Separator, method for manufacturing the same, and related secondary batteries and power consumption devices.

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] This application relates to a separator, a method for manufacturing the same, a secondary battery and a power consumption device related thereto.

Background Art

[0002] In recent years, secondary batteries have been widely used in many fields such as energy storage power systems such as hydraulic, thermal, wind, and solar power plants, electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. With the application and popularization of secondary batteries, their reliability issues, especially thermal stability issues, have attracted increasing attention. However, currently, the method of improving the thermal stability of secondary batteries is disadvantageous to the balance of the electrochemical performance of secondary batteries. Therefore, making a secondary battery have both high thermal stability and good electrochemical performance is an important issue in the design of secondary batteries.

Summary of the Invention

[0003] This application provides a separator that can achieve high thermal stability, long cycle life and good kinetic characteristics in a secondary battery, a method for manufacturing the same, and a secondary battery and a power consumption device related thereto.

[0004] The first aspect of this application provides a separator including a porous substrate and a coating provided on at least one surface of the porous substrate, the coating including a three-dimensional skeleton structure and a filler having a porous structure, and at least a part of the filler having the porous structure being filled in the three-dimensional skeleton structure.

[0005] By providing a coating including a three-dimensional skeleton structure and a filler having a porous structure on the surface of the porous substrate of the separator and filling at least a part of the filler having the porous structure in the three-dimensional skeleton structure, it is possible to make the separator have both high heat resistance, high adhesion, high ion conductivity and good impregnation and retention characteristics of the electrolyte, and further make the secondary battery have both high thermal stability, long cycle life and good kinetic characteristics.

[0006] In any embodiment of the present application, when 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 also be better balanced.

[0010] In any embodiment of the present application, when 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 filled in the three-dimensional skeleton structure, and is advantageous for forming an encapsulation effect, contributing to an increase in the heat resistance, adhesiveness, and ionic conductivity of the separator.

[0011] In any embodiment of this application, if D1 is the average diameter of the material constituting the three-dimensional skeletal structure, then D1 is 40 nm or less, preferably 5 nm to 35 nm. When the average diameter of the material constituting the three-dimensional skeletal structure is within the above range, the ionic conductivity and dielectric breakdown characteristics of the separator can be further improved, and it also contributes to forming an integrated effect by overlapping connection with a filler having a porous structure, thereby further improving the heat resistance of the separator.

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

[0013] In any embodiment of this application, the average pore size of the porous filler is 0.1 nm to 1.5 nm, preferably 0.3 nm to 1.0 nm. When the average pore size of the porous filler is within the above range, the ionic conductivity of the coating and the impregnation and retention characteristics of the electrolyte can be improved, contributing to further improvements in the cycle performance and dynamic characteristics of the secondary battery.

[0014] In any embodiment of this application, the true density of the porous filler is 1.0 g / cm³. 3 ~2.0g / cm 3 The concentration is preferably 1.2 g / cm³. 3 ~1.7g / cm 3 Therefore, if the true density of the porous filler is within the above range, the ionic conductivity of the coating and its impregnation and retention characteristics in the electrolyte can be improved, contributing to further improvements in the cycle performance and dynamic characteristics of the secondary battery.

[0015] In any embodiment of this application, the powder compression density of the porous filler at 30,000 N is 0.3 g / cm³. 3 ~1.5g / cm3 and preferably 0.5 g / cm 3 ~1.0 g / cm 3 When the bulk density of the filler having a porous structure is within the above range, the ionic conductivity of the coating and the impregnation and retention characteristics with respect to the electrolyte can be improved, contributing to further improvement in the cycle performance and kinetic characteristics 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 to 3000 m 2 / g, and preferably 800 m 2 / g to 2500 m 2 / g. When the specific surface area of the filler having a porous structure is within the above range, the affinity with the three-dimensional skeleton structure is better, the adhesion effect is improved on the premise of using less binder, the risk of the binder blocking the pores is effectively reduced, and the cycle performance and kinetic characteristics of the secondary battery can be improved.

[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 sieve, zeolite, and their modified materials.

[0019] In any embodiment of the present application, the organic porous particles include at least one of porous polymer materials, covalent organic framework materials, metal organic framework materials, and their respective modified materials.

[0020] In any embodiment of this 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 the above range, the heat resistance, ionic conductivity, and impregnation and retention properties of the electrolyte of the separator can be further improved.

[0021] In any embodiment of this application, the content of the three-dimensional skeletal 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 this application, the material constituting the three-dimensional skeletal structure includes at least one of linear, rod-shaped, tubular, and rod-shaped materials. A material of an appropriate shape is advantageous in that the three-dimensional skeletal structure and the porous filler form a more stable spatial network structure, thereby further improving the heat resistance, ionic conductivity, and impregnation and retention properties of the separator with respect to the electrolyte.

[0023] In any embodiment of this application, the aspect ratio of the material constituting the three-dimensional skeletal structure is 5 to 150, 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 of the separator and the impregnation and retention characteristics of the electrolyte can be further improved.

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

[0025] In any embodiment of this application, the organic material comprises at least one of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers, preferably the nanocellulose comprises at least one of cellulose nanofibers, cellulose nanowhiskers, and bacterial nanocellulose.

[0026] In any embodiment of this application, the inorganic material includes at least one of halloysite nanotubes, nano-rod alumina, nano-rod boehmite, nano-rod silica, and glass fibers.

[0027] In any embodiment of this application, the material constituting the three-dimensional skeletal structure includes nanocellulose, wherein the nanocellulose includes at least one of unmodified nanocellulose and modified nanocellulose.

[0028] In any embodiment of this application, 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, 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 is possible to effectively improve the heat resistance of the separator, improve the adhesive strength between the coating and the porous substrate, and is also advantageous in forming an integrated effect by overlap bonding of the nanocellulose and the filler having a porous structure.

[0029] In any embodiment of this 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 impregnation and retention properties of the electrolyte of the separator can be further improved.

[0030] In any embodiment of this application, the material constituting the three-dimensional skeletal structure contains sulfonic acid groups, and the sulfur element content 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 this application, the coating further comprises a non-particulate binder.

[0032] In any embodiment of this application, the non-particulate binder includes an aqueous solution type binder.

[0033] In any embodiment of this 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 in the coating can form a stable spatial network structure with a porous filler, etc., thereby maintaining high adhesion to the separator while reducing the amount of binder used.

[0034] In any embodiment of this application, the thickness of the porous substrate is 6 μm or less, preferably 3 μm to 5 μm. The coating of this application can significantly improve the heat resistance of the separator, thereby allowing the selection of a thinner porous substrate, which contributes to improving the energy density of the secondary battery.

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

[0036] In any embodiment of this 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 peeling off and improves the reliability of the secondary battery, but also improves the interface between the separator and the electrode, contributing to improved cycle performance of the secondary battery.

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

[0038] In any embodiment of this application, the particulate binder comprises at least one of the following: an acrylic acid ester monomer homopolymer or copolymer, an acrylic acid monomer homopolymer or copolymer, or a fluorine-containing olefin monomer homopolymer or copolymer.

[0039] In any embodiment of this application, the longitudinal thermal shrinkage rate of the separator at 135°C for 1 hour is 4% or less, preferably 0.5% to 3.8%.

[0040] In any embodiment of this application, the lateral thermal shrinkage rate of the separator at 135°C for 1 hour is 4% or less, preferably 0.5% to 3.8%.

[0041] In any embodiment of this application, the longitudinal tensile strength of the separator is 1600 kg / cm². 2 The above is preferable, preferably 1800 kg / cm². 2 ~4500 kg / cm 2 That is the case.

[0042] In any embodiment of this application, the lateral tensile strength of the separator is 1600 kg / cm². 2 The above is preferable, preferably 1800 kg / cm². 2 ~4500 kg / cm 2 That is the case.

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

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

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

[0046] A second aspect of this application provides a method for producing a separator according to the first aspect of this application, comprising the steps of: providing a porous substrate; preparing a coating slurry by mixing a material for constituting a three-dimensional skeletal structure and a filler having a porous structure in a solvent in a predetermined ratio; and applying the coating slurry to at least one surface of the porous substrate and drying 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 comprises 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 into the three-dimensional skeletal structure.

[0047] A third aspect of this application provides a secondary battery comprising a separator according to the first aspect of this application or a separator manufactured by the method of the second aspect of this application.

[0048] A fourth aspect of this application provides a power consumption device including a secondary battery according to the third aspect of this application.

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

[0050] To more clearly illustrate the technical concept of the embodiments of this application, the drawings that need to be used in the embodiments of this application are briefly described below. Obviously, the drawings described below represent only a few embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

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

[0052] The drawings are not always drawn to the actual scale. [Explanation of Symbols]

[0053] 1 Battery pack 2 Upper case 3. Lower case 4 Battery Modules 5 Secondary battery 51 Housing 52 Electrode Assembly 53 Cover Plate [Modes for carrying out the invention]

[0054] The following description details embodiments specifically disclosing the separator, its manufacturing method, and related secondary batteries and power consumption devices of this application, with appropriate reference to the attached drawings. However, unnecessary details may be omitted. For example, detailed explanations of already well-known matters and redundant explanations of substantially identical configurations may be omitted. This is to avoid the following description becoming unnecessarily verbose and to facilitate understanding by those skilled in the art. The attached drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter described in the claims.

[0055] The “range” disclosed in this application is limited in the form of a lower limit and an upper limit, and a given range is limited by selecting one lower limit and one upper limit, and the selected lower limit and upper limit define the boundary of a special range. The range thus limited may include or exclude end values, and may be any combination, that is, any lower limit may be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are given for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also expected. Also, if minimum range values ​​1 and 2 and maximum range values ​​3, 4 and 5 are given, the ranges 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5 may all be expected. In this application, unless otherwise stated, the numerical range “a-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" in this specification refers to all real numbers between "0 to 5," and "0 to 5" is an abbreviation for combinations of these numbers. Also, when a parameter is described as an integer greater than or equal to 2 (≧2), it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0056] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined to form new technical concepts. Such technical concepts should be considered to be included in the disclosures of this application.

[0057] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical concepts. Such technical concepts should be considered to be included in the disclosures of this application.

[0058] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but it is preferable that they be performed sequentially. For example, if it is stated that the above method includes steps (a) and (b), it means that the above method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if it is stated that the above method may further include step (c), it means that step (c) may be added to the above method in any order. For example, the above method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0059] Unless otherwise specified, the terms “equipped with” and “included” in this application mean open or closed. For example, the terms “equipped with” and “included” above may mean “equipped with” or “included” other components not listed, or “equipped with” or “included” only the listed components.

[0060] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, "A or B" is satisfied in any of the following cases: 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 specified, terms such as "first," "second," etc., in this application are used to distinguish different subjects and not to describe a specific order or hierarchical relationship.

[0062] Unless otherwise specified, terms used in this application have the common meanings that are ordinarily 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 the art, for example, according to the test methods provided in the embodiments 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 placed between the positive and negative electrode sheets and primarily serves to prevent short circuits between the positive and negative electrodes, while also allowing active ions to pass freely to form a circuit. As a crucial component of a secondary battery, the separator's performance directly affects the battery's overall performance.

[0065] Currently, separators used in commercially available rechargeable batteries are generally porous polyolefin membranes, which have poor heat resistance. When exposed to heat, they exhibit a significant thermal shrinkage effect, causing direct contact between the positive and negative electrodes inside the battery, resulting in an internal short circuit and increasing the safety risk of the rechargeable battery. Furthermore, the separator must also satisfy good impregnation and retention properties for the electrolyte.

[0066] To solve the above problems, the currently adopted measures mainly involve coating a heat-resistant inorganic ceramic layer onto a porous polyolefin membrane. However, inorganic ceramic layers still have a series of problems. For example, there is a high requirement for the thickness of the coating; when applied thinly, the improvement in the heat resistance of the separator is limited, and when the coating is thicker, the heat resistance can be improved, but this increases the internal resistance of the battery. There is also a high requirement for the density of the arrangement of inorganic ceramic particles; when the arrangement of inorganic ceramic particles is sparse, the improvement in the heat resistance of the separator is limited, and when the arrangement of inorganic ceramic particles is dense, the heat resistance can be improved, but this leads to pore clogging problems, affecting the cycle performance and dynamic characteristics of the secondary battery.

[0067] Therefore, conventional separators have difficulty achieving both high thermal stability, long cycle life, and good dynamic characteristics in secondary batteries.

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

[0069] Separator

[0070] A first embodiment of the present invention provides a separator comprising a porous substrate and a coating provided on at least one surface of the porous substrate, wherein the coating comprises 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 into the three-dimensional skeletal structure.

[0071] The term "three-dimensional skeletal structure" generally refers to a structure that has a three-dimensional spatial shape and a certain amount of void space, and the materials constituting the three-dimensional skeletal structure can be superimposed and connected to one another.

[0072] A filler having a porous structure typically refers to a filler that has a regular or irregular channel structure that allows ions to conduct. In the long-term charge-discharge process of secondary batteries, the gradual depletion and failure of the separator is a significant cause of reduced capacity and shortened service life. This is because, after the separator dries out, the internal resistance of the battery increases, charging and discharging are not completed, the capacity of the secondary battery deteriorates rapidly, and the service life is significantly shortened. The separator coating provided in the embodiment of this application includes a filler having a porous structure, which is advantageous for storing electrolyte and releasing electrolyte during the long-term charge-discharge process of the secondary battery. This improves the ionic conductivity of the coating and its impregnation and retention characteristics with respect to the electrolyte, contributing to improved cycle performance and dynamic characteristics of the secondary battery.

[0073] Fillers with a porous structure have the advantage of a large specific surface area and better affinity with three-dimensional skeletal structures. They improve the adhesive effect even with a small amount of binder used, effectively reduce the risk of the binder blocking the pores, and can improve the cycle performance and dynamic characteristics of secondary batteries.

[0074] By filling the three-dimensional skeletal structure with at least a portion of the porous filler, the heat resistance of the separator is improved, the degree of shrinkage when the separator is heated is reduced, the risk of short-circuiting between the positive and negative electrodes is reduced, the secondary battery has high thermal stability, and high adhesive strength is maintained between the coating and the porous substrate, contributing to a reduction in the probability of the porous filler falling off during the long-term charge-discharge process of the secondary battery. At the same time, because at least a portion of the porous filler is filled into the three-dimensional skeletal structure, the number of contact points between the porous filler and the three-dimensional skeletal structure is increased, the amount of binder used in the coating can be reduced, the risk of the binder blocking the pores can be effectively reduced, and the cycle performance and dynamic characteristics of the secondary battery can be further improved.

[0075] Therefore, the separator provided by the embodiments of this application can achieve high heat resistance, high adhesion, high ionic conductivity, and good electrolyte impregnation and retention characteristics simultaneously, and furthermore, a secondary battery using it can achieve high thermal stability, long cycle life, and good kinetic characteristics simultaneously.

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

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

[0078] By adjusting D1 / (d1 / √6) and d1 / (L1 / √2) within the above range, it is advantageous to form an integrated effect through the overlapping connection of the porous filler and the three-dimensional skeletal structure. As a result, the coating has a more stable spatial network structure, which further improves the heat resistance, adhesion, and ionic conductivity of the separator, and further improves the thermal stability, cycle performance, and dynamic characteristics 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, and 0.055 ≤ D1 / (d1 / √6) ≤ 0.45. This allows for better improvement of the heat resistance, adhesion, and ionic conductivity of the separator, and also enables a better balance of thermal stability, cycle performance, and dynamic characteristics in the secondary battery.

[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, and 0.15 ≤ d1 / (L1 / √2) ≤ 0.68. This allows for better improvement of the heat resistance, adhesion, and ionic conductivity of the separator, and also enables a better balance of thermal stability, cycle performance, and dynamic characteristics in the secondary battery.

[0081] In some embodiments, 0.05 ≤ D1 / (d1 / √6) ≤ 0.65 and 0.10 ≤ d1 / (L1 / √2) ≤ 0.7, preferably 0.055 ≤ D1 / (d1 / √6) ≤ 0.45 and 0.15 ≤ d1 / (L1 / √2) ≤ 0.68. This allows for better improvement of the heat resistance, adhesion, and ionic conductivity of the separator, and also enables a better balance of thermal stability, cycle performance, and dynamic characteristics in the secondary battery.

[0082] In some embodiments, if the volume distribution particle size Dv50 of the porous filler is denoted as d1, then d1 may be between 200 nm and 1500 nm, and preferably between 500 nm and 1200 nm. The porous filler has a small volume distribution particle size Dv50, which is advantageous for filling the three-dimensional skeletal structure and forming a nesting effect, contributing to an increase in the heat resistance, adhesion, and ionic conductivity of the separator.

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

[0084] Preferably, the porous structure of the filler having a porous structure may be a microporous structure. In some embodiments, the average pore diameter 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 diameter of the filler having a porous structure is within the above range, the ionic conductivity of the coating and the impregnation and retention characteristics 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 a porous filler is a known concept in the art and can be measured using instruments and methods known in the art. For example, it can be tested using the static volumetric method, referring to GB / T19587. During the test, both the adsorbent gas and the carrier gas may be nitrogen gas.

[0086] In some examples, the true density of the porous filler is 1.0 g / cm³. 3 ~2.0g / cm 3 It may be, preferably 1.2 g / cm³ 3 ~1.7g / cm 3 Therefore, if the true density of the porous filler is within the above range, the ionic conductivity of the coating and its impregnation and retention characteristics in the electrolyte can be improved, contributing to further improvements in the cycle performance and dynamic characteristics of the secondary battery.

[0087] The true density of a porous filler is a known concept in the art and can be measured using instruments and methods known in the art. For example, referring to GB / T24586-2009, the true volume V of a test sample is measured using a true density tester employing a gas displacement method with an inert gas (e.g., helium or nitrogen gas) as the medium. t The true density of a porous filler can be measured as: Mass of test sample / True volume of test sample V t That is the case.

[0088] In some embodiments, the powder compression density of the porous filler at 30,000 N was 0.3 g / cm³. 3 ~1.5g / cm 3 It may be, preferably 0.5 g / cm³ 3 ~1.0g / cm 3 Therefore, if the powder compression density of the porous filler is within the above range, the ionic conductivity of the coating and its impregnation and retention characteristics with respect to the electrolyte can be improved, contributing to further improvements in the cycle performance and dynamic characteristics of the secondary battery.

[0089] The powder compressibility density of a material is a known concept in the art and can be measured using instruments and methods known in the art. For example, it can be measured using an electronic pressure tester (e.g., UTM7305) referring to standard GB / T24533-2009. An exemplary test method involves weighing 1 g of material and measuring it with a base area of ​​1.327 cm². 2 The material is placed in a mold, pressurized to 30,000 N, held for 30 seconds, then the pressure is reduced and held for 10 seconds. After that, the powder compression density of the material under a 30,000 N force is recorded and calculated.

[0090] In some embodiments, the specific surface area of ​​the porous filler is 700 m². 2 / g~3000m 2 It may be / g, preferably 800m 2 / g~2500m 2The value is / g. When the specific surface area of ​​a porous filler is within the above range, it has better affinity with the three-dimensional skeletal structure, improves the binder effect assuming a small amount of binder is used, effectively reduces the risk of the binder clogging the pores, and improves the cycle performance and dynamic characteristics of the secondary battery.

[0091] The specific surface area of ​​a material has a meaning known in this art and can be measured using instruments and methods known in this art. For example, it can be tested using the nitrogen gas adsorption specific surface area analysis test method, referring to GB / T19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. Preferably, the nitrogen adsorption specific surface area analysis test can be performed using the Tri-Star3020 specific surface area pore size analyzer from Micromeritics, Inc., USA.

[0092] In some embodiments, the filler having the 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., type A, type X, type Y, type M and ZSM, etc.), zeolites, and their respective modifiers.

[0094] Preferably, the organic porous particles may include at least one of a porous polymer material, a covalent organic frame material (COF), a metal-organic frame material (MOF), and a modifier of each thereof. As an example, the organometallic frame material may include at least one of Prussian blue, the ZIF series (e.g., ZIF-8, ZIF-68, etc.), the UiO series, the CPL series, the MIL series, and a modifier of each thereof.

[0095] The modification method may be chemical modification and / or physical modification. Chemical modification methods include coupling agent modification (e.g., using silane coupling agents, titanate coupling agents, etc.), surfactant modification, polymer graft modification, etc. Physical modification methods 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 impregnation and retention properties of the electrolyte of the separator can be further improved.

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

[0098] In some embodiments, the material constituting the three-dimensional skeletal structure may include at least one of linear, rod-shaped, tubular, and rod-shaped materials. A material of an appropriate shape is advantageous in that the three-dimensional skeletal structure and the porous filler form a more stable spatial network structure, thereby further improving the heat resistance, ionic conductivity, and impregnation and retention properties of the separator with respect to the electrolyte.

[0099] In some embodiments, the material constituting the three-dimensional skeletal structure may include at least one of organic and inorganic materials.

[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, nano-rod alumina, nano-rod boehmite, nano-rod silica, and glass fibers.

[0102] In some embodiments, the material constituting the three-dimensional skeletal structure may include nanocellulose. Preferably, the nanocellulose may include at least one of the following: cellulose nanofibers (also called cellulose nanofibrils, CNF, nanofibril cellulose, or microfibril cellulose), cellulose nanowhiskers (also called cellulose nanocrystals, CNC, cellulose nanocrystals, or nanocrystalline cellulose), and bacterial nanocellulose (also called bacterial nanocellulose, BNC, bacterial cellulose, or microbial cellulose).

[0103] Nanocellulose is a general term for cellulose in the nano-order (e.g., within 100 nm) of any dimension, possessing both the properties of cellulose and nanoparticles. Nanocellulose may be polymer nanomaterials extracted from wood, cotton, etc., in nature by one or more means from chemistry, physics, or biology. It has advantages such as a wide range of sources, low cost, high biodegradability, high elastic modulus, and high specific surface area, making it an excellent substitute for conventional petrochemical resources and effectively mitigating problems such as environmental pollution and the shortage of petrochemical resources. Nanocellulose has good high-temperature resistance and small volume change after being heated, which can improve the heat resistance of separators. At the same time, because nanocellulose has a lower density than conventional inorganic ceramic particles, it can reduce the weight of secondary batteries and improve the gravimetric energy density of secondary batteries. Furthermore, the three-dimensional skeletal structure made of nanocellulose may have minute nanopores, which can prevent current leakage and enable the separator to have both good electrolyte impregnation and retention properties and good voltage breakdown properties.

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

[0105] Modified nanocellulose refers to nanocellulose containing a modifying group along with a hydroxyl group. In some examples, the modified nanocellulose contains a modifying group, and the modifying group may contain 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, preferably at least one of a sulfonic acid group, a boric acid group, and a phosphate group.

[0106] When nanocellulose has the above-mentioned specific modifying groups, it can effectively improve the heat resistance of the separator and enhance the thermal stability of the secondary battery, while also improving the adhesive strength between the coating and the porous substrate. When nanocellulose has the above-mentioned specific modifying groups, it is also advantageous to form an integrated effect by overlapping connection between the nanocellulose and the porous filler, thereby allowing the coating to have a more stable spatial network structure, improving the impregnation and retention properties of the separator in the electrolyte, and improving the ionic conductivity and voltage breakdown properties of the separator. Furthermore, the presence of the modifying groups can reduce the proportion of hydroxyl groups, thereby giving the coating slurry an appropriate viscosity, which is advantageous for application, and can improve the production efficiency of the separator and the uniformity of the coating.

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

[0108] The type of modifying group in nanocellulose can be measured by infrared spectroscopy. For example, the type of modifying group can be determined by measuring the infrared spectrum of the material and determining the characteristic peaks contained therein. Specifically, infrared spectroscopic analysis can be performed on the material using instruments and methods known in this field, and measurements can be made using an infrared spectrometer (for example, an IS10 Fourier transform infrared spectrometer from Nigel, Inc., USA) in accordance with the GB / T6040-2019 general rules for infrared spectroscopic analysis.

[0109] In some embodiments, the material constituting the three-dimensional skeletal structure contains sulfonic acid groups, and the sulfur content in the material constituting the three-dimensional skeletal structure 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 skeletal structure. Preferably, the material constituting the three-dimensional skeletal structure may also contain nanocellulose.

[0110] The sulfur content in the material constituting the three-dimensional skeletal structure can be determined by following a method in which the material is dried, ground in a mortar (e.g., an agate mortar) for 30 minutes, and then tested using an X-ray diffractometer (e.g., Miniflex600-C) to obtain the sulfur content. During the test, a Cu target material, Ni filter, tube voltage of 40KV, and tube current of 15mA are used, and the material is continuously scanned in the range of 5° to 80°.

[0111] In some embodiments, if D1 is the average diameter of the material constituting the three-dimensional skeletal structure, then D1 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 of the material constituting the three-dimensional skeletal structure is within the above range, the ionic conductivity and dielectric breakdown characteristics of the separator can be further improved, and it also contributes to forming an integrated effect through overlapping connection with a filler having a porous structure, thereby further improving the heat resistance of the separator. Furthermore, the following situations can be effectively avoided. If the average diameter of the materials constituting the three-dimensional skeletal structure is too large, the mutual wrapping effect of the formed three-dimensional skeletal structure will be insufficient, and the large voids may result in inadequate heat resistance and dielectric breakdown characteristics of the separator. At the same time, it is unfavorable for forming an integrated effect through overlapping connection with a porous filler. Furthermore, during the drying process of the coating, the three-dimensional skeletal structure is prone to collapse due to the lack of support from the porous filler. In addition, direct contact with the porous substrate can easily cause pore clogging problems, potentially affecting the ionic conductivity of the separator.

[0112] In some embodiments, the average length of the material constituting the three-dimensional skeletal structure is denoted as L1, where L1 may be between 300 nm and 3000 nm, and is preferably between 400 nm and 2500 nm, 800 nm and 2250 nm, 1000 nm and 2250 nm, or 1200 nm and 2250 nm. When the average length of the material constituting the three-dimensional skeletal structure is within the above range, the heat resistance and ionic conductivity of the separator can be further improved. Furthermore, the following situations can be effectively avoided. If the average length of the materials constituting the three-dimensional skeletal structure is too short, the overlapping connection effect with the porous filler will be poor, resulting in poor heat resistance of the coating. Furthermore, during the drying process of the coating, the three-dimensional skeletal structure will easily collapse because it does not provide support for the porous filler, and pore clogging problems are more likely to occur. This can hinder ion transport and moisture discharge, potentially affecting the thermal stability, cycle performance, and dynamic characteristics of the secondary battery. If the average length of the materials constituting the three-dimensional skeletal structure is too long, the viscosity of the coating slurry will be high and the flow will be poor, affecting the application of the coating slurry and potentially affecting the quality of the coating, 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 skeletal structure may be 5 to 150, preferably 30 to 95 or 40 to 90. When the aspect ratio of the material constituting the three-dimensional skeletal structure is within the above range, the ionic conductivity of the separator and the impregnation and retention characteristics of the electrolyte can be further improved. Furthermore, the following situations can be effectively avoided. If the aspect ratio of the material constituting the three-dimensional skeletal structure is too small, the overlapping connection effect with the porous filler is poor, the heat resistance of the coating is poor, and during the drying process of the coating, the three-dimensional skeletal structure is prone to collapse because it does not support the porous filler. In addition, pore clogging problems are likely to occur, which can hinder ion transport and moisture discharge, potentially affecting the thermal stability, cycle performance, and dynamic characteristics of the secondary battery. If the aspect ratio of the material constituting the three-dimensional skeletal structure is too large, the voids in the formed three-dimensional skeletal structure are small, which may result in a low ionic conductivity of the separator.

[0114] The average length and average diameter of the material constituting the three-dimensional skeletal structure can be measured by the following methods: A 3.6 mm × 3.6 mm sample is cut from any one region within the separator, and the microtopographic structure of the coating in the sample is mapped using a scanning electron microscope (e.g., ZEISS Sigma300). The high vacuum mode is selected, the operating voltage is 3 kV, and the magnification is 30,000x to obtain an SEM image. Based on the obtained SEM image, multiple (e.g., five or more) test regions are selected and length statistics are performed, with each test region having a size of 0.5 μm × 0.5 μm. Subsequently, the average value of the average length obtained in each test region is taken as the average length of the material constituting the three-dimensional skeletal structure. Based on the obtained SEM image, multiple (e.g., five or more) test regions are selected using Nano Measurer particle size distribution statistics software and diameter statistics are performed, with each test region having a size of 0.5 μm × 0.5 μm. Subsequently, the average value of the average diameter obtained in each test region is taken as the average diameter of the material constituting the three-dimensional skeletal structure.

[0115] When the material constituting the three-dimensional skeletal structure includes nanocellulose, the diameters at both ends in the longitudinal direction of the nanocellulose are generally small, while the diameters at intermediate positions are generally large. Therefore, the maximum diameter in the longitudinal direction of the nanocellulose can be used as the diameter of that nanocellulose, and the diameters of other nanocellulose can be processed according to a similar method. Subsequently, the average diameter of the nanocellulose can be obtained using Nano Measurer particle size distribution statistics software according to the method described above.

[0116] In some embodiments, the coating may further include a non-particulate binder. In this application, the type of non-particulate binder is not particularly limited, and any known material with good adhesion can be used. Preferably, the non-particulate binder may include an aqueous solution binder, which has the advantages of good thermodynamic stability and being environmentally friendly, thus advantageous for the preparation and application of the coating slurry. As an example, the aqueous solution binder may include at least one of an aqueous solution acrylic resin (e.g., acrylic acid, methacrylic acid, a copolymer with sodium acrylate monomer or other comonomers), polyvinyl alcohol (PVA), isobutylene-maleic anhydride copolymer, and 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 in the coating can form a stable spatial network structure with a porous filler, etc., 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. This contributes to improving the energy density of the secondary battery. The thickness of the coating 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 this application significantly improves the heat resistance of the separator, allowing for the selection of a thinner porous substrate and contributing to an improvement in the energy density of the secondary battery.

[0120] In this 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 may include at least one of porous polyolefin resin films (e.g., polyethylene, polypropylene, polyvinylidene fluoride), porous glass fibers, and porous nonwoven fabrics. The porous substrate may be a single-layer film or a multilayer composite film. If the porous substrate is a multilayer composite film, the materials of each layer may 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 the adhesive layer may include a particulate binder. The adhesive layer not only prevents the coating from peeling off and improves the reliability of the secondary battery, but also improves the interface between the separator and the electrode, contributing to improved cycle performance of the secondary battery.

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

[0123] Preferably, the particulate binder may include vinylidene fluoride polymers such as a homopolymer of vinylidene fluoride monomer (VDF) and / or a copolymer of vinylidene fluoride monomer and copolymer monomer. The copolymer monomer may be at least one of olefin monomers, fluorine-containing olefin monomers, chlorine-containing olefin monomers, acrylic acid ester monomers, acrylic monomers, and fluoroether monomers. Preferably, the copolymer monomer 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 longitudinal heat shrinkage rate of the separator at 135°C for 1 hour may be 4% or less, preferably 1.5% to 3.8%.

[0125] In some embodiments, the lateral thermal shrinkage rate of the separator at 135°C for 1 hour may be 4% or less, preferably 1.0% to 3.8%.

[0126] The separator can improve the reliability of secondary batteries by having a low thermal contraction rate in both the lateral and vertical directions at high temperatures of 135°C.

[0127] In some embodiments, the longitudinal tensile strength of the separator was 1600 kg / cm². 2 It may be greater than or equal to 1800 kg / cm², preferably 1800 kg / cm². 2 ~4500 kg / cm 2 That is the case.

[0128] In some embodiments, the lateral tensile strength of the separator was 1600 kg / cm². 2 It may be greater than or equal to 1800 kg / cm², preferably 1800 kg / cm². 2 ~4500 kg / cm 2 That is the case.

[0129] Because the separator has high tensile strength in both the lateral and vertical directions, the probability of the separator breaking when the secondary battery expands is reduced, thereby improving the reliability of the secondary battery.

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

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

[0132] By having good impregnation and retention characteristics of the electrolyte, the ionic conductivity and secondary battery capacity characteristics of the separator can be improved.

[0133] In some embodiments, the permeability of the separator may be 350 s / 100 mL or less, preferably 120 s / 100 mL to 260 s / 100 mL. By having good gas permeability in the separator, the ion conductivity and secondary battery capacity characteristics 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 ion conductivity of the separator can be better improved, and the heat stability, cycle performance and kinetic characteristics of the secondary battery can be better balanced.

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

[0136] The wetting length and wetting rate of the separator both have meanings known in this art and can be measured by methods known in this art. An example test method involves cutting the separator into a sample 5 mm wide and 100 mm long, fixing both ends of the sample and placing it horizontally, dropping 0.5 mg of electrolyte into the center of the sample, and after a predetermined time (1 min in this application), taking a photograph to measure the length over which the electrolyte diffuses, thereby obtaining the wetting length and wetting rate of the separator. For accuracy of the test results, the test can be performed using multiple samples (e.g., 5 to 10) and the average value can be calculated to obtain the 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 then dissolving thoroughly dried LiPF6 in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0137] Note that the coating parameters (e.g., thickness) of the separator described above are all coating parameters for one side of the porous substrate. If the coating is provided on both sides of the porous substrate, it is considered that the protection scope of this application is covered if the coating parameters on either side satisfy the requirements of this application.

[0138] Manufacturing method

[0139] A second embodiment of the present application provides a method for manufacturing a separator according to the first embodiment of the present application, comprising the steps of: providing a porous substrate; preparing a coating slurry by mixing a material for constituting a three-dimensional skeletal structure and a filler having a porous structure in a predetermined ratio in a solvent; and applying the coating slurry to at least one surface of the porous substrate and drying 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 comprises 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 into the three-dimensional skeletal structure.

[0140] In some examples, the solvent used to prepare the coating slurry may be water, for example, deionized water.

[0141] In some embodiments, the coating slurry may further contain other components, such as dispersants, wetting agents, binders, and so on.

[0142] In some embodiments, the material for constituting the three-dimensional skeletal structure may include at least one of organic and inorganic materials. Preferably, the organic material may include at least one of nanocellulose, polytetrafluoroethylene nanofibers, and polyamide nanofibers. Preferably, the inorganic material may include at least one of halloysite nanotubes, nanoalumina, nanoboehmite, nanosilica, and glass fibers.

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

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

[0145] Preferably, the cellulose powder having a whiteness of ≥80% may be commercially available, or it may be obtained by employing chemical methods (e.g., acid decomposition, alkali treatment, Tempo catalytic oxidation), biological methods (e.g., enzyme treatment), mechanical methods (e.g., ultrafine polishing, ultrasonic crushing, high-pressure homogenization), etc. The fiber raw material for producing the cellulose powder having a whiteness of ≥80% may include at least one of the following plant fibers: cotton fibers (e.g., cotton fibers, kapok fibers), hemp fibers (e.g., sisal fibers, ramie fibers, kouma fibers, flax fibers, cannabis fibers, Manila fibers, etc.), palm fibers, wood fibers, bamboo fibers, grass fibers, etc.

[0146] In some embodiments, the cellulose powder having a whiteness of ≥80% can also be produced by opening the fiber raw material to remove debris, steaming it in an alkaline solution (for example, an aqueous NaOH solution with a concentration of 4 wt% to 20 wt%, preferably 5 wt% to 15 wt%), then sequentially removing impurities by washing with water (for example, 3 to 6 washes), bleaching (for example, with sodium hypochlorite and / or hydrogen peroxide), removing impurities by pickling, removing impurities by washing with water, removing water, and air drying to obtain the cellulose powder.

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

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

[0149] Preferably, a cellulose powder having an amine group can be obtained by converting the urea organic solvent solution to a urea xylene solution.

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

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

[0152] In some examples, when the modification solution is an acidic solution, the reaction can be carried out under conditions of 80°C or lower, preferably 30°C to 60°C, and the reaction time between the cellulose powder and the modification solution may be 0.2h to 2.5h, preferably 0.5h to 1.5h.

[0153] In some examples, when the modification solution is an alkaline solution, the reaction can be carried out under conditions of 100°C to 145°C, and the reaction time between the cellulose powder and the modification solution may be 0.5h to 3.5h.

[0154] In some embodiments, polishing may be performed using a polishing machine, and cutting may be performed using a high-pressure homogenizer. By adjusting the polishing parameters of the polishing machine (e.g., number of polishing cycles, polishing 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 coating machine may be used when applying the coating slurry. The type of coating machine is not particularly limited in this application, and commercially available coating machines can be used, for example. The coating machine may include a gravure roll for transferring the slurry to a porous substrate.

[0156] In some embodiments, the coating slurry can be applied using methods such as transfer coating, rotary coating, or immersion coating.

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

[0158] The separator manufacturing method significantly simplifies the separator manufacturing process by creating the coating in a single application.

[0159] Some of the raw materials used in the method for manufacturing the separator, as well as parameters such as their content, can be found in the separator according to the first embodiment of this application, but their explanation is omitted here.

[0160] Unless otherwise specified, all raw materials used in the separator manufacturing process are commercially available.

[0161] secondary battery

[0162] A third 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 used continuously after discharge by activating the active material through charging. 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 placed between the positive and negative electrode sheets and primarily serves to prevent short circuits between the positive and negative electrodes, while also allowing active ions to pass through.

[0164] This 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, or a sodium metal battery, and in particular, the secondary battery may be a lithium-ion battery.

[0165] A secondary battery according to a third embodiment of the present invention includes a separator according to a first embodiment of the present invention or a separator manufactured by the method according to a second embodiment of the present invention, wherein the separator is interposed between a positive electrode sheet and a negative electrode sheet. Preferably, at least the side of the separator closer to the negative electrode sheet has the coating of the present invention. This enables the secondary battery of the present invention to achieve both 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 provided on at least one surface of the positive electrode current collector and containing a positive electrode active material. For example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode film layer is provided on one or both of the two opposing surfaces of the positive electrode current collector.

[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 respective modified compounds. Examples of lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate, lithium iron phosphate-carbon composites, lithium manganese phosphate, lithium manganese phosphate-carbon composites, lithium iron manganese phosphate, lithium iron manganese phosphate-carbon composites, and their respective 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 may contain at least one of lithium transition metal oxides and modified compounds thereof, having the general formula Li a Ni b Co c M d O e A f where 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] For example, the cathode active material for a lithium-ion battery may contain 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 contain at least one of sodium-containing transition metal oxides, polyanion materials (e.g., phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), Prussian blue-based materials, but is not limited thereto.

[0172] For example, the cathode active material for a sodium-ion battery may be 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 is X p M' q (PO4) r O x Y 3-x It may include at least one of the materials that are 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 + At least one selected from the following, where 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 modified compounds for each of the above-mentioned positive electrode active materials can be used to 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 contain a positive electrode conductive agent. In this application, the type of positive electrode conductive agent is not particularly limited, and as an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjenblack, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0175] In some embodiments, the positive electrode film layer may preferably further contain a positive electrode binder. The type of positive electrode binder is not particularly limited in this application, and as an example, the positive electrode binder may contain 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 resins.

[0176] In some embodiments, the positive electrode current collector can be a metal foil sheet or a composite current collector. An example of a metal foil sheet is aluminum foil. The composite current collector may include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. For example, the metal material may include at least one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. For example, the polymer material substrate 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 coating a positive electrode slurry onto a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing a positive electrode active material, a selectable conductive agent, a selectable binder, and any other components in a solvent and stirring uniformly. The solvent may, 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 containing a negative electrode active material. For example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode film layer is provided on one or both of the two opposing surfaces of the negative electrode current collector.

[0180] The negative electrode active material can be any negative electrode active material known in the art for secondary batteries. 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 elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy material.

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

[0182] In some embodiments, the negative electrode film layer may preferably further contain a negative electrode binder. The type of negative electrode binder is not particularly limited in this application, and as an example, the negative electrode binder may contain at least one of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylate PAA, polymethacrylate PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0183] In some embodiments, the negative electrode film layer may preferably further contain other additives. For example, the other additives may include thickeners such as sodium carboxymethylcellulose (CMC), PTC thermistor material, etc.

[0184] In some embodiments, the negative electrode current collector can be a metal foil sheet or a composite current collector. Copper foil can be used as an example of a metal foil sheet. The composite current collector may include a polymer material substrate and a metal material layer formed on at least one surface of the polymer material substrate. For example, the metal material may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. For example, the polymer material substrate 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 coating a negative electrode slurry onto a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, a selectable conductive agent, a selectable binder, and other selectable auxiliary agents in a solvent and stirring uniformly. The solvent may, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0186] The negative electrode sheet does not exclude any 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., consisting 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 some other embodiments, the negative electrode sheet described in this application further includes a protective layer covering the surface of the negative electrode film layer.

[0187] [Electrolyte]

[0188] During the charging and discharging process of a secondary battery, active ions reciprocate between the positive electrode sheet and the negative electrode sheet, being inserted and removed, while the electrolyte plays a role in conducting these active ions between the positive and negative electrode sheets. In this application, the type of electrolyte is not particularly limited and can be selected according to actual needs.

[0189] The electrolyte solution contains an electrolyte salt and a solvent. The types of electrolyte salts and solvents are not specifically limited and can be selected according to actual needs.

[0190] When the secondary battery is a lithium-ion battery, the electrolyte salt may, for example, include, but is not limited to, at least one of the following: lithium hexafluoride phosphate (LiPF6), lithium tetraborate tetrafluoride (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoride arsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium bisoxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0191] When the secondary battery is a sodium-ion battery, the electrolyte salt may, for example, include, but is not limited to, at least one of the following: sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bisfluorosulfonylimide (NaFSI), sodium bistrifluoromethanesulfonylimide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), sodium difluorooxalate borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorooxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0192] For example, the solvent may include, but is not limited to, at least one of the following: 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 contain additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performance characteristics of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature performance of the battery, and additives that improve the low-temperature output performance of the battery.

[0194] In some embodiments, the positive electrode sheet, separator, and negative electrode sheet can be manufactured into an electrode assembly by a winding process and / or a lamination process.

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

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

[0197] In this application, the shape of the secondary battery is not particularly limited and may be cylindrical, rectangular, or any other shape. Figure 1 shows a rectangular secondary battery 5 as an example.

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

[0199] Methods for manufacturing secondary batteries are well known. In some embodiments, a secondary battery can be formed by assembling a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. For example, a secondary battery can be obtained by forming an electrode assembly from a positive electrode sheet, a separator, and a negative electrode sheet using a winding or lamination process, placing the electrode assembly in an outer casing, injecting the electrolyte after drying, and then going through processes such as vacuum sealing, standing, chemical conversion, and shaping.

[0200] In some embodiments, the secondary battery according to this application may be assembled as 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] Figure 3 is a schematic diagram of a battery module 4 as an example. As shown in Figure 3, in the battery module 4, the multiple secondary batteries 5 may be arranged sequentially along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, these multiple secondary batteries 5 may be fixed together with fasteners.

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

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

[0204] Figures 4 and 5 are schematic diagrams of an example battery pack 1. As shown in Figures 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, the upper case 2 covering the lower case 3 and forming a sealed space for housing 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 embodiment of the present application provides a power consumption device comprising at least one of a secondary battery, battery module, or battery pack according to an embodiment of the present application. The secondary battery, battery module, or battery pack may be used as a power source for the power consumption device or as an energy storage unit for the power consumption device. The power consumption device may be, but is not limited to, mobile devices (e.g., mobile phones, laptop computers, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0207] Power consumption devices can be configured to use secondary batteries, battery modules, or battery packs, depending on their usage needs.

[0208] Figure 6 is a schematic diagram of an example power consumption device. This power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the requirements for high power output and high energy density of this power consumption device, a battery pack or battery module can be used.

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

[0210] Examples

[0211] The following examples are intended to illustrate the disclosures of this application in more detail, and are merely interpretive in nature, as it will be obvious to those skilled in the art that various modifications and changes can be made within the scope of the disclosures of this application. Unless otherwise specified, all parts, percentages, and ratios described in the following examples are based on mass, all reagents used in the examples are commercially available or can be synthesized according to conventional methods and used directly without requiring further processing, and the equipment used in the examples is commercially available.

[0212] Fabrication of nanocellulose

[0213] After opening the cotton linters using a cotton opening machine and removing the residue, the linters were pulverized at 150°C for 2 hours using a 5 wt% NaOH aqueous solution. Subsequently, the linters were washed with water to remove impurities (3 washes), bleached with sodium hypochlorite, washed with dilute hydrochloric acid to remove impurities, washed with water to remove impurities (1 wash), the water was removed, and the linters were air-dried to obtain cotton cellulose powder with a whiteness of 85% or higher.

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

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

[0216] The molar ratio of modifying groups to surface hydroxyl groups in nanocellulose can be measured by determining the hydroxyl value (the number of mg of potassium hydroxide equivalent to the hydroxyl group content per gram of sample) of raw cellulose and nanocellulose based on the phthalic anhydride method in GB / T12008.3-2009. The obtained value is converted to mgKOH / g, and then to mmol / g to obtain the hydroxyl group content. By subtracting the hydroxyl group content of nanocellulose from the hydroxyl group content of raw cellulose, the content of modifying groups (i.e., the content of modified hydroxyl groups) is obtained, and the molar ratio of modifying groups to hydroxyl groups is calculated from this.

[0217] Example 1

[0218] Fabrication of a separator

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

[0220] Preparation of coating slurry: A coating slurry was obtained by uniformly mixing a filler having a porous structure (commercially available) as shown in Table 1, nanocellulose, and an aqueous polyacrylic acid binder in a mass ratio of 80:18:2 in an appropriate amount of deionized water as a solvent.

[0221] Coating: The prepared coating slurry was applied to both sides of a porous PE substrate using a coating machine, and a separator was obtained by drying and slitting.

[0222] Fabrication of positive electrode sheet

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

[0224] Fabrication of negative electrode sheet

[0225] A negative electrode slurry was obtained by uniformly mixing artificial graphite, a conductive agent (Super P), and binders (styrene-butadiene rubber (SBR) and sodium carboxymethylcellulose (CMC)) in a suitable amount of deionized water as a solvent in a mass ratio of 96.4:0.7:1.8:1.1. The negative electrode slurry was then applied to copper foil, which served as the negative electrode current collector, and a negative electrode sheet was obtained through drying, cold pressing, stripe splitting, and cutting processes.

[0226] Preparation of electrolyte

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

[0228] Manufacturing of secondary batteries

[0229] A positive electrode sheet, a separator, and a negative electrode sheet are stacked in order and wound together to obtain an electrode assembly. The electrode assembly is then placed in an outer casing, dried, and then injected with electrolyte. After going through processes such as vacuum sealing, standing, chemical formation, and shaping, a secondary battery is obtained.

[0230] Examples 2-12

[0231] The secondary battery was fabricated in a manner similar to 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 in the fabrication of the separator were different. See Table 1 for specific parameters.

[0232] Examples 13-15

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

[0234] Examples 16-20

[0235] The secondary battery was fabricated in a manner similar to Example 1, except for differences in the mass content of the porous filler and nanocellulose used in the preparation of the separator. See Table 1 for specific parameters.

[0236] Comparative Example 1

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

[0238] Test section

[0239] (1) Cycle characteristics test of secondary batteries

[0240] At 45°C, the secondary battery was charged with a constant current of 1C to 4.2V, and then the constant voltage charging was continued until the current fell below 0.05C. At this point, the secondary battery was fully charged, and the charge capacity at this time, i.e., the first charge capacity, was recorded. After the secondary battery was left to stand for 5 minutes, it was discharged with a constant current of 1C to 2.8V. This constituted one charge-discharge cycle, and the discharge capacity at this time, i.e., the first discharge capacity, was recorded. A cycle charge-discharge test was performed on the secondary battery 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 of secondary batteries

[0242] At 0°C, the secondary battery is discharged at a constant current of 0.33C to 2.8V, left to stand for 30 minutes, charged at a constant current of 0.33C to 4.20V, then charged at a constant voltage until the current drops to 0.05C, left to stand for 30 minutes, discharged again at a constant current of 0.33C to 2.8V, left to stand for 30 minutes, and the discharge capacity A1 at this time is recorded. Subsequently, the secondary battery is charged at a constant current of 0.33C to 4.20V, then charged at a constant voltage until the current drops to 0.05C, left to stand for 30 minutes, discharged at a constant current of 2C to 2.8V, left to stand for 60 minutes, and the discharge capacity A2 at this time is recorded. The low-temperature discharge rate performance of the secondary battery is indicated by the ratio of the discharge capacity A2 at 0°C and a 2C rate to the discharge capacity A1 at 0°C and a 0.33C rate (A2 / A1).

[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 can have high thermal stability, as well as 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] It should be noted that this application is not limited to the above embodiments. The above embodiments are merely examples, and those having a configuration substantially the same as the technical idea and having the same operation and effect within the technical scope of this application are all included in the technical scope of this application. In addition, various modifications conceivable by those skilled in the art within the scope not departing from the gist of this application, or other forms constructed by combining some components in the embodiments are also included in the scope of this application.

[0247] [Table 1]

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