Bipolar stack unit cell structure and all-solid secondary battery including the same
A bipolar stack unit cell structure includes: 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 a plurality of the bicells are stacked, and a compression pad is provided between the first anode current collector and the second anode current collector of adjacent bicells of the plurality of bicells. The bipolar stack unit cell structure absorbs a volume change of an anode and suppresses or reduces a volume change of the entire cell to obtain a stable (or suitable) lifespan, and the capacity and voltage thereof can be freely (or suitably) designed by bipolar connection of the unit cells.
1 . 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 a plurality of the bicells comprise the bicell and are stacked, and an insulating compression pad is between the first anode current collector and the second anode current collector of adjacent bicells of the plurality of bicells,
wherein each of the first anode current collector and the second anode current collector contacts the compression pad,
wherein each of the first electrolyte layer and the second electrolyte layer is a solid electrolyte layer and comprises a solid electrolyte, a binder, and an alkyl acetate, and
wherein the solid electrolyte is an argyrodite-type solid electrolyte having a density of about 1.5 to about 2.0 gram per cubic centimeter (g/cc) and is independently represented in the first and second electrolyte layers by Formula 1:
Li + 12-n-x A n+ X 2− 6-x Y − x Formula 1
A is As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta;
X is S, Se, or Te;
Y is CI, Br, I, F. CN, OCN, SCN, or N 3 ;
1≤n≤5; and
0≤x≤2.
2 . The bipolar stack unit cell structure of claim 1 , further comprising:
a first bipolar plate on the first anode current collector and a second bipolar plate on the second anode current collector, the first anode current collector and the second anode current collector respectively being at corresponding ends of the bipolar stack unit cell structure,
wherein the compression pad is further between the first anode current collector at one of the ends of the bipolar stack unit cell structure and the first bipolar plate, and another compression pad is between the second anode current collector at another of the ends of the bipolar stack unit cell structure and the second bipolar plate.
3 . The bipolar stack unit cell structure of claim 1 , wherein the compression pad is made of an elastic material.
4 . The bipolar stack unit cell structure of claim 3 , wherein the elastic material comprises at least one selected from polyurethane, natural rubber, spandex, butyl rubber (isobutylene isoprene rubber, IIR), fluoroelastomer, elastomer, ethylene-propylene rubber (EPR), styrene-butadiene rubber (SBR), chloroprene, elastin, rubber epi Chlorohydrin, nylon, terpene, isoprene rubber, polybutadiene, nitrile rubber, thermoplastic elastomer, silicone rubber, ethylene-propylene-diene rubber (EPDM), ethylene vinyl acetate (EVA), halogenated butyl rubber, neoprene, and copolymers thereof.
5 . The bipolar stack unit cell structure of claim 1 , wherein the first anode active material layer and the second anode active material layer each independently comprise an anode active material and a binder, the anode active material has a particle form, and the anode active material has an average particle diameter of 4 μm or less.
6 . The bipolar stack unit cell structure of claim 5 , wherein the anode active material comprises at least one selected from a carbon-based anode active material, a metal anode active material, and a metalloid anode active material, and the carbon-based anode active material comprises amorphous carbon.
7 . The bipolar stack unit cell structure of claim 6 , wherein the metal anode active material and the metalloid anode active material each independently comprise at least one selected from gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (AI), bismuth (Bi), tin (Sn), and zinc (Zn).
8 . The bipolar stack unit cell structure of claim 5 , wherein the anode active material comprises a mixture of first particles of amorphous carbon and second particles of a metal or a metalloid, and
a content of the second particles is about 8 wt % to about 60 wt % based on a total weight of the mixture.
9 . The bipolar stack unit cell structure of claim 1 , further comprising: a fourth anode active material layer i) between the first anode current collector and the first anode active material layer, ii) between the first anode active material layer and the first electrolyte layer, iii) between the second electrolyte layer and the second anode active material layer, and/or iv) between the second anode active material layer and the second anode current collector, wherein the fourth anode active material layer is a metal layer, the metal layer comprising lithium or a lithium alloy.
10 . An all-solid secondary battery comprising: the bipolar stack unit cell structure of claim 1 ,
wherein a plurality of the bipolar stack unit cell structures comprises the bipolar stack unit cell structure and are stacked, and the stacked plurality of bipolar stack unit cell structures are electrically coupled.
11 . The all-solid secondary battery of claim 10 , further comprising a cathode terminal and an anode terminal, respectively at ends of the stacked plurality of bipolar stack unit cell structures,
wherein, between the cathode terminal and the first anode current collector or the second anode current collector, adjacent to the cathode terminal, a third cathode active material layer, a third electrolyte layer, a third anode active material layer, a third anode current collector, and a compression pad are further arranged sequentially from the cathode terminal.
12 . The bipolar stack unit cell structure of claim 1 , wherein an average particle diameter D50 of a solid electrolyte in the first and second cathode active material layers is less than an average particle diameter D50 of a solid electrolyte in the first and second electrolyte layers.
13 . The bipolar stack unit cell structure of claim 12 , wherein the average particle diameter D50 of the solid electrolyte in the first and second cathode active material layers is 90% or less than the average particle diameter D50 of the solid electrolyte in the first and second electrolyte layers.
14 . The bipolar stack unit cell structure of claim 12 , wherein the average particle diameter D50 of the solid electrolyte in the first and second cathode active material layers is 50% or less than the average particle diameter D50 of the solid electrolyte in the first and second electrolyte layers.
15 . The bipolar stack unit cell structure of claim 1 , wherein
the compression pad is to be pressed to have a thickness of about 40% to about 90% of an initial thickness thereof before being pressed, and
a thickness of the compression pad is 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.
16 . The bipolar stack unit cell structure of claim 1 , wherein the alkyl acetate is an octyl acetate.
17 . 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 a plurality of the bicells comprise the bicell and are stacked, and an insulating compression pad is between the first anode current collector and the second anode current collector of adjacent bicells of the plurality of bicells,
wherein each of the first anode current collector and the second anode current collector contacts the compression pad, and
wherein each of the first electrolyte layer and the second electrolyte layer independently comprises an argyrodite-type solid electrolyte having a density of about 1.5 gram per cubic centimeter (g/cc) to about 2.0 g/cc, and
wherein the argyrodite-type solid electrolyte is independently represented in the first and second electrolyte layers by Formula 1:
Li + 12-n-x A n+ X 2− 6-x Y − x Formula 1
A is As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta;
X is S, Se, or Te;
Y is CI, Br, I, F. CN, OCN, SCN, or N 3 ;
1≤n≤5; and
0≤x≤2.