PVDF polymer and preparation method thereof, electrode slurry, electrode, battery and electrical equipment

Abstract

The present disclosure relates to a PVDF polymer and a preparation method thereof, an electrode slurry, an electrode, a battery and an electrical device. The structural formula of the PVDF polymer includes a first repeating unit having a structure shown in the following formula (1), a second repeating unit having a structure shown in the following formula (2‑1) and / or formula (2‑2), and a third repeating unit having a structure shown in the following formula (3). The polymer provided by the present disclosure can avoid self-crosslinking of some monomers during the polymerization process, and the obtained polymer can be added in a lower amount in the positive electrode slurry, which can reduce the viscosity of the positive electrode slurry while improving the peeling force of the positive electrode sheet. Formula (1) Formula (2‑1) Formula (2‑2) Formula (3).

Description

Technical Field

[0001] The present disclosure relates to the technical field of polymer preparation, and in particular, to a PVDF-based polymer and a preparation method thereof, an electrode slurry, an electrode, a battery and an electrical device. Background Art

[0002] The positive electrode material of lithium-ion batteries is composed of active materials, conductive agents and binders. The main binder currently used is PVDF polymer. In the process of preparing the pole piece slurry, N-methylpyrrolidone (NMP) is generally used as a solvent, and a conductive agent (such as graphite) and a main material (such as lithium iron phosphate) are added for preparation. After the slurry is fully mixed, it is applied to the current collector, and then dried at a high temperature (such as 120°C) to remove the solvent NMP, and finally the pole piece is obtained. In order to improve its bonding performance, the commercially available PVDF binder generally has a large molecular weight, so the solution has a high viscosity. In the process of preparing the slurry, the extremely high viscosity of the PVDF NMP solution will make it difficult to fully mix the solution, which is not conducive to the uniform dispersion of various materials, resulting in a decrease in the uniformity of the pole piece surface density after drying. Therefore, it often takes a long time for stirring, dispersing and other processes, and it is difficult to ensure that the components in the solution are completely dispersed. If the same content of low molecular weight PVDF is used, the bonding force of PVDF will decrease while the viscosity of the solution decreases, which cannot meet the battery's use requirements. Using a large proportion of low molecular weight PVDF may squeeze out the proportion of active materials, resulting in poor toughness of the pole piece and reduced battery cycle performance. In addition, the use of high content PVDF will increase the proportion of NMP solvent in the slurry, reduce the solid content of the slurry, and further increase the cost.

[0003] The cross-linking process of polymers can improve the mechanical properties of polymers. Taking PVDF polymer as an example, the in-situ cross-linking process of PVDF catalyzed by zinc oxide / antimony trioxide has been reported, but the solubility of the cross-linked polymer is extremely poor and cannot be used as a binder for lithium-ion batteries; and because zinc oxide / antimony trioxide is solid, some of it will remain in the cross-linked PVDF and it is difficult to completely remove it. The introduction of a small amount of impurities will reduce the thermal stability of the PVDF material and affect the self-discharge process of the battery. Alternatively, a modified monomer (such as acrylic acid, etc.) that can undergo cross-linking can be introduced during the PVDF synthesis process, but at the conventional PVDF emulsion polymerization temperature, the functional groups between the polymer chains introduced with the modified monomer may have undergone cross-linking (such as acid-base catalyzed cross-linking) at the emulsion polymerization temperature, thereby obtaining a polymer that is difficult to dissolve and process. Summary of the invention

[0004] The purpose of the present disclosure is to provide a PVDF polymer and a preparation method thereof, an electrode slurry, an electrode battery and an electrical device, which can solve the problems existing in the above-mentioned prior art.

[0005] In order to achieve the above-mentioned object, the present disclosure provides a PVDF-based polymer in a first aspect, wherein the structural formula of the PVDF-based polymer comprises a first repeating unit having a structure represented by the following formula (1), a second repeating unit having a structure represented by the following formula (2-1) and / or formula (2-2), and a third repeating unit having a structure represented by the following formula (3):

[0006] Formula (1);

[0007] Formula (2-1), Formula (2-2);

[0008] In formula (2-2), R1 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms, and R2 is selected from hydrogen, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 11 carbon atoms;

[0009] Formula (3); In formula (3), R3 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms, and R4 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms.

[0010] Optionally, in the formula (2-2) of the second repeating unit, R1 is a methyl group or a hydrogen atom, and R2 is selected from a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a sec-butyl group, a 1-pentyl group, a 2-pentyl group, a neopentyl group, a benzyl group, a phenyl group, a cyclopentyl group, a cyclohexyl group, a 1-hexyl group, a 2-hexyl group, a 3-hexyl group, a 1-octyl group, a 2-octyl group, a 2-ethylhexyl group, a 3-octyl group, a n-decyl group, a 1-dodecyl group or a norbornyl group;

[0011] In the formula (3) of the third repeating unit, R3 is a methyl group or a hydrogen atom, and R4 is selected from a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a tert-butyl group, a sec-butyl group, a 1-pentyl group, a 2-pentyl group, a neopentyl group, a cyclopentyl group, a cyclohexyl group, a 1-hexyl group, a 2-hexyl group or a 3-hexyl group.

[0012] Optionally, based on the total number of the first repeating unit, the second repeating unit and the third repeating unit in the structural formula of the PVDF polymer, the content of the first repeating unit is 91-99%, the content of the second repeating unit is 0.5-4.5%, and the content of the third repeating unit is 0.5-4.5%.

[0013] Optionally, the structural formula of the PVDF polymer further includes a fourth repeating unit; the fourth repeating unit is selected from one or more of the following structures:

[0014] , , , ;

[0015] Wherein, based on the total molar number of all repeating units of the structural formula of the PVDF polymer, the molar content of the fourth repeating unit is 0.01-10%.

[0016] Optionally, the weight average molecular weight of the PVDF polymer is 5.2×10 5 ~1.13×10 6 .

[0017] The second aspect of the present disclosure provides a method for preparing the PVDF-based polymer as described in the first aspect of the present disclosure, comprising the following steps: mixing a first monomer, a second monomer, a third monomer, an initiator and a chain transfer agent, and performing a polymerization reaction to obtain a reaction product including the PVDF-based polymer;

[0018] Wherein, the first monomer is vinylidene fluoride; the second monomer is selected from one or more of the compounds having the structure represented by the following formula (B-1) or formula (B-2):

[0019] Formula (B-1), Formula (B-2);

[0020] In formula (B-2), R1 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms, and R2 is selected from hydrogen, an alkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 11 carbon atoms;

[0021] The third monomer is selected from one or more compounds having a structure represented by the following formula (C):

[0022] Formula (C); In formula (C), the substituent R3 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms, and R4 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms.

[0023] Optionally, the weight of the first monomer is M1, the total weight of the second monomer and the third monomer is M2, and M1:M2 is 100:(0.02-25);

[0024] The weight ratio of the second monomer to the third monomer is 1:(0.4-2.5).

[0025] Optionally, in the formula (B-2) of the second monomer, R1 is a methyl group or a hydrogen atom, and R2 is selected from a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a sec-butyl group, a 1-pentyl group, a 2-pentyl group, a neopentyl group, a benzyl group, a phenyl group, a cyclopentyl group, a cyclohexyl group, a 1-hexyl group, a 2-hexyl group, a 3-hexyl group, a 1-octyl group, a 2-octyl group, a 2-ethylhexyl group, a 3-octyl group, a n-decyl group, a 1-dodecyl group or a norbornyl group;

[0026] In the formula (C) of the third monomer, R3 is a methyl group or a hydrogen atom, and R4 is selected from a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a tert-butyl group, a sec-butyl group, a 1-pentyl group, a 2-pentyl group, a neopentyl group, a cyclopentyl group, a cyclohexyl group, a 1-hexyl group, a 2-hexyl group or a 3-hexyl group.

[0027] Optionally, the initiator is selected from an organic peroxide initiator, a persulfate initiator or a persulfate-sodium bisulfite composite initiation system; wherein the organic peroxide initiator is selected from one or more of di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, diethyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, dicyclopentyl peroxydicarbonate, tert-butyl peroxypivalate, tert-amyl peroxypivalate, diisobutyryl peroxide, benzoyl peroxide, tert-butyl hydroperoxide, di-tert-butyl peroxide and N,N-azobisisobutyronitrile; the persulfate initiator is selected from one or more of ammonium persulfate and potassium persulfate; based on the total weight of the first monomer, the total addition amount of the initiator is 0.05-1.5% by weight;

[0028] The chain transfer agent is selected from one or more of ethyl acetate, diethyl malonate, diethyl carbonate, dimethyl carbonate, methanol, ethanol, n-propanol, isopropanol, acetone and butanone; based on the total weight of the first monomer, the total addition amount of the chain transfer agent is 0.5-10 weight %.

[0029] Optionally, the method further comprises:

[0030] The first monomer, water, an emulsifier, a stabilizer and an optional fourth monomer are mixed to obtain a first mixture; wherein the fourth monomer is a fluorine-containing olefin having 3 to 6 carbon atoms;

[0031] The first mixture is mixed with the second monomer, the third monomer, the initiator and the chain transfer agent to perform a polymerization reaction.

[0032] Optionally, the fourth monomer is selected from one or more of hexafluoropropylene, chlorotrifluoroethylene, trifluoroethylene and tetrafluoroethylene;

[0033] Based on the total molar number of the first monomer, the second monomer, the third monomer and the fourth monomer, the added amount of the fourth monomer is 0-10.00 mol %; the molar ratio of the fourth monomer to the first monomer is (0-10):100.

[0034] Optionally, the emulsifier is selected from one or more of perfluorocarboxylic acid ammonium compounds, perfluorocarboxylic acid metal salts and perfluoropolyether compounds; based on the total weight of the first monomer, the added amount of the emulsifier is 0.05-0.3% by weight;

[0035] The stabilizer includes paraffin; based on the total weight of the first monomer, the added amount of the stabilizer is 0.2-0.6 weight %.

[0036] The third aspect of the present disclosure provides an electrode slurry, which includes the PVDF polymer described in the first aspect of the present disclosure or a PVDF polymer prepared according to the preparation method of the PVDF polymer described in the second aspect of the present disclosure; based on the total weight of the electrode slurry, the content of the PVDF polymer is 1.1~1.8% by weight; relative to 1 g of the added amount of the PVDF polymer, the amount of solvent in the electrode slurry is 20~33 g.

[0037] A fourth aspect of the present disclosure provides an electrode, which is prepared using the electrode slurry described in the third aspect of the present disclosure.

[0038] A fifth aspect of the present disclosure provides a battery, which includes the electrode described in the fourth aspect of the present disclosure.

[0039] A sixth aspect of the present disclosure provides an electrical device, which includes the battery described in the fifth aspect of the present disclosure.

[0040] Through the above technical scheme, the present invention provides a PVDF polymer and its preparation method, electrode slurry, electrode, battery and electrical equipment. The comonomer in the PVDF polymer is rich in polar groups. Compared with the conventional vinylidene fluoride homopolymer, the PVDF polymer of the present invention has better solubility in polar solvents (such as NMP); and the PVDF polymer can undergo in-situ crosslinking during high-temperature baking after being made into slurry by introducing specific pre-crosslinking groups (such as crosslinking between epoxy groups and acid anhydride, and crosslinking between epoxy groups and esters), thereby improving its bonding effect; the PVDF polymer is rich in more polar groups (such as epoxy groups, ester groups, etc.), and compared with the traditional straight-chain and branched PVDF, the PVDF polymer undergoes crosslinking during the heating process after slurry coating. After being linked, a network space structure can be formed, which can better wrap the metal ions in the active substance in the polymer, further enhancing the bonding force of the PVDF polymer in the pole piece; the PVDF polymer contains more polar groups, which can further enhance the electrostatic interaction with the metal ions, thereby attracting the metal ions into the polymer main chain to play a role of coating and bonding; the PVDF polymer has a stronger bonding force in the pole piece, so the amount of the polymer added in the slurry can be reduced while ensuring the performance of the pole piece, and the amount of NMP can be reduced while the solid content of the slurry remains unchanged, saving costs; the PVDF polymer has a lower addition amount and is not cross-linked during the slurrying process, so the slurry viscosity is lower, and other components are easier to be evenly dispersed on the pole piece surface;

[0041] In addition, the preparation method of PVDF polymers provided in the present invention has a second monomer and a third monomer with larger alkyl chain steric hindrance than conventionally used copolymer monomers (such as acrylic acid), which can reduce the probability of self-polymerization of the three monomers in the copolymer, making it easier for each monomer to copolymerize into the main chain of the PVDF polymer; the second monomer and the third monomer with a higher crosslinking temperature are used in the present invention, which can also avoid the problem of difficult processing of the polymer caused by PVDF crosslinking at the temperature of emulsion polymerization; compared with other crosslinked PVDFs, the polymer does not require additional processing during the preparation, synthesis and coating process, saving energy and manpower and material resources.

[0042] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings are used to provide further understanding of the present disclosure and constitute a part of the specification. They are used to explain the present disclosure together with the following detailed description, but do not constitute a limitation of the present disclosure.

[0044] Figure 1 This is the NMR spectrum of the product A2 prepared in Example 2 of the present disclosure;

[0045] Figure 2 This is the NMR spectrum of the product B3 prepared in Comparative Example 3 of the present disclosure. DETAILED DESCRIPTION

[0046] The specific embodiments of the present disclosure are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0047] The inventors of the present disclosure have found that, since PVDF has good heat resistance, it is possible to try to design PVDF that can achieve a thermal crosslinking process, thereby improving the adhesion of PVDF. The industrial synthesis of PVDF often uses emulsion polymerization (modified monomers may be introduced). The polymerization temperature of PVDF is between 50 and 70°C. Some crosslinking groups (the crosslinking temperature of conventional modified monomers is lower) may have been crosslinked at this temperature, thereby obtaining insoluble and difficult-to-process polymers. At the same time, it is difficult to completely remove additional crosslinking reagents, and the introduction of a small amount of impurities will reduce the thermal stability of PVDF materials. The inventors of the present disclosure also noted that during the slurry coating process, a temperature of about 120°C is required to completely volatilize NMP. The present disclosure uses this higher temperature baking stage as a thermal crosslinking process to cause the self-crosslinking of polymer molecular chains of PVDF polymers during the subsequent heating crosslinking process of the coating application, thereby avoiding the problem of PVDF polymers being difficult to dissolve due to pre-crosslinking during the polymer synthesis process. Therefore, the inventors of the present disclosure have designed a PVDF polymer that can achieve self-crosslinking under specific heating conditions, and can also avoid the phenomenon that the PVDF polymer is pre-crosslinked during the synthesis process of emulsion polymerization to obtain an insoluble crosslinked polymer. That is, the PVDF polymer will not be crosslinked during the emulsion polymerization process, but will be self-crosslinked at high temperature during the baking process to remove NMP when applied to the coating, which can improve the bonding strength.

[0048] In a first aspect, the present disclosure provides a PVDF-based polymer, wherein the structural formula of the PVDF-based polymer includes a first repeating unit having a structure represented by the following formula (1), a second repeating unit having a structure represented by the following formula (2-1) and / or formula (2-2), and a third repeating unit having a structure represented by the following formula (3):

[0049] Formula (1);

[0050] Formula (2-1), Formula (2-2);

[0051] In formula (2-2), R1 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms, and R2 is selected from hydrogen, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 11 carbon atoms;

[0052] Formula (3); In formula (3), R3 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms, and R4 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms.

[0053] The present disclosure provides a PVDF polymer. The PVDF polymer of the present disclosure has better solubility in polar solvents (such as NMP); and the PVDF polymer can undergo in-situ crosslinking during high-temperature baking after being made into slurry by introducing specific pre-crosslinking groups (such as crosslinking between epoxy groups and acid anhydrides, and crosslinking between epoxy groups and esters), thereby improving its bonding effect; the PVDF polymer is rich in more polar groups (such as epoxy groups, ester groups, etc.), and compared with traditional straight-chain and branched PVDF, the PVDF polymer can form a network space structure after crosslinking during the heating process after slurry coating, and the structure can better wrap the metal ions in the active substance in the polymer, In the material, the bonding force of the PVDF polymer in the electrode is further enhanced; the PVDF polymer contains more polar groups, which can further enhance the electrostatic interaction with metal ions, thereby attracting metal ions into the polymer main chain to play a role of coating and bonding; since the PVDF polymer has a stronger bonding force in the electrode, the amount of the polymer added in the slurry can be reduced while ensuring the performance of the electrode, and the amount of NMP can be reduced while the solid content of the slurry remains unchanged, saving costs; since the amount of PVDF polymer added is reduced and it is not cross-linked during the slurrying process, the slurry viscosity is lower, and other components added to the slurry are also easier to be evenly dispersed on the surface of the electrode.

[0054] According to the present disclosure, in the above structural formula Indicates a connection key.

[0055] In the present disclosure, in R1 to R4, the alkyl group may be a straight-chain alkyl group or a branched alkyl group; the aryl group may be an aryl group with a substituent or an aryl group without a substituent, the substituent on the aryl group may be an alkyl group with 1 to 4 carbon atoms, and the substituent on the aryl group may be one or more, and when there are multiple substituents, the multiple substituents may be the same or different. In addition, in the present disclosure, the number of carbon atoms of R1 to R4 refers to the total number of carbon atoms of the group and its substituents, for example, the number of carbon atoms of the benzyl group is 7.

[0056] In the present disclosure, the carbon number of 1-6 includes 1, 2, 3, 4, 5, 6; the carbon number of 1-12 includes 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12; the carbon number of 6-11 includes 6, 7, 8, 9, 10, 11.

[0057] In a specific embodiment, the formula (2-2) of the second repeating unit is derived from an acrylate compound; in the formula (2-2), R1 is a methyl group or a hydrogen atom, and R2 is selected from a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a sec-butyl group, a 1-pentyl group, a 2-pentyl group, a neopentyl group, a benzyl group, a phenyl group, a cyclopentyl group, a cyclohexyl group, a 1-hexyl group, a 2-hexyl group, a 3-hexyl group, a 1-octyl group, a 2-octyl group, a 2-ethylhexyl group, a 3-octyl group, a n-decyl group, a 1-dodecyl group or a norbornyl group; preferably, R1 is a methyl group, and R2 is selected from an alkyl group having 1 to 4 carbon atoms, and more preferably, R2 is selected from a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group or a tert-butyl group;

[0058] In the formula (3) of the third repeating unit, R3 is a methyl group or a hydrogen atom, and R4 is selected from a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a sec-butyl group, a 1-pentyl group, a 2-pentyl group, a neopentyl group, a cyclopentyl group, a cyclohexyl group, a 1-hexyl group, a 2-hexyl group, or a 3-hexyl group. The groups R1 to R4 in the second repeating unit and the third repeating unit have a wide range of applications, and when R1 to R4 are within the range provided in this embodiment, the PVDF polymer can have excellent performance.

[0059] In one embodiment, based on the total number of the first repeating unit, the second repeating unit and the third repeating unit in the structural formula of the PVDF polymer, the content of the first repeating unit is 91-99%, including but not limited to 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%; the content of the second repeating unit is 0.5-4.5%, including but not limited to 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%; the content of the third repeating unit is 0.5-4.5%, including but not limited to 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%. When the contents of the first repeating unit, the second repeating unit and the third repeating unit in the structural formula of the PVDF polymer are within the scope of this embodiment, the PVDF polymer can have excellent properties, such as high bonding force after being made into a pole piece and low slurry viscosity.

[0060] In a preferred embodiment, based on the total number of the first repeating unit, the second repeating unit and the third repeating unit in the structural formula of the PVDF polymer, the content of the first repeating unit is 94-97.5%, including but not limited to 94%, 95%, 96%, 97%, 97.5%, the content of the second repeating unit is 1-2%, including but not limited to 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, and the content of the third repeating unit is 1.5-4%, including but not limited to 1.5%, 2%, 2.5%, 3%, 3.5%, 4%. When the contents of the first repeating unit, the second repeating unit and the third repeating unit in the structural formula of the PVDF polymer are within the optimized range provided in this embodiment, the performance of the PVDF polymer is further improved.

[0061] In one embodiment, the structural formula of the PVDF polymer further includes a fourth repeating unit; the fourth repeating unit is selected from one or more of the following structures:

[0062] , , , By introducing the fourth repeating unit into the polymer structure, it has the effect of adjusting the polarity of the polymer and improving the solubility of the polymer.

[0063] In a preferred embodiment, based on the total molar number of all repeating units in the structural formula of the PVDF polymer, the molar content of the fourth repeating unit is 0.01-10%, including but not limited to 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%; preferably 2-5%, including but not limited to 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%. Introducing the fourth repeating unit within the content range of this embodiment into the PVDF polymer, especially the fourth repeating unit within the preferred content range, can further improve the effect of the fourth repeating unit in adjusting polarity and improving polymer solubility in the polymer.

[0064] In one embodiment, the weight average molecular weight of the PVDF polymer is 5.2×10 5 ~1.13×10 6 , including but not limited to 5.2×10 5 , 6×10 5 ,7×10 5 , 8×10 5 ,9×10 5 , 1×10 6 , 1.1×10 6 , 1.13×10 6 ; preferably 7.4×105 ~9.6×10 5 , including but not limited to 7.48×10 5 , 8×10 5 , 8.5×10 5 ,9×10 5 , 9.5×10 5 , 9.6×10 5 The PVDF-based polymer provided by the present disclosure has a weight average molecular weight suitable for electrode slurry, so that the electrode slurry has low viscosity and high bonding force.

[0065] The second aspect of the present disclosure provides a method for preparing the PVDF-based polymer as described in the first aspect of the present disclosure, comprising the following steps: mixing a first monomer, a second monomer, a third monomer, an initiator and a chain transfer agent, and performing a polymerization reaction to obtain a reaction product including the PVDF-based polymer;

[0066] Wherein, the first monomer is vinylidene fluoride;

[0067] The second monomer is selected from one or more compounds having a structure represented by the following formula (B-1) or formula (B-2):

[0068] Formula (B-1) (maleic anhydride), Formula (B-2);

[0069] In formula (B-2), R1 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms, and R2 is selected from hydrogen, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 11 carbon atoms;

[0070] The third monomer is selected from one or more compounds having a structure represented by the following formula (C):

[0071] Formula (C); In formula (C), the substituent R3 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms, and R4 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms.

[0072] The present disclosure provides a method for preparing PVDF-based polymers. Compared with conventionally used copolymer monomers (such as acrylic acid, etc.), the second monomer and the third monomer used in the present disclosure have larger alkyl chain steric hindrance, which can reduce the probability of self-polymerization of the three monomers in the copolymer, making it easier for each monomer to copolymerize into the main chain of the PVDF-based polymer; the present disclosure uses the second monomer and the third monomer with a higher cross-linking temperature, which can also avoid the problem of difficult processing of the polymer caused by PVDF cross-linking at the temperature of emulsion polymerization; compared with other cross-linked PVDFs, the preparation method of the polymer provided by the present disclosure does not require additional processing, saving energy and manpower and material resources.

[0073] In a specific embodiment, during the preparation process, each reaction monomer is slowly added dropwise (for example, the reaction raw materials are added dropwise to the reactor through an auxiliary agent pump) so that the monomer concentration in the reaction system is low and it is difficult to react with the comonomer itself, thereby ensuring a uniform reaction, thereby introducing the comonomer into the main chain of PVDF to form a random copolymer.

[0074] In a preferred embodiment, the method further comprises: during the polymerization reaction, continuously adding a first monomer to the reaction mixture to maintain a stable polymerization reaction pressure; wherein the first monomer is added to maintain the polymerization reaction pressure stable at a fluctuation percentage between 90% and 100% of the reaction pressure at the start of the reaction; wherein the fluctuation percentage between the reaction pressures refers to: (reaction start pressure - current system pressure) / reaction start pressure × 100%; preferably, the first monomer is added to maintain the polymerization reaction pressure stable at the same reaction pressure as the start of the reaction;

[0075] And in the polymerization reaction, initiator and chain transfer agent are added to the reaction mixture every 0.5 to 1 hour. The initiator is added in the same amount at a time, and the chain transfer agent is added in the same amount at a time. The addition of initiator and chain transfer agent during the polymerization reaction disclosed in the present invention is conducive to ensuring uniform polymer reaction and avoiding the consumption of initiator and chain transfer agent from having an adverse effect on the polymerization reaction.

[0076] In one embodiment, the total weight of the first monomer added in the polymerization reaction is M1, the total weight of the second monomer and the third monomer is M2, and M1:M2 is 100:(0.02-25), including but not limited to 100:0.02, 100:0.1, 100:0.5, 100:1, 100:5, 100:10, 100:15, 100:20, 100:25; preferably 100:(0.5-5), including but not limited to 100:0.5, 100:1, 100:1.5, 100:2, 100:2.5, 100:3, 100:3.5 , 100:4, 100:4.5, 100:5; the weight ratio of the second monomer: the third monomer is 1: (0.4~2.5), including but not limited to 1: 0.4, 1: 0.6, 1: 0.8, 1: 1, 1: 1.2, 1: 1.4, 1: 1.6, 1: 1.8, 1: 2, 1: 2.2, 1: 2.4, 1: 2.5, preferably 1: (0.7~1.2), including but not limited to 1: 0.7, 1: 0.75, 1: 0.8, 1: 0.85, 1: 0.9, 1: 0.95, 1: 1, 1: 1.05, 1: 1.1, 1: 1.15, 1: 1.2. According to the addition ratio range of the reaction monomers provided in this embodiment, especially according to the preferred addition ratio range of the reaction monomers, PVDF polymers with a more suitable content of repeating units can be obtained, and the obtained polymers have a more suitable molecular structure and molecular weight, thereby improving the performance of PVDF polymers.

[0077] In one embodiment, in the polymerization reaction, the total weight of the added initiator is 0.05-1.5 weight percent of the total weight of the added first monomer, including but not limited to 0.05 weight percent, 0.1 weight percent, 0.2 weight percent, 0.4 weight percent, 0.6 weight percent, 0.8 weight percent, 1 weight percent, 1.2 weight percent, 1.4 weight percent, 1.5 weight percent, preferably 0.8-1.2 weight percent, including but not limited to 0.8 weight percent, 0.9 weight percent, 1.0 weight percent, 1.1 weight percent, 1.2 weight percent;

[0078] In the polymerization reaction, the total added weight of the chain transfer agent is 0.5-10% by weight of the total weight of the first monomer added, including but not limited to 0.5% by weight, 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 1% by weight, preferably 1-5% by weight, including but not limited to 1% by weight, 1.5% by weight, 2% by weight, 2.5% by weight, 3% by weight, 3.5% by weight, 4% by weight, 4.5% by weight, 5% by weight. By controlling the added weight ratio between each raw material, the obtained polymer can be controlled to have a more suitable molecular structure and molecular weight, which is more suitable for application in the field of binders. And according to the optimized raw material addition ratio provided in this embodiment, a more effective PVDF polymer can be prepared.

[0079] In a specific embodiment, the formula (B-2) of the second monomer is derived from an acrylic acid ester compound; wherein R1 is a methyl group or a hydrogen atom, and R2 is selected from a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a sec-butyl group, a 1-pentyl group, a 2-pentyl group, a neopentyl group, a benzyl group, a phenyl group, a cyclopentyl group, a cyclohexyl group, a 1-hexyl group, a 2-hexyl group, a 3-hexyl group, a 1-octyl group, a 2-octyl group, a 2-ethylhexyl group, a 3-octyl group, a n-decane group, a 1-dodecyl group or a norbornyl group; preferably, R1 is a methyl group, and R2 is selected from an alkyl group having 1 to 4 carbon atoms, and further preferably, R2 is selected from a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group or a tert-butyl group; more preferably, the second monomer having the structure shown in formula (B-2) is selected from one or more of methyl methacrylate, isopropyl methacrylate, tert-butyl methacrylate and isobutyl methacrylate;

[0080] The third monomer is derived from a glycidyl acrylate compound, wherein in formula (C), R3 is a methyl group or a hydrogen atom, and R4 is selected from a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a tert-butyl group, a sec-butyl group, a 1-pentyl group, a 2-pentyl group, a neopentyl group, a cyclopentyl group, a cyclohexyl group, a 1-hexyl group, a 2-hexyl group or a 3-hexyl group; more preferably, the third monomer having the structure shown in formula (C) is selected from one or more of glycidyl methacrylate, glycidyl methyl methacrylate, glycidyl ethyl methacrylate, glycidyl n-propyl methacrylate and glycidyl isopropyl methacrylate.

[0081] In a specific embodiment, the initiator is selected from an organic peroxide initiator, a persulfate initiator or a persulfate-sodium bisulfite composite initiation system; wherein the organic peroxide initiator is selected from one or more of di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, diethyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, dicyclopentyl peroxydicarbonate, tert-butyl peroxypivalate, tert-amyl peroxypivalate, diisobutyryl peroxide, benzoyl peroxide, tert-butyl hydroperoxide, di-tert-butyl peroxide and N,N-azobisisobutyronitrile; the persulfate initiator is selected from one or more of ammonium persulfate and potassium persulfate; the chain transfer agent is selected from one or more of ethyl acetate, diethyl malonate, diethyl carbonate, dimethyl carbonate, methanol, ethanol, n-propanol, isopropanol, acetone and butanone.

[0082] The reactive monomers, initiators and chain transfer agents used in the present disclosure can be purchased through common commercial channels or prepared by known methods.

[0083] In one embodiment, the polymerization reaction conditions include: under a protective atmosphere, the polymerization reaction temperature is 50-70°C, the polymerization reaction pressure is 3-10 MPa, the polymerization reaction time is 6-10 h, and the rotation speed is 80-150 rpm / min; wherein the protective atmosphere is selected from nitrogen or argon.

[0084] In a preferred embodiment, the polymerization reaction conditions include: under a protective atmosphere, a polymerization reaction temperature of 55-65° C., a polymerization reaction pressure of 4-8 MPa, a polymerization reaction time of 7-8 h, and a rotation speed of 100-130 rpm / min. According to the preferred polymerization reaction conditions provided in this embodiment, better polymerization reaction effects can be obtained.

[0085] In a preferred embodiment, the method further comprises: mixing the first monomer, water, an emulsifier, a stabilizer and an optional fourth monomer to obtain a first mixture; wherein the fourth monomer is a fluorinated olefin having 3 to 6 carbon atoms; and then mixing the first mixture with the second monomer, the third monomer, the initiator and the chain transfer agent to carry out a polymerization reaction. The present disclosure adds a fourth monomer to the reaction system, which has the effect of enhancing the solubility of the polymer. In the present disclosure, the fourth monomer is added simultaneously with the first monomer, and the fourth monomer is added simultaneously with the first monomer during the polymerization reaction to maintain the pressure stability of the reaction system; specifically, the molar ratio of the added first monomer to the added fourth monomer is maintained the same as the molar ratio of the initially added first monomer to the fourth monomer.

[0086] In one embodiment, the fourth monomer is selected from one or more of hexafluoropropylene, monochlorotrifluoroethylene, trifluoroethylene and tetrafluoroethylene; based on the total molar number of the first monomer, the second monomer, the third monomer and the fourth monomer, the addition amount of the fourth monomer is 0.01-10.00 mol%, including but not limited to 0.01 mol%, 0.05 mol%, 0.1 mol%, 0.5 mol%, 1 mol%, 2 mol%, 3 mol%, 4 mol%, 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 10 mol%, preferably 2-5 mol%, including but not limited to 2 mol%, 2.5 mol%, 3 mol%, 3.5 mol%, 4 mol%, 4.5 mol%, 5 mol%; the molar ratio of the first monomer to the fourth monomer is 100:0.01-10, including but not limited to 100:0.01, 100:0.05, 100:0.1, 100:0.5, 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10; preferably 100:5-10, including but not limited to 100:5, 100:5.5, 100:6, 100:6.5, 100:7, 100:7.5, 100:8, 100:8.5, 100:9, 100:9.5, 100:10. Adding the fourth monomer according to the weight ratio range provided in this embodiment can ensure the thermal cross-linking properties of the polymer itself while also having better solubility.

[0087] In one embodiment, the emulsifier is selected from one or more of perfluorocarboxylic acid ammonium compounds, perfluorocarboxylic acid metal salts and perfluoropolyether compounds; preferably, the emulsifier is selected from one or more of ammonium perfluorohexanoate, sodium perfluorohexanoate, potassium perfluorohexanoate, ammonium perfluorooctanoate, sodium perfluorooctanoate, potassium perfluorooctanoate, ammonium perfluorodecanoate, sodium perfluorodecanoate, potassium perfluorodecanoate, ammonium perfluorooctadecanoate, sodium perfluorooctadecanoate and potassium perfluorooctadecanoate; based on the total weight of the first monomer, the added amount of the emulsifier is 0.05-0.3 weight%, including but not limited to 0.05 weight%, 0.1 weight%, 0.15 weight%, 0.2 weight%, 0.25 weight% and 0.3 weight%;

[0088] The stabilizer includes paraffin; based on the total weight of the first monomer, the amount of the stabilizer added is 0.2 to 0.6 weight percent, including but not limited to 0.2 weight percent, 0.3 weight percent, 0.4 weight percent, 0.5 weight percent, and 0.6 weight percent. By performing polymerization according to the amount of emulsifier and stabilizer added provided in this embodiment, a better polymerization reaction effect can be obtained.

[0089] In a specific embodiment, the method provided by the present disclosure further includes a post-treatment step, including: after stopping the polymerization reaction, repeatedly washing the polymerization product until the conductivity of the filtrate drops below 0.1 S / m, and then vacuum drying at 40-50° C. for 20-30 h. By post-treating the polymerization product, impurities can be removed to obtain a PVDF polymer product with higher purity.

[0090] The third aspect of the present disclosure provides an electrode slurry, which includes the PVDF polymer described in the first aspect of the present disclosure or a PVDF polymer prepared according to the preparation method of the PVDF polymer described in the second aspect of the present disclosure.

[0091] In one embodiment, based on the total weight of the electrode slurry, the content of the PVDF polymer is 1.1-1.8 wt %, including but not limited to 1.1 wt %, 1.2 wt %, 1.3 wt %, 1.4 wt %, 1.5 wt %, 1.6 wt %, 1.7 wt %, 1.8 wt %, preferably 1.3-1.5 wt %;

[0092] Relative to 1g of the PVDF polymer added, the amount of solvent used in the electrode slurry is 20-33g, including but not limited to 20g, 22g, 24g, 26g, 28g, 30g, 32g, 33g, preferably 25-30g, including but not limited to 25g, 26g, 28g, 30g. The electrode slurry provided by the present disclosure uses PVDF polymers, which can reduce the amount of the polymer added in the slurry and reduce the amount of solvent (such as NMP) under the premise of keeping the solid content of the slurry unchanged.

[0093] In a specific embodiment, the electrode slurry further comprises a positive electrode active material, a conductive agent, a dispersant and a solvent, wherein the solvent comprises NMP. Other components in the electrode slurry (such as the positive electrode active material, the conductive agent, the dispersant) can be selected from conventional reagents in the art.

[0094] A fourth aspect of the present disclosure provides an electrode, which is prepared using the electrode slurry described in the third aspect of the present disclosure.

[0095] In a specific embodiment, the electrode slurry provided by the present invention can be coated on a current collector and subjected to heat treatment to obtain an electrode; preferably, based on the total weight of the coating obtained by heat treatment, the content of the PVDF polymer is 1.8~3.0 weight%, including but not limited to 1.8 weight%, 2 weight%, 2.2 weight%, 2.4 weight%, 2.6 weight%, 2.8 weight%, and 3 weight%.

[0096] According to the present disclosure, the positive electrode active material can adopt materials widely used in the art, including but not limited to one or more of lithium transition metal oxides, lithium-containing phosphates and their respective modified compounds. These materials include but are not limited to the following compounds: one or more of lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium manganese cobalt oxide, lithium nickel cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide and their respective modified compounds; one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites and their respective modified compounds. The above-mentioned positive electrode active materials can be used alone or in combination of two or more.

[0097] According to the present disclosure, the positive electrode conductive agent may include one or more of conductive graphite, carbon black, acetylene black, carbon nanotubes, Ketjen black, carbon nanofibers, activated carbon, and graphene.

[0098] According to the present disclosure, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used as the metal foil, and the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0099] The present disclosure is further described in detail by way of examples. The raw materials used in the examples can all be obtained through commercial sources.

[0100] In the following examples, the polymerization reaction apparatus is a horizontal reactor with a stirring device and a volume of 50 L.

[0101] Example 1

[0102] The steps of preparing a self-crosslinked vinylidene fluoride copolymer A1 include:

[0103] First, 20 kg of pure water, 250 g of emulsifier (potassium perfluorooctanoate solution with a concentration of 4 wt%) and 40 g of stabilizer (paraffin, melting point: 60°C) were put into the reactor, nitrogen was filled in and vacuum was evacuated to deoxygenate until the oxygen content in the reactor was less than 20 ppm, the stirring speed was adjusted to 130 rpm / min, the reactor temperature was raised to 60°C, and the first monomer (vinylidene fluoride, VDF) was added until the reactor pressure reached 5.0 MPa; then 200 g of the second monomer (methyl methacrylate) and 200 g of the third monomer (glycidyl methacrylate) were dissolved in 1 kg of deionized water to prepare an aqueous solution, and the aqueous solution and 18 g of initiator (diisopropyl peroxydicarbonate, IPP) and 24 g of chain transfer agent (ethyl acetate) were added to the reactor through an auxiliary pump, and the addition time was controlled to be 0.5 h (the auxiliary pump was added while the reactor was reacting to ensure uniform reaction), and the reaction pressure was maintained at 5.0 by continuously adding the first monomer. MPa, 9 g of initiator (diisopropyl peroxydicarbonate, IPP) and 12 g of chain transfer agent (ethyl acetate) were added in batches every hour. A total of 10 kg of the first monomer (VDF) was added to the reaction. When the pressure dropped to 3.0 MPa, the gas was released and the material was collected. The total reaction time was 8 h. The total amount of initiator added in the polymerization reaction was 81 g, and the total amount of chain transfer agent added was 108 g. The polymer was filtered to remove wax, coagulated and demulsified, washed, dehydrated, and then dried to obtain the polymerization product A1.

[0104] Example 2

[0105] The self-crosslinked vinylidene fluoride copolymer A2 is prepared by the following steps:

[0106] First, 20 kg of pure water, 250 g of emulsifier (4 wt% potassium perfluorooctanoate solution) and 40 g of stabilizer (paraffin, melting point: 60°C) were put into the reactor, nitrogen was filled in and vacuum was evacuated to deoxygenate the reactor until the oxygen content in the reactor was less than 20 ppm, the stirring speed was adjusted to 130 rpm / min, the temperature of the reactor was raised to 60°C, and the first monomer (vinylidene fluoride, VDF) was added until the reactor pressure reached 5.0 MPa. 284g of the second monomer (tert-butyl methacrylate) and 200g of the third monomer (glycidyl methacrylate) were dissolved in 1kg of deionized water to prepare an aqueous solution. The aqueous solution and 18g of initiator (diisopropyl peroxydicarbonate, IPP) and 24g of chain transfer agent (ethyl acetate) were added to the reactor through an auxiliary pump. The addition time was controlled to be 0.5h (the auxiliary pump was added while the reactor was reacting to ensure uniform reaction). The reaction pressure was maintained at 5.0 MPa by continuously adding the first monomer. 9g of initiator (diisopropyl peroxydicarbonate, IPP) and 12g of chain transfer agent (ethyl acetate) were added in batches every hour. A total of 10kg of the first monomer (VDF) was added to the reaction. When the reaction pressure dropped to 3.0 MPa, the gas was released and the material was collected. The reaction time was 8h. The total amount of initiator added in the polymerization reaction was 81g, and the total amount of chain transfer agent added was 108g. The polymer was filtered to remove wax, coagulated and demulsified, washed, and dehydrated before drying. The polymerization product A2 was obtained.

[0107] Example 3

[0108] The self-crosslinked vinylidene fluoride copolymer A3 is prepared by the following steps:

[0109] First, 20 kg of pure water, 250 g of emulsifier (4 wt% potassium perfluorooctanoate solution) and 40 g of stabilizer (paraffin, melting point: 60°C) were put into the reactor, nitrogen was filled in and vacuum was evacuated to deoxygenate the reactor until the oxygen content in the reactor was less than 20 ppm, the stirring speed was adjusted to 130 rpm / min, the temperature of the reactor was raised to 60°C, and the first monomer (vinylidene fluoride, VDF) was added until the reactor pressure reached 5.0 MPa. 196 g of the second monomer (maleic anhydride) and 200 g of the third monomer (glycidyl methacrylate) were dissolved in 1 kg of deionized water to prepare an aqueous solution. The aqueous solution and 18 g of initiator (diisopropyl peroxydicarbonate, IPP) and 24 g of chain transfer agent (ethyl acetate) were added to the reactor through an auxiliary pump. The addition time was controlled to be 0.5 h (the auxiliary pump was added while the reactor was reacting to ensure uniform reaction). The reaction pressure was maintained at 5.0 MPa by continuously adding the first monomer. 9 g of initiator (diisopropyl peroxydicarbonate, IPP) and 12 g of chain transfer agent (ethyl acetate) were added in batches every hour. A total of 10 kg of the first monomer (VDF) was added to the reaction. When the reaction pressure dropped to 3.0 MPa, the gas was released and the material was collected. The reaction time was 8 h. The total amount of initiator added in the polymerization reaction was 81 g, and the total amount of chain transfer agent added was 108 g. The polymer was filtered to remove wax, coagulated and demulsified, washed, dehydrated, and then dried to obtain a polymer product A3.

[0110] Example 4

[0111] The self-crosslinked vinylidene fluoride copolymer A4 is prepared by the following steps:

[0112] First, 20 kg of pure water, 250 g of emulsifier (4 wt% potassium perfluorooctanoate solution) and 40 g of stabilizer (paraffin, melting point: 60°C) were put into the reactor, nitrogen was filled in and vacuum was evacuated to deoxygenate the reactor until the oxygen content was less than 20 ppm, the stirring speed was adjusted to 130 rpm / min, the temperature of the reactor was raised to 60°C, and the first monomer (vinylidene fluoride, VDF) was added until the reactor pressure reached 5.0 MPa. 196 g of the second monomer (maleic anhydride) and 220 g of the third monomer (methyl glycidyl methacrylate) were dissolved in 1 kg of deionized water to prepare an aqueous solution. The aqueous solution and 18 g of initiator (diisopropyl peroxydicarbonate, IPP) and 24 g of chain transfer agent (ethyl acetate) were added to the reactor through an auxiliary pump. The addition time was controlled to be 0.5 h (the auxiliary pump was added while the reactor was reacting to ensure uniform reaction). The reaction pressure was maintained at 5.0 MPa by continuously adding the first monomer (VDF). 9 g of initiator (diisopropyl peroxydicarbonate, IPP) and 12 g of chain transfer agent (ethyl acetate) were added in batches every hour. A total of 10 kg of the first monomer (VDF) was added to the reaction. When the reaction pressure dropped to 3.0 MPa, the gas was released and the material was collected. The reaction time was 8 h. The total amount of initiator added in the polymerization reaction was 81 g, and the total amount of chain transfer agent added was 108 g. The polymer is filtered to remove wax, coagulated and demulsified, washed, dehydrated and then dried to obtain a polymer product A4.

[0113] Example 5

[0114] The self-crosslinked vinylidene fluoride copolymer A5 is prepared by the following steps:

[0115] First, 20 kg of pure water, 250 g of emulsifier (4 wt% potassium perfluorooctanoate solution) and 40 g of stabilizer (paraffin, melting point: 60°C) were put into the reactor, and nitrogen was filled and vacuumed to deoxygenate the reactor until the oxygen content in the reactor was less than 20 ppm. The stirring speed was adjusted to 130 rpm / min, the temperature of the reactor was raised to 60°C, and a mixture of the first monomer (vinylidene fluoride, VDF) and the fourth monomer (hexafluoropropylene, HFP) was added (the molar ratio of the first monomer: the fourth monomer was 100:10) until the reactor pressure reached 5.0 MPa. 200 g of the second monomer (methyl methacrylate) and 200 g of the third monomer (glycidyl methacrylate) were dissolved in 1 kg of deionized water to prepare an aqueous solution, and the aqueous solution and 36 g of initiator (diisopropyl peroxydicarbonate, IPP) and 48 g of chain transfer agent (ethyl acetate) were added to the reactor through an auxiliary pump, and the addition time was controlled to be 0.5 h (the auxiliary pump was added while the reactor was reacting to ensure uniform reaction), and the reaction pressure was maintained at 5.0 MPa by continuously adding a vinylidene fluoride / hexafluoropropylene mixture (the molar ratio of the first monomer: the fourth monomer was 100:10), and 9 g of initiator (diisopropyl peroxydicarbonate, IPP) and 12 g of chain transfer agent (ethyl acetate) were added in batches intermittently every hour. A total of 10.4 kg of vinylidene fluoride / hexafluoropropylene mixture was added to the reaction (of which the total amount of vinylidene fluoride added as the first monomer was 8.427 kg, and the total amount of hexafluoropropylene added as the fourth monomer was 1.973 kg). When the pressure dropped to 4.0 MPa, the gas was released and the material was collected. The reaction time was 8 h. The total amount of initiator added in the polymerization reaction was 99 g, and the total amount of chain transfer agent added was 132 g. The polymer was filtered to remove wax, coagulated and demulsified, washed, dehydrated, and then dried to obtain a polymer product A5.

[0116] Embodiment 6-8

[0117] The preparation method according to Example 1 is different from that of Example 1 in that:

[0118] The polymers were prepared according to the raw material addition ratios in Table 1B below, and the rest of the process was the same as in Example 1 to obtain polymers A6 to A8.

[0119] Comparative Example 1

[0120] This comparative example refers to the preparation method in Example 1, but differs from Example 1 in that methyl methacrylate (the second monomer) is not added to obtain polymer B1.

[0121] Comparative Example 2

[0122] This comparative example refers to the preparation method in Example 1, but differs from Example 1 in that glycidyl methacrylate (the third monomer) is not added to obtain polymer B2.

[0123] Comparative Example 3

[0124] This comparative example refers to the preparation method in Example 1, but differs from Example 1 in that methyl methacrylate and glycidyl methacrylate are not added to obtain polymer B3.

[0125] The reaction conditions in the above examples and comparative examples are listed in the following Tables 1A-1B.

[0126] Table 1A

[0127]

[0128] Table 1B

[0129]

[0130] Test Example 1

[0131] (1) The polyvinylidene fluoride polymer obtained by drying in the above examples and comparative examples was sampled and dissolved in DMF to test its molecular weight and dispersion. The GPC test method includes: using DMF as the mobile phase and PMMA as the standard sample, and testing on an Agilent liquid chromatograph 1290.

[0132] (2) The polyvinylidene fluoride polymer obtained by drying in the above examples and comparative examples was dissolved in deuterated acetone, and the proportion of the comonomer was measured on a 600 M Bruker nuclear magnetic resonance spectrometer. Among them, 1 / 2 of the total integral of 3.1 ppm-2.8 ppm and 2.4 ppm-2.2 ppm was recorded as S1, which represented the number of the first repeating unit; the total integral of 3.4 ppm-3.3 ppm was recorded as S2, which represented the number of the second repeating unit; 1 / 3 of the total integral of 3.3 ppm-3.2 ppm was recorded as S3, which represented the number of the third repeating unit; the content of the first repeating unit was calculated as S1 / (S1+S2+S3)×100%, the content of the second repeating unit was calculated as S2 / (S1+S2+S3)×100%, and the content of the third repeating unit was calculated as S3 / (S1+S2+S3)×100%. In the present disclosure, the content of the fourth repeating unit in the PVDF polymer is obtained based on the nuclear magnetic resonance fluorine spectrum test.

[0133] (3) The polyvinylidene fluoride polymer obtained by drying in the above embodiments and comparative examples is applied to the positive electrode sheet. The preparation of the positive electrode sheet includes the following steps: 1 kg of lithium iron phosphate as the positive electrode active material, 10 g of carbon nanotubes as the positive electrode conductive agent and 24 g of the prepared self-crosslinking polymer are weighed and added into 600 g of N-methylpyrrolidone (NMP) as the solvent, and then stirred in a stirrer for 150 min to form a positive electrode slurry. The content of the PVDF polymer is 1.47% by weight based on the total weight of the electrode slurry; the amount of the solvent in the electrode slurry is 25 g relative to 1 g of the PVDF polymer added. The positive electrode slurry is evenly coated on the surface of the positive electrode current collector aluminum foil, and then placed in an oven and dried at 130°C to obtain a positive electrode sheet, and the adhesion of the sheet is tested. The adhesion test includes: using a 180° peeling force test method with a tensile speed of 50 mm / min; refer to GB / T2792.

[0134] The viscosity test of the positive electrode slurry includes: using an advanced rotational rheometer to test the viscosity of slurries prepared from different types of PVDF, recording 0.01 s -1 To 2000s -1 The viscosity of 50 s -1 As a standard for judging slurry viscosity.

[0135] The ratio of repeating units, weight average molecular weight, dispersity and adhesion data of the polymers prepared in the above examples and comparative examples are listed in Table 2 below.

[0136] Table 2

[0137]

[0138] According to the data in Table 2 above, we can see that:

[0139] Compared with polymers B1~B3 prepared in comparative examples 1 to 3, polymers A1~A8 prepared according to the method provided in the present disclosure in embodiments 1~8 simultaneously contain the first repeating unit, the second repeating unit and the third repeating unit. The positive electrode prepared using polymers A1~A8 has higher bonding force, that is, higher peel strength, and at the same addition amount, the viscosity of the positive electrode slurry obtained with polymers A1~A8 is lower.

[0140] Comparing Examples 1 to 4 with Example 5, it can be seen that the fourth repeating unit ( , hexafluoropropylene repeating unit), the polymer A5 in Example 5 has a higher dispersion and the viscosity of the prepared positive electrode slurry is lower, which shows that the introduction of the fourth repeating unit into the PVDF polymer is beneficial to improving the solubility of the polymer and reducing the slurry viscosity. In practical applications, the polymer can be selected and used according to the comprehensive properties such as the slurry viscosity and adhesion of the polymer.

[0141] Comparing Examples 1 to 4 with Example 6, it can be seen that the ratio of the total weight of the first monomer added in the polymerization reaction of Examples 1 to 4 to the total weight of the second monomer M1:M2 is within the preferred range of 100:(0.5-5) provided in the present disclosure, and the slurry prepared by using the polymers in Examples 1 to 4 has higher bonding force in positive electrode sheet applications;

[0142] Comparing Examples 1 to 4 with Examples 7 to 8, it can be seen that the weight ratio of the second monomer: the third monomer in the polymerization reaction of Examples 1 to 4 is within the preferred range provided in the present disclosure, and the slurry prepared using the polymers in Examples 1 to 4 has higher adhesion in positive electrode sheet applications.

[0143] Test Example 2

[0144] Taking the 0.382 N / 40 mm adhesion of polymer A1 in the positive electrode sheet in Table 2 as a benchmark, the addition amount and slurry viscosity required for polymers B1 to B3 prepared in the comparative example to achieve the same level of adhesion were tested. The results are listed in Table 3 below.

[0145] Table 3

[0146]

[0147] According to the data in Table 3 above,

[0148] When the polymers prepared by comparative examples 1 to 3 achieve the same level of bonding strength as the polymer prepared by example 1 of the present disclosure, the required addition amount of the polymers in comparative examples 1 to 3 in the positive electrode slurry is higher and the viscosity of the positive electrode slurry is also greater, indicating that the PVDF polymers provided by the present disclosure can achieve high bonding performance with a lower addition amount.

[0149] Test Example 3

[0150] This test example is used to perform nuclear magnetic resonance detection on polymer A2 prepared in Example 2 and polymer B3 prepared in Comparative Example 3. The detection instrument and conditions include using 1 H NMR test, 1 H NMR scans were performed 16 times, deuterated acetone was used as the solvent, the sample concentration was 10 mg / mL, and the sample was heated at 50°C for dissolution.

[0151] The NMR spectrum of polymer A2 is as follows Figure 1 As shown, the NMR spectrum of polymer B3 is shown in 2. Figure 1 and Figure 2 The comparison shows that Figure 1 The polymer A2 in Example 1 has a peak of the second repeating unit -(CH2CHCOOCH3)- at 3.4 ppm-3.3 ppm, a peak of the third repeating unit -(CH2CHCOOCH2CHCH2O)- at 3.3 ppm-3.2 ppm, and a structural unit of the main chain CH2 at 3.1 ppm-2.8 ppm and 2.4 ppm-2.2 ppm. This indicates that the first repeating unit, the second repeating unit and the third repeating unit exist in the polymer prepared according to the method provided in Example 1.

[0152] The preferred embodiments of the present disclosure are described in detail above; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0153] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0154] In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A PVDF polymer, characterized in that: The structural formula of the PVDF polymer includes a first repeating unit having a structure represented by the following formula (1), a second repeating unit having a structure represented by the following formula (2-1) and / or formula (2-2), and a third repeating unit having a structure represented by the following formula (3): Formula (1); Formula (2-1), Formula (2-2); In formula (2-2), R1 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms, and R2 is selected from hydrogen, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 11 carbon atoms; Formula (3); In formula (3), R3 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms, and R4 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms; Wherein, based on the total number of the first repeating unit, the second repeating unit and the third repeating unit in the structural formula of the PVDF polymer, the content of the first repeating unit is 91-99%, the content of the second repeating unit is 0.5-4.5%, and the content of the third repeating unit is 0.5-4.5%.

2. The PVDF polymer according to claim 1, characterized in that In the formula (2-2) of the second repeating unit, R1 is a methyl group or a hydrogen atom, and R2 is selected from a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a sec-butyl group, a 1-pentyl group, a neopentyl group, a benzyl group, a phenyl group, a 1-hexyl group, a 1-octyl group, a 2-ethylhexyl group, an n-decyl group or a 1-dodecyl group; In the formula (3) of the third repeating unit, R3 is a methyl group or a hydrogen atom, and R4 is selected from a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a tert-butyl group, a sec-butyl group, a 1-pentyl group, a neopentyl group or a 1-hexyl group.

3. The PVDF polymer according to claim 1, characterized in that The structural formula of the PVDF polymer also includes a fourth repeating unit; the fourth repeating unit is selected from one or more of the following structures: 、 、 、 ； Wherein, based on the total molar number of all repeating units of the structural formula of the PVDF polymer, the molar content of the fourth repeating unit is 0.01-10%.

4. The PVDF polymer according to claim 1, characterized in that: The weight average molecular weight of the PVDF polymer is 5.2×10 5 ~1.13×10 6 .

5. A method for preparing a PVDF polymer as claimed in claim 1 or 4, characterized in that: The following steps are involved: Mixing the first monomer, the second monomer, the third monomer, the initiator and the chain transfer agent to carry out a polymerization reaction to obtain a reaction product including the PVDF-based polymer; Wherein, the first monomer is vinylidene fluoride; the second monomer is selected from one or more of the compounds having the structure represented by the following formula (B-1) or formula (B-2): Formula (B-1), Formula (B-2); In formula (B-2), R1 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms, and R2 is selected from hydrogen, an alkyl group having 1 to 12 carbon atoms, or an aryl group having 6 to 11 carbon atoms; The third monomer is selected from one or more compounds having a structure represented by the following formula (C): Formula (C); In formula (C), the substituent R3 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms, and R4 is selected from hydrogen or an alkyl group having 1 to 6 carbon atoms.

6. The method for preparing a PVDF-based polymer according to claim 5, characterized in that: The weight of the first monomer is M1, the total weight of the second monomer and the third monomer is M2, and M1:M2 is 100:(0.02~25); The weight ratio of the second monomer to the third monomer is 1:(0.4-2.5).

7. The method for preparing a PVDF-based polymer according to claim 5, characterized in that: In the formula (B-2) of the second monomer, R1 is a methyl group or a hydrogen atom, and R2 is selected from a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a sec-butyl group, a 1-pentyl group, a neopentyl group, a benzyl group, a phenyl group, a 1-hexyl group, a 1-octyl group, a 2-ethylhexyl group, an n-decyl group, or a 1-dodecyl group; In the formula (C) of the third monomer, R3 is a methyl group or a hydrogen atom, and R4 is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, sec-butyl, 1-pentyl, neopentyl or 1-hexyl.

8. The method for preparing a PVDF-based polymer according to claim 5, characterized in that: The initiator is selected from an organic peroxide initiator, a persulfate initiator or a persulfate-sodium bisulfite composite initiation system; wherein the organic peroxide initiator is selected from one or more of di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, diethyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, dicyclopentyl peroxydicarbonate, tert-butyl peroxypivalate, tert-amyl peroxypivalate, diisobutyryl peroxide, benzoyl peroxide, tert-butyl hydroperoxide, di-tert-butyl peroxide and N,N-azobisisobutyronitrile; the persulfate initiator is selected from one or more of ammonium persulfate and potassium persulfate; based on the total weight of the first monomer, the total addition amount of the initiator is 0.05-1.5% by weight; The chain transfer agent is selected from one or more of ethyl acetate, diethyl malonate, diethyl carbonate, dimethyl carbonate, methanol, ethanol, n-propanol, isopropanol, acetone and butanone; based on the total weight of the first monomer, the total addition amount of the chain transfer agent is 0.5-10 weight %.

9. The method for preparing a PVDF-based polymer according to claim 5, characterized in that: The method further includes: The first monomer, water, an emulsifier, a stabilizer and an optional fourth monomer are mixed to obtain a first mixture; wherein the fourth monomer is selected from one or more of hexafluoropropylene, monochlorotrifluoroethylene, trifluoroethylene and tetrafluoroethylene; The first mixture is mixed with the second monomer, the third monomer, the initiator and the chain transfer agent to perform a polymerization reaction.

10. The method for preparing a PVDF-based polymer according to claim 9, characterized in that: Based on the total molar number of the first monomer, the second monomer, the third monomer and the fourth monomer, the added amount of the fourth monomer is 0-10.00 mol %; the molar ratio of the fourth monomer to the first monomer is (0-10):

100.

11. The method for preparing a PVDF-based polymer according to claim 9, characterized in that: The emulsifier is selected from one or more of perfluorocarboxylic acid ammonium compounds, perfluorocarboxylic acid metal salts and perfluoropolyether compounds; based on the total weight of the first monomer, the amount of the emulsifier added is 0.05-0.3% by weight; The stabilizer includes paraffin; based on the total weight of the first monomer, the added amount of the stabilizer is 0.2-0.6 weight %.

12. An electrode slurry, characterized in that: The invention relates to a PVDF polymer according to any one of claims 1 to 4 or a PVDF polymer prepared by the method for preparing a PVDF polymer according to any one of claims 5 to 11; based on the total weight of the electrode slurry, the content of the PVDF polymer is 1.1 to 1.8% by weight; relative to 1 g of the PVDF polymer added, the amount of solvent used in the electrode slurry is 20 to 33 g.

13. An electrode, characterized in that: The electrode is prepared using the electrode slurry as claimed in claim 12.

14. A battery, characterized in that: Comprising the electrode according to claim 13.

15. An electrical equipment, characterized in that: Comprising the battery of claim 14.

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