Lithium iron phosphorus / carbon composite material and preparation method and application thereof

Abstract

The invention relates to the technical field of resource utilization of environmental functional materials and industrial wastes, and discloses a lithium iron phosphorus / carbon composite material as well as a preparation method and application thereof. The invention relates to a preparation method of a lithium iron phosphorus / carbon composite material, which comprises the following steps: taking lithium-containing recycled waste liquid of a retired lithium ion battery as a lithium source, and mixing and reacting with a phosphorus source to obtain a lithium-containing precursor; and mixing the lithium-containing precursor, an iron source and a carbon source, dispersing in an aqueous medium, and carrying out hydrothermal reaction to obtain the lithium iron phosphorus / carbon composite material. According to the method, the lithium-rich waste liquid generated by wet recovery of the retired lithium battery is directly converted into the high-performance lithium iron phosphorus / carbon composite material, so that a resource closed loop of treating waste with waste is realized; in-situ synthesis of a lithium iron phosphorus active phase and compounding of a carbon carrier are synchronously completed under a mild condition by utilizing a hydrothermal method, the process is green, simple and convenient, a high-valued way is provided for dangerous waste liquid, the raw material cost of a functional material is reduced, the preparation process is efficient and controllable, and the preparation method has environmental and economic benefits and industrial application potential.

Description

Technical Field

[0001] This invention relates to the field of environmental functional materials and industrial waste resource utilization technology, and particularly to a lithium iron phosphate / carbon composite material, its preparation method and application. Background Technology

[0002] With the rapid global adoption of mobile electronic devices and electric vehicles, the production and disposal of lithium-ion batteries have exploded, leading to increasingly prominent issues related to resource recycling and environmental governance. The recycling process for retired lithium batteries typically involves extracting valuable metals through hydrometallurgy and acid-base leaching. However, this process often generates large quantities of lithium-containing wastewater or leaching solutions. These wastewaters still contain a certain concentration of lithium ions, and direct discharge not only wastes valuable strategic resources but also poses potential environmental pollution. Therefore, how to efficiently and economically recover lithium from such wastewaters and transform it into high-value-added functional materials has become a key issue in achieving a closed loop of "resources-materials-environment."

[0003] Carbon materials, due to their high specific surface area, abundant pore structure, good chemical stability, and electrical conductivity, are often used as catalyst supports, adsorbents, or electrode materials. Among them, porous carbon sources such as activated carbon and biochar are low-cost and widely available. Their surfaces can be pretreated to introduce or modulate oxygen-containing functional groups (such as -OH, -COOH, etc.), thereby enhancing their interaction with metal ions and promoting the uniform loading and stable binding of active components on their surfaces. Lithium iron Phosphorus (Li-Fe-P) system materials, especially lithium iron phosphate (LiFePO4) with an olivine structure, exhibit good structural stability and tunable interfacial properties in electrochemical energy storage, catalysis, and adsorption. Several existing studies have attempted to combine waste resources with carbon materials, but these methods typically rely on high-purity chemical raw materials, complex pretreatment processes, or complex chemical deposition and calcination processes. These methods suffer from problems such as complex processes, high energy consumption, high costs, and difficulty in controlling the morphology and size of the products. Furthermore, achieving uniform and confined growth of active components in porous supports is challenging, limiting their large-scale application in practical environmental remediation. Summary of the Invention

[0004] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, one objective of the present invention is to provide a method for preparing a lithium iron phosphate / carbon composite material.

[0005] The second objective of this invention is to provide a lithium iron phosphate / carbon composite material.

[0006] The third objective of this invention is to provide applications of this lithium iron phosphate / carbon composite material.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of the present invention provides a method for preparing a lithium iron phosphate / carbon composite material, comprising the following steps: S1. The lithium-containing waste liquid from retired lithium-ion batteries is used as a lithium source and mixed with a phosphorus source to react and obtain a lithium-containing precursor. S2. The lithium-containing precursor, iron source and carbon source are mixed and dispersed in an aqueous medium, and subjected to hydrothermal reaction to obtain the lithium iron phosphate / carbon composite material.

[0008] In some embodiments of the present invention, the lithium-containing waste liquid recovered from retired lithium-ion batteries includes lithium-rich mother liquor purified by hydrometallurgical processes.

[0009] Specifically, in the hydrometallurgical purification process, valuable metals such as Ni, Co, and Mn in the cathode materials of retired lithium-ion batteries are extracted in the form of high-purity products (such as nickel sulfate and cobalt sulfate), while lithium remains largely in the solution.

[0010] In some embodiments of the present invention, the mass ratio of the iron source to the carbon source is 1:(1-5); the ratio of the amount of lithium source, iron source and phosphorus source is 1:(0.8-1.2):(0.8-1.2) based on the elemental molar ratio of iron, lithium and phosphorus.

[0011] In some preferred embodiments of the present invention, the mass ratio of the iron source to the carbon source is 1:(1-3); the ratio of the amount of the lithium source, the iron source and the phosphorus source is 1:(0.9-1.1):(0.9-1.1) based on the elemental molar ratio of iron, lithium and phosphorus.

[0012] In some more preferred embodiments of the present invention, the ratio of the amount of lithium source, iron source and phosphorus source is 1:1.1:1 based on the elemental molar ratio of iron, lithium and phosphorus.

[0013] In some embodiments of the present invention, the iron source is selected from at least one of ferric nitrate, ferric chloride, ferric sulfate, and ferric phosphate.

[0014] In some embodiments of the present invention, the phosphorus source is selected from at least one of potassium phosphate, sodium phosphate, ammonium phosphate, dipotassium hydrogen phosphate, disodium hydrogen phosphate, diammonium hydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, and ammonium dihydrogen phosphate.

[0015] In some embodiments of the present invention, the carbon source is selected from porous carbon materials or soluble carbohydrates; wherein the porous carbon material includes at least one of activated carbon and biochar; and the soluble carbohydrates include at least one of starch and glucose.

[0016] In some embodiments of the present invention, when the carbon source is a porous carbon material, a pretreatment step is further included before use, wherein the pretreatment is selected from any of the following: 1) Place the carbon source in deionized water, acid, or alkaline solution and sonicate or stir for 10-180 min, then dry at 60-150℃; 2) The carbon source is subjected to light heat treatment at a temperature of 150-400℃ for 0.5-4 hours; 3) The carbon source is doped with nitrogen and / or oxygen.

[0017] In some embodiments of the present invention, the concentrations of the acid and alkali solutions are selected from 0.1-1.0 mol / L, respectively.

[0018] In some embodiments of the present invention, the acid solution is selected from sulfuric acid or hydrochloric acid.

[0019] In some embodiments of the present invention, the alkaline solution includes a sodium hydroxide solution.

[0020] Specifically, ultrasound can break up agglomerates in porous carbon materials, clear pores, and increase their dispersibility in the aqueous phase; acid / alkali treatment can introduce or increase oxygen-containing functional groups (such as -COOH, -OH) on the surface of porous carbon materials. These functional groups can improve hydrophilicity, making the surface of porous carbon materials easier to wet with aqueous precursor solutions, and can also provide anchoring points. Their negative charge or coordination ability can electrostatically adsorb or complex Fe in the solution. 3+ Li + These cations serve as "seed" sites for subsequent crystal growth.

[0021] In some embodiments of the present invention, in step S1, the temperature of the mixing reaction is 15-40°C, the time is 15-180 min, and the pH of the reaction system is 9-12.

[0022] In some preferred embodiments of the present invention, in step S1, the temperature of the mixing reaction is 20-30°C, the time is 30-120 min, and the pH of the reaction system is 10-11.

[0023] In some embodiments of the present invention, after the mixing reaction is completed in step S1, the solid phase is further separated by solid-liquid separation, washed and dried to obtain the lithium-containing precursor.

[0024] In some embodiments of the present invention, the washing agent includes water.

[0025] In some embodiments of the present invention, the drying temperature is 60-120°C.

[0026] In some embodiments of the present invention, in step S2, the dispersion process in the aqueous medium is carried out at 20-30°C or 40-80°C, and is supplemented by stirring for 10-120 min or ultrasonic dispersion for 5-60 min.

[0027] In some embodiments of the present invention, in step S2, the temperature of the hydrothermal reaction is 120-220°C and the time is 6-36 hours.

[0028] In some preferred embodiments of the present invention, in step S2, the temperature of the hydrothermal reaction is 160-200°C and the time is 12-24h.

[0029] In some embodiments of the present invention, in step S2, the solid-liquid ratio of the carbon source and the aqueous medium is 1g:(15-25)mL.

[0030] In some embodiments of the present invention, in step S2, before the hydrothermal reaction, a surfactant and / or a complexing agent are added to the reaction system; the amount of surfactant and complexing agent added is selected from 0.1%-5% of the total solid mass of the reaction system.

[0031] In some preferred embodiments of the present invention, the amounts of the surfactant and the complexing agent added are selected from 0.5% to 2% of the total solid mass of the reaction system.

[0032] In some more preferred embodiments of the present invention, the amounts of the surfactant and the complexing agent added are each selected from 1.5% of the total solid mass of the reaction system.

[0033] In some embodiments of the present invention, the surfactant includes at least one of polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), and hexadecyltrimethylammonium bromide (CTAB).

[0034] In some embodiments of the present invention, the complexing agent includes at least one selected from citric acid, oxalic acid, tartaric acid, ascorbic acid, and acetic acid.

[0035] In some embodiments of the present invention, after adding the surfactant and / or complexing agent, the process further includes stirring at room temperature for 30-60 minutes.

[0036] In some embodiments of the present invention, step S2, after the hydrothermal reaction is completed, further includes the operation of solid-liquid separation, collection of solid phase, washing, and drying.

[0037] In some embodiments of the present invention, the washing reagent includes water and ethanol.

[0038] In some embodiments of the present invention, the washing is performed 2-4 times.

[0039] In some embodiments of the present invention, the drying temperature is 60-120°C and the time is 0.5-6 hours.

[0040] In some embodiments of the present invention, after the hydrothermal reaction is completed in step S2, a heat treatment step is further included on the product; the heat treatment temperature is 200-600℃ and the time is 0.5-6h.

[0041] In some embodiments of the present invention, the heat treatment temperature is 300-500°C and the time is 1-2 hours.

[0042] In some embodiments of the present invention, the heat treatment is performed under an inert atmosphere; the inert atmosphere is selected from nitrogen or argon.

[0043] A second aspect of the present invention provides a lithium iron phosphate / carbon composite material, comprising a composite material prepared by the preparation method described in the first aspect of the present invention.

[0044] In some embodiments of the present invention, the lithium iron phosphate / carbon composite material includes a carbon phase matrix and lithium iron phosphate composite phase nanoparticles distributed in the carbon phase matrix; When the carbon source is a porous carbon material, the lithium iron phosphate composite phase nanoparticles are loaded on the surface and pores of the carbon phase matrix. When the carbon source is a soluble carbohydrate, the carbon phase matrix is ​​formed by hydrothermal carbonization of the soluble carbohydrate and coats the lithium iron phosphate composite phase nanoparticles.

[0045] In some embodiments of the present invention, when the carbon source is a porous carbon material, the specific surface area of ​​the lithium iron phosphate / carbon composite material is greater than 800 m². 2 / g; Total pore volume greater than 0.5cm³ 3 / g; average pore size is 4-5nm.

[0046] In some preferred embodiments of the present invention, when the carbon source is a porous carbon material, the specific surface area of ​​the lithium iron phosphate / carbon composite material is 800-1000 m². 2 / g; total pore volume is 0.5-0.7cm³. 3 / g; average pore size is 4-5nm.

[0047] The third aspect of the present invention provides the application of the lithium iron phosphate / carbon composite material described in the second aspect of the present invention as an adsorbent and / or catalyst in environmental pollution control.

[0048] In some embodiments of the present invention, the environmental pollution control includes the treatment of antibiotic-containing wastewater.

[0049] In some embodiments of the present invention, the antibiotic includes sulfadimethylpyrimidine.

[0050] The basic principles of this invention are explained as follows: The method for preparing lithium iron phosphate / carbon composite materials provided by this invention uses lithium-containing recycled waste liquid from retired lithium-ion batteries as a lithium source. It first mixes and reacts with a phosphorus source, and by controlling the pH (9-12) and reaction temperature (15-40℃), the precipitation reaction is promoted to be complete, while other impurity ions (such as Al) are suppressed. 3+ Fe 3+ The co-precipitation of lithium ions (such as iron, carbon, etc.) in the waste liquid converts low-concentration, free lithium ions into a solid, single-component Li3PO4 precursor. This step not only recovers lithium resources but also provides a stoichiometric, highly reactive lithium source and some phosphorus source for subsequent synthesis. Subsequently, the Li3PO4 precursor, iron source, and carbon source are subjected to a hydrothermal reaction. The hydrothermal reaction utilizes a high temperature (120-220℃) to provide the necessary activation energy, and the self-generated pressure increases the solubility of the reactants and accelerates mass transfer. Using water as a medium and reactants also has environmentally friendly characteristics. During the reaction: 1) When the carbon source is a porous carbon material, Fe 3+ Li + PO4 3- Plasma or ion clusters are adsorbed and diffused into the rich pores of the carbon support. Under high temperature and pressure, Li3PO4 reacts with the iron source to generate LiFePO4 crystal nuclei. The pore walls of the carbon exert a spatial confinement effect on the growth of the crystal nuclei, effectively inhibiting excessive growth and agglomeration of the grains. The growing crystals are tightly bonded to the functional group-rich carbon surface through the formation of chemical bonds such as Fe-OC and POC, thus forming a supported lithium iron phosphate / carbon composite material. The selective addition of surfactants and / or complexing agents can regulate the nucleation and growth of LiFePO4 particles in the pores and surface of the porous carbon material, preventing nanoparticles from clogging the pores or causing severe agglomeration, and ensuring their high dispersion and accessibility. Selective heat treatment can improve the crystallinity of LiFePO4 and strengthen the interfacial bonding between LiFePO4 and the carbon framework. 2) When the carbon source is soluble carbohydrate, under the same hydrothermal environment, the soluble carbohydrate undergoes dehydration, condensation, and carbonization to form an amorphous carbon network. Simultaneously, LiFePO4 crystal nuclei form and grow. These two processes are intertwined, and the generated carbon encapsulates or embeds LiFePO4 nanoparticles, forming a natural and close contact, thus forming a coated lithium iron phosphate / carbon composite material. At the same time, the small molecule gas released during carbonization forms micropores, and the generated carbon establishes continuous electronic conductive channels for LiFePO4 particles, forming a self-created pore and conductive network. The selective addition of surfactants and / or complexing agents can not only regulate the size and dispersion of LiFePO4 particles, but also affect the interaction between the carbohydrate carbonization process and the inorganic phase, promoting more uniform coating. Selective heat treatment can improve the crystallinity of LiFePO4 and completely carbonize the soluble carbohydrates to form a carbon network with good conductivity.

[0051] Compared with the prior art, the beneficial effects of the present invention are: The method for preparing lithium iron phosphate / carbon composite materials provided by this invention directly converts lithium-rich wastewater generated from the wet recycling of retired lithium batteries into high-performance lithium iron phosphate / carbon composite materials, realizing a closed-loop resource system of treating waste with waste. The method utilizes a hydrothermal approach to simultaneously synthesize the lithium iron phosphate active phase and composite with the carbon support under mild conditions, making the process green and simple. When using porous carbon materials as the carbon source, the resulting material possesses both a high specific surface area of ​​the porous carbon framework and a uniformly dispersed nano-active phase, forming a stable integrated structure of conductive network and active sites. Its adsorption and removal rate for typical sulfonamide antibiotics reaches as high as 91.7%. This method not only provides a high-value outlet for hazardous wastewater and significantly reduces the raw material cost of functional materials, but also offers a highly efficient and controllable preparation process, combining environmental benefits, economic benefits, and industrial application potential. Attached Figure Description

[0052] Figure 1 The image shows a SEM image of the supported lithium iron phosphate / carbon composite material prepared in Example 1. Figure 2 The image shows the XRD pattern of the supported lithium iron phosphate / carbon composite material prepared in Example 1. Figure 3 The O 1s plot of the X-ray photoelectron spectrum of the supported lithium iron phosphate / carbon composite material prepared in Example 1; Figure 4 The image shows the Fe 2p plot of the X-ray photoelectron spectroscopy of the supported lithium iron phosphate / carbon composite material prepared in Example 1. Figure 5 The image shows a SEM image of the coated lithium iron phosphate / carbon composite material prepared in Example 2. Figure 6 The image shows the CV curve of the coated lithium iron phosphate / carbon composite material prepared in Example 2. Detailed Implementation

[0053] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments can be obtained from conventional commercial sources or by existing technical methods. Unless otherwise specified, the experimental or testing methods are conventional methods in the art.

[0054] The lithium-containing waste liquid from retired lithium-ion batteries used in the following examples is a lithium-rich mother liquor obtained after hydrometallurgical purification of retired nickel-cobalt-manganese lithium oxide batteries. Most of the valuable metals (Ni, Co, Mn) in the cathode material have been precipitated and extracted, while lithium remains largely in the solution. Table 1 below shows the composition of the lithium-containing waste liquid from retired lithium-ion batteries used in the examples: Table 1. Composition of lithium-containing waste liquid from retired lithium-ion batteries used in the examples.

[0055] Example 1 This embodiment prepares a lithium iron phosphate / carbon composite material, and the steps are as follows: S11. At 25℃, lithium-containing waste liquid from retired lithium-ion batteries was reacted with sodium phosphate under magnetic stirring for 80 min. The pH of the system was adjusted to 9-12 to precipitate lithium as Li3PO4. The precipitate was collected by filtration, washed with deionized water and dried at 90℃ to obtain the Li3PO4 precursor. S21. Disperse the waste activated carbon (AC) in deionized water, sonicate for 60 min, and dry at 100℃ for later use. S22. Disperse the Li3PO4 precursor, ferric phosphate and pretreated activated carbon in water at room temperature, and stir magnetically for 30 min to make it evenly dispersed to form a dispersion. S23. The dispersion was transferred to a polytetrafluoroethylene-lined autoclave and hydrothermally reacted at 180°C for 15 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the solid phase was collected. The solid phase was washed three times with deionized water and ethanol, and dried at 80°C for 3 hours to obtain the supported lithium iron phosphate / carbon composite material, denoted as LEP@AC, which was then sealed and stored. The mass ratio of iron phosphate to pretreated activated carbon is 1:3; the ratio of lithium-containing waste liquid from retired lithium-ion batteries to iron phosphate and sodium phosphate is 1:1:1 based on the elemental molar ratio of iron, lithium, and phosphorus.

[0056] Figure 1 The image shows a SEM image of the supported lithium iron phosphate / carbon composite material prepared in Example 1. Figure 1It can be seen that a large number of fine Li-Fe-P phase nanoparticles are uniformly distributed on the rough surface and in the pores of activated carbon, indicating that the preparation method provided by the present invention achieves high dispersion loading of inorganic phase while retaining the porous structure of carbon skeleton, rather than agglomerated bulk.

[0057] Figure 2 The image shown is the XRD pattern of the supported lithium iron phosphate / carbon composite material prepared in Example 1. Figure 2 It can be seen that the position and intensity of the diffraction peaks of the supported lithium iron phosphate / carbon composite material prepared in Example 1 are completely consistent with the characteristic peaks of the standard olivine-type LiFePO4 (PDF card), which proves that the main phase of the inorganic active phase is crystalline lithium iron phosphate, and no obvious impurity peaks appear in the spectrum, indicating that the hydrothermal synthesis yielded a LiFePO4 phase with high purity.

[0058] Figure 3 The O 1s plot of the X-ray photoelectron spectrum of the supported lithium iron phosphate / carbon composite material prepared in Example 1 is shown below. Figure 3 It can be seen that the peak near 531 eV belongs to oxygen in Fe-OP or Fe-OC, which directly proves the chemical bonds (Fe-OP) inside the LiFePO4 crystal and the Fe-OC interface chemical bonds that may be formed between the inorganic phase and the carbon support.

[0059] Figure 4 The image shows the Fe 2p plot of the X-ray photoelectron spectroscopy of the supported lithium iron phosphate / carbon composite material prepared in Example 1. Figure 4 It can be seen that Fe 2p 3 / 2 and Fe 2p 1 / 2 The binding energy positions of the main peak (~711 eV and ~724 eV) and the structure of the satellite peaks are Fe 2+ The typical characteristics are consistent with the +2 valence state of Fe in LiFePO4, confirming the successful synthesis of the target product rather than a trivalent iron compound.

[0060] Table 2 Comparison of the supported lithium iron phosphate / carbon composite material and activated carbon prepared in Example 1

[0061] Table 2 compares the supported lithium iron phosphate / carbon composite material prepared in Example 1 with activated carbon. As shown in Table 2, the specific surface area of ​​the supported lithium iron phosphate / carbon composite material is significantly increased compared with that of activated carbon, indicating that the loading process of LiFePO4 nanoparticles is highly dispersed. The increase in total pore volume indicates that during the hydrothermal synthesis process, LiFePO4 nanoparticles grow and accumulate in situ on the surface and pores of activated carbon, forming new and additional pore spaces between particles and the carbon skeleton, as well as between particles. The slight decrease in average pore size is more conducive to enhancing the capillary coagulation and adsorption affinity for small and medium-sized pollutant molecules (such as antibiotics).

[0062] Example 2 This embodiment prepares a lithium iron phosphate / carbon composite material, and the steps are as follows: S11. At 25℃, lithium-containing waste liquid from retired lithium-ion batteries was reacted with sodium phosphate under magnetic stirring for 80 min. The pH of the system was adjusted to 9-12 to precipitate lithium as Li3PO4. The precipitate was collected by filtration, washed with deionized water and dried at 90℃ to obtain the Li3PO4 precursor. S21. Disperse Li3PO4 precursor, ferric nitrate and glucose (GLU) in water at room temperature, and add 1.5% of polyvinylpyrrolidone by the total solid mass of the reaction system. Sonicate for 30 min to make it uniformly dispersed to form a dispersion. S22. The dispersion was transferred to a polytetrafluoroethylene-lined high-pressure reactor and hydrothermally reacted at 200°C for 15 hours. During the reaction, glucose under heating conditions underwent dehydration, condensation and partial carbonization to form an amorphous carbon network, which nucleated and grew together with the Li–Fe–P nanophase in the sol to form a coated lithium iron phosphate / carbon composite material. S23. After the reaction is complete, cool to room temperature, filter and collect the solid phase, wash three times alternately with deionized water and ethanol, dry at 80℃ for 12h, and then heat-treat at 400℃ for 2h in N2 atmosphere to adjust the conductivity and crystallinity of the carbon layer. The resulting material is denoted as LEP@GLU and sealed for storage.

[0063] The mass ratio of ferric nitrate to pretreated activated carbon is 1:5; the ratio of lithium-containing waste liquid from retired lithium-ion batteries to ferric nitrate to sodium phosphate is 1:1:1 based on the elemental molar ratio of iron, lithium, and phosphorus.

[0064] Figure 5 The image shown is a SEM image of the coated lithium iron phosphate / carbon composite material prepared in Example 2. Figure 5 It can be seen that glucose forms a coated complex structure through in-situ carbonization.

[0065] Figure 6The image shows the CV curve of the coated lithium iron phosphate / carbon composite material prepared in Example 2. Figure 6 It can be seen that, compared with LiFePO4, LEP@GLU exhibits a higher redox peak current and a peak area increase of about 30%-50% in CV tests, indicating that it has a stronger interfacial charge migration ability.

[0066] Example 3 This embodiment investigates the effect of hydrothermal reaction temperature on the properties of lithium iron phosphate / carbon composite materials. The steps are as follows: The preparation method of the lithium iron phosphate / carbon composite material is the same as in Example 1, except that the hydrothermal reaction conditions are controlled at 120℃ for 18 h, 160℃ for 18 h, and 200℃ for 18 h, respectively. The resulting material is then used for the removal of sulfadiazine from water. Wastewater with an initial concentration of 4 μmol / L of sulfadiazine was prepared, and 5 mg of lithium iron phosphate / carbon composite material prepared under different hydrothermal reaction conditions was added. The reaction was carried out at room temperature (25°C) for 60 min. After the reaction, the residual concentration of sulfadiazine in the water was measured. Table 3 below shows the removal effect of lithium iron phosphate / carbon composite material on sulfadiazine under different hydrothermal reaction conditions. As shown in Table 3, the temperature of the hydrothermal reaction affects the removal effect of lithium iron phosphate / carbon composite material on sulfadiazine. The removal effect of sulfadiazine first increases and then decreases with increasing temperature, reaching the optimum at 160°C. This indicates that at this temperature, LiFePO4 forms well-crystallized nanoparticles, providing abundant and stable active sites. High temperature promotes the formation of interfacial chemical bonds such as Fe-OC, realizing efficient electron transport between the active phase and the conductive carbon skeleton. Moreover, this temperature is also conducive to the formation of a high specific surface area and abundant mesoporous structure, which provides a large number of adsorption sites and ensures smooth mass transfer.

[0067] Table 3. Removal effect of lithium iron phosphate / carbon composite materials prepared under different hydrothermal reaction conditions on sulfadiazine.

Claims

1. A method for preparing a lithium iron phosphate / carbon composite material, characterized in that, Includes the following steps: S1. The lithium-containing waste liquid from retired lithium-ion batteries is used as a lithium source and mixed with a phosphorus source to react and obtain a lithium-containing precursor. S2. The lithium-containing precursor, iron source and carbon source are mixed and dispersed in an aqueous medium, and subjected to hydrothermal reaction to obtain the lithium iron phosphate / carbon composite material.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the iron source to the carbon source is 1:(1-5); the ratio of the amount of lithium source, iron source and phosphorus source is 1:(0.8-1.2):(0.8-1.2) based on the elemental molar ratio of iron, lithium and phosphorus.

3. The preparation method according to claim 1, characterized in that, The iron source is selected from at least one of ferric nitrate, ferric chloride, ferric sulfate, and ferric phosphate; And / or, the phosphorus source is selected from at least one of potassium phosphate, sodium phosphate, ammonium phosphate, dipotassium hydrogen phosphate, disodium hydrogen phosphate, diammonium hydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, and ammonium dihydrogen phosphate.

4. The preparation method according to claim 1, characterized in that, The carbon source is selected from porous carbon materials or soluble carbohydrates; wherein the porous carbon material includes at least one of activated carbon and biochar; and the soluble carbohydrates include at least one of starch and glucose.

5. The preparation method according to claim 1, characterized in that, In step S1, the temperature of the mixing reaction is 15-40℃, the time is 15-180 min, and the pH of the reaction system is 9-12. And / or, in step S2, the temperature of the hydrothermal reaction is 120-220℃ and the time is 6-36h.

6. The preparation method according to any one of claims 1-5, characterized in that, In step S2, before the hydrothermal reaction, a surfactant and / or a complexing agent are added to the reaction system; the amount of surfactant and complexing agent added is selected from 0.1%-5% of the total solid mass of the reaction system.

7. The preparation method according to claim 6, characterized in that, In step S2, after the hydrothermal reaction is completed, the product is further subjected to heat treatment; the temperature of the heat treatment is 200-600℃ and the time is 0.5-6h.

8. A lithium iron phosphate / carbon composite material, characterized in that, It includes preparations made using the preparation method described in any one of claims 1-7.

9. The lithium iron phosphate / carbon composite material according to claim 8, characterized in that, The lithium iron phosphate / carbon composite material includes a carbon phase matrix and lithium iron phosphate composite phase nanoparticles distributed in the carbon phase matrix; When the carbon source is a porous carbon material, the lithium iron phosphate composite phase nanoparticles are loaded on the surface and pores of the carbon phase matrix. When the carbon source is a soluble carbohydrate, the carbon phase matrix is ​​formed by hydrothermal carbonization of the soluble carbohydrate and coats the lithium iron phosphate composite phase nanoparticles.

10. The application of the lithium iron phosphate / carbon composite material according to claim 8 or 9 as an adsorbent and / or catalyst in environmental pollution control.

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