Multi-layer composite structure for lithium-ion battery packaging and preparation method therefor, and lithium-ion battery

Abstract

A multi-layer composite structure for lithium-ion battery packaging and a preparation method therefor, and a lithium-ion battery. The multi-layer composite structure comprises an inner connection layer film and an outer framework structure layer film that are attached to each other; the inner connection layer film and the outer framework structure layer film each contain a water blocking additive. Metal aluminum foil is replaced with the water blocking additive, so that the objective of preventing vapor intrusion is achieved; moreover, because of the characteristic of good compatibility between outer and inner sides, the construction technology is reduced, the cost is reduced, and the safety performance is improved.

Description

Multilayer composite structure for lithium ion battery packaging, preparation method thereof, and lithium ion battery Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to a multi-layer composite structure for lithium-ion battery packaging, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] Lithium batteries (lithium secondary batteries) are batteries whose electrolytes are composed of solid polymers, gel polymers, and liquids, and charge transfer is generated by the movement of lithium ions. The positive and negative electrode active materials are formed from macromolecular polymers. A lithium secondary battery consists of a lithium battery body with the following composition: positive electrode current collector material (aluminum, nickel) / positive electrode active material layer (positive electrode materials such as metal oxides, carbon black, metal sulfides, electrolyte solutions, and polymers such as polypropylene) / electrolyte (carbonate electrolytes such as polypropylene carbonate, ethylene carbonate, dimethyl carbonate, and methylethylene carbonate, inorganic solid electrolytes made from lithium salts, or gel electrolytes) / negative electrode active material layer (negative electrode materials such as lithium metal, alloys, carbon, electrolyte solutions, and polymers) / negative electrode current collector material (copper, nickel, or stainless steel); and an outer sheath to house these components. Lithium secondary batteries, with their high volumetric and gravimetric efficiency, are widely used in electronic equipment, automobiles, and small aircraft. In the field of unmanned aerial vehicles, the balance between capacity and weight is particularly important, and current lithium-ion batteries cannot meet the long-term operating requirements of aircraft.

[0003] Layered products for lithium battery packaging need to comprehensively consider the properties required by lithium batteries, such as vapor-proof properties, sealing properties, anti-puncture properties, insulation properties, heat and cold resistance, electrolyte resistance (resistance to electrolyte solution properties) and corrosion resistance (resistance to hydrofluoric acid corrosion generated by electrolyte deterioration and hydrolysis).

[0004] Currently, there are three ways to package lithium-ion batteries: 1) Soft packaging using aluminum-plastic composite film. The aluminum-plastic composite film structure can be formed into a suitable shape to fit the space of an electronic device or electronic component, allowing for a certain degree of freedom in designing the shape of the electronic device or electronic component, achieving miniaturization and light weight. Invention patent CN101087687A relates to an outer layer packaging material for a secondary battery with an aluminum-plastic film structure. The packaging material described in this patent has three main functional layers. The outer layer uses a polymer film to improve mechanical strength. The material used is PET, PEN, or nylon. The middle layer is mainly used to prevent water vapor from embedding. Aluminum foil is usually used as the middle layer. The inner layer provides good heat sealing performance.

[0005] Existing layered products have a layered structure consisting of an outer base layer, an aluminum foil intermediate layer, and an inner layer. While using aluminum foil as the intermediate water-blocking layer provides excellent water-blocking performance, it also introduces new challenges. The addition of aluminum foil necessitates addressing the bonding between the outer and inner layers and the metal water-blocking layer to improve bonding strength. Current practices employ the addition of a thermally adhesive resin with excellent metal adhesion, such as an acid-modified olefin resin grafted with an unsaturated hydroxy acid, between the outer and metal water-blocking layers. For example, invention patent CN101087687A proposes optimizing the bond strength between the aluminum foil and the metal-adhesive olefin resin layer by forming a chemical conversion layer using a chemical conversion solution of an aminated phenolic polymer, a trivalent chromium compound, and a phosphorus compound.

[0006] The problems are as follows:

[0007] Problem 1: Safety issues arise. Because the layered structure of layered products consists of a base layer, a barrier layer made of metal foil, such as aluminum, and an inner layer, and the lithium hexafluorophosphate solution used as the electrolyte in the lithium battery, reacts with moisture to produce hydrofluoric acid. This hydrofluoric acid easily reacts with the aluminum foil and diffuses along the interface between the foil and the inner and outer layers, causing a decrease in the adhesion between the metal foil and the inner and outer layers, leading to delamination and decomposition, shortening the battery life.

[0008] Problem 2: There is a risk of short circuit. Existing products usually use thermal bonding to seal metal terminals. The metal terminals are sandwiched between layered products. Under the action of high heat, the metal terminals come into contact with the intermediate barrier layer of the layered product made of metal aluminum foil, which will cause short circuit problems. In addition, when external abnormal stress causes damage to the inner layer structure, microcracks are formed on the surface of the inner layer, and the liquid electrolyte invades the barrier layer of the metal aluminum foil through the cracked parts. Due to the high chemical activity of aluminum metal, the function of the battery is damaged. Metal aluminum foil has high ductility and processing properties, and can effectively block the invasion of external humid gas, but it also brings the disadvantages of complex processing technology, the risk of battery short circuit failure, and high cost. In addition, moisture penetration from the end face of the inner layer adhesive is also obvious. As a result, the moisture invading from the end face penetrates into the inner layer and reacts with the electrolyte solution to produce hydrofluoric acid, which causes separation between the barrier layer and the inner layer made of metal foil such as aluminum.

[0009] Problem three: High construction costs. The existing layered structure suffers from poor bonding between the middle layer and the inner and outer layers. To improve the bonding strength, other treatment processes and methods are needed to increase the surface activity of the barrier layer, such as chromium treatment, which inevitably increases processing technology and costs.

[0010] Summary of the Invention

[0011] In order to solve the problems existing in the prior art, the present invention provides a multi-layer composite structure for lithium-ion battery packaging, a preparation method thereof, and a lithium-ion battery. Generally, a lithium-ion battery contains an electrolyte, positive and negative electrode leads, and an external package. Existing external layered structure products usually adopt a composite structure of three or more layers, including an outer layer with high mechanical strength, an intermediate layer that prevents water vapor intrusion, an inner layer with good thermal bonding ability, and a transition layer between them. The purpose of the present invention is to simplify this structure and provide a multi-layer composite structure that uses a water-blocking additive instead of metal aluminum foil to achieve the purpose of preventing water vapor intrusion. At the same time, it takes advantage of the good compatibility between the outer and inner sides to reduce construction processes, reduce costs, and improve safety performance.

[0012] One of the purposes of the present invention is to provide a multi-layer composite structure for lithium-ion battery packaging, comprising an inner connecting layer film and an outer skeleton structure layer film bonded to each other; both the inner connecting layer film and the outer skeleton structure layer film contain a water-blocking additive.

[0013] In a preferred embodiment of the present invention,

[0014] The water-blocking additives in the inner connecting layer film and the outer skeleton structure layer film are the same or different, and are independently at least one of an inorganic water-blocking agent and an organic water-blocking agent;

[0015] The inorganic water-blocking agent is preferably at least one of titanium nitride, aluminum nitride, and a titanium aluminum nitride compound (Ti2AlN); and / or,

[0016] The organic water-blocking agent is preferably at least one of perfluorinated compounds (PFCs), more preferably at least one of perfluorooctane sulfonic acid, perfluorooctanoic acid, and Teflon.

[0017] In a preferred embodiment of the present invention,

[0018] The inner connecting layer film is prepared by mixing components including a thermal bonding polymer and the water-blocking additive, wherein the thermal bonding polymer is preferably at least one of polypropylene and modified polypropylene; the modified polypropylene is preferably at least one of ET20, ET70, and ET80 produced by Okamoto Co., Ltd. of Japan; and / or,

[0019] The outer skeleton structure layer film is prepared by mixing components including a high melting point polymer and the water-blocking additive. The high melting point polymer is a polymer with a melting point in the range of 200-350°C, preferably at least one of polyethylene terephthalate (PET) and nylon, and the nylon is preferably at least one of nylon 6 and nylon 66.

[0020] In a preferred embodiment of the present invention,

[0021] The amount of each component in the inner connecting layer film is calculated based on 100 parts by weight of the thermal adhesive polymer.

[0022] The water-blocking additive is 0.01-1 parts by weight, preferably 0.06-0.8 parts by weight; and / or,

[0023] When the water-blocking additive is an inorganic water-blocking agent, the amount used is preferably 0.01-0.3 parts by weight; more preferably 0.06-0.08 parts by weight; and / or,

[0024] When the water-blocking additive is an organic water-blocking agent, the amount used is preferably 0.1-1 parts by weight; more preferably 0.2-0.8 parts by weight;

[0025] The amount of each component in the outer skeleton structure film is calculated based on 100 parts by weight of the high melting point polymer.

[0026] The water-blocking additive is 0.01-1 parts by weight, preferably 0.06-0.8 parts by weight; and / or,

[0027] When the water-blocking additive is an inorganic water-blocking agent, the amount used is preferably 0.01-0.3 parts by weight; more preferably 0.06-0.08 parts by weight; and / or,

[0028] When the water-blocking additive is an organic water-blocking agent, the amount used is preferably 0.1-1 parts by weight; more preferably 0.2-0.8 parts by weight.

[0029] In a preferred embodiment of the present invention,

[0030] The inner connecting layer film and the outer skeleton structure layer film also contain conventional toughening agents, nucleating agents, antioxidants, silicone oils and modification aids in this field, and the amounts used are also conventional amounts. Those skilled in the art can add them according to actual conditions.

[0031] The toughening agents in the inner connecting layer film and the outer skeleton structure layer film are the same or different, and are independently preferably at least one of maleic anhydride and polyolefin elastomer (POE); the polyolefin elastomer is preferably Dow 7457; and / or,

[0032] The nucleating agents in the inner connecting layer film and the outer skeleton structure layer film are the same or different, preferably Milliken 3988i; and / or,

[0033] The antioxidants in the inner connecting layer film and the outer skeleton structure layer film are the same or different, preferably BASF Irgafos 168; and / or,

[0034] The silicone oil in the inner connecting layer film and the outer skeleton structure layer film is the same or different, preferably Dow Corning PMX-200; and / or,

[0035] The modifying agents in the inner connecting layer film and the outer skeleton structure layer film are the same or different, and are preferably Lanxess Mesamoll.

[0036] In the present invention, it is preferred that the amount of each component in the inner connecting layer film is calculated based on 100 parts by weight of the thermal adhesive polymer.

[0037] In the present invention, it is preferred that the amount of each component in the outer skeleton structure film is calculated based on 100 parts by weight of the high melting point polymer.

[0038] In a preferred embodiment of the present invention,

[0039] The total thickness of the multilayer composite structure is 50-200 μm, preferably 80-150 μm; and / or the thickness of the inner polymer film is 20-100 μm, preferably 40-80 μm; and / or the thickness of the outer skeleton structure layer film is 20-100 μm, preferably 40-80 μm.

[0040] Compared with the traditional process, the total thickness of the multi-layer composite structure of the present invention is reduced in film thickness, and the volume density of the battery can be increased under the same volume space conditions.

[0041] In a preferred embodiment of the present invention,

[0042] The multilayer composite structure further includes an intermediate water-blocking film, the material of which is preferably at least one of titanium nitride, copper, and polytetrafluoroethylene; the intermediate water-blocking film can further block the intrusion of water vapor; and / or,

[0043] The thickness of the intermediate water-blocking film is in the range of 3-20 μm, preferably 3-10 μm.

[0044] When the middle water-blocking film is made of polytetrafluoroethylene, the middle water-blocking film is formed by extrusion of the polytetrafluoroethylene. The extrusion molding can adopt conventional extrusion molding processes in the prior art, as long as the thickness of the middle water-blocking film obtained by extrusion is within the range of 3-20 μm.

[0045] When the material of the intermediate water-blocking film is at least one of titanium nitride and copper, the intermediate water-blocking film is formed by chemically plating or electroplating at least one of titanium nitride and copper on the side where the inner connecting layer film and the outer skeleton structure layer film are bonded, or on the side where the outer skeleton structure layer film and the inner connecting layer film are bonded. The chemical plating or electroplating can be conventional chemical plating or electroplating processes in the prior art, as long as the resulting intermediate water-blocking film has a thickness within a range of 3-20 μm.

[0046] The second object of the present invention is to provide a method for preparing a multilayer composite structure for lithium-ion battery packaging according to one of the objects of the present invention, comprising the steps of laminating film layers including an inner connecting layer film and an outer skeleton structure layer film and then hot-pressing them with double rollers to obtain the multilayer composite structure.

[0047] In a preferred embodiment of the present invention,

[0048] The method comprises:

[0049] Melting and mixing the components including the thermal bonding polymer and the water blocking additive and then extruding to form the inner connecting layer film; and / or,

[0050] The outer skeleton structure layer film is obtained by melt-mixing components including a high melting point polymer and a water-blocking additive and then extruding the mixture.

[0051] The extrusion molding of the inner connecting layer film and the outer skeleton structure layer film can adopt conventional extrusion molding processes in the prior art, as long as the thickness of the film layer obtained by extrusion meets the requirements.

[0052] In a preferred embodiment of the present invention,

[0053] The temperature range of the double-roll hot pressing is 140-200° C., preferably 160-180° C., and the pressure range is 1-3 MPa.

[0054] The present invention can preferably adopt the following specific technical solutions:

[0055] First, the thermal bonding polymer, water-blocking additive, toughening agent, and silicone oil are mixed in a high-speed homogenizer. Then, a nucleating agent, antioxidant, and modifying agent are added. After melt mixing, the mixture is uniformly melted and extruded in a twin-screw extruder. The mixture is then wound onto a metal drum and subjected to rapid cooling, shaping, trimming, and rolling to obtain the inner connecting layer film. The extrusion process includes: a drying temperature of 120-140°C; a drying time of 0.1-5 hours; a nozzle temperature of 240-280°C (staged control): 240-280°C in the first stage, 240-270°C in the second stage, and 250-280°C in the third stage; and a pressure of 5-10 MPa.

[0056] First, a high-melting-point polymer, a water-blocking additive, a toughening agent, and silicone oil are mixed in a high-speed homogenizer. Then, a nucleating agent, an antioxidant, and a modifying agent are added. After melt mixing and uniformity, the mixture is extruded through a twin-screw extruder and then wound onto a metal drum. After rapid cooling, shaping, trimming, and rolling, the outer skeleton structure layer film is obtained. Extrusion process: baking temperature 120-140°C; baking time 0.1-5 hours; nozzle temperature 240-280°C (stage control): 240-280°C for the first stage, 240-270°C for the second stage, and 250-280°C for the third stage; pressure 5-10 MPa.

[0057] After laminating the film layers including the outer skeleton structure layer film and the inner connecting layer film, as shown in FIG3 , the outer skeleton structure layer film containing the water-blocking additive and the inner connecting layer film are continuously passed through hot rolling rollers to realize the forming process and obtain a double-layer composite structure.

[0058] When the multilayer composite structure further includes an intermediate water-blocking film, the intermediate water-blocking film is placed between the outer skeleton structure film and the inner connecting layer film, and then laminated to each other and continuously passed through hot rolling rollers to achieve a molding process to obtain a multilayer composite structure including the intermediate water-blocking film.

[0059] A third object of the present invention is to provide a lithium-ion battery, which is encapsulated using the multi-layer composite structure of the first object of the present invention or the multi-layer composite structure prepared by the method of the second object of the present invention.

[0060] The method for packaging using the multi-layer composite structure of the present invention can adopt the conventional packaging method in the prior art. In the present invention, the multi-layer composite structure can preferably be made into a rectangular groove structure with one end open (the open end of the rectangular groove structure has an outer annular flange) and a groove cover structure that matches the open end of the rectangular groove structure, and then packaging can be performed.

[0061] The beneficial effects of the present invention are as follows:

[0062] The present invention improves upon the existing layered structure of aluminum-plastic film, enhancing product reliability and reducing costs while ensuring sufficient barrier properties. Based on the original structure of conventional aluminum-plastic film, the intermediate aluminum foil barrier layer is removed, along with the associated transition layer processing (a process for increasing the bonding strength between the aluminum-plastic film and the inner or outer layers). Furthermore, to enhance the effectiveness of blocking water vapor intrusion, the present invention incorporates a water-blocking additive in the inner and outer layers to improve the effectiveness of preventing water vapor from invading the internal electrolyte. By removing the intermediate metal aluminum foil layer, the multilayer composite film can be produced in a single pass using a double-roll hot-pressing method.

[0063] The multi-layer composite structure of the present invention replaces the metal foil water-blocking structure used in traditional aluminum-plastic film by adding a water-blocking component (water-blocking additive). On the basis of ensuring mechanical strength and electrolyte resistance, the existing layered structure construction method is changed to achieve rapid prototyping of the multi-layer film structure. Compared with the traditional method, this method, combined with the grid-like automobile chassis design, can reduce the process and construction difficulty, while increasing the thickness of the single cell, breaking through the limit thickness (10mm) of the single cell encapsulated by aluminum-plastic film. The thickness of the single cell using the multi-layer composite structure of the present invention can reach 14mm or more.

[0064] The multi-layer composite structure of the present invention has good support strength and does not soften when packaged, facilitating electrolyte injection. It also has strong water barrier properties, reducing the need for external environment (air moisture) during secondary packaging. The multi-layer composite structure of the present invention has high mechanical strength, electrolyte resistance, and thermal processing performance.

[0065] The multilayer composite structure of the present invention is suitable for packaging of automobile batteries, energy storage batteries and two-wheeled vehicle batteries (all of which are lithium-ion batteries), but is not suitable for packaging of small digital single batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] FIG1 is a schematic diagram of the structure of the multi-layer composite structure of the present invention excluding the intermediate water-blocking film; in the figure, 1 is the inner connecting layer film, and 2 is the outer skeleton structure layer film;

[0067] FIG2 is a schematic diagram of the structure of a multi-layer composite structure including an intermediate water-blocking film according to the present invention; in the figure, 1 is an inner connecting layer film, 2 is an outer skeleton structure layer film, and 3 is an intermediate water-blocking film;

[0068] FIG3 is a schematic diagram of a double-roll hot pressing process for forming a multi-layer composite structure according to the present invention;

[0069] FIG4 is a schematic diagram of a lithium-ion battery using a multilayer film structure;

[0070] FIG5 is a schematic diagram of an electrode extraction method for a lithium-ion battery using a multilayer film structure;

[0071] Figure 6 is a schematic diagram of a multi-layer film structure battery compression molding process;

[0072] FIG7 is a schematic diagram of a hot-pressing and sealing method for a battery using a multi-layer film structure. DETAILED DESCRIPTION

[0073] The present invention will be described in detail below with reference to specific embodiments and the accompanying drawings. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art to the present invention based on the contents of the present invention still fall within the scope of protection of the present invention.

[0074] The raw materials used in the examples and comparative examples are all conventional commercially available raw materials.

[0075] The reference standard for measuring the thickness of the multilayer composite structure in the examples and comparative examples is GB / T6672-2001;

[0076] The electrolyte solution resistance test process is as follows: the multi-layer composite structure specimen is immersed in an electrolyte solution containing 200ppm water (electrolyte composition EMC:DMC:LIF6P = 1:1:1) for 24 hours (temperature 60°C). The specimen is then cut into 15mm wide pieces and tested for peelability using a CTM8000 tensile testing machine under a tensile force of 10N. The reference standard for the tensile testing machine to determine whether the specimen is peelable is: GB / T 8808-1988;

[0077] The test process of the anti-rupture performance is as follows: After the multi-layer composite structure is heat-sealed, it is placed in a DZF6120 vacuum box at a pressure of 0.9 MPa to observe whether the product ruptures within 30 minutes.

[0078] Short-circuit resistance test process: Use a BT5300 internal resistance tester, connect the positive electrode to the inner layer of the multi-layer composite structure, and the negative electrode to the outer layer of the multi-layer composite structure. Apply a voltage of 500V and evaluate the conduction time.

[0079] Water vapor transmission rate test process: Use a water vapor transmission rate tester to test the moisture transmission rate of a multi-layer composite structure.

[0080] Formability test process: The cut multi-layer composite structure is placed between the punch and die of the MSK-120 soft-pack battery integrated molding machine (shell length and width 100mm*80mm), the punch is heated to 100℃, and the die is heated to 110℃, and the multi-layer composite structure is extruded for about 3 seconds and held for about 6 seconds. After extrusion molding, a rupture test is performed under a pressure of 30MPa in a DZF6120 vacuum box to test the ultimate forming depth of the multi-layer composite structure (that is, the maximum formable thickness of the multi-layer composite structure that can be extruded, at which it remains unbroken, and if it exceeds this thickness, it will rupture).

[0081] Example 1

[0082] 100 parts by weight of polypropylene (Yanshan Petrochemical K8303), 0.08 parts by weight of titanium nitride, 5 parts by weight of a toughening agent (Dow 7457), and 0.3 parts by weight of silicone oil were mixed in a high-speed homogenizer, and then 1.5 parts by weight of a nucleating agent (Milliken 3988i), 1.3 parts by weight of an antioxidant (BASF Irgafos 168), and 4 parts by weight of a modifying agent (Lanxess Mesamoll) were added. After melt mixing, the mixture was uniformly extruded in a twin-screw extruder and then wound onto a metal drum. After rapid cooling, shaping, trimming, and rolling, an inner connecting layer film was obtained. The extrusion process was as follows: a baking temperature of 130° C.; a baking time of 0.7 hours; a nozzle temperature (stage-controlled): 270° C. in the first stage, 250° C. in the second stage, and 270° C. in the third stage; and a pressure of 8.5 MPa.

[0083] 100 parts by weight of PET (Shanghai Yuanfang CB-602), 0.07 parts by weight of titanium nitride, 5 parts by weight of a toughening agent (Dow 7457), and 0.3 parts by weight of silicone oil were mixed in a high-speed homogenizer, and then 1.5 parts by weight of a nucleating agent (Milliken 3988i), 1.3 parts by weight of an antioxidant (BASF Irgafos 168), and 4 parts by weight of a modifying agent (Lanxess Mesamoll) were added. After melt mixing and uniformly mixing, the mixture was extruded in a twin-screw extruder and then wound onto a metal drum. After rapid cooling, shaping, trimming, and rolling, a film with an outer skeleton structure layer was obtained. Extrusion process: baking temperature 130°C; baking time 0.7 hour; nozzle temperature (stage-controlled): 270°C in the first stage, 250°C in the second stage, and 270°C in the third stage; pressure 8.5 MPa;

[0084] The outer skeleton structure film and the inner tie layer film obtained above were laminated and then continuously passed through hot rollers (temperature of 170°C and pressure of 2 MPa) to obtain a multilayer composite structure. The inner tie layer film in the multilayer composite structure had a thickness of 60 μm, and the outer skeleton structure film had a thickness of 80 μm. The properties of the multilayer composite structure are shown in Table 1.

[0085] Example 2

[0086] Example 2 was prepared using the same process as Example 1, differing only in that 0.16 parts by weight of titanium nitride was added to the inner connecting layer film, and 0.14 parts by weight of titanium nitride was added to the outer skeleton structure film. The resulting multilayer composite structure had an inner connecting layer thickness of 60 microns and an outer skeleton structure layer thickness of 80 microns. The properties of the multilayer composite structure are shown in Table 1.

[0087] Example 3

[0088] The preparation process of Example 3 was the same as that of Example 2, except that an intermediate water-blocking film was added. The preparation process of the intermediate water-blocking film was as follows: polytetrafluoroethylene (JTF-305, Zhejiang Juhua) was melted and extruded through a twin-screw extruder. The extruder was then wound around a metal drum. After rapid cooling and shaping, trimming, and rolling, the intermediate water-blocking film was obtained. The extrusion process was as follows: baking temperature 130°C; baking time 0.7 hour; nozzle temperature (staged control): 270°C in the first stage, 250°C in the second stage, and 270°C in the third stage; pressure 9 MPa.

[0089] The thickness of the inner connecting layer of the obtained multilayer composite structure is 60 microns, the thickness of the outer skeleton structure layer is 80 microns, and the thickness of the middle water-blocking film is 4 microns. The properties of the multilayer composite structure are shown in Table 1.

[0090] Example 4

[0091] The preparation process of Example 4 is the same as that of Example 1, except that the thickness of the inner connecting layer film in the obtained multilayer composite structure is 40 microns, and the thickness of the outer skeleton structure layer film is 60 microns. The properties of the multilayer composite structure are shown in Table 1.

[0092] Example 5

[0093] The preparation process of Example 5 is the same as that of Example 1, except that the thickness of the inner connecting layer film in the obtained multilayer composite structure is 40 microns, and the thickness of the outer skeleton structure layer film is 80 microns. The properties of the multilayer composite structure are shown in Table 1.

[0094] Comparative Example 1

[0095] Comparative Example 1 was prepared using the same process as Example 3, differing only in that neither the outer skeleton layer film nor the inner tie layer film contained a water-blocking additive. The resulting multilayer composite structure had an inner tie layer film thickness of 60 microns, an outer skeleton layer film thickness of 80 microns, and an intermediate water-blocking film thickness of 4 microns. The properties of the multilayer composite structure are shown in Table 1.

[0096] Table 1 Performance comparison of the multilayer composite structure of the embodiment and the comparative example

[0097] It can be seen from Examples 1-5, Comparative Example 1 and Table 1 that compared with the aluminum-plastic film in the prior art, the multi-layer composite structure of the present invention has excellent electrolyte solution resistance, and due to the use of double-roll hot pressing, the forming depth can reach 20 mm, which is much higher than the 8 mm that can be achieved by the aluminum-plastic film. In addition, the multi-layer composite structure of the present invention also has good anti-cracking performance, short-circuit resistance and water vapor resistance, and can meet the requirements of use; compared with Comparative Example 1, since its outer skeleton structure layer film and inner connecting layer film do not contain water-blocking additives, its electrolyte solution resistance and water vapor transmission rate are inferior to the multi-layer composite structures of Examples 1-5 of the present invention.

[0098] It can be seen that the multi-layer composite structure of the present invention replaces the metal foil water-blocking structure used in traditional aluminum-plastic film by adding water-blocking components (water-blocking additives). On the basis of ensuring mechanical strength and electrolyte resistance, it changes the construction method of the existing layered structure and realizes the rapid forming of the multi-layer film structure.

Claims

1. A multilayer composite structure for lithium-ion battery packaging, comprising an inner connecting layer film and an outer skeleton structure layer film bonded to each other; the inner connecting layer film and the outer skeleton structure layer film both contain a water-blocking additive.

2. The multilayer composite structure for lithium-ion battery packaging according to claim 1, wherein: The water-blocking additives in the inner connecting layer film and the outer skeleton structure layer film are the same or different, and are independently at least one of an inorganic water-blocking agent and an organic water-blocking agent; The inorganic water-blocking agent is preferably at least one of titanium nitride, aluminum nitride, and a nitrogen-aluminum-titanium compound; and / or, The organic water-blocking agent is preferably at least one of perfluorinated compounds, more preferably at least one of perfluorooctane sulfonic acid, perfluorooctanoic acid, and Teflon.

3. The multi-layer composite structure for lithium-ion battery packaging according to claim 1, wherein: The inner connecting layer film is prepared by mixing components including a thermal bonding polymer and the water blocking additive, wherein the thermal bonding polymer is preferably at least one of polypropylene and modified polypropylene; and / or, The outer skeleton structure layer film is prepared by mixing components including a high melting point polymer and the water blocking additive. The high melting point polymer is a polymer with a melting point in the range of 200-350° C., preferably at least one of polyethylene terephthalate and nylon.

4. The multi-layer composite structure for lithium-ion battery packaging according to claim 3, wherein: The amount of each component in the inner connecting layer film is calculated based on 100 parts by weight of the thermal adhesive polymer, and the amount of the water-blocking additive is 0.01-1 parts by weight, preferably 0.06-0.8 parts by weight; and / or, The amount of each component in the outer skeleton structure layer film is calculated based on 100 parts by weight of the high melting point polymer, and the amount of the water blocking additive is 0.01-1 parts by weight, preferably 0.06-0.8 parts by weight.

5. The multi-layer composite structure for lithium-ion battery packaging according to claim 1, wherein: The total thickness of the multi-layer composite structure is 50-200 μm, preferably 80-150 μm; and / or the thickness of the inner polymer film is 20-100 μm, preferably 40-80 μm.

6. The multi-layer composite structure for lithium-ion battery packaging according to claim 1, wherein: The multilayer composite structure further includes an intermediate water-blocking film, the material of which is preferably at least one of titanium nitride, copper, and polytetrafluoroethylene; and / or the thickness of the intermediate water-blocking film is in the range of 3-20 μm.

7. A method for preparing a multilayer composite structure for lithium-ion battery packaging as described in any one of claims 1 to 6, comprising the steps of laminating film layers including an inner connecting layer film and an outer skeleton structure layer film and then hot-pressing them with double rollers to obtain the multilayer composite structure.

8. The preparation method according to claim 7, wherein The method comprises: Melting and mixing the components including the thermal bonding polymer and the water blocking additive and then extruding to form the inner connecting layer film; and / or, The outer skeleton structure layer film is obtained by melt-mixing components including a high melting point polymer and a water-blocking additive and then extruding the mixture.

9. The preparation method according to claim 7, wherein: The temperature range of the double-roll hot pressing is 140-200° C., and the pressure range is 1-3 MPa.

10. A lithium-ion battery encapsulated by using the multilayer composite structure according to any one of claims 1 to 6 or the multilayer composite structure prepared by the method according to any one of claims 7 to 9.

Images