TechFront Research and Development in Manufacturing and Technology Battery Breakthrough: Stable Lithium Anodes A


Stanford University (Palo Alto, CA) research team has developed a stable pure lithium metal anode that could lead to the design of smaller, more efficient and less-expensive batteries for use in a wide range of applications from consumer electronics to electric vehicles. The researchers published their findings in a paper entitled “Interconnected hollow carbon nanospheres for stable lithium anodes” in the Nature Nanotechnology journal. It describes how lithium metal would be an optimal choice for anode materi- al because it has the highest specific capacity (3860 mAh g–1) and the lowest anode potential of all. The team’s pure lithium anode was developed with a protective layer of interconnected carbon domes. Current lithium batteries are made of lithium ion (Li-ion) but the lithium is in the electrolyte rather than in the anode. The researchers claim that a pure lithium anode holds the potential for a huge energy boost that could greatly extend battery life. “Of all the materials that one might use in an anode, lithium has the greatest potential. Some call it the Holy Grail,” said Yi Cui, a Stanford professor of materials science and engineering and leader of the research team. “It is very lightweight and it has the highest energy density. You get more power per volume and weight, leading to lighter, smaller bat- teries with more power.”


The problems in using lithium as an anode material have long vexed engineers. According to Guangyuan Zheng, a doctoral candidate in Cui’s lab and first author of the paper, “Lithium has major challenges that have made its use in anodes difficult. Many engineers had given up the search, but we found a way to protect the lithium from the problems that have plagued it for so long.” If engineers are successful in building future batteries with the anode material, the potential exists to greatly increase the energy density and dramatically lower costs, noted research team member Steven Chu, the former US Secretary of Energy and Nobel laureate who recently returned as a Stanford pro- fessor. “In practical terms, if we can triple the energy density


and simultaneously decrease the cost four-fold, that would be very exciting,” Chu said. “We would have a cell phone with triple the battery life and an electric vehicle with a 300-mile range that cost $25,000—and with better performance than an internal combustion engine car getting 40 mpg.” In the paper, the research team discussed the engineer- ing challenges posed by using lithium as anode material. Because lithium ions expand during charging, they haven’t been practical to use as material for anodes, which are


Professor Yi Cui said lithium has the greatest potential as an anode material. A Stanford research team has developed a stable lithium anode using hollow carbon nanospheres.


typically made of graphite and silicon and expand less than lithium during charging cycles. Researchers say that lithium’s expansion during charging is “virtually infinite” relative to the other materials. Its expan- sion is also uneven, causing pits and cracks to form in the outer surface, like paint on the exterior of a balloon that is be- ing inflated. The resulting fissures on the surface of the anode allow the lithium ions to escape, forming hair-like or mossy growths, called dendrites. Dendrites, in turn, short-circuit the battery and shorten its life. Preventing this buildup is the


October 2014 | ManufacturingEngineeringMedia.com 31


Photo courtesy Steve Castillo


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