title: Anodes for sodium ion batteries based on tin-germanium-antimony alloys.
abstract: Here we provide the first report on several compositions of ternary Sn-Ge-Sb thin film alloys for application as sodium ion battery (aka NIB, NaB or SIB) anodes, employing Sn50Ge50, Sb50Ge50, and pure Sn, Ge, Sb as baselines. Sn33Ge33Sb33, Sn50Ge25Sb25, Sn60Ge20Sb20, and Sn50Ge50 all demonstrate promising electrochemical behavior, with Sn50Ge25Sb25 being the best overall. This alloy has an initial reversible specific capacity of 833 mAhg(-1) (at 85 mAg(-1)) and 662 mAhg(-1) after 50 charge-discharge cycles. Sn50Ge25Sb25 also shows excellent rate capability, displaying a stable capacity of 381 mAhg(-1) at a current density of 8500 mAg(-1) (∼10C). A survey of published literature indicates that 833 mAhg(-1) is among the highest reversible capacities reported for a Sn-based NIB anode, while 381 mAhg(-1) represents the optimum fast charge value. HRTEM shows that Sn50Ge25Sb25 is a composite of 10-15 nm Sn and Sn-alloyed Ge nanocrystallites that are densely dispersed within an amorphous matrix. Comparing the microstructures of alloys where the capacity significantly exceeds the rule of mixtures prediction to those where it does not leads us to hypothesize that this new phenomenon originates from the Ge(Sn) that is able to sodiate beyond the 1:1 Na:Ge ratio reported for the pure element. Combined TOF-SIMS, EELS TEM, and FIB analysis demonstrates substantial Na segregation within the film near the current collector interface that is present as early as the second discharge, followed by cycling-induced delamination from the current collector.
authors.affiliation: Department of Chemical and Materials Engineering, University of Alberta , 9107 116th Street, Edmonton, Alberta, T6G 2V4, Canada.
authors.forename: Behdokht
authors.initials: B
authors.lastname: Farbod
authors.forename: Kai
authors.initials: K
authors.lastname: Cui
authors.forename: W Peter
authors.initials: WP
authors.lastname: Kalisvaart
authors.forename: Martin
authors.initials: M
authors.lastname: Kupsta
authors.forename: Beniamin
authors.initials: B
authors.lastname: Zahiri
authors.forename: Alireza
authors.initials: A
authors.lastname: Kohandehghan
authors.forename: Elmira Memarzadeh
authors.initials: EM
authors.lastname: Lotfabad
authors.forename: Zhi
authors.initials: Z
authors.lastname: Li
authors.forename: Erik J
authors.initials: EJ
authors.lastname: Luber
authors.forename: David
authors.initials: D
authors.lastname: Mitlin