Battery cell, separator, battery device, and electric device

Abstract

Embodiments of the present application provide a battery monomer, a separator, a battery device and a power utilization device. The battery monomer comprises a separator arranged between a negative electrode sheet and a positive electrode sheet; the separator comprises: a porous base film; a first coating layer arranged on the side of the porous base film close to the negative electrode sheet; and a second coating layer arranged on the side of the porous base film close to the positive electrode sheet; wherein the separator satisfies: ε 13 > ε 2； ε1 represents the average porosity of the first coating layer, ε2 represents the average porosity of the second coating layer, ε3 represents the average porosity of the porous base film, and ε 13 represents the average porosity of the first coating layer and the porous base film. The battery monomer of the present application has good reliability and prolongs the cycle life of the battery monomer.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a battery cell, a separator, a battery device, and an electrical device. Background Technology

[0002] In recent years, battery cells have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. With the increasing application and promotion of battery cells, the requirements for their reliability are becoming increasingly stringent.

[0003] Therefore, improving the reliability of individual battery cells is a problem that needs to be solved in this field. Summary of the Invention

[0004] This application provides a battery cell, a separator, a battery device, and an electrical device, which improves the reliability of the battery cell and extends its cycle life.

[0005] This application provides a battery cell including a separator disposed between a negative electrode and a positive electrode. The separator includes: a porous base film; a first coating disposed on the porous base film near the negative electrode; and a second coating disposed on the porous base film near the positive electrode. The separator satisfies the following condition: ε 13 >ε2 represents the average porosity of the second coating, and ε13 represents the average porosity of the first coating and the porous base film.

[0006] According to the embodiments of this application, during the electrochemical cycling process of a battery cell, the average porosity (ε) of the first coating and the porous base film near the negative electrode sheet is... 13 The average porosity (ε2) of the first coating is higher than that of the second coating near the positive electrode, which is beneficial for active ions such as sodium ions to pass through the separator from the negative electrode side. This facilitates the transport and deintercalation of active ions between the positive and negative electrodes, reduces dendrite formation in the first coating near the negative electrode, lowers the probability of short circuit in the battery cell, improves the reliability of the battery cell, and also improves the cycle life of the battery cell.

[0007] In some optional embodiments, the average porosity ε1 of the first coating is greater than the average porosity ε2 of the second coating. This greater average porosity ε1 of the first coating facilitates the passage of active ions, such as sodium ions, through the separator from the negative electrode side, enabling the transport and deintercalation of active ions between the positive and negative electrodes. It also helps reduce dendrite formation in the first coating near the negative electrode side, lowering the probability of short circuits in the battery cell and improving its reliability.

[0008] In some optional embodiments, the average porosity ε3 of the porous base film is greater than the average porosity ε2 of the second coating. The fact that the average porosity ε3 of the porous base film is greater than the average porosity ε2 of the second coating indicates that the average porosity ε3 is greater than the average porosity ε2 of the second coating, which extends the growth path of dendrites in the separator film, reduces the phenomenon that dendrites grow in the pores of the separator film and pierce the separator film, improves the short-circuit phenomenon of the battery cell, and enhances the reliability of the battery cell.

[0009] In some optional embodiments, the ratio a of the average porosity εl of the first coating to the average porosity ε2 of the second coating satisfies 1 < a ≤ 1.5. Thereby, it is beneficial for active ions such as sodium ions to pass through the separator film from the side of the negative electrode plate, that is, to pass through the separator film from the first coating, realizing the transmission and insertion / extraction of active ions between the positive electrode plate and the negative electrode plate, reducing the probability of short circuit of the battery cell, and enhancing the reliability of the battery cell.

[0010] In some optional embodiments, the average porosity ε2 of the second coating is 30% to 50%.

[0011] In some optional embodiments, the average porosity εl of the first coating is 40% to 60%.

[0012] In some optional embodiments, the average porosity ε3 of the porous base film is 30% to 55%.

[0013] In some optional embodiments, the average pore size rl of the first coating is greater than the pore size r2 of the second coating. Thereby, the average pore size rl of the first coating is greater than the pore size r2 of the second coating 2， It is beneficial for active ions to pass through the first coating on the side close to the negative electrode plate, reducing the crystallization phenomenon caused by the unsmooth passage of active ions through the separator film.

[0014] In some optional embodiments, the ratio b of the average pore size rl of the first coating to the pore size r2 of the second coating satisfies 1 < b ≤ 4. When the ratio b of the average pore size rl of the first coating to the pore size r2 of the second coating is within the above range, it is beneficial for active ions to pass through the first coating on the side close to the negative electrode plate, reducing the crystallization phenomenon caused by the unsmooth passage of active ions through the separator film, reducing the probability of short circuit of the battery cell, and enhancing the reliability of the battery cell.

[0015] In some optional embodiments, the average pore size r2 of the second coating is 30 nm to 70 nm.

[0016] In some optional embodiments, the average pore size rl of the first coating is 100 nm to 300 nm.

[0017] In some optional embodiments, the average pore size r3 of the porous base film is 40 nm to 150 nm.

[0018] In some optional embodiments, the tortuosity τ of the separator is 1 to 3, optionally 1.5 to 2.1. The tortuosity τ of the separator can be any value or a range of combinations thereof from 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, and 3. According to embodiments of this application, when the tortuosity τ of the separator is within the above range, it indicates that the separator has a suitable tortuosity, reducing the presence of through-holes in the separator, extending the growth path of dendrites, reducing the phenomenon of dendrites growing in the pores of the separator and piercing the separator, improving the short-circuit phenomenon of the battery cell, and improving the reliability of the battery cell.

[0019] In some optional embodiments, the tortuosity τ1 of the first coating is 1.2 to 2.2. A tortuosity τ1 within this range indicates that the first coating has a suitable tortuosity, which extends the dendrite growth path, reduces the phenomenon of dendrites growing in the pores of the separator and piercing the separator, improves the short-circuit phenomenon of the battery cell, and enhances the reliability of the battery cell.

[0020] In some optional embodiments, the tortuosity τ3 of the porous base membrane is 1.4 to 1.8. A tortuosity τ3 within this range indicates that the porous base membrane has suitable tortuosity, which extends the growth path of dendrites, reduces the phenomenon of dendrites growing in the pores of the separator and piercing the separator, improves the short-circuit phenomenon of the battery cell, and enhances the reliability of the battery cell.

[0021] In some optional embodiments, the tortuosity τ2 of the second coating is between 1 and 1.5. A tortuosity τ2 within this range elongates the dendrite growth path, reduces the phenomenon of dendrites growing in the pores of the separator and piercing the separator, improves the short-circuit phenomenon of the battery cell, and enhances the reliability of the battery cell.

[0022] In some optional embodiments, the ratio c of the thickness of the first coating and the thickness of the second coating is 1 to 2. A ratio of the thickness of the first coating to the thickness of the second coating within this range is beneficial for the separator to have suitable tortuosity while maintaining a suitable average porosity. This makes the path of active ions through the separator more complex and tortuous. Furthermore, the appropriate coating thickness can, to some extent, block dendrite growth and penetration, reducing the risk of battery short circuits and improving the reliability of the battery cell.

[0023] In some alternative embodiments, the thickness of the first coating is 1 to 3 μm.

[0024] In some optional embodiments, the thickness of the porous base film is 5 to 15 μm.

[0025] In some alternative embodiments, the thickness of the second coating is 1 to 3 μm.

[0026] In some alternative embodiments, the first coating comprises, by weight percentage, 5% to 15% of a first binder and 85% to 95% of a first inorganic filler, optionally 8% to 10% of the first binder and 90% to 92% of the first inorganic filler.

[0027] In some alternative embodiments, the second coating comprises, by weight percentage, 5% to 15% of a second binder and 85% to 95% of a second inorganic filler, optionally 8% to 10% of a second binder and 90% to 92% of a second inorganic filler.

[0028] In some alternative embodiments, the first adhesive and the second adhesive respectively comprise one or more of polypropylene, polyethylene glycol, polyvinyl alcohol, polystyrene, and ethylene propylene diene monomer (EPDM) rubber.

[0029] In some optional embodiments, the first inorganic filler and the second inorganic filler respectively include one or more of boehmite, alumina, aluminum oxide, silicon dioxide and zirconium oxide.

[0030] In some optional embodiments, the first inorganic filler volume particle size Dv 1 50 and the volumetric particle size Dv of the second inorganic filler 2 The ratio d of 50 ranges from 1.25 to 12.5. The first inorganic filler's volumetric particle size Dv 1 50 and the volumetric particle size Dv of the second inorganic filler 2 A ratio of 50 within the above range is beneficial for the first and second coatings in the separator to have the above-mentioned average porosity, tortuosity, and average pore size, thereby reducing the phenomenon of dendrites growing in the pores of the separator and piercing the separator, improving the short circuit phenomenon of the battery cell, and improving the reliability of the battery cell.

[0031] In some optional embodiments, the first inorganic filler volume particle size Dv 1 50 is 0.2μm to 0.5μm. The first inorganic filler volumetric particle size Dv 1 Within the aforementioned range, it is advantageous to ensure that the first coating in the separator has the aforementioned average porosity and average pore size, thereby reducing the phenomenon of dendrites growing in the pores of the separator and piercing the separator, improving the short circuit phenomenon of the battery cell, and enhancing the reliability of the battery cell.

[0032] In some optional embodiments, the volumetric particle size Dv of the second inorganic filler 2 50 ranges from 0.04 μm to 0.16 μm. The volumetric particle size Dv of the second inorganic filler... 2Within the aforementioned range, 50 is advantageous for the second coating to have the aforementioned average porosity and tortuosity, thereby improving the performance of the battery cell.

[0033] In some alternative embodiments, the first coating further includes inorganic particles, including one or more of silicon dioxide, magnesium chloride, and ferric chloride.

[0034] According to the embodiments of this application, the first coating has the above-mentioned inorganic particles, which can react with some of the dendrites formed in the first coating to dissolve some of the metal dendrites, such as sodium dendrites or lithium dendrites, thereby reducing the phenomenon of dendrites piercing the separator, improving the short circuit phenomenon of the battery cell, and improving the reliability of the battery cell.

[0035] In some alternative embodiments, the inorganic particles constitute 5% to 10% by mass in the first coating.

[0036] According to the embodiments of this application, the mass percentage of inorganic particles in the first coating is within the above-mentioned range. While taking into account the performance of the separator in the battery cell, it can dissolve some of the dendrites that may exist in the first coating, reduce the phenomenon of dendrites piercing the separator, improve the short circuit phenomenon of the battery cell, and improve the reliability of the battery cell.

[0037] In some alternative embodiments, the negative electrode sheet includes a negative current collector and a base coating disposed on at least one side of the negative current collector. When a battery cell includes such a negative electrode sheet, the uncontrolled growth of dendrites on the separator side near the negative electrode sheet is more severe, increasing the risk of dendrites penetrating the separator and causing a short circuit. The separator used in the embodiments of this application improves the reliability of the battery cell.

[0038] Secondly, embodiments of this application provide a separator, comprising: a porous base membrane; a first coating layer disposed on the porous base membrane near the negative electrode sheet; and a second coating layer disposed on the porous base membrane near the positive electrode sheet; wherein the separator satisfies: ε 13 >ε 2； ε2 represents the average porosity of the second coating, ε 13 This represents the average porosity of the first coating and the porous base film.

[0039] The average porosity of the first coating and the porous base film on the side of the separator closer to the negative electrode is higher than that of the second coating closer to the positive electrode (ε). 13 >ε2), during the electrochemical cycle of the battery cell, it is beneficial for active ions such as sodium ions to pass through the separator from the negative electrode side, realizing the transport and deintercalation of active ions in the positive and negative electrodes. This helps to reduce the formation of dendrites in the first coating on the side close to the negative electrode, reduces the probability of short circuit in the battery cell, improves the reliability of the battery cell, and also improves the cycle life of the battery cell.

[0040] Thirdly, embodiments of this application provide a battery device including the battery cell of the first aspect. The battery device includes the aforementioned battery cell and therefore possesses at least the beneficial effects of the battery cell.

[0041] Fourthly, embodiments of this application provide an electrical device that includes the battery device of the third aspect. This battery device includes the aforementioned battery device and therefore possesses at least the beneficial effects of a battery device. Attached Figure Description

[0042] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0043] Figure 1 The diagram shows a schematic of a battery cell provided in some embodiments of this application.

[0044] Figure 2 An exploded view of a battery cell provided in some embodiments of this application is shown.

[0045] Figure 3 This document shows schematic diagrams of battery modules provided in some embodiments of this application.

[0046] Figure 4 This illustration shows a schematic diagram of a battery pack provided in some embodiments of this application.

[0047] Figure 5 yes Figure 4 The diagram shown is an exploded view of the battery pack.

[0048] Figure 6 A schematic diagram of an electrical device provided in some embodiments of this application is shown.

[0049] The accompanying drawings are not necessarily drawn to scale.

[0050] The reference numerals in the attached drawings are explained as follows: 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Cover plate. Detailed Implementation

[0051] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, separator, battery assembly, and power-consuming device of this disclosure. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this disclosure and are not intended to limit the subject matter of the claims.

[0052] The "range" disclosed in this disclosure is defined by a lower limit and an upper limit, whereby a given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this disclosure, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥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.

[0053] Unless otherwise specified, all embodiments and optional embodiments of this disclosure may be combined with each other to form new technical solutions, and such technical solutions should be considered as included in the disclosure of this disclosure.

[0054] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions, and such technical solutions should be considered as included in the disclosure of this disclosure.

[0055] Unless otherwise specified, all steps of this disclosure may be performed sequentially or randomly, preferably sequentially. For example, if a method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if it is mentioned that the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0056] Unless otherwise specified, in this disclosure, the terms "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0057] In this application, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0058] In the embodiments of this application, the same reference numerals denote the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the thickness, length, width, and other dimensions of various components in the embodiments of this application shown in the accompanying drawings, as well as the overall thickness, length, width, and other dimensions of the integrated device, are merely illustrative and should not constitute any limitation on this application.

[0059] In this application, "multiple" refers to two or more (including two). Similarly, "various kinds" refers to two or more (including two), and "multiple items" refers to two or more (including two).

[0060] In this application, the battery cell may include a lithium-ion secondary battery cell, a lithium-ion primary battery cell, a lithium-sulfur battery cell, a sodium-lithium-ion battery cell, a sodium-ion battery cell, or a magnesium-ion battery cell, etc., and the embodiments of this application are not limited thereto. The battery cell may be cylindrical, flat, cuboid, or other shapes, etc., and the embodiments of this application are not limited thereto.

[0061] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0062] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0063] Unless otherwise stated, the testing instruments mentioned in this application shall be used in accordance with the requirements of the product specification sheet.

[0064] The battery mentioned in the embodiments of this application can be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, or battery packs.

[0065] A battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. A battery cell can be cylindrical, cuboid, or other shapes, etc., and the embodiments of this application are not limited in this respect. Figure 1 The example shown is a rectangular battery cell 5.

[0066] When there are multiple battery cells, they are connected in series, parallel, or mixed via a busbar. In some optional embodiments, the battery can be a battery module; when there are multiple battery cells, they are arranged and fixed to form a battery module. In some optional embodiments, the battery can be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed within the housing. In some optional embodiments, the housing can be part of the vehicle's chassis structure. For example, a portion of the housing can be at least part of the vehicle's floor, or a portion of the housing can be at least part of the vehicle's crossbeams and longitudinal beams.

[0067] In some alternative embodiments, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0068] A single battery cell generally includes an electrode assembly and an electrolyte. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of this application are not limited in this regard.

[0069] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode components and electrolyte. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0070] In some alternative embodiments, such as Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted according to requirements.

[0071] In some alternative embodiments, individual battery cells can be assembled into a battery module, and the number of individual battery cells contained in the battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module. Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0072] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0073] In some alternative embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0074] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the housing.

[0075] The battery cells provided in the embodiments of this application can be metal battery cells, such as lithium metal battery cells, negative electrode-free lithium metal battery cells, sodium metal battery cells, negative electrode-free sodium metal battery cells, etc.

[0076] A negative electrode-free battery cell typically refers to a battery cell in which no negative electrode active material layer is actively placed on the negative electrode side during the battery cell manufacturing process. For example, the negative electrode active material layer is not formed at the negative electrode through coating or deposition processes, nor is it formed by a carbonaceous active material layer. During the first charge, ions gain electrons on the negative electrode side and deposit metal on the surface of the negative electrode current collector. During discharge, the metal can be converted back into ions and return to the positive electrode, achieving cyclic charging and discharging. Compared to other battery cells, a negative electrode-free battery cell can achieve a higher energy density due to the absence of a negative electrode active material layer. In some optional embodiments, to improve the performance of the battery cell, some conventional materials that can be used as negative electrode active materials, such as carbon materials, can also be placed on the negative electrode side of the negative electrode-free battery cell. Although these materials have a certain capacity, because their content is small and they are not used as the main negative electrode active material in the battery cell, the battery cell constructed in this way can still be considered a negative electrode-free battery cell. The Cell Balance (CB) value of a negative electrode-free battery cell is typically very small; for example, in some alternative embodiments, the CB value of a negative electrode-free battery cell can be less than or equal to 0.1. The CB value is the capacity per unit area of ​​the negative electrode divided by the capacity per unit area of ​​the positive electrode in the battery cell. Because a negative electrode-free battery cell contains little or no negative electrode active material, the capacity per unit area of ​​the negative electrode is small, and therefore the CB value is very small, typically less than or equal to 0.1.

[0077] A single battery cell includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator located between the positive and negative electrode.

[0078] During electrochemical cycling, dendrites, such as lithium dendrites, inevitably form on the negative electrode side of a battery cell. These dendrites pierce the separator, increasing the risk of short circuits and affecting battery reliability. This is especially true for metal-free negative electrode cells, where the negative electrode typically includes a current collector and may have an undercoating. In these cells, the uncontrolled growth of negative electrode dendrites is more severe during electrochemical cycling, further increasing the risk of dendrites penetrating the separator and causing short circuits.

[0079] Research has revealed that when disassembling a short-circuited battery cell, dendrites were found to penetrate the separator. The average pore size of this type of separator coating is about 36 nm, and the deposited dendrites have a high aspect ratio. This type of short circuit usually occurs after more than 100 cycles, resulting in a low cycle life of the battery cell.

[0080] Based on this, this application provides a battery cell in which the separator has different average porosities on both the positive and negative sides of the battery cell, reducing dendrite growth in the separator pores, improving the short circuit phenomenon of the battery cell, and increasing the reliability of the battery cell; it also improves the cycle life of the battery cell.

[0081] This application provides a separator that can be used in metal batteries, such as lithium metal batteries, negative electrode-free lithium metal batteries, sodium metal batteries, negative electrode-free sodium metal batteries, etc., which can improve the reliability of battery cells and increase the cycle life of battery cells.

[0082] In some alternative embodiments, the separator membrane includes:

[0083] Porous base membrane;

[0084] The first coating is disposed on the side of the porous base film near the negative electrode sheet;

[0085] The second coating is disposed on the side of the porous base film near the positive electrode sheet;

[0086] Among them, the isolation membrane satisfies: ε 13 >ε2, where ε2 represents the average porosity of the second coating, ε 13 This represents the average porosity of the first coating and the porous base film.

[0087] According to embodiments of this application, during the electrochemical cycling of a battery cell, dendrites typically begin to form on the negative electrode side, resulting in a higher concentration of active ions on the separator side near the negative electrode. Consequently, the average porosity ε of the first coating and the porous base film on the separator side near the negative electrode is... 13 The average porosity of the second coating, which is closer to the positive electrode, is ε2 higher than that of the second coating. 13 >ε2 facilitates the passage of active ions, such as sodium ions, through the separator from the negative electrode side, enabling the transport and deintercalation of active ions between the positive and negative electrodes. This also helps reduce the formation of dendrites in the first coating near the negative electrode, reducing the probability of short circuits in the battery cell, improving the reliability of the battery cell, and increasing the cycle life of the battery cell.

[0088] The average porosity ε3 and average pore size r3 of the porous base membrane have meanings known in the art and can be measured using methods known in the art. For example, the test can be performed using a mercury porosimeter according to GB / T21650.1-2008. Alternatively, the test can be performed according to GB / T21650.2-2008, Determination of Pore Size Distribution and Porosity of Materials by Mercury Porosimeter and Gas Adsorption Methods Part 2: Analysis of Mesopores and Macropores by Gas Adsorption Method.

[0089] The average porosity ε1 of the first coating and the average porosity ε2 of the second coating have meanings known in the art and can be tested using methods known in the art. For example, using a Micromeritics AccuPycII 1340 fully automatic true density analyzer, referring to the national standard GB / T 24586-2009, the gas displacement method is employed for measurement. Average porosity = (V1-V2) / V1*100%, where V1 is the apparent volume of the sample and V2 is the true volume of the sample.

[0090] ε 13 This represents the average porosity of the first coating and the porous base film. As an example, ε... 13 The testing method includes: removing the second coating from the separator, then measuring the separator consisting only of the first coating and the porous base membrane using a Micromeritics AccuPyc II 1340 fully automated true density tester, referring to the national standard GB / T 24586-2009, using the gas displacement method. ε is calculated using the formula. 13 Average porosity = (V1-V2) / V1*100%, where V1 is the apparent volume of the sample and V2 is the actual volume of the sample.

[0091] The average pore size r1 of the first coating and the pore size r2 of the second coating can be measured using methods known in the art. For example, a TriStar II 3020 automatic adsorption analyzer can be used. Specific test methods can be found in the standards GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Materials by Gas Adsorption BET Method" and GB / T 21650.2-2008 "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Intrusion Porosimetry and Gas Adsorption Method".

[0092] In some optional embodiments, the average porosity ε1 of the first coating is greater than the average porosity ε2 of the second coating. This greater average porosity ε1 of the first coating facilitates the passage of active ions, such as sodium ions, through the separator from the negative electrode side, enabling the transport and deintercalation of active ions between the positive and negative electrodes. It also helps reduce dendrite formation in the first coating near the negative electrode side, lowering the probability of short circuits in the battery cell and improving its reliability.

[0093] In some optional embodiments, the average porosity ε3 of the porous base film is greater than the average porosity ε2 of the second coating. The greater average porosity ε3 of the porous base film also extends the growth path of dendrites in the separator, reducing the phenomenon of dendrites growing in the pores of the separator and piercing it, thus improving the short-circuit phenomenon of the battery cell and enhancing its reliability.

[0094] In some optional embodiments, the ratio a of the average porosity ε1 of the first coating and the average porosity ε2 of the second coating satisfies 1 < a ≤ 1.5. Optionally, a can be any value or a range of combinations thereof from 1.01, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5.

[0095] This facilitates the passage of active ions, such as sodium ions, through the separator from the negative electrode side, i.e., through the first coating layer, enabling the transport and deintercalation of active ions between the positive and negative electrodes, reducing the probability of short circuits in individual battery cells and improving the reliability of individual battery cells.

[0096] In some optional embodiments, the average porosity ε2 of the second coating is 30% to 50%. Optionally, the average porosity ε2 of the second coating can be any value or a range of combinations thereof from 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, and 50%.

[0097] In some optional embodiments, the average porosity ε1 of the first coating is 40% to 60%. Optionally, the average porosity ε1 of the first coating can be any value or a range of combinations thereof from 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, and 60%.

[0098] In some optional embodiments, the average porosity ε3 of the porous base membrane is 30% to 55%. Optionally, the average porosity ε3 of the porous base membrane can be any value or a range of combinations thereof from 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, and 55%.

[0099] In some alternative embodiments, the average pore size r1 of the first coating is greater than the pore size r2 of the second coating. Generally, dendrites begin to form on the negative electrode side, and the active ion concentration is higher on the side of the separator closer to the negative electrode. Therefore, the average pore size r1 of the first coating is greater than the pore size r2 of the second coating. 2， This facilitates the passage of active ions through the first coating on the side closest to the negative electrode, reducing crystallization caused by obstructed passage of active ions through the separator.

[0100] In some optional embodiments, the ratio b of the average pore size r1 of the first coating to the pore size r2 of the second coating satisfies 1 < b ≤ 4. Optionally, the ratio b can be any value from 1.01, 1, 1.5, 2, 2.5, 3, 3.5, 4, or a range thereof.

[0101] The ratio b of the average pore size r1 of the first coating to the pore size r2 of the second coating is within the above range, which is conducive to the passage of active ions through the first coating near the negative electrode sheet, reduces the crystallization phenomenon caused by the poor passage of active ions through the separator, reduces the probability of short circuit in the battery cell, and improves the reliability of the battery cell.

[0102] In some optional embodiments, the average pore size r2 of the second coating is 30 nm to 70 nm. The average pore size r2 of the second coating can be any value or a range of combinations thereof from 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, and 70 nm.

[0103] In some optional embodiments, the average pore size r1 of the first coating is from 100 nm to 300 nm. The average pore size r1 of the first coating can be any value or a range of combinations thereof from 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, 270 nm, 280 nm, 290 nm, and 300 nm.

[0104] In some optional embodiments, the average pore size r3 of the porous base film is from 40 nm to 150 nm. The average pore size r3 of the porous base film can be any value or a range of combinations thereof from 40 nm, 50 nm, 60 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 91 nm, 95 nm, 100 nm, 105 nm, 110 nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, and 150 nm.

[0105] In some alternative embodiments, the tortuosity τ of the separator is 1 to 3, optionally 1.5 to 2.1.

[0106] The tortuosity τ of the separator can be any value or a range thereof from 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3. According to the embodiments of this application, if the tortuosity τ of the separator is within the above range, it indicates that the separator has a suitable tortuosity, and the average porosity ε of the first coating and the porous base film near the negative electrode sheet is... 13 The average porosity ε2 of the second coating, which is closer to the positive electrode, is higher than that of the first coating and the porous base film. When active ions enter the second coating, which has a relatively low average porosity, from the first coating and the porous base film with higher average porosity, their conduction path will change. This will also reduce the presence of through pores in the separator, lengthen the growth path of dendrites, reduce the phenomenon of dendrites growing in the pores of the separator and piercing the separator, improve the short circuit phenomenon of the battery cell, and improve the reliability of the battery cell.

[0107] In some optional embodiments, the tortuosity τ1 of the first coating is between 1.2 and 2.2. Exemplarily, the tortuosity τ1 of the first coating can be 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, etc. When the tortuosity τ1 of the first coating is within the above range, it indicates that the first coating has a suitable tortuosity, which extends the growth path of dendrites, reduces the phenomenon of dendrites growing in the pores of the separator and piercing the separator, improves the short-circuit phenomenon of the battery cell, and enhances the reliability of the battery cell.

[0108] In some optional embodiments, the tortuosity τ3 of the porous base membrane is between 1.4 and 1.8. Exemplarily, the tortuosity τ3 of the porous base membrane can be 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, etc. A tortuosity τ3 within the above range indicates that the porous base membrane has a suitable tortuosity, which extends the dendrite growth path, reduces the phenomenon of dendrites growing in the pores of the separator and piercing the separator, improves the short-circuit phenomenon of the battery cell, and enhances the reliability of the battery cell.

[0109] In some optional embodiments, the tortuosity τ2 of the second coating is 1 to 1.5. Exemplarily, the tortuosity τ2 of the second coating can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, etc. When the tortuosity τ2 of the second coating is within the above range, it lengthens the growth path of dendrites, reduces the phenomenon of dendrites growing in the pores of the separator and piercing the separator, improves the short-circuit phenomenon of the battery cell, and enhances the reliability of the battery cell.

[0110] The tortuosity of the separator, porous base membrane, first coating, and second coating has a meaning well-known in the art and can be tested using known equipment and methods. For example, it can be calculated using the tortuosity formula τ = (R... ion ×ε) / R EL The tortuosity τ of the base membrane is calculated. In the above calculation formula:

[0111] ε represents the average porosity, which can be determined using a mercury porosimeter according to GB / T 21650.1-2008.

[0112] R ion The ionic resistance is expressed in Ω. It can be obtained using an electrochemical workstation (e.g., VMP3B electrochemical workstation) via symmetric cell electrochemical impedance spectroscopy (EIS). Specifically, any sample from the separator, porous base membrane, first coating, and second coating can be cut into samples of a certain size (e.g., 45.3mm * 33.7mm). The thickness of the sample is denoted as I, and the area as S. After drying, the sample is placed between two stainless steel electrodes and sealed to form a coin cell after absorbing a sufficient amount of electrolyte. The coin cell is then subjected to AC impedance spectroscopy experiments using an electrochemical workstation to obtain the ionic conductivity of the separator. A Shanghai Chenhua CHI 660C electrochemical workstation can be used. The test voltage can be -1V to 1V, the AC signal frequency can be 1MHz to 1kHz, and the sinusoidal potential amplitude is 5mV. To improve accuracy, the ion resistance of samples with different layer numbers N can be measured, and the slope obtained by plotting multiple ion resistance values ​​with multiple sample layer numbers N can be used as the ion resistance R of the base film. ion For accuracy, the average of five parallel samples can be used as the test result.

[0113] The electrolyte was prepared as follows: ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Sufficiently dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0114] R EL The ionic resistance of the electrolyte at 25°C can be expressed by the formula R. EL =I / (σ×S) is calculated, with the unit of measurement being Ω; I represents the thickness of the sample used in the above symmetrical cell (such as the first coating, second coating, or porous base membrane / separator, here referring to the thickness of a single-layer coating or single-layer porous base membrane sample), with the unit of measurement being μm; S represents the area of ​​the sample used in the above symmetrical cell, with the unit of measurement being mm. 2σ represents the conductivity of the electrolyte used in the above symmetrical battery, measured in ms / cm. It can be tested using a conductivity meter according to SJ / T 11723-2018 (test temperature is 25℃).

[0115] The tortuosity of porous base membranes can also be obtained by adjusting one or more of the intrinsic parameters of the base membrane (such as composition, average fiber diameter, average porosity, thickness, air permeability, density, etc.) and / or the preparation process parameters of the porous base membrane (such as one or more of stretching parameters, heat setting parameters, etc.). For example, under otherwise constant conditions, a larger average fiber diameter results in greater tortuosity; a larger thickness results in greater tortuosity; greater air permeability results in less tortuosity; a larger average porosity results in less tortuosity; a higher density results in greater tortuosity; and a larger stretching ratio during preparation results in less tortuosity, etc. Those skilled in the art can obtain base membranes with the desired tortuosity through a limited number of experiments.

[0116] In some optional embodiments, the ratio c of the thickness of the first coating and the thickness of the second coating is 1 to 2. Exemplarily, the ratio c can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, etc. A ratio of the thickness of the first coating to the thickness of the second coating within the above range is beneficial for the separator to have a suitable degree of tortuosity while maintaining a suitable average porosity. This makes the path of active ions through the separator more complex and tortuous. Furthermore, a coating of suitable thickness can, to some extent, block the growth and penetration of dendrites, reducing the risk of battery short circuits and improving the reliability of the battery cell.

[0117] In some optional embodiments, the thickness of the first coating is 1 to 3 μm. The thickness of the first coating can be any value or a range of combinations thereof from 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, and 3 μm.

[0118] In some optional embodiments, the thickness of the porous base film is 5 to 15 μm. The thickness of the porous base film can be any value or a range of combinations thereof from 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, and 15 μm.

[0119] In some optional embodiments, the thickness of the second coating is 1 to 3 μm. The thickness of the second coating can be any value or a range of combinations thereof from 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, and 3 μm.

[0120] The thicknesses of the first coating, the second coating, and the porous base film have meanings known in the art and can be determined using equipment and methods known in the art. For example, six parallel samples can be taken, and the thickness of each sample at different locations can be measured using a micrometer thickness gauge. At least 20 locations can be measured for each sample, and the average thickness of the six samples can be taken as the sample thickness.

[0121] In some optional embodiments, the first coating comprises, by weight percentage, 5% to 15% of a first binder and 85% to 95% of a first inorganic filler, optionally 8% to 10% of the first binder and 90% to 92% of the first inorganic filler. The inclusion of the above-mentioned weight percentages in the first coating is beneficial for having a suitable average porosity, facilitating the passage of active ions through the first coating near the negative electrode, and reducing crystallization caused by impaired passage of active ions through the separator.

[0122] In some optional embodiments, the second coating comprises, by weight percentage, 5% to 15% of a second binder and 85% to 95% of a second inorganic filler, optionally 8% to 10% of the second binder and 90% to 92% of the second inorganic filler. The inclusion of these weight percentages in the second coating is beneficial for the first coating to have a suitable average porosity, reduces the content of through-pores in the separator membrane, extends the path of active ions through the separator membrane, and reduces the probability of active ions forming dendrites that puncture the separator membrane.

[0123] In some alternative embodiments, the first adhesive and the second adhesive respectively comprise one or more of polypropylene, polyethylene glycol, polyvinyl alcohol, polystyrene, and ethylene propylene diene monomer (EPDM) rubber.

[0124] In some optional embodiments, the first inorganic filler and the second inorganic filler respectively include one or more of boehmite, alumina, aluminum oxide, silicon dioxide and zirconium oxide.

[0125] In some optional embodiments, the first inorganic filler volume particle size Dv 1 50 and the volumetric particle size Dv of the second inorganic filler 2 The ratio d of 50 ranges from 1.25 to 12.5. The first inorganic filler's volumetric particle size Dv 150 and the volumetric particle size Dv of the second inorganic filler 2 A ratio of 50 within the above range is beneficial for the first and second coatings in the separator to have the above-mentioned average porosity, tortuosity, and average pore size, thereby reducing the phenomenon of dendrites growing in the pores of the separator and piercing the separator, improving the short circuit phenomenon of the battery cell, and improving the reliability of the battery cell.

[0126] In some optional embodiments, the first inorganic filler volume particle size Dv 1 50 is 0.2 μm to 0.5 μm. Exemplarily, the first inorganic filler volumetric particle size Dv 1 50 can be 0.2μm, 0.25μm, 0.3μm, 0.35μm, 0.4μm, 0.45μm, 0.5μm, etc. The first inorganic filler's volumetric particle size Dv 1 Within the aforementioned range, it is advantageous to ensure that the first coating in the separator has the aforementioned average porosity and average pore size, thereby reducing the phenomenon of dendrites growing in the pores of the separator and piercing the separator, improving the short circuit phenomenon of the battery cell, and enhancing the reliability of the battery cell.

[0127] In some optional embodiments, the volumetric particle size Dv of the second inorganic filler 2 50 is 0.04 μm to 0.16 μm. Exemplarily, the volumetric particle size Dv of the second inorganic filler... 2 50 can be 0.04μm, 0.045μm, 0.05μm, 0.055μm, 0.06μm, 0.065μm, 0.07μm, 0.075μm, 0.08μm, 0.085μm, 0.09μm, 0.095μm, 0 .1μm, 0.105μm, 0.11μm, 0.115μm, 0.12μm, 0.125μm, 0.13μm, 0.135μm, 0.14μm, 0.145μm, 0.15μm, 0.155μm, 0.16μm, etc. Volume particle size Dv of the second inorganic filler 2 Within the aforementioned range, 50 is advantageous for the second coating to have the aforementioned average porosity and tortuosity, thereby improving the performance of the battery cell.

[0128] First inorganic filler volume particle size Dv 1 50. The volumetric particle size Dv of the second inorganic filler 2 The meaning of 50 is well-known in the art and can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer (such as the Malvern Mastersizer 3000) in accordance with GB / T 19077-2016. The physical definition of Dv50 is the particle size corresponding to a material's cumulative volume distribution percentage of 50%.

[0129] In some alternative embodiments, the first coating further includes inorganic particles, including one or more of silicon dioxide, magnesium chloride, and ferric chloride.

[0130] According to the embodiments of this application, the first coating has the above-mentioned inorganic particles, which can react with some dendrites in the separator, especially dissolving some metal dendrites, such as sodium dendrites or lithium dendrites, in the first coating, thereby reducing the phenomenon of dendrites piercing the separator, improving the short circuit phenomenon of the battery cell, and improving the reliability of the battery cell.

[0131] In some alternative embodiments, the inorganic particles constitute 5% to 10% by mass in the first coating.

[0132] Optionally, the mass percentage of inorganic particles in the first coating can be any value or range of the following: 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%.

[0133] According to the embodiments of this application, the mass percentage of inorganic particles in the first coating is within the above-mentioned range. While taking into account the performance of the separator in the battery cell, it can dissolve some of the dendrites that may exist in the first coating, reduce the phenomenon of dendrites piercing the separator, improve the short circuit phenomenon of the battery cell, and improve the reliability of the battery cell.

[0134] In some optional embodiments, the volumetric particle size Dv of the inorganic particles 3 50 is 0.05μm to 0.35μm, and can be any value among 0.05μm, 0.06μm, 0.07μm, 0.08μm, 0.09μm, 0.1μm, 0.2μm, and 0.3μm.

[0135] In some optional embodiments, the areal density D of the first coating and the second coating is ≤3 g / mm². 2 0.1g / mm can be selected. 2 Up to 2.8g / mm 2 .

[0136] The areal density of the first and second coatings has a well-known meaning in the art and can be measured using instruments and methods known in the art. For example, take a single-sided coated and cold-pressed release liner (if it is a double-sided coated release liner, the coating on one side can be wiped off first), cut it into small circular pieces with an area of ​​S1, weigh them, and record their weight as M1. Then wipe off the coating of the release liner after weighing, weigh the base film, and record it as M0. The areal density of the first or second coating = (weight of the release liner M1 - weight of the base film M0) / S1.

[0137] [Preparation method of the separating membrane]

[0138] This application also provides a method for preparing a separator membrane, which can prepare the separator membrane provided in this application.

[0139] The preparation method includes the following steps: providing a porous base membrane, a first coating slurry, and a second coating slurry; coating the first coating slurry and the second coating slurry onto both sides of the porous substrate to obtain the first coating and the second coating; and drying to obtain a separating membrane.

[0140] In some optional embodiments, the first coating slurry includes a first inorganic filler, and the second coating slurry includes a second inorganic filler; wherein the volumetric particle size Dv of the first inorganic filler is... 1 50 is greater than the volumetric particle size Dv of the second inorganic filler. 2 50. As a result, the average porosity of the first coating and the porous base film can be higher than that of the second coating near the positive electrode. This extends the dendrite growth path, reduces the phenomenon of dendrites growing in the pores of the separator and piercing the separator, improves the short circuit phenomenon of the battery cell, and enhances the reliability of the battery cell.

[0141] In some optional embodiments, the solvents in the first coating slurry and the second coating slurry may be, but are not limited to, one or more of deionized water, N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAC), and tetrahydrofuran (THF).

[0142] In some optional embodiments, the solid content of the first coating slurry and the second coating slurry can be 30%-60%, optionally 35%-45%. This facilitates coating.

[0143] In some alternative embodiments, the first coating slurry may further include a first binder and / or a first dispersant.

[0144] In some optional embodiments, the step of providing the first coating slurry may include the following steps: dispersing the first inorganic filler with a solvent to obtain a primary dispersion solution; adding a first binder and / or a first dispersant to the obtained primary dispersion solution for secondary dispersion to obtain the first coating slurry.

[0145] Optionally, the secondary dispersion process can be ultrasonic dispersion, during which stirring can be performed. Optionally, the stirring speed during ultrasonic dispersion can be 1000 rpm-1600 rpm, and the ultrasonic dispersion time can be 0.5 h-3 h.

[0146] In some alternative embodiments, the second coating slurry may further include a second binder and / or a second dispersant.

[0147] In some optional embodiments, the step of providing the second coating slurry may include the following steps: dispersing the second inorganic filler with a solvent to obtain a primary dispersion solution; adding a second binder and / or a second dispersant to the obtained primary dispersion solution for secondary dispersion to obtain the second coating slurry.

[0148] Optionally, the secondary dispersion process can be ultrasonic dispersion, during which stirring can be performed. Optionally, the stirring speed during ultrasonic dispersion can be 1000 rpm-1600 rpm, and the ultrasonic dispersion time can be 0.5 h-3 h.

[0149] In some optional embodiments, the drying temperature of the first coating slurry can be 60°C-80°C, and the drying time can be 5h-8h.

[0150] In some optional embodiments, the drying temperature of the second coating slurry can be 60°C-80°C, and the drying time can be 5 min-10 min.

[0151] In some optional embodiments, the coating method of the first coating slurry may include, but is not limited to, gravure transfer coating, rotary spraying, dip coating, and scraping coating.

[0152] In some optional embodiments, the second coating slurry may be applied by methods including but not limited to gravure transfer coating, rotary spraying, dip coating, and scraping coating.

[0153] The raw materials and their content parameters used in the preparation method of the separator provided in the embodiments of this application can be referred to the separator provided in the embodiments of this application, and will not be repeated here.

[0154] Unless otherwise specified, all raw materials used in the preparation of the separator membrane can be obtained commercially.

[0155] [Positive electrode plate]

[0156] In some alternative embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0157] In some alternative embodiments, the positive electrode active material includes a material capable of extracting and inserting lithium.

[0158] As examples, positive electrode active materials may include, but are not limited to, one or more of lithium transition metal oxides, metal chalcogenides, lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, lithium titanium oxides, and their respective modified compounds. Lithium transition metal oxides may include, but are not limited to, layered structures and spinel structures. Examples of lithium-containing phosphates may include, but are not limited to, lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, lithium iron manganese phosphate and carbon composites, and their respective modified compounds.

[0159] In some optional embodiments, to further improve the energy density of the battery, the positive electrode active material may include materials of the general formula Li. a Ni b Co c M d O e D f One or more of lithium transition metal oxides and their modified compounds. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M may include, but is not limited to, one or more of Ge, Mo, Sn, Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and D may include, but is not limited to, one or more of N, F, S and Cl.

[0160] In some alternative embodiments, the positive electrode active material may simultaneously comprise lithium transition metal oxide and lithium phosphate. This is advantageous for obtaining a battery that balances high capacity and high reliability.

[0161] As an example, the positive electrode active material may include, but is not limited to, LiCoO2, LiNiO2, LiMnO2, and LiNi 1 / 2 Mn 1 / 2O2, LiMn2O4, Li 4 / 3 Ti 5 / 3 O4, LiNi 1 / 2 Mn 1 / 2 O2, 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 0.2O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.80 Co 0.15 Al 0.05 O2, LiFePO4, LiMnPO4, Li 1.13 Ti 0.57 Fe 0.3 One or more of S2.

[0162] In some alternative embodiments, the positive electrode active material includes materials capable of extracting and inserting sodium. For example, the positive electrode active material may be one or more of the following: layered transition metal oxides (including but not limited to P2 type, O3 type, etc.), polyanionic materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian materials.

[0163] In some optional embodiments, as examples, the positive electrode active material may include, but is not limited to, NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, Na 0.67 MO2 (M includes at least two of Fe, Co, Cr, Mn, Ni, V, Ti, and Mo), NaMO2 (M includes at least two of Fe, Co, Ni, V, Ti, and Mo), NaFePO4, NaMnPO4, NaCoPO4, Na4Fe3(PO4)2O7, Na3V2(PO4)2F3, Na3V2(PO4)3, Prussian blue, Prussian white, and one or more of their respective modified compounds.

[0164] The modified compounds for the above-mentioned positive electrode active materials can be obtained by doping and / or surface coating of the positive electrode active materials.

[0165] In some optional embodiments, the positive electrode film layer may also optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0166] In some optional embodiments, the positive electrode film layer may also optionally include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene oxide, fluorinated acrylate resins, styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0167] In some optional embodiments, the positive current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include, but is not limited to, one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0168] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing positive electrode active materials, optional positive electrode conductive agents, optional positive electrode binders, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0169] [Negative electrode plate]

[0170] The structure and composition of the negative electrode can be adjusted according to the type of battery cell.

[0171] In some optional embodiments, the negative electrode sheet may include a negative current collector and a metal layer disposed on at least one surface of the negative current collector, wherein the metal material in the metal layer may include, but is not limited to, one or more of elemental lithium, lithium alloy, sodium, and sodium alloy.

[0172] Lithium alloys can be alloys formed from metallic lithium with other metallic or non-metallic elements. For example, other metallic elements in lithium alloys may include one or more of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, and platinum, while non-metallic elements may include one or more of boron, carbon, and silicon.

[0173] Sodium alloys can be alloys formed from metallic sodium with other metallic or non-metallic elements. For example, other metallic elements in a sodium alloy may include one or more of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, and platinum, while non-metallic elements may include one or more of boron, carbon, and silicon.

[0174] In some alternative embodiments, the negative electrode may include a negative current collector and may not include a metal layer, in order to assemble a negative electrode-free metal battery cell.

[0175] In some optional embodiments, the negative electrode sheet includes a negative current collector and a base coating disposed on at least one side of the negative current collector. When a battery cell includes such a negative electrode sheet, the uncontrolled growth of dendrites on the separator side near the negative electrode sheet is more severe, increasing the risk of dendrites penetrating the separator and causing a short circuit. The separator using the embodiments of this application improves the reliability of the battery cell. The base coating may include a negative electrode binder and a negative electrode conductive agent.

[0176] The negative electrode binder and negative electrode conductive agent can be binders and conductive agents commonly used in the art. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. As an example, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0177] The base coating typically does not contain negative electrode active materials, such as artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials can be selected from elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0178] In some alternative embodiments, to improve battery performance, the negative electrode side of the metal-free battery cell can also be provided with some conventional materials that can be used as negative electrode active materials, such as carbon materials. Although these materials have a certain capacity, since their content is small and they are not used as the main negative electrode active materials in the battery cell, the battery cell constructed in this way can still be regarded as a metal-free battery cell.

[0179] In some optional embodiments, the negative electrode current collector may include a metal foil, a three-dimensional porous current collector, or a composite current collector. Examples of metal foils include copper foil, copper alloy foil, nickel foil, nickel alloy foil, aluminum foil, and aluminum alloy foil. Examples of three-dimensional porous current collectors include copper mesh, nickel mesh, aluminum mesh, copper foam, nickel foam, and aluminum foam. The composite current collector may include a polymer substrate and a metal material layer formed on at least one surface of the polymer substrate. Examples of metal materials include, but are not limited to, one or more of copper, copper alloys, aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Examples of polymer substrates include, but are not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0180] [Electrolytes]

[0181] In some alternative embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and an organic solvent.

[0182] In some alternative embodiments, the electrolyte comprises anion, which may include bis(fluorosulfonyl)imide anion (FSI). - ), bis(trifluoromethanesulfonyl)imide anion (TFSI) - ), dioxaborate anion (BOB) - ), difluorooxalate borate anion (DFOB) - ), difluorodioxanol phosphate anion (DFOP) - ), tetrafluorooxalate phosphate anion (TFOP) - ), difluorophosphate anion (PO2F2) - ), hexafluorophosphate anion (PF6) - ), tetrafluoroborate anion (BF4) - ), hexafluoroarsenate anion (AsF6) - ), trifluoromethanesulfonate anion (CF3SO3) - One or more of the following.

[0183] In some alternative embodiments, the electrolyte comprises cations, which may include one or more of lithium ions and sodium ions.

[0184] In some optional embodiments, the concentration of the electrolyte salt can be 0.3 mol / L or higher, optionally 0.7 mol / L or higher, and further optionally 4 mol / L or lower, optionally 2.5 mol / L or lower, or 1.7 mol / L or lower. When the concentration of the electrolyte salt is within the above range, the electrolyte can have a suitable ionic conductivity.

[0185] Organic solvents may include, but are not limited to, one or more of esters, ethers, sulfones, and nitriles. Esters may include, but are not limited to, one or more of carbonates, phosphate esters, carboxylic esters, sulfate esters, and sulfonates. Carbonates may include cyclic carbonates and / or chain carbonates; optionally, carbonates may include both cyclic and chain carbonates. Chain carbonates may include low-viscosity polar chain carbonates, aliphatic branched carbonates, etc.

[0186] As an example, organic solvents may include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), butene carbonate, 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), diethyl sulfone (ESE), dimethyl ether tetraethylene glycol (TEGDME), ethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), trimethyl phosphate, 3-methoxypropionitrile, H(CF2)2OCH3, C4F9O CH3, H(CF2)2OCH2CH3, H(CF2)2OCH2CF3, H(CF2)2CH2O(CF2)2H, CF3CHFCF2OCH3, CF3CHFCF2OCH2CH3, 2-trifluoromethylhexafluoropropyl methyl ether, 2-trifluoromethylhexafluoropropyl ethyl ether, 2-trifluoromethylhexafluoropropyl propyl ether, 3-trifluoromethyloctafluorobutyl methyl ether, 3-trifluoromethyloctafluorobutyl ethyl ether, 3-trifluoromethyloctafluorobutyl propyl ether, 4-trifluoromethyl One or more of the following: decafluoropentyl methyl ether, 4-trifluoromethyl decafluoropentyl ethyl ether, 4-trifluoromethyl decafluoropentyl propyl ether, 5-trifluoromethyl dodecylfluorohexyl methyl ether, 5-trifluoromethyl dodecylfluorohexyl ethyl ether, 5-trifluoromethyl dodecylfluorohexyl propyl ether, 6-trifluoromethyl tetradecafluoroheptyl methyl ether, 6-trifluoromethyl tetradecafluoroheptyl ethyl ether, 6-trifluoromethyl tetradecafluoroheptyl propyl ether, 7-trifluoromethyl hexadecylfluorooctyl methyl ether, 7-trifluoromethyl hexadecylfluorooctyl ethyl ether, and 7-trifluoromethyl hexadecylfluorooctyl propyl ether.

[0187] In some optional embodiments, the electrolyte may also include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature power performance, etc.

[0188] The methods for preparing battery cells are well known. In some optional embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is placed in an outer packaging, dried, and then injected with the aforementioned electrolyte. After vacuum sealing, settling, and formation processes, a battery cell is obtained. Multiple battery cells can be further connected in series, parallel, or a combination thereof to form a battery module. Multiple battery modules can also be connected in series, parallel, or a combination thereof to form a battery pack. In some optional embodiments, multiple battery cells can also be directly assembled into a battery pack.

[0189] This application also provides an electrical device, which includes the battery provided in this application embodiment. The battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, mobile devices (such as mobile phones, tablets, laptops, etc.), electric vehicles (such as 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.

[0190] Electrical devices can choose the type of battery according to their usage needs, such as individual battery cells, battery modules, or battery packs.

[0191] Figure 6 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0192] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0193] Example

[0194] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0195] Example 1

[0196] Preparation of the first coating slurry

[0197] The first inorganic filler, alumina, has a D... v 1 A 0.3 μm alumina was uniformly dispersed in N-methylpyrrolidone (NMP). Then, the first binder, polyvinylidene fluoride (PVDF), and the first dispersant, hydrolyzed polymaleic anhydride, were added to the solution. The mixture was ultrasonically dispersed at 1100 rpm for 2 hours to obtain a first coating slurry with a solid content of approximately 40%. The weight ratio of the first inorganic filler, alumina, the first binder, and the first dispersant was 94.5:5:0.5.

[0198] Preparation of the second coating slurry

[0199] The second inorganic filler, boehmite, has a D... v 2 50 μm of the filler was uniformly dispersed in N-methylpyrrolidone (NMP). Then, polyvinylidene fluoride (PVDF) as a second binder and hydrolyzed polymaleic anhydride as a second dispersant were added to the solution. The mixture was ultrasonically dispersed at 1100 rpm for 2 hours to obtain a second coating slurry with a solid content of approximately 40%. The weight ratio of the second inorganic filler, the second binder, and the second dispersant was 94.5:5:0.5.

[0200] Preparation of the separating membrane

[0201] The second coating slurry was applied to one side of a wet-process PE porous substrate with an average porosity of 42.6% and a thickness of 7 μm using gravure transfer coating, and baked at 60℃-65℃ for about 10 min. Then, the first coating slurry was applied to the other side of the PE porous substrate in the same manner and baked at 60℃-65℃ for 10 min, resulting in a three-layer release film. The thickness of the first coating was 1 μm, and the thickness of the second coating was 1 μm.

[0202] Positive electrode preparation: The positive electrode active material sodium iron phosphate Na4Fe3(PO4)2P2O7, the conductive agent carbon black (Super P), and the binder polyvinylidene fluoride (PVDF) are thoroughly mixed in an appropriate amount of NMP solvent at a weight ratio of 90:5:5 to form a uniform positive electrode slurry; the positive electrode slurry is then coated onto the surface of the positive electrode current collector aluminum foil with a coating weight of 20 mg / cm². 2 After drying and cold pressing, a positive electrode sheet is obtained.

[0203] Preparation of negative electrode sheet:

[0204] Carbon nanotubes (CNTs) and sodium carboxymethyl cellulose (CMC) were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 50:50 to form an interface modification layer slurry. The interface modification layer slurry was coated onto the surface of an 8 μm thick copper foil anode current collector. After drying the interface modification layer slurry, a base coating with a thickness of 2 μm was formed.

[0205] Preparation of electrolyte: Dissolve fully dried NaPF6 in diethylene glycol dimethyl ether (DEGDME) to prepare an electrolyte with a NaPF6 concentration of 1 mol / L.

[0206] Assembly: The positive electrode, separator, and negative electrode are stacked in sequence to form an electrode assembly, wherein the second coating of the separator is disposed on the side close to the negative electrode, resulting in a sodium-free negative electrode battery cell.

[0207] Examples 2-5

[0208] The difference between this embodiment and embodiment 1 is that in embodiments 2-3, the volumetric particle size of the first inorganic filler in the first coating is adjusted so that the average porosity of the first coating is different; in embodiment 4, the volumetric particle size of the first inorganic filler and the second inorganic filler in the first coating and the second coating is adjusted so that the average porosity of the first coating and the second coating is different; in embodiment 5, the average porosity of the first coating, the second coating, and the porous base film is adjusted to be different, as shown in Table 1.

[0209] Examples 6-9

[0210] The difference between this embodiment and Embodiment 1 is that the thicknesses of the first coating, the second coating, and the porous base film are adjusted, as shown in Table 1.

[0211] Comparative Example 1

[0212] The difference between this comparative example and Example 1 is that the volumetric particle size of the second inorganic filler in the second coating is adjusted so that the average porosity of the second coating is different; the average porosity of the second coating is 60%, while the average porosity of the porous base film and the first coating is 52%.

[0213] Comparative Example 2

[0214] The difference between this comparative example and Example 3 is that the volumetric particle size of the second inorganic filler in the second coating is adjusted so that the average porosity of the second coating is different; the average porosity of the second coating is 50%, while the average porosity of the porous base film and the first coating is 49%.

[0215] Examples 10-15

[0216] The difference between this embodiment and Embodiment 1 is that: in Embodiments 10 to 13, the volumetric particle size and type of the first and second inorganic fillers in the first and second coatings are adjusted to make the average pore size of the first and second coatings different; in Embodiments 14 or 15, the average pore size of the porous base film is adjusted. Specifically, in Embodiment 10, the Dv of the first inorganic filler alumina is... 1 50 is 0.2 μ m; Dv of the first inorganic filler alumina in Example 11 1 50 is 0.5 μ m; Dv of the second inorganic filler boehmite in Example 12 2 50 is 0.04 μ m; Dv of the second inorganic filler boehmite in Example 13 2 50 is 0.16 μ m; In Example 14, the average pore size of the porous base membrane is 60 nm, and the tortuosity τ of the separator is 1.5; In Example 14, the average pore size of the porous base membrane is 40 nm, and the tortuosity τ of the separator is 2.1; The porosity of the first coating, the second coating, and the porous base membrane in Examples 10-15 is the same as that in Example 1, as shown in Table 2.

[0217] Examples 16-18

[0218] The difference between this embodiment and Embodiment 1 lies in the preparation of the first coating slurry. In Embodiment 16, the first inorganic filler, silica, has a Dv50 of 0.3. μ In step m, the first inorganic filler and silica were uniformly dispersed in N-methylpyrrolidone (NMP). Then, the first binder, polyvinylidene fluoride (PVDF), and the first dispersant, hydrolyzed polymaleic anhydride, were added to the solution. The mixture was ultrasonically dispersed at 1100 rpm for 2 hours to obtain a first coating slurry with a solid content of approximately 40%. The weight ratio of the first inorganic filler (silica), the first binder, and the first dispersant was 89.5:5:5:0.5. Example 17 differs from Example 16 in that magnesium chloride was substituted for silica by an equal mass. Example 18 differs from Example 16 in that ferric chloride was substituted for silica by an equal mass. See Table 3.

[0219] Performance testing

[0220] The above-mentioned separator and sodium-free battery cell were tested for the following performance characteristics.

[0221] (1) Average porosity ε of the isolation membrane, porous base membrane, first coating and second coating 13The average porosity ε3 and average pore size r3 of the porous base membrane can be tested according to GB / T21650.2-2008, Determination of Pore Size Distribution and Porosity of Materials by Mercury Intrusion Porosimetry and Gas Adsorption Method, Part 2: Analysis of Mesopores and Macropores by Gas Adsorption Method.

[0222] The average porosity ε1 of the first coating and the average porosity ε2 of the second coating can be measured using a Micromeritics AccuPyc II 1340 fully automatic true density analyzer, referring to the national standard GB / T 24586-2009, using the gas displacement method. The average porosity P = (V1-V2) / V1*100%, where V1 is the apparent volume of the sample and V2 is the actual volume of the sample. The average pore diameter r1 of the first coating and the pore diameter r2 of the second coating are determined according to the standards GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Materials by Gas Adsorption BET Method" and GB / T 21650.2-2008 "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Intrusion Porosimetry and Gas Adsorption Method".

[0223] (2) Detection of tortuosity of the separating membrane, porous base membrane, first coating, and second coating: Tortuosity calculation formula τ=(R ion ×ε) / R EL In the above calculation formula: ε represents the average porosity, which can be determined using a mercury porosimeter according to GB / T 21650.1-2008. R ion The ionic resistance, expressed in Ω, can be measured using an electrochemical workstation (e.g., VMP3B electrochemical workstation) via electrochemical impedance spectroscopy (EIS). Specifically, any sample from the separator, porous base membrane, first coating, and second coating can be cut into a sample of a certain size (e.g., 45.3mm * 33.7mm). The thickness of the sample is denoted as I, and the area as S. A lithium sheet, the aforementioned sample, and another lithium sheet are sequentially stacked to prepare a test sample. The test sample is placed in an outer packaging, and electrolyte is injected to obtain a symmetrical cell. To improve accuracy, the ionic resistance of the base membrane with different numbers of layers N can be measured. The slope obtained by plotting multiple ionic resistance values ​​against the number of base membrane layers N is taken as the ionic resistance R of the base membrane. ion The test voltage can be from -1V to 1V, and the AC signal frequency can be from 1MHz to 1KHz.

[0224] R ELThe ionic resistance of the electrolyte at 25°C can be calculated using the formula REL = I / (σ×S), with the unit of measurement being Ω; I represents the thickness of the sample used in the above symmetrical cell (if it is a coating or porous membrane, here it refers to the thickness of a single-layer coating or porous membrane sample), with the unit of measurement being μm; S represents the area of ​​the sample used in the above symmetrical cell, with the unit of measurement being mm. 2 σ represents the conductivity of the electrolyte used in the above symmetrical battery, measured in mS / cm. It can be tested using a conductivity meter according to 7SJ / T 11723-2018 (test temperature: 25℃). During testing, more than six coin cell samples can be used, and the average value of the test results should be taken.

[0225] (3) Cycle life of a single battery cell: At 25°C, the secondary battery is charged at a rate of 1C and discharged at a rate of 1C, and a cycle test of 3% to 97% SOC is performed until a short circuit occurs in the battery cell. The number of cycles is recorded as the cycle life of the battery cell.

[0226]

[0227] Table 2

[0228]

[0229] Table 3

[0230]

[0231] As shown in Table 1, the second coating is applied near the negative electrode, and the average porosity ε of the porous base film and the first coating are... 13 A porosity greater than the average porosity ε2 of the second coating is beneficial for improving the cycle life of the battery cells, making the battery cells less prone to short circuits, and improving the reliability of the battery cells.

[0232] Compared to the comparative example, the average porosity of the second coating in Example 1 is different, resulting in a difference in the average porosity ε between the porous base film of Comparative Example 1 and the first coating. 13 The average porosity ε2 of the second coating is less than that of the second coating, and the cycle life of Example 1 is much greater than that of Comparative Example 1.

[0233] Compared with Comparative Example 2, Examples 3-4 show different average porosities in the second coating, resulting in different average porosities ε between the porous base film of Comparative Example 1 and the first coating. 13 The average porosity ε2 of the second coating is less than that of the second coating, and the cycle life of Examples 3-4 is much greater than that of Comparative Example 2.

[0234] Table 2 shows that when the second coating is applied near the negative electrode, the average porosity ε of the porous base film and the first coating is... 13Under conditions where the average porosity ε2 of the second coating is greater than that of the first coating, the second coating, and the porous base film have different average pore sizes, resulting in different cycle lives for the battery cells.

[0235] Table 3 shows that when the second coating is applied near the negative electrode, the average porosity ε of the porous base film and the first coating is... 13 Under the condition that the average porosity ε2 of the second coating is greater than that of the second coating, adding a certain amount of inorganic particles to the first coating is beneficial to reduce dendrites in the separator or dissolve some of the formed dendrites, thus extending the cycle life of the battery cell.

[0236] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, comprising a positive electrode, a negative electrode, and a separator, wherein the separator is disposed between the negative electrode and the positive electrode; the separator comprises: Porous base membrane; A first coating is disposed on the porous base film near the negative electrode sheet; A second coating is disposed on the porous base film near the positive electrode sheet; Wherein, the isolation membrane satisfies: ε 13 >ε2, where ε2 represents the average porosity of the second coating, ε 13 This represents the average porosity of the first coating and the porous base film.

2. The battery cell according to claim 1, characterized in that, The average porosity ε1 of the first coating is greater than the average porosity ε2 of the second coating.

3. The battery cell according to claim 1 or 2, characterized in that, The average porosity ε3 of the porous base film is greater than the average porosity ε2 of the second coating.

4. The battery cell according to any one of claims 1 to 3, characterized in that, The ratio a of the average porosity ε1 of the first coating and the average porosity ε2 of the second coating satisfies 1 < a ≤ 1.

5.

5. The battery cell according to any one of claims 1 to 4, characterized in that, The average pore size r1 of the first coating is greater than the pore size r2 of the second coating.

6. The battery cell according to any one of claims 1 to 5, characterized in that, The ratio b of the average pore size r1 of the first coating to the pore size r2 of the second coating satisfies 1 < b ≤ 4.

7. The battery cell according to any one of claims 1 to 6, characterized in that, The isolation membrane meets one or more of the following conditions: (1) The average porosity ε2 of the second coating is 30% to 50%; (2) The average porosity ε1 of the first coating is 40% to 60%; (3) The average porosity ε3 of the porous base membrane is 30% to 55%; (4) The average pore size r2 of the second coating is 30 nm to 70 nm; (5) The average pore size r1 of the first coating is 100 nm to 300 nm; (6) The average pore size r3 of the porous base film is 40 nm to 150 nm.

8. The battery cell according to any one of claims 1 to 7, characterized in that, The isolation membrane meets one or more of the following conditions: (1) The tortuosity τ of the isolation membrane is 1 to 3, and can be selected as 1.5 to 2.1; (2) The tortuosity τ1 of the first coating is 1.2 to 2.2; (3) The tortuosity τ3 of the porous base membrane is 1.4 to 1.8; (4) The tortuosity τ2 of the second coating is 1 to 1.5; (5) The ratio c of the thickness of the first coating to the thickness of the second coating is 1 to 2; (6) The thickness of the first coating is 1 to 3 μm; (7) The thickness of the porous base film is 5 to 15 μm; (8) The thickness of the second coating is 1 to 3 μm.

9. The battery cell according to any one of claims 1 to 8, characterized in that, The first coating and the second coating satisfy one or more of the following conditions: (1) The first coating comprises, by weight percentage, 5% to 15% of a first binder and 85% to 95% of a first inorganic filler; (2) The second coating comprises, by weight percentage, 5% to 15% of a second binder and 85% to 95% of a second inorganic filler.

10. The battery cell according to claim 9, characterized in that, The first coating and the second coating satisfy one or more of the following conditions: (1) The first adhesive and the second adhesive respectively comprise one or more of polypropylene, polyethylene glycol, polyvinyl alcohol, polystyrene and ethylene propylene diene monomer (EPDM) rubber; (2) The first inorganic filler and the second inorganic filler respectively include one or more of boehmite, alumina, aluminum oxide, silicon dioxide and zirconium oxide; (3) The first inorganic filler volume particle size Dv 1 50 and the volumetric particle size Dv of the second inorganic filler 2 The ratio d of 50 ranges from 1.25 to 12.5; (4) The first inorganic filler volume particle size Dv 1 50 ranges from 0.2 μm to 0.5 μm; (5) The volumetric particle size Dv of the second inorganic filler 2 50 ranges from 0.04 μm to 0.16 μm.

11. The battery cell according to any one of claims 1 to 10, characterized in that, The first coating also includes inorganic particles, which include one or more of silicon dioxide, magnesium chloride, and ferric chloride.

12. The battery cell according to claim 11, characterized in that, The inorganic particles in the first coating have a mass percentage content of 5% to 10%.

13. The battery cell according to any one of claims 1 to 12, characterized in that, The negative electrode sheet includes a negative current collector and a base coating disposed on at least one side of the negative current collector.

14. A separating membrane, comprising: Porous base membrane; A first coating is applied to the porous base film on the side near the negative electrode sheet. The second coating is applied to the porous base film on the side near the positive electrode sheet. Wherein, the isolation membrane satisfies: ε 13 >ε2, where ε2 represents the average porosity of the second coating, ε 13 This represents the average porosity of the first coating and the porous base film.

15. A battery device comprising a battery cell according to any one of claims 1 to 13.

16. An electrical device comprising the battery device of claim 15.

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