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Title: Understanding the effects of oxygen defects on the redox reaction pathways in LiVPO 4 F by combining ab initio calculations with experiments

Abstract

Tavorite LiVPO 4F has great potential as a cathode material due to its high energy density, superior thermal stability and fast kinetics. It has been controversial whether the redox reaction pathway of LiVPO 4F is symmetric or not, but the origin of such symmetric/asymmetric redox reaction pathways has not been clearly understood. By combining ab initio calculations with experiments, we found that oxygen defects on fluorine sites, O F-, can be a key factor that affects the symmetry of the redox pathway of LiVPO 4F 1-δO δ (δ < 1). The computational results indicate that (1) the thermodynamically metastable ‘triclinic’ polymorph of VPO 4F 1-δO δ, which maintains the structural symmetry of LiVPO 4F, can be kinetically stabilized considering its marginally higher energy than the stable ‘monoclinic’ phase; and (2) the O F- defects slightly destabilize the intermediate phase ( x = 0.667) (Li 0.667VPO 4F versus Li 0.667VPO 4F 0.917O 0.083), inferring that the presence of O F- defects can induce the asymmetric redox pathway of LiVPO 4F 1-δO δ. We also experimentally found that the concentration of O F- defects is critically affected by the synthesis process of LiVPO 4F, and VPO 4F with lower O F- concentrationmore » can support the possible presence of the metastable (triclinic) phase, leading to the redox pathway being prone to being symmetric. Therefore, controlling oxygen defects by a synthesis processes can affect electrochemical performance via different redox reaction pathways of LiVPO 4F. This understanding provides further possibilities for improving the electrochemical performance.« less

Authors:
ORCiD logo [1];  [1]; ORCiD logo [2]; ORCiD logo [1]
  1. Pohang Univ. of Science and Technology (POSTECH), Pohang (Republic of Korea). Dept. of Materials Science and Engineering
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1569662
Alternate Identifier(s):
OSTI ID: 1512527
Report Number(s):
LLNL-JRNL-755434
Journal ID: ISSN 2050-7488; JMCAET; 942337
Grant/Contract Number:  
AC52-07NA27344
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Materials Chemistry. A
Additional Journal Information:
Journal Volume: 7; Journal Issue: 21; Journal ID: ISSN 2050-7488
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Park, Heetaek, Kim, Minkyung, Kang, ShinYoung, and Kang, Byoungwoo. Understanding the effects of oxygen defects on the redox reaction pathways in LiVPO 4 F by combining ab initio calculations with experiments. United States: N. p., 2019. Web. doi:10.1039/c9ta03070k.
Park, Heetaek, Kim, Minkyung, Kang, ShinYoung, & Kang, Byoungwoo. Understanding the effects of oxygen defects on the redox reaction pathways in LiVPO 4 F by combining ab initio calculations with experiments. United States. doi:10.1039/c9ta03070k.
Park, Heetaek, Kim, Minkyung, Kang, ShinYoung, and Kang, Byoungwoo. Tue . "Understanding the effects of oxygen defects on the redox reaction pathways in LiVPO 4 F by combining ab initio calculations with experiments". United States. doi:10.1039/c9ta03070k.
@article{osti_1569662,
title = {Understanding the effects of oxygen defects on the redox reaction pathways in LiVPO 4 F by combining ab initio calculations with experiments},
author = {Park, Heetaek and Kim, Minkyung and Kang, ShinYoung and Kang, Byoungwoo},
abstractNote = {Tavorite LiVPO4F has great potential as a cathode material due to its high energy density, superior thermal stability and fast kinetics. It has been controversial whether the redox reaction pathway of LiVPO4F is symmetric or not, but the origin of such symmetric/asymmetric redox reaction pathways has not been clearly understood. By combining ab initio calculations with experiments, we found that oxygen defects on fluorine sites, OF-, can be a key factor that affects the symmetry of the redox pathway of LiVPO4F1-δOδ (δ < 1). The computational results indicate that (1) the thermodynamically metastable ‘triclinic’ polymorph of VPO4F1-δOδ, which maintains the structural symmetry of LiVPO4F, can be kinetically stabilized considering its marginally higher energy than the stable ‘monoclinic’ phase; and (2) the OF- defects slightly destabilize the intermediate phase (x = 0.667) (Li0.667VPO4F versus Li0.667VPO4F0.917O0.083), inferring that the presence of OF- defects can induce the asymmetric redox pathway of LiVPO4F1-δOδ. We also experimentally found that the concentration of OF- defects is critically affected by the synthesis process of LiVPO4F, and VPO4F with lower OF- concentration can support the possible presence of the metastable (triclinic) phase, leading to the redox pathway being prone to being symmetric. Therefore, controlling oxygen defects by a synthesis processes can affect electrochemical performance via different redox reaction pathways of LiVPO4F. This understanding provides further possibilities for improving the electrochemical performance.},
doi = {10.1039/c9ta03070k},
journal = {Journal of Materials Chemistry. A},
number = 21,
volume = 7,
place = {United States},
year = {2019},
month = {4}
}

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