Patent Description:
Recently, in response to industrial demands, batteries having high energy density and safety have been actively developed. For example, lithium-ion batteries are being utilized not only in the fields of information-related apparatuses (e.g., appliances) and communication apparatuses (e.g., appliances), but also in the fields of automobiles. In the fields of automobiles, safety is especially important because it has an influence to driver and traffic safety.

Because commercially available lithium-ion batteries utilize an electrolyte solution including a flammable organic solvent, there is a possibility of overheating and catching fire when a short circuit occurs. In this regard, all-solid batteries utilizing a solid electrolyte instead of an electrolyte solution have been proposed.

Because all-solid batteries do not utilize flammable organic solvents, even when a short circuit occurs, the possibility of catching fire or explosion may be greatly reduced. Accordingly, safety of such all-solid secondary batteries may be greatly increased (e.g., improved) as compared with that of lithium-ion batteries utilizing an electrolyte solution.

Further, one of the characteristics of all-solid secondary batteries is that they can be easily built with a bipolar structure unlike related art lithium-ion batteries, and thus the number of parts may be reduced, and it is easier for large currents to flow, thus allowing the development of high-power, and high-energy-density cells having high voltages. However, with a bipolar structure in which electrodes are arranged in series, it is difficult to design a structure capable of absorbing a volume change due to a lithium deposition reaction utilized in the anode of an all-solid secondary battery.

<CIT> discloses an all-solid secondary battery with a current collector having a folded structure including one or more fold regions facing each other. An adhesive material is injected into the fold regions so as to prevent positional shifting or separation due to shock, vibration, and so forth, when manufacturing the battery or using the battery.

Aspects according to one or more embodiments are directed toward an electrode structure capable of absorbing a volume change of an anode in an all-solid-state secondary battery.

Aspects according to one or more embodiments are directed toward a bipolar all-solid secondary battery including the electrode structure.

Aspects according to one or more embodiments are directed toward a method of manufacturing the electrode structure.

According to one aspect of the present invention, an electrode structure is provided as defined in claim <NUM>. The electrode structure includes:.

The compression pad is made of an elastic material comprising at least one selected from polyurethane, natural rubber, spandex, butyl rubber (isobutylene isoprene rubber, IIR), fluoroelastomer, ethylene-propylene rubber (EPR), styrene-butadiene rubber (SBR), chloroprene, elastin, epichlorohydrin rubber, nylon, polyterpene, isoprene rubber, polybutadiene, nitrile rubber, thermoplastic elastomer, silicone rubber, ethylene-propylene-diene rubber (EPDM), ethylene vinyl acetate (EVA), halogenated butyl rubber, and neoprene. Further, the compression pad is capable of being pressed to have a thickness of <NUM>% to <NUM>% of an initial thickness thereof before being pressed. Further, a thickness of the compression pad is <NUM>% to <NUM>% of a thickness of a lithium deposition layer of an anode formed when charging an all-solid secondary battery comprising the electrode 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.

According to another aspect of the present invention, a bipolar all-solid secondary battery as defined in claim <NUM> is provided, which includes a stacked structure including a plurality of unit cells, wherein each unit cell of the plurality of unit cells includes the electrode structure; and a solid electrolyte layer on the cathode active material layer.

According to another aspect of the present invention, a method of manufacturing an electrode structure as defined in claim <NUM> is provided, the method includes:.

The above and other aspects, features, and enhancements of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:.

Reference will now be made in more detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.

The subject matter of the present disclosure will now be described more fully with reference to the accompanying drawings, in which example embodiments are illustrated. However, the subject matter of the present disclosure may be embodied in many different forms, should not be construed as being limited to the embodiments set forth herein.

The terms used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. Singular expressions include plural expressions unless the context clearly indicates otherwise. As used herein, the slash "/" or the term "and/or" includes any and all combinations of one or more of the associated listed items.

In the drawings, the thickness may be enlarged or reduced in order to clearly illustrate various layers and regions. Throughout the specification, the same reference numerals are used to refer to similar parts. Throughout the specification, when an element such as a layer, a film, a region or a component is referred to as being "on" another layer or element, it can be "directly on" the other layer or element, or intervening layers, regions, or components may also be present. Although the terms "first", "second", "third", etc., may be used herein to describe various elements, components, regions, and/or layers, these elements, components, regions, and/or layers should not be limited by these terms. These terms are used only to distinguish one component from another, and not for purposes of limitation.

Hereinafter, a bipolar stack unit cell structure according to embodiments and an all-solid secondary battery including the same will be described in more detail.

In related art, it is difficult to design a structure capable of absorbing a volume change due to a lithium deposition reaction utilized (e.g., happening) in an anode of an all-solid secondary battery with a bipolar structure, and without a buffer structure of an anode layer, a thickness variation inside a cell may become severe due to non-uniform lithium electrodeposition, and partial charge-discharge may occur, which may deteriorate battery performance and cause (e.g., increase) the risk of a short circuit.

In related art all-solid secondary batteries, a structure in which stacked cells are placed in a bipolar structure to increase the capacity of a cell has been proposed, but a structure for absorbing a volume change may be desired (e.g., may not have been proposed).

Accordingly, in order to solve the above problems in a bipolar cell utilizing the same current collector, the present discloser of the present inventive entity is intended to provide an electrode structure capable of having a buffer structure inside (e.g., a space formed by) the same current collector, a bipolar all-solid secondary battery including the same, and a method of manufacturing the electrode structure.

An electrode structure according to an embodiment includes:.

In the electrode structure according to an embodiment, the compression pad is provided inside the folded current collector to absorb a volume change of an anode layer during charging and discharging. Through this buffer structure of the current collector, the anode layer may be protected against a volume change during charging and discharging, thereby improving the durability of a bipolar all-solid secondary battery.

The electrode structure may be manufactured, for example, by the following method.

A method of manufacturing an electrode structure according to an embodiment includes:.

<FIG> is a schematic cross-sectional view of an electrode structure according to an embodiment. As shown in <FIG>, an electrode structure <NUM> has a current collector <NUM> having a folded structure, a cathode active material layer <NUM>, an anode active material layer <NUM>, and a compression pad <NUM> disposed inside the (e.g., inner space of) folded structure of the current collector <NUM>.

<FIG> is a schematic view illustrating a process of manufacturing an electrode structure according to an embodiment. As shown in <FIG>, the current collector <NUM> has both of a first surface <NUM> and a second surface <NUM>, and the first surface <NUM> includes a first portion 11a, a second portion 11b, and an intermediate portion 11c dividing (e.g., separating/connecting) the first portion 11a from the second portion 11b.

A cathode active material layer <NUM> is applied onto the first portion 11a of the first surface <NUM>, and an anode active material layer <NUM> is applied onto the second portion 11b. The intermediate portion 11c is an uncoated portion on which an active material layer is not applied. Meanwhile, the entire second surface <NUM> may be an uncoated portion.

When the current collector <NUM> is folded and bent around the intermediate portion 11c, the first portion 11a coated with the cathode active material layer <NUM> and the second portion 11b coated with the anode active material layer <NUM> are arranged toward the outside (e.g., form the outer surface of the collector <NUM>) in opposite directions to each other, and the second surface <NUM> is folded inward (e.g., forms the inner surface of the collector <NUM>).

As such, the compression pad <NUM> is disposed inside the folded structure of the current collector <NUM>, thereby forming the electrode structure <NUM> having a buffer structure. The compression pad <NUM> is provided inside the folded current collector <NUM>, thereby capable of absorbing a volume change of the anode active material layer <NUM> during charging and discharging.

A solid electrolyte layer <NUM> (<FIG>) is disposed on the cathode active material layer <NUM> of the electrode structure <NUM>, thereby forming a unit cell <NUM> constituting the all-solid secondary battery according to an embodiment.

Hereinafter, each component will be described in more detail.

As the current collector <NUM> of a bipolar battery, which may act as both a cathode and an anode, a current collector having a wide withstand voltage range (e.g., can withstand a wide voltage range) may be utilized. The voltage range (e.g., the withstand voltage range) of the current collector <NUM> may be, for example, about -<NUM> V to about <NUM> V, or about -<NUM> V to about <NUM> V. Within the above ranges, it may be suitably utilized as the current collector <NUM> of a bipolar battery.

The current collector <NUM> may be made of, for example, a material that does not react with lithium, that is, does not form an alloy and/or a compound with lithium. Examples of the material suitable for constituting the current collector <NUM> may include, but are not limited to, stainless steel, aluminum (Al), copper (Cu), titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), alloys thereof, and clads thereof. Any suitable material utilized to constitute a current collector of a bipolar battery in the related art may be utilized. The current collector <NUM> may be made of one of the above-described metals or an alloy of two or more metals, and/or may be made of a coating material.

According to an embodiment, the current collector <NUM> may be made of stainless steel. Because stainless steel has a wide withstand voltage range of about - <NUM> V to about <NUM> V, it may be suitably utilized as the current collector <NUM> of a bipolar battery. According to an embodiment, an alloy such as Al-Cu clad, which can withstand dislocations in a wide range, may also be suitably utilized for the current collector <NUM>.

The current collector <NUM> may be made in the form of a plate or foil.

The electrode structure <NUM> may further include, for example, a thin film containing an element capable of forming an alloy with lithium on the second portion 11b of the first surface <NUM> of the current collector <NUM>. The thin film may be disposed between the current collector <NUM> and the anode active material layer <NUM>. The thin film contains, for example, an element capable of forming an alloy with lithium. Examples of the element capable of forming an alloy with lithium may include, but are not limited to, gold, silver, zinc, tin, indium, silicon, aluminum, and bismuth. Any element in the related art that forms an alloy with lithium may be utilized. The thin film may be formed of one of these metals or may be formed of an alloy of several kinds (e.g., types) of metals. As the thin film is disposed between the current collector <NUM> and the anode active material layer <NUM>, for example, the deposition form of the second anode active material layer deposited between the thin film <NUM> and the anode active material layer <NUM> may be further flattened, and the cycle characteristics of the all-solid secondary battery <NUM> may be further improved.

The thickness of the thin film may be, for example, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. When the thickness of the thin film is less than about <NUM>, it may be difficult to exert a function as the thin film. When the thickness of the thin film is too thick, the thin film itself absorbs lithium such that the amount of lithium deposited in an anode decreases, so that the energy density of the all-solid secondary battery <NUM> decreases, and the cycle characteristics of the all-solid secondary battery <NUM> may be deteriorated. The thin film may be disposed on first and second anode current collectors <NUM> and <NUM>' by, for example, a vacuum deposition method, a sputtering method, a plating method, and/or the like, but the present disclosure is not necessarily limited to these methods. Any suitable method capable of forming the thin film in the related art may be utilized.

The compression pad <NUM> inside the folded structure of the current collector <NUM> may be made in the form of a sheet and it includes an elastic material.

The elastic material includes at least one selected from polyurethane, natural rubber, spandex, butyl rubber (isobutylene isoprene rubber, IIR), fluoroelastomer, ethylene-propylene rubber (EPR), styrene-butadiene rubber (SBR), chloroprene, elastin, epichlorohydrin rubber, nylon, polyterpene, isoprene rubber, polybutadiene, nitrile rubber, thermoplastic elastomer, silicone rubber, ethylene-propylene-diene rubber (EPDM), ethylene vinyl acetate (EVA), halogenated butyl rubber, and neoprene. According to an embodiment, the compression pad <NUM> may be made of a urethane-based material, for example, polyurethane.

According to an embodiment, the compression pad <NUM> may be formed of a urethane-based polymer sheet having a deformation rate of about <NUM>% to about <NUM>%.

The compression pad <NUM> is pressed (e.g., is capable of being pressed) to have a thickness of about <NUM>% to about <NUM>% of an initial thickness thereof before being pressed. For example, the compression pad <NUM> may be pressed to have a thickness of about <NUM>% to about <NUM>%, about <NUM>% to about <NUM>%, or about <NUM>% to about <NUM>% of the initial thickness thereof before being pressed. Because the volume change of the anode is effectively absorbed within the above ranges, it is possible to smoothly charge and discharge an all-solid secondary battery.

The thickness of the compression pad <NUM> is in a range of about <NUM>% to about <NUM>% of a thickness of a lithium deposition layer of an anode formed when charging an all-solid secondary battery. In an all-solid secondary battery, the thickness of the lithium deposition layer of the anode is determined in proportion to the current density of the cathode. That is, 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, and thereby the volume change of the anode occurs (e.g., the volume of the anode thereby increases). Accordingly, the thickness of the compression pad <NUM> may be determined to absorb the volume change of the anode. Therefore, the thickness of the compression pad <NUM> may be set to be in a range of about <NUM>% to about <NUM>% of a thickness of a lithium deposition layer of the anode formed when charging an all-solid secondary battery, thereby effectively absorbing the voltage change of the anode. For example, the thickness of the compression pad may be in a range of about <NUM>% to about <NUM>%, or, about <NUM>% to about <NUM>% of a thickness of a lithium deposition layer of the anode formed when charging an all-solid secondary battery.

The thickness of the compression pad <NUM> may be set in the range of about <NUM> to about <NUM>, and in some case, may be selectively set in the range of about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>.

As such, because the compression pad <NUM> is provided in the folded structure of the current collector, the volume change caused by a lithium (Li) deposition reaction used in the anode may be absorbed, and thus the anode layer may be protected, thereby improving the durability of a bipolar all-solid secondary battery.

As shown in <FIG>, in the electrode structure <NUM>, the cathode active material layer <NUM> is disposed on the first portion 11a of the first surface <NUM> of the current collector <NUM>.

The cathode active material layer <NUM> includes, for example, a cathode active material and a solid electrolyte. The solid electrolyte included in the cathode active material layer <NUM> may be similar to or different from the solid electrolyte included in the electrolyte layer <NUM>. For further details of the solid electrolyte, refer to those of the electrolyte layer <NUM>.

The cathode active material is a cathode active material capable of reversibly absorbing and desorbing lithium ions. The cathode active material may be, for example, a lithium transition metal oxide (such as a lithium cobalt oxide (LCO), a lithium nickel oxide, a lithium nickel cobalt oxide, a lithium nickel cobalt aluminum oxide (NCA), a lithium nickel cobalt manganese oxide (NCM), and/or lithium manganate), lithium and iron phosphate, a nickel sulfide, a copper sulfide, a lithium sulfide, an iron oxide, a vanadium oxide, and/or the like, but is not limited thereto, and any one available as a cathode active material in the related art may be utilized. The cathode active materials may each be utilized alone or as a mixture of two or more thereof.

The lithium transition metal oxide may be a compound represented by one of, for example, LiaA<NUM>-bBbD<NUM> (where <NUM>≤a≤ <NUM>, and <NUM>≤b≤<NUM>); LiaE<NUM>-<NUM>BbO<NUM>-cDc (where <NUM>≤a≤<NUM>, <NUM>≤b≤<NUM>, and <NUM>≤c≤<NUM>); LiE<NUM>-bBbO<NUM>-cDc (where <NUM>≤b≤<NUM>, and <NUM>≤c≤<NUM>); LiaNi<NUM>-b-cCobBcDα (where <NUM>≤a≤ <NUM>, <NUM>≤b≤<NUM>, <NUM>≤c≤<NUM>, and <NUM><α≤<NUM>); LiaNi<NUM>-b-cCobBcO<NUM>-αHα (where <NUM>≤a≤<NUM>, <NUM>≤b≤<NUM>, <NUM>≤c≤<NUM>, and <NUM><α<<NUM>); LiaNi<NUM>-b-cCobBcO<NUM>-αH<NUM> (where <NUM>≤a≤<NUM>, <NUM>≤b≤<NUM>, <NUM>≤c≤<NUM>, and <NUM><α< <NUM>); LiaNi<NUM>-b-cMnbBcDα (where <NUM>≤a≤<NUM>, <NUM>≤b≤<NUM>, <NUM>≤c≤<NUM>, and <NUM><α≤<NUM>); LiaN<NUM>-b-cMnbBcO<NUM>-αHα (where <NUM>≤a≤<NUM>, <NUM>≤b≤<NUM>, <NUM>≤c≤<NUM>, and <NUM><α<<NUM>); LiaNi<NUM>-b-cMnbBcO<NUM>-αH<NUM> (where <NUM>≤a≤<NUM>, <NUM>≤b≤<NUM>, <NUM>≤c≤<NUM>, and <NUM><α< <NUM>); LiaNibEcGdO<NUM> (where <NUM>≤a≤ <NUM>, <NUM>≤b≤<NUM>, <NUM>≤c≤<NUM>, and <NUM>≤d≤<NUM>); LiaNibCocMndGeO<NUM> (where <NUM>≤a≤<NUM>, <NUM>≤b≤<NUM>, <NUM>≤c≤<NUM>, <NUM>≤d≤<NUM>, and <NUM>≤e≤<NUM>); LiaNiGbO<NUM> (where <NUM>≤a≤ <NUM>, and <NUM>≤b≤ <NUM>); LiaCoGbO<NUM> (where <NUM>≤a≤ <NUM> and <NUM>≤b≤<NUM>); LiaMnGbO<NUM> (where <NUM>≤a≤ <NUM> and <NUM>≤ b≤<NUM>); LiaMn<NUM>GbO<NUM> (where, <NUM>≤a≤ <NUM> and <NUM>≤b≤<NUM>); LiaNibCocMndGeO<NUM> (where, <NUM> ≤ a ≤ <NUM>, <NUM> ≤ b ≤ <NUM>, <NUM> ≤ c ≤ <NUM>, <NUM> ≤ d ≤<NUM>, and <NUM> ≤ e ≤ <NUM>);LiaNiGbO<NUM> (where, <NUM> ≤ a ≤ <NUM> and <NUM> ≤ b ≤ <NUM>);LiaCoGbO<NUM> (where, <NUM> ≤ a ≤ <NUM> and <NUM> ≤ b ≤ <NUM>);LiaMnGbO<NUM> (where, <NUM> ≤ a ≤ <NUM> and <NUM> ≤ b ≤ <NUM>);LiaMn<NUM>GbO<NUM> (where, <NUM> ≤ a ≤ <NUM> and <NUM> ≤ b ≤ <NUM>);QO<NUM>; QS<NUM>; LiQS<NUM>; V<NUM>O<NUM>; LiV<NUM>O<NUM>; LiLO<NUM>; LiNiVO<NUM>; Li(<NUM>-f)J<NUM>(PO<NUM>)<NUM> (<NUM>≤f≤<NUM>); Li(<NUM>-f)Fe<NUM>(PO<NUM>)<NUM> (<NUM>≤f≤<NUM>); and LiFePO<NUM>. In these compounds, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combinations thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; H is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; L is Cr, V, Fe, Sc, Y, or a combination thereof; and J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof. A compound having a coating layer added on a surface thereof may be also utilized, and a mixture having the compound described above and a coating layer which are added thereto may be also utilized. The coating layer added to the surface of the compound includes, for example, a coating element compound of an oxide, a hydroxide, an oxyhydroxide, an oxycarbonate, and/or a hydroxycarbonate of the coating element. The compound forming the coating layer is amorphous or crystalline. The coating elements included in the coating layer may be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. A method of forming the coating layer may be any suitable one that does not adversely affect properties of the cathode active material. The coating method may be, for example, spraying, coating, and/or dipping. Because a specific coating method can be well understood by people in the art, detailed descriptions thereof will be omitted.

The cathode active material may include, for example, a lithium salt of a transition metal oxide having a layered rock salt kind (e.g., type) structure among the above-described lithium transition metal oxides. The "layered rock salt kind (e.g., type) structure", for example, is a structure wherein an oxygen atom layer and a metal atom layer are alternately and regularly arranged in the direction of <<NUM>> of a cubic rock salt kind (e.g., type) structure, whereby each atom layer forms a two-dimensional plane. "Cubic rock salt kind (e.g., type) structure" refers to a sodium chloride kind (e.g., type) (NaCl kind (e.g., type)) structure, which is a kind (e.g., type) of crystal structure, and, specifically, has a structure in which each of cations and anions are arranged in a face-centered cubic lattices (FCCs) and to be displaced from each other by <NUM>/<NUM> of a ridge of a unit lattice. A lithium transition metal oxide having the layered rock salt kind (e.g., type) structure may be a ternary lithium transition metal oxide, for example, LiNixCoyAlzO<NUM> (NCA) and/or LiNixCoyMnzO<NUM> (NCM) (<NUM><x< <NUM>, <NUM><y< <NUM>, <NUM><z<<NUM>, x+y+z=<NUM>). When the cathode active material includes a ternary lithium transition metal oxide having a layered rock salt kind (e.g., type) structure, the energy density and thermal stability of the all-solid secondary battery <NUM> are further improved.

The cathode active material may be covered by the coating layer as described above. The coating layer may be any one suitable as a coating layer of the cathode active material of the all-solid secondary battery. The coating layer may be, for example, Li<NUM>O-ZrO<NUM> and/or the like.

When the cathode active material includes nickel (Ni) as a ternary lithium transition metal oxide (such as NCA and/or NCM), the capacity density of the all-solid secondary battery <NUM> may be increased, whereby metal elution of the cathode active material in a charged state may be reduced. As a result, cycle characteristics in the charge state of the all-solid secondary battery <NUM> are improved.

The shape of the cathode active material may be, for example, a sphere or an elliptical sphere. The particle diameter of the cathode active material is not particularly limited and may be within a range applicable to a related art all-solid secondary battery. The content of the cathode active material in the cathode layer <NUM> is also not particularly limited and may be within a range applicable to a related art all-solid secondary battery.

The cathode active material layer <NUM> may include, for example, a solid electrolyte. The solid electrolyte included in the cathode active material layer <NUM> may be the same as or different from the solid electrolyte included in the electrolyte layer <NUM>. For details of the solid electrolyte, refer to those of the electrolyte layer <NUM>.

The solid electrolyte included in the cathode active material layer <NUM> may have a smaller average particle diameter D50 of particles of the solid electrolyte than that of the particles of the solid electrolyte included in the electrolyte layer <NUM>. For example, the average particle diameter D50 of the particles of the solid electrolyte included in the cathode active material layer <NUM> may be about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, or about <NUM>% or less of the average particle diameter D50 of the particles of the solid electrolyte included in the electrolyte layer <NUM>.

The average particle diameter D50 is, for example, a median particle diameter D50. The median particle diameter D50 is, for example, a particle size corresponding to a <NUM>% cumulative volume calculated from a particle having a small particle size in a particle size distribution measured by a laser diffraction method.

The cathode active material layer <NUM> may include a binder. Examples of the binder may include, but are not limited to, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. Any suitable binder utilized in the related art may be utilized.

The cathode active material layer <NUM> may include a conductive material. Examples of the conductive material may include, but are not limited to, graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and metal powder. Any suitable conductive material utilized in the related art may be utilized.

The cathode active material layer <NUM> may further include additives such as a filler, a coating agent, a dispersing agent, and/or an ion-conductive auxiliary agent in addition to the above-described cathode active material, solid electrolyte, binder, and conductive material.

Any suitable materials generally utilized in the related art for electrodes of all-solid secondary batteries may be utilized, as the filler, the coating agent, the dispersing agent and/or the ion-conductive auxiliary agent, included in the cathode active material layer <NUM>.

As shown in <FIG>, the electrolyte layer <NUM> is disposed on the cathode active material layer <NUM>, thereby forming the unit cell <NUM> including the electrode structure <NUM> and the electrolyte layer <NUM>. The electrolyte layer <NUM> may be a solid electrolyte layer.

The solid electrolyte may be, for example, a sulfide-based solid electrolyte. The sulfide-based solid electrolyte may be, for example, at least one selected from P<NUM>S<NUM>, Li<NUM>S-P<NUM>S<NUM>-LiX (where X is a halogen element), Li<NUM>S-P<NUM>S<NUM>-Li<NUM>O, Li<NUM>S-P<NUM>S<NUM>-Li<NUM>O-LiI, Li<NUM>S-SiS<NUM>, Li<NUM>S-SiS<NUM>-LiI, Li<NUM>S-SiS<NUM>-LiBr, Li<NUM>S-SiS<NUM>-LiCl, Li<NUM>S-SiS<NUM>-B<NUM>S<NUM>-LiI, Li<NUM>S-SiS<NUM>-P<NUM>S<NUM>-LiI, Li<NUM>S-B<NUM>S<NUM>, Li<NUM>S-P<NUM>S<NUM>-ZmSn (where m and n are each a positive number, and Z is one selected from Ge, Zn and Ga), Li<NUM>S-GeS<NUM>, Li<NUM>S-SiS<NUM>-Li<NUM>PO<NUM>, Li<NUM>S-SiS<NUM>-LipMOq (where p and q are each a positive number, and M is one selected from P, Si, Ge, B, Al, Ga, and In), Li<NUM>-xPS<NUM>-xClx (<NUM>≤x≤<NUM>), Li<NUM>-xPS<NUM>-xBrx (<NUM>≤x≤<NUM>), and Li<NUM>-xPS<NUM>-xIx (<NUM>≤x≤<NUM>). In some embodiments, the sulfide-based solid electrolyte may be prepared by treating a starting material such as Li<NUM>S and/or P<NUM>S<NUM> by a melt quenching method or a mechanical milling method. After this treatment, heat treatment may be performed. The solid electrolyte may be amorphous, crystalline, or a mixed state thereof. The solid electrolyte may include sulfur (S), phosphorus (P), and/or lithium (Li) as constituent elements among the above-described sulfide-based solid electrolyte materials. For example, the solid electrolyte may be a material including Li<NUM>S-P<NUM>S<NUM>. When a solid electrolyte including Li<NUM>S-P<NUM>S<NUM> as a material of the sulfide-based solid electrolyte forming the solid electrolyte, the mixing molar ratio of Li<NUM>S and P<NUM>S<NUM> may be, for example, in the range of Li<NUM>S: P<NUM>S<NUM>= about <NUM>:<NUM> to about <NUM>:<NUM>.

The sulfide-based solid electrolyte may include, for example, an argyrodite kind (e.g., type) solid electrolyte represented by the following Formula <NUM>:.

Formula <NUM>     Li+<NUM>-n-xAn+X<NUM>-<NUM>-xY-x,.

in Formula <NUM>, A is P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb or Ta; X is S, Se or Te; Y is Cl, Br, I, F, CN, OCN, SCN, or N<NUM>; and <NUM>≤n≤<NUM>, and <NUM>≤x≤<NUM> are satisfied. The sulfide-based solid electrolyte may be an argyrodite-kind (e.g., type) compound including at least one selected from Li<NUM>-xPS<NUM>-xClx (<NUM>≤x≤<NUM>), Li<NUM>-xPS<NUM>-xBrx (<NUM>≤x≤<NUM>), and Li<NUM>-xPS<NUM>-xIx (<NUM>≤x≤<NUM>). The sulfide-based solid electrolyte may be, for example, an argyrodite-kind (e.g., type) compound including at least one selected from Li<NUM>PS<NUM>Cl, Li<NUM>PS<NUM>Br, and Li<NUM>PS<NUM>I.

The density of the argyrodite-kind (e.g., type) solid electrolyte may be about <NUM>/cc to about <NUM>/cc. Because the argyrodite-kind (e.g., type) solid electrolyte has a density of <NUM>/cc or more, the internal resistance of the all-solid secondary battery may be reduced, and the penetration of the solid electrolyte by Li may be effectively suppressed.

The solid electrolyte layer <NUM> may include, for example, a binder. Examples of the binder included in the solid electrolyte layer may include, but are not limited to, styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. Any suitable binder utilized in the related art may be utilized. The binder included in the solid electrolyte layer may be the same as or different from the binder included in the cathode active material layer <NUM> and the anode active material layer <NUM>. In some embodiments, the binder may be omitted.

The content of the binder included in the solid electrolyte layer may be about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, or about <NUM> wt% to about <NUM> wt%, with respect to the total weight of the solid electrolyte layer.

As shown in <FIG>, in the electrode structure <NUM>, the anode active material layer <NUM> is disposed on the second portion 11b of the first surface <NUM> of the current collector <NUM>.

The anode active material layer <NUM> may include, for example, an anode active material and a binder.

The anode active material included in the anode active material layer <NUM> may have, for example, a particle shape. The average particle diameter of the anode active material having a particle shape may be, for example, about <NUM> or less, about <NUM> or less, about <NUM> or less, about <NUM> or less, or about <NUM> or less. The average particle diameter of the anode active material having a particle shape may be, for example, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. When the anode active material has an average particle diameter in these ranges, reversible absorbing and/or desorbing of lithium may be easier during charging and discharging. The average particle diameter of the anode active material is, for example, a median diameter (D50) measured utilizing a laser particle size distribution meter.

The anode active material included in the anode active material layer <NUM> may include, for example, at least one selected from a carbon-based anode active material and a metal or metalloid anode active material.

In some embodiments, the carbon-based anode active material may be amorphous carbon. Examples of amorphous carbon may include, but are not limited to, carbon black (CB), acetylene black (AB), furnace black (FB), ketjen black (KB), and graphene. Any material may be utilized as long as it is classified as amorphous carbon in the related art. Amorphous carbon is carbon that does not have crystallinity or has very low crystallinity, and is distinguished from crystalline carbon or graphite-based carbon.

The metal or metalloid anode active material may include at least one selected from gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn), but the present disclosure is not limited thereto. Any suitable material may be utilized as long as it is utilized as a metal anode active material or a metal or metalloid anode active material that forms an alloy or compound with lithium in the related art. For example, because nickel (Ni) does not form an alloy with lithium, it is not a metal anode active material.

The anode active material layer <NUM> may include a kind of anode active material among these anode active materials, or a mixture of a plurality of different anode active materials. For example, the anode active material layer <NUM> may include only amorphous carbon, or may include at least one selected from gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). In some embodiments, the anode active material layer <NUM> may include a mixture of amorphous carbon and at least one selected from gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). The mixing ratio of the mixture of amorphous carbon and gold and/or the like may be, for example, about <NUM>:<NUM> to about <NUM>:<NUM>, about <NUM>:<NUM> to about <NUM>:<NUM>, or about <NUM>:<NUM> to about <NUM>:<NUM> as a weight ratio, but the present disclosure is not limited thereto, and the mixing ratio may be selected according to the characteristics of the solid secondary battery <NUM>. When the anode active material has such a composition, cycle characteristics of the all-solid secondary battery are further improved.

The anode active material included in the anode active material layer <NUM> may include, for example, a mixture of first particles made of amorphous carbon and second particles made of metal or metalloid. Examples of the metal or metalloid may include gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn). In some embodiments, the metalloid may be a semiconductor. The content of the second particles may be about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, or about <NUM> wt% to about <NUM> wt% based on the total weight of the mixture. When the second particle has a content within these ranges, for example, the cycle characteristics of the all-solid-state secondary battery <NUM> are further improved.

Examples of the binder included in the anode active material layer <NUM> may include, but are not limited to, styrene-butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, vinylidene fluoride/hexafluoropropylene copolymers, polyacrylonitrile, and polymethyl methacrylate. Any suitable binder utilized in the related art may be utilized. The binder may be a single binder or a plurality of different binders.

When the anode active material layer <NUM> includes a binder, the anode active material layer <NUM> is stabilized on the current collector <NUM>. Further, cracking of the anode active material layer <NUM> is suppressed despite a volume change and/or relative position change of the anode active material layer <NUM> in the charging-discharging process. For example, when the anode active material layer <NUM> does not include a binder, it is possible for the anode active material layer <NUM> to be easily separated from the current collector <NUM>. When the anode active material layer <NUM> is separated from the current collector <NUM>, the current collector <NUM> comes into contact with the solid electrolyte layer <NUM> at the exposed portion of the current collector <NUM>, thereby increasing the possibility of a short circuit. The anode active material layer <NUM> may be prepared by applying a slurry, in which a material constituting the anode active material layer <NUM> is dispersed, on the current collector <NUM> and drying the slurry. When the binder is included in the anode active material layer <NUM>, it is possible to stably disperse the anode active material in the slurry. For example, when the slurry is applied on the current collector <NUM> by a screen printing method, it is possible to suppress the clogging of a screen (for example, clogging by aggregates of the anode active material).

The anode active material layer <NUM> may further include additives utilized in related art all-solid secondary batteries, for example, a filler, a coating agent, a dispersing agent, and/or an ion conductive auxiliary agent.

The thickness of the anode active material layer <NUM> may be, for example, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, or about <NUM>% or less of the thickness of the cathode active material layer <NUM>. The thickness of the anode active material layer <NUM> may be, for example, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. When the anode active material layer <NUM> is too thin, lithium dendrites formed between the anode active material layer <NUM> and the current collector <NUM> may collapse the anode active material layer <NUM>, so that it is difficult to improve the cycle characteristics of the all-solid secondary battery <NUM>. When the thickness of the anode active material layer <NUM> increases excessively (e.g., becomes too thick), the energy density of the all-solid secondary battery <NUM> decreases, and the internal resistance of the all-solid secondary battery <NUM> by the anode active material layer <NUM> increases, so that it is difficult to improve the cycle characteristics of the all-solid secondary battery <NUM>.

When the thickness of the anode active material layer <NUM> decreases, for example, the charging capacity of the anode active material layer <NUM> also decreases. The charging capacity of the anode active material layer <NUM> may be, for example, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, about <NUM>% or less, or about <NUM>% or less of the charging capacity of the cathode active material layer <NUM>. The charging capacity of the anode active material layer <NUM> may be, for example, about <NUM>% to about <NUM>%, about <NUM>% to about <NUM>%, about <NUM>% to about <NUM>%, about <NUM>% to about <NUM>%, about <NUM>% to about <NUM>%, about <NUM>% to about <NUM>%, or about <NUM>% to about <NUM>% of the charging capacity of the cathode active material layer <NUM>. When the charging capacity of the anode active material layer <NUM> is too small, the anode active material layer <NUM> becomes very thin. Therefore, lithium dendrites formed between the anode active material layer <NUM> and the current collector <NUM> during repeated charging and discharging processes may collapse the anode active material layer <NUM>, so that it is difficult to improve the cycle characteristics of the all-solid secondary battery <NUM>. When the charging capacity of the anode active material layer <NUM> increases excessively, the energy density of the all-solid secondary battery <NUM> decreases, and the internal resistance of the all-solid secondary battery <NUM> by the anode active material layer <NUM> increases, so that it is difficult to improve the cycle characteristics of the all-solid secondary battery <NUM>.

The charging capacity of the cathode active material layer <NUM> is obtained by multiplying the charging capacity density (mAh/g) of the cathode active material by the mass of the cathode active material in the cathode active material layer <NUM>. When several kinds (e.g., types) of cathode active materials are utilized, the values of charge capacity density x mass are calculated for respective cathode active materials, and the sum of these values is the charging capacity of the cathode active material layer <NUM>. The charging capacity of the anode active material layer <NUM> is calculated in the same way. That is, the charging capacity of the anode active material layer <NUM> is obtained by multiplying the charging capacity density (mAh/g) of the anode active material by the mass of the anode active material in the anode active material layer <NUM>. When several types of anode active materials are utilized, the values of charge capacity density x mass are calculated for respective anode active materials, and the sum of these values is the charging capacity of the anode active material layer <NUM>. Here, the charge capacity densities of the cathode active material and the anode active material are estimated utilizing an all-solid half-cell utilizing lithium metal as a counter electrode. The charging capacities of the cathode active material layer <NUM> and the anode active material layer <NUM> are directly measured by the measurement of the charging capacity utilizing the all-solid half-cell. When the measured charge capacity is divided by the mass of each active material, the charging capacity density is obtained. In some embodiments, the charging capacities of the cathode active material layer <NUM> and the anode active material layer <NUM> may be initial charging capacities measured during the first charging cycle.

In some embodiments, the all-solid-state secondary battery <NUM> may further include a second anode active material layer disposed between the current collector <NUM> and the anode active material layer <NUM> by charging. The second anode active material layer is a metal layer including lithium and/or a lithium alloy. The metal layer includes lithium and/or a lithium alloy. Accordingly, because the second anode active material layer is a metal layer including lithium, it functions as, for example, a lithium reservoir. Examples of the lithium alloy may include, but are not limited to, a Li-Al alloy, a Li-Sn alloy, a Li-In alloy, a Li-Ag alloy, a Li-Au alloy, a Li-Zn alloy, a Li-Ge alloy, and a Li-Si alloy. Any suitable lithium alloy utilized in the related art may be utilized. The second anode active material layer may be made of one of these alloys, lithium, and/or may be made of several kinds of alloys.

The thickness of the second anode active material layer is not particularly limited, but may be, for example, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. When the thickness of the second anode active material layer is too thin, it is difficult for the second anode active material layer to serve as a lithium reservoir. When the second anode active material layer is too thick, the mass and volume of the all-solid secondary battery <NUM> may increase, and the cycle characteristics thereof may be rather deteriorated. The second anode active material layer may be, for example, a metal foil having a thickness within these ranges.

In the all-solid secondary battery <NUM>, the second anode active material layer may be disposed between the current collector <NUM> and the anode active material layer <NUM> before assembly of the all-solid secondary battery <NUM> or may be deposited between the current collector <NUM> and the anode active material layer <NUM> by charging after assembly of the all-solid secondary battery <NUM>. When the second anode active material layer is disposed between the current collector <NUM> and the anode active material layer <NUM> before assembly of the all-solid secondary battery <NUM>, because the second anode active material layer is a metal layer including lithium, it functions as a lithium reservoir. For example, a lithium foil may be disposed between the current collector <NUM> and the anode active material layer <NUM> before assembly of the all-solid secondary battery <NUM>. Thus, the cycle characteristics of the all-solid secondary battery <NUM> including the second anode active material layer are further improved. When the second anode active material layer is deposited by charging after assembly of the all-solid secondary battery <NUM>, the second anode active material layer is not included during assembly of the all-solid secondary battery <NUM>, so that the energy density of the all-solid secondary battery <NUM> increases. For example, when charging the all-solid secondary battery <NUM>, the all-solid secondary battery <NUM> is charged to exceed the charging capacity of the anode active material layer <NUM>. That is, the anode active material layer <NUM> is overcharged. At the initial stage of charging, lithium is absorbed in the anode active material layer <NUM>. The anode active material included in the anode active material layer <NUM> forms an alloy or compound with lithium ions that have migrated from the cathode active material layer <NUM>. When the all-solid secondary battery <NUM> is charged to exceed the charging capacity of the anode active material layer <NUM>, for example, lithium is deposited on the rear surface of the anode active material layer <NUM>, that is, between the current collector <NUM> and the anode active material layer <NUM>, and a metal layer corresponding to the second anode active material layer is formed by the deposited lithium. The second anode active material layer is a metal layer mainly including lithium (that is, metal lithium). Such a result is obtained, for example, when the anode active material included in the anode active material layer <NUM> is composed of a material that forms an alloy or compound with lithium. During discharging, lithium in the anode active material layer <NUM> and the second anode active material layer, that is, the metal layer, is ionized and moves toward the cathode active material layer <NUM>. Accordingly, it is possible to utilize lithium as an anode active material in the all-solid secondary battery <NUM>. Further, because the anode active material layer <NUM> covers the second anode active material layer, it serves as a protective layer for the second anode active material layer, that is, the metal layer, and serves to suppress the deposition growth of lithium dendrites. Therefore, the short circuit and capacity reduction of the all-solid secondary battery <NUM> are suppressed, and as a result, the cycle characteristics of the all-solid secondary battery <NUM> are improved. Further, when the second anode active material layer is disposed by charging after assembly of the all-solid secondary battery <NUM>, the current collector <NUM> and the anode active material layer <NUM> and the region therebetween are, for example, Li-free regions that do not include lithium (Li) in the initial state or post-discharge state of the all-solid secondary battery.

The all-solid secondary battery, which is a bipolar cell utilizing the same current collector, has a buffer structure inside the same current collector (e.g., inside the inner space formed by folding one current collector), so that it is possible to protect an anode layer from a volume change during charging and discharging, thereby improving the durability of the battery.

<FIG> is a schematic cross-sectional view of an all-solid secondary battery according to an embodiment.

As shown in <FIG>, the all-solid secondary battery <NUM> is a bipolar all-solid secondary battery including: a unit cell <NUM> including the electrode structure <NUM>; and a solid electrolyte layer <NUM> disposed on the cathode active material layer <NUM>, wherein a plurality of the unit cells <NUM> are stacked. The all-solid secondary battery <NUM> has a structure in which a plurality of electrode structures <NUM> are stacked to have a bipolar connection structure, and a desired voltage design may be performed (e.g., obtained) by the bipolar connection structure.

According to an embodiment, <NUM> to <NUM> of the unit cells <NUM> may be stacked to constitute the all-solid secondary battery <NUM>. The all-solid secondary battery <NUM> having an appropriate voltage range may be manufactured by stacking <NUM> to <NUM> of the unit cells <NUM>.

The bipolar all-solid secondary battery <NUM> may further include: a first end plate <NUM> and a second end plate <NUM>' respectively disposed on an electrolyte layer <NUM> and an anode active material layer <NUM> existing at two opposite ends of the stacked unit cell <NUM>; a first half-cell <NUM> including a second anode active material layer <NUM>', a second current collector <NUM>', and a compression pad <NUM>' between the electrolyte layer <NUM> existing at one end of the unit cell stack and the first end plate <NUM>; and a second half-cell <NUM> including a second electrolyte layer <NUM>', a second cathode active material layer <NUM>', and a third current collector <NUM>" between the anode active material layer <NUM> existing at the other end of the unit cell stack and the second end plate <NUM>'.

Claim 1:
An electrode structure (<NUM>) comprising:
a current collector (<NUM>) having a folded structure comprising an outer surface (<NUM>) and an inner surface (<NUM>), the inner surface (<NUM>) defining an inner space, wherein the outer surface (<NUM>) comprises a first portion (11a), a second portion (11b) facing oppositely away from the first portion (11a), and an intermediate portion (11c) between the first portion (11a) and the second portion (11b);
a cathode active material layer (<NUM>) on the first portion (11a) of the outer surface (<NUM>);
an anode active material layer (<NUM>) on the second portion (11b) of the outer surface (<NUM>); and
a compression pad (<NUM>) disposed inside the inner space of the folded structure of the current collector (<NUM>),
wherein the compression pad (<NUM>) is made of an elastic material comprising at least one selected from polyurethane, natural rubber, spandex, butyl rubber (isobutylene isoprene rubber, IIR), fluoroelastomer, ethylene-propylene rubber (EPR), styrene-butadiene rubber (SBR), chloroprene, elastin, epichlorohydrin rubber, nylon, polyterpene, isoprene rubber, polybutadiene, nitrile rubber, thermoplastic elastomer, silicone rubber, ethylene-propylene-diene rubber (EPDM), ethylene vinyl acetate (EVA), halogenated butyl rubber, and neoprene,
the compression pad (<NUM>) is capable of being pressed to have a thickness of <NUM>% to <NUM>% of an initial thickness thereof before being pressed, and
a thickness of the compression pad (<NUM>) is <NUM>% to <NUM>% of a thickness of a lithium deposition layer of an anode formed when charging an all-solid secondary battery comprising the electrode structure (<NUM>), 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.