JP2003132943A - Nonaqueous electrolyte and nonaqueous electrolytic secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte which can improve a charge and discharge cycle life at a high temperature. SOLUTION: The nonaqueous electrolyte comprises a nonaqueous solvent and an electrolyte that is dissolved in the nonaqueous solvent, wherein the nonaqueous solvent includes ethylene carbonate (EC), propylene carbonate (PC), r-butyrolactone (GBL), and a fourth component that is a solvent other than the above EC, the above PC and the above GBL. Supposing that the percentage of the ethylene carbonate (EC), the propylene carbonate (PC), the r-butyrolactone (GBL) and the fourth component to the total volume of the nonaqueous solvent is x (volume %), y (volume %), z (volume %) and p (volume %), respectively, the above y, the above z and the above p satisfy 15<=x<=50, 30<=y<=75, 0<z<30 and 0<p<=5, respectively.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD 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, a lithium ion secondary battery is commercialized as a non-aqueous electrolyte secondary battery for mobile devices such as mobile phones. As an example of this lithium ion secondary battery, a lithium cobalt oxide (for example, LiCo
It is known to include a positive electrode containing O ₂ ), a negative electrode containing a graphite material or a carbonaceous material, a non-aqueous electrolyte mainly composed of an organic solvent in which a lithium salt is dissolved, and a porous membrane that is a separator. ing. 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 Laid-Open No. 14769/1992 discloses that
Propylene carbonate, ethylene carbonate and γ-
A non-aqueous electrolyte secondary battery is described which is mainly composed of a mixed solvent composed of butyrolactone and has an electrolytic solution in which the ratio of γ-butyrolactone is 10 to 50% by volume of the entire mixed solvent. In this publication, by adding γ-butyrolactone to a mixed solvent of propylene carbonate and ethylene carbonate, the conductivity of an electrolytic solution at a low temperature is increased and the low temperature discharge characteristics of a cylindrical non-aqueous electrolyte secondary battery are improved. .

However, the above-mentioned Japanese Unexamined Patent Publication No. 4-147
In the non-aqueous electrolyte secondary battery described in Japanese Patent Publication No. 69, a large amount of gas is generated from the negative electrode at the time of initial charging, or 60
When stored at an extremely high temperature of ℃ or more, the positive electrode reacts with the non-aqueous electrolyte to cause oxidative decomposition of the non-aqueous electrolyte to generate gas. Therefore, if the thickness of the container for accommodating the positive electrode, the negative electrode, the separator and the non-aqueous electrolyte is reduced in order to reduce the thickness of the battery, the generated gas causes a problem that the container is swollen and deformed. If the container is deformed, the battery may not fit in the electronic device or the electronic device may malfunction. Further, this non-aqueous electrolyte secondary battery has a problem that the reaction between the negative electrode and γ-butyrolactone is likely to proceed in a high temperature environment, and a long life cannot be obtained at a high temperature.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery capable of improving charge / discharge cycle life at high temperature.

[0006]

A first non-aqueous electrolyte according to the present invention is a non-aqueous electrolyte comprising a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent, wherein the non-aqueous solvent is , Ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and a fourth component that is a solvent other than the EC, the PC, and the GBL, with respect to the total volume of the non-aqueous solvent. The proportions of ethylene carbonate, propylene carbonate, γ-butyrolactone and the fourth component are respectively x (volume%) and y.
(Volume%), z (volume%), and p (volume%), x, y, z, and p are each 15 ≦ x ≦.
50, 30 ≦ y ≦ 75, 0 <z <30, 0 <p ≦ 5.

The second non-aqueous electrolyte according to the present invention is a non-aqueous electrolyte comprising a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent, and the non-aqueous solvent is ethylene carbonate (EC). And propylene carbonate (PC), γ
-Butyrolactone (GBL), vinylene carbonate (VC), and a fifth component which is a solvent other than the EC, the PC, the GBL and the VC, ethylene carbonate, propylene carbonate, relative to the total volume of the non-aqueous solvent, The ratios of γ-butyrolactone, vinylene carbonate, and the fifth component are x (volume%) and y, respectively.
(Volume%), z (volume%), w (volume%), q (volume%), the x, the y, the z, the w and the q are 15 ≦ x ≦ 50 and 30 ≦, respectively. y ≦ 75, 0 <
z <30, 0 <w ≦ 5, 0 <q ≦ 5 are satisfied.

A first non-aqueous electrolyte secondary battery according to the present invention comprises a container, an electrode group housed in the container, and a non-aqueous electrolyte containing a non-aqueous solvent and held by the electrode group. The non-aqueous electrolyte secondary battery, wherein the non-aqueous solvent is ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and E
C, the PC and the fourth component which is a solvent other than the GBL, and the proportions of ethylene carbonate, propylene carbonate, γ-butyrolactone and the fourth component with respect to the total volume of the non-aqueous solvent are x (volume%), y
(Volume%), z (volume%), and p (volume%), x, y, z, and p are each 15 ≦ x ≦.
50, 30 ≦ y ≦ 75, 0 <z <30, 0 <p ≦ 5.

A second non-aqueous electrolyte secondary battery according to the present invention comprises a container, an electrode group housed in the container, and a non-aqueous electrolyte that is held by the electrode group and contains a non-aqueous solvent. Non-aqueous electrolyte secondary battery, wherein the non-aqueous solvent is ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), vinylene carbonate (VC), the EC, the PC. , GBL and a fifth component which is a solvent other than VC, and the ratio of ethylene carbonate, propylene carbonate, γ-butyrolactone, vinylene carbonate and the fifth component to the total volume of the non-aqueous solvent is x (volume%). ), Y (volume%), z (volume%), w (volume%), q (volume%), the x, the y, the z, the w, and the q are respectively 15 ≦ x ≦ 50, 30
It is characterized by satisfying ≦ y ≦ 75, 0 <z <30, 0 <w ≦ 5, 0 <q ≦ 5.

A third non-aqueous electrolyte secondary battery according to the present invention comprises a container, a positive electrode housed in the container, a negative electrode housed in the container, and a space between the positive electrode and the negative electrode. Is a non-aqueous electrolyte secondary battery comprising a liquid non-aqueous electrolyte and an electrolyte layer containing a polymer having a function of gelling the liquid non-aqueous electrolyte, the liquid non-aqueous electrolyte, ethylene carbonate ( EC), propylene carbonate (PC), γ-butyrolactone (BL), and a non-aqueous solvent containing the EC, the PC and a fourth component that is a solvent other than the BL, and the entire non-aqueous solvent. The ratios of ethylene carbonate, propylene carbonate, γ-butyrolactone and the fourth component to x were defined as x (volume%), y (volume%), z (volume%) and p (volume%), respectively. Where, x, y, z
And p are 15 ≦ x ≦ 50 and 30 ≦ y ≦ 7, respectively.
5, 0 <z <30, 0 <p ≦ 5.

A fourth non-aqueous electrolyte secondary battery according to the present invention comprises a container, a positive electrode housed in the container, a negative electrode housed in the container, and a space between the positive electrode and the negative electrode. Is a non-aqueous electrolyte secondary battery comprising a liquid non-aqueous electrolyte and an electrolyte layer containing a polymer having a function of gelling the liquid non-aqueous electrolyte, the liquid non-aqueous electrolyte, ethylene carbonate ( EC), propylene carbonate (PC), γ-butyrolactone (GBL), vinylene carbonate (VC), and a fifth component that is a solvent other than the EC, the PC, the GBL, and the VC. Ratio of ethylene carbonate, propylene carbonate, γ-butyrolactone, vinylene carbonate and the fifth component containing a solvent, relative to the total volume of the non-aqueous solvent. X (volume%), y
(Volume%), z (volume%), w (volume%), q (volume%), the x, the y, the z, the w and the q are 15 ≦ x ≦ 50 and 30 ≦, respectively. y ≦ 75, 0 <
z <30, 0 <w ≦ 5, 0 <q ≦ 5 are satisfied.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A non-aqueous electrolyte secondary battery according to the present invention comprises a container, an electrode group housed in the container, and a non-aqueous electrolyte containing a non-aqueous solvent held by the electrode group. To have.

As the non-aqueous solvent, for example, any one of (A) to (B) described below is used.

(A) Non-Aqueous Solvent A This non-aqueous solvent A comprises ethylene carbonate (EC) and
Propylene carbonate (PC), γ-butyrolactone (GBL), and a fourth component that is a solvent other than the EC, the PC, and the GBL.

The proportions of ethylene carbonate, propylene carbonate, γ-butyrolactone and the fourth component with respect to the total volume of the non-aqueous solvent are x (volume%) and y, respectively.
(Volume%), z (volume%), and p (volume%), x, y, z, and p are each 15 ≦ x ≦.
50, 30 ≦ y ≦ 75, 0 <z <30, 0 <p ≦ 5 are satisfied.

(B) Non-Aqueous Solvent B This non-aqueous solvent B comprises ethylene carbonate (EC) and
It contains propylene carbonate (PC), γ-butyrolactone (GBL), vinylene carbonate (VC), and a fifth component that is a solvent other than the EC, the PC, the GBL, and the VC.

The proportions of ethylene carbonate, propylene carbonate, γ-butyrolactone, vinylene carbonate and the fifth component with respect to the total volume of the non-aqueous solvent are x (volume%), y (volume%), z (volume%) and w, respectively.
(Volume%) and q (volume%), the x, the y,
Z, w, and q are 15 ≦ x ≦ 50,
30 ≦ y ≦ 75, 0 <z <30, 0 <w ≦ 5, 0 <q ≦
5 is satisfied.

As the non-aqueous electrolyte, one having a substantially liquid or gel form can be used. Among them, the liquid non-aqueous electrolyte is preferable. By using the liquid non-aqueous electrolyte, the ionic conductivity can be increased, so that the interface resistance between the positive electrode and the separator and the interface resistance between the negative electrode and the separator can be reduced.

The non-aqueous electrolyte is, for example, the following (I)
It is prepared by the method described in (IV).

(I) A non-aqueous electrolyte is obtained by dissolving an electrolyte (for example, a lithium salt) in any of the above-mentioned non-aqueous solvents A to B (liquid non-aqueous electrolyte).

(II) A paste prepared by mixing any of the above-mentioned non-aqueous solvents A to B, an electrolyte and a polymer is formed into a film and then dried. The obtained thin film is interposed between the positive electrode and the negative electrode to produce an electrode group.
After impregnating this electrode group with a liquid non-aqueous electrolyte, the thin film is plasticized under reduced pressure.

(III) After impregnating a separator with a slurry containing any of the above-mentioned non-aqueous solvents A to B, an electrolyte and a gelling agent, the separator is interposed between a positive electrode and a negative electrode to form a gel state. An electrode group holding a non-aqueous electrolyte is obtained.

(IV) A gel containing a slurry containing any of the above-mentioned non-aqueous solvents A to B, an electrolyte and a gelling agent is applied to a positive electrode or a negative electrode, and a separator is interposed between the positive and negative electrodes. An electrode group holding a non-aqueous electrolyte is obtained.

Examples of the gelling agent include polyacrylonitrile (PAN).

Specific examples of the secondary battery according to the present invention (non-aqueous electrolyte secondary battery (I) and non-aqueous electrolyte secondary battery (II)) will be described below.

1. Non-Aqueous Electrolyte Secondary Battery (I) This non-aqueous electrolyte secondary battery includes a container, a separator housed in the container, and a separator interposed between a positive electrode that stores and releases lithium ions and a negative electrode that stores and releases lithium ions. It is provided with an electrode group arranged and a liquid non-aqueous electrolyte (non-aqueous electrolyte) containing at least the separator and a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent.

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

1) Electrode Group In this electrode group, the positive electrode, the negative electrode and the separator are preferably integrated. Such an electrode group is produced, for example, by the method described in (i) to (ii) below.

(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 between them.
It is compressed in the radial direction, or the positive electrode and the negative electrode are bent once or more with a separator interposed therebetween. By subjecting the flat material obtained by any one of the above-mentioned methods to thermoforming in the stacking 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, and the electrode group. To get

The heat molding may be carried out after the flat material is housed in a container or before it is housed in the container.

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

The molding can be carried out, for example, by press molding or fitting into a molding die.

The temperature of the heat molding is preferably in the range of 20 to 120 ° C. A more preferable range is 6
It is 0 to 100 ° C.

The molding pressure of the heat molding is 0.01 to 35.
It is desirable to set it within the range of kg / cm ² . A preferred range is 8 to 30 kg / cm ² , and a more preferred range is 12 to 25 kg / cm ² .

(Ii) 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 wound spirally with a separator interposed therebetween,
It is compressed in the radial direction, or the positive electrode and the negative electrode are bent once or more with a separator interposed therebetween. The flat material obtained by any of the methods described above is impregnated with a solution of a polymer having adhesiveness, and then vacuum dried to evaporate the solvent in the solution. Then, the positive electrode, the negative electrode, and the separator are integrated by performing heat molding to obtain an electrode group. In such an electrode group, the positive electrode and the separator are integrated by the polymer having an adhesive property that is scattered in the inside and the boundary thereof, and the adhesive property that the negative electrode and the separator are scattered in the inside and the boundary are formed. Since the secondary battery is integrated by the polymer, the adhesive strength can be increased while keeping the internal resistance of the secondary battery low.

The thermoforming may be carried out after the flat material is stored in a container or before it is stored in the container.

The solution of the adhesive polymer is prepared by dissolving the adhesive polymer in an organic solvent.

It is desirable that the above-mentioned adhesive polymer is capable of maintaining high adhesiveness while holding the non-aqueous electrolyte. Furthermore, it is more preferable that such a polymer has high lithium ion conductivity. Specifically, polyacrylonitrile (PAN), polyacrylate (PMM)
A), polyvinylidene fluoride (PVdF), polyvinyl chloride (PVC), or polyethylene oxide (PE)
O) etc. can be mentioned. Particularly, polyvinylidene fluoride is preferable. Polyvinylidene fluoride can hold a non-aqueous electrolytic solution, and when it contains a non-aqueous electrolytic solution, it partially gelates, so that the ionic conductivity can be further improved.

The boiling point of the solvent is preferably 200 ° C. or lower, more preferably 180 ° C. or lower. The lower limit of the boiling point is preferably 50 ° C, and the more preferable lower limit is 100 ° C.

The concentration of the adhesive polymer in the solution is preferably in the range of 0.05 to 2.5% by weight. The more preferable range of the concentration is 0.1 to 1.5% by weight.
Is.

The injection amount of the solution may be in the range of 0.1 to 2 ml per 100 mAh of battery capacity when the concentration of the adhesive polymer in the solution is 0.05 to 2.5% by weight. preferable. A more preferable range of the injection amount is 0.15 to 1 ml per 100 mAh of battery capacity.

The vacuum drying is preferably performed at 100 ° C. or lower. A more preferable vacuum drying temperature is 40 to 10
It is 0 ° C.

The total amount of the adhesive polymer contained in the battery is 0.1 to 6 mg per 100 mAh of battery capacity.
Is preferred. A more preferable range of the total amount of the adhesive polymer is 0. 0 per 100 mAh of battery capacity.
It is 2-1 mg.

2) Positive Electrode This positive electrode includes a current collector and a positive electrode layer which is carried on one side or both sides of the current collector and which contains an active material.

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,
Examples thereof include 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. . 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 (for example, LiM
It is preferable to use n ₂ O ₄ or LiMnO ₂ 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 to each other. 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 positive electrode active material, the conductive agent, and the binder are mixed in proportions of 80 to 95% by weight of the positive electrode active material and 3 to 2 of the conductive agent.
It is preferable that the content is 0% by weight and the binder is 2 to 7% by weight.

As the current collector, a porous conductive substrate or a non-porous conductive substrate can be used. These conductive substrates can be formed of, for example, aluminum, stainless steel, or nickel.

Above all, a hole having a diameter of 3 mm or less is 10 cm ²
It is preferable to use a conductive substrate having a two-dimensional porous structure, which is present at a ratio of 1 or more per one. More preferably, the diameter of the holes is in the range of 0.1 to 1 mm.
Further, it is more preferable that the existence ratio of the holes is in the range of 10 to 20 per 10 cm ² .

The above-mentioned hole having a diameter of 3 mm or less is 10 cm ²
The conductive substrate having a two-dimensional porous structure, which is present at a ratio of 1 or more per one, preferably has a thickness in the range of 15 to 100 μm. A more preferable range of the thickness is 30
˜80 μm.

The positive electrode is prepared, 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 it to form a thin plate. .

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

3) Negative Electrode The negative electrode includes a current collector and a negative electrode layer carried on one side or both sides of the current collector.

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

Examples of the carbonaceous material include graphite, coke,
Graphite material or carbonaceous material such as carbon fiber, spherical carbon, thermosetting resin, isotropic pitch, mesophase pitch, mesophase pitch carbon fiber, mesophase microsphere, etc. Discharge cycle characteristics are improved, which is preferable) to 500 to 3
Examples thereof include a graphite material or a carbonaceous material obtained by heat treatment at 000 ° C. Above all, it is preferable to use a graphite material having graphite crystals obtained by setting the heat treatment temperature to 2000 ° C. or higher and having a (002) plane spacing d ₀₀₂ of 0.34 nm or less. The non-aqueous electrolyte secondary battery including the negative electrode containing such a graphite material as a carbonaceous material can significantly improve the battery capacity and the large current discharge characteristics. The surface spacing 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-ptadiene 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.
It is preferably in the range of.

As the current collector, a porous conductive substrate or a non-porous conductive substrate can be used. These conductive substrates can be made of, for example, copper, stainless steel, or nickel.

Among them, a hole having a diameter of 3 mm or less is 10 cm ²
It is preferable to use a conductive substrate having a two-dimensional porous structure, which is present at a ratio of 1 or more per one. More preferably, the diameter of the holes is in the range of 0.1 to 1 mm.
Further, it is more preferable that the existence ratio of the holes is in the range of 10 to 20 per 10 cm ² .

The above-mentioned hole having a diameter of 3 mm or less is 10 cm ²
The conductive substrate having a two-dimensional porous structure, which is present at a ratio of one or more per one, preferably has a thickness in the range of 10 to 50 μm.

In the negative electrode, for example, a carbonaceous material that absorbs and releases lithium ions and a binder are kneaded in the presence of a solvent, and the obtained suspension is applied to a current collector and dried, It is produced by pressing once at a desired pressure or by multi-step pressing 2 to 5 times.

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

The negative electrode layer contains a metal such as aluminum, magnesium, tin, or silicon, a metal oxide, a metal sulfide, or a metal, in addition to the above-described material containing a carbon substance 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, tungsten oxide and the like.

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

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

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

4) Separator This separator is made of, for example, a porous sheet.

As the porous sheet, for example, a porous film or a non-woven fabric can be used. The porous sheet is preferably made of at least one material selected from polyolefin and cellulose, for example. Examples of the polyolefin include polyethylene and polypropylene. Above all, a porous film made of polyethylene, polypropylene, or both is preferable because it can improve the safety of the secondary battery.

The thickness of the porous sheet is preferably 30 μm or less, more preferably 25 μm.
It is the following. Further, the lower limit value of the thickness is preferably 5 μm, and more preferably the lower limit value is 8 μm.

The porous sheet preferably has a heat shrinkage ratio of 20% or less at 120 ° C. for 1 hour. The heat shrinkage rate is more preferably 15% or less.

The porous sheet has a porosity of 30 to 60.
It is preferably in the range of%. A more preferable range of porosity is 35 to 50%.

The porous sheet has an air permeability of 600.
It is preferably not more than seconds / 100 cm ³ . The air permeability means the time (second) required for 100 cm ³ of air to pass through the porous sheet. More preferably, the upper limit of the air permeability is 500 seconds / 100 cm ³ . The lower limit of the air permeability is preferably 50 seconds / 100 cm ³ , and the more preferable lower limit is 80 seconds / 10.
It is 0 cm ³ .

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

5) Liquid Non-Aqueous Electrolyte (Non-Aqueous Electrolyte Solution) This liquid non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent.

The non-aqueous solvent includes the above-mentioned (A) to (A).
Any of (B) can be used. First, the non-aqueous solvent A will be described.

The reason why the ratio of each solvent to the whole non-aqueous solvent is defined in the above range will be described.

A. γ-Butyrolactone (GBL) GBL mainly plays a role of controlling the reaction between the negative electrode and PC. When GBL is not added, the reaction between the negative electrode surface and PC proceeds from the time of initial charging, and the gas generated by the reaction induces the swelling of the battery container. GBL is added mainly for the purpose of controlling the reaction between the negative electrode and PC to suppress gas generation and swelling of the battery container during initial charging.
When the ratio of is 30 vol% or more, the reactivity between the negative electrode surface and GBL becomes high especially at high temperature, the reductive decomposition of the non-aqueous electrolyte proceeds, and a film that inhibits the charge-discharge reaction is formed on the negative electrode surface. It Therefore, long life cannot be obtained in a high temperature environment.

When the ratio (z) of GBL is less than 30% by volume, the cause is not clear, but the reaction of both PC and GBL with the negative electrode is suppressed, and the presence of the fourth component causes
The suppression effect is synergistic.

A more preferable ratio (z) is 1% by volume or more,
It is less than 30% by volume, more preferable ratio (z) is 1% by volume or more and 25% by volume or less, and most preferable ratio (z) is 2% by volume or more and 15% by volume or less.

B. Ethylene carbonate (EC) The ratio (x) of EC to the total volume of the non-aqueous solvent is 15% by volume.
If it is less than 1, it may be difficult to cover the surface of the negative electrode with a protective film derived from EC.
The reaction with the reaction proceeds with the generation of gas at the time of initial charging and the resulting expansion of the container. On the other hand, when the EC ratio (x) exceeds 50% by volume, the viscosity of the non-aqueous electrolyte may be increased and the ionic conductivity may be lowered, so that the low temperature discharge characteristics are significantly lowered. The more preferable range of the EC ratio (x) is 20.
It is from 50% by volume to 50% by volume, and a more preferable range is from 25% by volume to 50% by volume.

C. Propylene carbonate (PC) The ratio (y) of PC to the total volume of the non-aqueous solvent is 30% by volume.
If less than, the reaction between the negative electrode and GBL becomes dominant,
Even in the presence of the fourth component, it becomes difficult to improve the cycle life at high temperature. On the other hand, the PC ratio (y) is 7
When it exceeds 5% by volume, the reaction between the negative electrode and PC becomes predominant at the time of initial charging, and it is difficult to suppress gas generation and accompanying swelling of the battery container. A more preferable range of the ratio (y) of PC is 30% by volume or more and 70% by volume or less,
A more preferable range is 30% by volume or more and 65% by volume or less.

Note that PC moves from the non-aqueous solvent to the surface of the negative electrode during the initial charging / discharging step and adheres to the surface of the negative electrode. Therefore, in the non-aqueous solvent present in the secondary battery that has been subjected to the initial charge / discharge step, the
The ratio of is smaller than that before the secondary battery is assembled. The reduction rate increases as the amount of PC added decreases.

D. If the fourth component is not present in the fourth component non-aqueous solvent, the density or the lithium ion permeability of the protective film formed on the surface of the negative electrode is lowered, so that gas generation during initial charging and high temperature storage can be suppressed. In addition to disappearing, it is difficult to improve the charge / discharge cycle life at high temperature. However, when the ratio (p) of the fourth component to the total volume of the non-aqueous solvent exceeds 5% by volume,
It may promote gas generation during high temperature storage or initial charge, or the lithium ion permeability of the protective film formed on the negative electrode surface may decrease and the negative electrode impedance may increase, so long life may not be obtained. There is a nature. Therefore, the ratio (p) of the fourth component to the total volume of the non-aqueous solvent is preferably more than 0% by volume and 5% by volume or less.
The more preferable range of the fourth component is 4% by volume or less, the more preferable range is 3% by volume or less, and the most preferable range is 0.1% by volume to 2% by volume.

Fourth containing ethylene sulfite (ES)
According to the non-aqueous electrolyte containing the components, suppressing gas generation during high temperature storage and initial charging, and cycle life at high temperature,
Other charging / discharging characteristics such as storage characteristics and low temperature discharging characteristics can be simultaneously satisfied. Further, by containing VC in this non-aqueous electrolyte, the balance between suppression of gas generation, cycle life at high temperature, and other charge / discharge characteristics such as storage characteristics and low-temperature discharge characteristics is further improved. be able to.

As the fourth component, ethylene sulfite (E
When S) is used, the preferred range is 5% by volume or less,
A more preferred range is 3% by volume or less, and a most preferred range is 1.5% by volume or less.

As the fourth component, 12-crown-4 (Cr
If used, the preferred range is 5% by volume or less, the more preferred range is 4% by volume or less, and the most preferred range is 3% by volume or less.

When tetraethylene glycol dimethyl ether (Ether) is used as the fourth component, the preferred range is 5% by volume or less, the more preferred range is 4% by volume or less, and the most preferred range is 3% by volume or less.

As the fourth component, ES, Crown
And other solvents than Ether can be used.

Other solvents include, for example, vinylene carbonate (VC) and vinyl ethylene carbonate (VE
C), phenylethylene carbonate (phEC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), γ
-Valerolactone (VL), methyl propionate (M
P), ethyl propionate (EP), 2-methylfuran (2Me-F), furan (F), thiophene (TIO
P), catechol carbonate (CATC) and the like. The type of the other solvent used as the fourth component may be one type or two or more types.

By using the fourth component containing at least one kind of solvent selected from the group consisting of ES, Crown and Ether and one or more kinds of other solvents selected from the aforementioned kinds, The charging / discharging cycle life in can be further improved.

Next, the non-aqueous solvent B will be described.

The reason why the ratio of each solvent to the whole non-aqueous solvent is defined in the above range will be described.

A. γ-Butyrolactone (GBL) The existence ratio (z) of GBL in the non-aqueous solvent is set to less than 30% by volume for the same reason as explained for the non-aqueous solvent A described above. More preferable ratio (z) is 1% by volume or more and less than 30% by volume, further preferable ratio (z) is 1% by volume or more and 25% by volume or less, and most preferable ratio (z) is 2% by volume or more and 15% by volume. % Or less.

B. Ethylene carbonate (EC) The abundance ratio (x) of EC in the non-aqueous solvent is 15 to 50% by volume.
The reason why is set is for the same reason as explained for the non-aqueous solvent A described above. A more preferable range of the EC ratio (x) is 20% by volume or more and 50% by volume or less, and a more preferable range is 25% by volume or more and 50% by volume or less.

C. Propylene carbonate (PC) The abundance ratio (y) of PC in the non-aqueous solvent is 30 to 75% by volume.
The reason why it is set within the range is for the same reason as explained in the non-aqueous solvent A described above. A more preferable range of the ratio (y) of PC is 30% by volume or more and 70% by volume or less,
A more preferable range is 30% by volume or more and 65% by volume or less.

D. Vinylene carbonate (VC) VC improves the compactness of the protective film formed on the negative electrode surface, suppresses gas generation during initial charge and high temperature storage, cycle life at high temperature, storage characteristics and low temperature discharge characteristics. However, if the abundance ratio (w) of VC in the non-aqueous solvent exceeds 5% by volume, it may be added during high temperature storage or initial charging. It may promote gas generation, or the lithium ion permeability of the protective film formed on the surface of the negative electrode may decrease, increasing the impedance of the negative electrode and sufficiently improving the charge / discharge cycle life at high temperatures. It will be difficult. A preferred range of the ratio (w) of VC to the total volume of the non-aqueous solvent is 3% by volume or less, and a more preferred range is 2% by volume or less.

Note that VC moves from the non-aqueous solvent to the surface of the negative electrode and adheres to the surface of the negative electrode during the initial charge / discharge step. Therefore, in the non-aqueous solvent existing in the secondary battery that has been subjected to the initial charge / discharge step, V with respect to the total volume of the non-aqueous solvent is
The ratio of C is lower than that before the secondary battery is assembled. The reduction rate is, for example, 70 to 80 when the addition amount of VC is 1% by weight.
% (That is, the residual rate is 20 to 30%).

E. If the fifth component is not present in the fifth component non-aqueous solvent, the density or the lithium ion permeability of the protective film formed on the negative electrode surface is lowered, so that not only the generation of gas at the time of initial charging cannot be suppressed, It is also difficult to improve the cycle life at high temperature. However, if the ratio (q) of the fifth component to the total volume of the non-aqueous solvent exceeds 5% by volume, gas generation may be promoted during high temperature storage or initial charging, or protection formed on the negative electrode surface. There is a possibility that the lithium ion permeability of the film is lowered and the impedance of the negative electrode is increased, so that a sufficient cycle life cannot be obtained. Therefore, the ratio (q) of the fifth component to the total volume of the non-aqueous solvent is more than 0% by volume,
It is preferably within the range of 5% by volume or less. The more preferable range of the fifth component is 4% by volume or less, the more preferable range is 3% by volume or less, and the most preferable range is 0.1% by volume to 2% by volume.

Fifth containing ethylene sulfite (ES)
According to the non-aqueous electrolyte containing the components, suppressing gas generation during high temperature storage and initial charging, and cycle life at high temperature,
Other charging / discharging characteristics such as storage characteristics and low temperature discharging characteristics can be simultaneously satisfied.

As a fifth component, ethylene sulfite (E
When S) is used, the preferred range is 5% by volume or less,
A more preferred range is 3% by volume or less, and a most preferred range is 1.5% by volume or less.

As a fifth component, 12-crown-4 (Cr
If used, the preferred range is 5% by volume or less, the more preferred range is 4% by volume or less, and the most preferred range is 3% by volume or less.

When tetraethylene glycol dimethyl ether (Ether) is used as the fifth component, the preferred range is 5% by volume or less, the more preferred range is 4% by volume or less, and the most preferred range is 3% by volume or less.

As the fifth component, ES, Crown
And other solvents than Ether can be used.

Other solvents include, for example, vinyl ethylene carbonate (VEC), phenyl ethylene carbonate (phEC), diethyl carbonate (DEC),
Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), γ-valerolactone (VL), methyl propionate (MP), ethyl propionate (E
P), 2-methylfuran (2Me-F), furan (F), thiophene (TIOP), catechol carbonate (CATC) and the like. The type of the other solvent used as the fifth component may be one type or two or more types.

By using the fifth component containing at least one solvent selected from the group consisting of ES, Crown and Ether and one or more other solvent selected from the above-mentioned types, The charging / discharging cycle life in can be further improved.

Examples of the electrolyte dissolved in the non-aqueous solvents A to B include lithium perchlorate (LiClO ₄ ),
Lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium arsenic hexafluoride (LiA
sF ₆ ), lithium trifluorometasulfonate (Li
CF ₃ SO _3), bistrifluoromethylsulfonylimide lithium _{[(LiN (CF 3 SO 2} ) 2], LiN
Examples thereof include lithium salts such as (C ₂ F ₅ SO ₂ ) ₂ . The type of electrolyte used can be one type or two or more types.

Among them, those containing LiPF ₆ or LiBF ₄ are preferable. Further, (containing an imide salt composed of at least one of LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ and a salt composed of at least one of LiBF ₄ and LiPF ₆ When the mixed salt is used, the cycle life at high temperature can be further improved, and since the thermal stability of the electrolyte is improved, the voltage drop due to self-discharge during storage in a high temperature environment can be suppressed.

The amount of the electrolyte dissolved in the non-aqueous solvent is preferably 0.5 to 2.5 mol / L. A more preferable range is 1 to 2.5 mol / L.

The liquid nonaqueous electrolyte preferably contains a surfactant such as trioctyl phosphate (TOP) in order to improve the wettability with the separator. The amount of the surfactant added is preferably 3% or less, more preferably 0.1 to 1%.

The amount of the liquid non-aqueous electrolyte is preferably 0.2 to 0.6 g per 100 mAh of battery unit capacity. The more preferable range of the liquid non-aqueous electrolysis mass is 0.2
It is 5 to 0.55 g / 100 mAh.

6) Container (Accommodation Container) The shape of the container can be, for example, a cylinder with a bottom, a rectangular cylinder with a bottom, a bag shape, or the like.

This container can be formed from, for example, a sheet containing a resin layer, a metal plate, a metal film, or the like.

The resin layer contained in the sheet is, for example,
It can be formed from polyolefin (eg, polyethylene, polypropylene) or the like. As the sheet, it is desirable to use a sheet in which a metal layer and protective layers arranged on both surfaces of the metal layer are integrated. The metal layer serves to block moisture. Examples of the metal layer include aluminum, stainless steel, iron, copper, nickel and the like. Of these, aluminum is preferable because it is lightweight and has a high function of blocking moisture. The metal layer is
It may be formed from one kind of metal, but may be formed from one in which two or more kinds of metal layers are integrated. Of the two protective layers, the protective layer in contact with the outside serves to prevent damage to the metal layer. The external protective layer is formed of one type of resin layer or two or more types of resin layers. On the other hand, the internal protective layer plays a role of preventing the metal layer from being corroded by the non-aqueous electrolyte. This internal protective layer is 1
It is formed of one kind of resin layer or two or more kinds 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 formed of, for example, iron, stainless steel, or aluminum.

The thickness of the container (thickness of the wall of the container) is 0.3.
It is desirable that the thickness is less than or equal to mm. It has a thickness of 0.3
If it is thicker than mm, it becomes difficult to obtain high weight energy density and high volume energy density. The preferable range of the thickness of the container is 0.25 mm or less, the more preferable range is 0.15 mm or less, and the most preferable range is 0.12 mm.
mm or less. If the thickness is less than 0.05 mm, the container is likely to be deformed or damaged. Therefore, the lower limit of the container thickness is preferably 0.05 mm.

The thickness of the container is measured by the method described below. That is, in the area excluding the sealed portion of the container,
Arbitrarily select three points that are 1 cm or more apart from each other,
The thickness at each point is measured, the average value is calculated, and this value is used as the container thickness. If foreign matter (for example, resin) is attached to the surface of the container, the thickness is measured after removing the foreign matter. For example, when PVdF is attached to the surface of the container, the thickness of the container is measured after the PVdF is removed by wiping the surface of the container with a dimethylformamide solution.

It is preferable that an adhesive layer is formed on at least a part of the surface of the container, and the electrode group is adhered to the inner surface of the container by the adhesive layer. With such a configuration, the container can be fixed to the surface of the electrode group, so that the electrolytic solution can be prevented from penetrating between the electrode group and the container.

It is preferable that the secondary battery is initially charged at a rate of 0.05 C or more and 0.8 C or less under a temperature condition of 15 ° C. to 80 ° C. Charging under this condition may be performed for only one cycle or may be performed for two cycles or more. In addition, before the first charge, under the temperature condition of 15 ° C to 80 ° C for 1 hour
It may be stored for about 20 hours.

Here, 1C is a current value required to discharge the nominal capacity (Ah) in 1 hour.

The temperature of the initial charge is regulated within the above range for the following reason. First charge temperature is 15
If it is lower than 0 ° C, it becomes difficult to uniformly impregnate the liquid non-aqueous electrolyte into the positive electrode, the negative electrode and the separator because the viscosity of the liquid non-aqueous electrolyte remains high, the internal impedance increases, and the active material Utilization rate decreases. On the other hand, when the initial charging temperature exceeds 80 ° C., the binder contained in the positive electrode and the negative electrode deteriorates. The preferred charging temperature range is 15-6
The temperature is 0 ° C, and the more preferable range is 20 to 50 ° C.

By setting the rate of initial charge to be in the range of 0.05 to 0.8 C, the expansion of the positive electrode and the negative electrode due to charging can be moderately delayed, so that the liquid non-aqueous electrolyte can be uniformly applied to the positive electrode and the negative electrode. Can be penetrated. A preferable initial charge rate is 0.05 to 0.5C.

By providing such a step,
Since the liquid non-aqueous electrolyte can be uniformly impregnated into the voids of the electrodes and the separator, the internal impedance of the secondary battery can be reduced. As a result, the utilization rate of the active material can be increased, so that the substantial capacity of the battery can be increased. In addition, the charge / discharge cycle characteristics and the large current discharge characteristics of the battery can be improved.

A thin lithium-ion secondary battery as an example of the non-aqueous electrolyte secondary battery (I) according to the present invention is shown in FIGS. 1 and 2.
Will be described in detail with reference to.

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

As shown in FIG. 1, an electrode group 2 is housed in a container 1 having a desired thickness X. 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. The laminate is shown in FIG.
As shown in (from the bottom of the figure), the separator 3, the positive electrode layer 4, the positive electrode current collector 5, and the positive electrode 6 including the positive electrode layer 4, the separator 3, the negative electrode layer 7, the negative electrode current collector 8, and the negative electrode layer 7 Negative electrode 9, separator 3, positive electrode layer 4, positive electrode current collector 5, and positive electrode layer 4
The positive electrode 6 including the above, the separator 3, the negative electrode layer 7, and the negative electrode 9 including the negative electrode current collector 8 are laminated in this order. The negative electrode current collector 8 is located in the outermost layer of the electrode group 2. 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 thereof extends from the container 1. On the other hand, the strip-shaped negative electrode lead 11
Has one end connected to the negative electrode current collector 8 of the electrode group 2 and the other end extending from the container 1.

Next, the non-aqueous electrolyte secondary battery (II) according to the present invention will be described.

This non-aqueous electrolyte secondary battery comprises a container and an electrode group housed in the container. The electrode group is disposed between the positive electrode that absorbs and releases lithium ions, the negative electrode that absorbs and releases lithium ions, the positive electrode and the negative electrode, and gels the liquid non-aqueous electrolyte and the liquid non-aqueous electrolyte. And an electrolyte layer containing a polymer having a function.

As the container, the positive electrode, the negative electrode and the liquid non-aqueous electrolyte, the same ones as those explained in the non-aqueous electrolyte secondary battery (I) are used.

The electrolyte layer is produced, for example, by the method described below. First, a paste containing a polymer having a function of gelling a liquid non-aqueous electrolyte and a liquid non-aqueous electrolyte is formed and then dried. The obtained thin film is interposed between the positive electrode and the negative electrode to produce an electrode group. After impregnating the electrode group with a liquid non-aqueous electrolyte, the thin film is plasticized under reduced pressure to obtain the electrolyte layer.

The polymer preferably has thermoplasticity. Examples of such polymers include polyvinylidene fluoride (PVdF) and polyacrylonitrile (P
At least one selected from AN), polyethylene oxide (PEO), polyvinyl chloride (PVC), polyacrylate (PMMA) and polyvinylidene fluoride hexafluoropropylene (PVdF-HFP) can be used.

It is preferable that the secondary battery is initially charged at a rate of 0.05 C or more and 0.8 C or less under a temperature condition of 15 ° C. to 80 ° C. Charging under this condition may be performed for only one cycle or may be performed for two cycles or more. In addition, before the first charge, under the temperature condition of 15 ° C to 80 ° C for 1 hour
It may be stored for about 20 hours.

The first non-aqueous electrolyte secondary battery according to the present invention described above includes a container, an electrode group housed in the container, a non-aqueous solvent containing the non-aqueous solvent A and held by the electrode group. And an electrolyte.

The non-aqueous solvent A is ethylene carbonate (EC), propylene carbonate (PC), γ-
Butyrolactone (GBL) and a fourth component that is a solvent other than the EC, the PC, and the GBL. The proportions of ethylene carbonate, propylene carbonate, γ-butyrolactone and the fourth component with respect to the total volume of the non-aqueous solvent were x (volume%), y (volume%), z (volume%) and p (volume%), respectively. Where x, y, z and p are 15 ≦ x ≦ 50 and 30 ≦ y ≦ 7, respectively.
5, 0 <z <30 and 0 <p ≦ 5 are satisfied.

In order to improve the weight energy density and volume energy density of the non-aqueous electrolyte secondary battery, it is desirable that the thickness of the container be 0.3 mm or less. However, a container having a thickness of 0.3 mm or less easily swells due to the gas generated in the container.

By setting the ratio of γ-butyrolactone to the total volume of the non-aqueous solvent within the range of less than 30% by volume, the positive electrode and the non-aqueous electrolyte react with each other during storage under high temperature conditions and initial charging. As a result, it is possible to suppress the oxidative decomposition of the non-aqueous electrolyte. As a result, the amount of gas generated during high-temperature storage and initial charge can be reduced, so that the container can be prevented from swelling even when the container thickness is 0.3 mm or less, and high initial charge / discharge can be achieved. You can get efficiency.

Further, the ratio of ethylene carbonate to the whole non-aqueous solvent is 15% by volume or more and 50% by volume or less, the ratio of propylene carbonate is 30% by volume or more and 75% by volume or less, and the ratio of the fourth component is When the content is 5% by volume or less, a lithium ion-permeable protective film can be densely formed on the surface of the negative electrode. As a result, it is possible to reduce the reactivity of the negative electrode with respect to γ-butyrolactone under a high temperature environment, and thus it is possible to suppress the reductive decomposition of the non-aqueous electrolyte and suppress the increase in the interfacial impedance of the negative electrode. Therefore, the charge / discharge cycle life at high temperature can be improved.

The second non-aqueous electrolyte secondary battery according to the present invention comprises a container, an electrode group housed in the container, and a non-aqueous electrolyte containing the non-aqueous solvent B held by the electrode group. To have.

The non-aqueous solvent B is ethylene carbonate (EC), propylene carbonate (PC), γ-
Butyrolactone (GBL), vinylene carbonate (VC), and a fifth component which is a solvent other than the EC, the PC, the GBL, and the VC. The proportions of ethylene carbonate, propylene carbonate, γ-butyrolactone, vinylene carbonate and the fifth component with respect to the total volume of the non-aqueous solvent are x (volume%) and y, respectively.
(Volume%), z (volume%), w (volume%), q (volume%), the x, the y, the z, the w and the q are 15 ≦ x ≦ 50 and 30 ≦, respectively. y ≦ 75, 0 <
z <30, 0 <w ≦ 5, and 0 <q ≦ 5 are satisfied.

According to such a secondary battery, since a dense protective film excellent in lithium ion permeability can be formed on the surface of the negative electrode, the effect of suppressing gas generation at the time of initial charging or the charge / discharge cycle life at high temperature can be obtained. It can be higher.

[0143]

Embodiments of the present invention will now be described in detail with reference to the above-mentioned drawings.

Example 1 <Production of Positive Electrode> First, lithium cobalt oxide (Li _x
CoO ₂ ; where X is 0 <X ≦ 1) 91% by weight of powder, 3% by weight of acetylene black, 3% by weight of graphite, and polyvinylidene fluoride (PVdF) 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 have an electrode density of 3 g / cm ³ , and a positive electrode layer was carried on both sides of the current collector. A positive electrode having a structure was produced.

<Production of Negative Electrode> 3000 as carbonaceous material
93% by weight of powder of mesophase pitch-based carbon fiber (fiber diameter 8 μm, average fiber length 20 μm, average interplanar spacing (d ₀₀₂ ) 0.3360 nm) heat treated at ℃
And polyvinylidene fluoride (PVdF) 7 as a binder
% By weight to prepare a slurry. An electrode density of 1.4 g was obtained by applying the slurry on both sides of a current collector made of copper foil having a thickness of 12 μm, drying and pressing.
/ Cm ³ , a negative electrode having a structure in which the negative electrode layer was supported on the current collector was produced.

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

<Preparation of Non-Aqueous Electrolyte> Ethylene carbonate (EC), γ-butyrolactone (GBL), propylene carbonate (PC) and ethylene sulfite (E)
S) has a volume ratio (EC: GBL: PC: ES) of 31:
A non-aqueous solvent was prepared by mixing so as to be 6: 62: 1. Lithium tetrafluoroborate (Li
BF ₄ ) was dissolved so that its concentration was 1.5 mol / L to prepare a liquid non-aqueous electrolyte.

<Fabrication of Electrode Group> A strip-shaped positive electrode lead is welded to the positive electrode current collector, a strip-shaped negative electrode lead is welded to the negative electrode current collector, and the positive electrode and the negative electrode are interposed therebetween. After being wound in a spiral shape through the, it was formed into a flat shape to prepare an electrode group.

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

A 100 μm-thick laminated film in which both sides of an aluminum foil were covered with polypropylene was formed into a bag shape, and the electrode group was housed therein.

Then, the electrode group in the laminate film was vacuum dried at 80 ° C. for 12 hours to remove the water content contained in the electrode group and the laminate film.

The electrode group in the laminate film was charged with the liquid non-aqueous electrolyte in an amount of 4.8 g per 1 Ah of battery capacity.
And has the structure shown in FIGS. 1 and 2 described above, and has a thickness of 3.6 mm, a width of 35 mm, and a height of 62 mm.
The thin non-aqueous electrolyte secondary battery of was assembled.

This non-aqueous electrolyte secondary battery was subjected to the following treatment as an initial charge / discharge step. First, after leaving for 2 hours in a high temperature environment of 45 ° C, 0.2C (104
A constant current / constant voltage charge was performed up to 4.2 V for 15 hours. Then, it was left to stand at 20 ° C. for 7 days. Further, in a 20 ° C. environment, the battery was discharged at 0.2 C to 3.0 V to manufacture a non-aqueous electrolyte secondary battery.

(Examples 2 to 16) Thin non-aqueous electrolyte secondary batteries were produced in the same manner as in Example 1 except that the composition of the non-aqueous solvent was changed as shown in Tables 1 and 2 below. .

Comparative Examples 1 to 15 The compositions of the non-aqueous solvent and the lithium salt were changed as shown in Table 3 below, except that
A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 described above.

Obtained Examples 1 to 16 and Comparative Examples 1 to 1
Regarding the secondary battery of No. 5, the battery characteristics were evaluated by the methods described in (1) and (2) below.

1) Swelling of the container at the time of initial charging The above initial charging step, that is, 2 hours in a high temperature environment of 45 ° C.
Leave it alone, and in that environment, 0.2C (104mA) 4.2
After constant current / constant voltage charging to V for 15 hours, 20 ℃
The battery was left for 2 hours in the above environment, and then the battery thickness was measured. The device used to measure the battery thickness is Mit
The model number made by utoyo Corporation is IDF
The weight of the whole cell at the time of measurement was set to 300 grams with the apparatus of -130. The swelling rate (%) was calculated from the following formula (I), and the obtained results are also shown in Tables 1 to 3 below.

Swelling rate (%) = (T ₁ −T ₂ ) / T ₁ × 100 (I) However, in the formula (I), T ₁ represents the battery thickness after the initial charging step, and T ₂ represents the initial value. The battery thickness before a charging process is shown.

2) After 200 cycles under a 45 ° C. environment, the capacity retention rate was 4.2 V constant current / constant voltage charge at a current of 1 C, and then discharged to 3.0 V at a current of 1 C. Charge and discharge cycle is repeated in the environment of 45 ℃, maximum discharge capacity and 2
The capacity retention rate after 00 cycles was measured, and the results are also shown in Tables 1 to 3 below. The capacity retention rate after 200 cycles is a value when the discharge capacity in the first cycle is 100%.

In Tables 1 to 3, EC is ethylene carbonate, GBL is γ-butyrolactone, PC is propylene carbonate, ES is ethylene sulfite, and VC.
Indicates vinylene carbonate, EMC indicates ethyl methyl carbonate, and VEC indicates vinyl ethylene carbonate.

[0161]

[Table 1]

[0162]

[Table 2]

[0163]

[Table 3]

As is clear from Tables 1 to 3, EC, P
The ratio of C, GBL and ES is 15 ≦ x ≦ 50, 30 ≦ y
Liquid non-aqueous electrolyte containing a non-aqueous solvent satisfying ≦ 75, 0 <z <30, 0 <p ≦ 5, or a ratio of EC, PC, GBL, VC and ES of 15 ≦ x ≦ 50, 30 ≦ y ≦ 75 , 0 <z
The secondary batteries of Examples 1 to 16 provided with the liquid non-aqueous electrolyte containing the non-aqueous solvent satisfying <30, 0 <w ≦ 5, 0 <q ≦ 5 had less swelling at the time of initial charging and had a temperature of 45 ° C. It can be seen that the capacity retention rate after 200 cycles at such a high temperature is high.

From the results of Examples 1 to 6, the smaller the proportion of GBL, the higher the capacity retention rate after 200 cycles, whereas the larger the proportion of GBL, the smaller the swelling at the time of initial charging. I understand. Further, when the composition of the non-aqueous solvent is the same, the secondary battery of Example 1 using LiBF ₄ as the electrolyte has more swollenness at the time of initial charge than Example 2 using LiPF ₆ as the electrolyte. Can be made smaller.

On the other hand, the secondary batteries of Comparative Examples 1 to 15 have lower capacity retention rates at 45 ° C. than those of Examples 1 to 16.

Regarding the secondary battery of Example 12, after the initial charge / discharge step, the circuit was opened for 5 hours or more to allow the potential to settle sufficiently, after which the Ar concentration was 99.9% or more and the dew point was The electrode group was taken out by disassembling in a glove box at -50 ° C or lower. The electrode group was packed in a centrifuge tube, dimethylsulfoxide (DMSO) -d ₆ was added, and the tube was sealed, taken out from the glove box, and centrifuged.
Then, in the glove box, a mixed solution of the electrolytic solution and DMSO-d ₆ was collected from the centrifuge tube.
0.5 ml of the mixed solvent in a 5 mmφ sample tube for NMR
A certain amount was put in, and NMR measurement was performed. The apparatus used for the NMR measurement was JNM-LA400WB manufactured by JEOL Ltd., the observation nucleus was ¹ H, the observation frequency was 400 MHz, and the reference substance was dimethyl sulfoxide (DMSO) -d.
An internal standard of ₅ (2.5 ppm) was used. The measurement temperature was 25 ° C. ^{In the 1} HNMR spectrum, a peak corresponding to EC was observed around 4.5 ppm and a peak corresponding to VC was observed around 7.7 ppm, and the peak was observed in the non-aqueous solvent present in the secondary battery of Example 12 after the initial charge / discharge step. It was confirmed that VC was included. Further, the ratio of the NMR integrated intensity of the VC to the NMR integrated intensity of the EC was determined, and it was found that the ratio of VC to the whole non-aqueous solvent was smaller than that before the secondary battery was assembled.

(Example 17) <Preparation of liquid non-aqueous electrolyte> Ethylene carbonate (E
C), γ-butyrolactone (GBL), propylene carbonate (PC) and 12-crown-4 (Crow)
n) was mixed so that the volume ratio (EC: GBL: PC: Crown) was 31: 6: 62: 1 to prepare a non-aqueous solvent. Lithium tetrafluoroborate (LiBF ₄ ) was dissolved in the obtained non-aqueous solvent so as to have a concentration of 1.5 mol / L to prepare a liquid non-aqueous electrolyte.

A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that the liquid non-aqueous electrolyte was used.

(Examples 18 to 32) Thin non-aqueous electrolyte secondary batteries were manufactured in the same manner as in Example 1 except that the composition of the non-aqueous solvent was changed as shown in Tables 4 to 5 below. .

Regarding the obtained secondary batteries of Examples 17 to 32, the maximum discharge capacity, the swelling at the time of initial charging, and the 20% in the environment of 45 ° C. were performed in the same manner as described in Example 1 above.
The capacity retention rate after 0 cycle was measured, and the results are shown in Tables 4 to 5 below. In addition, Crown in Table 4 to Table 5
Indicates 12-crown-4.

[0172]

[Table 4]

[0173]

[Table 5]

As is clear from Tables 4 to 5, EC, P
The ratio of C, GBL and Crown is 15 ≦ x ≦ 50, 3
Liquid non-aqueous electrolyte containing a non-aqueous solvent satisfying 0 ≦ y ≦ 75, 0 <z <30 and 0 <p ≦ 5, EC, PC, GBL, V
The ratio of C and Crown is 15 ≦ x ≦ 50, 30 ≦ y ≦
Examples 17 to 3 provided with a liquid non-aqueous electrolyte containing a non-aqueous solvent satisfying 75, 0 <z <30, 0 <w ≦ 5, 0 <q ≦ 5.
The secondary battery of No. 2 has little swelling at the time of initial charging and is 45 ° C.
It can be seen that the capacity retention rate after 200 cycles at a high temperature as described above is high.

(Example 33) <Preparation of liquid non-aqueous electrolyte> Ethylene carbonate (E
C), γ-butyrolactone (GBL), propylene carbonate (PC) and tetraethylene glycol dimethyl ether (Ether) in volume ratio (EC: GBL:
A non-aqueous solvent was prepared by mixing such that PC: Ether) was 31: 6: 62: 1. Lithium tetrafluoroborate (LiBF ₄ ) was added to the obtained non-aqueous solvent at a concentration of 1.5.
A liquid non-aqueous electrolyte was prepared by dissolving so as to have a mol / L.

A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as described in Example 1 except that the liquid non-aqueous electrolyte was used.

(Examples 34 to 48) Thin non-aqueous electrolyte secondary batteries were manufactured in the same manner as in Example 1 except that the composition of the non-aqueous solvent was changed as shown in Tables 6 to 7 below. .

With respect to the obtained secondary batteries of Examples 34 to 48, the maximum discharge capacity, the swelling at the time of initial charge, and the secondary battery of 20 at 45 ° C. were performed in the same manner as described in Example 1 above.
The capacity retention rate after 0 cycle was measured, and the results are shown in Tables 6 to 7 below. In addition, Ether in Table 6 to Table 7
Represents tetraethylene glycol dimethyl ether.

[0179]

[Table 6]

[0180]

[Table 7]

As is clear from Tables 6 to 7, EC, P
The ratio of C, GBL and Ether is 15 ≦ x ≦ 50, 3
Liquid non-aqueous electrolyte containing a non-aqueous solvent satisfying 0 ≦ y ≦ 75, 0 <z <30 and 0 <p ≦ 5, EC, PC, GBL, V
The ratio of C and Ether is 15 ≦ x ≦ 50, 30 ≦ y ≦
Examples 33 to 4 provided with a liquid non-aqueous electrolyte containing a non-aqueous solvent satisfying 75, 0 <z <30, 0 <w ≦ 5, 0 <q ≦ 5.
The secondary battery of No. 8 has little swelling at the time of initial charging and is at 45 ° C
It can be seen that the capacity retention rate after 200 cycles at a high temperature as described above is high.

(Example 49) <Preparation of non-aqueous electrolyte> Ethylene carbonate (EC), γ-butyrolactone (GB)
L), propylene carbonate (PC) and ethylene sulfite (ES) in a volume ratio (EC: GBL: PC:
ES) was mixed at 31: 6: 62: 1 to prepare a non-aqueous solvent. Lithium tetrafluoroborate (LiBF ₄ ) was dissolved in the obtained non-aqueous solvent so as to have a concentration of 1.5 mol / L to prepare a liquid non-aqueous electrolyte. This liquid non-aqueous electrolyte was mixed with a solution obtained by dissolving polyvinylidene fluoride hexafluoropropylene (PVdF-HEP) in tetrahydroxyfuran (THF) to prepare a paste. A thin film was obtained by applying the obtained paste to a substrate and then drying it.

<Production of Electrode Group> A strip-shaped positive electrode lead was welded to a positive electrode current collector similar to that described in Example 1 above, and a negative electrode collector similar to that described in Example 1 above was welded. After welding a strip-shaped negative electrode lead to the electric body, the positive electrode and the negative electrode were spirally wound with the thin film interposed therebetween, and then flattened to form an electrode group.

This electrode group was immersed in the above-mentioned liquid non-aqueous electrolyte and the thin film was plasticized under reduced pressure to obtain an electrode group in which an electrolyte layer was interposed between the positive electrode and the negative electrode.

A laminate film having a thickness of 100 μm in which both sides of an aluminum foil were covered with polypropylene was formed into a bag, and the electrode group was housed therein, and the thickness was 3.6 mm.
A thin non-aqueous electrolyte secondary battery having a width of 35 mm and a height of 62 mm was assembled.

This non-aqueous electrolyte secondary battery was subjected to the following treatment as an initial charge / discharge step. First, after leaving for 2 h in a high temperature environment of 45 ° C, 0.2 C (84 m
In A), constant current / constant voltage charging was performed up to 4.2 V for 15 hours. Then, it was left to stand at 20 ° C. for 7 days. 2 more
Under a 0 ° C. environment, the battery was discharged at 0.2 C to 3.0 V to manufacture a non-aqueous electrolyte secondary battery.

(Examples 50 to 60) A thin non-aqueous electrolyte was prepared in the same manner as in Example 46, except that the composition of the non-aqueous solvent of the gelled non-aqueous electrolyte was changed as shown in Tables 8 to 9 below. A secondary battery was manufactured.

Comparative Examples 16 to 28 A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 46 described above except that the composition of the non-aqueous solvent and the lithium salt were changed as shown in Table 10 below. did.

Obtained Examples 49 to 60 and Comparative Example 1
The battery characteristics of the secondary batteries 6 to 28 were evaluated by the methods described in (1) and (2) below.

1) Swelling of the container at the time of initial charging The above initial charging step, that is, 2 hours in a high temperature environment of 45 ° C.
Leave it undisturbed and under that environment, 0.2V (84mA) 4.2V
After carrying out constant current / constant voltage charging for 15 hours, leave the battery in an environment of 20 ° C for 2 hours and measure the battery thickness.
The swelling rate (%) was calculated by the formula (I) described above, and the results are also shown in Tables 8 to 9 below. The device used for measuring the battery thickness and the weight applied to the cell during the measurement were the same as those described in Example 1 above.

2) Capacity maintenance factor after 200 cycles in an environment of 45 ° C. 4.2V constant current / constant voltage charge at a current of 1C was performed for 3 hours, and then discharged to 3.0V at a current of 1C. Charge and discharge cycle is repeated in the environment of 45 ℃, maximum discharge capacity and 2
The capacity retention rate after 00 cycles was measured, and the results are also shown in Tables 8 to 9 below. The capacity retention rate after 200 cycles is a value with the discharge capacity in the first cycle as 100%.

[0192]

[Table 8]

[0193]

[Table 9]

[0194]

[Table 10]

As is clear from Tables 8 to 10, EC,
The ratio of PC, GBL and ES is 15 ≦ x ≦ 50, 30 ≦
A gel non-aqueous electrolyte containing a non-aqueous solvent satisfying y ≦ 75, 0 <z <30, 0 <p ≦ 5, EC, PC, GBL, VC
And the ratio of ES is 15 ≦ x ≦ 50, 30 ≦ y ≦ 75, 0
The secondary batteries of Examples 49 to 60 provided with the gelled non-aqueous electrolyte containing the non-aqueous solvent satisfying <z <30, 0 <w ≦ 5, 0 <q ≦ 5 were less swollen at the time of initial charging, and It can be seen that the capacity retention rate after 200 cycles at a high temperature such as 45 ° C. is high.

On the other hand, the secondary batteries of Comparative Examples 16 to 28 all had a capacity retention rate at 45 ° C. of Examples 46 to 60.
It is lower than.

Example 61 <Preparation of Non-Aqueous Electrolyte (Liquid Non-Aqueous Electrolyte)> In a non-aqueous solvent having the same composition as described in Example 1 above, tetrafluoroboric acid was used as the first electrolyte. Lithium (LiBF ₄ ) was dissolved to a concentration of 1.5 mol / L, and
LiN (C ₂ F ₅ SO ₂ ) ₂ was dissolved as the first electrolyte so that its concentration was 0.2 mol / L to prepare a liquid non-aqueous electrolyte.

A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the liquid non-aqueous electrolyte was used.

Example 62 <Preparation of Non-Aqueous Electrolyte (Liquid Non-Aqueous Electrolyte)> In a non-aqueous solvent having the same composition as that described in Example 17, tetrafluoroboric acid was used as the first electrolyte. Lithium (LiBF ₄ ) is dissolved to a concentration of 1.5 mol / L, and LiN (C ₂ F ₅ SO ₂ ) ₂ is used as a first electrolyte to a concentration of 0.2 mol / L. And dissolved to prepare a liquid non-aqueous electrolyte.

A thin nonaqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the liquid nonaqueous electrolyte was used.

Example 63 <Preparation of Non-Aqueous Electrolyte (Liquid Non-Aqueous Electrolyte)> In a non-aqueous solvent having the same composition as described in Example 33, tetrafluoroboric acid was used as the first electrolyte. Lithium (LiBF ₄ ) is dissolved to a concentration of 1.5 mol / L, and LiN (C ₂ F ₅ SO ₂ ) ₂ is used as a first electrolyte to a concentration of 0.2 mol / L. And dissolved to prepare a liquid non-aqueous electrolyte.

A thin non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the liquid non-aqueous electrolyte was used.

With respect to the obtained secondary batteries of Examples 61 to 63, the maximum discharge capacity, the swelling at the time of initial charging, and the 20% in the environment of 45 ° C. were performed in the same manner as described in Example 1 above.
The capacity retention rate after 0 cycle was measured, and the results are shown in Table 11 below. In addition, in Table 11, the above-mentioned Examples 1 and 1
The results of 7, 33 are also shown.

[0204]

[Table 11]

As is clear from Table 11, comparison between Example 61 and Example 1, comparison between Example 62 and Example 17,
Comparing Example 63 and Example 33, it can be seen that when a mixed salt of LiBF ₄ and LiN (C ₂ F ₅ SO ₂ ) is used as the electrolyte, it is 45 compared with the case where only LiBF ₄ is used as the electrolyte. It can be seen that the capacity retention rate after 200 cycles at a high temperature such as ° C can be increased.

(Examples 64 to 66) Thin non-aqueous electrolyte secondary batteries were manufactured in the same manner as in Example 1 except that the composition of the non-aqueous solvent was changed as shown in Table 12 below.

Regarding the obtained secondary batteries of Examples 64 to 66, in the same manner as described in Example 1 above, the maximum discharge capacity, swelling at the time of initial charging, and 20 in an environment of 45 ° C.
The capacity retention rate after 0 cycle was measured, and the results are shown in Table 12 below. In addition, in Table 12, the above-mentioned Examples 1 and 1
The results of 7, 33 are also shown.

[0208]

[Table 12]

As is clear from Table 12, ES, Cro
wn or Ether and ES, Crown and Et
The secondary batteries of Examples 64-66 using the fourth component containing a solvent other than her were ES, Cro as the fourth component.
Examples 1, 17, 3 using only wn or Ether
Compared to the secondary battery of No. 3, 20 at high temperature such as 45 ℃
It can be seen that the capacity retention ratio after 0 cycle is high.

[0210]

As described above in detail, the non-aqueous electrolyte and the non-aqueous electrolyte secondary battery according to the present invention have remarkable effects such as improvement of charge / discharge cycle life at high temperature.

[Brief description of drawings]

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

FIG. 2 is an enlarged cross-sectional view showing a portion A of FIG.

[Explanation of symbols]

1 ... container, 2 ... Electrode group, 3 ... separator, 4 ... Positive electrode layer, 5 ... Positive electrode current collector, 6 ... Positive electrode, 7 ... Negative electrode layer, 8 ... Negative electrode current collector, 9 ... Negative electrode, 10 ... Positive electrode terminal, 11 ... Negative electrode terminal.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shun Kadoma             8th Shinsugita Town, Isogo Ward, Yokohama City, Kanagawa Prefecture             Ceremony company Toshiba Yokohama office (72) Inventor Masayuki Oguchi             1st Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa             Inside the Toshiba Research and Development Center F term (reference) 5H029 AJ05 AK03 AK05 AL06 AL07                       AL08 AM03 AM05 DJ09 HJ01                       HJ07

Claims (7)

[Claims] 1. A non-aqueous electrolyte comprising a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent, wherein the non-aqueous solvent is ethylene carbonate (EC), propylene carbonate (PC), and γ. -Butyrolactone (GBL) and a fourth component which is a solvent other than the EC, the PC and the GBL, and a ratio of ethylene carbonate, propylene carbonate, γ-butyrolactone and the fourth component to the total volume of the non-aqueous solvent. X (volume%), y (volume%),
When z (volume%) and p (volume%) are taken, the x, y, z and p are 15 ≦ x ≦ 50, 30 respectively.
A nonaqueous electrolyte characterized by satisfying ≦ y ≦ 75, 0 <z <30, 0 <p ≦ 5. 2. A non-aqueous electrolyte comprising a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent, wherein the non-aqueous solvent is ethylene carbonate (EC), propylene carbonate (PC), and γ. -Butyrolactone (GBL), vinylene carbonate (VC), and a fifth component that is a solvent other than the EC, the PC, the GBL, and the VC, ethylene carbonate, propylene carbonate with respect to the total volume of the non-aqueous solvent, The proportions of γ-butyrolactone, vinylene carbonate and the fifth component are respectively x (volume%), y (volume%), z (volume%), w (volume%),
When q (volume%), x, y, z, w and q are 15 ≦ x ≦ 50 and 30 ≦ y ≦ 7, respectively.
A non-aqueous electrolyte characterized by satisfying 5, 0 <z <30, 0 <w ≦ 5, 0 <q ≦ 5. 3. A non-aqueous electrolyte secondary battery comprising a container, an electrode group housed in the container, and a non-aqueous electrolyte containing a non-aqueous solvent and held by the electrode group. The solvent includes ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and a fourth component that is a solvent other than the EC, the PC, and the GBL, and the entire non-aqueous solvent. The ratio of ethylene carbonate, propylene carbonate, γ-butyrolactone and the fourth component to the product is x (volume%), y (volume%),
When z (volume%) and p (volume%) are taken, the x, y, z and p are 15 ≦ x ≦ 50, 30 respectively.
A non-aqueous electrolyte secondary battery characterized by satisfying ≦ y ≦ 75, 0 <z <30, 0 <p ≦ 5. 4. The fourth component according to claim 3, wherein the fourth component contains at least one solvent selected from the group consisting of ethylene sulfite, 12-crown-4 and tetraethylene glycol dimethyl ether. Non-aqueous electrolyte secondary battery. 5. A non-aqueous electrolyte secondary battery comprising a container, an electrode group housed in the container, and a non-aqueous electrolyte containing a non-aqueous solvent and held by the electrode group. The solvent is a solvent other than ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), vinylene carbonate (VC), the EC, the PC, the GBL and the VC. And a ratio of ethylene carbonate, propylene carbonate, γ-butyrolactone, vinylene carbonate and the fifth component to the total volume of the non-aqueous solvent, x (volume%), y (volume%), z (volume%), respectively. , W (% by volume),
When q (volume%), x, y, z, w and q are 15 ≦ x ≦ 50 and 30 ≦ y ≦ 7, respectively.
A non-aqueous electrolyte secondary battery satisfying 5, 0 <z <30, 0 <w ≦ 5, 0 <q ≦ 5. 6. The fifth component according to claim 5, wherein the fifth component contains at least one solvent selected from the group consisting of ethylene sulfite, 12-crown-4 and tetraethylene glycol dimethyl ether. Non-aqueous electrolyte secondary battery. 7. The non-aqueous electrolyte secondary battery according to claim 3, wherein the non-aqueous electrolyte has a substantially liquid or gel form.