Method for preparing dual-carbon modified sodium battery positive electrode material by using waste iron phosphate

Abstract

The invention provides a method for preparing a dual-carbon modified sodium battery positive electrode material by using waste iron phosphate, belongs to the field of lithium ion battery material recovery, and aims to solve the technical problem of low recovery utilization rate of lithium iron phosphate batteries. The preparation method of the double-carbon modified sodium battery positive electrode material comprises the following steps: extracting iron phosphate from a waste lithium iron phosphate material; the method comprises the following steps: adding iron phosphate into a sodium-containing solution, then adding a sodium source, a phosphorus source and a carbon source, performing sanding treatment, performing spray drying, and performing calcination I on a sample to obtain a sodium iron phosphate material; uniformly mixing the sodium ferric phosphate material with a functional carbon source, and calcining II. The waste iron phosphate is subjected to high-value recycling, the prepared sodium iron phosphate positive electrode material is subjected to multiple modification treatment, the conductivity and the rate capability of the sodium iron phosphate positive electrode material are improved, secondary pollution is not generated in the whole process, the process energy consumption is relatively low, the recovery process is green and efficient, and the method is suitable for industrial production. And high value-added recycling of the waste lithium iron phosphate battery is realized.

Description

Technical Field

[0001] The invention belongs to the field of lithium ion battery material recycling, and specifically relates to a method for preparing sodium battery positive electrode material by utilizing waste iron phosphate. Background Art

[0002] With the rise of the new energy vehicle industry and the guidance of national policies, new energy vehicles have shown explosive growth. It is estimated that the output of electric vehicles will reach 5.8 million in 2025, and the output value will exceed one trillion yuan. Among them, batteries account for 1 / 3 of the cost of the entire vehicle and 1 / 4 of the weight, and are rich in a variety of energy metals and strategic elements. If waste power batteries are not handled properly, the many metal elements they contain will not only cause serious harm to human health, but also cause waste of resources. The state has issued a series of policies to standardize the recycling and utilization of power batteries. Therefore, it is urgent to recycle and reuse waste batteries.

[0003] At present, the main methods for recycling lithium iron phosphate batteries are dry high-temperature solid-phase repair and hydrometallurgical recycling. The dry high-temperature repair method first mechanically crushes the positive electrode material by mechanical sorting, and then removes the organic binder by high-temperature calcination to separate the lithium iron phosphate powder from the aluminum foil to obtain the lithium iron phosphate positive electrode material. However, the entire recycling process is not very targeted to waste batteries, has high energy consumption, and the organic solvents in the battery are prone to cause serious environmental pollution after combustion. Hydrometallurgical recycling uses acid and alkali solutions as a medium to dissolve the waste lithium iron phosphate positive electrode, and mainly recycles lithium carbonate by precipitation, adsorption, ion exchange and other methods. Low-value iron phosphate slag is often landfilled, resulting in a huge waste of resources.

[0004] Patent publication number CN 115304042A discloses a method for recycling waste lithium iron phosphate to prepare battery-grade iron phosphate, comprising the following steps: using a leaching solution to leach and dissolve waste lithium iron phosphate materials, and after solid-liquid separation, obtaining a filtrate containing lithium and impurities and an iron phosphate residue; dissolving the obtained iron phosphate residue with sulfuric acid, adjusting the pH for recrystallization, and then filtering and separating to obtain a precipitated solid, drying, crushing, and calcining it to obtain battery-grade iron phosphate. This patent realizes the high-value recycling of waste iron phosphate. Patent Publication No. CN117886297A is a sodium iron fluorophosphate positive electrode material prepared by repairing and regenerating waste batteries. It adopts the reduction acid leaching method to achieve the effective and rapid separation of the conductive agent and the binder. The reducing environment is conducive to the dissolution of iron ions, avoiding the problem of low purity of the regenerated sodium iron fluorophosphate in the subsequent solid phase sintering process; the addition of surfactant effectively reduces the surface tension of the leaching solution, improves the hydrophilicity of the positive electrode active material, eliminates the phenomenon of waste powder floating on the surface of the solution, strengthens the mass transfer process, and increases the liquid-solid contact area, further improving the leaching rate and purity of the effective ingredients; the regenerated iron phosphate particles prepared by the precipitation method are solid-phase sintered with sodium fluoride to obtain the sodium iron fluorophosphate positive electrode material. This patent further uses waste iron phosphate to prepare sodium electric positive electrode materials. However, the conductivity and rate performance of the prepared sodium iron fluorophosphate positive electrode material need to be further improved. Summary of the invention

[0005] In response to the technical problem of low recycling rate of lithium iron phosphate batteries, the present invention proposes a method for preparing double-carbon modified sodium positive electrode materials using waste iron phosphate. On the one hand, the waste iron phosphate is recycled and utilized at a high value, and on the other hand, the prepared sodium iron phosphate positive electrode material is subjected to multiple modification treatments to improve the conductivity and rate performance of the sodium iron phosphate positive electrode material. No secondary pollution is generated in the whole process, the process energy consumption is low, the recycling process is green and efficient, and high value-added recycling of waste lithium iron phosphate batteries is achieved.

[0006] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A method for preparing a double-carbon modified sodium positive electrode material using waste iron phosphate, the steps are as follows:

[0008] (1) adding waste lithium iron phosphate material into a leaching solution for leaching and dissolution, and obtaining a lithium-containing filtrate and an iron phosphate residue after solid-liquid separation;

[0009] (2) After concentrating the lithium-containing solution, sodium carbonate is added to precipitate lithium carbonate, and after solid-liquid separation, sodium carbonate precipitate and sodium-containing solution are obtained;

[0010] (3) dissolving and regenerating the iron phosphate slag to obtain iron phosphate;

[0011] (4) adding ferric phosphate to the sodium-containing solution obtained in step (2), and then adding a sodium source, a phosphorus source, and a carbon source and grinding to obtain a pretreated mixed solution;

[0012] (5) spray drying the pretreated mixed solution, and calcining the spray-dried sample to obtain a sodium iron phosphate material;

[0013] (6) Mixing the sodium iron phosphate material with the functional carbon source, calcining after mixing evenly, and obtaining a double-carbon modified sodium iron phosphate positive electrode material.

[0014] The leachate comprises an acid solution and a catalyst; the acid in the acid solution is sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, citric acid, oxalic acid, formic acid or acetic acid; the catalyst is any one or more of hydrogen peroxide, sodium thiosulfate, sodium sulfite or ammonium thiosulfate.

[0015] The acid concentration in the leaching solution is 0.05-2 mol / L, and the catalyst concentration is 0.05-2 mol / L; the leaching and dissolving time is 0.5-4 hours, and the temperature is 20-60°C.

[0016] The molar ratio of iron, phosphorus and sodium in the pre-treated mixed solution in step (4) is (0.95-1):2:(1.95-2.1); the amount of the carbon source added is 0.5-10wt% of the total amount of iron, phosphorus and sodium.

[0017] The sodium source is sodium sulfate, sodium phosphate, sodium sulfite, sodium citrate or sodium hydroxide.

[0018] The phosphorus source is phosphoric acid, sodium phosphate, sodium dihydrogen phosphate, ammonium phosphate, and ammonium dihydrogen phosphate.

[0019] The carbon source is glucose, chitosan, sucrose and starch.

[0020] The calcination I includes two stages. The temperature of the first stage is 200-500° C. and the insulation time is 0.5-3 hours. The temperature of the second stage is 500-800° C. and the insulation time is 5-24 hours.

[0021] The functional carbon source is aminoacetate, glycine carbonate, polyvinyl pyrrolidone or urea; the added amount of the functional carbon source is 0.5-10wt% of the sodium iron phosphate material; the temperature of the calcination II is 600-800°C, and the insulation time is 0.5-4h.

[0022] The beneficial effects of the present invention are as follows: on the one hand, the present invention recycles waste lithium iron phosphate at a high value, extracts iron phosphate from waste lithium iron phosphate materials, and uses sodium-containing waste liquid generated in the lithium recovery process to prepare sodium iron phosphate positive electrode materials. On the other hand, the prepared sodium iron phosphate positive electrode materials are subjected to multiple modification treatments to obtain double-carbon modified sodium iron phosphate positive electrode materials, thereby improving the conductivity and rate performance of the sodium iron phosphate positive electrode materials. No secondary pollution is generated in the whole process, the process energy consumption is low, the recycling process is green and efficient, and high value-added recycling of waste lithium iron phosphate batteries is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 Schematic diagram of the process for preparing double-carbon modified sodium iron phosphate positive electrode material.

[0025] Figure 2 This is the SEM image of the double-carbon modified sodium iron phosphate positive electrode material in Example 1. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Example 1

[0028] A method for preparing a double carbon modified sodium positive electrode material using waste iron phosphate, the preparation process is as follows Figure 1 As shown, the specific production steps are as follows:

[0029] (1) 10 g of black powder material was added to a mixed solution of 100 ml of citric acid and hydrogen peroxide at a solid-liquid ratio of 100 g / L, wherein the concentration of citric acid was 1 mol / L, the concentration of hydrogen peroxide was 1 mol / L, the leaching temperature was 60° C., the leaching time was 2 h, and after dissolution, a lithium metal ion leachate and an iron phosphate residue were obtained by filtering;

[0030] (2) adding sodium carbonate having a lithium content 1.1 times that of the lithium content to the lithium-containing leachate obtained in step (1) to precipitate lithium carbonate, and filtering out the sodium carbonate precipitate after solid-liquid separation, and filtering out the sodium-containing solution;

[0031] (3) dissolving the iron phosphate slag obtained in step (1) with 3 mol / L hydrochloric acid, then adjusting the pH to 2.0 with 10 wt % sodium carbonate, and performing multiple dissolution precipitation regeneration processes. The precipitated iron phosphate slag is washed and dried and ground;

[0032] (4) adding the iron phosphate slag obtained in step (3) to the sodium-containing filtrate of step (2) to determine the sodium content in the sodium-containing filtrate, then adding sodium phosphate and sodium dihydrogen phosphate according to the molar ratio of iron, phosphorus and sodium in the final solution of 1:2:2.05, and finally adding glucose having a carbon content of 8 wt% of the total mass of iron, phosphorus and sodium elements after calcination, and obtaining a pretreated mixed solution after mechanical stirring;

[0033] (5) spray drying the pretreated mixed solution obtained in step (4), and calcining the spray-dried powder, wherein the first stage temperature is 260° C. and the second stage temperature is 600° C. and the temperature is 10 h. After the calcination is completed, the powder is ground and sieved to obtain a battery-grade sodium iron phosphate positive electrode material;

[0034] (6) The battery-grade sodium iron phosphate positive electrode material obtained in step (5) is contacted and mixed with urea in which the organic carbon accounts for 5 wt % after calcination. After mixing evenly, the mixture is calcined at 750° C. for 2 h to obtain a double-carbon modified sodium iron phosphate positive electrode material.

[0035] Example 2

[0036] A method for preparing a double-carbon modified sodium positive electrode material using waste iron phosphate, the specific production steps are as follows:

[0037] (1) 10 g of black powder material was added to a mixed solution of 100 ml of sulfuric acid and hydrogen peroxide at a solid-liquid ratio of 100 g / L, wherein the sulfuric acid concentration was 1 mol / L, the hydrogen peroxide concentration was 0.05 mol / L, the leaching temperature was 60° C., the leaching time was 2 h, and after dissolution, a lithium metal ion leachate and an iron phosphate residue were obtained by filtering;

[0038] (2) adding sodium carbonate having a lithium content 1.1 times that of the lithium content to the lithium-containing leachate obtained in step (1) to precipitate lithium carbonate, and filtering out the sodium carbonate precipitate after solid-liquid separation, and filtering out the sodium-containing solution;

[0039] (3) dissolving the iron phosphate slag obtained in step (1) with 3 mol / L hydrochloric acid, then adjusting the pH to 2.0 with 10 wt % sodium carbonate, and performing multiple dissolution precipitation regeneration processes. The precipitated iron phosphate slag is washed and dried and ground;

[0040] (4) adding the iron phosphate slag obtained in step (3) to the sodium-containing filtrate of step (2), determining the sodium content in the sodium-containing filtrate, then adding sodium sulfite and sodium phosphate in a molar ratio of 0.95:2:2.1 of iron, phosphorus and sodium in the final solution, and finally adding chitosan having a carbon content of 5 wt% of the total mass of iron, phosphorus and sodium elements after calcination, and obtaining a pretreated mixed solution after mechanical stirring;

[0041] (5) spray drying the pretreated mixed solution obtained in step (4), and calcining the spray-dried powder, wherein the first stage temperature is 260° C. and the second stage temperature is 600° C. and the temperature is 10 h. After the calcination is completed, the powder is ground and sieved to obtain a battery-grade sodium iron phosphate positive electrode material;

[0042] (6) The battery-grade sodium iron phosphate positive electrode material obtained in step (5) is added with aminoacetate in which the organic carbon accounts for 1 wt% of the calcined organic carbon, and the mixture is contacted and mixed. After the mixture is evenly mixed, the mixture is calcined at 600° C. for 2 h to obtain a double-carbon modified sodium iron phosphate positive electrode material.

[0043] Example 3

[0044] A method for preparing a double-carbon modified sodium positive electrode material using waste iron phosphate, the specific production steps are as follows:

[0045] (1) 10 g of black powder material was added to a mixed solution of 100 ml of hydrochloric acid and hydrogen peroxide at a solid-liquid ratio of 100 g / L, wherein the concentration of hydrochloric acid was 1 mol / L, the concentration of hydrogen peroxide was 1 mol / L, the leaching temperature was 20° C., the leaching time was 0.5 h, and after dissolution, a lithium metal ion leachate and an iron phosphate residue were obtained by filtering;

[0046] (2) adding sodium carbonate having a lithium content 1.1 times that of the lithium content to the lithium-containing leachate obtained in step (1) to precipitate lithium carbonate, and filtering out the sodium carbonate precipitate after solid-liquid separation, and filtering out the sodium-containing solution;

[0047] (3) dissolving the iron phosphate slag obtained in step (1) with 2 mol / L hydrochloric acid, and then adjusting the pH to 2.0 with 10 wt % sodium carbonate to perform multiple dissolution precipitation regeneration processes, and washing the precipitated iron phosphate slag and drying and grinding it;

[0048] (4) adding the iron phosphate slag obtained in step (3) to the sodium-containing filtrate of step (2), determining the sodium content in the sodium-containing filtrate, then adding sodium citrate and ammonium phosphate in a molar ratio of 0.98:2:1.95 of iron, phosphorus and sodium in the final solution, and finally adding sucrose having a carbon content of 10 wt% of the total mass of iron, phosphorus and sodium elements after calcination, and obtaining a pretreated mixed solution after mechanical stirring;

[0049] (5) spray drying the pretreated mixed solution obtained in step (4), and calcining the spray-dried powder, wherein the first stage temperature is 260° C. and the second stage temperature is 800° C. and the temperature is 10 h. After the calcination is completed, the powder is ground and sieved to obtain a battery-grade sodium iron phosphate positive electrode material;

[0050] (6) The battery-grade sodium iron phosphate positive electrode material obtained in step (5) is added with glycine carbonate in which the organic carbon accounts for 8 wt % after calcination, and the mixture is contacted and mixed. After the mixture is evenly mixed, the mixture is calcined at 800° C. for 2 h to obtain a double-carbon modified sodium iron phosphate positive electrode material.

[0051] Example 4

[0052] A method for preparing a double-carbon modified sodium positive electrode material using waste iron phosphate, the specific production steps are as follows:

[0053] (1) adding 10 g of black powder material to a mixed solution of 100 ml of acetic acid and sodium sulfite at a solid-liquid ratio of 100 g / L, wherein the acetic acid concentration is 1 mol / L, the sodium sulfite concentration is 1 mol / L, the leaching temperature is 40° C., the leaching time is 2 h, and after dissolution, filtering is performed to obtain a lithium metal ion leachate and an iron phosphate residue;

[0054] (2) adding sodium carbonate having a lithium content 1.1 times that of the lithium content to the lithium-containing leachate obtained in step (1) to precipitate lithium carbonate, and filtering out the sodium carbonate precipitate after solid-liquid separation, and filtering out the sodium-containing solution;

[0055] (3) dissolving the iron phosphate slag obtained in step (1) with 3 mol / L hydrochloric acid, then adjusting the pH to 2.0 with 10 wt % sodium carbonate, and performing multiple dissolution precipitation regeneration processes. The precipitated iron phosphate slag is washed and dried and ground;

[0056] (4) adding the iron phosphate slag obtained in step (3) to the sodium-containing filtrate of step (2), determining the sodium content in the sodium-containing filtrate, then adding sodium hydroxide and sodium dihydrogen phosphate in a molar ratio of 0.98:2:2.05 of iron, phosphorus and sodium in the final solution, and finally adding starch having a carbon content of 8 wt% of the total mass of iron, phosphorus and sodium elements after calcination, and obtaining a pretreated mixed solution after mechanical stirring;

[0057] (5) spray drying the pretreated mixed solution obtained in step (4), and calcining the spray-dried powder, wherein the first stage temperature is 260° C. and the second stage temperature is 600° C. and the temperature is 10 h. After the calcination is completed, the powder is ground and sieved to obtain a battery-grade sodium iron phosphate positive electrode material;

[0058] (6) The battery-grade sodium iron phosphate positive electrode material obtained in step (5) is added with polyvinyl pyrrolidone in which the organic carbon accounts for 5 wt % after calcination, and the mixture is contacted and mixed. After the mixture is evenly mixed, the mixture is calcined at 750° C. for 2 h to obtain a double-carbon modified sodium iron phosphate positive electrode material.

[0059] Example 5

[0060] A method for preparing a double-carbon modified sodium positive electrode material using waste iron phosphate, the specific production steps are as follows:

[0061] (1) adding 10 g of black powder material to a mixed solution of 100 ml of nitric acid and sodium thiosulfate at a solid-liquid ratio of 100 g / L, wherein the concentration of nitric acid is 1 mol / L, the concentration of sodium thiosulfate is 1 mol / L, the leaching temperature is 40° C., the leaching time is 2 h, and after dissolution, filtering is performed to obtain a lithium metal ion leachate and an iron phosphate filter residue;

[0062] (2) adding sodium carbonate having a lithium content 1.1 times that of the lithium content to the lithium-containing leachate obtained in step (1) to precipitate lithium carbonate, and filtering out the sodium carbonate precipitate after solid-liquid separation, and filtering out the sodium-containing solution;

[0063] (3) dissolving the iron phosphate slag obtained in step (1) with 5 mol / L hydrochloric acid, then adjusting the pH to 2.0 with 10 wt % sodium carbonate, and performing multiple dissolution precipitation regeneration processes. The precipitated iron phosphate slag is washed and dried and ground;

[0064] (4) adding the iron phosphate slag obtained in step (3) to the sodium-containing filtrate of step (2), determining the sodium content in the sodium-containing filtrate, then adding sodium phosphate and sodium dihydrogen phosphate in a molar ratio of 1:2:2.05 of iron, phosphorus and sodium in the final solution, and finally adding glucose having a carbon content of 8 wt% of the total mass of iron, phosphorus and sodium elements after calcination, and obtaining a pretreated mixed solution after mechanical stirring;

[0065] (5) spray drying the pretreated mixed solution obtained in step (4), and calcining the spray-dried powder, wherein the first stage temperature is 260° C. and the second stage temperature is 600° C. and the temperature is 10 h. After the calcination is completed, the powder is ground and sieved to obtain a battery-grade sodium iron phosphate positive electrode material;

[0066] (6) Add polyvinyl pyrrolidone in which the organic carbon accounts for 10 wt% after calcination to the battery-grade sodium iron phosphate positive electrode material obtained in step (5), mix well, and calcine at 750° C. for 0.5 h to obtain a double-carbon modified sodium iron phosphate positive electrode material.

[0067] Example 6

[0068] A method for preparing a double-carbon modified sodium positive electrode material using waste iron phosphate, the specific production steps are as follows:

[0069] (1) 10 g of black powder material was added to a mixed solution of 100 ml of formic acid and hydrogen peroxide at a solid-liquid ratio of 100 g / L, wherein the formic acid concentration was 0.05 mol / L, the hydrogen peroxide concentration was 1 mol / L, the leaching temperature was 60° C., the leaching time was 4 h, and after dissolution, a lithium metal ion leachate and an iron phosphate residue were obtained by filtering;

[0070] (2) adding sodium carbonate having a lithium content 1.1 times that of the lithium content to the lithium-containing leachate obtained in step (1) to precipitate lithium carbonate, and filtering out the sodium carbonate precipitate after solid-liquid separation, and filtering out the sodium-containing solution;

[0071] (3) dissolving the iron phosphate slag obtained in step (1) with 3 mol / L hydrochloric acid, then adjusting the pH to 2.0 with 10 wt % sodium carbonate, and performing multiple dissolution precipitation regeneration processes. The precipitated iron phosphate slag is washed and dried and ground;

[0072] (4) adding the iron phosphate slag obtained in step (3) to the sodium-containing filtrate of step (2), determining the sodium content in the sodium-containing filtrate, then adding sodium phosphate and sodium dihydrogen phosphate in a molar ratio of 1:2:2.05 of iron, phosphorus and sodium in the final solution, and finally adding glucose having a carbon content of 1 wt% of the total mass of iron, phosphorus and sodium elements after calcination, and obtaining a pretreated mixed solution after mechanical stirring;

[0073] (5) spray drying the pretreated mixed solution obtained in step (4), and calcining the spray-dried powder, wherein the first stage temperature is 260° C. and the second stage temperature is 600° C. and the temperature is 10 h. After the calcination is completed, the powder is ground and sieved to obtain a battery-grade sodium iron phosphate positive electrode material;

[0074] (6) The battery-grade sodium iron phosphate positive electrode material obtained in step (5) is contacted and mixed with urea in which the organic carbon accounts for 10 wt % after calcination. After mixing evenly, the mixture is calcined at 750° C. for 4 h to obtain a double-carbon modified sodium iron phosphate positive electrode material.

[0075] Comparative Example 1

[0076] A method for preparing a carbon-modified sodium cathode material using waste iron phosphate, the specific production steps are as follows:

[0077] (1) 10 g of black powder material was added to 100 ml of a mixed solution of formic acid and sodium thiosulfate at a solid-liquid ratio of 100 g / L, wherein the concentration of citric acid was 1 mol / L, the concentration of hydrogen peroxide was 1 mol / L, the leaching temperature was 40° C., the leaching time was 4 h, and after dissolution, a lithium metal ion leachate and an iron phosphate residue were obtained by filtering;

[0078] (2) adding sodium carbonate having a lithium content 1.1 times that of the lithium content to the lithium-containing leachate obtained in step (1) to precipitate lithium carbonate, and filtering out the sodium carbonate precipitate after solid-liquid separation, and filtering out the sodium-containing solution;

[0079] (3) dissolving the iron phosphate slag obtained in step (1) with 5 mol / L hydrochloric acid, then adjusting the pH to 2.0 with 10 wt % sodium carbonate, and performing multiple dissolution precipitation regeneration processes. The precipitated iron phosphate slag is washed and dried and ground;

[0080] (4) adding the iron phosphate slag obtained in step (3) to the sodium-containing filtrate of step (2), determining the sodium content in the sodium-containing filtrate, then adding sodium phosphate and sodium dihydrogen phosphate in a molar ratio of 1:2:2.05 of iron, phosphorus and sodium in the final solution, and finally adding glucose having a carbon content of 8 wt% of the total mass of iron, phosphorus and sodium elements after calcination, and obtaining a pretreated mixed solution after mechanical stirring;

[0081] (5) The pretreated mixed solution obtained in step (4) is spray dried, and the powder after spray drying is calcined. The temperature of the first stage is 260° C. and the temperature of the second stage is 600° C. and the temperature is kept for 10 hours. After the calcination is completed, the battery-grade sodium iron phosphate positive electrode material is obtained by grinding and screening.

[0082] Comparative Example 2

[0083] A method for preparing a carbon-modified sodium cathode material using waste iron phosphate, the specific production steps are as follows:

[0084] (1) adding 10 g of black powder material to a mixed solution of 100 ml of phosphoric acid and hydrogen peroxide at a solid-liquid ratio of 100 g / L, wherein the phosphoric acid concentration is 1 mol / L, the hydrogen peroxide concentration is 1 mol / L, the leaching temperature is 60° C., the leaching time is 2 h, and after dissolution, filtering is performed to obtain a lithium metal ion leachate and an iron phosphate filter residue;

[0085] (2) adding sodium carbonate having a lithium content 1.1 times that of the lithium content to the lithium-containing leachate obtained in step (1) to precipitate lithium carbonate, and filtering out the sodium carbonate precipitate after solid-liquid separation, and filtering out the sodium-containing solution;

[0086] (3) dissolving the iron phosphate slag obtained in step (1) with 3 mol / L hydrochloric acid, then adjusting the pH to 2.0 with 10 wt % sodium carbonate, and performing multiple dissolution precipitation regeneration processes. The precipitated iron phosphate slag is washed and dried and ground;

[0087] (4) adding the iron phosphate slag obtained in step (3) to the sodium-containing filtrate of step (2), determining the sodium content in the sodium-containing filtrate, and then adding sodium phosphate and sodium dihydrogen phosphate in a molar ratio of 1:2:2.05 of iron, phosphorus and sodium in the final solution, and after mechanical stirring, obtaining a pretreated mixed solution;

[0088] (5) The pretreated mixed solution obtained in step (4) is spray-dried, and the powder after spray drying is calcined. The temperature of the first stage is 260° C. and the temperature of the second stage is 600° C. and the temperature is kept for 10 hours. After the calcination is completed, the battery-grade sodium iron phosphate positive electrode material is obtained by grinding and sieving.

[0089] The electrochemical performance of the materials prepared in Examples 1-6 and Comparative Examples 1-2 was tested. The double carbon-modified sodium iron phosphate positive electrode material, carbon black, and polytetrafluoroethylene binder were ground and mixed in a mass ratio of 90:5:5, and then an electrode sheet was made and assembled into a button battery with a sodium sheet. The test results are shown in Table 1. The specific capacity of the sodium iron phosphate modified twice in Examples 1-6 can reach up to 110 mAh / g, which is significantly higher than that of the sodium iron phosphate without carbon modification and the sodium iron phosphate modified only once.

[0090] Table 1

[0091] Experimental protocol Carbon source Functional carbon source 0.2C capacity (mAh / g) Example 1 glucose Urea 110 Example 2 glucose Glycine 108 Example 3 sucrose Glycine carbonate 107 Example 4 starch Polyvinylpyrrolidone 106 Example 5 glucose Polyvinylpyrrolidone 107 Example 6 Chitosan Urea 108 Comparative Example 1 glucose / 97 Comparative Example 2 / / 95

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a double-carbon modified sodium cathode material using waste iron phosphate, characterized in that: Here are the steps: (1) adding waste lithium iron phosphate material into a leaching solution for leaching and dissolution, and obtaining a lithium-containing filtrate and iron phosphate residue after solid-liquid separation; (2) After concentrating the lithium-containing solution, sodium carbonate is added to precipitate lithium carbonate, and after solid-liquid separation, sodium carbonate precipitate and sodium-containing solution are obtained; (3) dissolving and regenerating the iron phosphate slag to obtain iron phosphate; (4) adding ferric phosphate to the sodium-containing solution obtained in step (2), and then adding a sodium source, a phosphorus source, and a carbon source and grinding to obtain a pretreated mixed solution; (5) spray drying the pretreated mixed solution, and calcining the spray-dried sample to obtain a sodium iron phosphate material; (6) Mixing the sodium iron phosphate material with the functional carbon source, calcining after mixing evenly, and obtaining a double-carbon modified sodium iron phosphate positive electrode material.

2. The method for preparing a double-carbon modified sodium positive electrode material using waste iron phosphate according to claim 1, characterized in that: The leachate comprises an acid solution and a catalyst; the acid in the acid solution is sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, citric acid, oxalic acid, formic acid or acetic acid; the catalyst is any one or more of hydrogen peroxide, sodium thiosulfate, sodium sulfite or ammonium thiosulfate.

3. The method for preparing a double-carbon modified sodium positive electrode material using waste iron phosphate according to claim 2, characterized in that: The acid concentration in the leaching solution is 0.05-2 mol / L, and the catalyst concentration is 0.05-2 mol / L; the leaching and dissolving time is 0.5-4 hours, and the temperature is 20-60°C.

4. The method for preparing a double-carbon modified sodium positive electrode material using waste iron phosphate according to claim 3, characterized in that: The molar ratio of iron, phosphorus and sodium in the pre-treated mixed solution in step (4) is (0.95-1):2:(1.95-2.1); the amount of the carbon source added is 0.5-10wt% of the total amount of iron, phosphorus and sodium.

5. The method for preparing a double-carbon modified sodium positive electrode material using waste iron phosphate according to claim 4, characterized in that: The sodium source is sodium sulfate, sodium phosphate, sodium sulfite, sodium citrate or sodium hydroxide.

6. The method for preparing a double-carbon modified sodium positive electrode material using waste iron phosphate according to claim 4, characterized in that: The phosphorus source is phosphoric acid, sodium phosphate, sodium dihydrogen phosphate, ammonium phosphate, and ammonium dihydrogen phosphate.

7. The method for preparing a double-carbon modified sodium positive electrode material using waste iron phosphate according to claim 4, characterized in that: The carbon source is glucose, chitosan, sucrose and starch.

8. The method for preparing a double-carbon modified sodium positive electrode material using waste iron phosphate according to any one of claims 1 to 7, characterized in that: The calcination I includes two stages. The temperature of the first stage is 200-500° C. and the insulation time is 0.5-3 hours. The temperature of the second stage is 500-800° C. and the insulation time is 5-24 hours.

9. The method for preparing a double-carbon modified sodium positive electrode material using waste iron phosphate according to claim 8, characterized in that: The functional carbon source is aminoacetate, glycine carbonate, polyvinyl pyrrolidone or urea; the added amount of the functional carbon source is 0.5-10wt% of the sodium iron phosphate material; the temperature of the calcination II is 600-800°C, and the insulation time is 0.5-4h.

10. A double-carbon modified sodium cathode material prepared by the method according to any one of claims 1 to 9.

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