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New nanowire-based hybrid battery/capacitor shows extreme cycle stability

Researchers funded by Nanostructures for Electrical Energy Storage (NEES), a DOE Energy Frontier Research Center, have developed a nanowire-based hybrid battery/capacitor that can be recharged hundreds of thousands of times. The team, based at the University of California, Irvine, coated gold nanowire in a manganese dioxide shell and encased the assembly in an electrolyte made of a Plexiglas-like gel. The combination is reliable and resistant to failure.

In a paper published in the journal ACS Energy Letters, they reported reversible cycle stability for up to 200 ,000 cycles with 94–96% average Coulombic efficiency for symmetrical δ-MnO2 nanowire capacitors operating across a 1.2 V voltage window in a poly(methyl methacrylate) (PMMA) gel electrolyte.

The nanowires have a Au@δ-MnO2 core@shell architecture in which a central gold nanowire current collector is surrounded by an electrodeposited layer of δ-MnO2 that has a thickness of between 143 and 300 nm. Identical capacitors operating in the absence of PMMA exhibited significantly reduced cycle stabilities ranging from 2000 to 8000 cycles. In the liquid PC electrolyte, the δ-MnO2 shell fractures, delaminates, and separates from the gold nanowire current collector. These deleterious processes are not observed in the PMMA electrolyte.

For electrode materials that rely on ion insertion for Faradaic charge storage, a nanowire morphology can enable higher power in either batteries or capacitors than is possible using a film of the same material. However, the Achilles heel of such nanowires for energy storage is cycle stability. The diminutive lateral dimension of nanowires increases their susceptibility to dissolution and corrosion, and these processes rapidly result in a loss of electrical continuity through the nanowire and an irreversible loss of capacity.

… Here, we report that the cycle stability of MnO2 all-nanowire capacitors can be extended from 2000 to 8000 cycles to more than 100000 cycles, simply by replacing a liquid electrolyte with a poly(methyl methacrylate) (PMMA) gel electrolyte.

—Thai et al.

Based on SEM analysis of cycled Au@MnO2 core@shell nanowires, the researchers suggested that one mechanism by which PMMA gel may extend cycle lifetime is simply the mechanical confinement of the MnO2 shell material on the gold nanowire current collector.

The high viscosity and elasticity of the PMMA gel appears to prevent the separation of MnO2 from the current collector while remaining transparent to fluxes of Li+ involved in insertion and deinsertion. The researchers also suggested that the PMMA gel electrolyte reduces the propensity for fracture of the MnO2 shell, increasing its fracture toughness.


  • Mya Le Thai, Girija Thesma Chandran, Rajen K. Dutta, Xiaowei Li and Reginald M. Penner (2016) “100k Cycles and Beyond: Extraordinary Cycle Stability for MnO2 Nanowires Imparted by a Gel Electrolyte” ACS Energy Letters Vol. 1: Pages 57-63 doi: 10.1021/acsenergylett.6b00029



Sooo does this transition into society in a useful way. Energy density, will this be useful in cars? Can it handle vibrations. Is it only good for stationary use? Is it highly expensive because it is so reliant on gold? Can something replace the gold to bring the cost down? Is this a model to substitute in other metals?


Good questions Jeff.


to me, this article doesn't really present anything new. There are many research articles coming out with new discoveries like this. However, very few of them ever make it to the commercial scale. The inherent nature of capacitors allow for high cyclability and fast charge/discharge cycles, because it's operating mechanism doesn't rely on the lithium chemistry that li ion batteries have. So that's nothing new. Also, since energy density was mentioned, supercapacitors tend to be much less energy dense than our modern day lithium ion batteries, by at least one order of magnitude, so if this ever sees commercial application, it will be used in conjunction with batteries, such as regenerative braking, or engine shutoff at intersections for hybrids. And considering commercial applications already exists, this will somehow have to prove itself to be superior to what's already available in performance or cost. So in short, while it's good that people are trying to find new ways to improve energy storage, very few of these ideas will ever stick.

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