A Method for Preparing a Solid Proton Electrolyte Membrane and Its Application

Abstract

The present invention provides a method for preparing a solid-state proton electrolyte membrane and its application. This electrolyte has various advantages such as high safety, the ability to broaden the voltage window, environmental friendliness, low cost, and long lifespan. Its synthesis method uses polyvinylidene fluoride and polyethylene oxide as the main synthesis components, and phosphoric acid is added thereto. The mixture is placed in an N,N-dimethylformamide solvent and heated and stirred to dissolve into a transparent and clear solution. Then, it is ultrasonically treated under heating conditions to remove a small amount of bubbles in the solution, obtaining a homogeneous and transparent solution. The solution is placed in a corresponding mold and the solvent is removed in a vacuum oven to obtain a solid electrolyte membrane with a uniform thickness. When the present invention is used in a proton battery, it can broaden the voltage window and improve its cycle lifespan. The present invention has the advantages of low cost, easy synthesis, and high safety, etc.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical technologies, and particularly to a method for preparing a solid proton electrolyte membrane and its applications. Background Art

[0002] Human over - reliance on fossil fuels is exacerbating global warming and ecological environment deterioration at an unprecedented rate. Facing this severe situation, the development of renewable energy has become a necessity. Among them, green energies such as solar energy, wind energy, and hydropower will gradually become the main body of the energy structure.

[0003] Among various energy storage technologies, electrochemical energy storage has become a key support for the construction of smart grids due to its flexible and efficient characteristics. However, traditional lithium - ion batteries are challenged in large - scale applications due to their high operation and maintenance costs, and the safety hazards brought by organic electrolytes and active anode materials. Similarly, lead - acid batteries have problems of environmental pollution and recycling due to their heavy metals and strongly corrosive electrolytes. In comparison, the energy storage system of proton batteries shows broader development prospects due to its economy, safety, and excellent ion - conduction performance. It should be noted that protons (H + ), due to their unique physical and chemical properties - including fast migration ability, extremely small molar mass, and hydration radius, perform outstandingly in aspects such as fast charge - discharge, cycle stability, and wide temperature adaptability, becoming a new generation of energy storage technologies with great potential. Among them, solid electrolytes, as a new generation of energy storage technologies, show broad application prospects due to their unique advantages. First of all, solid electrolytes completely eliminate the risks of leakage and volatilization of liquid electrolytes, fundamentally solving the safety hazards of battery systems; after composite modification, polymer - based electrolytes also show excellent flame - retardant properties, completely avoiding the thermal runaway problem of traditional batteries. Secondly, through material system optimization, solid - state proton batteries can operate stably in a wide temperature range from - 40°C to 120°C. Especially, polymer - based electrolytes still maintain a proton conductivity above 10 -4 S / cm at low - temperature environments through amorphous design and functional - group modification. The solid - state interface effectively suppresses side reactions such as hydrogen evolution / oxygen evolution, making the Coulomb efficiency stable above 99.5% and the cycle life reach more than 2000 times. Despite the above advantages of solid - state proton electrolytes, they also face some challenges. First of all, the room - temperature conductivity of most solid - state proton electrolytes still remains at the order of 10 -4 ~10 -3 S / cm, significantly lower than that of liquid electrolytes (>10 -2 S / cm); secondly, during the cycling process, the electrolyte is prone to cracking due to poor mechanical strength; and existing preparation processes such as ALD cost up to 500 / m 2 , exceeding the commercial requirements (<500 / m 2), the raw materials of the electrolyte are expensive, and the prices of raw materials such as high-purity ZrO2 are 3-5 times that of traditional materials, which makes it difficult in aspects such as large-scale production and practical applications. Therefore, developing solid-state proton electrolytes with low cost, high ionic conductivity, and long cycle life is of great significance in promoting the energy development in Hainan. Summary of the Invention

[0004] In view of this, the present invention provides a method for preparing a solid-state proton electrolyte membrane and its application. The purpose of the present invention is to overcome the deficiencies of the prior art and prepare a solid-state proton electrolyte with high safety, environmental friendliness, low cost, and long life. This method uses PVDF (polyvinylidene fluoride) and PEO (polyethylene oxide) as the main synthesis components, introduces phosphoric acid functional groups, dissolves them in an organic solvent DMF (N,N-dimethylformamide), and finally obtains a solid-state proton electrolyte membrane by drying the solvent. This method of introducing functional groups with PVDF and PEO as the main body can achieve large-scale production of solid electrolytes, realize low-cost and long-life solid-state proton batteries, and promote the practical application of solid-state proton batteries. This preparation method has significant scientific value and broad practical application prospects in the application of low-cost distributed energy storage systems in the South China Sea.

[0005] The technical solution of the present invention is realized as follows: A method for preparing a solid-state proton electrolyte membrane, comprising the following steps:

[0006] S1. Mix polyvinylidene fluoride, polyethylene oxide, and pure phosphoric acid in a mass ratio of 10:(1-5):(8-12);

[0007] S2. Add 5-15 mL of N,N-dimethylformamide solvent to the mixture in step S1, and heat and stir at 50-70 °C for 12-24 hours to obtain a transparent and clear solution;

[0008] S3. Ultrasonically treat the transparent and clear solution at 50-70 °C for 25-35 minutes to obtain a homogeneous and transparent solution;

[0009] S4. Place the homogeneous and transparent solution in a glass petri dish and dry it in a vacuum oven at 50-70 °C for 20-30 hours to obtain a solid-state proton electrolyte membrane.

[0010] Further, in step S1, the mass ratio of polyvinylidene fluoride, polyethylene oxide, and pure phosphoric acid is 10:1:10, and the concentration of the phosphoric acid ≥ 99%.

[0011] Further, in step S2, the volume-mass ratio of N,N-dimethylformamide to polyvinylidene fluoride is 10-11.67 mL / g, and the heating time is 24 hours.

[0012] Further, the stirring rate in step S2 is 150 - 250 r / min.

[0013] Further, the ultrasonic treatment power in step S3 is 100 - 500 W, and the ultrasonic frequency is 20 - 40 kHz.

[0014] Further, the degree of vacuum in step S4 is -0.08 to -0.1 MPa.

[0015] Further, the polyvinylidene fluoride is first pretreated by plasma, including the following steps:

[0016] Place the polyvinylidene fluoride in a reaction chamber with an argon atmosphere and evacuate to a pressure ≤ 10 Pa;

[0017] Perform plasma treatment at a radio frequency power of 50 - 200 W and a frequency of 13.56 MHz for 5 - 20 minutes;

[0018] After treatment, continue to pass argon for cooling for 3 - 7 minutes to obtain polyvinylidene fluoride with a 20 - 50% increase in the density of fluorine-containing groups on the surface and a roughness of 50 - 200 nm.

[0019] Further, the thickness of a solid-state proton electrolyte membrane is 50 - 100 μm, and the tensile strength ≥ 30 MPa.

[0020] Further, an application of a solid-state proton electrolyte membrane in the preparation of a deep-sea energy storage battery.

[0021] Further, the deep-sea energy storage battery includes a positive electrode active material, a negative electrode active material, and a solid-state proton electrolyte membrane, and the solid-state proton electrolyte membrane is located between the positive electrode active material and the negative electrode active material.

[0022] Principle of the present invention:

[0023] Semicrystalline PVDF (polyvinylidene fluoride) endows the material with high mechanical strength and thermal stability (melting temperature ~170 °C), and its hydrophobicity can reduce side reactions caused by electrolyte water absorption. The ether oxygen segments (-O-) in PEO (polyethylene oxide) form hydrogen bond networks with protons to enhance low-temperature ionic conductivity. High crystallinity is inhibited by blending to broaden the temperature range. The three hydroxyl groups (-OH) in the phosphate group can form hydrogen bond networks, and rapid proton hopping conduction is achieved through the Grotthuss mechanism (activation energy is reduced, significantly enhancing ionic conductivity (>10 -3 S / cm, at room temperature). The composite stabilization of the three reduces the tendency of phase separation, forming a continuous phase dominated by the amorphous state, maintaining stable proton conduction in the range of -20 °C to 80 °C (conductivity >10 -4 S / cm)

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] The present invention uses PVDF (polyvinylidene fluoride) and PEO (polyethylene oxide) as the synthesis main body, and introduces phosphoric acid functional groups. The combined action of the three significantly improves the ionic conductivity of the electrolyte, maintains stable proton conduction in the range of -20°C to 80°C, and greatly improves the cycle life of the proton battery.

[0026] The present invention has significant advantages such as low raw material cost, environmental protection in the process, high yield and large output, and exhibits excellent electrochemical performance. In the application of low-cost distributed energy storage systems in the South China Sea, it has significant scientific value and broad practical application prospects. Brief Description of the Drawings

[0027] Figure 1 is the X-ray diffraction pattern of the prepared polymer solid electrolyte;

[0028] Figure 2 is the scanning electron microscope image of the prepared solid electrolyte;

[0029] Figure 3 is the linear sweep voltammogram of the solid electrolyte prepared in Example 1;

[0030] Figure 4 is the variable-temperature electrochemical impedance spectrum of the solid electrolyte prepared in Example 1;

[0031] Figure 5 is the fitting of the variable-temperature electrochemical impedance spectrum of the solid electrolyte prepared in Example 1;

[0032] Figure 6 is the cycle performance graph of the solid-state proton battery assembled with the solid electrolyte material prepared in Example 2 at a current density of 50 mA / g;

[0033] Figure 7 is the rate performance graph of the solid-state proton battery assembled with the solid electrolyte material prepared in Example 2 at different current densities;

[0034] Figure 8 is the cycle performance graph of the solid-state proton battery assembled with the solid electrolyte material prepared in Example 2 at a current density of 200 mA / g;

[0035] Figure 9 is the cycle performance graph of the solid-state proton battery assembled with the solid electrolyte material prepared in Example 2 at a current density of 500 mA / g;

[0036] Figure 10 is the cycle performance graph of the solid-state proton battery assembled with the solid electrolyte material prepared in Example 2 at a current density of 1 A / g;

[0037] Figure 11 Cycling performance graph of the solid-state proton battery assembled with the solid-state electrolyte material prepared in Example 2 at a temperature of 60 °C and a current density of 50 mA / g;

[0038] Figure 12 Cycling performance graph of the solid-state proton battery assembled with the solid-state electrolyte material prepared in Example 2 at a temperature of -20 °C and a current density of 20 mA / g. Detailed implementation manners

[0039] To better understand the technical content of the present invention, specific examples are provided below to further illustrate the present invention.

[0040] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0041] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can all be obtained from commercial channels.

[0042] Example 1

[0043] A method for preparing a solid-state proton electrolyte membrane, using plasma-pretreated PVDF (polyvinylidene fluoride) and PEO (polyethylene oxide) as the synthesis main body, introducing phosphoric acid functional groups, dissolving in an organic solvent DMF (N,N-dimethylformamide), and finally obtaining the solid-state proton electrolyte membrane by drying the solvent. The specific steps are as follows:

[0044] 1) Place 1000 mg of PVDF (polyvinylidene fluoride), 100 mg of PEO (polyethylene oxide), and 1000 mg of phosphoric acid in a glass bottle;

[0045] 2) Add 10 mL of DMF (N,N-dimethylformamide) solvent to the glass bottle, heat and stir on a heating and stirring table at 60 °C for 24 h to obtain a white transparent clear solution.

[0046] 3) Place the glass bottle in an ultrasonic machine, heat to 60 °C, and ultrasonicate for 30 min to remove a little defoaming in the solution and obtain a homogeneous transparent solution.

[0047] 4) Place the homogeneous transparent solution in a glass petri dish with a diameter of 90 mm, and place it in a vacuum oven, set the temperature to 60 °C and the time to 24 h, and dry to obtain a white solid-state electrolyte membrane.

[0048] Perform performance analysis on the prepared solid-state electrolyte material

[0049] As Figure 1As shown, in the solid electrolyte synthesized by the present invention, PVDF is an amorphous structure, phosphoric acid molecules have a strong coordination ability with PVDF to form a solvated structure, and these molecules migrate through the interaction with the PVDF / PEO polymer chain, thereby achieving high room temperature ionic conductivity.

[0050] Figure 2 This is a scanning electron microscope image of the prepared solid electrolyte; the porous structure ensures the excellent mechanical properties of the electrolyte, and the hydrogen bonding force between phosphoric acid and PVDF / PEO chains contributes to the stability of the composite polymer framework.

[0051] Figure 3 This is the linear sweep voltammogram of the solid electrolyte prepared in Example 1. Compared with ordinary aqueous electrolytes, the voltage range of the solid electrolyte of the present invention is extended from 1V to 1.7V, which significantly broadens the operating voltage.

[0052] Electrochemical impedance spectroscopy from solid electrolytes Figure 4 It can be seen that the ionic conductivity shows a trend of increasing with increasing temperature, which is because the increase in temperature promotes the movement of chain segments in the polymer matrix.

[0053] Variable temperature electrochemical impedance spectroscopy fitting of the solid electrolyte prepared in Example 1 Figure 5 It can be seen that the change of ionic conductivity with temperature is very consistent with the Arrhenius behavior, and it is calculated that the ion migration rate promotion effect of the present invention is the most obvious.

[0054] Example 2

[0055] The solid-state proton battery was assembled using the solid-state electrolyte obtained in Example 1, as follows:

[0056] The solid electrolyte membrane prepared by the present invention is an electrolyte,

[0057] Positive electrode preparation: Synthesized copper iron Prussian blue analogs (CuFe-PBAs) are used as the active material of the positive electrode, conductive carbon black is used as the conductive agent, and polytetrafluoroethylene PTFE is used as the binder; the mass ratio of the active material, the conductive agent, and the binder is 7:2:1. After they are mixed in proportion, they are pressed into a pole piece with a thickness of 100-150um using a roller press.

[0058] Negative electrode preparation: activated carbon is used as the active material, conductive carbon black is used as the conductive agent, and polytetrafluoroethylene PTFE is used as the binder; the mass ratio of active material, conductive agent, and binder is 7:2:1. After mixing them in proportion, a roller press is used to press them into a pole piece with a thickness of 100-150um.

[0059] (2)Fabrication of the electrode sheets: The rolled positive and negative electrode sheets are dried, and the positive and negative electrode sheets are respectively cut into electrode sheets with a diameter of 6 mm and a diameter of 10 mm, and the mass loading of the electrode sheets is 5-10 mg / cm -2 .

[0060] (3)The CR2032 button battery is assembled in air, with Prussian blue as the positive electrode, activated carbon as the negative electrode, and the solid electrolyte membrane prepared in the present invention as the electrolyte.

[0061] See Figures 6 to 12 , the solid proton battery assembled in this example can provide 113.11 mAh / g at a small current density of 50 mA / g. After 200 cycles, the capacity is still 92.6 mAh / g, and the capacity retention rate is 81.86%. At a current density of 200 mA / g, after 1400 cycles, the capacity retention rate is 87.21%. At 500 mA / g, after 7000 cycles, the capacity retention rate is 82.15%. While having good rate performance, the electrolyte also has excellent cycling performance at different current densities. At a current density of 1 A / g, the capacity reaches 68.63 mAh / g, and after 19000 cycles, the capacity still remains 69.5%, and the cycle life reaches up to 7600 h, demonstrating its excellent cycling performance and long-life advantages.

[0062] Example 3

[0063] A preparation method of a solid proton electrolyte, the specific steps are as follows:

[0064] 1) Put 2 g of PVDF (polyvinylidene fluoride), 200 mg of PEO (polyethylene oxide) and 2 g of phosphoric acid into a glass bottle;

[0065] 2) Add 22 mL of DMF (N,N-dimethylformamide) solvent to the glass bottle, and heat and stir on a heating and stirring table at 60 °C for 24 h to obtain a white transparent and clear solution.

[0066] 3) Place the glass bottle in an ultrasonic machine and heat it to 60 °C for ultrasonic treatment for 30 min to remove a little defoaming in the solution and obtain a homogeneous and transparent solution.

[0067] 4) Place the white homogeneous and transparent solution in a glass petri dish with a diameter of 150 mm, and place it in a vacuum oven. Set the temperature to 60 °C and the time to 24 h, and dry it to obtain a white solid electrolyte membrane.

[0068] 5) Punch the obtained solid electrolyte membrane into a round sheet with a diameter of 17 mm, and assemble the CR2032 button battery in air, with Prussian blue as the positive electrode, activated carbon as the negative electrode, and the solid electrolyte membrane prepared in the present invention as the electrolyte.

[0069] Example 4

[0070] A preparation method of a solid-state proton electrolyte, the specific steps are as follows:

[0071] 1) Place 3 g of PVDF (polyvinylidene fluoride), 300 mg of PEO (polyethylene oxide), and 3 g of phosphoric acid in a glass bottle;

[0072] 2) Add 35 mL of DMF (N,N-dimethylformamide) solvent to the glass bottle, heat and stir on a heating and stirring table at 60 °C for 24 h to obtain a white, transparent, and clear solution.

[0073] 3) Place the glass bottle in an ultrasonic machine, heat it to 60 °C, and ultrasonicate for 30 min to remove a little defoaming in the solution to obtain a homogeneous and transparent solution.

[0074] 4) Place the white, homogeneous, and transparent solution in a glass petri dish with a diameter of 150 mm, and place it in a vacuum oven. Set the temperature to 60 °C and the time to 24 h, and dry it to obtain a white solid electrolyte membrane.

[0075] 5) Punch the obtained solid electrolyte membrane into circular pieces with a diameter of 17 mm, assemble a CR2032 button battery in the air, use Prussian blue as the positive electrode, activated carbon as the negative electrode, and the solid electrolyte membrane prepared by the present invention as the electrolyte.

[0076] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a solid-state proton electrolyte membrane, characterized in that: It includes the following steps: S1. Mix polyvinylidene fluoride, polyethylene oxide and pure phosphoric acid in a mass ratio of 10:(1-5):(8-12); S2. Add 5-15 mL of N,N-dimethylformamide solvent to the mixture in step S1, and heat and stir at 50-70 °C for 12-24 hours to obtain a transparent and clear solution; S3. Ultrasonically treat the transparent and clear solution at 50-70 °C for 25-35 minutes to obtain a homogeneous and transparent solution; S4. Place the homogeneous and transparent solution in a glass petri dish and dry it in a vacuum oven at 50-70 °C for 20-30 hours to obtain a solid proton electrolyte membrane.

2. The method for preparing a solid-state proton electrolyte membrane according to claim 1, wherein: In step S1, the mass ratio of polyvinylidene fluoride, polyethylene oxide and pure phosphoric acid is 10:1:

10.

3. The preparation method of a solid proton electrolyte membrane according to claim 1, characterized in that: In step S2, the volume-mass ratio of N,N-dimethylformamide to polyvinylidene fluoride is 10-11.67 mL / g, and the heating time is 24 hours.

4. The preparation method of a solid proton electrolyte membrane according to claim 1, characterized in that: In step S2, the stirring rate is 150-250 r / min.

5. The method for preparing a solid proton electrolyte membrane according to claim 1, characterized in that: In step S3, the ultrasonic treatment power is 100-500 W, and the ultrasonic frequency is 20-40 kHz.

6. The preparation method of a solid proton electrolyte membrane according to claim 1, wherein: In step S4, the vacuum degree is -0.08~-0.1 MPa.

7. The method for preparing a solid proton electrolyte membrane according to claim 1, characterized in that: The polyvinylidene fluoride is first pretreated by plasma, including the following steps: Place polyvinylidene fluoride in a reaction chamber with an argon atmosphere and evacuate to a pressure ≤10 Pa; Perform plasma treatment at a radio frequency power of 50-200 W and a frequency of 13.56 MHz for 5-20 minutes; After treatment, continue to cool with argon for 3-7 minutes to obtain polyvinylidene fluoride with a 20-50% increase in the density of fluorine-containing groups on the surface and a roughness of 50-200 nm.

8. A solid proton electrolyte membrane, characterized in that, Obtained by the preparation method according to any one of claims 1-7, the thickness of the solid proton electrolyte membrane is 50-100 μm, and the tensile strength ≥30 MPa.

9. Use of a solid proton electrolyte membrane as described in claim 8 in the preparation of a deep-sea energy storage battery.

10. The application according to claim 9, characterized in that, The battery includes a positive electrode active material, a negative electrode active material and a solid proton electrolyte membrane, and the solid proton electrolyte membrane is located between the positive electrode active material and the negative electrode active material.

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