Energy storage device and energy storage module

In the state where a positive electrode (18) and a separator (21) are held in a case, the value of the ratio of the tensile elongation in a first direction of the separator to the tensile elongation in the first direction of a positive electrode substrate (22) is from 4 to 68. In the same state, the value of the ratio of the tensile elongation in a second direction of the separator to the tensile elongation in the second direction of the positive electrode substrate is from 4 to 68. The value of the ratio of the thickness of a heat-resistant layer (31) to the thickness of the positive electrode substrate is from 0.25 to 0.70. The proportion by mass of heat-resistant particles contained in the heat-resistant layer is from 30 to 99% by mass of the heat-resistant layer.