JP2004342520A - Manufacturing method of secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a secondary battery in which the degasification with conditioning work or the like can be made steadily and airtightness after degassing can be secured sufficiently. <P>SOLUTION: The manufacturing method comprises a filling process in which a generating element is filled into the outer package by leaving the unjointed part 512 which communicates with inside and is separated from outside, and jointing the opening of the outer package film, a degassing process for opening a degassing hole while suppressing the thickness of the unjointed part 512 to a prescribed thickness t or less, and a refilling process for filling the generating element by jointing the unjointed part 512. In order to prevent that a large swelling or deformation are generated at the unjointed part by the increase of internal pressure due to the generated gas and the unjointed part does not return to the original shape at jointing and a part of the jointed part is separated by the concentration of stress at the surroundings of the unjointed part due to swelling of the unjointed part, the thickness of the unjointed part may be controlled when the internal pressure of the outer package is high, as a method of suppressing the swelling of the unjointed part and relieving the concentration of stress. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a secondary battery having an outer package constituted by a thin and lightweight outer film such as a laminate film, and relates to a method for manufacturing a secondary battery that can easily remove gas generated during conditioning. Also, the present invention relates to a method for manufacturing a secondary battery that can prevent the occurrence of liquid leakage or the like from a gas vent hole used at the time of gas venting.
[0002]
[Prior art]
With the miniaturization of personal computers, video cameras, mobile phones, etc., secondary batteries with a high energy density such as lithium secondary batteries have been put into practical use and widely used as power sources for these information-related devices and communication devices. I have. On the other hand, in the field of automobiles, the development of electric vehicles has been rushed due to environmental problems and resource problems, and various secondary batteries have been studied as power sources for electric vehicles.
[0003]
It is desirable that the secondary batteries used in the fields of the above-described portable devices, automobiles, and the like have a slightly high energy density, and attempts have been made to reduce the weight of battery cases and the like that are essentially unrelated to battery reactions. As a typical secondary battery, there is a secondary battery using a thin, lightweight, flexible exterior film instead of a rigid and large battery case.
[0004]
By the way, in a secondary battery such as a lithium secondary battery, gas may be generated from a power generating element due to conditioning or passage of time. Since the generated gas expands the flexible outer package, it is preferable to remove the generated gas from the inside of the secondary battery.
[0005]
The conventional degassing method is to provide a non-joined part that communicates with the inside of the outer body but does not communicate with the outside at a part of the joint of the thin and lightweight outer body that encloses the power generation element, A method is disclosed in which a gas vent hole is provided and gas is released, and then the unjoined portion is joined (Patent Document 1).
[0006]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2000-353497 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-325926 (Claim 1, FIG. 1, etc.)
[0007]
[Problems to be solved by the invention]
However, in the method of the related art, after the conditioning is completed, wrinkles may occur when joining the unjoined portions, and the generated wrinkles may be used as tunnels to leak electrolyte from the vent holes or to mix moisture into the battery. There was a fear.
[0008]
In addition, when the internal pressure of the exterior body increases during the degassing step, there is a possibility that the bonded portion may be separated from the unjoined portion of the exterior body. For example, there is disclosed a battery that aims to discharge gas when the internal pressure of a secondary battery is increased by utilizing the peeling of an unbonded portion (Patent Document 2).
[0009]
In view of the above problems, it is an object of the present invention to provide a method of manufacturing a secondary battery capable of reliably performing degassing accompanying conditioning or the like and ensuring sufficient hermeticity after degassing.
[0010]
Means for Solving the Problems and Effects of the Invention
The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result of closely examining the cause of wrinkles, large expansion and deformation have occurred in unbonded portions due to an increase in internal pressure due to gas generated in the secondary battery. It has been found that one factor is that the joint does not return to its original shape when joining. In addition, it was found that the stress was concentrated around the unjoined portion due to the expansion of the unjoined portion, and a part of the joined portion was peeled off. Therefore, as a method of suppressing the expansion of the unjoined portion and relieving the stress concentration, the present inventors have conceived to regulate the thickness of the unjoined portion when the internal pressure of the exterior body is high. That is, in the method for manufacturing a secondary battery of the present invention, the power generation element is wrapped with the exterior film, and the unjoined portion which is communicated with the inside and is isolated from the outside is joined, and the opening of the exterior film is joined. An enclosing step of enclosing the power generating element inside the exterior body,
A conditioning step of conditioning the power generating element;
A gas venting step of opening a gas vent hole in the non-joined portion to communicate the inside and the outside of the exterior body while restricting the thickness of the unjoined portion to a predetermined thickness or less,
A resealing step of joining the unjoined portion to close the gas vent hole, and enclosing the power generating element in the exterior body again.
[0011]
In other words, by providing an unjoined portion that forms a gas vent hole and constraining the thickness of the unjoined portion to a predetermined thickness or less at least during the degassing step, expansion and deformation of the unjoined portion, which is a major cause of wrinkling, is prevented. I am holding it down. Further, as an additional effect, by regulating the thickness of the unjoined portion, the gas inside the battery can be pressurized, and the speed of degassing from the gas vent hole can be improved. The unbonded portion can be easily formed together with the bonding of the exterior film.
[0012]
Further, it is desirable that the conditioning step is a step performed while restricting the thickness of the unbonded portion to the predetermined thickness or less. Since gas generation inside the secondary battery is generally generated in the conditioning step of the secondary battery, by regulating the thickness of the unbonded portion from the beginning of gas generation, the expansion or expansion of the unbonded portion, which is a major cause of wrinkling, is Deformation can be more reliably suppressed.
[0013]
Further, it is desirable that the thickness of the portion enclosing the power generation element together with the unjoined portion is also restricted to a second predetermined thickness or less. This is because, even in a portion other than the unjoined portion, peeling of the exterior film may occur due to stress concentration due to expansion of the exterior body. In addition, the gas inside the battery can be pressurized by regulating the thickness of the portion other than the unjoined portion, and the gas can be quickly released during the degassing process without increasing the size of the vent hole provided in the unjoined portion. It is possible to do.
[0014]
The preferred predetermined thickness is between 4 and 20 times the thickness of the exterior film. Further, it is desirable that the restraining method is performed by a restraining jig that restrains by holding in a thickness direction.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
A secondary battery to which the method for manufacturing a secondary battery of the present invention can be applied is a battery provided with an exterior body made of a flexible exterior film. Examples of the flexible exterior film include a laminated film such as an aluminum laminated film and a plastic film. The exterior body is formed by wrapping the power generation element of the secondary battery with these exterior films. It is desirable that these exterior films can be easily adhered by heat welding or ultrasonic welding, and have excellent airtightness and low moisture permeability.
[0016]
The lithium secondary battery will be described in detail as an example of a power generation element of the secondary battery. A lithium battery is obtained by superposing or winding a positive electrode and a negative electrode with a separator interposed therebetween. A solid electrolyte can be used instead of the separator. A lithium secondary battery is a non-aqueous battery, and generates gas by reacting with water mixed during the production. Further, gas may be generated due to evaporation of the organic solvent contained in the electrolytic solution or an electrode reaction in conditioning after battery production.
[0017]
The positive electrode is prepared by mixing a conductive material and a binder with a positive electrode active material capable of inserting and extracting lithium ions, adding an appropriate solvent as necessary, and forming a paste-like positive electrode mixture into a metal such as aluminum. It is formed by coating and drying on the surface of a current collector made of foil and then increasing the active material density by pressing.
[0018]
As the positive electrode active material, a known positive electrode active material such as a lithium transition metal composite oxide can be used. The lithium transition metal composite oxide is a preferable material for the present positive electrode active material because of its low electric resistance, excellent lithium ion diffusion performance, high charge / discharge efficiency and good charge / discharge cycle characteristics. For example, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, or a material to which a transition metal such as Li, Al, and Cr is added or substituted, respectively. When these lithium-metal composite oxides are used as the positive electrode active material, not only can they be used alone, but also a mixture of a plurality of them can be used.
[0019]
The conductive material is for ensuring the electrical conductivity of the positive electrode, and may be a mixture of one or more powdered carbon materials such as carbon black, acetylene black, and graphite. The binder plays a role of binding the active material particles and the conductive material particles, and may be a fluororesin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene. . An organic solvent such as N-methyl-2-pyrrolidone can be used as a solvent for dispersing the active material, the conductive material, and the binder.
[0020]
The material of the negative electrode is not particularly limited as long as a negative electrode active material that occludes lithium ions during charging and releases lithium ions during discharging can be used, and a known material can be used. For example, it is a carbon material such as lithium metal, graphite or amorphous carbon. Among them, it is particularly preferable to use a carbon material. Since the specific surface area can be made relatively large, and the lithium insertion and extraction speed is high, the charge / discharge characteristics at a large current and the output / regeneration density are good. In particular, in consideration of the balance between the output and the regenerative density, it is preferable to use a carbon material having a relatively large voltage change accompanying charging and discharging. Above all, it is preferable to use one made of natural graphite or artificial graphite having high crystallinity. By using such a highly crystalline carbon material, the lithium ion transfer efficiency of the negative electrode can be improved.
[0021]
When a carbon material is used as the negative electrode active material, a negative electrode mixture obtained by mixing the conductive material and the binder as described for the positive electrode is applied to the current collector, if necessary. It is preferable to use those obtained.
[0022]
The electrolytic solution is obtained by dissolving an electrolyte in an organic solvent. A gel electrolyte may be used instead of the electrolyte. As the gel electrolyte, one in which a polymer such as a vinylidene fluoride-hexafluoropropylene copolymer (p (VdF-HFP)) or the like is dispersed in an electrolyte solution described later can be used. p (VdF-HFP) gels by dispersing in the electrolytic solution.
[0023]
The organic solvent is not particularly limited as long as it is an organic solvent usually used for an electrolyte of a lithium secondary battery. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, oxolane compounds and the like can be used. In particular, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, tetrahydrofuran and the like, and a mixed solvent thereof are suitable. For example, a mixed organic solvent of a high dielectric constant main solvent such as ethylene carbonate and propylene carbonate and a low-viscosity auxiliary solvent such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate is preferable. Further, dimethoxyethane, tetrahydrofuran, butyl lactone, or the like may be used as a secondary solvent.
[0024]
The type of the electrolyte is not particularly limited, but an inorganic salt selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , a derivative of the inorganic salt, LiSO ₃ CF ₃ , LiC (SO ₃ CF ₃ ) _{2, LiN (SO 3 CF 3} ) 2, LiN (SO 2 C 2 F 5) 2 and _{LiN (SO} 2 CF ₃₎ organic salt selected from _{(SO 2 C 4 F 9)} , as well as derivatives of organic salts Preferably, at least one kind is used.
[0025]
By using these electrolytes, battery performance can be further improved, and the battery performance can be maintained even higher in a temperature range other than room temperature. The concentration of the electrolyte is also not particularly limited, and it is preferable to appropriately select the concentration in consideration of the type of the electrolyte and the organic solvent depending on the application.
[0026]
The separator serves to electrically insulate the positive electrode and the negative electrode and retain the electrolytic solution. For example, a porous synthetic resin film, particularly a porous film of a polyolefin polymer (polyethylene, polypropylene) may be used. Note that the separator is preferably larger than the positive electrode and the negative electrode in order to ensure insulation between the positive electrode and the negative electrode.
[0027]
[Secondary battery manufacturing method]
The method for manufacturing a secondary battery according to the present embodiment includes an encapsulation step, a degassing step, a resealing step, and other steps performed as necessary.
[0028]
(Encapsulation process)
The enclosing step is a step of enclosing the power generation element in the exterior body. The general method as described above can be used for the method of manufacturing the power generating element. The power generating element is manufactured before the main enclosing step. When a liquid electrolyte is used, the electrolyte can be injected into the exterior body during the encapsulation process.
[0029]
The exterior body is a member that isolates the power generation element from the outside of the exterior body. Generally, the power generation element is weak to moisture and the like, so that the exterior body is preferably made of a material having low moisture permeability so as to prevent moisture in the atmosphere from permeating into the exterior body. The exterior body has an unjoined portion that communicates with the inside of the exterior body and is isolated from the outside.
[0030]
As a method of enclosing the power generation element in the exterior body, the hermetically sealed exterior body can be obtained by wrapping the power generation element with an exterior film and then ultrasonically or thermally welding the opening. For example, a method of joining and closing an opening after inserting a power generation element into an exterior film formed in a bag shape in advance, and joining three sides of an opening after sandwiching the power generation element with a folded exterior film. There is a way to close.
[0031]
The unjoined portion is preferably provided at the same time as the opening is subjected to ultrasonic welding or the like. For example, the horn that irradiates ultrasonic waves or the part corresponding to the unjoined part of the mold when performing heat welding is easily formed by an operation such as ultrasonic welding by forming a shape that does not contact the unjoined part. Unjoined portions can be provided. Further, there is a method of forming an unbonded portion when a part of the outer periphery of the exterior film is bonded in advance and processed into a bag shape before enclosing the power generation element.
[0032]
The shape of the unjoined portion is not particularly limited. For example, a rectangular shape, a semicircular shape, an L-shape, and the like can be given. It is preferable that the size of the unjoined portion is large to some extent from the viewpoint of ease of degassing. For example, a case where the shape of the unjoined portion is rectangular will be described as an example. If the length (distance from the inner edge portion of the joined portion) or the width is small, the gas escapes at the same time as the electrolyte is drawn in and the electrolyte is discharged from the vent hole. May leak. If the unjoined portion is formed with a small width, the expansion of the unjoined portion can be reduced and the generation rate of wrinkles can be reduced. However, there is a possibility that the gas removal efficiency is reduced and the electrolyte solution leaks from the gas removal hole at the time of gas removal. Specifically, the size of the unjoined portion is preferably about 2 to 10 mm in length and about 5 to 30 mm in width. Further, the portion of the exterior body where the unjoined portion is provided is not particularly limited.
[0033]
(Conditioning process)
Conditioning can be performed by repeating charging and discharging of the power generating element for several cycles. Gas may be generated from the secondary battery due to conditioning.
[0034]
When performing the conditioning step, it is preferable to restrict the thickness and the like of the unjoined portion to a predetermined thickness or less, as in the gas release step described later. Since gas is generated in the conditioning step, if the exterior body is expanded without restricting the thickness of the unbonded portion and the like, inconveniences such as peeling of the bonded portion and generation of wrinkles in the resealing step may occur. Because. Further, it is preferable to restrict the thickness of the portion other than the unjoined portion of the exterior body to a second predetermined thickness or less, which will be described later.
[0035]
(Degassing process)
The degassing step is a step of discharging gas generated inside the exterior body. Degassing is performed by forming a degassing hole in the unjoined portion and connecting the inside and the outside of the exterior body. When the electrolyte of the secondary battery to be applied is a liquid, this step is performed while adjusting the position where the gas vent hole is formed to be upward so that the internal electrolyte does not leak.
[0036]
The gas vent hole can be formed by a method such as passing a needle through a predetermined portion. The location where the gas vent hole is formed is not particularly limited, but is desirably located farthest from the power generating element. The gas vent hole may be formed on either one or both of the two exterior films forming the unbonded portion. The size of the gas vent hole is not particularly limited, but is about 0.5 mm to 2.0 mm in diameter.
[0037]
The formation of the gas vent hole is performed while restricting the thickness of the unjoined portion to a predetermined thickness or less. By regulating the thickness of the unbonded portion, it is possible to suppress the occurrence of wrinkles in the unbonded portion and the separation of the bonded portion in the unbonded portion in the subsequent resealing step. The predetermined thickness is preferably between 4 and 20 times the thickness of the exterior film, and more preferably between 4 and 10 times.
[0038]
Furthermore, it is preferable that the thickness of the portion surrounding the power generating element together with the unjoined portion is also restricted to a certain thickness (second predetermined thickness) or less. By restraining the portion of the exterior body surrounding the power generation element, peeling of the exterior film can be suppressed, and gas pressure can be quickly released by pressing the exterior body. The second predetermined thickness is more preferably about the thickness of the exterior film and the power generating element.
[0039]
Further, it is preferable to restrain the joint portion of the exterior film. The degree of restraint is preferably such that the exterior film is pressed, more preferably about 1.5 to 2.0 times the thickness of the exterior film.
[0040]
There is no particular limitation on the method of regulating the thickness of the unjoined portion and the like. For example, it can be performed by a restraining jig that restrains an unjoined portion or the like by holding it in the thickness direction. FIG. 1 shows an example of the restraining jig. By sandwiching the power generating element 50 from the thickness direction with the restraining jigs 10 and 20, the thickness of the unjoined portion and the other parts of the exterior body can be regulated.
[0041]
In order to release gas more quickly, it is preferable to form a vacuum atmosphere after forming the gas release hole. By setting the entire exterior body in a vacuum atmosphere, gas generated or remaining in the interior of the exterior body can be removed.
[0042]
(Reseal process)
The resealing step is a step of joining the unjoined portions, closing the gas vent holes, and enclosing the power generating element again in the exterior body. As a method of closing the gas vent hole, a method in which the opening of the exterior film is joined in the encapsulation step can be used as it is.
[0043]
It is not particularly necessary to regulate the thickness of the unbonded portion when closing the gas vent hole. This is because the gas inside the exterior body is released and the internal pressure is low, so that the unbonded portion does not expand, and no wrinkles are generated even if thermal welding or ultrasonic welding is performed thereafter. For example, when the degassing step is performed by using the above-described restraining jig, the resealing step can be performed by taking out from the restraining jig.
[0044]
After closing the unjoined portion, the vicinity where the unjoined portion is formed can be cut to an appropriate size. When the electrolyte of the secondary battery to be applied is a liquid, this step is performed while adjusting the position where the gas vent hole is formed to be upward so that the internal electrolyte does not leak.
[0045]
(Function and effect)
With the above configuration, the method for manufacturing a secondary battery according to the present embodiment has the following operation and effects. First, in the enclosing step, the power generating element can be sealed inside the exterior body, and the influence of the external atmosphere (the influence of moisture and the like) on the power generating element is eliminated.
[0046]
A gas is generated from the power generating element due to a conditioning step performed after the enclosing step and a reaction of moisture mixed in the inside, and the exterior body is expanded. Here, the thickness of the unjoined portion and the thickness of the exterior body other than the unjoined portion can be regulated in advance, so that peeling of the joined portion can be prevented.
[0047]
In the degassing step, the gas inside the exterior body can be removed while suppressing the generation of wrinkles by forming a gas vent hole in the non-joined portion while restricting the thickness of the unjoined portion to a predetermined thickness or less. At the same time, the gas can be quickly and reliably removed from the exterior body by regulating the thickness of the exterior body other than the unjoined portion or by setting the atmosphere to a vacuum atmosphere. Since the gas vent hole is small and the internal pressure of the exterior body is high during the degassing step, the exterior body is less likely to be contaminated from the outside (such as mixing of moisture). Thereafter, by joining the unjoined portions, the inside and outside of the exterior body can be completely isolated.
[0048]
【Example】
Hereinafter, a method for manufacturing the secondary battery of the present invention will be described in detail with reference to FIGS.
[0049]
(Encapsulation process)
After bending the planar exterior film and sandwiching the power generation element 52, the three sides 511 were joined by heat welding. The thickness of the exterior film was 0.1 mm.
[0050]
First, both ends 511 in the direction perpendicular to the direction in which the exterior film was bent were joined to form an exterior film 51 enclosing the power generation element 52 therein, and then an electrolyte was injected into the exterior film 51.
[0051]
Thereafter, the remaining one side 511 was bonded while leaving the unbonded portion 512. The power generating element 52 has positive and negative external terminals electrically connected to the outside of the exterior body, but is omitted in the drawing.
[0052]
(Conditioning process)
The secondary battery 50 was conditioned while being held between the restraining jigs 10 and 20. The thickness t of the gap between the restraining jigs 10 and 20 at the portion holding the unjoined portion 512 was 2 mm, which was 20 times the thickness of the exterior film. In addition, portions of the restraining jigs 10 and 20 that sandwich the unjoined portion 512 have through holes 11 and 21 that are provided in the thickness direction of the unjoined portion 512. The size of the formed through holes 11 and 21 was 0.8 mm in diameter. Conditioning was performed by charging / discharging 5 cycles between 3.0 and 4.2 V at a current density of 10 A.
[0053]
(Degassing process)
A gas vent hole was formed in the unjoined portion 512 by passing a needle (diameter 0.5 mm) through the through holes 11 and 21. The penetration of the needle was performed so that the unbonded portion 512 was relatively higher than the power generation element 52 so that the electrolyte did not leak from the gas vent hole. In the following resealing step, the unbonded portion 512 was similarly set to be relatively higher.
[0054]
The portion of the exterior body 50 other than the unjoined portion 512 (the exterior body main body 513) is sandwiched between the restraining jigs 10 and 20 until the thickness of the power generation element 52 is added to the thickness of the exterior film. did. The gas in the exterior body was quickly discharged from the vent hole because the thickness of the exterior body was regulated. Further, the joint 511 was pressurized by being held between the restraining jigs 10 and 20.
[0055]
(Reseal process)
After taking out the secondary battery 50 from between the restraining jigs 10 and 20, the unbonded portion 512 was bonded by heat welding. The inside and outside of the exterior body 51 could be completely isolated. Thereafter, in the exterior body 51, a part where the unbonded part 512 was provided was long, so a part thereof was cut to shorten it.
[0056]
(Effect)
Since the thickness of the unbonded portion 512 was regulated during the degassing step, the expansion of the unbonded portion 512 due to the gas generated inside the exterior body 51 could be minimized. As a result, generation of wrinkles at the time of joining the unjoined portion 512 in the subsequent resealing step was able to be suppressed, and peeling of the joined portion 511 of the exterior body 51 was also able to be suppressed.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a secondary battery after an encapsulation step in the present embodiment.
FIG. 2 is a schematic view showing a conditioning step and a degassing step in the present embodiment.
[Explanation of symbols]
10, 20: restraining jigs 11, 21: through hole 50: secondary battery 51: exterior body (exterior film) 511: joined part 512: unjoined part 52: power generation element

Claims (5)

An enclosing step of enclosing the power generation element with an exterior film, leaving an unjoined portion communicating with the inside and isolated from the outside, joining an opening of the exterior film, and enclosing the power generation element inside the exterior body. When,
A conditioning step of conditioning the power generating element;
A gas venting step of opening a gas vent hole in the non-joined portion to communicate the inside and the outside of the exterior body while restricting the thickness of the unjoined portion to a predetermined thickness or less,
A resealing step of joining the unjoined portion, closing the gas vent hole, and enclosing the power generating element in the exterior body again. The method of manufacturing a secondary battery according to claim 1, wherein the conditioning step is a step performed while restricting the thickness of the unjoined portion to the predetermined thickness or less. 3. The method for manufacturing a secondary battery according to claim 1, wherein a thickness of a portion surrounding the power generation element together with the unjoined portion is also restricted to a second predetermined thickness or less. 4. The method for manufacturing a secondary battery according to claim 1, wherein the predetermined thickness is between 4 times and 20 times the thickness of the exterior film. The method for manufacturing a secondary battery according to claim 1, wherein the restraining is performed by a restraining jig restraining by holding in a thickness direction.

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