Polymer, electrode sheet, and related battery cells, batteries, and power consumption devices

Abstract

The present application provides a polymer, an electrode sheet, and a battery cell, a battery, and a power consumption device related thereto. The polymer includes a fluoropolymer, and the fluoropolymer has a crystallinity measured by differential scanning calorimetry of X C %, where 0 < X C ≦ 30, the melting temperature of the fluoropolymer is Tm, the unit thereof is °C, and 0

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular, to polymers, electrode sheets, and related battery cells, batteries, and power consumption devices.

Background Art

[0002] Battery cells have characteristics such as high capacity and long life, and are therefore widely applied to electronic devices, such as mobile phones, notebook computers, electric scooters, electric vehicles, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and electric tools.

[0003] As the application range of batteries becomes increasingly wide, the requirements for the performance of battery cells are also becoming increasingly strict. In order to improve the safety performance of battery cells, it is common to optimize the performance of the electrode sheets in the battery cells. However, the interfacial performance of the active material in the current electrode sheets is poor, and when applied to battery cells, the cycle performance and storage performance of the battery cells deteriorate.

Summary of the Invention

[0004] The present application has been made in view of the above problems, and its object is to provide a polymer, an electrode sheet, and related battery cells, batteries, and power consumption devices.

[0005] A first aspect of the present application is a polymer applied to a battery cell, including a fluoropolymer, wherein the fluoropolymer has a crystallinity of X C % measured by differential scanning calorimetry, 0 < X C ≦30, and the melting temperature of the fluoropolymer is Tm, with the unit of °C, and 0 < Tm ≦ 140, to provide a polymer.

[0006] As a result, the polymer of the present application has a relatively low crystallinity and melting temperature, the arrangement of the molecular chains is sparse, the interaction force between the molecular chains is small, adjacent molecular chains are easy to open, and segmental motion is realized by intermolecular rotation, forming a molecular chain structure with high flexibility. When the polymer is applied to the electrode sheet of the battery cell, the electrode sheet includes an active material layer containing the polymer and the active material. Since the affinity between the polymer and the electrolyte in the battery cell is good, the solvent in the electrolyte quickly diffuses between the molecular chains of the polymer, is wrapped by the molecular chains, forms an in-situ gel on the surface of the active material, and can adhere to the surface of the active material to protect the active material. Thereby, the active material and the electrolyte can be closely linked, the solid-liquid interface performance can be improved, the side reaction between the active material and the electrolyte can be reduced, and the cycle performance and storage performance of the battery cell can be improved.

[0007] In some embodiments, the glass transition temperature of the fluoropolymer is Tg, the unit thereof is °C, and -150 ≤ Tg ≤ 60. The glass transition temperature of the polymer is relatively low, the flexibility of the segments of the molecular chains is better, adjacent molecular chains are easier to open, it is easier to form an in-situ gel on the surface of the active material, and the solid-liquid interface performance is improved.

[0008] In some embodiments, the fluoropolymer includes at least one of the structural units represented by formula (I) to the structural units represented by formula (III).

Chemical formula

[0009] In formula (I) and formula (II), R1, R2, R3 and R4 each independently include 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 includes a fluorine atom. When substituted, the substituent includes a fluorine atom. In formula (III), R5 includes a single bond, a substituted or unsubstituted C1-C3 alkyl group. When substituted, the substituent includes a fluorine atom. p is a positive integer from 1 to 3. n is a positive integer from 1000 to 30000.

[0010] In some embodiments, R1, R2, R3 and R4 each independently include 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 selectively, R1, R2, R3 and R4 each independently include a hydrogen atom, a fluorine atom, a chlorine atom, a methyl group, a fluoromethyl group, a methoxy group or a perfluoromethoxy group.

[0011] In some embodiments, the fluoropolymer includes at least one of the structural units represented by formula (I-1) to the structural units represented by formula (I-11).

Chemical formula

[0012] In some embodiments, the fluoropolymer includes at least one of the structural units represented by formula (II-1) to the structural units represented by formula (II-5).

Chemical formula

[0013] In some embodiments, the fluoropolymer includes at least one of the structural units represented by formula (III-1) to the structural units represented by formula (III-3).

Chemical formula

[0014] In some embodiments, n is a positive integer from 5000 to 20000, and / or the molecular weight of the polymer is 2×10 5 g / mol to 1.5×10 6 g / mol. When the molecular weight of the polymer is within the above range, the polymer exhibits a certain solubility in the electrolyte and is difficult to be completely dissolved and dispersed in the electrolyte, which is advantageous for adjusting the distribution and dispersion of the polymer on the surface of the active material. In addition, the flexibility between the molecular chains of the polymer can be further improved, the acting force between the molecular chains is relatively weak, and it is advantageous for the solvent molecules in the electrolyte to open the molecular chains and enter between the molecular chains and be wrapped by the molecular chains. Thereby, it is advantageous for active ions to enter the active material through the solvent and realize smooth and rapid movement of the active ions.

[0015] In some embodiments, the polymer is added to a first solvent at a first temperature to form a polymer system. The polymer system is allowed to stand for 8 hours at the first temperature and then for ≧24 hours at a second temperature. After that, the polymer system is filtered through a 200-mesh filter, leaving a first substance. Here, the first temperature is higher than the second temperature, the mass of the polymer is n, with the unit of g, the mass of the first substance is m, with the unit of g, and the polymer and the first substance satisfy 5≦m / n≦1000. After undergoing a two-stage standing treatment, the polymer can form an in-situ gel in the first solvent, locking the solvent molecules inside the polymer and reducing the content overflowing from the filter. When the polymer meets the above conditions, the polymer is likely to form an in-situ gel in the first solvent, lock the solvent molecules inside the polymer, improve the liquid holding capacity, and further improve the cycle performance and storage performance of the battery cell.

[0016] A second aspect of the present application provides a positive electrode sheet including a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material and a polymer, and the polymer includes the polymer described in any one of the embodiments of the first aspect of the present application.

[0017] A third aspect of the present application provides a negative electrode sheet including a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material and a polymer, and the polymer includes the polymer described in any one of the embodiments of the first aspect of the present application.

[0018] A fourth aspect of the present application provides a battery cell including a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet includes the positive electrode sheet described in any one of the embodiments of the second aspect of the present application, and / or the negative electrode sheet includes the negative electrode sheet described in any one of the embodiments of the third aspect of the present application.

[0019] A fifth aspect of the present application provides a battery including the battery cell described in the fourth aspect of the present application.

[0020] A sixth aspect of the present application provides a power consumption device including the battery described in the fifth aspect of the present application.

Brief Description of the Drawings

[0021] To more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required in the embodiments of the present application are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can also obtain other drawings based on these drawings without creative efforts. The drawings are not necessarily drawn to actual scale.

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Figure 6

Explanation of Signs

[0022] 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. Power consumption device

Modes for Carrying Out the Invention

[0023] Hereinafter, embodiments specifically disclosing the polymer, the electrode sheet, and the related battery cell, battery, and power consumption device of the present application will be described in detail. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and duplicate descriptions of substantially the same configurations may be omitted. This is to avoid making the following description unnecessarily redundant and to facilitate the understanding of those skilled in the art. It should be noted that the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0024] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A predetermined range is defined by selecting one lower limit and one upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range thus defined may be a range that includes or does not include the end 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 given for a particular parameter, ranges of 60-110 and 80-120 are also understood to be contemplated. Also, if the minimum range values 1 and 2 and the maximum range values 3, 4, and 5 are given, ranges of 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 may all be contemplated. In this application, unless otherwise stated, the numerical range "a~b" is represented as an abbreviation for any combination of real numbers between a and b, and both a and b are real numbers. For example, the numerical range "0~5" indicates all real numbers between "0~5" in this specification, and "0~5" is an abbreviation for the combination of these numerical values. Also, when a certain parameter is expressed as an integer of 2 or more (≧2), it corresponds to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0025] Unless otherwise specified, all embodiments and selectable embodiments of this application may be combined with each other to form a new technical solution. Unless otherwise specified, all technical features and selectable technical features of this application can be combined with each other to form a new technical solution.

[0026] Unless otherwise specified, all steps of this application may be performed in order or randomly, but it is preferred to be performed in order. For example, the fact that the above method includes steps (a) and (b) may mean that the above method includes steps (a) and (b) performed in order, or may include steps (b) and (a) performed in order. For example, when it is mentioned that the above method may further include step (c), it means that step (c) may be added to the above method in any order. For example, the above method may include steps (a), (b) and (c), may include steps (a), (c) and (b), may include steps (c), (a) and (b), etc.

[0027] Unless otherwise specified, the terms "comprise" and "include" described in this application are open-ended and may also be closed-ended. For example, the above "comprise" and the above "include" can represent further "comprising" or "including" other components not listed, or "comprising" or "including" only the components listed.

[0028] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" represents "A, B, or both A and B". More specifically, any of the following conditions is satisfied: 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).

[0029] In this application, the terms "a plurality" and "a plurality of types" mean two or more.

[0030] The term "alkyl group" includes linear and branched 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. Further, the alkyl group may be optionally substituted. The substituent includes a fluorine atom.

[0031] The term "alkoxy group" means a group in which an alkyl group and an oxygen atom are linked by a single bond. For example, the alkoxy group may be a C1-C5 alkoxy group, a C1-C3 alkoxy group, or a C1-C2 alkoxy group. In some embodiments, the alkoxy group may include a methoxy group, an ethoxy group, a propoxy group. Further, the alkoxy group may be optionally substituted.

[0032] The term "halogen atom" means a fluorine atom, a chlorine atom, a bromine atom, etc.

[0033] The term "hydrogen" means 1H (light hydrogen, H), 2H (deuterium, D), or 3H (tritium, T). In each embodiment, "hydrogen" may be 1H (light hydrogen, H).

[0034] The battery cell includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. There is a solid-liquid contact interface between the electrode sheet and the electrolyte, and side reactions may occur at this contact interface, which may deteriorate the performance of the battery cell. Taking the positive electrode sheet as an example, there is a solid-liquid contact interface between the positive electrode active material contained in the positive electrode sheet and the electrolyte. At this interface, the positive electrode active material undergoes a side reaction with the electrolyte, resulting in the loss of the positive electrode active material, the reduction of the cycle performance of the battery cell, and the generation of products unfavorable to the cycle of the battery cell due to side reactions, which may deteriorate the storage performance of the battery cell.

[0035] Therefore, from the point of improving the interfacial performance of the solid-liquid contact interface, the inventors improve the cycle performance and storage performance of the battery cell. When applied to the positive electrode sheet and / or the negative electrode sheet, the inventors can form an in-situ gel on the surface of the solid-phase active material, that is, form a stable solid-liquid interface on the surface of the active material to reduce the risk of side reactions at the solid-liquid interface, and provide a polymer that improves the cycle performance and storage performance of the battery cell. Polymer

[0036] According to a first aspect, the present application provides a polymer. The polymer is applied to a battery cell and contains a fluoropolymer, where the crystallinity of the fluoropolymer measured by differential scanning calorimetry is X C %, 0 < X C ≦ 30, the melting temperature of the fluoropolymer is Tm, the unit is °C, and 0 < Tm ≦ 140.

[0037] Crystallization refers to the process in which atoms, ions or molecules in a material are arranged in a certain spatial order to form a regular pattern. The conformation of the polymer in the crystal is determined by two factors, intramolecular and intermolecular. The intermolecular force affects the packing density between molecular chains. The crystallinity X C % is used to represent the degree of crystallization in the material and can be measured by differential scanning calorimetry DSC. Specifically, the test steps are as follows: 0.5 g to 0.8 g of the sample is adopted, the sample is placed in a crucible, and the sample is heated and cooled under a nitrogen gas atmosphere. The temperature is raised from an initial temperature 20 °C lower than the material-specific Tg to an off-temperature of a process 20 °C higher than the material-specific Tm at a heating rate of 10 °C / min. Based on the endothermic and exothermic peak values or transition points of the material in the process, the actual glass transition temperature Tg and melting temperature Tm of the material are determined.

[0038] In contrast to the fluorine-based polymers commonly used in conventional secondary batteries having relatively high crystallinity and melting temperature, the polymer has good resistance to liquid electrolytes, thereby effectively providing an effect of suppressing adhesion or repulsion of the active material over a long period during the use process of the battery. The fluorine-based polymer used in the present application has relatively low crystallinity and melting temperature, the arrangement of the molecular chains is sparse, the acting force between the molecular chains is small, adjacent molecular chains are easy to open, and segmental motion is realized by intermolecular rotation, forming a molecular chain structure with high flexibility.

[0039] When the polymer is applied to the electrode sheet of the battery cell, the electrode sheet includes an active material layer containing the polymer and the active material. Since the affinity between the polymer and the electrolyte in the battery cell is good, the solvent in the electrolyte quickly diffuses between the molecular chains of the polymer and is wrapped by the molecular chains, forming an in-situ gel on the surface of the active material, which can adhere to the surface of the active material to protect the active material. Thereby, the active material and the electrolyte can be closely linked, the solid-liquid interface performance can be improved, the side reaction between the active material and the electrolyte can be reduced, and the cycle performance and storage performance of the battery cell can be improved.

[0040] Exemplarily, the crystallinity X C % measured by differential scanning calorimetry of the fluoropolymer may be 5%, 10%, 15%, 20%, 25%, 30%, or a range consisting of any two of the above numerical values.

[0041] Exemplarily, the melting temperature of the fluoropolymer may be 10°C, 20°C, 50°C, 70°C, 90°C, 100°C, 120°C, 140°C, or a range consisting of any two of the above numerical values.

[0042] In some embodiments, the glass transition temperature of the fluoropolymer is Tg, the unit is °C, and -150 ≤ Tg ≤ 60.

[0043] The glass transition temperature is the temperature at which the segments of the polymer transition from freezing to movement. The glass transition temperature has a certain influence 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). The glass transition temperature of the polymer is relatively low, the segments of the molecular chain are more flexible, and the adjacent molecular chains are more likely to be opened. Exemplarily, the glass transition temperature of the fluoropolymer may be -150°C, -140°C, -120°C, -100°C, -80°C, -60°C, -30°C, 0°C, 30°C, 60°C, or a range consisting of any two of the above numerical values.

[0044] In some embodiments, the fluoropolymer includes at least one of the structural units represented by formula (I) to the structural units represented by formula (III).

Chemical formula

[0045] In formula (I) and formula (II), R1, R2, R3, and R4 each independently include 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 includes a fluorine atom. When substituted, the substituent includes a fluorine atom.

[0046] In formula (III), R5 includes a single bond, a substituted or unsubstituted C1-C3 alkyl group. When substituted, the substituent includes a fluorine atom.

[0047] p is a positive integer from 1 to 3.

[0048] n is a positive integer from 1000 to 30000.

[0049] In some embodiments, R1, R2, R3, and R4 each independently include 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 one of R1, R2, R3, and R4 includes a fluorine atom.

[0050] In some embodiments, R1, R2, R3, and R4 each independently include a hydrogen atom, a fluorine atom, a chlorine atom, a methyl group, a fluoromethyl group, a methoxy group, or a perfluoromethoxy group.

[0051] In some embodiments, the fluoropolymer includes at least one structural unit represented by formula (I-1) to formula (I-11). [Chemical formula]

[0052] Optionally, the fluoropolymer includes at least two structural units represented by formula (I-1) to formula (I-11).

[0053] In some embodiments, the fluoropolymer includes at least one structural unit represented by formula (II-1) to formula (II-5). [Chemical formula]

[0054] In some embodiments, the fluoropolymer includes at least one structural unit represented by formula (III-1) to formula (III-3). [Chemical formula]

[0055] Exemplarily, the fluoropolymer includes one or more of polyperfluoroalkyl 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 (abbreviated as CYTOP).

[0056] Optionally, the fluoropolymer includes one or more of polyperfluorovinyl PTFE, polyvinylidene fluoride PVDF, perfluoroethylene propylene copolymer FEP, polyvinylidene fluoride - hexafluoropropylene copolymer PVDF - HFP, polyvinylidene fluoride - trifluoroethylene copolymer PVDF - TrFE.

[0057] The above fluoropolymer may be derived from one or more of monomers such as fluorocycloethane, fluoroethylene, 1,2 - difluoroethylene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, 3,3,3 - trifluoropropene, trifluoropropene, tetrafluoropropene, and pentafluoropropene. Optionally, the above fluoropolymer may be derived from at least two of monomers such as fluorocycloethane, fluoroethylene, 1,2 - difluoroethylene, vinylidene fluoride, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, hexafluoropropylene, 3,3,3 - trifluoropropene, trifluoropropene, tetrafluoropropene, and pentafluoropropene.

[0058] All of the monomers used in the above fluoropolymer are short-chain monomers, which are advantageous for forming a linear straight-chain structure or a short-chain structure by polymerization. The degree of entanglement of this type of structural type is low, which improves the flexibility of the molecular chain, and the molecular chain can be fully expanded in the electrolyte, thereby further improving the interfacial performance of the active material.

[0059] The groups of the polymers of the present application can be detected using infrared spectrophotometry IR. Specifically, the polymers are tested with a total reflection absorption Fourier transform infrared spectrophotometer (FTIR-ATR) of Thermo Nicolet Nexus 670, and then the test is carried out with reference to the standard GB / T6040-2002. Test range: ATR method 600 - 4000cm -1 , Reproducibility: ±2cm -1 , Resolution: 4cm -1 , Penetration depth: 0.2 - 0.6μm.

[0060] The structure of the polymers of the present application can be measured using nuclear magnetic resonance NMR. Specifically, it is carried out with a Varian Mercury Plus-400 nuclear magnetic resonance apparatus using 1H NMR and 13C NMR. The measurement temperature is 20°C, TMS is the internal standard, CDCl3 is the solvent, and the proton resonance frequency is 400MHz.

[0061] In some embodiments, n is a positive integer from 5000 to 20000.

[0062] In some embodiments, the molecular weight of the polymer is 2×10 5 g / mol to 1.5×10 6 g / mol.

[0063] When the molecular weight of the polymer is within the above range, the polymer exhibits a certain solubility in the electrolyte and is difficult to be completely dissolved and dispersed in the electrolyte, which is advantageous for adjusting the distribution and dispersion of the polymer on the surface of the active material. In addition, the flexibility between the polymer molecular chains can be further improved, the interaction force between the molecular chains is relatively weak, and the solvent molecules in the electrolyte can open the molecular chains and enter between the molecular chains, which is advantageous for being wrapped by the molecular chains. Thereby, it is advantageous for active ions to enter the active material through the solvent to realize smooth and rapid movement of the active ions. Exemplarily, the molecular weight of the polymer is 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 numerical values may also be acceptable.

[0064] The molecular weight of the polymer has the meaning known in the art and can be measured using equipment and methods commonly used in the art, and can be tested by adopting gel permeation chromatography GPC. The specific test steps are as follows: an appropriate amount of the sample to be measured (it is sufficient to ensure an absorbance of 8%-12% for the sample concentration) is adopted, 20 ml of deionized water is added, and at the same time, ultrasonic waves (53 KHz / 120 W) are applied outside for more than 5 minutes to completely disperse the sample, and then the sample is measured according to the GB / T19077-2016 / ISO 13320:2009 standard.

[0065] Alternatively, the test is carried out using a multi-angle light scattering detector MALLS. Specifically, a combined device of GPC and a DawnHeleos II type multi-angle light scattering detector, an Optilab T-rEX refractive index (RI) detector and a Visco Star II type viscometer (Wyatt Technology Corporation, USA) is adopted. The test is carried out under the condition of 30°, tetrahydrofuran is adopted as the mobile phase, the test is carried out at a flow rate of 1.0 ml / min, and the SEC-SAMLL data is processed using commercial software ASTRA6 to obtain the molecular weight parameters.

[0066] Through further research, the inventors found that when the polymer further satisfies one or more of the following conditions, the cycle performance and storage performance of the battery cell can be further improved.

[0067] In some embodiments, the polymer is added to a first solvent at a first temperature to form a polymer system. The polymer system is allowed to stand for 8 hours at the first temperature and then for ≧24 hours at a second temperature. After undergoing a two-stage standing treatment, a part of the polymer system is converted into a gel-like substance in-situ. Then, after the polymer system is filtered through a 200-mesh filter, a first substance remains. The first temperature is higher than the second temperature. The mass of the polymer is n, with the unit of g, and the mass of the first substance is m, with the unit of g. The polymer and the first substance satisfy 5≦m / n≦1000, optionally 10≦m / n≦1000, and further optionally 10≦m / n≦50. Exemplarily, m / n may be 5, 10, 20, 25, 28, 30, 32, 35, 40, 50, 80, 100, 200, 500, 1000, or a range consisting of any two of the above numerical values.

[0068] Exemplarily, based on the mass of the polymer system, the range of the ratio of the mass content of the polymer to the mass content of the first solvent is 1:100 to 1:10, for example, 3:50.

[0069] Exemplarily, the first solvent is the same as or similar to the solvent of the electrolyte, and the first solvent may include a carbonate-based solvent. The carbonate-based solvent includes, for example, a cyclic carbonate solvent and / or a linear carbonate solvent.

[0070] Examples of the cyclic carbonate solvent include that the cyclic carbonate solvent includes one or more of ethylene carbonate EC, vinylene carbonate VC, fluoroethylene carbonate FEC, difluoroethylene carbonate DFEC, vinyl ethylene carbonate VEC, and dioctyl carbonate CC.

[0071] Examples of linear carbonate solvents include linear carbonate solvents containing one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), diphenyl carbonate (DPC), methyl allyl carbonate (MAC), and polycarbonate VA.

[0072] Optionally, the first solvent may simultaneously contain a lithium salt and an electrolyte additive, such as lithium hexafluorophosphate, vinylene carbonate (VC), fluoroethylene carbonate (FEC), etc.

[0073] In the present application, m / n is also called the precipitation value and represents the ability of the polymer and the solvent to convert into a gel-like substance.

[0074] The first substance mainly contains a gel-like substance formed by the polymer and the first solvent. In such a gel-like substance, the molecular structure of the polymer hardly changes.

[0075] In some embodiments, the first substance is dried at 80 °C for 12 hours to remove the first solvent in the first substance, and detection by infrared spectrophotometry (IR) or testing by nuclear magnetic resonance (NMR) is performed. The main component of the dried first substance is the aforementioned polymer.

[0076] In the present application, the glass transition temperature of the polymer ≤ the first temperature ≤ the melting temperature of the polymer, and the first temperature is the normal operating temperature of the battery cell.

[0077] The first temperature is greater than the second temperature, and the first temperature and the second temperature may be set as the safe operating temperature range of the battery cell. Exemplarily, 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 the high operating temperature of the battery cell, and the second temperature approximates normal temperature or low temperature.

[0078] By increasing the temperature, the present application can achieve the expansion of polymer molecular chains within the safe operating temperature range of the battery cell, and promote the mutual attraction and physical bonding between the polymer molecular chains and the solvent. At room temperature, the activity of the molecular segments of the polymer decreases and is retained on the surface of the active material, locking the electrolyte in the environment of the space where the polymer exists to form a state similar to an in-situ gel, protecting the interface of the active material, and maintaining the normal transmission of lithium ions, thereby establishing interface protection, reducing side reactions on the surface, and improving cycle performance and storage performance. Positive electrode sheet

[0079] According to a second aspect, the present application provides a positive electrode sheet including a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material and a polymer, and the polymer includes the polymer described in any of the embodiments of the first aspect of the present application.

[0080] Exemplarily, the positive electrode current collector has both sides facing each other in its thickness direction, and the positive electrode active material layer is provided on one or both of the two sides of the positive electrode current collector.

[0081] The electrode sheet can be formed by applying a slurry to the current collector, drying it, and cold pressing it. Alternatively, the electrode sheet is derived from a battery cell, the battery cell is disassembled, the electrode sheet infiltrated with the electrolyte in the battery cell is taken out, and the electrode sheet infiltrated with the electrolyte is vacuum dried at 100 °C for 12 h to obtain the electrode sheet, which is used for electrode sheet tests such as liquid absorption rate.

[0082] The polymer can be synthesized by methods such as emulsion polymerization, suspension polymerization, bulk polymerization, solution polymerization, etc. Alternatively, if the polymer is derived from a battery cell, the battery cell is disassembled, the electrode sheet soaked in the electrolyte of the battery cell is taken out, the active material of the obtained electrode sheet is peeled off from the current collector by an external force to form a powder sample, added to DMC, stirred at 80 °C for 8 h at 500 rpm, after the stirring is completed, left standing at room temperature for 10 min, the supernatant is taken and dried at 80 °C for 12 h, and then the polymer can be obtained. There may be some lithium salts mixed in the obtained polymer, but basically it does not affect the infrared test and the precipitation value test. In order to guarantee the accuracy of the polymer, the lithium salts may be washed away and separated with DMC at room temperature.

[0083] In some embodiments, the positive electrode active material layer satisfies the following conditions. λ = 1 - P1 / P2 Formula (1) v = π×(d / 2) 2 ×h×(ρ / t) Formula (2) v / λ > 1.00 Formula (3) In Formulas (1) to (3), λ represents the porosity of the active material layer, P1 represents the actual compression density of the positive electrode active material layer, and its unit is g / cm 3 and P2 represents the true compression density of the positive electrode active material, and its unit is g / cm 3 and v represents the liquid absorption rate of the positive electrode active material layer, and its unit is mg / s, d represents the diameter of the capillary in the capillary test of the positive electrode active material layer, and its unit is mm, h represents the height of the liquid surface in the capillary, and its unit is mm, ρ represents the density of the electrolyte in the capillary test, and its unit is g / cm 3 and t represents the time for the electrolyte to be absorbed in the capillary tube, and its unit is s.

[0084] In the present application, the actual compression density P1 is the ratio of the mass to the thickness of the positive electrode active material layer per unit area in the electrode sheet. The actual compression density is determined by the force applied during roll pressing after the electrode sheet is coated, and the unit is g / cm 3 Specifically, as a test step, an electrode sheet with a certain area S is taken, the mass M of its positive electrode active material layer is weighed, the thickness D of the positive electrode active material layer is measured, and the actual compression density = M / (S × D).

[0085] In the present application, the true compression density P2 refers to the density of the positive electrode active material itself in the positive electrode active material layer. Specifically, in the consolidated state, it refers to the mass at a certain "actual volume of the solid material (excluding open pores, closed pores, and inter-particle pores)". The true volume V is obtained through testing, and then the true compression density is calculated based on P = m / V, and the test can be carried out with reference to GB / T24586-2009. Specifically, the test steps are as follows.

[0086] 1) Pretreatment: Place a clean and dry sample cup on the balance, tare it, put the powder sample into the sample cup, which occupies about 1 / 2 of the sample cup volume, and record the mass of the sample.

[0087] 2) Place the sample cup containing the sample in the true density tester, seal the test system, ventilate helium gas through the program, detect the gas pressure in the sample chamber and the expansion chamber, and further calculate the true volume based on Boyle's law (PV = nRT) to calculate the true compression density.

[0088] Here, the volume of the sample cup: 3.5 cm 3 , Analytical gas: Helium gas.

[0089] Equation (1) can calculate the porosity λ of the active material layer based on the actual compression density and the true compression density.

[0090] Specifically, λ = (V1 - V2) / V1 = 1 - V2 / V1 = 1 - (m / V1) / (m / V2) = 1 - P1 / P2.

[0091] Here, V1 represents the volume of the positive electrode active material layer at mass m, and its unit is cm 3 and V2 represents the volume occupied by the active material particles in the positive electrode active material layer at mass m, and its unit is cm 3 and

[0092] m represents the mass of the positive electrode active material layer, and its unit is g.

[0093] Equation (2) can represent the speed at which a certain point on the electrode sheet almost completely absorbs the liquid (such as the electrolyte) in the capillary within a unit time. A certain point on the electrode sheet of the present application is a region where the electrode sheet has a certain area, and the area corresponds to the cross-sectional area of the capillary.

[0094] In the present application, the method for detecting the liquid absorption speed of the electrode sheet is adsorbing a predetermined amount of electrolyte with a capillary, bringing the capillary into contact with the electrode sheet to be tested, and allowing the electrode sheet to be tested to absorb the electrolyte in the capillary by capillary action, after a predetermined time t has elapsed, recording the liquid level height h at which the electrolyte in the capillary has been absorbed, calculating the amount of the absorbed electrolyte based on the liquid level height h, diameter d, and density ρ of the electrolyte of the capillary, and quantitatively calculating the liquid absorption speed v of the electrode sheet based on the ratio of the absorbed amount to the predetermined time length t.

[0095] Exemplarily, the value of d is 0.2 to 1, for example, 0.2, and the value of h is 3 to 5, for example, 3.

[0096] The capillary has capillary pores, and since the capillary pores can directly adsorb the electrolyte by capillary action, it provides a liquid absorption power without the need for an external drive unit. Thus, when adsorbing the electrolyte by capillary action, the adsorption amount can be more accurately controlled. On the other hand, when the electrode sheet absorbs the electrolyte by its own capillary action, when the capillary is in contact with the electrode sheet to be tested, the electrode sheet sucks out the electrolyte from the capillary, and when not in contact, the electrolyte in the capillary does not flow out. Thereby, it can accurately reflect that the electrode sheet has absorbed the corresponding volume of electrolyte according to the absorption amount of the electrolyte in the capillary, further improving the accuracy of the test results and realizing quantitatively calculating the absorption rate at which the electrode sheet absorbs the electrolyte.

[0097] Equation (3) represents the liquid absorption rate of the electrode sheet at the porosity λ and can be used to represent the liquid absorption rate of the electrode sheet.

[0098] The polymer of the present application is introduced in the manufacturing process of the active material layer, can form a uniform high wetting point inside the active material layer, uniformly improves the wetting performance of the active material layer, improves the liquid absorption rate of the entire active material layer, and thereby improves the cycle performance of the battery cell using the electrode sheet.

[0099] Optionally, 1.00 < v / λ < 50.00.

[0100] In some embodiments, 1.00 < v / λ < 4.00, optionally, 1.20 ≤ v / λ ≤ 3.80, and further optionally 1.4 ≤ v / λ ≤ 3.6. Exemplarily, v / λ may be 1.20, 1.40, 1.80, 2.00, 2.50, 3.00, 3.50, 3.60, 3.80, 3.90 or a range consisting of any two of the above numerical values.

[0101] In some embodiments, based on the mass of the positive electrode active material layer, the mass percentage of the polymer is A%, where 0.1 ≤ A ≤ 1.5.

[0102] When the mass percentage of the polymer is within the above range, the interfacial performance of the positive electrode active material layer can be significantly improved. Exemplarily, the mass percentage of the polymer may be 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, or a range consisting of any two of the above numerical values.

[0103] The positive electrode active material layer contains a positive electrode active material, and as the positive electrode active material, a positive electrode active material used in a battery cell known in the art can be used. Exemplarily, the positive electrode active material may contain at least one of a positive electrode active material having a layered structure (for example, materials such as ternary, lithium nickelate / sodium, lithium cobaltate / sodium, lithium manganate / sodium, lithium-rich / sodium layered and rock salt phase layered), an olivine-type phosphate active material, and a positive electrode active material having a spinel structure (for example, lithium spinel manganate, lithium nickel manganese spinel, lithium-rich spinel manganate, and lithium nickel manganese spinel).

[0104] Exemplarily, the general formula of the positive electrode active material having a layered structure is Li x A y Ni a Co b Mn c M (1-a-b-c) Y z 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 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 positive electrode active material having a layered structure is lithium cobaltate LCO, lithium nickelate LNO, lithium manganate LMO, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.8 Co0.1 Mn 0.1 O2 (NCM811) and LiNi 0.5 Co 0.2 Mn 0.3 It may contain one or more of O2 (NCM523).

[0105] Exemplarily, the general formula of the olivine-type phosphate active material is Li x A y Me a M b P 1-c X c Y z where 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 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, and Y is one or more selected from O, F. Specifically, the olivine-type phosphate active material contains one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0106] Exemplarily, the general formula of the cathode active material with a spinel structure is Li x A y Mn a M 2-a Y zwhere 0 ≦ x ≦ 2, 0 ≦ y ≦ 1, and 0.9 ≦ x + y ≦ 2, 0.5 ≦ a ≦ 2, 3 ≦ z ≦ 5, A is one or more selected from Na, K, 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, Ce, and Y is one or more selected from O, F. Specifically, the cathode active material with a spinel structure includes one or more of LiMn2O4, LiNi 0.5 Mn 1.5 O4, LiCr 0.3 Mn 1.7 O4, Li 1.1 Al 0.1 Mn 1.9 O4, Li2Mn2O4, and Li 1.5 Mn2O4.

[0107] In some embodiments, a metal foil or a composite current collector can be used as the cathode current collector. As an example of the metal foil sheet, an aluminum foil or an aluminum alloy foil can be employed. The composite current collector may include a polymer material layer and a metal material layer formed on at least one surface of the polymer material layer. Exemplarily, the metal material may include one or more combinations selected from aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, and the polymer material layer may include one or more combinations selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0108] In some embodiments, the positive electrode active material layer may further selectively include a positive electrode conductive agent. The type of the positive electrode conductive agent in the present application is not particularly limited. Exemplarily, 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, based on the total mass of the positive electrode active material layer, the mass percentage of the positive electrode conductive agent is 5% or less.

[0109] In some embodiments, the positive electrode active material layer may further selectively include a positive electrode binder. In the present application, the type of the positive electrode binder is not particularly limited. Exemplarily, the positive electrode binder can include one or more combinations selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin. In some embodiments, based on the total mass of the positive electrode active material layer, the mass percentage of the positive electrode binder is 5% or less. The crystallinity of the positive electrode binder is higher than that of the fluoropolymer in the present application. The melting temperature of the positive electrode binder is higher than that of the fluoropolymer in the present application.

[0110] The positive electrode active material layer is usually formed by applying 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 a positive electrode active material, a selective conductive agent, a selective binder, and any other components in a solvent and stirring them uniformly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto. Negative electrode sheet

[0111] According to a third aspect, the present application provides a negative electrode sheet including a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, the negative electrode active material layer including a negative electrode active material and a polymer, and the polymer including the polymer described in any one of the examples of the first aspect of the present application.

[0112] Exemplarily, the negative electrode current collector has both sides facing each other in its thickness direction, and the negative electrode active material layer is provided on one or both of the opposite sides of the negative electrode current collector.

[0113] In some embodiments, the negative electrode active material layer satisfies formula (3). v / λ > 1.00 Formula (3) In formulas (1) to (3), λ represents the porosity of the negative electrode active material layer, v represents the liquid absorption rate of the negative electrode active material layer, and its unit is mg / s.

[0114] Since the detection methods of λ and v are the same as those described for the positive electrode active material layer, the description is omitted here.

[0115] In some embodiments, 3.00 < v / λ < 50.00, and optionally, 3.40 ≤ v / λ ≤ 30.00. Exemplarily, v / λ may be 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, or a range consisting of any two of the above numerical values.

[0116] In some embodiments, based on the mass of the negative electrode active material layer, the mass percentage of the polymer is B%, and 0.2 ≤ B ≤ 5.0.

[0117] When the mass percentage of the polymer is within the above range, the interfacial performance of the negative electrode active material layer can be significantly improved. Exemplarily, the mass percentage of the polymer may 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 consisting of any two of the above numerical values.

[0118] In some embodiments, the negative electrode current collector can use a metal foil or a composite current collector. For example, a copper foil can be employed as the metal foil sheet. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base (such as a base of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0119] In some embodiments, the negative electrode active material can employ a negative electrode active material known in the art for batteries. Exemplarily, the negative electrode active material may include at least one of 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 selected from elemental silicon, silicon oxygen compounds, silicon carbon composites, silicon nitrogen composites, and silicon alloys. The tin-based material is at least one selected from elemental tin, tin oxy compounds, and tin alloys. However, the present application is not limited to these materials, and other materials used as the negative electrode active material of the battery may also be used. These negative electrode active materials may be used alone, or two or more of them may be used in combination.

[0120] In some embodiments, the negative electrode active material layer may optionally further include a negative electrode binder. 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 (PMA), and carboxymethyl chitosan (CMCS).

[0121] In some embodiments, the negative electrode active material layer may optionally further include a conductive agent. The conductive agent may be at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0122] In some embodiments, the negative electrode active material layer may optionally further include other auxiliaries, such as a thickening agent (such as sodium carboxymethyl cellulose (CMC-Na)).

[0123] In some embodiments, components for manufacturing the negative electrode sheet, such as the negative electrode active material, the polymer, the conductive agent, the binder, and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry. The negative electrode slurry is applied to the negative electrode current collector, and after processes such as drying and cold pressing, a negative electrode sheet can be obtained, thereby manufacturing the negative electrode sheet. Battery cell

[0124] According to a fourth aspect, the present application provides a battery cell including a positive electrode sheet, a negative electrode sheet, a separator provided between the positive electrode sheet and the negative electrode sheet, and an electrolytic solution. The battery cell is a lithium-ion battery.

[0125] In some embodiments, the positive electrode sheet can adopt the positive electrode sheet according to any embodiment of the second aspect of the present application, thereby improving the cycle performance and storage performance of the battery cell. The negative electrode sheet can adopt a conventional negative electrode sheet.

[0126] In some other embodiments, the negative electrode sheet can adopt the negative electrode sheet according to any embodiment of the third aspect of the present application, thereby improving the cycle performance and storage performance of the battery cell. The positive electrode sheet can adopt a conventional positive electrode sheet.

[0127] In some other embodiments, the positive electrode sheet can adopt the positive electrode sheet according to any embodiment of the second aspect of the present application, and the negative electrode sheet can adopt the negative electrode sheet according to any embodiment of the third aspect of the present application, thereby improving the cycle performance and storage performance of the battery cell. [Electrolyte]

[0128] The battery cell further includes an electrolyte, and the electrolyte plays a role of conducting ions between the positive electrode sheet and the negative electrode sheet. The type of the electrolyte of the present application is not particularly limited and can be selected according to needs. The electrolyte may be, for example, liquid, gel-like or all-solid.

[0129] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution contains an electrolyte salt and a solvent.

[0130] Exemplarily, the lithium salt may include one or a combination of multiple types selected from 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 bis(oxalate)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorosilicate phosphate (LiTFOP).

[0131] Exemplarily, the organic solvent may include one or a combination of multiple types selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), 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), and diethyl sulfone (ESE).

[0132] In some embodiments, the electrolyte may further include an additive. For example, the additive may include a negative electrode film-forming additive and a positive electrode film-forming additive, and may also include additives that improve certain performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature or low-temperature performance of the battery, and the like. [Separator]

[0133] In some embodiments, the battery cell further includes a separator. The type of separator in the present application is not particularly limited, and any known porous structure separation membrane having good chemical stability and mechanical stability can be selected.

[0134] In some embodiments, the material of the separator can include one or a combination of multiple types selected from glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0135] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be made into an electrode assembly by a winding process or a lamination process.

[0136] The shape of the battery cell in the present application is not particularly limited, and it may be cylindrical, square, or any other arbitrary shape. FIG. 1 is an exemplary square-structured battery cell 5.

[0137] In some embodiments, as shown in FIGS. 1 and 2, the exterior can include a case 51 and a cover plate 53. The case 51 includes a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates surround to form an accommodation chamber. The case 51 has an opening communicating with the accommodation chamber, and the cover plate 53 closes the opening so as to close the accommodation chamber. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 by a winding process or a lamination process. The electrode assembly 52 is enclosed in the accommodation chamber. The electrolyte infiltrates the electrode assembly 52. The number of electrode assemblies 52 included in the battery cell 5 may be one or multiple types, and may be adjusted according to needs.

[0138] The manufacturing method of the battery cell of the present application is known. In some embodiments, a battery cell can be formed by assembling a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. Exemplarily, the positive electrode sheet, the separator, and the negative electrode sheet are formed into an electrode assembly by a winding process or a lamination process, the electrode assembly is placed in an exterior package, and after drying, the electrolyte is injected, and through processes such as vacuum encapsulation, standing, formation, and shaping, a battery cell can be obtained.

[0139] In some embodiments of the present application, the battery cell of the present application can be assembled into a battery module, and the number of battery cells included in the battery module may be plural, and the specific number may be adjusted according to the use and capacity of the battery module.

[0140] FIG. 3 is a schematic diagram of the exemplary battery module 4. As shown in FIG. 3, in the battery module 4, a plurality of battery cells 5 may be sequentially arranged along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by a fastener.

[0141] Optionally, the battery module 4 further includes a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0142] In some embodiments, the above battery module may be assembled as a battery pack, and the number of battery modules included in the battery pack may be adjusted according to the use and capacity of the battery pack.

[0143] Both the battery module 4 and the battery pack can be specific examples of the battery of the present application.

[0144] Figures 4 and 5 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 covers the lower box body 3 and forms a closed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner. Power consumption device

[0145] According to the fifth aspect, the present application provides a power consumption device including at least one of the battery cells, battery modules, and battery packs of the present application. The battery cells, battery modules, and battery packs may be a power source of the active power consumption device or an energy storage unit of the active power consumption device. The power consumption device may be a mobile device (e.g., a mobile phone, a notebook computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), a train, a ship, and a satellite, an energy storage system, etc., but is not limited thereto.

[0146] The power consumption device can select a battery cell, a battery module, or a battery pack according to demand. Figure 6 is a schematic diagram of an exemplary power consumption device. This power consumption device 6 is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the requirements for high power and high energy density of this power consumption device, the battery pack 1 or the battery module can be adopted. As another example, the power consumption device may be a mobile phone, a tablet computer, a notebook computer, etc. This power consumption device is usually required to be thin, and the battery cell can be adopted as a power source. Example

[0147] Hereinafter, examples of the present application will be described. The examples described below are exemplary and are only for interpreting the present application and cannot be understood as a limitation to the present application. Unless specific technologies or conditions are specified in the examples, the technologies or conditions described in the literature in this field or the product manuals are followed. The reagents or instruments used are not specified by the manufacturer, and all are ordinary commercially available products. Example 1 (1) Manufacture of the positive electrode sheet

[0148] As the positive electrode current collector, an aluminum foil with a thickness of 12 μm was used.

[0149] A fluoropolymer, the positive electrode active material LiFePO4, carbon black as a conductive agent, polyvinylidene fluoride (PVDF, crystallinity 48%, melting point 164 °C) as an example of a binder, and N-methylpyrrolidone (NMP) were prepared in the positive electrode slurry. The mass ratio of the fluoropolymer, LiFePO4, conductive carbon black, PVDF, and N-methylpyrrolidone (NMP) in the positive electrode slurry was 0.5:96.8:2:0.7:29. The positive electrode slurry was coated on the aluminum foil serving as the current collector, dried at 85 °C, then cold-pressed, and then subjected to trimming, cutting, and stripe splitting, and then dried under vacuum conditions at 85 °C for 4 h to prepare a positive electrode sheet. (2) Manufacture of the negative electrode sheet

[0150] As the negative electrode current collector, a copper foil with a thickness of 8 μm was used.

[0151] A fluoropolymer, artificial graphite as the negative electrode active material, carbon black as the conductive agent, styrene-butadiene rubber (SBR) as the binder, sodium carboxymethyl cellulose (CMC) as the thickener, and deionized water were uniformly mixed in a weight ratio of 2.5:94:0.5:2:1:100 to form a negative electrode slurry. The negative electrode slurry was coated on the copper foil current collector, dried at 85 °C, then cold-pressed, trimmed, cut, and stripe-split, and then dried under vacuum conditions at 120 °C for 12 h to prepare a negative electrode sheet. (3) Manufacture of the electrolyte

[0152] In an environment with a water content of less than 10 ppm, ethylene carbonate EC, a non-aqueous organic solvent, and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3:7 to obtain an electrolyte solvent, and then the solvent was mixed with LiPF6, a lithium salt, to obtain an electrolyte with a lithium salt concentration of 1 mol / L. (4) Manufacture of lithium-ion battery

[0153] As the separator, a 16-μm polyethylene film (PE) was used. The above positive electrode sheet, separator, and negative electrode sheet were laminated in sequence. After the separator was allowed to act as a separator between the positive electrode sheet and the negative electrode sheet, it was wound to obtain an electrode assembly. The electrode assembly was placed in an outer can, dried, and then an electrolyte was injected. After passing through processes such as vacuum encapsulation, standing, formation, and shaping, a lithium-ion battery was obtained. Comparative Example 1

[0154] A lithium-ion battery was manufactured in the same manner as in Example 1. Different from Example 1, polyvinylidene fluoride (PVDF, crystallinity 48%, melting point 164 °C), an example of a binder, was added to the positive electrode sheet of Comparative Example 1, and no other fluoropolymers were added. Styrene-butadiene rubber as a binder was added to the negative electrode sheet of Comparative Example 1, and no fluoropolymers were added. Comparative Example 2

[0155] A lithium-ion battery was manufactured in the same manner as in Example 1. Different from Example 1, the materials of the fluoropolymers on the positive electrode sheet and the negative electrode sheet of Comparative Example 2 were exchanged. Examples 2 to 4

[0156] A lithium-ion battery was manufactured in the same manner as in Example 1. Different from Example 1, the materials of the fluoropolymers on the positive electrode sheet and the negative electrode sheet of Examples 2 to 4 were exchanged. Example 5

[0157] A lithium-ion battery was manufactured in the same manner as in Example 1. Different from Example 1, a fluoropolymer was added to the positive electrode sheet of Example 5, and no fluoropolymer was added to the negative electrode sheet of Example 5. Example 6

[0158] A lithium-ion battery was manufactured in the same manner as in Example 1. Different from Example 1, a fluoropolymer was added to the negative electrode sheet of Example 6, and no fluoropolymer was added to the positive electrode sheet of Example 6.

[0159] The data of the examples and comparative examples are shown in Table 1. Test section 1. Test on the capacity retention rate of the lithium-ion battery

[0160] The above lithium-ion batteries manufactured in the examples and comparative examples were charged at a constant current of 1 / 3C to 4.25V in a normal temperature environment, and then charged at a constant voltage of 4.25V until the current reached 0.05C, left for 5 minutes, and then discharged at 1 / 3C to 2.8V. The obtained capacity was taken as the initial capacity C0. Then it was transferred to a 60°C environment for storage. The above steps were repeated for the same battery, and the discharge capacity Cn of each 30D battery was recorded simultaneously. The capacity retention rate Pn of the battery every 30D was Pn = Cn / C0 * 100%. Taking the six point values of P1, P2 ··· P6 as the vertical coordinates and the corresponding storage time as the horizontal coordinates, a spot diagram of the capacity retention rate of the battery and the number of storage days was obtained. The data of the capacity retention rate of the battery in Table 1 is the value of P6 measured after storage for 180D under the above test conditions. 2. Test on the DC impedance of the lithium-ion battery

[0161] The above lithium-ion batteries manufactured in the examples and comparative examples were charged at a constant current of 1 / 3C to 4.25V at 25°C, and then charged at a constant voltage of 4.25V until the current reached 0.05C. After standing for 5 minutes, the voltage V1 was recorded. Then, it was discharged at 1 / 3C for 30 seconds, and the voltage V2 was recorded. The internal resistance DCR1 of the battery after the first cycle can be obtained by (V2 - V1) / 1 / 3C. Then, it was transferred to a 60°C environment for storage. The above steps were repeated for the same battery, and at the same time, the internal resistance DCRn (n = 1, 2, 3···6) of the nth battery was recorded. Taking the six point values of DCR1, DCR2, DCR3···DCR6 as the vertical coordinates and the corresponding cycle numbers as the horizontal coordinates, a graph of the discharge DCIR of the battery and the number of storage days was obtained.

[0162] The internal resistance increase rate of the battery in Table 1 = (DCRn - DCR1) / DCR1 * 100%. The data in Table 1 are the data measured after storage for 180 days under the above test conditions. Test Results

[0163]

Table 1

[0164] In Table 1, VDF refers to vinylidene fluoride, HFP refers to hexafluoropropylene, TFE refers to tetrafluoroethylene, 90% VDF means that the molar percentage of VDF is 90% with respect to the total molar amount of VDF and HFP, and 10% FEP means that the molar percentage of FEP is 10%.

[0165] As can be seen from Table 1, compared with Comparative Example 1, in the examples of the present application, by adding the fluoropolymer of the present application to the positive electrode sheet and / or the negative electrode sheet, the cycle performance and storage performance of the lithium-ion battery are improved. Compared with Comparative Example 2, in the examples of the present application, 0 < X CWhen ≤ 30 and 0 < Tm ≤ 140 are satisfied, the arrangement of its molecular chains becomes sparse, the interaction force between the molecular chains is small, adjacent molecular chains are easy to open, and segmental motion is realized by intermolecular rotation to form a molecular chain structure with high flexibility, and the cycle performance and storage performance of the lithium-ion battery can be more significantly improved.

[0166] As described above, the present application has been described with reference to preferred embodiments. However, various improvements are possible without departing from the scope of the present application, and some of its components may be replaced with equivalents. In particular, as long as there is no structural contradiction, the technical features mentioned in each embodiment can be arbitrarily combined. The present application is not limited to the specific embodiments disclosed above, but includes all technical solutions included in the scope of the claims.

Claims

1. A polymer applicable to a battery cell, wherein the polymer contains a fluoropolymer, The fluoropolymer has a crystallinity of X measured by differential scanning calorimetry Ｃ %, where 0 < X Ｃ ≦ 30 the melting temperature of the fluoropolymer is Tm, the unit thereof is °C, and 0 < Tm ≤ 140, the polymer.

2. The glass transition temperature of the fluoropolymer is Tg, the unit thereof is °C, and -150 ≤ Tg ≤ 60. The polymer according to Claim 1.

3. The fluoropolymer contains at least one of the structural units represented by Formula (I) to the structural units represented by Formula (III), 【Chemical 1】 In Formula (I) and Formula (II), R １ , R ２ , R ３ and R ４ each independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C3 alkyl group, or a substituted or unsubstituted C1-C3 alkoxy group, and R １ , R ２ , R ３ and R ４ at least one of them includes a fluorine atom, and when being substituted, the substituent includes a fluorine atom, Optionally, R １ , R ２ , R ３ and R ４ each independently contains 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 more optionally, R １ , R ２ , R ３ and R ４ each independently contains a hydrogen atom, a fluorine atom, a chlorine atom, a methyl group, a fluoromethyl group, a methoxy group or a perfluoromethoxy group. In formula (III), R ５ represents a single bond, a substituted or unsubstituted C1-C3 alkyl group, and when it is substituted, the substituent contains a fluorine atom, p is a positive integer from 1 to 3, and n is a positive integer of 1000 to 30000. The polymer according to Claim 1 or 2.

4. The fluoropolymer contains at least one of the structural units represented by Formula (I-1) to the structural units represented by Formula (I-11). The polymer according to any one of Claims 1 to 3. 【Chemical 2】

5. The fluoropolymer further contains at least one of the structural units represented by Formula (II-1) to the structural units represented by Formula (II-5). The polymer according to any one of Claims 1 to 4. 【Chemical Formula 3】

6. The fluoropolymer further contains at least one of the structural units represented by Formula (III-1) to the structural units represented by Formula (III-3). The polymer according to any one of Claims 1 to 5. [Chemical Formula 4]

7. n is a positive integer of 5000 to 20000, and / or The molecular weight of the fluoropolymer is 2 × 10 ５ g / mol to 1.5 × 10 ６ g / mol, and the polymer according to any one of claims 3 to 6.

8. The polymer is added to a first solvent at a first temperature to form a polymer system, the polymer system is allowed to stand at the first temperature for 8 hours and at a second temperature for ≥ 24 hours, and after the polymer system is filtered through a 200-mesh filter, a first substance remains. The first temperature is higher than the second temperature, the mass of the polymer is n, the unit thereof is g, the mass of the first substance is m, the unit thereof is g, and the polymer and the first substance satisfy 5 ≤ m / n ≤ 1000. The polymer according to any one of Claims 1 to 7.

9. A positive electrode sheet including a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector, wherein the positive electrode active material layer contains a positive electrode active material and a polymer, and the polymer contains the polymer according to any one of Claims 1 to 8. The positive electrode sheet.

10. A negative electrode sheet including a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material and a polymer, and the polymer includes the polymer according to any one of claims 1 to 8.

11. A battery cell including a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet includes the positive electrode sheet according to claim 9, and / or the negative electrode sheet includes the negative electrode sheet according to claim 10.

12. A battery including the battery cell according to claim 11.

13. A power consumption device including the battery according to claim 12.

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