Boron-based polyelectrolyte, preparation method thereof and solid electrolyte membrane

Abstract

The invention relates to a boron-based polyelectrolyte, a preparation method thereof and a solid electrolyte membrane, and the preparation method of the boron-based polyelectrolyte comprises the step of carrying out a cross-linking reaction on a functional boron-based lithium salt and a cross-linking agent under the action of an initiator to obtain the boron-based polyelectrolyte. According to the preparation method provided by the invention, the functional boron-based lithium salt with a cross-shaped structure is taken as a raw material, the boron-based polyelectrolyte with a three-dimensional network structure and high regularity can be obtained through a cross-linking reaction with the cross-linking agent, an anion group of the lithium salt is fixed, and groups such as ether groups contained in the lithium salt can promote lithium ion transmission.

Description

Technical Field

[0001] The present disclosure relates to the technical field of lithium-ion batteries, and in particular to a boron-based polyelectrolyte and a preparation method thereof, and a solid electrolyte membrane. Background Art

[0002] The development of rechargeable batteries has brought great convenience to modern production and life. However, traditional rechargeable batteries generally use flammable and explosive low-boiling-point solvent electrolytes as the medium for lithium ion transmission, which poses a significant safety risk. Solid-state electrolytes are one of the effective ways to solve this problem.

[0003] At present, solid electrolytes include inorganic ceramic solid electrolytes and organic polymer solid electrolytes. Among them, inorganic ceramic solid electrolytes have strong ion conductivity, but the electrolytes are brittle and cannot be used in flexible devices; organic polymer solid electrolytes have good flexibility, but weak ion conductivity.

[0004] CN110556576A discloses a semi-interpenetrating network double salt solid electrolyte, synthesized by combining a linear ion-conducting polymer with a single-ion conducting polymer, using a certain ratio of diene borate lithium salt and a polythiol or polyene compound to form an in-situ polymerization reaction in a mixture of the linear ion-conducting polymer and a small-molecule lithium salt. While the solid electrolyte disclosed in this patent has high Li+ conductivity, it achieves this through the addition of a small-molecule lithium salt, which compromises the material's mechanical properties and stability, and increases production costs.

[0005] Therefore, there is a need to provide a solid electrolyte that has both ion conductivity and mechanical properties to meet application requirements. Summary of the Invention

[0006] In order to solve the above technical problems, the present disclosure provides a boron-based polyelectrolyte and a preparation method thereof, and a solid electrolyte membrane.

[0007] In a first aspect, the present disclosure provides a method for preparing a boron-based polyelectrolyte, the preparation method comprising the following steps:

[0008] The functional boron-based lithium salt and the cross-linking agent undergo a cross-linking reaction under the action of an initiator to obtain the boron-based polyelectrolyte;

[0009] Wherein, the functional boron-based lithium salt has the general structural formula shown in Formula I:

[0010]

[0011] 1≤n≤5;

[0012] The cross-linking agent is selected from at least one of polyethylene glycol, PVDF-HFP, pentaerythritol tetrakis(3-mercaptopropionate) or 2,2'-(1,2-ethylenedioxy)bis(ethylenethiol).

[0013] In the preparation method provided by the present disclosure, a functional boron-based lithium salt having a "cross" structure and containing terminal double bonds is used as a reaction raw material. It has abundant reaction sites. The introduced cross-linking agent can also provide reaction sites while enabling the product to fix the anionic groups of the lithium salt. In addition, the abundant ether groups and other groups in its flexible chain segments can promote lithium ion transmission. Therefore, the boron-based polyelectrolyte obtained by the preparation method of the present disclosure has excellent lithium ion transmission ability.

[0014] The preparation method of the boron-based polyelectrolyte disclosed in the present invention does not require the introduction of other commercial electrolyte lithium salts, is cost-controllable, safe and simple, environmentally friendly, and has the potential for industrial mass production.

[0015] As a preferred technical solution of the present disclosure, the molar ratio of the cross-linking agent to the functional boron-based lithium salt is 4-50:1.

[0016] As a preferred technical solution of the present disclosure, the temperature of the cross-linking reaction is 55-80° C., and the time of the cross-linking reaction is preferably 6-12 hours.

[0017] As a preferred technical solution of the present disclosure, the initiator is selected from thermal initiators, preferably azobisisobutyronitrile.

[0018] As a preferred technical solution of the present disclosure, the added amount of the initiator is 0.1-2% of the total solid reactant mass.

[0019] As a preferred technical solution of the present disclosure, the preparation method includes:

[0020] (1) dissolving a functional boron-based lithium salt in a solvent to obtain a solution;

[0021] (2) adding a crosslinking agent and an initiator to the solution to carry out a crosslinking reaction, and removing the solvent after the reaction to obtain the boron-based polyelectrolyte.

[0022] As a preferred technical solution of the present disclosure, the solution further includes a cosolvent, and the cosolvent is preferably selected from at least one of bisbenzenesulfonimide, fluorobisbenzenesulfonimide, benzenesulfonamide, benzenesulfonyl chloride, 4-phenoxybenzenesulfonyl fluoride or phenylmethylsulfonyl fluoride.

[0023] As a preferred technical solution of the present disclosure, the solvent is selected from at least one of ethanol, ether, dimethyl sulfoxide, N-methylpyrrolidone, acetone or N,N-dimethylformamide.

[0024] As a preferred technical solution of the present disclosure, in the solution, the concentration of the functional boron-based lithium salt is 0.1-1 mol / L.

[0025] In a second aspect, the present disclosure provides a boron-based polyelectrolyte prepared by the preparation method described in the first aspect.

[0026] As a preferred technical solution of the present disclosure, the boron-based polyelectrolyte has a lithium ion transference number greater than 0.6, an electrochemical stability window greater than or equal to 5.0 V, and an ionic conductivity greater than or equal to 2×10 -4 S cm -1 , ionic conductivity at 70℃≥1.0×10 - 4 S cm -1 , initial thermal decomposition temperature ≥350℃, tensile strength ≥4MPa.

[0027] In a third aspect, the present disclosure provides a solid electrolyte membrane, wherein components of the solid electrolyte membrane include the boron-based polyelectrolyte prepared by the preparation method described in the first aspect or the boron-based polyelectrolyte described in the second aspect.

[0028] In a fourth aspect, the present disclosure provides use of the boron-based polyelectrolyte described in the second aspect or the solid electrolyte membrane described in the third aspect in an electrochemical device.

[0029] In a fifth aspect, the present disclosure provides an electrochemical device comprising the boron-based polyelectrolyte described in the second aspect or the solid electrolyte membrane described in the third aspect.

[0030] In a sixth aspect, the present disclosure provides a vehicle comprising the boron-based polyelectrolyte described in the second aspect, the solid electrolyte membrane described in the third aspect, or the electrochemical device described in the fifth aspect.

[0031] The technical solution provided by the embodiments of the present disclosure has the following advantages over the prior art:

[0032] (1) The preparation method provided by the present disclosure uses a functional boron-based lithium salt with a "cross" structure as a raw material, and can obtain a boron-based polyelectrolyte with a highly regular three-dimensional network structure through a cross-linking reaction with a cross-linking agent, thereby fixing the anionic groups of the lithium salt, and the groups containing ether groups can promote lithium ion transmission;

[0033] (2) The boron-based polyelectrolyte provided by the present disclosure has a cross-linked network structure, excellent thermal stability and mechanical properties, and at the same time has relatively good ionic conductivity, which can meet the application requirements of lithium-ion batteries;

[0034] (3) The solid electrolyte membrane provided by the present disclosure has excellent thermal stability, high ionic conductivity and lithium ion transference number, and a wide electrochemical window. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0036] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0037] Figure 1 This is the X-ray diffraction spectrum of the boron-based polyelectrolyte obtained in Example 1 of the present disclosure;

[0038] Figure 2 This is a test chart of the lithium ion migration number of the boron-based polyelectrolyte obtained in Example 1 of the present disclosure;

[0039] Figure 3 This is a Fourier transform infrared spectrum of the boron-based polyelectrolyte obtained in Example 2 of the present disclosure;

[0040] Figure 4 This is a Fourier infrared spectrum of the product obtained in Comparative Example 2 of the present disclosure;

[0041] Figure 5 This is a graph showing the thermal stability test results of the boron-based polyelectrolyte obtained in Example 3 of the present disclosure;

[0042] Figure 6 This is an impedance test graph of the boron-based polyelectrolyte obtained in Example 3 of the present disclosure;

[0043] Figure 7 This is a diagram showing the tensile test results of the boron-based polyelectrolyte obtained in Example 4 of the present disclosure;

[0044] Figure 8 This is an impedance test diagram of the boron-based polyelectrolyte obtained in Example 4 of the present disclosure;

[0045] Figure 9 This is an impedance test diagram of the solid electrolyte film provided in Application Example 1 of the present disclosure;

[0046] Figure 10 A DSC test result diagram of the solid electrolyte film provided in Application Example 1 of the present disclosure;

[0047] Figure 11 A physical image of the film provided for comparative application example 1 of the present disclosure;

[0048] Figure 12A graph showing the test results of the lithium ion migration number of the solid electrolyte film provided in Application Example 2 of the present disclosure;

[0049] Figure 13 This is a graph showing the CV test results of the solid electrolyte film provided in Application Example 2 of the present disclosure. DETAILED DESCRIPTION

[0050] In order to more clearly understand the above-mentioned objectives, features and advantages of the present disclosure, the scheme of the present disclosure will be further described below. It should be noted that the embodiments of the present disclosure and the features therein can be combined with each other in the absence of conflict.

[0051] In the following description, many specific details are set forth to facilitate a full understanding of the present disclosure, but the present disclosure may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present disclosure, rather than all of the embodiments.

[0052] Currently, solid electrolytes in the existing technology are divided into inorganic solid electrolytes and organic polymer solid electrolytes. Among them, inorganic ceramic solid electrolytes have strong ion conductivity but are brittle and cannot be used in flexible devices; organic polymer solid electrolytes have good flexibility but weak ion conductivity. Therefore, the present disclosure provides a solid electrolyte with excellent mechanical properties and excellent ion conductivity.

[0053] The present disclosure provides a method for preparing a boron-based polyelectrolyte, the preparation method comprising the following steps:

[0054] The functional boron-based lithium salt and the cross-linking agent undergo a cross-linking reaction under the action of an initiator to obtain the boron-based polyelectrolyte;

[0055] Wherein, the functional boron-based lithium salt has the general structural formula shown in Formula I:

[0056]

[0057] 1≤n≤5, for example, 1, 2, 3, 4, 5, etc.

[0058] The cross-linking agent is selected from at least one of polyethylene glycol, PVDF-HFP, pentaerythritol tetrakis(3-mercaptopropionate) or 2,2'-(1,2-ethylenedioxy)bis(ethylenethiol).

[0059] In the preparation method provided by the present disclosure, a functional boron-based lithium salt having a "cross" structure and containing terminal double bonds is used as a reaction raw material. It has abundant reaction sites. The introduced cross-linking agent can also provide reaction sites while enabling the product to fix the anionic groups of the lithium salt. In addition, the abundant ether groups and other groups in its flexible chain segments can promote lithium ion transmission. Therefore, the boron-based polyelectrolyte obtained by the preparation method of the present disclosure has excellent lithium ion transmission ability.

[0060] The preparation method of the boron-based polyelectrolyte disclosed in the present invention does not require the introduction of other commercial electrolyte lithium salts, is cost-controllable, safe and simple, environmentally friendly, and has the potential for industrial mass production.

[0061] The preparation method of the functional boron-based lithium salt disclosed in the present invention may include the following steps:

[0062] (1) dissolving a lithium source and boric acid in deionized water to prepare solution a, and dissolving an unsaturated fatty acid in an organic solvent to prepare solution b, wherein the molar ratio of lithium contained in the lithium source to boron contained in the boric acid is 1:1, and the molar ratio of lithium contained in the lithium source to the unsaturated fatty acid is 1:4;

[0063] (2) mixing solution a and solution b obtained in step (1) in a flask, heating and stirring at 60-90° C. for 6-12 h under an inert atmosphere of nitrogen or argon to obtain a lithium salt solution;

[0064] (3) purifying and drying the lithium salt solution obtained in step (2) to remove residual solvent to obtain a boron-based lithium salt containing a terminal double bond;

[0065] In the above steps, as a preferred technical solution of the present disclosure, the lithium source is one or a combination of any two or more of lithium hydroxide, lithium carbonate, lithium borohydride, lithium tetrafluoroborate or butyl lithium.

[0066] As a preferred technical solution of the present disclosure, the unsaturated fatty acid is any one of acrylic acid, methacrylic acid, vinyl acetic acid, 3-pentenoic acid, 3-methyl-4-pentenoic acid, 4-pentenoic acid, 5-hexenoic acid, 6-heptenoic acid, 7-octenoic acid, 8-nonenoic acid, 9-decenoic acid, and undecenoic acid, or a combination of any two or more thereof.

[0067] As a preferred technical solution of the present disclosure, the organic solvent is any one of ethanol, acetonitrile, ether, dimethyl sulfoxide, N-methylpyrrolidone, acetone, and N,N-dimethylformamide, or a combination of any two or more thereof.

[0068] As a preferred technical solution of the present disclosure, the molar ratio of the cross-linking agent to the functional boron-based lithium salt is 4-50:1, for example, 4:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, etc.

[0069] As a preferred technical solution of the present disclosure, the temperature of the cross-linking reaction is 55-80°C, for example, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc., and the time of the cross-linking reaction is preferably 6-12h, for example, 6h, 7h, 8h, 9h, 10h, 11h, 12h, etc.

[0070] As a preferred technical solution of the present disclosure, the initiator is selected from thermal initiators, preferably azobisisobutyronitrile.

[0071] As a preferred technical solution of the present disclosure, the added amount of the initiator is 0.1-2% of the total solid reactant mass, for example, 0.1%, 0.3%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2%, etc.

[0072] As a preferred technical solution of the present disclosure, the preparation method includes:

[0073] (1) dissolving a functional boron-based lithium salt in a solvent to obtain a solution;

[0074] (2) adding a crosslinking agent and an initiator to the solution to carry out a crosslinking reaction, and removing the solvent after the reaction to obtain the boron-based polyelectrolyte.

[0075] As a preferred technical solution of the present disclosure, the solution further includes a cosolvent, and the cosolvent is preferably selected from at least one of bisbenzenesulfonimide, fluorobisbenzenesulfonimide, benzenesulfonamide, benzenesulfonyl chloride, 4-phenoxybenzenesulfonyl fluoride or phenylmethylsulfonyl fluoride.

[0076] The cosolvent introduced in the present disclosure contains abundant polar groups such as benzene rings and fluorine, which effectively promotes the dissociation and transmission of lithium ions in boron-based lithium salts.

[0077] As a preferred technical solution of the present disclosure, the solvent is selected from at least one of ethanol, ether, dimethyl sulfoxide, N-methylpyrrolidone, acetone or N,N-dimethylformamide.

[0078] As a preferred technical solution of the present disclosure, in the solution, the concentration of the functional boron-based lithium salt is 0.1-1 mol / L, for example, 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, etc.

[0079] In a second aspect, the present disclosure provides a boron-based polyelectrolyte prepared by the preparation method described in the first aspect.

[0080] The boron-based polyelectrolyte provided by the present disclosure has a regular cross-linked network structure, and has the advantages of good heat resistance, high strength, structural support, dimensional deformation, and pore fillability. At the same time, in the field of lithium-ion batteries, it has excellent thermal stability, high ionic conductivity and lithium ion migration number, and a wide electrochemical window, which can meet application requirements.

[0081] The boron-based polyelectrolyte provided by the present disclosure has the following general structural formula:

[0082]

[0083] In the above general structural formula, 1≤n≤5, for example, it can be 1, 2, 3, 4, 5, etc.

[0084] The above-mentioned general structural formula disclosed in the present invention only discloses part of the repeating units. It should be understood in the art that the general structural formula provided in the present invention does not mean that the degree of polymerization of the boron-based polyelectrolyte provided in the present invention is only 8. The average degree of polymerization needs to be determined based on the ratio of the initiator and the raw materials.

[0085] In the above general structural formula, each R group may correspond to a different raw material structural formula, including at least one of the following:

[0086]

[0087] Among them, 426400≤x≤1312000, for example, 430000, 450000, 500000, 600000, 700000, 800000, 900000, 1000000, 1100000, 1200000, etc.; 873600≤y≤2688000, for example, 900000, 10000 00, 1200000, 1500000, 1800000, 2000000, 2200000, 2500000, etc., 100000≤z≤4000000, for example, 500000, 1000000, 1500000, 2000000, 2500000, 3000000, 3500000, etc.

[0088] As a preferred technical solution of the present disclosure, the average molecular weight of the polymer is 7000-2000000 g / mol, for example, 8000 g / mol, 10000 g / mol, 50000 g / mol, 100000 g / mol, 500000 g / mol, 800000 g / mol, 1000000 g / mol, 1200000 g / mol, 1500000 g / mol, 1800000 g / mol, etc.

[0089] As a preferred technical solution of the present disclosure, the boron-based polyelectrolyte has a lithium ion transference number greater than 0.6, such as 0.7, 0.8, 0.9, 1.0, 1.2, 1.5, 2, 2.5, etc., an electrochemical stability window ≥ 5.0 V, such as 5.1 V, 5.2 V, 5.5 V, 5.8 V, 6.0 V, 6.2 V, 6.5 V, 6.8 V, 7 V, 8 V, etc., and an ionic conductivity at 30 ° C ≥ 2 × 10 -4 S cm -1 , for example 3×10 -4 S cm -1 , 4×10 -4 S cm -1 , 5×10 -4 S cm -1 , 6×10 -4 S cm -1 , 7×10 -4 S cm -1 , 8×10 -4 S cm -1 , 9×10 - 4 S cm -1 etc., the ionic conductivity at 70℃ is ≥1.0×10 -4 S cm -1 , for example 2×10 -4 S cm -1 , 5×10 -4 S cm -1 , 8×10 -4 S cm -1 , 9×10 -4 S cm -1 , 1×10 -3 S cm -1 , 6×10 -3 S cm -1 , 8×10 -3 S cm -1 , 1.0×10 - 2 S cm -1etc., the initial thermal decomposition temperature is ≥350°C, for example, 360°C, 380°C, 400°C, 420°C, 440°C, 450°C, 480°C, 500°C, etc., and the tensile strength is ≥4MPa, for example, 4.2MPa, 4.5MPa, 4.8MPa, 5.0MPa, 5.2MPa, 5.5MPa, 5.8MPa, 6MPa, 6.5MPa, 7MPa, etc.

[0090] The solid electrolyte provided by the present disclosure has excellent mechanical properties, good tensile strength, high ionic conductivity, lithium ion transference number and wide electrochemical window, which can meet the application requirements of batteries.

[0091] In a third aspect, the present disclosure provides a solid electrolyte membrane, the components of which include the boron-based polyelectrolyte described in the first aspect.

[0092] The preparation method of the solid electrolyte membrane disclosed in the present invention comprises: dissolving the boron-based polyelectrolyte in DMSO at a mass ratio of 1:5-15, such as 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, etc., stirring for 5-24 hours (such as 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, etc.) until completely dissolved, and then pouring into a polytetrafluoroethylene mold. , and dry at 50-70°C (52°C, 55°C, 58°C, 60°C, 62°C, 65°C, 68°C, etc.) for 24-48h (for example, 30h, 32h, 35h, 38h, 40h, 42h, 44h, etc.) to volatilize the solvent, and then transfer to Ar atmosphere and dry for 12h to obtain the solid electrolyte film, preferably with a thickness of 30-200μm, for example, 40, 50, 60, 80, 100, 120, 150, 180, etc.

[0093] In a fourth aspect, the present disclosure provides use of the boron-based polyelectrolyte described in the second aspect or the solid electrolyte membrane described in the third aspect in an electrochemical device.

[0094] In a fifth aspect, the present disclosure provides an electrochemical device comprising the boron-based polyelectrolyte described in the second aspect or the solid electrolyte membrane described in the third aspect.

[0095] In a sixth aspect, the present disclosure provides a vehicle comprising the boron-based polyelectrolyte described in the second aspect, the solid electrolyte membrane described in the third aspect, or the electrochemical device described in the fifth aspect.

[0096] The boron-based polyelectrolyte and its preparation method provided by the present disclosure are specifically described below through examples.

[0097] Example 1

[0098] This embodiment provides a boron-based polyelectrolyte comprising a polymer having a structure shown in the following formula:

[0099]

[0100] The preparation method is as follows:

[0101] (1) Dissolve 0.1M functional boron-based lithium salt in N,N-dimethylformamide solvent and stir at room temperature for 3 hours to obtain solution a, wherein the structural formula of the functional boron-based lithium salt is as follows:

[0102]

[0103] (2) 0.2 g of polyethylene oxide with an average molecular weight of 200w and 0.002 g of azobisisobutyronitrile were added to solution a, wherein the molar ratio of polyethylene oxide to Li was 10:1, and the mass of azobisisobutyronitrile accounted for 0.5% of the total mass of solid reactants. The reactants were heated and stirred at 55°C for 6 h to obtain a uniform viscous fluid, and dried at 50°C for 24 h to evaporate the solvent, thereby obtaining a boron-based polyelectrolyte.

[0104] The X-ray diffraction spectrum of the boron-based polyelectrolyte obtained in this example is shown in FIG. Figure 1 As shown in the figure, there is a set of sharp diffraction peaks at 2θ=19° and 23°, superimposed on the broad peak in the range of 10°<2θ<30°. The diffraction peaks belong to the crystalline phase and amorphous phase of PEO respectively; and the characteristic peaks of the boron-based lithium salt completely disappear, confirming that the functional boron-based lithium salt has undergone a cross-linking reaction with PEO.

[0105] The lithium ion migration number test of the boron-based polyelectrolyte obtained in this example is shown in FIG. Figure 2 ,exist Figure 2 The graph in the middle is a polarization current test graph of the material and an impedance test graph before and after the test. From the graph combined with the formula calculation, it can be seen that the lithium ion transference number of the boron-based polyelectrolyte obtained in this embodiment is 0.5.

[0106] Comparative Example 1

[0107] This comparative example provides a method for preparing a boron-based polyelectrolyte.

[0108] The difference from Example 1 is that in this example, the cross-linking reaction in step (2) is carried out at 50° C. for 5 h.

[0109] The final product obtained in this comparative example is a uniform liquid product, indicating that a large amount of unreacted functional boron-based lithium salt still exists in the product obtained by the preparation method provided in this comparative example, that is, the cross-linking reaction in this comparative example is incomplete.

[0110] Example 2

[0111] This embodiment provides a boron-based polyelectrolyte comprising a polymer having a structure shown in the following formula:

[0112]

[0113] The preparation method is as follows:

[0114] (1) 0.2 M functional boron-based lithium salt and 0.2 M bisbenzenesulfonimide were dissolved in dimethyl sulfoxide solvent and stirred at room temperature for 4 h to obtain solution a, wherein the structural formula of the functional boron-based lithium salt is as follows:

[0115]

[0116] (2) 0.4 g of polyethylene oxide with an average molecular weight of 40w and 0.005 g of azobisisobutyronitrile were added to solution a, wherein the molar ratio of polyethylene oxide to Li was 20:1, and the mass of azobisisobutyronitrile accounted for 1% of the total mass of solid reactants. The reactants were heated and stirred at 65°C for 10 h to obtain a uniform viscous fluid, and dried at 50°C for 24 h to evaporate the solvent, thereby obtaining a boron-based polyelectrolyte.

[0117] The Fourier transform infrared spectrum of the boron-based polyelectrolyte obtained in this example is shown in FIG. Figure 3 As shown. It can be clearly seen from the figure that the wave numbers are 1575 and 1556 cm -1 The C=C vibration characteristic peak at 3087cm -1 The CH(C=C) peak at 3439cm -1 The broad peak at is the NH stretching vibration peak of bisbenzenesulfonimide. As can be seen from the figure, the cross-linking reaction of the functional lithium salt in this embodiment is complete, and the target product, boron-based polyelectrolyte, has been successfully synthesized.

[0118] Comparative Example 2

[0119] This comparative example provides a method for preparing a boron-based polyelectrolyte.

[0120] The difference from Example 2 is that in this example, the co-solvent 0.2 M bisbenzenesulfonimide is not added.

[0121] The final product obtained in this comparative example contains undissolved functional lithium salt, and the Fourier infrared spectrum of the product obtained in this comparative example is as follows: Figure 4 As shown in the figure, the wave number is 3087cm -1 The CH(C=C) peak at 1575cm-1 completely disappears, but the peaks at 1575cm-1 and 1556cm-1 exist. -1 The C=C vibration characteristic peak at , indicates that in this comparative example, when the co-solvent bisbenzenesulfonimide is not introduced, the solubility of the functional lithium salt decreases and the cross-linking reaction is incomplete, and the target boron-based polyelectrolyte product is not synthesized.

[0122] Example 3

[0123] This embodiment provides a boron-based polyelectrolyte comprising a polymer having a structure shown in the following formula:

[0124]

[0125] The preparation method is as follows:

[0126] (1) 0.4 M functional boron-based lithium salt and 0.4 M benzenesulfonamide were dissolved in acetone solvent and stirred at room temperature for 6 h to obtain solution a, wherein the structural formula of the functional boron-based lithium salt is as follows:

[0127]

[0128] (2) 1.9 g of PVDF-HFP and 0.005 g of azobisisobutyronitrile were added to solution a, wherein the molar ratio of PVDF-HFP to Li was 20:1, and the mass of azobisisobutyronitrile accounted for 1.5% of the total mass of solid reactants. The reactants were heated and stirred at 65 °C for 10 h to obtain a uniform viscous fluid, and then dried at 60 °C for 30 h to evaporate the solvent, thereby obtaining a boron-based polyelectrolyte.

[0129] The thermal stability test results of the boron-based polyelectrolyte obtained in this example are shown in FIG. Figure 5 As can be seen from the figure, the initial thermal decomposition temperature of the boron-based polyelectrolyte provided in this embodiment is 363°C, which has excellent thermal stability; moreover, there is only one weight loss platform in the entire heating stage and the weight loss is relatively complete, indicating that the preparation process is completely reacted and the final product has a single composition.

[0130] The impedance test graph of the boron-based polyelectrolyte obtained in this example is shown in FIG. Figure 6 ,Depend on Figure 6 It can be seen from the calculation that the ionic conductivity of the boron-based polyelectrolyte provided in this embodiment at 30°C is ≥4.4×10 -4 S cm -1 The ionic conductivity at 70℃ is ≥7.9×10 -4 S cm -1 .

[0131] Example 4

[0132] This embodiment provides a boron-based polyelectrolyte comprising a polymer having a structure shown in the following formula:

[0133]

[0134] The preparation method is as follows:

[0135] (1) Dissolve 1M functional boron-based lithium salt and 1M 4-phenoxybenzenesulfonyl fluoride in acetone and dimethyl sulfoxide solvents, and stir at room temperature for 6 hours to obtain solution a, wherein the structural formula of the functional boron-based lithium salt is as follows:

[0136]

[0137] (2) 1 g of polyethylene oxide (PEO) with an average molecular weight of 100 W, 0.33 g of 2,2'-(1,2-ethylenedioxy)bis(ethylenethiol), and 0.02 g of azobisisobutyronitrile were added to solution a. The molar ratios of PEO, 2,2'-(1,2-ethylenedioxy)bis(ethylenethiol), and Li were 50:1 and 4:1, respectively. The mass of azobisisobutyronitrile accounted for 2% of the total mass of the solid reactants. The reactants were heated and stirred at 65°C for 12 h to obtain a uniform viscous fluid. The solvent was evaporated by drying at 70°C for 48 h to obtain a boron-based polyelectrolyte.

[0138] The gel chromatography test results of the boron-based polyelectrolyte obtained in this example are shown in Table 1. As can be seen from the data in Table 1, the average molecular weight of the boron-based polyelectrolyte obtained in this example is 1411234 g / mol, which is greater than the average molecular weight of the reactant PEO by 1000000, indicating that a cross-linking reaction occurs;

[0139] Table 1

[0140]

[0141] The tensile test results of the boron-based polyelectrolyte obtained in this example are shown in FIG. Figure 7 .Depend on Figure 7 From the tensile test stress-strain curve in , it can be seen that the tensile strength of the product obtained in this example is 4.02 MPa. Within the elastic range, the Young's modulus is 116 MPa according to the slope value of the tensile test stress-strain, which confirms that the boron-based polyelectrolyte has high mechanical strength.

[0142] The impedance test graph of the boron-based polyelectrolyte obtained in this example is shown in FIG. Figure 8 From the figure and calculation, it can be seen that the ionic conductivity of the boron-based polyelectrolyte provided in this embodiment at 30°C is ≥1.0×10 -4 S cm -1 The ionic conductivity at 70℃ is ≥1.9×10 -4 S cm -1 .

[0143] Example 5

[0144] This embodiment provides a boron-based polyelectrolyte.

[0145] Among them, the ionic conductivity of the boron-based polyelectrolyte at 30 ° C is 2.76×10 -4 S cm-1 The ionic conductivity at 70℃ is 1.53×10 -3 S cm -1 .

[0146] The preparation method is as follows:

[0147] (1) 0.3 M functional boron-based lithium salt and 0.35 M fluorobisbenzenesulfonimide were dissolved in N-methylpyrrolidone solvent and stirred at room temperature for 5 h to obtain solution a, wherein the structural formula of the functional boron-based lithium salt is as follows:

[0148]

[0149] (2) 0.6 g of polyethylene oxide (PEO) with an average molecular weight of 40 W and 0.01 g of azobisisobutyronitrile were added to solution a, where the molar ratio of PEO to Li was 30:1 and the mass of azobisisobutyronitrile accounted for 1% of the total mass of the solid reactants. The reactants were heated and stirred at 65°C for 8 h to obtain a uniform viscous fluid. The solvent was evaporated by drying at 60°C for 30 h, yielding a boron-based polyelectrolyte.

[0150] Application Example 1

[0151] This application example provides a solid electrolyte film prepared using the boron-based polyelectrolyte provided in Example 5.

[0152] Boron-based polyelectrolyte was dissolved in DMSO at a mass ratio of 1:15 and stirred for 8 h until completely dissolved. The viscous fluid was poured into a polytetrafluoroethylene mold and dried at 50 °C for 24 h to evaporate the solvent. The mold was then transferred to an Ar atmosphere and dried for 12 h to obtain a solid electrolyte film with a thickness of 110 μm.

[0153] The impedance test results of the solid electrolyte film provided in this application example are shown in the figure Figure 9 The figure shows the impedance of the single-ion conductor gel polymer electrolyte at 30°C, 40°C, 50°C, 60°C, and 70°C, and the calculated ionic conductivity. It can be seen from the figure that the impedance of the single-ion conductor gel polymer electrolyte decreases with increasing temperature, and its ionic conductivity suddenly increases around 60°C. As can be seen from the figure, the solid electrolyte film provided in this application example has high ionic conductivity, reaching 2.76×10 -4 S cm -1 , 1.53×10 at 70℃ -3 S cm -1 .

[0154] The DSC test results of the solid electrolyte film provided in this application example are shown in the figure below: Figure 10As shown in the figure, it can be seen that the initial melting point of the solid electrolyte film is 60°C, which is lower than that of pure PEO. A lower melting point is more conducive to improving the ionic conductivity and lithium ion transference number of the system.

[0155] Comparative Application Example 2

[0156] This comparative application example provides a method for preparing a boron-based polyelectrolyte.

[0157] The difference from the application example is that in this comparative application example, the amount of DMSO used is 30 times the mass of the boron-based polymer.

[0158] The actual picture of the film finally obtained in this comparative example is shown in FIG. Figure 11 ,exist Figure 11 In the process, since DMSO enters the network structure of the boron-based polyelectrolyte, even if appropriate drying temperature and drying time are used, the large amount of DMSO present in the network structure makes it impossible to peel the film from the polytetrafluoroethylene mold, and the solid electrolyte film cannot be prepared.

[0159] Example 6

[0160] This embodiment provides a boron-based polyelectrolyte comprising a polymer having a structure shown in the following formula:

[0161]

[0162] The lithium ion transference number of the boron-based polyelectrolyte is 0.62, the electrochemical stability window is 5V, and the ionic conductivity at 30℃ is 2.85×10 -4 S cm -1 .

[0163] The preparation method is as follows:

[0164] (1) 0.5 M functional boron-based lithium salt and 0.5 M phenylmethylsulfonyl fluoride were dissolved in acetone and dimethyl sulfoxide solvents, and stirred at room temperature for 6 h to obtain solution a, wherein the structural formula of the functional boron-based lithium salt is as follows:

[0165]

[0166] (2) 0.88 g of pentaerythritol tetrakis(3-mercaptopropionate) and 0.016 g of azobisisobutyronitrile were added to solution a, where the molar ratio of pentaerythritol tetrakis(3-mercaptopropionate) to lithium was 4:1, and the mass of azobisisobutyronitrile accounted for 1.5% of the total mass of the solid reactants. The reactants were heated and stirred at 65°C for 10 h to obtain a uniform viscous fluid. The solvent was evaporated by drying at 70°C for 40 h, yielding a boron-based polyelectrolyte.

[0167] Application Example 2

[0168] This application example provides a solid electrolyte film prepared using the boron-based polyelectrolyte provided in Example 6.

[0169] Boron-based polyelectrolyte was dissolved in DMSO at a mass ratio of 1:10 and stirred for 10 h until completely dissolved. The viscous fluid was poured into a polytetrafluoroethylene mold and dried at 65 °C for 10 h to evaporate the solvent. The mold was then transferred to an Ar atmosphere and dried for 24 h to obtain a solid electrolyte film with a thickness of 90 μm.

[0170] The lithium ion migration number test results of the solid electrolyte film provided in this application example are shown in the figure Figure 12 The lithium ion transfer number is a parameter used to evaluate the lithium ion transfer ability. A high ion transfer number is beneficial to reducing concentration polarization during charge and discharge, inhibiting lithium dendrite growth, improving active material utilization, and extending battery life. Figure 12 It can be clearly seen that the impedance difference of the single ion conductor gel polymer electrolyte film before and after polarization is small, indicating that the electrolyte has good electrochemical stability. The calculated lithium ion transference number is 0.62, and the ionic conductivity at 30°C reaches 2.85×10 -4 S cm -1 .

[0171] The CV test results of the solid electrolyte film provided in this application example are shown in the figure below. Figure 13 As shown in the figure, the current fluctuation does not exceed 0.1 mA within the potential range of 5V, and the multiple scanning CV curves are basically overlapped, indicating that the single ion conductor gel polymer electrolyte film obtained in Example 6 has excellent electrochemical stability and the electrochemical window reaches 5V.

[0172] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0173] The foregoing description is intended only to provide specific embodiments of the present disclosure, intended to enable those skilled in the art to understand and implement the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure is not intended to be limited to the embodiments described herein, but rather to be construed in the broadest manner consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a boron-based polyelectrolyte, characterized in that: The preparation method comprises the following steps: The functional boron-based lithium salt and the cross-linking agent undergo a cross-linking reaction under the action of an initiator to obtain the boron-based polyelectrolyte; Wherein, the functional boron-based lithium salt has the general structural formula shown in Formula I: 1≤n≤5； The cross-linking agent is selected from at least one of polyethylene glycol, PVDF-HFP, pentaerythritol tetrakis(3-mercaptopropionate) or 2,2'-(1,2-ethylenedioxy)bis(ethylenethiol).

2. The preparation method according to claim 1, characterized in that The molar ratio of the cross-linking agent to the functional boron-based lithium salt is 4-50:1; And / or, the temperature of the cross-linking reaction is 55-80° C., and preferably the time of the cross-linking reaction is 6-12 hours.

3. The preparation method according to claim 1 or 2, characterized in that The initiator is selected from thermal initiators, preferably azobisisobutyronitrile; And / or, the added amount of the initiator is 0.1-2% of the total solid reactant mass.

4. The preparation method according to any one of claims 1 to 3, characterized in that The preparation method comprises: (1) dissolving a functional boron-based lithium salt in a solvent to obtain a solution; (2) adding a crosslinking agent and an initiator to the solution to carry out a crosslinking reaction, and removing the solvent after the reaction to obtain the boron-based polyelectrolyte.

5. The preparation method according to claim 4, characterized in that The solution further comprises a cosolvent, and preferably the cosolvent is selected from at least one of bisbenzenesulfonimide, fluorobisbenzenesulfonimide, benzenesulfonamide, benzenesulfonyl chloride, 4-phenoxybenzenesulfonyl fluoride or phenylmethylsulfonyl fluoride.

6. The preparation method according to claim 4 or 5, characterized in that The solvent is selected from at least one of ethanol, ether, dimethyl sulfoxide, N-methylpyrrolidone, acetone or N,N-dimethylformamide; And / or, in the solution, the concentration of the functional boron-based lithium salt is 0.1-1 mol / L.

7. A boron-based polyelectrolyte, characterized in that The method is prepared according to any one of claims 1 to 6.

8. The boron-based polyelectrolyte according to claim 7, characterized in that The boron-based polyelectrolyte has a lithium ion transference number greater than 0.6, an electrochemical stability window greater than or equal to 5.0 V, and an ionic conductivity greater than or equal to 2×10 -4 S cm -1 , ionic conductivity at 70℃≥1.0×10 -4 S cm -1 , initial thermal decomposition temperature ≥350℃, tensile strength ≥4MPa.

9. A solid electrolyte membrane, characterized in that The components of the solid electrolyte membrane include the boron-based polyelectrolyte prepared by the preparation method according to any one of claims 1 to 6 or the boron-based polyelectrolyte according to claim 7 or 8.

10. Use of the boron-based polyelectrolyte according to claim 7 or 8 or the solid electrolyte membrane according to claim 9 in an electrochemical device.

11. An electrochemical device, characterized in that: The invention comprises the boron-based polyelectrolyte according to claim 7 or 8 or the solid electrolyte membrane according to claim 9.

12. A vehicle, characterized in that: The invention comprises the boron-based polyelectrolyte according to claim 7 or 8, the solid electrolyte membrane according to claim 9 or the electrochemical device according to claim 11.

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