METHOD FOR MANUFACTURING BATTERY

A method for manufacturing a battery includes: a first cutting step of cutting a laminate at a first cutting position to form a first cut surface, the laminate including at least one battery cell having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer; and a second cutting step of cutting the laminate cut in the first cutting step at a second cutting position inside the first cutting position to form a second cut surface. In the second cutting step, Rz1<W <5Rz1 is satisfied, where W denotes a distance between the first cut surface and the second cut surface to be formed and Rz1 denotes a surface roughness of the first cut surface.

BACKGROUND

1. Technical Field

The present disclosure relates to a method for manufacturing battery.

2. Description of the Related Art

Heretofore, there has been known a battery in which current collectors and active material layers are laminated.

For example, Japanese Unexamined Patent Application Publication No. 2020-13729 discloses a battery laminate formed by laminating unit batteries each including a positive current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative current collector layer laminated in this order.

SUMMARY

In order to increase the capacity density of a battery, it is necessary to increase the effective volume contributing to power generation. For this purpose, it is effective to cut a battery cell to remove portions thereof not contributing to power generation. However, when a battery cell is cut, there is a problem that burrs and a shear drop (so-called rollover) of battery constituent elements are generated on the cut surface and are prone to short-circuiting, thereby lowering the operational reliability of the battery. For example, Japanese Unexamined Patent Application Publication No. 2015-76315 discloses a method for manufacturing a battery including measuring a voltage after an edge portion of a battery cell is cut, and cutting the edge portion of the battery cell again in the case where the voltage gradually decreases. However, Japanese Unexamined Patent Application Publication No. 2015-76315 does not disclose a cutting method capable of inhibiting the generation of burrs and rollover on the cut surface.

One non-limiting and exemplary embodiment intends to solve the above problem, and has an object to provide a method for manufacturing a battery capable of achieving both a high capacity density and high reliability of a battery. A method for manufacturing a battery according to one aspect of the present disclosure includes: first cutting of cutting a laminate at a first cutting position to form a first cut surface, the laminate including at least one battery cell having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer; and second cutting of cutting the laminate cut in the first cutting at a second cutting position inside the first cutting position to form a second cut surface, in which Rz1<W<5Rz1is satisfied in the second cutting, where W denotes a distance between the first cut surface and the second cut surface to be formed and Rz1denotes a surface roughness of the first cut surface.

According to the present disclosure, it is possible to achieve both a high capacity density and high reliability of a battery.

DETAILED DESCRIPTIONS

Outline of Present Disclosure

A method for manufacturing a battery according to one aspect of the present disclosure includes: a first cutting step of cutting a laminate at a first cutting position to form a first cut surface, the laminate including at least one battery cell having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer located between the positive electrode layer and the negative electrode layer; and a second cutting step of cutting the laminate cut in the first cutting step at a second cutting position inside the first cutting position to form a second cut surface, in which Rz1<W<5Rz1is satisfied in the second cutting step, where W denotes a distance between the first cut surface and the second cut surface to be formed and Rz1denotes a surface roughness of the first cut surface.

Thus, in the first cutting step and the second cutting step, removal of a portion of a battery not contributing to power generation and the like can be achieved by cutting the laminate, and accordingly the ratio of an effective volume that is a volume contributing to power generation to the battery can be enhanced. In addition, the cutting in the second cutting step under the condition satisfying Rz1<W<5Rz1makes it possible to improve the flatness of the second cut surface, and to reduce the number and size of burrs and rollover of the constituent elements of the laminate generated on the second cut surface and thereby inhibit a short circuit from occurring between the positive electrode layer and the negative electrode layer. Therefore, the method for manufacturing a battery according to the present embodiment leads to achievement of a high capacity density and high reliability of a battery.

In addition, for example, the above W may be less than or equal to three times a thickness of the laminate.

This makes it possible to improve the flatness of the second cut surface and improve the quality of the second cut surface by reducing the generation of burrs and rollover.

Moreover, for example, the first cutting step and the second cutting step may be performed continuously as a series of steps.

This enables continuous cutting of the laminate without inserting another step, thereby improving the productivity.

Further, for example, when the position of the laminate is set as a reference, a first direction in which cutting of the laminate at the first cutting position proceeds may be different from a second direction in which cutting of the laminate at the second cutting position proceeds. For example, the second direction may be a direction perpendicular to the first direction.

In this case, since the laminate can be cut in different cutting directions in the first cutting step and the second cutting step, the laminate can be cut in directions adjusted depending on the quality of the cut surface, the ease of cutting, and the like.

Moreover, for example, the second direction may be a direction perpendicular to a laminating direction of the laminate.

In this case, even when burrs and the like are generated in the second cutting step, the burrs and the like are formed to extend orthogonally to the laminating direction of the laminate. For this reason, the occurrence of a short circuit is inhibited and accordingly the reliability of the battery thus manufactured can be improved.

Moreover, for example, the at least one battery cell may include multiple battery cells and the multiple battery cells may be laminated.

In this case, in the laminate in which the multiple battery cells are laminated, it is possible to inhibit short circuits between the positive electrode layer and the negative electrode layer from occurring between the multiple battery cells and in each battery cell, and also enhance the ratio of the effective volume to the battery. This enables a laminate-type high-capacity high-power battery to achieve both a high capacity density and high reliability.

Moreover, for example, the laminate may be cut by a shearing process in each of the first cutting step and the second cutting step.

In this case, the laminate can be cut only by shearing with a blade and the battery cell rarely deteriorates. Therefore, the productivity and the effective volume of the battery can be enhanced.

In addition, for example, the laminate may be cut with an ultrasonic cutter in the second cutting step. In this case, the flatness of the second cut surface can be further enhanced.

Furthermore, for example, the surface roughness of the second cut surface may be less than or equal to a thickness of the solid electrolyte layer. In addition, for example, the second cut surface may be flat.

In this case, the reliability of the battery can be further enhanced. For example, if the surface roughness of the second cut surface is less than or equal to the thickness of the solid electrolyte layer, the occurrence of a short circuit can be effectively inhibited, because even if a protrusion is formed on one of the positive electrode layer and the negative electrode layer on the second cut surface, the protrusion does not reach the other electrode layer when deformation or the like occurs.

Each of the embodiments to be described below presents a comprehensive or specific example. The numeric values, shapes, materials, constituent elements, layout positions and connection forms of the constituent elements, steps, the order of the steps, and so on described in the following embodiments are just examples and are not intended to limit the present disclosure. Among the constituent elements in the following embodiments, the constituent elements not described in the independent claim are described as optional constituent elements.

The drawings are schematic ones and are not necessarily illustrated exactly. Therefore, for example, the scales and the like are not always consistent among the drawings. Moreover, in the drawings, substantially the same constituent elements are denoted with the same reference signs and the repetitive description will be omitted or simplified.

In the present description, terms indicating relationships between elements such as parallel and perpendicular or orthogonal, terms indicating the shapes of elements such as a rectangle and a circle, and numerical ranges are not expressions specifying strict meanings only, but are expressions meaning substantially the equivalent ranges, for example, including a difference by about several percent.

In the present description and drawings, an x axis, a y axis, and a z axis represent three axes in a three-dimensional Cartesian coordinate system. When a shape in a plan view of a battery is a rectangle, the x axis coincides with a direction parallel to a first side of the rectangle, and the y axis coincides with a direction parallel to a second side orthogonal to the first side. The z axis coincides with a laminating direction of layers in a laminate and a battery.

In the present description, the “laminating direction” coincides with a direction normal to main surfaces of a current collector and an active material layer. In the present description, the “plan view” means a view seen from a direction perpendicular to the main surface of the battery or the laminate unless otherwise specified. However, an expression “a plan view of a certain surface” such as “a plan view of a cut surface” means a view of the “certain surface” seen from the front side.

In the present description, the terms “upper” and “lower” do not refer to an absolutely upper direction (vertically upper side) and an absolutely lower direction (vertically lower side) in a spatial recognition, but are used as terms specified according to a relative positional relationship based on a laminating order in a laminate structure. In addition, terms “above” and “below” are also applied to not only a case where two constituent elements are spaced from each other and another constituent element is present between the two constituent elements, but also a case where two constituent elements are in contact with each other by being closely attached to each other. In the following description, the negative side of the z axis is a “lower side” or “bottom side” and the positive side of the z axis is an “upper side” or “top side”.

Structure

First, a structure of a battery according to Embodiment 1 will be described by usingFIGS.1A and1B.

FIG.1Ais a sectional view illustrating a sectional structure of a battery1according to the present embodiment.FIG.1Bis a top view of the battery1according to the present embodiment.FIG.1Aillustrates a section taken along a IA-IA line inFIG.1B.

First, an outline of the battery1will be described.

As illustrated inFIGS.1A and1B, the battery1according to the present embodiment includes a battery cell10having a positive electrode layer11, a negative electrode layer12, and a solid electrolyte layer13located between the positive electrode layer11and the negative electrode layer12, and includes a positive current collector14and a negative current collector15. The battery1is, for example, an all-solid-state battery. The shape in the plan view of the battery1is a rectangle, for example. The shape of the battery1is, for example, a flat rectangular parallelepiped. The term flat herein means that the thickness (that is, the length in the z axis direction) is smaller than each side of the main surface (that is, the length in each of the x axis direction and the y direction) or the maximum width of the main surface. The shape in the plan view of the battery1may be another quadrangular shape such as a square, a parallelogram, or a rhombus or may be another polygonal shape such as a hexagon or an octagon. The shape of the battery1is, for example, the rectangular parallelepiped, but may be another shape such as a cube, a pyramidal frustum, or a polygonal column. In the present description, the sectional view such asFIG.1Aillustrates the thickness of each layer in an exaggerated manner in order to facilitate understanding of the layer structure of the battery1.

In the plan view of the battery1, the positive current collector14, the positive electrode layer11, the solid electrolyte layer13, the negative electrode layer12, and the negative current collector15have the same shape and the same size and their contours coincide with each other.

The battery1has parallel main surfaces16and17opposed to each other across the battery cell10and four side surfaces connecting the main surfaces16and17. The main surface16is the uppermost surface of the battery1. The main surface17is the lowermost surface of the battery1.

For example, the four side surfaces extend perpendicularly from the respective sides of the main surface17to the main surface16. The four side surfaces of the battery1are, for example, two pairs of side surfaces parallel to each other. Of the two pairs of the side surfaces, one pair of the side surfaces are second cut surfaces120and120aformed in a second cutting step to be described later. At least one side surface of the battery1only has to be the second cut surface. Instead, all the side surfaces of the battery1may be the second cut surfaces from the viewpoint that the capacity density and reliability can be enhanced.

The battery cell10is located between the positive current collector14and the negative current collector15. Although the battery1includes one battery cell10herein, the number of battery cells10is not limited to one but may be equal to or larger than two. For example, the battery according to the present embodiment may be a laminate-type battery in which multiple battery cells10are laminated with at least one of the positive current collector14and the negative current collector15interposed in between.

The battery1is manufactured by cutting an edge portion of a laminate1ato be described later. A laminate structure of the battery1is the same as a laminate structure of the laminate1a.Detailed description of each layer in the battery1will be provided later as description of the laminate1a.

In the battery1according to the present embodiment, a tab or lead, which is an electrode taken out to the outside, may be connected to at least one of the positive current collector14and the negative current collector15. Moreover, in order to keep the battery1airtight and protect the battery1, the battery1may be laminated with an outer package, or the battery1may be resin-sealed. In addition, the second cut surfaces120and120amay be at least partly covered with an insulating member in order to protect the cut surfaces. As the insulating material, a material having at least electrical insulation properties is used and a material also having impact resistance, heat resistance, flexibility and gas barrier properties may be used. As the insulating material, a polymer such, for example, as epoxy resin, acrylic resin, methacrylic resin, aramid resin, or polyimide resin, or an inorganic adhesive material may be used.

Method for Manufacturing a Battery

Next, a method of manufacturing the battery1according to the present embodiment will be described by usingFIGS.2A,2B,3and4.

The method of manufacturing the battery1according to the present embodiment includes, for example, a laminate forming step, a first cutting step, and a second cutting step.

First, the laminate forming step will be described.

FIG.2Ais a sectional view illustrating a sectional structure of the laminate1aaccording to the present embodiment.FIG.2Bis a top view of the laminate1aaccording to the present embodiment.FIG.2Aillustrates a section taken along a IIA-IIA line inFIG.2B. InFIG.2B, dashed lines depict the shape in the plan view of the battery cell10.

The laminate1ais formed in the laminate forming step. As illustrated inFIGS.2A and2B, the laminate1aaccording to the present embodiment includes a battery cell10having a positive electrode layer11, a negative electrode layer12, and a solid electrolyte layer13located between the positive electrode layer11and the negative electrode layer12and includes a positive current collector14and a negative current collector15.

The laminate1ahas parallel main surfaces16aand17aopposed to each other across the battery cell10. The main surface16ais the uppermost surface of the laminate1a.The main surface17ais the lowermost surface of the laminate1a.

The positive electrode layer11is located between the positive current collector14and the solid electrolyte layer13. The positive electrode layer11is arranged in contact with the main surface of the positive current collector14on the negative electrode layer12side. Here, another layer such as a conductive bonding layer may be provided between the positive electrode layer11and the positive current collector14.

The positive electrode layer11contains a positive electrode material such, for example, as a positive electrode active material. Various materials capable of releasing and inserting metal ions such as lithium ions or magnesium ions can be used as materials for the positive electrode active material. When a material capable of releasing and inserting lithium ions is used as the positive electrode active material, it is possible to use a positive electrode active material such, for example, as lithium cobalt composite oxide (LCO), lithium nickel composite oxide (LNO), lithium manganese composite oxide (LMO), lithium-manganese-nickel composite oxide (LMNO), lithium-manganese-cobalt composite oxide (LMCO), lithium-nickel-cobalt composite oxide (LNCO), lithium-nickel-manganese-cobalt composite oxide (LNMCO), or lithium-nickel-cobalt-aluminum composite oxide (LNCAO).

As a material contained in the positive electrode layer11, for example, a solid electrolyte such as an inorganic solid electrolyte may be contained. As the inorganic solid electrolyte, a sulfide solid electrolyte or an oxide solid electrolyte may be used. An example usable as the sulfide solid electrolyte is a mixture of lithium sulfide (Li2S) and diphosphorus pentasulfide (P2S5). In addition, as the sulfide solid electrolyte, it is possible to use a sulfide such as Li2S—SiS2, Li2S—B2S3, or Li2S—GeS2, or to use a sulfide in which at least one of Li3N, LiCl, LiBr, Li3PO4, and Li4SiO4is added as an additive to the above sulfide.

An example usable as the oxide solid electrolyte is Li7La3Zr2O12(LLZ), Li1.3Al0.3Ti1.7(PO4)3(LATP), (La,Li)TiO3(LLTO), or the like.

The surface of the positive electrode active material may be coated with a solid electrolyte.

As a material contained in the positive electrode layer11, at least one of conductive materials such, for example, as acetylene black, ketjenblack (registered trademark), and carbon nanofiber, binding binders such, for example, as polyvinylidene fluoride, and the like may be contained.

For example, the positive electrode layer11is produced by applying a paste-like paint in which the materials contained in the positive electrode layer11are kneaded together with a solvent onto the main surface of the positive current collector14and drying the paint. In order to increase the density of the positive electrode layer11, the positive electrode layer11applied on the positive current collector14and also called a positive electrode plate may be pressed after drying. The thickness of the positive electrode layer11is, for example, greater than or equal to 5 μm and less than or equal to 300 μm, but is not limited to this range.

The negative electrode layer12is located between the negative current collector15and the solid electrolyte layer13. The negative electrode layer12is arranged in contact with the main surface of the negative current collector15on the positive electrode layer11side. The negative electrode layer12is arranged opposed to the positive electrode layer11. Here, another layer such as a conductive bonding layer may be provided between the negative electrode layer12and the negative current collector15.

The negative electrode layer12contains, for example, a negative electrode active material as an electrode material. Various materials capable of releasing and inserting ions such as lithium ions or magnesium ions can be used as materials for the negative electrode active material. When a material capable of releasing and inserting lithium ions is used as a negative electrode active material contained in the negative electrode layer12, it is possible to use a negative electrode active material such, for example, as a single material such as graphite, metallic lithium, or silicon, a mixture of them, or lithium-titanium oxide (LTO).

As a material contained in the negative electrode layer12, for example, a solid electrolyte such as an inorganic solid electrolyte may be contained. As the inorganic solid electrolyte, for example, the inorganic solid electrolytes listed as the examples of the material contained in the positive electrode layer11may be used.

As a material contained in the negative electrode layer12, at least one of conductive materials such, for example, as acetylene black, ketjenblack, and carbon nanofiber, binding binders such, for example, as polyvinylidene fluoride, and the like may be contained.

For example, the negative electrode layer12is produced by applying a paste-like paint in which the materials contained in the negative electrode layer12are kneaded together with a solvent onto the main surface of the negative current collector15and drying the paint. In order to increase the density of the negative electrode layers12, the negative electrode layers12applied on the negative current collector15and also called a negative electrode plate may be pressed after drying. The thickness of the negative electrode layer12is, for example, greater than or equal to 5 μm and less than or equal to 300 μm, but is not limited to this range.

The positive electrode layer11is in contact with the main surface of the positive current collector14. The positive current collector14may include a current collector layer that is a layer containing a conductive material and provided on a portion to be in contact with the positive electrode layer11. The negative electrode layer12is in contact with the main surface of the negative current collector15. The negative current collector15may include a current collector layer that is a layer containing a conductive material and provided on a portion to be in contact with the negative electrode layer12.

Each of the positive current collector14and the negative current collector15is a conductive member in the form of a foil, a plate, or a mesh. Each of the positive current collector14and the negative current collector15may be, for example, a conductive thin film. As a material for constituting the positive current collector14and the negative current collector15, a metal such, for example, as stainless steel (SUS), aluminum (Al), copper (Cu), or nickel (Ni) may be used. The positive current collector14and the negative current collector15may be formed by using different materials.

The thickness of each of the positive current collector14and the negative current collector15is, for example, greater than or equal to 5 μm and less than or equal to 100 μm, but is not limited to this range.

The solid electrolyte layer13is located between the positive electrode layer11and the negative electrode layer12. The solid electrolyte layer13is in contact with both the positive electrode layer11and the negative electrode layer12. The solid electrolyte layer13is a layer containing an electrolyte material. As the electrolyte material, generally known electrolytes for battery may be used. The thickness of the solid electrolyte layer13may be greater than or equal to 5 μm and less than or equal to 300 μm or may be greater than or equal to 5 μm and less than or equal to 100 μm.

The solid electrolyte layer13contains a solid electrolyte. As the solid electrolyte, a solid electrolyte such, for example, as an inorganic solid electrolyte may be used. As the inorganic solid electrolyte, the inorganic solid electrolytes listed as the examples of the material contained in the positive electrode layer11may be used.

The solid electrolyte layer13may contain a binding binder such, for example, as polyvinylidene fluoride or the like in addition to the electrolyte material.

For example, the solid electrolyte layer13is produced by applying a paste-like paint in which the materials contained in the solid electrolyte layer13are kneaded together with a solvent onto the main surfaces of the positive electrode layer11and/or the negative electrode layer12and drying the paint. Instead, the solid electrolyte layer13may be formed by applying the paste-like paint onto a release film and drying the paste.

For example, the laminate1ais manufactured by laminating the positive current collector14, the positive electrode layer11, the solid electrolyte layer13, the negative electrode layer12, and the negative current collector15in this order and pressure-bonding them. As the pressurizing method, for example, a plate press, a roll press, or an isostatic press may be used. Moreover, from the viewpoint of improvement of the adhesion and density of each layer, heating may be performed during pressurization. The heating temperature may be set within a range where the materials of all the layers will not undergo a chemical change due to heat, and is, for example, higher than or equal to 60° C. and lower than or equal to 200° C.

In the present embodiment, the positive electrode layer11, the negative electrode layer12, and the solid electrolyte layer13are maintained in the forms of parallel flat plates. This makes it possible to inhibit the occurrence of a crack or collapse due to bending. Instead, the positive electrode layer11, the negative electrode layer12, and the solid electrolyte layer13may be smoothly curved all together.

The battery cell10is structured such that the side surfaces of the positive electrode layer11, the negative electrode layer12, and the solid electrolyte layer13are provided flush with each other, but is not limited to this. For example, in the plan view, the side surfaces of the positive electrode layer11, the negative electrode layer12, and the solid electrolyte layer13may be located at different positions. Instead, for example, the battery cell10may be structured such that the side surface of at least one of the positive electrode layer11and the negative electrode layer12is covered with the solid electrolyte layer13and the solid electrolyte layer13is in contact with at least one of the positive current collector14and the negative current collector15.

In the laminate1a,for example, the main surface of the positive current collector14on the battery cell10side includes a portion not provided with the positive electrode layer11. In addition, in the laminate1a,for example, the main surface of the negative current collector15on the battery cell10side includes a portion not provided with the negative electrode layer12. Although the regions on the current collectors incapable of functioning as a battery due to the absence of the positive electrode layer11and the negative electrode layer12are present in the laminate1a,the capacity density of the battery1can be enhanced by cutting off the edge portions of the laminate1aas will be described later. Here, the solid electrolyte layer13may be in contact with at least one of the portion of the positive current collector14not provided with the positive electrode layer11and the portion of the negative current collector15not provided with the negative electrode layer12.

Next, the first cutting step and the second cutting step will be described.

FIG.3is a sectional view for explaining a method of manufacturing the battery1according to the present embodiment.

In the first cutting step, as illustrated inFIG.3(a), the laminate1aformed in the laminate forming step is cut at first cutting positions111and111adepicted with dashed lines in the drawing, thereby forming first cut surfaces110and110a.As a result, a laminate1billustrated inFIG.3(b)is formed. The first cut surfaces110and110aare side surfaces connecting a main surface16band a main surface17bin the laminate1b.

In the first cutting step, for example, the laminate1ais cut at the first cutting position111passing the positive electrode layer11, the negative electrode layer12, and the solid electrolyte layer13in the battery cell10. Specifically, in the first cutting step, as illustrated inFIGS.3(a) and3(b), the planar first cut surface110is formed by collectively cutting all the constituent elements of the laminate1a,namely, the positive electrode layer11, the negative electrode layer12, the solid electrolyte layer13, the positive current collector14, and the negative current collector15. The first cutting position111is a position passing the two main surfaces16aand17aof the laminate1a.The direction in which the first cut surface110extends is not particularly limited. For example, the first cut surface110may be orthogonal to the main surfaces16aand17a.

The first cutting position111is not particularly limited. The first cutting position111may be a position for cutting off an edge portion of the laminate1aor a position for dividing the laminate1ainto multiple laminates.

An example of a usable cutting method in the first cutting step is, but is not limited to, shearing with a blade, cutting with an end mill, grinding, laser cutting, jet cutting, or the like. From the viewpoint of improvement of the productivity and the effective volume, the cutting method in the first cutting step may be a shearing process of shearing with a blade or the like.

In the first cutting step, for example, when the position of the laminate1ais used as a reference, the cutting proceeds at the first cutting position111along a first direction C10that is a fixed direction. In the case of the shearing process using a blade, for example, the direction in which the cutting proceeds is a direction in which the blade moves relative to the laminate1ain the plan view of the first cut surface110to be formed. The first direction C10is, for example, a direction orthogonal to the main surfaces16aand17ain the plan view of the first cut surface110, in other words, a direction parallel to the laminating direction of the laminate1a.Thus, it is possible to cut the laminate1aalong the direction connecting the main surface16aand the main surface17aat the shortest distance, thereby improving the productivity of the battery1. The first direction C10is not particularly limited, and may be a direction crossing the direction orthogonal to the main surfaces16aand17a.

Next, in the second cutting step, as illustrated inFIG.3(b), the laminate1bformed in the first cutting step is cut at second cutting positions121and121adepicted with dashed lines in the drawing, thereby forming second cut surfaces120and120a.The second cutting positions121and121aare located inside the first cut surfaces110and110aand at distances W and Wa from the first cut surfaces110and110a,respectively. As a result, the battery1illustrated inFIG.3(c)is formed.

In the second cutting step, as illustrated inFIGS.3(b) and3(c), the planar second cut surface120is formed by cutting the laminate1bat the second cutting position121located at the distance W inside from the first cut surface110. The distance W is a distance between the first cut surface110and the second cut surface120to be formed. Since the second cut surface120is formed at the second cutting position121, the distance W may be rephrased as a distance between the first cut surface110and the second cutting position121. The second cutting position121is a position not passing the first cut surface110. The first cut surface110and the second cut surface120(in other words, the second cutting position121) may be parallel to each other. In this case, since the distance between the first cut surface110and the second cutting position121is constant, the quality of the second cut surface can be stabilized and the volume cut off in the second cutting step can be reduced.

In the second cutting step, for example, the second cut surface120is formed by collectively cutting all the constituent elements of the laminate1b,namely, the positive electrode layer11, the negative electrode layer12, the solid electrolyte layer13, the positive current collector14, and the negative current collector15as in the first cutting step. The second cutting position121is a position passing the two main surfaces16band17bof the laminate1b.

The second cutting position121is close to the first cut surface110. In the second cutting step, a relationship between the surface roughness Rz1of the first cut surface110and the distance W satisfies Rz1<W<5Rz1. For example, in the second cutting step, the laminate1bis cut with the second cutting position121set to a position located at the distance W having the above relationship inside from the upper end side of the first cut surface110. When the distance W is less than or equal to the surface roughness Rz1of the first cut surface110, there is a risk that burrs and the like present on the surface of the first cut surface110cannot be fully removed. When the distance W is greater than or equal to five times the surface roughness Rz1of the first cut surface110, it is difficult to make the surface roughness Rz2of the second cut surface120small and obtain the effects of the present disclosure. The relationship between the surface roughness Rz1of the first cut surface110and the distance W satisfies Rz1<W<5Rz1, for example, at any position. In the present description, the surface roughness such as the surface roughness Rz1is a maximum surface roughness measured by a method in conformity to JIS B0601 2013.

In addition, the relationship between the surface roughness Rz1of the first cut surface110and the distance W may satisfy Rz1<W<4Rz1from the viewpoint of improvement of the flatness of the second cut surface.

Moreover, the distance W between the first cut surface110and the second cutting position121may be less than or equal to three times or two times the thickness of the laminate1b.This makes it possible to more effectively make the surface roughness Rz2of the second cut surface120small.

Further, for example, the second cut surface120is orthogonal to the main surfaces16band17bof the laminate1b.In this case, the positions of the end surfaces of the respective layers of the battery1exposed at the second cut surface120are aligned when viewed from the laminating direction, so that the effective volume of the battery can be increased. For example, in the second cut surface120, the side surfaces of the positive electrode layer11, the negative electrode layer12, the solid electrolyte layer13, the positive current collector14, and the negative current collector15of the battery1are exposed to be flush with each other. Moreover, for example, when viewed from the laminating direction of the battery1, the positions of the side surfaces of the positive electrode layer11, the negative electrode layer12, the solid electrolyte layer13, the positive current collector14, and the negative current collector15coincide with each other in the second cut surface120.

An example of a usable cutting method in the second cutting step is, but is not limited to, shearing with a blade, cutting with an end mill, grinding, laser cutting, jet cutting, or the like. From the viewpoint of improvement of the productivity and the effective volume, the cutting method in the second cutting step may be the shearing process of shearing with a blade or the like. In the shearing process, the temperature of the laminate1bhardly rises during cutting and accordingly the battery cell10rarely deteriorates during cutting. Moreover, from the viewpoint that the flatness of the second cut surface120can be improved, the shearing process may be cutting with an ultrasonic cutter that cuts by transmitting high-frequency vibration to the cutting edge.

In the second cutting step, for example, when the position of the laminate1bis used as a reference, the cutting proceeds at the second cutting position121along a second direction C20that is a fixed direction. In the case of the shearing process using a blade, for example, the direction in which the cutting proceeds is a direction in which the blade moves relative to the laminate1bin the plan view of the second cut surface120to be formed as in the first direction C10. For example, the second direction C20is a direction orthogonal to the main surfaces16band17bin the plan view of the second cut surface120. Thus, the second direction C20is parallel to and the same as the first direction C10. As a result, it is possible to cut the laminate1balong the direction connecting the main surface16band the main surface17bat the shortest distance, thereby improving the productivity of the battery1. In the case of a comparison of a relationship between the first direction C10and the second direction C20, the comparison is made on the assumption that the first cutting position111and the second cutting position121are parallel to each other even when the first cutting position111and the second cutting position121are not parallel to each other.

The second direction C20is not particularly limited, and the positional relationship between the first direction C10and the second direction C20is not limited to being parallel.FIG.4is a top view for explaining another example of the second direction in the second cutting step. As illustrated inFIG.4, the first direction C10and a second direction C21are not parallel but are different directions. Specifically, the second direction C21is a direction perpendicular to the first direction C10, and is a direction perpendicular to the laminating direction of the laminate1b(for example, a longitudinal direction of the first cut surface110). With the first direction C10and the second direction C21as described above, the first cutting position111in the first cutting step is easily set at a certain position of the laminate1a.In addition, the direction in which the cutting proceeds in the second cutting step is orthogonal to the laminating direction of the laminate1b.For this reason, even if burrs and the like are generated by cutting, the burrs and the like are formed so as to extend orthogonally to the laminating direction. As a result, the occurrence of a short circuit between the layers of the laminate1bcan be inhibited and the reliability of the battery1can be improved. The case where the first direction C10and the second direction C21are different directions is not limited to the aforementioned example. With the first direction C10and the second direction C21different from each other, the laminate1aand the laminate1bcan be cut in directions adjusted depending on the quality of the cut surface, the ease of cutting, and the like in the first cutting step and the second cutting step.

The surface roughness Rz2of the second cut surface120may be, for example, greater than 0 and less than or equal to the thickness of the solid electrolyte layer13. When the surface roughness Rz2of the second cut surface120is less than or equal to the thickness of the solid electrolyte layer13, the occurrence of a short circuit can be effectively inhibited. This is because, even if a protrusion is formed on one of the positive electrode layer11and the negative electrode layer12on the second cut surface120, the protrusion does not reach the other electrode layer when deformation or the like occurs.

In addition, the surface roughness Rz2of the second cut surface120may be less than the thickness of the solid electrolyte layer13.

The surface roughness Rz2of the second cut surface120may be less than or equal to 30 μm or be less than or equal to 20 μm. Moreover, the second cut surface120may be flat. In this case, the reliability of the battery1can be enhanced. In the present description, to be flat means to be substantially flat and means that the surface roughness Rz2is, for example, less than or equal to 10 μm.

Moreover, the first cutting step and the second cutting step may be performed continuously as a series of steps. This enhances the productivity. To perform continuously as a series of steps herein means to perform the first cutting step and the second cutting step without inserting execution of another step such as processing or measurement of the laminate1abetween the first cutting step and the second cutting step. For example, the laminate1amay be fixed for cutting in the first cutting step, and then the second cutting step may be performed while the resultant laminate is kept fixed after the cutting of the laminate1a.In addition, the first cutting step and the second cutting step may be performed with cutting devices on a continuous manufacturing line. The second cutting step may be performed within one minute after the end of the first cutting step.

Through the steps as described above, the battery1having the second cut surfaces120and120aas illustrated inFIG.3(c)is manufactured.

In the above description, the formation of the first cut surface110and the second cut surfaces120has been mainly described. Since the same applies to the first cut surface110aand the second cut surface120a,the detailed description thereof is omitted herein. Then, in the present embodiment, both the number of the first cut surfaces and the number of the second cut surfaces are two, but are not limited to two and each may be at least equal to or larger than one. In other words, at least one of the side surfaces of the battery1according to the present embodiment only has to be the second cut surface. All the side surfaces of the battery1may be the second cut surfaces from the viewpoint of further improvement of the capacity density and the reliability.

According to the method of manufacturing the battery1according to the present embodiment, the first cutting step of forming the first cut surface110and the second cutting step of forming the second cut surface120at the second cutting position121close to the first cut surface110are performed. This enables removal of the portions of the battery1not contributing to power generation and the like, and accordingly an increase in the ratio of the effective volume, which is a volume contributing to power generation, to the battery1. Moreover, with the relationship between the surface roughness Rz1of the first cut surface110and the distance W satisfying Rz1<W<5Rz1in the second cutting step, the portion near the first cut surface110susceptible to formation of burrs and rollover formed in the first cutting step is cut off, so that the battery1having the second cut surface120that has few burrs and rollover and is flatter than the first cut surface110can be manufactured. As a result, the high capacity density and high reliability of the battery1can be both achieved.

Next, a method for manufacturing a battery according to Embodiment 2 will be described. Embodiment 2 is different from Embodiment 1 in the number of battery cells included in a laminate. In the following description, different points will be described, and the description of the common points will be omitted or simplified.

FIG.5is a sectional view illustrating a sectional structure of a laminate2aaccording to the present embodiment. In the present embodiment, the laminate2ais formed in the laminate forming step and the laminate2ais cut in the first cutting step. As illustrated inFIG.5, the laminate2aincludes multiple battery cells10, a positive current collector14, and a negative current collector15. The multiple battery cells10are laminated such that the neighboring battery cells10are electrically connected to each other via the current collector. In the laminate2a,negative electrode layers12are arranged on the upper and lower main surfaces of the negative current collector15. In other words, the multiple battery cells10are laminated to be electrically connected in parallel by electrically connecting the same-polarity electrodes of the neighboring battery cells10via the current collector. Therefore, the laminating order is reversed between the neighboring battery cells10. Each battery cell10is sandwiched between the positive current collector14and the negative current collector15without another battery cell10interposed.

The negative electrode layers12are produced by applying a paste-like paint in which the materials contained in the negative electrode layers12are kneaded together with a solvent onto both main surfaces of the negative current collector15and drying the paint. In order to increase the density of the negative electrode layers12, the negative electrode layers12applied on the negative current collector15and also called negative electrode plates may be pressed after drying.

The solid electrolyte layers13and the positive electrode layers11are manufactured in the same methods as in Embodiment 1. Then, the laminate2ais pressure-bonded in the same method as in Embodiment 1.

The laminate2amay have a structure in which the positions of the negative electrode layers12and the positive electrode layers11are exchanged. The number of battery cells10in the laminate2ais two, but may be equal to or larger than three. For example, the number of multiple battery cells10can be increased by laminating the battery cells10with the positive electrode layers11arranged also on both surfaces of the positive current collector14. Moreover, in the laminate2a,the multiple battery cells10may be laminated to be electrically connected in series by electrically connecting the opposite-polarity electrodes of the neighboring battery cells10via the current collector. In this case, the positive electrode layer11is arranged on one of the main surfaces of at least one positive current collector14or negative current collector15and the negative electrode layer12is arranged on the other main surface.

In addition, in the case where the multiple battery cells10are laminated, the battery cells10may be laminated with a conductive layer interposed in between.FIG.6is a sectional view illustrating a sectional structure of a laminate3aaccording to the present embodiment. In the present embodiment, the laminate3amay be cut in the first cutting step.

As illustrated inFIG.6, the laminate3aincludes multiple laminates1aeach having a battery cell10and a conductive layer31. The multiple laminates1aare laminated such that the neighboring laminates1aare electrically connected to each other via the conductive layer31. In other words, the conductive layer31is located between the neighboring laminates1aamong the multiple laminates1a.In the laminate3a,the positive current collector14is arranged on one of the main surfaces of the conductive layer31and the negative current collector15is arranged on the other main surface. More specifically, in the laminate3a,the multiple battery cells10are laminated to be electrically connected in series by electrically connecting the opposite-polarity electrodes of the neighboring battery cells10via the positive current collector14, the negative current collector15, and the conductive layer31. Therefore, the multiple laminates1ahave the same laminating order.

A material for the conductive layer31is not particularly limited and, for example, a conductive adhesive agent having an electric conductivity and adhesiveness may be used. An example usable as the conductive adhesive agent is a mixture of metal particles and resin, a conductive polymer, or a metal with a low melting point. Instead, the laminate3adoes not have to include the conductive layer31, and the positive current collector14and the negative current collector15may be directly joined between the neighboring laminates1a.

For example, the laminate3ais produced by applying a conductive adhesive agent as a material for the conductive layer31onto the positive current collector14or the negative current collector15of the laminate1aformed in the above method and joining the two laminates1avia the conductive adhesive agent.

The number of the multiple laminates1ain the laminate3ais two, but may be equal to or larger than three. The number of the multiple laminates1ain the laminate3acan be adjusted by increasing the number of the laminates1aand the conductive layers31joined. Instead, in the laminate3a,the multiple battery cells10may be laminated to be electrically connected in parallel by electrically connecting the same-polarity electrodes of the neighboring battery cells10via the positive current collector14or the negative current collector15and the conductive layer31.

A laminate-type battery having a structure in which multiple battery cells10are laminated can be manufactured by performing the first cutting step and the second cutting step using the laminate2aor the laminate3athus produced.

FIG.7is a sectional view for explaining a method for manufacturing a battery according to the present embodiment. As illustrated inFIG.7, in the first cutting step, the laminate2ais cut at first cutting positions211and211adepicted with dashed lines in the drawing, thereby forming the first cut surfaces. Next, in the second cutting step, the cut laminate2ais further cut at second cutting positions221and221alocated inside the first cut surfaces and depicted with dashed lines in the drawing, thereby forming the second cut surfaces. In this case, all the multiple battery cells10included in the laminate2aare collectively cut in the first cutting step and the second cutting step. The details of the first cutting step and the second cutting step are as described in Embodiment 1. When a battery is manufactured through the same first cutting step and second cutting step as described above, the laminate-type battery thus manufactured can achieve both high capacity density and high reliability. Also, in the case of using the laminate3a,the laminate-type battery thus manufactured can achieve both high capacity density and high reliability as well.

EXAMPLES

Hereinafter, the details of the present disclosure will be specifically described based on Examples. However, the present disclosure should not be limited at all to Examples described below.

Production of Laminates for Evaluation

A positive electrode plate having a positive electrode layer was produced by mixing a lithium cobaltate powder as a positive electrode active material, a mixture of lithium sulfide and diphosphorus pentasulfide as a solid electrolyte, and a xylene solvent to form a slurry, applying the slurry onto an aluminum foil having a thickness of 12 μm as a positive current collector, and drying the slurry.

In addition, a negative electrode plate having a negative electrode layer was produced by mixing a graphite powder as a negative electrode active material and the same solid electrolyte and xylene solvent as the above to form a slurry, applying the slurry to a stainless steel foil having a thickness of 15 μm as a negative current collector, and drying the slurry.

Next, a solid electrolyte layer was produced by mixing the same solid electrolyte and xylene solvent as the above to form a slurry, applying the slurry onto the negative electrode layer, and drying the slurry. Then, the positive electrode plate and the negative electrode plate were laminated with the solid electrolyte layer on the negative electrode layer interposed in between and were pressurized under the condition with heating at 120° C., thereby producing a laminate. The thickness of the laminate at this time was 150 μm. The thickness of the solid electrolyte layer was 30 μm.

The produced laminate was cut with a shear to form a first cut surface. The surface roughness Rz1of the first cut surface was measured by using a laser microscope (manufactured by Keyence Corporation). The surface roughness Rz1of the first cut surface thus formed was 84 μm.

Further, the laminate with the first cut surface formed was divided into 15 pieces by cutting in a direction orthogonal to the first cut surface, and thus 15 laminates for evaluation in about 15 mm squares each having the divided first cut surface were obtained.

Next, the laminate for evaluation was cut by using an ultrasonic cutter at a second cutting position 100 μm inside from the first cut surface to form a second cut surface, and thereby a battery with the second cut surface formed was obtained. In other words, the aforementioned second cutting step was performed under the condition where the distance W between the first cut surface and the second cut surface to be formed was 100 μm. The same operation was repeated three times by using different laminates for evaluation to produce three batteries.

The surface roughness Rz2of the second cut surface of each of the produced batteries was measured by using a laser microscope (manufactured by Keyence Corporation). In addition, whether a short circuit occurred in each of the produced batteries was evaluated by measuring a potential difference between the positive electrode layer and the negative electrode layer in the battery with a tester. Table 1 presents the measurement result of the surface roughness Rz2of the second cut surface and the short circuit evaluation result. In Table 1, the surface roughness Rz2of the second cut surface is an average value of the three batteries. In Table 1, a short circuit count is the number of batteries in which short circuits were observed among the three batteries. Table 1 also presents the surface roughness Rz1of the first cut surface, the distance W, W/Rz1, and W/T where T denotes the thickness of the laminate for evaluation.

As presented in Table 1, in the batteries in Example 1, the surface roughness Rz2of the second cut surface was 9 μm and the short circuit count was 0.

Batteries were produced in the same method as in Example 1 except that the distance W was changed to 200 μm. In addition, the measurement of the surface roughness Rz2of the second cut surface and the short circuit evaluation for the batteries produced were made in the same method as in Example 1. Table 1 presents the measurement result of the surface roughness Rz2of the second cut surface and the short circuit evaluation result. As presented in Table 1, in the batteries in Example 2, the surface roughness Rz2of the second cut surface was 6 μm and the short circuit count was 0.

Batteries were produced in the same method as in Example 1 except that the distance W was changed to 300 μm. In addition, the measurement of the surface roughness Rz2of the second cut surface and the short circuit evaluation for the batteries produced were made in the same method as in Example 1. Table 1 presents the measurement result of the surface roughness Rz2of the second cut surface and the short circuit evaluation result. As presented in Table 1, in the batteries in Example 3, the surface roughness Rz2of the second cut surface was 10 μm and the short circuit count was 0.

Batteries were produced in the same method as in Example 1 except that the distance W was changed to 400 μm. In addition, the measurement of the surface roughness Rz2of the second cut surface and the short circuit evaluation for the batteries produced were made in the same method as in Example 1. Table 1 presents the measurement result of the surface roughness Rz2of the second cut surface and the short circuit evaluation result. As presented in Table 1, in the batteries in Example 4, the surface roughness Rz2of the second cut surface was 18 μm and the short circuit count was 0.

Comparative Example 1

Batteries were produced in the same method as in Example 1 except that the distance W was changed to 500 μm. In addition, the measurement of the surface roughness Rz2of the second cut surface and the short circuit evaluation for the batteries produced were made in the same method as in Example 1. Table 1 presents the measurement result of the surface roughness Rz2of the second cut surface and the short circuit evaluation result. As presented in Table 1, in the batteries in Comparative Example 1, the surface roughness Rz2of the second cut surface was 55 μm and the short circuit count was 2.

Summary

As presented above, it was found that the batteries in Examples 1 to 4 in which the second cut surfaces were formed under the condition satisfying W/Rz1greater than 1 and less than 5, that is, Rz1<W<5Rz1had the small surface roughness Rz2of the second cut surface of less than or equal to the thickness of the solid electrolyte layer and did not cause a short circuit, and thus had an ability to achieve high reliability. In this case, the distance W is less than or equal to three times the thickness T of the laminate for evaluation.

In addition, it was found that the batteries in Examples 1 to 3 in which the second cut surfaces were formed under the condition satisfying W/Rz1greater than 1 and less than 4, that is, Rz1<W<4Rz1had the surface roughness Rz2of the second cut surface of less than or equal to 10 μm and thus had an ability to achieve especially high reliability because the substantially flat second cut surfaces were formed. In this case, the distance W is less than or equal to two times the thickness T of the laminate for evaluation.

In contrast, in the batteries in Comparative Example 1 in which the second cut surfaces were formed under the condition having W/Rz1of greater than or equal to 5, that is, not satisfying Rz1<W<5Rz1, the surface roughness Rz2of the second cut surface was greater than in the batteries in Examples 1 to 4, and the short circuits occurred. Thus, it was found that the production condition of the batteries in Comparative Example 1 led to decreased reliability of the batteries as compared with Examples 1 to 4. As described above, it was confirmed that the reliability of the batteries may not be enhanced only by simply cutting the laminates for evaluation two times, but the reliability of the batteries can be enhanced by performing the second cutting under the condition satisfying Rz1<W<5Rz1.

Other Embodiments

Although the battery and method for manufacturing a battery according to the present disclosure have been described heretofore based on Embodiments and Examples, the present disclosure should not be limited to these Embodiments and Examples. The scope of the present disclosure includes various modifications of the embodiments conceivable by those skilled in the art and other modes constructed by combining some of the constituent elements in the embodiments, without departing from the gist of the present disclosure.

Further, in the foregoing embodiments, various changes, replacements, additions, omissions, or the like can be made within the scope of claims or the scope of the equivalents thereof.

Batteries according to the present disclosure are usable, for example, as batteries for electronic devices, electric appliance devices, electric vehicles, and the like.