Non-aqueous electrolyte secondary battery

Abstract

Provided is a non-aqueous electrolyte secondary battery in which the positions of a plurality of exposed parts are controlled so that it is possible to connect a plurality of tabs to predetermined positions in accordance with a thickness variation of electrodes. A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure comprises: an electrode body in which a positive electrode and a negative electrode are wound with a separator therebetween; an electrolyte; and a cylindrical outer can which accommodates the electrode body and the electrolyte, wherein the positive electrode has a current collector and a mixed layer laminated on at least a portion of the surface of the current collector, a plurality of exposed parts where the current collector is exposed are formed on the surface of the positive electrode, tabs are connected to the respective exposed parts, and when the rotation angle of the electrode body from a winding start-side end to a winding finish-side end of the exposed parts relative to the winding center is defined as an exposed part angle, the exposed part angle of the exposed parts positioned on the winding start side is greater than the exposed part angle of the exposed parts positioned on the winding finish side.

Description

[Technical Field]

[0001] This disclosure relates to a non-aqueous electrolyte secondary battery. [Background technology]

[0002] The positive and negative electrodes of a non-aqueous electrolyte secondary battery each consist of a current collector and a composite layer formed on the surface of the current collector. The composite layer contains an active material capable of reversibly intercalating and deintercalating Li ions. Furthermore, an exposed portion of the current collector is formed on the surface of the electrode, and a tab for connecting the electrode body to the battery terminals is attached to the exposed portion.

[0003] Patent documents 1 to 3 disclose a technique for providing multiple exposed portions for tab connections along the winding direction of the electrode body in order to suppress heat generation at the tab connection portion. Furthermore, patent document 3 describes that in the positive electrode, the length L in the winding direction of each exposed portion and the radius R of the portion of the electrode body that includes the exposed portion located closest to the end of the winding satisfy the relationship L ≥ 2πR. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-261439 [Patent Document 2] Japanese Patent Publication No. 2000-277155 [Patent Document 3] Japanese Patent Publication No. 2002-164044 [Overview of the project] [Problems that the invention aims to solve]

[0005] Incidentally, in order to connect the multiple tabs leading from the electrode body to the battery terminals, it is preferable that the multiple tabs are arranged in predetermined positions. Since the multiple tabs are connected to each exposed portion, exposed portions need to be formed on the electrode surface at the locations where the multiple tabs are arranged. However, the position of the exposed portions varies due to the influence of the electrode thickness, so when arranging each exposed portion on the electrode, it is necessary to consider the variation in electrode thickness between lots. The technologies disclosed in Patent Documents 1 to 3 do not consider the variation in the position of the exposed portions and still have room for improvement. Furthermore, as described in Patent Document 3, if the length of each exposed portion is increased, the mass of the composite layer decreases, and the battery capacity decreases significantly.

[0006] The purpose of this disclosure is to provide a non-aqueous electrolyte secondary battery in which the dimensions of multiple exposed parts are controlled so that multiple tabs can be connected in predetermined positions to accommodate variations in electrode thickness. [Means for solving the problem]

[0007] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure comprises an electrode body in which a first electrode and a second electrode having opposite polarities are wound with a separator between them, an electrolyte, and a cylindrical outer container housing the electrode body and the electrolyte. The first electrode has a current collector and a composite layer laminated on at least a portion of the surface of the current collector. Multiple exposed portions of the current collector are formed on the surface of the first electrode, and a tab is connected to each of the exposed portions. When the rotation angle from the winding start end to the winding end of the exposed portion with respect to the winding center of the electrode body is defined as the exposed portion angle, the exposed portion angle of the exposed portion located on the winding start side is larger than the exposed portion angle of the exposed portion located on the winding end side. [Effects of the Invention]

[0008] According to a non-aqueous electrolyte secondary battery in one aspect of this disclosure, multiple tabs can be connected at predetermined positions. [Brief explanation of the drawing]

[0009] [Figure 1]It is an axial cross-sectional view of a cylindrical secondary battery which is an example of an embodiment. [Figure 2] It is a perspective view of the wound electrode body included in the secondary battery shown in FIG. 1. [Figure 3] It is a front view showing the positive electrode constituting the electrode body shown in FIG. 2 in a developed state. [Figure 4] It is a plan view of the electrode body shown in FIG. 2 viewed from the axial direction.

Mode for Carrying Out the Invention

[0010] Hereinafter, an example of an embodiment of a cylindrical secondary battery according to the present disclosure will be described in detail with reference to the drawings. In the following description, specific shapes, materials, numerical values, directions, etc. are examples for facilitating the understanding of the present invention, and can be appropriately changed according to the specifications of the cylindrical secondary battery. Further, in the following description, when a plurality of embodiments and modification examples are included, it is initially assumed that the characteristic parts thereof can be used in appropriate combination.

[0011] FIG. 1 is an axial cross-sectional view of a non-aqueous electrolyte secondary battery 10 which is an example of an embodiment. In the secondary battery 10 shown in FIG. 1, an electrode body 14 and an electrolytic solution (not shown) are housed in an exterior can 15. The electrode body 14 has a wound structure in which strip-shaped electrodes (a positive electrode 11 and a negative electrode 12) are wound via a separator 13. As the non-aqueous solvent (organic solvent) of the electrolytic solution, carbonates, lactones, ethers, ketones, esters, etc. can be used, and two or more of these solvents can be mixed and used. When two or more solvents are mixed and used, it is preferable to use a mixed solvent containing a cyclic carbonate and a chain carbonate. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used as the cyclic carbonate, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), etc. can be used as the chain carbonate. As the electrolyte salt of the electrolytic solution, LiPF6, LiBF4, LiCF3SO3, etc. and mixtures thereof can be used. The dissolution amount of the electrolyte salt with respect to the non-aqueous solvent is, for example, 0.5 mol / L to 2.0 mol / L. Hereinafter, for the sake of convenience of explanation, the side of the sealing body 16 will be described as "upper" and the bottom side of the exterior can 15 will be described as "lower".

[0012] The sealing body 16 seals the opening at the upper end of the exterior can 15, so that the interior of the secondary battery 10 is sealed. Insulating plates 17 and 18 are provided above and below the electrode body 14, respectively. The positive electrode tab 19 extends vertically through the through hole of the insulating plate 17 and connects the filter 22 which is the bottom plate of the sealing body 16 and the positive electrode 11 contained in the electrode body 14. Thereby, the positive electrode 11 and the sealing body 16 are connected, and in the secondary battery 10, the cap 26 which is the top plate of the sealing body 16 electrically connected to the filter 22 serves as the positive electrode terminal. The material of the positive electrode tab 19 is, for example, aluminum. On the other hand, the negative electrode tab 20 extends to the bottom side of the exterior can 15 through the outside of the insulating plate 18 and is welded to the inner surface of the bottom of the exterior can 15. Thereby, the negative electrode 12 and the exterior can 15 are connected, and in the secondary battery 10, the exterior can 15 serves as the negative electrode terminal. The material of the negative electrode tab 20 is, for example, nickel.

[0013] In the electrode body 14, four positive electrode tabs 19a, 19b, 19c, and 19d are led out and electrically connected to each other. In this embodiment, only positive electrode tab 19a is connected to the filter 22, but the connection state of the positive electrode tabs 19 is not limited to this example. Furthermore, the positive electrode tabs 19 led out from the electrode body 14 may be directly connected to the sealing body 16 as in this embodiment, or they may be connected to the sealing body 16 via a known current collector.

[0014] The number of positive electrode tabs 19 derived from the electrode body 14 can be any number, i.e., two or more. By deriving multiple tabs from the electrode body 14, the connection resistance between the positive electrode 11 and the sealing body 16 can be reduced, thereby improving the output characteristics of the secondary battery 10. The number of positive electrode tabs 19 is preferably 2 to 10, and more preferably 3 to 6.

[0015] The configuration of the positive electrode tab 19 and the negative electrode tab 20 is not limited to the example of this embodiment. For example, multiple positive electrode tabs 19 and multiple negative electrode tabs 20 may be derived from the electrode body 14, or one positive electrode tab 19 and multiple negative electrode tabs 20 may be derived from the electrode body 14. In this embodiment, the case in which the first electrode is a positive electrode 11 and the second electrode is a negative electrode 12 is described, but the first electrode may also be a negative electrode 12. That is, it is sufficient that at least one of the positive electrode 11 and the negative electrode 12 corresponds to the first electrode.

[0016] The outer casing 15 is, for example, a metal cylindrical casing with a closed bottom. A gasket 27 is provided between the outer casing 15 and the sealing body 16 to ensure airtightness inside the secondary battery 10. The outer casing 15 has grooves 21 that support the sealing body 16, which are formed, for example, by pressing the side surface from the outside. The grooves 21 are preferably formed in an annular shape along the circumferential direction of the outer casing 15, and their upper surface supports the sealing body 16.

[0017] 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 the two. 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.

[0018] Next, the electrode body 14 will be described with reference to Figure 2. Figure 2 is a perspective view of the electrode body 14. As described above, 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 formed in a strip shape and are wound in a spiral shape around a winding core arranged along the winding axis, resulting in an alternate stacked state in the radial direction of the electrode body 14. In the radial direction, the side facing the winding axis is called the inner circumference, and the opposite side is called the outer circumference. In the electrode body 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the width direction of the positive electrode 11 and the negative electrode 12 is the axial direction. The positive electrode tab 19 is led out in the axial direction from four locations on the upper surface of the electrode body 14.

[0019] The negative electrode 12 included in the electrode body 14 is generally formed larger than the positive electrode 11 to prevent lithium deposition on the negative electrode 12. Specifically, the width of the negative electrode 12 is greater than the width of the positive electrode 11. Also, the longitudinal length of the negative electrode 12 is greater than the longitudinal length of the positive electrode 11. As a result, when wound as the electrode body 14, at least the portion of the positive electrode 11 where the positive electrode mixture layer 30 is formed is positioned opposite the portion of the negative electrode 12 where the negative electrode mixture layer is formed, via the separator 13.

[0020] The negative electrode 12 comprises a strip-shaped negative electrode current collector and a negative electrode mixture layer laminated on at least a portion of the surface of the negative electrode current collector. The negative electrode mixture layer is formed on at least one of the inner and outer circumferences of the negative electrode current collector, and preferably covers the entire surface of both sides of the negative electrode current collector, excluding the negative electrode exposed portion described later. For the negative electrode current collector, 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 current collector is, for example, 5 μm to 30 μm.

[0021] The negative electrode mixture layer preferably contains a negative electrode active material and a binder. The negative electrode mixture layer can be manufactured, for example, by coating both sides of a negative electrode current collector with a negative electrode mixture slurry containing a negative electrode active material, a binder, and a solvent such as water, drying it, and then rolling it.

[0022] The negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it can reversibly intercept and release lithium ions. For example, carbon-based materials such as natural graphite and artificial graphite, metals that alloy with lithium such as Si and Sn, or alloys and oxides containing these can be used.

[0023] The negative electrode active material may include carbon-based materials and silicon-based materials. Examples of silicon-based materials include Si, Si-containing alloys, and SiO2. x Examples include silicon oxides (where x is 0.8 to 1.6). Silicon-based materials are negative electrode active materials that can improve battery capacity compared to carbon-based materials. From the viewpoint of improving battery capacity and suppressing the deterioration of charge-discharge cycle characteristics, the content of silicon-based materials in the negative electrode active material is preferably 3% by mass or more relative to the mass of the negative electrode active material. The upper limit of the silicon-based material content is, for example, 20% by mass.

[0024] Examples of binders included in the negative electrode mixture layer include styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethylcellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., or partially neutralized salts), and polyvinyl alcohol (PVA). The binder may also include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. These may be used individually or in combination of two or more types.

[0025] At the winding end of the negative electrode 12, an exposed negative electrode portion is formed where the negative electrode current collector is exposed. The exposed negative electrode portion is the part where the surface of the negative electrode current collector is not covered by the negative electrode mixture layer, and it is preferable that it be provided on both sides of the negative electrode 12 so as to overlap in the thickness direction of the negative electrode 12. The exposed negative electrode portion is, for example, a part of the negative electrode current collector negative electrode It is provided by intermittent coating without applying the mixture slurry. The negative electrode tab 20 is connected to the exposed negative electrode portion by ultrasonic welding or the like.

[0026] 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 an olefin resin such as polyethylene or polypropylene. The thickness of the separator 13 is, for example, 10 μm to 50 μm. The separator 13 is trending toward thinner films as batteries become more high-capacity and high-power. The separator 13 has a melting point of, for example, 130°C to 180°C.

[0027] Next, the positive electrode 11 according to this embodiment will be described in detail with reference to Figures 3 and 4. Figure 3 is a front view of the positive electrode 11 that constitutes the electrode body 14. In Figure 3, the positive electrode 11 is shown in an unfolded state.

[0028] The positive electrode 11 has a strip-shaped positive electrode current collector 32 and a positive electrode mixture layer 30 laminated on at least a part of the surface of the positive electrode current collector 32. The positive electrode mixture layer 30 is preferably formed on at least one of the inner peripheral side and the outer peripheral side of the positive electrode current collector 32, and is preferably formed over the entire area of both surfaces of the positive electrode current collector 32 excluding the positive electrode exposed portions 34 described later. For the positive electrode current collector 32, for example, a metal foil such as aluminum or a film having the metal disposed on the surface layer is used. The thickness of the positive electrode current collector 32 is, for example, 10 μm to 30 μm. The variation in the thickness of the positive electrode 11 is, for example, -5% to +5% with respect to the design value.

[0029] The positive electrode mixture layer 30 preferably contains a positive electrode active material, a conductive agent, and a binder. The positive electrode mixture layer 30 can be produced, for example, 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 current collector 32, drying, and then rolling.

[0030] Examples of the positive electrode active material contained in the positive electrode mixture layer 30 include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni. The lithium transition metal oxide is, for example, Li x CoO2, Li x NiO2, Li x MnO2, Li x Co y Ni 1-y O2, Li x Co y M 1-y O z 、Li x Ni 1-y [[ID=,32]]M y O z 、Li x Mn2O4, Li x Mn 2-y M yO4, LiMPO4, Li2MPO4F (M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B; 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3). These may be used alone or in combination of multiple types. In terms of achieving a higher capacity of the non-aqueous electrolyte secondary battery, the cathode active material is Li x NiO2, Li x Co y Ni 1-y O2, Li x Ni 1-y M y O z (M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B; 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3), and it is preferable to include lithium nickel composite oxides such as these.

[0031] Examples of the conductive agent included in the cathode mixture layer 30 include carbon-based particles such as carbon black (CB), acetylene black (AB), ketjen black, carbon nanotube (CNT), graphene, and graphite. These may be used alone or in combination of two or more types.

[0032] Examples of the binder included in the cathode mixture layer 30 include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide-based resins, acrylic resins, polyolefin-based resins, etc. These may be used alone or in combination of two or more types. When preparing the cathode mixture slurry with an aqueous solvent, styrene-butadiene rubber (SBR), nitrile rubber (NBR), CMC or its salt, polyacrylic acid or its salt, polyvinyl alcohol, etc. may also be used.

[0033] Multiple exposed positive electrode portions 34 are formed on the surface of the positive electrode 11, along the winding direction of the electrode body 14, where the positive electrode current collector 32 is exposed. The exposed positive electrode portions 34 are parts where the surface of the positive electrode current collector 32 is not covered by the positive electrode mixture layer 30, and a positive electrode tab 19 is connected to each of the exposed positive electrode portions 34. The exposed positive electrode portions 34 are provided, for example, by intermittent coating, where the positive electrode mixture slurry is not applied to a part of the positive electrode current collector 32.

[0034] As shown in Figure 3, it is preferable that the positive electrode exposed portion 34 is provided along the entire length in the width direction, and that the positive electrode tab 19 is connected to the positive electrode exposed portion 34 over a long distance in the width direction. This increases the contact area between the positive electrode tab 19 and the positive electrode current collector 32, improving current collection performance. In the width direction, the ratio of the length of the positive electrode tab 19 in contact with the positive electrode exposed portion 34 to the total length of the positive electrode 11 is, for example, 0.5 to 0.9.

[0035] The positive electrode exposed portion 34 is formed to be wider in the longitudinal direction than the positive electrode tab 19. The width of the tab in the longitudinal direction is, for example, 1 mm to 7 mm, and the width of the positive electrode exposed portion 34 in the longitudinal direction is, for example, 5 mm to 40 mm. Preferably, the positive electrode exposed portion 34 is provided on both sides of the positive electrode 11 so as to overlap in the thickness direction of the positive electrode 11. The positive electrode tab 19 is joined to the positive electrode exposed portion 34 by, for example, ultrasonic welding.

[0036] In the example shown in Figure 3, four positive electrode exposed portions 34 are provided, starting from the winding start side: 34a, 34b, 34c, and 34d. The width of the longitudinal positive electrode exposed portions 34 decreases in the order of 34a, 34b, 34c, and 34d. Note that the size of each positive electrode exposed portion 34 is not limited to the example shown in Figure 3. For example, the longitudinal width of the positive electrode exposed portion 34 located at the winding end side may be larger than the longitudinal width of the positive electrode exposed portion 34 located at the winding start side.

[0037] Positive electrode tabs 19a, 19b, 19c, and 19d are connected to approximately the longitudinal center of the positive electrode exposed portions 34a, 34b, 34c, and 34d, respectively. Each of the positive electrode tabs 19a, 19b, 19c, and 19d is led out in the width direction from one end of the positive electrode 11.

[0038] A protective member 36 is provided on the surface of the positive electrode 11 so as to cover a portion of the positive electrode tab 19 and the positive electrode exposed portion 34. The protective member 36 is an insulating member that prevents the positive electrode tab 19 and the positive electrode exposed portion 34 from internally short-circuiting with the opposing negative electrode mixture layer in the event that the separator 13 is torn. Preferably, the protective member 36 is bonded to the surface of the positive electrode mixture layer 30 so as to straddle the positive electrode exposed portion 34 of the positive electrode 11 in the longitudinal direction. Furthermore, it is preferable that the protective member 36 is longer than the positive electrode 11 in the width direction of the positive electrode 11.

[0039] The protective member 36 is, for example, an adhesive tape having a base material and an adhesive portion formed on one surface of the base material. A heat-resistant layer containing inorganic particles such as metal oxides can be provided between the base material and the adhesive portion. The base material can be any insulating resin, such as PPS (polyphenylene sulfide), PEEK (polyether ether ketone), PI (polyimide), PP (polypropylene), PET (polyethylene terephthalate), PBT (polybutylene terephthalate), etc. The thickness of the base material is, for example, 5 μm to 50 μm.

[0040] The adhesive portion is the part for adhering the protective member 36 to the surface of the positive electrode 11. The thickness of the adhesive portion is, for example, 1 μm to 30 μm. The adhesive portion may contain at least one of a rubber-based polymer or an acrylic-based polymer. Since rubber-based polymers and acrylic-based polymers are adhesive, they can adhere the protective member 36 to the surface of the positive electrode 11. The adhesive portion may further contain, for example, a silicone-based polymer.

[0041] Figure 4 is a plan view of the electrode body 14 as seen from the axial direction in one example of an embodiment. When the rotation angle of the positive electrode exposed portion 34 from the winding start end to the winding end end with respect to the winding center C of the electrode body 14 is defined as the exposed portion angle θ, the exposed portion angles θ of each positive electrode exposed portion 34 satisfy the relationship: exposed portion angle θ of positive electrode exposed portion 34a > exposed portion angle θ of positive electrode exposed portion 34b > exposed portion angle θ of positive electrode exposed portion 34c > exposed portion angle θ of positive electrode exposed portion 34d. As a result, even if there is variation in the positions of the other positive electrode exposed portions 34a, 34b, and 34c relative to the positive electrode exposed portion 34d closest to the winding end, at least a portion of each positive electrode exposed portion 34a, 34b, and 34c can be included in the region P shown in Figure 4. The exposed portion angle θ of each positive electrode exposed portion 34 can be appropriately determined according to the expected variation range of the thickness of the positive electrode 11.

[0042] Since at least a portion of each positive electrode exposed portion 34 is included within the range of region P, any of the positive electrode tabs 19 can be positioned within the range of region P. The degree of variation in the positions of the positive electrode exposed portions 34a, 34b, and 34c relative to the positive electrode exposed portion 34d can be evaluated based on the measurement results of the thickness of the positive electrode 11. Based on the evaluation results, the position for connecting the positive electrode tabs 19 can be determined so that the positive electrode tabs 19 are positioned within the range of region P. Note that the exposed portion angle θ is the rotation angle from the winding start end to the winding end of the positive electrode exposed portion 34, and therefore may exceed 360°.

[0043] As described above, by controlling the dimensions of the positive electrode exposed portion 34, multiple positive electrode tabs 19 can be connected to predetermined positions in response to variations in the thickness of the positive electrode 11 without increasing the area of ​​the exposed portion, compared to the case where the longitudinal width of all positive electrode exposed portions 34 is increased as described in Reference 3. At the winding start side, even if the arc formed by the positive electrode 11 is small and the longitudinal width of the positive electrode exposed portion 34 is short, a sufficiently large exposed portion angle θ is formed. Therefore, by controlling the dimensions of the positive electrode exposed portion 34 as described above, multiple positive electrode tabs 19 can be connected to predetermined positions in response to variations in the thickness of the positive electrode 11 without increasing the area of ​​the exposed portion, compared to the case where the width of the exposed portion at the winding end is increased based on the exposed portion at the winding start side.

[0044] In Figure 4, the positive electrode tabs 19 are arranged in a nearly straight line radially from the winding center C, but the layout of the positive electrode tabs 19 is not limited to this example. For example, the positive electrode tabs 19 may be arranged in a nearly straight line radially with the winding center C in between, or they may be arranged at nearly equal angles around the winding center C. In that case, the arrangement of the positive electrode exposed portion 34 can be appropriately changed according to the arrangement direction of the positive electrode tabs 19. [Examples]

[0045] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0046] [Fabrication of the positive electrode] 100 parts by mass of LiNi 0.88 Co 0.09 Al 0.03 O2, 1.0 part by mass of acetylene black (AB), and 0.9 parts by mass of polyvinylidene fluoride (PVdF) were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. Next, this positive electrode mixture slurry was applied to both sides of a strip-shaped positive electrode current collector made of aluminum foil so that four positive electrode exposures were formed. After drying this coating film, it was rolled and cut to a predetermined electrode plate size to produce a positive electrode with a positive electrode mixture layer formed on both sides of a positive electrode current collector with a total length of 706 mm, and aluminum positive electrode tabs were welded to each positive electrode exposure. The longitudinal widths of the positive electrode exposures were set to 22 mm, 18 mm, 12 mm, and 8 mm in order from the winding start side so that at least a portion of each positive electrode exposure would be included within a predetermined range based on the positive electrode exposure closest to the end of the winding, even if there was variation in the thickness of the positive electrode. The longest positive electrode tab was welded to the 22mm wide positive electrode exposed section at the very beginning of the winding process, for welding to the sealing body.

[0047] [Fabrication of the negative electrode] A negative electrode mixture slurry was prepared by mixing 95 parts by mass of graphite, 5 parts by mass of SiO, 1 part by mass of carboxymethylcellulose (CMC), and 1 part by mass of styrene-butadiene rubber (SBR), and adding an appropriate amount of water. Next, this negative electrode mixture slurry was applied to both sides of a strip-shaped negative electrode current collector made of copper foil, so that a negative electrode exposure portion was formed at the end of the winding. After drying this coating film, it was rolled and cut to a predetermined electrode plate size to produce a negative electrode with a negative electrode mixture layer formed on both sides of a positive electrode current collector with a total length of 959 mm, and a nickel negative electrode tab was welded to the negative electrode exposure portion.

[0048] [Fabrication of electrode bodies] An electrode body was fabricated by winding the positive and negative electrodes via a separator made of polyolefin resin. The electrode body satisfied the relationship between the exposed angle θ of the positive electrode exposed portion 34a > the exposed angle θ of the positive electrode exposed portion 34b > the exposed angle θ of the positive electrode exposed portion 34c > the exposed angle θ of the positive electrode exposed portion 34d, similar to the example shown in Figure 4.

[0049] [Preparation of non-aqueous electrolytes] Ethylene carbonate (EC) and dimethyl Luca 100 parts by mass of a mixed solvent consisting of ionate (DMC) and (by volume ratio EC:DMC = 1:3) was mixed with 5 parts by mass of vinylene carbonate (VC). LiPF6 was dissolved in this mixed solvent to a concentration of 1.5 mol / L to prepare a non-aqueous electrolyte.

[0050] [Manufacturing of secondary batteries] Insulating plates were placed above and below the electrode body, and the electrode body was housed in a cylindrical outer casing. Next, the negative electrode tab was welded to the bottom of the outer casing, and after welding the positive electrode tabs together, the longest positive electrode tab was welded to the sealing body. After that, the electrolyte was injected into the outer casing using a reduced pressure method, and the open end of the outer casing was sealed by crimping it to the sealing body via a gasket to create a secondary battery. The design capacity of the fabricated secondary battery is 4850mAh.

[0051] <Comparative Example> In the fabrication of the positive electrode, even if variations in the thickness of the positive electrode occur, the longitudinal width of each positive electrode exposed portion was set to 8 mm, 12 mm, 26 mm, and 53 mm in order from the winding start side, so that at least a portion of each positive electrode exposed portion is included within a predetermined range based on the positive electrode exposed portion closest to the winding start side. Otherwise, the secondary battery was fabricated in the same manner as in the example.

[0052] [Battery capacity evaluation] The non-aqueous electrolyte secondary batteries of the examples and comparative examples were charged to 4.2V with a constant current of 1455mA (0.3C) at an ambient temperature of 25°C, and then charged to 97mA (0.02C) with a constant voltage of 4.2V. After standing for 20 minutes, they were discharged to 2.5V with a constant current of 2425mA (0.5C), and the discharge capacity at this time was defined as the battery capacity.

[0053] Table 1 summarizes the evaluation results of the battery capacity of the non-aqueous electrolyte secondary batteries in the examples and comparative examples.

[0054] [Table 1]

[0055] In the comparative example battery, even if variations in the position of the positive electrode exposed portion occur due to variations in the thickness of the positive electrode, the exposure angle of each positive electrode exposed portion is adjusted so that at least a portion of each positive electrode exposed portion is included within a predetermined range, using the positive electrode exposed portion closest to the winding start as a reference. However, the comparative example battery has a longer positive electrode exposed portion and a reduced mass of the positive electrode mixture layer compared to the example battery. Table 1 shows that the battery capacity of the comparative example battery is significantly lower than that of the example battery. Thus, as in the example battery, by increasing the exposure angle θ of the positive electrode exposed portion 34 located at the beginning of the winding compared to the exposure angle θ of the positive electrode exposed portion 34 located at the end of the winding, it is possible to connect multiple positive electrode tabs to predetermined positions in response to variations in the thickness of the positive electrode while suppressing a decrease in battery capacity. [Explanation of Symbols]

[0056] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Outer casing, 16 Sealing body, 17,18 Insulating plate, 19,19a,19b,19c,19d Positive electrode tab, 20 Negative electrode tab, 21 Grooved section, 22 Filter, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 26a Opening, 27 Gasket, 30 Positive electrode mixture layer, 32 Positive electrode current collector, 34,34a,34b,34c,34d Positive electrode exposed section, C Winding center, θ Exposed section angle

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode body in which a first electrode and a second electrode having opposite polarities are wound with a separator between them, an electrolyte, and a cylindrical outer container housing the electrode body and the electrolyte, The first electrode comprises a current collector and a composite layer laminated on at least a portion of the surface of the current collector. Multiple exposed portions of the current collector are formed on the surface of the first electrode along the winding direction of the electrode body, and a tab is connected to each of the exposed portions. When the rotation angle of the exposed portion relative to the winding center of the electrode body, from the beginning end to the end end of the exposed portion, is defined as the exposed portion angle, the exposed portion angle at the beginning of the winding is greater than the exposed portion angle at the end of the winding. A non-aqueous electrolyte secondary battery, wherein an insulating protective member is provided on the surface of the first electrode so as to cover a part of the tab and the exposed portion.

2. The surface of the first electrode is provided with three or more exposed portions, Each of the three or more exposed portions is connected to the tab, The non-aqueous electrolyte secondary battery according to claim 1, wherein the angle of the exposed portion of the three or more exposed portions decreases as you move from the winding start side to the winding end side of the first electrode.

3. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the first electrode is a positive electrode.