All-solid-state battery

Abstract

One embodiment provides an all-solid-state secondary battery including a buffer layer formed between battery cells adjacent to each other, wherein the all-solid-state secondary battery is in a stacked form having a plurality of battery cells stacked along a stacking direction, among the plurality of battery cells, a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are sequentially stacked.

Description

Technical Field

[0001] This invention relates to an all-solid-state battery. Background Technology

[0002] Recently, all-solid-state secondary batteries using solid electrolytes as electrolytes have attracted attention (e.g., patent reference 1). In all-solid-state secondary batteries, solid electrolyte powder is compressed and solidified to form an electrolyte layer.

[0003] Stacked all-solid-state secondary batteries are known as such batteries, in which multiple battery cells (also called individual cells) manufactured by sequentially stacking a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are stacked. In stacked all-solid-state secondary batteries, each cell repeatedly expands and contracts, generating pressure between adjacent cells during repeated charging and discharging. In this paper, because the expansion or contraction of each cell is not uniform but biased in the inward direction (perpendicular to the stacking direction) of the stacking surface, uneven pressure is applied to each cell in the inward direction of the stacking surface. Consequently, during repeated charging and discharging, the electrolyte layer of each cell gradually cracks or deforms, leading to problems such as deterioration of battery characteristics, including cycle performance.

[0004] (Patent Reference 1: Japanese Patent Publication No. 2011-086554) Summary of the Invention

[0005] Technical issues

[0006] One object of the present invention is to reduce the pressure bias applied to each of the battery cells involved in charging and discharging in a stacked all-solid-state secondary battery.

[0007] Technical solution

[0008] In other words, the all-solid-state secondary battery of the present invention is a stacked all-solid-state secondary battery, wherein multiple battery cells configured by sequentially stacking a positive electrode layer, a solid electrolyte layer and a negative electrode layer are stacked in the stacking direction, and a buffer layer is formed between adjacent battery cells.

[0009] With the above configuration, a buffer layer is provided between adjacent battery cells to charge the all-solid-state secondary battery, thereby distributing pressure when the battery cells expand and reducing the pressure bias applied to each battery cell according to charging and discharging. This suppresses the cracking or deformation of the electrolyte layer due to repeated charging and discharging, and also suppresses the degradation of battery characteristics such as cycle performance.

[0010] In all-solid-state secondary batteries, it is preferable that the sum of the thicknesses of the buffer layers along the stacking direction is greater than the sum of the thickness changes of the battery cells along the stacking direction during charging and discharging.

[0011] Therefore, the thickness changes of the battery cell during charging and discharging can be reliably absorbed by the buffer layer, and the bias voltage applied to each battery cell according to the pressure during charging and discharging can be further reduced.

[0012] On the other hand, "the change in charge and discharge" refers to the change in charge when the all-solid-state battery changes from a fully charged state to a discharged state. "Fully charged state" refers to a state where the SOC (State of Charge) of the all-solid-state battery is greater than or equal to 90%, while "discharged state" refers to a state where the SOC of the all-solid-state battery is less than or equal to 10%. Furthermore, "the SOC of the all-solid-state battery" refers to the ratio of the total remaining capacity of the battery cells to the total rated capacity of each battery cell.

[0013] Additionally, "the sum of the thicknesses of the buffer layers" refers to the sum of the thicknesses of multiple buffer layers when the all-solid-state secondary battery includes multiple buffer layers, and also refers to the thickness of a single buffer layer when only one buffer layer is provided. Furthermore, "the sum of the variations in the thickness of the battery cells" refers to the sum of the variations in the thickness of all battery cells included in the all-solid-state secondary battery.

[0014] As a specific embodiment of an all-solid-state secondary battery, lithium ions move between the positive electrode layer and the negative electrode layer in the battery cell to cause charging and discharging.

[0015] The buffer layer preferably has a lower elastic modulus than the positive electrode layer and the negative electrode layer. Therefore, when the battery cell expands due to charging and discharging, the buffer layer elastically deforms to more reliably absorb the volume change of the battery cell, thereby further reducing the pressure bias applied to each battery cell.

[0016] In one embodiment, in an all-solid-state secondary battery, the sum of the thicknesses of the positive electrode layer, the solid electrolyte layer, and the negative electrode layer in the stacking direction may be greater in the fully charged state than in the discharged state.

[0017] In one embodiment, the all-solid-state secondary battery may be in a state in which, in a fully charged state, a lithium metal layer is deposited between the negative electrode current collector and the negative electrode active material layer provided in the negative electrode layer.

[0018] Furthermore, in an all-solid-state secondary battery, in a fully charged state, the sum of the thicknesses of the negative electrode current collector and the negative electrode active material layer in the negative electrode layer along the stacking direction is preferably less than the thickness of the lithium metal layer deposited between the negative electrode current collector and the negative electrode active material layer along the stacking direction.

[0019] Therefore, it has a high volumetric energy density when fully charged and can stably repeat the dissolution and precipitation of lithium.

[0020] In one embodiment, in an all-solid-state secondary battery, when the specific capacity per unit area of ​​the positive electrode layer is X [mAh / cm²], -2 When fully charged, the thickness of the lithium metal layer along the stacking direction can be greater than or equal to 4.85 × X μm.

[0021] The all-solid-state secondary battery preferably further includes a rectangular housing for accommodating multiple battery cells and a buffer layer, wherein the housing has a bottom surface with the smallest area among three pairs of opposing surfaces, and the multiple battery cells and the buffer layer are accommodated in the housing for stacking along the height direction.

[0022] Therefore, the pressure bias applied to each of the battery cells can be further reduced as the battery cells expand due to charging and discharging.

[0023] In one embodiment, the area of ​​the buffer layer may be larger than the area of ​​the battery cell when viewed in the stacking direction.

[0024] In one embodiment, the battery cells may be connected in parallel with each other, and the buffer layer between the battery cells may be made of an insulating material. In this case, it is preferable that an insulating film having a thickness smaller than that of the buffer layer is installed between adjacent battery cells and the buffer layer.

[0025] In another embodiment, the battery cells may be connected in series with each other, and the buffer layer between the battery cells may be made of a conductive material.

[0026] Beneficial effects

[0027] This invention reduces the pressure bias applied to each of the battery cells involved in charging and discharging in a stacked all-solid-state secondary battery. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of an all-solid-state secondary battery according to one embodiment.

[0029] Figure 2 This is an exploded view of an all-solid-state secondary battery according to one embodiment.

[0030] Figure 3 This is a schematic diagram of the battery body of an all-solid-state secondary battery according to one embodiment.

[0031] Figure 4 It is based on different Figure 3 A schematic diagram of the battery body of an all-solid-state secondary battery according to one embodiment.

[0032] Figure 5 This is a schematic diagram of a sample of an all-solid-state secondary battery according to one embodiment.

[0033] Figure 6 The evaluation results of a battery characteristic evaluation according to one embodiment are shown. Detailed Implementation

[0034] An embodiment of the all-solid-state secondary battery of the present invention will be described below.

[0035] According to an exemplary embodiment, the all-solid-state secondary battery 100 is a lithium secondary battery, wherein lithium ions are charged and discharged while moving between the positive and negative electrodes. Figure 1 and Figure 2 As shown, the all-solid-state secondary battery 100 includes a battery casing C and a battery body 1 housed in the battery casing C.

[0036] The battery casing C can be prismatic (cubic prism) and made of a metal such as aluminum. The battery casing C has three pairs of opposing surfaces with different areas, and the opposing surface S with the smallest area serves as the bottom surface. On the bottom surface, the positive terminal P and the negative terminal N, which are electrically connected to the battery body 1, are mounted.

[0037] Battery body 1 is composed of multiple stacked ( Figure 1 It is a stacked type of 13 battery cells 11, and has a basically cuboid shape. For example... Figure 2 and Figure 3 As shown, each battery cell 11 is sheet-like and consists of a positive electrode layer 111, a solid electrolyte layer 112, and a negative electrode layer 113 stacked sequentially in the height direction. Furthermore, in the battery body 1, multiple battery cells 11 are stacked and overlapped in the height direction. In the battery body 1 housed in the battery casing C, the stacking direction of the battery cells 11 is aligned with the height direction of the battery casing C (i.e., the direction perpendicular to the bottom surface).

[0038] (Positive electrode layer)

[0039] The positive electrode layer 111 includes a positive electrode current collector layer 111a and a positive electrode active material layer 111b arranged sequentially toward the negative electrode layer 113.

[0040] The positive electrode current collector layer 111a has a rectangular shape in a plan view, such as a sheet, foil, or plate. There are no particular limitations on the material constituting the positive electrode current collector layer 111a; known materials used in all-solid-state batteries can be used, and for example, stainless steel, aluminum, copper, nickel, iron, titanium, carbon, or alloys thereof can be used.

[0041] The positive electrode active material layer 111b reversibly absorbs and releases lithium ions. The positive electrode active material layer 111b includes a minimum positive electrode active material and may further include a solid electrolyte. Additionally, if necessary, a conductive additive, a binder, a filler, a dispersant, etc. may be included, which are known materials contained in the positive electrode active material layer of the all-solid-state battery.

[0042] The material of the positive electrode active material is not particularly limited, and known materials that can be used for all-solid-state batteries can be used. For example, the positive electrode active material includes lithium salts such as lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium iron phosphate, nickel sulfide, copper sulfide, sulfur, iron oxide, or vanadium oxide. The positive electrode active materials can be used individually or in combination of two or more.

[0043] Additionally, the positive electrode active material preferably includes a lithium salt of a transition metal oxide having a layered rock salt structure in the lithium salt. "Layered" means in the form of flakes. Additionally, "rock salt structure" refers to the sodium chloride-type structure, which is a crystal structure, and particularly, a structure in which the face-centered cubic lattices formed by each of the cations and anions are offset by 1 / 2 of each unit grid ridge.

[0044] Examples of the lithium salt of the transition metal oxide having a layered rock salt structure may include lithium salts of ternary transition metal oxides, such as LiNi x Co y Al z O2 (NCA) or LiNi x Co y Mn z O2 (NCM) (assuming 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1).

[0045] When the positive electrode active material includes a lithium salt of a ternary transition metal oxide having a layered rock salt structure, the energy density and thermal stability of the all-solid-state secondary battery 100 can be improved.

[0046] The positive electrode active material may be coated with a coating. The coating can use any material known to be used as a coating for the positive electrode active material of the all-solid-state secondary battery 100 and may include, for example, Li2O-ZrO2, etc.

[0047] Additionally, the positive electrode active material is formed of a lithium salt such as NCA, NCM, etc. of a ternary transition metal oxide. When nickel (Ni) is included as the positive electrode active material, the capacity density of the all-solid-state secondary battery 100 can be increased, and the metal elution of the positive electrode active material can be reduced. Accordingly, the all-solid-state secondary battery 100 according to one embodiment can exhibit improved long-term reliability and cycle characteristics.

[0048] The positive electrode active material can have a particle shape such as spherical or elliptical. Furthermore, the particle size of the positive electrode active material is not particularly limited and can be within the range suitable for positive electrode active materials in conventional all-solid-state secondary batteries. Additionally, the content of the positive electrode active material in the positive electrode active material layer 111b is not particularly limited, but is within the range suitable for positive electrode layers 111 in conventional all-solid-state secondary batteries.

[0049] Furthermore, examples of conductive additives that can be mixed into the positive electrode active material layer 111b include, for example, graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and metal powder. Examples of binders that can be mixed into the positive electrode active material layer 111b include, for example, styrene-butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. Additionally, fillers, dispersants, and ion-conducting additives that can be mixed into the positive electrode active material layer 111b can be known materials commonly used in electrodes of all-solid-state secondary batteries.

[0050] (Solid electrolyte layer)

[0051] A solid electrolyte layer 112 is disposed between the positive electrode layer 111 and the negative electrode layer 113 (specifically, between the positive electrode active material layer 111b and the negative electrode active material layer 113a). The solid electrolyte layer 112 has a rectangular shape in plan view, such as sheet, foil, or plate, and comprises a solid electrolyte capable of ion movement. The solid electrolyte layer 112 contains a solid electrolyte capable of ion movement. The material of the solid electrolyte is not particularly limited, and known materials suitable for all-solid-state batteries can be used, examples of which include sulfide solid electrolytes, oxide solid electrolytes, and polymer electrolytes.

[0052] Sulfide-based solid electrolyte materials included in solid electrolytes can be, for example, Li₂S-P₂S₅, Li₂S-P₂S₅-LiX (where X is a halogen element (e.g., I or Cl)), Li₂S-P₂S₅-Li₂O, Li₂S-P₂S₅-Li₂O-LiI, Li₂S-SiS₂, Li₂S-SiS₂-LiI, Li₂S-SiS₂-LiBr, Li₂S-SiS₂-LiCl, Li₂S-SiS₂-B₂S₃-LiI, Li₂S-SiS₂-P₂S₅-LiI, Li₂S-B₂S₃, and Li₂S-P₂S₅-Z. m S n (m is an integer, Z is any one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q(p and q are integers, and M is P, Si, Ge, B, Al, Ga, or In, etc.) Sulfide-based solid electrolyte materials are prepared by processing raw materials (e.g., Li₂S, P₂S₅, etc.) using melt-quenching or mechanical grinding methods. Alternatively, heat treatment can be performed after this processing. Solid electrolytes can be amorphous or crystalline, and both can be in a mixed state.

[0053] Furthermore, as a solid electrolyte, a sulfide solid electrolyte material containing at least one element selected from sulfur, silicon, phosphorus, and boron is preferably used. This material improves the lithium conductivity of the solid electrolyte layer 112 and enhances the battery characteristics of the all-solid-state secondary battery 100. In particular, it is preferable to use a material containing sulfur (S), phosphorus (P), and lithium (Li) as the solid electrolyte, and more preferably, a material containing Li₂S-P₂S₅ is used.

[0054] When Li2S-P2S5 is included as the sulfide-based solid electrolyte material forming the solid electrolyte, the mixing molar ratio of Li2S and P2S5 can be, for example, in the range of Li2S:P2S5 = 50:50 to 90:10. Furthermore, the solid electrolyte layer 112 may further include a binder. The binder included in the solid electrolyte layer 112 may include, for example, styrene-butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene oxide, etc. The binder included in the solid electrolyte layer 112 may be the same as or different from the binder of the positive electrode active material layer 111b.

[0055] (Negative electrode layer)

[0056] The negative electrode layer 113 includes a negative electrode current collector layer 113b and a negative electrode active material layer 113a arranged sequentially in the direction of the positive electrode layer 111.

[0057] The negative electrode current collector layer 113b has a rectangular shape in the plan view, such as a sheet, foil, or plate. There are no particular limitations on the materials included in the negative electrode current collector layer 113b, and known materials suitable for all-solid-state batteries can be appropriately used. Examples of materials include stainless steel, aluminum, copper, nickel, iron, titanium, carbon, etc.

[0058] The negative electrode active material layer 113a may contain one or more negative electrode active materials that form alloys or compounds with lithium. When the all-solid-state secondary battery 100 according to one embodiment is overcharged, the negative electrode active material contained in the negative electrode active material layer 113a and the lithium ions moving from the positive electrode layer 111 may form alloys or compounds, and lithium metal may be deposited on one or both sides of the negative electrode active material layer 113a.

[0059] Specifically, during initial charging, the negative electrode active material and lithium ions in the negative electrode active material layer 113a can form an alloy or compound, allowing lithium to be absorbed into the negative electrode active material layer 113a. After absorption, when the capacity of the negative electrode active material layer 113a is exceeded, lithium metal precipitates on one or both sides of the negative electrode active material layer 113a. The lithium metal forms a metal layer. Because lithium metal is formed, and simultaneously diffuses through the negative electrode active material capable of forming alloys or compounds with lithium ions, the lithium metal forms uniformly along the surface of the negative electrode active material layer 113a, rather than a dendritic phase. During discharge, the lithium metal in the negative electrode active material layer 113a and the metal layer is ionized and migrates towards the positive electrode active material layer 111b. Accordingly, the lithium metal can ultimately be used as the negative electrode active material, improving energy density.

[0060] In one embodiment, when the all-solid-state battery is fully charged, the sum of the thicknesses of the negative electrode current collector and the negative electrode active material layer 113a in each battery cell 11 may be less than the thickness of the lithium metal layer deposited between the negative electrode current collector and the negative electrode active material layer 113a.

[0061] Additionally, when the specific capacity per unit area of ​​the positive electrode layer 111 is X [mAh / cm²] -2 When fully charged, the thickness of the lithium metal layer deposited from the negative electrode layer 113 in the stacking direction is 4.85 × X [μm].

[0062] The negative electrode active material used to achieve this function can be, for example, at least one selected from the group consisting of amorphous carbon, Au, Pt, Pd, Si, Al, Bi, Sn, In, and Zn. Specific examples of amorphous carbon may include, for example, carbon black such as acetylene black, furnace black, and Ketjen black, graphene, etc.

[0063] The shape of the negative electrode active material is not particularly limited, but it can be granular, wherein the negative electrode active material can form a uniform layer, such as a plating layer. When the negative electrode active material has a granular shape, lithium ions can pass through the gaps between the subdivided negative electrode active materials and form a lithium metal layer between the negative electrode active material layer 113a and the negative electrode current collector. On the other hand, when a plating layer is formed, the metal layer is deposited between the negative electrode active material layer 113a and the solid electrolyte layer 112.

[0064] The negative electrode active material layer 113a may further include an adhesive. By including the adhesive, the negative electrode active material layer 113a can be stabilized on the negative electrode current collector. The adhesive can be any of, for example, styrene-butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, and combinations thereof.

[0065] In addition, additives, such as fillers, dispersants and ion-conducting agents used in conventional all-solid-state secondary batteries, can be appropriately mixed into the negative electrode active material.

[0066] The battery body 1 may include a positive electrode current collector terminal 12 electrically connected to the positive electrode current collector layer 111a of each battery cell 11 and a negative electrode current collector terminal 13 electrically connected to the negative electrode current collector layer 113b. Both the positive electrode current collector terminal 12 and the negative electrode current collector terminal 13 are sheet-like and may be arranged along the stacking direction of the battery body 1. The positive electrode current collector terminal 12 and the negative electrode current collector terminal 13 may be connected to the positive terminal P and the negative terminal N protruding from the battery casing C, respectively, and the power generated in each battery cell 11 may be output to the outside through the positive electrode current collector terminal 12 and the negative electrode current collector terminal 13. Each battery cell 11 includes a positive electrode current collector tab 12a and a negative electrode current collector tab 13a protruding in a direction perpendicular to the stacking direction of each battery cell 11, which are respectively connected to the positive electrode current collector terminal 12 and the negative electrode current collector terminal 13. In one embodiment, each battery cell 11 of the battery body 1 may be connected in parallel with each other.

[0067] (Buffer layer)

[0068] According to one embodiment, the all-solid-state secondary battery 100 may include one or more buffer layers installed between adjacent battery cells 11 within the battery body 1. Buffer layers 14 may be installed between all adjacent battery cells 11, or between the battery cells 11 and the battery casing C at both ends along the stacking direction.

[0069] Each buffer layer 14 has a rectangular shape in a plan view, such as a sheet or plate, wherein the thickness direction of the buffer layer 14 may be aligned with the stacking direction of the battery cells 11. When viewed in the stacking direction of the battery cells 11, because each buffer layer 14 has an area larger than that of each battery cell 11, the buffer layer 14 can be mounted to cover the entire area except for the positive electrode current collector terminal 12a and the negative electrode current collector terminal 13a of the battery cells 11. Furthermore, the thickness of each buffer layer 14 can be set such that its sum is greater than the sum of the thickness variations of each battery cell 11 along the stacking direction during charging and discharging.

[0070] The buffer layer 14 absorbs the volume change (expansion) of the battery cell 11 during charging and discharging. It is composed of elastically deformable components and, in particular, may be formed of a material with an elastic modulus less than that of the positive and negative electrode current collectors. The buffer layer 14 may be formed of a material whose stress-displacement curve slope is less than or equal to 200 MPa or 50 MPa at less than or equal to 80% displacement, or less than or equal to 10 MPa at less than or equal to 50% displacement. The material of the buffer layer 14 may be epoxy resin, acrylic resin, polyimide resin, polyester resin, polypropylene resin, polyamide resin, polystyrene resin, polyvinyl chloride resin, polycarbonate resin, fluoropolymers such as PTFE, silicone rubber, etc., but is not limited to these. Each buffer layer 14 may consist of a single material or a combination of several materials. Furthermore, each buffer layer 14 may include the same material or may include different materials. Additionally, the buffer layer 14 may include an insulating material, which may insulate each battery cell 11. The insulating material may have a strength greater than or equal to 1.0 × 10⁻⁶. 17 Ω·cm 2 The surface resistivity, and in particular, fluoropolymers such as PTFE or silicone rubber.

[0071] In one embodiment, an insulating film with a thickness less than that of the buffer layer 14 may be installed between the battery cell 11 of the battery body 1. The insulating film may be made of materials such as PET (polyethylene terephthalate) film, PTFE (polytetrafluoroethylene) film, kapton film, polyimide film, imide film, etc., but is not limited thereto.

[0072] According to one embodiment of the all-solid-state secondary battery 100, because the buffer layer 14 is installed between the battery cells 11, the pressure generated when each battery cell 11 expands due to charging of the all-solid-state secondary battery 100 can be dispersed, reducing the pressure bias applied to each battery cell 11 due to charging and discharging. In addition, cracking or deformation of the electrolyte layer that may occur during repeated charging and discharging can be suppressed, thereby suppressing the degradation of battery characteristics such as cycle characteristics.

[0073] The present invention is not limited to the embodiments described above.

[0074] In one embodiment of the battery body 1, each battery cell 11 may be connected in parallel with each other, but is not limited thereto. In other words, each battery cell 11 may be connected in series with each other. In this case, each buffer layer 14 includes a conductive material to supply current between the battery cells 11. The conductive material may have a conductivity of less than or equal to 0.1 Ω / cm. 2 The thin-film resistivity value, and in particular, can be copper foil or aluminum foil, conductive double-sided tape, etc. Furthermore, each battery cell 11 can be connected to each other in a mixed manner of parallel and series connection.

[0075] Alternatively, the battery body 1 can be housed within the battery casing C, with the opposite side of the battery casing C having the smallest area serving as the bottom surface and the height direction serving as the stacking direction, but this is not a limitation. In another embodiment, the battery body 1 can be housed within the battery casing C, with one of the other opposite sides, rather than the opposite side of the battery casing C having the smallest area, serving as the bottom surface, and the height direction serving as the stacking direction, but this is not a limitation.

[0076] In one embodiment, the buffer layer 14 may be installed between the battery cells 11 and the battery casing C at both ends of the battery body 1 along the stacking direction of all battery cells 11 adjacent to the buffer layer 14 of the battery body 1, but is not limited thereto. In another embodiment, for example, as Figure 4 As shown, the buffer layer 14 can be mounted facing upwards and downwards along the stacking direction of the plurality of battery cells 11. In this document, an insulating layer, such as an insulating film, can be mounted between each battery cell 11.

[0077] In one embodiment, the lithium metal layer may not be deposited on the negative electrode layer 113 in the battery body 1. For example, when using a material capable of reversibly inserting / deintercalating large amounts of lithium ions, such as silicon, the volume of the negative electrode active material may change several times. In this document, the thickness of the positive electrode layer 111, the solid electrolyte layer 112, and the negative electrode layer 113 of each battery cell 11 may be greater in the fully charged state than in the discharged state.

[0078] Example

[0079] The invention will be described in more detail by way of the following examples. The invention is not limited to the following examples, but can be practiced with modifications suitable for the meanings above and below, and all of these are included within the technical scope of the invention.

[0080] Example 1

[0081] Battery characteristics are evaluated by the presence or absence of buffer layers between battery cells.

[0082] 1. Manufacturing of stacked all-solid-state secondary battery cells

[0083] (1) Preparation of positive electrode structure

[0084] LiNi, used as the positive electrode active material, was weighed at a mass ratio of 60:35:5. 0.8 Co 0.15 Al 0.05 O2(NCA) ternary powder, Li2S-P2S5 (80:20 mol%) amorphous powder as a sulfide-based solid electrolyte, and vapor-grown carbon fiber powder as a conductive material (conductive additive) for the positive electrode layer are mixed using a rotary mixer.

[0085] Subsequently, a dehydrated xylene solution containing styrene-butadiene rubber (hereinafter referred to as SBR) as a binder was added to the mixed powder, resulting in a total SBR content of 5.0 wt% based on the total weight of the mixed powder. Additionally, an appropriate amount of dehydrated xylene was added to the primary mixture to adjust the viscosity. Furthermore, to improve the dispersibility of the mixed powder, zirconia balls with a diameter of 5 mm were added to the mixed powder, such that the mixed powder, zirconia balls, and empty space were each 1 / 3 of the kneading container, thus preparing a third mixed solution. The third mixed solution was placed in a rotary mixer and stirred at 3000 rpm for 3 minutes to prepare a coating solution for the positive electrode layer.

[0086] Subsequently, after preparing a 20 μm thick aluminum film current collector as the positive electrode current collector and placing it on a benchtop screen printing machine, a coating solution for the positive electrode layer was applied to the positive electrode layer using a metal mask with a diameter of 2.0 cm × 2.0 cm and a thickness of 150 μm. The sheet coated with the coating solution for the positive electrode layer was dried on a hot plate at 60 °C for 30 minutes and then vacuum-dried at 80 °C for 12 hours to form a positive electrode layer on the positive electrode current collector. After drying, the positive electrode current collector and the positive electrode layer had a total thickness of approximately 165 μm.

[0087] (2) Fabrication of negative electrode structure

[0088] Graphite powder (vacuum-dried at 80°C for 24 hours) as the negative electrode active material and PVDF as the binder were weighed at a mass ratio of 95.0:5.0. Subsequently, the negative electrode active material, binder, and appropriate amount of NMP were placed in a rotary mixer and stirred at 3000 rpm for 3 minutes and degassed for 1 minute to prepare a coating solution for the negative electrode layer.

[0089] Subsequently, a 16 μm thick copper foil current collector was prepared as the negative electrode current collector, and a coating solution for the negative electrode layer was applied to the copper foil current collector using a doctor blade. The coating solution for the negative electrode layer on the copper foil current collector had a thickness (gap) of approximately 150 μm.

[0090] A sheet coated with a coating solution for the negative electrode layer was placed in a desiccator heated to 80°C and dried for 15 minutes. Subsequently, the dried sheet was vacuum-dried at 80°C for 24 hours to fabricate the negative electrode structure. The negative electrode structure has a thickness of approximately 140 μm.

[0091] (3) Manufacturing of the electrolyte layer

[0092] A solution of dehydrated xylene containing dissolved SBR was added to an amorphous powder of Li₂S-P₂S₅ (80:20 mol%), which served as a sulfide-based solid electrolyte, thereby including 2.0 wt% SBR based on the total weight of the primary mixture. Subsequently, an appropriate amount of dehydrated xylene was added to the primary mixture to adjust the viscosity, preparing a secondary mixture. Then, to improve the dispersibility of the mixed powder, zirconia balls with a diameter of 5 mm were added to the mixed powder, such that the mixed powder, zirconia balls, and empty space were each 1 / 3 of the kneading container, preparing a third mixed solution. The third mixed solution was placed in a rotary mixer and stirred at 3000 rpm for 3 minutes to prepare a coating solution for the electrolyte layer.

[0093] The negative electrode structure was placed on a benchtop screen printing machine, and a coating solution for the electrolyte layer was applied to the negative electrode structure using a 500 μm thick metal mask. The sheet coated with the electrolyte layer solution was dried on a hot plate at 40°C for 10 minutes, and then vacuum-dried again at 40°C for 12 hours to form the electrolyte layer on the negative electrode structure. After drying, the electrolyte layer had a total thickness of approximately 300 μm.

[0094] (4) Manufacturing of individual battery cells

[0095] Thin sheets consisting of a negative electrode structure, an electrolyte layer, and a positive electrode structure are pierced using a Thompson scraper and then pressed using a roller press with a 150 μm gap. The electrolyte layer and the positive electrode layer of the positive electrode structure are laminated using a dry lamination method to manufacture a single cell (cell) of an all-solid-state secondary battery. Each cell has a layer thickness of approximately 400 μm.

[0096] (5) Manufacturing of stacked all-solid-state secondary battery cells

[0097] Individual battery cells are stacked to create two stacked all-solid-state secondary battery cells.

[0098] like Figure 5 As shown in (a), one method involves preparing individual battery cells and placing a PTFE sheet of approximately 500 μm thickness between the individual battery cells as a buffer layer, then encapsulating them in an aluminum laminate with ends, evacuating the membrane to 100 Pa using a vacuum cleaner, and sealing the membrane to package them (sample A).

[0099] Another one is like Figure 5 As shown in (b), the stacked individual battery cells are packaged by not placing a buffer layer between them, enclosing the stacked individual battery cells in an aluminum laminate with ends, evacuating the membrane to 100 Pa using a vacuum cleaner, and sealing the membrane.

[0100] 2. Battery Characteristic Evaluation

[0101] The charge and discharge capacities (mAh) of each all-solid-state secondary cell in samples A and B were measured using a charge and discharge evaluation device (TOSCAT-3100, Dongyang system). The individual cells were charged to 4.25V at 0.1mA and discharged to 2.50V at 0.1mA at 60°C, followed by capacity measurement. Results are as follows: Figure 6 As shown.

[0102] like Figure 6 As shown, the solid-state secondary battery cells of sample A, where the buffer layer is disposed between the individual battery cells, exhibit the same charge and discharge capacity. However, the all-solid-state secondary battery cells of sample B, where the buffer layer is not disposed between the individual battery cells, exhibit increased charge capacity due to micro-short circuits, resulting in insufficient battery efficiency. Accordingly, the buffer layer disposed between the individual battery cells suppresses short circuits, thus improving the cycle characteristics of the all-solid-state secondary battery cells.

[0103] [Explanation of reference numerals in the attached figures]

[0104] 100: All-solid-state rechargeable lithium battery

[0105] 1: Battery body

[0106] 11: Battery Unit

[0107] 111: Positive electrode layer

[0108] 111a: Positive electrode current collector layer

[0109] 111b: Positive electrode active material layer

[0110] 112: Solid electrolyte layer

[0111] 113: Negative electrode layer

[0112] 113a: Negative electrode active material layer

[0113] 113b: Negative electrode current collector layer

[0114] 14: Buffer layer

Claims

1. An all-solid-state secondary battery, comprising: A stacked all-solid-state secondary battery, wherein multiple battery cells configured by sequentially stacking a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are stacked in a stacking direction, and a buffer layer is formed between adjacent battery cells. Lithium ions move between the positive electrode layer and the negative electrode layer to charge and discharge each of the battery cells, and In the fully charged state, the sum of the thicknesses of the negative electrode current collector and the negative electrode active material layer in the negative electrode layer along the stacking direction is less than the thickness of the lithium metal layer deposited between the negative electrode current collector and the negative electrode active material layer along the stacking direction.

2. The all-solid-state secondary battery according to claim 1, wherein... The sum of the thicknesses of the buffer layers along the stacking direction is greater than the sum of the thickness variations of the battery cells along the stacking direction during charging and discharging.

3. The all-solid-state secondary battery according to claim 1, wherein... The buffer layer has an elastic modulus that is smaller than that of the positive electrode layer and the negative electrode layer.

4. The all-solid-state secondary battery according to claim 1, wherein... The specific capacity per unit area of ​​the positive electrode layer is X [mAh / cm²]. -2 Furthermore, the thickness of the lithium metal layer in the fully charged state along the stacking direction is greater than or equal to 4.85 × X μm.

5. The all-solid-state secondary battery according to claim 1, The device further includes a rectangular housing for accommodating the plurality of battery cells and the buffer layer, wherein the housing has a bottom surface having a minimum area among three pairs of opposing surfaces, and the plurality of battery cells and the buffer layer are accommodated in the housing for stacking along the height direction.

6. The all-solid-state secondary battery according to claim 1, wherein... When viewed in the stacking direction, the area of ​​the buffer layer is larger than the area of ​​the battery cell.

7. The all-solid-state secondary battery according to claim 1, wherein... The battery cells are connected in parallel to each other, and the buffer layer between the battery cells comprises an insulating material.

8. The all-solid-state secondary battery according to claim 7, wherein An insulating film having a thickness smaller than that of the buffer layer is installed between adjacent battery cells and the buffer layer.

9. The all-solid-state secondary battery according to claim 1, wherein... The battery cells are connected in series with each other, and the buffer layer between the battery cells is made of a conductive material.

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