Battery cells, batteries and electrical devices

Abstract

This application provides a battery cell, a battery, and an electrical device. The battery cell includes an electrode assembly, which includes electrode plates and a separator. The electrode plates include a current collector and a membrane layer containing an active material and a liquid-absorbing polymer disposed on at least one surface of the current collector. The electrode plates satisfy: v / λ≥1.2; v represents the liquid absorption rate of the membrane layer, in mg / s; λ represents the porosity of the membrane layer. The separator includes a liquid-retaining polymer, and the separator satisfies: (m2-M) / (m1-M)≥25%; M represents the mass of the separator layer that has not absorbed electrolyte, in g; m1 represents the mass of the separator layer after immersion in electrolyte for 2 hours under ambient pressure, in g; m2 represents the mass of the separator layer after immersion in electrolyte for 2 hours under ambient pressure of 10000N, in g.

Description

Technical Field

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

[0002] Battery cells have characteristics such as high capacity and long lifespan, and are therefore widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and power tools, etc.

[0003] As batteries are used in a wider range of applications, the requirements for the performance of individual battery cells are becoming increasingly stringent. However, the current cycle performance of individual battery cells is relatively poor and still needs further improvement. Summary of the Invention

[0004] The embodiments of this application were made in view of the above-mentioned problems, and the purpose of this application is to provide a battery cell, a battery, and an electrical device.

[0005] A first aspect of this application provides a battery cell, the battery cell including an electrode assembly, the electrode assembly including electrode sheets and a separator; the electrode sheet including a current collector and a film layer containing an active material and a liquid-absorbing polymer disposed on at least one surface of the current collector, the electrode sheet satisfying: v / λ≥1.2; v represents the liquid absorption rate of the film layer, its unit is mg / s; λ represents the porosity of the film layer; the separator includes a liquid-retaining polymer, wherein the separator satisfies:

[0006]

[0007] Therefore, in the battery cell of this application embodiment, the electrode plates are provided with liquid-absorbing polymers, which help the electrode plates to absorb electrolyte back, and the electrolyte wets the electrode plates more evenly and fully, thereby improving the stability of the battery cell during cycling. The separator of the battery cell is provided with liquid-retaining polymers, which have strong liquid-retaining capacity. During the cyclic charging and discharging of the battery cell, the electrolyte is not easily squeezed out, reducing the liquid shortage during cyclic charging and discharging, reducing battery polarization, and improving the cycle performance of the battery cell.

[0008] In some embodiments, the active material includes a positive electrode active material, and the electrode sheet satisfies: 1.2 ≤ v / λ ≤ 4.50. When the electrode sheet meets the above range, its liquid absorption rate is faster, which can improve the electrolyte reabsorption rate and thus improve the cycle performance of the battery cell.

[0009] In some embodiments, the active material includes a negative electrode active material, and the electrode sheet satisfies: 3 ≤ v / λ < 50.00. When the electrode sheet meets the above range, its liquid absorption rate is faster, which can improve the electrolyte reabsorption rate and thus improve the cycle performance of the battery cell.

[0010] In some embodiments, the separating membrane satisfies:

[0011]

[0012] Therefore, when the separator of the present application meets the above conditions, its liquid retention capacity can be further improved, which can further reduce the liquid shortage during the cycle charge and discharge, reduce battery polarization, and improve the cycle performance of the battery cell.

[0013] In some embodiments, the separating membrane satisfies:

[0014]

[0015] Therefore, when the separator of the present application meets the above conditions, its liquid retention capacity can be further improved, which can further reduce the liquid shortage during the cycle charge and discharge, reduce battery polarization, and improve the cycle performance of the battery cell.

[0016] In some embodiments, the separating membrane satisfies:

[0017]

[0018] Therefore, when the separator of the present application meets the above conditions, its liquid retention capacity can be further improved, which can further reduce the liquid shortage during the cycle charge and discharge, reduce battery polarization, and improve the cycle performance of the battery cell.

[0019] In some embodiments, the separator further includes a liquid-absorbing polymer; optionally, the liquid-absorbing polymer in the electrode sheet has a unit volume mass of A1, and the liquid-absorbing polymer in the separator has a unit volume mass of A2, where 1.0 ≤ A1 / A2 ≤ 1.6; optionally, 1.2 ≤ A1 / A2 ≤ 1.5.

[0020] In some embodiments, the electrode sheet further includes a liquid-retaining polymer; optionally, the unit volume mass of the liquid-retaining polymer located in the electrode sheet is B1, and the unit volume mass of the liquid-retaining polymer located in the separator is B2, 0.4≤B1 / B2≤0.9; optionally, 0.5≤B1 / B2≤0.8.

[0021] In some embodiments, the unit volume mass of the liquid-absorbing polymer located in the electrode sheet is C1, and the unit volume mass of the liquid-retaining polymer located in the separator is C2, where 0.1 ≤ C1 / C2 ≤ 5.

[0022] In some embodiments, the liquid-retaining polymer includes ether polymers.

[0023] Optionally, the ether polymer comprises structural units represented by formula (BI) and / or formula (BII).

[0024]

[0025] In formula (BI), R 21 and R 22 Each independently comprises 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 groups;

[0026]

[0027] In formula (BII), R 24 To R 27 Each independently comprises 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 or ether group.

[0028] In some embodiments, the liquid-retaining polymer includes ester polymers.

[0029] Optionally, the ester polymer is formed into a sheet-like structure; the sheet-like structure is in (T m3 The elastic modulus G' - energy dissipation modulus G” curve was obtained by dynamic frequency scanning test at +20℃. The slope of the elastic modulus G' - energy dissipation modulus G” curve is K2, 1<K2<∞, T m3 ℃ represents the melting temperature of the ester polymer; optionally, 1 < K2 ≤ 100; further optionally, 1 < K2 ≤ 10.

[0030] In some embodiments, the ester polymer comprises structural units represented by formula (CI) and / or formula (CII).

[0031]

[0032] In formula (CI), R 31 R 32 and R 33Each independently comprises a hydrogen atom, or a substituted or unsubstituted C1-C8 alkyl group; R 34 Including substituted or unsubstituted C1-C8 alkyl groups, or substituted or unsubstituted C1-C8 hydroxyalkyl groups;

[0033]

[0034] In formula (CII), R 35 Includes substituted or unsubstituted C2-C6 methylene groups; optionally, R 35 Each independently includes substituted or unsubstituted C2-C4 methylene groups.

[0035] In some embodiments, the liquid-retaining polymer includes fluorinated polymers.

[0036] Optionally, the crystallinity of the fluorinated polymer, as determined by differential scanning calorimetry, is Xc1, where 0 < Xc1 ≤ 30%; the melting temperature of the fluorinated polymer is T. m1 Its unit is ℃, 0 < T m1 ≤140.

[0037] In some embodiments, the glass transition temperature of the fluorinated polymer is T. g1 Its unit is ℃, -150≤T g1 ≤60.

[0038] In some embodiments, the fluoropolymer includes at least one of the structural units represented by formula (A1) to formula (AIII).

[0039]

[0040] In equations (AI) and (AII), R 11 R 12 R 13 and R 14 Each independently comprises a hydrogen atom, a fluorine atom, a bromine 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;

[0041]

[0042] In formula (AIII),

[0043] R 15 Includes single-bonded, substituted or unsubstituted C1-C3 alkyl groups; p is a positive integer selected from 1 to 3; n is a positive integer selected from 1000 to 30000.

[0044] In some embodiments, the liquid-absorbing polymer further includes an ether polymer, wherein the ether polymer is formed into a sheet-like structure; the sheet-like structure is in (T m2 The elastic modulus G' - energy dissipation modulus G” curve was obtained by dynamic frequency scanning test at +20℃. The slope of the elastic modulus G' - energy dissipation modulus G” curve is K1, 1<K1<∞, T m2 ℃ represents the melting temperature of the ether polymer; optionally, 1 < K1 ≤ 100; further optionally, 1 < K1 ≤ 10.

[0045] In some embodiments, the liquid-retaining polymer includes aldehyde-ketone polymers.

[0046] Optionally, the aldehyde-ketone polymer is formed into a sheet-like structure; the sheet-like structure is in (T m4 The elastic modulus G' - energy dissipation modulus G” curve was obtained by dynamic frequency scanning test at +20℃. The slope of the elastic modulus G' - energy dissipation modulus G” curve is K3, 0.8≤K3<∞, T m4 ℃ represents the melting temperature of the aldehyde-ketone polymer; optionally, 0.8 ≤ K3 ≤ 100; further optionally, 0.8 ≤ K3 ≤ 10.

[0047] In some embodiments, the aldehyde-ketone polymer comprises structural units represented by formula (DI) and / or formula (DII).

[0048]

[0049] In formula (DI), R 41 Including single-bonded, substituted, or unsubstituted C1-C6 methylene groups; R 42 Includes hydrogen atoms, substituted or unsubstituted C1-C6 alkyl groups;

[0050]

[0051] 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 integers from 0 to 5, and at least one of r and s is selected from a positive integer.

[0052] In some embodiments, the insulating body includes a substrate, and the polymer layer is disposed on at least one surface of the substrate.

[0053] In some embodiments, the separator membrane comprises a porous substrate, and the liquid-retaining polymer is distributed in the pores of the porous substrate.

[0054] In some embodiments, the separator membrane includes a porous substrate and a polymer layer disposed on at least one surface of the porous substrate, the polymer layer including the liquid-retaining polymer.

[0055] In some embodiments, the coating basis weight of the liquid-retaining polymer is from 0.5 mg / 1540.25 mm² to 5 mg / 1540.25 mm². A coating basis weight within this range can further enhance the liquid-retaining capacity of the separator.

[0056] Secondly, this application proposes a battery comprising a battery cell as described in any embodiment of the first aspect of this application.

[0057] Thirdly, this application proposes an electrical device including a battery as described in any embodiment of the second aspect of this application. Attached Figure Description

[0058] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0059] Figure 1 This is a schematic diagram of one embodiment of the battery cell of this application.

[0060] Figure 2 yes Figure 1 An exploded view of the implementation method of the battery cell.

[0061] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0062] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0063] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0064] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses the battery cell of this application as a power source.

[0065] The accompanying drawings may not be drawn to scale.

[0066] The annotations in the attached figures are explained as follows:

[0067] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module;

[0068] 5. Battery cell; 51. Housing; 52. Electrode assembly;

[0069] 53. Cover plate;

[0070] 6. Electrical appliances. Detailed Implementation

[0071] The following detailed description discloses embodiments of the battery cell, battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0072] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0073] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0074] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0075] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0076] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0077] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0078] The term "alkyl" encompasses both straight-chain and branched alkyl groups. For example, an alkyl group can be C1-C5, C1-C4, C1-C3, or C1-C2 alkyl. In some embodiments, the alkyl group includes methyl, ethyl, propyl, isopropyl, butyl, isobutyl, etc. Additionally, the alkyl group may optionally be substituted. When substituted, the substituent includes a fluorine atom.

[0079] The term "alkoxy group" refers to a group in which an alkyl group is bonded to an oxygen atom by a single bond. For example, an alkoxy group can be a C1-C5 alkoxy group, a C1-C3 alkoxy group, or a C1-C2 alkoxy group. In some embodiments, an alkoxy group may include a methoxy group, an ethoxy group, or a propoxy group. Additionally, an alkoxy group may optionally be substituted.

[0080] The term "halogen atom" refers to fluorine atoms, chlorine atoms, bromine atoms, etc.

[0081] The term "hydrogen" refers to 1H (protium, H), 2H (deuterium, D), or 3H (tritium, T). In various embodiments, "hydrogen" may be 1H (protium, H).

[0082] A battery cell consists of a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is located between the positive and negative electrodes to isolate them. During the charge-discharge cycle of a battery cell, the electrode assembly undergoes volume expansion, especially in the later stages of the cycle when the expansion force is high. This causes the electrolyte to be squeezed out, making electrolyte reabsorption difficult. This increases the risk of electrolyte shortage and cell breakage, potentially deteriorating the cycle performance of the battery cell and shortening its cycle life.

[0083] In view of the above problems, this application proposes a battery cell in which the electrode plates are provided with a liquid-absorbing polymer. The liquid-absorbing polymer helps the electrode plates to absorb electrolyte, and the electrolyte wets the electrode plates more evenly and fully, thereby improving the stability of the battery cell during cycling. The separator of the battery cell is provided with a liquid-retaining polymer. The separator has a strong liquid-retaining capacity, and the electrolyte is not easily squeezed out during the cyclic charging and discharging of the battery cell, thereby reducing the liquid shortage during cyclic charging and discharging, reducing battery polarization, and improving the cycle performance of the battery cell.

[0084] battery cell

[0085] In a first aspect, embodiments of this application provide a battery cell including an electrode assembly, the electrode assembly including electrode plates and a separator;

[0086] The electrode sheet includes a current collector and a film layer containing an active substance and a liquid-absorbing polymer disposed on at least one surface of the current collector, and the electrode sheet satisfies: v / λ≥1.20;

[0087] v represents the liquid absorption rate of the membrane layer, with units of mg / s;

[0088] λ represents the porosity of the membrane layer;

[0089] The separator membrane comprises a liquid-retaining polymer, and the separator membrane satisfies the following:

[0090]

[0091] M represents the mass of the separator that did not absorb electrolyte, and its unit is g;

[0092] m1 represents the mass of the separator membrane after it has been immersed in the electrolyte for 2 hours and weighed under ambient pressure, and its unit is g;

[0093] m2 represents the mass of the separator membrane after it has been immersed in the electrolyte for 2 hours and weighed under an ambient pressure of 10000N, with the unit being g.

[0094] In actual calculations, the above formula only requires inputting the specific numerical values, without inputting the units of each parameter.

[0095] The battery cell of this application contains an absorbent polymer in its electrode plates. The absorbent polymer helps the electrode plates to absorb electrolyte, resulting in more uniform and sufficient wetting of the electrode plates by the electrolyte, thus improving the stability of the battery cell during cycling. The separator of the battery cell contains a liquid-retaining polymer. The separator has a strong liquid-retaining capacity, making it less likely for the electrolyte to be squeezed out during the cyclic charging and discharging of the battery cell. This reduces the possibility of electrolyte shortage during cyclic charging and discharging, reduces battery polarization, and improves the cycle performance of the battery cell.

[0096] In this application, the method for detecting the liquid absorption rate of the electrode includes the following steps:

[0097] A predetermined amount of electrolyte is drawn using a capillary tube;

[0098] When the capillary tube is brought into contact with the electrode plate, the electrode plate under test absorbs the electrolyte in the capillary tube under capillary action.

[0099] After a predetermined time t, the liquid level h of the electrolyte absorbed in the capillary is recorded. The amount of electrolyte absorbed is calculated based on the liquid level h, diameter d, and electrolyte density ρ of the capillary. The absorption rate v of the electrode is then quantitatively calculated based on the ratio of the absorbed amount to the predetermined time t.

[0100] For example, d takes a value from 0.2 to 1, such as 0.2; h takes a value from 3 to 5, such as 3.

[0101] The capillary has capillary channels, allowing it to directly absorb electrolyte through capillary action without the need for an external drive unit. This provides two advantages: firstly, it allows for more precise control of the absorbed electrolyte volume; secondly, since the electrode absorbs electrolyte through its own capillary action, and the electrolyte is only drawn out of the capillary when the capillary comes into contact with the electrode under test, and stops flowing out when the contact is broken, the amount of electrolyte absorbed within the capillary can accurately reflect the volume of electrolyte absorbed by the electrode. This further improves the accuracy of the test results and enables quantitative calculation of the electrolyte absorption rate of the electrode.

[0102] This application uses a standard electrolyte as the test sample. The specific formulation of the electrolyte can be found in the electrolyte formulation in the examples.

[0103] The liquid-absorbing polymer of this application is introduced during the preparation of the membrane layer, which can form a uniform high wetting point in the membrane layer, improve the overall liquid absorption rate of the membrane layer, and thus improve the cycle performance of the battery cell.

[0104] In the embodiments of this application, the porosity of the film layer in the electrode sheet is the ratio of the pore volume in the film layer to the overall volume of the film layer. It can be detected using equipment and methods known in the art, such as GB / T21650.2-2008 "Determination of pore size distribution and porosity of solid materials by mercury intrusion porosimetry and gas adsorption method - Part 2: Analysis of mesopores and macropores by gas adsorption method" and ASTM D2873-94e1 "Standard Test Method for Interior Porosity of Poly(VinylChoride)(PVC) Resins by Mercury Intrusion Porosimetry".

[0105] Alternatively, the porosity of the membrane can be calculated using the formula (1-P1 / P2);

[0106] P1 represents the actual compaction density of the membrane layer, with units of g / cm³. 3 The actual compaction density P1 refers to the ratio of the mass to the thickness of the active material layer per unit area in the electrode sheet. The actual compaction density is determined by the force applied during roller pressing after coating the electrode sheet, and the unit is g / cm³. 3 The specific testing steps are as follows: take an electrode sheet with a certain area S, weigh the mass M of its active material layer, and measure the thickness D of the film layer. The actual compaction density is M / (S×D).

[0107] P2 represents the actual compacted density of the active material, with units of g / cm³. 3 The actual compaction density P2 refers to the density of the active material itself in the active material layer.

[0108] Using graphite as an example, which is an active material used as the negative electrode, the density of graphite is 2.25 g / cm³. 3 The actual compacted density of the active material is 2.25 g / cm³. 3 .

[0109] Using the active material as the positive electrode active material for explanation, specifically, the true compacted density refers to the mass of a unit "actual volume of solid material (excluding open and closed pores and interparticle pores)" in a compacted state. The true volume V is obtained through testing, and the true compacted density is calculated using P = m / V. The testing can be performed according to GB / T24586-2009. Specifically, the testing steps are as follows:

[0110] 1) Pretreatment: Place a clean and dry sample cup on the balance, zero the balance, add the powder sample into the sample cup, filling about 1 / 2 of the sample cup volume, and record the sample mass;

[0111] 2) Place the sample cup containing the sample into the true density tester, seal the test system, and introduce helium gas according to the procedure. By detecting the pressure of the gas in the sample chamber and the expansion chamber, the true volume is calculated according to Bohr's law (PV=nRT), and thus the true compaction density is calculated.

[0112] The separator can be made from a substrate and a liquid-retaining polymer, etc. Alternatively, the separator can be derived from a battery cell. The battery cell is disassembled, the separator immersed in the electrolyte is removed, the separator is washed with deionized water and then vacuum dried at 80°C for 12 hours to obtain the separator, which is then used for separator testing such as mass weighing, liquid absorption rate, and porosity.

[0113] M represents the mass of the separator without absorbed electrolyte, which can also be understood as the mass of the separator itself. Specifically, the separator can be cut into 10 pieces of 1540.25mm thick material. 2 The mass of the disc is measured in an electronic balance.

[0114] m1 represents the mass of the separator membrane after immersion in the electrolyte for 2 hours, weighed under ambient pressure. Specifically, the separator membrane can be cut into 10 pieces of 1540.25 mm thick. 2 The discs were immersed in the electrolyte for 2 hours, then removed and suspended under ambient pressure for 2 minutes before being weighed.

[0115] m2 represents the mass of the separator membrane after it has been immersed in the electrolyte for 2 hours and then weighed under an ambient pressure of 10000N. Specifically, the separator membrane can be cut into 10 pieces of 1540.25mm thick. 2 The discs were immersed in the electrolyte for 2 hours, then removed and stacked in sequence. After applying a force of 10,000 N under ambient pressure, the mass of the separator was measured.

[0116] This application uses a standard electrolyte as a test sample for testing. The specific formulation of the electrolyte can be referred to the electrolyte formulation in the examples. For example, the electrolyte includes ethylene carbonate EC, ethyl methyl carbonate EMC, and dimethyl carbonate DMC in a volume ratio of 1:1:1. The electrolyte also includes lithium hexafluorophosphate LiPF6 with a molar concentration of 1 mol / L.

[0117] It can be defined as the liquid retention capacity Λ.

[0118] The separator in this embodiment includes a liquid-retaining polymer. The separator has a strong liquid-retaining capacity, and the electrolyte is not easily squeezed out during the cycle charging and discharging of the battery cell, which reduces the liquid shortage during the cycle charging and discharging, reduces battery polarization, and improves the cycle performance of the battery cell.

[0119] Optionally,

[0120]

[0121] When the separator meets the above conditions, the separator has a strong liquid retention capacity, which can reduce the liquid shortage during cycle charging and discharging, reduce battery polarization, and improve the cycle performance of individual battery cells.

[0122] For example, It can be:

[0123] 25.1%, 25.5%, 26%, 26.5%, 27%, 27.5%, 28%, 28.5%, 29%, 29.5%, 30%, 30.5%, 31%, 31.5%, 32%, 32.5%, 33%, 33.5%, 34%, 34.5%, 36%, 36.5%, 37%, 37.5%, 38%, 39% %, 40%, 41%, 42%, 45%, 46%, 48%, 50%, 52%, 55%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 96%, 97%, 98%, 99%, or a range consisting of any two of the above values.

[0124] In some implementations, the separator membrane satisfies:

[0125]

[0126] m1-M represents the ratio of the amount of liquid absorbed by the separator to the mass of the separator itself. It can characterize the liquid absorption capacity of the separator, that is, the amount of electrolyte absorbed by the separator, and its liquid retention capacity can also be relatively improved.

[0127] It can be defined as the liquid retention rate of the separating membrane.

[0128] When the separator meets the above conditions, the separator has relatively good liquid absorption capacity, which is conducive to improving the absorption rate of electrolyte and thus further improving the cycle performance of the battery cell.

[0129] For example,

[0130] 80%, 85%, 88%, 90%, 92%, 95%, 96%, 97%, 98%, 99%, 100%, 105%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190%, 200%, 210%, 220%, 230%, 240%, 250%, 260%, 270%, 280%, 290%, 300%, or a range consisting of any two of the above values.

[0131] In some implementations, the separator membrane satisfies:

[0132]

[0133] (m2-M) / M represents the ratio of the amount of liquid retained by the separator under external influence to the mass of the separator itself, which characterizes the separator's liquid retention capacity.

[0134] It can be defined as the liquid retention rate after the separator is pressurized.

[0135] When the separator meets the above conditions, even when the separator is under pressure, the separator has a relatively good liquid retention capacity, and the electrolyte adsorbed by the separator is not easily squeezed out, thereby improving the migration rate of active ions and further improving the cycle performance of the battery cell.

[0136] For example, It can be:

[0137] 20.0%, 22.5%, 25.1%, 25.5%, 26%, 26.5%, 27%, 27.5%, 28%, 28.5%, 29%, 29.5%, 30%, 30.5%, 31%, 31.5%, 32%, 32.5%, 33%, 33.5%, 34%, 34.5%, 36%, 36.5%, 37%, 37.5%, 38%, 39%, 40%, 41%, 42%, 45%, 46%, 48%, 50%, 52%, 55%, 60%, 62%, 65% 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 96%, 97%, 98%, 99%, 100%, 105%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190%, 200%, 210%, 220%, 230%, 240%, 250%, 260%, 270%, 280%, 290%, 300%, or a range consisting of any two of the above values.

[0138] In some embodiments, the separator further includes a liquid-absorbing polymer. The introduction of the liquid-absorbing polymer can improve the liquid absorption capacity of the separator, thereby increasing the rate at which the separator reabsorbs electrolyte.

[0139] In some implementations, the battery cell satisfies 0 ≤ y / V 总孔 ≤15%;

[0140] y represents the volume of free electrolyte in the battery cell, in mL.

[0141] V总孔 The value represents the pore volume of the electrode assembly, and its unit is mL.

[0142] When performing calculations using the formula, only the numerical value is substituted in, not the unit.

[0143] When a battery cell meets the above conditions, the content of free electrolyte in the battery cell is extremely low, or even virtually non-existent, thereby significantly improving the reliability and cycle performance of the battery cell.

[0144] 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 of any two of the above values. y / V 总孔 A value of 0 indicates that the amount of free electrolyte is 0 mL, meaning that there is essentially no free electrolyte in the battery cell.

[0145] The electrode assembly includes a positive electrode, a negative electrode, and a separator. The pore volume of the electrode assembly includes the sum of the pore volumes of the positive electrode, the negative electrode, and the separator. In the embodiments of this application, pore volume has a meaning known in the art and can be detected using equipment and methods known in the art, for example, by gas displacement method. The pore volume is denoted as vm, where v represents the apparent volume (i.e., the total volume) and m represents the actual volume.

[0146] In some implementations, the battery cell also satisfies: 0 ≤ y / Ah ≤ 15%;

[0147] y represents the volume of free electrolyte in the battery cell, in mL.

[0148] Ah represents the nominal capacity of the battery cell, and its unit is Ah.

[0149] When performing calculations using the formula, only the numerical value is substituted into the formula, without substituting its unit.

[0150] The volume y (mL) of free electrolyte can be determined by the following method: A fresh battery cell is filled to 0% SOC (State of Charge). A hole with a diameter of φ5-8mm is made in a localized area of ​​the battery cell. The battery cell is placed on top of a container with the hole facing down and directly above the container, allowing the free electrolyte inside the battery cell to drip into the container below. The battery cell is left to stand for 3 to 5 hours to allow all the free electrolyte to drip into the container. The volume of electrolyte in the container is then measured to obtain y. In this embodiment, the fresh battery cell can be a newly manufactured battery cell (not yet charged / discharged after formation) or a battery cell that has been installed in an electrical device and has been used for fewer than 10 cycles.

[0151] When a battery cell meets the above conditions, the content of free electrolyte in the battery cell is extremely low, or even virtually non-existent, thereby significantly improving the reliability and cycle performance of the battery cell.

[0152] 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 of any two of the above values. A y / Ah of 0 indicates that the amount of free electrolyte is 0, meaning that there is essentially no free electrolyte in the battery cell.

[0153] In some embodiments, after the battery cell undergoes a linear sweep frequency vibration test, it is charged to 100% state of charge (SOC), a hole is made in the battery cell, and the hole is set at the lowest point in the vertical direction. The volume of electrolyte flowing out of the battery cell is recorded as M1, where 0 mL ≤ M1 ≤ 0.5 mL. Optionally, M1 is 0 mL.

[0154] in,

[0155] The vibration direction of the linear sweep frequency vibration test is: single up-and-down vibration;

[0156] The vibration frequency of the linear sweep frequency vibration test is 10Hz to 55Hz.

[0157] The maximum acceleration in the linear sweep frequency vibration test was 30 m / s². 2 ;

[0158] The number of sweep cycles in the linear sweep vibration test is 10.

[0159] The vibration time for the linear sweep frequency vibration test was 3 hours.

[0160] In related technologies, during use, battery cells may vibrate under external forces. The electrolyte within the electrode assembly may detach from the assembly due to vibration, forming free electrolyte. This free electrolyte may leak, causing corrosion and potentially leading to battery cell failure. The embodiments of this application, by subjecting the battery cells to static and vibration treatments, effectively collect and eject the liquid electrolyte from within the cell. This allows for a more accurate determination of whether there is flowing liquid electrolyte between the cell casing and the electrode assembly, thus determining the content of free electrolyte. When the battery cells of this embodiment meet the above conditions, the content of free electrolyte within the cell is extremely low, or even virtually nonexistent, significantly improving the reliability and cycle performance of the battery cells.

[0161] 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 of any two of the above values. M1 of 0 mL indicates that the amount of free electrolyte is 0, meaning that after the linear sweep frequency vibration test, there is essentially no free electrolyte inside the battery cell.

[0162] In some embodiments, after the battery cell undergoes the above vibration test, the casing is removed, the electrode assembly is taken out and subjected to a compression test, and the volume of electrolyte flowing out of the electrode assembly is recorded as M2 (the compression equipment is suspended, and a weighing balance and an electrolyte collection container are set at the bottom), 0mL≤M2≤0.5mL, optionally, M2 is 0mL;

[0163] in,

[0164] The extrusion direction of the extrusion test is perpendicular to the thickness direction of the electrode assembly 52;

[0165] The degree of compression in the extrusion test was: extrusion pressure of 0.35 MPa.

[0166] In related technologies, battery cells may be subjected to external pressure during use. The electrolyte within the electrode assembly may detach from the assembly under this pressure, forming free electrolyte. This free electrolyte may leak, causing corrosion and potentially leading to battery cell failure. The embodiments of this application, by performing a compression test on the battery cell, can effectively squeeze out the liquid electrolyte inside the cell, thus more accurately determining whether there is flowing liquid electrolyte between the cell casing and the electrode assembly, and thus determining the content of free electrolyte. When the battery cell of the embodiments of this application meets the above conditions, after compression, the content of free electrolyte within the cell is extremely low, or even virtually non-existent, significantly improving the reliability and cycle performance of the battery cell.

[0167] 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 any range of two of the above values. M2 of 0 mL indicates that the amount of free electrolyte is 0, meaning that after the battery cell undergoes the compression test, there is essentially no free electrolyte inside.

[0168] In some implementations, a 200V voltage is supplied to the battery cell to form a circuit for 4 hours, and the absolute value of the temperature change of the battery cell is ≤4℃.

[0169] For example, when the negative terminal and casing of a battery cell are connected to a 200V voltage to form a current loop, the temperature fluctuation range of the battery cell within 4 hours is less than or equal to 4°C, and there are no failure behaviors such as fire or explosion. Especially when the free electrolyte y=0, the temperature fluctuation range is small, and the reliability of the battery cell is greatly improved.

[0170] In some embodiments, the unit volume mass of the liquid-absorbing polymer located in the electrode sheet is A1, and the unit volume mass of the liquid-absorbing polymer located in the separator is A2, where 1.0 ≤ A1 / A2 ≤ 1.6; alternatively, 1.2 ≤ A1 / A2 ≤ 1.5.

[0171] When a battery cell meets the above conditions, the electrode sheet has good liquid absorption performance and the separator has good liquid retention performance. The two work together to prevent the electrolyte from being squeezed out of the electrode assembly during the battery cell's cyclic charging and discharging process, and can also have a good wetting effect on the electrode sheet, thereby improving the cycle performance of the battery cell.

[0172] For example, A1 / A2 can be 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6 or a range of any two of the above values.

[0173] In some embodiments, the electrode sheet further includes a liquid-retaining polymer. The introduction of the liquid-retaining polymer can improve the liquid-retaining capacity of the electrode sheet, thereby improving the wetting performance of the electrolyte on the electrode sheet.

[0174] In some embodiments, the unit volume mass of the liquid-retaining polymer located in the electrode sheet is B1, and the unit volume mass of the liquid-retaining polymer located in the separator is B2, where 0.4 ≤ B1 / B2 ≤ 0.9; alternatively, 0.5 ≤ B1 / B2 ≤ 0.8.

[0175] When a battery cell meets the above conditions, the electrode sheet has good liquid absorption performance and the separator has good liquid retention performance. The two work together to prevent the electrolyte from being squeezed out of the electrode assembly during the battery cell's cyclic charging and discharging process, and can also have a good wetting effect on the electrode sheet, thereby improving the cycle performance of the battery cell.

[0176] For example, B1 / B2 can be 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or a range of any two of the above values.

[0177] In some embodiments, the absorbent polymer includes at least one of ether polymers and ester polymers.

[0178] [Ether polymers]

[0179] In some embodiments, the liquid-absorbing polymer comprises an ether polymer, which is formed into a sheet-like structure; the sheet-like structure is in (T m2 The elastic modulus G' - energy dissipation modulus G” curve was obtained by dynamic frequency scanning test at +20℃. The slope of the elastic modulus G' - energy dissipation modulus G” curve is K1, 1<K1<∞, T m2 °C represents the melting temperature of the ether polymer.

[0180] Specifically, the preparation process of the sheet-like structure is as follows: The ether polymer is vacuum dried at 80°C for 12 hours. The dried ether polymer is then hot-pressed into thin sheets using a flat vulcanizing machine, with the hot-pressing temperature set to (T...). m2 The temperature is +20℃, the calendering thickness is 1-2 min, the calendering time is 2 min, and the pressure is 8 MPa. After calendering for 2 min, the sample is removed and placed on another vulcanizing machine of the same model for cold pressing at a pressure of 10 MPa. Polymer discs (sheet-like structures) of a fixed size can be obtained using a circular mold with a diameter of 25 mm. For example, the sheet-like structure can be a disc with a thickness of 1-2 mm and a diameter of 25 mm; it can also be prepared according to the sample standard required by the testing equipment.

[0181] According to the conclusions of classical linear viscoelasticity, for polymers, especially linear polymers, the elastic modulus G'-energy dissipation modulus G” curve exhibits frequency dependence in the terminal region (the range approaching the maximum angular velocity), and the longest chain of the polymer plays a role in viscoelastic behavior.

[0182] The specific steps of the dynamic frequency scanning test are as follows: A TA-AR2000EX rotational rheometer (TA Instruments, USA) is used for the dynamic frequency scanning test. The parallel plate diameter is 25mm and the thickness is 0.9mm. To ensure the test is conducted within the linear springback region, the strain is 2% during the dynamic frequency scanning test, and the test temperature is T. m2 +20℃, test frequency sweep range: 500rad / s≤w 2 ≤0.05rad / s, so as to obtain data in the lowest possible frequency range.

[0183] Dynamic frequency scanning tests can characterize the degree of molecular chain entanglement during solid-state melting (molten state). Compared to linear or short-branched structures, long-branched, network, and low-crosslinked structures exhibit high entanglement and deviate from linear end-effector behavior, while ether polymers exhibit solid-state behavior. When the ether polymers of this application meet the above-mentioned range, they can further reduce the molecular chain entanglement state, which is beneficial for the diffusion of solvent molecules between molecular chains in the electrolyte. Furthermore, the ether polymers still maintain a certain degree of molecular chain entanglement, enabling them to form gel-like substances with the electrolyte, thus improving the cycle performance and storage performance of the battery cells.

[0184] In some implementations, 1 < K1 ≤ 100; alternatively, 1 < K1 ≤ 10. For example, K1 can be 1.01, 1.1, 2, 5, 10, 15, 20, 30, 50, 100, 200, 500, 1000, 5000, 10000 or a range of any two of the above values.

[0185] In some embodiments, the glass transition temperature of the ether polymer is T. g2 Its unit is ℃, -100≤T g2 ≤50; optionally, -80≤T g2 ≤30. For example, the glass transition temperature of the ether polymer can be -100°C, -80°C, -60°C, -30°C, 0°C, 30°C, 50°C, or a range of any two of the above values.

[0186] In some embodiments, the ether polymer comprises structural units represented by formula (BI).

[0187]

[0188] In formula (BI), R 21 and R 22 Each independently comprises a hydrogen atom, a substituted or unsubstituted C1-C3 alkyl group, or a substituted or unsubstituted C1-C3 alkoxy group; R 23 This includes substituted or unsubstituted C1-C5 methylene groups.

[0189] In some implementations, R 21 and R 22 Each independently includes a hydrogen atom and a substituted or unsubstituted C1-C2 alkyl group.

[0190] In some implementations, R 23 This includes single-bonded, substituted, or unsubstituted C1-C4 methylene groups.

[0191] For example, the ether polymer includes at least one of the structural units shown in formula (BI-1) to formula (BI-8).

[0192]

[0193] In some embodiments, the ether polymer comprises structural units represented by formula (BII).

[0194]

[0195] In formula (BII), R 24 To R 27 Each independently comprises 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 or ether group.

[0196] In some implementations, R 24 To R 27 Each independently comprises 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 or ether group.

[0197] In some embodiments, the ether polymer includes at least one of the structural units shown in formula (BII-1) to formula (BII-7).

[0198]

[0199] The monomers used in the above-mentioned ether polymers are polycyclic rings, such as six-membered rings or shorter-chain monomers, which are conducive to the polymerization to form a high content of -O- structures. This type of structure has a low degree of entanglement, which is beneficial to improving the flexibility of the molecular chain. The molecular chain can fully extend in the electrolyte and easily form a gel with the electrolyte, thereby improving the cycle performance and storage performance of the battery cell.

[0200] The polymers described above are merely examples of structural groups in the main molecular chains. In the embodiments of this application, the polymers may also be obtained by copolymerizing the above structural groups with other types of structural groups (such as olefin structural units, ester monomers, nitrile monomers, amide monomers, etc.).

[0201] When the above groups are substituted, the substituents may include one or more of the following: nitrile (-CN), nitro, sulfonic acid, sulfonyl, amide, carboxyl, ester, and halogen atom. These substituents are high-pressure resistant and more conducive to stabilizing the polymer structure. Halogen atoms may include fluorine, chlorine, bromine, etc.

[0202] In some embodiments, the degree of polymerization n of the ether polymer is selected from a positive integer from 1500 to 25000.

[0203] Optionally, the degree of polymerization n of the ether polymer is selected from a positive integer from 3000 to 18000.

[0204] In some embodiments, the polymer has a molecular weight of 1.2 × 10⁻⁶. 5 g / mol to 1.0 × 10 6 g / mol.

[0205] For example, the molecular weight of the polymer can be 1.2 × 10⁻⁶. 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.

[0206] [Ester polymers]

[0207] In some embodiments, the liquid-absorbing polymer comprises an ester polymer, wherein the ester polymer is formed into a sheet-like structure; the sheet-like structure is in (T m3 The elastic modulus G' - energy dissipation modulus G” curve was obtained by dynamic frequency scanning test at +20℃. The slope of the elastic modulus G' - energy dissipation modulus G” curve is K2, 1<K2<∞, T m3 °C represents the melting temperature of the ester polymer.

[0208] When the ester polymers of the embodiments of this application meet the above-mentioned range, the molecular chain entanglement state can be further reduced, which is beneficial to the diffusion of solvent molecules in the electrolyte between molecular chains; and the ether polymers still maintain a certain molecular chain entanglement state, which can form a gel-like substance with the electrolyte, thereby increasing the liquid absorption rate and improving the cycle performance and storage performance of the battery cell.

[0209] In some implementations, 1 < K2 ≤ 100; alternatively, 1 < K2 ≤ 10.

[0210] For example, K2 can be 1.01, 1.1, 1.2, 1.5, 2, 5, 10, 15, 20, 30, 50, 100, 200, 500, 1000, 5000, 10000 or a range of any two of the above values.

[0211] In some embodiments, the glass transition temperature of the ester polymer is T. g3 Its unit is ℃, -100≤T g3 ≤50; optionally, -80≤T g3 ≤30.

[0212] For example, the glass transition temperature of the ester polymer can be -100°C, -90°C, -80°C, -60°C, -30°C, 0°C, 30°C, 50°C, or a range of any two of the above values.

[0213] In some embodiments, the ester polymer comprises structural units represented by formula (CI).

[0214]

[0215] In formula (CI), R 31 R 32 and R 33 Each independently comprises a hydrogen atom, or a substituted or unsubstituted C1-C8 alkyl group; R 34 Includes substituted or unsubstituted C1-C8 alkyl groups, or substituted or unsubstituted C1-C8 hydroxyalkyl groups; optionally, R 34 This includes substituted or unsubstituted C1-C6 alkyl groups, or substituted or unsubstituted C1-C6 hydroxyalkyl groups.

[0216] Optionally, R 31 This includes hydrogen atoms, or substituted or unsubstituted methyl groups.

[0217] Optionally, R 32 and R 33 Each of them independently contains a hydrogen atom.

[0218] Optionally, R34 This includes substituted or unsubstituted C1-C4 alkyl groups, or substituted or unsubstituted C1-C4 hydroxyalkyl groups.

[0219] Exemplarily, the ester polymer includes at least one of the structural units shown in formula (CI-1) to formula (CI-15).

[0220]

[0221]

[0222] In some embodiments, the ester polymer comprises structural units represented by formula (CII).

[0223]

[0224] In formula (CII), R 35 This includes substituted or unsubstituted C2-C6 methylene groups.

[0225] Optionally, R 35 Each independently includes substituted or unsubstituted C2-C4 methylene groups.

[0226] For example, the ester polymer includes at least one of the structural units shown in formula (CII-1) to formula (CII-5).

[0227]

[0228] The aforementioned ester polymers have a low degree of molecular chain entanglement, which is beneficial to improving the flexibility of the molecular chains. The molecular chains can fully extend in the electrolyte and easily form a gel-like substance with the electrolyte.

[0229] The polymers described above are merely examples of structural groups in the main molecular chains. In the embodiments of this application, the polymers may also be obtained by copolymerizing the above structural groups with other types of structural groups (such as olefin structural units, ester monomers, nitrile monomers, amide monomers, etc.).

[0230] When the above-mentioned groups are substituted, the substituents may include one or more of the following: nitrile (-CN), nitro, sulfonic acid, sulfonyl, amide, carboxyl, ester, and halogen atoms (e.g., chlorine, fluorine, bromine). These substituents are high-pressure resistant, which is more beneficial for stabilizing the polymer structure.

[0231] In some embodiments, the degree of polymerization n of the ester polymer is selected from a positive integer from 800 to 20000.

[0232] Optionally, the degree of polymerization n of the ester polymer is selected from a positive integer from 1000 to 15000.

[0233] In some embodiments, the molecular weight of the ester polymer is 1.2 × 10⁻⁶. 5 g / mol to 1.0 × 10 6 g / mol.

[0234] For example, the molecular weight of the ester polymer can be 1.2 × 10⁻⁶. 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.

[0235] In some embodiments, the liquid-retaining polymer includes at least one of a fluorinated polymer and an aldehyde-ketone polymer.

[0236] In some embodiments, the liquid-retaining polymer comprises a fluorinated polymer, wherein the crystallinity of the fluorinated polymer, as determined by differential scanning calorimetry, is X. C1 , 0 < X C1 ≤30%; the melting temperature of the fluoropolymer is T m1 Its unit is ℃, 0 < T m1 ≤140.

[0237] Crystallization refers to the process by which atoms, ions, or molecules in a material arrange themselves in a specific spatial order to form an ordered structure. The conformation of polymers during crystallization is determined by both intramolecular and intermolecular factors. Intermolecular forces affect the packing density between molecular chains. Crystallinity X C1 The degree of crystallinity in a material is characterized by differential scanning calorimetry (DSC). Specifically, the testing procedure is as follows: Take 0.5g to 0.8g of sample, place the sample in a crucible, and subject the sample to heating and cooling at a nitrogen atmosphere, with a heating rate of 10℃ / min from the intrinsic temperature of the material (T0). g1 The initial temperature was 20°C lower than the material's intrinsic temperature, and the temperature was increased to the material's intrinsic temperature. m1 The cutoff temperature for the 20°C increase is determined by the actual glass transition temperature T of the material, based on the peak values ​​of heat absorption and release or the transition point during the process. g1 and melting temperature T m1 wait.

[0238] Therefore, fluorinated polymers have relatively low crystallinity and melting temperature, which makes the molecular chain arrangement tend to be loose, the interaction force between molecular chains is small, adjacent molecular chains are easily opened, and chain segment movement is achieved through intermolecular rotation, forming a molecular chain structure with high flexibility; and fluorinated polymers and electrolytes in battery cells can form gel-like substances, improving the cycle performance of battery cells.

[0239] For example, the crystallinity X of a fluorinated polymer, measured by differential scanning calorimetry. C1 It can be 5%, 10%, 15%, 20%, 25%, 30%, or a range of any two of the above values.

[0240] For example, the melting temperature of the fluoropolymer can be 10°C, 20°C, 50°C, 70°C, 90°C, 100°C, 120°C, 140°C, or any combination of two of the above values.

[0241] In some embodiments, the glass transition temperature of the fluorinated polymer is T. g1 Its unit is ℃, -150≤T g1 ≤60.

[0242] The glass transition temperature (GLT) is the temperature at which polymer chain segments transition from frozen to mobile. The GLT has a certain influence on the flexibility of polymer molecular chains; the lower the GLT, the better the flexibility of the polymer molecular chains at room temperature, and vice versa. The GLT can be measured using differential scanning calorimetry (DSC). Polymers with relatively low GLTs exhibit better chain segment flexibility, making it easier for adjacent molecular chains to open. For example, the GLT of fluorinated polymers can be -150℃, -120℃, -100℃, -80℃, -60℃, -30℃, 0℃, 30℃, 60℃, or any combination of two of these values.

[0243] In some embodiments, the fluoropolymer comprises structural units represented by formula (AI).

[0244]

[0245] In formula (AI), R 11 R 12 R 13 and R 14 Each independently comprises a hydrogen atom, a fluorine atom, a bromine 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.

[0246] In some embodiments, the fluoropolymer comprises structural units represented by formula (AII).

[0247]

[0248] In equations (AI) and (AII), R 11 R 12 R 13 and R 14 Each independently comprises a hydrogen atom, a fluorine atom, a bromine 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.

[0249] In some embodiments, the fluoropolymer comprises structural units represented by formula (AII).

[0250]

[0251] In equation (AIII), R 15 Includes single-bonded, substituted or unsubstituted C1-C3 alkyl groups.

[0252] When the above-mentioned groups are substituted, the substituents may include one or more of the following: nitrile (-CN), nitro, sulfonic acid, sulfonyl, amide, carboxyl, ester, and halogen atom. These substituents are high-pressure resistant and are more conducive to stabilizing the polymer structure. The halogen atom may include fluorine, chlorine, bromine, etc. Optionally, the halogen atom may include a fluorine atom.

[0253] In embodiments of this application, the polymer can also be obtained by copolymerizing the above-mentioned structural groups with a small amount of other types of structural groups (such as olefin structural units, ester monomers, nitrile monomers, amide monomers, etc.).

[0254] In some implementations, p is selected from positive integers from 1 to 3.

[0255] In some embodiments, the degree of polymerization n of the fluorinated polymer is selected from a positive integer from 1000 to 30000.

[0256] In some implementations, R 11 R 12 R 13 and R 14 Each independently comprises a hydrogen atom, a fluorine atom, a bromine atom, a substituted or unsubstituted C1-C2 alkyl group, or a substituted or unsubstituted C1-C2 alkoxy group; further optionally, R 11R 12 R 13 and R 14 Each of these atoms independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a methyl group, a fluoromethyl group, a methoxy group, or a perfluoromethoxy group.

[0257] In some embodiments, the fluorinated polymer includes at least one of the structural units shown in formula (AI-1) to formula (AI-11).

[0258]

[0259]

[0260] In some embodiments, the fluorinated polymer includes at least one of the structural units shown in formula (AII-1) to formula (AII-5).

[0261]

[0262] In some embodiments, the fluorinated polymer includes at least one of the structural units shown in formula (AIII-1) to formula (AIII-3).

[0263]

[0264] For example, the fluorinated polymer includes one or more of the following: perfluoroethylene (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).

[0265] Optionally, the fluorinated polymer includes one or more of perfluoroethylene (PTFE), polyvinylidene fluoride (PVDF), perfluoroethylene propylene copolymer (FEP), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE).

[0266] The aforementioned fluorinated polymers can be derived from one or more of the following monomers: fluorinated cyclohexane, fluorinated vinylidene, 1,2-difluoroethylene, vinylidene fluoride, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, hexafluoropropylene, 3,3,3-trifluoropropylene, trifluoropropylene, tetrafluoropropylene, and pentafluoropropylene. Optionally, the aforementioned fluorinated polymers can be derived from at least two of the following monomers: fluorinated cyclohexane, fluorinated vinylidene, 1,2-difluoroethylene, vinylidene fluoride, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, hexafluoropropylene, 3,3,3-trifluoropropylene, trifluoropropylene, tetrafluoropropylene, and pentafluoropropylene.

[0267] The monomers used in the above-mentioned fluorinated polymers are all short-chain monomers, which are conducive to the polymerization to form straight-chain linear structures or short-branched structures. This type of structure has a low degree of entanglement, which is conducive to improving the flexibility of the molecular chains. The molecular chains can fully extend in the electrolyte, which is conducive to the formation of a three-dimensional gel-like substance by the polymer and the electrolyte, and is conducive to further improving the liquid absorption rate.

[0268] In some embodiments, the degree of polymerization n of the fluorinated polymer is selected from a positive integer from 5000 to 20000.

[0269] In some embodiments, the molecular weight of the fluorinated polymer is 1.2 × 10⁻⁶. 5 g / mol to 1.5 × 10 6 g / mol; can be selected as 1.2×10 5 g / mol to 1.0 × 10 6 When the molecular weight of the polymer is within the above range, the polymerization exhibits excellent liquid retention capacity, which is beneficial for improving the liquid retention capacity of the separating membrane.

[0270] For example, the molecular weight of the polymer can be 1.2 × 10⁻⁶. 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.

[0271] [Ketone-aldehyde polymers]

[0272] In some embodiments, the liquid-retaining polymer comprises an aldehyde-ketone polymer, wherein the aldehyde-ketone polymer is formed into a sheet-like structure; the sheet-like structure is in (T m4 The elastic modulus G' - energy dissipation modulus G” curve was obtained by dynamic frequency scanning test at +20℃. The slope of the elastic modulus G' - energy dissipation modulus G” curve is K3, 0.8≤K3<∞, T m4°C represents the melting temperature of the aldehyde-ketone polymer.

[0273] In some implementations, 0.8 ≤ K3 ≤ 100; alternatively, 0.8 ≤ K3 ≤ 10.

[0274] For example, K3 can be 0.8, 0.9, 1, 2, 5, 10, 15, 20, 30, 50, 100, 200, 500, 1000, 5000, 10000 or a range of any two of the above values.

[0275] In some embodiments, the glass transition temperature of the aldehyde-ketone polymer is T. g4 Its unit is ℃, -100≤T g4 ≤50; optionally, -80≤T g4 ≤30.

[0276] For example, the glass transition temperature of the aldehyde-ketone polymer can be -100°C, -90°C, -80°C, -60°C, -30°C, 0°C, 30°C, 50°C, or a range of any two of the above values.

[0277] In some embodiments, the aldehyde-ketone polymer comprises structural units represented by formula (DI).

[0278]

[0279] In formula (DI), R 41 Including single-bonded, substituted, or unsubstituted C1-C6 methylene groups; R 42 Includes hydrogen atoms, substituted or unsubstituted C1-C6 alkyl groups;

[0280] Optionally, R 41 Including single-bonded, substituted, or unsubstituted C1-C2 methylene groups;

[0281] Optionally, R 42 Includes hydrogen atoms, substituted or unsubstituted C1-C3 alkyl groups.

[0282] In the embodiments of this 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, such as R. 41 A single bond, representing R 41 The carbon atoms on both sides are connected by single bonds.

[0283] Exemplarily, the aldehyde-ketone polymer includes at least one of the structural units shown in formula (DI-1) to formula (DI-6).

[0284]

[0285] Exemplarily, the aldehyde-ketone polymer comprises the structural unit shown in formula (DII).

[0286]

[0287] 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 integers from 0 to 5, and at least one of r and s is selected from a positive integer; optionally, R 43 To R 46 Each of these components 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.

[0288] In some embodiments, the aldehyde-ketone polymer includes at least one of the structural units shown in formula (DII-1) to formula (DII-4).

[0289]

[0290] The molecular chains of the aforementioned aldehyde-ketone polymers have a low degree of entanglement, which is beneficial to improving the flexibility of the molecular chains. The molecular chains can fully extend in the electrolyte, which is conducive to forming a gel-like substance with the electrolyte.

[0291] The polymers described above are merely examples of structural groups in the main molecular chains. In the embodiments of this application, the polymers can also be obtained by copolymerizing the above structural groups with other types of structural groups (such as olefin structural units, enol structural units, acrylonitrile structural units, etc.).

[0292] When the above groups are substituted, the substituents may include one or more of the following: nitrile (-CN), nitro, sulfonyl, carboxyl, ester, chlorine, fluorine, and bromine. These substituents are high-pressure resistant and are more conducive to stabilizing the polymer structure.

[0293] In some embodiments, the degree of polymerization n of the aldehyde-ketone polymer is selected from a positive integer from 500 to 15000.

[0294] Optionally, the degree of polymerization n of the aldehyde-ketone polymer is selected from a positive integer from 500 to 10000.

[0295] In some embodiments, the molecular weight of the aldehyde-ketone polymer is 1.2 × 10⁻⁶. 5 g / mol to 1.0 × 10 6 g / mol.

[0296] For example, the molecular weight of the aldehyde-ketone polymer can be 1.2 × 10⁻⁶. 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.

[0297] In some embodiments, the liquid-retaining polymer is added to a first solvent at 70°C to form a polymer system; the polymer system is allowed to stand at 70°C for 8 hours, and then allowed to stand at 25°C for ≥24 hours. After filtering the polymer system through a 200-mesh filter, the remaining substance is a first substance. The mass of the liquid-retaining polymer is q, and its unit is g; the mass of the first substance is m, and its unit is g; the liquid-retaining polymer and the first substance satisfy: 5≤m / q≤1000.

[0298] Liquid-retaining polymers have excellent liquid absorption and retention properties, which are beneficial for improving the liquid retention capacity of the separator membrane.

[0299] In some implementations, 10 ≤ m / q ≤ 1000; further optionally, 10 ≤ m / q ≤ 50. For example, m / q can be 5, 10, 20, 25, 28, 30, 32, 35, 40, 50, 80, 100, 200, 500, 1000 or a range of any two of the above values.

[0300] After the polymer system is left to stand at 70°C for 8 hours and then at 25°C for ≥24 hours, undergoing two stages of standing treatment, part of the polymer system swells and adsorbs, transforming into a gel state. When the polymer system comes into contact with the electrolyte, the polymer molecular chains unfold and open, allowing the electrolyte to diffuse between the molecular chains. The swelling and adsorption of the electrolyte by the polymer molecular chains improves the liquid absorption capacity and further enhances the cycle performance of the battery cells.

[0301] For example, based on the mass of the polymer system, the ratio of the mass content of the absorbent polymer to the mass content of the first solvent ranges from 1:100 to 1:10, for example, 3:50.

[0302] For example, the first solvent is the same as or similar to the solvent of the electrolyte, and the first solvent may include at least one of carbonate solvents and ether solvents. For example, carbonate solvents include cyclic carbonate solvents and / or linear carbonate solvents.

[0303] Examples of cyclic carbonate solvents include one or more of ethylene carbonate EC, vinylene carbonate VC, fluoroethylene carbonate FEC, difluoroethylene carbonate DFEC, vinyl ethylene carbonate VEC, and dioctyl carbonate CC.

[0304] As examples of linear carbonate solvents, linear carbonate solvents include one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), diphenyl carbonate (DPC), methyl allyl carbonate (MAC), and polycarbonate (VA).

[0305] Examples of ether solvents include one or more of tetrahydrofuran (THF), 2-methyltetrahydrofuran (2me-thf), 1,3-dioxolane (DOL), dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), and diethylene glycol dimethyl ether (DG).

[0306] Optionally, the first solvent may also contain lithium salts and electrolyte additives, such as lithium hexafluorophosphate, vinylene carbonate (VC), and fluorovinylene carbonate (FEC).

[0307] In this application, m / q is also referred to as the precipitation value, which characterizes the ability of the liquid-absorbing polymer and solvent to transform into a gel-like substance.

[0308] The first substance mainly includes a gel-state substance formed by a liquid-retaining polymer and a first solvent. In this type of gel-state substance, the molecular structure of the polymer remains basically unchanged.

[0309] In some embodiments, the first substance is dried at 80°C for 12 hours to remove the first solvent from the first substance, and then detected by infrared spectrophotometry (IR) or nuclear magnetic resonance (NMR). After drying, the main component of the first substance is the liquid-absorbing polymer described above.

[0310] This application's embodiments, by increasing the temperature, allow the liquid-retaining polymer molecular chains to expand within the safe operating temperature range of the battery cell, promoting mutual attraction and physical bonding between the polymer molecular chains and the electrolyte. At room temperature, the activity of the liquid-retaining and absorbing polymer molecular chain segments decreases, allowing them to remain attached to the separator and lock the electrolyte within the space of the liquid-retaining polymer, forming a gel or gel-like state. This can enhance the transport rate of active ions, such as lithium ions, and improve cycle performance.

[0311] The relevant parameters of the polymer in the embodiments of this application can be detected using the following methods:

[0312] The functional groups of the polymer in the embodiments of this application can be detected by infrared spectrophotometry (IR). Specifically, the liquid-retaining polymer is tested using a Thermo Nicolet Nexus 670 attenuated total reflectance Fourier transform infrared spectrometer (FTIR-ATR), and then tested according to standard GB / T6040-2002. The test range is 600–4000 cm⁻¹ using the ATR method. -1 Repeatability: ±2cm -1 Resolution: better than 4cm -1 ; Transmission depth 0.2~0.6μm.

[0313] The structure of the polymer in the embodiments of this application can be measured 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, with TMS as an internal standard, CDCl3 as a solvent, and a proton resonance frequency of 400MHz.

[0314] The polymer monomer type of the polymer in the embodiments of this application (especially suitable for monomers with a small proportion in the polymer) can be determined by pyrolysis-gas chromatography-mass spectrometry. The specific test steps are as follows: accurately weigh 0.5 mg of sample into a sample cup, fix it to the injection rod, and then insert it into the pyrolyzer installed near the GC (gas chromatography) injection port. After the pyrolyzer temperature reaches the set temperature, press the injection button. The sample cup will fall rapidly into the core of the pyrolysis furnace through free fall. In the inert gas N2 atmosphere, the volatile components will instantly vaporize and be carried into the gas chromatography column by the carrier gas for separation. Finally, it will be detected by flame ionization detector (FID) or mass spectrometer (MS) to obtain a gas chromatogram or total ion chromatogram.

[0315] The molecular weight of the polymer in the embodiments of this application has a meaning known in the art and can be determined using commonly used equipment and methods in the art. Gel permeation chromatography (GPC) can be used for testing. The specific testing steps are as follows: take an appropriate amount of the sample to be tested (the sample concentration should be 8%-12% opacity), add 20 ml of deionized water, and simultaneously incubate for 5 min (53 kHz / 120 W) to ensure that the sample is completely dispersed. Then, the sample is measured according to the standard GB / T19077-2016 / ISO 13320:2009.

[0316] Alternatively, a multi-angle laser scattering (MALLS) instrument can be used for testing. Specifically, an instrument combining a GPC with a Dawn Heleos II multi-angle laser light scattering device, an Optilab T-rEX refractive index (RI) detector, and a Visco Star II viscometer (Wyatt Technology Corporation, USA) is employed. Tests are conducted at 30°C using tetrahydrofuran as the mobile phase at a flow rate of 1.0 ml / min. SEC-SAMLL data are processed using the commercial software ASTRA6 to obtain molecular weight parameters.

[0317] In some embodiments, the separator membrane comprises a porous substrate, and the liquid-retaining polymer is distributed in the pores of the porous substrate.

[0318] In other embodiments, the separator includes a porous substrate and a polymer layer disposed on at least one surface of the porous substrate, the polymer layer comprising a liquid-retaining polymer. The polymer layer being disposed on at least one surface of the porous substrate means that the polymer layer can be disposed on one or both surfaces of the porous substrate. The liquid-retaining polymer can be dispersed in a solvent to form a polymer mixture system, which is then coated onto the porous substrate using coating processes such as atomization spraying or gravure coating.

[0319] This application does not impose any particular limitation on the material of the porous substrate. Any known porous substrate with good chemical and mechanical stability can be selected. For example, the porous substrate may include at least one of porous polyolefin-based resin membranes (e.g., polyethylene, polypropylene, polyvinylidene fluoride), porous glass fiber, and porous nonwoven fabric. The porous substrate can be a single-layer film or a multi-layer composite film. When the porous substrate is a multi-layer composite film, the materials of each layer can be the same or different.

[0320] In some embodiments, the porosity of the porous substrate is greater than or equal to 25%; optionally, it is between 25% and 50%. When the porosity of the porous substrate is within the above range, the air permeability of the porous substrate can be improved, which is beneficial to the migration of active ions. Furthermore, due to the relatively small porosity, the mechanical properties of the porous substrate can also be improved, and it provides good support for the polymer layer.

[0321] In some embodiments, the thickness of the porous substrate may be less than or equal to 16 μm, and may be selected from 5 μm to 12 μm. Exemplarily, the thickness of the porous substrate may be 1 μm, 2 μm, 3 μm, 5 μm, 10 μm, 12 μm, 15 μm, 16 μm, or any range of two of the above values.

[0322] Optionally, the polymer layer includes heat-resistant particles. The synergistic effect of the heat-resistant particles and the liquid-retaining polymer can further improve the overall heat resistance and ion transport performance of the separator. The liquid-retaining polymer and the heat-resistant particles can be dispersed in a solvent to form a polymer mixture system, which is then coated onto a porous substrate using coating processes such as atomization spraying or gravure coating.

[0323] In some embodiments, the mass percentage of the liquid-retaining polymer to the mass percentage of the heat-resistant particles, based on the total mass of the polymer layer, is (0.2 to 5.0):1; optionally, it is (0.5 to 2.0):1. When the contents of the heat-resistant particles and the liquid-retaining polymer are within the above ranges, the overall heat resistance and ion transport performance of the separator can be further improved. For example, the ratio of the mass percentage of the liquid-retaining polymer to the mass percentage of the heat-resistant particles can be 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.8:1, 1.0:1, 1.2:1, 1.5:1, 1.8:1, 2.0:1, 2.5:1, 2.8:1, 3.0:1, 3.2:1, 3.5:1, 3.8:1, 4.0:1, 4.2:1, 4.5:1, 4.8:1, 5.0:1, or a range of any two of the above values.

[0324] In some embodiments, the thickness of the polymer layer can be from 0.5 μm to 3.0 μm; optionally, it can be from 1.0 μm to 2.0 μm. When the thickness of the polymer layer is within the above range, the overall heat resistance and ion transport performance of the separator can be further improved. For example, the thickness of the polymer layer can be 0.5 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2.0 μm, 2.3 μm, 2.5 μm, 2.8 μm, 3.0 μm, or any combination of two of the above values.

[0325] Optionally, the separator may also include a heat-resistant coating located on at least one surface of the porous substrate, with a polymer layer located on the side of the heat-resistant coating facing away from the porous substrate.

[0326] The heat-resistant coating may include heat-resistant particles. In some embodiments, the heat-resistant particles include at least one of inorganic and organic particles. By incorporating heat-resistant particles, the heat resistance of the separator can be improved.

[0327] In some embodiments, the mass percentage of inorganic particles in the heat-resistant coating is ≤30%. Exemplarily, the mass percentage of inorganic particles in the heat-resistant coating is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, or a range of any two of the above values.

[0328] Inorganic particles may include at least one of the following: inorganic particles having a dielectric constant of 5 or higher, inorganic particles having the ability to transport active ions, and inorganic particles capable of undergoing electrochemical oxidation and reduction.

[0329] In some embodiments, inorganic particles having a dielectric constant of 5 or higher may include boehmite (γ-AlOOH), alumina (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), and silicon oxides (SiO2). x (0<x≤2), Tin dioxide (SnO2), Titanium oxide (TiO2), Calcium oxide (CaO), Zinc oxide (ZnO), Zirconia (ZrO2), Yttrium oxide (Y2O3), Nickel oxide (NiO), Hafnium dioxide (HfO2), Cerium oxide (CeO2), Zirconium titanate (ZrTiO3), Barium titanate (BaTiO3), Magnesium fluoride (MgF2), 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) and Pb (Mg3Nb) 2 / 3 At least one of O3-PbTiO3 (abbreviated as PMN-PT).

[0330] In some embodiments, the inorganic particles capable of transporting active ions may include lithium phosphate (Li3PO4) and lithium titanium phosphate (Li... x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium titanium aluminum phosphate (Li x Al y Ti z (PO4)3, 0<x<2, 0<y<1, 0<z<3), (LiAlTiP) x O y Glass-like materials (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2), SiS2 type glass (Li x Si y S z(0 < x < 3, 0 < y < 2, 0 < z < 4) and P2S5 type glass (Li x P y S z At least one of the following: 0 < x < 3, 0 < y < 3, 0 < z < 7.

[0331] In some embodiments, the inorganic particles capable of undergoing electrochemical oxidation and reduction may include at least one of lithium-containing transition metal oxides, lithium-containing phosphates with an olivine structure, carbon-based materials, silicon-based materials, tin-based materials, and lithium-titanium compounds.

[0332] In some embodiments, the heat-resistant coating may also include other organic particles, such as at least one of polystyrene, polyethylene, polyimide, melamine resin, phenolic resin, polypropylene, polyester (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), polyphenylene sulfide, polyarylamide, polyamide-imide, polyimide, copolymers of butyl acrylate and ethyl methacrylate, and mixtures thereof.

[0333] In some embodiments, the heat-resistant coating may also include an adhesive. As an example, the adhesive may include at least one of aqueous acrylic resins (e.g., homopolymers of acrylic acid, methacrylic acid, sodium acrylate monomers, or copolymers with other comonomers), polyvinyl alcohol (PVA), isobutylene-maleic anhydride copolymers, and polyacrylamide.

[0334] In some embodiments, the thickness of the heat-resistant coating is ≤4 μm. This helps to improve the energy density of the battery cell. In the embodiments of this application, the thickness of the heat-resistant coating refers to the thickness of the heat-resistant coating located on one side of the substrate. Exemplarily, the thickness of the heat-resistant coating can be 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, or any range of two of the above values.

[0335] In some embodiments, the coating basis weight of the liquid-retaining polymer is 0.5 mg / 1540.25 mm. 2 Up to 5mg / 1540.25mm 2 .

[0336] When the coating weight is within the above range, the liquid retention capacity of the separator can be further improved.

[0337] Optionally, the coating basis weight of the polymer layer can be 0.5 mg / 1540.25 mm. 2 Up to 3.5mg / 1540.25mm 2 .

[0338] For example, the coating basis weight of the polymer layer can be 0.5 mg / 1540.25 mm. 2 0.6mg / 1540.25mm 2 0.8mg / 1540.25mm 2 1.0mg / 1540.25mm 2 1.2mg / 1540.25mm 2 1.5mg / 1540.25mm 2 1.8mg / 1540.25mm 2 2.0mg / 1540.25mm 2 2.5mg / 1540.25mm 2 3mg / 1540.25mm 2 3.5mg / 1540.25mm 2 4mg / 1540.25mm 2 4.5mg / 1540.25mm 2 5mg / 1540.25mm 2 Or a range consisting of any two of the above values.

[0339] In this application, the coating basis weight refers to the coating basis weight of the liquid-retaining polymer on one side of the release liner. This can be measured using equipment and methods known in the art, for example, by cutting the same master roll substrate and release liner into 1540.25mm pieces. 2 Weigh 10 small discs of the separator film and calculate the coating weight of the superabsorbent polymer in the separator film.

[0340] [Positive electrode plate]

[0341] The battery cell includes a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on the positive current collector.

[0342] In some embodiments, the positive electrode film layer includes a positive electrode active material and a liquid-absorbing polymer.

[0343] As some examples, the positive electrode film layer includes a polymer layer containing a liquid-absorbing polymer and a positive electrode active material layer containing positive electrode active material particles, the positive electrode active material layer being disposed on at least one surface of the positive electrode current collector, and the polymer layer being disposed on the surface of the positive electrode active material layer opposite to the positive electrode current collector.

[0344] As other examples, there are multiple positive electrode active material particles, with pores between adjacent positive electrode active material particles, and the liquid-absorbing polymer is distributed within the pores.

[0345] In some embodiments, the positive electrode film layer may also include a liquid-retaining polymer.

[0346] As an example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0347] In some implementations, 1.20 ≤ v / λ ≤ 4.50. For example, v / λ can be 1.20, 1.40, 1.80, 2.00, 2.50, 3.00, 3.50, 3.60, 3.80, 3.90, 4.0, 4.2, 4.5 or a range of any two of the above values.

[0348] In some embodiments, the liquid-absorbing polymer has a mass percentage content of 0.1% to 1.5% based on the mass of the positive electrode active material layer.

[0349] When the mass percentage of the absorbent polymer is within the above-mentioned range, the absorbent capacity of the positive electrode active material layer can be significantly improved. For example, the mass percentage of the absorbent polymer can be 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, or any combination of two of the above values.

[0350] The positive electrode active material layer includes a positive electrode active material, which may be a positive electrode active material known in the art for use in battery cells. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphate compounds, lithium-containing transition metal oxides, sodium-containing phosphate compounds, and sodium-containing transition metal oxides.

[0351] For example, the general formula of olivine-type phosphate active substances (containing lithium phosphate compounds) is: Li x A y Me a M b P 1-c X c Y zWherein, 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; Y includes one or more of O and F. Specifically, olivine-type phosphate active substances include one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0352] For example, lithium transition metal oxides (layered materials such as ternary, lithium nickel oxide / sodium, lithium cobalt oxide / sodium, lithium manganese oxide / sodium, lithium-rich layered and rock salt phase layered materials, etc.). The general formula for layered cathode active materials 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), and LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 One or more of O2 (NCM811) and NCA.

[0353] In some embodiments, the positive current collector may be a metal foil or a composite current collector. Examples of metal foils include aluminum foil or aluminum alloy foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. Examples of the metal material include one or more combinations selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer substrate may include one or more combinations selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0354] In some embodiments, the positive electrode active material layer may optionally include a positive electrode conductive agent. This application does not impose particular limitations on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes one or more combinations 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.

[0355] In some embodiments, the positive electrode active material layer may optionally include a positive electrode binder. This application does not impose particular limitations on the type of positive electrode binder. As an example, the positive electrode binder may include one or more combinations selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. In some embodiments, the mass percentage of the positive electrode binder is less than 5% based on the total mass of the positive electrode active material layer. The positive electrode binder has a higher crystallinity than the fluorinated polymers of this application. The positive electrode binder has a higher melting temperature than the fluorinated polymers of this application.

[0356] The positive electrode active material layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, liquid-absorbing polymer, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it. Of course, the preparation of the positive electrode sheet is not limited to the above methods; the preparation methods described above can also be used.

[0357] [Negative electrode plate]

[0358] A single battery cell includes a negative electrode plate.

[0359] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0360] In some embodiments, the negative electrode film layer includes a negative electrode active material and a liquid-absorbing polymer.

[0361] As some examples, the negative electrode film layer includes a polymer layer containing a liquid-absorbing polymer and a negative electrode active material layer containing negative electrode active material particles, the negative electrode active material layer being disposed on at least one surface of the negative electrode current collector, and the polymer layer being disposed on the surface of the negative electrode active material layer opposite to the negative electrode current collector.

[0362] As other examples, there are multiple negative electrode active material particles, with pores between adjacent negative electrode active material particles, and the liquid-absorbing polymer is distributed within the pores.

[0363] In some embodiments, the negative electrode film layer may also include a liquid-retaining polymer.

[0364] In some implementations, 3.00 ≤ v / λ < 50.00. For example, v / λ can be 3.00, 3.20, 3.40, 3.50, 4.00, 4.50, 5.00, 5.50, 6.00, 6.50, 7.00, 8.00, 9.00, 9.50, 10.00, 10.50, 11.00, 12.00, 13.00, 14.00, 15.00, 20.00, 25.00, 28.00, 30.00, 35.00, 40.00, 45.00, 50.00, or a range of any two of the above values.

[0365] In some embodiments, the mass percentage of the absorbent polymer is from 0.2% to 5.0% based on the mass of the negative electrode active material layer. When the mass percentage of the absorbent polymer is within the above range, the liquid absorption capacity of the negative electrode active material layer can be significantly improved. For example, the mass percentage B% of the absorbent polymer can be 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, or a range of any two of the above values.

[0366] The negative electrode active material may be any negative electrode active material known in the art for use in battery cells. As an 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. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy materials.

[0367] In some embodiments, the negative electrode active material layer may optionally include a negative electrode conductive agent. This application does not impose particular limitations on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one selected from 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 is ≤5% based on the total mass of the negative electrode active material layer.

[0368] In some embodiments, the negative electrode active material layer may optionally include a negative electrode binder. This application does not impose particular limitations on the type of negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder is ≤5% based on the total mass of the negative electrode active material layer.

[0369] In some embodiments, the negative electrode active material layer may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc. In some embodiments, the mass percentage of the other additives is ≤2% based on the total mass of the negative electrode active material layer.

[0370] 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 polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0371] The negative electrode active material layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, liquid-absorbing polymer, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these. 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.

[0372] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode active material layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat (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 this application further includes a protective layer covering the surface of the negative electrode active material layer.

[0373] [Electrolytes]

[0374] During the charging and discharging process of a single battery cell, active ions repeatedly insert and extract between the positive and negative electrode plates, while the electrolyte acts as a conductor for these active ions. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to actual needs.

[0375] The electrolyte comprises an electrolyte salt and a solvent. The types of electrolyte salt and solvent are not specifically limited and can be selected according to actual needs.

[0376] When the battery cell of this 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 bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0377] When the battery cell of this 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 difluorooxalate borate (NaDFOB), sodium dioxalate borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorodioxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0378] 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), butyl ester carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), diethyl sulfone (ESE), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2me-thf), 1,3-dioxolane (DOL), dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), and diethylene glycol dimethyl ether (DG).

[0379] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0380] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process and / or a stacking process.

[0381] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0382] In some embodiments, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a soft package, such as a pouch. The material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0383] In some implementations, the positive electrode, separator, and negative electrode can be fabricated into an electrode assembly using a winding or stacking process.

[0384] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. Figure 1 The example shown is a square-structured battery cell 5.

[0385] In some embodiments, such as Figure 1 and Figure 2 As shown, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 may be one or more, and can be adjusted according to requirements.

[0386] The method for preparing the battery cell of this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process or a stacking process. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a battery cell is obtained.

[0387] In some embodiments of this application, the battery cells according to this application can be assembled into a battery module. The number of battery cells contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0388] Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0389] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0390] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0391] Both battery module 4 and battery pack can be used as specific examples of batteries in the embodiments of this application.

[0392] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0393] Electrical appliances

[0394] Thirdly, this application provides an electrical device, which includes at least one of the battery cell, battery module, and battery pack described in this application. The battery cell, battery module, and battery pack can be used as the power source for the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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 non-existent, placing the injection hole at the bottom of the battery cell in the vertical direction can improve the reliability of the battery cell, thereby improving the reliability of the electrical device.

[0395] Electrical devices can be equipped with individual battery cells, battery modules, or battery packs depending on their usage requirements. Figure 6 This is a schematic diagram of an example electrical device. The electrical device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device, a battery pack 1 or a battery module can be used. Another example electrical device could be a mobile phone, tablet, laptop, etc. These devices typically require a slim and lightweight design, and can use individual battery cells as their power source.

[0396] Example

[0397] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0398] Example 1: Preparation of Lithium-ion Batteries

[0399] (1) Preparation of the positive electrode sheet:

[0400] Aluminum foil with a thickness of 12μm was used as the positive electrode current collector.

[0401] Liquid-absorbing polymer and positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), conductive carbon black, and binder polyvinylidene fluoride (PVDF) are thoroughly mixed in an appropriate amount of N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. The mass ratio of the liquid-absorbing polymer, NCM622, conductive carbon black, and PVDF in the positive electrode slurry is 0:97.5:1.4:1.1. The positive electrode slurry is coated onto a current collector aluminum foil and vacuum dried at 100°C, followed by cold pressing. Then, it is trimmed, cut into sheets, slit, and dried under vacuum at 85°C for 4 hours to prepare the positive electrode sheet.

[0402] (2) Preparation of negative electrode sheet:

[0403] A copper foil with a thickness of 8μm was used as the negative electrode current collector.

[0404] A liquid-absorbing polymer, artificial graphite (negative electrode active material), carbon black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were mixed evenly in a weight ratio of 1.5:95.9:2:0.5:0.1 and then added to deionized water to prepare a negative electrode slurry. The negative electrode slurry was coated onto a copper foil current collector and dried at 85°C. After cold pressing, edge trimming, cutting, and slitting, it was dried under vacuum at 120°C for 12 hours to produce the negative electrode sheet.

[0405] (3) Preparation of electrolyte:

[0406] In an environment with a water content of less than 10 ppm, non-aqueous organic solvents ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate are mixed in a volume ratio of 1:1:1 to obtain an electrolyte solvent. Then, lithium salt LiPF6 is mixed with the mixed solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0407] (4) Preparation of the separating membrane

[0408] A 7μm polyethylene film (PE) was used as the substrate.

[0409] A liquid-retaining polymer was dispersed in dimethyl carbonate (DMC) solvent to form a mixture. This mixture was then atomized and sprayed onto both surfaces of a polyethylene film to form polymer layers. Water was used as the atomizing solvent, and the mass content of the mixture was 1%.

[0410] (5) Preparation of lithium-ion batteries:

[0411] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0412] Comparative Example 1

[0413] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference between Comparative Example 1 and Example 1 is that the positive electrode, negative electrode, and separator are all different. The separator in Comparative Example 1 is a 7 μm polyethylene film (PE).

[0414] The positive electrode sheet is prepared as follows:

[0415] Aluminum foil with a thickness of 12μm was used as the positive electrode current collector.

[0416] LiNi, the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2 (NCM622), conductive carbon black, and binder polyvinylidene fluoride (PVDF) are thoroughly mixed in an appropriate amount of N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. The mass ratio of NCM622, conductive carbon black, and PVDF in the positive electrode slurry is 97.5:1.4:1.1. The positive electrode slurry is coated onto a current collector aluminum foil and vacuum dried at 100°C, followed by cold pressing. Then, it is trimmed, cut into sheets, slit, and dried under vacuum at 85°C for 4 hours to produce the positive electrode sheet.

[0417] Preparation of negative electrode sheet:

[0418] A copper foil with a thickness of 8μm was used as the negative electrode current collector.

[0419] Artificial graphite (negative electrode active material), carbon black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were mixed evenly in a weight ratio of 97.4:2:0.5:0.1 and then added to deionized water to prepare a negative electrode slurry. The negative electrode slurry was coated onto a copper foil current collector and dried at 85°C. Then, it was cold-pressed, trimmed, cut into sheets, and slit. Finally, it was dried under vacuum at 120°C for 12 hours to prepare the negative electrode sheet.

[0420] Comparative Example 2

[0421] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 is that the liquid-retaining polymer in the separator of Comparative Example 2 was changed, and the liquid-absorbing polymer in the positive and negative electrode sheets was also changed.

[0422] Examples 1-2 to Examples 1-10

[0423] Lithium-ion batteries were prepared using a method similar to that of Example 1. The difference from Example 1 is that the content of the liquid-absorbing polymer in the positive and negative electrode sheets of Examples 1-2 to 1-10 was adjusted.

[0424] Examples 2-1 to 2-6

[0425] Lithium-ion batteries were prepared using a method similar to that of Example 1. The difference from Example 1 is that the types of at least one of the liquid-retaining polymer and the liquid-absorbing polymer were adjusted in Examples 2-1 to 2-6.

[0426] Examples 3-1 to 3-5

[0427] Lithium-ion batteries were prepared using a method similar to that of Example 1. The difference from Example 1 is that the coating weight of the liquid-retaining polymer in the separator was adjusted in Examples 3-1 to 3-5.

[0428] Example 4-1

[0429] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference between Example 4-1 and Example 4-1 is that the placement of the polymer layer in the separator was adjusted. Specifically, the preparation steps of the separator included:

[0430] A 7μm polyethylene film (PE) was used as the substrate for the release liner;

[0431] Silicon oxide particles and aqueous binder-type polyacrylic acid are mixed evenly in an appropriate amount of deionized water at a mass ratio of 20:80 to obtain a coating slurry.

[0432] The prepared coating slurry is applied to two surfaces of the PE substrate using a coating machine to form a heat-resistant coating.

[0433] The liquid-retaining polymer and binder are dispersed in dimethyl carbonate (DMC) solvent to form a mixed system. The mixed system is then atomized and sprayed onto the surface of the heat-resistant coating to form a polymer layer, thereby obtaining a release film.

[0434] Example 4-2

[0435] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference between Example 4-2 and Example 1 is that the preparation method of the separator was adjusted. Specifically, the preparation steps of the separator include:

[0436] A 7μm polyethylene film (PE) was used as the substrate for the release liner;

[0437] The liquid-retaining polymer, silica compound particles, and aqueous binder-type polyacrylic acid were mixed evenly in an appropriate amount of deionized water at a mass ratio of 80:20 to obtain the coating slurry. The mass ratio of the liquid-retaining polymer to the silica compound particles was 1.5:1.

[0438] The prepared coating slurry is applied to two surfaces of the PE substrate using a coating machine to form a heat-resistant coating.

[0439] The liquid-retaining polymer and binder are dispersed in dimethyl carbonate (DMC) solvent to form a mixed system. The mixed system is then atomized and sprayed onto the surface of the heat-resistant coating to form a polymer layer, thereby obtaining a release film.

[0440] The data for the examples and comparative examples are shown in Table 1.

[0441] Test section

[0442] 1. Wetting properties of electrodes and separators in lithium-ion batteries

[0443] Take a negative electrode sheet + separator structure after hot pressing at 80℃. The structure has a width of 2.0cm and a height of 10cm. Place the structure vertically in the electrolyte. The height of the electrode sheet in the electrolyte is 1mm. Record the height of the electrolyte rise after 2min. Record the liquid rise height / time to characterize the liquid absorption rate of the overall structure of negative electrode sheet + separator.

[0444] Take a positive electrode sheet + separator structure after hot pressing at 80℃. The structure has a width of 2.0cm and a height of 10cm. Place the structure vertically in the electrolyte. The height of the electrode sheet in the electrolyte is 1mm. Record the height of the electrolyte rise after 2min. Record the liquid rise height / time to characterize the liquid absorption rate of the overall structure of positive electrode sheet + separator.

[0445] 2. Cycle performance of lithium-ion batteries under 5C conditions

[0446] A lithium-ion battery was charged at 5C and discharged at 1C at 25°C. The capacity retention rate after 200 cycles was calculated, with the initial discharge capacity as 100%. Capacity retention rate (%) after 200 cycles = (Discharge capacity of the 200th cycle / Initial discharge capacity) × 100%.

[0447] Test Results

[0448] The test results are shown in Tables 1 and 2.

[0449] Table 1

[0450]

[0451] In Table 1, 60% methyl methacrylate refers to the methyl methacrylate molar percentage content of 60% based on the total molar amount of methyl methacrylate, butyl acrylate, and acrylonitrile.

[0452] Table 1 shows the liquid retention capacity.

[0453] The liquid retention rate (before pressurization) is (m1-M) / M×100%.

[0454] The liquid retention rate (after pressurization) is (m2-M) / M×100%.

[0455] Table 2

[0456]

[0457] In Table 2, 75% VDF refers to the molar percentage of vinylidene fluoride VDF based on the total molar amounts of vinylidene fluoride VDF, hexafluoropropylene HFP, and ethylene.

[0458] Table 3

[0459]

[0460]

[0461] In Table 3, the porosity of the positive electrode film in the positive electrode sheet of each embodiment and comparative example is 30.1%, and the porosity of the negative electrode film in the negative electrode sheet is 44.2%.

[0462] In Table 3, the ratio of the unit volume mass of the liquid-absorbing polymer in the electrode to the unit volume mass of the liquid-retaining polymer in the separator refers to the ratio of the sum of the monomer volume masses of the liquid-absorbing polymer in the positive and negative electrode to the unit volume mass of the liquid-retaining polymer in the separator.

[0463] Comparative Example 1: The separator did not contain the liquid-retaining polymer of this application, and the electrode did not contain the liquid-absorbing polymer, resulting in poor cycle performance of the battery cell.

[0464] Although Comparative Example 2 added polymers to the separator and electrode, the polymers had poor liquid retention and absorption capabilities, and could not effectively improve the cycle performance of the lithium-ion battery.

[0465] Compared to Comparative Example 1, the embodiments of this application include a liquid-absorbing polymer in the electrode sheet. The liquid-absorbing polymer helps the electrode sheet to absorb electrolyte, resulting in more uniform and sufficient wetting of the electrode sheet by the electrolyte, thus improving the stability of the battery cell during cycling. The separator of the battery cell is provided with a liquid-retaining polymer. The separator has a strong liquid-retaining capacity, making it less likely for the electrolyte to be squeezed out during the cyclic charging and discharging of the battery cell. This reduces the possibility of electrolyte shortage during cyclic charging and discharging, reduces battery polarization, and improves the cycle performance of the battery cell.

[0466] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery cell, comprising an electrode assembly, the electrode assembly comprising electrode plates and a separator; The electrode sheet includes a current collector and a film layer containing an active substance and a liquid-absorbing polymer disposed on at least one surface of the current collector. The electrode sheet satisfies: v / λ≥1.2; v represents the liquid absorption rate of the film layer, with units of mg / s. λ represents the porosity of the membrane layer; The separator membrane comprises a liquid-retaining polymer, and the separator membrane satisfies the following: ； M represents the mass of the separator that did not absorb electrolyte, and its unit is g; m1 represents the mass of the separator membrane after it has been immersed in the electrolyte for 2 hours and weighed under ambient pressure, and its unit is g; m2 represents the mass of the separator membrane after it has been immersed in the electrolyte for 2 hours and weighed under an ambient pressure of 10000N, with the unit being g.

2. The battery cell according to claim 1, wherein, The active material includes a positive electrode active material, and the electrode sheet satisfies: 1.2≤v / λ≤4.

50.

3. The battery cell according to claim 1 or 2, wherein, The active material includes a negative electrode active material, and the electrode sheet satisfies: 3≤v / λ<50.

00.

4. The battery cell according to claim 1, wherein, The isolation membrane satisfies: 。 5. The battery cell according to claim 1, wherein, The isolation membrane satisfies: 。 6. The battery cell according to claim 1, wherein, The isolation membrane satisfies: 。 7. The battery cell according to claim 1, wherein, The isolation membrane also includes a liquid-absorbing polymer.

8. The battery cell according to claim 7, wherein, The unit volume mass of the liquid-absorbing polymer located in the electrode sheet is A1, and the unit volume mass of the liquid-absorbing polymer located in the separator is A2, where 1.0 ≤ A1 / A2 ≤ 1.

6.

9. The battery cell according to claim 8, wherein, 1.2≤A1 / A2≤1.

5.

10. The battery cell according to claim 1, wherein, The electrode sheet also includes a liquid-retaining polymer.

11. The battery cell according to claim 10, wherein, The mass per unit volume of the liquid-retaining polymer located in the electrode sheet is B1. The mass per unit volume of the liquid-retaining polymer located in the isolation membrane is B2. 0.4≤B1 / B2≤0.

9.

12. The battery cell according to claim 11, wherein, 0.5≤B1 / B2≤0.

8.

13. The battery cell according to claim 1, wherein, The unit volume mass of the liquid-absorbing polymer located in the electrode plate is C1, and the unit volume mass of the liquid-retaining polymer located in the separator is C2, where 0.1≤C1 / C2≤5.

14. The battery cell according to claim 1, wherein, The absorbent polymer includes at least one of ether polymers and ester polymers.

15. The battery cell according to claim 14, wherein, The liquid-absorbing polymer is formed into a sheet-like structure; the sheet-like structure is in (T m2 The elastic modulus G' - energy dissipation modulus G” curve was obtained by dynamic frequency scanning test at +20℃. The slope of the elastic modulus G' - energy dissipation modulus G” curve is K1, 1 < K1 < ∞, T m2 °C represents the melting temperature of the absorbent polymer.

16. The battery cell according to claim 15, wherein, 1＜K1≤100。 17. The battery cell according to claim 16, wherein, 1＜K1≤10。 18. The battery cell according to claim 14, wherein, The ether polymer comprises at least one of the structural units shown in formula (BI) and formula (BII). Formula (BI); In formula (BI), n is selected from positive integers from 1500 to 25000; R 21 and R 22 Each independently comprises 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 groups; Formula (BII); In formula (BII), n is selected from positive integers from 1500 to 25000; R 24 To R 27 Each independently comprises 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 or ether group.

19. The battery cell according to claim 14 or 15, wherein, The ester polymer includes at least one of the structural units shown in formula (CI) and formula (CII). Formula (CI); In formula (CI), n is selected from positive integers from 1000 to 15000; R 31 R 32 and R 33 Each independently comprises a hydrogen atom, or a substituted or unsubstituted C1-C8 alkyl group; R 34 Including substituted or unsubstituted C1-C8 alkyl groups, or substituted or unsubstituted C1-C8 hydroxyalkyl groups; Formula (CII); In formula (CII), n is selected from positive integers from 1000 to 15000; R 35 This includes substituted or unsubstituted C2-C6 methylene groups.

20. The battery cell according to claim 19, wherein, R 35 Each independently includes substituted or unsubstituted C2-C4 methylene groups.

21. The battery cell according to claim 1, wherein, The liquid-retaining polymer includes at least one of fluorinated polymers and aldehyde-ketone polymers.

22. The battery cell according to claim 21, wherein, The aldehyde-ketone polymer is formed into a sheet-like structure; the sheet-like structure is in (T m3 The elastic modulus G' - energy dissipation modulus G” curve was obtained by dynamic frequency scanning test at +20℃. The slope of the elastic modulus G' - energy dissipation modulus G” curve is K3, 0.8≤K3<∞, T m3 °C represents the melting temperature of the aldehyde-ketone polymer.

23. The battery cell according to claim 22, wherein, 0.8≤K3≤100。 24. The battery cell according to claim 23, wherein, 0.8≤K3≤10。 25. The battery cell according to claim 21, wherein, The crystallinity of the fluorinated polymer, as determined by differential scanning calorimetry, is Xc1, where 0 < Xc1 ≤ 30%.

26. The battery cell according to claim 21, wherein, The melting temperature of the fluoropolymer is T. m1 Its unit is ℃, 0 < T m1 ≤140.

27. The battery cell according to claim 21, wherein, The glass transition temperature of the fluoropolymer is T. g1 Its unit is ℃, -150≤T g1 ≤60.

28. The battery cell according to claim 21, wherein, The fluoropolymer includes at least one of the structural units shown in formula (A1) to formula (AIII). Formula (AI) Formula (AII), In equations (AI) and (AII), n is selected from positive integers from 1000 to 30000, and R... 11 R 12 R 13 and R 14 Each independently comprises a hydrogen atom, a fluorine atom, a chlorine atom, a bromine 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; Formula (AIII); In equation (AIII), R 15 Includes single-bonded, substituted or unsubstituted C1-C3 alkyl groups; p is a positive integer selected from 1 to 3; n is a positive integer selected from 1000 to 30000.

29. The battery cell according to claim 21 or 22, wherein, The aldehyde-ketone polymer comprises at least one of the structural units shown in formula (DI) and formula (DII). Formula (DI); In formula (DI), n is selected from positive integers from 500 to 15000, and R 41 Including single-bonded, substituted, or unsubstituted C1-C6 methylene groups; R 42 Includes hydrogen atoms, substituted or unsubstituted C1-C6 alkyl groups; Formula (DII); In formula (DII), n is selected from positive integers from 500 to 15000, and 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 integers from 0 to 5, and at least one of r and s is selected from a positive integer.

30. The battery cell according to claim 1, wherein, The isolation membrane comprises a porous substrate, and the liquid-retaining polymer is distributed in the pores of the porous substrate.

31. The battery cell according to claim 1, wherein, The isolation membrane includes a porous substrate and a polymer layer disposed on at least one surface of the porous substrate, the polymer layer including the liquid-retaining polymer.

32. The battery cell according to claim 1, wherein, The coating basis weight of the liquid-retaining polymer is 0.5 mg / 1540.25 mm. 2 Up to 5mg / 1540.25mm 2 .

33. A battery comprising a battery cell according to any one of claims 1 to 32.

34. An electrical device comprising the battery according to claim 33.

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