Lithium secondary battery cell, electrical apparatus, and method for preparing lithium secondary battery

Abstract

Embodiments of the present application provide a lithium secondary battery cell, an electrical apparatus, and a method for preparing a lithium secondary battery. In particular, the embodiments of the present application provide a lithium secondary battery cell, characterized by comprising a negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The negative electrode material layer comprises a negative electrode active material and a linear fluorine-containing polyimide, and the linear fluorine-containing polyimide accounts for 0.5% to 3% by weight of the negative electrode material layer.

Description

Lithium-ion secondary battery cells, power-consuming devices, and methods for manufacturing lithium-ion secondary batteries

[0001] Cross-reference of related applications

[0002] This application is based on and claims priority to CN application number 202510217294.1 filed on February 26, 2025, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] This application relates to the field of battery technology, and in particular to lithium secondary battery cells, electrical devices, and methods for preparing lithium secondary batteries. Background Technology

[0004] With the continuous development of rechargeable batteries, the market demands increasingly higher lifespans for lithium-ion batteries. Currently, the main limitation to the cycle life of lithium iron phosphate batteries stems from the deterioration of the negative electrode's structural performance. During normal cycling, lithium loss at the negative electrode intensifies, and the accumulation of by-reaction products causes rapid volume expansion. Once this expansion is limited, the negative electrode's pore structure collapses rapidly, leading to a rapid reduction in the transport path between the electrolyte and active lithium within the electrode structure, and a rapid increase in polarization. This further triggers a significant drop in capacity and a rapid decline in lifespan. A critical factor is the stability of the SEI film. During cycling, the SEI film cannot remain stable due to the repeated extraction and insertion of lithium ions. The SEI film is continuously consumed, decomposed, and regenerated, a process that consumes a large amount of active lithium ions. This continuous loss of active lithium material causes a rapid decline in lifespan. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a lithium secondary battery cell, an electrical device, and a method for preparing a lithium secondary battery.

[0006] The first aspect of this application provides a lithium secondary battery cell, characterized in that it includes a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer including a negative electrode active material and a fluorinated polyimide; the fluorinated polyimide accounts for 0.5% to 3% of the weight of the negative electrode material layer.

[0007] In some embodiments, the fluorinated polyimide has a linear molecular chain.

[0008] In some embodiments, the fluorinated polyimide has a weight-average molecular weight of 20 kDa to 100 kDa.

[0009] In some embodiments, the fluorinated polyimide is a fluorinated aromatic polyimide.

[0010] In some embodiments, the fluorinated polyimide is formed by the condensation polymerization of a fluorinated aromatic diamine and a fluorinated aromatic dianhydride.

[0011] In some embodiments, the fluorinated aromatic diamine includes one or more of 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (6FODA), 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl, tetrafluoro-phenylenediamine, 4,4'-diamino-3,3'-difluorodiphenylmethane, 4,4'-diamino-2,2',3,3',5,5',6,6'-octafluorobiphenyl, 2,4-diamino-4'-fluorodiphenyl ether, and 3,5-diamino-trifluorotoluene.

[0012] In some embodiments, the fluorinated aromatic dianhydrides include, but are not limited to, hexafluorodianhydride (6FDA), 4,4'-(hexafluoroisopropene)phthalic anhydride, fluorinated derivatives of naphthalenetetracarboxylic dianhydride (NTDA), 1,2,4,5-benzenetetracarboxylic dianhydride, 4,4'-(hexafluoroisopropyl)bis(phthalic anhydride), and 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride.

[0013] In some embodiments, the fluorinated aromatic diamine is 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl.

[0014] In some embodiments, the fluorinated aromatic dianhydride is 4,4'-(hexafluoroisopropene)diphthalic anhydride.

[0015] In some embodiments, the molar ratio of the fluorinated aromatic diamine to the fluorinated aromatic dianhydride is 1:0.5 to 2.

[0016] In some embodiments, the fluorinated polyimide has a structure as shown in formula (1):

[0017] Where n is the degree of aggregation.

[0018] In some embodiments, the fluorinated polyimide is prepared by a method comprising the following steps:

[0019] (1) Dissolve fluorinated aromatic dianhydride and fluorinated aromatic dianhydride in a solvent, and heat at 65°C to 90°C for a certain time under inert gas protection to obtain polyamic acid solution;

[0020] (2) Add the chemical imidizing agent to the polyamic acid solution and stir to obtain the fluorinated polyimide;

[0021] (3) Separate, dry and pulverize the fluorinated polyimide into fluorinated polyimide particles.

[0022] In some implementations, the solvent is an aprotic solvent.

[0023] In some embodiments, the inert gas includes argon, helium, or nitrogen.

[0024] In some embodiments, the chemical imidizing agent includes a dehydrating agent and a dehydration catalyst.

[0025] In some embodiments, the volume average particle size (DV) of the fluorinated polyimide particles is... 50 The range is 0.1μm to 30μm, and can be selected as 0.5μm to 30μm, and further can be selected as 0.5μm to 8μm.

[0026] In some embodiments, the volume average particle size (DV) of the fluorinated polyimide particles is... 99 The range is 1μm to 50μm, and can be selected from 1μm to 30μm, and further can be selected from 7μm to 20μm.

[0027] In some embodiments, the negative electrode active material includes one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

[0028] In some embodiments, the negative electrode material layer further includes a binder and / or a conductive agent.

[0029] In some embodiments, the adhesive includes one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0030] In some embodiments, the conductive agent includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0031] In some embodiments, the negative electrode sheet is prepared by a method including the following steps: mixing negative electrode active material, conductive agent, binder, fluorinated polyimide and solvent evenly by stirring to obtain a negative electrode slurry; coating the negative electrode slurry on both sides of the negative electrode current collector; and obtaining the negative electrode sheet after cold pressing and cutting.

[0032] In some embodiments, the weight ratio of the fluorinated polyimide to the negative electrode active material is 0.5–3:92–94.5.

[0033] In some implementations, the stirring time is 8 hours to 24 hours.

[0034] The second aspect of this application provides an electrical device comprising any lithium secondary battery cell described in the first aspect of this application.

[0035] The third aspect of this application provides a method for preparing a lithium secondary battery, the method comprising preparing a negative electrode sheet, wherein the method for preparing the negative electrode sheet comprises the following steps: mixing a negative electrode active material, a conductive agent, a binder, a fluorinated polyimide and a solvent uniformly by stirring to obtain a negative electrode slurry, coating the negative electrode slurry on both sides of a negative electrode current collector, and obtaining a negative electrode sheet after cold pressing and cutting.

[0036] In some embodiments, the fluorinated polyimide is as defined in any one of claims 2-4;

[0037] In some embodiments, the weight ratio of fluorinated polyimide to negative electrode active material is 0.5–3:94.5–92; preferably, the stirring time is 8 h–24 h. Attached Figure Description

[0038] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the specific embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0039] Figure 1 is a schematic diagram of an electrode assembly with a wound structure inside a secondary battery cell according to an embodiment of this application.

[0040] Figure 2 is a schematic diagram of a secondary battery cell according to an embodiment of this application.

[0041] Figure 3 is an exploded view of a secondary battery cell according to an embodiment of this application, as shown in Figure 2.

[0042] Figure 4 is a schematic diagram of a battery module according to one embodiment of this application.

[0043] Figure 5 is a schematic diagram of a battery pack according to one embodiment of this application.

[0044] Figure 6 is an exploded view of a battery pack according to an embodiment of this application, as shown in Figure 5.

[0045] Figure 7 is a schematic diagram of an electrical device in which a secondary battery cell is used as a power source according to an embodiment of this application.

[0046] Figure 8 shows the Raman spectrum of a fluorinated polyimide according to an embodiment of this application.

[0047] The accompanying drawings are not drawn to scale.

[0048] Explanation of reference numerals in the attached drawings: 10 Corner section; 20 Flat section; 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Secondary battery cell; 51 Housing; 52 Electrode assembly; 53 End cap. Detailed Implementation

[0049] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0050] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, battery device, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0051] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0052] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0053] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0054] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0055] Unless otherwise specified, the terms "comprising" and "including" as used in this application are open-ended. For example, "comprising" and "including" may mean that other components not listed may also be included or contained.

[0056] Unless otherwise specified, the term "or" is inclusive in this application. For example, any of the following conditions satisfies the condition "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).

[0057] [Battery cell]

[0058] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0059] To address the limited lifespan of individual battery cells, appropriate additives can be used to slow down or alter the side reactions of the SEI film.

[0060] The first embodiment of this application provides a lithium secondary battery cell, characterized in that it includes a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer including a negative electrode active material and a fluorinated polyimide; the fluorinated polyimide accounts for 0.5% to 3% of the weight of the negative electrode material layer.

[0061] In lithium-ion battery cells, there is crystal water inside lithium-containing cathode active materials such as lithium iron phosphate that cannot be completely removed. This water reacts with lithium salts in the electrolyte (such as lithium hexafluorophosphate) to continuously generate proton acid. Proton acid inside the battery has always been the main culprit for damaging the anode SEI. The reaction of proton acid with alkyl lithium carbonate in the SEI leads to the dissolution of the SEI and damages the stability of the SEI interface.

[0062] The inventors discovered that fluorinated polyimide can improve the SEI film composition of the battery negative electrode during cycling. Polyimide contains imine bonds, which can absorb protic acids, and the F-containing groups can spontaneously react with lithium generated during battery cycling, converting the lithium into inorganic LiF. The LiF component in the SEI film effectively improves electrode stability and cycle life. Furthermore, the LiF-rich SEI structure also enhances the lithium-ion migration rate of the electrode, thereby improving the rate performance.

[0063] The above-mentioned method of transforming the by-reaction products into inorganic components that are beneficial to improving electrode performance can continue throughout the battery cycling process. Thus, during the dynamic cycling process, the components inside the electrode are transformed from waste into treasure, and the by-reaction is reused.

[0064] Polyimide (PI) refers to a class of polymers containing an imide ring (-CO-NR-CO-) in the main chain, which can be obtained by polymerization of dianhydrides and diamines. Based on the morphology of the molecular chain, it can include linear polyimides and cross-linked polyimides. Based on the chemical structure of the repeating units, polyimides can include aliphatic polyimides, semi-aromatic polyimides, and aromatic polyimides. Aromatic polyimides are polymerized from aromatic dianhydrides and diamines. In semi-aromatic polyimides, one of the dianhydrides or diamines is aromatic, while the other is aliphatic. Aliphatic polyimides are polymerized from aliphatic dianhydrides and aliphatic diamines.

[0065] In the negative electrode material layer, the fluorinated polyimide accounts for 0.5% to 3% of the weight of the negative electrode material layer (e.g., 0.5% to 0.8%, 0.8% to 1.0%, 1.0% to 1.5%, 1.5% to 2.0%, or 2.0% to 3.0%). When the content of fluorinated polyimide is within the above range, it has a significant effect on improving the SEI film of the battery negative electrode, and the cost caused by polyimide can be controlled within a reasonable range.

[0066] In some embodiments, the fluorinated polyimide accounts for 1.0% to 3.0% of the weight of the negative electrode material layer.

[0067] In some embodiments, the fluorinated polyimide has a linear molecular chain. Compared to cross-linked polyimides, linear polyimides have better processability and are easier to prepare.

[0068] The structure of polyimide can be characterized by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) to confirm the presence of cross-linked structures or characterize the degree of cross-linking. The presence of cross-linked structures or the degree of cross-linking can also be confirmed by testing the solubility or swelling of polyimide in organic solvents (e.g., methylpyrrolidone (NMP)).

[0069] The structure of fluorinated polyimide can also be characterized using Raman spectroscopy, with the following characteristic peaks: vibrational peak CF in the range of 1200–1300 cm⁻¹. -1 The characteristic peak of the imide ring is in the range of 1300–1400 cm⁻¹. -1 .

[0070] In some embodiments, the fluorinated polyimide has a weight-average molecular weight of 20 kDa to 100 kDa. Using a fluorinated polyimide with the above molecular weight can give the slurry a suitable viscosity, improve the adhesion of the electrode, reduce adverse phenomena such as electrode delamination, and help maintain the battery capacity. At the same time, it can give the slurry good processability, which facilitates the preparation of the electrode.

[0071] In some embodiments, the fluorinated polyimide has a weight-average molecular weight of 20kDa to 30kDa, 30kDa to 40kDa, 40kDa to 50kDa, 50kDa to 60kDa, 60kDa to 70kDa, 70kDa to 80kDa, 80kDa to 90kDa, or 90kDa to 100kDa.

[0072] In some embodiments, the fluorinated polyimide has a weight-average molecular weight of 50 kDa to 70 kDa (e.g., 50 kDa to 60 kDa or 60 kDa to 70 kDa).

[0073] The weight-average molecular weight of fluorinated polyimides can be determined using methods commonly used in the art, such as gel permeation chromatography. In some embodiments, gel permeation chromatography equipped with a differential refractive index detector or a light scattering detector is used to perform the measurement under the following conditions:

[0074] Chromatographic column: Polystyrene gel column

[0075] Test conditions solvent: tetrahydrofuran

[0076] Flow rate: 1.0 mL / min

[0077] Column temperature: 30-40℃

[0078] Standard sample: Monodisperse polystyrene standard, used for calibrating molecular weight distribution.

[0079] Exemplary test steps include:

[0080] 1. Sample preparation: Dissolve polyimide in THF at a concentration of approximately 2-5 mg / mL, and filter to remove insoluble matter;

[0081] 2. Injection analysis: Polymer chains of different molecular weights are separated by a chromatographic column, and the elution time is recorded by a detector;

[0082] 3. Data processing: Calculate the weight-average molecular weight based on the standard curve.

[0083] In some embodiments, the fluorinated polyimide is an aromatic polyimide. Aromatic polyimides have strong chemical stability and are structurally more stable within the electrolyte, reducing the possibility of side reactions.

[0084] In some embodiments, the aromatic polyimide is formed by the condensation polymerization of a fluorinated aromatic diamine and a fluorinated aromatic dianhydride.

[0085] Fluorinated aromatic diamines include, but are not limited to, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (6FODA), 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl, tetrafluoro-phenylenediamine, 4,4'-diamino-3,3'-difluorodiphenylmethane, 4,4'-diamino-2,2',3,3',5,5',6,6'-octafluorobiphenyl, 2,4-diamino-4'-fluorodiphenyl ether, and 3,5-diamino-trifluorotoluene. Fluorinated aromatic dianhydrides include, but are not limited to, hexafluorodianhydride (6FDA), 4,4'-(hexafluoroisopropene) phthalic anhydride, fluorinated derivatives of naphthalenetetracarboxylic dianhydride (NTDA), 1,2,4,5-benzenetetracarboxylic dianhydride, 4,4'-(hexafluoroisopropyl)bis(phthalic anhydride), and 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride.

[0086] In some embodiments, the fluorinated aromatic diamine is 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl. In some embodiments, the fluorinated aromatic dianhydride is 4,4'-(hexafluoroisopropene)phthalic anhydride.

[0087] In some embodiments, the molar ratio of the fluorinated aromatic diamine and the fluorinated aromatic dianhydride is 1:0.5 to 2 to obtain an aromatic polyimide having the above-mentioned selectable molecular weight.

[0088] In some embodiments, the aromatic polyimide has a structure as shown in formula (1):

[0089] Where n is the degree of aggregation.

[0090] Polyimides can be prepared in a two-step process: polyamic acid is obtained from diamine and dianhydride in an aprotic solvent, and then the polyamic acid undergoes thermal or chemical imidization, followed by dehydration and cyclization to obtain polyimides. Compared with thermal imidization, chemical imidization can be carried out at room temperature and is less prone to side reactions such as crosslinking or degradation.

[0091] In some embodiments, the aromatic polyimide is prepared by a method comprising the following steps:

[0092] (1) Dissolve fluorinated aromatic dianhydride and fluorinated aromatic dianhydride in a solvent, and heat at 65°C to 90°C for a certain time under inert gas protection to obtain polyamic acid solution;

[0093] (2) Add the chemical imidizing agent to the polyamic acid solution and stir to obtain the aromatic polyimide;

[0094] (3) The aromatic polyimide is separated, dried and crushed into aromatic polyimide particles.

[0095] The solvent used in the above method can be any aprotic solvent with good solubility for monomers and polymers. In some embodiments, the solvent is N-methylpyrrolidone.

[0096] The inert gases used in the above methods include, but are not limited to, helium, argon, and nitrogen. In some embodiments, the inert gas is nitrogen.

[0097] In some embodiments, the chemical imidizing agent comprises a dehydrating agent and a dehydration catalyst, wherein the dehydrating agent comprises an acid anhydride, such as acetic anhydride, propionic anhydride, or a mixture of the above anhydrides with aromatic monocarboxylic anhydrides; and the dehydration catalyst comprises a tertiary amine, such as triethylamine or pyridine.

[0098] In some embodiments, the chemical imidizing agent comprises acetic anhydride and triethylamine. Using this combination as the chemical imidizing agent reduces the likelihood of degradation of the polyamic acid and allows the imidization reaction to proceed rapidly at lower temperatures.

[0099] In some implementations, the reaction time for step (1) or step (2) is independently 0.5 h to 12 h.

[0100] In some embodiments, step (3) can be performed by separating the polyimide from the reaction solution through filtration (e.g., vacuum filtration) and drying (e.g., baking). To ensure uniform dispersion of the polyimide in the negative electrode slurry, the polyimide can be pulverized to obtain particles with the target particle size. In some embodiments, an air jet mill can be used for pulverization.

[0101] In some embodiments, the volume average particle size (DV) of the fluorinated polyimide particles is... 50 The range is 0.1μm to 30μm, for example, 0.1μm to 0.5μm, 0.5μm to 1μm, 1μm to 5μm, 5μm to 8μm, 8μm to 10μm, 10μm to 20μm or 20μm to 30μm.

[0102] In some embodiments, the volume average particle size (DV) of the fluorinated polyimide particles is... 99 The range is from 1μm to 50μm, for example, 1μm to 7μm, 7μm to 10μm, 10μm to 20μm, 20μm to 30μm, 30μm to 40μm, or 40μm to 50μm.

[0103] Fluorinated polyimide particles with a particle size within the above range can have a large specific surface area, which is beneficial for contact with protic acids and exerting an acid removal effect, while also being easier to prepare.

[0104] In some embodiments, the volume average particle size (DV) of the fluorinated polyimide particles is... 50 The diameter is 0.5 μm to 30 μm. In some embodiments, the volume average particle size (DV) of the fluorinated polyimide particles is... 50 The range is 0.5μm to 8μm.

[0105] In some embodiments, the volume average particle size (DV) of the fluorinated polyimide particles is... 99 The particle size ranges from 1 μm to 30 μm. In some embodiments, the volume average particle size (DV) of the fluorinated polyimide particles is... 99 The size ranges from 7μm to 20μm.

[0106] DV 50 and DV 99 Tests can be performed using methods known in the art. As an example, characterization tests can be performed using a Malvern laser particle size analyzer (e.g., Malvern's Mastersizer-3000) in accordance with GB / T 19077-2016.

[0107] [Negative electrode plate]

[0108] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0109] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0110] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil or copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0111] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0112] In some embodiments, the negative electrode can be made of foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, or foamed carbon, etc. When foamed metal is used as the negative electrode sheet, the surface of the foamed metal may or may not contain a negative electrode active material.

[0113] As an example, negative electrode active materials can be filled or / and deposited within the negative electrode current collector.

[0114] In some embodiments, the negative electrode film layer may optionally include an adhesive. The type of adhesive is not particularly limited, and those skilled in the art can choose flexibly according to actual needs. As an example, the adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0115] In some embodiments, the negative electrode film may optionally include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0116] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0117] In some embodiments, the negative electrode sheet can be prepared by: mixing the negative electrode active material, conductive agent, binder, fluorinated polyimide and solvent evenly by stirring to obtain a negative electrode slurry; coating the negative electrode slurry on both sides of the negative electrode current collector; and then cold pressing and cutting to obtain the negative electrode sheet.

[0118] In some embodiments, the weight ratio of the fluorinated polyimide to the negative electrode active material is 0.5–3:94.5–92. This weight ratio ensures that the negative electrode has sufficient active material to maintain a high energy density, and also allows for sufficient fluorinated polyimide to absorb protons.

[0119] In some embodiments, the weight ratio of the fluorinated polyimide to the negative electrode active material is 0.5–1:94–94.5, 1–1.5:93.5–94, 1.5–2:93–93.5, 2–2.5:92.5–93, or 2.5–3:92–92.5.

[0120] In some implementations, the stirring time is 8h to 24h (e.g., 8h to 16h, 16h to 20h, or 20h to 24h) to ensure that the components in the slurry are mixed uniformly.

[0121] In other embodiments, the current collector of the negative electrode sheet typically includes a current collector body and a base coating. The base coating can be disposed on at least one side of the current collector body. The base coating basically does not contain negative electrode active material, but may include a small amount of carbon material. However, the carbon material forms a thin coating and cannot function as a negative electrode active material. In this embodiment, the negative electrode sheet can be an electrode sheet without a negative electrode active material layer. For a negative electrode sheet without a negative electrode active material layer, when the current collector of the negative electrode sheet does not contain a base coating, the aforementioned film layer can be disposed on the surface of at least one side of the current collector; when the current collector of the negative electrode sheet includes a base coating, the aforementioned film layer can be disposed on the surface of the base coating away from the current collector.

[0122] [Positive electrode plate]

[0123] In some embodiments, the positive electrode can be a positive electrode sheet, which may include a positive current collector and a positive active material disposed on at least one surface of the positive current collector.

[0124] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material is disposed on either or both of the two opposite surfaces of the positive current collector.

[0125] As an example, the positive current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0126] In some embodiments, the secondary battery cell is a lithium-ion battery, and the positive electrode active material can be a positive electrode active material known in the art for lithium-ion batteries. The positive electrode active material may include at least one of the following materials: lithium phosphates, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium phosphates include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4, also referred to as LFP), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2, also known as NCM 333 LiNi 0.5 Co 0.2 Mn 0.3 O2, also known as NCM 523 LiNi 0.5 Co 0.25 Mn 0.25 O2, also known as NCM 211 LiNi 0.6 Co 0.2 Mn 0.2 O2, also known as NCM 622 LiNi 0.8 Co 0.1 Mn 0.1 O2, also known as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co0.05 Al 0.05 At least one of O2 and its modified compounds. Modified compounds refer to substances obtained by modification methods such as doping or coating based on the above-mentioned substances.

[0127] In the examples of positive electrode active materials in this application, the molar content of oxygen is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of oxygen will fluctuate.

[0128] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0129] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0130] In some embodiments, the positive electrode can be a foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, or foamed carbon, etc. When foamed metal is used as the positive electrode, the surface of the foamed metal may or may not contain a positive electrode active material. As an example, a positive electrode active material is filled and / or deposited within the foamed metal.

[0131] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0132] Electrolyte

[0133] The electrolyte plays a role in conducting ions between the positive and negative electrodes.

[0134] In some embodiments, the electrolyte includes an electrolyte salt and a solvent.

[0135] In some embodiments, the secondary battery cell is a lithium-ion battery, and the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0136] In some embodiments, the secondary battery cell is a sodium-ion battery, and the electrolyte salt may be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluorooxalate borate, sodium dioxalate borate, sodium difluorodioxalate phosphate, and sodium tetrafluorooxalate phosphate.

[0137] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. Ether solvents may also be selected. Ether solvents may include one or more of the following: ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 4-methyl-1,3-dioxolane, diphenyl ether, crown ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0138] In some embodiments, the electrolyte may optionally include additives. As examples, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0139] [shell]

[0140] In some embodiments, the secondary battery cell may include a casing. The casing may be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc. In some embodiments, the casing may be a sealed structure or a non-sealed structure. As an example, when the casing is a non-sealed structure, the casing serves to protect the electrode assembly, and a sealing bag is included between the casing and the electrode assembly to encapsulate the electrode assembly and electrolyte. Specifically, the sealing bag may be a bag-shaped insulating component or an aluminum-plastic film. When the casing is a sealed structure, it is used to encapsulate components such as the electrode assembly and electrolyte.

[0141] As an example, the secondary battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a secondary battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not have any particular limitations.

[0142] In some embodiments, the housing includes an end cap and a housing, the housing having an opening, and the end cap covering the opening. The housing may have one or more openings. The end cap may also have one or more.

[0143] In some embodiments, at least one electrode terminal is provided on the housing, and the electrode terminal is electrically connected to the tab. The electrode terminal can be directly connected to the tab, or it can be indirectly connected to the tab through a current collector. The electrode terminal can be provided on the end cap or on the housing.

[0144] In some embodiments, a pressure relief mechanism is provided on the casing. The pressure relief mechanism is used to release the internal gas of the secondary battery cell.

[0145] As an example, the internal pressure or temperature of a secondary battery cell is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the secondary battery cell reaches the predetermined threshold, the pressure relief mechanism is activated or a weak structure in the pressure relief mechanism is destroyed, thereby forming an opening or channel for the internal pressure or temperature to be released. The threshold design varies depending on the design requirements. The threshold may depend on the materials of one or more of the positive electrode, negative electrode, electrolyte, and separator in the secondary battery cell.

[0146] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0147] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0148] The term "actuation" as used in this application refers to the pressure relief mechanism being activated or undergoing a certain state, thereby releasing the internal pressure and temperature of the secondary battery cell. The actions of the pressure relief mechanism may include, but are not limited to: movement of components within the mechanism to form an exhaust channel, rupture, breakage, tearing, or opening of at least a portion of the mechanism, etc. When the pressure relief mechanism is actuated, the high-temperature, high-pressure substances inside the secondary battery cell are discharged as waste from the actuated portion. This method allows for pressure and temperature relief of the secondary battery cell under controllable pressure or temperature, thereby preventing potentially more serious accidents.

[0149] In some embodiments, when the housing is a non-sealed structure, the pressure relief mechanism can be configured as a through hole for discharging gas from inside the secondary battery cell.

[0150] The emissions from secondary battery cells mentioned in this application include, but are not limited to: electrolytes, dissolved or split positive and negative electrode plates, fragments of separators, high-temperature and high-pressure gases generated by the reaction, flames, etc.

[0151] Figure 2 shows a square-structured secondary battery cell 5 as an example.

[0152] In some embodiments, referring to FIG3, the housing may include a housing 51 and an end cap 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the end cap 53 can be closed by covering the opening to seal the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0153] [Battery Device]

[0154] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple secondary battery cells, which are connected in series, parallel, or mixed connections via a busbar.

[0155] In some embodiments, a battery cell assembly is typically formed by arranging multiple secondary battery cells.

[0156] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple secondary battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple secondary battery cells together with cable ties.

[0157] Figure 4 shows a battery module 4 as an example. Referring to Figure 4, in the battery module 4, multiple secondary battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other arbitrary way. Furthermore, these multiple secondary battery cells 5 can be fixed in place using fasteners.

[0158] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple secondary battery cells 5 are received.

[0159] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0160] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0161] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple secondary battery cells to the housing.

[0162] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0163] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0164] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0165] Figures 5 and 6 show a battery pack 1 as an example. Referring to Figures 5 and 6, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0166] The second embodiment of this application provides an electrical device that includes any of the lithium secondary battery cells provided in the first embodiment of this application.

[0167] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use secondary battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0168] Figure 7 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery cells in this device, a battery pack or battery module can be used.

[0169] [Methods for preparing secondary batteries]

[0170] The third embodiment of this application provides a method for preparing a lithium secondary battery, the method including the preparation of a negative electrode sheet, wherein the method for preparing the negative electrode sheet includes the following steps.

[0171] The negative electrode active material, conductive agent, binder, fluorinated polyimide and solvent are mixed evenly by stirring to obtain a negative electrode slurry. The negative electrode slurry is coated on both sides of the negative electrode current collector, and after cold pressing and cutting, a negative electrode sheet is obtained.

[0172] In some embodiments, the fluorinated polyimide is as described in the first embodiment of this application.

[0173] In some embodiments, the weight ratio of fluorinated polyimide to negative electrode active material is 0.5–3:94.5–92. This weight ratio ensures sufficient negative electrode active material in the negative electrode sheet to maintain a high energy density in the battery, while also allowing sufficient fluorinated polyimide to absorb protons.

[0174] In some implementations, the stirring time is 8 hours to 24 hours to ensure that the components in the slurry are mixed evenly.

[0175] [Example]

[0176] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0177] Synthesis of fluorinated polyimide

[0178] Fluorinated polyimide was synthesized according to the following reaction route.

[0179] Ar1: 4,4'-Diamino-2,2'-bis(trifluoromethyl)biphenyl (Mw = 320), Ar2: 4,4'-(hexafluoroisopropene)phthalic anhydride (Mw = 444.24)

[0180] First, Ar1 was added to a 500ml three-necked flask, followed by NMP solution and stirring until Ar1 was completely dissolved. Then, Ar2 monomer was added in the appropriate proportion. Nitrogen gas was completely introduced into the three-necked flask for the reaction, which was carried out at a temperature of 65℃ to 90℃. After heating for 1 hour, a polyamic acid solution was obtained. Then, acetic anhydride and triethylamine, chemical imidizing agents, were added to the polyamic acid solution, and the mixture was mechanically stirred to synthesize fluorinated polyimide. After vacuum filtration and drying, the particle size was broken down to the target level using an air jet mill. The obtained fluorinated polyimide has the following structure:

[0181] Following the method described above, the weight-average molecular weight and average particle size of the fluorinated polyimide were determined (see Table 1). The fluorinated polyimide was then characterized using Raman spectroscopy, and the characteristic peaks are as follows: Vibrational peaks are shown in the figure (CF is marked in the range of 1200–1300 cm⁻¹). -1 The characteristic peak of the imide ring is in the range of 1300–1400 cm⁻¹. -1 (Figure 8)

[0182] [Preparation of secondary battery cells]

[0183] The above-mentioned separator is used to prepare secondary battery cells. The composition or preparation method of the positive electrode, negative electrode, electrolyte and secondary battery cell are briefly introduced below.

[0184] Preparation method of positive electrode sheet

[0185] Lithium iron phosphate coated with soft carbon, conductive carbon black, and PVDF are mixed and then coated with N-methylpyrrolidone solvent. The mixture is then coated on both sides of aluminum foil, and after cold pressing and cutting, a positive electrode sheet is obtained. The weight ratio of soft carbon coated lithium iron phosphate: conductive carbon black: PVDF is 8:1:1.

[0186] Method for preparing negative electrode sheet

[0187] Artificial graphite, conductive carbon black, carboxymethyl cellulose (CMC) binder, fluorinated polyimide, and water solvent are mixed evenly by stirring and coated on both sides of copper foil. After cold pressing and cutting, the negative electrode sheet is obtained. The weight ratio of (artificial graphite + fluorinated polyimide): conductive carbon black: CMC: solvent is 95:2:3:100.

[0188] Separating membrane

[0189] A polyethylene film with a thickness of 7 μm was used as the separator.

[0190] Preparation of electrolyte

[0191] Ethylene carbonate, diethyl carbonate, and dimethyl carbonate were mixed in a volume ratio of 1:1:1. LiPF6 was then dissolved in this solution to obtain the electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L.

[0192] Battery assembly

[0193] The electrodes are arranged in the order of "separator-negative electrode-separator-positive electrode". One end of the positive electrode, negative electrode, and two separators is fixed to the discharge roller, and the other end is stacked together and fixed to the winding shaft. A motor is used to rotate the winding shaft, winding the positive electrode, negative electrode, and two separators to obtain the electrode assembly of the wound battery. The electrode assembly is placed in outer packaging, and the prepared electrolyte is injected into the dried secondary battery cell. After vacuum sealing, settling, formation, and aging processes, the secondary battery cell is obtained.

[0194] [Testing Method]

[0195] The properties / performance of the secondary battery cells in the above embodiments and comparative examples were tested.

[0196] Cyclic test: At 60℃, charge at a constant current of 1C to 3.65V, then switch to constant voltage test until the current is less than 0.05C, then discharge at 1C to 2.5V, and repeat this cycle 500 times.

[0197] The test results are shown in Table 1.

[0198] As can be seen from Examples 1-4, increasing the amount of fluorinated polyimide (its proportion in the dry weight of the negative electrode slurry) from 0.5% to 1.5% strengthens its ability to absorb proton acids, which is more beneficial for maintaining the high-temperature cycle performance of the battery. Increasing the amount of fluorinated polyimide from 1.5% to 3.0% can further increase its ability to absorb proton acids, but the improvement is relatively limited.

[0199] The capacity retention rates of Examples 8 and 9 were slightly lower than those of Example 1. This may be because the weight-average molecular weight of the fluorinated polyimide affects the viscosity of the slurry, which in turn affects the adhesion of the electrode and thus the retention of the battery capacity.

[0200] As can be seen from Examples 5, 6, and 7, the size of the fluorinated polyimide particles and the resulting difference in specific surface area may affect the ability to absorb proton acids, thereby affecting the high-temperature cycle performance of the battery.

[0201] Table 1

[0202] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A lithium secondary battery cell, characterized in that... The device includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The negative electrode material layer includes a negative electrode active material and a fluorinated polyimide. The fluorinated polyimide accounts for 0.5% to 3% of the weight of the negative electrode material layer.

2. The lithium secondary battery cell according to claim 1, wherein, The fluorinated polyimide has one or more of the following characteristics: (1) The fluorinated polyimide has a linear molecular chain; (2) The fluorinated polyimide has a weight-average molecular weight of 20kDa to 100kDa; (3) The fluorinated polyimide is a fluorinated aromatic polyimide.

3. The lithium secondary battery cell according to claim 1 or 2, wherein, The fluorinated polyimide is formed by the condensation polymerization of a fluorinated aromatic diamine and a fluorinated aromatic dianhydride; Preferably, the fluorinated aromatic diamine comprises one or more of the following: 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (6FODA), 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl, tetrafluoro-phenylenediamine, 4,4'-diamino-3,3'-difluorodiphenylmethane, 4,4'-diamino-2,2',3,3',5,5',6,6'-octafluorobiphenyl, 2,4-diamino-4'-fluorodiphenyl ether, and 3,5-diamino-trifluorotoluene; Preferably, the fluorinated aromatic dianhydrides include, but are not limited to, hexafluorodianhydride (6FDA), 4,4'-(hexafluoroisopropene)phthalic anhydride, fluorinated derivatives of naphthalenetetracarboxylic dianhydride (NTDA), 1,2,4,5-benzenetetracarboxylic dianhydride, 4,4'-(hexafluoroisopropyl)bis(phthalic anhydride), and 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride; Preferably, the fluorinated aromatic diamine is 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl; Preferably, the fluorinated aromatic dianhydride is 4,4'-(hexafluoroisopropene)phthalic anhydride; Preferably, the molar ratio of the fluorinated aromatic diamine to the fluorinated aromatic dianhydride is 1:0.5 to 2; Preferably, the fluorinated polyimide has a structure as shown in formula (1): Where n is the degree of aggregation.

4. The lithium secondary battery cell according to any one of claims 1-3, wherein, The fluorinated polyimide is prepared by a method comprising the following steps: (1) Dissolve fluorinated aromatic dianhydride and fluorinated aromatic dianhydride in a solvent, and heat at 65°C to 90°C for a certain time under inert gas protection to obtain polyamic acid solution; (2) Add the chemical imidizing agent to the polyamic acid solution and stir to obtain the fluorinated polyimide; (3) Separate, dry, and pulverize the fluorinated polyimide into fluorinated polyimide particles; Preferably, the solvent is an aprotic solvent; Preferably, the inert gas includes argon, helium, or nitrogen; Preferably, the chemical imidizing agent includes a dehydrating agent and a dehydration catalyst; Preferably, the volume average particle size DV of the fluorinated polyimide particles is... 50 The range is 0.1μm to 30μm, with a selectable range of 0.5μm to 30μm, and further selectable range of 0.5μm to 8μm; Preferably, the volume average particle size DV of the fluorinated polyimide particles is... 99 The range is 1μm to 50μm, and can be selected from 1μm to 30μm, and further can be selected from 7μm to 20μm.

5. The lithium secondary battery cell according to any one of claims 1-4, wherein, The negative electrode active material includes one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

6. The lithium secondary battery cell according to any one of claims 1-5, wherein, The negative electrode material layer also includes a binder and / or a conductive agent; Preferably, the adhesive comprises one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). Preferably, the conductive agent includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

7. The lithium secondary battery cell according to any one of claims 1-6, wherein, The negative electrode sheet is prepared by a method including the following steps: mixing negative electrode active material, conductive agent, binder, fluorinated polyimide and solvent evenly by stirring to obtain negative electrode slurry; coating the negative electrode slurry on both sides of the negative electrode current collector; and obtaining the negative electrode sheet after cold pressing and cutting. Preferably, the weight ratio of the fluorinated polyimide to the negative electrode active material is 0.5–3:92–94.5; Preferably, the stirring time is 8h to 24h.

8. An electrical device comprising a lithium secondary battery cell as described in any one of claims 1 to 7.

9. A method for preparing a lithium secondary battery, the method comprising preparing a negative electrode sheet, wherein, The method for preparing the negative electrode sheet includes the following steps: The negative electrode active material, conductive agent, binder, fluorinated polyimide and solvent are mixed evenly by stirring to obtain a negative electrode slurry. The negative electrode slurry is coated on both sides of the negative electrode current collector, and after cold pressing and cutting, a negative electrode sheet is obtained. Preferably, the fluorinated polyimide is as defined in any one of claims 2-4; Preferably, the weight ratio of fluorinated polyimide to negative electrode active material is 0.5-3:94.5-92; preferably, the stirring time is 8-24 hours.

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