JP7600557B2 - Wound type secondary battery - Google Patents

Description

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.

In recent years, secondary batteries such as lithium-ion batteries have come to be used in many situations in order to make efficient use of electricity. This has led to a need for improved performance, such as rapid charging and discharging, high current, large capacity, and long life. The most common structure of secondary batteries is 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 (see, for example, Patent Document 1).

However, secondary batteries, which are made by winding strip-shaped electrode material consisting of a positive electrode, a negative electrode, and a separator, tend to trap heat 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. As a result, a battery structure has been devised that expands the area of the current collector and efficiently exhausts the heat of the electrodes from a metallic core with good thermal conductivity (for example, Patent Document 2).

However, secondary batteries with the structure disclosed in Patent Document 2 have the problem that while they can release heat around the metal core, they are not effective at dissipating heat from other parts.

Japanese Patent Application Publication No. 10-321220 Japanese Patent Application Publication No. 10-092469

The present invention aims to provide a wound secondary battery that can improve the heat dissipation properties of the wound secondary battery and reduce the performance degradation caused by heat buildup.

To solve the above problems, the 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, the electrode laminate being characterized in that it is wound in a spiral shape.

In the above-mentioned wound secondary battery, a cone-shaped current collector may be in contact with the margins on both ends of the electrode laminate where no active material layer is formed, to allow current to flow and heat to diffuse.

The wound secondary battery of the present invention has a structure in which the strip-shaped electrode laminate is wound in a spiral shape while being shifted, so that the area of the portions at both ends of the strip-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 deterioration of battery performance due to temperature rise can be suppressed by improving heat dissipation.

FIG. 2 is an explanatory diagram of a layer structure of a wound type secondary battery. Schematic diagram of the relationship between the unwinding core and the winding core. 4A and 4B are schematic cross-sectional views of the winding shape of an electrode laminate as viewed from above and from the side. 3A and 3B are cross-sectional views of the first and second turns of the electrode laminate of the first embodiment. 11 is a cross-sectional view of the first and second turns of a conventional electrode laminate. FIG. FIG. 13 is a cross-sectional view of an electrode stack and a current collector that are wound with a staggered arrangement. Schematic diagram showing the battery shape. FIG. 11 is an explanatory diagram of a layer configuration according to a second embodiment. 13A and 13B are cross-sectional views of the first and second turns of an electrode laminate according to a second embodiment. FIG. 11 is a cross-sectional view of an electrode stack and a current collector according to a second embodiment.

The following describes in detail the embodiments of the present invention with reference to the drawings. Note that the present invention is not limited to the embodiments described below. In addition, in the embodiments described below, technically preferable limitations are imposed for carrying out the invention, but these limitations are not essential requirements for the present invention. Furthermore, equivalent members and the like may be given the same reference numerals and descriptions thereof may be omitted.

Figure 1 is an explanatory diagram of the layer structure of a wound secondary battery. Figure 1a shows the layer structure of one embodiment of the wound secondary battery of the present invention, and Figure 1b shows the layer structure of a conventional wound secondary battery. The basic layer structure is explained with reference to Figure 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 strip-shaped negative electrode 2, respectively.

The metal foil 5 may be, for example, 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 aforementioned metals, but is not limited to these.

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. Examples of inorganic compounds constituting the positive electrode active material include, but are not limited to, composite oxides represented by the composition formula Li _x MO ₂ or Li _y M ₂ O ₄ (where M is a transition metal, 0≦x≦1, 1≦y≦2), oxides having tunnel-shaped vacancies, metal chalcogenides with a layered structure, and chalcogen compounds containing lithium ions.

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.

As a method for forming each active material layer, any of the well-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.

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 depending on 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 layer structure is basically the same in conventional wound secondary batteries. 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 Figure 1a and the conventional wound secondary battery in Figure 1b.

(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. 1a. 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 figure) by the margin width a for each turn, and the negative electrode active material layer 7 and separator (short) 4 on the outer side of the negative electrode 2 wound on the outer side of the positive electrode 1 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, 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.

In contrast to this, Fig. 1b shows the positional relationship of the electrodes, which are wound without shifting and have a margin of width a at the end of the conventional band-shaped electrode. 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 Fig. 1b, since there is no margin of the substrate, only the end surface dissipates heat from the substrate.

To wind the positive electrode 1, separator 3, negative electrode 2, and separator (short) 4 inwardly and spirally around the core 10 on the side with the margin of the negative electrode 2 while maintaining the positional relationship of each layer shown in Figure 1a, 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, the positive electrode 1, separator 3, negative electrode 2, and separator (short) 4 can be wound in a spiral shape 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 Figure 2.

Schematic cross-sectional views of the electrode laminate 8 wound with offset and the electrode laminate 9 wound without offset, as seen from above and the side, are shown in Figures 3a and 3b, respectively. When the electrode laminate is 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. Figure 4 shows cross sections of the first and second turns of the electrode laminate 8 wound with offset. Figure 5 shows cross sections of the first and second turns of a normal electrode laminate 9 without offset. Although omitted in Figure 5, current-carrying tabs are generally installed periodically on the electrode laminate for current collection. When the electrode laminate is 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, even if the electrode positions shift, the surfaces of the active material layers of the positive electrode 1 and the negative electrode 2 can always be wound with their entire surfaces facing each other.

Conical collectors 12 and 13 for collecting current are placed in contact with the margins of the positive electrode 1 and negative electrode 2 of the spirally wound electrode laminate. Figure 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.

The inclination of the conical surfaces of the current collectors 12 and 13 is set at an angle that allows the current collectors 12 and 13 to contact the edges of the margins, 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, but are slightly offset, but this can be almost ignored if the width a is small. 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 of the base material is 0.02 mm, the length of the electrode laminate strip is 100 m, and the diameter of the winding core is 10 mm, the winding diameter of the secondary battery will be 196 mm.

In the above example, assuming that 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 a spiral offset and when it is wound without a spiral offset is shown in Table 1. By winding the metal foil with a spiral offset, the heat dissipation area increases by 100 m x 0.2 mm x 2 (positive and negative) = 40,000 ^mm2 to account for the margins, increasing the area from 8,000 ^mm2 to 48,000 ^mm2 , an increase of approximately six times. In addition, the circular portion of the top surface becomes conical by winding the metal foil with a spiral offset, increasing the surface area by approximately 1.2 times.

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

The electrode laminate, current collector, etc. are enclosed in a container such as a metal can or 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 materials and forming methods of the active material of the electrodes are not limited to those exemplified above. In other words, the present invention is characterized by the structure in which the electrodes are wound in a spiral shape and the shape of the conical collector, and the other components are not limited to the examples shown in this embodiment.

Second Embodiment
As the second embodiment, an example is shown in which only the metal foil 5, which is the substrate of the electrode laminate of the first embodiment, is enlarged to enlarge the margin, and a margin with a width b is provided on both sides of the electrode laminate where there is no active material layer. However, in order to prevent short circuits, the separator 3 and the 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.

The width of the blank portion, where there is no active material layer on either side, is b, and while maintaining the positional relationship shown in FIG. 8, the separator (short) 4 side is on the inside, and it is spirally wound around the core at the lower side of the figure, shifted by a width a per winding, as in the previous embodiment.

Figure 9 shows cross-sectional views of the first and second turns of the electrode, which is wound with the electrode laminate 8 shifted. Figure 10 shows a cross-sectional view of the state in which the conical collectors 12, 13 are in contact with the margins of the metal foil 5 from above and below. The margins of width b, which have no active material layers on either side, have space behind them, so by pressing the conical collectors 12, 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 collectors 12, 13. The increased contact area allows heat from the metal foil 5, which is the base material, to be more efficiently discharged to the collectors 12, 13. In addition, the extended margins are folded, so the volume of the battery does not increase.

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.

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

Claims (5)

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) a width of a margin on both ends of the electrode laminate where the active material layer is not formed; and b) a width of the electrode laminate that is spirally wound around a core, the electrode laminate being shifted by the width a per one winding . In the margin where the active material layer is not formed, the metal foil serving as the 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. The wound secondary battery according to claim 2, wherein the metal foil contains at least one of gold, silver, stainless steel, titanium, and platinum. 4. The wound secondary battery according to claim 1, wherein, in a state where the electrode laminate is wound in a spiral shape, both ends of the electrode laminate with which the current collector is in contact are inclined in the same direction relative to a winding axis to form inclined surfaces. 4. The wound secondary battery according to claim 1, wherein, in a state in which the electrode laminate is wound in a spiral shape, an end portion of the electrode laminate on a positive electrode side with which the current collector contacts and an end portion of the electrode laminate on a negative electrode side with which the current collector contacts are inclined in the same direction relative to a winding axis to form inclined surfaces.