Mechanism of electrochemical activity in Li2MnO3

A D Robertson, P G Bruce

Research output: Contribution to journalArticlepeer-review

411 Citations (Scopus)

Abstract

Lithium intercalation compounds based on lithium manganese oxides are of great importance as positive electrodes for rechargeable lithium batteries. It is widely accepted that Li+ may be extracted (deintercalated) from such lithium manganese oxides accompanied by oxidation of Mn up to a maximum oxidation state of +4. However, it has been suggested recently that further Li+ removal may be possible. Among the mechanisms that have been proposed to charge balance the removal of Li+ are Mn oxidation beyond +4 or loss of O-2(-). To investigate this phenomenon we have selected Li2MnO3, a layered compound Li[Li1/3Mn2/3]O-2.(2) with a ready supply of mobile Li+ ions but with all Mn already in the +4 oxidation state. We show that a substantial quantity of Li (at least 1.39 Li) may be removed. At 55 degreesC this occurs exclusively by oxidation of the nonaqueous electrolyte, thus generating H+ which exchange one-for-one with Li+ to form Li2-xHMnO3. The presence of H+ between the oxide layers results in a change of the layer stacking from O3 to P3, the latter being more stable for O-H-O bonding. At 30 degreesC initial Li removal is accompanied by oxygen loss (effective removal of Li2O) but further Li+ removal involves the same proton exchange mechanism as observed at 55 degreesC. The reaction is partially reversible. On extended cycling the material converts to spinel.

Original languageEnglish
Pages (from-to)1984-1992
Number of pages9
JournalChemistry of Materials
Volume15
Issue number9
DOIs
Publication statusPublished - 20 May 2003

Keywords

  • RECHARGEABLE LITHIUM BATTERIES
  • MANGANESE OXIDE
  • ION-EXCHANGE
  • ELECTRODES
  • SPINEL
  • INSERTION
  • INTERCALATION
  • PERFORMANCE
  • CHEMISTRY
  • CARBONATE

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