A pouch film stack according to the present invention includes a base layer, a gas barrier layer, and a sealant layer stacked in that order. The sealant layer includes a first sealant layer located adjacent to the gas barrier layer and a second sealant layer stacked on the first sealant layer, and ΔY according to Equation (1) is 66% to 120%. Δ Y = Yield strength of second sealant layer − Yield strength of first sealant layer / Yield strength of first sealant layer × 100