A negative electrode active material layer containing at least one selected from silicon and a silicon compound as a negative electrode active material is formed, and an amount of lithium exceeding an amount corresponding to a theoretical capacity of the negative electrode active material layer is brought into contact with the negative electrode active material layer so as to prepare a negative electrode. A positive electrode containing a lithium-absorption material capable of irreversibly absorbing lithium is prepared. The positive electrode, the negative electrode, a separator, and a nonaqueous electrolyte are enclosed inside an outer enclosure. A chemical conversion treatment of the negative electrode active material is performed with the lithium brought into contact with the negative electrode active material layer.