JP2002280077A - Method of producing sheet lithium secondary battery and sheet lithium secondary battery obtained by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a sheet lithium secondary battery for improving the bulging property during high-temperature standing and improving battery storage property as well as cycle property at a high temperature, and the sheet lithium secondary battery obtained by using the same. SOLUTION: The method of producing the sheet lithium secondary battery eased by a sheet casing material comprises the steps of charging the battery after assembled, of removing a gas generated during charge and of heating the battery from which the gas is removed at 30-120 deg.C for 0.5-50 hours in the state of being held at a voltage of 2.5-4.3 V. The sheet lithium secondary battery is obtained by using the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a sheet-shaped lithium ion secondary battery and a sheet-shaped lithium secondary battery obtained by the method.

[0002]

2. Description of the Related Art In a lithium secondary battery, it is known that a chemical reaction occurs at an interface between an electrode and an electrolytic solution during an initial charge to generate gas. Lithium secondary batteries are subjected to a degassing step to remove the generated gas, and then to an aging step (aging test). After the battery has a problem (for example, a voltage is rapidly increased during aging). Is dropped, and only non-defective good batteries are shipped as products.

[0003]

However, since it is difficult to completely remove the gas generated in the degassing step, a small amount of gas remains in the battery as a product. For this reason, the lithium secondary battery is made of an exterior material other than a metal (aluminum, iron (chrome plating), etc.) can (for example,
In the case of a so-called sheet-shaped lithium secondary battery (especially a laminated type) using a sheet-shaped exterior material such as an aluminum laminate film, the sheet-shaped lithium secondary battery as a product is exposed to a high-temperature (for example, 90 ° C.) atmosphere. When left for a long period of time, the remaining gas expands to cause blistering, and the expansion of the gas causes the positive and negative electrodes to separate, increasing the internal resistance, making charging and discharging unstable, causing battery performance,
In particular, there is a problem that the battery storage characteristics and the cycle characteristics under a high temperature atmosphere of about 100 ° C. are deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to improve the swelling characteristics (bulge characteristics) when left at high temperatures, as well as the battery storage characteristics and cycle characteristics at high temperatures. An object of the present invention is to provide a method for manufacturing a sheet-shaped lithium secondary battery having improved characteristics and a sheet-shaped lithium secondary battery.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, the assembled battery was charged to remove the gas generated during charging. While maintaining the voltage of 0.5 V to 4.3 V, 30
By heating for 0.5 hours to 50 hours in an atmosphere at a temperature of 120 ° C. to 120 ° C., it is possible to improve bulging characteristics (bulge characteristics) when left at high temperatures, and also to improve battery storage characteristics and cycle characteristics at high temperatures. And completed the present invention. That is, the present invention is as follows. (1) A method for manufacturing a sheet-like lithium secondary battery packaged with a sheet-like packaging material, comprising: charging the assembled battery; removing gas generated during the charging; Heating the battery in a temperature atmosphere of 30 ° C. to 120 ° C. for 0.5 hours to 50 hours while maintaining the battery from which voltage has been removed at a voltage of 2.5 V to 4.3 V. A method for manufacturing a lithium secondary battery. (2) After the step of heating while maintaining the voltage, a step of selecting non-defective batteries by an aging test in which the battery is left in a charged state for a predetermined period, and a step of further degassing the selected non-defective batteries. The method for producing a sheet-shaped lithium secondary battery according to the above (1), further comprising: (3) A sheet-shaped lithium secondary battery obtained by the production method according to the above (1) or (2). (4) A salt, a compatible solvent, and a fluoropolymer having vinylidene fluoride as a main unit as a main component, and the fluoropolymer has a density of 0.60 g / cm ^{3 to} 1.30 g / c.
The sheet-shaped lithium secondary battery according to the above (3), wherein a solid electrolyte layer, which is a porous body of m ³ , is interposed between the positive electrode and the negative electrode. (5) The salt is LiClO ₄ , LiBF ₄ , LiPF ₆ , Li
AsF ₆ , LiCF ₃ SO ₃ , LiAlCl ₄ and Li
At least one compound selected from (CF ₃ SO ₂ ) ₂ N, wherein the compatible solvent is one selected from ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethoxyethane, propylene carbonate, diethyl carbonate and dimethoxyethane Or 2
The sheet-shaped lithium secondary battery according to the above (3) or (4), which is at least one kind.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The present invention is a method for manufacturing a sheet-like lithium secondary battery packaged with a sheet-like package, charging the assembled battery, removing gas generated during the charging, and removing the gas. Remove the removed battery from 2.5 V to 4.3
And heating in a temperature atmosphere of 30 ° C. to 120 ° C. for 0.5 to 50 hours while maintaining the voltage of V.

[0007] The charging in the above-mentioned process varies depending on the size, capacity, shape and the like of the battery. For example, charging is performed at a constant current value until a constant voltage is reached, and then constant voltage charging is performed in that state. Perform under conditions.

In the subsequent step, for example, after discharging at a constant current at a constant current value until a constant voltage is reached, gas generated during charging is removed. For the degassing, for example, a rotary pump type vacuum suction device is used.

What is important in the present invention is that
After the step, the step of heating the battery from which the gas has been removed while maintaining the voltage is performed. The voltage retained by the battery from which the gas has been removed is 2.5 V to 4.3 V, preferably 3.0 V to 4.2 V, and more preferably 3.5 V.
~ 4.1V. When the voltage is less than 2.5 V,
The gas remaining when left in a high-temperature (for example, 90 ° C.) atmosphere expands to cause blisters. On the other hand, when the voltage exceeds 4.3 V, battery characteristics such as cycle characteristics and high-rate characteristics deteriorate. The voltage to be held is the open circuit voltage (open circuit voltage (OC)
V)). The temperature for heating while maintaining the voltage is 30 ° C to 120 ° C, preferably 40 ° C to 100 ° C.
° C, more preferably 60 ° C to 90 ° C. If the heating temperature is lower than 30 ° C., blisters will occur when left in the high-temperature atmosphere. When the heating temperature exceeds 120 ° C., battery characteristics such as cycle characteristics and high-rate characteristics deteriorate. The heating atmosphere during this voltage holding is not particularly limited, and examples thereof include air, nitrogen gas and the like. The heating is performed using, for example, a heating furnace or a thermostat. The heating time during the holding of the voltage is 0.5 hours to 50 hours, preferably 1 hour to 30 hours, more preferably 3 hours to 20 hours. If the heating time is less than 0.5 hour, blisters will occur when left in the high-temperature atmosphere.
If the heating time exceeds 50 hours, battery characteristics such as cycle characteristics and high-rate characteristics will deteriorate.

Through the above steps (1) to (4), it is possible to obtain a sheet-shaped lithium secondary battery having improved swelling characteristics (bulge characteristics) when left at high temperatures, and also improved battery storage characteristics and cycle characteristics at high temperatures. . The details of this reason are unknown, but the present inventors speculate as follows. After charging the assembled battery, the battery from which the gas has been removed is maintained at a voltage in a heated atmosphere, and a chemical bond is generated between the electrolyte and the surface of the porous hole due to electric energy and temperature energy. It is considered that the electrolytic solution is taken into the surface of the porous pores by the chemical bonding force, and the electrolyte does not easily volatilize even when the temperature of the electrolyte reaches a normal volatilization temperature. In fact, when the above process is not performed, when the charge and discharge are repeated, the electrolytic solution bleeds from the surface of the porous resin base material (the surface is sticky). No bleed occurs even if repeated. In addition, after charging the assembled battery, the battery from which the gas has been removed is maintained at a voltage in a heated atmosphere, so that the porous resin substrate (solid electrolyte layer or separator described later) holding the electrolytic solution is electrochemically protected. The electrolyte solution was physically retained in the porous part of the substrate physically (affinity was improved), and the performance of the electrolyte solution impregnated in the substrate was improved. It is considered that the battery storage characteristics at high temperature and the cycle characteristics are improved.

Further, in the present invention, after each of the above steps (1) to (4), a non-defective battery is selected by an aging test in which the battery is left in a charged state for a predetermined period, and degassing is further performed on the selected non-defective battery. The step of performing may be further performed.

The selection of good batteries in the step (1) can be carried out by removing the batteries (for example, those whose voltage has dropped sharply during this period) during the aging test. In the aging test, for example, recharging is performed in the same manner as the above charging, and in the charged state, for example,
It is allowed to stand for 1 to 2 weeks in an atmosphere of 23 ° C., and a product whose voltage drop from the charging voltage is within 0.1 V is regarded as a good product.

In the step (1), the non-defective battery is
Further, degassing is performed. This degassing can be performed, for example, using a rotary pump type vacuum suction device after discharging again in the same manner as the above-described discharging. In the present invention, even if this step is not performed, the blister of the battery can be suppressed, but gas may be generated in the step depending on the composition of the electrolytic solution. The gas can be reliably removed, and the blister characteristics can be further improved.

In the sheet-shaped lithium secondary battery of the present invention, the solid electrolyte layer or the separator may be interposed between the positive electrode and the negative electrode, but is preferably the solid electrolyte layer. The solid electrolyte layer means a polymer substrate impregnated with an electrolytic solution (lithium salt (electrolyte) + compatible solvent) to be gelled and prepared to exhibit ionic conductivity. When the solid electrolyte layer is interposed between the positive electrode and the negative electrode, the electrolyte does not exist in a liquid state (in a state where the electrolyte itself flows) in the battery, so that there is an advantage that there is no fear of liquid leakage from the battery. Can be In the present invention, among the solid electrolyte layer, a salt, a compatible solvent and a fluoropolymer having vinylidene fluoride as a main unit as a main component, and a fluoropolymer having the vinylidene fluoride as a main unit having a density of 0% .60 g / cm ³
It is preferable to use a solid electrolyte layer formed into a porous body of about 1.30 g / cm ³ . By interposing such a solid electrolyte layer between the positive electrode and the negative electrode, a sheet-shaped lithium secondary battery having further improved high-rate characteristics and low-temperature characteristics can be realized.

The high-rate characteristics and the low-temperature characteristics are improved by forming the fluoropolymer having vinylidene fluoride as a main unit in the solid electrolyte layer into a porous body having a specific density. It is thought that this further improves the ion transfer amount, which leads to a drastic increase. The density of the porous body of fluoropolymer to the vinylidene fluoride as a main unit is preferably ^{0.70g / cm 3 ~0.80g / cm 3} .

When the density of the porous body of the fluoropolymer having vinylidene fluoride as a main unit is less than 0.60 g / cm ³ , there is a concern that the mechanical strength is reduced and it becomes difficult to handle the battery during assembly. 1.3 density
If it is larger than 0 g / cm ^3, it is difficult to obtain a sufficient effect of improving high-rate characteristics and low-temperature characteristics.

The average pore diameter of the pores in the porous body is preferably from 0.01 μm to 10 μm, particularly preferably from 0.1 μm to 5 μm. This “average pore size” is
M observations were taken out of arbitrary 10 holes, and
It indicates the average value of the pore diameters of the pores.

If the average pore size is less than 0.01 μm, the liquid holding capacity tends to decrease, and if it exceeds 10 μm,
The mechanical strength of the porous body tends to decrease, and the handleability in the battery manufacturing process tends to decrease.

The fluoropolymer having vinylidene fluoride as a main unit is a homopolymer of vinylidene fluoride (polyvinylidene fluoride (PVdF)) or a mixture of vinylidene fluoride and another vinyl monomer having a fluorine atom. It means a copolymer, each of which may be used alone or in combination. Examples of the vinyl monomer having a fluorine atom other than the vinylidene fluoride include hexafluoropropylene (HFP),
Chlorotrifluoroethylene (CTFE), tetrafluoroethylene (TFE) and the like can be mentioned. The form of the copolymer may be any of a random form and a block form. In the case of a copolymer, the proportion of (units) of vinylidene fluoride is preferably at least 70 mol%, particularly preferably at least 75 mol%.

Fluoropolymers containing vinylidene fluoride as a main unit include carboxyl groups (—COO).
H) a vinyl group having a functional group consisting of a sulfonic acid group (—SO ₂ OH), a carboxylic acid ester group (—COOR), an amide group (—CONH ₂ ), or a phosphoric acid group (—PO (OH) ₂ ). A polymer of a monomer may be grafted (the substituent R in the carboxylic acid ester group (—COOR) is a lower alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, and a butyl group). . When the fluoropolymer is in a polymer form in which a polymer containing such a functional group is grafted, the adhesion of the solid electrolyte layer to the positive electrode or the negative electrode is improved, and the resistance between the electrodes is further reduced, so that the battery performance is further improved. . That is, high-rate characteristics and low-temperature characteristics are further improved. As the vinyl monomer having a functional group, a monomer composed of a compound having 4 or less carbon atoms in a portion excluding the functional group is preferable. As the carboxyl group-containing monomer, acrylic acid, methacrylic acid,
In addition to those having one carboxyl group such as crotonic acid, vinyl acetic acid and allyl acetic acid, those having two or more carboxyl groups such as itaconic acid and maleic acid can also be used. As the sulfonic acid group-containing monomer, styrene sulfonic acid, vinyl sulfonic acid and the like are preferable. As the carboxylic acid ester group-containing monomer, methyl acrylate, butyl acrylate, and the like are preferable. Acrylamide and the like are preferable as the amide group-containing monomer. As the phosphate group-containing monomer, triphenyl phosphate, tricresyl phosphate, and the like are preferable. Most preferred of these are acrylic acid or methacrylic acid.

As a grafting method, a radiation method is preferable. For example, the radiation is continuously or intermittently applied to the radiation in the coexistence of the polymer chain substrate (the polymer to be grafted) and the graft monomer material, or
More preferably, the polymer substrate is pre-irradiated with radiation prior to the coexistence of both. As the radiation, an electron beam, X-ray or γ-ray is used. Upon irradiation, the polymer substrate generates and activates free radicals.

The degree of grafting can be determined by several factors, but most importantly, the length of time the activated substrate is in contact with the graft monomer,
The extent of substrate preactivation by radiation, the extent to graft monomer material can penetrate the substrate, and is a temperature at which the substrate and the monomer is in contact. For example,
When the graft monomer is an acid, the degree of grafting can be observed by sampling the solution containing the monomer, titrating against the base, and measuring the residual monomer concentration. The degree of grafting is preferably from 2% to 20% of the final weight, particularly preferably from 3% to 1%.
It is 2%, particularly preferably 5% to 10%. In addition,
Grafting activates the polymer substrate (generating free radicals)
May be performed by light irradiation or heat.

The fluoropolymer having vinylidene fluoride as a main unit preferably has a melt flow index at 1.0 kg / 10 min or less at 230 ° C. and 10 kg, and is preferably 0.2 g / 10 min to 0.7 g / 10 m.
More preferably, it is in. The melt flow index is a value measured by a method described in standard ASTM D1238. When the melt flow index is 1.0 g / 10 min or less, the solid electrolyte layer exhibits more excellent mechanical strength, and the ionic conductivity at room temperature is further improved.

The salt (electrolyte) contained in the solid electrolyte layer
LiClO_Four, LiBF_Four, LiPF₆, LiAs
F₆, LiCF_ThreeSO_Three, LiAlCl_FourAnd Li (CF
_ThreeSO _Two)_TwoOne or more selected from the group consisting of N
It is preferred to use the above. Also, as a compatible solvent
Are ethylene carbonate, dimethyl carbonate,
Tyl methyl carbonate, diethoxyethane, diethyl
Carbonate, dimethoxyethane, propylene carbonate
Dimethyl sulfoxide, sulfolane, γ-butyro
Lactone, N, N-dimethylformamide, tetrahydrid
Lofran, 1,3-dioxolan, 2-methyltetrahi
Any selected from drofuran, diethyl ether, etc.
Or one or more of them are exemplified.
Carbonate, dimethyl carbonate, ethyl methyl carbonate
-Carbonate, diethoxyethane, propylene carbonate
G, diethyl carbonate and dimethoxyethane
It is preferable to use one or more selected ones.
The concentration of the salt (electrolyte) in the solution is from 0.5 mol / liter to
1.5 mol / l, preferably 0.7 mol / l
To 1.3 mol / l, more preferably 0.8 mol
/ L to 1.2 mol / l. Salt (electrolysis
Is less than 0.5 mol / l,
Battery conductivity has decreased and battery capacity cannot be obtained sufficiently
High-rate characteristics may be reduced, and 1.5 mol /
When the volume exceeds liters, high-
Properties and low-temperature properties tend to decrease.

The operating temperature of the battery (especially at low temperatures)
Together with the above compatible solvent for the purpose of preventing crystallization of the solution in
It is preferable to use a plasticizer such as -methyl-pyrrolidone (1-methyl-2-pyrrolidone), ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether. The amount of the plasticizer used is 1 to the compatible solvent.
It is preferably about 50% by weight to 50% by weight. By adding the plasticizer, crystallization of the solution impregnated (impregnated) with the fluoropolymer hardly occurs, and sufficient ion conductivity of the solid electrolyte layer can be secured.

When a mixed solvent is used as the compatible solvent,
In particular, a mixture containing at least one selected from diethyl carbonate (DEC) and ethyl methyl carbonate (EMC), and further containing ethylene carbonate (EC), propylene carbonate (PC), and dimethyl carbonate (DMC) is preferable. . In at least one kind selected from diethyl carbonate and ethyl methyl carbonate, the mixing ratio of each component constituting such a mixture is preferably 25% by volume to 50% by volume, and more preferably 30% by volume to 35% by volume. More preferred. Mixing ratio of 4% by volume in ethylene carbonate
-20% by volume, more preferably 6-18% by volume. In propylene carbonate, the mixing ratio is preferably from 3% by volume to 17% by volume, and more preferably from 5% by volume to 15% by volume.
In the case of dimethyl carbonate, the mixing ratio is preferably more than 40% by volume and 60% by volume or less.
More preferably, the content is in the range of volume% to 55 volume%.

In at least one selected from diethyl carbonate and ethyl methyl carbonate,
If the mixing ratio is less than 25% by volume, the freezing point of the solution in which the salt (electrolyte) is dissolved increases, and the internal resistance of the battery increases, particularly at low temperatures of -20 ° C or lower, and the low-temperature characteristics and charge / discharge Cycle characteristics tend to decrease, while
When the mixing ratio exceeds 50% by volume, the viscosity of the solution in which the salt (electrolyte) is dissolved increases, and the internal resistance of the battery increases.
The charge / discharge cycle characteristics tend to decrease.

In the case of ethylene carbonate, if the mixing ratio is less than 4% by volume, it is difficult to form a stable film on the surface of the negative electrode, and the cycle characteristics tend to be deteriorated. The viscosity of the solution in which the (electrolyte) is dissolved increases, the internal resistance of the battery increases, and the charge-discharge cycle characteristics tend to decrease.

In propylene carbonate, if the above mixing ratio is less than 3% by volume, the effect of suppressing the increase in impedance due to charge / discharge cycles becomes small, and the cycle characteristics tend to decrease. If it exceeds, the viscosity of the solution in which the salt (electrolyte) is dissolved increases, the internal resistance of the battery increases, and the charge / discharge cycle characteristics tend to decrease.

In dimethyl carbonate, when the mixing ratio is 40% by volume or less, the viscosity of the solution in which the salt (electrolyte) is dissolved increases, the internal resistance of the battery increases, and the charge / discharge cycle characteristics tend to decrease. And the mixing ratio is 6
When the content exceeds 0% by volume, the freezing point of the solution in which the salt (electrolyte) is dissolved increases, and particularly at a low temperature of −20 ° C. or lower, the internal resistance of the battery increases, and the cycle characteristics and low-temperature characteristics tend to decrease. Becomes

The thickness of the solid electrolyte layer varies depending on the shape and size of the positive electrode and the negative electrode, but is generally preferably 5 μm to 100 μm, particularly preferably 8 μm.
m to 50 μm, particularly preferably 10 μm to 30 μm
It is. Here, the thickness of the solid electrolyte layer is a thickness in a state where the solid electrolyte layer is interposed between the positive electrode and the negative electrode (in a state where the battery is actually assembled), and is equal to a separation distance between the positive electrode and the negative electrode.

The method of forming the solid electrolyte layer in the present invention is not particularly limited. For example, (a) a film is obtained by subjecting a fluoropolymer having vinylidene fluoride as a main unit as a main unit to a known foam molding method such as extrusion foam molding. Into a porous film by forming into a shape, or prepare a coating liquid (paste) in which a fluoropolymer, a suitable solvent and a foaming agent are mixed, and peel the coating liquid (paste) with a suitable coater. A coating film is formed by coating on the surface of the substrate, and the coating film is heated, dried, and then peeled from the peeling substrate to form a porous film, and the obtained porous film is dissolved with a salt in a compatible solvent. (B) dissolving the salt, the compatible solvent and the foaming agent in an appropriate solvent; Sa A fluoropolymer is added to the mixture, and the polymer is dissolved while heating, if necessary, to prepare a coating solution (paste), which is applied to the surface of the substrate for peeling using a suitable coater. A method in which the coating film is heated stepwise, heated and dried to evaporate the solvent, generate bubbles, and peel off the solid electrolyte layer from the peeling substrate. The above salt, directly on at least one surface of the positive electrode and / or the negative electrode formed in a
A method of forming a coating film of a solution in which a compatible solvent, a foaming agent, and a fluoropolymer are dissolved, and evaporating the solvent and generating bubbles to form a solid electrolyte layer may be used. In the method (b), the release substrate on which the coating film is formed may be dried by passing through a heating chamber having a different temperature.

As the foaming agent used in the methods (a) to (c), any of a decomposable foaming agent, a gaseous foaming agent and a volatile foaming agent can be used. Agents or volatile blowing agents are preferred, and gaseous blowing agents include nitrogen, carbon dioxide, propane, neopentane,
Methyl ether, difluoromethane dichloride, n-butane,
Isobutane and the like are preferable, and as a volatile foaming agent,
n-octanol, 1-pentanol, 3-methyl-1
-Butanol, 2-methyl-1-butanol, 2-pentanol, 3-pentanol, 2-methyl-2-butanol, 3-methyl-2-butanol and the like are preferred. In the methods (b) and (c), volatile foaming agents are preferred, and among them, n-octanol, 1-pentanol, 3-methyl-1-butanol and the like are particularly preferred.
n-Octanol is particularly preferred. Examples of the solvent in the methods (b) and (c) include, for example,
Tetrahydrofuran (THF), dimethylacetamide, dimethylformamide and the like are used.

The density of the porous body is adjusted by changing the amount of the foaming agent and various conditions during production. For example,
In the case of the method (a), the density (expansion degree) other than the amount of the foaming agent is used.
The manufacturing conditions that greatly affect the temperature include a molding temperature, a molding speed, and a molding pressure. In the case of the methods (b) and (c), the production conditions that greatly affect the density (expansion degree) other than the amount of the foaming agent include a coating speed, a drying temperature profile, a degree of exhaustion, and a molding speed. is there.

In the present invention, a separator may be used instead of the solid electrolyte layer as described above. Examples of the separator include a separator made of a polyethylene film, a separator made of a polypropylene film, and a conventionally known separator having a three-layer structure of a polypropylene / polyethylene / polypropylene film. When the above separator is used, as the salt (electrolyte) and the compatible solvent to be used, the same salt and compatible solvent as in the case of using the solid electrolyte layer can be suitably used.

As the positive electrode, the negative electrode and the sheet-like exterior material constituting the sheet-type lithium secondary battery in the present invention, conventionally known materials can be used. Examples of these are shown below.

For the positive electrode and the negative electrode, a positive electrode active material composition or a negative electrode active material composition in which a conductive material or a binder is mixed with the positive electrode active material or the negative electrode active material is applied on a current collector, and then dried and dried.
Rolling is performed to form a positive electrode active material layer or a negative electrode active material layer.

As the positive electrode active material, Li-Co-based composite oxide, Li-Mn-based composite oxide, Li-Ni-based composite oxide and the like can be used, and among them, they are chemically stable and easy to handle. It is preferable to use lithium cobalt oxide (LiCoO ₂ ) in view of the fact that a secondary battery having a high capacity can be manufactured. Examples of the conductive material include artificial or natural graphites, and granular carbon materials such as acetylene black, oil furnace black, and carbon black such as extra conductive furnace black ("granular" refers to flaky, spherical, pseudo spherical, Lump-like, whisker-like and the like are not particularly limited.) Can be used. Further, as the binder in the positive electrode, polytetrafluoroethylene, polyvinylidene fluoride, ethylene-propylene-diene-based polymer, or the like can be used. In the positive electrode active material composition, the conductive material is about 3 to 15 parts by weight, and the binder is 1 to 10 parts by weight based on 100 parts by weight of the total of the positive electrode active material, the conductive material, and the binder. It is preferred to be blended in about parts.

As the negative electrode active material, graphites such as fibrous graphite, flaky graphite and spherical graphite, preferably fibrous mesophase graphitized carbon can be used. As the binder for the negative electrode, the same binder as that for the positive electrode active material can be used. The amount of the negative electrode active material used may be about 80 to 96 parts by weight per 100 parts by weight of the total amount of the negative electrode active material and the binder.

As the current collector, a foil or a perforated foil formed of a conductive metal can be used, and its thickness may be about 5 μm to 100 μm. As the material of the positive electrode current collector, aluminum, stainless steel, or the like is used, and as the material of the negative electrode current collector, copper, nickel, silver, stainless steel, or the like is used.

The positive electrode and the negative electrode can be manufactured according to a known method. For example, for a positive electrode, a positive electrode active material, a binder, and a conductive material are mixed and processed, dispersed in an organic solvent such as N-methyl-2-pyrrolidone to form a paste, and the paste is applied to a positive electrode current collector and dried. Then, it can be obtained by pressing and cutting into an appropriate shape.

The form of the sheet-shaped lithium secondary battery includes a stacked type and a wound type. The method for manufacturing the sheet-shaped lithium secondary battery of the present invention, which includes the above-mentioned steps (1) to (4), is particularly applicable to the stacked type. Can be applied advantageously. FIG. 1 is a cross-sectional view schematically showing a sheet-shaped lithium secondary battery 20 when the present invention is realized as a stacked type. As shown in the cross-sectional view of FIG. 1, the laminated type is such that the positive electrode and the negative electrode are rectangular plate-like bodies (the positive electrode plate 1,
A negative electrode plate 2), and a solid electrolyte layer or separator 3 having a rectangular shape substantially the same size as the positive electrode plate 1 and the negative electrode plate 2 are prepared, and a solid electrolyte layer is provided between the positive electrode plate 1 and the negative electrode plate 2. Alternatively, a laminated structure 10 in which one or two or more units in which the separator 3 is interposed is repeated is prepared, and the laminated structure 10 is covered with the above-mentioned sheet-like packaging material 8 (along with an electrolytic solution when a separator is used). It has a configuration and usually has a plate-like shape.

In the present invention, the sheet-like exterior material refers to a material in which a resin layer is laminated on at least one surface of a metal foil. Examples of the metal foil include aluminum, copper, and iron. Examples of the resin include thermoplastic resins such as polyester and polypropylene. As long as it has such a thermoplastic resin layer, it can be sealed only by externally covering the laminated structure (stack) and heat-welding the periphery thereof,
The battery manufacturing operation is simple. The thickness of the metal foil is preferably 10 μm to 100 μm, more preferably 20 μm to
70 μm, and the thickness of the resin layer is preferably 5 μm to
100 μm, more preferably 10 μm to 50 μm, and the overall thickness is preferably 20 μm to 200 μm.
μm, more preferably 40 μm to 150 μm.

[0044]

The present invention will be described in detail with reference to the following examples, but the present invention is not limited to the following examples.

Example 1 [Preparation of positive electrode plate] 90 parts by weight of lithium cobaltate granules as a positive electrode active material, 5 parts by weight of polyvinylidene fluoride as a binder, 5 parts by weight of artificial graphite as a conductive material and N 70 parts by weight of -methyl-2-pyrrolidone were mixed to form a slurry. This slurry is applied on both sides of an aluminum foil (thickness: 20 μm) as a positive electrode current collector, dried, and then subjected to a rolling treatment (rolling temperature: 25 ° C., rolling ratio: 3)
0%) and 20 mg / c per side of aluminum foil
A positive electrode plate (width: 30 mm, length: 50 mm) having an m ² positive electrode active material layer (thickness: 70 μm) was prepared.

[Preparation of negative electrode plate] 95 parts by weight of fibrous graphitized carbon, 5 parts by weight of polyvinylidene fluoride and N-
A slurry was prepared by mixing 60 parts by weight of methyl-2-pyrrolidone. This slurry was applied to both sides of a copper foil (thickness: 14 μm) as a negative electrode current collector, dried, and then subjected to a rolling treatment (rolling temperature: 100 ° C., rolling ratio: 20%) to give 10 mg / cm ² negative electrode active material layer (thickness: 7
Negative electrode plate having a width of 5 μm (width: 32 mm, length: 52 m)
m) was prepared.

[Preparation of porous film for solid electrolyte layer]
30 parts by weight of polyvinylidene fluoride (PVdF), 170 parts by weight of dimethylformamide (DMF),
A coating liquid (paste) is prepared by mixing 30 parts by weight of n-octanol as a foaming agent with a screw-type mixer, and the coating liquid (paste) is transferred from a transfer-type coating machine to a release substrate made of Al. After coating at a coating speed of 1 m / min, the obtained coating film was heated at 160 ° C. for 6 minutes to volatilize and foam the solvent, and the obtained film was peeled from the peeling substrate. . The thickness of the film was 25 μm, and the density was 0.75 g / cm ³ . Such a polyvinylidene fluoride (PVdF) porous film having a thickness of 2
The film was cut into a rectangular film having a size of 5 μm, a width of 34 mm, and a length of 54 mm.

[Preparation of electrolyte solution] Ethylene carbonate 1
LiPF ₆ was added to a mixed solvent of 1% by volume, 9% by volume of propylene carbonate, 28% by volume of ethyl methyl carbonate, 47% by volume of dimethyl carbonate, and 5% by volume of diethyl carbonate at a concentration of 1.0 mol / mol. One liter (relative to the prepared electrolyte) was dissolved to prepare an electrolyte.

[Assembly of Laminated Sheet-Like Lithium Secondary Battery] The positive electrode plate and the negative electrode plate produced above, and a rectangular film of polyvinylidene fluoride (PVdF) (thickness: 25 μm, width: 34 mm, length: 54 mm) Using a positive electrode plate and a PV such that a unit in which a rectangular film of PVdF is sandwiched between a positive electrode plate and a negative electrode plate is repeated eight times.
The dF rectangular film and the negative electrode plate were stacked to produce a laminated structure. This laminated structure was immersed in the electrolytic solution prepared above for 1 hour to gel a rectangular film of PVdF.

Next, the laminated structure in which the rectangular film of PVdF was gelled was accommodated in an Al-laminated film in which a thermoplastic resin as an exterior material was laminated on one or both sides, and a laminated sheet-like lithium film was formed. The secondary battery was completed.

One group (100) of the above-prepared sheet-type lithium secondary batteries was charged at a constant current of 300 mA until the voltage reached 4.2 V, and further charged at a constant voltage of 4.2 V for 2 hours. Constant voltage charging was performed. After that, 300m
Constant current discharge was performed until the voltage reached 2.75 V at the constant current of A. Next, gas generated during charging was removed using a rotary pump type vacuum suction device. Subsequently, the laminated sheet-shaped lithium secondary battery from which the gas was removed was set to 3.5 V
At a temperature of 100 ° C. while maintaining the voltage
Heating was performed for hours.

Example 2 A laminated sheet-type lithium secondary battery from which gas was removed was
The same operation as in Example 1 was performed except that heating was performed for 5 hours in a temperature atmosphere of 80 ° C. while maintaining the voltage at 3.8 V.

Example 3 A laminated sheet-type lithium secondary battery from which gas was removed was replaced with 4
V at a temperature of 60 ° C. while maintaining the voltage of 5 V.
The procedure was the same as in Example 1, except that the heating was carried out for an hour.

Example 4 A laminated sheet-shaped lithium secondary battery from which gas was removed was
The same operation as in Example 1 was performed except that heating was performed for 5 hours in a temperature atmosphere of 40 ° C. while maintaining the voltage of 4.2 V.

Example 5 A laminated sheet-type lithium secondary battery from which gas was removed was replaced with 3
Example 1 was repeated except that heating was performed for 12 hours in a 100 ° C. temperature atmosphere while maintaining the voltage of V.

Example 6 A laminated sheet-shaped lithium secondary battery from which gas had been removed was used.
Example 1 was repeated except that heating was performed for 24 hours in a temperature atmosphere of 80 ° C. while maintaining the voltage at 2.5 V.

Example 7 A mixture of 20% by volume of ethylene carbonate, 30% by volume of propylene carbonate, 20% by volume of ethyl methyl carbonate, 20% by volume of dimethyl carbonate, and 10% by volume of diethyl carbonate was used as a mixed solvent for the electrolytic solution. The procedure was the same as in Example 1, except that was used.

Example 8 A laminated sheet-type lithium secondary battery from which gas was removed was
Example 7 was carried out in the same manner as in Example 7 except that heating was performed for 45 hours in a 100 ° C temperature atmosphere while maintaining the voltage of 3.5 V.

Example 9 The procedure of Example 9 was repeated except that a mixture of 10% by volume of ethylene carbonate, 20% by volume of propylene carbonate, 60% by volume of ethyl methyl carbonate and 10% by volume of diethyl carbonate was used as a mixed solvent for the electrolytic solution. Same as Example 2.

Example 10 A laminated sheet-shaped lithium secondary battery from which gas was removed was
Example 9 was carried out in the same manner as in Example 9, except that heating was performed for 5 hours in a temperature atmosphere of 60 ° C. while maintaining the voltage at 3.8 V.

Example 11 A laminated sheet-type lithium secondary battery from which gas was removed was
Example 9 was carried out in the same manner as in Example 9 except that heating was performed for 5 hours in a temperature atmosphere of 60 ° C. while maintaining the voltage at 4.2 V.

Example 12 A laminated sheet-type lithium secondary battery from which gas had been removed was used.
Example 9 was carried out in the same manner as in Example 9 except that heating was performed for 12 hours in a temperature atmosphere of 40 ° C while maintaining the voltage of 3.8 V.

Example 13 A laminated sheet-shaped lithium secondary battery from which gas was removed was
Example 9 was carried out in the same manner as in Example 9 except that heating was performed for 3 hours in a 100 ° C. temperature atmosphere while maintaining the voltage at 3.8 V.

Comparative Example 1 A laminated sheet-type lithium secondary battery from which gas was removed was
Example 1 was repeated except that heating was performed for 5 hours in a 25 ° C. temperature atmosphere while maintaining a voltage of 4.2 V.

Comparative Example 2 The same procedure as in Example 1 was carried out except that the laminated sheet-shaped lithium secondary battery from which the gas had been removed was heated for 5 hours in a temperature atmosphere of 25 ° C. without holding the voltage. I did the same.

Comparative Example 3 A laminated sheet-shaped lithium secondary battery from which gas was removed was
The same procedure as in Example 1 was performed, except that heating was performed for 0.05 hour in a temperature atmosphere of 60 ° C. while maintaining the voltage of 4.2 V.

Comparative Example 4 The same procedure as in Example 1 was carried out except that the laminated sheet-type lithium secondary battery from which the gas had been removed was heated for 5 hours in a temperature atmosphere of 60 ° C. without holding the voltage. I did the same.

Comparative Example 5 A laminated sheet-shaped lithium secondary battery from which gas was removed was
The same operation as in Example 1 was performed except that heating was performed for 5 hours in a 150 ° C. temperature atmosphere while maintaining the voltage at 4.2 V.

Comparative Example 6 A laminated sheet-shaped lithium secondary battery from which gas was removed was
The same operation as in Example 1 was performed except that heating was performed for 5 hours in a temperature atmosphere of 80 ° C. while maintaining the voltage at 4.5 V.

The following tests were performed on the respective samples of the laminated sheet-type lithium secondary batteries of Examples 1 to 13 and Comparative Examples 1 to 4 and 6 obtained above. Comparative Example 5
The sample No. could not be charged and discharged.

[Bulging Characteristics (Bulge Characteristics) Test] Each sample of the laminated sheet-type lithium secondary battery was allowed to stand in an atmosphere of 90 ° C. for 1 hour, and then expanded (m) in the thickness direction.
m) was measured.

[Test of Battery Storage Characteristics at High Temperature] Each sample of the laminated sheet-shaped lithium secondary battery was charged at room temperature, and then left in an air atmosphere at 100 ° C. for 5 hours. The charging was performed by supplying a current at a constant current of 1 C (680 mA) until the voltage reached 4.2 V, and then supplying a current at a constant voltage of 4.2 V until the total charging time reached 3 hours. Next, it is cooled to 20 ° C.
(680 mA) /2.75 V discharge at cutoff,
The discharge capacity [mA · H] at that time is obtained. Also, 100
Charge and discharge were performed at room temperature (20 ° C.) under the same conditions except that the battery was not left in an air atmosphere at a temperature of 20 ° C., and the discharge capacity [mA ·
H]. Furthermore, the discharge capacity after leaving at 100 ° C.
The discharge capacity change rate [%] was determined by dividing by the discharge capacity obtained in the same manner except that the battery was not left.

[High-Rate Characteristic Test] Each sample of the laminated sheet-type lithium secondary battery was charged at room temperature, and then discharged at room temperature (20 ° C.) at a cut-off of 2.5 V and 0.2 C (360 mA). And 2C (3600m
A) Discharge was performed, and a capacity retention ratio (%) with respect to a 0.2C discharge result was calculated from a 2C discharge result. In addition, charge
4.2V voltage at room temperature 1C (1800mA) constant current
Then, the current was supplied at a constant voltage of 4.2 V until the total charging time became 3 hours.

[Cycle Characteristics Test] Each sample of the laminated sheet-type lithium secondary battery was charged for 3 hours at a constant current of 1700 mA and the upper limit of the voltage was 4.2 V;
The four steps of a 0.5-hour pause after charging, a discharge until the voltage becomes 3 V at a constant current of 1700 mA, and a 0.5-hour pause after the discharge are defined as one cycle, and 60 cycles are defined as 60 cycles.
The cycle was repeated 500 times in an atmosphere of ° C., and the discharge capacity in the 500th cycle was divided by the initial discharge capacity to calculate the capacity retention rate [%]. Table 1 shows the results of Examples 1 to 13 and Table 2 shows the results of Comparative Examples 1 to 6.

[0075]

[Table 1]

[0076]

[Table 2]

[0077]

As is apparent from the above description, according to the present invention, the blistering characteristics (bulge characteristics) when left at high temperatures are improved, and the battery storage characteristics at high temperatures, high rate characteristics, and cycle characteristics are also improved. The present invention can provide a method for producing a sheet-shaped lithium secondary battery, and a sheet-shaped lithium secondary battery.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a sheet-shaped lithium secondary battery 20 when realized in a stacked type according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Negative electrode plate 3 Solid electrolyte layer or separator 8 Sheet-shaped exterior material 10 Laminated structure 20 Sheet-shaped lithium secondary battery

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Toshiki 4-3-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Cable Industries, Ltd. Itami Works (72) Inventor Shogo Tanno 4-3-1 Ikejiri, Itami-shi, Hyogo Mitsubishi Electric Wire (72) Inventor Mitsuhiro Marumoto 4-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Electric Wire Co., Ltd.Itami Works F-term (reference) 5H029 AJ04 AJ05 AJ06 AJ14 AK03 AL07 AM00 AM03 AM04 AM05 AM06 AM07 AM16 BJ04 CJ02 CJ12 CJ16 CJ28 DJ13 EJ12 HJ02 HJ08 HJ14 HJ18

Claims (5)

[Claims] 1. A method for manufacturing a sheet-like lithium secondary battery packaged with a sheet-like packaging material, comprising: charging a battery after assembly; and removing gas generated during the charging. The battery from which the gas was removed was changed to 2.5 V to 4.3.
Heating at a temperature of 30 ° C. to 120 ° C. for 0.5 hours to 50 hours while maintaining the voltage of V. 2. A step of selecting non-defective batteries by an aging test in which the battery is left in a charged state for a predetermined period after the step of heating while maintaining the voltage, and further degassing the selected non-defective batteries. The method according to claim 1, further comprising: performing a step of performing the method. 3. A sheet-shaped lithium secondary battery obtained by the method according to claim 1. 4. A salt, a compatible solvent and vinylidenefluoride.
And a fluoropolymer having a main unit of
The fluoropolymer has a density of 0.60 g / cm. ^Three~ 1.3
0 g / cm^ThreeThe solid electrolyte layer, which is a porous body of
4. The battery according to claim 3, wherein the battery is interposed between the anode and the anode.
4. The sheet-shaped lithium secondary battery according to 1. 5. The method according to claim 1, wherein the salt is LiClO ₄ , LiBF ₄ , LiPF
₆ , at least one compound selected from the group consisting of LiAsF ₆ , LiCF ₃ SO ₃ , LiAlCl ₄ and Li (CF ₃ SO ₂ ) ₂ N, wherein the compatible solvent is ethylene carbonate;
The sheet lithium secondary battery according to claim 3 or 4, wherein the lithium secondary battery is at least one selected from dimethyl carbonate, ethyl methyl carbonate, diethoxyethane, propylene carbonate, diethyl carbonate, and dimethoxyethane.