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

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, entitled "Separator, Manufacturing Method Thereof, and Related Secondary Battery, Power Consumption Device," filed on June 24, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to the field of battery technology, and in particular to a separator, a manufacturing method thereof, and related secondary batteries and power consuming devices. [Background technology]

[0003] In recent years, secondary batteries have been widely used in many fields, such as energy storage power systems for hydroelectric, thermal, wind and solar power plants, electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. With the application and popularity of secondary batteries, their service life and safety issues, especially thermal safety issues, have attracted more and more attention. However, currently, methods for improving the thermal safety performance of secondary batteries may be unfavorable to the balance of the energy density of secondary batteries. Therefore, it is an important task in the design of secondary batteries to provide secondary batteries with high energy density, high thermal safety performance and long life. Summary of the Invention

[0004] The present application aims to provide a separator, a manufacturing method thereof, and related secondary batteries and power consuming devices. The separator has characteristics such as excellent heat resistance, low water content, and good wettability with respect to an electrolyte, and therefore a secondary battery using the separator can have a high energy density, high heat safety performance, and long life.

[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, where 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 the 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 the 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 the improvement of the energy density of the secondary battery.

[0010] In any embodiment of the present 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 its hydrophilicity and further favor moisture evacuation during drying, and the separator of the present application can have a low moisture content.

[0011] In any embodiment of the present application, the nanocellulose comprises at least one of unmodified nanocellulose and modified nanocellulose, preferably modified nanocellulose.

[0012] In any embodiment of the present application, the modified nanocellulose comprises a modifying group, and 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, and preferably comprises 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, it can effectively improve the heat resistance of the separator and improve the thermal safety performance of the secondary battery, while it is also advantageous to have a low water content under the premise that the separator has good electrolyte wettability, and can further improve the electrochemical performance of the secondary battery.

[0013] In any embodiment of the present application, the modified nanocellulose contains a hydroxyl group and a modifying group, and the molar ratio of the modifying group to the hydroxyl group is 1:4 to 4:1, preferably 2:3 to 7:3. When the molar ratio of the modifying group to the hydroxyl group is within an appropriate range, the heat resistance and ion transport properties of the separator can be further improved, and the separator can have a low moisture content.

[0014] In any embodiment of the present 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 the present 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 in an appropriate range, the heat resistance, ion transport properties, and voltage breakdown properties of the separator can be further improved.

[0016] In any embodiment of the present 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 the present 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 the present 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, not only can nanocellulose be prevented from blocking the pore structure of the separator, but the viscosity of the coating layer slurry can be adjusted to an appropriate range, which makes the slurry have better fluidity and wetting properties during application, and is more advantageous in improving the quality of the coating layer.

[0020] In any embodiment of the present application, the content of the 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 the present 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 can ensure that the coating layer slurry has an appropriate viscosity, which is favorable for application, and it is also favorable for the separator to have a low moisture content and good electrolyte wettability, and it is also favorable for the filler and nanocellulose to form a stable spatial network structure.

[0023] In any embodiment of the present application, the filler includes at least one type selected from inorganic particles and organic particles.

[0024] In any embodiment of the present application, the decomposition temperature of said filler is equal to or greater than 200°C.

[0025] In any embodiment of the present application, the filler includes a first filler, and the first filler is a secondary particle topography formed by agglomeration of primary particles. At this time, the nanocellulose is also overlapped in the gaps between the primary particles constituting the filler of the secondary particle topography, and the nanocellulose and the first filler are overlapped to form an integrated effect, so that the coating layer can have a more stable space network structure, and the separator can have a suitable porosity and a stable pore structure, and the separator can also have both low moisture content and good electrolyte wettability.

[0026] In any embodiment of the present application, the content of the first filler is 50 wt% to 100 wt%, and preferably 90 wt% to 99 wt%, based on the total weight of the filler.

[0027] In any embodiment of the present application, the first filler has an average particle size Dv50 of 200 nm or less, and preferably 50 nm to 200 nm.

[0028] In any embodiment of the present application, the BET specific surface area of ​​the first filler is 20 m 2 / g or more, preferably 25m2 / g~50m 2 / g.

[0029] When at least one of the content, average particle diameter Dv50, and BET specific surface area of ​​the first filler is within the above range, the first filler can overlap with the nanocellulose to form an integrated effect, so that the coating layer can have a more stable spatial network structure and the separator can have better heat resistance and wettability to the electrolyte.

[0030] In any embodiment of the present application, the first filler comprises inorganic particles of a secondary particle topography, and the crystal type of the inorganic particles of the secondary particle topography comprises at least two of an α crystal type, a θ crystal type, a γ crystal type, and a crystal type, and preferably comprises at least two of an α crystal type, a θ crystal type, and a γ crystal type.

[0031] In any embodiment of the present application, the first filler includes inorganic particles of secondary particle topography, the crystal type of the inorganic particles of the secondary particle topography includes a θ crystal type, and the content of the θ crystal type 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] Selection of the first filler having a different crystal type contributes to improving at least one of the heat resistance and electrolyte wettability of the separator.

[0033] In any embodiment of the present application, the filler further includes a second filler, and the second filler is a primary particle topography, which can better exert the supporting effect of the second filler, improve the heat resistance of the separator, and also contribute to the coating layer having more pore structures and less moisture content when the amount of the second filler used is small.

[0034] In any embodiment of the present 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 the present application, the second filler has an average particle size Dv50 of 100 nm to 800 nm, preferably 200 nm to 400 nm.

[0036] In any embodiment of the present application, the BET specific surface area of ​​the second filler is 10 m 2 / g or less, preferably 4m 2 / g~9m 2 / g.

[0037] When at least one of the content, average particle diameter Dv50, and BET specific surface area of ​​the second filler is within the above range, the second filler can better exert its supporting effect, which is favorable for discharging moisture during the drying process, and can maintain an appropriate porosity and stable pore structure in the coating layer during long-term charge and discharge processes, and can further improve the ion transport properties and wettability of the separator with respect to the electrolyte.

[0038] In any embodiment of the present application, the second filler includes inorganic particles of primary particle topography, and the crystal type of the inorganic particles of the primary particle topography includes at least one of α crystal type and γ crystal type, and preferably includes α crystal type, which can further improve the heat resistance of the separator.

[0039] In any embodiment of the present application, the second filler comprises inorganic particles of a primary particle topography, the crystal type of the inorganic particles of the primary particle topography comprises an α crystal type, and the content of the α crystal type 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 comprises a non-particulate adhesive, and preferably, the non-particulate adhesive comprises an aqueous adhesive, which 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 also allows the separator to maintain high adhesion and good ion transport properties under the premise of reducing the amount of adhesive used.

[0042] In any embodiment of the present application, the thickness of the porous substrate is 6 μm or less, and preferably 3 μm to 5 μm, which 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%. If the porosity of the porous substrate is within an appropriate range, it is advantageous to further improve the ion transport properties 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.

[0044] In any embodiment of the present application, the areal density of the coating layer is 0.6 g / m 2 ~1.5g / m 2 and preferably 0.8 g / m 2 ~1.1g / m 2 This contributes to the formation of a coating layer with excellent heat resistance.

[0045] In any embodiment of the present application, the separator further includes an adhesive layer, the adhesive layer being provided on at least a portion of the surface of the coating layer, the adhesive layer including a particulate adhesive, and preferably the particulate adhesive including at least one of an acrylic acid ester monomer homopolymer or copolymer, an acrylic acid monomer homopolymer or copolymer, and a fluorine-containing olefin monomer homopolymer or copolymer. The adhesive layer can not only prevent the coating layer from falling off to improve the safety performance of the secondary battery, but also improve the interface between the separator and the electrodes, thereby improving the cycle performance of the secondary battery.

[0046] In any embodiment of the present application, the separator has a longitudinal heat shrinkage rate at 150° C. for 1 hour of 5% or less, and preferably 0.5% to 4%.

[0047] In any embodiment of the present application, the separator has a transverse heat shrinkage rate at 150° C. for 1 hour of 5% or less, and preferably 0.5% to 4%.

[0048] In any embodiment of the present application, the separator has a puncture strength of 350 gf or more, and preferably 370 gf to 450 gf.

[0049] In any embodiment of the present application, the separator has a longitudinal tensile strength of 2000 kg / cm 2 More than 2500kg / cm 2 ~4500kg / cm 2 It is.

[0050] In any embodiment of the present application, the separator has a transverse tensile strength of 2000 kg / cm 2 More than 2500kg / cm 2 ~4500kg / cm 2 It is.

[0051] In any embodiment of the present application, the separator has an air permeability of 300s / 100mL or less, and preferably 100s / 100mL to 200s / 100mL.

[0052] In any embodiment of the present application, the porosity of the separator is 30% to 45%, and preferably 32% to 36%.

[0053] In any embodiment of the present application, the wetted length of the separator is 30 mm or more, and preferably 30 mm to 80 mm.

[0054] In any embodiment of the present application, the wetting speed of the separator is 3 mm / s or more, and preferably 3 mm / s to 10 mm / s.

[0055] If the separator performance satisfies one or more of the above conditions, it is advantageous for improving at least one of the energy density, thermal safety performance, capacity development characteristics, and lifespan of the secondary battery.

[0056] A second aspect of the present application provides a method for producing a separator according to the first aspect of the present application, comprising: a step S1 of supplying a porous substrate; a step S2 of preparing a coating layer slurry by mixing nanocellulose and a filler in a solvent at a predetermined ratio to prepare the coating layer slurry; and a coating 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 comprising a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer comprising 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 method for producing a separator according to the present application produces a coating layer by a single application, greatly simplifying the separator production process.

[0057] In any embodiment of the present application, the coating is performed using a coater, the coater includes a gravure roll, and the ruling of the gravure roll is 100 LPI to 300 LPI, preferably 125 LPI to 190 LPI.

[0058] In any embodiment of the present application, the coating speed is from 30 m / min to 120 m / min, and preferably from 60 m / min to 90 m / min.

[0059] In any embodiment of the present application, the linear speed ratio of the coating is from 0.8 to 2.5, and preferably from 0.8 to 1.5.

[0060] In any embodiment of the present application, the drying temperature is from 40°C to 70°C, and preferably from 50°C to 60°C.

[0061] In any embodiment of the present application, the drying time is from 10 seconds to 120 seconds, and preferably from 20 seconds to 80 seconds.

[0062] By controlling each of the above process parameters within a predetermined range, the performance of the separator of the present application can be further improved.

[0063] In any embodiment of the present application, the method further includes a step S4 of applying a slurry containing a 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.

[0064] A third aspect of the present application provides a secondary battery comprising the separator of the first aspect of the present application or a separator produced by the method of the second aspect of the present application.

[0065] A fourth aspect of the present application provides a power consuming device including the secondary battery of the third aspect of the present application.

[0066] The separator provided in the present application has characteristics such as excellent heat resistance, low water content, and good wettability with respect to an electrolyte, so that a secondary battery using the separator can have a high energy density, high thermal safety performance, and a long life. The power consumption device of the present application includes the secondary battery of the present application, and therefore has at least the same advantages as the secondary battery. [Brief description of the drawings]

[0067] In order to more clearly describe the technical solutions of the embodiments of the present application, the drawings that need to be used in the embodiments of the present application are briefly described below. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on the drawings, even if they apply creative efforts.

[0068] [Figure 1] FIG. 1 is a schematic diagram of an embodiment of a secondary battery of the present application. [Diagram 2] FIG. 2 is an exploded schematic view of the embodiment of the secondary battery of FIG. 1. [Diagram 3] FIG. 1 is a schematic diagram of one embodiment of a battery module of the present application. [Figure 4] FIG. 1 is a schematic diagram of one embodiment of a battery pack of the present application. [Diagram 5] 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4. [Figure 6] 1 is a schematic diagram of an embodiment of a power consuming device including a secondary battery of the present application as a power source.

[0069] The drawings are not necessarily drawn to scale. 1 Battery pack 2 Upper case 3 Lower housing 4 Battery Module 5 Secondary battery 51 cases 52 Electrode Assembly 53 Lid plate DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0070] Hereinafter, with appropriate reference to the drawings, embodiments specifically disclosing the separator of the present application, its manufacturing method, and the related secondary battery and power consumption device will be described in detail. However, unnecessary detailed description may be omitted. For example, detailed description of known matters and duplicated description of substantially the same configuration may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the attached drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0071] The "ranges" disclosed in this application are defined in the form of lower and upper limits, where a given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such defined ranges may be inclusive or exclusive of the end values, and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, when ranges of 60-120 and 80-110 are recited for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Also, when minimum range values ​​1 and 2 and maximum range values ​​3, 4 and 5 are recited, ranges of 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 may all be contemplated. In this application, unless otherwise stated, the numerical range "a-b" is represented by the abbreviation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, with "0-5" being an abbreviation for combinations of these numerical values. Furthermore, expressing a parameter as an integer greater than or equal to 2 (≧2) is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0072] Unless otherwise specified, all the embodiments and optional embodiments of the present application may be combined with each other to form a new technical solution, and such technical solution should be considered as being included in the disclosure content of the present application.

[0073] Unless otherwise stated, all technical features and optional technical features of the present application may be combined with each other to form a new technical solution, and such technical solution should be considered as included in the disclosure content of the present application.

[0074] Unless otherwise stated, all steps in the present application may be performed in sequence or randomly, but are preferably performed in sequence. For example, the method includes steps (a) and (b) and may include steps (a) and (b) performed in sequence, or may include steps (b) and (a) performed in sequence. For example, when it is stated that the method may further include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0075] Unless otherwise specified, the terms "comprise" and "include" used in this application mean open-ended and may also be closed-ended. For example, the terms "comprise" and "include" can mean "comprise" or "include" other components not listed, or "comprise" or "include" only the listed components.

[0076] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, 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 "plurality" and "multiple types" mean two or more than two.

[0078] Unless otherwise explained, terms used in this application have the well-known meanings commonly understood by those of ordinary skill 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 field, 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 including a positive electrode sheet, a negative electrode sheet, and a separator, the separator being provided between the positive electrode sheet and the negative electrode sheet, mainly serves to prevent short circuit between the positive electrode and the negative electrode, and allows active ions to pass freely through the separator to form a circuit. With the application and popularization of secondary batteries, the requirements for the energy density of secondary batteries are also increasing. Thinning the separator is an effective measure to improve the energy density of secondary batteries. Currently, the separators used in commercialized secondary batteries are usually polyolefin porous membranes, such as polyethylene porous membranes, polypropylene porous membranes, or polypropylene / polyethylene / polypropylene three-layer composite membranes, with a melting point of 130°C to 160°C. Therefore, when the thickness is thinned, the heat resistance of the separator becomes poor, and when exposed to heat, it shrinks significantly, increasing the risk of short circuit between the positive electrode and the negative electrode.

[0081] To solve the above problems, the currently adopted measures are mainly to coat a heat-resistant inorganic ceramic layer on the polyolefin porous membrane, which can increase the mechanical strength of the separator, reduce the degree of shrinkage of the separator when exposed to heat, and reduce the risk of short circuit between the positive and negative electrodes. However, because the particle size of commercially available inorganic ceramic particles is large, the thickness of the entire separator increases, and the energy density of the secondary battery cannot be balanced, which is disadvantageous to improving the driving range, especially in the field of power batteries. In addition, because the particle size of commercially available inorganic ceramic particles is large, the number of deposited 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 of inorganic ceramic particles can reduce the thickness of the coating layer and alleviate the adverse effect on the energy density of the secondary battery, but the porosity of the coating layer formed by nano-sizing inorganic ceramic particles is low and is easy to block the pores of the polyolefin porous membrane, which reduces the porosity of the entire separator, increases the impedance of the ions, and is disadvantageous to the transport of active ions. At the same time, since the nano-sized inorganic ceramic particles have a high specific surface area and the contact between the particles is point contact, a large amount of adhesive needs to be used to ensure adhesion between the particles. However, if a large amount of adhesive is used, problems such as clogging of pores are likely to occur, which is detrimental to the rate performance of the secondary battery, for example, dendrites are likely to form on the surface of the negative electrode, and further detrimental to the capacity and energy density of the secondary battery.

[0082] In addition, inorganic ceramic particles have the property of easily absorbing water. In particular, when inorganic ceramic particles are nano-sized, their specific surface area increases significantly, which significantly increases the moisture content of the separator. During the long-term charge and discharge process of a secondary battery, the moisture in the separator is gradually released and enters the electrolyte. At present, the electrolyte system with the widest commercial application is a mixed carbonate ester solution of lithium hexafluorophosphate, which has poor thermal stability in high-temperature environments and decomposes at high temperatures to form PFs. 5 Generate and PF 5is highly sensitive to trace amounts of water in the electrolyte, and generates HF when it comes into contact with water, which increases the acidity of the electrolyte and is prone to corrode the positive electrode active material and the 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, the separator is required to have a low water content.

[0083] With the application and popularization of secondary batteries, the requirements for the service life of secondary batteries are also increasing. During the long-term charge and discharge process of secondary batteries, the separator gradually dries out and no longer functions, which is one of the main factors that cause the capacity of secondary batteries to decrease. This is because after the separator dries out, the internal resistance of the battery increases, so that charging and discharging are not completed, the capacity of the secondary battery is quickly attenuated, and the service life of the secondary battery is greatly reduced. Therefore, the separator is also required to have good electrolyte wettability.

[0084] However, prior art 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 the present application unexpectedly discovered that by providing a coating layer containing nanocellulose and a filler on the surface of a separator porous substrate and rationally controlling the ratio of the moisture content of the separator to the thickness of the coating layer, the separator can be endowed with high heat resistance, low moisture content, and good electrolyte wettability, and the secondary battery can be endowed with high energy density, high heat safety performance, and long life. Separator

[0086] Specifically, a first aspect of an embodiment of the present application provides a separator comprising a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer comprising nanocellulose and a filler, the moisture content of the separator being Appm, the thickness of the coating layer being H μm, and the separator satisfying 250≦A / H≦1500.

[0087] The inventors of the present application, after extensive research, 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 moisture content of the separator to the thickness of the coating layer within the above-mentioned specific range, the separator can be provided with high heat resistance, low moisture content, and good electrolyte wettability.

[0088] The nanocellulose structure contains many hydroxyl groups and has strong hydrophilicity, so if used alone, the moisture content of the separator is likely to be high, which affects the electrochemical performance of the secondary battery. The coating layer of the present application simultaneously contains nanocellulose and a filler, and the nanocellulose can overlap with the filler to form a stable spatial network structure, which is favorable for discharging moisture during the drying process, so that the separator of the present application can have a low moisture content.

[0089] The inventors of the present application, after extensive research, have found that when the moisture content Appm of the separator containing nanocellulose and a filler and the thickness Hμm of the coating layer are controlled so that A / H is between 250 and 1500, the coating layer can have a good spatial network structure and an appropriate content of hydroxyl functional groups, so that the separator has a low moisture content and good electrolyte wettability, and further, the secondary battery using the same can have good electrochemical performance, particularly a long cycle life and a long storage life. In addition, the coating layer of the present application simultaneously contains nanocellulose and a filler, and the nanocellulose and the filler are overlapped to give the coating layer a stable spatial network structure, so that the coating layer has high heat resistance, the degree of shrinkage when the separator is subjected to heat is reduced, the risk of short circuit between the positive electrode and the negative electrode is reduced, and the secondary battery can have high thermal safety performance. At the same time, because the coating layer of the present application has high heat resistance, a thinner porous substrate can be selected, and the secondary battery can have a high energy density.

[0090] The moisture content Appm of the separator and the thickness H μm of the coating layer satisfy 250≦A / H≦1500. For example, A / H may be in a range of any numerical value of 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1250, 1500 or more. Preferably, it is 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 content of hydroxyl functional groups, allowing the separator to have high heat resistance, low water content and good electrolyte wettability, and allowing the secondary battery to have high heat safety performance, long cycle life and long storage life.

[0091] The moisture content of the separator can be measured by a moisture meter, the measurement method can adopt the Karl Fischer moisture meter, and the test equipment can adopt the Swiss Wantong 831 Karl Fischer moisture meter.

[0092] In some embodiments, when the water content Appm of the separator satisfies A≦1000, the amount of water eluted from the separator and released into the electrolyte during charging and discharging of the secondary battery is small, which contributes to the secondary battery having good electrochemical performance. In particular, the secondary battery may have high capacity characteristics and a low volume expansion rate.

[0093] In addition, the inventors of the present application unexpectedly discovered in the course of their research that the lower the moisture content of the separator, the better it is. 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 will be poor, for example the separator's liquid absorption will decrease and its wettability to the electrolyte will be poor. As a result, during the long-term charge and discharge process of the secondary battery, the separator will rapidly dry out and no longer function; furthermore, the internal resistance of the secondary battery will rapidly increase, the capacity will rapidly decay, and the service life will be significantly shortened.

[0094] In some embodiments, the moisture content Appm of the separator satisfies 400≦A≦1000. For example, A may be any range of 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000 or more. Preferably, A 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, and the separator can be better equipped with high heat resistance, low moisture content and good electrolyte wettability, and the cycle life and storage life of the secondary battery can be further improved.

[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. Thereby, it 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 Thereby, it 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, thereby contributing to selecting a thinner porous substrate and further improving the energy density of the secondary battery.

[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, ensuring that the secondary battery has a high discharge rate and reducing the self-discharge of the battery.

[0099] In the present application, the material of the porous substrate is not particularly limited, and any well-known substrate having good chemical stability and mechanical stability can be selected, for example, the porous substrate can include at least one of a porous polyolefin resin film (e.g., at least one of polyethylene, polypropylene, and polyvinylidene fluoride), a porous glass fiber, and a porous nonwoven fabric. The porous substrate can be a single-layer film or a multi-layer composite film. When the porous substrate is a multi-layer composite film, the materials of each layer can be the same or different.

[0100] Another measure to improve the energy density of a secondary battery is to improve the voltage, for example by adopting a high-voltage positive electrode active material, but improving the voltage has a significant effect on the stability of the separator, so the separator needs to have good voltage breakdown characteristics. The separator coating layer of the present application includes nanocellulose, which is a general term for cellulose whose size in any dimension is nanoscale (for example, within 100 nm), and has both cellulose characteristics and nanoparticle characteristics. Nanocellulose may be a polymer nanomaterial extracted from wood, cotton, etc. in nature by one or more means of chemical, physical, biological, etc., and has the advantages of wide source, low cost, biodegradability, high elastic modulus, high specific surface area, etc., so it is an excellent alternative to traditional petrochemical resources, and can effectively alleviate problems such as environmental pollution and shortage of petrochemical resources. Nanocellulose also has good high temperature resistance properties and small volume change after being exposed to heat, so that the heat resistance of the separator can be improved, and at the same time, the density of nanocellulose is smaller than that of traditional inorganic ceramic particles, so that the weight of the secondary battery can be reduced and the gravimetric energy density of the secondary battery can be improved. Nanocellulose also provides the coating layer with tiny, uniform nanopores, which helps prevent current leakage, thereby providing the separator with both high ion transport properties and good voltage breakdown resistance.

[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, bacterial cellulose or microbial cellulose), and preferably includes cellulose nanowhiskers. Cellulose nanowhiskers have a high degree of crystallinity, which can reduce the hydrophilicity and is advantageous for water discharge during the drying process, thereby allowing the separator of the present application to have a low water content. In addition, cellulose nanowhiskers are easily overlapped with the filler, which can provide a more stable spatial network structure in the coating layer and further improve the performance of the separator.

[0102] In some embodiments, the nanocellulose may comprise at least one of unmodified nanocellulose (also referred to as hydroxylated nanocellulose) and modified nanocellulose, preferably modified nanocellulose.

[0103] The modified nanocellulose comprises a modifying group, which in some embodiments may comprise 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, and preferably comprises 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 improve the thermal safety performance of the secondary battery, while it is advantageous for the separator to have a low moisture content on the premise that it has good electrolyte wetting properties, thereby further improving the electrochemical performance of the secondary battery.

[0105] When nanocellulose has the above-mentioned specific modifying groups, the nanocellulose can form a more stable spatial network structure together with the filler, and can further improve the ion transport properties and voltage breakdown properties of the separator, which is also advantageous for matching with high-voltage positive electrode active materials, and can further improve the energy density of the secondary battery.

[0106] In addition, the presence of the modifying group can also reduce the proportion of hydroxyl groups, ensuring that the coating layer slurry has an appropriate viscosity, which is more convenient for application, and can also improve the production efficiency of the separator and the uniformity of the coating layer.

[0107] In some embodiments, the modified nanocellulose includes a hydroxyl group and a modifying group, and the molar ratio of the modifying group to the hydroxyl group may be 1:4 to 4:1, preferably 2:3 to 7:3. When the molar ratio of the modifying group to the hydroxyl group is within an appropriate range, the heat resistance and ion transport properties of the separator can be further improved, and the separator can have a low moisture content. In addition, the following situation can be effectively avoided. If the molar ratio of the modifying group to the hydroxyl group is too small, the further improvement effect on the heat resistance and ion transport properties of the separator by the modifying group may not be significant. If the molar ratio of the modifying group to the hydroxyl group is too large, the electrolyte wettability of the separator may be affected, for example, the ion transport properties of the separator may be deteriorated, which may affect the cycle life and storage life of the secondary battery, and may also reduce the heat resistance of the separator, and may even 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 determining the characteristic peaks contained therein. Specifically, infrared spectroscopy 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, USA, in accordance with GB / T6040-2019 Infrared Spectroscopic Analysis Method General Rules.

[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 properties of the separator can be further improved. In addition, 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 lead to poor heat resistance of the coating layer. In addition, during the drying process of the coating layer, some of the nanocellulose is prone to collapse due to lack of the support effect of the filler, and furthermore, the problem of pore clogging is likely to occur, which inhibits active ion transport and water discharge, and affects 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 lead to poor ion transport properties 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 in an appropriate range, the heat resistance, ion transport properties and voltage breakdown properties of the separator can be further improved. In addition, the following situation 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 are large, which may deteriorate the voltage breakdown properties of the separator, and the overlap effect with the filler may be poor, which may deteriorate the heat resistance of the coating layer. In addition, during the drying process of the coating layer, some of the nanocellulose is easily collapsed due to lack of the supporting effect of the filler, and is also prone to pore clogging problems, which inhibits active ion transport and water 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 a suitable range, the heat resistance and ion transport properties of the separator can be further improved. In addition, the following situations can be effectively avoided. If the average length of the nanocellulose is too short, the overlap effect with the filler may be poor, which may lead to poor heat resistance of the coating layer. In addition, during the drying process of the coating layer, some nanocellulose is prone to collapse due to lack of the supporting effect of the filler, and is more likely to cause pore clogging problems, which inhibits active ion transport and water 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 may affect the quality of the obtained 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 method. A sample of 3.6 mm x 3.6 mm is cut out from any one area in the separator, and the microtopography structure of the coating layer in the sample is measured using a scanning electron microscope (e.g., ZEISS Sigma 300), high vacuum mode is selected, the operating voltage is 3 kV, the magnification is 30,000 times, and an SEM image is obtained. Based on the obtained SEM image, multiple (e.g., 5 or more) test areas are selected to perform length statistics, and the size of each test area is 0.5 μm x 0.5 μm, and then the average value of the length obtained in each test area is taken as the average length of nanocellulose. Based on the obtained SEM image, multiple (e.g., 5 or more) test areas are selected to perform diameter statistics using Nano Measurer particle size distribution statistical software, and the size of each test area is 0.5 μm x 0.5 μm, and then the average value of the diameter obtained in each test area is taken as the average diameter of nanocellulose.

[0113] In some embodiments, the weight average molecular weight of the nanocellulose may be 10,000 to 60,000, preferably 30,000 to 50,000.

[0114] In some embodiments, the equilibrium degree of polymerization of the nanocellulose may be 150 DP to 300 DP, preferably 200 DP to 250 DP.

[0115] When the weight-average molecular weight and / or degree of polymerization of nanocellulose are within an appropriate range, not only can nanocellulose be prevented from blocking the pore structure of the separator, but the viscosity of the coating layer slurry can be set within an appropriate range, which makes the fluidity and wetting properties of the slurry better during application, and is more favorable 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-like shapes. Nanocellulose of a suitable shape is advantageous for forming a stable spatial network structure with the filler, which can further improve the ion transport properties and external force compression resistance of the separator.

[0117] In some embodiments, the content of the nanocellulose in the coating layer may be 6wt%-35wt%, preferably 10wt%-30wt%, based on the total weight of the coating layer. When the content of nanocellulose is within a suitable range, it can ensure that the coating layer slurry has a suitable viscosity, which is more convenient for application, and it is also convenient for the separator to have a low water content and good electrolyte wettability, and it is also convenient for the nanocellulose to build a stable space network structure together with the filler, which further improves the performance of the separator, for example, reducing the water content of the separator and improving the heat resistance, ion conduction ability, external force pressing ability and voltage breakdown ability of the separator.

[0118] In some embodiments, the content of the filler in the coating layer may be 60wt% or more, preferably 65wt% to 90wt%, based on the total weight of the coating layer. When the content of the filler is within a suitable range, it can ensure that the coating layer slurry has a suitable viscosity, which is more convenient for application, and it is also convenient for the separator to have a low water content and good electrolyte wettability, and it is also convenient for building a stable spatial network structure together with nanocellulose, which can further improve the performance of the separator, such as reducing the water content of the separator, and improving the heat resistance, tensile strength, puncture resistance, and external force pressing resistance of the separator.

[0119] In the secondary battery, the microstructural changes of the positive and negative active materials are irreversible during long-term charge and discharge, so that the volume of the entire battery increases. In particular, during rapid charging of the secondary battery, the negative active material has a higher degree of volume increase after inserting active ions. When the battery expands, a pressing and / or pulling action occurs on the separator, which makes the separator more likely to break, thereby increasing the risk of short circuit between the positive and negative electrodes. Therefore, the separator is also required to have good resistance to pressing force. The presence of the filler contributes to the coating layer having a stable spatial network structure, which can improve the ion transport properties and heat resistance of the separator, and can also improve the tensile strength, puncture resistance, and pressing force resistance of the separator.

[0120] In some embodiments, the filler can 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, so that the filler has excellent thermal stability and is less likely to decompose, and the heat resistance of the separator can be further improved.

[0122] Inorganic particles have high thermal stability and are difficult to decompose, and since they usually have hydroxyl groups on their surfaces, they tend to form a stable network structure of spaces together with nanocellulose. In some embodiments, the inorganic particles preferably include at least one of inorganic particles having a dielectric constant of 5 or more, inorganic particles having ion conductivity but not storing ions, or inorganic particles capable of undergoing electrochemical reactions.

[0123] Preferably, the inorganic particles having a dielectric constant of 5 or more are selected from the group consisting of boehmite, aluminum oxide, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, magnesium lithium silicate, magnesium sodium silicate, bentonite, hectorite, zirconium titanate, barium titanate, and Pb(Zr,Ti)O. 3 (abbreviated as PZT), Pb 1-m La m Zr 1-n Ti n O 3 (Abbreviated as PLZT, 0 <m<1、0<n<1)、Pb(Mg 3 Nb 2 / 3 )O 3 -PbTiO 3 (abbreviated as PMN-PT), and at least one of the modified inorganic particles. Preferably, the modification method of 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 be mechanical force dispersion, ultrasonic dispersion, high energy treatment, etc. The modification treatment reduces the aggregation of inorganic particles, thereby building a more stable and uniform space network structure together with nanocellulose, and also contributes to improving the wettability of the coating layer to the electrolyte and improving the adhesion of the coating layer by selecting a coupling agent, a surface active material, or a polymer-modified inorganic particle having a specific functional group.

[0124] Preferably, the inorganic particles having ion conductivity but not storing ions are Li 3 PO 4 , Lithium titanium phosphate Li x1 Ti y1 (PO4 ) 3 Lithium aluminum titanium phosphate Li x2 Al y2 Ti z1 (PO 4 ) 3 , (LiAlTiP) x3 O y3 type glass, lithium lanthanum titanate Li x4 La y4 TiO 3 , lithium germanium thiophosphate Li x5 Ge y5 P z2 S w , lithium nitride Li x6 N y6 , SiS 2 type glass Li x7 Si y7 S z3 or P 2 S 5 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] The organic particles have good thermal stability and are not easily decomposed, which can improve the heat resistance of the separator. At the same time, when the internal temperature of the secondary battery reaches the melting point of the organic particles due to overcharging, overheating, etc., the organic particles will melt and be absorbed into the micropores of the porous substrate through capillary action to play the role of closing and blocking the pores, which is advantageous in ensuring that the secondary battery has high safety performance.

[0127] In some embodiments, the organic particles include, but are not limited to, at least one of 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, polyamideimide 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 be preferably 130° C. or higher. This prevents the organic particles from transitioning from a glass state to a viscous flow state when the internal temperature of the secondary battery reaches 130° C., thereby preventing the separator from suddenly shrinking. More preferably, the organic particles include at least one of melamine formaldehyde resin particles, phenolic resin particles, polyester particles, silicone resin particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, and polyaryletherketone particles, but are not limited thereto.

[0129] In some embodiments, the filler includes a first filler, and the first filler is a secondary particle topography formed by agglomeration of primary particles. The filler of the secondary particle topography has a large specific surface area and a better affinity with nanocellulose, and the nanocellulose can overlap the gaps between the primary particles of the filler constituting the secondary particle topography to form an effect of overlapping and integrating the nanocellulose and the first filler, so that the coating layer can have a more stable space network structure, and the separator can have a suitable porosity and a stable pore structure, and the separator can also have both a low moisture content and good electrolyte wettability.

[0130] In some embodiments, the content of the first filler is 50wt% to 100wt%, preferably 90wt% to 99wt%, based on the total weight of the filler. When the content of the first filler is within an appropriate range, it is advantageous for the first filler to overlap with the nanocellulose to form an integrated effect, so that the coating layer can have a more stable spatial network structure, and the heat resistance, tensile strength, puncture resistance, and external pressure resistance of the separator can be further improved.

[0131] In some embodiments, the first filler has an average particle size Dv50 of 200 nm or less, preferably 50 nm to 200 nm, which allows the first filler to have a high specific surface area, increases the affinity between the first filler and nanocellulose, and is advantageous in forming an integrated effect by overlapping the first filler and nanocellulose, which allows the coating layer to have a more stable spatial network structure, and allows the separator to have better heat resistance and wettability to the electrolyte.

[0132] In some embodiments, the first filler has a BET specific surface area of ​​20 m 2 / g or more, preferably 25m 2 / g~50m2 / g, which is advantageous in that the affinity between the first filler and the nanocellulose is improved and the first filler overlaps with the nanocellulose to form an integrated effect, thereby allowing the coating layer to have a more stable space network structure and allowing the separator to have better heat resistance and wettability to the electrolyte.

[0133] In some embodiments, the first filler comprises inorganic particles of a secondary particle topography, and the crystal type of the inorganic particles of the secondary particle topography comprises at least two of α crystal type, θ crystal type, γ crystal type, or η crystal type, preferably at least two of α crystal type, θ crystal type, or γ crystal type.

[0134] The inorganic particles of the secondary particle topography of the α-crystal type have diffraction peaks at 2θ of 57.48°±0.2° and 43.34°±0.2° in an X-ray diffraction spectrum measured by an X-ray diffractometer. In some embodiments, the content of the α-crystal type 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 of the secondary particle topography.

[0135] The inorganic particles of the secondary particle topography of the θ crystal type have diffraction peaks at 2θ of 36.68°±0.2° and 31.21°±0.2° in an X-ray diffraction spectrum measured by an X-ray diffractometer. In some embodiments, the content of the θ crystal type 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 the secondary particle topography.

[0136] The inorganic particles of the secondary particle topography of the γ crystal type have diffraction peaks at 2θ of 66.95°±0.2° and 45.91°±0.2° in an X-ray diffraction spectrum measured by an X-ray diffractometer. In some embodiments, the content of the γ crystal type 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 of the secondary particle topography.

[0137] The inorganic particles of the secondary particle topography of the η crystal type have diffraction peaks at 2θ of 31.89°±0.2° and 19.37°±0.2° in an X-ray diffraction spectrum measured by an X-ray diffractometer. In some embodiments, the content of the η crystal type 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 of the secondary particle topography.

[0138] Inorganic particles with α crystal type secondary particle topography have the advantages of high hardness, good heat resistance, low dielectric constant, high safety, and high true density, inorganic particles with θ crystal type secondary particle topography have appropriate specific surface area and hardness, which can better improve the heat resistance and ion transport properties of the separator at the same time, and inorganic particles with γ crystal type and η crystal type secondary particle topography have the advantage of large specific surface area. Therefore, by selecting a first filler with a different crystal type, it contributes to improving at least one of the heat resistance and electrolyte wettability of the separator.

[0139] In some embodiments, the first filler comprises inorganic particles of secondary particle topography, the crystal type of the inorganic particles of the secondary particle topography comprises a θ crystal type, and the content of the θ crystal type 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 the secondary particle topography.

[0140] In some embodiments, the first filler comprises inorganic particles of secondary particle topography, and the crystal types of the inorganic particles of the secondary particle topography include α crystal type, θ crystal type, γ crystal type and η crystal type, and the content of α crystal type is 1.2 wt% to 5 wt%, the content of θ crystal type is 60 wt% to 82.5 wt%, the content of γ crystal type is 15 wt% to 35 wt%, and the content of η crystal type is 1 wt% or less, all calculated based on the total weight of the inorganic particles of the secondary particle topography.

[0141] The X-ray diffraction spectrum of inorganic particles of secondary particle topography can be obtained by drying the inorganic particles of secondary particle topography, polishing them in a mortar (e.g., an agate mortar) for 30 min, and then testing them using an X-ray diffraction device (e.g., Miniflex600-C) to obtain an X-ray diffraction spectrum. During the test, a Cu target, Ni filter, tube voltage 40 KV, tube current 15 mA, and continuous scanning range 5° to 80° can be adopted.

[0142] In some embodiments, the first filler includes inorganic particles having a secondary particle topography, and the inorganic particles having a secondary particle topography may be produced by oxidizing a precursor solution of inorganic particles using a high pressure sputtering method, then heating at 600°C to 900°C (e.g., for 1 hour to 3 hours) to form small particles, and then drying and solidifying at 150°C to 250°C (e.g., for 30 minutes to 60 minutes) to obtain inorganic particles having a secondary particle topography.

[0143] In some embodiments, the filler further comprises a second filler, and the second filler is a primary particle topography. The filler of the primary particle topography has a large particle size and high strength, so that it can better support the coating layer, reduce the amount of adhesive used, and improve the heat resistance of the separator. In addition, when the amount used is small, the separator has more pore structures and a smaller water content, which further improves 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, which allows the second filler to exert a better supporting effect, is favorable for discharging moisture during drying, allows the coating layer to maintain an appropriate porosity and stable pore structure during long-term charge / discharge, and further improves the ion transport properties and electrolyte wettability of the separator.

[0145] In some embodiments, the second filler has an average particle size Dv50 of 100 nm-800 nm, preferably 200 nm-400 nm, which allows the second filler to better exert its supporting effect, is favorable for discharging moisture during drying, allows the coating layer to maintain an appropriate porosity and stable pore structure during long-term charge / discharge, and further improves the ion transport properties and electrolyte wettability of the separator.

[0146] In some embodiments, the second filler has a BET specific surface area of ​​10 m 2 / g or less, preferably 4m 2 / g~9m 2 This allows the second filler to better exert its supporting effect, is favorable for the discharge of moisture during the drying process, and allows the coating layer to maintain an appropriate porosity and stable pore structure during long-term charge / discharge processes, thereby further improving the ion transport properties and wettability of the separator with respect to the electrolyte.

[0147] In some embodiments, the second filler comprises inorganic particles of primary particle topography, and the crystal type of the inorganic particles of primary particle topography comprises at least one of α crystal type and γ crystal type, and preferably comprises α crystal type. The inorganic particles of primary particle topography of α crystal type have the advantages of high hardness, good heat resistance, low dielectric constant, high safety, and high true density, which can further improve the heat resistance of the separator.

[0148] In some embodiments, the second filler comprises inorganic particles of a primary particle topography, the crystal type of the inorganic particles of the primary particle topography comprises an α crystal type, and the content of the α crystal type 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.

[0149] In some embodiments, the coating layer may further include a non-particulate adhesive. In the present application, the type of the non-particulate adhesive is not particularly limited, and any material having well-known good adhesive properties may be adopted. Preferably, the non-particulate adhesive includes an aqueous adhesive, which has the advantages of good thermodynamic stability and environmental friendliness, and is therefore advantageous for the preparation and application of the coating layer slurry. As an example, the aqueous adhesive includes at least one of an aqueous 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 the present application can form a stable spatial network structure, so that the separator can maintain high adhesion and good ion transport properties under the premise of 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 including a particulate adhesive. The adhesive layer can prevent the coating layer from falling off and improve the safety performance of the secondary battery, as well as improve the interface between the separator and the electrodes, thereby improving the cycle performance of the secondary battery.

[0152] Preferably, the particulate adhesive comprises at least one of acrylic ester monomer homopolymers or copolymers, acrylic acid monomer homopolymers or copolymers, and fluorine-containing olefin monomer homopolymers or copolymers. The copolymerization monomers include at least one of acrylic ester monomers, acrylic acid monomers, olefin monomers, halogen-containing olefin monomers, fluoroether monomers, etc., but are not limited thereto.

[0153] Preferably, the particulate adhesive comprises a vinylidene fluoride polymer, such as a homopolymer of vinylidene fluoride monomer (VDF) and / or a copolymer of vinylidene fluoride monomer and a comonomer. The comonomer may be at least one of an olefin monomer, a fluorine-containing olefin monomer, a chlorine-containing olefin monomer, an acrylate monomer, an acrylic monomer, and a fluoroether monomer. Preferably, the comonomer may comprise at least one of trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ether (e.g., perfluoro(methyl vinyl) ether PMVE, perfluoro(ethyl vinyl) ether PEVE, perfluoro(propyl vinyl) ether PPVE), perfluoro(1,3-dioxole), and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD).

[0154] In some embodiments, the separator has a machine direction (MD) heat shrinkage rate of 5% or less at 150° C. for 1 h, and preferably 0.5% to 4%.

[0155] In some embodiments, the separator has a transverse direction (TD) heat shrinkage rate of 5% or less at 150° C. for 1 h, and preferably 0.5% to 4%.

[0156] The separator of the present application has low thermal shrinkage rates in both the transverse and longitudinal directions, which can further improve the safety performance of the secondary battery.

[0157] In some embodiments, the separator has a puncture strength of 350 gf or more, and preferably 370 gf to 450 gf. The separator of the present application has a high puncture strength, which can further improve the safety performance of the secondary battery.

[0158] In some embodiments, the separator has a longitudinal tensile strength of 2000 kg / cm 2 More than 2500kg / cm 2 ~4500kg / cm 2 It is.

[0159] In some embodiments, the separator has a transverse tensile strength of 2000 kg / cm 2 More than 2500kg / cm 2 ~4500kg / cm 2 It is.

[0160] Since the separator of the present application has high tensile strength in both the horizontal 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 separator has an air permeability of 300s / 100mL or less, preferably 100s / 100mL to 200s / 100mL. The separator of the present application has a good air permeability, thereby improving the ion transport properties.

[0162] In some embodiments, the porosity of the separator is 30% to 45%, preferably 32% to 36%, which can improve the ion transport properties of the separator and reduce 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 speed of the separator is 3 mm / s or more, preferably 3 mm / s to 10 mm / s.

[0165] The separator of the present application has good electrolyte wettability, and therefore can improve ion transport properties 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 by using instruments and methods known in the art, for example, see GB / T19077-2016 Particle size distribution laser diffraction method, and can be tested by using a laser particle size analyzer (e.g., Master Size3000).

[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 according to the nitrogen gas adsorption specific surface area analysis test method with reference 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 a Tri-Star3020 type specific surface area pore size analysis tester manufactured by Micromeritics, USA.

[0168] In this application, the heat shrinkage rate, puncture strength, tensile strength and air permeability of the separator all have the meanings known in the art and can be measured by methods known in the art, for example, they can be tested with reference to standard GB / T36363-2018.

[0169] In this application, the wetting length and wetting speed of the separator both have meanings well known in the art and can be measured by methods well known in the art. An exemplary test method is to cut the separator into a sample with a width of 5 mm and a length of 100 mm, fix both ends of the sample and place it horizontally, drop 0.5 mg of electrolyte into the center of the sample, and after a predetermined time (1 min in this application), take a picture and measure the diffusion length of the electrolyte to obtain the wetting length and wetting speed of the separator. In order to ensure the accuracy of the test results, the test is performed using multiple samples (e.g., 5 to 10 samples) and the test results can be obtained by calculating the average value. 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 LiPF that has been thoroughly dried is then mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) to obtain an organic solvent. 6 was dissolved in the above organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L.

[0170] The coating layer parameters of the separator (eg, 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 the porous substrate, it is considered to be within the protection scope of the present application if the coating layer parameters of either one of the sides meet the present application. Manufacturing method

[0172] A second aspect of the embodiment of the present application provides a method for manufacturing a separator according to the first aspect of the embodiment of the present application, comprising the steps of: providing a porous substrate (S1); preparing a coating layer slurry by mixing nanocellulose and a filler in a solvent in a predetermined ratio to prepare the coating layer slurry (S2); and applying the coating layer slurry to at least one surface of the porous substrate (S3) to form a coating layer and dry the coating layer to obtain a separator, the separator comprising a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer comprising 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.

[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 include other ingredients, such as a dispersant, a wetting agent, an adhesive, and the like.

[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, the film surface problem of the coating layer can be effectively reduced, the probability of coating unevenness can be reduced, and the energy density and safety performance of the secondary battery can be further improved.

[0176] In some embodiments, the nanocellulose is obtained by a method including steps S21 of providing a cellulose powder having a whiteness of 80% or more, S22 of mixing the obtained cellulose powder with a modifying solution to react, and then washing to remove impurities to obtain cellulose nanowhiskers, and S23 of adjusting the pH of the obtained cellulose nanowhiskers to neutral (e.g., pH 6.5-7.5), grinding, and cutting to obtain nanocellulose.

[0177] Preferably, in S21, the cellulose powder having a whiteness of 80% or more may be commercially available or may be obtained by adopting a chemical method (e.g., acid decomposition method, alkali treatment method, Tempo catalytic oxidation method), a biological method (e.g., enzyme treatment method), a mechanical method (e.g., ultrafine grinding, ultrasonic crushing, high-pressure homogenization), etc. The fiber raw material for producing the cellulose powder having a whiteness of 80% or more may include at least one of plant fibers, such as cotton fibers (e.g., cotton fiber, cotton fiber), hemp fibers (e.g., sisal fiber, ramie fiber, jute fiber, flax fiber, hemp fiber, Manila hemp fiber, etc.), palm fibers, wood fibers, bamboo fibers, and grass fibers.

[0178] In some embodiments, the cellulose powder having a whiteness of 80% or more can be produced by opening the fiber raw material, removing the scum, digesting it with an alkaline solution (e.g., an aqueous NaOH solution having a concentration of 4 wt% to 20 wt%, preferably 5 wt% to 15 wt%), and then sequentially washing with water to remove impurities (e.g., washing with water 3 to 6 times), bleaching (which may be, for example, sodium hypochlorite and / or hydrogen peroxide), washing with an acid to remove impurities, washing with water to remove impurities, removing water, and flash drying to obtain a cellulose powder.

[0179] In some embodiments, in S22, the modifying solution may be an acid solution (e.g., sulfuric acid aqueous solution, boric acid aqueous solution, phosphoric acid aqueous solution, acetic acid aqueous solution) or an alkaline solution (e.g., urea organic solvent solution). Preferably, the modifying solution is an acid 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] In addition, since the urea organic solvent solution is a urea xylene solution, nanocellulose having an amine group can be obtained.

[0182] In some embodiments, in S22, the mass ratio of the cellulose powder to the modified solution may be 1:2.5 to 1:50, preferably 1:5 to 1:30.

[0183] When the modifying 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. When the modifying 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. When the modifying 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. When an aqueous acetic acid solution is used as the modifying solution, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30. When an organic urea solution is used as the modifying solution, the mass ratio of the cellulose powder to the organic urea solution may be 1:4 to 1:40.

[0184] In some embodiments, in S22, when the modifying solution is an acid solution, the reaction may be carried out under conditions of 80°C or less, 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, in S22, when the modifying solution 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 1h to 5h.

[0186] In some embodiments, in S23, the grinding may be performed using a grinder, and the cutting may be performed using a high-pressure homogenizer. By adjusting the grinding parameters of the grinder (e.g., grinding times, grinding time, etc.) and the cutting parameters of the high-pressure homogenizer, nanocellulose having different average diameters and / or different average lengths can be obtained.

[0187] In some embodiments, in S3, a coater is used for the coating. In the present application, the model number of the coater is not particularly limited, and for example, a commercially available coater can be adopted. Preferably, the coater includes a gravure roll for transferring the coating layer slurry to the porous substrate. Preferably, the gravure roll has a ruling of 100 LPI to 300 LPI, more preferably 125 LPI to 190 LPI.

[0188] In some embodiments, in S3, the coating method may be transfer coating, rotary spray coating, dip coating, etc.

[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 the above range, the film surface problem of the coating layer can be effectively reduced, the probability of occurrence of coating unevenness 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, in S3, the drying temperature may be between 40°C and 70°C, for example between 50°C and 60°C.

[0192] In some embodiments, in S3, the drying time may be between 10 seconds and 120 seconds, for example between 20 seconds and 80 seconds, or between 20 seconds and 40 seconds.

[0193] By controlling each of the above process parameters within a certain range, the performance of the separator of the present application can be further improved. Those skilled in the art can selectively adjust one or more of the above process parameters according to the actual production situation.

[0194] In some embodiments, the method further includes a step S4 of applying a slurry containing particulate adhesive to at least a portion of the surface of the coating layer in two applications so as to dry and form an adhesive layer.

[0195] The method for producing a separator according to the present application produces a coating layer by a single application, thereby greatly simplifying the separator production process.

[0196] The raw materials used in the separator manufacturing method of the present application and the parameters thereof such as their contents can be referred to the separator of the first aspect of the embodiment of the present application, but the description will be omitted here. Unless otherwise stated, each raw material used in the separator manufacturing method of the present application is available as a commercially available product. secondary battery

[0197] A third aspect of an embodiment of the present 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 after discharging by activating the active material through charging. In general, a secondary battery includes an electrode assembly and an electrolyte, the electrode assembly including a positive electrode sheet, a negative electrode sheet, and a separator, the separator being disposed between the positive electrode sheet and the negative electrode sheet and mainly serving to prevent short circuits between the positive electrode and the negative electrode, while allowing active ions to pass through.

[0199] In the present application, the type of the secondary battery is not particularly limited. 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 aspect of the present application includes a separator according to the first aspect of the present application or a separator produced by the method according to the second aspect of the present application, the separator being interposed between the positive electrode sheet and the negative electrode sheet. Preferably, at least the side of the separator close to the negative electrode sheet has the coating layer according to the first aspect of the present application. This allows the secondary battery according to the present application to have a high energy density, high thermal safety performance, and long life. [Positive electrode sheet]

[0201] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer that is provided on at least one surface of the positive electrode current collector and includes a positive electrode active material. For example, the positive electrode current collector has two surfaces that face each other in a thickness direction of the positive electrode current collector, and the positive electrode film layer is provided on one or both of the two facing 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 oxide can include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Examples of the lithium-containing phosphate can 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 having the general formula Li a Ni b Co c M d O e A f where 0.8 ≦ a ≦ 1.2, 0.5 ≦ b < 1, 0 < c < 1, 0 < d < 1, 1 ≦ e ≦ 2, 0 ≦ f ≦ 1, M is at least one selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, B, and A is at least one selected from N, F, S, Cl.

[0204] For example, the positive electrode active material for the lithium-ion battery is LiCoO 2 、LiNiO 2 、LiMnO 2 、LiMn 2 O 4 、LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O 2 , LiFePO 4 , LiMnPO 4 may contain at least one of the following:

[0205] When the secondary battery of the present application is a sodium ion battery, the positive electrode active material may include at least one of a sodium-containing transition metal oxide, a polyanion material (e.g., a phosphate, a fluorophosphate, a pyrophosphate, a sulfate, etc.), and a Prussian blue-based material, but is not limited thereto.

[0206] For example, the positive electrode active material for sodium-ion batteries is NaFeO 2 , NaCoO 2 , NaCrO 2 , NaMnO 2 , NaNiO 2 , NaNi 1 / 2 Ti 1 / 2 O 2 , NaNi 1 / 2 Mn 1 / 2 O 2 , Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O 2 , NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 , NaFePO 4 , NaMnPO 4 , NaCoPO 4 , Prussian blue-based materials, the general formula of which is X p M'q (PO 4 ) r O x Y 3-x The compound may include at least one of the materials represented by the general formula X p M' q (PO 4 ) r O x Y 3-x In, 0 <p≦4、0<q≦2、1≦r≦3、0≦x≦2であり、XはH + , Li + , Na + , K + , N.H. 4 + 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 the present application, the modifying compound of each of the above positive electrode active materials can 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 include a positive electrode conductive agent. In the present application, the type of the positive electrode conductive agent is not particularly limited, and for 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, based on the total mass of the positive electrode film layer, the mass percentage content of the positive electrode conductive agent is 5% or less.

[0209] In some embodiments, the positive electrode film layer may optionally include a positive electrode adhesive. In the present application, the type of the positive electrode adhesive is not particularly limited, 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, based on the total mass of the positive electrode film layer, the mass percentage content of the positive electrode adhesive is 5% or less.

[0210] In some embodiments, the positive electrode current collector may be a metal foil sheet or a composite current collector. An example of the metal foil sheet may be aluminum foil. The composite current collector may include a polymeric material base layer and a metal material layer formed on at least one surface of the polymeric material base layer. 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 polymeric material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0211] The positive electrode membrane layer is typically formed by applying a positive electrode slurry to a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing a positive electrode active material, an optional conductive agent, an optional adhesive, and any other components in a solvent, and stirring the mixture uniformly. The solvent may be, 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 that is provided on at least one surface of the negative electrode current collector and includes a negative electrode active material. For example, the negative electrode current collector has two surfaces that face each other in a thickness direction of the negative electrode current collector, and the negative electrode film layer is provided on one or both of the two facing surfaces of the negative electrode current collector.

[0213] The negative electrode active material may be any negative electrode active material known in the art for secondary batteries. For example, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate. The silicon-based material may include at least one of silicon elemental, 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 include a negative electrode conductive agent. In the present application, the type of the negative electrode conductive agent is not particularly limited, and for example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total mass of the negative electrode film layer, the mass percentage content of the negative electrode conductive agent is 5% or less.

[0215] In some embodiments, the negative electrode film layer may optionally include a negative electrode adhesive. In the present application, the type of the negative electrode adhesive is not particularly limited, and for example, the negative electrode adhesive may include at least one of styrene butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, based on the total mass of the negative electrode film layer, the mass percentage content of the negative electrode adhesive is 5% or less.

[0216] In some embodiments, the negative electrode membrane layer may optionally include other auxiliary agents. For example, the other auxiliary agents may include a thickener, such as sodium carboxymethylcellulose (CMC), a PTC thermistor material, etc. In some embodiments, based on the total mass of the negative electrode membrane layer, the mass percentage content of the other auxiliary agents is 2% or less.

[0217] In some embodiments, the negative electrode current collector may be a metal foil sheet or a composite current collector. An example of the metal foil sheet may be copper foil. The composite current collector may include a polymeric material base layer and a metal material layer formed on at least one surface of the polymeric material base layer. For example, the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. For example, the polymeric material base layer 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, an optional conductive agent, an optional adhesive, and other optional auxiliary agents in a solvent, and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0219] The negative electrode sheet does not exclude additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode sheet described in the present application further includes a conductive undercoat layer (e.g., made of a conductive agent and an adhesive) sandwiched between the negative electrode collector and the negative electrode film layer and provided on the surface of the negative electrode collector. In some other embodiments, the negative electrode sheet described in the present application further includes a protective layer covering the surface of the negative electrode film layer. [Electrolyte]

[0220] In the charging and discharging process of the secondary battery, active ions are inserted and removed between the positive electrode sheet and the negative electrode sheet, and the electrolyte serves to conduct the active ions between the positive electrode sheet and the negative electrode sheet. In the present application, the type of electrolyte is not particularly limited and can be selected according to actual needs.

[0221] The electrolyte solution includes an electrolyte salt and a solvent, and the types of the electrolyte salt and the solvent are not specifically limited and can be selected according to actual needs.

[0222] When the secondary battery of the present application is a lithium ion battery, for example, the electrolyte salt is lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6), lithium difluorosulfonylimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium difluoro(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorodisalophosphate (LiDFOP), and lithium tetrafluorooxalophosphate (LiTFOP).

[0223] When the secondary battery of the present application is a sodium ion battery, for example, the electrolyte salt is sodium hexafluorophosphate (NaPF 6 ), sodium tetrafluoroborate (NaBF 4 ), sodium perchlorate (NaClO 4 ), sodium hexafluoroarsenate (NaAsF 6 ), sodium difluorosulfonylimide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalyl borate (NaDFOB), Sodium difluoro(oxalato)borate (NaBOB), sodium difluorophosphate (NaPO 2 F 2 ), sodium difluorooxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0224] By way of example, the solvent may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0225] In some embodiments, the electrolyte may optionally include additives, such as an anode film-forming additive, a cathode film-forming additive, or an additive that can improve certain performance of the battery, such as an additive that improves the overcharge performance of the battery, an additive that improves the high temperature performance of the battery, or an additive that improves the low temperature power performance of the battery.

[0226] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be wound and / or stacked to produce an electrode assembly.

[0227] In some embodiments, the secondary battery may include an exterior case, which is used to seal the electrode assembly and the electrolyte.

[0228] In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the secondary battery may be a soft pack, such as a bag soft pack, etc. The material of the soft bag may be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0229] In the present application, the shape of the secondary battery is not particularly limited, and may be cylindrical, rectangular, or any other shape. Fig. 1 shows a secondary battery 5 having a rectangular structure as an example.

[0230] In some embodiments, as shown in FIG. 2, the exterior may include a case 51 and a cover plate 53. The case 51 includes a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate surround and form a receiving cavity. The case 51 has an opening communicating with the receiving cavity, and the cover plate 53 covers the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator may form an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and may be adjusted as needed.

[0231] The method for manufacturing the secondary battery of the present application is well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte solution can be assembled to form a secondary battery. For example, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly by a winding process or a lamination process, the electrode assembly can be placed in an outer casing, and the electrolyte solution can be injected after drying, and the secondary battery can be obtained through processes such as vacuum sealing, standing, chemical formation, and shaping.

[0232] In some embodiments of the present application, the secondary battery of the present application may be assembled into 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] Fig. 3 is a schematic diagram of an example battery module 4. As shown in Fig. 3, in the battery module 4, the multiple secondary batteries 5 may be arranged in sequence along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the multiple secondary batteries 5 may be fixed by fasteners.

[0234] Preferably, the battery module 4 may further include a housing having an accommodation space in which the multiple secondary batteries 5 are accommodated.

[0235] In some embodiments, the battery modules may be assembled into a battery pack, and the number of battery modules included in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0236] 4 and 5 are schematic diagrams of an example battery pack 1. As shown in Fig. 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, and the upper housing 2 covers the lower housing 3 to form an enclosed space for accommodating 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 aspect of the embodiment of the present application further provides a power consuming device including at least one of the secondary batteries, battery modules, or battery packs of the present application. The secondary batteries, battery modules, or battery packs may be used as a power source for the power consuming device, or may be used as an energy storage unit for the power consuming device. The power consuming device may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf car, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0239] The power consumption device can select a secondary battery, a battery module or a battery pack according to its usage needs.

[0240] 6 is a schematic diagram of an example power consuming device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. A battery pack or battery module may be employed to meet the high power and high energy density requirements of the power consuming device.

[0241] Other examples of power consuming devices may be mobile phones, tablet computers, notebook computers, etc. These power consuming devices are generally required to be thin and can use secondary batteries as their power source. Working Example

[0242] The following examples are provided to more specifically describe the disclosure of the present application, and are merely illustrative, since it is obvious to those skilled in the art that various modifications and changes may be made within the scope of the disclosure of the present application.Unless otherwise specified, all parts, percentages, and ratios described in the following examples are based on mass, and all reagents used in the examples are commercially available or obtained by synthesis according to conventional methods and can be used directly without further treatment, and the equipment used in the examples is commercially available. Preparation of nanocellulose C1 Preparation of cellulose powder

[0243] The cotton linters were opened using a cotton opener and the slag was removed, then they were digested in a 5 wt% NaOH aqueous solution at 150°C for 2 hours. Then, they were washed with water to remove impurities (three times), bleached with sodium hypochlorite, washed with dilute hydrochloric acid to remove impurities, washed with water to remove impurities (one time), removed the water, and air-dried to obtain cotton cellulose powder with a whiteness of 85% or more. Cellulose Esterification 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 hours. After the reaction was completed, impurities were removed by washing with water (three times), followed by filtration, acid removal, and impurities removal, to obtain cellulose nanowhiskers having sulfonic acid group-modifying groups. Neutralization of cellulose

[0244] First, the pH of the cellulose nanowhiskers with sulfonic acid group-modified groups was adjusted to neutral using a 10 wt% NaOH aqueous solution, and then the whiskers were dispersed by high-speed processing using a grinder for 2.5 hours, and the grinding was repeated twice. The whiskers were then cut into nanoscale particles using a high-pressure homogenizer to obtain nanocellulose C1 with sulfonic acid group-modified groups with an average length of 425 nm and an average diameter of 25 nm, and the molar ratio of sulfonic acid groups to hydroxyl groups was 5:3. Production of nanocellulose C2-C10 Nanocelluloses C2 to C10 were produced in a manner similar to that of nanocellulose C1, with differences being shown in Table 1. Preparation of nanocellulose C11 Preparation of cellulose powder

[0245] After the cotton linters were opened in a cotton opener and the slag was removed, they were digested in a 5wt% NaOH aqueous solution at 150℃ for 2h, then washed with water to remove impurities (3 washes), bleached with sodium hypochlorite, washed with dilute hydrochloric acid to remove impurities, washed with water to remove impurities (1 wash), removed water, and air-dried to obtain a cotton cellulose powder with a whiteness of 85% or more. The obtained cotton cellulose powder was mixed with a 20wt% NaOH aqueous solution at 10℃, stirred for 2 hours, filtered, and washed twice with water to obtain an alkali cellulose powder. Cellulose Esterification 50 g of the obtained alkali cellulose powder and 200 g of urea were placed in a three-necked reactor equipped with an oil-water separator. After the urea was dissolved, 5 g of xylene was added, and the temperature was raised to 137°C with stirring. The reaction was allowed to proceed for 4 hours, after which the reaction was stopped. After washing with water (three times), filtration, and drying, cellulose carbamate was obtained. Neutralization of cellulose

[0246] The obtained cellulose carbamate was dissolved in a 5 wt% NaOH aqueous solution to obtain a uniform cellulose carbamate solution, which was then dispersed by high-speed processing in a grinder for 2.5 h. The grinding was repeated twice, and the solution was then cut into nanoscale particles using a high-pressure homogenizer to obtain nanocellulose with amine group-modified groups having an average length of 425 nm and an average diameter of 25 nm, with a molar ratio of amine groups to hydroxyl groups of 4:3.

[0247] The molar ratio of the modifying group to the hydroxyl group can be measured by measuring the hydroxyl value (the number of mg of potassium hydroxide equivalent to the hydroxyl group content per 1 g of sample) of the raw cellulose and the modified nanocellulose based on the phthalic anhydride method in GB / T12008.3-2009, converting the obtained numerical value into mgKOH / g and converting it to mmol / g to obtain the hydroxyl group content. The content of the modifying group (i.e., the content of the modified hydroxyl group) is obtained by subtracting the hydroxyl group content of the modified nanocellulose from the hydroxyl group content of the raw cellulose, and the molar ratio of the modifying group to the hydroxyl group is calculated. Production of nanocellulose C12-C14

[0248] Unmodified nanocellulose is adopted, the product model number is CNWS-50, purchased from Zhongke Leiming (Beijing) Technology Co., Ltd., and can be further processed by a grinder and / or a 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) (Preparation of separator)

[0249] S1: Provide a PE porous substrate with a thickness of 4.8 μm and a porosity of 39%. S2: Preparation of coating layer slurry: Nanocellulose C1 prepared above, alumina as a filler (secondary particle topography, average particle size Dv50 is 140 nm, BET specific surface area is 30 m 2 / g) and aqueous polyacrylic acid as an adhesive were uniformly mixed in a suitable amount of deionized water as 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 coater, and the separator is obtained through a drying and slitting process. The surface density of the coating layer on one side of the PE porous substrate is 1.1 g / m 2The coating machine includes a gravure roll, the line number of the gravure roll is 175LPI, the coating speed is 90m / min, the coating line speed ratio is 1.2, the drying temperature is 55±5℃, and the drying time is 50 seconds. (2) Manufacturing of positive electrode sheets

[0250] Cathode active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 The positive electrode slurry is obtained by uniformly mixing (NCM811), the conductive agent carbon black (Super P), and the adhesive polyvinylidene fluoride (PVDF) in an appropriate amount of solvent N-methylpyrrolidone (NMP) in a mass ratio of 96.2:2.7:1.1. The positive electrode slurry is applied to an aluminum foil as a positive electrode current collector, and the 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 / mm 2 and the compressed density is 3.5 g / cm 3 It is. (3) Manufacturing of negative electrode sheets

[0251] The negative electrode active material, artificial graphite, the conductive agent, carbon black (Super P), the adhesive, styrene butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC), are mixed uniformly in a mass ratio of 96.4:0.7:1.8:1.1 with an appropriate amount of deionized water as a solvent to obtain a negative electrode slurry. The negative electrode slurry is applied to a copper foil as a negative electrode current collector, and the negative electrode sheet is obtained through drying, cold pressing, slitting, and cutting processes. The surface density of the negative electrode sheet is 0.126 mg / mm 2 and the compressed density is 1.7 g / cm 3 It is.

[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 the LiPF 6 was dissolved in the above organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L. (5) Manufacture of secondary batteries

[0253] The positive electrode sheet, separator, and negative electrode sheet are stacked in that order and rolled up to obtain an electrode assembly. The electrode assembly is placed in an outer casing, dried, and then an electrolyte is injected. The secondary battery is obtained through processes such as vacuum sealing, leaving it to stand, chemical formation, and shaping. Examples 2 to 6

[0254] The secondary battery was manufactured in a manner similar to that of Example 1, except that the amounts of nanocellulose C1 and filler added in the manufacture of the separator were different. See Table 2 for specific parameters. Examples 7 to 17

[0255] The secondary battery was manufactured in a manner similar to that of Example 1, except that the type of nanocellulose used to manufacture the separator was different. See Tables 1 and 2 for specific parameters. Examples 18 to 21

[0256] The secondary battery was manufactured in a manner similar to that of Example 1, except that the specific surface area of ​​the alumina filler used in the manufacture of the separator was different. See Table 2 for specific parameters.

[0257] The secondary particle topography of the alumina filler used in Example 18 had an average particle size Dv50 of 350 nm and a BET specific surface area of ​​15 m 2 The secondary particle topography of the alumina filler used in Example 19 has an average particle size Dv50 of 175 nm and a BET specific surface area of ​​20 m 2 The secondary particle topography of the alumina filler used in Example 20 has an average particle size Dv50 of 113 nm and a BET specific surface area of ​​35 m 2 The secondary particle topography of the alumina 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 similar manner to that in Example 1, except that the surface density of the coating layer in the manufacture of the separator was different. See Table 2 for specific parameters. Examples 27-28

[0259] The secondary battery is made of alumina with a secondary particle topography filler (average particle size Dv50 is 140 nm, BET specific surface area is 30 m 2 / g) and primary particle topography of alumina (average particle size Dv50 of 600 nm, BET specific surface area of ​​7 m 2 The preparation was carried out in a similar manner to Example 1, except that a mixture of 1,000 sucrose and 1,000 sucrose (g) was used. For the specific amounts added, see Table 2. Comparative Examples 1 to 4

[0260] The secondary batteries differ in the type of nanocellulose used in the manufacture of the separator, and the filler used is alumina with a primary particle topography (average particle size Dv50 of 1000 nm, BET specific surface area of ​​5 m 2 / g), the specific parameters are shown in Tables 1 and 2. [Table 2] JPEG2025515853000004.jpg132164 Testing Department

[0261] (1) Moisture content test of separator The empty plate was placed in a drying box and heated at 45°C for 8 hours, then placed in a dryer and cooled for 1 hour. 0.08g to 0.1g of separator sample was weighed and placed in the cooled empty plate, and the empty plate was 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 test method, and the test equipment used was the Swiss Wantong 831 Karl Fischer moisture meter.

[0262] (2) Thermal shrinkage rate test of separator Sample preparation: The separator prepared above was punched out into samples with a width of 50 mm and a length of 100 mm using a press, and five parallel samples were set and fixed on an A4 sheet of paper. The A4 sheet of paper containing the samples was then set on a piece of cardboard with a thickness of 1 mm to 5 mm. Sample test: Set the temperature of the blower 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 the cardboard into the blower oven, start timing, and after the set time (1 hour in this application) is reached, measure the length and width of the separator, and the values ​​are denoted as a and b respectively. Calculation of heat shrinkage: Machine direction (MD) heat shrinkage = [(100-a) / 100] x 100%, transverse direction (TD) heat shrinkage = [(50-b) / 50] x 100%, the average value of five parallel samples was used as the measurement result.

[0263] (3) Separator air permeability test The time required for 100 mL of air to pass through the separator at 25°C was measured, and the average value of five parallel samples was used as the measurement result. As the testing equipment, a Kumagai KRK (Kumagaya Riki Kogyo) Oken-type air permeability tester can be used.

[0264] (4) Testing the cycle performance of secondary batteries At 25°C, the secondary battery is charged at a constant current of 1C to 4.2V, and then the constant voltage charging is continued until the current becomes 0.05C or less. At this time, the secondary battery is in a fully charged state, and the charge capacity at this time, i.e., the first charge capacity, is recorded. After leaving the secondary battery to stand for 5 minutes, it is discharged at a constant current of 1C to 2.8V, which is one cycle of charge and discharge, and the discharge capacity at this time, i.e., the first discharge capacity, is recorded. The secondary battery was subjected to a cycle charge and discharge test according to the above method, and the discharge capacity after one cycle was recorded. 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 the high-temperature storage performance of secondary batteries At 25°C, the secondary battery is charged at a constant current of 1C to 4.2V, and constant voltage charging is continued until the current falls to 0.05C or less. The secondary battery is left to stand for 5 minutes, and then discharged at a constant current of 1C to 2.8V. The discharge capacity at this time is recorded as the capacity before storage. At 25°C, the secondary battery is charged at a constant current of 1C to 4.2V, and constant voltage charging is continued until the current falls to 0.05C or less. At this time, the secondary battery is fully charged. The secondary battery is then placed in a thermostatic chamber at 60°C, stored for 30 days, and then removed. The secondary battery is then discharged at a constant current of 1C to 2.8V. The discharge capacity at this time is recorded as the capacity after storage. Capacity retention rate (%) after storing the secondary battery at 60°C for 30 days = capacity after storage / capacity before storage x 100%.

[0266] (6) Heat box test for secondary batteries At 25°C, the secondary battery is charged at a constant current of 1C to 4.2V, and then charged at a constant voltage until the current is 0.05C or less, and then left to stand for 5min. Then, each secondary battery is measured with a jig in a DHG-9070A DHG series high-temperature oven, and the temperature is increased from room temperature to 80±2°C at a rate of 5°C / min, and kept at that temperature for 30min. After that, the temperature is increased at a rate of 5°C / min, and the temperature is kept at 30min for every 5°C increase until the secondary battery expires. The change in the surface temperature of the secondary battery during the temperature increase process is monitored, and the temperature of the oven corresponding to the time when the temperature starts to rise rapidly is the expiration temperature of the heat box of the secondary battery. The higher the expiration temperature of the heat box of the secondary battery, the better the 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 a 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 be 250≦A / H≦1500. This allows the thin separator to have a low moisture content, high heat resistance and high air permeability, and the secondary battery to have high heat safety performance and long life. 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 more, and the capacity retention rate of the secondary battery after 30 days of storage at 60°C is 84% ​​or more.

[0268] The present application is not limited to the above-mentioned embodiment. The above-mentioned embodiment is merely an example, and any configuration that has substantially the same technical idea and produces similar effects within the technical scope of the present application is included in the technical scope of the present application. In addition, various modifications that a person skilled in the art can conceive of to the embodiment, and other forms constructed by combining some of the components in the embodiment, are also included in the scope of the present application, as long as they do not deviate from the gist of the present application.

Claims

1. A separator comprising a porous substrate and a coating layer provided on at least one surface of the porous substrate, The coating layer contains nanocellulose and a 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; Separator.

2. 500≦A / H≦1500, preferably 600≦A / H≦1000; and / or 400≦A≦1000, preferably 500≦A≦800, and / or 0<H≦1.5, preferably 0.2≦H≦0.8; The separator according to claim 1 .

3. The nanocellulose comprises at least one of cellulose nanofibers, cellulose nanowhiskers, or bacterial nanocellulose, and is preferably cellulose nanowhiskers; The separator according to claim 1 or 2.

4. The nanocellulose comprises at least one of unmodified nanocellulose and modified nanocellulose, preferably modified nanocellulose; Preferably, the modified nanocellulose comprises a modifying group, and 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 or a phosphoric acid group, more preferably at least one of a sulfonic acid group, a boric acid group or a phosphoric acid group, and / or Preferably, 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, more preferably 2:3 to 7:3; The separator according to any one of claims 1 to 3.

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, preferably 10 to 40; (2) The average diameter of the nanocellulose is 10 nm to 40 nm, preferably 10 nm to 35 nm; (3) The average length of the nanocellulose is 100 nm to 600 nm, preferably 200 nm to 500 nm; (4) The weight average molecular weight of the nanocellulose is 10,000 to 60,000, preferably 30,000 to 50,000, (5) The equilibrium degree of polymerization of the nanocellulose is 150 DP to 300 DP, preferably 200 DP to 250 DP, The separator according to any one of claims 1 to 4.

6. The content of the 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; and / or 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. The separator according to any one of claims 1 to 5.

7. The filler includes 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 any one of claims 1 to 6.

8. The filler includes a first filler, and the first filler has a secondary particle topography formed by aggregation of primary particles, Preferably, the first filler satisfies at least one of the following conditions (1) to (5): (1) 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; (2) The average particle diameter Dv50 of the first filler is 200 nm or less, preferably 50 nm to 200 nm; (3) The BET specific surface area of ​​the first filler is 20 m ２ / g or more, preferably 25m ２ / g to 50m ２ / g, (4) The first filler includes inorganic particles having a secondary particle topography, and the crystal type of the inorganic particles having the secondary particle topography includes at least two of an α crystal type, a θ crystal type, a γ crystal type, or an η crystal type, and preferably includes at least two of an α crystal type, a θ crystal type, or a γ crystal type; (5) The first filler includes inorganic particles having a secondary particle topography, the crystal type of the inorganic particles having the secondary particle topography includes a θ crystal type, and the content of the θ crystal type is 50 wt % or more, preferably 60 wt % to 85 wt %, based on the total weight of the inorganic particles having the secondary particle topography. The separator according to claim 1 .

9. The filler further comprises a second filler, the second filler being a primary particle topography; Preferably, the second filler satisfies at least one of the following conditions (1) to (5): (1) 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; (2) The average particle diameter Dv50 of the second filler is 100 nm to 800 nm, preferably 200 nm to 400 nm; (3) The BET specific surface area of ​​the second filler is 10 m ２ / g or less, preferably 4m ２ / g ~ 9m ２ / g, (4) The second filler includes inorganic particles having a primary particle topography, and the crystal type of the inorganic particles having the primary particle topography includes at least one of an α crystal type and a γ crystal type, and preferably includes an α crystal type; (5) The second filler includes inorganic particles having a primary particle topography, the crystal type of the inorganic particles having the primary particle topography includes an α crystal type, and the content of the α crystal type is 90 wt % or more, preferably 95 wt % to 100 wt %, based on the total weight of the inorganic particles having the primary particle topography. The separator according to claim 8.

10. The coating layer further comprises a non-particulate adhesive; Preferably, the non-particulate adhesive comprises a water-based adhesive; 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 separator according to any one of claims 1 to 9.

11. The thickness of the porous substrate is 6 μm or less, preferably 3 μm to 5 μm, and / or The porosity of the porous substrate is between 32% and 48%, preferably between 34% and 39%, and / or The surface density of the coating layer is 0.6 g / m ２ ~1.5g / m ２ and preferably 0.8 g / m ２ ~1.1 g / m ２ That is, The separator according to any one of claims 1 to 10.

12. The separator further includes an adhesive layer, the adhesive layer being provided on at least a portion of the surface of the coating layer, the adhesive layer including a particulate adhesive, and preferably the particulate adhesive including at least one of an acrylic acid ester monomer homopolymer or copolymer, an acrylic acid monomer homopolymer or copolymer, and a fluorine-containing olefin monomer homopolymer or copolymer. The separator according to any one of claims 1 to 11.

13. At least one of the following conditions (1) to (9) is satisfied: (1) The longitudinal heat shrinkage rate of the separator at 150° C. for 1 h is 5% or less, and preferably 0.5% to 4%; (2) The separator has a transverse heat shrinkage rate of 5% or less at 150° C. for 1 h, and preferably 0.5% to 4%; (3) The separator has a puncture strength of 350 gf or more, preferably 370 gf to 450 gf; (4) The separator has a longitudinal tensile strength of 2000 kg / cm ２ More preferably, 2500 kg / cm ２ ~4500kg / cm ２ and (5) The separator has a lateral tensile strength of 2000 kg / cm ２ More preferably, 2500 kg / cm ２ ~4500kg / cm ２ and (6) The separator has an air permeability of 300 s / 100 mL or less, preferably 100 s / 100 mL to 200 s / 100 mL; (7) The porosity of the separator is 30% to 45%, preferably 32% to 36%, (8) The wet length of the separator is 30 mm or more, preferably 30 mm to 80 mm; (9) The wetting speed of the separator is 3 mm / s or more, preferably 3 mm / s to 10 mm / s. The separator according to any one of claims 1 to 12.

14. A method for producing the separator according to any one of claims 1 to 13, comprising the steps of: The method includes: a step S1 of supplying a porous substrate; a step S2 of preparing a coating layer slurry by mixing nanocellulose and a filler in a solvent in a predetermined ratio to prepare the coating layer slurry; and a coating 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 includes a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer includes nanocellulose and a 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; Manufacturing method.

15. The coating step satisfies at least one of the following conditions (1) to (5): (1) The coating is performed using a coater, the coater includes a gravure roll, and the ruling of the gravure roll is 100 LPI to 300 LPI, preferably 125 LPI to 190 LPI; (2) The coating speed is 30 m / min to 120 m / min, preferably 60 m / min to 90 m / min; (3) the linear speed ratio of the coating is 0.8 to 2.5, preferably 0.8 to 1.5; (4) The drying temperature is 40° C. to 70° C., preferably 50° C. to 60° C.; (5) The drying time is from 10 seconds to 120 seconds, preferably from 20 seconds to 80 seconds. The method of claim 14.

16. The method further includes a step S4 of applying a slurry containing a particulate adhesive to at least a part of the surface of the coating layer, and applying the slurry twice to form an adhesive layer after drying.

16. The method according to claim 14 or 15.

17. The separator according to any one of claims 1 to 13 or the separator produced by the method according to any one of claims 14 to 16, Secondary battery.

18. A power consuming device comprising the secondary battery according to claim 17.

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