New Sodium Ion Battery May Be Best Battery for Utility Grid

Whitacre's sodium-ion cells are similar in some ways to lithium-ion cells--the type used in portable electronics and in some electric vehicles. In both types of cell, ions are shuttled between the battery's positive and negative electrodes during charging and discharging, with an electrolyte serving as the medium for moving those ions. But because sodium is orders of magnitude more abundant than lithium, it is cheaper to use. To make the cells cheaper still, Whitacre plans to operate them at lower voltages, so that water-based electrolytes can be used instead of organic electrolytes. This should further decrease manufacturing costs, since water-based electrolytes are easier to work with.

The change to water-based electrolytes could also make it possible to eliminate much of the supporting material needed in conventional lithium-ion cells, again reducing costs. This is because increasing the ionic conductivity makes it possible to use thicker electrodes with fewer layers of separating and current-collecting materials inside the cell.

"In principle, a sodium-ion system can be low-cost, and with aqueous electrolytes, it could be really low-cost," says Jeff Dahn, a professor of physics and chemistry at Dalhousie University in Nova Scotia, Canada. _TechnologyReview

Jay Whitacre, a professor of Materials Science and Engineering at Carnegie Mellon University, is perfecting a sodium ion battery meant for use at utility-scale. It will contain no toxic materials, cost 1/3 as much as lithium ion cells per kwh stored, and will last longer through more charge-discharge cycles than conventional cells.

Aquion's battery uses an activated carbon anode and a sodium- and manganese-based cathode. A water-based electrolyte carries sodium ions between the two electrodes while charging and discharging. The principle is similar to lithium-ion, but sodium ions are more abundant and hence cheaper to use. Compared to solvent-based electrolytes, the aqueous electrolyte is also easier to work with and cheaper. Even better, the materials are nontoxic and the battery is 100 percent recyclable, Whitacre says.

Grid-scale trials of the technology are next. Aquion has started shipping pre-production battery prototypes to off-grid solar power companies. Next month, a 1,000-volt module will go to KEMA, a Dutch energy consulting and testing outfit, which has a facility outside Philadelphia.

...John Miller, an electrochemical capacitor expert and president of consulting firm JME in Shaker Heights, Ohio, says Aquion's battery could be the cheapest of the various battery technologies vying to provide grid storage. He compares it to today's most common grid storage technology, pumped hydro, which accounts for 95 percent of utility-scale energy storage. Pumped hydro involves moving water to an elevation when electricity demand is low, and releasing that water through turbines during peak periods. It is, however, limited by geology and space, and pumped hydro systems take many years and millions of dollars to build. Utilities are now starting to look at batteries because they can be delivered in months and, in principle, can be sited anywhere.

"Lead-acid is even too expensive," Miller says. "Aquion's technology is getting to the range of pumped hydro in cost, which is two cents per kilowatt-hour [over the system's lifetime]. They're unique. I would say it's very promising for grid storage."

So far, no available technology meets all grid energy storage requirements, says Haresh Kamath, a program manager for energy storage at the Electric Power Research Institute. "Each technology has a different sweet spot" in terms of cost, safety, reliability, lifespan, and efficiency, he says. _TechnologyReview

Here is more information about the new battery from Aquion:

Safe

The core Aquion technology contains zero toxic or otherwise hazardous materials. This facilitates battery installation and manufacturing facilities by preventing delays associated with hazardous material zoning issues. The technology was designed such that harvesting and recycling both the packaging and the active materials is easy. The batteries are also much more efficient than traditional batteries at both a cell and systems level; the end result is an energy storage system that makes better use of the energy it stores.

Reliable

The centerpiece of the technology is an innovative hybrid energy storage chemistry. Over the last two years, the chemistry has been rigorously proven in a laboratory environment and certified by independent third party testing. The electrochemical couple that has emerged from this process is one that combines a high capacity carbon anode with a sodium intercalation cathode capable of thousands of complete discharge cycles over extended periods of time. The materials couple can deliver over 30 Wh/l as packaged. The device functions in a broad range of ambient temperatures and can be repeatedly cycled with little to no loss in delivered capacity. Rapid cycle testing indicates at least 5000 cycles with no fade in delivered capacity, while ongoing calendar life testing shows stable performance for over a year of continuous deep cycle use.

Affordable

To minimize cost, only the cheapest raw materials were considered in the basic R&D phase. As a result, sodium interactive materials and water based electrolytes are used instead of the traditional lithium-based materials and organic solvents. We are also vertically integrated, with manufacturing that incorporates in-house electrode active materials production. Processes borrowed from the food and pharmaceutical industries are then used to create freestanding electrodes that are then packaged into large units. _Aquion

It is likely to take years more to perfect the technology for industrial and utility scale use and production. But this technology would seem to be the most promising battery technology seen recently, besides flow cell batteries -- which will take up to 10 more years to perfect.

In the meantime, the cryogenic storage technology being developed in the UK is felt to be the most promising non-battery utility storage technology.