Separator and electrochemical device

Abstract

The invention discloses a diaphragm and an electrochemical device, and belongs to the field of electrochemical energy storage. The diaphragm is used for the electrochemical device and comprises a base membrane and a coating arranged on one side or two sides of the base membrane in the thickness direction, the coating comprises a composite phase-change material, the composite phase-change material comprises a conductive polymer layer and a tubular material, the conductive polymer layer partially or completely coats the surface of the tubular material, and the tubular material is coated with the conductive polymer layer. A phase change material is contained in the tube of the tubular material. According to the diaphragm, the high-temperature thermal safety performance of the diaphragm can be improved under the condition that the high-temperature mechanical performance of the diaphragm is not damaged.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and particularly to membranes and electrochemical devices. Background Technology

[0002] With the widespread use of electronic products, people have increasingly stringent requirements for electrochemical devices, especially in terms of mechanical reliability and thermal safety. Lithium-ion batteries consist of a positive electrode, a negative electrode, and a separator. The separator acts as a physical barrier between the positive and negative electrodes, its core function being to prevent short circuits while allowing lithium ions to pass freely. Currently, diverse designs of separator coatings are giving separators more and more functions, among which the performance of the separator is crucial for improving thermal safety. Summary of the Invention

[0003] In view of the shortcomings of the prior art, this application provides a diaphragm and an electrochemical device, aiming to solve the problem of how to improve the high-temperature thermal safety performance of the diaphragm without compromising its high-temperature mechanical properties.

[0004] To achieve the above objectives, this application proposes a diaphragm for an electrochemical device. The diaphragm includes a base membrane and a coating disposed on one or both sides of the base membrane along its thickness direction. The coating includes a composite phase change material, which includes a conductive polymer layer and a tubular material. The conductive polymer layer partially or completely covers the surface of the tubular material, and the tubular material contains the phase change material.

[0005] In some embodiments, the tubular material comprises ceramic-based micro / nanotubular materials; and / or, the inner diameter of the tubular material is 10 nm to 30 nm; and / or, the length of the tubular material is 0.5 μm to 2.0 μm; and / or, the outer diameter of the tubular material is 30 nm to 100 nm; and / or, the specific surface area of ​​the tubular material is 20 m². 2 / g to 140m 2 / g.

[0006] In some embodiments, the thickness of the conductive polymer layer is 5 nm to 25 nm.

[0007] In some embodiments, the thickness of the coating is 0.5 μm to 1.5 μm.

[0008] In some embodiments, the composite phase change material has a mass percentage of 50% to 80% based on the coating.

[0009] In some embodiments, based on the composite phase change material, the mass ratio of the tubular material, the phase change material, and the conductive polymer is 1:(0.5~1):(0.3~1).

[0010] In some embodiments, the softening point of the phase change material is 50°C to 120°C.

[0011] In some embodiments, the conductive polymer includes at least one of polypyrrole, polyaniline, and poly(3,4-ethylenedioxythiophene); and / or, the phase change material includes at least one of mineral wax, biomass wax, polyolefin wax, and aliphatic polyester.

[0012] In some embodiments, the ceramic-like micro / nanotube material includes at least one of titanium dioxide nanotubes, boron nitride nanotubes, and aluminosilicate nanotubes.

[0013] To achieve the above objectives, this application also proposes an electrochemical device comprising a positive electrode, a negative electrode, an electrolyte, and the aforementioned separator, wherein the negative electrode comprises a silicon-carbon-containing negative electrode active material, and the coating thickness of the separator is 0.5% to 3% of the thickness of the active material layer of the negative electrode.

[0014] The beneficial effects of this application are as follows: This application provides a diaphragm for an electrochemical device. The diaphragm coating incorporates a composite phase change material, using a hollow tubular material as a carrier. The hollow tubular structure of the tubular material possesses ceramic fiber characteristics, and the incorporation of this material into the diaphragm coating improves its mechanical properties. Simultaneously, the hollow tubular structure provides a space to accommodate the phase change material. After the phase change material is contained within the tubular material, under conditions of locally generated high temperatures in the electrochemical device, the phase change material absorbs heat and melts, significantly slowing down the diaphragm's heating rate. The framework structure composed of the tubular material and the conductive polymer exhibits good thermal stability, maintaining the integrity of the coating structure even after the phase change material softens, preventing the diaphragm from shrinking at high temperatures. Therefore, the diaphragm of this application can soften the phase change material and absorb latent heat at lower heating temperatures, and at higher temperature ranges, the tubular material and conductive polymer layer maintain excellent dimensional stability and mechanical integrity of the diaphragm, preventing thermal runaway of the electrochemical device. Attached Figure Description

[0015] The embodiments described in this application are not limited to the accompanying drawings, which are only some of the embodiments described herein. Those skilled in the art can obtain drawings of other embodiments based on the content of this application.

[0016] Figure 1 This is a scanning electron microscope (SEM) image of a composite phase change material in one embodiment of this application. Detailed Implementation

[0017] The term "phase change material" refers to a substance that changes its physical state and provides latent heat while maintaining a constant temperature. The process of changing physical properties is called a phase change process, during which the phase change material absorbs or releases a large amount of latent heat.

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. The embodiments of this application may omit unnecessary detailed descriptions.

[0019] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0020] As used herein, the terms “approximately,” “generally,” “substantially,” and “about” are used to describe and indicate minor variations. When used in conjunction with an event or situation, these terms may refer to examples in which the event or situation occurred precisely or in examples in which the event or situation occurred very approximately.

[0021] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0022] In the detailed description and claims, a list of items connected by the terms "one of," "among," "a kind of," or other similar terms may mean any of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B, and C" means only A; only B; or only C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0023] In the detailed description and claims, the list of items connected by the term "at least one of" can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C.

[0024] Throughout this specification, references to “implementation,” “partial implementation,” “one implementation,” “another approach,” “specific approach,” or “partial approach” mean that at least one implementation or embodiment in this application includes the specific features, structures, materials, or characteristics described in that implementation or embodiment.

[0025] In this application, numerical ranges are involved. Unless otherwise specified, the numerical ranges mentioned above are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form a range not explicitly stated.

[0026] Currently, the diverse designs of diaphragm coatings are giving diaphragms more and more functions. Among them, the improvement of the thermal safety performance of diaphragms includes adding low-melting-point polymers to the diaphragm coating. Although this can provide thermal shutdown function, the melting and collapse of low-melting-point polymers at high temperatures will cause a significant decrease in the overall mechanical strength of the diaphragm, creating new thermal safety risks.

[0027] In view of this, this application proposes a diaphragm for an electrochemical device. The diaphragm includes a base membrane and a coating disposed on one or both sides of the base membrane. The coating includes a composite phase change material and a binder. The composite phase change material includes a tubular material and a conductive polymer. The conductive polymer partially or completely covers the surface of the tubular material, and the tubular material contains the phase change material.

[0028] refer to Figure 1The hollow tubular structure of the tubular material possesses ceramic fiber properties, and the coating incorporated into the diaphragm can improve its mechanical properties. Simultaneously, after the tubular material houses the phase change material, under the locally generated high temperatures of the electrochemical device, the phase change material absorbs heat and melts, significantly slowing down the diaphragm's heating rate. The framework structure composed of the tubular material and the conductive polymer exhibits good thermal stability, maintaining the integrity of the coating structure even after the phase change material softens, preventing the diaphragm from shrinking at high temperatures.

[0029] According to some embodiments of this application, a conductive polymer is coated on the opening of the tubular material to form a sealing layer, isolating the phase change material from the binder and effectively preventing leakage of the phase change material in a liquid state. In other embodiments, the conductive polymer completely covers the tubular material, serving as a fully encapsulated conductive polymer layer, which imparts a certain degree of conductivity to the composite phase change material, promoting uniform charge distribution within the battery and effectively reducing battery impedance.

[0030] According to some embodiments of this application, the volume conductivity of the conductive polymer at room temperature is 10. -3 S / cm up to 10 1 Within the range of S / cm.

[0031] According to some embodiments of this application, phase change material is filled into the interior of a tubular material by melt impregnation, achieving high loading capacity and uniform distribution.

[0032] According to some embodiments of this application, the preparation of composite phase change materials includes the following steps: S1: Vacuum dry the tubular material, mix the phase change material with the dried tubular material, heat it under vacuum to above the melting point of the phase change material, so that the phase change material melts and impregnates into the cavity of the tubular material, separate and remove the excess phase change material to obtain the tubular material-phase change material composite. S2: The tubular material-phase change material composite is immersed in a reaction solution containing the corresponding monomer of the conductive polymer and an oxidant. The oxidant can be a conventional self-polymerizing oxidant in the industry, so that the monomer undergoes a polymerization reaction on the surface of the composite to form a conductive polymer coating layer, thereby obtaining a composite phase change material.

[0033] The preparation method allows the conductive polymer to be generated in situ through self-polymerization. Compared with coating, there is no interface between different materials, resulting in better bonding.

[0034] According to some embodiments of this application, the preparation of composite phase change materials includes: firstly, passivating and modifying the interface of the tubular material to allow the monomers to preferentially react at the sealing point of the tubular material.

[0035] Therefore, the diaphragm of this application can soften the phase change material at a lower heating temperature to provide latent heat, while at a higher temperature range, it relies on the tubular material and conductive polymer layer to maintain the excellent dimensional stability and mechanical integrity of the diaphragm, preventing thermal runaway of the electrochemical device.

[0036] According to some embodiments of this application, the selection of the base membrane is not particularly limited, as long as it is a commonly used separator base membrane in secondary batteries. In particular, a base membrane with low resistance to electrolyte ion movement and excellent electrolyte permeability is preferred, including at least one of polyolefins, polyesters, polyacetals, polyamides, polyethylene terephthalate, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyoxymethylene, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polysulfone, and polymethyl methacrylate. Some non-limiting examples of polyolefins include at least one of polyethylene (PE), ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), polypropylene (PP), polyethylene-polypropylene copolymer (PE-PP), and polyethylene-polypropylene-polyethylene copolymer.

[0037] According to some embodiments of this application, the tubular material includes ceramic-based micro / nano tubular materials.

[0038] According to some embodiments of this application, the inner diameter of the tubular material is 10 nm to 30 nm, and the length of the tubular material is 0.5 μm to 2.0 μm. The load-bearing capacity of the tubular material is directly related to its inner cavity size. The aforementioned inner diameter and length ranges together define the volume range inside the tube, ensuring that the cavity of the nanotube is large enough to accommodate the phase change material capable of absorbing the target amount of latent heat.

[0039] For example, the inner diameter of the tubular material is 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm, 25nm, 26nm, 27nm, 28nm, 29nm, or 30nm, or falls within the range of any two of the above values.

[0040] For example, the length of the tubular material is 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2.0μm, or falls within the range of any two of the above values.

[0041] According to some embodiments of this application, the outer diameter of the tubular material is from 30 nm to 100 nm. An outer diameter within this range is beneficial for the tubular material to achieve good dispersibility in the coating, preventing agglomeration and facilitating the formation of a uniform three-dimensional network structure in the diaphragm coating, thus providing more uniform mechanical properties.

[0042] For example, the outer diameter of the tubular material is 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, or 100nm, or falls within the range of any two of the above values.

[0043] According to some embodiments of this application, the specific surface area of ​​the tubular material is 20m². 2 / g to 140m 2 / g.

[0044] For example, the specific surface area of ​​the tubular material is 20 m². 2 / g、40m 2 / g、60m 2 / g、80m 2 / g, 100m 2 / g, 120m 2 / g, 140m 2 / g, or within the range of any two of the above values.

[0045] According to some embodiments of this application, the thickness of the conductive polymer layer is from 5 nm to 25 nm.

[0046] The conductive polymer needs to form a continuous, dense film to effectively cover the openings at both ends and the outer surface of the tubular material, providing a physical seal and preventing leakage of the internal phase change material after melting. If the thickness is too thin (<5 nm), the coating layer may be discontinuous, containing defects or pores, failing to effectively prevent leakage of the phase change material and leading to functional failure. On the other hand, an excessively thick conductive polymer layer will affect the macroscopic pore structure of the membrane itself, hindering ion transport. An excessively thick coating layer will also reduce the adhesion to the tubular material, making the conductive polymer layer prone to peeling off due to stress during cycling.

[0047] According to some embodiments of this application, the thickness of the conductive polymer layer is controlled by adjusting the reaction time of the step of "immersing the tubular material-phase change material composite in a reaction solution containing monomers and oxidants". According to some embodiments of this application, the reaction time of the monomers is 12 h to 48 h.

[0048] For example, the thickness of the conductive polymer layer is 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm, or 25nm, or falls within the range of any two of the above values.

[0049] According to some embodiments of this application, the coating thickness is 0.5 μm to 1.5 μm. Coatings with a thickness of less than 0.5 μm contain less composite material and have poor thermal protection; excessively thick coatings will significantly increase the path and resistance of lithium ions shuttling between the positive and negative electrodes, and will also be detrimental to the flexibility of the separator, thus weakening the application effect of the separator in winding or stacking.

[0050] For example, the coating thickness is 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, or within any two of the above values.

[0051] According to some embodiments of this application, the mass percentage of the composite phase change material in the coating is 50% to 80%. This mass percentage maximizes the latent heat absorption capacity and mechanical properties of the coating, and through synergistic effects with other materials in the coating, it facilitates achieving the desired adhesion and ion conductivity of the coating to the base film.

[0052] According to some embodiments of this application, other materials in the coating include adhesives, such as polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride resin, polyester, polyether, polyphenylene ether, polyvinyl compounds, polyolefins, rubber, polyvinylpyrrolidone, polystyrene, nitrile rubber (NBR), styrene-butadiene rubber (SBR), acrylonitrile-styrene-butadiene copolymer, acrylate multi-element copolymers, polymethyl methacrylate, etc.

[0053] According to some embodiments of this application, other materials in the coating include dispersants, wetting agents, and other additives. This application does not impose special requirements on additives; those skilled in the art can select them based on conventional types and dosages. According to some embodiments of this application, additives include carboxymethyl cellulose, polyvinyl alcohol, polyacrylic acid compounds, etc.

[0054] For example, the mass percentage of the coating composite phase change material is 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, or within any two of the above values.

[0055] According to some embodiments of this application, based on a composite phase change material, the mass ratio of the tubular material, the phase change material, and the conductive polymer is 1:(0.5~1):(0.3~1). The composite phase change material uses the tubular material as its structural core, the phase change material as its latent heat absorption medium, and the conductive polymer as its leak-proof coating layer. Within the aforementioned mass ratio range, these three components synergistically provide the separator coating with a high-mechanical-strength tubular skeleton, a large specific surface area, thermal management capabilities, and leak-proof encapsulation capabilities. Ultimately, the separator coating formed by these components can provide active and reliable thermal safety protection without degrading the battery's electrical performance.

[0056] For example, based on composite phase change materials, the mass ratio of tubular material, phase change material, and conductive polymer can be 1:0.5:0.3, 1:0.5:0.4, 1:0.5:0.5, 1:0.5:0.6, 1:0.5:0.7, 1:0.5:0.8, 1:0.5:0.9, 1:0.5:1.0, 1:0.6:0.3, or 1:0.6:0. 4, 1:0.6:0.5, 1:0.6:0.6, 1:0.6:0.7, 1:0.6:0.8, 1:0.6:0.9, 1:0.6:1.0, 1:0.7:0.3, 1:0.7:0.4, 1:0.7:0.5, 1:0.7:0.6, 1:0.7:0.7, 1:0.7:0.8, 1:0.7:0.9, 1: 0.7:1.0, 1:0.8:0.3, 1:0.8:0.4, 1:0.8:0.5, 1:0.8:0.6, 1:0.8:0.7, 1:0.8:0.8, 1:0.8:0.9, 1:0.8:1.0, 1:0.9:0.3, 1:0.9:0.4, 1:0.9:0.5, 1:0.9:0.6, 1:0.9: 0.7, 1:0.9:0.8, 1:0.9:0.9, 1:0.9:1.0, 1:1.0:0.3, 1:1.0:0.4, 1:1.0:0.5, 1:1.0:0.6, 1:1.0:0.7, 1:1.0:0.8, 1:1.0:0.9, 1:1.0:1.0, or within the range of any two of the above values.

[0057] According to some embodiments of this application, the softening point of the phase change material is 50°C to 120°C. Many thermal runaways are caused by tiny internal short circuits. These short circuits generate localized high temperatures. When the local temperature reaches the softening point, the phase change material softens immediately at 50°C to 120°C, absorbing latent heat. If the overheating is temporary and does not cause permanent damage, the phase change material will re-solidify after the electrochemical device cools, preventing it from developing into a serious short circuit. If the softening point temperature is too low, the phase change material will soften prematurely or even melt into a liquid state, causing the coating to become sticky and adhere, making it impossible to wind properly. Even if a film is formed, the coating will become weak and easily peel off due to the loss of the phase change material's support, severely affecting the mechanical properties of the diaphragm. If the softening point temperature is too high, the latent heat absorption is not timely, making it difficult to effectively prevent tiny internal short circuits.

[0058] For example, the softening point of the phase change material is 50℃, 57℃, 64℃, 71℃, 78℃, 85℃, 92℃, 99℃, 106℃, 113℃, or 120℃, or falls within the range of any two of the above values.

[0059] Preferably, the softening point of the phase change material is 50~70℃.

[0060] According to some embodiments of this application, the full melting temperature of the phase change material is 42°C to 112°C.

[0061] For example, the full melting temperature is 42°C, 52°C, 62°C, 72°C, 82°C, 92°C, 102°C, or 112°C, or falls within the range of any two of the above values.

[0062] According to some embodiments of this application, the phase change material includes at least one of mineral wax, biomass wax, polyolefin wax, and aliphatic polyester.

[0063] According to some embodiments of this application, mineral wax includes montan wax, paraffin wax, etc.

[0064] According to some embodiments of this application, biomass wax includes waxes derived from animals or plants, such as beeswax, coconut wax, palm wax, etc.

[0065] According to some embodiments of this application, polyolefin waxes include polyethylene waxes, etc.

[0066] According to some embodiments of this application, aliphatic polyesters include polylactic acid (PLA), polyglycolic acid (PGA), polybutylene succinate (PBS), PBAT (polybutylene adipate-butylene terephthalate copolymer), PBST (polybutylene succinate-butylene terephthalate copolymer), PCL (polycaprolactone), and PPC (polypropylene carbonate), etc.

[0067] In some embodiments, the phase change material is preferably paraffin wax, which has the following advantages: First, its phase change temperature is well matched with the initial stage of thermal runaway in lithium batteries, enabling early intervention; second, paraffin wax has a high latent heat of phase change, which can effectively absorb a large amount of heat and significantly delay the temperature rise of the battery; third, paraffin wax has excellent chemical stability and electrical insulation, does not react with the internal components of the battery, and ensures the safety of the electrochemical system; fourth, paraffin wax has a low viscosity after melting, which allows it to fully wet the tubular material cavity and achieve high-efficiency loading. The softening point of paraffin wax is related to its molecular weight; a lower molecular weight results in a lower softening point. By adjusting the molecular weight of paraffin wax, paraffin materials with suitable softening points for this application can be screened. For example, paraffin wax with a softening point of 55°C has a carbon number of C... 18 - C 22 .

[0068] According to some embodiments of this application, the conductive polymer includes at least one of polypyrrole, polyaniline, and poly(3,4-ethylenedioxythiophene).

[0069] According to some embodiments of this application, poly(3,4-ethylenedioxythiophene) exhibits the best stability, but its cost is high. The electrochemical stability of polyaniline is limited by pH and potential, and its performance in applications is slightly inferior to that of polypyrrole. Polypyrrole demonstrates excellent stability within the voltage window of lithium batteries, and its synthesis process is mild and cost-effective. It forms a highly efficient synergistic system with tubular materials and paraffin: polypyrrole forms a tightly sealed coating layer on the surface of halloysite-paraffin composite through in-situ polymerization, which effectively prevents leakage of molten paraffin and, together with the tubular material, constructs a stable three-dimensional framework, maintaining the integrity of the coating structure even after the phase change material melts; at the same time, polypyrrole imparts moderate conductivity to the composite material, effectively balancing the charge distribution inside the battery and reducing interfacial impedance.

[0070] According to some embodiments of this application, ceramic micro / nanotube materials include at least one of titanium dioxide nanotubes, boron nitride nanotubes, and aluminosilicate nanotubes.

[0071] According to some embodiments of this application, aluminosilicate nanotubes include halloysite nanotubes, imogolite, etc. Halloysite nanotubes (Al2Si2O5(OH)4•nH2O, where n is 0-2, HNTs) are a two-layer aluminosilicate, while imogolite is a hydrous aluminosilicate mineral with the chemical formula Al2SiO3(OH)4, which has a single-walled nanotube structure.

[0072] To address the aforementioned problems, this application also proposes an electrochemical device, wherein the electrochemical device battery cell includes an electrode, an electrolyte, and the aforementioned separator. The electrochemical device is one of a battery cell, a battery module, or a battery pack.

[0073] An electrochemical device includes any device in which an electrochemical reaction occurs to convert chemical energy into electrical energy and vice versa. Specific, non-limiting examples include all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0074] According to some embodiments of this application, regardless of how the positive electrode, negative electrode and electrolyte are conventionally selected, as long as the battery cell includes the above-mentioned separator, the battery cell can obtain the aforementioned beneficial effects.

[0075] According to some embodiments of this application, the positive electrode sheet includes a positive current collector and a positive active material layer, wherein the positive active material layer includes a positive conductive agent, a positive active material, and a positive binder.

[0076] According to some embodiments of this application, the positive electrode conductive agent includes carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, mesoporous carbon, etc.

[0077] According to some embodiments of this application, the positive electrode active material is selected from LiCoO2, LiNiO2, and LiNi. x Mn y O2, Li 1+ z Ni x Mn y Co 1-x-y O2, LiNi x Co y Al z The group consisting of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, Li2MnO3, LiFeO2, LiFePO4, LiMnPO4, and combinations thereof, wherein each x is independently 0.2 to 0.9; each y is independently 0.1 to 0.45; and each z is independently 0 to 0.2. The positive electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as positive electrode active materials.

[0078] According to some embodiments of this application, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer. The positive electrode binder of this application is not limited to the above materials, but also includes other materials that can be used as battery positive electrode binders.

[0079] According to some embodiments of this application, the negative electrode sheet includes a negative current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes a negative electrode conductive agent, a negative electrode active material, and a negative electrode binder.

[0080] According to some embodiments of this application, the negative electrode conductive agent may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon tubes, carbon nanotubes, activated carbon, and mesoporous carbon.

[0081] According to some embodiments of this application, the negative electrode active material may include natural graphite particles, synthetic graphite particles, hard carbon, soft carbon, mesophase carbon microspheres (MCMB), Sn, SnO2, SnO, Li4Ti5O 12 The negative electrode active material is selected from at least one of LTO, Si material, silicon-carbon (Si-C) composite material, silicon-nitrogen (Si-N) composite material, and silicon-oxygen (Si-O) composite material. The negative electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as negative electrode active materials for batteries.

[0082] According to some embodiments of this application, the negative electrode binder may include at least one of polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyacrylamide, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylic acid-acrylonitrile-acrylamide copolymer, acrylic acid-acrylonitrile-acrylate copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acryloyl rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, carboxymethyl chitosan, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyurethane, alginate, fluorinated polymer, chlorinated polymer, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropylene. The negative electrode binder of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode binders.

[0083] According to some embodiments of this application, the electrolyte of the electrochemical device may include an organic solvent and a lithium salt. The use of organic solvents is not limited, as long as they can serve as a medium for the movement of ions participating in the battery's electrochemical reaction. Specifically, the organic solvent may be an ester-based solvent, such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone, etc.; an ether-based solvent, such as dibutyl ether, tetrahydrofuran, etc.; a ketone-based solvent, such as cyclohexanone; an aromatic hydrocarbon-based solvent, such as benzene, fluorobenzene, etc.; a carbonate-based solvent, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), etc.; an alcohol-based solvent, such as ethanol, isopropanol, etc.; or a nitrile, such as R-CN (where R is a straight-chain, branched, or cyclic C2 to C3 group). 20 The solvents include hydrocarbon groups (which may include double bonds, aromatic rings, or ether bonds); amide solvents, such as dimethylformamide; dioxolane solvents, such as 1,3-dioxolane; or sulfolane solvents, etc. Preferably, carbonate solvents are preferred, and more preferably cyclic carbonates with high ionic conductivity and high dielectric constant, such as ethylene carbonate or propylene carbonate, which can improve the charge-discharge performance of the battery, in mixtures with low-viscosity linear carbonate compounds (such as ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.).

[0084] The lithium salt can be any compound that can provide lithium ions for lithium secondary batteries, without any particular limitation. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. The concentration of the lithium salt is preferably in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, thereby exhibiting excellent electrolyte performance, and lithium ions can move effectively.

[0085] According to some embodiments of this application, the coating thickness of the separator is 0.5% to 3% of the thickness of the active material layer of the negative electrode. The coating is disposed on one or both sides of the separator base membrane, and the active material layer is disposed on one or both sides of the current collector of the negative electrode.

[0086] During charging and discharging, especially during high-current fast charging, the significant volume expansion / contraction of the anode (particularly silicon) generates substantial localized thermal stress and leads to heat accumulation. Paraffinic phase change materials encapsulated in tubular materials can effectively buffer localized temperature rises within the battery by absorbing a large amount of latent heat when the temperature rises to its melting point, acting as a "thermal buffer." This indirectly alleviates the overall anode expansion caused by the accumulation of by-reaction products and gas pressure by maintaining a more stable SEI film and reducing gas production.

[0087] For example, the coating thickness of the separator is 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 2.0%, 2.5%, 2.8%, or 3.0% of the thickness of the active material layer of the negative electrode, or falls within the range of any two of the above values.

[0088] According to some embodiments of this application, electrochemical devices are applied to electronic devices. These electronic devices include, but are not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robotic dogs, industrial robots, and android robots.

[0089] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the reagents used, unless otherwise specified, are commercially available reagents and materials. The source information of the raw materials used in the following examples and comparative examples is for illustrative purposes only and does not constitute any restriction on the procurement of raw materials. Those skilled in the art will know that the relevant raw materials can be obtained through other commercial channels or prepared by conventional methods in the art.

[0090] The CAS numbers of the main raw materials used in this application are as follows: Example 1 1. Preparation of the diaphragm (1) Preparation of composite phase change materials: a. Halloysite was vacuum dried at 100°C for 12 hours to remove adsorbed moisture. Then, paraffin wax (softening point 65°C) was cut into small pieces and placed in a 100 mL three-necked flask. Dried halloysite nanotubes (HNTs) (inner diameter 15 nm, outer diameter 45 nm, length 0.6 μm, specific surface area 70 m²) were added to the flask. 2 / g), the gas in the flask and the air in the halloysite were removed using a vacuum device, and then the device was heated in a water bath at 80°C until the paraffin melted. After 2 hours of impregnation, the internal cavity of the halloysite was gradually filled with the melted paraffin. The resulting halloysite / paraffin (HNTs-PW) composite was repeatedly collected on filter paper heated to 80°C. This step was repeated until no liquid paraffin residue remained on the filter paper, thus obtaining the HNTs-PW composite, wherein the mass ratio of HNTs to PW was 1:0.7; b. Weigh 114g of ammonium persulfate and place it in a 500mL beaker to prepare a 1mol / L ammonium persulfate solution A. Stir well and let stand for later use. Weigh 81g of ferric chloride powder and place it in a 500mL beaker to prepare a 1mol / L ferric chloride solution B. Stir well and let stand for later use. Weigh 33.5g of pyrrole monomer using a syringe and dissolve it in a 500mL beaker to obtain pyrrole solution C. Wrap it in aluminum foil to protect it from light and stir well. Let stand for later use. Prepare a 1mol / L hydrochloric acid solution D for later use. Use a syringe to draw 20mL of each of solutions A, B, and C, stir well, pour them into a petri dish, and add dilute hydrochloric acid to adjust the pH to 3. Then immerse the obtained HNTs-PW composite in the above solutions, store the petri dish in the dark, and let it stand at room temperature for 24h to form a polypyrrole (PPy) layer on HNTs-PW with a thickness of 15nm. Finally, the solid was centrifuged and washed three times with deionized water to obtain HNTs-PW@PPy, wherein the mass ratio of HNTs:PW:PPy was (1:0.7):0.5.

[0091] (2) Slurry preparation: Take 70g of the HNTs-PW@PPy prepared above and add 187g of deionized water. Stir at high speed for 30min to mix them evenly to obtain solution E. Add 3g of additives (CMC 1wt%, PVA 0.5wt%) to solution E. The purpose of adding is to increase the wettability of the slurry to the membrane and increase the viscosity of the slurry, which is beneficial for dispersion and subsequent coating to obtain solution F. Add 27g of PMMA to solution F and stir at high speed for 30min to obtain HNTs-PW@PPy-PMMA mixture, in which the mass ratio of HNTs-PW@PPy in the slurry is 70%.

[0092] (3) Separator coating: Using a 5μm PE base film as the substrate, gravure coating is performed. The base film coating thickness is 1μm. After drying and winding, the separator is obtained.

[0093] 2. Preparation of the positive electrode sheet Lithium cobalt oxide, superconducting carbon (Super-P) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are mixed evenly at a mass ratio of 97:1.5:1.5 to prepare a lithium-ion battery positive electrode slurry with a certain viscosity. The slurry is coated on a current collector aluminum foil, dried at 85°C, and then cold-pressed. Then, it is trimmed, cut into sheets, and slit. After slitting, it is dried at 110°C for 4 hours under vacuum conditions, and then the tabs are welded to form the positive electrode sheet.

[0094] 3. Preparation of negative electrode sheet Artificial graphite (anode active material), acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were thoroughly mixed in a deionized water solvent system at a mass ratio of 96:1:1.5:1.5 to obtain a cathode slurry with a solid content of 34.5%~37.5%. This slurry was coated on both sides of a 5μm Cu foil as a cathode current collector. After drying, cold pressing, and slitting, a cathode sheet was obtained with an active layer thickness of 50μm.

[0095] 4. Preparation of electrolyte In a dry argon atmosphere glove box, a solution prepared by mixing lithium salt LiPF6 with a non-aqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): propyl propionate (PP): ethylene carbonate (VC) = 20:30:20:28:2, mass ratio) at a mass ratio of 8:92 was used as the electrolyte for lithium-ion secondary batteries.

[0096] 5. Preparation of lithium-ion secondary batteries The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes for safety isolation. The electrode assembly is then wound to form the final electrode assembly. This assembly is placed in a packaging shell, infused with electrolyte, and sealed to obtain a lithium-ion secondary battery.

[0097] Examples 2 to 21 Examples 2-21 refer to the preparation method of Example 1, but differ from Example 1 in that the composition, microstructure and content of the coating material are different, as are the coating thickness. When the type of tubular material, phase change material or conductive polymer is changed, commercially available products are used as reagents.

[0098] Comparative Example 1 Comparative Example 1 is adapted and modified from the preparation method of Example 1, except that: based on coating quality, the coating includes 70 wt% halloysite nanotubes and does not include paraffin and polypyrrole layers.

[0099] Comparative Example 2 Comparative Example 2 is adapted and modified from the preparation method of Example 1, except that: based on the coating quality, the coating includes 41.2 wt% halloysite nanotubes and 28.8 wt% paraffin inside the tubes, excluding the polypyrrole layer.

[0100] Comparative Example 3 Comparative Example 3 was adapted and modified from the preparation method of Example 1, except that, based on the coating quality, the coating consisted of 46.7 wt% halloysite nanotubes and 23.3 wt% polypyrrole layer.

[0101] Comparative Example 4 Comparative Example 4 was adapted and modified from the preparation method of Example 1, except that: based on coating quality, the coating included 40.8 wt% paraffin and 29.2 wt% polypyrrole, but did not include halloysite nanotubes.

[0102] The parameters of the examples and comparative examples are recorded in Table 1.

[0103] Furthermore, performance tests were conducted on the above embodiments and comparative examples, and the test methods are as follows: (1) High-temperature cycle performance test: Five lithium-ion secondary batteries prepared in the comparative example and the embodiment were taken respectively. The lithium-ion secondary batteries were repeatedly charged and discharged through the following steps, and the 45℃ cycle capacity retention rate of the lithium-ion secondary batteries was calculated. First, in an environment of 45℃, the batteries were discharged to 3V at a constant current of 0.7C. Then, they were charged to 4.5V at a constant current and constant voltage of 0.7C, with a cutoff rate of 0.025C. After that, they were discharged to 3V at a discharge current of 0.7C, and the discharge capacity of the first cycle was recorded. Then, 800 charge and discharge cycles were performed under the same test environment and current, and the discharge capacity of the 800th cycle was recorded. Cycle capacity retention rate = (discharge capacity of the 800th cycle / discharge capacity of the first cycle) × 100%.

[0104] (2) Diaphragm heat shrinkage temperature test: Take 19mm round pieces of diaphragm from each embodiment and let them stand for 2 hours at 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, and 185℃ respectively. Calculate the test temperature of the diaphragm when the shrinkage rate is ≥5% as the diaphragm heat shrinkage temperature. Shrinkage rate = (D2-D1) / D1, where D1 is the diameter of the diaphragm round piece before the test, i.e., 19mm; D2 is the diameter of the diaphragm round piece after the test.

[0105] (3) Thermal shock test: Three lithium-ion secondary batteries prepared in the comparative example and the examples were taken and charged to 4.45V at a constant current and constant voltage rate of 0.2C, with a cutoff current of 0.025C. The cells were placed in an oven (suspended test) and heated by convection or circulating hot air at an initial temperature of 25±3℃. The oven temperature was increased to 116~136℃ at a rate of 5±2℃ / min, and then stopped after maintaining 2℃ for 30min. The temperature at which the cells ignited and exploded was recorded as the temperature of thermal shock failure. During the test, the surface temperature of the cells, the ambient temperature, and the voltage needed to be monitored. After resting for 1 hour, the OCV and IMP were measured, and the post-test photos were saved.

[0106] (4) Diaphragm porosity test: First, cut a sample of a certain area from the diaphragm to be tested. Record the geometric dimensions (length, width, thickness) of the sample and calculate its apparent volume V. Next, dry the sample under vacuum conditions to remove adsorbed moisture and volatile substances to ensure accurate testing. Place the dried diaphragm sample into the wetting solution n-butanol and immerse it in a vacuum environment for a sufficient time of more than 4 hours to ensure that the liquid fully fills all the open pores of the diaphragm. After immersion, take out the diaphragm sample, quickly wipe off the excess liquid droplets on the surface, and then immediately weigh the diaphragm mass saturated with the wetting solution at this time, and record it as M1. Dry the diaphragm sample saturated with the wetting solution again (to ensure that the wetting solution is completely evaporated), and then weigh its dry weight, and record it as M2. Based on the measured mass data, calculate the porosity (P) using the following formula: Porosity (P) = (M1-M2) / (ρ V) × 100% where ρ is the density of the wetting solution.

[0107] (5) Cell internal resistance test: The RO1100 automatic tester is used to measure the AC voltage drop across the battery by applying a 1A AC small current signal at a frequency of 1kHz to the battery, thereby measuring the battery internal resistance.

[0108] The results of the examples and comparative examples are recorded in Table 2.

[0109] Table 1. Parameters of Examples and Comparative Examples Table 2. Performance Results of Examples and Comparative Examples The performance results, as shown in Examples 1-3 and Comparative Examples 1-3, indicate that when the mass ratio of HNTs:PW:PPy is 1:0.7:0.5, the membrane's thermal shrinkage temperature can reach a maximum of 185°C, and its maximum thermal shock temperature can reach 136°C. This is mainly because the phase change material paraffin stored within the hollow halloysite nanotubes can absorb heat, thereby improving the membrane's thermal stability. However, the internal resistance data shows that as the proportion of PW increases, the corresponding cell internal resistance also increases. This is because excessive paraffin hinders the passage of lithium ions, increasing the interfacial impedance. Conversely, when the PW content is too low, the membrane's heat absorption effect decreases accordingly.

[0110] As shown in Tables 1 and 2, Examples 1 and 4-5, and Comparative Example 2, the minimum internal resistance of the cell is 16.3 mΩ. In-situ polymerization forms a polypyrrole (PPY) sealing layer on the surface of the halloysite nanotubes, effectively preventing leakage of the phase change material in its liquid state. This encapsulation process not only solves the core problem of phase change material leakage but also imparts a certain degree of conductivity to the material, which is beneficial for the uniformity of charge distribution inside the battery and effectively reduces battery impedance. When the PPY proportion decreases, the thickness of the Ppy sealing the phase change material at both ends of the halloysite nanotubes decreases, resulting in a corresponding decrease in the heat absorption effect of the separator. Furthermore, due to the conductivity of Ppy, the internal resistance increases to some extent. When the PPY proportion increases, in addition to sealing the phase change material at both ends of the halloysite nanotubes, additional PPY agglomerates, leading to a corresponding decrease in the heat absorption effect of the separator.

[0111] As shown in Tables 1 and 2, Examples 1 and 2-5 and Comparative Example 1, due to the synergistic effect of the self-encapsulation, heat absorption and low impedance of HNTs-PW@PPy, its high-temperature cycling capacity retention rate is significantly improved, reaching 93%. This increase in impedance is also a major factor restricting the reduction of high-temperature cycling capacity retention rate. The diaphragm of this design can avoid local high temperature of the diaphragm by absorbing heat. At the same time, the polypyrrole on the surface of the hollow halloysite can adjust the ion permeability, which can effectively reduce the internal resistance of the cell after cycling, thereby improving the cycling performance.

[0112] As shown in Tables 1 and 2, Examples 1 and 6-7, when the softening points of the phase change material are 110°C and 55°C respectively, the heat absorption effect of the membrane will decrease. The membrane heat shrinkage temperature decreases by 10°C, and the membrane heat shock maximum passing temperature decreases by 4°C. This is mainly because the heat absorption effect of the phase change material is best when the softening point is 65°C.

[0113] As shown in Tables 1 and 2, and Examples 1 and 8, when the conductive polymer is replaced by poly(3,4-ethylenedioxythiophene), the cell internal resistance increases by 0.5 mΩ and the cycle capacity retention decreases by 3%. This is mainly because PPy's unique spherical structure and large specific surface area result in the best synergistic effect of self-encapsulation, heat absorption, and low impedance among HNTs, PW, and PPy.

[0114] As shown in Tables 1 and 2, and Examples 1 and 9-12, when the mass percentage of the composite phase change material in the coating decreases, the overall heat absorption and low impedance effect of the membrane decreases. Conversely, when its mass percentage increases, the corresponding binder percentage in the membrane coating decreases, leading to coating detachment during cycling and consequently a decrease in membrane functionality. The optimal membrane coating thickness ratio to the negative electrode sheet is 2%. The reasons for excessively low or high ratios are the same as described above.

[0115] As shown in Tables 1 and 2, and Examples 1 and 13-18, when the inner diameter of the halloysite nanotube is 10 nm, the amount of phase change material stored in the corresponding membrane decreases, thus affecting the heat absorption function of the membrane. Example 16 is for the same reason. When the inner diameter of the halloysite nanotube is 30 nm, its specific surface area increases, which leads to the aggregation of halloysite nanotubes, thus affecting the PPy encapsulation of the halloysite nanotube opening. Examples 15 and 17 are for the same reason. When the length of the halloysite nanotube in Example 18 is too long, it leads to a decrease in the uniformity of the functional material slurry, thus affecting the functionality of the membrane.

[0116] As shown in Tables 1 and 2, and Examples 1 and 19, halloysite nanotubes, as a paraffin carrier, provide higher thermal stability to the diaphragm compared to titanium dioxide nanotubes, indicating that halloysite nanotubes have better compatibility with paraffin and polypyrrole, and the synergistic thermal stability of the three materials is superior.

[0117] When the term "embodiment" is used in the specification, it means that the invention has at least one embodiment that includes the specific feature, structure, material, or property. Therefore, expressions such as "in some embodiments," "in certain embodiments," and "exemplary" used throughout the document do not necessarily refer to the same embodiment. Furthermore, the specific feature, structure, material, or property can be combined in any suitable manner in one or more embodiments.

[0118] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the invention, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the invention.

Claims

1. A separator for use in an electrochemical device, characterized by, The diaphragm comprises a base film and a coating layer arranged on one side or both sides of the base film along the thickness direction, the coating layer comprises a composite phase change material, the composite phase change material comprises an electrically conductive polymer layer and a tubular material, The electrically conductive polymer layer is partially or entirely coated on the surface of the tubular material, The tubular material contains a phase change material in the tube.

2. The separator according to claim 1, characterized in that The tubular material comprises a ceramic micro-nano tubular material; And / or, the inner diameter of the tubular material is 10 nm to 30 nm; And / or, the length of the tubular material is 0.5 μm to 2.0 μm; And / or, the outer diameter of the tubular material is 30 nm to 100 nm; and / or the tubular material has a specific surface area of 20 m 2 / g to 140 m 2 / g.

3. The separator of claim 1, wherein The thickness of the electrically conductive polymer layer is 5 nm to 25 nm.

4. The separator of claim 1, wherein The thickness of the coating layer is 0.5 μm to 1.5 μm.

5. The diaphragm of claim 4, wherein The mass percentage of the composite phase change material based on the coating layer is 50% to 80%.

6. The diaphragm of claim 5, wherein The mass ratio of the tubular material, the phase change material and the electrically conductive polymer is 1: (0.5-1): (0.3-1).

7. The separator according to any one of claims 1 to 6, characterized in that, The softening point of the phase change material is 50℃ to 120℃.

8. The separator according to any one of claims 1 to 6, characterized in that, The electrically conductive polymer comprises at least one of polypyrrole, polyaniline, poly (3, 4-ethylenedioxythiophene) ; And / or, the phase change material comprises at least one of mineral wax, biomass wax, polyolefin wax, aliphatic polyester.

9. The diaphragm of claim 2, wherein, The ceramic micro-nano tubular material comprises at least one of titanium dioxide nanotube, boron nitride nanotube, silicate nanotube.

10. An electrochemical device, characterized by, The diaphragm comprises a base film and a coating layer arranged on one side or both sides of the base film along the thickness direction, the coating layer comprises a composite phase change material, the composite phase change material comprises an electrically conductive polymer layer and a tubular material, The electrically conductive polymer layer is partially or entirely coated on the surface of the tubular material, The tubular material contains a phase change material in the tube. The tubular material comprises a ceramic micro-nano tubular material; And / or, the inner diameter of the tubular material is 10 nm to 30 nm; And / or, the length of the tubular material is 0.5 μm to 2.0 μm; And / or, the outer diameter of the tubular material is 30 nm to 100 nm; The thickness of the electrically conductive polymer layer is 5 nm to 25 nm. The thickness of the coating layer is 0.5 μm to 1.5 μm. The mass percentage of the composite phase change material based on the coating layer is 50% to 80%. The mass ratio of the tubular material, the phase change material and the electrically conductive polymer is 1: (0.5-1): (0.3-1). The softening point of the phase change material is 50℃ to 120℃. The electrically conductive polymer comprises at least one of polypyrrole, polyaniline, poly (3, 4-ethylenedioxythiophene) ; And / or, the phase change material comprises at least one of mineral wax, biomass wax, polyolefin wax, aliphatic polyester. The ceramic micro-nano tubular material comprises at least one of titanium dioxide nanotube, boron nitride nanotube, silicate nanotube. The diaphragm comprises a base film and a coating layer arranged on one side or both sides of the base film along the thickness direction, the coating layer comprises a composite phase change material, the composite phase change material comprises an electrically conductive polymer layer and a tubular material, The electrically conductive polymer layer is partially or entirely coated on the surface of the tubular material, The tubular material contains a phase change material in the tube. The tubular material comprises a ceramic micro-nano tubular material; And / or, the inner diameter of the tubular material is 10 nm to 30 nm; And / or, the length of the tubular material is 0.5 μm to 2.0 μm; And / or, the outer diameter of the tubular material is 30 nm to 100 nm; The thickness of the electrically conductive polymer layer is 5 nm to 25 nm. The thickness of the coating layer is 0.5 μm to 1.5 μm. The mass percentage of the composite phase change material based on the coating layer is 50% to 80%. The mass

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