title: Charging/Discharging Nanomorphology Asymmetry and Rate-Dependent Capacity Degradation in Li-Oxygen Battery.
abstract: Liquid-cell in situ transmission electron microscopy (TEM) observations of the charge/discharge reactions of nonaqueous Li-oxygen battery cathode were performed with ∼5 nm spatial resolution. The discharging reaction occurred at the interface between the electrolyte and the reaction product, whereas in charging, the reactant was decomposed at the contact with the gold current collector, indicating that the lithium ion diffusivity/electronic conductivity is the limiting factor in discharging/charging, respectively, which is a root cause for the asymmetry in discharging/charging overpotential. Detachments of lithium oxide particles from the current collector into the liquid electrolyte are frequently seen when the cell was discharged at high overpotentials, with loss of active materials into liquid electrolyte ("flotsam") under minute liquid flow agitation, as the lithium peroxide dendritic trees are shown to be fragile mechanically and electrically. Our result implies that enhancing the binding force between the reaction products and the current collector to maintain robust electronic conduction is a key for improving the battery performance. This work demonstrated for the first time the in situ TEM observation of a three-phase-reaction involving gold electrode, lithium oxides, DMSO electrolyte and lithium salt, and O2 gas. The technique described in this work is not limited to Li-oxygen battery but also can be potentially used in other applications involving gas/liquid/solid electrochemical reactions.
authors.affiliation: Department of Nuclear Science and Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Kushima
authors.affiliation: Honda R&D Co. Ltd. , Automobile R&D Center, Wako-shi, Saitama 351-0193, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Koido
authors.affiliation: Honda R&D Co. Ltd. , Automobile R&D Center, Wako-shi, Saitama 351-0193, Japan.
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Fujiwara
authors.affiliation: Honda R&D Co. Ltd. , Fundamental Technology Research Center, Wako-shi, Saitama 351-0188, Japan.
authors.forename: Nariaki
authors.initials: N
authors.lastname: Kuriyama
authors.affiliation: Honda R&D Co. Ltd. , Automobile R&D Center, Wako-shi, Saitama 351-0193, Japan.
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Kusumi
authors.affiliation: Department of Nuclear Science and Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.|Department of Materials Science and Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Ju
authors.initials: J
authors.lastname: Li
keywords: electrochemistry; in situ; liquid cell; three-phase boundary; transmission electron microscopy (TEM)