A pvdf copolymer, its preparation method and application in lithium ion battery

Abstract

The application discloses a PVDF copolymer, a preparation method thereof and application thereof in a lithium ion battery, and relates to the technical field of lithium ion batteries. The PVDF copolymer is prepared by copolymerization of 1,1-vinylidene fluoride monomers and amino vinyl monomers, and the amount of the amino vinyl monomers is 0.05-10% of the mass of the 1,1-vinylidene fluoride monomers. The PVDF copolymer can reduce block polymerization of the monomers in the PVDF chain segment through the positive charge repulsion effect of the side chain of the amino vinyl monomers, realize uniform distribution of the monomers on the PVDF chain segment, form a network structure in the high-temperature baking process when the PVDF copolymer is used as an electrode piece adhesive, prevent the adhesive from floating, improve the peeling strength of the electrode piece, reduce the surface resistance of the electrode piece, and improve the battery performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, and more particularly to a PVDF copolymer, a preparation method thereof and application thereof in lithium ion batteries. BACKGROUND

[0002] The lithium ion battery slurry is mainly composed of active material and conductive agent particles, solvent, binder and other components. After being coated on the current collector aluminum foil, a small temperature gradient is formed on the surface and inside of the electrode during the drying process, and the surface temperature is higher than the internal temperature. During the drying process, the surface is dried first, and the concentration of the material is higher than that of the inside. Under such driving force, the binder in the electrode sheet will gradually migrate to the surface and precipitate on the surface of the active material and conductive agent, resulting in a large electrode sheet surface resistance, which seriously affects the battery performance. In addition, the distribution of the binder in the electrode sheet is uneven, and the binder on the side in contact with the aluminum foil is less, and the electrode sheet peeling strength is significantly reduced. In the actual production process, in order to reduce the floating of the binder, the drying temperature of the oven and the coating rate are reduced to reduce the floating of the binder. However, reducing the temperature and coating rate cannot completely solve the problem of the floating of the binder, and it also reduces the production efficiency of the product and increases the production cost. Therefore, it is necessary to improve the performance of the binder itself to solve the above problems.

[0003] In order to solve the problem of uneven distribution of the binder in the electrode sheet in the prior art, a polyurethane of a multi-block copolymer composed of alternating soft segments and hard segments is provided as a new binder for the electrode sheet. However, this technology does not solve the problem of uneven distribution of PVDF binder precipitation, which leads to a large electrode sheet surface resistance and a reduced sheet peeling strength. SUMMARY

[0004] The technical problem to be solved by the present application is to overcome the defects and deficiencies of the existing PVDF binder, such as uneven distribution of precipitation, which leads to a large electrode sheet surface resistance and a reduced sheet peeling strength. The present application provides a PVDF copolymer, which changes the spatial structure of the PVDF binder by using amino vinyl monomers to prevent the floating of the binder, improve the electrode sheet peeling strength, reduce the electrode sheet surface resistance, and improve the battery performance.

[0005] Another object of the present application is to provide a preparation method of the PVDF copolymer.

[0006] Still another object of the present application is to provide an application of the PVDF copolymer F in the preparation of lithium ion battery slurry.

[0007] Still another object of the present application is to protect a lithium ion battery slurry.

[0008] Still another object of the present application is to protect a lithium ion battery.

[0009] The above object of the present application is achieved by the following technical solutions.

[0010] A PVDF copolymer, the PVDF copolymer being copolymerized from 1,1-vinylidene fluoride monomers (VDF monomers) and amino vinyl monomers,

[0011] The amino vinyl monomer has the following structural formula:

[0012]

[0013] wherein R1, R2, R3 are independently selected from hydrogen, C1-C6 alkyl or halogenated C1-C6 alkyl; R4 is independently selected from C1-C6 alkyl, carbonyl, C1-C6 alkylamide or C1-C6 alkyl ester,

[0014] The amount of the amino vinyl monomer is 0.05-10% of the mass of the 1,1-vinylidene fluoride monomers.

[0015] It should be noted that:

[0016] The present application selects the amino vinyl monomer, which has a certain positive charge repulsion effect on the side chain, can reduce the block polymerization of the monomer in the PVDF segment, realize the uniform distribution of the monomer on the PVDF segment, and when used as a pole piece adhesive, the amino group can react with the carbon-hydrogen bond in the PVDF molecular chain during high-temperature baking, so that the molecular chain is quickly crosslinked, the adhesive forms a network structure, prevents the adhesive from floating, improves the pole piece peeling strength, reduces the surface resistance of the pole piece, and improves the battery performance.

[0017] The amount of the amino vinyl monomer must be strictly controlled, the amount of the amino vinyl monomer is too low to have crosslinking effect, and the amount of the amino vinyl monomer is too high, the crosslinking degree of the system is too high, and the prepared positive electrode slurry is prone to gelation and cannot be used.

[0018] In the specific embodiment, preferably, R1, R2 and R3 are all hydrogen. When R1, R2 and R3 are all hydrogen, the amino vinyl monomer has better polymerization effect with the vinylidene fluoride monomer, and is more conducive to forming a network structure.

[0019] In the specific embodiment, preferably, the amino vinyl monomer is one or more of allylamine, 2-aminoethyl acrylate and N-2(aminoethyl) acrylamide.

[0020] Preferably, the amount of the amino vinyl monomer is 0.5-2% of the mass of the 1,1-vinylidene fluoride monomer. For example, the amount of the amino vinyl monomer can be 0.1% of the mass of the 1,1-vinylidene fluoride monomer; or the amount of the amino vinyl monomer can be 1% of the mass of the 1,1-vinylidene fluoride monomer; or the amount of the amino vinyl monomer can be 2% of the mass of the 1,1-vinylidene fluoride monomer.

[0021] In the specific embodiment, the copolymerization monomer further comprises other fluorine-containing monomers, such as one or more of fluoroethylene, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, pentafluoropropylene, hexafluoropropylene, perfluoromethyl vinyl ether, and perfluoropropyl vinyl ether. The addition of the fluorine-containing monomers can reduce the crystallinity of the PVDF and improve the flexibility of the pole piece.

[0022] In another aspect, the present application also specifically protects a method for preparing the PVDF copolymer, and the PVDF copolymer of the present application can be prepared by emulsion polymerization or suspension polymerization.

[0023] The PVDF copolymer of the present application is prepared by emulsion polymerization or suspension polymerization, and the specific operation can refer to the following:

[0024] Under the reaction condition of less than 10 ppm of oxygen content, a part of the VDF monomer is added under closed stirring and temperature rising, and then the initiator and the chain transfer agent are added, and the copolymerization monomer is added at the same time, the polymerization reaction starts, and the reaction pressure is kept unchanged by continuously adding the VDF monomer. After a period of time, a certain amount of initiator and chain transfer agent is added. When the amount of VDF monomer reaches 3 kg, the reaction is stopped, the emulsion is collected, and the emulsion is repeatedly washed until the conductivity of the filtrate is reduced to below 0.1. Finally, drying for 24 h, the PVDF copolymer is obtained.

[0025] In the emulsion polymerization or suspension polymerization of the present application, the polymerization initiator can be selected from one of organic peroxide initiators, such as diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, diisobutyryl peroxide, tert-butyl peroxyneopentanoate, tert-amyl peroxyneopentanoate, etc. The emulsion polymerization system can also use a persulfate or persulfate / sodium bisulfite initiation system, and the preferred initiator is ammonium persulfate.

[0026] The chain transfer agent can be added in the polymerization system for adjusting the molecular weight of the polymer. The chemicals that can be used for chain transfer include ethyl acetate, diethyl malonate, diethyl carbonate, dimethyl carbonate, acetone, ethanol, n-propanol, etc.

[0027] Preferably, the chain transfer agent accounts for 0.01-1% of the mass of the polymerization monomer. The amount of the chain transfer agent is related to the molecular weight of the polymerization product. Too much, the molecular weight is small, and too little, the molecular weight is large.

[0028] In another aspect, the present application also specifically protects the use of the PVDF copolymer in the preparation of a lithium ion battery slurry.

[0029] The present application also specifically protects a lithium ion battery slurry comprising an active material, a conductive agent, a solvent and a binder, wherein the binder is the PVDF copolymer.

[0030] The present application also specifically protects a lithium ion battery, wherein the slurry of the lithium ion battery is the lithium ion battery slurry.

[0031] The lithium ion battery slurry of the present application contains a specific binder PVDF copolymer, which can form a network structure during high-temperature baking after being coated on the current collector aluminum foil. The binder in the electrode plate does not gradually migrate to the surface and precipitate on the surface of the active material and the conductive agent, and the electrode plate has a small surface resistance and excellent battery performance. In addition, the binder is uniformly distributed in the electrode plate, and the electrode plate has good peel strength, and can be widely used in the preparation of lithium ion batteries.

[0032] Compared with the prior art, the present application has the following advantages:

[0033] The PVDF copolymer of the present application can reduce the block polymerization of the monomer in the PVDF chain segment through the positive charge repulsion effect of the amino vinyl monomer side chain, realize the uniform distribution of the monomer in the PVDF chain segment, and form a network structure during high-temperature baking when used as an electrode plate binder, prevent the binder from floating, improve the peel strength of the electrode plate, and reduce the surface resistance of the electrode plate and improve the battery performance.

[0034] The positive electrode prepared from the PVDF copolymer of the present application has a bonding strength of 18.5-25.0 N / m and a surface resistance of 1.2-1.8 / Ω, and has higher bonding strength and lower surface resistance. DETAILED DESCRIPTION

[0035] The present application will be further described below in conjunction with specific embodiments, but the embodiments do not limit the present application in any form. Unless otherwise specified, the raw materials used in the embodiments of the present application are commercially available raw materials.

[0036] Example 1

[0037] A PVDF copolymer, wherein the PVDF copolymer is copolymerized from VDF monomers and an amino vinyl monomer, the amino vinyl monomer is allylamine, and the amount of the amino vinyl monomer is 0.5% of the mass of the VDF monomers.

[0038] The preparation method of the PVDF copolymer of the above-mentioned Example 1 is as follows:

[0039] In a 20L vertical polymerization reactor, 11.5kg of deionized water was added. The reactor was closed, vacuumed and purged with nitrogen several times until the oxygen content in the reactor was less than 10ppm. The reactor was heated to 85°C and the stirring was started at 400rpm. A certain amount of VDF monomer was injected into the reactor until the pressure reached 4.1MPa. 30g of the comonomer allylamine was dissolved in 500g of deionized water and was fed into the reactor by an additive pump at a rate of 150g / hour. At the same time, 0.64g of ammonium persulfate and 3.48g of diethyl malonate were added and the polymerization started. The pressure was kept constant by continuously feeding VDF monomer. After 1 hour, 0.28g of ammonium persulfate was added. After 2 hours, 0.28g of ammonium persulfate and 0.93g of diethyl malonate were added. When the amount of VDF monomer reacted reached 3kg, the reaction was stopped and the reaction time was 4.7 hours. The reactor was depressurized and the emulsion was collected. The emulsion was broken and washed repeatedly until the conductivity of the filtrate was below 0.1. Finally, the PVDF copolymer was dried in an oven at 95°C for 24 hours.

[0040] Example 2

[0041] A PVDF copolymer was prepared by copolymerizing VDF monomer and an amino vinyl monomer, which was allylamine, and the amount of the amino vinyl monomer was 1.0% of the mass of the VDF monomer.

[0042] The preparation method of the PVDF copolymer of Example 2 was as follows:

[0043] In a 20L vertical polymerization reactor, 11.5kg of deionized water was added. The reactor was closed, vacuumed and purged with nitrogen several times until the oxygen content in the reactor was less than 10ppm. The reactor was heated to 85°C and the stirring was started at 400rpm. A certain amount of VDF monomer was injected into the reactor until the pressure reached 4.1MPa. 30g of the comonomer allylamine was dissolved in 500g of deionized water and was fed into the reactor by an additive pump at a rate of 150g / hour. At the same time, 0.64g of ammonium persulfate and 3.48g of diethyl malonate were added and the polymerization started. The pressure was kept constant by continuously feeding VDF monomer. After 1 hour, 0.28g of ammonium persulfate was added. After 2 hours, 0.28g of ammonium persulfate and 0.93g of diethyl malonate were added. When the amount of VDF monomer reacted reached 3kg, the reaction was stopped and the reaction time was 4.7 hours. The reactor was depressurized and the emulsion was collected. The emulsion was broken and washed repeatedly until the conductivity of the filtrate was below 0.1. Finally, the PVDF copolymer was dried in an oven at 95°C for 24 hours.

[0044] Example 3

[0045] A PVDF copolymer, the PVDF copolymer is copolymerized from VDF monomer and amino vinyl monomer, the amino vinyl monomer is allyl amine, and the amount of the amino vinyl monomer is 2.0% of the mass of the VDF monomer.

[0046] The preparation method of the PVDF copolymer in the above embodiment 3 is as follows:

[0047] In a 20L vertical polymerization kettle, 11.5kg of deionized water was added. The reaction kettle was closed, vacuumized, and replaced with nitrogen several times until the oxygen content in the reaction kettle was less than 10ppm. The reaction kettle was heated to 85℃, and the stirring of the reaction kettle was started at a speed of 400r / min. A certain amount of VDF monomer was injected into the reaction kettle until the pressure was 4.1MPa. 120g of the comonomer allyl amine was dissolved in 500g of deionized water, and was added into the reaction kettle through an additive pump at a rate of 150g / hour. At the same time, 0.64g of ammonium persulfate and 3.48g of diethyl malonate were added, the polymerization reaction started, and the reaction pressure was kept constant by continuously adding VDF monomer. After 1h of reaction, 0.28g of ammonium persulfate was added, and after 2h of reaction, 0.28g of ammonium persulfate and 0.93g of diethyl malonate were added. When the amount of VDF monomer reacted was 3kg, the reaction was stopped, and the reaction time was 4.7h. The reaction kettle was depressurized, the emulsion was collected, broken, and repeatedly washed until the conductivity of the filtrate was reduced to below 0.1. Finally, it was dried in a 95℃ oven for 24h to obtain the PVDF copolymer.

[0048] Embodiment 4

[0049] A PVDF copolymer, the PVDF copolymer is copolymerized from VDF monomer and amino vinyl monomer, the amino vinyl monomer is allyl amine, and the amount of the amino vinyl monomer is 2.0% of the mass of the VDF monomer.

[0050] The preparation method of the PVDF copolymer in the above embodiment 4 is as follows:

[0051] In a 20L vertical polymerization reactor, 11.5kg of deionized water was added. The reactor was closed, vacuumed and purged with nitrogen several times until the oxygen content in the reactor was less than 10ppm. The reactor was heated to 85°C and the stirring was started at 400rpm. A certain amount of VDF / hexafluoropropylene mixed monomer was injected into the reactor until the pressure reached 4.1MPa. 120g of the co-monomer allylamine was dissolved in 500g of deionized water and was fed into the reactor by an additive pump at a rate of 150g / hour. At the same time, 0.64g of ammonium persulfate and 3.48g of diethyl malonate were added and the polymerization started. The reaction pressure was kept constant by continuously adding VDF / hexafluoropropylene monomer. After 1 hour of reaction, 0.28g of ammonium persulfate was added and after 2 hours, another 0.28g of ammonium persulfate and 0.93g of diethyl malonate were added. When the VDF monomer conversion reached 3kg, the reaction was stopped and the reaction time was 4.7 hours. The reactor was depressurized and the emulsion was collected. The emulsion was broken and repeatedly washed until the conductivity of the filtrate was below 0.1. Finally, the PVDF copolymer was dried in an oven at 95°C for 24 hours.

[0052] Example 5

[0053] A PVDF copolymer was prepared by copolymerizing VDF monomer and an amino vinyl monomer, which was 2-aminoethyl acrylate, in an amount of 5.0% by mass of the VDF monomer.

[0054] The PVDF copolymer of Example 5 was prepared by the following method:

[0055] In a 20L vertical polymerization reactor, 11.5kg of deionized water was added. The reactor was closed, vacuumed and purged with nitrogen several times until the oxygen content in the reactor was less than 10ppm. The reactor was heated to 85°C and the stirring was started at 400rpm. A certain amount of VDF monomer was injected into the reactor until the pressure reached 4.1MPa. 300g of the co-monomer 2-aminoethyl acrylate was dissolved in 500g of deionized water and was fed into the reactor by an additive pump at a rate of 150g / hour. At the same time, 0.64g of ammonium persulfate and 3.48g of diethyl malonate were added and the polymerization started. The reaction pressure was kept constant by continuously adding VDF monomer. After 1 hour of reaction, 0.28g of ammonium persulfate was added and after 2 hours, another 0.28g of ammonium persulfate and 0.93g of diethyl malonate were added. When the VDF monomer conversion reached 3kg, the reaction was stopped and the reaction time was 4.7 hours. The reactor was depressurized and the emulsion was collected. The emulsion was broken and repeatedly washed until the conductivity of the filtrate was below 0.1. Finally, the PVDF copolymer was dried in an oven at 95°C for 24 hours.

[0056] Example 6

[0057] A PVDF copolymer, the PVDF copolymer is copolymerized from VDF monomer and amino vinyl monomer, the amino vinyl monomer is N-2(aminoethyl)acrylamide, and the amount of the amino vinyl monomer is 2.0% of the mass of the VDF monomer.

[0058] The preparation method of the PVDF copolymer of the above embodiment 6 is as follows:

[0059] In a 20L vertical polymerization kettle, 11.5kg of deionized water was added. The reaction kettle was closed, vacuumized, and replaced with nitrogen for several times until the oxygen content in the reaction kettle was less than 10ppm. The reaction kettle was heated to 85℃, and the stirring of the reaction kettle was started with a speed of 400r / min. A certain amount of VDF monomer was injected into the reaction kettle until the pressure of the reaction kettle was 4.1MPa. 120g of the comonomer N-2(aminoethyl)acrylamide was dissolved in 500g of deionized water, and was added into the reaction kettle through an additive pump with an adding rate of 150g / hour. At the same time, 0.64g of ammonium persulfate and 3.48g of diethyl malonate were added, the polymerization reaction was started, and the reaction pressure was kept constant by continuously adding VDF monomer. After 1h of reaction, 0.28g of ammonium persulfate was added, and after 2h of reaction, 0.28g of ammonium persulfate and 0.93g of diethyl malonate were added. When the reaction amount of VDF monomer was 3kg, the reaction was stopped, and the reaction time was 4.7h. The reaction kettle was depressurized, the emulsion was collected, and was repeatedly washed until the conductivity of the filtrate was reduced to below 0.1. Finally, it was dried in a 95℃ oven for 24h to obtain the PVDF copolymer.

[0060] Comparative example 1

[0061] A PVDF copolymer, the PVDF copolymer is copolymerized from VDF monomer and amino vinyl monomer, the amino vinyl monomer is N-2(aminoethyl)acrylamide, and the amount of the amino vinyl monomer is 2.0% of the mass of the VDF monomer.

[0062] The preparation method of the PVDF copolymer of the above embodiment 1 is as follows:

[0063] In a 20L vertical polymerization reactor, 11.5kg of deionized water was added. The reactor was closed, vacuumed and purged with nitrogen several times until the oxygen content in the reactor was less than 10ppm. The reactor was heated to 85°C and the stirring was started at 400rpm. A certain amount of VDF monomer was injected into the reactor until the pressure reached 4.1MPa. 0.64g of ammonium persulfate and 3.48g of diethyl malonate were added and the polymerization started with a constant pressure maintained by continuous addition of VDF monomer. After 1h of reaction, 0.28g of ammonium persulfate was added and after 2h of reaction, 0.28g of ammonium persulfate and 0.93g of diethyl malonate were added. When the amount of VDF monomer reacted reached 3kg, the reaction was stopped and the reaction time was 4.7h. The reactor was depressurized and the emulsion was collected, broken and washed repeatedly until the conductivity of the filtrate was below 0.1. Finally, the PVDF copolymer was dried in an oven at 95°C for 24h.

[0064] Comparative Example 2

[0065] A PVDF copolymer was prepared by copolymerization of VDF monomer and an amino vinyl monomer, the amino vinyl monomer being allylamine, the amount of the amino vinyl monomer being 0.03% of the mass of the VDF monomer.

[0066] The PVDF copolymer of Comparative Example 2 was prepared as follows:

[0067] In a 20L vertical polymerization reactor, 11.5kg of deionized water was added. The reactor was closed, vacuumed and purged with nitrogen several times until the oxygen content in the reactor was less than 10ppm. The reactor was heated to 85°C and the stirring was started at 400rpm. A certain amount of VDF monomer was injected into the reactor until the pressure reached 4.1MPa. 10g of the comonomer allylamine was dissolved in 500g of deionized water and added to the reactor by an additive pump at a rate of 150g / hour. At the same time, 0.64g of ammonium persulfate and 3.48g of diethyl malonate were added and the polymerization started with a constant pressure maintained by continuous addition of VDF monomer. After 1h of reaction, 0.28g of ammonium persulfate was added and after 2h of reaction, 0.28g of ammonium persulfate and 0.93g of diethyl malonate were added. When the amount of VDF monomer reacted reached 3kg, the reaction was stopped and the reaction time was 4.7h. The reactor was depressurized and the emulsion was collected, broken and washed repeatedly until the conductivity of the filtrate was below 0.1. Finally, the PVDF copolymer was dried in an oven at 95°C for 24h.

[0068] Comparative Example 3

[0069] A PVDF copolymer, the PVDF copolymer is copolymerized from VDF monomer and an amino vinyl monomer, the amino vinyl monomer is allyl amine, and the amount of the amino vinyl monomer is 12% of the mass of the VDF monomer.

[0070] The preparation method of the PVDF copolymer of the above comparative example 2 is as follows:

[0071] In a 20L vertical polymerization kettle, 11.5kg of deionized water was added. The reaction kettle was closed, vacuumed, and replaced with nitrogen several times until the oxygen content in the reaction kettle was less than 10ppm. The reaction kettle was heated to 85℃, and the stirring speed was set to 400r / min. A certain amount of VDF monomer was injected into the reaction kettle until the pressure reached 4.1MPa. 720g of the comonomer allyl amine was dissolved in 500g of deionized water, and was added to the reaction kettle through an additive pump at a rate of 150g / hour. At the same time, 0.64g of ammonium persulfate and 3.48g of diethyl malonate were added, and the polymerization reaction started, and the reaction pressure was kept constant by continuously adding VDF monomer. After 1h of reaction, 0.28g of ammonium persulfate was added, and after 2h of reaction, 0.28g of ammonium persulfate and 0.93g of diethyl malonate were added. When the amount of VDF monomer reacted was 3kg, the reaction was stopped, and the reaction time was 4.7h. The reaction kettle was depressurized, and the emulsion was collected, broken, and repeatedly washed until the conductivity of the filtrate was reduced to below 0.1. Finally, it was dried in a 95℃ oven for 24h to obtain the PVDF copolymer.

[0072] Result detection

[0073] The PVDF copolymers of the above examples and comparative examples were prepared into positive electrodes according to the following electrode preparation method.

[0074] Electrode preparation process: 2g of PVDF was dissolved in 100g of NMP solution, and stirred until completely dissolved. Then, 2.8g of conductive agent carbon black and 56.2g of lithium iron phosphate were added under stirring, and ultrasonic stirring was performed for 2h to obtain a uniform slurry. The slurry was coated on a 12μm back electrode aluminum foil by a coating machine. Then, the aluminum foil was placed in a 100℃ vacuum oven for drying for 12h. The positive electrode was obtained.

[0075] The adhesive strength test was performed according to the test method in the national standard GB / T2790-1995 “Adhesive 180° peel strength test method flexible material against rigid material”.

[0076] The method for measuring the surface resistance is as follows:

[0077] Test instrument: electrode resistance meter, model BER2500 (IEST Energy Technology), electrode diameter 14mm, pressure 5-60MPa

[0078] Four-probe method: four probes are placed on the sample surface during testing, a direct current signal is input, the voltage signal between the probes is collected, and the sample resistivity is obtained through a conversion relationship.

[0079] The specific test results are shown in Table 1 below:

[0080] Table 1

[0081]

[0082]

[0083] The lower the melting point, the higher the copolymerization ratio of the amino vinyl monomer. As can be seen from the data in Table 1 above, the PVDF copolymer of the present application not only has good copolymerization effect, but also forms a network structure during high-temperature baking when used as a pole piece adhesive, preventing the adhesive from floating, improving the pole piece peel strength, and the bonding strength can reach more than 18.5 N / m, and the highest can reach 25.0 N / m. At the same time, it can also effectively reduce the surface resistance of the pole piece, and the surface resistance is 1.8 Ω or less, and the lowest can be reduced to 1.2 Ω, effectively improving the battery performance.

[0084] Among them, Comparative Example 1 is not added with amino vinyl monomer, the copolymerization effect is poor, the melting point is high, and the bonding strength as an adhesive is low, and the resistivity is also high, which cannot achieve the technical effect of the present application.

[0085] In Comparative Example 2, the amount of amino vinyl monomer is too low, which does not have good crosslinking effect, the copolymerization effect is poor, the melting point is high, and the bonding strength as an adhesive is low, and the resistivity is also high, which cannot achieve the technical effect of the present application.

[0086] In Comparative Example 3, the amount of amino vinyl monomer is too high, the crosslinking degree of the system is too high, and the prepared positive electrode slurry is easy to gel, and the bonding strength is significantly reduced.

[0087] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, it is not necessary and impossible to exhaust all the embodiments. Any modification, equivalent replacement and improvement made within the spirit and principles of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A PVDF copolymer, characterized in that, PVDF copolymers are synthesized by copolymerization of 1,1-vinylidene fluoride monomer and amino vinyl monomers. The aminovinyl monomer is one or more of allylamine, 2-aminoethyl acrylate and N-2-(aminoethyl)acrylamide; The amount of the aminovinyl monomer is 1, which is 0.5-2% of the mass of the 1-vinylidene fluoride monomer.

2. The PVDF copolymer as described in claim 1, characterized in that, The copolymer monomers also include one or more of the following: vinyl fluoride, trifluoroethylene, trifluorochloroethylene, tetrafluoroethylene, pentafluoropropylene, hexafluoropropylene, perfluoromethyl vinyl ether, and perfluoropropyl vinyl ether.

3. A method for preparing the PVDF copolymer according to any one of claims 1 or 2, characterized in that, It is prepared by emulsion polymerization or suspension polymerization.

4. The preparation method according to claim 3, characterized in that, In the specific synthesis, a chain transfer agent is added, and the amount of chain transfer agent added is 0.01 to 1% of the mass of the polymerizable monomer.

5. The application of the PVDF copolymer according to any one of claims 1 or 2 in the preparation of lithium-ion battery slurry.

6. A lithium-ion battery slurry, comprising active material, conductive agent particles, solvent, and binder, characterized in that, The adhesive is the PVDF copolymer according to any one of claims 1 or 2.

7. A lithium-ion battery, characterized in that, The slurry for the lithium-ion battery is the lithium-ion battery slurry of claim 6.

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