Startup Promises a Revolutionary Grid Battery

Technology Review
Jan 4, 2012

Long life: This kilowatt-scale zinc-air battery prototype can be charged and discharged 2,700 times with no physical degradation, its maker claims.

Battery developer Eos Energy Storage claims to have solved key problems holding back a battery technology that could revolutionize grid energy storage. If the company is right, its zinc-air batteries will be able to store energy for half the cost of additional generation from natural gas—the method currently used to meet peak power demands.

Company officials say that current prototypes demonstrate twice the energy density of lithium-ion batteries. They claim their final product will last for 30 years in grid-scale applications with a cycle life that is orders of magnitude greater than that of lead-acid batteries, making it one of the longest-lasting battery types around. CEO Michael Oster says Eos will soon complete a $10 million round of funding from several investors.

"If they can get what they are claiming, it would be revolutionary," says Steve Minnihan, an analyst with Lux Research, who says the technology shows promise for both grid storage and electric vehicles.

Zinc-air technology has long attracted battery developers because it's safe, it's inexpensive, and it offers high energy densities. Unlike conventional batteries, in which all reactants are packaged within the battery, zinc-air cells draw in oxygen from the air to generate current. Drawing on outside air gives the batteries a higher capacity-to-volume ratio and lowers the material costs. The battery's water-based chemistry also means it isn't prone to catching fire, unlike lithium-ion batteries.

Until now, however, these batteries have had low efficiencies and short life cycles, limiting their use to small, nonrechargeable applications such as hearing aids. Eos officials say they have solved several problems that have confounded previous efforts.

Eos's key advances involve changes in electrolyte chemistry and cell design. Zinc-air batteries typically use potassium hydroxide, a basic solution that absorbs carbon dioxide from the air. That causes potassium carbonate to build up, slowly clogging the cell's air pores. Because Eos's batteries use a novel pH-neutral electrolyte, Oster says, they do not absorb carbon dioxide. The company also uses a unique horizontal cell configuration that relies on gravity rather than a physical membrane to separate the liquid electrolyte from the air. The change, he says, prevents buildups on the zinc electrode from rupturing the membrane and causing cell failure.
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