Effect of Fluoride Doping on Lithium Diffusivity in Layered Molybdenum Oxide

Allison Wustrow, Justin C. Hancock, Jared T. Incorvati, John T. Vaughey, Kenneth R Poeppelmeier

Research output: Contribution to journalArticle

Abstract

The effects of cation doping on cathode performance has been extensively studied; however, the field of anion doping has historically received much less attention. Fluoride doping can greatly increase the initial diffusivity of the layered MoO 3 system. The first discharge cycle of the layered α-MoO 3 and MoO 2.8 F 0.2 phases were investigated and compared using the galvanostatic intermittent titration technique (GITT) in a lithium ion cell. The analysis revealed that a slight reduction of the oxide by fluoride doping to form a fluorobronze (MoO 2.8 F 0.2 ) eliminated a slow electrochemical process observed in α-MoO 3 . Galvanostatic cycling studies show that while α-MoO 3 has a higher initial capacity, it exhibits a first cycle Coulombic efficiency of only 86% with rapid capacity fade which has been associated with lithium trapping within the MoO 3 layer. In contrast, the Li + intercalation process in the fluorobronze was found to have a 94% Coulombic efficiency on the first cycle. By the third cycle Coulombic efficiencies greater than 99% were observed for five cycles. A thorough investigation of the synthesis of MoO 2.8 F 0.2 is also presented. Under mild hydrothermal conditions, the fluorination of α-MoO 3 to form MoO 2.8 F 0.2 is topotactic, while a competing reaction in solution forms MoO 2.4 F 0.6 (ReO 3 structure). Methods to prevent the solution phase reaction from occurring are discussed.

Original languageEnglish
Pages (from-to)2080-2086
Number of pages7
JournalACS Applied Energy Materials
Volume2
Issue number3
DOIs
Publication statusPublished - Mar 25 2019

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Keywords

  • batteries
  • fluoride doping
  • galvanostatic intermittent titration technique
  • lithium intercalation
  • molybdenum oxide

ASJC Scopus subject areas

  • Energy Engineering and Power Technology
  • Chemical Engineering (miscellaneous)
  • Electrochemistry
  • Materials Chemistry
  • Electrical and Electronic Engineering

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