Using nanoparticles of a copper compound to develop an inexpensive and durable high-powered battery electrode could be the breakthrough solution to the problem of sharp drop-offs in the output of wind and solar systems, scientists at Stanford University say.

Grid storage projects for renewable generation are getting bigger and more widespread, and many rely on lithium-ion battery technology. In late October, for example, AES Wind Generation and AES Energy Storage put into commercial operation AES Laurel Mountain, a wind generation plant in West Virginia comprising 98 MW of wind generation (from 61 GE 1.6-MW turbines) and 32 MW of A123 Systems energy storage devices (Figure 2).

2. Cost breakthrough. Stanford researchers have used nanoparticles of a copper compound to develop a high-power battery electrode that is reportedly so inexpensive to make that it could be used to build batteries big enough for economical large-scale energy storage on the grid. The development could result in a breakthrough for large-scale battery storage projects like AES Energy Storage’s newly built AES Laurel Mountain, a wind generation plant in West Virginia composed of 98 MW of wind generation and 32 MW of integrated battery-based energy storage. Courtesy: AES Energy Storage 

Most batteries fail because of accumulated damage to an electrode’s crystal structure, the Stanford researchers say. In laboratory tests, they found that a new electrode that employs crystalline nanoparticles of a copper compound survived 40,000 cycles of charging and discharging, after which it could still be charged to more than 80% of its original charge capacity. For comparison, the average lithium-ion battery can handle about 400 charge/discharge cycles before it deteriorates too much to be of practical use.

The electrode’s durability derives from the atomic structure of the crystalline copper hexacyanoferrate used to make it. The crystals have an open framework that allows ions—electrically charged particles whose movements en masse either charge or discharge a battery—to easily go in and out without damaging the electrode.

To maximize the benefit of the open structure, the researchers needed to use the right size ions. Too big, and the ions would tend to get stuck and could damage the crystal structure when they moved in and out of the electrode. Too small, and they might end up sticking to one side of the open spaces between atoms, instead of easily passing through. The right-sized ion turned out to be hydrated potassium, a much better fit than other hydrated ions such as sodium and lithium. The speed of the electrode is further enhanced because the particles of electrode material that the researchers synthesized are tiny even by nanoparticle standards—a mere 100 atoms across.

“At a rate of several cycles per day, this electrode would have a good 30 years of useful life on the electrical grid,” said Colin Wessells, a graduate student in materials science and engineering, who is the lead author of a paper describing the research, published in November in Nature Communications.

The research seeks to overcome cost concerns associated with grid energy storage as opposed to energy density. “We decided we needed to develop a ‘new chemistry’ if we were going to make low-cost batteries and battery electrodes for the power grid,” Wessells said. The researchers chose to use a water-based electrolyte, which Wessells described as “basically free compared to the cost of an organic electrolyte” such as is used in lithium-ion batteries. They made the battery electric materials from readily available precursors such as iron, copper, carbon, and nitrogen—all of which are extremely inexpensive compared with lithium.

The only major obstacle to finessing the new electrode is that its chemical properties cause it to be usable only as a high-voltage electrode, the researchers say. Every battery needs two electrodes—a high-voltage cathode and a low-voltage anode—in order to create the voltage difference that produces electricity. Efforts to find another material to use for the anode, which will be necessary before researchers can build an actual battery, are under way, and they have already uncovered “some promising candidates.”

—Sonal Patel is POWER’s senior writer.