Separator, its manufacturing method, and related secondary batteries and power consumption devices.

Abstract

The present application provides a separator including a porous substrate and a coating layer provided on at least one surface of the porous substrate, a manufacturing method thereof, and a secondary battery and a power consumption device related thereto, the coating layer including nanocellulose and a filler, the moisture content of the separator being Appm, the thickness of the coating layer being Hμm, and the separator satisfying 250≦A / H≦1500. The separator provided in the present application has characteristics such as excellent heat resistance, low moisture content, and good wettability with respect to the electrolyte, and therefore a secondary battery using the separator can have both high energy density, high thermal safety performance, and long life.

Description

[Technical Field] 【0001】 This application claims priority to patent application PCT / CN2022 / 101261, filed on 24 June 2022, titled "Separator, Method for Manufacturing the Same, and Related Secondary Battery, Power Consumption Device," all of which are incorporated herein by reference. 【0002】 This application belongs to the field of battery technology, and more specifically, relates to separators, methods for manufacturing the same, and related secondary batteries and power consumption devices. [Background technology] 【0003】 In recent years, rechargeable batteries have been widely used in many fields, including energy storage and power systems such as hydroelectric, thermal, wind, and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. With the application and widespread use of rechargeable batteries, their lifespan and safety issues, particularly thermal safety, are receiving increasing attention. However, current methods for improving the thermal safety performance of rechargeable batteries can sometimes compromise the balance of the battery's energy density. Therefore, achieving high energy density, high thermal safety performance, and long lifespan in rechargeable batteries has become a crucial design challenge. [Overview of the project] 【0004】 This application aims to provide a separator, a method for manufacturing the same, and related secondary batteries and power consumption devices. The separator has features such as excellent heat resistance, low moisture content, and good wetting properties with respect to the electrolyte, thereby enabling secondary batteries using the separator to possess high energy density, high thermal safety performance, and a long lifespan. 【0005】 A first aspect of the present application is a separator including a porous substrate and a coating layer provided on at least one surface of the porous substrate, wherein the coating layer includes nanocellulose and a filler, the water content of the separator is Appm, the thickness of the coating layer is H μm, and the separator satisfies 250 ≦ A / H ≦ 1500. 【0006】 As a result of intensive research, the inventors of the present application have found that by providing a coating layer containing nanocellulose and a filler on at least one surface of the porous substrate of the separator and controlling the ratio of the water content of the separator to the thickness of the coating layer within the above specific range, the separator can be made to have high heat resistance, low water content, and good electrolyte wetting properties. 【0007】 In any embodiment of the present application, 500 ≦ A / H ≦ 1500, preferably 600 ≦ A / H ≦ 1000. This contributes to the coating layer having a more stable network structure of space and a more appropriate content of hydroxyl functional groups, enabling the separator to have high heat resistance, low water content, and good electrolyte wetting properties, and enabling the secondary battery to have high thermal safety performance, long cycle life, and long storage life. 【0008】 In any embodiment of the present application, 400 ≦ A ≦ 1000, preferably 500 ≦ A ≦ 800. This contributes to the coating layer having a more stable network structure of space and a more appropriate content of hydroxyl functional groups, enabling the separator to better have high heat resistance, low water content, and good electrolyte wetting properties, and further improving the cycle life and storage life of the secondary battery. 【0009】 In any embodiment of the present application, 0 < H ≦ 1.5, preferably 0.2 ≦ H ≦ 0.8. This contributes to improving the energy density of the secondary battery. 【0010】 In any embodiment of this application, the nanocellulose comprises at least one of cellulose nanofibers, cellulose nanowhiskers, or bacterial nanocellulose, preferably cellulose nanowhiskers. Cellulose nanowhiskers can have a high degree of crystallinity, which can reduce their hydrophilicity and is advantageous for water removal during the drying process, and the separator of this application can have a low water content. 【0011】 In any embodiment of this application, the nanocellulose comprises at least one of unmodified nanocellulose and modified nanocellulose, and is preferably modified nanocellulose. 【0012】 In any embodiment of this application, the modified nanocellulose comprises a modifying group, wherein the modifying group comprises at least one of an amine group, a carboxylic acid group, an aldehyde group, a sulfonic acid group, a boric acid group, and a phosphoric acid group, preferably at least one of a sulfonic acid group, a boric acid group, and a phosphoric acid group. When the nanocellulose has the above-mentioned specific modifying group, the heat resistance of the separator can be effectively improved, thereby improving the thermal safety performance of the secondary battery. At the same time, assuming the separator has good electrolyte wetting characteristics, it is also advantageous to have a low moisture content, which can further improve the electrochemical performance of the secondary battery. 【0013】 In any embodiment of this application, the modified nanocellulose comprises hydroxyl groups and modifying groups, and the molar ratio of the modifying groups to the hydroxyl groups is 1:4 to 4:1, preferably 2:3 to 7:3. When the molar ratio of the modifying groups to the hydroxyl groups is within an appropriate range, it can further improve the heat resistance and ion transport properties of the separator and contribute to the separator having a low moisture content. 【0014】 In any embodiment of this application, the aspect ratio of the nanocellulose is 5 to 80, preferably 10 to 40. When the aspect ratio of the nanocellulose is within an appropriate range, the heat resistance and ion transport properties of the separator can be further improved. 【0015】 In any embodiment of this application, the average diameter of the nanocellulose is 10 nm to 40 nm, preferably 10 nm to 35 nm. When the average diameter of the nanocellulose is within an appropriate range, the heat resistance, ion transport characteristics, and voltage breakdown characteristics of the separator can be further improved. 【0016】 In any embodiment of this application, the average length of the nanocellulose is 100 nm to 600 nm, preferably 200 nm to 500 nm. When the average length of the nanocellulose is within an appropriate range, the heat resistance and ion transport properties of the separator can be further improved. 【0017】 In any embodiment of this application, the weight-average molecular weight of the nanocellulose is 10,000 to 60,000, preferably 30,000 to 50,000. 【0018】 In any embodiment of this application, the equilibrium degree of polymerization of the nanocellulose is 150DP to 300DP, preferably 200DP to 250DP. 【0019】 When the weight-average molecular weight and / or degree of polymerization of nanocellulose are within an appropriate range, it is possible to avoid the nanocellulose clogging the pore structure of the separator, as well as to maintain an appropriate viscosity for the coating layer slurry. This results in superior fluidity and wetting properties of the slurry during application, and is further advantageous for improving the quality of the coating layer. 【0020】 In any embodiment of this application, the content of nanocellulose in the coating layer is 6 wt% to 35 wt%, preferably 10 wt% to 30 wt%, based on the total weight of the coating layer. 【0021】 In any embodiment of this application, the content of the filler in the coating layer is 60 wt% or more, preferably 65 wt% to 90 wt%, based on the total weight of the coating layer. 【0022】 When the content of nanocellulose and / or filler is within an appropriate range, it is possible to ensure that the coating layer slurry has an appropriate viscosity, which is advantageous for application, and it is also advantageous that the separator has a low moisture content and good electrolyte wetting properties, and that the filler and nanocellulose form a stable spatial network structure. 【0023】 In any embodiment of this application, the filler comprises at least one selected from inorganic particles and organic particles. 【0024】 In any embodiment of this application, the decomposition temperature of the filler is 200°C or higher. 【0025】 In any embodiment of this application, the filler comprises a first filler, the first filler becoming a secondary particle topography formed by the aggregation of primary particles. In this case, the nanocellulose also overlaps in the voids between the primary particles constituting the filler of the secondary particle topography, creating an integrated effect by overlapping the nanocellulose and the first filler. This allows the coating layer to have a more stable spatial network structure, and furthermore, the separator can have an appropriate porosity and a stable pore structure, and the separator can also have a low moisture content and good electrolyte wetting properties. 【0026】 In any embodiment of this application, the content of the first filler is 50 wt% to 100 wt%, preferably 90 wt% to 99 wt%, based on the total weight of the filler. 【0027】 In any embodiment of this application, the average particle size Dv50 of the first filler is 200 nm or less, preferably 50 nm to 200 nm. 【0028】 In any embodiment of this application, the BET specific surface area of ​​the first filler is 20 m². 2 It is 1g or more, preferably 25m2 / g~50m 2 It is / g. 【0029】 If the first filler's content, average particle size Dv50, and BET specific surface area are within the above range, it can overlap with nanocellulose to form an integrated effect, thereby allowing the coating layer to have a more stable spatial network structure, and the separator to have better heat resistance and wettability to the electrolyte. 【0030】 In any embodiment of this application, the first filler comprises inorganic particles of secondary particle topography, and the crystalline form of the inorganic particles of secondary particle topography comprises at least two of the α-crystalline form, θ-crystalline form, γ-crystalline form, and crystalline form, preferably at least two of the α-crystalline form, θ-crystalline form, and γ-crystalline form. 【0031】 In any embodiment of this application, the first filler comprises inorganic particles of a secondary particle topography, the crystalline form of the inorganic particles of the secondary particle topography comprises the θ-crystalline form, and the content of the θ-crystalline form is 50 wt% or more, preferably 60 wt% to 85 wt%, based on the total weight of the inorganic particles of the secondary particle topography. 【0032】 By selecting a first filler with a different crystalline form, it is possible to improve at least one of the heat resistance and electrolyte wetting characteristics of the separator. 【0033】 In any embodiment of this application, the filler further comprises a second filler, the second filler being a primary particle topography. This allows the support function of the second filler to be better utilized, improving the heat resistance of the separator, and also contributes to the coating layer having more pore structures and a lower moisture content when used in small quantities. 【0034】 In any embodiment of this application, the content of the second filler is 50 wt% or less, preferably 1 wt% to 10 wt%, based on the total weight of the filler. 【0035】 In any embodiment of this application, the average particle size Dv50 of the second filler is 100 nm to 800 nm, preferably 200 nm to 400 nm. 【0036】 In any embodiment of this application, the BET specific surface area of ​​the second filler is 10 m². 2 / g or less, preferably 4m 2 / g~9m 2 It is / g. 【0037】 If at least one of the following is within the above range for the second filler: content, average particle size Dv50, and BET specific surface area, the second filler can better exert its supporting effect, which is advantageous for moisture discharge during the drying process, allows the coating layer to maintain an appropriate porosity and a stable pore structure during long-term charge-discharge processes, and further improves the ion transport characteristics and wettability of the separator to the electrolyte. 【0038】 In any embodiment of this application, the second filler comprises inorganic particles of primary particle topography, wherein the crystalline form of the inorganic particles of primary particle topography comprises at least one of α-crystalline and γ-crystalline forms, preferably α-crystalline. This can further improve the heat resistance of the separator. 【0039】 In any embodiment of this application, the second filler comprises inorganic particles of a primary particle topography, the crystalline form of the inorganic particles of the primary particle topography comprises an α-crystalline form, and the content of the α-crystalline form is 90 wt% or more, preferably 95 wt% to 100 wt%, based on the total weight of the inorganic particles of the primary particle topography. 【0040】 In any embodiment of the present application, the coating layer further includes a non-particulate adhesive, preferably, the non-particulate adhesive includes an aqueous adhesive. This is advantageous for the preparation and application of the coating layer slurry. 【0041】 In any embodiment of the present application, the content of the non-particulate adhesive in the coating layer is less than 1 wt% based on the total weight of the coating layer. The present application can also maintain high adhesiveness and good ion transport characteristics of the separator on the premise of reducing the usage amount of the adhesive. 【0042】 In any embodiment of the present application, the thickness of the porous substrate is 6 μm or less, preferably 3 μm to 5 μm. This contributes to further improving the energy density of the secondary battery. 【0043】 In any embodiment of the present application, the porosity of the porous substrate is 32% to 48%, preferably 34% to 39%. When the porosity of the porous substrate is within an appropriate range, it is advantageous for further improving the ion transport characteristics of the separator on the premise of ensuring high heat resistance of the separator. At the same time, it can ensure that the secondary battery has a high discharge rate and reduce the self-discharge of the battery. 【0044】 In any embodiment of the present application, the areal density of the coating layer is 0.6 g / m 2 ~1.5 g / m 2 and preferably 0.8 g / m 2 ~1.1 g / m 2 This contributes to the formation of a coating layer with excellent heat resistance. 【0045】 In any embodiment of this application, the separator further comprises an adhesive layer, the adhesive layer provided on at least a portion of the surface of the coating layer, the adhesive layer comprises a particulate adhesive, preferably the particulate adhesive comprises at least one of acrylic acid ester monomer homopolymers or copolymers, acrylic acid monomer homopolymers or copolymers, or fluorine-containing olefin monomer homopolymers or copolymers. The adhesive layer not only prevents the coating layer from falling off and improves the safety performance of the secondary battery, but also improves the interface between the separator and the electrode and improves the cycle performance of the secondary battery. 【0046】 In any embodiment of this application, the longitudinal thermal shrinkage rate of the separator at 150°C for 1 hour is 5% or less, preferably 0.5% to 4%. 【0047】 In any embodiment of this application, the lateral thermal shrinkage rate of the separator at 150°C for 1 hour is 5% or less, preferably 0.5% to 4%. 【0048】 In any embodiment of this application, the puncture strength of the separator is 350 gf or more, preferably 370 gf to 450 gf. 【0049】 In any embodiment of this application, the longitudinal tensile strength of the separator is 2000 kg / cm². 2 The above is preferable, preferably 2500 kg / cm². 2 ~4500 kg / cm 2 That is the case. 【0050】 In any embodiment of this application, the lateral tensile strength of the separator is 2000 kg / cm². 2 The above is preferable, preferably 2500 kg / cm². 2 ~4500 kg / cm 2 That is the case. 【0051】 In any embodiment of this application, the air permeability of the separator is 300 s / 100 mL or less, preferably 100 s / 100 mL to 200 s / 100 mL. 【0052】 In any embodiment of this application, the porosity of the separator is 30% to 45%, preferably 32% to 36%. 【0053】 In any embodiment of this application, the wetted length of the separator is 30 mm or more, preferably 30 mm to 80 mm. 【0054】 In any embodiment of this application, the wetting rate of the separator is 3 mm / s or more, preferably 3 mm / s to 10 mm / s. 【0055】 The performance of the separator, when it satisfies one or more of the above conditions, is advantageous in improving at least one of the following characteristics of the secondary battery: energy density, thermal safety performance, capacity characteristics, and lifespan. 【0056】 A second aspect of this application provides a method for manufacturing a separator according to the first aspect of this application, comprising: step S1 of supplying a porous substrate; step S2 of preparing a coating layer slurry by mixing nanocellulose and a filler in a solvent in a predetermined ratio to prepare a coating layer slurry; and application step S3 of applying the coating layer slurry to at least one surface of the porous substrate to form a coating layer and drying to obtain a separator, wherein the separator comprises a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer comprises nanocellulose and a filler, the water content of the separator is Appm, the thickness of the coating layer is Hμm, and the separator satisfies 250≦A / H≦1500. The method for manufacturing a separator according to this application greatly simplifies the separator manufacturing process because the coating layer is manufactured in a single application. 【0057】 In any embodiment of this application, the coating is performed using a coating machine, the coating machine includes a gravure roll, and the line count of the gravure roll is 100 LPI to 300 LPI, preferably 125 LPI to 190 LPI. 【0058】 In any embodiment of this application, the coating speed is 30 m / min to 120 m / min, preferably 60 m / min to 90 m / min. 【0059】 In any embodiment of this application, the linear velocity ratio of the coating is 0.8 to 2.5, preferably 0.8 to 1.5. 【0060】 In any embodiment of this application, the drying temperature is 40°C to 70°C, preferably 50°C to 60°C. 【0061】 In any embodiment of this application, the drying time is 10 to 120 seconds, preferably 20 to 80 seconds. 【0062】 By controlling each of the above process parameters within a predetermined range, the performance of the separator of this application can be further improved. 【0063】 In any embodiment of the present application, the method further includes step S4 of applying a slurry containing particulate adhesive to at least a portion of the surface of the coating layer, and performing two applications to form an adhesive layer after drying. 【0064】 A third aspect of this application provides a secondary battery comprising a separator according to the first aspect of this application or a separator manufactured by the method of the second aspect of this application. 【0065】 A fourth aspect of this application provides a power consumption device including a secondary battery according to the third aspect of this application. 【0066】 The separator provided in this application has excellent heat resistance, low moisture content, and good wettability to the electrolyte. Therefore, a secondary battery using this separator can have high energy density, high thermal safety performance, and a long lifespan. The power consumption device of this application includes the secondary battery according to this application and therefore has at least the same advantages as the secondary battery. [Brief explanation of the drawing] 【0067】 To more clearly illustrate the technical concepts of the embodiments of this application, the drawings that need to be used in the embodiments of this application are briefly described below. Obviously, the drawings described below represent only a few embodiments of this application, and those skilled in the art can obtain other drawings based on these, provided that they allow for creative effort. 【0068】 [Figure 1] This is a schematic diagram of one embodiment of the secondary battery of the present application. [Figure 2] Figure 1 is a schematic diagram of an exploded view of an embodiment of a secondary battery. [Figure 3] This is a schematic diagram of one embodiment of the battery module of this application. [Figure 4] This is a schematic diagram of one embodiment of the battery pack of this application. [Figure 5] Figure 4 is an exploded schematic diagram of an embodiment of the battery pack shown. [Figure 6] This is a schematic diagram of one embodiment of a power consumption device that includes a secondary battery as a power source according to the present application. 【0069】 The drawings are not always drawn to actual scale. The symbols are explained below. 1 Battery pack 2 Upper enclosure 3 Lower enclosure 4 Battery Modules 5 Secondary battery 51 cases 52 Electrode Assembly 53 Lid plate [Modes for carrying out the invention] 【0070】 The following description will detail embodiments specifically disclosing the separator, its manufacturing method, and related secondary batteries and power consumption devices of this application, with appropriate reference to the drawings. However, unnecessary details may be omitted. For example, detailed explanations of known matters or redundant explanations of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter described in the claims. 【0071】 The “range” disclosed in this application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting one lower limit and one upper limit, the selected lower limit and upper limit limiting the boundary of a particular range. The range thus limited may include or exclude endpoints, and may be any combination, that is, any lower limit may be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are given for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also expected. Also, if minimum range values ​​1 and 2 and maximum range values ​​3, 4 and 5 are given, the ranges 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 may all be expected. In this application, unless otherwise stated, the numerical range “a-b” is an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" in this specification refers to all real numbers between "0 to 5," and "0 to 5" is an abbreviation for combinations of these numbers. Also, when a parameter is described as an integer greater than or equal to 2 (≧2), it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. 【0072】 Unless otherwise specified, all embodiments and optional embodiments of this application may be combined to form new technical concepts. Such technical concepts should be considered to be included in the disclosures of this application. 【0073】 Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical concepts. Such technical concepts should be considered to be included in the disclosures of this application. 【0074】 Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but it is preferable that they be performed sequentially. For example, if it is stated that the above method includes steps (a) and (b), it means that the above method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if it is stated that the above method may further include step (c), it means that step (c) may be added to the above method in any order. For example, the above method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc. 【0075】 Unless otherwise specified, the terms “equipped with” and “included” in this application mean open or closed. For example, the terms “equipped with” and “included” above may mean “equipped with” or “included” other components not listed, or “equipped with” or “included” only the listed components. 【0076】 Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions are met: A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), or both A and B are true (or exist). 【0077】 In this application, the terms "multiple" and "multiple types" mean two or more. 【0078】 Unless otherwise specified, terms used in this application have the common meanings that are ordinarily understood by those skilled in the art. 【0079】 Unless otherwise specified, the numerical values ​​of each parameter mentioned in this application can be measured by various test methods commonly used in the art, for example, according to the test methods provided in this application. 【0080】 Typically, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is placed between the positive and negative electrode sheets and primarily serves to prevent short circuits between the positive and negative electrodes, while also allowing active ions to pass freely to form a circuit. With the application and widespread use of secondary batteries, the demand for energy density in secondary batteries is also increasing. Thinning the separator is an effective measure to improve the energy density of secondary batteries. Currently, separators used in commercially available secondary batteries are usually porous polyolefin membranes, such as porous polyethylene membranes, porous polypropylene membranes, or three-layer composite membranes of polypropylene / polyethylene / polypropylene. Their melting point is 130°C to 160°C. As a result, when the thickness is reduced, the heat resistance of the separator deteriorates, causing it to shrink significantly when heated, increasing the risk of short circuits between the positive and negative electrodes. 【0081】 To solve the above problems, the measures currently employed mainly involve coating a heat-resistant inorganic ceramic layer onto a polyolefin porous membrane. This increases the mechanical strength of the separator, reduces the degree of shrinkage when the separator is subjected to heat, and lowers the risk of short circuits between the positive and negative electrodes. However, because commercially available inorganic ceramic particles have a large particle size, the overall thickness of the separator increases, making it difficult to balance the energy density of the secondary battery, which is particularly detrimental to improving driving range in the field of power batteries. Also, because commercially available inorganic ceramic particles have a large particle size, the number of deposition layers in the polyolefin porous membrane is small (usually 5 layers or less), and the improvement effect on the heat resistance of the separator is limited. Nano-sizing the inorganic ceramic particles can reduce the thickness of the coating layer and mitigate the adverse effect on the energy density of the secondary battery. However, the porosity of the coating layer formed by nano-sizing the inorganic ceramic particles is low, and it easily clogs the pores of the polyolefin porous membrane. This reduces the overall porosity of the separator, increases the ion impedance, and is detrimental to the transport of active ions. At the same time, because nano-sized inorganic ceramic particles have a high specific surface area and the contact between particles is point contact, a large amount of adhesive is required to ensure adhesion between particles. However, using a large amount of adhesive makes pore clogging problems more likely, which is detrimental to the rate performance of the secondary battery. For example, dendrites are more likely to form on the negative electrode surface, and this is also detrimental to the capacity and energy density of the secondary battery. 【0082】 Furthermore, inorganic ceramic particles have a tendency to adsorb water, and in particular, when inorganic ceramic particles are nano-sized, their specific surface area increases significantly, leading to a substantial increase in the water content of the separator. During the long-term charge-discharge process of secondary batteries, water in the separator is gradually released and enters the electrolyte. Currently, the most widely used electrolyte system commercially is a mixed carbonate solution of lithium hexafluoride phosphate. However, lithium hexafluoride phosphate has poor thermal stability in high-temperature environments and decomposes at high temperatures to produce PF5. PF5 is highly sensitive to trace amounts of water in the electrolyte and generates HF upon contact with water, which increases the acidity of the electrolyte. This also makes it more corrosive to the positive electrode active material and positive electrode current collector, causing the elution of transition metal ions in the positive electrode active material and affecting the electrochemical performance of the secondary battery. Therefore, a low water content is required in the separator. 【0083】 With the increasing application and widespread use of rechargeable batteries, the demands on their lifespan are also growing. During the long-term charge-discharge process of rechargeable batteries, the gradual drying and failure of the separator is a significant factor causing a decrease in the battery's capacity. This is because, after the separator dries out, the battery's internal resistance increases, preventing complete charge and discharge, accelerating the decay of the battery's capacity, and significantly reducing its lifespan. Therefore, it is also required that the separator possess good electrolyte wetting characteristics. 【0084】 However, conventional separators often have difficulty combining high heat resistance, low moisture content, and good electrolyte wetting characteristics. 【0085】 In the course of research, the inventors of this application unexpectedly discovered that by providing a coating layer containing nanocellulose and fillers on the surface of a porous separator substrate, and by rationally controlling the ratio of the water content of the separator to the thickness of the coating layer, it is possible to give the separator high heat resistance, low water content, and good electrolyte wetting characteristics, and furthermore, to give the secondary battery high energy density, high thermal safety performance, and long lifespan. Separator 【0086】 Specifically, a first embodiment of the present invention provides a separator comprising a porous substrate and a coating layer provided on at least one surface of the porous substrate, wherein the coating layer comprises nanocellulose and a filler, the water content of the separator is Appm, the thickness of the coating layer is Hμm, and the separator satisfies 250 ≤ A / H ≤ 1500. 【0087】 The inventors of this application, after conducting extensive research, have found that by providing a coating layer containing nanocellulose and filler on at least one surface of the porous substrate of the separator, and by controlling the ratio of the moisture content of the separator to the thickness of the coating layer within the specified range, the separator can be made to possess high heat resistance, low moisture content, and good electrolyte wetting properties. 【0088】 Because nanocellulose structures contain many hydroxyl groups and have strong hydrophilicity, using them alone tends to increase the moisture content of the separator, affecting the electrochemical performance of secondary batteries. The coating layer of this application contains both nanocellulose and filler, and the nanocellulose can overlap with the filler to form a stable spatial network structure, which is advantageous for moisture discharge during the drying process. Therefore, the separator of this application can have a low moisture content. 【0089】 The inventors of this application, through diligent research, have found that by controlling the moisture content Appm of a separator containing nanocellulose and filler and the thickness Hμm of the coating layer so that the A / H ratio is between 250 and 1500, the coating layer can have a good spatial network structure and an appropriate amount of hydroxyl functional groups. As a result, the separator can have a low moisture content and good electrolyte wetting characteristics, and furthermore, a secondary battery using it can have good electrochemical performance, in particular, a long cycle life and a long storage life. In addition, the coating layer of this application contains nanocellulose and filler simultaneously, and the nanocellulose and filler overlap to give the coating layer a stable spatial network structure. As a result, the coating layer has high heat resistance, reduces the degree of shrinkage when the separator is subjected to heat, reduces the risk of short circuits between the positive and negative electrodes, and allows the secondary battery to have high thermal safety performance. At the same time, because the coating layer of this application has high heat resistance, a thinner porous substrate can be selected, allowing the secondary battery to have a high energy density. 【0090】 The moisture content Appm of the separator and the thickness Hμm of the coating layer satisfy 250≦A / H≦1500. For example, A / H may be in the range of any number of 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1250, 1500 or higher. Preferably, 300≦A / H≦1500, 500≦A / H≦1500, 500≦A / H≦1250, 500≦A / H≦1100, 500≦A / H≦1000, 600≦A / H≦1250, 600≦A / H≦1100, or 600≦A / H≦1000. This contributes to the coating layer having a more stable spatial network structure and a more appropriate amount of hydroxyl functional groups, enabling the separator to possess high heat resistance, low moisture content, and good electrolyte wetting characteristics, and allowing the secondary battery to possess high thermal safety performance, long cycle life, and long storage life. 【0091】 The moisture content of the separator can be measured using a moisture meter, and the measurement method can be the Karl Fischer moisture meter, and the test equipment can be a Swiss Mantong 831 Karl Fischer moisture meter. 【0092】 In some embodiments, when the water content Appm of the separator satisfies A ≤ 1000, less water is released from the separator into the electrolyte during the charging and discharging process of the secondary battery, contributing to the secondary battery having good electrochemical performance. In particular, the secondary battery can have high capacity characteristics and a low volume expansion rate. 【0093】 Furthermore, the inventors of this application discovered, during their research, that, surprisingly, a lower moisture content in the separator is not necessarily better. If the moisture content of the separator is too low, for example, less than 400 ppm, the interfacial properties between the separator and the electrolyte deteriorate. For example, the amount of liquid absorbed by the separator decreases, and the wetting properties to the electrolyte worsen. As a result, during the long-term charge-discharge process of the secondary battery, the separator dries out rapidly and becomes non-functional. Moreover, the internal resistance of the secondary battery increases rapidly, the capacity rapidly decreases, and the service life is significantly shortened. 【0094】 In some embodiments, the moisture content Appm of the separator satisfies 400 ≤ A ≤ 1000. For example, A may be in the range of any number from 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000 or higher. Preferably, it is 400 ≤ A ≤ 900, 400 ≤ A ≤ 800, 400 ≤ A ≤ 700, 400 ≤ A ≤ 600, 500 ≤ A ≤ 900, 500 ≤ A ≤ 800, or 500 ≤ A ≤ 700. This contributes to the coating layer having a more stable spatial network structure and a more appropriate content of hydroxyl functional groups, allowing the separator to better combine high heat resistance, low moisture content, and good electrolyte wetting characteristics, further improving the cycle life and storage life of the secondary battery. 【0095】 In some embodiments, the thickness H μm of the coating layer satisfies 0 < H ≦ 1.5. For example, H may be in the range consisting of any numerical value such as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 or more. Preferably, 0 < H ≦ 1.4, 0 < H ≦ 1.3, 0 < H ≦ 1.2, 0 < H ≦ 1.1, 0 < H ≦ 1.0, 0 < H ≦ 0.9, 0 < H ≦ 0.8, 0.1 ≦ H ≦ 0.8, 0.2 ≦ H ≦ 0.8, 0.3 ≦ H ≦ 0.8, 0.4 ≦ H ≦ 0.8 or 0.5 ≦ H ≦ 0.8. This contributes to the improvement of the energy density of the secondary battery. 【0096】 In some embodiments, the areal density of the coating layer is 0.6 g / m 2 ~1.5 g / m 2 and preferably 0.8 g / m 2 ~1.1 g / m 2 This contributes to the formation of a coating layer with more excellent heat resistance. 【0097】 In some embodiments, the thickness of the porous substrate may be 6 μm or less, and preferably may be 3 μm to 5 μm. The coating layer of the present application significantly improves the heat resistance of the separator, and thereby contributes to further improving the energy density of the secondary battery by selecting a thinner porous substrate. 【0098】 In some embodiments, the porosity of the porous substrate may be 32% to 48%, and preferably may be 34% to 39%. When the porosity of the porous substrate is within an appropriate range, it is advantageous for further improving the ion transport characteristics of the separator on the premise of ensuring high heat resistance of the separator, and at the same time, it can ensure that the secondary battery has a high discharge rate and reduce the self-discharge of the battery. 【0099】 In this application, the material of the porous substrate is not particularly limited, and any well-known substrate having good chemical and mechanical stability can be selected. For example, the porous substrate may include at least one of porous polyolefin resin films (e.g., polyethylene, polypropylene, and polyvinylidene fluoride), porous glass fibers, and porous nonwoven fabrics. The porous substrate may be a single-layer film or a multilayer composite film. If the porous substrate is a multilayer composite film, the materials of each layer may be the same or different. 【0100】 Another measure to improve the energy density of secondary batteries is to increase the voltage, for example, by employing a high-voltage positive electrode active material. However, increasing the voltage significantly affects the stability of the separator, so the separator needs to have good voltage breakdown characteristics. The separator coating layer of this application contains nanocellulose, which is a general term for cellulose in which the size of any dimension is nanoscale (e.g., within 100 nm), and possesses both the properties of cellulose and nanoparticles. Nanocellulose may also be polymer nanomaterials extracted from wood, cotton, etc. in nature by one or more means from chemical, physical, or biological sources, and has advantages such as a wide range of sources, low cost, biodegradability, high elastic modulus, and high specific surface area, making it an excellent substitute for conventional petrochemical resources and effectively mitigating problems such as environmental pollution and shortages of petrochemical resources. Furthermore, nanocellulose has good high-temperature resistance and small volume change after being heated, so it can improve the heat resistance of the separator. At the same time, because nanocellulose has a lower density than conventional inorganic ceramic particles, it can reduce the weight of the secondary battery and improve the gravimetric energy density of the secondary battery. Furthermore, nanocellulose contributes to preventing current leakage by providing the coating layer with fine and uniform nanopores, thereby enabling the separator to possess both high ion transport characteristics and good voltage breakdown characteristics. 【0101】 In some embodiments, the nanocellulose may include at least one of cellulose nanofibers (also called cellulose nanofibrils, CNF, nanofibril cellulose, or microfibril cellulose), cellulose nanowhiskers (also called cellulose nanocrystals, CNC, cellulose nanocrystals, or nanocrystalline cellulose), and bacterial nanocellulose (also called bacterial nanocellulose, BNC, or microbial cellulose), preferably containing cellulose nanowhiskers. Because cellulose nanowhiskers have a high degree of crystallinity, their hydrophilicity can be reduced, which is advantageous for water removal during the drying process, and thus the separator of this application can have a low moisture content. In addition, cellulose nanowhiskers easily overlap with fillers, and the coating layer can provide a stable spatial network structure, further improving the performance of the separator. 【0102】 In some examples, the nanocellulose may include at least one of unmodified nanocellulose (also called hydroxyl nanocellulose) and modified nanocellulose, preferably modified nanocellulose. 【0103】 The modified nanocellulose contains a modifying group. In some examples, the modifying group may include at least one of an amine group, a carboxylic acid group, an aldehyde group, a sulfonic acid group, a boric acid group, and a phosphate group, preferably at least one of a sulfonic acid group, a boric acid group, and a phosphate group. 【0104】 In further research, the inventors found that when nanocellulose has the above-mentioned specific modifying groups, it can effectively improve the heat resistance of the separator and enhance the thermal safety performance of the secondary battery. Furthermore, it is advantageous for the separator to have a low water content, provided that it has good electrolyte wetting properties, thereby further improving the electrochemical performance of the secondary battery. 【0105】 When nanocellulose has the specific modifying groups described above, it can form a more stable spatial network structure with fillers, further improving the ion transport and voltage breakdown characteristics of the separator. This is also advantageous for matching high-voltage cathode active materials and can further improve the energy density of secondary batteries. 【0106】 Furthermore, the presence of modifying groups can reduce the proportion of hydroxyl groups, ensuring that the coating layer slurry has an appropriate viscosity, which is advantageous for application and can improve the production efficiency of separators and the uniformity of the coating layer. 【0107】 In some embodiments, the modified nanocellulose contains hydroxyl groups and modifying groups, and the molar ratio of the modifying groups to the hydroxyl groups may be 1:4 to 4:1, preferably 2:3 to 7:3. When the molar ratio of the modifying groups to the hydroxyl groups is within an appropriate range, it can further improve the heat resistance and ion transport characteristics of the separator and contribute to the separator having a low moisture content. Furthermore, the following situations can be effectively avoided. If the molar ratio of the modifying groups to the hydroxyl groups is too small, the further improvement effect of the modifying groups on the heat resistance and ion transport characteristics of the separator may not be significant. If the molar ratio of the modifying groups to the hydroxyl groups is too large, the electrolyte wetting characteristics of the separator may be affected, for example, the ion transport characteristics of the separator may deteriorate, which may affect the cycle life and storage life of the secondary battery, as well as the heat resistance of the separator, which may further affect the thermal safety performance of the secondary battery. 【0108】 The type of modifying group in nanocellulose can be measured by infrared spectroscopy. For example, the type of modifying group can be determined by testing the infrared spectrum of the material and identifying the characteristic peaks contained therein. Specifically, infrared spectroscopic analysis of the material can be performed using instruments and methods well known in the art. For example, it can be tested using an infrared spectrophotometer such as the IS10 Fourier transform infrared spectrophotometer from Nicolet, Inc., in accordance with GB / T6040-2019 General Rules for Infrared Spectroscopic Analysis. 【0109】 In some embodiments, the aspect ratio of the nanocellulose may be 5 to 80, preferably 10 to 40. When the aspect ratio of the nanocellulose is within an appropriate range, the heat resistance and ion transport characteristics of the separator can be further improved. Furthermore, the following situations can be effectively avoided. If the aspect ratio of the nanocellulose is too small, the overlap effect with the filler is poor, which may result in poor heat resistance of the coating layer. Also, during the drying process of the coating layer, some nanocellulose is prone to collapse due to a lack of support from the filler, and pore clogging problems are also likely to occur. This inhibits active ion transport and moisture discharge, affecting the cycle performance and capacity of the secondary battery. If the aspect ratio of the nanocellulose is too large, the nanopores of the coating layer formed by overlapping with the filler are small, which may result in poor ion transport characteristics of the separator. 【0110】 In some embodiments, the average diameter of the nanocellulose may be 10 nm to 40 nm, preferably 10 nm to 35 nm. When the average diameter of the nanocellulose is within an appropriate range, the heat resistance, ion transport characteristics, and voltage breakdown characteristics of the separator can be further improved. Furthermore, the following situations can be effectively avoided. If the average diameter of the nanocellulose is too large, the nanopores of the coating layer formed by overlapping with the filler become large, which may worsen the voltage breakdown characteristics of the separator. In addition, the overlap effect with the filler is poor, which may worsen the heat resistance of the coating layer. Moreover, during the drying process of the coating layer, some nanocellulose is prone to collapse due to the lack of support from the filler, and pore clogging problems are likely to occur. This inhibits active ion transport and moisture discharge, affecting the cycle performance and capacity of the secondary battery. 【0111】 In some embodiments, the average length of the nanocellulose may be 100 nm to 600 nm, preferably 200 nm to 500 nm. When the average length of the nanocellulose is within an appropriate range, the heat resistance and ion transport properties of the separator can be further improved. Furthermore, the following situations can be effectively avoided. If the average length of the nanocellulose is too short, the overlap effect with the filler is poor, which may result in poor heat resistance of the coating layer. Also, during the drying process of the coating layer, some nanocellulose is prone to collapse due to a lack of support from the filler, and pore clogging problems are more likely to occur. This inhibits active ion transport and moisture discharge, affecting the cycle performance and capacity of the secondary battery. If the average length of the nanocellulose is too long, the viscosity of the coating layer slurry is high and the flow is poor, which may affect the application of the coating layer slurry and potentially affect the quality of the resulting coating layer, such as the heat resistance and ion transport properties of the separator. 【0112】 The average length and average diameter of nanocellulose can be measured by the following methods: A 3.6 mm × 3.6 mm sample is cut from any one region in the separator, and the microtopographic structure of the coating layer in the sample is measured using a scanning electron microscope (e.g., ZEISS Sigma 300). The high vacuum mode is selected, the operating voltage is 3 kV, and the magnification is 30,000x, and an SEM image is obtained. Based on the obtained SEM image, multiple (e.g., five or more) test regions are selected and length statistics are performed, with each test region having a size of 0.5 μm × 0.5 μm. The average value of the lengths obtained in each test region is then taken as the average length of the nanocellulose. Based on the obtained SEM image, multiple (e.g., five or more) test regions are selected using Nano Measurer particle size distribution statistics software and diameter statistics are performed, with each test region having a size of 0.5 μm × 0.5 μm. The average value of the diameters obtained in each test region is then taken as the average diameter of the nanocellulose. 【0113】 In some embodiments, the weight-average molecular weight of the nanocellulose may be 10,000 to 60,000, and preferably 30,000 to 50,000. 【0114】 In some examples, the equilibrium degree of polymerization of the nanocellulose may be 150DP to 300DP, and preferably 200DP to 250DP. 【0115】 When the weight-average molecular weight and / or degree of polymerization of nanocellulose are within an appropriate range, it is possible to avoid the nanocellulose clogging the pore structure of the separator, as well as to set the viscosity of the coating layer slurry within an appropriate range. This results in better fluidity and wetting properties of the slurry during application, and is advantageous for improving the quality of the coating layer, for example, by further improving the heat resistance and ion transport properties of the separator. 【0116】 In some embodiments, the shape of the nanocellulose may include at least one of tubular (e.g., hollow tubular), fibrous, or rod-shaped. Nanocellulose of an appropriate shape is advantageous in forming a stable spatial network structure with fillers, which can further improve the ion transport properties and external force resistance of the separator. 【0117】 In some embodiments, the nanocellulose content in the coating layer may be 6 wt% to 35 wt%, preferably 10 wt% to 30 wt%, based on the total weight of the coating layer. When the nanocellulose content is within an appropriate range, it is possible to ensure that the coating layer slurry has an appropriate viscosity, which is advantageous for application, and is also advantageous for the separator to have a low moisture content and good electrolyte wetting characteristics. Furthermore, it is advantageous for the nanocellulose to form a stable spatial network structure together with the filler, thereby further improving the performance of the separator. For example, it is possible to reduce the moisture content of the separator and improve the heat resistance, ion conductivity, external force resistance, and voltage breakdown resistance of the separator. 【0118】 In some embodiments, the filler content in the coating layer may be 60 wt% or more, preferably 65 wt% to 90 wt%, based on the total weight of the coating layer. When the filler content is within an appropriate range, it is possible to ensure that the coating layer slurry has an appropriate viscosity, which is advantageous for application, and is also advantageous for the separator to have a low moisture content and good electrolyte wetting characteristics. Furthermore, it is advantageous for constructing a stable spatial network structure together with nanocellulose, thereby further improving the performance of the separator. For example, the moisture content of the separator can be reduced, and the heat resistance, tensile strength, puncture resistance, and external force pressing resistance of the separator can be improved. 【0119】 In secondary batteries, the overall volume increases during long-term charge-discharge processes because the microstructural changes of the positive and negative electrode active materials are irreversible. In particular, during rapid charging of secondary batteries, the volume increase of the negative electrode active material after the insertion of active ions is even greater. When the battery expands, it creates pressing and / or tensile forces on the separator, making the separator susceptible to damage and increasing the risk of short circuits between the positive and negative electrodes. Therefore, the separator also requires good resistance to external forces. The presence of fillers contributes to the coating layer having a stable spatial network structure, thereby improving the ion transport characteristics and heat resistance of the separator, as well as improving the separator's tensile strength, puncture resistance, and resistance to external forces. 【0120】 In some embodiments, the filler may include at least one of inorganic particles and organic particles. 【0121】 In some embodiments, it is preferable that the decomposition temperature of the filler is 200°C or higher, thereby enabling the filler to have excellent thermal stability and resistance to decomposition, and further improving the heat resistance of the separator. 【0122】 Inorganic particles have high thermal stability and are resistant to decomposition, and typically have hydroxyl groups on their surface, making it easy to construct a stable spatial network structure together with nanocellulose. In some examples, preferably, the inorganic particles include at least one of the following: inorganic particles having a dielectric constant of 5 or more, inorganic particles that are ionic conductive but do not store ions, or inorganic particles that can undergo electrochemical reactions. 【0123】 Preferably, the inorganic particles having a dielectric constant of 5 or more are 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, lithium magnesium silicate, sodium magnesium 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 / 3 The material comprises O3-PbTiO3 (abbreviated as PMN-PT) and at least one of the modified inorganic particles. Preferably, the modification method for each inorganic particle may be chemical modification and / or physical modification. The chemical modification method includes coupling agent modification (e.g., silane coupling agent, titanate coupling agent, etc.), surfactant modification, polymer graft modification, etc. The physical modification method may include mechanical force dispersion, ultrasonic dispersion, high-energy treatment, etc. The modification treatment reduces aggregation of inorganic particles, thereby enabling the construction of a more stable and uniform network structure with nanocellulose. Furthermore, by selecting coupling agents, surfactants, or polymer-modified inorganic particles having specific functional groups, it is also possible to improve the wetting properties of the coating layer to the electrolyte and improve the adhesion of the coating layer. 【0124】 Preferably, the inorganic particles having ion conductivity but not storing ions are Li3PO4, lithium titanium phosphate Li x1 Ti y1 (PO4)3, Lithium Aluminum Titanium Phosphate x2 Al y2 Ti z1 (PO4)3, (LiAlTiP)x3 O y3 -type glass, lithium lanthanum titanate Li x4 La y4 TiO3, lithium germanium thiophosphate Li x5 Ge y5 P z2 S w , lithium nitride Li x6 N y6 , SiS2-type glass Li x7 Si y7 S z3 or P2S5-type glass Li x8 P y8 S z4 includes at least one of them, and includes 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 ion transport characteristics of the separator can be further improved. 【0125】 Preferably, the electrochemically reactive inorganic particles include at least one of lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials or lithium titanium compounds. 【0126】 Since the organic particles have good thermal stability and are difficult to decompose, the heat resistance of the separator can be improved. At the same time, when the internal temperature of the secondary battery reaches the melting point of the organic particles due to overcharge abuse, heat abuse, etc., the organic particles will melt and be sucked into the micropores of the porous substrate by capillary action to play the role of closing pores and blocking, which is beneficial to ensuring that the secondary battery has high safety performance. 【0127】 In some examples, the organic particles include, but are not limited to, at least one of the following: polyethylene particles, polypropylene particles, polystyrene particles, cellulose, cellulose modifiers (e.g., carboxymethylcellulose), melamine resin particles, phenolic resin particles, polyester particles (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), silicone resin particles, polyimide particles, polyamide-imide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, polyaryletherketone particles, and copolymers of butyl acrylate and ethyl methacrylate (e.g., crosslinked polymers of butyl acrylate and ethyl methacrylate). 【0128】 In some embodiments, the glass transition temperature of the organic particles may preferably be 130°C or higher. This prevents the organic particles from transitioning from a glassy state to a viscous flow state when the internal temperature of the secondary battery reaches 130°C, thus preventing the separator from shrinking rapidly. More preferably, the organic particles include, but are not limited to, at least one of melamine formaldehyde resin particles, phenolic resin particles, polyester particles, silicone resin particles, polyimide particles, polyamide-imide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, and polyaryletherketone particles. 【0129】 In some embodiments, the filler comprises a first filler, which is a secondary particle topography formed by the aggregation of primary particles. The filler of the secondary particle topography has a large specific surface area and better affinity with nanocellulose, and the nanocellulose can overlap in the voids between the primary particles of the filler constituting the secondary particle topography, forming an effect of overlapping and integrating the nanocellulose and the first filler. As a result, the coating layer can have a more stable spatial network structure, and furthermore, the separator can have an appropriate porosity and a stable pore structure, and the separator can also have a low moisture content and good electrolyte wetting properties. 【0130】 In some embodiments, the content of the first filler is 50 wt% to 100 wt%, preferably 90 wt% to 99 wt%, based on the total weight of the filler. When the content of the first filler is within an appropriate range, it is advantageous for overlapping with nanocellulose to form an integrated effect, which allows the coating layer to have a more stable spatial network structure, further improving the heat resistance, tensile strength, puncture resistance, and external force resistance of the separator. 【0131】 In some embodiments, the average particle size Dv50 of the first filler is 200 nm or less, preferably 50 nm to 200 nm. This allows the first filler to have a high specific surface area, increases the affinity between the first filler and nanocellulose, and is advantageous for overlapping the first filler and nanocellulose to form an integrated effect. As a result, the coating layer can have a more stable spatial network structure, and the separator can have better heat resistance and wettability to the electrolyte. 【0132】 In some embodiments, the BET specific surface area of ​​the first filler is 20 m². 2 It is 1g or more, preferably 25m 2 / g~50m2 This is / g. This improves the affinity between the first filler and nanocellulose, which is advantageous for forming an integrated effect by overlapping with the nanocellulose. As a result, the coating layer can have a more stable spatial network structure, and the separator can have better heat resistance and wettability to the electrolyte. 【0133】 In some embodiments, the first filler comprises inorganic particles of secondary particle topography, and the crystalline form of the inorganic particles of secondary particle topography comprises at least two of the α-crystalline form, θ-crystalline form, γ-crystalline form, or η-crystalline form, preferably at least two of the α-crystalline form, θ-crystalline form, or γ-crystalline form. 【0134】 In the α-crystalline type secondary particle topography, inorganic particles have diffraction peaks in the X-ray diffraction spectrum measured by an X-ray diffractometer at locations where 2θ is 57.48°±0.2° and 43.34°±0.2°. In some examples, the α-crystalline type content is 1.2 wt% or more, preferably 1.2 wt% to 10 wt%, and more preferably 1.2 wt% to 5 wt%, based on the total weight of the inorganic particles in the secondary particle topography. 【0135】 In the θ-crystalline secondary particle topography, inorganic particles have diffraction peaks in the X-ray diffraction spectrum measured by an X-ray diffractometer at locations where 2θ is 36.68°±0.2° and 31.21°±0.2°. In some examples, the θ-crystalline content is 50 wt% or more, preferably 60 wt% to 85 wt%, and more preferably 60 wt% to 82.5 wt%, based on the total weight of the inorganic particles in the secondary particle topography. 【0136】 In the γ-crystalline secondary particle topography, inorganic particles have diffraction peaks in the X-ray diffraction spectrum measured by an X-ray diffractometer at locations where 2θ is 66.95°±0.2° and 45.91°±0.2°. In some examples, the γ-crystalline content is 10 wt% or more, preferably 15 wt% to 60 wt%, and more preferably 15 wt% to 35 wt%, based on the total weight of the inorganic particles in the secondary particle topography. 【0137】 In the η-crystalline secondary particle topography, inorganic particles have diffraction peaks in the X-ray diffraction spectrum measured by an X-ray diffractometer at locations where 2θ is 31.89°±0.2° and 19.37°±0.2°. In some examples, the η-crystalline content is 5 wt% or less, preferably 2 wt% or less, and more preferably 1 wt% or less, based on the total weight of the inorganic particles in the secondary particle topography. 【0138】 Inorganic particles in α-crystalline secondary particle topography have advantages such as high hardness, good heat resistance, low dielectric constant, high safety, and high true density. Inorganic particles in θ-crystalline secondary particle topography have a moderate specific surface area and hardness, allowing for better and simultaneous improvement of the separator's heat resistance and ion transport properties. Inorganic particles in γ-crystalline and η-crystalline secondary particle topography have the advantage of a large specific surface area. Therefore, selecting a first filler of a different crystal type contributes to improving at least one of the separator's heat resistance and electrolyte wetting properties. 【0139】 In some embodiments, the first filler comprises inorganic particles of secondary particle topography, the crystalline form of the inorganic particles of secondary particle topography comprises the θ-crystalline form, and the content of the θ-crystalline form is 50 wt% or more, preferably 60 wt% to 85 wt%, and more preferably 60 wt% to 82.5 wt%, based on the total weight of the inorganic particles of secondary particle topography. 【0140】 In some embodiments, the first filler contains inorganic particles of secondary particle topography, and the crystalline forms of the inorganic particles of secondary particle topography include α-crystalline form, θ-crystalline form, γ-crystalline form, and η-crystalline form, with the α-crystalline form content being 1.2 wt% to 5 wt%, the θ-crystalline form content being 60 wt% to 82.5 wt%, the γ-crystalline form content being 15 wt% to 35 wt%, and the η-crystalline form content being 1 wt% or less, all of which are calculated based on the total weight of the inorganic particles of secondary particle topography. 【0141】 The X-ray diffraction spectrum of inorganic particles in secondary particle topography can be obtained by drying the inorganic particles, polishing them in a mortar (e.g., an agate mortar) for 30 minutes, and then testing them using an X-ray diffractometer (e.g., Miniflex600-C) to obtain the X-ray diffraction spectrum. During testing, a Cu target, Ni filter, tube voltage of 40KV, tube current of 15mA, and a continuous scanning range of 5° to 80° can be used. 【0142】 In some embodiments, the first filler comprises inorganic particles of secondary particle topography, which can be produced by oxidizing a precursor solution of inorganic particles by high-pressure sputtering, then heating at 600°C to 900°C (for example, 1 to 3 hours) to form small particles, and then drying and solidifying at 150°C to 250°C (for example, 30 to 60 minutes) to obtain inorganic particles of secondary particle topography. 【0143】 In some embodiments, the filler further comprises a second filler, the second filler being primary particle topography. Because the primary particle topography filler has a large particle size and high strength, it can better exert its support function in the coating layer, reduce the amount of adhesive used, and improve the heat resistance of the separator. Furthermore, when used in small amounts, the separator has a greater pore structure and a lower water content, which contributes to further improving the ion transport properties and wettability of the separator to the electrolyte. 【0144】 In some embodiments, the content of the second filler is 50 wt% or less, preferably 1 wt% to 10 wt%, based on the total weight of the filler. This allows the support function of the second filler to be better exercised, is advantageous for moisture discharge during the drying process, and allows the coating layer to maintain an appropriate porosity and a stable pore structure during the long-term charge-discharge process, further improving the ion transport characteristics and wettability of the separator to the electrolyte. 【0145】 In some embodiments, the average particle size Dv50 of the second filler is 100nm-800nm, preferably 200nm-400nm. This allows the second filler to better exhibit its support function, is advantageous for moisture discharge during the drying process, and enables the coating layer to maintain an appropriate porosity and stable pore structure during long-term charge-discharge processes, further improving the ion transport characteristics and wettability of the separator to the electrolyte. 【0146】 In some embodiments, the BET specific surface area of ​​the second filler is 10 m². 2 / g or less, preferably 4m 2 / g~9m 2 This allows the support function of the second filler to be better exercised, which is advantageous for the discharge of moisture during the drying process, and enables the coating layer to maintain an appropriate porosity and a stable pore structure during the long-term charge-discharge process, further improving the ion transport characteristics and wettability of the separator to the electrolyte. 【0147】 In some embodiments, the second filler comprises inorganic particles of primary particle topography, and the crystalline form of the inorganic particles of primary particle topography comprises at least one of α-crystalline form or γ-crystalline form, preferably α-crystalline form. Since α-crystalline inorganic particles of primary particle topography have advantages such as high hardness, good heat resistance, low dielectric constant, high safety, and high true density, the heat resistance of the separator can be further improved. 【0148】 In some embodiments, the second filler comprises inorganic particles of primary particle topography, the crystalline form of the inorganic particles of primary particle topography includes α-crystalline form, and the content of α-crystalline form is 90 wt% or more, preferably 95 wt% to 100 wt%, based on the total weight of the inorganic particles of primary particle topography. 【0149】 In some embodiments, the coating layer may further contain a non-particulate adhesive. In this application, the type of non-particulate adhesive is not particularly limited, and any well-known material with good adhesion can be used. Preferably, the non-particulate adhesive includes an aqueous solution adhesive, which has the advantages of good thermodynamic stability and being environmentally friendly, thus advantageous for the preparation and application of the coating layer slurry. As an example, the aqueous solution adhesive includes at least one of the following: aqueous solution acrylic resin (e.g., acrylic acid, methacrylic acid, sodium acrylate monomer homopolymer or other comonomer copolymer), polyvinyl alcohol (PVA), isobutylene-maleic anhydride copolymer, and polyacrylamide. 【0150】 Preferably, the content of the non-particulate adhesive in the coating layer is less than 1 wt% based on the total weight of the coating layer. The nanocellulose and filler in the coating layer of this application can form a stable spatial network structure, thereby maintaining high adhesion to the separator and good ion transport properties while reducing the amount of adhesive used. 【0151】 In some embodiments, the separator may further include an adhesive layer provided on at least a portion of the surface of the coating layer and containing particulate adhesive. The adhesive layer not only prevents the coating layer from falling off and improves the safety performance of the secondary battery, but can also improve the interface between the separator and the electrode and improve the cycle performance of the secondary battery. 【0152】 Preferably, the particulate adhesive comprises at least one of the following: an acrylic acid ester monomer homopolymer or copolymer, an acrylic acid monomer homopolymer or copolymer, or a fluorine-containing olefin monomer homopolymer or copolymer. The copolymer monomer comprises, but is not limited to, at least one of the following: an acrylic acid ester monomer, an acrylic acid monomer, an olefin monomer, a halogen-containing olefin monomer, a fluoroether monomer, etc. 【0153】 Preferably, the particulate adhesive includes a vinylidene fluoride polymer, such as a homopolymer of vinylidene fluoride monomer (VDF) and / or a copolymer of vinylidene fluoride monomer and comonomer. The copolymer monomer may be at least one of olefin monomers, fluorine-containing olefin monomers, chlorine-containing olefin monomers, acrylate monomers, acrylic monomers, and fluoroether monomers. Preferably, the comonomer may include at least one of trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ethers (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). 【0154】 In some examples, the longitudinal (MD) heat shrinkage rate of the separator at 150°C for 1 hour is 5% or less, preferably 0.5% to 4%. 【0155】 In some examples, the transverse (TD) thermal shrinkage rate of the separator at 150°C for 1 hour is 5% or less, preferably 0.5% to 4%. 【0156】 The separator of this application has a low thermal shrinkage rate in both the lateral and vertical directions, which can further improve the safety performance of secondary batteries. 【0157】 In some embodiments, the puncture strength of the separator is 350 gf or more, preferably 370 gf to 450 gf. The separator of this application has high puncture strength, which can further improve the safety performance of secondary batteries. 【0158】 In some embodiments, the longitudinal tensile strength of the separator was 2000 kg / cm². 2 The above is preferable, preferably 2500 kg / cm². 2 ~4500 kg / cm 2 That is the case. 【0159】 In some embodiments, the lateral tensile strength of the separator was 2000 kg / cm². 2 The above is preferable, preferably 2500 kg / cm². 2 ~4500 kg / cm 2 That is the case. 【0160】 Because the separator of this application has high tensile strength in both the lateral and vertical directions, the probability of the separator being damaged when the secondary battery expands is low, and the safety performance of the secondary battery can be further improved. 【0161】 In some embodiments, the permeability of the separator is 300 s / 100 mL or less, preferably 100 s / 100 mL to 200 s / 100 mL. The separator of this application can improve ion transport characteristics by having good permeability. 【0162】 In some embodiments, the porosity of the separator is 30% to 45%, preferably 32% to 36%. This improves the ion transport characteristics of the separator and reduces the self-discharge of the battery. 【0163】 In some embodiments, the wetted length of the separator is 30 mm or more, preferably 30 mm to 80 mm. 【0164】 In some embodiments, the wetting rate of the separator is 3 mm / s or more, preferably 3 mm / s to 10 mm / s. 【0165】 The separator of this application has good electrolyte wetting characteristics, which can improve ion transport characteristics and secondary battery capacity. 【0166】 In this application, the average particle size Dv50 of the material has a meaning well known in the art and can be measured using instruments and methods known in the art. For example, it can be tested using a laser particle size analyzer (e.g., Master Size 3000) by referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method. 【0167】 In this application, the specific surface area of ​​a material has a meaning well known in the art and can be measured using instruments and methods known in the art. For example, it can be tested by the nitrogen gas adsorption specific surface area analysis test method, referring to GB / T19587-2017, and calculated by the BET (Brunauer Emmett Teller) method. Preferably, the nitrogen adsorption specific surface area analysis test can be performed using the Tri-Star3020 specific surface area pore size analyzer from Micromeritics, Inc., USA. 【0168】 In this application, the thermal shrinkage rate, puncture strength, tensile strength, and air permeability of the separator are all well known in the art and can be measured by methods known in the art. For example, all can be tested by referring to standard GB / T36363-2018. 【0169】 In this application, the wetting length and wetting rate of the separator are both well known in the art and can be measured by methods known in the art. An example test method involves cutting the separator into a sample 5 mm wide and 100 mm long, fixing both ends of the sample and placing it horizontally, dropping 0.5 mg of electrolyte into the center of the sample, and after a predetermined time (1 min in this application), taking a photograph to measure the diffusion length of the electrolyte to obtain the wetting length and wetting rate of the separator. To ensure the accuracy of the test results, the test can be performed using multiple samples (e.g., 5 to 10) and the average value can be calculated to obtain the test results. The electrolyte can be prepared by the following method: 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, and thoroughly dried LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L. 【0170】 Note that the coating layer parameters of the separator described above (e.g., surface density, thickness, etc.) are all parameters of the coating layer on one side of the porous substrate. 【0171】 When a coating layer is provided on both sides of a porous substrate, it is considered that the protection scope of this application is reached if the coating layer parameters on either one of the sides satisfy the requirements of this application. Manufacturing method 【0172】 A second embodiment of the present application provides a method for producing a separator of the first embodiment of the present application, comprising: step S1 supplying a porous substrate; step S2 preparing a coating layer slurry by mixing nanocellulose and a filler in a predetermined ratio in a solvent to prepare the coating layer slurry; and step S3 coating the coating layer slurry onto at least one surface of the porous substrate to form a coating layer and dry it to obtain a separator, wherein the separator comprises a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer comprises nanocellulose and a filler, the water content of the separator is Appm, the thickness of the coating layer is Hμm, and the separator satisfies 250≦A / H≦1500. 【0173】 In some embodiments, in S2, the solvent may be water, such as deionized water. 【0174】 In some embodiments, in S2, the coating layer slurry may further contain other components, such as a dispersant, a wetting agent, an adhesive, and so on. 【0175】 In some embodiments, in S2, the solid content of the coating layer slurry can be controlled to 28% to 45%, for example, 30% to 38%. When the solid content of the coating layer slurry is within the above range, surface problems of the coating layer can be effectively reduced, the probability of uneven coating can be reduced, and the energy density and safety performance of the secondary battery can be further improved. 【0176】 In some examples, the nanocellulose is obtained by a method comprising S21, which involves supplying cellulose powder having a whiteness of 80% or more; S22, which involves mixing the obtained cellulose powder with a modification solution and reacting it, then washing to remove impurities and obtain cellulose nanowhiskers; and S23, which involves adjusting the pH of the obtained cellulose nanowhiskers to neutral (for example, pH 6.5 to 7.5), polishing, and cutting to obtain nanocellulose. 【0177】 Preferably, in S21, the cellulose powder having a whiteness of 80% or more may be commercially available, or it may be obtained by employing chemical methods (e.g., acid decomposition method, alkali treatment method, Tempo catalytic oxidation method), biological methods (e.g., enzyme treatment method), mechanical methods (e.g., ultrafine polishing, ultrasonic crushing, high-pressure homogenization), etc. The fiber raw material for producing the cellulose powder having a whiteness of 80% or more may include at least one of the following: plant fibers, such as cotton fibers (e.g., cotton fiber, cotton weed fiber), hemp fibers (e.g., sisal fiber, ramie fiber, jute fiber, flax fiber, cannabis fiber, Manila hemp fiber, etc.), palm fibers, wood fibers, bamboo fibers, and grass fibers. 【0178】 In some examples, the cellulose powder having a whiteness of 80% or more can also be produced by opening the fiber raw material, removing the dregs, then pulverizing it with an alkaline solution (for example, an aqueous NaOH solution with a concentration of 4 wt% to 20 wt%, preferably 5 wt% to 15 wt%), followed by sequentially removing impurities by washing with water (for example, 3 to 6 washes), bleaching (for example, with sodium hypochlorite and / or hydrogen peroxide), removing impurities by pickling, removing impurities by washing with water, removing water, and air drying to obtain the cellulose powder. 【0179】 In some embodiments, in S22, the modifying solution may be an acidic solution (e.g., an aqueous solution of sulfuric acid, an aqueous solution of boric acid, an aqueous solution of phosphoric acid, an aqueous solution of acetic acid) or an alkaline solution (e.g., an organic solvent solution of urea). Preferably, the modifying solution is an acidic solution. 【0180】 Preferably, the concentration of the acid solution may be 5 wt% to 80 wt%. When an aqueous sulfuric acid solution is used as the modifying solution, nanocellulose having sulfonic acid groups can be obtained by setting the concentration of the acid solution to 40 wt% to 80 wt%. When an aqueous boric acid solution is used as the modifying solution, nanocellulose having boric acid groups can be obtained by setting the concentration of the acid solution to 5 wt% to 10 wt%. When an aqueous phosphoric acid solution is used as the modifying solution, nanocellulose having phosphoric acid groups can be obtained by setting the concentration of the acid solution to 45 wt% to 75 wt%. When an aqueous acetic acid solution is used as the modifying solution, nanocellulose having carboxylic acid groups can be obtained by setting the concentration of the acid solution to 40 wt% to 80 wt%. 【0181】 Furthermore, by using a urea xylene solution as the urea organic solvent solution, nanocellulose having amine groups can be obtained. 【0182】 In some embodiments, in S22, the mass ratio of the cellulose powder to the modified solution may preferably be 1:2.5 to 1:50, and more preferably 1:5 to 1:30. 【0183】 If the modification solution is an aqueous sulfuric acid solution, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30. If the modification solution is an aqueous boric acid solution, the mass ratio of the cellulose powder to the acid solution may be 1:20 to 1:50. If the modification solution is an aqueous phosphoric acid solution, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30. If an aqueous acetic acid solution is used as the modification solution, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30. If a urea organic solvent solution is used as the modification solution, the mass ratio of the cellulose powder to the urea organic solvent solution may be 1:4 to 1:40. 【0184】 In some embodiments, when the modifying solution in S22 is an acidic solution, the reaction may be carried out under conditions of 80°C or lower, preferably 30°C to 60°C, and the reaction time between the cellulose powder and the modifying solution may be 0.5h to 4h, preferably 1h to 3h. 【0185】 In some embodiments, if the modifying solution in S22 is an alkaline solution, the reaction may be carried out under conditions 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. 【0186】 In some embodiments, in S23, polishing may be performed using a polishing machine, and cutting may be performed using a high-pressure homogenizer. By adjusting the polishing parameters of the polishing machine (e.g., number of polishing cycles, polishing time, etc.) and the cutting parameters of the high-pressure homogenizer, nanocellulose having different average diameters and / or different average lengths can be obtained. 【0187】 In some embodiments, in S3, the coating is performed using a coating machine. In this application, the model number of the coating machine is not particularly limited, and for example, a commercially available coating machine can be used. Preferably, the coating machine includes a gravure roll for transferring the coating layer slurry to a porous substrate. Preferably, the line count of the gravure roll is 100 LPI to 300 LPI, and more preferably 125 LPI to 190 LPI. 【0188】 In some embodiments, in S3, the coating method can be transfer coating, rotary spray coating, immersion coating, or the like. 【0189】 In some embodiments, in S3, the coating speed can be controlled between 30 m / min and 120 m / min, for example, between 60 m / min and 90 m / min. When the coating speed is within this range, surface problems of the coating layer can be effectively reduced, the probability of uneven coating can be reduced, and the energy density and safety of the secondary battery can be further improved. 【0190】 In some embodiments, in S3, the linear velocity ratio of the coating may be 0.8 to 2.5, for example, 0.8 to 1.5 or 1.0 to 1.5. 【0191】 In some embodiments, the drying temperature in S3 may be 40°C to 70°C, or for example, 50°C to 60°C. 【0192】 In some embodiments, the drying time in S3 may be 10 to 120 seconds, for example, 20 to 80 seconds or 20 to 40 seconds. 【0193】 The performance of the separator of this application can be further improved by controlling each of the above process parameters within a predetermined range. Those skilled in the art can selectively adjust one or more of the above process parameters according to actual production conditions. 【0194】 In some embodiments, the method further includes step S4, which involves applying a slurry containing particulate adhesive to at least a portion of the surface of the coating layer and applying it twice to allow it to dry and form an adhesive layer. 【0195】 The separator manufacturing method of this application significantly simplifies the separator manufacturing process by producing the coating layer in a single application. 【0196】 The raw materials and parameters such as their content used in the separator manufacturing method of this application can be found by referring to the separator of the first embodiment of this application, but such details are omitted here. Unless otherwise specified, each raw material used in the separator manufacturing method of this application is available commercially. secondary battery 【0197】 A third aspect of the embodiments of this application provides a secondary battery. 【0198】 A secondary battery, also called a rechargeable battery or storage battery, is a battery that can be used continuously by activating the active material through charging after discharge. Typically, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is placed between the positive electrode sheet and the negative electrode sheet and primarily serves to prevent short circuits between the positive and negative electrodes, while also allowing active ions to pass through. 【0199】 In this application, the type of secondary battery is not particularly limited, and for example, the secondary battery may be a lithium-ion battery, a sodium-ion battery, etc., and in particular, the secondary battery may be a lithium-ion secondary battery. 【0200】 A secondary battery according to a third embodiment of the present invention includes a separator according to a first embodiment of the present invention or a separator manufactured by the method of a second embodiment of the present invention, wherein the separator is interposed between the positive electrode sheet and the negative electrode sheet. Preferably, at least the side of the separator closer to the negative electrode sheet has a coating layer according to a first embodiment of the present invention. This makes it possible to provide the secondary battery of the present invention with high energy density, high thermal safety performance and long lifespan. [Positive electrode sheet] 【0201】 In some embodiments, the positive electrode sheet 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 opposing surfaces in its thickness direction, and the positive electrode film layer is provided on either or both of the two opposing surfaces of the positive electrode current collector. 【0202】 When the secondary battery of the present application is a lithium ion battery, the positive electrode active material can include, but is not limited to, one or more of lithium-containing transition metal oxides, lithium-containing phosphates, and their modified compounds. Examples of the lithium transition metal oxides 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 phosphates 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. 【0203】 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 lithium transition metal oxides and their modified compounds with 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, B, and A is at least one selected from N, F, S, Cl. 【0204】 As an example, the positive electrode active material for the lithium ion battery is LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3O2 (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. 【0205】 When the secondary battery of the present application is a sodium-ion battery, the positive electrode active material can include, but is not limited to, at least one of sodium-containing transition metal oxides, polyanion materials (e.g., phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue-based materials. 【0206】 As an example, the positive electrode active material for a sodium-ion battery is 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, materials with the general formula X p M’ q (PO4) r O x Y 3-x It can include at least one of the materials represented by the formula. In the general formula X p M’ q (PO4) r O x Y 3-x where 0 < p ≤ 4, 0 < q ≤ 2, 1 ≤ r ≤ 3, 0 ≤ x ≤ 2, and X is H + 、Li + 、Na + 、K + 、NH4 +At least one selected from the following, where M' is a transition metal cation, preferably at least one of V, Ti, Mn, Fe, Co, Ni, Cu, and Zn, and Y is a halogen anion, preferably at least one of F, Cl, and Br. 【0207】 In this application, the modifying compounds for each of the above-mentioned positive electrode active materials can be used to perform doping modification and / or surface coating modification on the positive electrode active material. 【0208】 In some embodiments, the positive electrode film layer may optionally contain a positive electrode conductive agent. In this application, the type of positive electrode conductive agent is not particularly limited, and as an example, the positive electrode conductive agent includes 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, the mass percentage content of the positive electrode conductive agent is 5% or less based on the total mass of the positive electrode film layer. 【0209】 In some embodiments, the positive electrode film layer may optionally include a positive electrode adhesive. The type of positive electrode adhesive is not particularly limited in this application, and 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 fluorine-containing acrylate resin. In some embodiments, the mass percentage content of the positive electrode adhesive is 5% or less based on the total mass of the positive electrode film layer. 【0210】 In some embodiments, the positive electrode current collector can 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 material substrate and a metal material layer formed on at least one surface of the polymer material substrate. For example, the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. For example, the polymer material substrate may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE). 【0211】 The positive electrode film layer is typically formed by applying a positive electrode slurry to a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is typically formed by dispersing a positive electrode active material, a selectable conductive agent, a selectable adhesive, and any other components in a solvent and stirring them uniformly. The solvent may, but is not limited to, N-methylpyrrolidone (NMP). [Negative electrode sheet] 【0212】 In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector and containing a negative electrode active material. For example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode film layer is provided on one or both of the two opposing surfaces of the negative electrode current collector. 【0213】 The anode active material can be an anode active material for secondary batteries that is well known in the art. For example, the anode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy material. 【0214】 In some embodiments, the negative electrode film layer may optionally contain a negative electrode conductive agent. The type of negative electrode conductive agent is not particularly limited in this application, and as an 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, the mass percentage content of the negative electrode conductive agent is 5% or less based on the total mass of the negative electrode film layer. 【0215】 In some embodiments, the negative electrode film layer may optionally include a negative electrode adhesive. The type of negative electrode adhesive is not particularly limited in this application, and for example, the negative electrode adhesive may include at least one of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylate PAA, polymethacrylate 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% or less based on the total mass of the negative electrode film layer. 【0216】 In some embodiments, the negative electrode film layer may optionally contain other additives. For example, the other additives may include thickeners such as sodium carboxymethylcellulose (CMC), PTC thermistor material, etc. In some embodiments, the mass percentage content of the other additives is 2% or less based on the total mass of the negative electrode film layer. 【0217】 In some embodiments, the negative electrode current collector can be a metal foil sheet or a composite current collector. Copper foil can be used as an example of a metal foil sheet. The composite current collector may include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. For example, the metal material may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. For example, the polymer material substrate may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE). 【0218】 The negative electrode film layer is typically formed by applying a negative electrode slurry to a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, a selectable conductive agent, a selectable adhesive, and other selectable auxiliary agents in a solvent and stirring uniformly. The solvent may, but is not limited to, N-methylpyrrolidone (NMP) or deionized water. 【0219】 The negative electrode sheet does not exclude any additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode sheet described in this application further includes a conductive undercoat layer (e.g., consisting of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and provided on the surface of the negative electrode current collector. In some other embodiments, the negative electrode sheet described in this application further includes a protective layer covering the surface of the negative electrode film layer. [Electrolyte] 【0220】 During the charging and discharging process of a secondary battery, active ions reciprocate between the positive electrode sheet and the negative electrode sheet, being inserted and removed, while the electrolyte plays a role in conducting these active ions between the positive and negative electrode sheets. In this application, the type of electrolyte is not particularly limited and can be selected according to actual needs. 【0221】 The electrolyte solution comprises an electrolyte salt and a solvent. The types of the electrolyte salt and the solvent are not specifically limited and can be selected according to actual needs. 【0222】 If the secondary battery of this application is a lithium-ion battery, the electrolyte salt may, for example, include, but is not limited to, at least one of the following: lithium hexafluoride phosphate (LiPF6), lithium tetraborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoride arsenate (LiAsF6), lithium difluorosulfonylimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium difluoro(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodisoxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). 【0223】 If the secondary battery of this application is a sodium-ion battery, for example, the electrolyte salt may be sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium difluorosulfonylimide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), It includes, but is not limited to, at least one of the following: sodium difluoro(oxalato)borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorooxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP). 【0224】 For example, the solvent may include, but is not limited to, at least one of the following: 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), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). 【0225】 In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performance characteristics of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature performance of the battery, and additives that improve the low-temperature output performance of the battery. 【0226】 In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be manufactured into an electrode assembly by a winding process and / or a lamination process. 【0227】 In some embodiments, the secondary battery may include an outer casing. This casing is used to seal the electrode assembly and the electrolyte. 【0228】 In some embodiments, the casing of the secondary battery may be a hard case such as a rigid plastic case, an aluminum case, or a steel case. The casing of the secondary battery may also be a soft pack, such as a soft bag. The material of the soft bag may be plastic, and may be at least one of polypropylene (PP), polybutylene terephthalate (PBT), or polybutylene succinate (PBS). 【0229】 In this application, the shape of the secondary battery is not particularly limited and may be cylindrical, rectangular, or any other shape. Figure 1 shows a rectangular secondary battery 5 as an example. 【0230】 In some embodiments, as shown in Figure 2, the exterior may include a case 51 and a cover plate 53. The case 51 includes a bottom plate and side plates connected to the bottom plate, and the bottom plate and side plates surround and form a housing cavity. The case 51 has an opening that communicates with the housing cavity, and the cover plate 53 covers the opening and closes the housing cavity. The positive electrode sheet, negative electrode sheet and separator can be formed into an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is packaged in the housing cavity. The 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. 【0231】 The method for manufacturing a secondary battery described in this application is well known. In some embodiments, a secondary battery can be formed by assembling a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. For example, a positive electrode sheet, a separator, and a negative electrode sheet can be formed as an electrode assembly by a winding process or a lamination process, the electrode assembly can be placed in an outer casing, the electrolyte can be injected after drying, and a secondary battery can be obtained through processes such as vacuum sealing, standing, chemical formation, and shaping. 【0232】 In some embodiments of this application, the secondary battery according to this application may be assembled as a battery module, and the number of secondary batteries included in the battery module may be multiple, and the specific number may be adjusted according to the application and capacity of the battery module. 【0233】 Figure 3 is a schematic diagram of a battery module 4 as an example. As shown in Figure 3, in the battery module 4, the multiple secondary batteries 5 may be arranged sequentially along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, these multiple secondary batteries 5 may be fixed together with fasteners. 【0234】 Preferably, the battery module 4 may further include a housing having a housing space for accommodating a plurality of secondary batteries 5. 【0235】 In some embodiments, the battery modules may be assembled as 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. 【0236】 Figures 4 and 5 are schematic diagrams of an example battery pack 1. As shown in Figures 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box. The battery box includes an upper housing 2 and a lower housing 3, the upper housing 2 covering the lower housing 3 and forming a sealed space for housing the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner. 【0237】 power consumption equipment 【0238】 A fourth embodiment of the present invention further provides a power consumption device comprising at least one of the secondary battery, battery module, or battery pack of the present invention. The secondary battery, battery module, or battery pack may be used as a power source for the power consumption device or as an energy storage unit for the power consumption device. The power consumption device may be, but is not limited to, mobile devices (e.g., mobile phones, laptop computers, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc. 【0239】 The aforementioned power consumption device can be configured to use a secondary battery, battery module, or battery pack, depending on its usage needs. 【0240】 Figure 6 is a schematic diagram of an example power consumption device. This power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the requirements for high power output and high energy density of this power consumption device, a battery pack or battery module can be used. 【0241】 Other examples of power-consuming devices may include mobile phones, tablet computers, and laptop computers. These power-consuming devices are generally required to be thin and can use rechargeable batteries as a power source. Examples 【0242】 The following examples are to explain the disclosure content of the present application more specifically. Since it is obvious to those skilled in the art that various modifications and changes can be made within the scope of the disclosure content of the present application, these examples are only for illustrative purposes. Unless otherwise specified, all parts, percentages, and ratios described in the following examples are based on mass. All reagents used in the examples are commercially available or obtained by synthesis according to conventional methods and can be directly used without further treatment. The equipment used in the examples is commercially available. Preparation of nanocellulose C1 Preparation of cellulose powder 【0243】 After the cotton linter was opened and defibered by an opener and the impurities were removed, it was retted at 150 °C for 2 h using a 5 wt% aqueous NaOH solution. Then, the impurities were removed by washing with water (the number of washing times was 3 times), followed by sodium hypochlorite bleaching, washing with dilute hydrochloric acid to remove impurities, washing with water to remove impurities (the number of washing times was 1 time), water removal, and air flow drying in sequence to obtain cotton cellulose powder with a whiteness of 85% or more. Esterification of cellulose 1 kg of the obtained cotton cellulose powder was mixed with 30 kg of a 60 wt% aqueous sulfuric acid solution and reacted at 60 °C for 1.5 h. After the reaction, impurities were removed by washing with water (the number of washing times was 3 times), filtration, acid removal, and impurity removal were carried out in sequence to obtain cellulose nanowhiskers with a sulfonic acid group modification group. Neutralization of cellulose 【0244】 First, the pH of the cellulose nanowhiskers with a sulfonic acid group modification group was adjusted to neutral with a 10 wt% aqueous NaOH solution, then it was dispersed by high-speed treatment with a grinder for 2.5 h, and the number of grinding times was 2 times. Next, it was cut to the nanoscale using a high-pressure homogenizer device to obtain nanocellulose C1 with a sulfonic acid group modification group having an average length of 425 nm and an average diameter of 25 nm, and the molar ratio of the sulfonic acid group to the hydroxyl group was 5:3. Manufacturing of nanocellulose C2-C10 Nanocellulose C2 to C10 is produced in a similar manner to nanocellulose C1. For the differences, refer to Table 1. Preparation of Nanocellulose C11 Preparation of cellulose powder 【0245】 After opening and removing impurities from cotton linter with an opener, it was digested at 150 °C for 2 h using a 5 wt% aqueous NaOH solution. Then, impurities were removed by washing with water (the number of water washings was 3 times), sodium hypochlorite bleaching, impurity removal by washing with dilute hydrochloric acid, impurity removal by washing with water (the number of water washings was 1 time), water removal, and air-flow drying were carried out in sequence to obtain cotton cellulose powder with a whiteness of 85% or more. The obtained cotton cellulose powder was mixed with a 20 wt% aqueous NaOH solution at 10 °C, stirred for 2 hours, filtered, and washed with water twice to obtain alkali cellulose powder. Esterification of cellulose 50 g of the obtained alkali cellulose powder and 200 g of urea were put into a three-neck reactor equipped with an oil-water separator. After urea was dissolved, 5 g of xylene was further added, and the temperature was raised to 137 °C while stirring. After reacting for 4 h, the reaction was terminated, and after washing with water (the number of water washings was 3 times), filtration, and drying, cellulose carbamate was obtained. Neutralization of cellulose 【0246】 The obtained cellulose carbamate was dissolved in a 5 wt% aqueous NaOH solution to obtain a uniform cellulose carbamate solution. Then, it was processed at high speed with a grinder for 2.5 h to disperse it, and the number of grinding times was 2 times. Furthermore, it was cut to the nanoscale using a high-pressure homogenizer device to obtain nanocellulose having an amine group-modified group with an average length of 425 nm and an average diameter of 25 nm, and the molar ratio of the amine group to the hydroxyl group was 4:3. 【0247】 The molar ratio of modifying groups to hydroxyl groups can be measured by determining the hydroxyl value (the number of mg of potassium hydroxide equivalent to the hydroxyl group content per gram of sample) of raw cellulose and modified nanocellulose based on the phthalic anhydride method in GB / T12008.3-2009. The obtained values ​​are converted to mgKOH / g, and then to mmol / g to obtain the hydroxyl group content. By subtracting the hydroxyl group content of modified nanocellulose from the hydroxyl group content of raw cellulose, the content of modifying groups (i.e., the content of modified hydroxyl groups) is obtained, and the molar ratio of modifying groups to hydroxyl groups can then be calculated. Manufacturing of nanocellulose C12-C14 【0248】 Unmodified nanocellulose, product model number CNWS-50, purchased from Zhongke Leiming (Beijing) Technology Co., Ltd., can be further processed with a polishing machine and / or high-pressure homogenizer to obtain nanocellulose with different average diameters and / or different average lengths. See Table 1 for details. [Table 1] Example 1 (1) (Fabrication of separators) 【0249】 S1: A porous PE substrate with a thickness of 4.8 μm and a void ratio of 39% is supplied. S2: Preparation of coating layer slurry: Nanocellulose C1 prepared above, alumina as filler (secondary particle topography, average particle size Dv50 is 140 nm, BET specific surface area is 30 m²) 2 A solution of polyacrylic acid (which is an adhesive), was uniformly mixed in an appropriate amount of deionized water containing a solvent in a mass ratio of 20:79.1:0.9 to obtain a coating layer slurry with a solid content of 35 wt%. S3: Coating: The prepared coating layer slurry is applied to both sides of the PE porous substrate using a coating machine, and a separator is obtained by drying and slitting. The surface density of the coating layer located on one side of the PE porous substrate is 1.1 g / m². 2The thickness is 0.8 μm. The coating machine includes a gravure roll, with a gravure roll line count of 175 LPI, a coating speed of 90 m / min, a coating linear speed ratio of 1.2, a drying temperature of 55 ± 5°C, and a drying time of 50 seconds. (2) Manufacturing of positive electrode sheets 【0250】 Cathode active material LiNi 0.8 Co 0.1 Mn 0.1 A positive electrode slurry is obtained by uniformly mixing O2 (NCM811), the conductive agent carbon black (Super P), and the adhesive polyvinylidene fluoride (PVDF) with an appropriate amount of the solvent N-methylpyrrolidone (NMP) according to a mass ratio of 96.2:2.7:1.1. The positive electrode slurry is applied to aluminum foil, which is the positive electrode current collector, and a positive electrode sheet is obtained through processes such as drying, cold pressing, slitting, and cutting. The surface density of the positive electrode sheet is 0.207 mg / mm². 2 The compressed density is 3.5 g / cm³. 3 That is the case. (3) Manufacturing of negative electrode sheets 【0251】 A negative electrode slurry is obtained by uniformly mixing artificial graphite, the negative electrode active material, carbon black (Super P), the conductive agent, styrene-butadiene rubber (SBR), the adhesive, and sodium carboxymethylcellulose (CMC) in an appropriate amount of deionized water, the solvent, according to a mass ratio of 96.4:0.7:1.8:1.1. The negative electrode slurry is applied to copper foil, which is the negative electrode current collector, and a negative electrode sheet is obtained by drying, cold pressing, slitting, and cutting. The surface density of the negative electrode sheet is 0.126 mg / mm². 2 The compressed density is 1.7 g / cm³. 3 That is the case. 【0252】 (4) Manufacturing of electrolyte Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 30:70 to obtain an organic solvent, and LiPF6, which had been thoroughly dried, was dissolved in the above organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L. (5) Manufacturing of secondary batteries 【0253】 The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an exterior package, and after drying, an electrolytic solution is injected. Through processes such as vacuum sealing, standing, formation, and shaping, a secondary battery is obtained. Examples 2 to 6 【0254】 The secondary battery is manufactured in a method similar to that of Example 1, except that the addition amounts of nanocellulose C1 and filler in the manufacture of the separator are different. Refer to Table 2 for specific parameters. Examples 7 to 17 【0255】 The secondary battery is manufactured in a method similar to that of Example 1, except that the types of nanocellulose used in the manufacture of the separator are different. Refer to Table 1 and Table 2 for specific parameters. Examples 18 to 21 【0256】 The secondary battery is manufactured in a method similar to that of Example 1, except that the specific surface areas of alumina, which is the filler used in the manufacture of the separator, are different. Refer to Table 2 for specific parameters. 【0257】 The secondary particle topography of alumina, which is the filler used in Example 18, has an average particle size Dv50 of 350 nm and a BET specific surface area of 15 m 2 / g. The secondary particle topography of alumina, which is the filler used in Example 19, has an average particle size Dv50 of 175 nm and a BET specific surface area of 20 m 2 / g. The secondary particle topography of alumina, which is the filler used in Example 20, has an average particle size Dv50 of 113 nm and a BET specific surface area of 35 m 2 / g. The secondary particle topography of alumina, which is the filler used in Example 21, has an average particle size Dv50 of 85 nm and a BET specific surface area of 40 m 2 / g. Examples 22 to 26 【0258】 The secondary battery was manufactured in a manner similar to Example 1, except for a difference in the surface density of the coating layer in the separator manufacturing process. Specific parameters are shown in Table 2. Examples 27-28 【0259】 The secondary battery uses alumina as a filler (average particle size Dv50 is 140 nm, BET specific surface area is 30 m²) as a secondary particle topography. 2 ( / g) and primary particle topography of alumina (average particle size Dv50 is 600nm, BET specific surface area is 7m²) 2 The preparation is similar to that of Example 1, except that a mixture with ( / g) is used; refer to Table 2 for specific amounts added. Comparative Examples 1-4 【0260】 The secondary batteries differ in the type of nanocellulose used in the manufacture of the separator, and the fillers used are all alumina (average particle size Dv50 is 1000 nm, BET specific surface area is 5 m²) in primary particle topography. 2 It is manufactured in a similar manner to Example 1, except that it is / g), and specific parameters are shown in Tables 1 and 2. [Table 2] JPEG0007872858000003.jpg132164 Testing Department 【0261】 (1) Test of the moisture content of the separator An empty dish was placed in a drying box and heated at 45°C for 8 hours, then cooled in a drying oven for 1 hour. A separator sample of 0.08g to 0.1g was weighed and placed in the cooled empty dish. The empty dish was then placed in a moisture meter and heated at 170°C for 10 minutes to measure the moisture content of the separator. The test method used was the Karl Fischer moisture meter, and the test instrument used was a Swiss Mantong 831 Karl Fischer moisture meter. 【0262】 (2) Test of the thermal shrinkage rate of the separator Sample preparation: The separators prepared above were punched out using a press machine into samples measuring 50 mm in width and 100 mm in length. Five parallel samples were set and fixed onto an A4 sheet of paper, and the A4 sheet containing the samples was then placed on corrugated cardboard with a thickness of 1 mm to 5 mm. Sample Test: Set the temperature of the forced-air oven to 150°C. After the temperature reaches the set temperature and stabilizes for 30 minutes, place an A4 sheet of paper on top of a piece of cardboard into the forced-air oven and start timing. After the set time (1 hour in this application) has been reached, measure the length and width of the separator and label the values ​​as a and b, respectively. Calculation of thermal shrinkage rate: Longitudinal (MD) thermal shrinkage rate = [(100-a) / 100] × 100%, transverse (TD) thermal shrinkage rate = [(50-b) / 50] × 100%, and the average value of 5 parallel samples was used as the measurement result. 【0263】 (3) Test of the air permeability of the separator At 25°C, the time required for 100 mL of air to pass through a separator was measured, and the average value of five parallel samples was used as the measurement result. A Kumagai KRK (Kumagai Riki Kogyo) Ouken-type air permeability tester can be used as the test equipment. 【0264】 (4) Testing of the cycle performance of secondary batteries At 25°C, the secondary battery was charged with a constant current of 1C to 4.2V, and then the constant voltage charging was continued until the current fell below 0.05C. At this point, the secondary battery was fully charged, and the charge capacity at this time, i.e., the first charge capacity, was recorded. After the secondary battery was left to stand for 5 minutes, it was discharged with a constant current of 1C to 2.8V. This constituted one charge-discharge cycle, and the discharge capacity at this time, i.e., the first 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 one cycle was recorded. The capacity retention rate (%) of the secondary battery after 500 cycles at 25°C = discharge capacity after 500 cycles / first discharge capacity × 100%. 【0265】 (5) Testing of the high-temperature storage performance of secondary batteries At 25°C, the secondary battery is charged with a constant current of 1C to 4.2V, and constant voltage charging is continued until the current falls below 0.05C. After the secondary battery is left standing for 5 minutes, it is discharged with a constant current of 1C to 2.8V, and the discharge capacity at this time is recorded as the capacity before storage. At 25°C, the secondary battery is charged with a constant current of 1C to 4.2V, and constant voltage charging is continued until the current falls below 0.05C, at which point the secondary battery is fully charged. After that, the secondary battery is placed in a constant temperature bath at 60°C and stored for 30 days, then removed, and after that, the secondary battery is discharged with a constant current of 1C to 2.8V, and the discharge capacity at this time is recorded as the capacity after storage. The capacity retention rate (%) after storage of a secondary battery after 30 days of storage = Capacity after storage / Capacity before storage × 100%. 【0266】 (6) Testing of the heat box of the secondary battery At 25°C, the secondary batteries are charged with a constant current of 1C up to 4.2V, and then the constant voltage charging is continued until the current falls below 0.05C, and they are left standing for 5 minutes. After that, each secondary battery is measured with a jig in a high-temperature oven of the DHG-9070A DHG series, and the temperature is raised from room temperature to 80±2°C at a rate of 5°C / min, held for 30 minutes, and then the temperature is raised at a rate of 5°C / min, with each 5°C increase followed by a 30-minute hold until the secondary battery becomes unusable. The change in surface temperature of the secondary battery is monitored during the heating process, and the oven temperature corresponding to when the temperature begins to rise rapidly is defined as the unusable temperature of the secondary battery's heat box. A higher unusable temperature of the secondary battery's heat box indicates better thermal safety performance of the secondary battery. [Table 3] 【0267】 As can be seen from Table 3, in Examples 1 to 28, a coating layer containing nanocellulose and filler is provided on both sides of the porous substrate of the separator, and the ratio of the moisture content of the separator to the thickness of the coating layer is controlled to 250 ≤ A / H ≤ 1500. As a result, the thinned separator has a low moisture content, high heat resistance and high air permeability, and the secondary battery can be given high thermal safety performance and a long lifespan. The heat box expiration temperature of the secondary battery is 150°C or higher, the capacity retention rate of the secondary battery after 500 cycles at 25°C is 88% or higher, and the capacity retention rate of the secondary battery after 30 days of storage at 60°C is 84% ​​or higher. 【0268】 Furthermore, this application is not limited to the embodiments described above. The embodiments described above are merely illustrative, and any configuration that is substantially identical to the technical idea and produces similar effects within the technical scope of this application is included. In addition, various modifications to the embodiments that can be conceived by a person skilled in the art, as long as they do not depart from the spirit of this application, and other forms constructed by combining some of the components of the embodiments are also included within the scope of this application.

Claims

[Claim 1] A separator comprising a porous substrate and a coating layer provided on at least one surface of the porous substrate, The coating layer comprises nanocellulose and filler, the moisture content of the separator is A ppm, the thickness of the coating layer is H μm, and the separator satisfies 250 ≤ A / H ≤ 1500. The average length of the nanocellulose is 100 nm to 600 nm. Separator. [Claim 2] 500 ≤ A / H ≤ 1500, and / or, 400 ≤ A ≤ 1000, and / or, 0 < H ≤ 1.5 The separator according to claim 1. [Claim 3] The nanocellulose comprises at least one of cellulose nanofibers, cellulose nanowhiskers, or bacterial nanocellulose. The separator according to claim 1. [Claim 4] The nanocellulose includes at least one of unmodified nanocellulose and modified nanocellulose. The separator according to claim 1. [Claim 5] The nanocellulose satisfies at least one of the following conditions (1) to (5): (1) The aspect ratio of the nanocellulose is 5 to 80. (2) The average diameter of the nanocellulose is 10 nm to 40 nm. (3) The average length of the nanocellulose is 200 nm to 500 nm. (4) The weight-average molecular weight of the nanocellulose is 10,000 to 60,000. (5) The equilibrium degree of polymerization of the nanocellulose is 150 DP to 300 DP. The separator according to claim 1. [Claim 6] The content of the nanocellulose in the coating layer is 6 wt% to 35 wt% based on the total weight of the coating layer, and / or The content of the filler in the coating layer is 60 wt% or more, based on the total weight of the coating layer. The separator according to claim 1. [Claim 7] The filler comprises at least one type selected from inorganic particles or organic particles, and / or The decomposition temperature of the filler is 200°C or higher. The separator according to claim 1. [Claim 8] The filler includes a first filler, the first filler forming a secondary particle topography created by the aggregation of primary particles. The separator according to claim 1. [Claim 9] The filler further comprises a second filler, the second filler being a primary particle topography. The separator according to claim 8. [Claim 10] The coating layer further comprises a non-particulate adhesive. The separator according to claim 1. [Claim 11] The thickness of the porous substrate is 6 μm or less, and / or The porosity of the porous substrate is 32% to 48%, and / or The surface density of the coating layer is 0.6 g / m². ２ ~1.5 g / m ２ That is, The separator according to claim 1. [Claim 12] The separator further includes an adhesive layer, the adhesive layer is provided on at least a portion of the surface of the coating layer, and the adhesive layer includes particulate adhesive. The separator according to claim 1. [Claim 13] Satisfying at least one of the following conditions (1) to (9), (1) The longitudinal thermal shrinkage rate of the separator at 150°C for 1 hour is 5% or less. (2) The lateral thermal shrinkage rate of the separator at 150°C for 1 hour is 5% or less. (3) The puncture strength of the separator is 350 gf or more. (4) The longitudinal tensile strength of the separator is 2000 kg / cm². ２ That's all. (5) The lateral tensile strength of the separator is 2000 kg / cm². ２ That's all. (6) The permeability of the separator is 300 s / 100 mL or less. (7) The porosity of the separator is 30% to 45%, (8) The wetted length of the separator is 30 mm or more. (9) The wetting rate of the separator is 3 mm / s or more. The separator according to claim 1. [Claim 14] A method for manufacturing a separator according to claim 1, The process includes: step S1 of supplying a porous substrate; step S2 of preparing a coating layer slurry by mixing nanocellulose and filler in a solvent in a predetermined ratio to prepare the coating layer slurry; and application step S3 of applying the coating layer slurry to at least one surface of the porous substrate to form a coating layer and drying to obtain a separator. The separator comprises a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer comprises nanocellulose and filler, the moisture content of the separator is A ppm, the thickness of the coating layer is H μm, and the separator satisfies 250 ≤ A / H ≤ 1500. The average length of the nanocellulose is 100 nm to 600 nm. Manufacturing method. [Claim 15] The coating step satisfies at least one of the following conditions (1) to (5): (1) The coating is carried out using a coating machine, the coating machine includes a gravure roll, and the number of lines on the gravure roll is 100 LPI to 300 LPI. (2) The coating speed is 30 m / min to 120 m / min, (3) The linear velocity ratio of the coating is 0.8 to 2.

5. (4) The drying temperature is 40°C to 70°C. (5) The drying time is 10 to 120 seconds. The method according to claim 14. [Claim 16] The process further includes step S4, which involves applying a slurry containing particulate adhesive to at least a portion of the surface of the coating layer and applying it twice to form an adhesive layer after drying. The method according to claim 14 or 15. [Claim 17] A separator comprising any one of claims 1 to 13, Secondary battery. [Claim 18] A power consumption device comprising a secondary battery as described in claim 17.

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