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New lithium polysulfide flow battery for large-scale energy storage

Battery_ross_labeled_v02b-902x1024
Stanford / SLAC’s new lithium-polysulfide flow battery design compared to conventional “redox” flow batteries. The new flow battery uses only one tank and pump and uses a simple coating instead of an expensive membrane to separate the anode and cathode. (Credit: Greg Stewart/SLAC). Click to enlarge.

Researchers from the US Department of Energy’s (DOE) SLAC National Accelerator Laboratory and Stanford University have designed a new lithium/polysulfide (Li/PS) semi-liquid (flow) battery for large-scale energy storage, with lithium polysulfide (Li2S8) in ether solvent as a catholyte and metallic lithium as an anode.

Unlike previous work on Li/S batteries with discharge products such as solid state Li2S2 and Li2S, the catholyte is designed to cycle only in the range between sulfur and Li2S4. Consequently, the team points out in a paper describing there work published in the RSC journal Energy & Environmental Science, all detrimental effects due to the formation and volume expansion of solid Li2S2/Li2S are avoided.

This novel strategy results in excellent cycle life and compatibility with flow battery design. The proof-of-concept Li/PS battery could reach a high energy density of 170 Wh kg−1 and 190 Wh L−1 for large scale storage at the solubility limit, while keeping the advantages of hybrid flow batteries. We demonstrated that, with a 5 M Li2S8 catholyte, energy densities of 97 Wh kg−1 and 108 Wh L−1 can be achieved. As the lithium surface is well passivated by LiNO3 additive in ether solvent, internal shuttle effect is largely eliminated and thus excellent performance over 2000 cycles is achieved with a constant capacity of 200 mA h g−1. This new system can operate without the expensive ion-selective membrane, and it is attractive for large-scale energy storage.

—Yang et al.

The work is some of the earliest supported by the DOE’s new Joint Center for Energy Storage Research battery hub (JCESR). (Earlier post.)

For solar and wind power to be used in a significant way, we need a battery made of economical materials that are easy to scale and still efficient. We believe our new battery may be the best yet designed to regulate the natural fluctuations of these alternative energies.

—Stanford Prof. Yi Cui

Currently the electrical grid cannot tolerate large and sudden power fluctuations caused by wide swings in sunlight and wind. As solar and wind’s combined contributions to an electrical grid approach 20%, energy storage systems must be available to smooth out the peaks and valleys of this intermittent power—storing excess energy and discharging when input drops.

Among the most promising batteries for intermittent grid storage today are “flow” batteries, as it is relatively simple to scale their tanks, pumps and pipes to the sizes needed to handle large capacities of energy. The new flow battery developed by Cui’s group has a simplified, less expensive design that presents a potentially viable solution for large-scale production.

Today’s flow batteries pump two different liquids through an interaction chamber where dissolved molecules undergo chemical reactions that store or give up energy. The chamber contains a membrane that only allows ions not involved in reactions to pass between the liquids while keeping the active ions physically separated.

This battery design has two major drawbacks: the high cost of liquids containing rare materials such as vanadium—especially in the huge quantities needed for grid storage—and the membrane, which is also very expensive and requires frequent maintenance.

The new Stanford/SLAC battery design uses only one stream of molecules and does not need a membrane at all. Its molecules mostly consist of the relatively inexpensive elements lithium and sulfur, which interact with a piece of lithium metal coated with a barrier that permits electrons to pass without degrading the metal. When discharging, lithium polysulfides absorb lithium ions; when charging, they lose them back into the liquid. The entire molecular stream is dissolved in an organic solvent, which doesn’t have the corrosion issues of water-based flow batteries.

Initial lab tests showed that the new battery retained excellent energy-storage performance through more than 2,000 charges and discharges, equivalent to more than 5.5 years of daily cycles, Cui said.

In the future, Cui’s group plans to make a laboratory-scale system to optimize its energy storage process and identify potential engineering issues, and to start discussions with potential hosts for a full-scale field-demonstration unit.

Resources

  • Yuan Yang, Guangyuan Zheng and Yi Cui (2013) A membrane-free lithium/polysulfide semi-liquid battery for large-scale energy storage. Energy Environ. Sci., 6, 1552-1558 doi: 10.1039/C3EE00072A

Comments

kelly

Is this the one? Is it cheap enough?

Sounds simple enough to commercialize on the weekend.

Nick Lyons

Sounds promising. I find this statement puzzling, however:

Initial lab tests showed that the new battery retained excellent energy-storage performance through more than 2,000 charges and discharges, equivalent to more than 5.5 years of daily cycles, Cui said.

I assume the use case they are talking about, "... to smooth out the peaks and valleys of this intermittent power..." means shaving peaks and filling in the sudden drops caused by clouds and wind changes, not filling in for solar overnight. Seems like more than one cycle/day is required.

soltesza

Sounds extremely promising. Is there any info about the roundtrip efficiency?

Flow batteries are usually very weak in that area (60%-70% roundtrip eff)

Also, this design seems easy to maintain after the 2000 cycles are gone (replacing the flow-through cell and possibly the electrolyte).

Brotherkenny4

Cost is everything for stationary applications. Certainly sulfur is as cheap as dirt, but we would need to know on a system level what the cost is.

HarveyD

Fraunhofer Institute of Materials of Dresden has found ways to make lower cost 600 Wh/Kg Lithium/Sulphur batteries, last for 1400+ cycles. When mass produced, it could become a better storage unit for affordable electrified vehicles?

Kit P

“Currently the electrical grid cannot tolerate large and sudden power fluctuations caused by wide swings in sunlight and wind. ”

Not true, The grid does just fine. What is true is that we can build wind and solar fast enough and them keep them working so that wind and solar would over load the capacity of the grid.

Worrying about storage is putting the cart before the cart. First you have to have excess wind.

“This battery design has two major drawbacks: ”

Just two? Well you might as well stop counting at the first show stopper.

“and the membrane, which is also very expensive and requires frequent maintenance. ”

Yes, the wind and sun is free but the electricity is not.

Bob Wallace

"Not true, The grid does just fine."

Right.

"What is true is that we can build wind and solar fast enough and them keep them working so that wind and solar would over load the capacity of the grid."

We'll simply do what we do right now with fossil fuel generation. When we don't need it all we'll turn some off. We have natural gas plants that run only a few hours a year. During parts of the year we turn some coal plants off for months.

At this point in time it's cheaper to build more wind generation than we need in low demand/high wind hours than to build storage. Cheap storage would change that math.

Unless storage gets very cheap we'll likely continue to overbuild.


Kit P

“We have natural gas plants that run only a few hours a year. ”

These are low capital cost, low maintenance, low labor, and very very reliable. The down side is that they are very inefficient. This is why SCGT are only used in standby as backup power.

I think wind and solar are great in the correct location. However, they are very high capital cost, high maintenance cost, and very, very unreliable. As a result they do not make very much electricity.

Making a little bit of power is great. If wind and solar ever produce enough power that coal and nuke plants are shut down, you will not hear me object. I figure I will be dead for several hundred years.

HarveyD

In the not too distant future, automated factories will mass produce small and large e-storage units for under $100 kWh.

Those low cost (under $100/kWh) higher energy density (1000+ Wh/Kg) increased duration (4,000+ cycles) units will find applications as small to very large (fixed) electricity storage, as mobile applications for electrified vehicles of all sizes and for a multitude of electronic gadgets.

High efficiency wireless chargers will make their use almost transparent.

Bob Wallace

"I think wind and solar are great in the correct location. However, they are very high capital cost, high maintenance cost, and very, very unreliable. As a result they do not make very much electricity."

Solar is uniquely low in terms of maintenance. Almost none. In most cases the panels don't even need cleaning if installed on an angle.

Wind does not have a high maintenance cost until about the time the turbines are worn out. That's somewhere in the 30 year range and likely longer with new turbine tech, especially those without gear trains.

Of course anything with moving parts tends to wear out. Adding thermal stress in the case of nuclear and fossil fuel plants compounds the problem.

Reliability is quite high for both solar and wind. (Perhaps you were thinking about variability?)

Overnight capital cost for onshore wind is 2x to 3x that of gas turbines. But the lack of fuel costs make wind cheaper than a simple turbine. Then with the low capacity of gas peakers the lack of sufficient operational hours over which to spread capex and financial costs makes their power quite expensive.

Natural gas run in a combined cycle plant and operated at high capacity is slightly cheaper than wind, but unlikely to stay cheaper. The overnight cost of NGCC is about 2x of onshore wind and the overnight cost of wind is headed downward. Wind is expected to get cheaper, gas prices will almost certainly rise.

Global investments in fossil fuel plants are dropping while investments in renewable are rising. While the total amount of fossil fuels continues to rise, the rate of increase is slowing. Bloomberg Energy is predicting global fossil fuel use peak by 2030.

Kit P

“Almost none. ”

Well that is how much power is produced by most solar panels.

“Wind does not have a high maintenance cost “

Sure it does.

BS Bob has belief system build on ignorance and wishful thinking.

“Adding thermal stress in the case of nuclear and fossil fuel plants compounds the problem. ”

There is thermal stress for wind and solar as well.

Reliability is quite high for both solar and wind. (Perhaps you were thinking about variability?)

What! Variability is the main reason that wind and solar are not reliable. After considering that wind and solar are 10% below where they should be based on design.

This is why putting them in the right place is so important.

“onshore wind ”

I do not live off shore. BS Bob is always talking about someplace else. If Denmark and Germany want to put a million wind turbines and store the power that is just fine with me..

“wind cheaper than a simple turbine ”

So what? It is not cheaper than steam turbines which is how 70% of the power is produced in the US.

“Global investments in fossil fuel plants ”

That is funny, you may want to check out China, Brazil, and India.

“Bloomberg Energy ”

Where do they produce power, never heard of them?

Engineer-Poet

Wrote the Twit:

Worrying about storage is putting the cart before the cart.
You need to worry about posting while drunk.  Why are you drunk in the early morning?

Kit P

Still waiting for E-P to tell us what he foolishly paid for his in his new PHEV with a power storage system so he can brag about using less gas while using more energy.

A brilliant plan to save the world by switching from one fossil fuel to another.

It is an indication of E-P's logic that he thinks ethanol impairs by prooof reading skils. If I need an English major to proof read for me, I know where to find a control system that likes to demonstrate he should have focused more on engineering. A bad poet and engineer.

Just for the record I had a beer with dinner. I saved gas by not driving anywhere because I stopped on the way home Friday to get the seeds I wanted.

Bob Wallace

Kit posts -

"“Wind does not have a high maintenance cost “

Sure it does.

BS Bob has belief system build on ignorance and wishful thinking."

Let's check the data....

Fixed maintenance costs - median $/kW

Onshore wind $10.95
Combined cycle NG $13.71
Nuclear $85.66
Scrubbed coal $27.50

A range of $11 to $86 dollars with wind being the least expensive. Even if we adjust the numbers for output capacity wind is lower than coal and, especially, nuclear.
--

Variable maintenance costs - median $/MWh

Onshore wind $6.45
Combined cycle NG $2.86
Nuclear $0.49
Scrubbed coal $3.70

Onshore wind is the highest of the four in variable maintenance costs. About $0.006/kWh which hardly rises to the level of expensive. Especially when one considers it has zero fuel costs.


Bob Wallace

Kit posts -

"“Adding thermal stress in the case of nuclear and fossil fuel plants compounds the problem. ”

There is thermal stress for wind and solar as well."

Right. Those boilers and steam pipes sure stress solar panels and wind turbines, don't they Kit?
---

Kit posts -

"“wind cheaper than a simple turbine ”

So what? It is not cheaper than steam turbines which is how 70% of the power is produced in the US."

It is important to compare like to like, Kit. Otherwise your argument has no value.

The median cost of new wind is $0.06/kWh.

The median cost of new coal and nuclear are over $0.10/kWh.
---

From the Bloomberg New Energy Financial annual Summit

http://bloom.bg/17gA7ia
--


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