2020)
2. 20 years of PHEVs (2010 - 2030)
3. 20 years of FCEVs (2015-2035) + extended period for heavy vehicle.

BEVS will probably start to dominate the market by 2020 or shortly thereafter and by 2030 it may very well become the incontestable leader and replace the last ICEVs, HEVs and PHEVs by 2040.

@E-P,
Superchargers is a poor business model because people mostly charge their PEV's at home, unlike a FCV that must always be filled up at a station.

Furthermore, frequent 3C charging can shorten the life of Lithium batteries. Look at the graph of drop in battery capacity vs. charging cycles in this article. You'll see that at only 0.5C charging and 1C discharging, the battery will wear out 3x faster than at 0.05C discharge rate. I am well aware of this because this also holds true for Li-Polymer batteries used in R/C as well.

Until battery can be much improved, PHEV will still be the most practical form of PEV's.

Furthermore, E-P, by the time this LiS or other advanced and low-cost battery will be commercially available, it will be at least 5-10 years. To ramp up production and to get the OEM's of auto to design PHEV's around it, it will take at least another 5 years...then it will take time to ramp up assembly lines and parts supply lines and refinements in new PHEV designs and manufacturing processes...will take at least another 5 years...So, at 1-1/2 to 2 decades away before PEV's will make any significant dent in the petroleum consumption.

Meanwhile, the oil and gas industry is figuring out that fossil fuels won't last that much longer, that people are looking into PEV's and FCV's, and that GW is wreaking havocs on all around the world (witness the most powerful Typhoon in history a few weeks ago wreaking untold damages and suffering in the Phillipines) and that gov's will likely put restraints on further CO2 emission... so the energy industry will naturally put their investments into batteries, H2 infrastructure, and zero-CO2 energy production in the next 2 decades...

RP...yes, energy firms with very deep pockets will progressively move to other fields such as, Hydrogen making + distribution, batteries + clean e-energy production and distribution.

Wouldn't be surprised to see $S$B from very large petroleum and NG producing countries such as Russia, Norway, Canada, the Arabian States and others + our own billionaires invest heavily in future clean energy and clean transportation infrastructure.

The Tesla Tube could be an interesting project for people with deep pockets. A vast country like USA, without any fast trains, could benefit and so could China, Brazil, India, Russia and most EU countries.

Superchargers is a poor business model because people mostly charge their PEV's at home

It's a perfectly fine business model.  People are almost certainly going to stop every couple of hours anyway.  Gasoline is already a very low-margin business, so who cares if there's only a small margin on electricity?  People "stuck" for 20 minutes let you make profit on a sandwich or $3 latte. If you can knock off half the fuel consumption of the next 2-hour leg with a quick battery top-up, that's more fuel displaced. Highway rest stops would be candidates for these things, since there's nothing to spill. Every bathroom break means full battery. frequent 3C charging can shorten the life of Lithium batteries. If the lost battery life costs less than the fuel that would be burned instead, people will still do it. Besides, this would be for the PHEV owner on long trips, not an every-day event. Someone who drives long legs all the time would get the Tesla-class battery and slow charge overnight, or just drive a diesel. I'm not sanguine about H2. The most natural sources for chemical energy are reformed natural gas and gasified coal, and if you think everyone is going to sequester their CO2 I think you're in for a rude awakening. We can't be talking about 500 or 1500 charge cycles here is such an untried technology is most likely to be scaled down and tried in a PHEV. We're talking about a much smaller battery taking on hundreds of charges and discharges in the course of one drive, with regenerative braking, idling, and other forms of possible regeneration from accessory motors and the transmission. My cell phone battery is recommended to have a full charge as often as possible for maximum life. It is small enough to throw away after the smallest matrix failure. Would a PHEV battery be robust enough to stand small defects? Would a driver have to settle almost immediately for suboptimal performance after driving off the showroom floor? ( A problem which I hear still dogs PV panels) Would rapid charging take as well as slow charging? And what optimal weight would be added by substituting the battery for a prorated share of the fuel and ICE plant? Hopefully if all these questions are settled, we could reduce ICE capacity by as little as 25% and have a battery and electric drive train that will pay for itself in accelleration, weight savings, and fuel savings. That will satisfy the pickup truck and SUV market, which require longer range and heavier/more variable loads than the minis where hybrid tech noaggregates. I'll be convinced when an automaker other than Tesla demonstrates this. Why bother with luxury markets for electric cars and space travel when the Joe Sixpack market will do? @E-P, Gasoline retail is a low-profit business, but at least the investment will pay for itself. A BEV with 80-kWh pack, when charged at 3C, will require 240 kW of power. Such a hefty power and current requirement will require expensive power electronics and local battery storage capacity...much more expensive than the low-tech gasoline pump and storage tank at the gas station. Therefore, to recoup this investment, either there will need to be a lot of volume or high markup for each charge. When most people will charge at home, local fast charging stations won't happen. Perhaps a few stations along the freeways at wide intervals will be able to recoup investment cost...but if intervals are too far apart, BEV owners won't be able to use it. Most people will end up buying PHEV-40's and charge at home for daily commute, and to fill up with gasoline for longer trips. When there is not critical mass, a reaction won't happen. Tesla subsidizes the fast charging stations with the high price of their cars, however, high-end BEV's will only be a niche market. So far, only a few Tesla fast-charge stations are available in the West coast area. Hyundai will also offer Tesla's style free fuel for the new Tucson FCEVs operating in California next spring. Could it be that fuel and maintenance would be included into the montly rent fees for future BEVs and FCEVs? A BEV with 80-kWh pack, when charged at 3C, will require 240 kW of power. The existing Tesla Supercharger runs at 80 kW. A 20-minute charge for a 17 kWh battery would require about 50 kW, less than the existing technology allows. Such a hefty power and current requirement will require expensive power electronics and local battery storage capacity... If the EOS zinc-air battery can be brought to market for anything close to the figures listed, this won't be a problem. Half-sizing the unit would cut power to 500 kW, allowing 10 hypothetical PHEVs or 6 Teslas to charge simultaneously. You can put a box the size of a 20-foot container just about anywhere. Therefore, to recoup this investment, either there will need to be a lot of volume or high markup for each charge. The volume comes with load-levelling and regulation for the grid; vehicle charging is an almost free option once the battery is installed. Siting the batteries to capture the automotive value stream is just good sense. When most people will charge at home, local fast charging stations won't happen. Perhaps a few stations along the freeways at wide intervals will be able to recoup investment cost...but if intervals are too far apart, BEV owners won't be able to use it. There's bound to be many geographic confluences of vehicle service stations or transient-customer retail (often combined with the former) and proximity to substations that makes good sites for a grid-scale battery. PHEVs don't require them at all, but being able to pick up a fast charge at most stops maximizes the benefit of the electric powertrain. It's true that most users not driving long distances will recharge at night. They may even stay plugged in all day and supply V2G services to help support fast chargers for drivers on the go. So far, only a few Tesla fast-charge stations are available in the West coast area. So far. Tesla has plans to put Superchargers on most major Interstate routes nationwide, allowing the 85 kWh Model S to drive coast to coast. And of course, if Li-S takes off and spawns the hypothetical PHEV-70, there is suddenly a mass market for such chargers. They will attract retail, restaurant and tourist traffic. Motels with connections for overnight charging will gain customers at the expense of those who don't. Virtuous cycles exist. @E-P, Your vision of a battery-dominated future is excellent, but you have not considered a future in which an-H2 piping system feeding local fuel-cells for local co-generation of heat and power, will be the dominant source of energy storage for winter and industrial use. In this H2-dominant future, FC's will be the grid's main backup power source, so you won't be needing grid-scale battery, so you won't be having readily-available high-powered source for BEV fast charging. Why is an H2-based e-storage system important? Because of the low cost of H2 as energy storage system in comparison to battery, having 1/10 to 1/100th the cost of a battery-based e-storage system, AND the massive capacity of an H2 e-storage system to provide seasonal scale of e-storage capacity, AND the durability of an H2 e-storage system. All what needed to be done is to dig up existing NG outdoor piping to replace them with H2-compatible piping, but for outdoor only, since H2 will not be allowed to enter the house, nor any building, nor enclosed space. The FC will be mounted outdoor to supply electricity and heat via wires and water piping only. This should be a fairly simple and easy task. Then, FCV's will be able to refuel at most major street corners. We will have name-plate capacity for RE at 3-5 folds average grid requirement. Yet, we will only need a much smaller power electronic capacity to make these RE capacity grid-compatible. The majority of these RE capaccity will be fed to H2 electrolyzers connected to the H2 piping system. Thus, the cost of RE fed directly to the H2 system will a lot lower than the cost of feeding RE to the grid. In the winters, most homes will have heat pump with COP of at least 3, and in combination with waste heat from the FC's, will be able to double the energy available from stored H2 as compared with when the NG is used currently for furnace combustion for space heating. Virtuous cycles indeed will exist. Quite a few votes here for the "plug in hybrid". I've driven a few and came away disappointed. Disappointed with the range, EV power, integration of the engine, and braking-regen. Especially so with the Ford Fusion Energi. I've driven the Tesla Model S, with the 85KWH battery and performance package. To say that I came away impressed is the understatement of the year. I'm in love with that car! Rather than see Tesla (and others) make use of a "smaller and lighter" battery as some here suggest, why not use the same physical size battery with 250% more Specific Energy? Instead of 250 practical miles, possibly 600 practical miles! Now, all of a sudden, you have a car that is practical for our immense interstate system. Charge at hotels/motels overnight, and be on your way in the morning. And a "once a week" charge becomes practical. This is nice. There are other ways to do sulfur too, so this is not last advance in this area. I think the ionic liquid is being somewhat overlooked here. The improved ionic liquid may actually be the most important aspect of the work. I'd personally like to see them couple the sulfur with a silicon anode, since then you wouldn't have free lithium in the cells. Ionic liquid plus silicon plus sulfur= very safe cells, and cheap base materials. In general people seem to concentrate too much on the long distance driving days. Those are rare events for most drivers. Smaller packs will cost more and weigh less. The very few days one drives all day will only be slightly lengthened by an addition stop to recharge. In real life we're probably talking an extra ten minutes on a ten hour drive day. Ten minutes. Not even enough time to check your messages and fire off a couple. Instead of thinking about how you might have to stop a bit longer on the few days you drive all day think about having your typical daily "fuel" bill drop from$4.81 to $1.89. That is what will matter to people.$1,755/yr vs. $690/yr. People will be willing to stop a bit longer on long trips if they are saving$1,000+ per year.

$4.81 (33 miles in a 24 MPG average US car burning$3.50/gallon gas).

$1.89 (33 miles in a 0.3 kWh/mile EV using$0.12/kWh electricity).

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