Lithium Insertion Processes of Orthorhombic Na_x MnO₂‐Based Electrode Materials

Electrochemical, thermal, and structural characterization of lithium insertion processes into orthorhombic ‐based materials is presented. "Chimie douce" oxidation, reduction, and/or exchange reactions of the precursor can be used to prepare high capacity (180 mAh/g), high potential compounds for use in secondary lithium batteries. Lithiated is quite stable; formation of spinel phases occurs only under conditions of prolonged severe abuse during cycling in electrochemical cells, or upon heating to 500°C. The lithium‐ion intercalation process is considerably more complex than that for sodium ions; features are seen in the electrochemical potential‐step experiments that may be attributed to several phase transitions. These results are interpreted in terms of the unusual structure, and implications for future use of these materials in lithium batteries are discussed.