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

Abstract

The present application provides a separator for a secondary battery, a manufacturing method thereof, and a secondary battery and an electric power utilization device including the separator. The separator according to the present application includes a porous substrate and a coating provided on at least one surface of the porous substrate, the coating including nanocellulose including a modified group including at least one of a sulfonic acid group, a boronic acid group, and a phosphate group.

Description

[Technical Field]

[0001] The present application relates to the technical field of secondary batteries, and more particularly to a separator, a manufacturing method thereof, and a secondary battery and an electric power utilization device related thereto. [Background technology]

[0002] Secondary batteries have the distinctive features of being light in weight, non-polluting, and having no memory effect, and are therefore widely used in various consumer electronic products and electric vehicles.

[0003] With the development of new energy industry, users are placing higher requirements on secondary batteries, such as increasing requirements for the safety performance of secondary batteries, but current methods for improving the safety performance of batteries are often unfavorable in balancing the energy density of batteries.

[0004] Therefore, how to simultaneously achieve good safety performance and high energy density in batteries is a key challenge in this field. Summary of the Invention

[0005] In view of the problems in the prior art, the present application provides a separator that has excellent thermal stability, high ionic conductivity, and good resistance to external pressure, allowing secondary batteries using the separator to achieve both good safety performance and high energy density.

[0006] To achieve the above object, according to a first aspect of the present application, there is provided a separator comprising a porous substrate and a coating provided on at least one surface of the porous substrate, wherein the coating comprises nanocellulose containing modified groups including at least one of a sulfonic acid group, a boronic acid group, and a phosphate group.

[0007] Compared to the prior art, the present invention has at least the following advantages. The separator of the present invention contains nanocellulose with specific modified groups (e.g., at least one of sulfonic acid groups, boronic acid groups, and phosphate groups) in the coating. This effectively improves the thermal stability of the separator, thereby improving the thermal stability of the battery and further enhancing safety during battery use. The nanocellulose with modified groups in the coating itself has a certain rigidity, ensuring adhesion between the separator substrate and the substrate while also ensuring ionic conduction efficiency and improving the separator's resistance to external pressure, thereby improving the battery's energy density and thermal stability. At the same time, the presence of modified groups reduces the proportion of hydroxyl groups in the raw material, thereby reducing the viscosity of the coating slurry, making it easier to apply the slurry, improving coating uniformity, and further improving separator production efficiency.

[0008] In any embodiment of the present application, the nanocellulose further contains hydroxy groups, and the ratio of the content of the modified groups to the hydroxy groups is 1:4 to 4:1. For example, the ratio of the modified groups to the hydroxy groups is 2:3 to 7:3. When the ratio of the modified groups to the unmodified hydroxy groups in the nanocellulose is within the above range, the thermal stability and ion conduction ability of the separator, as well as the thermal stability of the battery, can be further improved.

[0009] In any embodiment of the present application, the average diameter of the nanocellulose is ≦40 nm. For example, the average diameter of the nanocellulose may be 10 to 35 nm. When the average diameter of the nanocellulose is within the above-mentioned range, the thermal stability of the separator can be further improved and the thermal shrinkage rate of the separator can be reduced.

[0010] In any embodiment of the present application, the average length of the nanocellulose may be 100 to 600 nm. For example, the average length of the nanocellulose may be 200 to 500 nm. When the average length of the nanocellulose is within the above-mentioned range, the ion conduction ability of the separator can be further improved.

[0011] In any embodiment of the present application, the aspect ratio of the nanocellulose may be 5 to 60. For example, the aspect ratio of the nanocellulose may be 10 to 30. When the aspect ratio of the nanocellulose is within the above-mentioned range, the thermal stability of the separator and the safety performance of the battery can be further improved.

[0012] In any embodiment of the present application, the equilibrium degree of polymerization range of nanocellulose may be 150 to 300 DP. For example, the equilibrium degree of polymerization range of nanocellulose is 200 to 250 DP. When the equilibrium degree of polymerization range of nanocellulose is within the above-mentioned range, the viscosity of the nanocellulose solution is advantageously in a reasonable range, the fluidity and impregnation of the slurry during application are excellent, and further, the coating quality is improved, and the thermal stability and ion conduction capacity of the separator can be further improved.

[0013] In any embodiment of the present application, the molecular weight of the nanocellulose may be 20,000 to 60,000. For example, the molecular weight of the nanocellulose may be 30,000 to 50,000. When the molecular weight of the nanocellulose is within the above-mentioned range, not only can the nanocellulose prevent the porous channel structure of the separator from being blocked, but the viscosity of the nanocellulose solution can also be kept within a reasonable range. This provides excellent fluidity and impregnation of the slurry during application, which is advantageous for improving coating quality, and further improves the thermal stability and ion conduction capacity of the separator.

[0014] In any embodiment of the present application, the shape of the nanocellulose may be one or more selected from the group consisting of tubular, fibrous, and rod-shaped. Nanocellulose of an appropriate shape is more advantageous for forming a stable spatial network structure by itself or with other components in the coating, further increasing the ion conduction paths of the separator and improving external pressure resistance.

[0015] In some embodiments of the present application, the time period for the separator to exhibit leakage current is ≥ 12 days when the separator is heated to 65°C and applied to 4.3 V. A separator having the above characteristics can ensure that electrons are blocked at the separator edge, avoiding short or micro-short phenomena due to the appearance of breakdown points, and further improving the safety of the battery during use.

[0016] In any embodiment of the present application, the nanocellulose content in the coating may be ≥ 5 wt%. For example, the nanocellulose content in the coating may be 5-30 wt%, optionally 10-25 wt%. When the nanocellulose content in the coating is within the above-mentioned range, the coating slurry containing the nanocellulose can have a more appropriate viscosity, making it easier to apply. Nanocellulose, either by itself or with other components in the coating, is more advantageous in forming a stable spatial network structure, further increasing the ion conduction paths of the separator, improving external pressure resistance and voltage breakdown strength, and further improving the thermal safety of the battery.

[0017] In any embodiment of the present application, the coating further comprises a filler comprising at least one of inorganic particles, organic particles, and organic-inorganic hybrid particles.

[0018] In any embodiment of the present application, the inorganic particles may be at least one of inorganic particles having a dielectric constant of 5 or greater, inorganic particles having the ability to transmit active ions, and materials capable of undergoing electrochemical oxidation and reduction.

[0019] In any embodiment of the present application, the inorganic particles having a dielectric constant of 5 or greater include boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon oxide (SiO2), and the like. x(0 < x ≤ 2), tin dioxide (SnO2), titanium oxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), hafnium oxide (HfO2), cerium oxide (CeO2), zirconium titanate (ZrTiO3), barium titanate (BaTiO3), magnesium fluoride (MgF2), Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT), PB(Mg3Nb 2 / 3 )O3 - PbTiO3 (PMN - PT) may be at least one selected therefrom.

[0020] In any embodiment of the present application, the inorganic particles having the ability to transmit active ions are lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y glass - like (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x [[ID=3??]]La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2), SiS2 glass - like (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5 glass - like (Li x P<000002??]]S z , 0 < x < 3, 0 < y < 3, 0 < z < 7) may be at least one selected therefrom. It should be noted that there seems to be a small error in the original text where "La " in and "Zr " in etc. might be part of a chemical formula or something, and the translated text tries to maintain the integrity as much as possible. Also, there are some tags like 1-x etc. which are just preserved as they are. And in the translation of the chemical formula parts, the numbers and chemical symbols are translated according to common chemical naming conventions in English. If there are any specific requirements or corrections regarding the chemical content, it might need further clarification.

[0021] In any embodiment of the present application, the material capable of generating electrochemical oxidation and reduction may be at least one selected from a lithium-containing transition metal oxide, a lithium-containing phosphate having an olivine structure, a carbon-based material, a silicon-based material, a tin-based material, and a lithium-titanium compound.

[0022] In any embodiment of the present application, the organic particles may be at least one selected from polystyrene, polyethylene, polyimide, melamine resin, novolac resin, polypropylene, polyester, polyphenylene sulfide, aromatic polyamide, polyamideimide, polyimide, a copolymer of butyl acrylate and ethyl methacrylate, and mixtures thereof.

[0023] In any embodiment of the present application, the organic-inorganic hybrid particles may be selected from metal-organic framework materials, such as MOFs.

[0024] The presence of the filler in the coating can further build a stable spatial network structure in cooperation with the nanocellulose in the coating, further increasing the ion conduction paths, and at the same time further improving the thermal stability, antioxidant properties, puncture resistance and voltage breakdown strength of the separator, and further improving the thermal stability of the battery.

[0025] In any embodiment of the present application, the volume average particle diameter Dv50 of the filler is ≦2.5 μm. For example, the volume average particle diameter Dv50 of the filler may be 0.3 μm to 0.7 μm, 0.7 μm to 1.5 μm, or 1.5 μm to 2.5 μm. When the particle diameter of the filler is controlled within a predetermined range, the energy density of the battery can be further improved while ensuring good safety performance of the separator.

[0026] In any embodiment of the present application, the mass percentage of the filler in the coating is ≦95 wt% (based on the total mass of the coating). For example, the mass percentage of the filler in the coating may be 70 to 95 wt%, and optionally 75 to 90 wt%. When the mass percentage of the filler is controlled within a predetermined range, the energy density of the battery can be further improved while ensuring the safety performance of the separator.

[0027] In any embodiment of the present application, the thickness of the porous substrate is ≦12 μm, and optionally the thickness of the porous substrate is ≦7 μm. When the thickness of the substrate is within this range, the energy density of the battery can be further improved.

[0028] In any embodiment of the present application, the thickness of the coating is ≦3 μm, and optionally, the thickness of the coating is 0.5 to 2 μm. When the coating thickness is within the predetermined range, the energy density can be further improved while ensuring the safety performance of the battery.

[0029] In any embodiment of the present application, the separator has a heat shrinkage rate of ≦5% at 150° C. for 1 hour, optionally 0.5% to 3%.

[0030] In any embodiment of the present application, the separator has a wet length in 1 min of ≧20 mm, and optionally 30 to 80 mm.

[0031] In any embodiment of the present application, the separator has a peel force of ≧0.5 N / m, optionally between 0.5 and 100 N / m.

[0032] In any embodiment of the present application, the separator has a transverse tensile strength (MD) of ≥ 2000 kgf / cm 2 and selectable from 2500 to 4500 kgf / cm 2 is.

[0033] In any embodiment of the present application, the separator has a longitudinal tensile strength (TD) of ≥ 2000 kgf / cm 2 and selectable from 2500 to 4500 kgf / cm 2 is.

[0034] In any embodiment of the present application, the separator has an air permeability of ≦300 s / 100 ml, optionally between 100 s / 100 ml and 230 s / 100 ml.

[0035] If the separator's performance satisfies one or more of the above conditions, it will contribute to improving the safety performance and energy density of the battery.

[0036] In any embodiment of the present application, an adhesive layer comprising a particulate organic adhesive is further provided on at least a portion of the surface of the coating, and optionally the particulate organic adhesive comprises a polyvinylidene fluoride polymer, and further optionally the polyvinylidene fluoride polymer comprises a homopolymer of vinylidene fluoride monomer and / or a copolymer of vinylidene fluoride monomer and other comonomer, and even further optionally the other comonomer comprises a fluorine-containing monomer and / or a chlorine-containing monomer.

[0037] According to a second aspect of the present application, there is provided a method for producing a separator, comprising: 1) providing a porous substrate; 2) mixing modified nanocellulose with a solvent in a predetermined ratio to prepare a coating slurry; and 3) applying the coating slurry to at least one surface of the substrate and, after drying, obtaining a separator, wherein the separator obtained after drying comprises a porous substrate and a coating provided on at least one surface of the porous substrate, and the coating comprises modified nanocellulose having at least one modifying group selected from a sulfonic acid group, a boronic acid group, and a phosphate group.

[0038] In any embodiment of the present application, the modified nanocellulose is produced by the following method:

[0039] S1: Prepare cellulose powder with a whiteness of ≥ 85%. S2: The cellulose powder of step S1 is mixed with an acid solution and reacted, and then the mixture is deacidified and purified to obtain nanofiber whiskers having modified groups. S3: Adjust the pH of the obtained nanofiber whiskers having modified groups to neutral, and then polish and cut them to obtain the modified nanocellulose.

[0040] In any embodiment of the present application, in step S1, the cellulose powder can be obtained by the following method: For example, one or more fiber raw materials selected from sisal fiber, cotton fiber, and wood fiber are opened and deslag-removed, then cooked in an alkaline solution (for example, an aqueous NaOH solution, the concentration of which may be 4 to 20 wt%, optionally 5 to 15 wt%), washed and purified, and then bleached (for example, sodium hypochlorite and / or hydrogen peroxide solution can be used), pickled and purified, washed and purified, water-repellent, and air-dried to obtain the cellulose powder.

[0041] In any embodiment of the present application, in step S2, the acid solution may be an H2SO4 aqueous solution, an H3BO3 aqueous solution, or an H3PO4 aqueous solution, and the concentration of the acid solution may be 5 to 80 wt%.

[0042] In any embodiment of the present application, in step S2, the mass ratio of the cellulose powder to the acid solution may be 1:2.5 to 1:50, and optionally 1:5 to 1:30.

[0043] In any embodiment of the present application, in step S2, the reaction may be carried out at a temperature of 80° C. or less.

[0044] In any embodiment of the present application, in step S2, the reaction time of the cellulose powder and the acid solution may be 0.5 to 3 hours.

[0045] According to a third aspect of the present application, there is provided a secondary battery including the separator according to the first aspect of the present application or a separator manufactured by the manufacturing method according to the second aspect of the present application. As described above, the secondary battery according to the present application can improve energy density and safety, and at the same time, the manufacturing process has higher operability and significantly reduces production costs.

[0046] According to a fourth aspect of the present application, there is provided a power utilization device including the secondary battery provided by the third aspect of the present application.

[0047] In the separator of the present application, applying a modified nanocellulose coating to a porous substrate effectively improves the thermal stability of the separator and enhances safety during battery use. On the other hand, the nanocellulose with specific modified groups in the coating has a certain rigidity, which (or together with other components in the coating, such as fillers) can form a stable spatial network structure, thereby increasing the number of ion conduction paths and improving resistance to external pressure, further improving the energy density and thermal safety of the battery. Furthermore, the presence of modified groups reduces the proportion of hydroxyl groups in the raw material, thereby reducing the viscosity of the coating slurry and making it easier to apply, thereby improving separator production efficiency. [Brief explanation of the drawings]

[0048] In order to more clearly describe the technical solutions of the present application, the drawings used in the present application are briefly described below. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to the drawings without creative efforts.

[0049] [Figure 1] 1 is a schematic diagram of a separator according to an embodiment of the present invention. [Figure 2] 1 is a schematic diagram illustrating the configuration of a secondary battery according to an embodiment of the present application. [Figure 3] FIG. 3 is an exploded view of FIG. 2. [Figure 4]1 is a schematic configuration diagram of a battery module according to an embodiment of the present application. [Figure 5] 1 is a schematic diagram of a battery pack according to an embodiment of the present application. [Figure 6] FIG. 6 is an exploded view of FIG. 5. [Figure 7] 1 is a schematic diagram of an apparatus in which a secondary battery according to one embodiment of the present application is used as a power source. [Figure 8] FIG. 2 is a scanning electron microscope (SEM) view of a cross section of a separator according to one embodiment of the present application. [Figure 9] FIG. 1 is a scanning electron microscope (SEM) image of nanocellulose in a separator coating according to one embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0050] Hereinafter, with appropriate reference to the drawings, embodiments of the secondary battery separator and its manufacturing method, secondary battery, battery module, battery pack, and power utilization device according to the present application will be described in detail and specifically disclosed. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and redundant descriptions of actually similar structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the scope of the claims.

[0051] The "ranges" disclosed herein are defined by lower and upper limits, and a given range is defined by selecting one lower limit and one upper limit, with the selected lower and upper limits defining the boundaries of that particular range. Ranges defined in this manner may or may not include extreme values ​​and may be arbitrarily combined; that is, any lower limit may be combined with any upper limit to form a single range. For example, reciting ranges of 60 to 120 and 80 to 110 for a particular parameter is also contemplated as being within the ranges of 60 to 110 and 80 to 120. Furthermore, reciting minimum range values ​​of 1 and 2 and maximum range values ​​of 3, 4, and 5, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this specification, unless otherwise specified, the numerical range "a to b" is a shorthand notation for any combination of real numbers from a to b, where both a and b are real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers from "0 to 5" are listed in this specification, but "0 to 5" is merely an abbreviation for combinations of these numbers. Also, when a parameter is stated to be an integer ≧2, this is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0052] Unless otherwise specified, all embodiments and alternative embodiments of the present application can be combined with each other to form new technical solutions.

[0053] Unless otherwise specified, all technical features and optional technical features in the present application can be combined with each other to form new technical solutions.

[0054] Unless otherwise specified, all steps herein may be performed in order or randomly, but are preferably performed in order. For example, "the method includes steps (a) and (b)" means that the method may include steps (a) and (b) performed in order, or may include steps (b) and (a) performed in order. For example, "the method may further include step (c)" means that step (c) can be added to the method in any order, e.g., the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0055] Unless otherwise specified, the terms "comprise" and "comprises" used herein refer to open forms and may also be closed forms. For example, the terms "comprise" and "comprises" can indicate that other unlisted components may be further included or may be included, or that only the listed components may be included or may be included.

[0056] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions also satisfy the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or A and B are both true (or exist).

[0057] In the description of this specification, unless otherwise specified, the terms "more than or equal to" and "less than or equal to" are inclusive, and "multiple types" in "one or more types" means two types and more than two types.

[0058] Unless otherwise specified, the terms used herein have the meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of each parameter referred to herein can be measured by various measurement methods commonly used in the art (for example, they can be tested according to the methods shown in the examples of the present application).

[0059] secondary battery A secondary battery refers to a battery that can be continuously used by activating the active material through charging after discharging. The secondary battery may include a lithium ion secondary battery and a sodium ion secondary battery. Hereinafter, the secondary battery according to the present invention will be described in detail using a lithium ion secondary battery as an example.

[0060] Typically, a secondary battery includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. During the charge and discharge process, active ions are repeatedly inserted and removed between the positive and negative electrodes. The separator is placed between the positive and negative electrodes to separate them. The electrolyte conducts ions between the positive and negative electrodes.

[0061] [Separator] An embodiment of the present application provides a separator comprising a porous substrate and a coating formed on at least one surface of the porous substrate, the coating comprising nanocellulose containing modified groups that may include at least one selected from sulfonic acid groups, boronic acid groups, and phosphate groups. Figure 1 shows a schematic diagram of a separator in which a coating 12 is formed on one surface of a porous substrate 11.

[0062] Without wishing to be bound by theory, the inventors conducted extensive research and discovered that applying a coating containing nanocellulose with specific modified groups (including at least one of sulfonic acid groups, boronic acid groups, and phosphate groups) to at least one surface of a separator's porous substrate effectively improves the separator's thermal stability (e.g., significantly increases the battery's hot box failure temperature and / or significantly reduces the separator's thermal shrinkage). This significantly improves the safety performance of secondary batteries using such separators. Furthermore, the inclusion of nanocellulose with specific modified groups in the coating effectively reduces the amount of soft adhesive used in the coating, thereby effectively increasing the number of ion conduction paths and further improving the battery's cycle life and capacity retention. Furthermore, the presence of specific modified groups reduces the proportion of hydroxyl groups in the raw material, reducing the viscosity of the coating slurry and easing the difficulty of slurry application, further improving separator production efficiency.

[0063] The type of modifying group in nanocellulose can be determined using infrared spectroscopy. For example, the infrared spectrum of the material can be examined to determine the type of modifying group by determining the characteristic peaks contained therein. Specifically, infrared spectroscopy can be performed on the material using instruments and methods well known in the art. For example, infrared spectroscopy can be performed using an infrared spectrometer, such as an IS10 Fourier transform infrared spectrophotometer from Nicolet, USA, in accordance with GB / T 6040-2002, General Methods for Infrared Spectroscopy.

[0064] As a result of in-depth research, the present inventors have found that the separator according to the present application can further improve the performance of a secondary battery when it satisfies the above conditions and, optionally, when it further satisfies one or more of the following conditions:

[0065] In some embodiments, the nanocellulose further contains hydroxy groups, and the ratio of the modified groups to the hydroxy groups is 1:4 to 4:1. For example, the ratio of the modified groups to the hydroxy groups is 2:3 to 7:3. When the ratio of the modified groups to the unmodified hydroxy groups in the nanocellulose is within the above range, the thermal stability and ion conduction ability of the separator, as well as the thermal stability of the battery, can be further improved.

[0066] In some embodiments, the nanocellulose has an average diameter of ≦40 nm. For example, the nanocellulose may have an average diameter of 10 to 35 nm. When the average diameter of the nanocellulose is within this range, the thermal stability of the separator can be further improved and the thermal shrinkage of the separator can be reduced.

[0067] In some embodiments, the nanocellulose may have an average length of 100 to 600 nm. For example, the nanocellulose may have an average length of 200 to 500 nm. When the average length of the nanocellulose is within the above-mentioned range, the thermal stability and ion conduction ability of the separator can be further improved.

[0068] In some embodiments, the aspect ratio of the nanocellulose may be 5 to 60. For example, the aspect ratio of the nanocellulose may be 10 to 30. When the aspect ratio of the nanocellulose is within the above-mentioned range, the energy density of the battery can be further improved.

[0069] In some embodiments, the equilibrium degree of polymerization range of the nanocellulose may be 150 to 300 DP. For example, the equilibrium degree of polymerization range of the nanocellulose may be 200 to 250 DP. When the equilibrium degree of polymerization range of the nanocellulose is within the above-mentioned range, the viscosity of the nanocellulose solution is advantageously within a reasonable range, the fluidity and impregnation of the slurry during application are excellent, and further, the coating quality is improved, and the thermal stability and ion conduction capacity of the separator can be further improved.

[0070] In some embodiments, the molecular weight of the nanocellulose may be 20,000 to 60,000. For example, the molecular weight of the nanocellulose may be 30,000 to 50,000. When the molecular weight of the nanocellulose is within the above-mentioned range, not only can the nanocellulose prevent the porous channel structure of the separator from being blocked, but the viscosity of the nanocellulose solution can also be kept within a reasonable range. This provides excellent fluidity and impregnation of the slurry during application, which is advantageous for improving coating quality, and can further improve the thermal stability and ion conduction capacity of the separator.

[0071] In some embodiments, the nanocellulose may have one or more shapes selected from the group consisting of tubular, fibrous, and rod-like. Nanocellulose with an appropriate shape is more advantageous for forming a stable spatial network structure by itself or together with other components in the coating, further increasing the ion conduction paths and improving resistance to external pressure.

[0072] In some embodiments, the separator exhibits a leakage current for a period of ≥ 12 days at 65°C and 4.3 V. A separator with these characteristics ensures that electrons are blocked at the separator edge, preventing short or micro-short circuits due to the appearance of breakdown points, and further improving safety during battery use.

[0073] In some embodiments, the content of the nanocellulose in the coating may be ≧5 wt%. For example, the content of the nanocellulose in the coating may be 5 to 30 wt%, and optionally, 10 to 25 wt%. When the content of the nanocellulose in the coating is within the above-mentioned predetermined range, it is ensured that the slurry of the coating containing the nanocellulose has a more appropriate viscosity and can contribute to coating. Moreover, the nanocellulose itself or in combination with other components in the coating is more advantageous for constructing a stable spatial network structure, further increasing the ion conduction path, improving the external force resistance and voltage breakdown resistance, and further improving the thermal safety of the battery.

[0074] In some embodiments, the coating further includes a filler including at least one of inorganic particles, organic particles, and organic-inorganic hybrid particles.

[0075] In some embodiments, the inorganic particles may be at least one of inorganic particles having a dielectric constant of 5 or more, inorganic particles having the ability to transmit active ions, and materials capable of generating electrochemical oxidation and reduction.

[0076] In some embodiments, the inorganic particles having a dielectric constant of 5 or more are boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon oxide SiO x (0 < x ≦ 2), tin dioxide (SnO2), titanium oxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), hafnium oxide (HfO2), cerium oxide (CeO2), zirconium titanate (ZrTiO3), barium titanate (BaTiO3), magnesium fluoride (MgF2), Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Tiy O3(PLZT), PB(Mg3Nb 2 / 3 )O3-PbTiO3 (PMN-PT) may also be at least one selected therefrom.

[0077] In some embodiments, the inorganic particles having the ability to transmit active ions are lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y glass-like (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li<​​​​​​​​​​​​​​​​​​​​​​In some embodiments, the organic particles may be at least one selected from polystyrene, polyethylene, polyimide, melamine resin, novolac resin, polypropylene, polyester, polyphenylene sulfide, aromatic polyamide, polyamideimide, polyimide, copolymer of butyl acrylate and ethyl methacrylate, and mixtures thereof.

[0080] In some embodiments, the organic-inorganic hybrid particles may be selected from metal-organic framework materials, such as MOFs.

[0081] The presence of the filler in the coating can further build a stable spatial network structure in cooperation with the nanocellulose in the coating, further increasing the ion conduction paths. At the same time, the thermal stability, antioxidant properties, puncture resistance and voltage breakdown resistance of the separator can be further improved, and the safety performance of the battery can be further improved.

[0082] In some embodiments, the filler has a volume average particle diameter Dv50 of ≦2.5 μm. For example, the filler may have a volume average particle diameter Dv50 of 0.3 μm to 0.7 μm, 0.7 μm to 1.5 μm, or 1.5 μm to 2.5 μm. When the particle diameter of the filler is controlled within a predetermined range, the energy density of the battery can be further improved while ensuring good safety performance of the separator.

[0083] The volume average particle diameter Dv50 of the filler has a meaning well known in the art and can be measured by an instrument and method well known in the art, for example, GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method, and can be measured using a laser particle size analyzer (e.g., Master Size 3000).

[0084] In some embodiments, the weight percentage of the filler in the coating is ≦95 wt % (based on the total weight of the coating). For example, the weight percentage of the filler in the coating may be 70 to 95 wt %, and optionally 75 to 90 wt %. When the weight percentage of the filler is controlled within a predetermined range, the energy density of the battery can be further improved while ensuring the safety performance of the separator.

[0085] In some embodiments, the separator has a heat shrinkage rate of ≦5% after 1 hour at 150° C. For example, the separator may have a heat shrinkage rate of 0.5% to 3% after 1 hour at 150° C.

[0086] In some embodiments, the separator has a wet length of 20 mm or more in 1 minute. For example, the separator may have a wet length of 30 to 80 mm in 1 minute.

[0087] In this application, the method for measuring the wetting length of the separator in 1 minute (which reflects the separator's electrolyte impregnation performance) is as follows. a) Sample preparation: The separator was cut into samples 5 mm wide and 100 mm long using a sample cutter, obtaining five parallel samples. Both ends of the samples were attached parallel to a metal frame. b) Electrolyte preparation: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were uniformly mixed in a mass ratio of 3:5:2 to obtain a mixed solvent. Well-dried electrolyte salt LiPF6 was dissolved in the mixed solvent to obtain an electrolyte salt concentration of 1.0 mol / L. After uniform mixing, the electrolyte was obtained. c) The electrolyte was drawn into a burette, and 0.5 mg was dropped onto the center of the sample. Timing was started with a stopwatch. 1 minute after the set time, a photograph was taken, and the length of the electrolyte diffusion was measured with a steel ruler. This was marked as a, and the average of the values ​​measured for the five samples was taken.

[0088] In some embodiments, the separator has a peel force of ≧0.5 N / m, optionally between 0.5 and 100 N / m.

[0089] In some embodiments, the separator has a transverse tensile strength (MD) of ≥ 2000 kgf / cm 2 For example, the tensile strength in the transverse direction of the separator is 2500 to 4500 kgf / cm 2 may be.

[0090] In some embodiments, the separator has a longitudinal tensile strength (TD) of ≥ 2000 kgf / cm 2 For example, the longitudinal tensile strength of the separator is 2500 to 4500 kgf / cm 2 may be.

[0091] In some embodiments, the separator has an air permeability of ≦300 s / 100 mL. For example, the separator may have an air permeability of 100 s / 100 mL to 230 s / 100 mL.

[0092] The peel strength, transverse tensile strength (MD), longitudinal tensile strength (TD), and air permeability of the separator all have meanings well known in the art and can be measured by methods well known in the art, for example, by referring to the GB / T 36363-2018 standard.

[0093] In some embodiments, the coating thickness is ≦3 μm. For example, the coating thickness may be 0.5 μm to 1.0 μm, 1.0 μm to 1.5 μm, or 1.5 μm to 2.0 μm.

[0094] In some embodiments, the weight of the coating per unit area of ​​the separator is ≦3.0 g / m 2 For example, the coating weight on one side of a separator with a unit area is 1.0 g / m 2 ~1.5g / m 2 , 1.5g / m 2 ~2.5g / m 2 , 2.5g / m 2 ~3.0g / m 2 may be.

[0095] By controlling the coating thickness and / or coating weight within the above range, the energy density of the battery can be further improved, provided that the safety performance of the battery is ensured.

[0096] The above-mentioned coating thickness and coating weight are all within the control range of single-side coating. When the separator porous substrate has coatings on both surfaces, the coating on either surface is within the range of the present application as long as it satisfies the above range.

[0097] According to some embodiments, the coating may further include a non-particulate adhesive. The present application does not particularly limit the type of the non-particulate adhesive, and any known material having good improving properties may be selected and used.

[0098] According to some embodiments, the weight percentage of the non-particulate adhesive in the coating is <1%.

[0099] In some embodiments, the coating may further include a polymer for improving heat resistance, a dispersant, a wetting agent, etc. The present application does not particularly limit the type of the above-mentioned substance, and any known material having good improving properties may be selected and used.

[0100] In the embodiments of the present application, the material of the porous substrate is not particularly limited, and any substrate having good chemical and mechanical stability may be selected and used, such as one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The porous substrate may be a single-layer thin film or a multi-layer composite thin film. When the porous substrate is a multi-layer composite thin film, the materials of the layers may be the same or different.

[0101] In some embodiments, the thickness of the porous substrate is ≦12 μm, and optionally, the thickness of the porous substrate is ≦7 μm. For example, the thickness of the porous substrate may be 3 μm to 5 μm, 5 μm to 9 μm, or 9 μm to 12 μm. When the thickness of the substrate is controlled within a predetermined range, the energy density of the battery can be further improved while ensuring the safety performance of the battery.

[0102] In some embodiments, the porosity of the porous substrate may be 30% to 60%. When the porosity of the porous substrate is controlled within the above-mentioned range, the discharge ratio of the battery can be ensured and self-discharge can be prevented.

[0103] In some embodiments, an adhesive layer comprising a particulate organic adhesive is further provided on at least a portion of the surface of the coating. Optionally, the particulate organic adhesive may comprise a polyvinylidene fluoride polymer (PVDF-based polymer).

[0104] In some embodiments, the PVDF-based polymer may include homopolymers of vinylidene fluoride monomers and / or copolymers containing vinylidene fluoride monomers and other comonomers.

[0105] In some embodiments, the other comonomer may include a fluorine-containing monomer or a chlorine-containing monomer. Optionally, the comonomer may include at least one selected from polyvinyl fluoride, trifluoroethylene (VF3), hexafluoropropylene, trifluorochloroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE), and perfluoro(propyl vinyl) ether (PPVE), perfluoro(1,3-dioxole), and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD).

[0106] This application is 1) providing a porous substrate; 2) mixing the modified nanocellulose with a solvent in a predetermined ratio to provide a slurry of the coating to be prepared; 3) applying the coating slurry to at least one surface of the substrate and, after drying, obtaining a separator, The separator obtained after drying comprises a porous substrate and a coating provided on at least one surface of the porous substrate, the coating comprising modified nanocellulose having at least one modifying group selected from a sulfonic acid group, a boronic acid group, and a phosphate group. The present invention further provides a method for producing a separator.

[0107] In the present embodiment, the material of the porous substrate is not particularly limited, and any substrate having good chemical and mechanical stability may be selected, such as one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The porous substrate may be a single-layer thin film or a multi-layer composite thin film. When the porous substrate is a multi-layer composite thin film, the materials of each layer may be the same or different.

[0108] In some embodiments, in step 2), the solvent may be water, for example, ion-exchanged water.

[0109] In some embodiments, in step 2), the coating slurry further includes a filler. The types of fillers are as described above and are not described here. Optionally, the filler accounts for 95 wt% or less of the dry weight of the coating slurry. For example, it may be 70 to 95 wt%, or 75 to 90 wt%.

[0110] In some embodiments, in step 2), the coating slurry may further include a polymer for improving heat resistance, a dispersant, a wetting agent, an emulsion-type adhesive, or the like.

[0111] In some embodiments, in step 2), the solids content of the coating slurry may be controlled to 28% to 45%, for example, 30% to 38% by weight. When the solids content of the coating slurry is within this range, it can effectively reduce surface problems and the probability of non-uniform coating, thereby further improving the energy density and safety performance of the battery.

[0112] In some embodiments, in step 2), the modified nanocellulose is produced by the following method:

[0113] S1: Prepare cellulose powder with a whiteness of ≥ 85%. S2: The cellulose powder of step S1 is mixed with an acid solution and reacted, and then the mixture is deacidified and purified to obtain nanofiber whiskers having modified groups. S3: Adjust the pH of the obtained nanofiber whiskers having modified groups to neutral, and then polish and cut them to obtain the modified nanocellulose.

[0114] In any embodiment of the present application, in step S1, the cellulose powder can be obtained by purchasing it from the market, or can be produced as follows: After opening the fiber raw material and removing the slag, the raw material is steamed in an alkaline solution (for example, an aqueous NaOH solution, the concentration of which may be 4 to 20 wt%, and optionally 5 to 15 wt%), washed and purified, and then bleached (for example, using sodium hypochlorite and / or hydrogen peroxide), pickled and purified, washed and purified, water-repellent, and air-dried, thereby obtaining the cellulose powder.

[0115] In any embodiment of the present application, the fiber raw material may include at least one of plant fibers, such as cotton fibers (e.g., cotton wool fibers, cotton fiber), hemp fibers (e.g., sisal fibers, ramie fibers, jute fibers, flax fibers, hemp fibers, Manila hemp fibers, etc.), palm fibers, wood fibers, bamboo fibers, and grass fibers, and is preferably cotton fiber.

[0116] In any embodiment of the present application, in step S2, the acid solution may be an H2SO4 aqueous solution, an H3BO3 aqueous solution, or an H3PO4 aqueous solution, and the concentration of the acid solution may be 5 to 80 wt%.

[0117] When H2SO4 aqueous solution is selected, the concentration of the acid solution may be 40-80 wt%.

[0118] When H3BO3 aqueous solution is selected, the concentration of the acid solution may be 5-10 wt%.

[0119] When H3PO4 aqueous solution is selected, the concentration of the acid solution may be 45-75 wt%.

[0120] In any embodiment of the present application, in step S2, the mass ratio of the cellulose powder to the acid solution may be 1:2.5 to 1:50, and optionally 1:5 to 1:30.

[0121] When the H2SO4 aqueous solution is selected, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30.

[0122] When the H3BO3 aqueous solution is selected, the mass ratio of the cellulose powder to the acid solution may be 1:20 to 1:50.

[0123] When the H3PO4 aqueous solution is selected, the mass ratio of the cellulose powder to the acid solution may be 1:5 to 1:30.

[0124] In any embodiment of the present application, in step S2, the reaction may be carried out at a temperature of 80°C or less, or optionally at a temperature of 30 to 60°C.

[0125] In any embodiment of the present application, in step S2, the reaction time of the cellulose powder and the acid solution may be 0.5 to 3 hours, and optionally 1 to 2.5 hours.

[0126] In some embodiments, in step 3), the coating is performed using a coating device.

[0127] In the embodiment of the present application, there is no particular limitation on the model number of the coating device, and a commercially available coating device can be used.

[0128] In some embodiments, in step 3), the coating can be performed using a process such as transfer coating, spin coating, or dip coating.

[0129] In some embodiments, the coating device includes a gravure roll for transferring the coating slurry to the porous substrate.

[0130] In some embodiments, in step 3), the coating speed may be controlled to 30 m / min to 120 m / min, for example, 60 m / min to 90 m / min. When the coating speed is within this range, problems with the coating film surface can be effectively reduced, the probability of uneven coating can be reduced, and the energy density and safety performance of the battery can be further improved.

[0131] In some embodiments, in step 3), the linear velocity ratio of the coating may be controlled to 0.8 to 2.5, for example, 0.8 to 1.5, or 1.0 to 1.5.

[0132] In some embodiments, in step 3), the drying temperature may be 40°C to 70°C, for example, 50°C to 60°C.

[0133] In some embodiments, in step 3), the drying time may be 10 seconds to 120 seconds, for example, 20 seconds to 80 seconds, or 20 seconds to 40 seconds.

[0134] By controlling each of the above process parameters within a predetermined range, the performance of the separator of the present invention can be further improved. Those skilled in the art can selectively adjust one or more of the above process parameters according to the actual production situation.

[0135] The porous substrate, filler, cellulose powder, fiber raw material, non-particulate adhesive, etc. can all be obtained by purchasing from the market.

[0136] In the separator manufacturing method of the present invention, the coating is produced by a single application, which greatly simplifies the separator manufacturing process flow, and at the same time, by using the separator manufactured by the above method in a battery, the energy density and thermal stability of the battery can be effectively improved.

[0137] [Positive electrode] In a secondary battery, the positive electrode plate usually includes a positive electrode current collector and a positive electrode film layer provided on the positive electrode current collector and including a positive electrode active material.

[0138] The positive electrode current collector can be a conventional metal foil or a composite current collector (a composite current collector can be formed by providing a metal material on a polymer substrate.) For example, the positive electrode current collector can be an aluminum foil.

[0139] The specific type of the positive electrode active material is not limited, and any active material known in the art that can be used for the positive electrode of a secondary battery can be used. Those skilled in the art can select the material according to their actual needs.

[0140] For example, the positive electrode active material may include, but is not limited to, one or more of lithium-containing transition metal oxides, lithium-containing phosphates, and modified compounds thereof. Examples of lithium-containing transition metal oxides may include, but are not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof. Examples of lithium-containing phosphates may include, but are not limited to, lithium iron phosphate, lithium iron phosphate-carbon composite, lithium manganese phosphate, lithium manganese phosphate-carbon composite, lithium manganese iron phosphate, lithium manganese iron phosphate-carbon composite, and modified compounds thereof. All of these materials can be obtained commercially.

[0141] The modified compounds of the above-mentioned materials may be obtained by doping and / or surface coating the materials.

[0142] The positive electrode film layer usually further comprises optional adhesives, conductive agents, and other optional auxiliary agents.

[0143] By way of example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers.

[0144] By way of example, the adhesive may be one or more of styrene butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0145] [Negative electrode] In a secondary battery, the negative electrode plate usually includes a negative electrode current collector and a negative electrode film layer provided on the negative electrode current collector and including a negative electrode active material.

[0146] The negative electrode current collector can be a conventional metal foil or a composite current collector (e.g., a composite current collector can be formed by providing a metal material on a polymer substrate). For example, the negative electrode current collector can be a copper foil.

[0147] The specific type of the negative electrode active material is not limited, and active materials known in the art that can be used for secondary battery negative electrodes can be used. Those skilled in the art can select the material according to actual needs. For example, the negative electrode active material may include, but is not limited to, one or more of artificial graphite, natural graphite, hard carbon, soft carbon, silicon-based materials, and tin-based materials. The silicon-based material may be one or more selected from elemental silicon, silicon oxide (e.g., silicon monoxide), silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be one or more selected from elemental tin, tin-oxygen compounds, and tin alloys. All of these materials are commercially available.

[0148] In some embodiments, to further improve the energy density of the battery, the negative electrode active material may include a silicon-based material.

[0149] The negative electrode film layer usually further includes optional adhesives, conductive agents, and other optional auxiliary agents.

[0150] By way of example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0151] By way of example, the adhesive may be one or more of styrene butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0152] For example, other optional auxiliaries may be thickeners and dispersants (eg, sodium carboxymethylcellulose CMC-Na), PTC thermistor materials.

[0153] [Electrolyte] The secondary battery may include an electrolyte that functions to conduct ions between the positive electrode and the negative electrode. The electrolyte may include an electrolyte salt and a solvent.

[0154] By way of example, the electrolyte salt may be one or more selected from lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPOF), lithium bisoxalatodifluorophosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0155] By way of example, the solvent may be one or more selected from 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).

[0156] In some embodiments, the electrolyte solution further includes an additive, such as an additive that can improve certain battery performance, such as an additive that improves the overcharge performance of the battery, an additive that improves the high-temperature performance of the battery, or an additive that improves the low-temperature performance of the battery.

[0157] In some embodiments, the secondary battery may be a lithium ion secondary battery or a sodium ion secondary battery.

[0158] In the embodiment of the present application, there is no particular limitation on the shape of the secondary battery, and it may be cylindrical, rectangular, or any other shape. Figure 2 shows a secondary battery 5 having a rectangular structure as an example.

[0159] In some embodiments, the secondary battery may include an outer packaging that is used to hermetically encase the positive and negative plates and the electrolyte.

[0160] 3, in some embodiments, the outer packaging may include a case 51 and a cover plate 53. Specifically, the case 51 may include a base plate and side plates connected to the base plate, and the base plate and side plates surround and form a storage cavity. The case 51 has an opening communicating with the storage cavity, and the cover plate 53 may be installed to cover the opening to close the storage cavity.

[0161] The positive electrode plate, the negative electrode plate, and the separator can be wound or stacked to form an electrode assembly 52. ​​The electrode assembly 52 is sealed and packaged in the receiving cavity. The electrolyte may be an electrolytic solution impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 can be one or more, and can be adjusted as needed.

[0162] In some embodiments, the external packaging of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The external packaging of the secondary battery may be a flexible packaging material, such as a bag-type flexible packaging material. The material of the pouch may be plastic, and may include, for example, one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0163] In some embodiments, the secondary batteries may be assembled into a battery module, and the battery module may include multiple secondary batteries, the specific number of which may be adjusted depending on the application and capacity of the battery module.

[0164] Fig. 4 shows an example of a battery module 4. Referring to Fig. 4, in the battery module 4, the plurality of secondary batteries 5 may be arranged in order in the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed by fastening members.

[0165] The battery module 4 may further include a housing having an accommodating space, in which a plurality of secondary batteries 5 are accommodated.

[0166] In some embodiments, the battery modules may be further assembled into 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.

[0167] 5 and 6 show an example of a battery pack 1. Referring to FIGS. 5 and 6, the battery pack 1 may include a battery housing and a plurality of battery modules 4 provided in the battery housing. The battery housing includes an upper housing 2 and a lower housing 3, and the upper housing 2 is disposed over the lower housing 3, thereby forming an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery housing according to any method.

[0168] Electric power utilization equipment The present application further provides a power utilization device including at least one of the secondary battery, battery module, or battery pack. The secondary battery, battery module, or battery pack may be used as a power source for the power utilization device or as an energy storage unit for the power utilization device. The power utilization device may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop), an electric vehicle (e.g., a battery electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck), a train, a ship, a satellite, or an energy storage system.

[0169] The power utilization device can select a secondary battery, a battery module, or a battery pack according to its usage requirements.

[0170] 7 shows an example of a power utilization device, such as a battery electric vehicle, a hybrid vehicle, or a plug-in hybrid vehicle. To meet the high power and high energy density requirements of the secondary batteries of the power utilization device, a battery pack or battery module may be used.

[0171] Other examples of the power-utilizing device include a mobile phone, a tablet PC, and a notebook PC. Such power-utilizing devices are usually required to be lightweight and thin, and can use a secondary battery as a power source.

[0172] The effects of the present invention will be further explained below with reference to examples. [Example]

[0173] In order to clarify the technical problems, technical means, and effects solved by the embodiments of the present application, the following description will be made in more detail with reference to the embodiments and drawings. Obviously, the described embodiments are only some of the embodiments of the present application, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and does not impose any limitations on the present application and its applications. Any other embodiments that can be obtained by those skilled in the art based on the embodiments of the present application without any creative effort also fall within the scope of protection of the present application.

[0174] 1. Production of modified nanocellulose 1. Preparation of acid-modified cellulose S1. Preparation of cellulose powder: The cotton flock was opened using a cotton opener and the slag was removed. Then, it was steamed in a 5 wt% NaOH aqueous solution, washed and refined 3 to 6 times in sequence, bleached with sodium hypochlorite, pickled and refined, washed and refined, water-repellent, and air-dried, and cotton cellulose powder with a whiteness of ≥ 85% was obtained.

[0175] S2. Esterification of cellulose: 1 kg of the cotton cellulose powder obtained in step S1 was mixed with 30 kg of sulfuric acid solution (concentration: 60 wt%) and reacted for 2 hours at a temperature of 60°C. After the reaction was completed, the mixture was washed three times with water, filtered, and purified by deacidification to obtain nanofiber whiskers with sulfonated groups.

[0176] S3. Neutralization of cellulose: The pH of the sulfonated nanofiber whiskers was first adjusted to neutral using a 10% NaOH aqueous solution, and then they were dispersed by high-speed processing in a grinder for 2.5 hours. They were then cut into nanometer-sized pieces using a high-pressure homogenizer to obtain nanocellulose with sulfonate-modified groups. By adjusting the processing parameters using the grinder (e.g., the number of grinding times, as shown in Table 1) and the cutting parameters of the high-pressure homogenizer, modified nanocellulose with different average diameters, average lengths, and aspect ratios could be obtained. Water was added to prepare modified nanocellulose solutions of appropriate concentrations for preliminary use.

[0177] Following the same procedures as above, nanocellulose solutions modified with boronic acid groups, phosphate groups, and carboxyl groups were further prepared. The only difference between them was that to prepare nanocellulose modified with boronic acid groups, 7 wt% boronic acid was selected for oxidation and other reaction conditions remained unchanged; to prepare nanocellulose modified with phosphate groups, 70 wt% phosphoric acid was selected for oxidation and other reaction conditions remained unchanged; and to prepare nanocellulose modified with carboxyl groups, 60 wt% acetic acid was selected for oxidation and other reaction conditions remained unchanged.

[0178] 2. Preparation of alkali-modified cellulose S1. Preparation of cellulose powder: The cotton flock was opened using a cotton opener and the slag was removed, then it was steamed in a 5 wt% NaOH aqueous solution, washed and refined three times in sequence, bleached with sodium hypochlorite, pickled and refined, washed and refined, water-repellent, and air-dried to obtain cellulose powder with a whiteness of ≥ 85%. The cellulose powder was mixed with a 20 wt% sodium hydroxide aqueous solution at 10°C in a certain ratio, stirred for 2 hours, filtered and washed twice, and the cellulose powder was obtained.

[0179] S2. Preparation of cellulose carbamate: 50 g of the alkali cellulose powder obtained in step S1 and 200 g of urea were placed in a three-neck reactor equipped with an oil-water separator, heated to 137°C, and stirred for 4 hours. After the urea dissolved, 5 g of xylene was added. After the reaction was completed, the mixture was washed three times with water and filtered to obtain cellulose carbamate.

[0180] S3. Neutralization of cellulose sulfate: The cellulose carbamate obtained in S2 was dissolved in an appropriate 5 wt% NaOH solution to obtain a uniform cellulose carbamate solution, which was then dispersed by high-speed processing in a grinder for 2.5 hours and cut into nanometer-sized pieces in a high-pressure homogenizer to obtain nanocellulose with amino-modified groups. By adjusting the processing parameters in the grinder (e.g., the number of grinding times, as shown in Table 1) and the cutting parameters in the high-pressure homogenizer, modified nanocellulose with different average diameters, average lengths, and aspect ratios could be obtained. Water was added to prepare a modified nanocellulose solution of an appropriate concentration (e.g., 4.5 wt%) for preliminary use.

[0181] The ratio of modified group to hydroxyl group content in nanocellulose with modified groups produced using the following method was measured. Tests were conducted according to the phthalic anhydride method in the international standard GB / T12008.3-2009, and the hydroxyl values ​​(the number of milligrams of potassium hydroxide equivalent to the hydroxyl group content in 1 g of sample) of the raw cellulose and modified nanocellulose were obtained. The units of the obtained value are mg kOH / g, which can be converted to mmol / g as the hydroxyl group content. The modified group content (i.e., the content of modified hydroxyl groups) was obtained by subtracting the hydroxyl group content on the surface of the modified nanocellulose from the hydroxyl group content of the raw cellulose.

[0182] 2. Separator manufacturing Separator 1: 1) For example, a PE substrate having a thickness of 5 μm and a porosity of 37% was provided.

[0183] 2) Preparation of coating slurry: Aluminum oxide (Al2O3) as a filler, modified nanocellulose, and polyacrylate as a water-soluble non-particulate adhesive were uniformly mixed with an appropriate amount of ion-exchanged water as a solvent in a dry weight ratio of 79.2:20:0.8 to obtain a coating slurry. The type of modifying group contained in the modified nanocellulose, the ratio of modifying groups to hydroxyl groups, the average diameter, average length, and average aspect ratio of the nanocellulose are shown in Table 1 below.

[0184] 3) The coating slurry prepared in step 2) was applied to two surfaces of the PE substrate using an application device, and then dried and cut to obtain separator 1. The thickness of the single-side coating was 2 μm, and the weight of the single-side coating per unit area of ​​the separator was 1.0 g / m 2 FIG. 8 shows a scanning electron microscope (SEM) image of a cross section of a portion of the manufactured separator 1, and FIG. 9 shows a scanning electron microscope (SEM) image of the nanocellulose in the coating of the manufactured separator 1, which showed that the nanocellulose had formed a network structure in the coating.

[0185] All materials used in the examples can be obtained commercially. For example:

[0186] The PE substrate can be purchased from Shanghai Energy New Materials Co. Ltd.

[0187] Inorganic particles can be purchased from Estone Materials Technology Co., Ltd.

[0188] Alternatively, unmodified cellulose powder with a whiteness of ≧85% can be purchased from NORTHERN HUI TIAN CHEMICAL Co., Ltd., or produced by the above method.

[0189] The manufacturing methods for separators 2 to 24 and separator 1 are similar, but the differences lie in the type of modifying group contained in the modified nanocellulose, the ratio of the modifying group to the hydroxyl group content, and the average diameter, average length, and average aspect ratio of the nanocellulose, as shown in Table 1.

[0190] The length and diameter of the modified nanocellulose in the separator coating were measured using the following method. The micromorphology of the nanocellulose in the coating sample was plotted using a ZEISS Sigma 300 scanning electron microscope (SEM), with the high vacuum mode selected, the operating voltage set at 3 kV, and the magnification set at 30,000 times. Five data points were selected from the SEM scanning electron micrographs and averaged to determine the average length of the modified nanocellulose. The average diameter of the modified nanocellulose was calculated using Nano Measurer particle size distribution statistical software, with 20 data points selected and averaged to determine the average diameter of the modified nanocellulose.

[0191] 3. Secondary battery manufacturing Example 1 1. Manufacturing of positive electrode plates LiNi as the positive electrode active material0.8 Co 0.1 Mn 0.1 O2 (NCM811), carbon black (Super P) as a conductive agent, and polyvinylidene fluoride (PVDF) as an adhesive were mixed uniformly in a mass ratio of 96.2:2.7:1.1 with an appropriate amount of N-methylpyrrolidone (NMP) as a solvent to obtain a positive electrode slurry. The positive electrode slurry was applied to an aluminum foil positive electrode current collector, and then dried, cold pressed, slit, and cut to obtain a positive electrode plate. The areal density of the positive electrode was 0.207 mg / mm 2 and the compact density is 3.5 g / cm 3 It was.

[0192] 2. Manufacturing of negative electrode plates The negative electrode active material was artificial graphite, the conductive agent was carbon black (Super P), and the adhesives were styrene butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC-Na) in a mass ratio of 96.4:0.7:1.8:1.1. The mixture was uniformly mixed with an appropriate amount of ion-exchanged water as a solvent to obtain a negative electrode slurry. The negative electrode slurry was then applied to a copper foil negative electrode current collector, dried, cold-pressed, slit, and cut to obtain a negative electrode plate. The areal density of the negative electrode was 0.126 mg / mm 2 and the compact density is 1.7 g / cm 3 It was.

[0193] 3. Separator The separator used was the separator 1 produced above.

[0194] 4. Electrolyte production Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 30:70 to obtain an organic solvent. Well-dried electrolyte salt LiPF6 was dissolved in the mixed solvent to obtain an electrolyte salt concentration of 1.0 mol / L. After uniform mixing, an electrolyte solution was obtained.

[0195] 5. Secondary battery manufacturing The positive electrode plate, separator, and negative electrode plate were stacked in this order, and a separator was placed between the positive and negative electrodes to separate them, and then the stack was wound to obtain an electrode assembly. The electrode assembly was placed in an outer package, and the prepared electrolyte was injected into the dried secondary battery. The secondary battery was then vacuum-packaged, left to stand, chemically formed, and shaped, and the result was a secondary battery.

[0196] The manufacturing methods of the secondary batteries of Examples 2 to 21 and Comparative Examples 1 to 3 and the secondary battery of Example 1 are similar, but the difference is that different separators are used, as shown in Table 1 (Note: When adjusting the content of modified nanocellulose in the coating, the content of the filler can be adjusted at the same time while the content of the adhesive remains unchanged).

[0197] 4. Separator and battery performance testing 1. Separator heat shrinkage rate test 1) Sample preparation: Separator samples 50 mm wide and 100 mm long were punched using a press, and five parallel samples were placed on A4 paper and fixed in place. The A4 paper with the samples attached was then placed on a cardboard box 1 to 5 mm thick.

[0198] 2) Sample testing: The A4 paper placed on the cardboard was placed in a forced air hot box with the temperature set to 150°C. After the temperature reached the set temperature and stabilized for 30 minutes, timing began. After the set time was reached, the length and width of the separator were measured and the values ​​were marked as a and b respectively.

[0199] 3) Calculation of heat shrinkage rate: Longitudinal shrinkage rate A=(100-a) / 100*100%; Transverse shrinkage rate B=(50-b) / 50*100%;

[0200] The values ​​A and B were recorded and the average values ​​of the five samples were taken.

[0201] 2. Measure the time it takes for leakage current to appear when the separator is at 65°C and 4.3V.

[0202] 1) Discharged to 2.8V at a constant current of 0.2C.

[0203] 2) Allowed to stand for 30 minutes.

[0204] 3) The battery was initially charged at a constant current of 0.5C up to 4.3V, and then charged at a constant voltage down to 0.05C.

[0205] 4) Allowed to stand for 30 minutes.

[0206] 5) The battery was initially charged at a constant current of 0.2C up to 4.3V, and then charged at a constant voltage down to 0.02C.

[0207] 6) In the constant voltage charging step, the initial current was set to 0.02 C, the voltage was maintained at 4.3 V, and this was maintained for 120 days, and the current was monitored and recorded until leakage current appeared.

[0208] 7) The test was completed and the time when the separator leakage current appeared was recorded.

[0209] 3. Separator impregnation performance test 1) Preparation of sample pieces: The sample was cut into separator samples 5 mm wide and 100 mm long using a sample cutter to obtain five parallel samples, and both ends of the samples were attached parallel to a metal frame.

[0210] 2) Preparation of electrolyte solution: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of 3:5:2 to obtain a mixed solvent. Well-dried electrolyte salt LiPF6 was dissolved in the mixed solvent to obtain an electrolyte salt concentration of 1.0 mol / L. After uniform mixing, an electrolyte solution was obtained.

[0211] 3) Impregnation test: Take 0.5 mg of the prepared electrolyte and drop it onto the center of the sample piece fixed on the metal frame, start timing, and 1 minute after the set time has passed, take a photo and measure the length of diffusion of the electrolyte, mark it as a, and take the average value of the measurement results of five samples.

[0212] 4. Hot box test of secondary batteries At 25°C, the secondary batteries manufactured in the examples and comparative examples were charged at a constant current of 1C to a maximum charging voltage of 4.2V, then charged at a constant voltage until the current reached ≤0.05C and allowed to stand for 5 minutes. Each battery was then tested in a DHG-9070A DHG series high-temperature oven using a jig. The temperature was increased from room temperature to 80°C ±2°C at a rate of 5°C / min and maintained at this temperature for 30 minutes. The temperature was then increased at a rate of 5°C / min, and maintained for 30 minutes at each 5°C increase until the battery failed. The temperature at which the battery began to fail was recorded.

[0213] [Table 1] TIFF0007778162000002.tif248167TIFF0007778162000003.tif248167

[0214] As can be seen from Table 1, in Examples 1 to 21, nanocellulose containing specific modified groups was used as part of the separator coating, which significantly reduced the thermal shrinkage of the separator compared to Comparative Examples 1 to 3. The thermal shrinkage of the produced separators at 150°C for 1 hour was 3% or less, significantly improved the separator's electrolyte impregnation performance (under the test conditions, the separator's wetting length at 1 minute was ≥ 20 mm, the wetting length at 1 minute for the separator of Comparative Example 1 did not exceed 5 mm, and the wetting length at 1 minute for the separators of Comparative Examples 2 and 3 did not exceed 10 mm). This significantly extended the time until leakage current appeared at 65°C and 4.3 V. Furthermore, the ionic conductivity and thermal stability of secondary batteries produced from such separators were significantly improved. As shown in Table 1, the hot box failure temperatures of the batteries produced in Examples 1 to 21 were generally 125°C or higher. In particular, by further selecting parameters such as the ratio of modified groups to hydroxyl groups in the modified nanocellulose, the diameter, length, and aspect ratio of the modified nanocellulose, and the content of modified nanocellulose in the coating, the thermal stability of the separator and the thermal stability of the battery can be further improved. For example, when the ratio of modified groups to hydroxyl groups in the modified nanocellulose is 2:3 to 7:3 and the content of modified nanocellulose in the coating is in the range of 10 to 25 wt%, the thermal shrinkage of the separator at 150°C after 1 hour can be further reduced to 1.7% or less, and the hot box fail temperature of the secondary battery manufactured therefrom can be improved to 137°C or higher. Meanwhile, because the coating containing modified nanocellulose in the separator provided by the present invention has excellent thermal stability and ionic conductivity, the thickness of the separator substrate and the coating can be reduced to a certain extent, further improving the energy density of the battery while maintaining thermal stability.

[0215] The present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and all embodiments that have substantially the same configuration as the technical idea and exhibit similar effects within the scope of the technical means of the present application are included in the technical scope of the present application. Furthermore, various modifications that a person skilled in the art can make to the embodiments without departing from the scope of the gist of the present application, and other methods of constructing by combining some of the components in the embodiments, are also included in the scope of the present application.

Claims

1. A porous substrate; and a coating provided on at least one surface of the porous substrate, the coating comprising nanocellulose containing a modifying group comprising at least one of a sulfonic acid group, a boronic acid group, and a phosphate group; The nanocellulose further contains hydroxy groups, and the content ratio of the modified groups to the hydroxy groups is 1:4 to 4:1; A separator characterized by:

2. The average diameter of the nanocellulose is ≦40 nm; The separator according to claim 1 .

3. The average length of the nanocellulose is 100 to 600 nm; The separator according to claim 1 .

4. The aspect ratio of the nanocellulose is 5 to 60. The separator according to claim 1 .

5. The equilibrium degree of polymerization range of the nanocellulose is 150 to 300 DP, and / or The molecular weight of the nanocellulose is 20,000 to 60,000. The separator according to claim 1 .

6. The shape of the nanocellulose is one or more selected from tubular, fibrous, and rod-shaped. The separator according to claim 1 .

7. The separator exhibits leakage current for ≥12 days at 65°C and 4.3V. The separator according to claim 1 .

8. The content of the nanocellulose in the coating is ≧5 wt %; The separator according to claim 1 .

9. The coating further comprises a filler comprising at least one of inorganic particles, organic particles, and organic-inorganic hybrid particles. The separator according to claim 1 .

10. The thickness of the porous substrate is ≦12 μm, and / or The thickness of the coating is ≦3 μm. The separator according to claim 1 .

11. The separator satisfies one or more of the following (1) to (6): The separator according to claim 1 . (1) The separator has a thermal shrinkage rate of ≦5% after 1 hour at 150° C. (2) The wet length of the separator in 1 minute is ≧20 mm. (3) The peel strength of the separator is ≧0.5 N / m. (4) The separator has a transverse tensile strength (MD) of ≥ 2000 kg / cm ２ That is. (5) The separator has a longitudinal tensile strength (TD) of ≥ 2000 kg / cm ２ That is. (6) The separator has an air permeability of ≦300 s / 100 mL.

12. An adhesive layer containing a particulate organic adhesive is further provided on at least a portion of the surface of the coating. The separator according to claim 1 .

13. 1) providing a porous substrate; 2) mixing the modified nanocellulose with a solvent in a predetermined ratio to provide a slurry of the coating to be prepared; 3) applying the coating slurry to at least one surface of the substrate and, after drying, obtaining a separator, The separator obtained after drying comprises a porous substrate and a coating provided on at least one surface of the porous substrate, wherein the coating comprises modified nanocellulose containing at least one modifying group selected from a sulfonic acid group, a boronic acid group, and a phosphate group. The method for manufacturing a separator according to claim 1 .

14. The modified nanocellulose is produced by the following method: The method for manufacturing a separator according to claim 13. S1: Prepare cellulose powder with a whiteness of ≥ 85%. S2: The cellulose powder is mixed with an acid solution to cause a reaction, and then the resulting mixture is deacidified and purified to obtain nanofiber whiskers having modified groups. S3: Adjusting the pH of the nanofiber whiskers having the modifying group to neutral, and polishing and cutting them to obtain the modified nanocellulose.

15. In step S1, the alkaline solution is an aqueous NaOH solution, and the concentration of the alkaline solution is 4 to 20 wt %; and / or In step S2, the acid solution is ２ SO ４ Aqueous solution, H ３ BO ３ Aqueous solution or H ３ P.O. ４ an aqueous solution, the concentration of the acid solution being 5 to 80 wt %; and / or In step S2, the mass ratio of the cellulose powder to the acid solution is 1:2.5 to 1:50; and / or In step S2, the reaction is carried out at a temperature of ≦80° C. for 0.5 to 3 hours. The method for manufacturing a separator according to claim 14.

16. The separator according to any one of claims 1 to 12, A secondary battery characterized by:

17. The secondary battery according to claim 16, 1. A power utilization device comprising:

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