JP2002075445A - Nonaqueous electrolyte liquid and nonaqueous electrolyte liquid secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte liquid secondary cell enabled to restrain a swelling of a sheathing material by restraining a generation of gas during the reservation in high temperature, with high charge-discharge cycle property, and enabled to obtain a high capacity within short initial discharging period. SOLUTION: For the nonaqueous electrolyte liquid secondary cell comprising a sheathing material 1 with the thickness X of 0.3 mm or less, a host of electrodes 2, and a nonaqueous electrolyte liquid with which the host of electrodes 2 is impregnated, the nonaqueous electrolyte liquid contains a nonaqueous solvent containing γ-butyrolactone with a volume measure ratio of exceeding 60 volume %, and the electrolyte dissolved in the nonaqueous solvent with the concentration of 1.6 mol/L or more and 3 mol/L or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art At present, lithium ion secondary batteries have been commercialized as nonaqueous electrolyte secondary batteries for portable equipment such as mobile phones. This battery uses a lithium cobalt oxide (LiCoO ₂ ) for a positive electrode, a graphite material or a carbonaceous material for a negative electrode, an organic solvent in which a lithium salt is dissolved in a non-aqueous electrolyte, and a porous film for a separator. A non-aqueous solvent having a low viscosity and a low boiling point is used as a solvent for the electrolytic solution.

For example, Japanese Patent Application Laid-Open No. 4-14769 discloses that
Propylene carbonate, ethylene carbonate and γ-
It is possible to improve the low-temperature discharge characteristics of the cylindrical non-aqueous electrolyte secondary battery by using an electrolytic solution mainly composed of a mixed solvent composed of butyrolactone and having a ratio of γ-butyrolactone of 10 to 50% by volume of the whole solvent. It has been disclosed.

[0004] By the way, there is a demand for a reduction in the thickness of a battery along with a reduction in the thickness of a portable device. For this purpose, it is necessary to reduce the thicknesses of the positive electrode, the negative electrode, the separator, and the exterior material for storing the non-aqueous electrolyte. However, a lithium ion secondary battery provided with a non-aqueous electrolyte containing a solvent having a γ-butyrolactone content of 10 to 50% by volume described in Japanese Patent Application Laid-Open No. When the battery is stored at a high temperature of 60 ° C. or higher, the positive electrode reacts with the non-aqueous electrolyte to cause oxidative decomposition of the non-aqueous electrolyte, thereby generating gas. For this reason, when the thickness of the exterior material is reduced, there is a problem that the exterior material swells and deforms due to the generation of gas. When the exterior material is deformed, the battery may not fit in the electronic device or may cause malfunction of the electronic device.

[0005] By the way, the lecture of the 67th Annual Meeting of the Electrochemical Society of Japan
The 23 pages of the collection (published March 28, 2000)
Lencarbonate (EC) and γ-butyrolactone (GB
L) was mixed at a volume ratio of 2: 3.
LiBF as electrolyte salt in the medium _FourOr LiPF₆Dissolve
Electrolyte solution and a mixture of polyfunctional acrylate monomers
Polymer gel electrolysis obtained by polymerization and chemical cross-linking
Separator made of porous material, both positive and negative
Laminated on electrodes that have been crosslinked and packed with aluminum laminate
Lithium ion polymer secondary battery is disclosed
You. Also, here, high-rate discharge performance in gel electrolyte
In order to improve the low temperature performance, the electrolyte solvent should be EC /
GBF = 2/3 and LiBF as salt_Four2 when using
The optimum salt concentration must be in the high concentration range of mol / L or more.
It has been reported.

[0006]

DISCLOSURE OF THE INVENTION The present invention suppresses the generation of gas when stored at a high temperature to suppress the swelling of the exterior material, and has a high charge-discharge cycle characteristic and a high initial charge time. An object of the present invention is to provide a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery capable of obtaining a capacity.

[0007]

A non-aqueous electrolyte solution according to the present invention comprises: a non-aqueous solvent containing γ-butyrolactone in a volume ratio exceeding 60% by volume;
It is characterized by containing an electrolyte of 6 mol / L or more and 3 mol / L or less.

[0008] A non-aqueous electrolyte secondary battery according to the present invention has a package having a thickness of 0.3 mm or less, an electrode group housed in the package, and a non-aqueous electrolyte impregnated in the electrode group. Liquid, the non-aqueous electrolyte is dissolved in the non-aqueous solvent containing a non-aqueous solvent containing γ-butyrolactone in a volume ratio exceeding 60% by volume.
It is characterized by containing an electrolyte of 6 mol / L or more and 3 mol / L or less.

[0009] A non-aqueous electrolyte secondary battery according to the present invention comprises an outer package having a thickness of 0.3 mm or less, and an electrode group housed in the outer package and having a separator interposed between a positive electrode and a negative electrode. A non-aqueous electrolyte secondary battery including a non-aqueous electrolyte solution impregnated in the electrode group, wherein the positive electrode has a current collector and a positive electrode layer supported on one or both surfaces of the current collector. And the negative electrode has a current collector and a negative electrode layer supported on one or both surfaces of the current collector, and the nonaqueous electrolyte contains γ-butyrolactone in a volume ratio exceeding 60% by volume. And a non-aqueous solvent dissolved in the non-aqueous solvent.
It is characterized by containing an electrolyte of 6 mol / L or more and 3 mol / L or less.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A non-aqueous electrolyte secondary battery according to the present invention has an outer package having a thickness of 0.3 mm or less, and is housed in the outer package, and has a separator interposed between a positive electrode and a negative electrode. An electrode group and a non-aqueous electrolytic solution impregnated in the electrode group are provided. The non-aqueous electrolyte includes a non-aqueous solvent containing γ-butyrolactone at a volume ratio exceeding 60% by volume, and an electrolyte of 1.6 mol / L or more and 3 mol / L or less dissolved in the non-aqueous solvent. .

The electrode group, the positive electrode, the negative electrode, the separator, the non-aqueous electrolyte, and the packaging material will be described.

1) Electrode group In this electrode group, it is preferable that the positive electrode, the negative electrode, and the separator are integrated. Such an electrode group is produced, for example, by the method described in the following (i) or (ii).

Method (i) The positive electrode and the negative electrode are wound in a flat shape with a separator interposed therebetween, or the positive electrode and the negative electrode are spirally wound with a separator interposed therebetween and then compressed in the radial direction. Alternatively, the positive electrode and the negative electrode are bent at least once with a separator interposed therebetween. By subjecting the obtained flat article to heat molding in the laminating direction, the binder contained in the positive electrode and the negative electrode is thermoset to integrate the positive electrode, the negative electrode, and the separator to obtain an electrode group.

The heat molding may be performed after the flat object is stored in the exterior material, or may be performed before storing the flat material in the exterior material.

The atmosphere in which the heat molding is performed is desirably a reduced pressure atmosphere including a vacuum or a normal pressure atmosphere.

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

[0017] The temperature of the heat molding is preferably in the range of 40 to 120 ° C. A more preferred range is 6
0-100 ° C.

The molding pressure of the heat molding is 0.01 to 20.
It is desirable to be within the range of kg / cm ² . A more preferred range is 8 to 15 kg / cm ² .

Method (ii) Instead of producing the electrode group by the above-mentioned method, the electrode group may be obtained by integrating the positive electrode, the negative electrode, and the separator with an adhesive polymer. Examples of the polymer having the adhesive property include polyacrylonitrile (PA)
N), polyacrylate (PMMA), polyvinylidene fluoride (PVdF), polyvinyl chloride (PVC), or polyethylene oxide (PEO).

2) Positive Electrode This positive electrode has a structure in which a positive electrode layer containing an active material is supported on one or both sides of a current collector.

The positive electrode layer contains a positive electrode active material, a binder, and a conductive agent.

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.

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 positive electrode is produced, for example, by suspending a conductive agent and a binder in an appropriate solvent in a positive electrode active material, applying the suspension to a current collector, and drying to form a thin plate. .

When the electrode group is manufactured by the method described in the above-mentioned method (ii), the positive electrode further contains an adhesive polymer.

The thickness of the positive electrode layer is preferably in the range of 50 to 95 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, FIG.
As shown, if the positive electrode layer 4 on both sides of the current collector 5 is supported, the distance between the positive electrode layer surface 4 ₂ in contact with the positive electrode layer surface 4 ₁ and the collector 5 which faces the separator 3 is the positive electrode layer 4 has a thickness T _p . Therefore, when the positive electrode layer is supported on both surfaces of the positive electrode current collector, the thickness of one surface of the positive electrode layer is 50 to 95 μm.
m, the total thickness of the positive electrode layer is in the range of 100 to 190 μm. When the thickness of the positive electrode layer is less than 50 μm, the weight ratio and the volume ratio of the current collector become high, so that a high energy density may not be obtained. On the other hand, if the thickness of the positive electrode layer exceeds 95 μm, the distribution of the nonaqueous electrolyte in the positive electrode may become uneven, and the initial charging time may not be sufficiently reduced. A more preferable range of the positive electrode layer thickness is 55
７０70 μm.

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.

3) Negative Electrode The negative electrode has a structure in which a negative electrode layer is supported on one or both sides of a current collector.

The negative electrode layer contains a carbonaceous material that absorbs and releases lithium ions and a binder.

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 obtained by setting the temperature of the heat treatment at 2000 ° C. or higher and having a graphite crystal having a (002) plane spacing d ₀₀₂ of 0.34 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 the battery capacity and large current discharge characteristics. The surface distance d
₀₀₂ is more preferably 0.336 nm or less. In particular, the mesophase pitch-based carbon fiber is characterized by having a structure in which the surface on which lithium can be inserted and desorbed is directed to all surfaces, even when using the non-aqueous electrolyte defined in the present invention, Impregnation with a non-aqueous electrolyte is relatively easy compared to other carbonaceous materials, and is more preferable.

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.

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

When the electrode group is manufactured by the method described in the above method (ii), the negative electrode further contains a polymer having adhesiveness.

The thickness of the negative electrode layer is preferably in the range of 40 to 75 μm. Here, the thickness of the negative electrode layer is
It means the distance between the surface of the negative electrode layer facing the separator 3 and the surface of the negative electrode layer contacting the current collector. For example, as shown in FIG. 2 described later, when the negative electrode layer 7 is supported on both surfaces of the current collector 8, the negative electrode layer surface 7 ₁ facing the separator and the negative electrode layer surface 7 ₂ Is the thickness T _{N of the} negative electrode layer 7
It is. Therefore, when the negative electrode layer is carried on both surfaces of the negative electrode current collector, the thickness of one side of the negative electrode layer is 40 to 75 μm,
The total thickness of the negative electrode layer is in the range of 80 to 150 μm. If the thickness of the negative electrode layer is less than 40 μm, the weight ratio and the volume ratio of the current collector become high, so that a high energy density may not be obtained. On the other hand, when the thickness of the negative electrode layer is 75
If it exceeds μm, the distribution of the non-aqueous electrolyte in the negative electrode may become uneven, and the initial charging time may not be sufficiently reduced. A more preferable range of the negative electrode layer thickness is 45 to 65 μm.
m.

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.

The negative electrode layer may be made of a metal such as aluminum, magnesium, tin, silicon or the like, a metal oxide, a metal sulfide, or a metal, in addition to the above-mentioned carbon material that absorbs and releases lithium ions. It may include a metal compound selected from nitrides or a lithium alloy.

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.

4) Separator This separator is formed from a porous sheet.

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 and cellulose. Examples of the polyolefin include polyethylene and polypropylene. Among them, a porous film made of polyethylene, polypropylene, or both is preferable because the safety of the secondary battery can be improved.

When the electrode group is manufactured by the method described in the above-mentioned method (ii), the separator further contains an adhesive polymer.

5) Nonaqueous Electrolyte The nonaqueous solvent of this nonaqueous electrolyte contains γ-butyrolactone (GBL) in a volume ratio exceeding 60% by volume. If the volume ratio is less than 60% by volume, the non-aqueous electrolyte reacts with the charged electrode during high-temperature storage, causing oxidative decomposition of the non-aqueous electrolyte, generating gas and expanding the exterior material significantly. G
The solvent mixed with BL is a cyclic carbonate, and the volume ratio of the cyclic carbonate becomes relatively high, so that the solvent viscosity increases. As the solvent viscosity increases, the viscosity of the non-aqueous electrolyte increases. When the viscosity of the non-aqueous electrolyte becomes high, it becomes difficult to handle (particularly injecting) during production, and furthermore, the permeability of the non-aqueous electrolyte into the electrode group decreases, so that impregnation into the electrode group is hindered. In this case, normal charge / discharge characteristics are degraded. This is particularly apparent in the polarization resistance at the time of the first charge. In the case of a highly viscous non-aqueous electrolyte, impregnation of the electrolyte into the negative electrode is rate-determining, and it takes a long time for the first charge. In other words, under the same initial charge condition, the initial charge / discharge capacity decreases. A more preferable range of the volume ratio is 65% by volume or more, and more preferably 7% by volume.
5% by volume or more. Incidentally, the upper limit of the volume ratio of GBL is preferably set to 95% by volume. Volume ratio is 9
If the content exceeds 5% by volume, a reaction between the negative electrode and the GBL is likely to occur, which may make it difficult to sufficiently improve the charge / discharge cycle characteristics. That is, when the negative electrode (for example, a substance containing a carbonaceous substance that absorbs and releases lithium ions) reacts with the GBL to cause reductive decomposition of the nonaqueous 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 upper limit of the volume ratio is 90% by volume, and a still more preferred upper limit is 88% by volume. In particular, in the present invention, the viscosity of the non-aqueous electrolyte is preferably 3 cP or more and 20 cP or less in order to reduce the influence of the viscosity. More preferable viscosity of the non-aqueous electrolyte is 5 cP or more,
5 cP or less, more preferably 5 cP or more, 12
cP or less.

The cyclic carbonate which is a solvent mixed with GBL includes propylene carbonate (PC), ethylene carbonate (EC), vinylene carbonate (VC) and trifluoropropylene carbonate (TF).
It is preferable to use at least one selected from the group consisting of PC). In particular, when EC is used as a solvent mixed with GBL, charge / discharge cycle characteristics and large current discharge characteristics can be significantly improved. The volume ratio of EC in the non-aqueous solvent is preferably 5% by volume or more and less than 40% by volume. This is due to the following reasons. E
If the ratio of C is less than 5% by volume, it may be difficult to cover the surface of the negative electrode with a protective film densely.
A reaction with BL may occur, and it may be difficult to sufficiently improve charge / discharge cycle characteristics. On the other hand, when the EC ratio is 40% by volume or more, the viscosity of the non-aqueous electrolyte increases, and it may be difficult to sufficiently improve the charge / discharge cycle characteristics and the initial charge characteristics. A more preferable range of the EC ratio is 10 to 35% by volume, more preferably 10 to 35% by volume.
２５25% by volume.

From the viewpoint of further reducing the solvent viscosity, the non-aqueous solvent may contain a low-viscosity solvent in an amount of 20% by volume or less. Examples of the low-viscosity solvent include chain carbonate, chain ether, and cyclic ether.

Non-aqueous solvents include GBL exceeding 60% by volume.
, EC, PC, VC, TFPC, diethyl carbonate (DEC), methyl ethyl carbonate (MEC)
It is preferable to use a mixed solvent with a third solvent composed of at least one selected from the group consisting of benzene and aromatic compounds. Such a non-aqueous solvent can further enhance the charge / discharge cycle characteristics. DEC, MEC and V
The ratio of at least one solvent selected from the group consisting of C to the entire nonaqueous solvent is 0.01 to 10% by volume.
Is more preferable, and a more preferable range is 0.1 to 5% by volume.

More preferable compositions of the non-aqueous solvent include GBL and EC, GBL and PC, GBL and EC and DE.
C, GBL, EC, MEC, GBL, EC, MEC, V
C, GBL and EC and VC, GBL and PC and VC, GBL
, EC, PC, and VC.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ) and lithium hexafluorophosphate (L
iPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium trifluorometasulfonate (LiCF ₃ SO ₃ ), bistrifluoromethylsulfonylimithium [LiN (CF
₃ SO ₂ ) ₂ ]. Among them,
Preferably, LiBF ₄ is used.

The reason why the concentration of the electrolyte in the non-aqueous solvent is defined within the above range is as follows.
When the electrolyte concentration is less than 1.6 mol / L, the charge / discharge cycle characteristics deteriorate. On the other hand, when the electrolyte concentration is 3 mol /
If it exceeds L, even if the composition of the non-aqueous solvent is within the range of the present invention, the viscosity of the non-aqueous electrolyte increases, and handling (particularly injection)
This makes it difficult to uniformly infiltrate the electrolyte into the electrode group, so that the battery performance including the initial charge varies. A more preferable range of the electrolyte concentration is 1.8 mol / L.
As mentioned above, it is 2.5 mol / L or less, and the most preferable range is 2 mol / L or more and 2.2 mol / L or less.

In order to improve the wettability with the separator,
A surfactant such as trioctyl phosphate is used in an amount of 0.01
It is desirable to add within the range of 3%.

The amount of the non-aqueous electrolyte was 100 mA per unit cell capacity.
It is preferable to set the amount to 0.2 to 0.6 g per h. This is due to the following reasons. If the amount of the non-aqueous electrolyte is less than 0.2 g / 100 mAh, 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 amount of the non-aqueous electrolyte exceeds 0.6 g / 100 mAh, the amount of the electrolyte may increase and it may be difficult to seal with the sheet-made exterior material. A more preferable range of the amount of the non-aqueous electrolyte is 0.4 to 0.55 g / 100 mAh.

6) Exterior material The thickness of the exterior material is 0.3 mm or less. The exterior material can be formed, for example, from a sheet including a resin layer, a metal plate, a metal film, or the like. Here, the thickness of the exterior material means the thickness of a film material such as the sheet, the metal plate, and the metal film.

The resin layer contained in the sheet is, for example,
It can be formed from polyethylene, polypropylene or the like. As the sheet, it is desirable to use a sheet in which a metal layer and protective layers disposed on both sides of the metal layer are integrated. The metal layer serves to block moisture. 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 external protective layer is formed of one type of resin layer or two or more types of resin layers. On the other hand, the inner protective layer has a role of preventing the metal layer from being corroded by the non-aqueous electrolyte. This internal protective layer is formed from one type of resin layer or two or more types of resin layers. Further, a thermoplastic resin can be provided on the surface of the internal protective layer.

The metal plate and the metal film can be made of, for example, iron, stainless steel, or aluminum.

The reason why the thickness of the exterior material is specified in the above range will be described. When the thickness is more than 0.3 mm, it is difficult to obtain a high weight energy density and a high volume energy density. The thickness of the exterior material is preferably 0.25 mm or less, more preferably 0.15 mm or less,
The most preferred range is 0.12 mm or less. On the other hand, if the thickness is less than 0.05 mm, deformation and breakage are likely.
Therefore, the lower limit of the thickness is preferably set to 0.05 mm.

The thickness of the exterior material is measured by the method described below. That is, in a region other than the sealing portion (for example, the heat sealing portion) of the exterior material, three points that are separated from each other by 1 cm or more are arbitrarily selected, the thickness of each point is measured, and an average value is calculated. The value is the thickness of the exterior material. 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, when PVdF is attached to the surface of the exterior material,
After removing the PVdF by wiping the surface of the exterior material with a dimethylformamide solution, the thickness is measured.

It is preferable that the secondary battery is initially charged at a charging rate of 0.05 C or more and 0.5 C or less under a temperature condition of 30 ° C. to 60 ° C. Charging under this condition is 1
Only the cycle may be performed, or two or more cycles may be performed. In addition, before the first charge, 1
It may be stored for about 20 hours to about 20 hours. A more preferable range of the temperature condition is 30 to 50 ° 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 reason for defining the temperature of the first charge in the above range is as follows. Initial charge temperature is 30
When the temperature is lower than ℃, the effect of lowering the viscosity of the non-aqueous electrolyte cannot be sufficiently obtained, and it may be difficult to sufficiently reduce the initial charging time. On the other hand, when the initial charge temperature exceeds 60 ° C., the binder contained in the positive electrode and the negative electrode deteriorates.

The charge rate of the first charge is 0.05 to 0.5 C
By setting the range, it is possible to moderately delay the expansion of the positive electrode and the negative electrode due to charging, so that the nonaqueous electrolyte can be more uniformly penetrated into the positive electrode and the negative electrode, and the initial charging time can be further reduced. Can be.

A thin lithium ion secondary battery which is an example of the non-aqueous electrolyte secondary battery according to the present invention will be described in detail with reference to FIGS.

FIG. 1 is a sectional view showing a thin lithium ion secondary battery which is an example of the non-aqueous electrolyte secondary battery according to the present invention, and FIG. 2 is an enlarged sectional view showing a portion A in FIG.

As shown in FIG. 1, an electrode group 2 is accommodated in an exterior material 1 having a thickness X of 0.3 mm or less. The electrode group 2 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. 2, the laminate includes a separator 3 (from the lower side of the figure), a positive electrode 6 including a positive electrode layer 4, a positive electrode current collector 5, and a positive electrode layer 4, a separator 3, a negative electrode layer 7, and a negative electrode collector. Electric body 8 and negative electrode layer 7
, Separator 3, positive electrode layer 4, positive electrode current collector 5, positive electrode 6 including positive electrode layer 4, separator 3, negative electrode layer 7
And a negative electrode 9 provided with a negative electrode current collector 8 are stacked in this order. In the electrode group 2, the negative electrode current collector 8 is located in the outermost layer. One end of the strip-shaped positive electrode lead 10 is connected to the positive electrode current collector 5 of the electrode group 2, and the other end is extended from the exterior material 1. On the other hand, one end of the strip-shaped negative electrode lead 11 has one end of the negative electrode current collector 8 of the electrode group 2.
, And the other end extends from the exterior material 1.

In FIGS. 1 and 2 described above, an example is described in which the positive and negative electrodes and the electrode group in which the separator is flatly wound are used, but between the positive electrode, the negative electrode, and the positive electrode and the negative electrode. An electrode group composed of a laminate composed of a separator and a positive electrode, a negative electrode, and an electrode group having a structure in which a laminate composed of a separator disposed between the positive electrode and the negative electrode is bent at least once. Can be applied.

The non-aqueous electrolyte secondary battery according to the present invention described above has a package having a thickness of 0.3 mm or less, an electrode group housed in the package, and impregnated in the electrode group. A non-aqueous electrolyte. The non-aqueous electrolyte contains a non-aqueous solvent containing γ-butyrolactone (GBL) in a volume ratio exceeding 60% by volume, and 1.6 mo dissolved in the non-aqueous solvent.
1 / L or more and 3 mol / L or less of electrolyte.

According to such a secondary battery, since the volume ratio of GBL in the non-aqueous solvent exceeds 60% by volume, the oxidative decomposition of the non-aqueous electrolyte during high-temperature storage can be suppressed. As a result, the amount of gas generated during high-temperature storage can be reduced, so that the exterior material can be prevented from significantly expanding. At the same time, since the viscosity of the non-aqueous electrolyte can be reduced, the electrode group is uniformly impregnated with the non-aqueous electrolyte even when the positive electrode layer of the positive electrode and the negative electrode layer of the negative electrode are thickened for high capacity. Can be. Therefore, since the initial charging time can be shortened, it is possible to obtain a high discharge capacity from the beginning of the charge / discharge cycle with a short initial charging time. The electrolyte concentration is 1.6 mol / L or more and 3 mol / L.
Because of the following, the charge / discharge cycle characteristics can be improved.

In a non-aqueous solvent having a GBL volume ratio of more than 60% by volume, an electrolyte is used in an amount of 1.6 mol / L or more and 3 mol / L or more.
The reason why the charge / discharge cycle characteristics are improved by the dissolved non-aqueous electrolyte in the following is presumed to be as follows.

That is, the charge / discharge reaction is carried out by the positive and negative electrodes inserting and extracting lithium ions in the non-aqueous electrolyte held in the gaps between the positive electrode, the negative electrode and the separator. The transport of lithium ions is performed by the electrolyte flowing in and out of the gap every time the charge and discharge cycle is repeated. At the end of the cycle, the electrolyte does not move smoothly, so that the distribution of lithium ions becomes uneven.
In the region where the lithium ion concentration has decreased, the overvoltage associated with charging / discharging increases, so that the charging / discharging reaction is not performed. As a result, the capacity decreases as the charge / discharge cycle progresses, and the cycle life is shortened.

As in the present invention, the electrolyte concentration is set at 1.6 m.
ol / L or more and 3 mol / L or less,
Even when the distribution of lithium ions becomes uneven by repeating the cycle, a sufficient amount of lithium ions can be supplied to the positive and negative electrodes, so that the cycle life can be improved.

Therefore, according to the present invention, the non-aqueous electrolyte secondary battery in which the swelling of the exterior material during high temperature storage is suppressed, the charge / discharge cycle characteristics are excellent, and a high initial capacity can be obtained in a short initial charge time. Can be provided.

Further, another non-aqueous electrolyte secondary battery according to the present invention comprises an outer package having a thickness of 0.3 mm or less, a separator housed in the outer package, and a separator interposed between the positive electrode and the negative electrode. Electrode group, and a non-aqueous electrolyte impregnated in the electrode group, wherein the positive electrode has a current collector and a positive electrode layer having a thickness of 50 to 95 μm carried on one or both surfaces of the current collector. And the negative electrode has a current collector and a negative electrode layer having a thickness of 40 to 75 μm supported on one or both surfaces of the current collector, and the nonaqueous electrolyte contains 60% by volume. A non-aqueous solvent containing γ-butyrolactone at a volume ratio exceeding 1.6 mol / L or more and 3 mol / L dissolved in the non-aqueous solvent.
L or less of the electrolyte.

According to such a secondary battery, since the thicknesses of the positive electrode layer and the negative electrode layer are large, the weight energy density and the volume energy density can be improved. In addition, since the nonaqueous electrolyte can uniformly penetrate into the electrode group including the thick positive electrode layer and the negative electrode layer, it suppresses the swelling of the outer package when the secondary battery is stored at a high temperature. As a result, the initial charging time can be shortened, and the charge / discharge cycle characteristics can be improved. Therefore, swelling of the exterior material during high-temperature storage is suppressed, a high capacity can be obtained with a short initial charge, and excellent non-aqueous electrolyte secondary batteries with excellent charge / discharge cycle characteristics and high energy density can be realized. it can.

[0079]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

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 is 3% by weight of acetylene black, 3% by weight of graphite, and polyvinylidene fluoride (PVdF) is used as a binder.
3% by weight and N-methyl-2-pyrrolidone (N
MP) was added and mixed to prepare a slurry. The slurry was applied to both sides of a current collector made of an aluminum foil having a thickness of 15 μm, dried, and pressed to form a positive electrode layer having an electrode density of 3 g / cm ³ and a thickness of 60 μm. A positive electrode having a structure supported on both surfaces was produced. In addition,
In this case, the total thickness of the positive electrode layer is 120 μm.

<Preparation of Negative Electrode>
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 to prepare a slurry. The slurry was coated on both sides of a current collector made of copper foil having a thickness of 12 μm, dried, and pressed to obtain an electrode density of 1.4 g.
A negative electrode having a structure in which a negative electrode layer having a thickness of 52 μm / cm ³ and a thickness of 52 μm was supported on a current collector was produced. In this case, the total thickness of the negative electrode layer is 104 μm.

<Separator> Thickness: 25 μm, 120
A separator made of a polyethylene porous film having a heat shrinkage of 20% at 50 ° C. for 1 hour and a porosity of 50% was prepared.

<Preparation of Non-Aqueous Electrolyte> Lithium tetrafluoroborate (L) was added to a mixed solvent of ethylene carbonate (EC) and γ-butyrolactone (GBL) (mixing volume ratio 1: 2).
iBF ₄ ) was dissolved at a concentration of 1.6 mol / L to prepare a non-aqueous electrolyte.

<Preparation of Electrode Group> A band-shaped positive electrode lead was welded to the current collector of the positive electrode, and a band-shaped negative electrode lead was welded to the current collector of the negative electrode. To form a group of electrodes.

While heating this electrode group to 90 ° C., 13 k
Press molding was performed at a pressure of g / cm ² for 25 seconds to integrate the positive electrode, the negative electrode, and the separator.

A laminate film having a thickness of 0.1 mm in which both surfaces of an aluminum foil were covered with polypropylene was formed into a bag shape, and the electrode group was housed in the bag.

Next, moisture contained in the electrode group and the laminate film was removed by subjecting the electrode group in the laminate film to vacuum drying at 80 ° C. for 12 hours.

The above non-aqueous electrolyte was injected into the electrode group in the laminate film so that the amount per 1 Ah of battery capacity was 4.8 g, and the structure shown in FIGS.
A thin non-aqueous electrolyte secondary battery having a thickness of 3.6 mm, a width of 35 mm, and a height of 62 mm was assembled.

The following treatment was applied to this non-aqueous electrolyte secondary battery as an initial charge / discharge step. First, after leaving for 2 hours in a high-temperature environment of 45 ° C., 0.2 C (104
(mA) to 4.2 V at a constant current and a constant voltage for 15 hours. Then, it was left at 20 ° C. for 7 days. Further, the battery was discharged to 3 V at 0.2 C under an environment of 20 ° C. to produce a non-aqueous electrolyte secondary battery.

(Examples 2 to 6 and Comparative Examples 1 to 3) Except that the volume ratio of GBL in the non-aqueous solvent and the electrolyte concentration in the non-aqueous solvent were changed as shown in Table 1 below, A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1.

(Examples 7 and 8) A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the thicknesses of the positive electrode layer and the negative electrode layer were changed as shown in Table 1 below. did.

Comparative Example 4 <Preparation of Polymer Gel Electrolyte> Ethylene carbonate (EC) and γ-butyrolactone (GBL) were mixed at a volume ratio (EC: GBL) of 2: 3, and a nonaqueous solvent was added. Prepared. Lithium tetrafluoroborate (LiBF ₄ ) was dissolved in the obtained nonaqueous solvent so as to have a concentration of 4 mol / L to prepare a nonaqueous electrolyte. After mixing this non-aqueous electrolyte and the acrylate monomer solution,
By polymerizing and chemically cross-linking, a thin film as a polymer gel electrolyte precursor was obtained.

<Preparation of Electrode Group> A belt-like positive electrode lead was welded to the same positive electrode current collector as described in the first embodiment, and the same negative electrode collector as described in the first embodiment was used. After welding a strip-shaped negative electrode lead to the electric body, the positive electrode and the negative electrode were spirally wound between the positive electrode and the negative electrode with the thin film interposed therebetween, and then formed into a flat shape to produce an electrode group.

This electrode group was immersed in the above-described non-aqueous electrolyte, and the thin film was plasticized under reduced pressure to obtain an electrode group in which a polymer gel electrolyte was interposed between the positive electrode and the negative electrode.

A polymer secondary battery was manufactured with the same members and configuration as in Example 1 except that such an electrode group was used.

The obtained secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 4 were charged at a temperature of 40 ° C. and a charging current of 100 m.
At A (0.2 C), constant-current constant-voltage charging was performed up to 4.2 V for 12 hours. Then, after performing initial discharge at 250 mA and 3 V cut at room temperature, the battery was charged up to 4.2 V at a charging current of 500 mA for 3 hours, and discharged at 500 mA to 3 V in a 20 ° C. atmosphere. Eye discharge capacity (initial capacity) and capacity retention rate after 300 cycles (1st cycle discharge capacity is 100%)
Was measured, and the results are shown in Table 1 below. The viscosity is R
The results are shown in Table 1 below.

The charge / discharge cycle test was performed on the secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 4 in an atmosphere of 45 ° C., and the capacity retention rate after 300 cycles (discharge capacity in the first cycle) was measured. Is defined as 100%), and the results are shown in Table 1 below.

[0098]

[Table 1]

As is clear from Table 1, the thickness is 0.3 m
m or less, and an exterior material formed from a laminated film
The secondary batteries of Examples 1 to 8 provided with a nonaqueous electrolyte in which an electrolyte was dissolved in a nonaqueous solvent containing GBL at a volume ratio exceeding 60% by volume in an amount of 1.6 mol / L or more and 3 mol / L or less, It can be seen that the capacity and the capacity retention after 300 cycles at 20 ° C. and 45 ° C. are high.

On the other hand, it can be seen that the secondary batteries of Comparative Examples 1 to 4 in which the electrolyte concentration is out of the above range have lower capacity retention rates after 300 cycles than those of Examples 1 to 8. The secondary batteries of Comparative Examples 2 to 4 in which the volume ratio of GBL was less than 60% by volume had the initial capacity of Example 1.
It turns out that it becomes low compared with ８8.

[0101]

As described above in detail, according to the nonaqueous electrolyte and the nonaqueous electrolyte secondary battery according to the present invention, gas generation during high-temperature storage and during the first charge / discharge step is suppressed, and the exterior material is reduced. There is a remarkable effect that swelling can be suppressed, cycle life can be improved, and a high initial capacity can be obtained in a short initial charging time.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a thin lithium ion secondary battery as an example of a nonaqueous electrolyte secondary battery according to the present invention.

FIG. 2 is an enlarged sectional view showing a portion A in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... exterior material, 2 ... electrode group, 3 ... separator, 4 ... positive electrode layer, 5 ... positive electrode collector, 6 ... positive electrode, 7 ... negative electrode layer, 8 ... negative electrode current collector, 9 ... negative electrode, 10 ... positive electrode terminal , 11 ... negative electrode terminal.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kaoru Koiwa 8th Shinsugitacho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside the Toshiba Yokohama Office (72) Inventor Masahiro Sekino 8th Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa (72) Inventor Hiroyuki Hasebe 8 Shinsugita-machi, Isogo-ku, Yokohama-shi, Kanagawa Prefecture F-term (reference) 5H029 AJ02 AJ05 AJ07 AJ12 AK02 AK03 AK05 AL06 AL07 AM03 AM04 AM05 AM07 BJ04 BJ14 BJ15 CJ28 DJ02 EJ01 EJ12 HJ04 HJ07 HJ10 5H050 AA07 AA10 AA13 AA15 BA17 CA08 CB07 FA05 FA06 HA04 HA07 HA10

Claims (10)

[Claims] 1. A composition comprising: a non-aqueous solvent containing γ-butyrolactone in a volume ratio exceeding 60% by volume; and an electrolyte of 1.6 mol / L or more and 3 mol / L or less dissolved in the non-aqueous solvent. Characteristic non-aqueous electrolyte. 2. The non-aqueous electrolyte according to claim 1, wherein the non-aqueous solvent further contains ethylene carbonate. 3. The non-aqueous electrolyte according to claim 1, wherein the electrolyte is LiBF ₄ . 4. The non-aqueous electrolyte according to claim 1, wherein the viscosity is 3 cP or more and 20 cP or less. 5. A non-aqueous electrolyte secondary comprising: a packaging material having a thickness of 0.3 mm or less, an electrode group housed in the packaging material, and a non-aqueous electrolyte solution impregnated in the electrode group. In the battery, the non-aqueous electrolyte may have a volume ratio of γ-
A non-aqueous electrolyte secondary battery comprising: a non-aqueous solvent containing butyrolactone; and an electrolyte of 1.6 mol / L or more and 3 mol / L or less dissolved in the non-aqueous solvent. 6. An outer package having a thickness of 0.3 mm or less, an electrode group housed in the outer package and having a separator interposed between a positive electrode and a negative electrode, and a non-aqueous electrolyte impregnated in the electrode group. In a non-aqueous electrolyte secondary battery comprising a liquid, the positive electrode has a current collector and a positive electrode layer supported on one or both surfaces of the current collector, and the negative electrode has a current collector and A negative electrode layer supported on one or both surfaces of the current collector, wherein the non-aqueous electrolyte has a volume ratio of γ-
A non-aqueous electrolyte secondary battery comprising: a non-aqueous solvent containing butyrolactone; and an electrolyte of 1.6 mol / L or more and 3 mol / L or less dissolved in the non-aqueous solvent. 7. The non-aqueous electrolyte secondary battery according to claim 5, wherein the non-aqueous solvent further contains ethylene carbonate. 8. The non-aqueous electrolyte secondary battery according to claim 5, wherein the electrolyte is LiBF ₄ . 9. In the positive electrode, a positive electrode layer having a thickness of 50 to 95 μm is supported on one surface of the current collector, or a positive electrode layer having a thickness of 50 to 95 μm is provided on each surface of the current collector. The non-aqueous electrolyte secondary battery according to claim 6, which is carried. 10. In the negative electrode, a negative electrode layer having a thickness of 40 to 75 μm is supported on one surface of the current collector,
10. The non-aqueous electrolyte secondary battery according to claim 6, wherein a negative electrode layer having a thickness of 40 to 75 [mu] m is supported on each surface of the current collector.