Mylar film and lithium ion batteries

Abstract

The utility model provides a kind of Mylar film and lithium ion battery.The Mylar film has insulation, along the thickness direction of Mylar film, Mylar film includes sequentially arranged base layer, elastic buffer layer and protective layer, base layer is used to support elastic buffer layer, elastic buffer layer is configured to be able to elastically deform, protective layer is compounded on the surface of elastic buffer layer and can be deformed, protective layer is used to block electrolyte permeation to elastic buffer layer.The technical scheme of the utility model solves the problem of uneven distribution of electrolyte caused by the rigidity of Mylar film in the prior art.

Description

Technical Field

[0001] This utility model relates to the field of lithium-ion battery technology, and more specifically, to a Mylar film and a lithium-ion battery. Background Technology

[0002] Square lithium-ion batteries are widely used in consumer electronics (such as smartphones and laptops) and power batteries (such as new energy vehicles and energy storage devices) due to their advantages such as high energy density, regular size, and strong adaptability. Their core component, the Mylar membrane (mainly composed of polyethylene terephthalate, PET), is a key insulating component that ensures the safety and stable operation of the battery.

[0003] In existing technologies, the Mylar film of square lithium-ion batteries is wrapped around the outer periphery of the core. It generally adopts a single-layer or multi-layer PET substrate structure. The chemical stability is improved by coating with an electrolyte-resistant coating (such as PVDF coating). It mainly achieves three core functions: "isolation and insulation between the cell and the metal shell", "blocking electrolyte corrosion" and "assisting cell shaping". During the charging process of a square lithium-ion battery, the core expands in volume due to lithium ion insertion and extraction, causing dynamic changes in the gap between the core and the metal casing. In the early stages of charging, the core volume is small, and electrolyte tends to accumulate at the bottom and edges of the core. In the middle and later stages of charging, the core expands, squeezing the electrolyte in the gap. However, the existing Mylar film is a rigid PET structure and cannot adapt to the expansion of the core. It can only passively withstand the compression and cannot actively push the accumulated electrolyte to electrolyte-deficient areas on the core surface (such as the top and middle active material areas of the core). It will also exacerbate the accumulation of electrolyte in concave areas (such as the corner gaps between the core and the casing), leading to uneven electrolyte distribution. After long-term cycling, it is prone to local lithium plating, resulting in a shortened battery cycle life and a short circuit risk. Utility Model Content

[0004] The main objective of this invention is to provide a Mylar membrane and a lithium-ion battery to solve the problem of uneven electrolyte distribution caused by the rigidity of the Mylar membrane in the prior art.

[0005] To achieve the above objectives, this utility model provides a Mylar membrane. The Mylar membrane has insulating properties. Along the thickness direction of the Mylar membrane, the Mylar membrane includes a base layer, an elastic buffer layer, and a protective layer arranged sequentially. The base layer is used to support the elastic buffer layer. The elastic buffer layer is constructed to undergo elastic deformation. The protective layer is composited on the surface of the elastic buffer layer and is also capable of deformation. The protective layer is used to prevent electrolyte from penetrating into the elastic buffer layer.

[0006] Furthermore, the elastic buffer layer is provided with staggered micropores.

[0007] Furthermore, the Mylar membrane is bent to form a top covering surface, a bottom covering surface, and four side covering surfaces. The top covering surface, the bottom covering surface, and the four side covering surfaces are used to enclose a cuboid cell chamber. At least one of the following thicknesses is greater than the thickness of the remaining area of ​​the elastic buffer layer: the thickness of the elastic buffer layer in the area where the top covering surface is located, the thickness of the elastic buffer layer in the area where the bottom covering surface is located, and the thickness of the elastic buffer layer in the area where the corner of the cell chamber is located.

[0008] Furthermore, the thickness of the elastic buffer layer in the area where the top covering surface is located, the thickness of the elastic buffer layer in the area where the bottom covering surface is located, and the thickness of the elastic buffer layer in the area where the corner of the cell chamber is located are all 20μm-30μm thicker than the thickness of the remaining area of ​​the elastic buffer layer.

[0009] Furthermore, the Mylar membrane also includes a hot melt adhesive layer, with a hot melt adhesive layer provided between the base layer and the elastic buffer layer; and / or, with a hot melt adhesive layer provided between the elastic buffer layer and the protective layer.

[0010] Furthermore, the thickness of the hot melt adhesive layer ranges from 5μm to 8μm.

[0011] Furthermore, the base layer and the elastic buffer layer are connected by plasma surface treatment and hot-pressing composite bonding; and / or, the elastic buffer layer and the protective layer are connected by plasma surface treatment and hot-pressing composite bonding.

[0012] Furthermore, the thickness of the Mylar membrane ranges from 85 μm to 198 μm.

[0013] Furthermore, the thickness of the base layer ranges from 25μm to 50μm; or the thickness of the protective layer ranges from 5μm to 10μm; or the thickness of the elastic buffer layer ranges from 50μm to 130μm.

[0014] Furthermore, the compression resilience of the elastic buffer layer is ≥80%; or, the volume resistivity of the base layer is > Or, the electrolyte permeability of the protective layer is < .

[0015] According to another aspect of the present invention, the present invention provides a lithium-ion battery, including a battery cell, the aforementioned Mylar film, and a battery casing. The battery cell is located inside the battery casing, the Mylar film covers the battery cell, the protective layer is in contact with the surface of the battery cell, and the base layer is in contact with the inner wall surface of the battery casing.

[0016] By applying the technical solution of this utility model, the elastic buffer layer can undergo elastic deformation when the core expands. It can not only passively adapt to the expansion of the core, but also actively adjust the distribution of electrolyte through the rebound force after deformation. The compression ratio of the elastic buffer layer changes synchronously with the expansion ratio of the core. When the core expands and squeezes the Mylar film during charging, the elastic buffer layer has a large compression in the convex area of ​​the core, pushing the electrolyte to the electrolyte-deficient areas on the core surface (such as the top and corners of the core). In the concave area of ​​the core, the compression of the elastic buffer layer is smaller, and it absorbs the surrounding electrolyte through its rebound characteristics, thereby achieving a dynamic and uniform distribution of electrolyte on the core surface. In this way, the problem of uneven electrolyte distribution caused by the rigidity of the Mylar film in the prior art can be solved, the local lithium plating phenomenon can be reduced, the cycle life and safety of the battery can be improved, and the risk of short circuit can be reduced. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an undue limitation of the present invention. In the drawings: Figure 1 A schematic diagram of an embodiment of the Mylar membrane of this invention is shown; Figure 2 A schematic diagram of the unfolded structure of the Mylar membrane of this invention is shown.

[0018] The above figures include the following reference numerals: 11. Base layer; 12. Elastic buffer layer; 13. Protective layer; 14. Hot melt adhesive layer; 21. Top covering surface; 22. Bottom covering surface; 23. Side covering surface. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0020] This utility model provides a lithium-ion battery, including a battery cell, a Mylar film, and a battery casing. The battery cell is located inside the battery casing, the Mylar film covers the battery cell, a protective layer 13 is in contact with the surface of the battery cell, and a base layer 11 is in contact with the inner wall of the battery casing (aluminum or steel). By using the Mylar film described below, dynamic and uniform distribution of electrolyte on the surface of the battery cell can be achieved, effectively preventing local lithium plating and improving battery safety and cycle life.

[0021] In some embodiments, the lithium-ion battery is a square lithium-ion battery.

[0022] In some embodiments, the battery cell is a wound core, and its shape is square.

[0023] like Figure 1 and Figure 2 As shown, an embodiment of the present invention provides a Mylar membrane. The Mylar membrane has insulating properties. Along the thickness direction of the Mylar membrane, the Mylar membrane includes a base layer 11, an elastic buffer layer 12, and a protective layer 13 arranged sequentially. The base layer 11 is used to support the elastic buffer layer 12. The elastic buffer layer 12 is constructed to undergo elastic deformation. The protective layer 13 is composited on the surface of the elastic buffer layer 12 and is also capable of deformation. The protective layer 13 is used to prevent electrolyte from penetrating into the elastic buffer layer 12.

[0024] In the above technical solution, the elastic buffer layer 12 can undergo elastic deformation when the core expands. It can not only passively adapt to the expansion of the core, but also actively adjust the distribution of electrolyte through the rebound force after deformation. The compression ratio of the elastic buffer layer 12 changes synchronously with the expansion ratio of the core. When the core expands and squeezes the Mylar film during charging, the elastic buffer layer 12 has a large compression in the convex area of ​​the core, pushing the electrolyte to the electrolyte-deficient area on the surface of the core (such as the top and corners of the core). In the concave area of ​​the core, the compression of the elastic buffer layer 12 is smaller, and it absorbs the surrounding electrolyte through its rebound characteristics, thereby achieving a dynamic and uniform distribution of electrolyte on the surface of the core. In this way, the problem of uneven electrolyte distribution caused by the rigidity of the Mylar film in the prior art can be solved, the local lithium plating phenomenon can be reduced, the cycle life and safety of the battery can be improved, and the short circuit risk can be reduced.

[0025] Specifically, in the embodiments of this utility model, the working process when the square lithium-ion battery is charged is as follows: First, in the initial charging stage (before the core expands significantly): the elastic buffer layer 12 of the Mylar film is in its natural state, the protective layer 13 adheres to the surface of the core, and the electrolyte is evenly distributed between the core and the protective layer 13.

[0026] Then, in the later stages of charging (core volume expansion): the core expands due to lithium ion insertion, squeezing the protective layer 13 of the Mylar film outwards. The protective layer 13 transmits the squeezing force to the elastic buffer layer 12, which undergoes compression deformation under pressure (the compression rate changes synchronously with the core expansion rate, typically 0.5%-3%). At this time, the elastic buffer layer 12 stores elastic potential energy. During the compression process, the elastic buffer layer 12 actively squeezes the electrolyte between the core and the protective layer 13. Specifically, for the protruding areas of the core (e.g., the expanded areas), the compression amount of the elastic buffer layer 12 is larger, pushing the electrolyte in that area towards the surrounding concave areas (e.g., the top and corners of the core); for the concave areas of the core (e.g., the top and corners after the core has expanded), the compression amount of the elastic buffer layer 12 is smaller, absorbing the surrounding electrolyte through its own elastic potential energy to achieve dynamic adjustment of the electrolyte, thereby achieving dynamic and uniform distribution of the electrolyte on the surface of the core.

[0027] Finally, charging ends (core shrinks): After charging ends, the core volume shrinks and recovers, the pressure on the elastic buffer layer 12 disappears, and it returns to its natural state thanks to the resilience of the elastic buffer layer 12, preparing for electrolyte adjustment for the next charge.

[0028] It should be noted that when the battery cell expands, it compresses the Mylar membrane, increasing the pressure in the area where the elastic buffer layer 12 is located (forming a high-pressure zone). According to Bernoulli's principle, fluids flow from high-pressure areas to low-pressure areas, thus pushing the electrolyte to other areas on the battery cell surface (electrolyte-deficient areas, i.e., low-pressure zones). Conversely, when the battery cell contracts, the elastic buffer layer 12 returns to its original shape, reducing the pressure in these areas and attracting the surrounding electrolyte to flow back.

[0029] To alleviate the problem of uneven electrolyte distribution, existing technologies mainly improve the electrolyte injection process by optimizing it. One approach involves using high-pressure nitrogen to pulse-impact the injection hole, evacuating to -0.07MPa to -0.09MPa and maintaining this pressure for 30 to 150 seconds, followed by electrolyte injection and a settling period of 100 to 600 seconds. This pulse-impact method breaks the electrostatic adsorption between the positive electrode, separator, and negative electrode, promoting electrolyte penetration. However, this method increases production steps, leading to higher battery manufacturing costs. In contrast, the composite Mylar membrane with an elastic buffer layer in this invention integrates a compressible, resilient, and acid- and alkali-resistant elastic material layer into the traditional Mylar membrane structure. This eliminates the need for optimized electrolyte injection processes and allows for the active compression and uniform distribution of the electrolyte during core charging expansion, thus reducing battery manufacturing costs.

[0030] like Figure 1 and Figure 2As shown in the embodiment of this utility model, the elastic buffer layer 12 is provided with staggered micro-holes.

[0031] In the above technical solution, the introduction of micropores can increase the deformation capability of the elastic buffer layer 12, enabling it to compress and rebound more effectively when the core expands. At the same time, the presence of micropores helps the electrolyte to penetrate and distribute. Thus, with the assistance of micropores, the uniformity of electrolyte distribution can be improved, the risk of local lithium plating can be reduced, and the cycle stability and overall performance of the battery can be improved.

[0032] Furthermore, the micropore structure can store liquid like a sponge. In the Mylar membrane, the micropores of the elastic buffer layer 12 can temporarily hold excess electrolyte during the initial charging stage or in an unpressurized state. When the core expands during charging, the electrolyte stored inside the micropores is compressed, and the electrolyte is actively released and redistributed to electrolyte-deficient areas on the cell surface, such as the top and corners of the core. This release mechanism ensures that the electrolyte can uniformly cover the electrode material, promoting efficient lithium-ion transport between the positive and negative electrodes, avoiding localized drying, reducing the risk of lithium dendrite formation, and thus improving the battery's cycle performance and safety. Therefore, the liquid storage and release functions of the micropores enable the Mylar membrane to dynamically adjust the electrolyte distribution according to changes in the core state.

[0033] It should be noted that micropores generally refer to holes, channels, or cavities with sizes on the micrometer (μm) scale. The specific size of micropores typically ranges from hundreds of nanometers to tens of micrometers, which allows them to significantly affect the physical and chemical properties of materials at the microscale, while maintaining the integrity and continuity of materials at the macroscale.

[0034] like Figure 1 and Figure 2 As shown in the embodiment of this utility model, the Mylar membrane is bent to form a top covering surface 21, a bottom covering surface 22, and four side covering surfaces 23. The top covering surface 21, the bottom covering surface 22, and the four side covering surfaces 23 are used to enclose a cuboid cell chamber. At least one of the following thicknesses is greater than the thickness of the remaining area of ​​the elastic buffer layer 12: the thickness of the elastic buffer layer 12 in the area where the top covering surface 21 is located, the thickness of the elastic buffer layer 12 in the area where the bottom covering surface 22 is located, and the thickness of the elastic buffer layer 12 in the area where the corner of the cell chamber is located.

[0035] In the above technical solution, the areas where the top covering surface 21, the bottom covering surface 22, and the corners of the cell chamber are areas where electrolyte tends to accumulate. By increasing the thickness of the elastic buffer layer 12 in these areas, the squeezing effect in these areas can be enhanced. This makes it easier to push the electrolyte to electrolyte-deficient areas on the core surface (such as the top and corners of the core), thereby more effectively achieving a dynamic and uniform distribution of electrolyte on the core surface.

[0036] It should be noted that when the thickness of the elastic buffer layer 12 in the region where only the top covering surface 21 is located is greater than the thickness of the remaining region of the elastic buffer layer 12, the remaining region refers to all other parts of the elastic buffer layer 12 except for the region where the top covering surface 21 is located; when the thickness of the elastic buffer layer 12 in the region where only the bottom covering surface 22 is located is greater than the thickness of the remaining region of the elastic buffer layer 12, the remaining region refers to all other parts of the elastic buffer layer 12 except for the region where the bottom covering surface 22 is located; when the thickness of the elastic buffer layer 12 in the region where only the corner of the cell chamber is located is greater than the thickness of the remaining region of the elastic buffer layer 12... When the thickness is specified, the remaining area refers to all other parts of the elastic buffer layer 12 except for the area where the corner of the battery cell chamber is located. When the thickness of the elastic buffer layer 12 in the area where the top covering surface 21 is located, the thickness of the elastic buffer layer 12 in the area where the bottom covering surface 22 is located, and the thickness of the elastic buffer layer 12 in the area where the corner of the battery cell chamber is located are all greater than the thickness of the remaining area of ​​the elastic buffer layer 12, the remaining area refers to all other parts of the elastic buffer layer 12 except for the area where the top covering surface 21 is located, the area where the bottom covering surface 22 is located, and the area where the corner of the battery cell chamber is located. The same applies to other cases, which will not be elaborated here.

[0037] It should be noted that the top covering 21 covers the top wall of the square core, the bottom covering 22 covers the bottom wall of the square core, and the four side coverings 23 cover the four side walls of the square core.

[0038] like Figure 1 and Figure 2 As shown in the embodiment of this utility model, the thickness of the elastic buffer layer 12 in the area where the top covering surface 21 is located, the thickness of the elastic buffer layer 12 in the area where the bottom covering surface 22 is located, and the thickness of the elastic buffer layer 12 in the area where the corner of the cell chamber is located are all 20μm-30μm thicker than the thickness of the remaining area of ​​the elastic buffer layer 12.

[0039] In the above technical solution, the thickness difference enables the elastic buffer layer 12 to more effectively compress and distribute the electrolyte when the core expands. Especially in key areas such as the top, bottom and corners of the core, the thickened elastic buffer layer 12 can better adapt to the volume change of the core, prevent excessive accumulation of electrolyte in these areas, improve the uniformity of electrolyte wetting, and thus extend the cycle life of the battery.

[0040] like Figure 1 and Figure 2 As shown in the embodiments of this utility model, the Mylar film further includes a hot melt adhesive layer 14, which is provided between the base layer 11 and the elastic buffer layer 12; and / or, a hot melt adhesive layer 14 is provided between the elastic buffer layer 12 and the protective layer 13. Thus, through the adhesive effect of the hot melt adhesive layer 14, a stable bond can be ensured between the base layer 11, the elastic buffer layer 12, and the protective layer 13, thereby improving the overall structural strength and durability of the Mylar film.

[0041] In some embodiments, the hot melt adhesive layer 14 is a modified epoxy resin hot melt adhesive (electrolyte resistant type), which not only provides good adhesion but also ensures stability in an electrolyte environment.

[0042] In some embodiments, the base layer 11, the elastic buffer layer 12, and the protective layer 13 are connected by hot melt adhesive bonding and hot-pressing composite process. Specifically, the inner side of the base layer 11 (PET) (towards the core) is bonded to the outer side of the elastic buffer layer 12 (fluororubber-based TPE) with a modified epoxy resin hot melt adhesive (electrolyte resistant type) with a thickness of 5μm-8μm, and the inner side of the elastic buffer layer 12 is bonded to the outer side of the protective layer 13 (PTFE coating) with the same hot melt adhesive.

[0043] In the embodiments of this utility model, the thickness of the hot melt adhesive layer 14 ranges from 5μm to 8μm. By controlling the thickness of the hot melt adhesive layer 14 within the range of 5μm to 8μm, good bonding effect and structural stability can be ensured, while avoiding waste of internal battery space due to excessive thickness of the hot melt adhesive layer 14.

[0044] In some embodiments, the base layer 11 and the elastic buffer layer 12, and / or the elastic buffer layer 12 and the protective layer 13, are joined by plasma surface treatment and hot-press bonding. This achieves a tight connection between the base layer 11, the elastic buffer layer 12, and the protective layer 13. Furthermore, the plasma surface treatment and hot-press bonding eliminate the need for hot melt adhesives. By activating the surfaces of the base layer 11 and the elastic buffer layer 12 with plasma, interfacial adhesion can be improved, thereby increasing production efficiency. Specific implementations can utilize existing technologies.

[0045] In this embodiment of the invention, the thickness of the Mylar film ranges from 85μm to 198μm. Since the gap between the square battery casing and the core is typically 100μm-200μm, the overall thickness after lamination is 85μm-198μm, which meets the internal space requirements of the square battery casing. Specifically, the thickness ranges from 105μm to 198μm in the areas containing the top covering surface 21, the bottom covering surface 22, and the corners of the cell chamber; the thickness of the remaining areas of the Mylar film ranges from 85μm to 168μm.

[0046] In the embodiments of this utility model, the thickness of the base layer 11 ranges from 25μm to 50μm; or the thickness of the protective layer 13 ranges from 5μm to 10μm; or the thickness of the elastic buffer layer 12 ranges from 50μm to 130μm.

[0047] In the above technical solution, controlling the thicknesses of the base layer 11, protective layer 13, and elastic buffer layer 12 within the aforementioned range ensures a balance between insulation, electrolyte regulation capability, and structural stability of the Mylar membrane. Specifically, the thickness of the base layer 11 affects insulation performance and structural support; the thickness of the protective layer 13 affects electrolyte barrier properties and the coefficient of friction; and the thickness of the elastic buffer layer 12 affects electrolyte regulation and resilience. By optimizing the thickness of each layer, the optimal performance of the Mylar membrane under different functional requirements can be achieved.

[0048] Specifically, the thickness of the elastic buffer layer 12 in the area where the top covering surface 21 is located, the elastic buffer layer 12 in the area where the bottom covering surface 22 is located, and the elastic buffer layer 12 in the area where the corner of the cell chamber is located ranges from 70μm to 130μm; the thickness of the remaining area of ​​the elastic buffer layer 12 ranges from 50μm to 100μm.

[0049] In some embodiments, the compression rebound rate of the elastic buffer layer 12 is ≥80%; thus, the elastic buffer layer 12 is compressed when squeezed by the core and rebounds after the pressure is released, which can actively squeeze the electrolyte.

[0050] In some embodiments, the volume resistivity of the base layer 11 is greater than that of the substrate 11. This provides basic insulation.

[0051] In some embodiments, the electrolyte permeability of the protective layer 13 is < This prevents the electrolyte from penetrating into the elastic buffer layer 12, thereby reducing the aging of the elastic buffer layer 12.

[0052] In some embodiments, the coefficient of friction of the protective layer 13 is ≤0.15, which reduces the friction between the Mylar film and the core.

[0053] The above parameters directly affect the electrolyte regulation effect and battery safety.

[0054] In some embodiments, the base layer 11 is made of modified PET (meaning PET material with 10%-15% glass fiber and 1%-10% graphene added; or 10%-15% glass fiber and 1%-10% carbon nanotubes; or 10%-15% glass fiber and 1%-10% molten salt; or 10%-15% glass fiber and 1%-10% organic phase change material (paraffin or acetic acid) added). This allows the base layer 11 to have a tensile strength ≥65MPa, a temperature resistance range of -30℃ to 120℃, and a volume resistivity > This is so that the base layer 11 can provide basic insulation, structural support and thermal conductivity.

[0055] In some embodiments, the elastic buffer layer 12 is made of fluororubber-based thermoplastic elastomer (TPE) with a compression resilience ≥85% (25°C, 30% compression ratio) and good resistance to electrolyte corrosion (immersion in 1mol / L solution). In the electrolyte, the mass change rate is <2% after 25℃×1000h, and it has good acid and alkali resistance (no cracking after immersion in electrolyte with pH 2-12 for 25℃×500h).

[0056] In some embodiments, if it is necessary to improve the temperature resistance (such as to adapt to power batteries in high-temperature environments), the fluororubber-based TPE material of the elastic buffer layer 12 can be replaced with a perfluoroether rubber-based elastomer, which has a temperature resistance range of -50℃ to 200℃ and a compression rebound rate of ≥80%, as can be found in the prior art.

[0057] In some embodiments, the protective layer 13 is a polytetrafluoroethylene (PTFE) coating.

[0058] It should be noted that the base layer 11, the elastic buffer layer 12, and the protective layer 13 work together to achieve insulation, elastic compression, and resistance to electrolyte corrosion.

[0059] It should be noted that, to verify the effectiveness of this technical solution, a comparative experiment was conducted: Square lithium-ion batteries of the same specifications (model: ICR18650-3.7V-2000mAh, aluminum casing) were selected and divided into an experimental group (using the Mylar film of this application) and a control group (using existing single-layer PET Mylar film), with 10 batteries in each group. The electrolyte distribution uniformity and battery performance during charging were tested, and the results are shown in Table 1 below: Table 1

[0060] From the above description, it can be seen that the above embodiments of this utility model achieve the following technical effects: the elastic buffer layer can undergo elastic deformation when the core expands, which not only passively adapts to the expansion of the core, but also actively adjusts the distribution of electrolyte through the rebound force after the elastic buffer layer deforms; the compression ratio of the elastic buffer layer changes synchronously with the expansion ratio of the core. When the core expands and squeezes the Mylar film during charging, the elastic buffer layer has a large compression in the convex area of ​​the core, pushing the electrolyte to the electrolyte-deficient area on the surface of the core (such as the top and corners of the core); while in the concave area of ​​the core, the compression of the elastic buffer layer is smaller, and it absorbs the surrounding electrolyte through its rebound characteristics, thereby achieving a dynamic and uniform distribution of electrolyte on the surface of the core. In this way, the problem of uneven electrolyte distribution caused by the rigidity of the Mylar film in the prior art can be solved, the local lithium plating phenomenon can be reduced, the cycle life and safety of the battery can be improved, and the risk of short circuit can be reduced.

[0061] The above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Various modifications and variations can be made to this utility model by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A Mylar film characterized in that, The Mylar membrane is insulating. Along the thickness direction of the Mylar membrane, the Mylar membrane includes a base layer (11), an elastic buffer layer (12), and a protective layer (13) arranged sequentially. The base layer (11) is used to support the elastic buffer layer (12). The elastic buffer layer (12) is constructed to be able to undergo elastic deformation. The protective layer (13) is composited on the surface of the elastic buffer layer (12) and is able to undergo deformation. The protective layer (13) is used to prevent electrolyte from penetrating into the elastic buffer layer (12).

2. The Mylar film as claimed in claim 1, wherein, The elastic buffer layer (12) is provided with staggered micro-holes.

3. The Mylar membrane according to claim 1, characterized in that, The Mylar membrane is bent to form a top covering surface (21), a bottom covering surface (22), and four side covering surfaces (23). The top covering surface (21), the bottom covering surface (22), and the four side covering surfaces (23) are used to enclose a cuboid cell chamber. At least one of the following thicknesses is greater than the thickness of the elastic buffer layer (12) in the area where the top covering surface (21) is located, the elastic buffer layer (12) in the area where the bottom covering surface (22) is located, and the elastic buffer layer (12) in the area where the corner of the cell chamber is located:

4. The Mylar membrane according to claim 3, characterized in that, The thickness of the elastic buffer layer (12) in the area where the top covering surface (21) is located, the thickness of the elastic buffer layer (12) in the area where the bottom covering surface (22) is located, and the thickness of the elastic buffer layer (12) in the area where the corner of the cell chamber is located are all 20μm-30μm thicker than the thickness of the remaining area of ​​the elastic buffer layer (12).

5. The Mylar membrane according to any one of claims 1 to 4, characterized in that, The Mylar film also includes a hot melt adhesive layer (14), which is provided between the base layer (11) and the elastic buffer layer (12); and / or, the hot melt adhesive layer (14) is provided between the elastic buffer layer (12) and the protective layer (13).

6. The Mylar membrane according to claim 5, characterized in that, The thickness of the hot melt adhesive layer (14) ranges from 5μm to 8μm.

7. The Mylar membrane according to any one of claims 1 to 4, characterized in that, The base layer (11) and the elastic buffer layer (12) are connected by plasma surface treatment and hot pressing composite bonding; and / or the elastic buffer layer (12) and the protective layer (13) are connected by plasma surface treatment and hot pressing composite bonding.

8. The Mylar membrane according to any one of claims 1 to 4, characterized in that, The thickness of the Mylar membrane ranges from 85 μm to 198 μm.

9. The Mylar film as claimed in claim 8, wherein, The thickness of the base layer (11) is 25μm-50μm; or the thickness of the protective layer (13) is 5μm-10μm; or the thickness of the elastic buffer layer (12) is 50μm-130μm.

10. The Mylar membrane according to any one of claims 1 to 4, characterized in that, The compression resilience of the elastic buffer layer (12) is ≥80%; or, the volume resistivity of the base layer (11) is > ; Alternatively, the electrolyte permeability of the protective layer (13) is < .

11. A lithium-ion battery, characterized by, The battery includes a battery cell, a Mylar film as described in any one of claims 1 to 10, and a battery casing, wherein the battery cell is located inside the battery casing, the Mylar film covers the battery cell, the protective layer (13) is in contact with the surface of the battery cell, and the base layer (11) is in contact with the inner wall surface of the battery casing.

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