A lithium ion battery diaphragm and preparation method thereof, and a lithium ion battery

Abstract

The present invention provides a separator for a lithium-ion battery, comprising a substrate layer and a coating layer. The coating layer is coated on at least one side of the substrate layer. The coating layer comprises a first coating layer, a second coating layer, and a third coating layer, arranged in sequence. The third coating layer is connected to the substrate layer. The second coating layer is a thermally insulating aerogel layer, and the thermally insulating aerogel layer has a porosity of 80 to 99.5%. Compared to the prior art, the separator provided by the present invention adds a coating layer to the substrate layer and utilizes an aerogel coating with a porosity of 80 to 99.5%. By stacking the three coating layers, the separator's liquid absorption and liquid retention properties are improved, solving the problem of poor liquid absorption and liquid retention in existing separators. Furthermore, the present invention provides a method for preparing the separator and a lithium-ion battery containing the separator.

Description

Technical Field

[0001] The present invention relates to the field of lithium batteries, and in particular to a separator for lithium ion batteries, a preparation method thereof, and a lithium ion battery. Background Art

[0002] In the structure of lithium batteries, the diaphragm is one of the key internal components. The performance of the diaphragm determines the battery's interface structure, internal resistance, and other characteristics, directly affecting the battery's capacity, cycle life, and safety performance. A diaphragm with excellent performance plays an important role in improving the battery's overall performance. The main function of the diaphragm is to separate the positive and negative electrodes of the battery to prevent short circuits caused by contact between the two electrodes; it also needs to be able to allow electrolyte ions to pass through. Different types of batteries require different diaphragms, and the physicochemical properties of the diaphragm have a significant impact on the performance of the battery. Diaphragms are usually made of non-conductive materials. For lithium batteries, since the electrolyte is an organic solvent system, a diaphragm material that is resistant to organic solvents is required. Generally, a high-strength thin-film polyolefin porous membrane is used, mainly including polypropylene and polyethylene diaphragms, propylene and ethylene copolymers, and polyethylene copolymers.

[0003] However, existing battery separators lack the ability to absorb and retain liquid. Furthermore, as battery capacity increases, the number of chemical substances within the battery increases, and the density increases. This makes it increasingly difficult for the separator to absorb the electrolyte, preventing it from being fully soaked in electrolyte. This increases the battery's internal resistance, which in turn reduces the lithium battery's capacity and can easily cause the battery to explode. Furthermore, porous polyolefin membranes have high shrinkage, strong water absorption, and poor dimensional stability, making it difficult to manufacture high-precision products, limiting their long-term use.

[0004] To address the above issues, a Chinese utility model patent (CN201420868777.5) discloses a diaphragm comprising a diaphragm body and a groove disposed on at least one surface of the diaphragm body, wherein at least one end of the groove extends to the side of the diaphragm body. The groove is provided on the diaphragm surface to improve the diaphragm's liquid retention capacity. However, the design of the groove reduces the tensile strength of the diaphragm, making it prone to tearing when stretched, thereby causing a series of battery safety issues.

[0005] In view of this, it is indeed necessary to provide a technical solution to the above problems. Summary of the Invention

[0006] One of the purposes of the present invention is to solve the problem of poor liquid absorption and liquid retention capacity of existing diaphragms by providing a diaphragm for lithium-ion batteries, improve the liquid absorption and liquid retention performance of the diaphragm, thereby increasing the cycle life of the battery and reducing the cycle deterioration problem of the electrode.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A lithium-ion battery separator comprises a substrate layer and a coating layer, wherein the coating layer is coated on at least one side of the substrate layer, the coating layer comprising a first coating layer, a second coating layer, and a third coating layer arranged in sequence, the third coating layer being connected to the substrate layer, the second coating layer being an insulating aerogel layer, and the porosity of the insulating aerogel layer being 80 to 99.5%.

[0009] The diaphragm provided by the present invention adds a coating layer to the base layer. By stacking the three coating layers, the diaphragm's liquid absorption and liquid retention properties are improved, solving the problem of poor liquid absorption and liquid retention of existing diaphragms. After adding electrolyte to the bare battery cell, the residual liquid electrolyte in the shell is greatly reduced; at the same time, this diaphragm helps to firmly lock the electrolyte in the battery cell, thereby increasing the battery's cycle life and reducing the problem of cyclic deterioration of the electrode; in addition, the high-temperature performance and safety performance of the battery are also improved to a certain extent. When the battery is subjected to high temperature, puncture, impact, extrusion, etc., it can still be in a safe state. Among them, the use of an aerogel coating with a porosity of 80-99.5% can enable the diaphragm to absorb and retain more electrolyte, improve the battery's cycle performance, and also play a role in heat insulation. In addition, a third coating layer is provided between the heat-insulating aerogel layer and the base layer to improve the overall density of the diaphragm and ensure the safety performance of the battery.

[0010] Preferably, the coating layer is applied to both sides of the substrate layer. That is, the separator as a whole comprises a seven-layer structure, with three coating layers extending from the substrate layer at the center. Applying three coating layers on both sides of the substrate layer further improves the battery's liquid absorption and retention capabilities, ensuring that no liquid electrolyte remains within the housing after electrolyte addition.

[0011] Preferably, the coating layer is coated on one side of the substrate layer, and the second coating layer and the first coating layer are sequentially coated on the other side of the substrate layer. That is, the coating can also be performed in the order of the first coating layer, the second coating layer, the third coating layer, the substrate layer, the second coating layer, and the first coating layer, with the third coating layer only being coated on one side of the substrate layer.

[0012] Preferably, the thermal insulation aerogel layer includes inorganic nanoparticles, nanofibers and a cross-linking agent. Preferably, the thermal conductivity of the thermal insulation aerogel layer is less than or equal to 0.05W / m·k. Among them, the aerogel formed by inorganic nanoparticles has a high thermal insulation effect and is very hard, which improves the mechanical properties of the diaphragm and can avoid the problem of short circuit caused by thermal shrinkage of the diaphragm. The use of inorganic nanoparticles in conjunction with nanofibers provides the diaphragm with many small pore structures, helping the porosity of the diaphragm to reach at least 80% or even 99.5%, thereby improving the liquid absorption and liquid retention properties of the diaphragm. In addition, the thermal insulation aerogel layer also includes a binder.

[0013] Preferably, the specific surface area of ​​the inorganic nanoparticles is 50 to 500 m 2 / g, the particle size of the inorganic nanoparticles is 5 to 100 nm, and the inorganic nanoparticles are amorphous. 2 / g Inorganic nanoparticles with large specific surface area have a larger porosity at the same mass, or in other words, if the pore size is the same, the number of nanoparticles with large specific surface area will be greater, which will help the electrolyte to penetrate the gaps into the diaphragm and improve the liquid absorption performance of the diaphragm. Of course, the specific surface area should not be too large, which will lead to an excessively large pore size and will not be conducive to improving the liquid retention capacity of the diaphragm. More preferably, the specific surface area of ​​the inorganic nanoparticles is 150 to 400 m 2 In addition, the surface of the inorganic nanoparticles further includes at least two groups selected from the group consisting of carboxyl, amino and hydroxyl groups.

[0014] Preferably, the nanofibers are organic and / or inorganic fibers; the organic fibers include at least one of cellulose fibers, aramid fibers, polyamide fibers, polyester fibers, acrylic fibers, polypropylene fibers, ultra-high molecular weight polyethylene fibers, PBO fibers, PBI fibers, M5 fibers, and PI fibers; and the inorganic fibers include at least one of glass fibers, silica fibers, boron fibers, alumina fibers, and zinc oxide fibers. The nanofibers have a diameter of 5 to 500 nm and an aspect ratio of 1:10 to 1:500. The cellulose fibers include at least one of viscose fibers, acetate fibers, and cuprammonium fibers.

[0015] Preferably, the cross-linking agent is at least one of aziridines, isocyanates, glycerol ethers, polycarbodiimides and silanes. The addition of the cross-linking agent helps the cross-linking of the inorganic nanoparticles and the nanofibers, and the two molecules can be cross-linked together to form a three-dimensional network structure, which not only can improve the intensity of the barrier film, but also can improve its heat resistance. In addition, since the inorganic nanoparticle surface also includes at least two groups among carboxyl, amino and hydroxyl, the effect of at least two groups can help the cross-linking agent better to establish a three-dimensional network structure, and the chemical bonds generated by these several groups can also better retain the electrolyte, and the electrolyte is absorbed into the barrier film.

[0016] Preferably, the third coating layer includes ceramic particles. The porosity of the third coating layer is 30-70%. Properly reducing the porosity in the third coating layer can prevent the burrs and lithium dendrites of the pole piece from piercing the substrate layer, forming a relatively dense coating layer to protect the stability of the diaphragm. The third coating layer is arranged between the thermal insulation aerogel layer and the substrate layer, or it can be equivalent to the thermal insulation aerogel layer and then compounding a third coating layer, which can further enhance the strength and toughness of the diaphragm, making it less likely to be torn during stretching, thereby maintaining the stability of the battery. In addition, the third coating layer also includes a binder.

[0017] Preferably, the ceramic particles include at least one of alumina, boehmite, aluminum hydroxide, silicon dioxide, and titanium dioxide, wherein the particle size of the ceramic particles is 0.1 to 2 μm, and the coating thickness is 0.5 to 5 μm.

[0018] Preferably, the first coating layer comprises polymer particles, wherein the particle size of the polymer particles is 0.1 to 5 μm and the swelling degree is 5 to 100%. In addition, the first coating layer also comprises a binder.

[0019] Preferably, the polymer particles are fluoropolymers or acrylate polymers; the fluoropolymers include at least one of ethylene-tetrafluoroethylene copolymer (ETFE), polytetrafluoroethylene (PTFE), fluorinated ethylene-propylene copolymer (FEP), perfluoroalkoxy resin (PFA), polychlorotrifluoroethylene (PCTFE), ethylene chlorotrifluoroethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP); the acrylate polymers include at least one of polymethyl methacrylate, polyacrylate, acrylic acid-styrene copolymer, acrylic acid-organic silicon copolymer and acrylic acid-acrylonitrile copolymer.

[0020] Preferably, the pore sizes of the coating layers form a gradient distribution from large to small from the outer surface to the substrate layer. This effectively improves the membrane's liquid absorption efficiency and maintains the membrane's structural stability. Furthermore, the gradually decreasing pore size from the outside to the inside ensures that the membrane retains liquid effectively.

[0021] A second object of the present invention is to provide a method for preparing a lithium ion battery separator, comprising the following steps:

[0022] S1, first coating the third coating layer on at least one side of the substrate layer and drying;

[0023] S2, coating the second coating layer on the third coating layer, freeze-solidifying the second coating layer, and drying the second coating layer to obtain a diaphragm containing a thermal insulation aerogel layer; wherein the thermal insulation aerogel layer has a porosity of 80 to 99.5%;

[0024] S3, finally coating the first coating layer on the diaphragm containing the thermal insulation aerogel layer, and drying to obtain a diaphragm for a lithium ion battery.

[0025] This preparation method can make the three coating layers more tightly bonded, thereby improving the liquid absorption and liquid retention properties of the diaphragm while ensuring the strength and stability of the diaphragm.

[0026] A third object of the present invention is to provide a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, and a separator as described above, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet. With the separator, since the second coating layer on the separator has a porosity of 80 to 99.5%, the high porosity allows the separator to bond more tightly to the electrode sheet, ensuring that even if the thickness of the separator is increased, the overall bonding between the separator and the electrode sheet is not affected, thereby negligibly increasing the thickness of the battery. Furthermore, since the separator improves the battery's liquid retention performance, the battery's energy density is further increased.

[0027] The beneficial effects of the present invention are:

[0028] 1) The present invention provides a separator for a lithium-ion battery, comprising a substrate layer and a coating layer. The coating layer is coated on at least one side of the substrate layer and comprises a first coating layer, a second coating layer, and a third coating layer disposed sequentially. The third coating layer is connected to the substrate layer. The second coating layer is a thermally insulating aerogel layer having a porosity of 80 to 99.5%. Compared to the prior art, the separator provided by the present invention adds a coating layer to the substrate layer. By stacking the three coating layers, the separator's liquid absorption and liquid retention properties are significantly improved, addressing the poor liquid absorption and retention capabilities of prior separators. After adding electrolyte to a bare cell, residual liquid electrolyte within the casing is significantly reduced. Furthermore, the separator helps securely lock the electrolyte within the cell, extending the battery's cycle life and reducing the problem of cyclic degradation of the electrode. Furthermore, the battery's high-temperature performance and safety performance are significantly improved, allowing the battery to remain safe even when subjected to high temperatures, puncture, impact, or compression. Among them, the use of an aerogel coating with a porosity of 80 to 99.5% can enable the diaphragm to absorb and retain more electrolyte, thereby improving the battery cycle performance and also playing a role in heat insulation; in addition, a third coating layer is provided between the heat-insulating aerogel layer and the substrate layer, which can improve the overall density of the diaphragm and ensure the safety performance of the battery.

[0029] 2) The present invention also provides a lithium-ion battery. The lithium-ion battery using the above-mentioned separator has greatly improved liquid absorption and liquid retention performance, greatly improving the battery's cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is one of the structural schematic diagrams of the diaphragm of the present invention.

[0031] Figure 2 This is the second structural diagram of the diaphragm of the present invention.

[0032] Figure 3 This is the third structural diagram of the diaphragm of the present invention.

[0033] In the figure: 1-base material layer; 2-coating layer; 21-first coating layer; 22-second coating layer; 23-third coating layer. DETAILED DESCRIPTION

[0034] To make the technical solutions and advantages of the present invention more clear, the present invention and its beneficial effects will be described in further detail below with reference to specific implementation methods and accompanying drawings, but the implementation methods of the present invention are not limited thereto.

[0035] Example 1

[0036] like Figure 1As shown, a lithium-ion battery separator includes a substrate layer and a coating layer, wherein the coating layer is coated on one side of the substrate layer, and the coating layer includes a first coating layer, a second coating layer, and a third coating layer arranged in sequence from top to bottom, the third coating layer is connected to the substrate layer, and the second coating layer is an insulating aerogel layer. The porosity of the insulating aerogel layer is 80-99.5%, and the thermal conductivity of the insulating aerogel layer is less than or equal to 0.05 W / m·k; considering the difficulty and production cost of industrial production, the porosity of the insulating aerogel layer is preferably 85-96%.

[0037] The thermal insulation aerogel layer includes inorganic nanoparticles, nanofibers, a binder and a cross-linking agent. The specific surface area of ​​the inorganic nanoparticles is 50 to 500 m 2 / g, the particle size of the inorganic nanoparticles is 5 to 100 nm, the inorganic nanoparticles are amorphous, and their surface also includes at least two groups among carboxyl, amino and hydroxyl groups. Preferably, the specific surface area of ​​the inorganic nanoparticles is 150 to 400 m 2 / g. The diameter of the nanofiber is 5 to 500 nm, and the aspect ratio of the nanofiber is 1:10 to 1:500.

[0038] Specifically, the inorganic nanoparticles may be silica, alumina, chlorine dioxide, titanium dioxide, or calcium oxide; the nanofibers may be organic and / or inorganic fibers; the organic fibers may include at least one of cellulose fibers, aramid fibers, polyamide fibers, polyester fibers, acrylic fibers, polypropylene fibers, ultra-high molecular weight polyethylene fibers, PBO fibers, PBI fibers, M5 fibers, and PI fibers; and the inorganic fibers may include at least one of glass fibers, silica fibers, boron fibers, alumina fibers, and zinc oxide fibers. The crosslinking agent may be at least one of aziridines, isocyanates, glycerol ethers, polycarbodiimides, and silanes.

[0039] Furthermore, the third coating layer includes ceramic particles and a binder. The porosity of the third coating layer is 30-70%, the ceramic particles have a particle size of 0.1-2 μm, and the coating thickness is 0.5-5 μm. Specifically, the ceramic particles include at least one of alumina, boehmite, aluminum hydroxide, silicon dioxide, and titanium dioxide.

[0040] In addition, the first coating layer includes polymer particles and a binder. The polymer particles have a particle size of 0.1 to 5 μm and a swelling degree of 5 to 100%. Specifically, the polymer particles are fluoropolymers or acrylate polymers; the fluoropolymers include at least one of ethylene-tetrafluoroethylene copolymer (ETFE), polytetrafluoroethylene (PTFE), fluorinated ethylene-propylene copolymer (FEP), perfluoroalkoxy resin (PFA), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP); the acrylate polymers include at least one of polymethyl methacrylate, polyacrylate, acrylic acid-styrene copolymer, acrylic acid-organic silicon copolymer, and acrylic acid-acrylonitrile copolymer.

[0041] Preferably, the pore sizes of the coating layers form a gradient distribution from large to small from the outer surface to the substrate layer. That is, the pore sizes of the first coating layer, the second coating layer, and the third coating layer are distributed in a gradually decreasing gradient. By gradually reducing the pore size, the liquid absorption and liquid retention of the diaphragm are better improved.

[0042] Example 2

[0043] like Figure 2 As shown, unlike Example 1, the coating layer in this embodiment is applied to both sides of the substrate layer. This means the separator consists of a seven-layer structure, with three coating layers extending from the substrate layer to either side. Applying three coating layers on both sides of the substrate layer further improves the battery's liquid absorption and retention capabilities, ensuring that no liquid electrolyte remains within the housing after electrolyte addition.

[0044] The rest is the same as in Example 1 and will not be described again here.

[0045] Example 3

[0046] like Figure 3 As shown, the difference from Example 2 is that the coating layer of this embodiment is coated on one side of the substrate layer, and the other side of the substrate layer is coated with the second coating layer and the first coating layer in sequence. That is, compared with Example 2, the third coating layer is only coated on one side of the substrate layer.

[0047] The rest is the same as in Example 2 and will not be described again here.

[0048] Example 4

[0049] A method for preparing a lithium-ion battery separator comprises the following steps:

[0050] S1, first coating the third coating layer on at least one side of the substrate layer and drying;

[0051] S2, then applying the second coating layer on the third coating layer, then freezing and solidifying the second coating layer, and then drying it to obtain a diaphragm containing a thermal insulation aerogel layer; wherein the porosity of the thermal insulation aerogel layer is 80-99.5%; specifically, before coating, an aerogel slurry is first prepared, and the nanofibers and inorganic nanoparticles, a binder, a thickener and a cross-linking agent are fully mixed to prepare an aerogel slurry of a certain viscosity, and then the prepared aerogel slurry is evenly coated on the third coating layer. After the coating is completed, liquid nitrogen or dry ice is sprayed to freeze it. After the thermal insulation aerogel layer is frozen and solidified, it is dried to quickly vaporize the solvent in the thermal insulation aerogel layer to obtain a diaphragm containing a thermal insulation aerogel layer; in addition, if the thermal insulation aerogel layer is coated on both sides, the coating of the diaphragm containing the thermal insulation aerogel layer on one side can be completed first, and then the coating of the other side can be carried out;

[0052] S3, finally coating the first coating layer on the diaphragm containing the thermal insulation aerogel layer, and drying to obtain a diaphragm for a lithium ion battery.

[0053] The material of the substrate can be prepared by referring to existing materials.

[0054] Example 5

[0055] A lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, and any of the above-described separators, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet. The preparation of the lithium-ion battery can refer to the preparation of existing lithium-ion batteries and will not be described in detail here.

[0056] Specifically, the material selection of each embodiment is listed in the following Examples 6 to 20 and Comparative Examples 1 to 7, see Table 1. Among them, the coating structure of Examples 6 to 8 is the same as that of Example 1, and the coating structure of Examples 9 to 20 and Comparative Examples 1 to 7 is the same as that of Example 2.

[0057] Table 1

[0058]

[0059]

[0060] Separators from Examples 6-20 and Comparative Examples 1-7 were prepared according to the method described in Example 4. Lithium-ion batteries were then prepared using the resulting separators according to Example 5. The resulting lithium-ion batteries were tested, and the test results are shown in Table 2. The liquid retention capacities obtained in the following test results were calculated based on an initial battery capacity of approximately 5000 ng / L.

[0061] Table 2

[0062]

[0063]

[0064] The test results of the aforementioned examples and comparative examples demonstrate that lithium-ion batteries employing the present separator significantly improve both liquid retention and cycle retention. In particular, the double-sided, three-layer coating achieves a more pronounced liquid retention effect than a single-sided, three-layer coating. This demonstrates that the separator provided by the present invention significantly enhances both liquid absorption and retention. Furthermore, Comparative Examples 1-5 demonstrate that the separator of the present invention requires at least three layers of coating to achieve excellent results, while the absence of any one of these layers significantly impacts performance.

[0065] In addition, it can be seen from Examples 6 to 11 that as the porosity of the second coating layer gradually increases, the liquid retention capacity of the diaphragm also increases accordingly. However, if the porosity is too large, the liquid retention capacity actually decreases. It is speculated that this may be because the porosity is too large. Although the amount of electrolyte absorbed increases, the flow of the electrolyte will also be easier, resulting in subsequent electrolyte loss, and the liquid retention capacity is not further improved.

[0066] In addition, from the comparison of Examples 10 and 14-15, 16 and 17, it can be seen that when the substances added to the second coating layer are different, the performance of the battery is also affected to a certain extent. Whether it is different inorganic nanoparticles, different nanofibers, or different cross-linking agents, the liquid retention capacity of the diaphragm will be affected. This is mainly because the cross-linking agent cross-links the nanofibers and nanoparticles to form a network structure through cross-linking, but the effects of different substances are different. Some may have fewer carboxyl or amino groups and have an effect, and some substances may be caused by insufficient solubility of the cross-linking agent. In addition, the inventors also set up a comparative example in which the second coating layer and the third coating layer were swapped. The test results showed that the performance of the diaphragm was better when the thermal insulation aerogel layer was set in the second coating layer. This may be because the third coating layer is first compounded with the substrate layer to increase the strength of the substrate layer, and the second coating layer is close to the electrode. Since the porosity of the second coating layer is relatively high, the capillary force and the like can make the electrode and the second coating layer more tightly bonded. This structural design can help the diaphragm better absorb the electrolyte to improve the liquid retention capacity of the battery.

[0067] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0068] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A separator for a lithium ion battery, characterized in that The invention comprises a substrate layer and a coating layer, wherein the coating layer is coated on at least one side of the substrate layer, the coating layer comprises a first coating layer, a second coating layer and a third coating layer arranged in sequence, the third coating layer is connected to the substrate layer, the third coating layer comprises ceramic particles, the porosity of the third coating layer is 30-70%, the second coating layer is an insulating aerogel layer, the insulating aerogel layer comprises inorganic nanoparticles, nanofibers and a cross-linking agent, the porosity of the insulating aerogel layer is 80-99.5%, and the pore size of each layer of the coating layer forms a gradient distribution from large to small from the outer surface to the substrate layer.

2. A lithium ion battery separator according to claim 1, characterized in that: The coating layer is coated on both sides of the base material layer.

3. A lithium ion battery separator according to claim 1, characterized in that: The nanofibers are organic fibers and / or inorganic fibers; the organic fibers include at least one of cellulose fibers, aramid fibers, polyamide fibers, polyester fibers, acrylic fibers, nylon fibers, polypropylene fibers, ultra-high molecular weight polyethylene fibers, PBO fibers, PBI fibers, M5 fibers, and PI fibers; the inorganic fibers include at least one of glass fibers, silica fibers, boron fibers, alumina fibers, and zinc oxide fibers.

4. A lithium ion battery separator according to claim 1, characterized in that: The first coating layer includes polymer particles.

5. A lithium ion battery separator according to claim 4, characterized in that: The polymer particles are fluorine-containing polymers or acrylate polymers; the fluorine-containing polymers include at least one of ethylene-tetrafluoroethylene copolymers, polytetrafluoroethylene, fluorinated ethylene-propylene copolymers, perfluoroalkoxy resins, polychlorotrifluoroethylene, ethylene-chlorotrifluoroethylene copolymers, polyvinylidene fluoride, and polyvinylidene fluoride-hexafluoropropylene copolymers; the acrylate polymers include at least one of polymethyl methacrylate, polyacrylate, acrylic acid-styrene copolymers, acrylic acid-organic silicon copolymers, and acrylic acid-acrylonitrile copolymers.

6. A method for preparing the lithium ion battery separator according to any one of claims 1 to 5, It is characterized by: The following steps are involved: S1, first coating the third coating layer on at least one side of the substrate layer and drying; S2, coating the second coating layer on the third coating layer, freeze-solidifying the second coating layer, and drying the second coating layer to obtain a diaphragm containing a thermal insulation aerogel layer; wherein the thermal insulation aerogel layer has a porosity of 80 to 99.5%; S3, finally coating the first coating layer on the diaphragm containing the thermal insulation aerogel layer, and drying to obtain a diaphragm for a lithium ion battery.

7. A lithium-ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and the separator according to any one of claims 1 to 5, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet.

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