Regenerated lithium iron phosphate active material, preparation and use thereof

Abstract

The application belongs to the field of waste electrode recycling, and particularly relates to regenerated lithium iron phosphate active material and preparation and application thereof, wherein the preparation method of the regenerated lithium iron phosphate active material comprises the following steps: heating aluminum chloride, ethylene glycol and a phosphoric acid-based additive to obtain a modified solution, mixing and leaching the modified solution and waste electrode material containing lithium iron phosphate to separate a leaching liquor rich in Li, P and Fe; adding formula 1 ( ), a surfactant into the leaching liquor and performing first-stage precipitation treatment under a first pH and light irradiation, and then performing second-stage precipitation treatment under a second pH to obtain an iron-formula 1 complex lithium phosphate precursor; and performing calcination treatment on the iron-formula 1 complex lithium phosphate precursor to obtain the regenerated lithium iron phosphate active material. The regenerated lithium iron phosphate prepared by the application has performance comparable to or even superior to that of newly prepared lithium iron phosphate, and has excellent fast charging and long cycle stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of battery waste recycling, and particularly relates to the field of waste lithium iron phosphate battery material recycling. BACKGROUND

[0002] Lithium iron phosphate batteries have the advantages of long cycle life, economic safety, etc., and have become one of the mainstream positive electrode materials of power batteries, and the market share is continuously expanding. The market share of lithium iron phosphate batteries is nearly 70%, and the conventional service life of lithium ion batteries is generally 5 to 8 years. When the battery reaches the end-of-life state, if it is not disposed of, it will have adverse effects on human health and the ecological environment, and it is urgent to develop an efficient and environmentally friendly recycling method.

[0003] At present, the recycling methods of lithium iron phosphate batteries mainly include fire method and wet method. Among them, the fire method realizes the separation of valuable metals and materials in waste lithium ion batteries by means of high-temperature pyrolysis, smelting and other heat treatment methods, but such process has high energy consumption and poor economic efficiency; the current wet method mainly uses acid to dissolve the positive electrode material, and then prepares iron phosphate through precipitation and calcination, but such process has a long process flow, strong corrosion of acid system, involves many acid systems, and it is difficult to further treat the waste liquid.

[0004] For example, the patent document with publication number CN118610625A discloses a recycling and regeneration method of waste lithium iron phosphate positive electrode material and application, which specifically records detecting the element content of the recycled material, adding lithium source, iron source, phosphorus source and carbon source according to the element content, using a small amount of Fe element-deficient ratio, and then grinding, spray drying, sintering, removing magnetism, airflow crushing and mixing to obtain carbon-coated lithium iron phosphate positive electrode regenerated material. The patent document with publication number CN118137000A discloses a repairing and regenerating method of waste lithium iron phosphate battery positive electrode material, which adds pretreated lithium iron phosphate battery positive electrode material powder, CNT / GO / phosphorus iron concentrated solution and dispersed lithium-rich additive cyclopiperazine into a planetary ball mill for ball milling, dries the ball-milled sample to obtain a dried precursor powder; the dried precursor powder is placed in a tube furnace for high-temperature calcination to obtain a repaired and regenerated lithium iron phosphate battery positive electrode material. The patent document with publication number CN114824546A discloses a method for recycling and regenerating waste lithium iron phosphate, which first calcines waste high-carbon lithium iron phosphate powder or lithium iron phosphate pole piece to obtain oxidized lithium iron phosphate; then coats and sinter the oxidized lithium iron phosphate with carbon source substances twice to obtain regenerated lithium iron phosphate / carbon composite material; wherein the carbon source substances in the first coating and sintering include lithium source, iron source, phosphorus source and carbon source 1, and the carbon source substances in the second coating and sintering include carbon source 2.

[0005] In summary, the prior art discloses some solid or liquid resource recycling preparation schemes of waste lithium iron phosphate materials to prepare regenerated lithium iron phosphate materials, which can obtain certain regenerated electrochemical performance, however, the preparation scheme of the regenerated lithium iron phosphate material is difficult to effectively optimize the structure and the selective utilization of trace elements, and it is also difficult to obtain fast charging and long cycle performance comparable to or even better than that of the newly prepared lithium iron phosphate material. SUMMARY

[0006] In view of the problems existing in the recovery of the positive electrode of the waste lithium iron phosphate battery, the first object of the present application is to provide a preparation method of regenerated lithium iron phosphate active material, which aims to prepare regenerated lithium iron phosphate material with excellent fast charging and long cycle performance based on waste lithium iron phosphate material.

[0007] The second object of the present application is to provide the regenerated lithium iron phosphate active material prepared by the preparation method.

[0008] The third object of the present application is to provide the application of the regenerated lithium iron phosphate active material.

[0009] The fourth object of the present application is to provide a lithium ion battery comprising the regenerated lithium iron phosphate active material, and a positive electrode material and a positive electrode thereof.

[0010] A preparation method of regenerated lithium iron phosphate active material, comprising the following steps:

[0011] Step 1: leaching

[0012] The aluminum chloride, ethylene glycol and phosphoric acid additive are heated to obtain a modified solution; the modified solution and the waste electrode material containing lithium iron phosphate are mixed and leached to obtain a leaching solution rich in Li, P and Fe;

[0013] The phosphoric acid additive comprises at least one of phosphoric acid and its water-soluble salt, hypophosphorous acid and its water-soluble salt, pyrophosphoric acid and its water-soluble salt, water-soluble monohydrogen phosphate, water-soluble dihydrogen phosphate, C3~C 10 phosphoric acid ester;

[0014] Step 2: step-by-step precipitation

[0015] Formula 1, a surfactant is added to the leaching solution of step 1, and a first-stage precipitation treatment is carried out under a first pH and light irradiation, and then a second-stage precipitation treatment is carried out under a second pH to obtain an iron-formula 1 complex lithium phosphate precursor;

[0016] Formula 1;

[0017] In formula 1, M is H + , Na + , K +or NH4 + ;

[0018] The first pH is 1.5-4.5;

[0019] The second pH is 6-8.5;

[0020] Step 3: calcination

[0021] The iron-form 1 complex-lithium phosphate precursor prepared in step 2 is subjected to calcination treatment to obtain the regenerated lithium iron phosphate active material.

[0022] The waste electrode material is innovatively immersed in the modified solution formed by the hydrogen bond and / or coordination of aluminum chloride-ethylene glycol-phosphoric acid-based additives, which is conducive to the extraction of Fe, P and Li therein, and also conducive to the selective retention of electrochemical trace components therein. Further, in combination with the subsequent special step-by-step precipitation mode, an element gradient distribution precursor with iron as the core and lithium phosphate coating on the surface can be constructed. The precursor is subjected to calcination treatment, which can optimize the regenerated core of lithium iron phosphate, improve the atomic level distribution, and optimize the crystal and grain structure by using trace beneficial components. Therefore, the regenerated lithium iron phosphate can exhibit performance comparable to or even superior to newly prepared lithium iron phosphate, for example, it can exhibit excellent fast charging and long cycle stability.

[0023] In step 1, the waste electrode material is obtained by peeling off the electrode from the waste lithium iron phosphate battery.

[0024] Further, the waste electrode material can also contain negative electrode materials.

[0025] In the present application, the content of the waste lithium iron phosphate battery positive electrode material is not particularly required. Considering the economy of the process, the content of the active material is preferably above 50 wt.%, further preferably above 80 wt.%, and more preferably 80-95 wt.%.

[0026] Preferably, the waste electrode material is subjected to wet ball milling treatment in advance, and the solvent for wet ball milling includes a mixed solvent of solvent a and solvent b, wherein the solvent a includes at least one of dimethyl sulfoxide, dimethyl acetamide, dimethyl propionamide, gamma-butyrolactone, and limonene; and the solvent b includes at least one of water and ethanol. The present application research shows that the preferred wet ball milling is helpful to further strengthen the fast charging and long cycle performance of the regenerated LFP.

[0027] The volume ratio of the solvent a and the solvent b is not particularly required, for example, it can be 1:0.1-10, and further can be 1:0.5-2.

[0028] In the present application, the aluminum chloride, ethylene glycol and phosphoric acid-based additives form a co-solvent system based on coordination and hydrogen bonding between the components. The present application shows that the modified solution formed by the components can effectively extract Fe, P and Li, and is conducive to the selective use of beneficial ingredients, and further conducive to the fast charging and long cycle performance of the regenerated lithium iron phosphate.

[0029] In the present application, the phosphoric acid ester can be at least one of a monoester, a diester and a triester of phosphoric acid. The number of carbons in the phosphoric acid ester can be less than 10.

[0030] As an optional solution, in step 1, the phosphoric acid-based additive is at least one of phosphoric acid, phenylphosphonic acid, tributylphosphine, hypophosphorous acid.

[0031] Preferably, the aluminum chloride is aluminum chloride hexahydrate.

[0032] Preferably, the weight ratio of the aluminum chloride, ethylene glycol and phosphoric acid-based additive is 1:1~10:0.1~0.5; further can be 1:2~4:0.15~0.2. With the preferred ratio, the leaching behavior is optimized, the beneficial ingredients are selectively retained, and the fast charging and long cycle performance of the regenerated material are further improved.

[0033] Preferably, the heating temperature in step 1 is 25℃~90℃; further can be 45~85℃.

[0034] The heating time in step 1 can be 0.5h~5h; further can be 2~4h.

[0035] The liquid-solid ratio of the leaching process is controlled at 10~100ml / g; considering the cost, it can be further 30~50ml / g.

[0036] Preferably, the leaching temperature is 15~60℃; further can be 20~55℃.

[0037] Preferably, the leaching time is more than 1h, preferably 2~30h.

[0038] The surfactant is at least one of a cationic surfactant, an anionic surfactant and a neutral surfactant; for example, the surfactant is at least one of polyvinylpyrrolidone, polyethylene glycol, polyacrylamide, cetyltrimethylammonium bromide, sodium dodecyl sulfate, fatty alcohol polyoxyethylene ether, polysorbate and Span.

[0039] Preferably, the molar ratio of Fe to formula 1 in the leaching solution is 1:2~10, further can be 1:4~6; the weight ratio of iron to surfactant is 1:0.05~0.5, further can be 1:0.1~0.3.

[0040] The first pH can be regulated based on conventional means, for example, the pH of the system can be regulated by ammonia, diammonium hydrogen phosphate, calcium oxide.

[0041] Preferably, the first pH is 2-4; more preferably, 2-2.5.

[0042] Preferably, the power of the light source for light irradiation is 300-800 W, more preferably, 400-600 W.

[0043] Preferably, the time for light irradiation is 20-120 min, more preferably, 25-75 min, and more preferably, 30-60 min.

[0044] The second precipitation process also adds a buffer, wherein the buffer includes at least one of sodium dihydrogen phosphate-citric acid buffer, tris(hydroxymethyl)aminomethane-hydrochloric acid buffer, and ammonia-ammonium chloride buffer. In the present application, the buffer is added to perform the second precipitation process, which is conducive to constructing the precursor material with the coating structure and the element gradient distribution, and thus is more conducive to preparing the material with excellent fast charging and long cycle stability.

[0045] The initial pH of the buffer is not particularly limited, for example, it can be 7.2-8.5.

[0046] Preferably, the second precipitation process is carried out under positive pressure. In the present application, the second precipitation process is carried out under pressure, which is helpful to further optimize the element gradient distribution in the precursor material, and is more conducive to the fast charging and long cycle performance of the prepared regenerated LFP material.

[0047] The second pH is 7-8.5, and more preferably, 7.5-8.

[0048] Preferably, the temperature of the second precipitation process is 45-70℃.

[0049] In the present application, the time for the second precipitation can be reasonably adjusted as needed, for example, it can be 1-5 h.

[0050] In step 3, the molar ratio of Li, Fe, and P in the iron-form 1 complex lithium phosphate precursor is regulated to 1.05-1.10:1:1, and then a calcination process is performed to obtain the regenerated lithium iron phosphate active material.

[0051] In the present application, the raw materials used for regulating Li, Fe, and P can be raw materials known in the industry, for example, the lithium source can be one of lithium hydroxide, lithium phosphate, lithium nitrate, lithium acetate, and lithium carbonate. The iron source can be ferrous oxalate. The phosphorus source can be at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and lithium phosphate.

[0052] Preferably, the iron-form 1 complex lithium phosphate precursor with Li, Fe, P molar ratio and the carbon source are mixed and then subjected to calcination treatment.

[0053] Preferably, the calcination process comprises a three-stage gradient calcination process, which comprises a first-stage calcination process at a temperature of 300-400℃, a second-stage calcination process at a temperature of 500-650℃, and a third-stage calcination process at a temperature of 600-700℃.

[0054] Preferably, the calcination process is carried out in a protective atmosphere, such as at least one of nitrogen and a noble gas.

[0055] Preferably, the holding time of the first-stage calcination, the second-stage calcination and the third-stage calcination is 0.5-5h, respectively.

[0056] For example, the holding time at the first-stage calcination temperature is 1-3h, the holding time at the second-stage calcination temperature is 2-5h, and the holding time at the third-stage calcination temperature is 0.5-1h.

[0057] Preferably, a positive pressure pretreatment is carried out before the calcination, wherein the pressure of the positive pressure pretreatment is 1.5-5 MPa, the temperature is 150-250℃, and the time is 1-8h, and further can be 2-4h. Studies have shown that the fast charging and long-term stability of the prepared regenerated LFP can be further enhanced by pretreating the precursor material by the positive pressure pretreatment and then carrying out the subsequent calcination treatment.

[0058] The application further provides a regenerated lithium iron phosphate active material prepared by the preparation method.

[0059] The application further provides an application of the regenerated lithium iron phosphate active material prepared by the preparation method, which is used as a positive active material to prepare a lithium ion battery.

[0060] The application further provides a lithium ion battery comprising the regenerated lithium iron phosphate active material.

[0061] Advantages

[0062] The present application is based on the special modified solution for leaching the waste lithium iron phosphate, and further cooperating with the special two-stage precipitation process, the iron-form 1 complex lithium phosphate precursor with core-shell structure can be obtained, and the gradient distribution of lithium is promoted. The unique structure promotes the sufficient Li3PO4 outside the precipitate, and under the subsequent high-temperature pressurization and room temperature annealing process, a lithium-rich LiFePO4 layer is first formed on the outside of the particle, then Li diffuses from the outside to the inside to react, and a state of incomplete lithium diffusion is produced, so that the outside of the particle is slightly lithium-rich LiFePO4, and the lithium concentration gradually decreases towards the inside of the particle, forming a lithium concentration gradient from the outside to the inside. In addition, the process is also beneficial to the characteristics of the waste material, and can selectively retain the beneficial trace components therein, which is beneficial to the further modification of the material.

[0063] The process not only realizes the green recovery of waste lithium iron phosphate battery, but also realizes the upgrading and reconstruction from waste material to high-performance material through ingenious material design, and the electrochemical performance of the prepared gradient material exceeds that of the commercial material, especially the high first coulomb efficiency, 5C fast charging performance and long cycle characteristics of the material.

[0064] In the present application, the second stage precipitation is carried out under a buffer system, further cooperating with the positive pressure auxiliary precipitation and the positive pressure treatment before sintering, which is helpful to further improve the interface characteristics of the material and further improve the performance of the prepared regenerated material. BRIEF DESCRIPTION OF DRAWINGS

[0065] Figure 1 SEM graph of black powder before treatment in Example 1;

[0066] Figure 2 XRD graph of black powder before treatment in Example 1;

[0067] Figure 3 SEM graph of regenerated lithium iron phosphate prepared in Example 1;

[0068] Figure 4 TEM graph of regenerated lithium iron phosphate prepared in Example 1;

[0069] Figure 5 XRD graph of regenerated lithium iron phosphate prepared in Example 1;

[0070] Figure 6 First circle charge-discharge curve of regenerated lithium iron phosphate prepared in Example 1. DETAILED DESCRIPTION

[0071] As an optional solution, in the following case, the lithium iron phosphate black powder used is a mixed powder (also known as black powder, whose SEM is shown in FIG. 1) obtained by discharging, disassembling the positive electrode and negative electrode of the waste lithium iron phosphate battery, and mechanically crushing, and then simply screening to remove most of the current collector without fine sorting.Figure 1 XRD see Figure 2 The mass percentage of the main components is as follows: Li 4.2%, Fe 31.16%, Cu 1.78%, P 17.89%, Al 3.49%, Ni 0.1%, Mg 0.1%.

[0072] Example 1

[0073] Step 1 pretreatment:

[0074] Take 50 g of lithium iron phosphate black powder into a ball mill tank, add 20 ml of a mixed solution of dimethyl sulfoxide and water (volume ratio of dimethyl sulfoxide to water is 1:1), and ball mill at a speed of 400 rpm for 30 min, stopping every 10 min and standing for 5 min to cool. After ball milling, take out and wash with deionized water and ethanol alternately for three times, and dry in an oven.

[0075] Step 2 configuration of modification solution:

[0076] Weigh 8.35 g of aluminum chloride hexahydrate, take 16.70 g of ethylene glycol, and 1.25 g of phosphoric acid additive (phosphoric acid), and place them in a 50 mL beaker. Heat in a water bath to a clear and transparent modification solution. The heating time is 2 h and the heating temperature is 80°C;

[0077] Step 3 leaching:

[0078] Take 0.5 g of lithium iron phosphate black powder treated in step 1 and place it in 15 ml of the above modification solution. Stir in an air-tight manner to make the lithium iron phosphate black powder react with the modification solution, and leach lithium and iron. The stirring time is 24 h and the stirring temperature is 25°C. Then filter to obtain a leaching solution (filtrate 1), wherein the leaching rate of valuable metals is Fe 96.67% and Li 96.85%.

[0079] Step 4 stepwise precipitation:

[0080] Step 4a: first step deposition:

[0081] To the filtrate 1, dropwise add a solution of formula 1A (formula 1 with M being H) with a concentration of 1 mol / L until the molar amount of formula 1A is 5 times the molar amount of iron ions. At the same time, dropwise add a polyethylene glycol solution until the mass of polyethylene glycol is 0.1 times the mass of iron ions. After mixing evenly, add concentrated ammonia water to the solution to adjust the pH to 4, pour into a quartz colorimetric cell and place on a magnetic stirrer, irradiate under a xenon lamp (power is 500 W) for 30 min, and let the reacted mixture stand at room temperature for 2 h;

[0082] Step 4b: second step deposition:

[0083] Subsequently, a buffer system (ammonia and ammonium chloride, pH 8.25) was added to the solution of step 4a after standing for 2 h, the pH of the system was controlled at 7.5, the solution was poured into a flask, argon was introduced into the flask, the pressure in the flask was kept at 1.5 MPa, the temperature was 60°C, and the time was 2 h. The gas was introduced until the dispersed fine particles grew and the color changed to white, and the liquid part of the system was clarified. Subsequently, the obtained solution was centrifuged at 10000 rpm for 5 min to separate the filtrate and the filter residue (precursor material of the coating structure);

[0084] Step 5 two-stage regenerated lithium iron phosphate:

[0085] Step 5a: adjust the molar ratio of Li, Fe, and P in the filter residue obtained in step 4b to 1.05:1:1, and react with glucose (10wt% of the total weight of lithium source, iron source, and phosphorus source) in a high-pressure kettle under an argon atmosphere, 3 MPa, and 200°C for 3 h. After taking out, washing with water and anhydrous ethanol three times, and drying and grinding.

[0086] Step 5b: Put the ground material of step 5a into a tube furnace, heat at 300°C (T1) under an argon atmosphere (first-stage calcination) for 2 h, then heat at 500°C (T2) under an argon atmosphere (second-stage calcination) for 5 h to promote the formation of lithium iron phosphate with a gradient, and finally heat at 700°C (T3) under an argon atmosphere (third-stage calcination) for 0.5 h to obtain a regenerated lithium iron phosphate material (SEM is shown in Figure 3 ; TEM is shown in Figure 4 ; XRD is shown in Figure 5 ).

[0087] Use the regenerated material as an active material to prepare a button cell, the steps are as follows:

[0088] Positive electrode sheet preparation: The active material (regenerated lithium iron phosphate powder), conductive carbon black (SP), and binder (PVDF) are thoroughly ground in a mass ratio of 8:1:1 to make them uniformly mixed. A 100 μm applicator is used to slowly and uniformly apply the uniformly mixed slurry to a glass plate with an aluminum foil. The coated material is dried in a vacuum drying oven at 80°C for 10 h to obtain a dried positive electrode sheet. The dried positive electrode sheet is cut into small round pieces with a diameter of 1.2 cm using a button cell slicer.

[0089] Assembled button cell: The assembled button cell is a 2032 type button half cell with lithium metal negative electrode. In an argon-filled glove box, the button cell is assembled in the order of positive shell, positive sheet, separator (Celgard-2400), lithium sheet, gasket, spring and negative shell, and then packaged by a packaging machine. During the assembly process, electrolyte (1 mol / L LiPF6 organic solution, in which the solvent is a mixed solution of EC, DEC and DMC in a volume ratio of 1:1:1) is added before and after the placement of the separator, and a lithium ion secondary battery electrolyte is used.

[0090] After assembly, corresponding electrochemical tests are performed. The tests are performed in a constant temperature environment of 25°C.

[0091] The battery is charged at a rate of 0.1C to 3.65V, then converted to constant voltage charging until the current decreases to 0.05C cutoff, and then discharged at a constant current of 0.1C to 2.5V after 5 minutes of standing, which is one charge and discharge cycle. This process is repeated 2-3 cycles to complete activation, and the first coulombic efficiency is calculated.

[0092] The charge and discharge rate is unified to 0.2C for cycling, and the stable discharge capacity is taken as the reversible specific capacity at 0.2C. In the rate performance test, the battery is directly discharged at a high rate of 5C after being fully charged under the same charging system, and the measured discharge capacity is the reversible capacity at 5C.

[0093] Long cycle test, the battery is always cycled at a charge and discharge rate of 0.2C (the same as above), and the capacity is recorded every 100 cycles. After a total of 3000 cycles, the ratio of the discharge capacity to the initial 0.2C reversible specific capacity is calculated to obtain the capacity retention rate at 0.2C after 3000 cycles.

[0094] The first charge and discharge curve of the regenerated lithium iron phosphate prepared in Example 1 is shown in Figure 6 .

[0095] The specific performance is shown in Table 1.

[0096] Example 2

[0097] Compared with Example 1, the only difference is that the conditions of step 1 are changed, and the experimental groups are as follows:

[0098] Group A: The lithium iron phosphate black powder is not subjected to ball milling treatment with a mixed solution of dimethyl sulfoxide and water, and is directly mixed with the modified solution of step 2 to perform step 3 and subsequent treatment;

[0099] Group B: In step 1, the mixed solvent is only water; the amount of solvent is the same as that of the mixed solvent in Example 1.

[0100] Other operations and parameters are the same as those in Example 1.

[0101] Example 3

[0102] Compared with Example 1, the only difference is that the conditions of step 2 are changed, and the experimental groups are as follows:

[0103] Group A: the phosphorus-based additive is changed to a mixed solution of phenylphosphonic acid and tributyl phosphate, and the weight ratio of phenylphosphonic acid to tributyl phosphate is 1:1; the total amount of the phosphorus-based additive is unchanged;

[0104] Group B: the weight ratio of aluminum chloride hexahydrate, ethylene glycol and the phosphorus-based additive is changed to 1:7:0.3;

[0105] Group C: the heating temperature is changed to 50℃, and the heating time is changed to 3h;

[0106] Other operations and parameters are the same as those in Example 1.

[0107] Example 4

[0108] Compared with Example 1, the only difference is that the conditions of step 3 are changed, and the difference is that: the amount of the modification solution is changed, so that the liquid-solid ratio of the leaching process is 10:1ml / g, the leaching temperature is 50℃, and the leaching time is 6h; other operations and parameters are the same as those in Example 1.

[0109] Example 5

[0110] Compared with Example 1, the only difference is that the conditions of step 4 are changed, and the experimental groups are as follows:

[0111] Group A: in step 4a, the pH is changed to 2, and the light irradiation time is changed to 60min;

[0112] In step 4b, the buffer system is used to control the pH of the system to be 7.8, the temperature is 50℃, and the reaction time is 3h;

[0113] Group B: no buffer system is added, and the pH of the system is controlled to be 7.5 by using ammonia;

[0114] Group C: in step 4b, the buffer system is changed to tris(hydroxymethyl)aminomethane-hydrochloric acid, and the pH of the buffer system is 8;

[0115] Group D: step 4b is not treated under positive pressure, but is treated under normal pressure;

[0116] Other operations and parameters are the same as those in Example 1.

[0117] Example 6

[0118] Compared with Example 1, the only difference is that the conditions of step 5 are changed, and the experimental groups are as follows:

[0119] Group A: without the positive pressure treatment in step 5a, the mixed raw materials in step 5a are directly subjected to step 5b and subsequent treatments;

[0120] Group B: in step 5b, the temperature and time of the first-stage calcination to the third-stage calcination are changed, and are T1 400℃, the holding time 3h; T2 650℃, the holding time 5h; T3 800℃, the holding time 0.5h;

[0121] Group C: in step 5b, only the third-stage calcination is performed, and the time of the third-stage calcination is 7.5h;

[0122] The other operations and parameters are the same as in Example 1.

[0123] Comparative Example 1

[0124] Compared with Example 1, the only difference is that in step 2, no phosphoric acid-based additive is added, and the other operations and parameters are the same as in Example 1.

[0125] Comparative Example 2

[0126] Compared with Example 1, the only difference is that in step 2, silicic acid is used to replace the phosphoric acid-based additive, and the amount and the other operations and parameters are the same as in Example 1.

[0127] Comparative Example 3

[0128] Compared with Example 1, the only difference is that in step 2, sodium chloride is used to replace aluminum chloride, and the other operations and parameters are the same as in Example 1.

[0129] Comparative Example 4

[0130] Compared with Example 1, the only difference is that in step 3, a conventional acid leaching scheme is used to obtain the leaching solution: 0.5g of the lithium iron phosphate black powder treated in step 1 is placed in 15mL of 1mol / L sulfuric acid solution, stirring is performed in an air-tight manner, the lithium iron phosphate black powder reacts with the sulfuric acid solution, lithium and iron are leached, the stirring time is 24h, the stirring temperature is 25℃, and then filtration is performed to obtain the leaching solution (filtrate 1), wherein the valuable metal leaching rate is Fe 70.06%, Li 83.82%, and the other operations and parameters are the same as in Example 1.

[0131] Comparative Example 5

[0132] Compared with Example 1, the only difference is that in step 4, a single-stage precipitation method is used:

[0133] To the filtrate 1, drop by drop, add concentrated ammonia water until pH>12, and let the reacted mixture stand at room temperature for 2h until the liquid part of the system is clear. Then centrifuge the resulting solution at 6000rpm for 5min to separate the filtrate and the residue (precursor material), and the other operations and parameters are the same as in Example 1.

[0134] Comparative Example 6

[0135] Compared with Example 1, the only difference is that in step 4a, the added reagents and the regulated pH value are changed: the different step is:

[0136] To the filtrate 1, drop by drop, add a solution of citric acid with a concentration of 1 mol / L until the mass of citric acid is 4 times that of iron ions, and add concentrated ammonia water to the solution to adjust the pH to 6. After mixing well, add a 15%.wt solution of potassium ferricyanide to the above solution until the mass of potassium ferricyanide is 4 times that of iron ions. After mixing well, pour into a quartz cuvette and place on a magnetic stirrer, irradiate under a xenon lamp for 30min, and let the reacted mixture stand at room temperature for 2h; carry out step 4b and subsequent processing on the obtained product, and the other operations and parameters are the same as in Example 1.

[0137] The test results of each case are shown in Table 1:

[0138] ;

[0139] In summary, through the examples and comparative examples, it can be determined that the waste electrode material is innovatively immersed in the modified solution formed by the aluminum chloride-ethylene glycol-phosphoric acid-based additive hydrogen bond and / or coordination, which is conducive to the extraction of Fe, P and Li therein, and is also conducive to the selective retention of electrochemical trace components therein. Further, in combination with the subsequent special step-by-step precipitation method, a precursor with an iron core and a lithium phosphate coating on the surface and an element gradient distribution can be constructed. After calcination of the precursor, the regenerated lithium iron phosphate core can be optimized, the atomic distribution can be improved, and the crystal and grain structure can be optimized by using trace beneficial components. In this way, the regenerated lithium iron phosphate can exhibit performance comparable to or even superior to that of newly prepared lithium iron phosphate, for example, it can exhibit excellent fast charging and long cycle stability.

[0140] As can be seen from Example 1 and Example 2, pre-mechanical ball milling treatment of lithium iron phosphate black powder in a dimethyl sulfoxide-water mixed solution can be combined with the process of the present application, which is helpful to further strengthen the fast charging and long cycle performance of the regenerated lithium iron phosphate material.

[0141] As can be seen from Example 1 and Example 3, controlling the weight of aluminum chloride hexahydrate, ethylene glycol and phosphoric acid-based additive for further optimization control can be combined with the process of the present application, which is helpful to further strengthen the fast charging and long cycle performance of the regenerated lithium iron phosphate material.

[0142] From Example 1 and Example 5, it can be seen that, in the second precipitation process, the addition of the buffer system and / or positive pressure treatment helps to combine with the process of the application, and helps to further strengthen the fast charging and long cycle performance of the regenerated lithium iron phosphate material.

[0143] From Example 1 and Example 6, it can be seen that, by using positive pressure pre-sintering and then cooperating with subsequent three-stage sintering, it helps to further improve the physicochemical structure of lithium iron phosphate, and helps to further strengthen the fast charging and long cycle performance of the regenerated lithium iron phosphate material.

Claims

1. A method for preparing a regenerated lithium iron phosphate active material, characterized by the steps of The application relates to a method for preparing a regenerated lithium iron phosphate active material. The method comprises the following steps: Step 1: leaching aluminum chloride, ethylene glycol and a phosphoric acid-based additive are heated to obtain a modified solution; The phosphoric acid group additive includes at least one of phosphoric acid and a water-soluble salt thereof, hypophosphorous acid and a water-soluble salt thereof, pyrophosphoric acid and a water-soluble salt thereof, a water-soluble monohydrogen phosphate salt, a water-soluble dihydrogen phosphate salt, a C3-C6 alkyl phosphonate, and a C3-C6 alkyl phosphinate. 10 The phosphoric acid group additive includes at least one of phosphoric acid and a water-soluble salt thereof, hypophosphorous acid and a water-soluble salt thereof, pyrophosphoric acid and a water-soluble salt thereof, a water-soluble monohydrogen phosphate salt, a water-soluble dihydrogen phosphate salt the modified solution is mixed with waste electrode material containing lithium iron phosphate for leaching, and a leaching solution rich in Li, P and Fe is separated; Step 2: step-by-step precipitation Formula 1; In formula 1, the M is H + , Na + , K + , or NH4 + ; a formula 1 and a surfactant are added to the leaching solution of step 1, and a first-stage precipitation treatment is carried out under a first pH and light irradiation, and then a second-stage precipitation treatment is carried out under a second pH, so that an iron-formula 1 complex lithium phosphate precursor is obtained; the first pH is 1.5-4.5; the second pH is 6-8.5; Step 3: calcination 2. The method of claim 1, wherein the regenerated lithium-iron-phosphate active material is prepared by the steps of: the iron-formula 1 complex lithium phosphate precursor prepared in step 2 is subjected to calcination treatment, so that the regenerated lithium iron phosphate active material is prepared. ​ 3. The method of claim 1, wherein the regenerated lithium-iron-phosphate active material is prepared by the steps of: The waste electrode material is subjected to wet ball milling treatment in advance, and a solvent for the wet ball milling treatment comprises a mixed solvent of a solvent a and a solvent b, wherein the solvent a comprises at least one of dimethyl sulfoxide, dimethyl acetamide, dimethyl propionamide, gamma-butyrolactone and limonene; and the solvent b comprises at least one of water and ethanol. ​ In step 1, the phosphoric acid-based additive is at least one of phosphoric acid, phenylphosphonic acid, tributyl phosphate and hypophosphorous acid; The aluminum chloride is aluminum chloride hexahydrate; The weight ratio of the aluminum chloride, the ethylene glycol and the phosphoric acid-based additive is 1:1-10:0.1-0.5; The heating temperature is 25-90 DEG C; In step 1, the liquid-solid ratio of the leaching process is controlled to be 10-100 ml / g; The leaching temperature is 15-60 DEG C; 4. The method of claim 1, wherein the regenerated lithium-iron-phosphate active material is prepared by the steps of: The leaching time is more than 1 h. ​ In step 2, the surfactant is at least one of a cationic surfactant, an anionic surfactant and a neutral surfactant; The molar ratio of Fe in the leaching solution to formula 1 is 1:2-10; and the weight ratio of iron to the surfactant is 1:0.05-0.5; The power of the light source for the light irradiation is 300-800 W; 5. The method of claim 4, wherein the regenerated lithium-iron-phosphate active material is prepared by the steps of: The light irradiation time is 20-120 min. ​ 6. The method of producing a regenerated lithium-iron-phosphate active material according to claim 1, 4 or 5, characterized in that, In step 2, a buffer is further added in the second-stage precipitation process, wherein the buffer comprises at least one of sodium dihydrogen phosphate-lactic acid buffer, tris(hydroxymethyl)aminomethane-hydrochloric acid buffer and ammonia-ammonium chloride buffer.

7. The method of claim 1, wherein the regenerated lithium-iron-phosphate active material is prepared by the steps of: In step 2, the second-stage precipitation process is carried out under positive pressure. ​ In step 3, the molar ratio of Li, Fe and P in the iron-formula 1 complex lithium phosphate precursor is regulated to be 1.05-1.10:1:1 in advance, and then the calcination treatment is carried out, so that the regenerated lithium iron phosphate active material is prepared; The iron-formula 1 complex lithium phosphate precursor with the regulated molar ratio of Li, Fe and P is mixed with a carbon source, and then the calcination treatment is carried out; The calcination process comprises three-stage gradient calcination processes, which comprise a first-stage calcination process at a temperature of 300-400 DEG C, a second-stage calcination process at a temperature of 500-650 DEG C and a third-stage calcination process at a temperature of 600-700 DEG C; The calcination process is carried out in a protective atmosphere; The holding time of the first-stage calcination, the second-stage calcination and the third-stage calcination is respectively 0.5-5 h. The positive pressure pretreatment is carried out before roasting, wherein the pressure of the positive pressure pretreatment is 1.5-5 MPa, the temperature is 150-250 ℃, and the time is 1-8 h.

8. A regenerated lithium iron phosphate active material prepared by the preparation method in any one of claims 1-7.

9. The use of the regenerated lithium iron phosphate active material produced by the method according to any one of claims 1 to 7, characterized in that, It is used for preparing a lithium ion battery as a positive active material.

10. A lithium-ion battery, characterized by, A lithium ion battery comprising the regenerated lithium iron phosphate active material in claim 8.

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