title: Enhanced Lithiation Cycle Stability of ALD-Coated Confined a-Si Microstructures Determined Using In Situ AFM.
abstract: Microfabricated amorphous silicon (a-Si) pits ∼4 μm in diameter and 100 nm thick were fabricated to be partially confined in a nickel (Ni) current collector. Corresponding unconfined pillars were also fabricated. The samples were coated with 1.5, 3, or 6 nm of Al2O3 ALD. These samples were tested in electrolytes of 3:7 by weight ethylene carbonate:ethyl methyl carbonate (EC:EMC) with 1.2 M LiPF6 salt with and without 2% fluoroethylene carbonate (FEC) and in a pure FEC electrolyte with 10 wt % LiPF6. The samples were imaged with an atomic force microscope during electrochemical cycling to evaluate morphology evolution and solid electrolyte interphase (SEI) formation. The partially confined a-Si structures had superior cycle efficiency relative to the unconfined a-Si pillars. Additionally, samples with 3 nm of ALD achieved higher charge capacity and enhanced cycle life compared to samples without ALD, demonstrated thinner SEI formation, and after 10 cycles at a 1 C rate remained mostly intact and had actually decreased in diameter. Finally, the samples with 3 nm of ALD had better capacity retention in the baseline 3:7 EC:EMC than in either of the FEC containing electrolytes.
authors.affiliation: Electrochemistry Branch, US Army Research Laboratory , 2800 Powder Mill Road, Adelphi, Maryland 20783, United States.
authors.forename: Collin R
authors.initials: CR
authors.lastname: Becker
authors.affiliation: Electronic Science & Technology Division, US Naval Research Laboratory , Washington, DC 20375, United States.
authors.forename: S M
authors.initials: SM
authors.lastname: Prokes
authors.affiliation: Chemistry Division, US Naval Research Laboratory , Washington, DC 20375, United States.
authors.forename: Corey T
authors.initials: CT
authors.lastname: Love
keywords: atomic force microscopy; battery; in situ; lithium ion; silicon