JP2007128804A - battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery having a structure in which a heat generation amount of Joule heat due to an internal short circuit is small and a phenomenon in which a battery temperature rises excessively hardly occurs.
SOLUTION: The battery of the present invention includes a positive electrode in which a positive electrode active material is attached to the surfaces of positive current collector foils 30 and 34, and a negative electrode in which a negative electrode active material is attached to the surfaces of negative electrode current collector foils 40 and 42. And an electrode body including separators 22, 24, 26, 28 interposed between the positive electrode and the negative electrode. The separator is made of a thermoplastic resin, and at least one of the positive electrode current collector foil and the negative electrode current collector foil is made of a porous conductive sheet.
[Selection] Figure 3

Description

  The present invention relates to a battery. Specifically, the present invention relates to a battery with improved ability to suppress an excessive increase in temperature in the battery when an internal short circuit occurs.

When a physical impact such as dropping or damage is applied to a battery such as a lithium secondary battery, an internal short circuit may occur. When an internal short circuit occurs, Joule heat is generated at the location where the internal short circuit occurs, causing a phenomenon in which the battery temperature rises excessively. The excessive temperature rise here means rising to a temperature at which the active material constituting the electrode decomposes.
When an internal short circuit occurs, current concentrates on the internal short circuit. Joule heat is generated by the concentrated current. If current is concentrated to flow in a position where no active material exists, the temperature can be prevented from rising to a temperature at which the active material decomposes.
This type of technology is disclosed in Patent Document 1. In the technique of Patent Document 1, an exposed region where the positive electrode active material is not attached is provided in a part of the positive electrode where the positive electrode active material is attached. Similarly, an exposed region where the negative electrode active material is not attached is provided in a part of the negative electrode where the negative electrode active material is attached. The exposed area of the positive electrode and the exposed area of the negative electrode are provided at a position covering the outer periphery of the electrode body.
According to the battery disclosed in Patent Document 1, when an external physical impact such as dropping or damage is applied, an internal short circuit occurs between at least the positive electrode in the exposed region and the negative electrode in the exposed region covering the outer periphery of the electrode body. Arise. Since the current flows in a concentrated manner at a position where the active material does not exist, it should be possible to suppress the temperature rise to a temperature at which the active material decomposes.

JP-A-8-153543

According to the technique of Patent Document 1, a current can flow between the positive electrode in the exposed region and the negative electrode in the exposed region, and an excessive current does not flow through an internal short-circuited place where the active material exists. It should be. However, the effect is actually low.
When the present inventor researched the cause, an internal short-circuited portion generated between the positive electrode and the negative electrode in the exposed region covering the outer periphery of the electrode body is local, and the temperature becomes high in that portion, and the active material exists It was confirmed that the phenomenon of thermal decomposition of the active material by heat transfer occurred. Alternatively, the internal short-circuit location that occurs in the exposed area is local, and current alone cannot flow, and it is not possible to prevent the current from concentrating and flowing in the internal short-circuit location that occurs in the position where the active material exists. It was confirmed that the phenomenon occurred.

In the present invention, if an internal short circuit occurs, current concentration is prevented by performing a short circuit over a wide range.
The present invention is advantageously applied between the positive electrode in the exposed region and the negative electrode in the exposed region. In this case, current concentration that occurs in the exposed region can be mitigated, and a temperature increase in the exposed region can be suppressed. It is possible to suppress a phenomenon in which the active material is thermally decomposed by transferring heat to the location where the active material exists. Or it can suppress that an electric current concentrates on the internal short circuit location produced in the position where an active material exists, without flowing an electric current only in the internal short circuit location which arises in an exposure field.
The present invention may be applied to a place where an active material exists. If an internal short circuit occurs, current concentration can be prevented by short-circuiting over a wide range. In this case, a short-circuit current flows through the portion where the active material is present, but the concentration is mitigated and the temperature rise is suppressed.

  The battery of the present invention includes a positive electrode having a positive electrode active material attached to the surface of the positive electrode current collector foil, a negative electrode having a negative electrode active material attached to the surface of the negative electrode current collector foil, and a positive electrode and a negative electrode. An electrode body including the separator. The separator is made of a thermoplastic resin, and at least one of the positive electrode current collector foil and the negative electrode current collector foil is made of a porous conductive sheet.

When an internal short circuit occurs in the above electrode body, a short circuit current flows through the internal short circuit location, generating Joule heat. This heat causes the separator to melt. At the temperature at which the separator melts, the active material is not thermally decomposed.
If no holes are formed in the positive electrode current collector foil and the negative electrode current collector foil, the molten separator stays between the positive electrode and the negative electrode around the internal short-circuit point, and the molten separator moves between the positive electrode and the negative electrode around the internal short-circuit point. Keep insulation between them. The internal short circuit location remains in the local area where it first occurred, which causes high power concentrations.
In the above battery, since at least one of the positive electrode current collector foil and the negative electrode current collector foil is porous, the melted separator is absorbed by the pores. Short circuit to the periphery of the internal short circuit that occurred first. In the above battery, if an internal short circuit occurs, the battery is short-circuited over a wide range. For this reason, it is possible to prevent the short-circuit current from flowing in a concentrated manner.
In this specification, “porous” means having an opening on the surface in contact with the separator regardless of whether it is bottomed or bottomless. For example, the form which the continuous bubble penetrates the front and back of current collection foil may be sufficient, and the solid network shape branched in the current collection foil may be sufficient. If there is a hole having an opening on at least a surface in contact with the separator, the separator melt is absorbed into the hole.

The present invention is preferably applied to an exposed region where no active material is attached. That is, each of the positive electrode current collector foil and the negative electrode current collector foil is provided with an exposed region where no active material is attached, and at least one of the positive electrode current collector foil and the negative electrode current collector foil in the exposed region is It is preferable that it is composed of a porous conductive sheet.
In this case, if an internal short circuit occurs, a wide range of the exposed region is shorted. Since the short-circuit current flows through a wide short-circuit range formed in the exposed region, a large short-circuit current is prevented from flowing through a site where the active material exists. It is possible to suppress a temperature increase in the short-circuit range that occurs in the exposed region, and to prevent heat transfer to a temperature at which the active material decomposes.
The positive electrode current collector foil in the exposed region and the positive electrode current collector foil in the non-exposed region may be continuously extended from the same material, but may be different. There are no special restrictions as long as both are electrically connected. The positive electrode current collector foil in the exposed region and the positive electrode current collector foil in the non-exposed region may have the same thickness or different thicknesses. The same applies to the negative electrode current collector foil.

It is preferable that the positive electrode current collector foil and the negative electrode current collector foil in the exposed region cover the outer periphery of the electrode body.
The outer periphery of the electrode body is easily affected by external deformation and impact. When an internal short circuit occurs inside the electrode body, it is easy to obtain a relationship in which an internal short circuit has occurred even at the outer periphery. If an internal short circuit occurs, a wide area in the exposed area is shorted to prevent a large short circuit current from flowing through the active material. It is preferable that the current collector foil covers the outer periphery of the electrode body.

In the battery of the present invention, the porosity of the porous conductive sheet is particularly preferably not less than the volume% represented by the following formula.
Formula: A = {Y × (100−Z)} / X, in this formula:
X: Sum of the thickness of the porous positive electrode current collector foil and the porous negative electrode current collector foil Y: Thickness of the separator Z: Porosity (volume%) of the separator

  When the porosity of the porous conductive sheet was equal to or higher than the porosity represented by the above formula 1, when the separator was dissolved, it was dissolved in the pores of the conductive sheet adjacent to the dissolved separator. The separator can be absorbed. When the separator melt is absorbed into the pores, the substance that insulates between the positive electrode and the negative electrode disappears, and an internal short circuit occurs in a wide range.

The battery of the present invention is particularly preferably configured so that a load is applied from the outside to the inside of the electrode body.
When a load is applied from the outside to the inside of the electrode body, when the separator is melted, the melt is easily absorbed into the holes of the current collector foil. When the melt is absorbed into the pores, a wider contact area between the electrodes can be secured.
The method for applying a load to the electrode body is not particularly limited. For example, a load may be applied from the outside of the package that accommodates the electrode body, or an elastic member may be disposed inside the package and the load applied directly to the electrode body. Alternatively, a plurality of batteries may be assembled into an assembled battery, and a restraining load may be applied from the outside in the assembled battery state.

The main forms of the embodiments described in detail below are listed first.
(Mode 1) The battery is a lithium secondary battery.
(Mode 2) The electrode body is a wound electrode body that is wound with a separator interposed between the positive electrode and the negative electrode.
(Mode 3) The exposed region is formed on the entire outer peripheral surface of the electrode body.
(Mode 4) The current collector foil in the exposed region is thicker than the current collector foil in the power generation region.
By increasing the thickness of the outer current collector foil that is susceptible to external impact, the rigidity of the electrode body is improved. Even when an external impact is applied, the impact is less likely to be transmitted to the inside of the electrode body. An internal short circuit tends to occur at the outer periphery of the electrode body.
(Embodiment 5) Only one polarity current collector foil is porous.
(Mode 6) Only the current collector foil in the exposed region of one polarity is porous.
(Mode 7) Only the negative electrode current collector foil is porous.
In the lithium secondary battery, aluminum having a relatively low melting point is used for the positive electrode current collector foil. On the other hand, copper and nickel are employed for the negative electrode current collector foil, and the melting point is higher than that of aluminum, and it is difficult to melt even if an internal short circuit occurs. The holes disappear when the current collector foil melts. Therefore, in the lithium secondary battery, it is preferable that the negative electrode current collector foil using copper or nickel having a relatively high melting point is made porous rather than the positive electrode current collector foil using aluminum having a low melting point.
(Mode 8) In the porous sheet, the pores are formed in a three-dimensional network.
When an internal short circuit occurs when a metal such as a nail is pierced, the nail and the electrode sheet can be reliably in contact with each other.
(Mode 9) The pore diameter of the porous sheet is 1 mm or less.
When the area of the opening part of a void | hole is large, it will become difficult to ensure the contact area of a positive electrode sheet and a negative electrode sheet. If the hole diameter is 1 mm or less, loss of contact area due to opening of the hole can be suppressed during a short circuit.

<First embodiment>
The film package type lithium secondary battery of this example will be described.
FIG. 1 is a schematic diagram showing an outline of a lithium secondary battery 10 according to the present embodiment.
As shown in FIG. 1, the lithium secondary battery 10 according to the present embodiment roughly includes a package 12 made of a laminate film, an electrode body 20 accommodated in the package 12, and a projection protruding outside the package 12. A positive electrode lead terminal 13 and a negative electrode lead terminal 14 are provided.
The package 12 is configured by stacking two laminated films 16 and 17 and forming a heat welding portion 18 on the outside thereof.
An appropriate electrolyte is injected into the package 12 together with the electrode body 20. The electrolyte according to this example has a composition in which 1 mol / L LiPF ₆ is dissolved as a solute in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a ratio of 3: 7 (volume ratio). An electrolyte was used.

A rough configuration of the electrode body 20 will be described with reference to FIG. FIG. 2 is a schematic diagram showing the structure of the electrode body 20. As shown in FIG. 2, the electrode body 20 according to the present embodiment is a wound electrode body. The electrode body 20 includes a long positive electrode sheet 46, a long negative electrode sheet 36, and separators 22, 24, 26, and 28. The positive electrode sheet 46 includes a power generation region 42 to which an active material is attached and an exposed region 40 in which an active material layer is not formed and the current collector foil is exposed. The exposed area 40 of the positive electrode sheet constitutes the outermost periphery of the positive electrode sheet 46 in the electrode body 20. The negative electrode sheet 36 also includes a power generation region 34 where an active material is attached and an exposed region 30 where the current collector foil is exposed. The exposed area 30 of the negative electrode sheet is located on the outermost periphery of the negative electrode sheet 36 in the electrode body 20.
The electrode body 20 is first laminated in the order of the separator 24, the power generation region 34 of the negative electrode sheet 36, the separator 28, and the power generation region 42 of the positive electrode sheet, and is wound into a long shape using a winding machine or the like. Press. Next, along the broken line in FIG. 2, the power generation region 42 of the positive electrode sheet and the exposed region 40 of the positive electrode sheet are electrically connected, and the power generation region 34 of the negative electrode sheet 36 and the exposed region 30 of the negative electrode sheet are electrically connected. . The outermost separators 22 and 26 and the separators 24 and 28 interposed in the power generation regions 34 and 42 of both poles are also subjected to bonding treatment.

As described above, the positive electrode sheet 46 includes the power generation region 42 where the positive electrode active material is attached to both surfaces and the exposed region 40 where the positive electrode active material is not attached and the positive electrode current collector foil is exposed.
The power generation region 42 of the positive electrode sheet includes a positive electrode current collector foil made of a long aluminum foil having a thickness of 15 μm, and a positive electrode active material formed on both surfaces of the positive electrode current collector foil so that the total layer thickness is about 75 μm. It is composed of layers. By forming the positive electrode active material layer, the positive electrode active material is adhered to the positive electrode current collector foil.
The procedure for creating the power generation region 42 of the positive electrode sheet is as follows.
First, a positive electrode slurry for forming a positive electrode active material layer is prepared. The positive electrode slurry is prepared by mixing lithium nickelate (LiNiO ₂ ) as a positive electrode active material, carbon as a conductive material, carboxycellulose (CMC) and polytetrafluoroethylene (PTFE) as binders into water. adjust. Subsequently, it apply | coats on both surfaces of the aluminum foil which is current collection foil, and the porous layer by which the positive electrode active material was bound on both surfaces of current collection foil is obtained. And the power generation area | region 42 which has a positive electrode active material layer of the said layer thickness is formed by compressing the said porous layer with a roll press.
The exposed region 40 of the positive electrode sheet is composed of a long aluminum foil having a thickness of 100 μm. The exposed area 40 of the positive electrode sheet is wound so as to constitute the outermost periphery of the positive electrode sheet in the electrode body 20.

As described above, the negative electrode sheet 36 also includes the power generation region 34 in which the negative electrode active material is adhered to both surfaces and the exposed region 30 in which the negative electrode active material is not adhered and the current collector foil is exposed.
The power generation region 34 of the negative electrode sheet is composed of a negative electrode current collector foil made of a long copper foil having a thickness of about 10 μm and a negative electrode active material layer formed on both sides so that the total layer thickness is about 75 μm. ing. By forming the negative electrode active material layer, the negative electrode active material is adhered to the negative electrode current collector foil.
The procedure for creating the power generation region 34 of the negative electrode sheet is as follows.
First, a negative electrode slurry for forming a negative electrode active material layer is prepared. The negative electrode slurry is prepared by mixing carbon as a negative electrode active material, CMC as a binder and styrene butadiene block copolymer (SBR) with water. Subsequently, it apply | coats on both surfaces of copper foil which is current collection foil, and the porous layer by which the negative electrode active material was bound on both surfaces of current collection foil is obtained. Then, the porous layer is compressed by a roll press to form the power generation region 34 having the negative electrode active material layer having the layer pressure.
The exposed area 30 of the negative electrode sheet is composed of a long copper foil having a thickness of 100 μm. The exposed region of the negative electrode sheet is wound so as to constitute the outermost periphery of the negative electrode sheet in the electrode body. In the copper foil, a plurality of holes 38 are formed in a three-dimensional network (see FIG. 3). In FIG. 3, the three-dimensional network structure is schematically simplified and illustrated. The pores 38 are pores having a pore diameter of 1 mm or less. That is, the exposed region 30 of the negative electrode sheet is porous. The porosity of the exposed region 30 is 10% by volume. Therefore, the exposed region 30 of the negative electrode sheet 36 has an absorption volume of 0.010 cm ³ per cm ^2.

Separator 22, 24, 26, 28 is comprised from the microporous sheet | seat which consists of a composite resin of polyethylene (PE) which is polyolefin resin, and polypropylene (PP). When a microporous sheet is employed for the separators 22, 24, 26, 28, the separators 22, 24, 26, 28 can be impregnated with the electrolyte. The thickness of the separators 22, 24, 26 and 28 is about 25 μm. The porosity of the separators 22, 24, 26, and 28 is 60% by volume. When the 1 cm ² separators 22, 24, 26, and 28 are melted, 0.010 cm ³ of the melt flows out. The separators 22, 24, 26, and 28 are joined together with the separators 24 and 28 that are wound together with the power generation region of the positive electrode sheet and the power generation region of the negative electrode sheet, and the exposed region 40 of the positive electrode sheet and the exposed region 30 of the negative electrode sheet. The outermost separators 22 and 26 can be roughly divided. In the present embodiment, all the separators 22, 24, 26, and 28 have the same configuration.

As described above, the separators 22, 24, 26, and 28 are made of a composite resin of PP and PE. The melting point of polyolefin resin such as PP or PE is 130 ° C to 170 ° C. A separator made of a polyolefin resin melts in the range of 130 ° C to 170 ° C.
On the other hand, the active material uses LiNiO ₂ as the positive electrode active material and graphite as the negative electrode active material. Lithium composite oxides used as positive electrode active materials for lithium secondary batteries such as LiNiO ₂ and LiCoO ₂ decompose at about 180 ° C. or higher. When the positive electrode active material is locally heated at the internal short-circuited portion, the overheated state propagates to the surroundings and easily leads to a phenomenon in which a wide area of the electrode is overheated.
In the battery 10, the separator 26 is melted before the positive electrode active material is decomposed, and the area of the short-circuit portion is increased. If the area of the short circuit is large, current concentration at the time of short circuit does not occur. Therefore, in the battery 10 of this example, an excessive increase in the battery temperature due to the propagation of the decomposition of the positive electrode active material is unlikely to occur.
Note that a carbon material such as graphite used for the negative electrode active material of this example is hardly decomposed even under high temperature conditions. For this reason, in the battery 10, the excessive temperature rise resulting from decomposition | disassembly of a negative electrode active material does not arise easily.

  As shown in FIG. 1, the wound electrode body 20 including the positive electrode sheet 46, the separators 22, 24, 26, 28 and the negative electrode sheet 36 is accommodated in the package 12 together with the electrolyte. When the electrode body 20 of the lithium secondary battery of the present embodiment is housed in a case, a restraining load is applied from the outside of the electrode body 20 toward the winding center. In addition, when using as an assembled battery, you may restrain in the state which put together the some battery 10. FIG. Then, the package 12 is sealed, and the battery 10 according to this embodiment is completed.

<Second embodiment>
Since the battery of the second embodiment has the same configuration as that of the first embodiment except that the configuration of the separator is different, the overlapping description is omitted.
The separator is made of a material having a different melting point between the portion that is wound together with the power generation region of the positive electrode sheet and the power generation region of the negative electrode sheet, and the portion that is joined to the outside together with the exposed region of the positive electrode sheet and the exposed region of the negative electrode sheet. Yes. The part wound together with the power generation area of the electrode sheets of both electrodes employs a composite resin of polyethylene and polypropylene. The separator employs polyethylene that melts at a relatively low temperature in a portion sandwiched between the exposed region of the positive electrode sheet and the exposed region of the negative electrode sheet.

<Comparative example>
Since the lithium secondary battery of this comparative example has the same configuration as that of the first embodiment except that the configuration of the negative electrode sheet is different, the overlapping description is omitted.
The negative electrode sheet is composed of a power generation region in which the negative electrode active material is adhered to both surfaces and an exposed region in which the negative electrode active material is not adhered and the current collector foil is exposed, as in the above example.
The power generation region of the negative electrode sheet is composed of a negative electrode current collector foil made of a long copper foil having a thickness of about 10 μm and a negative electrode active material layer formed so that the total layer thickness is about 75 μm on both surfaces. Yes.
The exposed region of the negative electrode sheet is composed of a long copper foil having a thickness of 100 μm. The exposed region of the negative electrode sheet is wound so as to constitute the outermost periphery of the negative electrode sheet in the electrode body. No voids are formed in the copper foil in the exposed region according to this comparative example.

<Nail penetration test>
In order to investigate the effect of the battery of the present invention, a nail penetration test was performed on the lithium secondary batteries of Examples and Comparative Examples. In this test, the temperature of the battery was measured when an internal short circuit occurred due to nail penetration in the battery of the example and the comparative example. FIG. 3 is a schematic diagram showing a state in which a nail penetration test is performed on the battery of the first embodiment. FIG. 3A shows a state immediately after the nail 50 is inserted into the battery 10. FIG. 3B shows a state when the nail 50 is left in a state where it is stabbed.
The nail penetration test is a test in which a metal nail 50 is inserted from the outside of the battery 10 to forcibly short-circuit the inside. In this test, an iron nail 50 having a diameter of 2.5 mm was inserted at a speed of 100 mm / sec and left in a state where the nail 50 was stuck.

  In the battery of the first embodiment, the exposed region 30 of the negative electrode sheet has a porous structure. The exposed region 30 of the negative electrode sheet having such a structure has an absorption volume that can receive all of the melt when the separator 26 is melted. Even if the separator 26 melts due to the heat generated by the internal short circuit, the melt is absorbed in the holes 38 in the exposed region 30 of the negative electrode sheet. When a load is applied from the direction of the arrow X as in the battery 10 of the first embodiment, the melt of the separator 26 is easily absorbed by the holes 38 (see FIG. 3B). In the battery of the first embodiment, the melt of the separator 26 is absorbed by the holes 38, and a large contact area between the exposed area 40 of the positive electrode sheet and the exposed area 30 of the negative electrode sheet, that is, the area of the short-circuited portion can be ensured. It is thought that it was made.

In this test, as described above, the internal short circuit is forced by inserting the nail 50 into the battery 10, and the battery 10 is heated. Heat generation in the battery 10 first occurs from the outside of the electrode body 20 into which the nail 50 is inserted.
Further, as shown in FIG. 3A, in a state where the nail 50 is stuck in the electrode body 20, the short-circuit current flows through the contact between the nail 50 and the positive electrode sheet 46 and the contact between the nail 50 and the negative electrode sheet 36. . Such a contact is difficult to secure a connection state. For this reason, current concentration in which a short-circuit current flows in a narrow short-circuit portion occurs, and the battery temperature rises. The exposed region 40 of the positive electrode sheet is made of an aluminum foil having a relatively low melting point. In the exposed area 40 of the positive electrode sheet, the aluminum foil is melted by heat generation near the contact point with the nail 50. As shown in FIG. 3B, a gap 52 is formed between the nail 50 and the positive electrode sheet 46. When the gap 52 is formed, the connection state between the nail 50 and the positive electrode sheet is deteriorated. If the connection state deteriorates, the battery temperature may increase. On the other hand, since the exposed region 30 of the negative electrode sheet is made of a copper foil having a high melting point, it is unlikely to be melted by such heat generation.
In the battery 10 of the first embodiment, the exposed region 30 of the negative electrode sheet that is not easily melted is porous. Before the melting of the positive electrode sheet 46 proceeds, the melted product of the separator 26 is absorbed by the holes 38 in the exposed region 30 of the negative electrode sheet. For this reason, it is thought that the exposed area 40 of the positive electrode sheet and the exposed area 30 of the negative electrode sheet were able to contact in a wide area. As a result, in the battery 10 of the first example, it is considered that current concentration does not occur when an internal short circuit occurs, and heat generation due to Joule heat is suppressed.

The battery of the second embodiment employs a low melting point resin as a constituent material of the separator in the outer peripheral portion. In addition to the effect of the battery of the first embodiment, the separator melt is more quickly absorbed into the pores. Therefore, the contact area between the positive electrode sheet and the negative electrode sheet can be secured widely at an earlier stage. If the contact area between the positive electrode sheet and the negative electrode sheet is large, current concentration of the short-circuit current does not occur. As a result, it is considered that Joule heat was suppressed and an excessive temperature rise of the battery did not occur.
As described above, if the battery has a structure in which an internal short circuit occurs in a wide range, an excessive rise in temperature is suppressed.

In the battery of the comparative example, the positive electrode sheet and the negative electrode sheet in the outermost peripheral portion of the electrode body have a current collecting foil that is thicker than the inner side. However, no hole is formed in any polarity electrode sheet. In the battery of the comparative example as well, a restraining load is applied from the outside of the electrode body toward the center. However, if the pores are not formed, the separator melt is not absorbed and the intervening state is maintained. . Between the positive electrode sheet and the negative electrode sheet, a separator melt or a resin in which the melt solidifies is interposed between the positive electrode and the negative electrode. If such a substance is present, the area of the short-circuit portion between the positive electrode sheet and the negative electrode sheet is not ensured. If the area of the short circuit is small, current concentration occurs. Moreover, the aluminum used for the positive electrode sheet is melted and damaged when in the nail penetration state. Due to the melting damage of the current collector foil, the contact state between the nail and the positive electrode sheet becomes unclear and current concentration occurs. In the battery of the comparative example, current concentration at the time of short circuit is not eliminated. It is considered that Joule heat that reaches a battery temperature of 200 ° C. was generated because current concentration was not eliminated.
In addition, when the temperature in a battery rises to 200 degreeC or more, there exists a possibility that a positive electrode active material and a negative electrode active material may decompose | disassemble with a heat | fever. For example, the positive electrode active material of a lithium secondary battery undergoes decomposition in which the crystal of the active material itself collapses around 180 ° C. to 200 ° C. Since decomposition of the active material is accompanied by heat generation, it may propagate over the entire active material layer. The progress of the decomposition of the active material further increases the battery temperature. As a result, it causes overheating phenomena such as smoke.

  From the results of this test, the batteries of the first example and the second example having a structure in which the melt of the separator melted at the time of the internal short circuit is easily absorbed are internally short-circuited in a wide range, and the amount of Joule heat due to current concentration. Was found to be suppressed. By suppressing the generation of Joule heat, the battery temperature is unlikely to rise excessively. In the battery of the comparative example, the insulating material such as the separator melt remained between the positive and negative electrode sheets, so that it was considered that the contact area between the positive electrode sheet and the negative electrode sheet was not ensured and heat generation to a high temperature occurred.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
For example, in the battery of the above embodiment, an electrode body in which a set of a positive electrode, a separator, a negative electrode, and a separator is wound is adopted, but the present invention is not limited to this. The configuration of the present invention can also be applied to a battery that employs a laminated electrode body obtained by laminating a set of a positive electrode, a separator, a negative electrode, and a separator. When the technique of the present invention is applied to a battery having a stacked electrode body, an exposed region is formed in the bottom set in the stacking direction, the positive electrode and the negative electrode in the top set, and a plurality of holes are formed in the exposed portion. It is good to do so. With such a configuration, it is possible to suppress an increase in battery temperature as in the case of the battery of the above-described embodiment having a wound electrode body.
In the above embodiment, a battery having a laminate film package is employed, but the present invention is not limited to this configuration. For example, it may be a prismatic battery, a cylindrical battery having a metal package, or a battery having a synthetic resin package.

In the battery of the above embodiment, the thicknesses of the separators included in the same battery are all the same, but the thickness may be changed. The thickness may be changed for the purpose of giving priority to the separator interposed in the exposed areas of the positive electrode and the negative electrode. For example, only a region in contact with the holes of the current collector foil may employ a thinner separator than other regions.
Further, the porosity of the separator may be appropriately changed depending on the region. A separator with a high porosity has a low melt volume. If the volume of the separator melt is small, the proportion of pores in the conductive porous sheet can be reduced. By reducing the ratio of the holes, it is possible to secure a wider contact area between the positive electrode and the negative electrode when an internal short circuit occurs.

In the battery of the above embodiment, the power generation region and the exposed region of the positive electrode sheet are both made of aluminum, but both need not be made of aluminum. When applied to a general lithium secondary battery, aluminum excellent in stability at a high potential is preferable.
In the negative electrode sheet, both the power generation area and the exposed area are made of copper, but both need not be made of copper. These metal foils constituting the electrodes can be used without particular limitation as long as they are conductive metals. For example, metal materials such as aluminum, copper, titanium, nickel, iron, and stainless steel can be used.

  The technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings achieves a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

It is a side view of the battery which shows one Example of this invention. It is a schematic diagram which shows the structure of the electrode body which concerns on this invention. It is the schematic diagram which showed the mode of the nail penetration test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Battery 12 Film package 13 Positive electrode lead terminal 14 Negative electrode lead terminal 16, 17 Laminate film 18 Thermal welding part 20 Electrode body 22, 26 Separator of outer part 24, 28 Separator of electric power generation area 30 Exposed area of negative electrode sheet 34 Power generation of negative electrode sheet Area 36 Negative electrode sheet 38 Hole 40 Exposed area of positive electrode sheet 42 Power generation area of positive electrode sheet 46 Negative electrode sheet 50 Nail 52 Gap

Claims (6)

An electrode including a positive electrode having a positive electrode active material attached to the surface of the positive electrode current collector foil, a negative electrode having a negative electrode active material attached to the surface of the negative electrode current collector foil, and a separator interposed between the positive electrode and the negative electrode A battery having a body,
The separator is made of thermoplastic resin,
At least one of the positive electrode current collector foil and the negative electrode current collector foil is formed of a porous conductive sheet. Each of the positive electrode current collector foil and the negative electrode current collector foil is provided with an exposed region where no active material is attached,
2. The battery according to claim 1, wherein at least one of the positive electrode current collector foil and the negative electrode current collector foil in at least the exposed region is composed of a porous conductive sheet.   The battery according to claim 2, wherein the positive electrode current collector foil and the negative electrode current collector foil in the exposed region cover the outer periphery of the electrode body. The battery according to any one of claims 1 to 3, wherein the porosity of the porous conductive sheet is not less than the volume% represented by the following formula.
Formula: {Y × (100−Z)} / X
X: Sum of the thickness of the porous positive electrode current collector foil and the porous negative electrode current collector foil Y: Thickness of the separator Z: Porosity (volume%) of the separator   The battery according to any one of claims 2 to 4, wherein the separator in the exposed region is made of a material having a melting point lower than that of the remaining separator.   6. The battery according to claim 1, wherein a load is applied from the outside to the inside of the electrode body.

Images