Method for preparing cobalt-doped lithium iron vanadium phosphate from waste lithium iron phosphate battery powder

Abstract

The application discloses a method for preparing cobalt-doped lithium iron vanadium phosphate from waste lithium iron phosphate battery powder, and comprises the following steps: low-temperature acid immersion, copper removal, aluminum removal, activated carbon adsorption, vanadium and cobalt doping, adjustment of the lithium iron phosphate ratio, carbon doping and solid content adjustment to obtain slurry, superfine grinding of the slurry, spray drying to obtain precursor powder, sintering of the precursor powder, iron removal through sieving to obtain cobalt-doped lithium iron vanadium phosphate. The cobalt-doped lithium iron vanadium phosphate powder prepared by the method has a porous nano-particle structure and excellent rate performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of waste lithium ion battery material recycling and regeneration, and particularly relates to a method for preparing cobalt-doped iron lithium vanadium phosphate from waste iron lithium phosphate battery powder. BACKGROUND

[0002] With the rapid development of economy, energy and environmental problems have become the focus of attention. In recent years, the state has vigorously promoted new energy vehicles, and the sales of new energy vehicles have shown explosive growth. Most new energy vehicles mainly use lithium iron phosphate batteries, and the theoretical service life of lithium iron phosphate batteries is 7-8 years, which will inevitably bring a large number of waste batteries. How to effectively treat waste batteries and turn waste into treasure has become a topic of concern.

[0003] At present, the recycling of waste lithium iron phosphate batteries mainly has two recycling methods of fire method and wet method. The traditional fire method recovery is generally high-temperature incineration of electrode sheets, and the carbon and organic matter in the electrode fragments are burned off. The remaining ash that cannot be burned off is finally screened to obtain fine powder materials containing metals and metal oxides. The method has simple process, but the treatment process is long, and the comprehensive recovery rate of valuable metals is low. The wet recovery mainly dissolves the metal ions in the lithium iron phosphate battery through acid and alkali solution, and further extracts the dissolved metal ions in the form of oxides, salts and other forms by precipitation, adsorption and other methods. Most of the reagents used in the reaction process are H2SO4, NaOH and H2O2. The wet recovery process is simple, the equipment requirement is not high, and it is suitable for industrial scale production. It is the most studied by scholars and the mainstream treatment route of waste lithium ion batteries in China.

[0004] However, the lithium iron phosphate battery does not contain precious metals, and the cost of regenerating lithium iron phosphate is high, and the economic value is low. Iron lithium vanadium phosphate is considered to be a new generation of lithium ion battery positive electrode material due to its safety, non-toxicity, high specific capacity and good cycle performance. However, it has always been a difficult problem to limit its further development to research excellent and low-cost iron lithium vanadium phosphate. If waste lithium iron phosphate batteries can be used to prepare iron lithium vanadium phosphate materials, not only the production cost can be reduced, but also the recycling problem of waste lithium iron phosphate batteries can be solved. Patent application CN107579304A discloses a method for preparing iron lithium vanadium phosphate from waste lithium iron phosphate positive electrode sheets, but the specific capacity of the prepared iron lithium vanadium phosphate positive electrode material can only reach 110-135 mAh / g, which has no advantage compared with lithium iron phosphate. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a method for preparing cobalt-doped iron lithium vanadium phosphate from waste lithium iron phosphate battery powder, so as to improve the conductivity, specific capacity and rate performance of the recycled lithium iron phosphate regeneration material.

[0006] To achieve the above object, the application adopts the following technical scheme:

[0007] The application provides a method for preparing cobalt-doped lithium iron vanadium phosphate from waste lithium iron phosphate battery powder, comprising the following steps:

[0008] S1. The waste lithium iron phosphate battery powder is leached with inorganic acid, and carbon residue and mixed solution are obtained through solid-liquid separation;

[0009] S2. Iron powder is added to the mixed solution, and after sufficient reaction, the solid-liquid separation is performed to obtain crude sponge copper and a first filtrate; sodium sulfide solution is added to the first filtrate, and after sufficient reaction, the solid-liquid separation is performed to obtain a second filtrate;

[0010] S3. An antioxidant and an aluminum removal agent are added to the second filtrate, and after sufficient reaction, the solid-liquid separation is performed to obtain a third filtrate;

[0011] S4. Activated carbon powder is added to the third filtrate to remove organic matter in the solution, and after sufficient reaction, the solid-liquid separation is performed to obtain a fourth filtrate;

[0012] S5. NH4VO3 solid is added to the fourth filtrate, and n(V):n(Fe) is controlled to be (0.05-0.25):1; NH4CoPO4 solid is added, and the cobalt content in the finished product of lithium iron vanadium phosphate is controlled to be 800-2000 ppm; a phosphorus source, an iron source and a lithium source are further added, and the ratio of phosphorus, iron and lithium is adjusted to be n(Fe+V):n(P):n(Li)=(0.95-1):1:(1.02-1.1); a carbon source and pure water are further added, and the solid content of the solution is controlled to be 30-40 wt%, so as to obtain a slurry;

[0013] S6. The slurry is input into a sand mill for sand milling, and the sand milling is performed until D50≤0.2 μm and D99≤1.5 μm; and then spray drying is performed to obtain a precursor powder;

[0014] S7. The precursor powder is placed in a sintering furnace in a nitrogen atmosphere for high-temperature sintering, the oxygen content in the sintering furnace is controlled to be ≤1 ppm, the sintering temperature of the sintering constant temperature zone is controlled to be 730-780 ℃, and the sintering time is controlled to be 5-10 h; after sintering, the temperature is lowered to discharge the material, and the iron is removed through screening, so as to obtain cobalt-doped lithium iron vanadium phosphate.

[0015] Preferably, in step S1, the inorganic acid is one of sulfuric acid, phosphoric acid and hydrochloric acid, the amount of the inorganic acid is controlled to be 2.4-4.0 times the amount of substance of lithium ions in the battery powder, the amount of pure water is 3-7 times the mass of the battery powder, and the reaction time is 30-90 min.

[0016] Preferably, in step S2, the iron powder is 100-150 mesh, the adding amount is 1.2-1.5 times of the stoichiometric amount, and the reaction time is 60-120 min.

[0017] Preferably, in step S2, the concentration of the sodium sulfide solution is 20-25 g / L, the adding amount is 1.5-2.5% of the volume of the first filtrate, and the reaction time is 30-60 min.

[0018] Preferably, in step S3, the antioxidant is ascorbic acid, and the adding amount is 0.5 g / L; the aluminum removal agent is any one of 5wt% sodium hydroxide solution, 5wt% potassium hydroxide solution and 8wt% ammonia solution, and the pH at the reaction endpoint is controlled to be 3-5.5.

[0019] Preferably, in step S4, the adding amount of the activated carbon is 0.1-0.3% of the mass of the third filtrate.

[0020] Preferably, in step S5, the phosphorus source is any one of phosphoric acid, monobasic ammonium phosphate, monobasic potassium phosphate, monobasic sodium phosphate, dibasic ammonium phosphate, dibasic potassium phosphate and dibasic sodium phosphate; the iron source is ferrous sulfate heptahydrate, and the lithium source is lithium carbonate.

[0021] Preferably, in step S5, the carbon source is a mixture of sucrose and citric acid monohydrate, n(citric acid monohydrate):n(sucrose)=(0.08-0.13):1, and n(sucrose+ citric acid monohydrate):n(Fe+V)=(0.05-0.1):1.

[0022] Preferably, in step S6, the inlet air temperature of the spray drying is 250±2℃, and the outlet air temperature is 80±5℃.

[0023] Preferably, in step S7, the cooling is jacket water cooling, and the surface temperature of the discharged material is controlled to be ≤80℃.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] In the present application, ammonium metavanadate is used as the vanadium source. Since ammonium metavanadate is slightly soluble in cold water, the nanoscale ammonium metavanadate after grinding exists in the form of crystals in the reaction system, and can be used as the crystal nucleus for spray granulation. In the high-temperature sintering process, ammonium metavanadate is decomposed to generate V2O5(V6O 13), water vapor and ammonia gas, forming internal holes, while vanadium oxide is uniformly distributed in the holes, obtaining vanadium-doped porous vanadium iron lithium phosphate; a composite carbon source of sucrose and citric acid monohydrate is used, wherein the citric acid monohydrate can act as a dispersing agent, preventing material aggregation during superfine grinding, and obtaining uniform particles; superfine grinding is used, and the slurry particle size D50 reaches below 150 nm, shortening the lithium ion diffusion path and improving the rate performance of the material; vanadium and cobalt are doped into the interior of the iron lithium particles, and the doping elements are uniformly distributed, which can improve the electronic conductivity of the material and reduce the internal resistance of the material; at the same time, the electrolyte can enter the internal holes, which can effectively improve the migration rate of lithium ions and improve the rate performance. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 An electron microscope image of the cobalt-doped vanadium iron lithium phosphate positive electrode material of Example 1 is enlarged by 10,000 times.

[0027] Figure 2 An electron microscope image of the cobalt-doped vanadium iron lithium phosphate positive electrode material of Example 1 is enlarged by 5,000 times.

[0028] Figure 3 An electron microscope image of the cobalt-doped vanadium iron lithium phosphate positive electrode material of Example 1 is enlarged by 10,000 times. DETAILED DESCRIPTION

[0029] The present application will be further described in detail below in conjunction with specific examples, so that those skilled in the art can more clearly understand the present application. The examples are only used to explain the present application, and are not intended to limit the scope of the present application. In the examples of the present application, all raw material components are commercially available products well known to those skilled in the art, unless otherwise specified. If not specifically indicated, the technical means used are conventional means well known to those skilled in the art.

[0030] Example 1

[0031] The preparation method of the cobalt-doped vanadium iron lithium phosphate provided in this example is as follows:

[0032] Take 500 g of waste lithium iron phosphate battery powder with a lithium content of 2.9%, add 2500 g of pure water, stir evenly to make a slurry, then add 302.08 g of concentrated sulfuric acid with a concentration of 97.71% for leaching, react for 60 min, solid-liquid separation to obtain carbon residue and mixed solution containing phosphorus iron lithium 2954.3 g, the copper content of the solution is measured to be 677 ppm; 2.6 g of 100 mesh iron powder is added to the mixed solution, and the reaction is carried out for 75 min, and the solid-liquid separation is carried out to obtain crude sponge copper and the first filtrate; 59 ml of sodium sulfide solution with a concentration of 20 g / L is added to the first filtrate, and the reaction is carried out for 45 min, and the solid-liquid separation is carried out to obtain the second filtrate; 1.5 g of ascorbic acid and 5% sodium hydroxide solution are added to the second filtrate for reaction, and the pH of the reaction endpoint is controlled at 4.0, and the solid-liquid separation is carried out to obtain the third filtrate; 4.6 g of activated carbon powder is added to the third filtrate to remove organic matter in the solution, and the reaction is carried out for 30 min, and the solid-liquid separation is carried out to obtain the fourth filtrate; 20.2 g of NH4VO3 solid and 3.4 g of NH4CoPO4 solid are added to the fourth filtrate, and then 43.9 g of ammonium phosphate monohydrate, 20.1 g of lithium carbonate, 29.5 g of sucrose and 1.83 g of citric acid monohydrate are added, and finally pure water is added to control the solid content of the solution to be 30 wt%, and a slurry is obtained;

[0033] The slurry is input into a sand mill for sand milling, and zirconium balls with a diameter of 0.3 mm are used for sand milling, and the sand milling is carried out until D50≤0.2 μm and D99≤1.5 μm; the sand-milled slurry is transported to a spray tower for spray drying, and the inlet air temperature is controlled to be 250±2 ℃ and the outlet air temperature is controlled to be 80±5 ℃, to obtain a precursor powder with a moisture content of ≤0.5% and a particle size D50 of 6-8 μm; the precursor powder is placed in a sintering furnace in a nitrogen atmosphere for high-temperature sintering, the oxygen content in the sintering furnace is controlled to be ≤1 ppm, the sintering temperature of the sintering constant temperature zone is 750 ℃, and the sintering time is 6 h; after sintering, the material is discharged after cooling, the jacket water cooling is used for cooling in the cooling section, and the surface temperature of the discharged material is controlled to be ≤80 ℃; the sintered powder is subjected to iron removal by screening, the magnetic intensity of the iron remover is ≥12000 gs, the process magnetic foreign matter is ≤0.2 ppm, and a cobalt-doped lithium iron vanadium phosphate is obtained.

[0034] Example 2

[0035] The preparation method of the cobalt-doped lithium iron vanadium phosphate provided in this embodiment is as follows:

[0036] Take 500 g of waste lithium iron phosphate battery powder with a lithium content of 2.9%, add 2000 g of pure water, stir evenly to make a slurry, then add 314.03 g of concentrated sulfuric acid with a concentration of 97.71% for leaching, react for 90 min, solid-liquid separation to obtain carbon residue and mixed solution containing phosphorus iron lithium 2489.5 g, the copper content of the solution is measured to be 1004 ppm; add 3.3 g of 120 mesh iron powder to the mixed solution, react for 60 min, solid-liquid separation to obtain crude sponge copper and first filtrate; add 37.3 ml of sodium sulfide solution with a concentration of 25 g / L to the first filtrate, react for 45 min, solid-liquid separation to obtain second filtrate; add 1.2 g of ascorbic acid and 5% sodium hydroxide solution to the second filtrate for reaction, control the pH of the reaction endpoint to be 4.5, solid-liquid separation to obtain third filtrate; add 5 g of activated carbon powder to the third filtrate to remove organic matter in the solution, react for 30 min, solid-liquid separation to obtain fourth filtrate; add 48.7 g of NH4VO3 solid and 3.7 g of NH4CoPO4 solid to the fourth filtrate, then add 59.47 g of ammonium phosphate monohydrate, 34.68 g of lithium carbonate, then add 63.05 g of sucrose and 5.03 g of citric acid monohydrate, and finally add pure water to control the solid content of the solution to be 35 wt%, to obtain a slurry;

[0037] The slurry is input into a sand mill for sand milling, the grinding balls used for sand milling are zirconium balls with a diameter of 0.3 mm, and the sand milling is performed until D50≤0.2 μm and D99≤1.5 μm; the sand-milled slurry is transported to a spray tower for spray drying, the inlet air temperature is controlled to be 250±2℃, and the outlet air temperature is controlled to be 80±5℃, to obtain a precursor powder with a moisture content of ≤0.5% and a particle size D50 of 6-8 μm; the precursor powder is placed in a sintering furnace in a nitrogen atmosphere for high-temperature sintering, the oxygen content in the sintering furnace is controlled to be ≤1 ppm, the sintering temperature of the sintering constant temperature zone is 750℃, and the sintering time is 6 h, after sintering, the material is discharged after cooling, the jacket water cooling is used for cooling in the cooling section, and the surface temperature of the discharged material is controlled to be ≤80℃; the sintered powder is subjected to iron removal by screening, the magnetic intensity of the iron remover is ≥12000 gs, the process magnetic foreign matter is ≤0.2 ppm, and a cobalt-doped lithium iron vanadium phosphate is obtained.

[0038] Example 3

[0039] The preparation method of the cobalt-doped lithium iron vanadium phosphate provided in this embodiment is as follows:

[0040] Take 500g lithium content 2.9% of waste old lithium iron phosphate battery powder, add 1500g pure water, stir evenly to make slurry, then add 251.2g of concentrated sulfuric acid with a concentration of 97.71% for leaching, react for 90min, solid-liquid separation to get carbon residue and mixed solution containing phosphorus iron lithium 1952.4g, measured copper content of the solution is 1126.8ppm; Add 2.3g of 120 mesh iron powder to the mixed solution, react for 60min, solid-liquid separation to get crude sponge copper and first filtrate; Add 47.5ml of 25g / L sodium sulfide solution to the first filtrate, react for 45min, solid-liquid separation to get second filtrate; Add 0.95g of ascorbic acid and 5% sodium hydroxide solution to the second filtrate for reaction, control the pH of the reaction endpoint to be 3.5, solid-liquid separation to get third filtrate; Add 5.5g of activated carbon powder to the third filtrate to remove organic matter in the solution, react for 30min, solid-liquid separation to get fourth filtrate; Add 10.4g of NH4VO3 solid and 3.5g of NH4CoPO4 solid to the fourth filtrate, then add 17.06g of ammonium phosphate monohydrate, 13.6g of lithium carbonate, then add 41.47g of sucrose and 2.04g of citric acid monohydrate, finally add pure water to control the solid content of the solution to be 32wt%, get the slurry;

[0041] Put the slurry into a sand mill for sand milling, the grinding ball used for sand milling is zirconium ball with a diameter of 0.3mm, sand mill to D50≤0.2μm, D99≤1.5μm; The well-sand-milled slurry is transported to a spray tower for spray drying, control the inlet air temperature to be 250±2℃, the outlet air temperature to be 80±5℃, get the precursor powder with moisture content≤0.5%, particle size D50 of 6-8μm; Put the precursor powder into a sintering furnace in nitrogen atmosphere for high temperature sintering, control the oxygen content in the sintering furnace to be≤1ppm, the sintering temperature of the sintering constant temperature zone to be 750℃, the sintering time to be 6h, after sintering, cool down and discharge, the cooling section uses jacket water cooling, control the surface temperature of the discharged material to be≤80℃; The sintered powder is screened to remove iron, the magnetic strength of the iron remover is≥12000gs, the process magnetic foreign matter is≤0.2ppm, get the cobalt-doped lithium iron vanadium phosphate.

[0042] Comparative Example 1

[0043] This comparative example provides a method for preparing cobalt-doped lithium iron vanadium phosphate from waste old lithium iron phosphate battery powder, which has basically the same raw materials and steps as Example 1, the difference is that step S3 does not add antioxidant.

[0044] Comparative Example 2

[0045] This comparative example provides a method for preparing cobalt-doped lithium iron vanadium phosphate from waste old lithium iron phosphate battery powder, which has basically the same raw materials and steps as Example 1, the difference is that step S3 controls the reaction endpoint pH to be 2.5.

[0046] Comparative Example 3

[0047] The present comparative example provides a method for preparing cobalt-doped lithium iron vanadium phosphate from waste lithium iron phosphate batteries, which has the same raw materials and steps as Example 1, except that the ratio of n(V):n(Fe) is controlled to be 0.5:1 in step S5.

[0048] Performance test:

[0049] (1) The iron content of the aluminum-removed filter residue of Example 1 and Comparative Example 1 was analyzed. The iron content of the aluminum-removed filter residue in Example 1 was 8.57%, and the iron loss rate was 2.75%. The iron content of the aluminum-removed filter residue in Comparative Example 1 was 12.05%, and the iron loss rate was 4.59%. From the above results, it can be seen that the aluminum removal will increase the loss of iron without adding an antioxidant.

[0050] (2) The third filtrate after aluminum removal of Example 1-3 and Comparative Example 2 was detected, and the test results are shown in Table 1:

[0051] Table 1

[0052] Item Example 1 Example 2 Example 3 Comparative Example 2 Third filtrate aluminum content / ppm 14.22 7.98 26.54 789.26

[0053] From the above results, it can be seen that when the end point pH is lower than the range of the present patent, the residual amount of aluminum in the solution is higher, which ultimately leads to the aluminum content exceeding the standard in the product.

[0054] (3) The material prepared by Example 1-3 and Comparative Example 3 was analyzed, and the results are shown in Table 2:

[0055] Table 2

[0056] Item Example 1 Example 2 Example 3 Comparative Example 3 Fe (%) 30.97 27.22 32.48 22.73 P(％) 19.23 19.23 19.25 19.21 Li (%) 4.44 4.42 4.45 4.39 V(％) 3.1 6.81 1.62 11.37 C(％) 1.24 1.32 1.28 1.25 Co (ppm) 914.4 1237.2 1016.5 933.8 BET(m 2 / g) 33.1 31.8 35.4 32.9 Tap density (g / cm 3 )]]> 1.35 1.38 1.33 1.30 D50 (pm) 3.85 3.16 3.74 2.82 Al (ppm) 15.42 9.84 35.24 13.94 Cu (ppm) 0.98 1.24 1.11 1.34 0.1 C charge (mAh / g) 160.5 161.7 161.2 149.6 0.1 C discharge (mAh / g) 157.9 159.4 158.5 143.9 Initial efficiency (%) 98.38 98.58 98.33 96.19

[0057] From the data in Table 2, it can be seen that when the ratio of n(V):n(Fe) is higher than the range of the present patent, the charge-discharge capacity and the initial efficiency of Comparative Example 3 are lower than those of Examples 1-3.

[0058] Figures 1-3 The SEM electron micrograph of the cobalt-doped lithium iron vanadium phosphate prepared in Example 1 is shown in Figure 1, Figure 1 The electron micrograph at a magnification of 10,000 times can be seen that the particle D50 of the cobalt-doped lithium iron vanadium phosphate material is between 2-6 μm; Figure 2 The electron micrograph at a magnification of 50,000 times can be seen that the particles of the cobalt-doped lithium iron vanadium phosphate material are secondary particles formed by agglomeration of primary particles; Figure 3 The electron micrograph at a magnification of 100,000 times can be seen that the primary particles are spherical particles with uniform particle size, most of which are between 40-80 nm, thus the diffusion path of lithium ions can be shortened and the rate performance of the material can be improved.

[0059] The above merely describes preferred embodiments of the present application, and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing cobalt-doped lithium iron vanadium phosphate from waste lithium iron phosphate battery powder, characterized in that, The method comprises the following steps: S1. Leaching waste lithium iron phosphate battery powder with inorganic acid to obtain carbon residue and mixed solution through solid-liquid separation; S2. Adding iron powder to the mixed solution, and performing solid-liquid separation after sufficient reaction to obtain crude sponge copper and a first filtrate; adding sodium sulfide solution to the first filtrate, and performing solid-liquid separation after sufficient reaction to obtain a second filtrate; S3. Adding an antioxidant and an aluminum removal agent to the second filtrate, and performing solid-liquid separation after sufficient reaction to obtain a third filtrate; the antioxidant is ascorbic acid; S4. Adding activated carbon powder to the third filtrate to remove organic matter in the solution, and performing solid-liquid separation after sufficient reaction to obtain a fourth filtrate; S5. Adding NH4VO3 solid to the fourth filtrate, controlling n(V):n(Fe) = (0.05-0.25):1; adding NH4VO3 solid to control the cobalt content in the finished product of lithium iron phosphate vanadium phosphate to be 800-2000 ppm; further adding a phosphorus source, an iron source and a lithium source to adjust the ratio of phosphorus, iron and lithium to be n(Fe+V):n(P):n(Li) = (0.95-1):1:(1.02-1.1); further adding a carbon source and pure water to control the solid content of the solution to be 30-40 wt%, and obtaining a slurry; S6. Inputting the slurry into a sand mill to perform sand milling until D50≤0.2 μm and D99≤1.5 μm; and performing spray drying to obtain a precursor powder; S7. Placing the precursor powder in a sintering furnace in a nitrogen atmosphere to perform high-temperature sintering, controlling the oxygen content in the sintering furnace to be ≤1 ppm, the sintering temperature of the sintering constant temperature zone to be 730-780 ℃, and the sintering time to be 5-10 h; discharging after cooling, and removing iron through screening to obtain cobalt-doped lithium iron phosphate vanadium phosphate.

2. The process of claim 1, wherein the process of preparing cobalt doped lithium iron vanadium phosphate from spent lithium iron phosphate battery powder is characterized by, In step S1, the inorganic acid is one of sulfuric acid, phosphoric acid and hydrochloric acid, the amount of the inorganic acid added is controlled to be 2.4-4.0 times the amount of lithium ions in the battery powder in terms of the amount of substance of hydrogen ions, and the reaction time is 30-90 min.

3. The process for the preparation of cobalt doped lithium iron vanadium phosphate from spent and old lithium iron phosphate battery powder as claimed in claim 1 wherein, In step S2, the iron powder is 100-150 mesh, and the amount added is 1.2-1.5 times the stoichiometric amount, and the reaction time is 60-120 min. ​ 4. The process for the preparation of cobalt doped lithium iron vanadium phosphate from spent and old lithium iron phosphate battery powder as claimed in claim 1 wherein, In step S2, the concentration of the sodium sulfide solution is 20-25 g / L, the amount added is 1.5-2.5% of the volume of the first filtrate, and the reaction time is 30-60 min. ​ 5. The process for the preparation of cobalt doped lithium iron vanadium phosphate from spent and old lithium iron phosphate battery powder as claimed in claim 1 wherein, In step S3, the amount of ascorbic acid added is 0.5 g / L; the aluminum removal agent is any one of 5 wt% sodium hydroxide solution, 5 wt% potassium hydroxide solution and 8 wt% ammonia solution, and the pH at the end of the reaction is controlled to be 3-5.

5. ​ 6. The process of claim 1, wherein the process of preparation of cobalt doped lithium iron vanadium phosphate from spent and old lithium iron phosphate battery powder is characterized by, In step S4, the amount of activated carbon added is 0.1-0.3% of the mass of the third filtrate.

7. The process as claimed in claim 1, wherein the process for the preparation of cobalt doped lithium iron vanadium phosphate from spent and old lithium iron phosphate battery powder. In step S5, the phosphorus source is any one of phosphoric acid, monobasic ammonium phosphate, monobasic potassium phosphate, monobasic sodium phosphate, dibasic ammonium phosphate, dibasic potassium phosphate and dibasic sodium phosphate; the iron source is ferrous sulfate heptahydrate, and the lithium source is lithium carbonate.

8. The process for the preparation of cobalt doped lithium iron vanadium phosphate from spent and old lithium iron phosphate battery powder as claimed in claim 1 wherein, In step S5, the carbon source is a mixture of sucrose and citric acid monohydrate, n(citric acid monohydrate):n(sucrose)=(0.08-0.13):1, n(sucrose+ citric acid monohydrate):n(Fe+V)=(0.05-0.1):

1. ​ 9. The method for preparing cobalt-doped vanadium iron phosphate from waste lithium iron phosphate battery powder according to claim 1, characterized in that, In step S6, the spray drying inlet temperature is 250±2℃, and the outlet temperature is 80±5℃.

10. The process of claim 1, wherein the process of preparation of cobalt doped lithium iron vanadium phosphate from spent and old lithium iron phosphate battery powder is characterized by, In step S7, the cooling is jacket water cooling, and the surface temperature of the discharged material is controlled to be ≤80℃.

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