Separator, method for manufacturing the same, secondary battery and electric consumer device related thereto

Abstract

The present application provides a separator, a method for manufacturing the same, a secondary battery related thereto, and an electric consumption device. The separator includes a porous substrate and a coating layer provided on at least one surface of the porous substrate. The coating layer includes a three-dimensional skeleton structure and a filler, and at least a part of the filler is filled in the three-dimensional skeleton structure. The zeta potential of the coating layer is less than 0 mV. Since the separator according to the present application has characteristics such as excellent heat resistance, excellent uniformity, and excellent ion conductivity, a secondary battery using the separator can have a high energy density, high thermal safety, and a long service life.

Description

Technical Field

[0001] This application claims the priority of Chinese Patent Application PCT / CN2022 / 101261, titled "Separator, Method for Manufacturing the Same, Secondary Battery and Electric Consumption Device Related Thereby", filed on June 24, 2022, and all the contents of the said application are incorporated herein by reference.

[0002] This application belongs to the technical field of batteries, and specifically relates to a separator, a method for manufacturing the same, a secondary battery and an electric consumption device related therewith.

Background Art

[0003] In recent years, secondary batteries have been widely used in many fields such as energy storage power systems like hydropower, thermal power, wind power and solar power plants, and electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. As the application scope of secondary batteries is becoming increasingly wide, their safety issues, especially thermal safety issues, are attracting more and more attention. However, currently, the methods for improving the thermal safety performance of secondary batteries are disadvantageous to the balance of the energy density and the exertion of the capacity of secondary batteries. Therefore, enabling secondary batteries to have high energy density, high thermal safety performance and long service life is an important issue in the design of secondary batteries.

Summary of the Invention

[0004] The objective of this application is to provide a separator, a method for manufacturing the same, a secondary battery and an electric consumption device related therewith, which have characteristics such as excellent heat resistance, excellent uniformity, excellent ion conductivity, etc., so that the secondary battery using the said separator can have high energy density, high thermal safety performance and long service life.

[0005] A first aspect of the present application provides a separator including a porous substrate and a coating layer provided on at least one surface of the porous substrate. The coating layer includes a three-dimensional skeleton structure and a filler, at least a part of the filler is filled in the three-dimensional skeleton structure, and the zeta potential of the coating layer is less than 0 mV. The zeta potential of the coating layer can be measured by taking 30 g of the powder of the coating layer material, stirring and mixing it with 2000 g of deionized water to obtain a dispersion liquid, and measuring the zeta potential of the obtained dispersion liquid, that is, the zeta potential of the coating layer, by a zeta potential meter.

[0006] In the separator according to the present application, when the zeta potential of the coating layer is within an appropriate range, the slurry of the coating layer has good dispersibility. Therefore, after the slurry of the coating layer dries, a coating layer with good uniformity in areal density and thickness can be formed, improving the heat resistance of the separator. At the same time, it can ensure that the pore distribution of the coating layer is uniform and the ionic conductivity of the coating layer is good. As a result, the rate performance, thermal safety performance, and cycle performance of the secondary battery can be improved. When at least a part of the filler is filled in the three-dimensional skeleton structure, it contributes to the formation of an interlocking effect between the filler and the three-dimensional skeleton structure, improving the heat resistance of the separator, reducing the degree of shrinkage when the separator receives heat, reducing the risk of short circuit between the positive electrode and the negative electrode, enabling the secondary battery to have high thermal safety performance, and maintaining high adhesive strength between the coating layer and the porous substrate, thus avoiding the filler from falling off during long-term charge and discharge of the secondary battery. When at least a part of the filler is filled in the three-dimensional skeleton structure, the filler can also be lap-jointed with the three-dimensional skeleton structure. As a result, the coating layer can have a stable spatial network structure, increasing the ion conduction path of the separator, promoting ion transport, improving the infiltration and retention characteristics of the separator with respect to the electrolyte, and furthermore, the secondary battery using the separator of the present application can have a long service life. Since the coating layer of the present application has high heat resistance, a thinner porous substrate can be selected, and furthermore, the secondary battery using the separator of the present application can also achieve high energy density.

[0007] In any embodiment of the present application, the zeta potential of the coating layer is -50 mV to -5 mV, and optionally -25 mV to -5 mV. Thereby, in order to further improve the uniformity of the areal density and thickness and the pore uniformity of the coating layer, the ionic conductivity of the separator, and the energy density and cycle performance of the secondary battery can be further improved.

[0008] In any embodiment of the present application, the material constituting the three-dimensional skeleton structure includes at least one of organic rod-shaped materials and organic tubular materials. Materials with appropriate shapes are advantageous for better lap joining of the three-dimensional skeleton structure and the filler, whereby the coating layer can have a more stable spatial network structure, thereby further improving the heat resistance and ion conductivity of the separator.

[0009] In any embodiment of the present application, the material constituting the three-dimensional skeleton structure includes at least one of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers. Optionally, the nanocellulose includes at least one of cellulose nanofibers, cellulose nanowhiskers, and bacterial nanocellulose.

[0010] In any embodiment of the present application, the material constituting the three-dimensional skeleton structure includes nanocellulose, and the nanocellulose includes a hydroxy group and an anionic modification group. Optionally, the anionic modification group includes at least one of an amine group, a carboxy group, a sulfonic acid group, a borate group, and a phosphate group. More optionally, it includes at least one of a sulfonic acid group, a borate group, and a phosphate group. When the nanocellulose has the above specific anionic modification group, it can ensure that the slurry of the coating layer has an appropriate viscosity, which is advantageous for coating, so that the production efficiency of the separator can be improved, and it also contributes to the coating layer having an appropriate zeta potential, so that the uniformity of the surface density and thickness of the coating layer and the uniformity of the pores can be further improved, and the ion conductivity of the separator and the energy density and cycle performance of the secondary battery can be further improved.

[0011] In any embodiment of the present application, the molar ratio of the anionic modifying group to the hydroxy group is from 1:4 to 4:1, and optionally from 2:3 to 7:3. Thereby, the surface density and thickness uniformity of the coating layer and the pore uniformity can be further improved, and the heat resistance, ion conductivity, and infiltration and retention characteristics with respect to the electrolyte of the separator can be improved.

[0012] In any embodiment of the present application, the average diameter of the material constituting the three-dimensional skeleton structure is 40 nm or less, and optionally from 10 nm to 35 nm. Thereby, the ion conductivity and breakdown voltage resistance characteristics of the separator can be further improved, and the heat resistance of the separator can be further improved by contributing to the integration effect due to the lap joint between the material constituting the three-dimensional skeleton structure and the filler.

[0013] In any embodiment of the present application, the average length of the material constituting the three-dimensional skeleton structure is from 100 nm to 600 nm, and optionally from 200 nm to 400 nm. Thereby, the heat resistance and ion conductivity of the separator can be further enhanced.

[0014] Also in any embodiment of the present application, the aspect ratio of the material constituting the three-dimensional skeleton structure is from 5 to 60, and optionally from 15 to 30. Thereby, the ion conductivity of the separator can be further enhanced.

[0015] In any embodiment of the present application, the filler includes at least one of filler particles having a primary particle topography and filler particles having a secondary particle topography. Optionally, the filler includes filler particles having a secondary particle topography. More optionally, the filler simultaneously includes filler particles having a primary particle topography and filler particles having a secondary particle topography.

[0016] In any embodiment of the present application, the average particle diameter of the filler particles having a primary particle topography is from 200 nm to 800 nm, and optionally from 200 nm to 400 nm.

[0017] In any embodiment of the present application, the BET specific surface area of the filler particles of the primary particle topography is 10 m 2 / g or less, and optionally 3 m 2 / g to 7 m 2 / g.

[0018] In any embodiment of the present application, based on the total weight of the coating layer, the content of the filler particles of the primary particle topography is 30 wt% or less, and optionally 5 to 25 wt%.

[0019] Due to the large particle size of the filler particles of the primary particle topography, the supporting effect in the coating layer of the particles can be better exerted, the shrinkage of the filler particles of the secondary particle topography can be reduced, and the amount of binder used can be reduced, thereby improving the heat resistance of the separator. Due to the large particle size of the filler particles of the primary particle topography, when the usage amount is small, it contributes to the coating layer having more channel structures and less water content, and further improves the ion conductivity of the separator and the infiltration and retention characteristics with respect to the electrolyte.

[0020] In any embodiment of the present application, the average particle size of the filler particles of the secondary particle topography is 200 nm or less, and optionally 50 nm to 200 nm.

[0021] In any embodiment of the present application, the BET specific surface area of the filler particles of the secondary particle topography is 20 m 2 / g or more, and optionally 30 m 2 / g to 80 m 2 / g.

[0022] In any embodiment of the present application, based on the total weight of the coating layer, the content of the filler particles of the secondary particle topography is 60 wt% or more, and optionally 70 wt% to 90 wt%.

[0023] Since the filler particles of the secondary particle topography have the advantages of a large specific surface area and good affinity with the three-dimensional skeleton structure, they can better wrap and join with the three-dimensional skeleton structure, and the coating layer can have a more stable spatial network structure. Thereby, not only can the ion conduction path of the separator be increased to promote ion transport, but also the infiltration and retention characteristics of the electrolyte due to the heat resistance of the separator can be improved. Therefore, the secondary battery using the separator of the present application can have a long service life and good rate performance.

[0024] In any embodiment of the present application, the filler simultaneously includes filler particles of primary particle topography and filler particles of secondary particle topography, and the mass ratio of the filler particles of secondary particle topography to the filler particles of primary particle topography is 2:1 to 27:1, and optionally 5:1 to 15:1. This contributes to the coating layer having a more stable and uniform spatial network structure.

[0025] In any embodiment of the present application, the filler includes at least one of inorganic particles and organic particles. Optionally, the inorganic particles include at least one selected from inorganic particles having a dielectric constant of 5 or more, inorganic particles having a function of transporting active ions, and inorganic particles that can be electrochemically oxidized and reduced. Optionally, the organic particles include at least one selected from polystyrene, polyethylene, polyimide, melamine resin, phenol resin, polypropylene, polyester, polyphenylene sulfide, polyaramide, polyamideimide, polyimide, a copolymer of butyl acrylate and ethyl methacrylate, and mixtures thereof.

[0026] In any embodiment of the present application, based on the total weight of the coating layer, the content of the three-dimensional skeleton structure in the coating layer is 6 wt% to 35 wt%, and optionally 10 wt% to 30 wt%. Thereby, it is possible to ensure that the slurry of the coating layer has an appropriate viscosity, which is advantageous for coating, and is also advantageous for the integration effect due to the lap joint between the three-dimensional skeleton structure and the filler. Thereby, the coating layer can have a more stable spatial network structure.

[0027] In any embodiment of the present application, the mass ratio of the three-dimensional skeleton structure to the filler is 1:2 to 1:15.5, and optionally 1:5 to 1:10. Thereby, it contributes to the coating layer having an appropriate zeta potential, so that the uniformity of the areal density and thickness and the uniformity of the pores of the coating layer can be further improved. Thereby, the ion conductivity of the separator and the energy density and cycle performance of the secondary battery can be further improved.

[0028] In any embodiment of the present application, the coating layer further includes a non-particulate binder. Optionally, the non-particulate binder includes an aqueous solution type binder.

[0029] In any embodiment of the present application, based on the total weight of the coating layer, the content of the non-particulate binder in the coating layer is 2 wt% or less. The three-dimensional skeleton structure and the filler in the coating layer of the present application can be lap jointed so that the coating layer has a stable spatial network structure. Thereby, on the premise of reducing the usage amount of the binder, high adhesiveness to the separator can be maintained.

[0030] In any embodiment of the present application, the thickness of the porous substrate is 6 μm or less, and optionally 3 μm to 5 μm. Thereby, it contributes to the improvement of the energy density of the secondary battery.

[0031] In any embodiment of the present application, the thickness of the coating layer is 1 μm or less, and optionally 0.5 μm to 0.8 μm. This contributes to an improvement in the energy density of the secondary battery.

[0032] In any embodiment of the present application, the separator further includes an adhesive layer, the adhesive layer is disposed on at least a part of the surface of the coating layer, and the adhesive layer includes a particulate binder. Optionally, the particulate binder includes at least one of a homopolymer or copolymer of an acrylate monomer, a homopolymer or copolymer of an acrylic acid monomer, and a homopolymer or copolymer of a fluorine-containing olefin monomer. The adhesive layer can not only prevent the coating layer from falling off, improve the adhesiveness between the coating layer and the porous substrate and the safety performance of the secondary battery, but also improve the interface between the separator and the electrode and improve the cycle performance of the secondary battery.

[0033] In any embodiment of the present application, the longitudinal thermal shrinkage rate of the separator at 150 °C for 1 h is 5% or less, and optionally 0.5% to 3%.

[0034] In any embodiment of the present application, the transverse thermal shrinkage rate of the separator at 150 °C for 1 h is 5% or less, and optionally 0.5% to 3%.

[0035] In any embodiment of the present application, the longitudinal tensile strength of the separator is 2000 kg / cm 2 or more, and optionally 2500 kg / cm 2 ~4500 kg / cm 2 is.

[0036] In any embodiment of the present application, the transverse tensile strength of the separator is 2000 kg / cm 2 or more, and optionally 2500 kg / cm 2 ~4500 kg / cm 2 is.

[0037] In any embodiment of the present application, the wetting length of the separator is 30 mm or more, and optionally 30 mm to 80 mm.

[0038] In any embodiment of the present application, the wetting rate of the separator is 3 mm / s or more, and optionally 3 mm / s to 10 mm / s.

[0039] In any embodiment of the present application, the air permeability of the separator is 300 s / 100 mL or less, and optionally 100 s / 100 mL to 230 s / 100 mL.

[0040] By the performance of the separator satisfying one or more of the above conditions, it is advantageous for improving at least one of the energy density, thermal safety performance, and service life of the secondary battery.

[0041] The second aspect of the present application includes step S1 of providing a porous substrate, step S2 of preparing a slurry of a coating layer by mixing a material for forming a three-dimensional skeleton structure and a filler in a solvent at a predetermined ratio, and step S3 of applying the slurry of the coating layer to at least one surface of the porous substrate, forming a coating layer, and drying to obtain a separator. Here, the separator includes a porous substrate and a coating layer provided on at least one surface of the porous substrate. The coating layer includes a three-dimensional skeleton structure and a filler, at least a part of the filler is filled in the three-dimensional skeleton structure, and the zeta potential of the coating layer is less than 0 mV. A method for manufacturing the separator according to the first aspect of the present application is provided. The zeta potential of the coating layer can be measured by taking 30 g of the powder of the coating layer material, stirring and mixing it with 2000 g of deionized water to obtain a dispersion liquid, and measuring the zeta potential of the obtained dispersion liquid, that is, the zeta potential of the coating layer, with a zeta potential meter.

[0042] In any embodiment of the present application, the pH of the slurry of the coating layer is 5 to 10, and optionally 6 to 9.

[0043] In any embodiment of the present application, the static viscosity of the slurry of the coating layer is 1000 mPa·s or less.

[0044] In any embodiment of the present application, the slurry of the coating layer is obtained by a method including: a preparation step of a nanocellulose solution having a pH between 5 and 9 and a zeta potential of less than 0 mV, which includes step 1 of mixing nanocellulose having an anionic modification group with water to prepare the nanocellulose solution; a preparation step 2 of a filler solution having a pH of 7.5 or more and a zeta potential of less than 0 mV; and a mixing step 3 of mixing the nanocellulose solution and the filler solution at a predetermined ratio to obtain a slurry of the coating layer having a zeta potential of -5 mV or less.

[0045] In any embodiment of the present application, the concentration of the nanocellulose solution is 1 wt% to 10 wt%, optionally 2 wt% to 10 wt%.

[0046] In any embodiment of the present application, the concentration of the filler solution is 30 wt% to 60 wt%, optionally 35 wt% to 55 wt%.

[0047] In any embodiment of the present application, the nanocellulose having an anionic modification group is obtained by a method of mixing nanocellulose powder and a modification solution, reacting them, washing to remove impurities, obtaining cellulose nanowhiskers having an anionic modification group, adjusting the pH of the obtained cellulose nanowhiskers having an anionic modification group to neutral, and polishing and cutting to obtain nanocellulose having an anionic modification group. Optionally, the modification solution is an aqueous sulfuric acid solution, an aqueous boric acid solution, an aqueous phosphoric acid solution, an aqueous acetic acid solution, or a urea organic solvent solution.

[0048] In any embodiment of the present application, the filler solution is obtained by a method of mixing a filler, water, and a modifier containing at least one selected from a base, an anionic surfactant, and a nonionic surfactant to obtain a filler solution having a pH of 7.5 or more and a zeta potential of less than 0 mV.

[0049] In any embodiment of the present application, the base includes at least one selected from KOH, NaOH, NaHCO3, LiOH, NH4OH, Mg(OH)2, and Na2CO3.

[0050] In any embodiment of the present application, the anionic surfactant includes at least one selected from a sulfonate-type anionic surfactant, a carboxylate-type anionic surfactant, a sulfate ester salt-type anionic surfactant, and a phosphate ester salt-type anionic surfactant, and optionally includes at least one selected from an alkylbenzene sulfonate, a C12-C20 alkyl sulfonate, sodium polyacrylate, ammonium polyacrylate, sodium hydroxyethyl sulfate, and sodium C12-C20 alkyl sulfate.

[0051] In any embodiment of the present application, the nonionic surfactant includes at least one selected from a fluoroalkyl ethoxy glycol ether and an aliphatic alcohol polyoxyethylene ether.

[0052] In any embodiment of the present application, the method further includes two coating steps S4 of applying a slurry containing a particulate binder to at least a part of the surface of the coating layer and drying it to form an adhesive layer.

[0053] The method for manufacturing the separator of the present application significantly simplifies the manufacturing process of the separator because the coating layer is manufactured by single coating.

[0054] A third aspect of the present application provides a secondary battery including the separator of the first aspect of the present application or the separator manufactured by the method of the second aspect of the present application.

[0055] The fourth aspect of the present application provides an electric consumption device including the secondary battery according to the third aspect of the present application.

[0056] The present application provides a coating layer including a three-dimensional skeleton structure and a filler on the surface of the porous base material of the separator, and adjusts the zeta potential of the coating layer to less than 0 mV, so that the separator can have high heat resistance, high uniformity and good ion conductivity at the same time. Furthermore, the secondary battery can have high energy density, high thermal safety performance and long service life. Since the electric consumption device of the present application includes the secondary battery of the present application, it has at least the same advantages as the secondary battery.

Brief Description of the Drawings

[0057] To more clearly explain the technical solutions of the embodiments of the present application, the drawings required to be used in the examples of the present application are briefly described below. Obviously, the drawings described below are only some embodiments of the present application. Those skilled in the art can obtain other drawings based on these drawings without creative labor.

Figure 1

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Figure 5

Figure 6

Description of Reference Numerals

[0058] 1 Battery pack, 2 Upper box, 3 Lower box, 4 Battery module, 5 Secondary battery, 51 Housing, 52 Electrode assembly, 53 Cover plate

Mode for Carrying Out the Invention

[0059] Hereinafter, embodiments of the separator of the present application, a method for manufacturing the same, a secondary battery and an electric consumption device related thereto will be described in detail with appropriate reference to the drawings specifically disclosing the embodiments. However, detailed descriptions that are not necessary may be omitted. For example, detailed descriptions of known matters or redundant descriptions of substantially the same configuration may be omitted. This is to avoid the following description from becoming unnecessarily redundant and to facilitate the understanding of those skilled in the art. It should be noted that the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0060] The "range" disclosed in this application is defined in the form of a lower limit and an upper limit. A predetermined range is defined by selecting one lower limit and one upper limit, and the selected lower limit and upper limit limit the boundaries of a specific range. The range thus limited may be a range including or not including the end values, and may be arbitrarily combined, that is, 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 cited for a specific parameter, ranges of 60 - 110 and 80 - 120 are also understood to be anticipated. Also, when the minimum range values 1 and 2 and the maximum range values 3, 4, and 5 are cited, ranges of 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5 may all be anticipated. In this application, unless otherwise explained, the numerical range "a - b" is a shorthand notation for any combination of real numbers between a and b, and both a and b are real numbers. For example, the numerical range "0 - 5" indicates that all real numbers between "0 - 5" are cited in this specification, and "0 - 5" is a shorthand notation for combinations of these numerical values. Also, a notation that a certain parameter is 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.

[0061] Unless otherwise specified, all embodiments and selectable embodiments of this application may be combined with each other to form a new technical solution. Also, such a technical solution is considered to be included in the disclosure content of this application.

[0062] Unless otherwise specified, all technical features and selectable technical features of this application may be combined with each other to form a new technical solution. Also, such a technical solution is considered to be included in the disclosure content of this application.

[0063] Unless otherwise specified, all steps of this application may be performed in order or randomly, but it is preferred to perform them in order. For example, the fact that the above method includes steps (a) and (b) means that the above method may include steps (a) and (b) performed in order, or steps (b) and (a) performed in order. For example, when it is mentioned that the above method may further include step (c), it means that step (c) may be added to the above method in any order. For example, the above method may include steps (a), (b) and (c), may include steps (a), (c) and (b), may include steps (c), (a) and (b), etc.

[0064] Unless otherwise specified, the terms "comprise", "have" and "include" described in this application are open-ended and may also be closed-ended. For example, the above "comprise", "have" and "include" can mean further "comprising", "having" or "including" other components not listed, or only "comprising", "having" or "including" the listed components.

[0065] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" represents "A, B, or both A and B". More specifically, any of the following satisfies the condition "A or B". 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).

[0066] In this application, the terms "a plurality" and "a plurality of types" mean two or more.

[0067] Unless otherwise specified, the terms used in this application have the ordinary and well-known meanings understood by those skilled in the art.

[0068] Unless otherwise specified, the numerical values of the parameters mentioned in this application can be measured using various common measurement methods in this field. For example, they can be measured according to the methods described in the embodiments of this application.

[0069] Generally, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is provided between the positive electrode sheet and the negative electrode sheet, mainly playing a role in preventing short circuit between the positive electrode and the negative electrode, and at the same time, allowing active ions to pass freely to form a circuit.

[0070] With the application and popularization of secondary batteries, the requirements for the energy density and service life of secondary batteries are becoming increasingly high. Thinning of the separator is an effective measure to improve the energy density of secondary batteries. Currently, the separators used in commercialized secondary batteries are generally polyolefin porous membranes, such as polyethylene porous membranes, polypropylene porous membranes, or polypropylene / polyethylene / polypropylene three-layer composite membranes, and their melting points are 130°C to 160°C. Thus, when their thickness becomes thinner, the heat resistance of the separator deteriorates, and when heated, a significant heat shrinkage effect occurs, causing the positive electrode and the negative electrode inside the battery to come into direct contact and generate a short circuit inside, further increasing the safety risk of the secondary battery.

[0071] To solve the above problems, the currently adopted measures mainly involve coating 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 when the separator is heated, and reduce the risk of short circuit between the positive and negative electrodes inside the battery. However, due to the large particle size of commercially available inorganic ceramic particles, the overall thickness of the separator increases, and the energy density of the secondary battery cannot be balanced, which is particularly disadvantageous for improving the cruising range in the field of power batteries. Also, 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 furthermore, the improvement effect on the heat resistance of the separator is limited. Nanonization of inorganic ceramic particles can reduce the thickness of the coating layer and mitigate the adverse effects on the energy density of the secondary battery. However, the porosity of the coating layer formed by the nanonized inorganic ceramic particles is low, and it is easy to block the polyolefin porous membrane, resulting in a decrease in the overall porosity of the separator, an increase in ionic resistance, inhibition of ion transport, and further deterioration of the capacity and kinetic performance of the secondary battery. At the same time, due to the high specific surface area of the nanonized inorganic ceramic particles and the point contact form between the particles, a large amount of binder needs to be used to ensure the adhesion between the particles. However, when the amount of binder used is large, problems such as pore clogging are likely to occur, which is disadvantageous for the rate performance of the secondary battery. For example, dendrites are likely to form on the surface of the negative electrode, and it is also disadvantageous for the capacity, energy density, and service life of the secondary battery.

[0072] In addition, since the polyolefin porous membrane is a hydrophobic material and the inorganic ceramic particles are hydrophilic materials, when applying the slurry of inorganic ceramic on the surface of the polyolefin porous membrane, problems such as coating leakage and poor uniformity also exist, which affects the uniformity of the separator and further affects the capacity and kinetic performance of the secondary battery.

[0073] Therefore, it is difficult for the separators of the prior art to achieve both high energy density, high thermal safety performance, and long service life of the secondary battery.

[0074] In the process of research, the inventors of the present application surprisingly found that by providing a coating layer containing a three-dimensional skeleton structure and a filler on the surface of the separator porous substrate and adjusting the zeta potential of the coating layer within an appropriate range, the separator can be made to have high heat resistance, high uniformity, and good ion conductivity. Furthermore, it has been found that a secondary battery can achieve both high energy density, high thermal safety performance, and long service life. Separator

[0075] Specifically, the first aspect of the embodiment of the present application provides a separator including a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer including a three-dimensional skeleton structure and a filler, at least a part of the filler being filled in the three-dimensional skeleton structure, and the zeta potential of the coating layer being less than 0 mV.

[0076] The zeta potential of the coating layer can be measured by taking 30 g of the powder of the coating layer material, stirring and mixing it with 2000 g of deionized water to obtain a dispersion liquid, and measuring the zeta potential of the obtained dispersion liquid by a zeta potential meter, that is, the zeta potential of the coating layer.

[0077] The powder of the coating layer material is sampled by scraping the powder (for example, scraping the powder with a doctor blade), and the depth of scraping the powder does not exceed the boundary region between the coating layer and the porous substrate. The dispersion liquid is obtained by sufficiently stirring with a stirrer equipped with gears, and the stirring time may be 1 hour to 3 hours, and the stirring speed may be 1500 r / min to 3000 r / min.

[0078] The zeta potential meter can use the nano particle size and potential meter of the Zetasizer series of Malvern, for example, the nano particle size and potential meter of Zetasizer Advance. The sample cell can use the zeta potential capillary sample cell of DTS1070 of Malvern. Specifically, the obtained dispersion can be put into the zeta potential capillary cell of DTS1070 of Malvern for testing, and then the zeta potential of the dispersion can be measured by ZS Xplorer software. The test criteria can refer to GB / T 32671.2-2019 and ISO 13099-2-2012. In order to ensure the accuracy of the test results, multiple (for example, 5 or more) parallel samples are taken during the test and then the average value is taken.

[0079] Through a large number of studies, the inventors of the present application surprisingly found that by providing a coating layer containing a three-dimensional skeleton structure and a filler on the surface of the porous substrate of the separator and adjusting the zeta potential of the coating layer to less than 0 mV, the separator can have high heat resistance, high uniformity and good ion conductivity, and further, the secondary battery can have high energy density, high thermal safety performance and long service life.

[0080] The mechanism is not fully clear, but the inventors of the present application speculate the following points as possible reasons.

[0081] First, when the zeta potential of the coating layer is within an appropriate range, the slurry of the coating layer has good dispersibility. As a result, after the slurry of the coating layer dries, a coating layer with excellent uniformity in areal density and thickness can be formed, improving the heat resistance of the separator. At the same time, the pore distribution of the coating layer is uniform, and the ion conductivity of the coating layer can be ensured well, thereby improving the rate performance, thermal safety performance and cycle performance of the secondary battery.

[0082] Second, since at least a part of the filler is filled in the three-dimensional skeleton structure, it contributes to the formation of an intercalation effect between the filler and the three-dimensional skeleton structure, thereby improving the heat resistance of the separator, reducing the degree of shrinkage when the separator receives heat, reducing the risk of short circuit between the positive electrode and the negative electrode, enabling the secondary battery to have high thermal safety performance, maintaining high adhesive strength between the coating layer and the porous substrate, and avoiding the filler from falling off during long-term charge and discharge of the secondary battery.

[0083] Third, since at least a part of the filler is filled in the three-dimensional skeleton structure, the filler can also form a lap joint with the three-dimensional skeleton structure, thereby enabling the coating layer to have a stable spatial network structure, increasing the ion conduction pathway of the separator, promoting ion transport, improving the infiltration and retention characteristics of the separator with respect to the electrolyte, and furthermore, the secondary battery using the separator of the present application can have a long service life.

[0084] Fourth, since the coating layer of the present application has high heat resistance, a thinner porous substrate can be selected, and furthermore, the secondary battery using the separator of the present application can also achieve high energy density.

[0085] In some embodiments, the zeta potential of the coating layer may be -50 mV to -5 mV, optionally -25 mV to -5 mV, and further optionally -15 mV to -6 mV. Thereby, the uniformity of the surface density, thickness and pores of the coating layer is further improved, so that the ion conductivity of the separator, the energy density and cycle performance of the secondary battery can be further improved. Also, if the zeta potential of the coating layer is too low, the viscosity of the slurry of the coating layer is too high and the fluidity becomes poor, which can effectively avoid the possibility of affecting the application of the slurry of the coating layer and affecting the uniformity of the surface density, thickness and pores of the coating layer.

[0086] In some embodiments, the material constituting the three-dimensional skeleton structure may include at least one of organic rods and organic tubes. Materials with appropriate shapes are advantageous for better wrap-joining the three-dimensional skeleton structure and the filler, so that the coating layer can have a more stable spatial network structure, thereby further improving the heat resistance and ion conductivity of the separator.

[0087] In some embodiments, the material constituting the three-dimensional skeleton structure may include at least one of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers.

[0088] In some embodiments, the material constituting the three-dimensional skeleton structure may include nanocellulose. Optionally, the nanocellulose includes at least one of cellulose nanofibrils (also called Cellulose nanofibrils, CNF, nanofibrillar cellulose or microfibrillar cellulose), cellulose nanocrystals (also called Cellulose nanocrystals, CNC, cellulose nanocrystals or nanocrystalline cellulose), and bacterial nanocellulose (also called Bacterial nanocellulose, BNC, bacterial cellulose or microbial cellulose). Optionally, the nanocellulose includes cellulose nanocrystals having the advantage of high crystallinity, thereby better improving the heat resistance of the separator.

[0089] Nanocellulose is a general term for cellulose with a one-dimensional size in the nano-order (for example, within 100 nm). It has the characteristics of cellulose and the characteristics of nanoparticles. Nanocellulose may be a polymer nanomaterial extracted from wood, cotton, etc. in nature by one or more means such as chemistry, physics, and biology. It has a wide source, low cost, advantages such as biodegradability, high modulus, and high specific surface area. Therefore, it is an excellent alternative to conventional petrochemical resources and can effectively alleviate problems such as environmental pollution and the shortage of petrochemical resources.

[0090] In some embodiments, the nanocellulose may contain a hydroxy group and an anion-modified group. Optionally, the anion-modified group contains at least one of an amine group, a carboxyl group, a sulfonic acid group, a boric acid group, and a phosphate group. More optionally, it contains at least one of a sulfonic acid group, a boric acid group, and a phosphate group.

[0091] The inventors further found in further research that when nanocellulose has the above specific anion-modified group, it can ensure that the slurry of the coating layer has an appropriate viscosity, which is advantageous for coating. Therefore, it can improve the production efficiency of the separator and also contribute to the coating layer having an appropriate zeta potential. As a result, the uniformity of the surface density and thickness of the coating layer and the uniformity of the pores can be further improved. Furthermore, the ion conductivity of the separator, the energy density of the secondary battery, and the cycle performance can be further improved.

[0092] When nanocellulose has the above specific anion-modified group, it can also effectively improve the heat resistance of the separator and the adhesion strength between the coating layer and the porous substrate.

[0093] When the nanocellulose has the above-specified anionic modification group, it is also advantageous for the lap joint between the nanocellulose and the filler. Therefore, the coating layer has a more stable spatial network structure, and the infiltration and retention characteristics of the separator with respect to the electrolyte can be improved. As a result, the ion conductivity and breakdown voltage resistance characteristics of the separator can be further improved, which is advantageous for the matching of the high-voltage positive electrode active material and further improves the energy density of the secondary battery.

[0094] In some embodiments, the molar ratio of the anionic modification group to the hydroxy group may be 1:4 to 4:1, and optionally, 2:3 to 7:3. When the molar ratio of the anionic modification group to the hydroxy group is within an appropriate range, the uniformity of the surface density and thickness of the coating layer and the uniformity of the pores can be further improved, and the heat resistance, ion conductivity, and infiltration and retention characteristics of the separator with respect to the electrolyte can be improved. Also, if the molar ratio of the anionic modification group to the hydroxy group is too small, the further improvement effect on the uniformity of the surface density and thickness of the coating layer and the uniformity of the pores by the anionic modification group may not be obvious. If the molar ratio of the anionic modification group to the hydroxy group is too large, the infiltration and retention characteristics of the separator with respect to the electrolyte will deteriorate, which may in turn affect the cycle performance and safety performance of the secondary battery, and the heat resistance of the separator may decrease, further affecting the thermal safety performance of the secondary battery.

[0095] The type of the anionic modification group in the nanocellulose can be measured by infrared spectroscopy. For example, by testing the infrared spectrum of the material and determining the characteristic peaks contained therein, the type of the anionic modification group can be determined. Specifically, infrared spectrum analysis is performed on the material using known equipment and methods in this field. For example, it can be measured according to the general rules of the infrared spectrum analysis method of GB / T 6040-2019 using an infrared spectrophotometer (for example, the IS10 type Fourier transform infrared spectrophotometer of Thermo Fisher Scientific).

[0096] In some embodiments, the average diameter of the material constituting the three-dimensional skeleton structure may be 40 nm or less, and optionally 10 nm to 35 nm. When the average diameter of the material constituting the three-dimensional skeleton structure is within an appropriate range, the ion conductivity and breakdown voltage resistance characteristics of the separator can be further improved, and it also contributes to the integration effect due to the lap joint between the material constituting the three-dimensional skeleton structure and the filler, so the heat resistance of the separator can also be further improved. Also, if the average diameter of the material constituting the three-dimensional skeleton structure is too large, the winding effect of the formed three-dimensional skeleton structure is insufficient and the pores become large, so it is possible to effectively avoid the case where the breakdown voltage resistance characteristics of the separator are not sufficiently excellent.

[0097] In some embodiments, the average length of the material constituting the three-dimensional skeleton structure may be 100 nm to 600 nm, and optionally 200 nm to 400 nm. When the average length of the material constituting the three-dimensional skeleton structure is within an appropriate range, the heat resistance and ion conductivity of the separator can be further improved. Also, if the average length of the material constituting the three-dimensional skeleton structure is too short, the lap joint effect with the filler deteriorates, and the heat resistance of the coating layer may deteriorate. Moreover, in the drying process of the coating layer, some three-dimensional skeleton structures are likely to collapse due to insufficient support from the filler, easily blocking the pores of the porous substrate, inhibiting ion transport and water discharge, which may also affect the cycle performance and rate performance of the secondary battery. And if the average length of the material constituting the three-dimensional skeleton structure is too long, the viscosity of the slurry of the coating layer increases and the dispersibility deteriorates, so it is possible to effectively avoid the possibility that the uniformity of the surface density, thickness, and pores of the coating layer formed after drying the slurry of the coating layer deteriorates.

[0098] In some embodiments, the aspect ratio of the material constituting the three-dimensional skeleton structure may be 5 to 60, and optionally 15 to 30. When the aspect ratio of the material constituting the three-dimensional skeleton structure is within an appropriate range, the ion conductivity of the separator can be further improved. Also, if the aspect ratio of the material constituting the three-dimensional skeleton structure is too small, the wrap joint effect with the filler deteriorates, the heat resistance of the coating layer may deteriorate, and in the drying process of the coating layer, some of the three-dimensional skeleton structures are likely to collapse due to insufficient support from the filler, easily blocking the pores of the porous substrate, inhibiting ion transport and water discharge, which may affect the cycle performance and rate performance of the secondary battery. And, if the aspect ratio of the material constituting the three-dimensional skeleton structure is too large, since the pores of the formed three-dimensional skeleton structure are small, it is possible to effectively avoid the possibility that the ion conductivity of the separator deteriorates.

[0099] The average length and average diameter of the material constituting the three-dimensional skeleton structure can be measured by the following method. Cut out a 3.6 mm × 3.6 mm sample from any one region in the separator, map the microtopography structure of the coating layer in the sample using a scanning electron microscope (for example, ZEISS Sigma 300), select the high vacuum mode, with an operating voltage of 3 kV, a magnification of 30,000 times, and obtain an SEM image. Based on the obtained SEM image, select a plurality (for example, 5 or more) of test regions for length statistics, with the size of each test region being 0.5 μm × 0.5 μm. Then, take the average value of the lengths obtained in each test region as the average length of the material constituting the three-dimensional skeleton structure. Based on the obtained SEM image, use Nano Measurer particle size distribution statistics software to select a plurality (for example, 5 or more) of test regions for diameter statistics, with the size of each test region being 0.5 μm × 0.5 μm. Then, take the average value of the diameters obtained in each test region as the average diameter of the material constituting the three-dimensional skeleton structure.

[0100] In some embodiments, based on the total weight of the coating layer, the content of the three-dimensional skeleton structure in the coating layer may be 6 wt% to 35 wt%, and optionally 10 wt% to 30 wt%. When the content of the three-dimensional skeleton structure is within an appropriate range, it can ensure that the slurry of the coating layer has an appropriate viscosity, which is advantageous for coating. Also, it is advantageous for the integration effect due to the lap joint between the three-dimensional skeleton structure and the filler. Thus, the coating layer can have a more stable spatial network structure, thereby further improving the ion conductivity, the infiltration and retention characteristics with respect to the electrolyte, and the breakdown voltage resistance ability of the separator.

[0101] In a secondary battery, during the long-term charge-discharge process, the microstructural changes of the positive electrode active material and the negative electrode active material are irreversible, so the volume of the entire battery increases. In particular, during rapid charging of the secondary battery, the degree of volume increase after the negative electrode active material inserts active ions is higher. When the battery expands, a pressing and / or tensile action is generated on the separator, and the separator is likely to be damaged, thereby increasing the risk of short circuit between the positive electrode and the negative electrode. Therefore, the separator is also required to have good external force pressing resistance. At least a part of the filler is filled in the three-dimensional skeleton structure, which contributes to the coating layer having a stable spatial network structure, thereby improving the ion conductivity and heat resistance of the separator, and also improving the tensile strength, puncture resistance and external force pressing resistance of the separator.

[0102] In some embodiments, the filler may include at least one of filler particles with primary particle topography and filler particles with secondary particle topography. Optionally, the filler includes filler particles with secondary particle topography. More optionally, the filler simultaneously includes filler particles with primary particle topography and filler particles with secondary particle topography. Filler particles with secondary particle topography have the advantages of a large specific surface area and good affinity with the three-dimensional skeleton structure. Therefore, they can better wrap and join with the three-dimensional skeleton structure, enabling the coating layer to have a stable spatial network structure. Thereby, it can not only increase the ion conduction pathway of the separator and promote ion transport, but also improve the heat resistance of the separator and its infiltration and retention characteristics with respect to the electrolyte. As a result, the secondary battery employing the separator of the present application can have a long service life and good rate performance. Due to the large particle size of the filler particles with primary particle topography, the supporting effect in the particle coating layer can be better exerted, reducing the shrinkage of the filler particles with secondary particle topography and reducing the usage amount of the binder. Thereby, the heat resistance of the separator can be improved. Due to the large particle size of the filler particles with primary particle topography, it contributes to the coating layer having more channel structures and less water content when the usage amount is small, and further improving the ion conductivity of the separator and its infiltration and retention characteristics with respect to the electrolyte.

[0103] In some embodiments, the filler simultaneously includes filler particles with primary particle topography and filler particles with secondary particle topography, and the mass ratio of the filler particles with secondary particle topography to the filler particles with primary particle topography is from 2:1 to 27:1, optionally from 5:1 to 15:1. Thereby, it contributes to the coating layer having a more stable and excellent uniformity spatial network structure.

[0104] In some embodiments, the average particle size of the filler particles of the primary particle topography may be 200 nm to 800 nm, and optionally 200 nm to 400 nm. Thereby, the supporting effect of the filler particles of the primary particle topography can be better exerted, the coating layer can maintain a stable channel structure during the long-term charge and discharge process, and it is more favorable for ion transport.

[0105] In some embodiments, the BET specific surface area of the filler particles of the primary particle topography may be 10 m 2 / g or less, and optionally 3 m 2 / g to 7 m 2 / g. Thereby, the supporting effect of the filler particles of the primary particle topography can be better exerted, the coating layer can maintain a stable channel structure during the long-term charge and discharge process, and it is more favorable for ion transport.

[0106] In some embodiments, based on the total weight of the coating layer, the content of the filler particles of the primary particle topography is 30 wt% or less, and optionally 5 wt% to 25 wt%. Thereby, the supporting effect of the filler particles of the primary particle topography can be better exerted, the coating layer can maintain a stable channel structure during the long-term charge and discharge process, and it is more favorable for ion transport.

[0107] In some embodiments, the average particle size of the filler particles of the secondary particle topography may be 200 nm or less, and optionally 50 nm to 200 nm. Thereby, the filler particles of the secondary particle topography can have a high specific surface area, so that the affinity between the filler and the three-dimensional skeleton structure can be increased, and the filler and the three-dimensional skeleton structure can be better lap-joined. Thereby, the coating layer can have a more stable spatial network structure, and further, the separator can have better heat resistance, ion conductivity, and infiltration and retention characteristics for the electrolyte.

[0108] In some embodiments, the BET specific surface area of the filler particles of the secondary particle topography may be 20 m 2 / g or more, and optionally 30 m 2 / g to 80 m 2 / g. Thereby, the affinity between the filler and the three-dimensional skeleton structure becomes better, so that the coating layer can have a more stable spatial network structure, and the separator has better heat resistance, ion conductivity, and infiltration and retention characteristics with respect to the electrolyte.

[0109] In some embodiments, based on the total weight of the coating layer, the content of the filler particles of the secondary particle topography may be 60 wt% or more, and optionally 70 wt% to 90 wt%. Thereby, it is possible to ensure that the slurry of the coating layer has an appropriate viscosity, which is advantageous for coating. It is also advantageous for better lap-joining the filler and the three-dimensional skeleton structure, and the coating layer has a more stable spatial network structure, thereby further improving the tensile strength, puncture resistance and external force pressing resistance of the separator.

[0110] In some embodiments, the filler includes at least one of inorganic particles and organic particles.

[0111] In some embodiments, the inorganic particles may include at least one selected from inorganic particles having a dielectric constant of 5 or more, inorganic particles having a function of transporting active ions, and inorganic particles that can be electrochemically oxidized and reduced.

[0112] In some embodiments, examples of the inorganic particles having a dielectric constant of 5 or more include boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon oxygen compounds (SiOx (0 < x ≦ 2)), tin dioxide (SnO2), titanium dioxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), hafnium dioxide (HfO2), cerium oxide (CeO2), zirconium titanate (ZrTiO3), barium titanate (BaTiO3), magnesium fluoride (MgF2), Pb(Zr,Ti)O3 (abbreviated as PZT), Pb 1-m La m Zr 1-n Ti n O3 (abbreviated as PLZT, 0 < m < 1, 0 < n < 1), and Pb(Mg3Nb 2 / 3 )O3 - PbTiO3 (abbreviated as PMN - PT) may include one selected therefrom.

[0113] In some embodiments, examples of the inorganic particles having a function of transporting active ions include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium titanium aluminum phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y -based glass (0 < x < 4, 0 < y < 13), lanthanum lithium titanate (LixLayTiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2), SiS2 - based glass (Li x Si yS z 、 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5-based glass (Li x P y S z 、 0 < x < 3, 0 < y < 3, 0 < z < 7) may include one type selected therefrom.

[0114] In some embodiments, the electrochemically oxidizable and reducible inorganic particles may include at least one selected from lithium-containing transition metal oxides, olivine-structured lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials, and lithium titanium compounds.

[0115] In some embodiments, the organic particles may include at least one selected from polystyrene, polyethylene, polyimide, melamine resin, phenol resin, polypropylene, polyester (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), polyphenylene sulfide, polyaramide, polyamideimide, polyimide, a copolymer of butyl acrylate and ethyl methacrylate, and mixtures thereof.

[0116] In some embodiments, the mass ratio of the three-dimensional skeleton structure to the filler may be 1:2 to 1:15.5, and optionally 1:5 to 1:10. This contributes to the coating layer having an appropriate zeta potential, so that the uniformity of the surface density and thickness and the pore uniformity of the coating layer can be further improved, thereby further improving the ion conductivity of the separator and the energy density and cycle performance of the secondary battery.

[0117] In some embodiments, the coating layer may further include a non-particulate binder. In the present application, the type of the non-particulate binder is not particularly limited, and any material having known good adhesiveness can be adopted. Optionally, the non-particulate binder includes an aqueous solution type binder, which has good thermodynamic stability and environmental friendliness, and is thus advantageous for the preparation and coating of the slurry of the coating layer. As an example, the aqueous solution type binder may include at least one of an aqueous solution type acrylic resin (for example, a homopolymer of monomers such as acrylic acid, methacrylic acid, and sodium acrylate or a copolymer of these and other copolymerizable monomers), polyvinyl alcohol (PVA), an isobutylene-maleic anhydride copolymer, and polyacrylamide.

[0118] Optionally, based on the total weight of the coating layer, the content of the non-particulate binder in the coating layer is 2 wt% or less. The three-dimensional skeleton structure and the filler in the coating layer of the present application can be lap-jointed so that the coating layer has a stable spatial network structure. Thereby, on the premise of reducing the usage amount of the binder, high adhesiveness can be maintained for the separator.

[0119] In some embodiments, the thickness of the coating layer may be 1 μm or less, and optionally 0.5 μm to 0.8 μm. This contributes to the improvement of the energy density of the secondary battery. In the present application, the thickness of the coating layer refers to the thickness of the coating layer located on one side of the porous substrate.

[0120] In some embodiments, the thickness of the porous substrate may be 6 μm or less, and optionally 3 μm to 5 μm. The coating layer of the present application can significantly improve the heat resistance of the separator. Thereby, a thinner porous substrate can be selected, which contributes to the improvement of the energy density of the secondary battery.

[0121] In the present application, the material of the porous substrate is not particularly limited, and any known substrate having good chemical stability and mechanical stability can be selected. For example, the porous substrate may include at least one of a porous polyolefin-based resin film (e.g., at least one of polyethylene, polypropylene, and polyvinylidene fluoride), porous glass fiber, and porous nonwoven fabric. The porous substrate may be a single-layer film or a multilayer composite film. When the porous substrate is a multilayer composite film, the materials of each layer may be the same or different.

[0122] In some embodiments, the separator may further include an adhesive layer provided on at least a part of the surface of the coating layer and containing a particulate binder. The adhesive layer can not only prevent the coating layer from falling off, improve the adhesiveness between the coating layer and the porous substrate and the safety performance of the secondary battery, but also improve the interface between the separator and the electrode and the cycle performance of the secondary battery.

[0123] Optionally, the particulate binder may include at least one of a homopolymer or copolymer of an acrylate monomer, a homopolymer or copolymer of an acrylic acid monomer, and a homopolymer or copolymer of a fluorine-containing olefin monomer. The copolymer monomer includes, but is not limited to, at least one of an acrylate monomer, an acrylic acid monomer, an olefin monomer, a halogen-containing olefin monomer, and a fluoroether monomer.

[0124] Optionally, the particulate binder includes a vinylidene fluoride-based polymer, such as a homopolymer of vinylidene fluoride monomer (VDF) and / or a copolymer of vinylidene fluoride monomer and a comonomer. The comonomer may be at least one of an olefin monomer, a fluorine-containing olefin monomer, a chlorine-containing olefin monomer, an acrylate-based monomer, an acrylic monomer, and a fluoroether-based monomer. Optionally, the comonomer may include at least one of trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ether (e.g., perfluoro(methyl vinyl) ether PMVE, perfluoro(ethyl vinyl) ether PEVE, perfluoro(propyl vinyl) ether PPVE), perfluoro(1,3-m-dioxole), and perfluoro(2,2-dimethyl-1,3-m-dioxole) (PDD).

[0125] In some embodiments, the longitudinal thermal shrinkage rate of the separator at 150 °C for 1 h is 5% or less, and optionally 0.5% to 3%.

[0126] In some embodiments, the transverse thermal shrinkage rate of the separator at 150 °C for 1 h is 5% or less, and optionally 0.5% to 3%.

[0127] Since the separator of the present application has a low thermal shrinkage rate in both the transverse and longitudinal directions at a high temperature of 150 °C, the safety performance of the secondary battery can be improved.

[0128] In some embodiments, the longitudinal tensile strength of the separator is 2000 kg / cm 2 or more, and optionally 2500 kg / cm 2 ~4500 kg / cm 2 is.

[0129] In some embodiments, the transverse tensile strength of the separator is 2000 kg / cm 2 or more, and optionally 2500 kg / cm 2 to 4500 kg / cm 2 .

[0130] Since the separator of the present application has high tensile strength in both the transverse and longitudinal directions, the probability of the separator being damaged during the expansion of the secondary battery is small, and thereby, the safety performance of the secondary battery can be improved.

[0131] In some embodiments, the wetting length of the separator is 30 mm or more, and optionally 30 mm to 80 mm.

[0132] In some embodiments, the wetting rate of the separator is 3 mm / s or more, and optionally 3 mm / s to 10 mm / s.

[0133] Since the separator of the present application has good infiltration and retention characteristics with respect to the electrolyte, the ion conductivity of the separator and the capacity performance characteristics of the secondary battery can be improved.

[0134] In some embodiments, the air permeability of the separator is 300 s / 100 mL or less, and optionally 100 s / 100 mL to 230 s / 100 mL. Since the separator of the present application has good air permeability, the ion conductivity and the capacity performance characteristics of the secondary battery can be improved.

[0135] In the present application, the average particle size of the material is the known meaning in the art and can be measured using known devices and methods in the art. For example, a scanning electron microscope, a transmission electron microscope, and a particle size distribution apparatus are used to measure the material or the separator to obtain an image, and a plurality (for example, 10 or more) of test particles are randomly selected from the image, and the average value of the shortest diagonal line lengths of the particles can be statistically calculated as the average particle size.

[0136] In this application, the specific surface area of the material has the meaning known in the art and can be measured using the equipment and methods known in the art. For example, referring to GB / T 19587-2017, it can be measured by the nitrogen gas adsorption specific surface area analysis test method and calculated by the BET (Brunauer Emmett Teller) method. Optionally, the nitrogen gas adsorption specific surface area analysis test can be performed by a Tri-Star 3020 specific surface area and pore size analyzer manufactured by Micromeritics, USA.

[0137] In this application, the heat shrinkage rate, tensile strength, and air permeability of the separator all have the meaning known in the art and can be measured by the methods known in the art. For example, all of them can be tested with reference to the GB / T 36363-2018 standard.

[0138] In this application, both the wetting length and wetting rate of the separator have the meaning known in the art and can be measured by the methods known in the art. As an exemplary measurement method, the separator is cut into samples with a width of 5 mm and a length of 100 mm, the two ends of the sample are fixed and placed horizontally, 0.5 mg of electrolyte is dropped onto the center of the sample, and after reaching a predetermined time (1 min in this application), the length of the electrolyte diffusion is photographed and measured to obtain the wetting length and wetting rate of the separator. To ensure the accuracy of the test results, the test is performed using multiple (for example, 5 to 10) samples, and the test results can be obtained by calculating the average value. The electrolyte can be obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a mass ratio of 30:50:20 to obtain an organic solvent, and dissolving LiPF6 sufficiently dried in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0139] Note that all the parameters (such as thickness) of the coating layer of the separator are the parameters of the coating layer on one side of the porous substrate. When the coating layer is provided on both sides of the porous substrate, if the parameters of the coating layer on either side satisfy the present application, it is considered to be within the protection scope of the present application. Manufacturing method

[0140] The second aspect of the embodiment of the present application includes: a step S1 of providing a porous substrate; a step S2 of preparing a slurry of the coating layer by mixing a material for forming a three-dimensional skeleton structure and a filler in a solvent at a predetermined ratio; and a step S3 of applying the slurry of the coating layer to at least one surface of the porous substrate, forming the coating layer and drying it 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 a three-dimensional skeleton structure and a filler, at least a part of the filler is filled in the three-dimensional skeleton structure, and the zeta potential of the coating layer is less than 0 mV. A method for manufacturing a separator according to the first aspect of the embodiment of the present application is provided.

[0141] In some embodiments, in S2, the solvent may be water, for example, deionized water.

[0142] In some embodiments, in S2, the slurry may further include other components, for example, a dispersant, a wetting agent, a binder, etc.

[0143] In some embodiments, in S2, the material for forming the three-dimensional skeleton structure includes nanocellulose. The nanocellulose includes a hydroxy group and an anionic modified group. The anionic modified group includes at least one of an amine group, a carboxyl group, a sulfonic acid group, a boric acid group, and a phosphoric acid group, and optionally includes at least one of a sulfonic acid group, a boric acid group, and a phosphoric acid group.

[0144] Optionally, the nanocellulose is cellulose nanocrystals (also referred to as CNC, cellulose nanocrystals, or nanocrystalline cellulose).

[0145] In some embodiments, in S2, the slurry of the coating layer is obtained by a method comprising: a step 1 of preparing a nanocellulose solution having a pH between 5 and 9 and a zeta potential less than 0 mV, by mixing nanocellulose having an anionic modification group with water to prepare the nanocellulose solution; a step 2 of preparing a filler solution having a pH of 7.5 or more and a zeta potential less than 0 mV; and a mixing step 3 of mixing the nanocellulose solution and the filler solution at a predetermined ratio to obtain a slurry of the coating layer having a zeta potential of -5 mV or less.

[0146] In some embodiments, in step 1, the nanocellulose having an anionic modification group can be obtained by a method comprising: mixing and reacting nanocellulose powder with a modification solution, then washing to remove impurities to obtain cellulose nanocrystals having an anionic modification group, adjusting the pH of the obtained cellulose nanocrystals having an anionic modification group to neutral (for example, between 6.5 and 7.5), pulverizing, and cutting to obtain nanocellulose having an anionic modification group.

[0147] In some embodiments, the whiteness of the nanocellulose powder may be 80% or more. The cellulose powder may be obtained as a commercially available product, or by chemical methods (e.g., acid hydrolysis method, alkali treatment method, Tempo-mediated oxidation method), biological methods (e.g., enzymatic treatment method), mechanical methods (e.g., ultrafine grinding, ultrasonic grinding, high-pressure homogenization), etc. The fiber raw materials for producing the cellulose powder with a whiteness of 80% or more may include at least one of plant fibers, such as cotton fibers (e.g., cotton fiber, kapok fiber), hemp fibers (e.g., sisal fiber, columnar fiber, kouma fiber, flax fiber, hemp fiber, Manila hemp fiber, etc.), shuro fiber, wood fiber, bamboo fiber, and grass fiber.

[0148] In some embodiments, the cellulose powder is produced by a method in which the fiber raw material is opened and the debris is removed, then cooked with an alkali solution (e.g., an aqueous NaOH solution with a concentration of 4 wt% to 20 wt%, optionally 5 wt% to 15 wt%), then washed successively with water to remove impurities (e.g., the number of water washings is 3 to 6 times), bleached (e.g., using sodium hypochlorite and / or hydrogen peroxide solution), acid-washed to remove impurities, washed with water to remove impurities, water is removed, and air-dried to obtain the cellulose powder.

[0149] In some embodiments, the modification 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 alkali solution (e.g., urea organic solvent solution). Optionally, the modification solution is an acid solution.

[0150] In some embodiments, the concentration of the acid solution may be 5 wt% to 80 wt%.

[0151] When using an aqueous sulfuric acid solution as the denaturing solution, the concentration of the acid solution may be 40 wt% to 80 wt%, so that cellulose powder having a sulfonic acid group can be obtained. When using an aqueous boric acid solution as the denaturing solution, the concentration of the acid solution may be 5 wt% to 10 wt%, so that cellulose powder having a boric acid group can be obtained. When using an aqueous phosphoric acid solution as the denaturing solution, the concentration of the acid solution may be 45 wt% to 75 wt%, so that cellulose powder having a phosphate group can be obtained. When using an aqueous acetic acid solution as the denaturing solution, the concentration of the acid solution may be 40 wt% to 80 wt%, so that cellulose powder having a carboxylic acid group can be obtained.

[0152] Moreover, since the urea organic solvent solution is a urea xylene solution, cellulose powder having an amine group can be obtained.

[0153] In some embodiments, the mass ratio of the cellulose powder to the denaturing solution may be 1:2.5 to 1:50, and optionally 1:5 to 1:30.

[0154] When using an aqueous sulfuric acid solution as the denaturing solution, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30. When using an aqueous boric acid solution as the denaturing solution, the mass ratio of the cellulose powder to the acid solution may be 1:20 to 1:50. When using an aqueous phosphoric acid solution as the denaturing solution, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30. When using an aqueous acetic acid solution as the denaturing solution, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30. When using a urea organic solvent solution as the denaturing solution, the mass ratio of the cellulose powder to the urea organic solvent solution may be 1:4 to 1:40.

[0155] In some embodiments, when the denaturing solution is an acid solution, the reaction can be carried out under conditions of 80 °C or lower, and optionally under conditions of 30 °C to 60 °C. The reaction time between the cellulose powder and the denaturing solution can be 0.5 h to 4 h, and optionally 1 h to 3 h.

[0156] In some embodiments, when the denaturing solution is an alkaline solution, the reaction can be carried out under conditions of 100 °C to 145 °C, and the reaction time between the cellulose powder and the denaturing solution can be 1 h to 5 h.

[0157] In some embodiments, polishing may be performed using a polishing machine, and cutting may be performed using a high-pressure homogenizer. By adjusting the polishing parameters of the polishing machine (such as the number of polishing times, polishing time, etc.) and the cutting parameters of the high-pressure homogenizer, nanocellulose having different average diameters and / or different average lengths can be obtained.

[0158] In some embodiments, in Step 2, the filler solution can be obtained by a method of mixing a filler, water, and a denaturing agent containing at least one selected from a base, an anionic surfactant, and a nonionic surfactant to obtain a filler solution having a pH of 7.5 or higher and a zeta potential of less than 0 mV.

[0159] Optionally, the base includes at least one selected from KOH, NaOH, NaHCO3, LiOH, NH4OH, Mg(OH)2, and Na2CO3.

[0160] Optionally, the anionic surfactant includes at least one selected from sulfonate-type anionic surfactants, carboxylate-type anionic surfactants, sulfate ester salt-type anionic surfactants, and phosphate ester salt-type anionic surfactants, and further optionally includes at least one selected from alkylbenzene sulfonates (e.g., sodium butylnaphthalene sulfonate), C12-C20 alkyl sulfonates, sodium polyacrylate, ammonium polyacrylate, sodium hydroxyethyl sulfate, and sodium C12-C20 alkyl sulfate.

[0161] Optionally, the nonionic surfactant includes at least one selected from fluoroalkyl ethoxy glycol ethers and aliphatic alcohol polyoxyethylene ethers.

[0162] In some embodiments, the concentration of the nanocellulose solution may be 1 wt% to 10 wt%, and optionally 2 wt% to 10 wt%.

[0163] In some embodiments, the concentration of the filler solution may be 30 wt% to 60 wt%, and optionally 35 wt% to 55 wt%.

[0164] In some embodiments, in S2, the pH of the slurry of the coating layer may be 5 to 10, and optionally 6 to 9.

[0165] In some embodiments, in S2, the static viscosity of the slurry of the coating layer may be 1000 mPa·s or less.

[0166] Thereby, the film surface problem of the coating layer can be effectively reduced, and the occurrence probability of coating unevenness can be reduced, so that the energy density and safety performance of the secondary battery can be further improved.

[0167] In some embodiments, in S3, a coater is employed for the coating. In the present application, the model number of the coater is not particularly limited. For example, a commercially available coater can be adopted. The coater includes a gravure roll for transferring the slurry onto the porous substrate.

[0168] In some embodiments, in S3, the coating method can adopt transfer coating, rotary spray coating, dip coating, etc.

[0169] In some embodiments, the method further includes two coating steps S4 of applying a slurry containing a particulate binder onto at least a part of the surface of the coating layer and drying to form an adhesive layer.

[0170] Since the manufacturing method of the separator of the present application manufactures the coating layer by single coating, the manufacturing process of the separator is greatly simplified.

[0171] For parameters such as the raw materials used in the manufacturing method of the separator of the present application and their contents, reference can be made to the separator in the first aspect of the embodiment of the present application, and the description is omitted here.

[0172] Unless otherwise specified, each raw material used in the manufacturing method of the separator of the present application is commercially available. Secondary battery

[0173] The third aspect of the embodiment of the present application provides a secondary battery.

[0174] A secondary battery, also called a rechargeable battery or a storage battery, refers to a battery that can continue to be used by activating the active material through charging after discharging the battery. Usually, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is provided between the positive electrode sheet and the negative electrode sheet, mainly serving to prevent short circuit between the positive electrode and the negative electrode and allowing active ions to pass through.

[0175] 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. In particular, the secondary battery may be a lithium-ion secondary battery.

[0176] The secondary battery according to the third aspect of the embodiment of the present application includes a separator according to the first aspect of the embodiment of the present application or a separator manufactured by the method according to the second aspect of the embodiment of the present application, and the separator is interposed between the positive electrode sheet and the negative electrode sheet. Optionally, the coating layer of the present application is provided at least on the side of the separator close to the negative electrode sheet. Thereby, the secondary battery of the present application can have high energy density, high thermal safety performance and long service life. [Positive electrode sheet]

[0177] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector and containing a positive electrode active material. For example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode film layer is provided on one or both of the two opposing surfaces of the positive electrode current collector.

[0178] When the secondary battery of the present application is a lithium ion battery, the positive electrode active material includes, but is not limited to, at least one of lithium-containing transition metal oxides, lithium-containing phosphates, and their modified compounds. Examples of the lithium transition metal oxides include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Examples of the lithium-containing phosphates include, but are not limited to, at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their modified compounds.

[0179] 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 represented by the general formula Li a Ni b Co c M d O e A f and their modified compounds. 0.8 ≦ a ≦ 1.2, 0.5 ≦ b < 1, 0 < c < 1, 0 < d < 1, 1 ≦ e ≦ 2, 0 ≦ f ≦ 1, M is at least one selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is at least one selected from N, F, S, and Cl.

[0180] As an example, the positive electrode active material used in the lithium ion battery is LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O2, LiFePO4, LiMnPO4 may include at least one of them.

[0181] When the secondary battery of the present application is a sodium ion battery, the positive electrode active material includes, but is not limited to, at least one of sodium-containing transition metal oxides, polyanion materials (for example, phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue-based materials.

[0182] Examples of the positive electrode active material used in a sodium ion battery include, for example, NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, NaNi 1 / 2 Ti 1 / 2 O2, NaNi 1 / 2 Mn 1 / 2 O2, Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2, NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue-based materials, materials of the general formula X p M’ q (PO4) r O x Y 3-x It may include at least one of the materials represented by. In the general formula X p M’ q (PO4) r O x Y 3-x , 0 < p ≤ 4, 0 < q ≤ 2, 1 ≤ r ≤ 3, 0 ≤ x ≤ 2, and X is H + , Li + , Na + , K + and NH4 +At least one selected from, M' is a transition metal cation, optionally at least one of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, Y is a halogen anion, optionally at least one of F, Cl and Br.

[0183] In the present application, the modified compound of each of the above positive electrode active materials can be obtained by performing doping modification and / or surface coating modification on the positive electrode active material.

[0184] In some embodiments, the positive electrode film layer may optionally contain a positive electrode conductive agent. In the present application, the type of the positive electrode conductive agent is not particularly limited. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. In some embodiments, based on the total mass of the positive electrode film layer, the mass percentage of the positive electrode conductive agent is 5% or less.

[0185] In some embodiments, the positive electrode film layer may optionally contain a positive electrode binder. In the present application, the type of the positive electrode binder is not particularly limited. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin. In some embodiments, based on the total mass of the positive electrode film layer, the mass percentage of the positive electrode binder is 5% or less.

[0186] In some embodiments, the positive electrode current collector can be a metal foil sheet or a composite current collector. As an example of the metal foil sheet, an aluminum foil can be used. The composite current collector may include a polymer material layer and a metal material layer formed on at least one surface of the polymer material layer. As an example, the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0187] The positive electrode film layer is generally formed by applying a positive electrode slurry to a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring uniformly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto. [Negative electrode sheet]

[0188] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector and containing a negative electrode active material. For example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode film layer is provided on either one or both of the two opposing surfaces of the negative electrode current collector.

[0189] The negative electrode active material can adopt a negative electrode active material used in known secondary batteries in this field. As an example, the negative electrode active material includes, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy material.

[0190] 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. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber. In some embodiments, based on the total mass of the negative electrode film layer, the mass percentage of the negative electrode conductive agent is 5% or less.

[0191] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. In the present application, the type of the negative electrode binder is not particularly limited. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (for example, 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 of the negative electrode binder is 5% or less.

[0192] In some embodiments, the negative electrode film layer may optionally contain other auxiliaries. As an example, the other auxiliaries may include, for example, thickeners such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc. In some embodiments, based on the total mass of the negative electrode film layer, the mass percentage of the other auxiliaries is 2% or less.

[0193] In some embodiments, the negative electrode current collector can use a metal foil sheet or a composite current collector. As an example of the metal foil sheet, a copper foil can be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0194] The negative electrode film layer is generally formed by applying a negative electrode slurry to a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is generally formed by dispersing a negative electrode active material, an optional conductive agent, an optional binder, and any other auxiliaries in a solvent and stirring uniformly. The solvent may be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0195] The negative electrode sheet does not exclude other 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 (for example, composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and provided on the surface of the negative electrode current collector. In some other embodiments, the negative electrode sheet described in the present application further includes a protective layer covering the surface of the negative electrode film layer. [Electrolyte]

[0196] During the charge and discharge process of the secondary battery, active ions reciprocate between the positive electrode sheet and the negative electrode sheet for insertion and desorption, and the electrolyte plays a role in conducting the active ions between the positive electrode sheet and the negative electrode sheet. The present application does not particularly limit the type of the electrolyte, and it can be selected according to actual needs.

[0197] The electrolyte contains an electrolyte salt and a solvent. The types of the electrolyte salt and the solvent are not specifically limited and can be selected according to actual needs.

[0198] When the secondary battery of the present application is a lithium-ion battery, as an example, the electrolyte salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium difluoromethanesulfonimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoroborate (LiDFOB), lithium diborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodiphosphate (LiDFOP), and lithium tetrafluoroborate (LiTFOP), but is not limited thereto.

[0199] When the secondary battery of the present application is a sodium ion battery, as an example, the electrolyte salt includes, but is not limited to, at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium difluoromethanesulfonimide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluoroborate oxalate (NaDFOB), sodium diborate oxalate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorodiphosphate oxalate (NaDFOP), and sodium tetrafluorophosphate oxalate (NaTFOP).

[0200] As an example, the solvent includes, 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).

[0201] In some embodiments, the electrolyte may optionally contain additives. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, and additives that can improve certain performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature performance of the battery, and additives that improve the low-temperature output performance of the battery.

[0202] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be used to manufacture an electrode assembly by a winding process and / or a lamination process.

[0203] In some embodiments, the secondary battery may include an exterior. The exterior is used to seal the electrode assembly and the electrolyte.

[0204] In some embodiments, the exterior of the secondary battery may be a rigid package such as a rigid plastic case, an aluminum case, or a steel case. The exterior of the secondary battery may be a soft package such as a bag-type soft package. The material of the soft package may be at least one of plastics such as polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0205] In the present application, the shape of the secondary battery is not particularly limited and may be cylindrical, rectangular, or any other arbitrary shape. For example, FIG. 1 shows a secondary battery 5 having a rectangular structure as an example.

[0206] In some embodiments, as shown in FIG. 2, the exterior may include a housing 51 and a cover plate 53. The housing 51 includes a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates surround to form a receiving cavity. The housing 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 can form an electrode assembly 52 by a winding process and / or a lamination process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode body 52. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more and can be adjusted as needed.

[0207] The manufacturing method of the secondary battery of the present application is known. In some embodiments, a secondary battery can be formed by assembling a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. As an example, a positive electrode sheet, a separator, and a negative electrode sheet can be formed into an electrode assembly by a winding process and / or a lamination process. The electrode assembly is placed in an outer package, and after drying, the electrolyte is injected. Through processes such as vacuum sealing, standing, forming, and shaping, a secondary battery can be obtained.

[0208] In some embodiments of the present application, the secondary battery according to the present application may be assembled into a battery module, and the number of secondary batteries included in the battery module may be plural, and the specific number may be adjusted according to the use and capacity of the battery module.

[0209] FIG. 3 is a schematic diagram of a battery module 4 as an example. As shown in FIG. 3, in the battery module 4, a plurality of 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. Further, the plurality of secondary batteries 5 may be fixed by a fastener.

[0210] Optionally, the battery module 4 may further include a case having an accommodation space for accommodating a plurality of secondary batteries 5.

[0211] In some embodiments, the above battery module may be assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the use and capacity of the battery pack.

[0212] FIGS. 4 and 5 are schematic diagrams of a battery pack 1 as an example. As shown in FIGS. 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 box 2 and a lower box 3. The upper box 2 covers the lower box 3 and forms a sealed space for accommodating the battery module 4. The plurality of battery modules 4 may be arranged in the battery box in any manner. Electric consumption device

[0213] A fourth aspect of the embodiment of the present application provides an electric consumption device including at least one of a secondary battery, a battery module, or a battery pack of the present application. The secondary battery, battery module, or battery pack may be used as a power source of the electric consumption device or as an energy storage unit of the electric consumption device. The electric consumption device may be a mobile device (e.g., a mobile phone, a notebook computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), a train, a ship, a satellite, an energy storage system, etc., but is not limited thereto.

[0214] The electric consumption device can select a secondary battery, a battery module, or a battery pack according to its usage needs.

[0215] FIG. 6 is a schematic diagram of an electric consumption device as an example. The electric consumption device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the requirements for high output and high energy density of the electric consumption device, a battery pack or a battery module can be adopted.

[0216] Another example of the electric consumption device may be a mobile phone, a tablet computer, a notebook computer, etc. This electric consumption device is generally required to be thin, and a secondary battery can be used as a power source. Example

[0217] The following examples illustrate the content of this application in more detail. However, these examples are merely illustrative and it is obvious to those skilled in the art that various modifications and changes can be made within the scope of the disclosure of this application. All values of quantities, percentages, and ratios described in the following examples are based on mass unless otherwise specified. Also, all reagents used in the examples may be commercially available or synthesized according to conventional methods, and can be used as they are without further treatment. Moreover, all the devices used in the examples are commercially available. Preparation of Modified Nanocellulose C1 Preparation of Cellulose Powder

[0218] After opening cotton linter with an opener to remove debris, it is cooked at 150 °C for 2 h using a 5 wt% aqueous NaOH solution. Then, impurities are removed by washing with water (the number of water washings is 3 times), followed by sodium hypochlorite bleaching, removal of impurities by washing with dilute hydrochloric acid, removal of impurities by washing with water (the number of water washings is 1 time), removal of water, and air drying in sequence to obtain cotton cellulose powder with a whiteness of 85% or more. Esterification of Cellulose

[0219] 1 kg of the obtained cotton cellulose powder is mixed with 30 kg of a 60 wt% aqueous sulfuric acid solution and reacted at 60 °C for 1.5 h. After the reaction, impurities are removed by washing with water (the number of water washings is 3 times), filtration, acid removal, and impurity removal are carried out in sequence to obtain cellulose nanowhiskers having sulfonic acid groups. Neutralization of Cellulose

[0220] After adjusting the pH of the cellulose nanowhiskers having sulfonic acid groups to neutral with a 10 wt% aqueous NaOH solution, it is processed at high speed for 2.5 h with a grinder to disperse it. The number of grinding times is 2 times. Next, it is cut to the nanoscale using a high-pressure homogenizer device to obtain nanocellulose C1 having a sulfonic acid group modification group with an average length of 400 nm and an average diameter of 25 nm, and the molar ratio of the sulfonic acid group to the hydroxy group is 5:3. Preparation of Modified Nanocelluloses C2 - C4

[0221] Modified nanocellulose C2 - C4 is manufactured in a method similar to that of modified nanocellulose C1. For the differences, refer to Table 1. In the manufacturing process, by adjusting the parameters of the grinder treatment and the cutting parameters of the high - pressure homogenizer device, modified nanocellulose with different average diameters and / or different average lengths can be obtained. Preparation of Modified Nanocellulose C5 Preparation of Cellulose Powder

[0222] After opening cotton linter with an opener to remove debris, it is cooked at 150 °C for 2 h using a 5 wt% aqueous NaOH solution. Then, impurities are removed by washing with water (the number of water - washing times is 3), followed by sodium hypochlorite bleaching, removal of impurities by washing with dilute hydrochloric acid, removal of impurities by washing with water (the number of water - washing times is 1), removal of water, and air - flow drying in sequence to obtain cotton cellulose powder with a whiteness of 85% or more. The obtained cotton cellulose powder is mixed with a 20 wt% aqueous NaOH solution under the condition of 10 °C, stirred for 2 hours, filtered, washed with water twice, and then cellulose powder is obtained. Esterification of Cellulose

[0223] 50 g of the obtained cellulose powder and 200 g of urea are put into a three - necked reactor equipped with an oil - water separator. After urea is dissolved, 5 g of xylene is further added, and the temperature is raised to 137 °C with stirring and reacted for 4 h. After that, it is washed with water (the number of water - washing times is 3), filtered, and dried to obtain cellulose carbamate. Neutralization of Cellulose

[0224] The obtained cellulose carbamate is dissolved in a 5 wt% aqueous NaOH solution to obtain a uniform cellulose carbamate solution. Then, it is processed at high speed for 2.5 h with a grinder to disperse it, and the number of grinding times is 2. Furthermore, it is cut to the nanoscale using a high - pressure homogenizer device to obtain nanocellulose with an amine - modified group having an average length of 400 nm and an average diameter of 25 nm, and the molar ratio of the amine group to the hydroxy group is 4:3.

[0225] The molar ratio of the anionic modifying group to the hydroxy group can be measured by a method in which the hydroxy group valences (mg number of potassium hydroxide corresponding to the hydroxy group content per 1 g of the sample) of the raw cellulose and the modified nanocellulose are measured respectively based on the phthalic anhydride method in GB / T 12008.3-2009, the unit of the obtained numerical value is set as mgKOH / g, and this is converted to mmol / g to obtain the hydroxy group content. By subtracting the hydroxy group content of the modified nanocellulose from the hydroxy group content of the raw cellulose, the content of the anionic modifying group (i.e., the content of the modified hydroxy group) is obtained, and thereby, the molar ratio of the anionic modifying group to the hydroxy group is calculated. Preparation of Nanocellulose C6

[0226] Using unmodified nanocellulose, the average length is 400 nm and the average diameter is 25 nm. The product model number is CNWS-50, purchased from Zhongke Leiming (Beijing) Technology Co., Ltd., and can be further processed with a polishing machine and / or a high-pressure homogenizer to obtain nanocellulose with different average diameters and / or different average lengths.

[0227]

Table 1

[0228] Example 1 (1) Preparation of separator S1: Provide a PE porous substrate.

[0229] The thickness of the PE porous substrate is 5 μm and the porosity is 40%.

[0230] S2: Prepare a slurry of the coating layer.

[0231] In Step 1, 10 g of modified nanocellulose C1 and 190 g of water as a solvent are uniformly mixed to prepare a nanocellulose solution with a pH of 7.5 and a zeta potential of -35.7 mV. In Step 2, 6.6 g of a 10 wt% aqueous NaOH solution is added to 102 g of an aluminum oxide dispersion with a solid content of 50 wt% (secondary particle topography, average particle size 180 nm) and uniformly mixed to prepare a filler solution with a pH of 9.5 and a zeta potential of -10.1 mV. In Step 3, the prepared nanocellulose solution and the prepared filler solution are uniformly mixed at a solution mass ratio of 10:3 to form a mixed solution. Then, an aqueous solution type polyacrylic acid of 1 wt% binder (based on the total weight of the dried coating layer) is added to the mixed solution to obtain a slurry of the coating layer. S3. Coating

[0232] The prepared slurry of the coating layer is coated on both sides of a PE porous substrate with a coater, and a separator is obtained through drying and slitting processes. The thickness of the coating layer located on one side of the PE porous substrate is 0.8 μm. (2) Fabrication of the positive electrode sheet

[0233] Positive active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), carbon black (Super P) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are uniformly mixed in an appropriate amount of N-methylpyrrolidone (NMP) as a solvent at a mass ratio of 96.2:2.7:1.1 to obtain a positive electrode slurry. The positive electrode slurry is coated on an aluminum foil as a positive electrode current collector, and a positive electrode sheet is obtained through processes such as drying, cold pressing, strip splitting, and cutting. The areal density of the positive electrode sheet is 0.207 mg / mm 2 and the compression density is 3.5 g / cm 3 is obtained. (3) Fabrication of the negative electrode sheet

[0234] Artificial graphite as the negative electrode active material, carbon black (Super P) as the conductive agent, styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) as the binder are uniformly mixed in a mass ratio of 96.4:0.7:1.8:1.1 with an appropriate amount of solvent deionized water to obtain a negative electrode slurry. The negative electrode slurry is applied to a copper foil which is the negative electrode current collector, and through drying, cold pressing, strip splitting, and cutting processes, a negative electrode sheet is obtained. The areal density of the negative electrode sheet is 0.126 mg / mm 2 and the compression density is 1.7 g / cm 3 . (4) Preparation of the electrolyte

[0235] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 30:70 to obtain an organic solvent, and LiPF6 dried sufficiently is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L. (5) Fabrication of the secondary battery

[0236] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer package, and after drying, the electrolyte is injected. Through processes such as vacuum sealing, standing, forming, and shaping, a secondary battery is obtained. Examples 2 to 9

[0237] The secondary battery is manufactured in a method similar to Example 1, but the difference lies in the manufacturing parameters of the slurry of the coating layer in the manufacture of the separator. Specifically, refer to Table 2. Example 10

[0238] The secondary battery is manufactured in a method similar to Example 1, but the difference is that in the manufacture of the separator, aluminum oxide with primary particle topography is further added when preparing the slurry of the coating layer. Specific parameters can be referred to in Table 2.

[0239] In step 1, 10 g of modified nanocellulose C1 and 190 g of water as a solvent are uniformly mixed to prepare a nanocellulose solution with a pH of 7.5 and a zeta potential of -35.7 mV. In step 2, 6.6 g of a 10 wt% aqueous NaOH solution is added to 102 g of an aluminum oxide dispersion with a solid content of 50 wt% (a mixture of secondary particle topography and primary particle topography, with a mass ratio of 5:1, an average secondary particle size of 180 nm, and an average primary particle size of 400 nm), and uniformly mixed to prepare a filler solution with a pH of 9.5 and a zeta potential of -10.1 mV. In step 3, the prepared nanocellulose solution and the prepared filler solution are uniformly mixed at a solution mass ratio of 10:3 to form a mixture. Then, 1 wt% of an aqueous solution of binder polyacrylic acid (based on the total weight of the dried coating layer) is added to the mixture to obtain a slurry of the coating layer. Comparative Example 1

[0240] The secondary battery is prepared in a method similar to that of Example 1, but the difference is that in the preparation of the separator, when preparing the slurry of the coating layer, unmodified nanocellulose C6 and aluminum oxide with unmodified primary particle topography are used. For specific parameters, refer to Table 2.

[0241] In step 1, 10 g of unmodified nanocellulose C6 and 190 g of water as a solvent are uniformly mixed to prepare a nanocellulose solution with a pH of 8.6 and a zeta potential of 20.5 mV. In step 2, 102 g of an aluminum oxide dispersion with a solid content of 50 wt% (primary particle topography, with an average primary particle size of 800 nm) is used as a filler solution with a pH of 7.4 and a zeta potential of -5.5 mV. In step 3, the prepared nanocellulose solution and the prepared filler solution are uniformly mixed at a solution mass ratio of 10:3 to form a mixture. Then, 1 wt% of an aqueous solution of binder polyacrylic acid (based on the total weight of the dried coating layer) is added to the mixture to obtain a slurry of the coating layer. Comparative Example 2

[0242] The secondary battery is prepared in a method similar to that of Example 1, except that in the preparation of the separator, when preparing the slurry of the coating layer, untreated nanocellulose C6 and aluminum oxide with an untreated secondary particle topography are used. For specific parameters, refer to Table 2.

[0243] In Step 1, 10 g of untreated nanocellulose C6 and 190 g of water as a solvent are uniformly mixed to prepare a nanocellulose solution with a pH of 8.6 and a zeta potential of 20.5 mV. In Step 2, 102 g of an aluminum oxide dispersion with a solid content of 50 wt% (secondary particle topography, average particle size of secondary particles is 180 nm) is made into a filler solution with a pH of 5.6 and a zeta potential of 39.3 mV. In Step 3, the prepared nanocellulose solution and the prepared filler solution are uniformly mixed at a mass ratio of 10:3 of the solutions to form a mixture. Then, 1 wt% of an aqueous solution of a binder, polyacrylic acid (based on the total weight of the dried coating layer), is added to the mixture to obtain a slurry of the coating layer. Comparative Example 3

[0244] The secondary battery is prepared in a method similar to that of Example 1, except that in the preparation of the separator, untreated nanocellulose C6 is used when preparing the slurry of the coating layer. For specific parameters, refer to Table 2.

[0245] In Step 1, 10 g of unmodified nanocellulose C6 is uniformly mixed with 190 g of water as the solvent to prepare a nanocellulose solution with a pH of 8.6 and a zeta potential of 20.5 mV. In Step 2, 6.6 g of a 10 wt% aqueous NaOH solution is added to 102 g of an aluminum oxide dispersion with a solid content of 50 wt% (secondary particle topography, average particle size of 180 nm) and uniformly mixed to prepare a filler solution with a pH of 9.5 and a zeta potential of -10.1 mV. In Step 3, the prepared nanocellulose solution and the prepared filler solution are uniformly mixed at a solution mass ratio of 10:3 to form a mixture. Then, a 1 wt% aqueous solution of a binder, polyacrylic acid (based on the total weight of the dried coating layer), is added to the mixture to obtain a slurry of the coating layer. Comparative Example 4

[0246] The secondary battery is prepared in a method similar to Example 1, but the difference is that in the preparation of the separator, when preparing the slurry of the coating layer, aluminum oxide with an unmodified secondary particle topography is used. For specific parameters, refer to Table 2.

[0247] In Step 1, 10 g of modified nanocellulose C1 and 190 g of water as the solvent are uniformly mixed to prepare a nanocellulose solution with a pH of 7.5 and a zeta potential of -35.7 mV. In Step 2, 102 g of an aluminum oxide dispersion with a solid content of 50 wt% (secondary particle topography, average particle size of the secondary particles is 180 nm) is used as a filler solution with a pH of 5.6 and a zeta potential of 39.3 mV. In Step 3, the prepared nanocellulose solution and the prepared filler solution are uniformly mixed at a solution mass ratio of 10:3 to form a mixture. Then, a 1 wt% aqueous solution of a binder, polyacrylic acid (based on the total weight of the dried coating layer), is added to the mixture to obtain a slurry of the coating layer. Test Part (1) Test of the zeta potential of the coating layer

[0248] Using a blade, scrape 30 g of the coating layer material powder from the prepared separator (the scraping depth of the powder does not exceed the boundary region between the coating layer and the porous substrate), and then stir it with 2000 g of deionized water at a constant stirring speed (for example, it may be 2000 r / min) using a stirrer with gears. After stirring (the stirring time may be, for example, 1.5 hours), a dispersion is obtained. Place the obtained dispersion in a sample cell, and then use a zeta potential meter to test to obtain the zeta potential of the dispersion, that is, the zeta potential of the coating layer. The sample cell can use the DTS1070 zeta potential capillary sample cell from Malvern, and the zeta potential meter can use the Zetasizer Advance nanoparticle size and potential meter from Malvern.

[0249] The test standards can refer to GB / T 32671.2-2019 and ISO 13099-2-2012. For accuracy, five parallel samples can be selected for testing, and the average value can be calculated as the test result. (2) Test of the zeta potential of the nanocellulose solution, filler solution, and slurry of the coating layer

[0250] Put each of the above solutions into a sample cell, and then use a zeta potential meter to test to obtain the zeta potential of each solution. The sample cell can use the DTS1070 zeta potential capillary sample cell from Malvern, and the zeta potential meter can use the Zetasizer Advance nanoparticle size and potential meter from Malvern. The test standards can refer to GB / T 32671.2-2019 and ISO 13099-2-2012. For accuracy, five parallel samples can be selected for testing, and the average value can be calculated as the test result. (3) Thermal shrinkage rate test of the separator

[0251] Sample preparation: Punch out the separator prepared above into samples with a width of 50 mm and a length of 100 mm using a press, set 5 parallel samples on A4 paper and fix them, and set the A4 paper with the samples on cardboard with a thickness of 1 mm to 5 mm.

[0252] Sample test: Set the temperature of the forced-air oven to 150°C. After the temperature reaches the set temperature and stabilizes for 30 minutes, start timing. Put the A4 paper set on the upper surface of the corrugated paper into the forced-air oven. After reaching the set time (1 hour in this application), measure the length and width of the separator, and denote the values as a and b respectively.

[0253] Calculation of thermal shrinkage rate: Longitudinal direction (MD) thermal shrinkage rate = [(100 - a) / 100]×100%, transverse direction (TD) thermal shrinkage rate = [(50 - b) / 50]×100%. Take the average value of 5 parallel samples as the test result. (4) Test of the air permeability of the separator

[0254] At 25°C, measure the time required for 100 mL of air to pass through the separator. For accuracy, take the average value of 5 parallel samples as the test result. As the test equipment, the Kumagai KRK King Research type air permeability test equipment can be used. (5) Test of the cycle performance of the secondary battery

[0255] At 25°C, charge the secondary battery at a constant current of 1C to 4.2V and continue to charge at a constant voltage until the current becomes 0.05C or less. At this time, the secondary battery is in a fully charged state, and record the charging capacity at this time, that is, the first charging capacity. After standing the secondary battery for 5 minutes, discharge it at a constant current of 1C to 2.8V. This is regarded as one cycle of charge and discharge process, and record the discharge capacity at this time, that is, the first discharge capacity. Perform a cycle charge and discharge test on the secondary battery according to the above method, and record the discharge capacity after each cycle. Capacity retention rate (%) of the secondary battery after 500 cycles at 25°C = Discharge capacity after 500 cycles / First discharge capacity × 100%. For accuracy, take the average value of 5 parallel samples as the test result. (6) Heat box test of the secondary battery

[0256] 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 becomes 0.05C or less. After standing for 5 minutes, each secondary battery is measured with a jig in a high-temperature oven of the DHG-9070A DHG series. The temperature is raised from room temperature to 80 ± 2°C at a rate of 5°C / min, held for 30 minutes, and then the temperature is raised at a rate of 5°C / min, and kept warm for 30 minutes every time the temperature is raised by 5°C. Monitor the change in the surface temperature of the secondary battery during the heating process. The temperature of the oven corresponding to the time when the temperature starts to rise rapidly is the failure temperature of the heat box of the secondary battery. The higher the failure temperature of the heat box of the secondary battery, the better the thermal safety performance of the secondary battery. For accuracy, the average value of 5 parallel samples is used as the test result.

[0257] As can be seen from Table 2 and Table 3, in Examples 1 to 10, a coating layer containing nanocellulose (constituting a three-dimensional skeleton structure) and a filler is provided on both surfaces of the porous substrate, and the zeta potential of the coating layer is adjusted to less than 0 mV, so that the obtained separator can achieve both a low heat shrinkage rate and a high air permeability, and the obtained secondary battery can achieve both high thermal safety performance and good cycle performance. The inventors speculate that when the zeta potential of the coating layer is within an appropriate range, due to the good dispersibility of the slurry of the coating layer, a coating layer with good uniformity of surface density and thickness can be formed after the slurry of the coating layer is dried, improving the heat resistance of the separator, ensuring that the pore distribution of the coating layer is uniform and the ionic conductivity of the coating layer is good, which is the main reason why the secondary battery can achieve both high thermal safety performance and good cycle performance.

[0258] The coating layers of the separators manufactured in Comparative Examples 1 to 4 do not all satisfy the condition that the zeta potential is less than 0 mV. Furthermore, the separators cannot achieve both a low heat shrinkage rate and a high air permeability, and the secondary batteries also cannot achieve both high thermal safety performance and good cycle performance.

[0259] Note that the present application is not limited to the above embodiments. The above embodiments are merely illustrative, and any embodiments having a configuration substantially identical to the technical idea or exhibiting the same operational effects within the scope of the technical solution of the present application are all included within the technical scope of the present application. Furthermore, other forms constructed by adding various modifications conceivable by those skilled in the art to the embodiments or combining some of the components in the embodiments without departing from the spirit of the present application are also considered to be included within the scope of the present application.

[0260]

Table 2

[0261]

Table 3

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 comprising a three-dimensional skeleton structure and a filler, at least a part of the filler being filled in the three-dimensional skeleton structure, and the zeta potential of the coating layer being less than 0 mV, the zeta potential of the coating layer is measured by a method of taking 30 g of powder of the coating layer material, stirring and mixing it with 2000 g of deionized water to obtain a dispersion, and measuring the zeta potential of the obtained dispersion with a zeta potential meter to obtain the zeta potential of the coating layer, the separator.

2. the zeta potential of the coating layer is -50 mV to -5 mV, and optionally -25 mV to -5 mV, the separator according to claim 1.

3. the material constituting the three-dimensional skeleton structure includes at least one of organic rods and organic tubes, optionally, the material constituting the three-dimensional skeleton structure includes at least one of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers, optionally, the nanocellulose includes at least one of cellulose nanofibers, cellulose nanowhiskers, and bacterial nanocellulose, the separator according to claim 1 or 2.

4. the material constituting the three-dimensional skeleton structure includes nanocellulose, the nanocellulose includes a hydroxy group and an anionic modification group, optionally, the anionic modification group includes at least one of an amine group, a carboxyl group, a sulfonic acid group, a boric acid group, and a phosphoric acid group, and more optionally includes at least one of a sulfonic acid group, a boric acid group, and a phosphoric acid group, the separator according to any one of claims 1 to 3.

5. The molar ratio of the anionic modifying group to the hydroxy group is from 1:4 to 4:1, and optionally from 2:3 to 7:

3. The separator according to claim 4.

6. The average diameter of the material constituting the three-dimensional skeleton structure is 40 nm or less, and optionally from 10 nm to 35 nm. The separator according to any one of claims 1 to 5.

7. The average length of the material constituting the three-dimensional skeleton structure is from 100 nm to 600 nm, and optionally from 200 nm to 400 nm, and / or The aspect ratio of the material constituting the three-dimensional skeleton structure is from 5 to 60, and optionally from 15 to 30. The separator according to any one of claims 1 to 6.

8. The filler includes at least one of filler particles having a primary particle topography and filler particles having a secondary particle topography. Optionally, the filler includes filler particles having a secondary particle topography. Further optionally, the filler simultaneously includes filler particles having a primary particle topography and filler particles having a secondary particle topography. The separator according to any one of claims 1 to 7.

9. The filler particles having a primary particle topography satisfy at least one of the following conditions (1) to (3). (1) The average particle diameter of the filler particles having a primary particle topography is from 200 nm to 800 nm, and optionally from 200 nm to 400 nm. (2) The BET specific surface area of the filler particles having a primary particle topography is 10 m ２ / g or less, and optionally from 3 m ２ / g to 7 m ２ / g. (3) Based on the total weight of the coating layer, the content of the filler particles of the primary particle topography is 30 wt% or less, and optionally 5 wt% to 25 wt%. The separator according to claim 8.

10. The filler particles of the secondary particle topography satisfy at least one of the following conditions (1) to (3). (1) The average particle diameter of the filler particles of the secondary particle topography is 200 nm or less, and optionally 50 nm to 200 nm. (2) The BET specific surface area of the filler particles of the secondary particle topography is 20 m ２ / g or more, and optionally 30 m ２ / g to 80 m ２ / g. (3) Based on the total weight of the coating layer, the content of the filler particles of the secondary particle topography is 60 wt% or more, and optionally 70 wt% to 90 wt%. The separator according to claim 8 or 9.

11. The filler contains both the filler particles of the primary particle topography and the filler particles of the secondary particle topography, and the mass ratio of the filler particles of the secondary particle topography to the filler particles of the primary particle topography is 2:1 to 27:1, and optionally 5:1 to 15:

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

12. The filler contains at least one of inorganic particles and organic particles. Optionally, the inorganic particles include at least one selected from inorganic particles having a dielectric constant of 5 or more, inorganic particles having a function of transporting active ions, and inorganic particles that can be electrochemically oxidized and reduced. Optionally, the organic particles include at least one selected from polystyrene, polyethylene, polyimide, melamine resin, phenolic resin, polypropylene, polyester, polyphenylene sulfide, polyaramide, polyamideimide, polyimide, a copolymer of butyl acrylate and ethyl methacrylate, and mixtures thereof. The separator according to any one of claims 1 to 11,

13. Based on the total weight of the coating layer, the content of the three-dimensional skeleton structure in the coating layer is 6 wt% to 35 wt%, optionally 10 wt% to 30 wt%, and / or The mass ratio of the three-dimensional skeleton structure to the filler is 1:2 to 1:15.5, optionally 1:5 to 1:

10. The separator according to any one of claims 1 to 12.

14. The coating layer further includes a non-particulate binder. Optionally, the non-particulate binder includes an aqueous solution type binder. Optionally, based on the total weight of the coating layer, the content of the non-particulate binder in the coating layer is 2 wt% or less. The separator according to any one of claims 1 to 13.

15. The thickness of the porous substrate is 6 μm or less, optionally 3 μm to 5 μm, and / or The thickness of the coating layer is 1 μm or less, optionally 0.5 μm to 0.8 μm. The separator according to any one of claims 1 to 14.

16. The separator further includes an adhesive layer provided on at least a part of the surface of the coating layer, and the adhesive layer includes a particulate binder. Optionally, the particulate binder contains at least one of a homopolymer or copolymer of an acrylate monomer, a homopolymer or copolymer of an acrylic acid monomer, and a homopolymer or copolymer of a fluorine-containing olefin monomer. The separator according to any one of claims 1 to 15.

17. The separator satisfies at least one of the following conditions (1) to (7). (1) The longitudinal thermal shrinkage rate of the separator at 150°C for 1 h is 5% or less, and optionally 0.5% to 3%. (2) The transverse thermal shrinkage rate of the separator at 150°C for 1 h is 5% or less, and optionally 0.5% to 3%. (3) The longitudinal tensile strength of the separator is 2000 kg / cm ２ or more, and optionally 2500 kg / cm ２ to 4500 kg / cm ２ and (4) The transverse tensile strength of the separator is 2000 kg / cm ２ or more, and optionally 2500 kg / cm ２ to 4500 kg / cm ２ and (5) The wetting length of the separator is 30 mm or more, and optionally 30 mm to 80 mm. (6) The wetting rate of the separator is 3 mm / s or more, and optionally 3 mm / s to 10 mm / s. (7) The air permeability of the separator is 300 s / 100 mL or less, and optionally 100 s / 100 mL to 230 s / 100 mL. The separator according to any one of claims 1 to 16.

18. A method for manufacturing the separator according to any one of claims 1 to 17, comprising: Step S1 of providing a porous substrate; Mixing a material and a filler for forming a three-dimensional skeleton structure in a solvent at a predetermined ratio to prepare a slurry of a coating layer, a preparation step S2 of the slurry of the coating layer, Applying the slurry of the coating layer to at least one surface of the porous substrate to form a coating layer and drying to obtain a separator, an application step S3, and including, The separator includes a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer includes a three-dimensional skeleton structure and a filler, at least a part of the filler is filled in the three-dimensional skeleton structure, and the zeta potential of the coating layer is less than 0 mV, The zeta potential of the coating layer is obtained by a method of taking 30 g of powder of the coating layer material, stirring and mixing it with 2000 g of deionized water to obtain a dispersion liquid, and measuring the zeta potential of the obtained dispersion liquid with a zeta potential meter as the zeta potential of the coating layer, A method for manufacturing a separator.

19. The pH of the slurry of the coating layer is 5 to 10, optionally 6 to 9, and / or, The static viscosity of the slurry of the coating layer is 1000 mPa·s or less. The method according to claim 18.

20. The slurry of the coating layer is a preparation step of a nanocellulose solution having a pH between 5 and 9 and a zeta potential less than 0 mV, including step 1 of mixing nanocellulose having an anionic modification group with water to prepare the nanocellulose solution, step 2 of preparing a filler solution having a pH of 7.5 or more and a zeta potential less than 0 mV, and step 3 of mixing the nanocellulose solution and the filler solution at a predetermined ratio to obtain a slurry of a coating layer having a zeta potential of -5 mV or less, obtained by a method including, The method according to claim 18 or 19.

21. The concentration of the nano-cellulose solution is 1 wt% to 10 wt%, optionally 2 wt% to 10 wt%, and / or The concentration of the filler solution is 30 wt% to 60 wt%, optionally 35 wt% to 55 wt%. The method according to claim 20.

22. The nano-cellulose having the anionic modification group is obtained by a method in which nano-cellulose powder and a modification solution are mixed and reacted, then washed to remove impurities to obtain cellulose nanowhiskers having an anionic modification group, and the pH of the obtained cellulose nanowhiskers having an anionic modification group is adjusted to neutral, polished, and cut to obtain nano-cellulose having an anionic modification group. Optionally, the modification solution is an aqueous sulfuric acid solution, an aqueous boric acid solution, an aqueous phosphoric acid solution, an aqueous acetic acid solution, or a urea organic solvent solution. The method according to claim 20 or 21.

23. The filler solution is obtained by a method in which a filler, water, and a modifier containing at least one selected from a base, an anionic surfactant, and a nonionic surfactant are mixed to obtain a filler solution having a pH of 7.5 or more and a zeta potential of less than 0 mV. Optionally, the base contains at least one selected from KOH, NaOH, NaHCO ３ , LiOH, NH ４ OH, Mg(OH) ２ and Na ２ CO ３ and includes at least one selected from them. Optionally, the anionic surfactant contains at least one selected from a sulfonate-type anionic surfactant, a carboxylate-type anionic surfactant, a sulfate ester salt-type anionic surfactant, and a phosphate ester salt-type anionic surfactant. Further optionally, it includes at least one selected from alkylbenzene sulfonate, C12 - C20 alkyl sulfonate, sodium polyacrylate, ammonium polyacrylate, sodium hydroxyethyl sulfate, and sodium C12 - C20 alkyl sulfate. Optionally, the nonionic surfactant contains at least one selected from fluoroalkyl ethoxy glycol ethers and aliphatic alcohol polyoxyethylene ethers. The method according to claim 20 or 21.

24. The two - coating step S4 further includes applying a slurry containing a particulate binder to at least a part of the surface of the coating layer and drying to form an adhesive layer. The method according to any one of claims 18 to 23.

25. A separator including the separator according to any one of claims 1 to 17 or a separator manufactured by the method according to any one of claims 18 to 24. Secondary battery.

26. An electrical consumption device including the secondary battery according to claim 25. Electrical consumption device.

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