Electrochemical, thermal, and structural characterization of lithium insertion processes into orthorhombic Na2MnO2-based materials is presented. "Chimie douce" oxidation, reduction, and/or exchange reactions of the precursor Na0.44MnO2 can be used to prepare high capacity (180 mAh/g), high potential compounds for use in secondary lithium batteries. Lithiated Na2MnO2 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 degrees 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.