Electrodes and all-solid-state secondary batteries

Abstract

To provide an electrode which enables the rise in the initial charge / discharge efficiency of an all-solid secondary battery; and an all-solid secondary battery having the electrode and a high initial charge / discharge efficiency.SOLUTION: An electrode according to an aspect of the present invention comprises an electrode mixture layer having an electrode mixture containing an electrode active substance, a solid electrolyte and a conducting agent, provided that the conducting agent is 60 m2 / 100 g or less in surface area per mass of the electrode mixture, and having a porosity of 10% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to electrodes and all-solid-state secondary batteries. [Background technology]

[0002] In recent years, the demand for lithium-ion secondary batteries has been increasing as a power source for electric vehicles and hybrid vehicles. To simplify the safety system used in these batteries, there is a growing development of flame-retardant solid electrolytes. Known solid electrolytes include oxide solid electrolytes, sulfide solid electrolytes, and halide solid electrolytes. When these solid electrolytes are used to create electrodes for all-solid-state secondary batteries, it is known that a conductive agent (conductive additive, conductive material) is included together with the electrode active material (see, for example, Patent Documents 1 to 4).

[0003] Patent Document 1 describes a material comprising "an active material, a sulfide-based inorganic solid electrolyte having conductivity of ions of metal elements belonging to Group 1 or Group 2 of the periodic table, and a conductive additive having at least one metal atom belonging to Group 12, Group 13, or Group 14 of the periodic table, wherein the specific surface area of ​​the conductive additive is 1 to 500 m²." 2 Claim 1 describes an electrode material having a density of / g and a ratio of the long axis length to the short axis length of the particles constituting the conductive additive of 1.5 or more. The examples then include: "(Synthesis Example 3)...A conductive additive (Sample C) was obtained. The specific surface area was 80 m²." 2 The average value of the short axis length was 50 nm, and the aspect ratio was 25. (Paragraph

[0115] ) Table 1 (Paragraph

[0127] ) shows an electrode material (P-9) containing 30 mass% solid electrolyte (Li-PS), 69.5% active material (NCA), and 0.5 mass% conductive additive (Sample C). Furthermore, it is stated that "the positive electrode material (P-1) prepared above was applied to a 20 μm thick aluminum foil using an applicator, heated at 80°C for 1 hour, and then dried at 110°C for 1 hour. After that, a positive electrode sheet for an all-solid-state secondary battery having a laminated structure of positive electrode active material layer / aluminum foil was fabricated by using a heat press machine to apply pressure (10 MPa, 1 minute) while heating (120°C). ...In the same manner, Nos. 102~111 and c11~c13 described in Table 2 below were manufactured." (Paragraphs

[0132] to

[0133] ). Table 2 shows a battery using the positive electrode active material layer (P-9) as Test No. 109, and it is stated that "As is clear from Table 2, the all-solid-state secondary batteries of Test Nos. 101~111 that satisfy the provisions of the present invention have a large discharge capacity and excellent output characteristics." (Paragraph

[0140] ).

[0004] Patent Document 2 describes a positive electrode material comprising "a positive electrode active material, an inorganic solid electrolyte having conductivity of metal ions belonging to Group 1 or Group 2 of the periodic table, a conductive additive, and a dispersant comprising a compound having at least one selected from the following functional group (I)..." (Claim 1), and "the specific surface area of ​​the conductive additive is 50 m²." 2 Claim 2 describes a positive electrode material according to claim 1, which is less than or equal to / g. Furthermore, the example includes a specific surface area of ​​4 m². 2 Tests No. 103 and 104 used a positive electrode material (P-3, P-4) as the positive electrode active material layer, which consisted of a mixture of 4.95% by mass of a conductive additive ( / g) with 30% by mass of a solid electrolyte (Li-PS) and 65% by mass of a positive electrode active material (NMC). The all-solid-state secondary battery had a specific surface area of ​​1 m². 2 All-solid-state secondary batteries in Tests No. 105 to 110 are shown, in which a positive electrode material (P-5 to P-10) was used as the positive electrode active material layer, which was prepared by mixing 4.95% by mass of a conductive additive at / g with 30% by mass of a solid electrolyte (Li-PS) and 65% by mass of a positive electrode active material (NMC or NCA) (see Table 1 in paragraph

[0126] and Table 2 in paragraph

[0137] ). Furthermore, it is stated that "a positive electrode sheet for an all-solid-state secondary battery was fabricated by heating and pressurizing (10 MPa, 1 minute) using a heat press machine" (paragraph

[0132] ), and "as is clear from Table 2, the all-solid-state secondary batteries of Test Nos. 101 to 110 that satisfy the provisions of the present invention have a large discharge capacity and excellent output characteristics" (paragraph

[0139] ).

[0005] Patent Document 3 describes "an all-solid-state lithium-ion secondary battery, wherein the negative electrode is formed using a negative electrode composite material containing negative electrode active material particles, a conductive material, and a solid electrolyte, and the negative electrode active material particles are characterized in that..." (Claim 3). The example then describes the "negative electrode composite material formation process" as follows: "• Negative electrode active material particles: Si particles (Production Example 1)", "• Sulfide-based solid electrolyte: Li2S-P2S5 glass ceramic", "• Conductive material: VGCF", "The content of the conductive material in the mixture of negative electrode raw materials was adjusted so that the volume ratio of the conductive material was 2.5 volume% when the total volume of the obtained negative electrode composite material was taken as 100%", "...The negative electrode composite material raw materials were coated onto one side of copper foil (negative electrode current collector, manufactured by UACJ Foil Co., Ltd.). These negative electrode composite material raw materials were dried to form the negative electrode composite material." (Paragraph

[0074] ) Furthermore, it is stated that "a solid electrolyte material portion was further laminated on top of the negative electrode composite material formed on the negative electrode current collector (copper foil). This laminate was set in a roll press machine and pressed under the following pressing conditions to obtain the negative electrode side laminate I (solid electrolyte material portion / negative electrode composite material / negative electrode current collector)." "<Pressing conditions for negative electrode side laminate I>" "Pressing pressure: approximately 630 MPa (linear pressure: 20 kN / cm)" "Pressing temperature: 25°C" (paragraph

[0077] ). Furthermore, it is stated that "a solid electrolyte material portion was further laminated on top of the positive electrode composite material formed on the positive electrode current collector (aluminum foil). This laminate was set in a roll press machine and pressed under the following pressing conditions to obtain the positive electrode side laminate I (solid electrolyte material portion / positive electrode composite material / positive electrode current collector)." "<Pressing conditions for positive electrode side laminate I>" "Pressing pressure: approximately 710 MPa (linear pressure: 20 kN / cm)" "Pressing temperature: 165°C" (paragraph

[0078] ).

[0006] Patent Document 4 describes a method for manufacturing a sulfide all-solid-state battery, comprising the steps of: preparing the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer; and performing a roll press treatment at a press temperature of 100°C or higher with at least the negative electrode active material layer laminated on the solid electrolyte layer. (Claim 4) and a method for manufacturing a sulfide all-solid-state battery according to Claim 4, wherein the roll press treatment is performed at a press pressure of 2 to 6 tons / cm. (Claim 5) In Example 1, it is stated that "butyl butyrate as a dispersion medium, a 5% by mass butyl butyrate solution containing polyvinylidene fluoride as a binder, silicon particles (manufactured by Koshu Chemical) as a negative electrode active material, Li2S-P2S5 glass ceramic containing LiBr and LiI as a solid electrolyte, and VGCF (vapor-phase carbon fiber) as a conductive material were added to a polypropylene container and stirred for 30 seconds using an ultrasonic dispersion device. Then, the polypropylene container was shaken with a shaker for 30 minutes to prepare a paste for the negative electrode active material layer." and "The paste for the negative electrode active material layer was applied to copper foil (without graphite coating) as a negative electrode current collector using an applicator and the doctor blade method, and then dried to prepare a negative electrode (...) having a negative electrode active material layer and a negative electrode current collector." (Paragraph

[0029] ) Furthermore, it is stated that "from Examples 2 to 7, it can be seen that if the press pressure is 2 ton / cm or more, the desired initial charge-discharge efficiency can be obtained regardless of the press temperature." (paragraph

[0046] ), and the press pressure by the roll press treatment of the negative electrode active material layer is 2 ton / cm. 2Regarding Examples 2 to 7, the initial charge-discharge efficiency was 119% for Example 2, where the press temperature was 25°C (compared to Comparative Example 2), and 118% or 119% for Examples 3 to 7, where the press temperatures were 100°C, 165°C, 180°C, 195°C, and 210°C (see Table 1 in paragraph

[0044] ). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] WO2017 / 104405 [Patent Document 2] WO2016 / 194759 [Patent Document 3] Japanese Patent Publication No. 2019-16517 [Patent Document 4] Japanese Patent Publication No. 2018-142431 [Overview of the project] [Problems that the invention aims to solve]

[0008] Patent documents 1 and 2 describe that when a conductive additive is included along with the active material and solid electrolyte to form an electrode (positive electrode), a solid-state secondary battery with a large discharge capacity and excellent output characteristics can be obtained by setting the specific surface area of ​​the conductive additive to a specific value. However, the initial charge-discharge efficiency is not described. Furthermore, since these positive electrodes for solid-state secondary batteries are manufactured by heat pressing at a low pressure of 10 MPa, the porosity of the positive electrode active material layer (positive electrode mixture layer) is large and does not fall below 10%. On the other hand, Patent Documents 3 and 4 describe a method of incorporating a conductive material along with the active material and solid electrolyte to form an electrode (negative electrode), requiring a pressure of approximately 630 MPa or higher, or 2 ton / cm². 2 Although it is stated that the material should be pressurized at the high pressure mentioned above, there is no mention of the specific surface area of ​​the conductive material, nor is there any mention of reducing the porosity of the negative electrode active material layer (negative electrode mixture layer) to 10% or less, or reducing the surface area of ​​the conductive material per unit mass of negative electrode mixture.

[0009] The inventor of the present invention considered making the porosity of the electrode mixture layer 10% or less for the purpose of increasing the output of the all-solid-state secondary battery (see Table 1). In addition, the examples and comparative examples in Table 1 correspond to the examples and comparative examples described later.

[0010]

Table 1

[0011] However, when the porosity of the electrode mixture layer was reduced to 10% or less, an event in which the initial charge-discharge efficiency decreased was occasionally observed. As described above, in Patent Document 4, when the negative electrode is roll-pressed to form an all-solid-state secondary battery, it is described that "from Examples 2 to 7, if the pressing pressure is 2 ton / cm (a misprint of 2 ton / cm 2 ), the desired initial charge-discharge efficiency can be obtained without depending on the pressing temperature." However, as in the comparative examples described later, even when the pressing pressure is high and the porosity is 10% or less, the initial charge-discharge efficiency (first charge-discharge efficiency) may be low. In addition, Examples 2 to 7 in Patent Document 4 have the same or lower initial charge-discharge efficiency compared to when hot-pressed at 100 °C or higher and when pressed at 25 °C (room temperature). Therefore, they correspond to the comparative examples described in this specification, and it is estimated that the surface area per 100 g of the electrode mixture of the conductive agent is larger than 60 m 2 / 100 g.

[0012] An object of the present invention is to provide an electrode capable of increasing the first charge-discharge efficiency of an all-solid-state secondary battery and an all-solid-state secondary battery having high first charge-discharge efficiency equipped with the electrode.

Means for Solving the Problems

[0013] The electrode according to one aspect of the present invention has an electrode mixture containing an electrode active material, a solid electrolyte, and a conductive agent, and the surface area per 100 g of the electrode mixture of the conductive agent is 60 m 2 / 100 g or less, and is provided with an electrode mixture layer having a porosity of 10% or less. The all-solid-state secondary battery according to another aspect of the present invention includes the electrode.

Effects of the Invention

[0014] According to one aspect of the present invention, an all-solid-state secondary battery with high initial charge-discharge efficiency can be provided. According to another aspect of the present invention, an all-solid-state secondary battery can achieve high initial charge-discharge efficiency. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a schematic diagram showing one embodiment of a stacked all-solid-state secondary battery. [Figure 2] Figure 2 is a schematic diagram showing one embodiment of manufacturing an all-solid-state secondary battery. [Figure 3] Figure 3 is a schematic diagram showing one embodiment of an energy storage device composed of multiple all-solid-state secondary batteries. [Modes for carrying out the invention]

[0016] First, an overview of the electrodes disclosed herein and the all-solid-state secondary battery comprising such electrodes will be described.

[0017] As a result of diligent research, the inventors have found that when the porosity of the electrode is 10% or less, the surface area of ​​the conductive agent per unit mass of the electrode mixture is 60 m². 2 We discovered that the initial charge-discharge efficiency is improved by using a conductive agent with a density of "less than 100g," and thus completed the present invention. An electrode according to one aspect of the present invention comprises an electrode mixture containing an electrode active material, a solid electrolyte, and a conductive agent, wherein the surface area of ​​the conductive agent per unit mass of the electrode mixture is 60 m². 2 The electrode mixture layer has a weight of 100g or less and a porosity of 10% or less. The porosity referred to here is the porosity in the discharged state. "Discharged state" refers to the state in which the all-solid-state secondary battery has been discharged to a completely discharged state by adopting the charge and discharge conditions recommended or specified for the all-solid-state secondary battery.

[0018] The surface area per unit mass of the conductive agent electrode mixture is 60 m². 2 By keeping it below 100g, 60m2 Compared to cases where the weight exceeds 100g, the initial charge-discharge efficiency of the all-solid-state secondary battery is improved. The surface area is 52m². 2 / 100g or less is preferable. However, as the surface area decreases, the initial charge / discharge efficiency tends to decrease, so 15m 2 It is preferable to use 100g or more, and 20m 2 It is more preferable to use 100g or more.

[0019] As mentioned above, when the porosity of the electrode is 10% or less, the contact area between the solid electrolyte and the conductive agent (a material with high electronic conductivity) increases, which can promote side reactions of the solid electrolyte and reduce the initial charge-discharge efficiency. On the other hand, with the aforementioned electrode, even when the porosity of the electrode is 10% or less, the surface area of ​​the conductive agent per unit mass of the electrode mixture is 60 m². 2 By reducing the amount to less than 100g, the contact area is reduced, which is presumed to suppress side reactions of the solid electrolyte and improve the initial charge-discharge efficiency. The aforementioned electrode may be either a positive or negative electrode. If the negative electrode active material is a material with low electronic conductivity, such as Si, it can be said that it will produce the same effect as the positive electrode, based on the mechanism described above.

[0020] Here, the content of the conductive agent may be 10% by mass or less of the mass of the electrode mixture. The conductive agent content is preferably 8% by mass or less, more preferably 6% by mass or less, and even more preferably 4% by mass or less, based on the mass of the electrode mixture.

[0021] The conductive agent content in the electrode mixture is set to 10% by mass or less of the electrode mixture mass, and the surface area of ​​the conductive agent per unit mass of the electrode mixture is set to 60 m². 2 By keeping the amount below 100g, side reactions such as the decomposition reaction of the solid electrolyte contained in the electrode mixture can be suppressed, and the initial charge-discharge efficiency of the all-solid-state secondary battery equipped with this electrode mixture layer can be improved.

[0022] The surface area per unit mass of the conductive agent electrode mixture is 60 m². 2To keep the amount below 100g, it is preferable that the specific surface area of ​​the conductive agent is small. The specific surface area of ​​the conductive agent is 60m². 2 Preferably less than / g, 40m 2 Less than / g is more preferable, 20m 2 A value of less than / g is even more preferable.

[0023] <Method for measuring the specific surface area of ​​conductive materials> The specific surface area of ​​a conductive material may be a known value, such as a nominal value in a catalog, or it may be a measured value. The specific surface area of ​​a conductive material can be measured, for example, using a specific surface area measuring device (BELSORP-MR6, manufactured by Microtrac-Bel Corporation).

[0024] The conductive agent may be a carbonaceous material. As for carbonaceous materials, gas-phase carbon fibers with a small specific surface area, and carbon blacks such as acetylene black with a small specific surface area are preferred.

[0025] To achieve a porosity of 10% or less in the electrodes, the press pressure used when pressure molding the electrodes is preferably 200 MPa or higher, and more preferably 300 MPa or higher. The upper limit of the press pressure is preferably 1500 MPa. Furthermore, the press temperature when pressure molding the electrodes may be room temperature (for example, 20°C to 25°C), but it is preferable to set it to 100°C or higher, and more preferably to 150°C or higher. The upper limit of the press temperature is preferably 300°C.

[0026] <Method for measuring the porosity of electrode mixture layers> The porosity of the electrode mixture layer is calculated using the pore volume (Vp) obtained by the mercury intrusion method, the mass (W) of the electrode mixture layer, and the volume (Vm) of the electrode mixture layer. The pore volume (Vp) can be measured, for example, using an automated mercury porosimeter pore distribution analyzer (Autopore IV9510, Micromeristics). Electrodes with an electrode mixture layer formed on an electrode substrate of a predetermined size are sealed in a glass sample container and transported from the glove box to the pore distribution analyzer in a sealed state within an argon atmosphere to minimize contact with the atmosphere. The mercury intrusion pressure is set from 3 kPa to 400 MPa, and the measurement pore diameter is set from 4 nm to 1 μm. The pore distribution curve of the electrode mixture layer is obtained during the pressurization process. The pore volume (Vp) is calculated from the pore distribution of pores with a diameter of less than 5 μm. The porosity of the electrode mixture layer is calculated using the following formula, based on the pore volume (Vp), the mass (W) of the electrode mixture layer used for measurement, and the volume (Vm) of the electrode mixture layer calculated from its area and average thickness. (porosity / %)=Vp(cm 3 g -1 ) × W(g) / Vm(cm 3 ) × 100

[0027] The solid electrolyte contained in the electrode mixture layer may be a sulfide solid electrolyte. As sulfide solid electrolytes, Li6PS5Cl (argyrodite), Li2S-P2S5, Li2S-P2S5-LiI, and Li2S-P2S5-Z are used in the solid electrolyte layer described later. m S 2n (However, m and n are positive numbers, and Z is one of Ge, Zn, or Ga.) etc. can be used.

[0028] The surface area per unit mass of the conductive electrode mixture is 60 m². 2 By reducing the amount to 100g or less, even when the porosity of the electrode mixture layer is densified to 10% or less, side reactions such as the decomposition reaction of the sulfide solid electrolyte can be suppressed, thereby improving the initial charge-discharge efficiency of the all-solid-state secondary battery.

[0029] The electrode may be configured as a positive electrode by using the electrode active material as the positive electrode active material and the electrode mixture layer as the positive electrode mixture layer. Since positive electrode active materials are generally materials with low electronic conductivity, combining them with conductive materials, which have high electronic conductivity, can make them more effective.

[0030] Another aspect of the present invention relates to an all-solid-state secondary battery comprising the electrodes. The following embodiments describe an all-solid-state lithium-ion secondary battery, but the all-solid-state secondary battery may also be an all-solid-state sodium-ion secondary battery.

[0031] This all-solid-state rechargeable battery has high initial charge-discharge efficiency. <Method for measuring initial charge-discharge efficiency> The initial charge-discharge efficiency is measured by the method described below. For the initial charge and discharge cycle, an uncharged all-solid-state secondary battery will be charged at a temperature of 50°C with a charging current of 0.1C until it reaches the normal charging termination voltage. The charging termination condition will be when the charging current reaches 0.025C. After that, a 10-minute rest period will be observed. Subsequently, a constant-current discharge will be performed with a discharge current of 0.1C until it reaches the normal discharging termination voltage. After that, a 10-minute rest period will be observed. Normal usage refers to using the all-solid-state secondary battery under the charge and discharge conditions recommended or specified for that battery. The ratio of the discharge capacity to the amount of electricity charged during the initial charge and discharge is determined and defined as the initial charge and discharge efficiency.

[0032] This document describes in detail the configuration of an all-solid-state secondary battery, the configuration of an energy storage device, and a method for manufacturing an all-solid-state secondary battery, as well as other embodiments, according to one embodiment of the present invention (hereinafter referred to as "this embodiment"). Note that the names of the components (each element) used in each embodiment may differ from the names of the components (each element) used in the background art.

[0033] <Configuration of an all-solid-state secondary battery> The all-solid-state secondary battery according to this embodiment comprises an electrode body having a positive electrode, a negative electrode, and a solid electrolyte layer, and a container for housing the electrode body. The electrode body is usually a laminated type in which a positive electrode and a plurality of negative electrodes are laminated with a solid electrolyte layer in between. Alternatively, the electrode body may be a so-called "bipolar type" in which a positive electrode mixture layer is formed on one side of an electrode substrate and a negative electrode mixture layer is formed on the other side. Figure 1 shows an example of an all-solid-state secondary battery. The all-solid-state secondary battery 10 is a secondary battery in which a positive electrode 1 and a negative electrode 2 are laminated with a solid electrolyte layer 3 in between. The positive electrode 1 has a positive electrode substrate 4 and a positive electrode mixture layer 5. The negative electrode 2 has a negative electrode substrate 7 and a negative electrode mixture layer 6. In the all-solid-state secondary battery 10 shown in Figure 1, the negative electrode mixture layer 6, solid electrolyte layer 3, positive electrode mixture layer 5, and positive electrode substrate 4 are laminated on the negative electrode substrate 7 in this order.

[0034] (positive electrode) The positive electrode comprises a positive electrode substrate and a positive electrode mixture layer disposed directly on the positive electrode substrate or via an intermediate layer.

[0035] The positive electrode substrate is conductive. Whether or not it is conductive is determined by the volume resistivity measured in accordance with JIS-H-0505 (1975), which is 10 7 The determination is made using Ω·cm as the threshold. The positive electrode substrate material can be a metal such as aluminum, titanium, tantalum, or stainless steel, or an alloy thereof. Among these, aluminum or an aluminum alloy is preferred from the viewpoint of high potential resistance, high conductivity, and cost. Examples of positive electrode substrates include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30 as specified in JIS-H-4000 (2014) or JIS-H4160 (2006).

[0036] The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, it is possible to increase the strength of the positive electrode substrate while increasing the energy density per unit volume of the all-solid-state secondary battery.

[0037] The intermediate layer is a layer placed between the positive electrode substrate and the positive electrode mixture layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode mixture layer. The composition of the intermediate layer is not particularly limited and may include, for example, a binder and a conductive agent.

[0038] In this embodiment, the positive electrode mixture layer comprises a positive electrode active material, a solid electrolyte, and a conductive agent. The positive electrode mixture layer may optionally contain optional components such as a binder, a thickener, and a filler.

[0039] The positive electrode active material can be appropriately selected from known positive electrode active materials. For lithium-ion secondary batteries, materials capable of intercalating and releasing lithium ions are typically used as positive electrode active materials. Examples of positive electrode active materials include lithium transition metal composite oxides having an α-NaFeO2 crystal structure, lithium transition metal composite oxides having a spinel crystal structure, polyanionic compounds, chalcogen compounds, and sulfur. Examples of lithium transition metal composite oxides having an α-NaFeO2 crystal structure include Li[Li x Ni (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Co (1-x-γ) ]O2(0≦x<0.5, 0<γ<1), Li[Li x Co (1-x) ]O2(0≦x<0.5), Li[Li x Ni γ Mn (1-x-γ) ]O2(0≦x<0.5, 0<γ<1), Li[Li x Ni γ Mn β Co (1-x-γ-β)]O2(0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1), Li[Li x Ni γ Co β Al (1-x-γ-β) Examples include ]O2 (0≦x<0.5, 0<γ, 0<β, 0.5<γ+β<1). As a lithium transition metal composite oxide having a spinel-type crystal structure, Li x Mn2O4, Li x Ni γ Mn (2-γ) Examples include O4. Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. Some atoms or polyanions in these materials may be substituted with atoms or anions of other elements. The surfaces of these materials may be coated with other materials. As the positive electrode active material, one of these materials may be used alone, or two or more may be used in mixture form.

[0040] The positive electrode active material is usually in the form of particles (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. Setting the average particle size of the positive electrode active material to be above the lower limit makes it easier to manufacture or handle the positive electrode active material. Setting the average particle size of the positive electrode active material to be below the upper limit suppresses the decrease in battery capacity during high-rate discharge. When a composite material of the positive electrode active material and other materials is used, the average particle size of the composite material is used as the average particle size of the positive electrode active material. "Average particle size" refers to the value at which the volume-based integrated distribution calculated in accordance with JIS-Z-8819-2 (2001), based on the particle size distribution measured by laser diffraction / scattering method on a dilution of particles diluted with a solvent, in accordance with JIS-Z-8825 (2013), becomes 50%.

[0041] To obtain powder with a predetermined particle size, grinders and classifiers are used. Examples of grinding methods include using mortars, ball mills, sand mills, vibrating ball mills, planetary ball mills, jet mills, counter-jet mills, swirling airflow jet mills, or sieves. Wet grinding, which involves the coexistence of water or organic solvents such as hexane, can also be used during grinding. For classification, sieves and wind classifiers are used as needed, both dry and wet.

[0042] The content of the positive electrode active material in the positive electrode mixture layer is preferably 50% to 95% by mass, more preferably 60% to 90% by mass, and even more preferably 70% to 85% by mass. By setting the content of the positive electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the positive electrode mixture layer.

[0043] The solid electrolyte contained in the positive electrode mixture layer is not particularly limited. Sulfide solid electrolytes, halide solid electrolytes, oxide solid electrolytes, etc., used in the solid electrolyte layer described later can be used. Among these, sulfide solid electrolytes are preferred. The solid electrolyte content in the positive electrode mixture layer is preferably 5% by mass or more and 40% by mass or less, and more preferably 15% by mass or more and 25% by mass or less.

[0044] The conductive agent has conductivity, and the surface area per unit mass of the conductive agent electrode mixture is 60 m². 2The material is not particularly limited as long as it is less than 100g. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent can be in powder or fibrous form. One of these materials may be used alone as the conductive agent, or two or more may be used in mixture form. These materials may also be used in composite form. For example, a composite material of carbon black and CNTs may be used. Among these, vapor-processed carbon fiber (VGCF: registered trademark), which is a carbon nanofiber with a small specific surface area, is preferred. The surface area of ​​the conductive agent per unit mass of electrode mixture is 60m². 2 To keep the amount below 100g, the specific surface area of ​​the conductive agent should be 60m². 2 Preferably less than / g, 40m 2 Less than / g is more preferable, 20m 2 It is even more preferable that the amount be less than / g. Also, the lower limit of the specific surface area of ​​the conductive agent is 1m 2 / g is preferred, 4m 2 / g is preferable.

[0045] The content of the conductive agent in the positive electrode mixture layer is such that the surface area of ​​the conductive agent per unit mass of the electrode mixture is 60 m². 2 To keep the amount below 100g, it is preferable that the conductive agent content be 10% by mass or less, more preferably 1% by mass or more and 8% by mass or less, even more preferably 1% by mass or more and 6% by mass or less, and even more preferably 1% by mass or more and 4% by mass or less. By setting the conductive agent content within the above range, the initial charge-discharge efficiency of the all-solid-state secondary battery can be improved.

[0046] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0047] The binder content in the positive electrode mixture layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By keeping the binder content within the above range, the positive electrode active material can be stably maintained.

[0048] Examples of thickening agents include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. If the thickening agent has a functional group that reacts with lithium or the like, this functional group may be deactivated beforehand by methylation or the like.

[0049] The filler is not particularly limited. Examples of fillers include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, mineral resource-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof.

[0050] The positive electrode mixture layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, solid electrolyte, conductive agent, binder, thickener, and filler.

[0051] (Method of manufacturing the positive electrode) In this embodiment, the positive electrode is preferably a coated electrode. In other words, it is preferable to prepare a paste for forming a positive electrode mixture layer by kneading a positive electrode active material, a solid electrolyte, a conductive agent, optional components such as a binder, thickener, and filler as needed, and an organic solvent (dispersion medium), apply this paste to a substrate to form a coating layer, and dry it to form a positive electrode mixture layer, thereby forming the positive electrode.

[0052] Suitable organic solvents include aliphatic hydrocarbons such as heptane and decane, aromatic hydrocarbons such as toluene, tetralin, cumene, mesitylene, and anisole, dibutyl ether, diisobutyl ketone, and butyl butyrate. The mixing method is not particularly limited as long as a paste for forming a highly dispersible cathode mixture layer can be obtained. For example, general methods such as dissolvers, homomixers, kneaders, roll mills, sand mills, attritors, ball mills, vibrator mills, high-speed impeller mills, ultrasonic homogenizers, and shakers can be used.

[0053] The above-mentioned positive electrode substrate can be used as the substrate to which the paste for forming the positive electrode mixture layer is applied, but a solid electrolyte layer can also be used as the substrate. The method for applying the paste for forming the positive electrode mixture layer is not particularly limited, and general methods such as the doctor blade method, die coating method, gravure coating method, spray coating method, electrostatic coating method, and bar coating method can be employed. The thickness of the coating layer of the paste for forming the positive electrode mixture layer is appropriately selected according to the desired thickness of the electrode mixture layer.

[0054] The method for drying the coating layer of the paste for forming the positive electrode mixture layer is not particularly limited as long as it does not degrade the positive electrode mixture layer. For example, general methods such as hot air drying, infrared drying, reduced pressure drying, and dielectric heating drying can be used. As for the drying atmosphere, examples include inert gas atmospheres such as Ar gas atmosphere and nitrogen gas atmosphere, dry air atmosphere, and vacuum. For example, drying at 80°C to 150°C for 10 minutes to 12 hours is preferable. By the above method, a coated electrode (positive electrode) having a positive electrode mixture layer, which is a coated layer of paste for forming a positive electrode mixture layer on a substrate, can be manufactured.

[0055] (Negative electrode) The negative electrode comprises a negative electrode substrate and a negative electrode mixture layer disposed directly on the negative electrode substrate or via an intermediate layer. The configuration of the intermediate layer is not particularly limited and can be selected from, for example, the configurations exemplified in the positive electrode.

[0056] The negative electrode substrate is electrically conductive. Suitable materials for the negative electrode substrate include metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof, as well as carbonaceous materials. Among these, copper or copper alloys are preferred. Examples of negative electrode substrates include foil, vapor-deposited film, mesh, and porous materials, with foil being preferred from a cost perspective. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0057] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate while increasing the energy density per unit volume of the all-solid-state secondary battery.

[0058] The negative electrode mixture layer contains a negative electrode active material. In this embodiment, the negative electrode mixture layer preferably contains a solid electrolyte and a conductive agent. The negative electrode mixture layer may optionally contain optional components such as a binder, thickener, and filler. The solid electrolyte and conductive agent contained in the negative electrode mixture layer are the same as those contained in the positive electrode mixture layer. Furthermore, optional components such as the binder, thickener, and filler can be selected from the materials exemplified above for the positive electrode. The negative electrode can be manufactured using a negative electrode active material instead of a positive electrode active material, and by the same manufacturing method as for the positive electrode described above, to form a coated electrode electrode having a negative electrode mixture layer which is a coated layer of paste for forming the negative electrode mixture layer on a substrate. The negative electrode may also be manufactured by a dry method as in the conventional method.

[0059] The negative electrode mixture layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metallic elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, solid electrolyte, conductive agent, binder, thickener, and filler.

[0060] The negative electrode active material can be appropriately selected from known negative electrode active materials. For lithium-ion secondary batteries, materials capable of intercalating and releasing lithium ions are typically used as negative electrode active materials. Examples of negative electrode active materials include: metallic Li; metals or metalloids such as Si and Sn; metal oxides or metalloid oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 LiTiO 2、 Examples of materials include titanium-containing oxides such as TiNb2O7; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitizable carbon (easily graphitizable carbon or poorly graphitizable carbon). Among these materials, graphite and non-graphitizable carbon are preferred. In the negative electrode mixture layer, one of these materials may be used alone, or two or more may be used in mixture form.

[0061] "Graphite" refers to the average lattice plane spacing (d) of the (002) plane, determined by X-ray diffraction before charging or discharging, or during the discharge state.002 ) refers to carbon materials with a n-scale between 0.33 nm and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite. Artificial graphite is preferred from the standpoint of obtaining materials with stable physical properties.

[0062] "Non-graphite carbon" refers to the average lattice plane spacing (d) of the (002) plane, which is determined by X-ray diffraction before charging or during the discharge state. 002 This refers to carbon materials with a nautical radius of 0.34 nm or more and 0.42 nm or less. Non-graphitized carbons include poorly graphitizable carbons and easily graphitizable carbons. Examples of non-graphitized carbons include resin-derived materials, petroleum pitch or materials derived from petroleum pitch, petroleum coke or materials derived from petroleum coke, plant-derived materials, and alcohol-derived materials.

[0063] Here, "discharge state" refers to a state in which sufficient lithium ions that can be absorbed and released during charging and discharging are released from the carbon material, which is the negative electrode active material. For example, in a half-cell using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and metallic Li as the counter electrode, this is the state in which the open-circuit voltage is 0.7V or higher.

[0064] "Non-graphitizable carbon" refers to the above d 002 This refers to carbon materials with a wavelength between 0.36 nm and 0.42 nm.

[0065] "Easily graphitizable carbon" refers to the above d 002 This refers to carbon materials with a wavelength of 0.34 nm or more and less than 0.36 nm.

[0066] The negative electrode active material is usually in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm to 100 μm. If the negative electrode active material is a carbon material, titanium-containing oxide, or polyphosphate compound, its average particle size may be 1 μm to 100 μm. If the negative electrode active material is Si, Sn, Si oxide, or Sn oxide, its average particle size may be 1 nm to 1 μm. Setting the average particle size of the negative electrode active material above the lower limit makes it easier to manufacture or handle. Setting the average particle size of the negative electrode active material below the upper limit suppresses the decrease in battery capacity during high-rate discharge. To obtain powder with a predetermined particle size, a pulverizer or classifier is used. The pulverizing method and powder grading method can be selected from, for example, the methods exemplified above for the positive electrode. If the negative electrode active material is a metal such as metallic Li, the negative electrode active material may be in the form of foil.

[0067] The content of the negative electrode active material in the negative electrode mixture layer is preferably 40% by mass or more and 80% by mass or less, and more preferably 50% by mass or more and 70% by mass or less. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the negative electrode mixture layer.

[0068] (solid electrolyte layer) The solid electrolyte layer contains a solid electrolyte. The solid electrolyte used in the solid electrolyte layer is not particularly limited. As the solid electrolyte, sulfide solid electrolytes, halide solid electrolytes, oxide solid electrolytes, etc., can be used. Among these, sulfide solid electrolytes are preferred. The solid electrolyte layer can be manufactured by press molding in the same manner as in the past. Sulfide solid electrolytes include Li6PS5Cl, Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5 -Li3N, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z mS 2n (where m and n are positive numbers, and Z is one of Ge, Zn, or Ga.) Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (However, x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, or In.) These are some examples. As a solid halogen electrolyte, the general formula is Li x M y A compound represented by X6 is preferred, and examples include Li3YCl6, Li3YBr6, Li3YI6, Li3InCl6, Li3InBr6, Li3InF6, Li2ZrCl6, Li3ErCl6, Li3ErBr6, Li3DyCl6, Li3DyBr6, Li3GdCl6, Li3GdBr6, Li3HoCl6, Li3HoBr6, Li3LaCl6, Li3LaBr6, Li3NdCl6, Li3NdBr6, Li3ScCl6, Li3ScBr6, Li3ScF6, Li3SmCl6, Li3SmBr6, Li3TbCl6, Li3TbBr6, Li3TmCl6, Li3TmBr6, Li3AlF6, Li3TiF6, Li3GaF6, Li3GeF6, and the like. As an oxide solid electrolyte, Li7La3Zr2O 12 Li 0.5 La 0.5 Examples include TiO3, LiTi2(PO4)3, Li3BO3-Li2CO3, and Li3BO3-Li2SO4.

[0069] <Manufacturing method for all-solid-state secondary batteries> The method for manufacturing the all-solid-state secondary battery in this embodiment can be appropriately selected from known methods. This manufacturing method includes, for example, forming a positive electrode mixture layer by the positive electrode manufacturing method described above, forming a negative electrode mixture layer by the negative electrode manufacturing method, forming a solid electrolyte layer by the solid electrolyte layer manufacturing method, and forming an electrode body by stacking a positive electrode having a positive electrode mixture layer and a negative electrode having a negative electrode mixture layer via the solid electrolyte layer. Furthermore, in the method for manufacturing an all-solid-state secondary battery according to this embodiment, after forming a solid electrolyte layer, a positive electrode (coated electrode) may be formed on the solid electrolyte layer, and the all-solid-state secondary battery may be assembled using the laminate of the positive electrode and the solid electrolyte layer and a separately formed negative electrode. For example, as shown in Figure 2, a solid electrolyte layer is formed by pressing it at a pressure of 100 MPa at room temperature. Then, a positive electrode (coated electrode) obtained by coating a positive electrode mixture layer onto a substrate and drying it, as described above, is placed on top of the solid electrolyte layer and joined together by pressing at a pressure of 360 MPa at room temperature or 160°C to form a laminate. Finally, this laminate and the negative electrode are joined together by pressing at a pressure of 50 MPa to form an all-solid-state secondary battery. Conversely to the above manufacturing method, a negative electrode may be formed on a solid electrolyte layer, and an all-solid-state secondary battery may be assembled using a laminate of the negative electrode and the solid electrolyte layer, and a separately formed positive electrode.

[0070] <Shape and structure of all-solid-state rechargeable batteries> The shape of the all-solid-state secondary battery in this embodiment is not particularly limited, and examples include cylindrical batteries, prismatic batteries, flat batteries, coin-type batteries, button-type batteries, and the like. For example, an all-solid-state secondary battery 10, in which a positive electrode 1 and a negative electrode 2 are stacked via a solid electrolyte layer 3 as shown in Figure 1, can be housed in a rectangular container to form a rectangular battery.

[0071] <Configuration of the energy storage device> The all-solid-state secondary battery of this embodiment can be installed as a power storage unit (battery module) composed of multiple all-solid-state secondary batteries 10 in power supplies for vehicles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), power supplies for electronic devices such as personal computers and communication terminals, or power storage power supplies. In this case, it is sufficient that the technology of the present invention is applied to at least one of the all-solid-state secondary batteries 10 included in the power storage unit. Figure 3 shows an example of a power storage device 30 which is formed by further assembling power storage units 20, each of which is a collection of two or more electrically connected solid-state secondary batteries 10. The power storage device 30 may include busbars (not shown) that electrically connect two or more solid-state secondary batteries 10, busbars (not shown) that electrically connect two or more power storage units 20, etc. The power storage unit 20 or the power storage device 30 may include a condition monitoring device (not shown) that monitors the state of one or more solid-state secondary batteries 10.

[0072] <Other Embodiments> It should be noted that the all-solid-state secondary battery of the present invention is not limited to the above embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or with well-known technology. Furthermore, a part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment. [Examples]

[0073] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples.

[0074] (Fabrication of all-solid-state secondary batteries) As the positive electrode active material, LiNi 0.6 Co 0.2 Mn 0.2 I prepared O2 (NCM622). As a solid electrolyte, a sulfide solid electrolyte (Li6PS5Cl: argyrodite) was prepared. Acetylene black (AB) and vapor-phase carbon fiber (VGCF: registered trademark) were prepared as conductive materials. Styrene-butadiene rubber (SBR) was prepared as the binder. NCM622, Li6PS5Cl, AB or VGCF, and SBR were mixed in an agate mortar, and this mixture was kneaded with butyl butyrate, an organic solvent, to prepare a paste for forming the positive electrode mixture layer. The SBR content was 2% by mass of the positive electrode mixture mass. The obtained positive electrode mixture layer-forming paste was applied to an aluminum foil (average thickness 20 μm), which served as the positive electrode substrate, using a YBA type baker applicator to a basis weight of 15 mg / cm². -2 More than 25mg cm -2 The material was coated as follows. This was dried in an argon atmosphere oven set to the temperature at which the organic solvent evaporates, thereby forming a cathode mixture layer on the cathode substrate. This was then punched out into a 10 mm diameter circle to serve as the cathode for evaluation.

[0075] Next, 80 mg of sulfide solid electrolyte (Li6PS5Cl: argyrodite) was inserted into a ceramic powder molding machine with an inner diameter of 10 mm, and press-molded at a pressure of 100 MPa at room temperature for several seconds using a uniaxial press to form a solid electrolyte layer. After releasing the pressure, the prepared positive electrode was placed on one side of the solid electrolyte layer and press-molded at a pressure of 360 MPa at room temperature or 160°C for 5 minutes. After releasing the pressure, indium foil (average thickness 300 μm, diameter 8 mm, manufactured by Nilaco) and lithium foil (average thickness 300 μm, diameter 6 mm, manufactured by Honjo Metal) as the negative electrode, and SUS316 foil (manufactured by Nilaco) as the negative electrode base material were placed on the side opposite to the bonding surface of the positive electrode, and bonded together at a pressure of 50 MPa at room temperature for several seconds using a uniaxial press. By removing this from the ceramic powder molding machine, an all-solid-state secondary battery was obtained.

[0076] [Examples 1, 2, 4] As a conductive material, it has a specific surface area of ​​12 m². 2 Vapor-phase carbon fiber (VGCF: registered trademark, manufactured by Showa Denko Corporation) at a weight of / g (nominal value in the catalog) is mixed in amounts of 2% by mass, 3% by mass, and 4% by mass of the positive electrode mixture, respectively, and the surface area of ​​the conductive agent per unit mass of the positive electrode mixture is 24m² in each case. 2 / 100g, 36m 2 / 100g, 48m 2A positive electrode mixture layer at a concentration of 1 / 100g was formed on a positive electrode substrate under the above conditions to produce the positive electrodes according to Examples 1, 2, and 4. These positive electrodes according to Examples 1, 2, and 4 were placed on one side of the solid electrolyte layer prepared as described above, and pressure-molded at 160°C and a pressure of 360MPa for 5 minutes to obtain positive electrodes with porosity of 6.3%, 9.2%, and 9.5%, respectively. Subsequently, they were joined with the negative electrode under the above conditions to obtain an all-solid-state secondary battery. On the other hand, the positive electrodes according to Examples 1, 2, and 4, prepared as described above, were placed on one side of the solid electrolyte layer prepared as described above, and pressure-molded at room temperature under a pressure of 360 MPa for 5 minutes to obtain positive electrodes with porosity of 11.8%, 12.7%, and 13.9%, respectively. Subsequently, they were joined with the negative electrode under the above conditions to obtain an all-solid-state secondary battery.

[0077] [Example 3, Comparative Examples 1 and 3] As a conductive material, it has a specific surface area of ​​42 m². 2 Acetylene black (particulate AB, manufactured by Imerys) in amounts of 1% by mass, 2% by mass, and 4% by mass of the positive electrode mixture were mixed, respectively, with a surface area of ​​the conductive agent per unit mass of the positive electrode mixture of 42 m². 2 / 100g, 84m 2 / 100g, 168m 2 A positive electrode mixture layer at a concentration of 100g was formed on a positive electrode substrate under the above conditions to produce the positive electrodes according to Example 3, Comparative Examples 1 and 3. These positive electrodes according to Example 3, Comparative Examples 1 and 3 were placed on one side of the solid electrolyte layer prepared as described above, and pressure-molded at 160°C and a pressure of 360MPa for 5 minutes to obtain positive electrodes with porosity of 7.4%, 7.3%, and 9.7%, respectively. Subsequently, they were joined with the negative electrode under the above conditions to obtain an all-solid-state secondary battery. On the other hand, the positive electrodes of Example 3 and Comparative Examples 1 and 3, prepared as described above, were placed on one side of the solid electrolyte layer prepared as described above, and pressure-molded at room temperature under a pressure of 360 MPa for 5 minutes to obtain positive electrodes with porosity of 12.6%, 13.1%, and 13.0%, respectively. Subsequently, they were joined with the negative electrode under the above conditions to obtain an all-solid-state secondary battery.

[0078] [Comparative Example 2] As the conductive agent, acetylene black (granular AB, manufactured by Imerys) with a specific surface area of 58 m 2 / g was mixed at 2% by mass of the mass of the positive electrode mixture, and a positive electrode mixture layer with a surface area of 116 m 2 / 100 g per mass of the positive electrode mixture was formed on the positive electrode substrate under the above conditions to produce a positive electrode according to Comparative Example 2. The positive electrode according to Comparative Example 2 thus produced was overlaid on one surface of the solid electrolyte layer produced as described above, and pressure molding was performed at 160 °C under a pressure of 360 MPa for 5 minutes to obtain a positive electrode with a porosity of 7.3%. Thereafter, it was joined to the negative electrode under the above conditions to obtain an all-solid-state secondary battery. On the other hand, the positive electrode according to Comparative Example 2 produced as described above was overlaid on one surface of the solid electrolyte layer produced as described above, and pressure molding was performed at room temperature under a pressure of 360 MPa for 5 minutes to obtain a positive electrode with a porosity of 12.2%. Thereafter, it was joined to the negative electrode under the above conditions to obtain an all-solid-state secondary battery.

[0079] [Comparative Example 4] As the conductive agent, acetylene black (granular AB, manufactured by Denka) with a specific surface area of 125 m 2 / g was mixed at 2% by mass of the mass of the positive electrode mixture, and a positive electrode mixture layer with a surface area of 250 m 2 / 100 g per mass of the positive electrode mixture was formed on the positive electrode substrate under the above conditions to produce a positive electrode according to Comparative Example 4. The positive electrode according to Comparative Example 4 thus produced was overlaid on one surface of the solid electrolyte layer produced as described above, and pressure molding was performed at 160 °C under a pressure of 360 MPa for 5 minutes to obtain a positive electrode with a porosity of 9.1%. Thereafter, it was joined to the negative electrode under the above conditions to obtain an all-solid-state secondary battery. On the other hand, the positive electrode according to Comparative Example 4 produced as described above was overlaid on one surface of the solid electrolyte layer produced as described above, and pressure molding was performed at room temperature under a pressure of 360 MPa for 5 minutes to obtain a positive electrode with a porosity of 11.8%. Thereafter, it was joined to the negative electrode under the above conditions to obtain an all-solid-state secondary battery.

[0080] (Measurement of initial charge-discharge efficiency) For each of the obtained all-solid-state secondary batteries, the first charge and discharge were performed at 50 °C in the following manner, and the initial charge-discharge efficiency was measured. Constant current and constant voltage charging was performed with a charging current of 0.1C and a charging termination voltage of 3.75V. The charging termination condition was when the charging current became 0.025C. After that, a 10-minute rest period was observed. Subsequently, constant current discharge was performed with a discharge current of 0.1C and a discharge termination voltage of 2.25V. After that, a 10-minute rest period was observed. The ratio of discharge capacity to charge amount during the initial charge / discharge was determined and defined as the initial charge / discharge efficiency. Furthermore, for each of Examples 1 to 3 and Comparative Examples 1 to 4, the rate of change in initial charge-discharge efficiency was calculated by subtracting the initial charge-discharge efficiency of an all-solid-state secondary battery equipped with a positive electrode molded at 360 MPa pressure at room temperature from the initial charge-discharge efficiency of an all-solid-state secondary battery equipped with a positive electrode molded at 360 MPa pressure at 160°C.

[0081] The table shows the surface area per unit mass of the conductive agent positive electrode mixture, the porosity of the positive electrode molded at 160°C and 360 MPa, the initial charge-discharge efficiency of an all-solid-state secondary battery equipped with a positive electrode molded at 160°C and 360 MPa, and the rate of change of the initial charge-discharge efficiency. 2 This will be shown.

[0082] [Table 2]

[0083] table 2 Furthermore, the porosity of the positive electrodes of Examples 1 to 4 and Comparative Examples 1 to 4, which were pressure-molded at 160°C and a pressure of 360 MPa, was 10% or less in all cases, but the surface area of ​​the conductive agent per unit mass of the positive electrode mixture was 60 m². 2 The all-solid-state secondary batteries of Examples 1 to 4, which have a positive electrode weighing 100g or less, have a surface area of ​​60m² per unit mass of conductive agent in the positive electrode mixture. 2 Compared to the all-solid-state secondary batteries in Comparative Examples 1 to 4, which have positive electrodes exceeding 100g, the initial charge-discharge efficiency is clearly higher. Furthermore, the initial charge-discharge efficiency change rates in Examples 1 to 4 were positive, and the surface area of ​​the conductive agent per unit mass of positive electrode mixture was 60 m². 2When the positive electrode with less than 100 g / 100g is manufactured by pressure molding at 160 °C under a pressure of 360 MPa, and when the porosity of the positive electrode is 10% or less, the positive electrode is manufactured by pressure molding at the same pressure at room temperature. Compared with the case where the porosity of the positive electrode exceeds 10%, the initial charge-discharge efficiency is improved. In contrast, the change rates of the initial charge-discharge efficiency in Comparative Examples 1 to 4 are negative values, and the surface area per mass of the conductive agent in the positive electrode mixture is 60 m 2 When the positive electrode with more than 60 m 2 / 100g is manufactured by pressure molding at 160 °C under a pressure of 360 MPa, and when the porosity of the positive electrode is 10% or less, the positive electrode is manufactured by pressure molding at the same pressure at room temperature. Compared with the case where the porosity of the positive electrode exceeds 10%, the initial charge-discharge efficiency is not improved. When the porosity of the electrode is 10% or less, the contact area between the solid electrolyte and the conductive agent increases, and side reactions such as the decomposition reaction of the solid electrolyte are promoted. As in Comparative Examples 1 to 4, the initial charge-discharge efficiency is not improved. In contrast, in Examples 1 to 4, by setting the surface area per mass of the conductive agent in the electrode mixture to 60 m 2 / 100g or less, even when the porosity of the electrode is 10% or less, the contact area between the solid electrolyte and the conductive agent decreases, so side reactions such as the decomposition reaction of the solid electrolyte are suppressed, and it is presumed that the initial charge-discharge efficiency is improved. Particularly, in the positive electrode using particulate AB of Example 3, it is manufactured by pressure molding at 160 °C, and the initial charge-discharge efficiency of the all-solid-state secondary battery with an electrode porosity of 10% or less is significantly improved. This is because the porosity is large for an electrode manufactured by pressure molding at room temperature, and there is a shortage of electron conduction paths in the electrode, while for an electrode manufactured by pressure molding at 160 °C, the porosity is sufficiently small, and a good electron conduction path is formed in the electrode. Furthermore, when Examples 3, Comparative Examples 1 and 3 are compared, since the initial charge-discharge efficiency is improved with the reduction of the AB content, it is presumed that side reactions such as the decomposition reaction of the solid electrolyte are suppressed by reducing the surface area per mass of the conductive agent in the electrode mixture. Therefore, in the present embodiment, when the electrode porosity is 10% or less, it can be said that the effect of improving the initial charge-discharge efficiency of the all-solid-state secondary battery is achieved by using an electrode with a surface area per mass of the conductive agent in the electrode mixture of 60 m 2 / 100g or less. [Industrial applicability]

[0084] According to one aspect of the present invention, an all-solid-state secondary battery with high initial charge-discharge efficiency can be provided. This is useful as an all-solid-state secondary battery for hybrid vehicles, plug-in hybrid vehicles, and electric vehicles. [Explanation of symbols]

[0085] 1 positive electrode 2 negative electrode 3 Solid electrolyte layer 4. Positive electrode substrate 5. Positive electrode mixture layer 6. Negative electrode mixture layer 7. Negative electrode substrate 10 All-solid-state secondary battery 20 Energy storage units 30 Energy storage devices

Claims

1. The electrode mixture comprises an electrode active material, a solid electrolyte, and a conductive agent, wherein the surface area of ​​the conductive agent per unit mass of the electrode mixture is 60 m². ２ An electrode comprising an electrode mixture layer having a weight of 100g or less and a porosity of 10% or less.

2. The electrode according to claim 1, wherein the content of the conductive agent is 10% by mass or less of the mass of the electrode mixture.

3. The electrode according to claim 1 or 2, wherein the solid electrolyte is a sulfide solid electrolyte.

4. The electrode according to any one of claims 1 to 3, wherein the electrode active material is a positive electrode active material and the electrode mixture layer is a positive electrode mixture layer.

5. A solid-state secondary battery comprising the electrodes described in any one of claims 1 to 4.

6. A method for manufacturing an electrode, comprising kneading an electrode mixture containing an electrode active material, a solid electrolyte, and a conductive agent to form an electrode mixture layer in which the conductive agent has a surface area of ​​60 m² / 100 g or less per unit mass of the electrode mixture and a porosity of 10% or less.

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