title: In situ transmission electron microscopy probing of native oxide and artificial layers on silicon nanoparticles for lithium ion batteries.
abstract: Surface modification of silicon nanoparticles via molecular layer deposition (MLD) has been recently proved to be an effective way for dramatically enhancing the cyclic performance in lithium ion batteries. However, the fundamental mechanism of how this thin layer of coating functions is not known, which is complicated by the inevitable presence of native oxide of several nanometers on the silicon nanoparticle. Using in situ TEM, we probed in detail the structural and chemical evolution of both uncoated and coated silicon particles upon cyclic lithiation/delithation. We discovered that upon initial lithiation, the native oxide layer converts to crystalline Li2O islands, which essentially increases the impedance on the particle, resulting in ineffective lithiation/delithiation and therefore low Coulombic efficiency. In contrast, the alucone MLD-coated particles show extremely fast, thorough, and highly reversible lithiation behaviors, which are clarified to be associated with the mechanical flexibility and fast Li(+)/e(-) conductivity of the alucone coating. Surprisingly, the alucone MLD coating process chemically changes the silicon surface, essentially removing the native oxide layer, and therefore mitigates side reactions and detrimental effects of the native oxide. This study provides a vivid picture of how the MLD coating works to enhance the Coulombic efficiency, preserves capacity, and clarifies the role of the native oxide on silicon nanoparticles during cyclic lithiation and delithiation. More broadly, this work also demonstrates that the effect of the subtle chemical modification of the surface during the coating process may be of equal importance to the coating layer itself.
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory , 902 Battelle Boulevard, Richland, Washington 99352, United States.
authors.forename: Yang
authors.initials: Y
authors.lastname: He
authors.forename: Daniela Molina
authors.initials: DM
authors.lastname: Piper
authors.forename: Meng
authors.initials: M
authors.lastname: Gu
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Travis
authors.forename: Steven M
authors.initials: SM
authors.lastname: George
authors.forename: Se-Hee
authors.initials: SH
authors.lastname: Lee
authors.forename: Arda
authors.initials: A
authors.lastname: Genc
authors.forename: Lee
authors.initials: L
authors.lastname: Pullan
authors.forename: Jun
authors.initials: J
authors.lastname: Liu
authors.forename: Scott X
authors.initials: SX
authors.lastname: Mao
authors.forename: Ji-Guang
authors.initials: JG
authors.lastname: Zhang
authors.forename: Chunmei
authors.initials: C
authors.lastname: Ban
authors.forename: Chongmin
authors.initials: C
authors.lastname: Wang
keywords: aluminum glycerol; coating; in situ TEM; lithium ion battery; native oxide; silicon nanoparticle