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

[0003] In recent years, secondary batteries have been widely used in many fields, such as energy storage power systems such as hydroelectric power plants, thermal power plants, wind power plants, and solar power plants, as well as in electric tools, electric bicycles, electric motorcycles, electric vehicles, military supplies, and aerospace. With the application and popularity of secondary batteries, their safety issues, especially thermal safety issues, have attracted more and more attention. The separator is one of the main components that determine the safety of secondary batteries, and in this field, how to provide a separator with excellent heat resistance and stable structure remains an important issue. 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 producing the same, and related secondary batteries and power consuming devices, which have the characteristics of excellent heat resistance and high viscous strength, and thereby enable secondary batteries using the separator to have 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 disposed on at least one surface of the porous substrate, the coating comprising nanocellulose, the surface tension of the porous substrate being δ1 mN / m, the surface tension of the coating being δ2 mN / m, and the separator satisfying δ1 / δ2≧0.68.

[0006] As a result of research, the inventors of the present application have surprisingly found that by making the surface tension δ1 mN / m of the porous substrate and the surface tension δ2 mN / m of the coating satisfy δ1 / δ2≧0.68, the adhesive strength between the porous substrate and the coating is high, thereby avoiding the problem of peeling of the coating during long-term charging and discharging of the secondary battery, and also avoiding the problem of coating leakage when applying the coating slurry, thereby giving the coating the characteristics of high uniformity and high coverage of the porous substrate, and further imparting excellent heat resistance to the separator. Therefore, the separator according to the present application has the characteristics of excellent heat resistance and high viscosity strength, and therefore the secondary battery using the separator can have high energy density, high thermal safety, and long service life.

[0007] In any embodiment of the present application, 0.68≦δ1 / δ2≦1.8, preferably 0.7≦δ1 / δ2≦1.2, so that the separator can more reliably combine the characteristics of excellent heat resistance, high viscosity strength, and good ion transport properties, and so that the secondary battery using the separator can 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 a suitable range, coating leakage is unlikely to occur when applying the coating slurry, and the coverage area of ​​the porous substrate is large, so that the separator has better heat resistance, the secondary battery performance has higher safety, and it is also advantageous for 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 contains a modified group, and the modified group contains 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 contains at least one of a sulfonic acid group, a boric acid group, and a phosphoric acid group. When nanocellulose has the above-mentioned specific modified group, it can effectively improve the heat resistance of the separator and improve the thermal safety of the secondary battery, while 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 hydroxyl group and a modifying group, and the molar ratio of the modifying group to the hydroxyl group is 1:4 to 4:1, preferably 2:3 to 7:3. When the molar ratio of the modifying group to the hydroxyl group is within an appropriate range, the heat resistance and ion transport properties of the separator can be further improved, and the separator can also be provided with high adhesive strength.

[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 heat 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 content of nanocellulose is in an appropriate range, it can ensure that the coating slurry has a more appropriate viscosity and is more favorable for application, and can maintain high adhesive strength between the coating and the porous substrate, improving the structural stability of the separator. Furthermore, it is favorable for nanocellulose and other components (e.g., fillers, etc.) to build a stable spatial network structure, which can further improve the performance of the separator.

[0018] In any embodiment of the present application, the coating further comprises a filler, the filler comprising 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 filler in the form of secondary particles has a small particle size, a large specific surface area, and better affinity with nanocellulose. In addition, nanocellulose can be bound to the gaps between the primary particles that make up the filler in the form of secondary particles, thereby combining the nanocellulose and the filler in the form of secondary particles to achieve an integration effect. Thus, the coating has a more stable spatial network structure, and the performance of the separator can be further improved.

[0022] The primary particle filler has a large particle size and high strength, and therefore can better exert a supporting effect as a skeleton in the coating, reduce the amount of binder used, lower the thermal shrinkage rate of the separator, and improve the heat resistance of the separator. In addition, 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 the form of at least secondary particles.

[0026] In any embodiment of the present application, the crystal form of the inorganic particles in the form of primary particles includes at least one of an α crystal form and a γ crystal form, and preferably includes an α crystal 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 based binder, which provides advantages in 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 upon 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, thereby contributing to an improvement in 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 can prevent peeling of the coating and improve the safety of the secondary battery, as well as improve the interface between the separator and the electrodes, 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 16N / m to 40N / m, preferably 20N / m to 35N / 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 at 150° C. for 1 hour of 5% or less, preferably 0.5% to 3%.

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

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

[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 performance of the separator 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 disposing the coating slurry on 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, the surface tension of the porous substrate being δ1 mN / m, the surface tension of the coating being δ2 mN / m, and the separator satisfying 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 includes a step S4 of a second coating: 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.

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

[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 the separator produced by the method of the second aspect of the present application.

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

[0051] 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 a long service life. The power consuming device according to the present application includes the secondary battery according to the present application, and therefore has at least the same advantages as the secondary battery. [Brief description of the drawings]

[0052] In order to more clearly describe the technical solutions of the embodiments of the present application, the following briefly describes 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 creative efforts. [Figure 1] FIG. 1 is a schematic diagram of one embodiment of a secondary battery of the present application. [Diagram 2] FIG. 2 is an exploded schematic view of the secondary battery of FIG. 1 according to the embodiment. [Diagram 3]FIG. 1 is a schematic diagram of one embodiment of a battery module of the present application. [Figure 4] FIG. 1 is a schematic diagram of one embodiment of a battery pack of the present application. [Diagram 5] 5 is an exploded schematic diagram 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 including 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 case 3 Lower housing 4 Battery Module 5 Secondary battery 51 cases 52 Electrode Assembly 53 Cover plate DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] Hereinafter, the separator specifically disclosed in the present application, its manufacturing method, and the related secondary battery and power consumption device will be described in detail with appropriate reference to the drawings. However, unnecessary detailed description may be omitted. For example, detailed description of already known matters and duplicated description of the same actual configuration may be omitted. This is to avoid the following description from becoming unnecessarily redundant and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0055] A "range" disclosed in this application is defined by a lower limit and an upper limit, and a particular range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner may or may not include the endpoint values ​​and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also envisioned. Furthermore, if minimum range values ​​1 and 2 are listed and maximum range values ​​3, 4, and 5 are listed, then the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all envisioned. In this application, unless otherwise stated, the numerical range "a-b" represents an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed herein, and "0-5" is merely an abbreviation for combinations of these numbers. Additionally, when describing a parameter as an integer greater than or equal to 2, this is equivalent to disclosing that the parameter is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[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 as included in the disclosure of the present application.

[0057] Unless otherwise specified, all 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 considered as included in the disclosure of the present application.

[0058] Unless otherwise specified, all steps in the present application can be performed sequentially or randomly, and are preferably performed sequentially. For example, when the method includes steps (a) and (b), it means that the method can include steps (a) and (b) performed sequentially, or can include steps (b) and (a) performed sequentially. For example, a statement that the method may further include step (c) means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b).

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

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

[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] Generally, a secondary battery includes an electrode assembly and an electrolyte, the electrode assembly including a positive electrode plate, a negative electrode plate, and a separator, the separator being disposed between the positive electrode plate and the negative electrode plate and mainly serving to prevent short-circuiting between the positive electrode and the negative electrode, and also allowing active ions to pass freely through it to form a circuit. Therefore, the stability of the separator, particularly its thermal stability and structural stability, directly affect 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 a 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 the 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 disposed on at least one surface of the porous substrate, the coating comprising nanocellulose, the surface tension of the porous substrate being δ1 mN / m, the surface tension of the coating being δ2 mN / m, and the separator satisfying δ1 / δ2≧0.68.

[0067] Currently, the separators used in commercially available secondary batteries are usually polyolefin films with a melting point of 130°C to 160°C, such as polyethylene films, polypropylene films, or polypropylene / polyethylene / polypropylene three-layer composite films. For this reason, the separator has poor heat resistance and shrinks severely when exposed to heat, increasing the risk of short circuit between the positive and negative electrodes. The heat resistance of the separator can be improved by applying a heat-resistant inorganic ceramic layer onto a porous substrate (which may be, for example, a polyolefin film, a nonwoven fabric, etc.). However, since the particle size of commercially available inorganic ceramic particles is large, the number of inorganic ceramic particles stacked on the porous substrate is small (usually 5 layers or less), and as a result, the effect of improving the heat resistance of the separator is limited, and the thickness of the entire separator increases, making it difficult to balance with the energy density of the secondary battery, which has a negative effect on the increase in mileage, especially in the field of power batteries. In addition, the adhesive strength between the inorganic ceramic layer and the porous substrate is also low, and there is a high risk that the inorganic ceramic layer will be wetted by the electrolyte and peeled off due to 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 (for example, within 100 nm), and has both the properties of cellulose and nanoparticles. Nanocellulose may be a polymeric nanomaterial extracted from wood, cotton, straw, etc. in nature by any or multiple means such as chemical, physical, biological, etc., and has the advantages of a wide supply source, low cost, biodegradability, high elastic modulus, high specific surface area, etc., making it an excellent alternative to traditional petrochemical resources and effectively alleviating problems such as environmental pollution and shortage of petrochemical resources. Nanocellulose also has good high temperature resistance properties, and the change in volume when exposed to heat is small, thereby improving the heat resistance of the separator, reducing the degree of shrinkage of the separator when heated, reducing the risk of short circuit between the positive and negative electrodes, and providing high thermal safety to the secondary battery. Nanocellulose has a lower density than conventional inorganic ceramic particles, so that the weight of the secondary battery can be reduced.

[0069] Therefore, when the coating of the present application contains nanocellulose, it is advantageous for improving the heat resistance of the separator. In addition, the coating of the present application is thinner and heavier than conventional inorganic ceramic layers, which is advantageous for improving the volumetric energy density and weight energy density of the secondary battery. Furthermore, since 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, coating leakage is likely to occur, thereby reducing the mechanical strength of the produced separator and increasing the risk of short-circuiting between the positive and negative electrodes.

[0071] As a result of research, the inventors of the present application have surprisingly found that by satisfying δ1 mN / m of the surface tension of the porous substrate and δ2 mN / m of the coating (both of which are coatings after drying in the present application) of δ1 / δ2≧0.68, the adhesive strength between the porous substrate and the coating is high, thereby avoiding the problem of peeling of the coating during long-term charging and discharging of the secondary battery, and also avoiding the problem of coating leakage when applying the coating slurry, thereby giving the coating high uniformity and high coverage of the porous substrate, and further imparting excellent heat resistance to the separator. If the surface tension of the porous substrate is low and the surface tension of the coating is high, and δ1 / δ2 is less than 0.68, coating leakage is likely to occur when applying the coating slurry, in which case the separator has poor heat resistance and low adhesive strength, and there is a high risk of the coating peeling off during long-term charging and discharging of the secondary battery.

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

[0073] As a result of research, the inventors of the present application have 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, since this will deteriorate the air permeability and ion transport properties of the separator, and will 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 the characteristics of excellent heat resistance, high viscosity strength, and good ion transport properties, and therefore allows the secondary battery 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 a suitable range, coating leakage is unlikely to occur when applying the coating slurry, and the coverage area on the porous substrate is increased, so that the separator has better heat resistance, the secondary battery performance has higher safety, and it is also advantageous to maintain high adhesive strength between the porous substrate and the coating, and greatly reduces the risk of peeling off of the coating.

[0075] In some embodiments, the surface tension δ2 mN / m of the coating may satisfy 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 significantly reducing the risk of the coating peeling off, 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.

[0076] During the long-term charging and discharging of the secondary battery, the microstructure of the positive and negative active materials changes irreversibly, which increases the volume of the entire battery, and especially in the case of high-speed charging of the secondary battery, the volume further increases when ions are embedded in the negative active material. When the battery expands, the separator is subjected to a pressing and / or pulling action, which is likely to cause the separator to break, thereby increasing the risk of short circuit between the positive and negative electrodes. Therefore, the separator is also required to have good resistance to external pressure. In some embodiments, the coating further includes a filler. The presence of the filler contributes to imparting a stable spatial network structure to the coating, which can improve the ion transport properties and heat resistance of the separator, and can further improve the tensile strength, puncture resistance, and external pressure resistance of the separator.

[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, so that the filler has excellent thermal stability and is not easily decomposed, and the heat resistance of the separator can be further improved.

[0079] Inorganic particles have excellent thermal stability and are not easily decomposed, and usually have hydroxyl groups on their surfaces, so they are easy to form a stable spatial network structure with nanocellulose. In some embodiments, the inorganic particles preferably include at least one of inorganic particles having a dielectric constant of 5 or more, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of 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)O 3 (abbreviated as PZT), Pb 1-m La m Zr 1-n Ti n O 3 (Abbreviated as PLZT, 0 <m<1、0<n<1)、Pb(Mg 3 Nb 2 / 3 )O 3 -PbTiO 3 (abbreviated as PMN-PT), and at least one of these modified inorganic particles. Preferably, the modification method of each inorganic particle may be chemical modification and / or physical modification. The chemical modification method includes modification using a coupling agent (e.g., silane coupling agent, titanate coupling agent, etc.), modification by a surfactant, modification by polymer grafting, etc. The physical modification method may be mechanical force dispersion, ultrasonic dispersion, high energy treatment, etc. The modification treatment can reduce the aggregation of inorganic particles. Thereby, the inorganic particles and nanocellulose can build a more stable and uniform spatial network structure. In addition, modifying the inorganic particles with a coupling agent, a surface active material or a polymer having a specific functional group is also advantageous for improving the wettability 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 Li 3 PO 4 , Lithium titanium phosphate Li x1 Tiy1 (PO 4 ) 3 、 lithium aluminum titanium phosphate Li x2 Al y2 Ti z1 (PO 4 ) 3 、 (LiAlTiP) x3 O y3 type glass, lithium lanthanum titanate Li x4 La y4 TiO 3 、 lithium germanium thiophosphate Li x5 Ge y5 P z2 S w 、 lithium nitride Li x6 N y6 、 SiS 2 type glass Li x7 Si y7 S z3 、 and P 2 S 5 type glass Li x8 P y8 S z4 includes at least one of, 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 not easily decomposed, which can improve the heat resistance of the separator. In addition, when the internal temperature of the secondary battery reaches the melting point of the organic particles due to overcharging or overheating, the organic particles melt and are absorbed into the micropores of the porous substrate by capillary action, closing the pores and breaking 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, cellulose modifiers (e.g., carboxymethyl cellulose), melamine resin particles, phenolic resin particles, polyester particles (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), organic silicone resin particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, polyaryletherketone particles, and copolymers of butyl acrylate and ethyl methacrylate (e.g., crosslinked polymers of butyl acrylate and ethyl methacrylate).

[0085] In some embodiments, the glass transition temperature of the organic particles may be preferably 130° C. or higher. Thus, when the internal temperature of the secondary battery reaches 130° C., the organic particles do not change from a glass state to a viscous flow state, thereby avoiding severe shrinkage of the separator. More preferably, the organic particles include at least one of melamine formaldehyde resin particles, phenolic resin particles, polyester particles, organic silicone resin particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, and polyaryletherketone particles, but are not limited thereto.

[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 favors the filler and nanocellulose to build a stable spatial network structure, further improving the separator's heat resistance, tensile strength, puncture resistance, and external force pressing resistance.

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

[0088] The filler in the form of secondary particles has a small particle size, a large specific surface area, and better affinity with nanocellulose. In addition, nanocellulose can be bound to the gaps between the primary particles that make up the filler in the form of secondary particles, thereby combining the nanocellulose and the filler in the form of secondary particles to achieve an integration effect. Thus, the coating has a more stable spatial network structure, and the performance of the separator can be further improved.

[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. In addition, even with a small amount used, the channel structure of the coating can be increased, 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 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.

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

[0097] In an X-ray diffraction spectrum measured by an X-ray diffractometer for the inorganic particles in the secondary particle form of the γ crystal form, the particles have diffraction peaks at 2θ of 66.95°±0.2° and 45.91°±0.2°. In some embodiments, the content of the γ 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] In an X-ray diffraction spectrum measured by an X-ray diffractometer for inorganic particles in the form of secondary particles of the η crystal form, the particles have diffraction peaks at 2θ of 31.89°±0.2° and 19.37°±0.2°. In some embodiments, the content of the η crystal 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 form of secondary particles.

[0099] Inorganic particles in the form of secondary particles of α crystal form 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 form have appropriate specific surface area and hardness, and 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 form and η crystal form have the advantage of large specific surface area. Therefore, selecting fillers with different crystal forms contributes to improving the heat resistance and ion transport properties of the separator.

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

[0101] The X-ray diffraction spectrum of inorganic particles in the form of secondary particles can be tested by the following method. After baking the inorganic particles in the form of secondary particles, they are ground in a mortar (e.g., an agate mortar) for 30 min, and then tested with an X-ray diffraction device (e.g., Miniflex600-C) to obtain an X-ray diffraction spectrum. The test may be performed using a Cu target material, a Ni filter, a tube voltage of 40 KV, a tube current of 15 mA, and a continuous scanning 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 the 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 crystal form of the inorganic particles in the form of primary particles includes an α crystal form, and the content of the α crystal form is 90 wt % or more, preferably 95 wt % to 100 wt %, based on the total weight of the inorganic particles in the form of primary particles.

[0104] In some embodiments, the nanocellulose may include at least one of cellulose nanofibers (Cellulose nanofibrils, CNF, also called nanofibril cellulose or microfibrillated cellulose), cellulose nanowhiskers (Cellulose nanocrystals, CNC, also called cellulose nanocrystals or nanocrystalline cellulose), and bacterial nanocellulose (Bacterial nanocellulose, BNC, also called bacterial cellulose or microbial cellulose), and is preferably cellulose nanowhiskers. Cellulose nanowhiskers have a high degree of crystallinity, so they are less hydrophilic and are advantageous for the discharge of moisture during drying, allowing the moisture content of the coating of the present application to be low. In addition, cellulose nanowhiskers are easily bonded to fillers, which can impart a more stable spatial network structure to the coating, thereby 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 a modifying group, which in some embodiments may comprise at least one of an amine group, a carboxylic acid group, an aldehyde group, a sulfonic acid group, a boric acid group, and a phosphate group, and preferably comprises at least one of a sulfonic acid group, a boric acid group, and a phosphate group.

[0107] After further research, the inventors found that when nanocellulose has the above-mentioned specific modified group, it can effectively improve the heat resistance of the separator and improve the thermal safety of the secondary battery, while being favorable for maintaining a high adhesive strength between the porous substrate and the coating, and greatly reducing the risk of coating peeling. When nanocellulose has the above-mentioned specific modified group, nanocellulose can also build a more stable spatial network structure together with the filler, which can further improve the ion transport properties and voltage breakdown resistance of the separator, which is favorable for combination with high voltage positive electrode active materials, and also further improve the energy density of the secondary battery. In addition, the presence of the modified group can reduce the proportion of hydroxyl groups, which can ensure that the coating slurry has a more suitable viscosity and is more favorable for application, and can also improve the production efficiency and coating uniformity of the separator.

[0108] In some embodiments, the modified nanocellulose contains a hydroxy group and a modifying group, and the molar ratio of the modifying group to the hydroxy group may be 1:4 to 4:1, 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 the separator can also be provided with high adhesive strength.

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

[0110] In some embodiments, the average diameter of the nanocellulose may be 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 heat 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, and 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 sample of 3.6 mm x 3.6 mm is cut out from any region of the separator, and the microstructure of the coating in the sample is plotted using a scanning electron microscope (e.g., ZEISS Sigma 300), and an SEM image is obtained by selecting high vacuum mode, operating voltage of 3 kV, and magnification of 30,000 times. From the obtained SEM image, multiple test areas (e.g., 5 or more) with a size of 0.5 μm x 0.5 μm are selected and their lengths are statistically analyzed, and then the average value of the length obtained for each test area is taken as the average length of nanocellulose. From the obtained SEM image, multiple test areas (e.g., 5 or more) with a size of 0.5 μm x 0.5 μm are selected and their diameters are statistically analyzed using Nano Measurer particle size distribution statistical software, and then the average value of the diameters obtained for each test area is taken as the average diameter of nanocellulose.

[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 be prevented from causing clogging of the channel structure of the separator, 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 favorable for improving the quality of the coating, 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-shaped. The appropriate shape of the nanocellulose is more advantageous for building a stable spatial network structure together with the filler, thereby further improving the ion transport properties and external force compression resistance of the separator.

[0116] In some embodiments, the content of the nanocellulose in the coating may be 8 wt% or more, preferably 8 wt% to 35 wt%, more preferably 10 wt% to 25 wt%, based on the total weight of the coating. When the content of nanocellulose is in an appropriate range, it can ensure that the coating slurry has a more appropriate viscosity and is more favorable for application. When the content of nanocellulose is in an appropriate range, it can also maintain high adhesion strength between the coating and the porous substrate, and improve the structural stability of the separator. Furthermore, when the content of nanocellulose is in an appropriate range, it is favorable for nanocellulose and other components (e.g., fillers, etc.) to build a stable spatial network structure, and the ion conduction ability, external force pressing resistance, and voltage breakdown resistance of the separator can be further improved.

[0117] In some embodiments, the coating may further include a non-particulate binder. In the present application, the type of the non-particulate binder is not particularly limited and may be any material known to have good adhesion. Preferably, the non-particulate binder includes an aqueous binder having the advantages of good thermodynamic stability and environmental protection, thereby being advantageous in the preparation and application of the coating slurry. As an example, the aqueous binder includes 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), an isobutylene-maleic anhydride copolymer, and a 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 build 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, a polyoxyethylene-polyoxypropylene block copolymer wetting agent, etc. Wetting agents are usually compounds with low surface tension and high fluidity, which tend to cause clogging of the pores of the porous substrate during application and drying of the coating slurry. Since the coating of the present application does not contain a wetting agent, clogging of the pores of the porous substrate during application and drying of the coating slurry can be avoided. After conducting research, the present inventors have found that the coating slurry of the present application has excellent wettability, so that it is not necessary 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 stability and mechanical stability, such as at least one of glass fiber, nonwoven fabric, and polyolefin membrane (e.g., polyethylene, polypropylene, and polyvinylidene fluoride, etc.), may be used. The porous substrate may be a single layer membrane or a multilayer composite membrane. When the porous substrate is a multilayer 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 thinner, which contributes to improving 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 and preferably 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, and 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 can prevent peeling of the coating and improve the safety of the secondary battery, as well as improve the interface between the separator and the electrodes, 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 monomer, a homopolymer or copolymer of an acrylic monomer, and a homopolymer or copolymer of a fluorine-containing olefin monomer. The copolymerization monomer comprises at least one of an acrylate monomer, an acrylic monomer, an olefin monomer, a halogen-containing olefin monomer, a fluoroether monomer, and the like, but is not limited thereto.

[0126] Preferably, the particulate binder includes a vinylidene fluoride polymer, such as a homopolymer of vinylidene fluoride monomer (VDF) and / or a copolymer of vinylidene fluoride monomer and a copolymer monomer. The copolymer 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) ethers (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. Since 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, and the safety of the secondary battery is better.

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

[0130] The separator of the present application has a low thermal shrinkage rate in both the transverse and longitudinal directions at a high temperature of 150° C., which can further improve the safety of the secondary battery.

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

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

[0133] The separator of the present application has high tensile strength in both the transverse and longitudinal directions, which reduces the probability of the separator being broken when the secondary battery swells, thereby further improving the safety of the secondary battery.

[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 application 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, it can be tested using a laser particle size analyzer (e.g., Master Size 3000) with reference to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0139] In the present application, the specific surface area of ​​a material has a meaning known in the art and can be measured by instruments and methods known in the art. For example, it can be tested by the nitrogen adsorption specific surface area analysis test method with reference to GB / T 19587-2017 and calculated by the BET (Brunauer Emmett Teller) method. Preferably, the nitrogen adsorption specific surface area analysis test can be performed by a Tri-Star 3020 type specific surface area pore size analysis tester manufactured by Micromeritics, USA.

[0140] As used herein, the surface tension of the coating and the 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 by a tensile tester (e.g., a tensile tester from GOTECH, the starting jig interval of which can be 40 mm) at a tensile speed of 50 mm / min 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, they can be tested with reference to the GB / T 36363-2018 standard.

[0143] In the present application, the wetting length and wetting speed of the separator both have the meanings known in the art and can be measured by methods known in the art. As an example of a test method, the separator is cut into a sample with a width of 5 mm and a length of 100 mm, and both ends of the sample are fixed and placed horizontally. 0.5 mg of electrolyte is dropped into the center of the sample, and after a predetermined time (1 min in the present application), an image is taken to measure the diffusion length of the electrolyte, thereby obtaining the wetting length and wetting speed of the separator. In order to ensure the accuracy of the test results, multiple samples (e.g., 5 to 10 samples) can be selected for testing, and an average value is calculated as the test result. The electrolyte is LiPF2, which is an organic solvent obtained by mixing ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) in a mass ratio of 30:50:20, and is thoroughly dried. 6 The electrolyte can be prepared by dissolving the above in the organic solvent to prepare an electrolyte solution having a concentration of 1 mol / L.

[0144] It should be noted that the above separator coating parameters (eg, areal density, thickness, etc.) are all parameters for the coating on one side of the porous substrate.

[0145] When a coating is applied to both sides of a porous substrate, it is within the scope of protection of the present application if the coating parameters of either side meet 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, the separator comprising a porous substrate and a coating provided on at least one surface of the porous substrate, the surface tension of the porous substrate being δ1 mN / m, the surface tension of the coating being δ2 mN / m, and the separator satisfying 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, and preferably 23≦δ1≦45. When the surface tension of the porous substrate is within an appropriate range, coating leakage is unlikely to occur when applying the coating slurry, and the coverage area on the porous substrate is increased, so that the separator has better heat resistance, the secondary battery performance has higher safety, and it is also advantageous to maintain high adhesive strength between the porous substrate and the coating, and greatly reduces the risk of peeling off of the coating.

[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 between 18 mN / m and 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%. When the solid content of the coating slurry is within the above range, it can effectively reduce the problem of the coating film surface, reduce the probability of coating unevenness, and further improve 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 by a rotational viscometer.

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

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

[0158] In some embodiments, the cellulose powder having a whiteness of ≧80% 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 (e.g., an aqueous NaOH solution having a concentration of 4 wt% to 20 wt%, preferably 5 wt% to 15 wt%), and then the raw material is washed with water to remove impurities (e.g., 3 to 6 times), bleached (e.g., using sodium hypochlorite and / or hydrogen peroxide), pickled to remove impurities, washed with water to remove impurities, dehydrated, and flash dried to obtain a cellulose powder.

[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 an aqueous sulfuric acid 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 an aqueous boric acid 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 an aqueous phosphoric acid solution is used as the modifying solution, the concentration of the acid solution may be 45 wt% to 75 wt%, thereby obtaining nanocellulose having phosphoric acid groups. When an aqueous acetic acid solution is used as the 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 is 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 0.5h to 4h, preferably 1h to 3h.

[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 h to 5 h.

[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 different average diameters and / or different average lengths can be obtained.

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

[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 a second coating: 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.

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

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

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

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

[0174] A secondary battery, also called a rechargeable battery or storage battery, refers to a battery that can be used continuously after being discharged by activating the active material through charging. A secondary battery pack typically includes an electrode assembly and an electrolyte, the electrode assembly including a positive electrode plate, a negative electrode plate, and a separator, the separator being disposed between the positive electrode plate and the negative electrode plate and mainly serving to prevent short circuits between the positive electrode and the negative electrode, and also allowing active ions to pass through.

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

[0176] The secondary battery pack according to the third aspect of the present invention includes the separator according to the first aspect of the present invention or the separator produced 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, at least the negative electrode plate side of the separator has the coating of the present invention. Thereby, the secondary battery according to the present invention can have a 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 provided on at least one surface of the positive electrode current collector and containing a positive electrode active material. For example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode film layer is provided on one or both of the two opposing surfaces of the positive electrode current collector.

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

[0179] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for a lithium-ion battery may include at least one of a lithium transition metal oxide having the general formula Li a Ni b Co c M d O e A f and a modified compound thereof. 0.8 ≦ a ≦ 1.2, 0.5 ≦ b < 1, 0 < c < 1, 0 < d < 1, 1 ≦ e ≦ 2, 0 ≦ f ≦ 1, M is at least one selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is at least one selected from N, F, S, and Cl.

[0180] As an example, the positive electrode active material for lithium-ion batteries is LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O 2 , LiFePO 4 , LiMnPO 4 may contain at least one of the following:

[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., a phosphate, a fluorophosphate, a pyrophosphate, a sulfate, etc.), and a Prussian blue-type material, but is not limited thereto.

[0182] As an example, the positive electrode active material for sodium-ion batteries is NaFeO 2 , NaCoO 2 , NaCrO 2 , NaMnO 2 , NaNiO 2 , NaNi 1 / 2 Ti 1 / 2 O 2 , NaNi 1 / 2 Mn 1 / 2 O 2 , Na 2 / 3 Fe 1 / 3 Mn2 / 3 O 2 , NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 , NaFePO 4 , NaMnPO 4 , NaCoPO 4 , Prussian blue-based materials, the general formula of which is X p M' q (PO 4 ) r O x Y 3-x The material may include at least one of the materials represented by the general formula X p M' q (PO 4 ) r O x Y 3-x In, 0 <p≦4、0<q≦2、1≦r≦3、0≦x≦2であり、Xは、H + , Li + , Na + , K + , and N.H. 4 + 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. In the present application, the type of the positive electrode conductive agent is not particularly limited, and as an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the content of the positive electrode conductive agent is 5 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. In the present application, the type of the positive electrode binder is not particularly limited, and as an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. In some embodiments, the content of the positive electrode binder is 5 mass% or less based on the total mass of the positive electrode film layer.

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

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

[0188] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer including a negative electrode active material, the negative electrode current collector having two opposing surfaces in a thickness direction of the negative electrode current collector, for example, the negative electrode current collector having two opposing surfaces in a thickness direction of the negative electrode current collector, the negative electrode film layer being provided on either one or both of the two opposing surfaces of the negative electrode current collector.

[0189] The negative electrode active material can be any negative electrode active material for secondary batteries known in the art. As an example, the negative electrode active material can include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, but is not limited thereto. The silicon-based material can include at least one of silicon elemental, silicon oxide, silicon carbon composite, silicon nitrogen composite, and silicon alloy material. The tin-based material can 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. In the present application, the type of the negative electrode conductive agent is not particularly limited, and as an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the content of the negative electrode conductive agent may be 5 mass% or less based on the total mass of the negative electrode film layer.

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

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

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

[0194] The negative electrode film layer is usually obtained by applying a negative electrode slurry onto a negative electrode current collector, drying and cold rolling. The negative electrode slurry is usually formed by dispersing a negative electrode active material, an optional conductive agent, an optional binder, and any other auxiliary agent 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., made of a conductive agent and a binder) interposed between the negative electrode collector and the negative electrode film layer and provided on the surface of the negative electrode collector. In 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] In the charging and discharging process of the secondary battery, active ions are repeatedly absorbed and released between the positive and negative electrodes, and the electrolyte serves to conduct the active ions between the positive and negative 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 is lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium triflate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium disoxalate borate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorobis(oxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0199] When the secondary battery of the present application is a sodium ion battery, for example, the electrolyte salt is lithium hexafluorophosphate (NaPF 6 ), lithium tetrafluoroborate (NaBF 4 ), lithium perchlorate (NaClO 4 ), lithium hexafluoroarsenate (NaAsF 6 ), lithium bis(fluorosulfonyl)imide (NaFSI), lithium bistrifluoromethanesulfonylimide (NaTFSI), lithium triflate (NaTFS), lithium difluoro(oxalato)borate (NaDFOB), lithium bis(oxalato)borate (NaBOB), lithium difluorophosphate (NaPO 2 F 2 ), lithium difluorobis(oxalato)phosphate (NaDFOP), and lithium tetrafluoro(oxalato)phosphate (NaTFOP).

[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, may include a cathode film-forming additive, or may include an additive that can improve some performance of the battery, such as an additive that can improve the overcharge performance of the battery, an additive that can improve the high temperature performance of the battery, or an additive that can improve the power performance of the battery at low temperature.

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

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

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

[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. In one example, the positive electrode plate, the separator, and the negative electrode plate are wound and / or stacked into an electrode assembly, and the electrode assembly is placed in an outer casing and baked. After that, the 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 of the present application may be assembled into a battery module, and the number of secondary batteries included in the battery module may be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[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 be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed via a fastener.

[0210] Preferably, the battery module 4 may have a shell having a storage space, and the multiple secondary batteries 5 are stored in the 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 according to 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 Fig. 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box. The battery box includes an upper housing 2 and a lower housing 3, and the upper housing 2 is covered by the lower housing 3 to form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner. power consumption equipment

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

[0214] The power consuming 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, etc. To address the power consuming device's need for high power output and high energy density, a battery pack or battery module may be employed.

[0216] Other examples of power consuming devices may be mobile phones, tablets, laptops, etc. Such power consuming devices usually require light weight and thinness, and may be powered by secondary batteries. Working Example

[0217] The following examples are provided to more specifically illustrate the present disclosure, and these examples are merely illustrative, and various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise specified, all parts, percentages and ratios reported in the following examples are based on mass quantification, 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] Production of cellulose powder The cotton linters were opened in a cotton opener to remove foreign matter, then steamed in a 5 wt% NaOH aqueous solution at 150°C for 2 hours, followed by washing with water to remove impurities (three times), bleaching with sodium hypochlorite, washing with dilute hydrochloric acid to remove impurities, and washing with water to remove impurities (one time), followed by dehydration and air drying to obtain cotton cellulose powder with a whiteness of ≧85%.

[0219] Cellulose Esterification 1 kg of the obtained cotton cellulose powder was mixed with 30 kg of 60 wt % aqueous sulfuric acid solution and reacted at 60°C for 1.5 hours. After the reaction was completed, the mixture was washed with water to remove impurities (three times), filtered, deacidified and impurities removed, and cellulose nanowhiskers having modified groups, which are sulfonic acid groups, were obtained.

[0220] Neutralization of cellulose First, the pH of cellulose nanowhiskers having modified groups, which are sulfonic acid groups, was adjusted to neutral using a 10 wt% NaOH aqueous solution, then the whiskers were dispersed by high-speed processing in a grinder for 2.5 hours, the whiskers were ground twice, and the whiskers were cut at the nano level using a high-pressure homogenizer to obtain nanocellulose C1 having modified groups, which are sulfonic acid groups, with 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-C10

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

[0222] Production of cellulose powder The cotton linters were opened in a cotton opener to remove foreign matter, then steamed in 5wt% NaOH aqueous solution at 150℃ for 2h, followed by washing with water to remove impurities (3 times), bleaching with sodium hypochlorite, washing with dilute hydrochloric acid to remove impurities, and washing with water to remove impurities (1 time), followed by dehydration and air drying to obtain cotton cellulose powder with a whiteness of ≧85%. The obtained cotton cellulose powder was mixed with 20wt% NaOH aqueous solution at 10℃, stirred for 2h, filtered, and washed twice to obtain alkaline cellulose powder.

[0223] Cellulose Esterification 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. The mixture was then 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, which was then dispersed by high-speed processing in a grinder for 2.5 hours, with the number of grinding cycles being two. The resulting solution was then cut at the nano-level using a high-pressure homogenizer to obtain nanocellulose with modified groups that are amine groups, with an average length of 475 nm and an average diameter of 25 nm, and the molar ratio of amine groups to hydroxyl groups was 4:3.

[0225] The molar ratio of the modified group to the hydroxyl group can be measured by the following method. The hydroxyl value (the number of milligrams of potassium hydroxide equivalent to the hydroxyl group content per gram of sample) of the obtained raw cellulose and modified nanocellulose is tested by the phthalic anhydride method described in GB / T 12008.3-2009, and the obtained value is expressed in mg KOH / g. This value is converted to mmol / g to obtain the hydroxyl group content. The content of the modified group (i.e., the content of the hydroxyl group to be modified) is obtained by subtracting the content of the hydroxyl group of the modified nanocellulose from the content of the hydroxyl group of the raw cellulose, thereby obtaining the molar ratio of the modified group to the hydroxyl group. Production of nanocellulose C12 and C13

[0226] The unmodified nanocellulose product, model number CNWS-50, purchased from Zhongke Leiming (Beijing) Technology Co., Ltd., can be 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-based 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, coating: the prepared coating slurry was applied to the two surfaces of the PE porous substrate using a coater, and the separator was obtained through the process of drying and dividing. The thickness of the coating on one side of the PE porous substrate was 0.8 μm.

[0229] (2) Manufacturing of positive electrodes LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 O 2 A positive electrode slurry was obtained by uniformly mixing NCM811, carbon black (Super P) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a mass ratio of 96.2:2.7:1.1 with an appropriate amount of N-methylpyrrolidone (NMP) as a solvent. The positive electrode slurry was applied onto an aluminum foil positive electrode current collector, and the positive electrode plate was obtained through processes such as baking, cold rolling, slitting, and cutting. 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 electrodes The negative electrode active material was artificial graphite, the conductive agent was carbon black (Super P), and the binders were styrene butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC). The mixture was mixed uniformly in a mass ratio of 96.4:0.7:1.8:1.1 with an appropriate amount of deionized water as a solvent to obtain a negative electrode slurry. The negative electrode slurry was applied onto the copper foil of the negative electrode current collector, and the negative electrode plate was obtained through processes such as baking, cold rolling, slitting, and cutting. The negative electrode plate had an areal density of 0.126 mg / mm 2 , press density 1.7g / cm 3 It was.

[0231] (4) Manufacturing of electrolyte Ethylene carbonate (EC) and methyl ethyl carbonate (EMC) were mixed in a mass ratio of 30:70 to obtain an organic solvent, and the LiPF 6 was dissolved in the above organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L.

[0232] (5) Manufacture of secondary batteries The positive electrode plate, the separator, and the 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 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 manufactured in a similar manner to Example 3, except that the surface tensions of the porous substrates used to manufacture the separators were different, with the specific parameters being detailed in Table 2. 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. Examples 7 to 17

[0234] A secondary battery was manufactured in a manner similar to that of 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 preparation of the separator were different, and the specific parameters were as detailed in Table 2. Examples 21-22

[0236] In the manufacture of 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. Except for this, secondary batteries were manufactured by a method similar to that of Example 3. Comparative Example 1

[0237] A secondary battery was manufactured by a method similar to that of 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 alumina in the form of primary particles with an average particle size Dv50 of 1000 nm. Comparative Example 2

[0238] In the preparation of the separator, the surface tension of the PE porous substrate was 20 mN / m, and no filler was added to the coating slurry, but the secondary battery was prepared in a similar manner to that of Example 3. Comparative Example 3

[0239] In the preparation of the separator, the surface tension of the PE porous substrate was 20 mN / m, and the filler was alumina in the form of primary particles with an average particle size Dv50 of 400 nm. A secondary battery was prepared in the same manner as in Example 3. Comparative Example 4

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

[0241] [Table 2] JPEG2025517448000004.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 was an AMETEK rotational viscometer with a rotation speed of 12 r / min.

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

[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 by a tensile tester at 25°C. The separator sample size can be 100mm x 15mm, the separator peel speed can be 50mm / min, the peel angle can be 180°, and the tensile tester can be a GOTECH tensile tester with a starting jig interval of 40mm. GB / T 2792-2014 can be referred to as the test standard.

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

[0246] Sample test: Set the temperature of the blast oven to 150℃. After 30 minutes from when the temperature reaches the specified temperature and becomes stable, place an A4 sheet of paper placed on a piece of cardboard into the blast oven and start timing. After the specified time (1 hour in this application) is reached, measure the length and width of the separator and let these values ​​be a and b respectively.

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

[0248] (5) Separator breathability test The time required for 100 mL of air to pass through the separator at 25° C. is measured, and the average value of five parallel samples is taken as the test result. A Kumagaya KRK Oken type air permeability tester can be used as the test equipment.

[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 charged at a constant voltage until the current became 0.05C or less, at which 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, which constituted one cycle of charge and discharge, and the discharge capacity at this point was recorded as the discharge capacity at the first cycle. A charge and discharge cycle test of the secondary battery was carried out according to the above method, and the discharge capacity after each cycle was recorded. 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℃, the secondary battery was charged at 1C with constant current to 4.2V, then charged at constant voltage until the current was below 0.05C, and left for 5min, then tested in a high-temperature oven equipped with a DHG-9070A DHG series fixture, i.e., heated from room temperature to 100±2℃ at a rate of 5℃ / min, held for 30min, then heated at a rate of 5℃ / min, and kept for 30min every 5℃ until the secondary battery failed. The change in the surface temperature of the secondary battery during the heating process was monitored, and when the temperature began to rise rapidly, the corresponding oven temperature became the hot box failure temperature of the secondary battery. The higher the hot box failure temperature of the secondary battery, the better the thermal safety of the secondary battery.

[0251] [Table 3]

[0252] As can be seen from Table 3, in Examples 1 to 22, a coating containing nanocellulose is provided on 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 satisfy 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 viscous 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, and the particle size is large, so there is no binding effect between the alumina and nanocellulose, which leads to deterioration of the heat resistance of the separator and the thermal safety of the secondary battery. Furthermore, in Comparative Example 1, a high content of binder is required when producing the coating slurry, and if the amount of binder used is too large, clogging of the pores is likely to occur, which deteriorates 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 Example 3 and Comparative Example 4 to the surface tension of the prepared coating is less than 0.68, in which case there is a large area of ​​coating leakage when applying the coating slurry, which results in poor adhesive strength of the separator, poor heat resistance, and poor thermal safety of the secondary battery.

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

Claims

1. A separator, A porous substrate and a coating provided on at least one surface of the porous substrate, the coating comprising nanocellulose, the surface tension of the porous substrate being δ1 mN / m, the surface tension of the coating being δ2 mN / m, and the separator satisfying δ1 / δ2≧0.68; Separator.

2. 0.68≦δ1 / δ2≦1.8, preferably 0.7≦δ1 / δ2≦1.2, and / or δ1≧23, preferably 23≦δ1≦45, and / or 25≦δ2≦50, preferably 30≦δ2≦45; The separator according to claim 1 .

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

4. The nanocellulose is (1) The average diameter of the nanocellulose is 40 nm or less, preferably 10 nm to 35 nm; (2) The average length of the nanocellulose is 100 nm to 600 nm, preferably 200 nm to 500 nm; and (3) The aspect ratio of the nanocellulose is 5 to 60, preferably 15 to 30, and at least one of the following conditions is satisfied: The separator according to any one of claims 1 to 3.

5. 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; The separator according to any one of claims 1 to 4.

6. The coating further comprises a filler, the filler comprising at least one selected from inorganic particles and organic particles; The separator according to any one of claims 1 to 5.

7. 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; The separator according to claim 6.

8. The filler comprises primary particles, secondary particles, or a combination thereof, preferably the filler comprises at least secondary particles; Preferably, the average particle size Dv50 of the filler in the form of primary particles is 100 nm to 800 nm, more preferably 200 nm to 400 nm; Preferably, the average particle size Dv50 of the filler in the form of secondary particles is 200 nm or less, more preferably 50 nm to 200 nm. The separator according to claim 6 or 7.

9. 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 the form of at least secondary particles; Preferably, the crystal form of the inorganic particles in the form of primary particles includes at least one of an α crystal form and a γ crystal form, more preferably includes an α crystal form; Preferably, the crystal form of the inorganic particles in the form of secondary particles includes at least two of α crystal form, θ crystal form, γ crystal form, and η crystal form, more preferably includes at least two of α crystal form, θ crystal form, and γ crystal form. The separator according to any one of claims 6 to 8.

10. the coating further comprises a non-particulate binder; Preferably, the non-particulate binder comprises an aqueous binder, 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 separator according to any one of claims 1 to 9.

11. The coating does not contain a wetting agent. The separator according to any one of claims 1 to 10.

12. The thickness of the porous substrate is 6 μm or less, preferably 3 μm to 5 μm, and / or The areal density of the coating is 0.6 g / m ２ ~1.5g / m ２ , preferably 0.8 g / m ２ ~1.1 g / m ２ and / or The thickness of the coating is less than or equal to 1.5 μm, preferably between 0.5 μm and 0.8 μm; The separator according to any one of claims 1 to 11.

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

14. The separator is (1) 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; (2) The separator has a longitudinal heat shrinkage rate of 5% or less, preferably 0.5% to 3% at 150° C. for 1 h. (3) The separator has a transverse heat shrinkage rate of 5% or less, preferably 0.5% to 3% at 150° C. for 1 h. (4) The separator has a longitudinal tensile strength of 2000 kg / cm ２ More than 2500 kg / cm ２ ~4500kg / cm ２ The condition that (5) The separator has a lateral tensile strength of 2000 kg / cm ２ More than 2500 kg / cm ２ ~4500kg / cm ２ The condition that (6) The wet length of the separator is 30 mm or more, preferably 30 mm to 80 mm. (7) The wetting speed of the separator is 3 mm / s or more, preferably 3 mm / s to 10 mm / s. (8) 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 according to any one of claims 1 to 13.

15. Step S1 of providing a porous substrate; providing a coating slurry comprising nanocellulose; and step S3 of applying the coating slurry onto at least one surface of the porous substrate to form a coating, and then drying the coating to obtain a separator. The separator includes a porous substrate and a coating provided on at least one surface of the porous substrate, 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. A method for producing the separator according to any one of claims 1 to 14.

16. The coating slurry further comprises a filler. The method of claim 15.

17. The surface tension of the coating slurry is 18 mN / m to 52 mN / m; 17. The method according to claim 15 or 16.

18. 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; The method according to any one of claims 15 to 17.

19. The separator according to any one of claims 1 to 14 or the separator produced by the method according to any one of claims 15 to 18, Secondary battery.

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

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