Electrolyte-resistant high-fluorine-content fluororubber for lithium battery

Abstract

The present disclosure belongs to the technical field of new energy battery materials. Provided is an electrolyte-resistant high-fluorine-content fluororubber for a lithium battery. Specifically, vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene are used as polymerization monomers, and in a deoxidized high-purity water environment, a pH buffer agent, a chain transfer agent and an initiator are added thereto to perform a polymerization reaction, so as to prepare a raw rubber. The fluororubber raw rubber prepared by means of the method has a high fluorine content. An electrolyte-resistant high-fluorine-content fluororubber for a lithium battery is prepared by taking the high-fluorine-content fluororubber raw rubber as a raw material, adding a series of auxiliaries and mixing same for compounding, and is thus suitable for the field of sealing elements of power batteries.

Description

A high-fluorine-content fluororubber for lithium batteries, resistant to electrolyte.

[0001] Cross-reference to related applications

[0002] This disclosure is based on and claims priority to Chinese Patent Application No. 202411518556.X, filed on October 29, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of new energy battery materials technology, and in particular to a high-fluorine-content fluororubber for lithium batteries that is resistant to electrolytes. Background Technology

[0004] Electrolytes significantly impact the performance of lithium-ion batteries, and high-performance electrolyte rubber seals are crucial for their proper operation. The complex composition of electrolytes necessitates high-quality seal materials. Currently, seal materials primarily include peroxy-fluorinated rubber, nitrile rubber, perfluoroether rubber, and silicone rubber. Among these, peroxy-fluorinated rubber stands out due to its low compression set, excellent insulation properties, and low electrolyte volume expansion rate. Peroxy-fluorinated rubber is currently widely used in the sealing components of power batteries. However, with the rapid development of the power battery industry, the performance requirements for peroxy-fluorinated rubber are becoming increasingly stringent, especially its resistance to electrolytes. Therefore, there is an urgent need to develop a new method for preparing peroxy-fluorinated rubber to meet the demand for seal products suitable for different lithium-ion electrolyte environments.

[0005] Patent document CN115584141A discloses a bisphenol A high-fluorine fluororubber compound resistant to lithium battery electrolyte and its preparation method. The main improvement lies in using a dechlorinated bisphenol AF salt vulcanizing agent and the functional additive N325 carbon black to reduce compression set. The compound is prepared by using a pre-mixed bisphenol A high-fluorine rubber, thus reducing the volume expansion rate of the high-fluorine fluororubber in the electrolyte. Using bisphenol A high-fluorine fluororubber with a fluorine content of 70%–71% and the improved method, the resulting compound exhibits a high-temperature (200℃ × 70h) compression set of 19%–24% and a volume expansion rate in the electrolyte of 22%–29%. However, the volume resistivity of the lithium battery sealing component is relatively low (2.2 × 10⁻⁶). 10 Ω·cm~1.4×10 12 (Ω·cm), which cannot meet the requirements for electrolyte resistance.

[0006] Patent document CN111269511A discloses an insulating fluororubber material for sealing lithium batteries and its preparation method. The main improvement lies in using 0.75wt%–2.5wt% silica and / or barium sulfate as the insulating medium during compounding, resulting in a compound with excellent electrolyte resistance and a volume resistivity of 2 × 10⁻⁶. 12 The pressure is above Ω·cm, and the compression set at high temperature (200℃×70h) is below 20%, which meets the insulation and high temperature resistance requirements of the seal. However, the expansion rate after immersion in electrolyte is relatively high (volume expansion rate is 30%~35%, mass expansion rate is 15%~20%), which affects the performance of the seal.

[0007] For the electrolyte-resistant fluororubber currently required, the following requirements must be met: low high-temperature compression set, high material volume resistivity, low immersion volume expansion, and good vulcanization and physical-mechanical properties. However, the compounded fluororubbers disclosed in relevant patents cannot simultaneously achieve these excellent properties, resulting in each product being unsuitable for various lithium battery electrolyte environments. There is an urgent need to find a new preparation method that can improve the overall performance of fluororubber products.

[0008] In view of this, this disclosure proposes a high-fluorine-content fluororubber for lithium batteries that is resistant to electrolytes. Summary of the Invention

[0009] This disclosure aims to at least partially address one of the technical problems in the related art.

[0010] Therefore, the first objective of this disclosure is to provide a method for preparing fluororubber raw rubber with high fluorine content, which can produce fluororubber raw rubber with high fluorine content and excellent electrical properties.

[0011] The second objective of this disclosure is to provide a method for preparing a high-fluorine-content fluororubber resistant to electrolytes for lithium batteries. Using the aforementioned high-fluorine-content fluororubber raw material as raw material, a series of additives are mixed and compounded. The resulting fluororubber exhibits a high-temperature compression set (200℃×70h) ≤20% and a material volume resistivity ≥2.4×10⁻⁶. 12 Ω·cm, immersion volume expansion rate ≤30%, suitable for sealing components of power batteries.

[0012] To achieve the above objectives, the present disclosure adopts the following technical solution:

[0013] A high-fluorine-content fluororubber resistant to electrolyte for lithium batteries, characterized by comprising the following steps:

[0014] S1: According to the weight ratio, add 600-800 parts of deoxygenated high-purity water, 0.5-2 parts of pH buffer, and 0.1-1 parts of chain transfer agent to the polymerization reactor. Turn on the stirring and stir at 100-200 rpm. Heat the polymerization reactor to 60-100℃. Introduce the first mixed gas of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene until the pressure in the polymerization reactor is 2000-3000 kPa. Add 0.1-1 parts of initiator to initiate the copolymerization reaction.

[0015] S2: After polymerization begins, a second mixed gas of vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene is introduced to maintain the pressure of the polymerization reactor at 2000-3000 kPa. When the consumption of the second mixed monomer reaches 150-250 parts, the copolymerization reaction is terminated, the polymerization reactor is depressurized and discharged, and 20-30 parts of coagulant are added to the obtained emulsion for coagulation and washing. The emulsion is then dried in an oven to obtain raw rubber.

[0016] S3: Prepare the following compounding components: 100 parts raw rubber; 1-2 parts vulcanizing agent; 3-4 parts vulcanizing aid; 20-30 parts filler material MT carbon black N9900; 0.6-6 parts processing aid. Add the above components to a mixer and mix. After standing at room temperature for 15-30 hours, re-mill on a two-roll mill. The final electrolyte-resistant peroxyfluorinated rubber is obtained.

[0017] Furthermore, the pH buffer is selected from one of dipotassium hydrogen phosphate, potassium dihydrogen phosphate, and disodium hydrogen phosphate.

[0018] Furthermore, the chain transfer agent is selected from one or more mixtures of ethers, ketones, aromatics, and alkanes, including diethyl ether, propylene oxide, methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, isobutane, and cyclopropane.

[0019] Furthermore, the initiator is selected from one or more mixtures of organic and inorganic peroxides, including hydrogen peroxide, ammonium persulfate, potassium persulfate, tert-butyl hydroperoxide, di-tert-butane peroxide, and benzoyl peroxide.

[0020] Furthermore, an initiator synergist is added in step S1 to participate in the polymerization, and its preparation method is as follows:

[0021] a: Weigh 3-6 parts by weight of p-mercaptoterephthalic acid and 10-20 parts by weight of titanium tetrachloride, place them in a sealed reaction vessel, purge with nitrogen to replace the air, then add 100-150 parts by weight of ethanol and mix and stir; pour the mixture into a hydrothermal reaction vessel, place it in an oven, adjust the oven temperature to 200-220℃, after crystallization, take it out, let it stand and cool naturally to room temperature to obtain the precursor;

[0022] b: Weigh 5-10 parts of the precursor, 100-150 parts of toluene, 0.03-0.7 parts of dicyclopentene methacrylate, and 2-5 parts of sodium ethoxide by weight, place them in a sealed reaction vessel, purge with nitrogen to replace the air, adjust the temperature to 60-75℃, and heat for 30-100 minutes; then add 2-6 parts of titanium tetrachloride and heat for 30-60 minutes; remove the toluene by distillation, and dry to obtain the initiator synergist.

[0023] Furthermore, the amount of the initiating synergist added is 0.1-5 wt% of the initiator, optionally 0.5-2 wt%.

[0024] Furthermore, the molar ratio of hexafluoropropylene, vinylidene fluoride, and tetrafluoroethylene in the first mixture is 5–20:50–70:20–30; and the molar ratio of hexafluoropropylene, vinylidene fluoride, and tetrafluoroethylene in the second mixture is 15–30:30–50:30–60.

[0025] Furthermore, the coagulant is one or more mixtures of low-valent metal chlorides.

[0026] Further, the vulcanizing agent is one or a mixture of triallyl isocyanurate, dicumyl peroxide, and 1,3-bis(tert-butylperoxyisopropyl)benzene.

[0027] Further, the vulcanizing aid is one or a mixture of trimethylolpropane trimethacrylate, triallyl isocyanurate, and 2,5-di-tert-butylperoxide-2,5-dimethylethane.

[0028] Furthermore, the processing aid is one or more mixtures of fatty acid derivatives and silicones, palm wax, and stearic acid.

[0029] The synthesis principle of the synergist in this disclosure is as follows:

[0030] (1) Reaction of mercaptoterephthalic acid with titanium tetrachloride yields a mercaptoorganotitanium metal framework, which then undergoes a mercapto-olefin addition reaction with dicyclopentene methacrylate, followed by a secondary complexation with titanium tetrachloride to obtain a dicyclopenteneorganotitanium metal framework.

[0031] (2) The metal free radical that initiates the synergist is a stable free radical, which couples with the chain growth free radical to form an oxidized organometallic complex. The organometallic complex that initiates the synergist is equivalent to the chain transfer agent; it dominates the polymerization process and controls the free radical polymerization process of olefin monomers.

[0032] Compared with related technologies, the electrolyte-resistant, high-fluorine-content fluororubber for lithium batteries prepared according to the embodiments of this disclosure has the following beneficial effects:

[0033] 1. The high-fluorine peroxy fluororubber prepared in this disclosure has excellent vulcanization and physical and mechanical properties, with a fluorine content of 70%-71%, a TC90 time of ≤2.5 min, a tensile strength of ≥20 MPa, and an elongation at break of ≥220%.

[0034] 2. The high-fluorine peroxyfluororubber prepared in this disclosure exhibits excellent electrolyte resistance and is suitable for use in sealing components of power batteries. Its high-temperature compression set (200℃×70h) is ≤20%, and its volume resistivity is ≥2.4×10⁻⁶. 12 Ω·cm, soaking volume expansion rate ≤30%.

[0035] Additional aspects and advantages of this disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this disclosure. Attached Figure Description

[0036] Figure 1 shows the comparative tensile strength curves;

[0037] Figure 2 shows the vulcanization curve of Example 3. Detailed Implementation

[0038] Embodiments of this disclosure are described in detail below, with examples of these embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this disclosure, and should not be construed as limiting it.

[0039] <Example 1>

[0040] A method for preparing a high-fluorine-content fluororubber resistant to electrolyte for lithium batteries includes the following steps:

[0041] S1: In an 80L stainless steel polymerization reactor, add 52kg of deoxygenated high-purity water, 120g of pH buffer disodium hydrogen phosphate, and 35g of chain transfer agent isobutane. Start stirring at 180rpm and heat the polymerization reactor to 70℃. Purge the first mixed gas of hexafluoropropylene, vinylidene fluoride, and tetrafluoroethylene to a pressure of 2400kPa. The molar ratio of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene in the first mixture is 20:50:30. Add 20g of initiator potassium persulfate and 0.2g of initiator synergist mixture to initiate the copolymerization reaction.

[0042] The preparation method of the initiating synergist in this example is as follows:

[0043] a: Weigh 3g of p-mercaptoterephthalic acid and 10g of titanium tetrachloride, place them in a sealed reaction vessel, purge with nitrogen to replace the air, then add 100g of ethanol and mix and stir; pour the mixture into a hydrothermal reaction vessel, place it in an oven, adjust the oven temperature to 200℃, crystallize, remove it, and let it stand and cool naturally to room temperature to obtain the precursor;

[0044] b: Weigh 5g of precursor, 100g of toluene, 0.03g of dicyclopentene methacrylate, and 2g of sodium ethoxide, place them in a sealed reaction vessel, purge with nitrogen to replace the air, adjust the temperature to 60℃, and heat for 30 minutes; then add 2g of titanium tetrachloride and heat for 30 minutes; distill to remove toluene, dry, and obtain the initiator synergist.

[0045] S2: After polymerization begins, a second mixed gas of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene is introduced to maintain the polymerization reactor pressure at 2400 kPa. The molar ratio of hexafluoropropylene, vinylidene fluoride, and tetrafluoroethylene in the second mixture is 20:35:55. When the consumption of the second mixed monomer reaches 15 kg, the copolymerization reaction is terminated, the polymerization reactor is depressurized and discharged, and the resulting emulsion is coagulated and washed with 2 kg of MgCl2 coagulant. After drying in an oven, raw rubber is obtained.

[0046] S3: The following compounding components are prepared: (1) 10 kg raw rubber; (2) 0.15 kg vulcanizing agent triallyl isocyanurate; (3) 0.3 kg vulcanizing aid 2,5-di-tert-butylperoxide-2,5-dimethylethane; (4) 1.5 kg filler MT carbon black N9900; (5) 0.5 kg processing aid octadecanoic acid. The above components are added to a mixer and mixed. After standing at room temperature for 20 h, the mixture is re-milled on a two-roll mill. The final electrolyte-resistant peroxyfluorinated rubber is obtained.

[0047] <Example 2>

[0048] A method for preparing a high-fluorine-content fluororubber resistant to electrolyte for lithium batteries includes the following steps:

[0049] S1: In an 80L stainless steel polymerization reactor, add 52kg of deoxygenated high-purity water, 120g of pH buffer disodium hydrogen phosphate, and 70g of chain transfer agent isobutane. Start stirring at 180rpm and heat the polymerization reactor to 75℃. Purge the first mixed gas of hexafluoropropylene, vinylidene fluoride, and tetrafluoroethylene to a pressure of 2500kPa. The molar ratio of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene in the first mixture is 20:50:30. Add 70g of initiator ammonium persulfate and 0.4g of initiator synergist mixture to initiate the copolymerization reaction.

[0050] The preparation method of the initiating synergist in this example is as follows:

[0051] a: Weigh 4g of p-mercaptoterephthalic acid and 13g of titanium tetrachloride, place them in a sealed reaction vessel, purge with nitrogen to replace the air, then add 115g of ethanol and mix and stir; pour the mixture into a hydrothermal reaction vessel, place it in an oven, adjust the oven temperature to 200℃, crystallize, remove it, and let it stand and cool naturally to room temperature to obtain the precursor;

[0052] b: Weigh 7g of precursor, 115g of toluene, 0.18g of dicyclopentene methacrylate, and 3g of sodium ethoxide, place them in a sealed reaction vessel, purge with nitrogen to replace the air, adjust the temperature to 65℃, and heat for 50 minutes; then add 3g of titanium tetrachloride and heat for 40 minutes; remove toluene by distillation, dry, and obtain the initiator synergist.

[0053] S2: After polymerization begins, a second mixed gas of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene is introduced to maintain the polymerization reactor pressure at 2500 kPa. The molar ratio of hexafluoropropylene, vinylidene fluoride, and tetrafluoroethylene in the second mixture is 20:35:55. When the consumption of the second mixed monomer reaches 15 kg, the copolymerization reaction is terminated, the polymerization reactor is depressurized and discharged, and the resulting emulsion is coagulated and washed with 2 kg of MgCl2 coagulant. After drying in an oven, raw rubber is obtained.

[0054] S3: The following compounding components are prepared: (1) 10 kg raw rubber; (2) 0.1 kg vulcanizing agent triallyl isocyanurate; (3) 0.3 kg vulcanizing aid 2,5-di-tert-butylperoxide-2,5-dimethylethane; (4) 2 kg filler material MT carbon black N9900; (5) 0.5 kg processing aid octadecanoic acid. The above components are added to a mixer and mixed. After standing at room temperature for 20 h, the mixture is re-milled on a two-roll mill. The final electrolyte-resistant peroxyfluorinated rubber is obtained.

[0055] <Example 3>

[0056] A method for preparing a high-fluorine-content fluororubber resistant to electrolyte for lithium batteries includes the following steps:

[0057] S1: In an 80L stainless steel polymerization reactor, add 52kg of deoxygenated high-purity water, 60g of pH buffer disodium hydrogen phosphate, and 35g of chain transfer agent cyclopropane. Start stirring at 180rpm and heat the polymerization reactor to 70℃. Purge the first mixed gas of hexafluoropropylene, vinylidene fluoride, and tetrafluoroethylene to a pressure of 2400kPa. The molar ratio of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene in the first mixture is 15:60:25. Add 70g of initiator tert-butyl hydroperoxide and 0.7g of initiator synergist mixture to initiate the copolymerization reaction.

[0058] The preparation method of the initiating synergist in this example is as follows:

[0059] a: Weigh 5g of p-mercaptoterephthalic acid and 16g of titanium tetrachloride, place them in a sealed reaction vessel, purge with nitrogen to replace the air, then add 140g of ethanol and mix and stir; pour the mixture into a hydrothermal reaction vessel, place it in an oven, adjust the oven temperature to 220℃, crystallize, remove it, and let it stand and cool naturally to room temperature to obtain the precursor;

[0060] b: Weigh 8g of precursor, 140g of toluene, 0.5g of dicyclopentene methacrylate, and 4g of sodium ethoxide, place them in a sealed reaction vessel, purge with nitrogen to replace the air, adjust the temperature to 70℃, and heat for 65 minutes; then add 5g of titanium tetrachloride and heat for 45 minutes; distill to remove toluene, dry, and obtain the initiator synergist.

[0061] S2: After polymerization begins, a second mixed gas of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene is introduced to maintain the polymerization reactor pressure at 2400 kPa. The molar ratio of hexafluoropropylene, vinylidene fluoride, and tetrafluoroethylene in the second mixture is 25:35:50. When the consumption of the second mixed monomer reaches 15 kg, the copolymerization reaction is terminated, the polymerization reactor is depressurized and discharged, and the resulting emulsion is coagulated and washed with 2 kg of MgCl2 coagulant. After drying in an oven, raw rubber is obtained.

[0062] S3: The following compounding components are prepared: (1) 10 kg raw rubber; (2) 0.15 kg vulcanizing agent triallyl isocyanurate; (3) 0.3 kg vulcanizing aid 2,5-di-tert-butylperoxide-2,5-dimethylethane; (4) 1.5 kg filler MT carbon black N9900; (5) 0.55 kg processing aid octadecanoic acid. The above components are added to a mixer and mixed. After standing at room temperature for 24 h, the mixture is re-milled on a two-roll mill. The final electrolyte-resistant peroxyfluororubber is obtained.

[0063] <Example 4>

[0064] A method for preparing a high-fluorine-content fluororubber resistant to electrolyte for lithium batteries includes the following steps:

[0065] S1: In an 80L stainless steel polymerization reactor, add 52kg of deoxygenated high-purity water, 60g of pH buffer disodium hydrogen phosphate, and 70g of chain transfer agent cyclopropane. Start stirring at 180rpm and heat the polymerization reactor to 75℃. Purge the first mixed gas of hexafluoropropylene, vinylidene fluoride, and tetrafluoroethylene to a pressure of 2500kPa. The molar ratio of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene in the first mixture is 15:60:25. Add 20kg of potassium persulfate initiator and 1g of initiator synergist mixture to initiate the copolymerization reaction.

[0066] The preparation method of the initiating synergist in this example is as follows:

[0067] a: Weigh 6g of p-mercaptoterephthalic acid and 20g of titanium tetrachloride, place them in a sealed reaction vessel, purge with nitrogen to replace the air, then add 150g of ethanol and mix and stir; pour the mixture into a hydrothermal reaction vessel, place it in an oven, adjust the oven temperature to 220℃, crystallize, remove it, and let it stand and cool naturally to room temperature to obtain the precursor;

[0068] b: Weigh 10g of precursor, 150g of toluene, 0.7g of dicyclopentene methacrylate, and 5g of sodium ethoxide, place them in a sealed reaction vessel, purge with nitrogen to replace the air, adjust the temperature to 75℃, and heat for 100 minutes; then add 6g of titanium tetrachloride and heat for 60 minutes; distill to remove toluene, dry, and obtain the initiator synergist.

[0069] S2: After polymerization begins, a second mixed gas of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene is introduced to maintain the polymerization reactor pressure at 2500 kPa. The molar ratio of hexafluoropropylene, vinylidene fluoride, and tetrafluoroethylene in the second mixture is 25:35:50. When the consumption of the second mixed monomer reaches 15 kg, the copolymerization reaction is terminated, the polymerization reactor is depressurized and discharged, and the resulting emulsion is coagulated and washed with 2 kg of MgCl2 coagulant. After drying in an oven, raw rubber is obtained.

[0070] S3: The following compounding components are prepared: (1) 10 kg raw rubber; (2) 0.1 kg vulcanizing agent triallyl isocyanurate; (3) 0.3 kg vulcanizing aid 2,5-di-tert-butylperoxide-2,5-dimethylethane; (4) 2 kg filler material MT carbon black N9900; (5) 0.5 kg processing aid octadecanoic acid. The above components are added to a mixer and mixed. After standing at room temperature for 24 hours, the mixture is re-milled on a two-roll mill. The final electrolyte-resistant peroxyfluororubber is obtained.

[0071] <Comparative Example>

[0072] A method for preparing a high-fluorine-content fluororubber resistant to electrolyte for lithium batteries includes the following steps:

[0073] S1: In an 80L stainless steel polymerization reactor, add 52kg of deoxygenated high-purity water, 120g of pH buffer disodium hydrogen phosphate, and 35g of chain transfer agent isobutane. Start stirring at 180rpm and heat the polymerization reactor to 70℃. Purge the first mixed gas of hexafluoropropylene, vinylidene fluoride, and tetrafluoroethylene to a pressure of 2400kPa. The molar ratio of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene in the first mixture is 20:50:30. Add 20g of potassium persulfate as an initiator to initiate the copolymerization reaction.

[0074] S2: After polymerization begins, a second mixed gas of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene is introduced to maintain the polymerization reactor pressure at 2400 kPa. The molar ratio of hexafluoropropylene, vinylidene fluoride, and tetrafluoroethylene in the second mixture is 20:35:55. When the consumption of the second mixed monomer reaches 15 kg, the copolymerization reaction is terminated, the polymerization reactor is depressurized and discharged, and the resulting emulsion is coagulated and washed with 2 kg of MgCl2 coagulant. After drying in an oven, raw rubber is obtained.

[0075] S3: The following compounding components are prepared: (1) 10 kg raw rubber; (2) 0.15 kg vulcanizing agent triallyl isocyanurate; (3) 0.3 kg vulcanizing aid 2,5-di-tert-butylperoxide-2,5-dimethylethane; (4) 1.5 kg filler MT carbon black N9900; (5) 0.5 kg processing aid octadecanoic acid. The above components are added to a mixer and mixed. After standing at room temperature for 20 h, the mixture is re-milled on a two-roll mill. The final electrolyte-resistant peroxyfluorinated rubber is obtained.

[0076] The testing standards and methods for each indicator are as follows:

[0077] Fluorine content determination: 19F-NMR was used for detection. An analytical method was established by adding an internal standard to accurately test the fluorine content in fluororubber.

[0078] TC90: Heat the mold cavity to the set temperature and stabilize it; press the "Open Mold / Close Mold" switch to open the mold cavity; place a circular sample with a diameter of approximately 38mm, a thickness of 4-5mm, and a mass of approximately 6.5g into the mold cavity; press the "Open Mold / Close Mold" switch to close the mold cavity, the test will start automatically, and the test will end automatically after the set test time is reached, obtaining the vulcanization curve and reading the process positive vulcanization time TC90.

[0079] Tensile strength and elongation at break: The test was conducted in accordance with GBT528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber", with the sample type being type 1 and the tensile speed being (500±50) mm / min.

[0080] High-temperature compression set: The test shall be conducted in accordance with the provisions of GB / T7759-1998 "Determination of compression set of vulcanized rubber and thermoplastic rubber at room temperature, high temperature and low temperature", wherein the test temperature is 200℃ and the test time is 70 hours.

[0081] Material volume resistivity: Tested according to GB1410-89 "Test Methods for Volume Resistivity and Surface Resistivity of Solid Insulating Materials", with a test voltage of 1000V and a reading delay of 3 seconds.

[0082] Immersion volume expansion rate: The insulating fluororubber of this embodiment was immersed in lithium battery electrolyte at 85°C for 70 hours, and then the volume change of the insulating fluororubber was detected.

[0083] The above embodiments and comparative examples were tested and analyzed using the above methods, and the results are shown in the table below:

[0084] The test data from the above embodiments show that the fluorine content in the rubber increases to a certain extent after the addition of the initiator and synergist, and the immersion volume expansion rate is further improved. This is mainly because the organometallic complex of the initiator and synergist acts as a chain transfer agent, controlling the free radical polymerization process of olefin monomers.

[0085] The above are merely embodiments of this disclosure and do not limit the patent scope of this disclosure. Any equivalent modifications made using the content of this disclosure, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this disclosure.

Claims

1. A high-fluorine-content fluororubber resistant to electrolyte for lithium batteries, comprising the following steps: S1: According to the weight ratio, add 600-800 parts of deoxygenated high-purity water, 0.5-2 parts of pH buffer, and 0.1-1 parts of chain transfer agent to the polymerization reactor. Turn on the stirring and stir at 100-200 rpm. Heat the polymerization reactor to 60-100℃. Introduce the first mixed gas of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene until the pressure in the polymerization reactor is 2000-3000 kPa. Add 0.1-1 parts of initiator to initiate the copolymerization reaction. S2: After polymerization begins, a second mixed gas of vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene is introduced to maintain the pressure of the polymerization reactor at 2000-3000 kPa. When the consumption of the second mixed monomer reaches 150-250 parts, the copolymerization reaction is terminated, the polymerization reactor is depressurized and discharged, and 20-30 parts of coagulant are added to the obtained emulsion for coagulation and washing. The emulsion is then dried in an oven to obtain raw rubber. S3: Prepare the following compounding components: 100 parts raw rubber; 1-2 parts vulcanizing agent; 3-4 parts vulcanizing aid; 20-30 parts filler material MT carbon black N9900; 0.6-6 parts processing aid. Add the above components to a mixer and mix. After standing at room temperature for 15-30 hours, re-mill on a two-roll mill to finally produce electrolyte-resistant peroxyfluororubber.

2. The electrolyte-resistant, high-fluorine-content fluororubber for lithium batteries according to claim 1, wherein the pH buffer is selected from one of dipotassium hydrogen phosphate, potassium dihydrogen phosphate, and disodium hydrogen phosphate.

3. A high-fluorine-content fluororubber for lithium batteries according to claim 1 or 2, wherein the chain transfer agent is selected from diethyl ether, propylene oxide, methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, isobutane, and cyclopropane.

4. A high-fluorine-content fluororubber for lithium batteries according to any one of claims 1-3, characterized in that, The initiator is selected from hydrogen peroxide, ammonium persulfate, potassium persulfate, tert-butyl hydroperoxide, di-tert-butane peroxide, and benzoyl peroxide.

5. A high-fluorine-content fluororubber for lithium batteries resistant to electrolyte, as described in any one of claims 1-4, wherein the initiator synergist added in step S1 is added at an amount of 0.1-5 wt% of the initiator, and the preparation method is as follows: a: Weigh 3-6 parts by weight of p-mercaptoterephthalic acid and 10-20 parts by weight of titanium tetrachloride, place them in a sealed reaction vessel, purge with nitrogen to replace the air, then add 100-150 parts by weight of ethanol and mix and stir; pour the mixture into a hydrothermal reaction vessel, place it in an oven, adjust the oven temperature to 200-220℃, after crystallization, take it out, let it stand and cool naturally to room temperature to obtain the precursor; b: Weigh 5-10 parts of the precursor, 100-150 parts of toluene, 0.03-0.7 parts of dicyclopentene methacrylate, and 2-5 parts of sodium ethoxide by weight, place them in a sealed reaction vessel, purge with nitrogen to replace the air, adjust the temperature to 60-75℃, and heat for 30-100 minutes; then add 2-6 parts of titanium tetrachloride, heat for 30-60 minutes; remove toluene by distillation, dry, and obtain the initiator synergist.

6. A high-fluorine-content fluororubber for lithium batteries resistant to electrolyte, as claimed in any one of claims 1-5, wherein the molar ratio of hexafluoropropylene, vinylidene fluoride and tetrafluoroethylene in the first mixture is 5-20:50-70:20-30; and the molar ratio of hexafluoropropylene, vinylidene fluoride and tetrafluoroethylene in the second mixture is 15-30:30-50:30-60.

7. A high-fluorine-content fluororubber for lithium batteries according to any one of claims 1-6, wherein the coagulant is one or more of a low-valent metal chloride and sulfate.

8. A high-fluorine-content fluororubber for lithium batteries according to any one of claims 1-7, wherein the vulcanizing agent is one or more of triallyl isocyanurate, dicumyl peroxide, and 1,3-bis(tert-butylperoxyisopropyl)benzene.

9. A high-fluorine-content fluororubber for lithium batteries according to any one of claims 1-8, wherein the vulcanizing aid is one or more mixtures of trimethylolpropane trimethacrylate, triallyl isocyanurate, and 2,5-di-tert-butylperoxide-2,5-dimethylethane.

10. A high-fluorine-content fluororubber for lithium batteries according to any one of claims 1-9, wherein the processing aid is one or more mixtures of fatty acid derivatives and silicone, palm wax, and stearic acid.

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