Electrode could make large scale power storage a reality

Stanford researchers have developed an inexpensive and durable battery electrode that could be used to build batteries big enough for economical large scale energy storage on the electrical grid.

Made up of crystalline nanoparticles of a copper compound, the team's high power electrode is said to be capable of surviving 40,000 charge/discharge cycles, compared to a traditional lithium ion battery which can only survive about 400. "At a rate of several cycles per day, this electrode would have a good 30 years of useful life on the electrical grid," said Yi Cui, an associate professor of materials science and engineering at the university. "This is a breakthrough performance – a battery that will keep running for tens of thousands of cycles and never fail." The electrode's durability, according to Cui, 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," Cui explained. "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 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 compared with other hydrated ions such as sodium and lithium," noted Cui. "It fit perfectly – really, really nicely." Cui and his team have been able to readily synthesise the electrode material in gram quantities in the lab. He believes the process should easily be scaled up to commercial levels of production. "We put chemicals in a flask and you get this electrode material - you can do that on any scale," he concluded. "There are no technical challenges to producing this on a big enough scale to actually build a real battery."