Cylindrical battery

Abstract

Provided is a cylindrical battery comprising an electrode body in which a band-like first electrode (12) and a band-like second electrode which have different polarities are wound with a separator therebetween, the battery being characterized in that: the first electrode (11) has a first electrode core body (40); the first electrode core body (40) includes a mixture layer formation part (42) in which a first electrode mixture layer (41) is disposed on at least one surface of the first electrode core body (40); and the average value of the 0.2% proof stress of the innermost periphery (42A) of the mixture layer formation part (42) is larger than the average value of the 0.2% proof stress of regions other than the innermost periphery (42A) of the mixture layer formation part (42).

Description

Cylindrical battery

[0001] The present disclosure relates to a cylindrical battery.

[0002] A cylindrical battery is known that includes an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and a bottomed cylindrical outer can that houses the electrode assembly. Generally, the positive electrode includes a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core, and the negative electrode includes a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core. Patent Document 1 discloses a cylindrical battery in which the product of the yield strength value and the thickness value of the negative electrode core is equal to or greater than a predetermined value over the entire length of the negative electrode in the longitudinal direction.

[0003] International Publication No. 2013 / 047432

[0004] With the increase in capacity of cylindrical batteries in recent years, the volume change of the negative electrode during charge and discharge has become larger. As a result, the electrode plate is compressed during charging, and the electrode plate tends to expand outward along the axial direction particularly on the inner peripheral side of the electrode assembly. It has also been found that when the yield strength of the negative electrode core is increased over the entire longitudinal direction of the negative electrode as in Patent Document 1, although the expansion of the electrode plate is suppressed, charge and discharge performance such as load characteristics of the battery decreases. Therefore, there is a need for a technique that suppresses the axial expansion of the electrode plate while ensuring the charge and discharge performance of the battery.

[0005] A cylindrical battery according to one aspect of the present disclosure is a cylindrical battery including an electrode assembly in which a strip-shaped first electrode and a strip-shaped second electrode having different polarities are wound with a separator interposed therebetween, the first electrode includes a first electrode core, the first electrode core includes a mixture layer forming portion where a first electrode mixture layer is disposed on at least one surface of the first electrode core, and an average value of 0.2% yield strength at an innermost periphery of the mixture layer forming portion is larger than an average value of 0.2% yield strength in a region other than the innermost periphery of the mixture layer forming portion.

[0006] According to the cylindrical battery of one aspect of the present disclosure, it is possible to suppress outward expansion of the electrode plate in the axial direction while ensuring the charge and discharge performance of the battery.

[0007] This is an axial cross-sectional view of a cylindrical battery, which is an example of an embodiment. This is a perspective view of the electrode body of a cylindrical battery, which is an example of an embodiment. This is a cross-sectional view in the thickness direction of the negative electrode in the unfolded state, which constitutes a cylindrical battery, which is an example of an embodiment. This is a radial cross-sectional view of the negative electrode in the wound state, which constitutes a cylindrical battery, which is an example of an embodiment.

[0008] Hereinafter, an example of an embodiment of the cylindrical battery according to this disclosure will be described in detail with reference to the drawings. Figure 1 is an axial cross-sectional view of a cylindrical battery 10, which is an example of an embodiment, and Figure 2 is a perspective view of the electrode body 14 constituting the cylindrical battery 10.

[0009] As shown in Figure 1, the cylindrical battery 10 comprises an electrode body 14 in which a first electrode and a second electrode are wound around a separator 13, and a bottomed cylindrical outer casing 16 that houses the electrode body 14. The cylindrical battery 10 also comprises a non-aqueous electrolyte housed in the outer casing 16 and a sealing body 17 that closes the opening of the outer casing 16. For the sake of explanation, the side of the cylindrical battery 10 with the sealing body 17 will be referred to as "upper," and the bottom side of the outer casing 16 will be referred to as "lower." Furthermore, the following description will focus on the case where the first electrode is the negative electrode 12 and the second electrode is the positive electrode 11.

[0010] As shown in Figures 1 and 2, the electrode body 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound in a spiral shape via a separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are all elongated strip-shaped bodies that are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral shape. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in the longitudinal and width directions than the positive electrode 11. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and for example, two separators are arranged so as to sandwich the positive electrode 11.

[0011] The positive electrode 11 comprises a long positive electrode core 30 and a positive electrode mixture layer 31 formed on the positive electrode core 30. The positive electrode core 30 can be made of a metal foil that is stable within the potential range of the positive electrode 11, such as aluminum, aluminum alloy, stainless steel, or titanium, or a film on which such metal is arranged on the surface.

[0012] The positive electrode composite layer 31 preferably comprises a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF), and is formed on both sides of the positive electrode core 30. For the positive electrode active material, for example, a lithium transition metal composite oxide containing Ni, Co, Mn, Al, etc., is used.

[0013] In this embodiment, the thickness of the positive electrode 11 is substantially constant except for the region to which the positive electrode lead 20 is connected. The thickness of the positive electrode core 30 is, for example, 10 μm or more and 30 μm or less. The thickness of the positive electrode mixture layer 31 is, for example, 50 μm or more and 120 μm or less on one side of the positive electrode core 30. The positive electrode 11 can be manufactured by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode core 30, drying the coating film, and then compressing it to form the positive electrode mixture layer 31 on both sides of the positive electrode core 30.

[0014] As will be described in more detail later, the negative electrode 12 has a long negative electrode core 40 (first electrode core) and a negative electrode mixture layer 41 (first electrode mixture layer) formed on the negative electrode core 40. The negative electrode mixture layer 41 contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR).

[0015] The separator 13 is a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, polyolefins such as polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. A heat-resistant resin layer, such as aramid resin, may be formed on the surface of the separator 13. Furthermore, a filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12.

[0016] The electrode body 14 has a positive electrode lead 20 connected to a positive electrode 11 and a negative electrode lead 21 connected to a negative electrode 12. In this embodiment, the positive electrode lead 20 is connected to the longitudinal middle portion of the positive electrode 11, and the negative electrode lead 21 is connected to one longitudinal end of the negative electrode 12 located on the winding start side of the electrode body 14. Note that the current collection configuration of the positive electrode 11 and the negative electrode 12 is not limited to this. For example, the negative electrode lead 21 may be connected to one longitudinal end of the negative electrode 12 located on the winding end side of the electrode body 14, or it may be connected to the longitudinal middle portion of the negative electrode 12.

[0017] Non-aqueous electrolytes are lithium ion conductive. Non-aqueous electrolytes may be liquid electrolytes (electrolytes) or solid electrolytes.

[0018] A liquid electrolyte (electrolyte solution) comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. The non-aqueous solvent may also contain halogen-substituted solvents (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms of the solvent are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[0019] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc., can be used. As the inorganic solid electrolyte, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, etc.

[0020] Insulating plates 18 and 19 are positioned above and below the electrode body 14, respectively. In the example shown in Figure 1, the positive electrode lead 20 extends through a through-hole in the insulating plate 18 towards the sealing body 17, and the negative electrode lead 21 extends through a through-hole in the insulating plate 19 towards the bottom of the outer can 16. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, becomes the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 becomes the negative electrode terminal.

[0021] The outer casing 16 is a bottomed cylindrical metal container. A gasket 28 is provided between the outer casing 16 and the sealing body 17, sealing the inside of the battery. The outer casing 16 has, for example, a grooved portion 22 formed by pressing the side surface from the outside. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the outer casing 16, and its upper surface supports the sealing body 17. The upper end of the outer casing 16 is bent inward and crimped to the periphery of the sealing body 17.

[0022] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective radial centers, with the insulating member 25 interposed between their respective peripheral edges. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 towards the cap 27. This interrupts the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 ruptures, and gas is discharged from the opening of the cap 27.

[0023] The configuration of the negative electrode 12 (first electrode) will be described in detail below with reference to Figures 3 and 4. Figure 3 is a cross-sectional view in the thickness direction of the negative electrode 12 in an unfolded state, and Figure 4 is a cross-sectional view in the radial direction of the negative electrode 12 in a wound state.

[0024] As shown in Figures 3 and 4, the negative electrode 12 has a negative electrode core 40. As the negative electrode core 40, a foil of a metal that is stable in the potential range of the negative electrode 12, such as copper, copper alloy, stainless steel, nickel, or nickel alloy, or a film on which such a metal is arranged on the surface can be used. In particular, from the viewpoint of controlling the 0.2% proof strength of the negative electrode core 40 to a predetermined range described later, it is preferable to use copper or a copper alloy. The negative electrode core 40 has a uniform thickness in the longitudinal direction. The thickness of the negative electrode core 40 is, for example, 5 μm or more and 50 μm or less, and preferably 5 μm or more and 30 μm or less.

[0025] The negative electrode core 40 includes a compound layer forming section 42 on which a negative electrode compound layer 41 is disposed on at least one surface of the negative electrode core 40. In this embodiment, the negative electrode compound layer 41 is disposed on both sides of the negative electrode core 40, except for the winding start area to which the negative electrode lead 21 (see Figure 1) is connected. In addition, in at least one of the winding start and end areas of the compound layer forming section 42, the negative electrode compound layer 41 may be disposed on only one side of the negative electrode core 40. Furthermore, at the winding end side of the negative electrode core 40, there may be an area where the negative electrode compound layer 41 is not disposed on both sides of the negative electrode core 40. The number of turns of the compound layer forming section 42 can be appropriately set according to the size of the cylindrical battery 10, etc., but for example, it may be 5 or more and 30 or less, or 10 or more and 25 or less.

[0026] Here, when the volume of the negative electrode 12 changes during charging and discharging, the negative electrode 12 tends to expand circumferentially on the outer circumference side of the electrode body 14, and compress circumferentially on the inner circumference side of the electrode body 14. As a result, the negative electrode 12 on the inner circumference side is more likely to expand outward along the axial direction compared to the negative electrode 12 on the outer circumference side. If the negative electrode 12 expands axially, internal short circuits and other problems may occur.

[0027] In this embodiment, the negative electrode 12 has a 0.2% proof stress of the innermost circumference (first circumference) 42A of the compound layer forming section 42 which is greater than the average 0.2% proof stress of the regions of the compound layer forming section 42 other than the innermost circumference 42A. As a result, even if the inner negative electrode 12 is compressed in the circumferential or thickness direction due to a volume change in the negative electrode 12, the negative electrode 12 is less likely to stretch outward along the axial direction. As a result, internal short circuits and the like are suppressed, and a highly reliable cylindrical battery 10 can be realized. The 0.2% proof stress of the compound layer forming section 42 can be measured by the method described in the embodiment below.

[0028] Furthermore, it was found that increasing the 0.2% proof stress of the composite layer forming portion 42 over the entire longitudinal region of the negative electrode 12 reduces the charge and discharge performance, such as the load characteristics of the battery. This is presumed to be because increasing the 0.2% proof stress of the composite layer forming portion 42 over the entire longitudinal region of the negative electrode 12 excessively increases the surface pressure of the electrode body 14, making clogging of the separator 13 more likely. Therefore, by not increasing the 0.2% proof stress of the composite layer forming portion 42 over the entire longitudinal region of the negative electrode 12, and instead increasing the 0.2% proof stress of the inner region including the innermost circumference 42A of the composite layer forming portion 42 compared to the 0.2% proof stress of the outer region, it is possible to suppress the axial outward extension of the negative electrode 12 while ensuring charge and discharge performance.

[0029] Furthermore, in this embodiment, the average 0.2% proof stress of the outermost periphery 42B of the compound layer forming portion 42 of the negative electrode 12 is smaller than the average 0.2% proof stress of the regions of the compound layer forming portion 42 other than the outermost periphery 42B. As a result, the surface pressure of the electrode body 14 is further reduced, making it easier to ensure charge and discharge performance such as the load characteristics of the battery.

[0030] In this embodiment, the compound layer forming section 42 includes a first region 43 in which the 0.2% proof stress is approximately the same as the average value of the 0.2% proof stress of the innermost circumference 42A, and a second region 44 in which the 0.2% proof stress is approximately the same as the average value of the 0.2% proof stress of the outermost circumference 42B. The first region 43 is formed from the winding start end 42X toward the winding end of the compound layer forming section 42, and the second region 44 is formed from the winding end end 42Y toward the winding start end of the compound layer forming section 42. In this specification, the region in which the 0.2% proof stress is approximately the same as the average value of the 0.2% proof stress of the innermost circumference 42A (and the outermost circumference 42B) means the region in which the ratio of the measured value of the 0.2% proof stress to the average value of the 0.2% proof stress of the innermost circumference 42A is 0.95 or more and 1.05 or less.

[0031] The first region 43 only needs to be provided at least on the innermost circumference 42A of the compound layer forming section 42. For example, it is provided from the winding start end 42X of the compound layer forming section 42 to a point where the number of turns is 1 / 4 to 3 / 4 of the total number of turns. The larger the area where the first region 43 is provided, the less likely the negative electrode 12 is to extend outward along the axial direction during charging and discharging.

[0032] Furthermore, the second region 44 only needs to be provided at least on the outermost periphery 42B of the compound layer forming section 42. For example, it can be provided from the winding end 42Y of the compound layer forming section 42 to a point where the number of turns is 1 / 4 to 3 / 4 of the total number of turns. The larger the area where the second region 44 is provided, the lower the surface pressure of the electrode body 14 becomes, making it easier to ensure charge and discharge performance.

[0033] In this embodiment, the 0.2% yield strength changes significantly at the boundary (boundary point 45) between the first region 43 and the second region 44. Here, when N is the number of turns of the compound layer forming section 42, X is the integer part of 0.25N, and Y is the integer part of 0.75N, it is preferable that the boundary point 45 between the first region 43 and the second region 44 is located in the range from the Xth turn to the Yth turn. In this case, it is possible to improve the strength of the compound layer forming section 42 on the inner circumference side of the negative electrode 12 while suppressing an excessive increase in the overall strength of the compound layer forming section 42. As a result, it is possible to suppress the axial outward elongation of the negative electrode 12 while reducing the surface pressure of the electrode body 14. Note that if the 0.2% yield strength changes gradually between the first region 43 and the second region 44, the boundary point 45 is defined as the longitudinal center of the region between the first region 43 and the second region 44.

[0034] The average value of the 0.2% proof stress at the innermost circumference 42A of the compound layer forming section 42 is preferably 300 MPa or more, and more preferably 350 MPa or more. By setting the average value of the 0.2% proof stress at the innermost circumference 42A of the compound layer forming section 42 to 300 MPa or more, the axial outward elongation of the negative electrode 12 can be further suppressed. The upper limit of the average value of the 0.2% proof stress at the innermost circumference 42A of the compound layer forming section 42 is, for example, 500 MPa.

[0035] Furthermore, the average value of the 0.2% proof stress at the outermost periphery 42B of the composite layer forming section 42 is preferably 200 MPa or less, and more preferably 150 MPa or less. By setting the average value of the 0.2% proof stress at the outermost periphery 42B of the composite layer forming section 42 to 200 MPa or less, the surface pressure of the electrode body 14 is further reduced, making it easier to ensure charge and discharge performance. The lower limit of the average value of the 0.2% proof stress at the outermost periphery 42B of the composite layer forming section 42 is, for example, 30 MPa.

[0036] The ratio of the average value of the 0.2% proof stress of the innermost circumference 42A of the compound layer forming portion 42 to the average value of the 0.2% proof stress of the outermost circumference 42B of the compound layer forming portion 42 is, for example, 1.5 or more and 5 or less, and may be 2 or more and 4 or less. When this ratio is 1.5 or more and 5 or less, the axial outward extension of the negative electrode 12 can be further suppressed while ensuring charge and discharge performance.

[0037] The negative electrode mixture layer 41 contains a negative electrode active material and a binder. Preferably, the negative electrode active material contains a carbon material and a silicon-containing material. Including a silicon-containing material as the negative electrode active material makes it easier to achieve higher capacity. The negative electrode active material may also include, for example, a material containing at least one of an element that alloys with Li, such as Sn, and a material containing that element.

[0038] The carbon material that functions as the negative electrode active material is, for example, at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, and hard carbon. In particular, it is preferable to use artificial graphite such as massive artificial graphite (MAG) or graphitized mesophase carbon microbeads (MCMB), natural graphite such as flake graphite, massive graphite, or earthy graphite, or a mixture thereof as the carbon material. The volume-based D50 of the carbon material is, for example, 1 μm or more and 30 μm or less, preferably 5 μm or more and 25 μm or less.

[0039] Silicon-containing materials can be any material containing Si, and examples include silicon alloys, silicon compounds, and Si-containing composite materials. Among these, Si-containing composite materials are preferred. The D50 of composite materials is generally smaller than that of graphite. The volume-based D50 of composite materials is, for example, 1 μm or more and 15 μm or less. One type of silicon-containing material may be used alone, or two or more types may be used in combination.

[0040] From the viewpoint of increasing capacity, the silicon-containing material content is preferably 5% by mass or more, and more preferably 10% by mass or more, of the total mass of the negative electrode active material. Generally, silicon-containing materials undergo a larger volume change during charging and discharging compared to carbon materials. Therefore, when silicon-containing material is included as the negative electrode active material, the negative electrode mixture layer 41 tends to expand when charging and discharging is repeated. This compresses the negative electrode 12 on the inner circumference side, making it more prone to elongation on both axial sides. Thus, when silicon-containing material is included at a concentration of 5% by mass or more of the total mass of the negative electrode active material, the effect of suppressing the elongation of the negative electrode 12 is more pronounced.

[0041] A suitable silicon-containing material (composite material) is a composite particle including an ion conductive phase and an Si phase dispersed in the ion conductive phase. The ion conductive phase is, for example, at least one selected from the group consisting of a silicate phase, an amorphous carbon phase, a silicide phase, and a silicon oxide phase. The Si phase is formed by dispersing Si in the form of fine particles. The ion conductive phase is a continuous phase constituted by an aggregate of particles finer than the Si phase. Further, a conductive layer made of a material having higher conductivity than the ion conductive phase may be formed on the surface of the ion conductive phase.

[0042] An example of a suitable composite material containing Si has a sea-island structure in which fine Si is substantially uniformly dispersed in an amorphous silicon oxide phase, and is generally represented by the general formula SiO ｘ which is a composite particle represented by (0 < x ≤ 2). The main component of the silicon oxide may be silicon dioxide. The content ratio of oxygen to Si (x) is, for example, 0.5 ≤ x < 2.0, preferably 0.8 ≤ x ≤ 1.5.

[0043] As the binder contained in the negative electrode mixture layer 41, fluorine-containing resin, PAN, polyimide, acrylic resin, polyolefin, or the like may be used, but styrene-butadiene rubber (SBR) is preferably used. Further, the negative electrode mixture layer 41 preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like. Among these, it is suitable to use SBR in combination with CMC or a salt thereof, PAA or a salt thereof, or the like. Further, the negative electrode mixture layer 41 may contain a conductive agent such as CNT.

[0044] The negative electrode 12 of the present embodiment can be produced by the following method. The method for producing the negative electrode 12 includes, for example, a preparation step of preparing a negative electrode mixture slurry, an application step of applying the negative electrode mixture slurry to the surface of a negative electrode core 40 and drying the slurry, a rolling step of rolling the coating film produced in the application step, and a heating step of locally heating the coating film after rolling.

[0045] In the preparation step, the negative electrode active material and binder are mixed in a predetermined ratio, and a negative electrode mixture slurry is prepared using a dispersion medium such as water. In the coating step, the above negative electrode mixture slurry is applied to the surface of the negative electrode core 40, such as copper foil, and then dried to evaporate the dispersion medium. In the rolling step, the coating film prepared in the coating step is rolled with a roller or the like to adjust the thickness and density of the negative electrode mixture layer 41 to a desired range.

[0046] In the heating process, only a portion of the coating film after the rolling process, specifically the portion on the winding end side (second region 44), is locally heated. The method for heating the negative electrode 12 is not particularly limited, but for example, a contact heating method can be applied. For example, a heat roller or hot plate that sandwiches the negative electrode 12 from both sides in the thickness direction is used to locally heat a portion of the negative electrode 12 on the winding end side. By performing the heating process, the grain size of the negative electrode core 40 in the heated region can be increased, and the 0.2% yield strength of the heated region can be decreased.

[0047] The heating temperature in the heating process can be appropriately set depending on the material of the negative electrode core 40, but when the negative electrode core 40 is copper foil, it is preferable that the temperature is, for example, 130°C or higher and 250°C or lower, and 170°C or higher and 220°C or lower. When the heating temperature is 130°C or higher and 250°C or lower, it becomes easier to control the 0.2% yield strength of the negative electrode core 40 within an appropriate range.

[0048] In the method described above, the heating step is performed after applying the negative electrode mixture slurry onto the negative electrode core 40, but the heating step may be performed before applying the negative electrode mixture slurry. In other words, only the negative electrode core 40 may be heated.

[0049] As described above, in this embodiment, the average 0.2% proof stress of the innermost circumference 42A of the compound layer forming portion 42 of the negative electrode 12 is greater than the average 0.2% proof stress of the regions of the compound layer forming portion 42 other than the innermost circumference 42A. This makes it possible to improve the strength of the inner circumference side of the compound layer forming portion 42, where elongation of the negative electrode 12 is likely to occur, while suppressing an increase in the surface pressure of the electrode body 14. As a result, it is possible to suppress the axial outward elongation of the negative electrode 12 while ensuring the charge and discharge performance of the battery.

[0050] The above embodiments can be modified as appropriate within the scope of the purposes of this disclosure. For example, the compound layer forming portion 42 of the above embodiments includes only a first region 43 whose 0.2% proof stress is substantially the same as the average value of the 0.2% proof stress of the innermost circumference 42A, and a second region 44 whose 0.2% proof stress is substantially the same as the average value of the 0.2% proof stress of the outermost circumference 42B, but is not limited thereto. For example, the 0.2% proof stress of the region between the first region 43 and the second region 44 may be different from the 0.2% proof stress of the first region 43 and the second region 44, respectively.

[0051] Furthermore, although the above embodiment described the case where the first electrode is a negative electrode 12 and the second electrode is a positive electrode 11, the first electrode may be a positive electrode 11 and the second electrode may be a negative electrode 12. That is, the 0.2% yield strength of the positive electrode core 30 may differ in the longitudinal direction of the positive electrode 11. Note that the volume change of the negative electrode 12 during charging and discharging is larger than that of the positive electrode 11. Therefore, when the technology of this disclosure is applied to at least the negative electrode 12, the axial outward elongation of the electrode plate can be further suppressed.

[0052] Furthermore, when the first electrode is the positive electrode 11, it is preferable to use a metal mainly composed of aluminum for the positive electrode core 30. The positive electrode core 30 may also further contain iron. From the viewpoint of controlling the magnitude of the 0.2% proof stress, it is preferable that the mass of iron contained in the positive electrode core 30 is 1.2% by mass or more and 1.7% by mass or less of the total mass of the positive electrode core 30.

[0053] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0054] <Example 1> [Preparation of positive electrode] Lithium nickelate (LiNi) containing cobalt and aluminum was used as the positive electrode active material. ０．８８ Co ０．０９ Al ０．０３ O ２A positive electrode slurry was prepared by mixing 100 parts by mass of this positive electrode active material with 1 part by mass of acetylene black (AB) as a conductive agent and 1 part by mass of polyvinylidene fluoride (PVDF) as a binder, and then adding an appropriate amount of N-methyl-2-pyrrolidone (NMP). The positive electrode slurry was then applied to both sides of a positive electrode core made of aluminum alloy with a thickness of 15 μm, excluding the connection points of the positive electrode leads. After the coating film was dried, it was rolled using a roller and cut to a predetermined electrode size to produce a positive electrode.

[0055] [Fabrication of the negative electrode] As the negative electrode active material, a material was used which was a mixture of graphite and Si oxide (SiO) in a mass ratio of 95:5. 100 parts by mass of this negative electrode active material was mixed with 1 part by mass of styrene-butadiene rubber (SBR) and 1 part by mass of carboxymethylcellulose (CMC), and an appropriate amount of water was added to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was then applied to both sides of the negative electrode core, which was made of electrolytic copper foil with a thickness of 8 μm, except for the vicinity of the winding start end where the negative electrode leads were connected. After the coating film was dried, it was rolled using a roller and cut to the predetermined electrode size. Finally, only the portion corresponding to the second and subsequent turns when the negative electrode was wound was heated using a heat roller at 200°C at a speed of 0.1 m / min.

[0056] [Preparation of non-aqueous electrolyte] 100 parts by mass of a mixed solvent obtained by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 3:7, to which 5 parts by mass of vinylene carbonate (VC) is added, and LiPF ６ A non-aqueous electrolyte was prepared by dissolving 1.5 mol / liter of [the substance].

[0057] [Preparation of Test Cell (Non-Aqueous Electrolyte Secondary Battery)] Positive electrode leads and negative electrode leads were welded to the positive electrode and negative electrode, respectively. The positive electrode, negative electrode, and polyethylene separator were then wound in a spiral shape using a cylindrical winding core to obtain an electrode body. At this time, the number of turns in the compound layer forming section of the negative electrode was 18. Insulating plates were placed above and below the electrode body, and the electrode body was housed in an outer container (21 mm in diameter, 70 mm in height). The negative electrode leads were welded to the bottom of the bottomed cylindrical outer container, and the positive electrode leads were welded to the sealing body. After injecting the non-aqueous electrolyte into the outer container, the opening of the outer container was sealed with the sealing body via a gasket to prepare the test cell.

[0058] [Evaluation of Load Characteristics] Under a temperature environment of 25°C, the above test cell was charged with a constant current of 1A until the battery voltage reached 4.2V, and then charged again with a constant voltage of 4.2V until the current value was 0.25A. After that, the battery was discharged with a constant current of 1A until the battery voltage reached 2.5V, and the 1A discharge capacity was measured. Next, the battery was charged under the same conditions as above, and then discharged with a constant current of 5A until the battery voltage reached 2.5V, and the 5A discharge capacity was measured. Then, the load characteristics were calculated using the following formula: Load characteristics = 5A discharge capacity / 1A discharge capacity

[0059] [Evaluation of Negative Electrode Elongation] X-ray CT scans were performed on the test cells before and after the measurement of the load characteristics described above using a Shimadzu inspeXio SMX-255CT FPD HR. The axial length of the negative electrode at each circumference was measured from the X-ray CT images before and after the measurement, and the axial elongation of the negative electrode at each circumference was calculated. The maximum value of the axial elongation of the negative electrode at each circumference was defined as the maximum axial elongation.

[0060] [Evaluation of 0.2% yield strength of the compound layer formation section] After the elongation measurement described above, the test cell was disassembled, the negative electrode was removed, and the negative electrode compound layer was peeled off. The compound layer formation section (negative electrode core) was then cut out in the width direction (axial direction) to a width of 15 mm to form test specimens. Each test specimen was mounted on a tensile testing machine (Shimadzu Corporation, Autograph AG-IS10KN) and a tensile test was performed at a speed of 5 mm / min. The distance between the chucks when mounting the test specimens was 40 mm. The 0.2% yield strength was then determined from the correlation curve between elongation and stress obtained from the tensile test using the offset method described in JIS Z 2241. As a result, the 0.2% yield strength of the first turn of the compound layer formation section without heat treatment was 350 MPa throughout the entire area, while the 0.2% yield strength of the 2nd to 18th turns of the compound layer formation section with heat treatment was 150 MPa throughout the entire area.

[0061] <Example 2> In the preparation of the negative electrode, a test cell was prepared and evaluated in the same manner as in Example 1, except that only the portion corresponding to the area from the 4th turn onwards when the negative electrode was finally wound was heated using a heat roller. The 0.2% yield strength of the mixture layer formation section from the 1st to 3rd turns, which was not subjected to heat treatment, was 350 MPa throughout the entire area, while the 0.2% yield strength of the mixture layer formation section from the 4th to 18th turns, which was subjected to heat treatment, was 150 MPa throughout the entire area.

[0062] <Example 3> In the preparation of the negative electrode, a test cell was prepared and evaluated in the same manner as in Example 1, except that only the portion corresponding to the area from the 10th turn onwards when the negative electrode was finally wound was heated using a heat roller. The 0.2% yield strength of the mixture layer formation section from the 1st to the 9th turn, which was not subjected to heat treatment, was 350 MPa throughout the entire area, while the 0.2% yield strength of the mixture layer formation section from the 10th to the 18th turn, which was subjected to heat treatment, was 150 MPa throughout the entire area.

[0063] <Example 4> In the preparation of the negative electrode, a test cell was prepared and evaluated in the same manner as in Example 1, except that only the portion corresponding to the area from the 16th turn onwards when the negative electrode was finally wound was heated using a heat roller. The 0.2% yield strength of the mixture layer formation section from the 1st to the 15th turn, which was not subjected to heat treatment, was 350 MPa throughout the entire area, while the 0.2% yield strength of the mixture layer formation section from the 16th to the 18th turn, which was subjected to heat treatment, was 150 MPa throughout the entire area.

[0064] <Example 5> In the preparation of the negative electrode, a test cell was prepared and evaluated in the same manner as in Example 1, except that only the portion corresponding to the 18th turn when the negative electrode was finally wound was heated using a heat roller. The 0.2% yield strength of the mixture layer formation portion from the 1st to the 17th turn, which was not subjected to heat treatment, was 350 MPa throughout the entire area, and the 0.2% yield strength of the mixture layer formation portion at the 18th turn, which was subjected to heat treatment, was 150 MPa throughout the entire area.

[0065] <Comparative Example 1> In the preparation of the negative electrode, the test cell was prepared and evaluated in the same manner as in Example 1, except that the entire longitudinal region of the negative electrode was heated using a heat roller. The 0.2% yield strength of the mixture layer formation section from the 1st to the 18th turn, where the heat treatment was performed, was 150 MPa throughout the entire region.

[0066] <Comparative Example 2> In the preparation of the negative electrode, the test cell was prepared and evaluated in the same manner as in Example 1, except that the entire longitudinal region of the negative electrode was not heated. The 0.2% yield strength of the mixture layer formation portion from the 1st to the 18th turn, where no heat treatment was performed, was 350 MPa throughout the entire region.

[0067] Table 1 shows the load characteristics and evaluation results of the maximum axial elongation of the negative electrode for the test cells of the examples and comparative examples. The load characteristics and maximum axial elongation values ​​shown in Table 1 are relative values, with the values ​​for Comparative Example 1 set to 100. A larger load characteristic value indicates superior load characteristics. A smaller maximum axial elongation value indicates less elongation of the negative electrode. Table 1 also shows the regions where heat treatment was performed during the fabrication of the negative electrode.

[0068]

[0069] As shown in Table 1, the test cell of the example shows a reduced maximum axial elongation of the negative electrode compared to the test cell of Comparative Example 1. This is because the strength of the negative electrode core increased on the inner circumference side where the elongation of the negative electrode is significant, by making the 0.2% yield strength of the innermost circumference of the compound layer formation area greater than the average value of the 0.2% yield strength of other parts.

[0070] Furthermore, the test cell of Comparative Example 2, which was not heat-treated and had a high 0.2% yield strength throughout the entire longitudinal direction, showed a significant decrease in load characteristics. This is presumed to be because the surface pressure of the electrode body increased excessively, making it easier for the separator to clog. On the other hand, the test cell of the example in which the winding end region of the composite layer formation section was locally heated showed a significant improvement in load characteristics compared to the test cell of Comparative Example 2. In particular, the test cells of Examples 4 and 5 achieved a value equivalent to the maximum axial elongation of the negative electrode of Comparative Example 2 while showing a significant improvement in load characteristics.

[0071] The present disclosure is further illustrated by the following embodiments. Configuration 1: A cylindrical battery comprising an electrode body in which a strip-shaped first electrode and a strip-shaped second electrode with opposite polarities are wound around a separator, wherein the first electrode has a first electrode core, and the first electrode core includes a compound layer forming portion on at least one surface of the first electrode core, and the average value of the 0.2% proof stress of the innermost circumference of the compound layer forming portion is greater than the average value of the 0.2% proof stress of the region other than the innermost circumference of the compound layer forming portion. Configuration 2: The cylindrical battery according to Configuration 1, wherein the average value of the 0.2% proof stress of the outermost circumference of the compound layer forming portion is smaller than the average value of the 0.2% proof stress of the region other than the outermost circumference of the compound layer forming portion. Configuration 3: The cylindrical battery according to Configuration 1 or 2, wherein the compound layer forming portion includes a first region where the 0.2% proof stress is approximately the same as the average value of the 0.2% proof stress at the innermost circumference, and a second region where the 0.2% proof stress is approximately the same as the average value of the 0.2% proof stress at the outermost circumference. Configuration 4: The cylindrical battery according to Configuration 3, wherein the number of turns of the compound layer forming portion is N, and when the integer part of 0.25N is X and the integer part of 0.75N is Y, the boundary point between the first region and the second region is provided in the range from the Xth turn to the Yth turn. Configuration 5: The cylindrical battery according to any one of Configurations 1 to 4, wherein the average value of the 0.2% proof stress at the outermost circumference of the compound layer forming portion is 200 MPa or less. Configuration 6: The cylindrical battery according to any one of Configurations 1 to 5, wherein the average value of the 0.2% proof stress at the innermost circumference of the compound layer forming portion is 300 MPa or more. Configuration 7: A cylindrical battery according to any one of Configurations 1 to 6, wherein the first electrode is a negative electrode and the second electrode is a positive electrode. Configuration 8: A cylindrical battery according to any one of Configurations 1 to 7, wherein one of the first electrode and the second electrode is a negative electrode, the negative electrode comprises a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, the negative electrode mixture layer contains a carbon material and a silicon-containing material as negative electrode active materials, and the ratio of the mass of the silicon-containing material to the total mass of the negative electrode active materials is 5% by mass or more.

[0072] 10 Cylindrical battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer casing, 17 Sealing body, 18 Insulating plate, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved section, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode core body, 31 Positive electrode mixture layer, 40 Negative electrode core body, 41 Negative electrode mixture layer, 42 Mixture layer forming section, 42A Innermost circumference, 42B Outermost circumference, 42X Winding start end, 42Y Winding end end, 43 First region, 44 Second region, 45 Boundary point

Claims

1. A cylindrical battery comprising an electrode body in which a strip-shaped first electrode and a strip-shaped second electrode, each having opposite polarities, are wound around a separator, wherein the first electrode has a first electrode core, and the first electrode core includes a compound layer forming portion on at least one surface of the first electrode core, and the average value of the 0.2% proof stress of the innermost circumference of the compound layer forming portion is greater than the average value of the 0.2% proof stress of the region other than the innermost circumference of the compound layer forming portion.

2. The cylindrical battery according to claim 1, wherein the average value of the 0.2% proof stress of the outermost periphery of the compound layer forming portion is smaller than the average value of the 0.2% proof stress of the regions other than the outermost periphery of the compound layer forming portion.

3. The cylindrical battery according to claim 1, wherein the composite layer forming portion includes a first region whose 0.2% proof stress is substantially the same as the average value of the 0.2% proof stress of the innermost circumference, and a second region whose 0.2% proof stress is substantially the same as the average value of the 0.2% proof stress of the outermost circumference.

4. The cylindrical battery according to claim 3, wherein the number of turns of the composite layer forming portion is N, and when the integer part of 0.25N is X and the integer part of 0.75N is Y, the boundary point between the first region and the second region is provided in the range from the Xth turn to the Yth turn.

5. The cylindrical battery according to claim 1, wherein the average value of the 0.2% yield strength of the outermost periphery of the composite layer forming portion is 200 MPa or less.

6. The cylindrical battery according to claim 1, wherein the average value of the 0.2% yield strength at the innermost circumference of the composite layer forming portion is 300 MPa or more.

7. The cylindrical battery according to claim 1, wherein the first electrode is a negative electrode and the second electrode is a positive electrode.

8. The cylindrical battery according to claim 1, wherein one of the first electrode and the second electrode is a negative electrode, the negative electrode comprises a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, the negative electrode mixture layer contains a carbon material and a silicon-containing material as negative electrode active materials, and the ratio of the mass of the silicon-containing material to the total mass of the negative electrode active materials is 5% by mass or more.

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