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Title: Short-Range Order and Unusual Modes of Nickel Redox in a Fluorine-Substituted Disordered Rocksalt Oxide Lithium-Ion Cathode

Abstract

Fluorine substitution for oxygen in cation-disordered lithium-excess transition metal oxides (Li 1+xTM 1-xO 2) used as lithium-ion cathodes was recently demonstrated to improve the reversibility of the processes taking place on charge and discharge by reducing the amount of oxygen loss on charge and preventing major structural rearrangements at high voltage. Yet, little is understood about how fluorine incorporates the oxide structure and impacts its electrochemical properties. We use a combination of experimental (solid-state nuclear magnetic resonance (NMR) spectroscopy) and theoretical techniques (density functional theory (DFT) calculations and Monte Carlo simulations) to investigate the evolution of the local structure around fluorine and lithium and the oxidation state of redox-active nickel during charge and discharge of the Li 1.15Ni 0.45Ti 0.3Mo 0.1O 1.85F 0.15 (LNF15) cathode. We show that fluorine doping introduces short-range order in as-synthesized LNF15 by incorporating in lithium-rich sites with five or six lithium nearest neighbors. We observe the emergence of new signals in the ex situ 19F NMR spectra taken at high states of charge, which we tentatively assign to undercoordinated, diamagnetic fluorine environments seen in our computed models. Our theoretical results also suggest that octahedral nickel ions directly bonded to fluorine follow a different oxidation mechanismmore » than those surrounded by six oxygens, forming Ni 3+ intermediates instead of oxidizing from Ni 2+ directly to Ni 4+. While the oxidation of Ni 2+ toward Ni 4+ is incomplete in oxides, due to overlap between the oxygen and the nickel valence states, this result suggests that fluorination may be an efficient strategy to utilize the Ni 2+/Ni 4+ redox reservoir to a greater extent.« less

Authors:
ORCiD logo [1];  [2];  [3];  [4]
  1. Univ. of California, Berkeley, CA (United States). Dept. of Materials Science and Engineering; Univ. of California, Santa Barbara, CA (United States). Dept. of Materials
  2. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Dept. of Materials Science and Engineering
  3. Univ. of California, Berkeley, CA (United States). Dept. of Materials Science and Engineering; Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Dept. of Nuclear Science and Engineering
  4. Univ. of California, Berkeley, CA (United States). Dept. of Materials Science and Engineering; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (EE-3V); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Scientific User Facilities Division; Robert Bosch LLC, Farmington Hills, MI (United States); Umicore Cobalt & Specialty Materials (CSM), Brussels (Belgium); National Science Foundation (NSF)
OSTI Identifier:
1473706
Alternate Identifier(s):
OSTI ID: 1571113
Grant/Contract Number:  
AC02-05CH11231; DMR 1720256
Resource Type:
Accepted Manuscript
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 30; Journal Issue: 19; Journal ID: ISSN 0897-4756
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
25 ENERGY STORAGE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Li-ion batteries; Lithium transition metal oxides; NMR; disordered rocksalt cathodes; Monte Carlo simulations; density functional theory

Citation Formats

Clément, Raphaële J., Kitchaev, Daniil, Lee, Jinhyuk, and Ceder, Gerbrand. Short-Range Order and Unusual Modes of Nickel Redox in a Fluorine-Substituted Disordered Rocksalt Oxide Lithium-Ion Cathode. United States: N. p., 2018. Web. doi:10.1021/acs.chemmater.8b03794.
Clément, Raphaële J., Kitchaev, Daniil, Lee, Jinhyuk, & Ceder, Gerbrand. Short-Range Order and Unusual Modes of Nickel Redox in a Fluorine-Substituted Disordered Rocksalt Oxide Lithium-Ion Cathode. United States. doi:10.1021/acs.chemmater.8b03794.
Clément, Raphaële J., Kitchaev, Daniil, Lee, Jinhyuk, and Ceder, Gerbrand. Fri . "Short-Range Order and Unusual Modes of Nickel Redox in a Fluorine-Substituted Disordered Rocksalt Oxide Lithium-Ion Cathode". United States. doi:10.1021/acs.chemmater.8b03794. https://www.osti.gov/servlets/purl/1473706.
@article{osti_1473706,
title = {Short-Range Order and Unusual Modes of Nickel Redox in a Fluorine-Substituted Disordered Rocksalt Oxide Lithium-Ion Cathode},
author = {Clément, Raphaële J. and Kitchaev, Daniil and Lee, Jinhyuk and Ceder, Gerbrand},
abstractNote = {Fluorine substitution for oxygen in cation-disordered lithium-excess transition metal oxides (Li1+xTM1-xO2) used as lithium-ion cathodes was recently demonstrated to improve the reversibility of the processes taking place on charge and discharge by reducing the amount of oxygen loss on charge and preventing major structural rearrangements at high voltage. Yet, little is understood about how fluorine incorporates the oxide structure and impacts its electrochemical properties. We use a combination of experimental (solid-state nuclear magnetic resonance (NMR) spectroscopy) and theoretical techniques (density functional theory (DFT) calculations and Monte Carlo simulations) to investigate the evolution of the local structure around fluorine and lithium and the oxidation state of redox-active nickel during charge and discharge of the Li1.15Ni0.45Ti0.3Mo0.1O1.85F0.15 (LNF15) cathode. We show that fluorine doping introduces short-range order in as-synthesized LNF15 by incorporating in lithium-rich sites with five or six lithium nearest neighbors. We observe the emergence of new signals in the ex situ 19F NMR spectra taken at high states of charge, which we tentatively assign to undercoordinated, diamagnetic fluorine environments seen in our computed models. Our theoretical results also suggest that octahedral nickel ions directly bonded to fluorine follow a different oxidation mechanism than those surrounded by six oxygens, forming Ni3+ intermediates instead of oxidizing from Ni2+ directly to Ni4+. While the oxidation of Ni2+ toward Ni4+ is incomplete in oxides, due to overlap between the oxygen and the nickel valence states, this result suggests that fluorination may be an efficient strategy to utilize the Ni2+/Ni4+ redox reservoir to a greater extent.},
doi = {10.1021/acs.chemmater.8b03794},
journal = {Chemistry of Materials},
number = 19,
volume = 30,
place = {United States},
year = {2018},
month = {9}
}

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