Separator, method for producing the same, and related secondary battery and power consumption device

Abstract

The present application provides a separator, a method for manufacturing the same, and related secondary batteries and power consumption devices. The separator includes a porous substrate and a coating provided on at least one surface of the porous substrate, the coating including a three-dimensional framework and a filler having a porous structure, and at least a portion of the filler having a porous structure is filled in the three-dimensional framework.

Description

[Technical Field]

[0001] The present application relates to separators, methods for making the same, and related secondary batteries and power consuming devices. [Background technology]

[0002] In recent years, secondary batteries have been widely used in many fields, including energy storage power systems such as hydroelectric, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. As secondary batteries become more widely used, their reliability, particularly their thermal stability, has received increasing attention. However, current methods for improving the thermal stability of secondary batteries are unfavorable to the balance of their electrochemical performance. Therefore, achieving both high thermal stability and good electrochemical performance in secondary batteries is a key challenge in secondary battery design. Summary of the Invention

[0003] The present application provides a separator that can provide secondary batteries with high thermal stability, long cycle life, and good dynamic properties, a method for manufacturing the same, and related secondary batteries and power consuming devices.

[0004] A first aspect of the present application provides a separator comprising a porous substrate and a coating provided on at least one surface of the porous substrate, the coating including a three-dimensional skeletal structure and a filler having a porous structure, and at least a portion of the filler having the porous structure is filled in the three-dimensional skeletal structure.

[0005] By providing a coating containing a filler having a three-dimensional skeletal structure and a porous structure on the surface of the porous substrate of the separator and filling at least a portion of the filler having a porous structure into the three-dimensional skeletal structure, the separator can be made to have high heat resistance, high adhesion, high ionic conductivity, and good electrolyte impregnation and retention properties, and further, the secondary battery can be made to have high thermal stability, long cycle life, and good dynamic properties.

[0006] In any embodiment of the present application, if the volume distribution particle size Dv50 of the filler having the porous structure is d1 in nm units, the average diameter of the material constituting the three-dimensional skeleton structure is D1 in nm units, and the average length of the material constituting the three-dimensional skeleton structure is L1 in nm units, then 0 < D1 / (d1 / √6) ≤ 1 and 0 < d1 / (L1 / √2) ≤ 1. By adjusting D1 / (d1 / √6) and d1 / (L1 / √2) within the above ranges, it is advantageous to form an integration effect due to the overlapping connection between the filler having the porous structure and the three-dimensional skeleton structure. Since the coating has a more stable spatial network structure, the heat resistance, adhesiveness, and ionic conductivity of the separator can be further improved, and the thermal stability, cycle performance, and kinetic characteristics of the secondary battery can be further improved.

[0007] In any embodiment of the present application, 0.02 ≤ D1 / (d1 / √6) ≤ 0.85, and preferably, 0.05 ≤ D1 / (d1 / √6) ≤ 0.65.

[0008] In any embodiment of the present application, 0.04 ≤ d1 / (L1 / √2) ≤ 0.8, and preferably, 0.10 ≤ d1 / (L1 / √2) ≤ 0.7.

[0009] Thereby, the heat resistance, adhesiveness, and ionic conductivity of the separator can be better improved, and the thermal stability, cycle performance, and kinetic characteristics of the secondary battery can be better balanced.

[0010] In any embodiment of the present application, if the volume distribution particle size Dv50 of the filler having the porous structure is d1, then d1 is 200 nm to 1500 nm, and preferably 500 nm to 1200 nm. The filler having the porous structure has a small volume distribution particle size Dv50, is advantageously filled in the three-dimensional skeleton structure to form an inclusion effect, and contributes to an increase in the heat resistance, adhesiveness, and ionic conductivity of the separator.

[0011] In any of the examples of the present application, when the average diameter of the material constituting the three-dimensional framework is defined as D1, D1 is 40 nm or less, and preferably 5 nm to 35 nm. When the average diameter of the material constituting the three-dimensional framework is within the above range, the ionic conductivity and voltage breakdown characteristics of the separator can be further improved, and it also contributes to forming an integration effect by overlapping and connecting with the filler having a porous structure, thereby further improving the heat resistance of the separator.

[0012] In any embodiment of the present application, when the average length of the material constituting the three-dimensional framework is L1, L1 is 300 nm to 3000 nm, and preferably 400 nm to 2500 nm. When the average length of the material constituting the three-dimensional framework is within the above range, the heat resistance and ionic conductivity of the separator can be further improved.

[0013] In any embodiment of the present application, the average pore size of the filler having a porous structure is 0.1 nm to 1.5 nm, preferably 0.3 nm to 1.0 nm. When the average pore size of the filler having a porous structure is within the above range, the ionic conductivity of the coating and the impregnation and retention properties of the electrolyte can be improved, which contributes to further improvement of the cycle performance and dynamic properties of the secondary battery.

[0014] In any embodiment of the present application, the true density of the filler having a porous structure is 1.0 g / cm 3 ~2.0g / cm 3 and preferably 1.2 g / cm 3 ~1.7g / cm 3 When the true density of the filler having a porous structure is within the above range, the ionic conductivity of the coating and the impregnation and retention properties of the electrolyte can be improved, which contributes to further improvement of the cycle performance and dynamic properties of the secondary battery.

[0015] In any embodiment of the present application, the powder compression density of the filler having a porous structure at 30,000 N is 0.3 g / cm 3 ~1.5g / cm3 and preferably 0.5 g / cm 3 ~1.0g / cm 3 When the powder compressed density of the filler having a porous structure is within the above range, the ionic conductivity of the coating and the impregnation and retention properties of the electrolyte can be improved, which contributes to further improvement of the cycle performance and dynamic properties of the secondary battery.

[0016] In any embodiment of the present application, the specific surface area of ​​the filler having a porous structure is 700 m 2 / g~3000m 2 / g, preferably 800m 2 / g~2500m 2 When the specific surface area of ​​the porous filler is within the above range, it has a better affinity with the three-dimensional framework structure, improves the adhesion effect while using a small amount of binder, effectively reduces the risk of the binder blocking the pores, and improves the cycle performance and dynamic properties of the secondary battery.

[0017] In any embodiment of the present application, the filler having a porous structure includes at least one of inorganic porous particles and organic porous particles.

[0018] In any embodiment of the present application, the inorganic porous particles include at least one of porous alumina, porous silica, porous zirconia, porous titania, porous zinc oxide, porous magnesium oxide, porous calcium carbonate, molecular sieves, zeolites, and modified materials thereof.

[0019] In any embodiment of the present application, the organic porous particles comprise at least one of a porous polymer material, a covalent organic framework material, a metal organic framework material, and a respective modifying material.

[0020] In any embodiment of the present application, the content of the porous filler is 50 wt% to 97 wt%, preferably 63 wt% to 93 wt%, based on the total weight of the coating. When the content of the porous filler is within this range, the heat resistance, ionic conductivity, and electrolyte impregnation and retention properties of the separator can be further improved.

[0021] In any embodiment of the present application, the content of the three-dimensional framework structure is 1 wt% to 48 wt%, preferably 5 wt% to 35 wt%, based on the total weight of the coating.

[0022] In any embodiment of the present application, the material constituting the three-dimensional framework may be at least one of linear, rod-shaped, tubular, and rod-shaped. A material with an appropriate shape is advantageous for the three-dimensional framework and the filler having a porous structure to form a more stable spatial network structure, thereby further improving the heat resistance, ionic conductivity, and electrolyte impregnation and retention properties of the separator.

[0023] In any of the examples of the present application, the aspect ratio of the material constituting the three-dimensional skeletal structure is 5 to 150, and preferably 30 to 95. When the aspect ratio of the material constituting the three-dimensional skeletal structure is within the above range, the ionic conductivity and the impregnation and retention properties of the separator with respect to the electrolyte can be further improved.

[0024] In any embodiment of the present application, the material constituting the three-dimensional framework structure includes at least one of an organic material and an inorganic material.

[0025] In any embodiment of the present application, 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.

[0026] In any embodiment of the present application, the inorganic material comprises at least one of halloysite nanotubes, alumina nanorods, boehmite nanorods, silica nanorods, and glass fibers.

[0027] 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.

[0028] In any embodiment of the present application, the modified nanocellulose contains a modifying group, which includes at least one of an amine group, a carboxyl group, an aldehyde group, a sulfonic acid group, a boric acid group, and a phosphate group, and preferably at least one of a sulfonic acid group, a boric acid group, and a phosphate group. When the nanocellulose has the above-mentioned specific modifying group, it can effectively improve the heat resistance of the separator and improve the adhesive strength between the coating and the porous substrate, and it is also advantageous for forming an integrated effect by overlapping and bonding the nanocellulose with a filler having a porous structure.

[0029] In any embodiment of the present application, the modified nanocellulose contains hydroxyl groups and modifying groups, and the molar ratio of the modifying groups to the hydroxyl groups is 1:4 to 4:1, preferably 2:3 to 7:3. When the molar ratio of the modifying groups to the hydroxyl groups is within the above range, the heat resistance, ionic conductivity, and electrolyte impregnation and retention properties of the separator can be further improved.

[0030] 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.

[0031] In any embodiment of the present application, the coating further comprises a non-particulate binder.

[0032] In any embodiment of the present application, the non-particulate binder comprises an aqueous binder.

[0033] In any embodiment of the present application, the content of the non-particulate binder in the coating is 4 wt% or less based on the total weight of the coating. The three-dimensional skeletal structure of the coating can form a stable spatial network structure with a filler having a porous structure, thereby maintaining high adhesion to the separator while reducing the amount of binder used.

[0034] In any embodiment of the present application, the thickness of the porous substrate is 6 μm or less, preferably 3 μm to 5 μm. The coating of the present application can significantly improve the heat resistance of the separator, which allows the selection of a thinner porous substrate, contributing to an improvement in the energy density of the secondary battery.

[0035] In any embodiment of the present application, the thickness of the coating is 1.5 μm or less, preferably 0.5 μm to 1.2 μm, which contributes to improving the energy density of the secondary battery.

[0036] 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. The adhesive layer not only prevents the coating from falling off and improves the reliability of the secondary battery, but also improves the interface between the separator and the electrodes, contributing to improving the cycle performance of the secondary battery.

[0037] In any embodiment of the present application, the adhesive layer comprises a particulate binder.

[0038] In any embodiment of the present application, the particulate binder includes at least one of an acrylic acid ester-based monomer homopolymer or copolymer, an acrylic acid-based monomer homopolymer or copolymer, and a fluorine-containing olefin monomer homopolymer or copolymer.

[0039] In any embodiment of the present application, the separator has a longitudinal heat shrinkage rate of 4% or less at 135°C for 1 hour, and preferably 0.5% to 3.8%.

[0040] In any embodiment of the present application, the separator has a transverse heat shrinkage rate of 4% or less at 135°C for 1 hour, and preferably 0.5% to 3.8%.

[0041] In any embodiment of the present application, the longitudinal tensile strength of the separator is 1600 kg / cm 2 or more, preferably 1800 kg / cm 2 ~4500kg / cm 2 is.

[0042] In any embodiment of the present application, the separator has a transverse tensile strength of 1600 kg / cm 2 or more, preferably 1800 kg / cm 2 ~4500kg / cm 2 is.

[0043] In any embodiment of the present application, the wetted length of the separator is 20 mm or more, preferably 30 mm to 80 mm.

[0044] In any embodiment of the present application, the wetting speed of the separator is 3 mm / s or more, preferably 3 mm / s to 10 mm / s.

[0045] In any embodiment of the present application, the separator has an air permeability of 350 s / 100 mL or less, preferably 120 s / 100 mL to 260 s / 100 mL.

[0046] A second aspect of the present application provides a method for producing a separator according to the first aspect of the present application, comprising the steps of: providing a porous substrate; mixing a material for constituting a three-dimensional skeletal structure and a filler having a porous structure in a solvent at a predetermined ratio to prepare a coating slurry; and applying the coating slurry to at least one surface of the porous substrate and drying it to obtain a separator, wherein the separator comprises a porous substrate and a coating provided on at least one surface of the porous substrate, the coating comprising a three-dimensional skeletal structure and a filler having a porous structure, and at least a portion of the filler having a porous structure is filled in the three-dimensional skeletal structure.

[0047] A third aspect of the present application provides a secondary battery including the separator of the first aspect of the present application or a separator made by the method of the second aspect of the present application.

[0048] A fourth aspect of the present application provides a power consuming device including the secondary battery of the third aspect of the present application.

[0049] The separator according to the present application can provide a secondary battery with high thermal stability and good cycle performance and dynamic characteristics, and the power consumption device according to the present application includes the secondary battery according to the present application and therefore has at least the same advantages as the secondary battery. [Brief explanation of the drawings]

[0050] In order to more clearly explain 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 obtain other drawings based on the drawings without any creative efforts.

[0051] [Figure 1] 1 is a schematic diagram of an embodiment of a secondary battery of the present application. [Figure 2] FIG. 2 is an exploded schematic view of the embodiment of the secondary battery of FIG. 1. [Figure 3]1 is a schematic diagram of one embodiment of a battery module of the present application. [Figure 4] 1 is a schematic diagram of one embodiment of a battery pack of the present application. [Figure 5] 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4. [Figure 6] 1 is a schematic diagram of an embodiment of a power consuming device that includes a secondary battery of the present application as a power source.

[0052] The drawings are not necessarily drawn to scale. [Explanation of symbols]

[0053] 1 battery pack 2 Upper case 3 Lower case 4 Battery Module 5 Secondary battery 51 Housing 52 Electrode Assembly 53 Cover plate DETAILED DESCRIPTION OF THE INVENTION

[0054] Hereinafter, with appropriate reference to the accompanying drawings, embodiments specifically disclosing the separator of the present application, its manufacturing method, and related secondary batteries and power consumption devices will be described in detail. However, unnecessary detailed description may be omitted. For example, detailed description of already well-known matters or redundant description of substantially identical configurations 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 accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0055] The "ranges" disclosed in this application are defined in the form of lower and upper limits. 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 that 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, if ranges of 60 to 120 and 80 to 110 are recited for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 and maximum range values ​​of 3, 4, and 5 are recited, then ranges of 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all contemplated. In this application, unless otherwise specified, a numerical range "a to b" is an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" indicates that all real numbers between "0 and 5" are included herein, and "0 to 5" is 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.

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

[0057] Unless otherwise stated, all technical features and optional technical features of the present application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present application.

[0058] Unless otherwise specified, all steps in the present application may be performed in order or randomly, but are preferably performed in order. For example, when the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed in order, or may include steps (b) and (a) performed in order. 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.

[0059] 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.

[0060] 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 for "A or B": A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), or both A and B are true (or exist).

[0061] Unless otherwise stated, in this application, terms such as "first," "second," etc. are used to distinguish between different objects and not to describe a particular order or hierarchical relationship.

[0062] Unless otherwise explained, terms used in this application have the known meanings commonly understood by those skilled in the art.

[0063] Unless otherwise specified, the numerical values ​​of each parameter mentioned in this application can be measured by various test methods commonly used in this field, for example, according to the test methods provided in the examples of this application. Unless otherwise specified, the test temperature for each parameter is 25°C.

[0064] 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 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. As an important component of a secondary battery, its performance directly affects the performance of the secondary battery.

[0065] Currently, separators used in commercial secondary batteries are generally polyolefin porous membranes, which have poor heat resistance and undergo significant thermal contraction when exposed to heat, causing direct contact between the positive and negative electrodes inside the battery and resulting in an internal short circuit, increasing the safety risk of the secondary battery. Separators are also required to have good electrolyte impregnation and retention properties.

[0066] To solve the above problems, the solution currently adopted is mainly to coat a heat-resistant inorganic ceramic layer on polyolefin porous membrane.However, inorganic ceramic layer still has a series of problems, for example, the requirement for coating thickness is high, when coating is thin, the effect of improving the heat resistance of separator is limited, when coating is thick, heat resistance can be improved, but the internal resistance of battery increases; the requirement for the arrangement of inorganic ceramic particles is high, when the arrangement of inorganic ceramic particles is sparse, the effect of improving the heat resistance of separator is limited; when the arrangement of inorganic ceramic particles is dense, heat resistance can be improved, but pore clogging problem occurs, which affects the cycle performance and dynamic properties of secondary battery.

[0067] Therefore, it is difficult for the separators of the prior art to simultaneously achieve high thermal stability, long cycle life, and good dynamic properties for secondary batteries.

[0068] In the course of research, the inventors of the present application unexpectedly discovered that by providing a coating containing a filler having a three-dimensional skeletal structure and a porous structure on the surface of a separator porous substrate, and by having at least a portion of the filler having a porous structure filled in the three-dimensional skeletal structure, the separator can achieve high heat resistance, high adhesion, high ionic conductivity, and good electrolyte impregnation and retention properties, and further the secondary battery can achieve high thermal stability, long cycle life, and good dynamic properties.

[0069] Separator

[0070] A first aspect of an embodiment of the present application provides a separator including a porous substrate and a coating provided on at least one surface of the porous substrate, wherein the coating includes a three-dimensional skeletal structure and a filler having a porous structure, and at least a portion of the filler having the porous structure is filled in the three-dimensional skeletal structure.

[0071] The term "three-dimensional skeletal structure" generally refers to a structure having a three-dimensional spatial shape and a certain amount of void space, and can be formed by stacking and connecting materials that constitute the three-dimensional skeletal structure.

[0072] A porous filler generally refers to a filler with a regular or irregular channel structure that allows ions to pass through. During the long-term charge / discharge process of a secondary battery, the gradual drying and failure of the separator is a major cause of the decrease in capacity and shortened service life of the secondary battery. This is because, after the separator dries up, the battery's internal resistance increases, charging and discharging are incomplete, the secondary battery's capacity decays rapidly, and its service life is significantly shortened. The separator coating provided in the present application includes a porous filler, which is advantageous for storing electrolyte and releasing it during the long-term charge / discharge process of the secondary battery. This improves the ionic conductivity and electrolyte impregnation and retention properties of the coating, contributing to improved cycle performance and dynamic characteristics of the secondary battery.

[0073] Fillers with porous structures have the advantage of a large specific surface area and better affinity with three-dimensional skeletal structures, which can improve the adhesive effect while using a small amount of binder, effectively reducing the risk of binder blocking pores, and improving the cycle performance and dynamic properties of secondary batteries.

[0074] The porous filler is at least partially filled into the three-dimensional skeletal structure, which improves the heat resistance of the separator, reduces the degree of shrinkage of the separator when heated, reduces the risk of short-circuiting between the positive and negative electrodes, and contributes to high thermal stability of the secondary battery. It also maintains high adhesive strength between the coating and the porous substrate, contributing to a reduced likelihood of the porous filler falling off during long-term charge and discharge of the secondary battery. At the same time, the porous filler is at least partially filled into the three-dimensional skeletal structure, which increases the number of contact points between the porous filler and the three-dimensional skeletal structure, thereby reducing the amount of binder used in the coating and effectively reducing the risk of binder blocking the pores, thereby further improving the cycle performance and dynamic characteristics of the secondary battery.

[0075] Therefore, the separators provided by the examples of the present application can simultaneously achieve high heat resistance, high adhesion, high ionic conductivity, and good electrolyte impregnation and retention properties, and further, secondary batteries using the separators can simultaneously achieve high thermal stability, long cycle life, and good dynamic properties.

[0076] In some embodiments, at least a portion of the filler having a porous structure is filled into the three-dimensional framework, and another portion of the filler having a porous structure may be located on the surface of the three-dimensional framework and / or at the interface between the three-dimensional framework and the porous substrate. Alternatively, a portion of the filler having a porous structure may be embedded in the porous substrate at the interface between the three-dimensional framework and the porous substrate. For example, during the winding process of the electrode assembly, a portion of the filler having a porous structure at the interface may be embedded in the base and / or pores of the porous substrate under the action of external pressure.

[0077] In some embodiments, when the volume distribution particle diameter Dv50 of the filler having the porous structure is d1 in nm, the average diameter of the material constituting the three-dimensional skeletal structure is D1 in nm, and the average length of the material constituting the three-dimensional skeletal structure is L1 in nm, 0 <D1 / (d1 / √6)≦1、0<d1 / (L1 / √2)≦1である。

[0078] Adjusting D1 / (d1 / √6) and d1 / (L1 / √2) within the above ranges is advantageous in forming an integrated effect through overlapping connections between the porous filler and the three-dimensional framework structure, and the coating has a more stable spatial network structure, which can further improve the heat resistance, adhesion, and ionic conductivity of the separator, and further improve the thermal stability, cycle performance, and dynamic properties of the secondary battery.

[0079] Preferably, 0.02≦D1 / (d1 / √6)≦0.85, more preferably 0.03≦D1 / (d1 / √6)≦0.75, 0.05≦D1 / (d1 / √6)≦0.65, 0.052≦D1 / (d1 / √6)≦0.5, or 0.055≦D1 / (d1 / √6)≦0.45. This can further improve the heat resistance, adhesion, and ionic conductivity of the separator, and can also provide a secondary battery with better thermal stability, cycle performance, and dynamic properties.

[0080] Preferably, 0.04≦d1 / (L1 / √2)≦0.8, more preferably 0.10≦d1 / (L1 / √2)≦0.7, 0.12≦d1 / (L1 / √2)≦0.7, 0.14≦d1 / (L1 / √2)≦0.7, or 0.15≦d1 / (L1 / √2)≦0.68, thereby improving the heat resistance, adhesion, and ionic conductivity of the separator and enabling the secondary battery to achieve a good balance between thermal stability, cycle performance, and dynamic properties.

[0081] In some embodiments, 0.05≦D1 / (d1 / √6)≦0.65 and 0.10≦d1 / (L1 / √2)≦0.7, and preferably 0.055≦D1 / (d1 / √6)≦0.45 and 0.15≦d1 / (L1 / √2)≦0.68, which can improve the heat resistance, adhesion, and ionic conductivity of the separator and can also improve the thermal stability, cycle performance, and dynamic characteristics of the secondary battery.

[0082] In some embodiments, when the volume distribution particle diameter Dv50 of the filler having a porous structure is d1, d1 may be 200 nm to 1500 nm, and preferably 500 nm to 1200 nm. The filler having a porous structure has a small volume distribution particle diameter Dv50, and is advantageous in that it is filled into a three-dimensional skeletal structure to form a nesting effect, contributing to an increase in the heat resistance, adhesiveness, and ionic conductivity of the separator.

[0083] The volume distribution particle size Dv50 of a material has the meaning known in the art, and indicates the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%, and can be measured using instruments and methods known in the art. For example, the test can be performed using a laser particle size analyzer (e.g., Master Size 3000) in accordance with GB / T19077-2016.

[0084] Preferably, the porous structure of the filler having a porous structure may be a microporous structure. In some embodiments, the average pore size of the filler having a porous structure may be 0.1 nm to 1.5 nm, preferably 0.3 nm to 1.0 nm. When the average pore size of the filler having a porous structure is within the above range, the ionic conductivity of the coating and the impregnation and retention properties of the electrolyte can be improved, contributing to further improvement of the cycle performance and dynamic characteristics of the secondary battery.

[0085] The average pore size of the porous filler 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 using a static volumetric method in accordance with GB / T19587. During the test, both the adsorption gas and the carrier gas can be nitrogen gas.

[0086] In some embodiments, the true density of the filler having a porous structure is 1.0 g / cm 3 ~2.0g / cm 3 and preferably 1.2 g / cm 3 ~1.7g / cm 3 When the true density of the filler having a porous structure is within the above range, the ionic conductivity of the coating and the impregnation and retention properties of the electrolyte can be improved, which contributes to further improvement of the cycle performance and dynamic properties of the secondary battery.

[0087] The true density of a filler having a porous structure has a meaning known in the art and can be measured by instruments and methods known in the art. For example, referring to GB / T24586-2009, an inert gas (e.g., helium gas or nitrogen gas) is used as a medium, and a gas displacement method is adopted to measure the true volume V of a test sample using a true density tester. t The true density of a filler with a porous structure can be calculated by dividing the mass of the test sample by the true volume of the test sample, V. t is.

[0088] In some embodiments, the powder compaction density of the filler having a porous structure at 30,000 N is 0.3 g / cm 3 ~1.5g / cm 3 Preferably, it is 0.5 g / cm 3 ~1.0g / cm 3 When the powder compressed density of the filler having a porous structure is within the above range, the ionic conductivity of the coating and the impregnation and retention properties of the electrolyte can be improved, which contributes to further improvement of the cycle performance and dynamic properties of the secondary battery.

[0089] The powder compaction density of a material has a meaning known in the art and can be measured using equipment and methods known in the art. For example, it can be measured using an electronic pressure tester (e.g., UTM7305 type) with reference to standard GB / T24533-2009. An exemplary test method is to weigh 1 g of material and measure the density of the material with a base area of ​​1.327 cm. 2 The material is placed in a mold, pressurized to 30,000 N, and held for 30 seconds, after which the pressure is reduced and held for 10 seconds. The powder compression density of the material at 30,000 N is then recorded and calculated.

[0090] In some embodiments, the specific surface area of ​​the porous filler is 700 m 2 / g~3000m 2 / g, preferably 800m 2 / g~2500m 2When the specific surface area of ​​the porous filler is within the above range, it has a better affinity with the three-dimensional framework structure, and can improve the binder effect while using a small amount of binder, effectively reducing the risk of the binder blocking the pores, and improving the cycle performance and dynamic properties of the secondary battery.

[0091] 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, the specific surface area can be measured according to the nitrogen gas adsorption specific surface area analysis test method in accordance with GB / T19587-2017 and calculated using the Brunauer Emmett Teller (BET) method. Preferably, the nitrogen adsorption specific surface area analysis test can be performed using a Tri-Star 3020 specific surface area pore size analyzer manufactured by Micromeritics, Inc., USA.

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

[0093] Preferably, the inorganic porous particles may include at least one of porous alumina, porous silica, porous zirconia, porous titania, porous zinc oxide, porous magnesium oxide, porous calcium carbonate, molecular sieves (e.g., A-type, X-type, Y-type, M-type, ZSM-type, etc.), zeolite, and their respective modified materials.

[0094] Preferably, the organic porous particles may comprise at least one of porous polymer materials, covalent organic framework materials (COFs), metal organic framework materials (MOFs), and their respective modifiers. For example, the organometallic framework materials may comprise at least one of Prussian blue, ZIF series (such as ZIF-8, ZIF-68, etc.), UiO series, CPL series, MIL series, and their respective modifiers.

[0095] The modification may be chemical and / or physical. Chemical modification may include coupling agent modification (e.g., silane coupling agent, titanate coupling agent, etc.), surfactant modification, polymer graft modification, etc. Physical modification may include mechanical force dispersion, ultrasonic dispersion, high-energy treatment, etc.

[0096] In some embodiments, the content of the porous filler may be 50 wt% to 97 wt%, preferably 60 wt% to 95 wt%, or 63 wt% to 93 wt%, based on the total weight of the coating. When the content of the porous filler is within the above range, the heat resistance, ionic conductivity, and electrolyte impregnation and retention properties of the separator can be further improved.

[0097] In some embodiments, the content of the three-dimensional framework structure may be 1 wt% to 48 wt%, preferably 3 wt% to 38 wt%, 5 wt% to 35 wt%, based on the total weight of the coating.

[0098] In some embodiments, the material constituting the three-dimensional framework may include at least one of wires, rods, tubes, and rods. A material with an appropriate shape is advantageous for the three-dimensional framework and the filler having a porous structure to form a more stable spatial network structure, thereby further improving the heat resistance, ionic conductivity, and electrolyte impregnation and retention properties of the separator.

[0099] In some embodiments, the material constituting the three-dimensional framework structure can include at least one of an organic material and an inorganic material.

[0100] Preferably, the organic material may include at least one of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers.

[0101] Preferably, the inorganic material may include at least one of halloysite nanotubes, alumina nanorods, boehmite nanorods, silica nanorods, and glass fibers.

[0102] In some embodiments, the material constituting the three-dimensional framework may include nanocellulose, preferably at least one of cellulose nanofibers (Cellulose nanofibrils, CNF, also known as nanofibril cellulose or microfibril cellulose), cellulose nanowhiskers (Cellulose nanocrystals, CNC, also known as cellulose nanocrystals or nanocrystalline cellulose), and bacterial nanocellulose (Bacterial nanocellulose, BNC, also known as bacterial cellulose or microbial cellulose).

[0103] Nanocellulose is a general term for cellulose in the nano-order (e.g., within 100 nm) in any dimension, possessing both the properties of cellulose and nanoparticles. Nanocellulose can be a polymeric nanomaterial extracted from natural sources such as wood or cotton by one or more methods, including chemical, physical, and biological methods. It offers advantages such as a wide range of sources, low cost, high biodegradability, high elastic modulus, and high specific surface area, making it an excellent alternative to traditional petroleum resources and effectively alleviating issues such as environmental pollution and the shortage of petroleum resources. Nanocellulose has excellent high-temperature resistance and small volume change after heating, thereby improving the heat resistance of separators. At the same time, its lower density compared to conventional inorganic ceramic particles reduces the weight of secondary batteries and improves their weight-to-weight energy density. Furthermore, the three-dimensional framework structure of nanocellulose may have tiny nanopores, which prevent current leakage, allowing separators to achieve both good electrolyte impregnation and retention properties and good voltage breakdown resistance.

[0104] In some embodiments, the nanocellulose comprises at least one of unmodified nanocellulose (also called hydroxylated nanocellulose) and modified nanocellulose, preferably modified nanocellulose.

[0105] Modified nanocellulose refers to nanocellulose that includes modifying groups in addition to hydroxyl groups. In some embodiments, the modified nanocellulose includes modifying groups, and the modifying groups may include at least one of an amine group, a carboxyl group, an aldehyde group, a sulfonic acid group, a boric acid group, and a phosphate group, and preferably at least one of a sulfonic acid group, a boric acid group, and a phosphate group.

[0106] When nanocellulose contains the above-mentioned specific modifying groups, it can effectively improve the heat resistance of the separator, improving the thermal stability of the secondary battery, while also improving the adhesive strength between the coating and the porous substrate. When nanocellulose contains the above-mentioned specific modifying groups, it is also advantageous to form an integrated effect through overlapping connections between the nanocellulose and the porous filler, thereby providing the coating with a more stable spatial network structure, improving the separator's electrolyte impregnation and retention properties, and improving the separator's ionic conductivity and voltage breakdown characteristics. The presence of the modifying groups can also reduce the proportion of hydroxyl groups, which gives the coating slurry an appropriate viscosity, making it easier to apply, and improving separator production efficiency and coating uniformity.

[0107] In some embodiments, the molar ratio of the modifying groups to the hydroxyl groups may be 1:4 to 4:1, preferably 2:3 to 7:3. When the molar ratio of the modifying groups to the hydroxyl groups is within the above range, the heat resistance, ionic conductivity, and electrolyte impregnation and retention properties of the separator can be further improved. Furthermore, the following situation can be effectively avoided: If the molar ratio of the modifying groups to the hydroxyl groups is too small, the further improvement effect of the modifying groups on the separator's heat resistance and ionic conductivity may not be significant. If the molar ratio of the modifying groups to the hydroxyl groups is too large, the separator's electrolyte impregnation and retention properties may be deteriorated, which may further affect the cycle performance and reliability of the secondary battery, as well as the heat resistance of the separator, and may further affect the improvement effect on the thermal stability of the secondary battery.

[0108] The type of modifying group in nanocellulose can be determined by infrared spectroscopy. For example, the type of modifying group can be determined by measuring the infrared spectrum of the material and determining the characteristic peaks contained therein. Specifically, infrared spectroscopy of the material can be performed using equipment and methods known in the art. For example, infrared spectroscopy can be performed using an infrared spectrometer (e.g., an IS10 Fourier transform infrared spectrometer manufactured by Nigel, USA) in accordance with GB / T 6040-2019 General Rules for Infrared Spectroscopy.

[0109] In some embodiments, the material constituting the three-dimensional framework contains sulfonic acid groups, and the content of sulfur element in the material constituting the three-dimensional framework may be 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 framework. Preferably, the material constituting the three-dimensional framework may include nanocellulose.

[0110] The sulfur content of the materials that make up the three-dimensional framework can be determined by drying the materials, grinding them in a mortar (e.g., an agate mortar) for 30 minutes, and then testing them using an X-ray diffraction device (e.g., a Miniflex 600-C) to obtain the sulfur content. During the test, a Cu target, a Ni filter, a tube voltage of 40 kV, and a tube current of 15 mA are used, and the beam angle is continuously scanned from 5° to 80°.

[0111] In some embodiments, when the average diameter D1 of the material constituting the three-dimensional framework is 40 nm or less, preferably 5 nm to 35 nm, 8 nm to 35 nm, 10 nm to 35 nm, or 12 nm to 32 nm. When the average diameter D1 of the material constituting the three-dimensional framework is within the above range, the ionic conductivity and voltage breakdown characteristics of the separator can be further improved, and the stacked connection with the porous filler can contribute to forming an integration effect, thereby further improving the heat resistance of the separator. In addition, the following situations can be effectively avoided. If the average diameter of the material constituting the three-dimensional skeletal structure is too large, the inter-winding effect of the formed three-dimensional skeletal structure will be insufficient, and the voids will be large, which may result in the separator having insufficient heat resistance and voltage breakdown resistance characteristics. At the same time, this will be disadvantageous in forming an integrated effect through overlapping connections with the filler having a porous structure. Furthermore, during the drying process of the coating, the three-dimensional skeletal structure will be prone to collapse due to the lack of supporting effect of the filler having a porous structure. Furthermore, direct contact with the porous substrate will be likely to cause pore clogging problems, which may affect the ionic conductivity of the separator.

[0112] In some embodiments, the average length of the material constituting the three-dimensional framework is designated L1, and L1 may be 300 nm to 3000 nm, preferably 400 nm to 2500 nm, 800 nm to 2250 nm, 1000 nm to 2250 nm, or 1200 nm to 2250 nm. When the average length of the material constituting the three-dimensional framework is within the above range, the heat resistance and ionic conductivity of the separator can be further improved. In addition, the following situations can be effectively avoided. If the average length of the material constituting the three-dimensional framework is too short, the overlapping connection effect with the porous filler will be poor, the heat resistance of the coating will be poor, and during the drying process of the coating, the three-dimensional framework will be prone to collapse due to the lack of support from the porous filler, and pore clogging will be likely to occur, inhibiting ion transport and moisture discharge and potentially affecting the thermal stability, cycle performance and dynamic properties of the secondary battery. If the average length of the material constituting the three-dimensional framework is too long, the viscosity of the coating slurry will be high and the flow will be poor, which will affect the application of the coating slurry and further the quality of the coating, and may affect, for example, the heat resistance and ionic conductivity of the separator.

[0113] In some embodiments, the aspect ratio of the material constituting the three-dimensional framework may be 5 to 150, preferably 30 to 95 or 40 to 90. When the aspect ratio of the material constituting the three-dimensional framework is within the above range, the ionic conductivity and electrolyte impregnation and retention properties of the separator can be further improved. Furthermore, the following situation can be effectively avoided: If the aspect ratio of the material constituting the three-dimensional framework is too small, the overlapping connection effect with the porous filler is poor, the heat resistance of the coating is reduced, and during the drying process of the coating, the three-dimensional framework is prone to collapse due to the lack of support for the porous filler. Furthermore, pore clogging is likely to occur, which inhibits ion transport and moisture discharge and may affect the thermal stability, cycle performance, and dynamic characteristics of the secondary battery. If the aspect ratio of the material constituting the three-dimensional framework is too large, the voids in the formed three-dimensional framework are small, which may reduce the ionic conductivity of the separator.

[0114] The average length and average diameter of the material constituting the three-dimensional skeletal structure can be measured using the following method. A 3.6 mm × 3.6 mm sample is cut from any one area of ​​the separator, and the microtopography structure of the coating in the sample is mapped using a scanning electron microscope (e.g., ZEISS Sigma 300) in high vacuum mode with an operating voltage of 3 kV and a magnification of 30,000 times to obtain an SEM image. Based on the obtained SEM image, multiple test areas (e.g., five or more) are selected and length statistics are performed, with each test area measuring 0.5 μm × 0.5 μm. The average value of the average lengths obtained for each test area is then used as the average length of the material constituting the three-dimensional skeletal structure. Based on the obtained SEM image, multiple test areas (e.g., five or more) are selected and diameter statistics are performed using Nano Measurer particle size distribution statistical software, with each test area measuring 0.5 μm × 0.5 μm. The average value of the average diameters obtained for each test area is then used as the average diameter of the material constituting the three-dimensional skeletal structure.

[0115] When the material that makes up the three-dimensional skeletal structure contains nanocellulose, the diameter at both ends of the nanocellulose in the longitudinal direction is generally small and the diameter at the middle position is generally large, so the maximum diameter of the nanocellulose in the longitudinal direction can be used as the diameter of the nanocellulose. The diameters of other nanocelluloses can be processed in a similar manner, and then the average diameter of the nanocellulose can be obtained using the Nano Measurer particle size distribution statistical software according to the method described above.

[0116] In some embodiments, the coating may further include a non-particulate binder. In the present application, the type of non-particulate binder is not particularly limited, and any known material with good adhesive properties may be used. Preferably, the non-particulate binder may include an aqueous binder, which has the advantages of good thermodynamic stability and environmental friendliness, making it advantageous for preparing and applying a coating slurry. For example, the aqueous binder may include at least one of an aqueous acrylic resin (e.g., a homopolymer of acrylic acid, methacrylic acid, or sodium acrylate monomer or a copolymer with other comonomers), polyvinyl alcohol (PVA), an isobutylene-maleic anhydride copolymer, and a polyacrylamide.

[0117] Preferably, the content of the non-particulate binder in the coating may be 4 wt% or less based on the total weight of the coating. The three-dimensional skeletal structure of the coating can form a stable spatial network structure with a filler having a porous structure, thereby maintaining high adhesion to the separator while reducing the amount of binder used.

[0118] In some embodiments, the thickness of the coating may be 1.5 μm or less, preferably 0.5 μm to 1.2 μm, which contributes to improving the energy density of the secondary battery. The coating thickness refers to the thickness of the coating located on one side of the porous substrate.

[0119] In some embodiments, the thickness of the porous substrate may be 8 μm or less, preferably 6 μm or less, and more preferably 3 μm to 5 μm. The coating of the present application significantly improves the heat resistance of the separator, allowing the selection of a thinner porous substrate and contributing to an improvement in the energy density of the secondary battery.

[0120] In the present application, the material of the porous substrate is not particularly limited, and any known substrate having good chemical and mechanical stability can be selected. For example, the porous substrate 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 the layers can be the same or different.

[0121] In some embodiments, the separator may further include an adhesive layer, which may be provided on at least a portion of the surface of the coating, and which may include a particulate binder. The adhesive layer not only prevents the coating from falling off and improves the reliability of the secondary battery, but also improves the interface between the separator and the electrodes, contributing to improving the cycle performance of the secondary battery.

[0122] Preferably, the particulate binder may contain at least one of an acrylic acid ester-based monomer homopolymer or copolymer, an acrylic acid-based monomer homopolymer or copolymer, and a fluorine-containing olefin monomer homopolymer or copolymer. The copolymerizable monomer includes at least one of an acrylic acid ester-based monomer, an acrylic acid-based monomer, an olefin monomer, a halogen-containing olefin monomer, a fluoroether-based monomer, and the like, but is not limited thereto.

[0123] Preferably, the particulate binder may include 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 acrylic ester monomer, an acrylic monomer, and a fluoroether monomer. Preferably, the comonomer may include at least one of trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ethers (e.g., perfluoro(methyl vinyl) ether PMVE, perfluoro(ethyl vinyl) ether PEVE, perfluoro(propyl vinyl) ether PPVE), perfluoro(1,3-m-dioxole), and perfluoro(2,2-dimethyl-1,3-m-dioxole) (PDD).

[0124] In some embodiments, the separator may have a longitudinal heat shrinkage of 4% or less at 135° C. for 1 hour, and preferably has a heat shrinkage of 1.5% to 3.8%.

[0125] In some embodiments, the separator may have a transverse heat shrinkage of 4% or less at 135° C. for 1 hour, and preferably 1.0% to 3.8%.

[0126] The separator has low thermal shrinkage in both the transverse and longitudinal directions at a high temperature of 135° C., thereby improving the reliability of the secondary battery.

[0127] In some embodiments, the separator has a longitudinal tensile strength of 1600 kg / cm 2 or more, preferably 1800 kg / cm 2 ~4500kg / cm 2 is.

[0128] In some embodiments, the separator has a transverse tensile strength of 1600 kg / cm 2 or more, preferably 1800 kg / cm 2 ~4500kg / cm 2 is.

[0129] When the separator 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 reliability of the secondary battery can be improved.

[0130] In some embodiments, the wetted length of the separator may be 20 mm or more, preferably 30 mm to 80 mm.

[0131] In some embodiments, the wetting speed of the separator may be 3 mm / s or more, preferably 3 mm / s to 10 mm / s.

[0132] When the separator has good electrolyte impregnation and retention properties, the ionic conductivity of the separator and the capacity development properties of the secondary battery can be improved.

[0133] In some embodiments, the separator may have an air permeability of 350 s / 100 mL or less, preferably 120 s / 100 mL to 260 s / 100 mL. When the separator has good gas permeability, the ionic conductivity and the capacity development characteristics of the secondary battery can be improved.

[0134] In some embodiments, the separator includes a porous substrate and a coating provided on at least one surface of the porous substrate. The coating includes a three-dimensional skeleton structure and a filler having a porous structure. At least a part of the filler having the porous structure is filled in the three-dimensional skeleton structure. Let the volume distribution particle size Dv50 (unit: nm) of the filler having the porous structure be d1, the average diameter (unit: nm) of the material constituting the three-dimensional skeleton structure be D1, and the average length (unit: nm) of the material constituting the three-dimensional skeleton structure be L1. Then, 0 < D1 / (d1 / √6) ≦ 1 and 0 < d1 / (L1 / √2) ≦ 1. Preferably, 0.05 ≦ D1 / (d1 / √6) ≦ 0.65 and 0.10 ≦ d1 / (L1 / √2) ≦ 0.7. When the volume distribution particle size Dv50 of the filler having the porous structure is d1, d1 is 200 nm to 1500 nm, preferably 500 nm to 1200 nm. The material constituting the three-dimensional skeleton structure includes nanocellulose. When the average diameter of the material constituting the three-dimensional skeleton structure is D1, D1 is 40 nm or less, preferably 5 nm to 35 nm. When the average length of the material constituting the three-dimensional skeleton structure is L1, L1 is 300 nm to 3000 nm, preferably 400 nm to 2500 nm. Thereby, the heat resistance, adhesion, and ionic conductivity of the separator can be improved better, and the heat stability, cycle performance, and kinetic characteristics of the secondary battery can be made compatible better.

[0135] The heat shrinkage rate, tensile strength, and air permeability of the separator all have meanings known in the art and can be measured by methods known in the art. For example, all can be tested by referring to the standard GB / T36363~2018.

[0136] The separator wetting length and wetting rate have meanings known in the art and can be measured using methods known in the art. An exemplary test method involves cutting a separator into a 5 mm wide, 100 mm long specimen, fixing both ends of the specimen and placing it horizontally, dropping 0.5 mg of electrolyte onto the center of the specimen, and measuring the length of diffusion of the electrolyte after a predetermined time (1 min in this application) by photographing the specimen to obtain the separator wetting length and wetting rate. To ensure accuracy of the test results, multiple specimens (e.g., 5-10 specimens) are tested and averaged to obtain test results. The electrolyte may be prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a mass ratio of 30:50:20 to obtain an organic solvent, and dissolving thoroughly dried LiPF6 in the organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L.

[0137] The above separator coating parameters (e.g., thickness, etc.) are all coating parameters on one side of the porous substrate. When coatings are provided on both sides of the porous substrate, it is considered that the coating parameters on either side satisfy the present application and fall within the scope of protection of the present application.

[0138] Production method

[0139] 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 the steps of providing a porous substrate, mixing a material for constituting a three-dimensional skeletal structure and a filler having a porous structure in a predetermined ratio in a solvent to prepare a coating slurry, and applying the coating slurry to at least one surface of the porous substrate and drying it to obtain a separator, wherein the separator comprises the porous substrate and a coating provided on at least one surface of the porous substrate, the coating comprising a three-dimensional skeletal structure and a filler having a porous structure, and at least a portion of the filler having a porous structure is filled in the three-dimensional skeletal structure.

[0140] In some embodiments, the solvent used in preparing the coating slurry may be water, for example, deionized water.

[0141] In some embodiments, the coating slurry may further include other ingredients, such as dispersants, wetting agents, binders, and the like.

[0142] In some embodiments, the material for forming the three-dimensional framework structure may include at least one of an organic material and an inorganic material. Preferably, the organic material may include at least one of nanocellulose, polytetrafluoroethylene nanofiber, and polyamide nanofiber. Preferably, the inorganic material may include at least one of halloysite nanotubes, alumina nanorods, boehmite nanorods, silica nanorods, and glass fibers.

[0143] In some embodiments, the material comprising the three-dimensional scaffold structure may include nanocellulose.

[0144] In some embodiments, nanocellulose can be obtained by providing a cellulose powder with a whiteness of ≥ 80%, mixing the resulting cellulose powder with a modifying solution to react, washing to remove impurities, adjusting the pH to neutral, grinding, and cutting to obtain nanocellulose.

[0145] Preferably, the cellulose powder having a whiteness of 80% or greater may be commercially available or may be obtained by employing a chemical method (e.g., acid decomposition, alkali treatment, Tempo catalytic oxidation), a biological method (e.g., enzyme treatment), 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 greater may include at least one of plant fibers such as cotton fiber (e.g., cotton fiber, kapok fiber), hemp fiber (e.g., sisal fiber, ramie fiber, jute fiber, flax fiber, hemp fiber, Manila fiber, etc.), palm fiber, wood fiber, bamboo fiber, and grass fiber.

[0146] In some embodiments, the cellulose powder having a whiteness of 80% or greater can also be produced by opening a fiber raw material, removing debris, and then steaming the fiber raw material 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 the raw material with water to remove impurities (e.g., washing the raw material with water 3 to 6 times), bleaching the raw material with water (e.g., using sodium hypochlorite and / or hydrogen peroxide), pickling the raw material with an acid to remove impurities, washing the raw material with water to remove impurities, removing the water, and flash drying to obtain a cellulose powder.

[0147] In some embodiments, the modifying solution may be an acid solution (e.g., aqueous sulfuric acid, aqueous boric acid, aqueous phosphoric acid, aqueous acetic acid) or an alkaline solution (e.g., organic solvent urea solution). Preferably, the modifying solution is an acid solution.

[0148] Preferably, the concentration of the acid solution may be 5 wt% to 80 wt%. When a sulfuric acid aqueous solution is used as the modifying solution, a cellulose powder having sulfonic acid groups can be obtained by adjusting the concentration of the acid solution to 40 wt% to 80 wt%. When a boric acid aqueous solution is used as the modifying solution, a cellulose powder having boric acid groups can be obtained by adjusting the concentration of the acid solution to 5 wt% to 10 wt%. When a phosphoric acid aqueous solution is used as the modifying solution, a cellulose powder having phosphate groups can be obtained by adjusting the concentration of the acid solution to 45 wt% to 75 wt%. When an acetic acid aqueous solution is used as the modifying solution, a cellulose powder having carboxylic acid groups can be obtained by adjusting the concentration of the acid solution to 40 wt% to 80 wt%.

[0149] Preferably, the urea organic solvent solution is converted into a urea xylene solution, whereby a cellulose powder having an amine group can be obtained.

[0150] In some embodiments, the mass ratio of the cellulose powder to the modifying solution may be preferably 1:2.5 to 1:50, and more preferably 1:5 to 1:30.

[0151] When the modifying solution is a sulfuric acid aqueous solution, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30. When the modifying solution is a boric acid aqueous solution, the mass ratio of the cellulose powder to the acid solution may be 1:20 to 1:50. When the modifying solution is a phosphoric acid aqueous solution, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30. When the modifying solution is an acetic acid aqueous solution, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30. When the modifying solution is a urea organic solvent solution, the mass ratio of the cellulose powder to the urea organic solvent solution may be 1:4 to 1:40.

[0152] In some embodiments, when the modifying solution is an acid solution, the reaction can 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 can be 0.2 hours to 2.5 hours, preferably 0.5 hours to 1.5 hours.

[0153] In some embodiments, when the modifying 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 modifying solution may be 0.5 hours to 3.5 hours.

[0154] In some embodiments, grinding may be performed using a grinder, and cutting may be performed using a high-pressure homogenizer. By adjusting the grinding parameters of the grinder (e.g., grinding frequency, 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.

[0155] In some embodiments, a coater may be used to apply the coating slurry. In the present application, the model number of the coater is not particularly limited, and for example, a commercially available coater may be used. The coater may include a gravure roll for transferring the slurry to the porous substrate.

[0156] In some embodiments, the coating slurry may be applied by transfer coating, spin coating, dip coating, or the like.

[0157] In some embodiments, the method may further include applying a slurry including a particulate binder to at least a portion of the surface of the coating and drying to form an adhesive layer.

[0158] The separator fabrication method creates a coating in a single application, greatly simplifying the separator fabrication process.

[0159] Parameters such as some raw materials used in the method for producing the separator and their contents can be referenced in the separator according to the first aspect of the embodiment of the present application, but a description thereof will be omitted here.

[0160] Unless otherwise specified, each of the raw materials used in the method for producing the separator is commercially available.

[0161] secondary battery

[0162] A third aspect of an embodiment of the present application provides a secondary battery.

[0163] A secondary battery, also known as a rechargeable battery or storage battery, is a battery that can be continuously used by activating the active material through charging after discharging. 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 to prevent short circuits between the positive electrode and the negative electrode while allowing active ions to pass through.

[0164] The present application does not particularly limit the type of secondary battery, and for example, the secondary battery may be a lithium ion battery, a sodium ion battery, a lithium metal battery, a sodium metal battery, etc., and in particular, the secondary battery may be a lithium ion battery.

[0165] 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 prepared by the method according to the second aspect of the present application, the separator being interposed between a positive electrode sheet and a negative electrode sheet. Preferably, the separator has the coating of the present application on at least the side of the separator closest to the negative electrode sheet. This allows the secondary battery according to the present application to simultaneously achieve high thermal stability, long cycle life, and good dynamic characteristics.

[0166] [Positive electrode sheet]

[0167] In some embodiments, the positive electrode sheet may include a positive electrode current collector and a positive electrode film layer including a positive electrode active material and provided on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two surfaces facing each other in the 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.

[0168] When the secondary battery is a lithium-ion battery, the positive electrode active material may include, but is not limited to, at least one of lithium transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Examples of lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate, lithium iron phosphate and carbon composite, lithium manganese phosphate, lithium manganese phosphate and carbon composite, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composite, and their modified compounds.

[0169] 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 has the general formula Li a Ni b Co c M d O e A f and may include at least one of lithium transition metal oxides and modified compounds thereof. 0.8 ≦ a ≦ 1.2, 0.5 ≦ b < 1, 0 < c < 1, 0 < d < 1, 1 ≦ e ≦ 2, 0 ≦ f ≦ 1, M is at least one selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is at least one selected from N, F, S, and Cl.

[0170] As an example, the cathode active material for a lithium-ion battery may include at least one of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O₂ (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O₂ (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O₂ (NCM811), LiNi 0.80 Co 0.15 Al 0.05 O₂, LiFePO₄, and LiMnPO₄.

[0171] When the secondary battery is a sodium-ion battery, the cathode active material can include, but is not limited to, at least one of sodium-containing transition metal oxides, polyanion materials (e.g., phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue-based materials.

[0172] As an example, the cathode active material for a sodium-ion battery may include NaFeO₂, NaCoO₂, NaCrO₂, NaMnO₂, NaNiO₂, NaNi1 / 2 Ti 1 / 2 O2, NaNi 1 / 2 Mn 1 / 2 O2, Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2, NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue-based materials, general formula X p M' q (PO4) r O x Y 3-x The compound may include at least one material of the general formula X p M' q (PO4) r O x Y 3-x In, 0 <p≦4、0<q≦2、1≦r≦3、0≦x≦2であり、XはH + , Li + , Na + , K. + and NH4 + M' is a transition metal cation, preferably at least one of V, Ti, Mn, Fe, Co, Ni, Cu, and Zn; and Y is a halogen anion, preferably at least one of F, Cl, and Br.

[0173] The modifying compounds for the positive electrode active material can perform doping modification and / or surface coating modification on the positive electrode active material.

[0174] In some embodiments, the positive electrode film layer may preferably further include a positive electrode conductive agent. In the present application, the type of the positive electrode conductive agent is not particularly limited, and examples of the positive electrode conductive agent include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0175] In some embodiments, the positive electrode film layer may preferably further include a positive electrode binder. In the present application, the type of the positive electrode binder is not particularly limited, and for example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic ester resin.

[0176] In some embodiments, the positive electrode current collector may be a metal foil sheet or a composite current collector. An example of the metal foil sheet is 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).

[0177] The positive electrode film layer is typically formed by applying a positive electrode slurry to a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0178] [Negative electrode sheet]

[0179] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces facing each other in the 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.

[0180] The negative electrode active material may be any negative electrode active material for secondary batteries known in the art. For example, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of silicon elemental, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material may include at least one of tin elemental, tin oxide, and tin alloy material.

[0181] In some embodiments, the negative electrode film layer may preferably further include a negative electrode conductive agent. In the present application, the type of the negative electrode conductive agent is not particularly limited, and for example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0182] In some embodiments, the negative electrode film layer may preferably further include a negative electrode binder. In the present application, the type of the negative electrode binder is not particularly limited, and for example, the negative electrode binder 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).

[0183] In some embodiments, the negative electrode membrane layer may preferably further include other additives, such as a thickener, for example, sodium carboxymethyl cellulose (CMC), a PTC thermistor material, etc.

[0184] 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 is 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).

[0185] The negative electrode film layer is typically formed by applying a negative electrode slurry to a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, optional conductive agent, optional binder, 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.

[0186] 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 further includes a conductive undercoat layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and provided on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet described herein further includes a protective layer covering the surface of the negative electrode film layer.

[0187] [Electrolyte]

[0188] During the charge and discharge process of the secondary battery, active ions are inserted and released back and forth 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. In this application, the type of electrolyte is not particularly limited and can be selected according to actual needs.

[0189] 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.

[0190] When the secondary battery is a lithium-ion battery, for example, the electrolyte salt may include at least one of lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium difluorophosphate (LiPOF), lithium difluorooxalatophosphate (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP), but is not limited thereto.

[0191] When the secondary battery is a sodium ion battery, for example, the electrolyte salt may include at least one of sodium hexafluorophosphate (NaPF), sodium tetrafluoroborate (NaBF), sodium perchlorate (NaClO), sodium hexafluoroarsenate (NaAsF), sodium bisfluorosulfonylimide (NaFSI), sodium bistrifluoromethanesulfonylimide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), sodium difluorooxalate borate (NaBOB), sodium difluorophosphate (NaPOF), sodium difluorooxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP), but is not limited thereto.

[0192] By way of example, the solvent may include, but is not limited to, at least one 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).

[0193] In some embodiments, the electrolyte may preferably further include an additive. For example, the additive 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 that improves the overcharge performance of the battery, an additive that improves the high-temperature performance of the battery, or an additive that improves the low-temperature power performance of the battery.

[0194] In some embodiments, the positive electrode sheet, separator, and negative electrode sheet can be wound and / or stacked to form an electrode assembly.

[0195] In some embodiments, the secondary battery may include an outer casing, which is used to seal the electrode assembly and the electrolyte.

[0196] In some embodiments, the exterior of the secondary battery may be a hard case such as a hard plastic case, an aluminum case, or a steel case. The exterior of the secondary battery may be a soft pack, such as a soft pack bag. The material of the soft pack may be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0197] 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 with a rectangular structure as an example.

[0198] In some embodiments, as shown in FIG. 2 , the exterior may include a housing 51 and a cover plate 53. The housing 51 includes a bottom plate and a side plate connected to the bottom plate, and a storage cavity is formed by the bottom plate and the side plate. The housing 51 has an opening communicating with the storage cavity, and the cover plate 53 covers the opening to close the storage cavity. The positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged in the storage cavity. The electrode assembly 52 is impregnated with an electrolyte. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more and can be adjusted as needed.

[0199] Methods for fabricating secondary batteries are 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, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly by a winding process or a lamination process, the electrode assembly can be placed in a case, dried, and then an electrolyte can be injected. The secondary battery can be obtained by vacuum sealing, leaving it to stand, forming, shaping, and other processes.

[0200] In some embodiments, the secondary battery according to 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.

[0201] Fig. 3 is a schematic diagram of an example battery module 4. As shown in Fig. 3, in the battery module 4, the plurality of secondary batteries 5 may be arranged in order along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed by fasteners.

[0202] Preferably, the battery module 4 may further include a housing having an accommodating space for accommodating the plurality of secondary batteries 5.

[0203] In some embodiments, the battery modules may be assembled into a battery pack, and the number of battery modules included in the battery pack may be adjusted depending on the application and capacity of the battery pack.

[0204] 4 and 5 are schematic diagrams of an example battery pack 1. As shown in FIGS. 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box. The battery box includes an upper case 2 and a lower case 3, and the upper case 2 covers the lower case 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.

[0205] power consumption equipment

[0206] A fourth aspect of an embodiment of the present application provides a power consuming device including at least one of a secondary battery, a battery module, or a battery pack according to the embodiments of the present application. The secondary battery, the battery module, or the battery pack may be used as a power source for the power consuming device, or as an energy storage unit for the power consuming device. The power consuming device may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop, 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.

[0207] A power consuming device can select a secondary battery, a battery module, or a battery pack according to its usage needs.

[0208] 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, which may employ a battery pack or battery module to meet the high power and high energy density requirements of the power consuming device.

[0209] Other examples of power consuming devices include mobile phones, tablet computers, laptop computers, etc. These power consuming devices are generally required to be thin and can use secondary batteries as their power source.

[0210] Example

[0211] The following examples are provided to more specifically illustrate the disclosure of the present application, and are merely illustrative, since various modifications and variations within the scope of the disclosure of the present application will be apparent to those skilled in the art. 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 synthesized according to conventional methods and can be used directly without further treatment, and the equipment used in the examples is commercially available.

[0212] Preparation of nanocellulose

[0213] The cotton linters were opened using a cotton opener to remove the scum, then digested in a 5 wt% NaOH aqueous solution at 150°C for 2 hours. The cotton was then washed with water to remove impurities (three washes), bleached with sodium hypochlorite, washed with dilute hydrochloric acid to remove impurities, washed with water to remove impurities (one wash), removed water, and air-dried to obtain cotton cellulose powder with a whiteness of 85% or more.

[0214] 1 kg of the obtained cotton cellulose powder was mixed with 30 kg of 60 wt% aqueous sulfuric acid solution and reacted at 55-60°C for 0.5-0.8 hours. After the reaction was completed, impurities were removed by washing with water (three times), filtered, acid was removed, and impurities were removed. The pH was then adjusted to neutral with 10 wt% aqueous NaOH solution. The powder was then polished with a polishing machine and cut into nanoscale pieces using a high-pressure homogenizer to obtain nanocellulose with sulfonic acid group-modified groups, and the molar ratio of sulfonic acid groups to surface hydroxyl groups was 2:3-7:3.

[0215] During the preparation process, nanocellulose with different average diameters and / or different average lengths can be obtained by adjusting the reaction concentration, reaction time, processing parameters of the grinder, and cutting parameters of the high-pressure homogenizer device.

[0216] The molar ratio of modifying groups to surface hydroxyl groups in nanocellulose can be measured using the phthalic anhydride method in GB / T12008.3-2009 to obtain the hydroxyl values ​​(mg of potassium hydroxide equivalent to the hydroxyl group content per 1 g of sample) of raw cellulose and nanocellulose, respectively, in units of mgKOH / g, which is then converted to mmol / g to obtain the hydroxyl group content. The hydroxyl group content of nanocellulose is then subtracted from the hydroxyl group content of raw cellulose to obtain the modifying group content (i.e., the content of modified hydroxyl groups), from which the molar ratio of modifying groups to hydroxyl groups can be calculated.

[0217] Example 1

[0218] Preparation of separator

[0219] A PE porous substrate having a thickness of 4.8 μm is provided.

[0220] Preparation of coating slurry: Filler (commercially available) with the porous structure shown in Table 1, nanocellulose, and aqueous polyacrylic acid (a binder) were uniformly mixed in a mass ratio of 80:18:2 in an appropriate amount of deionized water (a solvent) to obtain a coating slurry.

[0221] Coating: The prepared coating slurry was applied to both sides of the PE porous substrate using a coater, and then dried and slit to obtain a separator.

[0222] Preparation of positive electrode sheet

[0223] Cathode active material LiNi 0.8 Co 0.1 Mn 0.1O2 (NCM811), conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are uniformly mixed in a mass ratio of 96.2:2.7:1.1 with an appropriate amount of solvent N-methylpyrrolidone (NMP) to obtain positive electrode slurry. This positive electrode slurry is then applied to aluminum foil, which serves as a positive electrode current collector, and after processes such as drying, cold pressing, strip division, and cutting, a positive electrode sheet is obtained.

[0224] Preparation of negative electrode sheet

[0225] The negative electrode active material, artificial graphite, the conductive agent, carbon black (Super P), the binder, styrene butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC), were uniformly mixed 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 then applied to copper foil as a negative electrode current collector, followed by drying, cold pressing, stripe division, and cutting processes to obtain a negative electrode sheet.

[0226] Preparation of electrolyte

[0227] An electrolyte solution with a concentration of 1.2 mol / L was prepared by dissolving thoroughly dried LiPF6 in an organic solvent in which ethylene carbonate (EC), dimethyl carbonate, and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 30:30:40.

[0228] Fabrication of secondary batteries

[0229] The positive electrode sheet, separator, and negative electrode sheet are stacked in this order and wound up to obtain an electrode assembly. The electrode assembly is then placed in an outer casing, dried, and then an electrolyte is injected. After vacuum sealing, leaving it to stand, chemical conversion, shaping, and other processes, a secondary battery is obtained.

[0230] Examples 2 to 12

[0231] The secondary battery was fabricated in a manner similar to that of Example 1, except that the volume distribution particle size Dv50, specific surface area, and / or average diameter and average length of the porous filler used to fabricate the separator were different. See Table 1 for specific parameters.

[0232] Examples 13 to 15

[0233] The secondary battery was fabricated in a manner similar to that of Example 1, except that the type of porous filler used to fabricate the separator and the average diameter and average length of the nanocellulose were different. See Table 1 for specific parameters.

[0234] Examples 16 to 20

[0235] The secondary battery was fabricated in a manner similar to that of Example 1, except that the mass content of the porous filler and nanocellulose used to fabricate the separator was different. The specific parameters are shown in Table 1.

[0236] Comparative Example 1

[0237] The secondary battery is fabricated in a similar manner to that of Example 6, except that ordinary primary particle alumina (solid structure) is used in place of the filler having a porous structure in the fabrication of the separator.

[0238] Test part

[0239] (1) Secondary battery cycle characteristic test

[0240] At 45°C, the secondary battery was charged at a constant current of 1C to 4.2V, and then continued to be charged at a constant voltage until the current fell below 0.05C. At this point, the secondary battery was fully charged, and the charge capacity at this point, i.e., the first charge capacity, was recorded. After allowing the secondary battery to stand for 5 minutes, it was discharged at a constant current of 1C to 2.8V. This constitutes one cycle of charge / discharge, and the discharge capacity at this point, i.e., the first discharge capacity, was recorded. The secondary battery was subjected to a cycle charge / discharge test according to the above method, and the discharge capacity after one cycle was recorded. The capacity retention rate (%) of the secondary battery after 1000 cycles at 45°C = discharge capacity after 1000 cycles / first discharge capacity × 100%. For accuracy, the average value of five parallel samples was used as the test result.

[0241] (2) Low-temperature discharge rate performance test for secondary batteries

[0242] At 0°C, the secondary battery was discharged at a constant current of 0.33C to 2.8V, allowed to stand for 30 minutes, charged at a constant current of 0.33C to 4.20V, charged at a constant voltage until the current reached 0.05C, allowed to stand for 30 minutes, discharged at a constant current of 0.33C to 2.8V, allowed to stand for 30 minutes, and recorded as discharge capacity A1. The secondary battery was then charged at a constant current of 0.33C to 4.20V, charged at a constant voltage until the current reached 0.05C, allowed to stand for 30 minutes, discharged at a constant current of 2C to 2.8V, allowed to stand for 60 minutes, and recorded as discharge capacity A2. The low-temperature discharge rate performance of the secondary battery was expressed as the ratio (A2 / A1) of the discharge capacity A2 at 0°C and 2C to the discharge capacity A1 at 0°C and 0.33C.

[0243] As can be seen from Table 1, by providing a coating containing a three-dimensional skeletal structure and a filler having a porous structure on the surface of the separator porous substrate and filling at least a portion of the filler having a porous structure into the three-dimensional skeletal structure, the secondary battery not only has high thermal stability, but also can achieve both a long cycle life and good dynamic characteristics.

[0244] As can be seen from the test results in Table 1, by further adjusting the parameters of the filler having nanocellulose and a porous structure to satisfy 0 < D1 / (d1 / √6) ≦ 1 and 0 < d1 / (L1 / √2) ≦ 1, the cycle performance and kinetic characteristics of the secondary battery can be improved better. In addition, by further adjusting one or more ranges of D1 / (d1 / √6), d1 / (L1 / √2), D1, d1, and L1, the cycle performance and kinetic characteristics of the secondary battery can be further improved.

[0245] As can be seen from the test results in Table 1, by further adjusting the mass content of the filler having nanocellulose and a porous structure, the cycle performance and kinetic characteristics of the secondary battery can be improved better.

[0246] Note that this application is not limited to the above embodiments. The above embodiments are merely illustrative, and those having substantially the same configuration as the technical idea and the same operational effects within the technical scope of this application are all included in the technical scope of this application. In addition, within the scope not departing from the gist of this application, various modifications conceivable by those skilled in the art applied to the embodiments, and other forms constructed by combining some components in the embodiments are also included in the scope of this application.

[0247] [Table 1]

Claims

1. A separator comprising a porous substrate and a coating provided on at least one surface of the porous substrate, the coating including a three-dimensional skeletal structure and a filler having a porous structure, and at least a portion of the filler having the porous structure is filled in the three-dimensional skeletal structure.

2. The volume distribution particle diameter Dv50 of the filler having the porous structure is expressed in nm as d １ year, The average diameter of the material constituting the three-dimensional framework structure is D in nm. １ year, The average length of the material constituting the three-dimensional framework is L １ Then, 0<D １ / (d １ / √6)≦1 and 0<d １ / (L １ / √2)≦1, The separator according to claim 1 .

3. 0.02≦D １ / (d １ / √6)≦0.85, preferably 0.05≦D １ / (d １ / √6)≦0.65, and / or 0.04≦d １ / (L １ / √2)≦0.8, preferably 0.10≦d １ / (L １ / √2)≦0.7, The separator according to claim 1 or 2.

4. The volume distribution particle diameter Dv50 of the filler having the porous structure is d １ Then, d １ is between 200 nm and 1500 nm, preferably between 500 nm and 1200 nm, and / or The average diameter of the material constituting the three-dimensional framework structure is D １ Then, D １ is 40 nm or less, preferably 5 nm to 35 nm, and / or The average length of the material constituting the three-dimensional framework is L １ Then, L １ is 300 nm to 3000 nm, preferably 400 nm to 2500 nm; The separator according to any one of claims 1 to 3.

5. The filler having a porous structure satisfies at least one of the following conditions (1) to (4): (1) The average pore size of the filler having a porous structure is 0.1 nm to 1.5 nm, preferably 0.3 nm to 1.0 nm; (2) The true density of the filler having a porous structure is 1.0 g / cm ３ ~2.0 g / cm ３ and preferably 1.2 g / cm ３ ~1.7g / cm ３ and (3) The powder compression density of the filler having the porous structure at 30,000 N is 0.3 g / cm ３ ~1.5g / cm ３ and preferably 0.5 g / cm ３ ~1.0 g / cm ３ and (4) The specific surface area of ​​the filler having a porous structure is 700 m ２ / g to 3000m ２ / g, preferably 800m ２ / g~2500m ２ / g, The separator according to any one of claims 1 to 4.

6. the filler having a porous structure includes at least one of inorganic porous particles and organic porous particles, Preferably, the inorganic porous particles include at least one of porous alumina, porous silica, porous zirconia, porous titania, porous zinc oxide, porous magnesium oxide, porous calcium carbonate, molecular sieves, zeolites, and modified materials thereof; Preferably, the organic porous particles comprise at least one of a porous polymer material, a covalent organic framework material, a metal organic framework material, and a respective modifying material; The separator according to any one of claims 1 to 5.

7. The content of the porous filler is 50 wt % to 97 wt %, preferably 63 wt % to 93 wt %, based on the total weight of the coating; and / or The content of the three-dimensional framework structure is 1 wt% to 48 wt%, preferably 5 wt% to 35 wt%, based on the total weight of the coating. The separator according to any one of claims 1 to 6.

8. The separator according to any one of claims 1 to 7, wherein the material constituting the three-dimensional framework structure includes at least one of linear, rod-shaped, tubular, and rod-shaped materials.

9. The separator according to any one of claims 1 to 8, wherein the aspect ratio of the material constituting the three-dimensional framework is 5 to 150, and preferably 30 to 95.

10. the material constituting the three-dimensional framework structure 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 comprises at least one of halloysite nanotubes, alumina nanorods, boehmite nanorods, silica nanorods, and glass fibers; The separator according to any one of claims 1 to 9.

11. 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 phosphate group, more preferably at least one of a sulfonic acid group, a boric acid group and a phosphate group; Preferably, the modified nanocellulose comprises hydroxyl groups and modifying groups, and the molar ratio of the modifying groups to the hydroxyl groups is 1:4 to 4:1, more preferably 2:3 to 7:3; The separator according to any one of claims 1 to 10.

12. The separator according to any one of claims 1 to 11, 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.

13. the coating further comprises a non-particulate binder; Preferably, the non-particulate binder comprises an aqueous binder; Preferably, the content of the non-particulate binder in the coating is 4 wt % or less, based on the total weight of the coating. The separator according to any one of claims 1 to 12.

14. The thickness of the porous substrate is 6 μm or less, preferably 3 μm to 5 μm, and / or The thickness of the coating is 1.5 μm or less, preferably 0.5 μm to 1.2 μm. The separator according to any one of claims 1 to 13.

15. The adhesive layer may further include an adhesive layer provided on at least a portion of the surface of the coating; Preferably, the adhesive layer comprises a particulate binder, Preferably, the particulate binder contains at least one of an acrylic acid ester-based monomer homopolymer or copolymer, an acrylic acid-based monomer homopolymer or copolymer, and a fluorine-containing olefin monomer homopolymer or copolymer. The separator according to any one of claims 1 to 14.

16. At least one of the following conditions (1) to (7) is satisfied: (1) The separator has a longitudinal heat shrinkage rate of 4% or less at 135°C for 1 hour, and preferably 0.5% to 3.8%. (2) The separator has a transverse heat shrinkage rate of 4% or less at 135°C for 1 hour, and preferably 0.5% to 3.8%. (3) The longitudinal tensile strength of the separator is 1600 kg / cm ２ or more, preferably 1800 kg / cm ２ ~4500kg / cm ２ and (4) The separator has a lateral tensile strength of 1600 kg / cm ２ or more, preferably 1800 kg / cm ２ ~4500kg / cm ２ and (5) The wet length of the separator is 20 mm or more, preferably 30 mm to 80 mm, (6) The wetting speed of the separator is 3 mm / s or more, preferably 3 mm / s to 10 mm / s, (7) The separator has an air permeability of 350 s / 100 mL or less, preferably 120 s / 100 mL to 260 s / 100 mL. The separator according to any one of claims 1 to 15.

17. A method for producing the separator according to any one of claims 1 to 16, comprising: A method comprising the steps of: providing a porous substrate; mixing a material for constituting a three-dimensional skeletal structure and a filler having a porous structure in a solvent at a predetermined ratio to prepare a coating slurry; and applying the coating slurry to at least one surface of the porous substrate and drying it to obtain a separator, wherein the separator comprises a porous substrate and a coating provided on at least one surface of the porous substrate, the coating comprising a three-dimensional skeletal structure and a filler having a porous structure, and at least a portion of the filler having a porous structure is filled in the three-dimensional skeletal structure.

18. A secondary battery comprising the separator according to any one of claims 1 to 16 or the separator produced by the method according to claim 17.

19. A power consuming device comprising the secondary battery according to claim 18.

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