JP2020145097A - Manufacturing method of laminated lithium ion secondary battery - Google Patents

Abstract

To provide a manufacturing method of a laminated secondary battery including a decompression step capable of shortening a decompression processing time and suppressing scattering of an electrolytic solution.SOLUTION: A manufacturing method of a laminated secondary battery includes: a step of injecting an electrolyte into an opening at one end of an exterior body accommodating an electrode laminate in which a positive electrode and a negative electrode are arranged in opposition to each other under atmospheric pressure; and a decompression step of reducing pressure from the atmospheric pressure to a set degree of vacuum after the injection of the electrolyte, and then returning to the atmospheric pressure. In the decompression step, (1) the set degree of vacuum is set to a specific degree of vacuum in a range of 1 kPa to 10 kPa, and (2) a holding time for holding within a range from the decompression reaching degree of 50% to the set degree of vacuum is set to 10 to 80 seconds when decompressing from the atmospheric pressure to the set degree of vacuum.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a laminated lithium ion secondary battery.

Lithium-ion secondary batteries are used as large-scale stationary power sources for power storage, power sources for electric vehicles, etc., and in recent years, research on miniaturization and thinning of batteries has been progressing. As a battery that meets the demand for miniaturization and weight reduction, there is a laminated lithium ion secondary battery that can reduce the thickness of the battery.

A laminated lithium-ion secondary battery uses a laminated film or the like as an exterior body, accommodates an electrode laminate including a positive electrode, a negative electrode, a separator, etc. in the exterior body, and then injects an electrolytic solution through the opening of the exterior body to open the opening. It is manufactured by sealing the part.

In this laminated lithium ion secondary battery, it is known that the electrolytic solution reacts with the negative electrode active material and decomposes to generate gas at the time of initial charging. When this gas is present between the electrodes, the internal resistance of the battery increases, the battery capacity decreases, and the battery characteristics such as cycle characteristics may deteriorate.

Therefore, it is common to inject the electrolytic solution into the exterior body and then perform decompression treatment to degas. This decompression treatment is a very important treatment in terms of preventing deterioration of battery characteristics due to gas generation, and various studies are required on the decompression method. For example, as a method of depressurizing, Patent Document 1 discloses a method of increasing the degree of decompression in a stepwise manner.

Japanese Unexamined Patent Publication No. 2002-11246

However, in the method of depressurizing in steps as in Patent Document 1, there is a concern that the depressurizing process will take a long time. On the other hand, if the decompression speed is simply increased in order to shorten the decompression time, the electrolytic solution tends to scatter from the exterior body, and as a result, the equipment is polluted.

From the above, it is an object of the present invention to provide a method for manufacturing a laminated secondary battery including a decompression step capable of shortening the decompression treatment time and suppressing scattering of an electrolytic solution.

As a result of diligent studies in view of the above problems, the present inventor sets the set vacuum degree at the time of depressurization to a specific vacuum degree, and reduces the pressure from atmospheric pressure to the set vacuum degree from 50% to the set vacuum degree. We have found that the above problems can be solved by setting the holding time within the range to a specific range, and have completed the following invention. That is, the present invention is as follows.

[1] An electrolytic solution injection step of injecting an electrolytic solution under atmospheric pressure into an opening at one end of an exterior body accommodating an electrode laminate in which a positive electrode and a negative electrode are arranged so as to face each other.
After the injection of the electrolytic solution, the pressure is reduced from the atmospheric pressure to the set vacuum degree, and then the pressure is returned to the atmospheric pressure.
In the decompression step
(1) The set vacuum degree is set to a specific vacuum degree in the range of 1 kPa to 10 kPa.
(2) Laminated lithium ion secondary battery having a holding time of 10 to 80 seconds for holding within the range from the decompression reaching degree of 50% when decompressing from the atmospheric pressure to the set vacuum degree to the set vacuum degree. Manufacturing method.
[2] The method for manufacturing a laminated lithium ion secondary battery according to [1], wherein the depressurizing speed when depressurizing from the atmospheric pressure to the set vacuum degree is 3 to 15 kPa / sec.
[3] The number of times the vacuum degree reaches the set vacuum degree is at least once before the pressure is reduced from the atmospheric pressure to the set vacuum degree and then returned to the atmospheric pressure. [1] or [2]. How to manufacture a laminated lithium-ion secondary battery.
[4] The method for manufacturing a laminated lithium ion secondary battery according to [3], wherein the number of arrivals is one.
[5] The laminated lithium ion according to any one of [1] to [4], wherein the time from the start of depressurization when depressurizing from the atmospheric pressure to the set vacuum degree to returning to the atmospheric pressure is within 100 seconds. How to manufacture a secondary battery.

According to the present invention, it is possible to provide a method for manufacturing a laminated secondary battery, which can shorten the depressurization treatment time and can suppress the scattering of the electrolytic solution, and includes a decompression step. That is, by shortening the depressurization processing time, the manufacturing time of the laminated secondary battery can be shortened. In addition, since the scattering of the electrolytic solution can be suppressed, the labor for cleaning and maintenance of the device can be reduced.

It is a figure which shows an example of the relationship between the degree of vacuum and the decompression time in the depressurization process. It is a figure which shows another example of the relationship between the degree of vacuum and the decompression time in the depressurization process.

The method for manufacturing a laminated secondary battery of the present invention includes an electrolytic solution injection step of injecting an electrolytic solution under atmospheric pressure into an opening at one end of an exterior body accommodating an electrode laminate in which a positive electrode and a negative electrode are arranged facing each other. ,
After the injection of the electrolytic solution, the pressure is reduced from the atmospheric pressure to the set vacuum degree, and then the pressure is returned to the atmospheric pressure. Then, in the above decompression step, (1) the set vacuum degree is set to a specific vacuum degree in the range of 1 kPa to 10 kPa, and (2) the decompression reaching degree when decompressing from atmospheric pressure to the set vacuum degree is from 50% to the set vacuum degree. The holding time for holding within the range of is 10 to 80 seconds.
Hereinafter, the electrolytic solution injection step, the decompression step, and the like will be described. In the present invention, the degree of vacuum is expressed as absolute pressure.

<Electrolyte injection process>
In the electrolytic solution injection step, the electrode laminate is housed in the exterior body prior to the injection of the electrolytic solution. In the electrode laminate, for example, the negative electrode and the positive electrode may be arranged facing each other via a separator, and an insulating layer may be provided between the negative electrode and the separator, or between the positive electrode and the separator. The electrode laminate may have a multilayer structure in which a plurality of negative electrodes and a plurality of positive electrodes are laminated. In this case, the negative electrode and the positive electrode may be provided alternately along the stacking direction. When a separator is used, the separator may be arranged between each negative electrode and each positive electrode.

The exterior body that accommodates the electrode laminate is not particularly limited, but an exterior film is preferable. The exterior film may be between two rectangular exterior films, or one rectangular exterior film may be folded in half, for example, and an electrode laminate may be arranged between the exterior films. After the arrangement, three of the four sides of the exterior film are sealed by laminating so that one end of the exterior body becomes an opening. Then, the electrolytic solution is injected under atmospheric pressure into the opening at one end of the exterior body.

The electrolytic solution is not particularly limited as long as it is an electrolytic solution used for a lithium ion secondary battery.
Examples of the electrolytic solution include an organic solvent and an electrolytic solution containing an electrolyte salt. Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate, dimethyl carbonate, diethyl carbonate (DEC), γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 1 , 2-Diethoxyethane, tetrohydrafuran, 2-methyltetraethylene, dioxolane, methylacetamide and other polar solvents, or mixtures of two or more of these solvents.
Electrolyte salts include LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ CO ₂ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ , LiN (COCF ₃ ). Examples include lithium-containing salts such as ₂ and LiN (COCF ₂ CF ₃ ) ₂ , lithium bisoxalate boronate (LiB (C ₂ O ₄ ) ₂ ), and lithium organic acid salt-boron trifluoride complex, LiBH. Complexes such as _{4 and the} like Complexes such as hydrides can be mentioned. These salts or complexes may be used alone or in admixture of two or more.

Further, the electrolyte may be a gel-like electrolyte in which the above-mentioned electrolyte solution further contains a polymer compound. Examples of the polymer compound include a fluorine-based polymer such as polyvinylidene fluoride and a polyacrylic polymer such as methyl poly (meth) acrylate. The gel electrolyte may be used as a separator.

<Decompression process>
In the depressurizing step, first, the exterior body after injecting the electrolytic solution is installed in the vacuum chamber. After that, the pressure is reduced from the atmospheric pressure to the set vacuum degree, and finally returned to the atmospheric pressure.
In the present invention, the above-mentioned conditions (1) and (2) are set in consideration of the efficiency of degassing from the exterior body, the suppression of scattering of the electrolytic solution, and the depressurization treatment time. First, a specific vacuum degree is set from a high vacuum degree range of 1 kPa to 10 kPa, but if the set vacuum degree is less than 1 kPa, the electrolytic solution scatters violently due to excessive decompression. The amount of scattering will increase. If it exceeds 10 kPa, the decompression becomes insufficient and the degassing efficiency decreases. Therefore, the number of depressurization treatments increases, and the total decompression treatment time becomes long. The set vacuum degree is preferably a specific vacuum degree in the range of 3 kPa to 8 kPa, more preferably a specific vacuum degree in the range of 4 kPa to 7.5 kPa, and a specific vacuum degree in the range of 4 kPa to 5.5 kPa. It is more preferable to set the degree of vacuum.
The set vacuum degree refers to the vacuum degree when the pressure is reduced from the atmospheric pressure and the set vacuum degree is first reached. Normally, the vacuum degree that has reached the set vacuum degree does not move up and down and is stable. , May fluctuate up and down. However, even if the degree of vacuum fluctuates up and down, the degree of vacuum is in the range of 1 kPa to 10 kPa.

In addition, the holding time for holding within the range from the decompression reaching degree of 50% to the set vacuum degree when decompressing from atmospheric pressure to the set vacuum degree (when holding multiple times, the total holding time) is 10 to 80 seconds. However, if the holding time is less than 10 seconds, a sufficient time for degassing cannot be obtained, and as a result, a plurality of depressurization treatments are required, resulting in a long decompression treatment time. If the holding time exceeds 80 seconds, it is not preferable from the viewpoint of tact time. The holding time is preferably 15 to 75 seconds, more preferably 20 to 70 seconds.
Further, when the set vacuum degree is reached, the maintenance time for maintaining the set vacuum degree can be appropriately set within the range in which the above-mentioned holding time can be maintained. That is, the depressurization may be stopped immediately after reaching the set vacuum degree (maintenance time 0 seconds), or a maintenance time of about 2 to 45 seconds may be provided.

The depressurizing speed when depressurizing from the atmospheric pressure to the set vacuum degree is preferably 3 to 15 kPa / sec, preferably 4.5 to 5.5 kPa / sec, from the viewpoint of suppressing scattering of the electrolytic solution and shortening the depressurizing treatment time. More preferably. The decompression rate is preferably constant without fluctuating in a step-like manner or repeating vertical movement.

The number of times the vacuum degree reaches the set vacuum degree is at least 1 time, 1 to 3 times, by depressurizing from the atmospheric pressure to the set vacuum degree and then returning to the atmospheric pressure to complete the decompression process. It is preferable, once or twice, more preferably once, and even more preferably once. Since the number of arrivals is only once, the effect of suppressing the scattering of the electrolytic solution can be further enhanced. The number of arrivals is the first time when the set vacuum is reached, then the decompression is stopped and the pressure rises, and after the decompression reach reaches a range of less than 50% to atmospheric pressure, the decompression is performed again to set the vacuum. The number of arrivals is the total number of times when the set vacuum degree is reached from the decompression achievement degree of 50% or less, such as the second time when the degree is reached.

Under the above conditions, the time from the start of decompression when decompressing from atmospheric pressure to the set vacuum degree to the final return to atmospheric pressure (end of the final decompression treatment), that is, the decompression treatment time is within 100 seconds. It is preferably present, and more preferably within 90 seconds. If it is within 100 seconds, the manufacturing time of the laminated secondary battery can be shortened.

After a predetermined holding time has passed, the electrode laminate and the electrolytic solution are contained in the exterior body by heat-sealing and sealing the opening at one end of the exterior body while maintaining the vacuum state. It will be in a sealed state. Then, the depressurization step is completed by stopping the depressurization and returning the inside of the vacuum chamber to the atmospheric pressure.

Here, in the decompression treatment according to the present invention, the relationship between the degree of vacuum and the decompression time will be described with reference to FIGS. 1 and 2. In the example shown in FIG. 1, first, the pressure is lowered from the atmospheric pressure A to the set vacuum degree B. After that, after maintaining the set vacuum degree for a certain period of time, the opening of the exterior body is sealed with the set vacuum degree C (the vacuum degree is the same as B) after the elapse of the certain time, and then the depressurization is stopped to move the inside of the vacuum chamber. Return to atmospheric pressure D. Here, the holding time for holding within the range from the decompression reaching degree of 50% to the set vacuum degree when decompressing from the atmospheric pressure to the set vacuum degree is 10 to 80 seconds, and the decompression reaching degree of 50% is defined as. It corresponds to the degree of vacuum of AB and CD. These correspond to the degree of vacuum of (AB) / 2. Then, the time T from AB to CD is the above-mentioned holding time.

The example shown in FIG. 2 is an example in which the degree of vacuum reaches the set degree of vacuum twice before the pressure is returned to atmospheric pressure and the decompression process is completed. As in the case of FIG. 1, the pressure is lowered from the atmospheric pressure E to the set vacuum degree F. Immediately after that, the depressurization in the vacuum chamber is stopped. By stopping the decompression, the degree of vacuum decreases and exceeds the degree of vacuum FG, which is the degree of reaching 50% of the decompression. After that, the pressure is reduced again from the degree of vacuum G, and the set degree of vacuum H (the degree of vacuum is the same as F) is reached through the degree of vacuum GH, which is the degree of reaching 50% of the degree of reduction. After reaching, after sealing the opening of the exterior body, the depressurization is stopped and the inside of the vacuum chamber is returned to the atmospheric pressure J. Here, the decompression reaching degree of 50% in the case of FIG. 2 corresponds to EF, FG, GH and HJ. These correspond to a degree of vacuum of (EF) / 2. Then, the sum of the time T1 from EF to FG and the time T2 from GH to HJ is the holding time.
In the case of FIG. 2, the decompression rate from E to F and the decompression rate from G to H are the same, but they do not have to be the same as long as they are in the above-mentioned preferable range of the decompression rate. Further, although the set vacuum degrees F and H are the same, they do not have to be the same as long as they are in the range of 1 kPa to 10 kPa.

A laminated secondary battery is manufactured through the above decompression process.
Here, as the electrode laminate housed in the exterior body in the electrolytic solution injection step, as described above, a configuration in which the negative electrode and the positive electrode are arranged facing each other via the separator and an insulating layer is appropriately provided can be mentioned. Hereinafter, the electrode laminate and a method for manufacturing the same will be described.

(Positive electrode)
The positive electrode in the electrode laminate preferably has a positive electrode current collector and a positive electrode active material layer laminated on the positive electrode current collector. The positive electrode active material layer typically includes a positive electrode active material and a binder for the positive electrode.
Examples of the positive electrode active material include lithium metallic acid compounds. Examples of the lithium metal acid compound include lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), and the like. Further, as the positive electrode active material, olivine-type lithium iron phosphate (LiFePO ₄ ) or the like may be used. Further, as the positive electrode active material, a material using a plurality of metals other than lithium may be used, and NCM (nickel cobalt manganese) oxide, NCA (nickel cobalt aluminum) oxide, etc., which are called ternary oxides, may be used. You may use it. As the positive electrode active material, these substances may be used alone or in combination of two or more.
The positive electrode active material is not particularly limited, but its average particle size is preferably 0.5 to 50 μm, and more preferably 1 to 30 μm. The average particle size means the particle size (D50) when the volume integration is 50% in the particle size distribution obtained by the laser diffraction / scattering method.
The content of the positive electrode active material in the positive electrode active material layer is preferably 50 to 98.5% by mass, more preferably 60 to 98% by mass, based on the total amount of the positive electrode active material layer.

Specific examples of the binder for the positive electrode include polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), fluorine-containing resin such as polytetrafluoroethylene (PTFE), and polymethyl acrylate (PMA). ), Acrylic resin such as polyvinylidene methacrylate (PMMA), polyvinylidene acetate, polyimide (PI), polyamide (PA), polyvinylidene chloride (PVC), polyethernitrile (PEN), polyethylene (PE), polypropylene (PP) , Polyacrylonitrile (PAN), acrylonitrile-butadiene rubber, styrene butadiene rubber (SBR), poly (meth) acrylic acid, carboxymethyl cellulose (CMC), hydroxyethyl cellulose, polyvinyl alcohol and the like. These binders may be used alone or in combination of two or more. Further, carboxymethyl cellulose and the like may be used in the form of a salt such as a sodium salt.
Among these, a fluorine-containing resin is preferable, and polyvinylidene fluoride is more preferable.
The content of the binder in the positive electrode active material layer is preferably 0.5% by mass or more, more preferably 0.5 to 20% by mass, and 1.0 to 10% based on the total amount of the positive electrode active material layer. Mass% is more preferred.

The positive electrode active material layer may further contain a conductive auxiliary agent. As the conductive auxiliary agent, a material having higher conductivity than the positive electrode active material and the negative electrode active material is used, and specific examples thereof include carbon materials such as Ketjen black, acetylene black (AB), carbon nanotubes, and rod-shaped carbon. Be done. The conductive auxiliary agent may be used alone or in combination of two or more. When the positive electrode active material layer contains a conductive auxiliary agent, the content of the conductive auxiliary agent is preferably 0.5 to 15% by mass, preferably 1.0 to 9% by mass, based on the total amount of the positive electrode active material layer. More preferably.

The positive electrode active material layer may contain an optional component other than the positive electrode active material, the conductive auxiliary agent, and the binder. However, the total content of the positive electrode active material, the conductive auxiliary agent, and the binder in the total mass of the positive electrode active material layer is preferably 90% by mass or more, and more preferably 95% by mass or more.
The thickness of the positive electrode active material layer (thickness of each of the plurality of positive electrode active material layers) is not particularly limited, but is preferably 10 to 100 μm, more preferably 20 to 80 μm.

Examples of the material used as the positive electrode current collector include conductive metals such as copper, aluminum, titanium, nickel, and stainless steel. Among these, aluminum, titanium, nickel and stainless steel are preferable, and aluminum is more preferable. The positive electrode current collector is generally made of a metal foil, and the thickness thereof is not particularly limited, but is preferably 1 to 50 μm, more preferably 5 to 20 μm. When the thickness of the electrode current collector is 1 to 50 μm, the handling of the electrode current collector can be facilitated and the decrease in energy density can be suppressed.

(Negative electrode)
The negative electrode in the electrode laminate preferably has a negative electrode current collector and a negative electrode active material layer laminated on the negative electrode current collector. The negative electrode active material layer typically includes a negative electrode active material and a binder for the negative electrode.
Examples of the negative electrode active material include carbon materials such as graphite and hard carbon, a composite of a tin compound, silicon and carbon, and lithium. Among these, a carbon material is preferable, and graphite is more preferable. As the negative electrode active material, these substances may be used alone or in combination of two or more.
The negative electrode active material is not particularly limited, but its average particle size is preferably 0.5 to 50 μm, more preferably 1 to 30 μm.
The content of the negative electrode active material in the negative electrode active material layer is preferably 50 to 98.5% by mass, more preferably 60 to 98% by mass, based on the total amount of the negative electrode active material layer.

Specific examples of the binder for the negative electrode are the same as those of the binder for the positive electrode, and one type may be used alone or two or more types may be used in combination. Further, carboxymethyl cellulose and the like may be used in the form of a salt such as a sodium salt.
Among these, a fluorine-containing resin is preferable, and polyvinylidene fluoride is more preferable.
The content of the binder in the negative electrode active material layer is preferably 0.5% by mass or more, more preferably 0.5 to 20% by mass, and 1.0 to 10% based on the total amount of the negative electrode active material layer. Mass% is more preferred.

The negative electrode active material layer may contain a conductive auxiliary agent. Specific examples of the conductive auxiliary agent include the same as in the case of the positive electrode active material layer. The conductive auxiliary agent may be used alone or in combination of two or more.
When the negative electrode active material layer contains a conductive auxiliary agent, the content of the conductive auxiliary agent is preferably 1 to 30% by mass, preferably 2 to 25% by mass, based on the total amount of the negative electrode active material layer. Is more preferable.
It should be noted that the negative electrode active material layer may contain an optional component other than the negative electrode active material, the conductive auxiliary agent, and the binder, which is the same as in the case of the positive electrode active material layer, and the content thereof is also the same.
The thickness of the negative electrode active material layer (thickness of each of the plurality of negative electrode active material layers) is not particularly limited, but is preferably 10 to 100 μm, more preferably 20 to 80 μm.

Examples of the material constituting the negative electrode current collector include conductive metals such as copper, aluminum, titanium, nickel, and stainless steel. Among these, copper, titanium, nickel and stainless steel are preferable, and copper is more preferable. The negative electrode current collector is also generally made of a metal foil like the positive electrode current collector, and its thickness is not particularly limited, but is preferably 1 to 50 μm, more preferably 5 to 20 μm. When the thickness of the electrode current collector is 1 to 50 μm, the handling of the electrode current collector can be facilitated and the decrease in energy density can be suppressed.
(Separator)
Examples of the separator include a porous polymer film, a non-woven fabric, and glass fiber, and among these, a porous polymer film is preferable. Examples of the porous polymer film include an olefin-based porous film. The separator may be heated by heat generated when the lithium ion secondary battery is driven and may undergo heat shrinkage. Even during such heat shrinkage, a short circuit can be easily suppressed by providing an insulating layer described later.

(Insulation layer)
An insulating layer may be provided between the positive electrode and the separator, or between the separator and the negative electrode. The insulating layer effectively prevents short circuits between the positive and negative electrodes. The insulating layer is preferably a layer having a porous structure containing insulating fine particles and a binder for an insulating layer, and the insulating fine particles are bound by a binder for an insulating layer.

The insulating fine particles are not particularly limited as long as they are insulating, and may be either organic particles or inorganic particles. Specific organic particles include, for example, crosslinked polymethyl methacrylate, crosslinked styrene-acrylic acid copolymer, crosslinked acrylonitrile resin, polyamide resin, polyimide resin, poly (lithium 2-acrylamide-2-methylpropanesulfonate), and the like. Examples thereof include particles composed of organic compounds such as polyacetal resin, epoxy resin, polyester resin, phenol resin, and melamine resin. Inorganic particles include silicon dioxide, silicon nitride, alumina, boehmite, titania, zirconia, boron nitride, zinc oxide, tin dioxide, niobium oxide (Nb ₂ O ₅ ), tantalum oxide (Ta ₂ O ₅ ), potassium fluoride, and foot. Examples thereof include particles composed of inorganic compounds such as lithium pentoxide, clay, zeolite, and calcium carbonate. Further, the inorganic particles may be particles composed of known composite oxides such as niobium-tantalum composite oxide and magnesium-tantalum composite oxide. One type of insulating fine particles may be used alone, or a plurality of types may be used in combination.
The average particle size of the insulating fine particles is not particularly limited as long as it is smaller than the thickness of the insulating layer, and is, for example, 0.001 to 1 μm, preferably 0.05 to 0.8 μm, and more preferably 0.1 to 0.6 μm. is there.
The content of the insulating fine particles contained in the insulating layer is preferably 15 to 95% by mass, more preferably 40 to 90% by mass, and further preferably 60 to 85% by mass based on the total amount of the insulating layer. When the content of the insulating fine particles is within the above range, the insulating layer can form a uniform porous structure and is provided with appropriate insulating properties.

As the binder for the insulating layer, the same type as the binder for the positive electrode described above can be used. The content of the binder for the insulating layer in the insulating layer is preferably 5 to 50% by mass, more preferably 10 to 45% by mass, still more preferably 15 to 40% by mass, based on the total amount of the insulating layer.
The thickness of the insulating layer is preferably 1 to 10 μm, more preferably 2 to 8 μm, and even more preferably 3 to 7 μm.

<Manufacturing method of electrode laminate>
[Preparation of positive electrode]
(Formation of positive electrode active material layer)
In the formation of the positive electrode active material layer, first, a composition for the positive electrode active material layer containing the positive electrode active material, the binder for the positive electrode, and the solvent is prepared. The composition for the positive electrode active material layer may contain other components such as a conductive additive to be blended if necessary. The positive electrode active material, the binder for the positive electrode, the conductive auxiliary agent and the like are as described above. The composition for the positive electrode active material layer is a slurry.

Water or an organic solvent is used as the solvent in the positive electrode active material layer composition. Specific examples of the organic solvent include one or more selected from N-methylpyrrolidone, N-ethylpyrrolidone, dimethylacetamide, and dimethylformamide. Of these, N-methylpyrrolidone is preferred.
The solid content concentration of the composition for the positive electrode active material layer is preferably 5 to 75% by mass, more preferably 20 to 65% by mass.

The positive electrode active material layer may be formed by a known method using the above-mentioned composition for the positive electrode active material layer. For example, the above-mentioned composition for the positive electrode active material layer is applied onto the positive electrode current collector and dried. Can be formed by
Further, the positive electrode active material layer may be formed by applying the composition for the positive electrode active material layer on a base material other than the positive electrode current collector and drying it. Examples of the base material other than the positive electrode current collector include known release sheets. For the positive electrode active material layer formed on the base material, preferably, after forming an insulating layer on the positive electrode active material layer, the positive electrode active material layer may be peeled off from the base material and transferred onto the positive electrode current collector.
The positive electrode active material layer formed on the positive electrode current collector or the base material is preferably pressure-pressed. By pressurizing, it becomes possible to increase the electrode density. The pressure press may be performed by a roll press or the like.

[Preparation of negative electrode]
(Formation of negative electrode active material layer)
In forming the negative electrode active material layer, first, a composition for the negative electrode active material layer containing the negative electrode active material, the negative electrode binder, and the solvent is prepared. The composition for the negative electrode active material layer may contain other components such as a conductive auxiliary agent to be blended as needed. The negative electrode active material, the binder for the negative electrode, the conductive auxiliary agent and the like are as described above. The composition for the negative electrode active material layer is a slurry.

As the solvent in the negative electrode active material layer composition, the same solvent as in the positive electrode active material layer composition can be used, and the solid content concentration thereof is also the same.

The negative electrode active material layer may be formed by a known method using the negative electrode active material layer composition. For example, the negative electrode active material layer composition is applied onto the negative electrode current collector and dried. Can be formed by
Further, the negative electrode active material layer may be formed by applying the composition for the negative electrode active material layer on a base material other than the negative electrode current collector and drying it. Examples of the base material other than the negative electrode current collector include known release sheets. For the negative electrode active material layer formed on the base material, preferably, after the insulating layer is formed on the negative electrode active material layer, the negative electrode active material layer may be peeled off from the base material and transferred onto the negative electrode current collector.
The negative electrode active material layer formed on the negative electrode current collector or the base material is preferably pressure-pressed. By pressurizing, it becomes possible to increase the electrode density. The pressure press may be performed by a roll press or the like.

(Formation of insulating layer)
The composition for an insulating layer used when forming the insulating layer contains inorganic particles, a binder for the insulating layer, and a solvent. The composition for the insulating layer may contain other optional components to be blended as needed. Details of the inorganic particles, the binder for the insulating layer, and the like are as described above. The composition for the insulating layer is a slurry. As the solvent, water or an organic solvent may be used, and the details of the organic solvent include those similar to those of the organic solvent in the positive electrode active material layer composition. The solid content concentration of the composition for the insulating layer is preferably 5 to 75% by mass, more preferably 15 to 50% by mass.

The insulating layer can be formed by applying the composition for an insulating layer on the positive electrode or negative electrode active material layer and drying it. The method of applying the composition for the insulating layer to the surface of the positive electrode or negative electrode active material layer is not particularly limited, and for example, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a bar coating method, a gravure coating method, etc. Screen printing method and the like can be mentioned.
The drying temperature is not particularly limited as long as the solvent can be removed, but is, for example, 40 to 120 ° C, preferably 50 to 90 ° C. The drying time is not particularly limited, but is, for example, 30 seconds to 20 minutes.

The positive electrode and the negative electrode obtained as described above are pressure-bonded via the separator of the present invention to form an electrode laminate. The specific method of crimping the positive electrode and the negative electrode is to press the positive electrode, the separator, and the negative electrode on top of each other (if there are multiple layers, they are alternately arranged and superposed) with a press or the like. It is good to do it by doing. The pressing conditions may be such that the positive electrode active material layer and the negative electrode active material layer are not compressed more than necessary. Specifically, the press temperature is 50 to 130 ° C., preferably 60 to 100 ° C., and the press pressure is, for example, 0.2 to 3 MPa, preferably 0.4 to 1.5 MPa. The press time is, for example, 15 seconds to 15 minutes, preferably 30 seconds to 10 minutes.
In the electrode laminate obtained as described above, for example, the positive electrode current collector is connected to the positive electrode terminal and the negative electrode current collector is connected to the negative electrode terminal.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

The obtained laminated lithium ion secondary battery was evaluated by the following evaluation method.
(Charging / discharging characteristics)
The batteries obtained in Examples and Comparative Examples were cycled at 1C and 1C charge / discharge rates, and the charge / discharge capacity and capacity retention rate were measured. If the charge / discharge capacity is 35.5 Ah or more and the 200-cycle capacity retention rate is 95% or more, it is evaluated as "good", and if any of them is inferior, it is evaluated as "bad".

[Example 1]
(Preparation of positive electrode)
92.8 parts by mass of LiFePO ₄ (average particle size 10 μm) as the positive electrode active material, 5 parts by mass of carbon black as the conductive auxiliary agent, 2.2 parts by mass of polyvinylidene fluoride as the electrode binder, and N as the solvent. -Methylpyrrolidone was mixed to obtain a slurry for a positive electrode active material layer adjusted to a solid content concentration of 55.5% by mass. This slurry for the positive electrode active material layer was applied to both sides of an aluminum foil having a thickness of 15 μm as a positive electrode current collector, pre-dried, and then vacuum dried at 120 ° C. After that, the positive electrode current collector coated with the slurry for the positive electrode active material layer on both sides is pressure-pressed by a roller at a linear pressure of 400 kN / m, and further punched into an electrode size of 467 mm × 175 mm square, and the positive electrode active material is punched on both sides. A positive electrode having a layer was used. Of the dimensions, the area to which the positive electrode active material was applied was 432 mm × 175 mm. The thickness of the positive electrode active material layer formed on both sides was 64.25 μm per side.

(Preparation of negative electrode)
100 parts by mass of graphite (average particle diameter 10 μm) as a negative electrode active material, 1.5 parts by mass of sodium salt of carboxymethyl cellulose (CMC) as an electrode binder, 1.5 parts by mass of styrene butadiene rubber (SBR), and a solvent. Was mixed with water to obtain a slurry for the negative electrode active material layer adjusted to have a solid content of 50% by mass. This slurry for the negative electrode active material layer was applied to both sides of a copper foil having a thickness of 12 μm as a negative electrode current collector and vacuum dried at 100 ° C. After that, the negative electrode current collector coated with the slurry for the negative electrode active material layer on both sides is pressure-pressed by a roller at a linear pressure of 500 kN / m, and further punched into an electrode size of 468 mm × 181 mm square, and the negative electrode active material is punched on both sides. It was a negative electrode having a layer. Of the dimensions, the area to which the negative electrode active material was applied was 439 mm × 181 mm. The thickness of the negative electrode active material layer formed on both sides was 43.5 μm per side.

(Preparation of electrolyte)
LiPF ₆ as an electrolyte salt is dissolved in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 3: 7 (EC: EMC) so as to be 1 mol / liter, and the electrolytic solution is prepared. Was prepared.

(Battery manufacturing)
The 18 negative electrodes, 17 positive electrodes, and 34 separators obtained above were laminated to obtain an electrode laminate. Here, the negative electrode and the positive electrode were arranged alternately, and a separator was arranged between each negative electrode and the positive electrode. Further, as the separator, a polyethylene porous film having a thickness of 12 μm was used.
The exposed ends of the positive electrode current collectors of each positive electrode were joined together by ultrasonic fusion, and the terminal tabs protruding to the outside were joined. Similarly, the exposed ends of the negative electrode current collectors of each negative electrode were joined together by ultrasonic fusion, and the terminal tabs protruding to the outside were joined.
Next, the electrode laminate was sandwiched between two aluminum laminate films, the terminal tabs were projected to the outside, three sides were sealed by laminating, and one end was used as an opening.

190 g of the electrolytic solution was injected through the injection nozzle under atmospheric pressure from the opening of the exterior body containing the electrode laminate with one end as an opening.

Subsequently, the exterior body was installed in the vacuum chamber, the vacuum pump connected to the exhaust pipe of the vacuum chamber was operated to start the depressurization process, and a laminated lithium ion secondary battery was produced. The time from the start of depressurization when depressurizing from the atmospheric pressure to the set vacuum degree to the end of the depressurization treatment and finally returning to the atmospheric pressure was measured (the same was measured for the following examples and comparative examples). The results are shown in Table 1.
The vacuum chamber used can adjust the decompression speed by opening and closing the valve interposed in the exhaust pipe and opening and closing the valve interposed in the atmosphere introduction pipe of the vacuum chamber.
The atmospheric pressure in each example and comparative example was 101.3 kPa.

As the conditions for the depressurization treatment, the set vacuum degree was 4.6 kPa and the decompression rate was 4.84 kPa / sec. In addition, the holding time for holding the pressure within the range from 50% (48.35 kPa) to the set vacuum degree (maintenance time of the set vacuum degree: 0 seconds) when decompressing from the atmospheric pressure to the set vacuum degree is 11 seconds. (The first time the set vacuum level was reached). Then, after returning to atmospheric pressure once, the pressure is reduced again at the above decompression rate and maintained within the range from the decompression reaching degree of 50% (48.35 kPa) to the set vacuum degree (maintenance time of the set vacuum degree: 25 seconds). After setting the holding time to 41 seconds (the second time when the set vacuum degree was reached), the opening was heat-sealed, the depressurization was stopped, and the inside of the vacuum chamber was returned to atmospheric pressure.
The amount of the electrolytic solution scattered after the reduced pressure treatment was determined from the difference between the weight before the reduced pressure treatment and the weight after the sealing treatment. From the amount of liquid scattered and the amount of injection electrolyte, the rate of decrease in the amount of electrolyte was calculated from the following formula. The results are shown in Table 1.
Equation) Reduction rate of electrolyte amount (%) = Liquid scattering amount / Liquid injection electrolyte amount x 100
In addition, the charge / discharge characteristics of the manufactured laminated secondary battery were evaluated. The results are shown in Table 1.

[Example 2]
The injection amount of the electrolytic solution is 170 g, the set vacuum degree (maintenance time for the first time to reach the set vacuum degree: 0 seconds, maintenance time for the second time to reach the set vacuum degree: 25 seconds) is 6.5 kPa, and the decompression speed is 4.74 kPa. A laminated lithium ion secondary battery was produced in the same manner as in Example 1 except that it was set to / sec.
In the same manner as in Example 1, the amount of liquid scattered and the rate of decrease in the amount of electrolytic solution were determined. In addition, the charge / discharge characteristics of the manufactured laminated secondary battery were evaluated. The results are shown in Table 1.

[Example 3]
In the same manner as in Example 1, an exterior body containing the electrode laminate was prepared with one end as an opening, and 210 g of the electrolytic solution was injected from the opening through an injection nozzle under atmospheric pressure. Subsequently, an exterior body was installed in the vacuum chamber, and a vacuum pump connected to the exhaust pipe of the vacuum chamber was operated to start the depressurization process to produce a laminated lithium ion secondary battery.

As the conditions for the depressurization treatment, the set vacuum degree was 4.6 kPa and the decompression rate was 4.84 kPa / sec. In addition, the holding time for holding the pressure within the range from 50% (48.35 kPa) to the set vacuum degree (maintenance time of the set vacuum degree: 0 seconds) when decompressing from the atmospheric pressure to the set vacuum degree is 21 seconds. (The first set vacuum degree was reached). After the lapse of the holding time, the opening was heat-sealed, the depressurization was stopped, and the inside of the vacuum chamber was returned to the atmospheric pressure to prepare a laminated lithium ion secondary battery.
In the same manner as in Example 1, the amount of liquid scattered and the rate of decrease in the amount of electrolytic solution were determined. In addition, the charge / discharge characteristics of the manufactured laminated secondary battery were evaluated. The results are shown in Table 1.

[Example 4]
The set vacuum degree is 6.5 kPa, the decompression speed is 4.74 kPa / sec, the first maintenance time when the set vacuum degree is reached is 0 seconds, the holding time is 11 seconds, and the second maintenance time when the set vacuum degree is reached is 25 seconds. A laminated lithium ion secondary battery was produced in the same manner as in Example 1 except that the time was set to 21 seconds.
In the same manner as in Example 1, the amount of liquid scattered and the rate of decrease in the amount of electrolytic solution were determined. In addition, the charge / discharge characteristics of the manufactured laminated secondary battery were evaluated. The results are shown in Table 1.

[Example 5]
In the same manner as in Example 1, an exterior body containing the electrode laminate was prepared with one end as an opening, and 190 g of an electrolytic solution was injected from the opening through an injection nozzle under atmospheric pressure. Subsequently, an exterior body was installed in the vacuum chamber, and a vacuum pump connected to the exhaust pipe of the vacuum chamber was operated to start the depressurization process to produce a laminated lithium ion secondary battery.

As the conditions for the depressurization treatment, the set vacuum degree was 4.6 kPa and the decompression rate was 4.84 kPa / sec. In addition, the holding time for holding the pressure within the range from 50% (48.35 kPa) to the set vacuum degree (maintenance time of the set vacuum degree: 40 seconds) when decompressing from the atmospheric pressure to the set vacuum degree is 56 seconds. (The first set vacuum degree was reached). After the lapse of the holding time, the opening was heat-sealed, the depressurization was stopped, and the inside of the vacuum chamber was returned to the atmospheric pressure to prepare a laminated lithium ion secondary battery.
In the same manner as in Example 1, the amount of liquid scattered and the rate of decrease in the amount of electrolytic solution were determined. In addition, the charge / discharge characteristics of the manufactured laminated secondary battery were evaluated. The results are shown in Table 1.

[Example 6]
In the same manner as in Example 1, an exterior body containing the electrode laminate was prepared with one end as an opening, and 190 g of an electrolytic solution was injected from the opening through an injection nozzle under atmospheric pressure. Subsequently, an exterior body was installed in the vacuum chamber, and a vacuum pump connected to the exhaust pipe of the vacuum chamber was operated to start the depressurization process to produce a laminated lithium ion secondary battery.

As the conditions for the decompression treatment, the set vacuum degree was 6.5 kPa and the decompression rate was 4.74 kPa / sec. In addition, the holding time for holding the pressure within the range from 50% (47.4 kPa) to the set vacuum degree (maintenance time of the set vacuum degree: 25 seconds) when decompressing from the atmospheric pressure to the set vacuum degree is 41 seconds. (The first set vacuum degree was reached). After the lapse of the holding time, the opening was heat-sealed, the depressurization was stopped, and the inside of the vacuum chamber was returned to the atmospheric pressure to prepare a laminated lithium ion secondary battery.
In the same manner as in Example 1, the amount of liquid scattered and the rate of decrease in the amount of electrolytic solution were determined. In addition, the charge / discharge characteristics of the manufactured laminated secondary battery were evaluated. The results are shown in Table 1.

[Example 7]
The injection amount of the electrolytic solution is 170 g, the set vacuum degree is 4.6 kPa, the decompression speed is 4.84 kPa / sec, the set vacuum degree is reached, the first maintenance time is 0 seconds, the holding time is 11 seconds, and the set vacuum degree is reached 2. A laminated lithium ion secondary battery was produced in the same manner as in Example 1 except that the holding time was 40 seconds and the holding time was 56 seconds.
In the same manner as in Example 1, the amount of liquid scattered and the rate of decrease in the amount of electrolytic solution were determined. In addition, the charge / discharge characteristics of the manufactured laminated secondary battery were evaluated. The results are shown in Table 1.

[Comparative Example 1]
In the same manner as in Example 1, an exterior body containing the electrode laminate was prepared with one end as an opening, and 170 g of the electrolytic solution was injected from the opening through an injection nozzle under atmospheric pressure. Subsequently, an exterior body was installed in the vacuum chamber, and a vacuum pump connected to the exhaust pipe of the vacuum chamber was operated to start the depressurization process to produce a laminated lithium ion secondary battery.

As the conditions for the decompression treatment, the set vacuum degree (maintenance time of the set vacuum degree: 5 seconds) was set to 0.6 kPa, and the decompression rate was set to 5.04 kPa / sec. In addition, the holding time for holding the pressure within the range from 50% (50.35 kPa) to the set vacuum degree when decompressing from the atmospheric pressure to the set vacuum degree was set to 21 seconds (the first set vacuum degree reached). .. After the lapse of the holding time, the opening was heat-sealed, the depressurization was stopped, and the inside of the vacuum chamber was returned to the atmospheric pressure to prepare a laminated lithium ion secondary battery.
In the same manner as in Example 1, the amount of liquid scattered and the rate of decrease in the amount of electrolytic solution were determined. In addition, the charge / discharge characteristics of the manufactured laminated secondary battery were evaluated. The results are shown in Table 1.

[Comparative Example 2]
In the same manner as in Example 1, an exterior body containing the electrode laminate was prepared with one end as an opening, and 170 g of the electrolytic solution was injected from the opening through an injection nozzle under atmospheric pressure. Subsequently, an exterior body was installed in the vacuum chamber, and a vacuum pump connected to the exhaust pipe of the vacuum chamber was operated to start the depressurization process to produce a laminated lithium ion secondary battery.

As the conditions for the depressurization treatment, the set vacuum degree (maintenance time of the set vacuum degree: 40 seconds) was set to 0.6 kPa, and the decompression rate was set to 4.74 kPa / sec. In addition, the holding time for holding within the range from 50% (50.35 kPa) to the set vacuum degree when decompressing from the atmospheric pressure to the set vacuum degree was set to 56 seconds (the first set vacuum degree reached). .. After the lapse of the holding time, the opening was heat-sealed, the depressurization was stopped, and the inside of the vacuum chamber was returned to the atmospheric pressure to prepare a laminated lithium ion secondary battery.
In the same manner as in Example 1, the amount of liquid scattered and the rate of decrease in the amount of electrolytic solution were determined. In addition, the charge / discharge characteristics of the manufactured laminated secondary battery were evaluated. The results are shown in Table 1.

[Comparative Example 3]
The injection amount of the electrolytic solution is 210 g, the set vacuum degree is 0.6 kPa, the decompression rate is 5.04 kPa / sec, the set vacuum degree is reached, the first maintenance time is 0 seconds, the holding time is 11 seconds, and the set vacuum degree is reached 2. A laminated lithium ion secondary battery was produced in the same manner as in Example 1 except that the holding time was 5 seconds and the holding time was 21 seconds.
In the same manner as in Example 1, the amount of liquid scattered and the rate of decrease in the amount of electrolytic solution were determined. In addition, the charge / discharge characteristics of the manufactured laminated secondary battery were evaluated. The results are shown in Table 1.

[Comparative Example 4]
The injection amount of the electrolytic solution is 210 g, the set vacuum degree is 0.6 kPa, the decompression rate is 5.04 kPa / sec, the set vacuum degree is reached, the first maintenance time is 0 seconds, the holding time is 11 seconds, and the set vacuum degree is reached 2. A laminated lithium ion secondary battery was produced in the same manner as in Example 1 except that the holding time was 40 seconds and the holding time was 56 seconds.
In the same manner as in Example 1, the amount of liquid scattered and the rate of decrease in the amount of electrolytic solution were determined. In addition, the charge / discharge characteristics of the manufactured laminated secondary battery were evaluated. The results are shown in Table 1.

[Comparative Example 5]
In the same manner as in Example 1, an exterior body containing the electrode laminate was prepared with one end as an opening, and 210 g of the electrolytic solution was injected from the opening through an injection nozzle under atmospheric pressure. Subsequently, an exterior body was installed in the vacuum chamber, and a vacuum pump connected to the exhaust pipe of the vacuum chamber was operated to start the depressurization process to produce a laminated lithium ion secondary battery.

As the conditions for the depressurization treatment, the set vacuum degree (maintenance time of the set vacuum degree: 0, 25 seconds) was set to 0.6 kPa, and the decompression rate was set to 5.04 kPa / sec. In addition, the holding time for holding within the range from 50% (50.35 kPa) to the set vacuum degree when decompressing from the atmospheric pressure to the set vacuum degree was set to 41 seconds (the first set vacuum degree reached). .. After the lapse of the holding time, the opening was heat-sealed, the depressurization was stopped, and the inside of the vacuum chamber was returned to the atmospheric pressure to prepare a laminated lithium ion secondary battery.
In the same manner as in Example 1, the amount of liquid scattered and the rate of decrease in the amount of electrolytic solution were determined. In addition, the charge / discharge characteristics of the manufactured laminated secondary battery were evaluated. The results are shown in Table 1.

Claims (5)

An electrolytic solution injection step of injecting an electrolytic solution under atmospheric pressure into an opening at one end of an exterior body accommodating an electrode laminate in which a positive electrode and a negative electrode are arranged facing each other.
After the injection of the electrolytic solution, the pressure is reduced from the atmospheric pressure to the set vacuum degree, and then the pressure is returned to the atmospheric pressure.
In the decompression step
(1) The set vacuum degree is set to a specific vacuum degree in the range of 1 kPa to 10 kPa.
(2) Laminated lithium ion secondary battery having a holding time of 10 to 80 seconds for holding within the range from the decompression reaching degree of 50% when decompressing from the atmospheric pressure to the set vacuum degree to the set vacuum degree. Manufacturing method. The method for manufacturing a laminated lithium ion secondary battery according to claim 1, wherein the decompression rate when depressurizing from the atmospheric pressure to the set vacuum degree is 3 to 15 kPa / sec. The laminated lithium ion according to claim 1 or 2, wherein the vacuum degree reaches the set vacuum degree at least once before the pressure is reduced from the atmospheric pressure to the set vacuum degree and then returned to the atmospheric pressure. How to manufacture a secondary battery. The method for manufacturing a laminated lithium ion secondary battery according to claim 3, wherein the number of arrivals is one. The laminated lithium ion secondary battery according to any one of claims 1 to 4, wherein the time from the start of depressurization when depressurizing from the atmospheric pressure to the set vacuum degree to returning to the atmospheric pressure is within 100 seconds. Manufacturing method.