CN115668604A - Packaging film, and tab lead and secondary battery using same - Google Patents
Packaging film, and tab lead and secondary battery using same Download PDFInfo
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- CN115668604A CN115668604A CN202180039809.3A CN202180039809A CN115668604A CN 115668604 A CN115668604 A CN 115668604A CN 202180039809 A CN202180039809 A CN 202180039809A CN 115668604 A CN115668604 A CN 115668604A
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- polypropylene
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- WABPQHHGFIMREM-UHFFFAOYSA-N lead(0) Chemical compound [Pb] WABPQHHGFIMREM-UHFFFAOYSA-N 0.000 claims description 2
- 238000009413 insulation Methods 0.000 abstract description 16
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- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 1
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- 229910052726 zirconium Inorganic materials 0.000 description 1
Images
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/10—Primary casings; Jackets or wrappings
- H01M50/183—Sealing members
- H01M50/186—Sealing members characterised by the disposition of the sealing members
- H01M50/188—Sealing members characterised by the disposition of the sealing members the sealing members being arranged between the lid and terminal
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/10—Primary casings; Jackets or wrappings
- H01M50/102—Primary casings; Jackets or wrappings characterised by their shape or physical structure
- H01M50/105—Pouches or flexible bags
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/10—Primary casings; Jackets or wrappings
- H01M50/183—Sealing members
- H01M50/19—Sealing members characterised by the material
- H01M50/195—Composite material consisting of a mixture of organic and inorganic materials
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/10—Primary casings; Jackets or wrappings
- H01M50/183—Sealing members
- H01M50/19—Sealing members characterised by the material
- H01M50/197—Sealing members characterised by the material having a layered structure
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/10—Primary casings; Jackets or wrappings
- H01M50/183—Sealing members
- H01M50/19—Sealing members characterised by the material
- H01M50/198—Sealing members characterised by the material characterised by physical properties, e.g. adhesiveness or hardness
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/10—Primary casings; Jackets or wrappings
- H01M50/116—Primary casings; Jackets or wrappings characterised by the material
- H01M50/124—Primary casings; Jackets or wrappings characterised by the material having a layered structure
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Composite Materials (AREA)
- Inorganic Chemistry (AREA)
- Materials Engineering (AREA)
- Sealing Battery Cases Or Jackets (AREA)
- Laminated Bodies (AREA)
Abstract
The packaging film of the present invention is characterized in that: the packaging film is a 3-layer multilayer packaging film composed of a core layer and surface layers formed on both surfaces of the core layer, wherein the core layer contains polypropylene having a melting point of 155-166 ℃ and a Melt Flow Rate (MFR) of 0.5-5 g/10min, the surface layers contain polypropylene having a melting point of 120-150 ℃ and a Melt Flow Rate (MFR) of 1-40 g/10min, and the core layer has a Charpy strength of 15kJ/m at 23 ℃ in a secondary battery covered with a packaging body 2 The thickness of the sealing film is 30 to 300 [ mu ] m, and the ratio of the thickness of the surface layer to the thickness of the core layer is 0.2 to 5. The packaging film can be used for making insulation and sealingA secondary battery having excellent characteristics.
Description
Technical Field
The present invention relates to a sealing film which is arranged between a lead conductor connected to a positive electrode or a negative electrode and an exterior package in a secondary battery covered with the exterior package and is heat-sealed. Also relates to a tab lead using the packaging film. Further relates to a secondary battery using the encapsulation film.
Background
In recent years, the size and function of mobile devices have been increasingly reduced, and the size and capacity of batteries mounted on such devices have been strongly desired. Conventionally, cylindrical batteries represented by 18650 batteries have been the mainstream of secondary batteries such as lithium ion batteries, but rectangular batteries have been developed to reduce the dead space in the device and extend the life. However, in order to further reduce the dead space and to make the battery lighter, a pouch type (pouch type) secondary battery using an exterior material in which a polyolefin film or a polyamide film is laminated with a metal foil has been developed as a new form of the secondary battery. The pouch-type secondary battery has been studied for use not only in portable devices but also in other fields, and has been put into practical use as a Storage battery for Electric Vehicles (EV) and a stationary Storage battery for Energy Storage Systems (ESS).
In order to safely use such a pouch-type secondary battery, when an abnormal reaction or a temperature increase occurs in the battery, it is necessary to prevent the electrolyte inside from leaking out, and sufficient sealing is required for the pouch. In particular, a portion of the lead conductor extending from the electrode to the outside tends to be insufficient in sealing property, and reliable packaging is required. On the other hand, if the temperature or pressure of the laminating operation is excessively high for reliable packaging, the metal foil contained in the outer package may come into contact with the lead conductor to cause short-circuiting. Therefore, various methods have been proposed, such as a method of sandwiching an encapsulating film between an outer package and a lead conductor and performing heat sealing.
Patent document 1 describes a metal terminal-coated resin film for a secondary battery, which is a laminate of metal terminals connected to a positive electrode or a negative electrode of a secondary battery, and which has a 3-layer structure of the resin film, an intermediate layer of the resin film being a core layer, and other layers being surface layers, wherein the melt flow rate of at least 1 resin layer constituting the resin film is 0.1 to 2.5g/10min, and the difference in melt flow rate between the core layer and the surface layers is 5 to 30g/10min. In the examples, acid-denatured polypropylene having a melt flow rate of 10 to 15g/10min is used for the surface layer, and polypropylene having a melt flow rate of 0.7 to 1g/10min is used for the core layer. This ensures insulation by the core layer and wrappability of the resin by the surface layer.
In recent years, the size of a pouch-type lithium ion secondary battery has been increased for EV use or ESS use. In the heat-sealing step of the exterior package in the production of such a large-sized battery, the heat-sealing step is performed with a larger amount of heat than in the case of a small-sized battery, and therefore, the risk of occurrence of a failure due to a short circuit is further increased. Further, there is a problem that the sealing film is broken by gas generated in the battery due to vaporization or decomposition of the electrolyte and the internal pressure rises, and the sealing property of the secondary battery cannot be maintained. The films and sealing materials described in patent documents 1 and 2 do not have sufficient performance to solve such problems.
Documents of the prior art
Patent document
Patent document 1: japanese patent laid-open No. 2014-132538
Patent document 2: japanese laid-open patent publication No. 2014-225378
Disclosure of Invention
Technical problem to be solved by the invention
The present invention has been made to solve the above problems, and an object of the present invention is to provide: a secondary battery excellent in insulation and sealing properties is provided, in which a sealing film is sandwiched between a lead conductor and an outer package and heat-sealed, whereby a short circuit between a metal layer in the outer package and the lead conductor can be prevented, and in which a sealed portion is prevented from being broken and leaking liquid when the pressure inside the battery rises. The invention also aims to: provided are an encapsulation film for such a secondary battery and a tab lead using the encapsulation film.
Technical solution for solving technical problem
The above technical problem can be solved by providing an encapsulating film characterized in that: a sealing film which is arranged between a lead conductor connected to a positive electrode or a negative electrode and an exterior package and is heat-sealed in a secondary battery covered with the exterior package; the packaging film is a 3-layer multilayer packaging film comprising a core layer and skin layers formed on both surfaces of the core layer, wherein the core layer contains polypropylene having a melting point of 155-166 ℃ and a Melt Flow Rate (MFR) of 0.5-5 g/10min, the skin layers contain polypropylene having a melting point of 120-150 ℃ and a Melt Flow Rate (MFR) of 1-40 g/10min, and the core layer has a Charpy strength of 15kJ/m at 23 DEG C 2 The thickness of the sealing film is 30 to 300 μm, and the ratio of the thickness of the surface layer to the thickness of the core layer is 0.2 to 5.
In this case, it is preferable that the core layer contains polypropylene having a melting point of 158 to 166 ℃ and a Melt Flow Rate (MFR) of 1 to 3g/10min, and the skin layer contains polypropylene having a melting point of 128 to 150 ℃ and a Melt Flow Rate (MFR) of 1 to 7g/10 min.
In this case, the polypropylene contained in at least one of the surface layers is also preferably modified with an unsaturated carboxylic acid, an unsaturated carboxylic acid anhydride or an unsaturated epoxy compound. The polypropylene contained in the core layer is also preferably a polypropylene block copolymer.
In this case, it is preferable that one of the surface layers is a metal adhesive layer to be bonded to the lead conductor, and the other surface layer is a package adhesive layer to be bonded to the outer package, the polypropylene contained in the metal adhesive layer is a polypropylene modified with an unsaturated carboxylic acid, an unsaturated carboxylic acid anhydride or an unsaturated epoxy compound, and the polypropylene contained in the package adhesive layer is a polypropylene modified with an unsaturated carboxylic acid, an unsaturated carboxylic acid anhydride or an unsaturated epoxy compound, or a polypropylene random copolymer.
The melting point of the polypropylene contained in the package adhesive layer is preferably higher than the melting point of the polypropylene contained in the metal adhesive layer. Preferably, the MFR of the polypropylene contained in the metal adhesive layer is higher than both the MFR of the polypropylene contained in the core layer and the MFR of the polypropylene contained in the package adhesive layer.
The above-described problems can also be solved by providing a tab lead in which both surfaces of a part of a lead conductor are covered with the above-described sealing film.
The above-described problems can also be solved by providing a secondary battery comprising: a power generation element including a positive electrode, a negative electrode, an electrolyte, and a separator; an outer package body which houses the power generating element and has a peripheral edge portion heat-sealed; a lead conductor connected to the positive electrode or the negative electrode and led out to the outside of the exterior package; and a sealing film disposed between the outer package and the lead conductor and heat-sealed, wherein the outer package is formed of a multilayer film including at least a metal layer and a sealing resin layer, and the sealing film is the sealing film.
Effects of the invention
The sealing film of the present invention is excellent in insulation and sealing properties. Therefore, by sandwiching and heat-sealing such an outer package film between the lead conductor of the secondary battery and the outer package, it is possible to prevent a short circuit between the metal layer in the outer package and the lead conductor, and to prevent the sealed portion from being broken and leaking when the pressure inside the battery rises. Therefore, a secondary battery having excellent insulation and sealing properties and a tab lead used for manufacturing the secondary battery can be provided. In particular, even when the secondary battery is increased in size, sufficient insulation and sealing properties can be exhibited.
Drawings
Fig. 1 is a cross-sectional view of a multilayer film.
Fig. 2 is a view showing the external appearance of the secondary battery of the present invention.
Fig. 3 is a sectional view of a heat-sealed portion of the secondary battery of the present invention.
Fig. 4 is an X-Y sectional view of fig. 2.
Fig. 5 is a view showing a method of measuring the development rate of the sealing film before and after heat sealing.
Fig. 6 is a diagram showing a method of measuring the adhesive strength.
Detailed Description
The present invention relates to a sealing film which is arranged between a lead conductor connected to a positive electrode or a negative electrode and an exterior package and is heat-sealed in a secondary battery covered with the exterior package. As shown in fig. 1, the sealing film 20 of the present invention is a 3-layer multilayer sealing film including a core layer 21 and surface layers 22 and 23 formed on both surfaces thereof.
Fig. 2 shows the appearance of the secondary battery 10 of the present invention using the sealing film 20. Fig. 3 is a sectional view of a heat-sealed portion of the secondary battery 10 of the present invention. The secondary battery 10 of the present invention includes: a power generation element including a positive electrode, a negative electrode, an electrolyte, and a separator; an outer package 40 in which the power generating element is housed and the peripheral edge portion of which is heat-sealed; a lead conductor 31 connected to the positive electrode or the negative electrode and led out to the outside of the exterior package 40; and an encapsulating film 20 disposed between the outer package 40 and the lead conductors 31 and heat-sealed. The outer package 40 in this case is composed of a multilayer film including a metal layer 42 for preventing permeation of oxygen and moisture and a sealing resin layer 41 for heat sealing, and is sealed in a bag shape in many cases. In this case, the sealing film 20 of the present invention may be used to prevent short-circuiting between the lead conductors 31 and the metal layer 42 in the outer package 40 and to improve the sealing between the lead conductors 31 and the outer package 40.
As described in the background section, in recent years, lithium ion secondary batteries have been increased in size, and in the heat sealing step of the outer package in this case, the risk of occurrence of a failure due to a short circuit is further increased because the heat sealing step is performed using a larger amount of heat than in the case of a small battery. Therefore, the sealing film is required to have higher insulation properties. As one of the proposals for improving the insulation properties, as described in patent documents 1 and 2, it is proposed to make the sealing film have a 3-layer structure of polypropylene and to make the melting point, melt viscosity, and load deformation temperature of the polypropylene in the core layer higher than those in the surface layer. This makes it possible to melt and flow the surface layer easily, to perform thermal bonding, and to maintain a sufficient thickness of the core layer while withstanding the pressure from the top, thereby ensuring insulation properties.
When a secondary battery is used, the pressure inside the secondary battery may increase when the temperature increases, the electrolyte decomposes and vaporizes, or an external force is applied. The present inventors have noticed that, when the internal pressure of the secondary battery is extremely high, if the sealing film having a 3-layer structure of polypropylene is used, the sealing film may be broken and the electrolyte may leak. In order to clarify the cause, the cross-sectional shape of the bonded portion of the sealing film was observed.
Fig. 4 is an X-Y sectional view of fig. 2 of a secondary battery having the structure described in comparative example 1 of the present invention. In fig. 4, the left side is a heat-sealed portion, and the right side is the battery interior. At this time, in the heat-sealed portion, the metal layer 42 in the outer package 40 is close to the lead conductor 31, and the thickness of the sealing resin layer 41 and the surface layers 22 and 23 is greatly reduced, but the core layer 21 maintains a sufficient thickness, and insulation between the metal layer 42 and the lead conductor 31 is secured. However, it was found that in the core layer 21 near the sealing portion, a partially protruding protrusion 5 was formed, and a notch 6 was formed beside it. This is presumably because the polypropylene having a low melting point, which forms the sealing resin layer 41 and the surface layer 23, easily flows out, whereas the polypropylene having a high melting point, which forms the core layer 21, cannot easily flow and is plastically deformed. Considering that this notch 6 becomes a weak point and promotes breakage, the inventors of the present invention have found that by using polypropylene having excellent impact resistance for the core layer 21, the encapsulating film 20 having excellent sealability can be obtained, and the above-mentioned technical problems can be solved.
The packaging film of the present invention thus found is characterized in that: which is a 3-layer multilayer packaging film composed of a core layer and skin layers formed on both surfaces thereof,
the core layer contains polypropylene having a melting point of 155 to 166 ℃ and a Melt Flow Rate (MFR) of 0.5 to 5g/10min,
the surface layer contains polypropylene having a melting point of 120 to 150 ℃ and a Melt Flow Rate (MFR) of 1 to 40g/10min,
the Charpy strength of the core layer at 23 ℃ is 15kJ/m 2 In the above-mentioned manner,
the thickness of the encapsulating film is 30 to 300 mu m, and,
the ratio of the thickness of the surface layer to the thickness of the core layer is 0.2 to 5.
In this way, in the encapsulating film 20 of the present invention, the kind of polypropylene is used separately for the core layer 21 and the skin layers 22 and 23. Among the polypropylenes used are polypropylene homopolymers (H-PP), polypropylene random copolymers (R-PP) and polypropylene block copolymers (B-PP), and are commercially available from various polypropylene manufacturers. The polypropylene homopolymer is a compound obtained by polymerizing only a propylene monomer, and has a high melting point and a high elastic modulus. The polypropylene random copolymer is a compound obtained by randomly copolymerizing propylene and a small amount of other comonomer, and the comonomer is randomly incorporated into a polypropylene chain. The random copolymer has a reduced melting point and a reduced elastic modulus compared to the homopolymer. The polypropylene block copolymer has a structure in which a chain of a polypropylene homopolymer is connected to a chain of a polymer of a small amount of another comonomer. The block copolymer shows a melting point and an elastic modulus similar to those of the homopolymer, and the impact resistance is improved. Polypropylene homopolymer, polypropylene random copolymer and polypropylene block copolymer are commercially available, and although the chemical composition is not clearly shown, the melting point, melt flow rate, elastic modulus, charpy strength, and the like are shown in the list, and therefore they can be appropriately selected and used.
The largest feature of the encapsulating film 20 of the present invention is: the core layer 21 contains polypropylene having a melting point of 155 to 166 ℃ and a Melt Flow Rate (MFR) of 0.5 to 5g/10min, and the summer strength of the core layer 21 at 23 ℃ is 15kJ/m 2 The above.
The melting point of polypropylene contained in the core layer 21 is 155 to 166 ℃. When the melting point is less than 155 ℃, the difference between the melting point and the melting point of the polypropylene contained in the surface layers 22 and 23 is small, which is not preferable. In the heat sealing step, after the surface layers 22 and 23 are melted, the surface layers 22 and 23 are heat-sealed with the lead conductor 31 or the outer package 40. In this case, since the melting point of the polypropylene contained in the core layer 21 is set to 155 ℃ or higher, the core layer 21 is less likely to flow than the surface layers 22 and 23 even when heated and pressurized in the heat sealing step, and thus a certain thickness can be secured as the core layer 21, and excellent insulation properties can be obtained. The melting point is preferably 158 ℃ or higher, more preferably 161 ℃ or higher, and still more preferably 163 ℃ or higher. On the other hand, the melting point is preferably 165 ℃ or lower. The melting point in the present specification means a melting peak temperature (. Degree. C.) measured at a temperature rise rate of 10 ℃/min in 2nd Run measurement using a Differential Scanning Calorimeter (DSC). When 2 or more melting peaks are observed, the temperature of the peak having the highest peak height based on the base line is set as the melting peak temperature (c) of the polypropylene contained in the core layer 21. The skin layers 22, 23 are also identical.
The polypropylene contained in the core layer 21 has an MFR of 0.5 to 5g/10min. When the MFR is less than 0.5g/10min, the viscosity becomes too high to stably form the sealing film 20. The MFR is preferably 1g/10min or more, more preferably 1.2g/10min or more, and still more preferably 1.5g/10min or more. On the other hand, when the MFR exceeds 5g/10min, the fluidity of polypropylene becomes too high in the heat-sealing step, and the thickness of the core layer 21 in the seal portion becomes too thin, so that excellent insulation properties cannot be obtained. The MFR is preferably 3g/10min or less, more preferably 2.8g/10min or less, still more preferably 2.5g/10min or less, and particularly preferably 2.0g/10min or less. The MFR in the present specification is a value measured at 230 ℃ under a load of 2.16kg in accordance with JIS K7210.
The core layer 21 has a Charpy strength of 15kJ/m at 23 DEG C 2 The above is important. The summer strength of the core layer 21 was set to 15kJ/m 2 As described above, the package film 20 can be prevented from breaking from the weak point formed in the core layer 21. The Charpy strength is preferably 20kJ/m 2 More preferably 40kJ/m or more 2 The concentration is more preferably 60kJ/m 2 The above. On the other hand, the Charpy strength is usually 200kJ/m 2 The following. The Charpy strength in the present specification is a value measured at 23 ℃ by the 1eA method (notched) according to JIS K7111-1.
The polypropylene contained in the core layer 21 is preferably a polypropylene block copolymer. Since the polypropylene contained in the core layer 21 is a polypropylene block copolymer, the encapsulating film 20 can be effectively prevented from being broken from the weak point of the core layer 21. Among them, polypropylene block copolymers are known to have relatively high melting point and elastic modulus and high charpy strength, and are generally used for injection molded articles requiring impact resistance. On the other hand, the extrusion moldability is not necessarily good, and the film is less suitable for a soft film in some cases. And a Charpy strength at 23 ℃ of 15kJ/m 2 The above are only some of the levels therein. Therefore, selecting polypropylene block copolymers, which are generally rarely used for film molding, and thus selecting compounds having a charpy strength above a certain level, and using them for the core layer 21 of the encapsulation film 20 of the present invention is a choice beyond the usual design.
In the encapsulating film 20 of the present invention, the skin layers 22 and 23 contain polypropylene having a melting point of 120 to 150 ℃ and a Melt Flow Rate (MFR) of 1 to 40g/10min.
The melting point of the polypropylene contained in the surface layers 22 and 23 is 120 to 150 ℃. When the melting point is less than 120 ℃, heat resistance to heat generation when the secondary battery 10 is used or heat from the outside is reduced. The melting point is preferably 128 ℃ or higher, more preferably 130 ℃ or higher, and still more preferably 135 ℃ or higher. On the other hand, when the melting point exceeds 150 ℃, the difference in melting point with the polypropylene contained in the core layer 21 becomes small, and therefore, the core layer 21 is also easily melted in the heat sealing step, and excellent insulation cannot be obtained. The melting point is preferably 148 ℃ or lower, more preferably 146 ℃ or lower.
The polypropylene contained in the skin layers 22, 23 has an MFR of 1 to 40g/10min. When the MFR is less than 1g/10min, the viscosity becomes too high, and the sealing film 20 cannot be stably formed. The MFR is preferably 1.5g/10min or more, more preferably 2g/10min or more. On the other hand, when the MFR exceeds 40g/10min, the difference from the MFR of the polypropylene contained in the core layer 21 becomes large, and in this case, the encapsulant film 20 cannot be stably formed, and the mechanical strength of the skin layers 22 and 23 also decreases. The MFR is preferably 7g/10min or less, more preferably 6.5g/10min or less, and still more preferably 6g/10min or less.
In the sealing film 20 of the present invention, the MFR of the polypropylene contained in the skin layers 22 and 23 s MFR relative to the polypropylene contained in the core layer 21 c Ratio of (MFR) s /MFR c ) Preferably 0.8 to 7. Ratio (MFR) s /MFR c ) If the amount is less than 0.8, the flowability of the polypropylene in the core layer 21 becomes too high in the heat-sealing step, and the thickness of the obtained core layer 21 becomes thin, which may lower the insulation properties. Ratio (MFR) s /MFR c ) More preferably 1 or more, and still more preferably 1.5 or more. On the other hand, in the ratio (MFR) s /MFR c ) If the viscosity exceeds 7, the viscosity of the surface layers 22 and 23 becomes too low, and the sealing film 20 may not be stably formed. Ratio (MFR) s /MFR c ) More preferably 6 or less, and still more preferably 4 or less.
The polypropylene contained in at least one of the surface layers 22, 23 is preferably modified with an unsaturated carboxylic acid, an unsaturated carboxylic acid anhydride or an unsaturated epoxy compound. These modifications may be random copolymerization or block copolymerization, or may be graft modification.
In the present invention, one of the surface layers 22 and 23 is preferably a metal adhesive layer 22 to which the lead conductor 31 is bonded, and the other is preferably a package adhesive layer 23 to which the outer package 40 is bonded. In this case, the polypropylene contained in the metal adhesive layer 22 is preferably polypropylene modified with an unsaturated carboxylic acid, an unsaturated carboxylic acid anhydride, or an unsaturated epoxy compound. This can improve adhesion to the lead conductor 31. Among them, the polypropylene is preferably a polypropylene modified with an unsaturated carboxylic acid or an unsaturated carboxylic acid anhydride.
The polypropylene contained in the metal adhesive layer 22 and the polypropylene contained in the package adhesive layer 23 may be the same type of polypropylene or different types of polypropylene. Since the same type of polypropylene is used, the metal adhesive layer 22 and the sealing body adhesive layer 23 are not distinguished from each other in the sealing film 20, it is not necessary to identify the front and back surfaces during sealing operation, workability is improved, and defective products due to incorrect identification of the front and back surfaces can be prevented.
On the other hand, in the case where different types of polypropylene are used for the metal adhesive layer 22 and the package adhesive layer 23, it is preferable that the polypropylene contained in the metal adhesive layer 22 is a polypropylene modified with an unsaturated carboxylic acid, an unsaturated carboxylic acid anhydride, or an unsaturated epoxy compound, and the polypropylene contained in the package adhesive layer 23 is a polypropylene random copolymer not so modified. This reduces the manufacturing cost of the sealing film 20, and ensures adhesion to the lead conductors 21.
The melting point of the polypropylene contained in the package adhesive layer 23 is preferably higher than the melting point of the polypropylene contained in the metal adhesive layer 22. In the heat sealing step, heat is applied from the outer package 40 side, but by making the melting point of the polypropylene contained in the package adhesive layer 23 higher than the melting point of the polypropylene contained in the metal adhesive layer 22, the polypropylene contained in the package adhesive layer 23 to which heat has been applied first can be prevented from excessively flowing and diffusing. In this case, the difference between the melting point of the polypropylene contained in the package adhesive layer 23 and the melting point of the polypropylene contained in the metal adhesive layer 22 is preferably 2 ℃.
Preferably, the MFR of the polypropylene contained in the metal adhesive layer 22 is higher than both the MFR of the polypropylene contained in the core layer 21 and the MFR of the polypropylene contained in the package adhesive layer 23. This allows the polypropylene contained in the metal adhesive layer 22 to be wound around the lead conductor 31 without a gap. The difference between the MFR of the polypropylene contained in the metal adhesive layer 22 and the MFR of the polypropylene contained in the core layer 21 and the MFR of the polypropylene contained in the package adhesive layer 23 is preferably 1 or more.
The core layer 21 or the skin layers 22 and 23 of the encapsulating film 20 of the present invention each contain polypropylene. The polypropylene content of each layer is usually 50% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more. Various additives that can be generally used, such as a filler and a colorant, may be contained in addition to the polypropylene. In addition, other resins other than polypropylene may be contained, and the content of the other resins in this case is usually 20% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, and preferably substantially none.
The thickness of the sealing film 20 is 30 to 300 μm. When the thickness of the sealing film 20 is less than 30 μm, short-circuiting between the lead conductor 31 and the metal layer 42 in the outer package 40 cannot be sufficiently prevented. The thickness of the sealing film 20 is preferably 50 μm or more, and more preferably 70 μm or more. On the other hand, when the thickness of the encapsulating film 20 exceeds 300 μm, not only the weight but also the cost increases. The thickness of the sealing film 20 is preferably 250 μm or less, more preferably 200 μm or less, and still more preferably 150 μm or less.
The ratio of the thickness of the surface layers 22 and 23 to the thickness of the core layer 21 is 0.2 to 5. If the ratio is less than 0.2, the adhesion of the sealing film 20 to the lead conductors 31 and the outer package 40 is reduced. The ratio is preferably 0.3 or more, and more preferably 0.5 or more. On the other hand, when the ratio exceeds 5, excellent insulation properties cannot be obtained. The ratio is preferably 4 or less, more preferably 3 or less. The thicknesses of the surface layers 22 and 23 are the thicknesses of the metal adhesive layer 22 and the package adhesive layer 23, respectively.
The lead conductor 31 used in the secondary battery of the present invention is a metal strip-shaped member connected to the positive electrode or the negative electrode, and can be charged and discharged therethrough. As the lead conductor 31 connected to the positive electrode, aluminum is mainly used. As the lead conductor 31 connected to the negative electrode, nickel, a material obtained by plating nickel on copper, or a clad material of copper and nickel is mainly used. In order to improve the corrosion resistance of these metal materials or to improve the adhesion to the sealing film 20, the metal materials may be treated with 6-valent chromate, 3-valent chromate, or a surface treatment agent based on zirconium or manganese, or an organic surface treatment agent containing polyvinyl alcohol or polyacrylic acid as a main component. The lead conductor 31 is generally 0.05 to 1mm thick and 2 to 100mm wide.
The tab lead 30 used in the secondary battery 10 of the present invention is formed by covering both surfaces of a part of the lead conductor 31 with the sealing film 20. By heat-sealing the package film 20 and the lead conductors 31 in advance, the space between the lead conductors 31 and the package film 20 can be reliably sealed, and positioning is facilitated when the outer package 40 is heat-sealed. Since one end of the lead conductor 31 is connected to the positive electrode or the negative electrode and the other end is connected to the charging/discharging device, the middle portion thereof is covered with the sealing film 20. The outer package 40 is heat-sealed at a position overlapping the sealing film 20.
The exterior package 40 used for the secondary battery 10 of the present invention is composed of a multilayer film including at least a metal layer 42 and a sealing resin layer 41. The metal layer 42 preferably further has a surface resin layer 43 on the outer side. The surface resin layer 43 may be appropriately printed, or the surface resin layer 43 may be formed of a plurality of resin layers. The overall thickness of the outer package 40 is usually 50 to 500 μm.
The resin constituting the sealing resin layer 41 may be any resin that can be heat-sealed, and a thermoplastic resin is usually used. Preferably, polyolefins are used, particularly preferably polypropylene. The thickness of the sealing resin layer 41 is usually 30 to 200 μm. The resin constituting the surface resin layer 43 is not particularly limited, and polyamide resin, polyester resin, polyolefin resin, polystyrene resin, thermoplastic polyimide resin, phenoxy resin, epoxy resin, acetal resin, fluorine resin, or the like can be used according to the application. The thickness of the surface resin layer 43 is usually 30 to 400 μm. The metal constituting the metal layer 42 is not particularly limited, and aluminum is preferable in view of workability, flexibility, cost, and the like. A metal foil having a thickness of 5 to 100 μm may be used, or a deposited film having a thickness of 0.1 to 2 μm may be used.
In the secondary battery 10 of the present invention, the power generating element including the positive electrode, the negative electrode, the electrolyte, and the separator is housed and sealed by heat-sealing the peripheral edge portion of the outer package. The type of the secondary battery 10 is not limited, and a lithium ion battery is preferable. The so-called bag-shaped state in which 2 outer packages 40 face each other and the power generating element is housed is preferable.
As a method for manufacturing the tab lead 30, a method may be employed in which the sealing film 20 is vertically disposed at a predetermined position of the lead conductor 31, and then the welded portion is heated and pressed from top to bottom. At this time, not only the heating from the top down, but also the lead conductors 31 are heated at the same time, so that the excessive flow of the sealing film 20 is suppressed, and the welding can be easily performed with the width almost the same as the width of the sealing film 20. Further, when the pressing is performed, a buffer material such as silicone rubber or a teflon sheet is disposed between the pressing head and the lead conductor 31, and the resin can be satisfactorily wound around the end of the lead conductor 31.
The outer package 40 housing the power generating element is stacked on the portion of the tab lead 30 thus obtained covered with the sealing film 20, and the peripheral edge portion of the outer package 40 is heated and pressurized from both sides, thereby manufacturing the secondary battery 10. Instead of manufacturing the tab lead 30 in advance, the lead conductor 31 and the sealing film 20 may be overlapped and heat-sealed at the same time when the exterior package 40 is closed.
The secondary battery 10 of the present invention thus obtained is a secondary battery 10 that can prevent a short circuit between the metal layer 42 and the lead conductor 31 in the exterior package 40 and has excellent sealing properties and insulating properties. The outer package 40 can be used particularly usefully in a large secondary battery or the like in which heat sealing conditions are strict and high reliability is required.
Examples
Example 1
[ production of packaging film ]
In the production of the encapsulating film 20, a 3-layer co-extrusion film production apparatus having 3 extruders was used. The polypropylene random copolymer pellets (R-PP) were fed into one extruder for the outer layer (for the package adhesive layer 23), and the acid-modified propylene random copolymer pellets (A-PP) were fed into the other extruder for the outer layer (for the metal adhesive layer 22). The polypropylene block copolymer pellets (B-PP) were put into the core layer 21 in an extruder. The extrusion temperature of 3 extruders was set at 200 ℃ and the temperature of a manifold-type T die was set at 220 ℃ to carry out coextrusion molding. In this manner, a multilayer film having a 3-layer structure with a total thickness of 100 μm, in which the thickness of the package adhesive layer 23 was 20 μm, the thickness of the core layer 21 was 30 μm, and the thickness of the metal adhesive layer 22 was 50 μm, was obtained, and the multilayer film was cut to obtain a 4mm × 8mm package film 20.
[ production of tab lead ]
An aluminum plate (A1050) having a thickness of 0.1mm was cut out to prepare a lead conductor 31 having a length of 13mm and a width of 4mm. As shown in fig. 5 (a), the lead conductors 31 are sandwiched between 2 sheets of the sealing film 20, and are sandwiched between a silicone rubber sheet having a thickness of 0.2 mm. At this time, the length a of the encapsulating film 20 is measured.
Subsequently, the tab lead 30 was heated and pressed at 170 ℃ for 5 seconds to obtain a tab lead having both surfaces covered with the sealing film 20. The resultant tab lead 30 is shown in fig. 5 (b). Outside the lead conductors 31 having a width of 4mm, the encapsulating films 20 were bonded to each other with a width of 4.1 mm. The length B was measured, and the development rate of the sealing film 20 was measured by the following equation. A smaller value indicates that the secondary battery 10 having excellent insulation properties can be obtained.
Development rate (%): [ ((Length B) - (Length A))/(Length A) ] × 100
[ measurement of adhesive Strength ]
As the outer package material, a multilayer film was used in which a polyamide layer 25 μm/an aluminum foil 50 μm/a polypropylene layer 25 μm was laminated in this order from the outermost layer. The resultant was cut into a rectangular shape having a length of 100mm × a width of 20mm, and then brought into contact with both surfaces of the portion of the sealing film 20 of the tab lead 30 thus produced (contact area: 3mm × 8 mm). At this time, 2 sheets of outer packaging material were arranged in the direction in which the polypropylene layer of the outer packaging material was in contact with the sealing film 20. Subsequently, the sample was heated and pressed at 180 ℃ and 0.3MPa for 5 seconds by a hot press having a width of 2mm to obtain a sample. Then, using the obtained sample, as shown in fig. 6, the outer packaging material of the portion which is not welded to the outer packaging film 20 was sandwiched by a chuck, and stretching was performed at a speed of 50 mm/min using a tensile tester. As a result, the force required for the destruction was 2.7kgf/4mm. The larger the force required for this destruction is, the more excellent the sealing property of the secondary battery 10 can be obtained. The broken portion was observed by an optical microscope, and the breakage was aggregation breakage of the outer package material (evaluation result a in table 1). The results are summarized in Table 1.
Examples 2 to 6 and comparative examples 1 to 4
An encapsulating film 20 was produced and evaluated in the same manner as in example 1, except that the types of polypropylene forming the encapsulant adhesive layer 23, the core layer 21, and the metal adhesive layer 22 were changed as shown in tables 1 and 2. As shown in table 1, 2 melting peaks (134 ℃ and 104 ℃) of the polypropylene contained in the package adhesive layer 23 of example 5 were observed. Since the peak height at 134 ℃ is higher than the peak height at 104 ℃,134 ℃ is used as the melting point of polypropylene contained in the package adhesive layer 23. The results are summarized in tables 1 and 2. Here, when the portion broken in the tensile test is aggregation breakdown of the sealing film 20, the evaluation result is B.
Description of the symbols
10. Secondary battery
20. Packaging film
21. Core layer
22. Surface layer (Metal bonding layer)
23. Surface layer (packaging body adhesive layer)
30. Tab lead wire
31. Lead conductor
40. External packing packaging body
41. Sealing resin layer
42. Metal layer
43. Surface resin layer
5. Projection part
6. And (4) a notch.
Claims (9)
1. An encapsulation film, characterized in that:
a sealing film which is arranged between a lead conductor connected to a positive electrode or a negative electrode in a secondary battery covered with an outer package and the outer package and is heat-sealed;
the packaging film is a 3-layer multilayer packaging film composed of a core layer and surface layers formed on both surfaces thereof,
the core layer contains polypropylene with a melting point of 155-166 ℃ and a melt flow rate MFR of 0.5-5 g/10min,
the surface layer contains polypropylene having a melting point of 120-150 ℃ and a melt flow rate MFR of 1-40 g/10min,
the core layer has a Charpy strength of 15kJ/m at 23 DEG C 2 In the above-mentioned manner,
the thickness of the encapsulation film is 30 to 300 mu m, and,
the ratio of the thickness of the surface layer to the thickness of the core layer is 0.2 to 5.
2. The encapsulation film of claim 1, wherein:
the core layer contains polypropylene having a melting point of 158 to 166 ℃ and a melt flow rate MFR of 1 to 3g/10min,
the skin layer contains polypropylene having a melting point of 128 to 150 ℃ and a melt flow rate MFR of 1 to 7g/10 min.
3. The encapsulation film of claim 1 or 2, wherein:
the polypropylene contained in at least one of the surface layers is modified with an unsaturated carboxylic acid, an unsaturated carboxylic acid anhydride or an unsaturated epoxy compound.
4. The encapsulation film according to any one of claims 1 to 3, wherein:
the polypropylene contained in the core layer is a polypropylene block copolymer.
5. The encapsulation film of claim 3 or 4, wherein:
one of the surface layers is a metal adhesive layer to which the lead conductor is adhered, and the other surface layer is a package adhesive layer to which the exterior package is adhered,
the polypropylene contained in the metal adhesive layer is a polypropylene modified with an unsaturated carboxylic acid, an unsaturated carboxylic acid anhydride or an unsaturated epoxy compound,
the polypropylene contained in the package adhesive layer is polypropylene modified with an unsaturated carboxylic acid, an unsaturated carboxylic acid anhydride or an unsaturated epoxy compound, or a polypropylene random copolymer.
6. The encapsulation film of claim 5, wherein:
the melting point of the polypropylene contained in the package adhesive layer is higher than the melting point of the polypropylene contained in the metal adhesive layer.
7. The encapsulation film of claim 5 or 6, wherein:
the MFR of the polypropylene contained in the metal adhesive layer is higher than both the MFR of the polypropylene contained in the core layer and the MFR of the polypropylene contained in the package adhesive layer.
8. A tab lead wire is characterized in that:
both faces of a part of the lead conductors are covered with the encapsulating film according to any one of claims 1 to 7.
9. A secondary battery is characterized by comprising:
a power generating element including a positive electrode, a negative electrode, an electrolyte, and a separator;
an outer package body which houses the power generating element and has a peripheral edge portion heat-sealed;
a lead conductor connected to the positive electrode or the negative electrode and led out to the outside of the exterior package; and
a sealing film disposed between the outer package and the lead conductors and heat-sealed,
the outer package is composed of a multilayer film including at least a metal layer and a sealing resin layer,
the encapsulating film according to any one of claims 1 to 7.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2019211553 | 2019-11-22 | ||
| PCT/JP2020/022093 WO2021100226A1 (en) | 2019-11-22 | 2020-06-04 | Sealing film, and tab lead and secondary battery which use same |
| JPPCT/JP2020/022093 | 2020-06-04 | ||
| PCT/JP2021/018980 WO2021246177A1 (en) | 2019-11-22 | 2021-05-19 | Sealing film, and tab lead and secondary battery which use same |
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| CN115668604A true CN115668604A (en) | 2023-01-31 |
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|---|---|---|---|
| CN202180039809.3A Pending CN115668604A (en) | 2019-11-22 | 2021-05-19 | Packaging film, and tab lead and secondary battery using same |
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| Country | Link |
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| CN (1) | CN115668604A (en) |
| WO (2) | WO2021100213A1 (en) |
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| JPWO2021246472A1 (en) * | 2020-06-03 | 2021-12-09 | ||
| CN116670899A (en) | 2021-12-27 | 2023-08-29 | 住友电气工业株式会社 | Lead wire for nonaqueous electrolyte battery, insulating film, and nonaqueous electrolyte battery |
| CN114497910B (en) * | 2022-01-10 | 2024-05-17 | 珠海冠宇电池股份有限公司 | Tab and battery comprising same |
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| JP2014019981A (en) * | 2012-07-19 | 2014-02-03 | Diatex Co Ltd | Method for manufacturing flat yarn and method for manufacturing cloth laminate |
| KR101327868B1 (en) * | 2012-11-21 | 2013-11-11 | 율촌화학 주식회사 | Sealing film for lead tab of secondary battery |
| JP2014225378A (en) * | 2013-05-16 | 2014-12-04 | 株式会社日立製作所 | Sealant for tab lead, tab lead and lithium ion secondary battery |
| JP2014229505A (en) * | 2013-05-23 | 2014-12-08 | 日立マクセル株式会社 | Sealing material for thin battery |
| JP6648400B2 (en) * | 2014-11-10 | 2020-02-14 | 凸版印刷株式会社 | Terminal resin film, tab and power storage device using the same |
| JP6699105B2 (en) * | 2015-08-04 | 2020-05-27 | 凸版印刷株式会社 | Resin film for terminal, tab using the same, and power storage device |
| JP6657732B2 (en) * | 2015-10-02 | 2020-03-04 | 大日本印刷株式会社 | Adhesive film for metal terminals |
-
2020
- 2020-01-30 WO PCT/JP2020/003530 patent/WO2021100213A1/en active Application Filing
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2021
- 2021-05-19 CN CN202180039809.3A patent/CN115668604A/en active Pending
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| WO2021100213A1 (en) | 2021-05-27 |
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