Mechanism of electrochemical activity in Li2MnO3

Alastair D. Robertson, Peter G. Bruce*

*Corresponding author for this work

Research output: Contribution to journalArticle

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 O2-. To investigate this phenomenon we have selected Li2MnO3, a layered compound Li[Li1/3Mn2/3]O2 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 °C this occurs exclusively by oxidation of the nonaqueous electrolyte, thus generating H+ which exchange one-for-one with Li+ to form Li2-xHxMnO3. 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 °C 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 °C. 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 number10
Early online date5 Apr 2003
DOIs
Publication statusPublished - 1 May 2003

Keywords

  • electrochemical activity
  • lithium batteries
  • oxidation

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