title: Lithiation-induced embrittlement of multiwalled carbon nanotubes.
abstract: Lithiation of individual multiwalled carbon nanotubes (MWCNTs) was conducted in situ inside a transmission electron microscope. Upon lithiation, the intertube spacing increased from 3.4 to 3.6 Å, corresponding to about 5.9% radial and circumferential expansions and ∼50 GPa tensile hoop stress on the outermost tube wall. The straight tube walls became distorted after lithiation. In situ compression and tension tests show that the lithiated MWCNTs were brittle with sharp fracture edges. Such a failure mode is in stark contrast with that of the pristine MWCNTs which are extremely flexible and fail in a "sword-in-sheath" manner upon tension. The lithiation-induced embrittlement is attributed to the mechanical effect of a "point-force" action posed by the intertubular lithium that induces the stretch of carbon-carbon bonds in addition to that by applied strain, as well as the chemical effect of electron transfer from lithium to the antibonding π orbital that weakens the carbon-carbon bond. The combined mechanical and chemical weakening leads to a considerable decrease of the fracture strain in lithiated MWCNTs. Our results provide direct evidence and understanding of the degradation mechanism of carbonaceous anodes in lithium ion batteries.
authors.affiliation: Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.forename: He
authors.initials: H
authors.lastname: Zheng
authors.forename: Xiao Hua
authors.initials: XH
authors.lastname: Liu
authors.forename: Shan
authors.initials: S
authors.lastname: Huang
authors.forename: Ting
authors.initials: T
authors.lastname: Zhu
authors.forename: Jiangwei
authors.initials: J
authors.lastname: Wang
authors.forename: Akihiro
authors.initials: A
authors.lastname: Kushima
authors.forename: Nicholas S
authors.initials: NS
authors.lastname: Hudak
authors.forename: Xu
authors.initials: X
authors.lastname: Huang
authors.forename: Sulin
authors.initials: S
authors.lastname: Zhang
authors.forename: Scott X
authors.initials: SX
authors.lastname: Mao
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Qian
authors.forename: Ju
authors.initials: J
authors.lastname: Li
authors.forename: Jian Yu
authors.initials: JY
authors.lastname: Huang