title: Microstructural evolution of tin nanoparticles during in situ sodium insertion and extraction.
abstract: The microstructural changes and phase transformations of tin nanoparticles during electrochemical sodiation were studied with a nanosized sodium ion battery using in situ transmission electron microscopy. It was found that the first sodiation process occurred in two steps; that is, the crystalline Sn nanoparticles were initially sodiated via a two-phase mechanism with a migrating phase boundary to form a Na-poor, amorphous Na(x)Sn alloy (x ~ 0.5), which was further sodiated to several Na-rich amorphous phases and finally to the crystallized Na(15)Sn(4) (x = 3.75) via a single-phase mechanism. The volumetric expansion was about 60% in the first step and 420% after the second step. However, despite the huge expansion, cracking or fracture was not observed, which is attributed to the second step of the single-phase sodiation that accommodates large portion of the sodiation-induced stress over the entire particle. Excellent cyclability was also observed during the reversible sodiation/desodiation cycles, showing great potential of Sn nanoparticles as a robust electrode material for rechargeable batteries.
authors.affiliation: Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
authors.forename: Jiang Wei
authors.initials: JW
authors.lastname: Wang
authors.forename: Xiao Hua
authors.initials: XH
authors.lastname: Liu
authors.forename: Scott X
authors.initials: SX
authors.lastname: Mao
authors.forename: Jian Yu
authors.initials: JY
authors.lastname: Huang