JOURNAL ARTICLE

Mechanism of Electrochemical Activity in Li<sub>2</sub>MnO<sub>3</sub>

Alastair D. Robertson (122829)Peter G. Bruce (1500148)

Year: 2016 Journal:   OPAL (Open@LaTrobe) (La Trobe University)   Publisher: La Trobe University

Abstract

Lithium intercalation compounds based on lithium manganese oxides are of great\nimportance as positive electrodes for rechargeable lithium batteries. It is widely accepted\nthat Li<sup>+</sup> may be extracted (deintercalated) from such lithium manganese oxides accompanied\nby oxidation of Mn up to a maximum oxidation state of +4. However, it has been suggested\nrecently that further Li<sup>+</sup> removal may be possible. Among the mechanisms that have been\nproposed to charge balance the removal of Li<sup>+</sup> are Mn oxidation beyond +4 or loss of O<sup>2-</sup>.\nTo investigate this phenomenon we have selected Li<sub>2</sub>MnO<sub>3</sub>, a layered compound Li[Li<sub>1/3</sub>Mn<sub>2/3</sub>]O<sub>2</sub>\nwith a ready supply of mobile Li<sup>+</sup> ions but with all Mn already in the +4 oxidation state.\nWe show that a substantial quantity of Li (at least 1.39 Li) may be removed. At 55 °C this\noccurs exclusively by oxidation of the nonaqueous electrolyte, thus generating H<sup>+</sup> which\nexchange one-for-one with Li<sup>+</sup> to form Li<sub>2</sub><sub>-</sub><i><sub>x</sub></i>H<i><sub>x</sub></i>MnO<sub>3</sub>. The presence of H<sup>+</sup> between the oxide\nlayers results in a change of the layer stacking from O3 to P3, the latter being more stable\nfor O−H−O bonding. At 30 °C initial Li removal is accompanied by oxygen loss (effective\nremoval of Li<sub>2</sub>O) but further Li<sup>+</sup> removal involves the same proton exchange mechanism as\nobserved at 55 °C. The reaction is partially reversible. On extended cycling the material\nconverts to spinel.

Keywords:
Nucleofection TSG101 Liquation Diafiltration Tubulopathy Hyporeflexia

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