Separator, manufacturing method thereof, and related secondary battery and power consumption device

Abstract

The present application provides a separator, a manufacturing method thereof, and related secondary batteries and power consumption devices, the separator including a porous substrate and a coating disposed on at least one surface of the porous substrate, the coating including a three-dimensional framework and a first filler, at least a portion of the first filler being filled into the three-dimensional framework, and the first filler having an average particle size of 200 nm or less. The present application enables secondary batteries to achieve high energy density, high thermal safety performance, long cycle life, and good dynamic performance.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to patent application PCT / CN2022 / 112580, entitled "Separator, Manufacturing Method Thereof, and Related Secondary Battery and Power Consumption Device," filed on August 15, 2022, the entire contents of which are incorporated herein by reference. [Technical Field]

[0002] The present application relates to the field of battery technology, and more particularly to separators, methods for manufacturing the same, and related secondary batteries and power consuming devices. [Background technology]

[0003] In recent years, secondary batteries have been widely used in energy storage power systems such as hydroelectric, thermal, wind, and solar power plants, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. As secondary batteries become more widely used and widespread, their safety issues, especially thermal safety issues, have received increasing attention. However, current methods for improving the thermal safety performance of secondary batteries often fail to balance the energy density and service life of secondary batteries. Therefore, how to achieve high energy density, high thermal safety performance, long cycle life, and good dynamic performance in secondary batteries is an important issue in secondary battery design. Summary of the Invention

[0004] An object of the present application is to provide a separator, a manufacturing method thereof, and related secondary batteries and power consumption devices, which can provide secondary batteries with high energy density, high thermal safety performance, long cycle life, and good dynamic performance.

[0005] A first aspect of the present application provides a separator, the separator including a porous substrate and a coating disposed on at least one surface of the porous substrate, wherein the coating includes a three-dimensional framework structure and a first filler, at least a portion of the first filler is filled in the three-dimensional framework structure, and the first filler has an average particle size of 200 nm or less.

[0006] During the course of research, the inventors surprisingly discovered that by applying a coating containing a three-dimensional framework structure and a first filler having an average particle size of 200 nm or less to the surface of a separator porous substrate, it is possible to achieve a separator with low weight, high heat resistance, and high ionic conductivity, and ultimately to achieve a secondary battery with high energy density, high thermal safety performance, long cycle life, and good dynamic performance.

[0007] In one embodiment of the present application, the average particle size of the first filler is 15 nm to 180 nm, and optionally 30 nm to 150 nm. When the average particle size of the first filler is within this range, the first filler can have a relatively high specific surface area, and the particle size of the first filler can be better matched with the three-dimensional skeleton structure, thereby better abutting the first filler and the three-dimensional skeleton structure to form an integrated effect, increasing the affinity between the first filler and the three-dimensional skeleton structure, and increasing the heat resistance and ionic conductivity of the separator, while also improving the separator's electrolyte penetration and retention properties.

[0008] In any embodiment of the present application, the first filler comprises at least one of primary particles and secondary particles.

[0009] In any embodiment of the present application, the first filler comprises a combination of primary particles and secondary particles.

[0010] In any embodiment of the present application, the content of the first filler in the form of primary particles is less than the content of the first filler in the form of secondary particles, based on the total weight of the first filler.

[0011] In any embodiment of the present application, the content of the first filler in the form of primary particles is 30 wt % or less, based on the total weight of the first filler.

[0012] In any embodiment of the present application, the average particle size of the first filler in the form of primary particles is 15 nm to 80 nm, and optionally 30 nm to 65 nm.

[0013] In any embodiment of the present application, the average particle size of the first filler in the form of secondary particles is 50 nm to 200 nm, and optionally 55 nm to 150 nm.

[0014] In any embodiment of the present application, the BET specific surface area of the first filler is ≥ 25 m 2 / g, and selectively 30m 2 / g~65m 2 When the specific surface area of the first filler is within the above range, the affinity between the first filler and the three-dimensional framework structure is better, which can increase the heat resistance and ionic conductivity of the separator, and simultaneously increase the electrolyte infiltration and retention properties of the separator.

[0015] In one embodiment of the present application, the content of the first filler is ≧50 wt%, preferably 60 wt% to 90 wt%, based on the total weight of the coating. When the content of the first filler is within this range, it can ensure that the coating slurry has an appropriate viscosity, which is advantageous for application, and is also advantageous for forming an integrated effect by contacting with the three-dimensional framework structure, which is advantageous for the coating to have a more stable spatial network structure, thereby further improving the heat resistance and ionic conductivity of the separator.

[0016] In one embodiment of the present application, the content of the three-dimensional framework structure is 5 wt% to 40 wt%, and optionally 8 wt% to 25 wt%, based on the total weight of the coating. When the content of the three-dimensional framework structure is within this range, it can ensure that the coating slurry has an appropriate viscosity, which is advantageous for application, and it is also advantageous for the three-dimensional framework structure and the first filler to abut against each other to form an integrated effect, which is advantageous for the coating to have a more stable spatial network structure, thereby further improving the heat resistance, ionic conductivity, electrolyte penetration and retention properties, and voltage breakdown capability of the separator.

[0017] In one embodiment of the present application, the first filler includes at least one of inorganic particles and organic particles. Optionally, the inorganic particles include at least one of boehmite, aluminum oxide, barium sulfate, magnesium oxide, magnesium hydroxide, silicone oxide, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, zirconium titanate, barium titanate, and magnesium fluoride. Further optional, the inorganic particles include at least one of boehmite, aluminum oxide, barium sulfate, magnesium oxide, silicone oxide, titanium oxide, zinc oxide, cerium oxide, and barium titanate. Optionally, the organic particles include at least one of polystyrene particles, polyacrylic wax particles, melamine formaldehyde resin particles, phenolic resin particles, polyester particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, and polyaryletherketone particles.

[0018] In any embodiment of the present application, the first filler comprises inorganic particles, and the crystalline form of the inorganic particles comprises at least one of a θ crystalline form, a γ crystalline form, and an η crystalline form, and optionally, the crystalline form of the inorganic particles comprises at least one of a θ crystalline form and a γ crystalline form.

[0019] In any embodiment of the present application, optionally, the content of the θ crystalline inorganic particles is ≧50 wt %, and more optionally, 55 wt % to 84 wt %, based on the total weight of the inorganic particles in the first filler.

[0020] In any embodiment of the present application, optionally, the content of the γ crystalline inorganic particles is ≧10 wt %, and further optionally 15 wt % to 44 wt %, based on the total weight of the inorganic particles in the first filler.

[0021] In any embodiment of the present application, optionally, the content of inorganic particles of the η crystalline form is ≦5 wt %, and further optionally ≦2.5 wt %, based on the total weight of the inorganic particles in the first filler.

[0022] In any embodiment of the present application, the three-dimensional framework structure is formed of a fibrous material, and the shape of the fibrous material optionally includes at least one of a rod-like shape, a tubular shape, a rod-like shape, and a fiber-like shape.

[0023] Selection of a first filler having a different crystal form contributes to improving at least one of the heat resistance, ionic conductivity, adhesive strength, and electrolyte wetting and retention properties of the separator.

[0024] In any embodiment of the present application, the material constituting the three-dimensional framework has an average diameter of ≦40 nm, and optionally 10 nm to 35 nm. When the average diameter of the material constituting the three-dimensional framework is within the above range, the ionic conductivity and voltage breakdown characteristics of the separator can be further improved, and the contact with the first filler also contributes to an integration effect, thereby further improving the heat resistance of the separator.

[0025] In any embodiment of the present application, the material constituting the three-dimensional framework has an average length of 100 nm to 600 nm, and optionally 200 nm to 500 nm. When the average length of the material constituting the three-dimensional framework is within the above range, the heat resistance and ionic conductivity of the separator can be further improved.

[0026] In any embodiment of the present application, the aspect ratio of the material constituting the three-dimensional framework is 5 to 60, and optionally 10 to 30. When the aspect ratio of the material constituting the three-dimensional framework is within the above range, the ionic conductivity and the electrolyte infiltration and retention properties of the separator can be further improved.

[0027] In any embodiment of the present application, the material constituting the three-dimensional framework structure includes at least one of an organic material and an inorganic material. Optionally, the organic material includes at least one of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers. Optionally, the nanocellulose includes at least one of cellulose nanofibers, cellulose nanocrystals, and bacterial nanocellulose. Optionally, the inorganic material includes at least one of halloysite nanotubes, nanorod-shaped aluminum oxide, nanorod-shaped boehmite, nanorod-shaped silica, and glass fibers.

[0028] In any embodiment of the present application, the material constituting the three-dimensional skeletal structure includes nanocellulose, and the nanocellulose includes at least one of unmodified nanocellulose and modified nanocellulose.

[0029] In any embodiment of the present application, optionally, the modified nanocellulose comprises a modifying group, the modifying group comprising at least one of an amine group, a carboxyl group, an aldehyde group, a sulfonic acid group, a boric acid group, and a phosphate group, and further optionally comprising at least one of a sulfonic acid group, a boric acid group, and a phosphate group.

[0030] When nanocellulose contains the above-mentioned specific modifying groups, it can effectively improve the heat resistance of the separator and improve the thermal safety performance of the secondary battery, while also improving the adhesive strength between the coating and the porous substrate. When nanocellulose contains the above-mentioned specific modifying groups, it is also advantageous for the nanocellulose and the first filler to abut against each other to form an integrated effect, thereby allowing the coating to have a more stable spatial network structure, thereby improving the separator's electrolyte wetting and retention properties, and improving the separator's ionic conductivity and voltage breakdown characteristics. The presence of modifying groups can also reduce the proportion of hydroxyl groups, thereby ensuring that the coating slurry has an appropriate viscosity, which is more advantageous for application, thereby improving separator production efficiency and coating uniformity.

[0031] In any embodiment of the present application, optionally, the modified nanocellulose contains hydroxyl groups and modifying groups, and the molar ratio of the modifying groups to the hydroxyl groups is 1:4 to 4:1, and more preferably 2:3 to 7:3. When the molar ratio of the modifying groups to the hydroxyl groups is within the above range, the heat resistance, ionic conductivity, and electrolyte infiltration and retention properties of the separator can be further improved. In any embodiment of the present application, the material constituting the three-dimensional framework contains sulfonic acid groups, and the content of sulfur element in the material constituting the three-dimensional framework is ≧0.1 wt%, and optionally 0.2 wt% to 0.5 wt%, based on the total weight of the material constituting the three-dimensional framework.

[0032] In any embodiment of the present application, the coating further comprises a second filler, at least a portion of which is embedded in the coating, and the average particle size of the first filler is denoted as d1, the average particle size of the second filler is denoted as d2, and d2 / d1 > 1. The second filler has a relatively large average particle size, which better exerts its supporting effect in the coating, reduces shrinkage of the first filler, and reduces the amount of adhesive used, thereby improving the heat resistance of the separator. When the second filler has a relatively large particle size and is used in a relatively small amount, it contributes to the coating having a more porous structure and a lower water content, which can further improve the ionic conductivity and electrolyte wetting and retention properties of the separator, and simultaneously improve the cycle performance and / or kinetic performance of the secondary battery.

[0033] In any embodiment of the present application, the first filler includes at least one of primary particles and secondary particles, and the average particle size of the first filler in the form of primary particles is d 11 and the average particle size of the first filler in the form of secondary particles is denoted by d 12 and 3.0≦d2 / d 11 ≦10.0, and optionally, 3.5≦d / d 11 ≦8.0 and / or 1.2≦d2 / d 12 ≦6.0, and optionally, 2.0≦d2 / d 12 ≦5.5.

[0034] The synergistic effect of the first filler and the second filler helps to reduce the moisture content of the coating, allowing the coating to maintain a stable pore structure during long-term charge and discharge, while also improving the heat resistance of the separator, thereby enabling the secondary battery to better achieve a combination of high energy density, high thermal safety performance, long cycle life, and good dynamic performance.

[0035] In any embodiment of the present application, the second filler has a primary particle morphology.

[0036] In any embodiment of the present application, the average particle size of the second filler is 120 nm to 350 nm, and optionally 150 nm to 300 nm, which can improve the supporting effect of the second filler, reduce the moisture content of the coating, maintain a stable pore structure in the coating during long-term charge / discharge processes, and simultaneously improve the heat resistance of the separator.

[0037] In any embodiment of the present application, the BET specific surface area of the second filler is ≦20 m 2 / g, and selectively 6m 2 / g~15m 2 This allows the second filler to better exert its supporting effect, reduces the moisture content of the coating, and allows the coating to maintain a stable pore structure during long-term charge and discharge, while also improving the heat resistance of the separator.

[0038] In any embodiment of the present application, the second filler comprises at least one of inorganic particles and organic particles.

[0039] In one embodiment of the present application, the second filler comprises inorganic particles in the form of primary particles, and the crystalline form of the inorganic particles in the form of primary particles comprises at least one of an α-crystalline form and a γ-crystalline form, and optionally comprises an α-crystalline form. The α-crystalline second filler has the advantages of high hardness, good heat resistance, low dielectric constant, high safety, and high true density, which can further improve the heat resistance of the coating.

[0040] In any embodiment of the present application, the second filler comprises inorganic particles in the form of primary particles, and the crystalline form of the inorganic particles in the form of primary particles comprises an α-crystalline form, and the content of the α-crystalline form is ≧70 wt %, and optionally 85 wt % to 100 wt %, based on the total weight of the inorganic particles in the form of primary particles in the second filler.

[0041] In one embodiment of the present application, the content of the second filler is ≦30 wt %, preferably 5 wt % to 25 wt %, based on the total weight of the coating. When the content of the second filler is within this range, the supporting effect of the second filler can be better exerted, the moisture content of the coating can be reduced, and the coating can maintain a stable pore structure during long-term charge and discharge.

[0042] In any embodiment of the present application, the coating further comprises a non-particulate adhesive. Optionally, the non-particulate adhesive comprises a water-based adhesive.

[0043] In one embodiment of the present application, the content of the non-particulate adhesive in the coating is ≦2 wt % based on the total weight of the coating. The three-dimensional framework structure and the first filler in the coating of the present application can form a stable spatial network structure, thereby allowing the separator to maintain high adhesiveness while reducing the amount of adhesive used.

[0044] In any embodiment of the present application, the thickness of the porous substrate is ≦6 μm, and optionally 3 μm to 5 μm. The coating of the present application can significantly improve the heat resistance of the separator, allowing for the selection of a thinner porous substrate, thereby contributing to improving the energy density of the secondary battery.

[0045] In any embodiment of the present application, the thickness of the coating is ≦2 μm, and optionally 0.5 μm to 1.5 μm, which contributes to improving the energy density of the secondary battery.

[0046] In one embodiment of the present application, the separator further includes an adhesive layer disposed on at least a portion of the surface of the coating, the adhesive layer including a particulate adhesive. The adhesive layer not only prevents the coating from peeling off and improves the safety performance of the secondary battery, but also improves the interface between the separator and the electrodes, thereby improving the cycle performance of the secondary battery.

[0047] In any embodiment of the present application, the particulate adhesive includes at least one of an acrylate-based monomer homopolymer or copolymer, an acrylic-based monomer homopolymer or copolymer, and a fluorine-containing olefin monomer homopolymer or copolymer.

[0048] In any embodiment of the present application, the separator has a longitudinal heat shrinkage rate at 150°C for 1 hour of ≦6%, and optionally 0.5% to 4%.

[0049] In any embodiment of the present application, the separator has a transverse heat shrinkage rate at 150°C for 1 hour of ≦6%, and optionally 0.5% to 4%.

[0050] The separator of the present application has low thermal shrinkage in both the transverse and longitudinal directions at a high temperature of 150° C., thereby improving the safety performance of the secondary battery.

[0051] In any embodiment of the present application, the separator has a longitudinal tensile strength of ≥ 2000 kg / cm 2 and selectively 2500 kg / cm 2 ~4500kg / cm 2 is.

[0052] In any embodiment of the present application, the separator has a transverse tensile strength of ≥ 2000 kg / cm 2 and selectively 2500 kg / cm 2 ~4500kg / cm 2 is.

[0053] The separator of the present application has high tensile strength in both the horizontal and vertical directions, so that the probability of the separator being damaged when the secondary battery expands is relatively low, thereby improving the safety performance of the secondary battery.

[0054] In any embodiment of the present application, the wetted length of the separator is ≧30 mm, and optionally 30 mm to 80 mm.

[0055] In any embodiment of the present application, the wetting speed of the separator is ≧3 mm / s, and optionally 3 mm / s to 10 mm / s.

[0056] The separator of the present application has good electrolyte infiltration and retention properties, and therefore can improve the ionic conductivity of the separator and the capacity development properties of the secondary battery.

[0057] In any embodiment of the present application, the separator has an air permeability of ≦300 s / 100 mL, and optionally 100 s / 100 mL to 230 s / 100 mL. The separator of the present application has good air permeability, which can improve ion conductivity and secondary battery capacity development characteristics.

[0058] In any embodiment of the present application, the separator has a voltage breakdown strength of ≧1 KV. The separator of the present application has a relatively high voltage breakdown strength, which can improve the safety performance of the secondary battery.

[0059] A second aspect of the present application provides a method for manufacturing the separator of the first aspect of the present application, the method comprising the steps of: providing a porous substrate; mixing a material for constituting a three-dimensional skeletal structure and a first filler in a predetermined ratio in a solvent to prepare a coating slurry; and applying the coating slurry to at least one surface of the porous substrate and drying it to obtain a separator, wherein the separator comprises a porous substrate and a coating disposed on at least one surface of the porous substrate, the coating comprising a three-dimensional skeletal structure and a first filler, at least a portion of the first filler being filled in the three-dimensional skeletal structure, and the average particle size of the first filler is 200 nm or less.

[0060] In any embodiment of the present application, the coating slurry further comprises a second filler, the average particle size of the first filler is denoted as d1, the average particle size of the second filler is denoted as d2, and d2 / d1>1.

[0061] A third aspect of the present application provides a secondary battery, the secondary battery comprising the separator of the first aspect of the present application or comprising a separator produced by the method of the second aspect of the present application.

[0062] A fourth aspect of the present application provides a power consuming device, the power consuming device including the secondary battery of the third aspect of the present application.

[0063] The separator of the present application can provide a secondary battery with high energy density, high thermal safety performance, and good cycle performance and dynamic performance at the same time, and the power consumption device of the present application includes a secondary battery according to the present application and therefore has at least the same advantages as the secondary battery. [Brief explanation of the drawings]

[0064] In order to more clearly explain the technical solutions of the embodiments of the present application, the following briefly introduces the drawings that need to be used in the embodiments of the present application. It is obvious that the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on the drawings without any creative efforts. [Figure 1] 1 is a schematic diagram of one embodiment of a secondary battery of the present application. [Figure 2] FIG. 2 is an exploded schematic view of an embodiment of the secondary battery of FIG. 1. [Figure 3] 1 is a schematic diagram of one embodiment of a battery module of the present application. [Figure 4] 1 is a schematic diagram of one embodiment of a battery pack of the present application. [Figure 5] FIG. 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4. [Figure 6]1 is a schematic diagram of one embodiment of the present application including a secondary battery-powered power consuming device. DETAILED DESCRIPTION OF THE INVENTION

[0065] Hereinafter, with appropriate reference to the drawings, specific disclosed embodiments of the separator of the present application, its manufacturing method, and related secondary batteries and power consumption devices will be described in detail. However, unnecessary detailed description may be omitted. For example, detailed description of well-known matters or repeated description of structures that are actually the same may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0066] The "ranges" disclosed in this application are defined in the form of lower and upper limits. A given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such defined ranges may be inclusive or exclusive, and may be arbitrarily combined; i.e., any lower limit may be combined with any upper limit to form a single range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if 1 and 2 are listed as minimum range values and 3, 4, and 5 are listed as maximum range values, the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all contemplated. In this application, unless otherwise specified, the numerical range "ab" is a shorthand notation for any combination of real numbers from a to b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have already been listed in this specification, and "0-5" is merely a shorthand representation of combinations of these numbers. Also, expressing a parameter as an integer ≧2 is equivalent to disclosing that this parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0067] Unless otherwise stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present application.

[0068] Unless otherwise stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present application.

[0069] Unless otherwise specified, all steps in this application may be performed in order or randomly, and are preferably performed in order. For example, when the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed in order, or steps (b) and (a) performed in order. For example, when the method mentioned above may further include step (c), it means that step (c) may be added to the method in any order, and for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0070] Unless otherwise specified, the terms "comprise" and "comprises" used in this application may be open ended or closed ended. For example, the terms "comprise" and "comprises" may indicate that other components not listed may be further included or included, or that only the listed components may be included or included.

[0071] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, "A or B" is satisfied when A is true (or exists) and B is false (or does not exist), when A is false (or does not exist) but B is true (or exists), or when both A and B are true (or exist).

[0072] Unless otherwise stated, in this application, the terms "first," "second," etc. are not intended to describe a particular order or hierarchy, but rather to distinguish between different objects.

[0073] Unless otherwise specified, terms used in this application have the known meanings commonly understood by those skilled in the art.

[0074] Unless otherwise specified, the numerical values of each parameter mentioned in this application can be measured using various test methods commonly used in the art, for example, according to the test methods given in the examples of this application.

[0075] Generally, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. The separator is installed between the positive electrode plate and the negative electrode plate and serves mainly to prevent short circuits between the positive and negative electrodes, while allowing active ions to pass freely through the separator to complete a circuit.

[0076] With the increasing application and popularity of secondary batteries, people's requirements for the energy density, service life, and dynamic performance of secondary batteries are increasing. Thinning the separator is an effective way to improve the energy density of secondary batteries. The separators currently used in commercial secondary batteries are generally polyolefin porous membranes, such as porous polyethylene membranes, porous polypropylene membranes, or polypropylene / polyethylene / polypropylene three-layer composite membranes, with melting points ranging from 130°C to 160°C. Therefore, as the separator becomes thinner, its heat resistance deteriorates. When exposed to heat, significant thermal contraction occurs, leading to direct contact between the positive and negative electrodes inside the battery, causing internal short circuits and increasing safety risks for secondary batteries.

[0077] To solve these problems, the current approach is to coat a heat-resistant inorganic ceramic layer on a polyolefin porous membrane, which increases the separator's mechanical strength, reduces its shrinkage when heated, and reduces the risk of short-circuiting between the positive and negative electrodes within the battery. However, commercially available inorganic ceramic particles have relatively large particle sizes, which increase the overall thickness of the separator and make it impossible to balance the energy density of the secondary battery, which is detrimental to improving range, especially in the field of power batteries. Furthermore, the effectiveness of commercially available inorganic ceramic particles in improving the separator's heat resistance is limited. While nano-sizing inorganic ceramic particles can reduce the coating thickness and mitigate the negative impact on the secondary battery's energy density, nano-sizing inorganic ceramic particles tends to clog the polyolefin porous membrane, resulting in a deterioration in the capacity and dynamic performance of the secondary battery. At the same time, since the specific surface area of nano-sized inorganic ceramic particles is relatively high and the contact between the particles is point contact, it is necessary to use a large amount of adhesive to ensure adhesion between the particles. However, when a relatively large amount of adhesive is used, pore clogging problems are likely to occur, which is detrimental to the dynamic performance of the secondary battery.

[0078] Therefore, the separators of the prior art often have difficulty in achieving high energy density, high thermal safety performance, long cycle life, and good dynamic performance of secondary batteries.

[0079] During the course of research, the inventors surprisingly discovered that by applying a coating containing a three-dimensional framework structure and a first filler having an average particle size of 200 nm or less to the surface of a separator porous substrate, it is possible to achieve a separator with low weight, high heat resistance, and high ionic conductivity, and ultimately to achieve a secondary battery with high energy density, high thermal safety performance, long cycle life, and good dynamic performance.

[0080] Separator Specifically, a first aspect of the present application provides a separator, the separator comprising a porous substrate and a coating disposed on at least one surface of the porous substrate, wherein the coating comprises a three-dimensional framework and a first filler, at least a portion of the first filler is filled in the three-dimensional framework, and the first filler has an average particle size of 200 nm or less. In the present application, the term "three-dimensional framework structure" refers to a structure having a three-dimensional spatial shape and a certain void, which can be formed by abutting materials constituting the three-dimensional framework structure with each other.

[0081] When the average particle size of the first filler is 200 nm or less, it has the advantages of a large specific surface area and high affinity with the three-dimensional skeletal structure, and is advantageous in forming a stable spatial network structure with the three-dimensional skeletal structure, which not only increases the ionic conductivity of the separator but also improves the heat resistance of the separator.

[0082] At least a portion of the first filler is filled into the three-dimensional framework, which contributes to the formation of a nesting effect between the first filler and the three-dimensional framework, thereby improving the heat resistance of the separator, reducing the degree of shrinkage of the separator when exposed to heat, reducing the risk of short circuits between the positive and negative electrodes, and providing the secondary battery with high thermal safety performance. This not only ensures high adhesive strength between the coating and the porous substrate, but also prevents the first filler from falling off during the long-term charge and discharge process of the secondary battery. At the same time, when at least a portion of the first filler is filled into the three-dimensional framework, the number of contact sites between the first filler and the three-dimensional framework is relatively large, which reduces the amount of adhesive used in the coating, thereby effectively reducing the risk of adhesive pore clogging and further improving the cycle performance and dynamic performance of the secondary battery.

[0083] The coating of the present application has high heat resistance, which allows the coating thickness to be reduced (for example, the coating thickness may be 2 μm or less), shortening the transmission distance of active ions, and further enabling the secondary battery to achieve higher energy density and good cycle performance and dynamic performance. Furthermore, the coating of the present application has high heat resistance, which allows the selection of thinner porous substrates, further improving the energy density of the secondary battery.

[0084] In some embodiments, at least a portion of the first filler is filled in the three-dimensional framework, and another portion of the first filler may be located on the surface of the three-dimensional framework and / or at the interface between the three-dimensional framework and the porous substrate, and a small amount of the first filler may be embedded in the porous substrate at the interface between the three-dimensional framework and the porous substrate, for example, during the winding process of the electrode assembly, due to the action of external pressure, the small amount of the first filler at the interface may be embedded in the base and / or pores of the porous substrate.

[0085] [Three-dimensional skeletal structure] In some embodiments, the three-dimensional framework may be formed of fibers, and the shape of the fibers may optionally include at least one of rod-like, tubular (e.g., hollow tubular), rod-like, and fibrous. A material with an appropriate shape is advantageous in that the three-dimensional framework and the first filler form a more stable spatial network structure, thereby further improving the heat resistance, ionic conductivity, and electrolyte wetting and retention properties of the separator. In this application, the term "fiber" refers to a material with an aspect ratio of 5 or more.

[0086] In some embodiments, the material constituting the three-dimensional framework structure includes at least one of an organic material and an inorganic material.

[0087] Optionally, the organic material includes at least one of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers. Optionally, the inorganic material includes at least one of halloysite nanotubes, nanorod aluminum oxide, nanorod boehmite, nanorod silica, and glass fibers.

[0088] In some embodiments, the material constituting the three-dimensional framework may include nanocellulose, optionally including at least one of cellulose nanofibers (Cellulose nanofibrils, CNF, also known as nanofibrillated cellulose or microfibrillated cellulose), cellulose nanocrystals (CNC, also known as nanocrystalline cellulose), and bacterial nanocellulose (BNC, also known as bacterial cellulose or microbial cellulose).

[0089] Nanocellulose is a general term for cellulose whose size in any dimension is nanoscale (e.g., within 100 nm), and it possesses the properties of cellulose but also nanoparticles. Nanocellulose can be a polymeric nanomaterial extracted from natural sources such as wood or cotton by one or more means, including chemical, physical, and biological methods. Its advantages include widespread availability, low cost, biodegradability, high elastic modulus, and high specific surface area. It is an excellent alternative to traditional petrochemical resources and can effectively alleviate issues such as environmental pollution and petrochemical resource shortages. Nanocellulose also has excellent high-temperature resistance and a relatively small volume change after heating, thereby improving the heat resistance of separators. At the same time, nanocellulose's density is relatively low compared to traditional inorganic ceramic particles, thereby reducing the weight of secondary batteries and improving their weight-to-weight energy density. Furthermore, the three-dimensional framework structure of nanocellulose has tiny nanopores that prevent current leakage, allowing separators to achieve both good electrolyte infiltration and retention properties and good voltage breakdown resistance.

[0090] In some embodiments, the nanocellulose may include at least one of unmodified nanocellulose (also called hydroxy nanocellulose) and modified nanocellulose, and optionally modified nanocellulose.

[0091] Modified nanocellulose refers to nanocellulose that includes both hydroxyl groups and modifying groups. In some embodiments, the modified nanocellulose includes modifying groups, and the modifying groups include at least one of an amine group, a carboxyl group, an aldehyde group, a sulfonic acid group, a boric acid group, and a phosphate group, and optionally at least one of a sulfonic acid group, a boric acid group, and a phosphate group.

[0092] Through further research, the inventors discovered that nanocellulose containing the specific modifying groups effectively improves the heat resistance of the separator, improving the thermal safety performance of the secondary battery, while also improving the adhesive strength between the coating and the porous substrate. The specific modifying groups in nanocellulose also help the nanocellulose and the first filler to form an integrated structure, resulting in a more stable spatial network structure for the coating, improving the separator's electrolyte penetration and retention properties, and improving the separator's ionic conductivity and voltage breakdown characteristics. The presence of the modifying groups also reduces the proportion of hydroxyl groups, ensuring that the coating slurry has an appropriate viscosity, which is more convenient for application and thereby improving separator production efficiency and coating uniformity.

[0093] In some embodiments, the molar ratio of the modifying groups to the hydroxyl groups is 1:4 to 4:1, and optionally 2:3 to 7:3. When the molar ratio of the modifying groups to the hydroxyl groups is within the above range, the heat resistance, ionic conductivity, and electrolyte penetration and retention properties of the separator can be further improved. The following situation can also be effectively avoided: if the molar ratio of the modifying groups to the hydroxyl groups is too low, the further improvement effect of the modifying groups on the separator's heat resistance and ionic conductivity may be unclear; if the molar ratio of the modifying groups to the hydroxyl groups is too high, the separator's electrolyte penetration and retention properties may be poor, affecting the cycle performance and safety performance of the secondary battery and further reducing the heat resistance of the separator, which may affect the improvement effect on the thermal safety performance of the secondary battery.

[0094] The type of modifying group in nanocellulose can be determined by infrared spectroscopy. For example, the type of modifying group can be determined by examining the infrared spectrum of the material and determining the characteristic peaks contained therein. Specifically, infrared spectroscopy can be performed on the material using instruments and methods known in the art, such as an infrared spectrometer (e.g., a Nicolet IS10 Fourier transform infrared spectrometer) in accordance with GB / T 6040-2019 General Methods for Infrared Spectroscopic Analysis.

[0095] In some embodiments, the material constituting the three-dimensional framework comprises a sulfonic acid group, and the content of sulfur element in the material constituting the three-dimensional framework is ≧0.1 wt %, optionally 0.2 wt % to 0.5 wt %, based on the total weight of the material constituting the three-dimensional framework, and optionally the material constituting the three-dimensional framework comprises nanocellulose.

[0096] The sulfur content of the three-dimensional framework material can be measured as follows: After drying the three-dimensional framework material, it is ground in a mortar (e.g., an agate mortar) for 30 minutes and then tested using an X-ray diffractometer (e.g., a Miniflex 600-C) to determine the sulfur content. The test uses a Cu target, a Ni filter, a tube pressure of 40 kV, a tube current of 15 mA, and a continuous scan range of 5°-80°.

[0097] In some embodiments, the average diameter of the material constituting the three-dimensional framework is ≦40 nm, and optionally may be 10 nm to 35 nm. When the average diameter of the material constituting the three-dimensional framework is within this range, the ionic conductivity and voltage breakdown characteristics of the separator can be further improved, and the integration effect due to contact with the first filler can be further improved, thereby further improving the heat resistance of the separator. The following situation can also be effectively avoided: if the average diameter of the material constituting the three-dimensional framework is too large, the resulting three-dimensional framework structure will have insufficient entanglement and relatively large voids, which may result in insufficient heat resistance and voltage breakdown characteristics of the separator. At the same time, it will be unfavorable for the integration effect due to contact with the first filler. Furthermore, during the drying process of the coating, the three-dimensional framework structure will be easily collapsed due to insufficient support from the first filler. Furthermore, direct contact with the porous substrate will easily cause pore clogging, which may affect the ionic conductivity of the separator.

[0098] In some embodiments, the average length of the material constituting the three-dimensional framework may be 100 nm to 600 nm, and optionally 200 nm to 500 nm. When the average length of the material constituting the three-dimensional framework is within this range, the heat resistance and ionic conductivity of the separator can be further improved. Furthermore, the following situation can be effectively avoided: if the average length of the material constituting the three-dimensional framework is too short, the contact effect between the three-dimensional framework and the first filler is relatively poor, resulting in poor heat resistance of the coating. Furthermore, during the drying process of the coating, the three-dimensional framework is prone to collapse due to insufficient support from the first filler, which is likely to cause pore clogging and hinder ion transmission and moisture discharge, thereby potentially affecting the thermal safety performance, cycle performance, and dynamic performance of the secondary battery. If the average length of the material constituting the three-dimensional framework is too long, the viscosity of the coating slurry is high and the fluidity is poor, which can affect the application of the coating slurry and further affect the quality of the coating, such as the heat resistance and ionic conductivity of the separator.

[0099] In some embodiments, the aspect ratio of the material constituting the three-dimensional framework may be 5 to 60, and preferably 10 to 30. When the aspect ratio of the material constituting the three-dimensional framework is within this range, the ionic conductivity and electrolyte infiltration and retention properties of the separator can be further improved. Furthermore, the following situations can be effectively avoided: if the aspect ratio of the material constituting the three-dimensional framework is too small, the contact effect between the three-dimensional framework and the first filler is relatively poor, resulting in poor heat resistance of the coating. Furthermore, during the drying process of the coating, the three-dimensional framework is prone to collapse due to insufficient support from the first filler, and furthermore, pore clogging problems are likely to occur, hindering ion transmission and moisture evacuation, which may affect the thermal safety performance, cycle performance, and dynamic performance of the secondary battery. If the aspect ratio of the material constituting the three-dimensional framework is too large, the resulting voids in the three-dimensional framework are small, which may result in low ionic conductivity of the separator.

[0100] The average length and average diameter of the material constituting the three-dimensional skeletal structure can be measured by the following method: a 3.6 mm × 3.6 mm sample is cut out from any region of the separator, and the micromorphology of the coating in the sample is mapped using a scanning electron microscope (e.g., ZEISS Sigma 300) in high vacuum mode at an operating voltage of 3 kV and a magnification of 30,000 times. SEM images are obtained based on the obtained SEM images, and length statistics are performed on multiple (e.g., five or more) test regions, each with a size of 0.5 μm × 0.5 μm. The average length value obtained in each test region is then used as the average length of the material constituting the three-dimensional skeletal structure. Based on the obtained SEM images, Nano Measurer particle size distribution statistical software is used to select multiple (e.g., five or more) test regions and perform diameter statistics, each with a size of 0.5 μm × 0.5 μm. The average diameter value obtained in each test region is then used as the average diameter of the material constituting the three-dimensional skeletal structure.

[0101] In some embodiments, the content of the three-dimensional framework may be 5 wt% to 40 wt%, or alternatively 8 wt% to 25 wt%, or 10 wt% to 25 wt%, based on the total weight of the coating. Because the material constituting the three-dimensional framework has a relatively large specific surface area, the coating formed with the same mass has a relatively large specific surface area and relatively many voids, resulting in relatively poor heat resistance of the separator. At the same time, the hydrogen bonding action of the material constituting the three-dimensional framework (e.g., nanocellulose) is very strong, and if the content is relatively high, the viscosity of the coating slurry will be relatively high, which is unfavorable for achieving a thin coating and is unfavorable for commercial production. When the content of the three-dimensional framework structure is within the above range, it can ensure that the coating slurry has an appropriate viscosity, which is advantageous for application, and it is also advantageous for the three-dimensional framework structure and the first filler to come into contact with each other to form an integrated effect, which is advantageous for the coating to have a more stable spatial network structure, thereby further improving the heat resistance, ionic conductivity, electrolyte penetration and retention properties, and voltage breakdown ability of the separator.

[0102] [First filler] In some embodiments, the first filler has an average particle size of 15 to 180 nm, optionally 20 to 170 nm, 25 to 160 nm, 30 to 150 nm, 40 to 140 nm, or 50 to 135 nm. When the average particle size of the first filler is within the above range, the first filler can have a relatively high specific surface area, and the particle size of the first filler can be better matched with the three-dimensional skeleton structure, thereby better abutting the first filler with the three-dimensional skeleton structure to form an integrated effect, increasing the affinity between the first filler and the three-dimensional skeleton structure, and increasing the heat resistance and ionic conductivity of the separator, while also improving the separator's electrolyte penetration and retention properties.

[0103] In some embodiments, the first filler comprises at least one of primary particles and secondary particles, and optionally the first filler comprises a combination of primary particles and secondary particles. The primary particle form of the first filler is advantageous for reducing the moisture content of the coating and improving the ionic conductivity of the coating, thereby better improving the cycle performance of the secondary battery. The secondary particle form of the first filler can better contact with the three-dimensional framework structure to form an integrated effect, thereby allowing the coating to have a more stable spatial network structure, thereby further improving the heat resistance of the separator.

[0104] In some embodiments, the first filler comprises a combination of primary particles and secondary particles, and the content of the first filler in the form of primary particles is less than the content of the first filler in the form of secondary particles, based on the total weight of the first filler.

[0105] In some embodiments, the first filler comprises a combination of primary particles and secondary particles, and based on the total weight of the first filler, the content of the first filler in the form of primary particles is 30 wt% or less, optionally 8 wt% to 30 wt%, 8 wt% to 28 wt%, 10 wt% to 30 wt%, 10 wt% to 28 wt%, 12 wt% to 30 wt%, 12 wt% to 28 wt%, 15 wt% to 30 wt%, 15 wt% to 28 wt%, 17.5 wt% to 30 wt%, or 17.5 wt% to 28 wt%.

[0106] In some embodiments, the average particle size of the first filler in the form of primary particles is 15 nm to 95 nm, optionally 15 nm to 80 nm, 20 nm to 80 nm, 30 nm to 75 nm, 35 nm to 75 nm, 35 nm to 70 nm, 30 nm to 70 nm, or 30 nm to 65 nm.

[0107] In some embodiments, the average particle size of the first filler in the form of secondary particles is 50 nm to 200 nm, and optionally 50 nm to 180 nm, 50 nm to 150 nm, 50 nm to 135 nm, 50 nm to 120 nm, 55 nm to 180 nm, 55 nm to 150 nm, 55 nm to 135 nm, 55 nm to 120 nm, 65 nm to 180 nm, 65 nm to 150 nm, 65 nm to 135 nm, or 65 nm to 120 nm.

[0108] In some embodiments, the BET specific surface area of the first filler is ≥ 25 m 2 / g, and selectively 30m 2 / g~80m 2 / g, 30m 2 / g~65m 2 When the specific surface area of the first filler is within the above range, it has better affinity with the three-dimensional framework structure and can abut against the three-dimensional framework structure to form an integrated effect, thereby increasing the heat resistance and ionic conductivity of the separator and simultaneously increasing the electrolyte infiltration and retention properties of the separator.

[0109] In some embodiments, the first filler comprises at least one of inorganic particles and organic particles, and optionally comprises inorganic particles or a combination of inorganic and organic particles. Inorganic particles have high hardness, high thermal stability, and resistance to decomposition. They typically have hydroxyl groups on their surfaces, making them easy to combine with materials (e.g., nanocellulose) that form three-dimensional frameworks to form stable spatial network structures. Organic particles have good thermal stability and resistance to decomposition. At the same time, when the internal temperature of a secondary battery reaches the melting point of the organic particles due to overcharging or thermal abuse, the organic particles can further melt and be drawn into the pores of the porous substrate by capillary action, thereby closing and blocking the pores, which is advantageous for improving the safety performance of the secondary battery.

[0110] Optionally, the inorganic particles include at least one of boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicone oxide SiOx (0 < x ≦ 2), tin dioxide (SnO2), titanium dioxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium dioxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), hafnium dioxide (HfO2), cerium oxide (CeO2), zirconium titanate (ZrTiO3), barium titanate (BaTiO3), and magnesium fluoride (MgF2). Further optionally, the inorganic particles are boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), silicone oxide SiO x (0 < x ≦ 2), and include at least one of titanium dioxide (TiO2), zinc oxide (ZnO), cerium oxide (CeO2), and barium titanate (BaTiO3).

[0111] Optionally, the organic particles include at least one of polystyrene particles, polyacrylic acid wax particles, melamine formaldehyde resin particles, phenol resin particles, polyester particles, polyimide particles, polyamideimide particles, polyaramide particles, polyphenylene sulfide particles, polysulfone particles, polyether sulfone particles, polyether ether ketone particles, and polyaryl ether ketone particles.

[0112] In some embodiments, the first filler includes inorganic particles, and the crystal form of the inorganic particles includes at least one of θ crystal form, γ crystal form, and η crystal form. Optionally, the crystal form of the inorganic particles includes at least one of θ crystal form and γ crystal form.

[0113] The inorganic particles of the θ crystal form have diffraction peaks at 2θ of 36.68°±0.2° and 31.21°±0.2° in an X-ray diffraction spectrum measured using an X-ray diffractometer. In some embodiments, the content of the inorganic particles of the θ crystal form in the first filler may be ≧50 wt%, and optionally 55 wt% to 84 wt%, based on the total weight of the inorganic particles in the first filler.

[0114] The γ-crystalline inorganic particles have diffraction peaks at 2θ of 66.95°±0.2° and 45.91°±0.2° in an X-ray diffraction spectrum measured using an X-ray diffractometer. In some embodiments, the content of the γ-crystalline inorganic particles in the first filler may be ≧10 wt %, and optionally 15 wt % to 44 wt %, based on the total weight of the inorganic particles in the first filler.

[0115] The inorganic particles of the η-crystalline form have diffraction peaks at 2θ of 31.89°±0.2° and 19.37°±0.2° in an X-ray diffraction spectrum measured using an X-ray diffractometer. In some embodiments, the content of the inorganic particles of the η-crystalline form in the first filler may be ≦5 wt %, optionally ≦2.5 wt %, and further optionally ≦1.5 wt %, based on the total weight of the inorganic particles in the first filler.

[0116] Inorganic particles with a θ crystal form have an appropriate specific surface area and hardness, which can better simultaneously improve the heat resistance and ionic conductivity of the separator, while inorganic particles with a γ crystal form and an η crystal form have the advantage of a large specific surface area.

[0117] Selection of a first filler having a different crystal form contributes to improving at least one of the heat resistance, ionic conductivity, adhesive strength, and electrolyte wetting and retention properties of the separator.

[0118] In some embodiments, the first filler may comprise inorganic particles, and the crystalline forms of the inorganic particles may include θ crystalline form, γ crystalline form, and η crystalline form, and the content of θ crystalline form inorganic particles in the first filler may be 55 wt% to 84 wt%, the content of γ crystalline form inorganic particles may be 15 wt% to 44 wt%, and the content of η crystalline form inorganic particles may be ≦2.5 wt%, all based on the total weight of the inorganic particles in the first filler.

[0119] X-ray diffraction spectra of inorganic particles can be obtained by the following method: After drying the inorganic particles, they are ground in a mortar (e.g., an agate mortar) for 30 minutes, and then tested using an X-ray diffractometer (e.g., a Miniflex 600-C) to obtain X-ray diffraction spectra. The test can be performed using a Cu target, a Ni filter, a tube pressure of 40 kV, a tube current of 15 mA, and a continuous scan range of 5°-80°.

[0120] In some embodiments, the first filler may include inorganic particles, which can be produced by the following method: a precursor solution of inorganic particles is oxidized by high-pressure sputtering, then heated at 600°C to 900°C (for example, for 1 hour to 3 hours) to form primary inorganic particles, and then further dried at 150°C to 250°C (for example, for 30 minutes to 60 minutes) to obtain secondary inorganic particles (obtained by aggregation of the primary particles).

[0121] In some embodiments, the content of the first filler is ≧50 wt%, and optionally 50 wt% to 90 wt%, 55 wt% to 90 wt%, 60 wt% to 90 wt%, 50 wt% to 85 wt%, 55 wt% to 85 wt%, 60 wt% to 85 wt%, 50 wt% to 82.5 wt%, 55 wt% to 82.5 wt%, or 60 wt% to 82.5 wt%, based on the total weight of the coating. When the content of the first filler is within the above range, it can ensure that the coating slurry has an appropriate viscosity, which is advantageous for application and for forming an integrated effect by contacting with the three-dimensional framework structure, which is advantageous for forming a more stable spatial network structure of the coating, thereby further improving the heat resistance and ionic conductivity of the separator.

[0122] [Second filler] In some embodiments, the coating further comprises a second filler at least partially embedded within the coating, and a portion of the second filler can protrude from the surface of the coating.

[0123] In some embodiments, the coating comprises a first filler and a second filler, wherein the average particle size of the first filler is denoted as d1 and the average particle size of the second filler is denoted as d2, where d2 / d1 > 1. The second filler has a relatively large average particle size, which can better support the coating, reduce shrinkage of the first filler, and reduce the amount of adhesive used, thereby improving the heat resistance of the separator. The second filler has a relatively large particle size and a relatively small amount used, which can contribute to the coating having a more porous structure and a lower water content, further improving the ionic conductivity and electrolyte wetting and retention properties of the separator, and simultaneously improving the cycling performance and / or kinetic performance of the secondary battery.

[0124] The first filler includes at least one of primary particles and secondary particles, and the average particle size of the first filler in the form of primary particles is defined as d 11and the average particle size of the first filler in the form of secondary particles is denoted by d 12 It is written as follows.

[0125] In some embodiments, 3.0≦d / d 11 ≦10.0, and optionally, 3.5≦d / d 11 ≦8.0 and 3.5≦d2 / d 11 The synergistic effect of the first filler and the second filler helps to reduce the moisture content of the coating, allowing the coating to maintain a stable pore structure during long-term charge and discharge, while also improving the heat resistance of the separator, thereby enabling the secondary battery to better achieve high energy density, high thermal safety performance, long cycle life, and good dynamic performance.

[0126] In some embodiments, 1.2≦d / d 12 ≦6.0, and optionally, 2.0≦d2 / d 12 ≦5.5 and 2.0≦d2 / d 12 ≦5.0, and 2.0≦d2 / d 12 The synergistic effect of the first filler and the second filler helps to reduce the moisture content of the coating, allowing the coating to maintain a stable pore structure during long-term charge and discharge, while also improving the heat resistance of the separator, thereby enabling the secondary battery to better achieve high energy density, high thermal safety performance, long cycle life, and good dynamic performance.

[0127] In some embodiments, the second filler has an average particle size d2 of 120 nm to 350 nm, preferably 150 nm to 300 nm, which can enhance the supporting effect of the second filler, reduce the moisture content of the coating, maintain a stable pore structure in the coating during long-term charge / discharge, and improve the heat resistance of the separator.

[0128] In some embodiments, the BET specific surface area of the second filler is ≦20 m 2 / g, and selectively 6m 2 / g~15m 2 This allows the second filler to better exert its supporting effect, reduces the moisture content of the coating, and allows the coating to maintain a stable pore structure during long-term charge and discharge, while also improving the heat resistance of the separator.

[0129] In some embodiments, the second filler comprises at least one of inorganic particles and organic particles.

[0130] In some embodiments, the inorganic particles may include at least one of inorganic particles having a dielectric constant of 5 or greater, inorganic particles that are ionic conductive but do not store ions, and inorganic particles that are capable of undergoing electrochemical reactions.

[0131] Alternatively, the inorganic particles having a dielectric constant of 5 or more may be boehmite, aluminum oxide, 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, magnesium lithium silicate, magnesium sodium silicate, bentonite, hectorite, zirconium titanate, barium titanate, Pb(Zr,Ti)O3 (abbreviated as PZT), Pb 1-m La m Zr 1-n Ti n O3 (abbreviated as PLZT, 0 <m<1、0<n<1)、Pb(Mg3Nb 2 / 3The coating composition includes at least one of )O3-PbTiO3 (abbreviated as PMN-PT) and modified inorganic particles. Optionally, the modification of each inorganic particle may be chemical and / or physical. The chemical modification may include coupling agent modification (e.g., using a silane coupling agent, a titanate coupling agent, etc.), surfactant modification, polymer graft modification, etc. The physical modification may include mechanical dispersion, ultrasonic dispersion, high-energy treatment, etc. The modification treatment can reduce the aggregation of inorganic particles, thereby resulting in a more stable and uniform spatial network structure of the coating. Furthermore, selecting a coupling agent, surfactant, or polymer with a specific functional group to modify the inorganic particles can improve the electrolyte wetting and retention properties of the coating and also contribute to improving the adhesion of the coating to the porous substrate.

[0132] Optionally, the inorganic particles that are ionically conductive but do not store ions include Li3PO4, lithium titanium phosphate, Li x1 Ti y1 (PO4)3, Lithium titanium aluminum phosphate Li x2 Al y2 Ti z1 (PO4)3, (LiAlTiP) x3 O y3 Glass, Lithium lanthanum titanate 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 z4including at least one of them, where 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. Thereby, the ionic conductivity of the separator can be further improved.

[0133] Optionally, the inorganic particles capable of undergoing an electrochemical reaction 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.

[0134] In some embodiments, the organic particles include, but are not limited to, at least one of polyethylene particles, polypropylene particles, cellulose, cellulose modifiers (such as carboxymethyl cellulose), melamine resin particles, phenol resin particles, polyester particles (such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), silicone resin particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, polyaryletherketone particles, and copolymers of butyl acrylate and ethyl methacrylate (such as cross-linked polymers of butyl acrylate and ethyl methacrylate).

[0135] In some embodiments, the second filler has a primary particle form.

[0136] In some embodiments, the second filler includes inorganic particles in primary particle form, and the crystal form of the inorganic particles in primary particle form includes at least one of α-crystal form and γ-crystal form, and optionally includes α-crystal form. The second filler in α-crystal form has the advantages of high hardness, good heat resistance, low dielectric constant, high safety, and large true density, thereby further improving the heat resistance of the coating.

[0137] In some embodiments, the second filler comprises inorganic particles in the form of primary particles, and the crystalline form of the inorganic particles in the form of primary particles comprises an α-crystalline form, and the content of the α-crystalline form is ≧70 wt%, optionally 75 wt% to 100 wt%, 85 wt% to 100 wt%, or 95 wt% to 100 wt%, based on the total weight of the inorganic particles in the form of primary particles in the second filler.

[0138] The α-crystalline inorganic particles have diffraction peaks at 2θ of 57.48°±0.2° and 43.34°±0.2° in an X-ray diffraction spectrum measured using an X-ray diffractometer.

[0139] In some embodiments, the content of the second filler is ≦30 wt %, and optionally 5 wt % to 25 wt %, 6 wt % to 22 wt %, 6 wt % to 20 wt %, or 8 wt % to 18 wt %, based on the total weight of the coating. When the content of the second filler is within the above range, the supporting effect of the second filler can be better exerted, the moisture content of the coating can be reduced, and the coating can maintain a stable pore structure during long-term charge and discharge.

[0140] In some embodiments, the coating may further include a non-particulate adhesive. The present application is not particularly limited to the type of non-particulate adhesive, and any known material with good adhesive properties may be selected. Optionally, the non-particulate adhesive may include a water-based adhesive, which has the advantages of high thermodynamic stability and environmental friendliness, making it advantageous for the preparation and application of coating slurries. For example, the water-based adhesive may include at least one of a water-based acrylic resin (e.g., a homopolymer of acrylic acid, methacrylic acid, or sodium acrylate monomer or a copolymer with other copolymerizable monomers), polyvinyl alcohol (PVA), an isobutylene-maleic anhydride copolymer, and polyacrylamide.

[0141] Optionally, the content of the non-particulate adhesive in the coating is ≦2 wt % based on the total weight of the coating. The three-dimensional framework structure and the first filler in the coating of the present application can form a stable spatial network structure, thereby allowing the separator to maintain high adhesiveness while reducing the amount of adhesive used.

[0142] In some embodiments, the thickness of the coating may be ≦2 μm, and optionally 0.5 μm to 1.5 μm, which contributes to improving the energy density of secondary batteries. In this application, the thickness of the coating refers to the thickness of the coating located on one side of the porous substrate.

[0143] In some embodiments, the thickness of the porous substrate may be ≦6 μm, and optionally 3 μm to 5 μm. The coating of the present application can significantly improve the heat resistance of the separator, allowing for the selection of a thinner porous substrate, thereby contributing to improving the energy density of the secondary battery.

[0144] The present application does not particularly limit the material of the porous substrate, and any known substrate having good chemical and mechanical stability can be selected. For example, the porous substrate may include at least one of a porous polyolefin resin film (e.g., at least one of polyethylene, polypropylene, and polyvinylidene fluoride), a porous glass fiber, and a 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.

[0145] 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 including a particulate adhesive. The adhesive layer not only prevents the coating from peeling off and improves the safety performance of the secondary battery, but also improves the interface between the separator and the electrodes, thereby improving the cycle performance of the secondary battery.

[0146] Optionally, the particulate adhesive includes at least one of an acrylate-based monomer homopolymer or copolymer, an acrylic-based monomer homopolymer or copolymer, and a fluorine-containing olefin monomer homopolymer or copolymer, and the copolymerizable monomer includes at least one of an acrylate-based monomer, an acrylic-based monomer, an olefin monomer, a halogen-containing olefin monomer, a fluoroether-based monomer, etc., but is not limited thereto.

[0147] Optionally, the particulate adhesive includes a vinylidene fluoride polymer, such as a homopolymer of vinylidene fluoride monomer (VDF) and / or a copolymer of a copolymerizable monomer with vinylidene fluoride monomer. The copolymerizable monomer may be at least one of an olefin monomer, a fluorine-containing olefin monomer, a chlorine-containing olefin monomer, an acrylate-based monomer, an acrylic-based monomer, and a fluoroether-based monomer. Optionally, the copolymerizable monomer may include at least one of trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ether (e.g., perfluoro(methyl vinyl) ether PMVE, perfluoro(ethyl vinyl) ether PEVE, perfluoro(propyl vinyl) ether PPVE), perfluoro(1,3-dioxole), and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD).

[0148] In some embodiments, the separator has a longitudinal heat shrinkage of ≦6%, optionally 0.5% to 4%, at 150° C. for 1 hour.

[0149] In some embodiments, the separator has a transverse heat shrinkage at 150° C. for 1 hour of ≦6%, optionally 0.5% to 4%.

[0150] The separator of the present application has low thermal shrinkage in both the transverse and longitudinal directions at a high temperature of 150° C., thereby improving the safety performance of the secondary battery.

[0151] In some embodiments, the separator has a longitudinal tensile strength of ≥ 2000 kg / cm 2 and selectively 2500 kg / cm 2 ~4500kg / cm 2 is.

[0152] In some embodiments, the separator has a transverse tensile strength of ≥ 2000 kg / cm 2 and selectively 2500 kg / cm 2 ~4500kg / cm 2 is.

[0153] The separator of the present application has high tensile strength in both the horizontal and vertical directions, so that the probability of the separator being damaged when the secondary battery expands is relatively low, thereby improving the safety performance of the secondary battery.

[0154] In some embodiments, the separator has a wetted length of ≧30 mm, optionally between 30 mm and 80 mm.

[0155] In some embodiments, the wetting rate of the separator is ≧3 mm / s, optionally between 3 mm / s and 10 mm / s.

[0156] The separator of the present application has good electrolyte infiltration and retention properties, and therefore can improve the ionic conductivity of the separator and the capacity development properties of the secondary battery.

[0157] In some embodiments, the separator has an air permeability of ≦300 s / 100 mL, and optionally 100 s / 100 mL to 230 s / 100 mL. The separator of the present application has good air permeability, which can improve ionic conductivity and secondary battery capacity development characteristics.

[0158] In some embodiments, the separator has a voltage breakdown strength of ≧1 KV. The separator of the present application has a relatively high voltage breakdown strength, which can improve the safety performance of the secondary battery.

[0159] In this application, the average particle size of a material has a meaning known in the art and can be measured using equipment and methods known in the art. For example, the material or separator may be measured using a scanning electron microscope, a transmission electron microscope, or a particle size distribution analyzer to obtain an image, and a plurality of (e.g., 10 or more) test particles (e.g., having a first filler, a second filler, etc.) may be randomly selected from the image, and the average length of the shortest diagonal lines of the particles may be calculated as the average particle size.

[0160] In this application, the specific surface area of a material has a meaning known in the art and can be measured using instruments and methods known in the art. For example, it can be tested using the nitrogen gas adsorption specific surface area analysis test method in accordance with GB / T 19587-2017 and calculated using the Brunauer Emmett Teller (BET) method. Alternatively, the nitrogen gas adsorption specific surface area analysis test can be performed using a Tri-Star 3020 specific surface area hole diameter analyzer manufactured by Micromeritics, Inc., USA.

[0161] In this application, the heat shrinkage rate, tensile strength, and air permeability of the separator all have meanings known in the art and can be measured using methods known in the art, for example, they may be tested in accordance with standard GB / T 36363-2018.

[0162] In this application, the separator wetting length and wetting rate have meanings known in the art and can be measured using methods known in the art. An exemplary test method is as follows: a separator is cut into a 5 mm wide, 100 mm long sample. Both ends of the sample are clamped and placed horizontally. 0.5 mg of electrolyte is dropped into the center of the sample. After a predetermined time (1 minute in this application), a photograph is taken to measure the diffusion length of the electrolyte, thereby obtaining the separator wetting length and wetting rate. To ensure the accuracy of the test results, multiple samples (e.g., 5-10) 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 organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L.

[0163] In this application, the voltage breakdown strength of a separator has a meaning known in the art and can be measured using a method known in the art. For example, it can be measured using a pressure tester with reference to GB / T 13542.2-2009 and GB / T 1408-2006. An exemplary test method is as follows: the separator is cut into a rectangular sample of 450 mm x 650 mm and measured using a pressure tester. The test equipment can be a CS2671AX pressure tester.

[0164] It should be noted that the coating parameters (such as thickness) of the separator are all the coating parameters of one side of the porous substrate. When the coating is applied to both sides of the porous substrate, if the coating parameters of either side satisfy the present application, it is considered to fall within the protection scope of the present application.

[0165] Manufacturing method A second aspect of the present application provides a method for manufacturing the separator of the first aspect of the present application, the method comprising the steps of: providing a porous substrate; mixing a material for constituting a three-dimensional skeletal structure and a first filler in a solvent in a predetermined ratio to prepare a coating slurry; and applying the coating slurry to at least one surface of the porous substrate and drying it to obtain a separator, wherein the separator comprises a porous substrate and a coating disposed on at least one surface of the porous substrate, the coating comprising a three-dimensional skeletal structure and a first filler, at least a portion of the first filler being filled in the three-dimensional skeletal structure, and the average particle size of the first filler is 200 nm or less.

[0166] In some embodiments, the coating slurry further comprises a second filler, wherein the average particle size of the first filler is denoted as d1 and the average particle size of the second filler is denoted as d2, and d2 / d1>1.

[0167] In some embodiments, the solvent used in preparing the coating slurry may be water, for example, deionized water.

[0168] In some embodiments, the coating slurry may further include other ingredients, such as dispersants, wetting agents, adhesives, and the like.

[0169] In some embodiments, the material for forming the three-dimensional framework structure includes at least one of an organic material and an inorganic material. Optionally, the organic material includes at least one of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers. Optionally, the inorganic material includes at least one of halloysite nanotubes, nanorod-shaped aluminum oxide, nanorod-shaped boehmite, nanorod-shaped silica, and glass fibers.

[0170] In some embodiments, the material comprising the three-dimensional framework comprises nanocellulose.

[0171] In some embodiments, the nanocellulose can be obtained by the following method: providing a cellulose powder with a whiteness of ≥ 80%, mixing the resulting cellulose powder with a modifying solution to react, washing to remove impurities, adjusting the pH to neutral, and then grinding and cutting to obtain nanocellulose.

[0172] Alternatively, the cellulose powder having a whiteness of 80% or greater may be commercially available or may be obtained using a chemical method (e.g., acid hydrolysis, alkali treatment, Tempo catalytic oxidation), a biological method (e.g., enzyme treatment), a mechanical method (e.g., ultrafine grinding, ultrasonic crushing, high-pressure homogenization), etc. The fiber raw material for producing the cellulose powder having a whiteness of 80% or greater may include at least one of plant fibers, such as cotton fibers (e.g., cotton wool fibers, cotton fiber), hemp fibers (e.g., sisal fibers, ramie fibers, jute fibers, flax fibers, hemp fibers, abaca fibers, etc.), braun fibers, wood fibers, bamboo fibers, and grass fibers.

[0173] In some embodiments, the cellulose powder having a whiteness of 80% or greater can also be produced by the following method: after opening the fiber raw material and removing the scum, the raw material is cooked in an alkaline solution (for example, an aqueous NaOH solution, the concentration of which may be 4 wt% to 20 wt%, and optionally 5 wt% to 15 wt%), and then sequentially washed with water to remove impurities (for example, washed 3 to 6 times), bleached (for example, sodium hypochlorite and / or hydrogen peroxide solution may be used), pickled to remove impurities, washed with water to remove impurities, drained, and dried in an air stream to obtain a cellulose powder.

[0174] In some embodiments, the modifying solution may be an acid solution (e.g., aqueous sulfuric acid, aqueous boric acid, aqueous phosphoric acid, aqueous acetic acid) or an alkaline solution (e.g., organic solvent urea solution). Optionally, the modifying solution is an acid solution.

[0175] Alternatively, the concentration of the acid solution may be 5 wt% to 80 wt%. When a sulfuric acid aqueous solution is selected as the modifying solution, a cellulose powder having sulfonic acid groups can be obtained by adjusting the concentration of the acid solution to 40 wt% to 80 wt%. When a boric acid aqueous solution is selected as the modifying solution, a cellulose powder having boric acid groups can be obtained by adjusting the concentration of the acid solution to 5 wt% to 10 wt%. When a phosphoric acid aqueous solution is selected as the modifying solution, a cellulose powder having phosphate groups can be obtained by adjusting the concentration of the acid solution to 45 wt% to 75 wt%. When an acetic acid aqueous solution is selected as the modifying solution, a cellulose powder having carboxylic acid groups can be obtained by adjusting the concentration of the acid solution to 40 wt% to 80 wt%.

[0176] Alternatively, the urea organic solvent solution is a urea xylene solution, thereby obtaining a cellulose powder having an amine group.

[0177] In some embodiments, optionally, the mass ratio of the cellulose powder to the modifying solution is 1:2.5 to 1:50, optionally 1:5 to 1:30.

[0178] When a sulfuric acid aqueous solution is selected as the modifying solution, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30. When a boric acid aqueous solution is selected as the modifying solution, the mass ratio of the cellulose powder to the acid solution may be 1:20 to 1:50. When a phosphoric acid aqueous solution is selected as the modifying solution, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30. When an acetic acid aqueous solution is selected as the modifying solution, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30. When a urea organic solvent solution is selected as the modifying solution, the mass ratio of the cellulose powder to the urea organic solvent solution may be 1:4 to 1:40.

[0179] In some embodiments, when the modifying solution is an acid solution, the reaction may be carried out at a temperature of 80°C or less, or optionally at a temperature of 30°C to 60°C, and the reaction time between the cellulose powder and the modifying solution may be 0.5 hours to 4 hours, or optionally 1 hour to 3 hours.

[0180] In some embodiments, when the modifying solution is an alkaline solution, the reaction may be carried out at a temperature of 100°C to 145°C, and the reaction time between the cellulose powder and the modifying solution may be 1 hour to 5 hours.

[0181] In some embodiments, grinding may be performed using a grinder, and cutting may be performed using a high-pressure homogenizer. By adjusting the grinding parameters of the grinder (e.g., grinding frequency, grinding time, etc.) and the cutting parameters of the high-pressure homogenizer, nanocellulose having different average diameters and / or different average lengths can be obtained.

[0182] In some embodiments, a coater may be used to apply the coating slurry. The present application does not particularly limit the model number of the coater, and for example, a commercially available coater may be used. The coater may include an intaglio roller, and the intaglio roller is used to transfer the slurry onto the porous substrate.

[0183] In some embodiments, the coating slurry may be applied by transfer coating, spin spray coating, dip coating, or the like.

[0184] In some embodiments, the method further comprises applying a slurry containing a particulate adhesive to at least a portion of the surface of the coating and allowing it to dry to form an adhesive layer.

[0185] The separator manufacturing method of the present application produces and obtains a coating in a single application, greatly simplifying the separator manufacturing process flow.

[0186] Parameters such as some raw materials used in the manufacturing method of the separator of the present application and their contents can be referred to the separator of the first aspect of the embodiment of the present application, and will not be further described here.

[0187] Unless otherwise specified, each of the raw materials used in the manufacturing method of the separator of the present application is commercially available.

[0188] secondary battery A third aspect of the present invention provides a secondary battery.

[0189] A secondary battery, also known as a rechargeable battery or storage battery, is a battery that can be continuously used by activating the active material through charging after discharging. Generally, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. The separator is disposed between the positive electrode plate and the negative electrode plate and mainly serves to prevent short circuits between the positive electrode and the negative electrode and allows active ions to pass through.

[0190] The present application is not particularly limited to the type of secondary battery, and for example, the secondary battery may be a lithium ion battery, a sodium ion battery, etc., and in particular may be the lithium ion secondary battery.

[0191] A secondary battery according to a third aspect of the present application includes the separator according to the first aspect of the present application or a separator manufactured by the method according to the second aspect of the present application, the separator being interposed between the positive electrode plate and the negative electrode plate, and optionally having the coating according to the present application on at least one side of the separator close to the negative electrode plate, thereby enabling the secondary battery according to the present application to simultaneously achieve high energy density, high thermal safety performance, long cycle life, and good dynamic performance.

[0192] [Positive electrode plate] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector and containing a positive electrode active material. For example, the positive electrode current collector has two opposite surfaces in its own thickness direction, and the positive electrode film layer is provided on either one or both of the two opposite surfaces of the positive electrode current collector.

[0193] When the secondary battery of the present application is a lithium ion battery, the positive electrode active material may include, but is not limited to, at least one of a lithium-containing transition metal oxide, a lithium-containing phosphate, and their modified compounds. Examples of the lithium transition metal oxide 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 modified compounds. Examples of the lithium-containing phosphate may include, but are not limited to, at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their modified compounds.

[0194] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material used in the lithium ion battery may include at least one of a lithium transition metal oxide and its modified compounds having the general formula Li a Ni b Co c M d O e A f where 0.8 ≦ a ≦ 1.2, 0.5 ≦ b < 1, 0 < c < 1, 0 < d < 1, 1 ≦ e ≦ 2, 0 ≦ f ≦ 1, M is at least one selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is at least one selected from N, F, S, and Cl.

[0195] For example, the positive electrode active materials used in lithium ion batteries are LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 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 It may contain at least one of O2, LiFePO4, and LiMnPO4.

[0196] When the secondary battery of the present application is a sodium ion battery, the positive electrode active material may include at least one of a sodium-containing transition metal oxide, a polyanion material (e.g., phosphate, fluorophosphate, pyrophosphate, sulfate, etc.), and a Prussian blue-based material, but is not limited thereto.

[0197] For example, the positive electrode active materials used in sodium ion batteries are NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, 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-based materials, general formula X p M' q (PO4) r O x Y 3-x The compound may contain at least one material represented by the general formula X p M' q (PO4)r O x Y 3-x In, 0 <p≦4、0<q≦2、1≦r≦3、0≦x≦2であり、Xは、H + , Li + , Na + , K. + and NH4 + wherein M' is a transition metal cation, optionally at least one of V, Ti, Mn, Fe, Co, Ni, Cu, and Zn; and Y is a halogen anion, optionally at least one of F, Cl, and Br.

[0198] In the present application, the modifying compound for each of the positive electrode active materials is a compound that modifies the positive electrode active material by doping and / or surface coating.

[0199] In some embodiments, the positive electrode film layer further optionally includes a positive electrode conductive agent. The present application does not particularly limit the type of the positive electrode conductive agent, and the positive electrode conductive agent may include at least one of 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%.

[0200] In some embodiments, the positive electrode film layer optionally further includes a positive electrode adhesive. The present application is not particularly limited to the type of the positive electrode adhesive. For example, the positive electrode adhesive 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 a fluorine-containing acrylate resin. In some embodiments, the mass percentage content of the positive electrode adhesive is ≦5 wt %, based on the total weight of the positive electrode film layer.

[0201] In some embodiments, the positive electrode current collector may be a metal foil sheet or a composite current collector. An example of a metal foil sheet is aluminum foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. For example, the metal layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. For example, the polymer base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0202] The positive electrode film layer is typically obtained by coating a positive electrode slurry on a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing a positive electrode active material, an optional conductive agent, an optional adhesive, and any other optional components in a solvent and stirring the resulting mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0203] [Negative electrode plate] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces facing each other in a thickness direction thereof, and the negative electrode film layer is disposed on one or both of the two facing surfaces of the negative electrode current collector.

[0204] The negative electrode active material may be any negative electrode active material for secondary batteries known in the art. For 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, a silicone-based material, a tin-based material, and lithium titanate. The silicone-based material may include at least one of a silicone element, a silicone oxide, a silicone carbon composite, a silicone nitrogen composite, and a silicone alloy material. The tin-based material may include at least one of a tin element, a tin oxide, and a tin alloy material.

[0205] In some embodiments, the negative electrode film layer optionally further includes a negative electrode conductive agent. The present application does not particularly limit the type of the negative electrode conductive agent, and for example, the negative electrode conductive agent may include at least one of 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%.

[0206] In some embodiments, the negative electrode film layer optionally further includes a negative electrode adhesive. The present application is not particularly limited to the type of the negative electrode adhesive, and for example, the negative electrode adhesive may include at least one of styrene butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-soluble acrylic acid-based resin (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 content of the negative electrode adhesive is ≦5 wt %, based on the total weight of the negative electrode film layer.

[0207] In some embodiments, the negative electrode membrane layer further optionally contains other additives. For example, the other additives may include a thickener, such as carboxymethylcellulose sodium (CMC-Na), a PTC thermistor material, etc. In some embodiments, the mass percentage content of the other additives is ≦2 wt %, based on the total weight of the negative electrode membrane layer.

[0208] In some embodiments, the negative electrode current collector may be a metal foil sheet or a composite current collector. An example of a metal foil sheet is copper foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. For example, the metal layer may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. For example, the polymer base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0209] The negative electrode film layer is typically obtained by coating a negative electrode slurry on a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, an optional conductive agent, an optional adhesive, and other optional auxiliary agents in a solvent and stirring the resulting mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0210] The negative electrode plate does not exclude additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode plate described herein further includes a conductive undercoating (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 plate described herein further includes a protective layer covering the surface of the negative electrode film layer.

[0211] [Electrolyte] During the charge and discharge process of the secondary battery, active ions are absorbed and released by moving back and forth between the positive and negative electrodes, and the electrolyte serves to conduct the active ions between the positive and negative electrodes. The present application does not particularly limit the type of electrolyte, and it can be selected according to actual needs.

[0212] The electrolyte solution includes an electrolyte salt and a solvent, and the types of the electrolyte salt and the solvent are not specifically limited and may be selected according to actual needs.

[0213] When the secondary battery of the present application is a lithium-ion battery, for example, the electrolyte salt may include at least one of lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPOF), lithium difluorobis(oxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP), but is not limited thereto.

[0214] When the secondary battery of the present application is a sodium-ion battery, for example, the electrolyte salt may include at least one of sodium hexafluorophosphate (NaPF), sodium tetrafluoroborate (NaBF), sodium perchlorate (NaClO), sodium hexafluoroarsenate (NaAsF), sodium bisfluorosulfonylimide (NaFSI), sodium bistrifluoromethanesulfonylimide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluoro(oxalato)borate (NaDFOB), sodium bis(oxalato)borate (NaBOB), sodium difluorophosphate (NaPOF), sodium difluorobis(oxalato)phosphate (NaDFOP), and sodium tetrafluoro(oxalato)phosphate (NaTFOP).

[0215] By way of 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), butylene 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), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0216] In some embodiments, the electrolyte solution may further optionally contain additives. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, and / or an additive that can improve some battery performance, such as an additive that improves the overcharge performance of the battery, an additive that improves the high-temperature performance of the battery, or an additive that improves the low-temperature power performance of the battery.

[0217] In some embodiments, the positive electrode plate, the separator, and the negative electrode plate may be fabricated into an electrode assembly by a winding process and / or a stacking process.

[0218] In some embodiments, the secondary battery may include an exterior body, which may be used to package the electrode assembly and the electrolyte.

[0219] In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the secondary battery may be a pouch, such as a bag-shaped pouch. The material of the pouch may be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0220] The present application does not particularly limit the shape of the secondary battery, and it may be cylindrical, rectangular, or any other shape. Figure 1 shows an example of a secondary battery 5 with a rectangular structure.

[0221] In some embodiments, as shown in FIG. 2 , the exterior body may include a case 51 and a cover plate 53. The case 51 may include a bottom plate and side plates connected to the bottom plate, which together form a surrounding accommodating cavity. The case 51 has an opening communicating with the accommodating cavity, and the cover plate 53 is used to cover the opening and seal the accommodating cavity. The positive electrode plate, the negative electrode plate, and the separator may be formed into an electrode assembly 52 through a winding process and / or a stacking process. The electrode assembly 52 is packaged in the accommodating cavity. An electrolyte is impregnated into the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more and can be adjusted as needed.

[0222] The method for manufacturing the secondary battery of the present application is well known. In some embodiments, a secondary battery can be formed by assembling a positive electrode plate, a separator, a negative electrode plate, and an electrolyte. For example, the positive electrode plate, the separator, and the negative electrode plate can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly can be placed in an outer casing, dried, and then injected with an electrolyte. The secondary battery can be obtained through processes such as vacuum packaging, standing, chemical formation, and shaping.

[0223] In some embodiments of the present application, the secondary battery according to the present application can be assembled into a battery module, and the number of secondary batteries included in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0224] Fig. 3 is a schematic diagram of an example battery module 4. As shown in Fig. 3, in the battery module 4, a plurality of secondary batteries 5 may be arranged in order along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed by fasteners.

[0225] Optionally, the battery module 4 may further include a housing having an accommodating space, and the plurality of secondary batteries 5 are accommodated in this accommodating space.

[0226] In some embodiments, the battery modules may be further assembled into a battery pack, and the number of battery modules included in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0227] 4 and 5 are schematic diagrams of an example battery pack 1. As shown in FIGS. 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 installed in the battery box. The battery box includes an upper housing 2 and a lower housing 3, and the upper housing 2 covers the lower housing 3 and is used to form a sealed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0228] power consumption equipment A fourth aspect of the present application provides a power consuming device, the power consuming device including at least one of the secondary battery, battery module, or battery pack of the present application. The secondary battery, battery module, or battery pack may be used as a power source for the power consuming device or as an energy storage unit for the power consuming device. The power consuming device may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0229] The power consumption device may select a secondary battery, a battery module, or a battery pack according to its usage needs.

[0230] 6 is a schematic diagram of an example power consuming device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, that may employ a battery pack or battery module to meet the high power and high energy density demands of the power consuming device.

[0231] Other examples of power consuming devices include mobile phones, tablet computers, notebook computers, etc. These power consuming devices generally require a thin design and can employ secondary batteries as their power source.

[0232] Example The following examples will more specifically describe the contents disclosed in this application, and these examples are for illustrative purposes only, as various modifications and variations within the scope of the contents disclosed in this application will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages and ratios reported in the following examples are by weight, and all reagents used in the examples can be obtained commercially or synthesized according to conventional methods and can be used directly without further treatment, and all equipment used in the examples can be obtained commercially.

[0233] Production of nanocellulose C1 The cotton linters were opened in a cotton opener to remove scum, then steamed in a 5 wt% NaOH aqueous solution at 150°C for 2 hours, then sequentially washed with water to remove impurities (washed three times), bleached with sodium hypochlorite, washed with dilute hydrochloric acid to remove impurities, washed with water to remove impurities (washed once), drained, and dried in an air stream to obtain cotton cellulose powder with a whiteness of ≥85%.

[0234] 1 kg of the obtained cotton cellulose powder is mixed with 30 kg of 60 wt% aqueous sulfuric acid solution and reacted at 55-60°C for 1.5 hours. After the reaction is completed, the mixture is washed with water to remove impurities (washed three times), filtered, and the acid is removed to remove impurities.

[0235] The pH was then adjusted to neutral with 10 wt% NaOH aqueous solution, followed by grinding with a grinder and nanoscale cutting using a high-pressure homogenizer to obtain nanocellulose C1 with sulfonic acid group-modified groups having an average length of 350 nm and an average diameter of 18 nm, and the molar ratio of sulfonic acid groups to hydroxyl groups was 5:3.

[0236] Production of nanocellulose C2 to C4 Nanocelluloses C2 to C4 were produced in a similar manner to nanocellulose C1, with the details of the differences being shown in Table 1. During the production process, nanocelluloses with different average diameters and / or lengths can be obtained by adjusting the grinder processing parameters and the cutting parameters of the high-pressure homogenizer equipment.

[0237] Production of nanocellulose C5 The cotton linters were opened in a cotton opener to remove scum, then steamed in 5 wt% NaOH aqueous solution at 150°C for 2 hours, then sequentially washed with water to remove impurities (three washes), bleached with sodium hypochlorite, washed with dilute hydrochloric acid to remove impurities, and washed with water to remove impurities (one wash). The water was drained and the cotton was dried in a stream of air to yield a cotton cellulose powder with a whiteness of ≥85%. The resulting cotton cellulose powder was mixed with 20 wt% NaOH aqueous solution at 10°C, stirred for 2 hours, filtered, and washed twice to yield a cellulose powder.

[0238] 50 g of the obtained cellulose powder and 200 g of urea were placed in a three-neck reactor equipped with an oil-water separator. After the urea was dissolved, 5 g of xylene was added, and the mixture was heated to 137°C with stirring. The reaction was stopped after 4 hours of reaction, followed by washing with water (three times), filtration, and drying to obtain cellulose urethane.

[0239] The obtained cellulose urethane was dissolved in a 5 wt% NaOH aqueous solution to obtain a uniform cellulose urethane solution, which was then polished with a polishing machine and further subjected to nanoscale cutting using a high-pressure homogenizer to obtain nanocellulose C5 with amine-modified groups having an average length of 350 nm and an average diameter of 18 nm, and the molar ratio of amine groups to hydroxyl groups was 4:3.

[0240] Production of nanocellulose C6 Unmodified nanocellulose, with an average length of 350 nm and an average diameter of 18 nm, product number CNWS-50, purchased from Zhongke Leiming (Beijing) Technology Co., Ltd., 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.

[0241] The molar ratio of modifying groups to hydroxyl groups in nanocelluloses C1-C5 can be measured using the following method: The hydroxyl group value (the number of milligrams of potassium hydroxide equivalent to the hydroxyl group content per gram of sample) of raw cellulose and nanocelluloses C1-C5 is measured according to the phthalic anhydride method in GB / T 12008.3-2009. The resulting value is expressed in mg KOH / g, which is then converted to mmol / g to represent the hydroxyl group content. Subtracting the hydroxyl group content of nanocelluloses C1-C5 from the hydroxyl group content of the raw cellulose yields the modifying group content (i.e., the content of modified hydroxyl groups), which can then be used to calculate the molar ratio of modifying groups to hydroxyl groups.

[0242] [Table 1]

[0243] Example 1 Separator manufacturing Provide a PE porous substrate: thickness is 5.2 μm.

[0244] Preparation of coating slurry: Mix the above-prepared nanocellulose C1, the first filler, the second filler, and the adhesive aqueous solution-type polyacrylic acid uniformly in a mass ratio of 16.0:62.5:20.0:1.5 with an appropriate amount of solvent deionized water to obtain the coating slurry.

[0245] The first filler is a mixture of aluminum oxide primary particles (average particle size 50 nm, content 12.5 wt% based on the total weight of the coating) and aluminum oxide secondary particles (average particle size 100 nm, content 50 wt% based on the total weight of the coating), and the contents of the α crystal form, the θ crystal form, the γ crystal form, and the η crystal form in the first filler are 1.5 wt%, 70.7 wt%, 27.3 wt%, and 0.5 wt%, based on the total weight of the first filler, respectively. The second filler is aluminum oxide primary particles (average particle size 240 nm), and the crystalline form of the second filler is mainly the α crystal form, and the mass proportion of the second filler is 99.5% or more based on the total weight of the second filler.

[0246] Coating: The prepared coating slurry was applied to two surfaces of the PE porous substrate using a coater, and then dried and slit to obtain a separator. The thickness of the coating on one side of the PE porous substrate was 1.0 μm.

[0247] Positive electrode plate manufacturing LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2 (NCM811), carbon black (Super P) as a conductive agent, and polyvinylidene fluoride (PVDF) as an adhesive were uniformly mixed in an appropriate amount of solvent N-methylpyrrolidone (NMP) in a mass ratio of 96.2:2.7:1.1 to obtain a positive electrode slurry. The positive electrode slurry was then applied to a positive electrode current collector aluminum foil, and after processes such as drying, cold pressing, slitting, and cutting, a positive electrode plate was obtained.

[0248] Negative electrode plate manufacturing The negative electrode active material, artificial graphite, the conductive agent, carbon black (Super P), the adhesive, styrene butadiene rubber (SBR) and carboxymethyl cellulose sodium (CMC-Na), were uniformly mixed in a mass ratio of 96.4:0.7:1.8:1.1 in an appropriate amount of deionized water solvent to obtain a negative electrode slurry. The negative electrode slurry was then applied to a negative electrode current collector copper foil, and the mixture was dried, cold pressed, slit, and cut to obtain a negative electrode plate.

[0249] Electrolyte production Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 30:70 to obtain an organic solvent, and thoroughly dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L.

[0250] Secondary battery manufacturing A positive electrode plate, a separator, and a negative electrode plate were stacked in this order and wound to obtain an electrode assembly. The electrode assembly was then placed in an outer casing, dried, and then an electrolyte was added. After undergoing processes such as vacuum packaging, standing, chemical conversion, and shaping, a secondary battery was obtained.

[0251] Examples 2-4 The secondary battery was manufactured in a similar manner to that of Example 1, except that the particle size of the first filler was different in the manufacture of the separator. The specific parameter details are as shown in Table 2.

[0252] Examples 5-14 The secondary battery was manufactured in a manner similar to that of Example 1, except that the types and / or amounts of nanocellulose and the first filler used in the separator were different. The specific parameter details are as shown in Table 2.

[0253] Example 15 The secondary battery was manufactured in a manner similar to that of Example 1, except that in the manufacture of the separator, the first filler was aluminum oxide secondary particles with an average particle size of 100 nm, and the contents of the α crystal form, θ crystal form, γ crystal form, and η crystal form in the first filler were 1.5 wt%, 70.7 wt%, 27.3 wt%, and 0.5 wt%, respectively, based on the total weight of the first filler.

[0254] Example 16 The secondary battery was fabricated in a manner similar to that of Example 1, except that aluminum oxide primary particles were used as the first filler in the separator fabrication. The average particle size of the aluminum oxide primary particles was 50 nm, and the contents of the α crystal form, θ crystal form, γ crystal form, and η crystal form were 1.5 wt%, 70.7 wt%, 27.3 wt%, and 0.5 wt%, respectively, based on the total weight of the aluminum oxide primary particles.

[0255] Comparative Example 1 The secondary battery was manufactured in the same manner as in Example 1, except for the manufacturing process of the separator.

[0256] Provide a PE porous substrate: thickness is 5.2 μm.

[0257] Preparation of coating slurry: Aluminum oxide primary particles (average particle size 700 nm, α-crystalline mass fraction ≥ 99.5%) and adhesive were mixed in a mass ratio of 94:6, and then dissolved in deionized water to obtain a coating slurry.

[0258] Coating: The prepared coating slurry was applied to two surfaces of the PE porous substrate using a coater, and then dried and slit to obtain a separator. The thickness of the coating on one side of the PE porous substrate was 1.8 μm.

[0259] Testing section (1) Separator heat shrinkage test Sample preparation: The separator prepared above is punched into samples with a width of 50 mm and a length of 100 mm using a press, and five parallel samples are placed on A4 paper and fixed in place. Next, the A4 paper containing the samples is placed on a cardboard box with a thickness of 1 mm to 5 mm.

[0260] Sample test: Place an A4 sheet of paper on a piece of cardboard and place it in a ventilated oven. Set the oven temperature to 150°C. After the temperature reaches the set temperature and stabilizes for 30 minutes, start timing. After the set time (1 hour in this application) is reached, measure the length and width of the separator and mark the values as a and b respectively.

[0261] Calculation of heat shrinkage rate: Machine direction (MD) heat shrinkage rate = [(100-a) / 100] x 100%, Transverse direction (TD) heat shrinkage rate = [(50-b) / 50] x 100%, the average value of five parallel samples is taken as the test result.

[0262] (2) Separator ionic conductivity test The ionic conductivity of the separator was measured using AC impedance spectroscopy. Specifically, the separator was cut into circular sheets of a certain area, dried, and then placed between two stainless steel electrodes. After absorbing a sufficient amount of electrolyte, the sheets were sealed to form a button cell battery. An AC impedance spectroscopy experiment was performed using an electrochemical workstation, a Shanghai Chenhua CHI 660C electrochemical workstation, with an AC signal frequency range of 0.01 Hz to 1 MHz and a sinusoidal potential amplitude of 5 mV. For accuracy, the average value of five parallel samples was taken as the test result.

[0263] The electrolyte solution used was prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a mass ratio of 30:50:20 to obtain an organic solvent, and then dissolving thoroughly dried LiPF6 in the organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L.

[0264] (3) Hot box test of secondary batteries At 25°C, the rechargeable batteries were charged at a constant current of 1C to 4.2V, and then continued constant voltage charging until the current reached ≤0.05C. After 5 minutes of rest, each rechargeable battery was then tested in a DHG-9070A DHG series high-temperature oven with a fixture. The temperature was increased from room temperature to 80°C + / -2°C at a rate of 5°C / min and maintained at that temperature for 30 minutes. The temperature was then increased at a rate of 5°C / min, with each 5°C increase being maintained for 30 minutes. The temperature change on the surface of the rechargeable battery was monitored during the heating process. The oven temperature at which the temperature began to rise rapidly was the hot box expiration temperature of the rechargeable battery. A higher hot box expiration temperature indicates better thermal safety performance of the rechargeable battery. For accuracy, the average value of five parallel samples was taken as the test result.

[0265] 4. Secondary battery cycle performance test At 25°C, the secondary battery was charged at a constant current of 1C to 4.2V, and then continued to be charged at a constant voltage of 0.05C. At this point, the secondary battery was fully charged. The charge capacity at this point, i.e., the first-cycle charge capacity, was recorded. After allowing the secondary battery to stand for 5 minutes, it was discharged at a constant current of 1C to 2.8V. This constitutes one cycle of charge-discharge, and the discharge capacity at this point, i.e., the first-cycle discharge capacity, was recorded. The secondary battery was subjected to a cycle charge-discharge test according to the above method, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) of the secondary battery after 1000 cycles at 25°C = discharge capacity after 1000 cycles / discharge capacity at first cycle × 100%. For accuracy, the average value of five parallel samples was taken as the test result.

[0266] As can be seen from Table 2, by applying a coating containing nanocellulose (which forms a three-dimensional skeletal structure) and a first filler with an average particle size of 200 nm or less to both surfaces of the separator's porous substrate, the separator can be made to have both low thermal shrinkage and high ionic conductivity, and the secondary battery can be made to have both high thermal safety performance and good cycle performance.

[0267] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiments that have substantially the same configuration as the technical idea and achieve the same effects within the scope of the technical solution of the present application are included within the technical scope of the present application. In addition, various modifications that a person skilled in the art can make to the embodiments and other methods constructed by combining some of the components of the embodiments are also included within the scope of the present application, as long as they do not deviate from the spirit of the present application. [Explanation of symbols]

[0268] 1: battery pack, 2: upper housing, 3: lower housing, 4: battery module, 5: secondary battery, 51: case, 52: electrode assembly, 53: cover plate.

[0269] [Table 2A] [Table 2B]

Claims

1. A separator comprising a porous substrate and a coating disposed on at least one surface of the porous substrate, wherein the coating comprises a three-dimensional framework and a first filler, and at least a portion of the first filler is filled in the three-dimensional framework. and the first filler has an average particle size of 200 nm or less.

2. 2. The separator according to claim 1, wherein the first filler has an average particle size of 15 nm to 180 nm, and optionally 30 nm to 150 nm.

3. the first filler includes at least one of primary particles and secondary particles; Optionally, the first filler comprises a combination of primary particles and secondary particles; Optionally, based on the total weight of the first filler, the content of the first filler in the form of primary particles is smaller than the content of the first filler in the form of secondary particles; Optionally, based on the total weight of the first filler, the content of the first filler in the form of primary particles is 30 wt % or less; Preferably, the average particle size of the first filler in the form of primary particles is 15 nm to 80 nm, more preferably 30 nm to 65 nm; 3. The separator according to claim 1, wherein the average particle size of the first filler in the form of secondary particles is preferably 50 nm to 200 nm, and more preferably 55 nm to 150 nm.

4. The BET specific surface area of the first filler is ≥ 25 m ２ / g, and optionally 30m ２ / g~65m ２ The separator according to claim 1 , wherein the tensile strength is 1 / g.

5. The content of the first filler is ≧50 wt %, optionally 60 wt % to 90 wt %, based on the total weight of the coating; and / or 5. The separator according to claim 1, wherein the content of the three-dimensional framework structure is 5 wt % to 40 wt %, and optionally 8 wt % to 25 wt %, based on the total weight of the coating.

6. the first filler includes at least one of inorganic particles and organic particles; Alternatively, the inorganic particles include at least one of boehmite, aluminum oxide, barium sulfate, magnesium oxide, magnesium hydroxide, silicone oxide, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, zirconium titanate, barium titanate, and magnesium fluoride; more preferably, the inorganic particles include at least one of boehmite, aluminum oxide, barium sulfate, magnesium oxide, silicone oxide, titanium oxide, zinc oxide, cerium oxide, and barium titanate; 6. The separator according to claim 1, wherein the organic particles optionally include at least one of polystyrene particles, polyacrylic wax particles, melamine formaldehyde resin particles, phenolic resin particles, polyester particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, and polyaryletherketone particles.

7. The first filler includes inorganic particles, and the crystalline form of the inorganic particles includes at least one of a θ crystalline form, a γ crystalline form, and an η crystalline form; Optionally, the crystalline form of the inorganic particles includes at least one of a θ crystalline form and a γ crystalline form; Preferably, the content of the inorganic particles having the θ crystal form is ≧50 wt %, more preferably 55 wt % to 84 wt %, based on the total weight of the inorganic particles in the first filler; Preferably, the content of inorganic particles in the gamma crystalline form is ≧10 wt %, more preferably 15 wt % to 44 wt %, based on the total weight of the inorganic particles in the first filler; 7. The separator according to claim 1, wherein the content of the inorganic particles of the η crystalline form is preferably ≦5 wt %, and more preferably ≦2.5 wt %, based on the total weight of the inorganic particles in the first filler.

8. The separator according to claim 1 , wherein the three-dimensional skeletal structure is formed of fibrous material, and the shape of the fibrous material selectively includes at least one of a rod shape, a tubular shape, a rod shape, and a fiber shape.

9. the average diameter of the material constituting the three-dimensional framework is ≦40 nm, optionally 10 nm to 35 nm; and / or the average length of the material constituting the three-dimensional framework is between 100 nm and 600 nm, and optionally between 200 nm and 500 nm; and / or 9. The separator according to claim 1, wherein the aspect ratio of the material constituting the three-dimensional framework is 5 to 60, and optionally 10 to 30.

10. the material constituting the three-dimensional framework includes at least one of an organic material and an inorganic material; Optionally, the organic material comprises at least one of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers; and optionally, the nanocellulose comprises at least one of cellulose nanofibers, cellulose nanocrystals, and bacterial nanocellulose; 10. The separator according to claim 1, wherein the inorganic material optionally includes at least one of halloysite nanotubes, nanorod-shaped aluminum oxide, nanorod-shaped boehmite, nanorod-shaped silica, and glass fibers.

11. The material constituting the three-dimensional framework structure includes nanocellulose, and the nanocellulose includes at least one of unmodified nanocellulose and modified nanocellulose; Optionally, the modified nanocellulose comprises a modifying group, the modifying group comprising at least one of an amine group, a carboxyl group, an aldehyde group, a sulfonic acid group, a boric acid group, and a phosphate group, and further optionally comprising at least one of a sulfonic acid group, a boric acid group, and a phosphate group; Optionally, the modified nanocellulose comprises a hydroxyl group and a modifying group, and the molar ratio of the modifying group to the hydroxyl group is 1:4 to 4:1, and further optionally 2:3 to 7:

3. The separator of any one of claims 1 to 10.

12. 12. The separator according to claim 1, wherein the material constituting the three-dimensional skeletal structure contains a sulfonic acid group, and the content of sulfur element in the material constituting the three-dimensional skeletal structure is ≧0.1 wt %, and optionally 0.2 wt % to 0.5 wt %, based on the total weight of the material constituting the three-dimensional skeletal structure.

13. The coating further comprises a second filler, at least a portion of the second filler being embedded in the coating, and the average particle size of the first filler is d １ and the average particle size of the second filler is d ２ and d ２ / d １ The separator of claim 1 , wherein the ρ is >1.

14. The first filler includes at least one of primary particles and secondary particles, and the average particle size of the first filler in the form of primary particles is defined as d １１ and the average particle size of the first filler in the form of secondary particles is represented by d １２ He wrote, 3.0≦d ２ / d １１ ≦10.0, and optionally 3.5≦d ２ / d １１ ≦8.0, and / or 1.2≦d ２ / d １２ ≦6.0, and optionally 2.0≦d ２ / d １２ 14. The separator of claim 13, wherein the .lambda.

15. The second filler is (1) The second filler has a primary particle form; (2) the average particle size of the second filler is 120 nm to 350 nm, and optionally 150 nm to 300 nm; (3) The BET specific surface area of the second filler is ≦20 m ２ / g, and optionally 6m ２ / g to 15m ２ / g, and (4) The second filler contains at least one of inorganic particles and organic particles; (5) The second filler contains inorganic particles in the form of primary particles, and the crystalline form of the inorganic particles in the form of primary particles includes at least one of an α-crystalline form and a γ-crystalline form, and selectively includes the α-crystalline form; (6) The second filler comprises inorganic particles in the form of primary particles, and the crystalline form of the inorganic particles in the form of primary particles comprises an α-crystalline form, and the content of the α-crystalline form is ≧70 wt %, and optionally 85 wt % to 100 wt %, based on the total weight of the inorganic particles in the form of primary particles in the second filler; (7) The separator according to claim 13 or 14, wherein the content of the second filler is ≦30 wt % based on the total weight of the coating, and optionally 5 wt % to 25 wt %.

16. the coating further comprises a non-particulate adhesive; Optionally, the non-particulate adhesive comprises a water-based adhesive; Optionally, the content of the non-particulate adhesive in the coating is ≦2 wt %, based on the total weight of the coating.

17. the thickness of the porous substrate is ≦6 μm, optionally 3 μm to 5 μm; and / or The separator of any one of claims 1 to 16, wherein the coating has a thickness of ≦2 μm, optionally between 0.5 μm and 1.5 μm.

18. the separator further includes an adhesive layer disposed on at least a portion of the surface of the coating, the adhesive layer including a particulate adhesive; Optionally, the particulate adhesive includes at least one of an acrylate-based monomer homopolymer or copolymer, an acrylic-based monomer homopolymer or copolymer, and a fluorine-containing olefin monomer homopolymer or copolymer.

19. The separator is (1) The separator has a longitudinal heat shrinkage rate of ≦6%, optionally 0.5% to 4%, at 150°C for 1 hour; (2) The separator has a transverse heat shrinkage rate of ≦6%, optionally 0.5% to 4%, at 150°C for 1 hour; (3) The separator has a longitudinal tensile strength of ≥ 2000 kg / cm ２ and optionally 2500 kg / cm ２ ~4500kg / cm ２ and (4) The separator has a lateral tensile strength of ≥ 2000 kg / cm ２ and optionally 2500 kg / cm ２ ~4500kg / cm ２ and (5) The wet length of the separator is ≧30 mm, and optionally 30 mm to 80 mm; (6) The wetting speed of the separator is ≧3 mm / s, and optionally 3 mm / s to 10 mm / s; (7) The separator has an air permeability of ≦300 s / 100 mL, and optionally 100 s / 100 mL to 230 s / 100 mL; (8) The separator according to any one of claims 1 to 18, which satisfies at least one of the conditions that the separator has a voltage breakdown strength of ≥ 1 KV.

20. 20. A method for producing a separator according to claim 1, the method comprising the steps of: providing a porous substrate; mixing a material for constituting a three-dimensional skeletal structure and a first filler in a predetermined ratio in a solvent to prepare a coating slurry; and applying the coating slurry to at least one surface of the porous substrate and drying it to obtain a separator, wherein the separator comprises a porous substrate and a coating disposed on at least one surface of the porous substrate, the coating comprising a three-dimensional skeletal structure and a first filler, at least a portion of the first filler being filled in the three-dimensional skeletal structure, and an average particle size of the first filler being 200 nm or less.

21. The coating slurry further comprises a second filler, and the average particle size of the first filler is d １ and the average particle size of the second filler is d ２ and d ２ / d １ 21. The method of claim 20, wherein:

22. 22. A secondary battery comprising a separator according to any one of claims 1 to 19 or a separator produced by the method according to any one of claims 20 to 21.

23. 23. A power consuming device comprising the secondary battery of claim 22.

Images