Composite diaphragm and preparation method thereof, battery cell, battery and battery pack

Abstract

The embodiment of the invention provides a composite diaphragm and a preparation method thereof, a battery cell, a battery and a battery pack. The composite diaphragm comprises: a base membrane having a first end and a second end opposite to each other; the first expansion layer is arranged on the surface of one side of the first end of the base film; and the second expansion layer is arranged on the surface of the other opposite side of the second end of the base film. The composite diaphragm can improve the structural stability of the battery cell, so that the cycle performance optimization of the battery cell is realized.

Description

Technical Field

[0001] The present application relates to the field of battery materials, and in particular to a composite diaphragm and a preparation method thereof, a battery cell, a battery, and a battery pack. Background Art

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

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

[0004] The present invention provides a composite diaphragm, a method for preparing the same, a battery cell, a battery, and a battery pack. The composite diaphragm includes a first end and a second end, with a first expansion layer provided on one surface of the first end and a second expansion layer provided on the opposite surface of the second end. The provision of the first and second expansion layers enables the composite diaphragm to improve the structural stability of the battery cell, thereby enhancing the battery's cycling performance.

[0005] In a first aspect, the present application provides a composite diaphragm, comprising:

[0006] a base membrane having opposing first and second ends;

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

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

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

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

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

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

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

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

[0015] In one possible embodiment, 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 a possible embodiment, the first expansion layer includes at least one of a cross-linked fluorinated polyether amine, a perfluoropolyether derivative, a fluorinated acrylate copolymer, and a cross-linked polyvinylidene fluoride;

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

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

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

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

[0022] In a possible embodiment, the composite diaphragm 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 expansion 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 a possible implementation, the first conductive layer and / or the second conductive layer includes a laser-induced graphene conductive layer.

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

[0027] In a possible implementation manner, 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 6 μm-10 μm;

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

[0031] In a second aspect, the present application provides a method for preparing the above-mentioned composite diaphragm, comprising:

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

[0033] In a possible embodiment, the composite diaphragm further includes a first conductive layer and / or a second conductive layer;

[0034] The preparation method of the composite diaphragm further comprises:

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

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

[0037] In a third aspect, the present application further provides a battery cell, which includes a positive electrode sheet, a negative electrode sheet, and the above-mentioned composite diaphragm or the composite diaphragm prepared by the above-mentioned preparation method.

[0038] In a possible implementation manner, the first expansion layer on the composite separator is close to the center of the battery core.

[0039] In a possible implementation manner, 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 area where the first expansion layer is located, and m is the number of winding turns in the area where the second expansion layer is located.

[0042] In a possible embodiment, in the battery core, the radius of the central hole of the battery core 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 windings of 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 core, the number of windings of 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 embodiment, 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 separator is greater than or equal to 200 μm and less than or equal to 250 μm.

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

[0048] In a fourth aspect, the present application also provides a battery comprising the above-mentioned battery cell.

[0049] In a fifth aspect, the present application also provides a battery pack comprising at least two of the above-mentioned batteries.

[0050] The composite diaphragm and its preparation method, battery cell, battery and battery pack provided in the present application, by respectively arranging a first expansion layer and a second expansion layer at both ends of the composite diaphragm, can not only prevent the internal collapse of the battery cell and avoid the increase of the gap between the positive and negative electrode sheets, but also fill the assembly gap between the outer layer of the battery cell and the shell through expansion, thereby improving the structural stability of the battery cell and thus improving the cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0053] Figure 2 A first end side view of the composite diaphragm provided in the present application;

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

[0055] Figure 4 A second end side view of the composite diaphragm provided in the present application;

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

[0057] Description of reference numerals:

[0058] 1-first conductive layer; 2-first expansion layer; 3-second conductive layer; 4-second expansion layer; 5-base film; a-thickness of first expansion layer; b-thickness of first conductive layer; H-thickness of base film; A-width of base film; c-width of first expansion layer; B-length of first expansion layer; d-thickness of second expansion layer; e-thickness of second conductive layer; f-width of second expansion layer; C-length of second expansion layer.

[0059] The above drawings illustrate specific embodiments of the present application, which will be described in more detail below. These drawings and the textual description are not intended to limit the scope of the present application in any way, but rather to illustrate the concepts of the present application to those skilled in the art by reference to specific embodiments. DETAILED DESCRIPTION

[0060] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.

[0061] In lithium-ion batteries, the main function of the separator of the battery cell is to physically isolate the positive and negative electrodes to prevent short circuits; block electron conduction; maintain electrolyte and optimize ion transmission; provide mechanical strength and structural support, etc., which can provide good charging and discharging conditions for the battery cell.

[0062] Currently, during the charge and discharge cycle of lithium batteries, the internal core expands due to the combined effects of materials and temperature, disrupting the internal stress balance, resulting in a shortened cell lifespan and reduced capacity. When the expansion force is large, the walls of the cell's central hole will sag inward, increasing the gap between the positive and negative electrodes, increasing the probability of thermal runaway and short circuits, and posing a high risk. Furthermore, the cell's unconstrained outer layer cannot provide the restraint necessary to ensure structural stability under harsh operating conditions.

[0063] The composite diaphragm and preparation method provided in the present application solve the support problem of the central hole of the cylindrical battery cell and the support problem of the assembly gap between the outer side of the battery cell and the shell by respectively arranging the first expansion layer and the second expansion layer on different sides of the two ends of the base membrane, thereby maintaining the overall structural stability of the battery cell and improving the cycle performance of the battery.

[0064] The following specific embodiments describe in detail the technical solution of the present application and how the technical solution of the present application solves the above-mentioned technical problems. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0065] The present application provides a composite diaphragm, comprising: a base membrane having a first end and a second end opposite to each other;

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

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

[0068] This application employs a first expansion layer and a second expansion layer, respectively, on opposite sides of the base film. During the battery cell cycle, the first or second expansion layer expands to better absorb and buffer the significant mechanical stress generated by the expansion of the electrode in the central hole area. Its own expansion and deformation provide more space for the internal electrode to expand, preventing it from caving inward. This reduces compression and damage (such as breakage and powder loss) to the electrode and composite separator at the bend point, thereby 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 battery cell as a whole. It also effectively fills the assembly gap between the battery cell and the battery housing, ensuring good contact with the battery housing (facilitating heat dissipation), thereby ensuring the structural stability of the battery cell and improving its cycling performance.

[0069] In some specific embodiments, the first and second expansion layers expand by absorbing liquid. This expansion allows for more space for the internal electrode sheets to expand, preventing them from collapsing inward. Furthermore, the expansion layer effectively fills the assembly gap between the battery cell and the battery housing, ensuring good contact with the battery housing (facilitating heat dissipation), thereby maintaining the structural stability of the battery cell and improving its cycling performance.

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

[0071] In the composite diaphragm provided in the present application, the first end where the first expansion layer is located is used as the head end for forming the central hole structure, and the second end where the second expansion layer is located is used as the tail end for forming the periphery of the battery cell. Since the electrolyte of the battery cell is injected from the central hole of the battery cell, the first expansion layer in the central hole area is more easily infiltrated by the electrolyte. When the electrolyte reaches the second expansion layer located on the periphery, it needs to overcome capillary force and gas resistance, penetrate from the inside to the outside, and infiltrate the second expansion layer. Therefore, controlling the expansion rate of the second expansion layer to be lower can not only avoid excessive expansion of the peripheral area and causing squeezing of the internal structure of the battery cell, but its lower expansion rate and denser structure help maintain the mechanical strength of the battery cell shell and provide a certain external thermal barrier. At the same time, the expansion rate of the first expansion layer is higher, and it can absorb the electrolyte and swell faster and to a greater extent.

[0072] In some embodiments, the expansion ratio 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 of the first expansion layer forms the leading end of the central pore structure, while the second end of the second expansion layer forms the trailing end of the battery cell's periphery. A first expansion layer with an expansion ratio of 150% or greater can store more electrolyte in the central pore area, acting as an additional heat buffer. It also provides a better ion transport path, reducing impedance and heat generation in the central region. Furthermore, a first expansion layer with this expansion ratio prevents internal collapse of the battery cell, improving battery cycle performance.

[0074] In some optional embodiments, the expansion rate of the first expansion layer can be less than or equal to 300%. In this case, a first expansion layer with an expansion rate greater than or equal to 150% and less than or equal to 300% can further prevent deformation of the battery cell structure during the battery's charge and discharge cycles, ensuring the integrity and insulation performance of the composite separator, maintaining electrolyte infiltration and ion conduction efficiency, and improving the battery cell's cycle performance.

[0075] Illustratively, the expansion thickness of the first expansion layer may be 150%, 160%, 170%, 180%, 190%, 200%, 210%, 220%, 230%, 240%, 250%, 260%, 270%, 280%, 290%, 300%, or a range consisting of any two thereof.

[0076] In some embodiments, the second expansion layer has an expansion ratio 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 infiltrate the battery cell, but also provides basic elasticity, absorbs part of the stress, helps to relieve the pressure between the electrode and the diaphragm, and increases the ion transmission rate, thereby improving the battery cell's cyclability and other performance.

[0078] In some optional embodiments, the expansion rate of the second expansion layer can 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% helps maintain the structural integrity of the electrode at the edge of the battery cell and protects the sealing structure of the battery cell. It also helps further improve the isolation function of the composite separator at lower operating temperatures, synergistically optimize the temperature field distribution, increase the ion conduction rate at the battery cell periphery, and improve the battery cell's cycling performance.

[0079] Illustratively, the expansion ratio of the second expansion layer may be 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190%, 200%, or a range consisting of any two thereof.

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

[0081] Standard samples were prepared in a glove box and immersed in electrolyte in a time-gradient manner at a constant temperature. The immersed samples were then placed in an inert atmosphere and the thickness was measured rapidly and non-contactly using a laser thickness gauge. The experiment was repeated 3 to 5 times and compared with a blank separator as a control. The thickness expansion ratio (ΔD% ± SD) was accurately calculated and the expansion rate (dΔD / dt) and the swelling equilibrium time (t 90 )'s dynamic characteristic curve.

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

[0083] In a cylindrical battery cell, the temperature in the center hole area is higher and the thermal expansion is more significant, while the peripheral area is lower in temperature and has greater strong constraints. Selecting a first expansion layer that is smaller in width than the width of the peripheral second expansion layer is beneficial for controlling high-temperature central expansion. The relatively wider width of the second expansion layer helps the peripheral area of ​​the battery cell accommodate more expansion under strong constraints. 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 the center hole area and peripheral area of ​​the entire battery cell can be made more uniform and controllable, further optimizing the structural stability of the battery cell and improving the cycle performance of the battery cell.

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

[0085] Because the composite diaphragm's bending radius is smallest in the central hole region, the maximum tensile stress is concentrated at the interface between the first expansion layer and the basement membrane. By selecting a width ratio of the first expansion layer to the basement membrane of 0.55-0.70:1, the area of ​​the basement membrane uncovered by the first expansion layer is retained as a flexible hinge. The elastic deformation of the basement membrane in this area absorbs over 60% of the bending stress, improving the interfacial integrity of the first expansion layer.

[0086] Illustratively, the width ratio of the first expansion layer to the base film may be 0.56:1, 0.63:1, 0.70:1, or a range consisting of any two thereof.

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

[0088] By limiting the width ratio of the second expansion layer (which serves as the peripheral area) to the base film within the aforementioned range, not only is a flexible buffer zone reserved to absorb lateral expansion stress, but the base film with a microporous structure is also able to better transfer heat. The base film area not covered by the second expansion layer forms an isothermal heat dissipation strip, which is beneficial for increasing the heat dissipation channel within the battery cell.

[0089] Illustratively, the width ratio of the second expansion layer to the base film may be 0.70:1, 0.78:1, 0.84:1, 0.87:1, or a range consisting of any two thereof.

[0090] In some embodiments, 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 initial winding end, is generally determined by the winding needle diameter and the wrap angle of the first diaphragm coil, while its minimum effective width must cover the peak stress region. By limiting the width of the first expansion layer to this range, the composite diaphragm's stress buffering and mechanical strength are balanced, further improving its electrochemical performance and structural reliability.

[0092] For example, the width of the first expansion layer may be 35 mm, 40 mm, 44 mm, or a range consisting of any two 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 end of the winding, considering its functions of stress buffering, edge liquid retention and heat dissipation, in order to obtain a battery cell with better cycle performance, the width of the second expansion layer of the composite separator can be limited to the above range.

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

[0096] In some embodiments, the first expansion layer includes at least one of cross-linked fluorinated polyether amine (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 polyether amine (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 expansion layer is 0.19 mol / m 3 -0.25mol / m 3 .

[0099] Within this crosslink density range, the first expansion layer swells more readily in the electrolyte, forming more interconnected channels and thereby improving ion transport. Furthermore, this crosslink density allows the first expansion layer to be more flexible, deforming with the expansion and contraction of the electrode, thus preventing interfacial delamination and localized stress concentration, thus preventing battery capacity degradation. Furthermore, the first expansion layer can also wrap around growing lithium dendrites through localized deformation, further reducing the risk of them piercing the separator.

[0100] For example, the crosslinking density of the first expansion layer may be 0.19 mol / m 3 , 0.20mol / 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 expansion layer is 0.24 mol / m 3 -0.28mol / m 3 .

[0102] The second expansion layer having the above cross-linking density can provide moderate swelling properties, keep the pores unobstructed, and prevent the pores from being completely blocked by sediments.

[0103] For example, the crosslinking density of the second expansion 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 embodiments, the crosslinking density of the first expansion layer is less than or equal to the crosslinking density of the second expansion layer.

[0105] The first expansion layer, at the leading end of the composite separator, features a relatively low crosslink density, making it more susceptible to swelling with the electrolyte and improving interfacial contact between the composite separator and the positive electrode. The second expansion layer, at the trailing end of the composite separator, features a relatively high crosslink density, resulting in a tighter network structure and greater dimensional stability. This facilitates rapid electrolyte infiltration, ensuring sufficient electrolyte retention and ultimately resulting in a battery with improved cycling performance.

[0106] In some embodiments, the composite separator further comprises a first conductive layer and / or a second conductive layer; at the 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 membrane and the first expansion layer / the base membrane and the second expansion layer, the connectivity of the conductive network of the composite membrane is maintained, the uniformity of ion transmission is guaranteed, the conductivity of the composite membrane is further improved, and the cycle performance of the battery is improved.

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

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

[0111] Furthermore, in order to obtain a composite diaphragm with better performance, the first conductive layer and / or the second conductive layer may be 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 0.8Ω / 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] Illustratively, the sheet resistance of the first conductive layer and / or the second conductive layer may be 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 a range consisting of any two 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, which is not limited here.

[0116] In some embodiments, 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 understood that the presence of the conductive layer is to improve the conductivity of the composite separator. Ensuring that the width of the first and / or second conductive layers is less than or equal to the width of the base film improves battery safety and also enables more uniform current distribution within the battery cell, thereby extending the battery's service life and reliability.

[0119] In some embodiments, the first conductive layer has a thickness of 6 μm to 10 μm.

[0120] In some embodiments, the second conductive layer has a thickness of 6 μm to 10 μm.

[0121] The thickness of the conductive layer will affect the migration path of the electrolyte ions. The first conductive layer and / or the second conductive layer having the above-mentioned thickness range can take into account both the improvement of its own ionic conductivity and the optimization of the interface contact between it and the base membrane, thereby realizing the construction of a more continuous electronic network and the formation of a dendrite physical barrier layer.

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

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

[0124] The composite diaphragm provided in the embodiment of the present application, by respectively arranging a first expansion layer and a second expansion layer on different side surfaces at opposite ends of the base film, enables the obtained composite base film to support the central hole structure of the battery cell when it is wound into a cylindrical battery cell, thereby preventing the central hole from sinking inward due to expansion of the electrode during the cycle operation, and can also fill the assembly gap between the outer layer of the battery cell and the shell, ensuring that a certain gap exists 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] The present application also provides a method for preparing the above-mentioned composite diaphragm, comprising: forming the first expansion layer on one side surface of the first end of the base membrane, and forming the second expansion layer on the other side surface opposite to the second end of the base membrane, to obtain the composite diaphragm.

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

[0127] Taking the cross-linked fluorinated polyetheramine as an example, the formation of the first expansion layer on one surface of the first end of the base film may include the following steps: mixing a polyetheramine prepolymer, a diluent perfluoropolyether, perfluorooctylsilane-modified nano-TiO2 (particle size 5 nm), and a photoinitiator Irgacure 184 in a mass ratio of 6:4:1:0.2 (high shear dispersion at 15°C and 3000 rpm), then vacuum dehydrating at 80°C to a moisture content of <200 ppm, grinding the mixture by three rollers to a slurry viscosity of 3500±200 cP and vacuum degassing, then forming a 25 μm wet film on a plasma-treated PE separator by micro-gravure coating at a speed of 8 m / min, and constructing a three-dimensional cross-linked network (cross-link density 0.22±0.03 mol / m2) by gradient UV curing (main peak at 365 nm, 120 mW / cm², total cumulative dose 6000 mJ / cm²) in a nitrogen atmosphere (O2 <200 ppm). 3 ), where the main curing zone UV cumulative dose is 4000mJ / cm²; finally it undergoes 80-120℃ step annealing and atmospheric pressure plasma fluorination treatment (C3F6 / He).

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

[0129] The second expansion layer can be formed on the opposite side of the second end of the base film by adjusting the process parameters based on the molding method of the first expansion layer. Specifically, a polyetheramine prepolymer, a diluent perfluoropolyether, perfluorooctylsilane-modified nano-TiO2 (particle size 5 nm), and a photoinitiator Irgacure 184 are mixed in stages in a planetary mixer (high shear dispersion at 15°C and 3000 rpm) at a mass ratio of 7:3:1.2:0.25. The mixture is then vacuum-dehydrated at 80°C to a moisture content of <200 ppm. The mixture is then triple-rolled to a slurry viscosity of 3500±200 cP and vacuum-degassed to obtain a slurry. Subsequently, a 25 μm wet film was formed on the plasma-treated PE membrane by micro-gravure coating at a speed of 8 m / min. A three-dimensional cross-linked network (cross-link density 0.26 ± 0.02 mol / m) was constructed by gradient UV curing (main peak at 365 nm, 120 mW / cm², total cumulative dose 6000 mJ / cm²) in a nitrogen atmosphere (O2 < 200 ppm). 3 ), where the main curing zone UV cumulative dose is 4500mJ / cm²; finally it undergoes 80-120℃ step annealing and atmospheric pressure plasma fluorination treatment (C3F6 / He).

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

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

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

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

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

[0135] In some embodiments, the composite diaphragm further includes a second conductive layer but does not include the first conductive layer. In this case, the method for preparing the composite diaphragm further includes: forming a second conductive layer on the surface of the second end of the base film where the second expansion layer is located.

[0136] Specifically, taking the example of LIG as the first and second conductive layers, the process of coating the LIG conductive layer on the base film surface includes: plasma etching (He / O2=95:5, 300W) and polydopamine coating (2g / L dopamine, polymerization at 50°C) at both ends of the base film to achieve base film activation and laser sensitization. Subsequently, spiral progressive scanning is performed using a dual-wavelength CO2 laser (10.6μm / 9.3μm, 4.0W / cm²), combined with in-situ boron doping (5wt% boric acid) to generate a 12μm-thick three-dimensional graphene layer (square resistance of 15Ω / sq). The conductivity is then enhanced by pulsed electroless copper plating (CuSO415g / L, 50°C to deposit a 1.8μm-thick copper layer) and microwave annealing (2.45GHz, 800W), ultimately obtaining a LIG conductive layer (square resistance of 0.8Ω / sq).

[0137] The LIG conductive layer prepared by the above process has excellent flexibility. Its conductivity retention rate after bending 5000 times is greater than 95%, and it passes the 100℃ / 1000h aging test. It is particularly suitable for high-rate flexible current collectors in power batteries. The mass production line speed can reach 1.2m / min and the yield rate exceeds 98%.

[0138] In some embodiments, the process for forming the first and second expansion layers on the surface of the LIG conductive layer includes: treating the surface of the LIG conductive layer with an inert element plasma, then applying the first and second expansion layers to the LIG conductive layer surface using a slot coater at a speed of 5 m / min, precisely controlling the wet film thickness of the first and second expansion layers to 18±2 μm. After coating, the layers are allowed to level for 90 seconds, followed by a 40°C preheating stage to eliminate shear stress. Subsequently, a gradient UV curing step (pre-curing at 365 nm / 80 mW / cm² for 120 seconds to form a surface crosslinking layer, followed by a main curing step at 385 nm / 120 mW / cm² for 300 seconds at a cumulative dose of 5200 mJ / cm²) is performed in a nitrogen atmosphere (O2 < 500 ppm) shielded box. The pre-curing step is performed with a UV curing agent (pre-curing at 365 nm / 80 mW / cm² for 120 seconds to form a surface crosslinking layer, followed by a main curing step at 385 nm / 120 mW / cm² for 300 seconds, for a cumulative dose of 5200 mJ / cm²). A roller pressure of 0.5 MPa is simultaneously applied to enhance the mechanical interlocking between the wet film and the porous structure of the LIG conductive layer. Finally, an annealing step is performed at 105°C for 1 hour to bond the first and second expansion layers to the LIG conductive layer.

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

[0140] The present application also provides a battery cell, which includes a positive electrode sheet, a negative electrode sheet and the above-mentioned composite diaphragm or the composite diaphragm prepared by the above-mentioned preparation method.

[0141] The composite separator and the positive and negative electrodes are the core components of the battery cell (single cell). They are formed into a battery cell through a specific structural design and assembly process. The core of this process is to build an internal environment that allows ions to shuttle freely but prevents electrons from flowing directly. The battery cell provided in some embodiments of the present application can be a wound cylindrical battery cell, which is wound in the order of a layer of positive electrode sheet, a layer of composite separator, and a layer of negative electrode sheet. The battery cell will be placed in a specific container, such as a cylindrical shell, and then an electrolyte will be injected into it. The electrolyte will penetrate into the micropores of the composite separator to form an ion transmission channel, and at the same time penetrate into the porous coating of the positive and negative electrode sheets, contact with the active material, and finally form a complete ion conduction path, which constitutes the basis for the occurrence of the electrochemical reaction.

[0142] In some embodiments, the first expansion layer on the composite separator is close to 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); wherein R is the radius of the central hole of the battery core; q is the expansion rate of the first expansion layer; and n is the number of winding turns in the area where the first expansion layer is located.

[0144] In some embodiments, the thickness d of the second expansion layer satisfies 1.0*G / (p*m)≤d≤1.25*G / (p*m); wherein 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 area 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 aforementioned nonlinear coupling relationship related to their own expansion rate, the circular radius of the central hole of the battery cell, the battery cell assembly gap, and the number of winding turns in the area where they are located, the expansion loss in the battery cell is minimized while the energy density of the battery cell is maximized, 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 is the assembly gap of the battery cell, wherein the assembly gap of the battery cell refers to the gap distance between the battery cell and the inner cavity of the housing after the battery cell is installed in the housing. Specifically, the gap distance can be determined by measuring the distance between the battery cell and the inner cavity of the housing multiple times and taking the average value.

[0151] In some embodiments, 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.

[0152] When the composite separator and electrode are wound together to form a battery cell, the radius of the center hole is minimized within a controllable range to increase the cell's energy density. By limiting the radius of the center hole within this range, the resulting battery cell achieves a high energy density while also balancing electrolyte wetting, mechanical strength, and cell capacity, resulting in excellent cycle performance and a long battery life.

[0153] For example, the radius of the central hole of the battery cell may be 2 mm, 3 mm, 4 mm, 5 mm, or a range consisting of any two of these.

[0154] In some embodiments, the number of windings 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 windings formed in the area where the first expansion layer is located, the total expansion amount and mechanical constraint strength of the area are reduced, the pressure on the physical space is relieved, more radial expansion space is left, and the stress distribution of the entire battery cell is made more uniform.

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

[0157] For example, the number of winding turns in the area where the first expansion layer is located may be 2, 3, 4, 5, 6, 7, or a range consisting of any two of these.

[0158] In some embodiments, the number of windings 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.

[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, and controlling the total expansion and mechanical load of the outer layer of the battery cell, the tensile stress on the periphery of the battery cell is further alleviated, and the deformation risk of the battery cell shell is reduced, it is beneficial to reduce the expansion gradient of the inner and outer layers of the battery cell, and improve the longitudinal flatness of the battery cell electrode and diaphragm during the battery cycle.

[0160] The number of windings formed in the area where the second expansion layer is located refers to the number of pre-wound turns of the separator at the end away from the center hole of the battery cell, i.e., the number of windings of the separator at the end of the battery cell. This portion of the separator is close to the battery cell casing in the wound battery cell. This portion of the separator does not correspond to the electrode sheet after being stacked and unfolded, i.e., the area where the separator extends beyond the electrode sheet. The second expansion layer is provided over this area. Furthermore, the second expansion layer may cover the entire area or only partially.

[0161] For example, the number of winding turns in the area where the second expansion layer is located may be 1, 2, 3, 4, 5, or a range consisting of any two of these.

[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 area, the first expansion layer it includes needs to meet the requirements of high-intensity 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 interface contact between the composite diaphragm and the electrode and the ion transmission efficiency in the battery cell, thereby ensuring the energy density and structural stability of the battery cell.

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

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

[0166] The second expansion layer, forming the outer periphery of the cell, must be able to absorb mechanical stress and maintain the shape stability of the outer portion of the wound cell. When the thickness of the second expansion layer falls within the aforementioned range, it balances electrode structural stability with electrolyte uniformity, synergizing with the first expansion layer to create a structurally stable cell system with improved cycling performance.

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

[0168] In addition, the length of the first expansion layer can be calculated based on the number of windings in the area where the first expansion layer is located, and the length of the second expansion layer can be calculated based on the number of windings in the area where the second expansion layer is located. The calculation method can be common means in this field.

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

[0170] The present application also provides a battery comprising the above-mentioned battery cell. The battery has excellent cycle performance, and its capacity retention rate can still reach over 80% after 1000 cycles.

[0171] The battery comprises a shell and a battery core, wherein the battery core is installed in the shell and has a gap between the battery core and the inner wall of the shell.

[0172] The present application also provides a battery pack, which includes at least two of the above-mentioned batteries.

[0173] The present application is further described below through specific examples.

[0174] Example 1

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

[0176] The preparation method of the composite diaphragm comprises the following steps:

[0177] Formation of the first expansion layer:

[0178] Slurry preparation: Polyetheramine prepolymer, diluent perfluoropolyether, perfluorooctylsilane-modified nano-TiO2 (particle size 5 nm), and photoinitiator Irgacure 184 were mixed in a mass ratio of 6:4:1:0.2 (high shear dispersion at 15°C and 3000 rpm), and then vacuum-dried at 80°C to a moisture content of <200 ppm.

[0179] Slurry coating: The obtained slurry was ground by three rollers to a viscosity of 3500 ± 200 cP and vacuum degassed. Then, a 25 μm wet film was formed on a plasma-treated PP base film using a micro-gravure coater at a speed of 8 m / min.

[0180] Curing molding: The wet film was cured in a nitrogen atmosphere (O2 < 200ppm) using gradient UV curing (365nm main peak, 120mW / cm², cumulative dose 6000mJ / cm²) to construct a three-dimensional cross-linked network, with the main curing zone UV cumulative dose of 4000mJ / cm²; a cross-linked fluorinated polyetheramine (cross-linking density 0.22mol / m 3 ); Finally, it was annealed at 90°C for 1 hour and fluorinated with atmospheric pressure plasma (C3F6 / He) to obtain the first expansion layer.

[0181] Formation of the second expansion layer:

[0182] The formation process of the first expansion layer is similar to that of the first expansion layer, except that the mass ratio of polyetheramine prepolymer, diluent perfluoropolyether, perfluorooctylsilane-modified nano-TiO2 and photoinitiator Irgacure184 is 7:3:1.2:0.25; the UV cumulative dose in the main curing zone is 4500mJ / cm², forming a cross-linked fluorinated polyetheramine (cross-linking density is 0.26mol / m 3 ), and finally a composite diaphragm was obtained.

[0183] The expansion ratio of the first expansion layer and the expansion ratio of the second expansion layer in the composite diaphragm are tested according to the following steps:

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

[0185] A battery cell comprises a positive electrode sheet with a width of 56 mm, a negative electrode sheet with a width of 58 mm, the above-mentioned composite diaphragm, an electrolyte and a cylindrical shell.

[0186] The positive electrode sheet, composite separator, and negative electrode sheet were stacked and wound to form a structural component, with 20 turns for the positive electrode and 21 turns for the negative electrode. The resulting structural component was assembled with a cylindrical shell, and electrolyte was injected into the shell to produce a test cylindrical cell.

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

[0188] The radius of the center hole of the battery cell is R=2mm, the assembly gap 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 a of the first expansion layer is 150 μm.

[0191] Example 3

[0192] Similar to Example 1, except that the thickness a of the first expansion layer is 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 a of the first expansion layer is 200 μm.

[0197] Example 6

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

[0199] Example 7

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

[0201] Example 8

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

[0203] Example 9

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

[0205] Example 10

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

[0207] Example 11

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

[0209] Example 12

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

[0211] Example 13

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

[0213] Example 14

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

[0215] Example 15

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

[0217] Example 16

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

[0219] Example 17

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

[0221] Example 18

[0222] Similar to Example 14, except that the composite diaphragm 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=10 μm.

[0223] The preparation method of the composite diaphragm comprises the following steps:

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

[0225] Base film activation: Plasma etching (He / O2=95:5, 300W) and polydopamine coating (2g / L dopamine, polymerization at 50°C) were used to activate and laser-sensitize the first and second ends of the PE base film.

[0226] Graphene layer formation: A dual-wavelength CO2 laser (10.6μm / 9.3μm, 4.0W / cm²) was used to perform spiral progressive scanning on the surface of the activated PE base film, combined with in-situ boron doping (5wt% boric acid) to generate a 12μm thick three-dimensional graphene layer (square resistance 15Ω / sq);

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

[0228] Formation of the first expansion layer:

[0229] Slurry coating: The slurry was prepared according to the steps in Example 1 and coated on the surface of the first conductive layer treated with argon plasma using a slot coater at a speed of 5 m / min. The wet film thickness was precisely controlled to be 18 ± 2 μm. The slurry was allowed to level for 90 seconds and then entered a 40°C preheating stage to eliminate shear stress.

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

[0231] Formation of the second expansion layer:

[0232] The formation process is similar to that of the first expansion layer, except that the mass ratio of the 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, and the cumulative UV dose in the main curing area is 4500mJ / cm², forming a cross-linked fluorinated polyetheramine, and finally obtaining a composite diaphragm.

[0233] Example 19

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

[0235] Example 20

[0236] Similar to Example 18, except that the assembly gap G of the battery cell is 0.3 mm. In this case, the thickness of the second expansion layer is 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, except that the expansion rate q of the first expansion layer is 250%, and the thickness a of the first expansion layer is 120 μm (based on 0.75*R / (q*n)≤a≤0.95*R / (q*n), it can be calculated that 120 μm≤a≤152 μm).

[0239] Example 22

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

[0241] Example 23

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

[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, except that the radius of the center hole of the battery cell is R=4 mm, the expansion rate of the second expansion layer is p=200%, and the thickness of the second expansion layer is d=190 μm.

[0247] Comparative Example 1

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

[0249] Comparative Example 2

[0250] Similar to Example 1, except 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 the first expansion layer and the second expansion layer are not provided at the first end and the second end of the base film.

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

[0254] Charge and discharge cycle test: The battery cell was placed at a test temperature of 60°C and allowed to stand for 2 hours. After standing, the battery cell was charged at a constant voltage of 3.45V, with a current limit of 3C and a cut-off current of 0.05C. After charging, the battery cell was discharged at a constant current of 1C to 20% SOC, forming a complete cycle. The cycle was repeated 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 the battery cell - capacity after cycle) / initial capacity of the battery cell. The test results are shown in Table 1.

[0255] Table 1

[0256]

[0257] As shown in Table 1, the battery cell provided in this application exhibits excellent cycling stability, maintaining a capacity retention rate exceeding 80% after 1,000 cycles. This is primarily due to the presence of a first expansion layer and a second expansion layer at the front and rear ends of the composite diaphragm contained in the battery cell provided in this application. These layers absorb the mechanical stress caused by the volume changes at the front and rear ends of the electrode during the battery's charge and discharge cycles, maintaining the structural integrity of the cell's central hole and ensuring good contact between the cell's periphery and the packaging shell. This improves the cell's structural stability and thus enhances its cycle capacity retention.

[0258] Compared with Example 1 and Example 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 shows that when the width of the first expansion layer is in the range of 35 mm to 44 mm, it can better cover the stress peak area at the first end of the base film without excessively increasing the stiffness of the first turn, thereby further reducing the possibility of fatigue cracking of the base film, thereby improving the cycle performance of the battery cell.

[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 cooperate with the first expansion layer with a thickness of 150 μm and a width of 40 mm to achieve better cycle performance of the obtained battery cell.

[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 44 mm to 53 mm, it is possible to better balance the stress buffering, liquid retention capacity, and heat dissipation effect on the outside of the battery cell, thereby obtaining a battery cell with better cycle performance.

[0262] Compared with Example 14, the cycle performance of the battery cell obtained in Example 18 is better, 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, which shows that changing the parameters of the central area of ​​the battery cell (increasing the central circle radius 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 indicates 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 capacity retention rate of the battery cell obtained in Example 10 after 1000 cycles is slightly higher. This indicates that when the radius of the central 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 achieve better cycle performance.

[0266] Compared with Comparative Examples 1 to 3, the battery cell obtained in Example 1 has better cycle performance, which shows that only by providing the first expansion layer and the second expansion layer on the base film at the same time can the battery cell obtain 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 those skilled in the art will readily identify other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art not disclosed herein. The present invention is not limited to the precise structure described above and illustrated in the accompanying drawings, and various modifications and variations may be made without departing from the scope thereof. The scope of the present invention is limited solely by the appended claims.

Claims

1. A composite diaphragm, characterized in that: include: a base membrane having opposing first and second ends; a first expansion layer, disposed on a surface of one side of the first end of the base film; The second expansion layer is disposed on the other side surface of the second end of the base film.

2. The composite diaphragm according to claim 1, characterized in that The expansion rate of the first expansion layer is greater than the expansion rate of the second expansion layer.

3. The composite diaphragm according to claim 1 or 2, characterized in that: The expansion rate of the first expansion layer is greater than or equal to 150%; And / or, the expansion ratio of the second expansion layer is greater than or equal to 120%.

4. The composite diaphragm according to claim 1, characterized in that The width of the first expansion layer is smaller than or equal to the width of the second expansion layer.

5. The composite diaphragm according to claim 4, characterized in that The width ratio of the first expansion layer to the base film is (0.55-0.70):1; And / or, a width ratio of the second expansion layer to the base film is (0.70-0.85):

1.

6. The composite diaphragm according to claim 5, characterized in that The width of the first expansion layer is greater than or equal to 35 mm and less than or equal to 44 mm; 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.

7. The composite diaphragm according to claim 1, characterized in that The first expansion layer comprises at least one of a cross-linked fluorinated polyether amine, a perfluoropolyether derivative, a fluorinated acrylate copolymer, and a cross-linked polyvinylidene fluoride; And / or, the crosslinking density of the first expansion layer is 0.19 mol / m 3 -0.25mol / m 3 ; And / or, the second expansion layer comprises at least one of a cross-linked fluorinated polyether amine, a perfluoropolyether derivative, a fluorinated acrylate copolymer, and a cross-linked polyvinylidene fluoride; And / or, the crosslinking density of the second expansion layer is 0.24 mol / m 3 -0.28mol / m 3 .

8. The composite diaphragm according to claim 1, characterized in that The crosslinking density of the first expansion layer is less than or equal to the crosslinking density of the second expansion layer.

9. The composite diaphragm according to claim 1, characterized in that The composite diaphragm 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 composite diaphragm according to claim 9, characterized in that: The first conductive layer and / or the second conductive layer includes a laser-induced graphene conductive layer.

11. The composite diaphragm according to claim 9, characterized in that 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 composite diaphragm according to claim 9, characterized in that 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 6 μm-10 μm; And / or, the thickness of the second conductive layer is 6 μm-10 μm.

13. A method for preparing the composite diaphragm according to any one of claims 1 to 12, characterized in that: include: The first expansion layer is formed on one side surface of the first end of the base film, and the second expansion layer is formed on the other side surface opposite to the second end of the base film to obtain the composite diaphragm.

14. The method for preparing a composite diaphragm according to claim 13, characterized in that: The composite diaphragm further comprises a first conductive layer and / or a second conductive layer; The preparation method of the composite diaphragm 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 base film opposite to the second end.

15. A battery cell, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and the composite diaphragm according to any one of claims 1 to 12 or the composite diaphragm prepared by the preparation method according to any one of claims 13 to 14.

16. The battery cell according to claim 15, characterized in that The first expansion layer on the composite separator is close to the center of the battery core.

17. The battery cell according to claim 15, characterized in that: The thickness a of the first expansion layer satisfies 0.75*R / (q*n)≤a≤0.95*R / (q*n); and / or, 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, p is the expansion rate of the second expansion layer; n is the number of winding turns in the area where the first expansion layer is located, and m is the number of winding turns in the area where the second expansion layer is located.

18. The battery cell according to claim 15, characterized in that The radius of the central hole of the battery core is greater than or equal to 2 mm and less than or equal to 5 mm; and / or, the number of winding turns of 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; And / or, the number of winding turns of 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.

19. The battery cell according to claim 15, characterized in that 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; And / or, the thickness of the second expansion layer of the composite separator is greater than or equal to 200 μm and less than or equal to 250 μm.

20. The battery cell according to claim 15, characterized in that The battery core is a wound battery core.

21. A battery, characterized in that: The battery cell comprises the battery cell according to any one of claims 15 to 20.

22. A battery pack, characterized in that: Comprising at least two batteries as claimed in claim 21.

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