Sulfur Polymers Could Enable Long-Lasting, High-Capacity Batteries

MTorrice writes "Lithium-sulfur batteries promise to store four to five times as much energy as today's best lithium-ion batteries. But their short lifetimes have stood in the way of their commercialization. Now researchers demonstrate that a sulfur-based polymer could be the solution for lightweight, inexpensive batteries that store large amounts of energy. Battery electrodes made from the material have one of the highest energy-storage capacities ever reported" Litihium Ion batteries should maintain capacity for about 1000 cycles, whereas Lithium-sulfur batteries traditionally went kaput after about 100. But it looks like they are getting pretty close to something feasible, from the article: "The best performing copolymer consisted of 90% sulfur by mass. Batteries using this copolymer had an initial storage capacity of 1,225 mAh per gram of material. After 100 charge-discharge cycles, the capacity dropped to 1,005 mAh/g, and after 500 cycles it fell to about 635 mAh/g. In comparison, a lithium-ion battery typically starts out with a storage capacity of 200 mAh/g but maintains it for the life of the battery, Pyun says."

Re:Still a ways to go

[Anonymous Coward]

I saw an interesting graph in Aviation Week some time ago about the energy density of batteries versus the same mass of hydrocarbon fuel. The article was in relation to the idea of creating (plug-in) hybrid airliners.

The batteries used in the 787 store four orders of magnitude less energy than the equivalent mass of jet fuel.

I'm mentioning this because it looks like these batteries would bring the difference up to three orders of magnitude.

Still a ways to go before batteries can compete against hydrocarbon/fossil fuels.

myke

Based on a back-of-the-envelope calculation, that number seems wrong. Could you have misread Aviation Week?

Jet fuel has an energy density close to 45 MJ/kg. A lithium-ion battery has an energy density of (approximately) 150 Wh/kg, which is 540 KJ/kg. That's about 1.2% of the energy density of the jet fuel, which is more like 2 orders of magnitude, not 4.

4 orders of magnitude below jet fuel is more in the range of supercapacitors than batteries.

Still a ways to go...until we get where?

[Immerman]

First off that's a bald-faced lie: Energy density of:
Gasoline: ~46 MJ/kg
Lithium-ion battery: 0.36-0.875 MJ/kg (1/127 - 1/52 times gasoline)
Lead-acid battery: 0.17 MJ/kg (1/270 times gasoline)

So even lead acid batteries are only two orders of magnitude less energy dense than gasoline.

As for the suitability in vehicles - that depends entirely on the application. For aircraft the energy density per both unit mass and unit volume is very important, so I doubt we'll see electric jetliners any time soon. For automobiles and other short-range land vehicles on the other hand batteries are already adequate for a lot of applications, and cost is the primary limiting factor. A measly 5x increase in capacity could extend the range of the 85kWh Tesla Model S from 265 miles to 1325 miles - still not enough for a long road trip on a single charge, but a lot further than most people care to drive in a single day, and overnight charging in hotel parking lots could be extremely convenient.

And for stationary applications the energy density per dollar is the only particularly important metric, and other battery technologies are probably more applicable to such applications.

Re:Still a ways to go...until we get where?

[strack]

Don't forget that gasoline engines typically turn only about 20-30% of the chemical energy into mechanical energy, whereas electric motors are about 90%. And you get rid of a heavy gasoline engine.

Re:Still a ways to go...until we get where?

[Anonymous Coward]

Energy density is more important here... not specific energy.

the Tesla model S will be using new Panasonic batteries, quoted at 735wh/L, or 2.65 MJ/Liter
Gasoline is ~36 MJ/Liter

so that's an order of magnitude difference.

BUT

Electric cars are 3 to 4 times more efficient at taking electricity and converting it to forward motion that an internal combustion engine. This is basically due to the fact that 1) electric motors are about 90% efficient, with IC about 30%, and electric cars can get energy back when braking.

So... instead of 36/2.65 = `3.6 times better for gas it's more like

36/(3*2.65) = 4.52 times better for gas

So yes... we are almost there.

Re:Still a ways to go...until we get where?

[Anonymous Coward]

that was supposed to be

  of 36/2.65 = 13.6

little typo there...