Lawrence Berkeley National Laboratory

LixMnO2 made from Na0.44MnO2 has an unusual tunnel structure which allows ion insertion processes to occur with minimal strain. It cycles very reversibly at an average voltage of about 3.2 vs. Li without undergoing phase conversion. The stability of this material makes it a promising candidate for use in electric vehicle applications, which not only have severe cost constraints, but also require long cycle life and abuse-tolerance. In practical lithium cells, however, the demonstrated capacity is typically less than the predicted 200 mAh/g for LixMnO2 cathode materials made by conventional solid-state reactions. This is due to kinetic limitations and to the sloping discharge characteristics. Attritor-milling of conventionally-made LixMnO2 and glycine-nitrate combustion synthesis have been used to produce powders with average particle size below 1 mm, improved rate capability, and a 15% improvement in utilization. Up to 55% of the Mn in LixMnO2 with the Na0.44MnO2 structure can also be replaced with Ti. Ti-doped analogs have modified discharge characteristics, with some exhibiting better utilization between set voltage limits than the parent compound.