Two-dimensional fluorine-doped carbon nanosheets, preparation and applications thereof

Abstract

The application discloses a preparation method and application of two-dimensional fluorine-doped carbon nanosheet. The preparation method of the two-dimensional fluorine-doped carbon nanosheet is as follows: a) synthesizing a hard template organic metal skeleton ZIF-L nanosheet, dispersing the ZIF-L nanosheet in an ethanol aqueous solution, adding a cationic surfactant, resorcinol, a fluorine-containing monomer, ammonia water and a formaldehyde solution into the dispersion liquid in sequence, reacting, centrifuging, and drying to obtain ZIF-L@ fluorine-doped phenolic resin composite nanosheet; b) calcining the composite nanosheet to obtain the two-dimensional fluorine-doped carbon nanosheet. The application prepares the two-dimensional fluorine-doped carbon nanosheet with a micron scale through a hard template method, the fluorine doping inhibits a hydrogen evolution reaction, the micron-level transverse size endows the two-dimensional fluorine-doped carbon nanosheet with long-range conductivity, improves the conductivity of a negative plate in a discharging state, reduces polarization, increases a charging receiving current, promotes electrochemical reduction of lead sulfate to metal lead, inhibits sulfatation, and finally prolongs the cycle life of a lead-carbon battery.

Description

Technical Field

[0001] This application relates to a method for preparing two-dimensional fluorine-doped carbon nanosheets and their application, belonging to the field of lead-carbon batteries and lead-acid batteries. Background Technology

[0002] Lead-acid batteries are a long-established and widely used energy storage technology. However, due to increasingly demanding performance requirements in various applications (such as automotive and large-scale energy storage), lead-acid batteries face the need for performance improvements. In particular, under high-rate partial state of charge (HRPSoC) loads, the negative electrode is considered the primary cause of the sharp decline in cycle capacity. This capacity decay is mainly attributed to the gradual accumulation of chemically inactive lead sulfate crystals on the negative electrode surface, especially at the bottom, a process known as sulfation. This is because lead sulfate cannot be completely and effectively converted into sponge lead during subsequent charging.

[0003] By incorporating up to ten times the usual amount of carbon material into the negative electrode, irreversible sulfation in lead-acid batteries can be significantly suppressed, resulting in a "lead-carbon battery." Moseley summarized the role of carbon in the negative electrode. Among various possible functions, carbon may promote lead nucleation. Pavlov confirmed that the electrochemical reduction of lead sulfate preferentially occurs on the surface of electrochemically active carbon. Furthermore, carbon can act as a steric hindrance for lead sulfate crystallization, thus maintaining its high specific surface area. Activated carbon increases the porosity of the negative electrode by providing an additional structural framework, promoting electrolyte migration from the surface to the interior. As a result, sufficient sulfuric acid can be provided to match the electrode reaction.

[0004] During lead-carbon battery charging, while the basic electrode reaction occurs at the negative electrode, the low hydrogen evolution potential of the carbon material leads to hydrogen evolution reaction (HER) on the carbon material surface. HER not only reduces coulombic efficiency but also disrupts the conductive connection between lead and carbon particles. Loading various materials with high HER overpotentials, such as lead and its derivatives, indium oxide, gallium oxide, and bismuth oxide, can mitigate these adverse effects. Alternatively, doping with other atoms, such as pyrrole nitrogen, oxygen, boron, and phosphorus, has proven to be an effective method for suppressing HER. However, the electronegativity of these doping elements is far lower than that of fluorine, meaning their effectiveness in suppressing HER is less than that of fluorine.

[0005] Given that the carbon materials currently incorporated into negative plates are generally several hundred nanometers in size, their ability to improve the conductivity of negative plates in the discharge state is limited.

[0006] This invention incorporates two-dimensional fluorine-doped carbon nanosheets with a lateral dimension of several micrometers into the negative electrode plate of a lead-carbon battery, which significantly improves the conductivity of the negative electrode plate in the discharge state, thereby increasing the charging current, promoting the reduction and conversion of lead sulfate crystals into sponge lead-acid batteries, inhibiting sulfation, and extending the battery cycle life. Summary of the Invention

[0007] Two-dimensional fluorine-doped carbon nanosheets with lateral dimensions of several micrometers were prepared by hard template method. Fluorine doping inhibited the hydrogen evolution reaction, and the micrometer-scale size endowed them with long-range conductivity, which improved the conductivity of the negative plate in the discharge state, reduced polarization, increased the charging current, promoted the electrochemical reduction of lead sulfate to metallic lead, inhibited sulfation, and thus extended the cycle life of lead-carbon batteries.

[0008] According to one aspect of the present invention, a method for preparing two-dimensional fluorine-doped carbon nanosheets is provided, comprising the following steps:

[0009] a) First, hard template metal-organic framework ZIF-L nanosheets were synthesized and dispersed in an ethanol aqueous solution. Cationic surfactant, resorcinol, fluorinated monomer, ammonia and formaldehyde solution were added to the dispersion in sequence. The reaction was carried out, centrifuged, and dried to obtain powder.

[0010] b) The powder is calcined to obtain two-dimensional fluorine-doped carbon nanosheets.

[0011] The above reaction was carried out in a glass container, centrifugation was carried out in a centrifuge, and the powder was placed in an open quartz boat and transferred to a tube furnace for calcination.

[0012] Optionally, the cationic surfactant is selected from at least one of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, hexadecylpyridine bromide, dodecyltrimethylammonium bromide, and tributylhexadecylphosphonium bromide.

[0013] Optionally, the fluorinated monomer is selected from at least one of 4-fluorophenol, 3-fluorophenol, 3-(trifluoromethoxy)phenol, and 4-(trifluoromethyl)phenol.

[0014] Optionally, the mass ratio of the cationic surfactant, resorcinol, fluorinated monomer, ammonia, and formaldehyde solution is 1:1-2:0.1-1:3-5:1-3.

[0015] Optionally, the mass ratio of the cationic surfactant, resorcinol, fluorinated monomer, ammonia and formaldehyde solution is any value or a range between two values ​​from 1:1 to 2:0.1 to 1:3 to 5:1 to 3.

[0016] Optionally, the reaction temperature is 15–50°C, and the reaction time is 6–10 h.

[0017] Optionally, the temperature of the reaction is any value among 15°C, 25°C, and 50°C, or a range between two values.

[0018] Optionally, the reaction time is any value among 6h, 8h, and 10h, or a range between two values.

[0019] Optionally, the centrifugation speed is 2000-5000 rpm, and the centrifugation time is 2-10 min.

[0020] Optionally, the centrifugation speed is any value among 2000 rpm, 3000 rpm, and 5000 rpm, or a range between two values.

[0021] Optionally, the centrifugation time is any value among 2 min, 6 min, and 10 min, or a range between two values.

[0022] Optionally, the drying temperature is 60–100°C, and the drying time is 24–36 hours.

[0023] Optionally, the drying temperature is any value among 60°C, 80°C, and 100°C, or a range between two values.

[0024] Optionally, the drying time is any value among 24h, 30h, and 36h, or a range between two values.

[0025] Optionally, the roasting includes a roasting stage;

[0026] The temperature of the first stage of roasting is 800-1000℃, and the roasting time is 2-4 hours.

[0027] Optionally, the temperature of the first roasting stage is any value among 800℃, 900℃, and 1000℃, or a range between two values.

[0028] Optionally, the temperature of the first roasting stage is any value among 2h, 3h, and 4h, or a range between two values.

[0029] According to another aspect of the present invention, the application of two-dimensional fluorine-doped carbon nanosheets obtained according to the above preparation method in a lead-carbon battery negative electrode plate is provided, comprising the following steps:

[0030] Step 1: Add water and sulfuric acid to a mixture containing two-dimensional fluorine-doped carbon nanosheets, additives, short fibers and lead powder, and stir to obtain lead paste;

[0031] Step 2: Apply the lead paste onto the grid, cure it, and dry it to obtain the negative electrode plate of the lead-carbon battery.

[0032] Optionally, the mass ratio of the two-dimensional fluorine-doped carbon nanosheets, additives, short fibers and lead powder is 1.5:1.4-1.6:0.06-0.08:100-150.

[0033] Optionally, the mass ratio of the two-dimensional fluorine-doped carbon nanosheets, additives, short fibers and lead powder is any value or a range between two values ​​from 1.5:1.4:0.06:100, 1.5:1.5:0.07:125, 1.5:1.6:0.08:150.

[0034] Optionally, the water accounts for 13% to 20% of the mass of the mixture; the sulfuric acid accounts for 7% to 12% of the mass of the mixture, and the density of the sulfuric acid is 1.4 g / cm³. -3 .

[0035] Optionally, the curing temperature is 45–55°C, and the curing time is 40–60 h.

[0036] Optionally, the curing temperature is any value among 45°C, 50°C, and 55°C, or a range between two values.

[0037] Optionally, the curing time is any value among 40h, 50h, and 60h, or a range between two values.

[0038] Optionally, the drying temperature is 60–85°C, and the drying time is 9–20 hours.

[0039] Optionally, the temperature of the drying process I is any value among 60°C, 70°C, and 85°C, or a range between two values.

[0040] Optionally, the drying time I is any value among 9h, 15h, and 20h, or a range between two values.

[0041] Optionally, the thickness of the lead paste is 2 to 4 mm.

[0042] This invention prepares micron-scale two-dimensional fluorine-doped carbon nanosheets using a hard template method. Fluorine doping inhibits the hydrogen evolution reaction, and the micron-scale lateral size endows them with long-range conductivity, improving the conductivity of the negative electrode plate in the discharge state, reducing polarization, increasing the charging current, promoting the electrochemical reduction of lead sulfate to metallic lead, inhibiting sulfation, and ultimately extending the cycle life of lead-carbon batteries.

[0043] The beneficial effects that this invention can produce include:

[0044] 1) The preparation method provided by this invention, which prepares two-dimensional fluorine-doped carbon nanosheets by hard template method, significantly improves the long-range conductivity of carbon materials, reduces the ohmic polarization of the battery, increases the charging receiving current, alleviates the sulfation of the negative plate, and greatly extends the cycle life of lead-carbon battery.

[0045] 2) The lead-carbon battery negative electrode plate provided by the present invention has better charge-discharge reversibility and charge receiving capability than the composite negative electrode plate prepared by two-dimensional carbon nanosheets and mesoporous carbon nanoparticles. Attached Figure Description

[0046] Figure 1 Schematic diagram of the synthesis of two-dimensional fluorine-doped carbon nanosheets (Example 1)

[0047] Figure 2 SEM images of ZIF-L, ZIF-L@PR, and ZIF-L@FPR and their carbonized products: (A) ZIF-L nanosheets; (B) ZIF-L@PR; (C) ZIF-L@FPR; (D) Carbon materials derived from ZIF-L; (E) Two-dimensional carbon nanosheets (2D C); (F) Two-dimensional fluorine-doped carbon nanosheets (2D FC) (Example 1 and Comparative Example 1)

[0048] Figure 3 Cyclic voltammetry (Example 1 and Comparative Example 1)

[0049] Figure 4 Electrochemical impedance spectroscopy (Example 1 and Comparative Example 1)

[0050] Figure 5 Coulombic efficiency and voltage efficiency (Example 1 and Comparative Example 1)

[0051] Figure 6 Energy efficiency (Example 1 and Comparative Example 1)

[0052] Figure 7 Discharge capacity variation (Example 1 and Comparative Example 1)

[0053] Figure 8 SEM images of negative electrode plates doped with two-dimensional carbon nanosheets and two-dimensional fluorine-doped carbon nanosheets: (A) 2D C-top-surface; (B) 2D FC-top-surface; (C) 2D C-top-interior; (D) 2D FC-top-interior.

[0054] Figure 9 XRD patterns of the top of the negative electrode plate doped with two-dimensional carbon nanosheets and two-dimensional fluorine-doped carbon nanosheets: (A) Top of 2D C negative electrode plate; (B) Top of 2D FC negative electrode plate; (C) Pb standard card; (D) PbSO4 standard card.

[0055] Table 1. Raw material ratios for preparing precursors of two-dimensional carbon nanosheets and two-dimensional fluorine-doped carbon nanosheets.

[0056] Table 2. Charging receive current of lead-carbon batteries with negative electrode plates doped with two-dimensional carbon nanosheets, two-dimensional fluorine-doped carbon nanosheets, and mesoporous fluorine-doped carbon nanoparticles.

[0057] Table 3 Hydrogen evolution reaction of a 5.7Ah rated capacity lead-carbon battery Detailed Implementation

[0058] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0059] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0060] Example 1

[0061] At room temperature, 7.35 g of Zn(NO3)2·6H2O was dissolved in 500 mL of deionized water, and 16.25 g of 2-methylimidazole (Hmim) was dissolved in 500 mL of deionized water. Both solutions were magnetically stirred for 0.5 h to ensure complete dissolution, yielding an aqueous solution of Hmim and an aqueous solution of Zn(NO3)2. The molar ratio of Zn in the two solutions was... 2+ The Hmim ratio was 1:8. The Hmim aqueous solution was rapidly poured into the Zn(NO3)2 aqueous solution, and the solution instantly turned milky white. After stirring for 0.5 h, a large amount of white flocculent matter appeared. Stirring continued for another 3.5 h (total reaction time controlled at 4.0 h). After the reaction was complete, the elliptical metal-organic framework ZIF-L nanosheets were separated using a centrifuge at 5000 rpm for 3.0 min.

[0062] 3.5 g of ZIF-L nanosheets were dispersed in an ethanol-water mixture (150 mL ethanol + 350 mL water) and stirred for 0.5 h. Then, 0.35 g of cetyltrimethylammonium bromide (CTAB) was added, and stirring continued for another 0.5 h. To ensure sufficient adsorption of CTAB onto the ZIF-L nanosheet surface, 0.6125 g of resorcinol, 0.208 g of 4-fluorophenol, and 1.75 mL of 28 wt% ammonia were added sequentially, and the mixture was magnetically stirred for 0.5 h. Finally, 0.90 mL of 37-40 wt% formaldehyde aqueous solution was added using a pipette. The reaction continued for 8.0 h, resulting in a fluorine-doped phenolic resin (FPR-1) coating on the ZIF-L nanosheet surface. Sufficient ZIF-L@FPR-1 composite nanosheets were synthesized, separated by vacuum membrane filtration, and dried in a 70 °C oven for 24 h. The dried ZIF-L@FPR-1 composite nanosheets were collected. Figure 2 C). Place it in an open quartz container, transfer it to a tube furnace, and in an inert nitrogen atmosphere, incubate at 5°C for 5 min. -1 The heating rate was increased from room temperature to 800℃, held at 800℃ for 2.0 h, and then allowed to cool naturally to room temperature to obtain two-dimensional fluorine-doped carbon nanosheets-1.

[0063] Milled lead oxide powder, two-dimensional fluorine-doped carbon nanosheets-1 (1.5 wt%, relative to the mass of milled lead oxide powder), polyester short fibers with a length of 3-5 mm (0.06 wt%, relative to the mass of milled lead oxide powder, polyester PET fiber), barium sulfate (1.2 wt%, relative to the mass of milled lead oxide powder), and lignin (0.2 wt%, relative to the mass of milled lead oxide powder) were loaded into a mixer and stirred thoroughly to ensure uniform mixing. Then, the mixture was poured into a paste mixer, and first, deionized water (13.3 wt%, relative to the mass of milled lead oxide powder) was slowly added, followed by dropwise addition of 1.4 g cm⁻¹. -3 H2SO4 solution (25℃), continue stirring for 25 minutes to obtain lead paste. Manually press the lead paste onto both sides of a 57.0mm × 38.0mm (length × width) lead-calcium alloy grid, ensuring the paste completely covers the surface. Use factory-coated paper to sandwich it in the middle, and then roll it flat with a rigid plastic tube, controlling the weight to 0.71g / cm². -2 After coating, the wet negative electrode plates are transferred to a constant temperature and humidity chamber for curing and drying. The curing process is as follows: 95% relative humidity, 45℃ for 36 hours; 70% relative humidity, 45℃ for 2 hours; 50% relative humidity, 45℃ for 2 hours. The drying process is as follows: 60℃ for 0.5 hours; 70℃ for 0.5 hours; 85℃ for 8.0 hours, resulting in the negative electrode plates. For each 2V test battery, four negative electrode plates (length × width × thickness = 57.0mm × 38.0mm × 2.0mm) are alternately stacked with three positive electrode plates (length × width × thickness = 57.0mm × 42.0mm × 2.0mm) purchased from Baoding Fengfan Group Co., Ltd. Each positive and negative electrode plate is wrapped with a 1.5mm thick absorbent glass fiber liner (AGM). The AGM compression ratio of the assembled battery is 20%. Then, using vacuum assistance, 80.3g of 1.275g of [unspecified substance] was injected into the battery (60.0mm long × 30.2mm wide × 70.4mm high). -3 The positive and negative electrodes and the separator were immersed in a sulfuric acid solution (25°C). Before electrochemical testing, the lead-carbon battery was formed using a constant-current charge-discharge method at a fixed rate. The specific process was as follows: 40 min of resting, 10 s of constant-voltage charging at 3.0 V, 18 h of constant-current charging at 901.3 mA, 3 h of constant-current discharging at 901.3 mA, 10 h of constant-current charging at 901.3 mA, 4 h of constant-current discharging at 901.3 mA, 9.5 h of constant-current charging at 901.3 mA, and finally 1 min of resting. Cyclic voltammetry was performed on an electrochemical workstation (BioLogic, VMP-300), with a scan voltage range of 0.0 to -1.5 V (relative to the Hg / Hg2SO4 reference electrode) and a scan rate of 10 mV / s. -1Electrochemical impedance spectroscopy (EIS) measurements were also performed on an electrochemical workstation (BioLogic, VMP-300), with a frequency range of 100 kHz to 0.1 Hz and a voltage amplitude of 10 mV. Constant current charge-discharge tests were conducted using a battery tester (CT2001A, 5V / 2A, LANHE), with charge and discharge cutoff voltages of 2.4 V and 1.8 V, respectively.

[0064] Example 2

[0065] At room temperature, 7.35 g of Zn(NO3)2·6H2O was dissolved in 500 mL of deionized water, and 16.25 g of Hmim was dissolved in 500 mL of deionized water. The solutions were stirred magnetically for 0.5 h until fully dissolved. The molar ratio of Zn... 2+ The Hmim ratio was 1:8. The Hmim aqueous solution was rapidly poured into the Zn(NO3)2 aqueous solution, and the solution instantly turned milky white. After stirring for 0.5 hours, a large amount of white flocculent matter appeared. The total reaction time was controlled at 4.0 hours. After the reaction was complete, ZIF-L nanosheets were separated using a centrifuge at 5000 rpm for 3.0 minutes.

[0066] 3.5 g of ZIF-L nanosheets were dispersed in an ethanol-water mixture (150 mL ethanol + 350 mL water) and stirred for 0.5 h. Then, 0.35 g of cetyltrimethylammonium bromide (CTAB) was added, and stirring continued for another 0.5 h. To ensure sufficient adsorption of CTAB onto the ZIF-L nanosheet surface, 0.652 g of resorcinol, 0.166 g of 4-fluorophenol, and 1.75 mL of ≥28% ammonia solution were added sequentially, and the mixture was magnetically stirred for 0.5 h. Finally, 0.90 mL of 37-40% formaldehyde aqueous solution was added using a pipette. The reaction was continued for 8.0 h, resulting in a fluorine-doped phenolic resin (FPR-2) coating on the ZIF-L nanosheet surface. Sufficient ZIF-L@FPR-2 composite nanosheets were synthesized, separated by vacuum membrane filtration, and dried in a 70 °C oven for 24 h. The dried ZIF-L@FPR-2 composite nanosheets were collected. Place it in an open quartz container, transfer it to a tube furnace, and in an inert nitrogen atmosphere, incubate at 5°C for 5 min. -1 The temperature was increased from room temperature to 800°C, held at 800°C for 2.0 h, and then allowed to cool naturally to room temperature to obtain two-dimensional fluorine-doped carbon nanosheets-2. Other implementation steps and methods were the same as in Example 1.

[0067] Example 3

[0068] At room temperature, 7.35 g of Zn(NO3)2·6H2O was dissolved in 500 mL of deionized water, and 16.25 g of Hmim was dissolved in 500 mL of deionized water. The solutions were stirred magnetically for 0.5 h until fully dissolved. The molar ratio of Zn... 2+The Hmim ratio was 1:8. The Hmim aqueous solution was rapidly poured into the Zn(NO3)2 aqueous solution, and the solution instantly turned milky white. After stirring for 0.5 h, a large amount of white flocculent matter appeared. The total reaction time was controlled at 1.0 h, yielding smaller ZIF-L nanosheets. After the reaction was complete, the ZIF-L nanosheets were separated using a centrifuge at 5000 rpm for 3.0 min.

[0069] 2.5 g of ZIF-L nanosheets were dispersed in an ethanol-water mixture (150 mL ethanol + 350 mL water) and stirred for 0.5 h. Then, 0.25 g of cetyltrimethylammonium bromide (CTAB) was added, and stirring continued for another 0.5 h. To ensure sufficient adsorption of CTAB onto the ZIF-L nanosheet surface, 0.4375 g of resorcinol, 0.149 g of 4-fluorophenol, and 1.25 mL of 28 wt% ammonia were added sequentially, and the mixture was magnetically stirred for 0.5 h. Finally, 0.64 mL of 37-40 wt% formaldehyde aqueous solution was added using a pipette. The reaction continued for 8.0 h, resulting in a fluorine-doped phenolic resin coating on the ZIF-L nanosheet surface. Sufficient ZIF-L@FPR composite nanosheets were synthesized, separated by vacuum membrane filtration, and dried in a 70 °C oven for 24 h. The dried ZIF-L@FPR-3 composite nanosheets were collected. Place it in an open quartz container, transfer it to a tube furnace, and in an inert nitrogen atmosphere, incubate at 5°C for 5 minutes. -1 The temperature was increased from room temperature to 800°C, held at 800°C for 2.0 h, and then allowed to cool naturally to room temperature to obtain two-dimensional fluorine-doped carbon nanosheets-3. Other implementation steps and methods were the same as in Example 1.

[0070] Comparative Example 1

[0071] At room temperature, 7.35 g of Zn(NO3)2·6H2O was dissolved in 500 mL of deionized water, and 16.25 g of Hmim was dissolved in 500 mL of deionized water. The solutions were stirred magnetically for 0.5 h until fully dissolved. The molar ratio of Zn... 2+The Hmim ratio was 1:8. The Hmim aqueous solution was rapidly poured into the Zn(NO3)2 aqueous solution, instantly turning the solution milky white. After stirring for 0.5 hours, a large amount of white flocculent matter appeared. The total reaction time was controlled at 4.0 hours. After the reaction was complete, ZIF-L nanosheets were separated using a centrifuge at 5000 rpm for 3.0 minutes. 3.5 g of ZIF-L nanosheets were dispersed in an ethanol-water mixture (150 mL ethanol + 350 mL water) and stirred for 0.5 hours. Then, 0.35 g of hexadecyltrimethylammonium bromide (CTAB) was added, and stirring continued for another 0.5 hours. To ensure sufficient adsorption of CTAB onto the ZIF-L nanosheet surface, 0.8168 g of resorcinol and 1.75 mL of ≥28% ammonia water were added sequentially, and the mixture was magnetically stirred for 0.5 hours. Finally, 0.90 mL of 37-40% formaldehyde aqueous solution was added using a pipette. The reaction continued for 8.0 h, and a layer of phenolic resin (PR) was coated onto the surface of the ZIF-L nanosheets. Figure 2 B). Sufficient ZIF-L@PR composite nanosheets were synthesized, separated by vacuum membrane filtration, and dried in a 70℃ oven for 24 h. The dried ZIF-L@PR composite nanosheets were collected and placed in an open quartz container, then transferred to a tube furnace and heated at 5℃ for 5 min under a nitrogen inert atmosphere. -1 The heating rate was increased from room temperature to 800°C, held at 800°C for 2.0 h, and then allowed to cool naturally to room temperature to obtain two-dimensional carbon nanosheets. Other implementation steps and methods were the same as in Example 1.

[0072] Comparative Example 2 (Mesoporous Fluorine-Doped Carbon)

[0073] 0.41 g of resorcinol, 0.14 g of 4-fluorophenol, and 0.21 g of hexamethylenetetramine were dissolved in 200 mL of deionized water using magnetic stirring. Subsequently, 0.40 g of the block copolymer Pluronic F127 was also dispersed and dissolved in the same solution. The mixture was transferred to a reactor and reacted at 120 °C for 4 h to obtain a brick-red suspension. The brick-red particles were separated by centrifugation at 11000 rpm for 10 min and dried at 80 °C for 24 h to obtain a brick-red powder. The brick-red powder was placed in a quartz boat and transferred to a tube furnace. Under a nitrogen atmosphere, the powder was heated from room temperature at 5 °C / min. -1 The temperature was raised to 350℃ and held for 1 hour, then raised to 800℃ and held for 2 hours to obtain mesoporous fluorine-doped carbon material. 1.5 g of mesoporous fluorine-doped carbon material, 1.4 g of additives (BaSO4 and lignin, mass ratio 6:1), 0.06 g of polyester staple fiber, and 100 g of lead powder were mixed using a high-speed shear mixer for 5 minutes. 13 g of water and 7 g of lead powder with a density of 1.4 g / cm³ were added to the mixture. –3Sulfuric acid was used to prepare lead paste by thorough stirring, with the material temperature controlled not to exceed 65°C. The lead paste was then pressed onto the grid, and after curing and drying, the negative electrode plate for a lead-carbon battery was obtained. Other implementation steps and methods were the same as in Example 1.

[0074] according to Figure 1 It can be seen that the preparation process and method of two-dimensional fluorine-doped carbon nanosheets are known.

[0075] Figure 2 The ZIF-L nanosheets synthesized at room temperature shown exhibit an elliptical leaf-like shape. Figure 2 A). After pure ZIF-L nanosheets undergo high-temperature carbonization at 800℃, their morphology is damaged and cannot be maintained. Figure 2 D). A layer of phenolic resin or fluorine-doped phenolic resin is coated onto the surface of ZIF-L. Figure 2 Two-dimensional carbon or fluorine-doped carbon nanosheets were obtained by high-temperature carbonization of B and C. Figure 2 The ZIF-L hard template morphology was well preserved (E and F). The transverse dimensions of the long axis of the ZIF-L nanosheets are at the micrometer level, concentrated in the range of 4–8 μm. After carbonization, the composite nanosheets shrink in size, but remain at the micrometer scale, concentrated in the range of 3–6 μm.

[0076] The lead paste was pressed into the topmost grid hole (12.3mm × 10.5mm) of the lead strip, with the total mass of the lead paste controlled at 1.28g. For example... Figures 3-4 As shown, the redox peak spacing is 0.801 V for the anode doped with two-dimensional carbon nanosheets, and 0.237 V for the anode doped with two-dimensional fluorine-doped carbon nanosheets. The introduction of fluorine increases the redox reversibility of Pb / PbSO4 and reduces the battery's internal resistance. The oxidation peak area is significantly larger than the reduction peak area in the CV curve, indicating that irreversible sulfation is inevitable. The ohmic resistance of the anode doped with two-dimensional fluorine-doped carbon nanosheets is significantly lower than that of the anode doped with two-dimensional carbon nanosheets.

[0077] Figures 5-6 As shown, compared with two-dimensional carbon nanosheets, the coulombic efficiency, voltage efficiency, and energy efficiency of lead-carbon batteries with two-dimensional fluorine-doped carbon nanosheets incorporated into the negative electrode are more stable. Figure 7 As shown, the lead-carbon battery with two-dimensional carbon nanosheets incorporated into the negative electrode plate has a charge-discharge cycle life of 33 cycles. In stark contrast, the lead-carbon battery with two-dimensional fluorine-doped carbon nanosheets incorporated into the negative electrode plate has a significantly longer cycle life of 96 cycles, approximately three times that of the former. It is worth noting that the lead-carbon battery with two-dimensional fluorine-doped carbon nanosheets incorporated into the negative electrode plate experienced an internal short circuit at 97 cycles, forcing it to cease operation. The experimental results indicate that incorporating two-dimensional fluorine-doped carbon nanosheets into the negative electrode plate results in superior cycle stability for lead-carbon batteries.

[0078] Figure 8As shown, numerous lead sulfate crystals were generated near the surface of the negative electrode containing two-dimensional carbon nanosheets, replacing the sponge lead. Figure 8 A), which was also verified by the obvious discharge effect observed during SEM. In stark contrast, the structure of the sponge lead was mostly retained within the negative electrode containing two-dimensional fluorine-doped carbon nanosheets. Figure 8 (B) This is mainly due to the suppression of the hydrogen evolution reaction and the improved electrochemical reversibility of the Pb / PbSO4 redox couple. Furthermore, in both cases, the sponge lead structure inside the negative electrode plate remains almost unchanged. Figure 8 (C and D). For both types of negative plates, PbSO4 crystal particles are clearly visible near the surface, and the sulfation phenomenon inside is significantly weaker than on the surface.

[0079] Figure 9 As shown, the top of the negative electrode plate containing two-dimensional carbon nanosheets and two-dimensional fluorine-doped carbon nanosheets has I PbSO4 / I Pb The figures were determined to be 13.6% and 11.9% respectively. Figure 9 (A and B). This indicates that incorporating two-dimensional fluorine-doped carbon nanosheets into the active material of the negative electrode plate can significantly suppress the sulfation process.

[0080] Table 1 shows that in the preparation of two-dimensional fluorine-doped carbon nanosheets, 4-fluorophenol was used to replace the same amount of resorcinol in the raw materials.

[0081] Table 2 shows that the charging current received by the lead-carbon battery with two-dimensional fluorine-doped carbon nanosheets incorporating the negative electrode plate is significantly higher than that of the two-dimensional carbon nanosheets and the mesoporous fluorine-doped carbon nanoparticles.

[0082] As shown in Table 3, fluorine doping inhibits the hydrogen evolution reaction.

[0083] Table 1

[0084]

[0085] Table 2

[0086]

[0087]

[0088] Table 3

[0089]

[0090] The results show that increasing the size of the carbon material in the negative electrode additive of lead-carbon batteries can improve the battery's charge acceptance capability, promote the electrochemical reduction of PbSO4 to metallic lead, inhibit sulfation, and extend the cycle life of lead-carbon batteries.

[0091] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A method for preparing two-dimensional fluorine-doped carbon nanosheets, characterized in that, Includes the following steps: a) First, rigid template elliptical metal-organic framework ZIF-L nanosheets were synthesized, with a major axis dimension of 4–8 μm, a minor axis dimension of approximately 2–4 μm, and a thickness of 200–300 nm. These nanosheets were dispersed in a 30–40 vol% ethanol-water solution, with a ZIF-L mass concentration of 7.0–9.0 mg / mL. −1 Add cationic surfactant, resorcinol, fluorinated monomer, ammonia and formaldehyde solution to the above dispersion, react, centrifuge, dry to obtain powder; b) Calcining the powder yields two-dimensional fluorine-doped carbon nanosheets; The calcination temperature is 800~1000℃, the major axis dimension is 3~7μm, the minor axis dimension is 1~3μm, and the thickness is 150~250nm.

2. The preparation method according to claim 1, characterized in that, The powder was calcined to obtain two-dimensional fluorine-doped carbon nanosheets; The roasting temperature is 800~900℃ and the roasting time is 2~3h.

3. The preparation method according to claim 1, characterized in that, The cationic surfactant is selected from at least one or more of hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride, hexadecylpyridine bromide, dodecyltrimethylammonium bromide, and tributylhexadecylphosphine bromide; The fluorinated monomer is selected from at least one or more of 4-fluorophenol, 3-fluorophenol, 3-(trifluoromethoxy)phenol, and 4-(trifluoromethyl)phenol; The mass ratio of the cationic surfactant, resorcinol, fluorinated monomer, 28-30% ammonia water and 37-40% formaldehyde solution is 1:1-2:0.1-1:3-5:1-3. The mass ratio of ZIF-L nanosheets to the precursor fluorine-doped phenolic resin is 6-8:

1.

4. The preparation method according to claim 3, characterized in that, The mass ratio of the cationic surfactant, resorcinol, fluorinated monomer, 28-30% ammonia water and 37-40% formaldehyde solution is 1:1-1.5:0.2-0.8:3.5-4.5:1.5-2.5; the mass ratio of ZIF-L nanosheets to the precursor fluorine-doped phenolic resin is 6.5-7.5:

1.

5. The preparation method according to claim 1, characterized in that, The reaction temperature is 15~50℃, and the reaction time is 6~10h; The centrifugation speed is 2000~5000 rpm, and the centrifugation time is 2~10 min; The drying temperature is 60~100℃, and the drying time is 24~36h.

6. The preparation method according to claim 1, characterized in that, The process for synthesizing the hard-template elliptical metal-organic framework ZIF-L nanosheets is as follows: 1) Dissolve 7.35g Zn(NO3)2·6H2O in 400~600mL of deionized water to obtain an aqueous solution of Zn(NO3)2; dissolve 16.25g 2-methylimidazole in 400~600mL of deionized water to obtain an aqueous solution of 2-methylimidazole. 2) Mass ratio Zn 2+ :2-Methylimidazole = 1:8; Mix 2-methylimidazole aqueous solution and Zn(NO3)2 aqueous solution and react for 2.0~6.0h, then centrifuge to separate ZIF-L nanosheets.

7. A two-dimensional fluorine-doped carbon nanosheet obtained by any one of claims 1 to 6.

8. The application of the two-dimensional fluorine-doped carbon nanosheets of claim 7 in the negative electrode plate of a lead-carbon battery.

9. The application according to claim 8, characterized in that, Includes the following steps: Step 1: Add water and sulfuric acid to a mixture containing two-dimensional fluorine-doped carbon nanosheets, additives, short fibers and lead powder, and stir to obtain lead paste; Step 2: Apply the lead paste onto the grid, cure it, and dry it to obtain the negative electrode plate of the lead-carbon battery.

10. The application according to claim 9, characterized in that, The mass ratio of the two-dimensional fluorine-doped carbon nanosheets, additives, polyester short fibers and lead powder is 1.5:1.4~1.6:0.06~0.08:100~150, and the additives are BaSO4 and lignin, with a mass ratio of 7~8:

1.

11. The application according to claim 10, characterized in that, The mass ratio of the two-dimensional fluorine-doped carbon nanosheets, additives, polyester short fibers and lead powder is 1.5:1.45~1.55:0.065~0.075:110~140.

12. The application according to claim 11, characterized in that, The water comprises 13% to 20% of the mixture by mass; the sulfuric acid comprises 7% to 12% of the mixture by mass, and the density of the sulfuric acid at 25°C is 1.4 g / cm³. −3 .

13. The application according to claim 12, characterized in that, The water accounts for 14% to 19% of the mass of the mixture; the sulfuric acid accounts for 8% to 11% of the mass of the mixture.

14. The application according to claim 9, characterized in that, The curing temperature is 45~55℃, and the curing time is 40~60h; The temperature of the drying process is 60~85℃, and the drying time is 9~20h; The thickness of the lead paste is 2-4 mm.

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