Polymer coating with thermal switch function and application thereof

Abstract

The invention relates to a polymer coating with a thermal switch function and application of the polymer coating in a secondary lithium battery pack. The polymer coating comprises a temperature-sensitive layer and a porous thermal insulation layer; wherein the temperature-sensitive layer is formed by N-isopropylacrylamide copolymer, the thickness of the temperature-sensitive layer is 50-200 [mu] m, and the temperature-sensitive layer accounts for 30-70% of the total mass of the coating, and the porous thermal insulation layer is formed on the basis of polyester terephthalate, the thickness of the porous thermal insulation layer is 100-200 [mu] m, and the porous thermal insulation layer accounts for 30-70% of the total mass of the coating. The pore diameter of the polymer coating can change along with the change of the external temperature, and the functions of heat preservation at low temperature and rapid heat dissipation at high temperature can be achieved. The invention also provides an application example of the polymer coating in a secondary lithium battery pack.

Description

Technical Field

[0001] The invention relates to the field of secondary lithium batteries, in particular to a polymer coating with a thermal switch function and application thereof in a secondary lithium battery pack. Background Art

[0002] Currently, electric vehicles powered by lithium-ion batteries have attracted widespread attention, and their sales have shown a steady growth trend. However, some electric vehicles, such as the Tesla Modal S, have experienced a number of serious fire accidents, casting a shadow on the commercialization of such electric vehicles. The failure of lithium battery packs to dissipate heat in time, which in turn leads to thermal runaway of battery cells, is an important cause of these safety accidents (Journal of The Electrochemical Society, 2019, 166, A2065-A2073).

[0003] In order to avoid the risk of thermal runaway of the battery, the main technical solution at present is to construct an insulation layer on the surface of the battery pack or configure a liquid cooling system. For example, patent CN202311792972.4 discloses an integrated structure of a new energy battery pack, which ensures that the heat is not conducted away through the bottom guard plate by spraying an insulation layer on the bottom of the liquid cooling plate, thereby avoiding affecting the thermal insulation performance of the battery pack; patent CN202311555338.9 discloses a safe and highly integrated liquid-cooled energy storage battery pack, which senses the ambient temperature through a thermistor by configuring a hot aerosol device, and starts working when the temperature reaches a predetermined value, thereby suppressing or preventing the occurrence of thermal runaway in the battery pack. However, although the method of constructing an insulation layer can insulate and keep warm, it lacks an efficient way to dissipate heat, and it is easy to cause thermal runaway of the battery under extreme conditions. Although configuring a liquid cooling system can effectively achieve thermal management of the battery pack, it will greatly reduce the energy density of the battery pack. Therefore, it is urgent to develop a method that has good thermal management capabilities and basically does not affect the energy density of the battery pack.

[0004] In summary, the failure of lithium battery packs to dissipate heat in a timely manner, which in turn leads to thermal runaway of the battery cells, is an important cause of these safety accidents. In order to avoid the risk of thermal runaway of batteries, the current main technical solution is to construct an insulation layer on the surface of the battery pack or configure a liquid cooling system. However, these methods have defects in dissipating heat to the outside, or affect the energy density of the battery pack. Therefore, the development of methods that have good thermal management capabilities and basically do not affect the energy density of the battery pack is of great significance to improving the safety of lithium battery packs and promoting the commercialization and popularization of power batteries. Summary of the invention

[0005] The object of the present invention is to provide a polymer coating with a thermal switch function and application thereof in a secondary lithium battery pack.

[0006] To achieve the above purpose, the present invention adopts the following technical solution:

[0007] A polymer coating with a thermal switch function, the polymer coating comprising a temperature-sensitive layer and a porous thermal insulation layer; wherein the temperature-sensitive layer is formed of an N-isopropylacrylamide-based copolymer, has a thickness of 50 to 200 μm, and accounts for 30% to 70% of the total mass of the coating; and the porous thermal insulation layer is formed based on polyethylene terephthalate, has a thickness of 100 to 200 μm, and accounts for 30% to 70% of the total mass of the coating.

[0008] The N-isopropylacrylamide-based copolymer is prepared by free radical polymerization of N-isopropylacrylamide and other monomers; wherein N-isopropylacrylamide accounts for 40-80% of the total mass of the N-isopropylacrylamide-based copolymer, and other monomers account for 20-60% of the mass of the N-isopropylacrylamide-based copolymer.

[0009] The other monomer is a monomer having two or three acrylamide structures, and the monomer contains a sulfone group, a phosphoric acid group or a 1,3,5-triazine-2,4,6-trione group.

[0010] The other monomers are selected from the monomers shown in the following structures,

[0011]

[0012] Among them, A is taken from H, C1-C 10 Alkyl or cyano; a is a natural number from 1 to 10.

[0013] The porous thermal insulation layer is formed based on polyethylene terephthalate; wherein,

[0014] The porous thermal insulation layer of polyethylene terephthalate is formed of polyethylene terephthalate having a porous structure, and the average pore diameter is 50 to 100 nm.

[0015] The polymer coating is coated on the surface of the battery pack, wherein the surface of the battery pack is sequentially composed of an N-isopropylacrylamide-based copolymer temperature-sensitive layer in the polymer coating and a porous thermal insulation layer based on polyethylene terephthalate.

[0016] The N-isopropylacrylamide-based copolymer temperature-sensitive layer is coated on the surface of the battery pack by spraying-UV irradiation;

[0017] The porous thermal insulation layer based on polyethylene terephthalate is prepared by coating polyethylene terephthalate having a porous structure dissolved in a solvent on an N-isopropylacrylamide-based copolymer temperature-sensitive layer through spraying, phase conversion or heat treatment.

[0018] An application of the polymer coating with thermal switch function, and an application of the polymer coating in a secondary lithium battery pack.

[0019] A secondary lithium battery pack comprises the polymer coating.

[0020] The polymer coating is located on the surface of the battery pack.

[0021] The working principle of the polymer coating with thermal switch function of the present invention is that the polymer coating is formed by a temperature-sensitive layer and a thermal insulation layer. It uses a heat-induced phase separation mechanism to promote the change of copolymers with specific structures in the polymer coating, so that the pore size on the surface of the polymer coating can change with the external temperature, thereby achieving the functions of heat preservation at low temperatures and rapid heat dissipation at high temperatures; thereby achieving temperature as a switch regulation, thereby avoiding the risk of thermal runaway of the battery.

[0022] The present invention has the following advantages:

[0023] In the thermosensitive layer of the polymer coating of the present invention, acrylamide is used as a thermal switch, so that it can control the change of the pore size formed by the polymerized cross-linking monomers in the coating as the external temperature changes, and then the coating is used to achieve the functions of heat preservation at low temperatures and rapid heat dissipation at high temperatures during the operation of the secondary battery pack.

[0024] At the same time, due to the selection of the coating components of the present invention, it can further achieve a certain flame retardancy.

[0025] The technical solution of the present invention is easy to operate, has strong innovation and important application value, and can be applied to secondary lithium battery packs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of a polymer coating formed on the surface of a battery pack provided in an embodiment of the present invention.

[0027] Figure 2 This is a graph of the average pore size of the polymer coating surface at 0°C provided in Example 1 of the present invention.

[0028] Figure 3 The average pore size diagram of the polymer coating surface at 80° C. provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0031] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0032] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0033] The raw materials used in the following examples of the present invention are all commercially available.

[0034] Example 1

[0035] N-isopropylacrylamide and (accounting for 40% and 60% of the total mass of the copolymer respectively) and mixed evenly to obtain a viscous liquid. The above liquid is sprayed onto the surface of the lithium battery pack, and then UV irradiated for 2h (UV irradiation parameters are 365nm UV light, power 50-200W) to obtain a temperature-sensitive layer (i.e., copolymer A1) on the surface of the battery pack; on this basis, polyethylene terephthalate is dissolved in N-methylpyrrolidone (mass fraction 8%), and a porous thermal insulation layer is obtained by spraying, soaking in water for 1-5min (phase inversion method), and drying at 50°C for 10-20min to form it on the surface of the above-mentioned temperature-sensitive layer. Among them, the thickness of the temperature-sensitive layer is 50μm, accounting for 30% of the total mass of the coating, and the thickness of the porous thermal insulation layer is 200μm, accounting for 70% of the total mass of the coating. For polymer coatings coated on the surface of battery packs, please refer to Figure 1 .

[0036] Studies have shown that at 0°C, the average pore size of the polymer coating on the surface of lithium battery packs is 22nm (e.g. Figure 2As shown), when at 80°C, the average pore size of the polymer coating on the surface of the lithium battery pack is 62 microns (as shown Figure 3 shown).

[0037] At the same time, the battery packs coated with the above-mentioned polymer coating and the uncoated battery packs were placed at 0°C for 12 hours. The internal temperature of the battery packs with the thermal switch functional polymer coating was 15°C higher than that of the uncoated battery packs. When the two battery packs were placed at 60°C for 12 hours, the internal temperature of the battery packs with the thermal switch functional polymer coating was 35°C lower than that of the uncoated battery packs.

[0038] Example 2

[0039] N-isopropylacrylamide and (50% and 50% of the total mass of the copolymer respectively) are mixed evenly to obtain a viscous liquid. The above liquid is sprayed onto the surface of the lithium battery pack, and then irradiated with UV for 2 hours to obtain a temperature-sensitive layer (i.e., copolymer A2); on this basis, polyterephthalate is dissolved in N-methylpyrrolidone, and a porous thermal insulation layer is prepared through spraying, phase conversion method, and heat treatment. Among them, the thickness of the temperature-sensitive layer is 100μm, accounting for 70% of the total mass of the coating, and the thickness of the porous thermal insulation layer is 150μm, accounting for 30% of the total mass of the coating, and then the polymer coating is coated on the surface of the battery pack (see Figure 1 ).

[0040] Studies have shown that at 0°C, the average pore size of the porous insulation layer on the surface of lithium battery packs is 30nm, and at 60°C, the average pore size of the porous insulation layer on the surface of lithium battery packs is 10 microns. When the battery pack at room temperature is placed at 0°C for 12 hours, the internal temperature of the battery pack with thermal switch functional coating is 16°C higher than that of the battery pack without coating. When the battery pack at room temperature is placed at 60°C for 12 hours, the internal temperature of the battery pack with thermal switch functional coating is 20°C lower than that of the battery pack without coating.

[0041] Example 3

[0042] N-isopropylacrylamide and (80% and 20% of the total mass of the copolymer respectively) are mixed evenly to obtain a viscous liquid. The above liquid is sprayed onto the surface of the lithium battery pack, and then irradiated with UV for 2 hours to obtain a temperature-sensitive layer (i.e., copolymer A3); on this basis, polyterephthalate is dissolved in N-methylpyrrolidone, and a porous thermal insulation layer is prepared through spraying, phase conversion method, and heat treatment. Among them, the thickness of the temperature-sensitive layer is 200μm, accounting for 60% of the total mass of the coating, and the thickness of the porous thermal insulation layer is 100μm, accounting for 40% of the total mass of the coating, and then the polymer coating is coated on the surface of the battery pack (see Figure 1 ).

[0043] Studies have shown that at 0°C, the average pore size of the porous insulation layer on the surface of lithium battery packs is 45nm, and at 60°C, the average pore size of the porous insulation layer on the surface of lithium battery packs is 35 microns. When the battery pack at room temperature is placed at 0°C for 12 hours, the internal temperature of the battery pack containing the thermal switch functional polymer coating is 20°C higher than that of the uncoated battery pack. When the battery pack at room temperature is placed at 60°C for 12 hours, the internal temperature of the battery pack containing the thermal switch functional polymer coating is 30°C lower than that of the uncoated battery pack.

[0044] Example 4

[0045] N-isopropylacrylamide and (accounting for 40% and 60% of the total mass of the copolymer respectively) and mixed evenly to obtain a viscous liquid. The above liquid is sprayed onto the surface of the lithium battery pack, and then irradiated with UV for 2 hours to obtain a temperature-sensitive layer (i.e., copolymer A4); on this basis, polyterephthalate is dissolved in N-methylpyrrolidone, and a porous thermal insulation layer is prepared through spraying, phase conversion method, and heat treatment. Among them, the thickness of the temperature-sensitive layer is 150μm, accounting for 50% of the total mass of the coating, and the thickness of the porous thermal insulation layer is 130μm, accounting for 50% of the total mass of the coating, and then the polymer coating is coated on the surface of the battery pack (see Figure 1 ).

[0046] Studies have shown that at 0°C, the average pore size of the porous insulation layer on the surface of lithium battery packs is 35nm, and at 80°C, the average pore size of the porous insulation layer on the surface of lithium battery packs is 50 microns. When the battery pack at room temperature is placed at 0°C for 12 hours, the internal temperature of the battery pack containing the thermal switch functional polymer coating is 20°C higher than that of the uncoated battery pack. When the battery pack at room temperature is placed at 80°C for 12 hours, the internal temperature of the battery pack containing the thermal switch functional polymer coating is 35°C lower than that of the uncoated battery pack.

Claims

1. A polymer coating with a thermal switch function, characterized in that: The polymer coating consists of a temperature-sensitive layer and a porous thermal insulation layer; wherein the temperature-sensitive layer is formed of an N-isopropylacrylamide-based copolymer, with a thickness of 50 to 200 μm, accounting for 30% to 70% of the total mass of the coating; the porous thermal insulation layer is formed based on polyethylene terephthalate, with a thickness of 100 to 200 μm, accounting for 30% to 70% of the total mass of the coating.

2. The polymer coating with thermal switch function according to claim 1, characterized in that: The N-isopropylacrylamide-based copolymer is prepared by free radical polymerization of N-isopropylacrylamide and other monomers; wherein N-isopropylacrylamide accounts for 40-80% of the total mass of the N-isopropylacrylamide-based copolymer, and other monomers account for 20-60% of the mass of the N-isopropylacrylamide-based copolymer.

3. The polymer coating with thermal switch function according to claim 2, characterized in that: The other monomers are monomers with two or three acrylamide structures, and the monomers contain sulfone groups, phosphoric acid groups or 1,3,5-triazine-2,4,6-trione groups.

4. The polymer coating with thermal switch function according to claim 3, characterized in that: The other monomers are selected from the monomers shown in the following structures, Among them, A is taken from H, C1-C 10 Alkyl or cyano; a is a natural number from 1 to 10.

5. The polymer coating with thermal switch function according to any one of claims 1 to 4, characterized in that: The polymer coating is coated on the surface of the battery pack, wherein the surface of the battery pack is sequentially composed of an N-isopropylacrylamide-based copolymer temperature-sensitive layer in the polymer coating and a porous thermal insulation layer based on polyethylene terephthalate.

6. The polymer coating with thermal switch function according to claim 5, characterized in that: The N-isopropylacrylamide-based copolymer temperature-sensitive layer is coated on the surface of the battery pack by spraying-UV irradiation; the porous thermal insulation layer based on polyethylene terephthalate is coated on the surface of the N-isopropylacrylamide-based copolymer temperature-sensitive layer by spraying, phase conversion method or heat treatment.

7. An application of the polymer coating with thermal switch function according to claim 1, characterized in that: Application of the polymer coating in a secondary lithium battery pack.

8. A secondary lithium battery pack, characterized in that: A polymer coating comprising the polymer coating of claim 1.

9. The secondary lithium battery pack according to claim 8, characterized in that: The polymer coating is located on the surface of the battery pack.

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