title: Reversible Li-Ion Conversion Reaction for a TixGe Alloy in a Ti/Ge Multilayer.
abstract: Group IV intermetallics electrochemically alloy with Li with stoichiometries as high as Li4.4M (M = Si, Ge, Sn, or Pb). This provides the second highest known specific capacity (after pure lithium metal) for lithium-ion batteries, but the dramatic volume change during cycling greatly limits their use as anodes in Li-ion batteries. We describe an approach to overcome this limitation by constructing electrodes using a Ge/Ti multilayer architecture. In operando X-ray reflectivity and ex situ transmission electron microscopy are used to characterize the heterolayer structure at various lithium stoichiometries along a lithiation/delithiation cycle. The as-deposited multilayer spontaneously forms a one-dimensional TixGe/Ti/TixGe core-shell planar structure embedded in a Ge matrix. The interfacial TixGe alloy is observed to be electrochemically active and exhibits reversible phase separation (i.e., a conversion reaction). Including the germanium components, the overall multilayer structure exhibits a 2.3-fold reversible vertical expansion and contraction and is shown to have improved capacity and capacity retention with respect to a Ge film with equivalent active material thickness.
authors.affiliation: Chemical Sciences and Engineering Division, Argonne National Laboratory , Lemont, Illinois 60439, United States.|Applied Physics Program and Materials Science and Engineering Department, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Xiao
authors.initials: X
authors.lastname: Chen
authors.affiliation: Chemical Sciences and Engineering Division, Argonne National Laboratory , Lemont, Illinois 60439, United States.
authors.forename: Tim T
authors.initials: TT
authors.lastname: Fister
authors.affiliation: Chemistry Department, University of Illinois Urbana-Champaign , Champaign, Illinois 61801, United States.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Esbenshade
authors.affiliation: Chemical Sciences and Engineering Division, Argonne National Laboratory , Lemont, Illinois 60439, United States.
authors.forename: Bing
authors.initials: B
authors.lastname: Shi
authors.affiliation: Applied Physics Program and Materials Science and Engineering Department, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Xianyi
authors.initials: X
authors.lastname: Hu
authors.affiliation: Applied Physics Program and Materials Science and Engineering Department, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Jinsong
authors.initials: J
authors.lastname: Wu
authors.affiliation: Chemistry Department, University of Illinois Urbana-Champaign , Champaign, Illinois 61801, United States.
authors.forename: Andrew A
authors.identifier: http://orcid.org/0000-0003-4400-9907
authors.initials: AA
authors.lastname: Gewirth
authors.affiliation: Applied Physics Program and Materials Science and Engineering Department, Northwestern University , Evanston, Illinois 60208, United States.
authors.forename: Michael J
authors.identifier: http://orcid.org/0000-0002-1026-4558
authors.initials: MJ
authors.lastname: Bedzyk
authors.affiliation: Chemical Sciences and Engineering Division, Argonne National Laboratory , Lemont, Illinois 60439, United States.
authors.forename: Paul
authors.identifier: http://orcid.org/0000-0002-6672-9748
authors.initials: P
authors.lastname: Fenter
keywords: Ge/Ti alloy; Li-ion battery; Patterson function; X-ray reflectivity; germanium; multilayer; thin film