CN114318009B - Method for recovering lithium from lithium iron phosphate - Google Patents
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Abstract
The invention discloses a method for recovering lithium from lithium iron phosphate, which comprises the following steps: s1, leaching lithium iron phosphate powder with heteropoly acid solution; s2, adding a precipitator into the leachate obtained in the step S1 to precipitate iron, and then carrying out solid-liquid separation; and S3, carrying out electrolysis treatment on the clear liquid obtained in the step S2, and obtaining a lithium-containing solution in a cathode chamber subjected to the electrolysis treatment, wherein the heteropoly acid solution comprises at least one of a phosphotungstic acid solution, a phosphomolybdic acid solution, a silicotungstic acid solution and a silicomolybdic acid solution. The method utilizes the heteropoly acid as a redox reaction medium, can recycle the heteropoly acid, and can solve the problems of long time consumption, low electric energy utilization rate and the like and the problem of high consumption of acid and oxidant in the prior art.
Description
Technical Field
The invention belongs to the technical field of waste material resource recycling, and particularly relates to a method for recycling lithium from lithium iron phosphate.
Background
Lithium iron phosphate (LiFePO)4) The high-power energy storage battery has the advantages of high theoretical capacity, theoretical energy density, high working voltage, excellent safety, low cost, no toxicity and the like, and is widely applied to the fields of electric automobiles and energy storage. Due to the rapid development of new energy industry, the scrappage of lithium iron phosphate batteries will increase rapidly in the future, and the large amount of stacked waste batteries not only greatly wastes resources, but also has great threat to the environment by potential fluorine-containing components (electrolyte). However, the lithium iron phosphate contains low value-added substances except lithium. Therefore, development of low-cost LiFePO4The high-efficiency lithium extraction technology of the anode material has important significance.
Hydrometallurgy prefers to leach lithium in acidic media by addition of oxidants and form FePO by controlling acidity4Precipitating, namely, decommissioning LiFePO4Conversion to FePO4. In addition to using inorganic acids as leaching agents, organic acids such as citric acid, succinic acid, malic acid, aspartic acid, oxalic acid, and the like can achieve complete dissolution by complexation with transition metal ions, and leaching efficiency depends on parameters such as acid concentration, temperature, reaction time, and solid-to-liquid ratio. It has been reported that the compounds are produced by Na2S2O8And H2O2By redox reaction of (3), LiFePO4Can be converted into FePO4And Li+Description of the Oxidation Process on waste LiFePO4Is of critical importance. However, a large amount of acid and oxidant such as H are needed to achieve the desired leaching effect, the acid concentration is between 1.0 and 3.0M2O2It is required to be 2 to 6 vol%. The precise recovery of the target metal by a large amount of acid or oxidizing agent is practically ineffective, and the unreacted acid or oxidizing agent eventually flows into the waste water, causing secondary pollution and increasing the cost of the recovery process. Therefore, the balance between the simplification of the recovery process and the saving of chemicals/energy consumption should be fully considered to achieve efficient, green recovery of the scrap metal. There have also been some studies showing that the electrochemical oxidation by pulp electrolysis can effectively promote the oxidation of lithium iron phosphate and the leaching of lithium, and avoid the addition of oxidant, but pulp electrolysis usually requires more than 6h because of the higher pulp viscosity and the lower reactivity of solid particles on the electrode surface.
Therefore, the method for rapidly extracting lithium from waste lithium iron phosphate is urgent at present, and can solve the problems of long time consumption, low electric energy utilization rate, large acid and oxidant consumption and the like in the prior art.
Disclosure of Invention
The present invention has been made to solve at least one of the above-mentioned problems occurring in the prior art. Therefore, the invention provides a method for recovering lithium from lithium iron phosphate, which is characterized in that heteropolyacid is matched with electrolysis treatment; on one hand, the purity and the recovery rate of the obtained lithium are high, on the other hand, no oxidant is required to be added additionally, the heteropoly acid can be recycled, and the consumption of the acid and the oxidant is obviously reduced.
According to one aspect of the present invention, there is provided a method of recovering lithium from lithium iron comprising the steps of:
s1, leaching lithium iron phosphate powder with heteropoly acid solution;
s2, adding a precipitator into the leachate obtained in the step S1 for iron precipitation treatment and then carrying out solid-liquid separation;
s3, carrying out electrolysis treatment on the clear liquid obtained after separation in the step S2, and obtaining a lithium-containing solution in a cathode chamber of the electrolysis treatment;
the heteropoly acid solution comprises at least one of a phosphotungstic acid solution, a phosphomolybdic acid solution, a silicotungstic acid solution and a silicomolybdic acid solution.
In the method provided by the invention, the mechanism is explained as follows:
in step S1: the heteropolyacid usually has acidity and oxidizability simultaneously, so that the lithium iron phosphate can be leached without adding an additional oxidant, and the heteropolyacid is converted from an oxidation state to a reduction state in the leaching process. The obtained leaching solution contains reduction heteropolyacid, lithium ions and iron ions;
in step S2: after the iron precipitation treatment, the iron is recovered in the form of solid compounds, and the participating clear liquid contains reduced heteropoly acid and lithium ions;
in step S3: when the clear liquid is electrolyzed, the reduced heteropoly acid in the anode chamber loses electrons and is converted from a reduced state to an oxidized state; li+Enrichment to the cathode chamber.
The method for recovering lithium from lithium iron phosphate has the following beneficial effects:
the heteropolyacid adopted by the invention has acidity and oxidizability, so that the lithium iron phosphate can be leached, an oxidant does not need to be additionally added, and the use amounts of the oxidant and the acid can be saved; by utilizing the electrolytic treatment, the lithium recovery effect is achieved, the heteropolyacid regeneration effect is achieved, the electric energy is saved, and the regenerated heteropolyacid is recycled, so that the acid consumption is reduced again.
In some embodiments of the present invention, the lithium iron phosphate powder in step S1 includes at least one of a mill tail and a retired power cell regrind.
In some embodiments of the invention, the retired power battery regrind includes at least one of a binder, a conductive agent, and an electrolyte in addition to the lithium iron phosphate powder.
In some embodiments of the present invention, the method further comprises pre-treating the lithium iron phosphate powder before step S1.
In some embodiments of the invention, the pre-treatment comprises washing the lithium iron phosphate powder with an organic solvent in step S1.
The organic solvent includes at least one of ethanol, styrene, triethanolamine, and N-methylpyrrolidone (NMP).
In some preferred embodiments of the present invention, the organic solvent comprises N-methylpyrrolidone.
In some embodiments of the present invention, the solid-to-liquid ratio of the lithium iron phosphate powder to the organic solvent is 50 to 1000 g/L.
In some embodiments of the present invention, the pre-treatment comprises washing the lithium iron phosphate powder with the organic solvent 2 to 4 times.
In some embodiments of the invention, the time period of each cleaning is 2-3 h.
The binder, the conductive agent and the electrolyte (fluorine-containing electrolyte) can be removed by cleaning with the organic solvent.
In some embodiments of the present invention, the temperature of the organic solvent washing is 60 to 70 ℃.
In some embodiments of the present invention, the pre-treatment further comprises, after the organic solvent washing, washing the obtained lithium iron phosphate powder with water.
In some embodiments of the invention, the solid-to-liquid ratio of the lithium iron phosphate powder to water is 50 to 1000 g/L.
In some embodiments of the present invention, the pre-treatment further includes washing the obtained lithium iron phosphate powder with water 1 to 2 times after the organic solvent is washed.
In some preferred embodiments of the present invention, in step S1, the heteropoly acid solution includes at least one of a phosphotungstic acid solution, a phosphomolybdic acid solution, a silicotungstic acid solution, and a silicomolybdic acid solution.
In some preferred embodiments of the present invention, in step S1, the heteropoly acid solution is a phosphomolybdic acid solution.
And mixing the lithium iron phosphate powder and the phosphomolybdic acid solution at normal temperature, and reacting to obtain the leaching solution containing Li and Fe. Precipitating iron by adding a precipitator, and then adding Li in filtrate+Under the action of an electric field, the phosphorus and the molybdenum are transferred to a cathode chamber to be recovered in a LiOH form, and electrons obtained by the reduced phosphomolybdate radical on the anode side are oxidized to be in an initial state. The method has the advantages of high reaction speed, high phosphomolybdic acid regeneration efficiency, high lithium recovery rate of over 99 percent and high iron content in the lithium-containing solution<1 percent, the regenerated phosphomolybdic acid can continuously react with the lithium iron phosphate raw material, the leaching effect is not reduced, and the circulation is realized.
In some embodiments of the present invention, in step S1, the concentration of the heteropoly acid solution is 50 to 500 mmol/L.
In some preferred embodiments of the present invention, in step S1, the concentration of the heteropoly acid solution is 150 mmol/L.
Too low a concentration of the heteropolyacid solution is insufficient to completely react the lithium iron phosphate powder, and too high a concentration may result in waste of the heteropolyacid solution.
In some preferred embodiments of the present invention, in step S1, the pH of the heteropoly acid solution is 1-2.5.
In some preferred embodiments of the present invention, in step S1, the pH of the heteropoly acid solution is 2.
The pH of the solution depends on the concentration of the heteropoly acid. When the pH value is too low, the concentration of the heteropoly acid is proved to be too high, and the waste of the heteropoly acid can be caused by the too high concentration; meanwhile, the structure of heteropoly acid is damaged by the over-high pH of heteropoly acid solution, so that the oxidability is weakened, and the heteropoly acid solution can not completely react with lithium iron phosphate powder.
In some embodiments of the present invention, in step S1, the molar ratio of the heteropoly acid in the heteropoly acid solution to the lithium iron phosphate powder is 1: 1 to 10.
The LiFePO4 content (moles) in the lithium iron phosphate powder was calculated based on ICP test data (Li, Fe, P content) and thermogravimetric data (carbon content).
In some preferred embodiments of the present invention, in step S1, the molar ratio of the heteropoly acid in the heteropoly acid solution to the lithium iron phosphate powder is 1: 2.
the LiFePO4 content (moles) in the lithium iron phosphate powder was calculated based on ICP test data (Li, Fe, P content) and thermogravimetric data (carbon content).
In some embodiments of the present invention, in step S1, the leaching time is 1-10 min.
In some preferred embodiments of the present invention, in step S1, the leaching time is 2 min.
Phosphomolybdic acid (H)3PMo12O40PMA) solution initially exhibits a yellow color (oxidation state) and its oxidation results from its anionic PMo12O40 3-The color of the hexavalent Mo in the alloy is derived from spherical Keggin structure anions (the heteropolyacid is in a classical structure and is spherical, the ratio of central atoms to hetero atoms is 1: 12, and the hexavalent Mo is named by the name of Keggin); lithium iron phosphate powder was added to the heteropoly acid solution at different molar ratios and the mixture was observed to immediately turn from yellow to dark blue. During the transition of PMA from the oxidized state to the reduced state, electrons are transferred from the reducing agent (LiFePO) via the O-Mo ligand-to-metal charge-transfer (O-Mo ligand-to-metal charge-transfer) pathway4) Is transferred to hexavalent Mo, with the result that part of Mo on the spherical structure6+Is reduced to Mo5+And the solution gradually changes from yellow to blue due to the change of the absorption of natural light wavelength of Keggin structural anions.
When the solute of the heteropoly-acid solution is phosphomolybdic acid, the reaction in step S1 includes the equation shown in formula (1):
2H++PMo12O40 3-(yellow) +2LiFePO4→2Li++PMo12O40 5-(blue) + Fe3++H2PO4 -+FePO4（1）。
In some embodiments of the present invention, in step S2, the precipitant includes at least one of a lithium hydroxide solution, a lithium phosphate solution, a lithium monohydrogen phosphate solution, and a lithium dihydrogen phosphate solution.
In some embodiments of the present invention, in step S2, the concentration of the precipitant is 100-500 mmol/L.
In some preferred embodiments of the present invention, in step S2, the precipitant has a concentration of 150 mmol/L.
The low concentration of the precipitating agent is not enough to completely precipitate Fe, and the high concentration can destroy the structure of the heteropoly acid solution and influence the regeneration of the heteropoly acid solution.
In some embodiments of the invention, in step S2, the time for depositing iron is 10-15 min.
In some embodiments of the present invention, in step S2, the molar ratio of the lithium iron phosphate raw material to the precipitant is 1: 0.15 to 0.45.
In some embodiments of the present invention, in step S2, the PH of the filtrate after the solid-liquid separation is 2 to 5.
The filtrate is related to the amount of precipitant added. The precipitation rate of Fe varies at different pH.
In some embodiments of the invention, in step S3, the electrolytic process is performed in an electrolytic cell.
In some embodiments of the invention, in step S3, the electrolytic cell includes an anode chamber, a cathode chamber, and a cation exchange membrane disposed between the anode chamber and the cathode chamber.
In some embodiments of the invention, the cation exchange membrane comprises at least one of HoCM G-0014, Nafion 117 proton exchange membrane, a wawter electrophoresis cell membrane.
In some preferred embodiments of the present invention, in step S3, the cation exchange membrane is HoCM G-0014.
In some embodiments of the invention, step S3 includes pumping a concentration of LiOH solution into the cathode chamber.
In the invention, the LiOH solution is added into the cathode chamber to increase the conductivity of the catholyte and reduce the overpotential of electrolysis on one hand; on the other hand, the purity of the LiOH product is improved.
In some embodiments of the invention, in step S3, the electrolytic cell further comprises an anode disposed within the anode chamber.
In some embodiments of the invention, in step S3, the electrolytic cell further comprises a cathode disposed within the cathode chamber.
In some embodiments of the invention, the anode and cathode are each individually selected from carbon felt electrodes.
In some embodiments of the present invention, in step S3, the voltage of the electrolysis process is 1.5-2.5V.
In some preferred embodiments of the present invention, in step S3, the voltage of the electrolytic process is 2V.
In some embodiments of the present invention, in step S3, the time of the electrolytic treatment is 2 to 60 min.
In some preferred embodiments of the present invention, in step S3, the time of the electrolytic treatment is 2 to 30 min.
In some preferred embodiments of the present invention, in step S3, the time of the electrolytic treatment is 2 min.
Drawings
The invention is further described with reference to the following figures and examples, in which:
FIG. 1 is a CV curve (sweep rate: 50 mV s) of PMA solution at pH =2.0 of test example 1-1）。
Fig. 2 shows the leaching rates of Li, Fe, and P elements and the pH change of the leachate at different ratios of lithium iron phosphate/phosphomolybdic acid in step a2 of example 1.
FIG. 3 is the XRD pattern of the residue from step A3 of example 1.
FIG. 4 is an electrolytic photograph of an anolyte solution (phosphomolybdic acid solution) at a constant pressure of 2V in step A4 of example 1.
FIG. 5 shows the change in the concentration of Li in the cathode chamber in step A4 in example 1.
Detailed Description
The concept and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments to fully understand the objects, features and effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive effort based on the embodiments of the present invention, and all embodiments are within the protection scope of the present invention.
The concept and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments to fully understand the objects, features and effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and other embodiments obtained by those skilled in the art without inventive efforts are within the protection scope of the present invention based on the embodiments of the present invention.
Example 1:
a1, mixing 100 g of lithium iron phosphate waste (the lithium iron phosphate waste consists of 70% of lithium iron phosphate, 5% of binder PVDF, 17.5% of carbon, 6% of electrolyte, 0.8% of metal copper scraps and 0.7% of aluminum scraps) with 100 mL of NMP (N-methyl pyrrolidone), stirring for 2 h at 60 ℃, repeatedly washing filter residues for 2 times under the above conditions after filtering, then washing the obtained solid for 1 time at normal temperature by 100 mL of deionized water, and drying the obtained solid to obtain a lithium iron phosphate raw material (the processed lithium iron phosphate waste consists of 84.1% of lithium iron phosphate, 1% of binder PVDF, 14% of carbon and 0.9% of electrolyte);
a2, adding 200mmol of phosphomolybdic acid (PMA) into 500 ml of deionized water, stirring and dissolving to obtain a leaching solution, wherein the leaching solution is yellow and has the pH value of 2; 52.6g (400 mmol) of lithium iron phosphate raw material (LFP) was added to the leachate, and it was observed that the leachate immediately changed from yellow to dark blue, and the filtrate was stirred at room temperature for 2min and then filtered. According to ICP analysis of the filtrate (fig. 2, the dotted line indicates that the leaching rates of Li, Fe, and P elements change with the molar ratio of lithium iron phosphate/phosphomolybdic acid, and the solid line indicates that the pH of the filtrate changes), when the amount of lithium iron phosphate added was 52.6g (400 mmol, n (LFP/PMA =2: 1)), the leaching rate of Fe was 22.4%, and the leaching rate of Li reached 99%.
A3, adding 75 mmol of lithium phosphate into the leachate (n (LFP/PMA =2: 1)) filtered in the step A2, stirring and reacting for 10min, and filtering to obtain filter residue and filtrate, wherein the pH value of the filtrate is 4.2; according to the ICP analysis of the filtrate (Table 1), Li was added3PO4After 10min, the content of Fe in the filtrate is reduced to 0.4%; according to XRD analysis of the residue (FIG. 3), the residue is mainly FePO4And (4) phase(s). The reaction equations are shown in formulas (2) and (3).
TABLE 1 ICP test result of Fe element in filtrate
A4, taking the filtrate obtained in the step A3, pumping the filtrate into an anode chamber of the electrolytic cell, pumping LiOH solution with certain concentration into a cathode chamber, and applying a constant voltage of 1.5V between the cathode and the anode; the cathode and the anode of the electrolytic cell both adopt carbon felt electrodes, and the membrane adopts a HoCM G-0014 cation exchange membrane. During electrolysis, the anode side PMoV 2MoVI 10O40 5-The anion losing electrons at the electrode, PMA Red Gradual transition from reduced to oxidized PMA ox The solution changed color from green to yellow as shown in equation (4). The basis for judging the completion of phosphomolybdic acid oxidation is as follows: the filtrate on the anode side is completely changed from dark blue to yellow and does not change color within 2min, and the electrolysis time is 30min when the voltage is 1.5V; according to the ICP test result, after 30min, Li is completely transferred to the cathodeSide (with LiOH, Li being deducted)3PO4As shown in fig. 5). The Li mobility was calculated as:
η=(cv-ma-mb)/mc；
wherein c represents the Li + concentration (mg/L) measured by ICP; v represents the volume (L) of the solution to be tested; m isa，mb，mcEach represents Li3PO4LiOH and Li leached in A2+Mass (mg).
PMo12O40 5-(blue) -2e- → PMo12O40 3-(yellow) (4);
example 2
In this example, the voltage in step a4 of example 1 was changed to 1.8v, and the other conditions were kept unchanged.
The basis for judging the completeness of phosphomolybdic acid oxidation in step A4 of example 2 is: the filtrate on the anode side changed from dark blue to yellow completely and did not change color within 2 min. When the voltage was 1.8V, the electrolysis time was 8 min, and Li had completely migrated to the cathode side.
Example 3
In this example, the voltage in step a4 in example 1 was changed to 2.0v, and the other conditions were kept unchanged.
The basis for judging the completeness of phosphomolybdic acid oxidation in step A4 of example 3 is: the filtrate on the anode side changed from dark blue to yellow completely and did not change color within 2min, and the test result is shown in fig. 4, when the voltage was 2V, the electrolysis time was 2min, and Li had completely migrated to the cathode side.
Example 4
This example provides a method for recovering lithium from lithium iron phosphate, in which phosphomolybdic acid was replaced with phosphotungstic acid (H) in example 33PW12O40PWA), keeping other conditions unchanged, and the specific process is as follows:
A1. adding 200mmol of phosphomolybdic acid (PMA) into 500 ml of deionized water, and stirring and dissolving to obtain a leaching solution; adding 52.6g of lithium iron phosphate raw material (400 mmol, n (LFP/PMA =2: 1)), stirring at room temperature for 2min, and filtering to obtain filtrate 1;
A2. taking the filtrate 1 in A1, adding 75 mmol of lithium phosphate into the filtrate, uniformly stirring the mixture, reacting the mixture for 10min, and filtering the mixture to obtain a filtrate 2;
A3. taking the filtrate 2 in the A2, pumping the filtrate into an anode chamber of an electrolytic cell, pumping LiOH solution with certain concentration into a cathode chamber, electrolyzing for 2min at a constant voltage of 2V, recovering anolyte and testing the mobility of element Li in the catholyte 3;
A4. to the anolyte in a3, 52.6g of a lithium iron phosphate raw material was added to obtain filtrate 4 and the leaching rate of element Li was tested.
And diluting the filtrate 1, the filtrate 2, the catholyte 3 and the filtrate 4 by 100 times, and then carrying out an ICP-OES test. The leaching rates of Li and Fe elements in the filtrate 1 are respectively 75.2% and 14.9%; the leaching rate of Fe in the filtrate 2 is reduced to 0.6 percent; the mobility of Li in the catholyte 3 is 98%; the leaching rates of Li and Fe elements in the filtrate 4 are respectively 63.1% and 8.6%.
The redox sequence of a common heteropolyacid is as follows: phosphomolybdic acid > silicomolybdic acid > phosphotungstic acid > silicotungstic acid. The iron lithium phosphate is leached by using the oxidation of the heteropoly acid, and the oxidability of the heteropoly acid is an important measurement standard. The leaching effect of the phosphomolybdic acid is better because the phosphomolybdic acid is more oxidizing. This also explains the difference in Li leaching solutions at the same molar ratio. After phosphomolybdic acid is replaced by phosphotungstic acid, the Li leaching rate in the filtrate 1 is reduced.
Test example 1
The present test example tested the reaction between phosphomolybdic acid regenerated in the anode chamber in step a3 of example 1 and the lithium iron phosphate raw material.
And D, taking the anolyte obtained in the step A3, adding 52.6g of lithium iron phosphate raw material, and observing that the leachate immediately changes from yellow to dark blue. ICP analysis of the leachate is shown in tables 2 and 3.
TABLE 2 result of ICP test of Li element in leach solution
TABLE 3 ICP test result of Fe element in leachate
According to ICP analysis of the filtrate, the leaching process was completed when the reaction time was 2 min. The leaching rate of Li was 99.2%, and the leaching rate of Fe was 22.1%. Therefore, the regenerated phosphomolybdic acid can continuously react with the lithium iron phosphate raw material to realize circulation.
Adding 75 mmol of lithium phosphate into the leaching solution, uniformly stirring, reacting for 10min, and measuring that the content of Fe in the solution in the filtrate is reduced from 22.1% to 0.2%.
Test example 2
The test example tested a CV curve for a PMA solution at pH = 2.0.
Phosphomolybdic acid (H)3PMo12O40PMA) can theoretically oxidize lithium iron phosphate. As shown in FIG. 1, there are 4 pairs of distinct redox peaks in the CV curve of PMA solution, the peaks have good symmetry, indicating that PMA ox /PMA red The reversibility of the redox couple is good. FePO is known4/LiFePO4The oxidation-reduction potential is 3.4V vs (Li/Li)+) About 0.2V vs (Ag/AgCl), and the potential corresponding to the PMA redox peak is about 0.4V vs (Ag/AgCl) as indicated by the arrow in FIG. 1. Thus, theoretically, PMA can convert LiFePO4And (4) oxidizing. Also, since PMAox/PM Ared The PMA solution has good reversibility and can be regenerated by electrolysis.
The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention. Furthermore, the embodiments of the present invention and the features of the embodiments may be combined with each other without conflict.
Claims (9)
1. A method for recovering lithium from lithium iron phosphate is characterized by comprising the following steps:
s1, leaching lithium iron phosphate powder with heteropoly acid solution;
s2, adding a precipitator into the leachate obtained in the step S1 to precipitate iron, and then carrying out solid-liquid separation;
s3, carrying out electrolysis treatment on the clear liquid obtained in the step S2, and obtaining a lithium-containing solution in a cathode chamber of the electrolysis treatment;
the heteropoly acid solution comprises at least one of a phosphotungstic acid solution, a phosphomolybdic acid solution, a silicotungstic acid solution and a silicomolybdic acid solution.
2. The method according to claim 1, wherein in step S1, the concentration of the heteropoly acid solution is 50-500 mmol/L.
3. The method of claim 1, wherein the molar ratio of lithium iron phosphate powder to heteropolyacid is 1: 1 to 10.
4. The method according to claim 1, wherein in step S1, the leaching time of the heteropoly acid solution is 1-10 min.
5. The method of claim 1, wherein in step S2, the precipitant comprises at least one of a lithium hydroxide solution, a lithium phosphate solution, a lithium monohydrogen phosphate solution, and a lithium dihydrogen phosphate solution.
6. The method according to claim 1, wherein the molar ratio of the lithium iron phosphate powder to the amount of precipitant is 1: 0.5 to 3.
7. The method according to claim 1, wherein in step S2, the concentration of the precipitating agent is 30 to 300 mmol/L.
8. The method according to claim 1, wherein the voltage of the electrolytic treatment in step S3 is 1.5-2.5V.
9. The method according to claim 1, wherein in step S3, the time of the electrolytic treatment is 2-60 min.
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