JP2007087814A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery whose safety is improved by reliably suppressing temperature rise of the battery due to internal short-circuiting by external shock and heat generation in excessive charging. <P>SOLUTION: A lithium secondary battery has an electrode body, having a positive electrode in which a positive electrode active material layer is formed on the surface of a positive electrode collector made of aluminum foil, and a negative electrode 30 in which negative electrode active material layers 34, 36 are formed on the surface of a negative electrode collector 32 made of copper foil. The layer thickness of the positive electrode active material layer to the thickness of the positive electrode collector and that of the negative electrode active material layer to the thickness of the negative electrode collector are 2.5 or smaller and 3.5 or smaller, respectively. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery. Specifically, when a local heat generation occurs in a lithium secondary battery, the lithium secondary battery has an improved ability to prevent the phenomenon of local overheating by transferring the heat to the surroundings. About.

  The lithium secondary battery includes a positive electrode having a positive electrode active material having the ability to occlude and release lithium ions, a negative electrode having a negative electrode active material having an ability to release and occlude lithium ions, and an electrolyte. A typical lithium secondary battery has a positive electrode in which a positive electrode active material layer is formed on the surface of a positive electrode current collector made of aluminum foil, and a negative electrode active material layer on the surface of a negative electrode current collector made of copper foil. A negative electrode. A large battery capacity can be obtained by ensuring a wide area where the positive electrode active material layer and the negative electrode active material layer face each other. In order to obtain a small-sized and large-capacity battery, it is necessary to accommodate a large-area positive electrode and a large-area negative electrode in a compact manner, and the positive electrode and the negative electrode (hereinafter collectively referred to as electrodes) are closely connected via a separator. It is housed in a sealed container in an overlapping state.

If the lithium secondary battery is overcharged or a mechanical impact is applied to the lithium secondary battery, an internal short circuit may occur, and a phenomenon may occur in which heat is generated locally at the location where the internal short circuit occurs. When an internal short circuit occurs, as described above, since the positive electrode and the negative electrode are accommodated in a closely overlapped state via the separator, locally generated heat is not easily transmitted to the surroundings, and overheating locally. The phenomenon is likely to occur. When a positive electrode active material or a negative electrode active material (hereinafter collectively referred to as an active material) is locally heated, the overheated state propagates to the surroundings, and is likely to lead to a phenomenon in which a wide area of the electrode is overheated.
There is a need for a technique for preventing the occurrence of local overheating by efficiently transferring heat to the surroundings even if local heat generation occurs.

  Therefore, a technique disclosed in Patent Document 1 has been proposed. In this technique, when the electrode body is configured by closely stacking the positive electrode and the negative electrode with a separator interposed therebetween, the current collector is thickened in the electrode located outside the electrode body, and the electrode located inside the electrode body is used. Reduce the thickness of the current collector. In the technique of Patent Document 1, if an internal short circuit occurs, it occurs in an outer portion of the electrode body, and the portion is overheated locally by increasing the thickness of the current collector. This prevents the occurrence of a phenomenon that propagates to In the technique of Patent Document 1, the electrode body is miniaturized by using a thin current collector at a portion located inside the electrode body where an internal short circuit is not caused.

JP 2002-110170 A

The battery described in Patent Document 1 requires two types of current collectors, one with a normal thickness and one with a thicker outer current collector than usual. Since two types of current collectors are required, the manufacturing work of the electrode body becomes complicated.
Further, in the technique of Patent Document 1, it is said that an internal short circuit does not occur inside the electrode body, but actually an internal short circuit also occurs inside the electrode body due to overcharge or the like. In the technique of Patent Document 1, when an internal short circuit occurs inside the electrode body, the current collector cannot be efficiently transferred to the surroundings because the current collector is thin, and the occurrence of a local overheating phenomenon can be prevented. Can not.

  If a thick current collector is used even inside the electrode body, the above problem is solved. However, when the thick outer current collector described in Patent Document 1 is used even inside the electrode body, the volume of the electrode body increases. In the technique described in Patent Document 1, quantitative research on the thickness of the electrode body necessary to prevent the occurrence of local overheating by transferring local heat generated due to an internal short circuit to the surroundings has advanced. Not in. Since there has been no research on the thickness necessary to prevent the occurrence of local overheating, the thickness of the outer current collector is set with a margin (to prevent the occurrence of local overheating). If it is used for the entire electrode body, the volume of the electrode body will increase.

  The lithium secondary battery of the present invention has a positive electrode in which a positive electrode active material layer is formed on the surface of a positive electrode current collector made of aluminum foil, and a negative electrode active material layer on the surface of a negative electrode current collector made of copper foil. The ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector is 2.5 or less, and the thickness of the negative electrode active material layer relative to the thickness of the negative electrode current collector is The ratio is 3.5 or less.

  According to the quantitative analysis of the present inventors, the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector made of aluminum foil is 2.5 or less, and the thickness of the negative electrode current collector made of copper foil When the ratio of the layer thickness of the negative electrode active material layer to 3.5 is 3.5 or less, even when local heat generation due to an internal short circuit occurs, the active material is overheated by efficiently transferring heat to the surroundings. It was confirmed that it can be prevented. It was confirmed that when the ratio of the thickness of the active material layer to the thickness of the current collector is controlled to the above-mentioned conditions in both the positive electrode and the negative electrode, the active material can be prevented from being overheated locally.

  If the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector is 3.1 or less, restrictions on the positive electrode current collector are lifted, and a normally used thin positive electrode current collector is sufficient. Was also confirmed.

  Copper constituting the negative electrode current collector has high thermal conductivity. When the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector is 3.1 or less, the heat capacity of the negative electrode current collector is large and the heat transfer efficiency is high. If the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector is 3.1 or less, local heat generation due to an internal short-circuit is absorbed by the negative electrode current collector and at the same time efficient around It is possible to prevent the active material from being overheated locally. If the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector is 3.1 or less, the active material is prevented from being overheated locally without increasing the thickness of the positive electrode current collector. it can.

According to the lithium secondary battery of the present invention, even if an internal short circuit occurs and local heat generation occurs, the heat is efficiently transferred to the surroundings using the current collector, and the active material is overheated. Can be prevented. Occurrence of a phenomenon that a wide range of the active material layer is overheated can be prevented, and a lithium secondary battery that can be used safely can be realized.
Moreover, it is sufficient to prepare one type of positive electrode current collector and one type of negative electrode current collector, which can be easily manufactured.

The main features of the embodiments described in detail below are listed first.
(Mode 1) A lithium composite oxide is used as a positive electrode active material. When lithium composite oxide is used for the positive electrode active material, high battery performance can be realized. However, when the lithium composite oxide is exposed to a high temperature (for example, 170 ° C. or higher), lithium ions are detached from the crystal lattice and the crystal structure is destroyed, and heat is generated at this time. When a short circuit occurs in a part of the electrode spreading in a plane and heat is generated, it is transferred to the surrounding lithium composite oxide to heat the surrounding lithium composite oxide. When the surrounding lithium composite oxide is overheated, the crystal structure of the surrounding lithium composite oxide is destroyed, and new heat is generated. As a result, the surrounding lithium composite oxide is overheated and a chain of heat is generated, and the crystal structure of the lithium composite oxide collapses (thermal runaway) in all of the electrodes that expand in a plane in a short time. Arise. When thermal runaway occurs, abnormal events such as smoke are likely to occur. A battery using a lithium composite oxide as a positive electrode active material requires a technique for preventing the occurrence of thermal runaway.
Therefore, even if a short circuit occurs in a part of the electrode spreading in a plane and local heat generation occurs, it is important to have a technology that prevents the crystal structure from being overheated to a temperature at which it collapses. Heat transfer technology is effective. Thermal runaway does not start if it can be efficiently transferred to the surroundings to prevent overheating to a temperature at which the crystal structure collapses.
The technique of the present invention is particularly useful for a battery using a lithium composite oxide as a positive electrode active material.
(Mode 2) A lithium composite oxide having a spinel crystal structure is used as the positive electrode active material. Lithium composite oxide having a spinel crystal structure achieves high battery performance, but thermal runaway tends to start. According to the technology of the present invention, it is possible to use a lithium composite oxide having a spinel type crystal structure that easily undergoes thermal runaway, and high battery performance can be obtained.
(Mode 3) A lithium composite oxide having a layered rock salt type crystal structure is used as the positive electrode active material. The lithium composite oxide having a layered rock salt type crystal structure realizes a high battery capacity, but is likely to start a thermal runaway. According to the technology of the present invention, it is possible to use a lithium composite oxide having a layered rock salt type crystal structure that is likely to be thermally runaway, and high battery performance can be obtained.
(Form 4) Any one of lithium nickelate (LiNiO ₂ ) having a layered rock salt type crystal structure, lithium cobaltate (LiCoO ₂ ), and lithium manganate (LiMn ₂ O ₄ ) having a spinel type crystal structure is used as a positive electrode Used for active materials.
(Form 5) The positive electrode active material layer is formed on both surfaces of the positive electrode current collector.
(Mode 6) The lithium secondary battery uses graphite as a negative electrode active material.
(Form 7) The negative electrode active material layer is formed on both surfaces of the negative electrode current collector.
(Embodiment 8) The electrode body of the lithium secondary battery is a wound electrode body.
(Embodiment 9) The sealed container of the lithium secondary battery is composed of a laminate film formed in a bag shape.
(Mode 10) A positive electrode current collector comprising an aluminum foil, a positive electrode active material comprising a lithium composite oxide having a crystal structure, a negative electrode current collector comprising a copper foil, and a negative electrode active material, The ratio of the thickness of the positive electrode active material layer to the thickness of the body is 0.3 to 2.5, and the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector is 1.0 to 3.5. It is.
(Form 11)
A negative electrode active material layer is formed on the surface of a negative electrode current collector made of copper foil, and the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector is 1.0 to 3.5.

<Example 1>
The film package type lithium secondary battery of this example will be described with reference to FIGS. FIG. 1 is a schematic diagram showing an outline of a lithium secondary battery 10 according to the present embodiment. FIG. 2 is a schematic view showing the electrode body 20. FIG. 2 shows a partially disassembled state in order to show the wound state of the electrode body 18. FIG. 3 is a schematic view showing a cross section of the positive electrode sheet 30 according to the present example. FIG. 4 is a schematic view showing a cross section of the negative electrode sheet 40 according to this example.

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 protrusion outside the package 12. And a negative electrode lead terminal 14 projecting out of the package.
The package 12 is configured by combining two laminate films 16 and 17 and forming a heat welding portion 18 over the outer periphery thereof.
An appropriate electrolyte is injected into the package 12 together with the electrode body 20. Electrolyte according to the present embodiment, ethylene carbonate (EC) and diethyl carbonate (DEC) is 3: 7 in a solvent are mixed in a ratio (volume ratio), a composition obtained by dissolving LiPF ₆ of 1 mol / L as a solute An electrolytic solution was used.

A rough configuration of the electrode body 20 will be described. 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 30, a long negative electrode sheet 40, and two long separators 22 and 24. These sheets are laminated in the order of the separator 22, the positive electrode sheet 30, the separator 24, and the negative electrode sheet 40, wound in a longitudinal direction using a winding machine or the like, and pressed in a radial direction to be wound in a flat shape. The electrode body 20 made is produced. The configurations of the positive electrode sheet 30 and the negative electrode sheet 40 will be described in detail later with reference to FIGS. 3 and 4.
At one end of the electrode body 20, one end of the positive electrode lead terminal 13 formed in a plate shape from an aluminum material is connected (fixed) to the positive electrode sheet 30. At the other end of the electrode body 20, one end of the negative electrode lead terminal 14 formed in a plate shape (the same shape as the positive electrode terminal 13) with a copper material is connected (fixed) to the negative electrode sheet 40. Connection between the terminals 13 and 14 and the electrode body 20 can be performed by ultrasonic welding or the like.

Next, the positive electrode sheet 30 will be described with reference to FIG. FIG. 3 shows the configuration of the positive electrode sheet 30 according to this example.
The positive electrode sheet according to this example includes a positive electrode current collector 32 made of a long aluminum foil having a thickness of about 33 μm (t3), a positive electrode active material layer 34 having a layer thickness of 36.5 μm (t1), a layer The positive electrode active material layer 36 has a thickness of 36.5 μm (t2). The total thickness (t1 + t2) of the positive electrode active material layers 34 and 36 is about 73 μm. The positive electrode sheet 30 is manufactured so that the ratio of the total thickness (t2 + t3) of the positive electrode active material layers 34 and 36 to the thickness (t1) of the positive electrode current collector 32 is about 2.2.

The production procedure of the positive electrode sheet 30 is as follows.
First, a positive electrode slurry for forming the positive electrode active material layers 34 and 36 was prepared. The positive electrode slurry was prepared by mixing LiNiO _{2 as} a positive electrode active material, acetylene black as a current collector, and carboxycellulose (CMC) and polyethylene tetrafluoroethylene (PTEE) as binders in water. The content of each component of the positive electrode slurry (other than water), LiNiO ₂ 87 wt%, acetylene black 10 wt%, CMC is 2 mass%, PTFE is 1% by mass. Next, the positive electrode slurry was applied to both surfaces of the positive electrode current collector 32 to obtain a porous layer in which the positive electrode active material was bound to both surfaces of the current collector. Then, the porous layer was compressed by a roll press to form the positive electrode active material layers 34 and 36 having the layer thickness. With the above procedure, the positive electrode sheet 30 having the above-described configuration was obtained.

Next, the negative electrode sheet 40 will be described with reference to FIG. FIG. 4 shows the configuration of the negative electrode sheet 40 according to this example.
The negative electrode sheet according to this example includes a negative electrode current collector 42 made of a long copper foil having a thickness of about 22 μm (T3), a negative electrode active material layer 44 having a layer thickness of 38.5 μm (T1), The negative electrode active material layer 46 has a thickness of 38.5 μm (T2). The total thickness (T1 + T2) of the negative electrode active material layers 44 and 46 is about 77 μm. The negative electrode sheet 40 is produced so that the ratio of the total thickness (T2 + T3) of the negative electrode active material layers 44 and 46 to the thickness (T1) of the negative electrode current collector 42 is about 3.5.

The production procedure of the negative electrode sheet 40 is as follows.
First, a negative electrode slurry for forming the negative electrode active material layers 44 and 46 was prepared. The negative electrode slurry was prepared by mixing graphite powder as a negative electrode active material, CMC as a binder and styrene-butadiene block copolymer (SBR) in water. The content of each component (other than water) contained in the negative electrode slurry was 98% by mass for graphite, 1% by mass for CMC, and 1% by mass for SBR. Next, the negative electrode slurry was applied to both surfaces of the negative electrode current collector 42 to obtain a porous layer in which the negative electrode active material was bound to both surfaces of the negative electrode current collector 42. Then, the porous layer was compressed by a roll press to form negative electrode active material layers 44 and 46 having the thickness. With the above procedure, the negative electrode sheet 40 having the above-described configuration was obtained.

The produced positive electrode sheet 30 and negative electrode sheet 40 are laminated together with two separator sheets 22 and 24 (here, a porous polyethylene sheet is used), and the laminated sheet is wound to produce a wound electrode body 20. did. The electrode body 20 was accommodated in the package 12 together with the electrolytic solution, and the lithium secondary battery 10 according to this example was completed.
The thickness of the positive electrode current collector in the lithium secondary battery of Example 1, the ratio of the layer thickness of the positive electrode active material layer to the thickness of the positive electrode current collector, the thickness of the negative electrode current collector, and the negative electrode current collector Table 1 shows the ratio of the layer thickness of the negative electrode active material layer to the thickness. Table 1 also shows positive electrode sheets and negative electrode sheets of other examples and comparative examples.

<Example 2>
The lithium secondary battery of this example includes the thickness of the positive electrode current collector, the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector, the thickness of the negative electrode current collector, Except that the ratio of the thickness of the negative electrode active material layer to the thickness was different, the configuration was the same as in Example 1, and the same procedure was used.
As shown in Table 1, the positive electrode sheet according to this example has a positive electrode current collector made of a long aluminum foil having a thickness of about 40.1 μm, and a total layer thickness of about 2 on both sides of the positive electrode current collector. It is comprised from the positive electrode active material layer formed so that it might become 73 micrometers. In the positive electrode sheet according to this example, the ratio of the total thickness of the positive electrode active material layers formed on both surfaces of the positive electrode current collector to the thickness of the positive electrode current collector is about 1.82.
The negative electrode sheet has a negative electrode current collector made of a long copper foil having a thickness of about 27.0 μm, and a negative electrode active material layer formed so that the total thickness is about 76 μm on both surfaces of the negative electrode current collector It is composed of In the negative electrode sheet according to this example, the ratio of the total thickness of the positive electrode active material layers formed on both surfaces of the negative electrode current collector to the thickness of the negative electrode current collector is about 2.82.

<Example 3>
The lithium secondary battery of this example includes the thickness of the positive electrode current collector, the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector, the thickness of the negative electrode current collector, Except that the ratio of the thickness of the negative electrode active material layer to the thickness was different, the configuration was the same as in Example 1, and the same procedure was used.
As shown in Table 1, the positive electrode sheet according to this example has a positive electrode current collector made of a long aluminum foil having a thickness of about 50 μm and a total layer thickness of about 73 μm on both surfaces of the positive electrode current collector. It is comprised from the positive electrode active material layer formed in this way. In the positive electrode sheet according to this example, the ratio of the total thickness of the positive electrode active material layers formed on both surfaces of the positive electrode current collector to the thickness of the positive electrode current collector is about 1.46.
The negative electrode sheet has a negative electrode current collector made of a long copper foil having a thickness of about 32.6 μm, and a negative electrode active material layer formed on both surfaces of the negative electrode current collector so that the total thickness is about 76 μm. It is composed of In the negative electrode sheet according to this example, the ratio of the total thickness of the negative electrode active material layers formed on both surfaces of the negative electrode current collector to the thickness of the negative electrode current collector is about 2.33.

<Example 4>
The lithium secondary battery of this example includes the thickness of the positive electrode current collector, the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector, the thickness of the negative electrode current collector, Except that the ratio of the thickness of the negative electrode active material layer to the thickness was different, the configuration was the same as in Example 1, and the same procedure was used.
As shown in Table 1, the positive electrode sheet according to this example has a positive electrode current collector made of a long aluminum foil having a thickness of about 40.1 μm, and a total layer thickness of about 73 μm on both surfaces of the positive electrode current collector. It is comprised from the positive electrode active material layer formed so that it may become. In the positive electrode sheet according to this example, the ratio of the total thickness of the positive electrode active material layers formed on both surfaces of the positive electrode current collector to the thickness of the positive electrode current collector is about 1.82.
The negative electrode sheet has a negative electrode current collector made of a long copper foil having a thickness of about 32.6 μm, and a negative electrode active material layer formed on both surfaces of the negative electrode current collector so that the total thickness is about 76 μm. It is composed of In the negative electrode sheet according to this example, the ratio of the total thickness of the negative electrode active material layers formed on both surfaces of the negative electrode current collector to the thickness of the negative electrode current collector is about 2.33.

<Example 5>
The lithium secondary battery of this example includes the thickness of the positive electrode current collector, the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector, the thickness of the negative electrode current collector, Except that the ratio of the thickness of the negative electrode active material layer to the thickness was different, the configuration was the same as in Example 1, and the same procedure was used.
As shown in Table 1, the positive electrode sheet according to this example has a positive electrode current collector made of a long aluminum foil having a thickness of about 30 μm and a total layer thickness of about 73 μm on both surfaces of the positive electrode current collector. It is comprised from the positive electrode active material layer formed in this way. In the positive electrode sheet according to this example, the ratio of the total thickness of the positive electrode active material layers formed on both surfaces of the positive electrode current collector to the thickness of the positive electrode current collector is about 2.43.
The negative electrode sheet has a negative electrode current collector made of a long copper foil having a thickness of about 32.6 μm, and a negative electrode active material layer formed on both surfaces of the negative electrode current collector so that the total thickness is about 76 μm. It is composed of In the negative electrode sheet according to this example, the ratio of the total thickness of the negative electrode active material layers formed on both surfaces of the negative electrode current collector to the thickness of the negative electrode current collector is about 2.33.

<Example 6>
The lithium secondary battery of this example includes the thickness of the positive electrode current collector, the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector, the thickness of the negative electrode current collector, The configuration is the same as that of Example 1 except that the ratio of the thickness of the negative electrode active material layer to the thickness is different.
As shown in Table 1, the positive electrode sheet according to this example has a positive electrode current collector made of a long aluminum foil having a thickness of about 50 μm, and a total layer thickness of about 73 μm on both surfaces of the positive electrode current collector. It is comprised from the positive electrode active material layer formed in this way. In the positive electrode sheet according to this example, the ratio of the total thickness of the positive electrode active material layers formed on both surfaces of the positive electrode current collector to the thickness of the positive electrode current collector is about 1.46.
The negative electrode sheet has a negative electrode current collector made of a long copper foil having a thickness of about 24.7 μm, and a negative electrode active material layer formed on both surfaces of the negative electrode current collector so that the total thickness is about 76 μm. It is composed of In the negative electrode sheet according to this example, the ratio of the total thickness of the negative electrode active material layers formed on both surfaces of the negative electrode current collector to the thickness of the negative electrode current collector is about 3.08.

<Example 7>
The lithium secondary battery of this example includes the thickness of the positive electrode current collector, the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector, the thickness of the negative electrode current collector, The configuration is the same as that of Example 1 except that the ratio of the thickness of the negative electrode active material layer to the thickness is different.
As shown in Table 1, the positive electrode sheet according to this example has a positive electrode current collector made of a long aluminum foil having a thickness of about 40.1 μm, and a total layer thickness of about 73 μm on both surfaces of the positive electrode current collector. It is comprised from the positive electrode active material layer formed so that it may become. In the positive electrode sheet according to this example, the ratio of the total thickness of the positive electrode active material layers formed on both surfaces of the positive electrode current collector to the thickness of the positive electrode current collector is about 1.82.
The negative electrode sheet has a negative electrode current collector made of a long copper foil having a thickness of about 24.7 μm, and a negative electrode active material layer formed on both surfaces of the negative electrode current collector so that the total thickness is about 76 μm. It is composed of In the negative electrode sheet according to this example, the ratio of the total thickness of the negative electrode active material layers formed on both surfaces of the negative electrode current collector to the thickness of the negative electrode current collector is about 3.08.

<Example 8>
The lithium secondary battery of this example includes the thickness of the positive electrode current collector, the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector, the thickness of the negative electrode current collector, The configuration is the same as that of Example 1 except that the ratio of the thickness of the negative electrode active material layer to the thickness is different.
As shown in Table 1, the positive electrode sheet according to this example has a positive electrode current collector made of a long aluminum foil having a thickness of about 30 μm and a total layer thickness of about 73 μm on both surfaces of the positive electrode current collector. It is comprised from the positive electrode active material layer formed in this way. In the positive electrode sheet according to this example, the ratio of the total thickness of the positive electrode active material layers formed on both surfaces of the positive electrode current collector to the thickness of the positive electrode current collector is about 2.43.
The negative electrode sheet has a negative electrode current collector made of a long copper foil having a thickness of about 24.7 μm, and a negative electrode active material layer formed on both surfaces of the negative electrode current collector so that the total layer thickness is about 76 μm. It is composed of In the negative electrode sheet according to this example, the ratio of the total thickness of the negative electrode active material layers formed on both surfaces of the negative electrode current collector to the thickness of the negative electrode current collector is about 3.08.

<Example 9>
The lithium secondary battery of this example includes the thickness of the positive electrode current collector, the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector, the thickness of the negative electrode current collector, Except that the ratio of the thickness of the negative electrode active material layer to the thickness was different, the configuration was the same as in Example 1, and the same procedure was used.
As shown in Table 1, the positive electrode sheet according to this example has a positive electrode current collector made of a long aluminum foil having a thickness of about 15 μm, and a total layer thickness of about 73 μm on both surfaces of the positive electrode current collector. It is comprised from the positive electrode active material layer formed in this way. In the positive electrode sheet according to this example, the ratio of the total thickness of the positive electrode active material layers formed on both surfaces of the positive electrode current collector to the thickness of the positive electrode current collector is about 4.87. This ratio is equivalent to the ratio of the positive electrode sheet that has been conventionally used.
The negative electrode sheet has a negative electrode current collector made of a long copper foil having a thickness of about 32.6 μm, and a negative electrode active material layer formed on both surfaces of the negative electrode current collector so that the total thickness is about 76 μm. It is composed of In the negative electrode sheet according to this example, the ratio of the total thickness of the negative electrode active material layers formed on both surfaces of the negative electrode current collector to the thickness of the negative electrode current collector is about 2.33.

<Example 10>
The lithium secondary battery of this example includes the thickness of the positive electrode current collector, the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector, the thickness of the negative electrode current collector, The configuration is the same as that of Example 1 except that the ratio of the thickness of the negative electrode active material layer to the thickness is different.
As shown in Table 1, the positive electrode sheet according to this example has a positive electrode current collector made of a long aluminum foil having a thickness of about 15 μm, and a total layer thickness of about 73 μm on both surfaces of the positive electrode current collector. It is comprised from the positive electrode active material layer formed in this way. In the positive electrode sheet according to this example, the ratio of the total thickness of the positive electrode active material layers formed on both surfaces of the positive electrode current collector to the thickness of the positive electrode current collector is about 4.87. This ratio is equivalent to the ratio of the positive electrode sheet that has been conventionally used.
The negative electrode sheet has a negative electrode current collector made of a long copper foil having a thickness of about 24.7 μm, and a negative electrode active material layer formed on both surfaces of the negative electrode current collector so that the total thickness is about 76 μm. It is composed of In the negative electrode sheet according to this example, the ratio of the total thickness of the negative electrode active material layers formed on both surfaces of the negative electrode current collector to the thickness of the negative electrode current collector is about 3.08.

<Comparative Example 1>
The lithium secondary battery of this comparative example includes the thickness of the positive electrode current collector, the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector, the thickness of the negative electrode current collector, The configuration is the same as that of Example 1 except that the ratio of the thickness of the negative electrode active material layer to the thickness is different.
As shown in Table 1, the positive electrode sheet according to this comparative example has a positive electrode current collector made of a long aluminum foil having a thickness of about 50 μm, and a total layer thickness of about 73 μm on both surfaces of the positive electrode current collector. It is comprised from the positive electrode active material layer formed in this way. In the positive electrode sheet according to this comparative example, the ratio of the total thickness of the positive electrode active material layers formed on both surfaces of the positive electrode current collector to the thickness of the positive electrode current collector is about 1.46.
The negative electrode sheet has a negative electrode current collector made of a long copper foil having a thickness of about 9.9 μm, and a negative electrode active material layer formed on both surfaces of the negative electrode current collector so that the total thickness is about 76 μm. It is composed of In the negative electrode sheet according to this comparative example, the ratio of the total thickness of the negative electrode active material layers formed on both surfaces of the negative electrode current collector to the thickness of the negative electrode current collector is about 7.70. Such a ratio is equivalent to the ratio of the negative electrode sheet conventionally used.

<Comparative example 2>
The lithium secondary battery of this comparative example includes the thickness of the positive electrode current collector, the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector, the thickness of the negative electrode current collector, The configuration is the same as that of Example 1 except that the ratio of the thickness of the negative electrode active material layer to the thickness is different.
As shown in Table 1, the positive electrode sheet according to this comparative example has a positive electrode current collector made of a long aluminum foil having a thickness of about 40.1 μm, and a total layer thickness of about 73 μm on both surfaces of the positive electrode current collector. It is comprised from the positive electrode active material layer formed so that it may become. In the positive electrode sheet according to this comparative example, the ratio of the total thickness of the positive electrode active material layers formed on both surfaces of the positive electrode current collector to the thickness of the positive electrode current collector is about 1.82.
The negative electrode sheet has a negative electrode current collector made of a long copper foil having a thickness of about 9.9 μm, and a negative electrode active material layer formed on both surfaces of the negative electrode current collector so that the total thickness is about 76 μm. It is composed of In the negative electrode sheet according to this comparative example, the ratio of the total thickness of the negative electrode active material layers formed on both surfaces of the negative electrode current collector to the thickness of the negative electrode current collector is about 7.70. Such a ratio is equivalent to the ratio of the negative electrode sheet conventionally used.

<Comparative Example 3>
The lithium secondary battery of this comparative example includes the thickness of the positive electrode current collector, the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector, the thickness of the negative electrode current collector, The configuration is the same as that of Example 1 except that the ratio of the thickness of the negative electrode active material layer to the thickness is different.
As shown in Table 1, the positive electrode sheet according to this comparative example has a positive electrode current collector made of a long aluminum foil having a thickness of about 30 μm, and a total layer thickness of about 73 μm on both surfaces of the positive electrode current collector. It is comprised from the positive electrode active material layer formed in this way. In the positive electrode sheet according to this comparative example, the ratio of the total thickness of the positive electrode active material layers formed on both surfaces of the positive electrode current collector to the thickness of the positive electrode current collector is about 2.43.
The negative electrode sheet has a negative electrode current collector made of a long copper foil having a thickness of about 9.9 μm, and a negative electrode active material layer formed on both surfaces of the negative electrode current collector so that the total thickness is about 76 μm. It is composed of In the negative electrode sheet according to this comparative example, the ratio of the total thickness of the negative electrode active material layers formed on both surfaces of the negative electrode current collector to the thickness of the negative electrode current collector is about 7.70. Such a ratio is equivalent to the ratio of the negative electrode sheet conventionally used.

<Comparative example 4>
The lithium secondary battery of this comparative example is a lithium secondary battery having the same specifications as a conventional lithium secondary battery. The lithium secondary battery of this comparative example includes the thickness of the positive electrode current collector, the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector, the thickness of the negative electrode current collector, The configuration is the same as that of Example 1 except that the ratio of the thickness of the negative electrode active material layer to the thickness is different.
As shown in Table 1, the positive electrode sheet according to this comparative example has a positive electrode current collector made of a long aluminum foil having a thickness of about 15 μm, and a total layer thickness of about 73 μm on both surfaces of the positive electrode current collector. It is comprised from the positive electrode active material layer formed in this way. In the positive electrode sheet according to this comparative example, the ratio of the total layer thickness of the positive electrode active material layers formed on both surfaces of the positive electrode current collector to the thickness of the positive electrode current collector is about 4.87.
The negative electrode sheet has a negative electrode current collector made of a long copper foil having a thickness of about 9.9 μm, and a negative electrode active material layer formed on both surfaces of the negative electrode current collector so that the total thickness is about 76 μm. It is composed of In the negative electrode sheet according to this comparative example, the ratio of the total thickness of the negative electrode active material layers formed on both surfaces of the negative electrode current collector to the thickness of the negative electrode current collector is about 7.70.

<Test 1: Nail penetration test>
In order to investigate the effect of the lithium secondary battery of the present invention, a nail penetration test was performed on the lithium secondary batteries of Examples 1 to 10 and Comparative Examples 1 to 4. In this test, when an internal short circuit occurs due to nail penetration in the batteries of Examples 1 to 10 and Comparative Examples 1 to 4, an overheating phenomenon (being heated to a temperature that causes battery rupture, smoke, and ignition) occurs. It was confirmed whether or not it occurred. The results are shown in Table 2. Table 2 also shows the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector and the ratio of the layer thickness of the negative electrode active material layer to the thickness of the negative electrode current collector. The battery indicated by a circle in Table 2 indicates that the overheating phenomenon did not occur even if an internal short circuit occurred, and the battery indicated by the x mark caused an overheating phenomenon due to the occurrence of an internal short circuit. It shows that.
The nail penetration test is a test in which a metal nail is inserted from the outside of the battery package to forcibly short-circuit the inside. In this test, a metal nail having a diameter of 2.5 mm was inserted at a speed of 350 mm / sec, and the nail was pierced and left for 2 hours. When the battery is internally short-circuited by nail penetration, the inside of the battery suddenly generates heat, and the temperature inside the battery rises. If the battery can efficiently transfer heat due to an internal short circuit, the temperature inside the battery is prevented from excessively rising. The battery having such a configuration is not easily overheated when an internal short circuit occurs.

As shown in Table 2, as a result of the nail penetration test, the batteries of Examples 1 to 10 were not overheated. For the batteries of Example 1 and Example 2, the battery temperature during the test was also examined. The maximum temperature during the test of the lithium secondary battery of Example 1 was about 130 ° C. The battery of Example 2 also had a maximum temperature of about 130 ° C. during this test.
In the batteries of Examples 1 to 8, the thicknesses of the positive electrode current collector and the negative electrode current collector are sufficiently secured. The ratio of the thickness of the active material layer to the current collectors of the batteries of Examples 1 to 8 is 2.5 or less on the positive electrode side and 3.5 or less on the negative electrode side. The local heat generation due to the internal short circuit is considered to have been suitably transferred by both the positive electrode current collector and the negative electrode current collector.

  In the batteries of Examples 9 and 10, the thickness of the positive electrode current collector is set to 15 μm, and a positive electrode sheet having a configuration equivalent to the conventional configuration is employed. In the battery of Example 9, the thickness of the negative electrode current collector was 33 μm (the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector was about 2.33), and the negative electrode sheet Is adopted. Also in the battery of Example 10, the thickness of the negative electrode current collector was set to 25 μm (the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector was about 3.08). Copper constituting the negative electrode current collector has a high heat absorption efficiency because of its large heat capacity per volume and high thermal conductivity. In the batteries of Example 9 and Example 10, since the thickness of the positive electrode current collector is thin but the thickness of the negative electrode current collector is sufficiently secured, local heat generation due to an internal short circuit is caused by the negative electrode current collector. It is thought that it was suitably dispersed.

In the batteries of Comparative Examples 1 to 4, an overheating phenomenon in which the temperature in the battery excessively increased occurred. In the lithium secondary batteries of Comparative Examples 1 to 3, the thickness of the negative electrode current collector was set to 10 μm (the ratio of the layer thickness of the negative electrode active material layer to the thickness of the negative electrode current collector was about 7.70. A negative electrode sheet having a configuration equivalent to the conventional configuration. The current collector on the positive electrode side is thicker than before, and the ratio of the current collector thickness to the active material layer is about 1.46 to about 2.43. However, in the lithium secondary batteries of Comparative Examples 1 to 3, since the current collector on the negative electrode side made of copper having good heat absorption efficiency is thin, rapid heat generation due to an internal short circuit is less likely to diffuse. In the batteries of Comparative Examples 1 to 3, it is considered that local heat generation due to an internal short circuit could not be transferred by the positive electrode current collector, resulting in an overheating phenomenon.
Moreover, the lithium secondary battery of Comparative Example 4 employs an electrode sheet having a configuration equivalent to the conventional configuration for both electrodes. In Comparative Example 4, the thickness of the negative electrode current collector is as thin as about 9.9 μm (the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector is about 7.70), and the positive electrode The current collector is as thin as about 15 μm (the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector is about 4.87). In the battery of Comparative Example 4, it is considered that local heat generated due to the internal short circuit could not be transferred by the current collector, resulting in an abnormality.

From the result of this test, the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector is about 2.43 or less, and the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector foil However, in the lithium secondary battery adopting a negative electrode of about 3.5 or less, local heat generation due to an internal short circuit is suitably transferred in both the positive electrode current collector and the negative electrode current collector, and an excessive temperature rise of the battery is caused. It was found to be suppressed.
In addition, in a lithium secondary battery employing a positive electrode sheet of a conventional specification (the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector is about 4.87), the thickness of the negative electrode current collector It was confirmed that an excessive increase in the temperature of the battery was suppressed by using a negative electrode sheet having a ratio of the thickness of the negative electrode active material layer to about 3.08 or less.

<Test 2: Overcharge test>
In order to investigate the effect of the lithium secondary battery of the present invention, overcharge tests were performed on the lithium secondary batteries of Examples 3 to 10 and Comparative Examples 1 to 4. When the battery is overcharged, the temperature in the lithium secondary battery increases. When the lithium secondary battery is overcharged, lithium ions are released from the crystal lattice of the positive electrode active material, resulting in a lithium deficient state. When the lithium secondary battery is overcharged, metallic lithium is deposited on the negative electrode surface. When the lithium secondary battery is overcharged, the separator may be damaged by heat generated by overcharge. As a result, an internal short circuit may occur at a microscopic portion in the battery. When an internal short circuit occurs, an overheating phenomenon tends to occur. In this test, whether or not the batteries of Examples 3 to 10 and Comparative Examples 1 to 4 are overheated (for example, overheated to a temperature causing explosion, smoke generation, or ignition) due to overcharge. I confirmed. The results are shown in Table 3. Table 3 also shows the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector and the layer thickness of the negative electrode active material layer relative to the thickness of the negative electrode current collector. The battery indicated by a circle in Table 3 indicates that the overheating phenomenon did not occur even when overcharged, and the battery indicated by the x mark caused an overheating phenomenon due to being overcharged. It shows that.
An overcharge test is a test in which a charging current is forced to flow through a lithium battery after charging is completed. In this test, the batteries of Examples 3 to 10 and Comparative Examples 1 to 4 were charged, and then a 20 A charging current was forcibly applied over 3 hours.

As a result of the overcharge test, the batteries of Examples 3 to 10 and Comparative Examples 1 to 3 did not generate an overheating phenomenon. Only in the battery of Comparative Example 4, the overheating phenomenon occurred.
In the batteries of Examples 3 to 8, the thicknesses of the positive electrode current collector and the negative electrode current collector are sufficiently secured. A current collector having a sufficient thickness has a sufficient heat capacity. For this reason, the heat which generate | occur | produced on the electrode surface by overcharge is spread | diffused suitably for the electrical power collector which comprises an electrode, and is transmitted. When the heat capacity of the current collector is large, the temperature of the battery is difficult to increase. If the battery temperature does not rise easily, the overheating phenomenon is suppressed. It is considered that the batteries of Examples 3 to 8 did not cause an overheating phenomenon because the positive electrode current collector and the negative electrode current collector had large heat capacities.
In the batteries of Examples 9 and 10, the thickness of the positive electrode current collector was set as thin as 15 μm (the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector was about 4.87). Yes. On the other hand, in the battery of Example 9, the thickness of the negative electrode current collector was set to be as thick as 33 μm (the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector was about 2.33). ing. In the battery of Example 10 as well, the thickness of the negative electrode current collector was set to 25 μm (the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector was about 3.08). Yes. In the batteries of Examples 9 and 10, since the thickness of the positive electrode current collector is thin but the thickness of the negative electrode current collector is sufficiently secured, the positive electrode current collector is sufficiently thick. It is considered that the heat generated by the heat was suitably diffused and transferred by the negative electrode current collector.

In the batteries of Comparative Examples 1 to 3, the thickness of the negative electrode current collector was set as thin as 10 μm (the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector was about 7.70). Yes. In the batteries of Comparative Examples 1 to 3, the thickness of the positive electrode current collector is 30 μm or more (the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector is about 2.43 or less). It is set thick. In the batteries of Comparative Examples 1 to 3, since the thickness of the negative electrode current collector is thin but the thickness of the positive electrode current collector is sufficiently secured, the heat generated by overcharging is suitably diffused by the positive electrode current collector. It is thought that the heat was transferred.
On the other hand, in the battery of Comparative Example 4, the thickness of the positive electrode current collector was 15 μm (the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector was about 4.87), and the negative electrode current collector. Was 10 μm (the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector was about 7.70). In the battery of Comparative Example 4, it is considered that the heat generated due to overcharging could not be diffused by the positive electrode current collector and the negative electrode current collector, resulting in an overheating phenomenon.

From the result of this test, in the lithium secondary battery employing the positive electrode sheet of the conventional specification (the positive electrode sheet in which the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector is about 4.87), the negative electrode current collector It was confirmed that a temperature increase during overcharge can be suppressed by using a negative electrode sheet having a ratio of the thickness of the negative electrode active material layer to the body thickness of about 3.08 or less.
Further, in a lithium secondary battery employing a negative electrode sheet of a conventional specification (a negative electrode sheet in which the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector is about 7.70), the thickness of the positive electrode current collector It was confirmed that a temperature increase during overcharging can be suppressed by using a positive electrode sheet having a ratio of the thickness of the positive electrode active material layer to the thickness of about 2.43 or less.

<Thermal analysis 1>
Thermal analysis was performed assuming several electrodes with different ratios of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector. This thermal analysis was performed assuming a lithium secondary battery made of the same material as in the previous example and having a capacity equivalent to 7 Ah. The analysis was performed assuming that the structure on the negative electrode side was constant and the ratio of the thickness of the active material layer to the thickness of the current collector was 7.70.
In this thermal analysis, based on the amount of heat generated when the structure of all LiNiO ₂ crystals contained in the positive electrode active material collapses and the specific heat and thermal conductivity of the aluminum constituting the positive electrode current collector, the crystal of the positive electrode active material We analyzed how the temperature inside the battery rose when the structure collapsed. FIG. 5 shows a graph of thermal analysis on the positive electrode side. In the graph of FIG. 5, the horizontal axis represents the ratio of the total thickness of the positive electrode active material layer to the thickness of the positive electrode current collector, and the vertical axis represents the highest battery in an abnormal state (when the crystal structure of the positive electrode active material collapses). Indicates temperature.

As shown in FIG. 5, from the result of the thermal analysis on the positive electrode side, when the ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector is about 3.0 or less, the crystal structure of the positive electrode active material It was analyzed that the heat generated by the collapse was suitably diffused by the positive electrode current collector, and the battery temperature did not rise above 170 ° C. In particular, when the ratio was about 2.5 or less, it was analyzed that the battery temperature at the time of abnormality did not rise to 150 ° C. or higher. As a result, even if heat is generated locally in the battery and the crystal structure of the positive electrode active material is locally broken, it is predicted that local heat is suitably diffused by the positive electrode current collector having a thickness. The When heat is diffused, a local temperature rise does not occur, and the crystal structure of the positive electrode active material is unlikely to collapse in a chain manner. If the collapse of the crystal structure of the positive electrode active material does not proceed, the overheating phenomenon in which the battery generates excessive heat is suppressed.
From this thermal analysis, it was found that a lithium battery equipped with a thick positive electrode current collector is less prone to overheating.

<Thermal analysis 2>
Thermal analysis was performed assuming several electrodes with different ratios of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector. This thermal analysis was performed assuming a lithium secondary battery made of the same material as in the previous example and having a capacity equivalent to 7 Ah. The analysis was performed assuming that the configuration on the positive electrode side was constant and the ratio of the active material layer to the thickness of the current collector was 4.87.
In this thermal analysis, based on specific heat and thermal conductivity of the material structure of all LiNiO ₂ crystals contained in the positive electrode active material constituting the heat and current collector occurs when collapsed, the positive electrode active material crystal structure We analyzed how the temperature inside the battery rose when the battery collapsed. FIG. 6 shows a graph of thermal analysis on the positive electrode side. In the graph of FIG. 6, the horizontal axis indicates the ratio of the total thickness of the negative electrode active material layer to the thickness of the negative electrode current collector, and the vertical axis indicates the highest battery in an abnormal state (when the crystal structure of the positive electrode active material collapses). Indicates temperature.

As shown in FIG. 6, from the result of the thermal analysis on the negative electrode side, when the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector is about 3.5 or less, the crystal structure of the positive electrode active material It was analyzed that the heat generated by the collapse was suitably diffused by the negative electrode current collector, and the battery temperature did not rise above 170 ° C. In particular, it was analyzed that the battery temperature did not rise above 150 ° C. when the ratio was about 3.1 or less. As a result, even if heat is generated locally in the battery and the crystal structure of the positive electrode active material locally collapses, it is predicted that local heat is suitably diffused by the thick negative electrode current collector. The When heat is diffused, a local temperature rise does not occur, and the crystal structure of the positive electrode active material is difficult to collapse in a chain manner. If the collapse of the crystal structure of the positive electrode active material does not proceed, the overheating phenomenon in which the battery generates excessive heat is suppressed.
From the thermal analysis, it was found that a lithium battery equipped with a thick negative electrode current collector is less prone to overheating.

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, the battery of the above embodiment uses a film package as a package, but is not limited thereto. The configuration of the present invention can also be applied to a battery employing a more rigid synthetic resin package or metal package.
Moreover, in the battery of the above-described 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.

In the battery of the above embodiment, LiNiO ₂ is used as the positive electrode active material, but the present invention is not limited to this. The configuration of the present invention can be applied to a lithium composite oxide that has been conventionally used as a positive electrode active material of a lithium secondary battery. The configuration of the present invention is useful for a positive electrode active material containing a lithium composite oxide having a layered rock salt type crystal structure. The structure of the present invention is also useful for a lithium composite oxide having a spinel crystal structure. Examples of the lithium composite oxide having a layered rock salt type crystal structure include LiNiO ₂ and LiCoO ₂ . LiMn ₂ O ₄ is an example of a lithium composite oxide having a spinel crystal structure. The oxide transition metal element in the lithium composite oxide contains two or more (e.g. general _formula: LiNi _{x Co 1-x O} oxide represented by ₂₎ may be used.

In the battery of the above example, a positive electrode in which a positive electrode active material layer is formed on both surfaces of the positive electrode current collector is applied. However, in the battery of the present invention, a positive electrode active material layer is formed only on one surface of the positive electrode current collector. The positive electrode that is used can also be applied.
The battery of the above example uses a negative electrode in which a negative electrode active material layer is formed on both sides of a negative electrode current collector, but the battery of the present invention has a negative electrode active material layer formed only on one side of the negative electrode current collector. The negative electrode which is made can also be applied.

  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 illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

1 is a side view showing an outline of a secondary battery of Example 1. FIG. 3 is a schematic diagram illustrating a configuration of an electrode body according to Example 1. FIG. 3 is a schematic diagram illustrating a configuration of a positive electrode sheet according to Example 1. FIG. 3 is a schematic diagram illustrating a configuration of a negative electrode sheet according to Example 1. FIG. It is a graph which shows the thermal analysis result by the side of a positive electrode. It is a graph which shows the thermal-analysis result by the side of a negative electrode.

Explanation of symbols

10: lithium secondary battery,
12: Package 13: Negative electrode lead terminal 14: Positive electrode lead terminal 16, 17: Laminate film,
20: Electrode body 30: Positive electrode sheet 32: Positive electrode current collector 34, 36: Positive electrode active material layer 40: Negative electrode 42: Negative electrode current collector 44, 46: Negative electrode active material layer

Claims (2)

Lithium secondary battery having a positive electrode having a positive electrode active material layer formed on the surface of a positive electrode current collector made of aluminum foil and a negative electrode having a negative electrode active material layer formed on the surface of a negative electrode current collector made of copper foil And
The ratio of the thickness of the positive electrode active material layer to the thickness of the positive electrode current collector is 2.5 or less, and the ratio of the layer thickness of the negative electrode active material layer to the thickness of the negative electrode current collector is 3.5 or less Rechargeable lithium battery. A lithium secondary battery having a negative electrode in which a negative electrode active material layer is formed on the surface of a negative electrode current collector made of copper foil,
A lithium secondary battery, wherein the ratio of the thickness of the negative electrode active material layer to the thickness of the negative electrode current collector is 3.1 or less.

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