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

1500_cy_s-go
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.

Li-s-go_cell
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

Comments

Roger Pham

If we ain't gonna put in ~$250 billions or so yearly in building RE collectors and H2-piping-FC-CHP sytem, PLUS $100 billions or so yearly in building new Nuclear Energy generation capacity, we ain't gonna be weaned off fossil fuels in 20 years!!!!WE ain't gonna be able to steer the Titanic 2 away from looming disaster. WE ain't gonna be abe to do it!!!!!

Meanwhile, our $500-700 billion yearly US Defense budget is spent on what? Imaginary and created enemies and useless defense systems...that will further threaten the fragile world peace...Russia and China are only spending a small fraction of the US defense budget on their own defense budget. Who will be our next enemies worthy of our enormous defense budget? The money is there to fight GW, if we so declare WAR on GW. We just have got to do it!

Roger Pham

I'd say, just match our Defense Budget to that of China or Russia to build and maintain human-killing weapons and tropps...and use the rest of the money on Defense against GW, our TRUE long-term ENEMY.

Roger Pham

Furthermore, the USA is already spending $700-1000 Billions yearly on oil, coal and gas YEARLY. According to: http://www.environmentamerica.org/reports/ame/high-cost-fossil-fuels

"The costs of continuing on our current energy path are steep. American consumers and businesses already spend roughly $700 billion to $1 trillion each year on coal, oil and natural gas, and suffer the incalculable costs of pollution from fossil fuels through damage to our health and environment. If America continues along a business-as-usual energy path, U.S. fossil fuel spending is likely to grow, totaling an estimated $23 trillion between 2010 and 2030."

Thus, after some years of using US Defense Budget to spend to defend against GW, we will start accumulating hundreds of billions of USD yearly of savings from spending on Fossil fuels, and that money can be plowed into building RE and NE generators and H2 infrastructures, without requiring any further spending any money on Defense budget. All the RE and NE and H2 projects will pay for themselves for decades after that...the money spent will be like investments, not like the money spent on useless weapon systems that will be total loss. Does any B-2 or B-52 or nuclear sub or aircraft carrier bring back any revenue for the US gov.? Nope! While money spent of RE and NE facilities will generate revenues years after years...

Engineer-Poet
At 90% capacity factor, it would take about 4,000 billion kWh x 0.9 / 8700 hours/year = 510 GW of nuclear capacity.

Math nit:  you multiplied by 0.9 when you should have divided.  You obviously did it right in the calculator, though.

Current US nuclear capacity is 107 GW, meaning that another 400 GW of nuclear capacity must be built.

Built, or converted.  Existing Rankine-cycle plants might be retrofitted with e.g. molten-salt or LEADIR boilers.

Wait a minute, total US electricity generation capacity is 1152 GW, for an average capacity factor of only 39%, because of tremendous variability in power demand.

A lot of this is due to the low capacity factor of RE.  The EIA states that installed US wind capacity hit 39.1 GW in 2010, yet net generation was only 2.3% of about 450 GW.  That's a bit over 10 GW average, or ~26% CF.  Average hydro generation in 2011 was 29.3 GW vs. installed capacity of 78.8 GW, or 37% CF.

My calculations were for an all-nuclear grid with a battery buffer sufficient to supply a daily min/max power ratio of more than 2:1.  Peak demand can also be managed relatively cheaply using ice storage in summer and backup cogenerating furnaces in winter.

If nuclear is to assume 100% of electricty production at all times and nothing else, you must build another 1000 GW of nuclear capacity. Can you estimate how long it would take to achieve that?

It would take only ~630 GW total capacity plus batteries to completely power the electric grid AND take on the bulk of ground-transport energy requirements.  If the EOS battery performs as claimed, it is a minor contributor to the net cost but can manage the whole day/night variation by itself.  How long that would take depends how you do it.  We can get a lot by mining our "waste".  For instance, there's about 60,000 tons of spent LWR fuel in the USA, which averages around 0.8% plutonium (480 tons).  At a fuel-cycle requirement for S-PRISM of perhaps 15 tons Pu per GW(e), that's 32 GW.  Building that out in 10 years requires 3.2 GW per year or a unit slightly less than once a month.  Existing LWRs provide enough plutonium in 60 GW-yr of generation to start about 1 GW of fast-spectrum reactors, so LWRs would allow the S-PRISM fleet to keep growing at about 1.5 GW/yr thereafter.  Call it 60 GW in 30 years.

That leaves about 570 GW to be met from other sources, but there are so many options it's hard to pick one.  Either LFTR or LEADIR (suitably modified) could supply drop-in boilers for existing steam plants.  Nuclearizing old steam plants makes it desirable to use them for base load.  Add EOS batteries to manage the demand curve and the total amount of nuclear generation soars.

570 GW in 30 years is 19 GW/yr.  Suppose your 100 MW(th) LEADIR comes off the line at one per day 250 days a year, and achieves 38% efficiency in practice.  That's 38 MW/d * 250 days/yr = 9.5 GW/yr, half the requirement from just one production line.  Fuel?  I dunno, how about thorium to take the heat off uranium?  Graphite has far better neutron economy than light water, and Shippingport still eked out a breeding gain despite H2O moderation.

This is doable, Roger.

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