Modified polyvinylidene fluoride binder and preparation method thereof

Abstract

The invention discloses a modified polyvinylidene fluoride binder and a preparation method thereof, and belongs to the technical field of polymers. The modified polyvinylidene fluoride binder disclosed by the invention comprises a polyvinylidene fluoride monomer and an acrylic acid monomer, the adhesive comprises 0.05%-10% by mole of repeating units of acrylic monomers, and the amount of randomly distributed acrylic monomer units is 1%-21%. The binder prepared by the invention has higher bonding force, can maintain the stability and uniformity of slurry, and can be used for a ternary positive electrode material system and a lithium iron phosphate material system.

Description

Technical Field

[0001] The invention belongs to the technical field of polymers, and in particular relates to a modified polyvinylidene fluoride binder and a preparation method thereof. Background Art

[0002] PVDF binder can bond active materials (lithium iron phosphate, ternary positive electrode materials, sodium positive electrode materials, etc.), conductive agents and current collectors on the positive electrode of the battery, maintain the uniformity and stability of the active materials during slurrying, provide the required electronic conduction in the electrode, and play a vital role in maintaining the capacity, service life, and stability of the battery. In order to improve the adhesion of PVDF and its alkali resistance in the high alkaline system of power batteries, polar comonomers such as acrylic acid are usually introduced into PVDF. In addition, for the lithium iron phosphate system, since traditional PVDF binders easily cause lithium salts to deposit on the negative electrode, they have strong interactions with lithium iron and conductive carbon, and are easy to swell, gel or dissolve in the electrolyte to form a viscous fluid or gel polymer electrolyte. While affecting the adhesion, it is easy to cause the electrode particles to delaminate, causing the battery capacity to decline and the cycle life to be shortened.

[0003] Solvay patent CN 101679563B discloses a vinylidene fluoride copolymer binder, which is prepared by copolymerizing hydrophilic (meth) acrylic acid monomer with vinylidene fluoride to prepare polyvinylidene fluoride resin. During the polymerization process, an aqueous solution of acrylic acid monomer is continuously added to prepare polyvinylidene fluoride resin, and the fraction of (meth) acrylic acid in the prepared PVDF randomly distributed unit is at least 40%. However, the continuous addition of (meth) acrylic acid copolymer monomer will seriously reduce the reaction rate and significantly reduce the production efficiency of PVDF. CN118667478 A discloses a PVDF binder, in which the portion of randomly distributed acrylic acid monomer units is greater than 22% and less than 40%, but the binder is suitable for use in ternary systems, easily forms gel in lithium iron phosphate systems, and has poor slurry stability. Summary of the invention

[0004] In order to solve the above problems in the prior art, the purpose of the present invention is to provide a modified polyvinylidene fluoride binder.

[0005] Another object of the present invention is to provide a method for preparing the modified polyvinylidene fluoride binder.

[0006] Another object of the present invention is to provide a modified polyvinylidene fluoride binder for use in preparing a positive electrode of a battery.

[0007] Another object of the present invention is to provide a positive electrode for a battery.

[0008] The above-mentioned object of the present invention is achieved by the following technical solutions:

[0009] A modified polyvinylidene fluoride binder, comprising a vinylidene fluoride monomer and an acrylic monomer;

[0010] The structural formula of the acrylic monomer is as follows:

[0011]

[0012] Among them, R 1 , R 2 , R 3 are independently hydrogen atoms, halogen elements or C 1 -C 3 Hydrocarbon group, R OH is a hydrogen atom or a C 1 -C 5 Hydrocarbon groups,

[0013] The binder comprises 0.05% to 10% by mole of repeating units of acrylic monomers, and the portion of randomly distributed acrylic monomer units is 1 to 21%;

[0014] Specifically, the acrylic monomer is selected from:

[0015]

[0016] At least one of .

[0017] Preferably, the modified polyvinylidene fluoride binder comprises at least 0.05 mol% of repeating units derived from the acrylic monomer.

[0018] Preferably, the modified polyvinylidene fluoride binder comprises at most 10 mol% of repeating units derived from the acrylic monomer.

[0019] Preferably, the randomly distributed acrylic monomer unit portion is 1 to 10%.

[0020] Preferably, the weight average molecular weight of the binder is 400,000 to 3.5 million.

[0021] In the present invention, if the weight average molecular weight of the binder is too low, the bonding force of the prepared binder is reduced; if the weight average molecular weight is too high, the viscosity of the adhesive solution is increased and the stability of the slurry is deteriorated.

[0022] Specifically, the polyvinylidene fluoride binder also includes at least one of vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, pentafluoropropylene, hexafluoropropylene, perfluoromethyl vinyl ether, and perfluoropropyl vinyl ether.

[0023] Specifically, the amount of the vinylidene fluoride is at least 95 mol %, thereby ensuring that the properties of the modified polyvinylidene fluoride binder will not be affected, especially when used in a lithium iron phosphate system.

[0024] A method for preparing a modified polyvinylidene fluoride binder comprises the following steps:

[0025] Mixing a polymerization initiator and a vinylidene fluoride monomer, and adding an acrylic monomer twice at the beginning and during the reaction to obtain the modified polyvinylidene fluoride binder;

[0026] The pressure in the reaction container is greater than the critical pressure of vinylidene fluoride.

[0027] The present invention can significantly improve the production efficiency of PVDF by adding the comonomer twice at the beginning of the reaction and during the reaction; by controlling the fraction of acrylic monomer units to 1-21%, the adhesive force can be improved and the slurry stability and uniformity can be maintained. In addition, the acrylic monomer distribution uniformity of the system is low, the interaction with lithium iron and conductive carbon is weak, and it is not easy to cause gelation, so it can be used in lithium iron phosphate material systems.

[0028] It should be noted that in the present invention, the first reaction is carried out after the acrylic monomer is added at the beginning of the reaction. The shorter the time of the first reaction is, the lower the portion of the randomly distributed acrylic monomer units is.

[0029] Specifically, the first reaction time is 0.5 to 1.5 hours.

[0030] Preferably, the amount of acrylic acid monomer added at the beginning of the reaction is 1% to 95% of the total amount of acrylic acid monomer; the amount of acrylic acid monomer added during the reaction is 1% to 95% of the total amount of acrylic acid monomer.

[0031] More preferably, the amount of acrylic monomer added at the beginning of the reaction is 5% to 90% of the total amount of acrylic monomer; the amount of acrylic monomer added during the reaction is 6% to 95% of the total amount of acrylic monomer.

[0032] More preferably, the amount of acrylic acid monomer added at the beginning of the reaction is 60% to 90% of the total amount of acrylic acid monomer; the amount of acrylic acid monomer added during the reaction is 6% to 10% of the total amount of acrylic acid monomer.

[0033] Specifically, the reaction adopts emulsion polymerization or suspension polymerization.

[0034] Specifically, the polymerization initiator is at least one of diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, diisobutyryl peroxide, tert-butyl peroxypivalate, and tert-amyl peroxypivalate.

[0035] Specifically, the initiator of the emulsion polymerization can also be a persulfate initiator or a persulfate / sodium bisulfite initiator. Preferably, an ammonium persulfate initiator is used.

[0036] Specifically, a chain transfer agent may be added to the polymerization reaction of the present invention to adjust the molecular weight of the polymer.

[0037] More specifically, the chain transfer agent is at least one of ethyl acetate, diethyl malonate, diethyl carbonate, dimethyl carbonate, acetone, ethanol, and n-propanol.

[0038] Preferably, the chain transfer agent accounts for 0.01% to 1% of the total mass of the vinylidene fluoride monomer and the acrylic acid monomer.

[0039] The present invention also protects the use of the modified polyvinylidene fluoride binder in preparing a positive electrode of a battery.

[0040] Specifically, the battery includes an NCM battery and / or an LFP battery.

[0041] The present invention also protects a positive electrode of a battery, comprising the modified polyvinylidene fluoride binder.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) The present invention can significantly improve the production efficiency of PVDF by adding the comonomer twice, at the beginning of the reaction and during the reaction;

[0044] (2) The randomly distributed acrylic monomer unit portion of the binder prepared by the present invention is 1 to 21%, which improves the adhesion of the cell plate and maintains the stability and uniformity of the slurry;

[0045] (3) The binder prepared by the present invention can be used in a ternary positive electrode material system and a lithium iron phosphate material system. DETAILED DESCRIPTION

[0046] The present invention is further described below with reference to specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0047] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0048] The portion of randomly distributed acrylic monomer units represents the percentage between the average number (%) of acrylic monomer sequences (the sequence being included between two repeating units derived from a vinylidene fluoride monomer) and the total average number (%) of acrylic monomer repeating units:

[0049] Randomly distributed acrylic monomer unit fraction = average number of acrylic monomer sequences (%) / total average number of acrylic monomer units (%)

[0050] When each acrylic monomer repeating unit is isolated, ie, contained between two repeating units of vinylidene fluoride monomer, the average number of acrylic monomer sequences is equal to the average total number of acrylic monomer repeating units, so the fraction of randomly distributed acrylic monomer units is 100%.

[0051] The total average number of acrylic monomer units in the polymer can be determined by acid-base titration of the carboxyl groups. 0.5 g of the polymer sample is weighed in acetone at a temperature of 70-80° C. 5 ml of water is then added dropwise under sufficient stirring to avoid polymer coagulation. It is then titrated with a 0.1 M NaOH solution until complete neutralization, with a titration endpoint of about -270 mV. Based on the measured acid equivalent, the acrylic monomer content is determined, and the total average number of acrylic monomer units (i.e., acrylic monomer unit % mole) is further determined.

[0052] The average number (%) of acrylic monomer sequences can be obtained by 19 F-NMR measurement. It has been found that the CF of the vinylidene fluoride unit adjacent to the isolated acrylic monomer unit 2 The partially related signal (in bold in the following chemical formula) corresponds to the peak at -94.8 ppm. 2 CF 2 -[CH 2 CH(COOH)] n -CH 2 CF 2 -CH 2 - The ratio of the intensity of this signal to all the peaks of this spectrum determines the average number of acrylic monomer sequences per 100 vinylidene fluoride monomer units (i.e. the mol% of acrylic monomer sequences), and thus ultimately determines the ratio between the mol% of the randomly distributed acrylic monomer units and the mol% of acrylic monomers.

[0053] Example 1

[0054] A method for preparing a modified polyvinylidene fluoride binder comprises the following steps:

[0055] In a 20L vertical polymerization reactor, add 10kg of deionized water and 4g of methylcellulose. Close the reactor, evacuate, and replace with nitrogen several times until the oxygen content in the reactor is less than 10ppm. Add 5g of diisopropyl peroxydicarbonate and 4kg of vinylidene fluoride until the pressure of the reactor is 6.0MPa. Heat the reactor to 45℃, start the reactor stirring, the speed is 800r / min, at the beginning of the reaction, dissolve 5g of acrylic acid monomer I-1 in 500g of deionized water at 45℃, add it to the reactor through the auxiliary pump, and maintain the pressure of 6.0MPa during the addition process. After 1h of reaction, add 95g of acrylic acid monomer I-2, and after 4h, release the pressure of the reactor, collect the suspended liquid, and wash it repeatedly until the conductivity of the filtrate drops below 0.1. Finally, dry it in an oven at 95℃ for 24h to obtain a modified polyvinylidene fluoride binder.

[0056] The weight average molecular weight of the prepared modified polyvinylidene fluoride binder is 1 million, the total average number of acrylic acid monomer units is 1.5%, and the randomly distributed acrylic acid monomer unit portion is 20%.

[0057] Example 2

[0058] A method for preparing a modified polyvinylidene fluoride binder comprises the following steps:

[0059] In a 20L vertical polymerization reactor, add 10kg of deionized water and 4g of methylcellulose. Close the reactor, evacuate, and replace with nitrogen several times until the oxygen content in the reactor is less than 10ppm. Add 5g of diisopropyl peroxydicarbonate and 4kg of vinylidene fluoride until the pressure of the reactor is 6.0MPa. Heat the reactor to 45℃, start the reactor stirring, the speed is 800r / min, at the beginning of the reaction, dissolve 90g of acrylic acid monomer I-1 in 500g of deionized water at 45℃, add it to the reactor through the auxiliary pump, and maintain the pressure of 6.0MPa during the addition process. After 1h of reaction, add 10g of acrylic acid monomer I-2, and after 4h, the reactor is depressurized, the suspended liquid is collected, and it is washed repeatedly until the conductivity of the filtrate drops below 0.1. Finally, dry it in an oven at 95℃ for 24h to obtain a modified polyvinylidene fluoride binder.

[0060] The weight average molecular weight of the prepared modified polyvinylidene fluoride binder is 1 million, the total average number of acrylic acid monomer units is 1.5%, and the randomly distributed acrylic acid monomer unit portion is 10%.

[0061] Example 3

[0062] A method for preparing a modified polyvinylidene fluoride binder comprises the following steps:

[0063] In a 20L vertical polymerization reactor, add 10kg of deionized water and 4g of methylcellulose. Close the reactor, evacuate, and replace with nitrogen several times until the oxygen content in the reactor is less than 10ppm. Add 5g of diisopropyl peroxydicarbonate and 4kg of vinylidene fluoride until the pressure of the reactor is 6.0MPa. Heat the reactor to 45℃, start the reactor stirring, the speed is 800r / min, at the beginning of the reaction, dissolve 60g of acrylic acid monomer I-1 in 500g of deionized water at 45℃, add it to the reactor through the auxiliary pump, and maintain the pressure of 6.0MPa during the addition process. After 1h of reaction, add 6g of acrylic acid monomer I-2, and after 4h, release the pressure of the reactor, collect the suspended liquid, and wash it repeatedly until the conductivity of the filtrate drops below 0.1. Finally, dry it in a 95℃ oven for 24h to obtain a modified polyvinylidene fluoride binder.

[0064] The weight average molecular weight of the prepared modified polyvinylidene fluoride binder is 1 million, the total average number of acrylic acid monomer units is 0.9%, and the randomly distributed acrylic acid monomer unit portion is 10%.

[0065] Example 4

[0066] A method for preparing a modified polyvinylidene fluoride binder comprises the following steps:

[0067] In a 20L vertical polymerization reactor, add 10kg of deionized water and 4g of methyl cellulose. Close the reactor, evacuate, and replace with nitrogen several times until the oxygen content in the reactor is less than 10ppm. Add 5g of diisopropyl peroxydicarbonate and 4kg of vinylidene fluoride / hexafluoropropylene monomer (the molar ratio of vinylidene fluoride to hexafluoropropylene is 98:2) until the pressure of the reactor is 6.0MPa. Heat the reactor to 45°C, start the reactor stirring, the speed is 800r / min, at the beginning of the reaction, dissolve 60g of acrylic acid monomer I-2 in 500g of deionized water at 45°C, add it to the reactor through the auxiliary pump, and maintain the pressure of 6.0MPa during the addition process. After 1h of reaction, add 6g of acrylic acid monomer I-1, and after 4h, the reactor is depressurized, the suspended liquid is collected, and it is washed repeatedly until the conductivity of the filtrate drops below 0.1. Finally, dry it in a 95°C oven for 24h to obtain a modified polyvinylidene fluoride binder.

[0068] The weight average molecular weight of the prepared modified polyvinylidene fluoride binder is 1 million, the total average number of acrylic acid monomer units is 0.9%, and the randomly distributed acrylic acid monomer unit portion is 10%.

[0069] Example 5

[0070] A method for preparing a modified polyvinylidene fluoride binder comprises the following steps:

[0071] In a 20L vertical polymerization reactor, add 10kg of deionized water and 4g of methylcellulose. Close the reactor, evacuate, and replace with nitrogen several times until the oxygen content in the reactor is less than 10ppm. Add 5g of diisopropyl peroxydicarbonate and 4kg of vinylidene fluoride / hexafluoropropylene monomer (the molar ratio of vinylidene fluoride to hexafluoropropylene is 98:2) until the pressure of the reactor is 6.0MPa. Heat the reactor to 45°C, start the reactor stirring, the speed is 800r / min, at the beginning of the reaction, dissolve 60g of acrylic acid monomer I-2 in 500g of deionized water at 45°C, add it to the reactor through the auxiliary pump, and maintain the pressure of 6.0MPa during the addition process. After 0.5h of reaction, add 6g of acrylic acid monomer I-1, and after 4.5h, the reactor is depressurized, the suspended liquid is collected, and it is repeatedly washed until the conductivity of the filtrate drops below 0.1. Finally, the mixture was dried in an oven at 95° C. for 24 hours to obtain a modified polyvinylidene fluoride binder.

[0072] The weight average molecular weight of the prepared modified polyvinylidene fluoride binder is 1 million, the total average number of acrylic acid monomer units is 0.9%, and the randomly distributed acrylic acid monomer unit portion is 5%.

[0073] Comparative Example 1

[0074] A method for preparing a modified polyvinylidene fluoride binder comprises the following steps:

[0075] In a 20L vertical polymerization reactor, add 10kg of deionized water and 4g of methyl cellulose. Close the reactor, evacuate, and replace with nitrogen several times until the oxygen content in the reactor is less than 10ppm. Add 5g of diisopropyl peroxydicarbonate and 4kg of vinylidene fluoride / hexafluoropropylene monomer (the molar ratio of vinylidene fluoride to hexafluoropropylene is 98:2) until the pressure of the reactor is 6.0MPa. Heat the reactor to 45°C, start the reactor stirring, the speed is 800r / min, and at the beginning of the reaction, dissolve 60g of acrylic acid monomer I-2 in 500g of deionized water at 45°C, add it to the reactor through the auxiliary pump, and maintain the pressure of 6.0MPa during the addition process. After 5h of reaction, the reactor is depressurized, the suspended liquid is collected, and it is washed repeatedly until the conductivity of the filtrate drops below 0.1. Finally, it is dried in an oven at 95°C for 24h to obtain a modified polyvinylidene fluoride binder.

[0076] The weight average molecular weight of the prepared modified polyvinylidene fluoride binder is 1 million, the total average number of acrylic acid monomer units is 0.9%, and the randomly distributed acrylic acid monomer unit portion is 22%.

[0077] Comparative Example 2

[0078] A method for preparing a modified polyvinylidene fluoride binder comprises the following steps:

[0079] In a 20L vertical polymerization reactor, add 10kg of deionized water and 4g of methyl cellulose. Close the reactor, evacuate, and replace with nitrogen several times until the oxygen content in the reactor is less than 10ppm. Add 5g of diisopropyl peroxydicarbonate and 4kg of vinylidene fluoride until the pressure of the reactor is 6.0MPa. Heat the reactor to 45°C, start the reactor stirring, the speed is 800r / min, and at the beginning of the reaction, dissolve 100g of acrylic acid monomer I-2 in 500g of deionized water at 45°C, add it to the reactor through an auxiliary pump, and maintain the pressure of 6.0MPa during the addition process. After 5h of reaction, the reactor is depressurized, the suspended liquid is collected, and it is repeatedly washed until the conductivity of the filtrate drops below 0.1. Finally, it is dried in an oven at 95°C for 24h to obtain a modified polyvinylidene fluoride binder.

[0080] The weight average molecular weight of the prepared modified polyvinylidene fluoride binder is 1 million, the total average number of acrylic acid monomer units is 1.5%, and the randomly distributed acrylic acid monomer unit portion is 22%.

[0081] Comparative Example 3

[0082] A method for preparing a modified polyvinylidene fluoride binder comprises the following steps:

[0083] In a 20L vertical polymerization reactor, add 10kg of deionized water and 4g of methylcellulose. Close the reactor, evacuate, and replace with nitrogen several times until the oxygen content in the reactor is less than 10ppm. Add 5g of diisopropyl peroxydicarbonate and 4kg of vinylidene fluoride until the pressure of the reactor is 6.0MPa. Heat the reactor to 45°C, start the reactor stirring, the speed is 800r / min, at the beginning of the reaction, dissolve 10g of acrylic acid monomer I-2 in 500g of deionized water at 45°C, add it to the reactor through the auxiliary pump, and maintain the pressure of 6.0MPa during the addition process. After 2h of reaction, add 90g of acrylic acid monomer I-2, and after 4h, release the pressure of the reactor, collect the suspended liquid, and wash it repeatedly until the conductivity of the filtrate drops below 0.1. Finally, dry it in an oven at 95°C for 24h to obtain a modified polyvinylidene fluoride binder.

[0084] The weight average molecular weight of the prepared modified polyvinylidene fluoride binder is 1 million, the total average number of acrylic acid monomer units is 1.5%, and the randomly distributed acrylic acid monomer unit portion is 30%.

[0085] Performance Testing

[0086] The modified polyvinylidene fluoride binder of the above examples and comparative examples is prepared into an electrode composition, which includes an electrode material, a conductive agent and the modified polyvinylidene fluoride binder.

[0087] 1. Melting point test:

[0088] The melting point of the polymer was measured by DSC.

[0089] 2. Cathode material (NCM8 series) electrode preparation process:

[0090] Dissolve 2g of modified polyvinylidene fluoride binder in 100g of NMP solution and stir to fully dissolve. Then add 2.8g of conductive agent carbon black and 56.2g of NCM811 under stirring, and then ultrasonically stir for 2h to obtain a uniform slurry. The slurry is coated on a 12μm thick electrode aluminum foil by a coater, and then the aluminum foil is placed in a 60℃ vacuum oven and dried for 12h to obtain a positive electrode.

[0091] 3. Cathode Material (LFP) Electrode Preparation

[0092] Dissolve 2g of modified polyvinylidene fluoride binder in 100g of NMP solution and stir to fully dissolve. Then add 2.8g of conductive agent carbon black and 56.2g of LFP under stirring, and then ultrasonically stir for 2h to obtain a uniform slurry. The slurry is coated on a 12μm thick electrode aluminum foil by a coater, and then the aluminum foil is placed in a 60℃ vacuum oven and dried for 12h to obtain a positive electrode.

[0093] 4. Bond strength test:

[0094] The bonding strength test was carried out in accordance with the test method in the national standard GB / T2790-1995 "Adhesive 180° Peel Strength Test Method Flexible Material to Rigid Material".

[0095] Table 1 Comparison of test performance results of Examples 1 to 5 and Comparative Examples 1 to 3

[0096]

[0097] It can be seen that Examples 1 to 5 have high bonding strength and good slurry stability in lithium iron phosphate and ternary systems. However, Comparative Examples 1 to 3, in which the fraction of randomly distributed acrylic monomers is greater than 21%, have very poor slurry stability in lithium iron phosphate systems.

[0098] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A modified polyvinylidene fluoride binder, characterized in that: Including vinylidene fluoride monomers and acrylic monomers; The structural formula of the acrylic monomer is as follows: Wherein, R1, R2, and R3 are independently hydrogen atoms, halogen elements, or C1-C3 hydrocarbon groups, R OH is a hydrogen atom or a C1-C5 hydrocarbon group including at least one hydroxyl group; The binder contains 0.05 to 10% by mole of repeating units of acrylic monomers, and the portion of randomly distributed acrylic monomer units is 1 to 21%.

2. The modified polyvinylidene fluoride binder according to claim 1, characterized in that: The acrylic monomer is selected from: At least one of .

3. The modified polyvinylidene fluoride binder according to claim 1 or 2, characterized in that: The randomly distributed acrylic monomer unit portion is 1 to 10%.

4. The modified polyvinylidene fluoride binder according to claim 1 or 2, characterized in that: The polyvinylidene fluoride binder further comprises at least one of vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, pentafluoropropylene, hexafluoropropylene, perfluoromethyl vinyl ether, and perfluoropropyl vinyl ether.

5. A method for preparing the modified polyvinylidene fluoride binder according to any one of claims 1 to 4, characterized in that: The following steps are involved: Mixing a polymerization initiator and a vinylidene fluoride monomer, and adding an acrylic monomer twice at the beginning of the reaction and during the reaction, respectively, to obtain the modified polyvinylidene fluoride binder; The pressure in the reaction container is greater than the critical pressure of vinylidene fluoride.

6. The preparation method according to claim 5, characterized in that: The first reaction is carried out after the acrylic monomer is added at the beginning of the reaction, and the reaction time is 0.5 to 1.5 hours.

7. The preparation method according to claim 5, characterized in that: The polymerization initiator is at least one of diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, diisobutyryl peroxide, tert-butyl peroxypivalate, and tert-amyl peroxypivalate.

8. Use of the modified polyvinylidene fluoride binder according to any one of claims 1 to 4 in the preparation of a positive electrode of a battery.

9. The use according to claim 8, characterized in that: The battery includes an NCM battery and / or an LFP battery.

10. A positive electrode of a battery, characterized in that: The invention comprises the modified polyvinylidene fluoride binder as described in any one of claims 1 to 4.

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