Separator, method for manufacturing the same, and related secondary batteries and power consumption devices.

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 priority to PCT / CN2022 / 101261, a Chinese patent application filed on 24 June 2022, entitled “Separator, Method for Manufacturing the Same, Related Secondary Battery and Electrical Consumption Device,” the entirety of which is incorporated herein by reference.

[0002] This application relates to the field of battery technology, and more specifically to separators, methods for manufacturing the same, and related secondary batteries and power consumption devices. [Background technology]

[0003] In recent years, rechargeable batteries have been widely used in many fields, including energy storage and power systems such as hydroelectric, thermal, wind, and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. As the range of applications for rechargeable batteries expands, safety issues, particularly thermal safety, are attracting increasing attention. However, current methods for improving the thermal safety performance of rechargeable batteries are often detrimental to balancing energy density and capacity. Therefore, achieving high energy density, high thermal safety, and a long service life in rechargeable batteries is a crucial challenge in battery design. [Overview of the Initiative]

[0004] The object of this application is to provide a separator having excellent heat resistance, excellent uniformity, and excellent ion conductivity, a method for manufacturing the same, and a secondary battery and an electrical consumption device related thereto, thereby enabling a secondary battery using the separator to have high energy density, high thermal safety performance, and a long service life.

[0005] A first aspect of the present invention provides a separator comprising a porous substrate and a coating layer provided on at least one surface of the porous substrate, wherein the coating layer comprises a three-dimensional skeletal structure and a filler, at least a portion of which is filled into the three-dimensional skeletal 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 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, i.e., the zeta potential of the coating layer, using a zeta potential meter.

[0006] In the separator according to the present invention, when the zeta potential of the coating layer is within an appropriate range, the slurry of the coating layer has good dispersibility, so that after the slurry of the coating layer dries, a coating layer with good uniformity of surface density and thickness can be formed, 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, thereby improving the rate performance, thermal safety performance and cycle performance of the secondary battery. By filling at least a portion of the filler into the three-dimensional skeletal structure, the filler and the three-dimensional skeletal structure contribute to forming a nesting effect, improving the heat resistance of the separator, reducing the degree of shrinkage when the separator is heated, reducing the risk of short-circuiting between the positive and negative electrodes, the secondary battery having high thermal safety performance, and maintaining high adhesive strength between the coating layer and the porous substrate, thereby preventing the filler from falling off during long-term charging and discharging of the secondary battery. Since at least a portion of the filler is filled into the three-dimensional skeletal structure, the filler can also lap-joint with the three-dimensional skeletal structure, thereby allowing the coating layer to have a stable spatial network structure, increasing the ion conduction passages of the separator and promoting ion transport, as well as improving the separator's penetration and retention characteristics in the electrolyte. Furthermore, secondary batteries using the separator of this invention can have a long service life. Because the coating layer of this invention has high heat resistance, a thinner porous substrate can be selected, and secondary batteries using the separator of this invention can also achieve high energy density.

[0007] In any embodiment of the present application, the zeta potential of the coating layer is -50mV to -5mV, and selectively -25mV to -5mV. This further improves the uniformity of the surface density and thickness of the coating layer, as well as the uniformity of the pores, thereby further improving the ion conductivity of the separator and the energy density and cycle performance of the secondary battery.

[0008] In any embodiment of the present application, the material constituting the three-dimensional skeletal structure includes at least one of organic rods and organic tubes. A material of an appropriate shape is advantageous for better lap-jointing the three-dimensional skeletal structure and the filler, thereby allowing the coating layer to have a more stable spatial network structure, which in turn can further improve the heat resistance and ion conductivity of the separator.

[0009] In any embodiment of the present application, the material constituting the three-dimensional skeletal structure comprises at least one of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers, wherein the nanocellulose optionally comprises 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 skeletal structure includes nanocellulose, wherein the nanocellulose includes a hydroxyl group and an anionic modifying group, and optionally the anionic modifying group includes at least one of an amine group, a carboxyl group, a sulfonic acid group, a boric acid group, and a phosphate group, and more optionally the anionic modifying group includes at least one of a sulfonic acid group, a boric acid group, and a phosphate group. When the nanocellulose has the above-mentioned specific anionic modifying group, it is possible to ensure that the slurry of the coating layer has an appropriate viscosity, which is advantageous for application and can improve the production efficiency of the separator. Furthermore, it contributes to the coating layer having an appropriate zeta potential, which can further improve the uniformity of the surface density and thickness of the coating layer and the uniformity of the pores, thereby further improving the ion conductivity of the separator and the energy density and cycle performance of the secondary battery.

[0011] In any embodiment of the present application, the molar ratio of the anionic modified group to the hydroxyl group is 1:4 to 4:1, and selectively 2:3 to 7:3. This further improves the uniformity of the surface density and thickness of the coating layer, as well as the uniformity of the pores, thereby improving the heat resistance, ion conductivity, and electrolyte penetration and retention properties of the separator.

[0012] In any embodiment of the present application, the average diameter of the material constituting the three-dimensional skeletal structure is 40 nm or less, and selectively between 10 nm and 35 nm. This further improves the ion conductivity and dielectric breakdown characteristics of the separator, and also contributes to the integration effect of the lap joint between the material constituting the three-dimensional skeletal structure and the filler, thereby further improving the heat resistance of the separator.

[0013] In any embodiment of the present application, the average length of the material constituting the three-dimensional skeletal structure is 100 nm to 600 nm, and selectively 200 nm to 400 nm. This makes it possible to further improve the heat resistance and ion conductivity of the separator.

[0014] In any embodiment of the present application, the aspect ratio of the material constituting the three-dimensional skeletal structure is 5 to 60, and selectively 15 to 30. This makes it possible to further enhance the ion conductivity of the separator.

[0015] In any embodiment of the present application, the filler comprises at least one of primary particle topography filler particles and secondary particle topography filler particles, selectively comprising secondary particle topography filler particles, and further selectively comprising both primary particle topography filler particles and secondary particle topography filler particles simultaneously.

[0016] In any embodiment of the present application, the average particle size of the filler particles in the primary particle topography is 200 nm to 800 nm, and selectively 200 nm to 400 nm.

[0017] In any embodiment of the present application, the BET specific surface area of ​​the filler particles in the primary particle topography is 10 m². 2 / g or less, and selectively, 3m 2 / g~7m 2 It is / g.

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

[0019] The larger particle size of the filler particles in primary particle topography allows for better support of the particles within the coating layer, reduces shrinkage of the filler particles in secondary particle topography, and reduces the amount of binder used, thereby improving the heat resistance of the separator. The larger particle size of the filler particles in primary particle topography contributes to the coating layer having more channel structures and less water content when used in small quantities, further improving the ion conductivity and electrolyte penetration and retention characteristics of the separator.

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

[0021] In any embodiment of the present application, the BET specific surface area of ​​the filler particles in the secondary particle topography is 20 m². 2 / g or more, and selectably 30m 2 / g~80m 2 It is / g.

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

[0023] The filler particles in secondary particle topography have the advantage of having a large specific surface area and good affinity with the three-dimensional skeletal structure. Therefore, they better lap-joint with the three-dimensional skeletal structure, allowing the coating layer to have a more stable spatial network structure. This not only increases the ion conduction pathways of the separator and promotes ion transport, but also improves the electrolyte penetration and retention characteristics due to the heat resistance of the separator. As a result, secondary batteries using the separator of this invention can have a long service life and good rate performance.

[0024] In any embodiment of the present application, the filler simultaneously comprises 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 selectively 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 comprises at least one of inorganic particles and organic particles. Optionally, the inorganic particles comprise at least one selected from inorganic particles having a dielectric constant of 5 or more, inorganic particles having the function of transporting active ions, and inorganic particles that are electrochemically oxidizable and reducible. Optionally, the organic particles comprise at least one selected from polystyrene, polyethylene, polyimide, melamine resin, phenolic resin, polypropylene, polyester, polyphenylene sulfide, polyaramid, polyamide-imide, polyimide, copolymers of butyl acrylate and ethyl methacrylate, and mixtures thereof.

[0026] In any embodiment of the present application, the content of the three-dimensional skeletal structure in the coating layer is 6 wt% to 35 wt%, and selectively 10 wt% to 30 wt%, based on the total weight of the coating layer. This ensures that the slurry of the coating layer has an appropriate viscosity, which is advantageous for application, and is also advantageous for the integration effect of the lap joint between the three-dimensional skeletal structure and the filler, thereby allowing the coating layer to have a more stable spatial network structure.

[0027] In any embodiment of the present application, the mass ratio of the three-dimensional skeletal structure to the filler is 1:2 to 1:15.5, and selectively 1:5 to 1:10. This contributes to the coating layer having an appropriate zeta potential, thereby further improving the uniformity of the surface density and thickness of the coating layer and the uniformity of the pores, which in turn further improves the ion conductivity of the separator and the energy density and cycle performance of the secondary battery.

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

[0029] In any embodiment of the present application, the content of the non-particulate binder in the coating layer is 2 wt% or less, based on the total weight of the coating layer. The three-dimensional skeletal structure and 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 maintaining high adhesion to the separator while reducing the amount of binder used.

[0030] In any embodiment of the present invention, the thickness of the porous substrate is 6 μm or less, and selectively between 3 μm and 5 μm. This contributes to improving 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 adhesion 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 is selectively between 30 mm and 80 mm.

[0038] In any embodiment of the present application, the wetting rate of the separator is 3 mm / s or more, and is selectively between 3 mm / s and 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 is selectively 100 s / 100 mL to 230 s / 100 mL.

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

[0041] A second aspect of the present invention provides a method for manufacturing a separator according to the first aspect of the present invention, comprising: step S1 providing a porous substrate; step S2 preparing a coating layer slurry by mixing a material for constituting a three-dimensional skeletal structure and a filler in a predetermined ratio in a solvent to prepare a coating layer slurry; and step S3 applying the coating layer slurry to at least one surface of the porous substrate to form a coating layer and dry it to obtain a separator, wherein the separator comprises a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer comprises a three-dimensional skeletal structure and a filler, at least a portion of the filler is filled into the three-dimensional skeletal 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 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, i.e., the zeta potential of the coating layer, using a zeta potential meter.

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

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

[0044] In any embodiment of the present application, the coating layer slurry is obtained by a method comprising: a step of preparing a nanocellulose solution having a pH between 5 and 9 and a zeta potential of less than 0 mV, the step of mixing nanocellulose having an anionic modification group with water to prepare the nanocellulose solution; a step of preparing a filler solution having a pH of 7.5 or higher and a zeta potential of less than 0 mV; and a mixing step of mixing the nanocellulose solution and the filler solution in a predetermined ratio to obtain a coating layer slurry 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%, and selectively 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%, and selectively 35 wt% to 55 wt%.

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

[0048] In any embodiment of the present application, the filler solution is obtained by mixing a filler, water, and a denaturant comprising 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.

[0049] In any embodiment of the present application, the base comprises 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 comprises at least one selected from sulfonate-type anionic surfactants, carboxylate-type anionic surfactants, sulfate-type anionic surfactants, and phosphate-type anionic surfactants, and optionally comprises at least one selected from alkylbenzene sulfonates, C12-C20 alkyl sulfonates, sodium polyacrylate, ammonium polyacrylate, sodium hydroxyethyl sulfate, and C12-C20 alkyl sulfates.

[0051] In any embodiment of the present application, the nonionic surfactant comprises at least one selected from fluoroalkyl ethoxyglycol ethers and aliphatic alcohol polyoxyethylene ethers.

[0052] In any embodiment of the present application, the method further comprises a two-coating step S4, in which a slurry containing particulate binder is applied to at least a portion of the surface of the coating layer and dried to form an adhesive layer.

[0053] The separator manufacturing method of this invention significantly simplifies the separator manufacturing process by producing the coating layer in a single application.

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

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

[0056] This invention provides a coating layer containing a three-dimensional skeletal structure and fillers on the surface of a porous substrate of a separator, and adjusts the zeta potential of the coating layer to less than 0 mV, thereby enabling the separator to simultaneously achieve high heat resistance, high uniformity, and good ion conductivity. Furthermore, it enables the secondary battery to possess high energy density, high thermal safety performance, and a long service life. The power consumption device of this invention, since equipped with the secondary battery of this invention, has at least the same advantages as the aforementioned secondary battery. [Brief explanation of the drawing]

[0057] To more clearly illustrate the technical concept of the embodiments of this application, the drawings that need to be used in the embodiments of this application are briefly described below. Clearly, the drawings described below represent only a few embodiments of this application, and those skilled in the art can obtain further drawings based on these drawings, even without any creative work. [Figure 1] This is a schematic diagram of one embodiment of the secondary battery of the present invention. [Figure 2] Figure 1 is a schematic diagram of an exploded view of an embodiment of a secondary battery. [Figure 3] This is a schematic diagram of one embodiment of the battery module of the present invention. [Figure 4] This is a schematic diagram of one embodiment of the battery pack of the present invention. [Figure 5] Figure 4 is an exploded schematic diagram of an embodiment of the battery pack shown. [Figure 6] This is a schematic diagram of one embodiment of an electrical consumption device that includes a secondary battery as a power source. The drawing is not necessarily drawn to actual scale. [Explanation of Symbols]

[0058] 1 Battery pack, 2 Upper box, 3 Lower box, 4 Battery module, 5 Rechargeable battery, 51 Housing, 52 Electrode assembly, 53 Cover plate [Modes for carrying out the invention]

[0059] Hereinafter, embodiments of the separator of the present application, its manufacturing method, and related secondary batteries and power consumption devices will be described in detail with appropriate reference to the drawings. However, unnecessary detailed explanations may be omitted. For example, detailed explanations of known matters or redundant explanations of substantially identical configurations may be omitted. This is to avoid the following explanation becoming unnecessarily verbose and to facilitate understanding by those skilled in the art. The accompanying drawings and the following explanation are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0060] The “range” disclosed in this application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting one lower limit and one upper limit, the selected lower limit and upper limit limit the boundary of a special range. The range thus limited may include or exclude endpoints, and may be any combination, that is, any lower limit may be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are given for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also expected. Also, if minimum range values ​​1 and 2 and maximum range values ​​3, 4 and 5 are given, the ranges 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 may all be expected. In this application, unless otherwise stated, the numerical range “a-b” is an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" indicates that in this specification, all real numbers between "0 and 5" are listed, and "0 to 5" is an abbreviated notation for combinations of these numbers. Also, the notation that a parameter is an integer greater than or equal to 2 (≧2) is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0061] Unless otherwise specified, all embodiments and optional embodiments of this Application may be combined to form new technical solutions. Such technical solutions are considered to be included in the disclosures of this Application.

[0062] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical concepts. Such technical concepts are considered to be included in the disclosures of this application.

[0063] Unless otherwise specified, all steps of this invention may be performed sequentially or randomly, but it is preferable that they be performed sequentially. For example, when it is mentioned that the above method includes steps (a) and (b), it means that the above method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, 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), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0064] Unless otherwise specified, the terms "equipment," "possess," and "include" as used in this application mean open-ended, but may also mean closed-ended. For example, the above terms "equipment," "possess," and "include" may mean further "equipment," "possess," or "include" other components not listed, or "equipment," "possess," or "include" only the listed components.

[0065] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following 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 "multiple" and "multiple types" refer to two or more types.

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

[0068] Unless otherwise specified, the numerical values ​​of each parameter referred to herein can be measured using various measurement methods commonly used in the art. For example, they can be measured according to the method 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 placed between the positive and negative electrode sheets and primarily serves to prevent short circuits between the positive and negative electrodes, while also allowing active ions to pass freely to form a circuit.

[0070] With the increasing application and widespread use of secondary batteries, the demands on their energy density and service life are constantly rising. Thinning the separator is an effective measure to improve the energy density of secondary batteries. Currently, the separators used in commercially available secondary batteries are generally porous polyolefin membranes, such as porous polyethylene membranes, porous polypropylene membranes, or three-layer composite membranes of polypropylene / polyethylene / polypropylene. Their melting point is 130°C to 160°C. As a result, if the thickness is reduced, the heat resistance of the separator deteriorates, and when heated, a significant thermal shrinkage effect occurs, causing the positive and negative electrodes inside the battery to come into direct contact, resulting in a short circuit and further increasing the safety risk of the secondary battery.

[0071] To solve the above problems, the measures currently employed mainly involve coating a heat-resistant inorganic ceramic layer onto a polyolefin porous membrane. This increases the mechanical strength of the separator, reduces the degree of shrinkage when the separator is subjected to heat, and lowers the risk of short circuits between the positive and negative electrodes inside the battery. However, because commercially available inorganic ceramic particles have a large particle size, the overall thickness of the separator increases, making it difficult to balance the energy density of the secondary battery, which is particularly detrimental to improving driving range in the field of power batteries. Furthermore, the large particle size of commercially available inorganic ceramic particles results in a small number of deposition layers in the polyolefin porous membrane (usually 5 layers or less), and the improvement effect on the heat resistance of the separator is finite. Nano-sizing the 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 nano-sized inorganic ceramic particles is low, making it easy to clog the polyolefin porous membrane. This reduces the overall porosity of the separator, increases ion resistance, inhibits ion transport, and further deteriorates the capacity and dynamic performance of the secondary battery. At the same time, because the specific surface area of ​​the nano-sized inorganic ceramic particles is high and the contact between particles is point contact, a large amount of binder is required to ensure adhesion between particles. However, using a large amount of binder makes pore clogging problems more likely, which is detrimental to the rate performance of the secondary battery. For example, dendrites are more likely to form on the negative electrode surface, and furthermore, it is detrimental to the capacity, energy density, and lifespan of the secondary battery.

[0072] Furthermore, since polyolefin porous membranes are hydrophobic materials and inorganic ceramic particles are hydrophilic materials, problems such as incomplete coating and poor uniformity can occur when applying inorganic ceramic slurry to the surface of the polyolefin porous membrane. This affects the uniformity of the separator and, in turn, impacts the capacity and dynamic performance of the secondary battery.

[0073] Therefore, conventional separators have difficulty achieving both high energy density, high thermal safety performance, and long service life in secondary batteries.

[0074] In the course of their research, the inventors of this invention have surprisingly discovered that by providing a coating layer containing a three-dimensional skeletal structure and fillers on the surface of a porous separator substrate, and by adjusting the zeta potential of the coating layer within an appropriate range, it is possible to give the separator high heat resistance, high uniformity, and good ion conductivity, and furthermore, to achieve high energy density, high thermal safety performance, and a long service life in the secondary battery. Separator

[0075] Specifically, a first embodiment of the present invention provides a separator comprising a porous substrate and a coating layer provided on at least one surface of the porous substrate, wherein the coating layer comprises a three-dimensional skeletal structure and a filler, at least a portion of which is filled into the three-dimensional skeletal structure, and the zeta potential of the coating layer is less than 0 mV.

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

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

[0078] The zeta potential meter can be a nanoparticle size potential meter from Malvern's Zetasizer series, such as the Zetasizer Advance, and the sample cell can be a Malvern DTS1070 zeta potential capillary sample cell. Specifically, the obtained dispersion is placed in a Malvern DTS1070 zeta potential capillary cell for testing, and then the zeta potential of the obtained dispersion can be measured using ZS Xplorer software. Test standards can be referenced from GB / T 32671.2-2019 and ISO 13099-2-2012. To ensure the accuracy of the test results, multiple (e.g., five or more) parallel samples should be taken and tested during the test, and the average value should be taken.

[0079] Through extensive research, the inventors of this invention have unexpectedly discovered that by providing a coating layer containing a three-dimensional skeletal structure and fillers on the surface of a porous substrate of a separator, and by adjusting the zeta potential of the coating layer to less than 0 mV, the separator can be endowed with high heat resistance, high uniformity, and good ion conductivity. Furthermore, the secondary battery can be endowed with high energy density, high thermal safety performance, and a long service life.

[0080] Although the mechanism is not fully understood, the inventors of this application speculate that the following are possible causes.

[0081] Firstly, 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 of surface density and thickness can be formed, improving the heat resistance of the separator. Furthermore, the pore distribution of the coating layer is uniform, ensuring good ion conductivity of the coating layer. This improves the rate performance, thermal safety performance, and cycle performance of the secondary battery.

[0082] Secondly, since at least a portion of the filler is filled into the three-dimensional skeletal structure, the filler and the three-dimensional skeletal structure contribute to forming a nesting effect, thereby improving the heat resistance of the separator, reducing the degree of shrinkage when the separator is subjected to heat, reducing the risk of short circuits between the positive and negative electrodes, and enabling the secondary battery to have high thermal safety performance. Furthermore, it is possible to maintain high adhesive strength between the coating layer and the porous substrate and prevent the filler from falling off during long-term charging and discharging of the secondary battery.

[0083] Thirdly, by filling at least a portion of the filler into the three-dimensional skeletal structure, the filler can also lap-joint with the three-dimensional skeletal structure, thereby enabling the coating layer to have a stable spatial network structure, increasing the ion conduction pathways of the separator and promoting ion transport, as well as improving the separator's penetration and retention characteristics in the electrolyte. Furthermore, secondary batteries using the separator of this invention can have a long service life.

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

[0085] In some embodiments, the zeta potential of the coating layer may be -50mV to -5mV, selectively -25mV to -5mV, and even more selectively -15mV to -6mV. This further improves the uniformity of the surface density and thickness of the coating layer and the uniformity of the pores, thereby further improving the ion conductivity of the separator and the energy density and cycle performance of the secondary battery. Furthermore, if the zeta potential of the coating layer is too low, the viscosity of the coating layer slurry will be too high and the fluidity will be poor, which can affect the application of the coating layer slurry and potentially affect the uniformity of the surface density and thickness of the coating layer and the uniformity of the pores.

[0086] In some embodiments, the material constituting the three-dimensional skeletal structure may include at least one of organic rods and organic tubes. A material with an appropriate shape is advantageous for better lap-jointing the three-dimensional skeletal structure and the filler, thereby allowing the coating layer to have a more stable spatial network structure, and thus further improving the heat resistance and ion conductivity of the separator.

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

[0088] In some embodiments, the material constituting the three-dimensional skeletal structure may include nanocellulose. Optionally, the nanocellulose includes at least one of cellulose nanofibers (also known as cellulose nanofibrils, CNF, nanofibril cellulose, or microfibril cellulose), cellulose nanowhiskers (also known as cellulose nanocrystals, CNC, cellulose nanocrystals, or nanocrystalline cellulose), and bacterial nanocellulose (also known as bacterial nanocellulose, BNC, or microbial cellulose). Optionally, the nanocellulose may include cellulose nanowhiskers, which have 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 on the nanoscale (e.g., within 100 nm), possessing the properties of both cellulose and nanoparticles. Nanocellulose may also be polymer nanomaterials extracted from wood, cotton, etc., in nature by one or more means from chemistry, physics, or biology. It has advantages such as a wide range of sources, low cost, biodegradability, high modulus, and high specific surface area, making it an excellent substitute for conventional petrochemical resources and effectively mitigating problems such as environmental pollution and the strain on petrochemical resources.

[0090] In some embodiments, the nanocellulose may contain a hydroxyl group and an anionic modified group, and selectively, the anionic modified group may contain at least one of an amine group, a carboxyl group, a sulfonic acid group, a boric acid group, and a phosphate group, and more selectively, at least one of a sulfonic acid group, a boric acid group, and a phosphate group.

[0091] In further research, the inventors found that when nanocellulose has the specific anion-modified groups described above, it is possible to ensure that the slurry of the coating layer has an appropriate viscosity, which is advantageous for application and can improve the production efficiency of separators. This also contributes to the coating layer having an appropriate zeta potential, thereby further improving the uniformity of the surface density and thickness of the coating layer and the uniformity of the pores. Furthermore, it is possible to further improve the ion conductivity of the separator and the energy density and cycle performance of the secondary battery.

[0092] When nanocellulose has the aforementioned specific anionic modified groups, it can also effectively improve the heat resistance of the separator and the adhesive strength between the coating layer and the porous substrate.

[0093] When nanocellulose has the aforementioned specific anion-modified groups, it is also advantageous for lap joints between nanocellulose and fillers, resulting in a more stable spatial network structure in the coating layer. This improves the separator's penetration and retention properties into the electrolyte, further enhancing the separator's ionic conductivity and voltage breakdown characteristics, which is advantageous for matching high-voltage positive electrode active materials and further improves the energy density of the secondary battery.

[0094] In some embodiments, the molar ratio of the anionic modifying group to the hydroxyl group may be 1:4 to 4:1, and selectively 2:3 to 7:3. When the molar ratio of the anionic modifying group to the hydroxyl 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 penetration and retention properties of the electrolyte of the separator can be improved. If the molar ratio of the anionic modifying group to the hydroxyl group is too small, the further improvement effect of the anionic modifying group on the uniformity of the surface density and thickness of the coating layer and the uniformity of the pores may not be clear. If the molar ratio of the anionic modifying group to the hydroxyl group is too large, the penetration and retention properties of the separator to the electrolyte may deteriorate, which may affect the cycle performance and safety performance of the secondary battery, and the heat resistance of the separator may decrease, which may further affect the thermal safety performance of the secondary battery.

[0095] The type of anionic modifying group in nanocellulose can be measured by infrared spectroscopy. For example, the type of anionic modifying group can be determined by testing the infrared spectrum of the material and identifying the characteristic peaks contained therein. Specifically, infrared spectral analysis can be performed on the material using known instruments and methods in this field, and measurements can be made using, for example, an infrared spectrophotometer (e.g., an IS10 Fourier transform infrared spectrophotometer from Nigaelic, Inc., USA) in accordance with the general rules of infrared spectroscopic analysis methods in GB / T 6040-2019.

[0096] In some embodiments, the average diameter of the material constituting the three-dimensional skeletal structure may be 40 nm or less, and is selectively between 10 nm and 35 nm. When the average diameter of the material constituting the three-dimensional skeletal structure is within an appropriate range, the ion conductivity and dielectric breakdown characteristics of the separator can be further improved, and the heat resistance of the separator can also be further improved because it contributes to the integration effect of the lap joint between the material constituting the three-dimensional skeletal structure and the filler. Furthermore, if the average diameter of the material constituting the three-dimensional skeletal structure is too large, the wrapping effect of the formed three-dimensional skeletal structure will be insufficient, resulting in larger pores, which can effectively avoid the problem of the separator's dielectric breakdown characteristics not being sufficiently good.

[0097] In some embodiments, the average length of the material constituting the three-dimensional skeletal structure may be 100 nm to 600 nm, and selectively 200 nm to 400 nm. When the average length of the material constituting the three-dimensional skeletal structure is within an appropriate range, the heat resistance and ion conductivity of the separator can be further improved. Furthermore, if the average length of the material constituting the three-dimensional skeletal structure is too short, the lap joint effect with the filler will be poor, which may result in poor heat resistance of the coating layer. Also, during the drying process of the coating layer, some of the three-dimensional skeletal structures may collapse due to insufficient support from the filler, easily clogging the pores of the porous substrate, hindering ion transport and moisture discharge, which may affect the cycle performance and rate performance of the secondary battery. Conversely, if the average length of the material constituting the three-dimensional skeletal structure is too long, the viscosity of the coating layer slurry will increase, resulting in poor dispersibility. This effectively avoids the possibility of poor surface density, thickness uniformity, and pore uniformity of the coating layer formed after the slurry has dried.

[0098] In some embodiments, the aspect ratio of the material constituting the three-dimensional skeletal structure may be 5 to 60, and is selectively 15 to 30. When the aspect ratio of the material constituting the three-dimensional skeletal structure is within an appropriate range, the ion conductivity of the separator can be further improved. Furthermore, if the aspect ratio of the material constituting the three-dimensional skeletal structure is too small, the lap joint effect with the filler will be poor, which may result in poor heat resistance of the coating layer. In addition, during the drying process of the coating layer, some of the three-dimensional skeletal structures may collapse due to insufficient support from the filler, easily clogging the pores of the porous substrate, hindering ion transport and moisture discharge, which may affect the cycle performance and rate performance of the secondary battery. Conversely, if the aspect ratio of the material constituting the three-dimensional skeletal structure is too large, the pores of the formed three-dimensional skeletal structure will be small, which may result in poor ion conductivity of the separator. These problems can be effectively avoided.

[0099] The average length and average diameter of the material constituting the three-dimensional skeletal structure can be measured by the following method: Cut a 3.6 mm × 3.6 mm sample from any one region of the separator, map the microtopographic structure of the coating layer in the sample using a scanning electron microscope (e.g., ZEISS Sigma 300), select high vacuum mode, set the operating voltage to 3 kV and the magnification to 30,000x, and acquire an SEM image; based on the acquired SEM image, select multiple (e.g., five or more) test regions and perform length statistics, with each test region having a size of 0.5 μm × 0.5 μm, and then use the average length obtained in each test region as the average length of the material constituting the three-dimensional skeletal structure; and based on the acquired SEM image, use Nano Measurer particle size distribution statistics software to select multiple (e.g., five or more) test regions and perform diameter statistics, with each test region having a size of 0.5 μm × 0.5 μm, and then use the average diameter obtained in each test region as the average diameter of the material constituting the three-dimensional skeletal structure.

[0100] In some embodiments, the content of the three-dimensional skeletal structure in the coating layer may be 6 wt% to 35 wt%, and selectively 10 wt% to 30 wt%, based on the total weight of the coating layer. When the content of the three-dimensional skeletal structure is within an appropriate range, it can be ensured that the slurry of the coating layer has an appropriate viscosity, which is advantageous for application, and is also advantageous for the integration effect of the lap joint between the three-dimensional skeletal structure and the filler. As a result, the coating layer can have a more stable spatial network structure, which can further improve the ion conductivity, penetration and retention characteristics of the electrolyte, and voltage breakdown capability of the separator.

[0101] In secondary batteries, the overall volume increases during long-term charge-discharge processes because the microstructural changes of the positive and negative electrode active materials are irreversible. In particular, the volume increase is greater after the negative electrode active material inserts active ions during rapid charging of secondary batteries. When the battery expands, it creates pressing and / or tensile forces on the separator, making the separator susceptible to damage, which increases the risk of short circuits between the positive and negative electrodes. Therefore, the separator is also required to have good resistance to external forces. At least a portion of the filler is filled into a three-dimensional skeletal structure, contributing to the coating layer having a stable spatial network structure. This can improve the ion conductivity and heat resistance of the separator, as well as the tensile strength, puncture resistance, and external force resistance of the separator.

[0102] In some embodiments, the filler may include at least one of primary particle topography filler particles and secondary particle topography filler particles, selectively including secondary particle topography filler particles, and further selectively including both primary particle topography and secondary particle topography filler particles simultaneously. The secondary particle topography filler particles have the advantage of having a large specific surface area and good affinity with the three-dimensional skeletal structure, so they can better lap-joint with the three-dimensional skeletal structure and provide a stable spatial network structure with the coating layer. This not only increases the ion conduction passages of the separator and promotes ion transport, but also improves the heat resistance and electrolyte penetration and retention characteristics of the separator. As a result, secondary batteries employing the separator of the present invention can have a long service life and good rate performance. The larger particle size of the filler particles in primary particle topography allows for better support of the particles within the coating layer, reduces shrinkage of the filler particles in secondary particle topography, and decreases the amount of binder used, thereby improving the heat resistance of the separator. The larger particle size of the filler particles in primary particle topography also contributes to the coating layer having more channel structures and less water content when used in small quantities, further improving the ion conductivity and electrolyte penetration and retention properties of the separator.

[0103] In some embodiments, the filler simultaneously contains 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 selectively 5:1 to 15:1. This contributes to the coating layer having a more stable and uniform spatial network structure.

[0104] In some embodiments, the average particle size of the filler particles in the primary particle topography may be 200 nm to 800 nm, and is selectively between 200 nm and 400 nm. This allows the support function of the filler particles in the primary particle topography to be better exhibited, the coating layer to maintain a stable channel structure during long-term charge-discharge processes, and is also advantageous for ion transport.

[0105] In some embodiments, the BET specific surface area of ​​the filler particles in the primary particle topography is 10 m². 2 It may be less than / g, and selectively 3m 2 / g~7m 2 This is / g. This allows the filler particles in primary particle topography to exert their supportive effect more effectively, the coating layer to maintain a stable channel structure during long-term charge-discharge processes, and is also advantageous for ion transport.

[0106] In some embodiments, the content of filler particles in the primary particle topography is 30 wt% or less, and selectively between 5 wt% and 25 wt%, relative to the total weight of the coating layer. This allows the support function of the filler particles in the primary particle topography to be better exercised, the coating layer to maintain a stable channel structure during long-term charge-discharge processes, and is also advantageous for ion transport.

[0107] In some embodiments, the average particle size of the filler particles in the secondary particle topography may be 200 nm or less, and is selectively between 50 nm and 200 nm. This allows the filler particles in the secondary particle topography to have a high specific surface area, thereby increasing the affinity between the filler and the three-dimensional skeletal structure, and enabling better lap jointing between the filler and the three-dimensional skeletal structure. As a result, the coating layer can have a more stable spatial network structure, and furthermore, the separator has better heat resistance, ion conductivity, and absorption and retention characteristics for the electrolyte.

[0108] In some examples, the BET specific surface area of ​​the filler particles in the secondary particle topography is 20 m². 2 It may be 30m or more, and selectively 30m 2 / g~80m 2 This results in better affinity between the filler and the three-dimensional skeletal structure, allowing the coating layer to have a more stable spatial network structure, and the separator to have even better heat resistance, ion conductivity, and electrolyte penetration and retention properties.

[0109] In some embodiments, the filler particle content of the secondary particle topography, based on the total weight of the coating layer, may be 60 wt% or more, and selectively 70 wt% to 90 wt%. This ensures that the slurry of the coating layer has an appropriate viscosity, which is advantageous for application. It is also advantageous for better lap jointing of the filler and the three-dimensional skeletal structure, resulting in a more stable spatial network structure in the coating layer, thereby further improving the tensile strength, puncture resistance, and external force resistance of the separator.

[0110] In some embodiments, the filler comprises 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 the function of transporting active ions, and inorganic particles that are electrochemically oxidizable and reducible.

[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 be included, and one type selected therefrom is acceptable.

[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), lithium lanthanum 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, further improving the uniformity of the surface density and thickness of the coating layer and the uniformity of the pores, 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 contain a non-particulate binder. In this application, the type of non-particulate binder is not particularly limited, and any material with known good adhesion can be used. Selectively, the non-particulate binder includes an aqueous solution type binder, which has the advantages of good thermodynamic stability and being environmentally friendly, thus advantageous for the preparation and application of the coating layer slurry. As an example, the aqueous solution type binder may contain at least one of the following: aqueous solution type acrylic resin (e.g., homopolymers of monomers of acrylic acid, methacrylic acid, sodium acrylate, or copolymers of these with other copolymer monomers), polyvinyl alcohol (PVA), isobutylene-maleic anhydride copolymer, and polyacrylamide.

[0118] Selectively, the content of the non-particulate binder in the coating layer is 2 wt% or less, based on the total weight of the coating layer. The three-dimensional skeletal structure and filler in the coating layer of the present invention can be lap-jointed so that the coating layer has a stable spatial network structure, thereby maintaining high adhesion to the separator while reducing the amount of binder used.

[0119] In some embodiments, the thickness of the coating layer may be 1 μm or less, and is selectively between 0.5 μm and 0.8 μm. This contributes to improving the energy density of the secondary battery. In this 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 is selectively between 3 μm and 5 μm. The coating layer of the present invention can significantly improve the heat resistance of the separator, thereby allowing for the selection of a thinner porous substrate, which contributes to improving the energy density of the secondary battery.

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

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

[0123] Selectively, the particulate binder comprises at least one of the following: a homopolymer or copolymer of an acrylic acid ester monomer, a homopolymer or copolymer of an acrylic acid monomer, or a homopolymer or copolymer of a fluorine-containing olefin monomer. The copolymer monomer comprises, but is not limited to, at least one of the following: an acrylic acid ester monomer, an acrylic acid monomer, an olefin monomer, a halogen-containing olefin monomer, or a fluoroether monomer.

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

[0125] In some examples, the longitudinal heat shrinkage rate of the separator at 150°C for 1 hour is 5% or less, and is selectively between 0.5% and 3%.

[0126] In some examples, the lateral thermal shrinkage rate of the separator at 150°C for 1 hour is 5% or less, and selectively between 0.5% and 3%.

[0127] The separator of this invention has a low thermal contraction rate in both the lateral and vertical directions at a high temperature of 150°C, and therefore can improve the safety performance of secondary batteries.

[0128] In some embodiments, the longitudinal tensile strength of the separator was 2000 kg / cm². 2 The above is the case, and it is possible to select 2500 kg / cm². 2 ~4500 kg / cm 2 That is the case.

[0129] In some embodiments, the lateral tensile strength of the separator was 2000 kg / cm². 2 The above is the case, and it is possible to select 2500 kg / cm². 2 ~4500 kg / cm 2 That is the case.

[0130] Since the separator of this invention has high tensile strength in both the lateral and vertical directions, the probability of the separator being damaged when the secondary battery expands is low, thereby improving the safety performance of the secondary battery.

[0131] In some embodiments, the wetted length of the separator is 30 mm or more, and is selectively between 30 mm and 80 mm.

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

[0133] The separator of this invention has good penetration and retention characteristics for the electrolyte, thereby improving the ion conductivity of the separator and the capacity performance characteristics of the secondary battery.

[0134] In some embodiments, the air permeability of the separator is 300 s / 100 mL or less, and selectively between 100 s / 100 mL and 230 s / 100 mL. The separator of this application has good air permeability, which can improve ion conductivity and the capacity performance characteristics of secondary batteries.

[0135] In this application, the average particle size of the material has a meaning known in the art and can be measured using instruments and methods known in the art. For example, the material or separator can be measured using a scanning electron microscope, transmission electron microscope, or particle size distribution device to acquire an image, and then multiple (e.g., 10 or more) test particles can be randomly selected from the image. The average of the shortest diagonal lengths of the particles can then be statistically determined as the average particle size.

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

[0137] In this application, the thermal shrinkage coefficient, tensile strength, and air permeability of the separator all have meanings known in the art and can be measured by methods known in the art. For example, all can be tested by referring to the GB / T 36363-2018 standard.

[0138] In this application, the wetting length and wetting rate of the separator both have meanings known in the art and can be measured by methods known in the art. An example measurement method includes cutting the separator into a sample with a width of 5 mm and a length of 100 mm, fixing both ends of the sample and placing it horizontally, dropping 0.5 mg of electrolyte into the center of the sample, and after a predetermined time (1 min in this application), photographing and measuring the length over which the electrolyte diffuses to obtain the wetting length and wetting rate of the separator. To ensure the accuracy of the test results, the test can be performed using multiple samples (e.g., 5 to 10) and the average value can be calculated to obtain the test results. The electrolyte can be 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 thoroughly dried LiPF6 in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0139] The parameters of the coating layer of the separator described above (e.g., thickness) are all parameters of the coating layer on one side of the porous substrate. When coating layers are provided on both sides of the porous substrate, it is considered that if the parameters of the coating layer on either side satisfy the requirements of this application, the application falls within the scope of protection. Manufacturing method

[0140] A second embodiment of the present invention provides a method for manufacturing a separator according to the first embodiment of the present invention, comprising: step S1 providing a porous substrate; step S2 preparing a coating layer slurry by mixing a material for constituting a three-dimensional skeletal structure and a filler in a predetermined ratio in a solvent to prepare a coating layer slurry; and step S3 applying the coating layer slurry to at least one surface of the porous substrate to form a coating layer and dry it to obtain a separator, wherein the separator comprises a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer comprises a three-dimensional skeletal structure and a filler, at least a portion of the filler is filled into the three-dimensional skeletal structure, and the zeta potential of the coating layer is less than 0 mV.

[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 contain other components, such as a dispersant, a wetting agent, a binder, and so on.

[0143] In some embodiments, in S2, the material constituting the three-dimensional skeletal structure includes nanocellulose, the nanocellulose includes a hydroxyl 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 phosphate group, and selectively includes at least one of a sulfonic acid group, a boric acid group and a phosphate group.

[0144] Selectively, the nanocellulose is cellulose nanowhiskers (also called cellulose nanocrystals, CNCs, cellulose nanocrystals, or nanocrystalline cellulose).

[0145] In some embodiments, in S2, the slurry of the coating layer can be obtained by a method comprising: a step of preparing a nanocellulose solution having a pH between 5 and 9 and a zeta potential of less than 0 mV, the step of mixing nanocellulose having an anionic modification group with water to prepare the nanocellulose solution; a step of preparing a filler solution having a pH of 7.5 or higher and a zeta potential of less than 0 mV; and a mixing step of mixing the nanocellulose solution and the filler solution in 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 modified group can be obtained by mixing nanocellulose powder and a modification solution and reacting them, then washing to remove impurities to obtain cellulose nanowhisker having an anionic modified group, adjusting the pH of the obtained cellulose nanowhisker having anionic modified group to neutral (for example, a pH between 6.5 and 7.5), grinding and cutting to obtain nanocellulose having anionic modified group.

[0147] In some embodiments, the whiteness of the nanocellulose powder may be 80% or more. The cellulose powder may be obtained commercially, or it can be obtained by chemical methods (e.g., acid hydrolysis, alkali treatment, Tempo contact oxidation), biological methods (e.g., enzymatic treatment), mechanical methods (e.g., ultrafine grinding, ultrasonic grinding, high-pressure homogenization), etc. The fiber raw material for producing the above-mentioned cellulose powder with a whiteness of 80% or more may include at least one of the following: plant fibers, for example, cotton fibers (e.g., cotton fibers, kapok fibers), hemp fibers (e.g., sisal fibers, ramie fibers, kouma fibers, flax fibers, cannabis fibers, Manila hemp fibers, etc.), palm fibers, wood fibers, bamboo fibers, and grass fibers.

[0148] In some embodiments, the cellulose powder may also be produced by opening the fiber raw material to remove debris, steaming it in an alkaline solution (for example, an aqueous NaOH solution with a concentration of 4 wt% to 20 wt%, and selectively 5 wt% to 15 wt%), then sequentially washing it with water to remove impurities (for example, 3 to 6 washes), bleaching it (for example, sodium hypochlorite and / or hydrogen peroxide may be used), pickling it to remove impurities, washing it with water to remove impurities, removing the water, and air-drying it to obtain the cellulose powder.

[0149] In some embodiments, the modification solution may be an acidic solution (e.g., an aqueous solution of sulfuric acid, boric acid, phosphoric acid, or acetic acid) or an alkaline solution (e.g., an organic solvent solution of urea). Optionally, the modification solution is an acidic solution.

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

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

[0152] Furthermore, by using a urea xylene solution as the urea organic solvent solution, a cellulose powder having an amine group can be obtained.

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

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

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

[0156] In some embodiments, when the modified 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 modified solution may be 1 to 5 hours.

[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 (e.g., number of polishing cycles, polishing time, etc.) and the cutting parameters of the high-pressure homogenizer, nanocellulose having different average diameters and / or different average lengths can be obtained.

[0158] In some embodiments, in step 2, the filler solution can be obtained by mixing the filler, water, and a denaturant comprising at least one selected from a base, anionic surfactant, and 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] Selectively, the base includes at least one selected from KOH, NaOH, NaHCO3, LiOH, NH4OH, Mg(OH)2, and Na2CO3.

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

[0161] Selectively, the nonionic surfactant comprises at least one selected from fluoroalkyl ethoxyglycol ethers and aliphatic alcohol polyoxyethylene ethers.

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

[0163] In some embodiments, the concentration of the filler solution may be 30 wt% to 60 wt%, or selectively 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 selectively 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] This effectively reduces surface coating problems and lowers the probability of uneven coating, thereby further improving the energy density and safety performance of secondary batteries.

[0167] In some embodiments, in S3, the coating is performed using a coater. In this application, the model number of the coating machine is not particularly limited, and for example, a commercially available coating machine can be used. The coating machine includes a gravure roll for transferring the slurry to a porous substrate.

[0168] In some embodiments, in S3, the coating method can be transfer coating, rotary spray coating, dip coating, or the like.

[0169] In some embodiments, the method further includes a two-coating step S4 in which a slurry containing particulate binder is applied to at least a portion of the surface of the coating layer and dried to form an adhesive layer.

[0170] The separator manufacturing method of this invention significantly simplifies the separator manufacturing process by producing the coating layer in a single application.

[0171] The raw materials and their content parameters used in the method for manufacturing the separator of this application can be found by referring to the separator of the first embodiment of this application, and are therefore omitted from this explanation.

[0172] Unless otherwise specified, the raw materials used in the method for manufacturing the separator of this application are commercially available. secondary battery

[0173] A third aspect of the embodiments of the present invention provides a secondary battery.

[0174] A secondary battery, also called a rechargeable battery or storage battery, is a battery that can be used continuously by activating the active material through charging after discharge. Typically, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is provided between the positive electrode sheet and the negative electrode sheet and primarily serves to prevent short circuits between the positive and negative electrodes, while also allowing active ions to pass through.

[0175] In this application, the type of secondary battery is not particularly limited, and for example, the secondary battery may be a lithium-ion battery, a sodium-ion battery, etc., and in particular, the secondary battery may be a lithium-ion secondary battery.

[0176] A secondary battery according to a third embodiment of the present invention includes a separator according to a first embodiment of the present invention or a separator manufactured by the method according to a second embodiment of the present invention, wherein the separator is interposed between the positive electrode sheet and the negative electrode sheet. Optionally, the coating layer of the present invention is provided at least on the side of the separator closest to the negative electrode sheet. This enables the secondary battery of the present invention to combine high energy density, high thermal safety performance, and a 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 opposing surfaces 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 It may contain at least one of O2, LiFePO4, and LiMnPO4.

[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 (e.g., 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 contain at least one of the materials represented by. In the general formula X p M’ q (PO4) r O x Y 3-x where 0 < p ≤ 4, 0 < q ≤ 2, 1 ≤ r ≤ 3, 0 ≤ x ≤ 2, and X is H + , Li + , Na + , K + and NH{4} +At least one of the following is selected, where M' is a transition metal cation, selectively at least one of V, Ti, Mn, Fe, Co, Ni, Cu, and Zn, and Y is a halogen anion, selectively at least one of F, Cl, and Br.

[0183] In this application, the modified compounds of each of the above positive electrode active materials may be obtained by doping modification and / or surface coating modification of the positive electrode active material.

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

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

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

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

[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 opposing surfaces in its thickness direction, and the negative electrode film layer is provided on either or both of the two opposing surfaces of the negative electrode current collector.

[0189] The anode active material can be anode active material used in secondary batteries known in this art. For example, the anode 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 selectively contain a negative electrode conductive agent. In this application, the type of negative electrode conductive agent is not particularly limited, and as an example, the negative electrode conductive agent may contain at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent is 5% or less of the total mass of the negative electrode film layer.

[0191] In some embodiments, the negative electrode film layer may optionally contain a negative electrode binder. In this application, the type of negative electrode binder is not particularly limited, and as an example, the negative electrode binder may contain at least one of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylate PAA, polymethacrylate PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder is 5% or less based on the total mass of the negative electrode film layer.

[0192] In some embodiments, the negative electrode film layer may optionally contain other additives. For example, the other additives may include thickeners such as sodium carboxymethylcellulose (CMC) or PTC thermistor material. In some embodiments, the mass percentage of the other additives is 2% or less based on the total mass of the negative electrode film layer.

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

[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, a selectable conductive agent, a selectable binder, and other optional auxiliary agents in a solvent and stirring uniformly. The solvent may, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0195] The negative electrode sheet does not exclude any additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode sheet described in this application further includes a conductive undercoat layer (e.g., consisting of a conductive agent and 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 this application further includes a protective layer covering the surface of the negative electrode film layer. [Electrolyte]

[0196] During the charging and discharging process of a secondary battery, active ions reciprocate between the positive electrode sheet and the negative electrode sheet, being inserted and removed, while the electrolyte plays a role in conducting these active ions between the positive and negative electrode sheets. This invention does not particularly limit the type of electrolyte and can be selected according to actual needs.

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

[0198] When the secondary battery of the present application is a lithium-ion battery, the electrolyte salt may include, as an example, at least one of the following: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium difluorosulfonylimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium disoxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodisoxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0199] When the secondary battery of the present application is a sodium-ion battery, the electrolyte salt may include, as an example, at least one of the following: sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium difluorosulfonylimide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), sodium disoxalate borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorodisoxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0200] As an example, the solvent includes, but is not limited to, at least one of the following: ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

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

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

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

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

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

[0206] In some embodiments, as shown in Figure 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 side plates surround and form a housing cavity. The housing 51 has an opening that communicates with the housing cavity, and the cover plate 53 covers the opening and closes the housing cavity. The positive electrode sheet, negative electrode sheet and separator can be formed into an electrode assembly 52 by a winding process and / or a lamination process. The electrode assembly 52 is packaged in the housing cavity. The electrolyte is impregnated into 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 method for manufacturing the secondary battery of the present invention 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. For example, an electrode assembly can be formed by winding and / or laminating processes of a positive electrode sheet, a separator, and a negative electrode sheet, the electrode assembly can be placed in an outer casing, the electrolyte can be injected after drying, and a secondary battery can be obtained through processes such as vacuum sealing, standing, chemical formation, and shaping.

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

[0209] Figure 3 is a schematic diagram of a battery module 4 as an example. As shown in Figure 3, in the battery module 4, the multiple secondary batteries 5 may be arranged sequentially along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, these multiple secondary batteries 5 may be fixed together with fasteners.

[0210] Optionally, the battery module 4 may further include a case having a housing space for accommodating multiple secondary batteries 5.

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

[0212] Figures 4 and 5 are schematic diagrams of an example battery pack 1. As shown in Figures 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 and forming a sealed space for housing the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner. Electrical consumption device

[0213] A fourth embodiment of the present invention provides an electrical consumption device comprising at least one of the secondary battery, battery module, or battery pack of the present invention. The secondary battery, battery module, or battery pack may be used as a power source for the electrical consumption device or as an energy storage unit for the electrical consumption device. The electrical consumption device may be, but is not limited to, mobile devices (e.g., mobile phones, laptop computers, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), trains, ships and satellites, energy storage systems, etc.

[0214] The aforementioned power consumption device can be configured to use a secondary battery, battery module, or battery pack, depending on its usage needs.

[0215] Figure 6 is a schematic diagram of an example of an electrical power consumption device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the requirements for high output and high energy density of this electrical power consumption device, a battery pack or battery module may be used.

[0216] Other examples of power-consuming devices may include mobile phones, tablet computers, and laptop computers. These power-consuming devices are generally required to be thin and can use rechargeable batteries as a power source. Examples

[0217] The following examples illustrate the contents of this application in more detail; however, these examples are merely illustrative, and it will be apparent to those skilled in the art that various modifications and changes can be made within the scope of the disclosure. All quantities, percentages, and ratios described in the following examples are based on mass unless otherwise specified. Furthermore, all reagents used in the examples may be commercially available or synthesized according to conventional methods, and may be used as is without requiring further processing. Furthermore, all apparatus used in the examples are commercially available. Preparation of modified nanocellulose C1 Preparation of cellulose powder

[0218] After opening the cotton linters using a cotton opening machine and removing debris, they are steamed at 150°C for 2 hours in a 5 wt% NaOH aqueous solution. Then, impurities are removed by washing with water (3 washes), bleached with sodium hypochlorite, impurities are removed by washing with dilute hydrochloric acid, impurities are removed by washing with water (1 wash), water is removed, and air-dried 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% sulfuric acid aqueous solution and reacted at 60°C for 1.5 hours. After the reaction is complete, impurities are removed by washing with water (3 washes), followed by filtration, deacidification, and impurity removal to obtain cellulose nanowhiskers containing sulfonic acid groups. Neutralization of cellulose

[0220] The pH of cellulose nanowhiskers having sulfonic acid groups was adjusted to neutral with a 10 wt% NaOH aqueous solution, then dispersed by high-speed processing in a polishing machine for 2.5 hours, with two polishing cycles. Next, it was cut into nanoscale using a high-pressure homogenizer to obtain nanocellulose C1 having sulfonic acid group-modified groups with an average length of 400 nm and an average diameter of 25 nm, and the molar ratio of sulfonic acid groups to hydroxyl groups was 5:3. Preparation of modified nanocellulose C2-C4

[0221] Modified nanocellulose C2-C4 are manufactured using a method similar to that of modified nanocellulose C1; see Table 1 for differences. By adjusting the parameters of the polishing machine and the cutting parameters of the high-pressure homogenizer during the manufacturing process, 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 the cotton linters using a cotton opening machine and removing debris, they are steamed at 150°C for 2 hours in a 5 wt% NaOH aqueous solution. Then, impurities are removed by washing with water (3 times), bleached with sodium hypochlorite, impurities are removed by washing with dilute hydrochloric acid, impurities are removed by washing with water (1 time), water is removed, and air-dried to obtain cotton cellulose powder with a whiteness of 85% or more. The obtained cotton cellulose powder is mixed with a 20 wt% NaOH aqueous solution at 10°C, stirred for 2 hours, filtered, and washed twice with water to obtain cellulose powder. Esterification of cellulose

[0223] 50 g of the obtained cellulose powder and 200 g of urea were placed in a three-port reactor equipped with an oil-water separator. After the urea dissolved, 5 g of xylene was added, and the mixture was heated to 137°C while stirring and reacted for 4 hours. After that, it was washed with water (3 times), filtered, and dried to obtain cellulose carbamate. Neutralization of cellulose

[0224] The obtained cellulose carbamate was dissolved in a 5 wt% NaOH aqueous solution to obtain a homogeneous cellulose carbamate solution, which was then dispersed by high-speed processing in a polishing machine for 2.5 hours (2 polishing cycles). Furthermore, it was cut into nanoscale pieces using a high-pressure homogenizer to obtain nanocellulose with amine-modified groups having an average length of 400 nm and an average diameter of 25 nm, with a molar ratio of amine groups to hydroxyl groups of 4:3.

[0225] The molar ratio of anionic modified groups to hydroxyl groups can be measured by determining the hydroxyl group value (the number of mg of potassium hydroxide equivalent to the hydroxyl group content per gram of sample) of raw cellulose and modified nanocellulose based on the phthalic anhydride method in GB / T 12008.3-2009. The obtained values ​​are converted to mgKOH / g, and then to mmol / g to obtain the hydroxyl group content. Subtracting the hydroxyl group content of modified nanocellulose from the hydroxyl group content of raw cellulose yields the anionic modified group content (i.e., the content of modified hydroxyl groups), from which the molar ratio of anionic modified groups to hydroxyl groups can be 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. Further processing with a polishing machine and / or high-pressure homogenizer can yield nanocellulose with different average diameters and / or different average lengths.

[0227] [Table 1]

[0228] Example 1 (1) Fabrication of separators S1: Provides a porous PE substrate.

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

[0230] S2: Prepare the slurry for 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 the 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) Manufacture of the positive electrode sheet

[0233] Positive electrode 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. (3) Manufacture of the negative electrode sheet

[0234] The negative electrode slurry is obtained by uniformly mixing artificial graphite (the negative electrode active material), carbon black (Super P) (the conductive agent), styrene-butadiene rubber (SBR) (the binder), and sodium carboxymethylcellulose (CMC) (the binder) in a mass ratio of 96.4:0.7:1.8:1.1 with an appropriate amount of solvent in deionized water. The negative electrode slurry is then applied to copper foil (the negative electrode current collector), and a negative electrode sheet is obtained by drying, cold pressing, stripping, and cutting. The surface density of the negative electrode sheet is 0.126 mg / mm². 2 The compressed density is 1.7 g / cm³. 3 That is the case. (4) Preparation of 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 thoroughly dried LiPF6 is dissolved in the above organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L. (5) Manufacturing of secondary batteries

[0236] A positive electrode sheet, a separator, and a negative electrode sheet are stacked in order and wound to obtain an electrode assembly. The electrode assembly is then placed in an outer casing, dried, and then injected with electrolyte. After processes such as vacuum sealing, standing, chemical formation, and shaping, a secondary battery is obtained. Examples 2-9

[0237] The secondary battery is manufactured using a method similar to that of Example 1, but the difference lies in the manufacturing parameters of the coating layer slurry in the separator manufacturing process; see Table 2 for details. Example 10

[0238] The secondary battery is manufactured in a manner similar to that of Example 1, but the difference is that in the manufacture of the separator, aluminum oxide for primary particle topography is further added when preparing the slurry of the coating layer. See Table 2 for specific parameters.

[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 10 wt% NaOH aqueous solution is added to 102 g of 50 wt% solids aluminum oxide dispersion (a mixture of secondary and primary particle topography, with a mass ratio of 5:1, an average particle size of secondary particles of 180 nm, and an average particle size of primary particles 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 in a mass ratio of 10:3 to form a mixture. Then, 1 wt% aqueous polyacrylic acid binder (based on the total weight of the coating layer after drying) is added to the mixture to obtain a coating layer slurry. Comparative Example 1

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

[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 a 50 wt% solids aluminum oxide dispersion (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 in a solution mass ratio of 10:3 to form a mixture. Then, 1 wt% aqueous polyacrylic acid binder (based on the total weight of the coating layer after drying) is added to the mixture to obtain a coating layer slurry. Comparative Example 2

[0242] The secondary battery is prepared in a similar manner to Example 1, but the difference is that in the preparation of the separator, unmodified nanocellulose C6 and unmodified secondary particle topography aluminum oxide were used when preparing the slurry for the coating layer. See Table 2 for specific parameters.

[0243] 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 a 50 wt% solid content aluminum oxide dispersion (secondary particle topography, with an average particle size of 180 nm for secondary particles) 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 in a mass ratio of 10:3 to form a mixture. Then, 1 wt% aqueous solution of polyacrylic acid (based on the total weight of the coating layer after drying) is added to the mixture to obtain a coating layer slurry. Comparative Example 3

[0244] The secondary battery is prepared in a similar manner to Example 1, but the difference is that unmodified nanocellulose C6 was used when preparing the slurry for the coating layer in the separator preparation. See Table 2 for specific parameters.

[0245] In Step 1, 10 g of unmodified nanocellulose C6 is uniformly mixed with 190 g of water as a 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 mixed solution. Then, a 1 wt% binder aqueous solution-type polyacrylic acid (based on the total weight of the dried coating layer) is added to the mixed solution 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 is uniformly mixed with 190 g of water as a solvent 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 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 mixed solution. Then, a 1 wt% binder aqueous solution-type polyacrylic acid (based on the total weight of the dried coating layer) is added to the mixed solution to obtain a slurry of the coating layer. Test Section[[ID=!13]] (1) Test of the zeta potential of the coating layer

[0248] Use a blade to 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 and a stirrer with a gear at a constant stirring speed (for example, it may be 2000 r / min), and then obtain a dispersion (the stirring time may be, for example, 1.5 hours). Place the obtained dispersion in a sample cell, and then use a zeta potentiometer 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 of Malvern, and the zeta potentiometer can use the Zetasizer Advance nanoparticle size potentiometer of 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 on 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 potentiometer to test to obtain the zeta potential of each solution. The sample cell can use the DTS1070 zeta potential capillary sample cell of Malvern, and the zeta potentiometer can use the Zetasizer Advance nanoparticle size potentiometer of 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) Test on the thermal shrinkage rate 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 with 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. Place an A4 sheet of paper, which has been placed on top of a piece of cardboard, into the forced-air oven. After the set time (1 hour in this application) has been reached, measure the length and width of the separator and denote the values ​​as a and b, respectively.

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

[0254] At 25°C, the time required for 100 mL of air to pass through the separator is measured, and for accuracy, the average value of five parallel samples is used as the test result. The Kumagai KRK Oken-type air permeability tester can be used as the test equipment. (5) Testing of the cycle performance of secondary batteries

[0255] At 25°C, the secondary battery is charged with a constant current of 1C to 4.2V, and then the constant voltage charging is continued until the current drops below 0.05C. At this point, the secondary battery is fully charged, and the charge capacity at this time, i.e., the first charge capacity, is recorded. After letting the secondary battery stand for 5 minutes, it is discharged with a constant current of 1C to 2.8V. This constitutes one charge-discharge cycle, and the discharge capacity at this time, i.e., the first discharge capacity, is recorded. The secondary battery is subjected to a cycle charge-discharge test according to the above method, and the discharge capacity after each cycle is recorded. The capacity retention rate (%) after 500 cycles of the secondary battery at 25°C = discharge capacity after 500 cycles / discharge capacity after 1st cycle × 100%. For accuracy, the average value of five parallel samples is used as the test result. (6) Heat box test of secondary batteries

[0256] At 25°C, the secondary batteries were charged with a constant current of 1C up to 4.2V, then continued with constant voltage charging until the current fell below 0.05C, and left to stand for 5 minutes. After that, each secondary battery was measured with a jig in a DHG-9070A DHG series high-temperature oven, and the temperature was raised from room temperature to 80±2°C at a rate of 5°C / min, held for 30 minutes, and then the temperature was raised at a rate of 5°C / min, with 30 minutes of holding for every 5°C increase. The change in surface temperature of the secondary battery was monitored during the heating process, and the oven temperature corresponding to when the temperature began to rise rapidly was the heat box expiration temperature of the secondary battery. A higher heat box expiration temperature indicates better thermal safety performance of the secondary battery. For accuracy, the average value of five parallel samples was used as the test result.

[0257] As can be seen from Tables 2 and 3, Examples 1 to 10 provide a coating layer containing nanocellulose (which constitutes a three-dimensional skeletal structure) and filler on both surfaces of the porous substrate, and adjust the zeta potential of the coating layer to less than 0 mV. This allows the resulting separator to have both low thermal shrinkage and high air permeability, and the resulting secondary battery to have both high thermal safety performance and good cycle performance. The inventors speculate that the main reason for this is that when the zeta potential of the coating layer is within an appropriate range, the slurry of the coating layer has good dispersibility, allowing for the formation of a coating layer with good surface density and thickness uniformity after drying of the slurry. This improves the heat resistance of the separator, and ensures that the pore distribution of the coating layer is uniform and the ionic conductivity of the coating layer is good, thus enabling the secondary battery to have both high thermal safety performance and good cycle performance.

[0258] The coating layers of the separators manufactured in Comparative Examples 1 to 4 all failed to satisfy the requirement of having a zeta potential of less than 0 mV. Furthermore, the separators could not achieve both low thermal shrinkage and high air permeability, and the secondary batteries could not achieve both high thermal safety performance and good cycle performance.

[0259] Furthermore, this application is not limited to the embodiments described above. The embodiments described above are merely illustrative, and any embodiment that has substantially the same configuration as the technical concept or exhibits the same effects within the scope of the technical solution provided by this application is included within the scope of this application. In addition, other forms constructed by adding various modifications to the embodiments that a person skilled in the art could conceive, or by combining some of the components of the embodiments, are also included within the scope of this application, as long as they do not depart from the spirit of this application.

[0260] [Table 2]

[0261] [Table 3]

Claims

1. A separator, The material comprises a porous substrate and a coating layer provided on at least one surface of the porous substrate, wherein the coating layer comprises a three-dimensional skeletal structure and a filler, at least a portion of the filler is filled into the three-dimensional skeletal structure, and the zeta potential of the coating layer is less than 0 mV. The zeta potential of the coating layer is obtained by measuring the zeta potential of the coating layer by taking 30 g of powder coating layer material, stirring and mixing it with 2000 g of deionized water to obtain a dispersion, and then measuring the zeta potential of the obtained dispersion using a zeta potential meter. Separator.

2. The zeta potential of the coating layer is -50 mV to -5 mV. The separator according to claim 1.

3. The material constituting the three-dimensional skeletal structure includes at least one type of organic rod-shaped material and organic tubular material. The separator according to claim 1.

4. The material constituting the three-dimensional skeletal structure includes at least one of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers. The separator according to claim 3.

5. The nanocellulose comprises at least one of cellulose nanofibers, cellulose nanowhiskers, and bacterial nanocellulose. The separator according to claim 4.

6. The material constituting the three-dimensional skeletal structure includes nanocellulose, The nanocellulose comprises a hydroxyl group and an anionic modified group. The separator according to claim 1.

7. The anionic modified group comprises at least one of an amine group, a carboxyl group, a sulfonic acid group, a boric acid group, and a phosphate group. The separator according to claim 6.

8. The molar ratio of the anionic modified group to the hydroxyl group is 1:4 to 4:

1. The separator according to claim 6.

9. The average diameter of the materials constituting the three-dimensional skeletal structure is 40 nm or less. The separator according to claim 1.

10. The average length of the material constituting the three-dimensional skeletal structure is 100 nm to 600 nm, and / or The aspect ratio of the material constituting the three-dimensional skeletal structure is 5 to 60. The separator according to claim 1.

11. The filler includes at least one type of filler particle for primary particle topography and filler particle for secondary particle topography. The separator according to claim 1.

12. The filler comprises both primary particle topography filler particles and secondary particle topography filler particles simultaneously. The separator according to claim 11.

13. The filler particles in the aforementioned primary particle topography satisfy at least one of the following conditions (1) to (3): (1) The average particle size of the filler particles in the primary particle topography is 200 nm to 800 nm. (2) The BET specific surface area of ​​the filler particles in the primary particle topography is 10 m². 2 / g or less, (3) Based on the total weight of the coating layer, the content of filler particles in the primary particle topography is 30 wt% or less. The separator according to claim 11.

14. The filler particles in the aforementioned secondary particle topography satisfy at least one of the following conditions (1) to (3): (1) The average particle size of the filler particles in the secondary particle topography is 200 nm or less. (2) The BET specific surface area of ​​the filler particles in the secondary particle topography is 20 m 2 / g or more, (3) Based on the total weight of the coating layer, the content of filler particles in the secondary particle topography is 60 wt% or more. The separator according to claim 11.

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

1. The separator according to claim 1.

16. The filler comprises at least one of inorganic particles and organic particles. The separator according to claim 1.

17. Based on the total weight of the coating layer, the content of the three-dimensional skeletal structure in the coating layer is 6 wt% to 35 wt%, and / or The mass ratio of the three-dimensional skeletal structure to the filler is 1:2 to 1:15.

5. The separator according to claim 1.

18. The coating layer further comprises a non-particulate binder. The separator according to claim 1.

19. The non-particulate binder comprises and / or an aqueous solution type binder. 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 claim 18.

20. The thickness of the porous substrate is 6 μm or less, and / or, The thickness of the coating layer is 1 μm or less. The separator according to claim 1.

21. The separator further includes an adhesive layer provided on at least a portion of the surface of the coating layer, and the adhesive layer includes a particulate binder. The separator according to claim 1.

22. The particulate binder comprises at least one of the following: a homopolymer or copolymer of an acrylic acid ester monomer, a homopolymer or copolymer of an acrylic acid monomer, or a homopolymer or copolymer of a fluorine-containing olefin monomer. The separator according to claim 21.

23. 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 hour is 5% or less. (2) The lateral thermal shrinkage rate of the separator at 150°C for 1 hour is 5% or less. (3) The longitudinal tensile strength of the separator is 2000 kg / cm². 2 That's all. (4) The lateral tensile strength of the separator is 2000 kg / cm². 2 That's all. (5) The wetted length of the separator is 30 mm or more. (6) The wetting rate of the separator is 3 mm / s or more. (7) The permeability of the separator is 300 s / 100 mL or less. The separator according to claim 1.

24. A method for manufacturing a separator according to claim 1, Step S1 provides a porous substrate, Step S2 involves preparing a coating layer slurry by mixing materials and fillers for forming a three-dimensional skeletal structure in a predetermined ratio in a solvent, The process includes a coating step S3, in which the slurry of the coating layer is applied to at least one surface of the porous substrate to form a coating layer, and then dried to obtain a separator. The separator comprises a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer comprising a three-dimensional skeletal structure and fillers, at least a portion of the fillers filling the three-dimensional skeletal structure, and the zeta potential of the coating layer being less than 0 mV. The zeta potential of the coating layer is obtained by measuring the zeta potential of the coating layer by taking 30 g of powder coating layer material, stirring and mixing it with 2000 g of deionized water to obtain a dispersion, and then measuring the zeta potential of the obtained dispersion using a zeta potential meter. A method for manufacturing separators.

25. The pH of the slurry of the coating layer is 5 to 10. and / or, The static viscosity of the slurry of the coating layer is 1000 mPa·s or less. The method according to claim 24.

26. The slurry of the coating layer is obtained by a method comprising: a step of preparing a nanocellulose solution having a pH between 5 and 9 and a zeta potential of less than 0 mV, the step of mixing nanocellulose having an anionic modified group with water to prepare the nanocellulose solution; a step of preparing a filler solution having a pH of 7.5 or higher and a zeta potential of less than 0 mV; and a mixing step of mixing the nanocellulose solution and the filler solution in a predetermined ratio to obtain a slurry of the coating layer having a zeta potential of -5 mV or less. The method according to claim 24.

27. The concentration of the nanocellulose solution is 1 wt% to 10 wt%, and / or The concentration of the filler solution is 30 wt% to 60 wt%. The method according to claim 26.

28. The nanocellulose having an anionic modifying group is obtained by a method in which nanocellulose powder and a modification solution are mixed and reacted, then washed to remove impurities to obtain cellulose nanowhisker having an anionic modifying group, the pH of the obtained cellulose nanowhisker having anionic modifying group is adjusted to neutral, polished, and cut to obtain nanocellulose having anionic modifying group. The method according to claim 26.

29. The modified solution is an aqueous solution of sulfuric acid, an aqueous solution of boric acid, an aqueous solution of phosphoric acid, an aqueous solution of acetic acid, or an organic solvent of urea. The method according to claim 28.

30. The filler solution is obtained by 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. The method according to claim 26.

31. The base comprises at least one selected from KOH, NaOH, NaHCO3, LiOH, NH4OH, Mg(OH)2 and Na2CO3, The anionic surfactant comprises at least one selected from sulfonate-type anionic surfactants, carboxylate-type anionic surfactants, sulfate-type anionic surfactants, and phosphate-type anionic surfactants, and further optionally comprises at least one selected from alkylbenzene sulfonate, C12-C20 alkyl sulfonate, sodium polyacrylate, ammonium polyacrylate, sodium hydroxyethyl sulfate, and C12-C20 alkyl sulfate sodium. The nonionic surfactant comprises at least one selected from fluoroalkyl ethoxyglycol ethers and aliphatic alcohol polyoxyethylene ethers. The method according to claim 30.

32. The process further includes a two-coating step S4, in which a slurry containing particulate binder is applied to at least a portion of the surface of the coating layer and dried to form an adhesive layer. The method according to claim 24.

33. A separator comprising the separator described in any one of claims 1 to 23, Secondary battery.

34. A secondary battery as described in claim 33, Electrical consumption device.

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