JP2000315481A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having improved safety. SOLUTION: This nonqeuous electrolyte secondary battery is constituted of a nonaqueous electrolyte held by the separator and an electrode group 5 provided with a positive electrode, a negative electrode and a porous separator disposed between the positive and negative electrodes having a property that the pores are closed by heating and; and a sheet in which at least a part of the inner surface is formed of a thermoplastic, resin layer. The battery also has an exterior material 3 for housing the electrode group 5 and heat-sealing the thermoplastic resin layers to seal the electrode group 5. The positive electrode, the negative electrode and the porous separator are integrally combined. The thermoplastic resin layer has a melting point higher than the pore close starting temperature of the separator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art At present, lithium ion secondary batteries have been commercialized as non-aqueous electrolyte secondary batteries for portable devices such as mobile phones. This battery has a lithium-cobalt oxide (LiCoO ₂ ) for the positive electrode, a graphite or carbonaceous material for the negative electrode, a non-aqueous electrolyte in which a lithium salt is dissolved in an organic solvent, a porous film for the separator, and a cylindrical or prismatic shape for the exterior material. Metal cans are used.

[0005] By the way, as portable equipment becomes thinner, there is a demand for making nonaqueous electrolyte secondary batteries thinner and lighter.
In order to reduce the thickness of the above-mentioned lithium ion secondary battery to 4 mm or less, it is necessary to reduce the thickness of the metal can.

However, if the thickness of the metal can is reduced, it becomes very difficult to form the metal can itself. For this reason, a metal can is provided as an exterior material and the thickness is 4 mm.
It has been almost difficult to put the following lithium ion secondary batteries to practical use.

On the other hand, US Pat. No. 5,437,692 discloses that an electrode group including a positive electrode, a negative electrode, and a gel-like polymer electrolyte layer disposed between the positive electrode and the negative electrode is provided in a battery housing member. Discloses a lithium ion secondary battery that is sealed in a battery. An object of the invention described in these U.S. Patents is to improve the cycle life by increasing the mobility of lithium ions. Also, no detailed description of the battery housing member is made.

However, a secondary battery provided with this gel polymer electrolyte layer has an internal short circuit, overcharge,
When abnormal heat generation or temperature rise is caused by leaving at a high temperature of 30 ° C. or more, the viscosity of the polymer electrolyte layer is reduced, and there is a risk that the positive electrode and the negative electrode come into contact with each other, that is, an internal short circuit occurs, leading to rupture.

[0007]

An object of the present invention is to provide a non-aqueous electrolyte secondary battery with improved safety.

[0008]

According to the present invention, there is provided an electrode group comprising a positive electrode, a negative electrode, and a porous separator disposed between the positive electrode and the negative electrode and having a property that pores are closed by heating. A non-aqueous electrolyte held by the separator; and a sheet in which at least a part of the inner surface is formed of a thermoplastic resin layer, which accommodates the electrode group and heat seals the thermoplastic resin layers together to form the electrode. An exterior material for sealing the group; wherein the positive electrode, the negative electrode, and the separator are integrated, and the thermoplastic resin layer has a higher melting point than a pore closing start temperature of the separator. A non-aqueous electrolyte secondary battery is provided.

According to the present invention, a positive electrode, a negative electrode, and at least one selected from polyolefin, cellulose, and polyvinylidene fluoride are disposed between the positive electrode and the negative electrode, and have an air permeability of 600 seconds / 100 cm.
^An electrode group comprising a porous sheet having a thickness of ³ or less and a thickness of 5 to 30 μm; a non-aqueous electrolyte held by the separator; and a sheet in which at least a part of the inner surface is formed of a thermoplastic resin layer. And an exterior material for housing the electrode group and sealing the electrode group by heat-sealing the thermoplastic resin layers with each other; and the positive electrode, the negative electrode, and the separator are integrated. In addition, there is provided a non-aqueous electrolyte secondary battery in which the thermoplastic resin layer has a higher melting point than a pore closing start temperature of the separator.

According to the present invention, there is provided a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, the separator comprising a porous sheet formed of at least one selected from polyolefin, cellulose, and polyvinylidene fluoride. A non-aqueous electrolyte held by the separator; and a sheet having at least a part of the inner surface formed of a polyolefin layer. The electrode group is housed, and the polyolefin layers are heat-sealed to each other. An exterior material for sealing an electrode group; wherein the positive electrode, the negative electrode, and the separator are integrated, and the polyolefin layer has a melting point higher than a pore closing start temperature of the separator. A water electrolyte secondary battery is provided.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode, a negative electrode, and a porous separator disposed between the positive electrode and the negative electrode and having a property that pores are closed by heating. A non-aqueous electrolyte held by the separator; and a sheet in which at least a part of the inner surface is formed of a thermoplastic resin layer. The electrode group is housed, and the thermoplastic resin layers are heat-sealed to each other. And an exterior material for sealing the electrode group. As the exterior material, a multilayer sheet including a thermoplastic resin layer forming at least a part of an inner surface or a sheet made of a thermoplastic resin can be used.

The positive electrode, the negative electrode, and the separator are integrated. Further, the thermoplastic resin layer,
It has a melting point higher than the pore closing start temperature of the separator.

Two specific examples of the secondary battery (hereinafter, referred to as a first non-aqueous electrolyte secondary battery and a second non-aqueous electrolyte secondary battery) will be described.

<First Non-Aqueous Electrolyte Secondary Battery> In the first non-aqueous electrolyte secondary battery, the positive electrode and the separator are formed of an adhesive polymer present at least at a part of their boundary. In addition to being integrated, the negative electrode and the separator are integrated by an adhesive polymer existing at least at a part of these boundaries. In particular, while the positive electrode and the separator are integrated by a polymer having adhesive properties scattered in the inside and the boundary thereof, the negative electrode and the separator have adhesive properties scattered in the inside and the boundary thereof. Desirably, they are integrated by a polymer.

1) Positive Electrode This positive electrode has a structure in which a positive electrode layer containing an active material, a conductive agent and a binder is supported on one or both surfaces of a current collector.

As the positive electrode active material, various oxides,
For example, manganese dioxide, lithium manganese composite oxide,
Lithium-containing nickel oxide, lithium-containing cobalt oxide, lithium-containing nickel-cobalt oxide, lithium-containing iron oxide, lithium-containing vanadium oxide, and chalcogen compounds such as titanium disulfide and molybdenum disulfide can be given. . Among them, lithium-containing cobalt oxide (for example, LiCoO ₂ ) and lithium-containing nickel cobalt oxide (for example, LiNi _0.8 Co _0.2
O ₂ ), lithium manganese composite oxide (eg, LiM
Use of n ₂ O ₄ and LiMnO ₂ ) is preferable because a high voltage can be obtained.

Examples of the conductive agent include acetylene black, carbon black, graphite and the like.

The binder has a function of holding the active material on the current collector and connecting the active materials. Examples of the binder include polytetrafluoroethylene (PTF)
E), polyvinylidene fluoride (PVdF), ethylene-
Propylene-diene copolymer (EPDM), styrene
Butadiene rubber (SBR) or the like can be used.

The mixing ratio of the positive electrode active material, the conductive agent and the binder is 80 to 95% by weight of the positive electrode active material, 3 to 2% of the conductive agent.
It is preferable that the content be in the range of 0% by weight and 2 to 7% by weight of the binder.

The thickness of the positive electrode layer is preferably in the range of 10 to 150 μm. Here, the thickness of the positive electrode layer means a distance between the surface of the positive electrode layer facing the separator and the surface of the positive electrode layer contacting the current collector. For example, as shown in FIG. 1, when the positive electrode layer P is supported on both surfaces of the current collector S, the distance between the positive electrode layer surface P ₁ facing the separator and the positive electrode layer surface P ₂ contacting the current collector is This is the thickness T of the positive electrode layer.
Therefore, when the thickness of the positive electrode layer is set to 10 to 150 μm,
For a positive electrode in which a positive electrode layer is supported on both surfaces of the current collector, the total thickness of the positive electrode layer is in the range of 20 to 300 μm. By making the thickness of the positive electrode layer in the range of 10 to 150 μm,
Large current discharge characteristics and cycle life can be improved. More preferably, the thickness of the positive electrode layer is in the range of 30 to 100 μm. By setting the content within this range, large current discharge characteristics and cycle life can be significantly improved.

The thickness of the positive electrode layer is measured by a method described below. First, the thickness of the positive electrode is measured by arbitrarily selecting 10 points existing at a distance of 1 cm or more from each other, measuring the thickness of each point, and calculating the average value. However,
When the positive electrode to be measured has a structure in which the positive electrode layer is supported on both surfaces of the current collector, one of the positive electrode layers is removed, and then the thickness of the positive electrode is measured. Next, the positive electrode layer is removed from the current collector, and the thickness of the current collector is measured. The thickness of the current collector can be determined by arbitrarily selecting 10 points that are separated from each other by 1 cm or more, measuring the thickness of each point, and calculating the average value. The difference between the thickness of the positive electrode and the thickness of the current collector is defined as the desired thickness of the positive electrode layer.

As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used. These conductive substrates can be formed from, for example, aluminum, stainless steel, or nickel. The current collector preferably has a thickness in the range of 5 to 20 μm. This is because within this range, the balance between the positive electrode strength and the weight reduction can be achieved.

2) Negative Electrode This negative electrode has a structure in which a negative electrode layer containing a carbonaceous material that occludes and releases lithium ions and a binder is supported on one or both sides of a current collector.

As the carbonaceous material, graphite, coke,
Graphite or carbonaceous materials such as carbon fiber and spherical carbon, thermosetting resin, isotropic pitch, mesophase pitch, mesophase pitch-based carbon fiber, mesophase spherules, etc. (particularly, mesophase pitch-based carbon fiber 500 to 3)
Graphite materials or carbonaceous materials obtained by performing a heat treatment at 000 ° C. can be exemplified. Among them, it is preferable to use a graphitic material having graphite crystals obtained by setting the temperature of the heat treatment to 2000 ° C. or higher and having a (002) plane spacing d ₀₀₂ of 0.340 nm or less. A non-aqueous electrolyte secondary battery provided with a negative electrode containing such a graphite material as a carbonaceous material can significantly improve battery capacity and large-current discharge characteristics. The surface distance d
₀₀₂ is more preferably 0.336 nm or less.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR),
Carboxymethyl cellulose (CMC) or the like can be used.

The mixing ratio of the carbonaceous material and the binder is 90 to 98% by weight of the carbonaceous material and 2 to 20% by weight of the binder.
Is preferably within the range. In particular, it is preferable that the carbonaceous material be in a range of 10 to 70 g / cm ^{2 on} one side in a state where the negative electrode is manufactured. The packing density is 1.20 to
It is preferable to set the range to 1.50 g / cm ³ .

The thickness of the negative electrode layer is preferably in the range of 10 to 150 μm. Here, the thickness of the negative electrode layer means the distance between the surface of the negative electrode layer facing the separator and the surface of the negative electrode layer contacting the current collector. When the thickness of the negative electrode layer is 10 to 150 μm, the total thickness of the negative electrode layer is 20 to 3 in the negative electrode in which the negative electrode layer is supported on both surfaces of the current collector.
The range is 00 μm. The thickness of the negative electrode layer is 10 to 150 μ
By setting it within the range of m, the large current discharge characteristics and the cycle life can be improved. The thickness of the negative electrode layer is
More preferably, it is within the range of 30 to 100 μm.
By setting the content within this range, large current discharge characteristics and cycle life can be significantly improved.

The thickness of the negative electrode layer is measured by the method described below. First, the thickness of the negative electrode is measured by arbitrarily selecting ten points existing at a distance of 1 cm or more from each other, measuring the thickness of each point, and calculating the average value. However,
When the negative electrode to be measured has a structure in which a negative electrode layer is supported on both surfaces of a current collector, one of the negative electrode layers is removed, and then the thickness of the negative electrode is measured. Next, the negative electrode layer is removed from the current collector, and the thickness of the current collector is measured. The thickness of the current collector can be determined by arbitrarily selecting 10 points that are separated from each other by 1 cm or more, measuring the thickness of each point, and calculating the average value. The difference between the thickness of the negative electrode and the thickness of the current collector is defined as the required thickness of the negative electrode layer.

As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used. These conductive substrates can be formed from, for example, copper, stainless steel, or nickel. The current collector preferably has a thickness in the range of 5 to 20 μm. This is because when the content is within this range, the balance between the strength of the negative electrode and the reduction in weight can be achieved.

The negative electrode layer includes a metal oxide, a metal sulfide, or a metal nitride, or a lithium metal or a lithium alloy, in addition to the above-described carbon material that absorbs and releases lithium ions. Can be used.

Examples of the metal oxide include tin oxide, silicon oxide, lithium titanium oxide, niobium oxide, and tungsten oxide.

Examples of the metal sulfide include tin sulfide and titanium sulfide.

Examples of the metal nitride include lithium cobalt nitride, lithium iron nitride, lithium manganese nitride and the like.

Examples of the lithium alloy include a lithium aluminum alloy, a lithium tin alloy, a lithium lead alloy, and a lithium silicon alloy.

3) Separator The separator is formed of a porous sheet having a property that pores are closed by heating.

The thermoplastic resin layer of the exterior material has a higher melting point than the opening start temperature of the separator. Here, the pore blocking start temperature of the separator is determined by disassembling the non-aqueous electrolyte secondary battery to take out the electrode group, disassembling the electrode group, taking out the separator, and washing the separator with an organic solvent. It is measured after removing the deposits such as the electrolyte and drying at 60 ° C. so that the separator does not thermally shrink. The drying of the separator can be performed under normal pressure or reduced pressure atmosphere.

The pore closing start temperature of the separator is measured by the method described below. After immersing the test cell obtained by sandwiching the separator between two electrodes made of a nickel plate in a non-aqueous solution having the same composition as the non-aqueous electrolyte contained in the secondary battery, vacuum is applied for 1 to 15 minutes in a desiccator. Impregnation is performed so that the non-aqueous solution does not evaporate. The size of the electrode is set to 10 × 15 mm, and the size of the separator is set to 20 × 25 mm. afterwards,
After standing at 100 ° C. for 10 minutes, the cell temperature and the cell resistance at an AC frequency of 1 KHz are measured while increasing the temperature at 2 ° C./min. FIG. 2 shows an example of the measurement result. The horizontal axis in FIG. 2 is the cell temperature, and the vertical axis is the cell resistance. As shown in FIG. 2, the temperature P at which the cell resistance value starts to rise sharply
Is the pore closing start temperature of the separator.

In the non-aqueous electrolyte secondary battery according to the present invention, the melting point of the thermoplastic resin layer of the outer package is measured by the method described above before the separator is incorporated into the electrode group, that is, before tension is applied. And the temperature at which the holes of the separator in the electrode group start to close. That is, in the non-aqueous electrolyte secondary battery according to the present invention, the separator before being incorporated in the electrode group, the separator in the electrode group and the separator obtained by disassembling the secondary battery, and the separator in any state, the separator The relationship is established that the melting point of the thermoplastic resin layer of the exterior material is higher than the temperature at which the holes start to close.

The pore closing start temperature of the separator is 10
The temperature is preferably from 0 ° C to 150 ° C. When the hole closing start temperature is set to less than 100 ° C., a normal high-temperature atmosphere (for example, 85 ° C.) without a risk of the secondary battery reaching an abnormally high temperature (runaway temperature of the non-aqueous electrolyte secondary battery, around 140 ° C.)
(In the vicinity), the battery impedance may increase. On the other hand, if the hole closing start temperature exceeds 150 ° C., the secondary battery may reach an abnormally high temperature, causing rupture or ignition. A more preferred range of the pore closing start temperature is 10
5 to 140 ° C. A more preferred range is 105 to
135 ° C. However, the opening temperature at which the separator is clogged means the temperature measured by the method described above after the secondary battery is disassembled by the method described above.

When the separator is incorporated into the electrode group, the separator is under tension, so that the size of the hole is increased.
For this reason, the hole closing start temperature of the separator and the temperature at which the holes of the separator in the electrode group start to close are higher than the hole closing start temperature measured by the method described above before the separator is incorporated into the electrode group. Tend to be.
The rise width varies depending on conditions such as the separator material, thickness, air permeability, heat shrinkage, and porosity.
0-15 ° C. Therefore, by setting the hole closing start temperature measured by the above-described method before the separator is incorporated into the electrode group within the range of 100 to 140 ° C., the hole closing start temperature (after disassembly of the secondary battery) of the separator is reduced. 1
It can be in the range of 00 to 150 ° C. Also, by setting the pore closing start temperature measured by the method described above before the separator is incorporated into the electrode group within the range of 110 to 135 ° C., the pore closing start temperature of the separator (after the secondary battery is disassembled) is reduced. 115-150 ° C. Further, before the separator is incorporated into the electrode group, the pore closing start temperature measured by the method described above is 105 to 105.
By setting the temperature within the range of 130 ° C., the pore closing start temperature (after disassembly of the secondary battery) of the separator is set to 120 to 140.
° C.

As the porous sheet, for example, a porous film or a nonwoven fabric can be used. The porous sheet is preferably made of, for example, at least one material selected from polyolefin, cellulose, and polyvinylidene fluoride (PVdF). Examples of the polyolefin include polyethylene and polypropylene. Among them, a porous film containing polyethylene or polypropylene is preferable. In particular, a porous film made of polyethylene, polypropylene, or both is preferable because the safety of the secondary battery can be improved.

The thickness of the separator is preferably in the range of 5 to 30 μm. This is due to the following reasons. When the thickness is less than 5 μm, it may be difficult to sufficiently increase the battery resistance after the pores of the separator are closed. For this reason, it takes time to stop the battery function, and the temperature may reach an abnormally high temperature, causing a burst or a fire. As the thickness of the separator increases, the battery resistance after closing the holes increases, so that the battery function can be stopped quickly. However, the thickness is 30 μm
If it exceeds, the weight energy density and the volume energy density of the secondary battery may decrease. The upper limit of the thickness is more preferably 25 μm, and the lower limit is more preferably 10 μm.

The separator preferably has an air permeability of 600 seconds / 100 cm ³ or less. The air permeability means the time (seconds) required for 100 cm ³ of air to pass through the separator. Air permeability is 600 seconds / 1
If it exceeds 00 cm ³ , it may be difficult to obtain high lithium ion mobility in the separator. The lower limit of the air permeability is preferably set to 100 seconds / 100 cm ³ . 100 seconds / 100c air permeability
If it is less than m ³ , sufficient separator strength may not be obtained, and the pore closing start temperature may increase. The upper limit of air permeability is 500 seconds / 100cm
More preferably, the upper limit is set to ^3, and the more preferable upper limit is 4.
00 seconds / 100 cm ³ . Further, the lower limit is more preferably set to 150 seconds / 100 cm ³ .

The separator preferably has a heat shrinkage at 120 ° C. for one hour of 20% or less. If the heat shrinkage exceeds 20%, it may be difficult to increase the bonding strength between the positive and negative electrodes and the separator. More preferably, the heat shrinkage is 15% or less.

The separator has a porosity of 30 to 60%.
Is preferably within the range. This is due to the following reasons. If the porosity is less than 30%, it may be difficult to obtain high electrolyte retention in the separator. On the other hand, if the porosity exceeds 60%, sufficient separator strength may not be obtained. A more preferred range of porosity is 35-50%.

As the separator, polyolefin, cellulose and polyvinylidene fluoride (PVdF) are used.
Consisting of at least one material selected from the group consisting of: a thickness of 5 to 30 μm, and an air permeability of 600 seconds / 100 c
It is preferable to use a porous sheet of m ³ or less. Such separators can have internal short circuits, overcharge, or 13
When abnormal heat generation or temperature rise occurs due to high temperature storage of 0 ° C or more, the holes are quickly closed, so that abnormally high temperatures can be avoided, and rupture and ignition should be reliably prevented. Can be. Also, this separator
An increase in impedance when used in a normal high-temperature atmosphere can be suppressed. Further, it is preferable that the porosity of the separator is in the range of 30 to 60%. By defining the material, air permeability, thickness and porosity of the separator, it is possible to optimize the temperature at which the separator starts to close holes.

4) Adhesive Polymer The adhesive polymer exists at least at a part of the boundary between the positive electrode and the separator and at least part of the boundary between the negative electrode and the separator. Further, it is preferable that the polymer having adhesiveness is held inside the positive electrode, the negative electrode, and the separator.

It is preferable that the polymer having adhesiveness can maintain high adhesiveness while holding the non-aqueous electrolyte. Further, such a polymer preferably has a high lithium ion conductivity. Specifically, polyacrylonitrile (PAN), polyacrylate (PMM
A), polyvinylidene fluoride (PVdF), polyvinyl chloride (PVC), or polyethylene oxide (PE)
O) and the like. As the polymer having the adhesive property, one or more kinds selected from the above-mentioned kinds can be used. Particularly, polyvinylidene fluoride is preferable. Polyvinylidene fluoride can hold a non-aqueous electrolyte, and if it contains a non-aqueous electrolyte, gelation occurs partially, so that the ionic conductivity can be further improved.

It is preferable that the polymer having adhesiveness has a porous structure having fine pores in the spaces between the positive electrode, the negative electrode, and the separator. An adhesive polymer having a porous structure can hold a nonaqueous electrolyte.

The total amount of the polymer having adhesiveness contained in the battery (including the one contained in the adhesive portion described later) is
It is preferable to set the amount to 0.1 to 6 mg per 100 mAh of battery capacity. This is due to the following reasons.
If the total amount of the polymer having adhesiveness is less than 0.1 mg per 100 mAh of battery capacity, it may be difficult to sufficiently improve the adhesion between the positive electrode, the separator, and the negative electrode. On the other hand, the total amount is 6 per 100 mAh of battery capacity.
If the amount exceeds mg, the lithium ion conductivity of the secondary battery may decrease, or the internal resistance may increase, and it may be difficult to improve the discharge capacity, large current discharge characteristics, and charge / discharge cycle characteristics. . A more preferable range of the total amount of the polymer having an adhesive property is 0.1 to 100 mAh per battery capacity.
2-1 mg.

5) Non-aqueous electrolyte The non-aqueous electrolyte is held at least in the separator. In particular, the non-aqueous electrolyte is preferably dispersed throughout the electrode group. As the non-aqueous electrolyte, a liquid non-aqueous electrolyte,
A gel non-aqueous electrolyte or a solid non-aqueous electrolyte can be used.

(1) Liquid Non-Aqueous Electrolyte The liquid non-aqueous electrolyte is impregnated into the electrode group.

This liquid non-aqueous electrolyte can be obtained by dissolving the electrolyte in a non-aqueous solvent.

As the non-aqueous solvent, a known non-aqueous solvent as a solvent for a lithium secondary battery can be used, and is not particularly limited. Propylene carbonate (PC) or ethylene carbonate (EC) and the PC or EC It is preferable to use a non-aqueous solvent mainly composed of a mixed solvent with one or more non-aqueous solvents having lower viscosity (hereinafter referred to as a second solvent).

As the second solvent, for example, chain carbon is preferable, and among them, dimethyl carbonate (DM
C), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate, methyl propionate, γ-butyrolactone (γ-BL), acetonitrile (AN), ethyl acetate (EA), toluene,
Xylene or methyl acetate (MA) is exemplified. These second solvents can be used alone or in the form of a mixture of two or more. In particular, the second type solvent more preferably has a donor number of 16.5 or less.

The viscosity of the second solvent is 2 at 25 ° C.
It is preferably 8 mp or less. The amount of the ethylene carbonate or propylene carbonate in the mixed solvent is preferably 10 to 80% by volume. More preferably, the blending amount of ethylene carbonate or propylene carbonate is 20 to 75 by volume.
%.

As the electrolyte, for example, lithium perchlorate
(LiClO_Four), Lithium hexafluorophosphate (Li
PF₆), Lithium borofluoride (LiBF_Four), Six foot
Lithium arsenide (LiAsF)₆), Trifluorometas
Lithium sulfonate (LiCF _ThreeSO_Three), Bistriflu
Lithium olomethylsulfonylimide [LiN (CF _Three
SO_Two)_Two] And other lithium salts. Among them, L
iPF₆, LiBF_FourIt is preferable to use

The amount of the electrolyte dissolved in the non-aqueous solvent is desirably 0.5 to 2.0 mol / 1.

A particularly preferred liquid non-aqueous electrolyte is one in which an electrolyte (eg, lithium salt) is dissolved in a mixed non-aqueous solvent containing γ-butyrolactone (BL), and the composition ratio of BL is 40% of the total mixed non-aqueous solvent. % By volume or more and 95% by volume or less. In the mixed non-aqueous solvent, it is preferable that the composition ratio of BL is maximized. If the ratio is less than 40% by volume, gas is likely to be generated at high temperatures. Further, when the mixed non-aqueous solvent contains BL and cyclic carbonate, the ratio of the cyclic carbonate becomes relatively high, so that the solvent viscosity may be significantly increased. When the solvent viscosity increases, the conductivity and permeability of the liquid non-aqueous electrolyte decrease, so that the charge / discharge cycle characteristics, large current discharge characteristics, and-
The discharge characteristics in a low-temperature environment around 20 ° C. decrease. On the other hand, when the ratio exceeds 95% by volume, the reaction between the negative electrode and BL is likely to occur, so that the charge / discharge cycle characteristics may be deteriorated. That is, when the negative electrode (for example, a carbonaceous material that absorbs and releases lithium ions) reacts with BL to cause reductive decomposition of the liquid non-aqueous electrolyte, a film that inhibits the charge / discharge reaction is formed on the surface of the negative electrode. You. As a result, current concentration tends to occur in the negative electrode, so that lithium metal is deposited on the negative electrode surface, or the impedance at the negative electrode interface increases, so that the charge / discharge efficiency of the negative electrode decreases and the charge / discharge cycle characteristics deteriorate. A more preferred range is 6
0 vol% or more and 90 vol% or less. By setting the content in this range, the effect of suppressing gas generation during high-temperature storage can be further enhanced, and the discharge capacity in a low-temperature environment around −20 ° C. can be further improved. A more preferable range is 75% by volume or more and 90% by volume or less.

As the solvent to be mixed with BL, cyclic carbonate is preferable in terms of increasing the charge / discharge efficiency of the negative electrode.

As the cyclic carbonate, propylene carbonate (PC), ethylene carbonate (E
C), vinylene carbonate (VC), trifluoropropylene carbonate (TFPC) and the like are desirable. In particular,
When EC is used as a solvent mixed with BL, charge / discharge cycle characteristics and large current discharge characteristics can be significantly improved. Other solvents to be mixed with BL include PC,
When a mixed solvent of EC and a third solvent, which is at least one selected from the group consisting of VC, TFPC, diethyl carbonate (DEC), methyl ethyl carbonate (MEC) and an aromatic compound, and EC, the charge / discharge cycle characteristics are improved. Is desirable.

Further, from the viewpoint of lowering the solvent viscosity, a low-viscosity solvent may be contained at 20% by volume or less. Examples of the low-viscosity solvent include chain carbonate, chain ether, and cyclic ether.

The more preferable composition of the non-aqueous solvent according to the present invention is BL and EC, BL and PC, BL and EC and DEC, B
L, EC, and MEC; BL, EC, MEC, and VC; BL, EC, and VC; BL, PC, and VC; or BL, EC, PC, and VC. At this time, the volume ratio of EC is 5 to 4
It is preferably 0% by volume. This is due to the following reasons. If the EC ratio is less than 5% by volume, it may be difficult to cover the negative electrode surface with a protective film densely, so that a reaction between the negative electrode and BL occurs and the charge / discharge cycle characteristics can be sufficiently improved. Can be difficult. On the other hand, if the EC ratio exceeds 40% by volume, the viscosity of the liquid non-aqueous electrolyte may increase and the ionic conductivity may decrease, so that the charge / discharge cycle characteristics, large current discharge characteristics, and low temperature discharge characteristics are sufficiently improved. It can be difficult to improve. A more preferred range of the EC ratio is 10 to 3
5% by volume. The ratio of the solvent composed of at least one selected from DEC, MEC and VC is 0.5
It is preferable to be within the range of 10 to 10% by volume.

Examples of the electrolyte include those similar to those described above. Among them, it is preferable to use LiPF ₆ or LiBF ₄ .

The amount of the electrolyte dissolved in the non-aqueous solvent is desirably 0.5 to 2.0 mol / l.

The liquid non-aqueous electrolyte containing γ-BL includes:
In order to improve the wettability with the separator, a surfactant such as trioctyl phosphate may be added in the range of 0.1 to 1%.

The amount of the liquid non-aqueous electrolyte having each of the above-mentioned compositions is 0.2 to 0.6 per 100 mAh of battery unit capacity.
g is preferable. This is due to the following reasons. 0.2 g / 100 mA of liquid non-aqueous electrolyte
If it is less than h, the ion conductivity of the positive electrode and the negative electrode may not be able to be sufficiently maintained. On the other hand, if the liquid non-aqueous electrolytic mass exceeds 0.6 g / 100 mAh, the amount of electrolyte becomes large, so that sealing may become difficult when a sheet-made exterior material is used. A more preferred range of the mass of the liquid non-aqueous electrolyte is 0.4 to 0.55 g / 100 mAh.

(2) Gel Non-Aqueous Electrolyte The gel electrolyte is present inside the separator, at the boundary between the separator and the positive electrode, and at the boundary between the separator and the negative electrode.

The gel non-aqueous electrolyte comprises a mixture of a polymer material, a non-aqueous solvent and an electrolyte.

The polymer materials include polyvinylidene fluoride (PVdF) and polyacrylonitrile (PA
N), at least one polymer selected from polyethylene oxide (PEO), polyvinyl chloride (PVC) and polyacrylate (PMMA) can be used. Further, as the non-aqueous solvent and the electrolyte,
Examples similar to those described above in the section of the liquid non-aqueous electrolyte can be given.

The gelled non-aqueous electrolyte also functions as a polymer having adhesive properties for integrating the positive electrode, the negative electrode and the separator. For this reason, when this gelled non-aqueous electrolyte is used, it is not necessary to add the polymer having adhesiveness described in the above section (4).

(3) Solid Nonaqueous Electrolyte The solid nonaqueous electrolyte exists inside the separator, at the boundary between the separator and the positive electrode, and at the boundary between the separator and the negative electrode.

The solid non-aqueous electrolyte comprises a mixture of a polymer material such as polyethylene oxide (PEO) and a lithium salt.

Examples of the lithium salt include those similar to those described in the section of the liquid non-aqueous electrolyte described above.

The solid non-aqueous electrolyte also has a function as an adhesive polymer for integrating the positive electrode, the negative electrode and the separator. Therefore, when this solid non-aqueous electrolyte is used, it is not necessary to add the polymer having adhesiveness described in the above section (4).

6) Exterior Material The electrode group and the non-aqueous electrolyte held by the electrode group are sealed in the exterior material. The exterior material is formed, for example, from one or two multilayer sheets having a thermoplastic resin layer formed on the periphery. Further, the thermoplastic resin layer has a higher melting point than the pore closing start temperature of the separator. When an exterior material is formed from one sheet, the sheet is folded, and the facing thermoplastic resin layers are thermally fused to each other to form a sealed structure, which is used as the exterior material. On the other hand, when the exterior material is composed of two sheets, the two sheets are overlapped, and the facing thermoplastic resin layers are thermally fused to each other to form a sealed structure, thereby forming an exterior material. When the lead is extended from the exterior material, the thermoplastic resin layers facing each other are thermally fused with the lead interposed therebetween.

An example of a method of sealing an electrode group with an exterior material will be described with reference to FIGS. An electrode group to which the positive electrode lead 1 and the negative electrode lead 2 are electrically connected, and a sheet having a thermoplastic resin layer formed on at least the periphery 4 (region shown by oblique lines in the figure) as an exterior material 3 are prepared. This sheet is provided in two at the center on the long side, and the electrode group is covered with this sheet so that the positive electrode lead 1 and the negative electrode lead 2 extend from the sheet. At this time, the surface including the thermoplastic resin layer of the sheet is positioned inside. Next, the openings are sealed by thermally fusing the thermoplastic resin layer in the openings along the longitudinal direction of the sheet and the openings from which the leads 1 and 2 extend. In addition, the sheet is folded in two at the center on the long side so that the thermoplastic resin layer is located inside, and then the thermoplastic resin layers at both openings along the longitudinal direction are thermally fused to form the sheet into a bag shape. After processing and storing the electrode group in the bag, the sealing may be performed by thermally fusing the thermoplastic resin layer in the opening from which the positive electrode lead 1 and the negative electrode lead 2 extend.

When the melting point of the thermoplastic resin layer is lower than the temperature at which the pores of the separator begin to close, when abnormal heat generation or temperature rise occurs due to internal short-circuiting, overcharging, or leaving at a high temperature of 130 ° C. or more. Because the thermoplastic resin is melted again before the holes of the separator are closed,
The airtightness of the exterior material is impaired. As a result, the electrode group in which the battery reaction is actively occurring is exposed to the atmosphere, so that moisture in the atmosphere and lithium react with each other, causing rapid heat generation and ignition. However, the opening temperature at which the separator is clogged means the temperature measured by the method described above after the secondary battery is disassembled by the method described above.

Examples of the thermoplastic resin include polyolefin. Examples of the polyolefin include polyethylene and polypropylene. As the thermoplastic resin, one type selected from the types described above, or two or more types such as a mixture of polyethylene and polypropylene can be used. The melting point of the polyolefin varies depending on the crystallinity. Therefore, it is desirable to use a polyolefin having a desired melting point for the thermoplastic resin. In particular, a polypropylene having a melting point of 150 ° C. or higher, or a thermoplastic resin made of a mixture of the polypropylene and the polyethylene, because the sealing strength can be increased,
preferable.

The melting point of the thermoplastic resin is preferably set to 120 ° C. or higher. When the melting point is lower than 120 ° C,
When the secondary battery is stored in a normal high-temperature atmosphere (for example, around 40 ° C.) that does not reach an abnormally high temperature, the thermoplastic resin may melt and the hermeticity of the exterior material may be impaired. A more preferred range is 140 ° C. or higher. By the way, the temperature of the heating and pressurizing for sealing the opening of the exterior material is set higher than the melting point of the thermoplastic resin in order to increase the productivity. The higher the melting point, the higher the airtightness at high temperatures, but the higher the sealing temperature. If the melting point exceeds 250 ° C., the non-aqueous electrolyte may be deteriorated by heat applied at the time of sealing, or the separator may be thermally contracted. Therefore, the upper limit of the melting point is preferably set to 250 ° C. A more preferred upper limit is 220 ° C.

The temperature difference between the pore closing start temperature of the separator and the melting point of the thermoplastic resin layer of the exterior material is 5 ° C.
It is preferable to make the above. When the temperature difference is less than 5 ° C., before the charge / discharge reaction is stopped by closing the holes of the separator, the thermoplastic resin layer in the sealing region of the exterior material is melted and the hermeticity of the exterior material is reduced. Might be. More preferably, the temperature difference is 20 ° C. or higher. However, the opening temperature at which the separator is clogged means the temperature measured by the method described above after the secondary battery is disassembled by the method described above.

A specific example of the exterior material is a multilayer sheet in which a layer having a function of blocking moisture and protective layers disposed on both sides of the moisture blocking layer are integrated.
Examples of the moisture blocking layer include a metal layer. Examples of the metal layer include aluminum, stainless steel, iron, copper, and nickel. Among them, aluminum which is lightweight and has a high function of blocking moisture is preferable. The metal layer may be formed from one type of metal, or may be formed from a combination of two or more types of metal layers. Of the two protective layers, a protective layer in contact with the outside serves to prevent damage to the metal layer. This outer protective layer is preferably formed of one or more resins selected from polyethylene and polypropylene. On the other hand, the internal protective layer serves to prevent the metal layer from being corroded by the non-aqueous electrolyte, and a part of the surface serves as a sealing region. The internal protective layer may be formed of only the above-described thermoplastic resin, or may be formed of only the above-described thermoplastic resin only near the surface. When the internal protective layer is formed of a thermoplastic resin, a material obtained by integrating two or more types of thermoplastic resin layers may be used.

It is preferable that the thickness of the exterior material is 500 μm or less. If it exceeds 500 μm, the capacity per unit weight of the battery may be reduced. Exterior material thickness is 3
The thickness is preferably not more than 00 μm, more preferably 2 μm.
It is 50 μm or less, most preferably 150 μm or less. On the other hand, if the thickness is less than 50 μm, deformation or breakage is likely. Therefore, the lower limit of the thickness is preferably set to 50 μm. A more preferred lower limit is 80 μm, and a most preferred range is 100 μm.

The thickness of the exterior material is measured by the method described below. That is, in the region other than the sealing portion of the exterior material, three points that are 1 cm or more apart from each other are arbitrarily selected, the thickness of each point is measured, an average value is calculated, and this value is calculated as the thickness of the exterior material. And When foreign matter (for example, resin) is attached to the surface of the exterior material, the thickness is measured after removing the foreign matter. For example, P
When VdF has adhered, the surface of the exterior material is wiped off with a dimethylformamide solution to remove PVdF, and then the thickness is measured.

The electrode group is desirably adhered to the inner surface of the exterior material by an adhesive layer formed on at least a part of the surface. With such a configuration, the exterior material can be fixed to the surface of the electrode group, so that it is possible to suppress the penetration of the electrolytic solution between the electrode group and the exterior material.

The first non-aqueous electrolyte secondary battery has a battery capacity (Ah) and a 1 kHz internal impedance (m
Ω) is preferably 10 mΩ · Ah or more and 110 mΩ · Ah or less. By setting the product of the capacity and the impedance within the above range, the large current discharge characteristics and the charge / discharge cycle characteristics can be further improved. Here, the battery capacity is the nominal capacity or the discharge capacity when discharging at 0.2C. A more preferred range is 20 mΩ · Ah
As described above, the value is 60 mΩ · Ah or less.

A thin lithium ion secondary battery which is an example of the first non-aqueous electrolyte secondary battery will be described in detail with reference to FIGS. 3 and 4 and FIGS.

FIG. 5 is a cross-sectional view of the thin lithium-ion secondary battery of FIG. 3 along the line VV, FIG. 6 is an enlarged cross-sectional view showing a part A of FIG. 5, and FIG. 7 is a part B of FIG. FIG. 7 is an enlarged cross-sectional view, and FIG. 7 is a schematic view showing the vicinity of the boundary between the positive electrode layer, the separator, and the negative electrode layer in the secondary battery of FIG.

The electrode group 5 having the positive electrode lead 1 and the negative electrode lead 2 is housed in the exterior material 3 with the positive electrode lead 1 and the negative electrode lead 2 extending from the exterior material 3. As shown in FIG. 6, for example, the exterior material 3 includes a thermoplastic resin layer 6, a metal layer 7 laminated on the thermoplastic resin layer 6, and an external protective layer 8 laminated on the metal layer 7. It consists of a laminated film. Therefore, in the exterior material 3, the entire inner surface is formed of the thermoplastic resin layer. The electrode group 5 has a structure in which a laminate including a positive electrode, a separator, and a negative electrode is wound into a flat shape. As shown in FIG. 7, the laminate includes a separator 9 (from the bottom of the figure), a positive electrode 12 including a positive electrode layer 10, a positive electrode current collector 11, and a positive electrode layer 10, a separator 9, a negative electrode layer 13, and a negative electrode collector. Electric body 14
, A negative electrode 15 having a negative electrode layer 13, a separator 9, a positive electrode layer 10, a positive electrode current collector 11 and a positive electrode 12 having a positive electrode layer 10,
The negative electrode 15 including the separator 9, the negative electrode layer 13 and the negative electrode current collector 14 is laminated in this order. In the electrode group 5, the negative electrode current collector 14 is located in the outermost layer.
On the surface of the electrode group 5, an adhesive portion 16 exists.
The inner surface of the exterior material 3 excluding the sealing region 4 is the bonding portion 1
6 is adhered. As shown in FIG. 8, the positive electrode layer 10,
In the gap between the separator 9 and the negative electrode layer 13, a polymer 17 having an adhesive property is held. The positive electrode 12 and the separator 9 are adhered to each other by an adhesive polymer 17 scattered inside the positive electrode layer 10 and the separator 9 and at the boundary between them. On the other hand, the negative electrode 15 and the separator 9
Are bonded to each other by an adhesive polymer 17 scattered inside the negative electrode layer 13 and the separator 9 and at the boundary between them. The liquid non-aqueous electrolyte is impregnated in the electrode group 5. The terminal of the positive electrode lead 1 is connected to the positive electrode current collector 11 of the electrode group 5. On the other hand, the end of the negative electrode lead 2 is connected to the negative electrode current collector 14 of the electrode group 5.
It is connected to the.

In FIG. 5, the electrode group 5
Although the bonding part 16 is formed on the entire surface of the electrode group 5, the bonding part 16 may be formed on a part of the electrode group 5. When forming the bonding portion 16 on a part of the electrode group 5, it is preferable to form the bonding portion 16 on at least the surface corresponding to the outermost periphery of the electrode group. In addition, the bonding portion 16
May not be required.

The first non-aqueous electrolyte secondary battery is manufactured, for example, by the method (I) described below. However,
The manufacturing method of the nonaqueous electrolyte secondary battery according to the present invention is not limited to the following embodiments as long as it is within the scope of the present invention.

<Production Method (I)> (First Step) An electrode group is produced by interposing a porous sheet as a separator between the positive electrode and the negative electrode.

The electrode group may be formed by spirally winding the positive electrode and the negative electrode through a non-polymer-holding separator having an adhesive property therebetween, or by spirally winding and then compressing in the radial direction. Alternatively, it is desirable that the positive electrode and the negative electrode are formed by bending a plurality of times through a non-polymer-holding separator having adhesiveness therebetween. When manufactured by such a method, in a second step described later, the positive electrode,
It is possible to prevent the solution from penetrating the entire boundary between the positive electrode and the separator and the entire boundary between the negative electrode and the separator while allowing the solution of the polymer having adhesiveness to permeate the negative electrode and the separator. As a result, it becomes possible to disperse the adhesive polymer on the positive electrode, the negative electrode and the separator, and to disperse the adhesive polymer on the boundary between the positive electrode and the separator and the boundary between the negative electrode and the separator. it can.

The positive electrode is produced, for example, by suspending a conductive agent and a binder in a suitable solvent in a positive electrode active material, applying the suspension to a current collector, and drying to form a thin plate. . Examples of the positive electrode active material, the conductive agent, the binder, and the current collector include those similar to those described in the section of (1) Positive electrode described above.

The negative electrode is prepared, for example, by kneading a carbonaceous substance that occludes / releases lithium ions and a binder in the presence of a solvent, applying the obtained suspension to a current collector, drying the resultant, It is produced by pressing once at a desired pressure or multi-stage pressing 2 to 5 times.

The carbonaceous material, the binder and the current collector may be the same as those described in the section of (2) Negative electrode.

As the porous sheet of the separator,
The same one as described in the section of (3) Separator described above can be used.

(Second Step) A sheet in which a sealing region is made of a thermoplastic resin is prepared as an exterior material, and the thermoplastic resin is melted and pressed to be processed into a bag shape. The electrode group is housed in the bag so that the lamination surface can be seen from the opening. A solution obtained by dissolving a polymer having adhesiveness in a solvent is injected into an electrode group in the exterior material through an opening to impregnate the electrode group with the solution.

Examples of the exterior material include those similar to those described in the section of (6) Exterior material described above.

Examples of the polymer having the adhesive property include the same polymers as those described in the section of the polymer having the adhesive property in (4) above. In particular, PVdF is preferable.

It is desirable to use an organic solvent having a boiling point of 200 ° C. or less as the solvent. Such organic solvents include:
For example, dimethylformamide (boiling point: 153 ° C.) can be mentioned. When the boiling point of the organic solvent exceeds 200 ° C., when the heating temperature described below is set to 100 ° C. or lower, the drying time may take a long time. The lower limit of the boiling point of the organic solvent is preferably set to 50 ° C. If the boiling point of the organic solvent is lower than 50 ° C., the organic solvent may evaporate while the solution is being injected into the electrode group. The upper limit of the boiling point is more preferably 180 ° C, and the lower limit of the boiling point is more preferably 100 ° C.

The concentration of the adhesive polymer in the solution is preferably in the range of 0.05 to 2.5% by weight. This is due to the following reasons. If the concentration is less than 0.05% by weight, it may be difficult to bond the positive and negative electrodes and the separator with sufficient strength.
On the other hand, if the concentration exceeds 2.5% by weight, it is difficult to obtain sufficient porosity to hold the nonaqueous electrolyte, and the interface impedance of the electrode may be significantly increased. When the interface impedance increases, the capacity and the large-current discharge characteristics are significantly reduced. A more preferred range of the concentration is from 0.1 to 1.5% by weight.

When the concentration of the adhesive polymer in the solution is 0.05 to 2.5% by weight, the injection amount of the solution is preferably in the range of 0.1 to 2 ml per 100 mAh of battery capacity. preferable. This is due to the following reasons. If the injection amount is less than 0.1 ml, it may be difficult to sufficiently increase the adhesion between the positive electrode, the negative electrode, and the separator. On the other hand, if the injection amount exceeds 2 ml, the lithium ion conductivity of the secondary battery may decrease, or the internal resistance may increase. It can be difficult. A more preferable range of the injection amount is 0.15 to 1 ml per 100 mAh of battery capacity.

(Third Step) The solvent in the solution is evaporated by heating the electrode group in a reduced pressure atmosphere including vacuum or a normal pressure atmosphere while pressing the electrode group to a predetermined thickness. A polymer having an adhesive property is present in the space between the positive electrode, the negative electrode and the separator. By this step, the positive electrode and the separator are bonded by a polymer having adhesive properties scattered in the inside and the boundary thereof, and the negative electrode and the separator have adhesive properties scattered in the inside and the boundary thereof. Glued by polymer. Further, by this heating, moisture contained in the electrode group can be removed at the same time.

The electrode group is allowed to contain a trace amount of solvent.

The heating is preferably performed at 100 ° C. or lower. This is due to the following reasons. If the heating temperature exceeds 100 ° C., the separator may be significantly shrunk. When the heat shrinkage increases, the porosity of the separator decreases, and the battery characteristics deteriorate. Further, the above-mentioned heat shrinkage tends to occur remarkably when a porous film containing polyethylene or polypropylene is used as a separator. Although the heat shrinkage of the separator can be suppressed as the heating temperature decreases, if the heating temperature is less than 40 ° C., it may be difficult to sufficiently evaporate the solvent. Therefore, the heating temperature is more preferably set to 40 to 100 ° C.

(Fourth Step) After injecting a liquid non-aqueous electrolyte into the electrode group in the exterior material, the opening of the exterior material is sealed by melting and pressing a thermoplastic resin to form a thin non-aqueous electrolyte. Assemble the next battery.

As the liquid non-aqueous electrolyte, those similar to those described in the section of (5) Non-aqueous electrolyte described above can be used.

In the above-described manufacturing method, the solution in which the polymer having the adhesive property is dissolved is injected after the electrode group is housed in the exterior material. good. In this case, first, an electrode group is prepared by interposing a separator between the positive electrode and the negative electrode. After the electrode group is impregnated with the solution, the solvent of the solution is evaporated by applying heat and drying while press-molding the electrode group, and a high adhesive having a high adhesiveness in the gap between the positive electrode, the negative electrode and the separator. Make the molecule exist. After storing such an electrode group in an exterior material, a liquid non-aqueous electrolyte is injected, sealing is performed, and the like, whereby a thin non-aqueous electrolyte secondary battery can be manufactured. An adhesive may be applied to the outer periphery of the electrode group before being housed in the exterior material. Thereby, the electrode group can be bonded to the exterior material.

(Fifth Step) The secondary battery assembled as described above is initially charged. In this first charge, the temperature is
80 ° C. and charge rate of 0.05 C or more, 0.5
C or less is preferable. Charging at such a temperature and a charging rate may be performed only in one cycle, or may be performed in two or more cycles. In addition, before the first charge,
It may be stored for about 1 to 20 hours under a temperature condition of ° C.

Here, the 1C charge rate is the nominal capacity (A
h) is the current value required to charge the battery in one hour.

The temperature of the first charge is defined in the above range for the following reason. Initial charge temperature is 30
When the temperature is lower than 0 ° C., the viscosity of the liquid non-aqueous electrolyte may remain high, so that it may be difficult to uniformly impregnate the positive electrode, the negative electrode, and the separator with the liquid non-aqueous electrolyte. Therefore, there is a possibility that the internal impedance increases and the utilization rate of the active material decreases. On the other hand, when the initial charge temperature exceeds 80 ° C., the binder contained in the positive electrode and the negative electrode may be deteriorated.

The charge rate of the first charge is 0.05 to 0.5 C
By setting the range, the expansion of the positive electrode and the negative electrode due to charging can be moderately delayed, so that the liquid nonaqueous electrolyte can uniformly penetrate the positive electrode and the negative electrode.

Under a temperature condition of 30 to 80 ° C., 0.05 to
By performing the initial charge at a charge rate of 0.5 C, the liquid non-aqueous electrolyte can be uniformly impregnated into the gaps of the electrodes and the separator.
Can be reduced, and the product of battery capacity and 1 kHz internal impedance is 10 mΩ · A
h and 110 mΩ · Ah or less. As a result, the utilization rate of the active material can be increased, so that the substantial capacity of the battery can be increased. Further, the charge / discharge cycle characteristics and the large current discharge characteristics of the battery can be improved.

<Second Non-Aqueous Electrolyte Secondary Battery> This second non-aqueous electrolyte secondary battery is arranged between a positive electrode, a negative electrode, and the positive electrode and the negative electrode, and has a property that pores are closed by heating. An electrode group comprising: a porous separator having: a non-aqueous electrolyte held by the separator; and at least a part of the inner surface is formed of a sheet formed of a thermoplastic resin layer,
A housing for accommodating the electrode group and heat-sealing the thermoplastic resin layers to seal the electrode group; As the exterior material, a multilayer sheet including a thermoplastic resin layer forming at least a part of an inner surface or a sheet made of a thermoplastic resin can be used.

The positive electrode, the negative electrode and the separator are integrated by thermosetting a binder contained in the positive electrode and the negative electrode. Further, the thermoplastic resin layer has a higher melting point than the pore closing start temperature of the separator.

As the positive electrode, the negative electrode, and the separator, the same ones as described in the first nonaqueous electrolyte secondary battery described above are used, except that an adhesive polymer is not contained. As the non-aqueous electrolyte and the exterior material, the same ones as described in the first non-aqueous electrolyte secondary battery described above are used.

The second non-aqueous electrolyte secondary battery has a battery capacity (Ah) and a 1 kHz internal impedance (m
Ω) is preferably 10 mΩ · Ah or more and 110 mΩ · Ah or less. By setting the product of the capacity and the impedance within the above range, the large current discharge characteristics and the charge / discharge cycle characteristics can be further improved. Here, the battery capacity is the nominal capacity or the discharge capacity when discharging at 0.2C. A more preferred range is 20 mΩ · Ah
As described above, the value is 60 mΩ · Ah or less.

This second non-aqueous electrolyte secondary battery is manufactured, for example, by the method (II) described below.

<Manufacturing Method (II)> (First Step) An electrode group is manufactured by the following methods (a) to (c).

(A) A positive electrode and a negative electrode are spirally wound with a separator interposed therebetween.

(B) The positive electrode and the negative electrode are spirally wound with a separator interposed therebetween, and then compressed in the radial direction.

(C) The positive electrode and the negative electrode are bent at least twice with a separator interposed therebetween.

(Second Step) A sheet in which the sealing region is made of a thermoplastic resin is prepared as an exterior material, and the thermoplastic resin is melted and pressed to be processed into a bag shape. The electrode group is stored in the obtained bag.

(Third Step) The above-mentioned electrode group was heated to 40 to 120 ° C.
While heating.

The molding is performed in the radial direction when the electrode group is produced by the method (a), and is laminated when the electrode group is produced by the method (b) or (c). The compression is performed in the direction.

The molding can be carried out, for example, by press molding or filling in a molding die.

The reason why the electrode group is heated when the electrode group is formed will be described. The electrode group does not include an adhesive polymer. For this reason, if the electrode group is molded at room temperature, springback occurs after molding,
That is, a gap is formed between the positive electrode and the separator and between the negative electrode and the separator. As a result, the contact area between the positive electrode and the separator and the contact area between the negative electrode and the separator decrease, so that the internal impedance increases. By forming the electrode group at a temperature of 40 ° C. or higher, the binder contained in the positive electrode and the negative electrode can be thermoset, so that the hardness of the electrode group can be increased. As a result, springback after molding can be suppressed, so that the contact area between the positive electrode and the separator and the contact area between the negative electrode and the separator can be improved, and the contact area can be maintained even after repeated charge / discharge cycles. Can be. On the other hand, when the temperature of the electrode group is 1
If the temperature exceeds 20 ° C., the separator may be significantly shrunk by heat. A more preferred temperature is 60 to 100 ° C.

The above-described molding while heating to the specific temperature can be performed, for example, under normal pressure, under reduced pressure, or under vacuum. It is preferable to perform the treatment under reduced pressure or under vacuum because the efficiency of removing water from the electrode group is improved.

When the molding is performed by press molding, the pressing pressure is preferably in the range of 0.01 to 20 kg / cm ² . This is due to the following reasons. If the press pressure is lower than 0.01 kg / cm ² ,
It may be difficult to suppress springback after molding. On the other hand, if the press pressure is higher than 20 kg / cm ² , the porosity in the electrode group may decrease, and the liquid nonaqueous electrolyte holding amount of the electrode group may be insufficient.

(Fourth Step) The liquid non-aqueous electrolyte is injected into the electrode group in the exterior material, and then the opening of the exterior material is sealed by melting and pressing a thermoplastic resin.
Assemble the non-aqueous electrolyte secondary battery.

In the above-described manufacturing method, the electrode group is housed in the exterior material and then molded while heating the electrode group to a specific temperature. However, the above-described heat molding may be performed before being housed in the exterior material. In this case, first, an electrode group is manufactured by the above-described first step. The electrode group is formed while being heated to 40 to 120 ° C. Next, the second nonaqueous electrolyte secondary battery can be assembled by housing the electrode group in an outer package, injecting a liquid nonaqueous electrolyte, performing sealing, and the like.

(Fifth Step) The secondary battery assembled as described above is initially charged. In this first charge, the temperature is
80 ° C. and charge rate of 0.05 C or more, 0.5
C or less is preferable. Charging at such a temperature and a charging rate may be performed only in one cycle, or may be performed in two or more cycles. In addition, before the first charge,
It may be stored for about 1 to 20 hours under a temperature condition of ° C.

The reason why the temperature of the initial charge and the charge rate of the initial charge are defined in the above ranges is for the same reason as described above.

Under a temperature condition of 30 to 80 ° C., 0.05 to
By performing the initial charge at a charge rate of 0.5 C, the liquid non-aqueous electrolyte can be uniformly impregnated into the gaps of the electrodes and the separator.
Can be reduced, and the product of battery capacity and 1 kHz internal impedance is 10 mΩ · A
h and 110 mΩ · Ah or less. As a result, the utilization rate of the active material can be increased, so that the substantial capacity of the battery can be increased. Further, the charge / discharge cycle characteristics and the large current discharge characteristics of the battery can be improved.

As described in detail above, the non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode, a negative electrode, a porous separator disposed between the positive electrode and the negative electrode, and having a property that pores are closed by heating. A non-aqueous electrolyte held by the separator; and a sheet in which at least a part of the inner surface is formed of a thermoplastic resin layer. The electrode group is housed, and the thermoplastic resin layers are separated from each other. An exterior material for heat sealing to seal the electrode group; The positive electrode, the negative electrode, and the separator are integrated. Further, the thermoplastic resin layer has a higher melting point than the pore closing start temperature of the separator.

In such a secondary battery, when abnormal heat generation or temperature rise occurs due to internal short circuit, overcharging, or leaving at a high temperature of 130 ° C. or more, the separator before the thermoplastic resin of the exterior material is melted. Holes can be closed. As a result, the movement of lithium ions in the separator is hindered in a state where the internal pressure is kept high and the airtightness is maintained, so that the battery reaction can be stopped. Therefore, a further rise in temperature can be avoided, so that rupture or ignition can be avoided beforehand, and safety can be ensured.

In the secondary battery according to the present invention, the lithium ion mobility of the separator can be improved by setting the air permeability of the separator to 600 seconds / 100 cm ³ or less. As a result, safety can be improved, and high-current discharge characteristics can be improved.

In the secondary battery according to the present invention, by setting the thickness of the separator in the range of 5 to 30 μm, the battery resistance after closing the hole of the separator can be increased. can do. As a result, a rise in temperature can be further suppressed, so that safety can be further improved. At the same time, the weight energy density and the volume energy density of the secondary battery can be increased.

In the secondary battery according to the present invention, by setting the opening temperature of the separator to be 100 to 150 ° C., the opening of the separator can be quickly closed when the temperature rises sharply. As a result, the battery function can be stopped earlier before the thermoplastic resin in the sealing region of the exterior material melts, so that the safety can be further improved. In addition, since the separator can suppress an increase in impedance when used in a normal high-temperature environment, excellent charge / discharge characteristics can be maintained at a high temperature.

In the secondary battery according to the present invention, the separator
Polyolefin, cellulose and polyfluorocarbon
At least one selected from vinylidene fluoride (PVdF)
5-30 μm thick and air permeable
Excess rate is 600 seconds / 100cm ^ThreeUse the following porous sheet
Allows for rapid temperature rise
The pores of the separator can be closed. as a result,
Earlier before the thermoplastic resin in the sealing area of the exterior material melts
Battery function can be stopped at an
Properties can be further improved. Also this separator
Is the impedance when used in a normal high temperature environment.
Excellent at high temperatures because it can suppress the rise
Charge / discharge characteristics can be maintained.

In the secondary battery according to the present invention, a porous sheet made of at least one kind of resin selected from polyolefin, cellulose and polyvinylidene fluoride is used as the separator, and a polyolefin is used as the thermoplastic resin of the exterior material. Thereby, when a rapid temperature rise occurs, the holes of the separator can be quickly closed. As a result, the battery function can be stopped earlier before the thermoplastic resin in the sealing region of the exterior material melts, so that the safety can be further improved. In addition, since the separator can suppress an increase in impedance when used in a normal high-temperature environment, excellent charge / discharge characteristics can be maintained at a high temperature. Further, since the corrosion of the thermoplastic resin in the sealing region by the non-aqueous electrolyte can be suppressed, the airtightness of the exterior material can be further improved.

In the secondary battery according to the present invention, by using a liquid non-aqueous electrolyte as the non-aqueous electrolyte, the impedance at the positive electrode interface and the negative electrode interface can be reduced as compared with a lithium ion secondary battery having a gel polymer electrolyte layer. Since the lithium ion conductivity can be increased and the lithium ion conductivity can be increased, the charge and discharge characteristics at a large current can be improved.

As the liquid non-aqueous electrolyte, a non-aqueous solvent,
By using a liquid containing a lithium salt dissolved in the non-aqueous solvent, and by including γ-butyrolactone in the non-aqueous solvent in an amount of 40% by volume or more and 95% by volume or less of the entire non-aqueous solvent, Since the water electrolyte can be uniformly permeated, the lithium ion mobility of the separator can be improved, and the large current discharge characteristics can be improved. In addition, since the non-aqueous electrolyte can enhance thermal stability, abnormal heat generation of the battery can be suppressed, and safety can be further improved.
Furthermore, since γ-butyrolactone is excellent in chemical stability, by containing a specific amount of γ-butyrolactone in a non-aqueous solvent, the positive electrode active material and the liquid non-aqueous electrolyte can be stored under high temperature conditions. Oxidative decomposition of the liquid non-aqueous electrolyte due to the reaction. as a result,
Since the amount of generated gas can be reduced, the swelling of the exterior material can be suppressed. For this reason, it is possible to avoid such a problem that the battery cannot be accommodated in the electronic device or a malfunction of the electronic device is caused.

When the secondary battery is initially charged, the charging temperature is set to 30 to 80 ° C., and the charging rate is set to 0.05 to 0.
By setting the temperature to 5C, it is possible to suppress the negative electrode and γ-butyrolactone from reacting and reducing and decomposing the liquid non-aqueous electrolyte. Therefore, the interface impedance of the negative electrode can be reduced, and the precipitation of metallic lithium can be reduced. Can be suppressed. Therefore, the large current discharge characteristics and the charge / discharge cycle characteristics of the secondary battery can be improved.

By using a gelled non-aqueous electrolyte as the non-aqueous electrolyte, internal short-circuiting, overcharging or 130 ° C. can be performed as compared with a secondary battery having a gelled polymer electrolyte.
Since the secondary battery can be prevented from generating heat at the time of abnormalities such as the high-temperature storage, safety can be further improved.

By the way, the exterior material included in the secondary battery according to the present invention is easily deformed following the expansion and contraction of the electrode group accompanying the charge / discharge reaction, and the force holding the electrode group is weak. For this reason, as the charge / discharge cycle progresses, the contact area between the positive electrode and the separator and the contact area between the negative electrode and the separator may decrease. The decrease in the contact area causes an increase in the internal resistance. The positive electrode and the separator are integrated by an adhesive polymer that is scattered inside and at the boundary thereof, and the negative electrode and the separator are integrated by an adhesive polymer that is scattered inside and at the boundary thereof. Thus, the internal impedance at the beginning of the charge / discharge cycle can be reduced, and the value can be maintained even when the charge / discharge cycle proceeds, so that the cycle life can be further improved.

Further, as shown in FIG. 8 described above, the non-aqueous electrolyte is held in the fine gaps formed by the polymer having the adhesive property, so that the battery characteristics can be improved even when a film-made packaging material is used. , And a lightweight and thin non-aqueous electrolyte secondary battery can be realized.

Further, in the secondary battery according to the present invention, the positive electrode, the negative electrode, and the separator are integrated by thermally curing the binder contained in the positive electrode and the negative electrode, so that the charge-discharge cycle can be started early. Can be reduced, and the value can be maintained even when the charge / discharge cycle proceeds, so that the cycle life can be further improved.

[0150]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail.

First, a description will be given of the temperature at which the separators included in the secondary batteries of Examples and Comparative Examples start to close holes.

A test cell obtained by sandwiching a separator between two electrodes made of a nickel plate was immersed in a non-aqueous solution having the same composition as the non-aqueous electrolyte used in each of the examples and comparative examples. Vacuum impregnation was performed for 10 minutes in a desiccator so that the non-aqueous solution did not volatilize. In addition,
The size of the electrode was 10 × 15 mm, and the size of the separator was 20 × 25 mm. Then, at 100 ° C, 1
After standing for 0 minutes, the cell temperature and the cell resistance at an AC frequency of 1 KHz were measured while increasing the temperature at 2 ° C./min.
The temperature at which the cell resistance value began to rise sharply was determined, and this temperature was defined as the separator blockage start temperature.

Example 1 <Preparation of Positive Electrode> First, lithium cobalt oxide (Li _x
CoO ₂ ; where X is 0 ≦ X ≦ 1) 91% by weight of powder, 2.5% by weight of acetylene black, 3% by weight of graphite, 4% by weight of polyvinylidene fluoride (PVdF) and N-methylpyrrolidone (NMP) ) Was added and mixed to prepare a slurry. The obtained slurry was applied to both sides of a current collector made of an aluminum foil having a thickness of 10 μm, dried, and pressed to carry a positive electrode layer having a thickness of 48 μm on each surface of the current collector. A positive electrode having a structure was prepared. In the obtained positive electrode, the electrode density was 3.0 g / c.
m ³ , the total thickness of the positive electrode layer was 96 μm.

<Preparation of Negative Electrode> 3000 carbonaceous materials were used.
93% by weight of a powder of mesophase pitch-based carbon fiber (fiber diameter: 8 μm, average fiber length: 20 μm, average plane spacing (d ₀₀₂ ): 0.3360 nm) heat-treated at ℃
And polyvinylidene fluoride (PVdF) 7 as a binder
% By weight and an N-methylpyrrolidone (NMP) solution were mixed to prepare a slurry. The obtained slurry is applied to both sides of a current collector made of a copper foil having a thickness of 10 μm, dried, and pressed, so that a thickness of 45 mm is applied to each surface of the current collector.
A negative electrode having a structure in which a negative electrode layer of μm was supported was produced. In the obtained negative electrode, the electrode density was 1.3 g / cm ³ and the total thickness of the negative electrode layer was 90 μm.

<Separator> A separator made of a polyethylene porous film having a thickness of 20 μm, a porosity of 40%, and a pore closing start temperature before assembling into an electrode group shown in Table 1 below was prepared.

<Preparation of Electrode Group> After the positive electrode and the negative electrode were spirally wound with the separator interposed therebetween, and then formed into a flat shape, the thickness was 2.5 mm.
Thus, an electrode group having a width of 30 mm and a height of 50 mm was prepared.

<Preparation of Liquid Nonaqueous Electrolyte> Lithium tetrafluoroborate (LiBF ₄ ) was converted to ethylene carbonate (E
1.5 mol / 1 was dissolved in a mixed solvent of C) and γ-butyrolactone (BL) (mixing volume ratio 25:75) to prepare a liquid non-aqueous electrolyte.

A 100 μm-thick laminated film was prepared in which both surfaces of an aluminum foil as a metal layer were covered with a thermoplastic resin layer made of polypropylene having a melting point of 160 ° C. The laminated film was processed into a bag shape by applying a heat press at 190 ° C. to thermally fuse the thermoplastic resin layers in the sealed region. The electrode group was housed in this, and both sides were sandwiched by a holder so that the thickness became 2.7 mm. 0.3% by weight of polyvinylidene fluoride (PVdF), a polymer having adhesive properties, in dimethylformamide (boiling point: 153 ° C.) as an organic solvent
Dissolved. The obtained solution was injected into the electrode group in the exterior material so that the amount per battery capacity of 100 mAh was 0.6 ml, and the solution was permeated into the electrode group, and was spread over the entire surface of the electrode group. Attached.

Then, the organic solvent is evaporated by subjecting the electrode group in the exterior material to vacuum drying at 80 ° C. for 12 hours, and the adhesive polymer is held in the gaps between the positive electrode, the negative electrode and the separator. A porous adhesive portion was formed on the surface of the electrode group.

After injecting 2 g of the liquid non-aqueous electrolyte into the electrode group in the exterior material, the opening of the exterior material was heated and pressed at 190 ° C. to thermally fuse the thermoplastic resin layers on the inner surface of the opening. Then, the opening is sealed, and a thin nonaqueous electrolyte secondary battery having a thickness of 2.7 mm, a width of 32 mm, and a height of 55 mm having the structure shown in FIGS. Was.

The following treatment was applied to the obtained nonaqueous electrolyte secondary battery of Example 1 as an initial charging step. First, after leaving for 5 hours in a high temperature environment of 40 ° C., 0.2 C
(120mA), constant current and constant voltage charging up to 4.2V
Performed for 0 hours. Thereafter, at 20 ° C. and 0.2 C.
Discharged to 7V. The discharge capacity at this time was 400 mAh. Further, charging was performed in a second cycle under the same conditions as in the first cycle except that the temperature was changed to 20 ° C., to produce a nonaqueous electrolyte secondary battery.

(Examples 2 to 4) Thin nonaqueous electrolyte secondary batteries were manufactured in the same manner as in Example 1 except that the pore closing start temperature of the separator was changed as shown in Table 1 below.

Example 5 A thin non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that the pore closing start temperature of the separator and the melting point of polypropylene of the exterior material were changed as shown in Table 1 below. A battery was manufactured.

Example 6 A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the composition of the liquid non-aqueous electrolyte was changed as shown in Table 2 below.

(Examples 7 and 8) Thin non-aqueous electrolyte secondary batteries were manufactured in the same manner as in Example 1 except that the pore closing start temperature of the separator was changed as shown in Table 1 below.

Comparative Example 1 A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the type of the thermoplastic resin of the exterior material was changed as shown in Table 1 below. .

(Comparative Examples 2-3) A thin non-woven fabric was prepared in the same manner as in Example 1 except that the material of the separator, the pore closing start temperature, and the melting point of the polyethylene of the exterior material were changed as shown in Table 1 below. A water electrolyte secondary battery was manufactured.

(Comparative Example 4) The material of the separator, the temperature at which the pores were closed, and the melting point of the polyethylene of the exterior material were as shown in Table 1 below.
A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 6 except that the structure was changed as shown in FIG.

Comparative Example 5 A liquid nonaqueous electrolyte and polyvinylidene fluoride having the same composition as in Example 6 described above
VdF) to form a gel by mixing and gelling.
A μm gel-like polymer electrolyte layer was prepared. An electrode group was prepared by interposing a gel polymer electrolyte layer between the positive electrode and the negative electrode as described in Example 1.

A laminated film similar to that described in Example 1 was processed into a bag shape in the same manner as described in Example 1. The electrode group is accommodated therein, and the opening of the exterior material is sealed in the same manner as described in Example 1. The thin non-aqueous liquid has a thickness of 2.7 mm, a width of 32 mm, and a height of 55 mm. An electrolyte secondary battery was manufactured.

The obtained secondary battery was subjected to the same initial charging step as described in Example 1 to produce a non-aqueous electrolyte secondary battery.

The obtained Examples 1 to 8 and Comparative Examples 1 to 5
The non-aqueous electrolyte secondary battery of No. was measured for a large current discharge characteristic (0.2 to 3 C) in a 4.2 V charged state.
The discharge capacity value in 3C discharge when the discharge capacity in 2C discharge was set to 100% was obtained, and the results are also shown in Table 2.

The non-aqueous electrolyte secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 5 were overcharged to 4.2 V and then subjected to an oven test at 140 ° C. to measure the maximum battery temperature at that time. The results are shown in Table 2 below.

Further, for the secondary batteries of Examples 1 to 8, after the initial charging step, the secondary battery was disassembled, the separator was taken out, the separator was immersed in a dimethylformamide solution, and the non-aqueous electrolyte and After the polyvinylidene fluoride was removed and the separator was dried under reduced pressure at 60 ° C. so as not to thermally shrink, the pore closing start temperature was measured by the above-described method. The results are also shown in Table 1 below. The drying of the separator is not limited to the drying under reduced pressure described above.
It can be performed at normal pressure. Drying under reduced pressure is more desirable in order to shorten the drying time.

[0175]

[Table 1]

[0176]

[Table 2]

As is clear from Tables 1 and 2, Example 1
The secondary batteries of Nos. To 8 are compared with the secondary batteries of Comparative Examples 1 to 5,
It can be seen that the battery has a low maximum temperature when stored in a high-temperature atmosphere of 140 ° C., has no liquid leakage, and has excellent safety. In particular,
It can be seen that the secondary batteries of Examples 1, 2, 4, and 5 do not generate heat in a high-temperature atmosphere of 140 ° C. and have extremely high safety because the opening-closing temperature (after disassembly of the secondary battery) of the separator is low. . In addition, it can be seen that the secondary batteries of Examples 1 to 8 can reduce a decrease in capacity when discharged with a large current as compared with the secondary battery of Comparative Example 5 including the gel polymer electrolyte layer.

Example 9 <Separator> A polyethylene porous material having a thickness of 20 μm, a porosity of 40%, an air permeability and a pore closing temperature before being incorporated into an electrode group, as shown in Table 3 below. A separator made of a high quality film was prepared.

<Preparation of Electrode Group> A positive electrode and a negative electrode similar to those described in the first embodiment are spirally wound with the separator interposed therebetween, and then formed into a flat shape to obtain a thick plate. An electrode group having a height of 2.5 mm, a width of 30 mm and a height of 50 mm was prepared.

A laminate film similar to that described in Example 1 was processed into a bag shape in the same manner as described in Example 1 above. The electrode group is housed in this,
Both surfaces were sandwiched between holders so that the thickness became 2.7 mm.
Polyvinylidene fluoride (P
VdF) was dissolved in an organic solvent, dimethylformamide (boiling point: 153 ° C.), at 0.3% by weight. The obtained solution was injected into the electrode group in the exterior material so that the amount per battery capacity of 100 mAh was 0.6 ml, and the solution was permeated into the electrode group, and was spread over the entire surface of the electrode group. Attached.

Next, the organic solvent was evaporated by performing vacuum drying at 80 ° C. for 12 hours on the electrode group in the exterior material, thereby holding the adhesive polymer in the gaps between the positive electrode, the negative electrode and the separator. A porous adhesive portion was formed on the surface of the electrode group.

The first embodiment described above was applied to the electrode group in the exterior material.
After injecting 2 g of the same liquid non-aqueous electrolyte as described in the above, the opening of the exterior material is sealed by the same method as described in Example 1 described above, and FIG. 3 to FIG. A thin nonaqueous electrolyte secondary battery having the structure shown in the figure, a thickness of 2.7 mm, a width of 32 mm, and a height of 55 mm was assembled.

The obtained non-aqueous electrolyte secondary battery of Example 9 was subjected to the same initial charging step as that described in Example 1 to produce a non-aqueous electrolyte secondary battery.

(Examples 10 to 12) A thin nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 9 except that the pore closing start temperature and the air permeability of the separator were changed as shown in Table 3 below. Manufactured.

Example 13 The same procedure as in Example 9 was carried out except that the opening temperature of the pores of the separator and the air permeability, and the melting point of the polypropylene of the exterior material were changed as shown in Table 3 below. A water electrolyte secondary battery was manufactured.

(Example 14) [0186] Example 9 described above was changed except that the composition of the liquid nonaqueous electrolyte was changed as shown in Table 4 below.
In the same manner as in the above, a thin non-aqueous electrolyte secondary battery was manufactured.

Example 15 A thin non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 9 except that the material of the separator, the temperature at which pores were closed, and the air permeability were changed as shown in Table 3 below. Manufactured.

Example 16 The same as Example 9 described above, except that the material of the separator, the temperature at which the pores were closed, the air permeability, and the type of the thermoplastic resin of the exterior material were changed as shown in Table 3 below. Thus, a thin non-aqueous electrolyte secondary battery was manufactured.

Example 17 The same procedures as in Example 9 were carried out except that the pore closing start temperature and the air permeability of the separator and the type of the thermoplastic resin of the exterior material were changed as shown in Table 3 below. A thin non-aqueous electrolyte secondary battery was manufactured.

(Example 18) The above-mentioned Example 9 was carried out except that the composition of the liquid non-aqueous electrolyte was changed as shown in Table 4 below.
In the same manner as in the above, a thin non-aqueous electrolyte secondary battery was manufactured.

Example 19 A gel was obtained by mixing 88 mol% of a liquid non-aqueous electrolyte having the same composition as described in Example 18 and 12 mol% of polyacrylonitrile as a polymer at 120 ° C. A non-aqueous electrolyte was prepared.

After impregnating the gel electrolyte in the separator similar to that described in Example 9, the separator was interposed between the positive electrode and the negative electrode similar to that described in Example 1,
An electrode group was prepared.

A laminated film similar to that described in Example 1 was processed into a bag shape in the same manner as described in Example 1. The electrode group is housed therein, and the opening of the exterior material is sealed in the same manner as described in Example 1,
A thin non-aqueous electrolyte secondary battery having a thickness of 2.7 mm, a width of 32 mm, and a height of 55 mm was manufactured.

Examples 20 and 21 Thin non-aqueous electrolyte secondary batteries were manufactured in the same manner as in Example 19 except that the air permeability of the separator was changed as shown in Table 3 below.

Comparative Example 6 A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 9 except that the kind of the thermoplastic resin of the exterior material was changed as shown in Table 3 below. .

(Comparative Examples 7 to 8) The same as in Example 9 described above, except that the material of the separator, the temperature at which the pores were closed, the air permeability, and the melting point of polyethylene as the exterior material were changed as shown in Table 3 below. Thus, a thin non-aqueous electrolyte secondary battery was manufactured.

(Comparative Example 9) The same procedure as in Example 14 was carried out except that the material of the separator, the pore closing temperature, the air permeability, and the melting point of the polyethylene of the exterior material were changed as shown in Table 3 below. A thin non-aqueous electrolyte secondary battery was manufactured.

(Comparative Example 10) A liquid non-aqueous electrolyte having the same composition as in Example 14 and polyvinylidene fluoride (PVdF) were mixed and gelled to form a gel polymer electrolyte layer having a thickness of 80 μm. Produced. An electrode group was prepared by interposing a gel polymer electrolyte layer between the positive electrode and the negative electrode as described in Example 1.

A laminate film similar to that described in Example 1 was processed into a bag shape in the same manner as described in Example 1. The electrode group is housed therein, the opening of the exterior material is sealed in the same manner as described in Example 1, and the thickness is 2.7 mm, the width is 32 mm, and the height is 55 mm. A water electrolyte secondary battery was manufactured.

The obtained secondary battery was subjected to the same initial charging step as described in Example 1 to produce a non-aqueous electrolyte secondary battery.

The obtained Examples 9 to 21 and Comparative Examples 6 to
Tenth Non-aqueous Electrolyte Secondary Battery of Example 1
The capacity retention at the time of 3C discharge and the maximum temperature in the 140 ° C. oven test were measured in the same manner as described above, and the results are also shown in Table 4 below.

Further, for the secondary batteries of Examples 9 to 21, after the initial charging step, the secondary battery was disassembled, the separator was taken out, the separator was immersed in a dimethylformamide solution, and the non-aqueous electrolyte attached to the separator and After the polyvinylidene fluoride was removed and the separator was dried under reduced pressure at 60 ° C. so as not to be thermally shrunk, the pore closing start temperature was measured by the method described above, and the results are also shown in Table 3 below. The drying of the separator is not limited to the drying under reduced pressure described above.
It can be performed at normal pressure. Drying under reduced pressure is more desirable in order to shorten the drying time.

[0203]

[Table 3]

[0204]

[Table 4]

As is clear from Tables 3 and 4, Example 9
It can be seen that the secondary batteries of Nos. To 21 have a lower maximum battery temperature when stored in a high-temperature atmosphere of 140 ° C., have no liquid leakage, and are excellent in safety, as compared with the secondary batteries of Comparative Examples 6 to 10. In particular, the secondary batteries of Examples 9, 10, 12, 13, and 17 are:
It can be seen that since the hole closing start temperature of the separator (after disassembly of the secondary battery) is low, no heat is generated in a high-temperature atmosphere of 140 ° C., and the safety is extremely high. Also, it can be seen that the secondary batteries of Examples 9 to 21 can reduce the capacity decrease when discharged with a large current as compared with the secondary battery of Comparative Example 10 including the gel polymer electrolyte layer.

(Example 22) A separator having a thickness of
10 μm, air permeability 90 sec / 100 cm
^ThreeAnd a porosity of 50% and a pore closing start temperature of 130
Other than using polyethylene porous film at ℃
Is a thin non-aqueous electrolyte secondary in the same manner as in Example 9 described above.
A battery was manufactured.

Example 23 A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 22 except that the air permeability of the porous film of the separator was set to 150 sec / 100 cm ³ .

Example 24 A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 22 except that the air permeability of the porous sheet of the separator was set to 400 sec / 100 cm ³ .

Example 25 A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 22 except that the air permeability of the porous sheet of the separator was 580 sec / 100 cm ³ .

Regarding the obtained secondary batteries of Examples 22 to 25, 3C was applied in the same manner as described in Example 1 described above.
The capacity retention ratio during discharge and the maximum temperature in a 140 ° C. oven test were measured, and the results are shown in Table 5 below.

For the secondary batteries of Examples 22 to 25, after the initial charging step, the secondary battery was disassembled, the separator was taken out, the separator was immersed in a dimethylformamide solution, and the non-aqueous electrolyte attached to the separator and After removing the polyvinylidene fluoride and drying under reduced pressure at 60 ° C. so that the separator did not thermally shrink, the pore closing start temperature was measured by the above-mentioned method. . The drying of the separator is not limited to the above-described drying under reduced pressure, and can be performed at normal pressure. Drying under reduced pressure is more desirable in order to shorten the drying time.

[0212]

[Table 5]

Examples 26 and 27 Thin nonaqueous electrolyte secondary batteries were manufactured in the same manner as in Example 1 except that the thickness of the separator was changed as shown in Table 6 below.

The obtained secondary batteries of Examples 26 and 27 were fabricated in the same manner as described in Example 1 above.
The maximum temperature in the 0 ° C. oven test was measured, and the results are shown in Table 6 below. Table 6 also shows the results of Example 1 described above.

The energy densities per unit weight of the secondary batteries of Examples 1, 26 and 27 were determined, and the results are also shown in Table 6 below.

[0216]

[Table 6]

As is clear from Table 6, the thicker the separator, the more the heat generation in a high temperature environment of 140 ° C. can be suppressed, but the lower the energy density per unit weight of the battery.

In the secondary battery of Example 19 provided with a separator impregnated with a gelled non-aqueous electrolyte, when the thickness of the separator was changed to 5 μm, the maximum temperature during the oven test increased by 10 ° C. The energy density per unit weight was increased by 12%. When the thickness of the separator was changed to 30 μm, the maximum temperature during the oven test was still 140 ° C., although the energy density per unit weight was reduced by 30%.

(Example 28) A positive electrode similar to that of Example 1 and a negative electrode similar to that of Example 1 are spirally wound with a separator similar to that of Example 9 interposed therebetween, and then formed into a flat shape. As a result, the thickness is 2.5 mm and the width is 30 mm
Thus, an electrode group having a height of 50 mm was prepared.

A laminate film similar to that described in Example 1 was processed into a bag shape in the same manner as described in Example 1 above. After accommodating the electrode group therein, the exterior material was pressed at a pressure of 10 kg / cm ² along the thickness direction of the electrode group in a high-temperature vacuum atmosphere at 80 ° C., thereby separating the positive electrode, the negative electrode, and the separator. The binder contained in the positive electrode and the negative electrode was thermally cured to be integrated.

2 g of a liquid non-aqueous electrolyte having the same composition as in Example 1 was injected into the electrode group in the exterior material, and the thickness was set to 2.
A thin nonaqueous electrolyte secondary battery having a size of 7 mm, a width of 32 mm, and a height of 55 mm was assembled.

Subsequently, a thin non-aqueous electrolyte secondary battery was manufactured by performing the same initial charge as described in Example 1.

With respect to the obtained secondary battery of Example 28,
When the capacity retention at the time of 3C discharge and the maximum temperature in the 140 ° C. oven test were measured in the same manner as described in Example 1 above, the capacity retention at the time of 3C discharge was 95%.
The maximum temperature was 140 ° C.

(Example 29) A positive electrode similar to that of Example 1 and a negative electrode similar to that of Example 1 are spirally wound with a separator similar to that of Example 9 interposed therebetween, and then formed into a flat shape. As a result, the thickness is 2.5 mm and the width is 30 mm
Thus, an electrode group having a height of 50 mm was prepared.

A laminate film similar to that described in Example 1 was processed into a bag shape in the same manner as described in Example 1 above. After accommodating the electrode group therein, the exterior material was pressed at a pressure of 10 kg / cm ² along the thickness direction of the electrode group in a high-temperature vacuum atmosphere at 80 ° C., thereby separating the positive electrode, the negative electrode, and the separator. The binder contained in the positive electrode and the negative electrode was thermally cured to be integrated.

33% by volume of ethylene carbonate (E
C), 66% by volume of γ-butyrolactone (BL) and 1
1.5 mol / l of lithium tetrafluoroborate (LiBF ₄ ) was dissolved in a nonaqueous solvent composed of volume% of vinylene carbonate to prepare a liquid nonaqueous electrolyte. 2 g of the liquid non-aqueous electrolyte was injected into the electrode group in the exterior material, and the thickness was 2.7 by closing the same manner as described in Example 1.
A thin nonaqueous electrolyte secondary battery having a thickness of 32 mm, a width of 32 mm, and a height of 55 mm was assembled.

Subsequently, a thin non-aqueous electrolyte secondary battery was manufactured by performing the same initial charge as described in Example 1.

With respect to the obtained secondary battery of Example 29,
When the capacity retention at the time of 3C discharge and the maximum temperature in the 140 ° C. oven test were measured in the same manner as described in Example 1 above, the capacity retention at the time of 3C discharge was 93%.
The maximum temperature was 140 ° C.

Example 30 A gel was prepared by mixing 38 mol% of polyethylene oxide (PEO), 5 mol% of LiPF ₆ , 38 mol% of ethylene carbonate, and 19 mol% of propylene carbonate at 120 ° C. A non-aqueous electrolyte was prepared.

After the obtained gelled non-aqueous electrolyte was impregnated in the same separator as in Example 9, this separator was interposed between the positive electrode and the negative electrode as in Example 1, and the separator was cooled to cool the non-aqueous electrolyte. By solidifying the water electrolyte, an electrode group was prepared in which the solid nonaqueous electrolyte was held by the separator and a solid nonaqueous electrolyte layer was interposed between the positive electrode and the separator and between the negative electrode and the separator.

A laminate film similar to that described in Example 1 was processed into a bag shape in the same manner as described in Example 1 above. After the electrode group is housed therein, the opening of the exterior material is sealed by the same method as described in the first embodiment, so that the thickness is 2.
A thin nonaqueous electrolyte secondary battery having a size of 5 mm, a width of 30 mm, and a height of 50 mm was assembled.

With respect to the obtained secondary battery of Example 30,
When the maximum temperature in the 140 ° C oven test was measured,
The maximum battery temperature was 140 ° C. At this time, there was no liquid leakage or gas ejection. Therefore, according to the present invention, the safety of a large non-aqueous electrolyte secondary battery such as an electric vehicle can be improved.

[0233]

As described in detail above, according to the present invention,
A non-aqueous electrolyte secondary battery having improved charge / discharge characteristics at a large current and improved safety can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view for explaining the thickness of a positive electrode layer in a nonaqueous electrolyte secondary battery according to the present invention.

FIG. 2 is a characteristic diagram showing an example of a relationship between a cell temperature and a cell resistance value in a hole closing start temperature measurement test.

FIG. 3 is a plan view showing an example of a first non-aqueous electrolyte secondary battery according to the present invention.

FIG. 4 is a plan view showing an exterior material of the nonaqueous electrolyte secondary battery in FIG. 3;

FIG. 5 is a sectional view taken along the line VV in FIG. 3;

FIG. 6 is an enlarged sectional view showing a portion A in FIG. 5;

FIG. 7 is an enlarged sectional view showing a portion B in FIG. 5;

8 is a schematic diagram showing the vicinity of a boundary between a positive electrode, a separator, and a negative electrode in the secondary battery of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... positive electrode lead, 2 ... negative electrode lead, 3 ... exterior material, 5 ... electrode group, 6 ... thermoplastic resin layer, 7 ... metal layer, 8 ... external protective layer, 9 ... separator, 10 ... positive electrode layer, 11 ... positive electrode Current collector, 12: Positive electrode, 13: Negative electrode layer, 14: Negative electrode current collector, 15: Negative electrode 16: Adhesive part, 17: Adhesive polymer.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takahisa Osaki 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Pref. F-term (reference) at Toshiba Kawasaki Office

Claims (16)

[Claims] 1. An electrode group comprising a positive electrode, a negative electrode, and a porous separator disposed between the positive electrode and the negative electrode and having a property that pores are closed by heating; a non-aqueous electrolyte held by the separator; And at least a part of the inner surface is made of a sheet formed of a thermoplastic resin layer, and accommodates the electrode group, and an exterior material for sealing the electrode group by heat-sealing the thermoplastic resin layers to each other. The non-aqueous electrolyte secondary, wherein the positive electrode, the negative electrode, and the separator are integrated, and the thermoplastic resin layer has a melting point higher than a pore closing start temperature of the separator. battery. 2. The temperature at which pores start to be clogged is 100 to 150 ° C.
The non-aqueous electrolyte secondary battery according to claim 1, wherein: 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein a material of the separator is at least one selected from polyolefin, cellulose, and polyvinylidene fluoride. 4. The air permeability of the separator is 600.
2. The method according to claim 1, wherein the speed is not more than seconds / 100 cm ^3.
The nonaqueous electrolyte secondary battery according to the above. 5. The melting point of the thermoplastic resin layer is 120 ° C.
The non-aqueous electrolyte secondary battery according to claim 1, wherein: 6. The non-aqueous electrolyte secondary battery according to claim 1, wherein the thermoplastic resin is a polyolefin. 7. A positive electrode, a negative electrode, and disposed between the positive electrode and the negative electrode, are made of at least one selected from polyolefin, cellulose, and polyvinylidene fluoride, and have an air permeability of 600 seconds / 100 cm ³ or less, An electrode group comprising: a separator made of a porous sheet having a thickness of 5 to 30 μm; a nonaqueous electrolyte held by the separator; and a sheet in which at least a part of the inner surface is formed of a thermoplastic resin layer, A housing for accommodating the group and heat-sealing the thermoplastic resin layers to seal the electrode group; and the positive electrode, the negative electrode, and the separator are integrated, The non-aqueous electrolyte secondary battery, wherein the plastic resin layer has a melting point higher than a pore closing start temperature of the separator. 8. The melting point of the thermoplastic resin layer is 120 ° C.
The non-aqueous electrolyte secondary battery according to claim 7, wherein: 9. The non-aqueous electrolyte secondary battery according to claim 7, wherein the thermoplastic resin is a polyolefin. 10. An electrode group comprising: a positive electrode; a negative electrode; and a separator disposed between the positive electrode and the negative electrode, the separator including a porous sheet formed of at least one selected from polyolefin, cellulose, and polyvinylidene fluoride. A non-aqueous electrolyte held by the separator; and a sheet in which at least a part of the inner surface is formed of a polyolefin layer. The electrode group is housed, and the polyolefin layers are heat-sealed to seal the electrode group. The positive electrode, the negative electrode, and the separator are integrated with each other, and the polyolefin layer has a higher melting point than a pore closing temperature of the separator. Non-aqueous electrolyte secondary battery. 11. The separator has an air permeability of 60.
11. The non-aqueous electrolyte secondary battery according to claim 10, wherein the time is 0 second / 100 cm ³ or less. 12. The melting point of the polyolefin layer is 12
The non-aqueous electrolyte secondary battery according to claim 10, wherein the temperature is 0 ° C. or higher. 13. The non-aqueous electrolyte comprises a liquid non-aqueous electrolyte,
9. The method according to claim 1, comprising at least one selected from a gel non-aqueous electrolyte and a solid non-aqueous electrolyte.
11. The non-aqueous electrolyte secondary battery according to any one of items 10 to 10. 14. The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent, wherein the non-aqueous solvent contains γ-butyrolactone at 40% by volume of the entire non-aqueous solvent.
The non-aqueous electrolyte secondary battery according to any one of claims 1, 7, and 10, wherein the content is 95% by volume or less. 15. The positive electrode and the separator are integrated by an adhesive polymer present on at least a part of these boundaries, and the negative electrode and the separator are present on at least a part of these boundaries. 11. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is integrated with a polymer having an adhesive property. 16. The positive electrode and the negative electrode include a binder, and the positive electrode, the negative electrode, and the separator are integrated by thermally curing the binder. Item 11. The non-aqueous electrolyte secondary battery according to any one of Items 1, 7, and 10.