Disclosed is a secondary battery. The secondary battery has a structure including an internal core portion containing an
electrolyte having a relatively lower crosslinking degree, and surrounded with a
peripheral portion containing an
electrolyte having a relatively higher crosslinking degree. It is possible to provide an effect of improving both
ion conductivity and mechanical properties by virtue of such structural characteristics. In addition, the
electrolyte portion having a lower crosslinking degree is confined by the electrolyte having a higher crosslinking degree to provide an effect of preventing
electrolyte leakage. In addition, the secondary battery can be obtained by a simple method that includes crosslinking only the
peripheral portion before the core portion reaches to a crosslinking temperature and is crosslinked under an environment preheated to the crosslinking temperature or higher. As a result, there is no
adverse effect upon the
processing efficiency, since any separate device or
system line is not required to carry out the crosslinking.