Relaxation ferroelectric polymer electrolyte film and preparation method and application thereof

Abstract

The invention discloses a relaxor ferroelectric polymer electrolyte film and a preparation method and application thereof, and belongs to the technical field of solid electrolyte. The method comprises the following steps: mixing an inorganic relaxor ferroelectric material, a polymer, a sodium salt and an organic solvent, heating and stirring to obtain a uniform bubble-free mixed solution; and pouring the mixed solution into a mold for shaping, and drying to obtain the relaxor ferroelectric polymer electrolyte film. The electrolyte film has high ionic conductivity, high ionic transference number and high mechanical property. The sodium metal battery prepared from the electrolyte film has excellent electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of solid electrolyte technology, and particularly relates to a relaxor ferroelectric polymer electrolyte film, its preparation method and application. Background Technology

[0002] Currently reported polymer solid electrolytes mainly include polyether systems based on polyethylene oxide and its derivatives, polyacrylonitrile systems, polycarbonate systems, and polyvinylidene fluoride and its copolymers. These systems offer advantages such as good flexibility and ease of chemical modification. However, compared to traditional liquid electrolytes, polymer solid electrolytes exhibit lower ionic conductivity, thermodynamic instability at the electrode interface, and poorer mechanical properties, which negatively impacts the electrochemical performance of the battery. Therefore, existing technologies still require improvement and development. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the purpose of this invention is to provide a relaxor ferroelectric polymer electrolyte film, its preparation method and application, in order to solve the problems of low ionic conductivity and thermodynamic instability at the electrode interface of existing polymer electrolyte films.

[0004] The technical solution adopted in this invention is as follows: In a first aspect, the present invention provides a method for preparing a relaxor ferroelectric polymer electrolyte thin film, comprising the steps of: Inorganic relaxor ferroelectric material, polymer, sodium salt and organic solvent are mixed, heated and stirred to obtain a mixture; The mixture is poured into a mold for shaping and drying to obtain the relaxor ferroelectric polymer electrolyte film.

[0005] Optionally, the polymer is selected from one of polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, and polyvinylidene fluoride-hexafluoropropylene copolymer.

[0006] Optionally, the organic solvent is selected from two of N,N-dimethylformamide, N-methylpyrrolidone, acetonitrile, tetrahydrofuran, acetone, ethanol, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, trimethyl phosphate, triethyl phosphate, and tripropyl phosphate.

[0007] Optionally, the mass ratio of the polymer, one organic solvent, and another organic solvent is 1:(1-100):(0.1-1).

[0008] Optionally, the sodium salt is selected from one of sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium hexafluorophosphate, and sodium perchlorate.

[0009] Optionally, the mass ratio of the polymer to the sodium salt is 1:(0.1-1).

[0010] Optionally, the inorganic relaxor ferroelectric material is selected from at least one of barium titanate, bismuth ferrite, and bismuth titanate.

[0011] Optionally, the mass ratio of the polymer to the inorganic relaxor ferroelectric material is 1:(0.01-0.2).

[0012] Optionally, the heating and stirring temperature is higher than the melting point of the polymer, and the heating and stirring time is 2-10 hours.

[0013] Optionally, the shaping and drying time is 1-48 hours.

[0014] Optionally, the drying temperature is 20-200°C.

[0015] Secondly, the present invention provides a relaxor ferroelectric polymer electrolyte film prepared by the above preparation method.

[0016] Optionally, the thickness of the relaxor ferroelectric polymer electrolyte film is 1-1000 μm.

[0017] Thirdly, the present invention provides an application of the relaxor ferroelectric polymer electrolyte film as described above in a sodium metal battery.

[0018] Fourthly, the present invention provides a sodium metal battery, wherein the battery includes the relaxor ferroelectric polymer electrolyte film described in the present invention.

[0019] Beneficial effects: The relaxor ferroelectric polymer electrolyte film prepared by the method provided in this invention possesses high ionic conductivity, high ion transport number, and high mechanical properties. The relaxor ferroelectric polymer electrolyte film prepared by this invention facilitates high-current rapid charging of sodium metal batteries. Attached Figure Description

[0020] Figure 1 EIS impedance diagrams of the relaxor ferroelectric polymer electrolyte films prepared in Examples 1-3.

[0021] Figure 2 The diagram shows the ion mobility spectra of the relaxor ferroelectric polymer electrolyte films prepared in Examples 1-3.

[0022] Figure 3 The tensile test images are of the relaxor ferroelectric polymer electrolyte films prepared in Examples 1-2.

[0023] Figure 4 The images show the test results of the constant current intermittent titration technique for the relaxor ferroelectric polymer electrolyte films prepared in Examples 1-2.

[0024] Figure 5The image shows the 10 C current density long-cycle diagram of the relaxor ferroelectric polymer electrolyte films prepared in Examples 1-2 assembled into sodium vanadium phosphate-sodium metal batteries.

[0025] Figure 6 The relaxor ferroelectric polymer electrolyte films prepared in Examples 1-2 were subjected to a 0.1 mA cm⁻¹ temperature range. -2 Image showing the results of deposition and stripping tests conducted at current density. Detailed Implementation

[0026] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0027] Currently, polymer electrolytes are often limited by their low ionic conductivity, preventing batteries assembled with these electrolytes from being rapidly charged and discharged at room temperature. Therefore, improving the degree of salt dissociation in polymer electrolytes, increasing their ionic conductivity, and lowering the desolvation energy barrier are particularly important. This embodiment develops a novel polymer solid-state electrolyte and improves its preparation process to achieve high room-temperature ionic conductivity, meeting the daily usage requirements of solid-state sodium metal batteries.

[0028] Specifically, this invention provides a method for preparing a relaxor ferroelectric polymer electrolyte film, comprising the following steps: S1. Mix the inorganic relaxor ferroelectric material, polymer, sodium salt and organic solvent, heat and stir to obtain a uniform, bubble-free mixture; S2. Pour the mixture into a mold, shape it, dry it, and prepare a film to obtain the relaxor ferroelectric polymer electrolyte film.

[0029] This embodiment introduces an inorganic relaxor ferroelectric material into a traditional polymer solid electrolyte, characterized by the non-coincidence of the positive and negative ion centers in the material molecules. A polarized electric field is formed between the oppositely charged ions, which promotes the dissociation of sodium salt, fixes anions, accelerates sodium ion transport, lowers the desolvation energy barrier, and promotes the directional deposition of sodium ions. Therefore, modifying the polymer electrolyte with an inorganic relaxor ferroelectric material accelerates sodium ion migration, thereby improving the ionic conductivity of the electrolyte. Furthermore, the relaxor ferroelectric polymer electrolyte film prepared by this method exhibits high ion transference number and high mechanical properties. Sodium metal batteries prepared with this electrolyte film demonstrate excellent electrochemical performance.

[0030] In one embodiment, the polymer is selected from, but is not limited to, polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, and polyvinylidene fluoride-hexafluoropropylene copolymer.

[0031] In one embodiment, the organic solvent is selected from two of N,N-dimethylformamide, N-methylpyrrolidone, acetonitrile, tetrahydrofuran, acetone, ethanol, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, trimethyl carbonate, triethyl phosphate, and tripropyl carbonate, but is not limited thereto.

[0032] In one embodiment, the mass ratio of the polymer, one organic solvent, and another organic solvent is 1:(1-100):(0.1-1).

[0033] In one embodiment, the inorganic relaxor ferroelectric material is selected from at least one of barium titanate, bismuth ferrite, and bismuth titanate, but is not limited thereto.

[0034] In one embodiment, the mass ratio of the polymer to the inorganic relaxor ferroelectric material is 1:(0.01-0.2), such as 1:0.01, 1:0.05, 1:0.1, 1:0.2, etc.

[0035] In one embodiment, the heating and stirring temperature is higher than the melting point of the polymer.

[0036] In one embodiment, the heating and stirring time is 2-10 hours, such as 2 hours, 5 hours, 10 hours, etc.

[0037] In one embodiment, the sodium salt is selected from at least one of sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium hexafluorophosphate, sodium perchlorate, etc., but is not limited thereto.

[0038] In one embodiment, the mass ratio of the polymer to the sodium salt is 1:(0.1-1), such as 1:0.1, 1:0.5, 1:0.8, 1:1, etc.

[0039] In one embodiment, the shaping and drying time is 1-48 hours, such as 3 hours, 6 hours, 10 hours, 14 hours, 25 hours, 47 hours, etc.

[0040] In one embodiment, the drying step is performed in air, vacuum, or an inert atmosphere (such as nitrogen atmosphere, argon atmosphere, etc.).

[0041] When the solvent removal step is carried out in an inert atmosphere, the resulting relaxor ferroelectric polymer electrolyte film can have dense and ultrathin characteristics, which helps to improve the compatibility of the relaxor ferroelectric polymer electrolyte film and the positive and negative electrode interfaces.

[0042] This invention provides a relaxor ferroelectric polymer electrolyte film prepared by the above-described preparation method.

[0043] In one embodiment, the thickness of the relaxor ferroelectric polymer electrolyte film is 1-1000 μm. This embodiment controls the thickness of the relaxor ferroelectric polymer electrolyte film to be 1-1000 μm by adjusting process parameters, such as 50 μm, 100 μm, 150 μm, 200 μm, 400 μm, 650 μm, 800 μm, 900 μm, and 1000 μm, thereby reducing the battery's bulk impedance and interface impedance.

[0044] This invention provides an application of the relaxor ferroelectric polymer electrolyte film described above in a sodium metal battery.

[0045] This invention provides a sodium metal battery, which includes the relaxor ferroelectric polymer electrolyte film described in this invention.

[0046] This embodiment uses a relaxor ferroelectric polymer electrolyte film matched with a cathode material (such as sodium nickel iron manganate, sodium vanadium phosphate, etc.), which exhibits excellent electrochemical stability.

[0047] In one embodiment, the relaxor ferroelectric polymer electrolyte film can be applied to at least one of the following types: pouch stacked type, pouch wound type, button cell type, square aluminum shell wound type, and cylindrical wound type, providing a new approach for the commercial application of solid polymer electrolytes.

[0048] The present invention will be further described below through specific embodiments.

[0049] Example 1 A method for preparing a relaxor ferroelectric polymer electrolyte thin film includes the following steps: 1g of polyvinylidene fluoride-hexafluoropropylene, 0.5g of sodium bis(trifluoromethanesulfonyl)imide, and 3g of ethylene carbonate were dissolved in 10g of acetonitrile. The solution was heated and stirred at 60°C for 5 hours until the polymer was completely dissolved, thus obtaining a polymer solution. The solution was poured into a mold for shaping and dried for 24 hours to prepare a film, which was named PH.

[0050] Example 2 A method for preparing a relaxor ferroelectric polymer electrolyte thin film includes the following steps: 0.1g bismuth titanate, 1g polyvinylidene fluoride-hexafluoropropylene, 0.5g sodium bis(trifluoromethanesulfonyl)imide, and 3g ethylene carbonate were dissolved in 10g acetonitrile. The solution was heated and stirred at 60°C for 5 hours until the polymer was completely dissolved to obtain a polymer solution. The solution was poured into a mold for shaping and dried for 24 hours to prepare a film, which was named PH-BiTO.

[0051] The difference between Example 2 and Example 1 is that this example introduces the inorganic relaxor ferroelectric material bismuth titanate.

[0052] Example 3 A method for preparing a relaxor ferroelectric polymer electrolyte thin film includes the following steps: 0.1g barium titanate, 1g polyvinylidene fluoride-hexafluoropropylene, 0.5g sodium bis(trifluoromethanesulfonyl)imide, and 3g ethylene carbonate were dissolved in 10g acetonitrile. The solution was heated and stirred at 60°C for 5 hours until the polymer was completely dissolved to obtain a polymer solution. The solution was poured into a mold for shaping and dried for 24 hours to prepare a film, which was named PH-BaTO.

[0053] The difference between Example 3 and Example 1 is that this example introduces the inorganic relaxor ferroelectric material barium titanate.

[0054] Performance testing The performance of the electrolyte films prepared in Examples 1-3 for pH, pH-BiTO, and pH-BaTO was tested using the following methods: (1) Ionic conductivity test: The electrolyte membrane was assembled into a steel sheet-electrolyte membrane-steel sheet battery in a glove box. The electrochemical impedance spectroscopy (EIS) test was performed using an electrochemical workstation, and the ionic conductivity was calculated using the following formula 1: (1) in R is the ionic conductivity, L is the thickness of the electrolyte membrane, R is the impedance of the battery, and S is the area of ​​the steel sheet.

[0055] (2) Ion transport number test: The electrolyte membrane was assembled into a sodium metal-electrolyte membrane-sodium metal battery in a glove box. An EIS test was performed using an electrochemical workstation, and the impedance R0 was recorded. Then, a polarization voltage of 10mV was continuously applied, and the initial current was recorded. When the steady-state current was reached, the voltage was stopped, and the EIS test was performed again. The impedance R0 was recorded at this time. s The ion transport number is calculated using the following formula 2: (2) Where t Na+ Where I is the sodium ion transport number, I0 is the initial current, R0 is the impedance before polarization, and I... s For steady-state current, R s The impedance at which steady-state current is achieved.

[0056] (3) Constant current intermittent titration test: The electrolyte membrane was assembled into a sodium nickel iron manganese oxide-electrolyte membrane-sodium metal battery in a glove box. During the charging test, a forward current with a current density of 0.1C was applied and kept constant for 10 min, then the current was interrupted and allowed to rest for 30 min. The constant current charging and resting relaxation were repeated until the charging cutoff voltage was reached. During the discharging test, a reverse current with a current density of 0.1C was applied and kept constant for 10 min, then the current was interrupted and allowed to rest for 30 min. The constant current discharging and resting relaxation were repeated until the discharging cutoff voltage was reached. The change in voltage over time was analyzed to infer the relationship between the solid phase ion concentration of the material and the voltage. The diffusion rate of ions was calculated using the following formula 3: (3) Where D is the ion diffusion rate, τ is the relaxation time, and n m It is the number of moles, V m It is the molar volume, and S is the contact area between the electrode and the electrolyte film. E s It is the change in total voltage caused by the pulse. E t It is the voltage change during constant current charging / discharging.

[0057] (4) Full cell cycle performance test: The above electrolyte films were assembled into sodium vanadium phosphate / sodium metal full cells and tested at 25°C and 10C rate.

[0058] (5) Symmetrical battery cycle performance test: The above electrolyte films were assembled into a sodium metal-electrolyte film-sodium metal battery and tested at 25℃ and 0.1 mA cm⁻¹. -2 Deposition stripping tests were performed at current density.

[0059] Results Analysis Figure 1 EIS impedance diagrams of the electrolyte films PH, PH-BiTO, and PH-BaTO are shown. Based on the impedance values, the room temperature ionic conductivity of the PH-BiTO electrolyte film is calculated to be 3.69 × 10⁻⁶. -4 S cm -1 The room temperature ionic conductivity of the PH-BaTO electrolyte membrane reaches 3.63 × 10⁻⁶. -4 S cm -1 This meets the conditions for normal operation of a full cell at room temperature. However, the room temperature ionic conductivity of the pH electrolyte membrane is only 2.90 × 10⁻⁶. -4 S cm -1 This indicates that the addition of bismuth titanate and barium titanate can promote the dissociation of sodium salt and improve ionic conductivity.

[0060] Figure 2The ion transport number diagrams for electrolyte films PH(a), PH-BiTO(b), and PH-BaTO(c) are shown. The sodium ion transport numbers for PH, PH-BiTO, and PH-BaTO are calculated to be 0.42, 0.71, and 0.58, respectively. The high sodium ion transport numbers indicate that sodium ions are the main conductor carriers, which can reduce battery polarization, improve rate performance and cycle stability, and are especially important in solid-state electrolytes.

[0061] Figure 3 Tensile test images of the electrolyte films PH-BiTO and PH show that the addition of the inorganic relaxor ferroelectric material bismuth titanate significantly improves the mechanical properties of the electrolyte. After introducing bismuth titanate into the electrolyte matrix, these bismuth titanate particles contain a large number of fine ferroelectric domains. These ferroelectric domains have a very stable structure and possess high strength and modulus. When the electrolyte material is subjected to tensile force, these high-strength ferroelectric domains dispersed in the electrolyte matrix effectively hinder dislocation movement and microcrack propagation, ultimately achieving a significant improvement in the material's mechanical strength. Therefore, PH-BiTO exhibits a tensile strength of 4.2 MPa and an elongation at break of 600%. The improved mechanical properties of the electrolyte provide a solid foundation for the safety and stability of solid-state sodium metal batteries.

[0062] Figure 4 The graphs show the galvanostatic intermittent titration test results for the electrolyte films PH-BiTO and pH, indicating the determination of the ion diffusion coefficients of each material. (The figure is related to pH 3.45 × 10⁻⁶). -11 cm 2 s -1 Compared to PH-BiTO, PH-BiTO exhibits a higher average diffusion coefficient (7.11 × 10⁻⁶). -11 cm 2 s -1 The results showed that bismuth titanate significantly improved the diffusion kinetics of sodium ions. This improvement was attributed to the modulation of the electrode microstructure by bismuth titanate, which enhanced the structural stability of the electrode material, thereby improving the sodium ion transport capacity.

[0063] Figure 5 The figure shows the long-cycle life of the electrolyte film PH-BiTO and PH assembled into a sodium vanadium phosphate-sodium metal battery. As can be seen from the figure, PH-BiTO has a longer cycle life and capacity retention under the high current density condition of 10C.

[0064] Figure 6 For electrolyte films, pH-BiTO and pH at 0.1 mA cm⁻¹ -2Deposition and stripping tests were conducted at current densities. The tests revealed that PH experienced a soft short circuit after 695 hours, with its polarization voltage gradually increasing. In contrast, PH-BiTO maintained stable cycling during a continuous deposition / stripping process of 1200 hours, with a subsequent stable polarization voltage of approximately 0.1V. The lower voltage polarization and longer cycle life demonstrate the good compatibility between PH-BiTO and the sodium metal anode. The interface between the sodium metal electrode and the electrolyte remained stable during repeated deposition / stripping, side reactions were effectively suppressed, and the interfacial impedance increased slowly.

[0065] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a relaxor ferroelectric polymer electrolyte thin film, characterized in that, Including the following steps: Inorganic relaxor ferroelectric material, polymer, sodium salt and organic solvent are mixed, heated and stirred to obtain a mixture; The mixture is poured into a mold for shaping and drying to obtain the relaxor ferroelectric polymer electrolyte film.

2. The method for preparing a relaxor ferroelectric polymer electrolyte thin film according to claim 1, characterized in that, The polymer is selected from one of polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, and polyvinylidene fluoride-hexafluoropropylene.

3. The method for preparing a relaxor ferroelectric polymer electrolyte thin film according to claim 1, characterized in that, The organic solvent is selected from two of N,N-dimethylformamide, N-methylpyrrolidone, acetonitrile, tetrahydrofuran, acetone, ethanol, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, trimethyl phosphate, triethyl phosphate, and tripropyl phosphate. The mass ratio of the polymer, one organic solvent, and another organic solvent is 1:(1-100):(0.1-1).

4. The method for preparing a relaxor ferroelectric polymer electrolyte thin film according to claim 1, characterized in that, The sodium salt is selected from one of sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium hexafluorophosphate, and sodium perchlorate.

5. The method for preparing a relaxor ferroelectric polymer electrolyte thin film according to claim 1, characterized in that, The inorganic relaxor ferroelectric material is selected from at least one of barium titanate, bismuth ferrite, and bismuth titanate.

6. The method for preparing a relaxor ferroelectric polymer electrolyte thin film according to claim 1, characterized in that, The mass ratio of the polymer to the sodium salt is 1:(0.1-1); The mass ratio of the polymer to the inorganic relaxor ferroelectric material is 1:(0.01-0.2).

7. The method for preparing a relaxor ferroelectric polymer electrolyte thin film according to claim 1, characterized in that, The heating and stirring temperature is higher than the melting point of the polymer, and the time is 2-10 hours; The shaping and drying time is 1-48 hours; The drying temperature is 20-200℃.

8. A relaxor ferroelectric polymer electrolyte film prepared by the preparation method according to any one of claims 1-7.

9. The application of the relaxor ferroelectric polymer electrolyte film of claim 8 in a sodium metal battery.

10. A sodium metal battery, characterized in that, Includes the relaxor ferroelectric polymer electrolyte film as described in claim 8.

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