FIG. 8A is a scanning electron microscope photograph of the surface of the produced active material film, and FIG. 8B is a scanning electron microscope photograph of the thickness cross section of the produced active material film. As seen from FIGS. 8A and 8B, it was found that since the active material film was produced by slicing the active material bulk which already had uniform characteristics, the porosities in the surface and thickness cross section of the active material film are substantially the same, and the active material film has an open pore structure. In addition, as a result of observing the surface resin and the central region in the thickness cross section of the produced active material film and measuring the pore area, it was confirmed that the porosities were substantially the same.
FIG. 9 is an optical photograph of a negative electrode in which the active material film of FIGS. 7 and 8 is adhered to a Cu foil which is the current collector. When producing the negative electrode of FIGS. 8A and 8B, the active material film is polished to be mirrored and the mirrored surface was adhered to the current collector, and as the conductive adhesive, a copper paste (65 wt % of 30 nm copper nanoparticles, 8 wt % of styrene-butadiene rubber) was used.
