Battery cell wrapping film and use thereof

Abstract

The application provides an electric core wrapping film and application thereof, and the electric core wrapping film comprises a substrate layer and a heat-sensitive layer; the heat-sensitive layer comprises polyethylene and polypropylene; the polyethylene comprises polyethylene elastomer, low-density polyethylene and polyethylene derivatives; the polyethylene derivatives comprise at least one of ethylene-acrylate copolymer and a copolymer of ethylene and vinyl acetate. By introducing polypropylene and various special polyethylene into the heat-sensitive layer, the electric core wrapping film can not only have suitable structural strength, good toughness and elasticity, but also has good electrolyte resistance and high-temperature resistance, that is, the electric core wrapping film still has good bonding strength under electrolyte immersion.

Description

Technical Field

[0001] This invention belongs to the field of battery cell coating film, and particularly relates to a battery cell coating film and its application. Background Technology

[0002] In battery manufacturing technology, the battery cell is the core component of a battery, and its quality directly affects the battery's performance and safety. A battery cell typically consists of a positive electrode, a negative electrode, a separator, and an electrolyte. The separator's function is to isolate the positive and negative electrodes, preventing direct contact and short circuits. However, during the cell assembly process, if the casing accidentally punctures the separator, it may cause the separator to rupture, leading to a partial short circuit within the cell. This can severely impact the battery's performance and safety.

[0003] To address this issue, several solutions already exist in the existing technology. For example, high-strength diaphragm materials can be used to improve the diaphragm's puncture resistance. Alternatively, special handling methods can be employed during the cell assembly process to prevent the casing from puncturing the diaphragm. Furthermore, some technical solutions involve improving the cell design, such as adding a protective layer, to prevent the casing from puncturing the diaphragm.

[0004] However, existing technical solutions still have some problems. First, while high-strength separator materials can improve the separator's puncture resistance, they may increase battery costs and potentially affect other battery performance aspects, such as electrolyte permeability and ion transport. Second, using special handling methods to prevent the casing from puncturing the separator not only increases operational complexity but may also affect the efficiency of cell insertion. While special cell treatments, such as wrapping the cells with a protective film, are convenient, they require high-quality films with specific requirements, including electrolyte resistance and adhesion. Therefore, selecting a suitable protective film to effectively prevent the casing from puncturing the separator while ensuring battery performance and safety is of great significance. Summary of the Invention

[0005] In order to provide a battery cell coating film with good structural strength and electrolyte resistance, the present invention provides a battery cell coating film and its application.

[0006] According to one aspect of the present invention, a battery cell coating film is provided, the battery cell coating film comprising a substrate layer and a thermosensitive layer; the thermosensitive layer comprises polyethylene and polypropylene, wherein the polyethylene comprises polyethylene elastomer, low-density polyethylene, and polyethylene derivatives; the polyethylene derivatives comprise at least one of ethylene-acrylate copolymers and copolymers of ethylene and vinyl acetate. The polyethylene elastomer is a thermoplastic elastomer having a narrow relative molecular mass distribution and a uniform short-chain distribution, and can be divided into two types: polymers of ethylene and butene, and polymers of ethylene and octene; while low-density polyethylene (LDPE) is a thermoplastic plastic obtained by free radical polymerization of ethylene under high pressure.

[0007] The inventors discovered that, in practical applications, in addition to requiring good electrolyte resistance, high-temperature resistance, and adhesion, the cell coating film also needs to achieve suitable structural strength to improve the problems of peeling and slippage that are common in existing cell coating films. Through experiments, the inventors found that when the cell coating film is too hard, it is prone to peeling at the corners during cell insertion. Furthermore, excessive hardness may reduce electrolyte permeability and ion transport during battery cycling, thus affecting the battery's cycle performance and other electrochemical properties. Conversely, when the cell coating film is too soft, it is prone to slippage and difficulty in securing during installation. Therefore, in view of the problems found in the prior art and by the inventors, the present invention introduces polypropylene and various special polyethylenes into the heat-sensitive layer, which not only provides suitable structural strength for the battery cell coating film, making the battery cell coating film have good toughness and elasticity and improving problems such as lifting and slippage, but also endows the battery cell coating film with good electrolyte resistance and high temperature resistance, that is, the battery cell coating film still has good bonding strength when immersed in electrolyte.

[0008] Preferably, the ethylene-acrylate copolymer includes at least one of ethylene-ethyl acrylate copolymer, ethylene-ethyl acrylate-maleic anhydride copolymer, and ethylene-butyl acrylate copolymer. The ethylene-acrylate copolymer can significantly improve the adhesion between the heat-sensitive layer and the adjacent layer, and improve the flexibility and high-temperature resistance of the heat-sensitive layer.

[0009] Preferably, the copolymer of ethylene and vinyl acetate includes ethylene vinyl acetate copolymer (EVM), in which the mass fraction of vinyl acetate is 0.4-0.6%. Compared with ethylene-vinyl acetate copolymer (EVA, with a mass fraction of vinyl acetate of 0.05-0.2%), EVM has lower branching and higher crystallinity, which helps to improve the temperature resistance, solvent resistance, and aging resistance of the heat-sensitive layer.

[0010] Preferably, the melt index of ethylene ethylene rubber (EVM) is 25-28 g / 10 min.

[0011] Preferably, the polyethylene elastomer is an ethylene-octene copolymer (POE), and the crystallinity of the octene end in the ethylene-octene copolymer is 30-50%.

[0012] Preferably, the density of the ethylene-octene copolymer is 0.89–0.95 g / cm³. 3 .

[0013] Preferably, the density of the ethylene-octene copolymer is 2.5 to 4.0 g / 10 min.

[0014] Preferably, the low-density polyethylene is linear low-density polyethylene (LDPE) with a crystallinity ≥24.5%. LDPE exhibits low-temperature toughness, high modulus, flexural strength, puncture strength, and tear strength. However, the presence of cross-linked polymers (such as cross-linked α-olefins in LDPE) or impurities in the heat-sensitive layer can reduce the crystallinity of the LDPE, affecting its melt dispersion and potentially forming crystal points in the heat-sensitive layer, thus impacting the film-forming properties of the battery cell coating. This invention addresses these issues by selecting LDPE with relatively high crystallinity and low cross-linked polymer and oxidizing impurity content.

[0015] Preferably, the linear low-density polyethylene has a melt index of 1.5–2.5 g / 10 min and a melting point of 110–130 °C.

[0016] Preferably, the polypropylene includes block copolymer polypropylene with a crystallinity of 75-90%. Block copolymerized polypropylene (PPB) is produced by copolymerizing polypropylene with another olefinic monomer. Industrially, it is mostly prepared by copolymerizing propylene with a small amount of ethylene, thus PPB has high toughness. However, its application in the battery cell field is greatly limited by its poor low-temperature impact resistance, large molding shrinkage, and poor heat resistance. This invention improves these problems by combining linear low-density polyethylene and polyethylene derivatives.

[0017] Preferably, the melt index of the block copolymer polypropylene is 5 to 12 g / 10 min.

[0018] Preferably, the heat-sensitive layer further includes at least one of a tackifying resin and a processing aid.

[0019] Preferably, the tackifying resin includes hydrogenated petroleum resin.

[0020] Preferably, the heat-sensitive layer comprises 25-35 parts polypropylene, 20-45 parts polyethylene elastomer, 10-25 parts low-density polyethylene, and 10-25 parts polyethylene derivative, calculated by weight.

[0021] Preferably, the heat-sensitive layer further includes 2 to 10 parts of tackifying resin and 0.05 to 1 part of processing aid, calculated by weight.

[0022] Preferably, the heat-sensitive layer is prepared by co-extrusion or blow molding.

[0023] Preferably, the substrate layer comprises a first film layer, a second film layer, and a third film layer arranged sequentially; wherein the first film layer comprises polyethylene terephthalate (PET); the second film layer comprises ethylene-vinyl acetate copolymer (EVA); and the third film layer comprises unstretched polypropylene (CPP). In the prior art, PET has good puncture resistance, and CPP has good stiffness, similar polarity to the separator, and good solvent resistance. However, in the prior art, the polarity difference between CPP and PET and the adhesive layer is large, resulting in poor adhesion and easy detachment of the CPP layer. In this invention, on the one hand, by utilizing EVA to tightly bond PET and CPP, a good protective effect can be provided for the battery cell coating film; on the other hand, in the battery cell coating film provided by this invention, the first film layer, the second film layer, the third film layer, and the thermosensitive layer are arranged sequentially. By introducing a polyethylene derivative into the thermosensitive layer, this invention enables the thermosensitive layer and the third film layer to have a good bonding effect, ensuring that they do not detach during long-term use.

[0024] Preferably, the thickness ratio is calculated as follows: first thin film layer: second thin film layer: third thin film layer = (1~3): 1: (0.5~2).

[0025] Preferably, the substrate layer is prepared by co-extrusion or blow molding.

[0026] Preferably, the raw materials for preparing the first film layer, the second film layer, and the third film layer are melt-blended and extruded into masterbatch at 200-250°C, and then co-extruded to obtain a substrate layer in which the first film layer, the second film layer, and the third film layer are stacked sequentially.

[0027] Preferably, the thickness of the cell coating film is 50–100 μm, and the thickness of the thermosensitive layer is 2–10 μm. In the prior art, the thickness of the cell coating film is generally above 100 μm. This is due to two factors: firstly, the practical requirements for the cell coating film to protect against punctures and resist electrolytes; and secondly, the need for ease of manufacturing processes using the protective film itself. However, thicker protective films increase material and manufacturing costs and encroach on valuable internal space within the cell, reducing its energy density. This invention, through the arrangement of the thermosensitive layer and the substrate layer, can maintain good electrolyte resistance, high-temperature resistance, and adhesion properties at a lower thickness, and improves upon the problems of peeling and slippage that easily occur in existing cell coating films.

[0028] A second aspect of the present invention provides a battery comprising a cell coating film as described above. Attached Figure Description

[0029] Figure 1 This is a cross-sectional view of the cell wrapping film provided in Embodiment 1 of the invention;

[0030] in, Figure 1 The markings have the following meanings: 1. Substrate layer; 11. First thin film layer; 12. Second thin film layer; 13. Third thin film layer; 2. Thermal layer. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0032] Example 1

[0033] 1. Raw materials for preparing the cell coating film

[0034] Prepare the raw materials required for the cell coating film according to the formula shown in Table 1.

[0035] Table 1. Formulation of cell coating film

[0036]

[0037] 2. Method for preparing the cell coating film

[0038] S1. The raw materials for preparing the first film layer, the second film layer, and the third film layer are melt-blended and extruded into masterbatch at 200-250°C, and then co-extruded to obtain a substrate layer in which the first film layer, the second film layer, and the third film layer are stacked sequentially; wherein, the thickness of the first film layer is 40 μm, the thickness of the second film layer is 20 μm, and the thickness of the third film layer is 20 μm;

[0039] S2. Subsequently, the materials are co-extruded into masterbatch according to the thermosensitive layer formula, and the thermosensitive layer is obtained by co-extrusion; wherein, the thickness of the thermosensitive layer is 5μm;

[0040] S3. Composite the thermal layer with the third thin film layer in the substrate layer to obtain the cell coating film, wherein the total thickness of the cell coating film is 85μm.

[0041] Example 2

[0042] This embodiment prepares the cell coating film with reference to the formula and method provided in Example 1. The difference from Example 1 is that in this embodiment, when preparing the heat-sensitive layer of the cell coating film, an equal mass fraction of ethylene-ethyl acrylate copolymer is used instead of ethylene-ethyl acrylate-maleic anhydride copolymer. Apart from the above differences, the operation steps for preparing the cell coating film in this embodiment are strictly consistent with those in Example 1.

[0043] Example 3

[0044] This embodiment prepares the cell coating film with reference to the formula and method provided in Example 1. The difference from Example 1 is that in this embodiment, when preparing the heat-sensitive layer of the cell coating film, an equal mass fraction of ethylene-butyl acrylate copolymer is used instead of ethylene-ethyl acrylate-maleic anhydride copolymer. Apart from the above differences, the operation steps for preparing the cell coating film in this embodiment are strictly consistent with those in Example 1.

[0045] Example 4

[0046] This embodiment prepares the cell coating film with reference to the formula and method provided in Example 1. The difference from Example 1 is that in this embodiment, when preparing the heat-sensitive layer of the cell coating film, an equal mass fraction of ethylene-vinyl acetate copolymer is used instead of ethylene-ethyl acrylate-maleic anhydride copolymer. Apart from the above differences, the operation steps for preparing the cell coating film in this embodiment are strictly consistent with those in Example 1.

[0047] Example 5

[0048] This embodiment prepares the cell coating film with reference to the formula and method provided in Embodiment 1. The difference from Embodiment 1 is that the VA mass fraction of EVM used in preparing the thermosensitive layer of the cell coating film in this embodiment is 0.7. Apart from the above differences, the operation steps for preparing the cell coating film in this embodiment are strictly consistent with those in Embodiment 1.

[0049] Example 6

[0050] This embodiment prepares a cell coating film with reference to the formula and method provided in Embodiment 1. The difference from Embodiment 1 is that in this embodiment, an equal mass fraction of EVA is used instead of EVM when preparing the thermosensitive layer of the cell coating film. Apart from the above differences, the operation steps for preparing the cell coating film in this embodiment are strictly consistent with those in Embodiment 1.

[0051] Example 7

[0052] This embodiment prepares the cell coating film with reference to the formula and method provided in Example 1. The difference from Example 1 is that in this embodiment, when preparing the heat-sensitive layer of the cell coating film, an equal mass fraction of ethylene-acrylate copolymer is used instead of the copolymer of ethylene and vinyl acetate. Apart from the above differences, the operation steps for preparing the cell coating film in this embodiment are strictly consistent with those in Example 1.

[0053] Example 8

[0054] This embodiment prepares the cell coating film with reference to the formula and method provided in Example 1. The difference from Example 1 is that in this embodiment, when preparing the heat-sensitive layer of the cell coating film, an equal mass fraction of a copolymer of ethylene and vinyl acetate is used instead of an ethylene-acrylate copolymer. Apart from the above differences, the operation steps for preparing the cell coating film in this embodiment are strictly consistent with those in Example 1.

[0055] Example 9

[0056] This embodiment prepares the cell coating film with reference to the formula and method provided in Example 1. The difference from Example 1 is that in this embodiment, when preparing the thermosensitive layer of the cell coating film, an equal mass fraction of ethylene-butene copolymer is used instead of POE. Apart from the above differences, the operation steps for preparing the cell coating film in this embodiment are strictly consistent with those in Example 1.

[0057] Example 10

[0058] This embodiment prepares a cell coating film with reference to the formula and method provided in Example 1. The difference from Example 1 is that in this embodiment, when preparing the thermosensitive layer of the cell coating film, an equal mass fraction of LLDPE with a crystallinity of 20% is used instead of LLDPE. Apart from the above differences, the operation steps for preparing the cell coating film in this embodiment are strictly consistent with those in Example 1.

[0059] Example 11

[0060] This embodiment prepares the cell coating film with reference to the formula and method provided in Example 1. The difference from Example 1 is that in this embodiment, random copolymer polypropylene (PPR) is used instead of PPB in equal parts by mass when preparing the heat-sensitive layer of the cell coating film. Apart from the above differences, the operation steps for preparing the cell coating film in this embodiment are strictly consistent with those in Example 1.

[0061] Example 12

[0062] This embodiment prepares a cell coating film with reference to the formula and method provided in Example 1. The difference from Example 1 is that the formula of the thermosensitive layer of the cell coating film prepared in this embodiment is shown in Table 2 (keeping the total mass fraction unchanged). Apart from the above differences, the operation steps for preparing the cell coating film in this embodiment are strictly consistent with those in Example 1.

[0063] Table 2. Formulation for preparing the thermosensitive layer in Example 12

[0064]

[0065] Example 13

[0066] This embodiment prepares a cell coating film with reference to the formula and method provided in Embodiment 1. The difference from Embodiment 1 is that in this embodiment, only a first thin film layer is set when preparing the substrate layer of the cell coating film, and the thickness of the first thin film layer is 80 μm. Apart from the above differences, the operation steps for preparing the cell coating film in this embodiment are strictly consistent with those in Embodiment 1.

[0067] Example 14

[0068] This embodiment prepares a cell coating film with reference to the formula and method provided in Embodiment 1. The difference from Embodiment 1 is that in this embodiment, only a third thin film layer is set when preparing the substrate layer of the cell coating film, and the thickness of the third thin film layer is 80 μm. Apart from the above differences, the operation steps for preparing the cell coating film in this embodiment are strictly consistent with those in Embodiment 1.

[0069] Comparative Example 1

[0070] This comparative example prepares a battery cell coating film using the formulation and method provided in Example 1. The difference between this comparative example and Example 1 is that, in preparing the heat-sensitive layer of the battery cell coating film, polypropylene, low-density polyethylene, and polyethylene elastomer are used in equal parts by mass to replace polyethylene derivatives (polyethylene derivatives are not added). Furthermore, the mass ratio of polypropylene, low-density polyethylene, and polyethylene elastomer in the formulation is maintained at 30:15:30. Apart from the above differences, the operation steps for preparing the battery cell coating film in this comparative example are strictly consistent with those in Example 1.

[0071] Comparative Example 2

[0072] This comparative example prepares a battery cell coating film using the formula and method provided in Example 1. The difference between this comparative example and Example 1 is that, in preparing the heat-sensitive layer of the battery cell coating film, polypropylene, polyethylene elastomer, and polyethylene derivative are used in equal parts by mass to replace low-density polyethylene (low-density polyethylene is not added). Furthermore, the mass ratio of polypropylene, polyethylene elastomer, and polyethylene derivative in the formula is maintained at 30:30:20. Apart from the above differences, the operation steps for preparing the battery cell coating film in this comparative example are strictly consistent with those in Example 1.

[0073] Comparative Example 3

[0074] This comparative example prepares a battery cell coating film using the formula and method provided in Example 1. The difference between this comparative example and Example 1 is that, in preparing the heat-sensitive layer of the battery cell coating film, polypropylene, low-density polyethylene, and polyethylene derivatives are used in equal parts by mass to replace polyethylene elastomer (polyethylene elastomer is not added), and the mass ratio of polypropylene, low-density polyethylene, and polyethylene derivatives in the formula is maintained at 30:15:20. Apart from the above differences, the operation steps for preparing the battery cell coating film in this comparative example are strictly consistent with those in Example 1.

[0075] Comparative Example 4

[0076] This comparative example prepares a battery cell coating film using the formula and method provided in Example 1. The difference between this comparative example and Example 1 is that, in preparing the heat-sensitive layer of the battery cell coating film, low-density polyethylene, polyethylene elastomer, and polyethylene derivative are used in equal parts by mass to replace polypropylene (polypropylene is not added). Furthermore, the mass ratio of low-density polyethylene, polyethylene elastomer, and polyethylene derivative in the formula is maintained at 15:30:20. Apart from the above differences, the operation steps for preparing the battery cell coating film in this comparative example are strictly consistent with those in Example 1.

[0077] Test case

[0078] 1. Test Object

[0079] The cell wrapping films prepared in Examples 1-14 and Comparative Examples 1-4 were cut into 25mm*150mm samples.

[0080] 2. Testing Methods

[0081] (1) Peel force test: According to the national standard GB / T88081988, the test object is subjected to peel force test at a speed of 300mm / min and 180° stretching in an environment of 23±2℃ and relative humidity of 50±5%.

[0082] (2) Electrolyte peel strength test: According to the national standard GB / T 11547-2008, the test object is hot-pressed with PP film at 0.5MPa and 150℃ for 2 seconds, then soaked in electrolyte at 85±5℃ for 4 hours, and then removed. The residual electrolyte is wiped off with lint-free paper, and then left to stand at room temperature for 12 hours. The PP film is then fixed to the steel plate with double-sided tape, and the tape is pulled apart with a peel strength tester at a speed of 300mm / min.

[0083] (3) Heat shrinkage rate test: According to the national standard GBT 34848-2017, the test object is kept at 110℃ for 48 hours and then naturally cooled to room temperature. The change rate of the length of the test object before and after heat preservation is tested.

[0084] (4) Puncture strength (RPS) test: According to the national standard GB / T 37841-2019, the test object is subjected to puncture resistance test at a speed of 50 mm / min in an environment of 23±2℃ and 50±10% relative humidity.

[0085] (5) Appearance performance of cell coating film: Observe whether the test object has problems such as falling off, slipping, delamination, or lifting during use (such as laying, hot pressing, and shell insertion). If there are no problems such as falling off, slipping, delamination, or lifting, “O” indicates qualified. If at least one of the following conditions occurs, “X” indicates unqualified.

[0086] 3. Test Results and Analysis

[0087] The test results for this test example are shown in Table 3. In Examples 1-8, the performance of the battery cell coating film provided in Examples 1-8 was affected because different polyethylene derivatives were selected to prepare the thermosensitive layer. Examples 1-4 show that when at least one of ethylene-ethyl acrylate copolymer, ethylene-ethyl acrylate-maleic anhydride copolymer, and ethylene-butyl acrylate copolymer is selected as the polyethylene derivative, the adhesion between the thermosensitive layer and the substrate layer, as well as its high-temperature resistance, can be significantly enhanced. The test data from Examples 1 and 5-6 show that although EVA is also a copolymer of ethylene and vinyl acetate, the introduction of EVM in the battery cell coating film provided by this invention can better enhance the high-temperature resistance of the thermosensitive layer. Furthermore, although the VA mass fraction of EVM can be between 0.4 and 0.8 in the prior art, experiments have shown that in the battery cell coating film provided by this invention, when the VA mass fraction of EVM is between 0.4 and 0.6, it has better electrolyte resistance. By comparing Examples 1 and 7-8, it can be seen that good electrolyte resistance can be achieved by using only ethylene-acrylate copolymer or ethylene and vinyl acetate copolymer in the thermosensitive layer; furthermore, when ethylene-acrylate copolymer and ethylene and vinyl acetate copolymer are used together, the electrolyte resistance of the cell coating film can be further enhanced.

[0088] Comparison of Examples 1 and 9-10 confirms that when the polyethylene elastomer is an ethylene-octene copolymer, and the crystallinity of the octene end in the ethylene-octene copolymer is 30-50%, the battery cell coating film exhibits better peel strength. Furthermore, when the low-density polyethylene is LLDPE and the crystallinity of LLDPE is ≥24.5%, the heat-sensitive layer in the battery cell coating film shows better toughness. In Example 10, it is evident that when the polypropylene is PPB and the crystallinity of PPB is 75-90%, it exhibits high toughness. Combined with Comparative Example 1, it is clear that by incorporating polyethylene derivatives, the poor high-temperature resistance of PPB can be improved.

[0089] As can be seen from Examples 1 and 12, the formulation of the thermosensitive layer also affects its performance. The thermosensitive layer provided in Example 12 has better puncture resistance due to its higher rigidity, but its electrolyte resistance and high temperature resistance are somewhat reduced.

[0090] As can be seen from Examples 13-14, compared with the multilayer structure of the substrate layer in Example 1, the overall performance of the cell coating film provided in Examples 13-14 is reduced to varying degrees.

[0091] Comparative Examples 1-3 show that polyethylene elastomer, low-density polyethylene, and polyethylene derivatives have a synergistic effect. The absence of any one of them will simultaneously lead to problems such as detachment, slippage, delamination, and warping of the battery cell coating film. Therefore, the combination of polyethylene elastomer, low-density polyethylene, and polyethylene derivatives can achieve a synergistic effect greater than the sum of its parts (1+1>2). Furthermore, as shown in Comparative Example 4, the addition of polypropylene can effectively improve the structural strength of the battery cell coating film, ensuring it reaches a suitable strength and preventing warping and slippage during use.

[0092] Table 3. Test Results of this Test Case

[0093]

[0094]

[0095] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An electrode core wrapping film, characterized by, The battery cell wrapping film comprises a substrate layer and a heat-sensitive layer; The substrate layer comprises a first film layer, a second film layer and a third film layer arranged in sequence, wherein the first film layer comprises polyethylene terephthalate; The second film layer comprises ethylene-vinyl acetate copolymer; The third film layer comprises unstretched polypropylene; The heat-sensitive layer comprises polyethylene and polypropylene, wherein the polyethylene comprises polyethylene elastomer, low-density polyethylene and polyethylene derivative; The polyethylene elastomer is ethylene-octene copolymer, The polyethylene derivative comprises ethylene-acrylate copolymer and ethylene-vinyl acetate copolymer, wherein the ethylene-vinyl acetate copolymer comprises ethylene-vinyl acetate rubber with a mass fraction of vinyl acetate of 0.4-0.

6.

2. The cell wrapping film of claim 1, wherein, The ethylene-acrylate copolymer comprises at least one of ethylene-ethyl acrylate copolymer, ethylene-ethyl acrylate-maleic anhydride copolymer and ethylene-butyl acrylate copolymer.

3. The cell wrapping film of claim 1, wherein, The ethylene-octene copolymer has a crystallinity of 30-50% at the octene end.

4. The cell wrapping film of claim 1, wherein, The low-density polyethylene is linear low-density polyethylene with a crystallinity of ≥24.5%.

5. The cell wrapping film of claim 1, wherein, The polypropylene comprises block copolymerized polypropylene with a crystallinity of 75-90%.

6. The cell wrapping film of claim 1, wherein, In the heat-sensitive layer, the polypropylene accounts for 25-35 parts by mass, the polyethylene elastomer accounts for 20-45 parts by mass, the low-density polyethylene accounts for 10-25 parts by mass and the polyethylene derivative accounts for 10-25 parts by mass.

7. The cell wrapping film of claim 6, wherein, In the substrate layer, the first film layer: the second film layer: the third film layer = (1-3): 1: (0.5-2) by thickness ratio.

8. The cell wrapping film according to any one of claims 1 to 7, wherein The battery cell wrapping film has a thickness of 50-100 μm, and the heat-sensitive layer has a thickness of 2-10 μm.

9. A battery, characterized by The battery comprises the battery cell wrapping film according to any one of claims 1-8.

Images