Method for producing ferric sodium pyrophosphate and extracting lithium from lithium iron phosphate black powder through replacement

Abstract

The invention relates to the technical field of lithium ion battery recovery, and discloses a method for producing ferric sodium pyrophosphate and extracting lithium from lithium iron phosphate black powder through replacement, and the method comprises the following steps: S1, weighing a certain amount of lithium iron phosphate black powder and a sodium source, dispersing in absolute ethyl alcohol, and carrying out ball milling and mixing to obtain solid powder; s2, dissolving the solid powder obtained in the step S1 in pure water, and performing suction filtration to obtain sodium ferric phosphate and lithium salt filtrate; s3, washing the sodium ferric phosphate obtained in the step S2, and drying; s4, adding sodium pyrophosphate into the sodium ferric phosphate, and calcining at high temperature to obtain a sodium ferric pyrophosphate product; s5, adding a phosphate ammonium salt into the lithium salt filtrate obtained in S2 until the pH value of the solution is 8-12, carrying out heat preservation reaction for a period of time, and carrying out suction filtration to obtain a lithium phosphate filter cake; and S6, washing the lithium phosphate filter cake obtained in the step S5, and drying to obtain a lithium phosphate product. According to the scheme, the problems existing in the existing lithium ion battery recovery technology can be solved, and a new way is provided for preparation of the sodium ion battery positive electrode material.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery recycling, and in particular to a method for producing sodium iron pyrophosphate by replacing lithium iron phosphate black powder and extracting lithium. Background Art

[0002] With the rapid development of the global new energy industry, lithium-ion batteries have become the main energy storage device due to their superior performance, and are widely used in new energy vehicles, portable electronic devices, and renewable energy storage. In lithium-ion batteries, lithium, as a key element, plays a vital role in battery performance. However, with the rapid expansion of the industry, the output and use of lithium-ion batteries have risen sharply, and the consumption of lithium resources has also shown an increasing trend year by year. At present, the reserves of natural lithium resources (such as salt lakes and lithium mines) are limited, and their supply speed cannot meet the market's growing demand for lithium, and the problem of lithium resource shortage is becoming increasingly prominent.

[0003] Among various lithium-ion battery products, lithium iron phosphate (LiFePO4) batteries have the advantages of high safety, long cycle life and good thermal stability, and their market share continues to rise, and their planned production capacity is also increasing. It is predicted that the amount of retired LiFePO4 batteries will reach 219.6GWh by 2030. For retired LiFePO4 batteries, the current mainstream recycling method is hydrometallurgy. This method is to leach the Li, Fe, and P elements in the battery material through strong acid, and then use sodium carbonate as a precipitant to recover lithium in the form of lithium carbonate in the leachate. However, this recycling method has significant disadvantages. Due to the high solubility of lithium carbonate, the precipitation rate of lithium carbonate is not high, and the lithium recovery rate is low. In addition, the iron phosphate slag mixture generated during the recycling process is a solid waste, and its slag volume is huge. Disposing of these solid wastes not only requires additional costs, but also causes waste of resources, which leads to high recycling costs.

[0004] In view of the shortage of lithium resources and the difficulties in recycling existing lithium-ion batteries, sodium-ion batteries have gradually attracted widespread attention as a potential alternative or supplementary energy storage technology. Especially in the field of new energy vehicles, with the increasing requirements for cost control and resource sustainability, sodium-ion batteries have attracted much attention due to their significant advantages of abundant sodium resources and low cost. In the positive electrode material system of sodium-ion batteries, sodium ferric pyrophosphate has been widely studied by many scientific research institutions and enterprises due to its advantages such as high theoretical capacity, good stable performance, low price, safety and reliability, and green environmental protection.

[0005] At present, there are two main synthetic routes for sodium ferric pyrophosphate, namely electrochemical ion exchange and traditional solid-state synthesis. Electrochemical ion exchange can produce electrochemically active sodium ferric pyrophosphate, but it is difficult to achieve large-scale production due to many factors.

[0006] In summary, developing efficient and environmentally friendly recycling technologies for waste lithium-ion batteries and exploring synthetic routes for new battery materials such as sodium pyrophosphate iron phosphate is of great strategic significance and technical value for ensuring resource supply security during the global energy transition, promoting the green development of the battery industry, and achieving a win-win situation for the economy and the environment. Summary of the Invention

[0007] The present invention aims to provide a method for producing sodium pyrophosphate iron phosphate by displacement from lithium iron phosphate black powder and extracting lithium, so as to solve the problems existing in the existing lithium-ion battery recycling technologies and provide a new approach for the preparation of the cathode material of sodium-ion batteries.

[0008] To achieve the above object, the present invention adopts the following technical solution: A method for producing sodium pyrophosphate iron phosphate by displacement from lithium iron phosphate black powder and extracting lithium, comprising the following steps:

[0009] S1: Weigh a certain amount of lithium iron phosphate black powder and a sodium source respectively, disperse them in absolute ethanol to form a mixed solution, and then perform a ball-milling mixing operation on the mixed solution to obtain solid powder;

[0010] S2: Dissolve the solid powder obtained in S1 in an appropriate amount of pure water, heat and stir for a period of time and then perform suction filtration to obtain sodium iron phosphate and a lithium salt filtrate;

[0011] S3: Wash the sodium iron phosphate obtained in S2, and then perform drying;

[0012] S4: Add sodium pyrophosphate to the sodium iron phosphate obtained in S3 and calcine it in a high-temperature and inert atmosphere to obtain a sodium pyrophosphate iron phosphate product;

[0013] S5: At a certain temperature, add an ammonium phosphate salt to the lithium salt filtrate obtained in S2 until the pH of the solution is 8-12, keep it warm and react for a period of time, and then perform suction filtration to obtain a lithium phosphate filter cake;

[0014] S6: Wash the lithium phosphate filter cake obtained in S5, and then perform drying to obtain a lithium phosphate product.

[0015] Preferably, in S1, the sodium source is any one of NaNO3, Na2SO4, NaCl, CH3COONa, and NaC2O4.

[0016] Preferably, in S1, the mass ratio of the sodium source to the lithium iron phosphate black powder is (1-3):1; the addition amount of absolute ethanol is 5% to 15% of the total mass of the sodium source and the lithium iron phosphate black powder.

[0017] Preferably, in S1, vacuum ball milling is adopted, the ball milling speed is 500-800 r / min, and the ball milling duration is 5-24 h.

[0018] Preferably, in S2, water bath heating is adopted, the heating temperature is 40-90°C, and the heating and stirring time is 0.5-5h.

[0019] Preferably, in S3, the mass of pure water for washing is 3-8 times the mass of sodium iron phosphate, and the number of water washing times is 2-4 times.

[0020] Preferably, in S3, the drying temperature is 40-100°C, and the drying time is 5-24h.

[0021] Preferably, in S4, the molar ratio of sodium iron phosphate to sodium pyrophosphate is (1-5):1.

[0022] Preferably, in S4, the calcination temperature is 500-1000°C, and the calcination time is 2-10h.

[0023] Preferably, in S5, the ammonium phosphate salt is any one of (NH4)2HPO4, NH4H2PO4, (NH4)3PO4; the concentration of the ammonium phosphate salt is 10%-30% wt.

[0024] Compared with the prior art, the beneficial effects of this solution are as follows:

[0025] (1) Under the background of the rapid development of the new energy vehicle industry, the treatment of retired lithium iron phosphate batteries has become an important issue. The prior art usually adopts hydrometallurgy to treat such batteries, and strong acids are required to leach the elements in the battery materials. However, the present invention uses an acid-free induced replacement method to extract lithium, avoiding the use of strong acids. Through a special mechanical force induced design, sodium elements replace lithium elements, which not only greatly reduces pollutant emissions and meets environmental protection requirements, but also simplifies the treatment process. At the same time, the consumption of chemical treatment agents is reduced, thereby reducing the overall treatment cost, and providing an economical and environmentally friendly method for the battery recycling link in the new energy vehicle industry.

[0026] (2) With the wide application of new energy vehicles, the resource utilization efficiency in the battery recycling process is crucial. The prior art will generate a large amount of iron phosphate slag mixture as solid waste during the recycling process, which not only causes resource waste, but also increases the treatment cost of solid waste. The present invention avoids the generation of solid waste iron phosphate slag mixture and realizes the recycling of multiple elements in the battery materials. This multi-element recycling method greatly improves the resource recycling rate, reduces the waste treatment and disposal costs, and provides a more sustainable resource guarantee for the new energy vehicle industry.

[0027] (3) As a potentially important energy storage technology in the new energy vehicle industry, the quality of the cathode material for sodium-ion batteries is crucial. There are limitations in the existing technology for preparing sodium iron pyrophosphate as the cathode material for sodium-ion batteries. While recycling lithium from waste lithium iron phosphate batteries, the present invention provides a preparation process for sodium iron pyrophosphate for sodium-ion batteries. This process can produce olivine-structured sodium iron phosphate with electrochemical activity, which has simple raw materials, a simple process, low cost, a short process, and is easy for large-scale production, showing excellent prospects for process application. This provides a better material basis for the development of sodium-ion batteries in the new energy vehicle industry and helps to promote the application of sodium-ion batteries in the field of new energy vehicles.

[0028] (4) Lithium resources are key strategic resources in the new energy vehicle industry. When recycling lithium using the existing technology with sodium carbonate as the precipitant, due to the relatively high solubility of lithium carbonate, the lithium recovery rate is low. The present invention uses ammonium phosphate salts to extract lithium, greatly reducing the solubility of the recovered lithium salts, thereby increasing the lithium recovery rate. This not only improves the economic value of recycling, reduces the dependence on primary resources, but also ensures the long-term supply security of lithium resources, providing a strong resource guarantee for the stable development of the new energy vehicle industry.

[0029] (5) The added sodium source in this technical solution is an affordable cementing reagent, which realizes the isomorphic substitution of Li in the crystal of retired LiFePO4 batteries through the mechanical force induction effect. + in the crystal of retired LiFePO4 batteries through the mechanical force induction effect.

[0030] (6) In this technical solution, ammonium phosphate salts are added to the lithium salt filtrate until the solution pH is 8 - 12 to reduce the solubility of the lithium salts. If the pH is too low, it is easy to cause incomplete precipitation of lithium ions and thus loss. If the pH is too high, it is easy to cause impure lithium salts and increased costs. The concentration of ammonium phosphate salts in this technical solution is set at 10% - 30% wt to prevent local over-concentration after the addition of ammonium phosphate salts due to excessive concentration, thus forming large particles that wrap impurities and making the lithium salts impure.

[0031] (7) In this technical solution, the ball milling speed is set at 500 - 800 r / min, which can prevent the lattice of lithium iron phosphate from being damaged due to too high a ball milling speed, thus making it impossible to prepare sodium iron phosphate again. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a flow chart of a method for producing sodium iron pyrophosphate and extracting lithium by replacing black powder of lithium iron phosphate in Example 1 of the present invention;

[0033] Figure 2 is an XRD diagram of the lithium phosphate prepared in Example 1 of the present invention;

[0034] Figure 3XRD pattern of sodium iron pyrophosphate prepared in Example 1 of the present invention;

[0035] Figure 4 Charge-discharge performance graph of the button cell assembled with the sodium iron pyrophosphate prepared in Example 1 of the present invention;

[0036] Figure 5 XRD pattern of lithium phosphate prepared in Example 2 of the present invention;

[0037] Figure 6 XRD pattern of sodium iron pyrophosphate prepared in Example 2 of the present invention;

[0038] Figure 7 Charge-discharge performance graph of the button cell assembled with the sodium iron pyrophosphate prepared in Example 2 of the present invention;

[0039] Figure 8 XRD pattern of lithium phosphate prepared in Example 3 of the present invention;

[0040] Figure 9 XRD pattern of sodium iron pyrophosphate prepared in Example 3 of the present invention;

[0041] Figure 10 Charge-discharge performance graph of the button cell assembled with the sodium iron pyrophosphate prepared in Example 3 of the present invention;

[0042] Figure 11 XRD pattern of lithium phosphate prepared in Example 4 of the present invention;

[0043] Figure 12 XRD pattern of sodium iron pyrophosphate prepared in Example 4 of the present invention;

[0044] Figure 13 Charge-discharge performance graph of the button cell assembled with the sodium iron pyrophosphate prepared in Example 4 of the present invention. Detailed Description of the Invention

[0045] The following is a further detailed description through specific embodiments:

[0046] Example 1

[0047] A method for producing sodium iron pyrophosphate by displacement from lithium iron phosphate black powder and extracting lithium, comprising the following steps:

[0048] S1: Weigh a certain amount of lithium iron phosphate black powder and sodium source respectively, disperse them in absolute ethanol to form a mixed solution, and then perform ball milling mixing operation on this mixed solution to obtain solid powder; among them, the sodium source is any one of NaNO3, Na2SO4, NaCl, CH3COONa and NaC2O4; the mass ratio of the sodium source to the lithium iron phosphate black powder is (1 - 3):1; the addition amount of absolute ethanol is 5% - 15% of the total mass of the sodium source and the lithium iron phosphate black powder; the ball milling operation uses a vacuum planetary ball mill, the ball milling speed is 500 - 800 r / min, and the ball milling duration is 5 - 24 h;

[0049] In this embodiment, 100.01 g of LiFePO4 black powder and 100.02 g of Na2SO4 are weighed and dispersed in absolute ethanol. Among them, the mass of absolute ethanol is 6% of the total mass of LiFePO4 black powder and Na2SO4, a mixed solution is prepared, and it is put into a vacuum planetary ball mill and ball milled at a speed of 500 r / min for 12 h to obtain solid powder;

[0050] S2: Dissolve the solid powder obtained in S1 in pure water, use water bath heating, the heating temperature is 40 - 90 °C, heat and stir for 0.5 - 5 h and then perform suction filtration to obtain sodium iron phosphate and lithium salt filtrate;

[0051] In this embodiment, the solid powder obtained in S1 is dissolved in pure water, the temperature of water bath heating is 70 °C, heat and stir for 3 h and then perform suction filtration to obtain sodium iron phosphate filter cake and lithium salt filtrate;

[0052] S3: Wash the sodium iron phosphate obtained in S2 and then dry it; among them, the mass of pure water for washing is 3 - 8 times the mass of sodium iron phosphate, and the number of water washing times is 2 - 4 times; use a blast drying oven for drying, the drying temperature is 40 - 100 °C, and the drying time is 5 - 24 h;

[0053] In this embodiment, the sodium iron phosphate obtained in S2 is washed 3 times with pure water, the mass of pure water for washing is 5 times the mass of sodium iron phosphate, and then it is dried using a blast drying oven, the drying temperature is 60 °C, and the drying time is 8 h.

[0054] S4: Add sodium pyrophosphate to the sodium iron phosphate obtained in S3 and calcine it in a high temperature and inert atmosphere to obtain sodium iron pyrophosphate product; among them, the molar ratio of sodium iron phosphate to sodium pyrophosphate is (1 - 5):1; use a tubular furnace to calcine in a nitrogen atmosphere, the calcination temperature is 500 - 1000 °C, and the calcination time is 2 - 10 h;

[0055] In this embodiment, sodium pyrophosphate is added to the sodium iron phosphate obtained in S3, and it is calcined using a tubular furnace in a nitrogen atmosphere, the calcination temperature is 1000 °C, the calcination time is 3 h, and the molar ratio of sodium iron phosphate to sodium pyrophosphate is 3:1;

[0056] S5: Under the condition of heating in a water bath at 40-90°C, slowly add ammonium phosphate salt to the lithium salt filtrate obtained in S2 until the pH of the solution is 8-12, keep the reaction warm for 0.5-1.5h, and then perform suction filtration to obtain a lithium phosphate filter cake; wherein the ammonium phosphate salt is any one of (NH4)2HPO4, NH4H2PO4, and (NH4)3PO4; and the concentration of the ammonium phosphate salt is 10%-30%wt.

[0057] In this embodiment, 20% wt of (NH4)3PO4 was slowly added to the lithium salt filtrate obtained from S2 under water bath heating at 70°C until the pH of the solution reached 11, and the reaction was kept warm for 1 hour, and then suction filtration was performed to obtain a lithium phosphate filter cake;

[0058] S6: washing the lithium phosphate filter cake obtained in S5 with pure water of 3-8 times its mass for 2-4 times respectively, and drying it in a blast oven at a drying temperature of 80-160° C. for a drying time of 2-8 hours to obtain a lithium phosphate product;

[0059] In this embodiment, the lithium phosphate filter cake obtained in S5 is washed three times with pure water of 4 times its mass, and then dried in a blast oven at a drying temperature of 80° C. for 4 hours to obtain a lithium phosphate product;

[0060] The sodium iron phosphate pyrophosphate product prepared in S4 and the lithium phosphate product prepared in S6 were tested by XRD. The test results are shown in Figure 2 , Figure 3 , Table 1 and Table 2. Figure 2 and Figure 3 It can be seen that the recovery rate of sodium iron pyrophosphate product is 90.37%, the main content is 99.24%, there are lithium ions that are not completely leached, and the purity can reach battery grade. The recovery rate of lithium phosphate product is 90.91%, the main content is 98.56%, which can be used as a lithium source to prepare lithium iron phosphate, lithium dihydrogen phosphate or lithium manganese iron phosphate.

[0061] Detection of the charge and discharge performance of the sodium iron pyrophosphate product prepared in S4

[0062] The sodium iron phosphate pyrophosphate product prepared in S4 is assembled into a CR2016 button battery. The specific assembly steps are as follows:

[0063] Step 1: Preparation of positive electrode sheet: According to the mass ratio of 7:2:1, weigh the sodium iron phosphate pyrophosphate (active substance), acetylene black and PVDF prepared in S4, mix them thoroughly, add appropriate amount of 1-methyl-2-pyrrolidone to make slurry, then coat the slurry on aluminum foil, dry it overnight in an environment of 120°C after coating, and make a positive electrode sheet;

[0064] Step 2: Battery assembly: Use sodium metal foil as the negative electrode, the positive electrode sheet prepared in Step 1 as the positive electrode, a glass microfiber membrane as the separator, and a 1 M NaClO4 solution (dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1 and adding 5% by volume of fluoroethylene carbonate (FEC)) as the electrolyte to assemble a CR2016 coin cell.

[0065] The test conditions are as follows: The voltage window for the NFPP half-cell test is 1.5 - 4.2 V.

[0066] It can be seen from Figure 4 that the sodium iron pyrophosphate recovered by this method has electrochemical activity when assembled into a coin cell and has a specific capacity of 99.87 mA·h / g at 0.1C.

[0067] Example 2

[0068] Different from Example 1, a method for producing sodium iron pyrophosphate by replacing lithium iron phosphate black powder and extracting lithium. In S1, 100.03 g of LiFePO4 black powder and 200.02 g of Na2SO4 are dispersed in absolute ethanol, where the mass of absolute ethanol is 6% of the total mass of LiFePO4 black powder and Na2SO4. Other steps are exactly the same as those in Example 1.

[0069] By performing XRD tests on the sodium iron pyrophosphate product obtained in S4 and the lithium phosphate product obtained in S6, the test results are shown in Figure 5 、 Figure 6 、Table 1 and Table 2. It can be seen from Figure 5 and Figure 6 that the recovery rate of the sodium iron pyrophosphate product is 92.55%, the main content is 99.35%, there are unextracted lithium ions, and the purity can reach battery grade. The recovery rate of the lithium phosphate product is 91.91%, and the main content is 98.12%.

[0070] Detect the charge-discharge performance of the sodium iron pyrophosphate product obtained in S4

[0071] The assembly method and test conditions of the coin cell are the same as those in Example 1, and will not be elaborated here.

[0072] It can be seen from Figure 7 that the sodium iron pyrophosphate recovered by this method has electrochemical activity when assembled into a coin cell and has a specific capacity of 95.4 mA·h / g at 0.1C.

[0073] Example 3

[0074] Different from Example 1, a method for producing sodium pyrophosphate iron phosphate by displacement from lithium iron phosphate black powder and extracting lithium. In S1, 100.03 g of LiFePO4 black powder and 200.01 g of NaNO3 are dispersed in absolute ethanol, where the mass of absolute ethanol is 6% of the total mass of LiFePO4 black powder and NaNO3. Other steps are exactly the same as those in Example 1.

[0075] By performing XRD tests on the sodium pyrophosphate iron phosphate product obtained in S4 and the lithium phosphate product obtained in S6, the test results are shown in Figure 8 、 Figure 9 、Table 1 and Table 2. From Figure 8 and Figure 9 it can be seen that the recovery rate of the sodium pyrophosphate iron phosphate product is 91.97%; the recovery rate of the lithium phosphate product is 91.19%, and the main content is 98.62%.

[0076] Detect the charge-discharge performance of the sodium pyrophosphate iron phosphate product obtained in S4

[0077] The assembly method and test conditions of the coin cell are the same as those in Example 1, and will not be elaborated here.

[0078] From Figure 10 it can be seen that the sodium pyrophosphate iron phosphate recovered by this method has electrochemical activity when assembled into a coin cell and has a specific capacity of 94.9 mA·h / g at 0.1C.

[0079] Example 4

[0080] Different from Example 1, a method for producing sodium pyrophosphate iron phosphate by displacement from lithium iron phosphate black powder and extracting lithium. In S1, 100.04 g of LiFePO4 black powder and 200.00 g of NaCl are dispersed in absolute ethanol, where the mass of absolute ethanol is 6% of the total mass of LiFePO4 black powder and NaCl. Other steps are exactly the same as those in Example 1.

[0081] By performing XRD tests on the sodium pyrophosphate iron phosphate product obtained in S4 and the lithium phosphate product obtained in S6, the test results are shown in Figure 11 、 Figure 12 、Table 1 and Table 2. From Figure 11 and Figure 12 it can be seen that the recovery rate of the sodium pyrophosphate iron phosphate product is 91.42%; the recovery rate of the lithium phosphate product is 92.03%, and the main content is 98.79%.

[0082] Detect the charge-discharge performance of the sodium pyrophosphate iron phosphate product obtained in S4

[0083] The assembly method and test conditions of the coin cell are the same as those in Example 1, and will not be elaborated here.

[0084] It can be seen from Figure 13 that the sodium iron pyrophosphate recovered by this method has electrochemical activity when assembled into a button battery, and has a specific capacity of 90.99 mA·h / g at 0.1C.

[0085] Comparative Example 1

[0086] Different from Example 1, a method for producing sodium iron pyrophosphate by displacing lithium iron phosphate black powder and extracting lithium. In S1, 100.01 g of LiFePO4 black powder and 400.02 g of Na2SO4 were dispersed in anhydrous ethanol, and the other steps were exactly the same as those in Example 1.

[0087] By performing XRD tests on the sodium iron pyrophosphate product obtained in S4 and the lithium phosphate product obtained in S6, the test results are shown in Tables 1 and 2.

[0088] Comparative Example 2

[0089] Different from Example 1, a method for producing sodium iron pyrophosphate by displacing lithium iron phosphate black powder and extracting lithium. In S1, the ball milling speed was 1000 r / min. The other steps were exactly the same as those in Example 1.

[0090] By performing XRD tests on the sodium iron pyrophosphate product obtained in S4 and the lithium phosphate product obtained in S6, the test results are shown in Tables 1 and 2.

[0091] Comparative Example 3

[0092] Different from Example 1, a method for producing sodium iron pyrophosphate by displacing lithium iron phosphate black powder and extracting lithium. In S5, 20% wt (NH4)3PO4 was slowly added to the lithium salt filtrate obtained in S2 until the solution pH reached 13. The other steps were exactly the same as those in Example 1.

[0093] By performing XRD tests on the sodium iron pyrophosphate product obtained in S4 and the lithium phosphate product obtained in S6, the test results are shown in Tables 1 and 2.

[0094] Comparative Example 4

[0095] Different from Example 1, a method for producing sodium iron pyrophosphate by displacing lithium iron phosphate black powder and extracting lithium. In S4, 20% wt (NH4)3PO4 was slowly added to the lithium salt filtrate obtained in S2 until the solution pH reached 7. The other steps were exactly the same as those in Example 1.

[0096] By performing XRD tests on the sodium iron pyrophosphate product obtained in S4 and the lithium phosphate product obtained in S6, the test results are shown in Tables 1 and 2.

[0097] Table 1

[0098]

[0099]

[0100] Table 2

[0101]

[0102] The above are only embodiments of the present invention. Specific technical solutions and / or common knowledge such as characteristics well known in the art are not described in detail herein. It should be noted that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application should be subject to the content of its claims, and the specific implementation manners described in the specification can be used to interpret the content of the claims.

Claims

1. A method for producing sodium iron pyrophosphate from lithium iron phosphate black powder and extracting lithium, characterized in that: The following steps are involved: S1: Weigh a certain amount of lithium iron phosphate black powder and sodium source respectively, disperse them in anhydrous ethanol to form a mixed solution, and then perform a ball milling operation on the mixed solution to obtain a solid powder; S2: dissolving the solid powder obtained in S1 in an appropriate amount of pure water, heating and stirring for a period of time, and then filtering to obtain sodium iron phosphate and lithium salt filtrate; S3: washing the sodium iron phosphate obtained in S2 and then drying it; S4: adding sodium pyrophosphate to the sodium iron phosphate obtained in S3 and calcining the mixture at a high temperature in an inert atmosphere to obtain a sodium iron pyrophosphate product; S5: at a certain temperature, adding ammonium phosphate to the lithium salt filtrate obtained in S2 until the pH of the solution is 8-12, keeping the temperature for a period of time, and then filtering to obtain a lithium phosphate filter cake; S6: washing the lithium phosphate filter cake obtained in S5, and then drying it to obtain a lithium phosphate product.

2. A method for producing sodium iron pyrophosphate and extracting lithium from lithium iron phosphate black powder by replacement according to claim 1, characterized in that: In S1, the sodium source is any one of NaNO3, Na2SO4, NaCl, CH3COONa and NaC2O4.

3. A method for producing sodium iron pyrophosphate and extracting lithium from lithium iron phosphate black powder by replacement according to claim 2, characterized in that: In S1, the mass ratio of the sodium source to the lithium iron phosphate black powder is (1-3):1; the amount of anhydrous ethanol added is 5% to 15% of the total mass of the sodium source and the lithium iron phosphate black powder.

4. A method for producing sodium iron pyrophosphate and extracting lithium from lithium iron phosphate black powder by replacement according to claim 3, characterized in that: In S1, vacuum ball milling is used, the ball milling speed is 500-800 r / min, and the ball milling time is 5-24 h.

5. A method for producing sodium iron pyrophosphate and extracting lithium from lithium iron phosphate black powder by replacement according to claim 4, characterized in that: In S2, water bath heating is adopted, the heating temperature is 40-90°C, and the heating stirring time is 0.5-5h.

6. A method for producing sodium iron pyrophosphate and extracting lithium from lithium iron phosphate black powder by replacement according to claim 5, characterized in that: In S3, the mass of pure water used for washing is 3-8 times the mass of sodium iron phosphate, and the number of water washings is 2-4 times.

7. A method for producing sodium iron pyrophosphate and extracting lithium from lithium iron phosphate black powder by replacement according to claim 6, characterized in that: In S3, the drying temperature is 40-100°C, and the drying time is 5-24h.

8. A method for producing sodium iron pyrophosphate and extracting lithium from lithium iron phosphate black powder by replacement according to claim 7, characterized in that: In S4, the molar ratio of sodium iron phosphate to sodium pyrophosphate is (1-5):

1.

9. A method for producing sodium iron pyrophosphate and extracting lithium from lithium iron phosphate black powder by replacement according to claim 8, characterized in that: In S4, the calcination temperature is 500-1000°C, and the calcination time is 2-10h.

10. A method for producing sodium iron pyrophosphate and extracting lithium from lithium iron phosphate black powder by replacement according to claim 9, characterized in that: In S5, the ammonium phosphate salt is any one of (NH4)2HPO4, NH4H2PO4, and (NH4)3PO4; the concentration of the ammonium phosphate salt is 10%-30%wt.

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