JP2012243567A - Lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lithium ion battery suppressing occurrence of cracks due to wound stress, thereby capable of reducing internal resistance of a battery.SOLUTION: In a lithium ion battery, a positive electrode 30 and a negative electrode 20 have recessed and projecting surfaces 23, 24, 33, 34 meshing each other with a separator 40 sandwiched therebetween. Each of the recessed and projecting surfaces 23, 24, 33, 34 has a shape such that gaps formed between the recessed and projecting surfaces 24, 34 on an inside of winding and the recessed and projecting surfaces 23, 33 on an outside of winding, which are deformed by winding to face with each other, are constant in the winding direction.

Description

  The present invention relates to a lithium ion battery, for example, a lithium ion battery having a wound electrode group wound with a separator interposed between a positive electrode and a negative electrode.

  Lithium ion batteries are high energy density secondary batteries that have a high operating voltage and are easy to obtain high output, and thus are increasingly important as in-vehicle power sources for hybrid vehicles and electric vehicles.

  One means for improving the output efficiency of a lithium ion battery is to reduce the internal resistance of the battery. One solution is to increase the area in which the positive electrode and the negative electrode face each other via a separator. As a lithium ion battery that focuses on this, the opposing surfaces of the positive electrode and the negative electrode are made uneven, and the positive electrode and the negative electrode are arranged so that the unevenness of the positive electrode and the negative electrode mesh with each other with a predetermined electrode gap (electrolyte phase gap). There is a lithium ion battery in which the area facing the negative electrode is increased (for example, Patent Document 1).

JP-A-11-162519

  In the coin-type battery disclosed in Patent Document 1, the positive electrode and the negative electrode are used without being bent in a flat shape. For example, a separator is provided between the positive electrode and the negative electrode, such as a cylindrical lithium ion battery. In a wound battery having a wound electrode group that is wound between, the positive electrode and the negative electrode are bent and used for winding, so that a bending moment acts on the positive electrode and the negative electrode, and the winding of the electrode A compressive stress is applied to the inner side of the winding, and a tensile stress is applied to the outer side of the winding.

  Therefore, the electrode gap between the irregularities of the positive electrode and the negative electrode is not constant, the number of portions that are not proper electrode gaps increases, the internal resistance increases, and the battery characteristics deteriorate.

  Further, the irregularities on the inner side of the winding have sharp corners due to compression deformation, and there is a risk that cracks are likely to occur in the portions due to stress concentration and contact with the separator. When cracks are formed in the unevenness, the internal resistance increases and the capacity decreases, and the battery characteristics deteriorate.

  The present invention has been made in view of such problems, and its object is to avoid irregularities in the electrode gap between the positive and negative electrodes due to the deformation of the unevenness caused by winding. In addition, an object of the present invention is to provide a battery having a small internal resistance by suppressing the occurrence of cracks due to winding stress.

  In order to achieve the above object, a lithium ion battery according to the present invention is a lithium ion battery having a wound electrode group wound with a separator interposed between a positive electrode and a negative electrode, wherein the positive electrode and the negative electrode are separators. Each of the uneven surfaces has a gap formed between the uneven surface on the inner side of the winding and the uneven surface on the outer side of the winding that is deformed by winding. It has a shape that is constant in the direction of rotation.

  According to the present invention, in the wound state, the uneven surface of the positive electrode and the uneven surface of the negative electrode adjacent to each other with the separator interposed therebetween mesh with each other with a certain gap. Thereby, generation | occurrence | production of the crack by winding stress can be suppressed and a battery with small internal resistance can be provided.

1 is a half sectional view showing one embodiment of a wound lithium ion battery according to the present invention. The perspective view which shows the electrode structure before winding of the lithium ion battery by this embodiment. Sectional drawing which shows the electrode structure before winding of the lithium ion battery by this embodiment. FIG. 3 is an enlarged cross-sectional view of a part of the electrode structure before winding of the lithium ion battery according to the present embodiment, showing a state before being combined. FIG. 3 is an enlarged cross-sectional view showing a part of the electrode structure before winding of the lithium ion battery according to the present embodiment, and showing a combined state. The figure which expands and shows a part of electrode structure in the state curved by winding. Explanatory drawing which shows the bending moment action state of an electrode. FIG. 8 is a plan view illustrating an example of a concavo-convex pattern, and is a diagram illustrating a negative electrode mixture layer on the outer side of a negative electrode. It is a top view which shows an example of an uneven | corrugated pattern, FIG. 9 (A) is a figure which shows the negative mix layer outside the winding of a negative electrode, FIG.9 (B) is a figure which shows the positive mix layer inside the winding of a positive electrode . Sectional drawing explaining the structure of the positive electrode used for the winding type battery of the comparative example 3, and a negative electrode.

First, the overall structure of a cylindrical lithium ion battery will be described with reference to FIG.
The lithium ion battery is an electrode structure in which a film separator 40 is sandwiched between a thin-film negative electrode 20 and a positive electrode 30 and wound in a spiral shape in a bottomed cylindrical metal battery can 10. (Winding electrode group) is loaded.

  A negative electrode insulating sheet 11 is laid on the bottom of the battery can 10. A metal battery lid 13 is attached to the opening end side of the battery can 10 by caulking through an insulating gasket 12 so as to close the opening. A positive electrode insulating sheet 14 is attached in the vicinity of the opening end in the battery can 10. The battery can 10 sealed by the insulating gasket 12 and the battery lid 13 is filled with an electrolytic solution.

  The negative electrode 20 includes a strip-shaped negative electrode current collector 21 and a negative electrode mixture layer 22 formed on the front and back surfaces of the negative electrode current collector 21 by coating or the like.

  As the negative electrode current collector 21, a metal foil or metal mesh of stainless steel, copper, nickel, titanium, or the like can be used. In particular, copper is preferable, and zirconia and zinc-containing copper having high heat resistance are also preferable. The negative electrode current collector 21 is conductively connected to the battery can 10 by a nickel negative electrode lead member 16 extending through the negative electrode insulating sheet 11.

  The negative electrode mixture layer 22 is composed of a negative electrode active material and a binder (binder resin). Examples of the negative electrode active material include natural graphite, a composite carbonaceous material in which a film formed by a dry CVD (Chemical Vapor Deposition) method or a wet spray method is formed on natural graphite, a resin raw material such as epoxy or phenol, petroleum, Carbonaceous materials such as artificial graphite and amorphous carbon materials made by firing pitch-based materials obtained from coal as raw materials, or lithium metals that can occlude and release lithium by forming lithium and compounds, lithium and compounds And oxides or nitrides of Group 4 elements such as silicon, germanium, and tin that can occlude and release lithium by being inserted into the crystal gap. In some cases, these are generally referred to as negative electrode active materials.

In particular, the carbonaceous material is a material having high conductivity, and excellent in terms of low temperature characteristics and cycle stability. Among the carbonaceous materials, a material having a wide carbon network surface layer (d ₀₀₂ ) is excellent in rapid charge / discharge and low-temperature characteristics, and is preferable. However, since a material having a wide carbon network surface layer (d ₀₀₂ ) may have a reduced capacity and low charge / discharge efficiency at the initial stage of charging, the carbon network surface layer (d ₀₀₂ ) is preferably 0.39 nm or less. Such a carbonaceous material may be referred to as pseudo-anisotropic carbon. Further, a carbonaceous material having high conductivity such as graphite, amorphous, activated carbon, etc., may be mixed to constitute the electrode. Alternatively, a material having the characteristics shown in (1) to (3) below may be used as the graphite material.

(1) peak in the range of 1300～1400Cm ^-1 measured by Raman spectrum intensity _{(I D)} and the peak intensity in the range of 1580～1620Cm ^-1 as measured by Raman spectroscopy spectra _{(I G)} and the R value (I _D / I _G ), which is an intensity ratio, is 0.2 or more and 0.4 or less.
(2) half-value width Δ value of the peak in the range of 1300～1400Cm ^-1 as measured by Raman spectroscopy spectra, 40 cm ^-1 or more 100 cm ^-1 or less.
(3) peak intensity of the X-ray diffraction (110) plane _{(I (110))} and (004) plane peak intensity _{(I (004))} the intensity ratio X value of _{(I (110)} / I ₍₀₀₄₎ ) Is 0.1 or more and 0.45 or less.

  Note that a conductive agent may be further added to the negative electrode mixture layer 22 in order to reduce electronic resistance. Examples of the conductive agent added to the negative electrode mixture layer 22 include carbon materials such as carbon black, graphite, carbon fiber, and metal carbide, which may be used alone or in combination.

  The binder of the negative electrode mixture layer 22 may be any material as long as it is in close contact with the material constituting the negative electrode mixture layer 22 and the negative electrode current collector 21. For example, vinylidene fluoride, tetrafluoroethylene, acrylonitrile, ethylene oxide Homopolymers or copolymers such as styrene-butadiene rubber. As a solvent constituting the binder resin solution, N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoamide, dioxane, tetrahydrofuran, tetramethylurea , Triethyl phosphate, trimethyl phosphate, and the like can be used. In particular, nitrogen-containing organic solvents such as N-methyl-2-pyrrolidone, N, N-dimethylformamide, and N, N-dimethylacetamide are preferable because of high solubility of the binder resin. These solvents may be used alone or in combination.

  The positive electrode 30 includes a strip-shaped positive electrode current collector 31 made of an aluminum foil, and a positive electrode mixture layer 32 formed by coating or the like on the front and back surfaces of the positive electrode current collector 31. The positive electrode current collector 31 is conductively connected to the battery lid 13 by an aluminum positive electrode lead member 15 extending through the positive electrode insulating sheet 14.

  The positive electrode mixture layer 32 is composed of a positive electrode active material and a binder. Further, a conductive agent may be further added to the positive electrode mixture layer 32 in order to reduce the electronic resistance.

The positive electrode active material has a composition formula Li _α Mn _x M 1 _y M 2 _z O ₂ (wherein M 1 is at least one selected from Co and Ni, and M 2 is Co, Ni, Al, B, Fe, Mg, Cr) X + y + z = 1, 0 <α <1.2, 0.2 ≦ x ≦ 0.6, 0.2 ≦ y ≦ 0.4, 0.05 ≦ z ≦ 0.4. ) Is preferable. Among these, it is more preferable that M1 is Ni or Co and M2 is Co or Ni. LiMn _1/3 Ni _1/3 Co _1/3 O ₂ is more preferable. In the composition, if Ni is increased, the capacity can be increased, if Co is increased, the output at a low temperature can be improved, and if Mn is increased, the material cost can be suppressed.

In addition, the additive element is effective in stabilizing the cycle characteristics. In addition, the general formula LiM _x PO ₄ (M: Fe or Mn, 0.01 ≦ X ≦ 0.4) and LiMn _1-x M _x PO ₄ (M: divalent cation other than Mn, 0.01 ≦ An orthorhombic phosphate compound having symmetry of the space group Pmnb where X ≦ 0.4) may be used. In particular, LiMn _1/3 Ni _1/3 Co _1/3 O ₂ has high low-temperature characteristics and high cycle stability, and is suitable as a lithium battery material for hybrid vehicles (HEV).

  The binder (binder resin) of the positive electrode mixture layer 32 may be any material as long as the material constituting the positive electrode mixture layer 32 and the positive electrode current collector 31 are brought into close contact with each other. For example, vinylidene fluoride, tetrafluoroethylene, Examples thereof include homopolymers or copolymers such as acrylonitrile and ethylene oxide, and styrene-butadiene rubber.

  The conductive agent of the positive electrode mixture layer 32 is, for example, a carbon material such as carbon black, graphite, carbon fiber, and metal carbide, and each may be used alone or in combination.

  As the separator 40, the separator currently used for the well-known lithium ion battery can be used. For example, examples of the separator 40 include microporous films made of polyolefin such as polyethylene and polypropylene, and nonwoven fabrics. From the viewpoint of increasing the capacity of the battery, the thickness of the separator 40 is preferably 20 μm or less, and more preferably 18 μm or less. By using the separator 40 having such a thickness, the capacity per volume of the battery can be increased. However, if the separator 40 is made too thin, the handleability is impaired, or the separation between the positive and negative electrodes is insufficient, and a short circuit is likely to occur. Therefore, the lower limit of the thickness is preferably 10 μm.

Solvents used for the electrolyte filled in the battery can 10 include ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and vinylene carbonate (from the viewpoint of low temperature characteristics and film formation on the negative electrode. VC) is preferable. The lithium salt used for the electrolytic solution is not particularly limited, but for inorganic lithium salts, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiI, LiCl, LiBr, etc., and for organic lithium salts, LiB [OCOCF ₃ ] ₄ , _{LiB [OCOCF 2 CF 3] 4} , LiPF 4 (CF 3) 2, LiN (SO 2 CF 3) 2, LiN (SO 2 CF 2 CF 3) may be used ₂ or the like. In particular, LiPF ₆ that is frequently used in consumer batteries is a suitable material because of its quality stability. LiB [OCOCF ₃ ] ₄ is an effective material because it has good dissociation and solubility and exhibits high conductivity at a low concentration.

  As shown in FIGS. 2 and 3, the lithium ion battery according to the present embodiment has the surface of the negative electrode 20 and the positive electrode 30 facing each other when the separator 40 is interposed between the negative electrode 20 and the positive electrode 30 and overlapped with each other. It has a concavo-convex shape that meshes with the surface.

  In the negative electrode 20, the negative electrode mixture layers 22 disposed on both the outer side and the inner side of the negative electrode current collector 21 in a wound state have uneven surfaces 23 and 24, respectively. The uneven surfaces 23 and 24 have a predetermined interval in the winding direction (the left-right direction in the drawing) which is the longitudinal direction of the negative electrode current collector 21 on the surface of the base portions 23B and 24B spreading in a plane with a constant thickness. It has a surface shape on which convex portions 23A and 24A projecting. The convex portions 23A, 24A have a substantially quadrangular tooth profile, and have a pair of side surfaces extending in a direction orthogonal to the winding direction and a top surface extending between the pair of side surfaces.

  In the positive electrode 30, each positive electrode mixture layer 32 arranged on both the outer side and the inner side of the positive electrode current collector 31 in a wound state has uneven surfaces 33 and 34, respectively. The uneven surfaces 33 and 34 have a predetermined interval in the winding direction (left and right direction in the drawing) which is the longitudinal direction of the positive electrode current collector 31 on the surface of the base portions 33B and 34B spreading in layers with a constant thickness. It has a surface shape on which projecting convex portions 33A and 34A are formed. The convex portions 33A and 34A have a tooth shape having a substantially square cross section, and have a pair of side surfaces extending in a direction orthogonal to the winding direction and a top surface extending between the pair of side surfaces.

  FIG. 4 is an enlarged cross-sectional view showing a part of the electrode structure before winding of the lithium ion battery in the present embodiment, and a positive electrode current collector and a positive electrode mixture layer disposed inside the winding, 1 shows a negative electrode current collector and a negative electrode mixture layer disposed on the outer side of the negative electrode current collector. FIG. 5 is a diagram illustrating a flat state in which the positive electrode and the negative electrode illustrated in FIG. 4 are overlapped with each other, and FIG. 6 is a diagram illustrating a state in which the positive electrode and the negative electrode are bent by winding. In FIGS. 4 to 6, the separator is omitted.

  The uneven shape of the uneven surfaces 23 and 24 of the negative electrode 20 and the uneven shape of the uneven surfaces 33 and 34 of the positive electrode 30 are different from each other in the flat state before winding, as shown in FIGS. ing.

  In the flat state before winding, the concavo-convex surfaces 23 and 33 have a rectangular cross-sectional shape of the convex portion 23A, whereas the concavo-convex surfaces 24 and 34 have a trapezoidal cross-sectional shape. ing.

  More specifically, the convex portion 34A (24A) of the concave and convex surface 34 (24) disposed on the winding inner side of the positive electrode current collector 31 shifts from the proximal end side to the distal end side in a flat state. Therefore, the pair of side surfaces have a shape that gradually approaches. And the convex part 23A (33A) of the concavo-convex surface 23 (33) disposed on the winding outer side of the negative electrode current collector 21 has each side surface perpendicular to the base part 23B (33B) in a flat state, or The pair of side surfaces have a shape in which the pair of side surfaces gradually separate as they move from the proximal end side to the distal end side.

  In the present embodiment, the base angle θa that is an angle formed between the side surfaces of the convex portions 23A and 33A and the base portions 23B and 33B is set to 90 degrees or less, for example, set to 88 to 87 degrees. ing. And base angle (theta) b which is an angle formed between the side surface of convex part 24A, 34A and base part 24B, 34B is set to an angle larger than 90 degree | times, for example, set to 91-93 degree | times. Yes. In FIGS. 4 and 5, for easy understanding, the angle is extremely shown at an angle larger than the set angle.

  The negative electrode 20 and the positive electrode 30 are curved by winding, and a bending moment acts on each of the negative electrode 20 and the positive electrode 30. For example, in the case of the negative electrode 20, as shown in FIG. 7, the negative electrode current collector 21 is considered to be a neutral surface, and the negative electrode mixture layer 22 wound outside the negative electrode current collector 21 has a tensile stress. σa acts, and compressive stress σb acts on the negative electrode mixture layer 22 on the inner side of the negative electrode current collector 21. The stresses σa and σb increase as the distance from the negative electrode current collector 21 increases.

  Similarly, in the case of the positive electrode 30, the tensile stress σa acts on the positive electrode mixture layer 32 outside the winding of the positive electrode current collector 31, and the positive electrode mixture layer on the inner side of the winding of the positive electrode current collector 31. Compressive stress σb acts on 32. The stresses σa and σb increase as the distance from the positive electrode current collector 31 increases.

  Therefore, if the negative electrode 20 and the positive electrode 30 with the base angles θa, θb of 90 degrees of the irregular surfaces 23, 24, 33, 34 before winding are wound, the current collector 21, Since the mixture layers 22 and 32 outside the winding 31 are pulled, the base angle θa of the uneven surfaces 23 and 33 changes to an angle larger than 90 degrees. Since the mixture layers 22 and 32 on the inner side of the current collectors 21 and 31 are compressed, the base angle θb of the uneven surfaces 23 and 33 changes to an angle smaller than 90 degrees.

  In the present embodiment, as shown in FIG. 5, in the flat state, the base angles θa of the concave and convex surfaces 23 and 33 are set to 90 degrees or an angle smaller than 90 degrees, and the bottoms of the concave and convex surfaces 24 and 34 are set. The angle θb is set to an angle larger than 90 degrees. Therefore, in the state curved by winding, the stress which acts on the mixture layers 22 and 32 can be reduced and generation | occurrence | production of a crack can be prevented.

  In the case of a wound battery, a positive electrode and a negative electrode are bent for use in winding. For this reason, a bending moment acts on the positive electrode and the negative electrode, compressive stress is applied to the inner side of the winding of the electrode, and tensile stress is easily applied to the outer side of the winding. Then, when an electrode having an uneven surface is used for a wound battery, as shown in FIG. 6, a convex portion 23A on the outer side of the winding is incorporated between the convex portions 34A and 34A on the inner side of the winding. Here, assuming that the respective base angles θb of the irregular surfaces 24 and 34 on the winding inner side are 90 degrees, the convex portions 34A and 34A are caused to protrude by the compressive stress generated on the winding inner electrode. The force which compresses (33A) from both sides works, and there is a possibility that a crack may occur in the convex portion 23A (33A) of the electrode on the outer side of the winding due to this force. On the other hand, in the present embodiment, the base angles θb of the irregular surfaces 24 and 34 on the winding inner side are larger than 90 degrees, and the base angle θa of the irregular surfaces 23 and 33 on the winding outer side is 90 degrees. By making it below, it is possible to suppress the force applied to the convex portion 23A (33A) of the outer electrode of the winding, and to prevent the occurrence of cracks.

  Then, as shown in FIG. 6, the side surfaces of the convex portions 34 </ b> A (24 </ b> A) that are adjacent to each other on the concave / convex surface 34 (24) that becomes the winding inner side are substantially parallel and the concave / convex surface that becomes the winding outer side. The pair of side surfaces of the projection 23A (33A) of the projection 23 (31) are substantially parallel, with the base end side of the projection 23A spreading more in the winding direction than the tip side, increasing the base angle θa.

  Therefore, in the curved state by winding, the uneven surfaces 23 and 24 of the negative electrode 20 and the uneven surfaces 33 and 34 of the positive electrode 30 adjacent to each other with the separator 40 interposed therebetween mesh with each other with a certain gap. Therefore, an appropriate electrode gap is maintained over a wide area, and the battery characteristics are improved under a decrease in internal resistance.

  Moreover, it is avoided that the corner | angular part c (refer FIG. 6) of the uneven | corrugated surface 24 (34) inside winding is sharpened at an acute angle of 90 degrees or less, and the stress concentration of the said part is relieve | moderated. In addition, since the corner portion c is not sharp, the contact with the separator 40 does not easily cause a crack in the portion. As a result, an increase in internal resistance and a decrease in capacity due to cracks in the uneven surfaces 24 and 34 are avoided, and battery characteristics are improved.

  The negative electrode mixture layer 22 having the concavo-convex surfaces 23 and 24 can be produced by, for example, the following method.

  First, the negative electrode mixture-containing composition is applied on at least one surface of the negative electrode current collector 21 and dried at 60 to 120 ° C. for 2 to 4 hours, for example. Then, the negative electrode mixture layer 22 is formed by adjusting the thickness and density by pressing. The uneven surfaces 23 and 24 can be formed by pressing the negative electrode mixture layer 22 using a mold or a roll having an uneven pattern. After applying a flat part by the said method, drying and pressing, only an uneven | corrugated | grooved part can be formed and dried by using an inkjet etc., and the uneven | corrugated surfaces 23 and 24 can also be formed. Further, the flat electrode may be applied to the current collector, and the electrode may be formed on the separator only at the convex portion.

  The concavo-convex surfaces 33 and 34 of the positive electrode 30 can be formed by using the positive electrode mixture-containing composition for forming the positive electrode mixture layer by the same method as the above-described negative electrode formation method.

  The height of the uneven surfaces 23, 24, 33, and 34 is desirably 50 μm or more. When the height of the uneven surfaces 23, 24, 33, and 34 is 50 to 100 μm, a battery having a low resistance and a high capacity can be obtained. It is more desirable because it can be realized. The electrode width is desirably 100 μm or more. An electrode width of 500 to 1000 μm is more desirable because a battery with low resistance and high capacity can be realized.

  The lithium ion battery of the present invention only needs to include the negative electrode 20 and the positive electrode 30 described above, and there are no particular limitations on other components and structures, and various components and structures that are applied to conventionally known lithium ion batteries. Can be adopted.

Example 1
LiMn _1/3 Ni _1/3 Co _1/3 O ₂ is used as the positive electrode active material, carbon black (CB1) and graphite (GF2) are used as the electronic conductive material, and polyvinylidene fluoride (PVDF) is used as the binder. The solid weight at the time of drying was set to NMP (N-- as a solvent so that the ratio of LiMn _1/3 Ni _1/3 Co _1/3 O ₂ : CB1: GF2: PVDF = 86: 9: 2: 3 A positive electrode material paste was prepared using methylpyrrolidone).

  This positive electrode material paste is applied to an aluminum foil to be the positive electrode current collector 31, dried at 80 ° C., and pressed with a pressure roller with a pattern to form a border pattern as shown in FIG. Then, it dried at 120 degreeC and formed the positive mix layer 32, 32 on both surfaces of the positive electrode current collector 31. FIG. 8 is a plan view showing an example of a concavo-convex pattern, and is a diagram showing a negative electrode mixture layer on the outer side of the negative electrode.

  Next, pseudo-anisotropic carbon, which is amorphous carbon, is used as the negative electrode active material, carbon black (CB2) is used as the conductive material, and PVDF is used as the binder. A slurry of the negative electrode mixture layer was prepared using NMP as a solvent so as to have a ratio of carbon: CB2: PVDF = 90: 5: 5.

  This negative electrode material slurry was applied to a copper foil to be the negative electrode current collector 21. Then, it is dried at 80 ° C. and pressed with a pressure roller with a pattern to give a concavo-convex pattern as shown in FIG. The uneven height was 100 μm, the uneven width was 500 μm, and the uneven space was 500 μm. Then, it dried at 120 degreeC and the negative mix layer 22 and 22 was formed in both surfaces of the negative electrode collector 21. As shown in FIG.

As the electrolytic solution, a solvent was mixed at a volume composition ratio EC: VC: DMC: EMC = 19.8: 0.2: 40: 40, and 1M LiPF ₆ was dissolved as a lithium salt to prepare an electrolytic solution. .

  A separator 40 was sandwiched between the produced negative electrode 20 and positive electrode 30 to form a wound group and inserted into the battery can 10. In order to collect current from the negative electrode 20, one end of a nickel negative electrode lead was welded to the negative electrode current collector 21, and the other end was welded to the battery can 10. In addition, one end of an aluminum positive electrode lead was welded to the positive electrode current collector 31 and the other end was electrically connected to the battery lid 13 in order to collect the positive electrode 30. Further, a wound battery of Example 1 as shown in FIG. 1 was produced by injecting and caulking the electrolytic solution.

(Battery characteristics evaluation)
<Battery capacity evaluation method>
The battery was charged at a constant current of 0.6 A to 4.1 V, charged at a constant voltage of 4.1 V until the current value reached 20 mA, and after 30 minutes of operation stop, discharged to 2.6 V at 0.6 A. This operation was repeated three times. Next, the battery was charged at a constant current of 0.6 A up to 4.1 V, left for 30 minutes, and the voltage was measured. The measurement results are shown in Table 1.

<Direct Current Resistance (DCR) Evaluation Method>
In the discharge DCR evaluation, the battery was charged at a constant current of 0.6 A up to 3.8 V, discharged at 0.6 A for 10 s, charged again at a constant current of 3.8 V, discharged at 1.8 A for 10 s, and again 3. The battery was charged to 8 V and discharged at 06 A for 10 s. The DCR of the battery was evaluated from the IV characteristics at this time. The measurement results are shown in Table 1.

(Example 2)
A wound battery of Example 2 was produced by the method described below.
Graphite was used as the negative electrode active material of the negative electrode mixture layer 22. A battery was fabricated and evaluated in the same manner as in Example 1 except for the above. The evaluation results are shown in Table 1.

(Example 3)
A wound battery of Example 3 was produced by the method described below.
The compositions of the positive electrode 30 and the negative electrode 20 are the same as in Example 1. The uneven height was 100 μm. Further, when the distance from the battery center to the current collector was d ₁ μm and the uneven width and uneven distance were d ₂ μm, the uneven width and uneven distance d ₂ were 60 × d ₁ μm. A battery was fabricated and evaluated in the same manner as in Example 1 except for the above. The evaluation results are shown in Table 1. Note that the uneven height refers to the height of the protrusions 23A, 24A, 33A, and 34A, the uneven width refers to the width of the protrusions, and the uneven space refers to the distance between the adjacent protrusions and protrusions.

Example 4
A wound battery of Example 4 was produced by the following method.
Graphite was used as the negative electrode active material of the negative electrode mixture layer 22. Except for this, the battery was fabricated and evaluated in the same manner as in Example 3. The evaluation results are shown in Table 1.

(Example 5)
A wound battery of Example 5 was produced by the method described below.
The compositions of the positive electrode 30 and the negative electrode 20 are the same as in Example 1. The uneven surfaces 23, 24, 33, and 34 are different from the first to fourth embodiments, as shown in FIG. 9, in the uneven pattern not only in the longitudinal direction (winding direction) but also in the lateral direction (lateral width direction). To make a matrix pattern. The uneven height was 100 μm. The electrode width in the longitudinal direction and the short direction was 500 μm, and the uneven width in the longitudinal direction and the short direction was 500 μm. Except for this, the battery was fabricated and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1. FIG. 9 is a plan view showing an example of a concavo-convex pattern, FIG. 9A is a diagram showing a negative electrode mixture layer on the outer side of the negative electrode, and FIG. 9B is a positive electrode mixture on the inner side of the positive electrode. It is a figure which shows a layer.

(Example 6)
The wound type battery of this example was manufactured by the method described below.
Graphite was used as the negative electrode active material of the negative electrode mixture layer. Except for this, the battery was fabricated and evaluated in the same manner as in Example 5. The evaluation results are shown in Table 1.

(Comparative Example 1)
A wound battery of Comparative Example 1 was produced by the method shown below.
First, LiMn _1/3 Ni _1/3 Co _1/3 O ₂ is used as the positive electrode active material, carbon black (CB1) and graphite (GF2) are used as the electronic conductive material, and polyvinylidene fluoride (PVDF) is used as the binder. And the solid content weight at the time of drying is NMP (as a solvent so that the ratio of LiMn _1/3 Ni _1/3 Co _1/3 O ₂ : CB1: GF2: PVDF = 86: 9: 2: 3 A positive electrode material paste was prepared using (N-methylpyrrolidone).

  This positive electrode material paste was applied to an aluminum foil serving as a positive electrode current collector, dried at 80 ° C., and pressed with a pressure roller. Then, it dried at 120 degreeC and formed the positive mix layer in the positive electrode electrical power collector. The positive electrode mixture layer has no uneven pattern.

  Next, pseudo-anisotropic carbon, which is amorphous carbon, is used as the negative electrode active material, carbon black (CB2) is used as the conductive material, and PVDF is used as the binder. A slurry of the negative electrode mixture layer was prepared using NMP as a solvent so as to have a ratio of carbon: CB2: PVDF = 90: 5: 5.

  This negative electrode material slurry was applied to a copper foil serving as a negative electrode current collector. Then, it dried at 80 degreeC and pressed with the pressure roller without an uneven | corrugated pattern. Then, it dried at 120 degreeC and formed the negative mix layer in the negative electrode collector. The negative electrode mixture layer also has no uneven pattern. Except for these, the battery was prepared and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

(Comparative Example 2)
A wound battery of Comparative Example 2 was produced by the method shown below.
The composition of the positive electrode and the negative electrode is the same as in Example 1. The concavo-convex pattern was a concavo-convex pattern as shown in FIG. The uneven height was 30 μm and the uneven width was 500 μm. Except for these, the battery was prepared and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

(Comparative Example 3)
A wound battery of Comparative Example 3 was produced by the method described below.
The composition of the positive electrode and the negative electrode is the same as in Example 1. As shown in FIG. 10, the uneven surface has a shape having convex portions 124A and 133A having a substantially triangular cross section. 10 is the same as the structure shown in FIG. 3 except for the shape of the convex portion, and the detailed description is omitted by changing the reference numeral shown in FIG. The uneven height was 100 μm and the uneven width was 500 μm. Except for these, the battery was prepared and evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

  As a result of evaluating the direct current resistance ratio and the capacity ratio with Comparative Example 1 being 100%, in Examples 1 to 6, the capacity ratio was not changed and the direct current resistance was reduced. In the case where graphite was used for the negative electrode active material of Example 6, the DC resistance ratio was 65% of Comparative Example 1.

  Since the lithium ion battery according to the present invention is a lithium ion battery with reduced internal resistance of the battery, it can be widely used as a power source for a hybrid vehicle requiring high output, a power source for an electric control system of a vehicle, and a backup power source. It is also suitable as a power source for industrial equipment such as railways, power tools and forklifts.

DESCRIPTION OF SYMBOLS 10 Battery can 20 Negative electrode 21 Negative electrode collector 22 Negative electrode mixture layer 23, 24 Uneven surface 23A, 24A, 33A, 34A Convex part 23B, 24B, 33B, 34B Base part 30 Positive electrode 31 Positive electrode collector 32 Positive electrode mixture layer 33, 34 Uneven surface

Claims (4)

A lithium ion battery having a wound electrode group wound with a separator interposed between a positive electrode and a negative electrode,
The positive electrode and the negative electrode have uneven surfaces that mesh with each other with the separator interposed therebetween,
Each of the uneven surfaces has a shape in which a gap formed between the uneven surface on the inner side of the winding and the uneven surface on the outer side of the winding that is deformed by winding is constant in the winding direction. Lithium ion battery. The concavo-convex surface has a base portion that spreads in layers with a constant thickness, and a convex portion that protrudes at a predetermined interval in the winding direction on the surface of the base portion,
The convex portion has a tooth profile having a pair of side surfaces extending in a direction orthogonal to the winding direction and a top surface extending between the pair of side surfaces,
The convex part of the irregular surface on the inner side of the winding has a shape in which the pair of side surfaces gradually approach as it moves from the proximal side to the distal side in a flat state,
In the flat state, the convex portions of the concavo-convex surface on the outer side of the winding have a shape in which each side surface is perpendicular to the base portion, or the pair of side surfaces gradually separate from each other as the base end side shifts to the distal end side. The lithium ion battery according to claim 1. As for the convex part of the uneven surface on the outer side of the winding, in a flat state, an angle formed between the side surface and the base part is set to 88 to 87 degrees,
The convex part of the uneven surface on the inner side of the winding has an angle formed between the side surface and the base part set to 91 to 93 degrees in a flat state. A lithium ion battery according to 1. In the positive electrode, a positive electrode mixture layer is formed on the inner side and outer side of the positive electrode current collector plate,
The negative electrode has a negative electrode mixture layer formed on the inner side and the outer side of the negative electrode current collector plate,
The positive electrode mixture layer on the outer side of the positive electrode current collector plate, and the negative electrode mixture layer on the outer side of the negative electrode current collector plate, having an irregular surface on the outer side of the winding,
The positive electrode mixture layer on the inner side of the winding of the positive electrode current collector plate and the negative electrode mixture layer on the inner side of the negative electrode current collector plate have uneven surfaces on the inner side of the winding. Item 4. The lithium ion battery according to any one of Items 3 to 3.

Images