Alumina particles, method for producing the same, and separator, battery, and electric device

Abstract

The present application provides an alumina particle, a preparation method thereof, a separator, a battery and an electric device, the alumina particle comprising primary particles; the average particle size of the primary particles is 15 nm to 80 nm. When the alumina particle is used in a separator of a secondary battery, the secondary battery can have high energy density, high thermal safety performance, good cycle performance and kinetic performance.

Description

[0001] This application is a divisional application based on the invention with application number 202280018074.0, application date December 5, 2022, applicant CATL, entitled "Separation membrane, preparation method thereof and related secondary battery and power-consuming device". Technical Field

[0002] This application belongs to the field of battery technology, specifically relating to an alumina particle, its preparation method and separator, battery and power-consuming device. Background Technology

[0003] In recent years, rechargeable batteries have been widely used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. With the application and promotion of rechargeable batteries, their safety issues, especially thermal safety, have received increasing attention. However, current methods for improving the thermal safety performance of rechargeable batteries often do not balance energy density and lifespan. Therefore, how to achieve high energy density, high thermal safety performance, and good cycle and kinetic performance in rechargeable batteries is a key challenge in rechargeable battery design. Summary of the Invention

[0004] The purpose of this application is to provide alumina particles, a method for preparing the alumina particles, a separator, a battery, and an electrical device. When the alumina particles are used as a separator in a secondary battery, the secondary battery can achieve high energy density, high thermal safety performance, and good cycle performance and kinetic performance.

[0005] The first aspect of this application provides alumina particles, wherein the alumina comprises primary particles; the average particle size of the primary particles is 15 nm to 80 nm.

[0006] The primary alumina particles have a small average particle size and a large specific surface area. When used as a separator coating in secondary batteries, these alumina particles exhibit good affinity with the three-dimensional framework formed by the fibrous material in the coating, resulting in a more stable spatial network structure. This not only increases the ion conductivity of the separator but also improves its heat resistance and electrolyte wetting and retention properties. Therefore, using these alumina particles in the separator of secondary batteries helps to achieve both high thermal safety performance and good cycle and kinetic performance.

[0007] In any embodiment of this application, the average particle size of the primary particles is 30 nm to 75 nm.

[0008] When the average particle size of primary particles is within the above range, when used as a coating for secondary battery separators, the coating can have a suitable average pore area and further improve the heat resistance and ion conductivity of the separator.

[0009] In any embodiment of this application, the alumina particles further include secondary particles formed from primary particles.

[0010] In any embodiment of this application, the average particle size of the secondary particles is 50 nm to 150 nm, and optionally 55 nm to 120 nm.

[0011] In any embodiment of this application, the average particle size of the alumina particles is ≤150nm, and can be selected as 15nm to 120nm.

[0012] In any embodiment of this application, the alumina particles have a crystal form including at least one of the θ crystal form, γ crystal form, and η crystal form; optionally, the alumina particles have a crystal form including at least one of the θ crystal form and γ crystal form.

[0013] In any embodiment of this application, the content of θ-type alumina particles is ≥50wt%, optionally from 60wt% to 82wt%, based on the total weight of the alumina particles.

[0014] In any embodiment of this application, the content of γ-crystalline alumina particles is ≥10wt%, optionally from 17wt% to 38wt%, based on the total weight of the alumina particles.

[0015] In any embodiment of this application, the content of n-crystal alumina particles is ≤5wt%, optionally ≤1.5wt%, based on the total weight of the alumina particles.

[0016] Selecting alumina particles with different crystal forms can help improve at least one of the following properties of the separator: heat resistance, ion conductivity, and wetting and retention properties of the electrolyte.

[0017] In any embodiment of this application, the BET specific surface area of ​​the alumina particles is ≥15m². 2 / g, optional 18m 2 / g to 65m 2 / g. When the BET specific surface area of ​​alumina particles is within the above range, the coating of the separator can have a suitable average pore area, and the heat resistance and ion conductivity of the separator can be further improved. In addition, the affinity between alumina particles and the three-dimensional skeleton structure formed by fibrous materials in the coating can be improved, so that the coating has a more stable spatial network structure, and the separator has better heat resistance and higher ion conductivity.

[0018] The second aspect of this application provides a method for preparing the alumina particles, comprising: oxidizing an alumina particle precursor solution by high-pressure sputtering, and then heating it at 600°C to 900°C to form alumina particles with a primary particle morphology.

[0019] In any embodiment of this application, the heating time for forming the alumina particles with a primary particle morphology is 1 hour to 3 hours.

[0020] In any embodiment of this application, the method for preparing the alumina particles further includes: drying and shaping the alumina particles with the primary particle morphology at 150°C to 250°C to obtain alumina particles with the secondary particle morphology formed from the primary particles.

[0021] In any embodiment of this application, the drying and setting time is 30 to 60 minutes.

[0022] In any embodiment of this application, the alumina particles can be prepared by the following method: the precursor solution of alumina particles is subjected to an oxidation reaction by high-pressure sputtering, and then heated at 600°C to 900°C (for example, 1 hour to 3 hours) to form alumina particles with a primary particle morphology. Then, it can be dried and shaped at 150°C to 250°C (for example, 30 minutes to 60 minutes) to obtain alumina particles with a secondary particle morphology after primary particle self-assembly.

[0023] A third aspect of this application provides a separating membrane comprising a porous substrate and a coating disposed on at least one surface of the porous substrate, wherein the coating comprises a filler, the filler comprising a first filler; the first filler being alumina particles as described in the first aspect of this application or alumina particles prepared according to the preparation method of the second aspect of this application.

[0024] In any embodiment of this application, the filler further includes a second filler, the second filler having an average particle size greater than that of the first filler. The larger particle size of the second filler allows it to better perform its supporting role in the coating, reducing the shrinkage of the first filler, decreasing the amount of binder required, and thus improving the heat resistance of the separator. The larger particle size of the second filler also helps to create a coating with more pore structures and less water content with a smaller amount used, thereby further improving the ion conductivity of the separator and its wetting and retention properties with the electrolyte.

[0025] In any embodiment of this application, the average particle size of the second filler is less than or equal to 400 nm, and may be selected as 100 nm to 300 nm.

[0026] In any embodiment of this application, the second filler has a primary particle morphology.

[0027] In any embodiment of this application, the BET specific surface area of ​​the second packing is ≤15m². 2 / g, optional 7m 2 / g to 12m 2 / g. When the BET specific surface area of ​​the second filler is within the above range, the coating can have a suitable average pore area, and the heat resistance and ion conductivity of the separator can be further improved. In addition, the supporting role of the second filler can be better utilized, the moisture content of the coating can be reduced, and the coating can maintain a stable pore structure during long-term charge and discharge, which is conducive to ion transport and can also improve the heat resistance of the separator.

[0028] In any embodiment of this application, the content of the second filler is ≤20wt%, optionally from 2wt% to 15wt%, based on the total weight of the coating. When the content of the second filler is within the above range, the coating can have a suitable average pore area, and the heat resistance and ion conductivity of the separator can be further improved; in addition, the supporting role of the second filler can be better utilized, the moisture content of the coating can be reduced, and the coating can maintain a stable pore structure during long-term charge and discharge, which is conducive to ion transport and can also improve the heat resistance of the separator.

[0029] In any embodiment of this application, the second filler comprises at least one of inorganic particles and organic particles.

[0030] In any embodiment of this application, the second filler comprises inorganic particles with a primary particle morphology, and the crystal form of the primary particle morphology inorganic particles includes at least one of α-crystal form and γ-crystal form, optionally including α-crystal form. The α-crystal form of the second filler has the advantages of high hardness, good heat resistance, low dielectric constant, high safety and high true density, thereby further improving the heat resistance of the coating.

[0031] In any embodiment of this application, the second filler comprises inorganic particles with a primary particle morphology, and the crystal form of the inorganic particles with the primary particle morphology includes the α crystal form, and the content of the α crystal form inorganic particles is ≥80wt%, optionally from 90wt% to 100wt%, based on the total weight of the inorganic particles with the primary particle morphology in the second filler.

[0032] In any embodiment of this application, the content of the first filler is ≥55wt%, optionally from 60wt% to 90wt%, based on the total weight of the coating. When the content of the first filler is within the above range, the coating can have a suitable average pore area, and the heat resistance and ion conductivity of the separator can be further improved; in addition, it is also beneficial for the coating to have a more stable spatial network structure, thereby further improving the heat resistance and ion conductivity of the separator.

[0033] In any embodiment of this application, the coating further includes fibrous material.

[0034] In any embodiment of this application, the content of the fibrous material is ≤40 wt%, optionally from 5 wt% to 25 wt%, based on the total weight of the coating. When the content of the fibrous material is within the above range, the coating can have a suitable average pore area, and the heat resistance and ion conductivity of the separator can be further improved.

[0035] In any embodiment of this application, the morphology of the fibrous material may optionally include at least one of rod-shaped, tubular, rod-shaped, and fibrous.

[0036] In any embodiment of this application, the average diameter of the fibrous material is ≤40 nm, and can be selected from 10 nm to 35 nm. When the average diameter of the fibrous material is within the above range, it helps to form an integrated effect by overlapping the fibrous material and the filler.

[0037] In any embodiment of this application, the average length of the fibrous material is from 100 nm to 800 nm, and optionally from 200 nm to 600 nm. When the average length of the fibrous material is within a suitable range, the heat resistance and ion conductivity of the separator can be further improved.

[0038] In any embodiment of this application, the aspect ratio of the fibrous material is 5 to 60, optionally 10 to 30. When the aspect ratio of the fibrous material is within a suitable range, the heat resistance and ion conductivity of the separator can be further improved.

[0039] In any embodiment of this application, the fibrous material comprises at least one of organic and inorganic materials. Optionally, the organic material comprises at least one of cellulose nanofibers, polytetrafluoroethylene nanofibers, and polyamide nanofibers; alternatively, the cellulose nanofibers comprise at least one of cellulose nanofibers, cellulose nanowhiskers, and bacterial cellulose nanofibers. Optionally, the inorganic material comprises at least one of halloysite nanotubes, nanorod-shaped alumina, nanorod-shaped boehmite, nanorod-shaped silica, and glass fibers.

[0040] In any embodiment of this application, the fibrous material comprises nanocellulose.

[0041] In any embodiment of this application, the nanocellulose includes hydroxyl groups and anionic modified groups.

[0042] In any embodiment of this application, the anionic modifying group includes at least one selected from amino, carboxyl, sulfonic acid, boric acid, and phosphoric acid groups, optionally including at least one selected from sulfonic acid, boric acid, and phosphoric acid groups. When nanocellulose has the above-mentioned specific anionic modifying groups, it can effectively improve the heat resistance of the separator and enhance the thermal safety performance of the secondary battery; on the other hand, it can also improve the adhesion strength between the coating and the porous substrate. When nanocellulose has the above-mentioned specific anionic modifying groups, it is also beneficial for nanocellulose to overlap with fillers to form an integrated effect, thereby enabling the coating to have a more stable spatial network structure, which can improve the wetting and retention characteristics of the separator to the electrolyte, improve the ion conductivity and voltage breakdown resistance of the separator, and also facilitate the matching of high-voltage positive electrode active materials, further improving the energy density of the secondary battery. In addition, the presence of anionic modifying groups can also reduce the proportion of hydroxyl groups, thereby ensuring that the coating slurry has a suitable viscosity, which is more conducive to coating, and thus can also improve the production efficiency of the separator and the uniformity of the coating.

[0043] In any embodiment of this application, the molar ratio of the anionic modifying group to the hydroxyl group is 1:4 to 4:1, and optionally 2:3 to 7:3. When the molar ratio of the anionic modifying group to the hydroxyl group is within a suitable range, the heat resistance, ionic conductivity, and wetting and retention properties of the separator can be further improved.

[0044] In any embodiment of this application, the coating further includes a non-particulate binder. Optionally, the non-particulate binder includes an aqueous solution-based binder.

[0045] In any embodiment of this application, the content of the non-particulate binder in the coating is ≤2 wt%, based on the total weight of the coating. The fibrous materials and fillers in the coating can form a stable spatial network structure, thereby enabling the release membrane to maintain high adhesion while reducing the amount of binder used.

[0046] In any embodiment of this application, the thickness of the porous substrate is ≤8μm, and can be selected from 3μm to 6μm. The coating of this application can significantly improve the heat resistance of the separator, thereby allowing the use of a thinner porous substrate, which helps to improve the energy density of the secondary battery.

[0047] In any embodiment of the present application, the thickness of the coating is ≤ 2 μm, and optionally 0.5 μm to 1.3 μm. The coating of the present application has high heat resistance, whereby the thickness of the coating can be reduced, and the energy density of the secondary battery can be further improved. In the present application, the thickness of the coating refers to the thickness of the coating on one side of the porous substrate.

[0048] In any embodiment of the present application, the separator further includes an adhesive layer, the adhesive layer is provided on at least a part of the surface of the coating, and the adhesive layer includes granular binders. The adhesive layer can not only prevent the coating from falling off and improve the safety performance of the secondary battery, but also improve the interface between the separator and the electrode and enhance the cycle performance of the secondary battery.

[0049] In any embodiment of the present application, the granular binder includes at least one of homopolymers or copolymers of acrylate monomers, homopolymers or copolymers of acrylic monomers, and homopolymers or copolymers of fluorinated olefin monomers.

[0050] In any embodiment of the present application, along the thickness direction of the separator, the average pore area of the coating is less than the average pore area of the porous substrate.

[0051] Making the average pore area S1 of the coating and the average pore area S2 of the porous substrate satisfy 0 < S1 / S2 < 1 (that is, the average pore area of the coating is less than the average pore area of the porous substrate) can enable the separator to have both high heat resistance and high ion conductivity, and enable the secondary battery to have both high energy density, high thermal safety performance, and good cycle performance and kinetic performance.

[0052] In any embodiment of the present application, 0.06 ≤ S1 / S2 < 1, optionally, 0.30 ≤ S1 / S2 ≤ 0.97.

[0053] In any embodiment of the present application, 0.0002 μm 2 ≤ S1 ≤ 0.0080 μm 2 , optionally, 0.0004 μm 2 ≤ S1 ≤ 0.0050 μm 2 . When the average pore area S1 of the coating is within the above range, on the one hand, it can improve the heat resistance of the separator, and on the other hand, it will not hinder the transport of active ions. Therefore, the secondary battery can better balance high energy density, high thermal safety performance, and good cycle performance and kinetic performance.

[0054] In any embodiment of the present application, 0.0005 μm 2 ≤ S2 ≤ 0.0100 μm 2 , optionally, 0.0008 μm 2 ≤ S2 ≤ 0.0080 μm2 When the average pore area S2 of the porous substrate is within the above range, it is beneficial to improve the ion conductivity of the separator and the capacity performance of the secondary battery.

[0055] In any embodiment of this application, the average pore size of the separator is denoted as d1, and the average pore size of the porous substrate is denoted as d2, then d1 / d2 < 1; optionally, 0.3 ≤ d1 / d2 ≤ 0.8. When the ratio d1 / d2 of the average pore size of the separator to the average pore size of the porous substrate is within the above range, it can ensure that the separator has high heat resistance while also having high ion conductivity.

[0056] In any embodiment of this application, 15nm ≤ d1 ≤ 50nm, and optionally, 20nm ≤ d1 ≤ 40nm. When the average pore size d1 of the separator is within the above range, it can improve the heat resistance of the separator on the one hand, and does not hinder the transport of active ions on the other hand, thereby enabling the secondary battery to better balance high energy density, high thermal safety performance, and good cycle performance and kinetic performance.

[0057] In any embodiment of this application, 25nm ≤ d2 ≤ 60nm, and optionally, 30nm ≤ d2 ≤ 50nm. When the average pore size d2 of the porous substrate is within the above range, it is beneficial to improve the ion conductivity of the separator and the capacity performance of the secondary battery.

[0058] In any embodiment of this application, the areal density of the coating is denoted as ρ1, and the areal density of the porous substrate is denoted as ρ2. Then, 0.15 ≤ ρ1 / ρ2 ≤ 0.80; optionally, 0.20 ≤ ρ1 / ρ2 ≤ 0.50. When ρ1 / ρ2 is within the above range, it is beneficial for the coating to have high heat resistance, and it is also beneficial for the secondary battery to have both high energy density and high thermal safety performance.

[0059] In any embodiment of this application, optionally, 0.50 g / m 2 ≤ρ1≤1.50g / m 2 Alternatively, 0.75g / m 2 ≤ρ1≤1.40g / m 2 When the areal density ρ1 of the coating is within the above range, it is beneficial for the secondary battery to achieve both high energy density and high thermal safety performance. It also enables the coating to have a suitable average pore area and further improves the heat resistance and ion conductivity of the separator.

[0060] In any embodiment of this application, optionally, 1.50 g / m 2 ≤ρ2≤4.50g / m 2 Alternatively, 2.00g / m 2 ≤ρ2≤4.00g / m2 When the areal density ρ2 of the porous substrate is within the above range, the porous substrate can have a suitable average pore area, which is also beneficial to improving the ion conductivity of the separator and the capacity performance of the secondary battery.

[0061] In any embodiment of this application, the porosity of the separator is denoted as P1, and the porosity of the porous substrate is denoted as P2, then 0.4 ≤ P2 / P1 < 1; optionally, 0.55 ≤ P2 / P1 ≤ 0.85. When P2 / P1 is within the above range, it is beneficial for the secondary battery to achieve both high thermal safety performance and good cycle performance and kinetic performance.

[0062] In any embodiment of this application, 20% ≤ P1 ≤ 60%, and optionally, 25% ≤ P1 ≤ 45%. When the porosity P1 of the separator is within the above range, it is beneficial for the secondary battery to achieve both high thermal safety performance and good cycle performance and kinetic performance.

[0063] In any embodiment of this application, 15% ≤ P2 ≤ 45%, and optionally, 20% ≤ P2 ≤ 40%. When the porosity P2 of the porous substrate is within the above range, it is beneficial to improve the ion conductivity of the separator and the capacity performance of the secondary battery.

[0064] In any embodiment of this application, the longitudinal thermal shrinkage rate of the separator at 150°C for 1 hour is ≤6%, and can be selected as 0.5% to 4%.

[0065] In any embodiment of this application, the lateral thermal shrinkage rate of the separator at 150°C for 1 hour is ≤6%, and can be selected as 0.5% to 4%.

[0066] The separator of this application has a low thermal shrinkage rate in both the lateral and longitudinal directions at a high temperature of 150°C, thereby improving the safety performance of the secondary battery.

[0067] In any embodiment of this application, the ion conductivity of the separator is ≥0.6 ms / cm 2 ≥0.9ms / cm 2 The separator of this application has high ion conductivity, thereby improving the cycle performance and / or kinetic performance of the secondary battery.

[0068] In any embodiment of this application, the resistance of the separator is ≤1.3Ω, optionally ≤1.0Ω. The separator of this application has a low resistance value, thereby improving the cycle performance and / or kinetic performance of the secondary battery.

[0069] In any embodiment of this application, the longitudinal tensile strength of the separator is ≥2000 kg / cm². 22500kg / cm² is available. 2 Up to 4500 kg / cm 2 .

[0070] In any embodiment of this application, the transverse tensile strength of the separator is ≥2000 kg / cm². 2 2500kg / cm² is available. 2 Up to 4500 kg / cm 2 .

[0071] The separator of this application has high tensile strength in both the transverse and longitudinal directions, which reduces the probability of the separator breaking when the secondary battery expands, thereby improving the safety performance of the secondary battery.

[0072] In any embodiment of this application, the wetting length of the separator is ≥30mm, and can be selected from 30mm to 80mm.

[0073] In any embodiment of this application, the wetting rate of the separator is ≥3 mm / s, and can be selected from 3 mm / s to 10 mm / s.

[0074] The separator of this application has good wetting and retention properties for electrolyte, thereby improving the ion conductivity of the separator and the capacity performance of the secondary battery.

[0075] In any embodiment of this application, the air permeability of the separator is ≤300s / 100mL, and can be selected from 100s / 100mL to 230s / 100mL. The separator of this application has good air permeability, thereby improving ion conductivity and the capacity performance of the secondary battery.

[0076] The fourth aspect of this application provides a secondary battery, including the separator membrane of the third aspect of this application.

[0077] The fifth aspect of this application provides an electrical device, including the secondary battery of the fourth aspect of this application.

[0078] When the alumina particles of this application are used in the separator of a secondary battery, the secondary battery can achieve high energy density, high thermal safety performance, and good cycle performance and kinetic performance. The electrical device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery. Attached Figure Description

[0079] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0080] Figure 1 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0081] Figure 2 yes Figure 1 An exploded view of the implementation method of the secondary battery.

[0082] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0083] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0084] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0085] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0086] The accompanying drawings are not necessarily drawn to scale. The reference numerals are as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Secondary battery, 51 Housing, 52 Electrode assembly, 53 Cover plate. Detailed Implementation

[0087] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the separator, its preparation method, and related secondary batteries and power-consuming devices of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0088] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0089] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0090] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0091] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0092] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0093] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0094] Unless otherwise specified, in this application, the terms "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0095] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0096] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application.

[0097] Typically, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The separator is placed between the positive and negative electrodes and mainly serves to prevent short circuits between the positive and negative electrodes, while also allowing active ions to pass freely to form a circuit.

[0098] With the application and promotion of rechargeable batteries, people have increasingly higher requirements for their energy density and kinetic performance. Thinning the separator is an effective measure to improve the energy density of rechargeable batteries. Currently, commercially available rechargeable batteries typically use polyolefin porous membranes, such as polyethylene porous membranes, polypropylene porous membranes, or polypropylene / polyethylene / polypropylene three-layer composite membranes, with melting points between 130℃ and 160℃. Therefore, when the thickness is reduced, the heat resistance of the separator decreases, and a significant thermal shrinkage effect occurs when heated, causing direct contact between the positive and negative electrodes inside the battery, leading to internal short circuits and increasing the safety risks of the rechargeable battery.

[0099] Therefore, existing separators often struggle to achieve high energy density, high thermal safety, and good cycle and kinetic performance in secondary batteries.

[0100] Alumina particles

[0101] Specifically, the first aspect of this application provides alumina particles, wherein the alumina particles comprise primary particles; the average particle size of the primary particles is 15 nm to 80 nm.

[0102] The primary alumina particles have a small average particle size and a large specific surface area. When used as a separator coating in secondary batteries, these alumina particles exhibit good affinity with the three-dimensional framework formed by the fibrous material in the coating, resulting in a more stable spatial network structure. This not only increases the ion conductivity of the separator but also improves its heat resistance and electrolyte wetting and retention properties. Therefore, using these alumina particles in the separator of secondary batteries helps to achieve both high thermal safety performance and good cycle and kinetic performance.

[0103] In some embodiments, the average particle size of the primary particles is 30 nm to 75 nm.

[0104] When the average particle size of primary particles is within the above range, when used as a coating for secondary battery separators, the coating can have a suitable average pore area and further improve the heat resistance and ion conductivity of the separator.

[0105] In some embodiments, the alumina particles may further include secondary particles formed from primary particles.

[0106] In some embodiments, the average particle size of the secondary particles is 50 nm to 150 nm, and can be selected as 50 nm to 135 nm, 50 nm to 120 nm, 55 nm to 150 nm, 55 nm to 135 nm, or 55 nm to 120 nm.

[0107] In some embodiments, the average particle size of the alumina particles is ≤150nm, and can be selected as 15nm to 150nm or 15nm to 120nm.

[0108] When the average particle size of alumina particles is within the above range, when used as a coating for secondary battery separators, the coating can have a suitable average pore area and further improve the heat resistance and ion conductivity of the separator.

[0109] In some embodiments, the alumina particles have a crystal form including at least one of the θ crystal form, γ crystal form, and η crystal form. Optionally, the alumina particles have a crystal form including at least one of the θ crystal form and γ crystal form.

[0110] The θ-type alumina particles exhibit diffraction peaks at 2θ of 36.68°±0.2° and 31.21°±0.2° in the X-ray diffraction pattern determined using an X-ray diffractometer. In some embodiments, the content of θ-type alumina particles in the alumina particles may be ≥50 wt%, optionally from 60 wt% to 82 wt%, based on the total weight of the alumina particles.

[0111] The γ-crystalline alumina particles exhibit diffraction peaks at 2θ of 66.95°±0.2° and 45.91°±0.2° in the X-ray diffraction pattern determined using an X-ray diffractometer. In some embodiments, the content of γ-crystalline alumina particles in the alumina particles may be ≥10 wt%, optionally from 17 wt% to 38 wt%, based on the total weight of the alumina particles.

[0112] The η-crystal alumina particles exhibit diffraction peaks at 2θ of 31.89°±0.2° and 19.37°±0.2° in the X-ray diffraction pattern determined using an X-ray diffractometer. In some embodiments, the content of η-crystal alumina particles in the alumina particles may be ≤5wt%, optionally ≤1.5wt%, and more preferably ≤1wt%, based on the total weight of the alumina particles.

[0113] Theta-type alumina particles have moderate specific surface area and hardness, which can better improve the heat resistance and ion conductivity of the separator at the same time; γ-type and η-type alumina particles have the advantage of large specific surface area.

[0114] Selecting alumina particles with different crystal forms can help improve at least one of the following properties of the separator: heat resistance, ion conductivity, and wetting and retention properties of the electrolyte.

[0115] In some embodiments, the alumina particles have crystal forms including θ, γ, and η crystal forms, and the content of θ crystal alumina particles can be 60wt% to 82wt%, the content of γ crystal alumina particles can be 17wt% to 38wt%, and the content of η crystal alumina particles can be ≤1.5wt%, all based on the total weight of the alumina particles.

[0116] The X-ray diffraction pattern of alumina particles can be obtained by the following method: After drying the alumina particles, grind them in a mortar (such as an agate mortar) for 30 minutes, and then use an X-ray diffractometer (such as a Miniflex 600-C) to obtain the X-ray diffraction pattern. During the test, a Cu target, a Ni filter, a tube voltage of 40 kV, a tube current of 15 mA, and a continuous scanning range of 5°–80° can be used.

[0117] In some embodiments, the BET specific surface area of ​​the alumina particles is ≥15m². 2 / g, optional 18m 2 / g to 65m 2 / g. When the BET specific surface area of ​​alumina particles is within the above range, the coating of the separator can have a suitable average pore area, and the heat resistance and ion conductivity of the separator can be further improved. In addition, the affinity between alumina particles and the three-dimensional skeleton structure formed by fibrous materials in the coating can be improved, so that the coating has a more stable spatial network structure, and the separator has better heat resistance and higher ion conductivity.

[0118] The second aspect of this application provides a method for preparing the alumina particles, comprising: oxidizing an alumina particle precursor solution by high-pressure sputtering, and then heating it at 600°C to 900°C to form alumina particles with a primary particle morphology.

[0119] In some embodiments, the heating time is 1 to 3 hours.

[0120] In any embodiment of this application, the method for preparing the alumina particles further includes: drying and shaping the alumina particles with the primary particle morphology at 150°C to 250°C to obtain alumina particles with the secondary particle morphology formed from the primary particles.

[0121] In some embodiments, the drying and setting time is 30 to 60 minutes.

[0122] In any embodiment of this application, the alumina particles can be prepared by the following method: the precursor solution of alumina particles is subjected to an oxidation reaction by high-pressure sputtering, and then heated at 600°C to 900°C (for example, 1 hour to 3 hours) to form alumina particles with a primary particle morphology. Then, it can be dried and shaped at 150°C to 250°C (for example, 30 minutes to 60 minutes) to obtain alumina particles with a secondary particle morphology after primary particle self-assembly.

[0123] Separating membrane

[0124] A third aspect of this application provides a separating membrane.

[0125] The isolation membrane includes a porous substrate and a coating disposed on at least one surface of the porous substrate, wherein the coating includes a filler, the filler including a first filler; the first filler is alumina particles provided in any embodiment of this application.

[0126] In some embodiments, the packing further includes a second packing, wherein the average particle size of the second packing is greater than the average particle size of the first packing.

[0127] The larger particle size of the second filler allows it to better support the coating, reduce the shrinkage of the first filler, and decrease the amount of binder required, thereby improving the heat resistance of the separator. The larger particle size of the second filler also helps to create a coating with more pore structures and less water content when used in smaller quantities, which further improves the ion conductivity of the separator and its wetting and retention properties with electrolyte.

[0128] In some embodiments, the average particle size of the second filler is less than or equal to 400 nm, and can be selected as 100 nm to 300 nm. When the average particle size of the second filler is within the above range, the coating can have a suitable average pore area, and the heat resistance and ion conductivity of the separator can be further improved. In addition, the supporting role of the second filler can be better utilized, the moisture content of the coating can be reduced, and the coating can maintain a stable pore structure during long-term charge and discharge, which is conducive to ion transport and can also improve the heat resistance of the separator.

[0129] In some embodiments, the BET specific surface area of ​​the second packing is ≤15m². 2 / g, optional 7m 2 / g to 12m 2 / g. When the BET specific surface area of ​​the second filler is within the above range, the coating can have a suitable average pore area, and the heat resistance and ion conductivity of the separator can be further improved. In addition, the supporting role of the second filler can be better utilized, the moisture content of the coating can be reduced, and the coating can maintain a stable pore structure during long-term charge and discharge, which is conducive to ion transport and can also improve the heat resistance of the separator.

[0130] In some embodiments, the second filler comprises at least one of inorganic particles and organic particles.

[0131] In some embodiments, the inorganic particles may include at least one of the following: inorganic particles having a dielectric constant of 5 or greater, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of undergoing electrochemical reactions.

[0132] Optionally, the inorganic particles having a dielectric constant of 5 or higher include boehmite, alumina, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hydropyrite, zirconium titanate, barium titanate, Pb(Zr,Ti)O3 (abbreviated as PZT), and Pb 1-m La m Zr 1-n Ti nO3 (abbreviated as PLZT, 0 < m < 1, 0 < n < 1), Pb (Mg3Nb) 2 / 3 The coating comprises at least one of PbTiO3 (abbreviated as PMN-PT) and its modified inorganic particles. Optionally, the modification of each inorganic particle can be chemical modification and / or physical modification. The chemical modification includes coupling agent modification (e.g., using silane coupling agents, titanate coupling agents, etc.), surfactant modification, polymer grafting modification, etc. The physical modification can be mechanical dispersion, ultrasonic dispersion, high-energy treatment, etc. Modification treatment can reduce the agglomeration of inorganic particles, thereby enabling the coating to have a more stable and uniform spatial network structure; in addition, by selecting coupling agents, surfactants or polymers with specific functional groups to modify inorganic particles, it is also helpful to improve the coating's wetting and retention properties with electrolytes and improve the coating's adhesion to porous substrates.

[0133] Optionally, the inorganic particles that have ion conductivity but do not store ions include Li3PO4 and lithium titanium phosphate (Li). x1 Ti y1 (PO4)3, Lithium aluminum titanium phosphate (Li) x2 Al y2 Ti z1 (PO4)3、(LiAlTiP) x3 O y3 Type glass, lithium lanthanum titanate (Li) x4 La y4 TiO3, lithium germanium thiophosphate (Li) x5 Ge y5 P z2 S w Lithium nitride (Li) x6 N y6 SiS2 type glass Li x7 Si y7 S z3 and P2S5 type glass Li x8 P y8 S z4 At least one of the following: 0 < x1 < 2, 0 < y1 < 3, 0 < x2 < 2, 0 < y2 < 1, 0 < z1 < 3, 0 < x3 < 4, 0 < y3 < 13, 0 < x4 < 2, 0 < y4 < 3, 0 < x5 < 4, 0 < y5 < 1, 0 < z2 < 1, 0 < w < 5, 0 < x6 < 4, 0 < y6 < 2, 0 < x7 < 3, 0 < y7 < 2, 0 < z3 < 4, 0 < x8 < 3, 0 < y8 < 3, 0 < z4 < 7. This can further improve the ion conductivity of the separator.

[0134] Optionally, the inorganic particles capable of undergoing electrochemical reactions include at least one of lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials, and lithium-titanium compounds.

[0135] In some embodiments, the organic particles include, but are not limited to, at least one of the following: polyethylene particles, polypropylene particles, cellulose, cellulose modifiers (e.g., carboxymethyl cellulose), melamine resin particles, phenolic resin particles, polyester particles (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), silicone resin particles, polyimide particles, polyamide-imide particles, polyarylamide particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, polyaryletherketone particles, and copolymers of butyl acrylate and ethyl methacrylate (e.g., crosslinked polymers of butyl acrylate and ethyl methacrylate).

[0136] In some embodiments, the second filler has a primary particle morphology.

[0137] In some embodiments, the second filler comprises inorganic particles with a primary particle morphology, and the crystal form of the primary particle morphology includes at least one of α-crystal and γ-crystal, optionally including α-crystal. The α-crystal second filler has the advantages of high hardness, good heat resistance, low dielectric constant, high safety and high true density, thereby further improving the heat resistance of the coating.

[0138] In some embodiments, the second filler comprises inorganic particles with a primary particle morphology, and the inorganic particles with a primary particle morphology have a crystal form including an α crystal form, and the content of the α crystal form inorganic particles is ≥80 wt%, optionally 85 wt% to 100 wt%, 90 wt% to 100 wt%, or 95 wt% to 100 wt%, based on the total weight of the inorganic particles with the primary particle morphology in the second filler.

[0139] The α-crystalline inorganic particles exhibit diffraction peaks at 2θ of 57.48°±0.2° and 43.34°±0.2° in the X-ray diffraction pattern determined by X-ray diffractometer.

[0140] In some embodiments, the content of the second filler is ≤20wt%, optionally from 2wt% to 15wt%, based on the total weight of the coating. When the content of the second filler is within the above range, the coating can have a suitable average pore area, and the heat resistance and ion conductivity of the separator can be further improved; in addition, the supporting role of the second filler can be better utilized, the moisture content of the coating can be reduced, and the coating can maintain a stable pore structure during long-term charge and discharge, which is conducive to ion transport and can also improve the heat resistance of the separator.

[0141] In some embodiments, the content of the first filler is ≥55 wt%, optionally from 60 wt% to 90 wt%, based on the total weight of the coating. When the content of the first filler is within the above range, the coating can have a suitable average pore area, and the heat resistance and ion conductivity of the separator can be further improved; in addition, it is also beneficial for the coating to have a more stable spatial network structure, thereby further improving the heat resistance and ion conductivity of the separator.

[0142] In some embodiments, the coating further includes fibrous material.

[0143] In some embodiments, the morphology of the fibrous material may optionally include at least one of rod-shaped, tubular (e.g., hollow tubular), rod-shaped, and fibrous. Materials with suitable shapes facilitate the formation of a stable spatial network structure between the fibrous material and the filler, thereby further improving the heat resistance and ion conductivity of the separator. In this application, "fibrous material" refers to a material with an aspect ratio of 5 or greater.

[0144] In some embodiments, the average diameter of the fibrous material is ≤40 nm, optionally from 10 nm to 35 nm. When the average diameter of the fibrous material is within the above range, it helps the fibrous material and the filler to overlap and form an integrated effect. Furthermore, it effectively avoids the following situation: when the average diameter of the fibrous material is too large, the mutual entanglement effect of the three-dimensional skeleton structure formed is insufficient, which may lead to insufficient heat resistance, voltage breakdown resistance, and other properties of the separator.

[0145] In some embodiments, the average length of the fibrous material is 100 nm to 800 nm, optionally 200 nm to 600 nm. When the average length of the fibrous material is within a suitable range, the heat resistance and ion conductivity of the separator can be further improved. Furthermore, it can effectively avoid the following situations: when the average length of the fibrous material is too short, its overlap with the filler is poor, the heat resistance of the coating deteriorates, and during the coating drying process, the three-dimensional skeleton structure formed by the fibrous material is prone to collapse due to the lack of filler support, which can easily lead to pore blockage, hindering ion transport and moisture removal, and potentially affecting the thermal safety, cycle performance, and kinetic performance of the secondary battery; when the average length of the fibrous material is too long, the coating slurry has high viscosity and poor flow, which may affect the coating slurry application and thus the coating quality, for example, potentially affecting the heat resistance and ion conductivity of the separator.

[0146] In some embodiments, the aspect ratio of the fibrous material is 5 to 60, optionally 10 to 30. When the aspect ratio of the fibrous material is within a suitable range, the heat resistance and ion conductivity of the separator can be further improved. Furthermore, it can effectively avoid the following situations: when the aspect ratio of the fibrous material is too small, its overlap with the filler is poor, the heat resistance of the coating deteriorates, and during the coating drying process, the three-dimensional skeleton structure formed by the fibrous material is prone to collapse due to the lack of filler support, which can easily lead to pore blockage, hindering ion transport and moisture removal, and potentially affecting the thermal safety, cycle performance, and kinetic performance of the secondary battery; when the aspect ratio of the fibrous material is too large, this may result in a decrease in the ion conductivity of the separator, thereby deteriorating the cycle performance and / or kinetic performance of the secondary battery.

[0147] The average length and average diameter of the fibrous material can be determined by the following method: A 3.6 mm × 3.6 mm sample is cut from any region of the separator. The microstructure of the coating in the sample is mapped using a scanning electron microscope (e.g., ZEISS Sigma 300). A high vacuum mode is selected, with a working voltage of 3 kV and a magnification of 30,000x to obtain a SEM image. Based on the obtained SEM image, multiple (e.g., more than 5) test regions are selected for length statistics. Each test region has a size of 0.5 μm × 0.5 μm. The average length of each test region is then taken as the average length of the fibrous material. Based on the obtained SEM image, multiple (e.g., more than 5) test regions are selected for diameter statistics using Nano Measurer particle size distribution statistical software. Each test region has a size of 0.5 μm × 0.5 μm. The average diameter of each test region is then taken as the average diameter of the fibrous material.

[0148] In some embodiments, the fibrous material includes at least one of organic and inorganic materials. The material used for the fibrous material is not particularly limited as long as it satisfies the requirements of electrical insulation, electrochemical stability, and stability to the electrolyte; it can be either organic or inorganic.

[0149] In some embodiments, the organic material includes at least one of cellulose nanofibers, polytetrafluoroethylene nanofibers, and polyamide nanofibers. In some embodiments, the inorganic material includes at least one of halloysite nanotubes, nanorod-shaped alumina, nanorod-shaped boehmite, nanorod-shaped silica, and glass fiber.

[0150] In some embodiments, the fibrous material comprises nanocellulose. Optionally, the nanocellulose comprises at least one of cellulose nanofibrils (CNF, also known as nanofibrillated cellulose or microfibrillated cellulose), cellulose nanocrystals (CNC, also known as cellulose nanocrystals or nanocrystalline cellulose), and bacterial nanocellulose (BNC, also known as bacterial cellulose or microbial cellulose). Optionally, the nanocellulose comprises cellulose nanocrystals, which have the advantage of high crystallinity, thereby better improving the heat resistance of the separator.

[0151] Nanocellulose refers to cellulose with any dimension within the nanometer range (e.g., within 100 nm), possessing both the characteristics of cellulose and those of nanoparticles. Nanocellulose can be a high-molecular-weight nanomaterial extracted from natural sources such as wood and cotton through one or more chemical, physical, or biological methods. It boasts advantages such as wide availability, low cost, biodegradability, high modulus, and high specific surface area, making it an excellent alternative to traditional petrochemical resources and effectively alleviating environmental pollution and petrochemical resource shortages. Nanocellulose also exhibits excellent high-temperature resistance and minimal volume change upon heating, thereby improving the heat resistance of the separator. Furthermore, compared to traditional inorganic ceramic particles, nanocellulose has a lower density, which can reduce the weight of the secondary battery and increase its gravimetric energy density. In addition, the three-dimensional framework structure formed by nanocellulose can possess tiny nanopores to prevent current leakage, enabling the separator to maintain both good electrolyte wetting and retention properties and excellent voltage breakdown resistance.

[0152] In some embodiments, the nanocellulose includes hydroxyl groups and anionic modifying groups.

[0153] In some embodiments, the anionic modifying group may optionally include at least one of amino, carboxyl, sulfonic acid, boric acid, and phosphoric acid groups, and more preferably at least one of sulfonic acid, boric acid, and phosphoric acid groups.

[0154] Further research by the inventors revealed that when nanocellulose possesses the aforementioned specific anionic modifying groups, it can effectively improve the heat resistance of the separator and enhance the thermal safety performance of the secondary battery. Furthermore, it can also improve the adhesion strength between the coating and the porous substrate. The presence of these specific anionic modifying groups also facilitates the integration of nanocellulose with fillers, resulting in a more stable spatial network structure in the coating. This enhances the separator's wetting and retention properties with the electrolyte, improves its ion conductivity and voltage breakdown resistance, and is beneficial for matching high-voltage positive electrode active materials, further increasing the energy density of the secondary battery. In addition, the presence of anionic modifying groups reduces the proportion of hydroxyl groups, ensuring the coating slurry has a suitable viscosity, which is more conducive to coating application, thereby improving the production efficiency and coating uniformity of the separator.

[0155] In some embodiments, the molar ratio of the anionic modifying group to the hydroxyl group is 1:4 to 4:1, optionally 2:3 to 7:3. When the molar ratio of the anionic modifying group to the hydroxyl group is within a suitable range, the heat resistance, ion conductivity, and electrolyte wetting and retention characteristics of the separator can be further improved. Furthermore, it effectively avoids the following situations: when the molar ratio of the anionic modifying group to the hydroxyl group is too small, the further improvement effect of the anionic modifying group on the heat resistance and ion conductivity of the separator may not be significant; when the molar ratio of the anionic modifying group to the hydroxyl group is too large, the electrolyte wetting and retention characteristics of the separator may deteriorate, which may affect the cycle performance and / or kinetic performance of the secondary battery, and may also lead to a decrease in the heat resistance of the separator, which may further affect the improvement effect on the thermal safety performance of the secondary battery.

[0156] The types of anionic modifying groups in nanocellulose can be determined using infrared spectroscopy. For example, the infrared spectrum of the material can be tested to identify its characteristic peaks, thereby determining the types of anionic modifying groups. Specifically, the material can be analyzed using infrared spectroscopy with instruments and methods known in the art, such as an infrared spectrometer (e.g., the Nicolet IS10 Fourier transform infrared spectrometer) according to the General Rules for Infrared Spectroscopic Analysis in GB / T 6040-2019.

[0157] In some embodiments, the fibrous material includes sulfonic acid groups, and the sulfur content in the fibrous material is ≥0.1 wt%, optionally from 0.2 wt% to 0.5 wt%, based on the total weight of the fibrous material.

[0158] The sulfur content in the fibrous material can be determined by the following method: After drying the fibrous material, grind it in a mortar (such as an agate mortar) for 30 minutes, and then use an X-ray diffractometer (such as a Miniflex 600-C) to determine the sulfur content. The test can be performed using a Cu target, a Ni filter, a tube voltage of 40 kV, a tube current of 15 mA, and a continuous scanning range of 5°–80°.

[0159] In some embodiments, the content of the fibrous material is ≤40 wt%, optionally from 5 wt% to 25 wt%, based on the total weight of the coating. When the fibrous material content is within the above range, the coating can have a suitable average pore area, and the heat resistance and ion conductivity of the separator can be further improved.

[0160] In some embodiments, the coating further includes a non-particulate binder. This application does not impose any particular limitation on the type of non-particulate binder; any known material with good adhesion can be selected. Optionally, the non-particulate binder includes an aqueous solution-based binder, which has the advantages of good thermodynamic stability and environmental friendliness, thereby facilitating the preparation and application of the coating slurry. As an example, the aqueous solution-based binder may include at least one of aqueous solution-based acrylic resins (e.g., homopolymers of acrylic acid, methacrylic acid, sodium acrylate monomers, or copolymers with other comonomers), polyvinyl alcohol (PVA), isobutylene-maleic anhydride copolymers, and polyacrylamide.

[0161] In some embodiments, the content of the non-particulate binder in the coating is ≤2 wt%, based on the total weight of the coating. The fibrous material and fillers in the coating can form a stable spatial network structure, thereby enabling the release membrane to maintain high adhesion while reducing the amount of binder used.

[0162] In some embodiments, the separator further includes an adhesive layer disposed on at least a portion of the surface of the coating, the adhesive layer comprising a particulate adhesive. The adhesive layer not only prevents the coating from peeling off, improving the safety performance of the secondary battery, but also improves the interface between the separator and the electrode, enhancing the cycle performance of the secondary battery.

[0163] Optionally, the particulate binder includes at least one of acrylate monomer homopolymers or copolymers, acrylate monomer homopolymers or copolymers, and fluorinated olefin monomer homopolymers or copolymers. The comonomer includes, but is not limited to, at least one of the following: acrylate monomers, acrylate monomers, olefin monomers, halogenated olefin monomers, fluoroether monomers, etc.

[0164] Optionally, the particulate binder comprises a vinylidene fluoride-based polymer, such as a homopolymer of vinylidene fluoride monomer (VDF) and / or a copolymer of vinylidene fluoride monomer and a comonomer. The comonomer may be at least one of an olefin monomer, a fluorinated olefin monomer, a chlorinated olefin monomer, an acrylate monomer, an acrylic monomer, and a fluoroether monomer. Optionally, the comonomer may include at least one of the following: trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ether (such as perfluoro(methyl vinyl) ether PMVE, perfluoro(ethyl vinyl) ether PEVE, perfluoro(propyl vinyl) ether PPVE), perfluoro(1,3-dioxolene), and perfluoro(2,2-dimethyl-1,3-dioxolene) (PDD).

[0165] In any embodiment of the present application, along the thickness direction of the separator membrane, the average pore area of the coating is less than the average pore area of the porous substrate.

[0166] Making the average pore area S1 of the coating and the average pore area S2 of the porous substrate satisfy 0 < S1 / S2 < 1 (that is, the average pore area of the coating is less than the average pore area of the porous substrate) can enable the separator membrane to have both high heat resistance and high ion conductivity, and enable the secondary battery to have both high energy density, high thermal safety performance, and good cycle performance and kinetic performance.

[0167] The coating comprises fibrous materials and fillers, which helps to form a nested effect between the fillers and the fibrous material structure. Thus, it can not only increase the heat resistance of the separator membrane, reduce the shrinkage degree of the separator membrane when heated, reduce the risk of short circuit between the positive and negative electrodes, and endow the secondary battery with high thermal safety performance, but also maintain a high bonding strength between the coating and the porous substrate, and prevent the fillers from falling off during the long-term charge and discharge process of the secondary battery. In addition, when at least a part of the fillers is filled in the three-dimensional skeleton structure formed by the fibrous materials, there are more contact sites between the fillers and the three-dimensional skeleton structure. Therefore, the amount of the binder used in the coating can be reduced, thereby effectively reducing the risk of binder plugging the pores, and further improving the cycle performance and kinetic performance of the secondary battery. In some embodiments, at least a part of the fillers is filled in the three-dimensional skeleton structure, and the other parts of the fillers may be located on the surface of the three-dimensional skeleton structure and / or the interface between the three-dimensional skeleton structure and the porous substrate. And at the interface position between the three-dimensional skeleton structure and the porous substrate, a small part of the fillers may be embedded in the porous substrate. For example, during the winding process of the electrode assembly, due to the action of external pressure, a small part of the fillers at the interface position are embedded in the matrix and / or pores of the porous substrate. In the present application, the "three-dimensional skeleton structure" refers to a structure with a three-dimensional spatial shape and certain pores, which can be formed by the mutual overlapping of fibrous materials.

[0168] The average pore area S1 of the coating is smaller than the average pore area S2 of the porous substrate (i.e., the average pore area of ​​the coating is smaller than the average pore area of ​​the porous substrate), which enables the coating to have high heat resistance. Because the coating of this application has high heat resistance, the coating thickness can be reduced (for example, the coating thickness can be less than or equal to 2 μm), shortening the active ion transport distance, so that the secondary battery can also achieve high energy density as well as good cycle performance and kinetic performance. In addition, because the coating of this application has high heat resistance, a thinner porous substrate can be selected, which can further improve the energy density of the secondary battery.

[0169] Further research by the inventors revealed that the ratio S1 / S2, which is the average pore area S1 of the coating to the average pore area S2 of the porous substrate, should not be too small. When S1 / S2 is too small, the average pore area of ​​the coating tends to be small, which may hinder the transport of active ions and affect the cycle performance and / or kinetic performance of the secondary battery. In some embodiments, 0.06 ≤ S1 / S2 < 1, and optionally, 0.10 ≤ S1 / S2 ≤ 0.99, 0.20 ≤ S1 / S2 ≤ 0.98, 0.30 ≤ S1 / S2 ≤ 0.97, 0.30 ≤ S1 / S2 ≤ 0.80, 0.30 ≤ S1 / S2 ≤ 0.70, 0.35 ≤ S1 / S2 ≤ 0.94, 0.35 ≤ S1 / S2 ≤ 0.85, 0.40 ≤ S1 / S2 ≤ 0.92, 0.40 ≤ S1 / S2 ≤ 0.80, 0.40 ≤ S1 / S2 ≤ 0.70, and 0.45 ≤ S1 / S2 ≤ 0.90.

[0170] In some embodiments, the average pore area S1 of the coating satisfies 0.0002 μm. 2 ≤S1≤0.0080μm 2 Optionally, 0.0004μm 2 ≤S1≤0.0050μm 2 0.0008μm 2 ≤S1≤0.0048μm 2 When the average pore area S1 of the coating is within the above range, it can improve the heat resistance of the separator on the one hand, and on the other hand, it will not hinder the transport of active ions. This allows the secondary battery to better balance high energy density, high thermal safety performance, and good cycle performance and kinetic performance.

[0171] In some embodiments, the average pore area S2 of the porous substrate satisfies 0.0005 μm. 2 ≤S2≤0.0100μm 2 Optionally, 0.0008μm 2 ≤S2≤0.0080μm 2When the average pore area S2 of the porous substrate is within the above range, it is beneficial to improve the ion conductivity of the separator and the capacity performance of the secondary battery.

[0172] In this application, the average pore area S1 of the coating of the separator and the average pore area S2 of the porous substrate of the separator can be obtained by testing a cross-sectional image of the separator.

[0173] The average pore area S1 of the separator coating refers to the ratio of the total pore area of ​​the coating in the cross-sectional image of the separator to the number of pores in the coating.

[0174] The average pore area S2 of the porous substrate of the separator refers to the ratio of the total pore area of ​​the porous substrate in the cross-sectional image of the separator to the number of pores in the porous substrate.

[0175] In this application, the cross-sectional image of the separator is an image along the thickness direction of the separator. A separator sample of a certain size (e.g., 15mm × 15mm) can be cut from any region of the separator. The cross-section of the separator is obtained by cutting it under freezing conditions (e.g., -80℃) using an ion beam polisher (e.g., Hitachi Arblade 5000). Referring to JY / T010-1996, a SEM image of the separator cross-section is obtained by scanning it with a scanning electron microscope (e.g., a Sigma 300 scanning electron microscope from ZEISS, Germany) (magnification can be 1000x to 30000x). The average pore area S1 of the separator coating and the average pore area S2 of the porous substrate of the separator are obtained using a multi-segment binarization method with an image processing detection system (e.g., Yihong separator detection system 2022-0408).

[0176] When cutting using an ion beam polisher, the test sample can be wrapped in copper or aluminum foil before cutting. To obtain a SEM image of the separator cross-section, the test sample can be sputtered with gold.

[0177] Using an image processing detection system, the pore area data of the separator coating and the porous substrate can be obtained separately. Then, using Mintab software, the pore area distribution map and average pore area of ​​the separator coating and the porous substrate can be obtained separately. The ratio of the total pore area of ​​the separator coating to the number of pores in the coating is the average pore area S1 of the separator coating, and the ratio of the total pore area of ​​the porous substrate to the number of pores in the porous substrate is the average pore area S2 of the porous substrate.

[0178] In some embodiments, the average pore size of the separator is denoted as d1, and the average pore size of the porous substrate is denoted as d2. Then, d1 / d2 < 1. Optionally, 0.2 ≤ d1 / d2 ≤ 0.9, 0.3 ≤ d1 / d2 ≤ 0.8, and 0.4 ≤ d1 / d2 ≤ 0.7. When the ratio d1 / d2 of the average pore size of the separator to the average pore size of the porous substrate is within the above range, it ensures that the separator has high heat resistance while also possessing high ion conductivity.

[0179] In some embodiments, the average pore size d1 of the separator satisfies 15nm≤d1≤50nm, and optionally, 20nm≤d1≤40nm. When the average pore size d1 of the separator is within the above range, it can improve the heat resistance of the separator on the one hand, and does not hinder the transport of active ions on the other hand, thereby enabling the secondary battery to better balance high energy density, high thermal safety performance, and good cycle performance and kinetic performance.

[0180] In some embodiments, the average pore size d2 of the porous substrate satisfies 25nm ≤ d2 ≤ 60nm, and optionally, 30nm ≤ d2 ≤ 50nm. When the average pore size d2 of the porous substrate is within the above range, it is beneficial to improve the ion conductivity of the separator and the capacity performance of the secondary battery.

[0181] The average pore size d1 of the separator and the average pore size d2 of the porous substrate can be tested using a capillary porosity analyzer (bubble point method). An exemplary testing method is as follows: Take a circular sample with a diameter of 25 mm and drop 3-5 drops of wetting solution onto it. After the sample is completely wetted, place it in a mold. Then, use inert gas to compress the wetting solution in the pores of the sample. The compression pressure and flow rate are inversely proportional to the pore size. The average pore size of the sample is obtained through software sampling and pressure-pore size conversion analysis. The testing instrument can be a PMI CFP 1500 pore size analyzer, with a testing pressure ranging from 100 psi to 350 psi.

[0182] In some embodiments, the areal density of the coating is denoted as ρ1, and the areal density of the porous substrate is denoted as ρ2. Then, 0.15 ≤ ρ1 / ρ2 ≤ 0.80, and optionally, 0.20 ≤ ρ1 / ρ2 ≤ 0.50. When ρ1 / ρ2 is within the above range, it is beneficial for the coating to have high heat resistance, and it is also beneficial for the secondary battery to achieve both high energy density and high thermal safety performance.

[0183] In some embodiments, the areal density ρ1 of the coating satisfies 0.50 g / m³. 2 ≤ρ1≤1.50g / m 2 Optionally, 0.60 g / m 2 ≤ρ1≤1.40g / m 2 0.75g / m 2≤ρ1≤1.40g / m 2 0.75g / m 2 ≤ρ1≤1.30g / m 2 When the areal density ρ1 of the coating is within the above-mentioned range, it is beneficial for the secondary battery to achieve both high energy density and high thermal safety performance. When the areal density ρ1 of the coating is within the above-mentioned range, it also enables the coating to have a suitable average pore area, and further improves the heat resistance and ion conductivity of the separator. In this application, the areal density of the coating refers to the areal density of the coating located on one side of the porous substrate.

[0184] In some embodiments, the areal density ρ2 of the porous substrate satisfies 1.50 g / m³. 2 ≤ρ2≤4.50g / m 2 Optionally, 2.00 g / m 2 ≤ρ2≤4.00g / m 2 When the areal density ρ2 of the porous substrate is within the above range, the porous substrate can have a suitable average pore area, which is also beneficial to improving the ion conductivity of the separator and the capacity performance of the secondary battery.

[0185] In some embodiments, the porosity of the separator is denoted as P1, and the porosity of the porous substrate is denoted as P2, then 0.4 ≤ P2 / P1 < 1; alternatively, 0.55 ≤ P2 / P1 ≤ 0.85. When P2 / P1 is within the above range, it is beneficial for the secondary battery to achieve both high thermal safety performance and good cycle performance and kinetic performance.

[0186] In some embodiments, the porosity P1 of the separator satisfies 20% ≤ P1 ≤ 60%, and optionally, 25% ≤ P1 ≤ 45%. When the porosity P1 of the separator is within the above range, it is beneficial for the secondary battery to achieve both high thermal safety performance and good cycle performance and kinetic performance.

[0187] In some embodiments, the porosity P2 of the porous substrate satisfies 15% ≤ P2 ≤ 45%, and optionally, 20% ≤ P2 ≤ 40%. When the porosity P2 of the porous substrate is within the above range, it is beneficial to improve the ion conductivity of the separator and the capacity performance of the secondary battery.

[0188] The porosity P1 of the separator and the porosity P2 of the porous substrate can be tested according to GB / T 24586-2009. The test method is as follows: Cut the separator or porous substrate into small circular samples with a diameter of 14mm, measure the thickness, and calculate the apparent volume V1 of the separator or porous substrate according to the formula for cylindrical volume. Referring to GB / T 24586-2009, using an inert gas such as helium or nitrogen as the medium, employ the gas displacement method and measure the true volume V2 of the separator or porous substrate using a true density meter. Then, the porosity of the separator or porous substrate = (V1-V2) / V1×100%. The testing instrument can be the AccuPyc II 1340 fully automatic true density meter from Micromeritics, USA.

[0189] In some embodiments, the thickness of the porous substrate is ≤8 μm, optionally from 3 μm to 6 μm. The coating of this application can significantly improve the heat resistance of the separator, thereby allowing for the use of a thinner porous substrate, which helps to improve the energy density of the secondary battery.

[0190] In some embodiments, the coating thickness is ≤2 μm, optionally from 0.5 μm to 1.3 μm. The coating of this application exhibits high heat resistance, thereby reducing the coating thickness and further improving the energy density of the secondary battery. In this application, the coating thickness refers to the thickness of the coating located on one side of the porous substrate.

[0191] This application does not impose any particular limitation on the material of the porous substrate; any known substrate with good chemical and mechanical stability can be selected. For example, the porous substrate may include at least one of porous polyolefin-based resin membranes (e.g., polyethylene, polypropylene, polyvinylidene fluoride), porous glass fiber, and porous nonwoven fabric. The porous substrate may be a single-layer film or a multi-layer composite film. When the porous substrate is a multi-layer composite film, the materials of each layer may be the same or different.

[0192] In some embodiments, the longitudinal thermal shrinkage rate of the separator at 150°C for 1 hour is ≤6%, optionally from 0.5% to 4%.

[0193] In some embodiments, the lateral thermal shrinkage rate of the separator at 150°C for 1 hour is ≤6%, optionally from 0.5% to 4%.

[0194] The separator of this application has a low thermal shrinkage rate in both the lateral and longitudinal directions at a high temperature of 150°C, thereby improving the safety performance of the secondary battery.

[0195] In some embodiments, the ion conductivity of the separator is ≥0.6 ms / cm 2 ≥0.9ms / cm2 .

[0196] The separator of this application has high ion conductivity, thereby improving the cycle performance and / or kinetic performance of the secondary battery.

[0197] In some embodiments, the resistance of the isolation membrane is ≤1.3Ω, and optionally ≤1.0Ω.

[0198] The separator of this application has a low resistance value, thereby improving the cycle performance and / or kinetic performance of the secondary battery.

[0199] In some embodiments, the longitudinal tensile strength of the separator is ≥2000 kg / cm². 2 2500kg / cm² is available. 2 Up to 4500 kg / cm 2 .

[0200] In some embodiments, the transverse tensile strength of the separator is ≥2000 kg / cm². 2 2500kg / cm² is available. 2 Up to 4500 kg / cm 2 .

[0201] The separator of this application has high tensile strength in both the transverse and longitudinal directions, which reduces the probability of the separator breaking when the secondary battery expands, thereby improving the safety performance of the secondary battery.

[0202] In some embodiments, the wetting length of the separator is ≥30mm, and can be selected from 30mm to 80mm.

[0203] In some embodiments, the wetting rate of the separator is ≥3 mm / s, optionally from 3 mm / s to 10 mm / s.

[0204] The separator of this application has good wetting and retention properties for electrolyte, thereby improving the ion conductivity of the separator and the capacity performance of the secondary battery.

[0205] In some embodiments, the air permeability of the isolation membrane is ≤300s / 100mL, and can be selected from 100s / 100mL to 230s / 100mL.

[0206] The separator membrane of this application has good air permeability, which can improve ion conductivity and the capacity of secondary batteries.

[0207] In this application, the average particle size of the material (e.g., the first filler, the second filler) has a meaning known in the art and can be measured using instruments and methods known in the art. For example, images can be obtained by measuring the material or the separator using a scanning electron microscope, a transmission electron microscope, or a particle size distribution instrument. Multiple (e.g., more than 10) test particles (e.g., those with the first filler and the second filler) can be randomly selected from the images, and the average value of the shortest diagonal length of the particles can be used as the average particle size.

[0208] In this application, the specific surface area of ​​materials (e.g., the first packing material, the second packing material) has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017 and calculated using the BET (Brunauer-Emmett-Teller) method. Optionally, the nitrogen adsorption specific surface area analysis can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc., USA.

[0209] In this application, the heat shrinkage rate, tensile strength, and air permeability of the separator have meanings known in the art and can be measured using methods known in the art. For example, they can all be tested with reference to the standard GB / T 36363-2018.

[0210] In this application, the wetting length and wetting speed of the separator have meanings known in the art and can be measured using methods known in the art. An exemplary test method is as follows: The separator is cut into samples with a width of 5 mm and a length of 100 mm. The two ends of the sample are fixed and placed horizontally. 0.5 mg of electrolyte is dropped into the center of the sample. After a specified time (1 min in this application), a photograph is taken and the length of electrolyte diffusion is measured, thereby obtaining the wetting length and wetting speed of the separator. To ensure the accuracy of the test results, multiple samples (e.g., 5 to 10) can be tested, and the test results are obtained by calculating the average value. The electrolyte can be prepared as follows: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of 30:50:20 to obtain an organic solvent. Thoroughly dried LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0211] The ion conductivity and resistance of the separator can be obtained through AC impedance spectroscopy. Specifically, the separator is cut into circular pieces of a certain area, dried, and placed between two stainless steel electrodes. After absorbing a sufficient amount of electrolyte, it is sealed to form a coin cell, and then AC impedance spectroscopy is performed.

[0212] It should be noted that the coating parameters (such as areal density and thickness) of the aforementioned separator are coating parameters for one side of the porous substrate. When the coating is applied to both sides of the porous substrate, if the coating parameters on either side meet the requirements of this application, it is considered to fall within the protection scope of this application.

[0213] Preparation method

[0214] In some embodiments of this application, a method for preparing a separator membrane according to a third aspect of this application is provided, comprising the following steps: providing a porous substrate; mixing a filler in a solvent and then stirring it uniformly at a certain shear rate to prepare a coating slurry; coating the coating slurry onto at least one surface of the porous substrate and drying it to obtain a separator membrane, wherein the separator membrane comprises a porous substrate and a coating disposed on at least one surface of the porous substrate, the coating comprising a filler.

[0215] In some embodiments, the coating further includes fibrous material, and the method for preparing the separator membrane includes the following steps: providing a porous substrate; mixing the fibrous material and filler in a solvent in a predetermined ratio, and then stirring evenly at a certain shear rate to prepare a coating slurry; applying the coating slurry to at least one surface of the porous substrate, and drying to obtain a separator membrane, wherein the separator membrane includes a porous substrate and a coating disposed on at least one surface of the porous substrate, and the coating includes fibrous material and filler.

[0216] In some embodiments, the solvent used when preparing the coating slurry can be water, such as deionized water.

[0217] In some embodiments, the coating slurry may also include other components, such as dispersants, wetting agents, binders, etc.

[0218] In some embodiments, the shear rate is ≤30 m / s, optionally from 15 m / s to 30 m / s. When the shear rate is within this range, the dried coating can have a suitable average pore area, and the heat resistance and ion conductivity of the separator can be further improved.

[0219] In some embodiments, the solid content of the coating slurry is 8% to 30%, optionally 10% to 20%.

[0220] In some embodiments, the surface density of the coating slurry on one side is 0.50 g / m². 2 Up to 1.50 g / m 2 0.75g / m 2 Up to 1.40 g / m 2When the surface density of the coating slurry is within the above range, the dried coating can have a suitable average pore area, and the heat resistance and ion conductivity of the separator can be further improved.

[0221] In some embodiments, the coating thickness on one side of the coating slurry is ≤2 μm, optionally from 0.5 μm to 1.3 μm. When the coating thickness of the coating slurry is within the above range, the dried coating can have a suitable average pore area, and the heat resistance and ion conductivity of the separator can be further improved.

[0222] In some embodiments, the fibrous material may include at least one of organic and inorganic materials. Optionally, the organic material includes at least one of cellulose nanofibers, polytetrafluoroethylene nanofibers, and polyamide nanofibers. Optionally, the inorganic material includes at least one of halloysite nanotubes, nanorod-shaped alumina, nanorod-shaped boehmite, nanorod-shaped silica, and glass fibers. In some embodiments, the fibrous material may include cellulose nanofibers, optionally cellulose nanocrystals (CNC, also known as cellulose nanocrystals or nanocrystalline cellulose).

[0223] In some embodiments, the nanocellulose can be obtained by the following method: providing cellulose powder with a whiteness ≥80%; mixing and reacting the obtained cellulose powder with a modified solution, followed by washing to remove impurities, to obtain cellulose nanowhiskers; adjusting the pH of the obtained cellulose nanowhiskers to neutral, and then grinding and cutting them to obtain nanocellulose.

[0224] Optionally, the cellulose powder with a whiteness ≥80% can be obtained commercially or by chemical methods (e.g., acid hydrolysis, alkali treatment, Tempo catalytic oxidation), biological methods (e.g., enzymatic treatment), or mechanical methods (e.g., ultrafine grinding, ultrasonic crushing, high-pressure homogenization). The fiber raw materials used to prepare the cellulose powder with a whiteness ≥80% may include at least one of plant fibers, such as cotton fibers (e.g., cotton fiber, kapok fiber), hemp fibers (e.g., sisal fiber, ramie fiber, jute fiber, flax fiber, hemp fiber, abaca fiber, etc.), palm fiber, wood fiber, bamboo fiber, and grass fiber.

[0225] In some embodiments, the cellulose powder with a whiteness of ≥80% can also be prepared by the following method: after the fiber raw material is opened and slag is removed, it is cooked with an alkaline solution (e.g., an aqueous solution of NaOH, the concentration of which can be 4wt% to 20wt%, optionally 5wt% to 15wt%), and then sequentially subjected to water washing to remove impurities (e.g., water washing 3 to 6 times), bleaching (e.g., sodium hypochlorite and / or hydrogen peroxide can be used), acid washing to remove impurities, water washing to remove impurities, water removal, and air drying to obtain cellulose powder.

[0226] In some embodiments, the modified solution may be an acid solution (e.g., aqueous solution of sulfuric acid, aqueous solution of boric acid, aqueous solution of phosphoric acid, aqueous solution of acetic acid) or an alkaline solution (e.g., urea organic solvent solution). Optionally, the modified solution is an acid solution.

[0227] Optionally, the concentration of the acid solution can be from 5 wt% to 80 wt%. When the modifying solution is an aqueous sulfuric acid solution, the concentration of the acid solution can be from 40 wt% to 80 wt%, thereby obtaining cellulose powder with sulfonic acid groups. When the modifying solution is an aqueous boric acid solution, the concentration of the acid solution can be from 5 wt% to 10 wt%, thereby obtaining cellulose powder with boric acid groups. When the modifying solution is an aqueous phosphoric acid solution, the concentration of the acid solution can be from 45 wt% to 75 wt%, thereby obtaining cellulose powder with phosphoric acid groups. When the modifying solution is an aqueous acetic acid solution, the concentration of the acid solution can be from 40 wt% to 80 wt%, thereby obtaining cellulose powder with carboxylic acid groups.

[0228] Optionally, the urea organic solvent solution is a urea xylene solution, thereby obtaining cellulose powder with amine groups.

[0229] In some embodiments, the mass ratio of the cellulose powder to the modified solution may be from 1:2.5 to 1:50, and optionally from 1:5 to 1:30.

[0230] When the modifying solution is an aqueous sulfuric acid solution, the mass ratio of the cellulose powder to the acid solution can be 1:5 to 1:30. When the modifying solution is an aqueous boric acid solution, the mass ratio of the cellulose powder to the acid solution can be 1:20 to 1:50. When the modifying solution is an aqueous phosphoric acid solution, the mass ratio of the cellulose powder to the acid solution can be 1:5 to 1:30. When the modifying solution is an aqueous acetic acid solution, the mass ratio of the cellulose powder to the acid solution can be 1:5 to 1:30. When the modifying solution is a urea organic solvent solution, the mass ratio of the cellulose powder to the urea organic solvent solution can be 1:4 to 1:40.

[0231] In some embodiments, when the modified solution is an acidic solution, the reaction can be carried out at a temperature not exceeding 80°C, preferably at a temperature between 30°C and 60°C, and the reaction time between the cellulose powder and the modified solution can be 0.5 h to 4 h, preferably 1 h to 3 h.

[0232] In some embodiments, when the modified solution is an alkaline solution, the reaction can be carried out at 100°C to 145°C, and the reaction time between the cellulose powder and the modified solution can be 1 h to 5 h.

[0233] In some embodiments, grinding can be performed using a grinding machine, and cutting can be performed using a high-pressure homogenizer. By adjusting the grinding parameters of the grinding machine (e.g., grinding times, grinding time, etc.) and the cutting parameters of the high-pressure homogenizer, nanocellulose with different average diameters and / or different average lengths can be obtained.

[0234] In some embodiments, a coating machine may be used to apply the coating slurry. This application does not impose any particular limitation on the type of coating machine; for example, a commercially available coating machine may be used. The coating machine includes a gravure roller; the gravure roller is used to transfer the slurry onto a porous substrate.

[0235] In some embodiments, the coating slurry can be applied by transfer coating, spin coating, dip coating, etc.

[0236] In some embodiments, the method further includes the step of: applying a slurry containing a particulate adhesive to at least a portion of the surface of the coating, and drying it to form an adhesive layer.

[0237] The method for preparing the separator membrane in this application simplifies the production process of the separator membrane by obtaining the coating through a single coating process.

[0238] The raw materials and their content parameters used in the preparation method of the separator membrane in this application can be referred to the separator membrane of the first aspect of the embodiments of this application, and will not be repeated here.

[0239] Unless otherwise specified, all raw materials used in the preparation method of the separator membrane in this application are commercially available.

[0240] Secondary batteries

[0241] The fourth aspect of the embodiments of this application provides a secondary battery.

[0242] A secondary battery, also known as a rechargeable battery or accumulator, is a battery that can be recharged after discharge to activate its active materials and continue to be used. Typically, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The separator is positioned between the positive and negative electrodes and primarily serves to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through.

[0243] This application does not impose any particular restrictions on the type of secondary battery. For example, the secondary battery can be a lithium-ion battery, a sodium-ion battery, etc. In particular, the secondary battery can be a lithium-ion secondary battery.

[0244] The secondary battery of the fourth aspect of this application includes a separator membrane of the third aspect of this application, the separator membrane being spaced between the positive electrode and the negative electrode. Optionally, at least the side of the separator membrane closest to the negative electrode has the coating of this application. Thus, the secondary battery of this application can achieve high energy density, high thermal safety performance, and good cycle performance and kinetic performance.

[0245] [Positive electrode plate]

[0246] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0247] When the secondary battery of this application is a lithium-ion battery, the positive electrode active material may include, but is not limited to, at least one of lithium transition metal oxides, lithium phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of lithium phosphates may include, but are not limited to, at least one of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds.

[0248] In some embodiments, to further improve the energy density of secondary batteries, the positive electrode active material for lithium-ion batteries may include materials with the general formula Li. a Ni b Co c M d O e A f At least one of lithium transition metal oxides and their modified compounds. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M is selected from at least one of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from at least one of N, F, S and Cl.

[0249] As an example, positive electrode active materials for lithium-ion batteries may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 At least one of O2, LiFePO4, and LiMnPO4.

[0250] When the secondary battery of this application is a sodium-ion battery, the positive electrode active material may include, but is not limited to, at least one of sodium-containing transition metal oxides, polyanionic materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.

[0251] As an example, positive electrode active materials for sodium-ion batteries may include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, and NaNi 1 / 2 Ti 1 / 2 O2, NaNi 1 / 2 Mn 1 / 2 O2, Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2, NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue materials, with the general formula X p M' q (PO4) r O x Y 3-x At least one of the materials in general formula X. p M' q (PO4) r O x Y 3-x In the given information, 0 < p ≤ 4, 0 < q ≤ 2, 1 ≤ r ≤ 3, 0 ≤ x ≤ 2, and X is selected from H. + Li + Na + K + and NH4 + At least one of the following, M' is a transition metal cation, optionally at least one of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halide anion, optionally at least one of F, Cl and Br.

[0252] In this application, the modified compounds of the above-mentioned positive electrode active materials may be those that have undergone doping modification and / or surface coating modification of the positive electrode active materials.

[0253] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total weight of the positive electrode film layer, the mass percentage content of the positive electrode conductive agent is ≤5 wt%.

[0254] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. In some embodiments, the mass percentage of the positive electrode binder is ≤5 wt% based on the total weight of the positive electrode film layer.

[0255] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. An example of the metal material may be at least one selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. An example of the polymeric material substrate may be at least one selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0256] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this.

[0257] [Negative electrode plate]

[0258] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0259] The negative electrode active material may be any negative electrode active material known in the art for use in secondary batteries. As an example, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy materials.

[0260] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total weight of the negative electrode film layer, the mass percentage content of the negative electrode conductive agent is ≤5 wt%.

[0261] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder is ≤5 wt% based on the total weight of the negative electrode film layer.

[0262] In some embodiments, the negative electrode film layer may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc. In some embodiments, the mass percentage of the other additives is ≤2 wt% based on the total weight of the negative electrode film layer.

[0263] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0264] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0265] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0266] Electrolyte

[0267] During the charging and discharging process of a secondary battery, active ions repeatedly insert and extract between the positive and negative electrode plates, while the electrolyte acts as a conductor for these active ions. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to actual needs.

[0268] The electrolyte comprises an electrolyte salt and a solvent. The types of electrolyte salt and solvent are not specifically limited and can be selected according to actual needs.

[0269] When the secondary battery of this application is a lithium-ion battery, as an example, the electrolyte salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0270] When the secondary battery of this application is a sodium-ion battery, as an example, the electrolyte salt may include, but is not limited to, at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), sodium dioxalate borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorodioxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0271] As an example, the solvent may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ester carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0272] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0273] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process and / or a stacking process.

[0274] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0275] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0276] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 1 This is an example of a square-structured secondary battery 5.

[0277] In some embodiments, such as Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process and / or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0278] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is placed in an outer packaging, dried, and then injected with an electrolyte. After vacuum sealing, settling, formation, and shaping processes, a secondary battery is obtained.

[0279] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0280] Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0281] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0282] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0283] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0284] Electrical appliances

[0285] A fifth aspect of this application provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0286] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0287] Figure 6 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0288] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0289] Example

[0290] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0291] Preparation of nanocellulose C1

[0292] Cellulose powder preparation

[0293] After the cotton linters are opened and the slag is removed by a cotton opener, they are cooked at 150°C for 2 hours using a 5wt% NaOH aqueous solution. Then, the cotton cellulose powder with a whiteness of ≥85% is obtained by sequentially washing and removing impurities (washing 3 times), bleaching with sodium hypochlorite, washing and removing impurities with dilute hydrochloric acid, washing and removing impurities (washing 1 time), water removal, and air drying.

[0294] esterification of cellulose

[0295] 1 kg of the obtained cotton cellulose powder was mixed with 30 kg of 60 wt% sulfuric acid aqueous solution and reacted at 55℃ to 60℃ for 1.5 h. After the reaction was completed, the mixture was then sequentially washed with water (washed 3 times), filtered, and deacidified to obtain cellulose nanocrystals with sulfonic acid groups.

[0296] Neutralization of cellulose

[0297] The pH of cellulose nanofibers with sulfonic acid groups was first adjusted to neutral using a 10wt% NaOH aqueous solution. Then, the nanofibers were ground using a grinder and then cut into nanoscale pieces using a high-pressure homogenizer to obtain cellulose nanofibers with sulfonic acid modified groups with an average length of 500nm and an average diameter of 22nm. The molar ratio of sulfonic acid groups to hydroxyl groups was 5:3.

[0298] The molar ratio of anionic modified groups to hydroxyl groups in nanocellulose can be determined by the following method: The hydroxyl value (equivalent to milligrams of potassium hydroxide per gram of sample) of the raw cellulose and nanocellulose is determined according to the phthalic anhydride method in GB / T12008.3-2009. The unit of the obtained value is mg KOH / g, which is then converted to mmol / g as the hydroxyl content. The content of anionic modified groups (i.e., the content of modified hydroxyl groups) is obtained by subtracting the hydroxyl content of nanocellulose from the hydroxyl content of the raw cellulose. The molar ratio of anionic modified groups to hydroxyl groups can then be calculated.

[0299] Preparation of nanocellulose C2

[0300] Unmodified nanocellulose with an average length of 500 nm and an average diameter of 22 nm, product model CNWS-50, was purchased from Zhongke Leiming (Beijing) Technology Co., Ltd. It can be further processed using a grinder and / or a high-pressure homogenizer to obtain nanocellulose with different average diameters and / or different average lengths.

[0301] Example 1

[0302] Preparation of the separating membrane

[0303] Porous PE substrate is available: 4.8μm thick, with a porosity of 32%.

[0304] Preparation of the coating slurry: The nanocellulose C1, the first filler alumina (secondary particle morphology, average particle size of 75 nm), and the binder aqueous solution-type polyacrylic acid prepared above were mixed evenly in an appropriate amount of deionized water at a mass ratio of 16:83:1. The mixture was then stirred at a shear rate of 23 m / s to obtain a coating slurry with a solid content of 15 wt%. The contents of α-crystal, θ-crystal, γ-crystal, and η-crystal forms in the first filler were 1.1 wt%, 68.7 wt%, 29.6 wt%, and 0.6 wt%, respectively, based on the total weight of the first filler.

[0305] Coating: The prepared coating slurry is applied to both surfaces of the PE porous substrate using a coating machine. After drying and slitting, a release film is obtained. The coating thickness on one side of the PE porous substrate is 0.8 μm, and the areal density is 1.25 g / m². 2 .

[0306] Preparation of positive electrode sheet

[0307] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed evenly in an appropriate amount of solvent N-methylpyrrolidone (NMP) at a mass ratio of 96.2:2.7:1.1 to obtain a positive electrode slurry. The positive electrode slurry is coated onto a positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through processes such as drying, cold pressing, slitting, and cutting.

[0308] Preparation of negative electrode sheet

[0309] Artificial graphite (anode active material), carbon black (Super P) (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (batch ratio 96.4:0.7:1.8:1.1) are mixed evenly in an appropriate amount of deionized water to obtain a cathode slurry. The cathode slurry is coated onto copper foil (cathode current collector), and the cathode sheet is obtained through drying, cold pressing, slitting, and cutting processes.

[0310] Preparation of electrolyte

[0311] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 30:70 to obtain an organic solvent. Fully dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0312] Preparation of secondary batteries

[0313] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0314] Example 2-16

[0315] The secondary batteries were prepared using a method similar to that of Example 1, with the differences shown in Table 1. The second filler in Examples 12-15 had a primary particle morphology, and the crystal form of the second filler was mainly α-crystal, accounting for more than 99% by mass, based on the total weight of the second filler.

[0316] Comparative Example 1

[0317] The secondary battery was prepared using a method similar to that in Example 1, except for the preparation process of the separator.

[0318] Porous PE substrate is available: 4.8μm thick, with a porosity of 32%.

[0319] Preparation of coating slurry: Alumina (average particle size of 600nm, primary particle morphology, α crystal form mass ratio of over 99%) and binder are mixed at a mass ratio of 94:6 and dissolved in deionized water. The mixture is then stirred at a shear rate of 23m / s to obtain a coating slurry with a solid content of 38wt%.

[0320] Coating: The prepared coating slurry is applied to both surfaces of the PE porous substrate using a coating machine. After drying and slitting, a release film is obtained. The coating thickness on one side of the PE porous substrate is 1.7 μm, and the areal density is 1.80 g / m³. 2 .

[0321] Test section

[0322] (1) Ion conductivity test of the separator

[0323] The ion conductivity of the separator was obtained through AC impedance spectroscopy. Specifically, the separator was cut into circular pieces of a certain area, dried, and placed between two stainless steel electrodes. After absorbing a sufficient amount of electrolyte, it was sealed to form a coin cell. AC impedance spectroscopy was then performed using an electrochemical workstation to obtain the ion conductivity of the separator. A Shanghai Chenhua CHI 660C electrochemical workstation was used, with an AC signal frequency range of 0.01Hz to 1MHz and a sinusoidal potential amplitude of 5mV. For accuracy, the average value of five parallel samples was taken as the test result.

[0324] The electrolyte was prepared as follows: ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of 30:50:20 to obtain an organic solvent. Fully dried LiPF6 was dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0325] (2) Average pore area test of coating and porous substrate

[0326] A sample of a certain size (e.g., 15mm × 15mm) is cut from a selected area of ​​the separator. The sample is then wrapped with copper foil and cut under freezing conditions (e.g., -80℃) using an ion beam polisher (e.g., Hitachi Arblade 5000) to obtain a cross-section. The sample is then sputter-coated with gold, and then, referring to JY / T010-1996, a scanning electron microscope (e.g., ZEISS Sigma 300 scanning electron microscope, Germany) is used to scan and obtain a SEM image of the separator cross-section (magnification can be 1000x to 30000x). An image processing detection system (e.g., Yihong separator detection system 2022-0408) is used to obtain the average pore area S1 of the separator coating and the average pore area S2 of the porous substrate of the separator using a multi-segment binarization method. The ratio of the total pore area of ​​the separator coating to the number of pores in the coating is the average pore area S1 of the separator coating, and the ratio of the total pore area of ​​the porous substrate of the separator to the number of pores in the porous substrate is the average pore area S2 of the porous substrate of the separator. For accuracy, the average value of 5 parallel samples is taken as the test result.

[0327] (3) Thermal shrinkage rate test of the separator film

[0328] Sample preparation: The separation membrane prepared above is punched into samples with a width of 50 mm and a length of 100 mm using a punching machine. Five parallel samples are placed on A4 paper and fixed. Then, the A4 paper containing the samples is placed on corrugated paper with a thickness of 1 mm to 5 mm.

[0329] Sample testing: Place the A4 paper placed on the corrugated paper into a forced-air drying oven. Set the temperature of the forced-air drying oven to 150℃. After the temperature reaches the set temperature and stabilizes for 30 minutes, start timing. After the set time (1 hour in this application), measure the length and width of the release film. The values ​​are marked as a and b, respectively.

[0330] Calculation of heat shrinkage rate: Longitudinal (MD) heat shrinkage rate = [(100-a) / 100]×100%, Transverse (TD) heat shrinkage rate = [(50-b) / 50]×100%, take the average value of 5 parallel samples as the test result.

[0331] (4) Thermal Box Test of Secondary Battery

[0332] At 25°C, charge the secondary battery at a constant current of 1C to 4.2V, continue constant voltage charging until the current is ≤0.05C, and let it stand for 5 minutes; then test each secondary battery with a fixture in a DHG-9070A DHG series high-temperature oven, heat from room temperature to 80°C ± 2°C at a rate of 5°C / min, and hold for 30 minutes; then continue heating at a rate of 5°C / min, and hold for 30 minutes every time the temperature rises by 5°C. Monitor the surface temperature change of the secondary battery during the heating process. The oven temperature corresponding to when the temperature starts to rise sharply is the thermal box failure temperature of the secondary battery. The higher the thermal box failure temperature of the secondary battery, the better the thermal safety performance of the secondary battery. For accuracy, take the average value of 5 parallel samples as the test result.

[0333] (5) Cycle Performance Test of Secondary Battery

[0334] At 25°C, charge the secondary battery at a constant current of 1C to 4.2V, continue constant voltage charging until the current is ≤0.05C. At this time, the secondary battery is in a fully charged state, and record the charging capacity at this time, which is the charging capacity of the first cycle; after letting the secondary battery stand for 5 minutes, discharge it at a constant current of 1C to 2.8V. This is a cycle of charge and discharge process, and record the discharge capacity at this time, which is the discharge capacity of the first cycle. Perform cycle charge and discharge tests on the secondary battery according to the above method, and record the discharge capacity after each cycle. The capacity retention rate (%) of the secondary battery after 1000 cycles at 25°C = discharge capacity after 1000 cycles / discharge capacity of the first cycle × 100%. For accuracy, take the average value of 5 parallel samples as the test result.

[0335] As can be seen from Table 2, in Examples 1-16, by providing coatings containing nanocellulose (constituting a three-dimensional skeleton structure) and fillers on both surfaces of the porous substrate of the separator membrane, and reasonably controlling the average pore area S1 of the coating and the average pore area S2 of the porous substrate to satisfy 0 < S1 / S2 < 1, the separator membrane can achieve both low thermal shrinkage rate and high ion conductivity, and the secondary battery can achieve both high thermal safety performance and good cycle performance.

[0336] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same structure and the same effect as the technical idea within the technical solution scope of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that those skilled in the art can think of to the embodiments, and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of this application.

[0337]

[0338] Table 2

[0339]

Claims

1. A separating membrane comprising a porous substrate and a coating disposed on at least one surface of the porous substrate, wherein, The coating includes fibrous material and filler, at least a portion of which is filled in the fibrous material, and the average pore area of ​​the coating is smaller than the average pore area of ​​the porous substrate along the thickness direction of the separator. Wherein, the average pore area of ​​the coating refers to the ratio of the total pore area of ​​the coating in the cross-sectional image of the separator to the number of pores in the coating; the average pore area of ​​the porous substrate refers to the ratio of the total pore area of ​​the porous substrate in the cross-sectional image of the separator to the number of pores in the porous substrate. The filler includes a first filler, which includes alumina particles; the alumina particles have a crystal form including the θ crystal form, and the content of the θ crystal form alumina particles is ≥50wt%, based on the total weight of the alumina particles.

2. The separator according to claim 1, wherein, The alumina particles include primary particles; the average particle size of the primary particles is 15 nm to 80 nm.

3. The separator according to claim 2, wherein, The average particle size of the primary particles is 30 nm to 75 nm.

4. The separator according to claim 1 or 2, wherein, The alumina particles also include secondary particles formed from primary particles.

5. The separator according to claim 4, wherein, The average particle size of the secondary particles is 50 nm to 150 nm.

6. The separator membrane according to claim 4, wherein, The average particle size of the secondary particles is 55 nm to 120 nm.

7. The separator according to claim 1, wherein, The average particle size of the alumina particles is ≤ 150 nm.

8. The separator according to claim 1, wherein, The alumina particles have an average particle size of 15 nm to 120 nm.

9. The separator according to claim 1, wherein, The content of the theta-type alumina particles is 60 wt% to 82 wt%, based on the total weight of the alumina particles.

10. The separator membrane according to claim 1, wherein, The alumina particles also include at least one of the γ-type and η-type crystal forms.

11. The separator according to claim 10, wherein, The content of γ-crystalline alumina particles is ≥10wt%, based on the total weight of the alumina particles.

12. The separator according to claim 10, wherein, The content of γ-crystalline alumina particles is 17 wt% to 38 wt%, based on the total weight of the alumina particles.

13. The separator according to claim 10, wherein, The content of η-crystal alumina particles is ≤5wt%, based on the total weight of the alumina particles.

14. The separator according to claim 10, wherein, The content of η-crystal alumina particles is ≤1.5wt%, based on the total weight of the alumina particles.

15. The separator membrane according to claim 1, wherein, The BET specific surface area of ​​the alumina particles is ≥ 15 m². 2 / g.

16. The separator membrane according to claim 1, wherein, The BET specific surface area of ​​the alumina particles is 18 m². 2 / g to 65 m 2 / g.

17. The separator membrane according to claim 1, wherein, The packing material further includes a second packing material, the average particle size of which is greater than that of the first packing material.

18. The separator membrane according to claim 17, wherein, The average particle size of the second filler is less than or equal to 400 nm.

19. The separator according to claim 17, wherein, The average particle size of the second filler is 100 nm to 300 nm.

20. The separator according to claim 17, wherein, The second packing material satisfies at least one of the following conditions (1) to (6): (1) The second filler has a primary particle morphology; (2) The BET specific surface area of ​​the second packing is ≤ 15m². 2 / g; (3) The content of the second filler is ≤ 20 wt%, based on the total weight of the coating; (4) The second filler comprises at least one of inorganic particles and organic particles; (5) The second filler comprises inorganic particles with a primary particle morphology, and the crystal form of the inorganic particles with the primary particle morphology includes at least one of α crystal form and γ crystal form; (6) The second filler comprises inorganic particles with a primary particle morphology, and the crystal form of the inorganic particles with a primary particle morphology includes α crystal form, and the content of α crystal form inorganic particles is ≥80 wt%, based on the total weight of the inorganic particles with a primary particle morphology in the second filler.

21. The separator according to claim 20, wherein, The BET specific surface area of ​​the second packing is 7 m². 2 / g to 12m 2 / g.

22. The separator according to claim 20, wherein, The content of the second filler is 2 wt% to 15 wt%, based on the total weight of the coating.

23. The separator according to claim 20, wherein, The crystal forms of the inorganic particles with the primary particle morphology include the α crystal form.

24. The separator according to claim 20, wherein, The inorganic particles with the primary particle morphology have a crystal form including α crystal form, and the content of α crystal form inorganic particles is 90 wt% to 100 wt%, based on the total weight of the inorganic particles with the primary particle morphology in the second filler.

25. The separator according to claim 1, wherein, The content of the first filler is ≥55 wt%, based on the total weight of the coating.

26. The separator membrane according to claim 1, wherein, The content of the first filler is 60 wt% to 90 wt%, based on the total weight of the coating.

27. The separator according to claim 1, wherein, The content of the fibrous material is ≤40 wt%, based on the total weight of the coating.

28. The separator membrane according to claim 1, wherein, The content of the fibrous material is from 5 wt% to 25 wt%, based on the total weight of the coating.

29. The separator membrane according to claim 1, wherein, The morphology of the fibrous material includes at least one of rod-shaped, tubular, rod-shaped, and fibrous.

30. The separator membrane according to claim 1, wherein, The average diameter of the fibrous material is ≤40 nm; The average length of the fibrous material is 100 nm to 800 nm; The aspect ratio of the fibrous material is 5 to 60.

31. The separator according to claim 30, wherein, The average diameter of the fibrous material is 10 nm to 35 nm.

32. The separator according to claim 30, wherein, The average length of the fibrous material is 200 nm to 600 nm.

33. The separator according to claim 30, wherein, The aspect ratio of the fibrous material is 10 to 30.

34. The separator membrane according to claim 1, wherein, The fibrous material includes at least one of organic and inorganic materials.

35. The separator according to claim 34, wherein, The organic material includes at least one of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers.

36. The separator according to claim 35, wherein, The nanocellulose includes at least one of cellulose nanofibers, cellulose nanowhiskers, and bacterial nanocellulose.

37. The separator membrane according to claim 34, wherein, The inorganic material includes at least one of halloysite nanotubes, nanorod alumina, nanorod boehmite, nanorod silica, and glass fiber.

38. The separator membrane according to claim 1, wherein, The fibrous material includes nanocellulose.

39. The separator according to claim 38, wherein, The nanocellulose includes hydroxyl groups and anionic modifying groups.

40. The separator according to claim 39, wherein, The anionic modifying group includes at least one of amino, carboxyl, sulfonic acid, boric acid, and phosphate groups.

41. The separator according to claim 39, wherein, The anionic modifying group includes at least one of sulfonic acid group, boric acid group and phosphate group.

42. The separator according to claim 39, wherein, The molar ratio of the anionic modifying group to the hydroxyl group is 1:4 to 4:

1.

43. The separator according to claim 39, wherein, The molar ratio of the anionic modifying group to the hydroxyl group is 2:3 to 7:

3.

44. The separator according to claim 1, wherein, The coating also includes a non-particulate binder.

45. The separator according to claim 44, wherein, The non-particulate adhesive includes aqueous solution-based adhesives.

46. ​​The separator according to claim 44, wherein, The content of the non-particulate binder in the coating is ≤2wt%, based on the total weight of the coating.

47. The separator according to claim 1, wherein, The thickness of the porous substrate is ≤8 μm; and / or, The thickness of the coating is ≤ 2 μm.

48. The separator membrane according to claim 47, wherein, The thickness of the porous substrate is 3 μm to 6 μm.

49. The separator according to claim 47, wherein, The coating thickness is from 0.5 μm to 1.3 μm.

50. The separator membrane according to claim 1, wherein, The isolation membrane further includes an adhesive layer disposed on at least a portion of the surface of the coating, the adhesive layer comprising a particulate adhesive.

51. The separator according to claim 50, wherein, The particulate binder includes at least one of acrylate monomer homopolymers or copolymers, acrylate monomer homopolymers or copolymers, and fluorinated olefin monomer homopolymers or copolymers.

52. The separator according to claim 1, wherein, Let the average pore area of ​​the coating be S1, and the average pore area of ​​the porous substrate be S2, then 0.06 ≤ S1 / S2 < 1.

53. The separator according to claim 52, wherein, 0.30 ≤ S1 / S2 ≤ 0.

97.

54. The separator according to claim 1, wherein, Let S1 be the average pore area of ​​the coating and S2 be the average pore area of ​​the porous substrate. 0.0002μm 2 ≤ S1 ≤ 0.0080μm 2 ; and / or, 0.0005μm 2 ≤ S2 ≤ 0.0100μm 2 。 55. The separator according to claim 54, wherein, 0.0004μm 2 ≤ S1 ≤ 0.0050μm 2 。 56. The separator according to claim 54, wherein, 0.0008μm 2 ≤ S2 ≤ 0.0080μm 2 。 57. The separator according to claim 1, wherein, Let the average pore size of the isolation membrane be denoted as d1, and the average pore size of the porous substrate be denoted as d2, then d1 / d2 < 1.

58. The separator according to claim 57, wherein, 0.3 ≤ d1 / d2 ≤ 0.

8.

59. The separator according to claim 57, wherein, 15nm ≤ d1 ≤ 50nm.

60. The separator according to claim 57, wherein, 20nm ≤ d2 ≤ 40nm.

61. The separator according to claim 57, wherein, 25nm ≤ d2 ≤ 60nm.

62. The separator according to claim 57, wherein, 30nm ≤ d2 ≤ 50nm.

63. The separator according to claim 1, wherein, The areal density of the coating is denoted as ρ1, and the areal density of the porous substrate is denoted as ρ2. Then, 0.15 ≤ ρ1 / ρ2 ≤ 0.

80.

64. The separator according to claim 63, wherein, 0.20 ≤ ρ1 / ρ2 ≤ 0.

50.

65. The separator according to claim 63, wherein, 0.50g / m 2 ≤ ρ1 ≤ 1.50g / m 2 。 66. The separator according to claim 63, wherein, 0.75g / m 2 ≤ ρ1 ≤ 1.40g / m 2 。 67. The separator according to claim 63, wherein, 1.50g / m 2 ≤ ρ2 ≤ 4.50g / m 2 。 68. The separator according to claim 63, wherein, 2.00g / m 2 ≤ ρ2 ≤ 4.00g / m 2 。 69. The separator according to claim 1, wherein, The porosity of the isolation membrane is denoted as P1, and the porosity of the porous substrate is denoted as P2. Then, 0.4 ≤ P2 / P1 < 1.

70. The separator according to claim 69, wherein, 0.55 ≤ P2 / P1 ≤ 0.

85.

71. The separator according to claim 69, wherein, 20% ≤ P1 ≤ 60%。 72. The separator according to claim 69, wherein, 25% ≤ P1 ≤ 45%。 73. The separator according to claim 69, wherein, 15% ≤ P2 ≤ 45%。 74. The separator according to claim 69, wherein, 20% ≤ P2 ≤ 40%。 75. The separator membrane according to claim 1, wherein, The isolation membrane satisfies at least one of the following conditions (1) to (9): (1) The longitudinal thermal shrinkage rate of the isolation membrane at 150℃ for 1 h is ≤6%; (2) The transverse thermal shrinkage rate of the isolation membrane at 150℃ for 1 h is ≤6%; (3) The ion conductivity of the isolation membrane is ≥ 0.6 ms / cm 2 ; (4) The resistance of the isolation membrane is ≤ 1.3 Ω; (5) The longitudinal tensile strength of the separator is ≥2000 kg / cm². 2 ; (6) The transverse tensile strength of the separator is ≥2000 kg / cm². 2 ; (7) The wetting length of the isolation membrane is ≥30 mm; (8) The wetting rate of the isolation membrane is ≥3 mm / s; (9) The air permeability of the isolation membrane is ≤300 s / 100mL.

76. The separator according to claim 75, wherein, The longitudinal thermal shrinkage rate of the isolation membrane at 150°C for 1 hour is 0.5% to 4%.

77. The separator membrane according to claim 75, wherein, The lateral thermal shrinkage rate of the isolation membrane at 150°C for 1 hour is 0.5% to 4%.

78. The separator according to claim 75, wherein, The ion conductivity of the isolation membrane is ≥ 0.9 ms / cm 2 .

79. The separator according to claim 75, wherein, The resistance of the isolation membrane is ≤ 1.0 Ω.

80. The separator according to claim 75, wherein, The longitudinal tensile strength of the separator is 2500 kg / cm². 2 Up to 4500 kg / cm 2 .

81. The separator according to claim 75, wherein, The lateral tensile strength of the separator is 2500 kg / cm². 2 Up to 4500 kg / cm 2 .

82. The separator according to claim 75, wherein, The wetting length of the isolation membrane is 30 mm to 80 mm.

83. The separator according to claim 75, wherein, The wetting rate of the isolation membrane is from 3 mm / s to 10 mm / s.

84. The separator according to claim 75, wherein, The air permeability of the isolation membrane is from 100 s / 100mL to 230 s / 100mL.

85. A secondary battery comprising the separator as described in any one of claims 1-84.

86. An electrical device comprising the secondary battery of claim 85.

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