Flat non-aqueous electrolyte secondary battery

Abstract

The disclosed positive electrode plate (40) and negative electrode plate (50) of the battery include positive electrode units (40a) and negative electrode units (50a) connected in a row. The electrode plates are bent in opposite directions by using the boundary portions of two adjacent positive electrode units (40a) and the boundary portions of two adjacent negative electrode units (50a) as bending portions (40ab) and (50ab), thereby bending the electrode plates in a zigzag manner. The electrode plates and separators (60) are arranged so that the active material layer of the positive electrode unit (40a) and the active material layer of the negative electrode unit (50a) are opposed to each other with the separator (60) sandwiched therebetween, and the bending portions (40ab) and the bending portions (50ab) are opposed to each other with the separator (60) sandwiched therebetween. The length of the positive electrode unit (40a) in the direction in which the positive electrode units (40a) are connected is longer than the length of the negative electrode unit (50a) in the direction in which the negative electrode units (50a) are connected.

Description

Technical Field

[0001] The present disclosure relates to a flat nonaqueous electrolyte secondary battery. Background Art

[0002] In the past, flat non-aqueous electrolyte secondary batteries have been used in power supplies of various electronic devices. Examples of flat non-aqueous electrolyte secondary batteries include batteries using a wound electrode group and batteries using a zigzag electrode group. The wound electrode group is formed by winding a positive electrode plate and a negative electrode plate with a separator sandwiched between them. A battery using a zigzag electrode group is disclosed, for example, in Patent Document 1.

[0003] Patent Document 1 discloses an example of forming an electrode group by folding the positive electrode plate and the negative electrode plate in a direction in which the positive electrode plate extends at an angle of 90 degrees (see Patent Document 1). Figure 2 In this example, no active material layer is formed on the bent portion of the electrode plate (see Patent Document 1). Figure 1 ).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2016-76329 Summary of the invention

[0007] In a zigzag-bent electrode group, if an active material layer is not formed on the bent portion of the electrode plate, this portion does not contribute to the battery capacity. On the other hand, if an active material layer is formed on the bent portion, lithium metal may be precipitated from the bent portion due to repeated charging and discharging. Such lithium metal precipitation may cause a battery short circuit and a reduction in battery capacity.

[0008] Under such circumstances, one of the objects of the present disclosure is to provide a flat nonaqueous electrolyte secondary battery using a zigzag-shaped electrode group, which has high battery capacity and reliability.

[0009] As a result of the research, the inventors of the present application found that the above-mentioned problems can be solved by adopting a specific structure. The present disclosure is based on this new finding.

[0010] One aspect of the present disclosure relates to a flat non-aqueous electrolyte secondary battery. The flat non-aqueous electrolyte secondary battery comprises: a flat shell; and a positive electrode plate, a negative electrode plate, a separator, and a non-aqueous electrolyte arranged in the shell, the positive electrode plate comprises more than three positive electrode units connected in a row, the negative electrode plate comprises more than three negative electrode units connected in a row, the more than three positive electrode units respectively comprise a positive electrode collector and a positive electrode active material layer arranged on the positive electrode collector, the more than three negative electrode units respectively comprise a negative electrode collector and a negative electrode active material layer arranged on the negative electrode collector, the positive electrode plate is bent in opposite directions by using the boundary portions of two adjacent positive electrode units as first bending portions, thereby zigzagging the positive electrode plate, The negative electrode plate is bent in a zigzag manner by bending the negative electrode plate in opposite directions by using the boundary portions of two adjacent negative electrode units as the second bending portions, respectively, and the positive electrode active material layer and the negative electrode active material layer are respectively arranged on the first and second bending portions, and the positive electrode plate, the negative electrode plate and the separator are arranged so that the positive electrode active material layer of the positive electrode unit and the negative electrode active material layer of the negative electrode unit are opposed to each other with the separator sandwiched therebetween, and the first bending portion and the second bending portion are opposed to each other with the separator sandwiched therebetween, and the length X of the positive electrode unit in the direction in which the positive electrode units are connected is longer than the length Y of the negative electrode unit in the direction in which the negative electrode units are connected.

[0011] Another aspect of the present disclosure relates to other flat non-aqueous electrolyte secondary batteries. The flat non-aqueous electrolyte secondary battery comprises: a flat shell; and a positive electrode plate, a negative electrode plate, a separator, and a non-aqueous electrolyte arranged in the shell, the positive electrode plate comprises more than three positive electrode units connected in a row, the negative electrode plate comprises more than three negative electrode units connected in a row, the more than three positive electrode units respectively comprise a positive electrode collector and a positive electrode active material layer arranged on the positive electrode collector, the more than three negative electrode units respectively comprise a negative electrode collector and a negative electrode active material layer arranged on the negative electrode collector, the positive electrode plate is bent in a zigzag manner by bending the positive electrode plate in opposite directions with the boundary portions of two adjacent positive electrode units as the first bending portions, and the negative electrode plate is bent in opposite directions with the boundary portions of two adjacent negative electrode units as the second bending portions. The negative electrode plate is bent in a zigzag manner, and the positive electrode active material layer and the negative electrode active material layer are arranged on the first and second bent portions, respectively. The positive electrode plate, the negative electrode plate and the separator are arranged so that the positive electrode active material layer of the positive electrode unit and the negative electrode active material layer of the negative electrode unit are opposed to each other with the separator sandwiched therebetween, and the first bent portion and the second bent portion are opposed to each other with the separator sandwiched therebetween, and a distance L1 between the positive electrode active material layer at the center of the first bent portion at the portion of the negative electrode plate wrapped by the positive electrode plate and the negative electrode active material layer at the center of the second bent portion is longer than a distance L2 between the positive electrode active material layer at the center of the first bent portion at the portion of the positive electrode plate wrapped by the negative electrode plate and the negative electrode active material layer at the center of the second bent portion.

[0012] According to the present disclosure, a flat nonaqueous electrolyte secondary battery using a zigzag-shaped electrode group can be obtained, which has high battery capacity and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a cross-sectional view schematically showing an example of the secondary battery according to the present embodiment.

[0014] Figure 2 It indicates Figure 1 2 is a cross-sectional view of an example of an electrode group of a secondary battery shown in FIG.

[0015] Figure 3A Yes Figure 2 The positive electrode plate of the electrode group shown is a top view when it is unfolded.

[0016] Figure 3B yes Figure 3A Cross-sectional view at line IIIB-IIIB.

[0017] Figure 4AYes Figure 2 The negative electrode plate of the electrode group shown is a top view when it is unfolded.

[0018] Figure 4B yes Figure 4A Cross-sectional view at line IVB-IVB of .

[0019] Figure 5 It is used to illustrate Figure 2 Schematic diagram of the configuration of the structural components of the electrode group is shown.

[0020] Figure 6 This is a schematic diagram for explaining the calculation method of the capacity loss rate. DETAILED DESCRIPTION

[0021] The following describes the embodiments of the present disclosure. In addition, in the following description, examples are given to illustrate the embodiments of the present disclosure, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials are sometimes exemplified, but other numerical values ​​and materials can be used as long as the effects of the present disclosure can be obtained.

[0022] (Flat non-aqueous electrolyte secondary battery)

[0023] The following describes a first flat nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure and a second flat nonaqueous electrolyte secondary battery according to another embodiment of the present disclosure. Hereinafter, the first flat nonaqueous electrolyte secondary battery may be referred to as the "first secondary battery" and the second flat nonaqueous electrolyte secondary battery may be referred to as the "second secondary battery". In addition, in one viewpoint, the first secondary battery and the second secondary battery characterize the battery of the present disclosure from different viewpoints. Therefore, at least a portion of the battery contained in the first secondary battery and at least a portion of the battery contained in the second secondary battery are repeated.

[0024] (Matters common to the first secondary battery and the second secondary battery)

[0025] The first and second secondary batteries (flat non-aqueous electrolyte secondary batteries) include: a flat shell; and a positive electrode plate, a negative electrode plate, a separator and a non-aqueous electrolyte arranged in the shell. The positive electrode plate includes more than three positive electrode units connected in a row. The negative electrode plate includes more than three negative electrode units connected in a row. The three or more positive electrode units respectively include a positive electrode collector and a positive electrode active material layer arranged on the positive electrode collector. The three or more negative electrode units respectively include a negative electrode collector and a negative electrode active material layer arranged on the negative electrode collector. The positive electrode plate is bent in a zigzag manner by bending the positive electrode plate in opposite directions by using the boundary between two adjacent positive electrode units as the first bending portion. The negative electrode plate is bent in a zigzag manner by using the boundary between two adjacent negative electrode units as the second bending portion. The positive electrode active material layer and the negative electrode active material layer are respectively arranged on the first and second bending portions. The positive electrode plate, the negative electrode plate, and the separator are arranged so that the positive electrode active material layer of the positive electrode unit and the negative electrode active material layer of the negative electrode unit face each other with the separator interposed therebetween, and the first bent portion and the second bent portion face each other with the separator interposed therebetween.

[0026] Here, bending the electrode plates (positive electrode plates and negative electrode plates) in opposite directions means bending the electrode plates by approximately 180 degrees. By bending the electrode plates in opposite directions at the bent portions, the electrode plates are bent in a zigzag manner.

[0027] In the first secondary battery, the length X of the positive electrode unit in the direction in which the positive electrode unit is connected is longer than the length Y of the negative electrode unit in the direction in which the negative electrode unit is connected. Here, the length X of the positive electrode unit in the direction in which the positive electrode unit is connected refers to the length along the positive electrode plate. In other words, the length X is the length of the positive electrode unit in the direction in which the positive electrode unit is connected when the positive electrode plate is flattened and unfolded. Similarly, the length Y of the negative electrode unit in the direction in which the negative electrode unit is connected is the length of the negative electrode unit in the direction in which the negative electrode unit is connected when the negative electrode plate is flattened and unfolded.

[0028] In the first secondary battery, more than three positive electrode units have the same planar shape (including substantially the same planar shape). That is, the length X of each positive electrode unit is substantially equal. Similarly, more than three negative electrode units have the same planar shape (including substantially the same planar shape). That is, the length Y of each negative electrode unit is substantially equal. The planar shapes of more than three positive electrode units of the second secondary battery are usually the same, but may be different. Similarly, the planar shapes of more than three negative electrode units of the second secondary battery are usually the same, but may be different.

[0029] In the second secondary battery, the distance L1 between the positive electrode active material layer at the center of the first bend portion at the portion where the negative electrode plate is wrapped by the positive electrode plate and the negative electrode active material layer at the center of the second bend portion is longer than the distance L2 between the positive electrode active material layer at the center of the first bend portion at the portion where the positive electrode plate is wrapped by the negative electrode plate and the negative electrode active material layer at the center of the second bend portion.

[0030] In the following, the portion where the negative electrode plate is surrounded by the positive electrode plate may be referred to as the “positive electrode active material excess portion”. Similarly, in the following, the portion where the positive electrode plate is surrounded by the negative electrode plate may be referred to as the “negative electrode active material excess portion”.

[0031] Here, the center of the bends (first and second bends) at the excess positive active material portion and the excess negative active material portion refers to the cross section along the direction in which the electrode units (positive electrode units and negative electrode units) are connected in a zigzag manner (i.e., Figure 2 For example, the center of the first bend at the excess portion of the positive electrode active material refers to the cross section along the direction in which the positive electrode units are connected in a zigzag manner (i.e., the center of the first bend at the excess portion of the positive electrode active material). Figure 2 In a typical example, the boundary between two adjacent positive electrode units becomes the center of the first bend, and the boundary between two adjacent negative electrode units becomes the center of the second bend.

[0032] In the first and second secondary batteries, the active material layers are also disposed in the first and second bent portions, so that the capacity of the battery can be increased.

[0033] Considering the battery characteristics, a given amount of active material is arranged per unit area on the positive plate and the negative plate. Therefore, when the positive plate and the negative plate are placed in parallel, the positive active material and the negative active material can be placed in an ideal ratio as designed. However, in the electrode group that is bent tortuously, the amount of positive active material is greater in the portion where the negative plate is wrapped by the positive plate than in the ideal ratio. The inventors of the present application have found that in this case, if charging and discharging are repeated, the negative active material layer will not absorb the lithium ions released from the positive active material layer cleanly, and lithium metal is easily precipitated between the active material layers. Such lithium metal precipitation may cause battery short circuit and reduced battery capacity. On the other hand, in the portion where the positive plate is wrapped by the negative plate, the amount of negative active material is greater than the ideal ratio. In this case, even if charging and discharging are repeated, the possibility of lithium metal precipitation between the active material layers is also very small.

[0034] In the first and second secondary batteries, the gap between the positive electrode active material layer and the negative electrode active material layer at the excess positive electrode active material portion can be made larger than the gap between the positive electrode active material layer and the negative electrode active material layer at the excess negative electrode active material portion. According to this structure, since the exchange of lithium ions at the excess positive electrode active material portion can be suppressed, the precipitation of lithium metal at this portion can be suppressed.

[0035] In the first and second secondary batteries, the number N of positive electrode units contained in one positive electrode plate is usually the same as the number M of negative electrode units contained in one negative electrode plate. In a preferred example, the number N of positive electrode units and the number M of negative electrode units are the same and are odd numbers, but these numbers may also be even numbers.

[0036] The planar shape of the positive electrode unit can be selected corresponding to the shape of the shell. The planar shape of the positive electrode unit can be a polygonal shape or a circular shape. When the shell is square, a preferred example of the planar shape of the positive electrode unit is a rectangle, for example, a rectangle slightly smaller than one main surface of the shell. When the shell is coin-shaped, a preferred example of the planar shape of the positive electrode unit is a polygonal shape (for example, a hexagonal shape, an octagonal shape, a decagonal shape, etc.) or a circular shape. The positive electrode unit may have a planar shape of a portion that further gives the above-mentioned planar shape a bent portion.

[0037] The planar shape of the negative electrode unit can be selected in the same manner as the planar shape of the positive electrode unit described above. In a preferred example, the planar shape of the positive electrode unit and the planar shape of the negative electrode unit are selected so that the area corresponding to the positive electrode active material and the negative electrode active material is maximized. For example, the planar shape of the positive electrode unit and the planar shape of the negative electrode unit can be set to substantially similar shapes. Among them, the planar shape of the positive electrode unit and the planar shape of the negative electrode unit are selected so as to satisfy the above-mentioned relationship between the length X and the length Y and / or the above-mentioned relationship between the distance L1 and the distance L2.

[0038] Generally, one positive electrode plate includes one positive electrode collector and a positive electrode active material layer disposed on the collector. In a preferred example, the positive electrode active material layer disposed on the positive electrode collector is continuous without interruption. Generally, one negative electrode plate includes one negative electrode collector and a negative electrode active material layer disposed on the collector. In a preferred example, the negative electrode active material layer formed on the negative electrode collector is continuous without interruption.

[0039] In the first and second secondary batteries, the difference (XY) between the length X and the length Y may be in the range of 0.1 to 0.3 mm. By setting the difference (XY) in this range, a secondary battery with less loss of battery capacity and high reliability can be obtained.

[0040] Without considering the thickness of the components (plates, collectors, separators) constituting the electrode group, the difference (L1-L2) between the distance L1 and the distance L2 can be regarded as equal to the difference (XY). Therefore, the difference (L1-L2) can also be set to the range of 0.1 to 0.3 mm in the same way as the difference (XY). If the thickness of the components constituting the electrode group is considered, the value of the difference (L1-L2) can be set to a value slightly smaller than the preferred value of the difference (XY). Preferably, L2 is small, for example, it can be the same degree as the thickness of the separator. In addition, when the electrode group has multiple different distances L1 and / or multiple different distances L2, it is preferred that all of these distances L1 and distance L2 satisfy the above relationship.

[0041] The maximum length of the positive electrode unit in the direction perpendicular to the direction connected to the positive electrode unit is set to width WX. In addition, the maximum length of the negative electrode unit in the direction perpendicular to the direction connected to the negative electrode unit is set to width WY. The width WX of the positive electrode unit in the direction perpendicular to the direction connected to the positive electrode unit and the width WY of the negative electrode unit in the direction perpendicular to the direction connected to the negative electrode unit can satisfy the relationship of WX>WY, but usually satisfy the relationship of WX≤WY. In addition, the area SP of one positive electrode unit and the area SN of one negative electrode unit can satisfy the relationship of SP>SN, but usually satisfy the relationship of SP≤SN.

[0042] In the first and second secondary batteries, at least a portion of the separator may be fixed to the negative electrode plate (negative electrode active material layer), or may be fixed to the positive electrode plate (positive electrode active material layer). According to these structures, the manufacture of the battery becomes easy. The method for fixing the separator is not particularly limited, and known techniques can be used. For example, the separator can be fixed to the negative electrode plate by hot pressing, etc. Alternatively, a separator having an adhesive layer on the surface can be used. The adhesive layer can use, for example, a layer containing a resin such as polyvinylidene fluoride.

[0043] The first and second secondary batteries may include at least one positive electrode plate and at least one negative electrode plate, so that the total number of positive electrode plates and the number of negative electrode plates is 2 or 3. Three examples (first to third configuration examples) related to the number of positive electrode plates and negative electrode plates and the configuration of active material layers are described below.

[0044] In the first configuration example, the number of positive plates and the number of negative plates are each 1. In this case, the positive active material layer is arranged only on one side of the positive current collector and the negative active material layer is arranged only on one side of the negative current collector. In the second configuration example, the number of positive plates is 2 and the number of negative plates is 1. In this case, the positive active material layer is arranged only on one side of the positive current collector and the negative active material layer is arranged on both sides of the negative current collector. In the second configuration example, the positive plates and the negative plates are arranged so that one negative plate is sandwiched by two positive plates. In the third configuration example, the number of negative plates is 2 and the number of positive plates is 1. In this case, the positive active material layer is arranged on both sides of the positive current collector and the negative active material layer is arranged only on one side of the negative current collector. In the third configuration example, the positive plates and the negative plates are arranged so that one positive plate is sandwiched by two negative plates.

[0045] In the first and second secondary batteries, in the portion where the positive electrode plate is wrapped by the negative electrode plate (the portion with excess negative active material), the positive electrode active material layer of the first bend portion and the negative electrode active material layer of the second bend portion can be in contact with the separator, respectively. In such a structure, it is also difficult for lithium metal to precipitate in the portion with excess negative active material.

[0046] In the first and second secondary batteries, there may or may not be a component preventing the penetration of non-aqueous electrolyte between the first bend and the second bend (especially between the two at the excess portion of positive active material). By arranging a component preventing the penetration of non-aqueous electrolyte (from other perspectives, a component preventing the movement of lithium ions or a component preventing the movement of non-aqueous electrolyte) between the first bend and the second bend, the precipitation of lithium metal at this part can be suppressed. However, since the first and second secondary batteries have a structure that suppresses the precipitation of lithium metal at the excess portion of positive active material, the necessity of using such a component is low. By making such a component unnecessary, manufacturing becomes easy and manufacturing costs can be reduced. In addition, space loss caused by the use of such a component can be prevented.

[0047] In addition to using the structure unique to this embodiment, the components of the first and second secondary batteries (shell, material constituting the positive electrode plate, material constituting the negative electrode plate, separator, non-aqueous electrolyte and other components, etc.) are not particularly limited. For example, the first and second batteries may include insulating components and other components that insulate the surroundings of the electrode group. In addition to having a structure unique to this embodiment, known materials and known structures can be used for the components of the first and second secondary batteries. With regard to these components, examples are given below, but this embodiment is not limited to the following examples.

[0048] (Positive plate)

[0049] The positive electrode plate includes a positive electrode collector and a positive electrode active material layer. A portion of the positive electrode collector may constitute a connecting portion electrically connected to a portion of the shell (shell body or sealing plate) that functions as a terminal. In this case, the connecting portion is connected to a portion of the shell by welding (e.g., ultrasonic welding) or the like.

[0050] Examples of the positive electrode current collector include a sheet (e.g., foil, mesh, or punched plate) made of a conductive material (e.g., a metal material). Examples of the metal material constituting the positive electrode current collector include aluminum, aluminum alloy, titanium, 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.

[0051] The positive electrode active material layer contains a positive electrode active material and may contain other substances (binders, conductive agents, etc.) as needed. Examples of positive electrode active materials include substances that reversibly release lithium ions, that is, substances that release and contain lithium ions. Specifically, examples of positive electrode active materials include metal oxides containing lithium, lithium-transition metal phosphate compounds, lithium-transition metal sulfate compounds, etc. 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 (such as LiMn2O4), lithium-nickel composite oxides (such as LiNiO2), lithium-cobalt composite oxides (such as LiCoO2), and composite oxides in which part of these transition metal elements are replaced with other metal elements (main group metal elements and / or transition metal elements).

[0052] Examples of the binder include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubber polymers. Examples of the fluororesins include polytetrafluoroethylene and polyvinylidene fluoride. The binder may be used alone or in combination of two or more.

[0053] Examples of the conductive agent include carbon materials. Examples of the carbon material used as the conductive agent include carbon black (acetylene black, Ketjen black, etc.), carbon nanotubes, and graphite. The conductive agent may be used alone or in combination of two or more.

[0054] (Negative plate)

[0055] The negative electrode plate includes a negative electrode collector and a negative electrode active material layer. A portion of the negative electrode collector may constitute a connection portion electrically connected to a portion of the housing (housing body or sealing plate) that functions as a terminal. In this case, the connection portion is connected to a portion of the housing by welding (e.g., ultrasonic welding) or the like.

[0056] Examples of negative electrode current collectors include sheets (e.g., foil, mesh, or punched plate) made of conductive materials (e.g., metal materials). The metal material of the negative electrode current collector may be a material that does not form lithium, alloys, or intermetallic compounds. Examples of metal materials of the negative electrode current collector include copper, nickel, iron, and alloys containing these metal elements (copper alloys, stainless steel, etc.). 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, for example, in the range of 5 to 300 μm.

[0057] The negative electrode active material layer includes a negative electrode active material and may include other materials (binder, conductive agent, thickener, etc.) as needed. Examples of negative electrode active materials include materials that reversibly encapsulate lithium ions, i.e., materials that encapsulate and release lithium ions. Specifically, examples of negative electrode active materials include carbon materials, silicon, silicon compounds, and lithium alloys. Examples of carbon materials include graphite, coke, graphitized intermediate carbon, graphitized carbon fibers, and amorphous carbon.

[0058] Examples of binders 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 forms of these rubbers. Examples of conductive agents include those exemplified in the description of the positive electrode active material layer. Examples of thickeners include water-soluble polymers containing carboxyl groups (e.g., carboxymethyl cellulose).

[0059] (Separator)

[0060] Examples of the separator include sheets having ion permeability and insulation. In addition, the separator may be obtained by laminating a plurality of sheets including sheets having ion permeability and insulation. The separator has a size required to insulate the positive electrode plate from the negative electrode plate.

[0061] The separator may be a microporous film, a woven fabric or a non-woven fabric. Examples of the material of the separator include insulating polymers, specifically polyolefin polymers, polyamide polymers, cellulose polymers, etc. The thickness of the separator may be in the range of 5 to 200 μm.

[0062] (Non-aqueous electrolyte)

[0063] As the non-aqueous electrolyte, a non-aqueous electrolyte having lithium ion conductivity is used. 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. The 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.

[0064] The gel-like non-aqueous electrolyte includes a liquid non-aqueous electrolyte and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and becomes gelled is used. Examples of such polymer materials include fluororesins, acrylic resins, and polyether resins.

[0065] Examples of anions of lithium salts include BF4 - 、ClO4 - PF6 - CF3SO3 - CF3CO2 - , imide anions, oxalate complex anions, etc.

[0066] Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and halogen-substituted products thereof (eg, fluorides), etc. The non-aqueous electrolyte may contain only one of these non-aqueous solvents, or may contain two or more of them.

[0067] Examples of esters include carbonates, carboxylates, etc. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, fluoroethylene carbonate (FEC), etc. Examples of chain carbonates include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, etc. Examples of cyclic carboxylates include γ-butyrolactone, γ-valerolactone, etc. Examples of chain carboxylates include ethyl acetate, methyl propionate, methyl fluoropropionate, etc.

[0068] The concentration of the lithium salt in the non-aqueous electrolyte can 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 can be in the range of 0.5 mol / L to 3.5 mol / L.

[0069] (case)

[0070] The flat housing may be a square (rectangular parallelepiped) or a coin (low cylindrical). That is, the first and second secondary batteries may be square batteries or coin-shaped batteries. The coin-shaped housing includes a so-called button-shaped housing.

[0071] A typical housing includes a housing body, a sealing plate, and a gasket disposed between the housing body and the sealing plate. Typically, the housing body and the sealing plate function as electrode terminals, respectively. For example, in the case of a general coin-shaped battery, the housing body functions as a positive terminal, and the sealing plate functions as a negative terminal. The housing body and the sealing plate can be formed using metal (e.g., conductive stainless steel), respectively.

[0072] The first and second secondary batteries and their manufacturing methods are described in detail below with reference to the accompanying drawings. The figures shown below are schematic diagrams and do not correctly reflect the actual structure. In addition, as mentioned above, since the basic structure and manufacturing method of the first and second secondary batteries are the same, they are collectively described as the secondary battery of embodiment 1. An example of a coin-shaped battery is described below, but the present disclosure is not limited to the example described below. The constituent elements of the example described below can be changed based on the above description. In addition, the matters described below can also be applied to the above embodiment.

[0073] (Implementation Method 1)

[0074] exist Figure 1 A cross-sectional view schematically shows the secondary battery according to Embodiment 1. Figure 1 The secondary battery 10 includes a flat (coin-shaped) case 20, an electrode group 30 and a non-aqueous electrolyte (not shown) disposed in the case 20. The case 20 includes a bottomed cylindrical case body 21, a sealing plate 22, and a gasket 23. The case body 21 is sealed by the sealing plate 22 and the gasket 23.

[0075] exist Figure 2 A cross-sectional view of the electrode group 30 is shown. Figure 2 The cross section is taken along the direction in which the positive electrode unit and the negative electrode unit are connected in a zigzag manner. The electrode group 30 includes a positive electrode plate 40, a negative electrode plate 50, and a separator 60 disposed therebetween. The positive electrode plate 40, the negative electrode plate 50, and the separator 60 are each bent in a zigzag manner.

[0076] (Positive plate)

[0077] exist Figure 3A The top view of the positive electrode plate 40 when it is flattened is shown. Figure 3B Show Figure 3A The positive electrode plate 40 includes a positive electrode collector 41 and a positive electrode active material layer 42 disposed on the positive electrode collector 41. The positive electrode plate 40 includes five positive electrode units 40a connected in a row. Each positive electrode unit 40a includes a positive electrode collector 41 and a positive electrode active material layer 42. Each positive electrode unit 40a has the same planar shape. Specifically, Figure 3A The positive electrode unit 40a in the example shown has an octagonal planar shape. Figure 3A In FIG. 4 , a dotted line indicates a boundary 40b between two adjacent positive electrode units 40a. Figure 3AAs shown in FIG. 1 , the length of each positive electrode unit 40a in the direction PD (long side direction) in which the positive electrode units 40a are connected is set to length X. In addition, the maximum length of each positive electrode unit 40a in the direction perpendicular to the direction PD is set to width WX. The length X of each of the five positive electrode units 40a is equal, and the width WX of each of the five positive electrode units 40a is equal.

[0078] The positive electrode plate 40 further includes a connection portion 43 for electrically connecting the positive electrode plate 40 to the case body 21. The connection portion 43 is connected to the ends of the positive electrode units 40a connected in a row, and in the example shown in the figure, is connected in the direction in which the positive electrode units 40a are connected.

[0079] In the example shown in the figure, the connecting portion 43 has a shape substantially the same as that of the positive electrode collector 41 of one positive electrode unit 40a. The connecting 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. As shown in the figure, a portion of a positive electrode collector 41 constitutes the connecting portion 43, and another portion constitutes the collector of the positive electrode unit 40a. The connecting portion 43 is a portion where the positive electrode mixture is not applied to the positive electrode collector 41 and where the positive electrode mixture is not applied. In addition, as long as the positive electrode collector 41 can be electrically connected to the case body 21, the structure of the connecting portion 43 is not particularly limited.

[0080] The positive electrode plate 40 is bent in opposite directions by using the boundary between two adjacent positive electrode units 40a as the first bent portion 40ab, so that the positive electrode plate 40 is formed as follows. Figure 2 In one viewpoint, the positive electrode unit 40a includes a first bent portion 40ab and a first overlapped portion 40aa. The first overlapped portion 40aa is along the stacking direction SD (reference direction) of the electrode group 30. Figure 2 ) overlapping parts.

[0081] In addition, if Figure 2 and the following Figure 5 As shown, the boundary between the connection portion 43 and the positive electrode unit 40 a is also bent as a bent portion.

[0082] The positive electrode active material layer 42 is formed on the surface of the positive electrode plate 40 on the side facing the negative electrode plate 50 except for the connection portion 43. That is, the positive electrode active material layer 42 is formed on both the first overlapped portion 40aa and the first bent portion 40ab.

[0083] (Negative plate)

[0084] exist Figure 4A FIG. 1 shows a top view of the negative electrode plate 50 when it is flattened and unfolded. Figure 4B Show Figure 4AThe negative electrode plate 50 includes a negative electrode collector 51 and a negative electrode active material layer 52 disposed on the negative electrode collector 51. The negative electrode plate 50 includes five negative electrode units 50a connected in a row. Each negative electrode unit 50a includes a negative electrode collector 51 and a negative electrode active material layer 52. Each negative electrode unit 50a has the same planar shape. Specifically, Figure 4A The negative electrode unit 50a in the example shown has an octagonal planar shape. Figure 4A In FIG. 5 , a boundary 50b between two adjacent negative electrode units 50a is shown by a dotted line. Figure 4A As shown in FIG. 1 , the length of each negative electrode unit 50a in the direction ND (longitudinal direction) in which the negative electrode units 50a are connected is set to length Y. In addition, the maximum length of each negative electrode unit 50a in the direction perpendicular to the direction ND is set to width WY. The length Y of each of the five negative electrode units 50a is equal, and the width WY of each of the five negative electrode units 50a is equal.

[0085] The negative electrode plate 50 further includes a connection portion 53 for electrically connecting the negative electrode plate 50 to the case body 21. The connection portion 53 is connected to the ends of the negative electrode units 50a connected in a row. In the example shown in the figure, the connection is in the direction in which the negative electrode units 50a are connected.

[0086] In the example shown in the figure, the connecting portion 53 has a shape substantially the same as that of the negative electrode collector 51 of one negative electrode unit 50a. The connecting portion 53 is a portion electrically connected to the sealing plate 22, and is connected to the sealing plate 22 by, for example, welding. As shown in the figure, a portion of a negative electrode collector 51 constitutes the connecting portion 53, and another portion constitutes the collector of the negative electrode unit 50a. The connecting portion 53 is a portion of the negative electrode mixture that is not coated on the negative electrode collector 51. In addition, as long as the negative electrode collector 51 can be electrically connected to the sealing plate 22, it is not particularly limited to the structure of the connecting portion 53.

[0087] The negative electrode plate 50 is bent in opposite directions by using the boundary between two adjacent negative electrode units 50a as the second bent portion 50ab, so that the negative electrode plate 50 is Figure 2 In one viewpoint, the negative electrode unit 50a includes a second bent portion 50ab and a second overlapped portion 50aa. The second overlapped portion 50aa is formed along the stacking direction SD (reference direction) of the electrode group 30. Figure 2 ) overlapping parts.

[0088] In addition, if Figure 2 and the following Figure 5 As shown, the boundary between the connection portion 53 and the negative electrode unit 50 a is also bent as a bent portion.

[0089] The negative electrode active material layer 52 is formed on one surface of the negative electrode plate 50 except for the connection portion 53. That is, the negative electrode active material layer 52 is formed on both the second overlapping portion 50aa and the second bent portion 50ab.

[0090] exist Figure 5 A schematic diagram for explaining the arrangement of the positive electrode plate 40 , the negative electrode plate 50 , and the separator 60 is shown. Figure 5 Schematically showing the Figure 2 The bent portion of the electrode group 30 shown is slightly expanded to separate the components. Figure 5 In FIG. 1 , the connection portions 43 and 53 are shown by dotted lines.

[0091] like Figure 5 As shown in FIG. 1 , the first bent portion 40ab of the positive electrode plate 40 and the second bent portion 50ab of the negative electrode plate 50 face each other with the separator 60 interposed therebetween. Figure 2 As shown, the positive electrode active material layer 42 and the negative electrode active material layer 52 face each other with the separator 60 interposed therebetween. The positive electrode plate 40, the negative electrode plate 50, and the separator 60 are arranged so as to satisfy these structures.

[0092] In addition, Figure 2 In the electrode group 30, the positive electrode current collector 41 and / or the negative electrode current collector 51 are in contact with the case 20, resulting in a short circuit. An insulating member (e.g., an insulating tape) for preventing such a short circuit may be arranged around the electrode group 30. For example, an insulating member for preventing the positive electrode current collector 41 and the negative electrode current collector 51 from contacting the case 20 may be arranged outside the respective bent portions.

[0093] like Figure 2 As shown, 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 of the positive electrode unit 40 a and the negative electrode active material layer 52 of the negative electrode unit 50 a face each other with the separator 60 interposed therebetween, and the first bent portion 40 ab and the second bent portion 50 ab face each other with the separator 60 interposed therebetween.

[0094] The length X of the positive electrode unit 40a is longer than the length Y of the negative electrode unit 50a. The difference (XY) between the length X and the length Y can be set to the above range. In addition, the width WX of the positive electrode unit and the width WY of the negative electrode unit usually satisfy the relationship WX≤WY.

[0095] like Figure 2As shown, the distance between the positive electrode active material layer 42 at the center of the first bend 40ab at the portion of the negative electrode plate 50 wrapped by the positive electrode plate 40 (positive electrode active material excess portion A) and the negative electrode active material layer 52 at the center of the second bend 50ab is set as distance L1. In addition, the distance between the positive electrode active material layer 42 at the center of the first bend 40ab at the portion of the positive electrode plate 40 wrapped by the negative electrode plate 50 (negative electrode active material excess portion B) and the negative electrode active material layer 52 at the center of the second bend 50ab is set as distance L2. Distance L1 is longer than distance L2. This can be achieved, for example, by making length X longer than length Y.

[0096] In the positive electrode active material excess portion A, the center portion of the first bent portion 40ab is the portion at which Figure 2 The outermost portion of the first bent portion 40ab in the positive electrode active material excess portion A in the cross section of FIG. Figure 2 In the cross section of the positive electrode active material excess portion A, the outermost portion of the second bend portion 50ab. Similarly, in the negative electrode active material excess portion B, the central portion of the first bend portion 40ab is the portion located at the outermost portion. Figure 2 The outermost portion of the first bent portion 40ab in the negative electrode active material excess portion B in the cross section of FIG. Figure 2 In the cross section of , the outermost portion of the second bend portion 50ab in the negative electrode active material excess portion B. In the positive electrode active material excess portion A, the center of the first bend portion 40ab and the center of the second bend portion 50ab are opposed to each other via the separator 60. In the negative electrode active material excess portion B, the center of the first bend portion 40ab and the center of the second bend portion 50ab are also opposed to each other via the separator 60.

[0097] In the excess positive active material portion A, a gap S is usually formed between the positive active material layer 42 and the separator 60 and / or between the negative active material layer 52 and the separator 60. On the other hand, in the excess negative active material portion B, the positive active material layer 42 and the negative active material layer 52 may be in contact with the separator 60 without a gap.

[0098] According to the secondary battery of embodiment 1, as described above, lithium metal precipitation (e.g., dendritic lithium metal precipitation) at the positive electrode active material excess portion A can be suppressed. As a result, a highly reliable battery can be obtained. In addition, in the secondary battery of embodiment 1, since the active material is also arranged in the bent portion, a high capacity can be achieved.

[0099] In addition, in Embodiment 1, the case where there is only one positive plate, one negative plate, and one separator constituting the electrode group is described. However, it is also possible that there is only one positive plate and one negative plate, and two on the other. In this case, active material layers are formed on both sides of only one electrode plate, and active material layers are formed on one side of each of the two electrode plates on the other side. Furthermore, in this case, two separators are used. When there is only one positive electrode plate and two negative electrodes, one positive electrode plate, two negative electrodes, and two separators are arranged in the order of 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 manner. Similarly, when there is only one negative electrode plate and two positive electrode plates, two positive electrode plates, one negative electrode plate, and two separators are arranged and folded in a zigzag manner in the order of positive electrode collector / positive electrode active material layer / separator / negative electrode active material layer / negative electrode collector / negative electrode active material layer / separator / positive electrode active material layer / positive electrode collector. When active material layers are formed on both sides of the positive electrode plate (or negative electrode plate), one positive electrode unit (or one negative electrode unit) includes a positive electrode collector (or negative electrode collector) and positive electrode active material layers (or negative electrode active material layers) arranged on both sides thereof.

[0100] (Method for manufacturing flat non-aqueous electrolyte secondary battery)

[0101] An example of a method for manufacturing a secondary battery of the present embodiment is described below. An example of a method for manufacturing the secondary battery 10 described in Embodiment 1 is described below. The first and second secondary batteries can be manufactured using the manufacturing method described below. Well-known techniques can be used in the manufacturing process described below. In addition, the method for manufacturing a secondary battery of the present embodiment is not limited to the manufacturing method described below.

[0102] First, prepare the positive electrode plate 40 and the negative electrode plate 50. In an example of a preferred method for manufacturing the positive electrode plate 40, first, the materials constituting the positive electrode active material layer 42 are mixed to prepare a positive electrode mixture. Next, the positive electrode mixture is applied to a conductive sheet (such as a metal foil) that becomes the positive electrode collector 41 to form the positive electrode active material layer 42. The positive electrode plate 40 is manufactured in this way. The positive electrode plate 40 is manufactured so that it has the above-mentioned structure (planar shape). After forming the positive electrode active material layer 42 in a given area of ​​a large-area conductive sheet, the conductive sheet and the positive electrode active material layer 42 are stamped together using a stamping die to manufacture the positive electrode plate 40.

[0103] Unlike the battery described in Patent Document 1 in which an active material layer is not formed on the bent portion of the electrode plate, in this embodiment, an active material layer is also formed on the first and second bent portions 40ab and 50ab. In this case, it is not necessary to separately apply the active material layer on the bent portion and the portion other than the bent portion. Therefore, the positive electrode plate used in this embodiment is easy to manufacture (the same applies to the negative electrode plate).

[0104] In an example of a preferred method for manufacturing the negative electrode plate 50, first, the materials constituting the negative electrode active material layer 52 are mixed to prepare a negative electrode mixture. Next, the negative electrode mixture is applied to a conductive sheet (e.g., metal foil) serving as the negative electrode current collector 51 to form the negative electrode active material layer 52. The negative electrode plate 50 is manufactured in this manner. The negative electrode plate 50 is manufactured so as to have the above-mentioned structure (planar shape). After forming the negative electrode active material layer 52 in a given area of ​​a large-area conductive sheet, the conductive sheet and the negative electrode active material layer 52 are stamped together using a stamping die to manufacture the negative electrode plate 50.

[0105] 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 are opposite to each other with the separator 60 sandwiched therebetween. And, they are bent together in a zigzag manner to produce an electrode group. In addition, the positive electrode plate 40, the negative electrode plate 50 and the separator 60 may be bent and then combined to produce the electrode group 30. In addition, in the production of the electrode group 30, at least a portion of the separator may be fixed to the positive electrode plate 40 or the negative electrode plate 50 before the electrode plate is bent. By fixing the separator, the production of the electrode group becomes easy. The fixing of the separator can be performed by the above-mentioned method.

[0106] Next, the connection portion 43 is electrically connected to the housing body 21. Similarly, the connection portion 53 is electrically connected to the sealing plate 22. These electrical connections can be implemented, for example, by welding (ultrasonic welding, etc.). In addition, as needed, before or after the connection of the connection portion, the surrounding of the electrode group 30 is protected by an insulating member.

[0107] Next, the electrode group 30 and the nonaqueous electrolyte are placed in the case body 21. Next, the case body 21 is sealed using the sealing plate 22 and the gasket 23. In this way, the secondary battery 10 of the first embodiment is obtained.

[0108] Example

[0109] The present disclosure is further described in detail through examples.

[0110] (Example 1)

[0111] In Example 1, a Figure 1A battery having the same structure as the secondary battery 10 shown in the figure. Here, the number of positive electrode units and negative electrode units is set to 5 respectively. The plane shapes of the positive electrode unit and the negative electrode unit are respectively set to be approximately regular octagons. Then, the values ​​of the length X and the length Y are changed to make multiple batteries. In addition, the widths WX and WY in the direction perpendicular to the long side direction of the electrode plate are set to 5.7 mm in both the positive electrode unit and the negative electrode unit.

[0112] Lithium cobalt oxide (LiCoO2) as a positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder were mixed at a mass ratio of 9:0.1:0.1 to prepare a positive electrode mixture constituting a positive electrode active material layer. Aluminum foil (thickness 13 μm) was used as a positive electrode current collector.

[0113] Graphite as a negative electrode active material, carboxymethyl cellulose as a thickener, and styrene butadiene rubber as a binder were mixed at a mass ratio of 9:0.1:0.1 to prepare a negative electrode mixture constituting a negative electrode active material layer. Copper foil (thickness 6 μm) was used as a negative electrode current collector.

[0114] A microporous film (thickness 14 μm) made of polyolefin was used as the separator. The non-aqueous electrolyte was prepared by dissolving LiPF6 in a non-aqueous solvent. Ethylene carbonate, propylene carbonate and ethyl methyl carbonate were mixed in the non-aqueous solvent at a volume ratio of 30:1:61.

[0115] The above-mentioned positive plate, negative plate and separator are used to make an electrode group by the above-mentioned method. Here, the electrode group is made so that there is substantially no gap between the positive electrode active material layer and the separator and between the negative electrode active material layer and the separator at the bend portion of the excess negative electrode active material. Then, using the electrode group, non-aqueous electrolyte and coin-shaped shell, a coin-shaped non-aqueous electrolyte secondary battery is made by the above-mentioned method. Regarding the size of the obtained secondary battery, the outer shape is 9.0 mm and the height is 2.0 mm.

[0116] In this embodiment, 5 types (samples 1 to 4 and comparative sample 1) of secondary batteries are produced by changing the length X and the length Y. Then, the 5 types of secondary batteries are subjected to a charge and discharge cycle test at 20°C. In the charge and discharge cycle test, charging and discharging are regarded as 1 cycle, and the charge and discharge cycle is repeated 1000 cycles. In addition, in the charge and discharge cycle test, charging is performed under the conditions of 4.35V and 6mA, and discharging is performed under the conditions of 3.0V and 6mA. Then, the battery capacity of each sample is measured before (initial), in the middle of, and after the charge and discharge cycle test.

[0117] Furthermore, after the five types of secondary batteries were subjected to the above-mentioned charge and discharge cycle for 500 cycles, the secondary batteries were disassembled and it was visually confirmed whether lithium metal was deposited between the electrode plates.

[0118] Table 1 shows the values ​​of length X and length Y in the five secondary batteries produced and the results of the above evaluation. The cycle number n in Table 1 is the cycle number at which the battery capacity reaches 80% of the initial battery capacity. Furthermore, Table 1 shows the calculation results of the capacity loss rate R (%) assuming that the difference between the length X and the length Y does not contribute to the battery capacity. In addition, the calculation results are based on the assumptions described later. The larger the value, the greater the loss of capacity, so it is preferred that the value is small. The capacity loss rate R becomes 0% when the length X and the length Y are equal.

[0119] [Table 1]

[0120]

[0121] Samples 1 to 4 correspond to the first secondary battery described above because the length X is longer than the length Y. Furthermore, by making the length X longer than the length Y, the distance L1 is longer than the distance L2. Therefore, samples 1 to 4 correspond to the second secondary battery described above.

[0122] As shown in Table 1, in samples 1 to 4 in which the length X was longer than the length Y, no lithium metal precipitation was observed after the charge-discharge cycle test. On the other hand, in comparative sample 1 in which the length X and the length Y were equal, lithium metal precipitation was observed in the excess portion of the positive electrode active material after the charge-discharge cycle test. Therefore, for comparative sample 1, when compared with samples 1 to 4, there is a high possibility that a short circuit and a decrease in capacity may occur due to repeated charge and discharge.

[0123] Furthermore, as shown in Table 1, the secondary batteries of samples 1 to 4 maintained a battery capacity higher than 80% of the initial capacity even after 1000 cycles. In contrast, the battery capacity of the secondary battery of comparative sample 1 became 80% of the initial capacity at 750 cycles. As a result, the secondary batteries of samples 1 to 4 showed little deterioration due to repeated charge and discharge.

[0124] On the other hand, as shown in Table 1, if the value of the difference (XY) between the length X and the length Y increases, the capacity loss rate also increases. Therefore, the difference (XY) is preferably set to a certain value or less. If the value of the capacity loss rate R is considered, the value of the difference (XY) is preferably less than 0.3 (for example, in the range of 0.1 to 0.3). In addition, the values ​​of the length X of the comparison sample 1 and samples 1 to 4 are different. Therefore, the result that (capacity loss rate of comparison sample 1) < (capacity loss rate of samples 1 to 4) does not mean that (battery capacity of comparison sample 1) > (battery capacity of samples 1 to 4). In addition, even if it is assumed that the active material layer of the bend portion of the excess positive active material portion does not contribute to the battery capacity, the active material layer of the bend portion of the excess negative active material portion also contributes to the increase of the battery capacity. Therefore, according to the battery of this embodiment, the battery capacity can be increased compared with the existing battery.

[0125] (Capacity loss rate R)

[0126] refer to Figure 6 To illustrate the calculation method of capacity loss rate R. As an example, Figure 6 Five positive electrode units 40a are shown. When the length X is longer than the length Y, the portion that becomes the excess positive electrode active material portion is Figure 6 The four trapezoidal portions T shown can be regarded as the positive electrode active material not facing the negative electrode active material. If the number of positive electrode units 40a is N (an odd number), the number of trapezoidal portions T is (N-1).

[0127] exist Figure 6 The width WX, the width WL, and the length D1 are shown. The width WX is the length of the positive electrode unit 40a in the width direction (5.7 mm in this embodiment). The width WL is the length of the border portion of two adjacent positive electrode units 40a in the width direction, that is, the length of one side of the positive electrode unit (octagon) at this portion. The length D1 is the length of one side of the octagon (including the hypotenuse of the trapezoidal portion T), and is the length in the direction PD in which the positive electrode units 40a are connected.

[0128] The size of the trapezoidal portion T is expressed by the following formula.

[0129] Upper: WL

[0130] Height: (XY)

[0131] Bottom: WL+(WX-WL)×(XY) / D1

[0132] Area ST: {(WL+(WX-WL)×(XY) / D1)+WL}×(XY) / 2

[0133] The total area of ​​all trapezoidal parts: ST×(N-1)

[0134] The dimensions of the positive electrode unit, which is a regular octagon and has a length X and a width WX of 5.7 mm, are as follows.

[0135] Area: 26.9mm 2

[0136] D1: 1.670mm

[0137] WL: 2.361mm

[0138] In addition, assuming that the values ​​of D1 and WL do not change even when X and Y change, the size of the trapezoidal portion T when WX is 5.7 mm is expressed as follows.

[0139] Upper sole: 2.361mm

[0140] Height: (XY)

[0141] Bottom: 2.361+(5.7-2.361)×(XY) / 1.670

[0142] Area ST: {(2.361+(5.7-2.361)×(XY) / 1.670)+2.361}×(XY) / 2

[0143] The above capacity loss rate R can be regarded as being equal to the ratio of the total area of ​​the trapezoidal portion T to the total area of ​​the positive electrode unit. Therefore, the capacity loss rate R is represented by the following formula. In addition, SP in the following formula is the area of ​​1 positive electrode unit. The capacity loss rate R in Table 1 is the value obtained in this way.

[0144] Capacity loss rate R (%) = 100 × ST × (N-1) / (N × SP)

[0145] Industrial Applicability

[0146] The present disclosure can be utilized in a flat nonaqueous electrolyte secondary battery.

[0147] Description of Reference Numerals

[0148] 10 Secondary battery (flat non-aqueous electrolyte secondary battery)

[0149] 20 Shell

[0150] 30 Electrode Group

[0151] 40 Positive plate

[0152] 40a positive unit

[0153] 40ab 1st bending section

[0154] 41. Positive electrode collector

[0155] 42 Positive electrode active material layer

[0156] 50 Negative plate

[0157] 50a negative unit

[0158] 50ab Second bending section

[0159] 51 negative electrode collector

[0160] 52 Negative electrode active material layer

[0161] 60 Dividers

[0162] X, Y length

[0163] L1, L2 distance.

Claims

1. A flat non-aqueous electrolyte secondary battery comprising: a flat housing; and The positive electrode plate, the negative electrode plate, the separator and the non-aqueous electrolyte are arranged in the housing. The positive electrode plate comprises three or more positive electrode units connected in a row. The negative electrode plate comprises three or more negative electrode units connected in a row. The three or more positive electrode units each include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The three or more negative electrode units each include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The positive electrode plate is bent in a zigzag manner by bending the positive electrode plate in opposite directions using the boundary between two adjacent positive electrode units as first bending portions, respectively. The negative electrode plate is bent in a zigzag manner by bending the negative electrode plate in opposite directions using the boundary between two adjacent negative electrode units as second bent portions. The positive electrode active material layer and the negative electrode active material layer are respectively arranged on the first bent portion and the second bent portion, The positive electrode plate, the negative electrode plate, and the separator are arranged so that the positive electrode active material layer of the positive electrode unit and the negative electrode active material layer of the negative electrode unit are opposed to each other with the separator interposed therebetween, and the first bent portion and the second bent portion are opposed to each other with the separator interposed therebetween, The length X of the positive electrode unit in the direction in which the positive electrode units are connected is longer than the length Y of the negative electrode unit in the direction in which the negative electrode units are connected. In the first bent portion and the second bent portion, a gap is formed between the positive electrode active material layer and the separator and / or between the negative electrode active material layer and the separator at a portion where the negative electrode plate is wrapped by the positive electrode plate.

2. The flat nonaqueous electrolyte secondary battery according to claim 1, wherein The difference (XY) between the length X and the length Y is in the range of 0.1 to 0.3 mm.

3. The flat nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein: A width WX of the positive electrode unit in a direction perpendicular to a direction in which the positive electrode units are connected and a width WY of the negative electrode unit in a direction perpendicular to a direction in which the negative electrode units are connected satisfy a relationship of WX≤WY.

4. The flat nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein: At least a portion of the separator is fixed to the negative electrode plate.

5. The flat nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein: When the number of the positive electrode plates and the number of the negative electrode plates are both 1, the positive electrode active material layer is arranged only on one side of the positive electrode collector and the negative electrode active material layer is arranged only on one side of the negative electrode collector, When the number of the positive electrode plates is 2, the positive electrode active material layer is arranged only on one side of the positive electrode collector and the negative electrode active material layer is arranged on both sides of the negative electrode collector. When the number of the negative electrode plates is two, the positive electrode active material layer is arranged on both surfaces of the positive electrode collector, and the negative electrode active material layer is arranged only on one surface of the negative electrode collector.

6. The flat nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein: In a portion where the positive electrode plate is surrounded by the negative electrode plate, the positive electrode active material layer at the first bent portion and the negative electrode active material layer at the second bent portion are in contact with the separator, respectively.

7. The flat nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein: There is no member preventing the nonaqueous electrolyte from passing therethrough between the first bent portion and the second bent portion.

8. A flat non-aqueous electrolyte secondary battery comprising: a flat housing; and The positive electrode plate, the negative electrode plate, the separator and the non-aqueous electrolyte are arranged in the housing. The positive electrode plate comprises three or more positive electrode units connected in a row. The negative electrode plate comprises three or more negative electrode units connected in a row. The three or more positive electrode units each include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The three or more negative electrode units each include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The positive electrode plate is bent in a zigzag manner by bending the positive electrode plate in opposite directions using the boundary between two adjacent positive electrode units as first bending portions, respectively. The negative electrode plate is bent in a zigzag manner by bending the negative electrode plate in opposite directions using the boundary between two adjacent negative electrode units as second bent portions. The positive electrode active material layer and the negative electrode active material layer are respectively arranged on the first bent portion and the second bent portion, The positive electrode plate, the negative electrode plate, and the separator are arranged so that the positive electrode active material layer of the positive electrode unit and the negative electrode active material layer of the negative electrode unit are opposed to each other with the separator interposed therebetween, and the first bent portion and the second bent portion are opposed to each other with the separator interposed therebetween, In the first bent portion and the second bent portion, a distance L1 between a surface of the positive electrode active material layer at the outermost portion, i.e., the center portion, of the first bent portion at the portion where the negative electrode plate is wrapped by the positive electrode plate on a side away from the positive electrode collector and a surface of the negative electrode active material layer at the outermost portion, i.e., the center portion, of the second bent portion on a side away from the negative electrode collector is longer than a distance L2 between a surface of the positive electrode active material layer at the outermost portion, i.e., the center portion, of the first bent portion at the portion where the positive electrode plate is wrapped by the negative electrode plate on a side away from the positive electrode collector and a surface of the negative electrode active material layer at the outermost portion, i.e., the center portion, of the second bent portion on a side away from the negative electrode collector. In the first bent portion and the second bent portion, a gap is formed between the positive electrode active material layer and the separator and / or between the negative electrode active material layer and the separator at a portion where the negative electrode plate is wrapped by the positive electrode plate.

9. The flat nonaqueous electrolyte secondary battery according to claim 8, wherein: A difference (XY) between a length X of the positive electrode unit in a direction in which the positive electrode units are connected and a length Y of the negative electrode unit in a direction in which the negative electrode units are connected is in a range of 0.1 to 0.3 mm.

10. The flat nonaqueous electrolyte secondary battery according to claim 8 or 9, wherein: A width WX of the positive electrode unit in a direction perpendicular to a direction in which the positive electrode units are connected and a width WY of the negative electrode unit in a direction perpendicular to a direction in which the negative electrode units are connected satisfy a relationship of WX≤WY.

11. The flat nonaqueous electrolyte secondary battery according to claim 8 or 9, wherein: At least a portion of the separator is fixed to the negative electrode plate.

12. The flat nonaqueous electrolyte secondary battery according to claim 8 or 9, wherein: When the number of the positive electrode plates and the number of the negative electrode plates are both 1, the positive electrode active material layer is arranged only on one side of the positive electrode collector and the negative electrode active material layer is arranged only on one side of the negative electrode collector, When the number of the positive electrode plates is 2, the positive electrode active material layer is arranged only on one side of the positive electrode collector and the negative electrode active material layer is arranged on both sides of the negative electrode collector. When the number of the negative electrode plates is two, the positive electrode active material layer is arranged on both surfaces of the positive electrode collector, and the negative electrode active material layer is arranged only on one surface of the negative electrode collector.

13. The flat nonaqueous electrolyte secondary battery according to claim 8 or 9, wherein: In a portion where the positive electrode plate is surrounded by the negative electrode plate, the positive electrode active material layer at the first bent portion and the negative electrode active material layer at the second bent portion are in contact with the separator, respectively.

14. The flat nonaqueous electrolyte secondary battery according to claim 8 or 9, wherein: There is no member preventing the nonaqueous electrolyte from passing therethrough between the first bent portion and the second bent portion.

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