Negative electrode for all-solid-state rechargeable battery, and all-solid-state rechargeable battery including same

Abstract

The present invention provides a negative electrode for an all-solid-state rechargeable battery in which shorting does not easily occur even if charged rapidly, and which can maintain a high battery capacity even if charging and discharging cycles are repeated. The negative electrode for an all-solid-state rechargeable battery includes a negative-electrode current collector and a negative-electrode mixture layer, wherein the negative-electrode mixture layer includes: a first layer forming a surface of the negative-electrode mixture layer toward the negative-electrode current collector; and a second layer forming a surface of the negative-electrode mixture layer opposite to the first layer, each of the first layer and the second layer contains a negative-electrode active material, a carbon material and a binder, content A of the binder in the first layer is 5 to 20 parts by weight with respect to 100 parts by weight of the total content of the negative-electrode active material and the carbon material in the first layer, content B of the binder in the second layer is 1 to 10 parts by weight with respect to 100 parts by weight of the total content of the negative-electrode active material and the carbon material in the second layer, content A is greater than content B, and the difference between content A and content B is in the range of 4 to 19 parts by weight.

Description

Anode for an all-solid-state secondary battery and an all-solid-state secondary battery comprising the same

[0001] The present invention relates to a negative electrode for an all-solid-state secondary battery and an all-solid-state secondary battery including the same.

[0002] All-solid-state secondary batteries are expected to significantly improve energy density compared to conventional secondary batteries using electrolytes. Furthermore, the recent rapid increase in demand for EV applications has created urgent challenges, such as improving rapid charging performance and suppressing cycle degradation.

[0003] As one of the factors affecting the battery performance of the all-solid-state secondary battery as described above, the peel strength between the negative electrode current collector and the negative electrode composite layer constituting the electrode of the all-solid-state secondary battery can be cited as an example.

[0004] If the peel strength between the negative electrode current collector and the negative electrode composite layer is excessively low, the negative electrode composite layer may peel off from the negative electrode current collector or become misaligned during the assembly process of an all-solid-state secondary battery. As a result, the negative electrode may not function properly or a short circuit may occur.

[0005] Accordingly, as shown in Patent Documents 1 to 3, an all-solid-state lithium secondary battery is being considered in which the peel strength between the negative electrode current collector and the negative electrode composite layer is increased by making the content of the binder contained in the negative electrode composite layer relatively larger than that of other parts in order to increase the peel strength between the negative electrode current collector and the negative electrode composite layer.

[0006] [Prior Art Literature]

[0007] [Patent Document]

[0008] Patent Document 1: Korean Patent No. 2071585

[0009] Patent Document 2: Korean Patent No. 2053063

[0010] Patent Document 3: Korean Patent No. 1527748

[0011] However, as a result of repeated examinations by the inventors of the present invention, it was found that if the peel strength between the negative electrode current collector and the negative electrode composite layer is excessively high, not only will the battery capacity decrease, but cracks may also occur in the negative electrode composite layer when lithium is precipitated during charging. If cracks occur in the negative electrode composite layer, for example, there is a risk that lithium precipitated in the negative electrode will concentrate at the location of the crack, resulting in a short circuit.

[0012] The inventors of the present invention also considered that not only the peel strength between the negative electrode current collector and the negative electrode composite layer, but also the peel strength between the negative electrode composite layer and the solid electrolyte layer are factors affecting the performance of the all-solid-state battery. The performance of the all-solid-state battery in this specification refers to battery capacity and suppression of short-circuiting during charging.

[0013] The present invention has been made in consideration of the aforementioned problems, and aims to provide a negative electrode for an all-solid-state secondary battery that is unlikely to cause a short circuit during rapid charging and can suppress cycle degradation.

[0014] An anode for an all-solid-state secondary battery according to one embodiment and an all-solid-state secondary battery including the same are as follows.

[0015] According to one embodiment, a negative electrode for an all-solid-state secondary battery comprising a negative electrode current collector and a negative electrode composite layer,

[0016] The above negative electrode composite layer includes a first layer forming a surface on the negative electrode collector side of the negative electrode composite layer, and a second layer forming a surface on the opposite side to the first layer.

[0017] The first layer and the second layer each contain a negative electrode active material, a carbon material, and a binder,

[0018] The content A of the binder in the first layer is 5 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the total weight of the negative electrode active material and the carbon material in the first layer,

[0019] The content B of the binder in the second layer is 1 part by weight or more and 10 parts by weight or less based on 100 parts by weight of the total weight of the negative electrode active material and the carbon material in the second layer,

[0020] Provided is an anode for an all-solid-state secondary battery, wherein the content A is greater than the content B, and the difference between the content A and the content B is in a range of 4 parts by weight or more and 19 parts by weight or less.

[0021] The above cathode composite layer may be composed of two layers: the first layer and the back layer.

[0022] The above negative electrode collector may be made of metal, and the binder may be a polyvinylidene fluoride polymer.

[0023] The peel strength between the negative electrode current collector and the negative electrode composite layer may be 35 mN / mm or more and 490 mN / mm or less.

[0024] According to another embodiment, an all-solid-state secondary battery is provided, which includes a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode, wherein the negative electrode is a negative electrode for the above-described all-solid-state secondary battery.

[0025] According to another embodiment, the cathode current collector and the cathode composite layer are included,

[0026] The above negative electrode composite layer is a method for manufacturing a negative electrode for an all-solid-state secondary battery, including a first layer forming a surface on the negative electrode collector side of the negative electrode composite layer, and a second layer forming a surface on the opposite side to the first layer,

[0027] A process of forming the first layer by applying the first cathode slurry onto the cathode current collector and drying it;

[0028] A process of forming the second layer by applying a second cathode slurry on the formed first layer and drying it,

[0029] The first negative electrode slurry and the second negative electrode slurry contain a negative electrode active material, a carbon material, a binder, and a solvent,

[0030] The content C of the binder in the first negative electrode slurry is 5 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the total weight of the negative electrode active material and the carbon material in the first negative electrode slurry,

[0031] The content D of the binder in the second negative electrode slurry is 1 part by weight or more and 10 parts by weight or less based on 100 parts by weight of the total weight of the negative electrode active material and the carbon material in the second negative electrode slurry,

[0032] A method for manufacturing a negative electrode for an all-solid-state secondary battery is provided, wherein the content C is greater than the content D, and the difference between the content C and the content D is in a range of 4 parts by weight or more and 19 parts by weight or less.

[0033] And, here, the phrases “first, second” are added for convenience to distinguish each component, and “first and second” have no special meaning in terms of order or anything else.

[0034] An all-solid-state secondary battery including the above-mentioned all-solid-state secondary battery negative electrode is unlikely to cause a short circuit even when rapidly charged, and can maintain a high battery capacity even when repeating charge and discharge cycles.

[0035] Figure 1 is a cross-sectional schematic diagram showing the structure of an all-solid-state secondary battery according to one embodiment.

[0036] Figure 2 is a cross-sectional schematic diagram showing the structure of an all-solid-state secondary battery according to another embodiment.

[0037] Figure 3 is a cross-sectional schematic diagram showing the structure of an all-solid-state secondary battery according to another embodiment.

[0038] Figure 4 is a cross-sectional schematic diagram showing the structure of an all-solid-state secondary battery according to one embodiment.

[0039] Hereinafter, specific implementation examples will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the implementation examples described herein.

[0040] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0041] Here, “combination of these” means a mixture, laminate, composite, copolymer, alloy, blend, reaction product, etc. of the components.

[0042] It should be understood that the terms "include," "comprising," or "having" herein are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0043] To clearly illustrate various layers and regions in the drawings, their thicknesses are enlarged, and similar parts are designated by the same drawing reference numerals throughout the specification. When an element such as a layer, film, region, or plate is said to be "over" or "on" another element, this includes not only the case where it is "directly over" the other element, but also the case where there are other elements in between. Conversely, when an element is said to be "directly over" another element, it means that there are no other elements in between.

[0044] Also, here, “layer” includes not only the shape formed on the entire surface when observed in a plan view, but also the shape formed on a portion of the surface.

[0045] In this specification, particle size may mean average particle size, and the average particle size may be measured by a method widely known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with a transmission electron microscope image or a scanning electron microscope image. Alternatively, the average particle size may be obtained by measuring using a dynamic light scattering method, performing data analysis, counting the number of particles for each particle size range, and calculating from the counted number. Unless otherwise defined, the average particle size is the diameter (D) of particles having a cumulative volume of 50% by volume in a particle size distribution. 50 ) can mean. In addition, unless otherwise defined, the average particle size is obtained by measuring the size (diameter or length of major axis) of about 20 particles randomly in a scanning electron microscope image to obtain a particle size distribution, and the diameter (D) of the particle having a cumulative volume of 50% by volume in the particle size distribution 50 ) may be taken as the average particle diameter.

[0046] Here, “or” is not interpreted in an exclusive sense, for example, “A or B” is interpreted to include A, B, A+B, etc.

[0047] “Metal” is interpreted as a concept that includes common metals, transition metals, and metalloids (semi-metals).

[0048] Below, a specific configuration of an all-solid-state secondary battery according to one embodiment of the present invention is described.

[0049] <1. Basic configuration of an all-solid-state secondary battery according to this embodiment>

[0050] The all-solid-state secondary battery according to the present embodiment is an all-solid-state secondary battery (1) including a positive electrode (10), a negative electrode (20), and a solid electrolyte layer (30), as shown in FIG. 1.

[0051] (1-1. Bipolar)

[0052] The positive electrode (10) includes a positive electrode current collector (11) and a positive electrode composite layer (12). Examples of the positive electrode current collector (11) include a plate-shaped body or a thin body made of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof. The positive electrode current collector (11) may be omitted.

[0053] The positive electrode composite layer (12) includes a positive electrode active material and a solid electrolyte. Meanwhile, the solid electrolyte included in the positive electrode (10) may be any solid electrolyte capable of conducting lithium ions, and may be a solid electrolyte of the same type as that described in the section on the solid electrolyte layer (30), or may be a solid electrolyte of a different type.

[0054] The cathode active material may be any cathode active material capable of reversibly absorbing and releasing lithium ions.

[0055] For example, the positive electrode active material can be formed using lithium salts such as lithium cobalt oxide (hereinafter referred to as LCO), lithium nickel oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide (hereinafter referred to as NCA), lithium nickel cobalt manganese oxide (hereinafter referred to as NCM), lithium manganate, lithium iron phosphate, nickel sulfide, copper sulfide, lithium sulfide, sulfur, iron oxide, or vanadium oxide. These positive electrode active materials may be used alone, or two or more types may be used in combination.

[0056] In addition, it is preferable that the positive electrode active material be formed by including a lithium salt of a transition metal oxide having a layered rock salt structure among the lithium salts described above. Here, the “layered rock salt structure” refers to a structure in which oxygen atomic layers and metal atomic layers are alternately and regularly arranged in the (111) direction of the cubic rock salt structure, and as a result, each atomic layer forms a two-dimensional plane. In addition, the “cubic rock salt structure” refers to a sodium chloride structure, which is a type of crystal structure, and specifically, refers to a structure in which face-centered cubic lattices formed by cations and anions respectively are arranged with a displacement of half of the corners of the unit cell.

[0057] Lithium salts of transition metal oxides having this layered rock salt structure include, for example, LiNi x Co y Al z O2(NCA), or LiNi x Co y Mn z O2(NCM)(but, 0 <x<1, 0<y<1, 0<z<1, 또한 x+y+z=1) 등의 삼원계 전이금속산화물의 리튬염을 들 수 있다.

[0058] When the positive electrode active material includes a lithium salt of a ternary transition metal oxide having the layered rock salt structure described above, the energy density and thermal stability of the all-solid-state secondary battery (1) can be improved.

[0059] The positive electrode active material may be covered by a covering layer. Here, the covering layer of the present embodiment may be any known covering layer for the positive electrode active material of an all-solid-state secondary battery. Examples of the covering layer include Li2O-ZrO2, for example.

[0060] In addition, when the positive electrode active material is formed by a lithium salt of a ternary transition metal oxide such as NCA or NCM and includes nickel (Ni) as the positive electrode active material, the capacity density of the all-solid-state secondary battery (1) can be increased and metal elution from the positive electrode active material in a charged state can be reduced. Accordingly, the all-solid-state secondary battery (1) according to the present embodiment can improve long-term reliability and cycle characteristics in a charged state.

[0061] Here, the shape of the positive electrode active material includes, for example, a spherical particle shape, an elliptical particle shape, etc. In addition, the particle size of the positive electrode active material is not particularly limited, and may be within the range applicable to positive electrode active materials of conventional all-solid-state secondary batteries. Meanwhile, the content of the positive electrode active material in the positive electrode (10) is also not particularly limited, and may be within the range applicable to positive electrodes of conventional all-solid-state secondary batteries.

[0062] In addition, in addition to the positive electrode active material and solid electrolyte described above, additives such as a conductive assistant, a binder, a filler, a dispersant, and an ionic conductive assistant may be appropriately mixed into the positive electrode (10).

[0063] Examples of conductive additives that can be mixed into the positive electrode (10) include graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder, etc. In addition, examples of binders that can be mixed into the positive electrode (10) include styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride (PVdF), polyethylene, etc. In addition, known materials that are generally used in electrodes of all-solid-state secondary batteries can be used as fillers, dispersants, ion conductive additives, etc. that can be mixed into the positive electrode (10).

[0064] (1-2. Cathode)

[0065] The negative electrode (20) includes a negative electrode current collector (21) and a negative electrode composite layer (22) laminated on the negative electrode current collector (21). The negative electrode current collector (21) is preferably composed of a material that does not react with lithium, i.e., does not form any alloy or compound with lithium. Examples of materials constituting the negative electrode current collector (21) include copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), and nickel (Ni). The negative electrode current collector is preferably composed of a metal as described above.

[0066] The negative electrode composite layer (22) includes a negative electrode active material, a carbon material, and a binder.

[0067] As a negative electrode active material, there is, for example, an alloy-forming element, which is an element that forms an alloy or compound with lithium through an electrochemical reaction during charging.

[0068] As the above alloy forming element, one or more selected from gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc may be cited as examples.

[0069] When using at least one of gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc as the alloy forming element, these negative electrode active materials have, for example, a particle shape, and the particle size is 4 μm or less, and more preferably 300 nm or less. In this case, the characteristics of the all-solid-state secondary battery (1) are further improved. Here, the particle size of the negative electrode active material is, for example, the median diameter (so-called D) measured using a laser particle size distribution meter. 50 ) can be used.

[0070] Examples of the above carbon materials include amorphous carbon such as carbon black and graphene. Examples of carbon black include acetylene black, furnace black, and ketjen black.

[0071] Examples of binders include styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc. The binder may be the same as or different from the binder in the positive electrode composite layer (12) and the solid electrolyte layer (30).

[0072] In addition to those described above, the negative electrode composite layer (22) may also contain appropriate additives used in conventional all-solid-state secondary batteries, such as fillers, dispersants, ion conductors, and solid electrolytes.

[0073] (1-3. Solid electrolyte layer)

[0074] The solid electrolyte layer (30) is formed between the positive electrode (10) and the negative electrode (20) and includes a solid electrolyte.

[0075] The above solid electrolyte may be any solid electrolyte usable in an all-solid-state secondary battery, such as one including a sulfide-based solid electrolyte material or an oxide-based solid electrolyte material, and is not particularly limited. In the present embodiment, as an example, a solid electrolyte in powder form and composed of a sulfide-based solid electrolyte material is described.

[0076] As the above sulfide-based solid electrolyte material, for example, Li2S-P2S5, Li2S-P2S5-LiX (X is a halogen element, for example, I, Br, 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, Li2S-P2S5-Z m S n (m and n are positive numbers, Z is either Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and q are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, or In). Here, the sulfide-based solid electrolyte material is manufactured by treating the starting material (e.g., Li2S, P2S5, etc.) by a melt-quenching method or a mechanical milling method. In addition, a heat treatment may be further performed after these treatments. The solid electrolyte may be amorphous, crystalline, or a mixture of the two.

[0077] In addition, as a solid electrolyte, it is preferable to use a material containing at least one element selected from sulfur, silicon, phosphorus, and boron among the above-mentioned sulfide-based solid electrolyte materials. Accordingly, the lithium conductivity of the solid electrolyte layer (30) is improved, and the battery characteristics of the all-solid-state secondary battery (1) are improved. In particular, it is preferable to use a solid electrolyte containing at least sulfur (S), phosphorus (P), and lithium (Li) as constituent elements, and it is more preferable to use a solid electrolyte containing Li2S-P2S5.

[0078] Here, when using a sulfide-based solid electrolyte material containing Li2S-P2S5 to form a solid electrolyte, the mixing molar ratio of Li2S and P2S5 may be selected in the range of, for example, Li2S:P2S5=50:50 to 90:10.

[0079] The solid electrolyte layer (30) may further contain a binder, and examples of the binder include styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, etc. The binder in the solid electrolyte layer (30) may be the same as or different from the binder in the positive electrode composite layer (12) and the negative electrode composite layer (22).

[0080] (1-4. Relationship between the charge capacity of the positive and negative electrodes)

[0081] It is preferable that the all-solid-state secondary battery (1) according to the present embodiment is configured such that the ratio of the charging capacity of the positive electrode composite layer (12) to the charging capacity of the negative electrode composite layer (22), i.e., the capacity ratio, satisfies the requirement of the following mathematical expression (1).

[0082] Mathematical formula (1)

[0083] 0.01

[0084] a: Charging capacity (mAh) of the positive electrode composite layer (12)

[0085] b: Charging capacity (mAh) of the negative electrode composite layer (22)

[0086] Meanwhile, the charge capacity of the positive electrode composite layer (12) and the negative electrode composite layer (22) can be measured by measurement using an all-solid-state half-cell.

[0087] ​For the all-solid-state secondary battery (1) according to the present embodiment, as described above, it is preferable to charge the all-solid-state secondary battery (1) to exceed the charge capacity of the negative electrode composite layer (22) by making the charge capacity of the positive electrode composite layer (12) excessive relative to the charge capacity of the negative electrode composite layer (22). That is, it is preferable to overcharge the negative electrode composite layer (22). In this case, at the initial stage of charging, lithium is absorbed into the negative electrode composite layer (22). That is, the negative electrode active material forms an alloy with lithium ions that have moved from the positive electrode (10). When further charging is performed beyond the capacity of the negative electrode composite layer (22), as illustrated in FIG. 2 or FIG. 3, lithium is deposited on the back of the negative electrode composite layer (22), that is, between the negative electrode current collector (21) and the negative electrode composite layer (22) and / or inside the negative electrode composite layer (22), and a lithium deposition layer (23) is formed by this lithium. The lithium deposition layer (23) is mainly composed of lithium (mainly metallic lithium), although it also contains trace amounts of elements other than lithium.

[0088] This phenomenon occurs because the negative electrode active material contains a specific substance, i.e., an alloy-forming element that forms an alloy or compound with lithium. During discharge, lithium in the negative electrode composite layer (22) and the lithium precipitation layer (23) is ionized and moves toward the positive electrode (10). Therefore, in the all-solid-state secondary battery (1) according to the present embodiment, the precipitated lithium can be used as the negative electrode active material. In addition, since the negative electrode composite layer (22) covers the lithium precipitation layer (23), it functions as a protective layer for the lithium precipitation layer (23) and can suppress the precipitation and growth of dendrites. Accordingly, short-circuiting and capacity reduction of the all-solid-state secondary battery (1) are suppressed, and further, the characteristics of the all-solid-state secondary battery (1) can be improved.

[0089] The thickness of the negative electrode composite layer (22) is preferably within a range that satisfies the requirements of the above mathematical formula (1), and is more preferably 1 μm or more and 20 μm or less, or 1 μm or more and 10 μm or less. If the thickness of the negative electrode composite layer (22) is 1 μm or more, the characteristics of the all-solid-state secondary battery (1) can be further improved. If the thickness of the negative electrode composite layer (22) is 20 μm or less, the resistance value of the negative electrode composite layer (22) can be suppressed to a small level, and as a result, the characteristics of the all-solid-state secondary battery (1) can be further improved.

[0090] The thickness of the aforementioned negative electrode composite layer (22) can be estimated, for example, by observing the average thickness of a cross-section after assembling and press-molding an all-solid-state secondary battery (1) using a scanning electron microscope (SEM).

[0091] <2. Characteristic configuration of the all-solid-state secondary battery according to the present embodiment>

[0092] As shown in Fig. 4, the all-solid-state secondary battery (1) according to the present embodiment has a binder content in the negative electrode composite layer (22) that is different between the first layer (221) forming the surface (22a) of the negative electrode composite layer (22) that is in contact with the negative electrode current collector (21) and the second layer (222) forming the surface (22b) of the side that is in contact with the solid electrolyte layer (30).

[0093] In this embodiment, the cathode composite layer (22) is formed from two layers, the first layer and the second layer.

[0094] The first layer (221) and the second layer (222) each contain a negative electrode active material, a carbon material, and a binder.

[0095] The above first layer (221) and the above second layer (222) each refer to the entirety of one layer formed by applying and drying one type of slurry of a certain composition, as described below.

[0096] The weight per unit area of ​​the cathode composite layer (22) is 0.2 mg / cm2 More than 2.5 mg / cm 2 It is desirable that it is less than 0.5 mg / cm 2 More than 2.0 mg / cm 2 Less than or equal to 0.8 mg / cm is more preferable. 2 More than 1.5 mg / cm 2 The following is more desirable.

[0097] The weight per unit area of ​​the first layer (221) is, for example, 0.1 mg / cm 2 More than 1 mg / cm 2 It is desirable that it is less than 0.1 mg / cm 2 More than 0.8 mg / cm 2 Less than or equal to 0.1 mg / cm is more preferable. 2 More than 0.5 mg / cm 2 The following is more desirable.

[0098] The weight per unit area of ​​the second layer (222) is, for example, 0.1 mg / cm 2 More than 1.5 mg / cm 2 It is desirable that it be less than 0.3 mg / cm 2 Above 1.3 mg / cm 2 Less than or equal to 0.5 mg / cm is more preferable. 2 More than 0.9 mg / cm 2 The following is more desirable.

[0099] The content A of the binder in the first layer (hereinafter also referred to as the first content) is 5 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the total content of the negative electrode active material and the carbon material in the first layer. The first content is preferably 10 parts by weight or more and 18 parts by weight or less, and more preferably 12 parts by weight or more and 16 parts by weight or less.

[0100] Meanwhile, the content B of the binder in the second layer forming the surface (22b) of the other layer, that is, the side in contact with the solid electrolyte layer (30) of the negative electrode composite layer (22) (hereinafter also referred to as the second content) is 1 part by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the total content of the negative electrode active material and the carbon material in the first layer. The second content is preferably 1 part by weight or more and 8 parts by weight or less, and more preferably 1 part by weight or more and 5 parts by weight or less.

[0101] In addition, the first content is greater than the second content, and the difference between the first content and the second content is 4 parts by weight or more and 19 parts by weight or less. The difference is preferably 6 parts by weight or more and 17 parts by weight or less, and more preferably 8 parts by weight or more and 15 parts by weight or less.

[0102] The peel strength between the negative electrode current collector (21) and the negative electrode composite layer (22) is preferably 35 mN / mm or more and 500 mN / mm or less, more preferably 50 mN / mm or more and 500 mN / mm or less, and even more preferably 100 mN / mm or more and 490 mN / mm or less. If it is difficult to measure this value, the result of a peel test using Kapton tape described in the examples described later may be used as an indicator, for example. Specifically, in the peel test using Kapton tape, when the test is performed multiple times, the peeling rate of the negative electrode composite layer (22) from the negative electrode current collector (21) is preferably 25% or less, more preferably 15% or less, and even more preferably, no peeling at all.

[0103] <3. Manufacturing method of all-solid-state secondary battery according to the present embodiment>

[0104] Next, a method for manufacturing an all-solid-state secondary battery (1) according to the present embodiment will be described. An all-solid-state secondary battery (1) according to the present embodiment can be manufactured by manufacturing a positive electrode (10), a negative electrode (20), and a solid electrolyte layer (30), respectively, and then laminating each of the above-described layers.

[0105] (3-1. Bipolar manufacturing process)

[0106] First, the materials (positive electrode active material, solid electrolyte, binder, etc.) that constitute the positive electrode composite layer (12) are mixed and processed into a sheet shape.

[0107] The positive electrode composite sheet obtained in this manner is cut into an appropriate shape and laminated as a positive electrode composite layer material on a positive electrode current collector, and the obtained laminate is pressed (for example, pressed using hydrostatic pressure) to manufacture a positive electrode (10) including a positive electrode current collector and a positive electrode composite layer.

[0108] (3-2. Cathode manufacturing process)

[0109] First, a slurry is prepared by adding the negative electrode composite layer materials (negative electrode active material, carbon material, binder, etc.) constituting the negative electrode composite layer (22) to a polar solvent or a non-polar solvent. Next, the obtained slurry is applied onto a negative electrode current collector (21) and dried. Next, the negative electrode (20) is prepared by pressurizing the obtained laminate (for example, pressing using hydrostatic pressure). The pressing process may be omitted. Alternatively, the negative electrode (20) may be prepared by forming the negative electrode composite layer (22) separately, laminating it on a negative electrode current collector (21), and then pressing it.

[0110] In the present embodiment, two types of slurries were used in the process of applying and drying the slurry on the negative electrode current collector (21). One of the two types of slurries (the first slurry) was adjusted so that the binder content C was 5 parts by weight or more and 20 parts by weight or less with respect to 100 parts by weight of the total weight of the negative electrode active material and the carbon material in the layer obtained after applying and drying the first slurry to remove the solvent. In addition, the other (the second slurry) was adjusted so that the binder content D was 1 part by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the total weight of the negative electrode active material and the carbon material after removing the solvent from the second slurry. Meanwhile, the weight ratios of the negative electrode active material, carbon material, and binder added when adjusting the first slurry and the second slurry, respectively, are directly reflected in the weight ratios of the negative electrode active material, carbon material, and binder in the layer obtained after removing the solvent.

[0111] In addition, the binder content C in the first slurry was set to be greater than the binder content D in the second slurry by 4 parts by weight or more and 19 parts by weight or less.

[0112] Then, the second slurry was applied and dried on top of the first slurry applied and dried on the negative electrode current collector (21), thereby forming a negative electrode composite layer (22) composed of two layers with different binder contents.

[0113] (3-3. Solid electrolyte layer manufacturing process)

[0114] The solid electrolyte layer (30) can be manufactured, for example, by the following order or process.

[0115] First, the starting raw material is processed by melt quenching or mechanical milling.

[0116] For example, when using the melt quenching method, a sulfide-based solid electrolyte material can be manufactured by mixing a predetermined amount of starting materials (e.g., Li2S, P2S5, etc.), forming them into a pellet shape, reacting them in a vacuum at a predetermined reaction temperature, and then quenching them. Meanwhile, the reaction temperature of the mixture of Li2S and P2S5 is preferably 400°C to 1000°C, and more preferably 800°C to 900°C. In addition, the reaction time is preferably 0.1 hour to 12 hours, and more preferably 1 hour to 12 hours. In addition, the quenching temperature of the reactants is usually 10°C or lower, and preferably 0°C or lower, and the quenching speed is usually about 1°C / sec to 10,000°C / sec, and preferably about 1°C / sec to 1000°C / sec.

[0117] In addition, when using a mechanical milling method, a sulfide-based solid electrolyte material can be produced by stirring and reacting starting materials (e.g., Li2S, P2S5, etc.) using a ball mill, etc. Meanwhile, the stirring speed and stirring time in the mechanical milling method are not particularly limited, but the faster the stirring speed, the faster the production speed of the sulfide-based solid electrolyte material can be, and the longer the stirring time, the higher the conversion rate of the raw material into the sulfide-based solid electrolyte material can be.

[0118] Thereafter, the mixed raw material obtained by the melt-quenching method or mechanical milling method is heat-treated at a predetermined temperature and then pulverized to produce a particle-shaped solid electrolyte. If the solid electrolyte has a glass transition point, it may change from an amorphous state to a crystalline state through heat treatment.

[0119] Subsequently, the solid electrolyte obtained by the above method can be formed into a film using a known film forming method such as an aerosol deposition method, a cold spray method, or a sputtering method, thereby producing a solid electrolyte layer (30). Meanwhile, the solid electrolyte layer (30) may also be produced by pressurizing a single solid electrolyte particle. In addition, the solid electrolyte layer (30) may also be produced by mixing a solid electrolyte, a solvent, and a binder, applying, drying, and pressurizing the solid electrolyte layer (30).

[0120] (3-4. Assembly process of all-solid-state secondary batteries)

[0121] An all-solid-state secondary battery (1) according to the present embodiment may be manufactured by stacking the positive electrode (10), the negative electrode (20), and the solid electrolyte layer (30) manufactured by the above-described method so that the solid electrolyte layer (30) is sandwiched between the positive electrode (10) and the negative electrode (20), and applying pressure (for example, applying pressure using hydrostatic pressure).

[0122] <4. Effect of this implementation example>

[0123] According to the positive electrode for an all-solid-state secondary battery or the all-solid-state secondary battery according to the present embodiment, the binder content in the first layer (221) forming the surface (22a) of the negative electrode composite layer (22) on the negative electrode current collector (21) side and the second layer (222) forming the surface (22b) of the solid electrolyte layer (30) side of the negative electrode composite layer (22) is set so that each peel strength is within an appropriate range, so that even in the case of rapid charging, peeling of the negative electrode composite layer (22) from the negative electrode current collector (21) can be suppressed within a range that does not interfere with lithium precipitation. In addition, the adhesion between the negative electrode composite layer (22) and the solid electrolyte layer (30) can be increased. As a result, it is possible to provide an all-solid-state secondary battery (1) that is less likely to cause a short circuit, which improves the capacity retention rate by suppressing peeling due to internal stress accompanying the short circuit and cycling of the battery, and can maintain a high battery capacity even when charge and discharge cycles are repeated. Since the negative electrode composite layer (22) has a two-layer structure, the manufacture of the negative electrode (20) or the all-solid-state secondary battery (1) can also be relatively simple.

[0124] <5. Regarding other embodiments of the present invention>

[0125] Above, the preferred embodiments of the present invention have been described in detail with reference to the attached drawings, but the present invention is not limited to these examples.

[0126] For example, in the above-described implementation example, the negative electrode composite layer (22) was described as a two-layer structure in which two types of slurries having different binder contents were applied twice in layers, but it may also be a three-layer structure in which three or more types of slurries having different binder contents were applied three or more times in layers.

[0127] In addition, it is clear that a person having ordinary knowledge in the technical field to which the present invention belongs can arrive at various modified or altered examples within the scope of the technical idea described in the scope of the patent claims, and these are also naturally understood to fall within the technical scope of the present invention.

[0128] [Example]

[0129] Hereinafter, the all-solid-state secondary battery according to the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0130] [Example 1]

[0131] [Making of the bipolar layer]

[0132] LiNi as a cathode active material 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 cathode layer conductive material (conductive assistant) were weighed at a weight ratio of 60:35:5 and mixed using a rotating-orbital mixer.

[0133] Next, a dehydrated xylene solution containing SBR as a binder was added to the mixture so that the SBR amount was 5.0 wt% based on the total weight of the mixture, thereby preparing a primary mixture.

[0134] A secondary mixture was prepared by adding an appropriate amount of dehydrated xylene to this primary mixture to adjust viscosity.

[0135] In addition, in order to improve the dispersibility of the mixed powder, zirconia balls with a diameter of 5 mm were added to the secondary mixing solution so that the space, mixed powder, and zirconia balls each occupied 1 / 3 of the total volume of the mixing vessel.

[0136] The resulting tertiary mixture was placed in a rotating mixer and stirred at 3000 rpm for 3 minutes to produce a coating solution for the positive electrode active material layer.

[0137] Next, an aluminum foil current collector having a thickness of 20 μm was prepared as a positive electrode current collector, the positive electrode current collector was mounted on a tabletop screen printer, and the positive electrode active material layer coating solution was applied onto the sheet using a metal mask having a thickness of 200 μm. Thereafter, the sheet on which the positive electrode active material layer coating solution was applied was dried on a hot plate at 60°C for 30 minutes and then vacuum-dried at 80°C for 12 hours. This was punched into a rectangular plate shape using a Thomson blade, thereby forming a positive electrode active material layer on the positive electrode current collector. The total thickness of the positive electrode current collector and positive electrode active material layer after drying was approximately 170 μm.

[0138] [Making of the cathode]

[0139] A stainless steel foil current collector with a thickness of 10 μm was prepared as a negative electrode current collector.

[0140] For cathode formation, CB2 (Asahi Carbon, specific surface area 52 m) was used as carbon. 2 / g, oil absorption (193 ml / 100g) 24g, silver (60 nm, manufactured by Dowa), 8g, PVdF (S5130, manufactured by Solvay) as a binder dissolved in N-methylpyrrolidone (NMP) at a concentration of 8 wt% were weighed out, and 90 g of NMP was further added, and a slurry 1 having a weight ratio of carbon / silver / binder = 75 / 25 / 14 was obtained using a rotating stirring device (manufactured by THINKY). In addition, the viscosity of the slurry 1 was 10,000 mP.s, which was in a range where there was no problem in application.

[0141] Next, 24 g of the above carbon, 8 g of the above silver, and 14 g of the above binder solution were weighed, and 112 g of NMP was also added, and stirred in the same manner to obtain slurry 2 containing carbon / silver / binder = 75 / 25 / 3.5 as a weight ratio. The viscosity of slurry 2 was 0.9 thousand mP.s, which was in a range where there was no problem in application.

[0142] The slurry 1 was applied onto the current collector using an applicator, dried at 80°C for 10 minutes, and a portion thereof was used for a peeling test from the current collector foil, and the remaining portion was similarly applied with the slurry 2 thereon, dried, and the desired electrode plate was obtained. The weight per unit area of ​​the sum of carbon, silver, and binder (i.e., the solid content of the negative electrode composite layer) was 0.5 mg / cm for both the first layer and the second layer. 2 , and 1.0 mg / cm as the entire cathode composite layer. 2 The above-mentioned electrode plate was vacuum dried at 103°C for 12 hours, stamped into a specified size using a pinnacle die, and the battery was assembled.

[0143] [Production of solid electrolyte layer coating solution]

[0144] As a sulfide-based solid electrolyte, amorphous powder of Li2S-P2S5 (80:20 mol%) was added with SBR binder dissolved in dehydrated xylene so as to be 1 wt% with respect to the solid electrolyte, thereby producing a first mixed slurry. Furthermore, a second mixed slurry was produced by adding an appropriate amount of dehydrated xylene and dehydrated diethylbenzene to this first mixed slurry for viscosity adjustment. Furthermore, in order to improve the dispersibility of the mixed powder, zirconia balls having a diameter of 5 mm were introduced into the third mixed slurry so that the space, the mixed powder, and the zirconia balls each occupied 1 / 3 of the total volume of the mixing vessel. The third mixed solution thus produced was introduced into a rotating-orbital mixer and stirred at 3000 rpm for 3 minutes, thereby producing a solid electrolyte layer coating solution.

[0145] [Production of solid electrolyte sheets]

[0146] The produced solid electrolyte layer coating solution was applied with a blade onto a PET film whose surface had been released, dried on a hot plate at 40°C for 10 minutes, and then vacuum-dried at 40°C for 12 hours to obtain a solid electrolyte sheet. The thickness of the solid electrolyte layer after drying was approximately 42 μm. The dried solid electrolyte sheet was punched with a Thomson blade and processed into a predetermined size.

[0147] [Fabrication of the electrolyte cathode structure]

[0148] A solid electrolyte sheet was placed on the surface of the cathode so that the solid electrolyte layer and the cathode were in contact, and these were mounted on a 3 mm thick aluminum plate (supporting material) to which a release film was bonded, and a vacuum laminate pack including the supporting material was performed. By immersing the solid electrolyte sheet in a pressurized medium and performing a hydrostatic pressure treatment (a pressing / compaction process using an isotropic press) at 50 MPa, the solid electrolyte layer (also called the SE layer) on the solid electrolyte sheet was integrated with the cathode. This will be referred to as an electrolyte cathode structure.

[0149] [Production of All-Solid-State Secondary Batteries]

[0150] An electrolyte cathode structure was placed at the center of an aluminum laminate, and an anode layer was placed thereon so that it was at the center of the electrolyte cathode structure. This was vacuum-degassed and sealed, mounted on a 3 mm thick aluminum plate (supporting material) to which a release film was bonded, and double vacuum laminate sealing was performed. This was immersed in a pressurized medium and subjected to an isostatic press (a pressing / compaction process using an isotropic press) at 490 MPa to obtain a single cell (single cell) of an all-solid-state secondary battery.

[0151] [Cathode peeling test]

[0152] The electrode plate manufactured from the above negative electrode was cut to 5 cm x 20 cm, mounted on a 3 mm thick aluminum plate (supporting material) to which a release film was bonded, and double vacuum laminate sealing was performed. This was immersed in a pressurized medium and subjected to an isostatic press treatment (a pressing / compaction process using an isostatic press) at 490 MPa. After the treatment, Kapton tape (1 cm x 5 cm, product number: 650S#25) was evenly pressed onto the electrode plate at eight points using a metal roller weighing 2 kg to bond it, and the state of the composite material peeling from the current collector was checked by pulling it vertically by hand. In addition, a 180-degree peel test was performed using a Shimadzu Autograph tensile tester, and the peel strength was quantified. The solid electrolyte layer was mounted on the electrode plate, the above-mentioned isostatic press treatment was performed, and a peel test of the solid electrolyte layer using the Kapton tape was performed in the same manner. The results are shown in Table 1. Meanwhile, the evaluation criteria are as follows. The unit of the binder content in Examples 1 to 7 and Comparative Examples 1, 2, 7, and 8 in Table 1 is parts by weight relative to 100 parts by weight of the total content of the negative electrode active material and the carbon material in the first layer or the second layer. In Comparative Examples 3 to 6, the negative electrode composite layer is composed of only one layer, so the unit of the binder content in Comparative Examples 3 to 6 in Table 1 is parts by weight relative to 100 parts by weight of the total content of the negative electrode active material and the carbon material in the negative electrode composite layer.

[0153] 1: No peeling

[0154] 2: Only the solid electrolyte layer is peeled off from the cathode.

[0155] 3: The entire solid electrolyte layer and part of the cathode are peeled off.

[0156] 4: The entire solid electrolyte layer and the entire cathode are peeled off.

[0157] [Cycle Evaluation of All-Solid-State Secondary Batteries]

[0158] The manufactured all-solid-state secondary battery was connected to a charge / discharge device (Toyo Systems, TOSCAT) and a cycle test was performed at 45°C.

[0159] Charge and discharge were performed at 0.33C (CCCV_0.1Ccut) / 0.33C (4.25V / 2.5V), and the ratio of the discharge capacity at 200 cycles when the first discharge capacity was 100 was defined as the capacity retention rate, and a comparison was performed. The results are shown in Table 1.

[0160] [Example 2]

[0161] An all-solid-state secondary battery was manufactured under the same conditions as Example 1, except for the negative electrode manufacturing process below.

[0162] [Cathode production]

[0163] A stainless steel foil current collector with a thickness of 10 μm was prepared as a negative electrode current collector.

[0164] For cathode formation, CB2 (Asahi Carbon, specific surface area 52 m) was used as carbon. 2 / g, oil absorption 193ml / 100g), 8 g of silver (60nm, manufactured by Dowa), and 80 g of a solution in which PVdF (S5130, manufactured by Solvay) as a binder was dissolved in N-methylpyrrolidone (NMP) at a concentration of 8 wt% were weighed, and 64 g of NMP was further added, and a slurry 3 having a weight ratio of carbon / silver / binder = 75 / 25 / 20 was obtained using a rotating stirring device (manufactured by THINKY). The viscosity of the slurry 3 was 12,000 mP.s, which was in a range where there was no problem in application.

[0165] Next, 24 g of the above carbon, 8 g of the above silver, and 4 g of the above binder solution were weighed, and 122 g of NMP was added and stirred to obtain slurry 4 having a weight ratio of carbon / silver / binder = 75 / 25 / 1. The viscosity of slurry 4 was 0.9 thousand mP.s, which was in a range where there was no problem in application.

[0166] The slurry 3 was applied onto the above-mentioned collector using an applicator, dried at 80°C for 10 minutes, and then the slurry 4 was applied thereon and dried to obtain the desired electrode plate. At this time, the weight per unit area of ​​the sum of carbon, silver, and binder was 0.5 mg / cm for both the first layer and the second layer. 2 , and 1.0 mg / cm for the entire cathode composite layer. 2 The above-mentioned electrode plate was vacuum dried at 103°C for 12 hours, stamped into a specified size using a pinnacle die, and the battery was assembled.

[0167] For the prepared all-solid-state secondary battery, a peeling test and cycle evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

[0168] [Example 3]

[0169] An all-solid-state secondary battery was manufactured under the same conditions as Example 1, except for the negative electrode manufacturing process below.

[0170] [Cathode production]

[0171] A stainless steel foil current collector with a thickness of 10 μm was prepared as a negative electrode current collector.

[0172] For cathode formation, CB2 (Asahi Carbon, specific surface area 52 m) was used as carbon. 2 / g, oil absorption 193ml / 100g) 24 g, silver (60nm, manufactured by Dowa) 8 g, and PVdF (S5130, manufactured by Solvay) as a binder were dissolved in N-methylpyrrolidone (NMP) at a concentration of 8 wt%, and 40 g of the solution was weighed, and further 92 g of NMP was added, and a slurry 5 consisting of carbon / silver / binder = 75 / 25 / 10 in a weight ratio was obtained using a rotating stirring device (manufactured by THINKY). The viscosity of the slurry 5 was 10,000 mP.s, which was in a range where there was no problem in application.

[0173] The slurry 5 was applied onto the above-mentioned collector using an applicator, dried at 80°C for 10 minutes, and then the slurry 4 used in Example 2 was applied thereon and dried to obtain the desired electrode plate. The weight per unit area of ​​the sum of carbon, silver, and binder was 0.5 mg / cm for both the first layer and the second layer. 2 , and 1.0 mg / cm for the entire cathode composite layer. 2 It was.

[0174] The above electrode plate was vacuum dried at 103°C for 12 hours, stamped into a specified size using a pinnacle die, and a battery was assembled.

[0175] For the prepared all-solid-state secondary battery, a peeling test and cycle evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

[0176] [Example 4]

[0177] An all-solid-state secondary battery was manufactured under the same conditions as Example 1, except for the negative electrode manufacturing process below.

[0178] [Cathode production]

[0179] A stainless steel foil current collector with a thickness of 10 μm was prepared as a negative electrode current collector. To form the negative electrode, CB2 (Asahi Carbon, specific surface area 52 m 2 / g, oil absorption 193ml / 100g) 24 g, silver (60nm, manufactured by Dowa) 8 g, and PVdF (S5130, manufactured by Solvay) as a binder were dissolved in N-methylpyrrolidone (NMP) at a concentration of 8 wt%, 20 g of the solution was weighed, and further 112 g of NMP was added, and a slurry 6 consisting of carbon / silver / binder = 75 / 25 / 5 in a weight ratio was obtained using a rotating stirring device (manufactured by THINKY). The viscosity of the slurry 6 was 10,000 mP.s, which was in a range where there was no problem in application.

[0180] The slurry 6 was applied onto the above-mentioned collector using an applicator, dried at 80°C for 10 minutes, and then the slurry 4 used in Example 2 was applied thereon and dried to obtain the desired electrode plate. The weight per unit area of ​​the sum of carbon, silver, and binder was 0.5 mg / cm for both the first layer and the second layer. 2 , and 1.0 mg / cm for the entire cathode composite layer. 2 It was.

[0181] The above electrode plate was vacuum dried at 103°C for 12 hours, stamped into a specified size using a pinnacle die, and a battery was assembled.

[0182] For the prepared all-solid-state secondary battery, a peeling test and cycle evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

[0183] [Example 5]

[0184] An all-solid-state secondary battery was manufactured under the same conditions as Example 1, except for the negative electrode manufacturing process below.

[0185] [Cathode production]

[0186] A stainless steel foil current collector with a thickness of 10 μm was prepared as a negative electrode current collector. To form the negative electrode, the slurry 3 used in Example 2 was applied onto the current collector using an applicator, dried at 80°C for 10 minutes, and then the slurry 5 used in Example 3 was applied thereon and dried to obtain the desired electrode plate. The unit area weight of the sum of carbon, silver, and binder was 0.5 mg / cm for both the first layer and the second layer. 2 , and 1.0 mg / cm for the entire cathode composite layer. 2 The above-mentioned electrode plate was vacuum dried at 103°C for 12 hours, stamped into a specified size using a pinnacle die, and the battery was assembled.

[0187] For the prepared all-solid-state secondary battery, a peeling test and cycle evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

[0188] [Example 6]

[0189] An all-solid-state secondary battery was manufactured under the same conditions as Example 1, except for the negative electrode manufacturing process below.

[0190] [Cathode production]

[0191] A stainless steel foil current collector with a thickness of 10 μm was prepared as a negative electrode current collector. To form the negative electrode, the slurry 1 used in Example 1 was applied onto the current collector using an applicator, dried at 80°C for 10 minutes, and then the slurry 5 used in Example 3 was applied thereon and dried to obtain the desired electrode plate. The unit area weight of the sum of carbon, silver, and binder was 0.5 mg / cm for both the first layer and the second layer. 2 , and 1.0 mg / cm for the entire cathode composite layer. 2 The above-mentioned electrode plate was vacuum dried at 103°C for 12 hours, stamped into a specified size using a pinnacle die, and the battery was assembled.

[0192] For the prepared all-solid-state secondary battery, a peeling test and cycle evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

[0193] [Example 7]

[0194] An all-solid-state secondary battery was manufactured under the same conditions as Example 1, except for the negative electrode manufacturing process below.

[0195] [Cathode production]

[0196] A stainless steel foil current collector with a thickness of 10 μm was prepared as a negative electrode current collector. To form the negative electrode, the slurry 1 used in Example 1 was applied onto the current collector using an applicator, dried at 80°C for 10 minutes, and then the slurry 4 used in Example 2 was applied thereon and dried to obtain the desired electrode plate. The unit area weight of the sum of carbon, silver, and binder was 0.5 mg / cm for both the first layer and the second layer.2 , and 1.0 mg / cm for the entire cathode composite layer. 2 The above-mentioned electrode plate was vacuum dried at 103°C for 12 hours, stamped into a specified size using a pinnacle die, and the battery was assembled.

[0197] For the prepared all-solid-state secondary battery, a peeling test and cycle evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

[0198] [Example 8]

[0199] An all-solid-state secondary battery was manufactured under the same conditions as Example 1, except for the negative electrode manufacturing process below.

[0200] [Cathode production]

[0201] A stainless steel foil current collector with a thickness of 10 μm was prepared as a negative electrode current collector. The unit area weight of the sum of carbon, silver, and binder was 0.1 mg / cm for the first layer. 2 , the second layer is 0.9 mg / cm 2 Except for this point, all of the questions were written in the same way as Example 1.

[0202] For the prepared all-solid-state secondary battery, a peeling test and cycle evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

[0203] [Example 9]

[0204] An all-solid-state secondary battery was manufactured under the same conditions as Example 1, except for the negative electrode manufacturing process below.

[0205] [Cathode production]

[0206] A 10 μm thick stainless steel foil current collector was prepared as a negative electrode current collector. The unit area weight of the sum of carbon, silver, and binder in the first layer was 0.4 mg / cm 2 , the second layer is 0.6 mg / cm 2 Except for this point, all of the questions were written in the same way as Example 1.

[0207] For the prepared all-solid-state secondary battery, a peeling test and cycle evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

[0208] [Example 10]

[0209] An all-solid-state secondary battery was manufactured under the same conditions as Example 1, except for the negative electrode manufacturing process below.

[0210] [Cathode production]

[0211] A 10 μm thick stainless steel foil current collector was prepared as a negative electrode current collector. The unit area weight of the sum of carbon, silver, and binder in the first layer was 0.9 mg / cm 2 , the second layer is 0.1 mg / cm 2 Except for this point, all of the questions were written in the same way as Example 1.

[0212] For the prepared all-solid-state secondary battery, a peeling test and cycle evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

[0213] [Comparative Example 1]

[0214] An all-solid-state secondary battery was manufactured under the same conditions as Example 1, except for the negative electrode manufacturing process below.

[0215] [Cathode production]

[0216] A stainless steel foil current collector with a thickness of 10 μm was prepared as a negative electrode current collector. To form the negative electrode, the slurry 2 used in Example 1 was applied onto the current collector using an applicator, dried at 80°C for 10 minutes, and then the slurry 1 used in Example 1 was applied thereon and dried to obtain the desired electrode plate. The unit area weight of the sum of carbon, silver, and binder was 0.5 mg / cm for both the first layer and the second layer. 2 , and 1.0 mg / cm for the entire cathode composite layer. 2 The above-mentioned electrode plate was vacuum dried at 103°C for 12 hours, stamped into a specified size using a pinnacle die, and the battery was assembled.

[0217] For the prepared all-solid-state secondary battery, a peeling test and cycle evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

[0218] [Comparative Example 2]

[0219] An all-solid-state secondary battery was manufactured under the same conditions as Example 1, except for the negative electrode manufacturing process below.

[0220] [Cathode production]

[0221] A stainless steel foil current collector with a thickness of 10 μm was prepared as a negative electrode current collector. To form the negative electrode, CB2 (Asahi Carbon, specific surface area 52 m) was used as carbon. 2 / g, oil absorption 193ml / 100g) 24 g, silver (60nm, manufactured by Dowa) 8 g, and PVdF (S5130, manufactured by Solvay) as a binder were dissolved in N-methylpyrrolidone (NMP) at a concentration of 8 wt%, 2 g was weighed, and further 122 g of NMP was added, and a slurry 7 composed of carbon / silver / binder = 75 / 25 / 0.5 as a weight ratio was obtained using a rotating stirring device (manufactured by THINKY). The slurry 7 had poor dispersibility and was in a coagulated state.

[0222] The slurry 6 used in Example 4 was applied onto the above-mentioned collector using an applicator, dried at 80°C for 10 minutes, and then the slurry 7 was applied thereon, but coagulation was severe, and the desired electrode plate could not be obtained.

[0223] [Comparative Example 3]

[0224] An all-solid-state secondary battery was manufactured under the same conditions as Example 1, except for the negative electrode manufacturing process below.

[0225] [Cathode production]

[0226] A stainless steel foil current collector with a thickness of 10 μm was prepared as a negative electrode current collector. To form the negative electrode, the slurry 1 used in Example 1 was applied onto the current collector using an applicator, dried, and the desired electrode plate was obtained. The unit area weight of the sum of carbon, silver, and binder was 0.5 mg / cm for both the first and second layers. 2 , and 1.0 mg / cm for the entire cathode composite layer. 2 The above-mentioned electrode plate was vacuum dried at 103°C for 12 hours, stamped into a specified size using a pinnacle die, and the battery was assembled.

[0227] For the prepared all-solid-state secondary battery, a peeling test and cycle evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

[0228] [Comparative Example 4]

[0229] An all-solid-state secondary battery was manufactured under the same conditions as Example 1, except for the negative electrode manufacturing process below.

[0230] [Cathode production]

[0231] A 10 μm thick stainless steel foil current collector was prepared as a negative electrode current collector. To form the negative electrode, CB2 (Asahi Carbon, specific surface area 52 m) was used as carbon. 2 / g, oil absorption 193ml / 100g) 24 g, silver (60nm, manufactured by Dowa) 8 g, and PVdF (S5130, manufactured by Solvay) as a binder were dissolved in N-methylpyrrolidone (NMP) at a concentration of 8 wt%, 100 g was weighed, and 20 g of NMP was further added, and a slurry 8 consisting of carbon / silver / binder = 75 / 25 / 25 in a weight ratio was obtained using a rotating stirring device (manufactured by THINKY). The viscosity of the slurry 8 was 15,000 mP.s, which was in a range where there was no problem in application.

[0232] The slurry 8 was applied onto the above-mentioned collector using an applicator, dried at 80°C for 10 minutes, and the desired electrode plate was obtained. The unit area weight of the sum of carbon, silver, and binder was 0.5 mg / cm for both the first layer and the second layer. 2 , and 1.0 mg / cm for the entire cathode composite layer. 2 The above-mentioned electrode plate was vacuum dried at 103°C for 12 hours, stamped into a specified size using a pinnacle die, and the battery was assembled.

[0233] For the prepared all-solid-state secondary battery, a peeling test and cycle evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

[0234] [Comparative Example 5]

[0235] An all-solid-state secondary battery was manufactured under the same conditions as Example 1, except for the negative electrode manufacturing process below.

[0236] [Cathode production]

[0237] A 10 μm thick stainless steel foil current collector was prepared as a negative electrode current collector. To form the negative electrode, CB2 (Asahi Carbon, specific surface area 52 m) was used as carbon. 2 / g, oil absorption 193ml / 100g) 24g, silver (60nm, manufactured by Dowa) 8g, and PVdF (S5130, manufactured by Solvay) as a binder were dissolved in N-methylpyrrolidone (NMP) at a concentration of 8 wt%, 28g of the solution was weighed, and further 102g of NMP was added, and a slurry 9 consisting of carbon / silver / binder = 75 / 25 / 7 in a weight ratio was obtained using a rotating stirring device (manufactured by THINKY). The viscosity was 11,000 mP.s, which was in a range where there was no problem in application.

[0238] Next, the slurry 9 was applied onto the entire body using an applicator and dried at 80°C for 10 minutes. The weight per unit area of ​​the total of carbon, silver, and binder was 0.5 mg / cm for both the first and second layers. 2 , and 1.0 mg / cm for the entire cathode composite layer.2 The above-mentioned electrode plate was vacuum dried at 103°C for 12 hours, stamped into a specified size using a pinnacle die, and the battery was assembled.

[0239] For the prepared all-solid-state secondary battery, a peeling test and cycle evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

[0240] [Comparative Example 6]

[0241] An all-solid-state secondary battery was manufactured under the same conditions as Example 1, except for the negative electrode manufacturing process below.

[0242] [Cathode production]

[0243] A stainless steel foil current collector with a thickness of 10 μm was prepared as a negative electrode current collector. The slurry 2 used in Example 1 was applied onto the current collector using an applicator and dried at 80°C for 10 minutes to obtain the desired electrode plate. The unit area weight of the sum of carbon, silver, and binder was 0.5 mg / cm for both the first and second layers. 2 , and 1.0 mg / cm for the entire cathode composite layer. 2 The above-mentioned electrode plate was vacuum dried at 103°C for 12 hours, stamped into a specified size using a pinnacle die, and the battery was assembled.

[0244] For the prepared all-solid-state secondary battery, a peeling test and cycle evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

[0245] [Comparative Example 7]

[0246] An all-solid-state secondary battery was manufactured under the same conditions as Example 1, except for the negative electrode manufacturing process below.

[0247] [Cathode production]

[0248] A stainless steel foil current collector with a thickness of 10 μm was prepared as a negative electrode current collector. The slurry 9 used in Example 1 was applied onto the current collector using an applicator, dried at 80°C for 10 minutes, and then the slurry 6 was applied thereon and dried to obtain the desired electrode plate. The unit area weight of the sum of carbon, silver, and binder was 0.5 mg / cm for both the first layer and the second layer. 2 , and 1.0 mg / cm for the entire cathode composite layer. 2 The above-mentioned electrode plate was vacuum dried at 103°C for 12 hours, stamped into a specified size using a pinnacle die, and the battery was assembled.

[0249] For the prepared all-solid-state secondary battery, a peeling test and cycle evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

[0250] [Comparative Example 8]

[0251] An all-solid-state secondary battery was manufactured under the same conditions as Example 1, except for the negative electrode manufacturing process below.

[0252] [Cathode production]

[0253] A stainless steel foil current collector with a thickness of 10 μm was prepared as a negative electrode current collector. The slurry 3 was applied onto the current collector using an applicator, dried at 80°C for 10 minutes, and then the slurry 7 was applied thereon and dried to obtain the desired electrode plate. The unit area weight of the sum of carbon, silver, and binder was 0.5 mg / cm for both the first and second layers. 2 , and 1.0 mg / cm for the entire cathode composite layer. 2 The above-mentioned electrode plate was vacuum dried at 103°C for 12 hours, stamped into a specified size using a pinnacle die, and the battery was assembled.

[0254] For the prepared all-solid-state secondary battery, a peeling test and cycle evaluation were performed in the same manner as in Example 1. The results are shown in Table 1.

[0255]

[0256] Cathode composite layer binder content (parts by weight) Weight per unit area of ​​composite (mg / cm) 2 ) Negative current collector - Negative electrode composite layer Solid electrolyte layer - Negative electrode composite layer Cycle short-circuit capacity retention rate 1st layer / 2nd layer 1st layer / 2nd layer Tape peeling presence / (mN / mm) Tape peeling presence / Peeling state Number / 10 % @ 0.33 Ccyc_200th Example 1 14% / 3.5% 0.5 / 0.5 None (0 / 8) 3 18 None (0 / 8) 10 / 1092 Example 2 20% / 1% 0.5 / 0.5 None (0 / 8) 4 90 None (0 / 8) 10 / 1088 Example 3 10% / 1% 0.5 / 0.5 None (0 / 8) 2 90 None (0 / 8) 10 / 1087 Example 45% / 1% 0.5 / 0.5 Mu(0 / 8) 160 Mu(0 / 8) 10 / 1086 Example 5 20% / 10% 0.5 / 0.5 Mu(0 / 8) 490 Mu(0 / 8) 10 / 1083 Example 6 14% / 10% 0.5 / 0.5 Mu(0 / 8) 318 Mu(0 / 8) 10 / 1082 Example 7 14% / 1% 0.5 / 0.5 Mu(0 / 8) 318 Mu(0 / 8) 10 / 1087 Example 8 14% / 3.5% 0.1 / 0.9 Mu(0 / 8) 318 Mu(0 / 8) 10 / 1095 Example 9 14% / 3.5% 0.4 / 0.6 Mu(0 / 8) 318 Mu(0 / 8) 10 / 1093 Example 1014% / 3.5%0.9 / 0.1No(0 / 8)318No(0 / 8)11 / 1088Comparative example 13.5% / 14%0.5 / 0.5Yes(5 / 8)30Yes(6 / 8)37 / 1073Comparative example 25% / 0.5%0.5 / 0.5No(0 / 8)160――――Comparative example 314% / 14%0.5 / 0.5No(0 / 8)318Yes(6 / 8)25 / 1081Comparative example 425% / 25%0.5 / 0.5No(0 / 8)580Yes(8 / 8)210 / 1050Comparative example 57% / 7%0.5 / 0.5Yes(3 / 8)55Yes(2 / 8)22 / 1078Comparative example 63.5% / 3.5%0.5 / 0.5Yu(5 / 8)30Mu(0 / 8)11 / 1065Comparative Example 77% / 5%0.5 / 0.5Yu(3 / 8)55Mu(1 / 8)21 / 1080Comparative Example 820% / 0.5%0.5 / 0.5Mu(0 / 8)490Mu(3 / 8)33 / 1078

[0257] [Consideration]

[0258] In Examples 1 to 10, neither the anode composite layer nor the solid electrolyte layer was peeled off from the anode current collector foil. Furthermore, the number of short circuits was sufficiently low, either 0 or 1, and a sufficiently high cycle life of over 80% was achieved in the battery cycle evaluation.

[0259] The weight per unit area of ​​the first layer is 0.9 mg / cm 2 , and the weight per unit area of ​​the second layer is increased to 0.1 mg / cm 2 From the comparison of the results of Example 10, which was reduced to 10, and Examples 1, 8, and 9, it was found that a smaller weight per unit area of ​​the first layer facilitates lithium diffusion and precipitation onto the current collector foil, resulting in better capacity retention and battery characteristics.

[0260] In contrast, in Comparative Example 1, which reversed the binder content of Example 1, since the binder content in the first layer was 3.5 parts by weight, the peel strength between the negative electrode current collector and the negative electrode composite layer decreased, resulting in a high probability of peeling between them. In addition, since the binder content in the second layer was 14 parts by weight, the binder covered the carbon material in the negative electrode composite layer, resulting in insufficient adhesion between the solid electrolyte layers. It is believed that the adhesiveness of the interface between the negative electrode composite layer and the solid electrolyte layer is mainly due to physical adhesion that occurs when the relatively soft solid electrolyte layer digs into the fine irregularities formed on the surface of the negative electrode composite layer, which is formed by solidifying and bonding the particulate material with the binder, by applying pressure. Accordingly, the irregularities are filled in by the binder, resulting in a small contact area and a decrease in adhesiveness. As a result, the number of battery short-circuit occurrences increased to 7 / 10, and the capacity retention rate also decreased to 65%.

[0261] In Comparative Example 3, since the binder content was uniformly 14 parts by weight throughout the entire negative electrode composite layer, sufficient peel strength was secured between the negative electrode current collector and the negative electrode composite layer. However, on the other hand, since the binder content covering the carbon of the negative electrode layer was large, the adhesion to the solid electrolyte layer was poor, and after hydrostatic pressure treatment, only the solid electrolyte was peeled off at a high rate of 6 / 8. As a result, a battery short circuit occurred in 50% of cases, and the capacity retention rate was also low at 81%.

[0262] In Comparative Example 4, the binder content was uniformly 25 parts by weight throughout the entire negative electrode composite layer, and the peel strength between the negative electrode current collector and the negative electrode composite layer was excessive. In addition, since the amount of binder covering the carbon of the negative electrode composite layer was large, the adhesion to the solid electrolyte layer was poor, and after the hydrostatic pressure treatment, only 8 / 8 of the solid electrolyte was peeled off. As a result, the precipitation of lithium in the negative electrode was hindered, cracks occurred in the negative electrode composite layer, and the battery was short-circuited prematurely.

[0263] In Comparative Example 5, the binder content was 7.0 parts by weight uniformly distributed throughout the entire negative electrode composite layer, and it was difficult to completely prevent peeling between the negative electrode current collector and the negative electrode composite layer.

[0264] In Comparative Example 6, the binder content was 3.5 parts by weight uniformly throughout the entire negative electrode composite layer, and in Comparative Example 6, the peel strength between the solid electrolyte layer and the negative electrode composite layer was sufficient, but peeling occurred between the negative electrode current collector and the negative electrode composite layer, resulting in a short circuit, similar to Comparative Example 5.

[0265] In Comparative Example 7, the binder content in the first layer is 7 parts by weight, and the adhesion between the negative electrode current collector and the negative electrode composite layer is sufficiently high. In addition, the binder content in the second layer is smaller than in Comparative Example 5, so the balance is better than in Comparative Example 5. However, since the difference in the binder content between the first layer and the second layer is small at 2.0, a short circuit occurs, albeit at a low frequency, and the capacity retention rate is also 80%.

[0266] In addition, in Comparative Example 8, where the difference between the binder content of the first layer and the binder content of the second layer was large at 19.5, the incidence of peeling and short-circuiting increased. It is believed that one of the factors is that the excessively low binder content of the second layer resulted in the deterioration of the dispersibility of the slurry, which in turn worsened the balance of the entire negative electrode composite layer and reduced the bonding strength.

[0267] From the above results, as shown in Examples 1 to 10, it was found that the content A (first content) of the binder in the first layer is 5 parts by weight or more and 20 parts by weight or less with respect to 100 parts by weight of the total content of the negative electrode active material and the carbon material in the first layer, the content B (second content) of the binder in the second layer is 1 part by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the total content of the negative electrode active material and the carbon material in the second layer, and the first content is greater than the second content, and the difference between the first content and the second content is in the range of 4 parts by weight or more and 19 parts by weight or less, thereby making it difficult for a short circuit to occur during rapid charging and also suppressing cycle deterioration.

[0268] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the following claims also fall within the scope of the present invention.

[0269] [Explanation of symbols]

[0270] 1: All-solid-state secondary battery

[0271] 10: Bipolar

[0272] 11: Positive current collector

[0273] 12: Bipolar composite layer

[0274] 20: Cathode

[0275] 21: Negative current collector

[0276] 22: Cathode composite layer

[0277] 221: 1st floor

[0278] 222: Second floor

[0279] 23: Lithium precipitation layer

[0280] 30: Solid electrolyte layer

Claims

1. A negative electrode for an all-solid-state secondary battery comprising a negative electrode current collector and a negative electrode composite layer, The above negative electrode composite layer includes a first layer forming a surface of the negative electrode collector side of the negative electrode composite layer, and a second layer forming a surface opposite to the first layer of the negative electrode composite layer. The first layer and the second layer each contain a negative electrode active material, a carbon material, and a binder, The content A of the binder in the first layer is 5 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the total content of the negative electrode active material and the carbon material in the first layer, The content B of the binder in the second layer is 1 part by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the total content of the negative electrode active material and the carbon material in the second layer, An anode for an all-solid-state secondary battery, wherein the content A is greater than the content B, and the difference between the content A and the content B is in a range of 4 parts by weight or more and 19 parts by weight or less.

2. In paragraph 1, The above cathode composite layer is composed of two layers, the first layer and the second layer. Cathode for all-solid-state secondary batteries.

3. In paragraph 1, The negative electrode current collector comprises a metal and the binder comprises a polyvinylidene fluoride polymer, Cathode for all-solid-state secondary batteries.

4. In paragraph 1, The peel strength between the negative electrode current collector and the negative electrode composite layer is 35 mN / mm or more and 490 mN / mm or less, Cathode for all-solid-state secondary batteries.

5. Including a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode, The above negative electrode is a negative electrode for an all-solid-state secondary battery as described in any one of claims 1 to 4. All-solid-state secondary battery.

6. Containing a negative electrode current collector and a negative electrode composite layer, A method for manufacturing a negative electrode for an all-solid-state secondary battery, wherein the negative electrode composite layer includes a first layer forming a surface of the negative electrode current collector side of the negative electrode composite layer, and a second layer forming a surface of the negative electrode composite layer opposite to the first layer. A process of forming the first layer by applying the first cathode slurry onto the cathode current collector and drying it; A process of forming the second layer by applying a second cathode slurry on the formed first layer and drying it, The first negative electrode slurry and the second negative electrode slurry contain a negative electrode active material, a carbon material, a binder, and a solvent, The content C of the binder in the first negative electrode slurry is 5 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the total weight of the negative electrode active material and the carbon material in the first negative electrode slurry, The content D of the binder in the second negative electrode slurry is 1 part by weight or more and 10 parts by weight or less based on 100 parts by weight of the total weight of the negative electrode active material and the carbon material in the second negative electrode slurry, The content C is greater than the content D, and the difference between the content C and the content D is in the range of 4 parts by weight or more and 19 parts by weight or less. Method for manufacturing a negative electrode for an all-solid-state secondary battery.

Images