Porous Mylar membrane

Abstract

The embodiment of the invention relates to a porous Mylar membrane which is suitable for a battery structure and comprises a membrane body and a plurality of pores formed in the membrane body, the porosity of the plurality of pores is 10%-50%; and the plurality of pores are uniformly distributed or distributed in a gradient manner. According to the porous Mylar film, the surface area of the film is greatly increased, efficient heat dissipation channels are formed, meanwhile, the electrolyte filled in the pores is also beneficial to heat transfer and diffusion, heat generated in the working process of a battery can be dissipated more timely, and the heat dissipation efficiency can be improved by 10%-50% compared with the prior art. According to the invention, the rising of the internal temperature of the battery can be effectively controlled, the stable performance of the battery is effectively maintained, the performance degradation and safety risk of the battery caused by overheating are reduced, and the service life of the battery is prolonged. The battery is simple in structure, the weight of the battery is reduced, the energy density of the battery is increased, and the liquid retention capacity of the battery is also effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a porous Mylar film. Background Art

[0002] In the context of the accelerating transformation of the current global energy pattern, energy storage battery cells, as the core of energy storage systems, play a decisive role in the development of the entire energy storage industry. Square lithium iron phosphate battery cells are currently the core products in the energy storage field, requiring not only high energy density but also longer cycle life and better safety performance.

[0003] In the structure of square energy storage batteries, the Mylar film plays a key insulation role in isolating the battery cells from the outer shell. Although traditional Mylar films have certain insulation properties, it is still difficult to meet the development needs of lithium battery technology for higher energy density, longer cycle life, and better safety, gradually exposing some limitations. For example, in terms of heat dissipation, the single structure of the Mylar film is difficult to meet the rapid heat dissipation requirements of the battery during high-power charging and discharging, easily leading to heat accumulation inside the battery, affecting battery performance and safety; in terms of electrolyte affinity, ordinary Mylar films have limited adsorption and retention capabilities for electrolytes, which is not conducive to the uniform distribution and long-term stability of electrolytes inside the battery, and thus affects the charge and discharge efficiency and cycle stability of the battery. Summary of the Invention

[0004] Based on this, the present invention provides a porous Mylar film, aiming to solve problems such as the low heat dissipation capacity, low liquid saturation capacity, poor electrolyte affinity, poor insulation performance balance of existing Mylar films, and difficulty in meeting the requirements of higher performance of lithium batteries.

[0005] To achieve the above object, the embodiments of the present invention propose the following technical solution: A porous Mylar film, applicable to a battery structure, includes a film body and a plurality of pores provided on the film body; the porosity of the plurality of pores is 10% - 50%; the plurality of pores are evenly distributed or the plurality of pores are distributed in a gradient.

[0006] As a preferred embodiment, when the plurality of pores are distributed in a gradient, along the thickness direction of the film body, the pore diameter of the pores on the side of the film body close to the battery cell of the battery structure is smaller than the pore diameter of the pores on the side of the film body close to the housing of the battery structure.

[0007] As a preferred embodiment, when the plurality of pores are distributed in a gradient, along the thickness direction of the film body, the density of the pores on the side of the film body close to the battery cell of the battery structure is greater than the density of the pores on the side of the film body close to the housing of the battery structure.

[0008] As a preferred embodiment, the thickness of the membrane body is 0.05 mm to 3 mm.

[0009] As a preferred embodiment, the pore diameter of the pores is 10 nm to 100 nm.

[0010] As a preferred embodiment, the membrane body is prepared from a polymer and a pore-forming agent, and the mass ratio of the polymer to the pore-forming agent is 1:0.1 to 1:0.5.

[0011] As a preferred embodiment, the polymer is one of polyethylene (PP) or polyethylene terephthalate (PET);

[0012] The pore-forming agent is one of paraffin oil, dichloromethane or polyvinyl alcohol.

[0013] As a preferred embodiment, the membrane body is prepared by the following method: mixing the polymer and the pore-forming agent evenly according to a mass ratio of 1:0.1 to 1:0.5 to obtain a mixed raw material; extruding the mixed raw material to obtain a prototype film; stretching the prototype film to obtain a Mylar film; soaking and drying the Mylar film to obtain the membrane body.

[0014] As a preferred embodiment, the mixing time is 10 min to 180 min, and the mixing speed is 500 revolutions per minute to 2500 revolutions per minute. The mixing is carried out in a high-speed mixer. Through high-speed mixing, it can ensure that the pore-forming agent is evenly dispersed in the raw materials, laying a foundation for the subsequent formation of pores.

[0015] As a preferred embodiment, the extrusion temperature is 250 °C to 300 °C, and the extrusion speed is 30 revolutions per minute to 80 revolutions per minute. The extrusion is carried out by melt extrusion in a twin-screw extruder; the extruded material can form a prototype film with the required shape through a required die.

[0016] As a preferred embodiment, the stretching temperature is 80 °C to 120 °C; the longitudinal stretching ratio of the stretching is 2 to 5, and the transverse stretching ratio of the stretching is 2 to 5. The prototype film is subjected to biaxial stretching (longitudinal stretching and transverse stretching) and the stretching conditions (including stretching temperature and stretching ratio) are controlled. During the stretching process, the pore-forming agent forms pores in the prototype film, and at the same time, by precisely controlling the stretching process parameters, a gradient distribution structure or a uniform distribution structure in the thickness direction of the prototype film is achieved.

[0017] As a preferred embodiment, the soaking is carried out by soaking with a cleaning solvent (such as ethanol, etc.); the soaking temperature is 40 °C to 60 °C; the soaking time is 2 h to 6 h. Through soaking, the pore-forming agent in the film can be removed.

[0018] As a preferred embodiment, the drying temperature is 60°C to 100°C; the drying time is 1h to 3h. Through the drying treatment, the residual solvent and moisture in the film can be removed, making the structure of the film stable.

[0019] As a preferred embodiment, the battery structure is a square battery structure.

[0020] As a preferred embodiment, the square battery structure is a square energy storage battery structure; the square energy storage battery structure is a square laminated lithium battery structure.

[0021] The beneficial effects achieved by the present invention: The porous Mylar film of the present application greatly increases the surface area of the film, forming an efficient heat dissipation channel. At the same time, the electrolyte filled in the pores also contributes to the transfer and diffusion of heat, and can more timely dissipate the heat generated during the operation of the battery. Its heat dissipation efficiency can be increased by 10% - 50% compared with the prior art. Through the present application, the rise of the internal temperature of the battery can be effectively controlled, the stable performance of the battery can be effectively maintained, the attenuation of battery performance and safety risks caused by overheating can be reduced, and the service life of the battery is extended. The structure of the present application is simple, which can effectively improve the heat dissipation efficiency of the surface of the battery core inside the battery, reduce the weight of the battery, increase the energy density of the battery, effectively improve the liquid retention capacity of the battery, and improve the cycle life of the battery structure; moreover, it is convenient to disassemble and assemble, easy to maintain, has good stability, is economical, safe and practical, and can well meet the actual use needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the structures shown in these drawings.

[0023] Figure 1 It is a schematic diagram of the overall structure of the porous Mylar film according to an embodiment of the present invention;

[0024] Figure 2 For Figure 1 it is a schematic diagram of the structure of the porous Mylar film from another angle;

[0025] Figure 3 For Figure 2 it is an enlarged schematic diagram at A.

[0026] The realization of the purpose, functional characteristics and advantages of the present invention will be further described in conjunction with the embodiments with reference to the drawings. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0028] It should be noted that if there are directional indications (such as up, down, left, right, front, back, top, bottom...) involved in the embodiments of the present invention, the directional indications are only used to explain the relative position relationship and movement conditions between components in a specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indications will also change accordingly.

[0029] In this application, unless otherwise clearly defined and limited, terms such as "installed", "connected", "connected", "fixed", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0030] It should be noted that when an element is referred to as "fixed to" or "disposed on" another element, it can be directly on the other element or there may also be an intermediate element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element at the same time.

[0031] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions between various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0032] In the prior art, in most cases, the surface of the Mylar film is coated or doped with materials having good thermal conductivity, or the Mylar film is made into a multi-layer composite structure, so as to improve the electrolyte absorption and thermal conductivity. The above methods not only increase the cost, but also have a relatively high difficulty in the transformation project and are difficult to be popularized in batches. Based on this, the present application provides a porous Mylar film.

[0033] Specifically, as Figures 1 to 3 shown, the embodiments of the present invention propose the following technical solution: a porous Mylar film, applicable to a battery structure, including a film body 10 and a plurality of pores 20 provided on the film body 10; the porosity of the plurality of pores 20 is 10% - 50%; the plurality of pores 20 are uniformly distributed or the plurality of pores are gradiently distributed.

[0034] When the porous Mylar film of the present application is applied to a battery structure, the porous Mylar film is disposed between the battery cell and the outer casing. At this time, the pores 20 are filled with an electrolyte. By providing the pores 20, the surface area of the porous Mylar film is greatly increased, forming an efficient heat dissipation channel. At the same time, the electrolyte filled in the pores also contributes to the transfer and diffusion of heat, and can more timely dissipate the heat generated during the operation of the battery. Its heat dissipation efficiency can be increased by 10% - 50% compared with the prior art.

[0035] The porosity of the pores 20 can be set according to actual needs, and can be 10%, or 20%, or 30%, or 40%, or 50%, etc. In the initial stage of the battery, the electrolyte can be stored through the pores 20, and the volume of the Mylar film is used for electrolyte storage. In the later stage of the use of the battery cell, the battery cell expands, and the stored electrolyte can be released by squeezing the Mylar film, maintaining the battery performance and further extending the battery service life; at the same time, by providing the pores, the surface area of the porous Mylar film structure is increased, and the heat transfer path is changed, so that when it acts synergistically with the electrolyte in convective heat conduction, the heat dissipation efficiency of the entire system can be significantly improved, ensuring the safety of the battery cell.

[0036] The porous Mylar film of the present application is made of a polymer material, and its insulation property is not affected under a certain porosity (10% - 50%). The Mylar film of the present application acts synergistically through the above-mentioned multiple dimensions, so as to improve the comprehensive performance of the Mylar film in lithium batteries, so as to meet the requirements of the battery for multi-functional integration such as insulation, heat dissipation, and electrolyte affinity under complex working conditions, thereby providing a key guarantee for the performance improvement and safe and stable operation of square batteries.

[0037] As a preferred embodiment, as Figure 3As shown, when multiple pores 20 are distributed in a gradient, along the thickness direction of the membrane body 10, the pore diameter of the pores 20 on the side of the membrane body 10 close to the battery cell of the battery structure is smaller than the pore diameter of the pores 20 on the side of the membrane body 10 close to the housing of the battery structure.

[0038] As a preferred embodiment, when multiple pores 20 are distributed in a gradient, along the thickness direction of the membrane body 10, the density of the pores 20 on the side of the membrane body 10 close to the battery cell of the battery structure is greater than the density of the pores 20 on the side of the membrane body 10 close to the housing of the battery structure.

[0039] Through the gradient distribution setting, the pores on the side close to the battery cell are relatively small and dense, and the pores on the side close to the housing are relatively large and sparse. In this way, it can effectively prevent the embedding of tiny particles of the electrode sheet on the side close to the battery cell, and the large pores on the side close to the housing are conducive to heat dissipation. On the premise of ensuring the insulation performance, better electrolyte adsorption and heat dissipation characteristics are achieved.

[0040] As a preferred embodiment, the thickness of the membrane body 10 is 0.05 mm to 3 mm. The thickness of the membrane body 10 can be set according to actual needs, and can be 0.05 mm, or 0.1 mm, or 0.9 mm, or 1.5 mm, or 2 mm, or 3 mm, etc.

[0041] As a preferred embodiment, the pore diameter of the pores 20 is 10 nm to 100 nm. The thickness of the pores 20 can be set according to actual needs, and can be 10 nm, or 20 nm, or 50 nm, or 70 nm, or 90 nm, or 100 nm, etc.

[0042] As a preferred embodiment, the membrane body 10 is prepared from a polymer and a pore-forming agent, and the mass ratio of the polymer to the pore-forming agent is 1:0.1 to 1:0.5. The mass ratio of the polymer to the pore-forming agent can be set according to actual needs, and can be 1:0.1, or 1:0.2, or 1:0.3, or 1:0.4, or 1:0.5, etc.

[0043] As a preferred embodiment, the polymer is one of polyethylene (PP) or polyethylene terephthalate (PET);

[0044] The pore-forming agent is one of paraffin oil, dichloromethane or polyvinyl alcohol.

[0045] As a preferred embodiment, the membrane body 10 is prepared by the following method: mixing a polymer and a pore former evenly at a mass ratio of 1:0.1 to 1:0.5 to obtain a mixed raw material; extruding the mixed raw material to obtain a prototype membrane; stretching the prototype membrane to obtain a Mylar membrane; soaking and drying the Mylar membrane to obtain the membrane body.

[0046] As a preferred embodiment, the mixing time is 10 min to 180 min, and the mixing speed is 500 revolutions per minute to 2500 revolutions per minute. The mixing time can be set according to actual needs and can be 10 min, or 30 min, or 60 min, or 120 min, or 180 min, etc. The speed can be set according to actual needs and can be 500 revolutions per minute, or 1000 revolutions per minute, or 1500 revolutions per minute, or 2500 revolutions per minute, etc. The mixing is carried out in a high-speed mixer. Through high-speed mixing, it can ensure that the pore former is evenly dispersed in the raw materials, laying a foundation for the subsequent formation of pores.

[0047] As a preferred embodiment, the extrusion temperature is 250 °C to 300 °C, and the extrusion speed is 30 revolutions per minute to 80 revolutions per minute. The extrusion temperature can be set according to actual needs and can be 250 °C, or 260 °C, or 280 °C, or 300 °C, etc. The speed can be set according to actual needs and can be 30 revolutions per minute, or 40 revolutions per minute, or 60 revolutions per minute, or 80 revolutions per minute, etc. The extrusion is a melt extrusion carried out in a twin-screw extruder; the extruded material can form a prototype membrane with a desired shape through a required die.

[0048] As a preferred embodiment, the stretching temperature is 80 °C to 120 °C; the longitudinal stretching ratio of the stretching is 2 to 5, and the transverse stretching ratio of the stretching is 2 to 5. The stretching temperature can be set according to actual needs and can be 80 °C, or 90 °C, or 100 °C, or 120 °C, etc. The longitudinal stretching ratio of the stretching can be 2, or 3, or 4, or 5, etc. The transverse stretching ratio of the stretching can be 2, or 3, or 4, or 5, etc. The prototype membrane is subjected to biaxial stretching (longitudinal stretching and transverse stretching) and the stretching conditions (including stretching temperature and stretching ratio) are controlled. During the stretching process, the pore former forms pores in the prototype membrane, and at the same time, by precisely controlling the stretching process parameters, a gradient distribution structure or a uniform distribution structure of the prototype membrane in the thickness direction is achieved.

[0049] As a preferred embodiment, the soaking is carried out with a cleaning solvent (such as ethanol, etc.); the temperature of the soaking is 40°C to 60°C; the time of the soaking is 2h to 6h. The soaking temperature can be set according to actual needs, and can be 40°C, or 45°C, or 50°C, or 60°C, etc. The soaking time can be 2h, or 3h, or 5h, or 6h, etc. Through soaking, the pore-forming agent in the membrane can be removed.

[0050] As a preferred embodiment, the drying temperature is 60°C to 100°C; the drying time is 1h to 3h. The drying temperature can be set according to actual needs, and can be 60°C, or 70°C, or 90°C, or 100°C, etc. The drying time can be 1h, or 1.5h, or 2h, or 3h, etc. Through the drying treatment, the residual solvent and moisture in the membrane can be removed, and the structure of the membrane can be stabilized.

[0051] As a preferred embodiment, the battery structure is a square battery structure.

[0052] As a preferred embodiment, the square battery structure is a square energy storage battery structure; the square energy storage battery structure is a square laminated lithium battery structure.

[0053] Through this application, the rise of the internal temperature of the battery can be effectively controlled, the stable performance of the battery can be effectively maintained, the attenuation of the battery performance and the safety risk caused by overheating can be reduced, and the service life of the battery is prolonged. The structure of this application is simple, the heat dissipation efficiency of the surface of the battery core inside the battery can be effectively improved, the weight of the battery is reduced, the energy density of the battery is increased, the liquid retention capacity of the battery is also effectively improved, and the cycle life of the battery structure is improved; moreover, it is convenient to disassemble and assemble, easy to maintain, has good stability, is economically safe and practical, and can well meet the actual use needs.

[0054] In the description of this specification, the description with reference to terms such as "one embodiment", "example", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example.

[0055] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0056] The above are only the preferred embodiments of the present invention, and do not thereby limit the patent scope of the present invention. Any equivalent structural transformation made under the inventive concept of the present invention by using the content of the specification and drawings of the present invention, or any direct / indirect application in other related technical fields, is included within the patent protection scope of the present invention.

Claims

1. A porous Mylar film, characterized in that: The invention is applicable to a battery structure, comprising a membrane body and a plurality of pores arranged on the membrane body; the porosity of the plurality of pores is 10% to 50%; the plurality of pores are evenly distributed or the plurality of pores are gradiently distributed.

2. The porous Mylar film according to claim 1, characterized in that When the plurality of pores are distributed in a gradient, along the thickness direction of the membrane body, the pore diameter of the pores on the side of the membrane body close to the battery core of the battery structure is smaller than the pore diameter of the pores on the side of the membrane body close to the shell of the battery structure.

3. The porous Mylar film according to claim 1, characterized in that When the plurality of pores are distributed in a gradient, along the thickness direction of the membrane body, the density of the pores on the side of the membrane body close to the battery core of the battery structure is greater than the density of the pores on the side of the membrane body close to the shell of the battery structure.

4. The porous Mylar film according to claim 1, characterized in that The thickness of the membrane body is 0.05 mm to 3 mm; the pore diameter is 10 nm to 100 nm.

5. The porous Mylar film according to claim 1, characterized in that The membrane body is prepared from a polymer and a pore-forming agent, and the mass ratio of the polymer to the pore-forming agent is 1:0.1 to 1:0.5; The polymer is one of polyethylene or polyethylene terephthalate; The pore-forming agent is one of paraffin oil, dichloromethane or polyvinyl alcohol.

6. The porous Mylar film according to claim 1, characterized in that The membrane body is prepared by the following method: polymer and pore former are mixed uniformly in a mass ratio of 1:0.1 to 1:0.5 to obtain a mixed raw material; the mixed raw material is extruded to obtain a prototype film; the prototype film is stretched to obtain a Mylar film; the Mylar film is soaked and then dried to obtain a membrane body.

7. The porous Mylar film according to claim 6, characterized in that The mixing time is 10 min to 180 min, and the mixing speed is 500 rpm to 2500 rpm; The extrusion temperature is 250° C. to 300° C., and the extrusion rotation speed is 30 rpm to 80 rpm.

8. The porous Mylar film according to claim 6, characterized in that The stretching temperature is 80° C. to 120° C.; the longitudinal stretching ratio is 2 to 5, and the transverse stretching ratio is 2 to 5.

9. The porous Mylar film according to claim 6, characterized in that The soaking is performed by soaking with a cleaning solvent; the soaking temperature is 40° C. to 60° C.; the soaking time is 2 hours to 6 hours; The drying temperature is 60° C. to 100° C.; the drying time is 1 h to 3 h.

10. The porous Mylar film according to claim 1, characterized in that The battery structure is a square battery structure; the square battery structure is a square energy storage battery structure.

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