A solid electrolyte is provided. The solid electrolyte includes inorganic ceramic electrolytes and an organic polymer. The organic polymer physically combines to the inorganic ceramic electrolytes. The organic polymer includes a repeat unit of formula (I),

##STR00001## wherein the A includes the following formula (II):

##STR00002## wherein each of R.sup.1 and R.sup.2 is independently selected at least one from the group consisting of the following groups: C.sub.2-C.sub.4 aliphatic alkyl, optionally substituted phenyl, bisphenol, bisphenol A, bisphenol F, and bisphenol S. The organic polymer is distributed uniformly between the inorganic ceramic electrolytes. The solid electrolyte has a conducting ion path. The solid electrolyte has a conducting ion path.

An epoxy resin composition (A), containing an epoxy resin having a structure represented by formula (1) described below and an epoxy resin having a structure represented by formula (2) described below and/or an epoxy resin having a structure represented by formula (3) described below. 89.0% to 99.9% by mass of the epoxy resin (1) and 0.1% to 11.0% by mass of the epoxy resin (2) and/or the epoxy resin (3) are contained in 100% by mass of a total of the epoxy resin (1) and the epoxy resin (2) and/or the epoxy resin (3). ##STR00001##