An object of the present invention is to provide a secondary battery that is able to inhibit the growth of a dendrite that can generate from an electrode comprising alkali metal and a separator used therein.A secondary battery, comprising:a positive electrode;a negative electrode comprising alkali metal;a separator comprising a layer of tetrafluoroethylene (TFE) polymer or copolymer that reacts with a dendrite of the alkali metal, the separator being hydrophilized at a rate of not less than 10% and not more than 80%; anda layer that does not react with a dendrite of the alkali metal located between the separator and the negative electrode, and a separator used therein.