Abstract: There are provided an electricity storage device, comprising a polymer electrolyte and polarizable electrodes, the polarizable electrodes each comprising an interface with the polymer electrolyte, the polarizable electrodes being metal electrodes, a negative electrode of the polarizable electrodes having, at its interface with the polymer electrolyte, a lithium alloy with a metal component contained in the negative electrode, the lithium alloy being capable of releasing lithium ions through a reversible electrochemical oxidation-reduction reaction; and a method for producing an electricity storage device, comprising: a structure forming step of obtaining an electrode-electrolyte structure where each of the polarizable electrodes is formed on a polymer electrolyte through an electroless plating method; and a layer forming step of applying voltage to the polarizable electrode while the electrode-electrolyte structure obtained by the structure forming step includes a solution containing lithium ions, to form a l