Battery and manufacturing method thereof

Abstract

This battery is provided with: a first electrode; a second electrode; and an electrolyte layer disposed between the first electrode and the second electrode so as to be in contact with the first electrode and the second electrode, the first electrode being a sintered body containing a first active material and a first oxide solid electrolyte, and the electrolyte layer being a sintered body containing a second oxide solid electrolyte. The electrolyte layer has a first region including an interface between the first electrode and the electrolyte layer, and a central region including a central position in the thickness direction, and has insulating properties in the first region, and the mass ratio of a carbide derived from the binder in the first electrode is lower than the mass ratio of a carbide derived from the binder in the central region of the electrolyte layer.

Description

Technical Field

[0001] This disclosure relates to batteries and methods of manufacturing them. Background Technology

[0002] As the next generation of batteries, solid-state batteries are being actively researched and developed.

[0003] As described in Patent Document 1, a solid-state battery is manufactured, for example, by stacking and firing multiple green sheets. The multiple green sheets include a positive electrode green sheet, a solid electrolyte green sheet, and a negative electrode green sheet.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 5803700 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] In the prior art, there is a need to improve the battery's resistance to damage.

[0009] Solution for solving the problem

[0010] This disclosure provides a battery having:

[0011] Electrode 1;

[0012] The second electrode; and,

[0013] An electrolyte layer disposed between the first electrode and the second electrode in a manner that contacts the first electrode and the second electrode.

[0014] The aforementioned first electrode is a sintered body containing a first active material and a first oxide solid electrolyte.

[0015] The aforementioned electrolyte layer is a sintered body containing a second oxide solid electrolyte, and has a first region including the interface between the aforementioned first electrode and the aforementioned electrolyte layer, and a central region including the center position in the thickness direction, and has insulation in the first region.

[0016] The battery satisfies at least one of the following conditions (a) and (b).

[0017] (a) The mass ratio of carbides derived from the binder in the first electrode is lower than the mass ratio of carbides derived from the binder in the central region of the electrolyte layer.

[0018] (b) When the ratio of the number of carbide-containing grain boundaries to the number of grain boundaries appearing in a cross section parallel to the thickness direction of the aforementioned battery is defined as exponent A, the aforementioned exponent A of the aforementioned first electrode is less than the aforementioned exponent A of the aforementioned central region of the aforementioned electrolyte layer.

[0019] The effects of the invention

[0020] According to the technology disclosed herein, the damage resistance of batteries can be improved. Attached Figure Description

[0021] Figure 1 A cross-sectional view illustrating a simplified configuration of a battery according to one embodiment of this disclosure.

[0022] Figure 2 A process diagram illustrating the battery manufacturing method. Detailed Implementation

[0023] (The insights that form the basis of this disclosure)

[0024] Solid-state batteries exhibit superior heat resistance compared to batteries using liquid electrolytes. New demands for solid-state batteries are anticipated. For example, there are plans to mount solid-state batteries onto electronic circuit boards for use in high-temperature environments. However, a significant difference in the coefficients of linear expansion between the solid-state battery and the electronic circuit board is anticipated. Therefore, stress based on this difference in coefficients of linear expansion could be applied to the solid-state battery, potentially causing damage.

[0025] Furthermore, the following manufacturing method is suitable for the mass production of solid-state batteries. A stack of green sheets corresponding to the size of individual solid-state batteries is obtained by cutting large-area green sheets into a laminate. Then, the laminate is fired to obtain a solid-state battery. Sometimes, burrs from the cutting remain in the solid-state battery; therefore, grinding is required after firing to remove these burrs. This grinding process applies impact to the solid-state battery, potentially causing damage.

[0026] The inventors focused on the amount of carbides derived from the binder in each layer. That is, the inventors believed that by adjusting the amount of carbides derived from the binder, it might be possible to improve the battery's resistance to damage, and thus conceived of the technology disclosed herein.

[0027] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. The present disclosure is not limited to the following embodiments.

[0028] (Implementation Method)

[0029] Figure 1 A cross-sectional view illustrating a simplified configuration of the battery 100 in one embodiment of this disclosure.

[0030] The battery 100 includes a positive electrode 20, a negative electrode 30, and an electrolyte layer 40. The electrolyte layer 40 is disposed between the positive electrode 20 and the negative electrode 30 in a manner that contacts the positive electrode 20 and the negative electrode 30. The battery 100 may also have multiple layers of positive electrode 20, multiple layers of negative electrode 30, and multiple layers of electrolyte layer 40. In this case, the battery 100 may also have an internal current collector.

[0031] In this embodiment, the positive electrode 20 corresponds to the first electrode, and the negative electrode 30 corresponds to the second electrode. However, the positive electrode 20 may also correspond to the second electrode, and the negative electrode 30 may also correspond to the first electrode.

[0032] In this specification, "sintering" refers to the phenomenon where bonding occurs between particles when a powder material is heated, resulting in densification of the molded body due to volume shrinkage. "Firing" refers to the heat treatment used for sintering.

[0033] The positive electrode 20 is a sintered body containing positive electrode active material and oxide solid electrolyte.

[0034] The positive electrode active material is a material capable of absorbing, storing, and releasing metal ions such as lithium ions. Examples of positive electrode active materials include lithium-containing transition metal oxides and lithium-containing transition metal phosphates. Among these, lithium-containing transition metal phosphates are suitable for positive electrode 20. Examples of lithium-containing transition metal phosphates include lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate.

[0035] In cathode 20, there are no particular limitations on the oxide solid electrolyte. Examples of oxide solid electrolytes include solid electrolytes with a NASICON-type structure, solid electrolytes with a perovskite-type structure, solid electrolytes with a LISICON-type structure, and solid electrolytes with a garnet-type structure. Among these, lithium-containing phosphate compounds with a NASICON-type structure are suitable for cathode 20.

[0036] Compared to other oxide solid electrolytes such as those with perovskite or garnet structures, NASICON-type solid electrolytes are materials that can be sintered at low temperatures. The ability to sinter at low temperatures is advantageous for suppressing reactions between the active material and the solid electrolyte.

[0037] Lithium-containing phosphate compounds can also have Li 1+x Al x Ge 2-x The composition of (PO4)3 (0≤x≤2). In this specification, compounds having the above composition are sometimes referred to as "LAGP". Another example of a lithium-containing phosphate compound is Li. 1+x Al x Ti 2-x(PO4)3 (0≤x≤2). This compound is sometimes referred to as "LATP" in this specification.

[0038] The electrolyte layer 40 is a sintered body containing an oxide solid electrolyte and carbides derived from the binder.

[0039] In the electrolyte layer 40, there is no particular limitation on the oxide solid electrolyte. The aforementioned substance, which serves as the oxide solid electrolyte of the positive electrode 20, may also be used in the electrolyte layer 40. For the same reasons as with the positive electrode 20, lithium-containing phosphate compounds having a NASICON-type structure are suitable for the electrolyte layer 40.

[0040] The electrolyte layer 40 has a first region 40a, a second region 40b, and a central region 40c. The first region 40a is the region containing the interface between the positive electrode 20 and the electrolyte layer 40. The second region 40b is the region containing the interface between the negative electrode 30 and the electrolyte layer 40. The central region 40c is the region containing the center position of the electrolyte layer 40 in the thickness direction. In this embodiment, the central region 40c is the region other than the first region 40a and the second region 40b.

[0041] The electrolyte layer 40 is insulating in the first region 40a. The central region 40c contains carbides derived from the binder. The binder is contained in the green sheet corresponding to the electrolyte layer 40 before firing. By adjusting the type of binder contained in the green sheet and the debinding temperature during firing, carbides derived from the binder can be intentionally retained in the central region 40c. Carbides as binder residue sometimes remain in the first region 40a as unavoidable impurities, but their amount does not impair the insulation of the first region 40a.

[0042] Similarly, the electrolyte layer 40 is insulating in the second region 40b. The central region 40c contains carbides derived from the binder. The binder is contained in the green sheet corresponding to the electrolyte layer 40 before firing. By adjusting the type of binder contained in the green sheet and the debinding temperature during firing, carbides derived from the binder can be intentionally left in the central region 40c. Carbides as binder residue sometimes remain in the second region 40b as unavoidable impurities, but their amount does not impair the insulation of the second region 40b.

[0043] The negative electrode 30 is a sintered body containing negative electrode active material and oxide solid electrolyte.

[0044] Negative electrode active materials are materials capable of absorbing, storing, and releasing metal ions such as lithium ions. Examples of negative electrode active materials include titanium dioxide (IV), composite oxides containing titanium and niobium, and lithium-containing transition metal phosphates. Examples of titanium dioxide (IV) include anatase (tetragonal), rutile (tetragonal), and brookite (orthorhombic) titanium dioxide. Composite oxides containing titanium and niobium, for example, have a composition of TiNb₂O₇. Examples of lithium-containing transition metal phosphates include lithium vanadium phosphate.

[0045] In the negative electrode 30, there is no particular limitation on the oxide solid electrolyte. The aforementioned substance, which is the oxide solid electrolyte used as the positive electrode 20, can also be used in the negative electrode 30. For the same reasons as with the positive electrode 20, lithium-containing phosphate compounds having a NASICON-type structure are suitable for the negative electrode 30.

[0046] The negative electrode 30 may also contain other materials such as conductive additives. Examples of conductive additives include the materials mentioned above.

[0047] The composition of the oxide solid electrolyte in the negative electrode 30 can be the same as or different from that in the positive electrode 20. The composition of the oxide solid electrolyte in the electrolyte layer 40 can also be the same as or different from that in the positive electrode 20. The positive electrode 20, electrolyte layer 40, and negative electrode 30 can also contain oxide solid electrolytes of the same composition. However, the compositions of the oxide solid electrolytes in the positive electrode 20, the electrolyte layer 40, and the negative electrode 30 can also differ from each other.

[0048] The battery 100 of this embodiment satisfies at least one of the following conditions (a1) and (b1). Condition (a1): The mass ratio M1 of carbides derived from the binder in the positive electrode 20 is lower than the mass ratio M2 of carbides derived from the binder in the central region 40c of the electrolyte layer 40. Condition (b1): When the exponent A is defined as the ratio of the number of carbide-containing grain boundaries to the number of grain boundaries appearing in a cross section parallel to the thickness direction of the battery 100, the exponent A of the positive electrode 20 is less than the exponent A of the central region 40c of the electrolyte layer 40. The electrolyte layer 40 is insulating in the first region 40a. In other words, the electrolyte layer 40 is not electronically conductive in this region. Therefore, the positive electrode 20 and the negative electrode 30 are electrically isolated, and self-discharge of the battery 100 is suppressed.

[0049] The properties of the electrolyte layer 40 have a significant impact on the damage resistance of the battery 100. This is because, compared to the positive electrode 20 and the negative electrode 30, the electrolyte layer 40 has lower porosity and acts as a support. Carbides derived from the binder remain in the central region 40c of the electrolyte layer 40. These carbides are present at the grain boundaries of the oxide solid electrolyte particles. When an impact is applied to the electrolyte layer 40, the carbides absorb the impact. When bending stress is applied to the electrolyte layer 40, the grain boundaries of the carbides slide, thereby promoting the deformation of the electrolyte layer 40. As a result, the damage resistance of the battery 100 is improved.

[0050] When the battery 100 satisfies at least one of the conditions selected from (a1) and (b1) above, the damage resistance of the battery 100 can be further improved. The reason is as follows. The sintered body serving as the positive electrode 20 is composed of a composite material of an active material and an oxide solid electrolyte. The positive electrode 20 arbitrarily contains a conductive additive. In contrast, the sintered body serving as the electrolyte layer 40, excluding carbides derived from the binder, is composed of an oxide solid electrolyte. Therefore, the porosity of the electrolyte layer 40 is lower than that of the positive electrode 20. As in this embodiment, the residual carbides in the electrolyte layer 40 with low porosity can improve the damage resistance of the battery 100. The starting point of damage to the battery 100 is located in the pores, but the lower the porosity, i.e. the higher the density, the easier it is for the grain boundaries where carbides are present to slide. On the other hand, the higher the porosity, i.e. the lower the density, the less likely it is for the carbides present at the grain boundaries to slide. The porosity of the electrolyte layer 40, the positive electrode 20, and the negative electrode 30 can be calculated using the following method: A cross-section parallel to the thickness direction of the battery 100 is observed using a scanning electron microscope to obtain a SEM image of the cross-section. Image processing is then performed to measure the total number of pixels and the number of pixels corresponding to pores in the SEM image. The ratio of the number of pixels corresponding to pores to the total number of pixels is the porosity.

[0051] The cathode 20 may or may not contain carbides derived from the binder. The binder is contained in the green sheet of the cathode 20 before firing. Most of the binder decomposes and is removed during firing, but carbides as binder residue sometimes remain in the cathode 20 as unavoidable impurities.

[0052] To ensure the required insulation properties of the electrolyte layer 40, the first region 40a has a thickness of, for example, 1 μm or more. There is no particular upper limit to the thickness of the first region 40a, but it can be, for example, 10 μm.

[0053] The battery 100 of this embodiment may also satisfy at least one of the following conditions (a2) and (b2). Condition (a2): The mass ratio M3 of carbides derived from the binder in the negative electrode 30 is lower than the mass ratio M2 of carbides derived from the binder in the central region 40c of the electrolyte layer 40. Condition (b2): When the exponent A is defined as the ratio of the number of grain boundaries containing carbides to the number of grain boundaries appearing in a cross section parallel to the thickness direction of the battery 100, the exponent A of the negative electrode 30 is less than the exponent A of the central region 40c of the electrolyte layer 40. According to this configuration, for the same reasons as the positive electrode 20, the damage resistance of the battery 100 is further improved.

[0054] The electrolyte layer 40 is insulating in the second region 40b. In other words, the electrolyte layer 40 is not electronically conductive in this region. As a result, the positive electrode 20 and the negative electrode 30 are more reliably electrically isolated, and the self-discharge of the battery 100 is suppressed.

[0055] The negative electrode 30 may or may not contain carbides derived from the binder. The binder is contained in the green sheet of the negative electrode 30 before firing. Most of the binder decomposes and is removed during firing, but carbides as binder residue sometimes remain in the negative electrode 30 as unavoidable impurities.

[0056] To ensure the insulation of the electrolyte layer 40, the second region 40b has a thickness of, for example, 1 μm or more. There is no particular upper limit to the thickness of the second region 40b, for example, 10 μm.

[0057] The central region 40c of the electrolyte layer 40 can be any region other than the first region 40a with a thickness of 1μm to 10μm and the second region 40b with a thickness of 1μm to 10μm.

[0058] The mass ratio M2a of carbides derived from the binder in the first region 40a of the electrolyte layer 40 is lower than the mass ratio M2 of carbides derived from the binder in the central region 40c of the electrolyte layer 40. With this configuration, insulation of the electrolyte layer 40 is easily ensured in the first region 40a. The mass ratio M2a of carbides derived from the binder in the first region 40a of the electrolyte layer 40 can also be equal to the mass ratio M1 of carbides derived from the binder in the positive electrode 20.

[0059] The mass ratio M2b of carbides derived from the binder in the second region 40b of the electrolyte layer 40 is lower than the mass ratio M2 of carbides derived from the binder in the central region 40c of the electrolyte layer 40. With this configuration, insulation of the electrolyte layer 40 in the second region 40b is easily ensured. The mass ratio M2b of carbides derived from the binder in the second region 40b of the electrolyte layer 40 can also be equal to the mass ratio M3 of carbides derived from the binder in the negative electrode 30.

[0060] The presence or absence of binder-derived carbides can be determined by observing the grain boundaries between particles of the sintered solid electrolyte and the grain boundaries between the particles of the sintered solid electrolyte and the active material. Binder-derived carbides exist at the grain boundaries with a thickness ranging from a few nm to several tens of nm.

[0061] The insulating nature of the first region 40a of the electrolyte layer 40 can be determined by observing the cross-section of the battery 100 using scanning spread resistance microscopy (SSRM). Specifically, the cross-section of the electrolyte layer 40 corresponding to the first region 40a is observed using SSRM. A histogram is constructed with the current value on the horizontal axis and the number of pixels on the vertical axis, based on the current values ​​in each pixel within the observation field. If a peak is observed only near 0 mA, it can be determined that the electrolyte layer 40 in the first region 40a corresponding to that observation field is insulating but not electronically conductive. The same method can also be used for the second region 40b and the central region 40c.

[0062] Next, the manufacturing method of battery 100 will be described. Figure 3 is a process diagram showing the manufacturing method of battery 100.

[0063] In step S1, a positive electrode green sheet, an electrolyte layer green sheet, and a negative electrode green sheet are prepared.

[0064] The positive electrode green sheet is obtained as follows: a positive electrode slurry is coated onto a substrate to form a coating film, and then the coating film is dried. The positive electrode slurry, for example, includes a positive electrode active material, an oxide solid electrolyte, a conductive additive, a first binder, and a solvent.

[0065] The electrolyte layer green sheet is obtained as follows: an electrolyte slurry is coated onto a substrate to form a coating film, and then the coating film is dried. The electrolyte slurry, for example, contains an oxide solid electrolyte, a second binder, and a solvent.

[0066] The negative electrode green sheet is obtained as follows: a negative electrode slurry is coated onto a substrate to form a coating film, and then the coating film is dried. The negative electrode slurry, for example, contains a negative electrode active material, an oxide solid electrolyte, a conductive additive, a first binder, and a solvent. Using a common binder in both the positive and negative electrode slurries is advantageous in terms of material cost and simplifies temperature management during the firing process.

[0067] As the first and second binders, thermoplastic resins such as polyvinyl butyral (PVB), polyvinylidene fluoride (PVdF), cellulose, acrylics, urethanes, and polyvinyl alcohol (PVA) can be used. Solvents are typically anhydrous alcohols (e.g., anhydrous ethanol), toluene, butyl acetate, NMP, and other organic solvents. Additionally, each slurry may contain a plasticizer. The type of plasticizer is not particularly limited; phthalates such as dioctyl phthalate and diisononyl phthalate can be used.

[0068] In this embodiment, the decomposition temperature of the second binder contained in the electrolyte slurry is higher than the decomposition temperature of the first binder contained in the positive electrode slurry and the negative electrode slurry. By selecting the first binder and the second binder in a manner that satisfies this relationship, the binder can be sufficiently removed from the positive electrode 20 and the negative electrode 30 by adjusting the temperature during firing, while carbides derived from the binder can be intentionally left in the electrolyte layer 40.

[0069] In one example, polyvinyl butyral can be used as the second binder, and acrylic resin can be used as the first binder. The decomposition temperature of polyvinyl butyral is 450℃–500℃. The decomposition temperature of high molecular weight acrylic resins is 350℃–400℃. The decomposition temperature of low molecular weight acrylic resins is 300℃–450℃. The decomposition temperature of the binder is the temperature at which weight loss ends during thermogravimetric analysis (TG) in atmosphere.

[0070] The difference between the decomposition temperature of the first binder and the decomposition temperature of the second binder is, for example, 100°C or more, or even 150°C or more. With this configuration, temperature management during firing is easy. There is no particular upper limit to the difference in decomposition temperatures; for example, it can be 200°C.

[0071] In step S2, the positive electrode green sheet, the electrolyte layer green sheet, and the negative electrode green sheet are stacked to form a laminate. The laminate is an assembly of multiple unburned finished products. By cutting the laminate, a laminate of the corresponding size to each battery 100 is obtained.

[0072] In the case of forming an MLCC (Multi-Layer Ceramic Capacitor) type stack by alternately stacking multiple positive electrode green sheets, multiple electrolyte layer green sheets, and multiple negative electrode green sheets, the stack may include an internal current collector. The internal current collector can be formed by coating the positive electrode green sheets and / or the negative electrode green sheets with a paste containing metals such as Ni and Ag.

[0073] In step S3, the laminate is pre-fired. Pre-firing is a process used to decompose and remove the binder contained in the laminate. During pre-firing, the laminate is heated at a specified binder-removing temperature to remove the first binder from the laminate. The specified binder-removing temperature is a temperature between the decomposition temperature of the first binder and the decomposition temperature of the second binder. When the laminate is fired at such a temperature, the first binder decomposes and is removed from the laminate. As a result, a large number of pores are formed in the positive and negative electrode green sheets. On the other hand, the second binder does not decompose and remains in the electrolyte green sheet. However, near the interface between the positive and electrolyte green sheets, the second binder contained in the electrolyte green sheet is discharged into the pores of the positive electrode green sheet and removed. Similarly, near the interface between the negative and electrolyte green sheets, the second binder contained in the electrolyte green sheet is discharged into the pores of the negative electrode green sheet and removed. As a result, the second binder can remain only in the central region of the electrolyte green sheet.

[0074] The debonding temperature during pre-firing depends on the decomposition temperatures of the first and second binders. Preferably, the debonding temperature during pre-firing is higher than the decomposition temperature of the first binder and lower than the decomposition temperature of the second binder. In one example, the debonding temperature (ambient temperature) during pre-firing is in the range of 250°C to 550°C. The pre-firing time is, for example, 1 hour to 60 hours. Pre-firing is carried out, for example, under atmospheric conditions or an inert atmosphere. The inert atmosphere is, for example, a nitrogen atmosphere or a rare gas atmosphere.

[0075] In step S4, the laminate is subjected to formal firing. During formal firing, the laminate is heated to a temperature higher than the aforementioned binder removal temperature. In one example, the firing temperature (ambient temperature) during formal firing is in the range of 600°C to 800°C. The formal firing time is, for example, 1 hour to 60 hours. Formal firing is performed, for example, in an inert atmosphere. An inert atmosphere is, for example, a nitrogen atmosphere or a rare gas atmosphere. When formal firing is performed under these atmospheres, if binder residue is present in any layer, the binder residue is carbonized, thereby allowing carbides to remain in that layer.

[0076] In step S5, the obtained sintered body is ground to remove burrs. The grinding method is not particularly limited, for example, barrel polishing.

[0077] The battery 100 of this embodiment is obtained through the above processes. According to the manufacturing method described above, carbides derived from the binder can be selectively retained in the central region c of the electrolyte layer 40. Therefore, the mass ratio M1 of carbides derived from the binder in the positive electrode 20 is lower than the mass ratio M2 of carbides derived from the binder in the central region 40c of the electrolyte layer 40. Similarly, the mass ratio M3 of carbides derived from the binder in the negative electrode 30 is lower than the mass ratio M2 of carbides derived from the binder in the central region 40c of the electrolyte layer 40.

[0078] (Other implementation methods)

[0079] (Postscript)

[0080] The following technology has been disclosed in the above description of the embodiments.

[0081] (Technology 1)

[0082] A battery that has the following features:

[0083] Electrode 1;

[0084] The second electrode; and,

[0085] An electrolyte layer disposed between the first electrode and the second electrode in a manner that contacts the first electrode and the second electrode.

[0086] The aforementioned first electrode is a sintered body containing a first active material and a first oxide solid electrolyte.

[0087] The aforementioned electrolyte layer is a sintered body containing a second oxide solid electrolyte, and has a first region including the interface between the aforementioned first electrode and the aforementioned electrolyte layer, and a central region including the center position in the thickness direction, and has insulation in the first region.

[0088] The battery satisfies at least one of the following conditions (a) and (b).

[0089] (a) The mass ratio of carbides derived from the binder in the first electrode is lower than the mass ratio of carbides derived from the binder in the central region of the electrolyte layer.

[0090] (b) When the ratio of the number of carbide-containing grain boundaries to the number of grain boundaries appearing in a cross section parallel to the thickness direction of the aforementioned battery is defined as exponent A, the aforementioned exponent A of the aforementioned first electrode is less than the aforementioned exponent A of the aforementioned central region of the aforementioned electrolyte layer.

[0091] This configuration improves the battery's resistance to damage.

[0092] (Technology 2)

[0093] According to the battery of technology 1, the aforementioned first oxide solid electrolyte and the aforementioned second oxide solid electrolyte comprise lithium-containing phosphate compounds having a NASICON-type structure. Such materials can be sintered at low temperatures, and are therefore suitable for the batteries of this disclosure.

[0094] (Technology 3)

[0095] According to the battery of technology 1 or 2, the aforementioned second electrode is a sintered body comprising a second active material and a third oxide solid electrolyte, wherein the mass ratio of carbides derived from the binder in the aforementioned second electrode is lower than the aforementioned mass ratio of carbides derived from the binder in the aforementioned central region of the aforementioned electrolyte layer. With this configuration, for the same reasons as the first electrode, the battery's resistance to damage is further improved.

[0096] (Technology 4)

[0097] According to the battery of technology 3, the aforementioned electrolyte layer further has a second region comprising the interface between the aforementioned second electrode and the aforementioned electrolyte layer, and the second region is insulating. With this configuration, the first electrode and the second electrode are more reliably electrically isolated, and the self-discharge of the battery is suppressed.

[0098] (Technology 5)

[0099] According to the battery of technology 3 or 4, the aforementioned third oxide solid electrolyte comprises a lithium-containing phosphate compound having a NASICON-type structure. For the same reason as the first electrode, the lithium-containing phosphate compound having a NASICON-type structure is suitable for the second electrode.

[0100] (Technology 6)

[0101] In the battery according to any one of techniques 1 to 5, the porosity of the electrolyte layer is lower than the porosity of the first electrode. With this configuration, the electrolyte layer can function as a support.

[0102] (Technology 7)

[0103] A method for manufacturing a battery, wherein the battery sequentially comprises a first electrode, an electrolyte layer, and a second electrode, the manufacturing method comprising the following steps:

[0104] A laminate comprising a first electrode sheet containing a first active material, a first solid electrolyte, and a first binder, and an electrolyte sheet containing a second solid electrolyte and a second binder is sintered.

[0105] The decomposition temperature of the second adhesive is higher than that of the first adhesive.

[0106] With this configuration, by adjusting the temperature during firing, the binder can be fully removed from the first and second electrodes, while the carbides derived from the binder can be intentionally left in the electrolyte layer.

[0107] (Technology 8)

[0108] According to the battery manufacturing method of Technology 7, the step of firing the aforementioned laminate includes, in the following order: heating the aforementioned laminate at a predetermined debinding temperature; and heating the aforementioned laminate at a temperature higher than the predetermined debinding temperature, wherein the predetermined debinding temperature is a temperature between the decomposition temperature of the first binder and the decomposition temperature of the second binder. With this configuration, the second binder can remain only in the central region of the electrolyte green sheet.

[0109] (Technology 9)

[0110] According to the battery manufacturing method described in technique 7 or 8, the difference between the decomposition temperature of the first binder and the decomposition temperature of the second binder is 100°C or more. With this configuration, temperature management during firing is easy.

[0111] Example

[0112] [Example 1]

[0113] (Preparation of electrode green sheets)

[0114] A mixture powder was prepared by mixing 40 parts by mass of lithium vanadium phosphate (Li3V2(PO4)3), 55 parts by mass of LAGP (amorphous), and 5 parts by mass of acetylene black (manufactured by Denka Company Limited, Li-400). The raw materials were mixed using a gyratory mill (manufactured by Seiwa Giken Co., Ltd., RM-05). The mixture powder was then mixed with a binder solution to prepare a slurry. The slurry was prepared using a rotary mixer (manufactured by THINKY CORPORATION, degassing mixer). The binder solution was prepared by mixing N-methylpyrrolidone and 15 parts by mass of high molecular weight acrylic acid (manufactured by Kyoeisha Chemical Co., Ltd., KC-7000F). The decomposition temperature of high molecular weight acrylic acid in atmosphere is approximately 350°C. The slurry was coated onto a PET film that had undergone a demolding process using a doctor blade to form a coated film. The thickness of the coated film was 200 μm. After the coated film is dried once in the atmosphere at 45°C, it is dried a second time in the atmosphere at 140°C. This yields the electrode green sheet.

[0115] (Preparation of electrolyte green sheets)

[0116] A slurry was prepared by mixing LAGP (amorphous polyvinyl chloride) with a binder solution. The slurry was prepared using a rotary mixer (THINKY CORPORATION, degassing mixer). The binder solution was prepared by mixing N-methylpyrrolidone and 15 parts by mass of polyvinyl butyral (Sekisui Chemicals Co., Ltd., BM-1). The decomposition temperature of polyvinyl butyral is approximately 500°C in atmospheric conditions. The slurry was coated onto a PET film that had undergone a demolding process using a doctor blade to form a coated film. The thickness of the coated film was 100 μm. After a first drying at 45°C in atmospheric conditions, the coated film was then a second drying at 140°C in atmospheric conditions. This yielded an electrolyte green sheet.

[0117] (Creating a layered body)

[0118] One electrode green sheet, one electrolyte green sheet, and two electrode green sheets are stacked sequentially to form a laminate. The laminate is held between 10mm thick SKD steel plates heated to 150℃ and pressurized for 5 minutes at 100MPa using a hydraulic press (Riken Machine Co., Ltd., CDM-5PA).

[0119] (Fabrication of the laminate for discharge experiments)

[0120] The laminate is punched with a φ12mm punch to produce a disc-shaped laminate for discharge testing.

[0121] (Fabrication of laminates for bending tests and drop tests)

[0122] The laminate was cut into dimensions of 6 mm in width and 60 mm in length to produce plate-shaped laminates for bending tests and drop tests.

[0123] (Pre-firing: Debinder)

[0124] The laminated body, which has been processed into a specified shape, is pre-fired in the atmosphere at 450°C for 2 hours.

[0125] (Official firing)

[0126] After pre-firing, the laminate was formally fired in a nitrogen atmosphere at 650°C for 2 hours. This yielded a sintered body for the battery used in evaluation.

[0127] (Install current collectors on the sintered body)

[0128] A 300 nm thick Au film was formed on both sides of the sintered body by sputtering.

[0129] [Example 2]

[0130] The binder for the electrode green sheet was changed to low molecular weight acrylic acid (manufactured by Kyoeisha Chemical Co., Ltd., KC-1700P). Otherwise, the battery (sintered body) of Example 2 was manufactured using the same method as in Example 1. The decomposition temperature of low molecular weight acrylic acid in atmosphere is approximately 300°C.

[0131] [Comparative Example 1]

[0132] The binder for the electrode green sheet was changed to polyvinyl butyral (manufactured by Sekisui Chemicals Co., Ltd., BM-1), and the pre-firing temperature was changed to 500°C. Otherwise, the battery (sintered body) of Comparative Example 1 was manufactured in the same manner as in Example 2.

[0133] [Comparative Example 2]

[0134] The pre-firing temperature was changed to 450°C, and the battery (sintered body) of Comparative Example 2 was made in the same way as Comparative Example 1.

[0135] [Evaluation of carbide content derived from binders]

[0136] The sintered body was cut along its thickness, and the cross-sections of the electrode and electrolyte layers were observed using a transmission electron microscope (TEM). Grain boundaries were determined from the TEM images, and the number of grain boundaries containing carbides was measured using carbon mapping images based on energy-dispersive X-ray analysis (EDX). Based on the following equation (1), an index A was calculated for both the electrode and electrolyte layers as a comparative index of the amount of carbides originating from the binder. The magnitude relationship of the amount of carbides originating from the binder was evaluated by comparing the index A in the electrode with that in the central region of the electrolyte layer. For the central regions of the electrode and electrolyte layers, more than 100 and less than 120 grain boundaries were observed. The “total number of observed grain boundaries” in the following equation (1) refers to the number of grain boundaries observed in the central regions of both the electrode and electrolyte layers. The “number of grain boundaries containing carbides” in the following equation (1) refers to the number of grain boundaries in the central regions of both the electrode and electrolyte layers in which carbon was detected. Then, the index A of the electrode and the index A of the central region of the electrolyte layer were compared, as shown in Table 1. When the difference between the index A of the electrode and the index A of the central region of the electrolyte layer is within 0.10, the amount of carbide contained in the electrode and the central region of the electrolyte layer is considered to be substantially equal, as shown in Table 1 as "electrode = electrolyte layer". When the difference between the index A of the electrode and the index A of the central region of the electrolyte layer is greater than 0.10, the magnitude relationship is shown in Table 1.

[0137] Index A = Number of grain boundaries with carbides / Total number of observed grain boundaries...(1)

[0138] Generally, a "grain boundary" refers to the interface between grains with different crystal orientations. The crystallization state of a sintered body at a grain boundary is irregular. Therefore, when observing a sintered body with TEM, regions with different contrasts can be observed between what appear to be fused grains. These regions can be identified as grain boundaries. It should be noted that the method for observing grain boundaries is not limited to TEM. Other methods, such as electron backscatter diffraction (EBSD), can also be used to observe grain boundaries.

[0139] [Determination of flexural strength]

[0140] The flexural strength of the sintered body was determined according to the three-point bending method specified in JIS R 1601. The results are shown in Table 1.

[0141] [Determination of crack initiation rate]

[0142] A 30mm diameter, 500mm long plastic tube was vertically placed on a 10mm thick stainless steel plate. The sintered body was repeatedly dropped through the tube. The test was conducted by having the short side of the same sintered body collide with the stainless steel plate. After repeating the test 10 times, the presence or absence of visually detectable cracks was confirmed. This test was performed on 100 samples, and the crack incidence rate was calculated. The results are shown in Table 1.

[0143] [Determination of the electronic conductivity of the electrolyte layer]

[0144] Electrodes formed from a single green sheet were used as positive electrodes, and electrodes formed from two green sheets were used as negative electrodes. The electronic conductivity of the electrolyte layer was measured. The sintered bodies of the examples and comparative examples were cut along the thickness direction, and the cross-section of the electrolyte layer was observed using a scanning extended resistance microscope (Bruker Nano Surface, Dimension Icon). The presence or absence of electronic conductivity was examined for the first region on the positive electrode side, the central region, and the second region on the negative electrode side. Specifically, a histogram was constructed using the current values ​​at each pixel within the field of view, with the horizontal axis representing the current value and the vertical axis representing the frequency. Electron conductivity was defined as the presence of a peak observed at a current value greater than 0 mA, except near 0 mA. No electronic conductivity was defined as the presence of a peak observed only near 0 mA. The results are shown in Table 1. The first region on the positive electrode side is the region containing the interface between the positive electrode and the electrolyte layer, with a thickness of 1 μm or more. The second region on the negative electrode side is the region containing the interface between the negative electrode and the electrolyte layer, with a thickness of 1 μm or more.

[0145] [Determination of discharge capacity]

[0146] Electrodes formed from a single green sheet were considered the positive electrode, and electrodes formed from two green sheets were considered the negative electrode. Charge-discharge tests were conducted on the sintered batteries. Charging was performed at 60°C, a current of 7 μA, and a termination voltage of 3.5 V. Discharge was then performed at 60°C, 7 μA, and a termination voltage of 0 V, and the discharge capacity was measured. The discharge capacity of 10 batteries was measured, and their average value was calculated. The results are shown in Table 1.

[0147] [Table 1]

[0148]

[0149] As shown in Table 1, the batteries of Examples 1 and 2 exhibit electronic conductivity in the central region of the electrolyte layer, but not in the first and second regions of the electrolyte layer. The bending strength of the batteries of Examples 1 and 2 is higher than that of the batteries of Comparative Examples 1 and 2. The crack incidence rate of the batteries of Examples 1 and 2 is 0%. The batteries of Examples 1 and 2 show a discharge capacity of 0.70 mAh.

[0150] In the batteries of Examples 1 and 2, the index A of the electrode is less than the index A of the central region of the electrolyte layer. That is, in the batteries of Examples 1 and 2, the mass ratio of carbides derived from the binder in the electrode is lower than the mass ratio of carbides derived from the binder in the central region of the electrolyte layer.

[0151] The battery of Example 2, which uses low molecular weight acrylic resin, has a higher bending strength than the battery of Example 1, which uses high molecular weight acrylic resin.

[0152] The battery of Comparative Example 1 lacks electronic conductivity throughout the entire electrolyte layer. However, the battery of Comparative Example 1 exhibits low flexural strength and a crack incidence rate as high as 5%.

[0153] The flexural strength of the battery in Comparative Example 2 was higher than that of the battery in Comparative Example 1. The crack incidence rate was also reduced to 2%. However, the battery in Comparative Example 2 exhibited electronic conductivity throughout the entire electrolyte layer. Therefore, the discharge capacity of the battery in Comparative Example 2 was as low as 0.50 mAh, which was suspected to be due to a short circuit between the positive and negative electrodes.

[0154] In the batteries of Comparative Examples 1 and 2, the index A of the electrode is equal to the index A of the central region of the electrolyte layer. That is, in the batteries of Comparative Examples 1 and 2, the mass ratio of carbides derived from the binder in the electrode is equal to the mass ratio of carbides derived from the binder in the central region of the electrolyte layer.

[0155] Industrial availability

[0156] The technology disclosed herein is suitable for solid-state batteries.

Claims

1. A battery comprising: Electrode 1; The second electrode; and, An electrolyte layer disposed between the first electrode and the second electrode in a manner that contacts the first electrode and the second electrode. The first electrode is a sintered body containing a first active material and a first oxide solid electrolyte. The electrolyte layer is a sintered body containing a second oxide solid electrolyte, and has a first region containing the interface between the first electrode and the electrolyte layer, and a central region containing the center position in the thickness direction, and is insulating in the first region. The battery satisfies at least one of the following conditions (a) and (b): (a) The mass ratio of carbides derived from the binder in the first electrode is lower than the mass ratio of carbides derived from the binder in the central region of the electrolyte layer; (b) When the ratio of the number of carbide-containing grain boundaries to the number of grain boundaries appearing in a cross section parallel to the thickness direction of the battery is defined as an exponent A, the exponent A of the first electrode is less than the exponent A of the central region of the electrolyte layer.

2. The battery according to claim 1, wherein, The first oxide solid electrolyte and the second oxide solid electrolyte contain lithium-containing phosphoric acid compounds having a NASICON-type structure.

3. The battery according to claim 1, wherein, The second electrode is a sintered body containing a second active material and a third oxide solid electrolyte. The mass ratio of carbides derived from the binder in the second electrode is lower than the mass ratio of carbides derived from the binder in the central region of the electrolyte layer.

4. The battery according to claim 3, wherein, The electrolyte layer also has a second region comprising the interface between the second electrode and the electrolyte layer, and is insulating in the second region.

5. The battery according to claim 3, wherein, The third oxide solid electrolyte contains a lithium-containing phosphoric acid compound with a NASICON-type structure.

6. The battery according to claim 1, wherein, The porosity of the electrolyte layer is lower than that of the first electrode.

7. A method for manufacturing a battery, wherein, The battery sequentially comprises a first electrode, an electrolyte layer, and a second electrode, and the manufacturing method includes the following steps: A laminate comprising a first electrode sheet containing a first active material, a first solid electrolyte, and a first binder, and an electrolyte sheet containing a second solid electrolyte and a second binder is sintered. The decomposition temperature of the second adhesive is higher than that of the first adhesive.

8. The method for manufacturing a battery according to claim 7, wherein, The firing steps for the laminated body are as follows: The step of heating the laminate at a specified binder release temperature; and, The step of heating the laminate at a temperature higher than the temperature of the adhesive remover. The specified debonding temperature is the temperature between the decomposition temperature of the first adhesive and the decomposition temperature of the second adhesive.

9. The method for manufacturing a battery according to claim 7, wherein, The difference between the decomposition temperature of the first adhesive and the decomposition temperature of the second adhesive is 100°C or more.

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