Cylindrical rechargeable battery

Abstract

A cylindrical secondary battery (10) comprises an outer package can (15) which has a cylindrical cylinder part (15a) and an electrode body (14) which is arranged within the cylinder part. The electrode body (14) is obtained by winding a positive electrode plate and a negative electrode plate, with a separator being interposed therebetween. With respect to the outer package can (15), the ratio of the minimum value of the outer diameters in the cylinder central part of the outer package can (15), the cylinder central part being positioned in the center in the axial direction, to the average value of the outer diameters in the cylinder bottom end part is 99.89% or more; and the ratio of the maximum value of the outer diameters in the cylinder central part to the average value of the outer diameters in the cylinder bottom end part is 100.80% or less. The outer diameters in the cylinder central part periodically change with respect to the angle of circumference; and the period in which the outer diameters in the cylinder central part change with respect to the angle of circumference is 0.4π to 1.0π.

Description

Technical Field

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

Background Art

[0002] Conventionally, cylindrical secondary batteries such as lithium-ion secondary batteries have been known, which include an electrode body (wound body) in which a positive electrode plate and a negative electrode plate are wound through a separator, and a cylindrical outer can that houses the electrode body and an electrolytic solution. In this secondary battery, each of the positive electrode plate and the negative electrode plate includes a core body that is a metal foil, and a mixture layer formed on both surfaces of the core body (see Patent Document 1).

[0003] Further, Patent Document 2 describes that, for example, when lithium ions are electrochemically inserted into a negative electrode mixture layer containing a silicon-based material, its volume expands about 3 to 4 times, contracts during discharge, and the change in expansion and contraction of the electrode body may become large.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a cylindrical secondary battery as described in Patent Document 1, if the expansion and contraction of the electrode body becomes large due to the use of a silicon-based material for the negative electrode active material forming the negative electrode plate, it is conceivable to take into account the expansion of the negative electrode plate and to increase the difference between the outer diameter of the electrode body and the inner diameter of the outer casing before the start of charging and discharging. However, in that case, the battery capacity may decrease, or the cycle characteristics, which are the capacity retention rate when repeating charge-discharge cycles, may deteriorate. On the other hand, it is conceivable to prevent the deterioration of cycle characteristics by suppressing the expansion of the electrode body with the confinement pressure of the outer casing, but if the confinement pressure is too high, there is a problem that the change in the outer circumference shape of the outer casing relative to the cylindrical surface will become large.

[0006] The purpose of this disclosure is to improve the cycle characteristics and battery capacity of a cylindrical secondary battery while suppressing changes in the outer casing shape relative to the cylindrical surface. [Means for solving the problem]

[0007] The cylindrical secondary battery according to this disclosure comprises an outer casing having a cylindrical tube portion and one end closed with a bottom plate portion, and an electrode body disposed inside the tube portion, wherein the electrode body has a positive electrode plate and a negative electrode plate wound around it with a separator in between, and the outer casing has a ratio of 99.89% or more of the minimum outer diameter of the center of the tube, which is the axial center of the outer casing, to the average outer diameter of the bottom end of the tube, and a ratio of 100.80% or less of the maximum outer diameter of the center of the tube to the average outer diameter of the bottom end of the tube, and the outer diameter of the center of the tube changes periodically with respect to the inscribed angle, and the period of change of the outer diameter of the center of the tube with respect to the inscribed angle is 0.4π to 1.0π. [Effects of the Invention]

[0008] According to the cylindrical secondary battery described herein, even when the expansion and contraction of the electrode body due to charging and discharging is large, the outer diameter of the electrode body can be increased in advance before charging and discharging begins, thereby increasing the battery capacity. Furthermore, the expansion of the electrode body can be suppressed by the confinement pressure of the outer casing, thus improving the cycle characteristics. In addition, it is possible to prevent the confinement pressure of the outer casing on the electrode body from becoming excessively high, thereby suppressing changes in the outer circumferential shape of the outer casing relative to the cylindrical surface. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view of a cylindrical secondary battery, which is an example of an embodiment. [Figure 2] This is a schematic diagram showing the cross-sectional shape of the cylindrical secondary battery of the embodiment before charging (a) and after charging (b). [Figure 3] This schematic diagram shows the cross-sectional shape before charging (a) and after charging (b) in a comparative example of a cylindrical secondary battery, where the outer diameter of the electrode body is made significantly smaller than the inner diameter of the outer casing to account for expansion due to charging. [Figure 4] This figure shows the measurement results of the outer diameter of the cylindrical portion and the test results of the volume retention rate in Comparative Example 1 and Examples 1 and 2. [Figure 5] This figure shows the measurement results of the outer diameter of the cylindrical portion and the test results of the volume retention rate in Example 3-5. [Figure 6] This figure shows the measurement results of the outer diameter of the cylindrical portion and the test results of the volume retention rate in Comparative Example 2. [Figure 7] This figure shows the relationship between the circumferential angle of the outer diameter at the bottom end of the cylindrical part and the outer diameter at the center of the cylindrical part in the cylindrical secondary battery of Comparative Example 1. [Figure 8] This figure corresponds to Figure 7 in the cylindrical secondary battery of Example 2. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the following description, specific shapes, materials, numerical values, directions, etc., are examples to facilitate understanding of the present invention and can be appropriately modified to suit the specifications of the cylindrical secondary battery. Furthermore, the term "abbreviated" below is used to include, for example, cases where they are exactly the same, as well as cases where they can be considered substantially the same. Moreover, when multiple embodiments and modifications are included below, it is intended from the outset that their characteristic parts may be appropriately combined and used.

[0011] Figure 1 is a cross-sectional view of a cylindrical secondary battery 10 according to an embodiment. As illustrated in Figure 1, the cylindrical secondary battery 10 comprises a wound electrode body 14, a non-aqueous electrolyte (not shown), an outer casing 15, and a sealing body 16. Hereinafter, "cylindrical secondary battery" will be referred to as "secondary battery." The wound electrode body 14 has a positive electrode plate 11, a negative electrode plate 12, and a separator 13, with the positive electrode plate 11 and the negative electrode plate 12 wound in a spiral shape via the separator 13. Hereinafter, one axial side of the electrode body 14 may be referred to as "upper," and the other axial side as "lower." The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte is not limited to a liquid electrolyte, but may also be a solid electrolyte using a gel-like polymer or the like.

[0012] The positive electrode plate 11 has a strip-shaped positive electrode core and a positive electrode tab 19 joined to the positive electrode core. The positive electrode tab 19 corresponds to a current-collecting metal tab. The positive electrode tab 19 is a conductive member for electrically connecting the positive electrode core and the positive electrode terminal, and extends from the upper end of the positive electrode core of the electrode body 14 to one side (upwards) in the axial direction α.

[0013] The positive electrode tab 19 is a strip-shaped conductive member. The constituent material of the positive electrode tab is not particularly limited. Preferably, the positive electrode tab 19 is made of a metal mainly composed of aluminum. Furthermore, the positive electrode plate 11 has positive electrode mixture layers formed on both the inside (inside of the radial direction β) and outside (outside of the radial direction β) of the winding of the positive electrode core body.

[0014] The negative electrode plate 12 has a strip-shaped negative electrode core body and a negative electrode tab 20 joined to the negative electrode core body. The negative electrode tab 20 is a conductive member for electrically connecting the negative electrode core body and an outer can 15 described later, and extends from the lower end of the negative electrode core body to the other side (downward) in the axial direction α among the electrode body 14. The outer can 15 serves as a negative electrode terminal. The negative electrode tab 20 is provided, for example, on the outer circumferential surface side portion of the outer wound portion of the electrode body 14. The negative electrode tab 20 is a strip-shaped conductive member. The constituent material of the negative electrode tab is not particularly limited. The negative electrode tab is preferably made of a metal mainly composed of nickel or copper, or a metal containing both nickel and copper. The negative electrode tab may be provided at a plurality of positions on the negative electrode core body. Further, on the inner side (radial direction inner side) and the outer side (radial direction outer side) of the winding of the negative electrode core body of the negative electrode plate 12, negative electrode active material layers (not shown) are formed respectively.

[0015] In addition, the negative electrode core body may be exposed on the outermost circumferential surface of the electrode body 14 to form an exposed portion, and the exposed portion may be brought into contact with the inner side surface of the cylindrical portion of the outer can 15 to be electrically connected to the outer can 15. At this time, better current collection performance can be ensured by the electrical connection between the negative electrode plate 12 and the cylindrical portion of the outer can 15.

[0016] As described above, the electrode body 14 has a winding structure in which the positive electrode plate 11 and the negative electrode plate 12 are wound in a spiral shape with a separator 13 interposed therebetween. The positive electrode plate 11, the negative electrode plate 12, and the separator 13 are all formed in a strip shape, and are alternately laminated in the radial direction β of the electrode body 14 by being wound in a spiral shape. In the electrode body 14, the longitudinal direction of each electrode plate 11, 12 becomes the winding direction γ (Figure 2), and the width direction of each electrode plate 11, 12 becomes the axial direction α (Figure 1).

[0017] On the outermost circumferential surface of the electrode body 14, a winding stop tape (not shown) that straddles the end of the winding in the winding direction of the electrode body 14 is adhered to fix the end of the winding of the electrode body 14. Also, a space 28 extending along the central axis O is formed at the central portion of the electrode body 14.

[0018] Furthermore, the outer casing 15 and the sealing body 16 constitute a metal battery case that houses the electrode body 14 and the non-aqueous electrolyte. Insulating plates 17 and 18 are provided above and below the electrode body 14, respectively. The positive electrode tab 19 extends through a through hole in the upper insulating plate 17 towards the sealing body 16 and is welded to the lower surface of the filter 22, which is the bottom plate of the sealing body 16. In the cylindrical secondary battery 10, the cap 26, which is the top plate of the sealing body 16 electrically connected to the filter 22, becomes the positive electrode terminal.

[0019] The outer casing 15 is a bottomed cylindrical metal container having a cylindrical section 15a, a bottom plate section 15b that closes one end of the section 15a, and an opening at the other end. The material of the outer casing is, for example, Fe. The electrode body 14 is arranged inside the section 15a. A gasket 27 is provided between the outer casing 15 and the sealing body 16 to ensure airtightness within the battery case. The outer casing 15 has a protruding section 21 that supports the sealing body 16, which is formed, for example, by pressing the side surface from the outside. The protruding section 21 is preferably formed in an annular shape along the circumferential direction of the outer casing 15, and its upper surface supports the sealing body 16. The sealing body 16 seals the opening of the outer casing 15.

[0020] The sealing body 16 has a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26, which are stacked in order from the electrode body 14 side. Each component of the sealing body 16 has, for example, a disc shape or a ring shape, and each component except the insulating member 24 is electrically connected to one another. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with the insulating member 24 interposed between their respective peripheries. If the internal pressure of the battery rises due to abnormal heat generation, for example, the lower valve body 23 may rupture, causing the upper valve body 25 to bulge towards the cap 26 and separate from the lower valve body 23, thereby interrupting the electrical connection between them. If the internal pressure rises further, the upper valve body 25 may rupture, and gas may be discharged from the opening 26a of the cap 26.

[0021] The components of the electrode body 14 will be described in detail below. For the positive electrode core of the positive electrode plate 11, a metal foil such as aluminum, a film having the metal disposed on the surface layer, or the like is used. A preferred positive electrode core is a metal foil mainly composed of aluminum or an aluminum alloy. The thickness of the positive electrode core is, for example, 10 μm to 30 μm.

[0022] The positive electrode mixture layer preferably contains a positive electrode active material, a conductive agent, and a binder. The positive electrode plate 11 is produced by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) to both surfaces of the positive electrode core, and then drying and rolling.

[0023] Examples of the positive electrode active material include lithium-containing transition metal oxides containing transition metal elements such as Co, Mn, and Ni. The lithium-containing transition metal oxide is not particularly limited, but is preferably a composite oxide represented by the general formula Li 1+x MO2 (where -0.2 < x ≤ 0.2 and M includes at least one of Ni, Co, Mn, and Al).

[0024] Examples of the above-mentioned conductive agent include carbon materials such as carbon black (CB), acetylene black (AB), ketjen black, and graphite. Examples of the above-mentioned binder include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide (PI), acrylic resins, and polyolefin resins. Further, these resins and carboxymethyl cellulose (CMC) or its salt, polyethylene oxide (PEO), etc. may be used in combination. These may be used alone or in combination of two or more.

[0025] The positive electrode tab 19 is disposed at the core exposed portion inside the winding of the positive electrode core, and is joined to the positive electrode core by welding such as ultrasonic welding and is electrically connected.

[0026] The negative electrode plate 12 has a strip-shaped negative electrode core and a negative electrode mixture layer (not shown) formed on the negative electrode core. For the negative electrode core, for example, a metal foil such as copper, or a film with the metal arranged on its surface, can be used. The thickness of the negative electrode core is, for example, 5 μm to 30 μm.

[0027] The negative electrode mixture layer preferably contains a negative electrode active material and a binder. The negative electrode plate 12 is manufactured by, for example, applying a negative electrode mixture slurry containing a negative electrode active material, a binder, and water to both sides of the negative electrode core, and then drying and rolling it.

[0028] The negative electrode active material is not particularly limited as long as it can reversibly intercept and release lithium ions. For example, graphite such as natural graphite or artificial graphite, metals that alloy with lithium such as Si and Sn, or alloys and composite oxides containing these can be used. The binder contained in the negative electrode active material layer is, for example, the same resin as in the case of the positive electrode plate 11. When preparing the negative electrode mixture slurry with an aqueous solvent, styrene-butadiene rubber (SBR), CMC or its salts, polyacrylic acid or its salts, polyvinyl alcohol, etc. can be used. These may be used individually or in combination of two or more.

[0029] For example, the negative electrode mixture layer may contain a Si material and graphite. The density of the mixture layer is preferably 1.3 to 1.75 g / cc. The Si material may include, for example, a first Si material (hereinafter referred to as "LSX") containing a lithium silicate phase and silicon dispersed within the lithium silicate phase. The Si material may also include, for example, a second silicon material (hereinafter referred to as "SiO") containing a silicon oxide phase and silicon dispersed within the silicon oxide phase.

[0030] When the Si material is included as the negative electrode active material, the content of the Si material is preferably 6 to 50% by mass based on the total mass of the negative electrode active material. When the negative electrode active material includes the Si material and graphite, the blending ratio of the Si material and graphite in the negative electrode binder layer is preferably 6:94 to 50:50 in terms of mass ratio. That is, the ratio of graphite in the negative electrode active material in the negative electrode binder layer is 50 to 94% by mass, and the ratio of the Si material in the negative electrode active material is 6 to 50%. If the blending ratio is within the above range, it becomes easy to achieve high capacity while maintaining good cycle characteristics.

[0031] SiO is, for example, particles in which fine Si particles are dispersed in a silicon oxide phase. Suitable SiO has a sea-island structure in which fine Si particles are substantially uniformly dispersed in an amorphous silicon oxide matrix, and has a general formula SiO x (0.5 ≦ x ≦ 1.6).

[0032] LSX is, for example, particles in which fine Si particles are dispersed in a lithium silicate phase. Suitable LSX has a sea-island structure in which fine Si particles are substantially uniformly dispersed in a matrix of lithium silicate represented by the general formula Li 2z SiO (2+z) (0 < z < 2).

[0033] For the binder included in the negative electrode binder layer, similar to the case of the positive electrode plate 11, fluorine-containing resins such as PTFE and PVdF, PAN, polyimide, acrylic resin, polyolefin, etc. may be used, but preferably a rubber-based binder such as styrene-butadiene rubber (SBR) is used. Further, the negative electrode binder layer 31 may contain CMC or its salt, polyacrylic acid (PAA) or its salt, PVA, etc. CMC or its salt functions as a thickener for adjusting the negative electrode binder slurry to an appropriate viscosity range, and also functions as a binder similar to SBR.

[0034] In the negative electrode binder layer, a conductive agent such as carbon nanotube (CNT), which is a carbon fiber, may be used.

[0035] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. The material of the separator 13 is preferably polyethylene, olefin resins such as polypropylene, or cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator 13.

[0036] Furthermore, the ratio (Dimin × 100 / D1a) of the minimum outer diameter Dimin at the axial center of the cylindrical section (position P2 in the axial direction of Figure 1), which is the axial center of the cylindrical section 15, to the average value D1a of the outer diameter at the bottom end of the cylindrical section (bottom end of the cylindrical section) (position P1 in the axial direction of Figure 1) of the cylindrical section 15a is 99.89% or higher. "Center of the cylindrical section" is the axial center position between the lower end and the upper end of the cylindrical section 15. In Figure 1, the outer circumferential surface of the cylindrical section 15a and the lower surface of the bottom plate section 15b of the cylindrical section 15 are connected by a circular arc-shaped R section 15c. "Bottom end of the cylindrical section" is the connection position between the outer circumferential surface of the cylindrical section 15a and the outer surface of the R section 15c. Note that "average value of the outer diameter of the cylindrical section 15a" means the average value of the outer diameter in the circumferential direction at the axial position of the cylindrical section 15a, for example, the bottom end of the cylindrical section or the center of the cylindrical section.

[0037] Furthermore, in the outer can 15, the ratio of the maximum outer diameter Dimax of the center of the cylindrical part to the average outer diameter D1a of the bottom end of the cylindrical part (Dimax × 100 / D1a) is 100.80% or less. In addition, the outer diameter Di of the center of the cylindrical part changes periodically with respect to the inscribed angle, and the period of change of the outer diameter Di of the center of the cylindrical part with respect to the inscribed angle is 0.4π to 1.0π, preferably 0.4π to 0.6π. The thickness of the outer can 15 is preferably 0.18 mm to 0.33 mm.

[0038] Furthermore, in the embodiment, the ratio of the average outer diameter Diav of the center of the cylindrical part to the average outer diameter D1a of the bottom end of the cylindrical part (Diav × 100 / D1a) of the outer casing 15 is 100.10% to 100.50%, preferably 100.20% to 100.50%. Also, the standard deviation σi of the outer diameter at the center of the cylindrical part is 0.020 mm to 0.050 mm. The above (Dimin × 100 / D1a), (Dimax × 100 / D1a), the period by which the outer diameter Di changes with respect to the inscribed angle, (Diav × 100 / D1a), and the standard deviation σi are preferably regulated when the secondary battery 10 is fully charged. The fully charged state refers to the state in which the secondary battery 10 is charged to the upper limit of its nominal capacity.

[0039] According to the secondary battery 10 described above, repeated charging and discharging of the secondary battery 10 causes repeated expansion and contraction of each electrode plate 11, 12, and charging causes the electrode body 14 to expand, increasing its outer diameter. At this time, the ratio of the minimum value Dimin of the outer diameter at the center of the cylinder (Dimin × 100 / D1a) to the average value D1a of the outer diameter at the bottom end of the cylinder is 99.89% or more. Also, the ratio of the maximum value Dimax of the outer diameter at the center of the cylinder (Dimax × 100 / D1a) to the average value D1a of the outer diameter at the bottom end of the cylinder is 100.80% or less. As a result, even if the axial center of the outer surface of the electrode body 14 bulges relative to the bottom end of the cylinder where the inner diameter is almost the same as the outer diameter of the electrode body 14 before charging and discharging, the bulge near the center of the cylinder of the outer casing 15 can absorb to some extent the expansion of the outer diameter of the electrode body 14. Therefore, even when the electrode body 14 expands, particularly so that its outer diameter increases near the axial center of the electrode body 14, it is possible to prevent the constraining pressure of the outer casing 15 on the electrode body 14 from becoming excessively high during charging, without having to pre-determine a significantly smaller outer diameter of the electrode body 14 relative to the inner diameter of the cylindrical portion 15a. This suppresses changes in the outer circumferential shape of the cylindrical portion 15a in the outer casing 15 relative to the cylindrical surface.

[0040] Therefore, the battery capacity can be increased, and the cycle characteristics of the secondary battery 10, i.e., the capacity retention rate, can be improved. This is thought to be because the current collection properties of each electrode plate can be made more uniform, resulting in better conductivity and reduced bias in the distribution of electrolyte between the electrode plates. Furthermore, since the ratio of the maximum value Dimax of the outer diameter at the center of the cylinder to the average value D1a of the outer diameter at the bottom end of the cylinder is 100.80% or less, changes in the outer circumference shape of the outer casing 15 relative to the cylindrical surface can be suppressed.

[0041] Furthermore, the ratio of the average outer diameter Diav of the center of the cylindrical portion to the average outer diameter D1a of the bottom end of the cylindrical portion of the outer casing 15 is 100.10% to 100.50%, preferably 100.20% to 100.50%. This allows the outer casing 15 to absorb to some extent the expansion of the outer diameter of the electrode body 14, even when the axial center of the outer circumferential surface of the electrode body 14 bulges relative to the bottom end of the cylindrical portion where the outer diameter of the electrode body 14 before charging and discharging is approximately the same as the inner diameter. Therefore, even when the electrode body 14 expands so that its outer diameter increases particularly near the axial center of the electrode body 14, it is possible to prevent the constraining pressure of the outer casing 15 on the electrode body 14 during charging from becoming excessively high, without having to significantly reduce the outer diameter of the electrode body 14 relative to the inner diameter of the cylindrical portion 15a beforehand. This suppresses changes in the outer circumferential shape of the cylindrical portion 15a relative to the cylindrical surface.

[0042] This also allows for increased battery capacity and improved cycle characteristics of the secondary battery 10. Furthermore, since the standard deviation σi of the outer diameter at the center of the cylindrical portion is 0.020 mm to 0.050 mm, changes in the outer shape of the cylindrical portion 15a relative to the cylindrical surface can be suppressed.

[0043] The first configuration is one in which the ratio of the minimum outer diameter Dimin of the center of the cylinder to the average outer diameter D1a of the bottom end of the cylinder (Dimin × 100 / D1a) is 99.89% or more, the ratio of the maximum outer diameter Dimax of the center of the cylinder to the average outer diameter D1a of the bottom end of the cylinder (Dimax × 100 / D1a) is 100.80% or less, the outer diameter Di of the center of the cylinder changes periodically with respect to the inscribed angle, and the period of change of the outer diameter Di of the center of the cylinder with respect to the inscribed angle is 0.4π to 1.0π. The second configuration is one in which the ratio of the average outer diameter Diav of the center of the cylinder to the average outer diameter D1a of the bottom end of the cylinder is 100.10% to 100.50%, and the standard deviation σi of the outer diameter σi of the center of the cylinder is 0.020 mm to 0.050 mm. In this case, the first configuration and the second configuration may be comprised of only one of them.

[0044] In this embodiment, the effect of increasing the confinement pressure of the outer casing 15 on the electrode body 14 will be explained using a schematic diagram. Figure 2 is a schematic diagram showing the cross-sectional shape of the secondary battery 10 of the embodiment before charging (a) and after charging (b). In Figure 2, to make the effect of the embodiment easier to understand, the entire outer casing 15 is represented as a cylindrical portion 15a. As shown in Figure 2(a), the inner diameter of the bottom end of the cylindrical portion 15a is d. The electrode body 14, with an outer diameter of d1, is housed inside the cylindrical portion 15a. In this embodiment, the difference between the inner diameter d of the cylindrical portion 15a and the outer diameter d1 of the electrode body 14 is made small. Then, as shown in Figure 2(b), when the secondary battery 10 is charged, the electrode body 14 expands, and the confinement pressure of the outer casing 15 on the electrode body 14 can be increased to a certain extent. This makes it possible to increase the battery capacity while preventing the outer circumferential surface of the electrode body 14 from deforming significantly due to the confinement pressure of the outer casing 15 when it expands. Furthermore, the expansion of the electrode body 14 can be suppressed by the restraining pressure of the outer casing 15, thus improving the cycle characteristics.

[0045] Figure 3 is a schematic diagram showing the cross-sectional shape before (a) and after (b) charging in the comparative example secondary battery 10a, where the outer diameter of the electrode body 14 is significantly smaller than the inner diameter d2 of the outer casing 15, taking into account the expansion due to charging. In the comparative example secondary battery 10a, as shown in Figure 3(a), before charging begins, the inner diameter d2 of the electrode body 14 is significantly smaller than the outer diameter d of the bottom end of the cylindrical portion 15a and the outer diameter d1 of the electrode body 14 in the embodiment. When the electrode body 14 expands due to charging, the electrode body 14 is held in place by a small restraining pressure from the cylindrical portion 15a. In such a comparative example, the battery capacity is low. Also, because the restraining pressure is small, the cycle characteristics tend to deteriorate.

[0046] Next, we will describe seven types of secondary batteries in total, including Comparative Examples 1-2 and Examples 1-5, which the inventors of this disclosure used in experiments to confirm the effects of the embodiments. [Examples]

[0047] [Example 1] [Fabrication of the positive electrode plate] A predetermined known paste-like cathode composite slurry was applied to both sides of a long cathode core made of aluminum foil and dried in a dryer. After that, it was cut to a predetermined electrode size and rolled using rollers to produce a cathode plate 11 in which cathode composite layers were formed on both sides of the cathode core.

[0048] [Fabrication of the negative electrode plate] A predetermined negative electrode mixture slurry was applied to both sides of a negative electrode core made of copper foil, dried in a dryer, and compressed to a predetermined thickness using the rollers of a roll press machine. At this time, the negative electrode active material was a mixed negative electrode of graphite and LSX. In addition, 0.01% of single-walled carbon nanotubes (CNTs) were contained in the negative electrode mixture layer as a conductive agent. Furthermore, the negative electrode mixture slurry was prepared by mixing 100 parts by mass of negative electrode active material, 1 part by mass of carboxymethylcellulose (CMC), 1 part by mass of polyacrylic acid (PAA), and 1 part by mass of styrene-butadiene rubber (SBR), using water as the dispersion medium. The ratio of Si material in the negative electrode active material was 6% by mass. The density of the negative electrode mixture layer (negative electrode density) was 1.6 g / cc. Then, the elongated negative electrode core with the negative electrode mixture layer formed on it was cut to a predetermined electrode size to produce a negative electrode plate 12.

[0049] [Fabrication of electrode bodies] A wound electrode body 14 was fabricated by winding the fabricated positive electrode plate 11 and negative electrode plate 12 in a spiral shape via a separator 13.

[0050] [Manufacturing of outer cans] The electrode body 14 described above was housed in a bottomed cylindrical outer casing 15, insulating plates 17 and 18 were placed above and below the electrode body, respectively, and a non-aqueous electrolyte was injected into the Fe outer casing 15. Then, the open end of the outer casing 15 was sealed with a gasket 27 and a sealing body 16 to fabricate a cylindrical lithium-ion secondary battery. In the column for Example 1 in Figure 4, the measurement results of the outer diameter at the center of the cylinder and the bottom end of the cylinder are shown. The measurements were taken in the fully charged state of the initial cell. In commercially available products, the "initial cell" corresponds to a secondary battery 10 that has been fully charged immediately after shipment. In the experiment, after confirming the initial capacity of the secondary battery 10, the secondary battery 10 that had undergone two charge-discharge cycles was assumed to be the initial cell, and the outer diameter of that secondary battery 10 in the fully charged state was measured. In Figure 4, "outer diameter of the center" represents the "outer diameter of the center of the cylinder". "Outer diameter of the bottom" represents the "outer diameter of the bottom end of the cylinder". In Figure 4, "Period" represents the period of the inscribed angle of the outer diameter at the center of the cylinder. Also, "Center outer diameter / Bottom outer diameter" in Figure 4 is the ratio (%) of the average outer diameter at the center of the cylinder to the average outer diameter at the bottom end of the cylinder.

[0051] As shown in Figure 4, in Example 1, the outer diameters of three test specimens were measured. For example, the ratio of the minimum outer diameter Dimin of the center of the cylinder to the average outer diameter D1a of the bottom end of the cylinder (Dimin × 100 / D1a) was 99.89% to 99.94%, which is 99.89% or higher. Also, the ratio of the maximum outer diameter Dimax of the center of the cylinder to the average outer diameter D1a of the bottom end of the cylinder (Dimax × 100 / D1a) was 100.32% to 100.44%, which is 100.80% or lower. The period of the outer diameter at the center of the cylinder is 0.95π or 0.96π. The ratio of the average outer diameter Diav of the center of the cylinder to the average outer diameter D1a of the bottom end of the cylinder (Diav × 100 / D1a) was 100.16% to 100.18%. The standard deviation σi of the outer diameter at the center of the cylinder is 0.025 mm to 0.034 mm. The thickness of the outer can 15 was set to 0.3 mm.

[0052] [Example 2] In Example 2, as shown in Figure 4, the ratio of Si material in the negative electrode active material was set to 10 mass%. The column for Example 2 in Figure 4 shows the measurement results of the outer diameter of the cylindrical portion 15a of the outer can 15. As shown in Figure 4, three test specimens were used in Example 2, and the outer diameter of each was measured. For example, the ratio of the minimum value Dimin of the outer diameter at the center of the cylindrical portion to the average value D1a of the outer diameter at the bottom end of the cylindrical portion (Dimin × 100 / D1a) is 99.90% to 100.11%, which is 99.89% or higher. Also, the ratio of the maximum value Dimax of the outer diameter at the center of the cylindrical portion to the average value D1a of the outer diameter at the bottom end of the cylindrical portion (Dimax × 100 / D1a) is 100.44% to 100.61%, which is 100.80% or lower. The period of the outer diameter at the center of the cylindrical portion is 0.43π or 0.51π. The ratio of the average outer diameter Diav of the center of the cylinder to the average outer diameter D1a of the bottom end of the cylinder (Diav × 100 / D1a) is 100.23% to 100.27%. The standard deviation σi of the outer diameter at the center of the cylinder is 0.023 mm to 0.035 mm. In Example 2, the other configurations are the same as in Example 1.

[0053] [Example 3] In Example 3, as shown in Figure 5, the ratio of Si material in the negative electrode active material was set to 20% by mass. The density of the negative electrode mixture layer (negative electrode density) was set to 1.55 g / cc. In the column for Example 3 in Figure 5, the measurement results of the outer diameter of the cylindrical portion 15a of the outer can 15 are shown. As shown in Figure 5, three test samples were used for Example 3, and the outer diameter of each was measured. For example, the ratio of the minimum value Dimin of the outer diameter at the center of the cylindrical portion to the average value D1a of the outer diameter at the bottom of the cylindrical portion (Dimin × 100 / D1a) was 99.97% to 100.18%, which is 99.89% or higher. Also, the ratio of the maximum value Dimax of the outer diameter at the center of the cylindrical portion to the average value D1a of the outer diameter at the bottom of the cylindrical portion (Dimax × 100 / D1a) was 100.46% to 100.63%, which is 100.80% or lower. The period of the outer diameter at the center of the cylinder is 0.44π to 0.51π. The ratio of the average outer diameter Diav at the center of the cylinder to the average outer diameter D1a at the bottom of the cylinder (Diav × 100 / D1a) is 100.31% to 100.33%. The standard deviation σi of the outer diameter at the center of the cylinder is 0.025 mm to 0.034 mm. In Example 3, the other configurations are the same as in Example 1.

[0054] [Example 4] In Example 4, as shown in Figure 5, the ratio of Si material in the negative electrode active material was set to 30% by mass. The density of the negative electrode mixture layer (negative electrode density) was set to 1.45 g / cc. In the column for Example 4 in Figure 5, the measurement results of the outer diameter of the cylindrical portion 15a of the outer can 15 are shown. As shown in Figure 5, three test samples were used for Example 4, and the outer diameter of each was measured. For example, the ratio of the minimum value Dimin of the outer diameter at the center of the cylindrical portion to the average value D1a of the outer diameter at the bottom of the cylindrical portion (Dimin × 100 / D1a) was 99.91% to 99.99%, which is 99.89% or higher. Also, the ratio of the maximum value Dimax of the outer diameter at the center of the cylindrical portion to the average value D1a of the outer diameter at the bottom of the cylindrical portion (Dimax × 100 / D1a) was 100.52% to 100.64%, which is 100.80% or lower. The period of the outer diameter at the center of the cylinder is 0.41π to 0.56π. The ratio of the average outer diameter Diav at the center of the cylinder to the average outer diameter D1a at the bottom end of the cylinder (Diav × 100 / D1a) is 100.25% to 100.27%. The standard deviation σi of the outer diameter at the center of the cylinder is 0.039 mm to 0.050 mm. In Example 4, the other configurations are the same as in Example 1.

[0055] [Example 5] In Example 5, as shown in Figure 5, the ratio of Si material in the negative electrode active material was set to 50% by mass. The density of the negative electrode mixture layer (negative electrode density) was set to 1.30 g / cc. Example 5The column shows the measurement results for the outer diameter of the cylindrical portion 15a of the outer can 15. As shown in Figure 5, in Example 5, the outer diameters of three test specimens were measured. For example, the ratio of the minimum value Dimin of the outer diameter at the center of the cylindrical portion to the average value D1a of the outer diameter at the bottom end of the cylindrical portion (Dimin × 100 / D1a) is 100.14% to 100.18%, which is 99.89% or higher. Also, the ratio of the maximum value Dimax of the outer diameter at the center of the cylindrical portion to the average value D1a of the outer diameter at the bottom end of the cylindrical portion (Dimax × 100 / D1a) is 100.68% to 100.74%, which is 100.80% or lower. The period of the outer diameter at the center of the cylindrical portion is 0.47π to 0.52π. The ratio of the average outer diameter Diav of the center of the cylinder to the average outer diameter D1a of the bottom end of the cylinder (Diav × 100 / D1a) is 100.43% to 100.50%. The standard deviation σi of the outer diameter at the center of the cylinder is 0.040 mm to 0.048 mm. In Example 5, the other configurations are the same as in Example 1.

[0056] [Comparative Example 1] As shown in Figure 4, Comparative Example 1 had a Si material ratio of 4% by mass in the negative electrode active material. The outer diameter of the cylindrical portion 15a of the outer can 15 is shown in the Comparative Example 1 column of Figure 4. The Comparative Example 1 column of Figure 4 shows the measurement results of the outer diameter of the cylindrical portion 15a of the outer can 15. As shown in Figure 4, three test samples were used as Comparative Example 1, and the outer diameter of each was measured. In Comparative Example 1, unlike Examples 1 to 5, the ratio of the minimum value Dimin of the outer diameter at the center of the cylindrical portion to the average value D1a of the outer diameter at the bottom end of the cylindrical portion in the outer can 15 was less than 99.89%, which is outside the range of the embodiment. Also, the period of change of the outer diameter at the center of the cylindrical portion with respect to the inscribed angle is 0.9π or more. Furthermore, in Comparative Example 1, unlike Examples 1 to 5, the ratio of the average value Diav of the outer diameter at the center of the cylindrical portion to the average value D1a of the outer diameter at the bottom end of the cylindrical portion was less than 100.10%, which is outside the range of the embodiment. Furthermore, the standard deviation σi of the outer diameter at the center of the cylindrical portion is 0.026 mm to 0.057 mm. In Comparative Example 1, the other configurations are the same as in Example 1.

[0057] [Comparative Example 2] In Comparative Example 2, as shown in Figure 6, the ratio of Si material in the negative electrode active material was set to 60% by mass. The density of the negative electrode mixture layer (negative electrode density) was set to 1.25 g / cc. The column for Comparative Example 2 in Figure 6 shows the measurement results of the outer diameter of the cylindrical portion 15a of the outer can 15. As shown in Figure 6, three test samples were used for Comparative Example 2, and their respective outer diameters were measured. In Comparative Example 2, unlike Examples 1-5, the ratio of the maximum outer diameter Dimax at the center of the cylindrical portion to the average outer diameter D1a at the bottom of the cylindrical portion in the outer can 15 exceeded 100.80%, falling outside the scope of the embodiment. Furthermore, in Comparative Example 2, unlike Examples 1-5, the ratio of the average outer diameter Diav at the center of the cylindrical portion to the average outer diameter D1a at the bottom of the cylindrical portion exceeded 100.50%, also falling outside the scope of the embodiment. Additionally, the standard deviation σi of the outer diameter at the center of the cylindrical portion exceeded 0.050 mm, also falling outside the scope of the embodiment. In Comparative Example 2, the other configurations are the same as in Example 1.

[0058] [Cycle Characteristics Evaluation] Using the secondary batteries prepared as described above for Examples 1-5 and Comparative Examples 1-2, the capacity retention rate after 100 cycles was measured. The measurement results for the capacity retention rate are shown in the cycle characteristics column of Figure 4-6. As can be seen from these test results, in the case of Comparative Example 1, the capacity retention rate was low at 89%, but in Examples 1-5, it was confirmed that the capacity retention rate was high at 96%.

[0059] Figure 7 shows the relationship between the outer diameter at the bottom end of the cylindrical part and the inscribed angle of the outer diameter at the center of the cylindrical part in the secondary battery of Comparative Example 1. Figure 8 is the corresponding figure for the secondary battery of Example 2. In Figure 7, the thin solid line La shows the change in the inscribed angle of the outer diameter at the bottom end of the cylindrical part in Comparative Example 1. In Figure 7, the thick solid line Lb shows the change in the inscribed angle of the outer diameter at the center of the cylindrical part in Comparative Example 1. In Figure 8, the thin solid line Lc shows the change in the inscribed angle of the outer diameter at the bottom end of the cylindrical part in Example 2. In Figure 8, the thick solid line Ld shows the change in the inscribed angle of the outer diameter at the center of the cylindrical part in Example 2. Also, arrows T1 and T2 indicate the period of the inscribed angle of the outer diameter at the center of the cylindrical part in Comparative Example 1 and Example 2, respectively.

[0060] As can be seen by comparing Figures 7 and 8, in Comparative Example 1, the minimum value of the outer diameter at the center of the cylinder is lower than the outer diameter at the bottom end of the cylinder, while in Example 2, the minimum value of the outer diameter at the center of the cylinder is higher than the outer diameter at the bottom end of the cylinder. This indicates that the constraining pressure of the outer can on the electrode body is higher in Example 2 than in Comparative Example 1. Furthermore, in Comparative Example 1, the period T1 of the outer diameter at the center of the cylinder is 0.90π, while in Example 2, the period T2 of the outer diameter at the center of the cylinder is 0.51π. This also indicates that the constraining pressure of the outer can on the electrode body is higher in Example 2 than in Comparative Example 1.

[0061] Furthermore, regarding the secondary battery of Comparative Example 2, although the figures corresponding to Figures 7 and 8 are omitted, the outer diameter of the center of the cylindrical part changes with respect to the inscribed angle with a period similar to that of Example 2 in Figure 8. On the other hand, the difference between the minimum and maximum values ​​of the outer diameter of the center of the cylindrical part is considerably larger than in the case of Figure 8. As a result, in Comparative Example 2, the outer circumferential shape of the cylindrical part changes significantly with respect to the cylindrical surface.

[0062] Furthermore, without being limited to the above Examples 1 to 5, if the ratio of graphite in the negative electrode active material is 50 to 94% by mass, the ratio of Si material in the negative electrode active material is 6 to 50% by mass, the density of the negative electrode mixture layer is 1.3 to 1.75 g / cc, the material of the outer can is Fe, and the thickness of the outer can is 0.18 mm to 0.33 mm, the same effects as in Examples 1 to 5 can be obtained. [Explanation of Symbols]

[0063] 10,10a Cylindrical secondary battery (secondary battery), 11 Positive electrode plate, 12 Negative electrode plate, 13 Separator, 14,14a Electrode body, 15 Outer casing, 15a Cylindrical section, 15b Bottom plate section, 15c R section, 16 Sealing body, 17,18 Insulating plate, 19 Positive electrode tab, 20 Negative electrode tab, 21 Protruding section, 22 Filter, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 27 Gasket, 28 Space.

Claims

1. A cylindrical secondary battery comprising an outer casing having a cylindrical tube portion and one end closed with a bottom plate portion, and an electrode body disposed inside the cylindrical portion, wherein the electrode body has a positive electrode plate and a negative electrode plate wound around each other with a separator in between, In a fully charged state, the outer can has a minimum outer diameter at the axial center of the cylindrical portion of the outer can that is 99.89% or more of the average outer diameter at the bottom end of the cylindrical portion, and a maximum outer diameter at the center of the cylindrical portion that is 100.80% or less of the average outer diameter at the bottom end of the cylindrical portion. The inner diameter of the bottom end of the cylindrical portion of the outer can matches the outer diameter of the electrode body before charging and discharging. The outer diameter of the center of the cylindrical portion changes periodically with respect to the inscribed angle, and the period of change in the outer diameter of the center of the cylindrical portion with respect to the inscribed angle is 0.4π to 1.0π. Cylindrical rechargeable battery.

2. In the cylindrical secondary battery described in claim 1, The period over which the outer diameter of the center of the cylindrical portion changes with respect to the inscribed angle is 0.4π to 0.6π. Cylindrical rechargeable battery.

3. In the cylindrical secondary battery according to claim 1 or claim 2, The negative electrode plate has a strip-shaped core and a composite layer formed on the core. The aforementioned composite layer is composed of an active material having graphite and Si material, The ratio of graphite in the active material is 50 to 94% by mass, the ratio of Si material in the active material is 6 to 50% by mass, the density of the mixture layer is 1.3 to 1.75 g / cc, the material of the outer can is Fe, and the thickness of the outer can is 0.18 mm to 0.33 mm. Cylindrical rechargeable battery.

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