Polymers, electrode sheets and related battery cells, batteries and power consumption devices

Abstract

The present application provides a polymer, an electrode sheet, and related battery cells, batteries, and power consumption devices. The polymer is added to a first solvent at a first temperature to form a polymer system, and the polymer system is allowed to stand at the first temperature for 8 hours and at a second temperature for 24 hours or more. After the polymer system is filtered through a 200-mesh filter, a first material remains. The first temperature is greater than the second temperature, where n is the mass of the polymer in grams, m is the mass of the first material in grams, and the ratio m / n of the polymer and the first material satisfies 5≦m / n≦1000. When the polymer is applied to a battery cell, it can improve the cycle performance of the battery cell.

Description

[Technical Field]

[0001] This application relates to the field of batteries, and in particular to polymers, electrode sheets and associated battery cells, batteries and power consuming devices. [Background technology]

[0002] Due to their characteristics such as high capacity and long life, battery cells are widely used in electronic devices such as mobile phones and laptops, electric scooters, electric cars, electric airplanes, electric boats, electric toy cars, electric toy boats, electric toy airplanes, and power tools.

[0003] As the range of battery applications expands, the requirements for battery cell performance are also becoming increasingly stringent. To improve the safety performance of battery cells, it is common to optimize the performance of electrode sheets in battery cells. However, the poor liquid storage performance of the active material in current electrode sheets results in poor cycle performance when used in battery cells. Summary of the Invention

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

[0005] A first aspect of the present application is a polymer for use in a battery cell, the polymer being added to a first solvent at a first temperature to form a polymer system, the polymer system being allowed to stand at the first temperature for 8 hours and at a second temperature for 24 hours or more, and then the polymer system being filtered through a 200-mesh filter to leave a first substance, the first temperature being greater than the second temperature, wherein the mass of the polymer is n in grams, the mass of the first substance is m in grams, and the polymer and the first substance satisfy the relationship 5≦m / n≦1000. When the polymer satisfies the above condition, the cycle performance and storage performance of the battery cell can be further improved.

[0006] As a result, the polymer of the present application realizes molecular chain expansion in the high safe operating temperature range of the secondary battery and promotes mutual attraction and physical bonding between the polymer molecular chain and the solvent in the electrolyte, which is advantageous for promoting bonding between the polymer molecular chain and the solvent, thereby storing the electrolyte in the active material layer.The polymer does not have mobility in the low safe operating temperature range of the secondary battery, and the polymer adheres to the active material surface, keeping the electrolyte locked in the space and environment where the polymer is located, improving the liquid storage capacity of the active material layer and improving the wetting ability of the electrolyte to the active material layer, thereby improving the cycle performance of secondary batteries using the polymer.

[0007] In some embodiments, 10≦m / n≦1000, and optionally 10≦m / n≦50. When the polymer satisfies the above conditions, the cycle performance and storage performance of the battery cell can be further improved.

[0008] In some embodiments, the first solvent comprises a cyclic carbonate solvent and / or a linear carbonate solvent.

[0009] Optionally, the cyclic carbonate solvent comprises one or more of ethylene carbonate EC, vinylene carbonate VC, fluoroethylene carbonate FEC, difluoroethylene carbonate DFEC, vinylethylene carbonate VEC, and dioctyl carbonate CC.

[0010] Optionally, the linear carbonate solvent comprises one or more of dimethyl carbonate DMC, diethyl carbonate DEC, ethyl methyl carbonate EMC, diphenyl carbonate DPC, methyl allyl carbonate MAC, polycarbonate VA.

[0011] In some embodiments, the polymer has a crystallinity of X, as measured by differential scanning calorimetry. C %, and 0 <X C≦30, the melting temperature of the polymer is Tm, and its unit is °C, and 0 <Tm≦140である。

[0012] As a result, the present application has good affinity between the polymer and the electrolyte in the battery cell, so that the solvent in the electrolyte quickly diffuses between the molecular chains of the polymer, is enveloped by the molecular chains, and forms an in-situ gel on the surface of the active material, improving the wetting performance of the electrolyte to the active material layer. This 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.

[0013] In some embodiments, the polymer has a glass transition temperature, Tg, in °C, in the range of -150≦Tg≦60. The polymer has a relatively low glass transition temperature, which allows the molecular chain segments to have better flexibility, allowing adjacent molecular chains to open more easily and form an in-situ gel, thereby improving the wetting ability of the electrolyte solution to the active material layer and improving the cycling performance of the battery cell.

[0014] In some embodiments, the polymer comprises at least one of structural units represented by formula (I) through (III). [ka]

[0015] In formula (I) and formula (II), R1, R2, R3, and R4 each independently contain 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 contains a fluorine atom, and when substituted, the substituent contains a fluorine atom. In formula (III), R5 contains a single bond or a substituted or unsubstituted C1-C3 alkyl group, and when substituted, the substituent contains a fluorine atom. p is a positive integer of 1 to 3. n is a positive integer of 1,000 to 30,000.

[0016] The monomers used in the polymers are all short-chain monomers, which are advantageous for forming a linear or short-branched structure upon polymerization. The low degree of entanglement in these structural types is advantageous for improving the flexibility of the molecular chains, allowing the molecular chains to fully unfold in the electrolyte, thereby further improving the liquid storage capacity of the active material.

[0017] 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 further 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.

[0018] In some embodiments, the polymer comprises at least one of structural units represented by formula (I-1) through (I-11). [ka]

[0019] In some embodiments, the polymer comprises at least one of structural units represented by formula (II-1) through (II-5). [ka]

[0020] In some embodiments, the polymer comprises at least one of structural units represented by formula (III-1) to structural units represented by formula (III-3). [ka]

[0021] In some embodiments, n is a positive integer between 5,000 and 20,000, and / or the molecular weight of the polymer is 2×10 5 g / mol ~ 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 not easily completely dissolved or dispersed in the electrolyte, which is advantageous for adjusting the distribution and dispersion of the polymer on the surface of the active material, and the flexibility of the polymer molecular chains can be further improved, and the interaction between the molecular chains is relatively weak, which is advantageous for the solvent molecules in the electrolyte to open the molecular chains and enter between them to be enveloped by them, which is advantageous for the active ions to enter the active material through the solvent and realize the smooth and rapid movement of the active ions.

[0022] A second aspect of the present application provides a positive electrode sheet including a positive electrode current collector and a positive electrode film layer provided on the positive electrode current collector, the positive electrode film layer including a positive electrode active material and a polymer, and the polymer including the polymer described in any one of the embodiments of the first aspect of the present application.

[0023] A third aspect of the present application provides a negative electrode sheet including a negative electrode current collector and a negative electrode film layer provided on the negative electrode current collector, the negative electrode film layer including a negative electrode active material and a polymer, the polymer including any of the polymers described in any of the embodiments of the first aspect of the present application.

[0024] 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 according to any one of the embodiments of the second aspect of the present application, and / or the negative electrode sheet includes the negative electrode sheet according to any one of the embodiments of the third aspect of the present application.

[0025] A fifth aspect of the present application provides a battery including the battery cell according to the fourth aspect of the present application.

[0026] A sixth aspect of the present application provides a power consuming device comprising a battery according to the fifth aspect of the present application. [Brief explanation of the drawings]

[0027] In order to more clearly explain the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on the drawings without any creative efforts.

[0028] [Figure 1] 1 is a schematic diagram of an embodiment of a battery cell of the present application. [Figure 2] FIG. 2 is an exploded schematic view of an embodiment of the battery cell of FIG. 1. [Figure 3] 1 is a schematic diagram of an embodiment of a battery module of the present application. [Figure 4] 1 is a schematic diagram of an embodiment of a battery pack of the present application. [Figure 5] 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4. [Figure 6] 1 is a schematic diagram of one embodiment of a power consuming device that includes a battery cell of the present application as a power source.

[0029] The drawings are not necessarily drawn to scale. [Explanation of symbols]

[0030] 1 battery pack, 2 upper case, 3 lower case, 4 battery module 5 Battery cell, 51 Case, 52 Electrode assembly 53 Cover plate 6 Power consumption equipment DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, detailed descriptions will be given of embodiments specifically disclosing the polymer, electrode sheet, and related battery cells, batteries, and power consumption devices of the present application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and redundant descriptions of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the accompanying drawings and the following description are provided 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.

[0032] "Ranges" disclosed herein are defined in the form of lower and upper limits, and a given range is defined by selecting one lower limit and one upper limit, with the selected lower and upper limits defining the boundaries of that particular range. Such defined ranges may be inclusive or exclusive of the end values, and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are recited for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 and maximum range values ​​of 3, 4, and 5 are recited, then ranges of 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all contemplated. In this application, unless otherwise specified, a numerical range "a to b" is represented by the abbreviation for any 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 and 5" are included herein, and "0 to 5" is an abbreviation for combinations of these numerical values. Furthermore, expressing a parameter as an integer greater than or equal to 2 (≧2) is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0033] Unless otherwise specified, all embodiments and optional embodiments of the present application may be combined with each other to form a new technical solution. Unless otherwise specified, all technical features and optional technical features of the present application may be combined with each other to form a new technical solution.

[0034] Unless otherwise specified, all steps in this application may be performed in order or randomly, but are preferably performed in order. For example, when a method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed in order, or steps (b) and (a) performed in order. For example, when a method is described as further including step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0035] Unless otherwise specified, the terms "comprise" and "include" used in this application mean open-ended and may also be closed-ended. For example, the terms "comprise" and "include" can mean "comprise" or "include" other components not listed, or "comprise" or "include" only the listed components.

[0036] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions satisfy "A or B": 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).

[0037] As used herein, the terms "plurality" and "plural types" mean two or more than two.

[0038] 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, and the like. The alkyl group may also be optionally substituted. The substituent may include a fluorine atom.

[0039] 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-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, or a propoxy group. The alkoxy group may also be optionally substituted.

[0040] The term "halogen atom" means a fluorine atom, a chlorine atom, a bromine atom, and the like.

[0041] The term "hydrogen" refers to 1H (protium, H), 2H (deuterium, D), or 3H (tritium, T). In each embodiment, "hydrogen" may be 1H (protium, H).

[0042] The secondary battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte, and the electrolyte permeates the positive electrode sheet and the negative electrode sheet, thereby realizing smooth movement of active ions between the positive electrode sheet and the negative electrode sheet.

[0043] The electrode sheet (e.g., a positive electrode sheet and / or a negative electrode sheet) includes a current collector and an active material layer provided on at least one surface of the current collector. The active material layer includes a pore structure. The electrolyte diffuses from the surface of the active material into the active material layer through the pore structure, thereby allowing the active material layer to be infiltrated with the electrolyte and allowing active ions to move smoothly from the positive electrode sheet to the negative electrode sheet.

[0044] The inventors have found that active material layers typically contain highly crystalline polymers, such as polyvinylidene fluoride (PVDF), which can bind the active material to the current collector and provide adhesion and support to the electrode sheet. However, active material layers containing such polymers generally exhibit poor affinity for the electrolyte, resulting in poor wettability of the electrolyte to the active material layer and poor liquid storage capacity. During use, transportation, or module assembly of secondary batteries, external pressure may be applied, which may cause the electrolyte in the active material layer to be pushed out of the active material layer, making it gradually difficult for the electrolyte to be absorbed back into the active material layer, resulting in a decrease in secondary battery capacity and a deterioration in the cycle performance of the secondary battery.

[0045] Therefore, from the viewpoint of improving the liquid storage capacity of the electrode sheet, the inventors improved the performance of the polymer in the electrode sheet, increased the affinity between the polymer and the electrolyte, and improved the infiltration performance of the electrolyte into the electrode sheet, thereby improving the cycle performance of a secondary battery using the polymer.

[0046] polymer

[0047] According to a first aspect, the present application provides a polymer for use in a battery cell. 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 or more. After undergoing this two-stage standing process, a portion of the polymer system is converted in situ into a gel-state substance. The polymer system is then filtered through a 200-mesh filter, leaving a first substance, where the first temperature is higher than the second temperature. After filtering the polymer system through the 200-mesh filter, the mobile phase solvent is filtered, and the residue, the first substance, is retained. The mass of the polymer is n (g), and the mass of the first substance is m (g), and the ratios of the polymer and the first substance satisfy 5≦m / n≦1000, optionally 10≦m / n≦1000, and optionally 10≦m / n≦50. Illustratively, 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 foregoing values.

[0048] Illustratively, based on the mass of the polymer system, the ratio of the mass content of the polymer to the mass content of the first solvent ranges from 1:100 to 1:10, for example, 3:50.

[0049] For example, the first solvent may be the same as or similar to the solvent of the electrolyte, and may include a carbonate-based solvent, such as a cyclic carbonate solvent and / or a linear carbonate solvent.

[0050] Examples of 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.

[0051] Examples of linear carbonate solvents include one or more of dimethyl carbonate DMC, diethyl carbonate DEC, ethyl methyl carbonate EMC, diphenyl carbonate DPC, methyl allyl carbonate MAC, and polycarbonate VA.

[0052] Optionally, the first solvent may contain both a lithium salt and an electrolyte additive, such as lithium hexafluorophosphate, vinylene carbonate (VC), or fluoroethylene carbonate (FEC).

[0053] In this application, m / n is also referred to as the sedimentation value, and represents the ability of the polymer and solvent to convert into a gel-state material.

[0054] The first substance includes a gel-state substance formed mainly by a polymer and a first solvent, and in such a gel-state substance, the molecular structure of the polymer hardly changes.

[0055] In some embodiments, the first material is dried at 80°C for 12 hours to remove the first solvent in the first material, and then detected by infrared spectroscopy (IR) or tested by nuclear magnetic resonance (NMR), and the main component of the first material after drying is the aforementioned polymer.

[0056] In this 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.

[0057] The first temperature is greater than the second temperature, and the first and second temperatures may be set as a safe operating temperature range of the battery cell, and 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 relatively high operating temperature of the battery cell, and the second temperature is close to room temperature or low temperature.

[0058] The polymer can realize molecular chain expansion within the high safe operating temperature range of the secondary battery, promote mutual attraction and physical bonding between the polymer molecular chain and the solvent in the electrolyte, and is advantageous for storing the electrolyte in the active material layer. The polymer may not be mobile within the low safe operating temperature range of the secondary battery, and the polymer can adhere to the active material surface to maintain the electrolyte in the space or environment in which the polymer is located, improving the liquid storage capacity of the active material layer and improving the wetting ability of the electrolyte to the active material layer, thereby improving the cycle performance of the secondary battery using the polymer.

[0059] The present invention achieves the expansion of polymer molecular chains within the safe operating temperature range of a battery cell by increasing the temperature, promoting mutual attraction and physical bonding between the polymer molecular chains and the solvent. The polymer molecular segments lose their activity at room temperature, adhere to the surface of the active material, and retain the electrolyte in the space or environment where the polymer is located, forming an in-situ gel-like state, improving the liquid storage capacity of the active material and improving cycle performance.

[0060] Through further research, the inventors have discovered that the cycling performance of the battery cell can be further improved if the polymer further satisfies one or more of the following conditions:

[0061] In some embodiments, the polymer has a crystallinity of X, as measured by differential scanning calorimetry. C %, and 0 <X C ≦30, the melting temperature of the polymer is Tm, in °C, and 0 <Tm≦140である。

[0062] Crystallization refers to the process in which atoms, ions, or molecules in a material are arranged in a certain spatial order to form an order. The conformation of polymers in a crystal is determined by two factors: intramolecular and intermolecular forces, and the intermolecular forces affect the stacking density between molecular chains. Crystallinity X CThe percentage represents the degree of crystallization in the material and can be measured by differential scanning calorimetry (DSC). Specifically, the test involves using a 0.5-0.8 g sample, placing the sample in a crucible, and heating the sample under a nitrogen gas atmosphere at a heating rate of 10°C / min from an initial temperature 20°C lower than the material's intrinsic Tg to a process off temperature 20°C higher than the material's intrinsic Tm. The actual glass transition temperature (Tg) and melting temperature (Tm) of the material are determined based on the heat absorption / dissipation peak value or transition point of the material during the process.

[0063] While fluoropolymers commonly used in conventional secondary batteries have relatively high crystallinity and melting temperatures, the polymers have good liquid-phase electrolyte resistance, thereby effectively providing adhesion or anti-repulsion effects for active materials over a long period of time during battery use. The fluoropolymers used in this application have relatively low crystallinity and melting temperatures, resulting in sparse molecular chain arrangements, small interchain forces, and easy opening of adjacent molecular chains, which allows segment motion through intermolecular internal rotation, forming a molecular chain structure with high flexibility.

[0064] Because the polymer has good affinity with the electrolyte in the battery cell, the solvent in the electrolyte quickly diffuses between the molecular chains of the polymer and is enveloped by the molecular chains, forming an in-situ gel on the surface of the active material. This adheres to the surface of the active material and protects the active material, thereby closely linking the active material with the electrolyte, improving the solid-liquid interface performance, reducing side reactions between the active material and the electrolyte, and improving the cycle performance of the battery cell.

[0065] Illustratively, the crystallinity X of a polymer measured by differential scanning calorimetry C The percentage may be 5%, 10%, 15%, 20%, 25%, 30%, or a range that is a combination of any two of the above values.

[0066] Illustratively, the melting temperature of the polymer may be 10°C, 20°C, 50°C, 70°C, 90°C, 100°C, 120°C, 140°C, or a combination of any two of the foregoing.

[0067] In some embodiments, the glass transition temperature of the polymer is Tg, in °C, where -150 < Tg < 60.

[0068] The glass transition temperature is the temperature at which a polymer segment transitions from frozen to mobile. 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. 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 lower the glass transition temperature of a polymer, the more flexible the molecular chain segments are, and the more likely adjacent molecular chains are to open. For example, the glass transition temperature of a 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 combining any two of the above values.

[0069] In some embodiments, the polymer comprises at least one of structural units represented by formula (I) through (III). [ka]

[0070] In formula (I) and formula (II), R1, R2, R3, and R4 each independently contain 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 contains a fluorine atom, and when substituted, the substituent contains a fluorine atom.

[0071] In formula (III), R5 includes a single bond or a substituted or unsubstituted C1 to C3 alkyl group, and when substituted, the substituent includes a fluorine atom.

[0072] p is a positive integer from 1 to 3.

[0073] n is a positive integer between 1,000 and 30,000.

[0074] 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.

[0075] 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.

[0076] In some embodiments, the polymer comprises at least one of structural units represented by formula (I-1) through (I-11). [ka]

[0077] Optionally, the polymer comprises at least two of the structural units represented by formula (I-1) to (I-11).

[0078] In some embodiments, the polymer comprises at least one of structural units represented by formula (II-1) through (II-5). [ka]

[0079] In some embodiments, the polymer comprises at least one of structural units represented by formula (III-1) to structural units represented by formula (III-3). [ka]

[0080] Exemplarily, the polymer includes one or more of polyperfluoroethylene PTFE, polyvinylidene fluoride PVDF, perfluoroethylenepropene 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).

[0081] Optionally, the polymer comprises one or more of polyperfluoroethylene PTFE, polyvinylidene fluoride PVDF, perfluoroethylene propene copolymer FEP, polyvinylidene fluoride-hexafluoropropylene copolymer PVDF-HFP, polyvinylidene fluoride-trifluoroethylene copolymer PVDF-TrFE.

[0082] The polymer may be derived from one or more of the following monomers: fluorocycloethane, fluoroethylene, 1,2-difluoroethylene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, 3,3,3-trifluoropropene, trifluoropropene, tetrafluoropropene, and pentafluoropropene. Optionally, the fluoropolymer may be derived from at least two of the following monomers: fluorocycloethane, fluoroethylene, 1,2-difluoroethylene, vinylidene fluoride, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, hexafluoropropylene, 3,3,3-trifluoropropene, trifluoropropene, tetrafluoropropene, and pentafluoropropene.

[0083] The monomers used in the above polymers are all short-chain monomers, which are advantageous in forming a linear straight-chain structure or a short-chain structure through polymerization. This type of structure has a low degree of entanglement, which is advantageous in improving the flexibility of the molecular chain, and the molecular chain can be sufficiently expanded in the electrolyte, which can further improve the interfacial performance of the active material.

[0084] The groups of the polymer of the present application can be detected by infrared spectroscopy IR, specifically, the polymer is tested by Thermo Nicolet Nexus 670 attenuated total reflection infrared Fourier transform infrared spectrophotometer (FTIR-ATR), and then the test is performed according to the standard GB / T6040-2002, the test range is ATR 600-4000 cm -1 , Reproducibility: ±2cm -1 , resolution: 4cm -1 More preferred than 0.2-0.6 μm penetration depth.

[0085] The structure of the polymer of the present application can be determined by nuclear magnetic resonance NMR, specifically, by H NMR and C NMR using a Varian Mercury Plus-400 nuclear magnetic resonance spectrometer, the measurement temperature is 20°C, TMS is the internal standard, CDCl is the solvent, and the proton resonance frequency is 400 MHz.

[0086] In some embodiments, n is a positive integer between 5,000 and 20,000.

[0087] In some embodiments, the molecular weight of the polymer is 2×10 5 g / mol to 1.5 × 10 6 g / mol.

[0088] When the molecular weight of the polymer is within the above range, the polymer exhibits a certain solubility in the electrolyte and is not easily completely dissolved or dispersed in the electrolyte, which is advantageous for adjusting the distribution and dispersion of the polymer on the surface of the active material; the flexibility of the polymer molecular chains can be further improved, and the interaction between the molecular chains is relatively weak, which is advantageous for the solvent molecules in the electrolyte to open the molecular chains, enter between the molecular chains, and be enveloped by the molecular chains, which is advantageous for the active ions to enter the active material through the solvent and realize smooth and rapid migration of the active ions. For example, 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 It may be g / mol or a range that is a combination of any two of the above values.

[0089] The molecular weight of polymer is a known meaning in the art, and can be measured by the equipment and methods commonly used in the art, and can be tested by gel permeation chromatography (GPC).The specific test steps are: take an appropriate amount of sample to be measured (ensure that the sample concentration is 8%-12% and the light shielding degree), add 20ml of deionized water, and simultaneously apply ultrasonic waves (53KHz / 120W) outside for 5 minutes to completely disperse the sample, and then measure the sample according to GB / T19077-2016 / ISO 13320:2009 standard.

[0090] Alternatively, the test was performed using a multi-angle light scattering detector MALLS, specifically, a GPC combined with a DawnHeleos II multi-angle light scattering detector, an Optilab T-rEX refractive index (RI) detector, and a Visco Star II viscometer (Wyatt Technology Corporation, USA). The test was performed at 30°C using tetrahydrofuran as the mobile phase at a flow rate of 1.0 ml / min, and the SEC-SAMLL data was processed using the commercial software ASTRA6 to obtain molecular weight parameters.

[0091] Positive electrode sheet

[0092] According to a second aspect, the present application provides a positive electrode sheet including a positive electrode current collector and a positive electrode film layer provided on the positive electrode current collector, the positive electrode film layer including a positive electrode active material and a polymer, and the polymer including the polymer described in any one of the embodiments of the first aspect of the present application.

[0093] For example, the positive electrode current collector has two surfaces facing each other in the thickness direction thereof, and the positive electrode active material layer is provided on one or both of the surfaces of the positive electrode current collector.

[0094] The electrode sheet can be obtained by applying the slurry to a current collector, drying the slurry, and cold-pressing the current collector. Alternatively, the electrode sheet can be derived from a battery cell, and the battery cell can be disassembled, and the electrode sheet soaked in the electrolyte can be removed from the battery cell and vacuum-dried at 100°C for 12 hours to obtain the electrode sheet, which can then be used for electrode sheet tests such as liquid absorption rate.

[0095] The polymer can be synthesized by emulsion polymerization, suspension polymerization, bulk polymerization, solution polymerization, etc. Alternatively, if the polymer is derived from a battery cell, the battery cell can be disassembled, and the electrode sheet soaked in the battery cell electrolyte removed. The active material of the resulting electrode sheet is peeled from the current collector by external force to form a powder sample, which is then added to dimethyl carbonate (DMC) and stirred at 500 rpm for 8 hours at 80°C. After stirring, the mixture is left to stand at room temperature for 10 minutes. The supernatant is then removed and dried at 80°C for 12 hours to obtain the polymer. The resulting polymer may contain a small amount of lithium salt, but this does not affect the infrared and sedimentation tests. To ensure the accuracy of the polymer, the lithium salt can be washed off and separated from the DMC at room temperature.

[0096] 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) 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 compressed density of the positive electrode active material layer, and its unit is g / cm 3 and P2 represents the true compressed 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 a capillary in a 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 indicates the density of the electrolyte in the capillary test, and its unit is g / cm 3 and t represents the time it takes for the electrolyte to be absorbed in the capillary tube, and its unit is s.

[0097] In the present application, the actual compressed density P1 is the ratio of the mass of the positive electrode active material layer per unit area of ​​the electrode sheet to the thickness. The actual compressed density is determined by the force with which the electrode sheet is roll-pressed after being coated, and its unit is g / cm. 3 The specific test steps are as follows: take an electrode sheet with a certain area S, weigh the mass M of its positive electrode active material layer, measure the thickness D of the positive electrode active material layer, and calculate the actual compressed density = M / (S × D).

[0098] In this application, the true compressed density P2 refers to the density of the positive electrode active material itself in the positive electrode active material layer, specifically, the mass per unit "actual volume of the solid material (not including open pores, closed pores, and inter-particle pores)" in a compacted state. The true volume V is obtained by testing, and the true compressed density is then calculated based on P = m / V, which can be tested in accordance with GB / T24586-2009. Specifically, the test steps are as follows:

[0099] 1) Pretreatment: Place a clean, dry sample cup on the balance, set it to zero, add the powder sample to the sample cup, occupying approximately half of the sample cup volume, and record the mass of the sample.

[0100] 2) Place the sample cup containing the sample in the true density tester, seal the test system, and use the program to infuse helium gas into the test cup, detect the gas pressure in the sample chamber and the expansion chamber, and then calculate the true volume based on Bohr's law (PV=nRT) to calculate the true compressed density.

[0101] Here, the volume of the sample cup is 3.5 cm 3 and the analysis gas is helium gas.

[0102] Formula (1) can calculate the porosity λ of the active material layer from the actual compressed density and the true compressed density.

[0103] Concrete area, λ=(V1-V2) / V1=1-V2 / V1=1-(m / V1) / (m / V2)=1-P1 / P2.

[0104] Here, V1 represents the volume of the positive electrode active material layer per 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 per mass m, and its unit is cm 3 is.

[0105] m represents the mass of the positive electrode active material layer, and its unit is g.

[0106] Equation (2) can express the rate at which a certain point on the electrode sheet almost completely absorbs the liquid (e.g., electrolyte) in the capillary within a unit time. The certain point on the electrode sheet in this application is a region of the electrode sheet having a certain area, and this area corresponds to the cross-sectional area of ​​the capillary.

[0107] In the present application, a method for detecting the liquid absorption rate of an electrode sheet includes: Adsorbing a predetermined amount of electrolyte with the capillary; The capillary is brought into contact with the electrode sheet, and the electrode sheet to be tested absorbs the electrolyte in the capillary by capillary action; After a predetermined time t has elapsed, the liquid level h of the absorbed electrolyte in the capillary is recorded, and the amount of the absorbed electrolyte is calculated based on the liquid level h, diameter d, and density ρ of the electrolyte in the capillary, and quantitatively calculates the liquid absorption rate v of the electrode sheet based on the ratio of the absorbed amount and the predetermined time length t.

[0108] Illustratively, the value of d is between 0.2 and 1, for example, 0.2, and the value of h is between 3 and 5, for example, 3.

[0109] The capillaries have capillary pores that can directly absorb the electrolyte through capillary action, providing the absorbing power without the need for an external drive unit. Thus, when the electrolyte is absorbed through capillary action, the amount of adsorption can be controlled more accurately. Meanwhile, the electrode sheet absorbs the electrolyte through its own capillary action. When the capillaries are in contact with the electrode sheet to be tested, the electrode sheet draws out the electrolyte from the capillaries, and when they are not in contact, the electrolyte in the capillaries does not flow out. This allows the amount of electrolyte absorbed in the capillaries to be accurately determined, further improving the accuracy of the test results and enabling the quantitative calculation of the absorption rate of the electrode sheet.

[0110] Equation (3) represents the liquid absorption rate of an electrode sheet at a porosity λ and can be used to represent the liquid absorption rate of an electrode sheet.

[0111] The polymer of the present application is introduced during the manufacturing process of the active material layer, and can form uniform high wetting points inside the active material layer, uniformly improving the wettability of the active material layer and increasing the liquid absorption rate of the entire active material layer, thereby improving the cycle performance of a battery cell using the electrode sheet.

[0112] Optionally, 1.00 <v / λ<50.00である。

[0113] 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 combined by any two of the above numerical values.

[0114] 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.

[0115] 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 combined by any two of the above numerical values.

[0116] The positive electrode film layer contains a positive electrode active material, and the positive electrode active material can be a positive electrode active material used in battery cells known in the art. Exemplarily, the positive electrode active material may include at least one of a positive electrode active material with a layered structure (such as 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 with a spinel structure (such as spinel lithium manganate, spinel nickel manganese lithium manganate, lithium-rich spinel lithium manganate, and nickel manganese lithium manganate).

[0117] Exemplarily, the general formula of the positive electrode active material with a layered structure is Li x A y Ni a Co b Mn c M (1-a-b-c) Y zwhere 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, and 1.8≦z≦3.5; A is one or more elements selected from Na, K, and Mg; M is one or more elements 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 elements selected from O and F. Optionally, y=0. Specifically, the layered positive electrode active material may be lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium manganese oxide (LMO), or 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 also contain one or more of O2 (NCM523).

[0118] For example, 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 zwherein 0≦x≦1.3, 0≦y≦1.3 and 0.9≦x+y≦1.3, 0.9≦a≦1.5, 0≦b≦0.5 and 0.9≦a+b≦1.5, 0≦c≦0.5, 3≦z≦5, A is one or more types selected from Na, K, and Mg, Me is one or more types selected from Mn, Fe, Co, and Ni, M is one or more types 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, and Ce, X is one or more types selected from S, Si, Cl, B, C, and N, and Y is one or more types selected from O and F. Specifically, the olivine-type phosphate active material includes one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0119] For example, the general formula of the positive electrode active material having a spinel structure is Li x A y Mn a M 2-a Y z where 0≦x≦2, 0≦y≦1, and 0.9≦x+y≦2, 0.5≦a≦2, 3≦z≦5, A is one or more elements selected from Na, K, and Mg, M is one or more elements 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 elements selected from O and F. Specifically, the positive electrode active material having a spinel structure is 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.

[0120] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. Examples of the metal foil sheet include aluminum foil or aluminum alloy foil. The composite current collector may include a polymeric material base layer and a metal material layer formed on at least one surface of the polymeric material base layer. For example, 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 polymeric material base layer may include one or more combinations selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0121] In some embodiments, the positive electrode film layer may further include an optional positive electrode conductive agent. The type of the positive electrode conductive agent is not particularly limited. For example, the positive electrode conductive agent may include one or more selected from the group consisting of superconducting carbon, conductive carbon black, conductive graphite, acetylene black, carbon black, Ketjen black, carbon particles, 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 film layer.

[0122] In some embodiments, the positive electrode film layer may further include an optional positive electrode binder. The type of positive electrode binder is not particularly limited herein, and the positive electrode binder may include, for example, one or a combination of materials 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, the mass percentage of the positive electrode binder is 5% or less, based on the total mass of the positive electrode film layer.

[0123] The positive electrode film 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 typically formed by dispersing a positive electrode active material, a conductive agent as an option, a binder as an option, 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

[0124] According to a third aspect, the present application provides a negative electrode sheet including a negative electrode current collector and a negative electrode film layer provided on the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material and a polymer, and the polymer includes the polymer described in any of the examples of the first aspect of the present application.

[0125] Exemplarily, the negative electrode current collector has two opposite surfaces in its thickness direction, and the negative electrode active material layer is provided on one or both of the two opposite surfaces of the negative electrode current collector.

[0126] 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.

[0127] 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.

[0128] 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 combined by any two of the above numerical values as well.

[0129] In some embodiments, the mass percentage of the polymer is B %, based on the mass of the negative electrode active material layer, and 0.2≦B≦5.0.

[0130] When the mass percentage of the polymer is in the above range, the interfacial performance of the negative electrode active material layer can be significantly improved. For example, 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 that combines any two of the above values.

[0131] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, a copper foil may be used as the metal foil sheet. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector may be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymeric material substrate (such as a substrate made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0132] In some embodiments, the negative electrode active material may be a battery negative electrode active material known in the art. For example, 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 may be at least one selected from elemental tin, tin oxy compounds, and tin alloys. However, the present application is not limited to these materials, and conventional materials used as negative electrode active materials in batteries may also be used. These negative electrode active materials may be used alone or in combination.

[0133] In some embodiments, the negative electrode membrane layer may further include an optional negative electrode binder, which 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).

[0134] In some embodiments, the negative electrode film layer may further include an optional conductive agent, which may be at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0135] In some embodiments, the negative electrode membrane layer may optionally further include other auxiliary agents, such as a thickener (eg, carboxymethylcellulose sodium (CMC-Na)).

[0136] In some embodiments, the negative electrode sheet can be manufactured by dispersing components for producing the above-described negative electrode sheet, such as the negative electrode active material, the polymer, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry, applying the negative electrode slurry to a negative electrode current collector, and then performing steps such as drying and cold pressing to obtain a negative electrode sheet. Battery cell

[0137] According to a fourth aspect, the present application provides a battery cell including a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet. The battery cell may be a lithium ion battery or the like.

[0138] In some embodiments, the positive electrode sheet may be a positive electrode sheet according to any one of the second aspects of the present application, thereby improving the cycle performance of the battery cell, and the negative electrode sheet may be a conventional negative electrode sheet.

[0139] In some other embodiments, the negative electrode sheet may be a negative electrode sheet according to any one of the third aspects of the present application, thereby improving the cycle performance of the battery cell, and the positive electrode sheet may be a normal positive electrode sheet.

[0140] In some other embodiments, the positive electrode sheet may be a positive electrode sheet according to any one of the second aspects of the present application, and the negative electrode sheet may be a negative electrode sheet according to any one of the third aspects of the present application, thereby improving the cycle performance of the battery cell. [Electrolyte]

[0141] The battery cell further includes an electrolyte, which serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte used in the present application is not particularly limited and can be selected according to needs. The electrolyte may be, for example, liquid, gel, or all-solid.

[0142] In some embodiments, the electrolyte is an electrolytic solution, which includes an electrolyte salt and a solvent.

[0143] Exemplarily, the lithium salt may include one or a combination of two or more selected from lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium disoxalate borate (LiBOB), lithium difluorophosphate (LiPOF), lithium difluorodisoxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0144] Illustratively, the organic solvent may include one or more combinations 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).

[0145] In some embodiments, the electrolyte solution may further contain additives. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, or an additive that improves certain battery performance, such as an additive that improves the overcharge performance of the battery or an additive that improves the high-temperature or low-temperature performance of the battery. [Separator]

[0146] In some embodiments, the battery cell further includes a separator. The type of separator used in the present application is not particularly limited, and any known porous structure separator having good chemical and mechanical stability can be selected.

[0147] In some embodiments, the separator may be made of one or a combination of materials selected from glass fiber, nonwoven 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.

[0148] In some embodiments, the positive electrode sheet, separator, and negative electrode sheet can be formed into an electrode assembly by a rolling or lamination process.

[0149] The shape of the battery cell of the present application is not particularly limited, and may be cylindrical, rectangular, or any other shape. Figure 1 shows an exemplary rectangular battery cell 5.

[0150] In some embodiments, as shown in FIGS. 1 and 2 , the exterior may include a case 51 and a cover plate 53. The case 51 includes a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a storage chamber. The case 51 has an opening communicating with the storage chamber, and the cover plate 53 closes the opening to close the storage chamber. The positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is sealed in the storage chamber. An electrolyte solution permeates the electrode assembly 52. ​​The number of electrode assemblies 52 included in the battery cell 5 may be one or more types and may be adjusted according to needs.

[0151] The method for manufacturing the battery cell of the present application is well 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. For example, the positive electrode sheet, the separator, and the negative electrode sheet can be wound or stacked to form an electrode assembly. The electrode assembly can then be placed in a housing, dried, and then injected with an electrolyte. The battery cell can then be obtained through processes such as vacuum sealing, standing, chemical conversion, and shaping.

[0152] In some embodiments of the present application, the battery cells of the present application can 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.

[0153] Fig. 3 is a schematic diagram of an example battery module 4. As shown in Fig. 3, in the battery module 4, the plurality of battery cells 5 may be arranged in order along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of battery cells 5 may be fixed by fasteners.

[0154] Optionally, the battery module 4 further includes a housing having an accommodating space, and the plurality of battery cells 5 are accommodated in the accommodating space.

[0155] In some embodiments, the battery modules may be assembled into a battery pack, and the number of battery modules included in the battery pack may be adjusted depending on the application and capacity of the battery pack.

[0156] The battery module 4 and the battery pack can both be specific examples of the battery of the present application.

[0157] 4 and 5 are schematic diagrams of an example battery pack 1. As shown in FIGS. 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, and the upper box body 2 covers the lower box body 3 to form 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 equipment

[0158] According to a fifth aspect, the present application provides a power consuming device including at least one of the battery cell, battery module, and battery pack of the present application. The battery cell, battery module, and battery pack may be a power source for the power consuming device or an energy storage unit for the power consuming device. The power consuming device may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop, 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, a satellite, an energy storage system, etc.

[0159] A power consuming device can be configured as a battery cell, a battery module, or a battery pack depending on its needs. FIG. 6 is a schematic diagram of an exemplary power consuming device. The power consuming device 6 may be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the power consuming device, a battery pack 1 or a battery module may be adopted. As another example, the power consuming device may be a mobile phone, a tablet computer, a laptop, etc. Such a power consuming device is usually required to be thin, and may adopt a battery cell as its power source. Example

[0160] The following examples are provided for illustrative purposes only and are not intended to limit the scope of the present application. Unless specific techniques or conditions are specified in the examples, the techniques, conditions, or product instructions described in the literature in this field are used. The reagents and instruments used are not specified by manufacturer, and are all commercially available, ordinary products. Example 1 (1) Manufacturing of positive electrode sheets

[0161] As the positive electrode current collector, an aluminum foil having a thickness of 12 μm was used.

[0162] A positive electrode slurry was prepared from fluoropolymer, the positive electrode active material LiFePO4, carbon black as a conductive agent, and polyvinylidene fluoride (PVDF) and N-methylpyrrolidone (NMP) as binders. The mass ratio of fluoropolymer, LiFePO4, conductive carbon black, PVDF, and N-methylpyrrolidone (NMP) in the positive electrode slurry was 0.5:96.8:2:0.5:0.2. The positive electrode slurry was applied to an aluminum foil current collector, dried at 85°C, cold-pressed, trimmed, cut, and divided into stripes, and then dried in a vacuum at 85°C for 4 hours to prepare a positive electrode sheet. (2) Manufacturing of negative electrode sheets

[0163] A copper foil with a thickness of 8 μm was used as the negative electrode current collector.

[0164] A fluoropolymer, artificial graphite as the negative electrode active material, carbon black as the conductive agent, styrene butadiene rubber (SBR) as the binder, sodium hydroxymethylcellulose (CMC) as the thickener, and deionized water were uniformly mixed in a weight ratio of 2.5:94:0.5:2:1:100 to prepare a negative electrode slurry. The negative electrode slurry was applied to a copper foil current collector and dried at 85°C. After that, the negative electrode sheet was cold pressed, trimmed, cut, and divided into stripes. It was then dried in a vacuum at 120°C for 12 hours to prepare a negative electrode sheet. (3) Electrolyte production

[0165] In an environment with a water content of less than 10 ppm, non-aqueous organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7 to obtain an electrolyte solvent, which was then mixed with lithium salt LiPF6 to obtain an electrolyte with a lithium salt concentration of 1 mol / L. (4) Lithium-ion battery manufacturing

[0166] A 16 μm polyethylene film (PE) was used as the separator. The positive electrode sheet, separator, and negative electrode sheet were stacked in this order, and the separator was placed between the positive electrode sheet and the negative electrode sheet to function as a separator. After that, the stack was wound up to obtain an electrode assembly. The electrode assembly was placed in an outer can, dried, and then an electrolyte was injected. After vacuum sealing, leaving it to stand, chemical conversion, shaping, and other processes, a lithium-ion battery was obtained.

[0167] The data for the examples and comparative examples are shown in Table 1. Testing section 1. Capacity retention rate test for lithium-ion batteries

[0168] The lithium-ion batteries prepared in the Examples and Comparative Examples were charged to 4.25V at room temperature using a 1.2C step charge, then further charged at a constant voltage of 4.25V until the current reached 0.05C, allowed to stand for 5 minutes, and then discharged at 0.33C to 2.8V. The resulting capacity was designated as the initial capacity, C0, and the initial clamping force of the lithium-ion battery was set to 10,000N. The same battery was repeatedly charged, and the discharge capacity, Cn, of the nth battery was recorded. The post-cycle capacity retention, Pn, was calculated as Cn / C0*100%, with the 200 points, P1, P2, ..., P200, as the ordinate and the corresponding cycle number as the abscissa, to plot the capacity retention versus cycle number for the batteries corresponding to the polymers used in the Examples and Comparative Examples.

[0169] In this test process, the first cycle corresponds to n=1, the second cycle corresponds to n=2, ... the 200th cycle corresponds to n=200. For example, the capacity retention data for the battery corresponding to Example 1 in Table 1 is data measured after 200 cycles under the above test conditions, i.e., the P200 value. The test process for Comparative Example 1 and other Examples is the same as above. 2. DC impedance test of lithium-ion batteries

[0170] The lithium-ion batteries prepared in the Examples and Comparative Examples were charged to 4.25 V at 25°C using an equivalent 1.2 C step charge, then further charged at a constant voltage of 4.25 V until the current reached 0.05 C. After 5 minutes of storage, the voltage V1 was recorded. They were then discharged at 1 / 3 C for 30 seconds, and the voltage V2 was recorded. The battery's internal resistance DCR1 after the first cycle was calculated using a discharge rate of (V2 - V1) / 1 / 3 C. The same battery was repeatedly charged, and the battery's internal resistance DCRn (n = 1, 2, 3, ... 200) after the nth cycle was recorded. The 200 values ​​of DCR1, DCR2, DCR3, ... DCR200 were plotted on the ordinate and the corresponding cycle number on the abscissa to plot the battery discharge DCIR versus cycle number for the polymers used in the Examples and Comparative Examples.

[0171] In this test process, the first cycle corresponds to n=1, the second cycle corresponds to n=2, and so on to the 200th cycle corresponds to n=200. For example, in Table 1, the internal resistance increase rate of the battery of Example 1 = (DCRn-DCR1) / DCR1*100%, and the test process of Comparative Example 1 and other Examples is the same as above. The data in Table 1 was measured after 200 cycles under the above test conditions. Test results

[0172] [Table 1]

[0173] In Table 1, VDF stands for vinylidene fluoride, HFP stands for hexafluoropropylene, TFE stands for tetrafluoroethylene, 90% VDF means that the molar percentage of VDF is 90% of the total molar amount of VDF and HFP, and 10% HEP means that the molar percentage of FEP is 10%.

[0174] As can be seen from Table 1, the addition of the polymer of the present invention to the positive electrode sheet and / or negative electrode sheet in the examples of the present application improves the cycle performance of lithium-ion batteries compared to Comparative Example 1. Compared to Comparative Example 2, when the examples of the present application satisfy 5≦m / n≦1000, particularly 10≦m / n≦50, the molecular chain arrangement is sparse, the inter-chain forces are small, adjacent molecular chains are easily opened, and segment motion is realized through intermolecular rotation, forming a molecular chain structure with high flexibility, which can more significantly improve the cycle performance of lithium-ion batteries.

[0175] Although the present application has been described above with reference to preferred embodiments, various modifications may be made without departing from the scope of the present application, and some of the components may be replaced with equivalents. In particular, as long as there is no structural contradiction, the technical features described in each embodiment may be arbitrarily combined. The present application is not limited to the specific embodiments disclosed above, but includes all technical solutions falling within the scope of the claims.

Claims

1. A polymer for use in a battery cell, 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 or more, and then the polymer system is filtered through a 200 mesh filter to leave a first substance, and the first temperature is greater than the second temperature; the mass of the polymer is n and its unit is g, the mass of the first substance is m and its unit is g, and the polymer and the first substance satisfy 5≦m / n≦1000; polymer.

2. 10≦m / n≦1000, and optionally 10≦m / n≦50; The polymer of claim 1.

3. the first solvent comprises a cyclic carbonate solvent and / or a linear carbonate solvent; Optionally, the cyclic carbonate solvent comprises one or more of ethylene carbonate EC, vinylene carbonate VC, fluoroethylene carbonate FEC, difluoroethylene carbonate DFEC, vinylethylene carbonate VEC, and dioctyl carbonate CC; Optionally, the linear carbonate solvent comprises one or more of dimethyl carbonate DMC, diethyl carbonate DEC, ethyl methyl carbonate EMC, diphenyl carbonate DPC, methyl allyl carbonate MAC, polycarbonate VA; The polymer according to claim 1 or 2.

4. The polymer has a crystallinity of X as measured by differential scanning calorimetry. Ｃ %, and 0<X Ｃ ≦30, The melting temperature of the polymer is Tm, and its unit is ° C., and 0 < Tm ≦ 140; The polymer of any one of claims 1 to 3.

5. The glass transition temperature of the polymer is Tg, and its unit is ° C., and −150≦Tg≦60. A polymer according to any one of claims 1 to 4.

6. The polymer contains at least one structural unit selected from 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 contains a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1 to C3 alkyl group, or a substituted or unsubstituted C1 to C3 alkoxy group, and R １ , R ２ , R ３ and R ４ at least one of contains a fluorine atom, and when substituted, the substituent contains a fluorine atom; Optionally, R １ , R ２ , R ３ and R ４ each independently comprises 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 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 comprises a single bond, a substituted or unsubstituted C1-C3 alkyl group, and if substituted, the substituent comprises a fluorine atom; and p is a positive integer from 1 to 3; n is a positive integer from 1,000 to 30,000; A polymer according to any one of claims 1 to 5.

7. The polymer contains at least one structural unit represented by formula (I-1) to formula (I-11), 【Chemistry 2】 The polymer of any one of claims 1 to 6.

8. The polymer further comprises at least one structural unit represented by formula (II-1) to formula (II-5), 【Chemistry 3】 A polymer according to any one of claims 1 to 7.

9. The polymer further comprises at least one structural unit represented by formula (III-1) to formula (III-3), 【Chemistry 4】 A polymer according to any one of claims 1 to 8.

10. n is a positive integer between 5,000 and 20,000, and / or The molecular weight of the polymer is 2×10 ５ g / mol~1.5×10 ６ g / mol, 10. The polymer of any one of claims 6 to 9.

11. A positive electrode sheet including a positive electrode current collector and a positive electrode film layer provided on the positive electrode current collector, The positive electrode film layer includes a positive electrode active material and a polymer, and the polymer includes the polymer according to any one of claims 1 to 10. Positive electrode sheet.

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

13. A battery cell including a positive electrode sheet and a negative electrode sheet, The positive electrode sheet comprises the positive electrode sheet according to claim 11 , and / or The negative electrode sheet includes the negative electrode sheet according to claim 12. Battery cell.

14. A battery cell comprising the battery cell of claim 13. battery.

15. A battery cell comprising the battery cell of claim 14. Power consumption equipment.

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