Secondary battery

Abstract

The secondary battery includes: a flexible outer casing; a flat battery element housed inside the outer casing, comprising a positive electrode and a negative electrode; a positive terminal connected to the positive electrode and extending to the outside of the outer casing; a negative terminal connected to the negative electrode and extending to the outside of the outer casing; and a fixing member disposed between the outer casing and the battery element, and respectively bonded to the outer casing and the battery element. The positive and negative electrodes are opposite each other and wound along a first direction, while the positive and negative terminals are separate from each other and extend along a second direction intersecting the first direction. When the battery element is divided into a first region further outward than the positive terminal, a second region further outward than the negative terminal, and a third region between the positive and negative terminals, the fixing member is not disposed in the third region, but is disposed in the first and second regions respectively. The size of the fixing member in the second direction is 50% or more and 100% or less of the size of the battery element in the second direction. The positive electrode includes: a positive current collector having a wound outer side and a wound inner side; and a positive active material layer respectively disposed on the wound outer side and the wound inner side. The positive and negative electrodes are wound with the positive electrode arranged on the outermost periphery. In the outermost positive electrode, no positive active material layer is disposed on the wound outer side, and the wound outer side is exposed. A positive active material layer is disposed on the wound inner side. Alternatively, the negative electrode includes: a negative current collector having a wound outer side and a wound inner side; and a negative active material layer respectively disposed on the wound outer side and the wound inner side. The positive and negative electrodes are wound with the negative electrode arranged on the outermost periphery. In the outermost negative electrode, no negative active material layer is disposed on the wound outer side, and the wound outer side is exposed. A negative active material layer is disposed on the wound inner side.

Description

Technical Field

[0001] This technology relates to a secondary battery. Background Technology

[0002] With the widespread use of mobile phones and other electronic devices, secondary batteries are being developed as small, lightweight power sources capable of achieving high energy density. These secondary batteries contain a positive electrode, a negative electrode, and an electrolyte, and various studies have been conducted on their structure.

[0003] Specifically, to prevent poor sealing of the battery casing, an insulating component is sandwiched between the battery casing and the housed object such as the power generation element, and this insulating component is fixed to the housed object (for example, see Patent Document 1). To prevent the electrode core from being cut, a wound fixing tape is attached to the curved portion (R portion) of the flat spiral electrode assembly (for example, see Patent Document 2). To suppress the movement (damage) of the electrode body due to vibration, a protrusion is provided on the inner side of the casing, and this protrusion is used to fix the electrode body (for example, see Patent Document 3). To prevent the electrode assembly from moving inside the casing, an outermost contour tape, including an adhesive tape such as an oriented polystyrene film, is attached to the electrode assembly (for example, see Patent Documents 4 and 5).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2006-278245

[0007] Patent Document 2: Japanese Patent Application Publication No. 2007-242519

[0008] Patent Document 3: Specification of Patent No. 6052574

[0009] Patent Document 4: Japanese Patent Application Publication No. 2015-118921

[0010] Patent Document 5: Japanese Patent Application Publication No. 2015-015236

[0011] Various studies have been conducted to improve the characteristics of secondary batteries, but there is still room for improvement as there are still shortcomings in terms of energy density, physical durability, and safety.

[0012] This technology was developed in view of the above-mentioned problems, and its purpose is to provide a secondary battery that can achieve excellent physical durability and excellent safety while ensuring energy density. Summary of the Invention

[0013] One embodiment of the present invention provides a secondary battery comprising: a flexible outer casing; a flat battery element housed within the outer casing, including a positive electrode and a negative electrode; a positive terminal connected to the positive electrode and extending to the outside of the outer casing; a negative terminal connected to the negative electrode and extending to the outside of the outer casing; and a fixing member disposed between the outer casing and the battery element, and respectively bonded to the outer casing and the battery element. The positive and negative electrodes are opposite each other and wound along a first direction, while the positive and negative terminals are separate and extend along a second direction intersecting the first direction. When the battery element is divided into a first region further outward than the positive terminal, a second region further outward than the negative terminal, and a third region between the positive and negative terminals, the fixing member is not disposed in the third region, but rather in the first and second regions respectively. The size of the fixing member in the second direction is 50% or more and 100% or less of the size of the battery element in the second direction. The positive electrode includes: a positive current collector having a wound outer side and a wound inner side; and a positive active material layer respectively disposed on the wound outer side and the wound inner side. The positive and negative electrodes are wound with the positive electrode arranged on the outermost periphery. In the outermost positive electrode, no positive active material layer is disposed on the wound outer side, and the wound outer side is exposed. A positive active material layer is disposed on the wound inner side. Alternatively, the negative electrode includes: a negative current collector having a wound outer side and a wound inner side; and a negative active material layer respectively disposed on the wound outer side and the wound inner side. The positive and negative electrodes are wound with the negative electrode arranged on the outermost periphery. In the outermost negative electrode, no negative active material layer is disposed on the wound outer side, and the wound outer side is exposed. A negative active material layer is disposed on the wound inner side.

[0014] According to one embodiment of the present technology, a secondary battery in which a flat battery element is housed inside a flexible outer casing, and a fixing member is disposed between the outer casing and the battery element. The fixing member is not disposed in a third region, but rather in both a first region and a second region, thereby bonding the fixing member to both the outer casing and the battery element. The size of the fixing member is 50% to 100% of the size of the battery element. The positive and negative electrodes are wound with the positive electrode positioned at the outermost periphery. In the outermost positive electrode, no positive electrode active material layer is provided on the outer surface of the winding, but a positive electrode active material layer is provided on the inner surface of the winding. Alternatively, the positive and negative electrodes are wound with the negative electrode positioned at the outermost periphery. In the outermost negative electrode, no negative electrode active material layer is provided on the outer surface of the winding, but a negative electrode active material layer is provided on the inner surface of the winding. This allows for excellent physical durability and excellent safety while ensuring energy density.

[0015] It should be noted that the effects of this technology are not necessarily limited to those described herein, but can be any of the series of effects related to this technology described later. Attached Figure Description

[0016] Figure 1 This is a perspective view showing the structure of a secondary battery in one embodiment of the present technology.

[0017] Figure 2 It is a three-dimensional diagram showing the structure of the battery components.

[0018] Figure 3 It is an enlarged representation Figure 2 A cross-sectional view of a portion of the structure of the battery element shown.

[0019] Figure 4 It is an enlarged representation Figure 2 A cross-sectional view of another part of the structure of the battery element shown.

[0020] Figure 5 It means Figure 2 A top view of the structure of the battery element shown (scale = 90%).

[0021] Figure 6 It means Figure 1 The diagram shows a cross-sectional view of the secondary battery structure.

[0022] Figure 7 It means Figure 5 The diagram shows a cross-sectional view of the structure of the battery element.

[0023] Figure 8 This is a top view showing the structure of the secondary battery of the first comparative example.

[0024] Figure 9 This is a top view showing the structure of the secondary battery of the second comparative example.

[0025] Figure 10 This is a top view showing the structure of the secondary battery of the third comparative example.

[0026] Figure 11 This is a top view showing the structure of the secondary battery of the fourth comparative example.

[0027] Figure 12 This is a top view showing the structure of the secondary battery of the fifth comparative example.

[0028] Figure 13 This is a top view showing the structure of the secondary battery of the sixth comparative example (scale = 30%).

[0029] Figure 14 This is a cross-sectional view showing the structure of the secondary battery (battery element) of the seventh comparative example.

[0030] Figure 15 This is a top view showing the structure of the secondary battery in Modified Example 2 (scale = 100%).

[0031] Figure 16 This is a top view showing the structure of the secondary battery in Modified Example 2 (scale = 50%).

[0032] Figure 17 This is a cross-sectional view showing the structure of the secondary battery (battery element) in Modified Example 3.

[0033] Figure 18 This is a cross-sectional view showing the structure of the secondary battery (battery element) of the ninth comparative example.

[0034] Figure 19 This is a top view showing the structure of the secondary battery in Modified Example 5.

[0035] Figure 20 This is a block diagram illustrating the structure of a secondary battery application example. Detailed Implementation

[0036] Hereinafter, an embodiment of the present technology will be described in detail with reference to the accompanying drawings. It should be noted that the description is presented in the following order.

[0037] 1. Secondary battery

[0038] 1-1. Structure

[0039] 1-2. Actions

[0040] 1-3. Manufacturing Method

[0041] 1-4. Functions and Effects

[0042] 2. Variations

[0043] 3. Uses of secondary batteries

[0044] <1. Secondary Battery>

[0045] First, a secondary battery according to one embodiment of this technology will be described.

[0046] The secondary battery described here is a secondary battery in which battery capacity is obtained by the intercalation and deintercalation of electrode reactants. It has a positive electrode, a negative electrode, and an electrolyte in liquid form. In this secondary battery, in order to prevent the electrode reactants from depositing on the surface of the negative electrode during charging, the charging capacity of the negative electrode is greater than the discharging capacity of the positive electrode. That is, the electrochemical capacity per unit area of ​​the negative electrode is set to be greater than the electrochemical capacity per unit area of ​​the positive electrode.

[0047] There are no particular restrictions on the types of substances used in the electrode reactions. Specifically, they are light metals such as alkali metals and alkaline earth metals. Alkali metals include lithium, sodium, and potassium, while alkaline earth metals include beryllium, magnesium, and calcium.

[0048] The following example uses lithium as the electrode reactant. A secondary battery that utilizes the insertion and extraction of lithium to obtain battery capacity is called a lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is inserted and extracted in an ionic state.

[0049] <1-1. Structure>

[0050] Figure 1 The three-dimensional structure of a secondary battery is shown. Figure 2 The three-dimensional structure of the battery element 20 is shown. Figure 3 as well as Figure 4 They were enlarged respectively Figure 2 A portion of the cross-sectional structure of the battery element 20 shown.

[0051] Figure 5 It shows Figure 2 The planar structure of the battery element 20 shown. Figure 6 It shows Figure 1 The cross-sectional structure of the secondary battery is shown. Figure 7 It shows Figure 5 The cross-sectional structure of the battery element 20 shown.

[0052] In addition, Figure 2 In the diagram, along with the battery element 20, a positive electrode lead 31 and a negative electrode lead 32 are also shown, and the cross-section of the battery element 20 along the XZ plane is shown with dashed lines.

[0053] Figure 3 A cross-section of the middle section of the winding of the battery element 20 is shown. Figure 4 A cross-section of the portion near the outermost periphery of the battery element 20 is shown. It should be noted that... Figure 3 as well as Figure 4 In the middle, the upper side is the outer side of the winding (the side away from the winding shaft P described later), and the lower side is the inner side of the winding (the side closer to the winding shaft P).

[0054] exist Figure 5 Along with the battery element 20, a positive electrode lead 31, a negative electrode lead 32, a fixing tape 50, and a straightening tape 60 are also shown. Figure 6 The cross-section of the secondary cell along the XZ plane is shown. Figure 7 A cross-section of the battery element 20 along the YZ plane is shown. It should be noted that... Figure 7 In the image, a corrective tape 60 is also shown together with the battery element 20.

[0055] like Figures 1 to 7As shown, the secondary battery includes an outer casing 10, a battery element 20, a positive electrode lead 31 and a negative electrode lead 32, sealing films 41 and 42, a fixing tape 50, and a straightening tape 60. The secondary battery described here is a laminated film type secondary battery that uses a flexible (or soft) outer casing 10 to house the battery element 20.

[0056] [Outer packaging film and sealing film]

[0057] like Figure 1 as well as Figure 2 As shown, the outer casing 10 is a flexible outer component that houses the battery element 20, and it has a pouch-like structure. Therefore, the outer casing 10 houses the positive electrode 21, the negative electrode 22, and the electrolyte, which will be described later.

[0058] The three-dimensional shape of the outer film 10 is not particularly limited, and corresponds to the three-dimensional shape of the battery element 20. Here, the three-dimensional shape of the outer film 10 is a flat, approximately cuboid, based on the three-dimensional shape of the flat battery element 20 described later.

[0059] The structure (material and number of layers, etc.) of the outer film 10 is not particularly limited; it can be a single-layer film or a multi-layer film. Here, the outer film 10 is a three-layer laminate consisting of a weld layer, a metal layer, and a surface protective layer, stacked sequentially from the inside. The weld layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protective layer contains a polymer compound such as nylon.

[0060] Insert the sealing film 41 between the outer film 10 and the positive lead 31, and insert the sealing film 42 between the outer film 10 and the negative lead 32.

[0061] The sealing membrane 41 is a sealing component used to prevent external air from entering the interior of the outer membrane 10, and contains one or more polymeric compounds such as polyolefins, which have a sealing effect on the positive electrode lead 31. The polyolefin is polyethylene, polypropylene, modified polyethylene, or modified polypropylene, etc. The sealing membrane 42 has the same structure as the sealing membrane 41, except that it is a sealing component that has a sealing effect on the negative electrode lead 32. That is, the sealing membrane 42 contains a polymeric compound such as a polyolefin that has a sealing effect on the negative electrode lead 32. Alternatively, sealing membranes 41 and 42 may be omitted.

[0062] [Battery Components]

[0063] like Figures 1-5 As shown, the battery element 20 is a flat power generation element containing a positive electrode 21, a negative electrode 22, a separator 23 and an electrolyte (not shown), housed inside the outer membrane 10.

[0064] Here, the battery element 20 is a so-called wound electrode body. That is, in the battery element 20, the positive electrode 21 and the negative electrode 22 are stacked on top of each other with a separator 23 in between, and the positive electrode 21, the negative electrode 22, and the separator 23 are wound around the winding axis P in the winding direction D1 (first direction). Therefore, the positive electrode 21 and the negative electrode 22 are opposite to each other with a separator 23 in between. In addition, the winding axis P is an imaginary axis extending along the Y-axis direction.

[0065] Because the battery element 20 has a flat, three-dimensional shape, therefore, Figure 2 As shown, the cross-section (along the XZ plane) of the battery element 20 intersecting the winding axis P has a flat shape defined by the major axis J1 and the minor axis J2. The major axis J1 is an imaginary axis extending in the X-axis direction and having a length greater than that of the minor axis J2, while the minor axis J2 is an imaginary axis extending in the Z-axis direction intersecting the X-axis direction and having a length less than that of the major axis J1. Here, the cross-sectional shape of the battery element 20 is a flat, approximately elliptical shape.

[0066] (positive electrode)

[0067] like Figure 3 as well as Figure 4 As shown, the positive electrode 21 includes a positive current collector 21A and a positive active material layer 21B.

[0068] The positive current collector 21A has one and two sides (an outer wound side F1 and an inner wound side F2) on which the positive active material layer 21B is disposed. The positive current collector 21A contains any one or more conductive materials such as metal materials, such as aluminum, nickel and stainless steel.

[0069] The positive electrode active material layer 21B is respectively disposed on the outer winding surface F1 and the inner winding surface F2, and contains positive electrode active material capable of lithium insertion and extraction. Furthermore, the positive electrode active material layer 21B may further contain a positive electrode binder and a positive electrode conductive agent. The method for forming the positive electrode active material layer 21B is not particularly limited; specifically, it can be any one or more of the following methods: coating method, etc.

[0070] The positive electrode active material is a lithium-containing compound, more specifically, a lithium transition metal compound. This is because a high energy density can be obtained. The lithium transition metal compound is a compound containing lithium and one or more transition metal elements as constituent elements. The types of lithium transition metal compounds are not particularly limited; specifically, they include oxides, phosphoric acid compounds, silicate compounds, and borate compounds. Specific examples of oxides are LiNiO2, LiCoO2, and LiMn2O4, while specific examples of phosphoric acid compounds are LiFePO4 and LiMnPO4.

[0071] The positive electrode binder includes any one or more of synthetic rubber and polymer compounds. The synthetic rubber is styrene-butadiene rubber, etc., and the polymer compound is polyvinylidene fluoride, etc. The positive electrode conductive agent includes any one or more of conductive materials such as carbon materials, including graphite, carbon black, acetylene black, and Ketjen black, etc. Alternatively, the conductive material can also be a metallic material or a polymer compound, etc.

[0072] Here, since the positive electrode 21 and the negative electrode 22 are wound with the positive electrode 21 positioned on the outside of the wound negative electrode 22, therefore, as Figure 4 As shown, the positive electrode 21 is located on the outermost periphery.

[0073] In this case, in the outermost positive electrode 21, the positive electrode active material layer 21B is only disposed on the inner winding surface F2 of one pair (the outer winding surface F1 and the inner winding surface F2) of the positive electrode current collector 21A. That is, in the outermost positive electrode 21, as... Figure 4 As shown, the positive electrode active material layer 21B is disposed on the inner side F2 of the winding. In contrast, the positive electrode active material layer 21B is not disposed on the outer side F1 of the winding, so the outer side F1 (positive electrode current collector 21A) of the winding is exposed.

[0074] This is because, compared to the case where the positive electrode active material layer 21B is not provided on either the outer winding surface F1 or the inner winding surface F2, when the secondary battery is impacted by drops or other events, the outermost positive electrode 21 is less likely to shift during winding, thus the secondary battery is less likely to move inside the outer casing 10. Furthermore, compared to the case where the positive electrode active material layer 21B is provided on both the outer winding surface F1 and the inner winding surface F2, the thickness (maximum dimension in the Z-axis direction) of the battery element 20 is reduced.

[0075] For the area where no positive electrode active material layer 21B is provided on the outer surface F1, it is sufficient to be at least one circumference of the outermost periphery of the positive electrode 21. Therefore, it can be one circumference of the outermost periphery of the positive electrode 21, or it can be a larger amount of wrapping than one circumference of the outermost periphery of the positive electrode 21. For example, "a larger amount of wrapping than one circumference of the outermost periphery" is 1.5 circumferences or 2 circumferences.

[0076] (negative electrode)

[0077] like Figure 3 as well as Figure 4 As shown, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B.

[0078] The negative current collector 22A has one and two sides (an outer wound side and an inner wound side) on which a negative active material layer 22B is disposed. The negative current collector 22A contains any one or more conductive materials such as metal materials, and the metal materials are copper, aluminum, nickel, and stainless steel.

[0079] The negative electrode active material layer 22B is respectively disposed on the outer and inner winding surfaces of the negative electrode current collector 22A, and contains negative electrode active material capable of lithium insertion and extraction. Furthermore, the negative electrode active material layer 22B may further contain a negative electrode binder and a negative electrode conductive agent. Details regarding the negative electrode binder and negative electrode conductive agent are the same as those regarding the positive electrode binder and positive electrode conductive agent. The method for forming the negative electrode active material layer 22B is not particularly limited; specifically, it can be any one or more of the following: coating method, vapor phase method, liquid phase method, spraying method, and firing method (sintering method).

[0080] The negative electrode active material includes one or more of carbon materials and metallic materials. This is because high energy density can be obtained. Carbon materials include easily graphitized carbon, difficult-to-graphitize carbon, and graphite (natural and artificial graphite). Metallic materials are materials containing one or more of a metallic element and a half-metallic element capable of forming an alloy with lithium as constituent elements; these metallic and half-metallic elements are silicon and tin, etc. Furthermore, metallic materials can be monomers, alloys, compounds, mixtures of two or more of them, or materials containing two or more of their phases. Specific examples of metallic materials are TiSi2 and SiO. x (0 < x ≤ 2, or 0.2 < x < 1.4), etc.

[0081] Here, as described above, since the positive electrode 21 and the negative electrode 22 are wound such that the positive electrode 21 is positioned on the outermost side of the negative electrode 22, the positive electrode 21 is located at the outermost periphery. Therefore, in the negative electrode 22, which is positioned opposite the outermost positive electrode 21 across the diaphragm 23, as... Figure 4 As shown, the negative electrode active material layer 22B is respectively disposed on the outer and inner sides of the negative electrode current collector 22A.

[0082] (Septum)

[0083] like Figure 3 as well as Figure 4 As shown, the separator 23 is an insulating porous membrane located between the positive electrode 21 and the negative electrode 22, allowing lithium to pass through while preventing contact between the positive electrode 21 and the negative electrode 22. The separator 23 contains any one or more of the following polymer compounds: polytetrafluoroethylene, polypropylene, and polyethylene.

[0084] (electrolyte)

[0085] The electrolyte permeates into each of the positive electrode 21, the negative electrode 22, and the membrane 23, and contains solvent and electrolyte salt.

[0086] The solvent includes any one or more non-aqueous solvents (organic solvents) such as carbonate compounds, carboxylic acid ester compounds, and lactone compounds. An electrolyte containing such a non-aqueous solvent is called a non-aqueous electrolyte. The electrolyte salt includes any one or more light metal salts such as lithium salts.

[0087] [Positive lead]

[0088] like Figure 1 , Figure 2 as well as Figure 5 As shown, the positive lead 31 is connected to the positive terminal of the battery element 20, and more specifically, to the positive electrode 21 (positive current collector 21A). This positive lead 31 extends from the inside of the outer casing 10 to the outside, and extends in a leading direction D2 (second direction) that intersects the winding direction D1. Here, the leading direction D2 corresponds to the Y-axis direction.

[0089] In addition, the positive electrode lead 31 comprises any one or more conductive materials such as aluminum. The shape of the positive electrode lead 31 is not particularly limited; specifically, it can be any one of the following: a thin plate shape or a mesh shape.

[0090] [Negative lead]

[0091] like Figure 1 , Figure 2 as well as Figure 5 As shown, the negative electrode lead 32 is connected to the negative terminal of the battery element 20, and more specifically, to the negative electrode 22 (negative current collector 22A). Similar to the positive electrode lead 31 described above, the negative electrode lead 32 is led out from the inside of the outer casing 10 to the outside and extends in the leading direction D2.

[0092] In addition, to prevent short circuits, the negative electrode lead 32 is separated from the positive electrode lead 31. That is, the positive electrode lead 31 and the negative electrode lead 32 are separated from each other and extend along the outgoing direction D2, thereby being led out to the outside of the outer casing membrane 10.

[0093] Furthermore, the negative electrode lead 32 comprises any one or more conductive materials such as copper, nickel, and stainless steel. It should be noted that the details regarding the shape of the negative electrode lead 32 are the same as the details regarding the shape of the positive electrode lead 31.

[0094] [Fixing tape]

[0095] like Figure 5 as well as Figure 6As shown, the fixing tape 50 is a strip-shaped fixing component that secures the battery element 20 to the outer film 10. The fixing tape 50 is disposed between the outer film 10 and the battery element 20, and is bonded to both the outer film 10 and the battery element 20. Thus, the surface of the battery element 20 is fixed to the inner side of the outer film 10 via the fixing tape 50.

[0096] As described above, the battery element 20 is housed inside the flexible outer film 10 and is a wound electrode body formed by winding the positive electrode 21 and the negative electrode 22. Furthermore, in the battery element 20, the positive electrode lead 31 is connected to the positive electrode 21, and the negative electrode lead 32 is connected to the negative electrode 22. In this case, the position of the fixing tape 50, i.e., the position where the battery element 20 is fixed to the outer film 10 via the fixing tape 50, is optimized to a predetermined position.

[0097] Specifically, such as Figure 5 As shown, in the planar structure of the battery element 20, which is connected to the positive electrode lead 31 and the negative electrode lead 32 respectively, the battery element 20 is divided into three regions (regions R1, R2, and R3) based on the respective positions of the positive electrode lead 31 and the negative electrode lead 32. Region R1 is located on the outer side of the positive electrode lead 31. Figure 5 The region R2 is the area to the left of the positive lead 31. Region R2 is the region further outward than the negative lead 32. Figure 5 (The middle section is to the right of negative lead 32). Region R3 is the area between positive lead 31 and negative lead 32. Figure 5 In the diagram, regions R1 to R3 are marked with light shading.

[0098] In this configuration, the fixing tape 50 is not disposed in region R3 but is disposed in regions R1 and R2 respectively, thus the secondary battery has two fixing tapes 50. That is, the secondary battery has fixing tape 50 disposed in region R1 and fixing tape 50 disposed in region R2. Figure 5 In the middle, the fixing tape 50 is marked with a darker shade than areas R1 to R3.

[0099] The fixing tape 50 is not disposed in region R3 but in regions R1 and R2 respectively. This is because, with the positive electrode lead 31 and the negative electrode lead 32 respectively connected to the battery element 20 (wound electrode body) and the battery element 20 housed inside the flexible outer film 10, the position of the battery element 20 fixed to the outer film 10 by the fixing tape 50 is optimized. Therefore, while ensuring the thinness of the secondary battery, the battery element 20 is less likely to move inside the outer film 10 when the secondary battery is impacted, and the temperature of the secondary battery is less likely to rise when heated. Details of the reasons explained here will be described later.

[0100] Here, as described above, the positive electrode 21 is disposed at the outermost periphery in the battery element 20, and the outer surface F1 of the positive current collector 21A is exposed in the outermost positive electrode 21. Therefore, the fixing tape 50 is adhered to the outer surface F1 of the positive current collector 21A.

[0101] Furthermore, for confirmation, it should be noted that the component of the secondary battery, which is not located in region R3 but is located in regions R1 and R2 respectively, is the fixing tape 50 instead of the straightening tape 60. As described above, since the fixing tape 50 is bonded to both the outer film 10 and the battery element 20, the placement of the fixing tape 50 needs to be controlled to regions R1 and R2 instead of region R3. In contrast, since the straightening tape 60 is not installed on the outer film 10 but only on the battery element 20, the placement of the straightening tape 60 is different from that of the fixing tape 50, and it does not need to be controlled to regions R1 and R2 instead of region R3.

[0102] The type of adhesive tape 50 is not particularly limited as long as it can bond the outer film 10 and the battery element 20 together. Preferably, the adhesive tape 50 includes one or more of the following: thermally adhesive components that exhibit adhesion upon heating and pressure. This is because the outer film 10 and the battery element 20 can be easily and firmly bonded together via the adhesive tape 50.

[0103] Specific examples of heat-bonding components include oriented polystyrene tape and hot melt adhesive tape. Oriented polystyrene tape is a strip-shaped adhesive component made of polystyrene extending in a specified direction; more specifically, it includes OPS (registered trademark) tape. Hot melt adhesive tape is an adhesive component that exerts its adhesive properties primarily by melting the adhesive components at a heating temperature of 80°C to 100°C.

[0104] The structure of oriented polystyrene tape is not particularly limited. Specifically, oriented polystyrene tape has a structure in which a substrate layer containing oriented polystyrene and an adhesive layer are stacked on top of each other. The substrate layer only needs to contain oriented polystyrene and can be a single layer or multiple layers. The thickness of oriented polystyrene tape is not particularly limited and can be set arbitrarily.

[0105] The structure of hot melt adhesive tape is not particularly limited. Specifically, hot melt adhesive tape has a structure in which a hot melt adhesive layer and a substrate layer are stacked on top of each other. The types of polymer compounds contained in the hot melt adhesive layer are not particularly limited; specifically, it can be any one or more of the following: styrene-isoprene-styrene block copolymer (SIS), ethylene-vinyl acetate copolymer (EVA), polyolefin elastomer (POE), styrene-butadiene block rubber (SBS), styrene-based thermoplastic elastomer (SEBS), polyurethane (PU), and amorphous polyalphaolefin (APAO). The styrene-based thermoplastic elastomer is a material with a basic unit structure of block copolymerization of polystyrene and flexible polyethylene-polybutene. The thickness of the hot melt adhesive tape is not particularly limited and can be arbitrarily set.

[0106] Alternatively, hot melt adhesive tape may have a structure in which a hot melt adhesive layer, a substrate layer, and a hot melt adhesive layer are stacked sequentially. This adhesive layer is a rubber-based adhesive layer containing a general rubber-based adhesive material. Details regarding the adhesive layer described here will also be provided later.

[0107] The placement (range) of the fixing tape 50 is not particularly limited, as long as the fixing tape 50 is disposed within each of regions R1 and R2. Preferably, the fixing tape 50 extends in the same output direction D2 as the positive electrode lead 31 and the negative electrode lead 32. This is because it prevents the fixing tape 50 from detaching from regions R1 and R2, and more specifically, it prevents the placement range of the fixing tape 50 from expanding into region R3. Furthermore, due to the increased placement area of ​​the fixing tape 50, it is easier to securely fix the battery element 20 to the outer film 10 via the fixing tape 50.

[0108] Furthermore, the relationship between the dimensions (length L1) of the battery element 20 in the output direction D2 and the dimensions (length L2) of the fixing tape 50 in the same output direction D2 meets the specified conditions. Specifically, the ratio of the length L2 of the fixing tape 50 to the length L1 of the battery element 20 is 50% to 100%. This is because, due to the sufficiently increased area of ​​the fixing tape 50, the battery element 20 is adequately fixed to the outer film 10 via the fixing tape 50. This ratio is calculated using the formula: ratio (%) = (L2 / L1) × 100. Figure 5 The example shown is a 90% proportion.

[0109] It should be noted that the length L2 of one fixing tape 50 and the length L2 of another fixing tape 50 can be the same or different from each other.

[0110] Furthermore, the size (width) of the fixing tape 50 in the direction intersecting the export direction D2 (Y-axis direction) (X-axis direction) is not particularly limited, as long as the fixing tape 50 does not detach from regions R1 and R2 respectively. Here, the width of the fixing tape 50 is smaller than the width of each of regions R1 and R2. It should be noted that the width of one fixing tape 50 and the width of another fixing tape 50 can be the same or different from each other.

[0111] Of course, the planar shape of the fixing tape 50 is not particularly limited. Here, as... Figure 5 As shown, the planar shape of the fixing tape 50 is rectangular. It should be noted that the planar shape of one fixing tape 50 and the planar shape of another fixing tape 50 can be the same as each other or different from each other.

[0112] [Corrective Tape]

[0113] like Figure 5 as well as Figure 7 As shown, the corrective tape 60 is a strip-shaped corrective component installed on the battery element 20 to maintain (correct) its three-dimensional shape (flat shape). The corrective tape 60 has an adhesive layer (adhesive surface) on one side, and is thus installed on the battery element 20 via the adhesive surface.

[0114] In the manufacturing process of battery element 20, as described later, after forming the wound body, the wound body is extruded (shaped) into a flat shape. Therefore, to prevent battery element 20 from deforming (restoring) in the direction opposite to the pressing direction, a straightening tape 60 is attached to battery element 20. This straightening tape 60 has one end 60A (first end) and another end 60B (second end), extending from one end 60A to the other end 60B in a direction along the minor axis J2. Furthermore, one end 60A and the other end 60B of the straightening tape 60 are respectively fixed to battery element 20. Additionally, the extending direction of the straightening tape 60 may also be inclined relative to the minor axis J2.

[0115] Specifically, such as Figure 7 As shown, the battery element 20 has an upper surface M1 and a lower surface M2 facing opposite directions, and a side surface M3 between the upper surface M1 and the lower surface M2. The side surface M3 is a side surface of the battery element 20 in the direction (Y-axis direction) intersecting the winding direction D1.

[0116] In addition, such as Figure 7 As shown, the corrective tape 60 includes one end 60A and another end 60B, and an intermediate portion 60C between the one end 60A and the other end 60B. The intermediate portion 60C is connected to one end 60A at one end and to the other end 60B at the other end.

[0117] In this configuration, with the middle portion 60C adjacent to the side surface M3, one end 60A of the straightening tape 60 is bonded to the upper surface M1, and the other end 60B is bonded to the lower surface M2. That is, the straightening tape 60 is bent along the upper surface M1 at one end and along the lower surface M2 at the other end. Furthermore, the middle portion 60C can be separated from the side surface M3. Thus, the straightening tape 60 is fixed to the battery element 20 via one end 60A and the other end 60B, thereby straightening the battery element 20 to prevent deformation, as described above. Therefore, the straightening tape 60 is used to maintain the flat shape of the battery element 20.

[0118] The number of corrective tape 60s is not particularly limited and can be set arbitrarily. Here, for example... Figure 5 As shown, the secondary battery has three corrective tapes 60. Figure 5 In the middle, the corrective tape 60 is marked with a darker shade than areas R1 to R3.

[0119] The first corrective tape 60 is positioned in the direction intersecting the winding direction D1 (Y-axis direction) on the side close to the positive lead 31 and the negative lead 32, more specifically, between the positive lead 31 and the negative lead 32 (region R3).

[0120] The second and third straightening tapes 60 are respectively positioned on the side away from the positive lead 31 and the negative lead 32 in a direction intersecting the winding direction D1 (Y-axis direction), and are separated from each other. Here, the second straightening tape 60 is positioned from region R1 to region R3, and the third straightening tape 60 is positioned from region R2 to region R3.

[0121] There are no particular restrictions on where the corrective tape 60 can be placed; it can be set arbitrarily.

[0122] Preferably, the straightening tape 60 is installed on the battery element 20 at locations other than where the positive lead 31 and the negative lead 32 are connected to the battery element 20. This is because, since the straightening tape 60 is installed on the battery element 20 without being obstructed by the positive lead 31 and the negative lead 32, the straightening tape 60 can be used to sufficiently straighten the battery element 20 to prevent deformation. In addition, the presence of the straightening tape 60 can prevent the thickness of the secondary battery from increasing, and can suppress excessively high temperatures caused by the presence of the straightening tape 60 when the secondary battery heats up.

[0123] Therefore, the first corrective tape 60 is installed on the battery element 20 in region R3, except for the locations where the positive lead 31 and the negative lead 32 are respectively connected to the battery element 20.

[0124] Furthermore, it is preferable that the corrective tape 60 is installed on the battery element 20 in a manner that does not overlap with the fixing tape 50. This is to ensure that the outer film 10 and the battery element 20 are bonded to each other via the fixing tape 50 without being obstructed by the corrective tape 60. In addition, it can prevent the thickness of the secondary battery from increasing due to the presence of the corrective tape 60.

[0125] Therefore, the second corrective tape 60 is installed on the battery element 20 in a manner that does not overlap with the fixing tape 50 disposed in region R1, and the third corrective tape 60 is installed on the battery element 20 in a manner that does not overlap with the fixing tape 50 disposed in region R2.

[0126] The structure of the corrective tape 60 is not particularly limited. Specifically, the corrective tape 60 has a structure in which a substrate layer and an adhesive layer are stacked on top of each other. Specific examples of the corrective tape 60 are polyethylene terephthalate (PET) tape and polypropylene (PP) tape, etc.

[0127] <1-2. Actions>

[0128] During charging of the secondary battery, lithium is deintercalated from the positive electrode 21 in battery element 20 and intercalated into the negative electrode 22 via the electrolyte. Conversely, during discharging of the secondary battery, lithium is deintercalated from the negative electrode 22 in battery element 20 and intercalated into the positive electrode 21 via the electrolyte. During these charging and discharging processes, lithium is intercalated and deintercalated in an ionic state.

[0129] <1-3. Manufacturing Method>

[0130] In the case of manufacturing a secondary battery, a positive electrode 21 and a negative electrode 22 are fabricated through the steps described below, and an electrolyte is prepared. The secondary battery is then fabricated using the positive electrode 21, the negative electrode 22, and the electrolyte. Here, since one end is open, an outer membrane 10 (not shown) having an opening at that end is used. Referring hereafter, the previously described... Figures 1 to 7 .

[0131] [The production of the positive electrode]

[0132] A positive electrode mixture is prepared by mixing positive electrode active material, positive electrode binder, and positive electrode conductive agent. This mixture is then added to an organic solvent to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry is coated onto both sides of the positive electrode current collector 21A to form a positive electrode active material layer 21B. It should be noted that after forming the positive electrode active material layer 21B, it can be compressed and molded using a roller press or similar device. In this case, the positive electrode active material layer 21B can be heated, or the compression molding process can be repeated multiple times. Thus, the positive electrode active material layer 21B is formed on both sides of the positive electrode current collector 21A, thereby producing the positive electrode 21.

[0133] In the case of manufacturing the positive electrode 21, as described above, when manufacturing the battery element 20 in a subsequent process, the formation range of the positive electrode active material layer 21B is adjusted so that the outer surface F1 of the positive electrode current collector 21A is exposed in the outermost positive electrode 21.

[0134] [Making the negative electrode]

[0135] By following the same steps as those used in the fabrication of the positive electrode 21, negative electrode active material layers 22B are formed on both sides of the negative electrode current collector 22A. Specifically, negative electrode active material, negative electrode binder, and negative electrode conductive agent are mixed to prepare a negative electrode mixture, which is then added to an organic solvent to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry is coated on both sides of the negative electrode current collector 22A to form the negative electrode active material layers 22B. Subsequently, the negative electrode active material layers 22B can be compressed and molded. Thus, negative electrode active material layers 22B are formed on both sides of the negative electrode current collector 22A, thereby fabricating the negative electrode 22.

[0136] [Preparation of Electrolyte]

[0137] An electrolyte salt is added to a solvent. The electrolyte salt then disperses or dissolves in the solvent, thus preparing an electrolyte solution.

[0138] [Assembly of a secondary battery]

[0139] First, the positive lead 31 is connected to the positive electrode 21 (positive current collector 21A) in a manner extending in the output direction D2 using a soldering method or the like, and the negative lead 32 is connected to the negative electrode 22 (negative current collector 22A) in a manner extending in the output direction D2 using a soldering method or the like.

[0140] Next, the positive electrode 21 and the negative electrode 22 are stacked on top of each other with the separator 23 in between, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound along the winding direction D1 with the winding axis P as the center, thereby forming a wound body. This wound body has the same structure as the battery element 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not permeated with electrolyte. In this case, as described above, the positive electrode 21 and the negative electrode 22 are wound with the positive electrode 21 arranged on the outermost periphery, and the outer surface F1 of the positive current collector 21A is exposed in the positive electrode 21 on the outermost periphery. Next, the wound body is pressed by using a press or the like to form a flat shape. As described above, a positive electrode lead 31 and a negative electrode lead 32 are respectively connected to this wound body (positive electrode 21 and negative electrode 22).

[0141] Next, fixing tape 50 and straightening tape 60 are installed on the winding body. In this case, when manufacturing the battery element 20 in a later process, the length L2 is adjusted so that the ratio of the length L2 of the fixing tape 50 to the length L1 of the battery element 20 is 50% to 100%. Here, as described above, two fixing tapes 50 and three straightening tapes 60 are installed on the winding body.

[0142] Next, the wound body is housed inside the outer film 10 through the opening, and then electrolyte is injected into the outer film 10 through the opening. Next, the outer films 10 (welded layers) facing each other at the opening are thermally fused together using a heat-sealing method. In this case, the positive electrode lead 31 and the negative electrode lead 32 are led out to the outside of the outer film 10. Furthermore, a sealing film 41 is inserted between the outer film 10 and the positive electrode lead 31, and a sealing film 42 is inserted between the outer film 10 and the negative electrode lead 32. Thus, electrolyte permeates into the wound body, thereby forming a battery element 20 as a wound electrode body, and since the outer film 10 is sealed, the battery element 20 is encapsulated inside the outer film 10.

[0143] Finally, using a heated press or similar device, the secondary battery is heated and pressurized at the location where the fixing tape 50 is applied. Various conditions, such as the heating temperature and the pressurizing pressure, can be arbitrarily set. Thus, the outer casing 10 and the battery element 20 are bonded together via the fixing tape 50, and the battery element 20 is fixed to the outer casing 10 via the fixing tape 50. Therefore, the secondary battery is assembled using the fixing tape 50.

[0144] Stabilization of secondary batteries

[0145] The assembled secondary battery is then charged and discharged. Various conditions, such as ambient temperature, number of charge / discharge cycles, and charge / discharge conditions, can be arbitrarily set. This forms a coating on the surface of the negative electrode 22, thereby stabilizing the state and electrochemical properties of the secondary battery.

[0146] Thus, a secondary battery using an outer membrane 10, namely a laminated membrane type secondary battery, was completed.

[0147] <1-4. Functions and Effects>

[0148] According to this secondary battery, a flat battery element 20 is housed inside a flexible outer casing film 10, and a fixing tape 50 is disposed between the outer casing film 10 and the battery element 20. This fixing tape 50 is not disposed in region R3, but rather in regions R1 and R2, thereby adhering to the outer casing film 10 and the battery element 20 respectively. The length L2 of the fixing tape 50 is 50% to 100% of the length L1 of the battery element 20. The positive electrode 21 and the negative electrode 22 are wound with the positive electrode 21 disposed on the outermost periphery, and in the outermost positive electrode 21, the positive electrode active material layer 21B is not disposed on the outer surface F1 of the winding, but rather on the inner surface F2 of the winding. Therefore, for the reasons explained below, excellent physical durability and excellent safety can be obtained while ensuring energy density.

[0149] Here, the function and effect of the secondary battery of this embodiment will be explained by comparing it with the secondary batteries of the first to eighth comparative examples described later.

[0150] Figure 8 The planar structure of the secondary battery in the first comparative example is shown, and... Figure 5 correspond. Figure 9 The planar structure of the secondary battery in the second comparative example is shown, and... Figure 5 correspond. Figure 10 The planar structure of the secondary battery in the third comparative example is shown, and... Figure 5 correspond. Figure 11 This illustrates the planar structure of the secondary battery in the fourth comparative example, and... Figure 5 correspond. Figure 12 This illustrates the planar structure of the secondary battery in the fifth comparative example, and... Figure 5 correspond. Figure 13 This shows the cross-sectional structure of the secondary battery in the sixth comparative example, and... Figure 5 correspond. Figure 14 This shows the cross-sectional structure of the secondary battery (battery element 20) of the seventh comparative example, and... Figure 4 correspond.

[0151] The secondary batteries of the first comparative examples to the eighth comparative examples have the same structure as the secondary battery of this embodiment, except as described below.

[0152] In the secondary battery of the first comparative example, such as Figure 8 As shown, a fixing tape 50 with a relatively large length L2 is disposed in region R3. In the secondary battery of the second comparative example, as... Figure 9 As shown, a fixing tape 50 with a shorter length L2 is disposed from region R3 to regions R1 and R2 respectively. In the secondary battery of the third comparative example, as... Figure 10 As shown, two fixing tapes 50 with a shorter length L2 are respectively disposed from region R3 to regions R1 and R2. In the secondary battery of the fourth comparative example, as Figure 11 As shown, a fixing tape 50 with a relatively large length L2 is disposed from region R3 to regions R1 and R2 respectively. In the secondary battery of the fifth comparative example, as Figure 12 As shown, since no fixing tape 50 is provided on the battery element 20, the battery element 20 is not fixed to the outer film 10.

[0153] In the secondary battery of the sixth comparative example, such as Figure 13 As shown, the proportion determined by the length L2 of the fixing tape 50 is 30%, therefore the condition of a proportion of 50% to 100% is not met. In the secondary battery of the seventh comparative example, as... Figure 14 As shown, in the outermost positive electrode 21, the positive electrode active material layer 21B is not disposed on the outer surface F1 of the positive electrode current collector 21A, nor is the positive electrode active material layer 21B disposed on the inner surface F2 of the positive electrode current collector 21A.

[0154] Although not specifically illustrated here, in the secondary battery of the eighth comparative example, the positive electrode 21 and the negative electrode 22 are wound with the separator 23 located on the outer side. That is, in the battery element 20, the separator 23 is disposed on the outermost periphery instead of the positive electrode 21 and the negative electrode 22 being disposed on the outermost periphery.

[0155] In the secondary battery of this embodiment, such as Figure 5 As shown, with the positive electrode lead 31 and the negative electrode lead 32 respectively connected to the battery element 20 (wound electrode body) and the battery element 20 housed inside the flexible outer film 10, the position of the battery element 20 fixed to the outer film 10 is optimized using the fixing tape 50. Furthermore, the ratio of the length L2 of the fixing tape 50 to the length L1 of the battery element 20 is optimized, and the state of the positive electrode 21 disposed on the outermost periphery (the presence or absence of the positive electrode active material layer 21B in the inner surface F2) is also optimized.

[0156] Therefore, firstly, since the fixing tape 50 is not provided in the region R3 that affects the thickness of the secondary battery (the maximum dimension in the Z-axis direction), the thickness of the secondary battery is reduced, thus ensuring the thinness of the secondary battery.

[0157] In detail, as described above, the cross-sectional shape of the battery element 20 is a flat, approximately elliptical shape. Therefore, as... Figure 6 As shown, in region R3, the surface of battery element 20 is basically flat, while in regions R1 and R2, the surface of battery element 20 is curved and gradually descends as it moves away from region R3.

[0158] In the secondary batteries of the first to fourth comparative examples, such as Figures 8-11 As shown, the fixing tape 50 is disposed in region R3. In this case, since the fixing tape 50 disposed in region R3 easily affects the thickness of the secondary battery, the presence of the fixing tape 50 easily increases the thickness of the secondary battery. In contrast, in the secondary battery of this embodiment, as... Figure 5 As shown, the fixing tape 50 is not disposed in region R3, but is disposed in regions R1 and R2 respectively. In this case, since the fixing tape 50 disposed in regions R1 and R2 respectively is less likely to affect the thickness of the secondary battery, the thickness of the secondary battery is not likely to increase even if the fixing tape 50 is used.

[0159] Therefore, in the secondary battery of this embodiment, where the fixing tape 50 is disposed in regions R1 and R2 instead of region R3, the thickness is smaller compared to the secondary batteries of the first to fourth comparative examples where the fixing tape 50 is disposed in region R3, even though the fixing tape 50 does not participate in the charge-discharge reaction. Thus, even though the secondary battery includes the fixing tape 50, the energy density per unit volume increases.

[0160] Secondly, since fixing tapes 50 are respectively arranged in the areas R1 and R2 of the outer film 10 that are not easily deformed even when subjected to external force, the battery element 20 is not easily damaged when the secondary battery is subjected to external force in the event of falling or other situations.

[0161] In detail, as described above, the battery element 20 is housed inside the outer casing 10. Therefore, when the secondary battery is impacted by an impact such as a drop, the battery element 20 may move inside the outer casing 10 due to the impact.

[0162] In the secondary battery of the fifth comparative example, such as Figure 12 As shown, since the fixing tape 50 is not used, the battery element 20 is not fixed to the outer film 10. In this case, the battery element 20 is prone to violent movement inside the outer film 10 due to impact, and therefore the battery element 20 is easily damaged.

[0163] Furthermore, in the secondary batteries of the first to fourth comparative examples, such as Figures 8-11 As shown, the battery element 20 is fixed to the outer film 10 via the fixing tape 50. However, the fixing tape 50 is positioned in region R3 of the outer film 10, which is prone to deformation due to movement of the battery element 20. In this case, if the outer film 10 deforms due to impact in region R3, the battery element 20 moves along with the deformation of the outer film 10. In particular, in the secondary battery of the first comparative example in which a fixing tape 50 is positioned in region R3, the outer film 10 is prone to significant deformation due to impact in region R3, and therefore the battery element 20 is also prone to significant movement. Thus, inside the outer film 10, the battery element 20 is still prone to violent movement due to impact, and therefore the battery element 20 is easily damaged.

[0164] In contrast, in the secondary battery of this embodiment, such as Figure 5 As shown, fixing tapes 50 are respectively provided in regions R1 and R2 of the outer film 10 that are not easily deformed by the movement of the battery element 20. In this case, since the outer film 10 is not easily deformed by impact in each of regions R1 and R2, the battery element 20 is not easily moved. In particular, if fixing tapes 50 are provided in regions R1 and R2, since the battery element 20 is fixed to the outer film 10 at two locations, the outer film 10 is not easily significantly deformed even if it is impacted in region R3, so the battery element 20 is not easily moved significantly. Thus, even if the battery element 20 is impacted inside the outer film 10, it is stable and not easily moved, so the battery element 20 is not easily damaged.

[0165] Therefore, in the secondary battery of this embodiment where the fixing tape 50 is not disposed in region R3 but in regions R1 and R2 respectively, compared with the secondary batteries of the first comparative example to the fourth comparative example where the fixing tape 50 is disposed in region R3 and the secondary battery of the fifth comparative example where the fixing tape 50 is not used, the probability of damage to the battery element 20 is reduced, and thus the physical durability is improved in the event of a drop or the like.

[0166] Third, since fixing tapes 50 are respectively arranged in regions R1 and R2 far from the center of the battery element 20, the temperature of the secondary battery is not easy to rise even if the secondary battery generates heat during charging and discharging.

[0167] In detail, as described above, since a charge-discharge reaction occurs in the battery element 20, the temperature of the battery element 20 rises due to the heat generated during the charge-discharge process. In particular, in the battery element 20, which serves as a wound electrode body, the temperature of the battery element 20 rises more easily in the region R3, which is closer to the heat-generating center, compared to the regions R1 and R2, which are respectively farther away from the heat-generating center.

[0168] In the secondary batteries of the first to fourth comparative examples, such as Figures 8-11 As shown, since the fixing tape 50 is disposed in region R3, the surface of the battery element 20 is covered by the fixing tape 50 in region R3 near the heat generation center. In this case, the heat generated by the heat generation is not easily released (dissipated) to the outside of the battery element 20, so the temperature of the secondary battery is prone to rise. In particular, the larger the size of the fixing tape 50, that is, the larger the coverage area of ​​the fixing tape 50 on the surface of the battery element 20, the easier it is for the temperature of the secondary battery to rise.

[0169] In contrast, in the secondary battery of this embodiment, such as Figure 5 As shown, since fixing tape 50 is provided in regions R1 and R2 respectively, the surface of battery element 20 is covered by fixing tape 50 in regions R1 and R2 that are far away from the heat generation center. In this case, the heat generated in region R3 due to heat generation is not hindered by fixing tape 50 and can be easily released (heat dissipated) to the outside of battery element 20, so the temperature of secondary battery is not easy to rise.

[0170] Therefore, in the secondary battery of this embodiment, where the fixing tape 50 is not disposed in region R3 but in regions R1 and R2 respectively, compared with the secondary batteries of the first to fourth comparative examples where the fixing tape 50 is disposed in region R3, the temperature is less likely to rise when the battery element 20 heats up, thus improving safety during use.

[0171] Fourth, since the ratio of the length L2 of the fixing tape 50 to the length L1 of the battery element 20 is 50% to 100%, the battery element 20 is not easily detached from the outer film 10 even if the secondary battery is impacted.

[0172] In detail, the adhesive force of the battery element 20 to the outer film 10 via the fixing tape 50 varies according to the above-mentioned ratio, and this ratio is determined according to the length L2 of the fixing tape 50.

[0173] In the secondary battery of the sixth comparative example, such as Figure 13As shown, because the length L2 is too small, the proportion is also too small, thus failing to meet the condition of a proportion between 50% and 100%. In this case, due to insufficient area of ​​the fixing tape 50, the adhesive force between the battery element 20 and the outer film 10 is also insufficient, making it difficult to fully fix the battery element 20 to the outer film 10. Consequently, when the secondary battery is subjected to impact, the battery element 20 is prone to detaching from the outer film 10.

[0174] In contrast, in the secondary battery of this embodiment, such as Figure 5 As shown, since the length L2 is sufficiently large, the proportion is also sufficiently large, thus satisfying the condition of a proportion of 50% to 100%. In this case, since the area of ​​the fixing tape 50 is ensured, the adhesive force of the battery element 20 relative to the outer film 10 is also ensured, making it easy to secure the battery element 20 firmly to the outer film 10. Therefore, even if the secondary battery is subjected to impact, the battery element 20 is not easily detached from the outer film 10.

[0175] Therefore, in the secondary battery of this embodiment that meets the condition of 50% to 100%, compared with the secondary battery of the sixth comparative example that does not meet the condition, even if the secondary battery is subjected to an impact, the battery element 20 is not easy to fall off, and therefore the battery element 20 is not easy to break.

[0176] Fifth, in the outermost positive electrode 21, the positive electrode active material layer 21B is not set on the outer side F1 of the winding, but on the inner side F2 of the winding. Therefore, when the secondary battery is subjected to external force such as falling, the battery element 20 is not easily damaged.

[0177] Specifically, when the secondary battery is impacted by falling or other events, whether the secondary battery inside the outer membrane 10 can easily move depends on the tightness of the seal between the positive electrode 21 and the separator 23.

[0178] In the secondary battery of the seventh comparative example, such as Figure 14 As shown, in the outermost positive electrode 21, the positive electrode active material layer 21B is not disposed on the inner winding surface F2, so the positive electrode current collector 21A is in direct contact with the separator 23. In this case, since the positive electrode 21 (positive electrode current collector 21A) is not sufficiently sealed with the separator 23, the winding of the positive electrode 21 is prone to shift when the secondary battery is subjected to an impact. As a result, the battery element 20 is prone to movement, and therefore the battery element 20 is easily damaged.

[0179] In contrast, in the secondary battery of this embodiment, such as Figure 5As shown, in the outermost positive electrode 21, the positive electrode active material layer 21B is disposed on the inner winding surface F2, so the positive electrode current collector 21A is indirectly in contact with the separator 23 through the positive electrode active material layer 21B. In this case, since the positive electrode 21 (positive electrode current collector 21A) and the separator 23 are sufficiently tightly bonded, the winding of the positive electrode 21 is less likely to shift when the secondary battery is impacted. Therefore, the battery element 20 is less likely to move, and thus the battery element 20 is less likely to break.

[0180] Therefore, in this embodiment, the secondary battery in which the positive electrode active material layer 21B in the outermost positive electrode 21 is provided on the inner winding surface F2, is less prone to movement of the battery element 20 even when the secondary battery is subjected to an impact, compared to the secondary battery of the seventh comparative example in which the positive electrode active material layer 21B in the outermost positive electrode 21 is not provided on the inner winding surface F2.

[0181] Sixth, since the positive electrode 21 is located on the outermost periphery in the battery element 20, the battery element 20 is not easily damaged when the secondary battery is subjected to external force such as falling.

[0182] In detail, whether the battery element 20 is easily damaged when the secondary battery is impacted in the event of a drop or other circumstances depends on whether the battery element 20 inside the outer casing 10 is easily movable.

[0183] In the secondary battery of the eighth comparative example, since the separator 23 is disposed on the outermost periphery in the battery element 20, the battery element 20 is prone to movement inside the outer membrane 10 when the secondary battery is subjected to an impact. As a result, the battery element 20 is easily damaged when the secondary battery is subjected to an impact.

[0184] In contrast, in the secondary battery of this embodiment, since the positive electrode 21 is disposed on the outermost periphery in the battery element 20, the battery element 20 is less likely to move inside the outer casing 10 when the secondary battery is impacted. Therefore, even if the secondary battery is impacted, the battery element 20 is less likely to break.

[0185] Therefore, in this embodiment, the secondary battery in which the positive electrode 21 is disposed on the outermost periphery in the battery element 20 is less likely to move even if the secondary battery is subjected to an impact, compared to the secondary battery in the eighth comparative example in which the separator 23 is disposed on the outermost periphery in the battery element 20. Thus, the battery element 20 is less likely to be damaged.

[0186] Based on the above description, the secondary battery of this embodiment, compared with the secondary batteries of the first to eighth comparative examples, not only has the energy density per unit volume increased, but also its physical durability under conditions such as drops is improved, and its safety during use is also enhanced. Therefore, it is possible to obtain excellent physical durability and excellent safety while ensuring energy density.

[0187] In particular, in the secondary battery of this embodiment, if the fixing tape 50 includes a heat-adhesive component that exhibits adhesion upon heating and pressurization, the battery element 20 can be easily and firmly fixed to the outer casing 10 using the fixing tape 50, thus achieving a higher efficiency. In this case, if the heat-adhesive component includes oriented polystyrene tape or the like, an even higher efficiency can be achieved because the battery element 20 is sufficiently fixed to the outer casing 10.

[0188] In addition, if the fixing tape 50 extends along the output direction D2, the battery element 20 can be easily and firmly fixed to the outer film 10 via the fixing tape 50, thus achieving a higher effect.

[0189] Furthermore, if the straightening tape 60 extending along the short axis J2 is installed on the battery element 20 at one end 60A and the other end 60B, the straightening tape 60 can be used to maintain the flat shape of the battery element 20. Therefore, the flat shape (thickness) of the battery element 20 is less likely to change, thus achieving a higher efficiency. In this case, if the straightening tape 60 is installed on the battery element 20 at locations other than where the positive electrode lead 31 and the negative electrode lead 32 are connected to the battery element 20, the straightening tape 60 can be used to sufficiently straighten the battery element 20 to prevent deformation, thus achieving a higher efficiency. In addition, if the straightening tape 60 is installed on the battery element 20 without overlapping with the fixing tape 50, the outer film 10 and the battery element 20 can be easily bonded to each other via the fixing tape 50, thus achieving a higher efficiency.

[0190] In addition, if the secondary battery is a lithium-ion secondary battery, sufficient battery capacity can be stably obtained by utilizing the insertion and extraction of lithium, thus achieving higher performance.

[0191] <2. Variations>

[0192] Next, variations of the secondary battery will be described. As explained below, the structure of the aforementioned secondary battery can be appropriately modified. Furthermore, any two or more of the variations described below can be combined with each other.

[0193] [Variation Example 1]

[0194] exist Figure 5In this design, the secondary battery has one positive electrode lead 31. However, although not specifically illustrated here, the number of positive electrode leads 31 is not particularly limited, and can be two or more. In this case, since the resistance of the secondary battery (battery element 20) decreases as the number of positive electrode leads 31 increases, a higher efficiency can be achieved. Furthermore, when the secondary battery has multiple positive electrode leads 31, regions R1 and R3 are positioned on the outermost side (…). Figure 5 The position of the positive lead 31 (leftmost in the middle) is used as a reference.

[0195] The modified example 1 regarding the positive electrode lead 31 can also be applied to the negative electrode lead 32. That is, the number of negative electrode leads 32 can be two or more, and as the number of negative electrode leads 32 increases, the resistance of the secondary battery (battery element 20) decreases. When the secondary battery has multiple negative electrode leads 32, regions R2 and R3 are arranged on the outermost side ( Figure 5 The position of the negative lead 32 (located on the far right) is used as the reference for the designation.

[0196] [Variation Example 2]

[0197] exist Figure 5 In this context, the proportion determined by the length L2 of the fixing tape 50 is not specifically limited, and therefore can be changed arbitrarily. Specifically, as with... Figure 5 corresponding Figure 15 as well as Figure 16 As shown, the scale can be changed. Figure 15 In this configuration, since the ratio is 100%, the length L1 of the battery element 20 equals the length L2 of the fixing tape 50. Figure 16 In this case, the proportion is 50%.

[0198] [Variation Example 3]

[0199] exist Figure 4 In this process, the positive electrode 21 and the negative electrode 22 are wound in such a way that the positive electrode 21 is disposed on the outer side of the negative electrode 22. In the outermost positive electrode 21, the positive electrode active material layer 21B is not disposed on the outer side F1 of the positive electrode current collector 21A, and the outer side F1 of the positive electrode current collector 21A is exposed.

[0200] However, it could also be, as with Figure 4 corresponding Figure 17As shown, the positive electrode 21 and negative electrode 22 are wound with the negative electrode 22 disposed on the outer side of the positive electrode 21. In the outermost negative electrode 22, the negative electrode active material layer 22B is not disposed on the outer surface F1 of the negative electrode current collector 22A, and the outer surface F1 is exposed. The negative electrode active material layer 22B is disposed on the inner surface F2 of the negative electrode current collector 22A. In this case, the same effect can be obtained as when the positive electrode active material layer 21B is not disposed on the outer surface F1 of the positive electrode current collector 21A, but is disposed on the inner surface F2.

[0201] That is, as with Figure 4 corresponding Figure 18 As shown, in the ninth comparative example secondary battery where the negative electrode active material layer 22B is not provided in the outermost negative electrode 22 and the inner surface F2 is not wound, the negative electrode 22 (negative electrode current collector 22A) is not sufficiently sealed with the separator 23. As a result, the winding of the negative electrode 22 is prone to misalignment, and the battery element 20 is easily damaged.

[0202] In contrast, such as Figure 17 As shown, in this embodiment of the secondary battery, the negative electrode active material layer 22B is disposed in the outermost negative electrode 22 and wound around the inner side F2, and the negative electrode 22 (negative electrode current collector 22A) is fully and tightly bonded to the separator 23. As a result, the winding of the negative electrode 22 is less likely to occur, and the battery element 20 is less likely to be damaged.

[0203] [Variation Example 4]

[0204] exist Figure 5 In the middle, on one side from the thickness direction (Z-axis direction) ( Figure 5 When observing the secondary battery from the near-front side (i.e., the surface side), the fixing tape 50 is not disposed in region R3 but is disposed in regions R1 and R2 respectively. Therefore, the secondary battery has two fixing tapes 50. That is, the secondary battery has two fixing tapes 50 disposed on the surface side in regions R1 and R2 respectively.

[0205] However, although there is no specific illustration here, on the other side from the thickness direction (Z-axis direction) ( Figure 5 When observing the secondary battery from the depth side (i.e., the inner side), the fixing tape 50 is not disposed in region R3 but is disposed in regions R1 and R2 respectively. Therefore, the secondary battery can also have two fixing tapes 50. That is, the secondary battery can also have two fixing tapes 50 disposed in regions R1 and R2 respectively on the inner side. In this case, the same effect can be obtained.

[0206] Alternatively, the secondary battery may have two fixing tapes 50 disposed on the outer side in regions R1 and R2 respectively, and two fixing tapes 50 disposed on the inner side in regions R1 and R2 respectively, thus having a total of four fixing tapes 50. In this case, since the battery element 20 is more securely fixed to the outer film 10 by the four fixing tapes 50, a higher efficiency can be achieved.

[0207] [Variation Example 5]

[0208] exist Figure 5 In this secondary battery, there is a fixing tape 50 and a straightening tape 60. However, as with Figure 5 corresponding Figure 19 As shown, the secondary battery only has the fixing tape 50, so the secondary battery may not need to have the straightening tape 60. In this case, the battery element 20 can be fixed to the outer film 10 using the fixing tape 50, thus achieving the same effect.

[0209] Additionally, as mentioned above, in order to maintain the flat shape of the battery element 20, such as Figure 5 As shown, the secondary battery preferably includes a fixing tape 50 and a straightening tape 60.

[0210] [Variation Example 6]

[0211] The aforementioned secondary battery uses a membrane 23 as a porous membrane. However, although not specifically illustrated here, a laminated membrane comprising layers of polymer compounds can be used instead of the porous membrane 23.

[0212] Specifically, the laminated separator includes a porous membrane with one and two faces and a polymer compound layer disposed on one or both sides of the porous membrane. This is because, due to the improved adhesion of the separator to each of the positive electrode 21 and the negative electrode 22, the winding misalignment of the battery element 20 is less likely to occur. Therefore, even if electrolyte decomposition reactions occur, the secondary battery is less likely to expand. The polymer compound layer contains a polymer compound such as polyvinylidene fluoride, which has excellent physical strength and is electrochemically stable.

[0213] It should be noted that one or both of the porous membrane and the polymer compound layer may contain any one or more of a variety of insulating particles. This is because multiple insulating particles dissipate heat when the secondary battery heats up, thus improving the safety (heat resistance) of the secondary battery. Insulating particles include inorganic particles and resin particles, etc. Specific examples of inorganic particles are particles of alumina, aluminum nitride, boehmite, silicon dioxide, titanium dioxide, magnesium oxide, and zirconium oxide, etc. Specific examples of resin particles are particles of acrylic resins and styrene resins, etc.

[0214] In the case of fabricating a layered membrane, a precursor solution containing a polymer compound and an organic solvent is prepared, and then the precursor solution is coated onto one or both sides of a porous membrane. Alternatively, the porous membrane can be immersed in the precursor solution. In this case, various insulating particles can also be added to the precursor solution as needed.

[0215] With the use of this layered separator, lithium ions can also move between the positive electrode 21 and the negative electrode 22, thus achieving the same effect.

[0216] [Variation Example 7]

[0217] The aforementioned secondary battery uses an electrolyte as a liquid. However, although not specifically illustrated here, an electrolyte layer as a gel-like electrolyte can also be used instead of the liquid electrolyte.

[0218] In the battery element 20 using an electrolyte layer, the positive electrode 21 and the negative electrode 22 are wound together with the electrolyte layer and the separator 23 in between. The electrolyte layer is located between the positive electrode 21 and the separator 23, and between the negative electrode 22 and the separator 23.

[0219] Specifically, the electrolyte layer comprises an electrolyte and a polymer compound, in which the electrolyte is held in place by the polymer compound. This is to prevent electrolyte leakage. The structure of the electrolyte is as described above. The polymer compound includes polyvinylidene fluoride, etc. In the case of forming the electrolyte layer, after preparing a precursor solution containing the electrolyte, polymer compound, and organic solvent, the precursor solution is coated on one or both sides of each of the positive electrode 21 and the negative electrode 22.

[0220] Even when this electrolyte layer is used, lithium ions can move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer, thus achieving the same effect.

[0221] <3. Uses of Secondary Batteries>

[0222] Next, the uses (application examples) of the above-mentioned secondary batteries will be explained.

[0223] The application of a secondary battery is any machinery, equipment, appliance, device, or system (a collection of multiple devices, etc.) that can primarily use it as a power source for driving or as a power storage source for energy accumulation; there are no particular limitations. A secondary battery used as a power source can be either a main power source or an auxiliary power source. The main power source is the preferred power source, regardless of the availability of other power sources. An auxiliary power source can be used to replace the main power source or can be switched from the main power source as needed. When using a secondary battery as an auxiliary power source, the type of main power source is not limited to a secondary battery.

[0224] Specific examples of the uses of rechargeable batteries are as follows: Electronic devices (including portable electronic devices) such as camcorders, digital still cameras, mobile phones, laptops, cordless phones, stereo headphones, portable radios, portable televisions, and portable information terminals. Portable household appliances such as electric shavers. Backup power supplies and storage devices such as memory cards. Power tools such as electric drills and chainsaws. Battery packs used as detachable power sources in laptops, etc. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric cars (including hybrid vehicles). Power storage systems such as home battery systems that pre-store power for emergencies. In these applications, one or multiple rechargeable batteries can be used.

[0225] Battery packs are effective in applications such as electric vehicles, energy storage systems, and larger equipment like power tools. Battery packs can use single cells or multiple battery banks. Electric vehicles are vehicles that operate (drive) using a secondary battery as their power source; as mentioned above, they can also be automobiles (hybrid vehicles, etc.) that have a power source other than a secondary battery. Energy storage systems are systems that use secondary batteries as their energy storage source. In household energy storage systems, since electricity is stored in the secondary battery that serves as the energy storage source, this electricity can be used to operate household electrical products, etc.

[0226] Here, a specific example of the application of secondary batteries is explained. The structure of the application example described below is only one example and can therefore be modified appropriately.

[0227] Figure 20 The frame structure of the battery pack is shown. The battery pack described here is a simplified type (so-called pouch) that uses a single rechargeable battery and is used in electronic devices such as smartphones.

[0228] like Figure 20 As shown, the battery pack includes a power supply 71 and a circuit board 72. The circuit board 72 is connected to the power supply 71 and includes a positive terminal 73, a negative terminal 74, and a temperature detection terminal 75 (so-called T terminal).

[0229] The power supply 71 includes a secondary battery. In this secondary battery, the positive lead is connected to the positive terminal 73, and the negative lead is connected to the negative terminal 74. Since the power supply 71 can be connected to an external source through the positive terminal 73 and the negative terminal 74, it can be charged and discharged through these terminals. The circuit board 72 includes a control unit 76, a switch 77, a thermistor (Positive Temperature Coefficient (PTC)) element 78, and a temperature detection unit 79. Alternatively, the PTC element 78 may be omitted.

[0230] The control unit 76 includes a central processing unit (CPU) and memory, and controls the overall operation of the battery pack. The control unit 76 detects and controls the operating status of the power supply 71 as needed.

[0231] It should be noted that when the voltage of the power supply 71 (secondary battery) reaches the overcharge detection voltage or the over-discharge detection voltage, the control unit 76 cuts off the switch 77, thereby preventing the charging current from flowing through the current path of the power supply 71. Additionally, when a large current flows during charging or discharging, the control unit 76 cuts off the charging current by cutting off the switch 77. The overcharge detection voltage and the over-discharge detection voltage are not particularly limited. For example, the overcharge detection voltage is 4.2V ± 0.05V, and the over-discharge detection voltage is 2.4V ± 0.1V.

[0232] The switch 77 includes a charging control switch, a discharging control switch, a charging diode, and a discharging diode, etc., and switches the connection between the power supply 71 and external devices according to the instructions of the control unit 76. The switch 77 includes a metal-oxide-semiconductor field-effect transistor (MOSFET), etc., and detects the charging and discharging current based on the on-resistance of the switch 77.

[0233] The temperature detection unit 79 includes a temperature detection element such as a thermistor, measures the temperature of the power supply 71 using the temperature detection terminal 75, and outputs the temperature measurement result to the control unit 76. The temperature measurement result measured by the temperature detection unit 79 is used for charging and discharging control by the control unit 76 when abnormal heating occurs, and for correction processing by the control unit 76 when calculating the remaining capacity.

[0234] Example

[0235] An embodiment of this technology will be described.

[0236] (Experimental Examples 1-6 and Comparative Examples 1-9)

[0237] After the secondary battery was manufactured, its various characteristics were evaluated.

[0238] [Making a Second-hand Battery]

[0239] The following steps were followed to create the product. Figures 1 to 7 The laminated film type secondary battery (lithium-ion secondary battery) shown in the figure.

[0240] (The production of the positive electrode)

[0241] First, 91 parts by mass of positive electrode active material (LiCoO2), 3 parts by mass of positive electrode binder (polyvinylidene fluoride), and 6 parts by mass of positive electrode conductive agent (graphite) are mixed to prepare a positive electrode mixture. Next, the positive electrode mixture is added to an organic solvent (N-methyl-2-pyrrolidone), and the organic solvent is stirred to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry is coated onto both sides of a positive electrode current collector 21A (a strip of aluminum foil with a thickness of 12 μm) using a coating device, and then the positive electrode mixture slurry is dried to form a positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B is compressed and molded using a roller press. Thus, a positive electrode active material layer 21B is formed on both sides of the positive electrode current collector 21A, forming the positive electrode 21.

[0242] When manufacturing the positive electrode 21, the formation range of the positive electrode active material layer 21B is adjusted depending on whether the positive electrode 21 is positioned on the outermost periphery during the subsequent manufacturing of the battery element 20 (wound body). Specifically, when the positive electrode 21 is positioned on the outermost periphery, the positive electrode active material layer 21B is not formed on the outer winding surface F1 of the positive electrode current collector 21A, but is formed only on the inner winding surface F2. Conversely, when the positive electrode 21 is not positioned on the outermost periphery, the positive electrode active material layer 21B is formed on both the outer winding surface F1 and the inner winding surface F2 of the positive electrode current collector 21A.

[0243] The "Outermost Periphery" column in Table 1 indicates the type of constituent element disposed on the outermost periphery (positive electrode 21, negative electrode 22, or separator 23). Furthermore, the "Active Material Layer (Outer Wrapping Side)" column indicates whether an active material layer is formed on the outer wrapping side (outer wrapping side F1) of the electrode disposed on the outermost periphery, and the "Active Material Layer (Inner Wrapping Side)" column indicates whether an active material layer is formed on the inner wrapping side (inner wrapping side F2) of the electrode disposed on the outermost periphery. When the electrode disposed on the outermost periphery is the positive electrode 21, this "active material layer" refers to the positive electrode active material layer 21B; when the electrode disposed on the outermost periphery is the negative electrode 22, this "active material layer" refers to the negative electrode active material layer 22B.

[0244] (Making the negative electrode)

[0245] First, 93 parts by mass of negative electrode active material (artificial graphite), 1.5 parts by mass of negative electrode binder (styrene-butadiene rubber), 4 parts by mass of negative electrode conductive agent (graphite), and 1.5 parts by mass of thickener (sodium carboxymethyl cellulose) are mixed to prepare a negative electrode mixture. Next, the negative electrode mixture is added to an aqueous solvent (pure water), and the organic solvent is stirred to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry is coated onto both sides of the negative electrode current collector 22A (a strip of copper foil with a thickness of 6 μm) using a coating device, and then the negative electrode mixture slurry is dried to form a negative electrode active material layer 22B. Finally, the negative electrode active material layer 22B is compressed and molded using a roller press. Thus, a negative electrode active material layer 22B is formed on both sides of the negative electrode current collector 22A, forming the negative electrode 22.

[0246] When fabricating the negative electrode 22, the formation range of the negative electrode active material layer 22B is adjusted depending on whether the negative electrode 22 is positioned on the outermost periphery during the subsequent fabrication of the battery element 20 (wound body). Specifically, when the negative electrode 22 is positioned on the outermost periphery, the negative electrode active material layer 22B is not formed on the outer winding surface F1 of the negative electrode current collector 22A, but is formed only on the inner winding surface F2. Conversely, when the negative electrode 22 is not positioned on the outermost periphery, the negative electrode active material layer 22B is formed on both the outer winding surface F1 and the inner winding surface F2 of the negative electrode current collector 22A.

[0247] The details of the items shown in the columns “Outermost Periphery”, “Active Material Layer (Wrapped Outer Side)” and “Active Material Layer (Wrapped Inner Side)” in Table 1 are as described above.

[0248] (Preparation of electrolyte)

[0249] An electrolyte salt (lithium hexafluorophosphate (LiPF6)) was added to a solvent (ethylene carbonate, propylene carbonate, propyl propionate, and ethyl propionate), and the solvent was then stirred. In this case, the solvent mixing ratio (by weight) was ethylene carbonate : propylene propylene carbonate : propyl propionate : ethyl propionate = 20 : 10 : 60 : 10, and the electrolyte salt concentration was 1 mol / kg relative to the solvent. Thus, the electrolyte salt dissolved or dispersed in the solvent, thereby preparing an electrolyte solution.

[0250] (Assembly of a secondary battery)

[0251] First, a positive electrode lead 31 made of aluminum is soldered to a positive electrode 21 (positive current collector 21A) in a manner extending in the output direction D2, and a negative electrode lead 32 made of nickel is soldered to a negative electrode 22 (negative current collector 22A) in a manner extending in the output direction D2.

[0252] Next, the positive electrode 21 and the negative electrode 22 are stacked on top of each other with a separator 23 (a microporous polyethylene membrane with a thickness of 15 μm) in between. Then, the positive electrode 21, the negative electrode 22, and the separator 23 are wound around the winding axis P along the winding direction D1, thereby creating a wound body. In this case, as shown in Table 1, the constituent elements arranged on the outermost periphery of the wound body are adjusted. More specifically, the positive electrode 21, the negative electrode 22, and the separator 23 are wound such that either the positive electrode 21 or the negative electrode 22 is arranged on the outermost periphery. Next, the wound body is pressed using a press to form a flat wound body.

[0253] Next, a fixing tape 50 was installed on the winding body. In this case, the structure when the fixing tape 50 is installed is the structure shown in the "Structure" column of Table 1 (Examples 1-6). Here, as shown in Table 1, oriented polystyrene tape (OPS) and hot melt tape (HM) were used as the fixing tape 50. In addition, the proportion (%) was adjusted by changing the length L2 of the fixing tape 50 while fixing the length L1 of the battery element 20.

[0254] As an oriented polystyrene tape, a tape (thickness = 56 μm) is used, which is formed by laminating a substrate layer containing oriented polystyrene and an adhesive layer (a rubber-based adhesive layer with a thickness of 5 μm). The substrate layer containing the oriented polystyrene is stacked sequentially from the side furthest from the adhesive layer: an oriented polystyrene layer (thickness = 40 μm), a rubber-based adhesive layer (thickness = 5 μm), and a PET layer (thickness = 6 μm). When this fixing tape 50 (oriented polystyrene tape) is mounted on a winding body, the substrate layer containing the oriented polystyrene is positioned opposite the winding body. In this case, the fixing tape 50 is bonded to the outer film 10 via the adhesive layer.

[0255] As a hot melt adhesive tape, a tape with a thickness of 80 μm is used, which consists of a hot melt adhesive layer (a styrene-isoprene-styrene block copolymer (SIS) layer with a thickness of 68 μm) and a substrate layer (a PET layer with a thickness of 12 μm) stacked sequentially. When this fixing tape 50 (hot melt adhesive tape) is mounted on a winding body, the hot melt adhesive layer is positioned opposite the winding body. In subsequent processes, when the fixing tape 50 (hot melt adhesive tape) is heated and pressurized, a portion of the hot melt adhesive layer protrudes around the fixing tape 50, thus the fixing tape 50 is bonded to the outer film 10, etc., via this protruding hot melt adhesive layer.

[0256] The "Correcting Tape (Present / Without)" column in Table 1 indicates whether correcting tape 60 is installed on the winding body. Here, for comparison purposes, correcting tape 60 is not installed on the winding body except that it is installed on the winding body.

[0257] Next, using a bag-shaped outer film 10 with an open end (opening), a wound body is received into the interior of the outer film 10 through the opening, and then an electrolyte is injected into the interior of the outer film 10 through the opening. The outer film 10 is an aluminum laminate consisting of a weld layer (30 μm thick polypropylene film), a metal layer (40 μm thick aluminum foil), and a surface protective layer (25 μm thick nylon film) stacked sequentially from the inside.

[0258] Next, the outer films 10 (welded layers) facing each other in the opening are thermally fused together, so that the positive electrode lead 31 and the negative electrode lead 32 are led out from the outer films 10 to the outside. In this case, a sealing film 41 (a polypropylene film with a thickness of 5 μm) is inserted between the outer films 10 and the positive electrode lead 31, and a sealing film 42 (a polypropylene film with a thickness of 5 μm) is inserted between the outer films 10 and the negative electrode lead 32. As a result, the electrolyte permeates into the winding body, thereby forming a battery element 20 as a wound electrode body, and since the outer films 10 are sealed, the battery element 20 is sealed inside the outer films 10.

[0259] Finally, using a heated press, the secondary battery is heated and pressurized at the location where the fixing tape 50 is applied. The heating temperature and pressurization pressure are adjusted to achieve the adhesive properties of the fixing tape 50. Thus, since the fixing tape 50 is bonded to the battery element 20, the outer film 10 and the battery element 20 are bonded together via the fixing tape 50. Therefore, the battery element 20 is fixed to the outer film 10 via the fixing tape 50, thereby assembling the secondary battery.

[0260] (Stabilization of secondary batteries)

[0261] The secondary battery was subjected to one charge-discharge cycle at room temperature (temperature = 23℃). During charging, a constant current of 0.1C was used until the voltage reached 4.45V, followed by constant voltage charging at that 4.45V until the current reached 0.05C. During discharging, a constant current of 0.1C was used until the voltage reached 3.0V. 0.1C refers to the current value required to fully discharge the battery (theoretical capacity) in 10 hours, and 0.05C refers to the current value required to fully discharge the battery (theoretical capacity) in 20 hours.

[0262] Thus, a coating is formed on the surface of the negative electrode 22, thereby stabilizing the state of the secondary battery. Therefore, a laminated film secondary battery is completed.

[0263] [Making a secondary battery for comparison]

[0264] It should be noted that, for comparison purposes, the following series of secondary batteries were also manufactured. Secondary batteries were manufactured using the same steps, except that the structure with the fixing tape 50 installed was the structure shown in the "Structure" column of Table 1 (Comparative Examples 1-4, 6). Secondary batteries were manufactured using the same steps, except that the fixing tape 50 was not installed on the winding body (Comparative Example 5). Secondary batteries were manufactured using the same steps, except that the positive electrode active material layer 21B (or negative electrode active material layer 22B) was not formed on the inner surface F2 of the winding in the outermost positive electrode 21 (or negative electrode 22). Secondary batteries were manufactured using the same steps, except that the battery element 20 was manufactured with the separator 23 positioned on the outermost periphery (Comparative Example 8).

[0265] [Evaluation of various characteristics]

[0266] Various characteristics of the secondary battery (size characteristics, drop durability characteristics, and temperature characteristics) were evaluated, and the results are shown in Table 1.

[0267] (Dimensional characteristics)

[0268] In evaluating dimensional characteristics, the secondary battery was charged at room temperature, and then the thickness (initial thickness (mm)) of the secondary battery was measured using a thickness gauge (PG-02J constant voltage thickness gauge manufactured by Teclock Co., Ltd.). The charging conditions were the same as those for stabilizing the secondary battery described above. This initial thickness is the maximum thickness of the secondary battery in a fully charged state.

[0269] (Drop durability characteristics)

[0270] In evaluating drop durability characteristics, 100 drop tests were conducted using a secondary battery, and the battery's condition was then repeatedly checked. The maximum number of drops the secondary battery could withstand without breakage (durability cycles) was investigated. In this case, the drop test was conducted according to JIS 60068-2-31:2013 (Environmental Test Methods - Electrical and Electronic - Part 2-31: Drop Tests and Tumble Tests) except that the drop height in the natural drop test - Method 2 (repeated) was changed to 0.5 m. When checking the secondary battery's condition, any of the following conditions were considered as battery breakage: the secondary battery could not charge or discharge due to violent movement inside the outer casing 10; the secondary battery's 1kHz impedance increased significantly; the outer casing 10 was damaged; and the secondary battery was short-circuited.

[0271] (Temperature characteristics)

[0272] In evaluating temperature characteristics, the secondary battery was charged and discharged at room temperature (temperature = 23℃ ± 3℃), and the temperature of approximately the center of the secondary battery (outer membrane 10) was measured during discharge. The highest value of this temperature (maximum temperature (℃)) was then measured. The charge and discharge conditions were the same as those during the stabilization treatment of the secondary battery, except that the discharge current was changed from 0.1C to 2C. 2C is the current value at which the battery capacity is fully discharged in 0.5 hours.

[0273]

[0274] [Inspection]

[0275] As shown in Table 1, the size characteristics, drop durability characteristics, and temperature characteristics of the secondary battery vary depending on the structure of the secondary battery.

[0276] Specifically, when the fixing tape 50 is not placed in any of the regions R1 to R3 (Comparative Example 5), the initial thickness does not increase and the maximum temperature decreases, but the number of durability cycles is significantly reduced.

[0277] Furthermore, in the cases where the fixing tape 50 is only disposed in region R3 (Comparative Example 1) and in the cases where the fixing tape 50 is disposed not only in region R3 but also in regions R1 and R2 respectively (Comparative Examples 2-4), the initial thickness increases, the number of durability tests decreases, or the maximum temperature increases. In particular, when the area of ​​the fixing tape 50 is large (Comparative Example 4), although the number of durability tests increases, the initial thickness also increases, and the maximum temperature also increases.

[0278] In addition, when the proportion is less than 50% (Comparative Example 6), the initial thickness does not increase and the maximum temperature also decreases, but the number of durability cycles is greatly reduced.

[0279] Furthermore, in the outermost positive electrode 21, when no positive electrode active material layer 21B is provided on the inner winding surface F2 (Comparative Example 7), the initial thickness does not increase, and the maximum temperature also decreases, but the number of durability cycles is significantly reduced. Moreover, in the outermost negative electrode 22, when no negative electrode active material layer 22B is provided on the inner winding surface F2 (Comparative Example 9), although the maximum temperature decreases, the initial thickness increases, and the number of durability cycles also decreases.

[0280] Furthermore, in the battery element 20, when the separator 23 is disposed on the outermost periphery (Comparative Example 8), the initial thickness is not increased and the maximum temperature is also reduced, but the number of durability cycles is significantly reduced.

[0281] In contrast, when the fixing tape 50 is not disposed in region R3 but in regions R1 and R2 respectively, at a ratio of 50% to 100%, and a positive electrode active material layer 21B (or negative electrode active material layer 22B) is provided on the inner winding surface F2 in the outermost positive electrode 21 (or negative electrode 22) (Examples 1 to 6), the initial thickness does not increase, the number of durability cycles increases, and the maximum temperature also decreases.

[0282] In this case, in particular, the following tendencies can be observed. Good results can be obtained regardless of the type of fixing tape 50 (oriented polystyrene tape and hot melt tape). Furthermore, when the straightening tape 60 is used, the number of durability cycles is further increased compared to when the straightening tape 60 is not used.

[0283] [Summarize]

[0284] As shown in Table 1, if a flat battery element 20 is housed inside the flexible outer casing 10, and the fixing tape 50 is disposed in regions R1 and R2 respectively, instead of region R3, and is bonded to the outer casing 10 and the battery element 20 respectively, with the length L2 of the fixing tape 50 being 50% to 100% of the length L1 of the battery element 20, and the positive electrode active material layer 21B (or negative electrode active material layer 22B) in the outermost positive electrode 21 (or negative electrode 22) is disposed on the inner winding side F2 instead of the outer winding side F1, then the initial thickness does not increase, the durability cycles increase, and the maximum temperature decreases. Therefore, in the secondary battery, excellent physical durability and excellent safety are achieved while ensuring the energy density per unit volume.

[0285] The above description, while illustrating the present technology with an example of one implementation method and embodiment, does not limit the structure of the present technology to the structure described in one implementation method and embodiment, and various modifications are possible.

[0286] Specifically, while the case where lithium is used as the electrode reactant has been described, this electrode reactant is not particularly limited. Therefore, as mentioned above, the electrode reactant can be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium, and calcium. Furthermore, the electrode reactant can also be other light metals such as aluminum.

[0287] The effects described in this specification are merely illustrative, and therefore the effects of this technology are not limited to those described in this specification. Thus, this technology can also achieve other effects.

Claims

1. A secondary battery, comprising: Flexible exterior components; The flat battery element is housed inside the outer component and includes a positive electrode and a negative electrode; The positive terminal is connected to the positive electrode and leads out to the outside of the external component; The negative terminal is connected to the negative electrode and leads out to the exterior of the external component; and A fixing component is disposed between the outer casing and the battery element, and is respectively bonded to the outer casing and the battery element. The positive and negative electrodes are opposite each other and are wound together along a first direction. The positive and negative terminals are separated from each other and extend along a second direction that intersects the first direction. When the battery element is divided into a first region further outward from the positive terminal, a second region further outward from the negative terminal, and a third region between the positive and negative terminals, the fixing component is not disposed in the third region, but is disposed in the first and second regions respectively. The size of the fixing component in the second direction is 50% to 100% of the size of the battery element in the second direction. The positive electrode includes: The positive current collector has a wound outer surface and a wound inner surface; and The positive electrode active material layers are respectively disposed on the outer surface of the winding and the inner surface of the winding. The positive electrode and the negative electrode are wound with the positive electrode positioned on the outermost periphery. In the outermost positive electrode, the positive electrode active material layer is not disposed on the outer surface of the winding, and the outer surface of the winding is exposed. The positive electrode active material layer is disposed on the inner surface of the winding. or, The negative electrode includes: The negative current collector has a wound outer surface and a wound inner surface; and The negative electrode active material layers are respectively disposed on the outer surface of the winding and the inner surface of the winding. The positive electrode and the negative electrode are wound with the negative electrode positioned on the outermost periphery. In the outermost negative electrode, the negative electrode active material layer is not provided on the outer side of the winding, the outer side of the winding is exposed, and the negative electrode active material layer is provided on the inner side of the winding.

2. The secondary battery according to claim 1, wherein, The fixing component includes a heat-adhesive component that exhibits adhesiveness upon heating and pressurization.

3. The secondary battery according to claim 2, wherein, The thermally adhesive component includes at least one of oriented polystyrene tape and hot melt adhesive tape.

4. The secondary battery according to any one of claims 1 to 3, wherein, The fixing component extends in the second direction.

5. The secondary battery according to any one of claims 1 to 3, wherein, The positive and negative electrodes are wound around the winding shaft. The cross-section of the battery element intersecting the winding axis has a flat shape defined by the major axis and the minor axis. It also includes a correction component that extends from a first end to a second end in a direction along the short axis, and is respectively mounted on the battery element at the first end and the second end.

6. The secondary battery according to claim 5, wherein, The correction component is installed on the battery element at a location other than where the positive terminal and the negative terminal are respectively connected to the battery element.

7. The secondary battery according to claim 5, wherein, The corrective component is mounted on the battery element in a manner that does not overlap with the fixing component.

8. The secondary battery according to any one of claims 1 to 3, The secondary battery is a lithium-ion secondary battery.

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