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

Abstract

The present application provides a separator including a porous substrate and a coating layer provided on at least one surface of the porous substrate, a manufacturing method thereof, and a secondary battery and a power consumption device related thereto, the coating layer including a three-dimensional skeleton structure and a filler, at least a portion of the filler being filled in the three-dimensional skeleton structure, and the filler being secondary particles formed by aggregation of primary particles. The separator provided by the present application has characteristics such as excellent heat resistance, high adhesive strength, and good electrolyte infiltration and retention properties, and therefore a secondary battery using the separator can achieve both high energy density, high thermal safety performance, long cycle life, and good rate performance.

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 Jun. 24, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to the field of battery technology, and in particular to separators, their manufacturing methods, 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 for hydroelectric, thermal, wind and solar power plants, electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. With the application and popularity of secondary batteries, their safety issues, especially thermal safety issues, have attracted more and more attention. However, currently, methods for improving the thermal safety performance of secondary batteries may be unfavorable to the balance between the energy density and service life of secondary batteries. Therefore, achieving high energy density, high thermal safety performance, long cycle life and good rate performance in secondary batteries has become an important issue in secondary battery design. Summary of the Invention

[0004] The object of the present application is to provide a separator, a manufacturing method thereof, and related secondary batteries and power consuming devices, which have characteristics such as excellent heat resistance, high adhesive strength, and good electrolyte infiltration and retention properties, thereby enabling secondary batteries using the separator to achieve both high energy density, high thermal safety performance, long cycle life, and good rate performance.

[0005] A first aspect of the present application provides a separator comprising a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer including a three-dimensional skeletal structure and a filler, at least a portion of the filler being filled into the three-dimensional skeletal structure, and the filler being secondary particles formed by aggregation of primary particles.

[0006] The filler in the coating layer is a secondary particle formed by agglomeration of primary particles, and the filler in the form of secondary particles has the advantage of having a large specific surface area and good affinity with the three-dimensional skeleton structure, so that it can form a stable spatial network structure with the three-dimensional skeleton structure, increase the ion conduction path of the separator, promote ion transport, and improve the electrolyte infiltration and retention properties of the separator, so that the secondary battery using the separator of the present application can have a long cycle life and good rate performance. At least a part of the filler is filled into the three-dimensional skeleton structure, which contributes to the formation of a nesting effect between the filler and the three-dimensional skeleton structure, improves the heat resistance of the separator, reduces the degree of shrinkage when the separator is subjected to heat, reduces the risk of short-circuiting between the positive electrode and the negative electrode, and the secondary battery has high thermal safety performance, and maintains high adhesive strength between the coating layer and the porous substrate, and can avoid the filler from falling off during long-term charging and discharging of the secondary battery. The coating layer of the present application includes a three-dimensional skeleton structure, and at least a part of the filler is filled in the three-dimensional skeleton structure, so that there are many contact sites between the filler and the three-dimensional skeleton structure, which can reduce the amount of adhesive used in the coating layer, effectively reduce the risk of pore clogging caused by the adhesive, and further improve the cycle life and rate performance of the secondary battery.The coating layer of the present application has high heat resistance, so that a thinner porous substrate can be selected, and the secondary battery can also have a high energy density.

[0007] In any embodiment of the present application, the average particle size of the primary particles constituting the filler is 8 nm to 30 nm, preferably 10 nm to 20 nm, which allows the filler to have a good secondary particle morphology, and within an appropriate range, the filler and the three-dimensional skeleton structure can be better overlapped to form an integration effect.

[0008] In any embodiment of the present application, the average particle size of the filler is 200 nm or less, preferably 50 nm to 200 nm, so that the filler has a high specific surface area and the filler having an average particle size within an appropriate range can be better matched with the length of the three-dimensional skeleton structure, so that the filler and the three-dimensional skeleton structure can be better overlapped to form an integrated effect, and the affinity between the filler and the three-dimensional skeleton structure can be increased, and the electrolyte infiltration and retention properties of the separator can be improved.

[0009] In any embodiment of the present application, the BET specific surface area of ​​the filler is 20 m 2 / g or more, preferably 30m 2 / g~80m 2 This improves the affinity between the filler and the three-dimensional framework structure, and increases the electrolyte infiltration and retention properties of the separator.

[0010] In any embodiment of the present application, the filler comprises at least one of inorganic particles and organic particles.

[0011] In any embodiment of the present application, the inorganic particles include at least one of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon-oxygen compounds, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, zirconium titanate, barium titanate, and magnesium fluoride, and more preferably, the inorganic particles include at least one of boehmite, alumina, barium sulfate, magnesium oxide, silicon-oxygen compounds, titanium oxide, zinc oxide, cerium oxide, and barium titanate.

[0012] In any embodiment of the present application, the organic particles include at least one of polystyrene and polyacrylic wax.

[0013] In any embodiment of the present application, the filler comprises inorganic particles in a secondary particle form, and the crystalline form of the inorganic particles in the secondary particle form comprises at least two of α-crystalline form, θ-crystalline form, γ-crystalline form, and η-crystalline form. Preferably, the crystalline form of the inorganic particles in the secondary particle form comprises at least two of α-crystalline form, θ-crystalline form, and γ-crystalline form.

[0014] In any embodiment of the present application, the content of the α-crystalline secondary inorganic particles in the secondary inorganic particles is 1.2 wt% or more, more preferably 1.2 wt% to 10 wt%, based on the total weight of the secondary inorganic particles.

[0015] In any embodiment of the present application, the content of the θ crystal form inorganic particles in the secondary particle form in the inorganic particles in the secondary particle form is 50 wt% or more, more preferably 60 wt% to 85 wt%, based on the total weight of the inorganic particles in the secondary particle form.

[0016] In any embodiment of the present application, the content of the inorganic particles in the form of secondary particles of γ crystal form in the inorganic particles in the form of secondary particles is 10 wt% or more, more preferably 15 to 60 wt%, based on the total weight of the inorganic particles in the form of secondary particles.

[0017] In any embodiment of the present application, the content of the inorganic particles in the form of secondary particles of the η crystal form in the inorganic particles in the form of secondary particles is 5 wt % or less, more preferably 2 wt % or less, based on the total weight of the inorganic particles in the form of secondary particles.

[0018] Selection of a filler having a different crystal form contributes to improving at least one of the heat resistance, adhesive strength, and electrolyte infiltration and retention properties of the separator.

[0019] In any embodiment of the present application, the average particle size of the primary particles constituting the filler is d 1 nm, and the average diameter of the material constituting the three-dimensional framework is d 2 nm, and the separator is JPEG2025517447000002.jpg1231. In this case, the material constituting the three-dimensional skeleton structure overlaps and connects to the gaps between the primary particles constituting the filler, thereby contributing to the integration effect due to the overlap between the filler and the three-dimensional skeleton structure, the coating layer can have a more stable spatial network structure, and the coating layer can also have a uniform nanopore structure, and the separator can better combine high heat resistance, high adhesive strength, and good electrolyte infiltration and retention properties.

[0020] In any embodiment of the present application, the three-dimensional framework structure is formed from fibrous materials, and preferably, the morphology of the fibrous materials includes at least one of rod-like, tubular, and fibrous.

[0021] In any embodiment of the present application, the material constituting the three-dimensional framework has an average diameter of 40 nm or less, preferably 10 nm to 35 nm, which can further improve the ion transport properties and voltage breakdown properties of the separator, and can also contribute to an integration effect due to the overlap between the material constituting the three-dimensional framework and the filler, thereby further improving the heat resistance of the separator.

[0022] In any embodiment of the present application, the average length of the material constituting the three-dimensional framework structure is 100 nm to 600 nm, and preferably 200 nm to 450 nm, which can further improve the heat resistance and ion transport properties of the separator.

[0023] In any embodiment of the present application, the aspect ratio of the material constituting the three-dimensional framework structure is from 5 to 60, and preferably from 10 to 30. This can further improve the electrolyte infiltration and retention properties of the separator.

[0024] In any embodiment of the present application, the fibrous material comprises at least one of an organic material and an inorganic material. Preferably, the organic material comprises at least one of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers, and preferably, the nanocellulose comprises at least one of cellulose nanofibers, cellulose nanowhiskers, and bacterial nanocellulose. Preferably, the inorganic material comprises at least one of halloysite nanotubes, nanorod-shaped alumina, nanorod-shaped boehmite, nanorod-shaped silica, and glass fibers.

[0025] In any embodiment of the present application, the material constituting the three-dimensional framework structure comprises nanocellulose, and the nanocellulose comprises at least one of unmodified nanocellulose and modified nanocellulose.

[0026] In any embodiment of the present application, the modified nanocellulose comprises a modified group, the modified group comprising at least one of an amine group, a carboxyl 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. When the nanocellulose has the above-mentioned specific modified group, it can effectively improve the heat resistance of the separator and improve the thermal safety performance of the secondary battery. Meanwhile, it can improve the adhesive strength between the coating layer and the porous substrate.

[0027] 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, more preferably 2:3 to 7:3. This can further improve the heat resistance, ion transport properties, and electrolyte infiltration and retention properties of the separator.

[0028] In any embodiment of the present application, the material constituting the three-dimensional skeletal structure contains a sulfonic acid group, and the content of sulfur element in the material constituting the three-dimensional skeletal structure is 0.1 wt% or more, preferably 0.2 wt% to 0.5 wt%, based on the total weight of the material constituting the three-dimensional skeletal structure.

[0029] In any embodiment of the present application, the content of the three-dimensional skeletal structure is 5 wt % to 40 wt %, and preferably 10 wt % to 25 wt %, based on the total weight of the coating layer.

[0030] In any embodiment of the present application, the content of the filler is 60 wt % or more, and preferably 70 wt % to 90 wt %, based on the total weight of the coating layer.

[0031] When the three-dimensional framework and the content of the filler are within a suitable range, the slurry of the coating layer can be ensured to have a suitable viscosity, which is more convenient for application, and the overlapping of the three-dimensional framework and the filler can be advantageously integrated, so that the coating layer can have a more stable spatial network structure.

[0032] In any embodiment of the present application, the coating layer further comprises inorganic particles in the form of primary particles, and at least a part of the inorganic particles in the form of primary particles is embedded in the coating layer, which can better exert its supporting effect in the coating layer, reduce the shrinkage of secondary particles, reduce the amount of adhesive used, and improve the heat resistance of the separator.

[0033] In any embodiment of the present application, the primary particle-type inorganic particles have an average particle size of 200 nm to 800 nm, preferably 200 nm to 400 nm, which can better exert the supporting effect of the primary particle-type inorganic particles, and the coating layer can maintain a stable pore structure during long-term charge and discharge, which is advantageous for ion transport and can improve the heat resistance of the separator.

[0034] In any embodiment of the present application, the inorganic particles in the form of primary particles have a BET specific surface area of ​​10 m 2 / g or less, preferably 3m 2 / g~7m 2 This allows the inorganic particles in the form of primary particles to better exert their supporting effect, and the coating layer maintains a stable pore structure during long-term charge and discharge processes, which is advantageous for ion transport and improves the heat resistance of the separator.

[0035] In any embodiment of the present application, the crystalline form of the inorganic particles in the form of primary particles includes at least one of α crystalline form and γ crystalline form, and preferably includes α crystalline form, which can further improve the heat resistance of the coating layer.

[0036] In any embodiment of the present application, the crystal form of the inorganic particles in primary particle form includes an α-crystal form, and the content of the α-crystal form inorganic particles in the inorganic particles in primary particle form is 90 wt% or more, more preferably 95 wt% to 100 wt%, based on the total weight of the inorganic particles in primary particle form.

[0037] In any embodiment of the present application, the inorganic particles in the form of primary particles include at least one of inorganic particles having a dielectric constant of 5 or more, inorganic particles having ionic conductivity but not storing ions, and inorganic particles capable of undergoing an electrochemical reaction.

[0038] In any embodiment of the present application, the content of the inorganic particles in the form of primary particles is 30 wt% or less, preferably 5 wt% to 25 wt% based on the total weight of the coating layer, so that the supporting effect of the inorganic particles in the form of primary particles can be better exhibited, the coating layer can maintain a stable pore structure during long-term charging and discharging, which is advantageous for ion transport and can improve the heat resistance of the separator.

[0039] In any embodiment of the present application, the coating layer further comprises a non-particulate adhesive.

[0040] In any embodiment of the present application, the non-particulate adhesive comprises a water-based adhesive.

[0041] In any embodiment of the present application, the content of the non-particulate adhesive in the coating layer is 2 wt% or less based on the total weight of the coating layer. The present application allows the separator to maintain high adhesiveness while reducing the amount of adhesive used.

[0042] In any embodiment of the present application, the thickness of the porous substrate is 6 μm or less, and preferably 3 μm to 5 μm, which contributes to improving the energy density of the secondary battery.

[0043] In any embodiment of the present application, the thickness of the coating layer is 1 μm or less, and preferably 0.5 μm to 0.8 μm, which contributes to improving the energy density of the secondary battery.

[0044] In any embodiment of the present application, the separator further includes an adhesive layer provided on at least a portion of the surface of the coating layer, the adhesive layer including a particulate adhesive. The adhesive layer can prevent the coating layer from falling off and improve the safety performance of the secondary battery, as well as improve the interface between the separator and the electrodes, thereby improving the cycle performance of the secondary battery.

[0045] In any embodiment of the present application, the particulate adhesive includes at least one of an acrylic ester monomer homopolymer or copolymer, an acrylic acid monomer homopolymer or copolymer, and a fluorine-containing olefin monomer homopolymer or copolymer.

[0046] In any embodiment of the present application, the separator has a longitudinal heat shrinkage rate of 5% or less at 150° C. for 1 hour, and preferably 0.5% to 3%.

[0047] In any embodiment of the present application, the separator has a transverse heat shrinkage rate of 5% or less at 150° C. for 1 hour, and preferably 0.5% to 3%.

[0048] 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.

[0049] 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.

[0050] In any embodiment of the present application, the wetted length of the separator is 30 mm or more, and preferably 30 mm to 80 mm.

[0051] In any embodiment of the present application, the wetting speed of the separator is 3 mm / s or more, and preferably 3 mm / s to 10 mm / s.

[0052] In any embodiment of the present application, the separator has an air permeability of 300s / 100mL or less, and preferably 100s / 100mL to 230s / 100mL.

[0053] If the separator performance satisfies one or more of the above conditions, it is advantageous for improving at least one of the energy density, thermal safety performance, cycle life, and rate performance of the secondary battery.

[0054] A second aspect of the present application provides a method for producing a separator according to the first aspect of the present application, comprising: a step S1 of supplying a porous substrate; a slurry supplying step S2 of mixing a material for constituting a three-dimensional skeletal structure and a filler in a solvent in a predetermined ratio to prepare the slurry; and a coating step S3 of applying the slurry to at least one surface of the porous substrate and drying to obtain a separator, the separator comprising a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer comprising a three-dimensional skeletal structure and a filler, at least a portion of the filler being filled in the three-dimensional skeletal structure, and the filler being secondary particles formed by aggregation of primary particles.

[0055] The method for producing a separator according to the present application produces a coating layer in a single application, greatly simplifying the separator production process.

[0056] In any embodiment of the present application, the slurry further comprises inorganic particles in the form of primary particles.

[0057] In any embodiment of the present application, the manufacturing method further includes a two-time coating step S4 of coating a slurry containing a particulate adhesive on at least a portion of the surface of the coating layer and drying to form an adhesive layer.

[0058] A third aspect of the present application provides a secondary battery comprising the separator of the first aspect of the present application or a separator produced by the method of the second aspect of the present application.

[0059] A fourth aspect of the present application provides a power consuming device including the secondary battery of the third aspect of the present application.

[0060] The separator provided by the present application can achieve high heat resistance, high adhesive strength, and good electrolyte infiltration and retention properties, and can also achieve high energy density, high thermal safety performance, long cycle life, and good rate performance in a secondary battery. The power consumption device of the present application is equipped with the secondary battery provided by the present application, and therefore has at least the same advantages as the secondary battery. [Brief description of the drawings]

[0061] In order to more clearly describe the technical solutions of the embodiments of the present application, the drawings that need to be used in the embodiments of the present application are briefly described below. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can also obtain other drawings based on the drawings without creative efforts.

[0062] [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 embodiment of the secondary battery of FIG. 1. [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 view of the embodiment of the battery pack shown in FIG. 4. [Figure 6]1 is a schematic diagram of one embodiment of a power consuming device that includes a secondary battery of the present application as a power source. [Figure 7] FIG. 2 is a transmission electron microscope (TEM) view of the secondary particle morphology of the filler according to the present application. [Figure 8] FIG. 2 is a scanning electron microscope (SEM) image of the coating layer of the separator produced in Example 1. [Figure 9] FIG. 2 is a scanning electron microscope (SEM) image of the coating layer of the separator produced in Example 23.

[0063] 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

[0064] Hereinafter, with appropriate reference to the drawings, an embodiment specifically disclosing the separator of the present application, its manufacturing method, and the related secondary battery and power consumption device will be described in detail. However, unnecessary detailed description may be omitted. For example, detailed description of known matters and duplicated description of substantially the same configuration may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the attached 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.

[0065] The "ranges" disclosed in this application are defined in the form of lower and upper limits, where a given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such defined ranges may be inclusive or exclusive of the end values, and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, when ranges of 60-120 and 80-110 are recited for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Also, when minimum range values ​​1 and 2 and maximum range values ​​3, 4 and 5 are recited, ranges of 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 may all be contemplated. In this application, unless otherwise stated, the numerical range "a-b" is represented by the abbreviation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, with "0-5" being an abbreviation for combinations of these numerical values. Furthermore, expressing a parameter as an integer greater than or equal to 2 (≧2) is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0066] Unless otherwise specified, all the embodiments and optional embodiments of the present application may be combined with each other to form a new technical solution, and such technical solution should be considered as being included in the disclosure content of the present application.

[0067] Unless otherwise stated, all technical features and optional technical features of the present application may be combined with each other to form a new technical solution, and such technical solution should be considered as included in the disclosure content of the present application.

[0068] Unless otherwise stated, all steps in the present application may be performed in sequence or randomly, but are preferably performed in sequence. For example, the method includes steps (a) and (b) and may include steps (a) and (b) performed in sequence, or may include steps (b) and (a) performed in sequence. For example, when it is stated that the method may further include step (c), it means that step (c) may 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), etc.

[0069] Unless otherwise specified, the terms "comprise" and "include" used in this application mean open-ended and may also be closed-ended. For example, the terms "comprise" and "include" can mean "comprise" or "include" other components not listed, or "comprise" or "include" only the listed components.

[0070] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions are met: 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).

[0071] Unless otherwise explained, terms used in this application have the known meanings commonly understood by those of ordinary skill in the art.

[0072] Unless otherwise specified, the numerical values ​​of each parameter mentioned in this application can be measured by various test methods commonly used in the field, for example, according to the test methods provided in the examples of this application.

[0073] Typically, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is disposed between the positive electrode sheet and the negative electrode sheet and serves mainly to prevent short circuits between the positive electrode and the negative electrode, while allowing active ions to pass freely through the separator to form a circuit.

[0074] With the application and popularization of secondary batteries, the requirements for the energy density, service life, and rate performance of secondary batteries are becoming higher and higher. Thinning the separator is an effective measure to improve the energy density of secondary batteries. Currently, the separators used in commercialized secondary batteries are usually polyolefin porous membranes, such as polyethylene porous membranes, polypropylene porous membranes, or polypropylene / polyethylene / polypropylene three-layer composite membranes, and their melting points are 130°C to 160°C. Therefore, when the thickness is thin, the heat resistance of the separator is poor, and when exposed to heat, a significant heat shrinkage effect occurs, causing direct contact between the positive and negative electrodes inside the battery, resulting in an internal short circuit, and further increasing the safety risk of the secondary battery.

[0075] The separator also needs to have good electrolyte infiltration and retention properties. During the long-term charge and discharge process of a secondary battery, the separator gradually dries up and no longer functions, which is an important factor in causing a decrease in the battery capacity and shortening of the service life of the secondary battery. This is because after the separator dries up, the internal resistance of the battery increases, charging and discharging are not completed, and the capacity of the secondary battery is rapidly attenuated, and the service life is significantly shortened. If the separator becomes thin, the electrolyte infiltration and retention properties become poor, which further accelerates the capacity attenuation.

[0076] To solve the above problems, the current approach is to coat a heat-resistant inorganic ceramic layer on the polyolefin porous membrane, which can increase the mechanical strength of the separator, reduce the degree of shrinkage of the separator when it is heated, and reduce the risk of short-circuiting between the positive and negative electrodes inside the battery. In addition, compared with the polyolefin porous membrane, the inorganic ceramic layer can improve the wetting and retention properties of the electrolyte due to the presence of hydroxyl groups on the surface, which can improve the cycle performance of the secondary battery to a certain extent.

[0077] However, because commercially available inorganic ceramic particles have a large particle size, the thickness of the entire separator increases, making it impossible to balance the energy density of the secondary battery, which is disadvantageous in improving the driving range, especially in the field of power batteries. In addition, because commercially available inorganic ceramic particles have a large particle size, the number of deposited layers in the polyolefin porous membrane is small (usually 5 layers or less), and the effect of improving the heat resistance of the separator is limited. Nano-sizing of inorganic ceramic particles can reduce the thickness of the coating layer and mitigate the adverse effect on the energy density of the secondary battery, but the porosity of the coating layer formed by nano-sizing inorganic ceramic particles is low and tends to block the polyolefin porous membrane, which reduces the porosity of the entire separator, increases the impedance of ions, inhibits ion transport, and further deteriorates the capacity and rate performance of the secondary battery. At the same time, because the specific surface area of ​​nano-sized inorganic ceramic particles is high and the contact form between particles is point contact, it is necessary to use a large amount of adhesive to ensure the adhesion between particles, but if the amount of adhesive used is large, it is easy to cause pore clogging problems, which is unfavorable to the rate performance of secondary batteries, such as the formation of dendrites on the surface of the negative electrode, and is also unfavorable to the capacity, energy density and service life of secondary batteries.In addition, the adhesion between the inorganic ceramic layer and the polyolefin porous membrane is poor, and during the long-term charge and discharge process of secondary batteries, the inorganic ceramic layer is easy to fall off, which causes a series of safety problems.

[0078] Therefore, it is difficult for the separators of the prior art to simultaneously achieve high energy density, high thermal safety performance, long cycle life, and good rate performance of the secondary battery.

[0079] In the course of research, the inventors of the present application unexpectedly discovered that by providing a coating layer containing a filler with a three-dimensional skeletal structure and secondary particle form on the surface of a separator porous substrate, it is possible to achieve a separator that combines high heat resistance, high adhesive strength, and good electrolyte infiltration and retention characteristics, and further to achieve a secondary battery that combines high energy density, high thermal safety performance, long cycle life, and good rate performance.

[0080] Separator

[0081] Specifically, a first aspect of an embodiment of the present application provides a separator including a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer including a three-dimensional skeletal structure and a filler, at least a portion of the filler being filled in the three-dimensional skeletal structure, and the filler being secondary particles formed by aggregation of primary particles. In the present application, the "three-dimensional skeletal structure" is a structure having a three-dimensional spatial shape and a certain amount of voids, and the materials constituting the three-dimensional skeletal structure are overlapped with each other.

[0082] As a result of intensive research, the inventors of the present application have unexpectedly discovered that by providing a coating layer containing a three-dimensional skeletal structure and a filler in the form of secondary particles on at least one surface of a porous substrate of a separator, and filling at least a portion of the filler into the three-dimensional skeletal structure, the resulting separator can achieve both high heat resistance, high adhesive strength, and good electrolyte infiltration and retention characteristics, and further, can achieve both high energy density, high thermal safety performance, long cycle life, and good rate performance in a secondary battery.

[0083] Although the mechanism behind this is not fully understood, the inventors of the present application speculate that the following reasons may be involved.

[0084] First, the filler in the coating layer is a secondary particle formed by aggregation of primary particles, and the filler in the form of secondary particles has the advantages of a large specific surface area and good affinity with the three-dimensional skeletal structure, and can form a stable spatial network structure with the three-dimensional skeletal structure, thereby increasing the ion conduction pathways of the separator, promoting the transport of ions, and improving the electrolyte infiltration and retention properties of the separator. As a result, a secondary battery using the separator of the present application can have a long cycle life and good rate performance.

[0085] Secondly, by filling at least a portion of the filler into the three-dimensional skeletal structure, the filler and the three-dimensional skeletal structure contribute to forming a nesting effect, which improves the heat resistance of the separator, reduces the degree of shrinkage of the separator when exposed to heat, reduces the risk of short-circuiting between the positive and negative electrodes, provides the secondary battery with high thermal safety performance, and maintains high adhesive strength between the coating layer and the porous substrate, thereby preventing the filler from falling off during long-term charging and discharging of the secondary battery.

[0086] Thirdly, since the coating layer of the present application includes a three-dimensional skeletal structure, and at least a portion of the filler is filled into the three-dimensional skeletal structure, there are many contact sites between the filler and the three-dimensional skeletal structure, so that the amount of adhesive used in the coating layer can be reduced, and the risk of pore clogging caused by the adhesive can be effectively reduced, and the cycle life and rate performance of the secondary battery can be further improved.

[0087] Fourth, since the coating layer of the present application has high heat resistance, a thinner porous substrate can be selected, and a high energy density can be achieved in the secondary battery.

[0088] In some embodiments, at least a portion of the filler is filled in the three-dimensional skeletal structure, and another portion of the filler can be located on the surface of the three-dimensional skeletal structure and / or at the interface between the three-dimensional skeletal structure and the porous substrate, and some of the filler may be embedded in the porous substrate at the interface between the three-dimensional skeletal structure and the porous substrate, for example, by being subjected to an external pressure during the rolling process of the electrode assembly, such that some of the filler at the interface is embedded in the matrix and / or pores of the porous substrate.

[0089] In some embodiments, the average particle size of the primary particles constituting the filler may be 8 nm to 30 nm, preferably 10 nm to 20 nm, which allows the filler to have a good secondary particle morphology, and within an appropriate range, the filler and the three-dimensional skeleton structure can be better overlapped to form an integrated effect, and after the three-dimensional skeleton structure collapses, the filler and the material constituting the three-dimensional skeleton structure enter the pores of the porous substrate, which can prevent the pores of the porous substrate from being clogged and affecting ion transport.

[0090] In some embodiments, the average particle size of the filler may be 200 nm or less, preferably 50 nm to 200 nm, so that the filler has a high specific surface area and the filler having an average particle size within an appropriate range can better match the length of the three-dimensional skeleton structure, so that the filler and the three-dimensional skeleton structure can better overlap to form an integrated effect, and the affinity between the filler and the three-dimensional skeleton structure can be increased, and the electrolyte infiltration and retention properties of the separator can be improved.

[0091] In some embodiments, the filler has a BET specific surface area of ​​20 m 2 / g or more, preferably 30m 2 / g~80m 2 / g, which improves the affinity between the filler and the three-dimensional skeleton structure and increases the infiltration and retention properties of the separator with respect to the electrolyte.

[0092] In some embodiments, the filler may include at least one of inorganic particles and organic particles.

[0093] Preferably, the inorganic particles are boehmite (γ-AlOOH), alumina (Al 2 O 3 ), barium sulfate (BaSO 4 ), magnesium oxide (MgO), magnesium hydroxide (Mg(OH) 2 ), silicon oxygen compound SiOx (0 < x ≤ 2), tin dioxide (SnO 2 ), titanium oxide (TiO 2 ), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO 2 ), yttrium oxide (Y 2 O 3 ), nickel oxide (NiO), hafnium dioxide (HfO 2 ), cerium oxide (CeO 2 ), zirconium titanate (ZrTiO 3 ), barium titanate (BaTiO 3 ), and magnesium fluoride (MgF 2 ) and includes at least one of them. More preferably, the inorganic particles are boehmite (γ-AlOOH), alumina (Al 2 O 3 ), barium sulfate (BaSO 4 ), magnesium oxide (MgO), silicon oxygen compound SiOx (0 < x ≤ 2), titanium oxide (TiO 2 ), zinc oxide (ZnO), cerium oxide (CeO 2 ), and barium titanate (BaTiO 3 ) and includes at least one of them.

[0094] Preferably, the organic particles include at least one of polystyrene and polyacrylic acid wax.

[0095] In some embodiments, the filler may include inorganic particles in a secondary particle form, and the crystalline form of the inorganic particles in the secondary particle form includes at least two of the α-crystalline form, the θ-crystalline form, the γ-crystalline form, and the η-crystalline form. Preferably, the crystalline form of the inorganic particles in the secondary particle form includes at least two of the α-crystalline form, the θ-crystalline form, and the γ-crystalline form.

[0096] The inorganic particles in the form of secondary particles of the α-crystal form have diffraction peaks at 2θ of 57.48°±0.2° and 43.34°±0.2° in an X-ray diffraction spectrum measured using an X-ray diffractometer. In some embodiments, the content of the inorganic particles in the form of secondary particles of the α-crystal form in the inorganic particles in the form of secondary particles may be 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.

[0097] The inorganic particles in the form of secondary particles of the θ crystal form have diffraction peaks at 2θ of 36.68°±0.2° and 31.21°±0.2° in an X-ray diffraction spectrum measured using an X-ray diffractometer. In some embodiments, the content of the inorganic particles in the form of secondary particles of the θ crystal form in the inorganic particles in the form of secondary particles may be 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.

[0098] The inorganic particles in the form of secondary particles of the γ crystal form have diffraction peaks at 2θ of 66.95°±0.2° and 45.91°±0.2° in an X-ray diffraction spectrum measured using an X-ray diffractometer. In some embodiments, the content of the inorganic particles in the form of secondary particles of the γ crystal form in the inorganic particles in the form of secondary particles may be 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 form of secondary particles.

[0099] The inorganic particles in the form of secondary particles of the η-crystal form have diffraction peaks at 2θ of 31.89°±0.2° and 19.37°±0.2° in an X-ray diffraction spectrum measured using an X-ray diffractometer. In some embodiments, the content of the inorganic particles in the form of secondary particles of the η-crystal form in the inorganic particles in the form of secondary particles is 5 wt% or less, preferably 2 wt% or less, more preferably 1 wt% or less, based on the total weight of the inorganic particles in the form of secondary particles.

[0100] Inorganic particles in the form of secondary particles of α crystal type have the advantages of high hardness, good heat resistance, low dielectric constant, high safety, and high true density. Inorganic particles in the form of secondary particles of θ crystal type have an appropriate specific surface area and hardness, and can simultaneously improve the heat resistance and ion transport properties of the separator. Inorganic particles in the form of secondary particles of γ crystal type and η crystal type have the advantage of a large specific surface area.

[0101] Therefore, the selection of a filler having a different crystal form contributes to improving at least one of the heat resistance, adhesive strength, and electrolyte infiltration and retention properties of the separator.

[0102] In some embodiments, the filler comprises inorganic particles in a secondary particle form, and the crystal forms of the inorganic particles in a secondary particle form include α crystal form, θ crystal form, γ crystal form and η crystal form, and the content of the inorganic particles in a secondary particle form of α crystal form may be 1.2 wt% to 5 wt%, the content of the inorganic particles in a secondary particle form of θ crystal form may be 60 wt% to 82.5 wt%, the content of the inorganic particles in a secondary particle form of γ crystal form may be 15 wt% to 35 wt%, and the content of the inorganic particles in a secondary particle form of η crystal form may be 1 wt% or less, all of which are calculated based on the total weight of the inorganic particles in a secondary particle form.

[0103] The X-ray diffraction spectrum of inorganic particles in the form of secondary particles is obtained by testing in the following manner. After drying 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 using an X-ray diffraction device (e.g., Miniflex600-C) to obtain an X-ray diffraction spectrum. During the test, a Cu target, Ni filter, tube pressure of 40 KV, and tube current of 15 mA are used to continuously scan in the range of 5° to 80°.

[0104] In some embodiments, the filler may include inorganic particles in the form of secondary particles, which may be produced by oxidizing a precursor solution of inorganic particles using a high pressure sputtering method, then heating at 600°C to 900°C (e.g., for 1 hour to 3 hours) to form small particles, and then drying at 150°C to 250°C (e.g., for 30 minutes to 60 minutes) to obtain inorganic particles in the form of secondary particles.

[0105] In some embodiments, the average particle size of the primary particles constituting the filler is d 1 nm, and the average diameter of the material constituting the three-dimensional framework is d 2 nm, and the separator is JPEG2025517447000003.jpg1231. In this case, the material constituting the three-dimensional skeleton structure overlaps the gap between the primary particles constituting the filler, thereby contributing to the integration effect due to the overlap between the filler and the three-dimensional skeleton structure, so that the coating layer can have a more stable spatial network structure, and the coating layer can also have a uniform nanopore structure, and the separator can better combine high heat resistance, high adhesive strength, and good electrolyte infiltration and retention properties.

[0106] In some embodiments, the shape of the filler may include at least one of beaded, chain-like, amorphous, spherical, roughly spherical, and pyramidal.

[0107] In some embodiments, the average diameter of the material constituting the three-dimensional skeleton structure may be 40 nm or less, preferably 10 nm to 35 nm. When the average diameter of the material constituting the three-dimensional skeleton structure is within an appropriate range, the ion transport properties and voltage breakdown properties of the separator can be further improved, and the material constituting the three-dimensional skeleton structure and the filler can be integrated by overlapping, and the heat resistance of the separator can be further improved. In addition, if the average diameter of the material constituting the three-dimensional skeleton structure is too large, the mutual winding effect of the formed three-dimensional skeleton structure is insufficient, and the voids are large, so that the separator's voltage breakdown properties are not sufficiently excellent, and it is disadvantageous to the integration effect by overlapping with the filler. In addition, during the drying process of the coating layer, the three-dimensional skeleton structure is easily collapsed due to the lack of the support effect of the filler, and further, it is easily in direct contact with the porous substrate, which causes the problem of pore clogging, which may affect the ion transport properties of the separator. This can be effectively avoided.

[0108] In some embodiments, the average length of the material constituting the three-dimensional framework may be 100 nm to 600 nm, preferably 200 nm to 450 nm. When the average length of the material constituting the three-dimensional framework is within an appropriate range, the heat resistance and ion transport properties of the separator can be further improved. In addition, if the average length of the material constituting the three-dimensional framework is too short, the overlap effect with the filler is poor, the heat resistance of the coating layer is poor, and in the drying process of the coating layer, the three-dimensional framework is prone to collapse due to insufficient support of the filler, and furthermore, the problem of pore clogging is likely to occur, which may inhibit ion transport and water discharge, and may affect the thermal safety performance, cycle performance and rate performance of the secondary battery. If the average length of the material constituting the three-dimensional framework is too long, the viscosity of the coating layer slurry is high and the flow is poor, which may affect the application of the coating layer slurry and further affect the quality of the coating layer, for example, the heat resistance and ion transport properties of the separator can be effectively avoided.

[0109] In some embodiments, the aspect ratio of the material constituting the three-dimensional framework may be 5 to 60, preferably 10 to 30. When the aspect ratio of the material constituting the three-dimensional framework is within an appropriate range, the electrolyte infiltration and retention properties of the separator can be further improved. In addition, when the aspect ratio of the material constituting the three-dimensional framework is too small, the overlap effect with the filler is poor, the heat resistance of the coating layer is poor, and in the drying process of the coating layer, the three-dimensional framework is prone to collapse due to insufficient support of the filler, and furthermore, the problem of pore clogging is likely to occur, which may inhibit ion transport and water discharge, and may affect the thermal safety performance, cycle performance and rate performance of the secondary battery. When the aspect ratio of the material constituting the three-dimensional framework is too large, the voids of the formed three-dimensional framework are small, which may effectively avoid the situation that the ion transport properties of the separator may be deteriorated.

[0110] The average length and average diameter of the material constituting the three-dimensional skeleton structure can be measured by the following method. An arbitrary area is selected from the separator, and a sample of 3.6 mm x 3.6 mm is cut out, and a scanning electron microscope (e.g., ZEISS Sigma 300) is used to map the microtopography structure of the coating layer in the sample, and a high vacuum mode is selected, the operating voltage is 3 kV, the magnification is 30,000 times, and an SEM diagram is obtained. Based on the obtained SEM diagram, multiple (e.g., five or more) test areas are selected to perform length statistics, and the size of each test area is 0.5 μm x 0.5 μm, and then the average value of the length obtained in each test area is taken as the average length of the material constituting the three-dimensional skeleton structure. Based on the obtained SEM diagram, multiple (e.g., five or more) test areas are selected to perform diameter statistics, and the size of each test area is 0.5 μm x 0.5 μm, and then the average value of the diameter obtained in each test area is taken as the average diameter of the material constituting the three-dimensional skeleton structure.

[0111] In some embodiments, the three-dimensional framework may be formed from a fibrous material, and the morphology of the fibrous material preferably includes at least one of a rod shape, a tube shape (e.g., a hollow tube shape) and a fiber shape. A material with an appropriate shape is advantageous in forming a more stable spatial network structure with the three-dimensional framework and the filler, particularly the primary particles constituting the filler, thereby further improving the heat resistance, ion transport properties, and electrolyte infiltration and retention properties of the separator.

[0112] In this application, "fibrous material" refers to a material with an aspect ratio of 5 or greater.

[0113] In some embodiments, the fibrous material may include at least one of an organic material and an inorganic material. As the fibrous material, there is no particular limitation on the material as long as it satisfies electrical insulation, electrochemical stability, and stability against an electrolyte, and the fibrous material may be an organic material or an inorganic material.

[0114] Preferably, the organic material comprises at least one of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers. Preferably, the inorganic material comprises at least one of halloysite nanotubes, nanorod-shaped alumina, nanorod-shaped boehmite, nanorod-shaped silica, and glass fibers.

[0115] In some embodiments, the material constituting the three-dimensional framework may include nanocellulose. Preferably, the nanocellulose includes at least one of cellulose nanofibers (Cellulose nanofibrils, CNF, also called nanofibril cellulose or microfibril 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). Preferably, the nanocellulose includes cellulose nanowhiskers, which have the advantage of having a high degree of crystallinity, thereby better improving the heat resistance of the separator.

[0116] Nanocellulose is a general term for cellulose whose size in any dimension is on the nano order (for example, within 100 nm), and has both the properties of cellulose and the properties of nanoparticles. Nanocellulose may be a polymeric nanomaterial extracted from wood, cotton, etc. in nature by one or more means of chemistry, physics, biology, etc., and has the advantages of wide source, low cost, biodegradability, high modulus, high specific surface area, etc., and can effectively alleviate problems such as environmental pollution and shortage of petrochemical resources as an excellent alternative to traditional petrochemical resources. Nanocellulose also has good high temperature resistance properties, and the volume change after being exposed to heat is small, so that the heat resistance of the separator can be improved. At the same time, the density of nanocellulose is smaller than that of traditional inorganic ceramic particles, so that the weight of the secondary battery can be reduced and the weight energy density of the secondary battery can be improved.

[0117] The three-dimensional skeletal structure made of nanocellulose may have tiny nanopores, which prevents current leakage, allowing the separator to have both good electrolyte infiltration and retention properties and good voltage breakdown resistance properties.

[0118] In some embodiments, the nanocellulose comprises at least one of unmodified nanocellulose (also called hydroxynanocellulose) and modified nanocellulose, preferably modified nanocellulose.

[0119] The modified nanocellulose comprises hydroxyl groups and modifying groups. In some embodiments, the modified nanocellulose comprises modifying groups, the modifying groups comprising at least one of amine groups, carboxyl groups, aldehyde groups, sulfonic acid groups, boric acid groups and phosphate groups, preferably at least one of sulfonic acid groups, boric acid groups and phosphate groups.

[0120] In further research, the inventors found that when nanocellulose has the above-mentioned specific modified groups, it can effectively improve the heat resistance of the separator and improve the thermal safety of the secondary battery, while also improving the adhesive strength between the coating layer and the porous substrate.

[0121] When the nanocellulose has the above-mentioned specific modified group, it is also advantageous for the integration effect due to the overlapping of the nanocellulose and the filler, which allows the coating layer to have a more stable spatial network structure, improves the electrolyte infiltration and retention properties of the separator, and improves the ion transport properties and voltage breakdown properties of the separator, which is advantageous for matching with high-voltage positive electrode active materials and can further improve the energy density of the secondary battery.

[0122] In addition, the presence of the modifying group can also reduce the proportion of hydroxyl groups, which can ensure that the coating layer slurry has an appropriate viscosity, which is more convenient for application, and can also improve the production efficiency of the separator and the uniformity of the coating layer.

[0123] In some embodiments, the molar ratio of the modifying group to the hydroxyl group may be 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, ion transport properties, and electrolyte infiltration and retention properties of the separator can be further improved. In addition, when the molar ratio of the modifying group to the hydroxyl group is too small, the effect of further improving the heat resistance and ion transport properties of the separator by the modifying group may not be significant. When the molar ratio of the modifying group to the hydroxyl group is too large, the separator may have poor electrolyte infiltration and retention properties, which may affect the cycle performance and safety performance of the secondary battery, and may also reduce the heat resistance of the separator, which may affect the thermal safety performance of the secondary battery. This can be effectively avoided.

[0124] The type of modified group in nanocellulose can be tested 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 can be performed on the material using instruments and methods known in the art, for example, an infrared spectrophotometer (e.g., an IS10 Fourier transform infrared spectrophotometer from Nicolet, USA) can be used to test according to GB / T6040-2019 Infrared Spectroscopic Analysis Method General Rules.

[0125] In some embodiments, the material constituting the three-dimensional skeleton contains a sulfonic acid group, and the content of sulfur element in the material constituting the three-dimensional skeleton is 0.1 wt% or more, preferably 0.2 wt% to 0.5 wt%, based on the total weight of the material constituting the three-dimensional skeleton. Preferably, the material constituting the three-dimensional skeleton contains nanocellulose, more preferably cellulose nanowhiskers.

[0126] The content of sulfur element in the material constituting the three-dimensional skeleton structure is obtained by testing in the following manner. After drying the material constituting the three-dimensional skeleton structure, it is ground in a mortar (e.g., an agate mortar) for 30 min, and then tested using an X-ray diffraction device (e.g., Miniflex600-C) to obtain the content of sulfur element. During the test, a Cu target, Ni filter, tube pressure of 40 KV, and tube current of 15 mA are used to continuously scan in the range of 5° to 80°.

[0127] In some embodiments, the content of the three-dimensional framework may be 5wt%-40wt%, preferably 10wt%-25wt%, based on the total weight of the coating layer. When the content of the three-dimensional framework is within a suitable range, it can ensure that the coating layer slurry has a suitable viscosity, which is more convenient for application. It is also advantageous for the integration effect due to the overlap between the three-dimensional framework and the filler, so that the coating layer can have a more stable spatial network structure, which can further improve the ion transport property, electrolyte infiltration and retention property, and voltage breakdown ability of the separator.

[0128] In the long-term charge and discharge process, the volume of the entire battery increases due to irreversible changes in the microstructure of the positive and negative active materials. In particular, during rapid charging of the secondary battery, the volume of the negative active material increases more after active ions are inserted. When the battery expands, pressure and / or tension is applied to the separator, making the separator more likely 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 pressure by external force. At least a part of the filler is filled into the three-dimensional skeleton structure, which contributes to the coating layer having a stable spatial network structure, thereby improving the ion transport properties and heat resistance of the separator, and also improving the tensile strength, puncture resistance, and external pressure resistance of the separator.

[0129] In some embodiments, the content of the filler may be 60wt% or more, preferably 70wt% to 90wt%, based on the total weight of the coating layer. When the content of the filler is within a suitable range, it can ensure that the coating layer slurry has a suitable viscosity, which is more convenient for application. It is also advantageous to overlap with the three-dimensional skeleton structure to form an integrated effect, so that the coating layer can have a more stable spatial network structure, and the tensile strength, puncture resistance and external force pressing resistance of the separator can be further improved.

[0130] In some embodiments, the coating layer may further include inorganic particles in the form of primary particles, at least a portion of the inorganic particles in the form of primary particles being embedded in the coating layer. The inorganic particles in the form of primary particles have a large particle size and high strength, and therefore can better exert a supporting effect in the coating layer, reduce the shrinkage of secondary particles, and reduce the amount of adhesive used, thereby improving the heat resistance of the separator. When the inorganic particles in the form of primary particles have a large particle size and are used in a small amount, they contribute to the coating layer having more pore structures and less water content, which can further improve the ion transport properties and electrolyte infiltration and retention properties of the separator, as well as the cycle performance of the secondary battery.

[0131] In some embodiments, at least a portion of the inorganic particles in the form of primary particles may be embedded in the coating layer, and a portion of the inorganic particles in the form of primary particles may protrude from the surface of the coating layer.

[0132] In some embodiments, the primary inorganic particles may have an average particle size of 200 nm to 800 nm, preferably 200 nm to 400 nm, so that the primary inorganic particles can better exert their supporting effect, and the coating layer can maintain a stable pore structure during long-term charge and discharge, which is advantageous for ion transport and improves the heat resistance of the separator.

[0133] In some embodiments, the inorganic particles in the form of primary particles have a BET specific surface area of ​​10 m 2 / g or less, preferably 3m 2 / g~7m 2 This allows the inorganic particles in the form of primary particles to better exert their supporting effect, and the coating layer maintains a stable pore structure during long-term charge and discharge processes, which is advantageous for ion transport and improves the heat resistance of the separator.

[0134] In some embodiments, the crystalline form of the inorganic particles in the form of primary particles may include 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, good heat resistance, low dielectric constant, high safety, and high true density, and therefore can further improve the heat resistance of the coating layer.

[0135] In some embodiments, the crystal form of the primary particle-form inorganic particles includes an α-crystal form, and the content of the α-crystal form primary particle-form inorganic particles in the primary particle-form inorganic particles may be 90 wt% or more, preferably 95 wt% to 100 wt%, based on the total weight of the primary particle-form inorganic particles.

[0136] In some embodiments, the shape of the inorganic particles in the form of primary particles may include at least one of a spherical shape, a dumbbell shape, and a polygonal shape.

[0137] In some embodiments, the inorganic particles in the form of primary particles may include at least one of inorganic particles having a dielectric constant of 5 or greater, inorganic particles having ionic conductivity but not storing ions, and inorganic particles capable of undergoing electrochemical reactions.

[0138] Preferably, the inorganic particles having a dielectric constant of 5 or more are boehmite, alumina, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, magnesium lithium silicate, magnesium sodium silicate, bentonite, hectorite, zirconium titanate, barium titanate, Pb(Zr,Ti)O 3 (abbreviated as PZT), Pb 1-m La m Zr 1-n Ti n O 3 (abbreviated as PLZT, 0 <m<1、0<n<1)、Pb(Mg 3 Nb 2 / 3 )O 3 -PbTiO 3 (abbreviated as PMN-PT), and at least one of the modified inorganic particles. Optionally, the modification method of each inorganic particle may be chemical modification and / or physical modification. The chemical modification method includes coupling agent modification (e.g., silane coupling agent, titanate coupling agent, etc.), surfactant modification, polymer graft modification, etc. The physical modification method may be mechanical force dispersion, ultrasonic dispersion, high energy treatment, etc. The modification treatment can reduce the aggregation of inorganic particles, so that the coating layer can have a more stable and uniform spatial network structure. In addition, by selecting a coupling agent, surfactant, or polymer having a specific functional group to modify the inorganic particles, it also contributes to improving the infiltration and retention properties of the coating layer in the electrolyte and improving the adhesion of the coating layer to the porous substrate.

[0139] 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 them, and 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.

[0140] Preferably, the electrochemically reactive inorganic particles 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.

[0141] In some embodiments, the content of the inorganic particles in the form of primary particles is 30wt% or less, preferably 5wt% to 25wt% based on the total weight of the coating layer. This allows the inorganic particles in the form of primary particles to better exert their supporting effect, and the coating layer maintains a stable pore structure during long-term charging and discharging, which is advantageous for ion transport and improves the heat resistance of the separator. In addition, when the content of the inorganic particles in the form of primary particles is high, the content of the filler in the form of secondary particles is reduced, which is disadvantageous in forming an integrated effect by overlapping the filler with the three-dimensional skeleton structure, and can effectively avoid a situation in which the heat resistance, ion transport properties, and electrolyte infiltration and retention properties of the separator are affected.

[0142] In some embodiments, the coating layer may further include a non-particulate adhesive. In the present application, the type of the non-particulate adhesive is not particularly limited, and any material having good known adhesive properties may be adopted. Preferably, the non-particulate adhesive includes an aqueous solution adhesive, which has the advantages of good thermodynamic stability and environmental friendliness, and is therefore advantageous for the preparation and application of the coating layer slurry. As an example, the aqueous solution adhesive may include at least one of an aqueous solution acrylic resin (e.g., a homopolymer of acrylic acid, methacrylic acid, sodium acrylate monomer or a copolymer with other copolymerizable monomers), polyvinyl alcohol (PVA), an isobutylene-maleic anhydride copolymer, and a polyacrylamide.

[0143] Preferably, the content of the non-particulate adhesive in the coating layer is 2 wt% or less based on the total weight of the coating layer. The three-dimensional skeleton structure in the coating layer of the present application can form a stable spatial network structure together with the filler, etc., thereby allowing the separator to maintain high adhesion while reducing the amount of adhesive used.

[0144] In some embodiments, the thickness of the coating layer may be 1 μm or less, and preferably 0.5 μm to 0.8 μm. This contributes to improving the energy density of the secondary battery. In the present application, the thickness of the coating layer refers to the thickness of the coating layer located on one side of the porous substrate.

[0145] In some embodiments, the thickness of the porous substrate may be 6 μm or less, and preferably 3 μm to 5 μm. The coating layer of the present application can significantly improve the heat resistance of the separator, which allows the selection of a thinner porous substrate, thereby contributing to the improvement of the energy density of the secondary battery.

[0146] In the present application, the material of the porous substrate is not particularly limited, and any known substrate having good chemical stability and mechanical stability can be selected, for example, the porous substrate can include at least one of a porous polyolefin resin film (e.g., at least one of polyethylene, polypropylene, and polyvinylidene fluoride), a porous glass fiber, and a porous nonwoven fabric. The porous substrate can be a single-layer film or a multi-layer composite film. When the porous substrate is a multi-layer composite film, the materials of each layer can be the same or different.

[0147] In some embodiments, the separator may further include an adhesive layer provided on at least a portion of the surface of the coating layer and including a particulate adhesive. The adhesive layer can prevent the coating layer from falling off and improve the safety performance of the secondary battery, as well as improve the interface between the separator and the electrodes, thereby improving the cycle performance of the secondary battery.

[0148] Preferably, the particulate adhesive comprises at least one of acrylic ester monomer homopolymers or copolymers, acrylic acid monomer homopolymers or copolymers, and fluorine-containing olefin monomer homopolymers or copolymers. The copolymerization monomers include at least one of acrylic ester monomers, acrylic acid monomers, olefin monomers, halogen-containing olefin monomers, and fluoroether monomers, but are not limited thereto.

[0149] Preferably, the particulate adhesive comprises a vinylidene fluoride polymer, such as a homopolymer of vinylidene fluoride monomer (VDF) and / or a copolymer of vinylidene fluoride monomer and a comonomer. The comonomer may be at least one of an olefin monomer, a fluorine-containing olefin monomer, a chlorine-containing olefin monomer, an acrylate monomer, an acrylic monomer, and a fluoroether monomer. Preferably, the comonomer may comprise at least one of trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ether (e.g., perfluoro(methyl vinyl) ether PMVE, perfluoro(ethyl vinyl) ether PEVE, perfluoro(propyl vinyl) ether PPVE), perfluoro(1,3-dioxole), and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD).

[0150] In some embodiments, the separator has a longitudinal heat shrinkage rate of 5% or less at 150° C. for 1 hour, and preferably 0.5% to 3%.

[0151] In some embodiments, the separator has a transverse heat shrinkage rate of 5% or less at 150° C. for 1 hour, and preferably 0.5% to 3%.

[0152] The separator of the present application has low thermal shrinkage in both the transverse and longitudinal directions at a high temperature of 150° C., and therefore can improve the safety performance of the secondary battery.

[0153] 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.

[0154] 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.

[0155] Since the separator of the present application has high tensile strength in both the transverse and longitudinal directions, the probability of the separator being damaged when the secondary battery expands is low, and the safety performance of the secondary battery can be improved.

[0156] In some embodiments, the wetted length of the separator is 30 mm or more, preferably 30 mm to 80 mm.

[0157] In some embodiments, the wetting speed of the separator is 3 mm / s or more, preferably 3 mm / s to 10 mm / s.

[0158] The separator of the present application has good electrolyte infiltration and retention properties, and therefore can improve the ion transport properties and secondary battery capacity exhibiting properties of the separator.

[0159] In some embodiments, the separator has an air permeability of 300s / 100mL or less, and preferably 100s / 100mL to 230s / 100mL. The separator of the present application has a good air permeability, and thus can improve ion transport properties and secondary battery capacity exhibiting properties.

[0160] In this application, the average particle size of a material has a meaning known in the art, and can be measured using instruments and methods known in the art. For example, a material or separator is measured using a scanning electron microscope, a transmission electron microscope, or a particle size distribution device to obtain an image, and a plurality of (e.g., 10 or more) test particles (e.g., a filler having a secondary particle form, inorganic particles having a primary particle form) are randomly selected from the image, and the average value of the shortest diagonal length of the particles can be statistically calculated as the average particle size.

[0161] In this application, the specific surface area of ​​a material has a meaning known in the art, and can be measured using instruments and methods known in the art. For example, it can be tested according to the nitrogen gas adsorption specific surface area analysis test method with reference to GB / T19587-2017, 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.

[0162] In this application, the heat shrinkage rate, tensile strength and air permeability of the separator all have the meanings known in the art and can be measured by methods known in the art, for example, they can be tested with reference to standard GB / T 36363-2018.

[0163] In this 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. An exemplary test method is as follows. 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 arranged horizontally. 0.5 mg of electrolyte is dropped into the center of the sample, and after a predetermined time (1 min in this application), the sample is photographed and the length of diffusion of the electrolyte is measured to obtain the wetting length and wetting speed of the separator. In order to ensure the accuracy of the test results, the test is performed using multiple samples (e.g., 5 to 10 samples) and the test results are obtained by calculating the average value. The electrolyte can be prepared by the following method. Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of 30:50:20 to obtain an organic solvent, and LiPF that has been thoroughly dried is then used. 6 was dissolved in the above organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L.

[0164] In addition, the coating layer parameters (e.g., thickness, etc.) of the above separators are all coating layer parameters on one side of the porous substrate. When coating layers are provided on both sides of the porous substrate, it is considered that the coating layer parameters on either one side of the coating layers satisfy the present application and fall within the scope of protection of the present application.

[0165] Manufacturing method

[0166] A second aspect of an embodiment of the present application provides a method for producing a separator according to the first aspect of an embodiment of the present application, comprising: a step S1 of supplying a porous substrate; a slurry supplying step S2 of mixing a material for constituting a three-dimensional skeletal structure and a filler in a solvent in a predetermined ratio to prepare the slurry; and a coating step S3 of applying the slurry to at least one surface of the porous substrate and drying to obtain a separator, the separator comprising a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer comprising a three-dimensional skeletal structure and a filler, at least a portion of the filler being filled in the three-dimensional skeletal structure, and the filler being secondary particles formed by aggregation of primary particles.

[0167] In some embodiments, in S2, the solvent may be water, for example deionized water.

[0168] In some embodiments, in S2, the slurry may further include other ingredients, such as dispersants, wetting agents, adhesives, inorganic particles in the form of primary particles, and the like.

[0169] In some embodiments, the solid content of the slurry in S2 can be controlled between 28% and 45%, for example, between 30% and 38%. When the solid content of the slurry is within the above range, the film surface problem of the coating layer can be effectively reduced, the probability of uneven coating can be reduced, and the energy density and safety performance of the secondary battery can be further improved.

[0170] In some embodiments, in S2, the material for forming the three-dimensional framework structure is a fibrous material, and the fibrous material may include at least one of an organic material and an inorganic material.

[0171] Preferably, the organic material includes at least one of nanocellulose, polytetrafluoroethylene nanofiber, and polyamide nanofiber. Preferably, the inorganic material includes at least one of halloysite nanotubes, nanorod-shaped alumina, nanorod-shaped boehmite, nanorod-shaped silica, and glass fiber. In some embodiments, the material constituting the three-dimensional framework structure may include nanocellulose, and cellulose nanowhiskers (also called Cellulose nanocrystals, CNC, cellulose nanocrystals, nanocrystalline cellulose) may be selected.

[0172] In some embodiments, the nanocellulose can be obtained by a method including steps S21 of providing a cellulose powder having a whiteness of 80% or more, S22 of mixing and reacting the obtained cellulose powder with a modifying solution, followed by washing to remove impurities to obtain cellulose nanowhiskers, and S23 of adjusting the pH of the obtained cellulose nanowhiskers to neutral, grinding and cutting them to obtain nanocellulose.

[0173] Preferably, in S21, the cellulose powder having a whiteness of 80% or more may be commercially available or may be obtained by adopting a chemical method (e.g., acid decomposition method, alkali treatment method, Tempo catalytic oxidation method), a biological method (e.g., enzyme treatment method), a mechanical method (e.g., ultrafine grinding, ultrasonic crushing, high-pressure homogenization), etc. The fiber raw material for producing the cellulose powder having a whiteness of 80% or more may include at least one of plant fibers, such as cotton fibers (e.g., cotton fiber, cotton fiber), hemp fibers (e.g., sisal fiber, ramie fiber, jute fiber, flax fiber, hemp fiber, Manila hemp fiber, etc.), palm fibers, wood fibers, bamboo fibers, and grass fibers.

[0174] In some embodiments, the cellulose powder having a whiteness of 80% or more can also be produced by opening the fiber raw material and removing debris, followed by steaming 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%), followed by sequentially washing with water to remove impurities (e.g., washing with water 3 to 6 times), bleaching (which may be, for example, sodium hypochlorite and / or hydrogen peroxide), washing with an acid to remove impurities, washing with water to remove impurities, removing water, and flash drying to obtain a cellulose powder.

[0175] In some embodiments, in S22, the denaturing solution may be an acid solution (e.g., an aqueous sulfuric acid solution, an aqueous boric acid solution, an aqueous phosphoric acid solution, an aqueous acetic acid solution) or an alkaline solution (e.g., an organic solvent solution of urea). Preferably, the denaturing solution is an acid solution.

[0176] 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 can be 40 wt% to 80 wt%, and a cellulose powder having a sulfonic acid group can be obtained. When an aqueous boric acid solution is used as the modifying solution, the concentration of the acid solution can be 5 wt% to 10 wt%, and a cellulose powder having a boric acid group can be obtained. When an aqueous phosphoric acid solution is used as the modifying solution, the concentration of the acid solution can be 45 wt% to 75 wt%, and a cellulose powder having a phosphoric acid group can be obtained. When an aqueous acetic acid solution is used as the modifying solution, the concentration of the acid solution can be 40 wt% to 80 wt%, and a cellulose powder having a carboxylic acid group can be obtained.

[0177] Preferably, the organic solvent solution of urea is a xylene solution of urea, so that a cellulose powder having an amine group can be obtained.

[0178] In some embodiments, in S22, the mass ratio of the cellulose powder to the modified solution may be 1:2.5 to 1:50, preferably 1:5 to 1:30.

[0179] 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.

[0180] In some embodiments, in S22, when the modifying solution is an acid solution, the reaction may be carried out under conditions of 80°C or less, preferably under conditions of 30°C to 60°C, and the reaction time between the cellulose powder and the modifying solution may be 0.5h to 4h, preferably 1h to 3h.

[0181] In some embodiments, in S22, when the denaturing solution is an alkaline solution, the reaction may be carried out under conditions of 100°C to 145°C, and the reaction time between the cellulose powder and the denaturing solution may be 1h to 5h.

[0182] In some embodiments, in S23, the grinding may be performed using a grinder, and the cutting may be performed using a high-pressure homogenizer. 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 having different average diameters and / or different average lengths can be obtained.

[0183] In some embodiments, a coater is used for the coating in S3. In the present application, the model number of the coater is not particularly limited, and for example, a commercially available coater can be used. The coater includes a gravure roll for transferring the slurry to the porous substrate.

[0184] In some embodiments, in S3, the coating method may be transfer coating, rotary spray coating, dip coating, etc.

[0185] In some embodiments, the method further includes a secondary coating step S4 in which a slurry containing particulate adhesive is applied to at least a portion of the surface of the coating layer and dried to form an adhesive layer.

[0186] The method for producing a separator according to the present application produces a coating layer in a single application, greatly simplifying the separator production process.

[0187] For parameters such as raw materials used in the manufacturing method of the separator of the present application and their contents, reference can be made to the separator of the first aspect of the embodiment of the present application, but a description thereof will be omitted here.

[0188] Each of the raw materials used in the manufacturing method of the separator of the present application is available as a commercially available product unless otherwise specified.

[0189] secondary battery

[0190] A third aspect of an embodiment of the present application provides a secondary battery.

[0191] A secondary battery, also called a rechargeable battery or storage battery, is a battery that can be used continuously after discharging by activating the active material through charging. In general, a secondary battery includes an electrode assembly and an electrolyte, the electrode assembly including a positive electrode sheet, a negative electrode sheet, and a separator, the separator being disposed between the positive electrode sheet and the negative electrode sheet and mainly serving to prevent short circuits between the positive electrode and the negative electrode, while allowing active ions to pass through.

[0192] 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.

[0193] A secondary battery according to a third aspect of the present application includes a separator according to the first aspect of the present application or a separator produced by the method according to the second aspect of the present application, the separator being interposed between the positive electrode sheet and the negative electrode sheet. Preferably, the separator has the coating layer according to the present application at least on the side closer to the negative electrode sheet. This allows the secondary battery according to the present application to achieve high energy density, high thermal safety performance, long cycle life, and good rate performance.

[0194] [Positive electrode sheet]

[0195] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer that is provided on at least one surface of the positive electrode current collector and includes a positive electrode active material. For example, the positive electrode current collector has two surfaces that face each other in a thickness direction of the positive electrode current collector, and the positive electrode film layer is provided on one or both of the two facing surfaces of the positive electrode current collector.

[0196] When the secondary battery of the present application is a lithium ion battery, the positive electrode active material includes at least one of lithium-containing transition metal oxides, lithium-containing phosphates, and modified compounds thereof, but is not limited thereto. Examples of the lithium transition metal oxides include 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, but is not limited thereto. Examples of the lithium-containing phosphates include at least one of lithium iron phosphate, lithium iron phosphate and carbon composite material, lithium manganese phosphate, lithium manganese phosphate and carbon composite material, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composite material, and modified compounds thereof, but is not limited thereto.

[0197] In some embodiments, in order to further improve the energy density of the secondary battery, the cathode active material used in the lithium-ion battery may include at least one of lithium transition metal oxides and modified compounds thereof having the general formula Li a Ni b Co c M d O e A f . 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.

[0198] As an example, the cathode active material used in the lithium-ion battery may include at least one of 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 M 0.1 O 2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O 2 , LiFePO 4 , LiMnPO 4 .

[0199] When the secondary battery of the present application is a sodium ion battery, the positive electrode active material includes at least one of a sodium-containing transition metal oxide, a polyanion material (e.g., a phosphate, a fluorophosphate, a pyrophosphate, a sulfate, etc.), and a Prussian blue-based material, but is not limited thereto.

[0200] 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 Mn 2 / 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 compound 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 selected from V, Ti, Mn, Fe, Co, Ni, Cu, and Zn; and Y is a halogen anion, preferably at least one selected from F, Cl, and Br.

[0201] In the present application, the modified compound of each of the positive electrode active materials can perform doping modification and / or surface coating modification on the positive electrode active material.

[0202] In some embodiments, the positive electrode film layer may contain a positive electrode conductive agent as necessary. In the present application, the type of the positive electrode conductive agent is not particularly limited, and for example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent is 5 wt% or less with respect to the total weight of the positive electrode film layer.

[0203] In some embodiments, the positive electrode film layer may include a positive electrode adhesive if necessary. In the present application, the type of the positive electrode adhesive is not particularly limited, and for example, the positive electrode adhesive may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. In some embodiments, the mass percentage of the positive electrode adhesive is 5 wt% or less with respect to the total weight of the positive electrode film layer.

[0204] In some embodiments, the positive electrode current collector may be a metal foil sheet or a composite current collector. An example of a metal foil sheet may be aluminum foil. The composite current collector may include a polymeric material base layer and a metal material layer formed on at least one surface of the polymeric material base layer. For example, the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. For example, the polymeric material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0205] The positive electrode membrane layer is usually formed by applying a positive electrode slurry to a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, a conductive agent if necessary, an adhesive if necessary, and any other components in a solvent, and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0206] [Negative electrode sheet]

[0207] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer that is provided on at least one surface of the negative electrode current collector and includes a negative electrode active material. For example, the negative electrode current collector has two surfaces that face each other in a thickness direction of the negative electrode current collector, and the negative electrode film layer is provided on one or both of the two facing surfaces of the negative electrode current collector.

[0208] The negative electrode active material may be any negative electrode active material for secondary batteries known in the art. For example, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate. The silicon-based material may include at least one of silicon elemental, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material may include at least one of tin elemental, tin oxide, and tin alloy material.

[0209] In some embodiments, the negative electrode film layer may include a negative electrode conductive agent if necessary. In the present application, the type of the negative electrode conductive agent is not particularly limited, and for example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent is 5 wt% or less with respect to the total weight of the negative electrode film layer.

[0210] In some embodiments, the negative electrode film layer may include a negative electrode adhesive, if necessary. In the present application, the type of the negative electrode adhesive is not particularly limited, and for example, the negative electrode adhesive may include at least one of styrene butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-soluble 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 mass percentage of the negative electrode adhesive is 5 wt% or less with respect to the total weight of the negative electrode film layer.

[0211] In some embodiments, the negative electrode membrane layer may include other additives as necessary. For example, the other additives may include a thickener, such as sodium carboxymethylcellulose (CMC), a PTC thermistor material, etc. In some embodiments, the mass percentage of the other additives is 2 wt % or less, based on the total weight of the negative electrode membrane layer.

[0212] In some embodiments, the negative electrode current collector may be a metal foil sheet or a composite current collector. An example of the metal foil sheet may be copper foil. The composite current collector may include a polymeric material base layer and a metal material layer formed on at least one surface of the polymeric material base layer. For example, the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. For example, the polymeric material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0213] The negative electrode film layer is usually formed by applying a negative electrode slurry to a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is usually formed by dispersing a negative electrode active material, a conductive agent if necessary, an adhesive if necessary, and other optional auxiliary agents in a solvent, and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0214] The negative electrode sheet does not exclude additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode sheet described in the present application further includes a conductive bottom coating layer (e.g., made of a conductive agent and an adhesive) sandwiched between the negative electrode collector and the negative electrode film layer and provided on the surface of the negative electrode collector. In some other embodiments, the negative electrode sheet described in the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0215] [Electrolyte]

[0216] In the charging and discharging process of the secondary battery, active ions are inserted and removed between the positive electrode sheet and the negative electrode sheet, and the electrolyte serves to conduct the active ions between the positive electrode sheet and the negative electrode sheet. The present application does not particularly limit the type of electrolyte, and it can be selected according to actual needs.

[0217] The electrolyte solution includes an electrolyte salt and a solvent, and the types of the electrolyte salt and the solvent are not specifically limited and can be selected according to actual needs.

[0218] When the secondary battery of the present application is a lithium ion battery, for example, the electrolyte salt is lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorooxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0219] When the secondary battery of the present application is a sodium ion battery, for example, the electrolyte salt is sodium hexafluorophosphate (NaPF 6 ), sodium tetrafluoroborate (NaBF 4 ), sodium perchlorate (NaClO 4 ), sodium hexafluoroarsenate (NaAsF 6), sodium bisfluorosulfonylimide (NaFSI), sodium bistrifluoromethanesulfonylimide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalyl borate (NaDFOB), sodium difluorooxalyl borate (NaBOB), sodium difluorophosphate (NaPO 2 F 2 ), sodium difluorooxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0220] By way of example, the solvent may include, but is not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0221] In some embodiments, the electrolyte may include additives as necessary. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, or an additive capable of improving certain performance of the battery, such as an additive for improving the overcharge performance of the battery, an additive for improving the high temperature performance of the battery, or an additive for improving the low temperature output performance of the battery.

[0222] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be wound and / or stacked to produce an electrode assembly.

[0223] In some embodiments, the secondary battery may include an exterior case that is used to seal the electrode assembly and the electrolyte.

[0224] In some embodiments, the exterior of the secondary battery may be a hard case such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the secondary battery may be a soft pack, such as a bag soft pack. The material of the soft pack may be at least one of plastic, such as polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0225] In the present application, the shape of the secondary battery is not particularly limited, and may be cylindrical, rectangular, or any other shape. Figure 1 shows a secondary battery 5 having a rectangular structure as an example.

[0226] In some embodiments, as shown in FIG. 2, the exterior may include a case 51 and a cover plate 53. The case 51 includes a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate surround and form a receiving cavity. The case 51 has an opening communicating with the receiving cavity, and the cover plate 53 covers the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator may form an electrode assembly 52 by a winding process and / or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. An electrolyte is infiltrated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and may be adjusted as needed.

[0227] The method for manufacturing the secondary battery of the present application is known. In some embodiments, a secondary battery can be formed by assembling a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. For example, a positive electrode sheet, a separator, and a negative electrode sheet are wound and / or laminated to form an electrode assembly, the electrode assembly is placed in an outer casing, and an electrolyte is injected after drying, and a secondary battery can be obtained through processes such as vacuum sealing, standing, chemical formation, and shaping.

[0228] 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 may be adjusted according to the application and capacity of the battery module.

[0229] Fig. 3 is a schematic diagram of an example battery module 4. As shown in Fig. 3, in the battery module 4, the multiple secondary batteries 5 may be arranged in sequence along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the multiple secondary batteries 5 may be fixed by fasteners.

[0230] Preferably, the battery module 4 may further include a case having an accommodation space for accommodating the plurality of secondary batteries 5.

[0231] In some embodiments, the battery modules may be assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0232] 4 and 5 are schematic diagrams of an example 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 covers 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.

[0233] power consumption equipment

[0234] A fourth aspect of an embodiment of the present application provides a 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 be used as a power source for the power consuming device, or may be used as an energy storage unit for the power consuming device. The power consuming device may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf car, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0235] The power consumption device can select a secondary battery, a battery module or a battery pack according to its usage needs.

[0236] 6 is a schematic diagram of an example power consuming device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. A battery pack or a battery module may be employed to meet the high power and high energy density requirements of the power consuming device.

[0237] Other examples of power consuming devices may be mobile phones, tablet computers, notebook computers, etc. These power consuming devices are generally required to be thin and can use secondary batteries as their power source.

[0238] Working Example

[0239] The following examples are provided to more specifically describe the disclosure of the present application, and are merely illustrative, since it is obvious to those skilled in the art that various modifications and changes may be made within the scope of the disclosure of the present application.Unless otherwise specified, all parts, percentages, and ratios described in the following examples are based on mass, and all reagents used in the examples are commercially available or can be synthesized according to conventional methods and can be used directly without further processing, and the equipment used in the examples is commercially available.

[0240] Production of nanocellulose C1

[0241] Production of cellulose powder

[0242] The cotton linters were opened using a cotton opener to remove debris, and then steamed in a 5 wt% NaOH aqueous solution at 150°C for 2 hours.Then, impurities were removed by washing with water (three times), bleached with sodium hypochlorite, impurities were removed by washing with dilute hydrochloric acid, impurities were removed by washing with water (one time), water was removed, and the product was air-dried, resulting in a cotton cellulose powder with a whiteness of 85% or more.

[0243] Cellulose Esterification

[0244] 1 kg of the obtained cotton cellulose powder was mixed with 30 kg of a 60 wt % aqueous sulfuric acid solution and reacted at 55°C to 60°C for 1.5 hours. After the reaction was completed, impurities were removed by washing with water (three times), filtered, and acid and impurities were removed in that order to obtain cellulose nanowhiskers having sulfonic acid groups.

[0245] Neutralization of cellulose

[0246] The pH of the cellulose nanowhiskers with sulfonic acid groups was adjusted to neutral with a 10 wt% NaOH aqueous solution, and then they were dispersed by high-speed processing in a grinder for 2.5 hours, and the number of grinding cycles was two. Then, they were cut into nanoscale pieces using a high-pressure homogenizer to obtain nanocellulose C1 with sulfonic acid group-modified groups with an average length of 450 nm and an average diameter of 25 nm. The molar ratio of sulfonic acid groups to hydroxyl groups was 5:3.

[0247] Production of nanocellulose C2-C13

[0248] Nanocelluloses C2 to C13 were produced in the same manner as nanocellulose C1, with the differences being shown in Table 1. During the production process, nanocelluloses with different average diameters and / or different average lengths can be obtained by adjusting the parameters of the grinder treatment and the cutting parameters of the high-pressure homogenizer device.

[0249] Production of nanocellulose C14

[0250] Production of cellulose powder

[0251] The cotton linters were opened using a cotton opener to remove debris, then steamed in 5wt% NaOH aqueous solution at 150°C for 2 hours, then washed with water to remove impurities (3 times), bleached with sodium hypochlorite, washed with dilute hydrochloric acid to remove impurities, washed with water to remove impurities (1 time), removed water, and air-dried to obtain cotton cellulose powder with a whiteness of 85% or more. The obtained cotton cellulose powder was mixed with 20wt% NaOH aqueous solution at 10°C, stirred for 2 hours, filtered, and washed twice with water to obtain cellulose powder.

[0252] Cellulose Esterification

[0253] 50 g of the obtained cellulose powder and 200 g of urea were placed in a three-necked reactor equipped with an oil-water separator. After the urea was dissolved, 5 g of xylene was added, and the mixture was heated to 137°C with stirring. After the reaction was completed for 4 hours, the mixture was washed with water (three times), filtered, and dried to obtain cellulose carbamate.

[0254] Neutralization of cellulose

[0255] 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. The grinding was repeated twice, and the cellulose carbamate was then cut into nanoscale particles using a high-pressure homogenizer to obtain nanocellulose C14 with amine-modified groups having an average length of 450 nm and an average diameter of 25 nm, with a molar ratio of amine groups to hydroxyl groups of 4:3.

[0256] Production of nanocellulose C15

[0257] Unmodified nanocellulose, with an average length of 450 nm and an average diameter of 25 nm, product model number CNWS-50, purchased from Zhongke Leiming (Beijing) Technology Co., Ltd., can be further processed with a grinder and / or a high-pressure homogenizer to obtain nanocellulose with different average diameters and / or different average lengths.

[0258] The molar ratio of modified groups to hydroxyl groups in nanocelluloses C1 to C14 can be measured by testing the hydroxyl values ​​(mg of potassium hydroxide equivalent to the hydroxyl group content per 1 g of sample) of raw cellulose and nanocelluloses C1 to C14 based on the phthalic anhydride method in GB / T 12008.3-2009, converting the units of the obtained values ​​to mg KOH / g and converting them to mmol / g to obtain the hydroxyl group content. The content of modified groups (i.e., the content of modified hydroxyl groups) is obtained by subtracting the hydroxyl group content of nanocelluloses C1 to C14 from the hydroxyl group content of raw cellulose, and the molar ratio of modified groups to hydroxyl groups is calculated.

[0259] [Table 1]

[0260] Example 1

[0261] Separator manufacturing

[0262] Provision of a PE porous substrate: its thickness is 4.5 μm and its porosity is 42%.

[0263] Preparation of coating layer slurry: Nanocellulose C1 produced as described above, alumina secondary particles as a filler, and aqueous polyacrylic acid as an adhesive were uniformly mixed in a mass ratio of 15:84.1:0.9 in an appropriate amount of deionized water as a solvent to obtain a coating layer slurry with a solid content of 35 wt%.

[0264] The alumina secondary particles, which are fillers, are manufactured by oxidizing an alumina precursor solution (e.g., an aluminum chloride solution) by high-pressure sputtering, heating at 830°C for 1.2 hours to form specific small particles, and then drying and shaping at 150°C for 45 minutes to obtain alumina secondary particles of a specific shape. The average particle size of the obtained alumina secondary particles is 150 nm, the average particle size of the primary particles constituting the secondary particles is 15 nm, and the contents of α crystal form, θ crystal form, γ crystal form, and η crystal form in the alumina secondary particles are 1.5 wt%, 74.7 wt%, 23.3 wt%, and 0.5 wt%, respectively, based on the total weight of the alumina secondary particles. A transmission electron microscope (TEM) image of the alumina secondary particles, which are fillers, is shown in FIG. 7, and the circles in the figure indicate the primary particles constituting the alumina secondary particles.

[0265] Coating: The prepared coating layer slurry was coated on both sides of the PE porous substrate using a coater, and the separator was obtained through a drying and slitting process. The thickness of the coating layer on one side of the PE porous substrate was 0.8 μm.

[0266] Manufacture of positive electrode sheets

[0267] Positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 A positive electrode slurry is obtained by uniformly mixing NCM811, carbon black (Super P) as a conductive agent, and polyvinylidene fluoride (PVDF) as an adhesive 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 is applied to an aluminum foil as a positive electrode current collector, and a positive electrode sheet is obtained through processes such as drying, cold pressing, slitting, and cutting. The surface density of the positive electrode sheet is 0.207 mg / mm 2 and the compressed density is 3.5 g / cm 3 It is.

[0268] Manufacture of negative electrode sheets

[0269] The negative electrode active material, artificial graphite, the conductive agent, carbon black (Super P), the adhesives, styrene butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC), were 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 to a copper foil as a negative electrode current collector, and a negative electrode sheet was obtained through drying, cold pressing, slitting and cutting processes. The surface density of the negative electrode sheet was 0.126 mg / mm 2 and the compressed density is 1.7 g / cm 3 It is.

[0270] Electrolyte production

[0271] Thoroughly dried LiPF was dissolved in an organic solvent consisting of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of 30:70. 6 was dissolved to prepare an electrolyte solution with a concentration of 1 mol / L.

[0272] Secondary battery manufacturing

[0273] The positive electrode sheet, separator, and negative electrode sheet are stacked in that order and rolled up to obtain an electrode assembly. The electrode assembly is placed in an outer casing, dried, and then an electrolyte is injected. The secondary battery is obtained through processes such as vacuum sealing, leaving it to stand, chemical formation, and shaping.

[0274] Examples 2 to 5

[0275] The secondary battery was manufactured in a manner similar to that of Example 1, except that the amounts of nanocellulose and filler added in the manufacture of the separator were different. See Table 2 for specific parameters.

[0276] Examples 6 to 8

[0277] The secondary battery is manufactured in a similar manner to that of Example 1, except that the filler used in manufacturing the separator is different.

[0278] The filler of Example 6 is manufactured by oxidizing an alumina precursor solution (e.g., an aluminum chloride solution) by high-pressure sputtering, heating at 750°C for 1.0 hour to form specific small particles, and then drying and shaping at 250°C for 60 minutes to obtain alumina secondary particles of a specific shape. The average particle size of the obtained alumina secondary particles is 100 nm, the average particle size of the primary particles constituting the secondary particles is 15 nm, and the contents of α crystal form, θ crystal form, γ crystal form and η crystal form in the alumina secondary particles are 1.2 wt%, 63.5 wt%, 34.5 wt% and 0.8 wt%, respectively, based on the total weight of the alumina secondary particles.

[0279] The filler of Example 7 is manufactured by subjecting an alumina precursor solution (e.g., an aluminum chloride solution) to an oxidation reaction by high-pressure sputtering, heating at 840°C for 1.5 hours to form specific small particles, and then drying and shaping at 200°C for 60 minutes to obtain alumina secondary particles of a specific form. The average particle size of the obtained alumina secondary particles is 200 nm, the average particle size of the primary particles constituting the secondary particles is 15 nm, and the contents of α crystal form, θ crystal form, γ crystal form and η crystal form in the alumina secondary particles are 1.8 wt%, 76.7 wt%, 21.0 wt% and 0.5 wt%, respectively, based on the total weight of the alumina secondary particles.

[0280] The filler of Example 8 is manufactured by subjecting an alumina precursor solution (e.g., an aluminum chloride solution) to an oxidation reaction by high-pressure sputtering, heating at 900°C for 2 hours to form specific small particles, and then drying and shaping at 150°C for 45 minutes to obtain alumina secondary particles of a specific form. The average particle size of the obtained alumina secondary particles is 300 nm, the average particle size of the primary particles constituting the secondary particles is 15 nm, and the contents of α crystal form, θ crystal form, γ crystal form and η crystal form in the alumina secondary particles are 2.5 wt%, 79.9 wt%, 17.1 wt% and 0.5 wt%, respectively, based on the total weight of the alumina secondary particles.

[0281] Examples 9 to 22

[0282] The secondary battery was manufactured in a manner similar to that of Example 1, except that the type of nanocellulose used in preparing the coating layer slurry in the manufacture of the separator was different, and the specific parameters are shown in Tables 1 and 2.

[0283] Example 23

[0284] The secondary battery was manufactured in a similar manner to that of Example 1, except that inorganic particles in the form of primary particles were further added when preparing the coating layer slurry in the manufacture of the separator.

[0285] Preparation of coating layer slurry: Nanocellulose C1 produced as described above, alumina secondary particles as a filler (the manufacturing process is the same as in Example 1), alumina in the form of primary particles (average particle size is 350 nm, the crystal form is mainly α crystal form, and the mass ratio is 99.9% or more), and aqueous polyacrylic acid as an adhesive were uniformly mixed in a mass ratio of 15:78.1:6:0.9 in an appropriate amount of deionized water as a solvent to obtain a coating layer slurry with a solid content of 35 wt%.

[0286] Comparative Example 1

[0287] The secondary battery is manufactured in a manner similar to that of Example 1, except that unmodified nanocellulose C15 is used in the manufacture of the separator and the alumina used is in the form of primary particles, with specific parameters shown in Table 2.

[0288] Preparation of coating layer slurry: Nanocellulose C15 produced as described above, primary particle form alumina (average particle size 650 nm, mainly α-crystalline form, mass ratio 99.9% or more), and aqueous polyacrylic acid as adhesive were uniformly mixed in a mass ratio of 15:80:5 in an appropriate amount of deionized water as a solvent to obtain a coating layer slurry with a solid content of 35 wt%.

[0289] Comparative Example 2

[0290] The secondary battery is manufactured in a similar manner to that in Example 1, except that the alumina used in manufacturing the separator is in the form of primary particles, and the specific parameters are shown in Table 2.

[0291] Preparation of coating layer slurry: Nanocellulose C1 produced as described above, primary particle form alumina (average particle size 650 nm, crystal form mainly α crystal form, mass ratio 99.9% or more), and aqueous polyacrylic acid as adhesive were uniformly mixed in a mass ratio of 15:80:5 in an appropriate amount of deionized water as a solvent to obtain a coating layer slurry with a solid content of 35 wt%.

[0292] Comparative Example 3

[0293] The secondary battery is manufactured in a manner similar to that of Example 1, except that nanocellulose is not added in the manufacture of the separator and the alumina is in the form of primary particles, and the specific parameters are shown in Table 2.

[0294] Preparation of coating layer slurry: Primary particle form alumina (average particle size 650 nm, mainly α-crystalline form, mass ratio 99.9% or more) and aqueous polyacrylic acid as adhesive were uniformly mixed in a mass ratio of 94:6 in an appropriate amount of deionized water as solvent to obtain a coating layer slurry with a solid content of 35 wt%.

[0295] [Table 2] JPEG2025517447000006.jpg25285

[0296] test

[0297] (1) Thermal shrinkage rate test of separator

[0298] Preparation of samples: The separator prepared as described 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 set and fixed on an A4 sheet of paper. The A4 sheet of paper on which the samples were set was then set on a piece of cardboard with a thickness of 1 mm to 5 mm.

[0299] Sample test: Place an A4 sheet of paper on top of the cardboard into a blast oven, set the temperature of the blast oven to 150°C, and after the temperature reaches the set temperature and stabilizes for 30 minutes, start timing. After the set time (1 hour in this application) is reached, measure the length and width of the separator, and the values ​​are denoted as a and b respectively.

[0300] 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 was taken as the test result.

[0301] (2) Separator air permeability test

[0302] The time required for 100 mL of air to pass through the separator at room temperature was measured, and the test result was the average of five parallel samples for accuracy. A Kumagaya KRK Oken air permeability tester can be used as the test equipment.

[0303] (3) Secondary battery heat box test

[0304] At 25℃, the secondary battery is charged at a constant current of 1C to 4.2V, and then charged at a constant voltage until the current is below 0.05C, and then left to stand for 5min. Then, each secondary battery is tested with a jig in a DHG-9070ADHG series high-temperature oven, and the temperature is raised from room temperature to 80℃±2℃ at a rate of 5℃ / min, and kept for 30min. Then, the temperature is raised at a rate of 5℃ / min, and the temperature is kept at 5℃ for 30min. During the heating process, the change in the surface temperature of the secondary battery is monitored, and the corresponding oven temperature when the temperature starts to rise rapidly is the expiration temperature of the heat box of the secondary battery. The higher the expiration temperature of the heat box of the secondary battery, the better the thermal safety performance of the secondary battery. For accuracy, the average value of five parallel samples is taken as the test result.

[0305] [Table 3]

[0306] As can be seen from Table 3, in Examples 1 to 23, by providing a coating layer containing nanocellulose (forming a three-dimensional skeleton structure) and a filler in the form of secondary particles on two surfaces of a porous substrate of a separator, the obtained separator can achieve both low thermal shrinkage and high air permeability, and the obtained secondary battery can have high thermal safety performance. FIG. 8 is a scanning electron microscope (SEM) image of the coating layer of the separator manufactured in Example 1. FIG. 9 is a scanning electron microscope (SEM) image of the coating layer of the separator manufactured in Example 23. As can be seen from FIGS. 8 and 9, the filler in the form of secondary particles used in the coating layer of the separator of the present application can overlap with the nanocellulose to form an integration effect, and the inorganic particles in the form of primary particles can perform a stable supporting function in the coating layer.

[0307] The filler in the form of secondary particles used in the coating layer of the separator of the present application overlaps with nanocellulose to form an integrated effect, thereby reducing the amount of adhesive used and reducing the thickness of the coating layer, and the separator can maintain its characteristics of excellent heat resistance and high adhesive strength, and the separator of the present application has high air permeability and is less likely to cause pore clogging problems. Therefore, a secondary battery using the separator of the present application can achieve high energy density, long cycle life, and good rate performance, provided that it has high thermal safety performance.

[0308] The alumina used in the coating layers of Comparative Example 1 and Comparative Example 2 is in the form of primary particles, in which case alumina and nanocellulose cannot form an integrated overlap effect, and the effect of improving the heat resistance of the separator and the thermal safety performance of the secondary battery is limited. In addition, since alumina and nanocellulose cannot form an integrated overlap effect, a relatively high content of adhesive needs to be used when preparing the coating layer slurry, and if the amount of adhesive used is large, pore clogging problems are likely to occur, which is also disadvantageous to the rate performance of the secondary battery.

[0309] In Comparative Example 3, an inorganic ceramic layer is used as the coating layer, and the inorganic ceramic particles are in the form of primary particles with large particle diameters. Therefore, the number of deposited layers of inorganic ceramic particles on the porous substrate during application is small, and the improvement effects on the heat resistance of the separator and the thermal safety performance of the secondary battery are limited.

[0310] Summarizing the test results of Examples 1 to 21 and 22, it can be seen that when nanocellulose has a specific type and / or a specific content of modifying groups of the present application, it contributes to further improving the heat resistance of the separator and the thermal safety performance of the secondary battery.

[0311] The present application is not limited to the above-mentioned embodiment. The above-mentioned embodiment is merely an example, and any configuration that has substantially the same technical idea and produces similar effects within the technical scope of the present application is included in the technical scope of the present application. In addition, various modifications that a person skilled in the art can conceive of to the embodiment, and other forms constructed by combining some of the components in 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 comprising a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer including a three-dimensional skeletal structure and a filler, at least a portion of the filler being filled into the three-dimensional skeletal structure, and the filler being secondary particles formed by aggregation of primary particles.

2. The separator according to claim 1, wherein the average particle size of the primary particles constituting the filler is 8 nm to 30 nm, and preferably 10 nm to 20 nm.

3. The separator according to claim 1 or 2, wherein the average particle size of the filler is 200 nm or less, preferably 50 nm to 200 nm.

4. The BET specific surface area of ​​the filler is 20 m ２ / g or more, preferably 30m ２ / g ~ 80m ２ The separator according to any one of claims 1 to 3, wherein the molecular weight is 1 / g.

5. The filler includes at least one of inorganic particles and organic particles, Preferably, the inorganic particles include at least one of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon-oxygen compounds, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, zirconium titanate, barium titanate, and magnesium fluoride; more preferably, the inorganic particles include at least one of boehmite, alumina, barium sulfate, magnesium oxide, silicon-oxygen compounds, titanium oxide, zinc oxide, cerium oxide, and barium titanate; The separator according to any one of claims 1 to 4, wherein the organic particles preferably include at least one of polystyrene and polyacrylic wax.

6. The filler comprises inorganic particles in a secondary particle form, and the crystal form of the inorganic particles in the secondary particle form comprises at least two of α crystal form, θ crystal form, γ crystal form, and η crystal form, and preferably, the crystal form of the inorganic particles in the secondary particle form comprises at least two of α crystal form, θ crystal form, and γ crystal form, Preferably, the content of the inorganic particles in the form of secondary particles having an α-crystal form is 1.2 wt % or more, more preferably 1.2 wt % to 10 wt %, based on the total weight of the inorganic particles in the form of secondary particles; Preferably, the content of the inorganic particles having a secondary particle form of the θ crystal form in the inorganic particles having a secondary particle form is 50 wt % or more, more preferably 60 wt % to 85 wt %, based on the total weight of the inorganic particles having a secondary particle form; Preferably, the content of the inorganic particles in the form of secondary particles having a gamma crystal form is 10 wt % or more, more preferably 15 to 60 wt %, based on the total weight of the inorganic particles in the form of secondary particles; The separator according to any one of claims 1 to 5, wherein the content of the inorganic particles in the secondary particle form of the η crystal form in the inorganic particles in the secondary particle form is preferably 5 wt % or less, more preferably 2 wt % or less, based on the total weight of the inorganic particles in the secondary particle form.

7. The average particle size of the primary particles constituting the filler is d １ nm, and the average diameter of the material constituting the three-dimensional framework structure is d ２ nm, and the separator is The separator according to any one of claims 1 to 6, which satisfies the above.

8. The separator according to any one of claims 1 to 7, wherein the three-dimensional skeletal structure is formed from fibrous materials, and preferably the form of the fibrous materials includes at least one of a rod-like form, a tubular form, and a fibrous form.

9. The separator according to any one of claims 1 to 8, wherein the material constituting the three-dimensional framework structure has an average diameter of 40 nm or less, preferably 10 nm to 35 nm.

10. The average length of the material constituting the three-dimensional framework is 100 nm to 600 nm, preferably 200 nm to 450 nm, and / or The separator according to any one of claims 1 to 9, wherein the aspect ratio of the material constituting the three-dimensional framework structure is 5 to 60, and preferably 10 to 30.

11. The fibrous material includes at least one of an organic material and an inorganic material, Preferably, the organic material comprises at least one of nanocellulose, polytetrafluoroethylene nanofibers and polyamide nanofibers, and preferably, the nanocellulose comprises at least one of cellulose nanofibers, cellulose nanowhiskers and bacterial nanocellulose; Preferably, the inorganic material includes at least one of halloysite nanotubes, nanorod-shaped alumina, nanorod-shaped boehmite, nanorod-shaped silica, and glass fiber.

12. The material constituting the three-dimensional framework structure includes nanocellulose, and the nanocellulose includes at least one of unmodified nanocellulose and modified nanocellulose; Preferably, the modified nanocellulose comprises a modifying group, the modifying group comprising at least one of an amine group, a carboxyl 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; Preferably, 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, more preferably 2:3 to 7:

3. The separator according to any one of claims 1 to 11.

13. The separator according to any one of claims 1 to 12, wherein the material constituting the three-dimensional skeletal structure contains a sulfonic acid group, and the content of sulfur element in the material constituting the three-dimensional skeletal structure is 0.1 wt % or more, preferably 0.2 wt % to 0.5 wt %, based on the total weight of the material constituting the three-dimensional skeletal structure.

14. The content of the three-dimensional framework structure is 5 wt % to 40 wt %, preferably 10 wt % to 25 wt %, based on the total weight of the coating layer; and / or The separator according to any one of claims 1 to 13, wherein the content of the filler is 60 wt % or more, preferably 70 wt % to 90 wt %, based on the total weight of the coating layer.

15. The separator according to any one of claims 1 to 14, wherein the coating layer further comprises inorganic particles in the form of primary particles, and at least a portion of the inorganic particles in the form of primary particles are embedded in the coating layer.

16. The separator according to claim 15, wherein the inorganic particles in the form of primary particles satisfy at least one of the following conditions (1) to (6): (1) The average particle size of the primary particle-form inorganic particles is 200 nm to 800 nm, and preferably 200 nm to 400 nm. (2) The BET specific surface area of ​​the inorganic particles in the form of primary particles is 10 m ２ / g or less, preferably 3m ２ / g ~ 7m ２ / g. (3) 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. (4) The crystal form of the primary particle-form inorganic particles includes an α-crystal form, and the content of the α-crystal form inorganic particles in the primary particle-form inorganic particles is 90 wt % or more, more preferably 95 wt % to 100 wt %, based on the total weight of the primary particle-form inorganic particles. (5) The inorganic particles in the form of primary particles include at least one of inorganic particles having a dielectric constant of 5 or more, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of undergoing an electrochemical reaction. (6) The content of the inorganic particles in the form of primary particles is 30 wt % or less, and preferably 5 wt % to 25 wt %, based on the total weight of the coating layer.

17. The coating layer further comprises a non-particulate adhesive; Preferably, the non-particulate adhesive comprises a water-based adhesive; The separator according to any one of claims 1 to 16, wherein the content of the non-particulate adhesive in the coating layer is preferably 2 wt % or less with respect to the total weight of the coating layer.

18. The thickness of the porous substrate is 6 μm or less, preferably 3 μm to 5 μm, and / or The separator according to any one of claims 1 to 17, wherein the coating layer has a thickness of 1 µm or less, preferably 0.5 µm to 0.8 µm.

19. The coating layer further includes an adhesive layer provided on at least a portion of the surface of the coating layer, the adhesive layer including a particulate adhesive, The separator according to any one of claims 1 to 18, wherein the particulate adhesive preferably includes at least one of an acrylic acid ester monomer homopolymer or copolymer, an acrylic acid monomer homopolymer or copolymer, and a fluorine-containing olefin monomer homopolymer or copolymer.

20. The separator according to any one of claims 1 to 19, which satisfies at least one of the following conditions (1) to (7): (1) The thermal shrinkage rate of the separator in the longitudinal direction at 150° C. for 1 hour is 5% or less, and preferably 0.5% to 3%. (2) The thermal shrinkage rate of the separator in the transverse direction at 150° C. for 1 hour is 5% or less, and preferably 0.5% to 3%. (3) The separator has a longitudinal tensile strength of 2000 kg / cm ２ More preferably, 2500 kg / cm ２ ~4500kg / cm ２ It is. (4) The separator has a lateral tensile strength of 2000 kg / cm ２ More preferably, 2500 kg / cm ２ ~4500kg / cm ２ It is. (5) The wet length of the separator is 30 mm or more, and preferably 30 mm to 80 mm. (6) The wetting speed of the separator is 3 mm / s or more, and preferably 3 mm / s to 10 mm / s. (7) The separator has an air permeability of 300 s / 100 mL or less, and preferably 100 s / 100 mL to 230 s / 100 mL.

21. A method for producing the separator according to any one of claims 1 to 20, comprising the steps of: A step S1 of providing a porous substrate; A slurry supply step S2 in which a material for constituting a three-dimensional skeleton structure and a filler are mixed in a solvent at a predetermined ratio to prepare the slurry; A coating step S3 of coating the slurry on at least one surface of the porous substrate and drying the slurry to obtain a separator; The separator includes a porous substrate and a coating layer provided on at least one surface of the porous substrate, the coating layer includes a three-dimensional skeletal structure and a filler, at least a portion of the filler is filled in the three-dimensional skeletal structure, and the filler is a secondary particle formed by aggregation of primary particles.

22. The method of claim 21 , wherein the slurry further comprises inorganic particles in primary particle form.

23. 23. The method of claim 21 or 22, further comprising a two-coating step S4 of applying a slurry containing particulate adhesive to at least a portion of the surface of the coating layer and drying to form an adhesive layer.

24. A secondary battery comprising the separator according to any one of claims 1 to 20 or the separator produced by the method according to any one of claims 21 to 23.

25. A power consuming device comprising the secondary battery of claim 24.

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