Battery cells, batteries and electrical devices

Abstract

The present application relates to a battery cell, a battery, and an electrical device. The battery cell includes an electrode assembly, the electrode assembly including a first electrode piece, a second electrode piece, and a separator, wherein the first electrode piece and the second electrode piece have opposite polarities, the separator is disposed between the first electrode piece and the second electrode piece, and at least one of the first electrode piece, the second electrode piece, and the separator contains a swelling polymer, wherein the swelling polymer satisfies the following conditions: 300% ≤ m2 / m1 ≤ 10000%; and m3 / m2 ≤ 50%.

Description

[0001] Citation of Related Applications

[0002] This application claims priority to the Chinese patent application entitled “Battery Cell, Battery and Electrical Device” filed on April 17, 2023, with application number 202310410916.3, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to a battery cell, a battery and an electrical device. Background Art

[0004] Battery cells have the characteristics of high capacity and long life, and are therefore widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric airplanes, electric boats, electric toy cars, electric toy boats, electric toy airplanes and power tools, etc.

[0005] As battery applications become increasingly widespread, the requirements for battery cell performance are becoming increasingly stringent. To improve battery cell performance, optimization and improvement are often performed on the battery cells; however, the reliability and cycle performance of battery cells remain poor. Summary of the Invention

[0006] The present application is made in view of the above-mentioned problems, and its object is to provide a battery cell, a battery, and an electric device.

[0007] In a first aspect, the present application proposes a battery cell, the battery cell including an electrode assembly, the electrode assembly including a first electrode piece, a second electrode piece, and a separator, the first electrode piece and the second electrode piece having opposite polarities, the separator being disposed between the first electrode piece and the second electrode piece, at least one of the first electrode piece, the second electrode piece, and the separator containing a swelling polymer, the swelling polymer satisfying: 300% ≤ m2 / m1 ≤ 10000%; m3 / m2 ≤ 50%,

[0008] in,

[0009] The swollen polymer was prepared into a film with a mass of m1 g, a width of 10 mm, a length of 10 mm, and a thickness of 1 mm.

[0010] The film was added to an excess of dimethyl carbonate DMC and allowed to stand at 25°C for 7 days to obtain a first swollen film. The mass of the first swollen film was m2 g.

[0011] The first swollen film was placed in an atmosphere with a humidity of less than or equal to 20% and allowed to stand at 25° C. for 7 days to obtain a dry film. The mass of the dry film was m 3 g.

[0012] Therefore, the swelling polymer of the embodiment of the present application can lock the electrolyte in the swelling polymer by physical adsorption through its own liquid locking and liquid releasing capabilities when satisfying 300%≤m2 / m1≤10000%; m3 / m2≤50%. The electrolyte can be locked on the surface of the active material particles to form a slow-release storage point to release the electrolyte into the electrode assembly, thereby improving the liquid shortage phenomenon of the electrolyte, so that the electrolyte continues to infiltrate the surface of the active material during the cyclic charge and discharge process of the battery cell; and on the basis of protecting the interface of the active material, it can also enable the active ions to be smoothly transmitted, thereby establishing interface protection, reducing side reactions at the solid-liquid interface, and improving the high-temperature storage performance, usage reliability and cycle performance of the battery cell.

[0013] In some embodiments, 500%≤m2 / m1≤5000%. When the embodiments of the present application meet the above range, the reliability and cycle performance of the battery cell can be further improved.

[0014] In some embodiments, the swelling polymer satisfies at least two of the following conditions,

[0015] (1) Film in T m The elastic modulus G'-energy loss modulus G" curve was obtained by dynamic frequency sweep test at +20℃. The slope of the elastic modulus G'-energy loss modulus G" curve is K, 0.5<K<5, and Tm represents the melting temperature of the film;

[0016] (2) The crystallinity of the swollen polymer measured by differential scanning calorimetry is Xc, 0<Xc≤30%; the glass transition temperature of the swollen polymer is T g , T g ≤25℃;

[0017] (3) The elastic modulus of the film is E, E≤1MPa; the elongation at break of the film is ε, ε≥100%.

[0018] When the embodiment of the present application meets the above range, the liquid locking and liquid releasing capabilities of the swelling polymer can be improved, and the use reliability and cycle performance of the battery cell can be further improved.

[0019] In some embodiments, the film is added to a preset electrolyte and allowed to stand at 25° C. for ≥24 h to obtain a second swollen film, wherein the preset electrolyte comprises dimethyl carbonate DMC, ethyl methyl carbonate EMC, ethylene carbonate EC, and lithium hexafluorophosphate LiPF6, the dimethyl carbonate, the ethyl methyl carbonate, and the ethylene carbonate have the same mass, and the molar amount of the lithium hexafluorophosphate LiPF6 is 1 mol / L;

[0020] The Shore hardness of the film is H a1 The Shore hardness of the second swollen film is Ha2 , the film and the second swollen film satisfy: 0≤H a2 / H a1 ≤0.5, and 0≤H a2 ≤45;

[0021] Optionally, 0≤H a2 / H a1 ≤0.45;

[0022] Further optionally, 20≤H a1 ≤100.

[0023] Therefore, in the embodiment of the present application, the swelling polymer can be arranged in at least one of the first pole piece and the second pole piece. The membrane layer of the first pole piece is a porous structure. For example, there are pores between the active material particles to form a porous structure. The swelling polymer can be dispersed in the porous structure of the first pole piece. On the one hand, the swelling polymer can rely on the porous structure to form a liquid-retaining network, while improving the interface performance of the active material particles, achieving a liquid locking effect, and can increase the transmission rate of lithium ions, reduce the interface side reactions of the active material layer, and improve the cycle performance of the battery cell; on the other hand, the swelling polymer swells after contacting the electrolyte, and its mechanical strength is reduced. During the cyclic charge and discharge process of the battery cell, it can effectively adapt to the expansion and deformation of the active material particles during the charge and discharge process, and can more effectively adhere to the surface of the active material particles, reducing problems such as solid-liquid interface peeling due to swelling to form a gel-like substance.

[0024] In some embodiments, the swelling polymer comprises a fluorinated polymer, and the fluorinated polymer comprises at least one of the compounds represented by formula (AI) to the compounds represented by formula (AIII),

[0025]

[0026] In formula (AI) and formula (AII), R 11 、R 12 、R 13 and R 14 Each independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C3 alkyl group, or a substituted or unsubstituted C1-C3 alkoxy group, and R 11 、R 12 、R 13 and R 14 At least one of the substituted groups comprises a fluorine atom; when substituted, the substituent comprises one or more of a nitrile group (-CN), a nitro group, a sulfonic acid group, a sulfonyl group, an amide group, a carboxyl group, an ester group, and a halogen atom;

[0027]

[0028] In formula (AIII), R15 Including single bonds, substituted or unsubstituted C1-C3 alkyl groups; when substituted, the substituents include one or more of nitrile groups (-CN), nitro groups, sulfonic acid groups, sulfonyl groups, amide groups, carboxyl groups, ester groups, and halogen atoms;

[0029] p is selected from any positive integer from 1 to 3.

[0030] In some embodiments, the swelling polymer includes an ether polymer, and the ether polymer includes a compound represented by formula (BI) and / or a compound represented by formula (BII).

[0031]

[0032] In formula (BI), R 21 and R 22 Each independently includes a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group, or a substituted or unsubstituted C1-C3 alkoxy group; R 23 Including substituted or unsubstituted C1-C5 alkylene;

[0033]

[0034] In formula (BII), R 24 to R 27 Each independently includes a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted C1-C3 alkoxy group or an ether group, and R 24 to R 27 At least one of them contains a substituted or unsubstituted C1-C3 alkoxy group or an ether group.

[0035] In some embodiments, the swelling polymer includes an ester polymer, and the ester polymer includes a compound represented by formula (CI) to a compound represented by formula (CIII),

[0036]

[0037] In formula (CI), R 31 、R 32 and R 33 Each independently includes a hydrogen atom, or a substituted or unsubstituted C1-C8 alkyl group; R 34 Including substituted or unsubstituted C1-C8 alkyl, or substituted or unsubstituted C1-C8 hydroxyalkyl;

[0038]

[0039] In formula (CII), R 35 including substituted or unsubstituted C2-C6 methylene; optionally, R 35Each independently comprises a substituted or unsubstituted C2-C4 methylene group;

[0040]

[0041] In formula (CIII), R 36 、R 37 and R 38 Each independently includes a hydrogen atom, or a substituted or unsubstituted C1-C8 alkyl group; R 39 Including substituted or unsubstituted C1-C8 alkyl;

[0042] Optionally, R 36 、R 37 and R 38 Each independently includes a hydrogen atom, a substituted or unsubstituted C1-C4 alkyl group.

[0043] In some embodiments, the swelling polymer comprises an aldehyde-ketone polymer, and the aldehyde-ketone polymer comprises a compound represented by formula (DI) and / or a compound represented by formula (DII),

[0044]

[0045] In formula (DI), R 41 Including single bonds, substituted or unsubstituted C1-C6 methylene; R 42 including hydrogen atoms, substituted or unsubstituted C1-C6 alkyl groups;

[0046]

[0047] In formula (DII), R 43 to R 46 Each independently includes a hydrogen atom, a hydroxyl group, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted C1-C3 hydroxyalkyl group, or a substituted or unsubstituted C1-C3 alkoxy group; r and s are each independently selected from an integer from 0 to 5, and at least one of r and s is selected from any positive integer.

[0048] In some embodiments, the first electrode sheet includes a current collector and a film layer disposed on at least one surface of the current collector, wherein the film layer includes a swelling polymer and active material particles.

[0049] In some embodiments, the membrane layer includes a polymer layer containing a swellable polymer and an active material layer containing active material particles. The active material layer is disposed on at least one surface of the current collector, and the polymer layer is disposed on the surface of the active material layer facing away from the current collector.

[0050] In some embodiments, there are multiple active material particles, there is a pore between two adjacent active material particles, and the swelling polymer is distributed in the pore.

[0051] In some embodiments, the isolation film includes a substrate and a coating disposed on at least one surface of the substrate;

[0052] In some embodiments, the swelling polymer is distributed in the pores of the substrate.

[0053] In some embodiments, the swelling polymer is distributed within the coating.

[0054] In some embodiments, the swelling polymer is disposed on the surface of the coating facing away from the substrate.

[0055] In some embodiments, the battery cell further includes a liquid electrolyte, and the liquid electrolyte is located within the electrode assembly.

[0056] In some embodiments, the battery cell satisfies: (m / ρ) / V 总孔 ≥80%;

[0057] V 总孔 The value indicating the pore volume of the electrode assembly, in mL;

[0058] m represents the difference between the mass of the battery cell before drying and the mass after drying, and its unit is g;

[0059] ρ represents the density of the liquid electrolyte, and its unit is g / mL.

[0060] Therefore, when the battery cell of the embodiment of the present application meets the above conditions, most of the liquid electrolyte is located in the pore structure of the electrode assembly, that is, the electrode assembly itself has good liquid absorption and liquid retention capabilities, which is conducive to the transmission of active ions and improves the dynamic performance of the battery cell; a small part of the liquid electrolyte can diffuse into the swelling polymer and release liquid during the cyclic charge and discharge process of the battery cell. Since the amount of liquid released is relatively small, the liquid electrolyte is not easy to flow out of the electrode assembly, and can make the electrolyte infiltration of the electrode assembly more uniform, thereby improving the cycle performance of the battery cell.

[0061] In some embodiments, the battery cell satisfies:

[0062] 0≤y / Ah≤15%;

[0063] y represents the volume of free electrolyte in the battery cell, and its unit is mL;

[0064] Ah represents the nominal capacity of a battery cell, and its unit is Ah.

[0065] Therefore, when the battery cell of the embodiment of the present application meets the above conditions, the free electrolyte content in the battery cell is extremely small, or even substantially free electrolyte is contained in the battery cell, thereby significantly improving the reliability and cycle performance of the battery cell.

[0066] In some embodiments, the battery cell satisfies:

[0067] 0≤y / V 总孔 ≤15%;

[0068] y represents the volume of free electrolyte in the battery cell, and its unit is mL;

[0069] V 总孔 A numerical value indicating the pore volume of the electrode assembly, with the unit being mL.

[0070] Therefore, when the battery cell of the embodiment of the present application meets the above conditions, the free electrolyte content in the battery cell is extremely small, or even substantially free electrolyte is contained in the battery cell, thereby significantly improving the reliability and cycle performance of the battery cell.

[0071] In some embodiments, after the battery cell is subjected to a linear frequency sweep vibration test, it is charged to 100% state of charge (SOC), a hole is opened on the battery cell, and the hole is set at the lowest point in the vertical direction, and the volume of liquid electrolyte flowing out of the battery cell is recorded as M1, 0 mL ≤ M1 ≤ 0.5 mL, and optionally, M1 is 0 mL;

[0072] in,

[0073] The vibration direction of the linear frequency sweep vibration test is: single vibration up and down;

[0074] The vibration frequency of the linear sweep vibration test is: 10Hz~55Hz;

[0075] The maximum acceleration of the linear sweep vibration test is: 30m / s 2 ;

[0076] The number of sweep cycles of the linear sweep vibration test is: 10 times;

[0077] The vibration time of the linear sweep frequency vibration test is: 3h.

[0078] Therefore, when the battery cell of the embodiment of the present application meets the above conditions, the free electrolyte content in the battery cell is extremely small, or even substantially free electrolyte is contained in the battery cell, thereby significantly improving the reliability and cycle performance of the battery cell.

[0079] In some embodiments, after the battery cell is subjected to the linear sweep vibration test, the electrode assembly is removed, and after the electrode assembly is subjected to the extrusion test, the volume of the electrolyte flowing out of the electrode assembly is recorded as M2, 0 mL≤M2≤0.5 mL, optionally, M2 is 0 mL;

[0080] in,

[0081] The extrusion direction of the extrusion test is: perpendicular to the thickness direction of the electrode assembly;

[0082] The extrusion degree of the extrusion test is: the extrusion pressure is 0.35MPa.

[0083] Therefore, when the battery cell of the embodiment of the present application meets the above conditions, the free electrolyte content inside the battery cell is extremely small after extrusion, or even the battery cell basically contains no free electrolyte, thereby significantly improving the reliability and cycle performance of the battery cell.

[0084] In a second aspect, the present application proposes a battery, which includes a battery cell according to any embodiment of the first aspect of the present application.

[0085] In a third aspect, the present application proposes an electrical device, which includes a battery according to any embodiment of the second aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0087] Figure 1 It is a schematic diagram of an embodiment of a battery cell of the present application.

[0088] Figure 2 yes Figure 1 An exploded schematic diagram of an embodiment of a battery cell.

[0089] Figure 3 It is a schematic diagram of an embodiment of a battery module of the present application.

[0090] Figure 4 It is a schematic diagram of an embodiment of the battery pack of the present application.

[0091] Figure 5 yes Figure 4 An exploded schematic diagram of an embodiment of a battery pack is shown.

[0092] Figure 6 It is a schematic diagram of an embodiment of an electric device including the battery cell of the present application as a power source.

[0093] The drawings are not necessarily drawn to scale.

[0094] The following are the descriptions of the reference numerals:

[0095] 1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module;

[0096] 5. Battery cell; 51. Housing; 52. Electrode assembly;

[0097] 53. Cover plate;

[0098] 6. Electrical equipment. DETAILED DESCRIPTION

[0099] Below, the embodiments of the battery cell, battery, and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0100] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0101] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0102] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0103] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which indicates that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0104] The battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator. The separator is arranged between the positive electrode sheet and the negative electrode sheet. Its main function is to prevent the positive electrode sheet and the negative electrode sheet from short-circuiting, while allowing active ions to pass freely to form a loop.

[0105] During the cyclic charge and discharge process of the battery cell, the volume of the electrode assembly may change (such as expansion and deformation) due to the embedding or removal of active ions from the active material, resulting in the electrolyte infiltrated in the electrode assembly being continuously squeezed out. The squeezed-out electrolyte may not be completely absorbed back into the electrode assembly, causing the electrolyte bridge to break in the electrode assembly. Due to the broken bridge of the electrolyte, the active material cannot be fully infiltrated, and the local lack of liquid in the active material makes it impossible to cyclically charge and discharge in this area. Its kinetic performance will deteriorate sharply, causing metal precipitation at the interface and increasing the risk of dendrites. As the dendrites grow, the dendrites may pierce the isolation membrane, causing a short circuit between the positive and negative electrode sheets, thereby deteriorating the reliability and cycle performance of the battery cell.

[0106] In response to the above issues, this application proposes a battery cell that incorporates a swelling polymer into the electrode assembly. Upon contact with the electrolyte, the swelling polymer can physically adsorb the electrolyte between the polymer molecular chains and release the electrolyte into the electrode assembly, thereby alleviating electrolyte starvation and reducing side reactions at the solid-liquid interface, thereby improving the reliability and cycle performance of the battery cell. The technical solution of this application is now described in detail.

[0107] battery cells

[0108] In a first aspect, the present application provides a battery cell, comprising an electrode assembly, the electrode assembly comprising a first electrode piece, a second electrode piece, and a separator, the first electrode piece and the second electrode piece having opposite polarities, the separator being disposed between the first electrode piece and the second electrode piece; at least one of the first electrode piece, the second electrode piece, and the separator comprising a swelling polymer,

[0109] in,

[0110] The swollen polymer was prepared into a film with a mass of m1 g, a width of 10 mm, a length of 10 mm, and a thickness of 1 mm.

[0111] The film was added to an excess of dimethyl carbonate DMC and allowed to stand at 25°C for 7 days to obtain a first swollen film. The mass of the first swollen film was m2 g.

[0112] The first swollen film is placed in an atmosphere with a humidity of less than or equal to 20% and allowed to stand at 25°C for 7 days to obtain a dry film having a mass of m3 g;

[0113] The swelling polymer satisfies: 300%≤m2 / m1≤10000%; m3 / m2≤50%.

[0114] In the embodiment of the present application, the swelling polymer includes a variety of materials, such as a polymer that is solid at room temperature (eg, 0 to 45° C.) or a polymer that is liquid at room temperature. Polymers of different forms can be prepared into films using different methods.

[0115] Specifically, a polymer that is solid at room temperature and soluble in a solvent is used. For example, 10 g of polymer is dissolved in 90 g of N-methylpyrrolidone (NMP), stirred at 1200 rpm for 2 hours, and then dried at 130°C for ≥ 8 hours to obtain a polymer film. A polymer film with a width of 10 mm, a length of 10 mm, and a thickness of 1 mm is used as the adhesive film. Dissolution refers to the process of mixing a solute and a solvent to form a uniform phase. The solubility of a polymer in a solvent generally refers to a solubility greater than 10 g of the polymer in the solvent.

[0116] A polymer that is solid at room temperature and is essentially insoluble in a solvent. 10 g of the polymer is taken and dissolved at (melting point T m +20℃) to form a 1mm solid polymer film. In particular, for polymers that are neither soluble nor meltable, a suitable softening temperature can be selected between Tg and Tb (Tb is the decomposition temperature of the polymer) for processing. The specific pressing process is: the polymer is vacuum dried at 80℃ for 12 hours. The dried polymer is hot-pressed into a thin sheet through a flat vulcanizer, and the hot pressing temperature is set to (T m +20°C), calendering thickness for 1-2 minutes, calendering time for 2 minutes, and pressure of 8 MPa. After calendering for 2 minutes, remove the sample and place it on another vulcanizer of the same model for cold pressing at a pressure of 10 MPa. A 10 cm x 10 cm square mold can produce a film of fixed size. The polymer is insoluble in the solvent, which can generally be understood as the polymer being poorly soluble in the solvent, with a solubility of less than 0.01 g in the solvent.

[0117] For polymers that are liquid at room temperature, take an appropriate amount of sample and dry it at the boiling point of a solvent such as NMP for ≥8 hours to obtain a polymer film. The thickness of the polymer film is related to the solid content of the liquid + the total height of the liquid before drying. You can prepare a liquid with a solid content of 50%, pour it into a solid container to a height of 2mm, and after drying, you can get a 2mm×50%=1mm film.

[0118] The film was added to an excess of dimethyl carbonate DMC (mass ratio of film to DMC was 1:100), where excess means that the film was added to dimethyl carbonate DMC and allowed to stand at 25° C. for 7 days to obtain a first swollen film which still contained free dimethyl carbonate DMC.

[0119] The film is swellable, meaning it absorbs DMC, causing a volume expansion. m2 represents the mass of the film after absorbing DMC. The ratio m2 / m1 characterizes the film's liquid absorption capacity, and thus the liquid absorption capacity of the swellable polymer. Therefore, m2 / m1 can be defined as the film's liquid absorption capacity. When 300% ≤ m2 / m1 ≤ 10000%, the swellable polymer exhibits excellent swelling properties, facilitating the absorption and locking of liquid electrolyte within the swellable polymer, thus enhancing liquid retention. The mass of free electrolyte within the battery cell is reduced, or even zero. As the mass of free electrolyte decreases, the risk of battery cell leakage and reliability issues decreases, improving the battery cell's reliability and cycle performance.

[0120] The first swollen film is dried in a relatively dry environment (humidity ≤ 20%), gradually releasing the solvent from the film. m3 represents the mass of the dried first swollen film. The ratio m3 / m2 can be used to characterize the film's ability to release liquid, and thus the swollen polymer's ability to release liquid. Therefore, m3 / m2 can be defined as the film's liquid release capacity. When m3 / m2 is ≤ 50%, the swollen polymer has a good ability to release liquid electrolyte. During the battery cell's charge and discharge cycles, the liquid electrolyte trapped in the swollen polymer can be released and released into the electrode assembly, promptly replenishing the liquid wetting performance of the electrode assembly's liquid-deficient locations. This ensures more uniform wetting performance throughout the electrode assembly, reduces side reactions at the solid-liquid interface, and improves the battery cell's reliability and cycle performance.

[0121] The swelling polymer of the embodiment of the present application can lock the electrolyte in the swelling polymer by physical adsorption through its own liquid locking and liquid releasing capabilities when satisfying 300%≤m2 / m1≤10000%; m3 / m2≤50%. The electrolyte can be locked on the surface of the active material particles to form a slow-release storage point to release the electrolyte into the electrode assembly, thereby improving the liquid shortage phenomenon of the electrolyte, so that the electrolyte continues to infiltrate the surface of the active material during the cyclic charge and discharge process of the battery cell; and on the basis of protecting the interface of the active material, it can also enable the active ions to be smoothly transmitted, thereby establishing interface protection, reducing solid-liquid interface side reactions, and improving the high-temperature storage performance, usage reliability and cycle performance of the battery cell.

[0122] In some embodiments, 500%≤m2 / m1≤5000%. When the embodiments of the present application meet the above range, the high-temperature storage performance, use reliability, and cycle performance of the battery cell can be further improved.

[0123] Illustratively, m2 / m1 can be 300%, 400%, 500%, 600%, 800%, 1000%, 1200%, 1400%, 1500%, 1600%, 1800%, 2000%, 2200%, 2400%, 2500%, 2600%, 2800%, 3000%, 3200%, 3300%, 3400%, 3500%, 3600%, 3700%, 3800%, 3900%, 4000%, 4200%, 4500%, 4600%, 4700%, 4800%, 4900%, 5000% or a range consisting of any two of the above values.

[0124] Optionally, 0<m3 / m2≤50%. Exemplarily, m3 / m2 can be 50%, 49%, 48%, 45%, 42%, 40%, 39%, 38%, 35%, 32%, 30%, 29%, 28%, 25%, 23%, 22%, 20%, 19%, 18%, 15%, 14%, 13%, 11%, 10%, 8%, 7%, 6%, 5%, 3%, 2%, 1%, or a range consisting of any two of the above values.

[0125] In order to further improve the liquid locking and liquid releasing capabilities of the swelling polymer, the swelling polymer may be further selected, for example, its physical and chemical properties may be further selected, so as to select a swelling polymer with excellent properties.

[0126] In some embodiments, the film is m The elastic modulus G'-energy loss modulus G" curve is obtained by dynamic frequency sweep test at +20℃. The slope of the elastic modulus G'-energy loss modulus G" curve is K, 0.5<K<5; T mIndicates the melting temperature of the film. In particular, for polymers that can neither dissolve nor melt, the melting temperature can be set at T g With T b (T b Select the appropriate softening temperature for testing.

[0127] According to the conclusions of classical linear viscoelasticity, for polymers, especially linear polymers, the elastic modulus G'-dissipation modulus G" in the terminal region of the elastic modulus G'-dissipation modulus G" curve (the interval approaching the maximum angular velocity) conforms to frequency dependence, and the longest chain of the polymer plays a role in the viscoelastic behavior.

[0128] The specific steps of the dynamic frequency sweep test are as follows: The dynamic frequency sweep test was performed using a TA-AR2000EX rotational rheometer (TAinstruments, USA) with a parallel plate diameter of 25 mm and a thickness of 0.9 mm. To ensure that the test was in the linear point-bounce region, the strain during the dynamic frequency sweep test was 2% and the test temperature was T m +20℃, test frequency sweep range: 500rad / s≤w 2 ≤0.05rad / s, so as to obtain data in the lowest possible frequency range.

[0129] The dynamic frequency sweep test can characterize the degree of entanglement of molecular chains under solid phase melting (melt state). When the swelling polymer of the embodiment of the present application meets the above range, the swelling polymer presents a low cross-linked network structure. The cross-linking degree is conducive to the swelling polymer to achieve continuous swelling and liquid absorption ability, and improve the stability of the swelling polymer liquid storage space, which is conducive to improving the cycle performance of the battery cell.

[0130] Illustratively, K may be 0.51, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 3, 3.5, 4, 4.5, 4.95, or a range consisting of any two of the above values.

[0131] In some embodiments, the crystallinity of the swollen polymer is Xc as measured by differential scanning calorimetry, 0<Xc≤30%.

[0132] Crystallization refers to the process in which atoms, ions or molecules in a material are arranged in a certain spatial order to form an orderly structure. The conformation of the polymer in the crystallization is determined by both intramolecular and intermolecular factors. Intermolecular forces affect the packing density between molecular chains. Crystallinity Xc is used to characterize the degree of crystallinity in the material. It can be measured by differential scanning calorimetry (DSC). Specifically, the test steps are as follows: take 0.5g to 0.8g of sample, place the sample in a carrier crucible, and heat and cool the sample in a nitrogen atmosphere, heating it at a rate of 10℃ / min from the intrinsic T of the material to the maximum temperature.g The initial temperature is 20℃ lower and then heated to the intrinsic T m The cut-off temperature of the process is 20℃ higher. The actual glass transition temperature T of the material is determined according to the endothermic and exothermic peak or transition point of the material in the process. g and melting temperature T m wait.

[0133] When the crystallinity of the swollen polymer is within the above range, the crystallinity is relatively low, the arrangement of the polymer molecular chains tends to be loose, the interaction force between the molecular chains is small, and adjacent molecular chains are easily opened, which is conducive to the liquid electrolyte entering between the polymer molecular chains, thereby improving the liquid absorption and release capacity of the swollen polymer, and further improving the cycle performance of the battery cell.

[0134] For example, the crystallinity X of the swollen polymer measured by differential scanning calorimetry is C % can be 1%, 2%, 5%, 10%, 15%, 20%, 25%, 30% or a range consisting of any two of the above values.

[0135] In some embodiments, the glass transition temperature of the swollen polymer is T g , T g ≤25℃; optionally, -60℃≤T g ≤25℃.

[0136] The glass transition temperature is the temperature at which the polymer chain segments change from frozen to moving. g Under such circumstances, the chain segments of the polymer enter a state of motion and have strong mobility. When the glass transition temperature of the swollen polymer is within the above range, the polymer chain segments have a certain mobility, so that the polymer gradually adapts to the volume deformation caused by the entry of the liquid electrolyte and is not prone to destructive deformation; and the polymer chain segments have a certain mobility, making room for the diffusion of the liquid electrolyte; and the network structure inside the polymer has strong flexibility, which is conducive to improving the swelling and liquid absorption capacity of the swollen polymer, and further improving the cycle performance of the battery monomer.

[0137] For example, the glass transition temperature of the swellable polymer may be -60°C, -30°C, -20°C, -10°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, or a range consisting of any two of the foregoing values.

[0138] In some embodiments, the elastic modulus of the film is E, E≤1 MPa; optionally, 0.01 MPa≤E≤1 MPa.

[0139] When the elastic modulus of the film is within the above range, the elastic strength of the film is low, and yield deformation can occur under a relatively low external force, which means that the molecular segments of the swollen polymer are more likely to rearrange under the action of external force. When the swollen polymer is immersed in a liquid electrolyte, the liquid electrolyte can solvate the molecular segments with a relatively low energy barrier, making it easier for the molecular segments to enter the swollen polymer.

[0140] Illustratively, the elastic modulus of the film may be 1 MPa, 0.9 MPa, 0.8 MPa, 0.7 MPa, 0.6 MPa, 0.5 MPa, 0.4 MPa, 0.3 MPa, 0.2 MPa, 0.1 MPa, 0.05 MPa, 0.02 MPa, 0.01 MPa, or a range consisting of any two of the above values.

[0141] In the embodiments of this application, the elastic modulus has a well-known meaning in the art and can be measured using known equipment and instruments. For example, a Shimadzu AGS-X tensile testing machine was used to conduct mechanical property tests on polymer inks and measure the stress-strain curve of the film. According to the national standard GB / T 1040.3-2006, samples were cut into strips approximately 5 mm wide and 50 mm long (the film thickness was controlled to be 1-2 mm), and tensile properties were measured at a rate of 50 mm / min. Elastic modulus E = stress max / (width * thickness), and elongation at break = strain / length.

[0142] In some embodiments, the elongation at break of the adhesive film is ε, ε≥100%. Optionally, 100%≤ε≤2000%.

[0143] When the elongation at break of the film is within the above range, it is conducive to continuous tensile deformation. This means that the network structure within the swollen polymer is resilient and has ample room for deformation. This allows for continuous molecular segment rearrangement under external forces, allowing for the absorption of more liquid electrolyte during the swelling process. Furthermore, the movement of the segments during the swelling process maintains the relative stability of the network structure, forming a stable liquid storage space. For polymers with the same monomer type and composition, the higher the elongation at break, the greater the corresponding swelling and liquid absorption capacity.

[0144] Illustratively, the elongation at break ε of the film can be 100%, 105%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190%, 200%, 220%, 240%, 250%, 270%, 280%, 300%, 320%, 350%, 400%, 450%, 480%, 500%, 600%, 700%, 800%, 900%, 1000%, 1500%, 2000%, or a range consisting of any two of the above values.

[0145] In the embodiments of this application, the term "elongation at break" is generally known in the art and can be tested using known equipment and instruments. For example, a Shimadzu AGS-X tensile testing machine is used to test the mechanical properties of the film and measure the film's stress-strain curve. In accordance with national standard GB / T 1040.3-2006, the film sample is cut into strips approximately 5 mm wide and 50 mm long (the film thickness is controlled to be 1-2 mm). The tensile properties are measured at a rate of 50 mm / min to determine the film's elongation at break.

[0146] In some embodiments, the film is added to a preset electrolyte and allowed to stand at 25° C. for ≥24 h to obtain a second swollen film, wherein the preset electrolyte includes dimethyl carbonate DMC, ethyl methyl carbonate EMC, ethylene carbonate EC, and lithium hexafluorophosphate LiPF6, the masses of dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate are the same, and the molar amount of lithium hexafluorophosphate LiPF6 is 1 mol / L;

[0147] The Shore hardness of the film is H a1 The Shore hardness of the second swollen film is H a2 , the film and the second swollen film meet: 0≤H a2 / H a1 ≤0.5, and 0≤H a2 ≤45;

[0148] The pre-set electrolyte has a composition similar to or substantially identical to that of the electrolyte in the battery. The film is immersed in the pre-set electrolyte to reveal its swelling state. Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) can be considered solvents for the pre-set electrolyte, and lithium hexafluorophosphate (LiPF6) is its lithium salt.

[0149] When immersed in a predetermined electrolyte, the film gradually absorbs the solvent, locking the solvent molecules within it. Swelling may cause the film to gel, which can reduce its mechanical strength. This reduction in mechanical strength becomes more pronounced as the degree of swelling increases. Therefore, in the present embodiment, the mechanical strength of the film before and after swelling can be used to measure the degree of swelling. Shore hardness is used to characterize the mechanical strength of the film.

[0150] In the embodiments of the present application, the Shore hardness of the film is well known in the art and can be tested using equipment and methods known in the art, such as in accordance with the standard GB / T531.1-2008 / ISO 7619-1:2004, "Rubber, vulcanized or thermoplastic—Test method for indentation hardness—Part 1: Shore durometer method (Shore hardness)." For example, three films or three second swollen films are stacked in the thickness direction to form a sample, such that the stacked thickness is 3 mm. The stacked sample is then placed in a Shore AM durometer for testing.

[0151] After testing, the film and the second swelling film of the embodiment of the present application meet the following conditions: 0≤H a2 / H a1 ≤0.5, and 0≤H a2 ≤40.

[0152] The swelling polymer can be arranged in at least one of the first pole piece and the second pole piece. The membrane layer of the first pole piece is a porous structure. For example, there are pores between the active material particles to form a porous structure. The swelling polymer can be dispersed in the porous structure of the first pole piece. On the one hand, the swelling polymer can rely on the porous structure to form a liquid-retaining network, while improving the interface performance of the active material particles, achieving a liquid locking effect, and can increase the transmission rate of lithium ions, reduce the interface side reactions of the active material layer, and improve the cycle performance of the battery cell; on the other hand, the swelling polymer swells after contacting the electrolyte, and its mechanical strength is reduced. During the cyclic charge and discharge process of the battery cell, it can effectively adapt to the expansion and deformation of the active material particles during the charge and discharge process, and can more effectively adhere to the surface of the active material particles, reducing problems such as solid-liquid interface peeling caused by swelling to form a gel-like substance.

[0153] The membrane layer of the second electrode is also a porous structure, and its structural form is similar to that of the first electrode. The porous structure can be a porous structure formed between the active material particles in the second electrode. The swelling behavior and mechanical properties of the swelling polymer are as described in the first electrode and will not be repeated here.

[0154] When the adhesive film and the second swelling adhesive film of the embodiment of the present application satisfy the above-mentioned relationship, they have a strong swelling ability and a better effect of locking the electrolyte. In addition, they can more effectively adapt to the expansion and deformation of the active material particles during the charging and discharging process of the battery cell, and can more effectively adhere to the surface of the active material particles, thereby reducing problems such as solid-liquid interface peeling caused by swelling to form a gel-like substance, and improving the cycle performance of the battery cell.

[0155] For example, the film and the second swollen film may satisfy 0≤H a2 / H a1 ≤0.2.

[0156] For example, Ha2 / H a1 It can be 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a range consisting of any two of the above values.

[0157] Further optionally, 20≤H a1 ≤100.

[0158] For example, the Shore hardness H of the film a1 It can be 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100 or a range consisting of any two of the above values.

[0159] 0≤H a2 ≤45. For example, the Shore hardness of the second swollen film is H a2 18.5, 19, 19.5, 20, 25, 30, 35, 40, 41, 42, 43, 44, 45, or a range consisting of any two of the above values.

[0160] In this application, Shore hardness H a1 and Shore hardness H a2 The measurement standards are the same.

[0161] In order to further improve the liquid absorption and storage capacity of the swelling polymer, the material of the swelling polymer can be further selected to improve the affinity between the swelling polymer and the electrolyte, thereby improving the liquid absorption and storage capacity of the swelling polymer.

[0162] In some embodiments, the swelling polymer may include at least one of a fluorinated polymer, an ether polymer, an ester polymer, and a ketone-aldehyde polymer.

[0163] [Fluorinated polymers]

[0164] In some embodiments, the swelling polymer comprises a fluorinated polymer.

[0165] In some embodiments, the crystallinity of the fluorinated polymer as measured by differential scanning calorimetry is X c1 ,0<

[0166] X c1 ≤30%. For example, the crystallinity X of the fluorinated polymer measured by differential scanning calorimetry is c1 % can be 1%, 5%, 10%, 15%, 20%, 25%, 30% or a range consisting of any two of the above values.

[0167] In some embodiments, the melting temperature of the fluoropolymer is T m1 ℃, 0<T m1 ≤140° C. For example, the melting temperature of the polymer may be 10° C., 20° C., 50° C., 70° C., 90° C., 100° C., 120° C., 140° C., or a range consisting of any two of the foregoing values.

[0168] In some embodiments, the glass transition temperature of the fluoropolymer is T g1 ℃, -60℃≤T g1 ≤25° C. For example, the glass transition temperature of the fluorinated polymer may be −60° C., −30° C., 0° C., 10° C., 25° C., or a range consisting of any two of the foregoing values.

[0169] Therefore, fluoropolymers have relatively low crystallinity, melting temperature or glass transition temperature. The better the flexibility of the fluoropolymer molecular chain, the better the flexibility of the molecular chain segments, and the easier it is for adjacent molecular chains to be opened. The solvent molecules in the electrolyte enter between the molecular chains of the fluoropolymer to form a gel-like substance, which effectively stores the electrolyte on the surface of the active material and improves the wetting performance of the active material.

[0170] In some embodiments, the fluorinated polymer includes at least one of the compounds represented by formula (AI) to the compounds represented by formula (AIII).

[0171] The compound represented by formula (AI) is shown below:

[0172]

[0173] In formula (AI), R 11 、R 12 、R 13 and R 14 Each independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted alkoxy group, and R 11 、R 12 、R 13 and R 14At least one of the substituted groups includes a fluorine atom. When substituted, the substituent includes one or more of a nitrile group (-CN), a nitro group, a sulfonic acid group, a sulfonyl group, an amide group, a carboxyl group, an ester group, and a halogen atom. The halogen atom may include a fluorine atom, a bromine atom, and the like, and may be a fluorine atom.

[0174] Optionally, R 11 、R 12 、R 13 and R 14 Each independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C10 alkyl group, or a substituted or unsubstituted C1-C10 alkoxy group.

[0175] Optionally, R 11 、R 12 、R 13 and R 14 Each independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C3 alkyl group, or a substituted or unsubstituted C1-C3 alkoxy group, and R 11 、R 12 、R 13 and R 14 At least one of them contains a fluorine atom.

[0176] In some embodiments, R 11 、R 12 、R 13 and R 14 Each independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C2 alkyl group or a substituted or unsubstituted C1-C2 alkoxy group; further optionally, R 11 、R 12 、R 13 and R 14 Each independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a methyl group, a fluoromethyl group, a methoxy group or a perfluoromethoxy group.

[0177] In some embodiments, the degree of polymerization n of the fluorinated polymer is any positive integer from 1000 to 30000, for example, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000, 21000, 22000, 23000, 24000, 25000, 26000, 27000, 28000, 29000, or a range consisting of any two of the above values.

[0178] In some embodiments, the fluorinated polymer includes at least one of the compounds represented by formula (AI-1) to the compounds represented by formula (AI-11),

[0179]

[0180] The compound represented by formula (AII) is shown below:

[0181]

[0182] In formula (AII), R 11 、R 12 、R 13 and R 14 Each independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted alkoxy group, and R 11 、R 12 、R 13 and R 14 At least one of the substituted groups includes a fluorine atom. When substituted, the substituent includes one or more of a nitrile group (-CN), a nitro group, a sulfonic acid group, a sulfonyl group, an amide group, a carboxyl group, an ester group, and a halogen atom. The halogen atom may include a fluorine atom, a bromine atom, and the like, and may be a fluorine atom.

[0183] Optionally, R 11 、R 12 、R 13 and R 14 Each independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C10 alkyl group, or a substituted or unsubstituted C1-C10 alkoxy group.

[0184] Optionally, R 11 、R 12 、R 13 and R 14 Each independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C3 alkyl group, or a substituted or unsubstituted C1-C3 alkoxy group, and R 11 、R 12 、R 13 and R 14 At least one of them contains a fluorine atom.

[0185] In some embodiments, R 11 、R 12 、R 13 and R 14 Each independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C2 alkyl group or a substituted or unsubstituted C1-C2 alkoxy group; further optionally, R 11 、R 12 、R 13and R 14 Each independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a methyl group, a fluoromethyl group, a methoxy group or a perfluoromethoxy group.

[0186] In some embodiments, the degree of polymerization n of the fluorinated polymer is any positive integer from 1000 to 30000, for example, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000, 21000, 22000, 23000, 24000, 25000, 26000, 27000, 28000, 29000, or a range consisting of any two of the above values.

[0187] In some embodiments, the fluorinated polymer includes at least one of the compounds represented by formula (AII-1) to the compounds represented by formula (AII-5),

[0188]

[0189] The compound represented by formula (AIII) is shown below,

[0190]

[0191] In formula (AIII), R 15 Includes single bonds, substituted or unsubstituted alkyl groups; when substituted, substituents include fluorine atoms.

[0192] In some embodiments, when substituted, the substituent may include one or more of a nitrile group (—CN), a nitro group, a sulfonic acid group, a sulfonyl group, an amide group, a carboxyl group, an ester group, and a halogen atom.

[0193] Optionally, R 15 This includes single bonds, substituted or unsubstituted C1-C10 alkyl groups.

[0194] Optionally, R 15 This includes single bonds, substituted or unsubstituted C1-C3 alkyl groups.

[0195] In some embodiments, p is selected from any positive integer from 1 to 3, such as 1, 2 or 3.

[0196] In some embodiments, the degree of polymerization n of the fluorinated polymer is any positive integer from 1000 to 30000, for example, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000, 21000, 22000, 23000, 24000, 25000, 26000, 27000, 28000, 29000, or a range consisting of any two of the above values.

[0197] In some embodiments, the fluorinated polymer includes at least one of the compounds represented by formula (AIII-1) to the compounds represented by formula (AIII-3),

[0198]

[0199] Exemplarily, the fluorinated polymer includes one or more of polyperfluoroethylene (PTFE), polyvinylidene fluoride (PVDF), perfluoroethylene propylene copolymer (FEP), perfluoroalkoxy polymer (PFA), perfluoropolyether (PFPE), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE) and perfluoro(1-butenyl vinyl ether) polymer (CYTOP for short).

[0200] Optionally, the fluorinated polymer includes one or more of polyperfluoroethylene (PTFE), polyvinylidene fluoride (PVDF), perfluoroethylene propylene copolymer (FEP), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE).

[0201] The fluoropolymer may be derived from one or more of the following monomers: fluorocycloethane, vinyl fluoride, 1,2-difluoroethylene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, 3,3,3-trifluoropropylene, trifluoropropylene, tetrafluoropropylene, and pentafluoropropylene. Alternatively, the fluoropolymer may be derived from at least two of the following monomers: fluorocycloethane, vinyl fluoride, 1,2-difluoroethylene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, 3,3,3-trifluoropropylene, trifluoropropylene, tetrafluoropropylene, and pentafluoropropylene.

[0202] The monomers used in the above-mentioned fluorinated polymers are all short-chain monomers, which are conducive to the polymerization to form a straight-chain linear structure or a short-chain branched structure. This type of structure has a low degree of entanglement, which is conducive to improving the flexibility of the molecular chain. The molecular chain can fully stretch in the electrolyte, thereby further improving the interfacial performance of the active material.

[0203] In some embodiments, the molecular weight of the swelling polymer is 2×10 5 g / mol to 1.5×10 6 g / mol.

[0204] When the molecular weight of the swelling polymer is within the above range, the interaction between the molecular chains is relatively weak, which is conducive to the solvent molecules in the electrolyte opening the molecular chains and entering between the molecular chains, thereby facilitating the active ions to enter the active material through the solvent, thereby achieving smooth and rapid migration of the active ions. For example, the molecular weight of the polymer can be 2×10 5 g / mol, 5×10 5 g / mol, 8×10 5 g / mol, 1×10 6 g / mol, 1.5×10 6 g / mol or a range consisting of any two of the above values.

[0205] The above-mentioned polymers are only examples of the structural groups of the main molecular chain. In the embodiments of the present application, the polymers can also be obtained by copolymerizing the above-mentioned structural groups with a small amount of other types of structural groups (such as olefin compounds, ester monomers, nitrile monomers, amide monomers and other compounds).

[0206] [Ether polymers]

[0207] In some embodiments, the swelling polymer comprises an ether polymer.

[0208] In some embodiments, the ether polymer is made into a sheet structure; the sheet structure is (T m2 The elastic modulus G'-energy loss modulus G" curve was obtained by dynamic frequency sweep test at +20)℃. The slope of the elastic modulus G'-energy loss modulus G" curve is K1, 1<K1<5, T m2 °C represents the melting temperature of the ether polymer. For example, K1 may be 1.01, 1.1, 2, 3, 4, 4.5, 4.8, 4.9, or a range consisting of any two of the above values.

[0209] In some embodiments, the glass transition temperature of the ether polymer is T g2 ℃, -20℃≤T g2≤25°C. For example, the glass transition temperature of the ether polymer can be -20°C, -15°C, -10°C, -5°C, -0°C, 5°C, 10°C, 15°C, 20°C, 25°C, or a range consisting of any two of the foregoing values. Ether polymers exhibit a certain degree of flexibility above the glass transition temperature, which facilitates the formation of a gel-like substance, improving the wetting effect on the electrode sheet and enhancing battery cycle performance.

[0210] In some embodiments, the ether polymer includes a compound represented by formula (BI),

[0211]

[0212] In formula (BI), R 21 and R 22 Each independently includes a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted alkoxy group; R 23 This includes single bonds, and substituted or unsubstituted methylene groups.

[0213] Optionally, R 21 and R 22 Each independently includes a hydrogen atom, a substituted or unsubstituted C1-C10 alkyl group, or a substituted or unsubstituted C1-C10 alkoxy group.

[0214] Optionally, R 21 and R 22 Each independently includes a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group, or a substituted or unsubstituted C1-C3 alkoxy group.

[0215] Optionally, R 23 It includes single bonds, substituted or unsubstituted C1-C10 methylene groups.

[0216] Optionally, R 23 It includes single bonds, substituted or unsubstituted C1-C5 methylene groups.

[0217] Illustratively, the ether polymer includes at least one of the compounds represented by formula (BI-1) to the compounds represented by formula (BI-8),

[0218]

[0219] In some embodiments, the ether polymer includes a compound represented by formula (BII),

[0220]

[0221] In formula (BII), R 24 to R 27 Each independently includes a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group or an ether group, and R24 to R 27 At least one of them contains a substituted or unsubstituted alkoxy group or an ether group.

[0222] Optionally, R 24 to R 27 Each independently includes a hydrogen atom, a substituted or unsubstituted C1-C10 alkyl group, a substituted or unsubstituted C1-C10 alkoxy group or an ether group.

[0223] Optionally, R 24 to R 27 Each independently includes a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted C1-C3 alkoxy group or an ether group, and R 24 to R 27 At least one of them contains a substituted or unsubstituted C1-C3 alkoxy group or an ether group.

[0224] Optionally, R 24 to R 27 Each independently includes a hydrogen atom, a substituted or unsubstituted C1-C2 alkyl group, a substituted or unsubstituted C1-C2 alkoxy group or an ether group, and R 24 to R 27 At least one of them contains a substituted or unsubstituted C1-C2 alkoxy group or an ether group.

[0225] In some embodiments, the ether polymer includes at least one of the compounds represented by formula (BII-1) to the compounds represented by formula (BII-7),

[0226]

[0227] When substituted, the substituent may include one or more of a nitrile group (-CN), a nitro group, a sulfonic acid group, a sulfonyl group, an amide group, a carboxyl group, an ester group, and a halogen atom; the halogen atom may include at least one of a fluorine atom, a bromine atom, and a chlorine atom.

[0228] The above-mentioned polymers are only examples of the structural groups of the main molecular chain. In the embodiments of the present application, the polymers can also be obtained by copolymerizing the above-mentioned structural groups with a small amount of other types of structural groups (such as olefin compounds, ester monomers, nitrile monomers, amide monomers and other compounds).

[0229] In some embodiments, the degree of polymerization n of the ether polymer is any positive integer from 1500 to 25000, for example, 1500, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000, 21000, 22000, 23000, 24000, 25000, or a range consisting of any two of the above values.

[0230] Optionally, the polymerization degree n of the ether polymer is any positive integer selected from 3,000 to 18,000.

[0231] In some embodiments, the molecular weight of the ether polymer is 1.2×10 5 g / mol to 1.0×10 6 g / mol.

[0232] For example, the molecular weight of the polymer may be 1.2×10 5 g / mol, 2×10 5 g / mol, 5×10 5 g / mol, 8×10 5 g / mol, 1×10 6 g / mol or a range consisting of any two of the above values.

[0233] [Ester polymer]

[0234] In some embodiments, the swelling polymer comprises an ester polymer.

[0235] In some embodiments, the ester polymer is made into a sheet structure; the sheet structure is (T m3 The elastic modulus G'-energy loss modulus G" curve was obtained by dynamic frequency sweep test at +20)℃. The slope of the elastic modulus G'-energy loss modulus G" curve is K2, 1<K2<5, T m3 °C represents the melting temperature of the ester polymer. For example, K2 may be 1.01, 1.1, 2, 3, 4, 4.5, or a range consisting of any two of the above values.

[0236] In some embodiments, the glass transition temperature of the ester polymer is T g3 ℃, -20℃≤T g3≤25°C; illustratively, the glass transition temperature of the ester polymer can be -20°C, -15°C, -10°C, -5°C, -0°C, 5°C, 10°C, 15°C, 20°C, 25°C, or a range consisting of any two of the foregoing values. Ester polymers exhibit a certain degree of flexibility above the glass transition temperature, which facilitates the formation of a gel-like substance, improving the wetting effect on the electrode sheet and enhancing battery cycle performance.

[0237] In some embodiments, the ester polymer includes a compound represented by formula (CI),

[0238]

[0239] In formula (CI), R 31 、R 32 and R 33 Each independently includes a hydrogen atom, or a substituted or unsubstituted alkyl group; R 34 It includes a substituted or unsubstituted alkyl group, or a substituted or unsubstituted hydroxyalkyl group.

[0240] Optionally, R 31 、R 32 and R 33 Each independently includes a hydrogen atom, or a substituted or unsubstituted C1-C10 alkyl group.

[0241] Optionally, R 31 、R 32 and R 33 Each independently includes a hydrogen atom, or a substituted or unsubstituted C1-C8 alkyl group; R 34 It includes substituted or unsubstituted C1-C8 alkyl groups, or substituted or unsubstituted C1-C8 hydroxyalkyl groups.

[0242] In some embodiments, R 34 It includes substituted or unsubstituted C1-C6 alkyl groups, or substituted or unsubstituted C1-C6 hydroxyalkyl groups.

[0243] In some embodiments, R 31 This includes a hydrogen atom, or a substituted or unsubstituted methyl group.

[0244] In some embodiments, R 32 and R 33 Each independently includes a hydrogen atom.

[0245] In some embodiments, R 34 It includes substituted or unsubstituted C1-C4 alkyl groups, or substituted or unsubstituted C1-C4 hydroxyalkyl groups.

[0246] Illustratively, the ester polymer includes at least one of the compounds represented by formula (CI-1) to the compounds represented by formula (CI-15),

[0247]

[0248]

[0249] In some embodiments, the ester polymer includes a compound represented by formula (CII),

[0250]

[0251] In formula (CII), R 35 This includes substituted or unsubstituted methylene groups.

[0252] Optionally, R 35 This includes substituted or unsubstituted C1-C10 methylene groups.

[0253] Optionally, R 35 This includes substituted or unsubstituted C2-C6 methylene groups.

[0254] Optionally, R 35 This includes substituted or unsubstituted C2-C4 methylene groups.

[0255] Illustratively, the ester polymer includes at least one of the compounds represented by formula (CII-1) to the compounds represented by formula (CII-5),

[0256]

[0257] In some embodiments, the ester polymer includes a compound represented by formula (CIII),

[0258]

[0259] In formula (CIII), R 36 、R 37 and R 38 Each independently includes a hydrogen atom, or a substituted or unsubstituted C1-C8 alkyl group; R 39 Including substituted or unsubstituted C1-C8 alkyl;

[0260] Optionally, R 36 、R 37 and R 38 Each independently includes a hydrogen atom, a substituted or unsubstituted C1-C4 alkyl group.

[0261] Illustratively, the ester polymer includes at least one of the compounds represented by formula (CIII-1) to the compounds represented by formula (CIII-5),

[0262]

[0263] When substituted, the substituent may include one or more of a nitrile group (-CN), a nitro group, a sulfonic acid group, a sulfonyl group, an amide group, a carboxyl group, an ester group, and a halogen atom. The halogen atom may include at least one of a fluorine atom, a bromine atom, and a chlorine atom.

[0264] The above-mentioned polymers are only examples of the structural groups of the main molecular chain. In the embodiments of the present application, the polymers can also be obtained by copolymerizing the above-mentioned structural groups with other types of structural groups (such as olefin compounds, acrylonitrile compounds, maleic anhydride and other monomers with functional groups).

[0265] In some embodiments, the degree of polymerization n of the ester polymer is selected from any positive integer from 800 to 20,000, for example, 800, 1,000, 1,500, 2,000, 3,000, 4,000, 5,000, 6,000, 7,000, 8,000, 9,000, 10,000, 11,000, 12,000, 13,000, 14,000, 15,000, 16,000, 17,000, 18,000, 19,000, 20,000, or a range consisting of any two of the above values.

[0266] In some embodiments, the degree of polymerization n of the ester polymer is any positive integer selected from 1,000 to 15,000.

[0267] In some embodiments, the molecular weight of the ester polymer is 1.2×10 5 g / mol to 1.0×10 6 g / mol.

[0268] For example, the molecular weight of the ester polymer may be 1.2×10 5 g / mol, 2×10 5 g / mol, 5×10 5 g / mol, 8×10 5 g / mol, 1×10 6 g / mol, 1.5×10 6 g / mol or a range consisting of any two of the above values.

[0269] [Ketone-aldehyde polymers]

[0270] In some embodiments, the swelling polymer comprises an aldehyde ketone polymer.

[0271] In some embodiments, the aldehyde-ketone polymer is made into a sheet structure; the sheet structure is (T m4The elastic modulus G'-energy loss modulus G" curve was obtained by dynamic frequency sweep test at +20)℃. The slope of the elastic modulus G'-energy loss modulus G" curve is K3, 0.8≤K3<5, T m4 °C represents the melting temperature of the aldehyde-ketone polymer. For example, K3 may be 0.8, 0.85, 0.9, 1, 1.01, 1.1, 2, 3, 4, 4.5, or a range consisting of any two of the above values.

[0272] In some embodiments, the glass transition temperature of the aldehyde-ketone polymer is T g4 ℃, -20℃≤T g4 ≤25°C; illustratively, the glass transition temperature of the aldehyde-ketone polymer can be -20°C, -15°C, -10°C, -5°C, -0°C, 5°C, 10°C, 15°C, 20°C, 25°C, or a range consisting of any two of the foregoing values. The aldehyde-ketone polymer exhibits a certain degree of flexibility above the glass transition temperature, which facilitates the formation of a gel-like substance, improving the wetting effect on the electrode sheet and enhancing the battery's cycling performance.

[0273] In some embodiments, the aldehyde-ketone polymer comprises a compound represented by formula (DI),

[0274]

[0275] In formula (DI), R 41 Including single bonds, substituted or unsubstituted C1-C6 methylene; R 42 This includes a hydrogen atom, and a substituted or unsubstituted C1-C6 alkyl group.

[0276] Optionally, R 41 It includes single bonds, substituted or unsubstituted C1-C2 methylene groups.

[0277] Optionally, R 42 This includes a hydrogen atom, and a substituted or unsubstituted C1-C3 alkyl group.

[0278] In the embodiments of the present application, a single bond indicates that the group does not exist, and the atoms on both sides of the group are connected by a single bond, for example, R 41 is a single bond, indicating R 41 The carbon atoms on both sides are connected by single bonds.

[0279] Illustratively, the aldehyde-ketone polymer includes at least one of the compounds represented by formula (DI-1) to the compounds represented by formula (DI-6),

[0280]

[0281] In some embodiments, the aldehyde-ketone polymer comprises a compound represented by formula (DII),

[0282]

[0283] In formula (DII), R 43 to R 46 Each independently includes a hydrogen atom, a hydroxyl group, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted C1-C3 hydroxyalkyl group, or a substituted or unsubstituted C1-C3 alkoxy group; r and s are each independently selected from an integer from 0 to 5, and at least one of r and s is selected from any positive integer.

[0284] Optionally, R 43 to R 46 Each independently includes a hydrogen atom, a hydroxyl group, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted C1-C2 hydroxyalkyl group, or a substituted or unsubstituted C1-C2 alkoxy group.

[0285] In some embodiments, the aldehyde-ketone polymer includes at least one of the compounds represented by formula (DII-1) to the compounds represented by formula (DII-4),

[0286]

[0287] The above polymers are only examples of the structural groups of the main molecular chain. In the embodiments of the present application, the polymers can also be obtained by copolymerizing the above structural groups with other types of structural groups (such as olefin compounds, enol compounds, acrylonitrile compounds, etc.).

[0288] When the above groups are substituted, the substituents may include one or more of a nitrile group (-CN), a nitro group, a sulfonic acid group, a sulfonyl group, an amide group, a carboxyl group, an ester group, and a halogen atom. The halogen atom may include at least one of a fluorine atom, a bromine atom, and a chlorine atom.

[0289] In some embodiments, the degree of polymerization n of the aldehyde-ketone polymer is selected from any positive integer from 500 to 15,000, for example, 500, 800, 1000, 1500, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, or a range consisting of any two of the above values.

[0290] Optionally, the degree of polymerization n of the aldehyde-ketone polymer is any positive integer selected from 500 to 10,000.

[0291] In some embodiments, the molecular weight of the aldehyde-ketone polymer is 1.2×10 5 g / mol to 1.0×10 6 g / mol.

[0292] For example, the molecular weight of the aldehyde-ketone polymer may be 1.2×10 5 g / mol, 2×10 5 g / mol, 5×10 5 g / mol, 8×10 5 g / mol, 1×10 6 g / mol, 1.0×10 6 g / mol or a range consisting of any two of the above values.

[0293] The relevant parameters of the swelling polymer according to the embodiment of the present application can be detected by the following methods:

[0294] The groups of the swellable polymers of the embodiments of the present application can be detected by infrared spectrophotometry IR. Specifically, the swellable polymers are tested using a Thermo Nicolet Nexus 670 attenuated total reflectance Fourier transform infrared spectrometer (FTIR-ATR), and then tested in accordance with the standard GB / T6040-2002. The test range is: ATR method 600-4000 cm -1 ; Repeatability: ±2cm -1 ; Resolution: better than 4cm -1 ; Transmission depth 0.2~0.6μm.

[0295] The structure of the swollen polymer according to the embodiment of the present application can be tested by nuclear magnetic resonance (NMR). Specifically, 1H NMR and 13C NMR are performed on a Varian Mercury Plus-400 NMR spectrometer at a test temperature of 20° C., TMS as an internal standard, CDCl 3 as a solvent, and a proton resonance frequency of 400 MHz.

[0296] The polymer monomer type of the swelling polymer in the embodiment of the present application (especially suitable for monomers with a relatively small proportion in the polymer) can be tested by pyrolysis-gas chromatography-mass spectrometry. The specific testing steps are as follows: accurately weigh 0.5 mg of sample and place it in a sample cup. After fixing it to the injection rod, place it in a pyrolyzer installed near the GC (gas chromatography) injection port. After the pyrolyzer temperature reaches the set temperature, press the injection button, and the sample cup quickly falls into the pyrolysis furnace core by free fall. In the inert gas N2 atmosphere, the volatile components are instantly vaporized and carried into the gas chromatography column by the carrier gas for separation. Finally, they are detected by a flame ionization detector FID or a mass spectrometer MS to obtain a gas chromatogram or a total ion current diagram.

[0297] The molecular weight of the swelling polymer in the embodiment of the present application is well known in the art and can be measured using commonly used equipment and methods in the art. Gel permeation chromatography (GPC) testing can be used. The specific testing steps are as follows: take an appropriate amount of the sample to be tested (the sample concentration is sufficient to ensure 8%-12% shading), add 20 ml of deionized water, and simultaneously supercharge for 5 minutes (53 KHz / 120 W) to ensure that the sample is completely dispersed, and then measure the sample in accordance with GB / T19077-2016 / ISO 13320:2009 standard.

[0298] The swelling polymer can be set in various locations, such as in the electrode, in the isolation membrane, etc. The following describes the setting form of the swelling polymer.

[0299] In some embodiments, the electrode sheet includes a swellable polymer. Specifically, the first electrode sheet includes a current collector and a film layer disposed on at least one surface of the current collector, the film layer including a swellable polymer and active material particles. The swellable polymer may be disposed only in the first electrode sheet, only in the second electrode sheet, or both. The first electrode sheet may be a positive electrode sheet, and accordingly, the second electrode sheet may be a negative electrode sheet; alternatively, the first electrode sheet may be a negative electrode sheet, and accordingly, the second electrode sheet may be a positive electrode sheet.

[0300] As some examples, the membrane layer includes a polymer layer and an active material layer, the polymer layer includes a swelling polymer, and the active material layer includes active material particles. The active material layer is arranged on at least one surface of the current collector, and the polymer layer is arranged on the surface of the active material layer away from the current collector. It can be understood that the active material particles and the binder are dried on the surface of the current collector to form an active material layer, and the swelling polymer is arranged on the surface of the active material layer away from the current collector. Such a setting is conducive to the swelling polymer locking the electrolyte on the surface of the active material particles to form a slow-release liquid storage point, thereby improving the active ion transfer rate while protecting the interface of the active material layer, reducing interfacial side reactions, and improving the high-temperature storage performance and cycle performance of the battery cell.

[0301] Specifically, the electrode preparation process includes:

[0302] adding active material particles into a solvent to prepare an active slurry;

[0303] Applying the active slurry to the surface of the current collector and drying and solidifying it into an active material layer;

[0304] The swelling polymer is placed on the surface of the active material layer to form an electrode.

[0305] As other examples, there are multiple active material particles, there are pores between two adjacent active material particles, and the swelling polymer is distributed in the pores; this setting can improve the liquid storage capacity of the active material layer, that is, the ability to lock the electrolyte, thereby improving the reliability and cycle performance of the battery cell.

[0306] Specifically, the preparation process of an embodiment of a pole piece includes:

[0307] dispersing the swelling polymer in a solvent to form a mixed system;

[0308] Adding active material particles into the mixed system to prepare a slurry;

[0309] The slurry is applied to the surface of the current collector and dried and solidified into a pole piece.

[0310] Specifically, the preparation process of another embodiment of the pole piece includes:

[0311] Dispersing the swelling polymer and active material particles in a solvent to prepare a slurry;

[0312] The slurry is applied to the surface of the current collector and dried and solidified into a pole piece.

[0313] As some further examples, the swelling polymer is distributed on the surface of the active material particles, and the swelling polymer is distributed in the pores between the active material particles.

[0314] Specifically, the preparation process of an embodiment of a pole piece includes:

[0315] Dispersing the swelling polymer and active material particles in a solvent to prepare a slurry;

[0316] Applying the slurry on the surface of the current collector and solidifying it into a film layer after drying;

[0317] The swelling polymer is placed on the surface of the film layer to form a pole piece.

[0318] In other embodiments, the isolation membrane includes a swellable polymer. Specifically, the isolation membrane may include a substrate; optionally, the isolation membrane may further include a coating disposed on at least one surface of the substrate.

[0319] As some examples, the substrate is generally a porous structure having pores, and the swelling polymer can be distributed in the pores of the substrate.

[0320] As further examples, the swelling polymer may be distributed within the coating.

[0321] As further examples, the swelling polymer can be disposed on a surface of the coating facing away from the substrate.

[0322] The specific distribution position of the swelling polymer can be any one of the above three forms, any two of them, or a combination of the above three positions.

[0323] In some embodiments, the isolation membrane includes a substrate, and the substrate includes a swellable polymer. The swellable polymer can be used as the main material of the substrate, or the swellable polymer can be blended with the main material of the substrate to prepare the substrate.

[0324] In some further embodiments, the swelling polymer may be disposed in the electrode and the isolation membrane. The specific disposition positions are as described above and will not be repeated here.

[0325] In some embodiments, the battery cell further includes a liquid electrolyte, and the liquid electrolyte is located within the electrode assembly.

[0326] Liquid electrolytes have fluidity, making it easier for them to flow around the active material particles, thereby increasing the transmission rate of active ions. In related technologies, liquid electrolytes generally have the following forms within battery cells: one is diffusion into the pore structure of the electrode assembly, such as being located in the pores of the pole piece and / or the separator; the other is free within the battery cell. The liquid electrolytes of the embodiments of the present application have the following forms: one is diffusion into the pore structure of the electrode assembly, such as being located in the pores of the pole piece and / or the separator; the other is diffusion into the swollen polymer, so that the liquid electrolytes of the embodiments of the present application are basically all located inside the electrode assembly, and there is basically no free electrolyte within the battery cell, thereby significantly improving the reliability and cycle performance of the battery cell.

[0327] In some embodiments, the battery cell also satisfies 0≤y / V 总孔 ≤15%;

[0328] y represents the volume of free electrolyte in the battery cell, and its unit is mL;

[0329] V 总孔 A numerical value indicating the pore volume of the electrode assembly, with the unit being mL.

[0330] When calculating in a formula, only the numerical value is substituted for the calculation, without substituting the unit for the calculation.

[0331] When the battery cell meets the above conditions, the content of free electrolyte in the battery cell is extremely small, or even the battery cell basically contains no free electrolyte, which can significantly improve the reliability and cycle performance of the battery cell.

[0332] For example, y / V 总孔It can be 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range consisting of any two of the above values. 总孔 A value of 0 indicates that the amount of free electrolyte is 0 mL, that is, there is basically no free electrolyte in the battery cell.

[0333] The electrode assembly includes a first electrode piece, a second electrode piece, and a separator. The pore volume of the electrode assembly includes the sum of the pore volume of the first electrode piece, the pore volume of the second electrode piece, and the pore volume of the separator. In the embodiments of the present application, pore volume has a meaning commonly known in the art and can be measured using equipment and methods commonly known in the art. For example, it can be obtained by a gas displacement method. The pore volume is vm, where v represents the apparent volume (i.e., the total volume) and m represents the true volume.

[0334] In some embodiments, the battery cell satisfies: (m / ρ) / V 总孔 ≥80%;

[0335] V 总孔 represents the pore volume of the electrode assembly 52, and its unit is mL;

[0336] m represents the difference between the mass of the battery cell before drying and the mass after drying, and its unit is g.

[0337] ρ represents the density of the electrolyte, and its unit is g / mL.

[0338] In the embodiments of the present application, m can be understood as the total amount of electrolyte in the battery cell. After the electrolyte is injected into the battery cell, the electrolyte mainly exists in the following forms: one is located in the pore structure of the electrode and / or the separator, and the other is diffused into the swollen polymer. m can be measured by the following method: take a fresh battery cell and fully discharge it to 0% SOC state of charge, weigh the battery cell, and the weighed mass is m1; open a hole with a diameter of The battery cell is placed on top of a container with the hole facing downward and directly above the container, so that the free electrolyte inside the battery cell can drip into the container below. The battery cell is left to stand for 3 to 5 hours so that all the free electrolyte inside can drip into the container. The battery cell is then dried at 60°C to 95°C for 24 to 48 hours, and the battery cell is immersed in dimethyl carbonate (DMC) solvent for 12 hours. The battery cell is then dried at 60°C to 95°C for 24 to 48 hours, and the dried battery cell is weighed. The weighed mass is recorded as m2, where m is m1-m2. For example, the battery cell is dried at 60°C for 5 hours, and the dried battery cell is weighed. In the embodiment of the present application, the fresh battery cell can be a battery cell that has just left the factory (not subjected to charge and discharge cycles after formation), or a battery cell that is assembled on an electrical device and has been cycled for less than 10 cycles.

[0339] In the embodiment of the present application, when there is free electrolyte in the battery cell, the electrolyte density ρ can be measured by the following method: a predetermined mass of electrolyte can be poured out from multiple battery cells in the battery, for example 10, and the volume of the poured electrolyte can be measured. The ratio of the predetermined mass to the volume is the electrolyte density ρ. When there is no free electrolyte in the battery cell, the electrolyte density ρ is the density of the electrolyte injected into the battery cell.

[0340] When the battery cell meets the above conditions, most of the liquid electrolyte is located in the pore structure of the electrode assembly, that is, the electrode assembly itself has good liquid absorption and liquid retention capabilities, which is conducive to the transmission of active ions and improves the dynamic performance of the battery cell; a small part of the liquid electrolyte can diffuse into the swelling polymer and release liquid during the battery cell's cyclic charge and discharge process. Since the amount of liquid released is relatively small, the liquid electrolyte is not easy to flow out of the electrode assembly, and can make the electrolyte infiltration of the electrode assembly more uniform, thereby improving the cycle performance of the battery cell.

[0341] For example, (m / ρ) / V 总孔 ≥80%, (m / ρ) / V 总孔 ≥82%, (m / ρ) / V 总孔 ≥85%, (m / ρ) / V 总孔 ≥86%, (m / ρ) / V 总孔 ≥88%, (m / ρ) / V 总孔 ≥90%, (m / ρ) / V 总孔 ≥92% or (m / ρ) / V 总孔 ≥95%.

[0342] In some embodiments, the battery cell further satisfies: 0≤y / Ah≤15%;

[0343] y represents the volume of free electrolyte in the battery cell, and its unit is mL;

[0344] Ah represents the nominal capacity of a battery cell, and its unit is Ah.

[0345] When calculating a formula, only the numerical value is substituted into the formula without its unit.

[0346] The volume of free electrolyte y (mL) can be measured by the following method: take a fresh battery cell and discharge it to 0% SOC state of charge. A hole with a diameter of The battery cell is placed on top of a container with the hole facing downward and directly above the container, so that the free electrolyte inside the battery cell can drip into the container below. The battery cell is left to stand in this manner for 3 to 5 hours to allow all the free electrolyte inside to drip into the container. The volume of the electrolyte in the container is then measured to obtain y. In the embodiments of the present application, a fresh battery cell can be a battery cell that has just left the factory (has not been charged and discharged after formation) or a battery cell that has been assembled in an electrical device and has been cycled less than 10 times.

[0347] When the battery cell meets the above conditions, the content of free electrolyte in the battery cell is extremely small, or even the battery cell basically contains no free electrolyte, which can significantly improve the reliability and cycle performance of the battery cell.

[0348] For example, y / Ah can be 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range consisting of any two of the foregoing values. A y / Ah of 0 indicates zero free electrolyte, i.e., substantially no free electrolyte is present in the battery cell.

[0349] In some embodiments, after the battery cell is subjected to a linear frequency sweep vibration test, it is charged to 100% state of charge (SOC), a hole is opened on the battery cell, and the hole is set at the lowest point in the vertical direction, and the volume of electrolyte flowing out of the battery cell is recorded as M1, 0 mL ≤ M1 ≤ 0.5 mL, and optionally, M1 is 0 mL;

[0350] in,

[0351] The vibration direction of the linear frequency sweep vibration test is: single vibration up and down;

[0352] The vibration frequency of the linear sweep vibration test is: 10Hz~55Hz;

[0353] The maximum acceleration of the linear sweep vibration test is: 30m / s 2 ;

[0354] The number of sweep cycles of the linear sweep vibration test is: 10 times;

[0355] The vibration time of the linear sweep frequency vibration test is: 3h.

[0356] In the related art, during use, battery cells may vibrate under the action of external forces, and the electrolyte in the electrode assembly may separate from the electrode assembly under the action of vibration, forming free electrolyte. The free electrolyte in the battery cell may leak, causing corrosion to the battery cell and leading to risks such as battery cell failure. However, the embodiments of the present application can effectively gather and throw out the liquid electrolyte inside the battery cell by subjecting the battery cell to static and vibration treatment, thereby more accurately judging whether there is flowing liquid electrolyte between the battery cell shell and the electrode assembly, and determining the content of free electrolyte. When the battery cell of the embodiments of the present application meets the above conditions, the content of free electrolyte in the battery cell is extremely small, or even the battery cell basically contains no free electrolyte, which can significantly improve the reliability and cycle performance of the battery cell.

[0357] For example, M1 can be 0 mL, 0.05 mL, 0.1 mL, 0.15 mL, 0.2 mL, 0.25 mL, 0.3 mL, 0.35 mL, 0.4 mL, 0.45 mL, 0.5 mL, or a range consisting of any two of the foregoing values. M1 of 0 mL indicates that the amount of free electrolyte is zero, meaning that there is essentially no free electrolyte inside the battery cell after the linear frequency sweep vibration test.

[0358] In some embodiments, after the battery cell undergoes the above-mentioned vibration test, the housing is removed, the electrode assembly is taken out and subjected to an extrusion test, and the volume of the electrolyte flowing out of the electrode assembly is recorded as M2 (the extrusion equipment is suspended, and a weighing balance and an electrolyte collection container are set at the bottom), 0 mL ≤ M2 ≤ 0.5 mL, optionally, M2 is 0 mL;

[0359] in,

[0360] The extrusion direction of the extrusion test is: perpendicular to the thickness direction of the electrode assembly 52;

[0361] The extrusion degree of the extrusion test is: the extrusion pressure is 0.35MPa.

[0362] In the related art, battery cells may be subjected to external squeezing during use, and the electrolyte in the electrode assembly may be separated from the electrode assembly under the action of squeezing, forming free electrolyte. The free electrolyte in the battery cell may leak, causing corrosion to the battery cell, leading to risks such as battery cell failure. However, the embodiment of the present application can effectively squeeze out the liquid electrolyte inside the battery cell by performing an squeezing test on the battery cell, thereby more accurately judging whether there is flowing liquid electrolyte between the battery cell shell and the electrode assembly, and determining the content of free electrolyte. When the battery cell of the embodiment of the present application meets the above conditions, after squeezing, the content of free electrolyte in the battery cell is extremely small, or even the battery cell basically contains no free electrolyte, which can significantly improve the reliability and cycle performance of the battery cell.

[0363] For example, M2 can be 0 mL, 0.05 mL, 0.1 mL, 0.15 mL, 0.2 mL, 0.25 mL, 0.3 mL, 0.35 mL, 0.4 mL, 0.45 mL, 0.5 mL, or a range consisting of any two of the foregoing values. An M2 of 0 mL indicates zero free electrolyte, meaning that substantially no free electrolyte remains within the battery cell after the extrusion test.

[0364] In some embodiments, a voltage of 200 V is applied to the battery cell to form a loop, and within 4 hours, the absolute value of the temperature change of the battery cell is ≤ 4°C.

[0365] For example, when the negative terminal and outer casing of a battery cell are connected to a 200V voltage to form a current loop, the battery cell's temperature fluctuates within 4°C over a 4-hour period, without any failures such as fire or explosion. In particular, when the free electrolyte y = 0, the temperature fluctuation range is minimal, significantly improving the reliability of the battery cell.

[0366] [Positive electrode]

[0367] The battery cell comprises a positive electrode plate, the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer arranged on the positive electrode current collector, and the positive electrode film layer comprises a positive electrode active material and a swelling polymer.

[0368] In some embodiments, the positive electrode film layer includes a polymer layer containing a swellable polymer and a positive electrode active material layer containing positive electrode active material particles. The positive electrode active material layer is arranged on at least one surface of the positive electrode current collector, and the polymer layer is arranged on the surface of the positive electrode active material layer facing away from the positive electrode current collector.

[0369] In some embodiments, there are multiple positive electrode active material particles, there is a pore between two adjacent positive electrode active material particles, the swelling polymer is distributed in the pore, and the positive electrode active material particles and the swelling polymer are located in the same film layer.

[0370] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two facing surfaces of the positive electrode current collector.

[0371] The positive electrode active material layer includes a positive electrode active material. The positive electrode active material can be a positive electrode active material commonly known in the art for use in battery cells. For example, the positive electrode active material includes at least one of a lithium-containing positive electrode active material and a sodium-containing positive electrode active material, and can include, for example, at least one of the following materials: a lithium-containing phosphate compound, a lithium-containing transition metal oxide, a sodium-containing phosphate compound, and a sodium-containing transition metal oxide.

[0372] For example, the general formula of the olivine-type phosphate active material (lithium-containing phosphate compound) is: Li x A y Me a M b P 1-c X c Y z , wherein 0≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of S, Si, Cl, B, C, and N; and Y includes one or more of O and F. Specifically, the olivine-type phosphate active material includes one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0373] For example, lithium transition metal oxides (layered materials such as ternary, lithium nickelate / sodium, lithium cobaltate / sodium, lithium manganate / sodium, lithium-rich layered and rock salt phase layered materials). The general formula of the layered structure positive electrode active material is: Li x A y Ni a Co b Mn c M (1-a-b-c) Y z, wherein 0≤x≤2.1, 0≤y≤2.1, and 0.9≤x+y≤2.1; 0≤a≤1, 0≤b≤1, 0≤c≤1, and 0.1≤a+b+c≤1; 1.8≤z≤3.5; A includes one or more of Na, K, and Mg; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; Y includes one or more of O and F. Optionally, y=0. Specifically, the layered structure positive electrode active material may include lithium cobalt oxide LCO, lithium nickel oxide LNO, lithium manganese oxide LMO, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NML33), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622),LiNi 0.8 Co 0.1 Mn 0.1 One or more of O2 (NCM811) and NCA.

[0374] During the charge and discharge process, battery cells are accompanied by the deintercalation and deintercalation of active ions, such as Li, and their molar content varies when the battery cells are discharged to different states. The molar content of Li in the examples of positive electrode active materials in the embodiments of this application refers to the material's initial state, i.e., the state before the materials are added. When the positive electrode active material is used in a battery system, the molar content of Li may change after charge and discharge cycles.

[0375] In the examples of the positive electrode active materials in the embodiments of the present application, the molar content of oxygen O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen O to change. In practice, the molar content of oxygen O will fluctuate.

[0376] In the embodiment of the present application, the modified compound can be modified by doping or coating. Doping modification can be adding doping elements such as transition metals to the compound, and coating modification can be surface coating with materials such as carbon, that is, forming a carbon coating layer on the outer surface of the particle.

[0377] In some embodiments, the mass content of the swelling polymer is ≤5% based on the total mass of the positive electrode film layer; optionally, it can be 0.05% to 1%. When the mass content of the swelling polymer is within the above range, the swelling polymer can effectively improve the interfacial properties and structural stability of the positive electrode sheet. In this case, the swelling polymer can be located in the same layer as the positive electrode active material particles, or in different layers. The case of being located in different layers means that the swelling polymer is located in the polymer layer and the positive electrode active material particles are located in the positive electrode active material layer. Optionally, the swelling polymer can be located in the same layer as the positive electrode active material particles.

[0378] For example, the mass content of the adsorbed polymer may be 0.05%, 0.08%, 0.10%, 0.11%, 0.12%, 0.15%, 0.16%, 0.18%, 0.20%, 0.22%, 0.25%, 0.28%, 0.30%, 0.32%, 0.35%, 0.38%, 0.40%, 0.42%, 0.45%, 0.48%, 0.50%, 0.55%, 0.58%, 0.60%, 0.70%, 0.80%, 0.90%, 0.95%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.6%, 1.7%, 1.8%, 1.9%, 1.9%, 1.10%, 1.111%, 1.12%, 1.13 ... %, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0% or a range consisting of any two of the above values.

[0379] In the embodiments of this application, the mass content of the polymer has a meaning well known in the art and can be tested using equipment and methods well known in the art. For example, it can be tested using thermogravimetric analysis (TGA) according to JYT014-1996. Specifically, a mass-temperature curve, i.e., a TG curve, is plotted based on the mass loss of the electrode during the heating process. The corresponding weight loss is read according to the polymer decomposition temperature, which is the total mass of the polymer in the electrode, and the mass content of the polymer is calculated from this. During the test, the test can be performed in a nitrogen atmosphere using the following temperature ramp program: 5°C / min, RT to 500°C; 10°C / min, 500 to 600°C; constant temperature at 600°C for 10 minutes, and then terminated.

[0380] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil or an aluminum alloy foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include a combination of one or more selected from aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. The polymer material base layer may include a combination of one or more selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0381] In some embodiments, the positive electrode active material layer may further optionally include a positive electrode conductive agent. The present application does not particularly limit the type of positive electrode conductive agent. For example, the positive electrode conductive agent may include a combination of one or more selected from superconducting carbon, conductive carbon black, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent is less than 5% based on the total mass of the positive electrode active material layer.

[0382] In some embodiments, the positive electrode active material layer may also optionally include a positive electrode binder. The present application embodiment has no particular restrictions on the type of positive electrode binder. As an example, the positive electrode binder may include a combination of one or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylic resin. In some embodiments, based on the total mass of the positive electrode active material layer, the mass percentage of the positive electrode binder is less than 5%. Compared to the crystallinity of the fluorinated polymer in the embodiment of the present application, the crystallinity of the positive electrode binder is higher.

[0383] The positive electrode active material layer is typically formed by coating the positive electrode slurry onto the positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional swelling polymer, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP). Of course, the preparation of the positive electrode sheet is not limited to the above method; the preparation methods described above may also be used.

[0384] [Negative electrode]

[0385] The battery cell includes a negative electrode plate.

[0386] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film disposed on at least one surface of the negative electrode current collector. For example, the negative electrode current collector has two opposing surfaces in the thickness direction of the negative electrode current collector, and the negative electrode film is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0387] In some embodiments, the negative electrode film layer includes a polymer layer containing a swellable polymer and a negative electrode active material layer containing negative electrode active material particles. The negative electrode active material layer is arranged on at least one surface of the negative electrode current collector, and the polymer layer is arranged on the surface of the negative electrode active material layer away from the negative electrode current collector.

[0388] In some embodiments, there are multiple negative electrode active material particles, there is a pore between two adjacent negative electrode active material particles, the swelling polymer is distributed in the pore, and the negative electrode active material particles and the swelling polymer are located in the same film layer.

[0389] The negative electrode active material can be any negative electrode active material known in the art for use in battery cells. For example, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include at least one of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include at least one of elemental tin, tin oxide, and tin alloys.

[0390] In some embodiments, the mass content of the swelling polymer is ≤5% based on the total mass of the negative electrode film layer; optionally, it can be 0.5% to 3.5%. When the mass content of the swelling polymer is within the above range, the swelling polymer can effectively improve the interfacial properties and structural stability of the negative electrode sheet. In this case, the swelling polymer can be located in the same layer as the negative electrode active material particles, or in different layers. The case of being located in different layers means that the swelling polymer is located in the polymer layer and the negative electrode active material particles are located in the negative electrode active material layer. Optionally, the swelling polymer can be located in the same layer as the negative electrode active material particles.

[0391] For example, the mass content of the adsorbed polymer may be 0.05%, 0.08%, 0.10%, 0.11%, 0.12%, 0.15%, 0.16%, 0.18%, 0.20%, 0.22%, 0.25%, 0.28%, 0.30%, 0.32%, 0.35%, 0.38%, 0.40%, 0.42%, 0.45%, 0.48%, 0.50%, 0.55%, 0.58%, 0.60%, 0.70%, 0.80%, 0.90%, 0.95%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.6%, 1.7%, 1.8%, 1.9%, 1.9%, 1.10%, 1.111%, 1.12%, 1.13 ... %, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0% or a range consisting of any two of the above values.

[0392] In some embodiments, the negative electrode active material layer may further optionally include a negative electrode conductive agent. The present embodiments do not particularly limit the type of negative electrode conductive agent. For example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent based on the total mass of the negative electrode active material layer is ≤5%.

[0393] In some embodiments, the negative electrode active material layer may further optionally include a negative electrode binder. The present application does not particularly limit the type of negative electrode binder. For example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), a water-soluble unsaturated resin SR-1B, a water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder based on the total mass of the negative electrode active material layer is ≤5%.

[0394] In some embodiments, the negative electrode active material layer may optionally include other additives. For example, the other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like. In some embodiments, the weight percentage of the other additives is ≤ 2% based on the total weight of the negative electrode active material layer.

[0395] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0396] The negative electrode active material layer is typically formed by coating the negative electrode slurry onto the negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional swelling polymer, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water. Of course, the preparation of the negative electrode sheet is not limited to the above method; the preparation methods described above can also be used.

[0397] The negative electrode sheet does not exclude other additional functional layers in addition to the negative electrode active material layer. For example, in some embodiments, the negative electrode sheet of the present application further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of the present application further includes a protective layer covering the surface of the negative electrode active material layer.

[0398] [Isolation film]

[0399] The battery cell includes a separator.

[0400] In some embodiments, the separator includes a substrate.

[0401] In some embodiments, a separator includes a substrate and a coating disposed on at least one surface of the substrate.

[0402] As some examples, the substrate is generally a porous structure having pores, and the swelling polymer can be distributed in the pores of the substrate.

[0403] As further examples, the swelling polymer may be distributed within the coating.

[0404] As further examples, the swelling polymer can be disposed on a surface of the coating facing away from the substrate.

[0405] The specific distribution position of the swelling polymer can be any one of the above three forms, any two of them, or a combination of the above three positions.

[0406] The embodiments of the present application are not particularly limited to the material of the substrate. Any known substrate with good chemical and mechanical stability may be selected, such as at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The substrate may be a single-layer film or a multi-layer composite film. When the substrate is a multi-layer composite film, the materials of each layer may be the same or different. The substrate typically has a porous structure having pores, and the swelling polymer may be distributed in the pores of the substrate.

[0407] In some embodiments, the coating may further include a filler. Further, the filler may include at least one of inorganic particles and organic particles. The swelling polymer may be distributed in the coating.

[0408] In some embodiments, the swelling polymer may be disposed on the surface of the coating facing away from the substrate.

[0409] In some embodiments, the decomposition temperature of the filler may be above 200° C., so that the filler has good thermal stability and is not easily decomposed, thereby further improving the heat resistance of the isolation membrane.

[0410] The inorganic particles have the characteristics of high thermal stability and non-decomposability. Optionally, the inorganic particles include at least one of inorganic particles having a dielectric constant of 5 or greater, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of undergoing electrochemical reactions.

[0411] Alternatively, the inorganic particles having a dielectric constant of 5 or more include boehmite, aluminum oxide, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hectorite, zirconium titanate, barium titanate, Pb(Zr,Ti)O3 (abbreviated as PZT), Pb 1-m La m Zr 1-n Ti n O3 (abbreviated as PLZT, 0<m<1, 0<n<1), Pb(Mg3Nb 2 / 3)O3-PbTiO3 (abbreviated as PMN-PT), and at least one of their respective modified inorganic particles. Optionally, the modification method of each inorganic particle may be chemical modification and / or physical modification. Chemical modification methods include coupling agent modification (for example, using silane coupling agent, titanate coupling agent, etc.), surfactant modification, polymer grafting modification, etc. Physical modification methods may be mechanical force dispersion, ultrasonic dispersion, high energy treatment, etc. The modification treatment can reduce the agglomeration of inorganic particles, thereby enabling them to form a more stable and uniform spatial network structure with nanocellulose; in addition, by selecting coupling agents, surfactants or polymer-modified inorganic particles with specific functional groups, it is also helpful to improve the coating's wetting properties for the electrolyte and improve the bonding strength between the coating and the substrate.

[0412] Alternatively, inorganic particles having ion conductivity but not storing ions include Li3PO4, lithium titanium phosphate Li x1 Ti y1 (PO4)3, lithium aluminum titanium phosphate Li x2 Al y2 Ti z1 (PO4)3, (LiAlTiP) x3 O y3 Type glass, lanthanum lithium titanate Li x4 La y4 TiO3, lithium germanium thiophosphate Li x5 Ge y5 P z2 S w , lithium nitride Li x6 N y6 、SiS2 type glass Li x7 Si y7 S z3 and P2S5 glass Li x8 P y8 S z4 At least one of the following: 0<x1<2, 0<y1<3, 0<x2<2, 0<y2<1, 0<z1<3, 0<x3<4, 0<y3<13, 0<x4<2, 0<y4<3, 0<x5<4, 0<y5<1, 0<z2<1, 0<w<5, 0<x6<4, 0<y6<2, 0<x7<3, 0<y7<2, 0<z3<4, 0<x8<3, 0<y8<3, 0<z4<7. This can further improve the ion transport properties of the isolation membrane.

[0413] Organic particles have good thermal stability and are not easy to decompose, which can improve the heat resistance of the isolation membrane; at the same time, when the internal temperature of the battery cell reaches the melting point of the organic particles due to overcharge abuse, heat abuse, etc., the organic particles can also melt and be absorbed into the micropores of the substrate due to capillary action to play a role in closing the pores and breaking the circuit, which is beneficial to ensure that the battery cell has high safety performance.

[0414] In some embodiments, the organic particles include, but are not limited to, at least one of polyethylene particles, polypropylene particles, polystyrene particles, melamine resin particles, phenolic resin particles, polyester particles (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, polyaryletherketone particles, and copolymers of butyl acrylate and ethyl methacrylate (e.g., cross-linked polymers of butyl acrylate and ethyl methacrylate).

[0415] In some embodiments, the coating further comprises a binder. The present application does not particularly limit the type of binder; any known material with good adhesive properties may be used. For example, the binder comprises at least one of an aqueous solution-based acrylic resin (e.g., a homopolymer of acrylic acid, methacrylic acid, or sodium acrylate, or a copolymer with other comonomers), polyvinyl alcohol, an isobutylene-maleic anhydride copolymer, and polyacrylamide.

[0416] Optionally, the binder content in the coating is <30%, based on the mass of the coating.

[0417] [Electrolyte]

[0418] In some embodiments, the battery cell includes an electrolyte, which may be locked by a swollen polymer and located on the surface of the active material particles, thus forming a non-free electrolyte.

[0419] During the charge and discharge process of a battery cell, active ions are embedded and released back and forth between the positive and negative electrodes, and the electrolyte conducts the active ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and it can be selected according to actual needs.

[0420] The electrolyte solution includes an electrolyte salt and a solvent. The types of the electrolyte salt and the solvent are not particularly limited and can be selected according to actual needs.

[0421] When the battery cell of the present application is a lithium-ion battery, as an example, the electrolyte salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0422] When the battery cell of the present application is a sodium ion battery, as an example, the electrolyte salt may include but is not limited to at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalatoborate (NaDFOB), sodium dioxalatoborate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorobis(oxalatophosphate) (NaDFOP) and sodium tetrafluorooxalatophosphate (NaTFOP).

[0423] As an example, the solvent may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0424] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0425] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly through a winding process and / or a lamination process.

[0426] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0427] In some embodiments, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell can also be a soft shell, such as a bag-type soft shell. The soft shell can be made of plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0428] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly by a winding process or a lamination process.

[0429] The present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape. Figure 1 The battery cell 5 is a square structure as an example.

[0430] In some embodiments, as Figure 1 and Figure 2 As shown, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be adjusted according to demand.

[0431] The manufacturing method of the battery cell of the present application is well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, separator, and negative electrode sheet can be wound or laminated to form an electrode assembly. The electrode assembly is then placed in an outer packaging, dried, and then injected with electrolyte. The battery cell is then vacuum packaged, allowed to stand, formed, and shaped to obtain a battery cell.

[0432] In some embodiments of the present application, the battery cells according to the present application can be assembled into a battery module. The battery module can contain multiple battery cells, and the specific number can be adjusted according to the application and capacity of the battery module.

[0433] Figure 3 FIG. 4 is a schematic diagram of a battery module 4 as an example. Figure 3As shown, in the battery module 4, the plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0434] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0435] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0436] Both the battery module 4 and the battery pack can be used as specific examples of batteries in the embodiments of the present application.

[0437] Figure 4 and Figure 5 FIG. 1 is a schematic diagram of a battery pack 1 as an example. Figure 4 and Figure 5 As shown, a battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 is used to cover the lower box body 3 and form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0438] Electrical devices

[0439] In a second aspect, the present application provides an electrical device, which includes at least one of the battery cells, battery modules and battery packs of the present application. The battery cells, battery modules and battery packs can be used as power sources for the electrical device, and can also be used as energy storage units for the electrical device. The electrical device may be, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc. In some embodiments, the battery cell includes an injection hole for injecting electrolyte; when the battery cell is applied to the electrical device, the injection hole is located at the bottom of the battery cell in the vertical direction. Since the amount of free electrolyte in the battery cell is extremely small, or even no free electrolyte, when the injection hole is set at the bottom of the battery cell in the vertical direction, the reliability of the battery cell can also be improved, thereby improving the reliability of the electrical device.

[0440] The electrical device can select battery cells, battery modules or battery packs according to its usage requirements. Figure 6This is a schematic diagram of an example electrical device. This electrical device 6 is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this electrical device, a battery pack 1 or battery module can be used. Another example electrical device can be a mobile phone, tablet computer, or laptop computer. These electrical devices typically require a thin and lightweight design and can use battery cells as their power source.

[0441] Example

[0442] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0443] Example 1 Preparation of lithium-ion battery

[0444] (1) Preparation of positive electrode sheet:

[0445] The swelling polymer, the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent carbon black, binder polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone (NMP) and mixed to prepare positive electrode slurry. 0.8 Co 0.1 Mn 0.1 The mass ratio of O2 (NCM811), conductive carbon black, and PVDF is 0.2:97.3:2:0.5. The positive electrode slurry is coated onto the current collector aluminum foil, dried at 85°C, and then cold-pressed. The cathode sheet is then trimmed, cut, and slit, and then dried under vacuum at 85°C for 4 hours to form the positive electrode. The binder, polyvinylidene fluoride (PVDF), has a crystallinity of 48%, a melting temperature of 164°C, and a glass transition temperature of 39°C.

[0446] (2) Preparation of negative electrode sheet:

[0447] The swelling polymer, artificial graphite (the negative electrode active material), carbon black (the conductive agent), styrene-butadiene rubber (SBR) (the binder), and sodium carboxymethyl cellulose (CMC) (the thickener) were mixed uniformly in a weight ratio of 2.5:94.9:2:0.5:0.1 in deionized water to form the negative electrode slurry. The negative electrode slurry was then coated onto the current collector copper foil and dried at 85°C. The negative electrode sheet was then cold-pressed, trimmed, cut, and slit, and then dried at 120°C under vacuum for 12 hours.

[0448] (3) Preparation of electrolyte:

[0449] In an environment with a water content of less than 10ppm, the non-aqueous organic solvents ethylene carbonate EC and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 3:7 to obtain an electrolyte solvent. Subsequently, the lithium salt LiPF6 and the mixed solvent are mixed to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0450] (4) Preparation of lithium-ion batteries:

[0451] Using a 16μm polyethylene film (PE) as a separator, the above-mentioned positive electrode sheet, separator, and negative electrode sheet are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer packaging shell, dried and then injected with electrolyte, and after vacuum packaging, standing, formation, shaping and other processes, a lithium-ion battery is obtained.

[0452] Example 2 to Example 4

[0453] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the amount of the swelling polymer used was adjusted in Examples 2 to 4.

[0454] Example 5 to Example 9

[0455] Lithium-ion batteries were prepared using a method similar to that of Example 1. The difference from Example 1 was that the types of swelling polymers were adjusted in Examples 5 to 9.

[0456] Example 10 and Example 11

[0457] Lithium-ion batteries were prepared using a method similar to that of Example 1. The difference from Example 1 was that the types of swelling polymers were adjusted in Examples 10 and 11.

[0458] Comparative Example 1

[0459] A lithium ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that no swelling polymer was used in Comparative Example 1.

[0460] (1) Preparation of positive electrode sheet:

[0461] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent carbon black, binder polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone (NMP) and mixed to form positive electrode slurry. 0.8 Co 0.1 Mn 0.1The mass ratio of O2 (NCM811), conductive carbon black, and PVDF is 97.5:2:0.5. The positive electrode slurry is coated on the current collector aluminum foil and dried at 85°C before cold pressing. The positive electrode sheet is then trimmed, cut, and slit, and then dried at 85°C under vacuum for 4 hours.

[0462] (2) Preparation of negative electrode sheet:

[0463] The negative electrode slurry was prepared by adding artificial graphite (the negative electrode active material), carbon black (the conductive agent), styrene-butadiene rubber (SBR) (the binder), and sodium carboxymethyl cellulose (CMC) (the thickener) to deionized water at a weight ratio of 94.9:2:0.5:2.6 and mixing them evenly. The negative electrode slurry was then coated onto the current collector copper foil and dried at 85°C. The negative electrode sheet was then cold-pressed, trimmed, cut, and slit, and then dried at 120°C under vacuum for 12 hours.

[0464] Comparative Example 2

[0465] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the type of swelling polymer was adjusted in Comparative Example 2.

[0466] Test section

[0467] 1. Battery cell capacity retention test

[0468] Taking Example 1 as an example, the prepared lithium-ion battery was first constant-capacity tested for C0: discharged to 2.8V at 1C, allowed to stand for 5 minutes, then charged to 4.25V at a constant current of 1 / 3C, and then charged to a current of 0.05C at a constant voltage of 4.25V. After standing for 5 minutes, the battery was discharged to 2.8V at 1C. The capacity released at this time was recorded as C0.

[0469] Then, the battery capacity retention rate test process is as follows: the battery corresponding to Example 1 is charged to 4.25V at room temperature with an equivalent 1.2C step charge (charge 0.5C0Ah at 1.2C constant current, then charge 0.3C0Ah at 0.87C constant current, and then charge to V2 at 1 / 3C constant current), then charge at 4.25V constant voltage to a current of 0.05C, stand for 5 minutes, and then discharge at 0.33C to 2.8V. The resulting capacity is recorded as the initial capacity C0, and the initial clamp force of the battery cell is set to 12000N. The above steps are repeated for the same battery, and the discharge capacity Cn of the battery after the nth cycle is recorded at the same time. The battery capacity retention rate after each cycle is Pn = Cn / C0*100%. The 250 point values ​​P1, P2...P250 are used as the vertical coordinates and the corresponding cycle number is used as the horizontal coordinates to obtain a curve of the battery capacity retention rate and cycle number corresponding to the polymer in Example 1.

[0470] During the test, the first cycle corresponds to n=1, the second cycle corresponds to n=2, ... and the 250th cycle corresponds to n=250. The battery capacity retention rate data corresponding to Example 1 in Table 3 is the data measured after 250 cycles under the above test conditions, that is, the value of P250.

[0471] The testing procedures of Comparative Example 1 and other embodiments are the same as above.

[0472] 2. Battery cell DC impedance test

[0473] Taking Example 1 as an example, the prepared lithium-ion battery was first constant-capacity tested for C0: discharged to 2.8V at 1C, allowed to stand for 5 minutes, then charged to 4.25V at a constant current of 1 / 3C, and then charged to a current of 0.05C at a constant voltage of 4.25V. After standing for 5 minutes, the battery was discharged to 2.8V at 1C. The capacity released at this time was recorded as C0.

[0474] The battery DC impedance test process is as follows: At 25°C, the battery cell corresponding to Example 1 is charged to 4.25V at an equivalent 1.2C step charge (0.5C0Ah at 1.2C constant current, 0.3C0Ah at 0.87C constant current, and then charged to V2 at 1 / 3C constant current). Then, it is charged to a current of 0.05C at 4.25V. After 5 minutes, the voltage V1 is recorded. The battery is then discharged at 1 / 3C for 30 seconds, and the voltage V2 is recorded. The internal resistance DCR1 of the battery after the first cycle is calculated as (V2-V1) / 1 / 3C. The initial clamping force of the battery cell is set to 12000N. Repeat the above steps for the same battery and simultaneously record the internal resistance DCRn (n=1, 2, 3...250) of the battery after the nth cycle. The 250 point values ​​of DCR1, DCR2, DCR3...DCR250 are plotted as the ordinate, and the corresponding number of cycles as the abscissa to obtain a curve of the battery discharge DCIR and cycle number corresponding to the polymer of Example 1. During this test, the first cycle corresponds to n=1, the second cycle corresponds to n=2, and so on. The 250th cycle corresponds to n=250. The internal resistance increase ratio of the battery of Example 1 in Table 3 = (DCRn-DCR1) / DCR1*100%,

[0475] The test process of Comparative Example 1 and other examples is the same as above. The data in Table 3 are measured after 250 cycles under the above test conditions.

[0476] Test results

[0477] The test results are shown in Tables 1 to 3.

[0478] Table 1

[0479]

[0480] In Table 1, "85% vinyl acetate + 15% ethylene" in the monomers means that, based on the total weight of the monomers, the weight content of vinyl acetate is 85% and the weight content of ethylene is 15%. Even when the same monomers are used, polymer properties, such as changes in glass transition temperature, may vary due to variations in polymerization conditions (such as polymerization temperature and pressure).

[0481] Table 2

[0482]

[0483] In Table 2, the swelling polymer content of the positive electrode sheet is 0.2%, which means that the mass content of the swelling polymer is 0.2% based on the total mass of the positive electrode film layer.

[0484] The amount of swelling polymer added to the positive electrode sheet is 0.0%, indicating that no swelling polymer is added to the positive electrode film layer.

[0485] Table 3

[0486]

[0487] As can be seen from Table 3, the positive electrode and negative electrode sheets of Comparative Example 1 do not have swelling polymer added. During the cycle of the lithium-ion battery, due to the volume change of the lithium-ion battery, the electrolyte in the electrode assembly may be squeezed out, causing a liquid shortage problem, thereby increasing the risk of lithium dendrites and deteriorating the reliability and cycle performance of the lithium-ion battery.

[0488] Although polyethylene oxide is added to the electrode in Comparative Example 2, the swelling capacity of the polymer is relatively low, resulting in low liquid retention efficiency and high impedance that deteriorates the battery kinetics.

[0489] The embodiment of the present application adds a swelling polymer to at least one of the positive electrode sheet, the negative electrode sheet and the isolation membrane. The swelling polymer can lock the electrolyte and release the electrolyte during the charge and discharge process, thereby improving the liquid retention capacity of the electrode assembly and the wettability of the electrolyte to the electrode assembly, thereby improving the reliability and cycle performance of the lithium-ion battery.

[0490] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications may be made to the embodiments without departing from the spirit, principles, and scope of the present application.

Claims

1. A battery cell, comprising an electrode assembly, the electrode assembly comprising a first electrode sheet, a second electrode sheet, and a separator, wherein the first electrode sheet and the second electrode sheet have opposite polarities, the separator is disposed between the first electrode sheet and the second electrode sheet, and at least one of the first electrode sheet, the second electrode sheet, and the separator comprises a swelling polymer, wherein the swelling polymer satisfies the following conditions: 300% ≤ m2 / m1 ≤ 10000%; m3 / m2 ≤ 50%, in, The swollen polymer is prepared into a film, the mass of the film is m1g, the width of the film is 10mm, the length is 10mm, and the thickness is 1mm; the film is a polymer film prepared from the swollen polymer; The film was added to an excess of dimethyl carbonate DMC, and allowed to stand at 25° C. for 7 days to obtain a first swollen film, wherein the mass of the first swollen film was m2g; The first swollen film was placed in an atmosphere with a humidity of less than or equal to 20% and allowed to stand at 25° C. for 7 days to obtain a dry film. The mass of the dry film was m3g.

2. The battery cell according to claim 1, wherein: 500%≤m2 / m1≤5000%.

3. The battery cell according to claim 1 or 2, wherein: The swelling polymer satisfies at least two of the following conditions, (1) The film is at T m The elastic modulus G'-energy loss modulus G" curve is obtained by dynamic frequency sweep test at +20°C. The slope of the elastic modulus G'-energy loss modulus G" curve is K, 0.5<K<5, T m Indicates the melting temperature of the film; (2) the crystallinity of the swollen polymer measured by differential scanning calorimetry is Xc, 0<Xc≤30%; The glass transition temperature of the swollen polymer is T g , T g ≤25℃; (3) The elastic modulus of the adhesive film is E, E≤1MPa; the elongation at break of the adhesive film is ε, ε≥100%.

4. The battery cell according to claim 1 or 2, wherein: Adding the film to a preset electrolyte and standing at 25° C. for ≥24 h to obtain a second swollen film, wherein the preset electrolyte includes dimethyl carbonate DMC, ethyl methyl carbonate EMC, ethylene carbonate EC and lithium hexafluorophosphate LiPF6, the dimethyl carbonate, the ethyl methyl carbonate and the ethylene carbonate have the same mass, and the molar amount of the lithium hexafluorophosphate LiPF6 is 1 mol / L; The Shore hardness of the film is H a1 The Shore hardness of the second swollen film is H a2 , the film and the second swollen film satisfy: 0≤H a2 / H a1 ≤0.5, and 0≤H a2 ≤4.

5. The battery cell according to claim 4, wherein: 0≤H a2 / H a1 ≤0.45。 The battery cell according to claim 4 , wherein: 20≤H a1 ≤100。 7. The battery cell according to claim 1 or 2, wherein: The swelling polymer includes a fluoropolymer, and the fluoropolymer includes at least one of the compounds represented by formula (AI) to the compounds represented by formula (AIII), In formula (AI) and formula (AII), R 11 、R 12 、R 13 and R 14 Each independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C3 alkyl group, or a substituted or unsubstituted C1-C3 alkoxy group, and R 11 、R 12 、R 13 and R 14 At least one of the substituted groups comprises a fluorine atom; when substituted, the substituent comprises one or more of a nitrile group (-CN), a nitro group, a sulfonic acid group, a sulfonyl group, an amide group, a carboxyl group, an ester group, and a halogen atom; In formula (AIII), R 15 Including single bonds, substituted or unsubstituted C1-C3 alkyl groups; when substituted, the substituents include one or more of nitrile groups (-CN), nitro groups, sulfonic acid groups, sulfonyl groups, amide groups, carboxyl groups, ester groups, and halogen atoms; p is any positive integer selected from 1 to 3; The polymerization degree n of the fluorinated polymer is selected from any positive integer from 5,000 to 20,000.

8. The battery cell according to claim 1 or 2, wherein: The swelling polymer includes an ether polymer, and the ether polymer includes a compound represented by formula (BI) and / or a compound represented by formula (BII), In formula (BI), R 21 and R 22 Each independently includes a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group, or a substituted or unsubstituted C1-C3 alkoxy group; R 23 Including substituted or unsubstituted C1-C5 alkylene; In formula (BII), R 24 to R 27 Each independently includes a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted C1-C3 alkoxy group or an ether group, and R 24 to R 27 At least one of them contains a substituted or unsubstituted C1-C3 alkoxy group or an ether group; The polymerization degree n of the ether polymer is selected from any positive integer from 1500 to 25000.

9. The battery cell according to claim 1 or 2, wherein: The swelling polymer includes an ester polymer, and the ester polymer includes a compound represented by formula (CI) to a compound represented by formula (CIII), In formula (CI), R 31 、R 32 and R 33 Each independently includes a hydrogen atom, or a substituted or unsubstituted C1-C8 alkyl group; R 34 Including substituted or unsubstituted C1-C8 alkyl, or substituted or unsubstituted C1-C8 hydroxyalkyl; In formula (CII), R 35 including substituted or unsubstituted C2-C6 methylene; In formula (CIII), R 36 、R 37 and R 38 Each independently includes a hydrogen atom, or a substituted or unsubstituted C1-C8 alkyl group; R 39 Including substituted or unsubstituted C1-C8 alkyl; The polymerization degree n of the ester polymer is selected from any positive integer from 800 to 20,000.

10. The battery cell according to claim 9, wherein: R 35 Each independently includes a substituted or unsubstituted C2-C4 methylene group.

11. The battery cell according to claim 9, wherein: R 36 、R 37 and R 38 Each independently includes a hydrogen atom, a substituted or unsubstituted C1-C4 alkyl group.

12. The battery cell according to claim 1 or 2, wherein: The swelling polymer includes an aldehyde-ketone polymer, and the aldehyde-ketone polymer includes a compound represented by formula (DI) and / or a compound represented by formula (DII), In formula (DI), R 41 Including single bonds, substituted or unsubstituted C1-C6 methylene; R 42 including hydrogen atoms, substituted or unsubstituted C1-C6 alkyl groups; In formula (DII), R 43 to R 46 Each independently includes a hydrogen atom, a hydroxyl group, a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted C1-C3 hydroxyalkyl group, or a substituted or unsubstituted C1-C3 alkoxy group; r and s are each independently selected from an integer from 0 to 5, and at least one of r and s is selected from any positive integer; The polymerization degree n of the aldehyde-ketone polymer is selected from any positive integer from 500 to 15,000.

13. The battery cell according to claim 1 or 2, wherein: The first pole piece includes a current collector and a film layer disposed on at least one surface of the current collector, and the film layer includes the swelling polymer and active material particles.

14. The battery cell according to claim 13, wherein: The membrane layer comprises a polymer layer containing a swelling polymer and an active material layer containing active material particles, the active material layer is disposed on at least one surface of the current collector, and the polymer layer is disposed on a surface of the active material layer facing away from the current collector; and / or There are a plurality of active material particles, and there is a gap between two adjacent active material particles. The swelling polymer is distributed in the gap.

15. The battery cell according to claim 1 or 2, wherein: The isolation film includes a substrate and a coating disposed on at least one surface of the substrate; The swelling polymer is distributed in the pores of the substrate; and / or The swelling polymer is distributed in the coating; and / or The swelling polymer is disposed on a surface of the coating layer facing away from the substrate. 16 . The battery cell according to claim 1 , further comprising a liquid electrolyte, wherein the liquid electrolyte is located within the electrode assembly.

17. The battery cell according to claim 16, wherein the battery cell satisfies: (m / ρ) / V 总孔 ≥80%; V 总孔 A value representing the pore volume of the electrode assembly, in mL; m represents the difference between the mass of the battery cell before drying and the mass after drying, and its unit is g; ρ represents the density of the liquid electrolyte, and its unit is g / mL.

18. The battery cell according to claim 1 or 2, wherein: The battery cell meets the following requirements: 0≤y / Ah≤15%; y represents the volume of free electrolyte in the battery cell, in mL; Ah represents the value of the nominal capacity of the battery cell, and its unit is Ah.

19. The battery cell according to claim 1 or 2, wherein: The battery cell meets the following requirements: 0≤y / V 总孔 ≤15%; y represents the volume of free electrolyte in the battery cell, in mL; V 总孔 The value representing the pore volume of the electrode assembly, with the unit being mL.

20. The battery cell according to claim 1 or 2, wherein: After the linear frequency sweep vibration test, the battery cell is charged to 100% state of charge (SOC). A hole is opened on the battery cell, and the hole is set at the lowest point in the vertical direction. The volume of liquid electrolyte flowing out of the battery cell is recorded as M1, where 0 mL ≤ M1 ≤ 0.5 mL. in, The vibration direction of the linear sweep vibration test is: single vibration up and down; The vibration frequency of the linear sweep vibration test is: 10Hz~55Hz; The maximum acceleration of the linear sweep vibration test is: 30m / s 2 ; The number of sweep cycles of the linear sweep vibration test is: 10 times; The vibration time of the linear sweep frequency vibration test is 3 hours.

21. The battery cell according to claim 20, wherein: M1 is 0 mL.

22. The battery cell according to claim 20, wherein After the battery cell has been subjected to the linear frequency sweep vibration test, the electrode assembly is removed. After the electrode assembly has been subjected to the extrusion test, the volume of the electrolyte flowing out of the electrode assembly is recorded as M2, where 0 mL ≤ M2 ≤ 0.5 mL; in, The extrusion direction of the extrusion test is: perpendicular to the thickness direction of the electrode assembly; The extrusion degree of the extrusion test is: the extrusion force is 0.35 MPa.

23. The battery cell according to claim 22, wherein: M2 is 0 mL.

24. A battery comprising the battery cell according to any one of claims 1 to 23.

25. An electrical device comprising the battery according to claim 24.

Images