Preparation method and application of solid proton electrolyte membrane

Abstract

The invention provides a solid proton electrolyte membrane preparation method and application thereof.The electrolyte has the advantages of being high in safety, capable of widening a voltage window, environmentally friendly, low in cost, long in service life and the like, and the synthesis method of the solid proton electrolyte membrane comprises the steps that polyvinylidene fluoride and polyethylene oxide serve as synthesis main bodies, phosphoric acid is added into the synthesis main bodies, and the mixture is placed in N, N-dimethyl formamide to be dissolved; heating, stirring and dissolving in an N, N-dimethylformamide solvent to obtain a transparent clear solution, and performing ultrasonic treatment under a heating condition to remove a small amount of bubbles in the solution, so as to obtain a uniform transparent solution; and placing the solution in a corresponding mold, and removing the solvent in a vacuum oven to obtain the solid electrolyte membrane with uniform thickness. When being used in the proton battery, the composite material can widen a voltage window and prolong the cycle life of the proton battery, and has the advantages of low cost, easiness in synthesis, high safety and the like.

Description

Technical Field

[0001] The present invention relates to the field of electrochemistry technology, and particularly relates to a preparation method and application of a solid proton electrolyte membrane. Background Art

[0002] Human's over - reliance on fossil fuels is exacerbating global warming and ecological environment deterioration at an unprecedented rate. Facing this severe situation, it has become necessary to develop renewable energy. 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 restricted by expensive operation and maintenance costs, and in addition, the safety hazards brought by organic electrolytes and active anode materials pose challenges to their large - scale application. Similarly, lead - acid batteries have problems of environmental pollution and recycling due to containing heavy metals and strongly corrosive electrolytes. In contrast, 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 technology with great potential. Among them, solid electrolytes, as a new generation of energy storage technology, show broad application prospects due to their unique advantages. First of all, solid electrolytes completely eliminate the risk 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 characteristics, completely avoiding the thermal runaway problem of traditional batteries. Secondly, through material system optimization, solid - state proton batteries can work 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. Although solid - state proton electrolytes have the above advantages, they also face some challenges. First of all, the room - temperature conductivity of most solid - state proton electrolytes still remains at the level 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 a solid-state proton electrolyte with low cost, high ionic conductivity, and long cycle life is of great significance in promoting the energy development of Hainan. Summary of the Invention

[0004] In view of this, the present invention proposes 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 synthesis main body, introduces a phosphoric acid functional group, dissolves it 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 a functional group with PVDF and PEO as the main body can realize the large-scale production of solid electrolytes, achieve 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: 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-state proton electrolyte membrane.

[0006] 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%.

[0007] 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.

[0008] Further, the stirring rate in step S2 is 150-250 r / min.

[0009] Further, in the step S3, the ultrasonic treatment power is 100 - 500 W, and the ultrasonic frequency is 20 - 40 kHz.

[0010] Further, in the step S4, the vacuum degree is -0.08 to -0.1 MPa.

[0011] Further, the polyvinylidene fluoride is first pretreated by plasma, including the following steps: Place the polyvinylidene fluoride in a reaction chamber with an argon atmosphere, and evacuate to a pressure ≤ 10 Pa; Perform plasma treatment for 5 - 20 minutes with a radio frequency power of 50 - 200 W and a frequency of 13.56 MHz; After the 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.

[0012] Further, the thickness of a solid-state proton electrolyte membrane is 50 - 100 μm, and the tensile strength ≥ 30 MPa.

[0013] Further, an application of a solid-state proton electrolyte membrane in the preparation of a deep-sea energy storage battery.

[0014] 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.

[0015] The principle of the present invention: Semicrystalline PVDF (polyvinylidene fluoride) gives the material 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 improve 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 improving 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 amorphous state, and maintaining stable proton conduction (conductivity >10 -4 S / cm) in the range of -20 °C to 80 °C Compared with the prior art, the beneficial effects of the present invention are: The present invention uses PVDF (polyvinylidene fluoride) and PEO (polyethylene oxide) as the main synthesis components, and introduces phosphoric acid functional groups. The combined effect 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.

[0016] The present invention has significant advantages such as low raw material cost, environmentally friendly 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

[0017] Figure 1 is the X-ray diffraction pattern of the prepared polymer solid electrolyte; Figure 2 is the scanning electron microscope image of the prepared solid electrolyte; Figure 3 is the linear sweep voltammogram of the solid electrolyte prepared in Example 1; Figure 4 is the variable-temperature electrochemical impedance spectrum of the solid electrolyte prepared in Example 1; Figure 5 is the fitting of the variable-temperature electrochemical impedance spectrum of the solid electrolyte prepared in Example 1; Figure 6 is the cycle performance graph of the button-type solid proton battery assembled with the solid electrolyte material prepared in Example 2 at a current density of 50 mA / g; Figure 7 is the rate performance graph of the button-type solid proton battery assembled with the solid electrolyte material prepared in Example 2 at different current densities; Figure 8 is the cycle performance graph of the button-type solid proton battery assembled with the solid electrolyte material prepared in Example 2 at a current density of 200 mA / g; Figure 9 is the cycle performance graph of the button-type solid proton battery assembled with the solid electrolyte material prepared in Example 2 at a current density of 500 mA / g; Figure 10 is the cycle performance graph of the button-type solid proton battery assembled with the solid electrolyte material prepared in Example 2 at a current density of 1 A / g; Figure 11 is the cycle performance graph of the button-type solid proton battery assembled with the solid electrolyte material prepared in Example 2 at a temperature of 60°C and a current density of 50 mA / g; Figure 12 is the cycle performance graph of the button-type solid proton battery assembled with the solid electrolyte material prepared in Example 2 at a temperature of -20°C and a current density of 20 mA / g. Detailed Embodiments

[0018] To better understand the technical content of the present invention, specific embodiments are provided below to further illustrate the present invention.

[0019] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0020] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can all be obtained from commercial channels.

[0021] Embodiment 1 A method for preparing a solid-state proton electrolyte membrane uses plasma-pretreated PVDF (polyvinylidene fluoride) and PEO (polyethylene oxide) as the synthesis main body, 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. The specific steps are as follows: 1) Place 1000 mg of PVDF (polyvinylidene fluoride), 100 mg of PEO (polyethylene oxide), and 1000 mg of phosphoric acid in a glass bottle; 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, and clear solution.

[0022] 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 and obtain a homogeneous and transparent solution.

[0023] 4) Place the homogeneous and 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 electrolyte membrane.

[0024] Perform performance analysis on the prepared solid electrolyte material As Figure 1 shown, for the solid electrolyte synthesized by the present invention, PVDF is in an amorphous structure, and phosphoric acid molecules have a strong coordination ability with PVDF, forming a solvation structure. These molecules migrate through the interaction with the PVDF / PEO polymer chain, thereby achieving a high room-temperature ionic conductivity.

[0025] Figure 2 is the scanning electron microscope image of the prepared solid electrolyte; the porous structure ensures excellent mechanical properties of the electrolyte, and the hydrogen bond force existing between phosphoric acid and the PVDF / PEO chain contributes to the stability of the composite polymer framework.

[0026] Figure 3This 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.

[0027] 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.

[0028] 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.

[0029] Example 2 The solid-state proton battery was assembled using the solid-state electrolyte obtained in Example 1, as follows: The solid electrolyte membrane prepared by the present invention is an electrolyte, 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.

[0030] 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.

[0031] (2) Preparation of electrode sheets: The positive and negative electrode sheets after rolling are dried, and the positive and negative electrode sheets are cut into electrode sheets with a diameter of 6 mm and a diameter of 10 mm respectively. The mass loading of the electrode sheets is 5-10 mg / cm -2 .

[0032] (3) CR2032 button cells were 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.

[0033] See also Figures 6 to 12, the solid-state 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, the capacity retention rate is 87.21% after 1400 cycles. At 500 mA / g, the capacity retention rate is 82.15% after 7000 cycles. 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 the capacity still remains 69.5% after 19000 cycles, and the cycle life reaches up to 7600 h, demonstrating its excellent cycling performance and long-life advantages.

[0034] Example 3 A preparation method of a solid-state proton electrolyte, the specific steps are as follows: 1) Put 2 g of PVDF (polyvinylidene fluoride), 200 mg of PEO (polyethylene oxide) and 2 g of phosphoric acid into a glass bottle; 2) Add 22 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.

[0035] 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.

[0036] 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.

[0037] 5) Punch the obtained solid electrolyte membrane into a disc with a diameter of 17 mm, and assemble a CR2032 button battery in the air. Prussian blue is used as the positive electrode, activated carbon is used as the negative electrode, and the solid electrolyte membrane prepared by the present invention is used as the electrolyte.

[0038] Example 4 A preparation method of a solid-state proton electrolyte, the specific steps are as follows: 1) Put 3 g of PVDF (polyvinylidene fluoride), 300 mg of PEO (polyethylene oxide) and 3 g of phosphoric acid into a glass bottle; 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.

[0039] 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.

[0040] 4) Place the white homogeneous 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.

[0041] 5) Punch the obtained solid electrolyte membrane into circular pieces with a diameter of 17 mm, and assemble the CR2032 button battery in the air. Prussian blue is used as the positive electrode, activated carbon is used as the negative electrode, and the solid electrolyte membrane prepared by the present invention is used as the electrolyte.

[0042] 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 in 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, characterized in that: 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 is ≥99%.

3. The method for preparing a solid-state 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 method for preparing a solid-state 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-state 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 method for preparing a solid-state proton electrolyte membrane according to claim 1, characterized in that: In step S4, the vacuum degree is - 0.08 ~ - 0.1 MPa.

7. The method for preparing a solid-state proton electrolyte membrane according to claim 1, characterized in that: The polyvinylidene fluoride is first pretreated by plasma, including the following steps: Place the 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 pass argon for cooling for 3 - 7 minutes to obtain polyvinylidene fluoride with a fluorine - containing group density on the surface increased by 20 - 50% and a roughness of 50 - 200 nm.

8. A solid-state 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 is ≥30 MPa.

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

10. The use 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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