Composite dispersing agent for sodium ion battery positive electrode and preparation method of composite dispersing agent

Abstract

The invention provides a composite dispersing agent for a sodium-ion battery positive electrode and a preparation method of the composite dispersing agent. The composite dispersant comprises 50-80 parts of a main dispersant and 20-50 parts of an auxiliary dispersant, the main dispersant is an acrylate terpolymer, and the auxiliary dispersant is an amphiphilic polymer. The composite dispersant for the sodium ion battery positive electrode can reduce the viscosity change rate of the slurry and improve the stability of the slurry when being applied to preparation of the positive electrode slurry, and can improve the peel strength and reduce the resistance of a pole piece when being applied to preparation of the positive pole piece, so that a more effective conductive path and a bonding network are obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion batteries, and particularly relates to a composite dispersant for a positive electrode of a sodium ion battery and a preparation method thereof. BACKGROUND

[0002] The booming development of large-scale energy storage systems and low-cost electric vehicles puts forward higher requirements for the performance, cost and resource sustainability of secondary batteries.

[0003] Although lithium ion batteries dominate the market, they are no longer the optimal choice for energy storage systems due to their small reserves on earth and high use cost. Sodium and lithium are both alkali metals, so they have similar chemical properties and energy storage mechanisms. The abundance of sodium on earth is much greater than that of lithium, so using sodium compounds to prepare sodium ion batteries can greatly reduce the manufacturing cost. However, the full play of the performance of sodium ion batteries highly depends on the performance of electrode materials, especially the performance of positive electrode materials. Currently, the positive electrode materials of sodium ion batteries include layered transition metal oxides, polyanion compounds, and prussian blue compounds. Although these materials have their own advantages, they all face the common challenge that the large radius of sodium ions leads to slow diffusion dynamics in the lattice of the positive electrode material, and the strong van der Waals force and electrostatic interaction during the preparation of the electrode can easily cause serious agglomeration. This agglomeration directly leads to the deterioration of the stability of the battery slurry, the processing difficulty, and the hindering of ion / electron transmission channels in the electrode.

[0004] In the prior art, although the addition of traditional single dispersants (such as carboxymethyl cellulose and polyvinylpyrrolidone) can improve the agglomeration phenomenon, it is difficult to effectively disperse the positive electrode material, the conductive agent and the binder, etc. at the same time, and it is still easy to cause problems such as flocculation or sedimentation of the slurry over time, increase of the internal resistance of the electrode, etc.

[0005] In view of the problems existing in the prior art, how to provide a composite dispersant for a positive electrode of a sodium ion battery, which can efficiently disperse the positive electrode slurry, improve the stability of the slurry, and improve the conductive path and the bonding network is a problem to be solved by the present application. SUMMARY

[0006] The purpose of the present application is to provide a composite dispersant for a positive electrode of a sodium ion battery and a preparation method thereof to solve the problems raised in the background.

[0007] To achieve the above-mentioned purpose, the present application provides a composite dispersant for a positive electrode of a sodium ion battery, characterized in that the composite dispersant comprises 50-80 parts of a main dispersant and 20-50 parts of a secondary dispersant.

[0008] The main dispersant is an acrylate terpolymer.

[0009] The secondary dispersant is an amphiphilic polymer.

[0010] As a further improvement, the structural formula of the acrylate terpolymer is shown as formula I:

[0011] n1 = 2-10, n2 = 1-6.

[0012] As a further improvement, the synthesis of the acrylate terpolymer comprises the following steps:

[0013] (1) Under a nitrogen atmosphere, add an organic solvent to a flask and stir to warm, then add dimethylaminoethyl methacrylate, butyl acrylate and initiator to the flask for stirring reaction;

[0014] (2) Slowly add a mixed solution of ethyl cyanoacrylate, initiator and organic solvent to step (1), continue stirring reaction, reaction is complete, post-treatment, to obtain an acrylate terpolymer.

[0015] As a further improvement, the molecular weight of the acrylate terpolymer is 1000-4000 g / mol.

[0016] As a further improvement, the amphiphilic polymer is prepared from polycaprolactone and acrylic acid.

[0017] As a further improvement, the preparation of the amphiphilic polymer comprises the following steps:

[0018] (1) Under a nitrogen atmosphere, add ε-caprolactone, benzyl (2-hydroxyethyl) trithiocarbonate, organic base and organic solvent to a dry flask, stir to react at 50-90°C, after the reaction is complete, post-treatment, to obtain polycaprolactone;

[0019] (2) Take the polycaprolactone prepared in step (1) in a flask, then add acrylic acid, initiator and organic solvent, stir to react at 70-90°C, after the reaction is complete, post-treatment, to obtain an amphiphilic polymer.

[0020] The present application provides a preparation method of a composite dispersant for sodium ion battery cathodes, characterized in that it comprises the following steps: stirring and mixing a primary dispersant and a secondary dispersant to obtain a composite dispersant for sodium ion battery cathodes.

[0021] As a further improvement, the preparation method of the composite dispersant for sodium ion battery cathodes further comprises 50-150 parts of an organic solvent.

[0022] As a further improvement, the organic solvent is at least one of N-methylpyrrolidone, cyclohexanone, N,N-dimethylformamide and methanol.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] The present application provides a composite dispersant for sodium ion battery cathode, which can reduce the viscosity change rate of the slurry, improve the stability of the slurry, and has a higher peeling strength and a lower electrode resistance when applied to the preparation of the cathode electrode sheet, indicating that the composite dispersant prepared by the present application has a better dispersing effect, which can make the conductive agent and the binder more dispersed on the electrode sheet, thereby having a more effective conductive path and bonding network.

[0025] The cyano group in the main dispersant can be combined with the surface of the conductive agent to form a stable adsorption layer, and the dimethylamino group in the main dispersant can form a weak coordination with the metal ions on the surface of the cathode material to enhance anchoring and prevent agglomeration, further improving the dispersibility of the cathode slurry; the hydrophobic chain segment in the secondary dispersant can interact with the hydrophobic groups on the surface of the conductive material to form a dispersion interface layer, and the hydrophilic chain segment can form hydrogen bonds with the solvent to make it more easily dispersed in the solvent. DETAILED DESCRIPTION

[0026] The present application will be described below in conjunction with specific embodiments. It should be noted that the following examples are examples of the present application and are only used to illustrate the present application, but not to limit the present application. Other combinations and various modifications within the concept of the present application can be made without departing from the spirit or scope of the present application.

[0027] In the following examples, the compound monomers and related reagents used, except for the acrylate terpolymer and butyl acrylate-ethyl cyanoacrylate copolymer, can be purchased from the market, wherein the polyvinylidene fluoride is purchased from Yuyao Fluorine Light New Material Co., Ltd., and the model number is Melos 5242F; the sodium ion layered oxide cathode material (NaNi 0.4 Fe 0.2 Mn 0.4 O2) is purchased from Xinwei Research Network, and the model number is sodium nickel manganese acid 424; the sodium polystyrene sulfonate is purchased from Shandong Keppler Biotechnology Co., Ltd., and the model number is kpl-88685.

[0028] The preparation of the acrylate terpolymer 1 comprises the following steps:

[0029] (1) Under a nitrogen atmosphere, 200 mL of ethyl acetate is added to a three-necked flask equipped with a condenser and a thermometer, and stirred to warm up to 60℃, then 39.3 g of dimethylaminoethyl methacrylate, 51.3 g of butyl acrylate and 0.5 g of azobisisobutyronitrile are added and stirred for 1 h;

[0030] (2) Slowly add a mixed solution of 25.0 g of ethyl cyanoacrylate, 0.5 g of azobisisobutyronitrile and 50 mL of ethyl acetate to step (1), dropwise complete within 1 h, continue to react at 75 °C for 3 h, after the reaction is completed, remove the ethyl acetate by rotary evaporation, then perform vacuum filtration at 185 °C to remove the impurity monomer, to obtain the acrylate terpolymer 1 (n1 = 8, n2 = 6).

[0031] Preparation of acrylate terpolymer 2, comprising the following steps:

[0032] (1) Under a nitrogen atmosphere, add 200 mL of ethyl acetate to a three-necked flask equipped with a condenser and a thermometer, stir and warm to 60 °C, then add 31.4 g of dimethylaminoethyl methacrylate, 51.3 g of butyl acrylate and 0.32 g of azobisisobutyronitrile to the flask and stir for 2 h;

[0033] (2) Slowly add a mixed solution of 18.8 g of ethyl cyanoacrylate, 0.5 g of azobisisobutyronitrile and 40 mL of ethyl acetate to step (1), dropwise complete within 1 h, continue to react at 75 °C for 3 h, after the reaction is completed, remove the ethyl acetate by rotary evaporation, then perform vacuum filtration at 185 °C to remove the impurity monomer, to obtain the acrylate terpolymer 2 (n1 = 6, n2 = 4).

[0034] Preparation of acrylate terpolymer 3, comprising the following steps:

[0035] (1) Under a nitrogen atmosphere, add 200 mL of ethyl acetate to a three-necked flask equipped with a condenser and a thermometer, stir and warm to 60 °C, then add 47.2 g of dimethylaminoethyl methacrylate, 51.3 g of butyl acrylate and 0.6 g of azobisisobutyronitrile to the flask and stir for 2 h;

[0036] (2) Slowly add a mixed solution of 37.5 g of ethyl cyanoacrylate, 0.55 g of azobisisobutyronitrile and 60 mL of ethyl acetate to step (1), dropwise complete within 1 h, continue to react at 75 °C for 4 h, after the reaction is completed, remove the ethyl acetate by rotary evaporation, then perform vacuum filtration at 185 °C to remove the impurity monomer, to obtain the acrylate terpolymer 3 (n1 = 14, n2 = 8).

[0037] Preparation of butyl acrylate-ethyl cyanoacrylate copolymer, comprising the following steps:

[0038] (1) Under a nitrogen atmosphere, add 120 mL of ethyl acetate to a three-necked flask equipped with a condenser and a thermometer, stir and warm to 60 °C, then add 51.3 g of butyl acrylate, 1.0 g of benzoyl peroxide to the flask and stir for mixing;

[0039] (2) slowly drop 18.8 g of ethyl cyanoacrylate and 40 mL of ethyl acetate into the solution in step (1), drop for 1 h, heat to 75 °C, continue to react for 3 h, after the reaction is completed, remove the solvent by rotary evaporation, then perform vacuum filtration at 80 °C to remove the impurity monomer, to obtain a butyl acrylate-ethyl cyanoacrylate copolymer.

[0040] Preparation of the amphiphilic polymer, comprising the following steps:

[0041] (1) under a nitrogen atmosphere, add 1.7 g of ε-caprolactone, 2.4 g of benzyl (2-hydroxyethyl)trithiocarbonate, 0.03 g of 4-dimethylaminopyridine and 30 mL of N,N-dimethylformamide into a dry flask, stir at 80 °C for 10 h, after the reaction is completed, cool to room temperature, add a large amount of methanol into the flask to precipitate, filter and collect the solid, vacuum dry at 40 °C for 24 h, to obtain intermediate one;

[0042] (2) take 2.7 g of the intermediate one prepared in step (1) into a flask, then add 3.2 g of acrylic acid, 0.07 g of azobisisobutyronitrile and 50 mL of N,N-dimethylformamide, react at 80 °C for 12 h, after the reaction is completed, cool to room temperature, add a large amount of diethyl ether into the flask to precipitate, filter and collect the solid, vacuum dry at 60 °C, to obtain the amphiphilic polymer.

[0043] The components and contents used in examples 1-3 and comparative examples 1-2 are shown in the following table 1:

[0044] Table 1

[0045]

[0046]

[0047] The composite dispersant prepared in examples 1-3 and comparative examples 1-2 is applied to the preparation of sodium-ion battery positive electrode slurry and the preparation of positive electrode sheet, and the viscosity, peel strength and sheet resistance are tested, and the specific method is as follows:

[0048] Preparation method of positive electrode slurry: mix 2 g of binder polyvinylidene fluoride, 2.5 g of the composite dispersant prepared in examples 1-3 and comparative examples 1-2, 21 g of N-methylpyrrolidone and stir for 1 h, then add 2.5 g of conductive carbon black (SP), 21 g of N-methylpyrrolidone and 93 g of sodium-ion layered oxide positive electrode material (NaNi 0.4 Fe 0.2 Mn 0.4 O2) into the mixture and continue to mix and stir for 3 h, to obtain a positive electrode slurry;

[0049] Positive electrode sheet: the positive electrode slurry was uniformly coated on the surface of the aluminum foil by a doctor blade, and dried in an oven at 90°C to obtain a positive electrode sheet;

[0050] Viscosity: the viscosity of the prepared positive electrode slurry was measured at 0h, 4h and 12h at 25°C using a DVNext type rotary viscometer rheometer with a No. 4 rotor at a test speed of 20 rpm;

[0051] Peeling strength: after the prepared positive electrode sheet was dried at 90°C for 5h, the peeling strength of the sheet was tested according to GB / T 2790-1995 using a KN type peeling force tester at a separation speed of 100mm / min in the 180° direction;

[0052] Sheet resistance: the sheet resistance of the positive electrode sheet was measured using a BER2500 type sheet resistance meter.

[0053] The test results are shown in Table 2 as follows:

[0054] Table 2

[0055]

[0056] As can be seen from the test results of Example 2 and Comparative Example 1 in Table 2, compared with using butyl acrylate-ethyl cyanoacrylate copolymer as the main dispersant, using the synthesized acrylate terpolymer of the application as the main dispersant to prepare the composite dispersant, applied to the preparation of the positive electrode slurry, it can be found that the change in slurry viscosity is small with the increase of time, which shows that the composite dispersant prepared by the application can significantly reduce the viscosity change rate of the sodium ion battery positive electrode slurry and improve the stability of the slurry; has a higher peeling strength and a lower sheet resistance, which shows that the composite dispersant prepared by the application has a good dispersion effect when applied to the positive electrode slurry, so that the conductive agent and the binder can be dispersed on the sheet to a greater extent, thereby having a more effective conductive path and adhesive network.

[0057] As can be seen from the test results of Example 2 and Comparative Example 2, compared with using a hydrophilic polymer as a secondary dispersant, using the synthesized amphiphilic polymer of the application as a secondary dispersant to prepare the composite dispersant, applied to the positive electrode slurry and the positive electrode sheet, has a lower viscosity change, a higher peeling strength and a lower sheet resistance, which shows that the composite dispersant prepared by the application has a better dispersion effect and a more stable performance.

[0058] As can be seen from the test results of examples 1-3, the present application provides a composite dispersant for sodium ion battery positive electrode, which is applied to the preparation of positive electrode slurry, and it can be found that the change of slurry viscosity is small with the increase of time, which shows that the composite dispersant prepared by the present application can significantly reduce the viscosity change rate of sodium ion battery positive electrode slurry and improve the stability of the slurry; it is applied to the preparation of positive electrode sheet, has high peeling strength and low sheet resistance, which shows that the composite dispersant prepared by the present application has good dispersion effect, can make the conductive agent and the binder disperse on the sheet to a greater extent, and then has more effective conductive path and bonding network.

[0059] The above embodiments are only for illustrating the technical concept and characteristics of the present application, the purpose is to let the person skilled in the art understand the content of the present application and implement it, and cannot limit the protection scope of the present application, any equivalent change or modification according to the spirit and essence of the present application should be covered in the protection scope of the present application.

Claims

1. A composite dispersant for a sodium-ion battery cathode, characterized by, The composite dispersant comprises 50-80 parts of a main dispersant and 20-50 parts of a secondary dispersant. The main dispersant is an acrylate terpolymer. The secondary dispersant is an amphiphilic polymer.

2. The composite dispersant for sodium-ion battery cathode according to claim 1, characterized in that, The structural formula of the acrylate terpolymer is shown as Formula I: n1= 2-10, n2= 1-6.

3. The composite dispersant for sodium-ion battery cathode according to claim 1, characterized in that, The synthesis of the acrylate terpolymer comprises the following steps: (1) Under a nitrogen atmosphere, an organic solvent is added to a flask and stirred to warm, and then dimethylaminoethyl methacrylate, butyl acrylate and an initiator are added thereto for stirring reaction; (2) A mixed solution of ethyl cyanoacrylate, an initiator and an organic solvent is slowly added dropwise to step (1), and stirring reaction is continued until the reaction is completed, and then post-treatment is performed to obtain the acrylate terpolymer.

4. The composite dispersant for sodium-ion battery cathode according to claim 1, characterized in that, The molecular weight of the acrylate terpolymer is 1000-4000 g / mol.

5. The composite dispersant for sodium-ion battery cathode according to claim 1, characterized in that, The amphiphilic polymer is prepared from polycaprolactone and acrylic acid.

6. The composite dispersant for sodium-ion battery cathode according to claim 1, characterized in that, The preparation of the amphiphilic polymer comprises the following steps: (1) Under a nitrogen atmosphere, ε-caprolactone, benzyl (2-hydroxyethyl) trithiocarbonate, an organic base and an organic solvent are added to a dry flask, and stirring reaction is performed at 50-90°C until the reaction is completed, and then post-treatment is performed to obtain polycaprolactone; (2) The polycaprolactone obtained in step (1) is taken into a flask, and then acrylic acid, an initiator and an organic solvent are added thereto, and stirring reaction is performed at 70-90°C until the reaction is completed, and then post-treatment is performed to obtain the amphiphilic polymer.

7. The method for preparing a composite dispersant for a sodium-ion battery cathode according to any one of claims 1-6, characterized in that, The preparation comprises the following steps: the main dispersant and the secondary dispersant are stirred and mixed to obtain a composite dispersant for sodium ion battery cathodes.

8. The method for preparing a composite dispersant for a sodium-ion battery cathode according to claim 7, characterized in that, It further comprises 50-150 parts of an organic solvent.

9. The method for preparing a composite dispersant for a sodium-ion battery cathode according to claim 8, characterized in that, The organic solvent is at least one of N-methylpyrrolidone, cyclohexanone, N,N-dimethylformamide and methanol. The organic solvent is at least one of N-methylpyrrolidone, cyclohexanone, N,N-dimethylformamide and methanol.

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