Separator and preparation method therefor, battery cell, battery device and electric device

Abstract

Provided in the present application are a separator and a preparation method therefor, a battery cell, a battery device and an electric device. The battery cell comprises: a casing; and an electrode assembly accommodated in the casing, wherein the electrode assembly comprises electrode sheets and a separator, and the electrode sheets and the separator are stacked; the separator comprises a base film and a modification layer located on at least one side of the base film; and the tortuosity of the base film ranges from 1.8 to 2.5, and the contact angle between the modification layer and an electrolyte ranges from 20° to 30°. The battery cell provided in the present application has improved cycle performance.

Description

Separator membrane and its preparation method, battery cell, battery device, electrical device

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411026899.4, filed on July 29, 2024, entitled “Separator membrane and preparation method thereof, battery cell, battery device, power device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, specifically to a separator and its preparation method, a battery cell, a battery device, and an electrical device. Background Technology

[0004] Battery cells are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric car toys, electric toy ships, electric toy airplanes, and power tools.

[0005] In the development of battery cells, improving the cycle performance of battery cells is one of the urgent problems to be solved. Summary of the Invention

[0006] This application provides a separator and its preparation method, a battery cell, a battery device, and an electrical device, which can improve the electrolyte retention capacity of the negative electrode of a metal battery cell and improve the cycle performance of the battery cell.

[0007] In a first aspect, embodiments of this application provide a battery cell, the battery cell comprising:

[0008] shell;

[0009] An electrode assembly, housed in the housing, includes an electrode sheet and a separator film, the electrode sheet and the separator film being stacked together; the separator film includes a base film and a modification layer located on at least one side of the base film, wherein...

[0010] The tortuosity of the base membrane is 1.8 to 2.5;

[0011] The contact angle between the modified layer and the electrolyte is 20° to 30°.

[0012] By depositing a modification layer on at least one side of the base film, the modification layer, having a low electrolyte contact angle, allows for excellent wetting and diffusion of the electrolyte on its surface. This improves the hydrophilic properties of the separator surface, enhancing its electrolyte retention capacity during battery cell cycling, thereby resulting in improved fast-charging performance and cycle performance for the battery cell. Simultaneously, the improved electrolyte retention capacity reduces dendrite growth and deterioration, lowering the risk of internal short circuits within the battery cell and enhancing its reliability.

[0013] In some embodiments, the tortuosity of the base film is 2.0 to 2.3.

[0014] In some embodiments, the contact angle between the modified layer and the electrolyte is 20° to 25°.

[0015] In some embodiments, the material of the modification layer comprises a solvophilic polymer having a swelling degree of 110% to 150% in an ether solvent.

[0016] In some embodiments, the solvophilic polymer contains polar functional groups, which include one or more of the following: carboxyl group, amide group, phenolic hydroxyl group, alcoholic hydroxyl group, ether bond, amide group, sulfonic acid group, halogen atom, ester group, and aromatic ring.

[0017] In some embodiments, the molar content of polar functional groups in the solvophilic polymer is 5% to 30%.

[0018] In some embodiments, the solvophilic polymer includes one or more of acrylic polymers, fluorinated hydrocarbon polymers, polyethersulfone, polyamide, and borane.

[0019] In some embodiments, the thickness of the modification layer is 1 μm to 2 μm.

[0020] In some embodiments, the electrode includes a positive electrode and a negative electrode, the separator is located between the positive electrode and the negative electrode, and the modification layer is located on the side of the separator closer to the negative electrode.

[0021] In some embodiments, the liquid retention capacity of the separator membrane is from 7.2 g / Ah to 8.8 g / Ah.

[0022] In some embodiments, the liquid absorption rate of the isolation membrane is from 5 g / s to 15 g / s.

[0023] In some embodiments, the air permeability of the isolation membrane is from 180s / 100mL to 280s / 100mL.

[0024] In some embodiments, the porosity of the base membrane is 40% to 50%.

[0025] In some embodiments, the battery cell further includes an electrolyte, which includes an organic solvent, including ether solvents.

[0026] In some embodiments, the ether solvent includes one or more of ethylene glycol dimethyl ether, dimethoxymethane, 1,2-dimethoxypropane, triethylene glycol dimethyl ether, 1,3-dioxocyclopentane, 4-methyl-1,3-dioxocyclopentane, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0027] Secondly, embodiments of this application provide a battery device, including a single battery cell from the first aspect of this application.

[0028] Thirdly, embodiments of this application provide an electrical device, including a battery according to embodiments of the second aspect of this application.

[0029] Fourthly, embodiments of this application provide a separating membrane, the separating membrane comprising a base film and a modification layer located on at least one side of the base film, wherein,

[0030] The tortuosity of the base membrane is 1.8 to 2.5;

[0031] The contact angle of the modified layer with water is 20° to 30°.

[0032] In some embodiments, the tortuosity of the base film is 2.0 to 2.3.

[0033] In some embodiments, the contact angle of the modification layer with water is 20° to 25°.

[0034] In some embodiments, the material of the modification layer comprises a solvophilic polymer having a swelling degree of 110% to 150% in an ether solvent.

[0035] In some embodiments, the solvophilic polymer contains polar functional groups, including one or more of carboxyl, amide, phenolic hydroxyl, alcoholic hydroxyl, ether bond, amide group, and sulfonic acid group.

[0036] In some embodiments, the molar content of polar functional groups in the solvophilic polymer is 5% to 30%.

[0037] In some embodiments, the solvophilic polymer includes one or more of acrylic polymers, fluorinated hydrocarbon polymers, polyethersulfone, polyamide, and borane.

[0038] In some embodiments, the thickness of the modification layer is 1 μm to 2 μm.

[0039] In some embodiments, the liquid retention capacity of the separator membrane is from 7.2 g / Ah to 8.8 g / Ah.

[0040] In some embodiments, the liquid absorption rate of the isolation membrane is from 5 g / s to 15 g / s.

[0041] In some embodiments, the air permeability of the isolation membrane is from 180s / 100mL to 280s / 100mL.

[0042] In some embodiments, the porosity of the base membrane is 40% to 50%.

[0043] In some embodiments, the battery cell further includes an electrolyte, which includes an organic solvent, including ether solvents.

[0044] In some embodiments, the ether solvent includes one or more of ethylene glycol dimethyl ether, dimethoxymethane, 1,2-dimethoxypropane, triethylene glycol dimethyl ether, 1,3-dioxocyclopentane, 4-methyl-1,3-dioxocyclopentane, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0045] Fifthly, embodiments of this application provide a method for preparing a separating membrane, comprising the following steps:

[0046] A surface-treated base film is provided, wherein the tortuosity of the base film is 1.8 to 2.5;

[0047] A modification layer is grafted in situ onto the surface of the base film, and the contact angle between the modification layer and the electrolyte is 20° to 30°.

[0048] In some embodiments, the method for surface treatment of the base film includes one or more of corona treatment, plasma treatment, laser treatment, and chemical etching. Attached Figure Description

[0049] 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 introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 is a schematic diagram of a battery cell provided in some embodiments of this application.

[0051] Figure 2 is an exploded view of a battery cell provided in some embodiments of this application.

[0052] Figure 3 is a schematic diagram of a battery module provided in some embodiments of this application.

[0053] Figure 4 is a schematic diagram of a battery pack provided in some embodiments of this application.

[0054] Figure 5 is an exploded view of the battery pack shown in Figure 4.

[0055] Figure 6 is a schematic diagram of an electrical device provided in some embodiments of this application.

[0056] The accompanying drawings are not necessarily drawn to scale.

[0057] The reference numerals in the attached diagram 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

[0058] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the separator, its preparation method, battery cell, battery device, and power-consuming device of this application. 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 for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0059] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a 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 included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 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 application, 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.

[0060] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0061] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0062] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates 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.

[0063] Unless otherwise specified, the terms "connected" and "linked" in this application should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0064] In this application, "multiple" refers to two or more, including two. "Multiple types" refers to two or more, including two.

[0065] The battery device mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells, which are connected in series, parallel, or mixed connections via a busbar.

[0066] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells; as an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells into a single module. As an example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0067] 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, and the embodiments of this application are not limited to this. Figure 1 shows a cuboid battery cell 5 as an example.

[0068] When there are multiple battery cells, they are connected in series, parallel, or mixed via a busbar. In some embodiments, the battery device can be a battery module; when there are multiple battery cells, they are arranged and fixed to form a battery module. In some embodiments, the battery device 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 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.

[0069] In some embodiments, individual battery cells can be assembled into a battery module. The number of battery cells in a battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Figure 2 is a schematic diagram of a battery module 4 as an example. As shown in Figure 2, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other arbitrary manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0070] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0071] In some 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.

[0072] Figures 3 and 4 are schematic diagrams of a battery pack 1 as an example. As shown in Figures 3 and 4, 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, with the upper housing 2 covering the lower housing 3 and forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the housing.

[0073] In some embodiments, the battery device may be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0074] The battery cells provided in the embodiments of this application are negative electrode-free battery cells, and may include at least one of negative electrode-free lithium metal battery cells and negative electrode-free sodium metal battery cells.

[0075] A negative electrode-free battery cell typically refers to a battery cell in which no negative electrode active material layer is actively formed on the negative electrode side during the 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 convert 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.

[0076] In some embodiments, to improve the performance of a single battery cell, the negative electrode side of the electrodeless battery cell may also contain some conventional materials that can be used as negative electrode active materials, such as carbon materials. Although these materials have a certain capacity, because 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 an electrodeless battery cell.

[0077] The Cell Balance (CB) value of a negative electrode-free battery cell is typically very small; for example, in some 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.

[0078] The battery cell includes an electrode assembly. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of this application are not limited to this.

[0079] Electrode assemblies generally include a positive electrode, a negative electrode, and a separator.

[0080] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode assembly. 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).

[0081] In some embodiments, as shown in FIG5, 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 as needed.

[0082] The separator, located between the positive and negative electrodes, primarily serves to prevent internal short circuits. Currently used separators generally include organic membranes, inorganic membranes, or organic-inorganic composite membranes. These membrane materials themselves have poor electrolyte adsorption properties, resulting in poor electrolyte retention capacity. During battery cell cycling, the electrolyte's conductivity is insufficient, failing to meet the requirements for long-cycle and fast-charging capabilities. For metal battery cells, poor electrolyte retention capacity leads to insufficient electrolyte storage at the top of the cell, resulting in uneven ion distribution during charging and discharging. This can easily cause non-uniform deposition of the active metal on the negative electrode, worsening dendrite growth and even causing internal short circuits.

[0083] In related technologies, to improve the poor liquid retention capacity of metal battery separators, a liquid-retaining coating is typically applied to the surface of the separator. This coating is bonded to the separator base film using an adhesive. However, this coating leads to a decrease in the conductivity of the separator and an increase in the impedance of the individual battery cells. Furthermore, the adhesive bonding of the coating has limited adhesion, and the coating is prone to detachment during cycling, reducing the liquid retention effect and deteriorating the cycle performance of the individual battery cells. Additionally, because different types of base films have different surface polarities, this adhesive coating method is not universally applicable to different types of base films.

[0084] Therefore, this application provides a battery cell in which the surface design of the separator is optimized to give the separator good liquid retention capacity, thereby improving the cycle performance of the battery cell.

[0085] [Isolation membrane]

[0086] In some embodiments, the separator includes a base membrane and a modification layer located on at least one side of the base membrane, wherein the tortuosity of the base membrane can be 1.8 to 2.5, and the electrolyte contact angle of the modification layer can be 20° to 30°.

[0087] The tortuosity of the base membrane is a parameter describing the degree of tortuosity of the pore channels inside the base membrane. The tortuosity is defined as the ratio of the actual length of the channel to the apparent length (macroscopic distance) through the seepage medium, that is, the true length of the trajectory of the seepage fluid particles in the channel when they pass through the medium unit.

[0088] In this application, the tortuosity of the base film can be measured using instruments and testing methods known in the art. As an example, the tortuosity τ can be calculated using the following formula:

[0089] Where, N m The McMullin number is denoted by ε, and ε is the porosity of the base membrane. Wherein, the McMullin number N... mThis is the ratio of the resistivity of the base film when immersed in the electrolyte to the resistivity of the electrolyte. The resistivity of the base film immersed in the electrolyte and the resistivity of the electrolyte can be obtained by the following method.

[0090] Base film resistivity test: An electrochemical workstation can be used to measure Rs for different base film layers (n) according to the resistance law formula Rs=ρ×L0 / (S×n) using the confined symmetric cell EIS method. Plot Rs and n to obtain the slope k=(ρ×L0) / S. Under the condition of known effective area S and separator thickness L0, the resistivity ρ=(k×S) / L0 can be obtained.

[0091] Electrolyte resistivity test: Using a conductivity meter, the resistance R of the electrolyte is tested at 25℃ and AC impedance 1kHz. The resistivity of the electrolyte is calculated using the formula ρ=R×S / L based on the length L and cross-sectional area S of the electrolyte being tested.

[0092] The contact angle of the modification layer with the electrolyte refers to the angle between the solid-liquid interface, the liquid interior, and the gas-liquid interface at the solid-liquid-gas three-phase interface when the electrolyte forms droplets on the surface of the modification layer. It can reflect the wetting performance of the electrolyte on the surface of the modification layer.

[0093] In this application, the contact angle can be measured using instruments and methods known in the art. For example, a contact angle measuring instrument can be used, with manual or automatic dropper operation to ensure that the volume of each drop is the same. A high-resolution camera is used for optical measurement, and the test results are analyzed in real time by measurement software. In this application, the liquid used to measure the electrolyte contact angle can be dimethyl ethylene glycol (DME).

[0094] In this embodiment, a modification layer is formed on at least one side of the base film. This modification layer has a low electrolyte contact angle, allowing the electrolyte to wet and diffuse effectively on the surface of the modification layer. This improves the hydrophilic properties of the separator surface, enhances the separator's liquid retention capacity during battery cell cycling, and consequently enables the battery cell to exhibit higher fast-charging performance and improved cycle performance. Simultaneously, the improved liquid retention capacity of the separator reduces dendrite growth and deterioration, lowers the risk of internal short circuits within the battery cell, and enhances the reliability of the battery cell.

[0095] By controlling the tortuosity of the base film within the range of 1.8 to 2.5, the modification layer can have better adhesion performance on the surface of the base film, reduce the shedding of the modification layer during the charge and discharge cycle of the battery cell, improve the structural stability of the separator, and thus improve the cycle performance of the battery cell.

[0096] For example, the tortuosity of the base film can be 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, or any value within the range of the above; optionally, the tortuosity of the base film can be 2.0 to 2.3. By limiting the tortuosity of the base film to the above range, the modification layer can have better adhesion performance on the surface of the base film, further reducing the shedding of the modification layer during battery cell cycling. In addition, limiting the tortuosity of the base film to the above range results in better ion permeability of the separator, which can further improve the cycle performance of the battery cell.

[0097] For example, the contact angle between the modification layer and the electrolyte can be 20°, 21°, 22°, 23°, 24°, 25°, 26°, 27°, 28°, 29°, 30°, or any value within the range of the above. Optionally, the contact angle between the modification layer and the electrolyte can be 19° to 23°. By limiting the contact angle between the modification layer and the electrolyte to the above range, the electrolyte exhibits better wetting properties on the modification layer, which can further improve the hydrophilic and liquid-retaining performance of the separator, thereby improving the cycle performance and reliability of the battery cell.

[0098] In some embodiments, the material of the modification layer may include a solvophilic polymer having a swelling degree of 110% to 150% in an ether solvent, optionally 115% to 140%.

[0099] In this application, the solubilophilic polymer refers to a polymer that has a good affinity for the electrolyte, such as a polymer that can be well dispersed in organic solvents, a polymer that can effectively adsorb organic solvents, or a polymer that can be grafted or bonded to organic solvents. Using a solubilophilic polymer as the material for the modification layer allows the electrolyte to effectively wet the modification layer, thereby improving the liquid retention and absorption capacity of the separator.

[0100] Swelling degree refers to the ratio of the volume of a polymer molecule after swelling to its volume before swelling when the polymer molecules adsorb solvent and reach swelling equilibrium. The swelling degree of the liquid-retaining polymer can be tested using methods known in the art. For example, the liquid-retaining polymer can be placed on a glass plate and a film can be scraped. A 1cm × 1cm polymer film can be taken, and its thickness can be measured with calipers or a micrometer. The volume can be calculated as V1. The polymer film can then be immersed in an ether solvent at room temperature for 12 hours. After removal, the length, width, and height of the polymer film can be measured, and its volume can be calculated as V2. The swelling degree s of the liquid-retaining polymer can then be calculated using the formula s = V2 / V1 × 100%. Solvophilic polymers with swelling degrees in ether solvents within the above range have good liquid absorption and retention properties. Using them as a material for the modification layer can further improve the liquid retention capacity of the separator, thereby improving the cycle performance of the battery cell. In the embodiments of this application, the ether solvent can be dimethyl ethylene glycol (DME).

[0101] In some embodiments, the solvophilic polymer may contain polar functional groups, which may include one or more of the following: carboxyl groups, amide groups, phenolic hydroxyl groups, alcoholic hydroxyl groups, ether bonds, amide groups, sulfonic acid groups, halogen atoms, ester groups, and aromatic rings. The polar functional groups in the solvophilic polymer can form hydrogen bonds with the surface and interior of the base film, thereby further enhancing the bonding strength of the modification layer on the base film surface, reducing the shedding of the modification layer during battery cell cycling, and further improving the cycle performance of the battery cell.

[0102] In some embodiments, the molar content of polar functional groups in the solvophilic polymer can be from 5% to 30%, and optionally from 8% to 27%. By controlling the content of polar functional groups in the solvophilic polymer within the above range, the modified layer and the base film can have a high bonding strength, while the modified layer can maintain good liquid absorption and retention capacity, which is beneficial to further improve the liquid retention performance and structural stability of the separator, thereby improving the cycle performance of the battery cell.

[0103] In some embodiments, the solvophilic polymer may include one or more of acrylic polymers, fluorinated hydrocarbon polymers, polyethersulfone (PES), polyamides, and boranes.

[0104] In this application, acrylic polymer refers to polymers of acrylic acid and its derivatives. For example, acrylic polymer may include, but is not limited to, one or more of polymethyl acrylate, polymethyl methacrylate (may), polyethylene glycol dimethacrylate (PEGDMA), polymethyl methacrylate, polymethyl alpha chloroacrylate, and polymethyl alpha cyanoacrylate.

[0105] As an example, fluorinated hydrocarbon polymers may include, but are not limited to, one or more of the following: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride-trifluorochloroethylene copolymer (PVDF-CTFE), tetrafluoroethylene, hexafluoropropylene-vinylidene fluoride copolymer (THV), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA).

[0106] Polyethersulfone may include, but is not limited to, one or more of polyphenylene terephthalamide (MPIA), poly(p-phenylene terephthalamide) (PPTA), modified polyethersulfone, and polyphenylene sulfone.

[0107] In this application, borane refers to boron-containing hydrocarbons with the chemical formula BxHy, such as, but not limited to, diborane (B2H6), pentoborane (B5H9), and decaborane (B...). 10 H 14 One or more of the following.

[0108] In some embodiments, the thickness of the modification layer can be from 1 μm to 2 μm. A modification layer thickness within this range can provide good electrolyte absorption and retention capabilities, further improving the cycle performance of the battery cell. When the modification layer is thinner, its electrolyte adsorption capacity is lower, resulting in lower electrolyte retention by the separator, making it difficult to meet the electrolyte requirements during battery cell charge-discharge cycles. When the modification layer is thicker, the migration path of active ions in the electrolyte becomes longer, affecting the ion migration rate during battery cell charge-discharge cycles, thus impacting the cycle and fast-charging performance of the battery cell.

[0109] In some embodiments, the modification layer may be disposed on one side surface of the base film or on both sides surface of the base film.

[0110] In some embodiments, when the modification layer is located on one side of the base film, the modification layer is located on the side of the base film closer to the negative electrode. Positioning the modification layer on the side of the base film closer to the negative electrode allows the negative electrode to have good electrolyte wettability during the charge-discharge cycle of the battery cell, slows down lithium dendrite growth, and helps improve the cycle performance and reliability of the battery cell.

[0111] In some embodiments, the liquid retention capacity of the separator membrane can be from 7.2 g / Ah to 8.8 g / Ah, and optionally from 7.5 g / Ah to 8.5 g / Ah.

[0112] In this application, the electrolyte retention capacity of the separator refers to the mass of electrolyte that the separator can adsorb and hold, which reflects the separator's electrolyte retention capacity. The electrolyte retention capacity of the separator can be detected using methods known in the art. For example, take an unfilled battery cell and record its mass as m1 (in grams). After filling the battery cell with electrolyte and cycling it a certain number of times (200 or 500 cycles), record the mass of the battery cell as m2 (in grams). The electrolyte retention capacity ρ = (m2 - m1) / Wh, where Wh is the capacity of the battery cell, in Ah.

[0113] In some embodiments, the liquid absorption rate of the separator can be from 5 g / s to 15 g / s, and optionally from 8 g / s to 12 g / s. The liquid absorption rate of the separator refers to the rate at which the separator absorbs electrolyte per unit time, and can be detected using methods known in the art. For example, take a separator of a certain specification, record the original mass (mass before liquid absorption) m3 (in grams), immerse the separator in the electrolyte for a certain time t (in seconds), and record the mass m4 (in seconds) of the separator after liquid absorption. The liquid absorption rate of the separator is then determined.

[0114] In some embodiments, the air permeability of the separator can be from 180s / 100mL to 280s / 100mL, and optionally from 200s / 100mL to 250s / 100mL.

[0115] The air permeability of a separator membrane refers to the time required for 100 mL of gas to pass through a certain area of ​​the membrane. The air permeability can be tested using instruments and methods known in the art. An exemplary test method is as follows: Cut the separator membrane into 5 cm × 5 cm samples, apply a pressure of 1.21 kPa using an air permeability meter, and test the passage of 100 mL of gas at 6.45 cm. 2 The time required for the isolation membrane to be sealed is used to obtain its air permeability value, expressed in seconds per 100 mL.

[0116] In some embodiments, the porosity of the base membrane is 40% to 50%. The porosity of the base membrane is defined in a way known in the art and can be tested using instruments and methods known in the art. An exemplary test method is as follows: Take five 100mm × 100mm base membrane samples, measure their weights, and take the average as the base membrane weight M (mg). Calculate the porosity X of the base membrane using the formula X = [1 - M / (T × S × ρ)] × 100%, where T is the thickness of the base membrane, S is the area of ​​the base membrane, and ρ is the density of the polymer in the base membrane formulation.

[0117] In some embodiments, the base membrane can be any known porous structure separator membrane with good chemical and mechanical stability.

[0118] In some embodiments, the base film may be made of one or more of the following materials: glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The base film may be a single-layer film or a multi-layer composite film. When the base film is a multi-layer composite film, the materials of each layer may be the same or different.

[0119] In some embodiments, the base film can be a surface-treated film material. Surface treatment of the base film can increase its surface roughness and surface energy, thereby improving the adhesion of the modification layer to the base film surface, reducing the shedding of the modification layer during battery cell cycling, improving the structural stability of the separator, and ultimately improving the cycle performance of the battery cell.

[0120] In some embodiments, the separator membrane can be prepared by the following method:

[0121] S10 provides a surface-treated base film, wherein the tortuosity of the base film is 1.8 to 2.5;

[0122] S20, a modification layer is formed by in-situ grafting on the surface of the base film, and the contact angle between the modification layer and the electrolyte is 20° to 30°.

[0123] In some embodiments, the method for surface treatment of the base film may include one or more of corona treatment, plasma treatment, laser treatment, and chemical etching. By surface treating the base film, the surface energy of the base film can be increased, thereby enhancing the adhesion of the modification layer to the base film surface, reducing the shedding of the modification layer during battery cell cycling, and improving the cycle stability of the battery cell.

[0124] In some embodiments, the modification layer can be applied to the surface of the base film by methods such as gravure roller coating, extrusion coating, dip coating, or electrospinning.

[0125] [Positive electrode plate]

[0126] In some 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 electrode 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.

[0127] In some embodiments, the positive electrode active material includes a material capable of extracting and inserting lithium, thereby obtaining a negative electrode-free lithium metal battery cell.

[0128] 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.

[0129] In some embodiments, to further improve the energy density of a single battery cell, the positive electrode active material may include materials of the general formula Li. a Ni b Co c M d O e D fOne 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.

[0130] In some embodiments, the positive electrode active material may simultaneously comprise lithium transition metal oxide and lithium phosphate. This is advantageous for obtaining battery cells that balance high capacity and high reliability.

[0131] As an example, the positive electrode active material may include, but is not limited to, LiCoO2, LiNiO2, LiMnO2, and LiNi 1 / 2 Mn 1 / 2 O2, 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 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.80 Co 0.15 Al 0.05 O2, LiFePO4, LiMnPO4, Li 1.13 Ti 0.57 Fe 0.3 One or more of S2.

[0132] In some embodiments, the positive electrode active material includes a material capable of both sodium extraction and insertion. This results in a sodium-free negative electrode battery cell. For example, the positive electrode active material may include, but is not limited to, one or more of 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.

[0133] In some embodiments, as an example, 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.

[0134] 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.

[0135] In some embodiments, the positive electrode film may 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.

[0136] In some embodiments, the positive electrode film layer may 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).

[0137] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a first layer of polymeric material and a layer of metallic material formed on at least one surface of the first layer of polymeric material. As an example, the metallic 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 first layer of polymeric material may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0138] 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, positive electrode conductive agents, 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 this.

[0139] [Negative electrode plate]

[0140] In some embodiments, the negative electrode sheet may include a negative current collector and a first metal layer disposed on at least one surface of the negative current collector, wherein the metal element in the first metal layer may include one or more of alkali metal elements and alkaline earth metal elements.

[0141] In some embodiments, the metallic material in the first metal layer may include one or more of elemental lithium, lithium alloy, sodium, and sodium alloy.

[0142] 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.

[0143] 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.

[0144] In some embodiments, the negative electrode sheet may include a negative current collector and exclude the first metal layer to assemble a negative electrode-free metal battery cell.

[0145] In some 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 material substrate and a metal material layer formed on at least one surface of the polymer material 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 material substrates include, but are not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0146] [Electrolytes]

[0147] A single battery cell includes an electrolyte.

[0148] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and an organic solvent.

[0149] In some embodiments, the electrolyte includes 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.

[0150] In some embodiments, the electrolyte includes cations, which may include one or more of lithium ions and sodium ions.

[0151] In some embodiments, the concentration of the electrolyte salt may 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.

[0152] 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.

[0153] As an example, organic solvents may include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), butenyl 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.

[0154] In some embodiments, the electrolyte may optionally 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.

[0155] Methods for preparing battery cells are well known. In some 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 package, dried, and then injected with the 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 embodiments, multiple battery cells can also be directly assembled into a battery pack.

[0156] This application also provides an electrical device, which includes the battery device provided in this application. The battery device can be used as the power source for 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.

[0157] Electrical devices can choose the type of battery device according to their usage needs, such as individual battery cells, battery modules, or battery packs.

[0158] Figure 6 is a schematic diagram of an example electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0159] 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.

[0160] Example

[0161] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0162] Example 1

[0163] Separating membrane

[0164] S10, using a PE film with a thickness of 12μm as the base film, the surface of the base film is subjected to corona treatment at a voltage of 60kV, and the tortuosity of the resulting base film is 2.2.

[0165] S20, polymethyl methacrylate (PMMA) is coated on the surface of the base film to form a modification layer with a thickness of 2 μm, thus obtaining the isolation film.

[0166] Positive electrode sheet

[0167] Sodium iron pyrophosphate (positive electrode active material), carbon nanotubes (conductive agent), polyvinylidene fluoride (PVDF) (binder), conductive carbon black (dispersant), and benzoic acid (alkali removal agent) were mixed in a mass ratio of 93.8:3:2.5:0.3:0.4. Then, N-methylpyrrolidone (NMP) (organic solvent) was added and stirred until uniformly dispersed to obtain a positive electrode slurry. The positive electrode slurry was then coated on both sides of the aluminum foil surface of the positive electrode current collector, with a coating amount of 200 mg / 1540.25 cm². 2 The positive electrode sheet is obtained after drying, cold pressing, and slitting.

[0168] Negative electrode sheet

[0169] Carbon nanotubes (CNTs) are coated on both sides of the copper foil of the negative electrode current collector to serve as the negative electrode sheet, with a coating thickness of 3 μm on one side.

[0170] electrolyte

[0171] The electrolyte salt is sodium hexafluorophosphate (NaPF6) with a concentration of 1 mol / L, and the solvent for the electrolyte is dimethyl ethylene glycol (DME).

[0172] battery cell

[0173] In an argon-protected glove box, the above-mentioned positive electrode, negative electrode and separator are assembled and then injected with electrolyte to form a button cell.

[0174] Examples 2 to 15

[0175] The difference from Example 1 is that the parameters of the separator are different, as detailed in Table 1.

[0176] Example 16

[0177] The difference from Example 1 is that the battery cell is a lithium metal battery cell, and the positive electrode and electrolyte are different:

[0178] Positive electrode sheet

[0179] Lithium iron phosphate (LFP), carbon black (Super P), and polyvinylidene fluoride (PVDF) binder are mixed evenly in an appropriate amount of N-methylpyrrolidone (NMP) at a weight ratio of 8:1:1 to obtain a positive electrode slurry. The positive electrode slurry is coated onto aluminum foil for the positive electrode current collector, and then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0180] electrolyte

[0181] The electrolyte salt is LiFSI with a concentration of 1 mol / L, and the solvent for the electrolyte is dimethyl ethylene glycol ether (DME).

[0182] Comparative Examples 1 to 4

[0183] The difference from Example 1 is that the parameters of the separator are different, as detailed in Table 1.

[0184] Comparative Example 5

[0185] The difference from Example 1 is that no modification layer is provided on the surface of the base film.

[0186] Comparative Example 6

[0187] The difference from Example 16 is that no modification layer is provided on the surface of the base film.

[0188] Test section

[0189] (1) Liquid retention capacity of the separating membrane

[0190] Record the mass of the battery cell (capacity Wh) before electrolyte injection as m1. After injecting electrolyte into the battery cell, circulate it 200 times and then record the mass of the battery cell as m2. Calculate the electrolyte retention of the battery cell ρ = (m2-m1) / Wh, in g / Ah.

[0191] (2) Liquid absorption rate of the separating membrane

[0192] Take a separator membrane with dimensions of 5cm × 5cm and record its initial mass m3. Immerse the separator membrane in the electrolyte for a certain time t. After removing it, record the mass m4 of the separator membrane after absorbing the electrolyte. Record the electrolyte absorption rate of the separator membrane. The unit is g / s.

[0193] (3) Air permeability of the separator

[0194] The separator membrane was cut into 5cm x 5cm squares. Using a permeability meter, a pressure of 1.21 kPa was applied, and the permeability of 100ml of gas was measured to be 6.45cm. 2 The time required for the isolation membrane to be used is used to obtain its air permeability value, expressed in seconds per 100 ml.

[0195] (4) Porosity of the base film

[0196] Take 5 100mm×100mm base film samples, test their weight and take the average value as the base film weight M (mg). Calculate the porosity X of the base film using the formula X=[1-M / (T×S×ρ)]×100%, where T is the thickness of the base film, S is the area of ​​the base film, and ρ is the density of the polymer in the base film formulation.

[0197] (5) Battery cell cycle performance

[0198] At 25℃, a single battery cell is charged at a constant current of 0.33C to 3.65V, and then discharged at a rate of 0.33C to 1.5V. The reversible capacity is measured as C1. This charging and discharging process is repeated until the discharge capacity of the single battery cell, Cn / C1, is ≤80%, and the total number of cycles is recorded. Here, Cn is the reversible capacity at the nth cycle.

[0199] (6) Battery cell fast charging performance

[0200] At 25℃, the battery cell was charged to 3.65V at a constant current of 0.33C, allowed to stand for 30 minutes, then discharged to 1.5V at a constant current of 0.33C, allowed to stand for another 30 minutes, charged to 3.65V at a constant current of 0.33C, then charged to 0.05C at a constant voltage, allowed to stand for 30 minutes, and discharged to 1.5V at a constant current of 0.33C. The reversible capacity was recorded as C0.

[0201] The battery cell was charged to 3.65V with a constant current of 4C0, left to stand for 120 minutes, and then discharged to 1.5V with a constant current of 0.33C0, left to stand for 30 minutes. The reversible capacity Cm of the battery cell during charging and discharging was recorded. The fast charging capacity retention rate was Cm / C0*100%.

[0202] The performance test results are shown in Table 1.

[0203] Based on the data in Table 1, by setting a modification layer on the surface of the separator base film and adjusting the contact angle of the modification layer and the tortuosity of the base film, the separator can have good liquid retention capacity and stability, thereby improving the cycle performance and reliability of the battery cells.

[0204] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery cell, comprising: a housing; an electrode assembly accommodated in the housing, the electrode assembly comprising a pole piece and a separator, the pole piece and the separator being stacked, the separator comprising a base film and a modification layer on at least one side of the base film, wherein the tortuosity of the base film is 1.8 to 2.5; and the contact angle of the modification layer with electrolyte is 20° to 30°. The tortuosity of the base film is 2.0 to 2.3; and / or the contact angle of the modification layer with electrolyte is 20° to 25°. The material of the modification layer comprises a solventophilic polymer, and the solventophilic polymer has a swelling degree of 110% to 150% in an ether solvent. The solventophilic polymer contains a polar functional group, and the polar functional group comprises one or more of a carboxyl group, an amide group, a phenolic hydroxyl group, an alcoholic hydroxyl group, an ether bond, an amide group, a sulfonic acid group, a halogen atom, an ester group, and an aromatic ring. The molar content of the polar functional group in the solventophilic polymer is 5% to 30%.

2. The battery cell of claim 1, wherein, The solventophilic polymer comprises one or more of an acrylic polymer, a fluorinated hydrocarbon polymer, a polyether sulfone, a polyamide, and a borane. The thickness of the modification layer is 1 μm to 2 μm.

3. The battery cell of claim 1 or 2, wherein, The pole piece comprises a positive pole piece and a negative pole piece, the separator is located between the positive pole piece and the negative pole piece, and the modification layer is located on the side of the separator close to the negative pole piece.

4. The battery cell of claim 3, wherein, The liquid retention amount of the separator is 7.2 g / Ah to 8.8 g / Ah; and / or the liquid absorption rate of the separator is 5 g / s to 15 g / s; and / or the air permeability of the separator is 180 s / 100 mL to 280 s / 100 mL; and / or the porosity of the base film is 40% to 50%.

5. The battery cell of claim 4, wherein, The battery cell further comprises electrolyte, and the electrolyte comprises an organic solvent, and the organic solvent comprises an ether solvent.

6. The battery cell of any one of claims 3 to 5, wherein, The ether solvent comprises one or more of ethylene glycol dimethyl ether, dimethoxymethane, 1,2-dimethoxypropane, triethylene glycol dimethyl ether, 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran.

7. The battery cell of any one of claims 1 to 6, wherein, The battery cell comprises the battery cell of any one of claims 1 to 11.

8. The battery cell of any one of claims 1 to 7, wherein, 13.A device powered by electricity, comprising the battery device of claim 12.

9. The battery cell of any one of claims 1 to 8, wherein, 14.A separator, comprising a base film and a modification layer on at least one side of the base film, wherein the tortuosity of the base film is 1.8 to 2.5; and the contact angle of the modification layer with water is 20° to 30°. The tortuosity of the base film is 2.0 to 2.3; and / or the contact angle of the modification layer with water is 20° to 25°. The material of the modification layer comprises a solventophilic polymer, and the solventophilic polymer has a swelling degree of 110% to 150% in an ether solvent. The solventophilic polymer contains a polar functional group, and the polar functional group comprises one or more of a carboxyl group, an amide group, a phenolic hydroxyl group, an alcoholic hydroxyl group, an ether bond, an amide group, a sulfonic acid group, a halogen atom, an ester group, and an aromatic ring.

10. The battery cell of any one of claims 1 to 9, wherein, The molar content of the polar functional group in the solventophilic polymer is 5% to 30%.

11. The battery cell of claim 10, wherein, The solventophilic polymer comprises one or more of an acrylic polymer, a fluorinated hydrocarbon polymer, a polyether sulfone, a polyamide, and a borane.

12. A battery device, wherein, ​ ​ ​ ​ ​ 15. The separator film according to claim 14, wherein ​ ​ 16. The separator film according to claim 14 or 15, wherein ​ 17. The separator film according to claim 16, wherein ​ 18. The separator film according to claim 17, wherein ​ 19. The separator membrane according to claims 16 to 18, wherein, ​ 20. The separator membrane according to any one of claims 14 to 19, wherein, The thickness of the modification layer is 1-2 μm.

21. The separator membrane according to any one of claims 14 to 20, wherein, The liquid retention amount of the separation film is 180-220 g; and / or The liquid absorption rate of the separation film is 5-15 g / s; and / or The air permeability of the separation film is 180-280 s / 100 mL; and / or The porosity of the base film is 40-50%.

22. A method for preparing a separation film, comprising the following steps: A surface-treated base film is provided, wherein The tortuosity of the base film is 1.8-2.5; A modification layer is grafted in situ on the surface of the base film, and the contact angle of the modification layer with electrolyte is 20-30°.

23. The method of making according to claim 22, wherein, The method for surface treatment of the base film comprises one or more of corona treatment, plasma treatment, laser treatment, and chemical etching treatment.

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