Battery cell, polyolefin elastomer preparation method, battery device, and electric device

Abstract

The present application discloses a battery cell, a polyolefin elastomer preparation method, a battery device, and an electric device. The battery cell comprises a positive electrode sheet and a negative electrode sheet. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material and a polyolefin elastomer; the polyolefin elastomer includes a first polyolefin elastomer having a first molecular weight and a second polyolefin elastomer having a second molecular weight, the first molecular weight is higher than the second molecular weight, and a mass ratio of the first polyolefin elastomer to the second polyolefin elastomer in the polyolefin elastomer is 1:(0.2-5.0). Embodiments of the present application can improve the specific capacity of electrode sheets and ensure the stability of the electrode sheets.

Description

Battery cell, method for preparing polyolefin elastomer, battery device, and electric device TECHNICAL FIELD

[0001] The present application belongs to the field of secondary batteries, and particularly relates to a battery cell, a method for preparing a polyolefin elastomer, a battery device, and an electric device. BACKGROUND

[0002] In recent years, with the continuous development of various electronic products, new energy vehicles, and energy storage devices, the demand for secondary batteries has also rapidly increased. Secondary batteries charge and discharge through the reciprocal deintercalation of active ions between positive and negative active materials. The positive and negative active materials are usually bonded to the current collector by a binder to facilitate the export of electrical energy and help the secondary battery achieve a higher energy density. As an important component of the battery cell, the electrode sheet has a huge impact on the electrochemical performance of the secondary battery, especially the cycle performance, which in turn affects the working performance and efficiency of the device using the secondary battery.

[0003] However, the electrode sheet has problems of reduced specific capacity and insufficient stability. SUMMARY

[0004] The embodiments of the present application provide a battery cell, a method for preparing a polyolefin elastomer, a battery device, and an electric device, which can improve the specific capacity of the electrode sheet and ensure the stability of the electrode sheet.

[0005] In a first aspect, the embodiments of the present application provide a battery cell, comprising a positive electrode sheet and a negative electrode sheet; the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector; wherein the positive electrode active material layer comprises a positive electrode active material and a polyolefin elastomer, the polyolefin elastomer comprises a first polyolefin elastomer of a first molecular weight and a second polyolefin elastomer of a second molecular weight, the first molecular weight is higher than the second molecular weight, and the mass ratio of the first polyolefin elastomer to the second polyolefin elastomer in the polyolefin elastomer is 1:(0.2-5.0).

[0006] The polyolefin elastomers with different molecular weights are mixed in the present application, wherein the polyolefin elastomer with small molecular weight can be used as a dispersant to stabilize the dispersion state of the materials inside the pole piece and prevent particle agglomeration, and the polyolefin elastomer with large molecular weight can be used as a binder to bind the active material, the conductive agent and the current collector in the pole piece together; and under the compounding of the polyolefin elastomer with a specific content, the polyolefin elastomers with different molecular weights can jointly coat the surface of the active material, reduce the active sites on the surface of the active material, thereby reducing the contact reaction of the active material with O2 and CO2 in the air, improving the gram capacity of the pole piece and ensuring the stability of the pole piece, while avoiding the continuous HF removal reaction of the fluorine-containing binder with sodium clusters in the system, further improving the gram capacity of the pole piece and ensuring the stability of the pole piece.

[0007] In any embodiment of the present application, the first polyolefin elastomer and the second polyolefin elastomer are independently selected from unmodified or modified polyolefin elastomers.

[0008] In any embodiment of the present application, the mass ratio of the first polyolefin elastomer to the second polyolefin elastomer in the polyolefin elastomer is 1:(0.5-1). The mass ratio of the first polyolefin elastomer to the second polyolefin elastomer within the above range can better coat the surface of the active material, reduce the active sites on the surface of the active material, thereby reducing the contact reaction of the active material with O2 and CO2 in the air, improving the gram capacity of the pole piece and ensuring the stability of the pole piece, while avoiding the continuous HF removal reaction of the fluorine-containing binder with sodium clusters in the system, further improving the gram capacity of the pole piece and ensuring the stability of the pole piece.

[0009] In any embodiment of the present application, the first molecular weight is 40-100 W, and the second molecular weight is 1-10 W. The first molecular weight within the above range can have good adhesion and cohesion, and the second molecular weight within the above range can have good viscosity.

[0010] In any embodiment of the present application, the first molecular weight is 50-70 W, and the second molecular weight is 3-5 W. The first molecular weight within the above range can have good adhesion and cohesion, and the second molecular weight within the above range can have good viscosity.

[0011] In any embodiment of the present application, the modified polyolefin elastomer includes an anhydride-modified polyolefin elastomer and / or a carboxyl-modified polyolefin elastomer. The anhydride-modified polyolefin elastomer and / or the carboxyl-modified polyolefin elastomer can improve the binding property, elasticity and stability of the polyolefin elastomer.

[0012] In any embodiment of the present application, the modified polyolefin elastomer comprises at least one of maleic anhydride, glycidyl methacrylate and acrylic acid. The at least one of maleic anhydride, glycidyl methacrylate and acrylic acid modified polyolefin elastomer can further improve the adhesion, elasticity and stability of the polyolefin elastomer.

[0013] In any embodiment of the present application, the grafting rate of the anhydride modified polyolefin elastomer and / or the carboxyl modified polyolefin elastomer is 0.1% to 3.0%. The grafting rate of the anhydride modified polyolefin elastomer and / or the carboxyl modified polyolefin elastomer within the above range can ensure sufficient adhesion strength and avoid excessive grafting rate leading to excessive entanglement between molecular chains and causing side reactions.

[0014] In any embodiment of the present application, the adhesion strength between the positive electrode tab and the positive electrode current collector is 12 to 25 N / m.

[0015] In any embodiment of the present application, the positive electrode active material layer is prepared from a slurry, and the slurry comprises a positive electrode active material, a polyolefin elastomer and a solvent.

[0016] In any embodiment of the present application, the polyolefin elastomer has a repeating structural unit as shown in Formula 1,

[0017] In Formula 1, R2 is selected from C1-C5 alkyl; the polyolefin elastomer has a repeating structural unit as shown in Formula 2,

[0018] In Formula 2, R1 is selected from C1-C8 alkyl; the polyolefin elastomer further has a polar segment structural unit; wherein the content of the structural unit shown in Formula 1 is 5% to 45%, the content of the structural unit shown in Formula 2 is 45% to 94%, and the content of the polar segment structural unit is 1% to 10%. The polyolefin elastomer having Formula 1, Formula 2 and the polar segment structural unit can self-repair minor damage during the charging and discharging process of the battery, thereby improving the reliability and durability of the battery.

[0019] In any embodiment of the present application, the solvent comprises aromatic hydrocarbon-containing and / or aromatic hydrocarbon-free solvent oil.

[0020] In any embodiment of the present application, the positive electrode active material comprises phosphate and / or pyrophosphate of NACISON type structure.

[0021] In any embodiment of the present application, the positive active material comprises at least one of Na3MnTi(PO4)3, Na3MnV(PO4)3, Na3TiV(PO4)3, Na3Fe2(PO4)3, Na3MnZr(PO4)3 and Na2MP2O7, wherein M is selected from at least one of Fe, Co, Mn and Cu.

[0022] In a second aspect, the embodiments of the present application provide a preparation method of the polyolefin elastomer, comprising the following steps: providing polymer monomers, the polymer monomers comprising olefins having the structure shown in the above Formula 1 or the above Formula 2; mixing the polymer monomers, a modifier and a catalyst, and then allowing the polymer monomers to polymerize under the action of the catalyst to obtain the polyolefin elastomer.

[0023] In the present application, by introducing the olefins having the structure shown in Formula 1 and Formula 2, the glass transition temperature (Tg) of the polyolefin elastomer can be controlled, the movement of the molecular chain segments of the polyolefin elastomer is facilitated, the transmission of sodium ions or other ions is facilitated, and thus the electrical conductivity and electrochemical performance of the battery are improved. Meanwhile, the appropriate Tg can make the polyolefin elastomer have good adhesion, and the shedding and failure of the electrode material can be reduced, and thus the cycle life of the battery is prolonged.

[0024] In any embodiment of the present application, the modifier comprises at least one of maleic anhydride, glycidyl methacrylate and acrylic acid.

[0025] In any embodiment of the present application, the catalyst comprises at least one of a metallocene catalyst, a bridged bis-cyclopentadienyl catalyst and methylaluminoxane.

[0026] In a third aspect, the embodiments of the present application provide a battery device comprising the battery monomer.

[0027] In a fourth aspect, the embodiments of the present application provide a power utilization device comprising the battery monomer or the battery device. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments of the present application will be briefly introduced as follows. Those skilled in the art can also obtain other drawings according to these drawings without any creative labor.

[0029] FIG. 1 shows a schematic diagram of a battery monomer according to some embodiments of the present application.

[0030] FIG. 2 shows an exploded schematic diagram of a battery monomer according to some embodiments of the present application.

[0031] FIG. 3 shows a schematic diagram of a battery module according to some embodiments of the present application.

[0032] FIG. 4 shows a schematic diagram of a battery pack according to some embodiments of the present application.

[0033] FIG. 5 is an exploded schematic diagram of the battery pack shown in FIG. 4.

[0034] FIG. 6 shows a schematic diagram of an electric device according to some embodiments of the present application.

[0035] FIG. 7 is a plot of the change in the gravimetric capacity of the electrode sheet after formation in Example 1 and Comparative Example 1.

[0036] FIG. 8 is a SEM image of the positive electrode sheet in Example 1.

[0037] FIG. 9 is a schematic diagram of the polyolefin elastomer and the active material in the positive electrode sheet in Example 1.

[0038] FIG. 10 is a plot of the change in the gravimetric capacity of the electrode sheet in Comparative Example 1 in air / argon, oxygen environments.

[0039] FIG. 11 is a plot of the change in the gravimetric capacity of the electrode sheet in Comparative Example 1 in different oxygen content environments.

[0040] In the drawings, the drawings are not necessarily drawn to scale.

[0041] Reference signs are explained as follows: 1, battery pack; 2, upper case; 3, lower case; 4, battery module; 5, battery cell; 51, case; 52, electrode assembly; 53, cover plate. DETAILED DESCRIPTION

[0042] In order to more clearly understand the above-mentioned objects, features and advantages of the present application, the schemes of the present application will be further described below. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0043] In the following description, a lot of specific details are set forth in order to provide a thorough understanding of the present disclosure, but the present application can also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some of the embodiments of the present application, not all the embodiments.

[0044] Hereinafter, specific embodiments of the battery cell, the method for producing a polyolefin elastomer, the battery device, and the electric device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known well, repeated description of substantially the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided in order for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0045] The ranges disclosed herein are intended to be "open" ranges, i.e., the end values are not included in the range. For example, if a range of 60-120 is listed for a particular parameter, it is understood that 60 and 120 are not included in the range. In addition, if a minimum range value of 1 is listed and a maximum range value of 3 is listed, then the following ranges are all contemplated: 1-3, 1-2, and 1-1.5. In this application, unless otherwise indicated, a numerical range "a-b" means a range of any combination of the numbers a and b, wherein both a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between 0 and 5 have been listed herein, and "0-5" is merely a shorthand for listing all of those numbers. Also, when a parameter is stated to be an integer > 2, it is equivalent to stating that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0046] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application, if not specifically stated otherwise.

[0047] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application, if not specifically stated otherwise.

[0048] All steps of the present application can be performed in sequence or randomly, and preferably in sequence, if not specifically stated otherwise. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0049] The term "alkyl" refers to saturated hydrocarbon groups, both straight-chain and branched-chain. C1-8alkyl means an alkyl group having 1 to 8 carbon atoms, examples of which include, but are not limited to, methyl, ethyl, propyl (e.g., n-propyl, i-propyl), butyl (e.g., n-butyl, i-butyl, sec-butyl, t-butyl), pentyl (e.g., n-pentyl, i-pentyl, neopentyl), and the like.

[0050] The term "arene" refers to a hydrocarbon having a benzene ring basic structure.

[0051] The term "recurring structural unit", also known as a repeat unit or mer, is a structural unit covalently linked to adjacent repeating units and occurring more than once. These units are identical in chemical composition and structure and are the building blocks of the polymer.

[0052] Throughout this specification, substituents of compounds are disclosed in groups or in ranges. It is specifically intended that where a group or range of substituents is disclosed, each and every individual subcombination of that group or range is also disclosed. For example, the term "C1-C8alkyl" is specifically intended to individually disclose C1, C2, C3, C4, C5, C6, C7, C8, C1-C8, C1-C7, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C8, C2-C7, C2-C6, C2-C5, C2-C4, C2-C3, C3-C8, C3-C7, C3-C6, C3-C5, C3-C4, C4-C8, C4-C7, C4-C6, C4-C5, C5-C8, C5-C7, C5-C6, C6-C8, C6-C7, and C7-C8alkyl.

[0053] In this application, a battery refers to a single physical module that includes one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include a battery module or a battery pack, etc. The battery generally includes a box for packaging one or more battery cells. The box can avoid the influence of liquid or other foreign matters on the charging or discharging of the battery cells.

[0054] The battery cell can be in the shape of a cylinder, a flat body, a cuboid, or other shapes, which are not limited by the embodiments of the present application. The battery cell is generally divided into three types according to the packaging method: cylindrical battery cells, square battery cells, and soft package battery cells, which are not limited by the embodiments of the present application.

[0055] The battery cell includes an electrode assembly and an electrolyte, and the electrode assembly is composed of a positive electrode sheet, a negative electrode sheet, and a separator. The battery cell mainly works by moving metal ions between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet includes a positive current collector and a positive active material layer, and the positive active material layer is coated on the surface of the positive current collector. The positive current collector without the positive active material layer protrudes from the positive current collector with the positive active material layer, and the positive current collector without the positive active material layer serves as a positive electrode tab.

[0056] In addition, the battery cell also includes a shell for accommodating the electrode assembly and the electrolyte, wherein the electrolyte can play a role in transmitting electrons between the positive electrode sheet and the negative electrode sheet.

[0057] During the research and development, the inventors found that the ordinary pole piece showed significant difference in air / argon environment, as shown in FIG. 10, the pole piece stored for 30D in the argon environment, and the charging gram capacity was almost lost, while the charging gram capacity was lost by 15% when stored for 7D in the oxygen atmosphere. Further positive verification found that, as shown in FIG. 11, the pole piece was stored for 7D in the environment with different oxygen concentrations, and the charging capacity would decrease with the increase of oxygen concentration.

[0058] Therefore, the embodiments of the present application provide a battery monomer, the pole piece of which has polyolefin elastomers with different molecular weights and different mass ratios, so as to improve the gram capacity of the pole piece and ensure the stability of the pole piece.

[0059] The battery monomer, battery and the like disclosed by the present application can be assembled into a power supply system of an electric device, so as to improve the safety performance and service life of the electric device.

[0060] A battery monomer

[0061] In a first aspect, the embodiments of the present application provide a battery monomer, which includes a positive pole piece and a negative pole piece. The positive pole piece includes a positive current collector and a positive active material layer arranged on at least one surface of the positive current collector, wherein the positive active material layer includes a positive active material and a polyolefin elastomer, the polyolefin elastomer includes a first polyolefin elastomer with a first molecular weight and a second polyolefin elastomer with a second molecular weight, the first molecular weight is higher than the second molecular weight, and the mass ratio of the first polyolefin elastomer to the second polyolefin elastomer in the polyolefin elastomer is 1:(0.2-5.0).

[0062] In the embodiments of the present application, the polyolefin elastomers with different molecular weights are mixed and used, wherein the polyolefin elastomer with a small molecular weight can be used as a dispersant to stabilize the dispersion state of the materials in the pole piece and prevent particle agglomeration, and the polyolefin elastomer with a large molecular weight can be used as a binder to bond the active material, the conductive agent and the current collector in the pole piece together, and under the compounding of a specific content of the polyolefin elastomer, the polyolefin elastomers with different molecular weights jointly act to coat the surface of the active material, reduce the active sites on the surface of the active material, and thus reduce the contact reaction of the active material with O2 and CO2 in the air, so as to improve the gram capacity of the pole piece and ensure the stability of the pole piece. Meanwhile, the continuous HF removal reaction caused by the contact of the PVDF binder with sodium clusters in the system can be avoided, and the gram capacity of the pole piece is further improved, and the stability of the pole piece is ensured.

[0063] Polyolefin elastomer (POE) is an elastomer obtained by random copolymerization of olefins, possessing properties of both plastics and rubber. In this application, a high molecular weight first polyolefin elastomer and a low molecular weight second polyolefin elastomer are compounded at a mass ratio of 1:(0.2–5.0). This ensures optimal dispersibility and adhesion, while also guaranteeing the formation of the electrode's pore structure and ion channels, thus reducing membrane resistance.

[0064] In some embodiments, the mass ratio of the first polyolefin elastomer to the second polyolefin elastomer in the polyolefin elastomer is independently selected from 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0, 1:2.1, 1:2.2, 1:2.3, 1: 2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9, 1:3.0, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9, 1:4.0, 1:4.1, 1:4.2, 1:4.3, 1:4.4, 1:4.5, 1:4.6, 1:4.7, 1:4.8, 1:4.9, 1:5.0, or any value within a range of any two.

[0065] In some embodiments, both the first polyolefin elastomer and the second polyolefin elastomer are independently selected from unmodified or modified polyolefin elastomers.

[0066] Optionally, the first polyolefin elastomer is an unmodified polyolefin elastomer, and the second polyolefin elastomer is an unmodified polyolefin elastomer.

[0067] Optionally, the first polyolefin elastomer is an unmodified polyolefin elastomer, and the second polyolefin elastomer is a modified polyolefin elastomer.

[0068] Optionally, the first polyolefin elastomer is a modified polyolefin elastomer, and the second polyolefin elastomer is an unmodified polyolefin elastomer.

[0069] Optionally, the first polyolefin elastomer is a modified polyolefin elastomer, and the second polyolefin elastomer is a modified polyolefin elastomer.

[0070] In the embodiments of the present application, by introducing the modified polyolefin elastomer, the adhesion of the electrode material can be improved, and the components such as the electrode active material, the conductive agent and the current collector can be tightly bonded together to form a stable electrode structure. Such strong bonding helps to prevent the electrode material from falling off and peeling off during the charging and discharging process, thereby improving the cycle stability and service life of the battery. The microstructure of the electrode can also be optimized to promote particle dispersion, which helps to form a more uniform and dense electrode layer, thereby improving the specific surface area of the electrode and the utilization rate of the active material. The porosity can also be adjusted to provide more channels for ion and electron transmission, which helps to improve the ion transmission efficiency and electrochemical reaction rate of the battery. The overall stability of the electrode can also be enhanced, and the capacity decay caused by the falling off or structural damage of the electrode material can be reduced, which helps to improve the cycle stability and service life of the battery. In addition, polyolefin elastomers with different modification groups can also be adapted to different battery systems, such as lithium ion batteries, sodium ion batteries, etc.

[0071] In some embodiments, the mass ratio of the first polyolefin elastomer to the second polyolefin elastomer in the polyolefin elastomer is 1:(0.5-1). The mass ratio of the first polyolefin elastomer to the second polyolefin elastomer in the above range can better coat the surface of the active material, reduce the active sites on the surface of the active material, thereby reducing the contact reaction of the active material with O2 and CO2 in the air, improving the gram capacity of the electrode sheet, ensuring the stability of the electrode sheet, and avoiding continuous HF removal reaction of the fluorine-containing binder with sodium clusters in the system, further improving the gram capacity of the electrode sheet and ensuring the stability of the electrode sheet.

[0072] The mass ratio of the first polyolefin elastomer to the second polyolefin elastomer in the above range can also optimize the porosity of the electrode, improve the transmission efficiency of ions, and thus improve the specific capacity and rate performance of the battery.

[0073] In some embodiments, the first molecular weight is 40-100 W, and the second molecular weight is 1-10 W. The first molecular weight in the above range can balance the entanglement of the high molecular chains in the first polyolefin elastomer and the effective contact with the electrode surface, and can have good adhesion and cohesion at the same time to ensure the integrity of the electrode material and reduce the falling off of the active material, thereby improving the cycle stability and capacity retention rate of the battery.

[0074] The first molecular weight in the above range can avoid forming a denser layer, reduce the transmission path length of electrons and ions in the electrode, and thus reduce the internal resistance.

[0075] The second molecular weight in the above range can better dissolve and disperse various materials in the electrode sheet, while obtaining a slurry with a suitable viscosity, which is convenient for coating and drying. The charging and discharging efficiency and the cycle stability.

[0076] Optionally, the first molecular weight is independently selected from any value or a range between any two values of 40W, 45W, 50W, 55W, 60W, 65W, 70W, 75W, 80W, 85W, 90W, 95W, 100W.

[0077] Optionally, the second molecular weight is independently selected from any value or a range between any two values of 1W, 2W, 3W, 4W, 5W, 6W, 7W, 8W, 9W, 10W.

[0078] In some embodiments, the first molecular weight is 50-70W and the second molecular weight is 3-5W. Within the above ranges, the first polyolefin elastomer has suitable bonding strength and adhesion, which can ensure that the electrode has sufficient porosity to support efficient ion transport. The second polyolefin elastomer can more easily penetrate into the gaps between the electrode material particles, improving dispersion uniformity, and can also improve solubility in solvents, improving dispersion effect.

[0079] The polyolefin elastomer in the electrode sheet can be detected by separating the polyolefin elastomer in the coating. As an example, a certain amount of coating is taken, and then the coating is placed in a mixed solution of water and ethanol, the volume ratio of water to ethanol is 1:1, and the mass ratio of the coating to the mixed solution is about 1:10. The mixed solution containing the coating is subjected to ultrasonic treatment for 20-40 min, the ultrasonic frequency is 20-40 HZ, which can be 25 HZ, then washed and filtered, and the polymer after the coating is stripped is collected. Then mass spectrometry is used: by ionizing the polymer molecules and measuring their mass, the molecular weight of the polyolefin elastomer can be determined.

[0080] The obtained polymer sample to be tested is nitrated to prepare a suitable sample solution, and then the sample solution is ionized, mass analyzed, data processed and result analyzed to obtain the mass and proportion of each molecule in the sample solution. The ionization, mass analysis, data processing and result analysis are as follows:

[0081] Ionization: Under the action of an electric field, the molecules in the sample solution are ionized into charged ions.

[0082] Mass analysis: The ionized ions are sent to a mass spectrometer for mass analysis. In the mass spectrometer, the ions are focused in a narrow area, and then by measuring the mass and speed of the ions, the mass of the ions can be calculated.

[0083] Data processing: The ion mass data measured by the mass spectrometer can be processed and analyzed by a computer, for example, by searching the mass-to-charge ratio vs. intensity plot, the mass of various molecules in the sample can be determined.

[0084] Result analysis: According to the mass spectrometry data, the mass proportion of the first polyolefin elastomer and the second polyolefin elastomer can be analyzed.

[0085] In some embodiments, the modified polyolefin elastomer includes an anhydride-modified polyolefin elastomer and / or a carboxyl-modified polyolefin elastomer.

[0086] The introduction of anhydride or carboxyl functional groups can enable the modified polyolefin elastomer to form stronger chemical bonds or hydrogen bonds with the surface of the electrode material, thereby improving the adhesion of the binder. This enhanced adhesion helps to firmly bond the electrode active material, conductive agent, and current collector together, preventing the active material from falling off during charging and discharging.

[0087] The introduction of anhydride or carboxyl functional groups can improve the dispersibility of the polyolefin elastomer in the slurry medium, helping to form a uniform and dense electrode structure, and improving the energy density and cycle stability of the battery.

[0088] The introduction of anhydride or carboxyl functional groups can further enhance the elasticity of the polyolefin elastomer. During the charging and discharging process of the battery, the electrode material will undergo volume changes. The modified polyolefin elastomer can effectively buffer such changes, prevent the destruction of the electrode structure, prolong the service life of the battery, and improve the cycle stability and safety of the battery.

[0089] The anhydride-modified polyolefin elastomer and / or the carboxyl-modified polyolefin elastomer has good chemical stability and can resist the corrosion of the electrolyte, maintaining the integrity of the electrode structure. In a high-temperature environment, the modified polyolefin elastomer still maintains stable performance, preventing battery safety problems caused by thermal runaway.

[0090] The anhydride-modified polyolefin elastomer and / or the carboxyl-modified polyolefin elastomer can improve the ionic conductivity of the electrode sheet and improve the charging and discharging performance of the battery.

[0091] The grade of the anhydride-modified polyolefin elastomer includes at least one of MA8510, MD715, MA9015, MH7510, FUSABOND N416, FUSABOND N216, AMPLIFY GR216, and AMPLIFY GR217.

[0092] In some embodiments, the modified polyolefin elastomer includes at least one of maleic anhydride, glycidyl methacrylate, and acrylic acid.

[0093] In some embodiments, the grafting rate of the anhydride-modified polyolefin elastomer and / or the carboxyl-modified polyolefin elastomer is 0.1% to 3.0%.

[0094] Grafting generally means more polar groups are introduced onto the macromolecular chains of the polyolefin elastomer, which can enhance the interaction forces between the elastomer and the electrode active material, the conductive agent, and the current collector, thereby improving the bonding strength.

[0095] The grafting rate within the above range can ensure sufficient bonding strength and avoid excessive grafting rate leading to excessive entanglement between molecular chains, causing side reactions.

[0096] Optionally, the grafting rate of the anhydride-modified polyolefin elastomer and / or the carboxyl-modified polyolefin elastomer is independently selected from any value or a range value between any two values in 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 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%.

[0097] In some embodiments, the bonding strength between the positive electrode tab and the positive electrode current collector is 12-25 N / m.

[0098] Optionally, the bonding strength between the positive electrode tab and the positive electrode current collector is independently selected from any value or a range value between any two values in 12 N / m, 13 N / m, 14 N / m, 15 N / m, 16 N / m, 17 N / m, 18 N / m, 19 N / m, 20 N / m, 21 N / m, 22 N / m, 23 N / m, 24 N / m, 25 N / m.

[0099] In some embodiments, the positive electrode active material layer is prepared from a slurry, and the slurry comprises a positive electrode active material, a polyolefin elastomer, and a solvent.

[0100] In some embodiments, the polyolefin elastomer has a repeating structural unit as shown in Formula 1,

[0101] In Formula 1, R2 is selected from C1-C5 alkyl; the polyolefin elastomer has a repeating structural unit as shown in Formula 2,

[0102] In Formula 2, R1 is selected from C1-C8 alkyl; the polyolefin elastomer further has a polar segment structural unit; wherein the content of the structural unit as shown in Formula 1 is 5%-45%, the content of the structural unit as shown in Formula 2 is 45%-94%, and the content of the polar segment structural unit is 1%-10%.

[0103] The structure and content of the structural unit of Formula 1, the structural unit of Formula 2 and the polar segment structural unit can be determined by methods known in the art, such as nuclear magnetic resonance spectroscopy. Nuclear magnetic resonance spectroscopy is the study of the absorption of radio frequency radiation by atomic nuclei in a strong magnetic field, and is one of the most powerful tools for qualitative analysis of the composition and structure of various organic and inorganic substances, and sometimes quantitative analysis can also be performed. At the same time, it can also be combined with infrared spectroscopy, such as Fourier transform infrared spectroscopy (FTIR), which can test the interaction of infrared radiation with the molecular vibration or rotation of the substance, and perform structural analysis by recording the infrared absorption spectrum of the sample. In the detection of organic functional groups by infrared testing, the following test steps can be referred to: When the infrared light beam penetrates the surface of the polar piece by a few microns deep (ATR is Ge crystal), when it is irradiated by infrared light with continuous frequency change, the molecules on the surface of the polar piece absorb some frequencies of radiation, and the net change of the dipole moment caused by the vibration or rotation movement produces the transition of the molecular vibration and rotation energy level from the ground state to the excited state, which weakens the transmission intensity of the corresponding absorption area, and records the curve of the percentage transmission ratio of infrared light with wave number, and the infrared spectrum is obtained; the infrared spectrum and the functional group analysis result are obtained. For example, reference can be made to the national standard GB / T6040-2002 General Rules for Infrared Spectroscopy Analysis Method. ICP testing can also be used, for example, reference can be made to the standards YS / T1006.2-2014, GB / T23367.2-2009 or YS / T1028.5-2015. Specifically, according to the embodiments of the present application, ICP inductively coupled plasma emission spectrometer (device model iCAP 740) can be used to measure according to the manufacturer's instructions. Further, pyrolysis gravimetric analysis and gas chromatography-mass spectrometry can also be used for analysis.

[0104] Optionally, the content of the structural unit of Formula 1 is independently selected from any value or a range value between any two of 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%.

[0105] Optionally, the content of the structural unit of Formula 2 is independently selected from any value or a range value between any two of 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 94%.

[0106] Optionally, the content of the polar segment structural unit is independently selected from any value or a range value between any two of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%.

[0107] In the embodiments of the present application, the polar segment structural unit is a structural unit containing a polar group, and the polar group can be a carboxyl group.

[0108] In the embodiments of the present application, the content of the structural unit shown in Formula 1, the structural unit shown in Formula 2, and the polar segment structural unit is specially selected so that the polyolefin elastomer has a suitable glass transition temperature.

[0109] In some embodiments, the solvent includes aromatic hydrocarbon-containing and / or aromatic hydrocarbon-free solvent oil.

[0110] The solvent includes at least one of D20 solvent, D40 solvent, D60 solvent, D80 solvent, D100 solvent, D120 solvent, and D200 solvent.

[0111] In some embodiments, the positive electrode active material includes a phosphate and / or pyrophosphate of NACISON type structure.

[0112] When the positive electrode active material is in this range, the phosphate and pyrophosphate of NACISON type structure can be oxidized by O2 and CO2 in the air to generate sodium-depleted sodium pyrophosphate iron and Na2O2 / NaO2, thereby reducing the gram capacity and stability of the electrode sheet. In addition, the basic Na2O2 / NaO2 can also react with the fluorine-containing binder to cause the binder to lose fluorine and form a double bond, further reducing the gram capacity and stability of the electrode sheet.

[0113] Therefore, the polyolefin elastomer is arranged in the positive electrode active material layer, the polyolefin elastomer includes a first polyolefin elastomer of a first molecular weight and a second polyolefin elastomer of a second molecular weight, the first molecular weight is higher than the second molecular weight, and the mass ratio of the first polyolefin elastomer to the second polyolefin elastomer in the polyolefin elastomer is 1:(0.2-5.0), so as to improve the gram capacity of the electrode sheet and ensure the stability of the electrode sheet.

[0114] In some embodiments, the positive electrode active material includes at least one of Na3MnTi(PO4)3, Na3MnV(PO4)3, Na3TiV(PO4)3, Na3Fe2(PO4)3, Na3MnZr(PO4)3, and Na2MP2O7, wherein M is selected from at least one of Fe, Co, Mn, and Cu.

[0115] [Positive electrode sheet]

[0116] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector and including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite in the thickness direction of the positive electrode current collector, and the positive electrode film layer is arranged on any one or both of the two opposite surfaces of the positive electrode current collector.

[0117] In some embodiments, the positive electrode active material includes a material capable of deintercalating and intercalating lithium.

[0118] As an example, the positive electrode active material can include, but is not limited to, one or more of lithium transition metal oxides, metal chalcogenides, lithium-containing phosphates, and modified compounds thereof. Examples of the lithium transition metal oxides can include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, lithium titanium oxides, and modified compounds thereof. The lithium transition metal oxides can include, but are not limited to, layered structures, spinel structures. Examples of the lithium-containing phosphates can include, but are not limited to, one or more of lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese phosphate, a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon, and modified compounds thereof.

[0119] In some embodiments, in order to further enhance the energy density of the battery cell, the positive electrode active material can include one or more of lithium transition metal oxides of a general formula of Li a Ni b Co c M d O e D f 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M can include, but is not limited to, one or more of Ge, Mo, Sn, Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and D can include, but is not limited to, one or more of N, F, S, and Cl.

[0120] In some embodiments, the positive electrode active material can include both lithium transition metal oxides and lithium-containing phosphates. This is advantageous in obtaining a battery that has both large capacity and high reliability.

[0121] As an example, the positive electrode active material can include, but is not limited to, LiCoO2, LiNiO2, LiMnO2, LiNi 1 / 2 Mn 1 / 2 O2, LiMn2O4, Li 4 / 3 Ti 5 / 3 O4, LiNi 1 / 2 Mn 1 / 2 O2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.80 Co 0.15 Al 0.05 O2, LiFePO4, LiMnPO4, Li 1.13 Ti 0.57 Fe 0.3 one or more of S2.

[0122] In some embodiments, the positive electrode active material includes a material capable of deintercalating and intercalating sodium. For example, the positive electrode active material can include, but is not limited to, one or more of a layered transition metal oxide (including but not limited to P2-type, O3-type, etc.), a polyanion material (such as a phosphate, a fluorophosphate, a pyrophosphate, a sulfate, etc.), a Prussian-type material.

[0123] In some embodiments, as an example, the positive electrode active material can include, but is not limited to, one or more of NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, Na 0.67 one or more of MO2(M includes at least two of Fe, Co, Cr, Mn, Ni, V, Ti, Mo), NaMO2(M includes at least two of Fe, Co, Ni, V, Ti, Mo), NaFePO4, NaMnPO4, NaCoPO4, Na4Fe3(PO4)2O7, Na3V2(PO4)2F3, Na3V2(PO4)3, Prussian blue, Prussian white, and respective modified compounds thereof.

[0124] The modified compounds of each of the above positive electrode active materials can be a doping modification and / or a surface coating modification to the positive electrode active material.

[0125] In some embodiments, the positive electrode film layer can also optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent can include, but is not limited to, one or more of super P, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, carbon nanofibers.

[0126] In some embodiments, the positive current collector can employ a metal foil or a composite current collector. As an example of a metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material can include, but is not limited to, one or more of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy. As an example, the polymer material base layer can include, but is not limited to, one or more of polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE).

[0127] The positive electrode film layer is typically formed by coating a positive electrode slurry on a positive electrode current collector, drying, and cold-pressing. The positive electrode slurry is typically formed by dispersing and uniformly stirring a positive electrode active material, a positive electrode conductive agent, a positive electrode binder, and any other components in a solvent. The solvent can be N-methyl pyrrolidone (NMP), but is not limited thereto.

[0128] [Negative electrode tab]

[0129] The structure and composition of the negative electrode tab can be adjusted according to the type of the battery cell.

[0130] In some embodiments, the negative electrode tab can include a negative electrode current collector and a metal layer disposed on at least one surface of the negative electrode current collector, and the metal material in the metal layer can include, but is not limited to, one or more of lithium monomer, a lithium alloy, sodium, a sodium alloy.

[0131] The lithium alloy can be an alloy of metallic lithium and other metal elements or non-metal elements. As an example, the other metal elements in the lithium alloy can include one or more of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, platinum, and the non-metal elements in the lithium alloy can include one or more of boron, carbon, silicon.

[0132] The sodium alloy can be an alloy of metallic sodium and other metal elements or non-metal elements. As an example, the other metal elements in the sodium alloy can include one or more of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, platinum, and the non-metal elements in the sodium alloy can include one or more of boron, carbon, silicon.

[0133] In some embodiments, the negative electrode tab can include a negative electrode current collector and not include a metal layer, to assemble a negative electrode metal-free battery cell.

[0134] In some embodiments, in order to improve the performance of the battery, some conventional materials that can be used as negative active materials, such as carbon materials, etc., can also be arranged on the negative side of the metal anode-free battery cell. Although these materials have a certain capacity, due to their small amount and not being used as the main negative active material in the battery cell, the battery cell thus formed can still be regarded as a metal anode-free battery cell.

[0135] In some embodiments, the negative current collector can include a metal foil, a three-dimensional porous current collector, or a composite current collector. As examples of the metal foil, copper foil, copper alloy foil, nickel foil, nickel alloy foil, aluminum foil, and aluminum alloy foil can be used. As examples of the three-dimensional porous current collector, copper mesh, nickel mesh, aluminum mesh, foamed copper, foamed nickel, and foamed aluminum can be used. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As examples, the metal material can include, but is not limited to, one or more of copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As examples, the polymer material base layer can include, but is not limited to, one or more of polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0136] [Electrolyte]

[0137] The kind of the electrolyte is not specifically limited in the present application and can be selected according to the needs. For example, the electrolyte can be selected from at least one of a solid-state electrolyte and a liquid electrolyte (i.e., electrolyte solution).

[0138] In some embodiments, the electrolyte uses an electrolyte solution including an electrolyte salt and a solvent.

[0139] The kind of the electrolyte salt is not specifically limited and can be selected according to the actual needs. In some embodiments, as examples, the electrolyte salt can include at least one of NaPF6, NaClO4, NaBCl4, NaSO3CF3, and Na(CH3)C6H4SO3.

[0140] The kind of the solvent is not particularly limited, and can be selected according to actual needs. In some embodiments, the solvent can include, by way of example, at least one of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene 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).

[0141] In some embodiments, the electrolyte can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and an additive capable of improving certain performance of the battery, such as an additive capable of improving overcharge performance of the battery, an additive capable of improving high-temperature performance of the battery, an additive capable of improving low-temperature power performance of the battery, and the like.

[0142] [Separator]

[0143] The battery cell using the electrolyte, and some battery cells using a solid-state electrolyte, also include a separator. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and mainly functions to prevent short circuiting of the positive and negative electrodes, while allowing metal ions to pass through. The kind of the separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0144] In some embodiments, the material of the separator can include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of the layers can be the same or different.

[0145] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet can be made into an electrode assembly by a winding process or a stacking process.

[0146] In some embodiments, the battery cell can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0147] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the battery cell can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), or the like.

[0148] The shape of the battery cell is not particularly limited in the present application, which can be cylindrical, square, or any other shape. FIG. 1 is a battery cell 5 in a square structure as an example.

[0149] In some embodiments, as shown in FIG. 2, the outer package can include a shell 51 and a cover plate 53. The shell 51 can include a bottom plate and a side plate connected to the bottom plate, which enclose a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to seal the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator film can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or several, which can be adjusted according to requirements.

[0150] The preparation method of the battery cell of the present application is known. In some embodiments, the positive electrode sheet, the separator film, the negative electrode sheet, and the electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, the separator film, and the negative electrode sheet can be formed into an electrode assembly through a winding process or a stacking process, the electrode assembly is placed in the outer package, the electrolyte is injected after drying, and the battery cell is obtained after processes such as vacuum packaging, standing, formation, and shaping.

[0151] In some embodiments, the battery cell according to the present application can be assembled into a battery module, and the number of battery cells contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0152] FIG. 3 is a schematic diagram of a battery module 4 as an example. As shown in FIG. 3, in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be used. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0153] Optionally, the battery module 4 can further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0154] In some embodiments, the above-mentioned battery module 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.

[0155] FIGS. 4 and 5 are schematic diagrams of the battery pack 1 as an example. As shown in FIGS. 4 and 5, the battery pack 1 can include a battery case and a plurality of battery modules 4 disposed in the battery case. The battery case includes an upper case 2 for capping a lower case 3 and forms an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery case in any manner.

[0156] A method for preparing the polyolefin elastomer

[0157] In a second aspect, an embodiment of the present application provides a method for preparing the polyolefin elastomer, including the following steps: providing polymer monomers, the polymer monomers including olefins having the structure shown in the above Formula 1 or the above Formula 2; mixing the polymer monomers, a modifier, and a catalyst, and allowing the polymer monomers to polymerize under the action of the catalyst to obtain the polyolefin elastomer.

[0158] In some embodiments, the modifier includes at least one of maleic anhydride, glycidyl methacrylate, and acrylic acid.

[0159] In some embodiments, the catalyst includes at least one of a metallocene catalyst, a bridged bis-met catalyst, and methylaluminoxane.

[0160] A battery device

[0161] In a third aspect, an embodiment of the present application provides a battery device including the battery monomer of the first aspect. The battery monomer can be assembled into a battery.

[0162] A power consuming device

[0163] In a fourth aspect, an embodiment of the present application provides a power consuming device including the battery monomer of the first aspect and at least one of a battery module and a battery pack assembled from the battery monomer. The battery monomer, the battery module, and the battery pack can be used as a power source of the power consuming device or as an energy storage unit of the power consuming device. The power consuming device can be, but is not limited to, a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0164] The power consuming device can select the battery monomer, or the battery module or the battery pack assembled from the battery monomer according to the use requirement of the power consuming device.

[0165] FIG. 6 is a schematic diagram of an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the demand of the electric device for high power and high energy density, a battery pack or a battery module can be used.

[0166] The electric device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The electric device usually requires thinning, and a battery monomer can be used as a power source.

[0167] Embodiments

[0168] The following examples more specifically describe the present disclosure, which are only used for illustrative purposes, because various modifications and changes within the scope of the present disclosure are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods, and can be used directly without further treatment, and the instruments used in the examples are commercially available.

[0169] The MH7510, MH7511, MH75102, MH7513, and MA8510 in the examples are all purchased from Dow Chemical.

[0170] Example 1

[0171] Preparation of positive electrode tab: the positive electrode active material sodium iron pyrophosphate, the conductive agent carbon black (Super P), MH7510, and MA8510 are mixed in a weight ratio of 95.5:3.0:0.5:1.0, solvent oil D80 is added, and the system is stirred to be uniform under the action of a stirrer, to obtain a positive electrode slurry with a solid content of 60wt%. The positive electrode slurry is uniformly coated on an aluminum foil current collector and high-temperature dried, and then cold-pressed to obtain a positive electrode tab.

[0172] Preparation of negative electrode tab: carbon nanotubes (CNT) and sodium carboxymethyl cellulose (CMC) are mixed in a weight ratio of 50:50 in an appropriate amount of solvent deionized water to form an interface modification layer slurry. The interface modification layer slurry is coated on the surface of a negative electrode current collector copper foil, with a thickness of 5μm.

[0173] Preparation of separator film: a porous polyethylene film is used as a separator film, and an organic / inorganic composite coating layer, including a ceramic particle coating layer, a metal oxide coating layer, and a glue layer, can be provided on the separator film.

[0174] Preparation of electrolyte: NaPF6 that is fully dried is dissolved in diethylene glycol dimethyl ether (DEGDME) to prepare an electrolyte with a concentration of 1mol / L.

[0175] Assembly: the positive electrode sheet, the separator and the copper foil prepared in the above steps are stacked in sequence, so that the separator is between the positive electrode sheet and the copper foil and can isolate the positive electrode sheet and the copper foil, and then the stacked components are wound to obtain the battery cell; the electrode assembly is arranged in the shell, and after drying, the electrolyte is injected; after the processes such as formation and standing, the battery monomer is obtained.

[0176] Examples 2-7

[0177] The implementation steps are basically the same as those of Example 1, except that the compounding of the binder / dispersant is different, and the specific formula is shown in Table 1.

[0178] Examples 8-10

[0179] The implementation steps are basically the same as those of Example 1, except that the compounding of the binder / dispersant is different, and the specific formula is shown in Table 1, wherein,

[0180] Preparation method of polyolefin elastomer in Example 8: after mixing hexene, octene, maleic anhydride and metallocene catalyst in a ratio of 7:2:0.8:0.2, polymerization for 48h, anhydride modified POE is obtained,

[0181] Preparation method of polyolefin elastomer in Example 9: after mixing hexene, octene, glycidyl methacrylate and metallocene catalyst in a ratio of 7:2:0.8:0.2, polymerization for 48h, carboxyl modified POE is obtained,

[0182] Preparation method of polyolefin elastomer in Example 10: after mixing hexene, octene, acrylic acid and metallocene catalyst in a ratio of 7:2:0.8:0.2, polymerization for 48h, carboxyl modified POE is obtained.

[0183] Comparative Examples 1-4

[0184] The implementation steps are basically the same as those of Example 1, except that the compounding of the binder / dispersant is different, and the specific formula is shown in Table 1.

[0185] Data testing and analysis

[0186] 1. The positive electrode sheet in Examples 1-10 and Comparative Examples 1-4 is tested for performance, and the test method is as follows, and the test results are shown in Table 1.

[0187] Adhesive force

[0188] Parameter definition: the adhesive force refers to the maximum force required for peeling the materials pasted together from the contact surface per unit width.

[0189] National standard for parameter testing: the adhesion between the film layer and the current collector can be characterized by the peeling strength, which can be measured by instruments and methods known in the art, for example, refer to GB / T 2792-2014.

[0190] Test procedure for parameters: according to the embodiments of the present application, the test of the adhesion of the pole piece includes: immersing the pole piece in ethyl methyl carbonate (EMC) for cleaning. About 15-20 cm of the pole piece coated with negative material on both sides is taken; the pole piece is attached to a steel plate with 3M double-sided tape; the pole piece is tested by a material testing machine INSTRON3365 to obtain the relationship between force and distance; and the adhesion value of the pole piece is calculated.

[0191] Membrane resistance

[0192] Parameter definition: the resistivity of the pole piece refers to a physical quantity representing the resistance characteristics of the pole piece.

[0193] National standard for parameter testing: the resistivity of the pole piece is a known meaning in the art, which can be measured by instruments and methods known in the art, and the test method can refer to GB / T 30835-2014 or T / CASAS 019-2021. The test instrument verification regulation can refer to JJG 508-2004.

[0194] Test procedure for parameters: according to the embodiments of the present application, the resistivity of the pole piece is determined by the four-probe method. Specifically, according to the embodiments of the present application, the resistivity is determined by the following method: immersing the pole piece in ethyl methyl carbonate (EMC) for cleaning, filling in specific equipment, fixing four copper plates with a length of 1.5 cm* width of 1 cm* thickness of 2 mm equidistantly on a line, the distance between the middle two copper plates is L (1 cm to 2 cm), the base material of the fixed copper plate is insulating material, the lower end surface of the four copper plates is pressed on the measured pole piece during testing, the two end copper plates are connected with direct current I, the voltage V is measured on the middle two copper plates, the average value of I and V is read for three times, and V / I is the resistance of the pole piece at the test position.

[0195] 2. The performance of the battery cell in Example 1 and Comparative Example 1 was tested, and the test method is as follows, and the test results are shown in Table 2.

[0196] Formation first efficiency test: each battery cell is charged at 0.33C rate to a voltage equal to 3.65V at room temperature, and the first charge capacity C1 is tested, then discharged at 0.33C rate to a voltage equal to 1.5V, and the first discharge reversible capacity D1 is measured, and the ratio of the first discharge capacity D1 / C1 is the first efficiency of the battery;

[0197] Cycling performance test: each battery monomer is charged at room temperature at 0.33C rate to voltage equal to 3.65V, and then discharged at 0.33C rate to voltage equal to 1.5V, and the reversible capacity is measured as C0. Keep repeating the charge and discharge until the discharge capacity Cn of a certain cycle is less than or equal to 95% of C0, and the total cycle number is recorded as X-Cycle. Wherein, Cn is the reversible capacity of the nth cycle; n C0≤95% is reached. Cn / C0 is the capacity retention rate of the battery monomer. n Cn is the reversible capacity of the nth cycle;

[0198] Battery storage life test: each battery monomer is charged at room temperature at 0.33C rate to voltage equal to 3.65V, and then discharged at 0.33C rate to voltage equal to 1.5V, and the reversible capacity is measured as C0. Then store the battery monomer in an environment of 25℃, and every 30 days, charge at 0.33C rate to voltage equal to 3.65V, and then discharge at 0.33C rate to voltage equal to 1.5V, and the reversible capacity is measured as Cn. Cn / C0 is the storage life decay rate of the battery monomer. Keep storing and repeating the charge and discharge until the discharge capacity Cn of a certain cycle is less than or equal to 80% of C0. Record the storage days Dn of the battery. 0， n， n

[0199] From Table 1 and Table 2, it can be seen that:

[0200] In Comparative Example 1, PVDF is used as the binder, which is easy to react with air and continuously react with sodium clusters in the system to release HF, thereby increasing the membrane resistance and reducing the stability of the pole piece. In Examples 1-10, polyolefin elastomers with different molecular weights are used as dispersants and binders respectively, which can better coat the surface of the active material, reduce the active sites on the surface of the active material, and thereby reduce the contact reaction of the active material with O2 and CO2 in the air, so as to improve the adhesion and ensure the stability of the pole piece.

[0201] From Examples 1-10 and Comparative Examples 2, 3 and 4, it can be seen that only when the polyolefin elastomers with different molecular weights are mixed and used, and the polyolefin elastomers with different molecular weights are compounded according to a specific mass ratio, can the adhesion be improved and the stability of the pole piece be ensured.

[0202] 3, the pole pieces in Example 1 and Comparative Example 1 are subjected to formation verification and morphology analysis, and the test results are shown in Figures 7-9. Figure 7 is the formation verification, Figure 8 is the SEM diagram of the positive pole piece in Example 1, and Figure 9 is a schematic diagram of the polyolefin elastomer and the active material in the positive pole piece in Example 1.

[0203] From Figure 7, it can be seen that the capacity of the pole piece in Example 1 remains basically unchanged after formation.

[0204] ​​​As can be seen from FIGS. 8 and 9, the polyolefin elastomer in the embodiment 1 coats the surface of the active material, reduces the active sites on the surface of the active material, reduces the contact reaction of the active material with O2 and CO2 in the air, improves the specific capacity of the pole piece, and ensures the stability of the pole piece.

[0205] Table 1

[0206] Table 2

[0207] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0208] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features, but these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A battery cell, characterized by, The positive electrode sheet and the negative electrode sheet; The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector; The positive electrode active material layer comprises a positive electrode active material and a polyolefin elastomer, the polyolefin elastomer comprises a first polyolefin elastomer with a first molecular weight and a second polyolefin elastomer with a second molecular weight, the first molecular weight is higher than the second molecular weight, and the mass ratio of the first polyolefin elastomer to the second polyolefin elastomer in the polyolefin elastomer is 1:(0.2-5.0).

2. The battery cell of claim 1, wherein, The first polyolefin elastomer and the second polyolefin elastomer are independently selected from unmodified or modified polyolefin elastomers.

3. The battery cell of claim 1, wherein, The mass ratio of the first polyolefin elastomer to the second polyolefin elastomer in the polyolefin elastomer is 1:(0.5-1).

4. The battery cell of claim 1, wherein, The first molecular weight is 40-100 W, and the second molecular weight is 1-10 W. Preferably, the first molecular weight is 50-70 W, and the second molecular weight is 3-5 W.

5. The battery cell of claim 2, wherein, The modified polyolefin elastomer comprises an anhydride-modified polyolefin elastomer and / or a carboxyl-modified polyolefin elastomer; and / or, The modified polyolefin elastomer comprises at least one of maleic anhydride, glycidyl methacrylate, and acrylic acid.

6. The battery cell of claim 5, wherein, The grafting rate of the anhydride-modified polyolefin elastomer and / or the carboxyl-modified polyolefin elastomer is 0.1%-3.0%.

7. The battery cell of claim 1, wherein, The bonding strength between the positive electrode sheet and the positive electrode current collector is 12-25 N / m.

8. The battery cell of claim 1, wherein, The positive electrode active material layer is prepared from a slurry, and the slurry comprises the positive electrode active material, the polyolefin elastomer, and a solvent.

9. The battery cell of claim 1, wherein, The polyolefin elastomer has a repeating structural unit as shown in Formula 1, In formula 1, R2 is selected from C1-C5 alkyl; The polyolefin elastomer has a repeating structural unit as shown in Formula 2, In formula 2, R1 is selected from C1-C8 alkyl; The polyolefin elastomer also has a polar segment structural unit; In formula 1, the content of the structural unit is 5%-45%, the content of the structural unit in formula 2 is 45%-94%, and the content of the polar segment structural unit is 1%-10%.

10. The battery cell of claim 8, wherein, The solvent comprises aromatic hydrocarbon-containing and / or aromatic hydrocarbon-free solvent oil.

11. The battery cell of claim 1, wherein, The positive electrode active material comprises phosphate and / or pyrophosphate of the NACISON type structure.

12. The battery cell of claim 11, wherein, The positive electrode active material comprises at least one of Na3MnTi(PO4)3, Na3MnV(PO4)3, Na3TiV(PO4)3, Na3Fe2(PO4)3, Na3MnZr(PO4)3, and Na2MP2O7, Wherein, M is selected from at least one of Fe, Co, Mn, and Cu.

13. A process for the preparation of a polyolefin elastomer as claimed in claim 9, characterized in that, The method comprises the following steps: Providing a polymer monomer, the polymer monomer comprising an olefin with the structure shown in formula 1 or formula 2 described above; Mixing the polymer monomer, a modifier, and a catalyst, and then allowing the polymer monomer to polymerize under the action of the catalyst to obtain the polyolefin elastomer.

14. The method of claim 13, wherein, The modifier comprises at least one of maleic anhydride, glycidyl methacrylate, and acrylic acid. Optionally, the catalyst comprises at least one of a metallocene catalyst, a bridged bis-met catalyst, and methylaluminoxane.

15. A battery device comprising the battery cell of any one of claims 1-12.

16. An electrically powered device comprising the battery cell of any one of claims 1-12 or the battery device of claim 15.

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