title: Coupling In Situ TEM and Ex Situ Analysis to Understand Heterogeneous Sodiation of Antimony.
abstract: We employed an in situ electrochemical cell in the transmission electron microscope (TEM) together with ex situ time-of-flight, secondary-ion mass spectrometry (TOF-SIMS) depth profiling, and FIB-helium ion scanning microscope (HIM) imaging to detail the structural and compositional changes associated with Na/Na(+) charging/discharging of 50 and 100 nm thin films of Sb. TOF-SIMS on a partially sodiated 100 nm Sb film gives a Na signal that progressively decreases toward the current collector, indicating that sodiation does not proceed uniformly. This heterogeneity will lead to local volumetric expansion gradients that would in turn serve as a major source of intrinsic stress in the microstructure. In situ TEM shows time-dependent buckling and localized separation of the sodiated films from their TiN-Ge nanowire support, which is a mechanism of stress-relaxation. Localized horizontal fracture does not occur directly at the interface, but rather at a short distance away within the bulk of the Sb. HIM images of FIB cross sections taken from sodiated half-cells, electrically disconnected, and aged at room temperature, demonstrate nonuniform film swelling and the onset of analogous through-bulk separation. TOF-SIMS highlights time-dependent segregation of Na within the structure, both to the film-current collector interface and to the film surface where a solid electrolyte interphase (SEI) exists, agreeing with the electrochemical impedance results that show time-dependent increase of the films' charge transfer resistance. We propose that Na segregation serves as a secondary source of stress relief, which occurs over somewhat longer time scales.
authors.affiliation: Chemical and Materials Engineering, University of Alberta , Edmonton, Alberta T6G 2 V4, Canada.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Li
authors.affiliation: Chemical and Materials Engineering, University of Alberta , Edmonton, Alberta T6G 2 V4, Canada.
authors.forename: Xuehai
authors.initials: X
authors.lastname: Tan
authors.affiliation: nanoFAB Fabrication and Characterization Facility, University of Alberta , Edmonton, Alberta T6G 2 V4, Canada.
authors.forename: Peng
authors.initials: P
authors.lastname: Li
authors.affiliation: Chemical and Materials Engineering, University of Alberta , Edmonton, Alberta T6G 2 V4, Canada.
authors.forename: Peter
authors.initials: P
authors.lastname: Kalisvaart
authors.affiliation: Department of Materials Science and Engineering, University of Connecticut , Storrs, Connecticut 06269, United States.
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Janish
authors.affiliation: Center for Integrated Nanotechnologies, Sandia National Laboratories , Albuquerque, New Mexico 87185, United States.
authors.forename: William M
authors.initials: WM
authors.lastname: Mook
authors.affiliation: Department of Chemistry, University of Alberta , Edmonton, Alberta T6G 2 V4, Canada.
authors.forename: Erik J
authors.initials: EJ
authors.lastname: Luber
authors.affiliation: Center for Integrated Nanotechnologies, Sandia National Laboratories , Albuquerque, New Mexico 87185, United States.
authors.forename: Katherine L
authors.initials: KL
authors.lastname: Jungjohann
authors.affiliation: Department of Materials Science and Engineering, University of Connecticut , Storrs, Connecticut 06269, United States.
authors.forename: C Barry
authors.initials: CB
authors.lastname: Carter
authors.affiliation: Chemical & Biomolecular Engineering and Mechanical Engineering, Clarkson University , 8 Clarkson Avenue, Potsdam, New York 13699, United States.
authors.forename: David
authors.initials: D
authors.lastname: Mitlin
keywords: antimony; in situ TEM; lithium ion battery; operando; sodium ion battery