In recent years, as down sizing and multi-functionalization of portable equipments have advanced, increase of capacity of batteries has been demanded accordingly.
Si—O negative electrodes are promising as a high-capacity negative electrode in lithium batteries since lithium can show a large amount of storage, and thus a number of types of such electrodes have been investigated. Examples of the method of forming Si—O on a collector include methods in which Si—O particles are mixed with a binder and a solvent to prepare a paste, which is then coated, dried and flat-rolled, as well as vapor deposition methods, and the like.
Among these technical methods, the vapor deposition method is a dry process that is advantageous in increase of the energy density without including a binder, and is also superior in productivity since it can achieve a high film formation rate. Patent Document 1 discloses a method of forming an Si—O film by vacuum vapor deposition, sputtering or ion plating.
Patent Document 2 discloses a negative electrode for secondary cells including a negative electrode active material layer provided on a collector, in which the negative electrode active material layer contains Si and Fe, with the ratio of the number of both atoms being 19:1 to 1:9, in other words, the number of moles of Fe accounting for no less than 5.3% with respect to that of Si. In addition, the negative electrode active material layer is disclosed to be formed into a film by binary simultaneous vapor deposition.
Also, in connection with an oxide of a multicomponent material containing Si, Patent Document 3 discloses a method of film formation by a vapor deposition process using a material prepared by mixing Fe and Si with the ratio of the atoms being Fe:Si=98:2 to 65:35, as an evaporation source to obtain a Fe—Si—O based magnetic film.
Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2004-349237
Patent Document 2: Japanese Unexamined Patent Application, First Publication No. 2007-26805
Patent Document 3: Japanese Unexamined Patent Application, First Publication No. Hei 10-92683