Preparation method of modified porous carbon for lead-carbon battery and lead-carbon battery

Abstract

The application relates to a preparation method of modified porous carbon for lead-carbon batteries and a lead-carbon battery, and the preparation method of the modified porous carbon comprises five steps: pretreatment, impregnation, carbonization, oxidation and surface modification. The pretreated biomass is impregnated by using a high-permeability activator formed by compounding phosphoric acid, imidazolium salt and a permeation aid, and then carbonized and oxidized; finally, the surface is modified by melamine polyphosphate and ammonia gas at high temperature, so that the modified porous carbon with a nitrogen content of more than 7%, micropore rate of more than 23% and mesopore rate of 65% to 73% is prepared. The prepared modified porous carbon is used as a negative electrode additive of the lead-carbon battery, can obviously inhibit the hydrogen evolution reaction, improve the cycle capacity retention rate, further slow down the performance attenuation of the lead-carbon battery, and the cycle capacity retention rate of 500 times at 2C under HRPSoC is more than 90%.

Description

Technical Field

[0001] The invention belongs to the technical field of lead-carbon batteries, and particularly relates to a preparation method of modified porous carbon for a lead-carbon battery and a lead-carbon battery. Background Art

[0002] To alleviate the energy crisis and environmental pollution, countries around the world are developing new energy vehicles, with hybrid vehicles being a key component. Traditional lead-acid batteries are used in mild hybrid vehicles due to their low price and excellent high-current discharge performance. However, the negative electrode of traditional lead-acid batteries is susceptible to irreversible sulfation under high-rate charge / discharge (HRPSoC) conditions, which shortens the battery's lifespan. Lead-carbon batteries, which combine the advantages of supercapacitors and lead-acid batteries, can effectively slow down irreversible sulfation of the negative electrode. The positive electrode of a lead-carbon battery is the same as that of a conventional lead-acid battery—PbO2—while the negative electrode is a hybrid electrode of lead and carbon. Leveraging the carbon material's excellent conductivity, capacitance, and high specific surface area, the utilization and dispersion of the negative electrode active material are improved, thereby inhibiting the accumulation and deactivation of lead sulfate and extending the battery's lifespan. However, the hydrogen evolution potential of carbon materials is much lower than that of lead, and the hydrogen evolution current is much higher than that of lead. Therefore, the incorporation of carbon materials exacerbates the hydrogen evolution phenomenon at the negative electrode. Hydrogen evolution not only causes serious loss of electrolyte during the cycle, but also affects the battery's charging efficiency, destroys the structure of the negative plate, and increases the internal resistance of the negative plate, thereby causing the battery's performance to degrade rapidly. Therefore, it is particularly important to increase the hydrogen evolution overpotential of the carbon material and delay the hydrogen evolution reaction at the negative plate.

[0003] The existing technology mainly starts from the modification of biomass carbon, such as the introduction of materials with high hydrogen evolution overpotential, such as silver oxide, zinc oxide or rare earth oxide, into activated carbon by blending, loading, coating or in-situ method; and heteroatom-doped activated carbon, the specific surface area and multi-porous structure of the carbon are appropriate, such as the specific surface area should be within an appropriate range, and the ratio of micropores to mesopores should be appropriate. The effect of introducing materials with high hydrogen evolution overpotential by blending, loading and coating in the above methods is limited; the general effect of introducing materials with high hydrogen evolution overpotential by in-situ method is better, but the process is often more complicated and the preparation cost is relatively high; carbon with appropriate specific surface area and multi-porous structure is conducive to inhibiting hydrogen evolution reaction, but the process is generally more strictly controlled; the method for preparing heteroatom-doped activated carbon is mainly to use plasma treatment, impregnation with heteroatom-containing compounds to modify the surface of activated carbon to achieve the purpose of introducing heteroatoms. The general process operation is more complicated, and the content of heteroatoms on the surface of the prepared activated carbon is not high.

[0004] Chinese patent CN106629721A discloses a method for producing nitrogen-containing super activated carbon, which includes introducing ammonia into the KOH activation process for activation. This method not only utilizes the high-temperature reaction between ammonia and carbon to produce a well-developed pore structure, but also utilizes the reaction between ammonia and potassium to resolve the potassium release problem during KOH activation, while also achieving the purpose of doping the activated carbon surface with nitrogen. The ammonia activation method disclosed in this patent simply introduces ammonia into the activation step of the conventional super activated carbon preparation process. KOH activation and ammonia activation compete with each other, and cannot produce activated carbon with a high surface nitrogen content. Summary of the Invention

[0005] In view of the above problems, the purpose of the present invention is to provide a method for preparing modified porous carbon for lead-carbon batteries. The prepared modified porous carbon has the characteristics of high specific surface area and microporosity, appropriate mesopore ratio and high nitrogen content. The modified porous carbon is used as an additive in the negative electrode of the lead-carbon battery to effectively increase the hydrogen evolution overpotential of the carbon, thereby inhibiting irreversible sulfation and improving the cycle performance of the lead-carbon battery under HRPSoC working conditions. The present invention provides the following technical solutions to solve the above technical problems:

[0006] A method for preparing modified porous carbon for lead-carbon batteries comprises the following steps:

[0007] (S1) Pretreatment: The biomass raw material is crushed, washed, and dried in sequence to obtain pretreated biomass;

[0008] (S2) impregnation: placing the pretreated biomass into an impregnation solution for 1 to 2 hours, and then granulating and drying in sequence to obtain a preform; the impregnation solution is a mixed aqueous solution of phosphoric acid, imidazolium salt and a penetration enhancer prepared in a mass ratio of 100: (20 to 40): (1 to 3), and the penetration enhancer is a polyoxyethylene fatty acid ester;

[0009] (S3) carbonizing: carbonizing the prefabricated material at 500-700° C. under an inert atmosphere, cooling, washing, and drying to obtain a carbonized material;

[0010] (S4) Oxidation: Soaking the carbonized material in an oxidant solution for 3 to 6 hours, rinsing, and drying to obtain an oxidized material;

[0011] (S5) Surface modification: The obtained oxidized material and melamine polyphosphate are uniformly mixed in a mass ratio of 100:3 to 8, heat-treated at 850 to 950° C. for 2 to 4 hours under an ammonia atmosphere, and then cooled and ground to obtain modified porous carbon for lead-carbon batteries.

[0012] The present invention forms a high-osmotic activator by compounding phosphoric acid, imidazolium salt and a penetration enhancer to impregnate the pretreated biomass, and then carbonize, oxidize and surface modify the biomass to prepare a modified porous carbon. The obtained modified porous carbon has a high specific surface area and microporosity, and an appropriate mesopore ratio. Imidazolium salts have good solubility for biomass raw materials, but not all organic salts can be activated in synergistic manner with phosphoric acid to prepare porous carbon with a high specific surface area, microporosity and an appropriate mesopore ratio. The inventors found that imidazolium salts can synergize with phosphoric acid to activate biomass. The possible reason is that the imidazole ring in the imidazolium salt and the benzene ring in the biomass produce a certain force, thereby promoting the activation of phosphoric acid on the biomass raw material. In addition, adding polyoxyethylene fatty acid ester penetration enhancers can significantly enhance the activation ability of phosphoric acid and imidazolium salts, which may be because polyoxyethylene fatty acid ester penetration enhancers have a good solubilization and wetting effect on biomass.

[0013] Oxidation of the carbonized material increases surface acidic functional groups and lowers the isoelectric point, facilitating the reaction between ammonia and carbon during surface modification. Melamine polyphosphate decomposes at 300-400°C to produce large amounts of ammonia and water, which further increase the porosity of the carbonized material and reduce its bulk density. Simultaneously, the generated ammonia reacts with the carbonized material at high temperatures, introducing pyridine, pyrrole, and quaternary nitrogen-containing functional groups onto the carbon surface, thereby producing a modified porous carbon with a high nitrogen content. However, excessive nitrogen content can compromise the skeletal strength of the porous carbon.

[0014] Furthermore, the biomass in step (S1) is at least one of coconut shells, rice shells, and walnut shells; the crushing is to crush to 100-400 mesh, and the crushing method adopts air flow crushing, high-speed crushing, or ball milling; the water washing is to wash 2-4 times; and the drying is to dry in an oven at 80-100° C. for 24-36 hours.

[0015] Furthermore, in step (S2), the solid-liquid ratio of the pretreated biomass to the impregnation liquid is 1 kg: 1 to 3 L, the concentration of the impregnation liquid is 50 to 75 wt %; the impregnation temperature is 170 to 240° C., and the biomass undergoes a maturation transformation during the impregnation process, producing plasticity.

[0016] Furthermore, the imidazolium salt in step (S2) is at least one of 1-ethyl-3-methylimidazolium chloride, 1,3-dimethylimidazolium chloride, and 1-(2-hydroxyethyl)-3-methylimidazolium chloride, preferably 1-(2-hydroxyethyl)-3-methylimidazolium chloride; and the polyoxyethylene fatty acid ester is at least one of Mize49 or Mize52.

[0017] Furthermore, the granulation in step (S2) is to obtain columnar or spherical granules by a granulator, for example, by a plunger granulator, cutting into rods or strips with a diameter of 2 to 5 mm, such as 2 mm, 3 mm, 4 mm, and a length of 100 to 150 mm; by a needle granulator, spherical particles are formed, and the particle size can be 1.5 mm, 2 mm, 2.5 mm, or 3 mm; and the drying is drying in an oven at 100 to 150° C. for 24 to 36 hours.

[0018] Furthermore, the carbonization conditions in step (S3) are as follows: heating to 500-700°C in a rotary kiln at a heating rate of 3-8°C / min, keeping warm for 1-2.5h, the rotary kiln speed is 15-20rpm, the carbonization atmosphere is an inert atmosphere, and the inert atmosphere is an oxygen content of less than 1%, preferably less than 0.1%, such as nitrogen and / or argon; the washing is boiling in water for 30-60min to remove residual phosphoric acid in the carbonized material, so that the phosphoric acid in the carbonized material is less than 200ppm, and the residual phosphoric acid can also be recovered for use in step (S1); the drying is drying to a moisture content of <5wt%, such as baking in an oven at 100-150°C for 24-36h.

[0019] Furthermore, in step (S4), the oxidant solution is 10wt% to 20wt% hydrogen peroxide, and the solid-liquid ratio of the carbonized material to the oxidant is 1kg:2 to 4L; the rinsing is rinsing with water 3 to 5 times to wash away the residual oxidant; and the drying is drying to a moisture content of <5wt%, such as baking in an oven at 100 to 150°C for 24 to 36 hours.

[0020] Furthermore, the surface modification conditions in step (S5) are as follows: ammonia is introduced into a horizontal induction furnace, the temperature is raised to 850-950° C. at a heating rate of 3-8° C. / min, and the temperature is kept for 2-4 hours; the grinding is performed using a jet mill, and the particle size D50 after grinding is 6-10 μm.

[0021] The present invention also provides a lead-carbon battery, the negative electrode material of which comprises the modified porous carbon prepared by the above preparation method.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention uses a high-osmotic activator formed by compounding phosphoric acid, imidazolium salt and a penetration enhancer to impregnate the pretreated biomass, and then carbonizes, oxidizes and surface-modifies it to prepare a modified porous carbon. The nitrogen content of the prepared modified porous carbon is more than 7%; the specific surface area and microporosity are significantly improved, with a specific surface area of ​​1420m 2 / g or more, with a microporosity of over 23% and a mesoporosity of 65% to 73%. The modified porous carbon prepared by the present invention is used as a negative electrode additive for lead-carbon batteries, significantly inhibiting the hydrogen evolution reaction and improving the cycle capacity retention rate, thereby slowing down the performance degradation of lead-carbon batteries; the capacity retention rate after 500 cycles at 2C under HRPSoC reaches over 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the SEM image of the modified porous carbon prepared in Example 1.

[0025] Figure 2 This is the particle size distribution diagram of the modified porous carbon prepared in Example 1.

[0026] Figure 3 This is the pore size distribution diagram of the modified porous carbon prepared in Example 1. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with specific examples. Unless otherwise specified, the "parts" in the examples of the present invention are all parts by weight. All reagents used are commercially available reagents in this area.

[0028] Mai Ze 49 is a polyoxyethylene fatty acid ester surfactant, a non-ionic surfactant with an HLB of 16.9.

[0029] Span 20 is sorbitan monolaurate, a nonionic surfactant with an HLB of 8.6.

[0030] Example 1

[0031] Modified porous carbon for lead-carbon batteries, comprising the following steps:

[0032] (S1) Pretreatment: The rice husk was crushed to 200 mesh using air flow, washed twice with water, and then dried in an oven at 90°C for 24 h;

[0033] (S2) impregnation: first, 20 parts of 1-ethyl-3-methylimidazolium chloride and 1 part of a penetration enhancer, Mei Ze 49, are dissolved in 167 parts of a 60 wt% phosphoric acid solution to form an impregnation solution, i.e., the mass ratio of phosphoric acid, 1-ethyl-3-methylimidazolium chloride, and the penetration enhancer, Mei Ze 49, is 100:20:1; then, the pretreated rice husk is placed in the impregnation solution at a solid-liquid ratio of 1 kg:2 L, and impregnated in a kneader at 170° C. for 2 h to obtain a kneaded material; then, the kneaded material is formed into spherical particles with a particle size of 2.5 mm by a pin granulator, and dried in an oven at 100° C. for 36 h to obtain a prefabricated material;

[0034] (S3) Carbonization: The preform was placed in a rotary kiln, heated to 600°C at a heating rate of 6°C / min under a nitrogen atmosphere, and kept at this temperature for 2.5 hours. The rotary kiln speed was 20 rpm. After carbonization, the preform was naturally cooled to room temperature, boiled in water for 40 minutes, and dried in an oven at 120°C for 24 hours to obtain a carbonized material.

[0035] (S4) Oxidation: Soak the carbonized material in 10% hydrogen peroxide for 5 hours at a solid-liquid ratio of 1 kg:3 L. Rinse with water three times after soaking, and then bake in an oven at 120° C. for 24 hours to obtain an oxidized material.

[0036] (S5) Surface modification: The obtained oxidizing material was uniformly mixed with melamine polyphosphate in a mass ratio of 100:3 and placed in a horizontal induction furnace. Ammonia gas was introduced and the temperature was increased to 850°C at a heating rate of 6°C / min and kept at this temperature for 3 h. After the modification was completed, the mixture was naturally cooled to room temperature and then ground with a jet mill to obtain a modified porous carbon for lead-carbon batteries with a particle size D50 of 7.8 μm.

[0037] The SEM images of the modified porous carbon are shown in Figure 2. Figure 1 As shown in the particle size distribution diagram Figure 2 As shown, the pore size distribution diagram is as follows Figure 3 shown.

[0038] Example 2

[0039] The rest is the same as Example 1, except that 1,3-dimethylimidazolium chloride is used instead of 1-ethyl-3-methylimidazolium chloride in step (S2), and finally a modified porous carbon for lead-carbon batteries with a particle size D50 of 6.8 μm is obtained.

[0040] Example 3

[0041] The rest is the same as Example 1, except that 1-(2-hydroxyethyl)-3-methylimidazolium chloride is used instead of 1-ethyl-3-methylimidazolium chloride in step (S2), and finally a modified porous carbon for lead-carbon batteries with a particle size D50 of 7.2 μm is obtained.

[0042] Example 4

[0043] The rest is the same as Example 3, except that the mass ratio of phosphoric acid, 1-(2-hydroxyethyl)-3-methylimidazolium chloride and the penetration enhancer Mize 49 in the impregnation solution in step (S2) is 100:30:2, and finally a modified porous carbon for lead-carbon batteries with a particle size D50 of 7.0 μm is obtained.

[0044] Example 5

[0045] The rest is the same as Example 3, except that the mass ratio of phosphoric acid, 1-(2-hydroxyethyl)-3-methylimidazolium chloride and the penetration enhancer Mize 49 in the impregnation solution in step (S2) is 100:40:3, and finally a modified porous carbon for lead-carbon batteries with a particle size D50 of 7.3 μm is obtained.

[0046] Example 6

[0047] The rest is the same as Example 3, except that in step (S5), the oxidizing material and melamine polyphosphate are in a mass ratio of 100:5, and finally a modified porous carbon for lead-carbon batteries with a particle size D50 of 7.1 μm is obtained.

[0048] Example 7

[0049] The rest is the same as Example 3, except that in step (S5), the oxidizing material and melamine polyphosphate are in a mass ratio of 100:8, and finally a modified porous carbon for lead-carbon batteries with a particle size D50 of 6.9 μm is obtained.

[0050] Example 8

[0051] The rest is the same as Example 1, except that the biomass raw material in step (S1) is coconut shell.

[0052] Comparative Example 1

[0053] The rest is the same as Example 1, except that in step (S2), no imidazolium salt and no penetration aid are used, that is, the impregnation solution is a phosphoric acid solution.

[0054] Comparative Example 2

[0055] The rest is the same as Example 1, except that imidazolium salt is not used in step (S2), that is, the impregnation solution is a mixture of phosphoric acid solution and a penetration enhancer.

[0056] Comparative Example 3

[0057] The rest is the same as Example 1, except that step (S2) uses the disk 20 instead of the pump 49.

[0058] Comparative Example 4

[0059] The rest is the same as Example 1, except that melamine polyphosphate is not used in step (S5), and only ammonia is used for surface modification.

[0060] Application Example 1

[0061] Lead powder, acetylene black, barium sulfate, humic acid, short carbon fiber, H2SO4 (1.28g / cm 3) was mixed evenly with the modified porous carbon obtained in the embodiment and the comparative example, and a certain volume of polytetrafluoroethylene (PTFE) emulsion and water were added in a mass ratio of 100:0.2:0.6:0.15:0.05:2 (i.e., 2 wt% of the modified porous carbon was added to the conventional negative electrode formula), and mechanically stirred for 10 hours to form a paste (density of approximately 4.4 g / ml), and the paste was evenly applied to the negative electrode grid. The negative electrode plate with the paste was placed in a constant temperature and humidity chamber and cured at 50°C for 10 hours (humidity 80%) to prepare a lead-carbon battery negative electrode.

[0062] Application Example 2-8

[0063] Other conditions are the same as those in Application Example 1, except that the modified porous carbons are prepared according to Examples 2-8, respectively.

[0064] Comparative Application Examples 1-4

[0065] Other conditions are the same as those in Application Example 1, except that the modified porous carbons are prepared according to Comparative Examples 1-4.

[0066] Results and Analysis

[0067] Specific surface area and pore size determination: Low-temperature nitrogen adsorption experiments were performed on the modified porous carbons prepared in Examples and Comparative Examples using a Tristar II 3020 fully automatic specific surface and pore size analyzer manufactured by Micromeritics Instrument Corporation, USA, to determine the specific surface area and pore size distribution of the porous carbons. Pores with a diameter less than 2 nm are micropores; pores with a diameter in the range of 2 to 50 nm are mesopores. Specific data are shown in Table 1. The pore size distribution of the modified porous carbon prepared in Example 1 is shown in Table 1. Figure 3 shown.

[0068] Determination of nitrogen content: The nitrogen content of the modified porous carbons prepared in the examples and comparative examples was analyzed using a vario EL cube elemental analyzer from Elementar, Germany. The data are shown in Table 1.

[0069] Electrochemical performance test:

[0070] (1) Hydrogen evolution overpotential polarization curve test: The hydrogen evolution overpotential polarization curve test was conducted on the lead-carbon battery negative electrode prepared in the corresponding application example and the comparative application example using an electrochemical tester. A three-electrode system was used, with the lead-carbon battery negative electrode prepared in the application example and the comparative application example as the working electrode, a platinum electrode as the counter electrode, and a calomel electrode as the reference electrode. The electrolyte was a 1.12 g / ml sulfuric acid solution. The scan rate was 5 mV / s, and the scan range was -0.3 V to -1.5 V. The test results are shown in Table 2.

[0071] (2) Battery performance test: The lead-carbon battery negative electrode prepared in the application example and the comparative application example, the conventional positive electrode, and the electrolyte were used to form a battery, and then the battery was subjected to the HRPSoC cycle life test. The test results are shown in Table 2.

[0072] The HRPSoC cycle life test conditions are as follows: a battery with a 0% state of charge is charged at 0.1C to a cutoff voltage of 2.4V, then charged at a constant voltage of 2.4V for 12 hours, followed by a 10-minute rest. It is then discharged at 1C to 50% of its theoretical capacity, or 50% SoC. Finally, a high-rate charge-discharge cycle is performed, with the following cycle sequence: charging at 2C for 60 seconds, resting for 10 seconds, discharging at 2C for 60 seconds, and resting for 10 seconds. The voltage across the battery is recorded during the charge-discharge cycle. The battery is considered dead when the discharge voltage reaches the cutoff voltage of 1.7V.

[0073] Table 1 Specific surface area and pore size data of modified porous carbon

[0074]

[0075] By comparing Comparative Examples 1 to 3 with the embodiments of the present invention, it can be seen from Table 1 that the present invention uses a high-osmotic activator formed by compounding phosphoric acid, imidazolium salt and a penetration enhancer to impregnate biomass, and then carbonizes, oxidizes and surface-modifies the biomass. The specific surface area and microporosity of the modified porous carbon are significantly improved, and the specific surface area reaches 1420 m 2 / g or more, the microporosity is more than 23%, and the mesoporosity is maintained at 65% to 73%.

[0076] By comparing Comparative Example 4 with Example 1, it can be seen that surface modification of the oxidized carbonized material by using melamine polyphosphate and ammonia can increase the nitrogen content of the porous carbon to more than 7%.

[0077] Table 2 Electrochemical performance

[0078]

[0079] As can be seen from Table 2, compared with the comparative application examples, the hydrogen evolution overpotential of the lead-carbon battery negative electrodes prepared in Application Examples 1 to 8 after being assembled into batteries is significantly improved, and the 500 cycle capacity retention rate at 2C under HRPSoC reaches more than 90%, indicating that the modified porous carbon prepared by the present invention significantly reduces the hydrogen evolution reaction in the lead-carbon battery, significantly improves the cycle capacity retention rate, and slows down the performance degradation of the lead-carbon battery.

[0080] Combining the data in Table 1 and Table 2, it can be seen that the modified porous carbon prepared by the preparation method of the present invention has a high microporosity and an appropriate mesopore ratio, that is, a microporosity of more than 23% and a mesoporosity of 65% to 73%, and at the same time has a nitrogen content of more than 7%. The lead-carbon battery prepared from the modified porous carbon increases the hydrogen evolution overpotential to more than 1.20v, and the 500 cycle capacity retention rate at 2C under HRPSoC reaches more than 90%. A higher microporosity has a better effect on inhibiting the hydrogen reaction. It may be that during the hydrogen evolution reaction, the hydrogen produced is not easy to escape in the micropores, but is easier to escape in the mesopores. Therefore, the ratio of micropores to mesopores should be properly controlled. At the same time, a higher microporosity and an appropriate mesopore ratio give the porous carbon a higher porosity and specific surface area. The pores, especially the mesopores, in the high-porosity carbon can store a large amount of electrolyte, so that when sulfuric acid is blocked from entering the interior from the surface of the plate, the electrolyte in the pores can provide a large amount of H + and HSO4 - , which makes the lead-carbon battery have a higher cycle capacity retention rate.

[0081] In summary, the modified porous carbon prepared by the preparation method of the present invention has a microporosity of more than 23% and a mesoporosity of 65% to 73%, and at the same time has a nitrogen content of more than 7%. Its application as an additive in the negative electrode of a lead-carbon battery can effectively increase the hydrogen evolution overpotential of the carbon, thereby inhibiting irreversible sulfation and improving the cycle performance of the lead-carbon battery under HRPSoC conditions.

[0082] The above detailed description is a specific description of one feasible embodiment of the present invention. This embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not depart from the present invention should be included in the scope of the technical solution of the present invention.

Claims

1. A method for preparing modified porous carbon for lead-carbon batteries, characterized in that: The following steps are involved: (S1) Pretreatment: The biomass raw material is crushed, washed, and dried in sequence to obtain pretreated biomass; (S2) impregnation: placing the pretreated biomass into an impregnation solution for 1-2 hours, followed by granulation and drying to obtain a preform; the impregnation solution is a mixed aqueous solution of phosphoric acid, imidazolium salt and a penetration enhancer prepared in a mass ratio of 100:(20-40):(1-3), wherein the penetration enhancer is a polyoxyethylene fatty acid ester; (S3) Carbonization: Carbonizing the prefabricated material at 500-700°C under an inert atmosphere, cooling, washing, and drying to obtain a carbonized material; (S4) Oxidation: Soaking the carbonized material in an oxidant solution for 3 to 6 hours, rinsing and drying after soaking to obtain an oxidized material; (S5) Surface modification: The obtained oxidized material and melamine polyphosphate are uniformly mixed in a mass ratio of 100:3-8, heat-treated at 850-950°C for 2-4 h under an ammonia atmosphere, and then cooled and ground to obtain modified porous carbon for lead-carbon batteries.

2. The preparation method according to claim 1, characterized in that In step (S1), the biomass is at least one of coconut shells, rice shells, and walnut shells; the crushing is to crush to 100-400 mesh, and the crushing method adopts air flow crushing, high-speed crushing, or ball milling; the water washing is 2-4 times; and the drying is drying in an oven at 80-100° C. for 24-36 hours.

3. The preparation method according to claim 1, characterized in that In step (S2), the solid-liquid ratio of the pretreated biomass to the impregnation liquid is 1 kg: 1-3 L, the concentration of the impregnation liquid is 50-75 wt %; and the impregnation temperature is 170-240° C.

4. The preparation method according to claim 1, characterized in that In step (S2), the imidazolium salt is at least one of 1-ethyl-3-methylimidazolium chloride, 1,3-dimethylimidazolium chloride, and 1-(2-hydroxyethyl)-3-methylimidazolium chloride; and the polyoxyethylene fatty acid ester is at least one of MaiZe49 or MaiZe52.

5. The preparation method according to claim 4, characterized in that The imidazolium salt is 1-(2-hydroxyethyl)-3-methylimidazolium chloride.

6. The preparation method according to claim 1, characterized in that In step (S2), the granulation is performed by a granulator to obtain columnar or spherical granules; and the drying is performed in an oven at 100-150° C. for 24-36 hours.

7. The preparation method according to claim 1, characterized in that The carbonization conditions of step (S3) are as follows: heating to 500-700°C in a rotary kiln at a heating rate of 3-8°C / min, keeping warm for 1-2.5 hours, rotating the rotary kiln at 15-20 rpm, and carbonizing in an inert atmosphere with an oxygen content of less than 1%; washing is performed by boiling in water for 30-60 minutes to remove residual phosphoric acid in the carbonized material, so that the phosphoric acid in the carbonized material is less than 200 ppm; and drying is performed to a moisture content of less than 5wt%.

8. The preparation method according to claim 1, wherein In step (S4), the oxidant solution is 10wt%~20wt% hydrogen peroxide, and the solid-liquid ratio of the carbonized material to the oxidant is 1 kg:2~4L; the rinsing is to rinse with water 3~5 times to wash away the residual oxidant; and the drying is to dry until the moisture content is less than 5wt%.

9. The preparation method according to claim 1, characterized in that The surface modification conditions in step (S5) are as follows: introducing ammonia gas into a horizontal induction furnace, heating the temperature to 850-950°C at a heating rate of 3-8°C / min, and keeping the temperature for 2-4 hours; the grinding is performed using a jet mill, and the particle size D50 after grinding is 6-10 μm.

10. A lead-carbon battery, characterized in that: The negative electrode material of the lead-carbon battery comprises the modified porous carbon prepared by any one of the preparation methods of claims 1-9.

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