Non-aqueous electrolyte secondary battery

Abstract

The present invention is characterized by comprising an electrode body (14) in which a positive electrode (11) and a negative electrode (12) are wound with a separator interposed therebetween, and is characterized in that: the negative electrode (12) includes a negative electrode current collector (40) and a negative electrode mixture layer (41) that is disposed on the negative electrode current collector (40); the negative electrode (12) has a non-facing portion (42) that is wound in a state of not facing the positive electrode (11) across the separator on the winding-start side of the electrode body (14); and, in the non-facing portion (42), a mixture-uncoated portion (44) in which the negative electrode current collector (40) is exposed is provided in a region closer to the winding-end side than the mixture starting end (41X) of the negative electrode mixture layer (41).

Description

Nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery.

[0002] Conventionally, non-aqueous electrolyte secondary batteries have been known that include an electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound with a separator interposed therebetween, and a bottomed cylindrical outer can that houses the electrode assembly. Generally, the negative electrode includes a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector. Patent Document 1 discloses a non-aqueous electrolyte secondary battery in which, for the purpose of increasing the battery output and suppressing heat generation during charging and discharging, multiple current collector exposed portions, in which the negative electrode current collector is exposed and no negative electrode mixture layer is disposed, are arranged at intervals along the longitudinal direction of the negative electrode.

[0003] Japanese Patent Application Laid-Open No. 2006-24375

[0004] In recent years, with the spread of electric vehicles and other factors, there has been an increasing demand for improved cycle characteristics of non-aqueous electrolyte secondary batteries. During battery charge and discharge, stress tends to concentrate more easily at the winding start side (winding center side) of the electrode assembly than at the winding end side, which makes the electrode plates more likely to deform. When electrode plate deformation occurs, the distance between the positive and negative electrodes becomes uneven, making it more likely that charge and discharge reactions will become uneven within the electrode assembly. As a result, the cycle characteristics of non-aqueous electrolyte secondary batteries deteriorate.

[0005] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes an electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound longitudinally with a separator interposed therebetween, a non-aqueous electrolyte, and a bottomed cylindrical outer can that accommodates the electrode assembly and the non-aqueous electrolyte. The negative electrode includes a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, and has a non-facing portion at the winding start side of the electrode assembly that is wound so as not to face the positive electrode via the separator. The non-facing portion is characterized in that a region of the non-facing portion that is closer to the winding end side than the mixture start end, which is the end on the winding start side of the negative electrode mixture layer, has an uncoated portion where no negative electrode mixture layer is disposed and where the negative electrode current collector is exposed.

[0006] According to the nonaqueous electrolyte secondary battery of one aspect of the present disclosure, unevenness in the charge / discharge reaction inside the electrode assembly is suppressed, and cycle characteristics can be improved.

[0007] 1 is a plan view showing a positive electrode and a negative electrode in an expanded state, the plan view showing an enlarged winding start side of the positive electrode and the negative electrode in an expanded state, and a plan view showing an axial cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention;

[0008] Hereinafter, an example of an embodiment of a nonaqueous electrolyte 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 understanding of the present invention and can be appropriately changed according to the specifications of the nonaqueous electrolyte secondary battery. Furthermore, when the following description includes multiple embodiments and modified examples, it is initially assumed that the characteristic portions thereof will be used in appropriate combination.

[0009] Fig. 1 is an axial cross-sectional view of an example of a nonaqueous electrolyte secondary battery 10. As shown in Fig. 1, the nonaqueous electrolyte secondary battery 10 includes a wound electrode assembly 14, a nonaqueous electrolyte (not shown), and an exterior body 16 that accommodates the electrode assembly 14 and the nonaqueous electrolyte.

[0010] The electrode assembly 14 has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The positive electrode 11, the negative electrode 12, and the separator 13 are all long strips that are spirally wound and alternately stacked in the radial direction of the electrode assembly 14. 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 direction and width direction 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 13 are arranged to sandwich the positive electrode 11.

[0011] The positive electrode 11 has a long positive electrode current collector 30 and a positive electrode mixture layer 31 disposed on the positive electrode current collector 30. The positive electrode current collector 30 can be a foil of a metal stable within the potential range of the positive electrode 11, such as aluminum, an aluminum alloy, stainless steel, or titanium, or a film having such a metal disposed on its surface. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF), and is preferably formed on both sides of the positive electrode current collector 30. For example, a lithium transition metal composite oxide containing Ni, Co, Mn, Al, or the like is used as the positive electrode active material.

[0012] The thickness of the positive electrode 11 is, for example, 100 μm or more and 200 μm or less. 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 current collector 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 100 μm or less on one side of the positive electrode current collector 30. The positive electrode 11 can be produced by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode current collector 30, drying the coating, and then compressing it to form the positive electrode mixture layer 31 on both sides of the positive electrode current collector 30.

[0013] The negative electrode 12 has a long negative electrode current collector 40 and a negative electrode mixture layer 41 disposed on the negative electrode current collector 40. The negative electrode current collector 40 can be a foil of a metal that is stable within the potential range of the negative electrode 12, such as copper, a copper alloy, stainless steel, nickel, or a nickel alloy, or a film having such a metal disposed on its surface. The negative electrode mixture layer 41 contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR), and is preferably formed on both sides of the negative electrode current collector 40.

[0014] The negative electrode active material preferably contains a silicon-containing material in addition to a carbon material. The inclusion of a silicon-containing material facilitates achieving both high capacity and excellent cycle characteristics. From the viewpoint of achieving high capacity, the content of the silicon-containing material is preferably 5% by mass or more, more preferably 10% by mass or more, relative to the total mass of the negative electrode active material. Generally, silicon-containing materials undergo larger volume changes during charge and discharge than carbon materials. Therefore, when a silicon-containing material is included as the negative electrode active material, deformation of the electrode plate is likely to occur at the winding start side of the electrode assembly 14. Therefore, when a silicon-containing material is included as the negative electrode active material, the effect of improving the cycle characteristics described below is significantly exhibited.

[0015] The carbon material functioning 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. Among them, it is preferable to use at least artificial graphite such as massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB), natural graphite such as flake graphite, massive graphite, and amorphous graphite, or a mixture thereof as the carbon material.

[0016] The silicon-containing material may 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 volume-based average particle size (D50) of the composite material is generally smaller than the D50 of graphite. The volume-based D50 of the composite material 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.

[0017] A suitable silicon-containing material (composite material) is a composite particle containing an ion-conducting phase and a Si phase dispersed in the ion-conducting phase. The ion-conducting 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-conducting phase is a continuous phase composed of a collection of particles finer than the Si phase. The silicon-containing material may also have a conductive layer covering the surface of the ion-conducting phase. The conductive layer is made of a material with higher conductivity than the ion-conducting phase and forms a good conductive path in the negative electrode mixture layer 41.

[0018] An example of a suitable Si-containing composite material has a sea-island structure in which fine Si is dispersed almost uniformly in an amorphous silicon oxide phase, and the overall structure is represented by the general formula SiO ｘ The silicon oxide may be mainly composed of silicon dioxide. The oxygen to silicon content (x) is, for example, 0.5≦x<2.0, preferably 0.8≦x≦1.5.

[0019] The thickness of the negative electrode 12 is, for example, 100 μm or more and 300 μm or less. In this embodiment, the thickness of the negative electrode 12 is substantially constant except for a current collector exposed portion 43 (see FIG. 2 ) and a mixture uncoated portion 44 (see FIG. 2 ), which will be described later. The thickness of the negative electrode current collector 40 is, for example, 5 μm or more and 15 μm or less. The thickness of the negative electrode mixture layer 41 is, for example, 50 μm or more and 150 μm or less on one side of the negative electrode current collector 40. The negative electrode 12 can be produced, similarly to the positive electrode 11, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder onto the negative electrode current collector 40, drying the coating, and then compressing it to form the negative electrode mixture layer 41 on both sides of the negative electrode current collector 40.

[0020] The electrode assembly 14 has a positive electrode lead 20 connected to the positive electrode 11 and a negative electrode lead 21 connected to the negative electrode 12. The positive electrode lead 20 is, for example, an aluminum tab, and the negative electrode lead 21 is, for example, a nickel tab. In this embodiment, the positive electrode lead 20 is connected to approximately the center of the positive electrode 11 in the longitudinal direction. The negative electrode lead 21 is provided at one longitudinal end of the negative electrode 12 located at the winding start side of the electrode assembly 14. The negative electrode lead 21 may also be provided at one longitudinal end of the negative electrode 12 located at the winding end side of the electrode assembly 14.

[0021] The non-aqueous electrolyte has lithium ion conductivity and may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0022] The liquid electrolyte (electrolytic solution) contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. Examples of the electrolyte salt include LiPF ６ Lithium salts such as

[0023] 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, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, 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 the non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0024] The exterior body 16 is a cylindrical metal container with a bottom and an opening at one axial end, and the opening of the exterior body 16 is closed by a sealing body 17. For ease of explanation, the sealing body 17 side of the nonaqueous electrolyte secondary battery 10 will be referred to as the "top" and the bottom side of the exterior body 16 will be referred to as the "bottom" below.

[0025] Insulating plates 18 and 19 are disposed above and below the electrode body 14. In the example shown in Fig. 1 , the positive electrode lead 20 passes through a through hole in the insulating plate 18 and extends toward the sealing body 17, and the negative electrode lead 21 passes through a through hole in the insulating plate 19 and extends toward the bottom side of the exterior body 16. The positive electrode lead 20 is connected to the underside of an internal terminal plate 23 of the sealing body 17 by welding or the like, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the exterior body 16 by welding or the like, and the exterior body 16 serves as the negative electrode terminal.

[0026] A gasket 28 is provided between the exterior body 16 and the sealing body 17 to ensure airtightness inside the battery. The exterior body 16 has a grooved portion 22 formed on its side surface that protrudes inward and supports the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the exterior body 16, and supports the sealing body 17 on its upper surface. The sealing body 17 is fixed to the top of the exterior body 16 by the grooved portion 22 and the open end of the exterior body 16 that is crimped to the sealing body 17.

[0027] The sealing body 17 has a structure in which, in order from the electrode body 14 side, 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. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for 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 centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the battery increases due to abnormal heat generation, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged through a vent hole in the cap 27.

[0028] Next, the electrode assembly 14 will be described in detail with further reference to Figures 2 and 3. Figure 2 is a diagram showing a portion of a radial cross section of the electrode assembly 14, and Figure 3 is a plan view showing the positive electrode 11 and negative electrode 12 in a developed state, with an enlarged view of the winding start side. Note that in Figure 2, the separator 13, positive electrode current collector 30, and positive electrode mixture layer 31 are omitted for clarity.

[0029] 2 and 3 , the negative electrode 12 has a non-facing portion 42 at the winding start side of the electrode assembly 14, where the negative electrode 12 is wound without facing the positive electrode 11 via the separator 13. In other words, the negative electrode 12 extends toward the winding start side of the electrode assembly 14 beyond a position facing the positive electrode starting end 11X, which is the end of the positive electrode 11 at the winding start side.

[0030] The non-facing portion 42 of the negative electrode 12 includes a region where the negative electrode mixture layer 41 is provided and a region where the negative electrode current collector 40 is exposed. A current collector exposed portion 43 where the negative electrode current collector 40 is exposed is provided closer to the winding start side than the mixture starting end 41X, which is the end of the negative electrode mixture layer 41 on the winding start side. The current collector exposed portion 43 is wound, for example, 0.5 to 2.0 turns. The negative electrode lead 21 is connected to the current collector exposed portion 43.

[0031] Here, in the non-facing portion 42, a region closer to the winding end side than the mixture starting end 41X of the negative electrode mixture layer 41 has a mixture uncoated portion 44 where the negative electrode mixture layer 41 is not disposed and the negative electrode current collector 40 is exposed. That is, in the longitudinal direction of the negative electrode 12, the mixture uncoated portion 44 is formed by being sandwiched between regions where the negative electrode mixture layer 41 is disposed. In the present embodiment, the mixture uncoated portion 44 is provided across the width direction of the negative electrode 12. The mixture uncoated portion 44 can be formed, for example, by intermittent application in which the negative electrode mixture slurry is not applied to a portion of the negative electrode current collector 40.

[0032] During charging and discharging of the battery, stress is more likely to concentrate at the winding start side of the electrode assembly 14 than at the winding end side, which makes the electrode plate more likely to deform. In particular, the negative electrode 12 is more likely to stretch toward the winding start side due to expansion and contraction of the negative electrode mixture layer 41 during charging and discharging. Therefore, stress is more likely to concentrate at the winding start side of the negative electrode 12, making it more likely to deform. When the negative electrode 12 deforms, the inter-electrode distance between the positive electrode 11 and the negative electrode 12 becomes uneven, which makes it more likely that the distribution of the nonaqueous electrolyte inside the electrode assembly 14 will become uneven, especially during rapid charging and discharging. As a result, uneven charge and discharge reactions occur inside the electrode assembly 14, and the cycle characteristics of the nonaqueous electrolyte secondary battery 10 will deteriorate.

[0033] In this embodiment, by providing the negative electrode 12 with the uncoated composite portion 44, when the negative electrode 12 stretches toward the winding start side, the uncoated composite portion 44 deforms preferentially. That is, when the negative electrode 12 stretches toward the winding start side, the uncoated composite portion 44 functions as a readily deformable portion. This is because the negative electrode mixture layer 41, which is stronger than the uncoated composite portion 44, is disposed on both sides of the uncoated composite portion 44. The preferential deformation of the uncoated composite portion 44 alleviates stress concentration at the winding start side of the negative electrode 12. This suppresses deformation of the region of the negative electrode 12 facing the positive electrode 11 via the separator 13, thereby maintaining a uniform inter-electrode distance between the positive electrode 11 and the negative electrode 12. As a result, unevenness in the charge / discharge reaction within the electrode assembly 14 is less likely to occur, improving cycle characteristics.

[0034] The mixture uncoated portion 44 may be provided on only one side of the negative electrode 12, but is preferably provided on both sides of the negative electrode 12. By providing the mixture uncoated portion 44 on both sides of the negative electrode 12, when the negative electrode 12 stretches toward the winding start side due to repeated charge and discharge, the mixture uncoated portion 44 becomes more likely to deform, and the effects of the present disclosure can be significantly exhibited.

[0035] As shown in FIG. 2 , in the radial cross section of the electrode assembly 14, the uncoated portion 44 is preferably located in a range sandwiched between a line X1 extending radially from the winding center Z of the electrode assembly 14 through the positive electrode starting end 11X and a line X2 extending radially from the winding center Z of the electrode assembly 14 through the lead end 21Y, which is the end of the winding end of the negative electrode lead 21. The inventors' investigations revealed that deformation of the negative electrode 12 is significant within the range sandwiched between the lines X1 and X2 on the winding start side of the negative electrode 12. Therefore, by locating the uncoated portion 44 within the range sandwiched between the lines X1 and X2, deformation of the negative electrode 12 can be further suppressed. As a result, the inter-electrode distance between the positive electrode 11 and the negative electrode 12 can be maintained uniform, thereby further improving the cycle characteristics of the nonaqueous electrolyte secondary battery 10.

[0036] The uncoated portion 44 is preferably wound 0.10 or more times, more preferably 0.15 or more times. In this case, the amount of deformation of the uncoated portion 44 can be increased, and stress concentration at the start of winding of the negative electrode 12 can be further alleviated. Furthermore, the uncoated portion 44 is preferably wound 0.25 or less times, more preferably 0.20 or less times. If the uncoated portion 44 is wound more than 0.25 times, the amount of deformation of the uncoated portion 44 increases excessively, which may result in uneven inter-electrode distances between the positive electrode 11 and the negative electrode 12. Therefore, the uncoated portion 44 is preferably wound 0.10 or more times and 0.25 or less times, more preferably 0.15 or more times and 0.20 or less times.

[0037] As shown in FIG. 3 , in the non-facing portion 42 of the negative electrode 12, the negative electrode mixture layer 41 provided closer to the start of winding of the negative electrode 12 than the uncoated portion 44 is referred to as the first negative electrode mixture layer 41A, and the negative electrode mixture layer 41 provided closer to the end of winding of the negative electrode 12 than the uncoated portion 44 is referred to as the second negative electrode mixture layer 41B. The first negative electrode mixture layer 41A is wound, for example, 0.05 or more turns, and preferably 0.5 or more turns. Increasing the length of the first negative electrode mixture layer 41A makes the uncoated portion 44 more likely to deform. The second negative electrode mixture layer 41B is wound, for example, 0.05 or more turns, and preferably 0.5 or more turns. Increasing the length of the second negative electrode mixture layer 41B can prevent the positive electrode 11 and the mixture uncoated portion 44 from facing each other via the separator 13, which makes it easier to prevent lithium from being deposited in the mixture uncoated portion 44 during charging. Note that the second negative electrode mixture layer 41B does not necessarily have to be provided.

[0038] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0039] Example 1 [Fabrication of Positive Electrode] As a positive electrode active material, lithium nickel oxide (LiNi) containing cobalt and aluminum was used. ０．８８ Co ０．０９ Al ０．０３ O ２ ) was used. The positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed in a solids mass ratio of 98:1:1, and N-methylpyrrolidone (NMP) was used as a dispersion medium to prepare a positive electrode mixture slurry. The slurry was applied to both sides of a positive electrode current collector made of a long aluminum foil with a thickness of 15 μm, and the coating was dried and compressed to obtain a positive electrode in which a positive electrode mixture layer was formed on both sides of the positive electrode current collector. An exposed current collector portion where no positive electrode mixture layer was present was provided in the center of the positive electrode in the longitudinal direction, and an aluminum positive electrode lead was ultrasonically welded to the exposed current collector portion.

[0040] [Negative Electrode Fabrication] A mixture of graphite and silicon oxide in a mass ratio of 95:5 was used as the negative electrode active material. The negative electrode active material, a dispersion of styrene butadiene rubber, and sodium carboxymethyl cellulose were mixed in a solids mass ratio of 98:1:1, and water was used as the dispersion medium to prepare a negative electrode mixture slurry. The slurry was applied to both sides of a negative electrode current collector made of a long copper foil with a thickness of 8 μm, and the coating was dried and compressed to obtain a negative electrode with a negative electrode mixture layer formed on both sides of the negative electrode current collector. As shown in FIGS. 2 and 3 , a current collector exposed portion was provided at one longitudinal end of the negative electrode located at the winding start side, and a nickel negative electrode lead was ultrasonically welded to the current collector exposed portion. Furthermore, an uncoated mixture portion was provided on the inner peripheral surface of the negative electrode at the winding start side, so as to form 0.1 turns during winding.

[0041] [Fabrication of Electrode Assembly] The positive electrode, the negative electrode, and a polyethylene separator were spirally wound around a cylindrical winding core member to obtain an electrode assembly. The uncoated portion of the electrode assembly was wound so as to be located within a range sandwiched between a line X1 extending from the winding center Z of the electrode assembly, passing through the starting end of the positive electrode, and a line X2 extending from the winding center Z of the electrode assembly, passing through the lead end (the end of the winding end of the negative electrode lead 21), and extending along the radial direction of the electrode assembly 14. After forming the wound structure of the electrode assembly, the winding core member was removed to obtain a wound-type electrode assembly with a cavity formed in the winding core portion.

[0042] [Preparation of non-aqueous electrolyte] 5 parts by mass of vinylene carbonate (VC) was added to 100 parts by mass of a mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:7, and LiPF ６ was dissolved in a concentration of 1.5 mol / L to prepare a non-aqueous electrolyte solution.

[0043] [Fabrication of Cylindrical Battery] After placing insulating plates above and below the electrode assembly, the negative electrode lead was welded to the inner bottom surface of a cylindrical outer can with a bottom, and the positive electrode lead was welded to the internal terminal plate of a sealing member, and the electrode assembly was housed in the outer can. Thereafter, a nonaqueous electrolyte solution was injected into the outer can under reduced pressure, and the opening of the outer can was sealed with a sealing member via a gasket, thereby obtaining a cylindrical battery.

[0044] [Evaluation of Cycle Characteristics (Capacity Retention)] The fabricated nonaqueous electrolyte secondary batteries were charged to 4.2 V at a constant current of 1.0 C in a temperature environment of 25° C., and then charged at a constant voltage of 4.2 V until the current value reached 0.02 C. Thereafter, the batteries were discharged to 2.5 V at a constant current of 1.0 C. This constituted one cycle, and the discharge capacity at 1.0 C after 500 cycles was measured. The capacity retention was then calculated using the following formula: Capacity retention [%] = (Discharge capacity after 500 cycles / Discharge capacity at first cycle) × 100

[0045] [Evaluation of Shape of Winding Core Portion After Cycle Test] The fabricated nonaqueous electrolyte secondary batteries were charged, and the vicinity of the winding core of the electrode body was observed using an X-ray CT scanner (Shimadzu Corporation, SMX-225CT FPD HR). From the captured image of the vicinity of the winding core, the area of ​​the space in the winding core portion and the perimeter of the space were calculated, and the circularity before the cycle test was determined. Then, for the nonaqueous electrolyte secondary batteries after 500 cycles, the batteries were charged, and the vicinity of the winding core of the electrode body was observed using an X-ray CT scanner (Shimadzu Corporation, SMX-225CT FPD HR). From the captured image of the vicinity of the winding core, the area of ​​the space in the winding core portion and the perimeter of the space were calculated, and the circularity after the cycle test was determined. Then, the circularity maintenance rate of the winding core portion was calculated using the following formula: Circularity maintenance rate [%] = (Circularity after 500 cycles / Circularity before cycles) × 100

[0046] Example 2 A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that in fabricating the negative electrode, an uncoated portion of the mixture was provided on the inner peripheral surface of the winding start side of the negative electrode so as to form 0.16 turns during winding.

[0047] Example 3 A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that in fabricating the negative electrode, an uncoated portion of the negative electrode mix was provided on the inner peripheral surface of the winding start side so as to extend 0.25 turns during winding.

[0048] Example 4 A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that in fabricating the negative electrode, an uncoated portion of the negative electrode mix was provided on the outer peripheral surface of the winding start side so as to form 0.16 turns during winding.

[0049] Example 5 A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that in fabricating the negative electrode, an uncoated portion of the mixture was provided on both surfaces of the winding start side of the negative electrode so as to be wound 0.16 turns during winding.

[0050] Example 6 A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that in fabricating the negative electrode, an uncoated portion of the negative electrode mix was provided on the inner peripheral surface of the winding start side so as to extend 0.05 turns during winding.

[0051] Example 7 A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that in fabricating the negative electrode, an uncoated portion of the mixture was provided on the inner circumferential surface of the winding start side of the negative electrode so as to be wound for 0.29 turns during winding.

[0052] Comparative Example 1 A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that no uncoated portion of the mixture was provided on the winding start side of the negative electrode.

[0053] The evaluation results of the capacity retention rate and the circularity retention rate of the winding core portion of the nonaqueous electrolyte secondary batteries of Examples and Comparative Examples are shown in Table 1. Table 1 also shows the position and length of the uncoated portion.

[0054]

[0055] As can be seen from Table 1, the nonaqueous electrolyte secondary batteries of the Examples have improved capacity retention rates compared to the nonaqueous electrolyte secondary batteries of the Comparative Examples. Furthermore, the nonaqueous electrolyte secondary batteries of the Examples have higher circularity retention rates compared to the nonaqueous electrolyte secondary batteries of the Comparative Examples. From this, it is presumed that the test cells of the Examples have suppressed deformation of the positive and negative electrodes due to preferential deformation of the uncoated portions of the composite, even when repeatedly charged and discharged, and thus maintained a uniform inter-electrode distance between the positive and negative electrodes.

[0056] Furthermore, the test cells of Examples 1 to 5, in which the uncoated portion of the composite was wound 0.10 to 0.25 times, showed a significantly improved capacity retention rate compared to Example 6, in which the uncoated portion of the composite was wound less than 0.10 times, and Example 7, in which the uncoated portion of the composite was wound more than 0.25 times. Furthermore, Example 5, in which the uncoated portion of the composite was formed on both sides of the negative electrode, showed an improved capacity retention rate compared to Examples 2 and 4, in which the uncoated portion of the composite was formed on one side of the negative electrode.

[0057] The present disclosure is further described by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery including: an electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound longitudinally with a separator interposed therebetween; a non-aqueous electrolyte; and a bottomed cylindrical outer can that accommodates the electrode assembly and the non-aqueous electrolyte, wherein the negative electrode includes a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, and the electrode assembly has a non-facing portion wound at a winding start side thereof so as not to face the positive electrode via the separator, and a mix-uncoated portion in which the negative electrode mixture layer is not disposed and the negative electrode current collector is exposed is provided in a region of the non-facing portion that is closer to the winding end side than the mix-start end, which is the end at the winding start side of the negative electrode mixture layer. Configuration 2: The mix-uncoated portion is provided on both sides of the negative electrode. Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the material mixture uncoated portion is wound 0.10 to 0.25 times.Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein a negative electrode lead is joined to a region of the negative electrode that is closer to the winding center of the electrode body than the material mixture starting end.Configuration 5: The nonaqueous electrolyte secondary battery according to Configuration 4, wherein, in a radial cross section of the electrode body, the material mixture uncoated portion is provided in a range sandwiched between a straight line extending in the radial direction of the electrode body from the winding center of the electrode body, passing through a positive electrode starting end that is the end of the positive electrode where winding starts, and a straight line extending in the radial direction of the electrode body from the winding center of the electrode body, passing through a lead terminal end that is the end of the negative electrode lead where winding ends. Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the negative electrode mixture layer contains a silicon-containing material as a negative electrode active material, and the content of the silicon-containing material is 5 mass% or more relative to the total mass of the negative electrode active material.

[0058] REFERENCE SIGNS LIST 10 Cylindrical battery, 11 Positive electrode, 11X Positive electrode starting end, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer can, 17 Sealing body, 18 Insulating plate, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 21Y Lead end, 22 Grooved portion, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode current collector, 31 Positive electrode mixture layer, 40 Negative electrode current collector, 41 Negative electrode mixture layer, 41A First negative electrode mixture layer, 41B Second negative electrode mixture layer, 41X Mixture starting end, 42 Non-facing portion, 43 Current collector exposed portion, 44 Mixture uncoated portion, Z Winding center

Claims

1. A non-aqueous electrolyte secondary battery comprising: an electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound longitudinally with a separator interposed therebetween; a non-aqueous electrolyte; and a bottomed cylindrical outer can that accommodates the electrode assembly and the non-aqueous electrolyte, wherein the negative electrode includes a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, and has a non-facing portion at a winding start side of the electrode assembly that is wound so as not to face the positive electrode via the separator, and wherein a region of the non-facing portion is provided on the winding end side of a mixture start end, which is the end on the winding start side of the negative electrode mixture layer, on the winding end side, where the negative electrode mixture layer is not disposed, and where the negative electrode current collector is exposed, an uncoated portion is provided.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the uncoated portion is provided on both sides of the negative electrode.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the uncoated portion is wound 0.10 to 0.25 times.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein a negative electrode lead is joined to a region of the negative electrode closer to the winding start side of the electrode body than the starting end of the material mixture.

5. The nonaqueous electrolyte secondary battery according to claim 4, wherein, in a radial cross section of the electrode body, the uncoated portion is provided in a range sandwiched between a straight line extending in the radial direction of the electrode body from the winding center of the electrode body, passing through a positive electrode starting end which is the end of the positive electrode at the winding start side, and a straight line extending in the radial direction of the electrode body from the winding center of the electrode body, passing through a lead ending end which is the end of the negative electrode lead at the winding end side.

6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode mixture layer contains a silicon-containing material as a negative electrode active material, and the content of the silicon-containing material is 5 mass % or more relative to the total mass of the negative electrode active material.

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