Method for synthesizing titanium-doped iron phosphate

Abstract

The invention discloses a method for synthesizing titanium-doped iron phosphate, and belongs to the technical field of recycling of lithium battery positive electrode materials. The technical problems to be solved are to reduce the recycling cost of the waste phosphate positive electrode material, improve the economic benefit, improve the electrochemical performance and powder compaction of the titanium-doped lithium iron phosphate / carbon composite material and improve the yield of the finished product titanium. According to the technical scheme, the method comprises the following steps: reacting the waste phosphate positive electrode material in a phosphoric acid solution, and performing solid-liquid separation after the reaction to obtain filter residues 1 and filtrate 1; reacting an iron source with the filtrate 1, and performing solid-liquid separation after the reaction is finished to obtain filter residues 2 and filtrate 2; mixing the filtrate 2 with a titanium source, heating, and adding an oxidizing agent to obtain slurry; aging the slurry, and then washing, drying and sintering to obtain titanium-doped iron phosphate; wherein the ratio of the mass content of titanium provided by the titanium source in the titanium-doped iron phosphate to the mass content of titanium in the waste phosphate positive electrode material is (1-3): (1-3).

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of recycling and reusing lithium battery cathode materials, and particularly relates to a method for synthesizing titanium-doped iron phosphate. BACKGROUND

[0002] For understanding the technical content of the application: Phosphate cathode materials (such as lithium iron phosphate, LiFePO4) have become an ideal choice for power batteries and energy storage systems due to their high safety, long cycle life, low cost and environmental friendliness, and are widely used in electric vehicles, energy storage power stations, aerospace and other fields. In recent years, with the rapid development of the new energy industry, the production of lithium iron phosphate has increased rapidly, and a large amount of waste lithium iron phosphate material has been generated. If the waste lithium iron phosphate cathode material from the disassembled retired power batteries and energy storage batteries cannot be effectively recycled, not only will it cause waste of resources such as lithium, iron and phosphorus, but also it may cause serious pollution to the ecological environment due to the leakage of heavy metals and electrolyte. Therefore, it is of great significance to develop efficient and environmentally friendly lithium iron phosphate recycling technology.

[0003] The existing lithium iron phosphate recycling technology has high limitations, and the recycling methods of waste lithium iron phosphate mainly include high-temperature roasting method and hydrometallurgical leaching method, but these methods still have the following problems: (1) The high-temperature roasting method decomposes lithium iron phosphate at high temperature (700℃), releases harmful gases (such as HF, P2O5), pollutes the environment; the energy consumption is high, and iron and phosphorus are mainly in the form of mixed oxides, which are difficult to be directly regenerated into high-purity lithium iron phosphate; the recovery rate of lithium is low, and part of the lithium is lost by volatilization at high temperature. (2) The wet acid leaching method usually uses strong acids such as sulfuric acid and hydrochloric acid for leaching, which generates a large amount of acidic wastewater, and the subsequent treatment cost is high; iron and phosphorus are mainly precipitated in the form of iron phosphate (FePO4), but the purity of iron phosphate obtained by the traditional method is low, containing impurities such as Na + , K + , Ca² + , which affects the electrochemical performance of the regenerated material; the existing technology focuses more on the recovery of lithium (such as the preparation of lithium carbonate), and less on the high-value recovery of iron and phosphorus, resulting in low resource utilization rate. (3) Performance problems of regenerated lithium iron phosphate The regenerated lithium iron phosphate by the traditional recycling method often has lattice defects, poor electrical conductivity and other problems, which leads to its electrochemical performance (such as specific capacity, cycle stability) not as good as that of newly prepared materials; for example, the initial discharge capacity of some regenerated LFP at 0.1C rate is only 140mAh / g, which is much lower than that of commercial LFP (~160mAh / g).

[0004] As the journal title or book title "Green Mining and Metallurgy", February 2023, the literature name "Research Progress on Recycling Technology of Waste Lithium Iron Phosphate Battery Positive Material", volume number "Volume 39, Issue 1", the literature in the form of strong acid + oxidizing agent converts all metal elements in lithium iron phosphate from solid form to ions in liquid, and then according to the properties of different metal ions, further uses precipitation, adsorption, ion exchange and other methods to extract metal ions in the solution in the form of oxide, salt, etc., so as to realize the recycling of all components of waste lithium iron phosphate positive material. Although the full component dissolution and precipitation method can realize the recycling of all components of waste lithium iron phosphate positive material, it has the advantages of high metal recovery rate and high purity of recovered products, but in the dissolution process, strong acid needs to be added to completely destroy the material structure, usually with large acid consumption, long process, large wastewater discharge and high cost. When the price of lithium salt falls, the economic efficiency of this process is not ideal.

[0005] The potential advantages of titanium doping in lithium iron phosphate recycling. Research has found that introducing titanium (Ti) elements into lithium iron phosphate can significantly improve its electrochemical performance: Ti 4+ Doping can stabilize the crystal structure, reduce the volume change during lithium ion deintercalation, and improve the cycle stability; the introduction of Ti can enhance the electronic conductivity, reduce the polarization, and improve the rate performance; Ti-doped lithium iron phosphate (LiFe 1-x Ti x PO4) performs better at high temperature and high voltage, suitable for long-life energy storage batteries. However, existing lithium iron phosphate recycling technologies have not fully utilized the advantages of titanium doping: most recycling methods only focus on the separation of lithium and iron, without considering optimizing the performance of regenerated materials through doping; in the traditional wet recycling process, iron and phosphorus are mostly precipitated in amorphous FePO4 form, which is difficult to be directly used for preparing high-performance Ti-doped LFP; if titanium source (such as titanium dioxide, titanyl sulfate, etc.) can be introduced in situ during the recycling process, combined with optimized sintering process, it is expected to directly regenerate high-performance Ti-doped lithium iron phosphate, and improve the added value of recycled products.

[0006] Yet another Chinese patent publication No. CN120172374A discloses a method for titanium-doped iron phosphate, comprising the following steps: step one: dissolving titanium white by-product ferrous sulfate powder in water to prepare a titanium-containing iron source solution; step two: adding water to a reaction kettle and stirring; step three: adding the titanium-containing iron source solution, a phosphorus source solution, ammonia water and an oxidizing agent to the reaction kettle to prepare a primary slurry; step four: filtering and washing the primary slurry until the electrical conductivity is less than or equal to 2000 us / cm, and then adding water to prepare a secondary slurry; step five: adding phosphoric acid to the reaction kettle and heating to 60-70℃; step six: adding the secondary slurry to the reaction kettle and performing a heat preservation reaction with the phosphoric acid; and step seven: filtering and washing the reaction product obtained in step six until the electrical conductivity is less than or equal to 500 us / cm, and then drying and sintering. The present application simplifies the titanium doping process and improves the utilization rate of titanium in titanium white by-products and the purity of titanium-doped iron phosphate products. However, the process is relatively complex, and ammonia water is needed to control the pH of the system during the reaction process. Acidic by-products will also be produced.

[0007] Therefore, there is an urgent need in the art to provide a method that can improve the titanium yield of the finished product, has a simple process, high purity of the finished product, and better environmental protection. SUMMARY

[0008] The present application aims to provide: A method for preparing titanium-doped iron phosphate from waste phosphate positive electrode materials, and related technologies, to solve the technical problems of reducing the cost of recycling waste phosphate positive electrode materials, improving economic benefits, improving the electrochemical performance of titanium-doped iron lithium / carbon composite materials, improving powder compaction, and improving the titanium yield of the finished product.

[0009] Term explanation: Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the subject matter of the claims belongs. Unless otherwise indicated, all patents, patent applications, publications cited herein are hereby incorporated by reference in their entirety. If there is a plurality of definitions for a term herein, the definition in this section applies.

[0010] It should be understood that the above brief summary and the following detailed description are exemplary and explanatory only and are not restrictive of the subject matter of the present application. In the present application, the use of the singular includes the plural unless specifically stated otherwise. It should also be noted that the use of "or" means "and / or" unless otherwise stated. Furthermore, the use of the term "including" as well as other forms such as "contain" "comprise" and "comprises" are not limiting.

[0011] The definitions of standard chemical terms can be found in the reference "Applied Electrochemistry" by Yang Hui and Lu Wenqing, Science Press.

[0012] Unless otherwise indicated, conventional methods within the skill of the art are employed, such as compaction density measurements, electrochemical performance measurements, and the like.

[0013] Unless specifically defined, the use of each term herein is to be given its ordinary meaning in the art. For example, the use of a vendor's instructions for the use of a reagent kit, or the like, is to be assumed, unless otherwise indicated. Standard techniques are employed in the methods and procedures described herein, such as those described in the various publications referenced and discussed below, and in the Examples. The techniques and procedures are generally performed according to conventional methods well known in the art and as described in the various publications referenced and discussed below, unless otherwise indicated.

[0014] As used herein, the term "washing" refers to the removal of impurities or other soluble contaminants from the surface of a material using a solvent, thereby increasing the purity of the material and the efficiency of subsequent processing.

[0015] As used herein, the term "drying" refers to the removal of water or other volatile solvents from a material, thereby preventing the degradation of material properties or abnormal reactions due to the presence of water during subsequent processing.

[0016] As used herein, the term "sintering" refers to the physical and chemical bonding between particles of a material through high-temperature treatment, resulting in a dense solid.

[0017] As used herein, the term "solid-liquid separation" refers to the process of separating solid particles from a liquid. It is a common physical operation widely used in various fields such as chemistry, chemical engineering, pharmacy, food science, and environmental science. The purpose of solid-liquid separation is to separate solid particles from a liquid in order to recover the solid, purify the liquid, or achieve separation processing of both.

[0018] In a first aspect, the present application provides a method for preparing titanium-doped iron phosphate from waste phosphate cathode material, comprising the following steps: S1, reacting the waste phosphate cathode material with a phosphoric acid solution, and then performing solid-liquid separation to obtain a filter residue 1 and a filtrate 1; S2, reacting the iron source with the filtrate 1, and then performing solid-liquid separation to obtain a filter residue 2 and a filtrate 2; S3, mixing the filtrate 2 with a titanium source, heating, and then adding an oxidizing agent to obtain a slurry; S4, aging the slurry, and then washing, drying, and sintering to obtain titanium-doped iron phosphate; In the titanium-doped iron phosphate, the mass content of titanium provided by the titanium source and the mass content of titanium provided by the waste phosphate cathode material are in a ratio of 1-3:1-3.

[0019] In the first aspect, the waste phosphate cathode material is selected from at least one of the following: waste lithium iron phosphate, waste iron phosphate, and the residual phosphate material after lithium extraction from waste lithium iron phosphate.

[0020] The technical feature of the waste phosphate positive material is preferably: the waste phosphate positive material with Al element content < 300 ppm, Cu element content 0-500 ppm; and / or the waste phosphate positive material with Al element content 300-10000 ppm, Cu element content 0-500 ppm, Ti element content 2000-6000 ppm.

[0021] The technical feature of the phosphoric acid solution is preferably: the mass concentration of 30-35%.

[0022] The technical feature of the phosphoric acid solution is preferably: the mass concentration of 30-35%.

[0023] The technical feature of the phosphoric acid solution is further preferably: the mass concentration of 30%, 31%, 32%, 33%, 34%, 35%.

[0024] The technical feature of the phosphoric acid solution is further preferably: the mass concentration of 30%.

[0025] The technical feature of the reaction temperature of step S1 is preferably: 90-100℃.

[0026] The technical feature of the reaction temperature of step S1 is preferably: 90-100℃.

[0027] The technical feature of the reaction temperature of step S1 is further preferably: 90℃, 91℃, 92℃, 93℃, 94℃, 95℃, 96℃, 97℃, 98℃, 99℃, 100℃.

[0028] The technical feature of the reaction temperature of step S1 is further preferably: 90℃.

[0029] The technical feature of the reaction time of step S1 is preferably: 3-12h.

[0030] The technical feature of the reaction time of step S1 is preferably: 3-6h.

[0031] The technical feature of the reaction time of step S1 is further preferably: 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h.

[0032] The technical feature of the reaction time of step S1 is further preferably: 3h.

[0033] The technical feature of the iron source is at least one of: iron powder, iron sheet, iron ingot.

[0034] The technical feature of the iron source is preferably: iron powder, iron sheet.

[0035] The technical feature of the iron source is further preferably: iron powder.

[0036] wherein the technical feature is that the total phosphorus content and the total iron content in the filtrate 2 after adding the iron source have a molar ratio of 2.8:1-3.2:1.

[0037] wherein the technical feature is that the total phosphorus content and the total iron content after adding the iron source have a molar ratio of 2.8:1-3.0:1.

[0038] wherein the technical feature is that the molar ratio of iron in the waste phosphate positive electrode material and phosphorus in phosphoric acid is selected from 1:5-10.

[0039] wherein the technical feature is that the molar ratio of iron in the waste phosphate positive electrode material and phosphorus in phosphoric acid is preferably 1:5, 1:6, 1:7, 1:8, 1:9 and 1:10.

[0040] wherein the technical feature is that the molar ratio of iron in the waste phosphate positive electrode material and phosphorus in phosphoric acid is further preferably 1:5-1:8.

[0041] wherein the technical feature is that the titanium source added in step S3 is selected from at least one of titanium dioxide, titanyl sulfate, and tetrabutyl titanate.

[0042] wherein the technical feature is that the titanium source added in step S3 is preferably titanyl sulfate and titanium dioxide.

[0043] wherein the technical feature is that the amount of titanium source added is that the titanium content in the titanium-doped iron phosphate is 3000ppm-5000ppm.

[0044] wherein the technical feature is that the titanium content in the titanium-doped iron phosphate is preferably 3000ppm, 3100ppm, 3200ppm, 3300ppm, 3400ppm, 3500ppm, 3600ppm, 3700ppm, 3800ppm, 3900ppm, 4000ppm, 4100ppm, 4200ppm, 4300ppm, 4400ppm, 4500ppm, 4600ppm, 4700ppm, 4800ppm, 4900ppm, 5000ppm.

[0045] wherein the technical feature is that the mass ratio of the titanium content in the waste phosphate positive electrode material to the titanium content of the added titanium source is preferably 0.5-1.0:1.

[0046] wherein the technical feature is that the mass ratio of the titanium content in the waste phosphate positive electrode material to the titanium content of the added titanium source is further preferably 0.5:1, 0.6:1, 0.7:1, 0.8:1 and 0.9:1.

[0047] wherein the technical feature is that the mass of the titanium source is 0.15-0.80% of the mass of the iron phosphate prepared by co-precipitation.

[0048] The oxidizing agent is preferably hydrogen peroxide.

[0049] The hydrogen peroxide is preferably added dropwise.

[0050] The dropwise addition is preferably for 30-120 minutes.

[0051] The dropwise addition is more preferably for 90-120 minutes.

[0052] The molar ratio of the oxidizing agent to the iron in the filtrate 2 is preferably 0.6-0.7:1.

[0053] The molar ratio of the oxidizing agent to the iron in the filtrate 2 is preferably 0.6-0.7:1.

[0054] The molar ratio of the oxidizing agent to the iron in the filtrate 2 is preferably 0.6-0.7:1.

[0055] The mass concentration of the hydrogen peroxide is preferably 20-30%.

[0056] The mass concentration of the hydrogen peroxide is preferably 20-30%.

[0057] The mass concentration of the hydrogen peroxide is preferably 20-30%.

[0058] The mass concentration of the hydrogen peroxide is preferably 20-30%.

[0059] The heating in step S3 is preferably 55-65°C.

[0060] The heating in step S3 is preferably 55-65°C.

[0061] The heating in step S3 is preferably 55-65°C.

[0062] The heating in step S3 is preferably 55-65°C.

[0063] The temperature of the aging in step S4 is preferably 90-95°C.

[0064] The temperature of the aging in step S4 is preferably 90-95°C.

[0065] The temperature of the aging of the technical feature step S4 is further preferably 90℃, 91℃, 92℃, 93℃, 94℃, 95℃.

[0066] The temperature of the aging of the technical feature step S4 is further preferably 90℃, 91℃, 92℃, 93℃, 94℃, 95℃.

[0067] The time of the aging of the technical feature step S4 is selected from 60-180min.

[0068] The time of the aging of the technical feature step S4 is preferably 60-100min.

[0069] The time of the aging of the technical feature step S4 is further preferably 60min, 65min, 70min, 75min, 80min, 85min, 90min, 95min, 100min.

[0070] The time of the aging of the technical feature step S4 is further preferably 60min, 65min, 70min, 75min, 80min, 85min, 90min, 95min, 100min.

[0071] The temperature of the sintering of the technical feature is selected from 400-700℃.

[0072] The temperature of the sintering of the technical feature is preferably 500-600℃.

[0073] The temperature of the sintering of the technical feature is further preferably 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃.

[0074] The temperature of the sintering of the technical feature is further preferably 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃.

[0075] The time of the sintering of the technical feature is selected from 3-6h.

[0076] The time of the sintering of the technical feature is further preferably 3-4h.

[0077] The time of the sintering of the technical feature is further preferably 4h. Based on further solving or simultaneously solving multiple technical problems of the technical problem of the present application, in the technical scheme provided by the first aspect of the present application, the preferred scheme comprises: The first preferred solution is: the titanium source added in step S3. This technical solution further solves the technical problem of "further reducing the cost of recycling waste phosphate positive electrode materials, improving economic benefits, improving the electrochemical performance and powder compaction of titanium-doped lithium iron phosphate / carbon composite materials, and improving the yield of finished titanium" on the basis of solving the technical problem of "reducing the cost of recycling waste phosphate positive electrode materials, improving economic benefits, improving the electrochemical performance and powder compaction of titanium-doped lithium iron phosphate / carbon composite materials, and improving the yield of finished titanium".

[0078] The second preferred solution is: the amount of titanium source added. This technical solution further solves the technical problem of "further reducing the cost of recycling waste phosphate positive electrode materials, improving economic benefits, improving the electrochemical performance and powder compaction of titanium-doped lithium iron phosphate / carbon composite materials, and improving the yield of finished titanium" on the basis of solving the technical problem of "reducing the cost of recycling waste phosphate positive electrode materials, improving economic benefits, improving the electrochemical performance and powder compaction of titanium-doped lithium iron phosphate / carbon composite materials, and improving the yield of finished titanium".

[0079] The third preferred solution is: the ratio of the titanium content in the generated lithium iron phosphate to the titanium content in the waste phosphate. This technical solution further solves the technical problem of "further reducing the cost of recycling waste phosphate positive electrode materials, improving economic benefits, improving the electrochemical performance and powder compaction of titanium-doped lithium iron phosphate / carbon composite materials, and improving the yield of finished titanium" on the basis of solving the technical problem of "reducing the cost of recycling waste phosphate positive electrode materials, improving economic benefits, improving the electrochemical performance and powder compaction of titanium-doped lithium iron phosphate / carbon composite materials, and improving the yield of finished titanium".

[0080] In a second aspect, the embodiments of the present application provide that: the iron element accounts for 35.00-37.00% of the mass of the titanium-doped lithium iron phosphate, the phosphorus element accounts for 20.00-21.00% of the mass of the titanium-doped lithium iron phosphate, and the molar ratio of the iron element to the phosphorus element is 0.950-0.980; the specific surface area of the titanium-doped lithium iron phosphate is 6-14 m 2 / g, and the titanium content of the titanium-doped lithium iron phosphate is 3000-5000 ppm.

[0081] Among them, the technical features include: the composition and specific surface area of the titanium-doped lithium iron phosphate.

[0082] Among them, the technical features of the composition of the titanium-doped lithium iron phosphate are selected from: the iron element accounts for 35.00-37.00% of the mass of the titanium-doped lithium iron phosphate, the phosphorus element accounts for 20.00-21.00% of the mass of the titanium-doped lithium iron phosphate, and the specific surface area is 6-14 m 2 / g.

[0083] The composition of the titanium-doped iron phosphate is preferably: iron element accounts for 35.51-36.5% of the mass of the titanium-doped iron phosphate, phosphorus element accounts for 20.42-21% of the mass of the titanium-doped iron phosphate, and the specific surface area is 10.37-14 m 2 / g.

[0084] The composition of the titanium-doped iron phosphate is further preferably: iron element accounts for 35.51-36.07% of the mass of the titanium-doped iron phosphate, phosphorus element accounts for 20.42-20.72% of the mass of the titanium-doped iron phosphate, and the specific surface area is 10.37-13.23 m 2 / g.

[0085] In a third aspect, the present application provides a preparation method of titanium-doped lithium iron phosphate / carbon composite material, comprising the following steps: mixing, grinding and drying the titanium-doped iron phosphate, lithium source and carbon source, and then sintering in an inert gas atmosphere to obtain the lithium iron phosphate / carbon composite material.

[0086] The lithium source, the carbon source and the sintering are technical features.

[0087] The lithium source is selected from one or more of lithium carbonate, lithium acetate and lithium hydroxide.

[0088] The lithium source is preferably lithium carbonate and lithium acetate.

[0089] The lithium source is further preferably lithium carbonate.

[0090] The molar ratio of lithium in the lithium source to iron in the titanium-doped iron phosphate is selected from 1.02-1.06:1.

[0091] The molar ratio of lithium in the lithium source to iron in the titanium-doped iron phosphate is preferably 1.02:1, 1.03:1, 1.04:1, 1.05:1 or 1.06:1.

[0092] The carbon source is selected from at least one of glucose, sucrose, citric acid, polyethylene glycol, polyvinyl alcohol, starch, cellulose and fructose.

[0093] The carbon source is preferably glucose, sucrose and citric acid.

[0094] The carbon source is further preferably glucose.

[0095] The mass percentage of the carbon source in the titanium-doped iron phosphate is selected from 8-20%.

[0096] The mass percentage of the carbon source in the titanium-doped iron phosphate is preferably 8-15%.

[0097] The mass percentage of the technical feature carbon source in the titanium-doped iron phosphate is further preferably 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%.

[0098] The technical feature of the grinding system is at least one of a water system or an ethanol system.

[0099] The technical feature of the grinding is selected from coarse grinding and fine grinding.

[0100] The technical feature of the coarse grinding is preferably a coarse grinding time of 30-60 min.

[0101] The technical feature of the fine grinding is further preferably a particle size of 560-860 nm after fine grinding.

[0102] The technical feature of the sintering temperature and time is selected from a temperature of 740-850℃ and a time of 6-10h.

[0103] The technical feature of the sintering temperature and time is preferably a temperature of 740-800℃ and a time of 6-10h.

[0104] The technical feature of the sintering temperature and time is further preferably a temperature of 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, or 800℃ and a time of 6h, 7h, 8h, 9h, or 10h.

[0105] In a fourth aspect, the application provides a titanium-doped lithium iron phosphate / carbon composite material prepared by the preparation method.

[0106] In a fifth aspect, the application provides application of the titanium-doped lithium iron phosphate and the titanium-doped lithium iron phosphate / carbon composite material in battery preparation.

[0107] The application has the following beneficial effects: 1. Compared with the prior art, the application has better technical effects in reducing the cost of recycling waste phosphate positive electrode materials, improving economic benefits, improving the electrochemical performance of the titanium-doped lithium iron phosphate / carbon composite material, and improving powder compaction and titanium yield of finished products. On the basis of recycling waste lithium iron phosphate to prepare iron phosphate, two titanium sources are introduced, one part of which uses the titanium source of waste lithium iron phosphate (the titanium source recycling rate is as high as 98% or more), and the other part is prepared by doping a titanium source to prepare a titanium-doped iron phosphate, which avoids the titanium removal process in the traditional recycling of waste lithium iron phosphate to prepare iron phosphate, reduces the recycling cost, improves the utilization value of titanium, and through the synergistic effect of the secondary titanium source doping, the utilization rate of the secondary titanium source is as high as 87% or more, which is conducive to improving the electrochemical performance and powder compaction of lithium iron phosphate.

[0108] 2. The application uses a specific amount of titanium compound to control the amount of titanium content added in the synthesis stage of iron phosphate, and at the same time optimizes the ratio of atomic-level titanium source (the titanium source in the waste phosphate completely dissolves in the phosphoric acid solution) in the waste phosphate to the formed molecular-level titanium source by adding titanium source, to ensure that the titanium elements of the two titanium sources are uniformly dispersed in the product.

[0109] Titanium doping can inhibit the excessive growth of FePO4 precursor during high-temperature synthesis, forming more uniform particles; titanium doping can reduce the particle agglomeration tendency of FePO4 precursor when sintered into LiFePO4, reduce the "hard agglomeration" phenomenon of secondary particles, maintain the independence of primary particles, and is beneficial to powder compaction (the powder after titanium doping can reach 2.50 g / cm 3 and above), while titanium doping can improve the electrochemical performance of lithium iron phosphate.

[0110] 3. The application uses recycled phosphate positive electrode material to regenerate and synthesize titanium-doped iron phosphate, and the prepared lithium iron phosphate has good electrochemical performance and powder compaction density, and can reach the product level of market iron phosphate. BRIEF DESCRIPTION OF DRAWINGS

[0111] Figure 1 SEM image of the titanium-doped iron phosphate sample of Example 1 at 80K magnification.

[0112] Figure 2 XRD characterization spectrum of the titanium-doped iron phosphate sample of Example 1.

[0113] Figure 3 XRD comparison chart of the titanium-doped lithium iron phosphate / carbon composite material of Application Example 1 and Comparative Example 1.

[0114] Figure 4 Electrochemical performance of the lithium iron phosphate / carbon composite material prepared in Application Example 1. DETAILED DESCRIPTION

[0115] The following non-limiting examples can enable those of ordinary skill in the art to more fully understand the present application, but in no way limit the present application. The following content is only an exemplary description of the scope of the present application, and those skilled in the art can make various changes and modifications to the present application based on the disclosed content, and it should also belong to the scope of the present application.

[0116] The present application will be further described in the following specific examples. The various instruments, devices, equipment, reagents, products, etc. used in the examples of the present application are obtained through conventional commercial channels unless otherwise specified.

[0117] Example 1 The embodiment uses lithium iron phosphate waste powder with Al content of 104.2 ppm, Cu content of 9.1 ppm, C content of 1.20%, and Ti content of 3039 ppm.

[0118] 3825.0 g of a 30% phosphoric acid solution was weighed into a glass reaction kettle, stirring was started, and then 369.5 g of waste lithium iron phosphate powder was added. The mixture was heated to 90°C and reacted for 3 h. After the reaction, filtration was performed, and a small amount of water was used for washing. The filtrate 1 and the filter residue 1 were obtained. The filter residue 1 was dried and weighed, and the mass was 8.1 g. This indicated that the dissolution and leaching rate of the phosphoric acid solution was as high as 97.8%. The filter residue 1 could be redissolved in the phosphoric acid solution for reuse.

[0119] According to the molar ratio of phosphorus / iron = 3.0, 132.6 g of iron powder was added to the filtrate 1, and the mixture was heated at 55°C for 2 h. After the reaction, filtration was performed, and the bright green ferrous phosphate filtrate 2 and the filter residue 2 were obtained.

[0120] The filtrate 2 was placed in a reaction kettle, 4.0 g (2500 ppm) of titanium dioxide powder was added, and the system was heated to 55°C. After stabilization, 475.0 g of a 20% hydrogen peroxide solution was added through a peristaltic pump, and the time control was 90 min. After the dropwise addition was completed, the mixture was heated to 90°C and aged for 60 min.

[0121] After the reaction, the mixture was filtered and washed until the conductivity of the filtrate was below 300 us / cm. The filter cake was dried in an oven at 120°C and then dehydrated in a muffle furnace at 650°C for 4 h.

[0122] The specific surface area of the titanium-doped iron phosphate after dehydration was 11.57 m 2 / g, the Fe% was 36.07%, the P% was 20.7%, the molar ratio of iron to phosphorus was 0.964, and the titanium content was 3825 ppm. At this time, the yield of the second addition of titanium was 81.0%.

[0123] Example 2 The embodiment uses lithium iron phosphate waste powder with Al content of 111.5 ppm, Cu content of 10.8 ppm, C content of 1.20%, and Ti content of 3207 ppm.

[0124] 3825.0 g of a 30% phosphoric acid solution was weighed into a glass reaction kettle, stirring was started, and then 369.5 g of waste lithium iron phosphate powder was added. The mixture was heated to 90°C and reacted for 3 h. After the reaction, filtration was performed, and a small amount of water was used for washing. The filtrate 1 and the filter residue 1 were obtained. The filter residue 1 was dried and weighed, and the mass was 8.1 g. This indicated that the dissolution and leaching rate of the phosphoric acid solution was as high as 97.8%. The filter residue 1 could be redissolved in the phosphoric acid solution for reuse.

[0125] Take 132.8g iron powder according to the molar ratio of phosphorus / iron=3.0, add it to the filtrate 1, and react for 2h under the condition of heating at 55℃. After the reaction is completed, filtration is carried out to obtain bright green ferrous phosphate filtrate 2 and filter residue 2.

[0126] Put the filtrate 2 into the reaction kettle, add 4.80g (3000ppm) titanium dioxide powder, and then raise the system to 55℃. After stabilization, add 475.00g hydrogen peroxide solution with a concentration of 20% through a peristaltic pump, and control the time to be 90min. After the dropwise addition is completed, heat to 90℃ and age for 60min.

[0127] After the reaction is completed, wash by suction filtration until the conductivity of the filtrate is below 300us / cm. Dry the filter cake in an oven at 120℃, and then dehydrate in a muffle furnace at 600℃ for 5h.

[0128] The specific surface area of the titanium-doped iron phosphate after dehydration is 11.29m 2 / g, Fe%=35.86%, P%=20.66%, the molar ratio of iron to phosphorus is 0.960, and the titanium content is 4348ppm. At this time, the yield of the second addition of titanium element is 81.6%.

[0129] Example 3 In this example, the Al element content in the lithium iron phosphate waste powder is 114.5ppm, the Cu element content is 12.7ppm, the C element content is 1.16%, and the Ti element content is 3883ppm.

[0130] Take 3825.0g phosphoric acid solution with a concentration of 30% and place it in a glass reaction kettle. After stirring is started, add 369.5g waste lithium iron phosphate powder, heat to 90℃, and react for 3h. After the reaction is completed, filtration is carried out, and a small amount of water is washed. The filter cake 1 is dried and weighed, and the mass is 7.75g, indicating that the dissolution leaching rate of the phosphoric acid solution is as high as 97.9%. The filter cake 1 can be dissolved again in the phosphoric acid solution for reuse.

[0131] Take 132.8g iron powder according to the molar ratio of phosphorus / iron=3.0, add it to the filtrate 1, and react for 2h under the condition of heating at 55℃. After the reaction is completed, filtration is carried out to obtain bright green ferrous phosphate filtrate 2 and filter residue 2.

[0132] Put the filtrate 2 into the reaction kettle, add 4.80g (3000ppm) titanium dioxide powder, and then raise the system to 55℃. After stabilization, add 475.00g hydrogen peroxide solution with a concentration of 20% through a peristaltic pump, and control the time to be 90min. After the dropwise addition is completed, heat to 90℃ and age for 60min.

[0133] After the reaction, the filter cake was washed until the conductivity of the filtrate was less than 300 us / cm, and then dried in an oven at 120°C. After drying, the filter cake was dehydrated in a muffle furnace at 600°C for 4h.

[0134] The specific surface area of the titanium-doped iron phosphate after dehydration was 9.87 m 2 / g, Fe%=35.9%, P%=20.72%, the molar ratio of iron to phosphorus was 0.958, and the titanium content was 4889 ppm, and the yield of the second titanium element was 82.0% at this time.

[0135] Example 4 In this example, the lithium iron phosphate waste powder had an Al content of 122.2 ppm, a Cu content of 14.6 ppm, a C content of 1.2%, and a Ti content of 3545 ppm.

[0136] 3825.0g of a 30% phosphoric acid solution was weighed into a glass reaction kettle, and after stirring was started, 369.5g of waste lithium iron phosphate powder was added. The reaction was heated to 90°C and carried out for 3h. After the reaction, filtration was carried out, and a small amount of water was used for washing, obtaining filtrate 1 and residue 1. The residue 1 was dried and weighed, and the mass was 7.02g, indicating that the dissolution and leaching rate of the phosphoric acid solution was as high as 98.1%. The residue 1 could be dissolved in the phosphoric acid solution again for reuse.

[0137] According to the molar ratio of phosphorus / iron=3.0, 132.3g of iron powder was added to the filtrate 1, and the reaction was carried out at 55°C for 2h. After the reaction, filtration was carried out, obtaining bright green ferrous phosphate filtrate 2 and residue 2. The filtrate 2 was placed in a reaction kettle, 5.4g (theoretical 3400 ppm) of titanium dioxide powder was added, and the system was raised to 55°C. After stabilization, 475.0g of a 20% hydrogen peroxide solution was added through a peristaltic pump, and the time was controlled at 90min. After the dropwise addition was completed, the temperature was raised to 90°C and aged for 60min.

[0138] After the reaction, the filter cake was washed until the conductivity of the filtrate was less than 300 us / cm, and then dried in an oven at 120°C. After drying, the filter cake was dehydrated in a muffle furnace at 600°C for 4h.

[0139] The specific surface area of the titanium-doped iron phosphate after dehydration was 9.87 m 2 / g, Fe%=35.9%, P%=20.72%, the molar ratio of iron to phosphorus was 0.958, and the titanium content was 4889 ppm, and the yield of the second titanium element was 82.0% at this time.

[0140] Example 5 In this example, the lithium iron phosphate waste powder had an Al content of 120.2 ppm, a Cu content of 13.7 ppm, a C content of 1.21%, and a Ti content of 4220 ppm.

[0141] Take 3825.0 g of phosphoric acid solution with a concentration of 30% and place it in a glass reaction kettle. After stirring, add 369.5 g of waste lithium iron phosphate powder, heat to 90°C and react for 3h. After the reaction is complete, filter and wash with a small amount of water to obtain filtrate 1 and residue 1. Dry the residue 1 and weigh it, which is 9.6 g, indicating that the dissolution leaching rate of the phosphoric acid solution is as high as 97.4%. The residue 1 can be redissolved in the phosphoric acid solution for reuse.

[0142] According to the molar ratio of phosphorus / iron = 3.0, add 132.9 g of iron powder to the filtrate 1 and react at 55°C for 2h. After the reaction is complete, filter to obtain bright green ferrous phosphate filtrate 2 and residue 2.

[0143] Place the filtrate 2 in the reaction kettle, add 1.6 g (theoretical 1000 ppm) of titanium dioxide powder, and then raise the system to 55°C. After stabilizing, add 475.0 g of hydrogen peroxide solution with a concentration of 20% through a peristaltic pump, and control the time to be 90 min. After the dropwise addition is complete, heat to 90°C and age for 60 min.

[0144] After the reaction is complete, filter and wash until the conductivity of the filtrate is below 300 us / cm. Dry the filter cake in an oven at 120°C and then dehydrate it in a muffle furnace at 600°C for 5h.

[0145] After dehydration, the titanium-doped iron phosphate is detected to have a specific surface area of 10.37 m 2 / g, Fe%=35.79%, P%=20.65%, the molar ratio of iron to phosphorus is 0.959, and the titanium content is 3318 ppm. At this time, the yield of the second addition of titanium element is 81.8%.

[0146] Example 6 This example uses lithium iron phosphate waste powder with Al element content of 104.2 ppm, Cu element content of 9.1 ppm, C element content of 1.2%, and Ti element content of 3039 ppm.

[0147] Take 3825.0 g of phosphoric acid solution with a concentration of 30% and place it in a glass reaction kettle. After stirring, add 369.5 g of waste lithium iron phosphate powder, heat to 90°C and react for 3h. After the reaction is complete, filter and wash with a small amount of water to obtain filtrate 1 and residue 1. Dry the residue 1 and weigh it, which is 9.6 g, indicating that the dissolution leaching rate of the phosphoric acid solution is as high as 97.4%. The residue 1 can be redissolved in the phosphoric acid solution for reuse.

[0148] According to the molar ratio of phosphorus / iron = 3.0, add 132.9 g of iron powder to the filtrate 1 and react at 55°C for 2h. After the reaction is complete, filter to obtain bright green ferrous phosphate filtrate 2 and residue 2.

[0149] The filtrate 2 was placed in a reaction kettle, 8.5 g (theoretical 2500 ppm) of titanyl sulfate powder was added, and the system was raised to 55°C. After stabilization, 475.0 g of 20% hydrogen peroxide solution was added by peristaltic pump, and the time control was 90 min. After the dropwise addition was completed, it was heated to 90°C and aged for 60 min.

[0150] After the reaction was completed, the filter cake was dried in a 120°C oven and then dehydrated in a muffle furnace at 550°C for 6 h.

[0151] The specific surface area of the titanium-doped iron phosphate after dehydration was 13.23 m 2 / g, Fe%=35.51%, P%=20.42%, the molar ratio of iron to phosphorus was 0.962, and the titanium content was 3985 ppm, and the titanium yield was 87.4%.

[0152] Example 7 The Al element content in the lithium iron phosphate waste powder used in this example was 104.2 ppm, the Cu element content was 9.1 ppm, the C element content was 1.20%, and the Ti element content was 3039 ppm. 3825.0 g of 30% phosphoric acid solution was weighed into a glass reaction kettle, stirring was started, and then 369.5 g of waste lithium iron phosphate powder was added. It was heated to 90°C and reacted for 3 h. After the reaction was completed, it was filtered and washed with a small amount of water to obtain filtrate 1 and residue 1. The residue 1 was dried and weighed, and the mass was 8.1 g, indicating that the dissolution leaching rate of the phosphoric acid solution was as high as 97.8%. The residue 1 could be dissolved in phosphoric acid solution again for reuse.

[0153] According to the molar ratio of phosphorus / iron=3.0, 132.6 g of iron powder was added to the filtrate 1, and the reaction was carried out at 55°C for 2 h. After the reaction was completed, it was filtered to obtain bright green ferrous phosphate filtrate 2 and residue 2.

[0154] The filtrate 2 was placed in a reaction kettle, 25.9 g (theoretical 3700 ppm) of tetrabutyl titanate was added, and the system was raised to 55°C. After stabilization, 475.0 g of 20% hydrogen peroxide solution was added by peristaltic pump, and the time control was 90 min. After the dropwise addition was completed, it was heated to 90°C and aged for 60 min.

[0155] After the reaction was completed, the filter cake was dried in a 120°C oven and then dehydrated in a muffle furnace at 600°C for 4 h.

[0156] The specific surface area of the titanium-doped iron phosphate after dehydration was 12.04 m 2 / g, Fe%=35.60%, P%=20.51%, the molar ratio of iron and phosphorus is 0.960, and the titanium content is 4015ppm, and the titanium yield is 88.6% at this time.

[0157] Application Example 1 A lithium iron phosphate / carbon composite material includes the titanium-doped iron phosphate prepared in Example 1, a lithium source, and an organic carbon source.

[0158] The lithium iron phosphate / carbon composite material preparation method includes the following steps: 24.7g of lithium carbonate (99.5wt%), 100.0g of titanium-doped iron phosphate, 8.0g of glucose, and 4.0g of polyethylene glycol are weighed according to the molar ratio of lithium / iron=1.03, and then added to a basket mill containing 800mL of ethanol. After grinding at a speed of 1000r / min for 60min, the slurry is transferred to a fine grinder. After the particle size of the slurry reaches 660nm, it is transferred out and subjected to spray drying.

[0159] The spray-dried material is sieved and then sintered in a tube furnace under a nitrogen environment. The sintering temperature is 790℃, and the temperature is kept constant for 10h. After the tube furnace naturally cools to room temperature, the sintered material is subjected to classification crushing and then sent for inspection.

[0160] Application Example 2 A lithium iron phosphate / carbon composite material includes the titanium-doped iron phosphate prepared in Example 2, a lithium source, and an organic carbon source.

[0161] The lithium iron phosphate / carbon composite material preparation method includes the following steps: 24.8g of lithium carbonate (99.5wt%), 100.0g of titanium-doped iron phosphate, 8.0g of glucose, and 4.0g of polyethylene glycol are weighed according to the molar ratio of lithium / iron=1.04, and then added to a basket mill containing 800mL of ethanol. After grinding at a speed of 1000r / min for 60min, the slurry is transferred to a fine grinder. After the particle size of the slurry reaches 660nm, it is transferred out and subjected to spray drying.

[0162] The spray-dried material is sieved and then sintered in a tube furnace under a nitrogen environment. The sintering temperature is 790℃, and the temperature is kept constant for 10h. After the tube furnace naturally cools to room temperature, the sintered material is subjected to classification crushing and then sent for inspection.

[0163] Application Example 3 A lithium iron phosphate / carbon composite material includes the titanium-doped iron phosphate prepared in Example 3, a lithium source, and an organic carbon source.

[0164] The lithium iron phosphate / carbon composite material preparation method includes the following steps: Take 24.7g of lithium carbonate (99.5wt%), 100.0g of titanium-doped iron phosphate, 8.0g of glucose, and 4.0g of polyethylene glycol according to the molar ratio of lithium / iron=1.04, and add them to a basket mill containing 800mL of pure water. Grind at a speed of 1000r / min for 60min, then transfer to a fine grinder. When the particle size of the slurry reaches 660nm, transfer it out and perform spray drying.

[0165] After sieving, the spray-dried material is placed in a tube furnace under a nitrogen environment for sintering. The sintering temperature is 800℃, and the temperature is kept constant for 8h. After the tube furnace naturally cools to room temperature, the sintered material is subjected to graded crushing and then sent for inspection.

[0166] Application Example 4 A lithium iron phosphate / carbon composite material includes titanium-doped iron phosphate prepared in Example 4, a lithium source, and an organic carbon source.

[0167] The preparation method of the lithium iron phosphate / carbon composite material includes the following steps: Take 24.8g of lithium carbonate (99.5wt%), 100.0g of titanium-doped iron phosphate, 8.0g of glucose, and 4.0g of polyethylene glycol according to the molar ratio of lithium / iron=1.04, and add them to a basket mill containing 800mL of ethanol. Grind at a speed of 1000r / min for 60min, then transfer to a fine grinder. When the particle size of the slurry reaches 660nm, transfer it out and perform spray drying.

[0168] After sieving, the spray-dried material is placed in a tube furnace under a nitrogen environment for sintering. The sintering temperature is 790℃, and the temperature is kept constant for 10h. After the tube furnace naturally cools to room temperature, the sintered material is subjected to graded crushing and then sent for inspection.

[0169] Application Example 5 A lithium iron phosphate / carbon composite material includes titanium-doped iron phosphate prepared in Example 5, a lithium source, and an organic carbon source.

[0170] The preparation method of the lithium iron phosphate / carbon composite material includes the following steps: Take 24.5g of lithium carbonate (99.5wt%), 100.0g of titanium-doped iron phosphate, 8.0g of glucose, and 4.0g of polyethylene glycol according to the molar ratio of lithium / iron=1.03, and add them to a basket mill containing 800mL of ethanol. Grind at a speed of 1000r / min for 60min, then transfer to a fine grinder. When the particle size of the slurry reaches 660nm, transfer it out and perform spray drying.

[0171] After sieving, the spray-dried material is placed in a tube furnace under a nitrogen environment for sintering. The sintering temperature is 790℃, and the temperature is kept constant for 10h. After the tube furnace naturally cools to room temperature, the sintered material is subjected to graded crushing and then sent for inspection.

[0172] Application Example 6 A lithium iron phosphate / carbon composite material comprises the titanium-doped lithium iron phosphate prepared in Example 6, a lithium source and an organic carbon source.

[0173] The lithium iron phosphate / carbon composite material preparation method comprises the following steps: 24.3 g of lithium carbonate (99.5 wt%) and 100.0 g of titanium-doped lithium iron phosphate were weighed according to a molar ratio of lithium / iron = 1.03, 8.0 g of glucose and 4.0 g of polyethylene glycol were added to a basket mill containing 800 mL of ethanol, and the mixture was ground at a speed of 1000 r / min for 60 min, and then transferred to a fine grinder. After the particle size of the slurry reached 660 nm, it was transferred out and subjected to spray drying.

[0174] The spray-dried material was sieved and then sintered in a tube furnace under a nitrogen environment. The sintering temperature was 790°C, and the temperature was kept constant for 9 h. After the tube furnace naturally cooled to room temperature, the sintered material was subjected to classification crushing and then sent for inspection.

[0175] Application Example 7 A lithium iron phosphate / carbon composite material comprises the titanium-doped lithium iron phosphate prepared in Example 7, a lithium source and an organic carbon source.

[0176] The lithium iron phosphate / carbon composite material preparation method comprises the following steps: 24.1 g of lithium carbonate (99.5 wt%) and 100.0 g of titanium-doped lithium iron phosphate were weighed according to a molar ratio of lithium / iron = 1.02, 8.0 g of glucose and 4.0 g of polyethylene glycol were added to a basket mill containing 800 mL of ethanol, and the mixture was ground at a speed of 1000 r / min for 60 min, and then transferred to a fine grinder. After the particle size of the slurry reached 660 nm, it was transferred out and subjected to spray drying.

[0177] The spray-dried material was sieved and then sintered in a tube furnace under a nitrogen environment. The sintering temperature was 790°C, and the temperature was kept constant for 10 h. After the tube furnace naturally cooled to room temperature, the sintered material was subjected to classification crushing and then sent for inspection.

[0178] Comparative Example 1 Comparative Example 1 did not add a titanium source during the synthesis of titanium-doped lithium iron phosphate, and then prepared a lithium iron phosphate / carbon composite material using the titanium-doped lithium iron phosphate of Comparative Example 1 according to the method of Application Example 1.

[0179] Comparative Example 2 Comparative Example 2 did not add a titanium source during the preparation of titanium-doped lithium iron phosphate. Comparative Example 2 added 3000 ppm of titanium dioxide in the final product lithium iron phosphate during the preparation of the lithium iron phosphate / carbon composite material, specifically: Take 24.9g of lithium carbonate (99.5wt%), 100.0g of titanium-doped iron phosphate, 8.0g of glucose, 4.0g of polyethylene glycol, and 4.0g of titanium dioxide according to the molar ratio of lithium / iron = 1.04, and add them to a basket mill containing 800mL of pure water. Grind at a speed of 1000r / min for 60min, then transfer to a fine grinder. When the particle size of the slurry reaches 660nm, transfer it out and perform spray drying.

[0180] After sieving, the spray-dried material is placed in a tube furnace under a nitrogen environment for sintering. The sintering temperature is 800℃, and the temperature is kept constant for 8h. After the tube furnace naturally cools to room temperature, the sintered material is crushed and sent for inspection.

[0181] Comparative Example 3 The preparation method of titanium-doped iron phosphate in Comparative Example 3 is the same as that in Example 1. In Comparative Example 3, titanium dioxide is added as a titanium source during the preparation of lithium iron phosphate / carbon composite material. The titanium content of the titanium source is 1000ppm of titanium dioxide based on the mass of lithium iron phosphate / carbon composite material. Specifically: Take 24.9g of lithium carbonate (99.5wt%), 100.0g of titanium-doped iron phosphate, 8.0g of glucose, 4.0g of polyethylene glycol, and 4.0g of titanium dioxide according to the molar ratio of lithium / iron = 1.04, and add them to a basket mill containing 800mL of pure water. Grind at a speed of 1000r / min for 60min, then transfer to a fine grinder. When the particle size of the slurry reaches 660nm, transfer it out and perform spray drying.

[0182] After sieving, the spray-dried material is placed in a tube furnace under a nitrogen environment for sintering. The sintering temperature is 800℃, and the temperature is kept constant for 8h. After the tube furnace naturally cools to room temperature, the sintered material is crushed and sent for inspection.

[0183] Comparative Example 4 Comparative Example 4 is compared with Example 1. Only titanium source is added during the preparation of titanium-doped iron phosphate. The titanium content of the titanium source is 5000ppm of titanium dioxide based on the mass of lithium iron phosphate / carbon composite material. Then, according to the method of Application Example 1, lithium iron phosphate / carbon composite material is prepared using the titanium-doped iron phosphate of Comparative Example 4.

[0184] Comparative Example 5 Comparative Example 5 is compared with Example 1. Only titanium source is added during the preparation of titanium-doped iron phosphate. The titanium content of the titanium source is 1000ppm of titanium dioxide based on the mass of lithium iron phosphate / carbon composite material. Then, according to the method of Application Example 1, lithium iron phosphate / carbon composite material is prepared using the titanium-doped iron phosphate of Comparative Example 5.

[0185] Comparative Example 6 Compared with Example 1, the total amount of waste lithium iron phosphate and iron element added with pure iron powder used in Example 1 was completely replaced with an equal amount of pure iron powder and reacted with an equal amount of phosphoric acid in Example 1 to generate filtrate 2. After heating this filtrate 2, an oxidant and a titanium source were added to synthesize titanium-doped iron phosphate. The titanium content of the titanium source was 4000 ppm of titanium dioxide per unit mass of the lithium iron phosphate / carbon composite material. Then, following the method of Application Example 1, lithium iron phosphate / carbon composite material was prepared using the titanium-doped iron phosphate of Comparative Example 6.

[0186] Comparative Example 7 Compared to Example 1, the total amount of waste lithium iron phosphate and iron element added with pure iron powder used in Example 1 was completely replaced with an equal amount of pure iron powder, which reacted with an equal amount of phosphoric acid in Example 1 to generate filtrate 2. This filtrate 2 was then heated and an oxidant was added to synthesize iron phosphate. In Comparative Example 7, a titanium dioxide source was added during the preparation of the lithium iron phosphate / carbon composite material. The titanium content of the titanium source was 4000 ppm of titanium dioxide per unit mass of the lithium iron phosphate / carbon composite material. Specifically: Weigh out 24.7g of lithium carbonate (99.5wt%), 100.0g of titanium-doped iron phosphate, 8.0g of glucose, 4.0g of polyethylene glycol, and titanium dioxide in sequence at a lithium / iron ratio of 1.04. Add them to a basket mill containing 800mL of pure water and grind at 1000r / min for 60min. Then transfer to fine grinding and remove the slurry when the particle size reaches 660nm. Spray dry the slurry.

[0187] The dried material was then crushed and sintered in a tube furnace under nitrogen atmosphere at 800℃ for 8 hours. After the tube furnace cooled naturally to room temperature, the sintered material was graded, crushed, and sent for testing.

[0188] Detection Example 1 1. Using the lithium iron phosphate / carbon composite material prepared in the application example as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder, electrode sheets were fabricated at a mass ratio of 90:5:5. Lithium metal was used as the negative electrode, and the cells were assembled into coin cells. The initial discharge capacity was tested under different charge / discharge current conditions at room temperature (2-3.75V) with charging at 0.1C, 0.2C, and 1C.

[0189] 2. Compacted density measurement: The compacted density was measured using a Sansi longitudinal and transverse compacted density meter.

[0190] 3. Table 1 shows the physicochemical data of iron phosphate.

[0191] 4. Table 2 shows the electrochemical performance, compaction density, and titanium content of the finished product of lithium iron phosphate; Table 3 shows the titanium yield of waste phosphate, the yield of titanium added twice during the preparation of iron phosphate, and the yield of titanium added during the preparation of lithium iron phosphate.

[0192] 5、The detection method of the yield of waste phosphate titanium is: (1) dissolving the filtrate 1 after solid-liquid separation in S1 in hydrochloric acid and then detecting by ICP to obtain the mass concentration of titanium element, which is converted into mass and then compared with the titanium content in the added waste lithium iron phosphate to obtain the yield of titanium element; (2) detecting the filter residue 1 by ICP to obtain the mass concentration of titanium element in the undissolved part, which is converted into mass and then compared with the titanium content in the added waste lithium iron phosphate to obtain the proportion of residual titanium, which can be used to prove the yield of waste phosphate titanium. (The sum of the proportions of titanium elements in the filtrate 1 and the filter residue 1 is theoretically 1) Since the waste phosphate is dissolved in phosphoric acid, titanium exists in the form of ions, and in the later process of synthesizing iron phosphate, almost 100% exists in titanium-doped iron phosphate, so the titanium yield of the waste phosphate in examples 1-7 and comparative examples 2-7 is equivalent to the effect of comparative example 1.

[0193] 6, The yield of the second addition of titanium is: The yield of the second addition of titanium in the preparation of iron phosphate is: The ratio of the difference between the total titanium content of titanium-doped iron phosphate and the titanium content provided by the waste phosphate positive material in the titanium-doped iron phosphate and the titanium content of the second titanium source. The yield of the addition of titanium in the preparation of lithium iron phosphate / carbon composite material process: The ratio of the difference between the total titanium content of titanium-doped lithium iron phosphate and the titanium content provided by the waste phosphate positive material in the titanium-doped lithium iron phosphate and the titanium content of the second addition of titanium in the preparation of iron phosphate and the titanium content of the addition of titanium in the preparation of lithium iron phosphate / carbon composite material process. (The contents here are mass contents) Table 1

[0194] Table 2

[0195] Table 3

[0196] Verification of technical effects and / or analysis of technical problems It can be seen from Figure 1 It can be seen from

[0197] Figure 2 The XRD pattern shown in Table 1 shows that no impurity peak appears, and the XRD pattern of the recovered and prepared titanium-doped iron phosphate is completely consistent with the standard hexagonal system iron phosphate pattern (PDF card No. #29-0715), which shows that the titanium-doped iron phosphate prepared by the method is hexagonal system iron phosphate.

[0198] Figure 3The XRD of the lithium iron phosphate prepared in Comparative Example 1 and Application Example 1 is compared, and the peak shape and diffraction peak position of the lithium iron phosphate standard card (PDF card No. #40-1499) are consistent, and no other impurity peak exists, indicating that the recovered material can be used to prepare pure-phase lithium iron phosphate. It can be seen that the peak intensity of Application Example 1 is obviously higher than that of Comparative Example 1, indicating that the lithium iron phosphate prepared by doping titanium has better crystallinity, larger grain size, and the synthesized sample has a perfect olivine structure, indicating that titanium is not simply physically mixed in the lithium iron phosphate cathode material, but enters the lithium iron phosphate crystal lattice, so it does not affect the crystal structure of LiFePO4.

[0199] Table 1 is the main content titration, ICP impurity, and specific surface area data of the precursor iron phosphate in the examples and comparative examples. Tables 2-3 are the data summary of the finished products of the application examples and comparative examples. It can be seen that the yield of the secondary addition of titanium in this type of titanium doping is between 81.0-88.6%, and the titanium content of the finished product is controlled at 3000-5000ppm. The electrochemical data has a slight change trend, and the general rule is that with the increase of Ti content, it first increases and then decreases, but when the titanium content is between 3000-5000ppm, the electrochemical values are very small and can be ignored. When the titanium content is <3000ppm or >5000ppm, Comparative Example 5 and Comparative Example 4 are prepared, wherein the powder pressure and electrochemical data of Comparative Example 5 are significantly lower than those of the application examples; the powder pressure in Comparative Example 4 changes little, but the electrochemical data has a downward trend.

[0200] In general, the addition of an appropriate amount of titanium element can effectively improve the uniform distribution of lithium iron phosphate particles, thereby improving the electrochemical performance, but too high will have a negative impact, and too little will not achieve the ideal performance.

[0201] Application Examples 6 and 7 use titanyl sulfate and tetrabutyl titanate as the same control, and the data in Table 1 show that the electrochemical data and powder pressure are similar to those of Application Examples 1, 2, 3, 4, and 5, indicating that under the synergistic effect of this type of titanium doping, using different titanium sources can obtain products with better performance. Comparative Example 1 is a control without additional titanium doping in the recovery group, and Comparative Examples 2, 3, 4, and 5 are comparisons of different ways of titanium doping in the recovery group. Comparative Examples 6 and 7 are the finished lithium iron phosphate prepared from the iron phosphate obtained by the iron method.

[0202] Overall, compared with the powder pressing test, the electrochemical performance of the examples is better than that of the comparative examples, indicating that the titanium element is uniformly distributed in the iron phosphate nucleation stage, and the titanium distribution in the prepared lithium iron phosphate is also more uniform, which reduces the particle size of the lithium iron phosphate positive material, reduces the migration distance of Li, improves the electronic conductivity of the lithium iron phosphate positive material, and improves the electrochemical performance; the titanium doping in this method not only improves the particle crystallinity, but also reduces the particle agglomeration tendency of the FePO4 precursor when sintered into LiFePO4, reduces the "hard agglomeration" phenomenon of the particles, maintains the independence of the particles, and is beneficial to powder compaction.

[0203] Overall, based on the comparison of examples 1 and comparative examples 1-7, the present application adopts technical means of adding titanium source, specific titanium source dosage, and combination of waste phosphate positive material, etc., to achieve new technical effects of reducing the cost of recycling waste phosphate positive material, improving economic benefits, improving the electrochemical performance of titanium-doped lithium iron phosphate / carbon composite material, powder compaction, and improving the titanium yield of finished products. The combined technical effects are more superior than the sum of the effects of each technical means.

[0204] Finally, it should be noted that the above content is only used to illustrate the technical solutions of the present application, and is not a limitation on the protection scope of the present application. Simple modifications or equivalent replacements of the technical solutions of the present application made by those skilled in the art do not deviate from the essence and scope of the technical solutions of the present application.

Claims

1. A method for synthesizing titanium-doped iron phosphate by recycling waste phosphate cathode materials, characterized in that, The specific steps are as follows: S1. Waste phosphate cathode material reacts with phosphoric acid solution. After the reaction is complete, solid and liquid are separated to obtain filter residue 1 and filtrate 1. S2, the iron source reacts with filtrate 1, and after the reaction is completed, solid and liquid separation is obtained to obtain filter residue 2 and filtrate 2; S3, filtrate 2 are mixed with titanium source, heated and then oxidant is added to obtain slurry; S4. The slurry is aged, then washed, dried and sintered to obtain titanium-doped iron phosphate; In the titanium-doped iron phosphate, the ratio of the mass content of titanium provided by the titanium source to the mass content of titanium provided by the waste phosphate cathode material is 1-3:1-3.

2. The method according to claim 1, characterized in that... The phosphoric acid solution has a mass concentration of 10%-40%; and / or The waste phosphate cathode material is selected from at least one of waste lithium iron phosphate, waste iron phosphate, and phosphate material remaining after lithium extraction from waste lithium iron phosphate; and / or The Ti content of the waste phosphate cathode material is 3000-5000 ppm; and / or The molar ratio of iron to phosphorus in the waste phosphate cathode material is 1:5-10; and / or The iron source mentioned in step S2 is selected from one or more of iron powder, iron sheets, and iron ingots; and / or The amount of iron source added is such that the molar ratio of total phosphorus to total iron in filtrate 2 is 2.8:1-3.2:

1.

3. The method according to claim 1, characterized in that, The titanium source mentioned in step S3 is at least one of titanium dioxide, titanium oxysulfate, and tetrabutyl titanate; and / or The mass of the titanium source is 0.15-0.80% of the mass of the iron phosphate prepared by co-precipitation.

4. The method according to claim 1, characterized in that, The oxidant mentioned in step S3 is hydrogen peroxide; and / or The heating temperature in step S3 is 50-65°C; and / or The molar ratio of H2O2 in the hydrogen peroxide to iron in filtrate 2 is 0.5-1.0:1; and / or The hydrogen peroxide has a mass concentration of 5%-30%, and is added by dripping over a period of 30-120 minutes.

5. The method according to claim 1, characterized in that, The aging temperature in step S4 is 80-100℃, and the aging time is 60-180 min; and / or The washing process involves washing until the conductivity of the filtrate is <300 μS / cm; and / or The drying temperature is 80-120℃ and the time is 10-14 hours; the sintering temperature is 400-700℃ and the time is 3-6 hours.

6. A titanium-doped iron phosphate, characterized in that, Iron comprises 35.00-37.00% of the mass of titanium-doped iron phosphate, and phosphorus comprises 20.0-21.0% of the mass of titanium-doped iron phosphate, with a molar ratio of iron to phosphorus of 0.950-0.980; the specific surface area of ​​the titanium-doped iron phosphate is 6-14 m². 2 / g, wherein the titanium content of the titanium-doped iron phosphate is 3000-5000ppm.

7. A method for preparing a titanium-doped lithium iron phosphate / carbon composite material, characterized in that, Includes the following steps: The titanium-doped iron phosphate prepared by the method according to any one of claims 1-5 is mixed with a lithium source and a carbon source, ground, dried, and then sintered in an inert gas atmosphere to obtain a lithium iron phosphate / carbon composite material.

8. The preparation method according to claim 7, characterized in that, The grinding system is at least one of water or ethanol; and / or The lithium source is one or more of lithium carbonate, lithium acetate, and lithium hydroxide; and / or The molar ratio of lithium in the lithium source to iron in titanium-doped iron phosphate is 1.02-1.06:1; and / or The carbon source is selected from at least one of glucose, sucrose, citric acid, polyethylene glycol, polyvinyl alcohol, starch, cellulose, and fructose; and / or The carbon source accounts for 8-20% of the mass of iron phosphate. and / or The grinding process involves coarse grinding followed by fine grinding, wherein the coarse grinding particle size is <2µm, and the fine grinding produces a slurry particle size of 560-860nm; and / or The sintering temperature is 740-850℃, and the sintering time is 6-10h.

9. The titanium-doped lithium iron phosphate / carbon composite material prepared by the preparation method according to any one of claims 7-8.

10. The application of the titanium-doped lithium iron phosphate prepared by the method of any one of claims 1-6 and / or the titanium-doped lithium iron phosphate / carbon composite material prepared by the preparation method of any one of claims 7-8 in battery preparation.

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