A bipolar stack unit cell structure comprising: a bicell in which a first anode current collector, a first anode active material layer, a first electrolyte layer, a first cathode active material layer, a cathode current collector, a second cathode active material layer, a second electrolyte layer, a second anode active material layer, and a second anode current collector are sequentially arranged, wherein the first electrolyte layer and the second electrolyte layer include a solid electrolyte, wherein a plurality of the bicells are stacked, and a compression pad is provided between the first anode current collector and second anode current collector of adjacent bicells of the plurality of bicells, wherein the compression pad is made of an elastic material including at least one selected from polyurethane, natural rubber, spandex, butyl rubber (isobutylene isoprene rubber, IIR), fluoroelastomer, elastomer, ethylene-propylene rubber, styrene-butadiene rubber, chloroprene, elastin, rubber epi Chlorohydrin, nylon, terpene, isoprene rubber, polybutadiene, nitrile rubber, thermoplastic elastomer, silicone rubber, ethylene-propylene-diene rubber (EPDM), ethylene vinyl acetate, halogenated butyl rubber, neoprene, and copolymers thereof, wherein the compression pad is pressed to have a thickness of about 40% to about 90% of an initial thickness thereof before being pressed, and wherein a thickness of the compression pad is set in a range of about 200% to about 500% of a thickness of a lithium deposition layer of an anode formed when charging an all-solid secondary battery comprising the bipolar stack unit cell structure, wherein the thickness of the lithium deposition layer of the anode is determined according to the amount of lithium moving from the cathode to the anode. a bicell in which a first anode current collector, a first anode active material layer, a first electrolyte layer, a first cathode active material layer, a cathode current collector, a second cathode active material layer, a second electrolyte layer, a second anode active material layer, and a second anode current collector are sequentially arranged, wherein the first electrolyte layer and the second electrolyte layer include a solid electrolyte, wherein a plurality of the bicells are stacked, and a compression pad is provided between the first anode current collector and second anode current collector of adjacent bicells of the plurality of bicells, wherein the compression pad is made of an elastic material including at least one selected from polyurethane, natural rubber, spandex, butyl rubber (isobutylene isoprene rubber, IIR), fluoroelastomer, elastomer, ethylene-propylene rubber, styrene-butadiene rubber, chloroprene, elastin, rubber epi Chlorohydrin, nylon, terpene, isoprene rubber, polybutadiene, nitrile rubber, thermoplastic elastomer, silicone rubber, ethylene-propylene-diene rubber (EPDM), ethylene vinyl acetate, halogenated butyl rubber, neoprene, and copolymers thereof, wherein the compression pad is pressed to have a thickness of about 40% to about 90% of an initial thickness thereof before being pressed, and wherein a thickness of the compression pad is set in a range of about 200% to about 500% of a thickness of a lithium deposition layer of an anode formed when charging an all-solid secondary battery comprising the bipolar stack unit cell structure, wherein the thickness of the lithium deposition layer of the anode is determined according to the amount of lithium moving from the cathode to the anode.