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Proc Natl Acad Sci U S A. 2015 Jun 30;112(26):7914-9. doi: 10.1073/pnas.1503546112. Epub 2015 Jun 15.

Rescaling of metal oxide nanocrystals for energy storage having high capacitance and energy density with robust cycle life.

Author information

1
Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea;
2
Materials and Process Simulation Center, California Institute of Technology, Pasadena, CA 91125;
3
Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720;
4
Graduate School of Energy, Environment, Water and Sustainability, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea;
5
Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; Department of Chemical Engineering, University of Texas at Austin, Austin, TX 78712.
6
Materials and Process Simulation Center, California Institute of Technology, Pasadena, CA 91125; wag@wag.caltech.edu jeung@kaist.ac.kr.
7
Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea; Graduate School of Energy, Environment, Water and Sustainability, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea; wag@wag.caltech.edu jeung@kaist.ac.kr.

Abstract

Nanocrystals are promising structures, but they are too large for achieving maximum energy storage performance. We show that rescaling 3-nm particles through lithiation followed by delithiation leads to high-performance energy storage by realizing high capacitance close to the theoretical capacitance available via ion-to-atom redox reactions. Reactive force-field (ReaxFF) molecular dynamics simulations support the conclusion that Li atoms react with nickel oxide nanocrystals (NiO-n) to form lithiated core-shell structures (Ni:Li2O), whereas subsequent delithiation causes Ni:Li2O to form atomic clusters of NiO-a. This is consistent with in situ X-ray photoelectron and optical spectroscopy results showing that Ni(2+) of the nanocrystal changes during lithiation-delithiation through Ni(0) and back to Ni(2+). These processes are also demonstrated to provide a generic route to rescale another metal oxide. Furthermore, assembling NiO-a into the positive electrode of an asymmetric device enables extraction of full capacitance for a counter negative electrode, giving high energy density in addition to robust capacitance retention over 100,000 cycles.

KEYWORDS:

energy storage; in situ electrochemical spectroscopy; metal oxide nanocrystals; molecular dynamic simulation; rescaled atomic clusters

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