JP4599070B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

In recent years, with the reduction in size and weight of various electronic devices such as VTRs, mobile phones, and personal computers, and cordless portable electronic devices, there is an increasing demand for higher energy density for the power sources of these electronic devices. For this reason, nonaqueous electrolyte secondary batteries such as lithium secondary batteries using metallic lithium as the negative electrode active material and lithium ion secondary batteries using carbon as the negative electrode active material have been proposed. Among lithium ion secondary batteries, carbonaceous materials such as coke, graphite, fired resin, and pyrolytic vapor phase carbon are used as the negative electrode active material, and chalcogens such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ are used as the positive electrode active material. Lithium ion secondary batteries using compounds have already been put into practical use.

  As a lithium ion secondary battery, for example, Patent Document 1 discloses a secondary battery using carbon as a negative electrode. Patent Document 2 discloses a lithium ion secondary battery having excellent charge / discharge characteristics using a carbon fiber having a lamellar structure in the cross-sectional direction of the fiber diameter as a negative electrode active material. In addition, a lithium ion secondary battery having high charging energy is known in which graphite having a high degree of graphite is used as the negative electrode active material.

  Such a lithium ion secondary battery is widely used as a power source for various portable terminals because it is safer than a secondary battery using metallic lithium as a negative electrode. In particular, since the demand for a power source for small portable terminals is increasing, there is an increasing demand for increasing the capacity of secondary batteries. On the other hand, there is a demand for small size and light weight. Since these requirements are contradictory, in order to obtain a secondary battery having a small size, a light weight, and a high capacity, the packing density of the electrodes is increased.

  However, when the electrode density is increased, the electrolyte holding capacity of the electrode is lowered, and the charge / discharge cycle maintenance ratio is deteriorated.

  In Patent Document 3, a large number of grooves are formed by embossing on the surface of the positive electrode mixture (positive electrode material layer) and / or the negative electrode mixture (negative electrode material layer) so that the electrolyte quickly penetrates into the element. It is disclosed to form.

  However, when a groove is formed on the surface of the composite material using embossing, the groove portion is strongly pressed, so that the density becomes higher than the others and the reactivity decreases. For this reason, since a non-uniform reaction occurs, deterioration of the active material contained in the composite material has progressed, and excellent charge / discharge cycle characteristics could not be obtained.

On the other hand, it is also known to form a groove on the surface of the composite material using a cutter or a needle. However, when the grooves are formed in this way, the active material or the like is likely to fall off while repeating the charge / discharge cycle, and thus the charge / discharge cycle characteristics have not been improved.
Japanese Unexamined Patent Publication No. Sho 63-121260 JP-A-5-89879 JP 2001-357836 A

  An object of the present invention is to provide a nonaqueous electrolyte secondary battery excellent in charge / discharge cycle characteristics.

A non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous electrolyte secondary battery comprising a positive electrode including a positive electrode current collector, a negative electrode including a negative electrode current collector, and a non-aqueous electrolyte,
At least one of the positive electrode current collector and the negative electrode current collector is provided with grooves at intervals of 0.1 to 5 mm, and the depth d (μm) of the grooves is (1 ) Is satisfied.

d = at (1)
However, t is the thickness (μm) of the current collector in which the groove is formed, and a is a proportionality coefficient and is in the range of 0.03 to 0.16.

Another non-aqueous electrolyte secondary battery according to the present invention includes an electrode group in which a laminate including a positive electrode including a positive electrode current collector and a negative electrode including a negative electrode current collector is wound, and a non-electrode held by the electrode group. A non-aqueous electrolyte secondary battery comprising a water electrolyte,
At least one of the positive electrode current collector and the negative electrode current collector is provided with grooves parallel to the winding direction at intervals of 0.1 to 5 mm, and the depth d of the grooves (Μm) satisfies the above formula (1).

  ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte secondary battery excellent in the charge / discharge cycle characteristic can be provided.

  The nonaqueous electrolyte secondary battery according to the present invention includes a container, an electrode group that is housed in the container and includes a positive electrode and a negative electrode, and a nonaqueous electrolyte that is held by the electrode group. For example, the electrode group may be formed by alternately stacking positive and negative electrodes with a separator interposed therebetween, winding the positive and negative electrodes in a cylindrical or flat shape with a separator interposed therebetween, or by combining the positive and negative electrodes. It is produced by bending one or more times with a separator interposed.

  At least one of the positive electrode current collector and the negative electrode current collector is provided with grooves at intervals of 0.1 to 5 mm, and the groove depth d (μm) is The expression (1) is satisfied.

  Hereinafter, the positive electrode, the negative electrode, the nonaqueous electrolyte, and the separator will be described.

1) Positive electrode The positive electrode includes a positive electrode current collector and a positive electrode material layer formed on one or both surfaces of the positive electrode current collector.

  As the positive electrode current collector, it is preferable to use the current collector having the grooves described above. When using the current collector in which the groove is formed as the negative electrode current collector, a current collector in which the groove is not formed may be used. For example, a metal foil or a metal mesh material can be used for the positive electrode current collector provided with no groove. Examples of the metal include aluminum, an aluminum alloy, and stainless steel.

  Hereinafter, the positive electrode current collector provided with the grooves will be described.

  For the substrate on which the grooves are formed, for example, aluminum, an aluminum alloy, or a stainless metal plate can be used.

  The groove can be provided on the surface of the substrate on which the positive electrode material layer is formed. Moreover, although a groove | channel can also be provided in the surface in which the positive electrode material layer of a board | substrate is not formed, it is preferable to provide a groove | channel only in the surface in which a positive electrode material layer is formed from the point of ensuring the intensity | strength of a collector.

  This groove is formed using, for example, a needle or a cutter. Industrially, for example, there is a method of pulling out one end of a hoop-shaped substrate while pressing a comb or a brush on the surface of the substrate.

  The groove forming direction (length direction) is preferably parallel to the sides of the current collector in order to reduce the variation in groove spacing. In particular, in the case of an electrode group wound in a cylindrical shape or a flat shape, current collection during winding is performed by making the winding direction (long side direction of the current collector) parallel to the groove forming direction. It can prevent body deformation, tearing and breaking.

  The cross-sectional shape of the groove can be, for example, rectangular, semicircular, U-shaped, or V-shaped.

  The reason why the depth d (μm) of the groove is in a range satisfying the expression (1) is as follows.

  When the depth d of the groove is less than 0.03 t, the groove becomes shallow, so that a sufficiently large void cannot be provided in the positive electrode, and the diffusibility of the nonaqueous electrolyte in the positive electrode material layer is reduced. For this reason, the permeation rate of the nonaqueous electrolyte into the positive electrode material layer becomes slow. For this reason, the amount of nonaqueous electrolyte retained cannot be secured sufficiently, and the nonaqueous electrolyte is depleted while the charge / discharge cycle is repeated, so that excellent charge / discharge cycle characteristics cannot be obtained. On the other hand, when the depth d of the groove exceeds 0.16 t, the strength of the current collector is reduced because the groove becomes deeper. Therefore, when the electrode group is manufactured or the battery is assembled, The incidence of tearing or breaking increases. A more preferable range of the groove depth d is a range in which the proportionality coefficient a in the equation (1) is 0.06 to 0.12.

  The reason why the interval between the grooves is within the above range is for the reason described below.

  If the groove spacing is less than 0.1 mm, the amount of voids in the positive electrode increases, so that the internal diffusion of the nonaqueous electrolyte is promoted and the nonaqueous electrolyte easily penetrates into the positive electrode material layer. While the holding amount can be increased, the strength of the current collector is reduced, so that the rate of occurrence of deformation, tearing or breaking of the current collector is increased. On the other hand, when the groove interval exceeds 5 mm, the amount of voids in the positive electrode decreases, and the internal diffusion of the nonaqueous electrolyte is difficult to proceed, so that excellent charge / discharge cycle characteristics cannot be obtained. A more preferable range of the groove interval is 0.5 to 2 mm.

  The width of the groove is preferably smaller than the average particle diameter of the positive electrode active material in order to prevent the groove from being clogged with the active material.

  When providing a groove | channel in a positive electrode collector, it is preferable that the thickness t of a positive electrode collector shall be the range of 12-20 micrometers. This is because when the thickness t of the current collector is less than the above range, the strength decreases, and therefore there is a risk of deformation, tearing or breaking by providing the groove, while the thickness t of the current collector If the value exceeds the above range, the workability deteriorates and the ratio of the current collector in the positive electrode increases, so that sufficient capacity may not be obtained.

  Next, the positive electrode material layer will be described.

  The positive electrode material layer can contain a positive electrode active material and a binder.

Examples of the positive electrode active material include chalcogen compounds such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ . These chalcogen compounds can be used in combination of two or more.

  The average particle diameter of the positive electrode active material is preferably in the range of 10 to 14 μm.

  Examples of the binder include a fluororesin, a polyolefin resin, a styrene resin, a thermoplastic elastomer resin such as an acrylic resin, and a rubber resin such as fluororubber. Specifically, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polyacrylonitrile, nitrile rubber, polybutadiene, butyl rubber, polystyrene, styrene-butadiene rubber, hydrogenated styrene-butadiene rubber, polysulfide rubber, nitrocellulose , Cyanoethyl cellulose, carboxymethyl cellulose and the like. Among these binders, an elastomer, a rubber cross-linked body, or a modified body into which a polar group is introduced is suitable from the viewpoint of improving the adhesion between the current collector and the positive electrode material layer and improving the resistance increasing effect during overcharging. It is.

  The positive electrode material layer may further contain acetylene black, graphite such as powdered expanded graphite, pulverized carbon fiber, pulverized graphitized carbon fiber and the like as a conductive auxiliary material.

  When providing a groove | channel in a positive electrode electrical power collector, this positive electrode can be produced by the method demonstrated below, for example.

That is, a groove having a depth d (μm) satisfying the expression (1) is formed on a belt-like substrate in a length of 0.1 to 0.1 so that the length direction of the groove is parallel to the length direction of the substrate. Obtaining a positive electrode current collector by forming at intervals of 5 mm;
And a step of forming a positive electrode material layer on the positive electrode current collector.

  The manufacturing method may further include a step of cutting the positive electrode current collector on which the positive electrode material layer is formed into a desired size. When cutting, it may be cut perpendicular to the length direction of the groove or may be cut in parallel. Further, the positive electrode current collector on which the positive electrode material layer is formed can be used as it is without being cut.

  More specifically, this positive electrode can be produced as described below.

  The positive electrode active material, the binder, and if necessary, the conductive auxiliary material are suspended in a suitable organic solvent to form a positive electrode coating slurry, and this positive electrode coating slurry is applied to one or both sides of the belt-like positive electrode current collector. It can be produced by cutting a coated, dried and pressed product into a desired size.

  In addition, for example, a positive electrode can be produced by kneading a positive electrode active material together with a binder and, if necessary, a conductive auxiliary material, and sticking a sheet into a strip-shaped positive electrode current collector.

  According to the manufacturing method described above, since the length direction of the groove and the length direction of the strip-shaped positive electrode current collector are parallel, when winding the positive electrode current collector having the groove formed, Even when a tensile force parallel to the length direction of the positive electrode current collector is applied, such as when forming the positive electrode current collector or cutting the positive electrode current collector on which the positive electrode material layer is formed, Deformation, tearing and breaking can be avoided. Therefore, it is possible to manufacture a positive electrode including a current collector in which grooves satisfying the above-described expression (1) are formed at intervals of 0.1 to 5 mm with a high yield.

2) Negative electrode This negative electrode includes a negative electrode current collector and a negative electrode material layer formed on one or both sides of the negative electrode current collector.

  As the negative electrode current collector, it is preferable to use a current collector in which grooves satisfying the formula (1) are formed at intervals of 0.1 to 5 mm. However, the current collector in which the grooves described above are formed as the positive electrode current collector. In the case of using a body, a current collector in which the aforementioned grooves are not formed may be used. Examples of the negative electrode current collector in which no groove is provided include a copper foil or a copper mesh material, and a copper foil, particularly an electrolytic copper foil is suitable. The thickness of the negative electrode current collector can be in the range of 5 to 20 μm.

  Hereinafter, the negative electrode current collector provided with the grooves will be described.

  For the substrate on which the groove is formed, for example, a copper metal plate can be used. In particular, electrolytic copper is suitable as copper.

  The groove can be provided on the surface of the substrate on which the negative electrode material layer is formed. Moreover, although a groove | channel can also be provided in the surface in which the negative electrode material layer of a board | substrate is not formed, it is preferable to provide a groove | channel only in the surface in which a negative electrode material layer is formed from the point of ensuring the intensity | strength of a collector.

  As a method for forming the groove, the same method as described for the positive electrode can be used.

  The groove forming direction (length direction) and the cross-sectional shape of the groove can be the same as described for the positive electrode.

  The reason why the depth d (μm) of the groove is within the range satisfying the expression (1) and the interval between the grooves is within the range is the same as described for the positive electrode.

  The width of the groove is preferably smaller than the average particle diameter of the negative electrode active material in order to prevent the groove from being clogged with the active material.

  When providing a groove in the negative electrode current collector, the thickness t of the negative electrode current collector is preferably in the range of 5 to 20 μm for the same reason as described for the positive electrode.

  Next, the negative electrode material layer will be described.

  The negative electrode material layer can contain a negative electrode active material and a binder.

  Examples of the negative electrode active material include spherical artificial graphite, scaly graphite, and fibrous carbon material. These may be used in combination of two or more.

  The average particle diameter of the negative electrode active material is preferably in the range of 10 to 50 μm.

  As the binder, the same binders as those mentioned above for the positive electrode can be used.

  The negative electrode material layer may further contain graphite or the like as a conductive auxiliary material.

  In the case where a groove is provided in the negative electrode current collector, this negative electrode can be produced, for example, by the method described below.

That is, a groove having a depth d (μm) satisfying the expression (1) is formed on a belt-like substrate in a length of 0.1 to 0.1 so that the length direction of the groove is parallel to the length direction of the substrate. Obtaining a negative electrode current collector by forming at intervals of 5 mm;
And a step of forming a negative electrode material layer on the negative electrode current collector.

  This manufacturing method may further include a step of cutting the negative electrode current collector on which the negative electrode material layer is formed into a desired size. The cutting direction can be the same as described for the positive electrode. Further, the negative electrode current collector on which the negative electrode material layer is formed can be used as it is without being cut.

  More specifically, this negative electrode can be produced as described below.

  The negative electrode active material, the binder, and, if necessary, the conductive auxiliary material are suspended in a suitable organic solvent to form a negative electrode coating slurry, and this negative electrode coating slurry is applied to one or both sides of the strip-shaped negative electrode current collector. It can be produced by cutting a coated, dried and pressed product into a desired size.

  Further, for example, the negative electrode can also be produced by kneading a negative electrode active material together with a binder and, if necessary, a conductive auxiliary material, and sticking the sheet into a strip-shaped negative electrode current collector.

  According to the manufacturing method described above, since the length direction of the groove and the length direction of the strip-shaped negative electrode current collector are parallel, when winding the negative electrode current collector with the groove formed, Even when a negative electrode current collector is formed, or when a negative electrode current collector formed with a negative electrode material layer is cut, even if a tensile force parallel to the length direction of the negative electrode current collector is applied, the negative electrode current collector Deformation, tearing and breaking can be avoided. Therefore, it is possible to manufacture a negative electrode including a current collector in which grooves satisfying the above-described expression (1) are formed at intervals of 0.1 to 5 mm with a high yield.

3) Non-aqueous electrolyte As the non-aqueous electrolyte, a non-aqueous electrolyte in which an electrolyte (for example, lithium salt) is dissolved in a non-aqueous solvent can be used. However, the non-aqueous electrolyte is not limited to this and has a liquid form at the time of injection. Anything can be used. An example of this is a gel electrolyte precursor obtained by adding a gelling agent to a non-aqueous electrolyte.

  Examples of the non-aqueous solvent include those containing as a main component at least one selected from the group consisting of ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and γ-butyrolactone. The non-aqueous solvent is preferably used in a mixture of two to three types rather than being used alone because of its viscosity.

As the electrolyte, for example, lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), or the like is used. Can do. The electrolyte can be used alone or in the form of a mixture.

  The concentration of the electrolyte dissolved in the non-aqueous solvent is preferably in the range of 0.5 to 1.5 mol / L.

4) Separator Examples of the separator include a polyethylene porous film or a polypropylene porous film having a thickness of 20 to 30 μm.

  Examples of the non-aqueous electrolyte secondary battery according to the present invention include those having various structures such as a square shape, a thin shape, a cylindrical shape, and a coin shape. An example of a prismatic nonaqueous electrolyte secondary battery is shown in FIG. 1, an example of a thin nonaqueous electrolyte secondary battery is shown in FIGS. 2 and 3, and an example of a cylindrical nonaqueous electrolyte secondary battery is shown in FIG.

  FIG. 1 is a partially cutaway perspective view showing a prismatic nonaqueous electrolyte secondary battery which is an example of a nonaqueous electrolyte secondary battery according to the present invention.

  As shown in FIG. 1, a bottomed rectangular tube-shaped outer can 1 made of metal, for example, aluminum also serves as a positive electrode terminal, for example, and an insulator 2 is disposed on the inner surface of the bottom. The flat electrode group 3 is housed in the outer can 1. The electrode group 3 is prepared by laminating a negative electrode 4, a separator 5, and a positive electrode 6, winding in a spiral shape so that the positive electrode 6 is located on the outermost periphery, and then press-molding it into a flat shape. is there.

  A spacer 7 made of, for example, synthetic resin having a lead extraction hole in the vicinity of the center is disposed on the electrode group 3 in the outer can 1. The metal lid 8 is liquid-tightly joined to the upper end opening of the outer can 1 by, for example, laser welding. The lid 8 has a liquid injection hole 10 for injecting a nonaqueous electrolyte. A sealing lid 11 is joined to the lid body 8 including the liquid injection hole 10 in a liquid-tight manner by, for example, laser welding so as to close the liquid injection hole 10. Further, an extraction hole 9 for a negative electrode terminal is opened near the center of the lid body 8. The negative electrode terminal 12 is hermetically sealed in the extraction hole 9 via an insulating material 13 made of glass or resin. A negative electrode lead 14 is connected to the lower end surface of the negative electrode terminal 12, and the other end of the negative electrode lead 14 is connected to the negative electrode 4. The insulating sealing plate 15 is disposed on the upper surface of the lid body 8. The insulating outer tube 16 covers the side and bottom edges of the outer can 1 and the insulating sealing plate 15.

  2 is a cross-sectional view showing a thin non-aqueous electrolyte secondary battery which is an example of the non-aqueous electrolyte secondary battery according to the present invention, and FIG. 3 is an enlarged cross-sectional view showing part A of FIG.

  As shown in FIG. 2, an electrode group 22 is accommodated in a container 21 made of, for example, a laminate film. The electrode group 22 has a structure wound in a spiral shape so that a laminate composed of a positive electrode, a separator, and a negative electrode has a flat shape. As shown in FIG. 3, the laminate includes a separator 23, a positive electrode material layer 24, a positive electrode current collector 25, and a positive electrode material layer 24, a separator 23, and a negative electrode material layer (from the lower side of the figure). 27, a negative electrode 29 having a negative electrode current collector 28 and a negative electrode material layer 27, a separator 23, a positive electrode material layer 24, a positive electrode 26 having a positive electrode current collector 25 and a positive electrode material layer 24, a separator 23, and a negative electrode material layer 27 and a negative electrode 29 having a negative electrode current collector 28 are laminated in this order. In the electrode group 22, the negative electrode current collector 28 is located in the outermost layer. One end of the strip-like positive electrode lead 30 is connected to the positive electrode current collector 25 of the electrode group 22, and the other end extends from the container 21. On the other hand, one end of the strip-shaped negative electrode lead 31 is connected to the negative electrode current collector 28 of the electrode group 22, and the other end is extended from the container 21.

  FIG. 4 is a partially cutaway perspective view showing a cylindrical nonaqueous electrolyte secondary battery which is an example of the nonaqueous electrolyte secondary battery according to the present invention.

  For example, an insulator 42 is disposed at the bottom of a bottomed cylindrical metal container 41 made of stainless steel. The electrode group 43 is accommodated in the container 41. The electrode group 43 has a structure in which a belt-like material in which a positive electrode 44, a separator 45, and a negative electrode 46 are laminated in this order is wound in a spiral shape so as to have a cylindrical shape.

  A non-aqueous electrolyte is accommodated in the container 41. A PTC element 47 having a hole in the center, a safety valve 48 disposed on the PTC element 47, and a cap-shaped positive terminal 49 disposed on the safety valve 48 are provided with an insulating gasket at the upper opening of the container 41. 50 is fixed by caulking. The safety valve 48 has a structure that breaks when the battery internal pressure reaches a predetermined value and releases the internal pressure. The positive terminal 49 has a gas vent hole (not shown). One end of the positive electrode lead 51 is connected to the positive electrode 44, and the other end is connected to the PTC element 47. The negative electrode 46 is connected to the container 41, which is a negative electrode terminal, through a negative electrode lead (not shown).

  As described in detail above, the non-aqueous electrolyte secondary battery according to the present invention has at least one of the positive electrode current collector and the negative electrode current collector with grooves at intervals of 0.1 to 5 mm. Near the boundary between the current collector and the electrode material layer without reducing the strength of the current collector because the depth d (μm) of the groove satisfies the above-mentioned formula (1). It is possible to increase the amount of voids in the electrode by forming voids in the electrode. As a result, the non-aqueous electrolyte easily diffuses into the electrode material layer, so that the non-aqueous electrolyte can easily penetrate into the electrode material layer, and the amount of the non-aqueous electrolyte retained in the electrode can be increased. Furthermore, since the electrode material layer is not locally pressed or scraped in order to form a groove on the surface of the electrode material layer, the nonaqueous electrolyte retention ability can be improved without deteriorating the electrode characteristics. it can. As a result, excellent charge / discharge cycle characteristics can be realized. In particular, it is possible to improve charge / discharge cycle characteristics by providing a groove in the positive electrode current collector than in providing a groove in the negative electrode current collector.

  Further, when the laminate including the positive electrode and the negative electrode is wound and accommodated in the container, the length direction of the groove is made parallel to the winding direction, thereby adding to the current collector when the positive and negative electrodes are wound. Since the current collector can be prevented from being deformed, cracked or broken by a tensile force, a wound electrode group having excellent nonaqueous electrolyte retention capability can be provided at a high yield.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

[Example]
Example 1
<Preparation of positive electrode>
As shown in FIGS. 5 and 6, a positive electrode current collector 60 is formed by forming grooves 62 having a depth of d = 0.10 t using a needle on both surfaces of a strip-shaped aluminum foil 61 having a thickness t of 15 μm. Got. At this time, the length direction of the groove and the length direction of the aluminum foil were made parallel, the groove interval L was 1 mm, and the groove width W was 2 μm.

  The depth d, width W, and interval L of the grooves were measured as described below.

  The current collector was embedded in a resin and cut to expose the cross section of the current collector, and the depth of the groove was measured by observing with a microscope. This measurement was performed for a total of 10 arbitrary points, and the average value was calculated to calculate the groove depth d. The groove width W and the interval L were also calculated under the same conditions. In addition, this observation confirmed that the cross-sectional shape of the groove was V-shaped as shown in FIG.

On the other hand, with respect to 41.7 parts by weight of an N-methylpyrrolidone solution containing 12% by weight of polyvinylidene fluoride resin (PVdF), as a positive electrode active material, 100 parts by weight of LiCoO ₂ powder having an average particle size of 12 μm, As an auxiliary material, 5 parts by weight of graphite powder (trade name, KS4 manufactured by Lonza) was mixed and kneaded. Subsequently, 15 parts by weight of N-methylpyrrolidone was further added to the mixture, and the solid matter was dispersed using a bead mill to prepare a positive electrode coating slurry.

Next, the positive electrode current application slurry is applied to both surfaces of the positive electrode current collector so as to be 194 g / m ² , dried, pressed, and cut into a predetermined size to obtain a thickness. A belt-like positive electrode having a thickness of 130 μm and a width of 49.5 mm was produced.

<Production of negative electrode>
To 100 parts by weight of spherical artificial graphite, 3 parts by weight of flake graphite, 1.5 parts by weight of carboxymethyl cellulose and 1.3 parts by weight of styrene-butadiene rubber latex were added and mixed and stirred uniformly. Prepared.

  As a negative electrode current collector, the negative electrode coating slurry is uniformly applied to both surfaces of an electrolytic copper foil having a thickness of 10 μm. Subsequently, the solvent of the negative electrode coating slurry is dried, and further press-molded with a roll press. After that, a strip-shaped negative electrode was produced by cutting into a predetermined size.

<Preparation of non-aqueous electrolyte (non-aqueous electrolyte)>
Trioctyl phosphate (TOP) was added to a mixed solution adjusted so that the composition ratio was ethylene carbonate / methyl ethyl carbonate / LiPF ₆ = 34.9 / 53.1 / 12 (mass ratio) under reduced pressure. By adding 5% by weight, a nonaqueous electrolytic solution having a LiPF ₆ concentration of 1.0 mol / L was obtained.

<Assembly of secondary battery>
Lead tabs are joined to the strip-shaped positive electrode and the strip-shaped negative electrode current collector, respectively, and the positive electrode and the negative electrode are made of a polyethylene microporous film having a thickness of 25 μm, a porosity of 50%, and an air permeability of 300 seconds / 100 cc. Are laminated in the order of positive electrode / separator / negative electrode / separator, and spirally using a winding core having a flat cross section so that the winding direction is parallel to the length direction of the groove. It was wound, further heated and compressed with a hydraulic press, and formed into a flat spiral electrode group.

  Next, this electrode group was inserted into a thin aluminum outer can having a thickness of 0.2 mm, an outer dimension of 4.1 mm, a width of 30 mm, and a height of 50 mm, and a lid was laser-seamed welded to the upper end opening of the outer can. After sealing the electrode group, the non-aqueous electrolyte is injected through the liquid injection hole of the lid, and the liquid injection hole is sealed by laser seam welding to the lid body including the liquid injection hole. As a result, a rectangular nonaqueous electrolyte secondary battery having a non-rated dimension of the structure shown in FIG. 1 having a thickness of 4.4 mm, a width of 30 mm, and a height of 48 mm was assembled.

(Examples 2-5, Comparative Examples 2-3)
A square nonaqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that the groove depth d and the interval L of the positive electrode current collector were changed to the values shown in Table 1 below.

(Comparative Example 1)
A square nonaqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that a positive electrode current collector without a groove was used.

(Comparative Example 4)
The battery configuration was the same as that of Example 1, except that the groove depth d and interval L of the positive electrode current collector were changed to the values shown in Table 1 below.

  In Comparative Example 4, since the positive electrode current collector broke during the production of the electrode group, the secondary battery could not be assembled.

About the obtained square non-aqueous electrolyte secondary battery of Examples 1-5 and Comparative Examples 1-3, after initial charge, it was charged / discharged under the conditions of 1.0 C / 1.0 C at 20 ° C. (charging conditions; 620 mA, 4 (2V, 3 hours, discharge conditions; 620 mA, 3.0 V cut-off), the discharge capacities at the first cycle and the 500th cycle were measured, and the discharge capacity maintenance rate at the 500th cycle relative to the first cycle was calculated. The results are shown in Table 1 below.

  As can be seen from Table 1, the secondary batteries of Examples 1 to 5 including the positive electrode current collector provided with the grooves satisfying the formula (1) at intervals of 0.1 to 5 mm are in the 500th cycle. The discharge capacity retention rate was high, and the charge / discharge cycle characteristics were excellent. In addition, from the secondary batteries of Example 1 and Example 3, when the groove interval L is constant, increasing the value of the groove depth d from 0.03t to 0.10t improves the discharge capacity retention rate. It was confirmed that it was possible.

  In contrast, Comparative Example 1 in which neither the positive electrode current collector nor the negative electrode current collector was provided with grooves, Comparative Example 2 in which the groove depth d was less than 0.03 t, and Comparative Example in which the groove interval L exceeded 5 mm Since the secondary battery of No. 3 had a small amount of non-aqueous electrolyte retained on the positive electrode, the discharge capacity retention rate at the 500th cycle was lower than that of the secondary batteries of Examples 1 to 5.

  In Example 1 described above, a groove having a V-shaped cross section was obtained because the groove was formed with a needle. However, the groove shape is not particularly limited, and the groove depth and interval are within the scope of the present invention. Any shape can be used as long as it is within.

The partial notch perspective view which shows the square nonaqueous electrolyte secondary battery which is an example of the nonaqueous electrolyte secondary battery which concerns on this invention. Sectional drawing which shows the thin nonaqueous electrolyte secondary battery which is an example of the nonaqueous electrolyte secondary battery which concerns on this invention. The expanded sectional view which shows the A section of FIG. The partial notch perspective view which shows the cylindrical nonaqueous electrolyte secondary battery which is an example of the nonaqueous electrolyte secondary battery which concerns on this invention. 4 is a schematic diagram showing a positive electrode current collector of the nonaqueous electrolyte secondary battery of Example 1. FIG. FIG. 6 is a schematic cross-sectional view of the positive electrode current collector of FIG. 5 cut along a VI-VI line.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Exterior can, 2, 42 ... Insulator, 3, 22, 43 ... Electrode group, 4, 29, 46 ... Negative electrode, 5, 23, 45 ... Separator, 6, 26, 44 ... Positive electrode, 7 ... Spacer, 8 DESCRIPTION OF SYMBOLS ... Lid, 9 ... Extraction hole, 10 ... Injection hole, 11 ... Sealing lid, 12 ... Negative electrode terminal, 13 ... Insulating material, 14, 31 ... Negative electrode lead, 15 ... Insulation sealing plate, 16 ... Outer tube, 21 , 41 ... Container, 24 ... Positive electrode material layer, 25, 60 ... Positive electrode current collector, 27 ... Negative electrode material layer, 28 ... Negative electrode current collector, 30, 51 ... Positive electrode lead, 47 ... PTC element, 48 ... Safety valve, 49 ... positive electrode terminal, 50 ... insulating gasket, 61 ... substrate (aluminum foil), 62 ... groove.

Claims (2)

A non-aqueous electrolyte secondary battery comprising a positive electrode including a positive electrode current collector, a negative electrode including a negative electrode current collector, and a non-aqueous electrolyte,
At least one of the positive electrode current collector and the negative electrode current collector is provided with grooves at intervals of 0.1 to 5 mm, and the depth d (μm) of the grooves is (1 A non-aqueous electrolyte secondary battery characterized by satisfying the formula:
d = at (1)
However, t is the thickness (μm) of the current collector in which the groove is formed, and a is a proportionality coefficient and is in the range of 0.03 to 0.16. A non-aqueous electrolyte secondary battery comprising: an electrode group in which a laminate including a positive electrode including a positive electrode current collector and a negative electrode including a negative electrode current collector is wound; and a non-aqueous electrolyte held in the electrode group. And
At least one of the positive electrode current collector and the negative electrode current collector is provided with grooves parallel to the winding direction at intervals of 0.1 to 5 mm, and the depth d of the grooves (Μm) satisfies the following formula (1): a non-aqueous electrolyte secondary battery.
d = at (1)
However, t is the thickness (μm) of the current collector in which the groove is formed, and a is a proportionality coefficient and is in the range of 0.03 to 0.16.

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