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

Abstract

The present application provides a separator, a manufacturing method thereof, and a secondary battery and a power consuming device related thereto. The separator includes a porous substrate and a coating provided on at least one surface of the porous substrate, the coating including nanocellulose, the surface tension of the porous substrate is δ1 mN / m, the surface tension of the coating is δ2 mN / m, and the separator satisfies δ1 / δ2≧0.68. The separator according to the present application is characterized by excellent heat resistance and high viscosity strength, and therefore a secondary battery using the separator can have high energy density, high thermal safety, and long service life.

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] This application relates to the field of battery technology, and more particularly to separators, methods for their manufacture, and related secondary batteries and power consuming devices. [Background technology]

[0003] In recent years, secondary batteries have been widely used in many fields, including energy storage power systems such as hydroelectric power plants, thermal power plants, wind power plants, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. As secondary batteries become more widely used, their safety, especially their thermal safety, has attracted increasing attention. Separators are one of the key components that determine the safety of secondary batteries. Therefore, developing separators with excellent heat resistance and stable structures remains a key challenge in this field. Summary of the Invention [Problem to be solved by the invention]

[0004] The object of the present application is to provide a separator, a method for manufacturing the same, and related secondary batteries and power consumption devices. The separator is characterized by excellent heat resistance and high viscosity strength, and thereby a secondary battery using the separator can have a high energy density, high thermal safety, and a long service life. [Means for solving the problem]

[0005] A first aspect of the present application provides a separator comprising a porous substrate and a coating provided on at least one surface of the porous substrate, wherein the coating comprises nanocellulose, the surface tension of the porous substrate is δ1 mN / m, the surface tension of the coating is δ2 mN / m, and the separator satisfies δ1 / δ2≧0.68.

[0006] The inventors of the present application have surprisingly found, through extensive research, that by ensuring that the surface tension δ1 mN / m of the porous substrate and the surface tension δ2 mN / m of the coating satisfy the relationship δ1 / δ2 ≧ 0.68, the adhesive strength between the porous substrate and the coating is high, thereby avoiding the problem of coating peeling during long-term charge / discharge of the secondary battery and the problem of coating leakage when applying the coating slurry, thereby imparting the characteristics of high coating uniformity and high coverage of the porous substrate, and further imparting excellent heat resistance to the separator. Therefore, the separator of the present application is characterized by excellent heat resistance and high viscosity strength, and thereby secondary batteries using this separator can combine high energy density, high thermal safety, and a long service life.

[0007] In any embodiment of the present application, 0.68≦δ1 / δ2≦1.8, preferably 0.7≦δ1 / δ2≦1.2, thereby enabling the separator to more reliably combine the characteristics of excellent heat resistance, high viscosity strength, and good ion transport properties, and thereby enabling a secondary battery using the separator to more reliably combine high energy density, high thermal safety, and long service life.

[0008] In any embodiment of the present application, δ1≧23, preferably 23≦δ1≦45. When the surface tension of the porous substrate is within an appropriate range, coating leakage is less likely to occur when applying the coating slurry, and the coverage area of ​​the porous substrate is increased, which results in a separator with better heat resistance, a secondary battery with higher safety, and is also advantageous in maintaining high adhesive strength between the porous substrate and the coating.

[0009] In any embodiment of the present application, 25≦δ2≦50, preferably 30≦δ2≦45. When the surface tension of the coating is within an appropriate range, it is advantageous for maintaining high adhesive strength between the porous substrate and the coating, and is also advantageous for wetting the separator with the electrolyte, improving the ion transport properties of the separator, and improving the capacity development properties of the secondary battery.

[0010] In any embodiment of the present application, the nanocellulose comprises at least one of unmodified nanocellulose and modified nanocellulose, preferably modified nanocellulose.

[0011] In any embodiment of the present application, the modified nanocellulose includes a modifying group, which includes at least one of an amine group, a carboxylic acid group, an aldehyde group, a sulfonic acid group, a boric acid group, and a phosphoric acid group, and preferably includes at least one of a sulfonic acid group, a boric acid group, and a phosphoric acid group. When nanocellulose has the above-mentioned specific modifying group, it can effectively improve the heat resistance of the separator and improve the thermal safety of the secondary battery, while also being advantageous in maintaining high adhesive strength between the porous substrate and the coating.

[0012] In any embodiment of the present application, the modified nanocellulose contains a hydroxy group and a modifying group, and the molar ratio of the modifying group to the hydroxy group is 1:4 to 4:1, preferably 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, and high adhesive strength can also be imparted to the separator.

[0013] In any embodiment of the present application, the average diameter of the nanocellulose is 40 nm or less, preferably 10 nm to 35 nm. When the average diameter of the nanocellulose is within an appropriate range, the heat resistance of the separator can be further improved and the thermal shrinkage rate of the separator can be reduced.

[0014] In any embodiment of the present application, the average length of the nanocellulose is 100 nm to 600 nm, preferably 200 nm to 500 nm. When the average length of the nanocellulose is within an appropriate range, the heat resistance and ion transport properties of the separator can be further improved.

[0015] In any embodiment of the present application, the aspect ratio of the nanocellulose is 5 to 60, preferably 15 to 30. When the aspect ratio of the nanocellulose is within an appropriate range, the ion transport properties of the separator can be further improved.

[0016] In any embodiment of the present application, the content of the nanocellulose in the coating is 8 wt% or more, preferably 10 wt% to 25 wt%, based on the total weight of the coating.

[0017] When the nanocellulose content is within an appropriate range, the coating slurry has a more appropriate viscosity, which makes it easier to apply, and it can maintain high adhesive strength between the coating and the porous substrate, improving the structural stability of the separator. Furthermore, it is advantageous for nanocellulose and other components (e.g., fillers, etc.) to build a stable spatial network structure, further improving the performance of the separator.

[0018] In any embodiment of the present application, the coating further comprises a filler, and the filler comprises at least one selected from inorganic particles and organic particles.

[0019] In any embodiment of the present application, the content of the filler in the coating is 60 wt% or more, preferably 65 wt% to 90 wt%, based on the total weight of the coating.

[0020] In any embodiment of the present application, the filler comprises primary particles, secondary particles, or a combination thereof, and preferably, the filler comprises at least secondary particles.

[0021] The secondary particle form filler has a small particle size, a large specific surface area, and better affinity with nanocellulose. Furthermore, nanocellulose can bind to the voids between the primary particles that make up the secondary particle form filler, thereby bonding the nanocellulose and the secondary particle form filler together to achieve an integrated effect. As such, the coating has a more stable spatial network structure, further improving the performance of the separator.

[0022] The primary particle filler has a large particle size and high strength, and therefore can better perform the supporting function as a skeleton in the coating, reducing the amount of binder used and reducing the thermal shrinkage rate of the separator, thereby improving the heat resistance of the separator. Furthermore, even with a small amount used, the filler can increase the channel structure of the coating and contribute to reducing the moisture content, thereby further improving the ion transport properties and wettability of the separator to the electrolyte.

[0023] In any embodiment of the present application, the average particle size Dv50 of the filler in the form of primary particles is 100 nm to 800 nm, preferably 200 nm to 400 nm.

[0024] 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, preferably 50 nm to 200 nm.

[0025] In any embodiment of the present application, the filler comprises inorganic particles in the form of primary particles, inorganic particles in the form of secondary particles, or a combination thereof, and preferably, the filler comprises inorganic particles in at least the form of secondary particles.

[0026] In any embodiment of the present application, the crystalline form of the inorganic particles in the form of primary particles includes at least one of an α crystalline form and a γ crystalline form, and preferably includes an α crystalline form.

[0027] In any embodiment of the present application, the crystalline form of the inorganic particles in the form of secondary particles includes at least two of the α crystalline form, the θ crystalline form, the γ crystalline form, and the η crystalline form, and preferably includes at least two of the α crystalline form, the θ crystalline form, and the γ crystalline form.

[0028] In any embodiment of the present application, the coating further comprises a non-particulate binder, and preferably the non-particulate binder comprises an aqueous binder, which is advantageous for the preparation and application of the coating slurry.

[0029] 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, and the separator according to the present application can maintain high adhesive strength and good ion transport properties of the separator while reducing the amount of binder used.

[0030] In any embodiment of the present application, the coating may be free of a wetting agent, thereby avoiding clogging of the pores of the porous substrate during application and drying of the coating slurry.

[0031] In any embodiment of the present application, the thickness of the porous substrate is 6 μm or less, preferably 3 μm to 5 μm, which contributes to improving the energy density of the secondary battery.

[0032] In any embodiment of the present application, the areal density of the coating is 0.6 g / m 2 ~1.5g / m 2, preferably 0.8 g / m 2 ~1.1g / m 2 This results in a separator with superior heat resistance and ion transport properties.

[0033] In any embodiment of the present application, the thickness of the coating is 1.5 μm or less, preferably 0.5 μm to 0.8 μm, which contributes to improving the energy density of the secondary battery.

[0034] 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, the adhesive layer including a particulate binder, and preferably the particulate binder including 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 adhesive layer not only prevents peeling of the coating and improves the safety of the secondary battery, but also improves the interface between the separator and the electrodes, thereby improving the cycle characteristics of the secondary battery.

[0035] In any embodiment of the present application, the adhesive strength between the coating and the porous substrate is 16 N / m to 40 N / m, preferably 20 N / m to 35 N / m.

[0036] In any embodiment of the present application, the separator has a longitudinal heat shrinkage rate of 5% or less, preferably 0.5% to 3%, at 150°C for 1 hour.

[0037] In any embodiment of the present application, the separator has a transverse heat shrinkage rate of 5% or less, preferably 0.5% to 3%, at 150°C for 1 hour.

[0038] In any embodiment of the present application, the separator has a longitudinal tensile strength of 2000 kg / cm 2 More than 2500 kg / cm 2 ~4500kg / cm 2 is.

[0039] In any embodiment of the present application, the separator has a transverse tensile strength of 2000 kg / cm 2 More than 2500 kg / cm 2 ~4500kg / cm 2 is.

[0040] In any embodiment of the present application, the wetted length of the separator is 30 mm or more, preferably 30 mm to 80 mm.

[0041] In any embodiment of the present application, the wetting speed of the separator is 3 mm / s or more, preferably 3 mm / s to 10 mm / s.

[0042] In any embodiment of the present application, the separator has an air permeability of 300 s / 100 mL or less, preferably 100 s / 100 mL to 230 s / 100 mL.

[0043] When the separator performance satisfies one or more of the above conditions, it is advantageous for improving at least one of the energy density, thermal safety, capacity development characteristics, and service life of the secondary battery.

[0044] A second aspect of the present application provides a method for producing a separator according to the first aspect of the present application, comprising step S1 of providing a porous substrate, step S2 of providing a coating slurry containing nanocellulose, and step S3 of applying the coating slurry to at least one surface of the porous substrate, wherein the separator comprises a porous substrate and a coating provided on at least one surface of the porous substrate, wherein the surface tension of the porous substrate is δ1 mN / m, the surface tension of the coating is δ2 mN / m, and the separator satisfies δ1 / δ2≧0.68.

[0045] In any embodiment of the present application, the coating slurry further comprises a filler.

[0046] In any embodiment of the present application, the surface tension of the coating slurry is 18 mN / m to 52 mN / m.

[0047] In any embodiment of the present application, the method further comprises step S4 of applying a second coating: a slurry containing a particulate binder onto at least a portion of the surface of the coating and drying to form an adhesive layer.

[0048] The present separator manufacturing method produces a coating in a single application, greatly simplifying the process flow for producing separators.

[0049] A third aspect of the present application provides a secondary battery comprising the separator according to the first aspect of the present application or a separator produced by the method according to the second aspect of the present application.

[0050] A fourth aspect of the present application provides a power consumption device including the secondary battery according to the third aspect of the present application.

[0051] The separator according to the present application is characterized by excellent heat resistance and high viscosity strength, and as a result, a secondary battery using the separator can have high energy density, high thermal stability, and a long service life. 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 explanation of the drawings]

[0052] In order to more clearly describe the technical solutions of the embodiments of the present application, the following will briefly describe the drawings that need to be used in the embodiments of the present application. 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 any creative efforts. [Figure 1] 1 is a schematic diagram of one embodiment of a secondary battery of the present application. [Figure 2] FIG. 2 is an exploded schematic view of the embodiment of the secondary battery of FIG. 1. [Figure 3]1 is a schematic diagram of one embodiment of a battery module of the present application. [Figure 4] 1 is a schematic diagram of one embodiment of a battery pack of the present application. [Figure 5] 5 is a schematic exploded view of the embodiment of the battery pack shown in FIG. 4. [Figure 6] 1 is a schematic diagram of one embodiment of a power consuming device that includes a secondary battery of the present application as a power source. [Explanation of symbols]

[0053] It should be noted that the drawings are not necessarily drawn to scale. 1 battery pack 2 Upper housing 3 Lower housing 4 Battery Module 5 Secondary battery 51 cases 52 Electrode Assembly 53 Cover plate DETAILED DESCRIPTION OF THE INVENTION

[0054] Hereinafter, embodiments of a separator, a manufacturing method thereof, and a related secondary battery and power consumption device specifically disclosed in the present application will be described in detail with appropriate reference to the drawings. However, unnecessary details may be omitted. For example, detailed descriptions of already known matters and redundant descriptions of the same actual configurations may be omitted. This is to avoid unnecessary redundancy in the following description 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.

[0055] "Ranges" disclosed herein are defined by lower and upper limits, and a particular range is defined by selecting a lower and upper limit, with the selected lower and upper limits defining the boundaries of the particular range. Ranges defined in this manner may or may not include the endpoints 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 to 120 and 80 to 110 are listed for a particular parameter, it is understood that the ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed and maximum range values ​​of 3, 4, and 5 are listed, the ranges of 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all contemplated. In this application, unless otherwise specified, a 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 a shorthand notation for combinations of these numbers. Also, describing a parameter as an integer greater than or equal to 2 is equivalent to disclosing that the parameter is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0056] Unless otherwise specified, all and any embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0057] Unless otherwise specified, all technical features and any technical features of the present application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present application.

[0058] Unless otherwise specified, all steps herein can be performed sequentially or randomly, and are preferably performed sequentially. For example, if the method includes steps (a) and (b), this 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).

[0059] Unless otherwise specified, the terms "including" and "comprises" in this application are intended to represent open expressions, but may also be closed expressions. For example, "including" and "comprises" may mean that other elements not listed are also included or comprised, or that only the listed elements are included or comprised.

[0060] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), or both A and B are true (or exist).

[0061] As used herein, the terms "plurality" and "plurality" refer to two or more than two.

[0062] Unless otherwise specified, terms used in this application have their commonly understood meanings as commonly understood by those of ordinary skill in the art.

[0063] Unless otherwise specified, the values ​​of each parameter referred to in this application can be measured using various test methods commonly used in the art, for example, according to the test methods shown in the examples of this application.

[0064] Typically, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. The separator is disposed between the positive electrode plate and the negative electrode plate and serves to prevent short circuits between the positive electrode and the negative electrode, while also allowing active ions to pass freely through the separator to form a circuit. Therefore, the stability of the separator, particularly its thermal stability and structural stability, directly affects the safety of the secondary battery.

[0065] As a result of their research, the inventors of the present application have surprisingly found that by providing a coating containing nanocellulose on the surface of the porous substrate of a separator and controlling the ratio of the surface tension of the porous substrate to the surface tension of the coating within an appropriate range, the separator can combine the characteristics of excellent heat resistance and high viscosity strength, and as a result, a secondary battery using this separator can combine high energy density, high thermal safety, and a long service life. Separator

[0066] Specifically, a first aspect of an embodiment of the present application provides a separator comprising a porous substrate and a coating provided on at least one surface of the porous substrate, wherein the coating comprises nanocellulose, the surface tension of the porous substrate is δ1 mN / m, the surface tension of the coating is δ2 mN / m, and the separator satisfies δ1 / δ2≧0.68.

[0067] Currently, separators used in commercially available secondary batteries are typically polyolefin films with melting points between 130°C and 160°C, such as polyethylene films, polypropylene films, or polypropylene / polyethylene / polypropylene trilayer composite films. This results in poor heat resistance and severe shrinkage when exposed to heat, increasing the risk of short circuits between the positive and negative electrodes. While the heat resistance of separators can be improved by coating a heat-resistant inorganic ceramic layer on a porous substrate (e.g., a polyolefin film or nonwoven fabric), the large particle size of commercially available inorganic ceramic particles limits the number of inorganic ceramic particle layers on the porous substrate (usually five or fewer). This limits the effectiveness of improving the separator's heat resistance and increases the overall thickness of the separator, making it difficult to balance with the secondary battery's energy density, which, particularly in the field of power batteries, negatively impacts mileage. Furthermore, the adhesive strength between the inorganic ceramic layer and the porous substrate is low, increasing the risk of the inorganic ceramic layer becoming wetted by the electrolyte and peeling off during long-term charging and discharging of the secondary battery.

[0068] Nanocellulose is a general term for cellulose whose size in any dimension is at the nano-level (e.g., within 100 nm) and combines the properties of cellulose with those of nanoparticles. Nanocellulose can be a polymeric nanomaterial extracted from natural sources such as wood, cotton, and straw by chemical, physical, or biological means. It offers advantages such as widespread availability, low cost, biodegradability, high elastic modulus, and high specific surface area. It is therefore an excellent alternative to traditional petrochemical resources and can effectively alleviate issues such as environmental pollution and the shortage of petrochemical resources. Nanocellulose also has excellent high-temperature resistance and exhibits minimal volume change when heated, thereby improving the heat resistance of separators, reducing the degree of separator shrinkage during heating, reducing the risk of short circuits between the positive and negative electrodes, and providing high thermal safety for secondary batteries. Nanocellulose also has a lower density than conventional inorganic ceramic particles, allowing for the weight reduction of secondary batteries.

[0069] Therefore, when the coating of the present application contains nanocellulose, it is advantageous for improving the heat resistance of the separator. Furthermore, the coating of the present application is thinner and lighter than conventional inorganic ceramic layers, which is advantageous for improving the volumetric energy density and weight energy density of the secondary battery. Furthermore, because the coating of the present application has high heat resistance, it is possible to further thin the porous substrate, which can further reduce the weight of the secondary battery and improve the volumetric energy density and weight energy density of the secondary battery.

[0070] As a result of their research, the inventors of the present application have found that when a coating slurry containing nanocellulose is applied to the surface of a porous substrate, it is easy for the coating to leak out, which reduces the mechanical strength of the produced separator and increases the risk of short-circuiting between the positive and negative electrodes.

[0071] Through their research, the inventors of the present application have surprisingly found that when the surface tension δ1 mN / m of the porous substrate and the surface tension δ2 mN / m of the coating (in this application, both are the dried coatings) satisfy the relationship δ1 / δ2 ≥ 0.68, the adhesive strength between the porous substrate and the coating is high, thereby avoiding the problem of coating peeling during long-term charge / discharge of the secondary battery. This also avoids the problem of coating leakage when applying the coating slurry, thereby providing the coating with high uniformity and high coverage of the porous substrate, and further imparting excellent heat resistance to the separator. When the surface tension of the porous substrate is low and the surface tension of the coating is high, resulting in a δ1 / δ2 ratio of less than 0.68, coating leakage is likely to occur when applying the coating slurry. In this case, the separator has poor heat resistance and low adhesive strength, and is at a high risk of coating peeling during long-term charge / discharge of the secondary battery.

[0072] Therefore, the separator according to the present invention is characterized by excellent heat resistance and high viscosity strength, and as a result, a secondary battery using the separator can have a high energy density, high thermal safety, and a long service life.

[0073] Through research, the inventors of the present application surprisingly found that the ratio of the surface tension of the porous substrate to the surface tension of the coating should not be too high, because this would deteriorate the breathability and ion transport properties of the separator and adversely affect the electrochemical and mechanical properties of the secondary battery, such as the cycle characteristics of the secondary battery. In some embodiments, the ratio is preferably 0.68≦δ1 / δ2≦1.8, 0.7≦δ1 / δ2≦1.5, 0.7≦δ1 / δ2≦1.2, 0.7≦δ1 / δ2≦1.0, or 0.7≦δ1 / δ2≦0.9. This allows the separator to more reliably combine excellent heat resistance, high viscosity strength, and good ion transport properties, thereby allowing secondary batteries using the separator to more reliably combine high energy density, high thermal safety, and long service life.

[0074] In some embodiments, the surface tension δ1 mN / m of the porous substrate may satisfy δ1≧23, preferably 23≦δ1≦45. When the surface tension of the porous substrate is within an appropriate range, coating leakage is less likely to occur when applying the coating slurry, and the coverage area on the porous substrate is increased, which results in a separator with better heat resistance and a secondary battery with higher safety. This is also advantageous in maintaining high adhesive strength between the porous substrate and the coating, and significantly reduces the risk of coating peeling.

[0075] In some embodiments, the surface tension δ2 mN / m of the coating may satisfy the relationship 25≦δ2≦50, preferably 30≦δ2≦45. When the surface tension of the coating is within the appropriate range, it is advantageous for maintaining high adhesive strength between the porous substrate and the coating and significantly reducing the risk of coating peeling, and it is also advantageous for wetting the separator with the electrolyte, improving the ion transport properties of the separator, and improving the capacity development properties of the secondary battery.

[0076] During long-term charge and discharge of a secondary battery, irreversible changes in the microstructure of the positive and negative electrode active materials cause the overall volume of the battery to increase. Particularly during high-speed charging of the secondary battery, the volume further increases when ions are embedded in the negative electrode active material. Battery expansion can cause compression and / or tension on the separator, potentially causing separator damage and increasing the risk of short-circuiting between the positive and negative electrodes. Therefore, the separator must also have good resistance to external pressure. In some embodiments, the coating further contains a filler. 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 improving the separator's tensile strength, puncture resistance, and resistance to external pressure.

[0077] In some embodiments, the filler may include at least one selected from inorganic particles and organic particles.

[0078] In some embodiments, the decomposition temperature of the filler may be 200° C. or higher, which provides the filler with excellent thermal stability and resistance to decomposition, thereby further improving the heat resistance of the separator.

[0079] Inorganic particles have excellent thermal stability and are resistant to decomposition, and typically have hydroxyl groups on their surfaces, which facilitate the formation of a stable spatial network structure with nanocellulose. In some embodiments, the inorganic particles preferably include at least one of inorganic particles having a dielectric constant of 5 or greater, inorganic particles that are ionic conductive but do not store ions, and inorganic particles capable of undergoing electrochemical reactions.

[0080] Preferably, the inorganic particles having a dielectric constant of 5 or more are boehmite, alumina, zinc oxide, silicon oxide, titanium oxide, zirconia, 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)O3 (abbreviated as PZT), Pb 1-m La m Zr 1-n Ti n O3 (abbreviated as PLZT, 0 <m<1、0<n<1)、Pb(Mg3Nb 2 / 3 )O3-PbTiO3 (abbreviated as PMN-PT), and at least one of these modified inorganic particles. Preferably, the inorganic particles may be modified chemically and / or physically. Chemical modification methods include modification using a coupling agent (e.g., a silane coupling agent, a titanate coupling agent, etc.), modification with a surfactant, and modification by polymer grafting. Physical modification methods include mechanical dispersion, ultrasonic dispersion, high-energy treatment, etc. Modification treatment can reduce the aggregation of inorganic particles, thereby enabling the inorganic particles and nanocellulose to form a more stable and uniform spatial network structure. Furthermore, modifying the inorganic particles with a coupling agent, surface-active material, or polymer having a specific functional group is advantageous for improving the wettability of the coating to the electrolyte and the adhesive strength between the coating and the porous substrate.

[0081] Preferably, the inorganic particles having ion conductivity but not storing ions are Li3PO4, lithium titanium phosphate Li x1 Ti y1 (PO4)3, Lithium titanium aluminum phosphate Li x2 Al y2 Ti z1(PO4)3, (LiAlTiP) x3 O y3 type glass, lithium lanthanum titanate Li x4 La y4 TiO3, lithium germanium thiophosphate Li x5 Ge y5 P z2 S w , lithium nitride Li x6 N y6 , SiS2 type glass Li x7 Si y7 S z3 , and P2S5 type glass Li x8 P y8 S z4 includes 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.

[0082] Preferably, 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.

[0083] The organic particles have excellent thermal stability and are difficult to decompose, thereby improving the heat resistance of the separator. Also, when the internal temperature of the secondary battery reaches the melting point of the organic particles due to overcharging or overheating, etc., the organic particles melt and are absorbed into the micropores of the porous substrate by capillary action, closing the pores and playing a role in cutting off the circuit, thereby ensuring the high safety of the secondary battery.

[0084] In some examples, the organic particles may include, but are not limited to, at least one of polyethylene particles, polypropylene particles, polystyrene particles, cellulose, a cellulose modifier (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 a copolymer of butyl acrylate and ethyl methacrylate (e.g., a crosslinked polymer of butyl acrylate and ethyl methacrylate).

[0085] In some embodiments, the glass transition temperature of the organic particles may be 130° C. or higher. Therefore, when the internal temperature of the secondary battery reaches 130° C., the organic particles do not change from a glassy state to a viscous flow state, thereby preventing severe shrinkage of the separator. More preferably, the organic particles include, but are not limited to, 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.

[0086] In some embodiments, the content of the filler in the coating may be 60 wt % or more, preferably 65 wt % to 90 wt %, 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, and further promote the formation of a stable spatial network structure between the filler and nanocellulose, thereby further improving the separator's heat resistance, tensile strength, puncture resistance, and resistance to external pressure.

[0087] In some embodiments, the filler comprises primary particles, secondary particles, or a combination thereof, preferably the filler comprises at least secondary particles.

[0088] The secondary particle form filler has a small particle size, a large specific surface area, and better affinity with nanocellulose. Furthermore, nanocellulose can bind to the voids between the primary particles that make up the secondary particle form filler, thereby bonding the nanocellulose and the secondary particle form filler together to achieve an integrated effect. As such, the coating has a more stable spatial network structure, further improving the performance of the separator.

[0089] The filler in the form of primary particles has a large particle size and high strength, and therefore can better exert a supporting effect as a skeleton in the coating, thereby reducing the amount of binder used, lowering the thermal shrinkage rate of the separator, and improving the heat resistance of the separator. Furthermore, even with a small amount used, the filler can increase the channel structure of the coating, contributing to reducing the moisture content, and further improving the ion transport properties and wettability of the separator to the electrolyte.

[0090] In some embodiments, the content of the filler in the form of secondary particles is 50 wt% to 100 wt%, preferably 90 wt% to 99 wt%, based on the total weight of the filler.

[0091] In some embodiments, the filler in the form of primary particles has an average particle size Dv50 of 100 nm to 800 nm, preferably 200 nm to 400 nm.

[0092] In some embodiments, the average particle size Dv50 of the filler in the form of secondary particles is 200 nm or less, preferably 50 nm to 200 nm.

[0093] In some embodiments, the filler comprises inorganic particles in primary particle form, inorganic particles in secondary particle form, or a combination thereof, and preferably, the filler comprises inorganic particles in at least secondary particle form.

[0094] In some embodiments, the crystalline form of the inorganic particles in the form of secondary particles includes at least two of the α-crystalline form, the θ-crystalline form, the γ-crystalline form, and the η-crystalline form, and preferably includes at least two of the α-crystalline form, the θ-crystalline form, and the γ-crystalline form.

[0095] The X-ray diffraction spectrum of the α-crystalline inorganic particles in the form of secondary particles measured by an X-ray diffractometer has diffraction peaks at 2θ of 57.48°±0.2° and 43.34°±0.2°. In some embodiments, the content of the α-crystalline inorganic particles in the form of secondary particles is 1.2 wt% or more, preferably 1.2 wt% to 10 wt%, and more preferably 1.2 wt% to 5 wt%, based on the total weight of the inorganic particles in the form of secondary particles.

[0096] In an X-ray diffraction spectrum measured by an X-ray diffractometer, the inorganic particles in the secondary particle form of the θ crystal form have diffraction peaks at 2θ of 36.68°±0.2° and 31.21°±0.2°. In some embodiments, the content of the θ crystal form is 50 wt% or more, preferably 60 wt% to 85 wt%, and more preferably 60 wt% to 82.5 wt%, based on the total weight of the inorganic particles in the secondary particle form.

[0097] The X-ray diffraction spectrum of the inorganic particles in the secondary particle form of the gamma crystal form measured by an X-ray diffractometer has diffraction peaks at 2θ of 66.95°±0.2° and 45.91°±0.2°. In some embodiments, the content of the gamma crystal form is 10 wt% or more, preferably 15 wt% to 60 wt%, and more preferably 15 wt% to 35 wt%, based on the total weight of the inorganic particles in the secondary particle form.

[0098] The X-ray diffraction spectrum of the inorganic particles in the secondary particle form of the η crystalline form measured by an X-ray diffractometer has diffraction peaks at 2θ of 31.89°±0.2° and 19.37°±0.2°. In some embodiments, the content of the η crystalline form is 5 wt% or less, preferably 2 wt% or less, and more preferably 1 wt% or less, based on the total weight of the inorganic particles in the secondary particle form.

[0099] Inorganic particles in the form of secondary particles of α-crystal structure have the advantages of high hardness, excellent heat resistance, low dielectric constant, high safety, and high true density. Inorganic particles in the form of secondary particles of θ-crystal structure have appropriate specific surface area and hardness, which can better improve both the heat resistance and ion transport properties of the separator. Inorganic particles in the form of secondary particles of γ-crystal structure and η-crystal structure have the advantage of large specific surface area. Therefore, selecting fillers with different crystalline structures contributes to improving the heat resistance and ion transport properties of the separator.

[0100] In some embodiments, the crystalline forms of the inorganic particles in secondary particle form include α crystalline form, θ crystalline form, γ crystalline form, and η crystalline form, and the content of α crystalline form is 1.2 wt% to 5 wt%, the content of θ crystalline form is 60 wt% to 82.5 wt%, the content of γ crystalline form is 15 wt% to 35 wt%, and the content of η crystalline form is 1 wt% or less, all based on the total weight of the inorganic particles in secondary particle form.

[0101] The X-ray diffraction spectrum of secondary inorganic particles can be measured using the following method. After baking the secondary inorganic particles, they are ground in a mortar (e.g., an agate mortar) for 30 minutes and then measured using an X-ray diffractometer (e.g., a Miniflex 600-C) to obtain an X-ray diffraction spectrum. The test may use a Cu target, a Ni filter, a tube voltage of 40 kV, a tube current of 15 mA, and a continuous scan range of 5° to 80°.

[0102] In some embodiments, the crystalline form of the inorganic particles in the form of primary particles includes at least one of α-crystalline form and γ-crystalline form, and preferably includes α-crystalline form. The inorganic particles in the form of primary particles in the form of α-crystalline form have advantages of high hardness, excellent heat resistance, low dielectric constant, high safety, and high true density, which can further improve the heat resistance of the separator.

[0103] In some embodiments, the crystalline form of the inorganic particles in primary particle form includes an α-crystalline form, and the content of the α-crystalline form is 90 wt % or more, preferably 95 wt % to 100 wt %, based on the total weight of the inorganic particles in primary particle form.

[0104] In some embodiments, the nanocellulose may include at least one of cellulose nanofibers (cellulose nanofibrils, CNF, also known as nanofibrillated cellulose or microfibrillated cellulose), cellulose nanowhiskers (cellulose nanocrystals, CNC, also known as cellulose nanocrystals or nanocrystalline cellulose), and bacterial nanocellulose (bacterial nanocellulose, BNC, also known as bacterial cellulose or microbial cellulose), preferably cellulose nanowhiskers. Cellulose nanowhiskers have a high degree of crystallinity and therefore low hydrophilicity, which is advantageous for moisture release during drying and allows the moisture content of the coating to be low. Furthermore, cellulose nanowhiskers easily bond to fillers, imparting a more stable spatial network structure to the coating and further improving the performance of the separator.

[0105] In some embodiments, the nanocellulose comprises at least one of unmodified nanocellulose (also called hydroxynanocellulose) and modified nanocellulose, preferably modified nanocellulose.

[0106] The modified nanocellulose comprises modifying groups, which in some embodiments may comprise at least one of an amine group, a carboxylic acid group, an aldehyde group, a sulfonic acid group, a boric acid group, and a phosphate group, and preferably at least one of a sulfonic acid group, a boric acid group, and a phosphate group.

[0107] After further research, the inventors discovered that nanocellulose containing the above-mentioned specific modified groups can effectively improve the heat resistance of separators and enhance the thermal safety of secondary batteries, while also maintaining high adhesion strength between the porous substrate and the coating, significantly reducing the risk of coating peeling. When nanocellulose contains the above-mentioned specific modified groups, it can also form a more stable spatial network structure with the filler, further improving the ion transport properties and voltage breakdown resistance of the separator, which is advantageous for combination with high-voltage positive electrode active materials and further improving the energy density of secondary batteries. Furthermore, the presence of the modified groups reduces the proportion of hydroxy groups, thereby ensuring that the coating slurry has a more appropriate viscosity, making it easier to apply, and also improving separator production efficiency and coating uniformity.

[0108] In some embodiments, the modified nanocellulose contains hydroxyl groups and modifying groups, and the molar ratio of the modifying groups to the hydroxyl groups may be 1:4 to 4:1, preferably 2:3 to 7:3. When the molar ratio of the modifying groups to the hydroxyl groups is within an appropriate range, the heat resistance and ion transport properties of the separator can be further improved, and the separator can also be endowed with high adhesive strength.

[0109] The type of modifying group in nanocellulose can be measured by infrared spectroscopy. For example, the type of modifying group can be determined by measuring the infrared spectrum of the material and determining the characteristic peaks contained therein. Specifically, infrared spectroscopy of the material can be performed using instruments and methods 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 General Methods for Infrared Spectroscopy.

[0110] In some embodiments, the nanocellulose may have an average diameter of 40 nm or less, preferably 10 nm to 35 nm. When the average diameter of the nanocellulose is within an appropriate range, the heat resistance of the separator can be further improved and the thermal shrinkage rate of the separator can be reduced.

[0111] In some embodiments, the average length of the nanocellulose may be 100 nm to 600 nm, preferably 200 nm to 500 nm. When the average length of the nanocellulose is within an appropriate range, the heat resistance and ion transport properties of the separator can be further improved.

[0112] In some embodiments, the aspect ratio of the nanocellulose may be 5 to 60, preferably 15 to 30. When the aspect ratio of the nanocellulose is within an appropriate range, the ion transport properties of the separator can be further improved.

[0113] The average length and average diameter of nanocellulose can be measured by the following method. A 3.6 mm x 3.6 mm sample is cut 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). SEM images are obtained using high vacuum mode, an operating voltage of 3 kV, and a magnification of 30,000. From the obtained SEM image, multiple test regions (e.g., five or more) with a size of 0.5 μm x 0.5 μm are selected and their lengths are calculated. The average length obtained for each test region is then used to determine the average length of nanocellulose. From the obtained SEM image, multiple test regions (e.g., five or more) with a size of 0.5 μm x 0.5 μm are selected and their diameters are calculated using Nano Measurer particle size distribution statistical software. The average diameter obtained for each test region is then used to determine the average diameter of nanocellulose.

[0114] In some embodiments, the weight-average molecular weight of the nanocellulose may be 10,000 to 60,000, preferably 30,000 to 50,000. When the weight-average molecular weight of the nanocellulose is within an appropriate range, not only can the nanocellulose prevent clogging of the separator channel structure, but the viscosity of the coating slurry can be maintained within an appropriate range, thereby improving the fluidity and wettability of the slurry during application, which is beneficial for improving the coating quality and further improving the heat resistance and ion transport properties of the separator.

[0115] In some embodiments, the shape of the nanocellulose may include at least one of tubular (e.g., hollow tubular), fibrous, and rod-like shapes. The appropriate shape of nanocellulose is more advantageous for building a stable spatial network structure together with the filler, thereby further improving the ion transport properties and external pressure resistance of the separator.

[0116] In some embodiments, the nanocellulose content in the coating may be 8 wt% or more, preferably 8 wt% to 35 wt%, and more preferably 10 wt% to 25 wt%, based on the total weight of the coating. A nanocellulose content within an appropriate range can ensure that the coating slurry has a more appropriate viscosity, making it easier to apply. A nanocellulose content within an appropriate range can also maintain high adhesion strength between the coating and the porous substrate, improving the structural stability of the separator. Furthermore, a nanocellulose content within an appropriate range can help nanocellulose and other components (e.g., fillers, etc.) form a stable spatial network structure, further improving the ion conduction capacity, external force resistance, and voltage breakdown resistance of the separator.

[0117] In some embodiments, the coating may further include a non-particulate binder. The type of non-particulate binder is not particularly limited herein and may be any material known to have good adhesion. Preferably, the non-particulate binder includes an aqueous binder, which has the advantages of good thermodynamic stability and environmental protection, thereby making it convenient for manufacturing and applying the coating slurry. For example, the aqueous binder may include at least one of an aqueous acrylic resin (e.g., a homopolymer of acrylic acid, methacrylic acid, or sodium acrylate monomer, or a copolymer of these monomers with other copolymerizable monomers), polyvinyl alcohol (PVA), isobutylene-maleic anhydride copolymer, and polyacrylamide.

[0118] Preferably, 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 form a stable spatial network structure, thereby reducing the amount of binder used while maintaining high adhesive strength and good ion transport properties of the separator.

[0119] In some embodiments, the coating does not contain a wetting agent, such as a common acrylate or a polyoxyethylene-polyoxypropylene block copolymer wetting agent. Wetting agents are typically compounds with low surface tension and high fluidity, which can easily cause clogging of pores in a porous substrate during application and drying of the coating slurry. Because the coating of the present application does not contain a wetting agent, clogging of pores in a porous substrate during application and drying of the coating slurry can be avoided. Through research, the inventors have found that the coating slurry of the present application has excellent wetting properties, making it unnecessary to use a wetting agent.

[0120] In the present application, the material of the porous substrate is not particularly limited, and any substrate known to have good chemical and mechanical stability, such as at least one of glass fiber, nonwoven fabric, and polyolefin membrane (e.g., polyethylene, polypropylene, polyvinylidene fluoride, etc.), 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 materials of each layer may be the same or different.

[0121] In some embodiments, the thickness of the porous substrate may be 6 μm or less, and preferably 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 made even thinner, contributing to an improvement in the energy density of the secondary battery.

[0122] In some embodiments, the coating has an areal density of 0.6 g / m 2 ~1.5g / m 2 Preferably, it is 0.8 g / m 2 ~1.1g / m 2 This results in a separator with superior heat resistance and ion transport properties.

[0123] In some embodiments, the thickness of the coating may be 1.5 μm or less, preferably 0.5 μm to 0.8 μm, thereby contributing to an improvement in the energy density of the secondary battery.

[0124] In some embodiments, the separator further includes 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 not only prevents peeling of the coating and improves the safety of the secondary battery, but also improves the interface between the separator and the electrodes, thereby improving the cycle characteristics of the secondary battery.

[0125] Preferably, the particulate binder comprises 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 copolymerizable monomer includes at least one of an acrylate-based monomer, an acrylic-based monomer, an olefin monomer, a halogen-containing olefin monomer, a fluoroether-based monomer, etc., but is not limited thereto.

[0126] Preferably, the particulate binder contains a vinylidene fluoride polymer, such as a homopolymer of vinylidene fluoride monomer (VDF) and / or a copolymer of vinylidene fluoride monomer and a copolymerizable monomer. The copolymerizable monomer may be at least one of an olefin monomer, a fluorine-containing olefin monomer, a chlorine-containing olefin monomer, an acrylate monomer, an acrylic monomer, and a fluoroether monomer. Preferably, the comonomer may include at least one of trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ether (e.g., perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE), perfluoro(propyl vinyl) ether (PPVE)), perfluoro(1,3-dioxole), and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD).

[0127] In some embodiments, the adhesive strength between the coating and the porous substrate is 16 N / m to 40 N / m, preferably 20 N / m to 35 N / m. Because the separator of the present application has high adhesive strength, the coating is less likely to peel off during long-term charge-discharge cycles of the secondary battery, improving the safety of the secondary battery.

[0128] In some embodiments, the separator has a longitudinal heat shrinkage of 5% or less, preferably 0.5% to 3%, at 150° C. for 1 hour.

[0129] In some embodiments, the separator has a transverse heat shrinkage of 5% or less, preferably 0.5% to 3%, at 150° C. for 1 hour.

[0130] The separator of the present invention 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 secondary batteries.

[0131] In some embodiments, the separator has a longitudinal tensile strength of 2000 kg / cm 2 More than 2500 kg / cm 2 ~4500kg / cm 2 is.

[0132] In some embodiments, the separator has a transverse tensile strength of 2000 kg / cm 2 More than 2500 kg / cm 2 ~4500kg / cm 2 is.

[0133] The separator of the present application has high tensile strength in both the horizontal and vertical directions, which reduces the probability of separator breakage when the secondary battery expands, further improving the safety of the secondary battery.

[0134] In some embodiments, the wetted length of the separator is 30 mm or more, preferably 30 mm to 80 mm.

[0135] In some embodiments, the wetting speed of the separator is 3 mm / s or more, preferably 3 mm / s to 10 mm / s.

[0136] The separator of the present invention has excellent electrolyte wettability, which can improve the ion transport properties of the secondary battery and the capacity of the secondary battery.

[0137] In some embodiments, the separator has an air permeability of 300 s / 100 mL or less, preferably 100 s / 100 mL to 230 s / 100 mL. The separator of the present application has good air permeability, which can improve the ion transport properties of the separator.

[0138] In this application, the average particle size Dv50 of a material has a meaning known in the art and can be measured by instruments and methods known in the art, for example, by testing using a laser particle size analyzer (e.g., Master Size 3000) in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0139] 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 according to the nitrogen adsorption specific surface area analysis test method in accordance with GB / T 19587-2017 and calculated by the Brunauer Emmett Teller (BET) method. Preferably, the nitrogen adsorption specific surface area analysis test can be performed using a Tri-Star 3020 specific surface area pore size analyzer manufactured by Micromeritics, Inc., USA.

[0140] As used herein, the surface tension of a coating and a porous substrate both have the meaning known in the art and can be measured by methods known in the art, for example, by testing with a dyne test pen.

[0141] In the present application, the adhesive strength between the coating and the porous substrate has a meaning known in the art and can be measured by a method known in the art, for example, referring to the GB / T 2792-2014 standard, a 180° peel test can be performed at a tensile speed of 50 mm / min using a tensile tester (for example, a tensile tester manufactured by GOTECH, in which the starting jig distance can be 40 mm) to calculate the adhesive strength.

[0142] In this application, the heat shrinkage rate, tensile strength, and air permeability of the separator all have meanings known in the art and can be measured by methods known in the art, for example, by testing them in accordance with GB / T 36363-2018 standard.

[0143] In this application, the wetting length and wetting rate of the separator have meanings known in the art and can be measured by methods known in the art. As an example of a test method, a separator is cut into a sample 5 mm wide and 100 mm long, and both ends of the sample are fixed and placed horizontally. 0.5 mg of electrolyte is dropped onto the center of the sample. After a predetermined time (1 min in this application), an image is taken to measure the diffusion length of the electrolyte, thereby obtaining the wetting length and wetting rate of the separator. To ensure the accuracy of the test results, multiple samples (e.g., 5 to 10) can be selected for testing, and the test results are averaged. The electrolyte can be prepared by mixing ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) in a mass ratio of 30:50:20 to obtain an organic solvent, dissolving thoroughly dried LiPF6 in the organic solvent, and preparing an electrolyte solution with a concentration of 1 mol / L.

[0144] The above-mentioned separator coating parameters (for example, surface density, thickness, etc.) are all parameters of the coating on one side of the porous substrate.

[0145] When a coating is applied to both sides of a porous substrate, the coating parameters on either side must meet the present application to be within the scope of protection of the present application. Manufacturing method

[0146] A second aspect of the present embodiment provides a method for producing a separator according to the first aspect of the present embodiment, comprising step S1 of providing a porous substrate, step S2 of providing a coating slurry containing nanocellulose, and step S3 of applying the coating slurry onto at least one surface of the porous substrate to form a coating, followed by drying to obtain a separator, wherein the separator comprises a porous substrate and a coating provided on at least one surface of the porous substrate, wherein the surface tension of the porous substrate is δ1 mN / m, the surface tension of the coating is δ2 mN / m, and the separator satisfies δ1 / δ2≧0.68.

[0147] In some embodiments, 0.68≦δ1 / δ2≦1.8, 0.7≦δ1 / δ2≦1.5, 0.7≦δ1 / δ2≦1.2, 0.7≦δ1 / δ2≦1.0, or 0.7≦δ1 / δ2≦0.9.

[0148] In some embodiments, in step S1, the surface tension δ1 mN / m of the porous substrate may satisfy δ1 ≧ 23, preferably 23 ≦ δ1 ≦ 45. When the surface tension of the porous substrate is within an appropriate range, coating leakage is less likely to occur when applying the coating slurry, and the coverage area of ​​the porous substrate is increased, which results in better heat resistance of the separator and higher safety of the secondary battery performance. This is also advantageous for maintaining high adhesive strength between the porous substrate and the coating, and greatly reduces the risk of coating peeling.

[0149] In the present application, porous substrates with different surface tensions are commercially available, and the surface of the porous substrate can be treated with an oxidizing agent or irradiated with ultraviolet light to give it the required surface tension.

[0150] In some embodiments, in step S2, the solvent may be water, for example, deionized water.

[0151] In some embodiments, in step S2, the coating slurry may include other components such as a binder, a filler, etc. Preferably, the binder includes an aqueous binder. Preferably, the filler includes at least secondary particles.

[0152] In some embodiments, in step S2, the coating slurry does not use a wetting agent.

[0153] In some embodiments, in step S2, the surface tension of the coating slurry may be 18 mN / m to 52 mN / m.

[0154] In some embodiments, in step S2, the solid content of the coating slurry can be controlled to be between 28% and 45%, for example, between 30% and 38%, which can effectively reduce problems with the coating surface and reduce the probability of uneven coating, thereby further improving the energy density and safety of the secondary battery.

[0155] In some embodiments, in step S2, the viscosity of the coating slurry may be 300 mPa·s to 1800 mPa·s, preferably 500 mPa·s to 1300 mPa·s. The viscosity of the coating slurry can be tested using a rotational viscometer.

[0156] In some embodiments, the nanocellulose is obtained by the following method: S21: Provide a cellulose powder with a whiteness of 80% or more. S22: Mix the obtained cellulose powder with a modifying solution to react, then wash to remove impurities, and obtain cellulose nanowhiskers. S23: Adjust the pH of the obtained cellulose nanowhiskers to neutral (e.g., pH 6.5 to 7.5), and further crush and cut them to obtain nanocellulose.

[0157] Preferably, in step S21, the cellulose powder having a whiteness of 80% or greater may be commercially available or may be obtained by a chemical method (e.g., acid hydrolysis, alkali treatment, or Tempo contact oxidation), a biological method (e.g., enzyme treatment), or a mechanical method (e.g., ultrafine grinding, ultrasonic disruption, or high-pressure homogenization). The fiber raw material for producing the cellulose powder having a whiteness of 80% or greater 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, and abaca fiber), palm fiber, wood fiber, bamboo fiber, and grass fiber.

[0158] In some embodiments, the cellulose powder having a whiteness of 80% or greater may be produced by the following method: After opening the fiber raw material to remove foreign matter, the raw material is steamed in an alkaline solution (for example, an NaOH aqueous solution with a concentration of 4 wt% to 20 wt%, preferably 5 wt% to 15 wt%), followed by washing with water to remove impurities (for example, washing with water 3 to 6 times), bleaching (for example, using sodium hypochlorite and / or hydrogen peroxide), pickling to remove impurities, washing with water to remove impurities, dehydration, and flash drying, to obtain a cellulose powder.

[0159] In some embodiments, in step S22, the denaturing solution may be an acid solution (e.g., sulfuric acid aqueous solution, boric acid aqueous solution, phosphoric acid aqueous solution, acetic acid aqueous solution) or an alkaline solution (e.g., urea organic solvent solution). Preferably, the denaturing solution is an acid solution.

[0160] Preferably, the concentration of the acid solution may be 5 wt% to 80 wt%. When a sulfuric acid aqueous solution is used as the modifying solution, the concentration of the acid solution may be 40 wt% to 80 wt%, thereby obtaining nanocellulose having sulfonic acid groups. When a boric acid aqueous solution is used as the modifying solution, the concentration of the acid solution may be 5 wt% to 10 wt%, thereby obtaining nanocellulose having boric acid groups. When a phosphoric acid aqueous solution is used as the modifying solution, the concentration of the acid solution may be 45 wt% to 75 wt%, thereby obtaining nanocellulose having phosphate groups. When an acetic acid aqueous solution is used as the modifying solution, the concentration of the acid solution may be 40 wt% to 80 wt%, thereby obtaining nanocellulose having carboxylic acid groups.

[0161] Preferably, the urea organic solvent solution is a urea xylene solution, thereby obtaining nanocellulose having amine groups.

[0162] In some embodiments, in step S22, the mass ratio of the cellulose powder to the modified solution may be preferably 1:2.5 to 1:50, and more preferably 1:5 to 1:30.

[0163] 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.

[0164] In some embodiments, in step S22, when the denaturing solution is an acid solution, the reaction may be carried out under conditions of 80°C or less, preferably 30°C to 60°C, and the reaction time between the cellulose powder and the denaturing solution may be 0.5 hours to 4 hours, preferably 1 hour to 3 hours.

[0165] In some embodiments, in step 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 hour to 5 hours.

[0166] In some embodiments, a grinder may be used for grinding and a high-pressure homogenizer may be used for cutting in step 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 various average lengths can be obtained.

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

[0168] In some embodiments, in step S3, the coating method may be transfer coating, spin coating, dip coating, or the like.

[0169] In some embodiments, the method may further include step S4 of applying a second coating: a slurry containing a particulate binder onto at least a portion of the surface of the coating and drying to form an adhesive layer.

[0170] The present separator manufacturing method produces a coating in a single application, greatly simplifying the process flow for producing separators.

[0171] Parameters such as some of the raw materials used in the manufacturing method of the separator of the present application and their contents can be referenced to the separator described in the first aspect of the embodiment of the present application, so they will not be described in detail here.

[0172] Unless otherwise specified, all of the raw materials used in the manufacturing method of the separator of the present invention are commercially available. secondary battery

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

[0174] A secondary battery, also known as a rechargeable battery or storage battery, is a battery that can continue to be used after discharge by activating the active material through charging. Typically, a secondary battery pack includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. The separator is disposed between the positive electrode plate and the negative electrode plate and mainly serves to prevent short circuits between the positive electrode and the negative electrode, and also allows active ions to pass through.

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

[0176] A secondary battery pack according to a third aspect of the present invention includes the separator according to the first aspect of the present invention or a separator manufactured by the method according to the second aspect of the present invention, the separator being interposed between the positive electrode plate and the negative electrode plate. Preferably, the separator has the coating of the present invention on at least the negative electrode plate side. This allows the secondary battery of the present invention to have high energy density, high thermal safety, and a long service life. [Positive electrode plate]

[0177] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer including a positive electrode active material, the positive electrode current collector having two opposing surfaces in a thickness direction of the positive electrode current collector, and the positive electrode film layer being provided on one or both of the two opposing surfaces of the positive electrode current collector.

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

[0179] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for the lithium-ion battery may include at least one of lithium transition metal oxides having the general formula Li a Ni b Co c M d O e A f and modified compounds 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.

[0180] As an example, the positive electrode active material for the lithium-ion battery is LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 At least one of O2, LiFePO4, and LiMnPO4 may be included.

[0181] 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., phosphate, fluorophosphate, pyrophosphate, sulfate, etc.), and a Prussian blue material, but is not limited to these.

[0182] As an example, positive electrode active materials for sodium ion batteries include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, NaNi 1 / 2 Ti 1 / 2 O2, NaNi 1 / 2 Mn 1 / 2 O2, Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2, NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue-based materials, general formula X p M' q (PO4) r O x Y 3-x The compound may contain at least one of the materials represented by the general formula X p M' q (PO4) 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 NH4 +wherein M' is a transition metal cation, preferably at least one of V, Ti, Mn, Fe, Co, Ni, Cu, and Zn; and Y is a halogen anion, preferably at least one of F, Cl, and Br.

[0183] 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.

[0184] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. The type of the positive electrode conductive agent is not particularly limited in the present application. For example, the positive 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 positive electrode conductive agent is 5% by mass or less, based on the total mass of the positive electrode film layer.

[0185] In some embodiments, the positive electrode film layer may further include a positive electrode binder. The type of the positive electrode binder is not particularly limited in the present application. For example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorinated acrylate resin. In some embodiments, the content of the positive electrode binder is 5% by mass or less, based on the total mass of the positive electrode film layer.

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

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

[0188] In some embodiments, the negative electrode plate 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 its thickness direction, and the negative electrode film layer is provided on either one or both of the two opposing surfaces of the negative electrode current collector.

[0189] The negative electrode active material may be any negative electrode active material for secondary batteries known in the art. For example, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of silicon elemental, silicon oxide, silicon carbon composite, silicon nitrogen composite, and silicon alloy material. The tin-based material may include at least one of tin elemental, tin oxide, and tin alloy material.

[0190] In some embodiments, the negative electrode film layer preferably further includes a negative electrode conductive agent. The type of the negative electrode conductive agent is not particularly limited herein. 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% by mass or less, based on the total mass of the negative electrode film layer.

[0191] In some embodiments, the negative electrode film layer preferably further includes a negative electrode binder. The type of the negative electrode binder is not particularly limited in the present application. For 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% by mass or less, based on the total mass of the negative electrode film layer.

[0192] In some embodiments, the negative electrode membrane layer preferably further contains other additives. For example, the other additives include a thickener, such as sodium carboxymethyl cellulose (CMC), a PTC thermistor material, etc. In some embodiments, the content of the other additives is 2% by mass or less, based on the total mass of the negative electrode membrane layer.

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

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

[0195] The negative electrode plate may include an additional functional layer other than the negative electrode film layer. For example, in some embodiments, the negative electrode plate of the present application may include a conductive primer (e.g., composed of a conductive agent and a binder) interposed between the negative electrode current collector and the negative electrode film layer and provided on the surface of the negative electrode current collector. In other embodiments, the negative electrode plate of the present application may further include a protective layer coated on the surface of the negative electrode film layer. [Electrolyte]

[0196] During the charge and discharge 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 electrodes. In the present application, the type of electrolyte is not particularly limited and can be selected according to actual needs.

[0197] 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.

[0198] When the secondary battery of the present application is a lithium-ion battery, for example, the electrolyte salt may include at least one of lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium triflate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium disoxalate borate (LiBOB), lithium difluorophosphate (LiPOF), lithium difluorobis(oxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP), but is not limited to these.

[0199] When the secondary battery of the present application is a sodium ion battery, for example, the electrolyte salt may include at least one of lithium hexafluorophosphate (NaPF), lithium tetrafluoroborate (NaBF), lithium perchlorate (NaClO), lithium hexafluoroarsenate (NaAsF), lithium bis(fluorosulfonyl)imide (NaFSI), lithium bistrifluoromethanesulfonylimide (NaTFSI), lithium triflate (NaTFS), lithium difluoro(oxalato)borate (NaDFOB), lithium bis(oxalato)borate (NaBOB), lithium difluorophosphate (NaPOF), lithium difluorobis(oxalato)phosphate (NaDFOP), and lithium tetrafluoro(oxalato)phosphate (NaTFOP), but is not limited to these.

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

[0201] In some embodiments, the electrolyte preferably includes an additive. For example, the additive may include an anode film-forming additive, a cathode film-forming additive, or 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.

[0202] In some embodiments, the positive electrode plate, the separator, and the negative electrode plate may be formed into an electrode assembly by a winding process and / or a stacking process.

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

[0204] In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, or a steel case. The exterior of the secondary battery may be a soft bag, such as a pouch-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).

[0205] In the present application, the shape of the secondary battery is not particularly limited, and it may be cylindrical, rectangular, or any other shape. Fig. 1 illustrates a secondary battery 5 having a rectangular structure.

[0206] 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 side plates connected to the bottom plate, and the bottom plate and side plates define a storage chamber. The case 51 has an opening communicating with the storage chamber, and the cover plate 53 covers the opening to seal the storage chamber. The positive electrode plate, the negative electrode plate, and the separator may be formed 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 electrode assembly 52 is impregnated with an electrolyte. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and can be adjusted as needed.

[0207] The method for manufacturing the secondary battery of the present application is well known. In some embodiments, a positive electrode plate, a separator, a negative electrode plate, and an electrolyte can be assembled into a secondary battery. For example, the positive electrode plate, the separator, and the negative electrode plate are wound and / or stacked to form 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.

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

[0209] 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 also be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed together using a fastener.

[0210] Preferably, the battery module 4 may have a shell having a storage space, and the plurality of secondary batteries 5 are stored in this storage space.

[0211] 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 depending on the application and capacity of the battery pack.

[0212] 4 and 5 are schematic diagrams of an example of a battery pack 1. As shown in FIGS. 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box. The battery box includes an upper 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

[0213] A fourth aspect of an embodiment of the present application 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 as an energy storage unit for the power consuming device. The power consuming device may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck), an electric train, a ship, a satellite, an energy storage system, etc.

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

[0215] 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. 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.

[0216] Other examples of power consuming devices may be mobile phones, tablets, laptops, etc. Such power consuming devices usually need to be lightweight and thin, and may therefore be powered by secondary batteries. Example

[0217] The following examples are provided to more specifically illustrate the present disclosure, and are merely illustrative, with various modifications and variations within the scope of the present disclosure being apparent to those skilled in the art. Unless otherwise specified, all parts, percentages, and ratios reported in the following examples are based on mass, 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. Production of nanocellulose C1

[0218] Cellulose powder production The cotton linters were opened in a cotton opener to remove foreign matter, and then steamed for 2 hours at 150°C using a 5 wt% NaOH aqueous solution. Subsequently, the cotton was washed with water to remove impurities (three times), bleached with sodium hypochlorite, washed with dilute hydrochloric acid to remove impurities, and washed with water (one time) to remove impurities. The cotton was then dehydrated and air-dried to obtain cotton cellulose powder with a whiteness of ≥85%.

[0219] esterification of cellulose 1 kg of the obtained cotton cellulose powder was mixed with 30 kg of 60 wt% sulfuric acid aqueous 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, deoxidized, and impurities were removed, yielding cellulose nanowhiskers with modified groups, which are sulfonic acid groups.

[0220] Neutralization of cellulose First, the pH of cellulose nanowhiskers modified with sulfonic acid groups was adjusted to neutral using a 10 wt% NaOH solution. The nanowhiskers were then dispersed in a grinder at high speed for 2.5 hours, crushed twice, and then cut into nanometer-level pieces using a high-pressure homogenizer. Nanocellulose C1, modified with sulfonic acid groups, had an average length of 475 nm and an average diameter of 25 nm. The molar ratio of sulfonic acid groups to hydroxyl groups was 5:3. Production of nanocellulose C2 to C10

[0221] Nanocelluloses C2 to C10 were produced by a method similar to that for nanocellulose C1, except for the details shown in Table 1. During the production process, nanocelluloses of various average diameters and / or lengths were produced by adjusting the processing parameters in the grinder and the cutting parameters in the high-pressure homogenizer. Production of nanocellulose C11

[0222] Cellulose powder production The cotton linters were opened in a cotton opener to remove foreign matter, then steamed in a 5 wt% NaOH solution at 150°C for 2 hours. The cotton was then washed three times to remove impurities, bleached with sodium hypochlorite, washed with dilute hydrochloric acid, and washed once to remove impurities. The cotton was then dehydrated and air-dried to obtain a cotton cellulose powder with a whiteness of 85% or greater. The resulting cotton cellulose powder was mixed with a 20 wt% NaOH solution at 10°C, stirred for 2 hours, filtered, and washed twice to obtain an alkaline cellulose powder.

[0223] esterification of cellulose 50 g of the obtained alkaline cellulose powder and 200 g of urea were placed in a three-necked flask equipped with an oil-water separator, and after dissolving the urea, 5 g of xylene was added. The mixture was heated to 137°C with stirring and reacted for 4 hours, after which the reaction was stopped. After that, the mixture was washed with water (three times), filtered, and dried to obtain cellulose carbamate.

[0224] Neutralization of cellulose The obtained cellulose carbamate was dissolved in a 5 wt% NaOH aqueous solution to obtain a uniform cellulose carbamate solution. It was then dispersed by high-speed processing in a grinder for 2.5 hours, and the number of grinding cycles was increased to two. It was then further cut at the nano-level using a high-pressure homogenizer to obtain nanocellulose with modified groups, which were amine groups, with an average length of 475 nm and an average diameter of 25 nm. The molar ratio of amine groups to hydroxyl groups was 4:3.

[0225] The molar ratio of modifying groups to hydroxyl groups can be measured using 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 raw cellulose and modified nanocellulose obtained is tested using the phthalic anhydride method described in GB / T 12008.3-2009. The resulting value is expressed in mg KOH / g and converted to mmol / g to determine the hydroxyl group content. Subtracting the hydroxyl group content of the modified nanocellulose from the hydroxyl group content of the raw cellulose gives the modifying group content (i.e., the content of modified hydroxyl groups), thereby determining the molar ratio of modifying groups to hydroxyl groups. Production of nanocellulose C12 and C13

[0226] The unmodified nanocellulose product, model number CNWS-50, purchased from Zhongke Leiming (Beijing) Technology Co., Ltd., was further processed in a grinder and / or a high-pressure homogenizer to obtain nanocellulose with different average diameters and / or different average lengths, as shown in Table 1.

[0227] [Table 1] Example 1

[0228] (1) Separator manufacturing In S1, a PE porous substrate with a thickness of 5 μm and a surface tension of 25 mN / m was provided. In S2, preparation of coating slurry: The nanocellulose C1 produced above, filler alumina (secondary particle form with an average particle size Dv50 of 160 nm), and binder aqueous solution polyacrylic acid were uniformly mixed in a mass ratio of 15:84.1:0.9 with an appropriate amount of deionized water as the solvent to obtain a coating slurry with a solid content of 35 wt% and a viscosity of 854 mPa·s. In S3, the coating slurry was applied to both surfaces of the porous PE substrate using a coater, and the substrate was dried and divided to obtain a separator. The thickness of the coating on one side of the porous PE substrate was 0.8 μm.

[0229] (2) Manufacturing of positive electrode plates LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2 (NCM811), carbon black (Super P) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were uniformly mixed in a mass ratio of 96.2:2.7:1.1 with an appropriate amount of N-methylpyrrolidone (NMP) as a solvent to obtain a positive electrode slurry. The positive electrode slurry was applied to an aluminum foil positive electrode current collector, and then baked, cold-rolled, slit, and cut to obtain a positive electrode plate. The positive electrode plate had an areal density of 0.207 mg / mm. 2 , press density 3.5g / cm 3 It was.

[0230] (3) Manufacturing of negative electrode plates 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). A 96.4:0.7:1.8:1.1 mass ratio of these materials was mixed uniformly with an appropriate amount of deionized water as a solvent to obtain a negative electrode slurry. The negative electrode slurry was then applied to a copper foil negative electrode current collector, followed by baking, cold rolling, slitting, and cutting to obtain a negative electrode plate. The negative electrode plate had an areal density of 0.126 mg / mm. 2 , press density 1.7g / cm 3 It was.

[0231] (4) Electrolyte production Ethylene carbonate (EC) and methyl ethyl carbonate (EMC) were mixed in a mass ratio of 30:70 to obtain an organic solvent, and LiPF6 that had been thoroughly dried was dissolved in the organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L.

[0232] (5) Secondary battery manufacturing The positive electrode plate, separator, and negative electrode plate were stacked in this order and wound to obtain an electrode assembly. The electrode assembly was placed in an outer casing, dried, and then an electrolyte solution was injected. The secondary battery was obtained through processes such as vacuum packaging, standing, formation, and shaping. Examples 2 to 6

[0233] Secondary batteries were fabricated in a similar manner to Example 3, except that the surface tensions of the porous substrates used to fabricate the separators were different, with the specific parameters being detailed in Table 2. Porous substrates with different surface tensions are commercially available, and the required surface tension can also be achieved by treating the surface of the porous substrate with an oxidizing agent or irradiating it with ultraviolet light. Examples 7 to 17

[0234] A secondary battery was manufactured in a similar manner to Example 3, except that the type of nanocellulose used to manufacture the separator was different and the specific parameters were as detailed in Tables 1 and 2. Examples 18 to 20

[0235] A secondary battery was manufactured in the same manner as in Example 3, except that the amounts of nanocellulose and filler added in the separator were different, and the specific parameters were as detailed in Table 2. Examples 21-22

[0236] In manufacturing the separator, a mixture of secondary particle-form alumina (average particle size Dv50 is 160 nm) and primary particle-form alumina (average particle size Dv50 is 400 nm) was used as a filler, and in Example 21, the mass ratio of the two was 90:10, and in Example 22, the mass ratio of the two was 70:30. Secondary batteries were manufactured by a method similar to that of Example 3, except that Comparative Example 1

[0237] A secondary battery was manufactured in a similar manner to Example 3, except that the manufacturing parameters of the separator were different: the surface tension of the PE porous substrate was 20 mN / m, the nanocellulose was unmodified nanocellulose number C12, and the filler was primary particle-form alumina with an average particle size Dv50 of 1000 nm. Comparative Example 2

[0238] A secondary battery was manufactured in the same manner as in Example 3, except that in the manufacture of the separator, the surface tension of the PE porous substrate was 20 mN / m and no filler was added to the coating slurry. Comparative Example 3

[0239] A secondary battery was manufactured in a similar manner to Example 3, except that the surface tension of the PE porous substrate in the manufacture of the separator was 20 mN / m, and primary particle-form alumina with an average particle size Dv50 of 400 nm was used as the filler. Comparative Example 4

[0240] A secondary battery was fabricated in the same manner as in Example 3, except that the surface tension of the PE porous substrate in the preparation of the separator was 20 mN / m.

[0241] [Table 2] JPEG0007785202000003.jpg92170 Test part

[0242] (1) Viscosity test of coating slurry The viscosity of the coating slurry was tested by a rotational viscometer at 25° C. The test equipment used was an AMETEK rotational viscometer with a rotation speed of 12 r / min.

[0243] (2) Surface tension of coatings and porous substrates Tested at 25°C with a dyne test pen.

[0244] (3) Testing the adhesive strength between the coating and the porous substrate The adhesive strength between the coating in the separator and the porous substrate was tested at 25°C using a tensile tester. The separator sample size may be 100 mm x 15 mm, the separator peel speed may be 50 mm / min, and the peel angle may be 180°. The tensile tester may be a GOTECH tensile tester with a starting jig distance of 40 mm. GB / T 2792-2014 may be used as the test standard.

[0245] (4) Separator heat shrinkage rate test Sample preparation: The separator prepared above was punched out into samples 50 mm wide and 100 mm long using a press, and five parallel samples were placed on A4 paper and fixed in place. Next, the A4 paper with the samples placed on it was placed on cardboard with a thickness of 1 mm to 5 mm.

[0246] Sample test: Set the temperature of the blast oven to 150°C. After 30 minutes, when the temperature has reached the predetermined temperature and stabilized, place an A4 sheet of paper placed on a piece of cardboard into the blast oven. Start timing. After the predetermined time (1 hour in this application), measure the length and width of the separator. These values ​​are a and b, respectively.

[0247] Calculation of heat shrinkage rate: Machine direction (MD) heat shrinkage rate = [(100-a) / 100] x 100%, Transverse direction (TD) heat shrinkage rate = [(50-b) / 50] x 100%. The average value of five parallel samples is taken as the test result.

[0248] (5) Separator breathability test The time required for 100 mL of air to pass through the separator is measured at 25°C, 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.

[0249] (6) Testing the cycle characteristics of secondary batteries At 25°C, the secondary battery was charged at a constant current of 1C to 4.2V, and then at a constant voltage until the current fell to 0.05C or less. At this point, the secondary battery was fully charged, and the charge capacity at this point was recorded as the charge capacity at the first cycle. After leaving the secondary battery stationary for 5 minutes, it was discharged at a constant current of 1C to 2.8V. This constituted one charge / discharge cycle, and the discharge capacity at this point was recorded as the discharge capacity at the first cycle. A charge / discharge cycle test was conducted on the secondary battery according to the method described above, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) of the secondary battery after 500 cycles at 25°C = discharge capacity after 500 cycles / discharge capacity at the first cycle × 100%.

[0250] (7) Hot box test of secondary batteries At 25°C, the rechargeable batteries were charged at 1C to 4.2V, then at constant voltage until the current fell below 0.05C. After 5 minutes of charging, the batteries were tested in a high-temperature oven equipped with a DHG-9070A DHG series fixture. The temperature was increased from room temperature to 100±2°C at a rate of 5°C / min, held for 30 minutes, and then increased at a rate of 5°C / min, with each 5°C increase being maintained for 30 minutes until the rechargeable battery failed. The surface temperature of the rechargeable battery was monitored during the heating process; when the temperature began to rise rapidly, the corresponding oven temperature reached the hot box failure temperature of the rechargeable battery. A higher hot box failure temperature indicated better thermal safety of the rechargeable battery.

[0251] [Table 3]

[0252] As can be seen from Table 3, in Examples 1 to 22, a coating containing nanocellulose was applied to two surfaces of the porous substrate of the separator, and the surface tension δ1 mN / m of the porous substrate and the surface tension δ2 mN / m of the coating satisfied the relationship δ1 / δ2≧0.68, preferably 0.68≦δ1 / δ2≦1.8, and more preferably 0.7≦δ1 / δ2≦1.2. This allows the separator to have low thermal shrinkage, high viscosity strength, and high breathability, and further allows the secondary battery to have high thermal safety and good cycle characteristics.

[0253] The alumina used in the coating of Comparative Example 1 is in the form of primary particles with large particle diameters, which means that the alumina and nanocellulose do not bond together, resulting in a deterioration of the heat resistance of the separator and the thermal safety of the secondary battery. Furthermore, Comparative Example 1 requires the use of a high content of binder when preparing the coating slurry, and if the amount of binder used is too high, pore clogging is likely to occur, thereby deteriorating the cycle characteristics of the secondary battery.

[0254] In Comparative Example 2, no alumina was used in the coating. In this case, the viscosity of the nanocellulose solution was high, resulting in poor breathability of the coating, poor cycle characteristics of the secondary battery, and poor heat resistance of the separator and thermal safety of the secondary battery.

[0255] The ratio of the surface tension of the porous substrate used in Comparative Examples 3 and 4 to the surface tension of the produced coating was less than 0.68, and in this case, there was a large area of ​​coating leakage when applying the coating slurry, resulting in poor adhesive strength of the separator, poor heat resistance, and poor thermal safety of the secondary battery.

[0256] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiment that has substantially the same configuration as the technical idea or exhibits the same effects within the scope of the technical solution of the present application is included within the technical scope of the present application. Furthermore, various modifications that a person skilled in the art may make to the embodiments or other forms constructed by combining some of the components of the embodiments are also included within the scope of the present application, as long as they do not deviate from the spirit of the present application.

Claims

1. A separator, A porous substrate and a coating provided on at least one surface of the porous substrate, wherein the coating comprises nanocellulose and a filler, the surface tension of the porous substrate is δ1 mN / m, the surface tension of the coating is δ2 mN / m, and the separator satisfies 0.68≦δ1 / δ2≦1.8; The content of the nanocellulose in the coating is 8 wt % to 40 wt %, based on the total weight of the coating; Separator.

2. 0.7≦δ1 / δ2≦1.2, and / or δ1≧23, and / or 25≦δ2≦50; The separator according to claim 1 .

3. 23≦δ1≦45, and / or 30≦δ2≦45; The separator according to claim 2 .

4. The nanocellulose includes at least one of unmodified nanocellulose and modified nanocellulose; The separator according to claim 1 .

5. 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 phosphate group; and / or The modified nanocellulose contains hydroxy groups and modifying groups, and the molar ratio of the modifying groups to the hydroxy groups is 1:4 to 4:1; The separator according to claim 4.

6. The nanocellulose is (1) The average diameter of the nanocellulose is 40 nm or less; (2) The average length of the nanocellulose is 100 nm to 600 nm; and (3) The aspect ratio of the nanocellulose satisfies at least one of the conditions of 5 to 60; The separator according to claim 1 .

7. The nanocellulose is (1) The average diameter of the nanocellulose is 10 nm to 35 nm; (2) The average length of the nanocellulose is 200 nm to 500 nm; and (3) The aspect ratio of the nanocellulose satisfies at least one of the conditions of 15 to 30; The separator according to claim 6.

8. The content of the nanocellulose in the coating is 10 wt % to 25 wt %, based on the total weight of the coating; The separator according to claim 1 .

9. The filler comprises at least one selected from inorganic particles and organic particles. The separator according to claim 1 .

10. The content of the filler in the coating is 59.1 wt% to 91.1 wt% based on the total weight of the coating. The separator according to claim 1 .

11. The content of the filler in the coating is 65 wt % to 90 wt % based on the total weight of the coating. The separator according to claim 10.

12. The filler comprises primary particles, secondary particles, or a combination thereof. The separator according to claim 1 .

13. The filler includes at least secondary particles, The average particle size Dv50 of the primary particle filler is 100 nm to 800 nm, The average particle size Dv50 of the secondary particle filler is 200 nm or less. The separator according to claim 12.

14. The filler comprises inorganic particles in the form of primary particles, inorganic particles in the form of secondary particles, or a combination thereof. The separator according to claim 1 .

15. The filler comprises inorganic particles in at least a secondary particle form, The crystalline form of the inorganic particles in the form of primary particles includes at least one of an α crystalline form and a γ crystalline form, The crystalline form of the inorganic particles in the form of secondary particles includes at least two of an α crystalline form, a θ crystalline form, a γ crystalline form, and an η crystalline form. The separator according to claim 14.

16. the coating further comprises a non-particulate binder; The separator according to claim 1 .

17. The coating does not contain a wetting agent. The separator according to claim 1 .

18. The thickness of the porous substrate is 6 μm or less, and / or The areal density of the coating is 0.6 g / m ２ and / or up to 1.5 g / m 2 ; The thickness of the coating is 1.5 μm or less. The separator according to claim 1 .

19. The thickness of the porous substrate is 3 μm to 5 μm, and / or the areal density of the coating is between 0.8 g / m 2 and 1.1 g / m 2 , and / or The thickness of the coating is 0.5 μm to 0.8 μm. The separator of claim 18.

20. 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; The separator according to claim 1 .

21. 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 separator of claim 20.

22. The separator is (1) The adhesive strength between the coating and the porous substrate is 16 N / m to 40 N / m; (2) The separator has a longitudinal heat shrinkage rate of 5% or less at 150°C for 1 hour. (3) The separator has a transverse heat shrinkage rate of 5% or less at 150°C for 1 hour. (4) The separator has a longitudinal tensile strength of 2000 kg / cm ２ The condition is equal to or greater than (5) The separator has a transverse tensile strength of 2000 kg / cm ２ The condition is equal to or greater than (6) The wet length of the separator is 30 mm or more. (7) The wetting speed of the separator is 3 mm / s or more. (8) The separator has an air permeability of 300 s / 100 mL or less. The separator according to claim 1 .

23. The separator is (1) The adhesive strength between the coating and the porous substrate is 20 N / m to 35 N / m; (2) The separator has a longitudinal heat shrinkage rate of 0.5% to 3% at 150°C for 1 hour. (3) The separator has a transverse heat shrinkage rate of 0.5% to 3% at 150°C for 1 hour. (4) The separator has a longitudinal tensile strength of 2500 kg / cm 2 to 4500 kg / cm 2 ; (5) The separator has a tensile strength in the transverse direction of 2500 kg / cm 2 to 4500 kg / cm 2 ; (6) The wet length of the separator is 30 mm to 80 mm. (7) The wetting speed of the separator is 3 mm / s to 10 mm / s. (8) The separator satisfies at least one of the following conditions: the air permeability is 100 s / 100 mL to 230 s / 100 mL; The separator of claim 22.

24. Step S1 of providing a porous substrate; Step S2 of providing a coating slurry comprising nanocellulose and a filler; and step S3 of applying the coating slurry onto at least one surface of the porous substrate to form a coating, followed by drying to obtain a separator, wherein the separator comprises a porous substrate and a coating provided on at least one surface of the porous substrate, wherein the surface tension of the porous substrate is δ1 mN / m, the surface tension of the coating is δ2 mN / m, the content of the nanocellulose in the coating is 8 wt% to 40 wt%, based on the total weight of the coating, and the separator satisfies 0.68≦δ1 / δ2≦1.

8. A method for producing the separator according to claim 1.

25. The surface tension of the coating slurry is 18 mN / m to 52 mN / m.

25. The method of claim 24.

26. Secondary application: further comprising step S4 of applying a slurry containing a particulate binder onto at least a portion of the surface of the coating and drying to form an adhesive layer; 25. The method of claim 24.

27. The separator according to any one of claims 1 to 23, Secondary battery.

28. The secondary battery according to claim 27, Power consumption equipment.

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