Oxidation and reduction reactions are commonly utilized for the synthesis of inorganic crystalline materials. This is especially true for the synthesis of electrode materials for Li-ion batteries including cathode and anode materials. Conventionally, cathode materials such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide and the mixed oxides are synthesized under oxidative environments. These materials are more readily obtainable since control of an oxidative heat treatment environment (e.g. heat treatment in open air environment) is not difficult. In contrast, a reductive environment is less feasible since control of a reductive heat treatment atmosphere is difficult. The difficulty stems from the fact that during the heat treatment steps of the synthesis, especially at elevated temperatures (e.g. >500° C.), a slight leakage of air during the heat treatment would be detrimental for the reaction and therefore degrade the quality of the synthesized materials. The difficulties in controlling a reductive atmosphere make mass production unlikely or very expensive. One example is the synthesis of lithium iron phosphate that is conventionally synthesized in a reducing or inert atmosphere. A LiFePO4 type cathode material has been discussed for replacing LiCoO2 for lithium ion battery applications because of the potentially lower cost (Fe replacing Co) and the safer operating characteristics of the material (no decomposition of the material during charging). However, processing issues such as high temperature heat treatment (>600° C.) under an inert or reducing atmosphere makes the material expensive and it is not widely accepted. Until the present, the maintenance of a reducing or an inert atmosphere at a high temperature was still a key factor limiting good control of the quality of the synthesized materials. To ensure a complete seal of the furnace, especially when heat treated at high temperatures, is very difficult.
Prior arts such as U.S. Pat. Nos. 5,910,382, 6,723,470, 6,730,281, 6,815,122, 6,884,544, and 6,913,855, in general, teach methods and precursors utilized for the formation of stoichiometric LiFePO4, or the substitution of cations for iron. The above mentioned patents only show how the materials are synthesized. None of the prior art teaches how to control the heat treatment environment efficiently and cost effectively.
USPTO Backgrounds
USPTO Backgrounds