Modified polyvinylidene fluoride and preparation method therefor, active material composition, positive electrode sheet, and energy storage device

Abstract

The present application provides modified polyvinylidene fluoride and a preparation method therefor, an active material composition, a positive electrode sheet, and an energy storage device. The modified polyvinylidene fluoride provided by the present application is a copolymer of vinylidene fluoride and 4-vinyl-4'-substituent-bis-benzenesulfonimide lithium, and the mass fraction of the 4-vinyl-4'-substituent-bis-benzenesulfonimide lithium in the modified vinylidene fluoride ranges from 2% to 10%. The modified vinylidene fluoride not only has good binding power, but also has relatively strong lithium ion conduction capability, thereby improving the rate performance of the energy storage device.

Description

Modified polyvinylidene fluoride and preparation method thereof, active material composition, positive electrode sheet and energy storage device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on July 12, 2023, with application number 2023108518484 and application name “Modified polyvinylidene fluoride and its preparation method, active material composition, positive electrode sheet and energy storage device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to a modified polyvinylidene fluoride and a preparation method thereof, an active material composition, a positive electrode sheet and an energy storage device. Background Art

[0003] Polyvinylidene fluoride (PVDF) is widely used as a binder in battery electrodes, bonding and retaining active materials. With the continuous advancement of battery technology, higher rate performance requirements are being placed on batteries. However, the binders currently used are chemically inert and lack the ability to conduct lithium ions. This can affect the electrochemical performance of the positive and negative electrode materials, limiting improvements in battery rate performance.

[0004] Summary of the Invention

[0005] In response to the above problems, an embodiment of the present application provides a modified polyvinylidene fluoride, which has a strong lithium ion conductivity effect and improves the rate performance of the energy storage device.

[0006] The first aspect of the present application provides a modified polyvinylidene fluoride, comprising: the modified polyvinylidene fluoride is a copolymer of vinylidene fluoride and 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium, and the mass fraction of the 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium in the modified polyvinylidene fluoride ranges from 2% to 10%.

[0007] A second embodiment of the present application provides a method for preparing modified polyvinylidene fluoride, which comprises:

[0008] Providing lithium 4-vinyl-4'-substituted-bisbenzenesulfonyl imide and vinylidene fluoride; and

[0009] 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium is copolymerized with vinylidene fluoride to obtain modified polyvinylidene fluoride, wherein the mass fraction of 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium in the modified vinylidene fluoride ranges from 2% to 10%.

[0010] A third embodiment of the present application provides an active material composition, which includes: active particles, a conductive agent, and a binder, wherein the binder is the modified polyvinylidene fluoride described in the embodiment of the present application.

[0011] A fourth embodiment of the present application provides a positive electrode sheet, which includes: a current collector and an active material layer, wherein the active material layer is arranged on the surface of the current collector, and the active material layer includes the active material composition described in the embodiment of the present application.

[0012] The fifth aspect of the present application provides an energy storage device, comprising: an electrolyte, a negative electrode plate, a diaphragm, and the positive electrode plate described in the embodiment of the present application, wherein the negative electrode plate is at least partially immersed in the electrolyte, the diaphragm is located on one side of the negative electrode plate and is at least partially immersed in the electrolyte, and the positive electrode plate is arranged on the side of the diaphragm away from the negative electrode plate and is at least partially immersed in the electrolyte.

[0013] The modified polyvinylidene fluoride of the embodiment of the present application is a copolymer of vinylidene fluoride and 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium. The bisbenzenesulfonyl imide lithium group is introduced into the polyvinylidene fluoride molecular chain by random copolymerization. The two ends of the lithium sulfonyl imide are connected to the benzene ring with a high degree of negative charge delocalization through chemical bonds, thereby enhancing the degree of electron delocalization of the entire structure, making Li+ easily dissociated, thereby giving the modified polyvinylidene fluoride a strong ability to conduct lithium ions. The mass fraction of the 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium ranges from 2% to 10%. The modified vinylidene fluoride has both good adhesion and strong ability to conduct lithium ions, which can improve the rate performance of the energy storage device. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0015] FIG1 is a flow chart of a method for preparing modified polyvinylidene fluoride according to an embodiment of the present application.

[0016] FIG2 is a schematic structural diagram of a pole piece according to an embodiment of the present application.

[0017] FIG3 is a schematic cross-sectional view of a pole piece according to an embodiment of the present application along the AA direction in FIG2 .

[0018] FIG4 is a schematic structural diagram of an energy storage device according to an embodiment of the present application.

[0019] FIG5 is a schematic cross-sectional view of the energy storage device according to an embodiment of the present application along the BB direction in FIG4 .

[0020] FIG6 is an electrochemical impedance spectroscopy graph of the energy storage device of the present application.

[0021] Explanation of reference numerals: 100 - positive electrode sheet, 110 - current collector, 120 - active material layer, 200 - energy storage device, 210 - separator, 220 - negative electrode sheet. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0023] The terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish between different objects, not to describe a particular order. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0024] The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings.

[0025] It should be noted that, for the convenience of explanation, in the embodiments of the present application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0026] Polyvinylidene fluoride (PVDF) is widely used as a binder in battery electrodes, bonding and retaining active materials. With the continuous advancement of battery technology, higher rate performance requirements are being placed on batteries. However, the binders currently used are chemically inert and lack the ability to conduct lithium ions. This can affect the electrochemical performance of the positive and negative electrode materials, limiting improvements in battery rate performance.

[0027] The first aspect of the present application provides a modified polyvinylidene fluoride, comprising: the modified polyvinylidene fluoride is a copolymer of vinylidene fluoride and 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium, and the mass fraction of the 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium in the modified polyvinylidene fluoride ranges from 2% to 10%.

[0028] The modified polyvinylidene fluoride is a copolymer of vinylidene fluoride and lithium 4-vinyl-4'-substituted-bisbenzenesulfonyl imide. The lithium bisbenzenesulfonyl imide groups are introduced into the polyvinylidene fluoride molecular chain through random copolymerization. The ends of the lithium sulfonyl imide are chemically bonded to benzene rings with a high degree of negative charge delocalization, enhancing the electron delocalization of the entire structure. This facilitates the dissociation of Li+, resulting in a strong lithium ion conductivity in the modified polyvinylidene fluoride. The mass fraction of the lithium 4-vinyl-4'-substituted-bisbenzenesulfonyl imide ranges from 2% to 10%. The modified polyvinylidene fluoride exhibits both good bonding strength and strong lithium ion conductivity, improving the rate performance of energy storage devices.

[0029] In some embodiments, the electrical conductivity of the modified polyvinylidene fluoride is 1.67×10 -4 S / cm to 6.0×10 -4 S / cm. Specifically, the conductivity of the modified polyvinylidene fluoride can be 1.67×10 -4 S / cm, 2×10 -4 S / cm, 3×10 -4 S / cm, 4×10 -4 S / cm, 5×10 -4 S / cm, 6×10 -4 S / cm, and any values ​​between the above values.

[0030] When the electrical conductivity of the modified polyvinylidene fluoride is less than 1.67×10 -4 S / cm, the lithium bis(benzenesulfonyl)imide groups are relatively few, and the modified polyvinylidene fluoride has a poor ability to conduct lithium ions. When the conductivity of the modified polyvinylidene fluoride is greater than 6×10 -4 S / cm, the lithium bis(benzenesulfonyl)imide groups are more, and the adhesive force of the modified polyvinylidene fluoride becomes poor. When the conductivity of the modified polyvinylidene fluoride is 1.67×10 -4 S / cm to 6.0×10 -4 S / cm, the modified vinylidene fluoride has both good bonding strength and strong ability to conduct lithium ions, thereby improving the rate performance of the energy storage device.

[0031] In some embodiments, the modified polyvinylidene fluoride has the structural formula:

[0032] Wherein, R is H or an electron-withdrawing group, and the electron-withdrawing group is CN or F, etc. The modified polyvinylidene fluoride has polyvinylidene fluoride as the main chain, and the length of the molecular chain can be made very long, and the molecular weight is high, which will not affect the adhesive force of the modified polyvinylidene fluoride.

[0033] Furthermore, when R is CN or F, CN or F is a strong electron-withdrawing group, which enhances the degree of electron delocalization, making Li+ more easily dissociated, thereby making the modified polyvinylidene fluoride have a stronger ability to conduct lithium ions.

[0034] In some embodiments, the weight average molecular weight of the modified polyvinylidene fluoride ranges from 500,000 to 800,000. Specifically, the weight average molecular weight of the modified polyvinylidene fluoride can be 500,000, 550,000, 600,000, 650,000, 700,000, 750,000, 800,000, and any value therebetween.

[0035] When the weight-average molecular weight of the modified polyvinylidene fluoride is less than 500,000, the adhesive force of the modified polyvinylidene fluoride is low. When the weight-average molecular weight of the modified polyvinylidene fluoride is greater than 800,000, the solubility of the modified polyvinylidene fluoride is low and the processing performance is poor. When the weight-average molecular weight of the modified polyvinylidene fluoride is between 500,000 and 800,000, the adhesive force of the modified polyvinylidene fluoride is good, the solubility is also high, and the processing performance is good.

[0036] In some embodiments, the copolymer is a random copolymer. In other words, the modified polyvinylidene fluoride is a random copolymer of vinylidene fluoride and lithium 4-vinyl-4'-substituted-bisbenzenesulfonyl imide.

[0037] The modified polyvinylidene fluoride is prepared by random copolymerization, and the synthesis process is simple and the cost is low.

[0038] In some embodiments, the median particle size of the modified polyvinylidene fluoride ranges from 0.5 μm to 1.5 μm. Specifically, the median particle size of the modified polyvinylidene fluoride can be 0.5 μm, 0.7 μm, 0.9 μm, 1.1 μm, 1.3 μm, 1.5 μm, and any value therebetween.

[0039] When the median particle size of the modified polyvinylidene fluoride is less than 0.5 μm, the modified polyvinylidene fluoride particles are too small and easily clump together during dissolution, encapsulating the particles inside, making it difficult to dissolve and affecting processing performance. When the median particle size of the modified polyvinylidene fluoride is greater than 1.5 μm, the modified polyvinylidene fluoride is difficult to dissolve, affecting processing performance. When the median particle size of the modified polyvinylidene fluoride is between 0.5 μm and 1.5 μm, the modified polyvinylidene fluoride is easier to dissolve and has good processing performance.

[0040] Referring to FIG1 , a second embodiment of the present application provides a method for preparing modified polyvinylidene fluoride, which comprises:

[0041] S201, providing lithium 4-vinyl-4'-substituted-bisbenzenesulfonyl imide and vinylidene fluoride; and

[0042] Optionally, the substituent in the lithium 4-vinyl-4'-substituted-bisbenzenesulfonyl imide may be, but is not limited to, -H, -CN or -F.

[0043] S202, copolymerizing 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium with vinylidene fluoride to obtain modified polyvinylidene fluoride, wherein the mass fraction of 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium in the modified vinylidene fluoride ranges from 2% to 10%.

[0044] The modified polyvinylidene fluoride is a copolymer of vinylidene fluoride and lithium 4-vinyl-4'-substituted-bisbenzenesulfonyl imide. The lithium bisbenzenesulfonyl imide groups are introduced into the polyvinylidene fluoride molecular chain through random copolymerization. The ends of the lithium sulfonyl imide are chemically bonded to benzene rings with a high degree of negative charge delocalization, enhancing the electron delocalization of the entire structure. This facilitates the dissociation of Li+, resulting in a strong lithium ion conductivity in the modified polyvinylidene fluoride. The mass fraction of the lithium 4-vinyl-4'-substituted-bisbenzenesulfonyl imide ranges from 2% to 10%. The modified polyvinylidene fluoride exhibits both good bonding strength and strong lithium ion conductivity, improving the rate performance of energy storage devices.

[0045] Furthermore, the reaction formula for the copolymerization reaction of the 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium and vinylidene fluoride is as follows:

[0046] In some embodiments, 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium is copolymerized with vinylidene fluoride to obtain modified polyvinylidene fluoride, comprising:

[0047] S2011, introducing a first mass of vinylidene fluoride gas into a reaction container, and polymerizing the vinylidene fluoride at a first temperature of 40° C. to 60° C. and a first pressure of 3.2 MPa to 3.7 MPa; and

[0048] Optionally, the copolymerization reaction of 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium and vinylidene fluoride to obtain modified polyvinylidene fluoride further comprises: adding an initiator, a chain transfer agent and a dispersant into the reaction container.

[0049] Optionally, the initiator may be a low temperature initiator, a medium temperature initiator, or a high temperature initiator. Specifically, the medium temperature initiator may be, but is not limited to, diisopropyl peroxydicarbonate.

[0050] Optionally, the chain transfer agent may be, but is not limited to, acetone.

[0051] Optionally, the dispersant may be a cellulose ether dispersant or a polyvinyl alcohol dispersant.

[0052] S2012, introducing a second mass of vinylidene fluoride gas and 4-vinyl-4'-substituted-bis-benzenesulfonyl imide lithium into a reaction vessel, and causing the vinylidene fluoride and 4-vinyl-4'-substituted-bis-benzenesulfonyl imide lithium to undergo a copolymerization reaction under the initiation of an initiator at a second temperature of 40°C to 60°C and a second pressure of 3.2 MPa to 3.7 MPa to form modified polyvinylidene fluoride; wherein the mass ratio of the first mass of vinylidene fluoride to the second mass of vinylidene fluoride is in the range of 0.1 to 0.25.

[0053] First, a first mass of vinylidene fluoride gas is introduced into a reaction vessel (such as a stainless steel autoclave) to cause a polymerization reaction. Then, a second mass of vinylidene fluoride gas and 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium are added to obtain modified polyvinylidene fluoride by seed polymerization, thereby obtaining a moderate particle size and a narrow particle size distribution with good processing performance.

[0054] Specifically, the first temperature may be 40°C, 45°C, 50°C, 55°C, 60°C, or any value in between.

[0055] When the first temperature is less than 40°C, the polymerization reaction is slow. When the first temperature is greater than 60°C, the initiator is too active, the polymerization reaction is too fast, and implosion is likely to occur, resulting in a large amount of gel. When the first temperature is between 40°C and 60°C, the polymerization reaction speed is appropriate.

[0056] Specifically, the first pressure can be 3.2 MPa, 3.3 MPa, 3.4 MPa, 3.5 MPa, 3.6 MPa, 3.7 MPa, and any value in between.

[0057] When the first pressure is less than 3.2 MPa, the amount of vinylidene fluoride gas introduced is relatively small, the polymerization reaction is vigorous, and implosion is likely to occur, resulting in the production of a large amount of gel. When the first pressure is greater than 3.2 MPa, the amount of vinylidene fluoride gas introduced is relatively large, which may damage the generated seeds. When the first pressure is between 3.2 MPa and 3.7 MPa, the polymerization reaction is less likely to implode, thus preventing the production of gel and the generation of seeds.

[0058] Specifically, the second temperature may be 40°C, 45°C, 50°C, 55°C, 60°C, or any value in between.

[0059] When the second temperature is less than 40°C, the copolymerization reaction is slow. When the second temperature is greater than 60°C, the initiator is too active, the copolymerization reaction is too fast, and implosion is likely to occur, resulting in the formation of a large amount of gel. When the second temperature is between 40°C and 60°C, the copolymerization reaction speed is appropriate.

[0060] Specifically, the second pressure can be 3.2 MPa, 3.3 MPa, 3.4 MPa, 3.5 MPa, 3.6 MPa, 3.7 MPa, and any value in between.

[0061] When the second pressure is less than 3.2 MPa, the amount of vinylidene fluoride gas introduced is relatively small, resulting in a vigorous copolymerization reaction and a high probability of implosion, which can produce a large amount of gel. When the second pressure is greater than 3.2 MPa, the amount of vinylidene fluoride gas introduced is relatively large, which can easily damage the generated seeds. When the second pressure is between 3.2 MPa and 3.7 MPa, the copolymerization reaction is less likely to implode, thus avoiding the formation of gel and also preventing the generated seeds from being damaged.

[0062] Specifically, the mass ratio of the first mass of vinylidene fluoride to the second mass of vinylidene fluoride is 0.1, 0.15, 0.2, 0.25, and any value in between.

[0063] When the mass ratio of the first mass of vinylidene fluoride to the second mass of vinylidene fluoride is less than 0.1, the particles of the modified polyvinylidene fluoride obtained are larger, resulting in poor dissolution during use. When the mass ratio of the first mass of vinylidene fluoride to the second mass of vinylidene fluoride is greater than 0.25, the particles of the modified polyvinylidene fluoride obtained are smaller, resulting in poor dissolution during use. When the mass ratio of the first mass of vinylidene fluoride to the second mass of vinylidene fluoride is between 0.1 and 0.25, the particle size of the modified polyvinylidene fluoride obtained is suitable and has good processing performance.

[0064] In some embodiments, the preparation of the lithium 4-vinyl-4'-substituted-bisbenzenesulfonyl imide comprises:

[0065] The p-substituted benzenesulfonamide and p-styrenesulfonyl chloride are mixed and reacted at a third temperature of 10° C. to 30° C. to form lithium 4-vinyl-4'-substituted-bisbenzenesulfonyl imide, wherein the molar ratio of the p-substituted benzenesulfonamide to the p-styrenesulfonyl chloride is 0.9 to 1.1.

[0066] Furthermore, the reaction formula for the preparation of the lithium 4-vinyl-4'-substituted-bisbenzenesulfonyl imide is as follows:

[0067] A third embodiment of the present application provides an active material composition, which includes: active particles, a conductive agent, and a binder, wherein the binder is the modified polyvinylidene fluoride described in the embodiment of the present application.

[0068] Optionally, the active particles include one or more of transition metal oxides, polyanionic compounds, and Prussian blue materials.

[0069] Optionally, the conductive agent may be, but is not limited to, acetylene black, conductive carbon black, carbon nanotubes, carbon fibers, graphene, and the like.

[0070] Please refer to Figures 2 and 3. The fourth embodiment of the present application provides a positive electrode sheet 100, which includes: a current collector 110 and an active material layer 120. The active material layer 120 is arranged on the surface of the current collector 110, and the active material layer 120 includes the active material composition described in the embodiment of the present application.

[0071] Optionally, in some embodiments, the current collector 110 may be, but is not limited to, aluminum foil.

[0072] It can be understood that the active material layer 120 is obtained by dispersing the active material composition described in the embodiment of the present application in a solvent to prepare a slurry, which is then coated on the current collector 110 .

[0073] Please refer to Figures 4 and 5. The fifth embodiment of the present application provides an energy storage device 200, which includes: an electrolyte, a negative electrode plate 220, a diaphragm 210 and the positive electrode plate 100 described in the embodiment of the present application, the negative electrode plate 220 is at least partially immersed in the electrolyte, the diaphragm 210 is located on one side of the negative electrode plate 220 and is at least partially immersed in the electrolyte, and the positive electrode plate 100 is arranged on the side of the diaphragm 210 away from the negative electrode plate 220 and is at least partially immersed in the electrolyte.

[0074] The energy storage device 200 of the embodiment of the present application may be, but is not limited to, a lithium-ion secondary energy storage device 200 , a lithium-ion primary energy storage device 200 , a lithium-sulfur energy storage device 200 , or the like.

[0075] It is understandable that the energy storage device 200 may be, but is not limited to, a battery cell, a battery module, a battery pack, etc.

[0076] Optionally, the diaphragm 210 may be, but is not limited to, at least one of a polypropylene film (PP) and a polyethylene film (PE).

[0077] Optionally, the electrolyte includes electrolyte salt, solvent and additives.

[0078] The electrolyte is a medium for active ion migration and charge transfer, and plays a role in conducting ions between the positive electrode plate 100 and the negative electrode plate 220 of the energy storage device 200 .

[0079] Optionally, the solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, methyl acetate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, sulfolane, and dimethyl sulfoxide. Using these substances as solvents can dissolve more electrolyte salts, resulting in the electrolyte having higher conductivity and viscosity, which is beneficial for improving the dynamic performance of the energy storage device 200.

[0080] Optionally, the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalatoborate), and lithium difluorooxalatoborate. When these materials are used as electrolyte salts, they release a large amount of active ions after being dissolved in a solvent. The active ions migrate between the positive electrode sheet 100 and the negative electrode sheet 220 to realize the charge and discharge process of the energy storage device 200.

[0081] Optionally, in some specific embodiments, the active ions are at least one of lithium ions and sodium ions.

[0082] Optionally, the additive includes at least one of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, vinyl sulfite, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, 1,3-propane sultone, and the like. Using these materials as additives can improve the performance of the electrolyte, facilitate the formation of electrode protective films (passivation films of the negative electrode plate 220 and the positive electrode plate 100), prevent thermal runaway of the energy storage device 200, and prevent overcharging, thereby enhancing the stability and safety of the energy storage device 200.

[0083] Optionally, the negative electrode plate 220 includes a negative electrode current collector 110 and a negative electrode active material layer 120 covering the surface of the negative electrode current collector 110 . The negative electrode current collector 110 may be, but is not limited to, copper foil.

[0084] Examples 1 to 3 and Comparative Examples 1 and 2

[0085] 1) Preparation of lithium 4-vinyl-4'-cyano-bisbenzenesulfonyl imide:

[0086] Under an argon atmosphere, 4.01 g of p-cyanobenzenesulfonamide was added to 10 ml of acetonitrile solution, followed by the addition of 2.69 g of dimethylaminopyridine and 6.68 g of triethylamine. The mixture was evenly dispersed and then cooled to 0°C to obtain a mixed acetonitrile solution. P-styrenesulfonyl chloride in an equal molar ratio to p-cyanobenzenesulfonamide was dissolved in acetonitrile and added dropwise to the mixed acetonitrile solution. After the addition was complete, the mixture was heated to room temperature and reacted for 24 hours to obtain 4-vinyl-4'-cyano-bisbenzenesulfonyl imide, which was then neutralized with a lithium hydroxide aqueous solution to obtain lithium 4-vinyl-4'-cyano-bisbenzenesulfonyl imide.

[0087] 2) Preparation of modified polyvinylidene fluoride:

[0088] In the first step, 300 g of deionized water and 0.5% of the monomer weight of a dispersant were added to a 500 ml stainless steel autoclave;

[0089] In the second step, the reactor was sealed, evacuated and filled with nitrogen, the temperature was raised to 50°C, 20% vinylidene fluoride was added to increase the pressure of the reactor to 3.5 MPa, and the initiator (diisopropyl peroxydicarbonate) and chain transfer agent (acetone) were added to start the polymerization reaction;

[0090] In the third step, the remaining 80% of the vinylidene fluoride, the initiator, and lithium 4-vinyl-4'-cyano-bisbenzenesulfonyl imide are added at a certain rate, and the temperature and pressure are maintained until the vinylidene fluoride is added and the pressure drops to 2.8 MPa. The copolymerization reaction is completed to obtain modified polyvinylidene fluoride. The mass fraction of the lithium 4-vinyl-4'-cyano-bisbenzenesulfonyl imide is shown in Table 1:

[0091] 3) Preparation of positive electrode sheet 100:

[0092] The positive electrode active material lithium iron phosphate (LFP) particles, modified polyvinylidene fluoride, and conductive agent super carbon black (SP) were dispersed in N-methylpyrrolidone (NMP) at a mass ratio of 93:5:2 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was coated on the current collector 110 aluminum foil. The coating weight of the positive electrode slurry was 254 mg / 1540.25 mm 2 After drying, rolling and punching, the positive electrode sheet 100 is obtained.

[0093] 4) Preparation of negative electrode sheet 220: A circular lithium sheet is used.

[0094] 5) Preparation of the diaphragm 210:

[0095] A 16 μm polyethylene film is used as the separator 210 .

[0096] 6) Preparation of electrolyte:

[0097] The organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain a mixed solvent, and then dry lithium salt LiPF6 is added thereto to prepare an electrolyte with a concentration of 1 mol / L.

[0098] 7) Preparation of energy storage device 200: The positive electrode sheet 100, separator 210, and negative electrode sheet 220 are stacked in order and placed in a button battery casing in sequence, so that the separator 210 is located between the positive and negative electrodes to act as an insulator. After assembling them, two drops of electrolyte are dripped into the button battery, and the button battery lid is covered to obtain the energy storage device 200 described in Examples 1 to 3 and Comparative Examples 1 and 2.

[0099] Example 4

[0100] 1) Preparation of lithium 4-vinyl bisbenzenesulfonyl imide:

[0101] Under an argon atmosphere, 4.01 g of benzenesulfonamide was added to 10 ml of acetonitrile solution, followed by the addition of 2.69 g of dimethylaminopyridine and 6.68 g of triethylamine. The mixture was evenly dispersed and then cooled to 0°C to obtain a mixed acetonitrile solution. P-styrenesulfonyl chloride in an equal molar ratio to benzenesulfonamide was dissolved in acetonitrile and added dropwise to the mixed acetonitrile solution. After the addition was complete, the mixture was heated to room temperature and reacted for 24 hours to obtain 4-vinylbisbenzenesulfonyl imide, which was then neutralized with a lithium hydroxide aqueous solution to obtain lithium 4-vinylbisbenzenesulfonyl imide.

[0102] 2) Preparation of modified polyvinylidene fluoride:

[0103] In the first step, 300 g of deionized water and 0.5% of the monomer weight of a dispersant were added to a 500 ml stainless steel autoclave;

[0104] In the second step, the reactor was sealed, evacuated and filled with nitrogen, the temperature was raised to 50°C, 20% vinylidene fluoride was added to increase the pressure of the reactor to 3.5 MPa, and the initiator (diisopropyl peroxydicarbonate) and chain transfer agent (acetone) were added to start the polymerization reaction;

[0105] In the third step, the remaining 80% of the vinylidene fluoride, the initiator, and lithium 4-vinyl bisbenzenesulfonyl imide are added at a certain rate, and the temperature and pressure are maintained until the vinylidene fluoride is added and the pressure drops to 2.8 MPa. The copolymerization reaction is completed to obtain modified polyvinylidene fluoride. The mass fraction of the lithium 4-vinyl bisbenzenesulfonyl imide is shown in Table 1:

[0106] 3) Preparation of the positive electrode sheet 100: the same as the preparation of the positive electrode sheet 100 in Example 1.

[0107] 4) Preparation of the negative electrode sheet 220: The preparation of the negative electrode sheet 220 is the same as that in Example 1.

[0108] 5) Preparation of the diaphragm 210: The preparation of the diaphragm 210 is the same as that in Example 1.

[0109] 6) Preparation of electrolyte: the same as the preparation of electrolyte in Example 1.

[0110] 7) Preparation of the energy storage device 200: The preparation is the same as that of the energy storage device 200 in Example 1.

[0111] Performance Testing

[0112] 1) Infrared test

[0113] The modified polyvinylidene fluoride was dissolved into a film using a Fourier transform infrared spectrometer, and the infrared spectrum curve of the modified polyvinylidene fluoride was tested using attenuated total reflection.

[0114] 2) MRI test

[0115] The test was carried out using a nuclear magnetic resonance spectrometer.

[0116] The modified polyvinylidene fluoride was dissolved in dimethyl sulfoxide (DMSO), and the H spectrum of the nuclear magnetic resonance spectrum was tested to obtain the H spectrum chemical shift value in the benzene ring.

[0117] 3) Conductivity test

[0118] The modified polyvinylidene fluoride was dissolved in NMP to prepare a glue solution with a solid content of 8%. After vacuum degassing, the glue solution was coated on aluminum foil, dried and cut into 12 mm small discs to obtain a polymer film.

[0119] The obtained polymer film is prepared into a button battery: a steel sheet, a polymer film, and a steel sheet are stacked in sequence to assemble into a steel-to-steel ion-blocking button battery.

[0120] The electrochemical impedance spectroscopy of the obtained buckle was tested using an electrochemical workstation with a scanning frequency ranging from 1 Hz to 10 MHz, and the lithium ion conductivity of the polymer film was obtained by Nyquist fitting.

[0121] 4) Positive electrode sheet 100 peeling force test

[0122] The positive electrode sheet 100 is cut into strips of 15×150 mm and peeled 180° using a tensile testing machine at a speed of 50 mm / min and a peeling length of 100 mm. After the test is completed, the peeling force can be obtained.

[0123] 5) Rate performance of the energy storage device 200

[0124] The energy storage device 200 obtained in the above embodiment was subjected to a rate test on a charge-discharge instrument at a test temperature of 25°C. The device was cycled three times at a rate of 0.5C (i.e., both the charge rate and the discharge rate were 0.5C), and the third discharge capacity was recorded as C1. The device was then fully charged at a rate of 0.5C and discharged at a rate of 2C, with the discharge capacity recorded as C2. The 2C rate capacity retention ratio was C2 / C1.

[0125] 6) Electrochemical impedance spectroscopy (EIS) test

[0126] At 25° C., the energy storage device 200 obtained in the above embodiment was connected to an electrochemical workstation, and an electrochemical impedance spectroscopy curve was obtained by scanning from a high frequency of 800 kHz to a low frequency of 50 MHz with an AC amplitude of 10 mV.

[0127] The performance test data of Examples 1 to 4 and Comparative Examples 1 to 2 are shown in Table 1 and Table 2:

[0128] Table 1:

[0129] Table 2:

[0130] It can be seen from the data of Comparative Example 1, Comparative Example 2 and Examples 1 to 3 that as the mass fraction of 4-vinyl-4'-cyano-bisbenzenesulfonyl imide lithium increases, the conductivity of the modified polyvinylidene fluoride continues to increase and the peeling force of the positive electrode sheet 100 decreases. When the mass fraction of the 4-vinyl-4'-cyano-bisbenzenesulfonyl imide lithium is between 2% and 10%, the modified polyvinylidene fluoride can take into account both higher conductivity and good peeling force of the positive electrode sheet 100, thereby making the energy storage device 200 have good rate performance.

[0131] From the data of Example 2 and Example 4, it can be seen that the conductivity of the modified PVDF obtained using lithium 4-vinylbisbenzenesulfonyl imide is slightly worse than that of the modified PVDF obtained using lithium 4-vinyl-4'-cyano-bisbenzenesulfonyl imide. This is because CN is a strong electron-withdrawing group, which enhances the degree of electron delocalization, making Li+ more easily dissociated, thereby making the modified polyvinylidene fluoride have a stronger ability to conduct lithium ions.

[0132] The electrochemical impedance spectroscopy curves of the energy storage device 200 of Example 1, Example 2 and Comparative Example 1 are shown in FIG6 :

[0133] As can be seen from Figure 6, as the content of 4-vinyl-4'-cyano-bisbenzenesulfonyl imide lithium added to the modified PVDF increases, Rs in the energy storage device 200 does not change significantly, and Rct gradually decreases, indicating that 4-vinyl-4'-cyano-bisbenzenesulfonyl imide lithium has a significant effect on improving the transmission of lithium ions and can reduce the polarization of the energy storage device 200.

[0134] Mentioning "embodiments" and "implementation methods" in this application means that the specific features, structures or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrases in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments. In addition, it should be understood that the features, structures or characteristics described in the various embodiments of the present application can be arbitrarily combined to form another embodiment that does not deviate from the spirit and scope of the technical solution of the present application, unless there is a contradiction between them.

[0135] Finally, it should be noted that the above implementation modes are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the above preferred implementation modes, ordinary technicians in this field should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A modified polyvinylidene fluoride, wherein: The modified polyvinylidene fluoride is a copolymer of vinylidene fluoride and 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium. In the modified polyvinylidene fluoride, the mass fraction of the 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium is in the range of 2% to 10%.

2. The modified polyvinylidene fluoride according to claim 1, wherein The conductivity of the modified polyvinylidene fluoride is 1.67×10 -4 S / cm to 6.0×10 -4 S / cm.

3. The modified polyvinylidene fluoride according to claim 1, wherein The structural formula of the modified polyvinylidene fluoride is: Wherein, R is H or an electron-withdrawing group, and the electron-withdrawing group is CN or F.

4. The modified polyvinylidene fluoride according to claim 1, wherein The weight average molecular weight of the modified polyvinylidene fluoride is in the range of 500,000 to 800,000.

5. The modified polyvinylidene fluoride according to claim 1, wherein The median particle size of the modified polyvinylidene fluoride is in the range of 0.5 μm to 1.5 μm.

6. A method for preparing modified polyvinylidene fluoride, wherein: include: Providing 4-vinyl-4'-substituted-bis-benzenesulfonyl imide lithium and vinylidene fluoride; as well as The 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium is copolymerized with vinylidene fluoride to obtain modified polyvinylidene fluoride, wherein the mass fraction of the 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium in the modified polyvinylidene fluoride is in the range of 2% to 10%.

7. The method for preparing modified polyvinylidene fluoride according to claim 6, wherein: The method of copolymerizing 4-vinyl-4'-substituted-bisbenzenesulfonyl imide lithium with vinylidene fluoride to obtain modified polyvinylidene fluoride comprises: Passing a first mass of vinylidene fluoride gas into a reaction container, at a first temperature of 40° C. to 60° C. and a first pressure of 3.2 MPa to 3.7 MPa, to polymerize the vinylidene fluoride; and A second mass of vinylidene fluoride gas and 4-vinyl-4'-substituted-bis-benzenesulfonyl imide lithium are introduced into a reaction container, and the vinylidene fluoride and 4-vinyl-4'-substituted-bis-benzenesulfonyl imide lithium are copolymerized under the initiation of an initiator at a second temperature of 40° C. to 60° C. and a second pressure of 3.2 MPa to 3.7 MPa to form modified polyvinylidene fluoride; wherein the second mass of vinylidene fluoride gas and 4-vinyl-4'-substituted-bis-benzenesulfonyl imide lithium are copolymerized at a second temperature of 40° C. to 60° C. and a second pressure of 3.2 MPa to 3.7 MPa to form modified polyvinylidene fluoride; The mass ratio of the first mass of vinylidene fluoride to the second mass of vinylidene fluoride ranges from 0.1 to 0.

25.

8. The method for preparing modified polyvinylidene fluoride according to claim 6, wherein: The preparation of the 4-vinyl-4'-substituted-bis-benzenesulfonyl imide lithium comprises: The p-substituted benzenesulfonamide and p-styrenesulfonyl chloride are mixed and reacted at a third temperature of 10° C. to 30° C. to form 4-vinyl-4'-substituted-bis-benzenesulfonyl imide lithium, wherein the molar ratio of the p-substituted benzenesulfonamide to the p-styrenesulfonyl chloride is 0.9 to 1.

1.

9. An active material composition, wherein: The active material composition comprises: Active particles; Conductive agent; and The binder is the modified polyvinylidene fluoride according to any one of claims 1 to 5.

10. A positive electrode sheet, wherein: include: current collector; as well as An active material layer, wherein the active material layer is disposed on the surface of the current collector, and the active material layer comprises the active material composition according to claim 9.

11. An energy storage device, wherein: include: Electrolyte; A negative electrode plate, wherein the negative electrode plate is at least partially immersed in the electrolyte; A diaphragm, located on one side of the negative electrode plate and at least partially immersed in the electrolyte; as well as The positive electrode plate as described in claim 10 is arranged on the side of the diaphragm away from the negative electrode plate and is at least partially immersed in the electrolyte.

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