A polyionic liquid binder suitable for vulcanized polyacrylonitrile and its preparation method and application

Abstract

The application relates to a polyionic liquid binder suitable for vulcanized polyacrylonitrile and a preparation method and application thereof, which is obtained by carrying out an alkylation reaction and a polymerization reaction on bromo-n-butane and 1-vinylimidazole, and then carrying out an anion exchange reaction on lithium bis(trifluoromethylsulfonyl) imide and sodium anthraquinone-2-sulfonate. The polyionic liquid binder can anchor polysulfide on the polymer chain through the electrostatic interaction between the lone pair electrons in the molecular chain and the polysulfide, effectively inhibits the shuttle effect, contains a quinoid structure which can act as a redox medium to accelerate the electron transfer process and improve the interface kinetic performance of the SPAN positive electrode, has excellent bonding performance and mechanical strength, can significantly improve the structural integrity and electronic conduction continuity of the electrode in the cycle process, and prolongs the cycle life of the electrode. The obtained binder can be widely applied to SPAN-based positive electrodes of lithium ion batteries and provides effective technical support for solving key problems such as volume expansion and poor conductivity of SPAN materials.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery binder technology, specifically relating to a polyionic liquid binder suitable for vulcanized polyacrylonitrile, its preparation method, and its application. Background Technology

[0002] With the miniaturization of electronic devices, the widespread adoption of electric vehicles, and the rapid development of large-scale energy storage, higher demands are being placed on the energy density, cycle life, and rate performance of lithium-ion batteries. Sulphurized polyacrylonitrile (SPAN), as a cathode material with high theoretical capacity, is considered a strong candidate for next-generation high-energy-density lithium metal batteries. However, it faces three major challenges in application: first, the soluble lithium polysulfides (LiPSs) generated during charge and discharge are prone to shuttle effects, leading to loss of active material and corrosion of the lithium anode; second, the poor conductivity of the material itself and its products, along with slow charge transfer kinetics, limits the battery's rate performance; and third, significant volume changes during cycling can easily damage the integrity of the electrode structure, affecting cycle life.

[0003] Currently, research often addresses these issues by modifying active materials (e.g., using cross-linked polymers) or adding electrolyte additives (e.g., redox media). However, these methods are often complex or may introduce side reactions. It is noteworthy that the role of binders, a key component of the electrode, has not received sufficient attention. Traditional binders (such as PVDF and CMC) have limited functionality, only providing physical adhesion and failing to simultaneously address issues such as polysulfide shuttle, sluggish kinetics, and volume expansion.

[0004] Polymer ionic liquids combine the high ionic conductivity and electrochemical stability of ionic liquids with the excellent mechanical properties of polymers, making it possible to develop novel multifunctional binders. Therefore, developing a polymer ionic liquid binder that integrates efficient bonding, polysulfide anchoring, ion conduction, and volume buffering functions is of great significance for improving the overall performance of SPAN-based lithium metal batteries and promoting their practical application. Summary of the Invention

[0005] The present invention aims to provide a polyionic liquid binder suitable for vulcanized polyacrylonitrile, its preparation method and application, to solve the problems of LiPSs dissolution, low sulfur utilization and SPAN electrode volume expansion buffering.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The primary objective of this invention is to provide a polyionic liquid binder, wherein the polyionic liquid binder is poly(1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonylimide)anthraquinone-2-sulfonic acid); the general structural formula is shown below: .

[0007] A second objective of this invention is to provide a method for preparing a polyionic liquid binder, comprising the following steps: S1, alkylation reaction of bromobutane with 1-vinylimidazol by heating to obtain ionic liquid monomer 1-butyl-3-vinylimidazol bromide ([BVIm][Br]). S2, The ionic liquid monomer is dissolved in a solvent, an appropriate amount of initiator is added, and a free radical polymerization reaction is carried out under inert gas protection to obtain polyionic liquid poly(1-vinyl-3-butylimidazolium bromide) ([PBVIm][Br]). S3, poly(1-vinyl-3-butylimidazolium bromide) ([PBVIm][Br]), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and sodium anthraquinone-2-sulfonate (SAS) are dissolved in deionized water and poly(1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide anthraquinone-2-sulfonic acid) ([PBVIm][TFSI][AS]) is obtained by anion exchange reaction.

[0008] Preferably, in the above steps: In step S1, the molar ratio of bromobutane to 1-vinylimidazole is 1:1 to 1.5.

[0009] In step S1, the alkylation reaction is carried out at a temperature of 60-80°C.

[0010] In step S1, the alkylation reaction takes 1-3 hours.

[0011] In step S2, the initiator is one of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, azoisobutylcyanoformamide, ammonium persulfate, potassium persulfate, or sodium persulfate, and the amount used is 1%-5% of the monomer mass.

[0012] In step S2, the reaction solvent is at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), methanol, or acetonitrile.

[0013] In step S2, the reaction time for the free radical polymerization reaction is 15-45 min.

[0014] In step S3, the molar ratio of poly(1-vinyl-3-butylimidazolium bromide), lithium bis(trifluoromethanesulfonyl)imide, and sodium anthraquinone-2-sulfonate is 1:0.1~1.5:0.1-1.5.

[0015] In step S3, the reaction time for the anion exchange reaction is 5-30 min.

[0016] A third objective of this invention is to provide the application of a polyionic liquid binder in a vulcanized polyacrylonitrile electrode. Based on this application, a vulcanized polyacrylonitrile electrode is obtained.

[0017] The vulcanized polyacrylonitrile electrode further includes vulcanized polyacrylonitrile and conductive carbon black, wherein the mass ratio of the vulcanized polyacrylonitrile, conductive carbon black and polyionic liquid binder is 50~95: 4~40: 1~10.

[0018] A fourth objective of this invention is to provide a lithium metal battery having the sulfurized polyacrylonitrile electrode described above in this application.

[0019] Technical principle of the invention: (1) The ionic liquid segments contained in the molecular chain of the polyionic liquid binder of the present invention have abundant lone pairs of electrons, which can bind with negatively charged polysulfides (such as Li2S). n (n=4-8) form strong electrostatic interactions, firmly anchoring the polysulfides to the polymer chain.

[0020] (2) The quinone structure introduced into the polyionic liquid binder molecule of the present invention has excellent redox activity and can participate in the charge transfer process on the electrode surface as a redox medium, thereby reducing the electron transfer energy barrier.

[0021] (3) The polyionic liquid binder of the present invention forms a stable cross-linked network structure during the polymerization process, which has excellent mechanical strength and elastic deformation ability.

[0022] Compared with the prior art, the beneficial effects of the present invention are: (1) High efficiency in suppressing polysulfide shuttle effect: The polyionic liquid binder of this invention effectively prevents it from desorbing from the positive electrode and diffusing into the electrolyte, thereby suppressing the shuttle effect from the source and significantly reducing the battery capacity decay and coulombic efficiency decline caused by polysulfide loss.

[0023] (2) Redox-mediated enhancement of interfacial dynamics: The polyionic liquid binder of this invention reduces the electron transfer energy barrier, accelerates the transfer of electrons between the SPAN active material and the current collector, and promotes the insertion and extraction and migration of lithium ions in the electrolyte, significantly enhancing the interfacial dynamics performance of the SPAN cathode, effectively improving the defect of poor conductivity of the SPAN material itself, and improving the rate performance of the battery.

[0024] (3) Enhanced SPAN cathode structure integration capability: The polyionic liquid binder of this invention effectively buffers and inhibits the volume expansion and contraction of the SPAN-based cathode during charge and discharge cycles, preventing electrode structure collapse, active material shedding and current collector peeling off from the active layer, significantly improving the structural integrity and cycle stability of the electrode, and extending the service life of the electrode.

[0025] (4) Stable electrochemical performance: Thanks to the synergistic effect of the above three core advantages, the SPAN cathode and lithium metal battery prepared using the polyionic liquid binder of this invention can maintain a high capacity retention rate (the capacity retention rate can still reach more than 99% after 100 cycles at 1C rate) and good rate performance (it can still release 300 mAh g at 10C high rate). -1 Specific capacity). Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0027] Figure 1 This is the synthesis route diagram for Example 1; Figure 2 Thermogravimetric curves of the polyionic liquid binders prepared in Examples 1, 3, and 4 are shown. Figure 3 Peel force-displacement curves for Examples 1-4 and Comparative Example 1 applied to vulcanized polyacrylonitrile electrodes; Figure 4 The images are scanning electron microscope (SEM) images of the polyacrylonitrile electrodes used in Example 1 and Comparative Example 1.

[0028] Figure 5 This is a comparison chart of the cycle performance of Example 1 and Comparative Example 1.

[0029] Figure 6 This is a comparison chart of the rate performance of Example 1 and Comparative Example 1. Detailed Implementation

[0030] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention. Example 1

[0031] See appendix Figure 1 This example provides a polyionic liquid binder, its preparation method, and its application, including the following steps: Step 1: Under vigorous stirring at 70 °C, 20.55 g (0.15 mol) of n-butane bromide was added dropwise to 14.13 g (0.15 mol) of 1-vinylimidazolium in a 100 mL beaker. The alkylation reaction was then continued for 2 hours, followed by cooling the mixture to room temperature to obtain a yellow viscous solution. This yellow viscous solution was then diluted with 50 mL of acetone at room temperature and stirred vigorously. The mixture was then stored in a refrigerator for 1 hour. A white solid precipitated from the cooled solution, which was separated by filtration through a Buchner funnel, washed with acetone, and dried at 40 °C for 1 hour to obtain a white powder of 1-butyl-3-vinylimidazolium bromide ([BVIm][Br]).

[0032] Step 2: 18.48 g of 1-butyl-3-vinylimidazolium bromide ([BVIm][Br]), 67 mg of azobisisobutyronitrile (AIBN), and 30 mL of DMF were added to a 250 mL round-bottom flask. The flask was sealed and polymerized by purging with N2 at 80 °C for 30 minutes. A brownish-red viscous sol was formed at the end of the reaction. Then, equal volumes of deionized water and ethyl acetate were added to the sol sequentially, and the mixture was stirred vigorously. Subsequently, poly(1-vinyl-3-butylimidazolium bromide) [PBVIm][Br] was purified by static layer separation. The mixed solution separated into two layers: an upper layer of colorless transparent liquid and a lower layer of pale yellow transparent liquid. The lower yellow liquid was then separated and dried in a vacuum oven at 95 °C for 6 hours to obtain a pale yellow powder.

[0033] Step 3: 1.45 g (5.06 mmol) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1.58 g (5.06 mmol) of sodium anthraquinone-2-sulfonate (SAS) were dissolved in 5 ml of deionized water. Then, 2 g (9.2 mmol) of [PBVIm][Br] dissolved in 100 ml of deionized water was added dropwise while stirring at room temperature for 10 minutes. The resulting white precipitate was then separated from the solution and collected as a white powder by filtration. Finally, the white powder was dried in a vacuum oven to obtain poly(1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide anthraquinone-2-sulfonic acid) ([PBVIm][TFSI][AS]) topaz solid.

[0034] Step 4: Vulcanized polyacrylonitrile (SPAN), conductive carbon black, and [PBVIm][TFSI][AS] binder are mixed in a mass ratio of 90:5:5, with NMP as the solvent, and stirred to obtain a uniform slurry. The slurry is then coated onto carbon-coated aluminum foil using a scraping method and vacuum dried at 90°C for 12 hours. The dried electrode is then cut into 10mm round pieces for later use.

[0035] Step 5: Using the above-mentioned disc as the positive electrode and the lithium sheet as the negative electrode, a Celgard separator and an electrolyte of (1M LiTFSIin DME:DOL=1:1 Vol% with 2%LiNO3) are matched and assembled into a 2032 type button battery in an argon glove box with a water and oxygen content of less than 0.01 ppm. Example 2

[0036] This embodiment provides a polyionic liquid binder, its preparation method, and its application, referring to Example 1. The difference between this embodiment and Example 1 is that 2.9 g (10.12 mmol) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is used instead of 1.45 g (5.06 mmol) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1.58 g (5.06 mmol) of sodium anthraquinone-2-sulfonate (SAS) in Example 1. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1. Example 3

[0037] This embodiment provides a polyionic liquid binder, its preparation method, and its application, referring to Example 1. The difference between this embodiment and Example 1 is that 0.73 g (2.53 mmol) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 2.37 g (7.59 mmol) of sodium anthraquinone-2-sulfonate (SAS) are used instead of 1.45 g (5.06 mmol) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1.58 g (5.06 mmol) of sodium anthraquinone-2-sulfonate (SAS) in Example 1. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1. Example 4

[0038] This embodiment provides a polyionic liquid binder, its preparation method, and its application, referring to Example 1. The difference between this embodiment and Example 1 is that 2.18 g (7.59 mmol) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 0.79 g (2.53 mmol) of sodium anthraquinone-2-sulfonate (SAS) are used instead of 1.45 g (5.06 mmol) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1.58 g (5.06 mmol) of sodium anthraquinone-2-sulfonate (SAS) in Example 1. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1. Example 5

[0039] This embodiment provides a polyionic liquid binder, its preparation method, and its application, referring to Example 1. The difference between this embodiment and Example 1 is that 2.18 g (7.59 mmol) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 0.79 g (2.53 mmol) of sodium anthraquinone-2-sulfonate (SAS) are used instead of 1.45 g (5.06 mmol) of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1.58 g (5.06 mmol) of sodium anthraquinone-2-sulfonate (SAS) in Example 1. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1. Example 6

[0040] This embodiment provides a polyionic liquid binder, its preparation method, and its application, with reference to Embodiment 1. The difference between this embodiment and Embodiment 1 is that the alkylation reaction time is 1 hour instead of 2 hours in Embodiment 1, while the remaining raw material ratios and preparation methods are strictly consistent with those in Embodiment 1. Example 7

[0041] This embodiment provides a polyionic liquid binder, its preparation method, and its application, with reference to Embodiment 1. The difference between this embodiment and Embodiment 1 is that the reaction time of the free radical polymerization reaction is 1 hour instead of the alkylation reaction time of 2 hours in Embodiment 1. The remaining raw material ratios and preparation methods are strictly consistent with those in Embodiment 1. Example 8

[0042] This embodiment provides a polyionic liquid binder, its preparation method, and its application, with reference to Embodiment 1. The difference between this embodiment and Embodiment 1 is that the alkylation reaction time is 15 min instead of 30 min in Embodiment 1. The remaining raw material ratios and preparation methods are strictly consistent with those in Embodiment 1. Example 9

[0043] This embodiment provides a polyionic liquid binder, its preparation method, and its application, with reference to Embodiment 1. The difference between this embodiment and Embodiment 1 is that the reaction time of the anion exchange reaction is 5 min instead of the alkylation reaction time of 10 min in Embodiment 1. The remaining raw material ratios and preparation methods are strictly consistent with those of Embodiment 1.

[0044] Comparative Example 1 This embodiment refers to Example 1 to provide a polyionic liquid binder, its preparation method and application. The difference between this embodiment and Example 1 is that polyvinylidene fluoride (PVDF) binder is used instead of poly(1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonylimide)anthraquinone-2-sulfonic acid) [PBVIm][TFSI][AS] binder, and the proportions of the remaining raw materials are strictly consistent with those in Example 1.

[0045] Performance tests were performed on Examples 1-9 and Comparative Example 1 as described above: Thermogravimetric analysis (TGA): The thermal stability of an adhesive is evaluated by continuously and accurately measuring the changes in the adhesive with temperature or time under programmed temperature control (usually at a constant rate of temperature increase).

[0046] Peel force test: The force-displacement curve is recorded using a universal testing machine, and the average peel force and peel strength are calculated.

[0047] Electrode integrity test: The plane of the electrode is observed by scanning electron microscopy.

[0048] Rate performance testing: Assembled Li-SPAN batteries were tested at room temperature. A Blue Battery testing system was used, operating within a voltage range of 1–3V at 1C, 2C, 3C, 4C, and 5C (1C = 560 mAh g). -1 Charge and discharge tests were conducted using current density.

[0049] Cyclic performance testing: Assembled Li-SPAN batteries were subjected to room temperature cycle testing. A Blue Electricity testing system was used, operating at 3C (1C = 560 mAh g⁻¹) within a voltage range of 1–3V. -1 Charge and discharge tests were conducted using current density.

[0050] Results analysis: (1) such as Figure 2 As shown, Figure 2 These are the thermogravimetric curves of three polyionic liquid binders measured in argon gas. The results show that all three polyionic liquid binders have certain thermal stability, and their initial decomposition temperatures are all above 300℃.

[0051] (2) such as Figure 3 and Figure 4 As shown, Figure 3Peel force-displacement curves were compared between SPAN cathodes using [PBVIm][TFSI][AS] polyionic liquid binder and SPAN cathodes using PVDF binder. The peel force of Example 1 (0.6 N) was 1.5 times that of Comparative Example 1 (0.4 N). Figure 4 A comparison of the SPAN positive electrode using [PBVIm][TFSI][AS] polyionic liquid binder and the SPAN positive electrode using PVDF binder using planar scanning electron microscopy revealed that the electrode of Example 1 (i.e., the [PBVIm][TFSI][AS] polyionic liquid binder) had a dense and smooth surface, while the electrode of Comparative Example 1 (PVDF binder) exhibited obvious wide and deep cracks. The results indicate that Example 1, using the [PBVIm][TFSI][AS] polyionic liquid binder, possesses stronger bonding performance and mechanical strength.

[0052] (3) such as Figure 5 and Figure 6 As shown, Figure 5 and Figure 6 The electrochemical performance of the [PBVIm][TFSI][AS] polyionic liquid binder in Comparative Example 1 and the PVDF binder in Comparative Example 1 applied to the vulcanized polyacrylonitrile electrode was compared. The lithium metal battery of Example 1 using the [PBVIm][TFSI][AS] polyionic liquid binder maintained a high capacity retention rate (more than 99% capacity retention rate after 100 cycles at 1C) and good rate performance (300 mAh g-1 specific capacity can still be released at a high rate of 10C).

[0053] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A polyionic liquid binder suitable for vulcanized polyacrylonitrile, characterized in that, The polyionic liquid binder is poly(1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide anthraquinone-2-sulfonic acid), and its general structural formula is shown below: 。 2. The method for preparing the polyionic liquid binder suitable for vulcanized polyacrylonitrile according to claim 1, characterized in that, The preparation method specifically includes the following steps: S1, alkylation reaction of bromobutane with 1-vinylimidazol by heating to obtain ionic liquid monomer 1-butyl-3-vinylimidazol bromide; S2, Dissolve the ionic liquid monomer in a solvent, add an appropriate amount of initiator, and carry out a free radical polymerization reaction under inert gas protection to obtain polyionic liquid poly(1-vinyl-3-butylimidazolium bromide); S3, poly(1-vinyl-3-butylimidazolium bromide), lithium bis(trifluoromethanesulfonyl)imide, and sodium anthraquinone-2-sulfonate are dissolved in deionized water and poly(1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide anthraquinone-2-sulfonic acid) is obtained by anion exchange reaction.

3. The preparation method according to claim 2, characterized in that, In step S1, the molar ratio of bromobutane to 1-vinylimidazole is 1:1 to 1.5; The alkylation reaction temperature is 60-80℃; The reaction time is 1-3 hours.

4. The preparation method according to claim 2, characterized in that, In step S2, the initiator is one of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, azoisobutylcyanoformamide, ammonium persulfate, potassium persulfate, or sodium persulfate, and the amount used is 1%-5% of the monomer mass.

5. The preparation method according to claim 2, characterized in that, In step S2, the reaction solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, methanol, or acetonitrile.

6. The preparation method according to claim 2, characterized in that, In step S2, the reaction time for the free radical polymerization reaction is 15-45 min.

7. The preparation method according to claim 2, characterized in that, In step S3, the molar ratio of poly(1-vinyl-3-butylimidazolium bromide), lithium bis(trifluoromethanesulfonyl)imide, and sodium anthraquinone-2-sulfonate is 1:0.1~1.5:0.1-1.5; The reaction time for anion exchange is 5-30 minutes.

8. A vulcanized polyacrylonitrile electrode, characterized in that, Includes the polyionic liquid binder as described in claim 1.

9. The vulcanized polyacrylonitrile electrode as described in claim 8, characterized in that, It also includes vulcanized polyacrylonitrile and conductive carbon black, wherein the mass ratio of the vulcanized polyacrylonitrile, conductive carbon black and polyionic liquid binder is 50~95: 4~40: 1~10.

10. A lithium metal battery, characterized in that, Includes the vulcanized polyacrylonitrile electrode as described in claim 8 or 9.

Images