Novel ALD Chemistry Enabled Low-Temperature Synthesis of Lithium Fluoride Coatings for Durable Lithium Anodes Lin Chen, †,‡ Kan-Sheng Chen, § Xinjie Chen, § Giovanni Ramirez, †,¶ Zhennan Huang, ∥ Natalie R. Geise, #,∇ Hans-Georg Steinrü ck, # Brandon L. Fisher, ⊥ Reza Shahbazian-Yassar, ∥ Michael F. Toney, # Mark C. Hersam, § and Jeffrey W. Elam* ,†,‡ † Energy System Division, ‡ Joint Center for Energy Storage Research, and ⊥ Nanoscience & Technology Division, Argonne National Laboratory, Lemont, Illinois 60439, United States § Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States ∥ Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, Illinois 60607, United States # Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Center, Menlo Park, California 94025, United States ∇ Department of Chemistry, Stanford University, Stanford, California 94305, United States * S Supporting Information ABSTRACT: Lithium metal anodes can largely enhance the energy density of rechargeable batteries because of the high theoretical capacity and the high negative potential. However, the problem of lithium dendrite formation and low Coulombic efficiency (CE) during electrochemical cycling must be solved before lithium anodes can be widely deployed. Herein, a new atomic layer deposition (ALD) chemistry to realize the low-temperature synthesis of homogeneous and stoichiometric lithium fluoride (LiF) is reported, which then for the first time, as far as we know, is deposited directly onto lithium metal. The LiF preparation is performed at 150 °C yielding 0.8 Å/cycle. The LiF films are found to be crystalline, highly conformal, and stoichiometric with purity levels >99%. Nanoindentation measurements demonstrate the LiF achieving a shear modulus of 58 GPa, 7 times higher than the sufficient value to resist lithium dendrites. When used as the protective coating on lithium, it enables a stable Coulombic efficiency as high as 99.5% for over 170 cycles, about 4 times longer than that of bare lithium anodes. The remarkable battery performance is attributed to the nanosized LiF that serves two critical functions simultaneously: (1) the high dielectric value creates a uniform current distribution for excellent lithium stripping/plating and ultrahigh mechanical strength to suppress lithium dendrites; (2) the great stability and electrolyte isolation by the pure LiF on lithium prevents parasitic reactions for a much improved CE. This new ALD chemistry for conformal LiF not only offers a promising avenue to implement lithium metal anodes for high-capacity batteries but also paves the way for future studies to investigate failure and evolution mechanisms of solid electrolyte interphase (SEI) using our LiF on anodes such as graphite, silicon, and lithium. KEYWORDS: lithium metal anode, atomic layer deposition, new chemistry, lithium fluoride, high shear modulus 1. INTRODUCTION Societal demands for energy storage in portable electronics, electric vehicles, and renewable energy are driving the development of advanced battery technologies. 1−3 For instance, the modest charge storage capacity of the graphite anodes used in commercial lithium ion batteries (372 mAh/g) has motivated research to discover a higher-capacity alternative anode material. 4−7 Lithium metal is an ideal anode for rechargeable lithium-based batteries because of its high theoretical capacity (3860 mAh/g) and low redox potential (−3.04 V vs standard hydrogen electrode). 5,8,9 Lithium metal anodes also facilitate high-energy cathodes (e.g., sulfur or air) for next-generation systems. 10 However, the large-scale deployment of lithium metal anodes in rechargeable batteries has been hindered by severe technical hurdles, including large volumetric changes and lithium dendrite formation during cycling, 11,12 resulting in low Coulombic efficiency and short cycling life. 13,14 Many of the problems plaguing lithium metal anodes result from deficiencies in the solid electrolyte interphase (SEI) that can form spontaneously when lithium metal contacts the organic electrolyte. For instance, this spontaneous SEI is Received: March 23, 2018 Accepted: July 9, 2018 Published: July 9, 2018 Research Article www.acsami.org Cite This: ACS Appl. Mater. Interfaces 2018, 10, 26972-26981 © 2018 American Chemical Society 26972 DOI: 10.1021/acsami.8b04573 ACS Appl. Mater. Interfaces 2018, 10, 26972−26981 Downloaded via NORTHWESTERN UNIV on November 6, 2018 at 00:05:19 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.