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Title: Structure Stabilization by Mixed Anions in Oxyfluoride Cathodes for High-Energy Lithium Batteries

Mixed-anion oxyfluorides (i.e., FeOxF2-x) are an appealing alternative to pure fluorides as high-capacity cathodes in lithium batteries, with enhanced cyclability via oxygen substitution. Yet, it is still unclear how the mixed anions impact the local phase transformation and structural stability of oxyfluorides during cycling due to the complexity of electrochemical reactions, involving both lithium intercalation and conversion. Herein, we investigated the local chemical and structural ordering in FeO0.7F1.3 at length scales spanning from single particles to the bulk electrode, via a combination of electron spectrum-imaging, magnetization, electrochemistry, and synchrotron X-ray measurements. The FeO0.7F1.3 nanoparticles retain a FeF2-like rutile structure but chemically heterogeneous, with an F-rich core covered by thin O-rich shell. Upon lithiation the O-rich rutile phase is transformed into Li—Fe—O(—F) rocksalt that has high lattice coherency with converted metallic Fe, a feature that may facilitate the local electron and ion transport. The O-rich rocksalt is highly stable over lithiation/delithiation and thus advantageous to maintain the integrity of the particle, and due to its predominant distribution on the surface, it is expected to prevent the catalytic interaction of Fe with electrolyte. Our findings of the structural origin of cycling stability in oxyfluorides may provide insights into developing viable high-energymore » electrodes for lithium batteries.« less
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [4] ;  [3] ;  [2] ;  [2] ;  [2]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States); Korea Atomic Energy Research Institute, Daejeon (Korea)
  2. Rutgers Univ., New Brunswick, NJ (United States)
  3. State Univ. of New York at Binghampton, Binghampton, NY (United States)
  4. Brookhaven National Lab. (BNL), Upton, NY (United States)
Publication Date:
OSTI Identifier:
1239785
Report Number(s):
BNL--111677-2015-JA
Journal ID: ISSN 1936-0851; YN0100000
Grant/Contract Number:
SC0012704
Type:
Accepted Manuscript
Journal Name:
ACS Nano
Additional Journal Information:
Journal Volume: 9; Journal Issue: 10; Journal ID: ISSN 1936-0851
Publisher:
American Chemical Society
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
25 ENERGY STORAGE lithium batteries; mixed-anion cathodes; iron oxyfluoride; scanning transmission electron microscopy (STEM); electron energy loss spectroscopy (EELS)