The polycyclic aromatic compound in the solution B reacts with the lithium contained in the silicon compound to form a complex. Since the complex is stable, the lithium desorption from the silicon compound proceeds. Further, in the solvent as was described above, since the complex between the polycyclic aromatic compound and the lithium may be present stable instantaneously or sustainably, without causing a rapid reaction (a reaction accompanying ignition or boiling of the solvent), the lithium is softly desorbed from the silicon compound.

Thus, in the step 3, by desorbing a part of active Li from the silicon compound, a violent reaction is prevented from occurring in the following step 4. It is to be noted that, only by passing the step 3, the desorption of the active Li is insufficient, when an electrode is prepared in this state, during preparation of an aqueous slurry, a reaction occurs with moisture in the slurry or a binder, sometimes, a large heat generation is caused, that is, an aqueous slurry capable of coating is not obtained, or if obtained, since the Li portion in the active material is eluted by the heat generation, the battery characteristics may not be improved. Since what has undergone the step 3 after forming the silicon compound into the electrode is also insufficient in the deactivation of the Li portion, when left in dry air (dew point: ?20° C. or lower), the Li portion is gradually deactivated, lithium oxide, hydroxide or carbonate is generated on a surface to cause deterioration of the battery characteristics. Therefore, it is necessary to further deactivate the active lithium by carrying out a step 4 that is a next step like in the present invention.