Sodium-ion battery, binder and preparation method thereof, and electric device

Abstract

The application relates to a sodium ion battery, a binder and a preparation method thereof, and an electric device. A primer layer is arranged between a positive electrode film layer and a current collector; the positive electrode film layer comprises a positive electrode active material; and the primer layer comprises a carboxyl-modified polyvinylidene fluoride. The ductility of the positive electrode film layer and the current collector layer is inconsistent when subjected to pressure, and generally the ductility of the current collector is greater than that of the active layer. The relationship between the ductility of the current collector and the pressure is generally nonlinear, and when close to the critical value of the ductility, the ductility shows a rapid growth trend. Therefore, when the compaction density increases, that is, the pressure on the positive electrode sheet increases to a certain degree, the ductility of the current collector is greater than that of the positive electrode film layer, and thus the demolding condition occurs. The introduction of the primer layer containing the carboxyl-modified polyvinylidene fluoride can enhance the connection between the current collector and the positive electrode film layer, reduce the difference in the ductility of the two to a certain extent, reduce the demolding condition, and thus improve the compaction density.

Description

Technical Field

[0001] This application relates to a sodium-ion battery, an adhesive and its preparation method, and an electrical device. Background Technology

[0002] Sodium-ion batteries, as an emerging sustainable energy storage technology, are characterized by low cost and environmental friendliness, and therefore their application has been increasingly developed in recent years.

[0003] Therefore, higher requirements are placed on the compaction density of sodium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide a sodium-ion battery, a binder, a method for preparing the same, and an electrical device.

[0005] The embodiments of this application are implemented as follows:

[0006] In a first aspect, embodiments of this application provide a sodium-ion battery, including: a positive electrode sheet;

[0007] The positive electrode includes: a positive electrode film layer, a current collector, and a base coating layer; the base coating layer is disposed between the positive electrode film layer and the current collector; the positive electrode film layer includes a positive electrode active material;

[0008] The base coating consists of carboxyl-modified polyvinylidene fluoride.

[0009] Research has found that one of the reasons why it is difficult to increase the compaction density of the positive electrode sheet of sodium-ion batteries is that the positive electrode active material of sodium-ion batteries, especially polyanionic materials, has a large cohesive force (intermolecular force), which is often greater than the adhesive force between the positive electrode active material itself and the current collector. When the compaction density of the positive electrode sheet is increased, the positive electrode film often detaches from the current collector before it can be increased to a high level, thus making it difficult to increase the compaction density of the positive electrode sheet of sodium-ion batteries.

[0010] Based on this, in the above technical solution of this application, the base coating includes: carboxyl-modified polyvinylidene fluoride; this carboxyl-modified polyvinylidene fluoride has stronger adhesive properties; and it can react with residual alkali in the positive electrode active material to reduce the amount of residual alkali at the interface (residual alkali itself causes conventional PVDF to be intolerant, and on the other hand, residual alkali will absorb water from the air, deteriorating the adhesion); by setting it in the base coating and placing the base coating between the positive electrode film layer and the current collector, the adhesion between the positive electrode film layer and the current collector can be enhanced, thereby improving the problem of positive electrode film layer detachment. The elongation rates of the positive electrode film and the current collector layer are inconsistent under pressure. Generally, the elongation rate of the current collector (usually a metal foil) is greater than that of the active layer. The relationship between the elongation rate of the current collector and pressure is usually non-linear, and it will show a rapid growth trend when approaching its critical elongation rate value. Therefore, when the compaction density increases, that is, when the pressure on the positive electrode increases to a certain extent, the elongation of the current collector is much greater than that of the positive electrode film, which will lead to demolding. The introduction of the carboxyl-modified polyvinylidene fluoride undercoating can enhance the connection between the current collector and the positive electrode film, reduce the difference in elongation rates between the two to a certain extent, reduce demolding, and thus improve the compaction density.

[0011] In some alternative embodiments, the general structural formula of carboxyl-modified polyvinylidene fluoride includes:

[0012] (CH2CF2)n1-(CR1R2-CR3R4)n2;

[0013] Wherein, n1:n2 = (85-90):(15-10); at least one of R1, R2, R3 or R4 contains a carboxyl group; R1, R2, R3, R4 are hydrogen, alkyl or branched.

[0014] The above technical solution can obtain carboxyl-modified polyvinylidene fluoride with higher molecular weight and relatively longer chains, resulting in a better network structure. This makes the carboxyl-modified polyvinylidene fluoride more adhesive, thereby enhancing the adhesion strength of the undercoat layer and improving the adhesion strength between the positive electrode film and the current collector. This effectively improves the problem of easy demolding of the positive electrode film in sodium-ion batteries, thus helping to increase the compaction density of the positive electrode sheet in sodium-ion batteries.

[0015] In some alternative implementations, the molecular weight of the carboxyl-modified polyvinylidene fluoride is 300,000 to 700,000.

[0016] In the above technical solution, the molecular weight of carboxyl-modified polyvinylidene fluoride is 300,000-700,000. Within this range, it has a higher molecular weight (the molecular weight of common polyvinylidene fluoride is 200,000-500,000, with generally poor adhesion) and a relatively long chain, which can obtain carboxyl-modified polyvinylidene fluoride with a better network structure. This makes the carboxyl-modified polyvinylidene fluoride have stronger adhesion, thereby enhancing the adhesion strength of the undercoating layer, and further improving the adhesion strength between the positive electrode film and the current collector. This effectively improves the problem of easy demolding of the positive electrode film of sodium-ion batteries, and thus helps to improve the compaction density of the positive electrode sheet of sodium-ion batteries.

[0017] In some alternative implementations, the base coating also includes a conductive agent.

[0018] In some alternative embodiments, the base coating also includes, by weight percentage: 43%-50% conductive agent and 50%-57% carboxyl-modified polyvinylidene fluoride.

[0019] In some alternative implementations, the positive electrode active material includes: a polyanionic material.

[0020] In some alternative embodiments, the positive electrode active material includes at least one of the following: sodium iron pyrophosphate, sodium iron pyrophosphate, sodium iron phosphate, sodium iron sulfate, sodium vanadium phosphate, and sodium fluorophosphate.

[0021] Secondly, this application provides a method for preparing an adhesive, comprising:

[0022] Carboxyl-containing monomers were cross-linked with polyvinylidene fluoride monomers to obtain carboxyl-modified polyvinylidene fluoride.

[0023] In some alternative embodiments, a crosslinking reaction is carried out between a monomer containing a carboxyl group and a polyvinylidene fluoride monomer, including:

[0024] Crosslinking reaction is carried out using a first monomer and a second monomer;

[0025] The first monomer includes: (CH2CF2)n1;

[0026] The second monomer includes: (CR1R2-CR3R4)n2;

[0027] Wherein, n1:n2 = (85-90):(15-10), and at least one of R1, R2, R3 or R4 contains a carboxyl group; R1, R2, R3, R4 are hydrogen, alkyl or branched.

[0028] In some alternative embodiments, the amount of carboxyl substitution in the carboxyl-modified polyvinylidene fluoride is 3.0% to 10.0%.

[0029] In some alternative implementations, the molecular weight of the carboxyl-modified polyvinylidene fluoride is 300,000 to 700,000.

[0030] Thirdly, this application provides an adhesive, the general formula of which includes:

[0031] (CH2CF2)n1-(CR1R2-CR3R4)n2;

[0032] Wherein, n1:n2 = (85-90):(15-10); at least one of R1, R2, R3 or R4 contains a carboxyl group; R1, R2, R3, R4 are hydrogen, alkyl or branched.

[0033] In some alternative implementations, the molecular weight of the adhesive is 300,000 to 700,000.

[0034] In some alternative embodiments, the amount of carboxyl substitution in the adhesive is 3.0% to 10.0%.

[0035] Fourthly, this application provides an electrical device that includes a sodium-ion battery provided in any of the foregoing embodiments, the sodium-ion battery being used to provide electrical energy. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application;

[0038] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0039] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0040] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0041] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown;

[0042] Figure 6 This is a schematic diagram of an electrical device in which a battery is used as a power source according to one embodiment of this application.

[0043] icon:

[0044] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0045] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0047] In the description of the embodiments of this application, the technical terms "first", "second", etc. are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0048] In the description of the embodiments of this application, the technical terms "inner" and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0049] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0050] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0051] In the embodiments of this application, the same reference numerals denote the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the height, length, width, and other dimensions of various components in the embodiments of this application shown in the accompanying drawings, as well as the overall height, length, width, and other dimensions of the integrated device, are merely illustrative and should not constitute any limitation on this application.

[0052] Research has found that one of the reasons why it is difficult to increase the compaction density of the positive electrode sheet of sodium-ion batteries is that the positive electrode active material of sodium-ion batteries, especially polyanionic materials, has a large cohesive force (intermolecular force), which is often greater than the adhesive force between the positive electrode active material itself and the current collector. When the compaction density of the positive electrode sheet is increased, the positive electrode film often detaches from the current collector before it can be increased to a high level, thus making it difficult to increase the compaction density of the positive electrode sheet of sodium-ion batteries.

[0053] Based on this, some embodiments of this application provide a sodium-ion battery, including: a positive electrode sheet;

[0054] The positive electrode includes: a positive electrode film layer, a current collector, and a base coating layer; the base coating layer is disposed between the positive electrode film layer and the current collector; the positive electrode film layer includes a positive electrode active material;

[0055] The base coating consists of carboxyl-modified polyvinylidene fluoride.

[0056] The above technical solution, by setting the base coating to include: carboxyl-modified polyvinylidene fluoride; this carboxyl-modified polyvinylidene fluoride has stronger adhesive properties; and can react with residual alkali in the positive electrode active material to reduce the amount of residual alkali at the interface (residual alkali itself causes conventional PVDF to be intolerant, and on the other hand, residual alkali will absorb water from the air, deteriorating the adhesion); setting it in the base coating and placing the base coating between the positive electrode film layer and the current collector can enhance the adhesion between the positive electrode film layer and the current collector, thereby improving the problem of positive electrode film layer detachment. The elongation rates of the positive electrode film and the current collector layer are inconsistent under pressure. Generally, the elongation rate of the current collector (usually a metal foil) is greater than that of the active layer. The relationship between the elongation rate of the current collector and pressure is usually non-linear, and it will show a rapid growth trend when approaching its critical elongation rate value. Therefore, when the compaction density increases, that is, when the pressure on the positive electrode increases to a certain extent, the elongation of the current collector is much greater than that of the positive electrode film, which will lead to demolding. The introduction of the carboxyl-modified polyvinylidene fluoride undercoating can enhance the connection between the current collector and the positive electrode film, reduce the difference in elongation rates between the two to a certain extent, reduce demolding, and thus improve the compaction density.

[0057] In some embodiments of this application, the aforementioned "sodium-ion battery" can be a single sodium-ion battery cell. Typically, a single battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode includes a positive current collector and a positive electrode film; the negative electrode includes a negative current collector and a negative electrode film. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrode cells. The electrolyte acts as a conductor between the positive and negative electrode cells. The separator is disposed between the positive and negative electrode cells, primarily to prevent short circuits between the positive and negative electrodes, while simultaneously allowing ions to pass through.

[0058] Furthermore, in some embodiments of this application, the general formula of the carboxyl-modified polyvinylidene fluoride described above includes:

[0059] (CH2CF2)n1-(CR1R2-CR3R4)n2;

[0060] Wherein, n1:n2 = (85-90):(15-10); at least one of R1, R2, R3 or R4 contains a carboxyl group; R1, R2, R3, R4 are hydrogen, alkyl or branched.

[0061] In some embodiments of this application, the carboxyl-modified polyvinylidene fluoride described above is obtained by reacting a first monomer and a second monomer;

[0062] The first monomer includes: (CH2CF2)n1;

[0063] The second monomer includes: (CR1R2-CR3R4)n2;

[0064] Wherein, n1:n2 = (85-90):(15-10), and at least one of R1, R2, R3 or R4 contains a carboxyl group; R1, R2, R3, R4 are hydrogen, alkyl or branched.

[0065] In the above technical solution, the first monomer includes (CH2CF2)n1; the second monomer includes (CR1R2-CR3R4)n2. Under the above conditions, a carboxyl-modified polyvinylidene fluoride with a higher molecular weight and a relatively longer chain can be obtained, resulting in a better network structure. This makes the carboxyl-modified polyvinylidene fluoride more adhesive, thereby enhancing the adhesion strength of the undercoating layer and improving the adhesion strength between the positive electrode film and the current collector. This effectively improves the problem of easy demolding of the positive electrode film of sodium-ion batteries, thus helping to increase the compaction density of the positive electrode sheet of sodium-ion batteries.

[0066] For example, in some embodiments of this application, n1:n2 = (85, 86, 87, 88, 89, 90 or any range between any two of the aforementioned values) : (15, 14, 13, 12, 11, 10 or any range between any two of the aforementioned values).

[0067] For example, in some embodiments of this application, the above n1:n2 = 85:15; n1:n2 = 86:14; n1:n2 = 87:13; n1:n2 = 88:12; n1:n2 = 89:11; n1:n2 = 90:10 or any range between the two aforementioned ratios.

[0068] Further optionally, in some embodiments of this application, any one of R1, R2, R3 or R4 contains a carboxyl group; or optionally, in some embodiments of this application, multiple groups of R1, R2, R3 or R4 contain carboxyl groups; for example, both R1 and R2 contain carboxyl groups; or both R3 and R4 contain carboxyl groups; or all of R1, R2, R3 and R4 contain carboxyl groups.

[0069] Further, optionally, and exemplary, in some embodiments of this application, the above-described carboxyl-modified polyvinylidene fluoride comprises:

[0070] (CH2CF2)85-(CR1R2-CR3R4)15;

[0071] (CH2CF2)86-(CR1R2-CR3R4)14;

[0072] (CH2CF2)87-(CR1R2-CR3R4)13;

[0073] Among them, at least one of R1, R2, R3 or R4 contains a carboxyl group; R1, R2, R3, R4 are hydrogen, alkyl or branched.

[0074] Furthermore, in some embodiments of this application, the molecular weight of the carboxyl-modified polyvinylidene fluoride is 300,000 to 700,000.

[0075] In the above technical solution, the molecular weight of carboxyl-modified polyvinylidene fluoride is 300,000-700,000. Within this range, it has a higher molecular weight (the molecular weight of common polyvinylidene fluoride is 200,000-500,000, with generally poor adhesion) and a relatively long chain, which can obtain carboxyl-modified polyvinylidene fluoride with a better network structure. This makes the carboxyl-modified polyvinylidene fluoride have stronger adhesion, thereby enhancing the adhesion strength of the undercoating layer, and further improving the adhesion strength between the positive electrode film and the current collector. This effectively improves the problem of easy demolding of the positive electrode film of sodium-ion batteries, and thus helps to improve the compaction density of the positive electrode sheet of sodium-ion batteries.

[0076] For example, in some embodiments of this application, the molecular weight of the carboxyl-modified polyvinylidene fluoride is 300,000, 350,000, 400,000, 450,000, 500,000, 550,000, 600,000, 650,000, 700,000 or any two of the aforementioned values.

[0077] Furthermore, in some embodiments of this application, the thickness of the base coating is 1 μm to 3 μm.

[0078] In the above technical solution, the thickness of the base coating is 1μm to 3μm; within this range, it is beneficial to the compaction density of the positive electrode sheet.

[0079] For example, in some embodiments of this application, the thickness of the base coating is 1 μm, 1.1 μm, 1.2 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3 μm, or a range between any two of the aforementioned values.

[0080] Furthermore, in some embodiments of this application, the base coating layer further includes a conductive agent.

[0081] In the above technical solution, the base coating also includes a conductive agent; by combining the conductive agent with carboxyl-modified polyvinylidene fluoride, it is beneficial to improve the processing performance of the base coating, such as improving the processing performance of the base coating such as easy gelation, thereby making it easier to obtain a base coating with better overall performance; and further beneficial to improve the compaction density of the positive electrode sheet of sodium-ion battery.

[0082] Furthermore, in some embodiments of this application, the base coating layer further comprises, by weight percentage: 43%-50% conductive agent and 50%-57% carboxyl-modified polyvinylidene fluoride.

[0083] In the above technical solution, the base coating also includes, by mass percentage: 43%-50% conductive agent and 50%-57% carboxyl-modified polyvinylidene fluoride; the combination of conductive agent and carboxyl-modified polyvinylidene fluoride within the above ratio range is beneficial to improving the processing performance of the base coating, such as improving the processing performance of the base coating such as easy gelation, thereby helping to obtain a base coating with better overall performance; and further helping to improve the compaction density of the positive electrode sheet of sodium-ion battery.

[0084] For example, in some embodiments of this application, the base coating further includes, by weight percentage: 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50% or any two of the foregoing values ​​of conductive agent and 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57% or any two of the foregoing values ​​of carboxyl-modified polyvinylidene fluoride.

[0085] Furthermore, in some embodiments of this application, the conductive agent includes at least one of acetylene black, conductive carbon black SP, superconducting carbon, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0086] For example, in some embodiments of this application, the conductive agent is any one of acetylene black, conductive carbon black SP, superconducting carbon, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers. Alternatively, in some embodiments of this application, the conductive agent is a mixture of acetylene black and conductive carbon black SP; or in some embodiments of this application, the conductive agent is a mixture of superconducting carbon, carbon black, and Ketjen black; or in some embodiments of this application, the conductive agent is a mixture of carbon dots, carbon nanotubes, and graphene. The raw materials in each of the above mixtures can be mixed in any proportion.

[0087] In some alternative implementations, the adhesion between the positive electrode film and the undercoat layer is 16.3 N / M to 27 N / M.

[0088] In the above technical solution, the adhesion between the positive electrode film layer and the base coating layer is 16.3 N / M to 27 N / M. The increased adhesion between the positive electrode film layer and the base coating layer is beneficial for obtaining a higher compaction density of the positive electrode sheet.

[0089] For example, in some embodiments of this application, the adhesive strength between the positive electrode film layer and the base coating layer is 16.3 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, 26 N / M, 27 N / M, or any two of the aforementioned values, of carboxyl-modified polyvinylidene fluoride.

[0090] Furthermore, in some embodiments of this application, the aforementioned "adhesive force between the positive electrode film layer and the undercoat layer" has a meaning known in the art and can be tested using methods known in the art. An exemplary test method is as follows:

[0091] First, attach double-sided tape to the stainless steel plate, then attach the positive electrode sheet (positive electrode film side) to the double-sided tape, and use a tensile testing machine to clamp the electrode sheet and peel it off 180°.

[0092] Furthermore, in some embodiments of this application, the positive electrode active material includes: a polyanionic material.

[0093] In the above technical solution, polyanionic materials refer to materials that can insert and release sodium ions, and whose structure contains anionic groups that can interact with sodium ions. Polyanionic cathode materials typically have high electrochemical activity, enabling high-capacity sodium ion storage.

[0094] However, common polyanionic materials have relatively large cohesive forces (intermolecular forces). By adding a base coating, the adhesion between the positive electrode film and the current collector can be enhanced, which is beneficial for the positive electrode sheet to obtain a higher compaction density.

[0095] In some embodiments of this application, the aforementioned polyanionic material may be Na x-a A a V y-b M b (PO4)2(DO4)2F z-d Q d Wherein, element A represents an alkali metal element that substitutes for element Na, element M represents a metal element that substitutes for element V, element D represents a dopant element that substitutes for element P, and element Q represents a dopant element that substitutes for element F. Element D includes at least one of Si and S, and element Q includes at least one of Cl and O; 3.5 ≤ x ≤ 4.5, 0 ≤ a ≤ 0.15x, 0.8 ≤ y ≤ 1.1, 0 ≤ b ≤ 0.3y, 0.8 ≤ z ≤ 1.1, and 0 ≤ d ≤ 0.2z. Optionally, element A includes at least one of K and Li; element M includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0096] In some embodiments of this application, the above-mentioned positive electrode active materials may be modified by doping and / or surface coating.

[0097] Furthermore, in some embodiments of this application, the above-mentioned positive electrode active material includes at least one of the following: sodium iron pyrophosphate, sodium iron pyrophosphate, sodium iron phosphate, sodium iron sulfate, sodium vanadium phosphate, and sodium fluorophosphate.

[0098] Further optionally, in some embodiments of this application, the sodium iron pyrophosphate class includes: sodium iron pyrophosphate, dopants of sodium iron pyrophosphate; exemplarily, iron site dopants of sodium iron pyrophosphate.

[0099] Further optionally, in some embodiments of this application, the iron-site doping element of sodium iron pyrophosphate includes at least one of Ti, V, Cr, Mn, Co, Ni, Ca, Mg, Al, or Nb.

[0100] Further optionally, in some embodiments of this application, the positive electrode active material is selected as sodium iron pyrophosphate Na4Fe3(PO4)2P2O7(NFPP).

[0101] Further optionally, in some embodiments of this application, sodium iron pyrophosphate includes: sodium iron pyrophosphate, dopants of sodium iron pyrophosphate; exemplarily, iron site dopants of sodium iron pyrophosphate.

[0102] Further optionally, in some embodiments of this application, the iron-site doping element of sodium iron pyrophosphate includes at least one of Ti, V, Cr, Mn, Co, Ni, Ca, Mg, Al, or Nb.

[0103] Further optionally, in some embodiments of this application, sodium iron phosphate includes: sodium iron phosphate, dopants of sodium iron phosphate; exemplarily, iron site dopants of sodium iron phosphate.

[0104] Further optionally, in some embodiments of this application, the iron-site doping element of sodium iron phosphate includes at least one of Ti, V, Cr, Mn, Co, Ni, Ca, Mg, Al, or Nb.

[0105] In other optional embodiments of this application, the sodium ferric sulfate, sodium vanadium phosphate, and sodium fluorophosphate described above also include similar doping methods.

[0106] During the charging and discharging process of a battery, sodium (Na) undergoes insertion / extraction and consumption, resulting in varying molar Na content at different discharge states. In the examples of cathode materials in this application, the molar Na content refers to the initial state of the material, i.e., the state before feeding. When the cathode material is applied to the battery system, the molar Na content changes after charge-discharge cycles.

[0107] In the examples of cathode materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0108] The positive electrode active material inevitably contains a high amount of residual alkali (including NaOH and Na2CO3). Excessive residual alkali not only causes incompatibility with conventional PVDF, but also absorbs moisture from the air, further deteriorating adhesion. The amount of carboxyl groups introduced into PVDF is related to the amount of residual alkali in the positive electrode active material. Carboxyl groups can react with NaOH and Na2CO3 in the residual alkali, thereby reducing the amount of residual alkali at the interface, improving adhesion, and benefiting compaction density.

[0109] Some embodiments of this application provide a method for preparing an adhesive, including:

[0110] Carboxyl-containing monomers were cross-linked with polyvinylidene fluoride monomers to obtain carboxyl-modified polyvinylidene fluoride.

[0111] In the above technical solution, a carboxyl-containing monomer is used to crosslink with polyvinylidene fluoride monomer to obtain carboxyl-modified polyvinylidene fluoride. Compared with ordinary polyvinylidene fluoride, this carboxyl-modified polyvinylidene fluoride has a higher molecular weight, longer chains, and a better network structure, which makes the carboxyl-modified polyvinylidene fluoride have stronger adhesion. This can enhance the adhesion strength of the undercoat layer, thereby improving the adhesion strength between the positive electrode film and the current collector, effectively improving the problem of easy demolding of the positive electrode film of sodium-ion battery; thus, it is beneficial to improve the compaction density of sodium-ion battery.

[0112] Furthermore, carboxyl-modified polyvinylidene fluoride can react with residual alkali in the positive electrode film (e.g., to generate sodium carboxylate), which effectively enhances the adhesion between the positive electrode film and the current collector, thus improving the compaction density of sodium-ion batteries.

[0113] Furthermore, in some embodiments of this application, a crosslinking reaction is carried out between a monomer containing a carboxyl group and a polyvinylidene fluoride monomer, including:

[0114] Crosslinking reaction is carried out using a first monomer and a second monomer;

[0115] The first monomer includes: (CH2CF2)n1;

[0116] The second monomer includes: (CR1R2-CR3R4)n2;

[0117] Wherein, n1:n2 = (85-90):(15-10), and at least one of R1, R2, R3 or R4 contains a carboxyl group; R1, R2, R3, R4 are hydrogen, alkyl or branched.

[0118] In the above technical solution, by introducing a second monomer containing -COOH groups into the PVDF main body (first monomer), the group can neutralize the high residual alkali in NFPP and undergo a cross-linking reaction, which makes the primer and the cathode coating have better adhesion.

[0119] For example, in some embodiments of this application, the above n1:n2 = 85:15; n1:n2 = 86:14; n1:n2 = 87:13; n1:n2 = 88:12; n1:n2 = 89:11; n1:n2 = 90:10 or any range between the two aforementioned ratios.

[0120] Further optionally, in some embodiments of this application, any one of R1, R2, R3 or R4 contains a carboxyl group; or optionally, in some embodiments of this application, multiple groups of R1, R2, R3 or R4 contain carboxyl groups; for example, both R1 and R2 contain carboxyl groups; or both R3 and R4 contain carboxyl groups; or all of R1, R2, R3 and R4 contain carboxyl groups.

[0121] In some alternative embodiments, the amount of carboxyl substitution in the carboxyl-modified polyvinylidene fluoride is 3.0% to 10.0%.

[0122] In the above technical solution, the amount of carboxyl substitution in carboxyl-modified polyvinylidene fluoride is 3.0% to 10.0%, which can effectively increase the molecular weight of polyvinylidene fluoride, increase the chain length, improve its network structure, thereby increasing its adhesive properties, and thus increasing the compaction density of the positive electrode sheet.

[0123] For example, in some embodiments of this application, the amount of carboxyl substitution in carboxyl-modified polyvinylidene fluoride is 3.0%, 3.1%, 3.2%, 3.5%, 3.8%, 4.0%, 4.2%, 4.5%, 4.8%, 5.0%, 5.2%, 5.5%, 5.8%, 6.0%, 6.5%, 7.0%, 8.0%, 8.5%, 9.0%, 9.5%, 9.8%, 10.0%, or a range between any two of the aforementioned ratios.

[0124] Furthermore, in some embodiments of this application, the molecular weight of the carboxyl-modified polyvinylidene fluoride described above is 300,000 to 700,000.

[0125] For example, in some embodiments of this application, the molecular weight of the carboxyl-modified polyvinylidene fluoride is 300,000, 350,000, 400,000, 450,000, 500,000, 550,000, 600,000, 650,000, 700,000 or any two of the aforementioned values.

[0126] Some embodiments of this application provide an adhesive, the general formula of which includes:

[0127] (CH2CF2)n1-(CR1R2-CR3R4)n2;

[0128] Wherein, n1:n2 = (85-90):(15-10); at least one of R1, R2, R3 or R4 contains a carboxyl group; R1, R2, R3, R4 are hydrogen, alkyl or branched.

[0129] Furthermore, in some embodiments of this application, the molecular weight of the adhesive is 300,000 to 700,000. Exemplarily, the molecular weight of the adhesive is 300,000, 350,000, 400,000, 450,000, 500,000, 550,000, 600,000, 650,000, 700,000, or any range between the aforementioned two values.

[0130] Furthermore, in some embodiments of this application, the amount of carboxyl group substitution in the adhesive is 3.0% to 10.0%. Exemplarily, the amount of carboxyl group substitution in the adhesive is 3.0%, 3.5%, 4.0%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 8.0%, 9.0%, 10.0%, or a range between any two of the aforementioned values.

[0131] In some embodiments of this application, a positive electrode sheet containing a positive electrode film layer can be obtained by coating a positive electrode slurry onto at least one surface of a positive electrode current collector and then performing processes such as drying and cold pressing.

[0132] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0133] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0134] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0135] [Negative electrode plate]

[0136] The negative electrode sheet includes a negative current collector and a negative electrode film layer formed on at least one surface of the negative current collector.

[0137] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0138] In some optional embodiments of this application, the aforementioned negative electrode active material may include at least one of the following: hard carbon, graphite, soft carbon, carbon fiber, silicon-based materials, tin-based materials, sodium titanate, or other metals that can form alloys with sodium, optionally, hard carbon.

[0139] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0140] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0141] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0142] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0143] In other embodiments, the current collector of the negative electrode sheet typically includes a current collector body and a base coating. The base coating can be disposed on at least one side of the current collector body. The base coating essentially does not contain negative electrode active material, but may include a small amount of carbon material. However, the carbon material forms a thin coating and cannot function as a negative electrode active material. When the current collector of the negative electrode sheet includes a base coating, the film layer can be disposed on the surface of the base coating away from the current collector. In this embodiment, the negative electrode sheet can be an electrode sheet without a negative electrode active material layer. For a negative electrode sheet without a negative electrode active material layer, when the current collector of the negative electrode sheet does not contain a base coating, the film layer can be disposed on the surface of at least one side of the current collector; when the current collector of the negative electrode sheet includes a base coating, the film layer can be disposed on the surface of the base coating away from the current collector.

[0144] In some embodiments, the film layer may further include a binder for fixing the additive to the negative electrode sheet. The type of binder is not particularly limited, and those skilled in the art can choose flexibly according to actual needs.

[0145] [Electrolytes]

[0146] This application does not impose any particular limitation on the type of electrolyte, which can be selected according to actual needs. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions). This includes battery cells using electrolyte solutions and some battery cells using solid electrolytes.

[0147] The electrolyte plays a role in conducting ions between the positive and negative electrode plates.

[0148] In some embodiments, the electrolyte salt may be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium difluorosulfonamide, sodium ditrifluoromethanesulfonamide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluorooxalate borate, sodium dioxalate borate, sodium difluorodioxalate phosphate, and sodium tetrafluorooxalate phosphate.

[0149] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0150] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0151] [Isolation membrane]

[0152] In some embodiments, this application does not have a particular limitation on the type of separator membrane, and any known porous separator membrane with good chemical and mechanical stability can be selected.

[0153] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0154] In some embodiments of this application, the positive electrode, the negative electrode, and the separator can be formed into an electrode assembly 52 by a winding process or a stacking process.

[0155] In some embodiments, the sodium-ion battery cell may include an outer packaging. This outer packaging can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0156] 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; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0157] 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. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0158] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. An electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0159] In the above technical solutions, the term "sodium-ion battery" can also refer to a battery module or battery pack.

[0160] For example, in some embodiments, battery cells can be assembled into battery modules, and the number of battery cells contained in a battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0161] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 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.

[0162] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0163] 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 one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0164] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 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, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0165] Some embodiments of this application provide an electrical device, which includes a sodium-ion battery provided in any of the foregoing embodiments, the sodium-ion battery being used to provide electrical energy; or the electrical device includes a positive electrode sheet prepared by the method for preparing a positive electrode sheet provided in any of the foregoing embodiments.

[0166] The sodium-ion battery can be at least one of a battery cell, a battery module, or a battery pack. The battery cell, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can include, but is not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships and satellites, energy storage systems, etc.

[0167] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0168] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0169] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a battery as their power source.

[0170] Example

[0171] 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.

[0172] Example 1

[0173] A sodium-ion battery is provided, prepared according to the following steps:

[0174] [Preparation of positive electrode sheet]:

[0175] 1. Preparation of carboxyl-modified polyvinylidene fluoride:

[0176] A certain amount of PVDF was added to a 10% KOH / anhydrous ethanol mixed solution (the volume ratio of water to anhydrous ethanol was 1:1), stirred at 60℃ for 10 min, washed with a large amount of water, filtered, and dried to obtain powder.

[0177] The polymerization reaction was carried out by adding the PVDF powder obtained above and alkyl carboxylic acid (mass ratio of 6:1) to a mixed solution of 10% water and anhydrous ethanol. After stirring for 30 min under nitrogen protection, the system was heated to 70 °C and reacted for 10 h under nitrogen protection. The mixture was repeatedly washed with deionized water and dried under vacuum at 60 °C for 12 h to obtain carboxyl-modified polyvinylidene fluoride; the carboxyl substitution amount was 7.0%; see Table 1 for details.

[0178] 2. Preparation of the primer coating:

[0179] Aluminum foil is used as the current collector.

[0180] By weight percentage, 40% conductive agent (acetylene black) and 60% of the aforementioned carboxyl-modified polyvinylidene fluoride were compounded to obtain a base coating slurry. The base coating slurry was uniformly coated onto aluminum foil and then dried.

[0181] 3. Formation of the positive electrode plate:

[0182] By mass percentage, a positive electrode material is prepared by compounding 95.10% of the positive electrode active material (Na4Fe3(PO4)2P2O7), 2.30% of the binder (polyvinylidene fluoride), 1.00% of the surfactant (dodecyl dimethyl ammonium bromide), and 1.60% of the conductive agent (conductive carbon black). This mixture is then added to the solvent N-methylpyrrolidone (NMP) and uniformly mixed to form a positive electrode slurry. This slurry is then uniformly coated onto the aluminum foil containing the base coating obtained in step 2 above, with a coating thickness of 200 μm. After drying, cold pressing, winding, assembly, and formation processes, a positive electrode sheet is formed. See Table 1 for details.

[0183] [Preparation of negative electrode sheet]:

[0184] The negative electrode active material hard carbon, conductive agent acetylene black, binder styrene-butadiene rubber (SBCs), and thickener carboxymethyl cellulose (CMC) are thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 90:5:4:1 to form a uniform negative electrode slurry. The negative electrode slurry is coated onto a negative electrode current collector copper foil with a thickness of 12μm, dried at 100℃, and then pressed to obtain a negative electrode sheet.

[0185] [Electrolyte preparation]:

[0186] In an argon-filled glove box, ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a mass ratio of EC:DEC:EMC = 4:2:4, and then 1.0 mol / L sodium hexafluorophosphate (NaPF6) was added.

[0187] [Isolation membrane]:

[0188] The separator is a polyethylene separator.

[0189] [Battery Assembly]:

[0190] The positive electrode, separator, and negative electrode are stacked and wound in sequence to form a single battery cell.

[0191] Example 2-11

[0192] The difference from Example 1 is that the binder, positive electrode active material, or performance parameters are different, as detailed in Table 1.

[0193] Comparative Example 1

[0194] The difference from Example 1 lies in the preparation of the positive electrode sheet, as detailed below:

[0195] 1. Preparation of the primer coating:

[0196] Aluminum foil is used as the current collector.

[0197] A primer coating slurry is prepared by compounding 40% conductive agent (acetylene black) and 60% polyvinylidene fluoride (PVDF) by weight percentage. The primer coating slurry is then uniformly coated onto aluminum foil and dried.

[0198] 2. Formation of the positive electrode plate:

[0199] By mass percentage, a positive electrode material is prepared by compounding 95.10% of the positive electrode active material (Na4Fe3(PO4)2P2O7), 2.30% of the binder (polyvinylidene fluoride), 1.00% of the surfactant (dodecyl dimethyl ammonium bromide), and 1.60% of the conductive agent (conductive carbon black). This mixture is then added to the solvent N-methylpyrrolidone (NMP) and uniformly mixed to form a positive electrode slurry. This slurry is then uniformly coated onto the aluminum foil containing the base coating obtained in step 2 above, with a coating thickness of 200 μm. After drying, cold pressing, winding, assembly, and formation processes, a positive electrode sheet is formed. See Table 1 for details.

[0200] Comparative Example 2

[0201] The difference from Example 1 lies in the preparation of the positive electrode sheet, as detailed below:

[0202] Aluminum foil is used as the current collector.

[0203] By mass percentage, a positive electrode material is prepared by compounding 95.10% of the positive electrode active material (Na4Fe3(PO4)2P2O7), 2.30% of the binder (polyvinylidene fluoride), 1.00% of the surfactant (dodecyl dimethyl ammonium bromide), and 1.60% of the conductive agent (conductive carbon black). This mixture is then added to the solvent N-methylpyrrolidone (NMP) and uniformly mixed to form a positive electrode slurry. This slurry is then uniformly coated onto the aluminum foil containing the base coating obtained in step 2 above, with a coating thickness of 200 μm. After drying, cold pressing, winding, assembly, and formation processes, a positive electrode sheet is formed. See Table 1 for details.

[0204] [Performance Testing]:

[0205] Performance tests of each embodiment and comparative sample:

[0206] 1. Test method for adhesion between the positive electrode film and the base coating (unit: N / M):

[0207] First, attach double-sided tape to the stainless steel plate, then attach the positive electrode sheet (positive electrode film side) to the double-sided tape, and use a tensile testing machine to clamp the electrode sheet and peel it off 180°.

[0208] 2. Test method for cohesion of the base coating (unit: N / M):

[0209] First, attach double-sided tape to the stainless steel plate, then attach the electrode to the double-sided tape. Next, attach a layer of green adhesive (copper adhesive) to the surface of the electrode on the double-sided tape. Then, use a tensile testing machine to clamp the green adhesive (copper adhesive) and peel it off at 180°.

[0210] 3. Test method for DC internal resistance (DCR) of positive electrode plate

[0211] Charge the battery at 25℃ with a constant current of 0.33C to 3.65V, then charge with a constant voltage to a current of 0.05C, allow it to rest for 1 hour, then discharge at 1C for 60 minutes (50% SOC), followed by another 1 hour of rest. Then discharge at 0.1C for 10 seconds, recording the voltage V1 at the end. Finally, discharge at 1C for 1 second, recording the voltage V2 at the end. Calculate the battery's DCR. The DCR calculation formula is: DCR=(V1-V2) / (I 1C -I 0.1C (), the unit is mOhm.

[0212] 4. Test method for compacted density

[0213] A positive electrode sheet with a diameter of 14mm was punched out using a stamping machine. The mass mc and thickness dc of the positive electrode sheet were measured using an electronic balance and a benchtop digital thickness gauge, respectively. A sufficient number of aluminum foil substrates with a diameter of 14mm were punched out using a stamping machine. The mass mA1 and thickness dAl of the aluminum foil substrates were measured using an electronic balance and a benchtop digital thickness gauge, respectively.

[0214] The compaction density of the positive electrode sheet is calculated using the following formula:

[0215]

[0216] Where: ρ c This refers to the compaction density of the positive electrode sheet, expressed in grams per cubic centimeter (g / cm³). 3 );

[0217] m c The mass of the positive electrode is expressed in grams (g).

[0218] m Al The mass of the aluminum foil substrate is expressed in grams (g).

[0219] This refers to the diameter of the positive electrode plate, in millimeters (mm).

[0220] dc represents the thickness of the positive electrode plate, in micrometers (μm).

[0221] dAl represents the thickness of the aluminum foil substrate, measured in micrometers (μm).

[0222] The performance test results of each embodiment and comparative example are shown in Table 2.

[0223] Table 1

[0224]

[0225]

[0226] Table 2

[0227]

[0228] As can be seen from the data in the table above:

[0229] The compaction density of each embodiment of this application is higher than that of Comparative Example 1 and Comparative Example 2; this demonstrates that the solutions of the embodiments of this application can effectively improve the compaction density.

[0230] Furthermore, under the premise of the same base coating thickness, compared with Comparative Example 1 and Comparative Example 2, the solutions of the various embodiments of this application will not lead to an increase in the DC internal resistance (DCR) of the positive electrode sheet, and thus are beneficial to battery performance.

[0231] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A sodium-ion battery, characterized in that, include: Positive electrode sheet; The positive electrode sheet includes: a positive electrode film layer, a current collector, and a base coating layer; the base coating layer is disposed between the positive electrode film layer and the current collector; the positive electrode film layer includes a positive electrode active material; The base coating comprises: carboxyl-modified polyvinylidene fluoride.

2. The sodium-ion battery according to claim 1, characterized in that, The general structural formula of the carboxyl-modified polyvinylidene fluoride includes: (CH2CF2)n1-(CR1R2-CR3R4)n2; Wherein, n1:n2 = (85-90):(15-10); at least one of R1, R2, R3 or R4 contains a carboxyl group; R1, R2, R3, R4 are hydrogen, alkyl or branched.

3. The sodium-ion battery according to claim 1 or 2, characterized in that, The molecular weight of the carboxyl-modified polyvinylidene fluoride is 300,000 to 700,000.

4. The sodium-ion battery according to any one of claims 1-3, characterized in that, The base coating also includes: a conductive agent; Optionally, the base coating may further comprise, by weight percentage: 43%-50% conductive agent and 50%-57% carboxyl-modified polyvinylidene fluoride; Optionally, the conductive agent includes at least one of acetylene black, conductive carbon black, superconducting carbon, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

5. A method for preparing an adhesive, characterized in that, include: Carboxyl-containing monomers were cross-linked with polyvinylidene fluoride monomers to obtain carboxyl-modified polyvinylidene fluoride.

6. The method for preparing the adhesive according to claim 5, characterized in that, The cross-linking reaction involving a monomer containing a carboxyl group and a polyvinylidene fluoride monomer includes: Crosslinking reaction is carried out using a first monomer and a second monomer; The first monomer comprises: (CH2CF2)n1; The second monomer comprises: (CR1R2-CR3R4)n2; Wherein, n1:n2 = (85-90):(15-10), and at least one of R1, R2, R3 or R4 contains a carboxyl group; R1, R2, R3, R4 are hydrogen, alkyl or branched.

7. The method for preparing the adhesive according to claim 5 or 6, characterized in that, The amount of carboxyl substitution in the carboxyl-modified polyvinylidene fluoride is 3.0% to 10.0%; Optionally, the molecular weight of the carboxyl-modified polyvinylidene fluoride is 300,000 to 700,000.

8. An adhesive, characterized in that, The general formula of the adhesive includes: (CH2CF2)n1-(CR1R2-CR3R4)n2; Wherein, n1:n2 = (85-90):(15-10); at least one of R1, R2, R3 or R4 contains a carboxyl group; R1, R2, R3, R4 are hydrogen, alkyl or branched.

9. The adhesive according to claim 8, characterized in that, The molecular weight of the adhesive is 300,000 to 700,000; Optionally, the amount of carboxyl substitution in the adhesive is 3.0% to 10.0%.

10. An electrical device, characterized in that, The electrical device includes a sodium-ion battery as described in any one of claims 1-4, wherein the sodium-ion battery is used to provide electrical energy.

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