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

Abstract

The present application provides a separator, a method for producing the same, and related secondary batteries and power consuming devices, the separator comprising a porous substrate and a coating disposed on at least one surface of the porous substrate, the coating comprising nanocellulose and a filler, the coating having an areal density of σg / m 2 the thickness of the coating located on one side of the porous substrate is H μm, and the separator satisfies 0.3≦σ≦1.65 and 0.7≦σ / H≦2.2. The separator provided by the present application is characterized by good heat resistance, high ionic conductivity, and good wettability and retention of an electrolyte, and thus a secondary battery using the separator can have high energy density, high thermal safety, and good capacity development characteristics.

Description

[Technical field]

[0001] This application claims priority to patent application PCT / CN2022 / 101261, entitled "Separator, Manufacturing Method Thereof, and Related Secondary Battery and Power Consumption Device," filed on June 24, 2022, the entire contents of which are incorporated herein by reference.

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

[0003] In recent years, secondary batteries have been widely used in energy storage power systems such as hydroelectric power plants, thermal power plants, wind power plants, and solar power plants, as well as in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military supplies, and aerospace. With the application and popularity of secondary batteries, their safety issues, especially thermal safety issues, have attracted more and more attention. However, the current methods used to improve the thermal safety of secondary batteries often do not help to balance the energy density and capacity performance of secondary batteries. Therefore, how to manufacture secondary batteries that combine the characteristics of high energy density, high thermal safety, and good capacity performance has become an important issue in secondary battery design. Summary of the Invention

[0004] The present application provides a separator, a method for producing the same, and a secondary battery and a power consuming device related thereto. The separator has the characteristics of good heat resistance, high ionic conductivity, and good wettability and retention of an electrolyte, and thus a secondary battery using the separator can have high energy density, high thermal safety, and good capacity.

[0005] A first aspect of the present application is a separator, comprising a porous substrate and a coating provided on at least one surface of the porous substrate, the coating comprising nanocellulose and a filler, and the areal density of the coating located on one side of the porous substrate is σ g / m 2 and the thickness of the coating located on one side of the porous substrate is H μm, and the separator satisfies 0.3 ≦ σ ≦ 1.65 and 0.7 ≦ σ / H ≦ 2.2, and provides a separator.

[0006] As a result of much research, the inventors of the present application have surprisingly found that a coating containing nanocellulose and a filler is provided on at least one surface of the porous substrate of the separator, and the areal density σ g / m 2 and the thickness H μm of the coating satisfy 0.3 ≦ σ ≦ 1.65 and 0.7 ≦ σ / H ≦ 2.2, and the obtained separator can have excellent heat resistance, high ionic conductivity, and excellent wettability and retention characteristics with respect to the electrolyte. As a result, it has been found that the secondary battery can have high energy density, high thermal safety, and good capacity performance characteristics.

[0007] In any embodiment of the present application, 0.6 ≦ σ ≦ 1.5, and optionally, 0.7 ≦ σ ≦ 1.3. Thereby, it is advantageous for obtaining the effect that the nanocellulose and the filler in the coating are more reliably connected.

[0008] In any embodiment of the present application, 0.9 ≦ σ / H ≦ 1.8, and optionally, 0.9 ≦ σ / H ≦ 1.6. Thereby, it is advantageous for obtaining the effect that the nanocellulose and the filler in the coating are more reliably connected.

[0009] In any embodiment of the present application, 0 < H ≦ 1.5, and optionally, 0.5 ≦ H ≦ 0.8. Thereby, it contributes to the improvement of the energy density of the secondary battery.

[0010] In any embodiment of the present application, the ionic conductivity of the porous substrate is λ 1mS / cm, and the ionic conductivity of the separator is λ 2 mS / cm, and the separator has a resistance of 1<λ 1 / λ 2 ≦3, optionally, 1.05≦λ 1 / λ 2 ≦1.8, which contributes to the transport of active ions and the capacity of the secondary battery.

[0011] In any embodiment of the present application, 0.5≦λ 1 ≦1.8, optionally, 1.0≦λ 1 ≦1.4.

[0012] In any embodiment of the present application, 0.2≦λ 2 ≦1.5, optionally, 0.5≦λ 2 ≦1.2.

[0013] In any embodiment of the present application, the nanocellulose comprises at least one of unmodified nanocellulose and modified nanocellulose, and optionally is modified nanocellulose.

[0014] In any embodiment of the present application, the modified nanocellulose comprises a modified group, the modified group comprising at least one of an amine group, a carboxylic acid group, an aldehyde group, a sulfonic acid group, a boric acid group, and a phosphoric acid group, and optionally comprising at least one of a sulfonic acid group, a boric acid group, and a phosphoric acid group. When nanocellulose has the above-mentioned specific modified group, it can effectively improve the heat resistance of the separator and improve the thermal safety of the secondary battery, while it is advantageous for nanocellulose and the filler to build a more stable spatial network structure, thereby further improving the ion transport properties and voltage breakdown resistance of the separator.

[0015] In any embodiment of the present application, the modified nanocellulose comprises a hydroxyl group and a modifying group, and the molar ratio of the modifying group to the hydroxyl group is 1:4 to 4:1, optionally 2:3 to 7:3, thereby further improving the heat resistance and ion transport properties of the separator.

[0016] In any embodiment of the present application, the aspect ratio of the nanocellulose is 5 to 80, optionally 10 to 40. This can further improve the ion transport properties of the separator.

[0017] In any embodiment of the present application, the average diameter of the nanocellulose is 40 nm or less, optionally 10 nm to 35 nm, which can further improve the ion transport properties and voltage breakdown resistance of the separator.

[0018] In any embodiment of the present application, the average length of the nanocellulose is 100 nm to 600 nm, optionally 200 nm to 450 nm, thereby further improving the heat resistance and ion transport properties of the separator.

[0019] In any embodiment of the present application, the filler includes at least one of inorganic particles and organic particles. The presence of the filler contributes to imparting a stable spatial network structure to the coating, thereby improving the ion transport properties and heat resistance of the separator, as well as the tensile strength, puncture resistance, and external pressure resistance of the separator.

[0020] In any embodiment of the present application, the decomposition temperature of the filler is 200° C. or higher. This allows the filler to have excellent thermal stability and to be less susceptible to decomposition, and can further improve the heat resistance of the separator.

[0021] In any embodiment of the present application, the inorganic particles include at least one of inorganic particles having a dielectric constant of 5 or greater, inorganic particles that are ionically conductive but do not store ions, and inorganic particles capable of undergoing electrochemical reactions.

[0022] In any embodiment of the present application, the inorganic particles having a dielectric constant of 5 or more are selected from the group consisting of boehmite, aluminum oxide, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, magnesium lithium silicate, magnesium sodium silicate, bentonite, hectorite, zirconium titanate, barium titanate, and Pb(Zr,Ti)O. 3 , Pb 1-m La m Zr 1-n Ti n O 3 , Pb(Mg 3 Nb 2 / 3 )O 3 -PbTiO 3 and at least one of these modified inorganic particles, <m<1、0<n<1である。

[0023] In any embodiment of the present application, the inorganic particles that are ionically conductive but do not store ions are Li 3 PO 4 , Lithium titanium phosphate Li x1 Ti y1 (PO 4 ) 3 , Lithium titanium aluminum phosphate Li x2 Al y2 Ti z1 (PO 4 ) 3 , (LiAlTiP) x3 O y3 Glass, Lithium lanthanum titanate Li x4 La y4 TiO 3 , Lithium germanium thiophosphate Li x5 Ge y5 P z2 S w , Lithium nitride Li x6 N y6 , SiS2 Mold Glass Li x7 S y7 S z3 , and P 2 S 5 Mold Glass Li x8 P y8 S z4 At least one of the following is included: <x1<2、0<y1<3、0<x2<2、0<y2<1、0<z1<3、0<x3<4、0<y3<13、0<x4<2、0<y4<3、0<x5<4、0<y5<1、0<z2<1、0<w<5、0<x6<4、0<y6<2、0<x7<3、0<y7<2、0<z3<4、0<x8<3、0<y8<3、0<z4<7である。

[0024] In any embodiment of the present application, the inorganic particles capable of undergoing an electrochemical reaction include at least one of a lithium-containing transition metal oxide, a lithium-containing phosphate, a carbon-based material, a silicon-based material, a tin-based material, and a lithium titanium compound.

[0025] In any embodiment of the present application, the organic particles include at least one of polyethylene particles, polypropylene particles, polystyrene particles, cellulose, cellulose modifiers, melamine resin particles, phenolic resin particles, polyester particles, organic silicone resin particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, polyaryletherketone particles, and copolymers of butyl acrylate and ethyl methacrylate, and optionally at least one of melamine formaldehyde resin particles, phenolic resin particles, polyester particles, organic silicone resin particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, and polyaryletherketone particles.

[0026] In any embodiment of the present application, the content of the nanocellulose in the coating is 8 wt% or more, optionally 10 wt% to 35 wt%, based on the total weight of the coating. When the content of nanocellulose is in a suitable range, it can ensure that the coating slurry has a more suitable viscosity and is more favorable for application. In addition, it is also favorable for the nanocellulose and the filler to build a stable spatial network structure, which can further improve the ion conducting ability, external force pressing resistance, and voltage breakdown resistance of the separator.

[0027] In any embodiment of the present application, the content of the filler in the coating is 50wt% or more, optionally 65wt%-90wt% based on the total weight of the coating, which can ensure that the coating slurry has a more suitable viscosity and is more convenient for application. In addition, it is advantageous to build a stable spatial network structure together with nanocellulose, which further improves the tensile strength, puncture resistance, and external pressure resistance of the separator.

[0028] In any embodiment of the present application, the mass ratio of the nanocellulose to the filler in the coating is 0.1 to 0.95, optionally 0.18 to 0.6, thereby further improving the overall properties of the separator, for example, the separator can have high tensile strength and good puncture resistance, external force pressure resistance and voltage breakdown resistance.

[0029] In any embodiment of the present application, the filler has a primary particle form, a secondary particle form formed by aggregation of primary particles, or a combination thereof. The filler in the form of secondary particles has a large specific surface area and is more compatible with nanocellulose, and can therefore build a stable spatial network structure together with nanocellulose, thereby further improving the performance of the separator. The filler in the form of primary particles has a large particle size, and can therefore better exert a supporting effect as a skeleton in the coating, thereby imparting an appropriate porosity and channel structure to the coating.

[0030] In any embodiment of the present application, the content of the filler in the form of primary particles in the coating is 50 wt% to 100 wt%, optionally 90 wt% to 99 wt%, based on the total weight of the filler.

[0031] In any embodiment of the present application, the average particle size Dv50 of the filler in the form of primary particles is from 100 nm to 800 nm, optionally from 200 nm to 400 nm.

[0032] In any embodiment of the present application, the average particle size Dv50 of the filler in the form of secondary particles is 200 nm or less, optionally 50 nm to 200 nm.

[0033] In any embodiment of the present application, the filler in the form of primary particles has a specific surface area of ​​10 m 2 / g or less, selectively, 4m 2 / g~9m 2 / g.

[0034] In any embodiment of the present application, the specific surface area of ​​the filler in the form of secondary particles is 20 m 2 / g or more, selectively, 25m 2 / g~50m 2 / g.

[0035] In any embodiment of the present application, the thickness of the porous substrate is 6 μm or less, and optionally 3 μm to 5 μm, which contributes to improving the energy density of the secondary battery.

[0036] In any embodiment of the present application, the porosity of the porous substrate is 30% to 60%, which is advantageous in further improving the ion transport properties of the separator while ensuring high heat resistance of the separator.

[0037] In any embodiment of the present application, the coating further comprises a non-particulate binder. Optionally, the non-particulate binder comprises an aqueous based binder, which provides advantages in the preparation and application of the coating slurry.

[0038] In any embodiment of the present application, the content of the non-particulate binder in the coating is less than 1 wt %, based on the total weight of the coating, which allows the use of less binder while maintaining high adhesion and good ion transport properties of the separator.

[0039] In any embodiment of the present application, the separator further includes an adhesive layer, the adhesive layer being provided on at least a portion of the surface of the coating, and the adhesive layer includes a particulate binder. The adhesive layer can prevent peeling of the coating and improve the safety of the secondary battery, as well as improve the interface between the separator and the electrodes, and improve the cycle characteristics of the secondary battery. Optionally, the particulate binder includes at least one of a homopolymer or copolymer of an acrylate monomer, a homopolymer or copolymer of an acrylic monomer, and a homopolymer or copolymer of a fluorine-containing olefin monomer.

[0040] In any embodiment of the present application, the separator has a longitudinal heat shrinkage rate at 150° C. for 1 hour of 6.5% or less, optionally 0.5% to 3%.

[0041] In any embodiment of the present application, the separator has a transverse heat shrinkage rate at 150° C. for 1 h of 6.5% or less, optionally 0.5% to 3%.

[0042] The separator of the present application has a low thermal shrinkage rate in both the transverse and longitudinal directions at a high temperature of 150° C., which can further improve the safety of the secondary battery.

[0043] In any embodiment of the present application, the separator has a longitudinal tensile strength of 2000 kg / cm 2 Above 2500kg / cm 2 ~4500kg / cm 2 It is.

[0044] In any embodiment of the present application, the separator has a transverse tensile strength of 2000 kg / cm 2 Above 2500kg / cm 2 ~4500kg / cm 2 It is.

[0045] The separator of the present application has high tensile strength in both the transverse and longitudinal directions, which reduces the probability of the separator being broken when the secondary battery swells, thereby further improving the safety of the secondary battery.

[0046] In any embodiment of the present application, the wetted length of the separator is 30 mm or more, optionally 30 mm to 80 mm.

[0047] In any embodiment of the present application, the wetting speed of the separator is 3 mm / s or more, optionally 3 mm / s to 10 mm / s.

[0048] The separator of the present invention has excellent electrolyte wettability, which can improve the ion transport properties and the capacity of the secondary battery.

[0049] In any embodiment of the present application, the separator has an air permeability of 220 s / 100 mL or less, optionally 100 s / 100 mL to 180 s / 100 mL. The separator of the present application has good air permeability, thereby improving ion transport properties.

[0050] A second aspect of the present application is a method for producing the separator according to the first aspect of the present application, Step S1 of providing a porous substrate; A coating slurry preparation step S2 in which nanocellulose and a filler are mixed in a solvent in a predetermined ratio to prepare a coating slurry; A coating step S3 of coating the coating slurry onto at least one surface of the porous substrate to form a coating, and then drying to obtain a separator; The separator comprises a porous substrate and a coating disposed on at least one surface of the porous substrate, the coating comprising nanocellulose and a filler, the coating having an areal density of σg / m 2 a thickness of the coating located on one side of the porous substrate is H μm, and the separator satisfies 0.3≦σ≦1.65 and 0.7≦σ / H≦2.2.

[0051] The present method of manufacturing the separator produces a coating in a single application, greatly simplifying the process flow for producing the separator.

[0052] In an optional embodiment of the present application, the method further includes a secondary application step S4 in which a slurry including a particulate binder is applied to at least a portion of the surface of the coating and dried to form an adhesive layer.

[0053] A third aspect of the present application provides a secondary battery comprising the separator according to the first aspect of the present application or the separator produced by the method of the second aspect of the present application.

[0054] A fourth aspect of the present application provides a power consuming device including the secondary battery according to the third aspect of the present application. Effect of the Invention

[0055] The separator according to the present application has the characteristics of good heat resistance, high ionic conductivity, and good wettability and retention of electrolyte, which allows the secondary battery to have high energy density, high thermal safety, and good capacity. The power consumption device according to the present application includes the secondary battery according to the present application, and therefore has at least the same advantages as the secondary battery. [Brief description of the drawings]

[0056] In order to more clearly describe the technical solutions of the embodiments of the present application, the drawings that need to be used in the embodiments of the present application are briefly described below. It is obvious that the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on these drawings without creative efforts. [Figure 1] 1 is a schematic diagram of an embodiment of a secondary battery of the present application. [Diagram 2] FIG. 2 is an exploded schematic view of the secondary battery of FIG. 1 according to the embodiment. [Diagram 3] FIG. 1 is a schematic diagram of an embodiment of a battery module of the present application. [Figure 4] FIG. 1 is a schematic diagram of an embodiment of a battery pack of the present application. [Diagram 5] 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4. [Figure 6] 1 is a schematic diagram of an embodiment of a power consuming device including a secondary battery of the present application as a power source. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] Hereinafter, the separator specifically disclosed in the present application, its manufacturing method, and the related secondary battery and power consumption device will be described in detail with appropriate reference to the drawings. However, unnecessary detailed description may be omitted. For example, detailed description of already known matters and duplicated description of the same actual configuration may be omitted. This is to avoid the following description from becoming unnecessarily redundant and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0058] A "range" disclosed in this application is defined by a lower limit and an upper limit, and a particular range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner may or may not include the endpoint values ​​and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also envisioned. Furthermore, if minimum range values ​​1 and 2 are listed and maximum range values ​​3, 4, and 5 are listed, then the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all envisioned. In this application, unless otherwise stated, the numerical range "a-b" represents 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 "0-5" means that all real numbers between "0-5" are listed herein, and "0-5" is merely an abbreviation for combinations of these numbers. Additionally, when describing a parameter as an integer greater than or equal to 2, this is equivalent to disclosing that the parameter is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0059] Unless otherwise specified, all and any embodiments of the present application can be combined with each other to form a new technical solution, and such solution should be considered as being included in the disclosure of the present application.

[0060] Unless otherwise specified, all and any technical features of the present application can be combined with each other to form a new technical solution, and such technical solution should be considered as included in the disclosure of the present application.

[0061] Unless otherwise specified, all steps in the present application can be performed sequentially or randomly, and are preferably performed sequentially. For example, when the method includes steps (a) and (b), it means that the method can include steps (a) and (b) performed sequentially, or can include steps (b) and (a) performed sequentially. For example, a statement that the method may further include step (c) means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b).

[0062] Unless otherwise specified, the terms "including," "having," and "comprising" in this application are intended to be open-ended but may also be closed-ended. For example, "including," "having," and "comprising" may mean that other elements not listed are included or included, or that only the listed elements are included, included, or included.

[0063] In this application, unless otherwise specified, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions satisfy 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).

[0064] As used herein, the terms "plurality" and "plurality" refer to two or more than two.

[0065] Unless otherwise specified, terms used in this application have their commonly understood meanings as commonly understood by those of ordinary skill in the art.

[0066] Unless otherwise specified, the values ​​of each parameter referred to in this application can be measured using various test methods commonly used in the field, for example, according to the test methods shown in the examples of this application.

[0067] 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 disposed between the positive electrode sheet and the negative electrode sheet and serves mainly to prevent short circuits between the positive electrode and the negative electrode, and also allows active ions to pass freely through the separator to form a circuit.

[0068] With the application and popularization of secondary batteries, the requirements for the energy density of secondary batteries are increasing. Thinning the separator is an effective means for improving the energy density of secondary batteries and reducing the internal resistance of the battery. Currently, the separators used in commercially available secondary batteries are usually polyolefin porous films with melting points between 130°C and 160°C, such as polyethylene porous films, polypropylene porous films, or polypropylene / polyethylene / polypropylene three-layer composite films. As a result, when the thickness of the separator becomes thin, the heat resistance of the separator becomes poor, and when the separator is exposed to heat, it undergoes severe shrinkage, resulting in an increased risk of short circuit between the positive and negative electrodes.

[0069] Furthermore, the separator is also required to have good wettability and retention of the electrolyte. The gradual drying and failure of the separator due to long-term charging and discharging of the secondary battery is an important cause of the capacity reduction of the secondary battery. If the separator dries out, the internal resistance of the battery increases, making it impossible to sufficiently charge and discharge the battery, which in turn accelerates the capacity reduction of the secondary battery and significantly shortens the service life of the secondary battery. Furthermore, if the separator becomes thin, the wettability and retention of the electrolyte of the separator becomes even worse, which also accelerates the capacity reduction.

[0070] To solve the above problems, the main countermeasure currently used is to coat a heat-resistant inorganic ceramic layer on the polyolefin porous membrane to increase the mechanical strength of the separator, reduce the degree of shrinkage when the separator is subjected to heat, and reduce the risk of short circuit between the positive and negative electrodes. However, the large particle size of commercially available inorganic ceramic particles causes an increase in the overall thickness of the separator, making it difficult to balance with the energy density of the secondary battery, and especially in the field of power batteries, adversely affecting the increase in mileage. In addition, the large particle size of commercially available inorganic ceramic particles means that the number of ceramic layers on the polyolefin porous membrane is small (usually 5 layers or less), and as a result, the improvement effect on the heat resistance of the separator is limited.

[0071] Nano-sizing inorganic ceramic particles can reduce the thickness of the coating and reduce the adverse effect on the energy density of the secondary battery, but the coating formed with nano-sizing inorganic ceramic particles has a low porosity and is prone to clogging the micropores of the polyolefin porous membrane, leading to a decrease in the porosity of the entire separator and an increase in ion impedance, and is also disadvantageous to the transport of active ions. In addition, nano-sizing inorganic ceramic particles have a large specific surface area and contact each other in the form of point contact, so a large amount of binder is required to ensure adhesion between the particles, but if the amount of binder used is too large, the pores are likely to be clogged, which is disadvantageous to the rate characteristics of the secondary battery, for example, dendrites are likely to form on the surface of the negative electrode, and is also disadvantageous to the capacity and energy density of the secondary battery.

[0072] Therefore, it is difficult for the separators in the prior art to achieve high energy density, high thermal safety, and good capacity performance in a secondary battery.

[0073] As a result of their research, the inventors of the present application have surprisingly found that by providing a coating containing nanocellulose and a filler on the surface of the porous substrate of the separator, and by optimizing the relationship between the surface density and thickness of the coating, the separator can have good heat resistance, high ionic conductivity, and excellent wettability and retention of the electrolyte, and further, the secondary battery can have high energy density, high thermal safety, and good capacity display properties. Separator

[0074] Specifically, a first aspect of an embodiment of the present application includes a porous substrate and a coating provided on at least one surface of the porous substrate, the coating comprising nanocellulose and a filler, the coating having an areal density of σg / m 2 the coating located on one side of the porous substrate has a thickness of H μm, and the separator satisfies 0.3≦σ≦1.65 and 0.7≦σ / H≦2.2.

[0075] As a result of much research, the inventors of the present application have unexpectedly discovered that a coating containing nanocellulose and a filler is provided on at least one surface of a porous substrate of a separator, and the surface density of the coating is σg / m 2 They have found that when the σ / H thickness H μm satisfies 0.3≦σ≦1.65 and 0.7≦σ / H≦2.2, the obtained separator can have excellent heat resistance, high ionic conductivity, and excellent wettability and retention of the electrolyte, and as a result, the secondary battery can have high energy density, high thermal safety, and good capacity display properties.

[0076] Although the mechanism is not yet fully clear, the inventors of the present application speculate that possible causes include the following points. First, by adjusting the surface density and thickness of the coating within the above range of the present application, the nanocellulose and filler in the coating contribute to constructing a stable spatial network structure, thereby increasing the ion conduction channel, which is favorable for the transport of active ions and the capacity of the secondary battery. Second, since the nanocellulose and filler in the coating construct a stable spatial network structure, the coating can have uniform nanopores, and the separator can also have good liquid absorption properties, wettability and retention properties for the electrolyte. Third, by adjusting the surface density and thickness of the coating within the above range of the present application, the coating can also contribute to having high heat resistance, reducing the degree of shrinkage of the separator when heated, reducing the risk of short circuit between the positive and negative electrodes, and providing high thermal safety to the secondary battery. Fourth, since the coating of the present application has high heat resistance, it is possible to select a thinner porous substrate, and the secondary battery can also have a high energy density.

[0077] The areal density of said coating, σg / m 2 and thickness H μm satisfy 0.7≦σ / H≦2.2. For example, σ / H may be 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, or a range of values ​​greater than or equal to 0.8. In some embodiments, the areal density σ g / m 2 and the thickness Hμm satisfies 0.8≦σ / H≦2.0, 0.85≦σ / H≦1.8, 0.9≦σ / H≦1.8, 0.9≦σ / H≦1.7, 0.9≦σ / H≦1.6, or 0.9≦σ / H≦1.5, which is advantageous for obtaining the effect of more reliably connecting the nanocellulose and the filler in the coating, and for example, a coating having better heat resistance and wettability and retention to the electrolyte can be formed.

[0078] The areal density of said coating, σg / m 2satisfies 0.3 ≦ σ ≦ 1.65. For example, σ may be in the range consisting of any of the numerical values such as 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, or more. In some embodiments, optionally, the areal density σ g / m of the coating 2 satisfies 0.4 ≦ σ ≦ 1.5, 0.5 ≦ σ ≦ 1.5, 0.6 ≦ σ ≦ 1.5, 0.7 ≦ σ ≦ 1.5, 0.7 ≦ σ ≦ 1.4, 0.7 ≦ σ ≦ 1.3, or 0.7 ≦ σ ≦ 1.2. Thereby, it is advantageous for obtaining the effect that the nanocellulose and the filler in the coating are more reliably connected, and for example, a coating excellent in heat resistance, wettability with respect to the electrolyte, and retention can be formed.

[0079] In some embodiments, optionally, the thickness H μm of the coating satisfies 0 < H ≦ 1.5. For example, H may be in the range consisting of any of the numerical values such as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, or more. More optionally, 0 < H ≦ 1.4, 0 < H ≦ 1.3, 0 < H ≦ 1.2, 0 < H ≦ 1.1, 0 < H ≦ 1.0, 0 < H ≦ 0.9, 0 < H ≦ 0.8, 0.1 ≦ H ≦ 0.8, 0.2 ≦ H ≦ 0.8, 0.3 ≦ H ≦ 0.8, 0.4 ≦ H ≦ 0.8, or 0.5 ≦ H ≦ 0.8. Thereby, it contributes to the improvement of the energy density of the secondary battery.

[0080] As a result of further research, the inventors found that the ionic conductivity λ of the porous substrate 1 mS / cm and the ionic conductivity λ of the separator 2 mS / cm satisfy 1 < λ 1 / λ 2 ≦ 3, the separator can ensure good air permeability, wettability with respect to the electrolyte, and retention, and thereby contribute to the transport of active ions and the capacity performance of the secondary battery. Also, λ 1 / λ 2If λ is greater than 3, the porosity of the coating is too small, or the coating has poor wettability and retention of the electrolyte, which increases the ion impedance of the separator and effectively avoids the transport of active ions and the capacity of the secondary battery. 1 / λ 2 ≦2, 1.0<λ 1 / λ 2 ≦1.8, 1.0<λ 1 / λ 2 ≦1.7, 1.0<λ 1 / λ 2 ≦1.6, 1.0<λ 1 / λ 2 ≦1.5, 1.0<λ 1 / λ 2 ≦1.4, 1.0<λ 1 / λ 2 ≦1.3, 1.05≦λ 1 / λ 2 ≦2, 1.05≦λ 1 / λ 2 ≦1.8, 1.05≦λ 1 / λ 2 ≦1.7, 1.05≦λ 1 / λ 2 ≦1.6, 1.05≦λ 1 / λ 2 ≦1.5, 1.05≦λ 1 / λ 2 ≦1.4 or 1.05≦λ 1 / λ 2 ≦1.3.

[0081] In some embodiments, the ionic conductivity, λ, of the porous substrate is 1 mS / cm is 0.5≦λ 1 ≦1.8, and optionally, 1.0≦λ 1 ≦1.4.

[0082] In some embodiments, the separator has an ionic conductivity λ 2 mS / cm is 0.2≦λ 2 ≦1.5, and optionally, 0.5≦λ 2 ≦1.2.

[0083] The ionic conductivity of the porous substrate and separator can be measured through an AC impedance spectrum experiment. Specifically, the porous substrate or separator is cut into a disk of a given area, baked, and then placed between two stainless steel electrodes to absorb a sufficient amount of electrolyte, and then sealed to obtain a coin cell, and an AC impedance spectrum experiment is performed. The intersection point between the central straight line part of the obtained AC impedance spectrum and the real axis is the self-resistance of the electrolyte. The ionic conductivity of the porous substrate or separator is then calculated by the formula σ=(L / A)×R, where L is the thickness of the porous substrate or separator (cm), and A is the contact area between the stainless steel electrodes and the porous substrate or separator (cm). 2 ), R represents the self-resistance (mS) of the electrolyte. The electrolyte used was an organic solvent obtained by mixing ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) in a mass ratio of 30:50:20, and then thoroughly dried LiPF 6 In the above organic solvent, an electrolyte solution having a concentration of 1 mol / L can be prepared.

[0084] In some embodiments, the porosity of the porous substrate may be 30% to 60%. When the porosity of the porous substrate is within an appropriate range, it is advantageous to further improve the ion transport properties of the separator while ensuring high heat resistance of the separator.

[0085] In some embodiments, the thickness of the porous substrate may be 6 μm or less, and optionally 3 μm to 5 μm. The coating of the present application can significantly improve the heat resistance of the separator, thereby enabling the porous substrate to be further thinned, thereby contributing to improving the energy density of the secondary battery.

[0086] In the present application, the material of the porous substrate is not particularly limited, and any substrate having good known chemical stability and mechanical stability, such as at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, may be used.The porous substrate may be a single layer membrane or a multi-layer composite membrane.When the porous substrate is a multi-layer composite membrane, the material of each layer may be the same or different.

[0087] One way to improve the energy density of secondary batteries is to increase the voltage, e.g., use of a high-voltage positive electrode active material. However, as the voltage increases, the stability of the separator is significantly affected, so the separator is also required to have good voltage breakdown resistance.

[0088] The separator coating of the present application includes nanocellulose, which is a general term for cellulose with a one-dimensional size at the nano level (for example, within 100 nm), and combines the properties of cellulose with the properties of nanoparticles. Nanocellulose may be a polymeric nanomaterial extracted from wood, cotton, etc. in nature by any one or more means such as chemical, physical, biological, etc., and has advantages such as a wide supply source, low cost, biodegradability, high modulus, and high specific surface area, making it an excellent alternative to traditional petrochemical resources and effectively alleviating problems such as environmental pollution and shortage of petrochemical resources. Nanocellulose also has good high temperature resistance properties, and the change in volume when exposed to heat is small, thereby improving the heat resistance of the separator. In addition, nanocellulose has a smaller density than conventional inorganic ceramic particles, so that the weight of the secondary battery can be reduced, and the weight energy density of the secondary battery can be improved. In addition, nanocellulose can also form minute nanopores in the coating to prevent current leakage, thereby allowing the separator to have both high ion transport properties and good voltage breakdown resistance.

[0089] In some embodiments, the nanocellulose may comprise at least one of cellulose nanofibers (Cellulose nanofibrils, CNF, also called nanofibrillated cellulose or microfibrillated cellulose), cellulose nanowhiskers (Cellulose nanocrystals, CNC, also called cellulose nanocrystals or nanocrystalline cellulose), and bacterial nanocellulose (BNC, also called bacterial cellulose or microbial cellulose), and optionally cellulose nanowhiskers. Cellulose nanowhiskers have a high degree of crystallinity and therefore a low hydrophilicity, which is favorable for the evacuation of moisture during drying, thereby allowing the coating of the present application to have a low moisture content.

[0090] In some embodiments, the nanocellulose comprises at least one of unmodified nanocellulose (also called hydroxynanocellulose) and modified nanocellulose, and optionally is modified nanocellulose.

[0091] The modified nanocellulose comprises modifying groups, in some embodiments, the modifying groups comprise at least one of an amine group, a carboxylic acid group, an aldehyde group, a sulfonic acid group, a boric acid group, and a phosphate group, and optionally at least one of a sulfonic acid group, a boric acid group, and a phosphate group.

[0092] After further research, the inventors found that when nanocellulose has the above-mentioned specific modified group, it can effectively improve the heat resistance of the separator and improve the thermal safety of the secondary battery, while nanocellulose and filler are favorable for constructing a more stable spatial network structure, so that the ion transport properties and voltage breakdown resistance of the separator can be further improved, which is favorable for cooperation with high-voltage positive electrode active materials and improves the energy density of the secondary battery. In addition, the presence of the modified group can also reduce the proportion of hydroxyl groups, which can ensure that the coating slurry has a more suitable viscosity and is more favorable for application, and can further improve the production efficiency and coating uniformity of the separator.

[0093] In some embodiments, the modified nanocellulose comprises a hydroxy group and a modifying group, and the molar ratio of the modifying group to the hydroxy group may be 1:4 to 4:1, and optionally 2:3 to 7:3. When the molar ratio of the modifying group to the hydroxy group is within an appropriate range, the heat resistance and ion transport properties of the separator can be further improved. In addition, if the molar ratio of the modifying group to the hydroxy group is too small, the effect of further improving the heat resistance and ion transport properties of the separator by the modifying group may be insufficient, and if the molar ratio of the modifying group to the hydroxy group is too large, the wettability and retention of the separator with respect to the electrolyte may be deteriorated, thereby deteriorating the ion transport properties of the separator, further adversely affecting the cycle properties and safety of the secondary battery, and may also cause a decrease in the heat resistance of the separator, and further adversely affecting the thermal safety of the secondary battery. This can be effectively avoided.

[0094] The type of modified group in nanocellulose can be measured by infrared spectroscopy. For example, the type of modified group can be determined by measuring the infrared spectrum of the material and determining the characteristic peaks contained therein. Specifically, the infrared spectrum analysis of the material can be measured using instruments and methods known in the art, for example, an infrared spectrometer (e.g., an IS10 Fourier transform infrared spectrometer manufactured by Nicolet, USA) in accordance with GB / T 6040-2019 Infrared Spectroscopy General Methods.

[0095] In some embodiments, the aspect ratio of the nanocellulose may be 5 to 80, and optionally 10 to 40. When the aspect ratio of the nanocellulose is within a suitable range, the ion transport properties of the separator can be further improved. In addition, if the aspect ratio of the nanocellulose is too small, the connection effect between the nanocellulose and the filler is poor, the heat resistance of the coating is poor, and during the baking process of the coating, a part of the nanocellulose is easily collapsed due to the lack of support by the filler, which is likely to cause the problem of clogging of the pores, inhibiting the transport of active ions and adversely affecting the cycle characteristics and capacity of the secondary battery. If the aspect ratio of the nanocellulose is too large, the nanopores caused by the nanocellulose become small, which can effectively avoid the deterioration of the ion transport properties of the separator.

[0096] In some embodiments, the average diameter of the nanocellulose may be 40 nm or less, and optionally 10 nm to 35 nm. When the average diameter of the nanocellulose is within a suitable range, the ion transport properties and voltage breakdown resistance of the separator can be further improved. In addition, when the average diameter of the nanocellulose is too large, the nanopores caused by the nanocellulose become large, which may cause deterioration of the voltage breakdown resistance of the separator, and further, the connection effect between the nanocellulose and the filler becomes poor, leading to deterioration of the heat resistance of the coating. In addition, during the baking process of the coating, a part of the nanocellulose is easily collapsed due to the lack of support by the filler, which is likely to cause problems such as clogging of the pores, which inhibits the transport of active ions, and adversely affects the cycle characteristics and capacity of the secondary battery.

[0097] In some embodiments, the average length of the nanocellulose may be 100 nm to 600 nm, and optionally 200 nm to 450 nm. When the average length of the nanocellulose is within a suitable range, the heat resistance and ion transport properties of the separator can be further improved. In addition, if the average length of the nanocellulose is too short, the connection effect between the nanocellulose and the filler is poor, leading to deterioration of the heat resistance of the coating, and during the baking process of the coating, a part of the nanocellulose is easily collapsed due to the lack of support by the filler, which is likely to cause problems with clogging of the pores, inhibiting the transport of active ions and adversely affecting the cycle characteristics and capacity of the secondary battery. If the average length of the nanocellulose is too long, the viscosity of the coating slurry increases and the fluidity deteriorates, which affects the application of the coating slurry, thereby affecting the quality of the obtained coating, for example, the heat resistance and ion transport properties of the separator.

[0098] The average length and average diameter of nanocellulose can be measured by the following method. A sample of 3.6 mm x 3.6 mm is cut out from any region of the separator, and the microstructure of the coating in the sample is plotted using a scanning electron microscope (e.g., ZEISS Sigma 300), and an SEM image is obtained by selecting high vacuum mode, operating voltage of 3 kV, and magnification of 30,000 times. From the obtained SEM image, multiple test areas (e.g., 5 or more) with a size of 0.5 μm x 0.5 μm are selected and their lengths are statistically analyzed, and then the average value of the length obtained for each test area is taken as the average length of nanocellulose. From the obtained SEM image, multiple test areas (e.g., 5 or more) with a size of 0.5 μm x 0.5 μm are selected and their diameters are statistically analyzed using Nano Measurer particle size distribution statistical software, and then the average value of the diameters obtained for each test area is taken as the average diameter of nanocellulose.

[0099] In some embodiments, the shape of the nanocellulose may include at least one of tubular (e.g., hollow tubular), fibrous, and rod-shaped. The appropriate shape of the nanocellulose is more advantageous for building a stable spatial network structure together with the filler, thereby further improving the ion transport properties and external force compression resistance of the separator.

[0100] In some embodiments, the content of the nanocellulose in the coating may be 8 wt% or more, optionally 10 wt% to 35 wt%, based on the total weight of the coating. When the content of nanocellulose is in a suitable range, it can ensure that the coating slurry has a more suitable viscosity and is more convenient for application, and further, it is favorable for the nanocellulose and the filler to build a stable spatial network structure, thereby further improving the ion conducting ability, external force pressing resistance, and voltage breakdown resistance of the separator.

[0101] During the long-term charge and discharge of the secondary battery, the microstructure of the positive and negative active materials changes irreversibly, which increases the volume of the entire battery, and especially in the case of high-speed charging of the secondary battery, the volume further increases when active ions are embedded in the negative active material. When the battery expands, the separator is subjected to a pressing and / or pulling action, which is likely to cause the separator to break, thereby increasing the risk of short circuit between the positive and negative electrodes. Therefore, the separator is also required to have good resistance to external pressure. The presence of the filler contributes to imparting a stable spatial network structure to the coating, which can improve the ion transport properties and heat resistance of the separator, and can also improve the tensile strength, puncture resistance, and external pressure resistance of the separator.

[0102] In some embodiments, the filler may include at least one of inorganic particles and organic particles.

[0103] In some embodiments, the decomposition temperature of the filler is selectively 200° C. or higher, so that the filler has excellent thermal stability and is not easily decomposed, and the heat resistance of the separator can be further improved.

[0104] Inorganic particles have excellent thermal stability and are not easily decomposed, and usually have hydroxyl groups on their surfaces, so they are easy to form a stable spatial network structure with nanocellulose. In some embodiments, the inorganic particles selectively include at least one of inorganic particles having a dielectric constant of 5 or more, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of electrochemical reactions.

[0105] Alternatively, the inorganic particles having a dielectric constant of 5 or more may be boehmite, aluminum oxide, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, magnesium lithium silicate, magnesium sodium silicate, bentonite, hectorite, zirconium titanate, barium titanate, Pb(Zr,Ti)O 3 (abbreviated as PZT), Pb 1-m La m Zr 1-n Ti n O 3 (Abbreviated as PLZT, 0 <m<1、0<n<1)、Pb(Mg 3 Nb 2 / 3 )O 3 -PbTiO 3 (abbreviated as PMN-PT), and at least one of these modified inorganic particles. Optionally, the modification method of each inorganic particle may be chemical modification and / or physical modification. The chemical modification method includes modification by a coupling agent (e.g., a silane coupling agent, a titanate coupling agent, etc.), modification by a surfactant, modification by polymer grafting, etc. The physical modification method may be mechanical force dispersion, ultrasonic dispersion, high energy treatment, etc. The modification treatment can reduce the aggregation of inorganic particles, so that the inorganic particles and nanocellulose can build a more stable and uniform spatial network structure. In addition, modifying the inorganic particles with a coupling agent, a surface active material, or a polymer having a specific functional group is also advantageous for improving the wettability and retention of the coating to the electrolyte, and the adhesion between the coating and the porous substrate.

[0106] Optionally, the inorganic particles that are ionically conductive but do not store ions are Li 3 PO 4 , Lithium titanium phosphate Li x1Ti y1 (PO 4 ) 3 、 lithium titanium aluminum phosphate Li x2 Al y2 Ti z1 (PO 4 ) 3 、 (LiAlTiP) x3 O y3 type glass, lithium lanthanum titanate Li x4 La y4 TiO 3 、 lithium germanium thiophosphate Li x5 Ge y5 P z2 S w 、 lithium nitride Li x6 N y6 、 SiS 2 type glass Li x7 Si y7 S z3 、 and P 2 S 5 type glass Li x8 P y8 S z4 may include at least one of them, where 0 < x1 < 2, 0 < y1 < 3, 0 < x2 < 2, 0 < y2 < 1, 0 < z1 < 3, 0 < x3 < 4, 0 < y3 < 13, 0 < x4 < 2, 0 < y4 < 3, 0 < x5 < 4, 0 < y5 < 1, 0 < z2 < 1, 0 < w < 5, 0 < x6 < 4, 0 < y6 < 2, 0 < x7 < 3, 0 < y7 < 2, 0 < z3 < 4, 0 < x8 < 3, 0 < y8 < 3, 0 < z4 < 7. Thereby, the ion transport characteristics of the separator can be further improved.

[0107] Optionally, the inorganic particles capable of causing the electrochemical reaction include at least one of lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials, and lithium titanium compounds.

[0108] The organic particles have excellent thermal stability and are not easily decomposed, which can improve the heat resistance of the separator. In addition, when the internal temperature of the secondary battery reaches the melting point of the organic particles due to overcharging or overheating, the organic particles melt and are absorbed into the micropores of the porous substrate by capillary action, which closes the pores and plays a role in breaking the circuit, which is advantageous in ensuring high safety of the secondary battery.

[0109] In some examples, the organic particles may include, but are not limited to, at least one of polyethylene particles, polypropylene particles, polystyrene particles, cellulose, cellulose modifiers (e.g., carboxymethyl cellulose), melamine resin particles, phenolic resin particles, polyester particles (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), organic silicone resin particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, polyaryletherketone particles, and copolymers of butyl acrylate and ethyl methacrylate (e.g., crosslinked polymers of butyl acrylate and ethyl methacrylate).

[0110] In some embodiments, the glass transition temperature of the organic particles may be 130° C. or higher, so that when the internal temperature of the secondary battery reaches 130° C., the organic particles do not change from a glass state to a viscous flow state, thereby avoiding severe shrinkage of the separator. More preferably, the organic particles include at least one of melamine formaldehyde resin particles, phenolic resin particles, polyester particles, organic silicone resin particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, and polyaryletherketone particles, but are not limited thereto.

[0111] In some embodiments, the content of the filler in the coating may be 50 wt% or more, optionally 65 wt% to 90 wt%, based on the total weight of the coating, to ensure that the coating slurry has a more suitable viscosity and is more convenient for application, and further favorably allows the filler and nanocellulose to build a stable spatial network structure, further improving the tensile strength, puncture resistance, and external pressure resistance of the separator.

[0112] In some embodiments, the mass ratio of nanocellulose to the filler in the coating may be 0.1 to 0.95, optionally 0.18 to 0.6, more preferably 0.18 to 0.6, thereby further improving the overall properties of the separator, for example, the separator can have high tensile strength and good puncture resistance, external force pressure resistance, and voltage breakdown resistance.

[0113] In some embodiments, the filler includes a primary particle form, a secondary particle form formed by aggregation of primary particles, or a combination thereof. The filler in the form of secondary particles has a large specific surface area and is more compatible with nanocellulose, and can therefore build a stable spatial network structure together with nanocellulose, thereby further improving the performance of the separator. The filler in the form of primary particles has a large particle size, and can therefore better exert a supporting effect as a skeleton in the coating, allowing the coating to have an appropriate porosity and channel structure.

[0114] In some embodiments, the amount of filler in the form of primary particles in the coating may be 50 wt% to 100 wt%, and optionally 90 wt% to 99 wt%, based on the total weight of the filler. In some embodiments, the amount of filler in the form of secondary particles in the coating may be less than 50 wt%, and optionally 1 wt% to 10 wt%, based on the total weight of the filler.

[0115] In some embodiments, the filler in the form of primary particles has an average particle size Dv50 of 100 nm to 800 nm, optionally 200 nm to 400 nm. In some embodiments, the filler in the form of secondary particles has an average particle size Dv50 of 200 nm or less, optionally 50 nm to 200 nm.

[0116] In some embodiments, the filler in the form of primary particles has a specific surface area of ​​10 m 2 / g or less, and optionally, 4m 2 / g~9m 2 In some embodiments, the specific surface area of ​​the filler in the form of secondary particles is 20 m 2 / g or more, and optionally, 25m 2 / g~50m 2 / g.

[0117] In some embodiments, the coating further comprises a non-particulate binder. In the present application, the type of the non-particulate binder is not particularly limited, and any material having good known adhesion can be selected.

[0118] Optionally, the non-particulate binder comprises an aqueous binder having the advantages of good thermodynamic stability and environmental protection, which is advantageous for the preparation and application of the coating slurry.As an example, the aqueous binder comprises at least one of an aqueous acrylic resin (e.g., a homopolymer of acrylic acid, methacrylic acid, sodium acrylate monomer, or a copolymer thereof with other comonomers), polyvinyl alcohol, isobutylene-maleic anhydride copolymer, and polyacrylamide.

[0119] Optionally, the content of the non-particulate binder in the coating is less than 1 wt % based on the total weight of the coating. The nanocellulose and filler in the coating of the present application can build a stable spatial network structure, so that the separator can maintain high adhesion and good ion transport properties under the premise of reducing the amount of binder used.

[0120] In some embodiments, the separator may further include an adhesive layer, the adhesive layer being provided on at least a portion of the surface of the coating, the adhesive layer including a particulate binder. The adhesive layer can prevent peeling of the coating to improve the safety of the secondary battery, as well as improve the interface between the separator and the electrodes to improve the cycle characteristics of the secondary battery.

[0121] Optionally, the particulate binder comprises at least one of a homopolymer or copolymer of an acrylate monomer, a homopolymer or copolymer of an acrylic monomer, and a homopolymer or copolymer of a fluorine-containing olefin monomer. The copolymerization monomer comprises at least one of an acrylate monomer, an acrylic monomer, an olefin monomer, a halogen-containing olefin monomer, a fluoroether monomer, and the like, but is not limited thereto.

[0122] Optionally, 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 another copolymerizable monomer, which may be at least one of an olefin monomer, a fluorine-containing olefin monomer, a chlorine-containing olefin monomer, an acrylate monomer, an acrylic monomer, and a fluoroether monomer. Optionally, the other comonomer may include at least one of trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ethers (e.g., perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE), perfluoro(propyl vinyl) ether (PPVE), perfluoro(1,3-m-dioxole), and perfluoro(2,2-dimethyl-1,3-m-dioxole) (PDD).

[0123] In some embodiments, the separator has a longitudinal heat shrinkage rate at 150° C. for 1 h of 6.5% or less, optionally 0.5% to 3%.

[0124] In some embodiments, the separator has a transverse heat shrinkage of 6.5% or less at 150° C. for 1 h, optionally 0.5% to 3%.

[0125] The separator of the present application has low thermal shrinkage in both the transverse and longitudinal directions at a high temperature of 150° C., which can further improve the safety of the secondary battery.

[0126] In some embodiments, the separator has a longitudinal tensile strength of 2000 kg / cm 2 Above 2500kg / cm 2 ~4500kg / cm 2 It is.

[0127] In some embodiments, the separator has a transverse tensile strength of 2000 kg / cm 2 Above 2500kg / cm 2 ~4500kg / cm 2 It is.

[0128] The separator of the present application has high tensile strength in both the horizontal and vertical directions, which reduces the probability of the separator being damaged when the secondary battery swells, thereby further improving the safety of the secondary battery.

[0129] In some embodiments, the separator has an air permeability of 220 s / 100 mL or less, optionally 100 s / 100 mL to 180 s / 100 mL. The separator of the present application has good air permeability, which can improve the ion transport properties.

[0130] In some embodiments, the wetted length of the separator is greater than or equal to 30 mm, optionally between 30 mm and 80 mm.

[0131] In some embodiments, the wetting rate of the separator is greater than or equal to 3 mm / s, optionally between 3 mm / s and 10 mm / s.

[0132] The separator of the present invention has excellent electrolyte wettability, which can improve the ion transport properties and the capacity of the secondary battery.

[0133] In this application, the average particle size Dv50 of the material has a meaning known in the art and can be measured by instruments and methods known in the art, for example, it can be tested using a laser particle size analyzer (e.g., Master Size 3000) with reference to the particle size distribution laser diffraction method of GB / T 19077-2016.

[0134] In this application, the specific surface area of ​​a material has a meaning known in the art and can be measured by instruments and methods known in the art. For example, it can be tested by the nitrogen gas adsorption specific surface area analysis test method with reference to GB / T 19587-2017 and calculated by the BET (Brunauer Emmett Teller) method. Alternatively, the nitrogen gas adsorption specific surface area analysis test can be performed by a specific surface area pore size analysis tester of Tri-Star 3020 type manufactured by Micromeritics, USA.

[0135] In this application, the heat shrinkage rate, tensile strength, and air permeability of the separator all have the meanings known in the art and can be measured by methods known in the art, for example, they can be tested with reference to the GB / T 36363-2018 standard.

[0136] In the present application, the wetting length and wetting speed of the separator both have the meanings known in the art and can be measured by methods known in the art. As an example of a test method, the separator is cut into a sample with a width of 5 mm and a length of 100 mm, and both ends of the sample are fixed and placed horizontally. 0.5 mg of electrolyte is dropped into the center of the sample, and after a predetermined time (1 min in the present application), an image is taken to measure the diffusion length of the electrolyte, thereby obtaining the wetting length and wetting speed of the separator. In order to ensure the accuracy of the test results, multiple samples (e.g., 5 to 10 samples) can be selected for testing, and an average value is calculated as the test result. The electrolyte is LiPF 2000, which is an organic solvent obtained by mixing ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) in a mass ratio of 30:50:20, and is thoroughly dried. 6 The electrolyte can be prepared by dissolving the above in the organic solvent to prepare an electrolyte solution having a concentration of 1 mol / L.

[0137] The above separator coating parameters (e.g., areal density, thickness, etc.) are all parameters of the coating on one side of the porous substrate. When the coating is provided on both sides of the porous substrate, it is considered to be within the scope of protection of the present application if the parameters of the coating on either side satisfy the present application. Manufacturing method

[0138] A second aspect of the present embodiment provides a method for producing a separator according to the first aspect of the present embodiment, comprising: a step S1 of providing a porous substrate; a step S2 of preparing a coating slurry by mixing nanocellulose and a filler in a solvent in a predetermined ratio; and a step S3 of applying the coating slurry onto at least one surface of the porous substrate to form a coating, which is then dried to obtain a separator, the separator comprising a porous substrate and a coating provided on at least one surface of the porous substrate, the coating comprising nanocellulose and a filler, and an areal density of the coating located on one side of the porous substrate being σg / m.2 the coating on one side of the porous substrate has a thickness of H μm, and the separator satisfies 0.3≦σ≦1.65 and 0.7≦σ / H≦2.2.

[0139] In some embodiments, in S2, the solvent may be water, for example, deionized water.

[0140] In some embodiments, the coating slurry in S2 may include other ingredients such as dispersants, wetting agents, binders, and the like.

[0141] In some embodiments, in S2, the solid content of the coating slurry can be controlled between 28% and 45%, for example, between 30% and 38%. When the solid content of the coating slurry is within the above range, it can effectively reduce problems with the coating film surface and reduce the probability of uneven coating, thereby further improving the energy density and safety of the secondary battery.

[0142] In some embodiments, in S2, nanocellulose can be obtained by the following method: S21: providing a cellulose powder having a whiteness of 80% or more; S22: mixing the obtained cellulose powder with a modifying solution to react, and then washing to remove impurities to obtain cellulose nanowhiskers; S23: adjusting the pH of the obtained cellulose nanowhiskers to neutral (e.g., pH 6.5 to 7.5), and further grinding and cutting to obtain nanocellulose.

[0143] Optionally, in S21, the cellulose powder having a whiteness of 80% or more may be commercially available or may be obtained by a chemical method (e.g., acid hydrolysis method, alkali treatment method, Tempo contact oxidation method), a biological method (e.g., enzyme treatment method), a mechanical method (e.g., ultrafine grinding, ultrasonic crushing, high-pressure homogenization), etc. The fiber raw material for producing the cellulose powder having a whiteness of 80% or more may include at least one of plant fibers, such as cotton fibers (e.g., cotton fiber, kapok fiber), hemp fibers (e.g., sisal fiber, ramie fiber, jute fiber, flax fiber, hemp fiber, Manila hemp fiber, etc.), palm fiber, wood fiber, bamboo fiber, and grass fiber.

[0144] In some embodiments, the cellulose powder having a whiteness of 80% or more may be produced by the following method: After opening the fiber raw material to remove foreign matter, the fiber raw material is steamed in an alkaline solution (e.g., a NaOH aqueous solution having a concentration of 4 wt% to 20 wt%, optionally 5 wt% to 15 wt%), and then the fiber is washed with water to remove impurities (e.g., 3 to 6 times of washing), bleached (e.g., using sodium hypochlorite and / or hydrogen peroxide), pickled to remove impurities, washed with water to remove impurities, dehydrated, and flash dried to obtain a cellulose powder.

[0145] In some embodiments, in S22, the denaturing solution may be an acid solution (e.g., an aqueous sulfuric acid solution, an aqueous boric acid solution, an aqueous phosphoric acid solution, an aqueous acetic acid solution) or an alkaline solution (e.g., an organic solvent solution of urea). Optionally, the denaturing solution is an acid solution.

[0146] Alternatively, the concentration of the acid solution may be 5 wt% to 80 wt%. When an aqueous sulfuric acid solution is used as the modified solution, the concentration of the acid solution may be 40 wt% to 80 wt%, thereby obtaining nanocellulose having sulfonic acid groups. When an aqueous boric acid solution is used as the modified solution, the concentration of the acid solution may be 5 wt% to 10 wt%, thereby obtaining nanocellulose having boric acid groups. When an aqueous phosphoric acid solution is used as the modified solution, the concentration of the acid solution may be 45 wt% to 75 wt%, thereby obtaining nanocellulose having phosphoric acid groups. When an aqueous acetic acid solution is used as the modified solution, the concentration of the acid solution may be 40 wt% to 80 wt%, thereby obtaining nanocellulose having carboxylic acid groups.

[0147] Alternatively, the urea organic solvent solution may be a urea xylene solution, thereby obtaining nanocellulose having amine groups.

[0148] In some embodiments, in S22, optionally, the mass ratio of the cellulose powder to the denaturing solution is 1:2.5 to 1:50, and optionally, is 1:5 to 1:30.

[0149] When a sulfuric acid aqueous solution is used as the modifying solution, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30. When a boric acid aqueous solution is used as the modifying solution, the mass ratio of the cellulose powder to the acid solution may be 1:20 to 1:50. When a phosphoric acid aqueous solution is used as the modifying solution, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30. When an acetic acid aqueous solution is used as the modifying solution, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30. When a urea organic solvent solution is used as the modifying solution, the mass ratio of the cellulose powder to the urea organic solvent solution may be 1:4 to 1:40.

[0150] In some embodiments, in S22, when the denaturing solution is an acid solution, the reaction may be carried out under conditions of 80°C or less, optionally at 30°C to 60°C, and the reaction time between the cellulose powder and the denaturing solution may be 0.5h to 4h, optionally at 1h to 3h.

[0151] In some embodiments, in S22, when the denaturing solution is an alkaline solution, the reaction may be carried out under conditions of 100°C to 145°C, and the reaction time between the cellulose powder and the denaturing solution may be 1 h to 5 h.

[0152] In some embodiments, a grinder may be used for grinding and a high-pressure homogenizer may be used for cutting in S23. By adjusting the grinding parameters of the grinder (e.g., grinding times, grinding time, etc.) and the cutting parameters of the high-pressure homogenizer, nanocellulose with various average diameters and / or different average lengths may be obtained.

[0153] In some embodiments, a coater is used for the coating in S3. In the present application, the model number of the coater is not particularly limited, and for example, a commercially available coater can be adopted. The coater includes a gravure roller for transferring the coating slurry onto the porous substrate.

[0154] In some embodiments, in S3, the coating method may be transfer coating, spin coating, dip coating, or the like.

[0155] In some embodiments, the method may further include a secondary coating step S4 of applying a slurry containing a particulate binder to at least a portion of the surface of the coating and drying to form an adhesive layer. Optionally, spin coating is used as the coating method.

[0156] The present method of manufacturing the separator produces a coating in a single application, greatly simplifying the process flow for producing the separator.

[0157] Some of the raw materials used in the manufacturing method of the separator of the present application and parameters such as their contents can be referred to the separator described in the first aspect of the embodiment of the present application, so they will not be described in detail here.

[0158] Unless otherwise specified, all of the raw materials used in the manufacturing method of the separator of the present application are commercially available. secondary battery

[0159] A third aspect of an embodiment of the present application provides a secondary battery.

[0160] A secondary battery, also called a rechargeable battery or storage battery, refers to a battery that can be used continuously after being discharged by activating the active material through charging. A secondary battery typically includes an electrode assembly and an electrolyte, the electrode assembly including a positive electrode sheet, a negative electrode sheet, and a separator, the separator being disposed between the positive electrode sheet and the negative electrode sheet and mainly serving to prevent short circuits between the positive electrode and the negative electrode, and also allowing active ions to pass through.

[0161] In the present application, the type of the secondary battery is not particularly limited. For example, the secondary battery may be a lithium ion battery, a sodium ion battery, etc., and in particular, the secondary battery may be a lithium ion secondary battery.

[0162] The secondary battery according to the third aspect of the present invention includes a separator according to the first aspect of the present invention or a separator produced by the method according to the second aspect of the present invention, the separator being interposed between the positive electrode sheet and the negative electrode sheet. Optionally, at least the negative electrode sheet side of the separator has the coating according to the present invention. Thereby, the secondary battery according to the present invention can have high energy density, high thermal safety, and good capacity development characteristics. [Positive electrode sheet]

[0163] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector and containing a positive electrode active material. For example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode film layer is provided on either one or both of the two opposing surfaces of the positive electrode current collector.

[0164] 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 a lithium-containing transition metal oxide, a lithium-containing phosphate, and a modified compound thereof. Examples of the lithium transition metal oxide 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 modified compounds thereof. Examples of the lithium-containing phosphate 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 modified compounds thereof.

[0165] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for a lithium ion battery may include at least one of a lithium transition metal oxide having the general formula Li a Ni b Co c M d O e A f and a modified compound thereof. 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.

[0166] As an example, the positive electrode active material for lithium-ion batteries is LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O 2 , LiFePO 4 , LiMnPO 4 may contain at least one of the following:

[0167] When the secondary battery of the present application is a sodium ion battery, the positive electrode active material may include at least one of a sodium-containing transition metal oxide, a polyanionic material (e.g., a phosphate, a fluorophosphate, a pyrophosphate, a sulfate, etc.), and a Prussian blue-type material, but is not limited thereto.

[0168] As an example, the positive electrode active material for sodium-ion batteries is NaFeO 2 , NaCoO 2 , NaCrO 2 , NaMnO 2 , NaNiO 2 , NaNi 1 / 2 Ti 1 / 2 O 2 , NaNi 1 / 2 Mn 1 / 2 O 2 , Na 2 / 3 Fe 1 / 3 Mn2 / 3 O 2 , NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 , NaFePO 4 , NaMnPO 4 , NaCoPO 4 , Prussian blue-based materials, the general formula of which is X p M' q (PO 4 ) r O x Y 3-x The material may include at least one of the materials represented by the general formula X p M' q (PO 4 ) r O x Y 3-x In, 0 <p≦4、0<q≦2、1≦r≦3、0≦x≦2であり、Xは、H + , Li + , Na + , K + , and N.H. 4 + where M' is a transition metal cation, optionally at least one of V, Ti, Mn, Fe, Co, Ni, Cu, and Zn, and Y is a halogen anion, optionally at least one of F, Cl, and Br.

[0169] In the present application, the modified compound of each of the above positive electrode active materials may be a compound that modifies the positive electrode active material by doping and / or by surface coating.

[0170] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. In the present application, the type of the positive electrode conductive agent is not particularly limited, and for example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the content of the positive electrode conductive agent is 5 mass% or less based on the total mass of the positive electrode film layer.

[0171] In some embodiments, the positive electrode film layer may further include a positive electrode binder. In the present application, the type of the positive electrode binder is not particularly limited, and as an example, the positive electrode binder may include 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 resin. In some embodiments, the content of the positive electrode binder is 5 mass% or less based on the total mass of the positive electrode film layer.

[0172] In some embodiments, the positive electrode current collector may employ a metal foil or a composite current collector. An example of a metal foil may employ an aluminum foil. The composite current collector may include a polymer base layer and a metal material layer formed on at least one surface of the polymer base layer. As an example, the metal material may include at least one of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. As an example, the polymer base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0173] The positive electrode membrane layer is usually obtained by applying a positive electrode slurry onto a positive electrode current collector, drying and cold rolling. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP). [Negative electrode sheet]

[0174] 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 including a negative electrode active material. For example, the negative electrode current collector has two opposing surfaces in the thickness direction of the negative electrode current collector, and the negative electrode film layer is provided on either one or both of the two opposing surfaces of the negative electrode current collector.

[0175] The negative electrode active material may be any negative electrode active material for secondary batteries known in the art. As an example, the negative electrode active material may include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, but is not limited thereto. The silicon-based material may include at least one of silicon elemental, silicon oxide, silicon carbon composite, silicon nitrogen composite, and silicon alloy material. The tin-based material may include at least one of tin elemental, tin oxide, and tin alloy material.

[0176] In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent. In the present application, the type of the negative electrode conductive agent is not particularly limited, and for example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the content of the negative electrode conductive agent may be 5 mass% or less based on the total mass of the negative electrode film layer.

[0177] In some embodiments, the negative electrode film layer optionally further includes a negative electrode binder. In the present application, the type of the negative electrode binder is not particularly limited, and as an example, the negative electrode binder may include at least one of styrene butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the content of the negative electrode binder is 5 mass% or less based on the total mass of the negative electrode film layer.

[0178] In some embodiments, the negative electrode membrane layer optionally further includes other auxiliary agents. For example, the other auxiliary agents include a thickener, such as sodium carboxymethylcellulose (CMC), a PTC thermistor material, etc. In some embodiments, the content of the other auxiliary agents is 2% by mass or less, based on the total mass of the negative electrode membrane layer.

[0179] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. An example of the metal foil may be a copper foil. The composite current collector may include a polymer base layer and a metal material layer formed on at least one surface of the polymer base layer. As an example, the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0180] The negative electrode film layer is usually obtained by applying a negative electrode slurry onto a negative electrode current collector, drying and cold rolling. The negative electrode slurry is usually formed by dispersing a negative electrode active material, an optional conductive agent, an optional binder, and optional other auxiliary agents in a solvent and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0181] The negative electrode sheet does not exclude additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of the present application further includes a conductive primer (e.g., made of a conductive agent and a binder) interposed between the negative electrode collector and the negative electrode film layer and provided on the surface of the negative electrode collector. In some other embodiments, the negative electrode sheet of the present application further includes a protective layer coated on the surface of the negative electrode film layer. [Electrolyte]

[0182] In the charging and discharging process of the secondary battery, active ions are repeatedly absorbed and released between the positive and negative electrodes, and the electrolyte serves to conduct the active ions between the positive and negative electrode sheets. In the present application, the type of electrolyte is not particularly limited and can be selected according to actual needs.

[0183] The electrolyte solution includes an electrolyte salt and a solvent, and the types of the electrolyte salt and the solvent are not particularly limited and can be selected according to actual needs.

[0184] When the secondary battery of the present application is a lithium ion battery, for example, the electrolyte salt is lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6), lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium disoxalate borate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorodisalophosphate (LiDFOP), and lithium tetrafluorooxalophosphate (LiTFOP).

[0185] When the secondary battery of the present application is a sodium ion battery, the electrolyte salt is, for example, sodium hexafluorophosphate (NaPF 6 ), sodium tetrafluoroborate (NaBF 4 ), sodium perchlorate (NaClO 4 ), sodium hexafluoroarsenate (NaAsF 6 ), sodium bisfluorosulfonylimide (NaFSI), sodium bistrifluoromethanesulfonylimide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalyl borate (NaDFOB), sodium disalyl borate (NaBOB), sodium difluorophosphate (NaPO 2 F 2 ), sodium difluorooxalic acid phosphate (NaDFOP), and sodium tetrafluorooxalic acid phosphate (NaTFOP).

[0186] By way of example, the solvent may include, but is not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0187] In some embodiments, the electrolyte solution optionally further includes an additive. For example, the additive may include an anode film-forming additive, may include a cathode film-forming additive, or may include an additive that can improve some performance of the battery, such as an additive that can improve the overcharge performance of the battery, an additive that can improve the high temperature performance of the battery, or an additive that can improve the power performance of the battery at low temperatures.

[0188] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly by a winding process and / or a lamination process.

[0189] In some embodiments, the secondary battery may include an exterior body that can be used to house the electrode assembly and the electrolyte.

[0190] In some embodiments, the exterior body of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior body of the secondary battery may be a soft bag, such as a bag-shaped soft bag. The material of the soft bag may be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0191] In the present application, the shape of the secondary battery is not particularly limited, and may be cylindrical, rectangular, or any other shape. Fig. 1 illustrates a secondary battery 5 having a rectangular structure.

[0192] In some embodiments, as shown in FIG. 2, the exterior body may include a case 51 and a cover plate 53. The case 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate define a storage chamber. The case 51 has an opening communicating with the storage chamber, and the cover plate 53 is placed over the opening to seal the storage chamber. The positive electrode sheet, the negative electrode sheet, and the separator may be made into an electrode assembly 52 by a winding process and / or a stacking process. The electrode assembly 52 is sealed in the storage chamber. The electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and can be adjusted as needed.

[0193] The method for manufacturing the secondary battery of the present application is well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled into a secondary battery. As an example, a positive electrode sheet, a separator, and a negative electrode sheet are wound and / or stacked into an electrode assembly, and the electrode assembly is placed in an outer casing and baked. After that, an electrolyte is injected, and the secondary battery is obtained through processes such as vacuum packaging, standing, formation, and shaping.

[0194] In some embodiments of the present application, the secondary battery of the present application may be assembled into a battery module, and the number of secondary batteries included in the battery module may be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0195] Fig. 3 is a schematic diagram of an example of a battery module 4. As shown in Fig. 3, in the battery module 4, a plurality of secondary batteries 5 may be arranged in sequence in the length direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed via a fastener.

[0196] Alternatively, the battery module 4 may have a shell having a storage space, and the multiple secondary batteries 5 are stored in the storage space.

[0197] In some embodiments, the above 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.

[0198] 4 and 5 are schematic diagrams of an example of a battery pack 1. As shown in Fig. 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box. The battery box includes an upper housing 2 and a lower housing 3, and the upper housing 2 is covered by the lower housing 3 to form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner. power consumption equipment

[0199] A fourth aspect of the present embodiment provides a power consuming device, the power consuming device including at least one of the secondary battery, battery module, or battery pack of the present application. The secondary battery, battery module, or battery pack may function as a power source for the power consuming device, or may function as an energy storage unit for the power consuming device. The power consuming device may be, but is not limited to, a mobile device (e.g., mobile phone, laptop), an electric vehicle (e.g., pure electric vehicle, hybrid electric vehicle, plug-in hybrid electric vehicle, electric bicycle, electric scooter, electric golf cart, electric truck), an electric train, a ship, a satellite, an energy storage system, etc.

[0200] The power consuming device can select a secondary battery, a battery module, or a battery pack according to its usage needs.

[0201] 6 is a schematic diagram of an example of a power consuming device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To address the power consuming device's need for high power output and high energy density, a battery pack or battery module may be employed.

[0202] Other examples of power consuming devices may be mobile phones, tablets, laptops, etc. Such power consuming devices usually require light weight and thinness, and may be powered by secondary batteries. Working Example

[0203] The following examples are provided to more specifically illustrate the present disclosure, and these examples are merely illustrative, and various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise specified, all parts, percentages and ratios reported in the following examples are based on mass metering, all reagents used in the examples are commercially available or can be synthesized by conventional methods and can be used directly without further treatment, and all instruments used in the examples are commercially available. Preparation of modified nanocellulose C1

[0204] (1) Production of cellulose powder: Cotton linters were opened in a cotton opener to remove foreign matter, and then steamed in a 5 wt% NaOH aqueous solution at 150°C for 2 hours. Then, impurities were removed by washing with water (three times), bleached with sodium hypochlorite, impurities were removed by washing with dilute hydrochloric acid, and impurities were removed by washing with water (one time). The cotton was dehydrated and air-dried to obtain cotton cellulose powder with a whiteness of 85% or more.

[0205] (2) Esterification of cellulose: 1 kg of the obtained cotton cellulose powder was mixed with 30 kg of 60 wt % aqueous sulfuric acid solution and reacted at 60°C for 1.5 hours. After the reaction was completed, the mixture was washed with water to remove impurities (three times), filtered, deacidified and impurities were removed, and cellulose nanowhiskers having modified sulfonic acid groups were obtained.

[0206] (3) Neutralization of cellulose: First, the pH of cellulose nanowhiskers having modified sulfonic acid groups was adjusted to neutral using a 10 wt% NaOH aqueous solution, and then the cellulose nanowhiskers were dispersed by high-speed processing in a grinder for 2.5 hours. The nanowhiskers were then cut at the nano level using a high-pressure homogenizer to obtain nanocellulose having modified sulfonic acid groups with an average length of 375 nm and an average diameter of 25 nm. The molar ratio of sulfonic acid groups to hydroxyl groups was 5:3. Preparation of modified nanocellulose C2

[0207] (1) Production of cellulose powder: Cotton linters were opened in a cotton opener to remove foreign matter, and then steamed in a 5 wt% NaOH aqueous solution at 150°C for 2 hours. Then, impurities were removed by washing with water (three times), bleached with sodium hypochlorite, and impurities were removed by washing with dilute hydrochloric acid, and impurities were removed by washing with water (one time). The cotton was dehydrated and air-dried to obtain cotton cellulose powder with a whiteness of 85% or more.

[0208] (2) Esterification of cellulose: 1 kg of the obtained cotton cellulose powder was mixed with 30 kg of a 7 wt % aqueous boric acid solution and reacted at 60°C for 1.5 hours. After the reaction was completed, the mixture was washed with water to remove impurities (three times), filtered, deacidified and impurities removed, yielding nanofiber whiskers with boric acid groups.

[0209] (3) Neutralization of cellulose: First, the pH of nanofiber whiskers with boric acid groups was adjusted to neutral using a 10 wt% NaOH aqueous solution, then the whiskers were dispersed by high-speed processing in a grinder for 2.5 hours, and further cut at the nano level using a high-pressure homogenizer to obtain nanocellulose with modified groups of boric acid groups, with an average length of 375 nm and an average diameter of 25 nm. The molar ratio of boric acid groups to hydroxyl groups was 2:3. Preparation of modified nanocellulose C3

[0210] (1) Production of cellulose powder: Cotton linters were opened in a cotton opener to remove foreign matter, and then steamed in a 5 wt% NaOH aqueous solution at 150°C for 2 hours. Then, impurities were removed by washing with water (three times), bleached with sodium hypochlorite, and impurities were removed by washing with dilute hydrochloric acid, and impurities were removed by washing with water (one time). The cotton was dehydrated and air-dried to obtain cotton cellulose powder with a whiteness of 85% or more.

[0211] (2) Esterification of cellulose: 1 kg of the obtained cotton cellulose powder was mixed with 30 kg of 75 wt % aqueous phosphoric acid solution and reacted at 60°C for 4 hours. After the reaction was completed, the mixture was washed with water to remove impurities (three times), filtered, deoxidized and impurities were removed, and nanofiber whiskers having phosphate groups were obtained.

[0212] (3) Neutralization of cellulose: First, the pH of nanofiber whiskers with phosphate groups was adjusted to neutral using a 10 wt% NaOH aqueous solution, then the whiskers were dispersed by high-speed processing in a grinder for 2.5 hours, and then cut at the nano level using a high-pressure homogenizer to obtain nanocellulose with modified phosphate groups with an average length of 375 nm and an average diameter of 25 nm. The molar ratio of phosphate groups to hydroxyl groups was 7:3.

[0213] The molar ratio of the modified group to the hydroxyl group can be measured by the following method. The hydroxyl value (the number of milligrams of potassium hydroxide equivalent to the hydroxyl group content per gram of sample) of the obtained raw cellulose and modified nanocellulose is tested by the phthalic anhydride method described in GB / T 12008.3-2009, and the obtained value is expressed in mg KOH / g. This value is converted to mmol / g to obtain the hydroxyl group content. The content of the modified group (i.e., the content of the hydroxyl group to be modified) is obtained by subtracting the content of the hydroxyl group of the modified nanocellulose from the content of the hydroxyl group of the raw cellulose, thereby obtaining the molar ratio of the modified group to the hydroxyl group. Example 1 Separator manufacturing

[0214] Provide a PE porous substrate: thickness 4μm, porosity 40%, ionic conductivity 1.20mS / cm. Preparation of coating slurry: The modified nanocellulose C1 produced above, filler aluminum oxide (primary particle form, average particle size Dv50 300 nm), and aqueous polyacrylic acid as a binder were mixed uniformly in a mass ratio of 15:84.2:0.8 with deionized water as a suitable solvent to obtain a coating slurry with a solid content of 35 wt%. Coating: The prepared coating slurry was coated on two surfaces of the PE porous substrate using a coater, and the separator was obtained through a drying and dividing process. The coating on one side of the PE porous substrate had an areal density of 0.9 g / m 2 , and the thickness was 0.45 μm. Manufacture of positive electrode sheets

[0215] LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 O 2A positive electrode slurry was obtained by uniformly mixing NCM811, carbon black (Super P) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a mass ratio of 96.2:2.7:1.1 with an appropriate amount of N-methylpyrrolidone (NMP) as a solvent. The positive electrode slurry was applied onto an aluminum foil positive electrode current collector, and the positive electrode sheet was obtained through processes such as baking, cold rolling, slitting, and cutting. The positive electrode sheet had an areal density of 0.207 mg / mm 2 , compressed density 3.5g / cm 3 It was. Manufacture of negative electrode sheets

[0216] The negative electrode active material was artificial graphite, the conductive agent was carbon black (Super P), and the binders were styrene butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC). The mixture was mixed uniformly in a mass ratio of 96.4:0.7:1.8:1.1 with an appropriate amount of deionized water as a solvent to obtain a negative electrode slurry. The negative electrode slurry was applied onto the copper foil of the negative electrode current collector, and the negative electrode sheet was obtained through processes such as baking, cold rolling, slitting, and cutting. The negative electrode sheet had an areal density of 0.126 mg / mm 2 , compressed density 1.7g / cm 3 It was. Electrolyte production

[0217] Ethylene carbonate (EC) and methyl ethyl carbonate (EMC) were mixed in a mass ratio of 30:70 to obtain an organic solvent, and the LiPF 6 was dissolved in the above organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L. Secondary battery manufacturing

[0218] The positive electrode sheet, the separator, and the negative electrode sheet were laminated in this order and wound to obtain an electrode assembly. The electrode assembly was placed in an outer casing, dried, and then an electrolyte was injected. The secondary battery was obtained through processes such as vacuum packaging, standing, formation, and shaping. Examples 2 to 18 and Comparative Examples 1 to 5

[0219] Except for the different manufacturing parameters of the separator, the secondary battery was manufactured in a similar manner to that in Example 1. The specific parameters are shown in Table 1. Example 19

[0220] A secondary battery was manufactured in the same manner as in Example 3, except that aluminum oxide in the form of secondary particles having an average particle size Dv50 of 150 nm was used as the filler. Example 20

[0221] A secondary battery was manufactured in a similar manner to Example 3, except that both primary particle-form aluminum oxide (average particle size Dv50 of 300 nm) and secondary particle-form aluminum oxide (average particle size Dv50 of 150 nm) were used as the filler, and the mass ratio of primary particle-form aluminum oxide to secondary particle-form aluminum oxide was 1:1. Test part

[0222] (1) Thermal shrinkage rate test of separator Preparation of samples: The separator prepared above was punched out into samples with a width of 50 mm and a length of 100 mm using a press, and five parallel samples were placed on an A4 sheet of paper and fixed in place. Next, the A4 sheet of paper with the samples placed on it was placed on a cardboard sheet with a thickness of 1 mm to 5 mm.

[0223] Sample test: Set the temperature of the blast oven to 150℃. After 30 minutes from when the temperature reaches the specified temperature and becomes stable, place an A4 sheet of paper placed on a piece of cardboard into the blast oven and start timing. After the specified time (1 hour in this application) is reached, measure the length and width of the separator and let these values ​​be a and b respectively.

[0224] Calculation of heat shrinkage: Machine direction (MD) heat shrinkage = [(100-a) / 100] x 100%, transverse direction (TD) heat shrinkage = [(50-b) / 50] x 100%. The average value of five parallel samples is taken as the test result.

[0225] (2) Separator breathability test The time required for 100 mL of air to pass through the separator at room temperature is measured, and the average value of five parallel samples is taken as the test result. A Kumagaya KRK Oken type air permeability tester can be used as the test equipment.

[0226] (3) Testing the ionic conductivity of porous substrates and separators The ionic conductivity of the porous substrate and separator is tested by AC impedance spectrum experiments. Specifically, the porous substrate or separator is cut into a disk of a given area, baked, and then placed between two stainless steel electrodes. After absorbing sufficient electrolyte, the electrodes are sealed to form a coin cell, and an AC impedance spectrum experiment is performed. The intersection point between the central straight line part of the obtained AC impedance spectrum and the real axis is taken as the self-resistance of the electrolyte, and the ionic conductivity of the porous substrate or separator is calculated by the formula σ = (L / A) × R. L is the thickness of the porous substrate or separator (cm), and A is the contact area between the stainless steel electrode and the porous substrate or separator (cm). 2 ), R represents the electrolyte's inherent resistance (mS).

[0227] The electrolyte used was an organic solvent obtained by mixing ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) in a mass ratio of 30:50:20, and then thoroughly dried LiPF 6 The above is dissolved in the organic solvent to prepare an electrolyte solution having a concentration of 1 mol / L.

[0228] As can be seen from Table 1, in Examples 1 to 20, a coating containing nanocellulose and a filler was provided on two surfaces of the porous substrate of the separator, and the surface density of the coating was σg / m 2 When the thickness H μm satisfies both 0.3≦σ≦1.65 and 0.7≦σ / H≦2.2, the obtained separator can have a low thermal shrinkage rate and high air permeability, and further, a secondary battery using the separator can have a high energy density, high thermal safety, and good capacity development characteristics.

[0229] As can be seen from the test results of Examples 1 to 8 and Comparative Examples 1 to 2, Examples 9 to 13 and Comparative Example 3, and Examples 14 to 18 and Comparative Examples 4 to 5, the surface density of the coating σg / m 2 and thickness H μm do not satisfy the above relationship, for example, σ / H is greater than 2.2, or σ / H is less than 0.7, or σ is greater than 1.65, the combination of surface density and thickness of the coating is not reasonable, resulting in poor connection effect between nanocellulose and filler in the coating, and failure to form a stable spatial network structure with an appropriate channel structure. The separator cannot have low thermal shrinkage and high air permeability, and the secondary battery using the separator also cannot have high energy density, high thermal safety, and good capacity performance.

[0230] The present application is not limited to the above-mentioned embodiment. The above-mentioned embodiment is merely an example, and any embodiment that has substantially the same configuration as the technical idea or exhibits the same effect within the scope of the technical solution of the present application is included in the technical scope of the present application. Furthermore, various modifications that a person skilled in the art may make to the embodiment or other forms constructed by combining some of the components of the embodiment are also included in the scope of the present application, as long as they do not deviate from the gist of the present application.

[0231] [Table 1] JPEG2025517454000003.jpg245170 [Explanation of symbols]

[0232] It should be noted that the drawings are not necessarily drawn to scale. 1 Battery pack 2 Upper case 3 Lower case 4 Battery Module 5 Secondary battery 51 cases 52 Electrode Assembly 53 Cover plate

Claims

1. A separator, A porous substrate; a coating disposed on at least one surface of the porous substrate; The coating comprises nanocellulose and a filler, The areal density of the coating on one side of the porous substrate is σ g / m ２ and the thickness of the coating located on one side of the porous substrate is H μm, and the separator satisfies 0.3≦σ≦1.65 and 0.7≦σ / H≦2.2; Separator.

2. 0.6≦σ≦1.5, optionally 0.7≦σ≦1.3; and / or 0.9≦σ / H≦1.8, optionally 0.9≦σ / H≦1.6; and / or 0<H≦1.5, optionally 0.5≦H≦0.8; The separator according to claim 1 .

3. The ionic conductivity of the porous substrate is λ １ mS / cm, and the ionic conductivity of the separator is λ ２ mS / cm, and the separator has a viscosity of 1<λ １ / λ ２ ≦3, optionally, 1.05≦λ １ / λ ２ ≦1.8 is satisfied, The separator according to claim 1 or 2.

4. 0.5≦λ １ ≦1.8, optionally 1.0≦λ １ ≦1.4, and / or 0.2≦λ ２ ≦1.5, optionally 0.5≦λ ２ ≦1.2, The separator according to claim 3 .

5. The nanocellulose comprises at least one of unmodified nanocellulose and modified nanocellulose, and optionally is modified nanocellulose; Optionally, the modified nanocellulose comprises a modifying group, the modifying group comprising at least one of an amine group, a carboxylic acid group, an aldehyde group, a sulfonic acid group, a boric acid group, and a phosphoric acid group, and further optionally comprising at least one of a sulfonic acid group, a boric acid group, and a phosphoric acid group; Optionally, the modified nanocellulose comprises hydroxy groups and modifying groups, and the molar ratio of the modifying groups to the hydroxy groups is from 1:4 to 4:1, more preferably from 2:3 to 7:3; The separator according to any one of claims 1 to 4.

6. The nanocellulose is (1) The aspect ratio of the nanocellulose is 5 to 80, optionally 10 to 40; (2) The average diameter of the nanocellulose is 40 nm or less, optionally, 10 nm to 35 nm; (3) The average length of the nanocellulose is 100 nm to 600 nm, and optionally, satisfies at least one of the following conditions: 200 nm to 450 nm; The separator according to any one of claims 1 to 5.

7. The filler comprises at least one of inorganic particles and organic particles, and / or The decomposition temperature of the filler is 200° C. or higher. The separator according to any one of claims 1 to 6.

8. The inorganic particles include at least one of inorganic particles having a dielectric constant of 5 or more, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of causing an electrochemical reaction; Alternatively, the inorganic particles having a dielectric constant of 5 or more may be boehmite, aluminum oxide, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, magnesium lithium silicate, magnesium sodium silicate, bentonite, hectorite, zirconium titanate, barium titanate, Pb(Zr,Ti)O ３ , Pb １－ｍ La ｍ Zr １－ｎ Ti ｎ O ３ , Pb(Mg ３ Nb ２／３ ) O ３ -PbTiO ３ and at least one of these modified inorganic particles, wherein 0<m<1 and 0<n<1; Optionally, the inorganic particles that are ionically conductive but do not store ions are Li ３ P.O. ４ , Lithium titanium phosphate Li ｘ１ Ti ｙ１ (P.O. ４ ) ３ , Lithium aluminum titanium phosphate Li ｘ２ A ｙ２ Ti ｚ１ (P.O. ４ ) ３ , (LiAlTiP) ｘ３ O ｙ３ Mold glass, lithium lanthanum titanate Li ｘ４ La ｙ４ TiO ３ , Lithium germanium thiophosphate Li ｘ５ Ge ｙ５ P ｚ２ S ｗ , Lithium nitride Li ｘ６ N ｙ６ , SiS ２ Molded Glass Li ｘ７ S ｙ７ S ｚ３ , and P ２ S ５ Molded Glass Li ｘ８ P ｙ８ S ｚ４ and wherein 0<x1<2, 0<y1<3, 0<x2<2, 0<y2<1, 0<z1<3, 0<x3<4, 0<y3<13, 0<x4<2, 0<y4<3, 0<x5<4, 0<y5<1, 0<z2<1, 0<w<5, 0<x6<4, 0<y6<2, 0<x7<3, 0<y7<2, 0<z3<4, 0<x8<3, 0<y8<3, 0<z4<7; Optionally, the inorganic particles capable of electrochemical reaction include at least one of lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials, and lithium titanium compounds; The separator according to claim 7.

9. The organic particles include at least one of polyethylene particles, polypropylene particles, polystyrene particles, cellulose, a cellulose modifier, melamine resin particles, phenolic resin particles, polyester particles, organic silicone resin particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, polyaryletherketone particles, and a copolymer of butyl acrylate and ethyl methacrylate, and optionally include at least one of melamine formaldehyde resin particles, phenolic resin particles, polyester particles, organic silicone resin particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, and polyaryletherketone particles; The separator according to claim 7.

10. The content of the nanocellulose in the coating is 8 wt % or more, optionally 10 wt % to 35 wt %, based on the total weight of the coating; and / or The content of the filler in the coating is 50 wt % or more, alternatively 65 wt % to 90 wt %, based on the total weight of the coating; and / or The mass ratio of the nanocellulose to the filler in the coating is 0.1 to 0.95, optionally 0.18 to 0.6; The separator according to any one of claims 1 to 9.

11. The filler has a primary particle form, a secondary particle form formed by aggregation of primary particles, or a combination thereof; Optionally, the filler is (1) the content of the filler in the form of primary particles in the coating is 50 wt % to 100 wt %, optionally 90 wt % to 99 wt %, based on the total weight of the filler; (2) The average particle diameter Dv50 of the filler in the form of primary particles is 100 nm to 800 nm, optionally 200 nm to 400 nm; (3) The average particle diameter Dv50 of the filler in the form of secondary particles is 200 nm or less, and optionally 50 nm to 200 nm; (4) The specific surface area of ​​the filler in the form of primary particles is 10 m ２ / g or less, optionally 4m ２ / g ~ 9m ２ / g, (5) The specific surface area of ​​the filler in the form of secondary particles is 20 m ２ / g or more, optionally, 25m ２ / g to 50m ２ / g, The separator according to any one of claims 1 to 10.

12. The thickness of the porous substrate is 6 μm or less, optionally 3 μm to 5 μm, and / or The porosity of the porous substrate is 30% to 60%. The separator according to any one of claims 1 to 11.

13. the coating further comprises a non-particulate binder; Optionally, the non-particulate binder comprises an aqueous based binder; Optionally, the content of the non-particulate binder in the coating is less than 1 wt %, based on the total weight of the coating. The separator according to any one of claims 1 to 12.

14. the separator further includes an adhesive layer, the adhesive layer being provided on at least a portion of a surface of the coating, the adhesive layer including a particulate binder, and optionally the particulate binder including at least one of a homopolymer or copolymer of an acrylate-based monomer, a homopolymer or copolymer of an acrylic-based monomer, and a homopolymer or copolymer of a fluorine-containing olefin monomer; The separator according to any one of claims 1 to 13.

15. The separator is (1) The separator has a longitudinal heat shrinkage rate of 6.5% or less at 150° C. for 1 h, and optionally has a heat shrinkage rate of 0.5% to 3%. (2) The separator has a transverse heat shrinkage rate of 6.5% or less at 150° C. for 1 h, and optionally, 0.5% to 3%; (3) The separator has a longitudinal tensile strength of 2000 kg / cm ２ or more, optionally 2500 kg / cm ２ ~4500kg / cm ２ The condition that (4) The separator has a lateral tensile strength of 2000 kg / cm ２ or more, optionally 2500 kg / cm ２ ~4500kg / cm ２ The condition that (5) The wet length of the separator is 30 mm or more, and optionally, 30 mm to 80 mm; (6) The wetting speed of the separator is 3 mm / s or more, and optionally, 3 mm / s to 10 mm / s; (7) The separator satisfies at least one of the following conditions: the air permeability is 220 s / 100 mL or less, and optionally, 100 s / 100 mL to 180 s / 100 mL; The separator according to any one of claims 1 to 14.

16. A method for producing the separator according to any one of claims 1 to 15, comprising the steps of: Step S1 of providing a porous substrate; A coating slurry production step S2 in which nanocellulose and a filler are mixed in a solvent in a predetermined ratio to prepare a coating slurry; A coating step S3 of coating the coating slurry onto at least one surface of the porous substrate to form a coating, and then drying to obtain a separator; The separator comprises a porous substrate and a coating disposed on at least one surface of the porous substrate, the coating comprising nanocellulose and a filler, the coating having an areal density of σg / m ２ and the thickness of the coating located on one side of the porous substrate is H μm, and the separator satisfies 0.3≦σ≦1.65 and 0.7≦σ / H≦2.2; A method for manufacturing a separator.

17. The method further includes a second coating step S4 of coating a slurry containing a particulate binder on at least a portion of the surface of the coating and drying the slurry to form an adhesive layer.

17. The method of claim 16.

18. The separator according to any one of claims 1 to 15 or the separator produced by the method according to claim 16 or 17, Secondary battery.

19. The secondary battery according to claim 18, Power consuming device.

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