A composite separator and its preparation method, a battery cell, a battery, and a battery pack.

Abstract

This application provides a composite separator, its preparation method, a battery cell, a battery, and a battery pack. The composite separator includes: a base membrane having a first end and a second end opposite to each other; a first expansion layer disposed on one side surface of the first end of the base membrane; and a second expansion layer disposed on the opposite side surface of the second end of the base membrane. This composite separator can improve the structural stability of the battery cell, thereby optimizing the cycle performance of the battery cell.

Description

Technical Field

[0001] This application relates to the field of battery materials, and in particular to a composite separator and its preparation method, a battery cell, a battery, and a battery pack. Background Technology

[0002] In lithium-ion batteries, the main functions of the separator in the cell include physically isolating the positive and negative electrodes to prevent short circuits; blocking electron conduction; maintaining the electrolyte and optimizing ion transport; and providing mechanical strength and structural support, thus providing good charging and discharging conditions for the cell.

[0003] However, current cylindrical battery cells suffer from problems such as center collapse and expansion deformation. These problems lead to uneven stress distribution within the cell, and when the expansion force and stress within the cell are high, it will seriously affect the battery's cycle life and safety. Summary of the Invention

[0004] This application provides a composite separator and its preparation method, a battery cell, a battery, and a battery pack. The composite separator includes a first end and a second end opposite to each other. A first expansion layer is provided on one side surface of the first end, and a second expansion layer is provided on the opposite side surface of the second end. The provision of the first expansion layer and the second expansion layer enables the composite separator to improve the structural stability of the battery cell, thereby improving the cycle performance of the battery.

[0005] In a first aspect, this application provides a composite separator, comprising:

[0006] The base membrane has a first end and a second end that are opposite each other;

[0007] A first expansion layer is disposed on one side surface of the first end of the base film;

[0008] A second expansion layer is disposed on the opposite side surface of the second end of the base film.

[0009] In one possible implementation, the expansion rate of the first expansion layer is greater than that of the second expansion layer.

[0010] In one possible implementation, the expansion rate of the first expansion layer is greater than or equal to 150%;

[0011] And / or, the expansion rate of the second expansion layer is greater than or equal to 120%.

[0012] In one possible implementation, the width of the first expansion layer is less than or equal to the width of the second expansion layer.

[0013] In one possible implementation, the width ratio of the first expanded layer to the base film is (0.55-0.70):1;

[0014] And / or, the width ratio of the second expanded layer to the base film is (0.70-0.85):1.

[0015] In one possible implementation, the width of the first expansion layer is greater than or equal to 35 mm and less than or equal to 44 mm;

[0016] And / or, the width of the second expansion layer is greater than or equal to 44 mm and less than or equal to 53 mm.

[0017] In one possible implementation, the first expansion layer comprises at least one of cross-linked fluorinated polyetheramine, perfluorinated polyether derivative, fluorinated acrylate copolymer, and cross-linked polyvinylidene fluoride;

[0018] And / or, the crosslinking density of the first expanded layer is 0.19 mol / m³. 3 -0.25mol / m 3 ;

[0019] And / or, the second expansion layer comprises at least one of cross-linked fluorinated polyetheramine, perfluoropolyether derivative, fluorinated acrylate copolymer, and cross-linked polyvinylidene fluoride;

[0020] And / or, the crosslinking density of the second expanded layer is 0.24 mol / m 3 -0.28mol / m 3 .

[0021] In one possible implementation, the crosslinking density of the first expanded layer is less than or equal to the crosslinking density of the second expanded layer.

[0022] In one possible implementation, the composite membrane further includes a first conductive layer and / or a second conductive layer;

[0023] At the first end of the base film, the first conductive layer is located between the base film and the first expanded layer;

[0024] And / or, at the second end of the base film, the second conductive layer is located between the base film and the second expansion layer.

[0025] In one possible implementation, the first conductive layer and / or the second conductive layer comprises a laser-induced graphene conductive layer.

[0026] In one possible implementation, the sheet resistance of the first conductive layer and / or the second conductive layer is less than or equal to 0.8 Ω / sq.

[0027] In one possible implementation, the width of the first conductive layer is less than or equal to the width of the base film;

[0028] And / or, the width of the second conductive layer is less than or equal to the width of the base film;

[0029] And / or, the thickness of the first conductive layer is 6μm-10μm;

[0030] And / or, the thickness of the second conductive layer is 6μm-10μm.

[0031] Secondly, this application provides a method for preparing the above-mentioned composite separator, comprising:

[0032] The first expansion layer is formed on one side surface of the first end of the base membrane, and the second expansion layer is formed on the opposite side surface of the second end of the base membrane to obtain the composite membrane.

[0033] In one possible implementation, the composite membrane further includes a first conductive layer and / or a second conductive layer;

[0034] The method for preparing the composite diaphragm further includes:

[0035] The first conductive layer is formed on one side surface of the first end of the base film;

[0036] And / or, the second conductive layer is formed on the opposite side surface of the second end of the base film.

[0037] Thirdly, this application also provides a battery cell, which includes a positive electrode, a negative electrode, and the above-mentioned composite separator or a composite separator prepared by the above-mentioned preparation method.

[0038] In one possible implementation, the first expansion layer on the composite separator is located near the center of the battery cell.

[0039] In one possible implementation, the thickness 'a' of the first expansion layer satisfies 0.75*R / (q*n)≤a≤0.95*R / (q*n);

[0040] And / or, the thickness d of the second expansion layer satisfies 1.0*G / (p*m)≤d≤1.25*G / (p*m);

[0041] Wherein, R is the radius of the center hole of the battery cell; G is the assembly gap of the battery cell; q is the expansion rate of the first expansion layer, p is the expansion rate of the second expansion layer; n is the number of winding turns in the region where the first expansion layer is located, and m is the number of winding turns in the region where the second expansion layer is located.

[0042] In one possible implementation, the radius of the central hole of the battery cell is greater than or equal to 2 mm and less than or equal to 5 mm.

[0043] And / or, in the battery cell, the number of winding turns in the region where the first expansion layer of the composite separator is located is greater than or equal to 2 and less than or equal to 7;

[0044] And / or, in the battery cell, the number of winding turns in the region where the second expansion layer of the composite separator is located is greater than or equal to 1 and less than or equal to 5.

[0045] In one possible implementation, the thickness of the first expansion layer of the composite diaphragm is greater than or equal to 150 μm and less than or equal to 190 μm;

[0046] And / or, the thickness of the second expansion layer of the composite diaphragm is greater than or equal to 200 μm and less than or equal to 250 μm.

[0047] In one possible implementation, the battery cell is a wound battery cell.

[0048] Fourthly, this application also provides a battery comprising the aforementioned battery cell.

[0049] Fifthly, this application also provides a battery pack comprising at least two of the aforementioned batteries.

[0050] The composite separator and its preparation method, cell, battery and battery pack provided in this application, by setting a first expansion layer and a second expansion layer at both ends of the composite separator, can not only prevent the cell from collapsing and avoid the gap between the positive and negative electrodes from increasing, but also fill the assembly gap between the outer layer of the cell and the shell through expansion, thereby improving the stability of the cell structure and thus improving the cycle performance of the battery. Attached Figure Description

[0051] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0052] Figure 1 This is a schematic diagram of the structure of the composite diaphragm provided in this application;

[0053] Figure 2 This is a first end side view of the composite diaphragm provided in this application;

[0054] Figure 3 This is a top view of the first end of the composite diaphragm provided in this application;

[0055] Figure 4 This is a second end side view of the composite diaphragm provided in this application;

[0056] Figure 5 This is a top view of the second end of the composite diaphragm provided in this application.

[0057] Explanation of reference numerals in the attached figures:

[0058] 1-First conductive layer; 2-First expanded layer; 3-Second conductive layer; 4-Second expanded layer; 5-Base film; a-Thickness of the first expanded layer; b-Thickness of the first conductive layer; H-Thickness of the base film; A-Width of the base film; c-Width of the first expanded layer; B-Length of the first expanded layer; d-Thickness of the second expanded layer; e-Thickness of the second conductive layer; f-Width of the second expanded layer; C-Length of the second expanded layer.

[0059] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0060] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0061] In lithium-ion batteries, the separator of the cell mainly functions to physically isolate the positive and negative electrodes to prevent short circuits; block electron conduction; maintain the electrolyte and optimize ion transport; and provide mechanical strength and structural support. It can provide good charging and discharging conditions for the cell.

[0062] Currently, during the charge-discharge cycle of lithium batteries, the internal structure of the cell expands due to the combined effects of materials and temperature. This disrupts the internal stress balance, leading to a decrease in cell lifespan and capacity. When the expansion force is large, the wall of the cell's central hole will indent inward, increasing the spacing between the positive and negative electrodes and raising the probability of thermal runaway and short circuits, posing a high risk. Furthermore, the lack of restraint design on the outer layer of the cell fails to provide adequate constraint to ensure structural stability under harsh operating conditions.

[0063] The composite separator and its preparation method provided in this application solve the problem of supporting the central hole of the cylindrical cell and the problem of supporting the assembly gap between the outer side of the cell and the shell by setting a first expansion layer and a second expansion layer on different sides at both ends of the base membrane, thereby maintaining the overall structural stability of the cell and improving the cycle performance of the battery.

[0064] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will now be described with reference to the accompanying drawings.

[0065] This application provides a composite membrane, comprising: a base membrane having opposing first and second ends;

[0066] A first expansion layer is disposed on one side surface of the first end of the base film;

[0067] A second expansion layer is disposed on the opposite side surface of the second end of the base film.

[0068] This application provides a first expansion layer and a second expansion layer on different sides at opposite ends of the base film. During cell cycling, the expansion of the first or second expansion layer allows for better absorption and buffering of the significant mechanical stress generated by the expansion of the electrode in the central hole area. Through its own expansion deformation, it provides more space for the expansion of the internal electrode, preventing inward concavity and reducing pressure and damage (such as breakage or powder shedding) on ​​the electrode and composite separator at bending points, thus lowering the risk of internal short circuits. The second or first expansion layer helps maintain the tightness and rigidity of the external winding structure, preventing excessive expansion and deformation of the cell as a whole. It also effectively fills the assembly gap between the cell and the casing and ensures good contact with the battery casing (facilitating heat dissipation), thereby ensuring the structural stability of the cell and improving its cycle performance.

[0069] In some specific embodiments, the first expansion layer and the second expansion layer expand by absorbing liquid. The first and second expansion layers can expand by absorbing liquids such as electrolyte, providing more space for the expansion of the internal electrode sheets, preventing them from sinking inward, and effectively filling the assembly gap between the cell and the casing, ensuring good contact with the battery casing (facilitating heat dissipation), thereby ensuring the structural stability of the cell and improving the cycle performance of the cell.

[0070] In some specific implementations, the expansion rate of the first expansion layer is greater than that of the second expansion layer.

[0071] In the composite separator provided in this application, the first end where the first expansion layer is located serves as the beginning of the central hole structure, and the second end where the second expansion layer is located serves as the end forming the periphery of the battery cell. Since the electrolyte in the battery cell is injected through the central hole, the first expansion layer in the central hole region is more easily wetted by the electrolyte. However, for the electrolyte to reach the second expansion layer located on the periphery, it needs to overcome capillary forces and gas resistance, permeating from the inside out to wet the second expansion layer. Therefore, controlling the expansion rate of the second expansion layer to be lower avoids excessive expansion in the peripheral region, which could compress the internal structure of the battery cell. Its lower expansion rate and denser structure help maintain the mechanical strength of the battery cell casing and provide a certain degree of external thermal insulation. Simultaneously, the higher expansion rate of the first expansion layer allows it to absorb the electrolyte and swell more quickly and significantly.

[0072] In some implementations, the expansion rate of the first expansion layer is greater than or equal to 150%.

[0073] When the composite separator is fabricated into a cylindrical battery cell, the first end containing the first expansion layer is used as the starting end for forming the central hole structure, and the second end containing the second expansion layer is used as the ending end for forming the outer periphery of the battery cell. When the expansion rate of the first expansion layer is greater than or equal to 150%, more electrolyte can be stored in the central hole region, acting as an additional heat capacity buffer; it also provides better ion transport channels, which helps reduce the impedance and heat generation in the central region. In addition, the first expansion layer with the above expansion rate can also prevent the battery cell from collapsing, which helps improve the cycle performance of the battery.

[0074] In some optional embodiments, the expansion rate of the first expansion layer may be less than or equal to 300%. In this case, the first expansion layer with an expansion rate greater than or equal to 150% and less than or equal to 300% can further prevent cell structure deformation during battery cycle charging and discharging, ensure the integrity and insulation performance of the composite separator, help maintain electrolyte wetting and ion conduction efficiency, and improve the cycle performance of the cell.

[0075] For example, the expansion layer of the first expansion layer can be a range of 150%, 160%, 170%, 180%, 190%, 200%, 210%, 220%, 230%, 240%, 250%, 260%, 270%, 280%, 290%, 300%, or any two of these.

[0076] In some implementations, the expansion rate of the second expansion layer is greater than or equal to 120%.

[0077] When the expansion rate of the second expansion layer is greater than or equal to 120%, it not only allows the electrolyte to quickly wet the cell, but also provides basic elasticity, absorbs some stress, helps to relieve the pressure between the electrode and the separator, improves the ion transport rate, and thus improves the cell's cycle performance and other properties.

[0078] In some optional embodiments, the expansion rate of the second expansion layer can also be less than or equal to 200%. In this case, selecting an expansion rate of the second expansion layer greater than or equal to 120% and less than or equal to 200% is beneficial for maintaining the structural integrity of the electrode in the cell edge region and protecting the cell's sealing structure. It also helps to further improve the isolation function of the composite separator at lower operating temperatures, synergistically optimize the temperature field distribution, increase the ion conduction rate around the cell, and improve the cell's cycle performance.

[0079] For example, the expansion rate of the second expansion layer can be a range of 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190%, 200%, or any combination thereof.

[0080] Specifically, the expansion rate can be tested using the following method:

[0081] Standard samples were prepared in a glove box and then immersed in an electrolyte solution at a constant temperature using a time-gradient method. The immersed samples were then placed in an inert atmosphere using a laser thickness gauge for non-contact, rapid thickness measurement. The experiment was repeated 3-5 times, with a blank diaphragm as a control. The thickness expansion rate (ΔD%±SD) was accurately calculated, and the expansion rate (dΔD / dt) and swelling equilibrium time (t) were plotted. 90 The dynamic characteristic curve of ).

[0082] In some implementations, the width of the first expansion layer is less than or equal to the width of the second expansion layer.

[0083] In cylindrical battery cells, the central hole region experiences higher temperatures and more significant thermal expansion, while the peripheral region has lower temperatures and is subject to greater constraint. Choosing a first expansion layer with a width smaller than the second expansion layer helps control the high-temperature expansion at the center. A wider second expansion layer allows the peripheral region to accommodate more expansion under strong constraint. By controlling the width of the first expansion layer to be less than or equal to the width of the second expansion layer, the spatial distribution of expansion in both the central hole and peripheral regions of the cell becomes more uniform and controllable, further optimizing the cell's structural stability and improving its cycle performance.

[0084] In some embodiments, the width ratio of the first expanded layer to the base film is (0.55-0.70):1.

[0085] Since the composite membrane in the central hole region has the smallest bending radius, the maximum tensile stress is concentrated at the interface between the first expansion layer and the base membrane. By selecting a width ratio of (0.55-0.70):1 for the first expansion layer and the base membrane, the area on the base membrane not covered by the first expansion layer is retained as a flexible hinge. The elastic deformation of the base membrane in this area absorbs more than 60% of the bending stress, which helps to improve the interface integrity of the first expansion layer.

[0086] For example, the width ratio of the first expanded layer to the base film can be a range of 0.56:1, 0.63:1, 0.70:1, or any two of these.

[0087] In some embodiments, the width ratio of the second expanded layer to the base film is (0.70-0.85):1.

[0088] By limiting the width ratio of the second expansion layer to the base film within the aforementioned range, a flexible buffer zone can be reserved to absorb lateral expansion stress. This also allows the base film with its microporous structure to better transfer heat, and the base film area not covered by the second expansion layer forms an isothermal heat dissipation strip, which helps to increase the heat dissipation channels inside the battery cell.

[0089] For example, the width ratio of the second expanded layer to the base film can be a range of 0.70:1, 0.78:1, 0.84:1, 0.87:1, or any two of these.

[0090] In some implementations, the width of the first expansion layer is greater than or equal to 35 mm and less than or equal to 44 mm.

[0091] The maximum width of the first expansion layer, which serves as the beginning of the winding, is generally determined by the diameter of the winding needle and the wrap angle of the first turn of the diaphragm, while its minimum effective width needs to cover the stress peak region. By limiting the width of the first expansion layer within the above range, the stress buffering and mechanical strength of the composite diaphragm can be balanced, further improving its electrochemical performance and structural reliability.

[0092] For example, the width of the first expansion layer can be a range of 35 mm, 40 mm, 44 mm, or any combination thereof.

[0093] In some embodiments, the width of the second expansion layer is greater than or equal to 44 mm and less than or equal to 53 mm.

[0094] As the second expansion layer at the winding tail end, considering its functions of stress buffering, edge liquid retention and heat dissipation, the width of the second expansion layer of the composite separator can be limited within the above range in order to obtain a battery cell with better cycle performance.

[0095] For example, the width of the second expansion layer can be a range of 44 mm, 49 mm, 53 mm, or any combination thereof.

[0096] In some embodiments, the first expansion layer includes at least one of cross-linked fluorinated polyetheramine (CL-PEA), perfluoropolyether derivative (PFPE), fluorinated acrylate copolymer (FAC), and cross-linked polyvinylidene fluoride (CL-PVDF).

[0097] In some embodiments, the second expansion layer includes at least one of cross-linked fluorinated polyetheramine (CL-FPEA), perfluoropolyether derivative (PFPE), fluorinated acrylate copolymer (FAC), and cross-linked polyvinylidene fluoride (CL-PVDF).

[0098] In some embodiments, the crosslinking density of the first expanded layer is 0.19 mol / m³. 3 -0.25mol / m 3 .

[0099] Within this crosslinking density range, the first expansion layer swells more easily in the electrolyte, forming more interconnected channels and thus improving the ion transport rate. Moreover, the first expansion layer at this crosslinking density is more flexible and can deform with the expansion or contraction of the electrode, avoiding interface peeling or local stress concentration and preventing battery capacity decay; during lithium dendrite growth, it can also wrap the dendrites through local deformation, further reducing the risk of them puncturing the separator.

[0100] For example, the crosslinking density of the first expanded layer can be 0.19 mol / m 3 0.20 mol / m 3 0.21mol / m 3 0.22mol / m 3 0.23mol / m 3 0.24mol / m 3 0.25mol / m 3 Or a range consisting of any two of them.

[0101] In some embodiments, the crosslinking density of the second expanded layer is 0.24 mol / m³. 3 -0.28mol / m 3 .

[0102] The second expansion layer with the aforementioned cross-linking density provides moderate swelling, keeps the pores open, and prevents deposits from completely clogging the pores.

[0103] For example, the crosslinking density of the second expanded layer can be 0.24 mol / m 3 0.25mol / m 3 0.26mol / m3 0.27mol / m 3 0.28mol / m 3 Or a range consisting of any two of them.

[0104] In some specific implementations, the crosslinking density of the first expanded layer is less than or equal to the crosslinking density of the second expanded layer.

[0105] The first expansion layer, as the beginning of the composite separator, has a relatively low cross-linking density, making it easier for the electrolyte to swell and improving the interfacial contact between the composite separator and the positive electrode. The second expansion layer, as the end of the composite separator, has a relatively high cross-linking density, representing a tighter network structure and greater dimensional stability. This facilitates rapid electrolyte wetting, ensuring a more sufficient electrolyte retention and resulting in a battery with better cycle performance.

[0106] In some embodiments, the composite membrane further includes a first conductive layer and / or a second conductive layer; at a first end of the base membrane, the first conductive layer is located between the base membrane and the first expansion layer.

[0107] In some embodiments, at the second end of the base film, a second conductive layer is located between the base film and the second expansion layer.

[0108] By introducing a conductive layer between the base film and the first expansion layer / the base film and the second expansion layer, the conductivity of the conductive network of the composite separator is maintained, the uniformity of ion transport is ensured, the conductivity of the composite separator is further improved, and the cycle performance of the battery is improved.

[0109] Figure 1 This is a schematic diagram of the structure of the composite diaphragm provided in some embodiments of this application, such as... Figure 1 As shown, the composite membrane includes:

[0110] The first conductive layer 1, the first expansion layer 2, the second conductive layer 3, the second expansion layer 4, and the base film 5.

[0111] Furthermore, in order to obtain a composite membrane with better performance, the first conductive layer and / or the second conductive layer can be selected as a laser-induced graphene conductive layer (LIG conductive layer).

[0112] In some embodiments, the sheet resistance of the first conductive layer and / or the second conductive layer is less than or equal to 0.8 Ω / sq.

[0113] By limiting the sheet resistance of the first conductive layer and / or the second conductive layer to the above range, it is beneficial to protect the ion-dominated current path, thereby improving the cycle performance of the battery.

[0114] For example, the sheet resistance of the first conductive layer and / or the second conductive layer may be a range of 0.1Ω / sq, 0.2Ω / sq, 0.3Ω / sq, 0.4Ω / sq, 0.5Ω / sq, 0.6Ω / sq, 0.7Ω / sq, 0.8Ω / sq, or any combination thereof.

[0115] It should be noted that the sheet resistance of the first conductive layer and the second conductive layer may be the same or different, and no limitation is made here.

[0116] In some implementations, the width of the first conductive layer is less than or equal to the width of the base film.

[0117] In some embodiments, the width of the second conductive layer is less than or equal to the width of the base film.

[0118] It is understandable that the conductive layer exists to improve the conductivity of the composite separator. Ensuring that the width of the first conductive layer and / or the second conductive layer is less than or equal to the width of the base film improves the safety of battery use and also allows for a more uniform current distribution within the cell, which helps extend the battery's lifespan and reliability.

[0119] In some embodiments, the thickness of the first conductive layer is 6 μm-10 μm.

[0120] In some embodiments, the thickness of the second conductive layer is 6 μm-10 μm.

[0121] The thickness of the conductive layer affects the migration path of electrolyte ions. The first conductive layer and / or the second conductive layer with the above-mentioned thickness range can simultaneously improve its own ionic conductivity and optimize the interface contact between it and the base film, thereby realizing the construction of a more continuous electronic network and the formation of a dendritic physical barrier layer.

[0122] For example, the thickness of the first conductive layer can be in the range of 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any combination thereof. The thickness of the second conductive layer can be in the range of 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any combination thereof.

[0123] It should be noted that the thicknesses of the first conductive layer and the second conductive layer may be the same or different, which is not limited here.

[0124] The composite separator provided in this application embodiment, by setting a first expansion layer and a second expansion layer on different sides at opposite ends of the base film, enables the resulting composite base film to support the central hole structure of the battery cell when wound into a cylindrical battery cell, preventing the central hole from collapsing inward due to electrode expansion during cyclic operation. It can also fill the assembly gap between the outer layer of the battery cell and the shell, ensuring that there is a certain gap between the battery cell and the shell, thereby improving the structural stability of the battery cell in the shell and ultimately achieving the technical effect of optimizing the cycle performance of the battery cell.

[0125] This application also provides a method for preparing the above-mentioned composite separator, comprising: forming a first expansion layer on one side surface of a first end of the base membrane, and forming a second expansion layer on the opposite side surface of a second end of the base membrane, thereby obtaining the composite separator.

[0126] In some embodiments, the base film can be polyethylene (PE), polypropylene (PP), polyethylene / polypropylene composite film, aramid (poly(p-phenylene terephthalamide, PPTA), polyimide (PI), etc.

[0127] Taking cross-linked fluorinated polyetheramine as the first expansion layer as an example, the formation of the first expansion layer on one side surface of the first end of the base film may include the following steps: mixing polyetheramine prepolymer, diluent perfluoropolyether, perfluorooctylsilane modified nano-TiO2 (particle size of 5nm) and photoinitiator Irgacure184 at a mass ratio of 6:4:1:0.2 (high shear dispersion at 15℃ and 3000rpm), then vacuum dehydrating at 80℃ to a moisture content of <200ppm, grinding with three rollers to a slurry viscosity of 3500±200cP and vacuum degassing, then forming a 25μm wet film on a plasma-treated PE membrane by microgravure coating at a speed of 8m / min, and constructing a three-dimensional cross-linked network (cross-linking density of 0.22±0.03mol / m²) by gradient UV curing (365nm main peak, 120mW / cm², total cumulative dose of 6000mJ / cm²) under a nitrogen atmosphere (O2<200ppm). 3 The UV cumulative dose in the main curing zone is 4000 mJ / cm²; it is finally subjected to step annealing at 80-120℃ and atmospheric pressure plasma fluorination treatment (C3F6 / He).

[0128] It should be noted that the raw materials and molding process conditions for the preparation of the first expansion layer in the above process can be adjusted according to the actual application requirements, and are not limited here.

[0129] The second expansion layer can be formed on the second end of the base film relative to the other side by adjusting the process parameters based on the forming method of the first expansion layer. Specifically, polyetheramine prepolymer, perfluoropolyether diluent, perfluorooctylsilane modified nano-TiO2 (particle size of 5nm), and photoinitiator Irgacure184 are mixed in stages in a planetary mixer at a mass ratio of 7:3:1.2:0.25 (high shear dispersion at 15℃ and 3000rpm), then vacuum dehydrated at 80℃ until the moisture content is <200ppm, and then milled by three rollers until the slurry viscosity is 3500±200cP and vacuum degassed to obtain the slurry. Subsequently, a 25 μm wet film was formed on the plasma-treated PE diaphragm using microgravure coating at a speed of 8 m / min. A three-dimensional cross-linked network (cross-linking density 0.26 ± 0.02 mol / m²) was then constructed under a nitrogen atmosphere (O₂ < 200 ppm) using gradient UV curing (365 nm main peak, 120 mW / cm², total cumulative dose 6000 mJ / cm²). 3 The UV cumulative dose in the main curing zone is 4500 mJ / cm²; it is finally subjected to step annealing at 80-120℃ and atmospheric pressure plasma fluorination treatment (C3F6 / He).

[0130] It should be noted that the raw materials and molding process conditions for the preparation of the second expansion layer in the above process can be adjusted according to the actual application requirements, and are not limited here.

[0131] In some embodiments, the composite separator further includes a first conductive layer and a second conductive layer; in this case, the method for preparing the composite separator further includes:

[0132] The conductive layer is formed on one side surface of the first end of the base film;

[0133] The conductive layer is formed on the opposite side surface of the second end of the base film.

[0134] In some embodiments, the composite membrane further includes a first conductive layer but does not include a second conductive layer; in this case, the method for preparing the composite membrane further includes forming a first conductive layer on one side surface of the first end of the base membrane.

[0135] In some embodiments, the composite membrane further includes a second conductive layer but does not include the first conductive layer; in this case, the method for preparing the composite membrane further includes forming a second conductive layer on the surface of the second expansion layer at the second end of the base membrane.

[0136] Specifically, taking the example where both the first and second conductive layers are LIG conductive layers, the process of depositing a LIG conductive layer on the surface of the base film includes: activating the base film and laser sensitizing it by performing plasma etching (He / O2=95:5, 300W) and polydopamine coating (2g / L dopamine, polymerization at 50℃) at both ends of the base film; then performing a spiral progressive scan using a dual-wavelength CO2 laser (10.6μm / 9.3μm, 4.0W / cm²) in conjunction with in-situ boron doping (5wt% boric acid) to generate a 12μm thick three-dimensional graphene layer (sheet resistance 15Ω / sq); then enhancing conductivity through pulsed chemical copper plating (CuSO4 15g / L, deposition of a 1.8μm thick copper layer at 50℃) and microwave annealing (2.45GHz, 800W), finally obtaining a LIG conductive layer (sheet resistance 0.8Ω / sq).

[0137] The LIG conductive layer prepared by the above process has excellent flexibility, with a conductivity retention rate of >95% after 5000 bends, and has passed the aging test at 100℃ / 1000h. It is particularly suitable for high-rate flexible current collectors for power batteries, and the mass production line speed can reach 1.2m / min with a yield rate of over 98%.

[0138] In some embodiments, the process of forming the first and second expansion layers on the surface of the LIG conductive layer includes: treating the LIG conductive layer surface with inert element plasma, then precisely controlling the thickness of the first and second expansion layer wet films to 18±2μm at a speed of 5m / min using a slot coater on the LIG conductive layer surface, allowing it to stand and level for 90 seconds after coating, and then entering a 40℃ preheating section to eliminate shear stress; subsequently, performing gradient UV curing in a nitrogen-protected chamber (O2<500ppm) (pre-curing at 365nm / 80mW / cm² for 120s to form a surface crosslinking layer, then switching to 385nm / 120mW / cm² for 300s main curing, with a cumulative dose of 5200mJ / cm²), while simultaneously applying 0.5MPa roller pressure to enhance the mechanical interlocking between the wet film and the porous structure of the LIG conductive layer; finally, annealing at 105℃ / 1h to bond the interface between the first and second expansion layers and the LIG conductive layer.

[0139] It should be noted that the raw materials and molding process conditions for the conductive layer can be adjusted according to the actual application requirements, and the above process does not limit them.

[0140] This application also provides a battery cell, which includes a positive electrode, a negative electrode, and the above-described composite separator or a composite separator prepared by the above-described preparation method.

[0141] Composite separators, positive and negative electrodes are the core components of a battery cell (single cell). They are formed into a cell through specific structural design and assembly processes. The core of this process lies in creating an internal environment that allows ions to move freely but prevents electrons from flowing directly. In some embodiments of this application, the battery cell can be a wound cylindrical cell, wound in the order of a positive electrode layer, a composite separator layer, and a negative electrode layer. The cell is placed in a specific container, such as a cylindrical shell, and then an electrolyte is injected into it. The electrolyte permeates into the micropores of the composite separator, forming ion transport channels, and simultaneously permeates into the porous coatings of the positive and negative electrodes, contacting the active materials, ultimately forming a complete ion conduction path, which constitutes the basis for the electrochemical reaction.

[0142] In some embodiments, the first expansion layer on the composite separator is located near the center of the battery cell.

[0143] In some embodiments, the thickness 'a' of the first expansion layer satisfies 0.75*R / (q*n)≤a≤0.95*R / (q*n); where R is the radius of the circle of the center hole of the battery cell; q is the expansion rate of the first expansion layer; and n is the number of turns of the first expansion layer in the region.

[0144] In some embodiments, the thickness d of the second expansion layer satisfies 1.0*G / (p*m)≤d≤1.25*G / (p*m); where G is the assembly gap of the battery cell; p is the expansion rate of the second expansion layer; and m is the number of winding turns in the region where the second expansion layer is located.

[0145] By limiting the thickness 'a' of the first expansion layer and the thickness 'd' of the second expansion layer to the nonlinear coupling relationship related to their own expansion rate, the radius of the center hole of the battery cell, the battery cell assembly gap, and the number of winding turns in their respective regions, the expansion loss in the battery cell is minimized while maximizing the energy density of the battery cell, thereby improving the cycle life of the battery cell.

[0146] like Figure 2 As shown, a represents the thickness of the first expansion layer 2, b represents the thickness of the first conductive layer 1, and H represents the thickness of the base film 5.

[0147] like Figure 3 As shown, c represents the width of the first expansion layer 2, A represents the width of the base film 5, and B represents the length of the first expansion layer 2.

[0148] like Figure 4 As shown, d represents the thickness of the second expansion layer 4, and e represents the thickness of the second conductive layer 3.

[0149] like Figure 5 As shown, f represents the width of the second expansion layer 4, and C represents the length of the second expansion layer 4.

[0150] G represents the assembly gap of the battery cell, which refers to the distance between the battery cell and the inner cavity of the casing after the battery cell is installed. Specifically, this gap distance can be determined by taking the average value of multiple measurements of the distance between the battery cell and the inner cavity of the casing.

[0151] In some implementations, the radius of the center hole of the battery cell is greater than or equal to 2 mm and less than or equal to 5 mm.

[0152] When the composite separator is wound together with the electrode sheet to form a battery cell, the radius of the circle of the central hole of the battery cell is minimized within a controllable range to improve the energy density of the battery cell. By limiting the radius of the circle of the central hole of the battery cell within the above range, the resulting battery cell can achieve high energy density while taking into account properties such as electrolyte wetting, mechanical strength and cell capacity, so that the battery has good cycle performance and service life.

[0153] For example, the radius of the center hole of the battery cell can be 2 mm, 3 mm, 4 mm, 5 mm, or any combination thereof.

[0154] In some embodiments, the number of turns in the region where the first expansion layer of the composite diaphragm is located is greater than or equal to 2 and less than or equal to 7.

[0155] By limiting the number of winding turns in the area where the first expansion layer is located, the total expansion and mechanical constraint strength in that area are reduced, the pressure in the physical space is relieved, more radial expansion space is left, and the stress distribution of the entire cell is made more uniform.

[0156] The number of winding turns in the area where the first expansion layer is located refers to the number of pre-wound turns of the composite separator at the end closest to the center hole of the battery cell. This portion of the separator, after being stacked and unfolded with the electrode, does not correspond to the electrode; that is, the separator extends beyond the electrode area. The first expansion layer is disposed in this area. Furthermore, the first expansion layer may cover the entire area or only partially cover it.

[0157] For example, the number of turns in the region where the first expansion layer is located can be a range of 2, 3, 4, 5, 6, 7 or any two of them.

[0158] In some embodiments, the number of turns in the region where the second expansion layer of the composite diaphragm is located is greater than or equal to 1 and less than or equal to 5.

[0159] By limiting the number of winding turns in the area where the second expansion layer is located, reducing the number of electrode layers in the winding tail area, controlling the total expansion and mechanical load of the outer layer of the cell, further alleviating the tensile stress on the periphery of the cell, reducing the deformation risk of the cell shell, and helping to reduce the expansion gradient between the inner and outer layers of the cell, and improving the longitudinal flatness of the cell electrode and separator during battery cycling.

[0160] The number of winding turns in the area where the second expansion layer is located refers to the number of turns of the separator pre-wound at the end away from the center hole of the cell, i.e., the number of extra turns of the separator at the tail end of the cell. This part of the separator is close to the cell casing during the winding of the cell. After being stacked with and unfolded with the electrode, this part of the separator does not correspond to the electrode, i.e., the area where the separator extends beyond the electrode. The second expansion layer is disposed in this area. Furthermore, the second expansion layer may cover the entire area or only partially cover this area.

[0161] For example, the number of turns in the region where the second expansion layer is located can be a range of 1, 2, 3, 4, 5 or any two of them.

[0162] In some embodiments, the thickness of the first expansion layer is greater than or equal to 150 μm and less than or equal to 190 μm.

[0163] As the first end forming the central hole region, the first expansion layer it includes needs to meet the requirements of high-strength electrolyte absorption capacity, sufficient buffer space and rapid thermal response capability. When the thickness of the first expansion layer is within the above range, it can take into account the interfacial contact between the composite separator and the electrode and the ion transport efficiency in the cell, thus ensuring the energy density and structural stability of the cell.

[0164] For example, the thickness of the first expansion layer can be a range of 150 μm, 160 μm, 170 μm, 180 μm, 190 μm or any combination thereof.

[0165] In some embodiments, the thickness of the second expansion layer is greater than or equal to 200 μm and less than or equal to 250 μm.

[0166] As the second end forming the periphery of the battery cell, its second expansion layer needs to be able to absorb mechanical stress and maintain the shape stability of the wound battery cell exterior. When the thickness of the second expansion layer is within the above-mentioned range, it can take into account both the stability of the electrode structure and the uniformity of electrolyte distribution, and work together with the first expansion layer to construct a battery cell system with a stable structure and better cycle performance.

[0167] For example, the thickness of the second expansion layer can be 200μm, 210μm, 220μm, 230μm, 240μm, 250μm, etc.

[0168] In addition, the length of the first expansion layer can be calculated based on the number of turns in the region where the first expansion layer is located, and the length of the second expansion layer can be calculated based on the number of turns in the region where the second expansion layer is located. The calculation method can be the commonly used method in this field.

[0169] In some embodiments, the battery cell provided in this application is a wound battery cell, which has structural stability and excellent cycle performance.

[0170] This application also provides a battery comprising the aforementioned battery cell. This battery exhibits excellent cycle performance, retaining over 80% of its capacity after 1000 cycles.

[0171] The battery includes a casing and a cell, with the cell installed inside the casing and having a gap between it and the inner wall of the casing.

[0172] This application also provides a battery pack comprising at least two of the aforementioned batteries.

[0173] The present application will be further described below through specific embodiments.

[0174] Example 1

[0175] A composite membrane includes a first expansion layer, a second expansion layer, and a base membrane; the first expansion layer is made of cross-linked fluorinated polyetheramine (CL-PEA), and the second expansion layer is also made of cross-linked fluorinated polyetheramine (CL-PEA); the base membrane is made of PP material.

[0176] The preparation method of this composite membrane includes the following steps:

[0177] Formation of the first expansion layer:

[0178] Slurry preparation: Polyetheramine prepolymer, diluent perfluoropolyether, perfluorooctylsilane modified nano-TiO2 (particle size of 5nm) and photoinitiator Irgacure184 were mixed at a mass ratio of 6:4:1:0.2 (high shear dispersion at 15℃ and 3000rpm), and then vacuum dehydrated at 80℃ until the moisture content was <200ppm;

[0179] Slurry coating: The obtained slurry is milled to a viscosity of 3500±200cP by three rollers and degassed under vacuum. Then, it is coated with a microgravure coating machine at a speed of 8m / min to form a 25μm wet film on the plasma-treated PP base film.

[0180] Curing and molding: The above wet film was cured under a nitrogen atmosphere (O2 < 200 ppm) using gradient UV curing (365 nm main peak, 120 mW / cm², cumulative dose 6000 mJ / cm²) to construct a three-dimensional cross-linked network. The cumulative UV dose in the main curing region was 4000 mJ / cm². Cross-linked fluorinated polyetheramine (cross-linking density 0.22 mol / m²) was formed. 3 Finally, the first expansion layer was obtained by annealing at 90℃ for 1h and fluorination by atmospheric pressure plasma (C3F6 / He).

[0181] Formation of the second expansion layer:

[0182] Similar to the formation process of the first expansion layer, the difference lies in the mass ratio of polyetheramine prepolymer, diluent perfluoropolyether, perfluorooctylsilane-modified nano-TiO2, and photoinitiator Irgacure184: 7:3:1.2:0.25; the cumulative UV dose in the main curing zone is 4500 mJ / cm², forming a cross-linked fluorinated polyetheramine (cross-linking density of 0.26 mol / m²). 3 ), ultimately resulting in a composite membrane.

[0183] The expansion rates of the first and second expansion layers in the composite diaphragm were tested according to the following steps:

[0184] Standard samples (20 mm × 50 mm) were prepared in a glove box (H2O / O2 < 0.1 ppm). The prepared samples were then immersed in an electrolyte (1 mol / L LiPF6 / EC:DMC) at a time-gradient (0.5 h, 1 h, 2 h, 4 h, 8 h, 24 h) under constant temperature. The immersed samples were then placed in an inert atmosphere and subjected to non-contact rapid thickness measurement using a laser thickness gauge. The experiment was repeated 3-5 times, with a blank diaphragm as a control. The thickness expansion rate (ΔD% ± SD) was accurately calculated, and the expansion rate (dΔD / dt) and swelling equilibrium time (t) were plotted. 90 The dynamic characteristic curves of the first expansion layer were measured; the expansion rate of the first expansion layer was q=200%, and the expansion rate of the second expansion layer was p=150%.

[0185] A battery cell includes a positive electrode sheet with a width of 56 mm, a negative electrode sheet with a width of 58 mm, the aforementioned composite separator, an electrolyte, and a cylindrical shell.

[0186] The positive electrode, composite separator, and negative electrode are stacked sequentially and then wound to form a structural component. The positive electrode has 20 turns and the negative electrode has 21 turns. After assembling the resulting structural component with a cylindrical shell, electrolyte is injected into it to obtain a test cylindrical battery cell.

[0187] In the composite membrane, the thickness of the base membrane is H=20μm and the width of the base membrane is A=63mm; the thickness of the first expansion layer is a=140μm and the width is c=30mm; the thickness of the second expansion layer is d=190μm and the width is f=40mm.

[0188] The radius of the center hole of the battery cell is R=2mm, the assembly gap is G=0.6mm, the number of winding turns n in the area where the first expansion layer is located is 5 turns, and the number of winding turns m in the area where the second expansion layer is located is 2 turns.

[0189] Example 2

[0190] Similar to Example 1, except that the thickness of the first expansion layer is a = 150 μm.

[0191] Example 3

[0192] Similar to Example 1, except that the thickness of the first expansion layer is a = 170 μm.

[0193] Example 4

[0194] Similar to Example 1, except that the thickness of the first expansion layer is a = 190 μm.

[0195] Example 5

[0196] Similar to Example 1, except that the thickness of the first expansion layer is a = 200 μm.

[0197] Example 6

[0198] Similar to Example 2, except that the width of the first expansion layer is c=35mm.

[0199] Example 7

[0200] Similar to Example 2, except that the width of the first expansion layer is c=40mm.

[0201] Example 8

[0202] Similar to Example 2, except that the width of the first expansion layer is c=44mm.

[0203] Example 9

[0204] Similar to Example 2, except that the width of the first expansion layer is c=50mm.

[0205] Example 10

[0206] Similar to Example 7, except that the thickness of the second expansion layer is d=200μm.

[0207] Example 11

[0208] Similar to Example 7, except that the thickness of the second expansion layer is d=230μm.

[0209] Example 12

[0210] Similar to Example 7, except that the thickness of the second expansion layer is d=250μm.

[0211] Example 13

[0212] Similar to Example 7, except that the thickness of the second expansion layer is d=260μm.

[0213] Example 14

[0214] Similar to Example 11, except that the width of the second expansion layer is f = 44 μm.

[0215] Example 15

[0216] Similar to Example 11, except that the width of the second expansion layer is f = 49 μm.

[0217] Example 16

[0218] Similar to Example 11, except that the width of the second expansion layer is f = 53 μm.

[0219] Example 17

[0220] Similar to Example 11, except that the width of the second expansion layer is f = 55 μm.

[0221] Example 18

[0222] Similar to Example 14, the difference is that the composite membrane further includes a first conductive layer and a second conductive layer, both of which are LIG conductive layers; the thickness b of the first conductive layer and the thickness e of the second conductive layer satisfy b=e=10μm.

[0223] The preparation method of this composite membrane includes the following steps:

[0224] Formation of the first conductive layer and the second conductive layer:

[0225] Base film activation: The first and second ends of the PE base film were activated and laser-sensitized by plasma etching (He / O2=95:5, 300W) and polydopamine coating (2g / L dopamine, polymerization at 50℃);

[0226] Formation of graphene layer: The surface of the activated PE base film was spirally scanned using a dual-wavelength CO2 laser (10.6μm / 9.3μm, 4.0W / cm²) and in situ boron doping (5wt% boric acid) was combined to generate a 12μm thick three-dimensional graphene layer (sheet resistance 15Ω / sq).

[0227] Post-processing: Pulse chemical copper plating (15 g / L CuSO4, 50 °C to deposit a 1.8 μm copper layer) and microwave annealing (2.45 GHz, 800 W) were performed on the surface of the graphene layer to obtain a membrane intermediate with the first and second conductive layers deposited.

[0228] Formation of the first expansion layer:

[0229] Slurry coating: Prepare the slurry according to the steps in Example 1. Coat the surface of the first conductive layer treated with argon plasma at a speed of 5 m / min using a slot coater. Precisely control the wet film thickness to be 18 ± 2 μm. Allow it to stand and level for 90 s before entering the 40°C preheating section to eliminate shear stress.

[0230] Curing: The wet film was subjected to gradient UV curing in a nitrogen-protected chamber (O2 < 500 ppm) (pre-curing at 365 nm wavelength and 80 mW / cm² energy for 120 s to form a surface cross-linked layer, followed by main curing at 385 nm wavelength and 120 mW / cm² energy for 300 s to form cross-linked fluorinated polyetheramine (CL-PEA); cumulative dose reached 5200 mJ / cm², and the UV cumulative dose in the main curing zone was 4000 mJ / cm²); simultaneously, 0.5 MPa roller pressing was applied to enhance the mechanical interlocking of the porous structure between the wet film and the first conductive layer; finally, annealing at 105 °C for 1 h was performed to bond the interface between CL-PEA and the first conductive layer, and fluorination was performed using atmospheric pressure plasma (C3F6 / He) to obtain a composite membrane precursor with a deposited first expansion layer.

[0231] Formation of the second expansion layer:

[0232] Similar to the formation process of the first expansion layer, the difference lies in that the mass ratio of polyetheramine prepolymer, diluent perfluoropolyether, perfluorooctylsilane modified nano-TiO2 and photoinitiator Irgacure184 in the slurry is 7:3:1.2:0.25; the slurry is coated on the surface of the second conductive layer treated with argon plasma, the UV cumulative dose in the main curing area is 4500mJ / cm², forming a cross-linked fluorinated polyetheramine, and finally obtaining a composite membrane.

[0233] Example 19

[0234] Similar to Example 18, the difference is that the radius R of the circle of the center hole of the battery cell is 3mm, and the number of winding turns n in the area where the first expansion layer is located is 7.5.

[0235] Example 20

[0236] Similar to Example 18, the difference is that the assembly gap of the battery cell G = 0.3 mm. At this time, the thickness of the second expansion layer d = 115 μm (based on 1.0*G / (p*m) ≤ d ≤ 1.25*G / (p*m), it can be calculated that 100 μm ≤ d ≤ 125 μm).

[0237] Example 21

[0238] Similar to Example 18, the difference is that the expansion rate of the first expansion layer is q=250%, and the thickness of the first expansion layer is a=120μm (based on 0.75*R / (q*n)≤a≤0.95*R / (q*n), it can be calculated that 120μm≤a≤152μm).

[0239] Example 22

[0240] Similar to Example 18, the difference is that the expansion rate of the second expansion layer is p=200%, and the thickness of the second expansion layer is d=165μm (based on 1.0*G / (p*m)≤d≤1.25*G / (p*m), it can be calculated that 150μm≤d≤187.2μm).

[0241] Example 23

[0242] Similar to Example 10, except that the expansion rate of the second expansion layer is p=125%, and the thickness of the second expansion layer is d=300μm.

[0243] Example 24

[0244] Similar to Example 10, except that the cell filling gap G = 0.9 mm, and the thickness of the second expansion layer d = 375 μm.

[0245] Example 25

[0246] Similar to Example 10, the difference is that the radius of the central hole of the battery cell is R=4mm, and the expansion rate of the second expansion layer is p=200%, and the thickness of the second expansion layer is d=190μm.

[0247] Comparative Example 1

[0248] Similar to Example 1, the difference is that a second expansion layer is not provided at the second end of the base film.

[0249] Comparative Example 2

[0250] Similar to Example 1, the difference is that the first expansion layer is not provided at the first end of the base film.

[0251] Comparative Example 3

[0252] Similar to Example 1, the difference is that neither the first expansion layer nor the second expansion layer is provided at the first end or the second end of the base film.

[0253] The following performance tests were performed on the batteries obtained in Examples 1-25 and Comparative Examples 1-3:

[0254] Charge-discharge cycle test: The cell was placed at a test temperature of 60℃ and left to stand for 2 hours. After standing, the cell was charged at a constant voltage of 3.45V, with a current limit of 3C and a cutoff current of 0.05C. After charging, the cell was discharged at a constant current of 1C to 20% SOC, forming one complete cycle. The cells were cycled 200 times, 400 times, and 1000 times respectively, and the capacity retention rate was recorded. The capacity retention rate was calculated as follows: Capacity retention rate = (Initial capacity of cell - Capacity after cycle) / Initial capacity of cell. The test results are detailed in Table 1.

[0255] Table 1

[0256]

[0257] As shown in Table 1, the battery cell provided in this application exhibits excellent cycle stability, maintaining a capacity retention rate of over 80% after 1000 cycles. This is primarily due to the composite separator within the battery cell, which incorporates a first expansion layer and a second expansion layer at its two ends. These layers absorb the mechanical stress caused by volume changes at the beginning and end of the electrode plates during battery cycle charging and discharging, ensuring both structural integrity in the central hole area and good contact between the cell periphery and the casing. This improves the structural stability of the battery cell and thus enhances its cycle capacity retention performance.

[0258] Compared with Examples 1 and 5, the battery cells obtained in Examples 2 to 4 have better cycle performance. This indicates that when the thickness a of the first expansion layer satisfies 0.75*R / (q*n)≤a≤0.95*R / (q*n), the energy density and structural stability of the obtained battery cell can be better guaranteed, resulting in better cycle performance of the battery cell.

[0259] Compared with Examples 2 and 9, the battery cells obtained in Examples 6 to 8 have better cycle performance. This indicates that when the width of the first expansion layer is in the range of 35mm to 44mm, it can better cover the stress peak area at the beginning of the base film without excessively increasing the stiffness of the first cycle, thereby reducing the possibility of fatigue cracking of the base film to a greater extent and making the battery cell have better cycle performance.

[0260] Compared with Examples 7 and 13, the battery cells obtained in Examples 10 to 12 have better cycle performance. This indicates that when the thickness d of the second expansion layer satisfies 1.0*G / (p*m)≤d≤1.25*G / (p*m), it can better balance the structural stability and liquid retention capacity of the battery cell periphery, and can also work in synergy with the first expansion layer with a thickness of 150μm and a width of 40mm to make the obtained battery cell have better cycle performance.

[0261] Compared with Examples 11 and 17, the battery cells obtained in Examples 14 to 16 have better cycle performance. This indicates that when the width of the second expansion layer is in the range of 44mm to 53mm, it can better balance the stress buffering, liquid retention capacity and heat dissipation effect of the battery cell, thereby obtaining a battery cell with better cycle performance.

[0262] Compared with Example 14, the battery cell obtained in Example 18 has better cycle performance, which shows that introducing a conductive layer into the composite separator can further improve the cycle performance of the obtained battery cell.

[0263] Compared with Example 18, the battery cells obtained in Examples 19 and 21 have better cycle performance. This shows that changing the parameters of the central region of the battery cell (increasing the radius of the central circle or increasing the expansion rate of the first expansion layer) is beneficial to improving the cycle performance of the battery cell.

[0264] Compared with Examples 20 and 22, the battery cell obtained in Example 18 has better cycle performance, which shows that increasing the filling gap or reducing the expansion rate of the second expansion layer is beneficial to improving the cycle performance of the battery cell.

[0265] Compared with Example 25, the battery cell obtained in Example 10 has a slightly higher capacity retention rate after 1000 cycles. This indicates that when the radius of the center hole of the battery cell and the expansion rate of the second expansion layer are changed, the thickness a of the first expansion layer satisfies 0.75*R / (q*n)≤a≤0.95*R / (q*n), and the thickness d of the second expansion layer satisfies 1.0*G / (p*m)≤d≤1.25*G / (p*m), the obtained battery cell can also obtain better cycle performance.

[0266] Compared with Comparative Examples 1 to 3, the battery cell obtained in Example 1 has better cycle performance. This shows that by simultaneously setting the first expansion layer and the second expansion layer on the base film, the battery cell can achieve a capacity retention rate of more than 96% after 200 cycles, a capacity retention rate of more than 91% after 400 cycles, and a capacity retention rate of more than 80% after 1000 cycles.

[0267] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. An electric cell, characterized by, The positive electrode sheet, the negative electrode sheet, and the composite separator; The composite separator comprises: a base film having opposite first and second ends; a first expansion layer disposed on one side surface of the first end of the base film; a second expansion layer disposed on the opposite other side surface of the second end of the base film; The composite separator is wound with the positive electrode sheet and the negative electrode sheet in a winding direction to form a battery cell, and the first end forms a center hole of the battery cell; The thickness a of the first expansion layer satisfies 0.75 R / (q n) ≤ a ≤ 0.95 R / (q n); The thickness d of the second expansion layer satisfies 1.0 G / (p m) ≤ d ≤ 1.25 G / (p m); wherein R is the radius of the center hole of the battery cell; G is the assembly gap of the battery cell; q is the expansion rate of the first expansion layer, and p is the expansion rate of the second expansion layer; n is the number of winding turns in the region where the first expansion layer is located, and m is the number of winding turns in the region where the second expansion layer is located.

2. The electric cell of claim 1, wherein, The expansion rate of the first expansion layer is greater than the expansion rate of the second expansion layer.

3. The cell of claim 1 or 2, wherein, The expansion rate of the first expansion layer is greater than or equal to 150%; And / or, the expansion rate of the second expansion layer is greater than or equal to 120%.

4. The electric cell of claim 1, wherein, The width of the first expansion layer is less than or equal to the width of the second expansion layer.

5. The electric cell of claim 4, wherein, The width ratio of the first expansion layer to the base film is (0.55-0.70):1; And / or, the width ratio of the second expansion layer to the base film is (0.70-0.85):

1.

6. The electric cell of claim 5, wherein, The width of the first expansion layer is greater than or equal to 35mm and less than or equal to 44mm; And / or, the width of the second expansion layer is greater than or equal to 44mm and less than or equal to 53mm.

7. The electric cell of claim 1, wherein, The first expansion layer comprises at least one of cross-linked fluorinated polyether amine, perfluoropolyether derivative, fluorine-containing acrylate copolymer, and cross-linked polyvinylidene fluoride; and / or the crosslinking density of the first intumescent layer is 0.19 mol / m 3 -0.25 mol / m 3 ; And / or, the second expansion layer comprises at least one of cross-linked fluorinated polyether amine, perfluoropolyether derivative, fluorine-containing acrylate copolymer, and cross-linked polyvinylidene fluoride; and / or the crosslinking density of the second intumescent layer is 0.24 mol / m 3 -0.28 mol / m 3 .

8. The electric cell of claim 1, wherein, The cross-linking density of the first expansion layer is less than or equal to the cross-linking density of the second expansion layer.

9. The electric cell of claim 1, wherein, The composite separator further comprises a first conductive layer and / or a second conductive layer; At the first end of the base film, the first conductive layer is located between the base film and the first expansion layer; And / or, at the second end of the base film, the second conductive layer is located between the base film and the second expansion layer.

10. The electric cell of claim 9, wherein, The first conductive layer and / or the second conductive layer comprise a laser-induced graphene conductive layer.

11. The electric cell of claim 9, wherein, The sheet resistance of the first conductive layer and / or the second conductive layer is less than or equal to 0.8Ω / sq.

12. The electric cell of claim 9, wherein, The width of the first conductive layer is less than or equal to the width of the base film; And / or, the width of the second conductive layer is less than or equal to the width of the base film; And / or, the thickness of the first conductive layer is 6μm-10μm; And / or, the thickness of the second conductive layer is 6μm-10μm.

13. The electrically charged cell of claim 1, wherein, The preparation method of the composite separator comprises: forming the first expansion layer on one side surface of the first end of the base film and forming the second expansion layer on the opposite other side surface of the second end of the base film to obtain the composite separator.

14. The electric cell of claim 13, wherein, The composite separator further comprises a first conductive layer and / or a second conductive layer; The preparation method of the composite separator further comprises: forming the first conductive layer on one side surface of the first end of the base film; and / or, the second conductive layer is formed on the other side surface of the second end of the base film.

15. The electrically charged cell of claim 1, wherein, The first expansion layer of the composite separator is close to the center of the battery cell.

16. The electrically charged cell of claim 1, wherein, The circular radius of the center hole of the battery cell is greater than or equal to 2mm and less than or equal to 5mm; and / or, the number of winding turns of the area where the first expansion layer of the composite separator is located is greater than or equal to 2 and less than or equal to 7; and / or, the number of winding turns of the area where the second expansion layer of the composite separator is located is greater than or equal to 1 and less than or equal to 5.

17. The electrically charged cell of claim 1, wherein, The thickness of the first expansion layer of the composite separator is greater than or equal to 150μm and less than or equal to 190μm; and / or, the thickness of the second expansion layer of the composite separator is greater than or equal to 200μm and less than or equal to 250μm.

18. The electrically core of claim 1, wherein, The battery cell is a winding type battery cell.

19. A battery, characterized by A battery cell according to any one of claims 1-18.

20. A battery pack, characterized by A battery according to claim 19, comprising at least two battery cells.

Images