SECONDARY BATTERY, BATTERY PACK, ELECTRIC VEHICLE, POWER STORAGE SYSTEM, POWER TOOL, AND ELECTRONIC DEVICE

A secondary battery includes a battery element including a positive electrode, a negative electrode, and an electrolytic solution, a housing member configured to accommodate the battery element, and a safety valve mechanism attached to the housing member. The safety valve mechanism includes a valve member including an opening valve portion configured to be opened; and an opening member including a plurality of opening portions radially arranged in a region opposed to the opening valve portion from a center of the region as a base point, and a plurality of protrusion portions radially arranged in a region outside the plurality of opening portions from the center and the plurality of protrusion portions protrude toward the plurality of opening portions. A number of the opening portions and a number of the protrusion portions are equal to each other, and each of the plurality of opening portions and each of the plurality of protrusion portions are opposed to each other in a direction toward the center.