Electrode sheets and related battery cells, batteries, and electrical devices

Abstract

The present application provides an electrode sheet and related battery cells, batteries, and electric devices. The electrode sheet comprises a current collector and an active material layer disposed on at least one surface of the current collector, wherein the active material layer comprises an active material and a polymer, and wherein the active material layer satisfies Equations (1) to (3), and the polymer, as a component of the active material layer, can form uniform high-wetting points within the active material layer, thereby uniformly improving the wetting performance of the active material layer and increasing the overall liquid absorption rate of the active material layer, so as to improve the cycle performance of the battery cell. Equation (1) Equation (2) v / λ>1.00 Equation (3)

Description

Technology Field

[0001] This application relates to the field of batteries, and in particular to electrode sheets and related battery cells, batteries, and electric devices. Background Technology

[0002] Battery cells possess characteristics such as high capacity and long lifespan, so they are widely used in electronic devices such as mobile phones, laptop computers, battery cars, electric vehicles, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and power tools.

[0003] As the range of battery applications expands, requirements for battery cell performance are becoming increasingly stringent. To enhance the safety performance of battery cells, improvements are generally made to optimize the performance of the electrode sheets within the cells. However, current active materials in electrode sheets have poor liquid absorption performance, resulting in poor cycle performance when applied to battery cells.

[0004] The present application has been made in consideration of the above-mentioned problem and aims to provide an electrode sheet and related battery cells, batteries, and electric devices.

[0005] A first aspect of the present application provides an electrode sheet, wherein the electrode sheet comprises a current collector and an active material layer disposed on at least one surface of the current collector, the active material layer comprises an active material and a polymer, and the active material layer satisfies formulas (1) to (3).

[0006] Equation (1)

[0007] Equation (2)

[0008] v / λ>1.00 Equation (3)

[0009] In formulas (1) to (3),

[0010] λ represents the porosity of the active material layer;

[0011] P1 represents the actual compressed density of the active material layer, and the unit is g / cm³ 3 is;

[0012] P2 represents the true compressed density of the active substance, and the unit is g / cm³ 3 is;

[0013] v represents the liquid absorption rate of the active material layer, and the unit is mg / s;

[0014] d represents the diameter of the capillary in the capillary test of the active material layer, and the unit is mm;

[0015] h represents the height of the liquid level within the capillary tube, and the unit is mm;

[0016] ρ represents the density of the electrolyte in the above capillary test, and the unit is g / cm³ 3 is;

[0017] t represents the time during which the electrolyte is absorbed into the capillary tube, and the unit is s.

[0018] Accordingly, the polymer of the present application is introduced into the process of manufacturing an active material layer to form a uniform high-moisture point within the active material layer and uniformly improve the wetting performance of the active material layer, thereby improving the overall liquid absorption rate of the active material layer and thereby improving the cycle performance of a battery cell using the electrode sheet.

[0019] In some embodiments, the active material comprises a positive electrode active material, and the active material layer is 1.00 <v / λ<4.00를 만족시키고; 선택적으로, 1.20≤v / λ≤3.80을 만족시킨다.

[0020] In some embodiments, the active material comprises a positive electrode active material, and based on the mass of the active material layer, the mass percentage of the polymer is A%; where 0.1 ≤ A ≤ 1.5. When the mass percentage of the polymer is within the above range, the liquid absorption capacity of the positive electrode active material layer can be significantly improved.

[0021] In some embodiments, the active material comprises a negative active material, and the active material layer is 3.00 <v / λ<50.00을 만족시키고; 선택적으로, 3.40≤v / λ≤30.00을 만족시킨다.

[0022] In some embodiments, the active material comprises a negative active material, and the mass percentage of the polymer is B% based on the mass of the active material layer; where 0.2 ≤ B ≤ 5.0. When the mass percentage of the polymer is within the above range, the liquid absorption capacity of the negative active material layer can be significantly improved.

[0023] In some embodiments, the degree of crystallinity of the polymer measured by differential scanning calorimetry is X C % and 0 <X C ≤30; the melting temperature of the polymer is Tm, the unit is °C, and 0 <Tm≤140이다.

[0024] Accordingly, since the polymer and the electrolyte in the battery cell have good affinity, the solvent in the electrolyte can rapidly diffuse between the molecular chains of the polymer and be wrapped by the molecular chains, forming an in-situ gel on the surface of the active material and improving the wetting performance of the electrolyte on the active material layer, thereby improving the liquid absorption rate of the entire active material layer and improving the cycle performance of the battery cell using the electrode sheet.

[0025] In some embodiments, the glass transition temperature of the polymer is Tg, the unit is °C, and -150≤Tg≤60. Since the glass transition temperature of the polymer is relatively low, the flexibility of the chain segments of the molecular chains is better, adjacent molecular chains open more easily, and an in-situ gel is formed more easily, thereby improving the wetting performance of the electrolyte on the active material layer and improving the cycle performance of the battery cell.

[0026] In some embodiments, the polymer comprises at least one of the structural units represented by Formula (III) from the structural unit represented by Formula (I), and

[0027] Equation (I), Formula (II), Equation (III);

[0028] In formulas (I) and (II), R1, R2, R3 and R4 each independently comprise a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C3 alkyl group or a substituted or unsubstituted C1-C3 alkoxy group, at least one of R1, R2, R3 and R4 comprises a fluorine atom, and if substituted, the substituent comprises a fluorine atom; in formula (III), R5 comprises a single bond, a substituted or unsubstituted C1-C3 alkyl group, and if substituted, the substituent comprises a fluorine atom, p is selected from a positive integer of 1 to 3, and n is selected from a positive integer of 1000 to 30000.

[0029] Accordingly, the polymer of the present application has a straight linear structure or a short branched chain structure, and this type of structure has a low degree of entanglement, which is advantageous for improving the flexibility of the molecular chains, and since the molecular chains can be fully stretched in the electrolyte, the wetting performance of the electrolyte for the active material can be further improved.

[0030] In some embodiments, R1, R2, R3 and R4 each independently comprise a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C2 alkyl group or a substituted or unsubstituted C1-C2 alkoxy group; more optionally, R1, R2, R3 and R4 each independently comprise a hydrogen atom, a fluorine atom, a chlorine atom, a methyl group, a fluoromethyl group, a methoxy group or a perfluoromethoxy group.

[0031] In some embodiments, the polymer comprises at least one of the structural units represented by formula (I-11) from the structural unit represented by formula (I-1).

[0032] Equation (I-1), Equation (I-2), Equation (I-3),

[0033] Equation (I-4), Equation (I-5), Equation (I-6),

[0034] Formula (I-7), Formula (I-8), Formula (I-9),

[0035] Formula (I-10), Equation (I-11).

[0036] In some embodiments, the polymer comprises at least one of the structural units represented by Formula (II-5) from the structural unit represented by Formula (II-1).

[0037] Equation (II-1), Formula (II-2),

[0038] Equation (II-3), Formula (II-4),

[0039] Formula (II-5).

[0040] In some embodiments, the polymer comprises at least one of the structural units represented by Formula (III-3) from the structural unit represented by Formula (III-1).

[0041] Equation (III-1), Equation (III-2),

[0042] Equation (III-3).

[0043] In some embodiments, n is selected from a positive integer between 5000 and 20000.

[0044] In some embodiments, the molecular weight of the polymer is 2×10 5 g / mol~1.5×10 6 When the molecular weight of the polymer is within the above range, it is possible to ensure that the polymer exhibits a constant solubility in the electrolyte, and at the same time, it is not easy for the polymer to be completely dissolved and dispersed by the electrolyte, which helps to control the distribution and dispersion of the polymer on the surface of the active material, and allows the electrolyte to be uniformly infiltrated into the active material layer, thereby increasing the liquid absorption rate of the entire active material layer and improving the cycle performance of the battery cell adopting the electrode sheet. Furthermore, the flexibility between the molecular chains of the polymer can be further improved, and since the forces between the molecular chains are relatively weak, solvent molecules in the electrolyte enter between the molecular chains and are wrapped by the molecular chains, which helps active ions enter the active material through the solvent, thereby realizing smooth and rapid movement of active ions and improving the kinetic performance of the battery cell.

[0045] A second aspect of the present application provides a battery cell, said battery cell comprising an electrode sheet of any embodiment of the first aspect of the present application.

[0046] A third aspect of the present application provides a battery, said battery comprising a battery cell according to a second aspect of the present application.

[0047] A fourth aspect of the present application provides an electric device, said electric device comprising a battery cell according to a third aspect of the present application. Brief explanation of the drawing

[0048] To further clarify the technical solution means of the embodiments of the present application, the drawings to be used in the embodiments of the present application are briefly introduced below. Of course, the drawings described below are merely some embodiments of the present application, and those skilled in the art can obtain other drawings based on the drawings without creative effort. The attached drawings may not be drawn to actual scale. FIG. 1 is a schematic diagram of one embodiment of a battery cell of the present application. Figure 2 is an exploded schematic diagram of an embodiment of the battery cell of Figure 1. FIG. 3 is a schematic diagram of one embodiment of the battery module of the present application. FIG. 4 is a schematic diagram of one embodiment of the battery pack of the present application. Figure 5 is an exploded schematic diagram of an embodiment of the battery pack shown in Figure 4. FIG. 6 is a schematic diagram of one embodiment of an electric device including a battery cell of the present application as a power source. Specific details for implementing the invention

[0049] The following describes and specifically discloses embodiments of the polymer, electrode sheet, and related battery cell, battery, and electric device of the present application. However, unnecessary detailed descriptions are omitted where necessary. For example, detailed descriptions of well-known facts and redundant descriptions of structures that are practically identical may be omitted. This is intended to prevent unnecessary duplication of the following description and to enable those skilled in the art to understand it easily. Furthermore, the attached drawings and the following description are intended to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0050] The “ranges” disclosed in this application are defined in the form of lower and upper limits, and a given range is defined by the selection of one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of a specific range. A range defined in this manner may or may not include endpoint values ​​and may be arbitrarily combined. That is, any lower limit may 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 should be understood that ranges of 60–110 and 80–120 are also considered. Furthermore, if minimum range values ​​1 and 2 are listed and maximum range values ​​3, 4, and 5 are listed, all ranges of 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5 are expected. In this application, unless otherwise specified, numeric ranges “a–b” represent a shortened expression of a combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range “0 to 5” indicates that all real numbers between “0 to 5” are listed in this specification, and “0 to 5” is merely an abbreviated expression for combinations of such numerical values. Additionally, if a specific parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is an integer, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0051] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with one another to form a new technical solution. Unless otherwise specified, all technical features and optional technical features of this application may be combined with one another to form a new technical solution.

[0052] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, and sequentially is preferred. For example, the statement that a method comprises steps (a) and (b) indicates that the method may comprise steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the statement that the mentioned method further comprises step (c) indicates that step (c) may be added to the method in any order, for example, the method may comprise steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), etc.

[0053] Unless otherwise specified, the terms “comprehensive” and “include” as used in this application may be open or closed. For example, the terms “comprehensive” and “include” indicate that the product may further comprise or include other unlisted components, or may comprise or include only the listed components.

[0054] Unless otherwise specified, the term “or” in this application is inclusive. For example, the phrase “A or B” indicates “A, B, or both A and B.” More specifically, “A or B” satisfies any one of the conditions that A is true (or exists) and B is false (or absent), A is false (or absent) and B is true (or exists), or A and B are both true (or exist).

[0055] In this application, the terms “plural” and “multiple types” refer to two or more types.

[0056] The term “alkyl group” includes straight-chain and branched-chain alkyl groups. For example, the alkyl group may be a C1-C5 alkyl group, a C1-C4 alkyl group, a C1-C3 alkyl group, or a C1-C2 alkyl group. In some embodiments, the alkyl group includes a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, etc. Additionally, the alkyl group may be optionally substituted. When substituted, the substituent includes a fluorine atom.

[0057] The term “alkoxy group” refers to a group in which an alkyl group and an oxygen atom are connected by a single bond. For example, the alkoxy group may be a C1 to C5 alkoxy group, a C1 to C3 alkoxy group, or a C1 to C2 alkoxy group. In some embodiments, the alkoxy group may include a methoxy group, an ethoxy group, or a propoxy group. Additionally, the alkoxy group may be optionally substituted.

[0058] The term “halogen atom” refers to fluorine atoms, chlorine atoms, bromine atoms, etc.

[0059] The term “hydrogen” represents 1H (light hydrogen, H), 2H (deuterium, D), or 3H (tritium, T). In each embodiment, “hydrogen” may be 1H (light hydrogen, H).

[0060] A battery cell comprises an electrode assembly and an electrolyte, and the electrode assembly comprises a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet. The electrode assembly belongs to a gap pore structure, and the electrolyte infiltrates into the electrode assembly, and the driving force of the infiltration is mainly a spontaneous infiltration and suction process by capillary force. Since the electrolyte infiltrates and is sucked into the interior of the electrode assembly through the separator from the cross-section of the electrode assembly due to the barrier of the current collector of the electrode sheet, the layer spacing of the electrode assembly acts as an induction agent and the separator acts as a classification agent. The infiltration step of the electrolyte inside the electrode assembly includes (1) the electrolyte being delivered into the gap between the electrode sheet and the separator by the action of capillary force, (2) the electrolyte preferentially infiltrating into the pores of the separator (the infiltration rate of the electrolyte is much greater in the separator than in the active material layer of the electrode sheet), and (3) the electrolyte diffusing through the separator to the surfaces of both the positive electrode sheet and the negative electrode sheet and infiltrating into the pores of the active material layer.

[0061] The applicant has discovered that in order to bond an active material to the surface of a current collector, a polymer must be used as a binder in the active material layer. Since the polymer must be immersed in the electrolyte for a long time, a polymer with high crystallinity is generally used to ensure the performance of the polymer and maintain excellent bonding and support effects in the active material layer. However, there is a problem in that the affinity between the electrode sheet using the above-mentioned polymer and the electrolyte is poor, resulting in poor wettability of the electrode sheet, slowing down the diffusion rate of the electrolyte from the surface of the active material layer to the interior of the active material layer, and degrading the liquid absorption performance of the active material, thereby degrading the cycle performance of the battery cell.

[0062] Considering these points, the applicant has improved the cycle performance of a battery cell by improving the liquid absorption rate of a material such as a polymer within the active material layer, with the aim of improving the liquid absorption rate of the active material layer.

[0063] electrode sheet

[0064] In a first embodiment, the present application proposes an electrode sheet, wherein the electrode sheet comprises a current collector and an active material layer disposed on at least one surface of the current collector, and the active material layer comprises an active material and a polymer. The electrode sheet may be a positive electrode sheet and / or a negative electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer.

[0065] The electrode sheet can be manufactured by coating a slurry onto a current collector and then drying and cold rolling. Alternatively, the electrode sheet is derived from a battery cell, the battery cell is disassembled to remove the electrode sheet immersed in the electrolyte from the battery cell, and the electrode sheet immersed in the electrolyte is vacuum dried at 100°C for 12 hours to obtain the electrode sheet, which is then used for measuring the electrode sheet, such as liquid absorption rate.

[0066] Polymers can be synthetically produced by emulsion polymerization, suspension polymerization, bulk polymerization, solution polymerization, etc. Alternatively, the polymer can be derived from a battery cell, the battery cell is disassembled to remove the electrode sheet infiltrated with the electrolyte from the battery cell, the active material of the obtained electrode sheet is removed from the current collector by external force to form a powder sample, this is added to dimethyl carbonate (DMC) and stirred at 500 rpm at 80°C for 8 hours, after which the stirring is stopped and left at room temperature for 10 minutes, then the clear liquid of the upper layer is taken and dried at 80°C for 12 hours to obtain the polymer. Although the obtained polymer may contain a small amount of lithium salt, it basically does not affect infrared measurement and precipitation value measurement, and to ensure the precision of the polymer, the lithium salt may be separated by washing with DMC at room temperature.

[0067] The above active material layer satisfies the following.

[0068] Equation (1)

[0069] Equation (2)

[0070] v / λ>1.00 Equation (3)

[0071] In formulas (1) to (3),

[0072] λ represents the porosity of the active material layer;

[0073] P1 represents the actual compressed density of the active material layer, and the unit is g / cm³ 3 is;

[0074] P2 represents the true compressed density of the active substance, and the unit is g / cm³ 3 is;

[0075] v represents the liquid absorption rate of the active material layer, and the unit is mg / s;

[0076] d represents the diameter of the capillary in the capillary test of the active material layer, and the unit is mm;

[0077] h represents the height of the liquid level within the capillary tube, and the unit is mm;

[0078] ρ represents the density of the electrolyte in the above capillary test, and the unit is g / cm³ 3 is;

[0079] t represents the time during which the electrolyte is absorbed into the capillary tube, and the unit is s.

[0080] In the present application, the actual compression density (P1) represents the ratio of the mass and thickness of the active material layer per unit area of ​​the electrode sheet, the actual compression density is determined by the force of overall compression after the electrode sheet is coated, and the unit is g / cm² 3 And, in the specific measurement step, an electrode sheet of a certain area (S) is taken, the mass (M) of the active material layer is measured, and the thickness (D) of the active material layer is measured, so the actual compressive density = M / (S×D).

[0081] In the present application, the true compressive density (P2) represents the density of the active material itself in the active material layer, and assuming the active material is a negative electrode active material such as graphite, the density of graphite is 2.25 g / cm³ 3 And, the true compressed density of the active substance is 2.25 g / cm³ 3 am.

[0082] Taking a positive electrode active material as an example, specifically, it refers to the mass of the unit “actual volume of solid material (excluding open pores, closed pores and inter-particle pores)” in a compressed state, and the true volume (V) is obtained through measurement, and then the true compressed density is calculated according to P=m / V, and the measurement can be performed by referring to GB / T24586-2009, and specifically the measurement steps are as follows.

[0083] (1) Pretreatment: Place a clean, dry sample cup on a scale and reset it to zero, then add the powder sample to the sample cup at about half the volume of the sample cup and record the sample mass.

[0084] (2) Place the sample cup containing the sample on the true density meter, seal the measurement system, pass helium gas through it according to the procedure, detect the pressure of the gas in the sample chamber and the expansion chamber, and then calculate the true volume according to Bohr's law (PV=nRT) to calculate the true compressible density.

[0085] Here, sample cup volume: 3.5 cm 3 , analyzed gas: is helium.

[0086] Equation (1) can calculate the porosity (λ) of the active material layer through the actual compressive density and the true compressive density.

[0087] Specifically,

[0088] Here, V1 represents the volume of the active material layer at mass m, and the unit is cm³ 3 is;

[0089] V2 represents the volume occupied by active particles in the active material layer at mass m, and the unit is cm³ 3 is;

[0090] m represents the mass of the active material layer, and the unit is g.

[0091] Equation (2) can indicate the rate at which a point on the electrode sheet substantially completely absorbs the liquid (e.g., electrolyte) within the capillary within a unit time. In this application, a point on the electrode sheet refers to a region of the electrode sheet having a constant area corresponding to the cross-sectional area of ​​the capillary.

[0092] In the present application, a method for detecting the liquid absorption rate of an electrode sheet comprises the following steps.

[0093] A predetermined amount of electrolyte is drawn in using a capillary tube.

[0094] The capillary is brought into contact with the electrode sheet, and the electrode sheet under test absorbs the electrolyte from the capillary through capillary action.

[0095] After a predetermined time (t) has elapsed, the liquid level height (h) at which the electrolyte is absorbed within the capillary is recorded, the amount of absorbed electrolyte is calculated based on the liquid level height (h), diameter (d), and density (ρ) of the capillary, and the liquid absorption rate (v) of the electrode sheet is quantitatively calculated based on the ratio of the absorbed amount to the predetermined time (t).

[0096] For example, d takes a value from 0.2 to 1, for example, 0.2, and h takes a value from 3 to 5, for example, 3.

[0097] The capillary has a capillary channel, allowing it to directly draw in the electrolyte through capillary action, thus eliminating the need for an external drive unit to provide the power for liquid suction. In this way, on the one hand, the amount of electrolyte absorbed can be controlled more accurately when drawn in by capillary action, and on the other hand, since the electrode sheet absorbs the electrolyte through its own capillary action, the electrode sheet absorbs the electrolyte from within the capillary when the capillary contacts the electrode sheet under test, and the electrolyte within the capillary no longer flows out when the contact is removed. Consequently, the amount of electrolyte absorbed within the capillary accurately reflects that the electrode sheet has absorbed a corresponding volume of electrolyte, thereby further improving the accuracy of the measurement results and enabling the quantitative calculation of the liquid absorption rate of the electrode sheet.

[0098] Equation (3) represents the liquid absorption rate of the electrode sheet at porosity (λ), which can be used to indicate the liquid absorption rate of the electrode sheet.

[0099] The polymer of the present application is introduced into the process of manufacturing an active material layer to form a uniform high-moisture point within the active material layer and uniformly improve the wetting performance of the active material layer, thereby improving the overall liquid absorption rate of the active material layer and thus improving the cycle performance of a battery cell using the electrode sheet.

[0100] Optionally, 1.00 <v / λ<50.00이다.

[0101] In some embodiments, the degree of crystallinity of the polymer measured by differential scanning calorimetry is X C % and 0 <X C≤ 30; the melting temperature of the polymer is Tm, the unit is °C, and 0 <Tm≤140이다.

[0102] Crystallization refers to the process in which atoms, ions, or molecules within a material are arranged in a specific spatial order to form an ordered structure. In crystallization, the shape of a polymer is determined by intramolecular and intermolecular factors, and intermolecular forces influence the packing density between molecular chains. Degree of crystallization (X C % is used to indicate the degree of crystallization of the material, which can be measured by differential scanning calorimetry (DSC). Specifically, the measurement steps are as follows: a sample of 0.5 g to 0.8 g is taken, the sample is placed in a carrier crucible, and the sample is heated / deheated in a nitrogen atmosphere. The temperature is raised at a rate of 10°C / min from an initial temperature 20°C lower than the material's intrinsic Tg to a cutoff temperature of 20°C higher than the material's intrinsic Tm. During the process, the actual glass transition temperature (Tg) and melting temperature (Tm) of the material are determined based on the endothermic and exothermic peaks or transition points of the material.

[0103] Compared to fluorine-based polymers commonly used in secondary batteries in related technologies, the degree of crystallization and melting temperature are relatively higher, allowing the polymer to possess good resistance to liquid electrolytes and effectively provide active material bonding or repulsion suppression effects for a long period during battery use. The polymer (fluorine-based polymer) used in this application has a relatively low degree of crystallization and melting temperature, which tends to result in a loose molecular chain arrangement and weak forces between molecular chains, allowing for chain segment flexibility and enabling adjacent molecular chains to open easily.

[0104] Since the polymer and the electrolyte in the battery cell have good affinity, the solvent in the electrolyte can rapidly diffuse between the molecular chains of the polymer and be wrapped by the molecular chains, thereby forming an in-situ gel on the surface of the active material, improving the wetting performance of the electrolyte on the active material layer, and improving the liquid absorption rate of the entire active material layer, thereby improving the cycle performance of the battery cell using the electrode sheet.

[0105] For example, the degree of crystallinity of the polymer measured by differential scanning calorimetry (X C %) can be a range consisting of 5%, 10%, 15%, 20%, 25%, 30%, or any two of the above values.

[0106] For example, the melting temperature of the polymer may be a range consisting of 10°C, 20°C, 50°C, 70°C, 90°C, 100°C, 120°C, 140°C, or any two of the above values.

[0107] In some embodiments, the glass transition temperature of the polymer is Tg, the unit is °C, and -150≤Tg≤60.

[0108] The glass transition temperature is the temperature at which a polymer chain segment transitions from freezing to movement. The glass transition temperature has a certain effect on the flexibility of the polymer molecular chain; the lower the glass transition temperature, the better the flexibility of the polymer molecular chain at room temperature, and the higher the glass transition temperature, the worse the flexibility of the molecular chain at room temperature. The glass transition temperature can be measured by differential scanning calorimetry (DSC). A relatively low glass transition temperature of the polymer results in better flexibility of the molecular chain segments, allowing adjacent molecular chains to open more easily and facilitating the formation of an in-situ gel, thereby improving the wetting performance of the electrolyte for the active material layer and enhancing the cycle performance of the battery cell. For example, the glass transition temperature of a fluoropolymer may be a range consisting of -150°C, -140°C, -120°C, -100°C, -80°C, -60°C, -30°C, 0°C, 30°C, 60°C, or any two of the above values.

[0109] In some embodiments, the polymer comprises at least one of the structural units represented by Formula (III) from the structural unit represented by Formula (I).

[0110] Equation (I), Formula (II), Equation (III);

[0111] In formulas (I) and (II), R1, R2, R3 and R4 each independently comprise a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C3 alkyl group or a substituted or unsubstituted C1-C3 alkoxy group, and at least one of R1, R2, R3 and R4 comprises a fluorine atom, and when substituted, the substituent comprises a fluorine atom.

[0112] In formula (III), R5 comprises a single bond, substituted or unsubstituted C1-C3 alkyl group, and if substituted, the substituent comprises a fluorine atom, and p is selected from a positive integer between 1 and 3.

[0113] n is selected from positive integers between 1,000 and 30,000.

[0114] In some embodiments, R1, R2, R3 and R4 each independently comprise a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C2 alkyl group or a substituted or unsubstituted C1-C2 alkoxy group, and at least one of R1, R2, R3 and R4 comprises a fluorine atom.

[0115] In some embodiments, R1, R2, R3 and R4 each independently comprise a hydrogen atom, a fluorine atom, a chlorine atom, a methyl group, a fluoromethyl group, a methoxy group, or a perfluoromethoxy group.

[0116] In some embodiments, the polymer comprises at least one of the structural units represented by formula (I-11) from the structural unit represented by formula (I-1).

[0117] Equation (I-1), Equation (I-2), Equation (I-3),

[0118] Equation (I-4), Equation (I-5), Equation (I-6),

[0119] Formula (I-7), Formula (I-8), Formula (I-9),

[0120] Formula (I-10), Equation (I-11).

[0121] Optionally, the polymer comprises at least two of the structural units represented by Formula (I-11) from the structural unit represented by Formula (I-1).

[0122] In some embodiments, the polymer comprises at least one of the structural units represented by Formula (II-5) from the structural unit represented by Formula (II-1).

[0123] Equation (II-1), Formula (II-2),

[0124] Equation (II-3), Formula (II-4),

[0125] Formula (II-5).

[0126] In some embodiments, the polymer comprises at least one of the structural units represented by Formula (III-3) from the structural unit represented by Formula (III-1).

[0127] Equation (III-1), Equation (III-2),

[0128] Equation (III-3).

[0129] For example, the polymer comprises one or more of polyperfluoroethylene PTFE, polyvinylidene fluoride PVDF, perfluoroethylene propylene copolymer FEP, perfluoroalkoxy polymer PFA, perfluoropolyether PFPE, polyvinylidene fluoride-hexafluoropropylene copolymer PVDF-HFP, polyvinylidene trifluoroethylene copolymer PVDF-TrFE, and perfluoro(1-butenyl vinyl ether) polymer (abbreviated as CYTOP).

[0130] Optionally, the polymer comprises one or more of polyperfluoroethylene PTFE, polyvinylidene fluoride PVDF, perfluoroethylene propylene copolymer FEP, polyvinylidene fluoride-hexafluoropropylene copolymer PVDF-HFP, and polyvinylidene trifluoroethylene copolymer PVDF-TrFE.

[0131] The polymer may be derived from one or more types of monomers selected from fluorocycloethane, fluoroethylene, 1,2-difluoroethylene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, 3,3,3-trifluoropropylene, trifluoropropylene, tetrafluoropropylene, and pentafluoropropylene. Optionally, the polymer may be derived from at least two types of monomers selected from fluorocycloethane, fluoroethylene, 1,2-difluoroethylene, vinylidene fluoride, trifluoroethylene, trifluoroethylene chloride, tetrafluoroethylene, hexafluoropropylene, 3,3,3-trifluoropropylene, trifluoropropylene, tetrafluoropropylene, and pentafluoropropylene.

[0132] All monomers used in the above polymer are short-chain monomers, which are advantageous for polymerizing to form a straight-chain linear structure or a short-branched-chain structure. These structural types have a low degree of entanglement, which is advantageous for improving the flexibility of the molecular chains. Since the molecular chains can be fully stretched in the electrolyte, the wetting performance of the electrolyte for the active material can be further improved, and the interfacial performance of the active material can be improved.

[0133] The atomic groups of the polymer of the present application can be detected by an infrared spectrophotometer (IR); specifically, the polymer is measured using a Thermo Nicolet Nexus 670 attenuated total reflection Fourier transform infrared spectrometer (FTIR-ATR) and the measurement range is determined by referring to the standard GB / T6040-2002, with an ATR method of 600–4000 cm⁻¹. -1 ; Repeatability: ±2cm -1 ; Resolution: 4cm -1 Superior; penetration depth is 0.2~0.6μm.

[0134] The structure of the polymer of the present application can be measured by nuclear magnetic resonance NMR, specifically using 1H NMR and 13C NMR on a Varian Mercury Plus-400 nuclear magnetic resonance instrument, with a measurement temperature of 20℃, using TMS as an internal standard and CDCl3 as a solvent, and a proton resonance frequency of 400MHz.

[0135] In some embodiments, n is selected from a positive integer between 5000 and 20000.

[0136] In some embodiments, the molecular weight of the polymer is 2×10 5 g / mol~1.5×10 6 It is g / mol.

[0137] When the molecular weight of the polymer is within the above range, it is possible to ensure that the polymer exhibits a constant solubility in the electrolyte. At the same time, since it is not easily completely dissolved and dispersed by the electrolyte, it helps control the distribution and dispersion of the polymer on the surface of the active material. Furthermore, by allowing the electrolyte to infiltrate the active material layer uniformly, the liquid absorption rate of the entire active material layer is increased, thereby improving the cycle performance of the battery cell adopting the electrode sheet. Moreover, the flexibility between the molecular chains of the polymer can be further enhanced. Since the forces between the molecular chains are relatively weak, solvent molecules in the electrolyte open the molecular chains and enter between them, enveloping them. This facilitates the entry of active ions into the active material through the solvent, thereby enabling the smooth and rapid movement of active ions. For example, the molecular weight of the polymer is 2×10⁻⁶. 5 g / mol, 5×10 5 g / mol, 8×10 5 g / mol, 1×10 6 g / mol, 1.5×10 6 It may be a range consisting of g / mol or any two of the above values.

[0138] The molecular weight of the polymer is a well-known meaning in the industry and can be measured using equipment and methods commonly used in the industry, and can be measured using gel permeation chromatography (GPC). The specific measurement steps are as follows: Take an appropriate amount of the sample to be tested (the sample concentration should ensure a light blocking degree of 8% to 12%), add 20 ml of deionized water, and simultaneously apply external ultrasound to the sample for 5 minutes (53 KHz / 120 W) to ensure the sample is completely dispersed, and then measure the sample according to the GB / T19077-2016 / ISO 13320:2009 standard.

[0139] Alternatively, measurements can be performed using a multi-angle laser light scattering system (MALLS). Specifically, measurements were carried out using an instrument (Wyatt Technology Corporation, USA) combining a GPC and a Dawn Heleos II type multi-angle laser light scattering device, an Optilab T-rEX refractive index (RI) detector, and a Visco Star II type viscometer. Measurements were performed using tetrahydrofuran as the flow phase at a flow rate of 1.0 ml / min at 30°, and the SEC-SAMLL data was processed using the commercial software ASTRA6 to obtain molecular weight parameters.

[0140] As a result of further research, the inventors discovered that the cycle performance of the battery cell can be further improved when the polymer satisfies one or more of the following conditions.

[0141] In some embodiments, the polymer is added to a first solvent at a first temperature to form a polymer system; the polymer system is left standing at the first temperature for 8 hours and then left standing at a second temperature for 24 hours or more, after undergoing two stages of standing treatment, the polymer system is converted in situ into a gel-state material partially or wholly, and then the polymer system is filtered through a 200 mesh screen to leave a first material, wherein the first temperature is greater than the second temperature; the mass of the polymer is n and the unit is g; the mass of the first material is m and the unit is g; the polymer and the first material satisfy 5≤m / n≤1000; optionally, 10≤m / n≤1000; more optionally, 10≤m / n≤50. For example, m / n may be a range consisting of 5, 10, 20, 25, 28, 30, 32, 35, 40, 50, 80, 100, 200, 500, 1000 or any two of the above values.

[0142] For example, based on the mass of the polymer system, the ratio range of the mass content of the polymer to the mass content of the first solvent is 1:100 to 1:10, and for example, 3:50.

[0143] For example, the first solvent is identical or similar to the solvent of the electrolyte, and the first solvent may include a carbonate-based solvent. For example, the carbonate-based solvent includes a cyclic carbonate solvent and / or a linear carbonate solvent.

[0144] As examples of cyclic carbonate solvents, cyclic carbonate solvents include one or more of ethylene carbonate EC, vinylene carbonate VC, fluoroethylene carbonate FEC, difluoroethylene carbonate DFEC, vinylethylene carbonate VEC, and dioctyl carbonate CC.

[0145] As examples of linear carbonate solvents, linear carbonate solvents include one or more of dimethyl carbonate DMC, diethyl carbonate DEC, methyl ethyl carbonate EMC, diphenyl carbonate DPC, methylallyl carbonate MAC, and polycarbonate VA.

[0146] Optionally, the first solvent may additionally contain a lithium salt and an electrolyte additive such as lithium hexafluorophosphate, vinylene carbonate VC, fluorovinylene carbonate FEC, etc.

[0147] In this application, m / n is also referred to as a precipitation value indicating the ability of a polymer and a solvent to convert into a gel-state material.

[0148] The first material comprises a gel-state material formed mainly by a polymer and a first solvent, and in this type of gel-state material, the molecular structure of the polymer does not substantially change.

[0149] In some embodiments, the first material is dried at 80°C for 12 hours to remove the first solvent from the first material, which is detected by infrared spectrophotometry IR or measured by nuclear magnetic resonance NMR, and after drying, the main component of the first material is a polymer as described above.

[0150] In the present application, the glass transition temperature of the polymer ≤ first temperature ≤ melting temperature of the polymer, and the first temperature is the normal operating temperature of the battery cell.

[0151] The first temperature is greater than the second temperature, and the first temperature and the second temperature can be set to a safe operating temperature range of the battery cell. For example, the first temperature may be 60°C to 80°C, for example, 70°C, and the second temperature may be -30°C to 30°C, for example, 25°C. That is, the first temperature is a high operating temperature of the battery cell, and the second temperature is close to room temperature or low temperature.

[0152] The present application can achieve elongation of polymer molecular chains within a safe operating temperature range of the battery cell by increasing the temperature, and can improve liquid absorption capacity by promoting mutual attraction and physical bonding between the polymer molecular chains and the solvent. The activity of the polymer molecular chain segments decreases at room temperature and remains attached to the surface of the active material, locking the electrolyte in the spatial environment where the polymer is located and forming a state similar to an in-situ gel, thereby improving the ability to lock the liquid and improving cycle performance.

[0153] [Straight Play Sheet]

[0154] The above positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material and a polymer. In the present application, the polymer comprises a polymer as described above.

[0155] For example, the positive electrode current collector has two surfaces facing each other in the direction of its own thickness, and a positive electrode active material layer is disposed on one or both of the two facing surfaces of the positive electrode current collector.

[0156] In some embodiments, 1.00 <v / λ<4.00; 선택적으로, 1.20≤v / λ≤3.80; 더 선택적으로, 1.4≤v / λ≤3.6이다. 예시적으로, v / λ는 1.20, 1.40, 1.80, 2.00, 2.50, 3.00, 3.50, 3.60, 3.80, 3.90 또는 위의 임의의 두 값으로 구성된 범위일일 수 있다.

[0157] In some embodiments, the mass percentage of the polymer based on the mass of the positive electrode active material layer is A%, where 0.1≤A≤1.5.

[0158] When the mass percentage of the polymer is within the above range, the liquid absorption capacity of the positive electrode active material layer can be significantly improved. For example, the mass percentage (A%) of the polymer may be in a range consisting of 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, or any two of the above values.

[0159] The above positive electrode active material layer comprises a positive electrode active material, and the positive electrode active material may be a positive electrode active material for a battery cell known in the art. For example, the positive electrode active material may include at least one type of layered positive electrode active material (e.g., ternary, lithium nickelate / sodium, lithium cobaltate / sodium, lithium manganate / sodium, lithium-rich / sodium layered and rock salt layered materials), olivine-type phosphate active material, and spinel-structured positive electrode active material (e.g., spinel lithium manganate, spinel nickel-manganate, lithium-rich spinel lithium manganate, nickel-manganate, etc.).

[0160] For example, the general formula of a layered positive electrode active material is as follows: Li x A y Ni a Co b Mn c M (1-a-b~C) Y zAnd, where, 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 also 0.1≤a+b+c≤1; 1.8≤z≤3.5; A is one or more selected from Na, K, and Mg; M is one or more selected from 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; and Y is one or more selected from O and F. Optionally, Y=0. Specifically, the layered positive electrode active material is lithium cobaltate LCO, lithium nickelate LNO, lithium manganate LMO, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811) and LiNi 0.5 Co 0.2 Mn 0.3 It may include one or more types of O2(NCM523).

[0161] For example, the general formula of an olivine-type phosphate active substance is Li x A y Me a M b P 1-C X c Y zAnd, where, 0≤x≤1.3, 0≤y≤1.3, also 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, also 0.9≤a+b≤1.5; 0≤c≤0.5, 3≤z≤5; A is one or more selected from Na, K, Mg; Me is one or more selected from Mn, Fe, Co, Ni; M is one or more selected from 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, Ce; X is one or more selected from S, Si, Cl, B, C, N; Y is one or more selected from O, F. Specifically, the olivine-type phosphate active material includes one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0162] For example, the general formula of a spinel-structured positive electrode active material is Li x A y Mn a M 2-a Y z And, where, 0≤x≤2, 0≤y≤1, and also 0.9≤x+y≤2; 0.5≤a≤2; 3≤z≤5; A is one or more selected from Na, K, and Mg; M is one or more selected from Ni, Co, 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; and Y is one or more selected from O and F. Specifically, the positive electrode active material of the spinel structure is LiMn2O4, LiNi 0.5 Mn 1.5 O4, LiCr 0.3 Mn 1.7 O4, Li1.1 Al 0.1 Mn 1.9 O4, Li2Mn2O4 and Li 1.5 It includes one or more types of Mn2O4.

[0163] In some embodiments, the positive electrode current collector may use a metal foil or a composite current collector. As an example of the metal foil, an aluminum foil or an aluminum alloy foil may be used. The composite current collector may include a base layer of a polymer material and a metal material layer formed on at least one surface of the base layer of the polymer material, wherein, as an example, the metal material may include one or a combination of several types selected from aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, and the base layer of the polymer material may include one or a combination of several types selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0164] In some embodiments, the positive electrode active material layer optionally further comprises a positive electrode conductive agent. The present application does not particularly limit the type of positive electrode conductive agent, and as an example, the positive electrode conductive agent comprises one or a combination of several types 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 5% or less based on the total mass of the positive electrode active material layer.

[0165] In some embodiments, the positive electrode active material layer further comprises a positive electrode binder as an option. The present application does not particularly limit the type of positive electrode binder, and as an example, the positive electrode binder may comprise one type or a combination of several types selected from polyvinylidene fluoride (PVDF). In some embodiments, the mass percentage of the positive electrode binder is 5% or less based on the total mass of the positive electrode active material layer. The degree of crystallization of the positive electrode binder is higher than the degree of crystallization of the polymer described earlier in the present application, and the melting temperature of the positive electrode binder is higher than the melting temperature of the polymer described earlier in the present application.

[0166] The positive electrode active material layer is generally formed by coating a positive electrode slurry onto a positive electrode current collector, drying, and cold rolling. The positive electrode slurry is generally formed by dispersing the positive electrode active material, the polymer, an optional conductive agent, an optional positive electrode binder, and other components in a solvent and mixing them uniformly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.

[0167] [Polar Sheet]

[0168] The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, and the negative electrode active material layer comprises a negative electrode active material and a polymer. In this application, the polymer comprises a polymer as described above.

[0169] For example, the negative current collector has two surfaces facing each other in the direction of its thickness, and a negative active material layer is disposed on one or both of the two facing surfaces of the negative current collector.

[0170] In some embodiments, 3.00 <v / λ<50.00; 선택적으로, 3.40≤v / λ≤30.00이다. 예시적으로, v / λ는 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 또는 위의 임의의 두 값으로 구성된 범위일일 수 있다.

[0171] In some embodiments, the mass percentage of the polymer is B% based on the mass of the negative electrode active material layer; where 0.2 ≤ B ≤ 5.0. When the mass percentage of the 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 of the polymer (B%) may be a range consisting of 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 any two of the above values.

[0172] In some embodiments, the negative electrode current collector may use a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a base layer of a polymer material and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material substrate (e.g., a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0173] In some embodiments, the negative electrode active material may be a negative electrode active material for batteries known in the art. As an example, the negative electrode active material may include at least one type of material selected from artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be at least one type selected from elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be at least one type selected from elemental tin, tin oxide, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. Such negative electrode active materials may be used individually or in combination of two or more.

[0174] In some embodiments, the negative electrode active material layer further comprises a negative electrode binder as an option. The negative electrode binder may be at least one selected from styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The degree of crystallization of the negative electrode binder is higher than the degree of crystallization of the polymer described earlier in this application, and the melting temperature of the negative electrode binder is higher than the melting temperature of the polymer described earlier in this application.

[0175] In some embodiments, the negative electrode active material layer optionally further comprises a conductive agent. The conductive agent may be at least one type selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0176] In some embodiments, the negative electrode active material layer may optionally include other auxiliary agents, such as a thickener (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0177] In some embodiments, a negative electrode sheet can be manufactured in the following manner. A negative electrode slurry is formed by dispersing, for example, a negative electrode active material, the polymer, a conductive agent, a negative electrode binder, and any other components used to manufacture the negative electrode sheet in a solvent (e.g., deionized water); and after coating the negative electrode slurry onto a negative electrode current collector, a negative electrode sheet can be obtained after undergoing processes such as drying and cold rolling.

[0178] battery cell

[0179] In a second aspect, the present application provides a battery cell, said battery cell comprising a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte. The battery cell may be a lithium-ion battery, etc.

[0180] In some embodiments, the positive electrode sheet may use a positive electrode sheet of any embodiment of the first aspect of the present application, thereby improving the cycle performance of the battery cell. The negative electrode sheet may use a conventional electrode sheet.

[0181] In some embodiments, the negative electrode sheet may use a negative electrode sheet of any embodiment of the first aspect of the present application, thereby improving the cycle performance of the battery cell. The positive electrode sheet may use a conventional electrode sheet.

[0182] In some embodiments, the positive electrode sheet may use a positive electrode sheet of any embodiment of the first aspect of the present application, and the negative electrode sheet may use a negative electrode sheet of any embodiment of the first aspect of the present application, thereby improving the cycle performance of the battery cell.

[0183] [Electrolyte]

[0184] The battery cell further comprises an electrolyte, which acts as an ion conductor between the positive electrode sheet and the negative electrode sheet. The present application does not specifically limit the type of electrolyte and may be selected as necessary. For example, the electrolyte may be a liquid, a gel, or all solid.

[0185] In some embodiments, the electrolyte uses an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0186] As an example, the lithium salt may include one or a combination of several types selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluorocenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate phosphate (LiDFOB), lithium bisoxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0187] As an example, the organic solvent may include one or a combination of several types selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0188] In some embodiments, the electrolyte further includes additives as an option. For example, the additives may include negative electrode film-forming additives and positive electrode film-forming additives, and may further include additives that can improve some performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high or low temperature performance of the battery, etc.

[0189] [Separator]

[0190] In some embodiments, the battery cell further comprises a separator. The present application does not particularly limit the type of separator, and any known porous separator having good chemical and mechanical stability may be selected and used.

[0191] In some embodiments, the material of the separator may include one or a combination of several types selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film. If the separator is a multilayer composite film, the material of each layer may be the same or different.

[0192] In some embodiments, the positive electrode sheet, separator, and negative electrode sheet may be manufactured into an electrode assembly through a winding process or a lamination process.

[0193] The present application does not specifically limit the shape of the battery cell, and it may be cylindrical, square, or any other shape. FIG. 1 illustrates a square battery cell (5) as an example.

[0194] In some embodiments, as illustrated in FIGS. 1 and 2, the outer packaging may include a case (51) and a cover plate (53). Here, the case (51) may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate surround to form a receiving cavity. The case (51) has an opening communicating with the receiving cavity, and the cover plate (53) covers the opening to seal the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator undergo a winding process or a lamination process to form an electrode assembly (52). The electrode assembly (52) is packaged within the receiving cavity. An electrolyte is infiltrated into the electrode assembly (52). The number of electrode assemblies (52) included in the battery cell (5) may be one or multiple, and this can be adjusted as needed.

[0195] The method for manufacturing the battery cell of the present application is known. In some embodiments, a battery cell may be formed by assembling a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. As an example, the positive electrode sheet, the separator, and the negative electrode sheet undergo a winding process or a lamination process to form an electrode assembly, the electrode assembly is placed in an outer package and dried, an electrolyte is injected, and a battery cell is obtained through processes such as vacuum packaging, settling, formation, and molding.

[0196] In some embodiments of the present application, the battery cells of the present application may be assembled into a battery module, and the number of battery cells included in the battery module may be multiple, and the specific number may be adjusted according to the application and capacity of the battery module.

[0197] FIG. 3 is a schematic diagram of a battery module (4) as an example. As shown in FIG. 3, in the battery module (4), a plurality of battery cells (5) may be arranged sequentially along the length direction of the battery module (4). Of course, they may also be arranged in any other arbitrary manner. In addition, the plurality of battery cells (5) may be secured through a fastener.

[0198] Optionally, the battery module (4) may further include a housing having a receiving space, and a plurality of battery cells (5) are received in the receiving space.

[0199] In some embodiments, the battery module may also be assembled into a battery pack, and the number of battery modules included in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0200] FIGS. 4 and 5 are schematic diagrams of a battery pack (1) as an example. As illustrated in FIGS. 4 and 5, the battery pack (1) may include a battery box and a plurality of battery modules (4) disposed within the battery box. The battery box includes an upper box body (2) and a lower box body (3), wherein the upper box body (2) covers the lower box body (3) to form a sealed space for accommodating the battery modules (4). The plurality of battery modules (4) may be arranged within the battery box in any manner.

[0201] Battery modules and battery packs can both be cited as examples of the battery of the present application.

[0202] electrical device

[0203] In a fifth aspect, the present application provides an electric device, wherein the electric device comprises at least one type of the battery cell, battery module, or battery pack of the present application. The battery cell, battery module, or battery pack may be used as a power source for the electric device or as an energy storage unit for the electric device. The electric device may be, but is not limited to, a mobile device (e.g., mobile phone, laptop computer, etc.), an electric vehicle (e.g., pure electric vehicle, hybrid electric vehicle, plug-in hybrid electric vehicle, electric bicycle, electric scooter, electric golf cart, electric truck, etc.), an electric train, a ship and satellite, an energy storage system, etc.

[0204] The electric device may select a battery cell, a battery module, or a battery pack depending on the usage needs. FIG. 6 is a schematic diagram of an electric device as an example. The electric device (6) is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To satisfy the requirements of the electric device for high power and high energy density, a battery pack (1) or a battery module may be used. Another example of an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. The electric device should generally be thin and light, and may use a battery cell as a power source.

[0205] Examples

[0206] The following describes embodiments of the present application. The embodiments described below are illustrative and are intended for use only in interpreting the present application and should not be construed as a limitation thereof. Where specific technical or conditional descriptions are not specified in the embodiments, they should be performed in accordance with technical or conditional descriptions in the literature of the art or in the product description. Unless otherwise indicated by the manufacturer, the reagents or equipment used are all commercially available generic products.

[0207] Example 1

[0208] (1) Manufacturing of positive electrode sheet

[0209] An aluminum foil with a thickness of 12㎛ is used as the positive electrode current collector.

[0210] A positive electrode slurry is prepared using a fluoropolymer, LiFePO4 as a positive electrode active material, carbon black as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone (NMP). The mass ratio of the fluoropolymer, LiFePO4, conductive carbon black, PVDF, and N-methylpyrrolidone (NMP) in the positive electrode slurry is 0.5:96.8:2:0.7:29. The positive electrode slurry is coated onto an aluminum foil current collector, dried at 85°C, then cold-rolled to cut the edges, cut into sheets, slit, and then dried under vacuum at 85°C for 4 hours to produce a positive electrode sheet.

[0211] (2) Manufacture of negative electrode sheet

[0212] A copper foil with a thickness of 8㎛ is used as the negative electrode current collector.

[0213] A negative electrode slurry is prepared by uniformly mixing a fluoropolymer, artificial graphite as a negative electrode active material, carbon black as a conductive agent, styrene butadiene rubber (SBR) as a binder, sodium carboxymethylcellulose (CMC) as a thickener, and deionized water in a weight ratio of 2.5:94:0.5:2:1:100. The negative electrode slurry is coated onto a copper foil as a current collector and dried at 85°C, then cold-rolled, edge-cut, cut into a sheet, slit, and dried under vacuum at 120°C for 12 hours to produce a negative electrode sheet.

[0214] (3) Preparation of electrolyte

[0215] In an environment with a water content of less than 10 ppm, an electrolyte solvent is obtained by mixing non-aqueous organic solvents, ethylene carbonate EC and methyl ethyl carbonate (EMC), in a volume ratio of 3:7, and then a lithium salt LiPF6 is mixed with the solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0216] (4) Manufacturing of lithium-ion batteries

[0217] A 16 μm polyethylene film (PE) is used as a separator. The positive electrode sheet, separator, and negative electrode sheet are laminated in sequence so that the separator acts as an isolation agent between the positive electrode sheet and the negative electrode sheet, and then wound to obtain an electrode assembly. The electrode assembly is placed in an outer packaging shell, dried, and then an electrolyte is injected. A lithium-ion battery is obtained through processes such as vacuum packaging, settling, formation, and molding.

[0218] Comparative Example 1

[0219] A lithium-ion battery was manufactured using a method similar to that of Example 1, but the difference from Example 1 is that polyvinylidene fluoride (PVDF, crystallinity 48%, melting point 164°C), which is a binder, is added to the positive electrode sheet of Comparative Example 1 and no other fluoropolymer is added, and styrene butadiene rubber, which is a binder, is added to the negative electrode sheet of Comparative Example 1 and no fluoropolymer is added.

[0220] Comparative Example 2

[0221] A lithium-ion battery was manufactured using a method similar to that of Example 1, but the difference from Example 1 is that the materials of the positive and negative electrode sheets of Comparative Example 2 are replaced with fluoropolymer.

[0222] Examples 2 to 4

[0223] The lithium-ion battery was manufactured in a manner similar to Example 1, but the difference from Example 1 is that the material of the positive electrode sheet and the negative electrode sheet in Examples 2 to 4 is replaced with a fluoropolymer.

[0224] Examples 5 to 7

[0225] The lithium-ion battery was manufactured using a method similar to that of Example 1, but the difference from Example 1 is that the content of the fluoropolymer in the positive electrode sheet of Examples 5 to 7 is adjusted.

[0226] Examples 8 to 10

[0227] The lithium-ion battery was manufactured using a method similar to that of Example 1, but the difference from Example 1 is that the content of the fluoropolymer in the negative electrode sheet of Examples 8 to 10 is adjusted.

[0228] The data for the examples and comparative examples are as shown in Table 1.

[0229] Measurement part

[0230] 1. Measurement of lithium-ion battery capacity maintenance

[0231] The lithium-ion battery prepared in the examples and comparative examples is charged to 4.25V with a full current of 1C in a room temperature environment, then charged to 0.05C with a constant voltage of 4.25V, left for 5 minutes, and then discharged to 2.8V with 1C, and the resulting capacity is recorded as the initial capacity C0. The above steps are repeated for the same battery, and the discharge capacity Cn of the battery after the nth cycle is recorded simultaneously. The battery capacity retention rate Pn after each cycle is Pn = Cn / C0 * 100%, and a point graph of the battery capacity retention rate and the number of cycles is plotted with the 1200 point values ​​of P1, P2......P1200 as the vertical coordinate and the corresponding number of cycles as the horizontal coordinate.

[0232] In this measurement process, the first cycle corresponds to n=1, the second cycle to n=2, ...... the 1200th cycle to n=1200. For example, the battery capacity retention rate data corresponding to Example 1 in Table 1 is the data measured after 1200 cycles under the above measurement conditions, i.e., the value of P1200. The measurement procedure for Comparative Example 1 and other examples is the same as above.

[0233] 2. Measurement of DC Impedance of Lithium-Ion Batteries

[0234] The lithium-ion battery prepared in the examples and comparative examples is charged to 4.25V at 25°C with a constant current of 1 / 3C, then charged to a constant voltage of 4.25V until the current becomes 0.05C, left for 5 minutes, and then the voltage V1 is recorded. Then, after discharging at 1 / 3C for 30 seconds, the voltage V2 is recorded, which is (V2-V1) / 1 / 3C, and the internal resistance DCR1 of the battery after the first cycle is obtained. The above steps are repeated for the same battery, and the internal resistance DCRn (n=1, 2, 3......1200) of the battery after the nth cycle is recorded simultaneously. The 1200 point values ​​of DCR1, DCR2, DCR3....... DCR1200 are set as the vertical coordinate, and the corresponding number of cycles is set as the horizontal coordinate to obtain a graph of the battery discharge DCIR and the number of cycles corresponding to the polymers of the examples and comparative examples.

[0235] In this measurement process, the first cycle corresponds to n=1, the second cycle to n=2, ..., the 1200th cycle to n=1200. For example, the increase ratio of the battery internal resistance of Example 1 in Table 1 is (DCRn-DCR1) / DCR1*100%, and the measurement procedure for Comparative Example 1 and other examples is the same as above. The data in Table 1 is the data measured after 1200 cycles under the above measurement conditions.

[0236] Measurement results

[0237] Table 1

[0238]

[0239] In Table 1, VDF represents vinylidene fluoride, HFP represents hexafluoropropylene, and TFE represents tetrafluoroethylene, where 90% VDF means that the molar ratio of VDF is 90% based on the total molar amount of VDF and HFP, and 10% FEP means that the molar ratio of FEP is 10%.

[0240] As can be seen from Table 1, compared to Comparative Example 1, the embodiment of the present application adds the fluoropolymer of the present application to the positive electrode sheet and / or negative electrode sheet, and the fluoropolymer can form uniform high-wetting points within the active material layer, thereby uniformly improving the wetting performance of the active material layer and increasing the overall liquid absorption rate of the active material layer, which can improve the cycle performance of the battery cell using the electrode sheet.

[0241] Compared to Comparative Example 2, the embodiment of the present application can significantly improve the cycle performance of a lithium-ion battery when v / λ > 1 is satisfied.

[0242] Although this application has been described with reference to preferred embodiments, various improvements may be made without departing from the scope of this application, and equivalents may replace any parts thereof. In particular, each technical feature mentioned in each embodiment may be combined in any way, 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. Explanation of the symbols

[0243] 1: Battery pack; 2: Upper box body; 3: Lower box body; 4: Battery module; 5: Battery cell; 51: Case; 52: Electrode assembly; 53: Cover plate; 6: Electrical device.

Claims

Claim 1 An electrode sheet comprises a current collector and an active material layer disposed on at least one surface of the current collector, wherein the active material layer comprises an active material and a polymer, and the active material layer satisfies Equations (1) to (3). Equation (1) Equation (2) v / λ > 1.00 Equation (3) In Equations (1) to (3), λ represents the porosity of the active material layer; P1 represents the actual compressive density of the active material layer, and the unit is g / cm² 3 ..., and the actual compressed density represents the ratio of the mass to the thickness of the active material layer per unit area of ​​the electrode sheet; P2 represents the true compressed density of the active material, and the unit is g / cm³ 3 ..., and the true compressive density represents the density of the active material itself in the active material layer; v represents the liquid absorption rate of the active material layer, with a unit of mg / s; d represents the diameter of the capillary in the capillary test of the active material layer, with a unit of mm; h represents the height of the liquid level inside the capillary, with a unit of mm; and ρ represents the density of the electrolyte in the capillary test, with a unit of g / cm³ 3 t represents the time during which the electrolyte is absorbed into the capillary, the unit is s, and the polymer comprises at least one of the structural units represented by Formula (III-3) and the structural unit represented by Formula (III-1), an electrode sheet. Equation (III-1) Equation (III-2) Equation (III-3) Claim 2 In claim 1, the active material comprises a positive electrode active material, and the active material layer is 1.00 <v / λ<4.00를 만족시키는, 전극 시트. Claim 3 In claim 1, the active material comprises a positive electrode active material, and based on the mass of the active material layer, the mass percentage of the polymer is A%; wherein 0.1 ≤ A ≤ 1.5, an electrode sheet. Claim 4 In claim 1, the active material comprises a negative electrode active material, and the active material layer is 3.00 <v / λ<50.00을 만족시키는, 전극 시트. Claim 5 An electrode sheet according to claim 1, wherein the active material comprises a negative electrode active material, and the mass percentage of the polymer is B% based on the mass of the active material layer; wherein 0.2 ≤ B ≤ 5.

0. Claim 6 In any one of claims 1 to 5, the degree of crystallization of the polymer measured by differential scanning calorimetry is X C % and 0 <X C ≤30; the melting temperature of the polymer is Tm, the unit is °C, and 0 <Tm≤140인, 전극 시트. Claim 7 An electrode sheet according to any one of claims 1 to 5, wherein the glass transition temperature of the polymer is Tg, the unit is °C, and -150≤Tg≤60. Claim 8 In any one of claims 1 to 5, the polymer further comprises at least one of the structural unit represented by formula (I) and the structural unit represented by formula (II), and Equation (I) Formula (II) in Formulas (I) and (II), wherein R1, R2, R3 and R4 each independently comprise a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C3 alkyl group or a substituted or unsubstituted C1-C3 alkoxy group, at least one of R1, R2, R3 and R4 comprises a fluorine atom, and when substituted, the substituent comprises a fluorine atom; n is selected from a positive integer of 1000 to 30000, electrode sheet. Claim 9 An electrode sheet according to any one of claims 1 to 5, wherein the polymer comprises at least one of the structural units represented by formula (I-1) and the structural unit represented by formula (I-11). Equation (I-1) Equation (I-2) Equation (I-3) Equation (I-4) Equation (I-5) Equation (I-6) Formula (I-7) Formula (I-8) Formula (I-9) Formula (I-10) Equation (I-11) Claim 10 An electrode sheet according to any one of claims 1 to 5, wherein the polymer further comprises at least one structural unit from the structural unit represented by formula (II-1) to the structural unit represented by formula (II-5). Equation (II-1) Formula (II-2) Equation (II-3) Equation (II-4) Formula (II-5) Claim 11 In claim 8, n is selected from a positive integer of 5,000 to 20,000; and / or the molecular weight of the polymer is 2×10 5 g / mol~1.5×10 6 Electrode sheet, g / mol. Claim 12 A battery cell comprising an electrode sheet according to any one of claims 1 to 5. Claim 13 A battery comprising a battery cell according to claim 12. Claim 14 An electric device comprising a battery according to paragraph 13. Claim 15 delete

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