Binder and preparation method thereof, secondary battery and electrical equipment

Abstract

The present application discloses a binder and a preparation method thereof, a secondary battery, and an electrical device. The binder includes modified cellulose, a cross-linking agent, and a photoinitiator, wherein the modified cellulose includes cellulose modified with a halogenated olefin. The binder of the present application is an environmentally friendly, functional, water-soluble binder. On the one hand, the raw materials used are abundant in resources, low in cost, and environmentally friendly. On the other hand, the binder has good dispersibility and excellent bonding properties. In addition, the present application can not only improve the toughness of the battery's positive electrode sheet and reduce the resistance of the positive electrode sheet, but also improve the battery's cycle performance.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a binder and a preparation method thereof, a secondary battery and an electrical device. Background Art

[0002] Binders are a crucial component of lithium battery electrodes. Although used in small quantities, they significantly impact the performance of lithium-ion batteries and are a crucial factor in determining battery performance. Currently, polyvinylidene fluoride (PVDF) is a commonly used binder for secondary battery positive electrodes. However, PVDF requires N-methylpyrrolidone (NMP) as a solvent, which has drawbacks such as high cost, toxicity, and environmental pollution. Furthermore, PVDF's high molecular weight can result in poor conductivity, low mechanical properties, and insufficient elasticity in the electrode sheets, impacting battery cycling performance. Summary of the Invention

[0003] The present application provides a binder and a preparation method thereof, a secondary battery and an electrical device, which solve the problems of current binders polluting the environment and having insufficient performance.

[0004] According to the binder in the first embodiment of the present application, the binder includes modified cellulose, a cross-linking agent, and a photoinitiator, and the modified cellulose includes cellulose modified with a halogenated olefin.

[0005] Optionally, in other embodiments of the present application, the halogenated olefin includes allyl chloride, allyl bromide, butyl bromide or butyl chloride.

[0006] Optionally, in other embodiments of the present application, the cross-linking agent is selected from at least one of polyethylene glycol diacrylate, trimethylene diamine, and diaminodiphenyl sulfone.

[0007] Optionally, in other embodiments of the present application, the number average relative molecular weight of polyethylene glycol diacrylate is 500-100,000. Further, the number average relative molecular weight of polyethylene glycol diacrylate may be 10,000-90,000, 20,000-80,000, or 50,000-70,000.

[0008] Optionally, in other embodiments of the present application, the number average relative molecular mass of the modified cellulose may be 10,000 to 900,000, or 50,000 to 800,000, or 100,000 to 500,000.

[0009] Optionally, in other embodiments of the present application, based on the mass content of the binder, the modified cellulose accounts for 24% to 64%, the cross-linking agent accounts for 32% to 72%, and the photoinitiator accounts for 2% to 8%.

[0010] Optionally, in other embodiments of the present application, the mass ratio of modified cellulose to cross-linking agent is (1:3) to (2:1), preferably 1:(1 to 2).

[0011] Optionally, in other embodiments of the present application, the photoinitiator includes at least one of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone or ethyl 2,4,6-trimethylbenzoylphenylphosphonate.

[0012] According to the second embodiment of the present application, the method for preparing the adhesive includes:

[0013] Adding halogenated olefins to cellulose for reaction, adding a precipitant, and precipitating to obtain modified cellulose;

[0014] mixing modified cellulose, a cross-linking agent, and a photoinitiator to obtain a binder;

[0015] The cross-linking agent includes polyethylene glycol diacrylate.

[0016] According to the secondary battery in the third embodiment of the present application, it includes a positive electrode sheet, and the positive electrode sheet includes the above-mentioned binder.

[0017] Optionally, in other embodiments of the present application, the binder accounts for 2% to 10% of the total mass of the positive electrode sheet.

[0018] According to the electric device in the fourth embodiment of the present application, the electric device includes the above-mentioned secondary battery, and the secondary battery serves as a power supply for the electric device.

[0019] The adhesive according to the embodiment of the present application has at least the following technical effects:

[0020] (1) The present application uses modified cellulose, which includes cellulose modified with halogenated olefins. Compared with traditional cellulose, the present application reduces the intermolecular hydrogen bonding force and reduces its polarity by grafting vinyl groups, thereby improving the flexibility of cellulose and enhancing processing capabilities.

[0021] (2) The raw materials of the adhesive of the present application are biodegradable, non-toxic, harmless and environmentally friendly.

[0022] (3) Using the adhesive of the present application as a positive electrode plate adhesive can improve the flexibility of the plate, while also reducing the impedance of the positive electrode plate, thereby improving the cycle performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 This is a nuclear magnetic resonance spectroscopy characterization diagram of the propylene-modified cellulose in the examples of the present application;

[0025] Figure 2 1 is a diagram showing the bending test results of the positive electrode sheets provided in the examples and comparative examples of the present application. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0027] The present invention provides a binder and a method for preparing the same, a secondary battery, and an electrical device. The following describes each of the embodiments in detail. It should be noted that the order in which the embodiments are described below does not limit the preferred order of the embodiments.

[0028] In this specification, a numerical range expressed using “to” means a range including the numerical values ​​described before and after “to” as the minimum value and the maximum value, respectively.

[0029] The embodiment of the present application provides a binder, which includes modified cellulose, a cross-linking agent and a photoinitiator, and the modified cellulose includes cellulose modified with halogenated olefins. The present application adopts modified cellulose, and the modified cellulose includes cellulose modified with halogenated olefins, while traditionally, carboxymethyl cellulose (CMC) is generally used. CMC has a rigid structure and poor bonding flexibility, which makes it difficult to meet the performance requirements of batteries. The present application synthesizes and modifies cellulose by grafting halogenated olefins to obtain a modified cellulose with a double bond structure having flexible groups, thereby reducing the intermolecular hydrogen bonding force and reducing its polarity, thereby improving the flexibility of cellulose and improving processing capabilities. In addition, the binder of the present application is water-soluble, degradable, non-toxic, harmless and environmentally friendly.

[0030] In some embodiments of the present application, the crosslinking agent is selected from at least one of polyethylene glycol diacrylate (PEGDA), trimethylenediamine, and diaminodiphenyl sulfone. Preferably, the crosslinking agent is PEGDA, which can reduce interfacial resistance in lithium-ion batteries, allowing lithium ions to be more easily inserted into and removed from the active material through the electrolyte during charging, thereby improving the battery's cycle performance.

[0031] Specifically, compared to traditional polyvinylidene fluoride (PVDF), the PEGDA used in this application contains acrylate functional groups, which helps improve the kinetics. PEGDA can undergo polymerization under the action of light, heat and radiation, and in the presence of a certain amount of initiator.

[0032] Specifically, cellulose is a natural polymer material with abundant resources. Cellulose can be modified through crosslinking. Modified cellulose refers to a product with a three-dimensional network structure constructed through crosslinking points using a crosslinking agent. This application introduces a certain amount of non-polar double bonds through substitution modification of cellulose, thereby improving flexibility. Furthermore, the curing and crosslinking technology of PEGDA enhances the mechanical properties of the electrode and exhibits certain excellent electrical properties.

[0033] In some embodiments of the present application, the halogenated olefin includes allyl chloride. The halogenated olefin may also be an olefin substituted with other halogens, such as fluorine, chlorine, bromine, or iodine. For example, the halogenated olefin may also be allyl bromide, butyl bromide, or butyl chloride. The carbon chain length of the olefin should not be too long, otherwise it will cause certain difficulties in grafting.

[0034] In some embodiments of the present application, the number average relative molecular mass of the modified cellulose may be 10,000 to 900,000, or 50,000 to 800,000, or 100,000 to 500,000.

[0035] In some embodiments of the present application, the number average relative molecular weight of PEGDA is 500 to 100,000, for example, the number average relative molecular weight of PEGDA can be 10,000 to 90,000, or 20,000 to 80,000, or 50,000 to 70,000. In some embodiments of the present application, based on the weight content of the binder, the modified cellulose accounts for 24% to 64%, the cross-linking agent accounts for 32% to 72%, and the photoinitiator accounts for 2% to 8%.

[0036] In some embodiments of the present application, the mass ratio of the modified cellulose to the crosslinking agent can be (1:3) to (2:1), preferably 1:(1-2). When the mass ratio of the modified cellulose to the crosslinking agent is within this preferred range, the binder has good electrical conductivity and mechanical properties.

[0037] In some embodiments of the present application, the photoinitiator includes at least one of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone (photoinitiator 2959) or ethyl 2,4,6-trimethylbenzoylphenylphosphonate. Photoinitiator 2959 is a highly efficient, non-yellowing UV photoinitiator used to initiate UV polymerization reactions in unsaturated prepolymer systems.

[0038] Accordingly, the present invention also provides a method for preparing a binder, comprising:

[0039] Adding halogenated olefins to cellulose for reaction, adding a precipitant, and precipitating to obtain modified cellulose;

[0040] mixing modified cellulose, a cross-linking agent, and a photoinitiator to obtain a binder;

[0041] The cross-linking agent includes PEGDA.

[0042] Specifically, the precipitating agent includes acetone.

[0043] In a specific implementation, the preparation method of the binder includes:

[0044] (1) adding cellulose powder to distilled water containing NaOH and urea, cooling and mixing uniformly to obtain a cellulose solution;

[0045] (2) adding allyl chloride to the cellulose solution at 30±5°C for reaction, adding acetone for precipitation, washing the obtained precipitate and freeze-drying it to obtain modified cellulose powder;

[0046] (3) The modified cellulose was added to a dimethyl sulfoxide solvent and mixed, and a photoinitiator 2959 and PEGDA were added and mixed to obtain a binder.

[0047] In addition, an embodiment of the present application further provides a positive electrode plate, comprising a binder, an active material, and a conductive agent, wherein the binder is the binder described above or the binder prepared by the preparation method described above.

[0048] Specifically, the binder may account for 2% to 10% of the total mass of the positive electrode sheet, 3% to 9% of the total mass of the positive electrode sheet, or 5% to 8% of the total mass of the positive electrode sheet. The binder in this application has excellent bonding properties, so only a small amount of binder needs to be added to the positive electrode sheet to achieve bonding.

[0049] Accordingly, the present invention also provides a method for preparing a positive electrode sheet, comprising:

[0050] mixing a binder, an active material, and a conductive agent to obtain a slurry;

[0051] The slurry is coated and then UV-cured and cross-linked, and dried to obtain a positive electrode sheet;

[0052] Wherein, the binder is the above-mentioned binder or the binder prepared by the above-mentioned preparation method.

[0053] Specifically, the mass ratio of binder:conductive agent:active material is 1:1:8.

[0054] Specifically, the conductive agent includes one or more of KB carbon, conductive carbon black, conductive graphite, carbon fiber, carbon nanotubes or graphene; the active material includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium vanadium phosphate, lithium manganese phosphate, nickel cobalt manganese lithium oxide and nickel cobalt aluminum lithium oxide.

[0055] In specific implementation, the method for preparing the positive electrode sheet includes:

[0056] (1) Mixing a binder, an active material, and a conductive agent in a certain mass ratio to obtain a slurry;

[0057] (2) The slurry is coated and placed in a UV curing machine for light curing. After drying and cutting, the positive electrode sheet is obtained.

[0058] An embodiment of the present application further provides a secondary battery, comprising the above-mentioned positive electrode sheet or the positive electrode sheet prepared by the above-mentioned preparation method.

[0059] The present application also provides an electrical device including the aforementioned secondary battery, which serves as a power source for the electrical device. The electrical device of the present application includes, but is not limited to, backup power supplies, motors, electric vehicles, electric motorcycles, power-assisted bicycles, bicycles, power tools, and large household batteries.

[0060] The following describes the details in conjunction with specific embodiments.

[0061] Example 1

[0062] (1) Preparation of experimental reagents:

[0063] (a) Cellulose powder, aqueous solution of NaOH and urea, allyl chloride, acetone, DMSO solvent, PEGDA, and photoinitiator 2959 (i.e., 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone).

[0064] (2) Preparation of cellulose solution:

[0065] (a) Pour 150 ml of distilled water into a 250 ml round-bottom beaker and add 12.35 g of NaOH and 14.12 g of urea. Stir thoroughly with a glass rod to mix. Then add 6 g of cellulose powder.

[0066] (b) Place the prepared solution in a refrigerator and allow it to cool slowly while stirring continuously to mix thoroughly. Freeze the solution at -20°C for 24 hours. Thaw at room temperature. The cellulose solution is now ready.

[0067] (3) Preparation of modified cellulose:

[0068] (a) The round-bottom flask containing the cellulose solution was fixed to a thermostatically heated magnetic stirrer using an iron stand and heated to 30°C. 15 g of allyl chloride was weighed using an electronic balance and poured into the round-bottom flask to react with the cellulose solution for 72 h.

[0069] (b) Add acetone to the reacted solution to allow for complete precipitation. The resulting precipitate is placed on a filter and rinsed three times with deionized water. Remove the rinsed precipitate, place it in plastic wrap, poke small holes in the plastic wrap, and place it in a freeze dryer for freeze-drying.

[0070] (c) After freeze drying, the modified cellulose is taken out and placed in a bag. The bag is then wrapped in tin foil, labeled, and stored in a refrigerator for future use.

[0071] (4) Preparation of binder solution:

[0072] (a) Preparation of 5% modified cellulose solution

[0073] 5 g of modified cellulose was slowly added into 100 ml of DMSO solvent and mixed, and slowly stirred with a magnetic stirrer to dissolve the cellulose, thereby preparing a 5% modified cellulose solution.

[0074] (b) Preparation of binder

[0075] A small reagent bottle was taken, 3 ml of the modified cellulose solution (ie, containing 0.15 g of modified cellulose), 0.0125 g of photoinitiator 2959, and 0.15 g of PEGDA were added, and the mixture was mixed with a magnetic stirrer for 25 minutes to obtain a binder.

[0076] (5) Preparation of positive electrode sheets for lithium-ion batteries:

[0077] The positive electrode material (lithium iron phosphate), conductive agent (KB carbon), and the prepared binder were mixed at a mass ratio of 80:10:10 to obtain a positive electrode slurry. The positive electrode slurry was applied to the surface of aluminum foil and then placed in a UV curing machine for 90 seconds. The temperature of the forced air oven was adjusted to 80°C. After the temperature stabilized, the material was removed and dried for 6 hours. After roller pressing and cutting, the positive electrode sheet was produced.

[0078] Example 2

[0079] The method is the same as Example 1, except that, in the preparation process of the binder, the amounts of modified cellulose solution, photoinitiator 2959, and PEGDA used are 2 mL, 0.0125 g, and 0.2 g, respectively.

[0080] Example 3

[0081] The method is the same as Example 1, except that, in the preparation process of the binder, the amounts of modified cellulose solution, photoinitiator 2959, and PEGDA used are 1.5 mL, 0.0125 g, and 0.225 g, respectively.

[0082] Example 4

[0083] The method is the same as Example 1, except that, in the preparation process of the binder, the amounts of modified cellulose solution, photoinitiator 2959, and PEGDA used are 4 mL, 0.0125 g, and 0.1 g, respectively.

[0084] Example 5

[0085] The method is the same as Example 1, except that, in the preparation process of the binder, the amounts of modified cellulose solution, photoinitiator 2959, and PEGDA used are 3 mL, 0.003 g, and 0.15 g, respectively.

[0086] Example 6

[0087] The method is the same as Example 1, except that, in the preparation process of the binder, the amounts of modified cellulose solution, photoinitiator 2959, and PEGDA used are 3 mL, 0.006 g, and 0.15 g, respectively.

[0088] Example 7

[0089] The method is the same as Example 1, except that, in the preparation process of the binder, the amounts of modified cellulose solution, photoinitiator 2959, and PEGDA used are 3 mL, 0.018 g, and 0.15 g, respectively.

[0090] Example 8

[0091] The method is the same as Example 1, except that, in the preparation process of the binder, the amounts of modified cellulose solution, photoinitiator 2959, and PEGDA used are 3 mL, 0.024 g, and 0.15 g, respectively.

[0092] Example 9

[0093] The method is the same as Example 1, except that, in the preparation process of the binder, the amounts of modified cellulose solution, photoinitiator 2959, and PEGDA used are 3 mL, 0.03 g, and 0.15 g, respectively.

[0094] Example 10

[0095] The method is the same as Example 1, except that, during the preparation of the positive electrode sheet, the mass ratio of the positive electrode material, the conductive agent, and the binder is 87:11:2.

[0096] Example 11

[0097] The method is the same as Example 1, except that, during the preparation of the positive electrode sheet, the mass ratio of the positive electrode material, the conductive agent, and the binder is 84.5:10.5:5.

[0098] Example 12

[0099] The method is the same as Example 1, except that, during the preparation of the positive electrode sheet, the mass ratio of the positive electrode material, the conductive agent, and the binder is 82:10:8.

[0100] Example 13

[0101] The method is the same as Example 1, except that, in the preparation process of the binder, the cross-linking agent used is trimethylenediamine.

[0102] Example 14

[0103] The method is the same as Example 1, except that, in the preparation process of the adhesive, the cross-linking agent used is diaminodiphenyl sulfone.

[0104] Example 15

[0105] The same as Example 1, except that, in the preparation process of the binder, the modifier for modifying the cellulose is allyl bromide.

[0106] Example 16

[0107] The method is the same as Example 1, except that, in the preparation process of the binder, bromobutylene is used as the modifier for modifying the cellulose.

[0108] Example 17

[0109] The method is the same as Example 1, except that, in the preparation process of the binder, chloroprene is used as the modifier for modifying the cellulose.

[0110] Comparative Example 1

[0111] The method is the same as Example 1, except that no cross-linking agent is added during the preparation of the adhesive.

[0112] Comparative Example 2

[0113] The same as Example 1, except that no modified cellulose was added during the preparation of the binder.

[0114] Comparative Example 3

[0115] The same as Example 1, except that unmodified cellulose is added during the preparation of the binder.

[0116] The main preparation parameters involved in the preparation process of Examples 1 to 17 and Comparative Examples 1 to 3 are recorded in Table 1, wherein the amount of binder refers to the percentage of the binder in the positive electrode slurry.

[0117] Table 1

[0118]

[0119]

[0120] The positive electrode sheets prepared in Examples 1 to 17 and Comparative Examples 1 to 3 were subjected to resistance and bending tests, and the test results are recorded in Table 2.

[0121] The negative electrode sheet (lithium sheet), separator, electrolyte, and the positive electrode sheets prepared in Examples 1 to 17 and Comparative Examples 1 to 3 were assembled into button cells, and the charge and discharge cycle performance of the button cells was tested. The test results are recorded in Table 2.

[0122] The diaphragm uses PE / PP film.

[0123] The electrolyte was prepared by the following method: ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed uniformly in a mass ratio of 30:40:30 to obtain a non-aqueous organic solvent, 1 mol / L LiPF6 was dissolved in the above non-aqueous organic solvent, and the mixture was mixed uniformly to obtain an electrolyte.

[0124] The specific test methods are as follows:

[0125] 1) Test method for positive electrode resistance: Use the two-probe method to test the positive electrode to obtain the positive electrode resistance.

[0126] 2) Positive electrode bending test method: Place the positive electrode on the rotating needle, bend it 45°, and observe the surface appearance of the positive electrode.

[0127] 3) Cycling performance test method: At 25±2°C, place the secondary battery aside for 5 minutes, charge at a constant current rate of 1C to 4.2V, then charge at a constant voltage until the current is less than or equal to 0.05C. Then place it aside for 5 minutes, and then discharge at a constant current rate of 1C to 3.0V. This is considered one charge and discharge cycle. The discharge capacity at this time is recorded as the discharge capacity of the lithium-ion secondary battery in the first cycle. The lithium-ion secondary battery is subjected to 100 and 200 cycle charge and discharge tests according to the above method. The discharge capacity of each cycle is recorded and the capacity retention rate is calculated.

[0128] Table 2

[0129]

[0130]

[0131] Based on the above data, it can be seen that the binder provided by this application, due to the presence of modified cellulose, can make the positive electrode sheet have good flexibility. Due to the presence of the crosslinking agent, it can reduce the resistance value of the positive electrode sheet, thereby reducing the interfacial impedance of the lithium-ion battery. The use of the binder of this application can better enable lithium ions to be embedded in and released from the active material through the electrolyte during the battery's charge and discharge process, significantly improving the battery's cycle performance.

[0132] The above is a detailed introduction to a binder and its preparation method, secondary battery and electrical equipment provided by the present application. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea; at the same time, for technical personnel in this field, based on the ideas of the present application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A binder, characterized in that: The invention comprises modified cellulose, a crosslinking agent and a photoinitiator, wherein the modified cellulose comprises cellulose modified with a halogenated olefin, the halogenated olefin comprises allyl chloride, allyl bromide, butylene bromide or butylene chloroate, the mass ratio of the modified cellulose to the crosslinking agent is (1:3) to (2:1), and based on the mass content of the binder, the modified cellulose accounts for 24% to 64%, and the crosslinking agent accounts for 32% to 72%; wherein the crosslinking agent comprises at least one of polyethylene glycol diacrylate, trimethylene diamine and diaminodiphenyl sulfone.

2. The adhesive according to claim 1, characterized in that The number average relative molecular weight of the polyethylene glycol diacrylate is 500 to 100,000; the number average relative molecular weight of the modified cellulose is 10,000 to 900,000.

3. The adhesive according to claim 1, characterized in that Based on the mass content of the binder, the photoinitiator accounts for 2% to 8%.

4. The adhesive according to claim 1, characterized in that The photoinitiator includes at least one of 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone or ethyl 2,4,6-trimethylbenzoylphenylphosphonate.

5. A method for preparing the adhesive according to any one of claims 1 to 4, characterized in that: include: Adding halogenated olefins to cellulose for reaction, adding a precipitant, and precipitating to obtain modified cellulose; The modified cellulose, a cross-linking agent and a photoinitiator are mixed to obtain the binder; wherein the cross-linking agent includes polyethylene glycol diacrylate.

6. A secondary battery, characterized in that: The invention comprises a positive electrode sheet, wherein the positive electrode sheet comprises the binder according to any one of claims 1 to 4, and the binder accounts for 2% to 10% of the total mass of the positive electrode sheet.

7. An electrical device, characterized in that: The secondary battery as claimed in claim 6 is included, and the secondary battery is used as a power supply for the electrical device.

Images