A method for preparing lithium manganese iron phosphate by using waste lithium iron phosphate battery powder

Abstract

The application provides a method for preparing lithium manganese iron phosphate by using waste lithium iron phosphate battery powder, and comprises the following steps: calcining waste lithium iron phosphate battery powder, water immersion, filtration, obtaining filtrate I and residue I; adding ammonia water into the residue I, filtration, obtaining filtrate and residue II, adding a reducing agent into the filtrate, filtration, obtaining filtrate II and crude sponge copper; adding dilute sulfuric acid into the crude sponge copper, filtration, obtaining filtrate III and refined sponge copper; adding alkali liquor I into the residue II, filtration, rinsing the residue with alkali liquor II, obtaining Fe2O3 and FePO4; mixing the above-mentioned filtrate I, II, Fe2O3 and FePO4, controlling the ratio of P, Fe, Mn and Li, obtaining mixed slurry; grinding, spray drying, sintering, crushing and packaging the mixed slurry, and lithium manganese iron phosphate positive electrode material is obtained. The preparation process does not need acid immersion, the amount of acid is reduced, and the waste residue generated by various wet impurity removal is reduced; the prepared product has excellent performance and meets the demand of the battery industry.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of waste battery recycling, and particularly relates to a method for preparing lithium manganese iron phosphate from waste lithium iron phosphate battery powder. BACKGROUND

[0002] With the rapid development of new energy vehicles, a large number of lithium ion power batteries are applied to new energy vehicles, and the service life of lithium ion power batteries is generally 5-8 years, and even shorter. The development of new energy vehicles has a history of nearly 10 years, so a large number of waste lithium ion power batteries are generated over time. At present, there are many reports on the recycling of waste lithium ion batteries.

[0003] Chinese patent CN116119638A discloses a method for preparing lithium manganese iron phosphate from waste lithium iron phosphate powder. The disassembled waste lithium iron phosphate powder is calcined in a reducing atmosphere, further combined with phosphoric acid leaching, the pH of the leaching solution is regulated to 2-3 by using metal Fe and / or Mn, and the matching continuous spray-calcination after the oxidation-reduction of hydrogen peroxide is adopted, so that the lithium manganese iron phosphate product is finally obtained. The method first calcines and then performs acid leaching reaction, and the pH value needs to be regulated in the middle, so that the overall process steps are complicated and difficult to control. The calcination process needs to be performed in an atmosphere containing hydrogen, and hydrogen needs to be additionally prepared or purchased, which undoubtedly increases the calcination cost. In addition, most of the traditional wet recovery is mainly based on organic acid or inorganic acid leaching, and after impurity removal treatment, the three elements of lithium, iron and phosphorus are treated by sedimentation, respectively. The pH of the solution in each stage needs to be controlled and wastewater is generated. SUMMARY

[0004] In view of this, the application provides a method for preparing lithium manganese iron phosphate from waste lithium iron phosphate battery powder

[0005] To achieve the above purpose, the following technical scheme is adopted in the application.

[0006] A method for preparing lithium manganese iron phosphate from waste lithium iron phosphate battery powder, comprising the following steps:

[0007] S1, calcine the waste lithium iron phosphate battery powder at 400-800 DEG C for 10-30 h, add water after the calcination is completed, and react at 40-90 DEG C, filter to obtain a lithium-containing filtrate I and a filter residue I;

[0008] S2, add ammonia water to the filter residue I to react, filter to obtain a copper-lithium-containing filtrate and a filter residue II, add a reducing agent to the filtrate to react, filter to obtain a lithium-containing filtrate II and crude sponge copper;

[0009] S3, add dilute sulfuric acid to the crude sponge copper to react, filter to obtain a filtrate III and refined sponge copper;

[0010] S4, adding alkali liquor I to the above residue II to react, filtering, rinsing the residue with alkali liquor II to obtain Fe2O3 and FePO4;

[0011] S5, taking the above lithium-containing filtrate I, lithium-containing filtrate II, Fe2O3 and FePO4 to mix, controlling n(P):n(Fe+Mn):n(Li)=1:(0.95-1.0):(1.02-1.05) by adding external phosphorus source, manganese source, iron source and lithium source, wherein n(Fe):n(Mn)=(1-X):X(0X≤0.7), and adding carbon source to obtain mixed slurry; the amount of carbon source added is 1-2% of the carbon content in the finished product manganese iron lithium phosphate;

[0012] S6, taking the above mixed slurry to grind, spray dry, sinter, crush and package to obtain the lithium manganese iron phosphate positive electrode material.

[0013] Further, the amount of water added in step S1 is added according to the mass ratio of material to liquid of 1:(2-5).

[0014] Further, the concentration of ammonia water in step S2 is 13-23wt%, and the amount of ammonia water added is according to the mass ratio of material to liquid of 1:(1-2).

[0015] Further, the reducing agent in step S2 is iron powder or aluminum powder, and the amount of reducing agent added is 1.3-1.7 times the amount required for the theoretical reaction.

[0016] In some embodiments, preferably, when the reducing agent is iron powder, the filtrate III in step S3 is ferrous sulfate solution, which is used to adjust the ratio of Li, Fe and P in step S5.

[0017] When the reducing agent is aluminum powder, the filtrate III in step S3 is aluminum sulfate solution, which is mixed with the filtrate obtained after filtering in step S4 to extract aluminum metal.

[0018] Further, the concentration of dilute sulfuric acid in step S3 is 5-20wt%, and the amount of dilute sulfuric acid added is 1.3-2.0 times the amount of the reducing agent.

[0019] Further, the concentration of alkali liquor I in step S4 is 15-30wt%, and the amount of alkali liquor I added is according to the mass ratio of material to liquid of 1:(1-2).

[0020] Further, the concentration of alkali liquor II in step S4 is 2-5wt%, and the amount of alkali liquor II used is 1-3 times the mass of the residue to be rinsed, and the washing water after rinsing is used to prepare alkali liquor I.

[0021] Further, the phosphorus source in step S5 is at least one of phosphoric acid, ammonium dihydrogen phosphate, ammonium hydrogen phosphate, potassium dihydrogen phosphate, potassium hydrogen phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate;

[0022] The iron source is at least one of analytical reagent ferrous sulfate and iron oxide;

[0023] The manganese source is at least one of manganese sulfate, manganese carbonate, manganese oxalate and manganese oxide;

[0024] The lithium source is lithium carbonate;

[0025] The carbon source is at least one of graphite, glucose and sucrose.

[0026] Further, the grinding control D50 of the mixture in step S6 is between 300 and 600 nm; and the gas produced by the spray drying is absorbed by water to be reused as ammonia water to step S2.

[0027] Compared with the prior art, the present application has the following advantages:

[0028] (1) The preparation process of the present application does not need acid immersion, thereby reducing the amount of acid used and the waste residue produced by various wet method impurity removal; in the process, all C is changed into gas, so that no carbon residue is formed, and the carbon residue is a hazardous waste, thereby reducing the generation of waste.

[0029] (2) In the preparation process of the present application, the reducing agent is iron powder or aluminum powder; when iron powder is used, the filtrate produced can be used to adjust the Li, Fe and P ratio in the mixed slurry; when aluminum powder is used, the filtrate produced can be combined with the subsequent aluminum-containing filtrate to extract aluminum; the gas produced in the spray drying process is absorbed by water to be reused as an ammonia water solution in the copper removal process; the entire process fully utilizes the waste residue, waste liquid and waste gas produced, reduces pollution, reduces investment and generates additional value.

[0030] (3) The manganese iron lithium phosphate obtained by the preparation process of the present application has excellent indexes and stable performance, and meets the requirements of battery-grade manganese iron lithium phosphate raw materials. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The technical scheme flowchart of the present application. DETAILED DESCRIPTION

[0032] The present application will be further described in detail below in combination with specific embodiments, so that those skilled in the art can more clearly understand the present application.

[0033] Key test material sources and physicochemical parameters:

[0034] The main components of the waste lithium iron phosphate battery powder are shown in the following table:

[0035] Table 1 waste old lithium iron phosphate battery powder each component situation

[0036] Component Lithium Carbon Copper Aluminum Content (%) 2.2～4.0 6～45 ≤3 ≤3

[0037] The specific raw materials in the present application are all existing substances, which can be directly purchased from the market.

[0038] A method for preparing lithium manganese iron phosphate from waste old lithium iron phosphate battery powder, comprising the following steps:

[0039] S1, calcination: the waste old lithium iron phosphate battery powder is calcined in air or oxygen atmosphere to completely oxidize it, the calcination temperature is controlled to be 400-800℃, and the calcination time is controlled to be 10-30h. The main reaction occurring is: C+O2=CO2, 2C+O2=2CO, 2Cu+O2=2CuO, 4Al+3O2=2Al2O3, 8LiFePO4+2O2=Li2O+Fe2O3+2Li3PO4+6FePO4.

[0040] S2, water immersion: the calcined material is mixed with water, the solid-liquid mass ratio is controlled to be 1:2-5, the reaction temperature is controlled to be 40-90℃, and the reaction time is controlled to be 30-120min, and solid-liquid separation is performed to obtain filter residue 1 and lithium-containing solution 1, and the reaction is: Li2O+H2O=2LiOH.

[0041] S3, copper removal: the filter residue 1 is added to an ammonia water solution with a concentration of 13-23wt% and reacts for 1-6h, the solid-liquid ratio is controlled to be 1:1-2, the cupric oxide and lithium phosphate in the filter residue 1 are fully dissolved in the ammonia water, and then solid-liquid separation is performed to obtain filter residue 2 and filtrate 2.

[0042] S4, sponge copper preparation: a reducing agent is added to the filtrate 2 to reduce copper to copper single element, the reaction time is controlled to be 45-90min, solid-liquid separation is performed to obtain crude sponge copper (the main components of the crude sponge copper are Cu, Al, Al(OH)3 or Cu, Fe, Fe(OH)2) and lithium-containing filtrate 3, and the lithium-containing filtrate 3 and the lithium-containing filtrate 1 are mixed for standby use, wherein the reducing agent is iron powder or Al powder, and the amount of the reducing agent added is controlled to be 1.3-1.7 times the theoretical amount of the reducing agent required for the chemical reaction.

[0043] S5, sponge copper refining: the sponge copper is added to a dilute sulfuric acid solution with a concentration of 5-20wt%, the impurities on the sponge copper are removed, the amount of the acid added is controlled to be 1.3-2.0 times the amount of the reducing agent added in step 4, the reaction time is controlled to be 60-150min, solid-liquid separation is performed to obtain filter residue 4 (refined sponge copper) and filtrate 4, and if the filtrate 4 is an aluminum sulfate solution, it is used together with the filtrate 5 to refine metallic aluminum, and if the filtrate 4 is a ferrous sulfate solution, it is used to adjust the Li, Fe and P ratio.

[0044] S6, aluminum removal: the filter residue 2 is added to a 15-30 wt% liquid alkali solution and reacted for 30-60 min, with a solid-liquid ratio of 1:1-2, so that the aluminum oxide is converted into metavanadate and dissolved in the solution, and the solid-liquid separation obtains filter residue 5 and aluminum-containing filtrate 5, which is used for refining aluminum.

[0045] S7, water washing: the filter residue 5 is rinsed with 2-5% liquid alkali solution, and the amount of rinsing water is controlled to be 1-3 times the mass of the filter residue 5, and the filter residue after washing is Fe2O3 and FePO4, and the washing water is used to prepare liquid alkali and reused in step 6.

[0046] S8, mixing and proportion adjustment: the iron source obtained in step 7, the lithium-containing filtrate 1 obtained in step 2, and the lithium-containing filtrate 3 obtained in step 4 are mixed, and then the phosphorus source, iron source, manganese source and lithium source are added, and the n(P):n(Fe+Mn):n(Li) is controlled to be 1:(0.95-1.0):(1.02-1.05), wherein n(Fe):n(Mn)=(1-X):X(0X≤0.7), and then the carbon source is added, and stirred for 45-90 min, wherein the added phosphorus source is one or more of phosphoric acid, monoammonium phosphate, diammonium phosphate, monopotassium phosphate, dipotassium phosphate, monosodium phosphate, disodium phosphate, the added iron source is analytical reagent ferrous sulfate, iron oxide or the filtrate 4 of step 5, the added manganese source is one or more of manganese sulfate, manganese carbonate, manganese oxalate, manganese oxide, and the added lithium source is lithium carbonate, wherein the carbon source is one or more of graphite, glucose and sucrose, and the amount of carbon source added is determined according to the carbon content of 1-2% in the finished product lithium manganese iron phosphate.

[0047] S9, sand milling: the slurry of step 8 is ground with a sand mill, and the slurry D50 is controlled to be between 300-600 nm.

[0048] S10, the sand milling slurry obtained in step 9 is subjected to spray drying, roller furnace sintering, air flow crushing and packaging to obtain lithium manganese iron phosphate positive electrode material, the gas produced by spray drying is mainly water vapor and ammonia, which is absorbed with water and used in step 3 to remove copper.

[0049] Example 1

[0050] The embodiment provides a method for preparing lithium manganese iron phosphate from waste lithium iron phosphate battery powder, and the specific steps are as follows:

[0051] S1, the waste lithium iron phosphate battery powder is calcined in an air atmosphere to completely oxidize, the calcination temperature is controlled to be 550°C, and the calcination time is 20h, and the calcined material is obtained.

[0052] S2, add water to the calcined material above according to a solid-liquid mass ratio of 1:3, control the temperature to be 70 DEG C, and react for 80 min, to obtain a lithium-containing filtrate 1 and a filter residue 1 after separation.

[0053] S3, add an ammonia water solution with a concentration of 20 wt% to the filter residue 1 above according to a solid-liquid mass ratio of 1:1.5, react for 3 h, to make the copper oxide and lithium phosphate in the filter residue 1 fully dissolved in the ammonia water, filter to obtain a filter residue 2 and a filtrate 2.

[0054] S4, add iron powder to the filtrate 2 above, control the reaction time to be 60 min, to reduce the copper to elemental copper, and obtain a crude sponge copper (the main components of the crude sponge copper are Cu, Fe and Fe(OH)2) and a lithium-containing filtrate 3 after solid-liquid separation. The amount of the iron powder added is 1.3 times the amount required by the theoretical reaction.

[0055] S5, add a dilute sulfuric acid solution with a concentration of 8 wt% to the crude sponge copper above in an amount of 1.5 times the amount of the iron powder, react for 100 min, and obtain a filter residue 4 (refined sponge copper) and a ferrous sulfate solution after solid-liquid separation. The ferrous sulfate solution can be used as an iron source to adjust the Fe content in the mixed slurry in the subsequent step S8.

[0056] S6, add a sodium hydroxide solution with a concentration of 20 wt% to the filter residue 2 above according to a solid-liquid mass ratio of 1:1.5, react for 45 min, to make the aluminum oxide change into metaborate and dissolve in the solution, and obtain a filter residue 5 and an aluminum-containing filtrate 5 after solid-liquid separation. The aluminum-containing filtrate 5 is used to extract metallic aluminum.

[0057] S7, add a sodium hydroxide solution with a concentration of 3 wt% to the filter residue 5 above according to a solid-liquid mass ratio of 1:2 for washing, and the filter residue after washing is Fe2O3 and FePO4. The washing water is used to prepare liquid caustic and is reused in step S6.

[0058] S8, mix the iron source in step S7, the lithium-containing filtrate 1 in step 2 and the lithium-containing filtrate 3 in step S4, and additionally add phosphoric acid, manganese sulfate, lithium carbonate and glucose, control P:(Fe+Mn):Li=1:0.98:1.05 and n(Fe):n(Mn)=0.3:0.7, and stir for 60 min to obtain a mixed slurry. The amount of the glucose added is such that the carbon content in the finished product lithium manganese iron phosphate is 1.5%.

[0059] S9, grind the mixed slurry obtained in step S8 with a sand mill, control the D50 of the slurry to be 400-500 nm, and then perform spray drying, roller furnace sintering, air flow crushing and packaging to obtain the lithium manganese iron phosphate positive electrode material. The gas generated in the spray drying is mainly water vapor and ammonia, which is absorbed with water and used to remove copper in step S3.

[0060] Example 2

[0061] The embodiment provides a method for preparing lithium manganese iron phosphate by using waste lithium iron phosphate battery powder, and the raw materials and steps are basically the same as those of the embodiment 1, and the difference lies in that aluminum powder is used to replace iron powder in step S4, and the addition amount of the aluminum powder is 1.5 times of the required amount in the theoretical reaction. At this time, the main components of the crude sponge copper in step S4 are Cu, Al and Al(OH)3; the solid-liquid separation in step S5 obtains the filter residue 4 and the aluminum sulfate solution, and the aluminum sulfate solution is used together with the aluminum-containing filtrate 5 in step S6 to refine metal aluminum.

[0062] Embodiment 3

[0063] The embodiment provides a method for preparing lithium manganese iron phosphate by using waste lithium iron phosphate battery powder, and the specific steps are as follows:

[0064] S1, the waste lithium iron phosphate battery powder is calcined in an oxygen atmosphere to completely oxidize the waste lithium iron phosphate battery powder, and the calcination temperature is controlled to be 400 DEG C, and the calcination time is 20 h.

[0065] S2, according to the solid-liquid mass ratio 1:5, water is added to the calcined material in step S1, the temperature is controlled to be 90 DEG C, and the reaction is carried out for 30 min, and then the lithium-containing filtrate 1 and the filter residue 1 are separated.

[0066] S3, according to the solid-liquid mass ratio 1:2, the filter residue 1 obtained in step S2 is added with an ammonia water solution with a concentration of 15wt%, and the reaction is carried out for 3h, so that the copper oxide and lithium phosphate in the filter residue 1 are fully dissolved in the ammonia water, and then the filter residue 2 and the filtrate 2 are obtained by filtration.

[0067] S4, iron powder is added to the filtrate 2 obtained in step S3, and the reaction time is controlled to be 90 min, so that the copper is reduced to copper single element, and after the reaction is completed, the solid-liquid separation is carried out to obtain crude sponge copper and lithium-containing filtrate 3. The addition amount of the iron powder is 1.3 times of the required amount in the theoretical reaction.

[0068] S5, the crude sponge copper obtained in step S4 is added with 1.3 times of the amount of iron powder and a dilute sulfuric acid solution with a concentration of 10wt%, and the reaction is carried out for 120 min, so that the filter residue 4 (refined sponge copper) and the ferrous sulfate solution are obtained by solid-liquid separation. The ferrous sulfate solution can be used as an iron source to adjust the Fe content in the mixed slurry in the subsequent step S8.

[0069] S6, according to the solid-liquid mass ratio 1:2, the above filter residue 2 is added with a sodium hydroxide solution with a concentration of 30wt%, and the reaction is carried out for 60 min, so that the aluminum oxide is changed into metaborate and dissolved in the solution, and then the filter residue 5 and the aluminum-containing filtrate 5 are obtained by solid-liquid separation. The aluminum-containing filtrate 5 is used to refine metal aluminum.

[0070] S7, the filter residue 5 obtained in step S6 is washed with a 2wt% sodium hydroxide solution according to a solid-liquid mass ratio of 1:3, and the filter residue after washing is Fe2O3 and FePO4, and the washing water is used to prepare liquid caustic soda and reused in step S6.

[0071] S8, the iron source of step S7, the lithium-containing filtrate 1 of step 2, and the lithium-containing filtrate 3 of step S4 are mixed, and diammonium phosphate, manganese carbonate, lithium carbonate, and sucrose are added, and the P:(Fe+Mn):Li is controlled to be 1:0.98:1.05, and n(Fe):n(Mn) is 0.5:0.5, and stirring is performed for 90 minutes to obtain a mixed slurry. The amount of sucrose added is such that the carbon content in the finished product of lithium manganese iron phosphate is 2%.

[0072] S9, the mixed slurry obtained in step S8 is ground with a sand mill, and the slurry D50 is controlled to be 500-600nm, and then spray drying, roller furnace sintering, jet milling, and packaging are performed to obtain lithium manganese iron phosphate positive electrode material. The gas produced by spray drying is mainly water vapor and ammonia, which is absorbed with water and used for copper removal in step S3.

[0073] Example 4

[0074] This example provides a method for preparing lithium manganese iron phosphate using waste lithium iron phosphate battery powder, which has the same raw materials and steps as example 1, except that in step S8, n(Fe):n(Mn)=(1-X):X(0X≤0.7), where X=0.1, then n(Fe):n(Mn)=0.9:0.1, and the rest is the same as example 1.

[0075] Comparative Example 1

[0076] This comparative example provides a method for preparing lithium manganese iron phosphate (high-temperature solid-phase method), the specific steps are as follows:

[0077] (1) Grinding: analytical pure Li2CO3, FeC2O4·2H2O, MnSO4·H2O, NH4H2PO4, C6H 12 O6·H2O and pure water are put into a sand mill for sand grinding, and the particle size D50 is controlled to be 200-300nm, and D99≤1.5μm, the amount of each raw material is added according to P:(Fe+Mn):Li=1:0.98:1.05, n(Fe):n(Mn)=0.3:0.7, and the sand grinding solid content is controlled to be 35%, and the amount of dextrose is added to make the carbon content in the finished product of lithium manganese iron phosphate be 1.5wt%.

[0078] (2) Spray drying, atmosphere sintering, pulverization, iron removal, and packaging to obtain lithium manganese iron phosphate material; the control conditions of atmosphere sintering are as follows: pre-sintering at 400℃ for 4h under N2 atmosphere, and then sintering at 750℃ for 12h.

[0079] Comparative Example 2

[0080] The present comparative example provides a method for preparing lithium manganese iron phosphate using waste lithium iron phosphate battery powder, which has the same raw materials and steps as Example 1, except that the calcination temperature in step S1 is 300°C.

[0081] Comparative Example 3

[0082] The present comparative example provides a method for preparing lithium manganese iron phosphate using waste lithium iron phosphate battery powder, which has the same raw materials and steps as Example 1, except that the calcination temperature in step S1 is 350°C.

[0083] Comparative Example 4

[0084] The present comparative example provides a method for preparing lithium manganese iron phosphate using waste lithium iron phosphate battery powder, which has the same raw materials and steps as Example 1, except that the amount of iron powder added in step S4 is 1.1 times the theoretical amount.

[0085] Comparative Example 5

[0086] The present comparative example provides a method for preparing lithium manganese iron phosphate using waste lithium iron phosphate battery powder, which has the same raw materials and steps as Example 1, except that the concentration of sulfuric acid solution in step S5 is 50wt%.

[0087] Comparative Example 6

[0088] The present comparative example provides a method for preparing lithium manganese iron phosphate using waste lithium iron phosphate battery powder, which has the same raw materials and steps as Example 1, except that the filter residue 5 is washed with pure water in step S7.

[0089] Comparative Example 7

[0090] The present comparative example provides a method for preparing lithium manganese iron phosphate using waste lithium iron phosphate battery powder, which has the same raw materials and steps as Example 1, except that in step S8, n(Fe):n(Mn)=(1-X):X(0X=0.9, then n(Fe):n(Mn)=0.1:0.9.

[0091] Performance Test

[0092] (1) The copper content of the lithium-containing filtrate 3 obtained in step S4 of the present application Example 1, 2 and Comparative Example 4 was detected. The lithium-containing filtrate 3 of Example 1 had a copper content of 18.4 ppm; the lithium-containing filtrate 3 of Example 2 had a copper content of 11.7 ppm. From the above results, it can be seen that the iron powder or aluminum powder can effectively reduce the copper in the solution, and the Cu ion in the solution can be controlled at a lower level. The lithium-containing filtrate 3 of Comparative Example 4 had a copper content of 7422 ppm, which was significantly higher than that of Examples 1-2. This shows that if the amount of reducing agent added is lower than the optimal range given in the patent, the copper recovery rate will be reduced.

[0093] (2) The carbon residue in the calcined material of step S1 of the present application Examples 1-3 and Comparative Examples 2-3 was detected, and the test results are shown in Table 2.

[0094] Table 2 Carbon residue in the calcined material of step S1 of Examples 1-3 and Comparative Examples 2-3

[0095] Sample Example 1 Example 2 Example 3 Comparative Example 2 Comparative Example 3 Carbon Exclusion Rate (%) 97.25 97.34 98.94 38.66 45.31

[0096] Table 2 shows the effect of high-temperature calcination for carbon removal in step S1 of Examples 1-3 and Comparative Examples 2-3. From the above results, it can be seen that the two comparative examples with a calcination temperature lower than the range of the present patent have poor high-temperature carbon removal effect, with a carbon removal rate of only 38.66% and 45.31%, which do not meet the requirements of the present process for carbon removal.

[0097] (3) The copper content of the ferrous sulfate solution in step S5 of the present application Example 1 and Comparative Example 5 was detected. The copper content of the ferrous sulfate solution in Example 1 was 27.6 ppm, and the copper content of the ferrous sulfate solution in Comparative Example 5 was 8.04 g / L. From the above results, it can be seen that a too high concentration of sulfuric acid will cause the dissolution of the sponge copper, and at the same time, the ferrous sulfate solution cannot be used as an iron source to adjust the Fe content in the mixed slurry in subsequent step S8.

[0098] (4) The aluminum content of the filter residue (Fe2O3 and FePO4) in step S7 of the present application Example 1 and Comparative Example 6 was detected. In Example 1, the aluminum content in Fe2O3 and FePO4 was 9.4 ppm, and in Comparative Example 6, the aluminum content in Fe2O3 and FePO4 was 0.88%. From the test results, it can be seen that if pure water is used for washing, the aluminum content in the filter residue of Fe2O3 and FePO4 will exceed the standard, and the lithium iron manganese phosphate material prepared will not meet the requirements for battery production and use.

[0099] (5) The material prepared in Example 1, 3, 4, Comparative Example 1, 7 of the present application is used as an active material, the binder is PVDF, and the conductive agent is SP, and the slurry is prepared by dissolving the active material, the binder and the conductive agent in NMP solvent according to the mass ratio of active material: binder: conductive agent = 8: 1: 1, and then the slurry is uniformly coated on a metal aluminum foil, vacuum dried, and finally punched into a circular electrode with a diameter of 14 mm as a positive electrode by using a punch. In an Ar-filled glove box (O2 content less than 0.1 ppm, H2O content less than 0.1 ppm), a metal lithium sheet is used as a negative electrode, Celgard2400 porous propylene film is used as a separator, and the electrolyte is a 1 mol / L lithium hexafluorophosphate (LiP Li6) solution, and the solvent is a volume mixture of ethylene carbonate (EC): ethyl carbonate (DMC) = 1:1, and a button cell (CR2032) is prepared according to a certain assembly process, and after completion, it is left to stand for 24 h to allow the electrolyte to fully soak the electrode material; under room temperature conditions (25±1℃), the test conditions are a voltage of 2.5-4.5V, and the test results are shown in Table 3

[0100] Table 3 Performance parameters of the batteries prepared using the lithium manganese iron phosphate obtained in Example 1, 3, 4, Comparative Example 1, 7 as raw material

[0101]

[0102] As can be seen from Table 3, compared with Comparative Example 1, the lithium manganese iron phosphate material prepared by the preparation method of the present application (Example 1, 3, 4) has a similar first charge-discharge efficiency and cycle performance, i.e., the lithium manganese iron phosphate material prepared from the waste lithium iron phosphate battery powder meets the use requirements; compared with Comparative Example 7, the lithium manganese iron phosphate material prepared by the preparation method of the present application (Example 1, 3, 4) has better first charge-discharge efficiency and cycle performance.

[0103] The above are only preferred embodiments of the present application, and are not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing lithium manganese iron phosphate using waste lithium iron phosphate battery powder, characterized in that, Comprise the following steps: S1, take the waste lithium iron phosphate battery powder in 400~800 ℃ conditions calcination 10~30h, after calcination add water, in 40~90 ℃ conditions reaction, filtration, get lithium-containing filtrate I and filter residue I; S2, to the above filter residue I add ammonia water reaction, filtration, get copper lithium-containing filtrate and filter residue II, to the filtrate add reducing agent reaction, filtration, get lithium-containing filtrate II and crude sponge copper; S3, to the above crude sponge copper add dilute sulfuric acid reaction, filtration, get filtrate III and refined sponge copper; S4, to the above filter residue II add lye I reaction, filtration, with lye II to filter residue bleaching, get Fe2O3 and FePO4; S5, take the above lithium-containing filtrate I, lithium-containing filtrate II, Fe2O3, FePO4 mixing, through the additional phosphorus source, manganese source, iron source, lithium source control n (P) : n (Fe+Mn) : n (Li) =1: (0.95~1.0) : (1.02~1.05), wherein n (Fe) : n (Mn) = (1-X) : X (0X≤0.7), and add carbon source, get mixed slurry;Carbon source added amount to the finished product manganese iron phosphate lithium carbon content is 1~2% as the criterion; S6, take the above mixed slurry grinding, spray drying, sintering, crushing, packaging, namely get manganese iron phosphate lithium positive electrode material.

2. The method of claim 1, wherein, The water added in step S1 is added according to the mass ratio of material to liquid of 1: (2~5).

3. The method of claim 1, wherein, The ammonia water concentration in step S2 is 13~23wt%, and the ammonia water added amount is added according to the mass ratio of material to liquid of 1: (1~2).

4. The method of claim 1, wherein, The reducing agent in step S2 is iron powder or aluminum powder, and the reducing agent added amount is 1.3-1.7 times of the theoretical reaction required amount.

5. The method of claim 4, wherein, When the reducing agent is iron powder, the filtrate III in step S3 is ferrous sulfate solution, which is used to adjust the Li, Fe and P ratio in step S5. When the reducing agent is aluminum powder, the filtrate III in step S3 is aluminum sulfate solution, which is mixed with the filtrate obtained after filtration in step S4 to refine aluminum.

6. The method of claim 1, wherein, The dilute sulfuric acid concentration in step S3 is 5~20wt%, and the dilute sulfuric acid added amount is 1.3~2.0 times of the amount of the reducing agent.

7. The method of claim 1, wherein, The lye I concentration in step S4 is 15~30wt%, and the lye I added amount is added according to the mass ratio of material to liquid of 1: (1~2).

8. The method of claim 1, wherein, The lye II concentration in step S4 is 2~5wt%, and the lye II amount is 1~3 times of the mass of the filter residue to be bleached, and the washing water after bleaching is used to prepare lye I.

9. The method of claim 1, wherein, The phosphorus source in step S5 is at least one of phosphoric acid, monoammonium phosphate, dihydrogen ammonium phosphate, monopotassium phosphate, dipotassium phosphate, monosodium phosphate, disodium phosphate; The iron source is at least one of analytical pure ferrous sulfate and iron oxide; The manganese source is at least one of manganese sulfate, manganese carbonate, manganese oxalate and manganese oxide; The lithium source is lithium carbonate; The carbon source is at least one of graphite, glucose and sucrose.

10. The method of claim 1, wherein, The grinding control mixture D50 in step S6 is between 300~600nm; The gas produced by spray drying is absorbed with water and reused as ammonia water in step S2.

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