Electrode plates and coin-type secondary batteries

Abstract

Disclosed is a positive electrode plate which comprises a positive electrode collector and an active material layer arranged on the positive electrode collector. The positive electrode collector comprises a plurality of repeating units that are aligned in a row, and an active material layer is arranged on each of the plurality of repeating units. The positive electrode collector has an outer edge which, at a boundary portion between two adjacent repeating units, has a shape that protrudes toward the inside of the boundary part and is composed of a smooth line. Each one of the plurality of repeating units has a generally circular shape or a generally polygonal shape.

Description

[Technical field]

[0001] The present disclosure relates to an electrode plate and a coin-type secondary battery. [Background technology]

[0002] Flat secondary batteries have been used as power sources for various electronic devices. Examples of flat secondary batteries include batteries using a wound electrode group and batteries using a zigzag folded electrode group. A wound electrode group is formed by sandwiching a separator between a positive electrode plate and a negative electrode plate and winding them. A battery using a zigzag folded electrode group is disclosed in, for example, Patent Document 1.

[0003] Patent Document 1 discloses an example in which a positive electrode plate and a negative electrode plate are arranged so that their extension directions are shifted by 90°, and then folded to form an electrode group (see FIG. 2 of Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-76329 A Summary of the Invention

[0005] In the field of batteries, improving yield is important. One of the objects of the present disclosure is to provide an electrode plate that enables batteries to be manufactured with high yield, and a coin-type secondary battery that can be manufactured with high yield.

[0006] One aspect of the present disclosure relates to an electrode plate including a current collector and an active material layer disposed on the current collector, the current collector including a number of repeat units aligned in a row, the active material layer disposed on each of the repeat units, an outer edge of a boundary between two adjacent repeat units among the outer edges of the current collector has a convex shape toward the inside of the boundary and is formed by a smooth line, and each of the repeat units is substantially circular or substantially polygonal.

[0007] Another aspect of the present disclosure relates to a coin-type secondary battery, the coin-type secondary battery including a coin-shaped case and a positive electrode plate and a negative electrode plate disposed in the case, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, the positive electrode current collector includes a plurality of repeat units A aligned in a row, the negative electrode current collector includes a plurality of repeat units B aligned in a row, the positive electrode active material layer is disposed on each of the plurality of repeat units A, the negative electrode active material layer is disposed on each of the plurality of repeat units B, and the positive electrode plate and the negative electrode plate are disposed such that the positive electrode active material layer and the negative electrode active material layer face each other. the positive electrode current collector is folded at a boundary X between two adjacent repeating units A, and the negative electrode current collector is folded at a boundary Y between two adjacent repeating units B, when the positive electrode current collector is developed flat, an outer edge of the boundary X among the outer edges of the positive electrode current collector has a convex shape toward the inside of the boundary X and is configured with a smooth line, when the negative electrode current collector is developed flat, an outer edge of the boundary Y among the outer edges of the negative electrode current collector has a convex shape toward the inside of the boundary Y and is configured with a smooth line, and each of the plurality of repeating units A and the plurality of repeating units B is substantially circular or substantially polygonal.

[0008] According to the present disclosure, it is possible to obtain an electrode plate that enables batteries to be manufactured with high yield, and a coin-type secondary battery that can be manufactured with high yield. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view illustrating a schematic example of a coin-type secondary battery according to the present disclosure. [Diagram 2] 2 is a cross-sectional view showing a schematic diagram of an electrode group of the coin-type secondary battery shown in FIG. 1. [Figure 3A] 2 is a plan view showing a schematic diagram of an example of a positive electrode plate of the coin-type secondary battery shown in FIG. 1. [Figure 3B] 3B is a schematic cross-sectional view taken along line IIIB-IIIB in FIG. 3A. FIG. [Figure 3C] FIG. 3B is a partially enlarged view of the positive electrode current collector shown in FIG. 3A. [Figure 4A] 2 is a plan view showing a schematic diagram of an example of a negative electrode plate of the coin-type secondary battery shown in FIG. 1. [Figure 4B] 4B is a diagram showing a cross section taken along line IVB-IVB in FIG. 4A. FIG. [Figure 4C] FIG. 4B is a partially enlarged view of the negative electrode current collector shown in FIG. 4A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present disclosure will be described. In the following description, an embodiment of the present disclosure will be described by way of example, but the present disclosure is not limited to the example described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure can be obtained.

[0011] (Pole plate) The electrode plate of the present disclosure is an electrode plate used in a coin-type secondary battery, and is a positive electrode plate and / or a negative electrode plate. The electrode plate includes a current collector and an active material layer disposed on the current collector. The current collector includes a plurality of repeat units aligned in a row. An active material layer is disposed on each of the plurality of repeat units. Each of the plurality of repeat units is substantially circular or substantially polygonal. In the battery, the current collector is folded with the boundary between two adjacent repeat units as the folding portion. That is, the electrode plate is folded with the boundary as the folding portion.

[0012] When the electrode plate is a positive electrode plate, the current collector, the repeating unit, the boundary portion, and the active material layer can be read as a positive electrode current collector, the repeating unit A, the boundary portion X, and the positive electrode active material layer, respectively. When the electrode plate is a negative electrode plate, the current collector, the repeating unit, the boundary portion, and the active material layer can be read as a negative electrode current collector, the repeating unit B, the boundary portion Y, and the negative electrode active material layer, respectively.

[0013] The electrode plate of the present disclosure can be used in a coin-type secondary battery described later. The positive electrode plate and / or negative electrode plate of the coin-type secondary battery described later is an example of the electrode plate of the present disclosure. Therefore, the configuration of the positive electrode plate and / or negative electrode plate of the coin-type secondary battery described later can be applied as the configuration of the electrode plate of the present disclosure. There is no particular limitation on the current collector and active material layer, and they may be selected according to the type of secondary battery in which the electrode plate is used and the type of electrode plate (positive electrode plate, negative electrode plate). The materials of the current collector and active material layer may be publicly known current collector and active material materials. Examples of the current collector and active material layer will be described later.

[0014] Among the outer edges of the current collector, the outer edge of the boundary between two adjacent repeating units may be referred to as the “outer edge (P)” hereinafter. The outer edge (P) may have the following feature (1). (1) The outer edge (P) has a convex shape toward the inside of the boundary (or, from another perspective, toward the center of the boundary).

[0015] The outer edge (P) has at least one of the following characteristics (2) to (6). In addition to the above characteristic (1), the outer edge (P) may have at least one of the characteristics (2) to (6). In addition to the above characteristic (1), the outer edge (P) may have any one of the characteristics (2) to (6). For example, the outer edge (P) may have the above characteristic (1) and the following characteristic (2). (2) The outer edge (P) is composed of smooth lines. (3) The outer edge (P) has no corners. (4) The outer edge (P) is rounded. (5) At the outer edge (P), the tangent vector of the outer edge (P) is not discontinuous. For example, the tangent vector of the outer edge (P) may change continuously. (6) The outer edge (P) has a shape with rounded corners formed by two straight lines. Here, the two straight lines are two sides of two polygons when the two polygons are joined so as to share two vertices. The two sides are two unshared sides that have a single shared vertex as their end point. These will be specifically described in the first embodiment described below.

[0016] In the electrode plate of the present disclosure, the boundary portion of the repeating unit is folded when the electrode group is produced. Therefore, when the electrode group is produced, a force (such as tension) is applied to the boundary portion. If a corner portion is present at the outer edge (P) of the boundary portion, the force is concentrated at the corner portion, and the current collector is likely to break. A current collector including an outer edge (P) having the above characteristics does not have a portion at the boundary portion where the force is particularly likely to concentrate, and therefore is less likely to break when the electrode group is produced. Therefore, the electrode group and secondary battery can be produced with a high yield. Furthermore, by using the electrode plate of the present disclosure, a highly reliable secondary battery can be obtained.

[0017] Each of the multiple repeating units is substantially circular or substantially polygonal. An example of a substantially circular shape is a shape formed by two equal arc-shaped curves arranged in line symmetry and point symmetry so as to be convex outward, and two straight lines connecting the curves. An example of such a shape is a shape obtained by cutting a circle (or an ellipse) by two parallel lines that are equidistant from the center of the circle (or ellipse). In the case of an ellipse, the two parallel lines are parallel to the major axis or minor axis of the ellipse.

[0018] An example of the substantially polygonal shape includes a polygonal portion (a polygonal portion) and a portion that fills the area between the polygonal portion and the outer edge (P). Hereinafter, the portion that fills the area between the polygonal portion and the outer edge (P) may be referred to as a "rounded portion." The number of sides that constitute the polygonal portion may be in the range of 6 to 12. For example, the polygonal portion may be a hexagon (e.g., a regular hexagon), an octagon (e.g., a regular octagon), or a decagon (e.g., a regular decagon). That is, the repeating unit may be a substantially octagon or a substantially decagon.

[0019] Examples of the substantially circular and substantially polygonal shapes include the above shapes and shapes that include a portion that will become a bent portion. For example, examples of the substantially polygonal shapes include shapes that include a polygon and a portion that will become a bent portion.

[0020] From one point of view, the shape of the repeating unit may be the following shape. That is, when the innermost diameter of a coin-shaped case in which the electrode plates are arranged is F, consider a first circle with a diameter of F and a second circle that is concentric with the first circle and has a diameter of 0.4F. In this case, the shape of the repeating unit may be such that the entire outer edge of the repeating unit falls within the area between the first circle and the second circle (specifically, the area between the circumference of the first circle and the circumference of the second circle). In one example of this case, the diameter of the second circle may be 0.5F. There is no particular limitation on the innermost diameter F of the case. The innermost diameter F may be in the range of 6 mm to 9 mm (for example, 7 mm to 9 mm).

[0021] The shape of the repeating unit A of the positive plate and the shape of the repeating unit B of the negative plate may be the same or different. When the shape of the repeating unit A is different from the shape of the repeating unit B, the outer edge of the repeating unit A and the outer edge of the repeating unit B may both be in the region between the first circle and the second circle.

[0022] The area of ​​repeat unit A may be greater than the area of ​​repeat unit B. Alternatively, the area of ​​repeat unit A may be smaller than the area of ​​repeat unit B. For example, the width WB (see FIG. 4C) of repeat unit B may be greater or smaller than the width WA (see FIG. 3C) of repeat unit A. Also, the length LB (see FIG. 4C) of repeat unit B may be greater or shorter than the length LA (see FIG. 3C) of repeat unit A. In one example, the area of ​​repeat unit B is greater than the area of ​​repeat unit A.

[0023] A current collector including multiple repeat units can be formed of a single metal sheet. The active material layers arranged on the multiple repeat units may or may not be connected. For example, the active material layer may not be formed on the folded portion of the current collector.

[0024] There is no particular limitation on the number of repeating units contained in one current collector, and it may be in the range of 2 to 30, or may be 3 or more (for example, in the range of 3 to 30 or 3 to 15).

[0025] The repeating unit at one end of the multiple repeating units may be connected to a portion (connecting portion) for electrically connecting the current collector to an electrode terminal. The multiple repeating units and the connecting portion may be formed from a single metal sheet.

[0026] The multiple repeating units may have a shape in which multiple polygons are lined up in a row so that two adjacent polygons share two vertices, and further the outer corners of the two vertices are rounded.

[0027] (Coin-type secondary battery) The coin-type secondary battery of the present disclosure includes a coin-type case, and a positive electrode plate and a negative electrode plate disposed in the case. The positive electrode plate includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The positive electrode current collector includes a plurality of repeat units (hereinafter sometimes referred to as "repeat unit A") aligned in a row. The negative electrode current collector includes a plurality of repeat units (hereinafter sometimes referred to as "repeat unit B") aligned in a row. A positive electrode active material layer is disposed on each of the plurality of repeat units A. A negative electrode active material layer is disposed on each of the plurality of repeat units B. The positive electrode plate and the negative electrode plate are disposed such that the positive electrode active material layer and the negative electrode active material layer face each other.

[0028] The coin-type secondary battery of the present disclosure also includes secondary batteries having a shape called a button type. That is, the coin-type case also includes a case used for a battery called a button type.

[0029] The positive electrode current collector is folded at the boundary between two adjacent repeat units A (hereinafter sometimes referred to as "boundary X"), and the negative electrode current collector is folded at the boundary between two adjacent repeat units B (hereinafter sometimes referred to as "boundary Y"),.

[0030] The positive and negative electrode plates are formed by folding the electrode plates of the present disclosure at their boundaries, and therefore, redundant description may be omitted.

[0031] When the current collectors (positive electrode current collector, negative electrode current collector) are laid out flat, the outer edge (P) of the boundary (boundary X, boundary Y) between two adjacent repeat units (repeat unit A, repeat unit B) among the outer edges of the current collectors has the above-mentioned shape. Also, each of the repeat units (repeat unit A, repeat unit B) is substantially circular or substantially polygonal as described above.

[0032] When the positive electrode plate is developed flat, the outer edge of boundary X among the outer edges of the positive electrode plate may have a convex shape toward the inside of boundary X and may be configured as a smooth line. When the negative electrode plate is developed flat, the outer edge of boundary Y among the outer edges of the negative electrode plate may have a convex shape toward the inside of boundary Y and may be configured as a smooth line.

[0033] When the positive electrode current collector is developed flat, the repeating units A may have a shape in which a plurality of first polygons are arranged in a row such that two adjacent first polygons share two vertices, and the outer corners at the two vertices are rounded. When the negative electrode current collector is developed flat, the repeating units B may have a shape in which a plurality of second polygons are arranged in a row such that two adjacent second polygons share two vertices, and the outer corners at the two vertices are rounded. The number of sides of the first polygon may be the same as the number of sides of the second polygon. The first polygon and the second polygon may be polygons having substantially the same shape (for example, congruent polygons).

[0034] The outer edge (outer edge (P)) of boundary portion X and the outer edge (outer edge (P)) of boundary portion Y may each be rounded with a curve (e.g., a circular arc) having a radius of curvature R. For example, the above-mentioned corners of outer edge (P) may be rounded with a curve (e.g., a circular arc) having a radius of curvature R. Note that the radius of curvature of the curve that rounds the outer edges does not have to be constant.

[0035] The radius of curvature R may be 0.1 mm or more, 0.3 mm or more, or 1 mm or more. The radius of curvature R may be 2.5 mm or less, or 2 mm or less. The radius of curvature R may be in the range of 0.1 to 2.5 mm (for example, in the range of 0.3 to 2.0 mm). By rounding the outer edge (P) with a curve having a radius of curvature R of 0.3 mm or more, damage to the current collector when preparing the electrode assembly can be particularly reduced. By rounding the outer edge (P) with a curve having a radius of curvature R of 2.0 mm or less, it becomes easy to bend the electrode plate when preparing the electrode assembly.

[0036] Consider a case where multiple polygons, each with a side length of S (mm), are lined up in a row so that two adjacent polygons share two vertices, and the outer corners at the two vertices are rounded with a curve with a radius of curvature R (mm) (see FIG. 3C). In this case, the length S and the radius of curvature R may satisfy the formula 0.04S≦R≦S, or 0.12S≦R≦0.8S.

[0037] The secondary battery of the present disclosure may include a separator disposed between the positive electrode plate and the negative electrode plate. The secondary battery of the present disclosure may further include a separator disposed between the positive electrode plate and the negative electrode plate, and a non-aqueous electrolyte disposed in the case. That is, the secondary battery of the present disclosure may be a non-aqueous electrolyte secondary battery.

[0038] The positive and negative electrode plates may each be zigzag folded or wound. In these cases, a separator may be disposed between the positive and negative electrode plates.

[0039] At least a part of the separator may be fixed to the negative electrode active material layer or the positive electrode active material layer. By fixing the separator to the active material layer, the battery can be manufactured easily. There is no particular limitation on the method of fixing the separator, and a known technique may be used. For example, the separator may be fixed to the active material layer by heat pressing or the like. Alternatively, a separator having an adhesive layer on its surface may be used. For the adhesive layer, for example, a layer containing a resin such as polyvinylidene fluoride may be used.

[0040] When the positive electrode plate and the negative electrode plate are each folded in a zigzag pattern, the positive electrode active material layer may be disposed on only one side of the positive electrode current collector, and / or the negative electrode active material layer may be disposed on only one side of the negative electrode current collector.

[0041] The secondary battery of the present disclosure may include at least one positive electrode plate and at least one negative electrode plate such that the total number of positive electrode plates and negative electrode plates is 2 or 3. Three examples (first to third arrangement examples) regarding the number of positive electrode plates and negative electrode plates and the arrangement of active material layers will be described below.

[0042] In the first arrangement example, the number of positive electrode plates and the number of negative electrode plates are each one. In this case, a positive electrode active material layer is disposed on only one side of the positive electrode collector, and a negative electrode active material layer is disposed on only one side of the negative electrode collector. In the second arrangement example, the number of positive electrode plates is two, and the number of negative electrode plates is one. In this case, a positive electrode active material layer is disposed on only one side of the positive electrode collector, and a negative electrode active material layer is disposed on both sides of the negative electrode collector. In the second arrangement example, the positive electrode plates and the negative electrode plates are arranged so that one negative electrode plate is sandwiched between two positive electrode plates. In the third arrangement example, the number of negative electrode plates is two, and the number of positive electrode plates is one. In this case, a positive electrode active material layer is disposed on both sides of the positive electrode collector, and a negative electrode active material layer is disposed on only one side of the negative electrode collector. In the third arrangement example, the positive electrode plates and the negative electrode plates are arranged so that one positive electrode plate is sandwiched between two negative electrode plates.

[0043] When the positive electrode plate and the negative electrode plate are each wound, a positive electrode active material layer may be disposed on both sides of the positive electrode current collector, and a negative electrode active material layer may be disposed on both sides of the negative electrode current collector.

[0044] The type of secondary battery of the present disclosure is not particularly limited, and may be a nickel-metal hydride secondary battery or a non-aqueous electrolyte secondary battery. Examples of non-aqueous electrolyte secondary batteries include lithium secondary batteries and lithium ion secondary batteries.

[0045] Except for the use of the configuration specific to the present disclosure, there is no particular limitation on the components of the secondary battery of the present disclosure (such as the case, the material constituting the positive electrode plate, the material constituting the negative electrode plate, and other components). Except for the use of the configuration specific to the present disclosure, the components of the secondary battery of the present disclosure may be made of publicly known materials or configurations. Examples of components when the secondary battery of the present disclosure is a lithium ion secondary battery are given below, but the present disclosure is not limited to the following examples.

[0046] (Positive plate) Examples of the positive electrode current collector include a sheet-like object (for example, a foil, a mesh, or a punched sheet) made of a conductive material (for example, a metal material). Examples of the metal material constituting the positive electrode current collector include aluminum, an aluminum alloy, titanium, a titanium alloy, and stainless steel. The thickness of the positive electrode current collector may be, for example, in the range of 5 to 300 μm.

[0047] The positive electrode active material layer contains a positive electrode active material, and may contain other materials (such as a binder and a conductive agent) as necessary. Examples of positive electrode active materials include materials that reversibly absorb and release lithium ions. Specifically, examples of positive electrode active materials include metal oxides containing lithium, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. Examples of metal oxides containing lithium include lithium transition metal composite oxides and lithium-nickel-cobalt-aluminum composite oxides. Examples of lithium transition metal composite oxides include lithium-manganese composite oxides (e.g., LiMn 2 O 4 ), lithium-nickel composite oxides (e.g. LiNiO 2 ), lithium-cobalt composite oxides (e.g. LiCoO 2 ), and composite oxides in which some of these transition metal elements are replaced with other metal elements (main group metal elements and / or transition metal elements).

[0048] Examples of the binder include fluororesin, polyacrylonitrile, polyimide resin, acrylic resin, polyolefin resin, and rubber polymer. Examples of the fluororesin include polytetrafluoroethylene and polyvinylidene fluoride. Only one type of binder may be used, or two or more types may be used.

[0049] Examples of the conductive agent include carbon materials. Examples of the carbon materials used as the conductive agent include carbon black (such as acetylene black and ketjen black), carbon nanotubes, and graphite. The conductive agent may be used alone or in combination of two or more kinds.

[0050] (Negative electrode plate) The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer. A part of the negative electrode current collector may constitute a connection part that is electrically connected to a part of the case (case body or sealing plate) that functions as a terminal. In that case, the connection part is connected to a part of the case by welding (such as ultrasonic welding).

[0051] Examples of the negative electrode current collector include sheet-like materials (such as foils, meshes, or punched sheets) made of conductive materials (such as metal materials). The metal material of the negative electrode current collector may be a material that does not form any alloys or intermetallic compounds with lithium. Examples of the metal materials of the negative electrode current collector include copper, nickel, iron, and alloys containing these metal elements (such as copper alloys and stainless steels). In a preferred example, the metal material of the negative electrode current collector is copper or a copper alloy. The thickness of the negative electrode current collector may be in the range of, for example, 5 to 300 μm.

[0052] The negative electrode active material layer contains a negative electrode active material and may contain other substances (such as binders, conductive agents, and thickeners) as necessary. Examples of the negative electrode active material include substances that can reversibly occlude and release lithium ions. Specifically, examples of the negative electrode active material include carbon materials, silicon, silicon compounds, and lithium alloys. Examples of the carbon materials include graphite, coke, carbon in the process of graphitization, graphitized carbon fibers, and amorphous carbon.

[0053] Examples of the binder include fluororesins such as polyvinylidene fluoride (PVDF), acrylic resins such as polymethyl acrylate and ethylene-methyl methacrylate copolymer, styrene butadiene rubber, acrylic rubber, and modified versions of these rubbers. Examples of the conductive agent include the conductive agents exemplified in the explanation of the positive electrode active material layer. Examples of the thickener include water-soluble polymers containing a carboxyl group (e.g., carboxymethyl cellulose).

[0054] (Separator) Examples of the separator include a sheet having ion permeability and insulation. The separator may be a laminate of a plurality of sheets including a sheet having ion permeability and insulation. The separator has a size necessary for insulating the positive electrode plate from the negative electrode plate.

[0055] The separator may be a microporous film, a woven fabric, or a nonwoven fabric. Examples of materials for the separator include polymers having insulating properties, specifically, polyolefin-based polymers, polyamide-based polymers, cellulose-based polymers, etc. The thickness of the separator may be in the range of 5 to 200 μm.

[0056] (Non-aqueous electrolyte) The non-aqueous electrolyte used has lithium ion conductivity. A typical non-aqueous electrolyte includes a non-aqueous solvent and lithium ions and anions dissolved in the non-aqueous solvent. The non-aqueous electrolyte may be liquid or gel-like. A liquid non-aqueous electrolyte can be prepared by dissolving a lithium salt in a non-aqueous solvent. Lithium ions and anions are generated by dissolving a lithium salt (a salt of lithium ions and anions) in a non-aqueous solvent.

[0057] The gelled non-aqueous electrolyte includes a liquid non-aqueous electrolyte and a matrix polymer. For example, a polymer material that absorbs a non-aqueous solvent and gels is used as the matrix polymer. Examples of such polymer materials include fluororesins, acrylic resins, and polyether resins.

[0058] Examples of anions of lithium salts include BF 4 - , ClO 4 - , P.F. 6 - , C.F. 3 SO 3 - , C.F. 3 CO 2 - , anions of imides, anions of oxalate complexes, and the like.

[0059] Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and halogen-substituted derivatives thereof (e.g., fluorides), etc. The non-aqueous electrolyte may contain only one type of these non-aqueous solvents, or may contain two or more types.

[0060] Examples of esters include carbonate esters, carboxylate esters, etc. Examples of cyclic carbonate esters include ethylene carbonate, propylene carbonate, fluoroethylene carbonate (FEC), etc. Examples of linear carbonate esters include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, etc. Examples of cyclic carboxylate esters include γ-butyrolactone, γ-valerolactone, etc. Examples of linear carboxylate esters include ethyl acetate, methyl propionate, methyl fluoropropionate, etc.

[0061] The concentration of the lithium salt in the non-aqueous electrolyte may be, for example, in the range of 0.5 mol / L to 3.5 mol / L. Here, the concentration of the lithium salt is the sum of the concentration of the dissociated lithium salt and the concentration of the undissociated lithium salt. The concentration of the anion in the non-aqueous electrolyte may be in the range of 0.5 mol / L to 3.5 mol / L.

[0062] (case) A typical case includes a case body, a sealing plate, and a gasket disposed between the case body and the sealing plate. Usually, the case body and the sealing plate each function as an electrode terminal. For example, in the case of a typical coin-shaped battery, the case body functions as a positive electrode terminal, and the sealing plate functions as a negative electrode terminal. The case body and the sealing plate can each be formed using a metal (e.g., stainless steel having electrical conductivity).

[0063] An example of a secondary battery of the present disclosure and a method for manufacturing the same will be specifically described below with reference to the drawings. The secondary battery described below includes the electrode plate of the present disclosure. The components of the secondary battery described below can be modified based on the above description. The matters described below may also be applied to the above embodiment. Components that are not essential to the secondary battery of the present disclosure can be omitted.

[0064] (Embodiment 1) A cross-sectional view of a coin-type secondary battery of embodiment 1 is shown typically in Fig. 1. The secondary battery 10 of Fig. 1 includes a coin-type case 20, and an electrode group 30 and a non-aqueous electrolyte (not shown) disposed within the case 20. The case 20 includes a cylindrical case body 21 with a bottom, a sealing plate 22, and a gasket 23. The case body 21 is sealed by the sealing plate 22 and the gasket 23.

[0065] A cross-sectional view of the electrode group 30 is shown in FIG. 2. FIG. 2 is a cross-section along the direction in which the repeating units 41A and 51B (see FIG. 3A and FIG. 4A) are connected in a zigzag pattern. The electrode group 30 includes a positive electrode plate 40, a negative electrode plate 50, and one separator 60 disposed therebetween. The positive electrode plate 40, the negative electrode plate 50, and the separator 60 are each folded in a zigzag pattern. The positive electrode active material layer 42 and the negative electrode active material layer 52 face each other with the separator 60 sandwiched therebetween.

[0066] (Positive plate) A plan view of the positive electrode plate 40 when it is developed flat is shown in Fig. 3A, and a cross-sectional view taken along line IIIB-IIIB in Fig. 3A is shown in Fig. 3B. A partially enlarged view of the positive electrode current collector 41 is shown in Fig. 3C. The positive electrode plate 40 includes a positive electrode current collector 41 and a positive electrode active material layer 42 disposed on the positive electrode current collector 41.

[0067] The positive electrode current collector 41 includes a plurality of repeat units 41A aligned in a line. FIGS. 3A and 3C show a boundary 41k between two adjacent repeat units 41A. The repeat units 41A are aligned in one direction PD. A positive electrode active material layer 42 is formed on each repeat unit 41A. The positive electrode active material layers 42 disposed on the respective repeat units 41A are connected to each other. In the electrode group 30, the positive electrode current collector 41 and the positive electrode plate 40 are folded with the entire boundary 41X (the area around the boundary 41k) between two adjacent repeat units 41A as a folded portion.

[0068] A connection portion 43 is connected to the repeating unit 41A at one end. In the illustrated example, the connection portion 43 has approximately the same shape as one of the repeating units 41A. The connection portion 43 is a portion connected to the case body 21, and is connected to the case body 21 by, for example, welding or the like. The positive electrode active material layer 42 is not disposed on the connection portion 43. There is no particular limitation on the structure of the connection portion 43 as long as the positive electrode current collector 41 can be electrically connected to the case body 21. As shown in FIG. 2, the boundary portion between the connection portion 43 and the repeating unit 41A is also folded as a folding portion.

[0069] Referring to FIG. 3C, one repeating unit 41A includes an octagonal portion 41Aa, which is an octagon, and a rounded portion 41Ab. In FIG. 3C, the rounded portion 41Ab is hatched. The shape formed by the multiple repeating units 41A has a shape in which multiple octagonal portions 41Aa are lined up in a row such that two adjacent octagonal portions 41Aa share two vertices, and the corners of the outer edges at the two vertices are rounded. The rounded corners become the rounded portions 41Ab. In the example shown in FIG. 3C, the corners are rounded with a curve (arc) having a radius of curvature R.

[0070] When the positive electrode current collector 41 is laid out flat, the outer edge of the boundary portion 41X (folded portion) has a shape that protrudes toward the inside of the boundary portion 41X and is configured with a smooth line. The outer edge of the boundary portion 41X has no corners. The tangent vector of the outer edge of the boundary portion 41X is not discontinuous but changes continuously. A part of the outer edge of the boundary portion 41X may be a straight line.

[0071] (Negative plate) A plan view of the negative electrode plate 50 when it is developed flat is shown in Fig. 4A, and a cross-sectional view taken along line IVB-IVB in Fig. 4A is shown in Fig. 4B. A partially enlarged view of the negative electrode current collector 51 is shown in Fig. 4C. The negative electrode plate 50 includes a negative electrode current collector 51 and a negative electrode active material layer 52 disposed on the negative electrode current collector 51.

[0072] The negative electrode current collector 51 includes a plurality of repeat units 51B aligned in a line. FIGS. 4A and 4C show a boundary 51k between two adjacent repeat units 51B. The repeat units 51B are aligned in one direction ND. A negative electrode active material layer 52 is formed on each repeat unit 51B. The negative electrode active material layers 52 disposed on the respective repeat units 51B are connected to each other. In the electrode group 30, the negative electrode current collector 51 and the negative electrode plate 50 are folded with the entire boundary 51Y (the area around the boundary 51k) between two adjacent repeat units 51B as a folded portion.

[0073] A connection portion 53 is connected to the repeating unit 51B at one end. In the example shown in the figure, the connection portion 53 has approximately the same shape as one of the repeating units 51B. The connection portion 53 is a portion connected to the sealing plate 22, and is connected to the sealing plate 22 by, for example, welding or the like. The negative electrode active material layer 52 is not disposed in the connection portion 53. There is no particular limitation on the structure of the connection portion 53 as long as the negative electrode current collector 51 can be electrically connected to the sealing plate 22. As shown in FIG. 2, the boundary portion between the connection portion 53 and the repeating unit 51B is also folded as a folding portion.

[0074] 4C, one repeating unit 51B includes an octagonal portion 51Ba and a rounded portion 51Bb. The octagonal portion 51Ba and the rounded portion 51Bb have the same shapes as the octagonal portion 41Aa and the rounded portion 41Ab, respectively. Therefore, a description of the shape of the repeating unit 51B is omitted.

[0075] In the positive electrode current collector 41 and the negative electrode current collector 51, the outer edges of the boundaries X and Y, which are the bent parts, are formed with smooth lines. Therefore, even when stress is applied to the boundaries X and Y when forming the electrode group 30, damage to the boundaries X and Y can be suppressed. On the other hand, if corners are present on the outer edges, stress may be concentrated at the corners, making the current collectors more susceptible to breakage.

[0076] It should be noted that a short circuit may occur if the positive electrode plate 40 and / or the negative electrode plate 50 come into contact with the case 20. An insulating member (e.g., insulating tape) may be placed around the electrode group 30 to prevent such a short circuit.

[0077] In the first embodiment, the case where the electrode group includes only one positive electrode plate, one negative electrode plate, and one separator is described. However, one of the positive electrode plate and the negative electrode plate may be only one, and the other may be two. In that case, an active material layer may be formed on both sides of only one electrode plate, and an active material layer may be formed on one side of each of the other two electrode plates. In that case, two separators may be used. In the case where there is only one positive electrode plate and two negative electrode plates, the one positive electrode plate, the two negative electrode plates, and the two separators may be arranged in the following order: negative electrode collector / negative electrode active material layer / separator / positive electrode active material layer / positive electrode collector / positive electrode active material layer / separator / negative electrode active material layer / negative electrode collector, and folded in a zigzag pattern. Similarly, when there is only one negative electrode plate and two positive electrode plates, the two positive electrode plates, one negative electrode plate, and two separators may be arranged in the following order and folded in a zigzag: positive electrode current collector / positive electrode active material layer / separator / negative electrode active material layer / negative electrode current collector / negative electrode active material layer / separator / positive electrode active material layer / positive electrode current collector. When active material layers are formed on both sides of the positive electrode plate (or negative electrode plate), one repeat unit A (or one repeat unit B) includes a positive electrode current collector (or negative electrode current collector) and positive electrode active material layers (or negative electrode active material layers) arranged on both sides thereof.

[0078] (Method of manufacturing coin-type secondary battery) An example of a method for manufacturing the secondary battery of this embodiment will be described below. An example of a method for manufacturing the secondary battery 10 described in embodiment 1 will be described below. Known techniques can be applied to the manufacturing process described below. Note that the method for manufacturing the secondary battery of this embodiment is not limited to the following manufacturing method.

[0079] First, the positive electrode plate 40 and the negative electrode plate 50 are prepared. In one example of a method for producing the positive electrode plate 40, first, materials constituting the positive electrode active material layer 42 are mixed to prepare a positive electrode mixture. Next, the positive electrode mixture is applied onto a conductive sheet (e.g., metal foil) that becomes the positive electrode current collector 41 to form the positive electrode active material layer 42. In this manner, the positive electrode plate 40 is produced. The positive electrode plate 40 and the positive electrode current collector 41 are produced so as to have the above-mentioned structure (planar shape). The positive electrode plate 40 may be produced by forming the positive electrode active material layer 42 in a predetermined region of a large-area conductive sheet, and then punching out the conductive sheet and the positive electrode active material layer 42 together using a punching die.

[0080] In one example of a method for producing the negative electrode plate 50, first, materials constituting the negative electrode active material layer 52 are mixed to prepare a negative electrode mixture. Next, the negative electrode mixture is applied onto a conductive sheet (e.g., metal foil) that becomes the negative electrode current collector 51 to form the negative electrode active material layer 52. In this manner, the negative electrode plate 50 is produced. The negative electrode plate 50 and the negative electrode current collector 51 are produced so as to have the above-mentioned structure (planar shape). The negative electrode plate 50 may be produced by forming the negative electrode active material layer 52 in a predetermined region of a large-area conductive sheet, and then punching out the conductive sheet and the negative electrode active material layer 52 together using a punching die.

[0081] Next, the positive electrode plate 40, the negative electrode plate 50, and the separator 60 are arranged so that the positive electrode active material layer 42 and the negative electrode active material layer 52 face each other with the separator 60 interposed therebetween. Then, they are folded together in a zigzag pattern to produce the electrode group 30. The positive electrode plate 40, the negative electrode plate 50, and the separator 60 may be folded and then combined to produce the electrode group 30. In addition, in producing the electrode group 30, at least a part of the separator may be fixed to the positive electrode plate 40 or the negative electrode plate 50 before folding the electrode plates. Fixing the separator makes it easier to produce the electrode group. The separator can be fixed by the method described above.

[0082] Furthermore, sealing plate 22 is fitted into gasket 23 to form a fitted body. Next, connection portion 43 is electrically connected to case body 21. Similarly, connection portion 53 is electrically connected to sealing plate 22. These electrical connections can be implemented by, for example, welding (ultrasonic welding, etc.). If necessary, the periphery of electrode group 30 is protected with an insulating member before or after connecting the connection portions.

[0083] Next, the electrode group 30 and the nonaqueous electrolyte are placed in the combination of the sealing plate 22 and the gasket 23. Next, the case body 21 is placed so as to seal the opening of the combination, and then the open end of the case body 21 is crimped to seal the opening. In this manner, the secondary battery 10 of the first embodiment is obtained.

[0084] When the electrode group 30 is a wound type electrode group, first, the positive electrode plate 40, the negative electrode plate 50, and the separator 60 are wound together to prepare a wound body, so that the separator 60 is disposed between the positive electrode plate 40 and the negative electrode plate 50. Then, the wound body is crushed to have a flat shape. At this time, the wound body is crushed so that the boundary portion (rounded portion) of the repeating unit becomes a folded portion of the flat shape. In this manner, the wound type electrode group 30 can be prepared. EXAMPLES

[0085] The present disclosure will be described in more detail with reference to examples. In these examples, secondary batteries having the same structure as the secondary battery 10 shown in FIG. 1 were fabricated and evaluated. In these examples, multiple types of secondary batteries (batteries A1 to A6 and C1) with different shapes of current collectors were fabricated. The fabrication and evaluation of these secondary batteries will be described below.

[0086] (Battery A1) In Example 1, a battery having the same structure as the secondary battery 10 shown in FIG. 1 was produced. The planar shape of the repeating unit A (corresponding to the repeating unit 41A in FIG. 3A) was a substantially regular octagon with one side of 2.5 mm. The length LA of the repeating unit A along the direction PD and the width WA perpendicular to the direction PD (see FIG. 3C) were each 6 mm. The positive electrode current collector had a shape in which 15 regular octagons were connected in a row, and the corners of the outer edge of the boundary between two adjacent regular octagons were rounded. Specifically, the corners were rounded with a curve with a curvature radius R of 1.0 mm. The number of repeating units B (corresponding to the repeating unit 51B in FIG. 4A) of the negative electrode current collector was the same as the number of repeating units A. The length LB of the repeating unit B in the direction ND (see FIG. 4C) was the same as the length LA. The width WB perpendicular to the direction ND was slightly larger than the width WA.

[0087] The positive electrode mixture constituting the positive electrode active material layer is made of lithium cobalt oxide (LiCoO 2 ), acetylene black as a conductive agent, and polyvinylidene fluoride as a binder were mixed in a mass ratio of lithium cobalt oxide:acetylene black:polyvinylidene fluoride=9:0.1:0.1 to prepare the positive electrode current collector. Aluminum foil was used as the positive electrode current collector. A positive electrode active material layer having a thickness of 55 μm was formed by applying a positive electrode mixture to one side of the positive electrode current collector. Of the 15 regular octagonal parts, the active material layer was not placed on two parts at one end, and they were used as connection parts for welding. That is, the number of repeating units A on which the positive electrode active material layer was placed was 13.

[0088] The negative electrode mixture constituting the negative electrode active material layer was prepared by mixing graphite as the negative electrode active material, carboxymethyl cellulose (CMC) as the thickener, and styrene butadiene rubber (SBR) as the binder in a mass ratio of graphite:CMC:SBR=9:0.1:0.1. Copper foil was used as the negative electrode current collector.

[0089] The separator was a microporous polyolefin membrane (thickness 14 μm). The nonaqueous electrolyte was LiPF 6The non-aqueous solvent was prepared by mixing ethylene carbonate, propylene carbonate, and methyl ethyl carbonate in a volume ratio of ethylene carbonate:propylene carbonate:methyl ethyl carbonate=30:1:61.

[0090] The positive and negative electrode plates were produced using the above materials. Then, an electrode group (see FIG. 2) was produced in which the positive and negative electrode plates and the separator were folded in a zigzag pattern. Next, a coin-shaped nonaqueous electrolyte secondary battery was produced by the above-mentioned method using the electrode group, nonaqueous electrolyte, and a coin-shaped case. The size of the obtained secondary battery was 9.5 mm in outer diameter and 2.0 mm in height. The innermost diameter of the case was 7.5 mm.

[0091] (Batteries A2~A6) Batteries A2 to A6 were produced under the same conditions as battery A1, except that the shape of the boundary between two adjacent repeating units A was changed. Specifically, the curvature of the curved line that rounded the outer edge of the boundary was changed in the range of 0.1 to 2.5 mm. The curvature used in each battery is shown in Table 1 below.

[0092] (Battery C1) Battery C1 was produced under the same conditions as Battery A1, except that the outer corners of the boundary between the two adjacent regular octagons were not rounded.

[0093] (Yield evaluation during electrode group production) Ten electrode groups were produced for each of the above batteries A1 to A6 and C1. The current-carrying state of each of the positive and negative electrode current collectors was then confirmed, and whether or not the current collectors were broken was evaluated. In other words, if current was not allowed to flow, the product was judged to be defective, and if current was allowed to flow, the product was judged to be non-defective. The yield (%) was then calculated from the number of electrode groups produced and the number of non-defective products. The yield is expressed by the following formula: Yield (%) = 100 x (number of good products) / (number produced) (Charge / discharge test) For the above-described batteries A1 to A6 and C1, charge-discharge cycle tests were performed. In the charging process, charging was carried out at a current value of 6 mA until the battery voltage reached 4.35 V, and then a constant voltage of 4.35 V was applied until the current value became 0.5 mA. The discharging process was carried out by discharging at a current value of 6 mA until the battery voltage reached 3.0 V. One charge-discharge cycle consisting of one charging process and one discharging process was defined as one cycle, and charge-discharge was repeated. Then, the number of charge-discharge cycles n until the battery capacity reached 80% of the initial battery capacity was evaluated. For batteries (batteries A3, A1, A4, A5, A6) whose battery capacity was greater than 80% of the initial battery capacity at the stage after 1000 cycles, the number of charge-discharge cycles n in Table 1 was set to 1000. The evaluation results are shown in Table 1.

[0094]

Table 1

[0095] As shown in Table 1, compared with the battery C1 without a rounded portion, the batteries A1 to A6 in which the corner portions of the boundary portions were rounded had a higher yield of the electrode group and a larger number of charge-discharge cycles. When the radius of curvature was in the range of 0.3 to 2.5 mm, the yield of the electrode group was particularly high and the number of charge-discharge cycles was particularly large.

Industrial Applicability

[0096] The present disclosure can be applied to electrode plates and coin-shaped secondary batteries.

Explanation of Signs

[0097] 10: Secondary battery 20: Case 40: Positive electrode plate 41: Positive electrode current collector 41A, 51B: Repeating unit 41Aa, 51Ba: Octagonal portion (polygonal portion) 41Ab, 51Bb: Rounded portion 41k, 51k: Boundary 41X, 51Y: Boundary portion 42: Positive electrode active material layer 50: Negative plate 51: Negative electrode current collector 52: Negative electrode active material layer 60: Separator

Claims

1. An electrode plate including a current collector and an active material layer disposed on the current collector, The current collector includes a plurality of repeat units connected in a line, the active material layer is disposed on each of the plurality of repeating units, an outer edge of a boundary between two adjacent repeating units among the outer edges of the current collector has a convex shape toward the inside of the boundary, each of the plurality of repeat units is substantially polygonal; the plurality of repeating units have a shape in which a plurality of polygons are aligned in a row such that two adjacent polygons share two vertices, and further, corners of the outer edges at the two vertices are rounded; The corners of the outer edge at the two vertices are rounded with a curve having a radius of curvature R, A pole plate, wherein the length S of one side of the polygon and the radius R of curvature satisfy 0.04S≦R≦S.

2. An electrode plate as described in claim 1, wherein the length S and the radius of curvature R satisfy 0.12S≦R≦0.8S.

3. A coin-type secondary battery including a coin-type case and a positive electrode plate and a negative electrode plate disposed within the case, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, The positive electrode current collector includes a plurality of repeating units A connected in a line, The negative electrode current collector includes a plurality of repeating units B arranged in a row, the positive electrode active material layer is disposed on each of the plurality of repeating units A, the negative electrode active material layer is disposed on each of the plurality of repeating units B, the positive electrode plate and the negative electrode plate are arranged such that the positive electrode active material layer and the negative electrode active material layer face each other, the positive electrode current collector is folded at a boundary portion X between two adjacent repeating units A, the negative electrode current collector is folded at a boundary Y between two adjacent repeating units B as a folding portion, When the positive electrode current collector is developed flat, an outer edge of the boundary portion X among the outer edges of the positive electrode current collector has a convex shape toward an inside of the boundary portion X, When the negative electrode current collector is developed flat, an outer edge of the boundary portion Y among the outer edges of the negative electrode current collector has a convex shape toward an inside of the boundary portion Y, each of the plurality of repeating units A and the plurality of repeating units B is substantially polygonal; When the positive electrode current collector is developed flat, the plurality of repeating units A have a shape in which a plurality of first polygons are aligned in a row such that two adjacent first polygons share two vertices, and further, corner portions αA on outer edges of the two vertices are rounded; When the negative electrode current collector is developed flat, the plurality of repeating units B have a shape in which a plurality of second polygons are aligned in a row such that two adjacent second polygons share two vertices, and further, corner portions αB on outer edges of the two vertices are rounded; the number of sides of the first polygon is the same as the number of sides of the second polygon, The corner αA is rounded with a curve having a radius of curvature R 1 , The corner αB is rounded with a curve having a radius of curvature R 2 , the length S 1 of one side of the first polygon and the radius of curvature R 1 satisfy 0.04S 1 ≦R 1 ≦S 1 ; A coin-type secondary battery, wherein the length S 2 of one side of the second polygon and the radius of curvature R 2 satisfy 0.04S 2 ≦R 2 ≦S 2 .

4. The length S 1 and the radius of curvature R 1 satisfy 0.12S 1 ≦R 1 ≦0.8S 1 , The coin-type secondary battery according to claim 3 , wherein the length S 2 and the radius of curvature R 2 satisfy 0.12S 2 ≦R 2 ≦0.8S 2 .

5. The coin-type secondary battery according to claim 3, wherein the radius of curvature R 1 and the radius of curvature R 2 are each in the range of 0.3 to 2.0 mm.

6. The coin-type secondary battery according to any one of claims 3 to 5, further comprising a separator disposed between the positive electrode plate and the negative electrode plate, and a non-aqueous electrolyte disposed within the case.

7. 7. The coin-type secondary battery according to claim 3, wherein the positive electrode plate and the negative electrode plate are each zigzag folded or wound.

8. The positive electrode plate and the negative electrode plate are each folded in a zigzag pattern, The coin-type secondary battery according to any one of claims 3 to 6, wherein the positive electrode active material layer is disposed on only one surface of the positive electrode current collector, and / or the negative electrode active material layer is disposed on only one surface of the negative electrode current collector.

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