Battery monomer, battery and electric device

Abstract

The invention relates to a battery monomer, a battery and a power utilization device. The battery monomer comprises an electrode pole piece, the electrode pole piece comprises a current collector and a film layer arranged on at least one side of the current collector, the film layer comprises an active substance and a plurality of fluorinated polymers, the crystallinity of one of the fluorinated polymers is marked as Xc1%, the cold crystallization temperature is marked as Tc1 DEG C, and the crystallinity of the other fluorinated polymer is marked as Xc1%. The crystallinity of another fluorinated polymer in the multiple fluorinated polymers is marked as Xc2%, the cold crystallization temperature is marked as Tc2 DEG C, and the multiple fluorinated polymers meet the following conditions: (Xc2-Xc1) / Xc1 is more than or equal to 20% and less than or equal to 400%, and (Tc2-Tc1) / Tc1 is more than or equal to 30% and less than 250%.

Description

[0001] This application is a divisional application based on the invention with application number 202311460439.8, application date November 3, 2023, applicant CATL, and invention title "Electrode Sheet, Battery and Electrical Device". Technical Field

[0002] This application relates to a battery cell, a battery, and an electrical device. Background Technology

[0003] Batteries have the characteristics of high capacity and long life, so they are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and power tools, etc.

[0004] As batteries are used in a wider range of applications, the requirements for battery performance are becoming increasingly stringent. However, the cycle life and storage life of batteries are still relatively poor and need further improvement. Summary of the Invention

[0005] This application is made in view of the above-mentioned issues, and its purpose is to provide a battery cell, a battery, and an electrical device.

[0006] In a first aspect, this application proposes a battery cell, which includes an electrode sheet. The electrode sheet includes a current collector and a film layer disposed on at least one side of the current collector. The film layer includes an active material and a variety of fluorinated polymers. The crystallinity of one of the fluorinated polymers is denoted as X. c1 %, the cold crystallization temperature is denoted as T c1 ℃; The crystallinity of one of the various fluorinated polymers is denoted as X. c2 %, the cold crystallization temperature is denoted as T c2 ℃, Among them, many fluorinated polymers satisfy: 20% ≤ (X c2 -X c1 ) / X c1 ≤400%, 30%≤(T) c2 -T c1 ) / T c1 <250%.

[0007] Therefore, the crystallinity X of the first fluorinated polymer in the embodiments of this application is... c1 The percentage is relatively small, and the cold crystallization temperature T c1The relatively low temperature (℃) allows for greater flexibility of the molecular chains, which is more conducive to the formation of in-situ gels on the surface of active material particles by the primary fluorinated polymer, thus improving solid-liquid interface properties. The primary and secondary fluorinated polymers have similar structures, but the secondary fluorinated polymer exhibits higher crystallinity (X) compared to the primary fluorinated polymer. c2 The percentage is relatively large, and the cold crystallization temperature T is relatively high. c2 The higher the temperature, the higher the energy required to release the intermolecular bonds, which is more conducive to increasing its own cohesive energy density, reducing swelling deformation, and enhancing the binding force between active materials. Therefore, the embodiments of this application can effectively improve the cycle performance and storage performance of battery cells through the synergy of various fluorinated polymers.

[0008] In some implementations, 40% ≤ (X c2 -X c1 ) / X c1 <400%; optionally, X c2 -X c1 ≥10; Further optionally, 10≤X c2 -X c1 ≤45; Further optionally, 10≤X c2 -X c1 ≤40. The embodiments of this application, through further selection of the crystallinity and cold crystallization temperature of the fluorinated polymer, can further improve the cycle performance and storage performance of the electrode sheets when applied to battery cells.

[0009] In some implementations, 0 < X c1 ≤28; optionally, 10≤X c1 ≤25; and / or 30≤X c2 ≤50; optionally, 35≤X c2 ≤50.

[0010] In some implementations, 35% ≤ (T c2 -T c1 ) / T c1 <250%; optionally, 39%≤(T) c2 -T c1 ) / T c1 ≤213%; optionally, T c2 -T c1 ≥25; further optionally, 25≤T c2 -T c1 ≤100; further optionally, 35≤T c2 -T c1 ≤85.

[0011] In some implementations, 35 < T is further optionally specified. c1 ≤100; optionally, 40≤T c1≤90; and / or 115≤T c2 ≤140; optionally, 125≤T c2 ≤135.

[0012] In some embodiments, the glass transition temperature of one of the multiple fluorinated polymers is T. g1 ℃, -30≤T g1 ≤40.

[0013] In some embodiments, the glass transition temperature of one of the multiple fluorinated polymers is T. g2 ℃, -30≤T g2 ≤40.

[0014] In some embodiments, each of the multiple fluorinated polymers independently includes at least one of the compounds represented by formula (A1) to formula (AIII). Formula (AI) Formula (AII), In equations (AI) and (AII), R 11 R 12 R 13 and R 14 Each independently comprises a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a substituted or unsubstituted C1-C3 alkyl group, or a substituted or unsubstituted C1-C3 alkoxy group, and R 11 R 12 R 13 and R 14 At least one of them contains a fluorine atom; Formula (AIII) In equation (AIII), R 15 Includes single-bonded, substituted or unsubstituted C1-C3 alkyl groups; p is a positive integer from 1 to 3; n is a positive integer selected from 1000 to 30000.

[0015] In some embodiments, the molecular weight of one of the multiple fluorinated polymers is W1 g / mol, the molecular weight of another of the multiple fluorinated polymers is W2 g / mol, and the multiple fluorinated polymers satisfy: 0 < W 1 / W2 < 1; optionally, 2.0 × 10 5 ≤W1≤1.0×10 6 5.0×10 5 ≤W2≤1.2×10 6The first fluorinated polymer has a relatively small molecular weight and a stronger affinity for solvents, but it is also more susceptible to solvent dispersion, making it difficult to control its positional distribution. The second fluorinated polymer has a relatively high molecular weight and longer molecular chain segments, increasing the probability of contact and entanglement between molecular chain segments and enhancing intermolecular forces. This improves the binding force between active materials and significantly reduces the interaction with solvent molecules, making it easier to control their dispersion position. Using both in combination is more conducive to improving interfacial side reactions and structural stability in the positive electrode, thereby improving the cycle performance and storage performance of the battery cell.

[0016] In some embodiments, the total mass content of the various fluorinated polymers is ≤5% based on the total mass of the film layer; optionally, it is 0.05% to 5%; optionally, the mass content of the first fluorinated polymer is ≤4% based on the total mass of the film layer; optionally, the mass content of the second fluorinated polymer is ≤4% based on the total mass of the film layer. When the mass content of the various fluorinated polymers is within the above range, the various fluorinated polymers can effectively improve the interfacial properties and structural stability of the electrode sheet. The mass content of the various fluorinated polymers refers to the sum of the mass contents of each fluorinated polymer in the various fluorinated polymers.

[0017] In some embodiments, the electrode sheet includes a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive active material, a first fluorinated polymer, and a second fluorinated polymer.

[0018] In some embodiments, the mass content of the first fluorinated polymer and the total mass content of the second fluorinated polymer are 0.05% to 2.5% based on the total mass of the positive electrode film.

[0019] In some implementations, the mass content of the first fluorinated polymer is less than the mass content of the second fluorinated polymer based on the total mass of the positive electrode film.

[0020] In some embodiments, the total mass content of the first fluorinated polymer is ≤2% based on the total mass of the positive electrode film; it may be 0.05% to 2%; or it may be 0.05% to 1%.

[0021] In some embodiments, the total mass content of the second fluorinated polymer is ≤2% based on the total mass of the positive electrode film; it can be 1% to 2%; or it can be 1.2% to 2%.

[0022] In some embodiments, the positive electrode active material includes at least one of lithium phosphate compounds and layered positive electrode active materials.

[0023] In some embodiments, the electrode sheet includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, a first fluorinated polymer, and a second fluorinated polymer.

[0024] In some embodiments, the mass content of the first fluorinated polymer and the total mass content of the second fluorinated polymer are 0.05% to 5% based on the total mass of the negative electrode film.

[0025] In some implementations, the mass content of the first fluorinated polymer is greater than the mass content of the second fluorinated polymer, based on the total mass of the negative electrode film.

[0026] In some implementations, the mass content of the first fluorinated polymer is less than the mass content of the second fluorinated polymer, based on the total mass of the negative electrode film.

[0027] In some embodiments, the mass content of the first fluorinated polymer is ≤4% based on the total mass of the negative electrode film; it can be selected as 0.5% to 4%.

[0028] In some embodiments, the mass content of the second fluorinated polymer is ≤4% based on the total mass of the negative electrode film; it can be selected as 0.4% to 2%.

[0029] In some embodiments, the negative electrode active material includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

[0030] Secondly, this application proposes a battery including a battery cell according to any embodiment of the first aspect of this application.

[0031] Thirdly, this application proposes an electrical device including a battery as described in the second aspect of this application. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of one embodiment of the battery cell of this application.

[0034] Figure 2 yes Figure 1 An exploded view of the implementation method of the battery cell.

[0035] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0036] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0037] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0038] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses the battery cell of this application as a power source.

[0039] The accompanying drawings may not be drawn to scale.

[0040] The annotations in the attached figures are explained as follows: 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Cover plate; 6. Electrical appliances. Detailed Implementation

[0041] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the electrode plates, battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of 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 the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0042] 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 the 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 to 120 and 80 to 110 are listed for a specific parameter, it is also expected that ranges of 60 to 110 and 80 to 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 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise stated, the numerical range "a to b" 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 to 5" means that all real numbers between "0 and 5" have been listed in this article; "0 to 5" is just a shortened representation of these numerical combinations. In addition, when a parameter is stated as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0044] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0045] 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.

[0046] In the embodiments of this application, the terms "multiple" or "multi-type" refer to two or more kinds.

[0047] The term "alkyl" encompasses both straight-chain and branched alkyl groups. For example, alkyl groups can be C1 to C5 alkyl, C1 to C4 alkyl, C1 to C3 alkyl, or C1 to C2 alkyl. In some embodiments, alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, etc. Additionally, alkyl groups may optionally be substituted. When substituted, the substituents include fluorine atoms.

[0048] The term "alkoxy group" refers to a group in which an alkyl group is bonded to an oxygen atom by a single bond. For example, an alkoxy group can be a C1-C5 alkoxy group, a C1-C3 alkoxy group, or a C1-C2 alkoxy group. In some embodiments, an alkoxy group may include a methoxy group, an ethoxy group, or a propoxy group. Additionally, an alkoxy group may optionally be substituted.

[0049] The term "halogen atom" refers to fluorine atoms, chlorine atoms, bromine atoms, etc.

[0050] The term "hydrogen" refers to 1H (protium, H), 2H (deuterium, D), or 3H (tritium, T). In various embodiments, "hydrogen" may be 1H (protium, H).

[0051] The battery includes an electrode assembly and an electrolyte. The electrode assembly includes electrode plates and a separator. The electrode plates include a positive electrode plate and a negative electrode plate. The positive electrode plate includes a positive electrode film layer containing a positive active material that can provide active ions. The negative electrode plate includes a negative electrode film layer containing a negative active material. The separator is placed between the positive and negative electrode plates and mainly serves to prevent short circuits between the positive and negative electrode plates, while allowing active ions to pass freely to form a circuit.

[0052] There is a solid-liquid interface between the electrode and the electrolyte. During the battery cycle charge and discharge, the electrode may expand in volume, which will cause the interface to be damaged and a new interface to be formed. The formation of the new interface will lead to the continuous occurrence of interfacial side reactions, which will deteriorate the cycle performance and storage performance of the battery cell.

[0053] In view of the above problems, the embodiments of this application improve the cycle performance and storage performance of battery cells by improving the interfacial performance of the solid-liquid interface. The embodiments of this application propose an electrode sheet comprising multiple fluorinated polymers, at least two of which are made of different materials. One of the fluorinated polymers can form an in-situ gel on the surface of the solid-phase active material, i.e., a stable solid-liquid interface is formed on the surface of the active material, reducing the risk of side reactions at the solid-liquid interface. However, this fluorinated polymer is not conducive to the bonding between the active materials, resulting in poor structural stability of the electrode sheet. Another fluorinated polymer can enhance the bonding force between the active materials, playing a supporting role in the electrode sheet, thereby improving the structural stability of the electrode sheet and thus improving the cycle performance and storage performance of the battery cell.

[0054] The technical solution of this application will now be described in detail.

[0055] Electrode plates In a first aspect, this application proposes an electrode sheet.

[0056] The electrode includes a current collector and a film layer disposed on at least one side of the current collector. The film layer includes an active material and various fluorinated polymers, wherein the crystallinity of one of the fluorinated polymers is denoted as X. c1 %, the cold crystallization temperature is denoted as T c1 ℃, the crystallinity of one of the fluorinated polymers in a variety of fluorinated polymers is denoted as X. c2 %, the cold crystallization temperature is denoted as T c2 ℃, where many fluorinated polymers satisfy: 20% ≤ (X c2 -X c1 ) / X c1 <400%, 30%≤(T) c2 -T c1 ) / T c1 <250%.

[0057] The electrode sheet may include at least one of a positive electrode sheet and a negative electrode sheet; for example, the electrode sheet includes a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector, the positive electrode film layer including a positive active material and a variety of fluorinated polymers. As another example, the electrode sheet includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector, the negative electrode film layer including a negative active material and a variety of fluorinated polymers. As yet another example, the electrode sheet includes both a positive and a negative electrode sheet; the positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector, the positive electrode film layer including a positive active material and a variety of fluorinated polymers; the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector, the negative electrode film layer including a negative active material and a variety of fluorinated polymers.

[0058] In this application, each of the multiple fluorinated polymers is a polymer containing fluorine atoms. One of the multiple fluorinated polymers is defined as the first fluorinated polymer, another as the second, and so on, when the multiple fluorinated polymers also include a third, which is defined as the third fluorinated polymer. The more types of fluorinated polymers used, the better the cycle performance and storage performance of the battery cells can be improved through their combined use.

[0059] The first fluorinated polymer has good affinity with the electrolyte in the battery cell. When the first fluorinated polymer comes into contact with the electrolyte, it swells. The solvent in the electrolyte can quickly diffuse into the molecular chains of the first fluorinated polymer and be encapsulated by the molecular chains, forming an in-situ gel on the surface of the active material. This gel adheres to the surface of the active material, providing protection and thus tightly bonding the active material and electrolyte, improving the solid-liquid interface performance and reducing side reactions between the active material and electrolyte. However, due to the poor solvent resistance of the first fluorinated polymer, it is not conducive to tightly bonding the active materials together, especially during the expansion and contraction of the active materials in the later stages of cycling. The weak bonding force between the active materials leads to poor structural stability of the electrode sheet. This application also includes a second fluorinated polymer. The second fluorinated polymer has better solvent resistance and a higher cohesive energy density, which can slow down its own swelling and deformation, improve the bonding force between the active materials, and thus improve the structural stability of the electrode sheet, enhancing the cycle performance and storage performance of the battery cell.

[0060] Crystallinity X of the first fluorinated polymer c1 The percentage is relatively small, and the cold crystallization temperature T c1 The relatively low temperature (℃) allows for greater flexibility of the molecular chains, which is more conducive to the formation of in-situ gels on the surface of active material particles by the primary fluorinated polymer, thus improving solid-liquid interface properties. The primary and secondary fluorinated polymers have similar structures, but the secondary fluorinated polymer exhibits higher crystallinity (X) compared to the primary fluorinated polymer. c2 The percentage is relatively large, and the cold crystallization temperature T is relatively high. c2 The higher the temperature, the higher the energy required to release the intermolecular bonds, which is more conducive to increasing its own cohesive energy density, reducing swelling deformation, and enhancing the binding force between active materials. Therefore, the embodiments of this application can effectively improve the cycle performance and storage performance of battery cells through the synergy of various fluorinated polymers.

[0061] Crystallization refers to the process by which atoms, ions, or molecules in a material arrange themselves in a specific spatial order to form an ordered structure. The conformation of polymers during crystallization is determined by both intramolecular and intermolecular factors. Intermolecular forces affect the packing density between molecular chains. Crystallinity X C % is used to characterize the degree of crystallinity in a material, and the cold crystallization temperature T is used to characterize the degree of crystallinity in a material. c ℃ is the crystallization temperature of the material during the cooling process after melting. Both parameters can be measured using differential scanning calorimetry (DSC). Specifically, the testing procedure is as follows: Take 0.5g to 0.8g of sample, place the sample in a crucible, and subject the sample to heating and cooling treatments under a nitrogen atmosphere at a heating rate of 10℃ / min, starting from the intrinsic temperature of the material at ℃. g The initial temperature is 20°C lower than the material's intrinsic temperature. mThe temperature was increased by 20°C and held constant for 5 minutes, and the first heating curve was recorded. Then, the temperature was decreased at a rate of 10°C / min to a temperature lower than the intrinsic temperature of the material. g Record the cooling curve at a cutoff temperature 20°C lower than the specified temperature. The peak value or transition point of the heat absorption and release during the cooling process is the actual cold crystallization temperature T of the material. c By calculating the peak area corresponding to each peak on the cooling curve at ℃, the enthalpy of crystallization can be obtained. The ratio of the enthalpy of crystallization to the standard enthalpy is the degree of crystallinity X. C % etc. The crystallinity in the embodiments of this application refers to the crystallinity measured by differential scanning calorimetry.

[0062] The embodiments of this application can further improve the cycle performance and storage performance of electrode sheets when applied to battery cells by further selecting the crystallinity and cold crystallization temperature of fluorinated polymers.

[0063] In this embodiment of the application, 20% ≤ (X) c2 -X c1 ) / X c1 <400%; optionally, 40%≤(X) c2 -X c1 ) / X c1 <400%. For example, (X c2 -X c1 ) / X c1 The percentages can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 105%, 110%, 115%, 120%, 125%, 130%, 135%, 140%, 145%, 150%, 155%, 160%, 165%, 170%, 175%, 180%, 185%, 190%, 195%, 200%, 205%, 210%, 220%, 2 25%, 230%, 235%, 240%, 245%, 250%, 255%, 260%, 265%, 270%, 275%, 280%, 285%, 290%, 295%, 300%, 305%, 310%, 315%, 320%, 325%, 330%, 335%, 340%, 345%, 350%, 355%, 360%, 365%, 370%, 375%, 380%, 385%, 390%, 395%, or a range consisting of any two of the above values.

[0064] In some implementations, X c2 -X c1 ≥10; optionally, 10≤X c2 -X c1 ≤45. For example, X c2 -Xc1 The crystallinity can be 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, or any combination of two of the above values. In other words, the difference between the crystallinity of the second fluorinated polymer and the crystallinity of the first fluorinated polymer is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any combination of two of the above values.

[0065] In some implementations, 0 < X c1 ≤28. The crystallinity of the primary fluorinated polymer, as determined by differential scanning calorimetry, can be 5%, 10%, 15%, 20%, 25%, 28%, or a range of any two of the above values. X c1 When the percentage is less than 10%, the fluorinated polymer has virtually no melting peak, and the melting temperature may not be detectable.

[0066] In some implementations, 30 ≤ X c2 ≤50. The crystallinity of the second fluorinated polymer, as determined by differential scanning calorimetry, can be 30%, 35%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, or any range of two of the above values. X c2 When the percentage is less than 10%, the fluorinated polymer has virtually no melting peak, and the melting temperature may not be detectable.

[0067] In this embodiment of the application, 30%≤(T) c2 -T c1 ) / T c1 <250%; optionally, 35%≤(T) c2 -T c1 ) / T c1 <250%. For example, (T c2 -T c1 ) / T c1 It can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 105%, 110%, 115%, 120%, 125%, 130%, 135%, 140%, 145%, 150%, 155%, 160%, 165%, 170%, 175%, 180%, 185%, 190%, 195%, 200%, 205%, 210%, 220%, 225%, 230%, 235%, 240%, 245%, 250%, or a range of any two of the above values.

[0068] In some implementations, T c2 -T c1 ≥25; further optionally, 25≤Tc2 -T c1 ≤100; for example, T c2 -T c1 The temperature difference between the cold crystallization temperature of the second fluorinated polymer and the first fluorinated polymer can be 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, or any combination of two of the above values. In other words, the difference between the cold crystallization temperature of the second fluorinated polymer and the first fluorinated polymer is 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, or any combination of two of the above values.

[0069] In some implementations, 35 < T c1 ≤100. The cold crystallization temperature of the first fluoropolymer can be 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 81℃, 85℃, 90℃, 95℃, 100℃ or any combination of two of the above values.

[0070] In some implementations, 115≤T c2 ≤140. The cold crystallization temperature of the second fluorinated polymer can be 115℃, 118℃, 120℃, 122℃, 125℃, 128℃, 130℃, 132℃, 135℃, 138℃, 140℃ or any combination of two of the above values.

[0071] In some embodiments, the glass transition temperature of the first fluorinated polymer is T. g1 ℃, -30≤T g1 ≤40. For example, the glass transition temperature of the first fluorinated polymer can be -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, or a range of any two of the above values.

[0072] In some embodiments, the glass transition temperature of the second fluorinated polymer is T. g2 ℃, -30≤T g2 ≤40. For example, the glass transition temperature of the second fluorinated polymer can be -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, or a range of any two of the above values.

[0073] In some embodiments, each of the multiple fluorinated polymers independently includes at least one of the compounds shown in formula (A1) to formula (AIII).

[0074] When multiple fluorinated polymers include a first fluorinated polymer and a second fluorinated polymer, each of the first fluorinated polymer and the second fluorinated polymer independently includes at least one of the compounds shown in formula (A1) to formula (AIII), and the first fluorinated polymer and the second fluorinated polymer are different in material, which can be distinguished by the difference in structural units and / or the difference in degree of polymerization.

[0075] When multiple fluorinated polymers include a first fluorinated polymer, a second fluorinated polymer, and a third fluorinated polymer, the first fluorinated polymer and the second fluorinated polymer each independently include at least one of the compounds shown in formula (A1) to the compounds shown in formula (AIII), and the materials of the first fluorinated polymer, the second fluorinated polymer, and the third fluorinated polymer are different from each other, specifically by the difference in structural units and / or the difference in degree of polymerization.

[0076] The compounds represented by formula (AI) are as follows: Formula (AI) In formula (AI), R 11 R 12 R 13 and R 14 Each independently comprises a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted alkoxy group, and R 11 R 12 R 13 and R 14 At least one of them contains a fluorine atom.

[0077] Optionally, R 11 R 12 R 13 and R 14 Each of them independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C10 alkyl group, or a substituted or unsubstituted C1-C10 alkoxy group.

[0078] Optionally, R 11 R 12 R 13 and R 14 Each of them independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C3 alkyl group, or a substituted or unsubstituted C1-C3 alkoxy group.

[0079] Further optional, R 11 R12 R 13 and R 14 Each of these atoms independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a methyl group, a fluoromethyl group, a methoxy group, or a perfluoromethoxy group.

[0080] In some embodiments, the degree of polymerization n of the fluoropolymer is selected from positive integers from 1000 to 30000, such as 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000, 21000, 22000, 23000, 24000, 25000, 26000, 27000, 28000, 29000, or a range of any two of the above values.

[0081] Optionally, when substituted, the substituent may include one or more of the following: nitrile (-CN), nitro, sulfonic acid, sulfonyl, amide, carboxyl, ester, and halogen atom. The halogen atom may include fluorine, bromine, etc., and may be a fluorine atom.

[0082] In some embodiments, the fluorinated polymer includes at least one of the compounds shown in formula (AI-1) to the compounds shown in formula (AI-11). Formula (AI-1) Formula (AI-2) Formula (AI-3) Formula (AI-4) Formula (AI-5) Formula (AI-6) Formula (AI-7) Formula (AI-8) Formula (AI-9) Formula (AI-10) Formula (AI-11).

[0083] The compounds represented by formula (AII) are as follows: Formula (AII), In formula (AII), R 11 R 12 R 13 and R 14 Each independently comprises a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted alkoxy group, and R 11 R12 R 13 and R 14 At least one of them contains a fluorine atom.

[0084] Optionally, R 11 R 12 R 13 and R 14 Each of them independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C10 alkyl group, or a substituted or unsubstituted C1-C10 alkoxy group.

[0085] Optionally, R 11 R 12 R 13 and R 14 Each of them independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a substituted or unsubstituted C1-C3 alkyl group, or a substituted or unsubstituted C1-C3 alkoxy group.

[0086] Further optional, R 11 R 12 R 13 and R 14 Each of these atoms independently includes a hydrogen atom, a fluorine atom, a chlorine atom, a methyl group, a fluoromethyl group, a methoxy group, or a perfluoromethoxy group.

[0087] In some embodiments, the degree of polymerization n of the fluoropolymer is selected from positive integers from 1000 to 30000, such as 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000, 21000, 22000, 23000, 24000, 25000, 26000, 27000, 28000, 29000, or a range of any two of the above values.

[0088] Optionally, when substituted, the substituent may include one or more of the following: nitrile (-CN), nitro, sulfonic acid, sulfonyl, amide, carboxyl, ester, and halogen atom. The halogen atom may include fluorine, bromine, etc., and may be a fluorine atom.

[0089] In some embodiments, the fluorinated polymer includes at least one of the compounds shown in formula (AII-1) to formula (AII-5). Formula (AII-1) Formula (AII-2) Formula (AII-3) Formula (AII-4) Formula (AII-5).

[0090] The compounds represented by formula (AIII) are as follows: Formula (AIII) In equation (AIII), R 15 Includes single bonds, substituted or unsubstituted alkyl groups; when substituted, the substituents include fluorine atoms.

[0091] In some embodiments, when substituted, the substituent may include one or more of the following: nitrile (-CN), nitro, sulfonic acid, sulfonyl, amide, carboxyl, ester, and halogen atom.

[0092] Optionally, R 15 Includes single-bonded, substituted or unsubstituted C1-C3 alkyl groups.

[0093] In some implementations, p is selected from positive integers from 1 to 3, such as 1, 2, or 3.

[0094] In some embodiments, the degree of polymerization n of the fluoropolymer is selected from positive integers from 1000 to 30000, such as 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000, 21000, 22000, 23000, 24000, 25000, 26000, 27000, 28000, 29000, or a range of any two of the above values.

[0095] In some embodiments, the fluorinated polymer includes at least one of the compounds shown in formula (AIII-1) to formula (AIII-3). Formula (AIII-1) Formula (AIII-2) Formula (AIII-3).

[0096] For example, fluorinated polymers include one or more of the following: perfluoroethylene (PTFE), polyvinylidene fluoride (PVDF), perfluoroethylene-propylene copolymer (FEP), perfluoroalkoxy polymer (PFA), perfluoropolyether (PFPE), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE), and perfluoro(1-butenyl vinyl ether) polymer (CYTOP).

[0097] Optionally, the fluorinated polymer includes one or more of the following: perfluoroethylene (PTFE), polyvinylidene fluoride (PVDF), perfluoroethylene propylene copolymer (FEP), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE).

[0098] The aforementioned fluorinated polymers can be derived from one or more of the following monomers: fluorinated cyclohexane, fluorinated vinylidene, 1,2-difluoroethylene, vinylidene fluoride, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, hexafluoropropylene, 3,3,3-trifluoropropylene, trifluoropropylene, tetrafluoropropylene, and pentafluoropropylene. Optionally, the aforementioned fluorinated polymers can be derived from at least two of the following monomers: fluorinated cyclohexane, fluorinated vinylidene, 1,2-difluoroethylene, vinylidene fluoride, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, hexafluoropropylene, 3,3,3-trifluoropropylene, trifluoropropylene, tetrafluoropropylene, and pentafluoropropylene.

[0099] In embodiments of this application, the polymer can also be obtained by copolymerizing the above-mentioned structural groups with small amounts of other types of structural groups (e.g., olefin compounds, ester monomers, nitrile monomers such as acrylonitrile, amide monomers such as acrylamide, acrylic acid, etc.). These small amounts of monomers have relatively poor hydrophilic properties; copolymerizing the monomers of the above-mentioned fluorinated polymer with these monomers can improve the swelling ratio and compressive modulus of the fluorinated polymer.

[0100] In some embodiments, the molecular weight of the fluorinated polymer is 2 × 10⁻⁶. 5 g / mol to 1.5 × 10 6 g / mol.

[0101] For example, the molecular weight of the fluoropolymer can be 2 × 10⁻⁶. 5 g / mol, 5×10 5 g / mol, 8×10 5 g / mol, 1×10 6 g / mol, 1.2×10 6 g / mol or a range consisting of any two of the above values.

[0102] In some embodiments, the molecular weight of the first fluorinated polymer is W1 g / mol, the molecular weight of the second fluorinated polymer is W2 g / mol, and multiple fluorinated polymers satisfy: 0 < W 1 / W2 < 1. The first fluorinated polymer has a relatively small molecular weight and a stronger affinity for the solvent, but it is also more susceptible to solvent dispersion, making it difficult to control its positional distribution. The second fluorinated polymer has a relatively high molecular weight and longer molecular chains, increasing the probability of contact and entanglement between molecular chains and enhancing intermolecular forces. This improves the binding force between active materials and significantly reduces interaction with solvent molecules, making it easier to control their dispersion position. Using both in combination is more beneficial for balancing the improvement of interfacial side reactions and structural stability in the positive electrode, thereby improving the cycle performance and storage performance of the battery cell. For example, W... 1 / W2 < can be 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, or a range consisting of any two of the above values.

[0103] In some implementations, 2.0 × 10 5 ≤W1≤1.0×10 6 For example, the molecular weight of the first fluorinated polymer can be 2 × 10⁻⁶. 5 g / mol, 5×10 5 g / mol, 8×10 5 g / mol, 1.0×10 6 g / mol or a range consisting of any two of the above values.

[0104] In some implementations, 5.0 × 10 5 ≤W2≤1.5×10 6 For example, the molecular weight of the second fluorinated polymer can be 5 × 10⁻⁶. 5 g / mol, 6×10 5 g / mol, 8×10 5 g / mol, 1×10 6 g / mol, 1.5×10 6 g / mol or a range consisting of any two of the above values.

[0105] The relevant parameters of the fluoropolymers in the embodiments of this application can be detected using the following methods: The functional groups of the fluorinated polymers in this application embodiment can be detected using infrared spectrophotometry (IR). Specifically, the fluorinated polymers are tested using a Thermo Nicolet Nexus 670 attenuated total reflectance Fourier transform infrared spectrometer (FTIR-ATR), and then tested according to standard GB / T6040-2002. The test range is 600~4000 cm⁻¹ using the ATR method. -1 Repeatability: ±2cm -1 Resolution: better than 4cm -1 ; Transmission depth 0.2~0.6μm.

[0106] The structure of the fluorinated polymer in the embodiments of this application can be determined by nuclear magnetic resonance (NMR). Specifically, 1H NMR and 13C NMR are performed on a Varian Mercury Plus-400 NMR spectrometer at a test temperature of 20°C, with TMS as an internal standard, CDCl3 as a solvent, and a proton resonance frequency of 400MHz.

[0107] The polymer monomer type of the fluorinated polymer in this application (especially suitable for monomers with a small proportion in the polymer) can be determined by pyrolysis-gas chromatography-mass spectrometry. The specific test steps are as follows: accurately weigh 0.5 mg of sample into a sample cup, fix it to the injection rod, and then insert it into the pyrolyzer installed near the GC (gas chromatograph) injection port. After the pyrolyzer temperature reaches the set temperature, press the injection button. The sample cup will fall rapidly into the core of the pyrolysis furnace through free fall. In the inert gas N2 atmosphere, the volatile components will instantly vaporize and be carried into the gas chromatography column by the carrier gas for separation. Finally, it will be detected by flame ionization detector (FID) or mass spectrometer (MS) to obtain a gas chromatogram or total ion chromatogram.

[0108] The molecular weight of the fluorinated polymers in this application embodiment has a meaning known in the art and can be determined using commonly used equipment and methods in the art. It can be tested by gel permeation chromatography (GPC) according to GB / T21863-2008. The specific test steps are as follows: take an appropriate amount of the sample to be tested (the sample concentration should be 8%-12% opacity), add 20 ml of deionized water, and simultaneously incubate for 5 min (53 kHz / 120 W) to ensure that the sample is completely dispersed. Then, the sample is measured according to GB / T19077-2016 / ISO 13320:2009.

[0109] [Positive electrode plate] In some embodiments, the electrode sheet includes a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive active material and a variety of fluorinated polymers. In this case, the negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative active material and a variety of fluorinated polymers. Alternatively, the negative electrode sheet may include a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative active material, i.e., it does not contain fluorinated polymers.

[0110] In other embodiments, the electrode assembly includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material and a variety of fluorinated polymers. In this case, the positive electrode film layer may include a positive electrode active material, i.e., it does not contain fluorinated polymers.

[0111] Further research revealed that when both the positive and negative electrode films contain multiple fluorinated polymers, these polymers can improve the interfacial performance and structural stability of both the positive and negative electrode films, thereby effectively enhancing the cycle performance and storage performance of the battery cells.

[0112] In some embodiments, the total mass content of the various fluorinated polymers is ≤5% based on the total mass of the positive electrode film; optionally, it is 0.05% to 3%; optionally, it is 0.05% to 2.5%. When the mass content of the various fluorinated polymers is within the above range, the various fluorinated polymers can effectively improve the interfacial properties and structural stability of the positive electrode sheet. The mass content of the various fluorinated polymers refers to the sum of the mass contents of each fluorinated polymer in the various fluorinated polymers.

[0113] For example, the total mass content of various fluorinated polymers can be 0.05%, 0.08%, 0.10%, 0.11%, 0.12%, 0.15%, 0.16%, 0.18%, 0.20%, 0.22%, 0.25%, 0.28%, 0.30%, 0.32%, 0.35%, 0.38%, 0.40%, 0.42%, 0.45%, 0.48%, 0.50%, 0.55%, 0.58%, 0.60%, 0.70%, 0.80%, 0.90%, 0.95%, 1%, 1.1%, 1.2%, 1 0.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, or a range consisting of any two of the above values.

[0114] In some embodiments, the mass content of the first fluorinated polymer is less than the mass content of the second fluorinated polymer based on the total mass of the positive electrode film; when multiple fluorinated polymers meet the above conditions, the interfacial performance and structural stability of the positive electrode sheet can be further improved.

[0115] In some embodiments, the mass content of the first fluorinated polymer is ≤2% based on the total mass of the positive electrode film; it can be selected from 0.05% to 2%; it can be selected from 0.05% to 1%, for example 0.05%, 0.08%, 0.10%, 0.11%, 0.12%, 0.15%, 0.16%, 0.18%, 0.20%, 0.22%, 0.25%, 0.28%, 0.30%, 0.32%, 0.35%, 0.38%, 0.40%, 0.42%, 0.45%, 0.48%, 0.50%, 0.55%, 0.58%, 0.60%, 0.70%, 0.80%, 0.90%, 0.95%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, or a range of any two of the above values.

[0116] In some embodiments, the mass content of the second fluorinated polymer is ≤2% based on the total mass of the positive electrode film; it can be selected from 1% to 2%; it can be selected from 1.2% to 2%, for example 0.05%, 0.08%, 0.10%, 0.11%, 0.12%, 0.15%, 0.16%, 0.18%, 0.20%, 0.22%, 0.25%, 0.28%, 0.30%, 0.32%, 0.35%, 0.38%, 0.40%, 0.42%, 0.45%, 0.48%, 0.50%, 0.55%, 0.58%, 0.60%, 0.70%, 0.80%, 0.90%, 0.95%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, or a range of any two of the above values.

[0117] In this application, the polymer mass content has a meaning known in the art and can be detected using equipment and methods known in the art. For example, it can be detected using thermogravimetric analysis (TGA) according to JYT014-1996. Specifically, based on the mass loss of the electrode during the heating process, a mass-temperature curve, i.e., a TG curve, is plotted. The mass loss corresponding to the polymer decomposition temperature is read as the total mass of the polymer in the electrode, thereby calculating the polymer mass content and coating weight. During the test, the following temperature rise program can be used in a nitrogen atmosphere: 5℃ / min, RT~500℃; 10℃ / min, 500~600℃; constant temperature at 600℃ for 10 min, then end.

[0118] The positive electrode film includes a positive electrode active material, which may be a positive electrode active material known in the art for use in battery cells. As an example, the positive electrode active material is a lithium-containing positive electrode active material, which may include at least one of the following materials: lithium phosphate compounds and layered positive electrode active materials.

[0119] For example, the general formula of olivine-type phosphate active substances (containing lithium phosphate compounds) is: Li x A y Me a M b P 1-c X c Y zWherein, 0≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of S, Si, Cl, B, C, and N; Y includes one or more of O and F. Specifically, olivine-type phosphate active substances include one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0120] For example, layered cathode active materials (such as ternary, lithium nickel oxide / sodium, lithium cobalt oxide / sodium, lithium manganese oxide / sodium, lithium-rich layered, and rock salt phase layered materials). The general formula for layered cathode active materials is: Li x A y Ni a Co b Mn c M (1-a-b-c) Y z Wherein, 0≤x≤2.1, 0≤y≤2.1, and 0.9≤x+y≤2.1; 0≤a≤1, 0≤b≤1, 0≤c≤1, and 0.1≤a+b+c≤1; 1.8≤z≤3.5; A includes one or more of Na, K, and Mg; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; Y includes one or more of O and F. Optionally, y=0. Specifically, the layered structure positive electrode active material may include lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium manganese oxide (LMO), and LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NML33), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 One or more of O2 (NCM811) and NCA.

[0121] During the charging and discharging process, active ions such as Li undergo insertion / extraction and consumption, resulting in varying molar Li content in the battery cell at different discharge states. In the embodiments of this application regarding the positive electrode active material, the molar Li content refers to the initial state of the material, i.e., the state before feeding. After charge-discharge cycles, the molar Li content may change when the positive electrode active material is applied to the battery system.

[0122] In the embodiments of this application, the molar content of oxygen (O) in the positive electrode active materials is only a theoretical value. Oxygen release from the crystal lattice will cause the molar content of oxygen (O) to change. In reality, the molar content of oxygen (O) will fluctuate.

[0123] In the embodiments of this application, the modified compound may be modified by doping or coating. Doping modification may involve adding doping elements such as transition metals to the compound, while coating modification may involve surface coating with materials such as carbon, that is, forming a carbon coating layer on the outer surface of the particles.

[0124] In some embodiments, the mass content of the positive electrode active material is 80% to 99.9%, optionally 90% to 99%, based on the total mass of the positive electrode film. When the mass content of the positive electrode active material is within the above range, it is beneficial to improve the energy density of the battery cell.

[0125] In some embodiments, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer can be disposed on either or both of the two opposite surfaces of the positive current collector.

[0126] In some embodiments, the positive current collector may be a metal foil or a composite current collector. Examples of metal foils include aluminum foil or aluminum alloy foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. Examples of the metal material include one or more combinations selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The polymer substrate may include one or more combinations selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0127] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose particular limitations on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes one or more combinations selected from superconducting carbon, conductive carbon black, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent is less than 5% based on the total mass of the positive electrode film layer.

[0128] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, various fluorinated polymers, optional conductive agents, optional binders, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to this. Of course, the preparation of the positive electrode sheet is not limited to the above methods; the preparation methods described earlier can also be used.

[0129] [Negative electrode plate] In some embodiments, the electrode sheet includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material and a variety of fluorinated polymers.

[0130] The negative electrode active material may be any negative electrode active material known in the art for use in battery cells. As an example, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include at least one of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include at least one of elemental tin, tin oxide, and tin alloys.

[0131] In some embodiments, the mass content of the negative electrode active material is 80% to 99.9%, optionally 90% to 99%, based on the total mass of the negative electrode film. When the mass content of the negative electrode active material is within the above range, it is beneficial to improve the energy density of the battery cell.

[0132] In some embodiments, the mass content of the various fluorinated polymers is ≤5% based on the total mass of the negative electrode film; it can be selected as 0.05% to 5%. When the mass content of the various fluorinated polymers is within the above range, the various fluorinated polymers can effectively improve the interfacial properties and structural stability of the negative electrode sheet. The mass content of the various fluorinated polymers refers to the sum of the mass contents of each fluorinated polymer in the various fluorinated polymers.

[0133] For example, the mass content of various fluoropolymers can be 0.05%, 0.08%, 0.10%, 0.11%, 0.12%, 0.15%, 0.16%, 0.18%, 0.20%, 0.22%, 0.25%, 0.28%, 0.30%, 0.32%, 0.35%, 0.38%, 0.40%, 0.42%, 0.45%, 0.48%, 0.50%, 0.55%, 0.58%, 0.60%, 0.70%, 0.80%, 0.90%, 0.95%, 1%, 1.1%, 1.2%, 1%. 3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, or a range consisting of any two of the above values.

[0134] In some embodiments, when an aqueous solvent is used for the negative electrode slurry, the mass content of the first fluorinated polymer is greater than the mass content of the second fluorinated polymer based on the total mass of the negative electrode film. When multiple fluorinated polymers meet the above conditions, the interfacial properties and structural stability of the negative electrode sheet can be further improved.

[0135] In some embodiments, the mass content of the first fluorinated polymer is ≤4% based on the total mass of the negative electrode film; it can be optionally from 0.5% to 4%, or from 2% to 4%. For example, the mass content of the first fluorinated polymer can be 0.05%, 0.08%, 0.10%, 0.11%, 0.12%, 0.15%, 0.16%, 0.18%, 0.20%, 0.22%, 0.25%, 0.28%, 0.30%, 0.32%, 0.35%, 0.38%, 0.40%, 0.42%, 0.45%, 0.48%, 0.50%, or 0.55%. 0.58%, 0.60%, 0.70%, 0.80%, 0.90%, 0.95%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, or a range consisting of any two of the above values.

[0136] In some embodiments, the mass content of the second fluorinated polymer is ≤4% based on the total mass of the negative electrode film; it can be optionally 0.4% to 4%, more preferably 0.4% to 2%, and even more preferably 0.4% to 1%. For example, the mass content of the first fluorinated polymer can be 0.05%, 0.08%, 0.10%, 0.11%, 0.12%, 0.15%, 0.16%, 0.18%, 0.20%, 0.22%, 0.25%, 0.28%, 0.30%, 0.32%, 0.35%, 0.38%, 0.40%, 0.42%, 0.45%, 0.48%, 0. 0.50%, 0.55%, 0.58%, 0.60%, 0.70%, 0.80%, 0.90%, 0.95%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, or a range consisting of any two of the above values.

[0137] In some embodiments, when an oil-based solvent is used in the negative electrode slurry, the mass content of the first fluorinated polymer is greater than the mass content of the second fluorinated polymer based on the total mass of the negative electrode film. When multiple fluorinated polymers meet the above conditions, the interfacial properties and structural stability of the negative electrode sheet can be further improved.

[0138] In some embodiments, the mass content of the first fluorinated polymer is ≤4% based on the total mass of the negative electrode film; it can be selected as 0.5% to 2%.

[0139] In some embodiments, the mass content of the second fluorinated polymer is ≤4% based on the total mass of the negative electrode film; it can be selected from 0.4% to 4%, and more preferably from 2% to 4%.

[0140] In some embodiments, the negative electrode current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0141] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose particular limitations on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the negative electrode conductive agent is ≤5% based on the total mass of the negative electrode film layer.

[0142] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc. In some embodiments, the mass percentage of other additives is ≤2% based on the total mass of the negative electrode film.

[0143] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0144] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, various fluorinated polymers, optional conductive agents, optional binders, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these. Of course, the preparation of the negative electrode sheet is not limited to the above methods; the preparation methods described earlier can also be used.

[0145] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoating layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0146] battery cell Secondly, this application proposes a battery cell in its embodiments.

[0147] The battery cell includes electrode plates as described in any embodiment of the first aspect of this application, which can effectively improve the cycle performance and storage performance of the battery cell.

[0148] [Isolation membrane] In some implementations, the battery cell includes a separator.

[0149] In some embodiments, the separator includes a substrate.

[0150] In some embodiments, the separator includes a substrate and a coating disposed on at least one surface of the substrate.

[0151] The embodiments of this application do not have particular limitations on the material of the substrate. Any known substrate with good chemical and mechanical stability can be selected, such as at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The substrate can be a single-layer film or a multi-layer composite film. When the substrate is a multi-layer composite film, the materials of each layer can be the same or different.

[0152] In some embodiments, the coating may also include heat-resistant fillers. Further, the heat-resistant fillers may include at least one of inorganic particles and organic particles.

[0153] In some embodiments, the decomposition temperature of the heat-resistant filler can be above 200°C, thereby giving the heat-resistant filler good thermal stability and resistance to decomposition, which can further improve the heat resistance of the separator.

[0154] Inorganic particles possess high thermal stability and are not easily decomposed. Optionally, the inorganic particles include at least one of the following: inorganic particles with a dielectric constant of 5 or higher, inorganic particles with ionic conductivity but without ion storage, and inorganic particles capable of undergoing electrochemical reactions.

[0155] Optionally, inorganic particles with a dielectric constant of 5 or higher include boehmite, alumina, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hydropyrite, zirconium titanate, barium titanate, Pb(Zr,Ti)O3 (abbreviated as PZT), and Pb 1-m La m Zr 1-n Ti n O3 (abbreviated as PLZT, 0 < m < 1, 0 < n < 1), Pb(Mg3Nb) 2 / 3 The inorganic particles are selected from at least one of PbTiO3 (PMN-PT) and its modified inorganic particles. Optionally, the modification of each inorganic particle can be chemical and / or physical. Chemical modification methods include coupling agent modification (e.g., using silane coupling agents, titanate coupling agents, etc.), surfactant modification, polymer grafting modification, etc. Physical modification methods can include mechanical dispersion, ultrasonic dispersion, high-energy treatment, etc. Modification treatment can reduce the agglomeration of inorganic particles, thereby enabling them to form a more stable and uniform spatial network structure with nanocellulose. Furthermore, by selecting coupling agents, surfactants, or polymers with specific functional groups to modify the inorganic particles, it is also helpful to improve the coating's wetting properties to the electrolyte and enhance the adhesion strength between the coating and the substrate.

[0156] Optionally, inorganic particles that are ion-conductive but do not store ions include Li3PO4 and lithium titanium phosphate (Li). x1 Ti y1 (PO4)3, Lithium aluminum titanium phosphate (Li) x2 Al y2 Ti z1 (PO4)3、(LiAlTiP) x3 O y3 Type glass, lithium lanthanum titanate (Li) x4 La y4 TiO3, lithium germanium thiophosphate Li x5 Ge y5 P z2 S w Lithium nitride (Li) x6 N y6 SiS2 type glass Li x7 Si y7 S z3 and P2S5 type glass Li x8 P y8 S z4 At least one of the following: 0 < x1 < 2, 0 < y1 < 3, 0 < x2 < 2, 0 < y2 < 1, 0 < z1 < 3, 0 < x3 < 4, 0 < y3 < 13, 0 < x4 < 2, 0 < y4 < 3, 0 < x5 < 4, 0 < y5 < 1, 0 < z2 < 1, 0 < w < 5, 0 < x6 < 4, 0 < y6 < 2, 0 < x7 < 3, 0 < y7 < 2, 0 < z3 < 4, 0 < x8 < 3, 0 < y8 < 3, 0 < z4 < 7. This can further improve the ion transport characteristics of the separator.

[0157] Organic particles have good thermal stability and are not easily decomposed, which can improve the heat resistance of the separator. At the same time, when the internal temperature of the battery cell reaches the melting point of the organic particles due to overcharging, abuse, or thermal abuse, the organic particles can melt and be drawn into the micropores of the substrate by capillary action, thus playing a role in closing the pores and breaking the circuit, which helps to ensure that the battery cell has high safety performance.

[0158] In some embodiments, the organic particles include, but are not limited to, at least one of the following: polyethylene particles, polypropylene particles, polystyrene particles, melamine resin particles, phenolic resin particles, polyester particles (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), polyimide particles, polyamide-imide particles, polyarylamide particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, polyaryletherketone particles, and copolymers of butyl acrylate and ethyl methacrylate (e.g., crosslinked polymers of butyl acrylate and ethyl methacrylate).

[0159] In some embodiments, the coating also includes an adhesive. This application does not impose any particular limitation on the type of adhesive; any known material with good adhesion can be selected. As an example, the adhesive includes at least one of aqueous acrylic resins (e.g., homopolymers of acrylic acid, methacrylic acid, sodium acrylate monomers, or copolymers with other comonomers), polyvinyl alcohol, isobutylene-maleic anhydride copolymers, and polyacrylamide.

[0160] Optionally, the binder content in the coating is <30%, based on the mass of the coating.

[0161] Electrolyte In some implementations, the battery cell includes an electrolyte.

[0162] During the charging and discharging process of a single battery cell, active ions repeatedly insert and extract between the positive and negative electrode plates, while the electrolyte acts as a conductor for these active ions. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to actual needs.

[0163] Electrolytes consist of electrolyte salts and solvents. The types of electrolyte salts and solvents are not specifically limited and can be selected according to actual needs.

[0164] As an example, the electrolyte salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0165] As an example, the solvent may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ester carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0166] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0167] In some implementations, the positive electrode, separator, and negative electrode can be fabricated into an electrode assembly using a winding process and / or a stacking process.

[0168] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0169] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0170] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. Figure 1 The example shown is a square-structured battery cell 5.

[0171] In some embodiments, such as Figure 1 and Figure 2 As shown, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 may be one or more, and can be adjusted according to requirements.

[0172] The method for preparing the battery cell of this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process or a stacking process. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a battery cell is obtained.

[0173] In some embodiments of this application, the battery cells according to this application can be assembled into a battery module. The number of battery cells contained in the battery module can be one or more, and the specific number can be adjusted according to the application and capacity of the battery module.

[0174] Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0175] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0176] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0177] Both battery module 4 and battery pack can be used as specific examples of batteries in the embodiments of this application.

[0178] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0179] Electrical appliances Thirdly, this application provides an electrical device, which includes at least one of the battery cell, battery module, and battery pack described in this application. The battery cell, battery module, and battery pack can be used as the power source for the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc. In some embodiments, the battery cell includes an injection hole for injecting electrolyte; when the battery cell is applied to the electrical device, the injection hole is located at the bottom of the battery cell in the vertical direction. Since the amount of free electrolyte in the battery cell is extremely small, or even non-existent, placing the injection hole at the bottom of the battery cell in the vertical direction can improve the reliability of the battery cell, thereby improving the reliability of the electrical device.

[0180] Electrical devices can be equipped with individual battery cells, battery modules, or battery packs depending on their usage requirements. Figure 6 This is a schematic diagram of an example electrical device. The electrical device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device, a battery pack 1 or a battery module can be used. Another example electrical device could be a mobile phone, tablet, laptop, etc. These devices typically require a slim and lightweight design, and can use individual battery cells as their power source.

[0181] Example 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.

[0182] Example 1: Preparation of Lithium-ion Batteries (1) Preparation of the positive electrode sheet: A positive electrode slurry was prepared by mixing various fluorinated polymers, lithium iron phosphate (LiFePO4) as the positive electrode active material, and carbon black as the conductive agent in an N-methylpyrrolidone (NMP) mixture at a mass ratio of 2.2:96.8:1. The positive electrode slurry was coated onto a current collector aluminum foil, dried at 85°C, and then cold-pressed. After edge trimming, cutting, and slitting, the foil was dried under vacuum at 85°C for 4 hours to produce the positive electrode sheet.

[0183] (2) Preparation of negative electrode sheet: A mixture of various fluorinated polymers, artificial graphite (the negative electrode active material), and carbon black (the conductive agent) in water at a weight ratio of 2.4:97.3:0.3 was prepared to form a negative electrode slurry. The negative electrode slurry was coated onto a copper foil current collector and dried at 85°C. After cold pressing, edge trimming, cutting, and slitting, the slurry was dried under vacuum at 120°C for 12 hours to form the negative electrode sheet.

[0184] (3) Preparation of electrolyte: The electrolyte consists of an organic solvent and a lithium salt. The organic solvent consists of ethylene carbonate EC and ethyl methyl carbonate (EMC) (volume ratio 3:7), and the lithium salt consists of 1 mol / L LiPF6.

[0185] (4) Preparation of lithium-ion batteries: Using polyethylene film (PE) as a separator, the positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrode. The electrode assembly is then wound up. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0186] Examples 2 to 6 Lithium-ion batteries were prepared using a method similar to that of Example 1. The difference from Example 1 is that the types of fluorinated polymers were adjusted in Examples 2 to 6.

[0187] Examples 7 to 9 Lithium-ion batteries were prepared using a method similar to that of Example 1, except that the amount of fluorinated polymer used in Examples 7 to 10 was adjusted.

[0188] Example 10 A lithium-ion battery was prepared using a method similar to that of Example 1. The difference is that the negative electrode sheet in Example 10 was prepared using the following method: Oily anode: Various fluorinated polymers, artificial graphite (anode active material), and carbon black (conductive agent) are mixed evenly in N-methylpyrrolidone (NMP) at a weight ratio of 2.4:97.3:0.3 to prepare a negative electrode slurry. The negative electrode slurry is coated onto a current collector copper foil and dried at 85°C. Then, it is cold-pressed, trimmed, cut into sheets, and slit. Finally, it is dried under vacuum at 120°C for 12 hours to prepare the negative electrode sheet.

[0189] Comparative Example 1 Lithium-ion batteries were prepared using a method similar to that of Example 1, except that Comparative Example 1 did not use multiple fluorinated polymers. (1) Preparation of the positive electrode sheet: A positive electrode slurry was prepared by mixing the positive electrode active material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) in a mass ratio of 97.5:0.7:1.8 with N-methylpyrrolidone (NMP). The positive electrode slurry was coated onto a current collector aluminum foil, dried at 85°C, and then cold-pressed. After edge trimming, cutting, and slitting, the foil was dried under vacuum at 85°C for 4 hours to form the positive electrode sheet. The crystallinity of the binder polyvinylidene fluoride (PVDF) was 48%.

[0190] (2) Preparation of negative electrode sheet: Aqueous anode: Polyvinylidene fluoride (PVDF) binder, artificial graphite (anode active material), styrene-butadiene rubber (SBR) binder, and carbon black (conductive agent) are mixed evenly in water at a weight ratio of 0.4:97.3:2:0.3 to prepare a cathode slurry. The cathode slurry is coated onto copper foil (current collector) and dried at 85°C. After cold pressing, edge trimming, cutting, and slitting, it is dried under vacuum at 120°C for 12 hours to produce the cathode sheet. The crystallinity of the PVDF binder is 48%.

[0191] Comparative Example 2 Lithium-ion batteries were prepared using a method similar to that of Example 1, except that the type of polymer was adjusted in Comparative Example 2.

[0192] Comparative Example 3 A lithium-ion battery was prepared using a method similar to Comparative Example 1. The difference between Comparative Example 3 and Comparative Example 1 is that the negative electrode sheet was prepared using the following method: Oily anode: Polyvinylidene fluoride (PVDF) binder, artificial graphite (anode active material), and carbon black (conductive agent) are mixed evenly in an N-methylpyrrolidone (NMP) solution at a weight ratio of 2:97.3:0.7 to prepare a negative electrode slurry. The negative electrode slurry is coated onto a copper current collector foil and dried at 85°C. After cold pressing, edge trimming, cutting, and slitting, it is dried under vacuum at 120°C for 12 hours to produce the negative electrode sheet. The crystallinity of the PVDF binder is 48%.

[0193] Test section 1. Lithium-ion battery capacity retention test The lithium-ion batteries prepared in the examples and comparative examples were charged to 3.8V at a constant current of 1 / 3C at room temperature, left to stand for 5 minutes, and then discharged to 2.0V at 1 / 3C. The resulting capacity was recorded as the initial capacity C0. The batteries were then stored at 60°C. The above steps were repeated for the same battery, and the discharge capacity Cn of the battery was recorded every 30 days. The battery capacity retention rate after 30 days was calculated as Pn = Cn / C0 * 100%. A dot plot of battery capacity retention rate versus storage days was obtained with the six points P1, P2...P6 as the ordinate and the corresponding storage time as the abscissa. The battery capacity retention rate data in Table 4 were measured after 180 days of storage under the above test conditions, i.e., the value of P6.

[0194] 2. Lithium-ion battery DC impedance test The lithium-ion batteries prepared in the examples and comparative examples were charged to 3.8V at a constant current of 1 / 3C at 25°C, and after resting for 5 minutes, the voltage V1 was recorded. Then, they were discharged at 1 / 3C for 30 seconds, and the voltage V2 was recorded. The internal resistance DCR1 of the battery after the first cycle was obtained by calculating (V2-V1) / 1 / 3C. The batteries were then transferred to a 60°C environment for storage. The above steps were repeated for the same battery, and the internal resistance DCRn of the battery in the nth cycle (n=1, 2, 3...6) was recorded simultaneously. The values ​​of the six points DCR1, DCR2, DCR3...DCR6 were plotted on the ordinate, and the corresponding number of cycles was plotted on the abscissa to obtain a curve of the battery discharge DCIR and the number of storage days.

[0195] The battery internal resistance increase rate in Table 4 is calculated as (DCRn - DCR1) / DCR1 * 100%. The data in Table 4 were obtained after 180 days of storage under the above test conditions.

[0196] Test Results The test results are shown in Tables 1 to 4.

[0197] Table 1

[0198] Table 2

[0199] Table 3

[0200] Table 4

[0201] As shown in Table 4, since no fluorinated polymers were added to the positive and negative electrode sheets of Comparative Example 1, the electrode sheets may expand in volume during the lithium-ion battery cycle, which may lead to the destruction of the interface and the formation of a new interface. The formation of the new interface will lead to the continuous occurrence of interfacial side reactions, which will deteriorate the cycle performance and storage performance of the battery cell.

[0202] Although polymers were added to the electrodes in Comparative Examples 2 and 3, the polymers could not effectively form in-situ gels on the surface of the active material, could not effectively slow down the interfacial reaction, and their high impedance would deteriorate the battery dynamics performance.

[0203] This application embodiment adds multiple fluorinated polymers to at least one of the positive and negative electrode sheets. The first fluorinated polymer can form an in-situ gel on the surface of the solid active material, that is, a stable solid-liquid interface is formed on the surface of the active material, reducing the risk of side reactions at the solid-liquid interface. However, the first fluorinated polymer is not conducive to the bonding between active materials, resulting in poor structural stability of the electrode sheet. The second fluorinated polymer can improve the bonding force between active materials, play a supporting role for the electrode sheet, thereby improving the structural stability of the electrode sheet, and thus improving the cycle performance and storage performance of the battery cell.

[0204] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. A battery cell, comprising an electrode sheet, the electrode sheet comprising a current collector and a film layer disposed on at least one side of the current collector, the film layer comprising an active material and a plurality of fluorinated polymers. The crystallinity of one of the fluorinated polymers is denoted as X. c1 %, the cold crystallization temperature is denoted as T c1 ℃; The crystallinity of one of the various fluorinated polymers is denoted as X. c2 %, the cold crystallization temperature is denoted as T c2 ℃, in, The various fluorinated polymers satisfy: 20% ≤ (X) c2 -X c1 ) / X c1 ≤400%, 30%≤(T) c2 -T c1 ) / T c1 <250%.

2. The battery cell according to claim 1, wherein, 40%≤(X c2 -X c1 ) / X c1 <400%; Optionally, X c2 -X c1 ≥10; Further optionally, 10≤X c2 -X c1 ≤45; Further optionally, 10≤X c2 -X c1 ≤40.

3. The battery cell according to claim 2, wherein, 0 < X c1 ≤28; optionally, 10≤X c1 ≤25; and / or 30≤X c2 ≤50; optionally, 35≤X c2 ≤50.

4. The battery cell according to any one of claims 1 to 3, wherein, 35%≤(T c2 -T c1 ) / T c1 <250%; optionally, 39%≤(T) c2 -T c1 ) / T c1 ≤213%; Optionally, T c2 -T c1 ≥25; further optionally, 25≤T c2 -T c1 ≤100; further optionally, 35≤T c2 -T c1 ≤85.

5. The battery cell according to claim 4, wherein, 35 < T c1 ≤100; optionally, 40≤T c1 ≤90; and / or 115≤T c2 ≤140; optionally, 125≤T c2 ≤135.

6. The battery cell according to any one of claims 1 to 5, wherein, The glass transition temperature of one of the various fluorinated polymers is T. g1 ℃, -30≤T g1 ≤40; and / or The glass transition temperature of one of the various fluorinated polymers is T. g2 ℃, -30≤T g2 ≤40; Optionally, Each of the plurality of fluorinated polymers independently includes at least one of the compounds represented by formula (A1) to formula (AIII). Formula (AI) Formula (AII), In equations (AI) and (AII), R 11 R 12 R 13 and R 14 Each independently comprises a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, a substituted or unsubstituted C1-C3 alkyl group, or a substituted or unsubstituted C1-C3 alkoxy group, and R 11 R 12 R 13 and R 14 At least one of them contains a fluorine atom; Formula (AIII) In equation (AIII), R 15 Includes single-bonded, substituted or unsubstituted C1-C3 alkyl groups; p is a positive integer from 1 to 3; n is a positive integer selected from 1000 to 30000.

7. The battery cell according to any one of claims 1 to 6, wherein, One of the fluorinated polymers has a molecular weight of W1 g / mol. One of the various fluorinated polymers has a molecular weight of W2 g / mol. The various fluorinated polymers satisfy: 0 < W 1 / W2 < 1; Optionally, 2.0×10 5 ≤W1≤1.0×10 6 ; 5.0×10 5 ≤W2≤1.2×10 6 。 8. The battery cell according to any one of claims 1 to 7, wherein, Based on the total mass of the membrane layer, the total mass content of the various fluorinated polymers is ≤5%; optionally, it is 0.05% to 5%. Optionally, Based on the total mass of the membrane layer, the mass content of the first fluorinated polymer is ≤4%; Optionally, Based on the total mass of the membrane layer, the mass content of the second fluorinated polymer is ≤4%.

9. The battery cell according to any one of claims 1 to 8, wherein, The electrode sheet includes a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive active material, a first fluorinated polymer, and a second fluorinated polymer. Optionally, Based on the total mass of the positive electrode film, the mass content of the first fluorinated polymer and the total mass content of the second fluorinated polymer are between 0.05% and 2.5%. Optionally, Based on the total mass of the positive electrode film, the mass content of the first fluorinated polymer is less than the mass content of the second fluorinated polymer; Further optional, Based on the total mass of the positive electrode film, the mass content of the first fluorinated polymer is ≤2%; optionally, it is 0.05% to 2%; optionally, it is 0.05% to 1%. Further optional, Based on the total mass of the positive electrode film, the mass content of the second fluorinated polymer is ≤2%; optionally 1% to 2%; optionally 1.2% to 2%. Further optionally, the positive electrode active material includes at least one of lithium phosphate compounds and layered positive electrode active materials.

10. The battery cell according to any one of claims 1 to 8, wherein, The electrode sheet includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The negative electrode film layer includes a negative electrode active material, a first fluorinated polymer, and a second fluorinated polymer. Optionally, Based on the total mass of the negative electrode film, the mass content of the first fluorinated polymer and the total mass content of the second fluorinated polymer are 0.05% to 5%; Optionally, Based on the total mass of the negative electrode film, the mass content of the first fluorinated polymer is greater than the mass content of the second fluorinated polymer; or Based on the total mass of the negative electrode film, the mass content of the first fluorinated polymer is less than the mass content of the second fluorinated polymer. Further optional, Based on the total mass of the negative electrode film, the mass content of the first fluorinated polymer is ≤4%; optionally, it is 0.5% to 4%; optionally, it is 2% to 4%. Optionally, Based on the total mass of the negative electrode film, the mass content of the second fluorinated polymer is ≤4%; optionally 0.4% to 2%; further optionally 0.4% to 1%. Further optionally, the negative electrode active material includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

11. A battery comprising a battery cell according to any one of claims 1 to 10.

12. An electrical device comprising the battery according to claim 11.

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