Wound type secondary battery

Abstract

To provide a winding type secondary battery that can improve the heat dissipation of the winding type secondary battery and reduce the performance degradation caused by heat buildup.SOLUTION: The winding type secondary battery has a structure in which an electrode laminate 8, in which a positive electrode 1 and a negative electrode 2 are stacked via separators 3, 4, is wound. The electrode laminate is wound in a spiral shape. The area at both ends of the electrode laminate where an active material layer is not formed and a metal foil is exposed is increased, thereby increasing a heat dissipation area. The improved heat dissipation can suppress the deterioration of battery performance due to temperature rise.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a wound type secondary battery in which a positive electrode laminate and a negative electrode laminate are wound with a separator interposed therebetween. [Background technology]

[0002] In recent years, from the viewpoint of efficient use of electricity, secondary batteries such as lithium-ion batteries have come to be used in many situations. Therefore, there is a need for improved performance such as rapid charging and discharging, large current, large capacity, and long life. The structure of secondary batteries is generally a wound type in which a strip-shaped electrode material consisting of a positive electrode, a negative electrode, and a separator is rolled up and stored in a battery case together with an electrolyte (for example, Patent Document 1).

[0003] However, in secondary batteries in which strip-shaped electrode materials consisting of positive and negative electrodes and a separator are wound, heat is likely to build up inside the wound electrodes, and the generated heat deteriorates the battery performance, so it is necessary to efficiently exhaust the generated heat to lower the temperature, which is an issue. Therefore, a battery structure has been devised in which the area of ​​the current collector is enlarged and the heat of the electrodes is efficiently exhausted from a metallic shaft core with good thermal conductivity (for example, Patent Document 2).

[0004] However, in a secondary battery having a structure such as that disclosed in Patent Document 2, although it can dissipate heat around the metal shaft core, it has the problem that it is not effective in dissipating heat from other parts. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-321220 [Patent Document 2] Japanese Patent Application Publication No. 10-092469 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a wound secondary battery that can improve the heat dissipation property of the wound secondary battery and reduce the performance degradation caused by heat buildup. [Means for solving the problem]

[0007] In order to solve the above problems, a first aspect of the present invention is a wound secondary battery having a structure in which an electrode laminate in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween is wound, characterized in that the electrode laminate is wound in a spiral shape.

[0008] In the above-mentioned wound secondary battery, a cone-shaped current collector may be in contact with margins on both ends of the electrode laminate where no active material layer is formed, for current flow and heat diffusion. Effect of the Invention

[0009] According to the wound secondary battery of the present invention, since the band-shaped electrode laminate is spirally wound while being shifted, the area of ​​the portions at both ends of the band-shaped electrode laminate where no active material layer is formed and the metal foil is exposed is increased, thereby increasing the heat dissipation area, and a secondary battery can be obtained in which the improved heat dissipation can suppress deterioration of battery performance due to temperature rise. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is an explanatory diagram of a layer structure of a wound type secondary battery. [Diagram 2] Schematic diagram of the relationship between the unwinding core and the winding core. [Diagram 3] 4A and 4B are schematic cross-sectional views of the winding shape of an electrode laminate as viewed from above and from the side. [Figure 4] 3A and 3B are cross-sectional views of the first and second turns of the electrode laminate of the first embodiment. [Diagram 5] FIG. 1 is a cross-sectional view of the first and second turns of a conventional electrode laminate. [Figure 6] FIG. 13 is a cross-sectional view of an electrode stack and a current collector with offset winding. [Figure 7] Schematic diagram showing the battery shape. [Figure 8] FIG. 6 is an explanatory diagram of a layer configuration according to a second embodiment. [Figure 9] 6A and 6B are cross-sectional views of the first and second turns of an electrode laminate according to a second embodiment. [Figure 10] FIG. 6 is a cross-sectional view of an electrode stack and a current collector according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below. In addition, in the embodiments shown below, technically preferable limitations are imposed for carrying out the invention, but these limitations are not essential requirements for the present invention. Furthermore, the same reference numerals may be used to designate equivalent members, and descriptions thereof may be omitted.

[0012] Fig. 1 is an explanatory diagram of the layer structure of a wound type secondary battery. Fig. 1a is an explanatory diagram of the layer structure of one embodiment of the wound type secondary battery of the present invention, and Fig. 1b is an explanatory diagram of the layer structure of a conventional wound type secondary battery. The basic layer structure is explained with Fig. 1a. A positive electrode active material layer 6 or a negative electrode active material layer 7 is formed on both sides of a metal foil 5, which is a substrate, to form a strip-shaped positive electrode 1 and a negative electrode 2, respectively.

[0013] The metal foil 5 may be a single metal foil made of one of several metals, such as aluminum, gold, silver, copper, nickel, stainless steel, titanium, and platinum, or an alloy of two or more of the several metals, but is not limited to these.

[0014] The positive electrode active material layer 6 may contain a positive electrode active material, a conductive auxiliary, a binder resin, a dispersant, etc., and the positive electrode active material is not particularly limited as long as it is a compound capable of absorbing and releasing lithium ions. The inorganic compound constituting the positive electrode active material is represented by the composition formula Li x MO2, or Li y Examples of the oxide include, but are not limited to, a composite oxide represented by M2O4 (wherein M is a transition metal, 0≦x≦1, 1≦y≦2), an oxide having tunnel-shaped vacancies, a metal chalcogenide having a layered structure, and a chalcogen compound containing lithium ions.

[0015] The negative electrode active material layer 7 may contain a negative electrode active material, a conductive auxiliary, a binder resin, a dispersant, etc., and examples thereof include, but are not limited to, carbon black, ketjen black, acetylene black, carbon whiskers, carbon fibers, natural graphite, artificial graphite, carbon nanoparticles and nanotubes, titanium oxide, ruthenium oxide, aluminum, and nickel.

[0016] As a method for forming each active material layer, any of the known methods can be suitably applied, such as screen printing, metal spraying, plating, vapor deposition, inkjet printing, spraying, gravure printing, thermal transfer, letterpress printing, intaglio printing, offset printing, sputtering, ion plating, or plasma chemical vapor deposition.

[0017] The area where the active material is applied is provided with a margin on each of the opposite sides of the positive electrode 1 and the negative electrode 2, and the metal foil 5 is exposed in the margin. The width of the margin is a. The separator 3 and the separator (short) 4 are provided on the active material layers of the positive electrode 1 and the negative electrode 2. In order to reduce the risk of electrical shorts, it is desirable to make the separator 3 and the separator (short) 4 slightly larger than the area of ​​the active material layer according to the accuracy of the winding position control. This structure of the positive electrode 1 / separator 3 / negative electrode 2 / separator (short) 4 is called the electrode laminate 8. The conventional wound secondary battery also has a similar layer structure. Note that the width of the entire band-shaped member (vertical direction in the figure) is the same in the wound secondary battery of the present invention in FIG. 1a and the conventional wound secondary battery in FIG. 1b.

[0018] (First embodiment) The positional relationship between the positive electrode, negative electrode, and separator of a wound secondary battery according to one embodiment of the present invention is shown in FIG. la. When the electrode laminate 8 of the wound secondary battery according to this embodiment is wound, it is shifted in the width direction (downward in the drawing) by the margin width a for each turn, and the outer negative electrode active material layer 7 of the negative electrode 2 wound on the outer side of the layer of the outer positive electrode active material layer 6 of the positive electrode 1 and the separator (short) 4 are wound so that they overlap exactly, so that the electrode laminate is wound in a spiral shape shifted by the width a for each turn. To avoid ambiguity in the term, it should be noted that the "spiral" referred to here is a three-dimensional curve that moves (up or down) in a direction perpendicular to the plane of rotation while rotating, and is not a simple spiral.

[0019] In contrast, conventional strip-shaped electrodes have a margin of width a at the end, and the positional relationship of the electrodes wound without shifting is shown in Figure 1b. The electrode laminate 9 has a structure in which the positive electrode 1' / separator 3' / negative electrode 2' / separator 3' are stacked without shifting, and when this is wound as shown in Figure 1b, since there is no margin of the substrate, only the end surface dissipates heat from the substrate.

[0020] To wind the positive electrode 1, separator 3, negative electrode 2, and separator (short) 4 in a spiral manner around the core 10 on the side where there is a margin of the negative electrode 2 while maintaining the positional relationship of each layer shown in Fig. 1a, with the separator (short) 4 on the inside, with a shift of width a per turn, the position of the unwinding core 11 is controlled so that the relative positions of the positive electrode 1, separator 3, negative electrode 2, and separator (short) 4 do not shift. By controlling the winding in conjunction with the position of the winding core 10, it is possible to wind the positive electrode 1, separator 3, negative electrode 2, and separator (short) 4 in a spiral manner with a shift of width a per turn. A schematic diagram of the relationship between the unwinding core 11 and the core 10 is shown in Fig. 2.

[0021] 3a and 3b are schematic cross-sectional views of the top and side of the electrode laminate 8 wound with offset and the electrode laminate 9 wound without offset, respectively. When the electrodes are wound with offset, the outer shape becomes a cylindrical shape with inclined conical surfaces at the top and bottom, but the volume does not change compared to the simple cylindrical shape without offset. FIG. 4 shows cross sections of the first and second turns of the electrode laminate 8 wound with offset. FIG. 5 shows cross sections of the first and second turns of a normal electrode laminate 9 without offset. Although omitted in FIG. 5, current-carrying tabs are generally installed periodically on the electrode laminate for current collection. When the electrodes are wound with offset, the position of the electrode laminate 8 gradually shifts as it is wound, and it shifts by a width a for each turn, but because there is a margin of a width a, the surfaces of the active material layers of the positive electrode 1 and the negative electrode 2 can always be wound facing each other even if the electrode positions shift.

[0022] The current collectors 12 and 13, which are conical surfaces, are brought into contact with the margins of the positive electrode 1 and the negative electrode 2 of the spirally wound electrode laminate. FIG. 6 shows a cross-sectional view of the strip-shaped electrode laminate and the current collectors 12 and 13, which are wound 2.5 turns in a spirally offset manner. Here, the positive electrode 1 is in contact with the current collector 12, and the negative electrode 2 is in contact with the current collector 13. More specifically, the current collector 12 is in contact with the metal foil 5a exposed in the margin of the positive electrode 1, and the current collector 13 is in contact with the metal foil 5b exposed in the margin of the negative electrode 2. These conical surfaces collect current and dissipate heat from the electrode laminate. The current collectors 12 and 13 are made of a conductive material, typically a metal.

[0023] The inclination of the conical surfaces of the current collectors 12 and 13 is set to an angle at which the current collectors 12 and 13 come into contact with the edges of the margin, etc., depending on the electrode laminate and the width a of the margin. At this time, since the current collectors are wound with a spiral offset, the central axis of the conical collector and the central axis of the winding core do not coincide and there is a slight offset, but if the width a is small, this can be almost ignored. As an example, if the thickness of the electrode laminate is 0.3 mm, the margin is 0.2 mm, the thickness of the metal foil substrate is 0.02 mm, the length of the strip of the electrode laminate is 100 m, and the diameter of the winding core is 10 mm, the winding diameter of the secondary battery will be 196 mm.

[0024] In the above example, if the margins and sides of the metal foil 5 are used as the heat dissipation area, a comparison of the heat dissipation area when the metal foil is wound with and without a spiral offset is shown in Table 1. By winding the metal foil with a spiral offset, the heat dissipation area is increased by 100 mm × 0.2 mm × 2 (positive and negative) = 40,000 mm, taking into account the margins. 2 increased by 8,000 mm 2 From 48,000mm 2 The circular part on the top surface is spirally shifted and wound to form a cone shape, increasing the surface area by about 1.2 times.

[0025] [Table 1]

[0026] The shape of a battery when staggered in a spiral shape is shown in Fig. 7(a), and the shape of a battery when wound without staggering is shown in Fig. 7(b). Both are the shapes when three batteries are lined up in series. When batteries are connected with staggering in a spiral shape, the space occupied by batteries other than the first battery is the same as when wound without staggering. Since there is no difference in the volume of each battery, the space created by the conical shape can be effectively utilized for other purposes, and there is no significant loss of volume.

[0027] The electrode laminate, the current collector, etc. are enclosed in a container such as a metal can or a flexible film, the inside of the container is filled with an electrolyte, and the container is packaged to form a secondary battery. Any known container may be appropriately adopted and used. In this case, the electrolyte may be a solid electrolyte or a gel electrolyte. The material of the active material of the electrode and the method of formation are not limited to those exemplified above. That is, the present invention is characterized by the structure in which the electrodes are wound in a spiral shape and the shape of the conical current collector, and other components are not limited to the examples shown in this embodiment.

[0028] Second embodiment As the second embodiment, an example is shown in which only the metal foil 5, which is the base material of the electrode laminate of the first embodiment described above, is enlarged to enlarge the margin, and a margin with width b is provided on both sides where there is no active material layer. However, to prevent short circuits, the separator 3 and separator (short) 4 are larger than those in the first embodiment. The positional relationship of the positive electrode 1, negative electrode 2, separator 3, and separator (short) 4 that constitute this electrode laminate is shown in FIG. 8.

[0029] The blank portion has a width b of the portion having no active material layer on either side, and while maintaining the positional relationship shown in FIG. 8, the separator (short) 4 side is on the inside, and the blank portion is spirally wound at the lower side of the figure with a shift of width a per winding around the core, as in the previously described embodiment.

[0030] FIG. 9 shows cross-sectional views of the first and second turns of the electrode in which the electrode laminate 8 is wound with a shifted shape. FIG. 10 shows a cross-sectional view of the state in which the conical current collectors 12 and 13 are in contact with the margins of the metal foil 5 from above and below. The margins of width b on both sides of which there is no active material layer have space behind them, so by pressing the conical current collectors 12 and 13 against the metal foil 5, the margins of the metal foil 5 are folded along the angle of the cone surface, and the margins can come into surface contact with the surfaces of the current collectors 12 and 13. The increased contact area allows heat from the metal foil 5, which is the substrate, to be more efficiently discharged to the current collectors 12 and 13. In addition, the extended margins are folded, so the volume of the battery does not increase.

[0031] In the battery structure of the present invention, the band-shaped electrode laminate is wound in a spiral shape while being shifted, so that the exposed area of ​​both ends of the band can be increased to increase the heat dissipation area, and the deterioration of battery performance due to temperature rise can be suppressed by improving heat dissipation. In addition, by making the current collector into a conical surface shape, the marginal part of the electrode can be brought into contact with the current collector, and electricity can be passed and heat can be discharged through the current collector. [Explanation of symbols]

[0032] 1...Positive electrode 2...Negative electrode 3. Separator 4. Separator (short) 5...Metal foil (base material) 6...Cathode active material layer 7...Negative electrode active material layer 8, 9: Electrode laminate 10....Core 11. Unwinding core 12, 13... Current collector

Claims

1. In a wound type secondary battery having a structure in which an electrode laminate in which a positive electrode and a negative electrode are laminated with a separator interposed therebetween is wound, the electrode laminate is wound in a spiral shape, a conical surface-shaped current collector is in contact with the margins on both ends of the electrode laminate on which no active material layer is formed, thereby conducting current and diffusing heat; a width of a margin on both ends of the electrode laminate on which the active material layer is not formed is defined as a, and the electrode laminate is spirally wound around a core with a shift of the width a per one winding.

2. In a margin on which the active material layer is not formed, a metal foil that is a base material of the electrode laminate is exposed, 2. The wound secondary battery according to claim 1, wherein the current collector is in contact with the metal foil.

3. A wound secondary battery as described in claim 2, characterized in that the metal foil contains at least one of gold, silver, stainless steel, titanium, and platinum.

4. A wound secondary battery as described in any one of claims 1 to 3, characterized in that when the electrode laminate is spirally wound, both ends of the electrode laminate with which the current collector contacts are inclined in the same direction relative to the winding axis to form inclined surfaces.

5. A wound secondary battery as described in any one of claims 1 to 3, characterized in that when the electrode laminate is spirally wound, the end of the electrode laminate on the positive electrode side with which the current collector contacts and the end of the electrode laminate on the negative electrode side with which the current collector contacts are inclined in the same direction relative to the winding axis to form an inclined surface.

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