Lithium-ion batteries are a rechargeable battery that is essential to smartphones and small electronic devices that are widely used in our real life. Recently, lithium-ion batteries have even been applied to electric vehicles, and their importance is growing higher. It is necessary to replace the graphite anode material that is currently commercialized, in order to develop a battery with larger capacity. Metal oxides are heavily researched as the next-generation anode material owing to their large theoretical capacity and chemical stability. In this thesis, the lithiation mechanism of tin oxide ($SnO_2$) and cobalt oxide ($Co_3O_4$) are to be analyzed using in situ transmission electron microscopy.