title: Pore collapse and regrowth in silicon electrodes for rechargeable batteries.
abstract: Structure and composition of an 11 nm thick amorphous silicon (a-Si) thin film anode, capped with 4 nm of alumina are measured, in operando, by neutron reflectivity (NR) and electrochemical impedance spectroscopy in a lithium half-cell. NR data are analyzed to quantify the a-Si thickness and composition at various states of charge over six cycles. The a-Si anode expands and contracts upon lithiation and delithiation, respectively, while maintaining its integrity and low interfacial roughness (≤1.6 nm) throughout the cycling. The apparently non-linear expansion of the a-Si layer volume versus lithium content agrees with previous thin-film a-Si anode studies. However, a proposed pore collapse and regrowth (PCRG) mechanism establishes that the solid domains in the porous LixSi film expand linearly with Li content at 8.48 cm(3) mol(-1) Li, similar to crystalline Si. In the PCRG model, porosity is first consumed by expansion of solid domains upon lithiation, after which the film as a whole expands. Porosity is reestablished at 5-28% upon delithiation. Data show that the alumina protective layer on the a-Si film functions as an effective artificial solid electrolyte interphase (SEI), maintaining its structural integrity, low interfacial roughness, and relatively small transport resistance. No additional spontaneously-formed SEI is observed in this study.
authors.affiliation: Department of Mechanical Engineering, Colorado School of Mines, Golden, CO, USA.
authors.forename: S C
authors.initials: SC
authors.lastname: DeCaluwe
authors.forename: B M
authors.initials: BM
authors.lastname: Dhar
authors.forename: L
authors.initials: L
authors.lastname: Huang
authors.forename: Y
authors.initials: Y
authors.lastname: He
authors.forename: K
authors.initials: K
authors.lastname: Yang
authors.forename: J P
authors.initials: JP
authors.lastname: Owejan
authors.forename: Y
authors.initials: Y
authors.lastname: Zhao
authors.forename: A A
authors.initials: AA
authors.lastname: Talin
authors.forename: J A
authors.initials: JA
authors.lastname: Dura
authors.forename: H
authors.initials: H
authors.lastname: Wang