A polymer electrolyte membrane, its preparation method, and a lithium-ion battery

Abstract

This invention relates to the field of polymer electrolyte technology, and in particular to a polymer electrolyte membrane, its preparation method, and a lithium-ion battery. The polymer electrolyte membrane of this invention is mainly prepared from polyvinylidene fluoride hexafluoropropylene and a single-ion polymer, wherein the single-ion polymer has the following general structural formula; where the ratio of x to y is 1:(0.25~0.5). This invention provides a composite polymer electrolyte membrane based on a single-ion polymer with a specific structure. By introducing nitrile bonds into the single-ion polymer structure and adding a polyvinylidene fluoride hexafluoropropylene polymer matrix, the lithium-ion battery's lithium electrolyte capacity is improved. + The polymer electrolyte membrane exhibits excellent ionic conductivity, migrating ability, and film-forming properties.

Description

Technical Field

[0001] This invention relates to the field of polymer electrolyte technology, and in particular to a polymer electrolyte membrane, its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries (LIBs) are a high-density energy storage solution widely used in power plants and vehicle electric fields. Commercial liquid electrolytes used in lithium-ion batteries typically dissolve lithium salts in carbonate solvents to achieve high ionic conductivity; however, the low flash point of non-aqueous solvents can easily lead to safety issues such as leakage and combustion. Solid-state electrolytes, due to their unique physical properties, can avoid these problems.

[0003] Solid electrolytes can be classified into inorganic solid electrolytes (ISE), solid polymer electrolytes (SPE), and inorganic filler composite solid polymer electrolytes based on their composition. Compared with inorganic solid electrolytes, solid polymer electrolytes offer greater flexibility in shape and packaging design. However, the ionic conductivity of solid polymer electrolytes at room temperature is too low (10⁻⁶). -7 ~10 -6 The lithium transfer rate (S / cm) is insufficient for practical applications. Solid polymer electrolytes are mainly based on complexes of lithium salts and macromolecules, which are typically dual-ion conductors where anions and cations migrate simultaneously. The lithium-ion transference number is usually around 0.3. Due to the deposition of anions on the anode surface and side reactions, concentration gradients and battery polarization occur. Therefore, single-ion conductors have attracted widespread attention.

[0004] Single-ion conductive solid polymer electrolytes (SIPEs) are electrolytes that use lithium ions as the main conducting ions. In this electrolyte, anions are fixed on the polymer backbone, and lithium ions are correlated with anions. Lithium ions are the only charge carriers that are conducted through the electrolyte, eliminating anion polarization at the electrode interface. The performance of single-ion conductors is even ten times less ionic conductivity than that of dual-ion conductive electrolytes. However, compared with traditional organic liquid electrolytes, their room temperature ionic conductivity is still low, and their impedance at the interface with the positive and negative electrodes is high, which hinders their application in lithium-ion batteries.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The first objective of this invention is to provide a polymer electrolyte membrane, which is a composite polymer electrolyte membrane based on a single-ion polymer with a specific structure, and has excellent Li... + Its migration ability, ionic conductivity and film-forming properties.

[0007] The second objective of this invention is to provide a method for preparing the above-mentioned polymer electrolyte membrane, which is simple in process.

[0008] A third objective of this invention is to provide a lithium-ion battery that uses the polymer electrolyte membrane described above, thereby reducing battery polarization and improving battery cycle life and stability.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0010] This invention provides a polymer electrolyte membrane, mainly made of polyvinylidene fluoride hexafluoropropylene and a single-ion polymer, wherein the single-ion polymer has the following general structural formula;

[0011] In the formula, the ratio of x to y is 1:(0.25~0.5).

[0012] Furthermore, the mass ratio of the polyvinylidene fluoride hexafluoropropylene to the single-ion polymer is 1:(0.5-2).

[0013] The present invention also provides a method for preparing the polymer electrolyte membrane as described above, comprising the following steps:

[0014] S1, 2-acrylamido-2-methylpropanesulfonic acid and lithium salt were subjected to a lithiation reaction in an organic solvent to obtain a solution containing lithium 2-acrylamido-2-methylpropanesulfonic acid;

[0015] S2. The solution containing lithium 2-acrylamide-2-methylpropanesulfonate, acrylonitrile, and an initiator react to obtain a reaction solution. The reaction solution is mixed with the precipitation solvent to obtain a polymer precipitate. The polymer precipitate is purified and dried to obtain a single-ion polymer.

[0016] S3, a mixture of polyvinylidene fluoride hexafluoropropylene, the single-ion polymer, and an organic solvent is poured onto a substrate and dried to obtain the polymer electrolyte membrane.

[0017] Further, in step S1, the molar ratio of 2-acrylamide-2-methylpropanesulfonic acid to the lithium salt is 2:(1 to 1.5).

[0018] Preferably, in step S1, the lithium salt includes lithium carbonate.

[0019] Further, in step S2, the molar ratio of the acrylonitrile and the lithium 2-acrylamide-2-methylpropanesulfonate is 1:(2-4).

[0020] Further, in step S2, the molar ratio of the initiator to the 2-acrylamide-2-methylpropanesulfonic acid is (0.005~0.015):1.

[0021] Furthermore, in step S2, the reaction temperature is 55–65°C, and the reaction time is 10–15 h.

[0022] Further, in step S2, the initiator includes at least one of azobisisobutyronitrile, dimethyl azobisisobutyrate, and diacyl peroxide.

[0023] Preferably, in step S2, the precipitating solvent includes icy diethyl ether.

[0024] Further, in step S3, the mass percentage of polyvinylidene fluoride hexafluoropropylene in the mixture is 10% to 20%.

[0025] The present invention also provides a lithium-ion battery comprising the polymer electrolyte membrane described above.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] The polymer electrolyte membrane provided by this invention is a composite polymer electrolyte membrane based on a single-ion polymer with a specific structure. By designing and optimizing the structure of the single-ion polymer, nitrile bonds are introduced into the single-ion polymer structure. Furthermore, by adding a polymer matrix of polyvinylidene fluoride hexafluoropropylene to the polymer electrolyte membrane, the Li- content of the polymer electrolyte membrane is improved. + It exhibits excellent migration ability and film-forming properties, with superior ionic conductivity > 1.0 × 10⁻⁶. -4 S / cm -1 .

[0028] The polymer electrolyte membrane of the present invention fixes anions on the polymer backbone, making lithium ion migration easier and improving ionic conductivity; when used in ion batteries, it can reduce battery polarization and improve battery cycle life and stability. Attached Figure Description

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0030] Figure 1 This is the NMR spectrum of P(AN-AMPSLi) in Embodiment 1 of the present invention.

[0031] Figure 2 The above are the AMPS and P(AN-AMPSLi) Fourier transform infrared spectra of Embodiment 1 of the present invention.

[0032] Figure 3 This is a symmetry stability test diagram of the polymer electrolyte membranes of Comparative Example 1 and Example 2 of the present invention.

[0033] Figure 4 The PVDF-HFP polymer electrolyte membrane of Comparative Example 1 and the P(AN-AMPSLi) membrane of Example 2 are examples of the present invention. 0.5 SEM image of lithium anode after repeated peeling / deposition of polymer electrolyte membrane. Detailed Implementation

[0034] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0035] The following describes in detail a polymer electrolyte membrane, its preparation method, and a lithium-ion battery according to an embodiment of the present invention.

[0036] In some embodiments of the present invention, a polymer electrolyte membrane is provided, which is mainly made of polyvinylidene fluoride hexafluoropropylene and a single-ion polymer having the following general structural formula;

[0037] In the formula, the ratio of x to y is 1:(0.25~0.5).

[0038] In the general structural formula of a single-ion polymer, x and y represent the molar ratio of the two materials, not their actual chemical structure.

[0039] In some embodiments of the present invention, typical but not limiting measurements, for example, the ratio of x to y can be 1:0.25, 1:0.3, 1:0.35, 1:0.4, 1:0.45, or 1:0.5, etc.

[0040] The polymer electrolyte membrane of this invention is a composite polymer electrolyte membrane based on a single-ion polymer with a specific structure. By designing and optimizing the structure of the polymer electrolyte membrane, nitrile bonds are introduced into the single-ion polymer structure. As a flexible group, the nitrile bond can promote the migration of lithium ions and also give the polymer membrane good toughness. Polyvinylidene fluoride hexafluoropropylene is electrically neutral as the polymer matrix. The addition of PVDF-HFP is beneficial to improving the film-forming properties of the polymer electrolyte. This provides extremely high protection for the membrane that inhibits lithium dendrite penetration. These excellent properties give it good ionic conductivity and processing performance.

[0041] This invention designs a specific structure for a single-ion polymer to fix anions in the polymer backbone, making lithium ion migration easier, which is beneficial to improving ionic conductivity and eliminating anion polarization at the electrode interface.

[0042] In some embodiments of the present invention, the mass ratio of polyvinylidene fluoride hexafluoropropylene to monoionic polymer is 1:(0.5-2).

[0043] In some specific embodiments of the present invention, the mass ratio of polyvinylidene fluoride hexafluoropropylene to the single-ion polymer is 1:(1 to 1.5). Using a mass ratio within the above range, a polymer electrolyte membrane with higher conductivity and better mechanical properties can be obtained.

[0044] In some embodiments of the present invention, the polymer electrolyte membrane has an ionic conductivity > 1.0 × 10⁻⁶ at room temperature. - 4 S / cm -1 Preferably, the polymer electrolyte membrane has an ionic conductivity of 1.3 × 10⁻⁶ at room temperature. -4 ~2.0×10 -4 S / cm -1 .

[0045] In some embodiments of the present invention, the polymer electrolyte membrane has a tensile strength of 15-50 MPa, an elongation at break of 8%-30%, and a Young's modulus of 40-70 MPa.

[0046] In some embodiments of the present invention, a method for preparing the above-mentioned polymer electrolyte membrane is also provided, comprising the following steps:

[0047] S1, 2-acrylamide-2-methylpropanesulfonic acid (AMPS) and lithium salt were subjected to a lithiation reaction in an organic solvent to obtain a solution containing lithium 2-acrylamide-2-methylpropanesulfonate (AMPSLi);

[0048] S2, a solution containing lithium 2-acrylamide-2-methylpropanesulfonate (AMPSLi), acrylonitrile (AN) and an initiator are reacted to obtain a reaction solution. The reaction solution is mixed with the precipitating solvent to obtain a polymer precipitate. The polymer precipitate is purified and dried to obtain a single-ion polymer.

[0049] A mixture of S3, polyvinylidene fluoride hexafluoropropylene (PVDF-HFP), monoionic polymer and organic solvent is poured onto a substrate and dried to obtain a polymer electrolyte membrane.

[0050] In some embodiments of the present invention, the single-ion polymer in step S2 is named P(AN-AMPSLi), and the polymer electrolyte membrane is named P(AN-AMPSLi)a, where a is the ratio of the mass of P(AN-AMPSLi) to the total mass of the polymer electrolyte membrane.

[0051] This invention lithiates AMPS to obtain AMPSLi through Lewis acid-base reaction, then copolymerizes it with nitrile functional monomers to form a polyanionic salt through free radical polymerization, and then mixes it with a polyvinylidene fluoride hexafluoropropylene matrix to obtain a composite polymer electrolyte membrane based on P(AN-AMPSLi).

[0052] P(AN-AMPSLi) is a single-ion polymer. Since lithium ions dominate the conductive sites, it is advantageous to reduce polarization by immobilizing anions on the polymer main chain. Since the anions cannot move, the negative ion depletion layer near the lithium anode does not generate a large electric field. The reduction in polarization allows the addition of P(AN-AMPSLi) to promote the formation of the solid-electrolyte interphase (SEI) layer between the polymer electrolyte membrane and the electrode, and the Li... + The formation of transport channels reduces interfacial resistance. PVDF-HFP is electrically neutral, and its addition improves the film-forming properties of the polymer electrolyte.

[0053] The preparation method of the present invention is simple, and the film can be directly formed after drying without complicated process flow. The prepared polymer electrolyte membrane has excellent processing performance and ionic conductivity.

[0054] In some embodiments of the present invention, in step S1, the molar ratio of 2-acrylamide-2-methylpropanesulfonic acid and lithium salt is 2:(1 to 1.5).

[0055] In some embodiments of the present invention, in step S1, the lithium salt includes lithium carbonate (Li2CO3).

[0056] In some embodiments of the present invention, in step S1, the organic solvent includes N,N-dimethylformamide (DMF).

[0057] In some embodiments of the present invention, in step S1, the temperature of the lithiation reaction is 15-35°C and the time of the lithiation reaction is 1-3 hours.

[0058] In some embodiments of the present invention, in step S2, the molar ratio of acrylonitrile to lithium 2-acrylamide-2-methylpropanesulfonate is 1:(2-4); preferably, the molar ratio of acrylonitrile to lithium 2-acrylamide-2-methylpropanesulfonate is 1:3.

[0059] In some embodiments of the present invention, in step S2, the molar ratio of the initiator to 2-acrylamide-2-methylpropanesulfonic acid is (0.005 to 0.015):1; preferably, the molar ratio of the initiator to 2-acrylamide-2-methylpropanesulfonic acid is 0.01:1.

[0060] In some embodiments of the present invention, in step S2, the reaction temperature is 55-65°C and the reaction time is 10-15 h; preferably, the reaction temperature is 60°C and the reaction time is 12 h.

[0061] In some embodiments of the present invention, in step S2, the reaction is carried out in an inert gas atmosphere; preferably, the inert gas includes nitrogen.

[0062] In some embodiments of the present invention, in step S2, the initiator includes at least one of azobisisobutyronitrile, dimethyl azobisisobutyrate, and diacyl peroxide.

[0063] In some embodiments of the present invention, in step S2, the precipitated solvent includes icy diethyl ether.

[0064] In some embodiments of the present invention, in step S2, the volume ratio of the reaction solution to the precipitated solvent is 1:(7-9).

[0065] In some embodiments of the present invention, step S2, mixing the reaction solution with the precipitation solvent, includes adding the reaction solution dropwise into the precipitation solvent.

[0066] In some embodiments of the present invention, in step S2, purification includes dissolving the polymer precipitate in an organic solvent and then adding it dropwise to icy diethyl ether for precipitation; preferably, the number of dissolutions and precipitations is ≥3 times, and preferably, the organic solvent includes N,N-dimethylformamide (DMF).

[0067] In some embodiments of the present invention, in step S2, the drying temperature is 50-100°C and the drying time is 40-60 hours; preferably, the drying includes vacuum drying.

[0068] In some embodiments of the present invention, in step S3, the mass ratio of polyvinylidene fluoride hexafluoropropylene to monoionic polymer is 1:(0.5-2); preferably, the mass ratio of polyvinylidene fluoride hexafluoropropylene to monoionic polymer is 1:(1-1.5).

[0069] In some embodiments of the present invention, in step S3, the mass percentage of polyvinylidene fluoride hexafluoropropylene in the mixture is 10% to 20%; preferably, the mass percentage of polyvinylidene fluoride hexafluoropropylene in the mixture is 15%.

[0070] In some embodiments of the present invention, in step S3, the organic solvent includes N,N-dimethylformamide (DMF).

[0071] In some embodiments of the present invention, step S3, the method for preparing the mixture includes: dissolving polyvinylidene fluoride hexafluoropropylene in an organic solvent, then adding P(AN-AMPSLi), and stirring evenly at room temperature.

[0072] In some embodiments of the present invention, in step S3, drying includes vacuum drying; preferably, the drying temperature is 50-100°C and the drying time is 20-30 hours.

[0073] In some specific embodiments of the present invention, when the mass ratio of PVDF-HFP to P(AN-AMPSLi) is 2:1, 1:1, and 1:2, and the value of a is 0.3, 0.5, and 0.7, respectively, the prepared polymer electrolyte membrane is named P(AN-AMPSLi). 0.3 , P(AN-AMPSLi 0.5 , P(AN-AMPSLi 0.7 .

[0074] In some embodiments of the present invention, a lithium-ion battery is also provided, comprising the above-described polymer electrolyte membrane.

[0075] The polymer electrolyte membrane of the present invention can be used in lithium-ion batteries, which helps to reduce battery polarization and improve battery cycle performance and stability.

[0076] Example 1

[0077] The polymer electrolyte membrane P(AN-AMPSLi) provided in this embodiment 0.3 The preparation method includes the following steps:

[0078] S1. Dry AMPS under vacuum at 60℃ for 48h, weigh 3g AMPS and add it to a 100mL flask, then add 10mL DMF and stir for 2h until AMPS is completely dissolved to obtain an AMPS solution; then add Li2CO3 to the AMPS solution according to the stoichiometric ratio of AMPS to Li2CO3 of 2:1 and perform a lithiation reaction at room temperature under ultrasonic dispersion for 2h to obtain a solution containing AMPSLi.

[0079] S2. Add the above solution containing AMPSLi to a three-necked flask, add AN monomer according to the molar ratio of AN to AMPSLi of 1:3, and then add AIBN. The amount of AIBN added is 1 mol% of the amount of AMPS added. Heat to 60°C in a silicone oil bath under nitrogen atmosphere and stir for 12 h to obtain the reaction solution.

[0080] The above reaction solution was slowly added dropwise to ice-cold ether to precipitate the copolymer, resulting in a white polymer precipitate. The volume ratio of the reaction solution to ice-cold ether was 1:8. The white polymer precipitate was then dissolved in DMF and added dropwise to ice-cold ether for precipitation. The dissolution and precipitation were repeated at least three times. The precipitate was then dried in a vacuum oven at 80°C for 2 days to obtain the monoionic polymer P(AN-AMPSLi).

[0081] S3. Dissolve 1g of PVDF-HFP in DMF to form a 15wt% polymer solution. Then weigh 0.5g of P(AN-AMPSLi) and add it to the solution. Stir well at room temperature, pour the solution onto a glass plate, and vacuum dry at 80℃ for 24h to obtain the polymer electrolyte membrane P(AN-AMPSLi). 0.3 .

[0082] Example 2

[0083] The polymer electrolyte membrane P(AN-AMPSLi) provided in this embodiment 0.5 The preparation method is the same as in Example 1, except that in step S3, the mass of P(AN-AMPSLi) is 1g.

[0084] Example 3

[0085] The polymer electrolyte membrane P(AN-AMPSLi) provided in this embodiment 0.7 The preparation method is the same as in Example 1, except that in step S3, the mass of P(AN-AMPSLi) is 1.5g.

[0086] Example 4

[0087] The preparation method of the polymer electrolyte membrane provided in this embodiment is the same as that in Example 1, except that in step S2, the molar ratio of AN to AMPSLi is 1:4.

[0088] Example 5

[0089] The preparation method of the polymer electrolyte membrane provided in this embodiment is the same as that in Example 1, except that in step S2, the molar ratio of AN to AMPSLi is 1:2.

[0090] Comparative Example 1

[0091] The method for preparing the polymer electrolyte membrane provided in this comparative example includes the following steps:

[0092] 1 g of PVDF-HFP and 0.4 g of lithium bis(trifluoromethanesulfonyl)imide (TFSILi) were dissolved in 30 mL of DMF. The resulting solution was poured onto the surface of a glass plate and dried under vacuum at 60 °C for 24 h to obtain a polymer electrolyte membrane.

[0093] Experimental Example 1

[0094] The NMR test of P(AN-AMPSLi) in Example 1 was performed, and the results are as follows: Figure 1 As shown. Infrared tests were performed on AMPS and P(AN-AMPSLi) of Example 1, and the results are as follows. Figure 2 As shown.

[0095] from Figure 1 and Figure 2 It can be seen that P(AN-AMPSLi) with a specific structure was obtained by using the preparation method of the present invention.

[0096] Experimental Example 2

[0097] The symmetry stability of the polymer electrolyte membrane of Comparative Example 1 and the polymer electrolyte membrane of Example 2 was tested, and the results are as follows: Figure 3 As shown.

[0098] from Figure 3 It can be seen that P(AN-AMPSLi) 0.5 The polymer electrolyte membrane exhibits high electrochemical cycling stability, maintaining a stable voltage-time curve at ±20 mV for 500 h. In contrast, the PVDF-HFP polymer electrolyte membrane shows significant fluctuations in the initial cycle, with the polarization voltage increasing sharply after approximately 200 h of constant current cycling. Therefore, P(AN-AMPSLi) 0.5 Polymer electrolyte membranes can promote the formation of a solid-electrolyte interphase (SEI) layer and Li between the solid electrolyte membrane and the electrode. + The formation of a transmission channel reduces the interface resistance.

[0099] The PVDF-HFP polymer electrolyte membrane of Comparative Example 1 and the P(AN-AMPSLi) membrane of Example 2 were used respectively. 0.5 A polymer electrolyte membrane is assembled with a lithium metal sheet to form Li|P(AN-AMPSLi). 0.5 |Li symmetric cells and Li|PVDF-HFP|Li symmetric cells, for PVDF-HFP polymer electrolyte membranes and P(AN-AMPSLi) 0.5 SEM analysis was performed on the lithium anode after repeated peeling / deposition of the polymer electrolyte membrane, and the results are as follows: Figure 4 As shown. Figure 4 In this context, 'a' represents P(AN-AMPSLi). 0.5 SEM images of lithium anodes after repeated peeling / deposition of polymer electrolyte membranes, b is SEM image of lithium anodes after repeated peeling / deposition of PVDF-HFP polymer electrolyte membranes.

[0100] from Figure 4 As can be seen from this, Li|P(AN-AMPSLi) 0.5 The lithium electrode surface of a Li-symmetric cell exhibits virtually no lithium dendrite formation due to the immobility of anions; therefore, the depletion layer of negative ions near the lithium anode does not generate a large electric field, resulting in dendrite-free lithium deposition. In contrast, the lithium electrode surface of a Li|PVDF-HFP|Li-symmetric cell is rough, exhibiting pits and protrusions, which is due to branching growth caused by free lithium ion deposition. This result is consistent with... Figure 3 The voltage-time curves of the symmetrical cells are consistent, further indicating that P(AN-AMPSLi) 0.5 Polymer electrolyte membranes exhibit high electrochemical cycling stability.

[0101] Using lithium iron phosphate as the positive electrode and lithium metal sheet as the negative electrode, 2025 model button batteries were assembled using polymer electrolyte membranes from Examples 1-3 and Comparative Example 1, respectively. Performance tests were conducted to obtain the ionic conductivity of the polymer electrolyte membrane at 25°C and the first discharge specific capacity of the battery at a 0.1C rate. The results are shown in Table 1.

[0102] Table 1

[0103] <![CDATA[Ionic conductivity (S / cm -1 )]]> <![CDATA[Initial discharge specific capacity (mAh·g -1 )]]> Example 1 <![CDATA[1.3×10 -4 ]]> 135 Example 2 <![CDATA[1.89×10 -4 ]]> 152 Example 3 <![CDATA[2.0×10 -4 ]]> 150 Comparative Example 1 <![CDATA[3.57×10 -5 ]]> 102

[0104] As shown in Table 1, the ionic conductivity of the polymer electrolyte of this invention is significantly higher than that of Comparative Example 1. With the increase in the number of lithium ions attached to sulfonate groups in the electrolyte system, the carrier concentration also increases, leading to higher conductivity. P(AN-AMPSLi) is a single-ion polymer. Since lithium ions dominate the conductive sites, it is advantageous to reduce polarization by fixing anions on the polymer chain backbone, as the anions cannot move. Therefore, the negative ion depletion layer near the lithium anode does not generate a large electric field. The reduction in polarization allows the addition of P(AN-AMPSLi) to promote the formation of the solid-electrolyte interphase (SEI) layer between the solid electrolyte membrane and the electrode, and the Li... + The formation of transport channels reduces the interface resistance. In Comparative Example 1, because the PVDF-HFP matrix is ​​electrically neutral, the added TFSI- anions and Li... + Cations can migrate bidirectionally, leading to a decrease in the conductivity of polymer electrolytes.

[0105] Experimental Example 3

[0106] The tensile strength, elongation at break, and Young's modulus of the polymer electrolyte membranes in Examples 1-3 and Comparative Example 1 were tested. The prepared solid polymer electrolyte membranes were cut into 1×5cm rectangular strips, clamped in the mold of the testing machine, and stretched at a certain rate to obtain stress-strain test data. Test conditions: 15 mm / s, 25℃. The results are shown in Table 2.

[0107] Table 2

[0108] Tensile strength (MPa) Elongation at break (%) Young's modulus (MPa) Example 1 15.2 22.5 43.4 Example 2 27.1 28.2 46.6 Example 3 42.5 8.4 68.5 Comparative Example 1 8.7 11.2 35.8

[0109] As shown in Table 2, with the increase of P(AN-AMPSLi) content, the tensile strength and elastic modulus of the polymer electrolyte membrane of the present invention both increase. The introduction of P(AN-AMPSLi) enhances the structural stability of the composite membrane and regulates the transfer and stacking of polymer chains. However, when the amount of P(AN-AMPSLi) added, a, reaches 0.7, the flexibility of the polymer electrolyte membrane of the present invention decreases sharply, and the elongation at break is even lower than that of the PVDF-HFP polymer electrolyte membrane. The overall results show that the polymer electrolyte membrane of the present invention has excellent processing performance.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A polymer electrolyte membrane, characterized in that, It is mainly made of polyvinylidene fluoride hexafluoropropylene and a single-ion polymer, which has the following general structural formula; In the formula, the ratio of x to y is 1:(0.25~0.5).

2. The polymer electrolyte membrane according to claim 1, characterized in that, The mass ratio of the polyvinylidene fluoride hexafluoropropylene to the monoionic polymer is 1:(0.5~2).

3. The method for preparing the polymer electrolyte membrane according to claim 1 or 2, characterized in that, Includes the following steps: S1, 2-acrylamido-2-methylpropanesulfonic acid and lithium salt were subjected to a lithiation reaction in an organic solvent to obtain a solution containing lithium 2-acrylamido-2-methylpropanesulfonic acid; S2. The solution containing lithium 2-acrylamide-2-methylpropanesulfonate, acrylonitrile, and an initiator react to obtain a reaction solution. The reaction solution is mixed with the precipitation solvent to obtain a polymer precipitate. The polymer precipitate is purified and dried to obtain a single-ion polymer. S3, a mixture of polyvinylidene fluoride hexafluoropropylene, the single-ion polymer, and an organic solvent is poured onto a substrate and dried to obtain the polymer electrolyte membrane.

4. The method for preparing the polymer electrolyte membrane according to claim 3, characterized in that, In step S1, the molar ratio of 2-acrylamide-2-methylpropanesulfonic acid to the lithium salt is 2:(1~1.5).

5. The method for preparing the polymer electrolyte membrane according to claim 3, characterized in that, In step S1, the lithium salt includes lithium carbonate.

6. The method for preparing the polymer electrolyte membrane according to claim 3, characterized in that, In step S2, the molar ratio of acrylonitrile to lithium 2-acrylamide-2-methylpropanesulfonate is 1:(2~4).

7. The method for preparing the polymer electrolyte membrane according to claim 3, characterized in that, In step S2, the molar ratio of the initiator to the 2-acrylamide-2-methylpropanesulfonic acid is (0.005~0.015):

1.

8. The method for preparing the polymer electrolyte membrane according to claim 3, characterized in that, In step S2, the reaction temperature is 55~65℃ and the reaction time is 10~15h.

9. The method for preparing the polymer electrolyte membrane according to claim 3, characterized in that, In step S2, the initiator includes at least one of azobisisobutyronitrile, dimethyl azobisisobutyrate, and diacyl peroxide.

10. The method for preparing the polymer electrolyte membrane according to claim 3, characterized in that, In step S2, the precipitating solvent includes icy diethyl ether.

11. The method for preparing the polymer electrolyte membrane according to claim 3, characterized in that, In step S3, the mass percentage of polyvinylidene fluoride hexafluoropropylene in the mixture is 10% to 20%.

12. A lithium-ion battery, characterized in that, Includes the polymer electrolyte membrane as described in claim 1 or 2.

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