Electrode binder composition, positive electrode material composition, positive electrode, and battery

Abstract

The application relates to the technical field of batteries, in particular to an electrode binder composition, a positive electrode material composition, a positive electrode and a battery. The electrode binder composition comprises polyacrylate and polyvinylpyrrolidone; wherein the polyacrylate is obtained by polymerization of polymerizable monomers comprising alkyl acrylate, acrylic acid and allyl polyether. The electrode binder composition has good adhesion, can significantly improve the peeling strength of the electrode sheet, can improve the coating area density of the electrode material, ensures that the electrode sheet does not crack under the condition of high area density, and effectively improves the energy density of the electrode sheet; in addition, experiments prove that the use of polyacrylate and polyvinylpyrrolidone can significantly improve the viscosity rebound of the electrode material slurry, which can effectively reduce the coating difficulty of the electrode material slurry.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to an electrode binder composition, a positive electrode material composition, a positive electrode and a battery. Background Art

[0002] Lithium manganese iron phosphate positive electrode materials are gradually being used in the battery field, including automotive batteries, due to their advantages such as high gram capacity, good safety and low cost.

[0003] However, compared with lithium iron phosphate positive electrode materials, lithium manganese iron phosphate positive electrode materials have worse processability. In the process of using them to prepare lithium-ion battery positive electrodes, there are usually problems such as easy rebound of slurry viscosity, easy cracking, and low compaction. These problems limit the large-scale promotion and application of lithium manganese iron phosphate positive electrode materials. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the problems existing in the prior art when using lithium iron manganese phosphate positive electrode materials to prepare lithium-ion battery positive electrodes, such as easy rebound of slurry viscosity, easy cracking, and low compaction degree, thereby providing an electrode binder composition, a positive electrode material composition, a positive electrode and a battery.

[0005] To this end, the present invention provides an electrode binder composition, comprising polyacrylate and polyvinyl pyrrolidone; wherein the polyacrylate is obtained by polymerizing polymerizable monomers comprising alkyl acrylate, acrylic acid and allyl polyether.

[0006] Optionally, the weight ratio of the polyacrylate to the polyvinyl pyrrolidone is (3-5):(0.3-0.8).

[0007] Optionally, in the polymerizable monomer, the molar ratio of alkyl acrylate, acrylic acid, and allyl polyether is (1-3):(7-10):(1-3);

[0008] Preferably, in the polymerizable monomer, the molar ratio of alkyl acrylate, acrylic acid and allyl polyether is (1.5-2.5):(6-9):(1-1.5), wherein the molar amount of the allyl polyether is calculated based on the molar amount of allyl groups, and the allyl polyether is preferably a monoallyl allyl polyether.

[0009] Optionally, the weight average molecular weight of the polyacrylate is 50,000 to 80,000, preferably 65,000 to 75,000.

[0010] Optionally, the number of carbon atoms in the alkyl acrylate is not less than 7;

[0011] Optionally, the alkyl acrylate includes at least one of butyl acrylate, pentyl acrylate, octyl acrylate, hexyl acrylate, heptyl acrylate and octadecyl acrylate;

[0012] Optionally, the allyl polyether includes at least one of allyl polyethylene glycol, allyl epoxy polyether and allyl alcohol polyoxyalkyl ether.

[0013] Optionally, the preparation method of the polyacrylate comprises:

[0014] Take a dispersion medium, an emulsifier and 50-80% of a polymerizable monomer, raise the temperature to a first polymerization temperature under stirring, and add 20-50% of an initiator to initiate a polymerization reaction;

[0015] After the first effective reaction time, the remaining polymerizable monomers and the initiator are added respectively, and the temperature is raised to the second polymerization temperature, and the temperature is kept to react for the second effective reaction time.

[0016] Optionally, the above-mentioned “50-80% of polymerizable monomer” means that in the corresponding step, the added weight of the polymerizable monomer is 50-80% of the total weight of the polymerizable monomer; “20-50% of initiator” means that in the corresponding step, the added weight of the initiator is 20-50% of the total weight of the initiator.

[0017] Optionally, in parts by weight, the ratio of the dispersion medium, the emulsifier, the polymerizable monomer, and the initiator is (40-350):(0.5-10):(80-100):(0.1-0.7);

[0018] Optionally, the first polymerization temperature is 75-78°C;

[0019] Optionally, the first effective duration is 1 to 2 hours;

[0020] Optionally, the second polymerization temperature is 85-90°C;

[0021] Optionally, the second effective duration is 2 to 3 hours;

[0022] Optionally, after the heat preservation reaction is carried out for the second effective time, the preparation method of the polyacrylate further comprises the steps of cooling the temperature to 40-50° C. and adjusting the pH value to 8-9;

[0023] Optionally, the dispersion medium includes at least one of water, ethanol, styrene, acetone, butyl acetate and ether;

[0024] Optionally, the emulsifier includes at least one of fatty acid soap, alkyl sulfate, alkylbenzene sulfonate, polyol fatty acid ester and phosphate;

[0025] Optionally, the initiator includes at least one of ammonium persulfate, potassium persulfate, benzoyl peroxide, cumene hydroperoxide and dicarbonate peroxide.

[0026] Optionally, after adjusting the pH value, the preparation method of the polyacrylate may further include operations such as solid-liquid separation, washing, drying, crushing, and screening.

[0027] The present invention also provides a positive electrode material composition, which includes the binder composition described above.

[0028] Optionally, based on the total weight of the positive electrode material composition, the weight percentage of the binder composition is 2.2 to 4.2 wt %;

[0029] Optionally, the positive electrode material composition further comprises a positive electrode active material and a positive electrode conductive agent, and based on the total weight of the positive electrode material composition, the weight percentage of the positive electrode active material is 94-97 wt%, and the weight percentage of the positive electrode conductive agent is 0.8-1.8 wt%;

[0030] Optionally, the positive electrode active material includes at least one of lithium manganese iron phosphate, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt oxide and lithium manganese oxide, preferably lithium manganese iron phosphate.

[0031] Optionally, the positive electrode conductive agent includes at least one of carbon nanotubes, carbon black and graphene.

[0032] The present invention also provides a positive electrode, which comprises the positive electrode material composition described above.

[0033] The present invention also provides a battery, which optionally includes the positive electrode.

[0034] The technical solution of the present invention has the following advantages:

[0035] 1. The electrode binder composition provided by the present invention comprises a polyacrylate and polyvinyl pyrrolidone. The polyacrylate is obtained by polymerizing polymerizable monomers including alkyl acrylate, acrylic acid, and allyl polyether. This results in the polyacrylate containing carboxyl groups and ether bonds on its main chain. The carboxyl groups can enhance the adhesive strength and ionic conductivity of the binder, while the ether bonds can improve the binder's brittleness and lower its glass transition temperature. Polyvinyl pyrrolidone can ionize positive charges in the solvent and interact with the negative charges on the carboxyl groups to generate electrostatic attraction. Polyvinyl pyrrolidone can also generate hydrogen bonds. Therefore, the combination of polyvinyl pyrrolidone and the polyacrylate can further enhance the adhesive properties of the binder.

[0036] Therefore, the electrode binder composition of the present invention has good bonding properties and can significantly improve the peel strength of the electrode sheet; at the same time, it can also increase the coating surface density of the electrode material, ensuring that the electrode sheet will not crack even with a high surface density, thereby effectively improving the energy density of the electrode sheet; in addition, it has been experimentally verified that the compound use of the above-mentioned polyacrylate and polyvinyl pyrrolidone can also significantly improve the viscosity rebound of the electrode material slurry, which can effectively reduce the difficulty of coating the electrode material slurry.

[0037] 2. The electrode binder composition provided by the present invention, when the molecular weight of the polyacrylate is 50,000-80,000, can also effectively improve the flexibility of the electrode material layer, thereby achieving the effect of greatly improving the peel strength of the electrode sheet while ensuring the flexibility of the electrode material layer.

[0038] 3. The electrode binder composition provided by the present invention controls the number of carbon atoms of the alkyl acrylate to be no less than 7, which can further improve the flexibility of the electrode material layer. DETAILED DESCRIPTION

[0039] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0040] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0041] Example 1

[0042] Prepare lithium manganese iron phosphate positive electrode sheet as follows:

[0043] (1) 256 g of butyl acrylate, 432 g of acrylic acid, and 498 g of allyl polyether (allyl polyethylene glycol, n=10) were mixed uniformly to obtain a polymerizable monomer, wherein the molar ratio of butyl acrylate, acrylic acid, and allyl polyether was 2:6:1;

[0044] (2) 2000 g of dispersion medium (water), 10 g of emulsifier (fatty acid soap) and 800 g of the above-mentioned polymerizable monomer were added to a reactor as initial raw materials, and the temperature was raised to a first polymerization temperature of 75° C. under stirring;

[0045] (3) Add 0.4 g of initiator (benzoyl peroxide) to initiate the polymerization reaction. After 2 h of reaction, the reaction is basically completed. Then, 200 g of polymerizable monomer and 1.6 g of initiator (benzoyl peroxide) are evenly added, and the temperature is raised to the second polymerization temperature of 85 ° C. and the reaction is kept at this temperature for 3 h;

[0046] Wherein, in the above steps (2) and (3), the ratio of the amount of dispersion medium, emulsifier, polymerizable monomer, and initiator is 200:1:100:0.2;

[0047] (4) After the reaction in step (3) is completed, the temperature is lowered to about 45°C, and a buffer is added to adjust the pH value to 8.0;

[0048] (5) The reaction mixture was centrifuged to separate the polymer product, and then the polymer product was washed with hot water to remove the residual additives on the surface of the polymer product. The obtained polymer product was dried, crushed, and passed through a 150-mesh sieve to obtain a polyacrylate. The molecular weight of the polyacrylate was determined to be 75,000;

[0049] (6) 150 g of lithium manganese iron phosphate, 1.6 g of carbon black, 1.1 g of carbon nanotubes, 4.2 g of the above-mentioned polyacrylate, and 0.5 g of polyvinyl pyrrolidone were added to 160 g of N-methyl pyrrolidone to prepare a positive electrode material slurry; wherein the weight ratio of polyacrylate to polyvinyl pyrrolidone was 4.2:0.5;

[0050] (7) The positive electrode material slurry obtained in step (6) was mixed with 18 mg / cm 2 The surface density of the film was coated on the surface of the aluminum current collector, dried at 100°C, and hot-pressed at 30N to prepare a lithium manganese iron phosphate positive electrode sheet.

[0051] In the positive electrode material of the lithium manganese iron phosphate positive electrode sheet, the weight percentage of lithium manganese iron phosphate is approximately 95.3wt%, the weight percentage of carbon black is approximately 1.0wt%, the weight percentage of carbon nanotubes is approximately 0.7wt%, the weight percentage of polyacrylate is approximately 2.7wt%, and the weight percentage of polyvinyl pyrrolidone is approximately 0.3wt%.

[0052] Example 2

[0053] A lithium iron manganese phosphate positive electrode sheet was prepared according to the method of Example 1, except that in step (6) of this example, the amount of polyacrylate used was 3.2 g and the amount of polyvinyl pyrrolidone used was 0.8 g, that is, the weight ratio of polyacrylate to polyvinyl pyrrolidone was 3.2:0.8; the remaining steps were exactly the same as in Example 1.

[0054] Example 3

[0055] A lithium iron manganese phosphate positive electrode sheet was prepared according to the method of Example 1, except that in step (6) of this example, the amount of polyacrylate used was 4.72 g and the amount of polyvinyl pyrrolidone used was 0.3 g, that is, the weight ratio of polyacrylate to polyvinyl pyrrolidone was 4.72:0.3; the remaining steps were exactly the same as in Example 1.

[0056] Example 4

[0057] A lithium iron manganese phosphate positive electrode sheet was prepared according to the method of Example 1, except that in step (1) of this embodiment, the amount of butyl acrylate used was 128 g, the amount of acrylic acid used was 504 g, and the amount of allyl polyether (allyl polyethylene glycol, n=10) used was 498 g, that is, the molar ratio of butyl acrylate, acrylic acid, and allyl polyether was 1:7:1. The remaining steps were exactly the same as in Example 1.

[0058] Example 5

[0059] A lithium iron manganese phosphate positive electrode sheet was prepared according to the method of Example 1, except that in step (1) of this embodiment, the amount of butyl acrylate used was 384 g, the amount of acrylic acid used was 720 g, and the amount of allyl polyether (allyl polyethylene glycol, n=10) used was 1494 g, that is, the molar ratio of butyl acrylate, acrylic acid, and allyl polyether was 3:10:3. The remaining steps were exactly the same as in Example 1.

[0060] Example 6

[0061] A lithium iron manganese phosphate positive electrode sheet was prepared according to the method of Example 1, except that in step (1) of this example, the amount of butyl acrylate used was 192 g, the amount of acrylic acid used was 504 g, and the amount of allyl polyether (allyl polyethylene glycol, n=10) used was 498 g, that is, the molar ratio of butyl acrylate, acrylic acid, and allyl polyether was 1.5:7:1. The remaining steps were exactly the same as in Example 1.

[0062] Example 7

[0063] A lithium iron manganese phosphate positive electrode sheet was prepared according to the method of Example 1, except that in step (1) of this embodiment, the amount of butyl acrylate used was 320 g, the amount of acrylic acid used was 648 g, and the amount of allyl polyether (allyl polyethylene glycol, n=10) used was 747 g, that is, the molar ratio of butyl acrylate, acrylic acid, and allyl polyether was 2.5:9:1.5. The remaining steps were exactly the same as in Example 1.

[0064] Example 8

[0065] A lithium iron manganese phosphate positive electrode sheet was prepared according to the method of Example 1, except that the first polymerization temperature in step (4) of this embodiment was controlled to 78° C., the first effective reaction time in step (3) was 1 h, the second polymerization temperature was 90° C., and the second effective reaction time was 2 h, ultimately resulting in the polyacrylate obtained in step (5) having a molecular weight of 50,000; the remaining steps were exactly the same as in Example 1.

[0066] Example 9

[0067] A lithium iron manganese phosphate positive electrode sheet was prepared according to the method of Example 1, except that the first polymerization temperature in step (4) of this embodiment was controlled to 78° C., the first effective reaction time in step (3) was 2 h, the second polymerization temperature was 85° C., and the second effective reaction time was 3 h, ultimately resulting in the polyacrylate obtained in step (5) having a molecular weight of 80,000; the remaining steps were exactly the same as in Example 1.

[0068] Example 10

[0069] A lithium iron manganese phosphate positive electrode sheet was prepared according to the method of Example 1, except that the alkyl acrylate used in step (1) of this example was hexyl acrylate and the allyl polyether was allyl epoxy polyether; the remaining steps were exactly the same as in Example 1.

[0070] Comparative Example 1

[0071] Prepare lithium manganese iron phosphate positive electrode sheet as follows:

[0072] (1) 150 g of lithium manganese iron phosphate, 1.6 g of carbon black, 1.1 g of carbon nanotubes, and 4.7 g of polyvinylidene fluoride were added to 170 g of N-methylpyrrolidone to prepare a positive electrode material slurry;

[0073] (3) The positive electrode material slurry obtained in step (1) was mixed with 18 mg / cm 2 The film was coated on the surface of the aluminum current collector with a thickness of , dried at 100°C, and hot pressed at 30N to prepare a lithium manganese iron phosphate positive electrode sheet.

[0074] Comparative Example 2

[0075] Prepare lithium manganese iron phosphate positive electrode sheet as follows:

[0076] (1) Take 150g of lithium manganese iron phosphate, 1.6g of carbon black, 1.1g of carbon nanotubes, and 4.7g of polyvinyl pyrrolidone, add them to 170g of N-methylpyrrolidone, and prepare a positive electrode material slurry;

[0077] (3) The positive electrode material slurry obtained in step (1) was mixed with 18 mg / cm 2The thickness was coated on the surface of the aluminum current collector, dried at 100°C, and hot pressed at 30N. Since polyvinyl pyrrolidone has no adhesiveness, it cannot be pressed to obtain a positive electrode sheet.

[0078] Comparative Example 3

[0079] Prepare lithium manganese iron phosphate positive electrode sheet as follows:

[0080] (1) 150 g of lithium manganese iron phosphate, 1.6 g of carbon black, 1.1 g of carbon nanotubes, and 4.7 g of the polyacrylate obtained in step (5) of Example 1 were added to 160 g of N-methylpyrrolidone to prepare a positive electrode material slurry;

[0081] (2) The positive electrode material slurry obtained in step (1) was mixed with 18 mg / cm 2 The film was coated on the surface of the aluminum current collector with a thickness of , dried at 100°C, and hot pressed at 30N to prepare a lithium manganese iron phosphate positive electrode sheet.

[0082] Comparative Example 4

[0083] A lithium iron manganese phosphate positive electrode sheet was prepared according to the method of Example 1, except that step (1) of this comparative example was: 256 g of butyl acrylate and 432 g of acrylic acid were mixed uniformly to obtain a polymerizable monomer, wherein the molar ratio of butyl acrylate to acrylic acid was 2:6; the remaining steps were exactly the same as in Example 1.

[0084] Comparative Example 5

[0085] A lithium iron manganese phosphate positive electrode sheet was prepared according to the method of Example 1, except that, in step (1) of this comparative example, 256 g of butyl acrylate and 498 g of allyl polyether (allyl polyethylene glycol, n=10) were mixed uniformly to obtain a polymerizable monomer, wherein the molar ratio of butyl acrylate to allyl polyether was 2:1; and the remaining steps were exactly the same as in Example 1.

[0086] Comparative Example 6

[0087] A lithium iron manganese phosphate positive electrode sheet was prepared according to the method of Example 1, except that step (1) of this comparative example was: 432 g of acrylic acid and 498 g of allyl polyether (allyl polyethylene glycol, n=10) were mixed uniformly to obtain a polymerizable monomer, wherein the molar ratio of acrylic acid to allyl polyether was 6:1; and the remaining steps were exactly the same as in Example 1.

[0088] Experimental Example 1

[0089] (1) The freshly prepared positive electrode material slurry in each embodiment or comparative example was taken and the initial viscosity (cp) was measured using a digital viscometer with a 4# rotor at a speed of 60r. The slurries were then allowed to stand for 10 hours and the viscosity (cp) after standing was measured again. The measurement results are shown in Table 1.

[0090] (2) The minimum crack density (g / cm) of the positive electrode sheets prepared by the methods of each embodiment or comparative example was measured. 2 ), the determination method is as follows: on the aluminum current collector at different surface densities (18 mg / cm 2 The positive electrode material slurry was applied as described above and dried at 100°C. The cracking of the electrode was observed. The results are shown in Table 1.

[0091] (3) The peel strength (N / cm) of the positive electrode sheets prepared in each Example or Comparative Example was measured as follows: tape was applied to the electrode sheet, one end of the electrode sheet was fixed to one end of a tensile testing machine, and the tape was peeled off 180° from the other end. The tensile force used in the test was the peel strength. The results are shown in Table 1.

[0092] (4) The number of times the positive electrode sheets prepared in each Example or Comparative Example were folded in half to allow light to pass through was measured. The measurement method was as follows: the electrode sheet was folded in half 180°, and a flashlight was used to illuminate the electrode sheet. The number of times the electrode sheet was folded in half to allow light to pass through was recorded. The measurement results are shown in Table 1.

[0093] Table 1 Measurement results of Experimental Example 1

[0094]

[0095] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. An electrode binder composition, characterized in that Comprising polyacrylate and polyvinyl pyrrolidone; wherein the polyacrylate is obtained by polymerizing polymerizable monomers including alkyl acrylate, acrylic acid and allyl polyether, and the weight average molecular weight of the polyacrylate is 50,000 to 80,000; the weight ratio of the polyacrylate to the polyvinyl pyrrolidone is (3 to 5): (0.3 to 0.8); In the polymerizable monomer, the molar ratio of alkyl acrylate, acrylic acid, and allyl polyether is (1-3):(7-10):(1-3), wherein the molar amount of the allyl polyether is calculated based on the molar amount of allyl groups; The number of carbon atoms in the alkyl acrylate is not less than 7; The alkyl acrylate includes at least one of butyl acrylate, pentyl acrylate, octyl acrylate, hexyl acrylate, heptyl acrylate and octadecyl acrylate; The allyl polyether includes at least one of allyl polyethylene glycol, allyl epoxy polyether and allyl alcohol polyoxyalkyl ether.

2. The adhesive composition according to claim 1, wherein The molar ratio of the alkyl acrylate, acrylic acid and allyl polyether is (1.5-2.5): (6-9): (1-1.5).

3. The adhesive composition according to claim 1 or 2, characterized in that The weight average molecular weight of the polyacrylate is 65,000 to 75,000.

4. The adhesive composition according to claim 1 or 2, characterized in that The preparation method of the polyacrylate comprises: Take a dispersion medium, an emulsifier and 50-80% of a polymerizable monomer, heat it to a first polymerization temperature under stirring, and add 20-50% of an initiator to initiate a polymerization reaction; After the first effective reaction time, the remaining polymerizable monomers and the initiator are added respectively, and the temperature is raised to the second polymerization temperature, and the temperature is kept to react for the second effective reaction time.

5. The adhesive composition according to claim 4, characterized in that In parts by weight, the ratio of the dispersion medium, the emulsifier, the polymerizable monomer, and the initiator is (40-350): (0.5-10): (80-100): (0.1-0.7).

6. The adhesive composition according to claim 4, characterized in that The first polymerization temperature is 75-78°C; And / or, the first effective duration is 1 to 2 hours; and / or, the second polymerization temperature is 85-90° C.; And / or, the second effective duration is 2 to 3 hours; And / or, after the heat preservation reaction is carried out for the second effective time, the preparation method of the polyacrylate further comprises the steps of cooling the temperature to 40-50° C. and adjusting the pH value to 8-9; and / or, the dispersion medium comprises at least one of water, ethanol, styrene, acetone, butyl acetate and ether; and / or, the emulsifier comprises at least one of fatty acid soap, alkyl sulfate, alkylbenzene sulfonate, polyol fatty acid ester and phosphate; And / or, the initiator includes at least one of ammonium persulfate, potassium persulfate, benzoyl peroxide, cumene hydroperoxide and dicarbonate peroxide.

7. A positive electrode material composition, characterized in that The positive electrode material composition includes the binder composition according to any one of claims 1 to 6.

8. The positive electrode material composition according to claim 7, characterized in that Based on the total weight of the positive electrode material composition, the weight percentage of the binder composition is 2.2-4.2 wt %.

9. The positive electrode material composition according to claim 7, characterized in that The positive electrode material composition further includes a positive electrode active material and a positive electrode conductive agent. Based on the total weight of the positive electrode material composition, the weight percentage of the positive electrode active material is 94-97 wt %, and the weight percentage of the positive electrode conductive agent is 0.8-1.8 wt %. And / or, the positive electrode active material includes at least one of lithium manganese iron phosphate, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium cobalt oxide and lithium manganese oxide.

10. The positive electrode material composition according to claim 9, characterized in that The positive electrode active material is lithium manganese iron phosphate.

11. A positive electrode, characterized in that The positive electrode comprises the positive electrode material composition according to any one of claims 7 to 10.

12. A battery, characterized in that: The battery comprises the positive electrode according to claim 11.

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