JP2000285965A - Nonaqueous electrolyte secondary battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery and its manufacturing method capable of increasing mechanical strength of an electrode group and suppressing bulging of a battery, deformation or short circuit by mechanical shock without changing the shape and decreasing battery characteristics in a thin battery. SOLUTION: This nonaqueous electrolyte secondary battery has an electrode group 2 having a positive electrode, a negative electrode, and a separator placed between the positive electrode and the negative electrode and nonaqueous electrolyte, holds an adhesive polymer in at least voids in the positive electrode, the negative electrode, and the separator, and integrates them by adhesion. The adhesive polymer in the outermost periphery has higher density or larger molecular weight than that on the inside.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art At present, a thin lithium ion secondary battery has been commercialized as a nonaqueous electrolyte secondary battery for portable equipment such as a mobile phone. 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 an electrolytic solution, and a porous film for a separator.

[0003] With the reduction in thickness and weight of portable devices, there is a demand for reduction in thickness and weight of batteries themselves. Therefore, in a thin battery, not only a can but also a laminate film including a thin metal layer is used as an exterior material. In the case of using the laminate film packaging material, problems such as battery swelling occur. As means for solving such problems and reducing the thickness of the battery, claims in Japanese Patent Application Laid-Open No. 10-177865 disclose a positive electrode, a negative electrode, a separator having an opposing surface holding an electrolytic solution, and an electrolytic solution. A lithium ion secondary battery comprising a liquid phase, a mixed phase of a polymer gel phase and a polymer phase containing an electrolytic solution, and comprising an adhesive resin layer for joining the positive electrode and the negative electrode to the opposite surface of the separator is described. ing. In addition, the claims of JP-A-10-198054 include a step of forming each electrode formed on the positive electrode and the negative electrode current collector, and a step of forming a binder resin solution obtained by dissolving polyvinylidene fluoride as a main component in a solvent. A method for producing a lithium ion secondary battery comprising a step of applying to a separator, a step of superposing the above-mentioned electrodes on the separator, and a step of impregnating the battery laminate with an electrolyte with drying and evaporating the solvent while keeping the electrodes in contact with each other is described. Have been.

Since the adhesive is porous, it has a considerable amount of voids, and together with the separator, the electrolyte held in the voids enables charging and discharging of the nonaqueous electrolyte secondary battery. . Therefore, in order to maintain battery characteristics, it is necessary to reduce the density per unit area of the adhesive inside the electrode group as much as possible.

[0005] However, there is a problem in that the mechanical strength of the electrode group cannot be obtained to secure sufficient safety with the amount of the adhesive capable of obtaining sufficient battery characteristics.

Further, when the density per unit area of the adhesive is increased in order to improve the mechanical strength of the electrode group, the amount of electrolyte held in the voids decreases, and the charge / discharge characteristics are significantly reduced. Occurs.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to minimize the change in the battery shape by effectively utilizing the gap of the adhesive layer on the outermost periphery of the electrode group which is not involved in charging / discharging inside the battery. By increasing the rigidity of the non-aqueous electrolyte battery electrode without deteriorating the battery characteristics, it is possible to prevent internal short circuit due to deformation or deformation of the battery when dropped, and to suppress swelling of the battery during high temperature storage. And a method for producing the non-aqueous electrolyte secondary battery.

[0008]

According to the present invention, there is provided an electrode group including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. In the gap between the negative electrode and the separator, a polymer having adhesiveness is held, respectively, and the positive electrode, the negative electrode, and the separator are bonded and integrated to form a non-aqueous electrolyte secondary battery, The outermost periphery of the electrode group is a non-aqueous electrolyte secondary battery in which a polymer having an adhesive property at a higher density than the inside of the electrode group exists.

The present invention also provides an electrode group including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein at least the positive electrode,
In the nonaqueous electrolyte secondary battery, a polymer having adhesiveness is held in the gap between the negative electrode and the separator, and the positive electrode, the negative electrode, and the separator are bonded and integrated. The non-aqueous electrolyte secondary battery is characterized in that the outermost periphery of the electrode group contains an adhesive polymer having a molecular weight larger than that of the inside of the electrode group.

The present invention also provides a process for preparing an electrode group by interposing a separator between a positive electrode and a negative electrode, a process for impregnating the electrode group with a solution in which an adhesive polymer is dissolved, Applying a solution in which a polymer having a higher concentration than the adhesive-containing solution is dissolved to the outermost periphery of the electrode group, and / or applying the solution inside the battery exterior member, and vacuum-drying the electrode group And a step of impregnating the electrode group with a non-aqueous electrolyte.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a non-aqueous electrolyte secondary battery (for example, a thin lithium ion secondary battery) according to the present invention will be described.
This will be described in detail with reference to FIG. 1, FIG. 2, FIG. 4, and FIG.

FIG. 1 is a sectional view showing a non-aqueous electrolyte secondary battery (for example, a thin lithium ion secondary battery) according to the present invention, FIG. 2 is an enlarged view showing part A of FIG. 1, and FIG. FIG. 3 is a schematic view showing the vicinity of a boundary between a separator and a negative electrode layer.

FIG. 4 is a perspective view showing a non-aqueous electrolyte secondary battery having a structure in which a positive electrode, a negative electrode and a separator are wound.

FIG. 5 is a perspective view showing a non-aqueous electrolyte secondary battery having a structure in which a positive electrode, a negative electrode and a separator are wound or bent.

As shown in FIG. 1, an exterior material 1 made of, for example, a laminate film surrounds an electrode group 2. 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, a positive electrode layer 4, a positive electrode current collector 5, a positive electrode layer 4, a separator 3, a negative electrode layer 6, and a negative electrode current collector.
7, a negative electrode layer 6, a separator 3, a positive electrode layer 4, a positive electrode current collector 5, a positive electrode layer 4, a separator 3, a negative electrode layer 6, and a negative electrode current collector 7 are laminated in this order. In the electrode group 2, the negative electrode current collector 7 is located in the outermost layer. However, the outermost layer of the electrode group 2 may be any of a positive electrode, a negative electrode and a separator. The outermost peripheral portion 8 exists on the surface of the electrode group 2. As shown in FIG. 3, the positive electrode layer
4. In the gap between the separator 3 and the negative electrode layer 6, a polymer 9 having an adhesive property is held. Thereby, the electrode group is integrated and fixed. It is desirable that a polymer having the same component adhesiveness is used for the positive electrode layer, the separator, and the negative electrode layer. Thereby, the electrode group can be more firmly integrated. The non-aqueous electrolyte is
Has been extended from one. On the other hand, the strip-shaped negative electrode lead 11
One end is connected to the negative electrode current collector 7 of the electrode group 2, and the other end is extended from the exterior material 1.

The non-aqueous electrolyte secondary battery of the present invention is shown in FIG.
As shown in FIG. 3, a pair of a positive electrode 41, a negative electrode 43, and a separator 42
May have an electrode group formed by winding the laminate. Also, as shown in FIG. 5, one set of the positive electrode 51 and the negative electrode
A stacked body of the separator 53 and the separator 52 may have an electrode group formed by bending. As a result, the production of the electrode group is facilitated, and an electrode group having high mechanical strength is obtained. The area of the negative electrode 43 is preferably larger than the area of the positive electrode 41. With such a configuration, the negative electrode end extends from the positive electrode end, but current concentration on the negative electrode end is suppressed, and cycle performance and safety are improved.
Further, it is preferable that the short side of the separator extends from the short side of the strip electrode of the negative electrode by 0.25 mm to 2 mm, respectively, and the polymer having adhesiveness according to the present invention is present in the extended separator portion. As a result, the strength of the extending portion of the separator is increased, and short-circuit between the positive electrode and the negative electrode hardly occurs even when an impact is applied to the battery. Further, even when the battery is under a high temperature condition (100 ° C. or higher), the separator does not easily shrink, so that the short circuit between the positive electrode and the negative electrode can be prevented, and the safety is improved.

Next, the positive electrode, the negative electrode, the separator 3, the outermost peripheral portion 8, the adhesive polymer 9, the non-aqueous electrolyte, and the package 1 will be described in detail.

1) Positive Electrode This positive electrode has a structure in which a positive electrode layer 4 containing an active material is supported on one or both sides of a current collector 5. The positive electrode holds the polymer 9 having adhesiveness in the void. The positive electrode layer,
It contains a positive electrode active material and a conductive agent. In addition, the positive electrode layer may contain a binder that binds the positive electrode active material, in addition to the polymer 9 having an adhesive property.

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. . Above all, when a lithium-containing cobalt oxide (eg, LiCoO ₂ ), a lithium-containing nickel-cobalt oxide (eg, LiNi _0.8 Co _0.2 O ₂ ), or a lithium manganese composite oxide (eg, LiMn ₂ O ₄ , LiMnO ₂ ) is used, a high voltage is obtained. Is preferred because

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

Examples of the binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVd).
F), ethylene-propylene-diene copolymer (EPD
M), styrene-butadiene rubber (SBR) and 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 and 3 to 20% by weight of the conductive agent.
%, And a binder within a range of 2 to 7% by weight.

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.

Among them, it is preferable to use a conductive substrate having a two-dimensional porous structure in which holes having a diameter of 3 mm or less exist at a rate of 1 or more per 10 cm ² . That is, if the diameter of the hole formed in the conductive substrate is larger than 3 mm, sufficient positive electrode strength may not be obtained. Meanwhile, the diameter
If the proportion of holes having a diameter of 3 mm or less is less than the above range, it becomes difficult to uniformly infiltrate the non-aqueous electrolyte into the electrode group, and thus a sufficient cycle life may not be obtained. 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 aforementioned conductive substrate having a two-dimensional porous structure in which one or more holes having a diameter of 3 mm or less exist at a rate of one or more per 10 cm ² preferably has a thickness in a range of 15 to 100 μm. If the thickness is less than 15 μm, sufficient positive electrode strength may not be obtained. On the other hand, when the thickness exceeds 100 μm, the weight of the battery and the thickness of the electrode group increase, and it may be difficult to sufficiently increase the weight energy density and the volume energy density of the thin secondary battery. A more preferable range of the thickness is 30 to 80 μm.

It is desirable that the polymer having adhesiveness can maintain high adhesiveness while holding the non-aqueous electrolyte. Further, such a polymer is more preferably high in lithium ion conductivity. Specifically, polyacrylonitrile (PAN), polyacrylolate (PMMA), polyvinylidene fluoride (PVdF), polyvinyl chloride (PV
C) or polyethylene oxide (PEO). Particularly, polyvinylidene fluoride is preferable. Polyvinylidene fluoride can hold a non-aqueous electrolyte, and if it contains a non-aqueous electrolyte, it partially gels, so that the ion conductivity in the positive electrode can be further improved.

It is preferable that the adhesive polymer exists in a porous structure in the space of the positive electrode. The adhesive polymer having a porous structure can hold a non-aqueous electrolyte.

2) Negative Electrode The negative electrode has a structure in which a negative electrode layer 6 is supported on one side or both sides of a current collector 7. The negative electrode carries a polymer having adhesiveness in the gap.

[0029] The negative electrode layer contains carbonaceous material that stores and releases lithium ions. Further, the negative electrode layer may include a binder for binding the negative electrode material, in addition to the polymer 9 having adhesiveness.

Examples of the carbonaceous material include graphite, coke,
For graphitic or carbonaceous materials such as carbon fiber and spherical carbon, thermosetting resin, isotropic pitch, mesophase pitch, mesophase pitch-based carbon fiber, mesophase pitch sphere, etc. (especially, mesophase pitch-based carbon fiber is preferable) Graphite materials or carbonaceous materials obtained by performing a heat treatment at 500 to 3000 ° C. can be mentioned.
Above all, it is obtained by setting the temperature of the heat treatment at 2000 ° C. or higher, and the plane distance d ₀₀₂ of the (002) plane is 0.340 nm or less.
It is preferable to use a graphitic material having graphite crystals. A non-aqueous electrolyte secondary battery including a negative electrode containing such a graphite material as a carbonaceous material can significantly improve battery capacity and large current characteristics. The surface distance d ₀₀₂ is 0.336n
More preferably, it is not more than m.

Examples of the binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVd).
F), ethylene-propylene-diene copolymer (EPD
M), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC) and the like can be used. The mixing ratio of the carbonaceous material and the binder is 90 to 98 for the carbonaceous material.
% By weight and 2 to 20% by weight of the binder. In particular, the carbonaceous material is 5 to 20 g in a state where the negative electrode is manufactured.
/ m ² is preferable.

As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used. These conductive substrates are, for example, copper, stainless steel,
Or it can be formed from nickel.

Above all, it is preferable to use a conductive substrate having a two-dimensional porous structure in which the following holes are present at a rate of one or more per 10 cm ² . That is, if the diameter of the hole in the conductive substrate is larger than 3 mm, sufficient negative electrode strength may not be obtained. On the other hand, when the proportion of holes having a diameter of 3 mm or less is smaller than the above range, it becomes difficult to uniformly infiltrate the non-aqueous electrolyte into the electrode group, and thus a sufficient cycle life may not be obtained. The diameter of the hole is
More preferably, it 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 conductive substrate having a two-dimensional porous structure in which one or more holes having a diameter of 3 mm or less exist at a rate of one or more per 10 cm ² preferably has a thickness in the range of 10 to 50 μm. If the thickness is less than 10 μm, sufficient negative electrode strength may not be obtained. On the other hand, when the thickness exceeds 50 μm, the weight of the battery and the thickness of the electrode group increase, and it may be difficult to sufficiently increase the weight energy density and the volume energy density of the thin secondary battery.

It is desirable that the polymer having adhesiveness can maintain high adhesiveness while holding the non-aqueous electrolyte. Further, such a polymer is more preferably high in lithium ion conductivity. Specifically, those similar to those described for the positive electrode described above can be mentioned.
In particular, PVdF is preferred.

It is preferable that the adhesive polymer exists in the form of a porous structure in the space of the negative electrode. The adhesive polymer having a porous structure can hold a non-aqueous electrolyte. As the negative electrode, in addition to those containing a carbonaceous substance that occludes and releases lithium ions, those containing a metal oxide, a metal sulfide, or a metal nitride, and those made of lithium metal or a lithium alloy are used. be able to.

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

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

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

3) Separator This separator is formed of a porous sheet in which an adhesive polymer is held in the voids.

As the porous sheet, for example, a porous film containing polyethylene, polypropylene or PVdF, a synthetic resin nonwoven fabric, or the like can be used. Among them, a porous film made of polyethylene, polypropylene, or both is preferable because the safety of the secondary battery can be improved.

It is desirable that the polymer having adhesiveness can maintain high adhesiveness while holding the non-aqueous electrolyte. Further, such a polymer preferably has a high lithium ion conductivity. Specifically, those similar to those described for the positive electrode described above can be mentioned. In particular, PVdF is preferred.

It is preferable that the adhesive polymer exists in the form of a porous structure in the voids of the separator. The adhesive polymer having a porous structure can hold a non-aqueous electrolyte.

The thickness of the porous sheet is preferably 30 μm or less. If the thickness exceeds 30 μm, the distance between the positive electrode and the negative electrode increases, and the internal resistance may increase. The lower limit of the thickness is preferably set to 5 μm. When the thickness is less than 5 μm, the strength of the separator is significantly reduced, and an internal short circuit may easily occur.
The upper limit of the thickness is more preferably 25 μm, and the lower limit is more preferably 10 μm.

The porous sheet preferably has a heat shrinkage of not more than 20% at 120 ° C. for one hour. The heat shrinkage is 2
If it exceeds 0%, it may be difficult to increase the adhesive strength between the positive and negative electrodes and the separator. More preferably, the heat shrinkage is 15% or less.

The porous sheet preferably has a porosity in the range of 30 to 60%. This is due to the following reasons. If the porosity is less than 30%, it may be difficult to obtain high electrolyte retention in the separator. A more preferred range of porosity is 35-50%.

The porous sheet has an air permeability of 600 seconds /
It is preferably 100 cm ³ or less. Air permeability is 600 seconds /
If it exceeds 100 cm ³ , it may be difficult to obtain high lithium ion mobility in the separator. Also,
The lower limit of the air permeability is preferably set to 100 seconds / 100 cm ³ . If the air permeability is less than 100 seconds / 100 cm ³ , sufficient separator strength may not be obtained. The upper limit of the air permeability is more preferably 500 seconds / 100 cm ³ , and the lower limit is more preferably 150 seconds / 100 cm ³ .

4) Non-aqueous electrolyte The non-aqueous electrolyte is a liquid electrolyte prepared by dissolving an electrolyte in a non-aqueous solvent.

As the non-aqueous solvent, a known non-aqueous solvent as a solvent for a lithium secondary battery can be used, and although not particularly limited, propylene carbonate (PC)
Non-aqueous solvent mainly composed of a mixed solvent of ethylene or ethylene carbonate (EC) and one or more non-aqueous solvents having a lower viscosity than that of the PC or EC and having a donor number of 18 or less (hereinafter abbreviated as a second solvent) It is preferable to use

As the second type of solvent, for example, a chain carbonate is preferable. Among them, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), ethyl propionate, methyl propionate, γ-butyrolactone are preferable. (Γ-BL), acetonitrile (AN), ethyl acetate (EA), toluene, xylene or methyl acetate (MA). These second solvents can be used alone or in the form of a mixture of two or more. In particular, the second solvent has a donor number of 1
More preferably, it is 6.5 or less. The viscosity of the second solvent is preferably 28 mp or less at 25 ° C.
The amount of the ethylene carbonate or propylene carbonate in the mixed solvent is preferably 10 to 80% by volume. More preferably, the blending amount of the ethylene carbonate or propylene carbonate is 20 to 75% by volume.

The more preferable composition of the mixed solvent is EC and
MEC, EC and PC and MEC, EC and MEC and DEC, EC and MEC and DMC, EC and
In a mixed solvent of MEC, PC and DEC, the volume ratio of MEC is preferably 30 to 80%. A more preferred MEC volume ratio is 4
It is in the range of 0-70%.

Examples of the electrolyte contained in the non-aqueous electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), and the like.
Lithium salts (electrolytes) such as lithium arsenic hexafluoride (LiAsF ₆ ), lithium trifluorometasulfonate (LiCF ₃ SO ₃ ), and lithium bistrifluoromethylsulfonylimide [LiN (CF ₃ SO ₂ ) ₂ ]. Among them, LiPF ₆ and LiBF ₄
It is preferable to use

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

The amount of the non-aqueous electrolyte was 100 m
It is preferably 0.2 to 0.6 g per Ah. This is due to the following reasons. 0.2 g / 100 non-aqueous electrolyte
If it is less than mAh, the ionic conductivity between 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 become so large that it may be difficult to seal with the film-shaped exterior material.
A more preferable range of the amount of the nonaqueous electrolyte is 0.4 to 0.55 g / 100 mA.
h.

5) Outermost portion 8 This outermost portion 8 exists on the surface of the electrode group 2 and can be mainly formed of a polymer having adhesiveness. Further, the polymer having adhesiveness at the outermost periphery has a higher areal density or a larger molecular weight than the polymer having adhesiveness inside the electrode group. As a result, deformation of the battery due to gas generation can be reduced, and furthermore, deformation and short circuit due to mechanical collision caused by dropping or the like can be suppressed.

Further, it is preferable that the outermost peripheral portion is bonded to the exterior material. This is due to the following reasons. When the outermost peripheral portion is bonded and integrated with the exterior material, the electrode group does not move inside the battery, so that deformation and short circuit due to mechanical collision caused by dropping or the like can be further suppressed. .

It is desirable that the polymer having adhesiveness at the outermost periphery is hardly dissolved in the non-aqueous electrolyte and has high mechanical strength.

It is desirable that the polymer having adhesiveness can maintain high adhesiveness while holding the non-aqueous electrolyte. Further, such a polymer preferably has a high lithium ion conductivity. Specifically, those similar to those described above for the positive electrode can be mentioned.
Particularly, PVdF is preferable.

The outermost peripheral portion may have a porous structure. The porous outermost peripheral portion can hold the non-aqueous electrolyte in the void.

The total amount of the adhesive polymer contained in the battery is preferably 0.2 to 6 mg per 100 mAh of battery capacity. This is due to the following reasons. If the total amount of the polymer having adhesiveness is less than 0.2 mg per 100 mAh of battery capacity, it may be difficult to improve the adhesion between the positive electrode, the separator, and the negative electrode and the mechanical strength of the electrode group. On the other hand, if the total amount exceeds 6 mg per 100 mAh of battery capacity, the lithium ion conductivity of the secondary battery may decrease, or the internal resistance may increase, and the discharge capacity, large current characteristics, and charge / discharge cycle life are greatly reduced. Might be.
A more preferred range of the total amount of the polymer having adhesiveness is 0.5 to 3 mg per 100 mAh of battery capacity.

6) Exterior Material 1 As the exterior material 1, for example, a thin film made of a flexible synthetic resin or metal can be used. In particular, in the case of a non-aqueous electrolyte battery, a multilayer film in which a barrier layer such as aluminum is inserted into a layer made of a synthetic resin is preferable. It is preferable to include an aluminum layer, particularly in the case of a non-aqueous electrolyte battery, since it is possible to prevent water from being mixed into the electrolyte and to extend the battery life.

It is preferable that the thickness of the exterior material is in the range of 50 to 300 μm. If it is too thin, it tends to be deformed or damaged, and if it is too thick, the effect of thinning is reduced. Hereinafter, a method for manufacturing the nonaqueous electrolyte secondary battery according to the present invention will be described.

(First Step) An electrode group is formed by interposing a porous sheet as a separator between a positive electrode and a negative electrode.
The positive electrode is produced, for example, by suspending a conductive agent and a binder in a suitable solvent in a positive electrode active material, applying the suspension to a current collector, and drying to form a thin plate. Examples of the positive electrode active material, the conductive agent, the binder, and the current collector include the same ones as described in the above section (1) Positive electrode.

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

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

As the porous sheet of the separator,
Examples similar to those described in the section of (3) Separator described above can be given.

(Second Step) A solution obtained by dissolving an adhesive polymer in a solvent is injected into the electrode group, and the solution is impregnated into the electrode group.

Examples of the polymer having adhesiveness include those similar to those described in the section of the positive electrode in (1) above. In particular, PVdF is preferred.

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

The concentration of the adhesive polymer in the solvent is 0.1
Preferably, it is in the range of ~ 2.5% by weight. This is due to the following reasons. If the concentration is less than 0.1% by weight, it may be difficult to bond the positive and negative electrodes and the separator with sufficient strength. On the other hand, if the concentration exceeds 2.5% by weight, it is difficult to obtain sufficient porosity to hold the non-aqueous electrolyte, and the sea surface impedance of the electrode may be significantly increased. When the interface impedance increases, the capacity and the large-current discharge characteristics are significantly reduced. A more preferred range of the concentration is from 0.5 to 1.5% by weight.

When the concentration of the adhesive polymer in the solution was 0.1 to 2.5% by weight, the battery capacity was 100 mA.
It is preferred to be in the range of 0.2 ml to 2 ml per h. This is due to the following reasons. The injection amount is 0.2m
If it is less than l, it may be difficult to sufficiently enhance the adhesion between the positive electrode, the negative electrode and the separator. On the other hand, if the injection amount is more than 2 ml, the lithium ion conductivity of the secondary battery may be reduced, or the internal resistance may be increased, and the discharge capacity, large current discharge characteristics and charge / discharge cycle life may be improved. It can be difficult. A more preferable range of the injection amount is 0.3 ml to 1 ml per 100 mAh of battery capacity.

(Third Step) While the electrode group is pressed to a predetermined thickness and dried under normal pressure or under reduced pressure including vacuum, the solvent in the solution is evaporated to form the positive electrode, the negative electrode and the separator. The adhesive polymer is held in the gap, and the electrode group is molded, integrated and fixed. Further, by this drying, the water contained in the electrode group can be removed at the same time.

Note that the porous outermost peripheral portion is allowed to contain a small amount of solvent.

The drying is preferably performed at 100 ° C. or lower. This is due to the following reasons. When the drying temperature exceeds 100 ° C., the separator may be significantly shrunk by heat. When the heat shrinkage becomes large, the separator warps, and it becomes difficult to firmly bond the positive electrode, the negative electrode, and the separator. Further, the above-mentioned heat shrinkage tends to occur remarkably when a porous film containing polyethylene or polypropylene is used as a separator. Although the heat shrinkage of the separator can be suppressed as the drying temperature decreases, if the drying temperature is less than 40 ° C., it may be difficult to sufficiently evaporate the solvent. For this reason, the drying temperature is more preferably set to 40 to 100 ° C. Also,
Drying is desirably performed under reduced pressure including vacuum.

(Fourth Step) A solution obtained by dissolving a polymer having an adhesive property in a solvent at a higher concentration than the solution used in (Second Step) is used for the outermost periphery of the electrode group and / or the exterior material. Apply to inner surface. Examples of the exterior material include those similar to those described in the section of (6) Exterior material described above.

It is desirable that the polymer having the adhesive property is hardly dissolved in the non-aqueous electrolyte and has high mechanical strength.

Further, as the polymer having the adhesive property,
Examples similar to those described in the section of the positive electrode in (1) above can be given. Particularly, PVdF is preferable.

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

The concentration of the adhesive polymer in the solution is preferably 0.2% by weight or more. A more preferred range is from 2.5 to 15% by weight. This is due to the following reasons.
If the concentration is less than 2.5%, the viscosity of the solution is too low, and there is a possibility that an adhesive amount for obtaining sufficient strength may not be applied. On the other hand, if the concentration exceeds 15%, the adhesive may not be completely dissolved in the solvent, or the viscosity of the solution may be too high to apply a necessary minimum amount of adhesive. A more preferred range of the concentration is between 5 and 12% by weight.

[0080] wherein the amount of adhesive per unit area of the outermost periphery of the electrode group of the adhesive ^{3.2 × 10 - 6 g / cm} 2 or more. A more preferred range is 4 × 10 ^{−5 to} 2.4 × 10 ⁻⁴ g / cm ₂ . This is due to the following reasons. When the amount of the adhesive per unit area of the outermost periphery is less than 4 × 10 ⁻⁵ g / cm ₂ , deformation or short circuit due to battery swelling or drop impact may not be sufficiently suppressed. On the other hand, if it exceeds 2.4 × 10 ⁻⁴ g / cm ₂ , it may be difficult to apply the coating sufficiently thin so as not to change the battery thickness. A more preferred range is 8 × 10
^{-5 to} 2 × 10 ^-4 g / cm ₂ .

(Fifth Step) The electrode group is housed in the package, and dried under normal pressure or reduced pressure including vacuum while press-molding to a predetermined thickness to evaporate the solvent in the solution. The electrode group and the exterior material are formed and fixed. Further, by this drying, the water contained in the electrode group and the exterior material can be removed at the same time.

The porous outermost peripheral portion is allowed to contain a small amount of solvent.

The drying is preferably performed at 100 ° C. or lower. This is due to the following reasons. When the drying temperature exceeds 100 ° C., the separator may be significantly shrunk by heat. When the heat shrinkage becomes large, the separator warps, and it becomes difficult to firmly bond the positive electrode, the negative electrode, and the separator. Further, the above-mentioned heat shrinkage tends to occur remarkably when a porous film containing polyethylene or polypropylene is used as a separator. Although the heat shrinkage of the separator can be suppressed as the drying temperature decreases, if the drying temperature is less than 40 ° C., it may be difficult to sufficiently evaporate the solvent. For this reason, the drying temperature is more preferably set to 40 to 100 ° C. Further, drying is desirably performed under reduced pressure including vacuum.

(Sixth step) After a non-aqueous electrolyte is injected into the electrode group in the package, a thin non-aqueous electrolyte secondary battery is manufactured by sealing the opening of the package.

As the non-aqueous electrolyte, the same one as described above can be used.

The manufacturing method according to the present invention is the same as that shown in FIGS.
Alternatively, a thin non-aqueous electrolyte secondary battery having the structure shown in FIGS. 3 and 4 can be manufactured.

According to the non-aqueous electrolyte secondary battery according to the present invention described above, the adhesive is densely applied to the outermost periphery of the electrode group without increasing the amount of the adhesive inside the electrode more than necessary. Can be present. Therefore, it is possible to provide a nonaqueous electrolyte secondary battery including an electrode group having excellent mechanical strength while suppressing the internal resistance caused by the adhesive polymer.

Further, according to the non-aqueous electrolyte secondary battery according to the present invention, it is possible to change the type of the adhesive inside the electrode group and the type of the adhesive at the outermost periphery of the electrode group. An adhesive polymer having a higher molecular weight than the inside of the electrode group can be present. Therefore, it is possible to provide a nonaqueous electrolyte secondary battery including an electrode group having excellent mechanical strength while suppressing the internal resistance caused by the adhesive polymer.

[0089]

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; however, X is 0 ≦ X ≦ 1) powder 91 wt% of acetylene black 3.5 wt%, were mixed together by adding graphite 3.5% by weight and ethylene propylene diene monomer powder 2 wt% of toluene, 10 cm ² per After applying a current collector made of porous aluminum foil (thickness: 15 μm) having holes of 0.5 mm in diameter at a ratio of 10 to both sides, the electrode having an electrode density of 3 g / cm ³ was pressed by pressing. Were produced.

<Preparation of Negative Electrode> Mesophase pitch-based carbon fiber heat-treated at 3000 ° C. as a carbonaceous material (having a fiber diameter of 8
μm, average fiber length is 20 μm, average spacing (d ₀₀₂ ) is 0.3360
nm of the powder was mixed with 93 wt% of polyvinylidene fluoride (PVdF) 7 wt% as a binder, 10 cm ² per 10 this
Each electrode is coated on a current collector made of a porous copper foil (thickness: 15 μm) having holes with a diameter of 0.5 mm, dried, and pressed to obtain an electrode having an electrode density of 1.3 g / cm ^3. Were produced.

<Separator> The thickness is 25 μm,
Two separators made of a polyethylene porous film having a heat shrinkage over time of 20% and a porosity of 50% were prepared. Each side of the separator is 2 mm from each side of the positive and negative electrodes.
1.5mm long, 1mm and 0.75mm from both ends of positive and negative electrodes respectively
Is extended.

<Production of Flat Electrode Coil> The positive electrode, the separator, and the negative electrode were stacked, spirally wound as an electrode group, and then formed into a flat shape to produce a coil.

<Preparation of Nonaqueous Electrolyte> Lithium tetrafluoroborate (LiBF4) was mixed with a mixed solvent of ethylene carbonate (EC) and γ-butyrolactone (BL) (mixing volume ratio 25:75).
1.5 mol / l was dissolved to prepare a non-aqueous electrolyte.

<Adhesion of Electrode Group> 0.3% by weight of polyvinylidene fluoride (PVdF), a polymer having adhesive properties, was dissolved in dimethylformamide (DMF) (boiling point: 153 ° C.) as an organic solvent. The obtained solution is injected into the electrode group so as to be 0.18 ml per 100 mAh of battery capacity, and the solution is permeated into the electrode group. Thereafter, both surfaces of the electrode group were sandwiched by a holder so that the thickness of the electrode could be fixed at 2.8 mm.

Next, the electrode group was vacuum dried at 80 ° C. for 12 hours.
By applying for a while, the organic solvent was evaporated, and the adhesive polymer was held in the gaps between the positive electrode, the negative electrode and the separator.

<Attachment of Exterior Material to Electrode Group> Polyvinylidene fluoride (PVdF), which is an adhesive polymer, was converted to dimethylformamide (DMF), an organic solvent, having a boiling point of 153.
6 ° C.). The obtained solution was applied to the outer periphery of the electrode group so as to be 0.01 ml per 100 mAh of battery capacity. Thereafter, a laminate film having a thickness of 100 μm in which both surfaces of the aluminum foil were covered with polypropylene was formed into a bag shape, and the electrode group was housed in the bag, and both surfaces of the battery were sandwiched by holders so that the battery thickness could be fixed at 3 mm.

Next, the electrode group was vacuum dried at 80 ° C. for 12 hours.
After the application, the organic solvent was evaporated, and the adhesive polymer was held in the gaps between the positive electrode, the negative electrode and the separator near the outermost periphery.

2 g of the non-aqueous electrolyte was injected into the electrode group in the laminate film, and the thin non-aqueous electrolyte having the structure shown in FIGS. 1 and 2 having a thickness of 3 mm, a width of 40 mm and a height of 70 mm was obtained. An electrolyte secondary battery was assembled.

The following treatment was applied to this non-aqueous electrolyte secondary battery as an initial charging step. First, after being left for 5 hours in a high temperature environment of 40 ° C., constant current and constant voltage charging was performed at 0.2 C (110 mA) to 4.2 V for 10 hours under the environment. Then at 0.2C
The battery was discharged to 2.7 V, and the second cycle was charged under the same conditions as the first cycle to obtain a non-aqueous electrolyte secondary battery.

The blister after storage at 85 ° C. for 120 hours at a high temperature was measured. Also, when the outer material of the laminate film is used, the mechanical strength of the fused portion of the laminate film is high, but the mechanical strength of the other parts is low, and the mechanical strength of the electrode group is lower than the mechanical strength of the battery. Greatly influences
Therefore, in this case, an offset drop collision test was performed in which a portion other than the fused portion was subjected to a drop collision, and the drop safety of the nonaqueous electrolyte secondary battery was evaluated. The non-aqueous electrolyte secondary battery charged to 4.2 V as described above is dropped from a height of 1.9 m, and the widest surface is on the falling surface concrete. The safety was confirmed by falling and colliding at 0 to 80 °. This is, for example, as shown in FIG.
This is to prevent the collision between the concrete 63 as the falling surface and the falling collision portion 62 at the time of the battery falling collision and the exterior material fusion portion 62 to collide. The drop test was performed with 10 batteries, and if no internal short circuit occurred due to deformation, it was evaluated as ○,
The case where an internal short circuit occurred due to the deformation was evaluated as x.

The type of the internal adhesive, the surface density, the weight average molecular weight, the type of the outermost adhesive,
Table density, solution concentration, weight average molecular weight, and test results
Shown in 1.

[Table 1] (Examples 2 to 8, Comparative Examples 1 to 3) The type and surface density of the adhesive inside the electrode group and the type and surface density of the adhesive at the outermost periphery of the electrode group were changed as shown in Table 1. A thin nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1 except for the above, and a drop test and a high-temperature storage test were performed. Table 1 also shows the type of the internal adhesive, the surface density, the weight average molecular weight, the type of the outermost adhesive, the surface density, the solution concentration, the weight average molecular weight, and the test results of the batteries of the examples.

[0103]

As described in detail above, according to the present invention,
Provided is a non-aqueous electrolyte secondary battery in which the mechanical strength of the battery is increased without changing the battery shape, the battery is mechanically resistant to impact such as falling, and the battery swelling during storage under high temperature conditions is suppressed. be able to.

[Brief description of the drawings]

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

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

FIG. 3 is a schematic diagram showing the vicinity of a boundary between a positive electrode layer, a separator, and a negative electrode layer in the electrode group of the nonaqueous electrolyte secondary battery in FIG.

FIG. 4 is a perspective view showing a nonaqueous electrolyte secondary battery having a structure in which one set of a positive electrode, a negative electrode, and a separator is wound.

FIG. 5 is a perspective view showing a non-aqueous electrolyte secondary battery having a structure in which one set of a positive electrode, a negative electrode, and a separator is wound or bent.

FIG. 6 is a schematic diagram illustrating an example of a collision state during an offset drop test of the nonaqueous electrolyte secondary battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Exterior material 2 ... Electrode group 3 ... Separator 4 ... Positive electrode layer 5 ... Positive electrode current collector 6 ... Negative electrode layer 7 ... Negative electrode current collector 8 ... Outer periphery 9 ... Polymer having adhesiveness 10 ... Positive electrode lead 11 ... Negative electrode lead 41… Positive electrode 42… Separator 43… Negative electrode 51… Positive electrode 52… Separator 53… Negative electrode 61… Exterior material fusion part 62… Drop impact part 63… Concrete

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takahisa Osaki 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture F-term (reference) 5H029 AJ04 AJ11 AJ12 AK02 AK03 AK05 AL01 AL02 AL03 AL04 AL06 AL07 AL08 AL12 AM02 AM03 AM04 AM05 AM07 BJ04 CJ02 CJ06 CJ13 CJ22 DJ08 DJ12 EJ11 HJ10 HJ12

Claims (3)

[Claims] An electrode group comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein at least a space between the positive electrode, the negative electrode, and the separator is provided. In the non-aqueous electrolyte secondary battery, wherein the polymer having adhesiveness is held, and the positive electrode, the negative electrode, and the separator are bonded and integrated, the outermost periphery of the electrode group is A non-aqueous electrolyte secondary battery comprising a polymer having an adhesive property at a higher density than inside the electrode group. 2. An electrode group comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein at least a space between the positive electrode, the negative electrode, and the separator is provided. In the non-aqueous electrolyte secondary battery, wherein the polymer having adhesiveness is held, and the positive electrode, the negative electrode, and the separator are bonded and integrated, the outermost periphery of the electrode group is A non-aqueous electrolyte secondary battery comprising an adhesive polymer having a higher molecular weight than the inside of the electrode group. 3. A step of forming an electrode group by interposing a separator between a positive electrode and a negative electrode; a step of impregnating the electrode group with a solution in which an adhesive polymer is dissolved; A step of applying a solution in which molecules are dissolved at a concentration higher than that of the adhesive-containing solution to the outermost periphery of the electrode group, and / or a step of applying a vacuum drying to the electrode group; The method for producing a non-aqueous electrolyte secondary battery according to claim 1, further comprising: impregnating the electrode group with a non-aqueous electrolyte.