JP5403020B2 - Secondary battery electrode - Google Patents

Description

  The present invention relates to a secondary battery electrode, and more particularly to a secondary battery electrode in which an active material is applied to the surface of a metal foil.

  Secondary batteries are widely used as a power source because they can be recharged and used repeatedly. In recent years, there has been a demand for reduction in the use of fossil fuels (restriction of carbon dioxide emissions). Secondary batteries used for main and auxiliary power sources such as electric vehicles and hybrid vehicles are charged and discharged with large currents and secondary batteries. Increased capacity of batteries is required.

  2. Description of the Related Art Secondary batteries such as nickel metal hydride secondary batteries and lithium ion secondary batteries use an electrode in which an active material is applied (supported) on a current collector made of metal foil. And by increasing the amount of the active material applied to the current collector, the output of the secondary battery (the value obtained by multiplying the discharge current by the discharge voltage) can be increased. However, the thickness of the active material applied to the metal foil cannot be increased too much. Therefore, many holes are formed in the active material application region of the metal foil to increase the application amount per unit area (see, for example, Patent Document 1).

  Further, in Patent Document 1, holes are uniformly formed in the metal foil except for a portion where the lead piece is formed or a portion where the lead piece is welded, and a non-penetrating protrusion is provided in a region where the hole is not formed. Is disclosed. This non-penetrating protrusion is formed by pressing the burr generated around the hole when a large number of holes are formed by pulling the metal foil from one side to the other side. It is formed for the purpose of performing smooth flattening when crushing and flattening.

JP 2011-40568 A

  Conventionally, the holes formed in the metal foil in order to increase the coating amount of the active material have been uniformly formed in the active material coating region. On the other hand, in general, as shown in FIG. 6, a lead portion 52 for connecting a current collecting lead (not shown) is formed on one end side in the width direction of the band-shaped current collector 51. The area excluding the area is an active material application area 53. In the secondary battery using the electrode having such a configuration, the current density flowing through the current collector (electrode) is high on the lead portion 52 side and on the side away from the lead portion 52, as indicated by arrows in FIG. Lower.

  However, since a plurality of holes (not shown) are uniformly formed in the metal foil in the active material application region 53 and the conductivity of the active material is smaller than the conductivity of the metal foil, the discharge of the secondary battery Sometimes power cannot flow toward the lead portion 52 in a state where the current density is large, and the current collection efficiency deteriorates. As a result, the output density of the secondary battery, that is, the output per unit volume or the unit weight of the secondary battery is reduced.

  The present invention has been made in view of the above problems, and its purpose is to improve the current collection efficiency, and to achieve both the improvement of the output density and the energy density of the secondary battery. It is to provide an electrode.

To achieve the above object, the invention according to claim 1, a secondary battery electrode active material is made from a coated electrode together with the sheet-like or plate-like metal in the hole is formed, the The electrode is formed in a band shape or a rectangular shape, the electrode is electrically connected to one long side of the pair of long sides of the electrode, and the hole has a hole area ratio per unit area. The hole is formed so as to become larger from the side where the electrode is electrically connected, and the hole extends from the long side opposite to the long side where the electrode is electrically connected. It is formed in an elliptical shape that is long in the direction perpendicular to the current collecting direction toward the long side on the electrically connected side . Here, “the side on which the electrodes are electrically connected” means the side where the current collecting member is connected by welding, soldering, or the like, or the portion that is integrally formed and serves as the current collecting member It means the side to do. The phrase “becomes larger with increasing distance” includes not only the case where the rate of increase changes continuously but also the case where it changes stepwise.

  In this invention, the hole is not formed uniformly in the sheet-like or plate-like metal constituting the electrode, but the opening rate per unit area of the hole is separated from the side where the electrode is electrically connected. It is formed to be as large as possible. That is, as the electrode is closer to the side where the electrode is electrically connected, for example, the portion connected to the current collecting member, the area of the portion where the hole is not formed in the metal is increased, the electric resistance is reduced, and the current is reduced. It becomes easy to flow. When discharging with a secondary battery, the current flows in a state where the current density increases as the electrode is closer to the portion connected to the electrode terminal of the secondary battery (for example, the portion connected to the current collecting member). However, in the past, the porosity was increased to increase the amount of active material applied (supported amount) per unit area with a constant porosity, so the electrode was connected to the electrode terminal of the secondary battery. I could not increase the amount of current flowing through the part. However, in this invention, since the electrical resistance per unit area of the electrode closer to the side where the electrode is electrically connected is smaller, the current collection efficiency is improved and the output density of the secondary battery is improved. In addition, the energy density can be improved.

The invention according to claim 2 is the invention according to claim 1, wherein the maximum value of the hole area ratio is 50% and the minimum value is 20%.
If the hole area ratio is too large, the electrode is easily damaged during the electrode pressing process after the active material is applied in the electrode manufacturing process, resulting in poor yield. In the present invention, if the maximum value of the hole area ratio is 50%, which is a normally used material or thickness, the electrode is set to a value that makes it difficult to damage the electrode during press working. A secondary battery electrode can be obtained. Further, when the hole area ratio is 20% or more, preferable values can be obtained as the capacity per unit electrode volume and the discharge performance.

The invention described in claim 3 is the invention described in claim 1 or 2, wherein the active material is applied in a state of filling the holes.
According to a fourth aspect of the present invention, in the third aspect of the present invention, the hole is formed in a state in which there is a burr around the hole, and the burr protrudes in the thickness direction of the metal. Conventionally, when forming a hole in the electrode, it is formed by etching or laser treatment so as not to generate burrs, or when burrs are generated by forming holes by punching, the burrs are crushed and flattened by pressing. It was. However, in this invention, since the burr protrudes in the thickness direction of the sheet-like or plate-like metal, the active material and the burr come into contact with each other, and the electric resistance is smaller than that of the active material in the thickness direction of the electrode. Therefore, the current can be collected also in the thickness direction of the electrode, and the current collection efficiency is higher than that in the case where there is no burr.

The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the electrode has a sheet shape, and one of the pair of long sides of the electrode has a long side. It is electrically connected to the current collecting member in a band shape, and the active material is applied to a portion other than the current collecting member that is electrically connected. As the configuration of the secondary battery, a positive electrode sheet formed of a strip-shaped secondary battery electrode and a negative electrode sheet formed of a strip-shaped secondary battery electrode are substantially stacked in a stacked state with a strip-shaped separator interposed therebetween. There is an electrode body that is wound into a long cylindrical shape, and the electrode body is housed in a battery case. In the configuration, a plurality of current collecting members are connected to one end side in the width direction of the secondary battery electrode, and the current collecting members are connected to the non-coated portion of the active material. In this invention, the electrode is in the form of a sheet, one end side is electrically connected to the current collecting member in a strip shape, and the active material is applied to a portion other than the current collecting member that is electrically connected Even if the secondary battery electrode is manufactured without previously setting the connection position of the current collecting member, the current collecting member can be connected to a desired position.

  A sixth aspect of the present invention is the invention according to any one of the first to fifth aspects, wherein the electrode is a wound type. In this invention, a winding type secondary battery is obtained by winding a positive electrode and a negative electrode formed of a sheet-like metal electrode formed in a band shape through a separator.

  ADVANTAGE OF THE INVENTION According to this invention, current collection efficiency improves and the electrode for secondary batteries which can make the improvement of the output density of a secondary battery and the improvement of an energy density compatible can be provided.

(A) is the schematic diagram which abbreviate | omitted a part of active material of the electrode for secondary batteries of one Embodiment, (b) is the partial expansion schematic diagram which shows the state of the burr | flash around a hole. The schematic perspective view of the electrode body by which the positive electrode sheet and the negative electrode sheet were wound on both sides of the separator. The schematic diagram of the state into which an electric current flows into a positive electrode sheet. The schematic diagram of the electrode for secondary batteries of another embodiment. The schematic diagram of the electrode for secondary batteries of another embodiment. The schematic diagram which shows the state of the current density of the electric current which flows into a collector.

Hereinafter, an embodiment embodying the present invention will be described with reference to FIGS.
As shown in FIG. 1A, the electrode for a secondary battery is composed of an electrode sheet 11 as an electrode. The electrode sheet 11 is formed with a hole 13 in a metal foil 12 as a sheet-like metal and an active material 14. It has been applied. An active material 14 is applied to the metal foil 12 so as to fill the holes 13. The width and length of the metal foil 12 are set corresponding to the size of the secondary battery in which the secondary battery electrode is used. In FIG. 1A, in order to make the hole 13 easier to understand, the ratio of the hole diameter to the width of the metal foil 12 is shown as about 1:13. The number of holes 13 formed to be 1/100 or less and formed per unit area of the metal foil 12 is much larger.

  In this embodiment, the electrode sheet 11 is formed in a band shape, and a connection portion 16 to which a current collecting lead 15 as a current collecting member is electrically connected is formed in a band shape on one end side. Is applied to portions other than the connecting portion 16. That is, one end side of the electrode sheet 11 is electrically connected to the current collecting lead 15 in a strip shape, and the active material 14 is applied to a portion other than the belt-shaped portion electrically connected to the current collecting lead 15. ing. The applied active material differs depending on the type of secondary battery such as a nickel metal hydride battery and a lithium ion battery. Moreover, even if it is the same kind of secondary battery, what is applied to the electrode sheet 11 for the positive electrode is different from that applied to the electrode sheet 11 for the negative electrode.

  The holes 13 are not formed uniformly on the entire metal foil 12, but the opening ratio per unit area is farther from the side where the electrode sheet 11 is electrically connected, that is, the current is collected from the current collecting leads 15. It is formed so that it becomes large, so that it leaves | separates from the strip-shaped part currently connected.

  The maximum value of the open area ratio is set to a value that does not damage the electrode sheet 11 when the metal foil 12 is pressed after the active material 14 is applied in the manufacturing process of the electrode sheet 11, and the minimum value is a value per unit electrode volume. It is set to a value at which a preferable value is obtained as the capacity and the discharge performance. The maximum value of the open area ratio is 50%, and the minimum value is 20%.

  As shown in FIG. 1B, the hole 13 is formed in a state where there are burrs 17 around it, and the burrs 17 and the holes 13 are formed with the burrs 17 protruding in the thickness direction of the metal foil 12. An active material 14 is applied to the metal foil 12 so as to be buried.

Next, the operation of the secondary battery electrode configured as described above will be described.
As shown in FIG. 2, an electrode body 19 is formed by winding in a substantially long cylindrical shape in a laminated state in which a strip-shaped separator 18 is sandwiched between a positive electrode sheet 11p and a negative electrode sheet 11n. Is housed in a battery case (not shown) together with an electrolyte solution (not shown) to form a secondary battery. In FIG. 2, the current collecting lead of the negative electrode sheet 11n is not shown.

  When the secondary battery is discharged (output), the current is taken out from the current collecting lead 15 of the positive electrode sheet 11p. As shown by the arrows in FIG. 3, the current is connected to the current collecting lead 15. The current flows from the side opposite to the portion 16 toward the connecting portion 16 side, and the current density is larger at the closer to the connecting portion 16 than at the far side. The holes 13 are not uniformly formed in the metal foil 12 constituting the electrode sheet 11p for the positive electrode, but are electrically connected to the current collecting leads 15 as the opening ratio of the holes 13 is far from the connecting portion 16. It is formed so that it becomes large, so that it leaves | separates from the strip-shaped part currently made. Therefore, the closer the electrode sheet 11p for the positive electrode is to the connection portion 16, the larger the area of the portion where the hole 13 is not formed in the metal foil 12, the electric resistance is reduced, and the current easily flows.

  When discharging with a secondary battery, the current flows in a state where the current density increases as it is closer to the connecting portion 16 of the current collecting lead 15. Conventionally, however, the open area ratio is constant and the active material 14 per unit area is constant. Since the hole area ratio was increased in order to increase the coating amount (loading amount), the amount of current flowing through the portion near the connection portion 16 of the current collecting lead 15 could not be increased. However, in the embodiment, since the positive electrode sheet 11p has a smaller electrical resistance per unit area in the portion closer to the connection portion 16, the current collection efficiency is improved, the output density of the secondary battery is improved, and the energy density is increased. Can be improved at the same time. The power density means the power (unit W) divided by the weight or volume of the battery (W / kg or W / l). The energy density means a value obtained by dividing the amount of energy of the battery by the weight or volume of the battery (Wh / kg or Wh / l).

<Example>
In order to confirm the influence of the aperture ratio of the holes 13 formed in the metal foil 12, a secondary battery is formed using an electrode sheet in which the holes 13 are uniformly formed, and the capacity per electrode volume of the secondary battery The high rate discharge performance at 1000 mAh discharge was measured. Table 1 shows the results obtained by changing the thickness of the metal foil 12 and the aperture ratio of the holes 13 as an electrode sheet. The hole diameter of each hole 13 was 1.5 μm. In addition, the capacity | capacitance per electrode volume in Table 1, and the value of the high-rate discharge performance at the time of 1000 mAh discharge are relative values.

表１から、電極体積当たりの容量は、金属箔１２の厚さが薄い方が大きくなる傾向が確認された。また、金属箔１２の厚さが同じ場合は、開孔率が大きい方が大きくなる傾向があり、開孔率が２０％より小さい場合は、９００未満となり不合格となった。

From Table 1, the capacity | capacitance per electrode volume confirmed the tendency for the one where the thickness of the metal foil 12 is thin to become large. Moreover, when the thickness of the metal foil 12 was the same, the one with a large hole area ratio had a tendency to become large, and when the hole area ratio was smaller than 20%, it was less than 900 and it failed.

  Regarding the high rate discharge performance at 1000 mAh discharge, the influence of the thickness of the metal foil 12 and the hole area ratio is not as great as in the case of the capacity per electrode volume, but when the hole area ratio is less than 20%, it is less than 80. Passed.

  Further, when the hole area ratio is 50%, wrinkles are generated in the connection portion 16 where the active material 14 is not applied during electrode pressing. When the hole area ratio is larger than 50%, the electrode sheet is easily damaged during electrode pressing. Conceivable.

From the above, it was confirmed that the aperture ratio of the holes 13 is preferably 20% or more and 50% or less.
According to this embodiment, the following effects can be obtained.
(1) The electrode for the secondary battery is composed of an electrode (electrode sheet 11) in which a hole 13 is formed in a sheet-like metal (metal foil 12) and an active material 14 is applied, and the hole 13 per unit area. Is formed such that the larger the distance from the side to which the electrode is electrically connected (the connecting portion 16 to which the current collecting lead 15 is electrically connected), the greater the distance is. Accordingly, the current collection efficiency is improved, and both the improvement of the output density and the energy density of the secondary battery can be achieved.

  (2) The maximum value of the hole area ratio is set to 50%. When the aperture ratio is too large, the electrode is easily damaged during the electrode pressing process after the active material 14 is applied in the manufacturing process of the electrode (electrode sheet 11), and the yield deteriorates. However, if the maximum value of the hole area ratio is 50%, the electrode is difficult to be damaged at the time of pressing the electrode with a normally used material or thickness, and an electrode for a secondary battery can be obtained with a high yield.

(3) Since the minimum value of the hole area ratio is set to 20%, preferable values can be obtained as the capacity per unit electrode volume and the discharge performance.
(4) The active material 14 is applied in a state of filling the holes 13, and the holes 13 are formed in a state where there are burrs 17 around them, and the burrs 17 protrude in the thickness direction of the metal foil 12. . Therefore, the burr 17 protruding in the thickness direction of the metal foil 12 comes into contact with the active material 14, and there is a portion where the electric resistance is smaller than that of the active material 14 in the thickness direction of the electrode (electrode sheet 11). It will be. Accordingly, the current can be collected also in the thickness direction of the electrode sheet 11, and the current collection efficiency is higher than when the burr 17 is not provided.

  (5) The electrode has a sheet shape, and one end side is electrically connected to the current collecting member (current collecting lead 15) in a band shape, and the active material 14 is electrically connected to the current collecting member. It is applied to the part. Therefore, even if the secondary battery electrode is manufactured without previously setting the connection position of the current collecting lead 15, the current collecting lead 15 can be connected to a desired position.

  (6) The electrode is a wound type. Therefore, the positive electrode (the positive electrode sheet 11p) and the negative electrode (the negative electrode sheet 11n) formed of a sheet-like metal electrode formed in a belt shape are wound by winding them through the separator 18. A type electrode body 19 is obtained, and a wound type secondary battery is obtained using the electrode body 19.

The embodiment is not limited to the above, and may be embodied as follows, for example.
The electrode sheet 11 is not limited to the configuration in which the connection portion 16 is formed in a band shape on one end side. For example, as shown in FIG. 4, the connecting portion 16 may be formed so as to extend substantially from the one end side in the width direction of the strip-shaped metal foil 12 to the other end side by the width of the current collecting lead 15. In this case, it is preferable that a plurality of connection portions 16 are provided. And the hole 13 is formed so that the hole area ratio may become so large that it is away from the connection part 16 instead of changing from the one end side of the width direction of the metal foil 12 toward the other end side.

  As shown in FIG. 5, a plurality of connection portions 16 may be provided at predetermined positions on one end side in the width direction of the strip-shaped metal foil 12. In this case, it is determined in advance in which position of the electrode sheet 11 the current collecting lead 15 is provided, and the hole 13 is formed with reference to that position. In this embodiment, the application area of the active material 14 can be increased in the metal foil 12 having the same size as compared with the case where the connection portion 16 is provided on the entire one end side of the metal foil 12.

The hole diameter is not limited to 1.5 μm in the embodiment, and may be larger or smaller than 1.5 μm.
The hole 13 is not limited to a circular shape such as an elliptical shape or an oval shape, and may be formed in an elliptical shape having a long vertical direction with respect to the current collecting direction. In that case, it is hard to damage at the time of electrode manufacture.

The thickness of the metal foil 12 is not limited to 20 μm to 100 μm used in the examples, and may be thicker than 100 μm or thinner than 20 μm.
A structure in which the active material 14 is applied to the metal foil 12 in the state where the burr 17 does not exist around the hole 13 may be adopted.

  The electrode sheet 11 is formed in a belt shape, and is a winding type in which the electrode body 19 is configured by winding the electrode sheet 11p for the positive electrode and the electrode sheet 11n for the negative electrode 11n in a laminated state in a substantially long cylindrical shape with the separator 18 in between. It is not limited to those suitable for secondary batteries. For example, the positive electrode sheet 11p, the negative electrode sheet 11n, and the separator 18 may be wound into a cylindrical shape and applied to a cylindrical secondary battery, or the rectangular positive electrode sheet 11p, the negative electrode sheet 11n, and the separator It may be applied to a secondary battery in which a rectangular parallelepiped electrode body 19 configured by stacking 18 in a plurality of layers is used.

  ○ The configuration in which the aperture ratio per unit area of the holes 13 formed in the metal foil 12 is a target value is a configuration in which the number of the holes 13 formed per unit area of the metal foil 12 is changed with the same hole diameter. However, the number of holes 13 formed per unit area is the same, and the hole diameter may be changed, or both the structures may be used in combination.

○ The hole area ratio is not limited to a continuously changing configuration, and may be a configuration that changes stepwise or a configuration in which both are mixed.
The electrode may have a structure in which the hole 13 is formed in a plate-like metal instead of a sheet and the active material 14 is applied.

The following technical idea (invention) can be understood from the embodiment.
(1) A secondary battery comprising the secondary battery electrode according to any one of claims 1 to 6.

  DESCRIPTION OF SYMBOLS 11 ... Electrode sheet | seat as an electrode, 12 ... Metal foil as a sheet-like metal, 13 ... Hole, 14 ... Active material, 15 ... Current collection lead as a current collection member, 17 ... Burr.

Claims (6)

An electrode for a secondary battery comprising an electrode in which holes are formed in a sheet-like or plate-like metal and an active material is applied,
The electrode is formed in a band shape or a rectangular shape, and the electrode is electrically connected on one long side of the pair of long sides of the electrode,
The hole is formed so that a hole area ratio per unit area increases as the distance from the side to which the electrode is electrically connected increases .
The hole is long in a direction perpendicular to the current collecting direction from the long side opposite to the long side on the side to which the electrode is electrically connected to the long side on the side to which the electrode is electrically connected. An electrode for a secondary battery, characterized by being formed in an elliptical shape .   The secondary battery electrode according to claim 1, wherein the maximum value of the aperture ratio is 50% and the minimum value is 20%.   The secondary battery electrode according to claim 1, wherein the active material is applied so as to fill the hole.   4. The electrode for a secondary battery according to claim 3, wherein the hole is formed with a burr around the hole, and the burr protrudes in a thickness direction of the metal. 5. The electrode has a sheet shape, and is electrically connected to the current collecting member in a strip shape on one of the long sides of the electrode, and the active material is electrically connected to the current collecting member The electrode for a secondary battery according to any one of claims 1 to 4, wherein the electrode is applied to a portion other than being applied.   The electrode for a secondary battery according to claim 1, wherein the electrode is a wound type.

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