Computational and Experimental Investigation of the Electrochemical Stability and Li-Ion Conduction Mechanism of LiZr 2 (PO 4 ) 3 Yusuke Noda,* ,† Koki Nakano, ‡ Hayami Takeda, ‡,§ Masashi Kotobuki, ∥,⊥ Li Lu, ∥,⊥ and Masanobu Nakayama †,‡,§,# † Center for Materials Research by Information Integration (CMI 2 ), Research and Services Division of Materials Data and Integrated System (MaDIS), National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan ‡ Frontier Research Institute for Materials Science (FRIMS), Nagoya Institute of Technology, Gokiso, Showa, Nagoya, Aichi 466-8555, Japan § Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, 1-30 Goryo-Ohara, Nishikyo, Kyoto 615-8245, Japan ∥ Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117575, Singapore ⊥ National University of Singapore Suzhou Research Institute, Dushu Lake Science and Education Innovation District, Suzhou 215123, P. R. China # Global Research Center for Environment and Energy Based on Nanomaterials Science (GREEN), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0047, Japan * S Supporting Information ABSTRACT: Solid electrolytes possessing sufficient ionic conductivity and electrochemical stability are urgently needed for the fabrication of all-solid-state Li-ion batteries (LIBs). In this study, we focus on a solid-state oxide electrolyte LiZr 2 (PO 4 ) 3 (LZP), which has NASICON structure and electrochemically stable Zr 4+ ions. Using density functional theory (DFT) to calculate the electrochemical window of LZP, we find that it is unstable against Li metal, in accordance with our experimental results. The Li-ion transport is investigated using first-principles molecular dynamics (FPMD) simulations. The calculated Li-ion conductivity at room temperature (5.0 × 10 −6 S/cm) and the activation energy for Li-ion diffusion (0.43 eV) are in fair agreement with experimental results. The mechanism of Li-ion conduction in LZP is revealed by analyzing the Li-ion trajectories in the FPMD simulations. It is found that each Li ion migrates between 6b sites as it is pushed out or repelled by other Li ions around these 6b sites. Hence, the high Li-ion conductivity is attributed to a migration mechanism driven by Frenkel-like defect. 1. INTRODUCTION The Li-ion battery (LIB) is one of the most popular types of rechargeable batteries with high energy density, long cycle life, and good safety. LIBs have been widely used for electric vehicles, smartphones, laptops, and so on. 1 At present, the prevailing electrolytes for LIBs are organic liquid solvents, such as dimethyl carbonate and ethylene carbonate. However, these electrolytes are at risk of liquid leakage, inflammation, and/or explosion caused by short circuit. 2 One attractive and important solution to this problem is replacing the organic liquid electrolytes with inorganic solid electrolytes. Such solid electrolytes are indispensable for all- solid-state batteries. Sulfide-based solid electrolytes such as Li 10 GeP 2 S 12 (LGPS) are well-known as good ionic conductors with high Li-ion conductivity (10 −2 S/cm) because of their three-dimensional diffusion channels. 3−5 However, sulfides present difficulties in the fabrication of all-solid-state batteries, as they tend to react with water and generate hydrogen sulfide gas. From this point of view, it is advisable to use oxide-based solid electrolytes instead. Unfortunately, compared with sulfide- based solid electrolytes, the oxide-based ones exhibit lower Li- ion conductivity at room temperature (in the order of 10 −3 S/ cm at the highest). Therefore, it is essential to improve their ionic conductivity. Na super ionic conductor (NASICON)-type oxide-based solid electrolytes, as well as perovskite-type and garnet-type Received: April 26, 2017 Revised: October 18, 2017 Published: October 18, 2017 Article pubs.acs.org/cm © 2017 American Chemical Society 8983 DOI: 10.1021/acs.chemmater.7b01703 Chem. Mater. 2017, 29, 8983−8991 Cite This: Chem. Mater. 2017, 29, 8983-8991 Downloaded via NAGOYA INST OF TECHNOLOGY on November 8, 2019 at 02:50:32 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.