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Enhanced Lithiation Cycle Stability of ALD-Coated Confined a‑Si Microstructures Determined Using In Situ AFM

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journal contribution
posted on 13.01.2016, 00:00 by Collin R. Becker, S.M. Prokes, Corey T. Love
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.