Perfluoropolyether-based polymer solid electrolyte film regulated and controlled by mixed solvent as well as preparation method and application of perfluoropolyether-based polymer solid electrolyte film

Abstract

The invention discloses a perfluoropolyether-based polymer solid electrolyte film regulated and controlled by a mixed solvent as well as a preparation method and application of the perfluoropolyether-based polymer solid electrolyte film, and belongs to the field of organic polymer solid electrolyte preparation. Reacting under the action of an initiator and an RAFT (reversible addition-fragmentation chain transfer) reagent to obtain a perfluoropolyether-based copolymer; the method comprises the following steps: adding a perfluoropolyether-based copolymer into a polyvinylidene fluoride-hexafluoropropylene copolymer solution in which lithium salt is dissolved, the mass of the polyvinylidene fluoride-hexafluoropropylene copolymer accounts for 10%-30% of the mass of the polyvinylidene fluoride-hexafluoropropylene copolymer, the mass of the N, N '-dimethylformamide, the mass of the trifluorotoluene and the mass of the perfluoropolyether-based copolymer account for 10%-30% of the mass of the polyvinylidene fluoride-hexafluoropropylene copolymer, and the perfluoropolyether-based polymer solid-state electrolyte film is obtained by uniformly mixing and then preparing a film. And the comprehensive performance of the composite solid electrolyte serving as the film is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of organic polymer solid-state electrolyte preparation, and relates to a mixed solvent regulated perfluoropolyether-based polymer solid-state electrolyte film and a preparation method and application thereof. BACKGROUND

[0002] Lithium metal batteries have become an indispensable part of daily life, and are widely used in portable electronic devices such as mobile phones and computers, as well as in electric vehicles and smart grids, showing good development prospects.

[0003] Although the lithium metal anode has advantages such as high theoretical specific capacity and low electrochemical potential, it is prone to side reactions when in contact with traditional organic liquid electrolytes, which can induce the formation of lithium dendrites and further cause short circuits, seriously affecting the safety and service life of the battery. In contrast, polymer solid-state electrolytes have attracted widespread attention due to their non-volatility, non-flammability, good thermal stability, and high mechanical strength. Perfluoropolyether has good thermal stability and can maintain its good properties under high temperature or low temperature conditions. The van der Waals radius of the fluorine atom in the perfluoropolyether molecular chain is small, and it has advantages such as strong electronegativity and low polarization. In addition, perfluoropolyether can form a LiF-rich SEI layer (solid-state compound film) at the interface, which can effectively inhibit the growth of lithium dendrites. However, the polarity of perfluoropolyether is relatively low, and its solubility for lithium salt is also relatively weak, so it is difficult to achieve high ionic conductivity when used as an electrolyte alone. Polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) is widely used as a polymer matrix to form a solid-state electrolyte due to its high dielectric constant, good mechanical stability and low crystallization characteristics.

[0004] However, the pure PVDF-HFP electrolyte usually has the problems of low room temperature ionic conductivity and large interface impedance, and needs to be modified by compounding to improve the performance. Early studies successfully prepared porous PVDF-HFP-based electrolytes by non-solvent induced phase separation, which showed the potential of the polymer solid-state electrolyte matrix. However, such systems usually rely on liquid electrolyte to achieve high ionic conductivity, which has certain safety hazards. And it cannot realize the precise control of the nano-scale microphase separation structure. The selection of film-forming solvent has a decisive influence on the microstructure and performance of the electrolyte. The boiling point, solubility parameter and polarity of the solvent will directly affect the arrangement of the polymer chain and the phase separation behavior. The slow evaporation degree of high boiling point solvents (such as DMF) and medium boiling point solvents (such as BTF, trifluorotoluene) is different, which provides different transmission paths for lithium ions, thus showing different results in electrochemical performance. However, the influence of the solvent on the microstructure and performance of the pure PVDF-HFP electrolyte is rarely reported. Therefore, how to modify the pure PVDF-HFP electrolyte by solvent regulation to meet the development needs of high-performance lithium metal batteries needs to be solved. SUMMARY

[0005] In view of the problems in the prior art, the application provides a mixed solvent regulated perfluoropolyether-based polymer solid-state electrolyte film, a preparation method and application, which modifies the pure PVDF-HFP electrolyte by solvent regulation to meet the development needs of high-performance lithium metal batteries.

[0006] The application is realized by the following technical scheme: A preparation method of a mixed solvent regulated perfluoropolyether-based polymer solid-state electrolyte film, comprising the following steps: Step 1. Perfluoropolyether acrylate and methoxy polyethylene glycol acrylate are reacted by reversible addition-fragmentation chain transfer polymerization method under the action of an initiator and a RAFT agent to obtain a perfluoropolyether-based copolymer. Step 2. The perfluoropolyether-based copolymer is added to a polyvinylidene fluoride-hexafluoropropylene copolymer solution in which lithium salt is dissolved, the solvent of the solution is N,N'-dimethylformamide and trifluorotoluene, and the mass fraction of the perfluoropolyether-based copolymer in the polyvinylidene fluoride-hexafluoropropylene copolymer is 10%-30%, and then a film is prepared after being uniformly mixed to obtain a perfluoropolyether-based polymer solid-state electrolyte film.

[0007] The application is further improved in that: The mass ratio of the perfluoropolyether acrylate and the methoxy polyethylene glycol acrylate in step 1 is 1:1, and the perfluoropolyether acrylate and the methoxy polyethylene glycol acrylate are reacted at 68-70 DEG C for 14-16 h to obtain the perfluoropolyether-based copolymer.

[0008] The initiator and the RAFT agent are azobisisobutyronitrile and 2-[[(butylthio)thioxomethyl]thio]propanoic acid, respectively.

[0009] The mass ratio of the azobisisobutyronitrile, 2-[[(butylthio)thioxomethyl]thio]propanoic acid and perfluoropolyether acrylate is 0.31:0.11:7.8.

[0010] The molecular weight of the perfluoropolyether acrylate and the methoxypolyethylene glycol acrylate is 1000 g / mol and 480 g / mol, respectively, and the molecular weight of the obtained perfluoropolyether-based copolymer is 100000.

[0011] The lithium salt is lithium bistrifluoromethanesulfonimide, and the lithium bistrifluoromethanesulfonimide accounts for 40% to 50% of the mass of the polyvinylidene fluoride-hexafluoropropylene copolymer.

[0012] In the polyvinylidene fluoride-hexafluoropropylene copolymer solution, the ratio of polyvinylidene fluoride-hexafluoropropylene and solvent is 1 g:10 ml.

[0013] The volume ratio of the N,N'-dimethylformamide and the trifluorotoluene is 1:1.

[0014] A perfluoropolyether-based polymer solid-state electrolyte thin film prepared by the preparation method of the perfluoropolyether-based polymer solid-state electrolyte thin film regulated by the mixed solvent.

[0015] The perfluoropolyether-based polymer solid-state electrolyte thin film is applied to the preparation of a full-solid-state lithium metal battery.

[0016] Compared with the prior art, the present application has the following beneficial technical effects: The preparation method of the perfluoropolyether-based polymer solid-state electrolyte thin film regulated by the mixed solvent, the perfluoropolyether acrylate and the methoxypolyethylene glycol acrylate are two monomers, which are reacted to obtain a perfluoropolyether-based copolymer by using a reversible addition-fragmentation chain transfer polymerization method under the action of an initiator and a RAFT agent. The perfluoropolyether-based copolymer can be used as an organic filler and is added to a polyvinylidene fluoride-hexafluoropropylene copolymer solution in which a lithium salt is dissolved. The solvent is designed as a mixed solvent composed of N,N'-dimethylformamide and trifluorotoluene. The perfluoropolyether-based copolymer accounts for 10% to 30% of the mass of the polyvinylidene fluoride-hexafluoropropylene copolymer, so as to adjust the microphase separation state of the polymer solid-state electrolyte. The problems of low ionic conductivity and poor thermal stability are solved, and the interaction between the PVDF-HFP and the lithium salt is adjusted, and the comprehensive performance of the composite solid-state electrolyte as a thin film is improved.

[0017] The prepared full-fluoropolyether-based polymer solid electrolyte thin film has full-fluoropolyether-based copolymer as an organic filler, PVDF-HFP / lithium salt as a matrix, and after being assembled into a full-solid-state lithium metal battery, exhibits the highest ionic conductivity (1.19×10 -3 S / cm) at 60 ℃ when the amount of the organic filler is 20 wt.%. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The nuclear magnetic resonance spectrum of the full-fluoropolyether-based copolymer obtained in Example 1 of the present application.

[0019] Figure 2 The small-angle X-ray two-dimensional diffraction pattern of the full-fluoropolyether-based polymer solid electrolyte obtained in Example 2 of the present application.

[0020] Figure 3 The one-dimensional scattering curve of the full-fluoropolyether-based polymer solid electrolyte obtained in Example 2 of the present application. DETAILED DESCRIPTION

[0021] In order to enable those skilled in the art to better understand the scheme of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments.

[0022] A preparation method of a full-fluoropolyether-based polymer solid electrolyte thin film regulated by a mixed solvent, comprising the following steps: Step 1: using the method of RAFT polymerization, an initiator, a RAFT agent, full-fluoropolyether acrylate (PFPEAA, molecular weight 1000 g / mol, 7.8 g, 7.8 mmol) and methoxy polyethylene glycol acrylate (PEGMA, molecular weight 480 g / mol, 3.74 g, 7.8 mmol) are sequentially added in an organic solvent trifluorotoluene (BTF), the initiator is azobisisobutyronitrile (AIBN, 0.051 g, 0.31 mmol), the RAFT agent is 2-[[(butylthio)thioxomethyl]thio]propionic acid (PABTC, 0.027 g, 0.11 mmol), after three times of freeze-thaw degassing, the reaction is carried out at a control temperature of 68-70 ℃ (oil bath heating) under the protection of nitrogen for 14-16 h, the process is as follows, the obtained reaction liquid is used in the way of rotary evaporation (temperature at 50-60 ℃, time for 0.5-1.5 h) to remove the solvent, so as to realize the separation of the product, and the full-fluoropolyether-based copolymer with a molecular weight of 100000 is obtained.

[0023]

[0024] Step 2: Perfluoropolyether-based copolymer was added as filler into the polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) solution (1 g PVDF-HFP solid, 10 ml solvent) of lithium salt (lithium bis(trifluoromethanesulfonyl)imide, LiTFSI) in two different solvents at different ratios, the mass of perfluoropolyether-based copolymer accounted for 10%, 20%, 30% of the mass of polyvinylidene fluoride-hexafluoropropylene copolymer, the lithium salt was 40-50 wt.% of the PVDF-HFP substrate, and the two different organic solvents were N,N'-dimethylformamide (DMF) and a mixed solvent of N,N'-dimethylformamide and trifluorotoluene (v:v = 1:1), referred to as TD, and stirred at 65-67 °C for 8-10 h to form a uniform solution. A solution casting method was used to prepare a composite solid-state electrolyte, i.e., pouring into a mold, the solution was solidified at room temperature to form a film, and then dried in a vacuum oven at 65-70 °C to remove the solvent to obtain a uniformly dispersed perfluoropolyether-based polymer solid-state electrolyte film. The film was cut into a circular piece with a diameter of 18-20 mm and stored in a glove box for use in the preparation of a full-solid-state lithium metal battery.

[0025] Example 1 A method for preparing a perfluoropolyether-based polymer solid-state electrolyte film regulated by a mixed solvent, the method comprising the following steps: Step 1: Under the premise of a 1:1 molar ratio of two monomers, azobisisobutyronitrile (0.051 g, 0.31 mmol), 2-[[(butylthio)thioxomethyl]thio]propionic acid (0.027 g, 0.11 mmol), perfluoropolyether acrylate (7.8 g, 7.8 mmol), and methoxy polyethylene glycol acrylate (3.74 g, 7.8 mmol) were sequentially added to trifluorotoluene (17.10 g), and the mixture was subjected to three freeze-thaw degassing processes. The resulting mixture was then reacted under nitrogen protection at a controlled temperature of 68 °C for 16 h. The solvent was removed from the mixture by rotary evaporation (temperature 50 °C, time 1 h) to obtain a perfluoropolyether-based copolymer.

[0026] Figure 1 The figure is the nuclear magnetic resonance spectrum of the perfluoropolyether-based copolymer. As can be seen from the figure, the allyl peak characteristic of the acrylate end group (5.6-6.6 ppm) is significantly weakened, and the -CH2- segment (3.5-3.8 ppm) and methoxy (3.3 ppm) peaks are retained, indicating the successful synthesis of the perfluoropolyether-based copolymer.

[0027] Step 2: Perfluoropolyether-based copolymer poly (PFPEAA- coA mixed solvent regulated preparation method of perfluoropolyether-based polymer solid-state electrolyte thin film, the method comprising the following steps:

[0028] Example 2 A mixed solvent regulated preparation method of perfluoropolyether-based polymer solid-state electrolyte thin film, the method comprising the following steps: Step 1: under the premise of the amount-of-substance ratio of two monomers being 1:1, azobisisobutyronitrile (0.051 g, 0.31 mmol), 2-[[(butylthio)thioxomethyl]thio]propionic acid (0.027 g, 0.11 mmol), perfluoropolyether acrylate (7.8 g, 7.8 mmol) and methoxy polyethylene glycol acrylate (3.74 g, 7.8 mmol) were sequentially added into trifluorotoluene (17.10 g) respectively, the mixed system was obtained by reacting under the protection of nitrogen for 16 h at a controlled temperature of 68 ℃ after three times of freeze-thaw degassing, and the solvent was removed from the mixed system by rotary evaporation (temperature at 60 ℃ for 1 h) to obtain a perfluoropolyether-based copolymer.

[0029] Step 2: the perfluoropolyether-based copolymer poly (PFPEAA- co A mixed solvent regulated preparation method of perfluoropolyether-based polymer solid-state electrolyte thin film, the method comprising the following steps:

[0030] Figure 2 Small-angle X-ray two-dimensional diffraction patterns of perfluoropolyether-based polymer solid-state electrolyte in two different film-forming solvent states, respectively. The left image is the image measured in DMF as the solvent environment, and the right image is the image measured in the mixed solvent environment. Both two-dimensional scattering patterns show approximately uniform concentric rings. The intensity distribution of the sample with DMF as the solvent is wider, while the scattering ring of the sample with mixed solvent is brighter and slightly shrunk, and the peak shape is slightly sharp, indicating that the microphase separation structures of the two composite solid-state electrolytes have certain differences. From the scattering intensity distribution of the two-dimensional scattering pattern, it can be seen that the scattering intensity of the sample with mixed solvent is higher than that of the sample with DMF as the solvent, which indicates that the perfluoropolyether-based polymer solid-state electrolyte with mixed solvent has better crystallinity. Figure 3 It can be seen that there are two clear diffraction peaks at 0.58 nm -1 and 0.74 nm -1 , respectively (the blue line is measured in DMF as the solvent environment, and the red line is measured in the mixed solvent as the solvent environment), which is consistent with the two-dimensional diffraction pattern, indicating that the two composite solid-state electrolytes have obvious microphase separation structures and certain differences.

[0031] Example 3 A preparation method of a perfluoropolyether-based polymer solid-state electrolyte thin film regulated by a mixed solvent, the method comprising the following steps: Step 1: Under the premise of the amount-of-substance ratio of two monomers being 1:1, azobisisobutyronitrile (0.051 g, 0.31 mmol), 2-[[(butylthio)thioxomethyl]thio]propionic acid (0.027 g, 0.11 mmol), perfluoropolyether acrylate (7.8 g, 7.8 mmol), and methoxy polyethylene glycol acrylate (3.74 g, 7.8 mmol) are sequentially added in trifluorotoluene (17.10 g), and after three times of freeze-thaw degassing, the mixed system is reacted under the protection of nitrogen at a control temperature of 68°C for 16 h. The obtained mixed system is subjected to rotary evaporation (temperature at 55°C, time for 1 h) to remove the solvent, and a perfluoropolyether-based copolymer is obtained.

[0032] Step 2: The perfluoropolyether-based copolymer poly (PFPEAA- coThe PVDF-HFP solution of LiTFSI in two different solvents, N,N'-dimethylformamide (DMF) and a mixed solvent of N,N'-dimethylformamide and trifluorotoluene (v:v = 1:1) respectively, with a mass ratio of 30% of PEGMA to the PVDF-HFP solution, was prepared by adding 1 g of PVDF-HFP solid and 10 ml of solvent, with the amount of lithium salt being 50 wt.% of the PVDF-HFP substrate. After stirring at 65 °C for 10 h, the solution was poured into a mold and solidified at room temperature, and then dried in a vacuum oven at 65 °C to remove the solvent. The obtained composite solid electrolyte film was cut into a circular piece with a diameter of 19 mm, and stored in a glove box.

[0033] The films obtained in the above three examples were assembled into lithium metal batteries in a glove box, and a stainless steel symmetric battery was assembled with the composite solid electrolyte film sandwiched between two stainless steel electrodes. The ion conductivity test was performed, and the results are shown in Table 1.

[0034] Table 1 Ion conductivity test data

[0035] wherein the ion conductivity can be calculated by the formula: wherein σ represents the ion conductivity of the electrolyte material, in units of siemens per centimeter (S / cm); L represents the thickness of the electrolyte material, in units of centimeters (cm); R represents the resistance of the electrolyte material, in units of ohms (Ω); and S represents the cross-sectional area of the electrolyte material, in units of square centimeters (cm 2 ).

[0036] The number of lithium ion transfers was measured according to the constant potential polarization method, and the applied voltage was 10 mV. The number of lithium ion transfers was calculated by the following equation:

[0037] wherein: I0— initial current (μA) I ss — steady-state current (μA) ΔV— applied voltage (mV) R0— initial resistance (Ω) Rss— steady-state resistance (Ω) The films obtained in the above three examples were assembled into lithium metal batteries in a glove box, and a lithium metal symmetric battery was assembled with the composite solid electrolyte film sandwiched between two lithium metal electrodes. The number of ion transfers was tested, and the results are shown in Table 2.

[0038] Table 2 Ion transference number test data

[0039] According to the data in Table 1 and Table 2, it can be seen that the lithium metal battery prepared by using the perfluoropolyether-based copolymer provided by the application has excellent electrochemical performance, and the electrochemical performance is greater than that of the pure solvent under the condition that the film-forming solvent is a mixed solvent. Specifically, the perfluoropolyether-based copolymer electrolyte filler obtained by Examples 1-3 has an ionic conductivity of 1.67-4.15 x 10 -5 S / cm at 25°C when the film-forming solvent is DMF, and an ionic conductivity of 0.98-1.81 x 10 -4 S / cm at 60°C, and the lithium ion transference number t Li+ is 0.43-0.5; when the film-forming solvent is a mixed solvent, the ionic conductivity at 25°C is 1.51-3.91 x 10 -4 S / cm, and the ionic conductivity at 60°C is 0.62-1.19 x 10 -3 S / cm, and at the same time, the lithium ion transference number also increases to different degrees, indicating that the selection of the film-forming solvent has a certain influence on the microphase separation state existing in the preparation of the polymer solid electrolyte on the electrochemical performance level of the lithium metal battery. In terms of the present application, compared with the DMF solvent, the polymer solid electrolyte prepared under the condition of the mixed solvent has a higher ionic conductivity and a higher lithium ion transference number.

Claims

1. A method for preparing a perfluoropolyether-based polymer solid electrolyte film controlled by a mixed solvent, characterized in that, Includes the following steps: S1, perfluoropolyether acrylate and methoxy polyethylene glycol acrylate are reacted by reversible addition-fragmentation chain transfer polymerization under the action of an initiator and RAFT reagent to obtain a perfluoropolyether-based copolymer; S2, a perfluoropolyether copolymer is added to a polyvinylidene fluoride-hexafluoropropylene copolymer solution containing dissolved lithium salt. The solvent of the solution is N,N'-dimethylformamide and trifluorotoluene. The perfluoropolyether copolymer accounts for 10% to 30% of the mass of the polyvinylidene fluoride-hexafluoropropylene copolymer. After uniform mixing, a film is formed to obtain a perfluoropolyether polymer solid electrolyte film.

2. The method for preparing a perfluoropolyether-based polymer solid electrolyte film controlled by a mixed solvent according to claim 1, characterized in that, The molar ratio of the perfluoropolyether acrylate and the methoxy polyethylene glycol acrylate in S1 is 1:

1. The perfluoropolyether acrylate and the methoxy polyethylene glycol acrylate are reacted at 68-70 °C for 14-16 h to obtain a perfluoropolyether-based copolymer.

3. The method for preparing a perfluoropolyether-based polymer solid electrolyte film controlled by a mixed solvent according to claim 2, characterized in that, The initiator and RAFT reagent are azobisisobutyronitrile and 2-[[(butylthio)thiomethyl]thio]propionic acid, respectively.

4. The method for preparing a perfluoropolyether-based polymer solid electrolyte film controlled by a mixed solvent according to claim 3, characterized in that, The molar ratio of the azobisisobutyronitrile, 2-[[(butylthio)thiomethyl]thio]propionic acid and perfluoropolyether acrylate is 0.31:0.11:7.

8.

5. The method for preparing a perfluoropolyether-based polymer solid electrolyte film controlled by a mixed solvent according to claim 1, characterized in that, The molecular weights of the perfluoropolyether acrylate and methoxy polyethylene glycol acrylate in S1 are 1000 g / mol and 480 g / mol, respectively, and the molecular weight of the resulting perfluoropolyether-based copolymer is 100,000.

6. The method for preparing a perfluoropolyether-based polymer solid electrolyte film controlled by a mixed solvent according to claim 1, characterized in that, The lithium salt described in S2 is lithium bis(trifluoromethanesulfonyl)imide, which is 40% to 50% of the mass of polyvinylidene fluoride-hexafluoropropylene copolymer.

7. The method for preparing a perfluoropolyether-based polymer solid electrolyte film controlled by a mixed solvent according to claim 6, characterized in that, In the polyvinylidene fluoride-hexafluoropropylene copolymer solution, the ratio of polyvinylidene fluoride-hexafluoropropylene to solvent is 1 g: 10 ml.

8. The method for preparing a perfluoropolyether-based polymer solid electrolyte film controlled by a mixed solvent according to claim 7, characterized in that, The volume ratio of N,N'-dimethylformamide to trifluorotoluene is 1:

1.

9. A perfluoropolyether-based polymer solid electrolyte film obtained by the preparation method of a perfluoropolyether-based polymer solid electrolyte film controlled by a mixed solvent as described in any one of claims 1 to 8.

10. The application of the perfluoropolyether-based polymer solid electrolyte film as described in claim 9 in the preparation of all-solid-state lithium metal batteries.

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