Binder, negative electrode sheet, and sodium-ion battery

Abstract

The application belongs to the technical field of sodium ion batteries, and particularly relates to a binder, a negative electrode sheet and a sodium ion battery. The binder is a copolymer of acrylic monomer-derived repeating units, acrylamide monomer-derived repeating units and dopamine-acrylic acid-derived repeating units, has carboxyl, amino and hydroxyl structures, can form strong hydrogen bonds and covalent bonds with a negative electrode active material, conductive carbon and a negative electrode current collector, and the strong hydrogen bond interaction between the carboxyl and the surface functional groups of the active material, together with the strong adsorption of dopamine in the binder to the material surface, is conducive to enhancing the adhesion between the negative electrode active material layer and the current collector and between the components of the negative electrode, effectively improving the peeling capacity of the negative electrode sheet, and the carboxyl component is also conducive to enhancing the migration rate of sodium ions, thereby improving the cycle performance, stability performance and rate performance of the sodium ion battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion batteries, and particularly relates to a binder, a negative electrode sheet and a sodium ion battery. BACKGROUND

[0002] In recent years, due to the scarcity of lithium resources, the continuous rise of raw materials and the outbreak of the energy storage market, it is very crucial to develop other related energy storage technologies that can replace lithium ion batteries at a low cost. At the same time, sodium ion batteries are developing into a new energy storage technology solution. Sodium ion batteries have a wide application prospect in the energy storage field due to their advantages such as abundant sodium resources, low cost and good safety performance. For sodium ion batteries, the negative electrode material plays an important role in loading and releasing sodium ions, which directly affects the overall kinetic performance of the battery, such as rate performance and power density.

[0003] At present, the practical application of sodium ion batteries is still limited by the lack of suitable binders, especially binders with excellent adhesion and ion conductivity. Graphite carbon-based materials commonly used in lithium ion battery negative electrodes have abundant raw materials, low price and large reversible capacity. However, due to the large radius of sodium ions and the thermodynamic instability of sodium and graphite compounds, they cannot be used as negative electrode materials for sodium ion batteries. Although the unique structure of non-graphite carbon-based materials can exhibit excellent electrochemical performance in sodium batteries, their low compaction density, many surface defects and pores can lead to poor peel strength of the negative electrode sheet, which seriously affects the cycle life of the sodium ion battery. SUMMARY

[0004] The purpose of the present application is to provide a binder that has strong hydrogen bond interactions between the carboxyl groups and the surface functional groups of the active material, and the dopamine of the binder has an adsorption effect on the surface of the material, which can enhance the adhesion between the negative electrode active material layer, the current collector and the components of the negative electrode, effectively improving the peel strength of the negative electrode sheet.

[0005] To achieve the above purpose, the following technical solutions are adopted in the present application:

[0006] The binder of the present application is a copolymer of acrylic monomer-derived repeating units, acrylamide monomer-derived repeating units and dopamine acrylic acid-derived repeating units, and the molecular formula of the binder is as follows:

[0007]

[0008] In the formula, R1 is H, -CH3, -COOH, -CH2COOH or -CH2CH2CH2CH2CH2CH2CH3,

[0009] R2 is H, Li, Na or K,

[0010] R3 is H, -CH3 or -CH2CH2CH2CH2CH2CH2CH3,

[0011] R4 is H, -CH3, -COOH, -CH2COOH or -CH2CH2CH2CH2CH2CH2CH3.

[0012] Preferably, in the molecular formula of the binder, x is an integer of 5-5000, y is an integer of 5-1000, and z is an integer of 5-1000.

[0013] The second object of the present application is to provide a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material, a conductive agent, a dispersing agent and the binder as described above.

[0014] Preferably, the mass percentage of the negative electrode active material, the conductive agent, the dispersing agent and the binder is (90%-98%):(0.5%-5%):(0.1%-2%):(0.5%-5%).

[0015] Preferably, the negative electrode active material is at least one of hard carbon and soft carbon.

[0016] Preferably, the peeling strength of the negative electrode sheet is D (N / m), wherein 2

[0017] Preferably, the resistivity of the negative electrode active material layer is E (Ω·cm), wherein 0.05≤E≤1.

[0018] Preferably, the conductive agent comprises at least one of carbon black, activated carbon, carbon molecular sieve, acetylene black, carbon black, Ketjen black, graphene, carbon nanotube and carbon nanofiber.

[0019] Preferably, the negative electrode current collector comprises at least one of carbon-coated foil, metal foil or composite foil.

[0020] The third object of the present application is to provide a sodium ion battery, wherein the sodium ion battery comprises an electrolyte, a positive electrode sheet, the negative electrode sheet as described above and a separator arranged between the negative electrode sheet and the positive electrode sheet.

[0021] The application has the beneficial effects that the binder provided by the application has carboxyl, amino and hydroxyl structures, can form strong hydrogen bonds and covalent bonds with the negative active material, conductive carbon and negative current collector, and can form strong hydrogen bonds and covalent bonds between the molecules of the binder, the strong hydrogen bond interaction between the carboxyl and the surface functional groups of the active material, and the strong adsorption of dopamine in the binder to the surface of the material, are beneficial to enhancing the adhesion between the negative active material layer and the current collector and between the components of the negative electrode, effectively improving the peeling capacity of the negative electrode sheet, and the carboxyl component is also beneficial to enhancing the migration rate of sodium ions, thereby improving the cycle performance, stability and rate performance of the sodium ion battery. DETAILED DESCRIPTION

[0022] In order to make the technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described clearly and completely below in conjunction with specific embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0023] According to an aspect of the present application, the present application provides a binder, which is a copolymer of a repeating unit derived from an acrylic monomer, a repeating unit derived from an acrylamide monomer and a repeating unit derived from dopamine acrylic acid, and the molecular formula of the binder is as follows:

[0024]

[0025] In the formula, R1 is H, -CH3, -COOH, -CH2COOH or -CH2CH2CH2CH2CH2CH2CH3,

[0026] R2 is H, Li, Na or K,

[0027] R3 is H, -CH3 or -CH2CH2CH2CH2CH2CH2CH3,

[0028] R4 is H, -CH3, -COOH, -CH2COOH or -CH2CH2CH2CH2CH2CH2CH3.

[0029] The carboxyl, amino and hydroxyl structures can not only form strong hydrogen bonds and covalent bonds with the negative active material, conductive carbon and negative current collector, but also form strong hydrogen bonds and covalent bonds between the molecules of the binder. The strong hydrogen bond interaction between the carboxyl and the surface functional groups of the active material, together with the strong adsorption of dopamine in the binder to the material surface, is conducive to enhancing the adhesion between the negative active material layer and the current collector and between the components of the negative electrode, effectively improving the peeling capacity of the negative electrode sheet, and thus improving the cycle performance of the battery.

[0030] In an embodiment according to the present application, in the molecular formula of the binder, the number x of the acrylic monomer-derived repeating units is an integer from 5 to 5000, the number y of the acrylamide monomer-derived repeating units is an integer from 5 to 1000, and the number z of the piperazine acrylic acid-derived repeating units is an integer from 5 to 1000, for example, 5, 10, 20, 50, 80, 100, 500, 1000, 2000, 3000, 4000, 5000.

[0031] According to a second aspect of the present application, a negative electrode sheet is provided, comprising a negative current collector and a negative active material layer arranged on at least one surface of the negative current collector, wherein the negative active material layer comprises a negative active material, a conductive agent, a dispersing agent and the binder as described above.

[0032] In an embodiment according to the present application, the mass percentage of the negative active material, the conductive agent, the dispersing agent and the binder is (90% to 98%) : (0.5% to 5%) : (0.1% to 2%) : (0.5% to 5%).

[0033] The content of each component in the negative active material layer can be adjusted according to the performance requirements. For example, the negative active material can be 90%, 91%, 92%, 93%, 94%, 96% or 98%; the conductive agent can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4% or 5%; the dispersing agent can be 0.1%, 0.5%, 1%, 1.5% or 2%; and the binder can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4% or 5%.

[0034] In an embodiment according to the present application, the negative active material is at least one of hard carbon and soft carbon.

[0035] In an embodiment according to the present application, the peeling strength of the negative electrode sheet is D (N / m), wherein 2 < D < 40, for example, 2 N / m, 5 N / m, 8 N / m, 10 N / m, 15 N / m, 18 N / m, 20 N / m, 25 N / m, 28 N / m, 30 N / m, 35 N / m, 38 N / m or 40 N / m.

[0036] In an embodiment according to the present application, the negative active material layer has a resistivity of E (Ω·cm), wherein 0.05≤E≤1, for example, 0.05Ω·cm, 0.06Ω·cm, 0.08Ω·cm, 0.1Ω·cm, 0.3Ω·cm, 0.5Ω·cm, 0.81Ω·cm, 0.85Ω·cm, or 1Ω·cm.

[0037] In an embodiment according to the present application, the conductive agent includes at least one of carbon black, activated carbon, carbon molecular sieve, acetylene black, carbon black, ketjen black, graphene, carbon nanotube, and carbon nanofiber. A certain amount of conductive agent is added when the electrode sheet is made, for increasing the conductivity of electrons and sodium ions, accelerating the electron transmission rate by forming a conductive network on the surface of the active material, and absorbing and retaining electrolyte, thereby providing more electrolyte interface for sodium ions, and improving the charging efficiency and cycle life of the battery.

[0038] In an embodiment according to the present application, the negative current collector includes at least one of carbon-coated foil, metal foil, or composite foil. The carbon-coated aluminum foil is used as the current collector. After the carbon-coated aluminum foil is treated, the carbon-coated layer can act as a bridge to tightly bond the negative active material and the aluminum foil, and the particles are embedded in each other, thereby improving the conductivity of the negative electrode sheet and ultimately reducing the internal resistance of the battery.

[0039] According to a third aspect of the present application, the present application provides a sodium-ion battery, including an electrolyte, a positive electrode sheet, the negative electrode sheet according to any one of the preceding embodiments, and a separator arranged between the negative electrode sheet and the positive electrode sheet.

[0040] The positive electrode sheet is prepared by using N-methyl pyrrolidone (NMP) as a solvent to prepare an active material slurry, adding a conductive agent binder to stir to form a positive electrode slurry, and then performing coating, drying, and other processes to form the electrode sheet.

[0041] The separator is a single-layer or multi-layer separator made of at least one of polypropylene, polyethylene, polyester substrate, polyacrylonitrile, non-woven fabric, polyvinylidene fluoride, and glass fiber.

[0042] The electrolyte includes a sodium salt, a carbonate solvent, and an additive. The carbonate solvent includes a cyclic carbonate solvent and a chain carbonate solvent. The sodium salt is at least one of NaPF6, NaClO4, NaBF4, NaFSI, NaTFSI, NaSO3CF3, and Na(CH3)C6H4SO3. The additive includes a first additive and a second additive. The first additive is fluoroethylene carbonate or difluoroethylene carbonate. The second additive is at least one of fluoro-cyclotriphosphazene, hexafluoro-cyclotriphosphazene, pentafluoroethoxy-cyclotriphosphazene, and pentafluorophenoxy-cyclotriphosphazene.

[0043] The technical solutions and beneficial effects of the present application will be described in detail below in combination with specific examples and comparative examples.

[0044] Example 1

[0045] The binder provided in the present example is a copolymer of acrylic monomer-derived repeating units, acrylamide monomer-derived repeating units and dopamine acrylic monomer-derived repeating units, and the molecular formula of the binder is as follows:

[0046]

[0047] In the formula, R1-R3 are all H, R4 is -COOH, x is 1023, y is 408, and z is 415, and the mass content of the binder in the active material layer is 4%;

[0048] The preparation method of the negative electrode sheet containing the binder is as follows: hard carbon, the binder and carbon black are uniformly mixed in a weight ratio of 94:4:2 in a proper amount of deionized water to obtain a negative electrode slurry. Then the negative electrode slurry is coated on a negative electrode current collector aluminum foil, and after baking and rolling, a negative electrode sheet is obtained. The thickness of the negative electrode current collector is 20 μm, and the thickness of the negative electrode active material layer is 70 μm.

[0049] The preparation method of the positive electrode sheet is as follows: prussian blue, nitrile rubber and acetylene black are uniformly mixed in a weight ratio of 92:4:4 in a proper amount of NMP to obtain a positive electrode slurry; then the positive electrode slurry is coated on a carbon-coated aluminum foil as the positive electrode current collector, and after drying and rolling, a positive electrode sheet is obtained.

[0050] The preparation method of the sodium ion battery containing the binder is as follows: the aforementioned negative electrode sheet, a separator (polyethylene film) and the positive electrode sheet are sequentially stacked or wound to obtain an electric core, the electric core is placed in a packaging shell, an electrolyte (ethylene carbonate + NaPF6) is added and packaged, and after processes such as formation, hot and cold pressing and capacity distribution, a sodium ion battery is obtained.

[0051] Example 2

[0052] The difference between the present example and Example 1 is the value of the binder-related parameters.

[0053] The binder provided in the present example is a copolymer of acrylic monomer-derived repeating units, acrylamide monomer-derived repeating units and dopamine acrylic monomer-derived repeating units, and the molecular formula of the binder is as follows:

[0054]

[0055] In the formula, R1 is -CH3, R2 is Li, R3 is -CH3, R4 is -CH2COOH, x is 2109, y is 542, and z is 765, and the mass content of the binder in the active material layer is 3%.

[0056] The rest is the same as example 1, which is not described here.

[0057] Example 3

[0058] The difference between example 1 is the value of the binder related parameters.

[0059] The binder provided in this embodiment is a copolymer of acrylic monomer derived repeating units, acrylamide monomer derived repeating units and dopamine acrylic acid derived repeating units, and the molecular formula of the binder is as follows:

[0060]

[0061] In the formula, R1 is -COOH, R2 is Na, R3 is -CH3, R4 is H, x is 821, y is 625, and z is 356. The mass content of the binder in the active material layer is 3.5%;

[0062] The rest is the same as example 1, which is not described here.

[0063] Example 4

[0064] The difference between example 1 is the value of the binder related parameters.

[0065] The binder provided in this embodiment is a copolymer of acrylic monomer derived repeating units, acrylamide monomer derived repeating units and dopamine acrylic acid derived repeating units, and the molecular formula of the binder is as follows:

[0066]

[0067] In the formula, R1 is -CH2COOH, R2 is K, R3 is H, R4 is -CH3, x is 3405, y is 385, and z is 145. The mass content of the binder in the active material layer is 2%;

[0068] The rest is the same as example 1, which is not described here.

[0069] Example 5

[0070] The difference between example 1 is the value of the binder related parameters.

[0071] The binder provided in this embodiment is a copolymer of acrylic monomer derived repeating units, acrylamide monomer derived repeating units and dopamine acrylic acid derived repeating units, and the molecular formula of the binder is as follows:

[0072]

[0073] In the formula, R1 is -CH2CH2CH2CH2CH2CH2CH3, R2 is Na, R3 is -CH3, R4 is H, x is 4752, y is 143, and z is 95. The mass content of the binder in the active material layer is 1.6%.

[0074] The rest is the same as in Example 1, which will not be repeated here.

[0075] Example 6

[0076] The difference between Example 1 is the value of the binder-related parameters.

[0077] The binder provided in this example is a copolymer of acrylic monomer-derived repeating units, acrylamide monomer-derived repeating units, and dopamine acrylic acid-derived repeating units. The molecular formula of the binder is as follows:

[0078]

[0079] In the formula, R1 is -CH3, R2 is Na, R3 is -CH3, R4 is -CH3, x is 4232, y is 633, and z is 559. The mass content of the binder in the active material layer is 0.6%.

[0080] The rest is the same as in Example 1, which will not be repeated here.

[0081] Example 7

[0082] The difference between Example 1 is the value of the binder-related parameters.

[0083] The binder provided in this example is a copolymer of acrylic monomer-derived repeating units, acrylamide monomer-derived repeating units, and dopamine acrylic acid-derived repeating units. The molecular formula of the binder is as follows:

[0084]

[0085] In the formula, R1 is -CH3, R2 is Na, R3 is -CH3, R4 is -CH3, x is 4232, y is 633, and z is 559. The mass content of the binder in the active material layer is 0.6%.

[0086] The rest is the same as in Example 1, which will not be repeated here.

[0087] Example 8

[0088] The difference between Example 1 is the value of the binder-related parameters.

[0089] The adhesive provided by the embodiment is a copolymer of acrylic monomer derived repeating units, acrylamide monomer derived repeating units and dopamine acrylic acid derived repeating units, and the molecular formula of the adhesive is as follows:

[0090]

[0091] In the formula, R1 is -COOH, R2 is K, R3 is H, R4 is -COOH, x is 485, y is 725, and z is 624, and the mass content of the adhesive in the active material layer is 2.3%;

[0092] The rest is the same as in Example 1, which will not be repeated here.

[0093] Example 9

[0094] The difference between Example 1 and the present embodiment is the value of the adhesive-related parameters.

[0095] The adhesive provided by the embodiment is a copolymer of acrylic monomer derived repeating units, acrylamide monomer derived repeating units and dopamine acrylic acid derived repeating units, and the molecular formula of the adhesive is as follows:

[0096]

[0097] In the formula, R1 is -CH2COOH, R2 is H, R3 is -CH3, R4 is -CH2COOH, x is 1456, y is 332, and z is 216, and the mass content of the adhesive in the active material layer is 4.6%;

[0098] The rest is the same as in Example 1, which will not be repeated here.

[0099] Example 10

[0100] The difference between Example 1 and the present embodiment is the value of the adhesive-related parameters.

[0101] The adhesive provided by the embodiment is a copolymer of acrylic monomer derived repeating units, acrylamide monomer derived repeating units and dopamine acrylic acid derived repeating units, and the molecular formula of the adhesive is as follows:

[0102]

[0103] In the formula, R1 is -CH2COOH, R2 is H, R3 is -CH3, R4 is -CH2COOH, x is 1456, y is 332, and z is 216, and the mass content of the adhesive in the active material layer is 4.6%;

[0104] The rest is the same as in Example 1, which will not be repeated here.

[0105] Example 11

[0106] The difference between this example and Example 1 is the value of the binder-related parameters.

[0107] The binder provided in this example is a copolymer of acrylic monomer-derived repeating units, acrylamide monomer-derived repeating units, and dopamine acrylic acid-derived repeating units, and the molecular formula of the binder is as follows:

[0108]

[0109] In the formula, R1 is H, R2 is Na, R3 is H, R4 is H, x is 2509, y is 453, and z is 387. The mass content of the binder in the active material layer is 3.6%.

[0110] The rest is the same as Example 1, which will not be repeated here.

[0111] Example 12

[0112] The difference between this example and Example 1 is the value of the binder-related parameters.

[0113] The binder provided in this example is a copolymer of acrylic monomer-derived repeating units, acrylamide monomer-derived repeating units, and dopamine acrylic acid-derived repeating units, and the molecular formula of the binder is as follows:

[0114]

[0115] In the formula, R1 is -CH3, R2 is K, R3 is -CH3, R4 is -CH3, x is 3416, y is 785, and z is 612. The mass content of the binder in the active material layer is 2.5%.

[0116] The rest is the same as Example 1, which will not be repeated here.

[0117] Example 13

[0118] The difference between this example and Example 1 is the value of the binder-related parameters.

[0119] The binder provided in this example is a copolymer of acrylic monomer-derived repeating units, acrylamide monomer-derived repeating units, and dopamine acrylic acid-derived repeating units, and the molecular formula of the binder is as follows:

[0120]

[0121] In the formula, R1 is -COOH, R2 is H, R3 is -CH3, R4 is -COOH, x is 4135, y is 264, and z is 826. The mass content of the binder in the active material layer is 1.8%.

[0122] The rest is the same as example 1, which is not described here.

[0123] Example 14

[0124] The difference between example 1 is the value of the binder related parameters.

[0125] The binder provided in this embodiment is a copolymer of acrylic monomer derived repeating units, acrylamide monomer derived repeating units and dopamine acrylic acid derived repeating units, and the molecular formula of the binder is as follows:

[0126]

[0127] In the formula, R1 is -CH2OOH, R2 is Li, R3 is H, R4 is -CH2OOH, x is 658, y is 768, and z is 494. The mass content of the binder in the active material layer is 0.9%;

[0128] The rest is the same as example 1, which is not described here.

[0129] Example 15

[0130] The difference between example 1 is the value of the binder related parameters.

[0131] The binder provided in this embodiment is a copolymer of acrylic monomer derived repeating units, acrylamide monomer derived repeating units and dopamine acrylic acid derived repeating units, and the molecular formula of the binder is as follows:

[0132]

[0133] In the formula, R1 is H, R2 is K, R3 is H, R4 is -CH3, x is 1802, y is 156, and z is 637. The mass content of the binder in the active material layer is 1.6%;

[0134] The rest is the same as example 1, which is not described here.

[0135] Example 16

[0136] The difference between example 1 is the value of the binder related parameters.

[0137] The binder provided in this embodiment is a copolymer of acrylic monomer derived repeating units, acrylamide monomer derived repeating units and dopamine acrylic acid derived repeating units, and the molecular formula of the binder is as follows:

[0138]

[0139] wherein R1 is -CH3, R2 is H, R3 is H, R4 is -CH2CH2CH2CH2CH2CH2CH3, x is 2318, y is 625, and z is 738, and the mass content of the binder in the active material layer is 3.4%;

[0140] The rest is the same as in Example 1, which is not repeated here.

[0141] Comparative Example 1

[0142] The binder provided in this comparative example is composed of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, sodium alginate, and sodium polyacrylate in a mass content ratio of 1.2%: 1.6%: 0: 0: 0;

[0143] The negative electrode sheet, the separator (polyethylene film), and the positive electrode sheet containing the binder are stacked in order or wound to obtain a battery cell, the battery cell is placed in a packaging shell, an electrolyte (ethylene carbonate + NaPF6) is added and packaged, and after processes such as formation, hot and cold pressing, and capacity distribution, a sodium ion battery is obtained.

[0144] Comparative Example 2

[0145] The binder provided in this comparative example is composed of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, sodium alginate, and sodium polyacrylate in a mass content ratio of 0.8%: 2.1%: 0%: 0%: 0%;

[0146] The negative electrode sheet, the separator (polyethylene film), and the positive electrode sheet containing the binder are stacked in order or wound to obtain a battery cell, the battery cell is placed in a packaging shell, an electrolyte (ethylene carbonate + NaPF6) is added and packaged, and after processes such as formation, hot and cold pressing, and capacity distribution, a sodium ion battery is obtained.

[0147] Comparative Example 3

[0148] The binder provided in this comparative example is composed of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, sodium alginate, and sodium polyacrylate in a mass content ratio of 0%: 0%: 2.8%: 0%: 0%;

[0149] The negative electrode sheet, the separator (polyethylene film), and the positive electrode sheet containing the binder are stacked in order or wound to obtain a battery cell, the battery cell is placed in a packaging shell, an electrolyte (ethylene carbonate + NaPF6) is added and packaged, and after processes such as formation, hot and cold pressing, and capacity distribution, a sodium ion battery is obtained.

[0150] Comparative Example 4

[0151] The binder provided by the present comparative example is composed of carboxymethyl cellulose sodium, styrene butadiene rubber, polyacrylic acid, sodium alginate and polyacrylic acid sodium with a mass content ratio of 0%:0%:0%:3.2%:0%;

[0152] The negative electrode sheet, the separator (polyethylene film) and the positive electrode sheet containing the binder are stacked in order or wound to obtain a battery cell, the battery cell is placed in a packaging shell, an electrolyte (ethylene carbonate + NaPF6) is added and packaged, and after processes such as formation, hot and cold pressing, and capacity distribution, a sodium ion battery is obtained.

[0153] Comparative Example 5

[0154] The binder provided by the present comparative example is composed of carboxymethyl cellulose sodium, styrene butadiene rubber, polyacrylic acid, sodium alginate and polyacrylic acid sodium with a mass content ratio of 0%:0%:0%:0%:3.0%;

[0155] The negative electrode sheet, the separator (polyethylene film) and the positive electrode sheet containing the binder are stacked in order or wound to obtain a battery cell, the battery cell is placed in a packaging shell, an electrolyte (ethylene carbonate + NaPF6) is added and packaged, and after processes such as formation, hot and cold pressing, and capacity distribution, a sodium ion battery is obtained.

[0156] The sodium ion batteries obtained in Examples 1-16 and Comparative Examples 1-5 are subjected to electrochemical performance tests, and the experimental results are shown in Table 1.

[0157] (1) Mechanical property test of negative electrode sheet:

[0158] The double-sided adhesive tape is pasted on a flat steel plate, and then a negative electrode sheet with a length of 200 mm and a width of 30 mm is pasted on the double-sided adhesive tape. Then the steel plate with the bonded electrode sheet is placed in the test area of the tensile testing machine, and the tensile testing machine peels the electrode sheet from the steel plate at an angle of 180°. The peeling length is 150 mm and the peeling speed is 50 mm / min.

[0159] (2) Cycle performance test of sodium ion battery:

[0160] At 25°C, the sodium ion battery is charged at 1C constant current to the upper limit of the cut-off voltage, then charged at constant voltage to a current of 0.2C, and then discharged at 1C constant current to the lower limit of the cut-off voltage after standing for 5 min. The discharge capacity is the initial capacity of the sodium ion battery. The battery is subjected to 500 cycles of charge and discharge tests according to the above steps, and the discharge capacity of the 500th cycle is obtained. The capacity retention rate of the sodium ion battery at the 500th cycle at 25°C = the discharge capacity of the 500th cycle / the discharge capacity of the 1st cycle x 100%.

[0161] (3) Rate performance test of sodium ion battery:

[0162] The sodium ion battery was charged and discharged at 0.2C and 1C rates at 25°C, wherein 1C = 160 mAh / g, and the cut-off voltage of the charge and discharge was 1.5V-3.8V. The specific steps were as follows: the sodium ion battery was charged at a constant current to the upper limit of the cut-off voltage at a set rate, then charged at a constant voltage until the current was 0.05C, and then rested for 5 min, and then discharged at a constant current to the lower limit of the cut-off voltage at a set rate, and then rested for 5 min, which was one cycle of charge and discharge. The sodium ion battery was repeatedly tested for 5 cycles of charge and discharge according to the above steps, and the discharge specific capacity of the 5th cycle was recorded. The rate discharge capacity ratio (%) of the sodium ion battery after 5 cycles = the discharge specific capacity of the 5th cycle of 1C charge and discharge / the discharge specific capacity of the 5th cycle of 0.2C charge and discharge x 100%.

[0163] wherein P is the peeling strength of the negative electrode tab, C is the capacity retention rate of the sodium ion battery after 500 cycles, and R is the rate discharge capacity ratio of the sodium ion battery after 5 cycles.

[0164] Table 1 - Sodium ion battery performance test table

[0165]

[0166]

[0167] As can be seen from Table 1, when the binder is a copolymer of the repeating units derived from the acrylic monomer, the repeating units derived from the acrylamide monomer, and the repeating units derived from the dopamine acrylic acid, the negative electrode tab has good adhesion and ion conduction performance, while when the negative electrode binder is sodium carboxymethyl cellulose, styrene butadiene rubber, polyacrylic acid, sodium alginate, and sodium polyacrylate, the adhesion and ion conduction performance of the negative electrode tab is poor, resulting in poor cycle performance and rate performance of the sodium ion battery.

[0168] Based on the disclosure and teachings of the above specification, a person of ordinary skill in the art can make changes and modifications to the above embodiments. Therefore, the present application is not limited to the above specific embodiments, and any obvious improvements, replacements or modifications made by those skilled in the art based on the present application are within the scope of the present application. In addition, although some specific terms are used in the specification, these terms are only for convenience of explanation and do not constitute any limitation on the present application.

Claims

1. An adhesive, characterized in that, The adhesive is a copolymer of repeating units derived from acrylic monomers, repeating units derived from acrylamide monomers, and repeating units derived from dopamine acrylic monomers. The molecular formula of the adhesive is as follows: In the formula, R1 is H, -CH3, -COOH, -CH2COOH, or -CH2CH2CH2CH2CH2CH2CH3. R2 is H, Li, Na, or K. R3 can be H, -CH3, or -CH2CH2CH2CH2CH2CH2CH3. R4 can be H, -CH3, -COOH, -CH2COOH, or -CH2CH2CH2CH2CH2CH2CH3; In the molecular formula of the adhesive, x is an integer from 5 to 5000, y is an integer from 5 to 1000, and z is an integer from 5 to 1000.

2. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material, a conductive agent, a dispersant and the binder as described in claim 1.

3. The negative electrode sheet according to claim 2, characterized in that, The mass percentages of the negative electrode active material, conductive agent, dispersant, and binder are (90%–98%): (0.5%–5%): (0.1%–2%): (0.5%–5%).

4. The negative electrode sheet according to claim 2, characterized in that, The negative electrode active material is at least one of hard carbon and soft carbon.

5. The negative electrode sheet according to claim 2, characterized in that, The peel strength of the negative electrode is D, and the unit of peel strength D is N / m, where 2 < D < 40.

6. The negative electrode sheet according to claim 2, characterized in that, The resistivity of the negative electrode active material layer is E, and the unit of resistivity E is Ω·cm, wherein 0.05≤E≤1.

7. The negative electrode sheet according to claim 2, characterized in that, The conductive agent includes at least one of carbon black, activated carbon, carbon molecular sieve, acetylene black, Ketjen black, graphene, carbon nanotubes, and carbon nanofibers.

8. The negative electrode sheet according to claim 2, characterized in that, The negative electrode current collector includes at least one of carbon-coated foil, metal foil, or composite foil.

9. A sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The negative electrode is the negative electrode as described in any one of claims 2-8.

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