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USA: Li-ion’s Roar: Is the Affordable Long-Haul Electric Car Almost at Hand?

Recently, Newark, California-based Envia Systems unveiled a 400-watt-hour/kilogram rechargeable lithium-ion battery that it said could be delivered for as little as $125/kilowatt-hour. That’s roughly twice the density at half the cost of the current state of the art. Magic, or the fruit of wise investments by the Department of Energy, GM, and a handful of venture capitalists?
Perhaps both. Envia didn’t announce a production-ready 300-mile EV battery, but rather the promising results of prototype battery testing conducted by the Naval Service Warfare Center. Production is about two years off. So how has Envia managed this leapfrog improvement? There’s a bit of alchemy in the manganese-rich lithium cathode and the silicon-carbon nanocomposite anode, and a lot of magic in the as-yet-undisclosed organic electrolyte that has been developed to resist the oxidation that typically occurs at higher voltages in today’s lithium-ion electrolytes. Another trick is that in the new anode chemistry developed at Envia, lithium ions form an alloy with the silicon component of the nanostructured-composite anode without expanding enough to damage the structure, leading to a battery with long cycle life.
Cycle life will be the focus of continuing development. USABC standards dictate 1000 cycles minimum for EV batteries and 4000 for plug-in hybrids, but Envia has only achieved “greater than 500 cycles” for EVs. Granted, at 300 miles per charge, that equates to 150,000 miles; but such a battery won’t give you 1500 cycles at 100 miles each, and owners won’t always deep-cycle their batteries, so Envia needs to hit 1000-plus cycles. The batteries prefer room temperature but work between -4 and 130 degrees F. The lithium cathode is also fire-safe, should the battery be punctured.
PolyPlus of Berkeley, California, is developing a lithium-air battery promising even greater energy density that could be ready for EVs in 10 years. Using oxygen from the air means that, as with gasoline, these batteries don’t have to carry around their oxidation medium.
The bugaboo has always been that lithium reacts violently with water–even with humidity. PolyPlus has solved this problem with a low-cost titanium-phosphate ceramic membrane surrounding the lithium anode that lets lithium ions pass freely but is impervious to other contaminants. The highly porous gas-diffusion cathode is composed of carbon and Teflon. Pour water in, and it wets the carbon pores, not the Teflon ones, allowing air to flow through these and marry the lithium ions (becoming about 10 percent heavier as it discharges).



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