Lithium-sulfur batteries could give about five times the energy density of their lithium-ion cousins, researchers say. But they've got to solve the pesky problem of a deteriorating work environment.

That is, lithium-sulfur chemistries tend to clog up, break down, and otherwise degrade, limiting cycle life, or the number of times they can be recharged. For electric and plug-in hybrid vehicle applications, that's a no-no.

Sion Power Corp. is looking for an answer to that problem, and on Friday announced an $800,000 Department of Energy research grant to help.

That comes on top of the Tucson, Ariz.-based battery maker's joint development agreement with German chemicals giant BASF, announced earlier this year.

The common goal is to bring lithium-sulfur's promised benefits to automakers in the form of a battery, one Sion hopes can offer driving ranges three times greater than those from lithium-ion batteries now available, on a kilogram-to-kilogram basis.

One big problem with lithium-sulfur batteries is cycle life. Simply put, these batteries tend to generate chemicals in the discharge process that clog the system, speeding anode disintegration and weakening battery performance over time. It's also hard to chemically reverse that clogging in the recharging process (see Green Light post).

Sion says it's tackling the problem with high-energy lithium metal anodes that are kept clean, so to speak, by components in its unique electrolyte system.

That electrolyte formula also enhances the performance of the sulfur cathode, letting the battery use more than 90 percent of the sulfur, up from about 46 percent for previous chemistries, the company says (see Green Car Congress).

BASF has been working with Sion on new anode design, as well as more stable cathodes and new membranes to protect the lithium in the batteries.

All these improvements put together could allow Sion to boost the energy density of its lithium-sulfur cells from about 350 watt-hours per kilogram to 550 watt-hours per kilogram, while speeding up recharging time to less than three hours, the company says (see Green Car Congress).

Sulfur is a lot cheaper than the cobalt, manganese and other metals used in lithium-ion batteries, which could make lithium-sulfur a lower-cost alternative (see What's Next in Lithium Batteries?)

But a mass-market battery remains to be built, though Sion has tested its products in unmanned aerial vehicles – military drone planes – made by QinetiQ (see Cleantech Group).

Similar efforts are underway to find anti-clogging formulas for metal-air batteries, including lithium-air and its potentially cheaper cousin, zinc-air (see A Car Powered By Zinc?).

BASF is working with ReVolt Technology to develop rechargeable zinc-air batteries (see Green Light post).

And Japanese researchers have developed a longer-lived lithium-air battery using a water-based solution that can be pumped out and refilled (see Japanese Research Examines Anti-Clogging Lithium-Air Battery Tech).

Photo of a lithium-sulfur battery via Sion Power Corp.

Tags: basf, lithium-air, lithium-ion, lithium-sulfur, powerair, revolt, sion, zinc-air