Provided is a secondary battery including an electrode including silicon or a silicon compound. The electrode includes, for example, a current collector formed using metal and a silicon film as an active material provided over the current collector. The hydrogen concentration in the silicon film of the electrode may be higher than or equal to 1.0×1018 cm−3 and lower than or equal to 1.0×1021 cm−3. Such a silicon film is formed over a current collector by a plasma CVD method or the like for example, and hydrogen is contained as little as possible in the silicon film, which is preferable. In order to contain hydrogen as little as possible in the silicon film, the silicon film may be formed over the current collector under a high temperature environment.