title: In situ transmission electron microscopy investigation of the electrochemical lithiation-delithiation of individual Co9S8/Co-filled carbon nanotubes.
abstract: Carbon nanotube (CNT)-encapsulated metal sulfides/oxides are promising candidates for application as anode materials in lithium ion battery (LIB), while their electrochemical behavior and mechanism still remain unclear. A comprehensive understanding of the lithiation mechanism at nanoscale of this type of composites will benefit the design and development of high-performance LIB materials. Here, we use Co9S8/Co nanowire-filled CNTs as a model material to investigate the lithium storage mechanism by in situ transmission electron microscopy. For a Co9S8/Co nanowire-filled closed CNT, the reaction front propagates progressively during lithiation, causing an axial elongation of 4.5% and a radial expansion of 32.4%, while the lithiated nanowire core is still confined inside the CNT. Contrastingly, for an open CNT, the lithiated Co9S8 nanowire shows an axial elongation of 94.2% and is extruded out from the open CNT. In particular, a thin graphite shell is drawn out from the CNT wall by the extruded lithiated Co9S8. The thin graphite shell confines the extruded filler and protects the filler from pulverization in the following lithiation-delithiation cycles. During multiple cycles, the Co segment remains intact while the Co9S8 exhibits a reversible transformation between Co9S8 and Co nanograins. Our observations provide direct electrochemical behavior and mechanism that govern the CNT-based anode performance in LIBs.
authors.affiliation: Institute of Physical Chemistry, Zhejiang Normal University , Jinhua 321004, China.
authors.forename: Qingmei
authors.initials: Q
authors.lastname: Su
authors.forename: Gaohui
authors.initials: G
authors.lastname: Du
authors.forename: Jun
authors.initials: J
authors.lastname: Zhang
authors.forename: Yijun
authors.initials: Y
authors.lastname: Zhong
authors.forename: Bingshe
authors.initials: B
authors.lastname: Xu
authors.forename: Yuehai
authors.initials: Y
authors.lastname: Yang
authors.forename: Suman
authors.initials: S
authors.lastname: Neupane
authors.forename: Kamal
authors.initials: K
authors.lastname: Kadel
authors.forename: Wenzhi
authors.initials: W
authors.lastname: Li