A self-supporting sodium-ion battery electrode material and a sodium-ion battery

Abstract

This invention relates to the field of sodium-ion battery technology, specifically to a self-supporting sodium-ion battery electrode material and a sodium-ion battery. The preparation method includes the following steps: pouring a PVA solution into an iron-based polyanion suspension, adjusting the pH to acidic, and performing PVA hydroxyl-Fe... 3+ Coordination reaction; pyrrole monomer is added dropwise to the obtained coordination system, allowing the pyrrole monomer to adsorb onto the PVA hydroxyl group-Fe 3+ A composite slurry is obtained at the coordination sites; an oxidant is added dropwise to initiate a polymerization reaction; the composite slurry after freeze-polymerization is then allowed to thaw naturally at room temperature, and this freezing and thawing process is repeated to obtain a composite gel film, i.e., a self-supporting sodium-ion battery electrode material. This invention solves the problem of easy free aggregation of PPy through coordination-guided design, while simultaneously strengthening the interfacial bonding between NaFePO4 and the PVA / PPy network, resulting in an electrode with high specific capacity, high rate capability, long cycle life, and excellent self-support, meeting the assembly and cycling requirements of practical applications.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a self-supporting sodium-ion battery electrode material and a sodium-ion battery. Background Technology

[0002] The demand for low-cost, high-safety rechargeable batteries for large-scale energy storage and power batteries is increasing year by year. Sodium-ion batteries, due to the abundance, wide distribution, and low cost of sodium resources, have become an important alternative to lithium-ion batteries. Polyanionic sodium iron phosphate (NaFePO4) is a core candidate material for the cathode of sodium-ion batteries due to its stable crystal structure, high theoretical specific capacity (approximately 154 mAh / g), and excellent thermal safety. However, NaFePO4 has extremely low intrinsic conductivity (10 mAh / g). -9 ~10 -6 The slow ion transport rate (S / cm) necessitates conductivity modification and electrode structure optimization for practical application. Traditional NaFePO4 electrode fabrication relies on insulating binders (such as PVDF and CMC) and metal current collectors (such as aluminum foil). On one hand, binders not only increase the electrode interfacial impedance but are also prone to detachment during cycling due to electrolyte swelling and interfacial stress, leading to active material deactivation and accelerated capacity decay. Furthermore, PVDF requires the use of toxic organic solvents (N-methylpyrrolidone), posing environmental and cost issues. On the other hand, metal current collectors increase electrode weight and cost, and the interface between the current collector and the active material easily forms a passivation layer, hindering electron transport and potentially causing corrosion during long-term cycling, thus reducing battery stability.

[0003] To improve the mechanical and electrical properties of sodium-ion battery cathode materials, patent application CN116534829A discloses a method for preparing double-layer coated sodium-ion battery cathode materials from FePO4 using a liquid-phase method. By coating Na4Fe3(PO4)2(P2O7) twice, the conductivity of the electrode material is enhanced while its stability in the electrolyte is improved. Patent application CN117334828A discloses a self-supporting, current collector-free thick electrode for secondary batteries based on conductive nanocellulose. The electrode uses the battery active material as the active substance, and conductive polymer composite nanocellulose as a dispersant, conductive agent, and film-forming medium, resulting in a flexible, self-supporting thick electrode for secondary batteries. Patent application CN119905546A discloses a self-supporting negative electrode material. Polyaniline is coated onto a phosphorus-carbon composite material by in-situ polymerization of aniline to obtain a dispersion of polyaniline-coated phosphorus-carbon. Graphene oxide is added to the dispersion of polyaniline-coated phosphorus-carbon and then reduced by heating to obtain a polyaniline-coated phosphorus-carbon / graphene aerogel. The polyaniline-coated phosphorus-carbon / graphene aerogel is sliced ​​to obtain a self-supporting negative electrode of polyaniline-coated phosphorus-carbon / graphene aerogel.

[0004] In existing technologies, on the one hand, the traditional process of introducing polypyrrole (PPy) makes PPy prone to free aggregation, failing to form a continuous and uniform conductive network, resulting in uneven electron transport paths and limited improvement in rate performance. On the other hand, existing PVA-based self-supporting electrodes mostly rely on simple freeze-thaw physical cross-linking, providing mechanical support only through molecular chain crystallization, which results in insufficient mechanical strength and Fe... 3+ Problems such as easy hydrolysis and weak bonding between the active material and the polymer interface lead to active material stripping and framework cracking during cycling, making it difficult to balance mechanical and electrochemical performance. Therefore, there is an urgent need to develop a self-supporting electrode that combines high mechanical strength, a uniform conductive network, and no binder / current collector, to achieve a dual improvement in electrode performance and process economy. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a self-supporting sodium-ion battery electrode without binder or current collector. The electrode overcomes the limitations of insufficient mechanical strength and easy cracking of the skeleton of the existing self-supporting electrode through a dual network design of coordination crosslinking and freeze-thaw physical crosslinking. At the same time, the self-supporting design without current collector enables the electrode to achieve high specific capacity, high rate capability and long cycle performance.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, this application provides a self-supporting sodium-ion battery electrode material, the preparation method of which includes the following steps: S1: Add the sodium-ion battery iron-based polyanion cathode material to water and adjust the pH to acidic to obtain an iron-based polyanion suspension; S2: Add polyvinyl alcohol (PVA) powder to water, heat to completely dissolve PVA, and cool to obtain a PVA solution; S3: Pour the PVA solution into the iron-based polyanionic suspension, adjust the pH to acidic, and proceed with the PVA hydroxyl-Fe... 3+ Coordination reaction; S4: After the coordination reaction is complete, pyrrole monomer is added dropwise to the obtained coordination system, allowing the pyrrole monomer to be adsorbed onto the PVA hydroxyl-Fe 3+ At the coordination sites, a composite slurry is obtained; S5: Add an oxidant to the composite slurry to carry out a polymerization reaction and obtain the polymerized composite slurry; S6: The composite slurry after freeze polymerization is thawed naturally at room temperature. Repeated freezing and thawing yields a composite gel film, which is a self-supporting sodium-ion battery electrode material.

[0007] Furthermore, the molar ratio / mass ratio of the sodium-ion battery iron-based polyanionic cathode material to PVA is 6:1-12, wherein the PVA is of type 1750 or type 2480.

[0008] Furthermore, the mass ratio of the iron-based polyanionic cathode material, oxidant, and pyrrole monomer is 4:1-10:1.

[0009] Furthermore, the sodium-ion battery iron-based polyanionic cathode material is selected from at least one of NaFePO4, Na3Fe2(PO4)3, Na2FeP2O7, Na2FePO4F, Na2Fe2(SO4)3, Na2Fe2(SO4)3 and Na3Fe2(SO4)3F.

[0010] Furthermore, after adding the sodium-ion battery iron-based polyanion cathode material to water, it is dispersed using an ultrasonic cell disruptor for 30-40 minutes; Furthermore, in step S1, the pH is adjusted to acidity by slowly adding 0.1~1 mol / L acid solution to adjust the pH to <5; Furthermore, the acid solution is added dropwise and then stirred for 10-20 minutes; Furthermore, the acid solution is selected from at least one of dilute hydrochloric acid, dilute sulfuric acid, dilute nitric acid, acetic acid, formic acid, and carbonic acid; Further, the heating completely dissolves the PVA by heating to 70-90°C and stirring in a constant-temperature water bath for 30-60 minutes until the solution is completely transparent and free of particles. The cooling process yields a PVA solution, which is then cooled to below 30°C. Furthermore, after the PVA solution is poured into the iron-based polyanionic suspension, it is stirred at a speed of 300-400 rpm for 10-20 minutes. Furthermore, in step S3, the pH is adjusted by adding dilute hydrochloric acid dropwise to adjust the pH to 3-4, with the concentration of the dilute hydrochloric acid being 0.5 mol / L-1.0 mol / L. Furthermore, the coordination reaction is carried out simultaneously with stirring for 30-60 minutes at a room temperature of 25℃±2℃. The coordination reaction is a PVA hydroxyl-Fe... 3+ Coordination reaction; Furthermore, the dropping rate of the pyrrole (Py) monomer is 0.1-1.0 mL / min, and after adding the Py monomer to the coordination system, the mixture is stirred for 20-30 minutes to allow the Py monomer to be fully adsorbed onto the PVA-Fe complex. 3+ At the coordination site; Furthermore, the oxidant is added at a rate of 0.5-1 mL / min, and the oxidant is selected from at least one of ferric chloride, ammonium persulfate, and hydrogen peroxide. After the addition is completed, stirring is continued for 1-3 hours at a temperature of room temperature (25℃±2℃), and the system gradually turns dark black. Furthermore, the composite slurry after freeze polymerization is first poured into a polytetrafluoroethylene mold for defoaming treatment, and then the mold is placed in a freezer at -50℃ to -10℃ for 16-20 hours. The mold is then removed and allowed to thaw naturally at room temperature for 8-12 hours to complete the first "freeze-thaw" cycle. The above freeze-thaw cycle is repeated ≥3 times, and finally the composite gel film is removed from the mold. Furthermore, the defoaming treatment method is to allow the mixture to stand at 25℃±3℃ for ≥30 minutes for natural defoaming, or to perform vacuum defoaming at -0.09 MPa to -0.07 MPa for 5 to 10 minutes.

[0011] Furthermore, after obtaining the composite gel membrane, the surface residual oxidant and acid are rinsed with deionized water and soaked for 3-5 hours (with water changed more than twice during this period) to remove unreacted impurities and avoid electrochemical side reactions. After washing, the gel membrane is transferred to a vacuum drying oven and vacuum dried for 12-24 hours. The moisture content of the dried gel membrane is ≤8%, and the thickness of the composite gel membrane is 120-150 μm.

[0012] Secondly, this application provides a self-supporting sodium-ion battery electrode, which is obtained by punching the dried composite gel film into a circular electrode sheet using a Φ3mm-Φ24mm punching machine.

[0013] Thirdly, this application provides a sodium-ion battery comprising the aforementioned self-supporting sodium-ion battery electrode material.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By constructing a uniform and continuous PPy conductive network, the problems of low intrinsic conductivity and slow ion transport of NaFePO4 are solved, thereby improving the electron / ion transport efficiency of the electrode and enhancing rate performance and cycle stability.

[0015] 2. No insulating binder or metal current collector is added. On the one hand, it reduces the electrode interface impedance and avoids capacity decay caused by binder swelling and detachment and current collector corrosion and passivation. On the other hand, it reduces electrode weight and manufacturing cost, and does not rely on toxic organic solvents such as NMP, thus improving the environmental friendliness of the process.

[0016] 3. The problem of easy PPy dispersion and aggregation is solved by coordination-guided design, while strengthening the interfacial bonding force between NaFePO4 and PVA / PPy network. PVA provides a three-dimensional support framework, PPy constructs a continuous conductive network, and NaFePO4 is uniformly distributed as an active material, avoiding the stripping of active material during cycling, and taking into account the self-supporting mechanical strength and structural stability of the electrode.

[0017] 4. By using a dual network design of coordination crosslinking and freeze-thaw physical crosslinking, the limitations of insufficient mechanical strength and easy cracking of the skeleton of existing self-supporting electrodes are overcome, and an electrode with high specific capacity, high rate capability, long cycle life and excellent self-support is obtained to meet the assembly and cycling requirements in practical applications. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited thereto. It should be noted that the implementation steps in the embodiments can be further adjusted according to the specific experimental environment, and the implementation steps not specified are usually conditions in conventional experiments. All compounds involved in the following embodiments are commercially available pharmaceutical products.

[0019] Example 1 Take 3.1g NaFePO4 and add it to 8 mL of deionized water. Disperse the mixture in an ultrasonic cell disruptor for 30 minutes (300 W power, 5 s working time / 3 s intermittent time) to form a uniform suspension. Add 0.5 mol / L acetic acid to the suspension to adjust the pH to 2-3. Stir for 10 minutes to obtain an iron-based polyanion suspension. Add 3.1g of PVA to 60 mL of deionized water, stir in a 90℃ constant temperature water bath for 60 minutes until the solution is completely transparent and free of particles, then cool to 30℃ to obtain a PVA solution. The cooled PVA clear solution was poured into the iron-based polyanionic suspension, magnetically stirred (400 rpm) for 10 minutes, and the pH of the mixture was adjusted to 3.0-3.5 with 0.5 mol / L HCl. Stirring was continued for 60 minutes to complete the "PVA hydroxy-Fe" solution. 3+ "Coordination reaction."

[0020] To "PVA-Fe 3+ In the "-NaFePO4" coordination system, purified Py monomer was added dropwise (dropping rate 1.0 mL / min). After magnetic stirring (300 rpm) for 20 minutes, hydrogen peroxide oxidant solution was slowly added dropwise (dropping rate 0.8 mL / min). The mass ratio of iron-based polyanionic cathode material, added Py monomer and oxidant was 4:1:1. After the addition was completed, stirring was continued for 2 hours (room temperature). The system gradually changed from light brownish-yellow to dark black.

[0021] Pour the polymerized composite slurry into a polytetrafluoroethylene mold and let it stand at room temperature for 40 minutes. Place the mold in a -28℃ freezer and freeze for 20 hours. Remove the mold and let it thaw naturally at room temperature for 8 hours. Repeat this cycle 3 times. Remove the composite gel membrane from the mold and rinse the surface with deionized water to remove residual oxidants and acids. Soak the membrane for 3 hours (changing the water twice during this period). After cleaning, transfer the gel membrane to a vacuum drying oven and vacuum dry at 35℃ for 12 hours.

[0022] Example 2 Take 3.1g of Na3Fe2(SO4)3F and add it to 8 mL of deionized water. Disperse the mixture in an ultrasonic cell disruptor for 30 minutes (300W power, 5 s working time / 3 s intermittent time) to form a uniform suspension. Add 0.25 mol / L dilute sulfuric acid to the suspension to adjust the pH to 3-4. Stir for 10 minutes to obtain an iron-based polyanionic suspension. Add 6.2g of PVA to 120 mL of deionized water, stir in a 90℃ constant temperature water bath for 60 minutes until the solution is completely transparent and free of particles, then cool to 30℃ to obtain a PVA solution. The cooled PVA clear solution was poured into the iron-based polyanionic suspension, magnetically stirred (400 rpm) for 10 minutes, and the pH of the mixture was adjusted to 3.5-4.0 with 0.5 mol / L HCl. Stirring was continued for 60 minutes to complete the "PVA hydroxy-Fe" solution. 3+ "Coordination reaction."

[0023] To "PVA-Fe 3+ In the "-NaFePO4" coordination system, purified Py monomer was added dropwise (dropping rate 0.1 mL / min). After magnetic stirring (300 rpm) for 20 minutes, ferric chloride oxidant solution was slowly added dropwise (dropping rate 0.5 mL / min). The mass ratio of iron-based polyanionic cathode material, added Py monomer and oxidant was 4:5:1. After the addition was completed, stirring was continued for 2 hours (room temperature). The system gradually changed from light brownish-yellow to dark black.

[0024] Pour the polymerized composite slurry into a polytetrafluoroethylene mold and let it stand at room temperature for 40 minutes. Place the mold in a -10℃ freezer and freeze for 16 hours. Remove the mold and allow it to thaw naturally at room temperature for 12 hours. Repeat this cycle 3 times. Remove the composite gel membrane from the mold and rinse the surface with deionized water to remove any residual oxidant and acid. Soak the membrane for 3 hours (changing the water twice during this period). After cleaning, transfer the gel membrane to a vacuum drying oven and vacuum dry at 35℃ for 12 hours.

[0025] Example 3 Take 3.1g of Na3Fe2(PO4)3 and add it to 8 mL of deionized water. Disperse the mixture in an ultrasonic cell disruptor for 30 minutes (300W power, 5 s working time / 3 s intermittent time) to form a uniform suspension. Add 0.5 mol / L HCl dropwise to the suspension to adjust the pH to 4-5. Stir for 10 minutes to obtain an iron-based polyanion suspension. Add 0.55g PVA to 10 mL of deionized water, stir in a 90℃ constant temperature water bath for 60 minutes until the solution is completely transparent and free of particles, then cool to 30℃ to obtain a PVA solution. The cooled PVA clear solution was poured into the iron-based polyanionic suspension, magnetically stirred (400 rpm) for 10 minutes, and the pH of the mixture was adjusted to 3.0-3.5 with 0.5 mol / L HCl. Stirring was continued for 60 minutes to complete the "PVA hydroxy-Fe" solution. 3+ "Coordination reaction."

[0026] To "PVA-Fe 3+ In the "-NaFePO4" coordination system, purified Py monomer was added dropwise (dropping rate 0.5 mL / min). After magnetic stirring (300 rpm) for 20 minutes, ammonium persulfate (APS) oxidant solution was slowly added dropwise (dropping rate 1 mL / min). The mass ratio of iron-based polyanionic cathode material, added Py monomer and oxidant was 4:10:1. After the addition was completed, stirring was continued for 2 hours (room temperature). The system gradually changed from light brownish-yellow to dark black.

[0027] Pour the polymerized composite slurry into a polytetrafluoroethylene mold and let it stand at room temperature for 40 minutes. Place the mold in a -50℃ freezer and freeze for 16 hours. Remove the mold and let it thaw naturally at room temperature for 12 hours. Repeat this cycle 5 times. Remove the composite gel membrane from the mold and rinse the surface with deionized water to remove residual oxidants and acids. Soak the membrane for 3 hours (changing the water twice during this period). After cleaning, transfer the gel membrane to a vacuum drying oven and vacuum dry at 35℃ for 12 hours.

[0028] Comparative Example 1 Take 4.0 g NaFePO4 and add it to 6 mL of deionized water. Disperse it by sonication for 30 min to form a uniform suspension. Add 0.3 mL of purified Py monomer to the NaFePO4 suspension and stir magnetically (400 rpm) for 15 min. Adjust the pH of the system to 2-3 with 1 mol / L HCl. Slowly add APS solution (dropping rate 1 mL / min) and stir at room temperature for 2 h until the system turns dark black. Vacuum filter the dark black system to collect the PPy / NaFePO4 composite powder. Wash it three times with deionized water and vacuum dry it at 60℃ for 12 h.

[0029] The dried PPy / NaFePO4 composite powder was mixed with the binder solution and magnetically stirred for 60 min to form a uniform viscous slurry (solid-liquid ratio ≈ 1:1.2, viscosity 5000-8000 mPa). s); use a scraper to evenly coat the slurry onto the aluminum foil, let it stand at room temperature for 30 min; vacuum dry at 60℃ for 12 h, roll it with a roller press to make it dense; use a Φ16mm punching machine to punch it into a circular electrode film with a thickness of 100 μm.

[0030] Experimental Example Experimental Methods: The dried films prepared in Examples 1-3 and Comparative Example 1 were punched into circular electrode sheets using a Φ16 mm punching machine to obtain electrode films. The electrode films were used as the positive electrode to construct coin cells with a separator, electrolyte, and hard carbon negative electrode for testing. Under constant temperature conditions of 25℃, the assembled coin cells were charged to 3.6V at a constant current of 0.1C, allowed to stand for 15 minutes, and then discharged to 1.5V at a constant current of 0.1C, completing one charge-discharge cycle. This charge-discharge process was then repeated for multiple cycles, and the charge-discharge capacity, coulombic efficiency, and capacity retention were continuously recorded for each cycle.

[0031] The electrode materials prepared in Example 1 and Comparative Example 1 were subjected to bending tests to examine the surface condition and mechanical damage behavior of the electrodes under a 180° dynamic bending condition (50 cycles).

[0032] The experimental results are shown in the table below: Table 1 Performance Test Results Statistics

[0033] As shown in Table 1, compared with the battery in Comparative Example 1, the binder-free self-supporting electrode prepared in Example 1 is superior to the electrode material prepared in Comparative Example 1 in both electrochemical and mechanical performance, which is attributed to the structural design and repeated freeze-thaw experimental scheme of Example 1.

Claims

1. A self-supporting sodium-ion battery electrode material, characterized in that, The preparation method includes the following steps: The iron-based polyanion cathode material of sodium-ion battery was added to water and the pH was adjusted to acidic to obtain an iron-based polyanion suspension. PVA powder is added to water, heated to completely dissolve the PVA, and then cooled to obtain a PVA solution. PVA solution was poured into an iron-based polyanionic suspension, and the pH was adjusted to acidic to proceed with the PVA hydroxyl-Fe... 3+ Coordination reaction; After the coordination reaction is complete, pyrrole monomer is added dropwise to the resulting coordination system, allowing the pyrrole monomer to adsorb onto the PVA hydroxyl-Fe 3+ At the coordination sites, a composite slurry is obtained; An oxidant is added dropwise to the composite slurry to carry out a polymerization reaction, resulting in a polymerized composite slurry. The composite slurry after freeze polymerization is thawed naturally at room temperature. Repeated freezing and thawing yields a composite gel film, which is a self-supporting sodium-ion battery electrode material.

2. The self-supporting sodium-ion battery electrode material according to claim 1, characterized in that, The mass ratio of the iron-based polyanionic cathode material to PVA is 6:1-12.

3. The self-supporting sodium-ion battery electrode material according to claim 1 or 2, characterized in that, The mass ratio of the iron-based polyanionic cathode material, oxidant, and pyrrole monomer is 4:1-10:

1.

4. The self-supporting sodium-ion battery electrode material according to claim 1 or 2, characterized in that, The polyanionic cathode material is selected from at least one of NaFePO4, Na3Fe2(PO4)3, Na2FeP2O7, Na2FePO4F, Na2Fe2(SO4)3 and Na3Fe2(SO4)3F.

5. The self-supporting sodium-ion battery electrode material according to claim 1 or 2, characterized in that, The sodium-ion battery iron-based polyanion cathode material is added to water, and the pH is adjusted to acidity, then to pH 2-5.

6. The self-supporting sodium-ion battery electrode material according to claim 1 or 2, characterized in that, After pouring the PVA solution into the iron-based polyanionic suspension, the pH is adjusted to acidity, and then adjusted to pH 3-4.

7. The self-supporting sodium-ion battery electrode material according to claim 1 or 2, characterized in that, The dropping rate of the pyrrole monomer is 0.1-1.0 mL / min.

8. The self-supporting sodium-ion battery electrode material according to claim 1 or 2, characterized in that, The rate of adding the oxidant is 0.5-1 mL / min, and the oxidant is selected from at least one of ferric chloride, ammonium persulfate, and hydrogen peroxide.

9. The self-supporting sodium-ion battery electrode material according to claim 1 or 2, characterized in that, The composite slurry after freeze polymerization is frozen at -50℃ to -10℃ for 16-20 hours, and then thawed naturally for 8-12 hours. This freeze-thaw cycle is repeated ≥3 times.

10. A sodium-ion battery, characterized in that, It includes the sodium-ion battery electrode material as described in any one of claims 1-9.

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