title: Rescaling of metal oxide nanocrystals for energy storage having high capacitance and energy density with robust cycle life.
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.
authors.affiliation: Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea;
authors.forename: Hyung Mo
authors.initials: HM
authors.lastname: Jeong
authors.affiliation: Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea;
authors.forename: Kyung Min
authors.initials: KM
authors.lastname: Choi
authors.affiliation: Materials and Process Simulation Center, California Institute of Technology, Pasadena, CA 91125;
authors.forename: Tao
authors.initials: T
authors.lastname: Cheng
authors.affiliation: Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea;
authors.forename: Dong Ki
authors.initials: DK
authors.lastname: Lee
authors.affiliation: Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720;
authors.forename: Renjia
authors.initials: R
authors.lastname: Zhou
authors.affiliation: Graduate School of Energy, Environment, Water and Sustainability, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea;
authors.forename: Il Woo
authors.initials: IW
authors.lastname: Ock
authors.affiliation: Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; Department of Chemical Engineering, University of Texas at Austin, Austin, TX 78712.
authors.forename: Delia J
authors.initials: DJ
authors.lastname: Milliron
authors.affiliation: Materials and Process Simulation Center, California Institute of Technology, Pasadena, CA 91125; wag@wag.caltech.edu jeung@kaist.ac.kr.
authors.forename: William A
authors.initials: WA
authors.lastname: Goddard
authors.affiliation: 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.
authors.forename: Jeung Ku
authors.initials: JK
authors.lastname: Kang
keywords: energy storage; in situ electrochemical spectroscopy; metal oxide nanocrystals; molecular dynamic simulation; rescaled atomic clusters