?-MnO2 for Li batteries

g-MnO₂ for Li batteries
Part II - Some aspects of the lithium insertion process into g-MnO₂
and electrochemically lithiated g-Li_xMnO₂compounds.

S. Sarciaux, A. Le Gal La Salle, A. Verbaere, Y. Piffard and D. Guyomard.

Laboratoire de Chimie des Solides, Institut des MatÈriaux de Nantes,

B.P. 32229, 44322 Nantes Cedex 3, France

The first Li insertion into various g-MnO₂ compounds, characterized by their rates of De Wolff and microtwinning defects, and the reversible Li intercalation process into the resulting g-Li_xMnO₂ materials have been investigated.

The first Li insertion into g-MnO₂ is a first order reaction which occurs via a nucleation and growth mechanism. When the concentration of De Wolff defects increases, the thermodynamic potential of this reaction decreases and its kinetics becomes slower. The resulting g-Li_xMnO₂ materials exhibit a very close structural relationship with so-called CDMO materials.

The reversible Li intercalation process into g-Li_xMnO₂ occurs in two steps that both operate via a two-phased mechanism. The concentration of De Wolff defects also plays a detrimental role in the kinetics of reversible lithium intercalation in electrochemically formed g-Li_xMnO₂.

Structural characterization of materials at the end of the first discharge have shown that g-MnO₂ materials with a high rate of De Wolff defects are subjected to deeper structural rearrangements.

Keywords: g-MnO₂, g-Li_xMnO₂, Li insertion process, thermodynamics, kinetics, structural changes.