Advanced electrode may aid large-scale power storage

Advanced electrode may aid large-scale power storage

Electrode with copper nanoparticles handles 40,000 charge/discharge cycles

The sun doesn’t always shine and the breeze doesn’t always blow and therein lie perhaps the biggest hurdles to making wind and solar power usable on a grand scale. Stanford researchers have developed a new electrode that employs crystalline nanoparticles of a copper compound that could be part of a dream battery to store large quantities of excess power generated on windy or sunny days until we needed it.

The average lithium-ion battery can handle about 400 charge/discharge cycles before it deteriorates too much to be of practical use. Grid tied batteries would have to handle much more that this. In laboratory tests, the new electrode survived 40,000 cycles of charging and discharging, and after which could still be charged to more than 80% of its original capacity.

Colin Wessells, a graduate student in materials science and engineering, is the lead author of a paper describing the research, published in Nature Communications. “That is a breakthrough performance – a battery that will keep running for tens of thousands of cycles and never fail,” said Yi Cui, an associate professor of materials science and engineering, who is Wessell’s adviser and a coauthor of the paper.

Yi Cui, an associate professor of materials science and engineering. (Credit: Linda A. Cicero / Stanford News Service)

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 to easily go in and out without damaging the electrode. Most batteries fail because of accumulated damage to an electrode’s crystal structure. Because the ions can move so freely, the electrode’s cycle of charging and discharging is extremely fast, which is important because the power you get out of a battery is proportional to how fast you can discharge 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. 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 compared with other hydrated ions such as sodium and lithium.

The researchers used a water-based electrolyte — which is basically free compared to the cost of an organic electrolyte in lithium ion batteries. The significant limitation to the new electrode is that its chemical properties cause it to be usable only as a high-voltage electrode. But every battery needs two electrodes — a high-voltage cathode and a low-voltage anode. The researchers need to find another material to use for the anode before they can build an actual battery. But Cui said they have already been investigating various materials for an anode and have some promising candidates. For more information see http://mse.stanford.edu
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Jim Harrison