Method for preparing ferric manganese phosphate precursor by regenerating waste phosphate positive electrode material as well as product and application of ferric manganese phosphate precursor

Abstract

The invention belongs to the technical field of resource recovery, and particularly relates to a method for preparing a lithium ferric manganese phosphate precursor by recycling a waste phosphate positive electrode material as well as a product and application thereof. The method comprises the following steps: S1, dispersing waste phosphate positive electrode material powder in a phosphoric acid solution for reaction, and filtering after the reaction is finished to obtain filter residue 1 and filtrate 1; s2, adding a metal source into the filtrate 1 for reaction, continuously heating, and filtering after the reaction is finished to obtain filter residues 2 and filtrate 2; and S3, drying the filter cake to obtain the rhodochrosite type ferric manganese phosphate precursor. The method for preparing the ferric manganese phosphate precursor by regenerating the waste phosphate positive electrode material is more environment-friendly, more elements are recycled, and the comprehensive utilization rate of the elements is high.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling technology, specifically relating to a method for preparing lithium iron manganese phosphate precursor by recycling waste phosphate cathode materials, and its products and applications. Background Technology

[0002] In recent years, with the rapid development of the electric vehicle and energy storage markets, lithium iron phosphate cathode material has seen its market output gradually increase due to its advantages such as low price, good safety performance, stable structure and long cycle life. Meanwhile, lithium iron manganese phosphate material, which is regarded as an upgraded version of lithium iron phosphate with high energy density, is also increasingly favored by the market, and its demand is gradually increasing.

[0003] With the rapid growth of phosphate cathode materials, their recycling and reuse have become increasingly crucial. Commercial phosphate cathode material recycling mainly focuses on lithium iron phosphate (LFP) recovery and regeneration into iron phosphate. This is primarily achieved through leaching with strong acids, strong alkalis, or oxidants, or high-temperature calcination. The leaching process with strong acids, strong alkalis, or oxidants places high demands on the recycling equipment and introduces a large number of impurity ions and generates significant amounts of wastewater, which is detrimental to environmental protection. Similarly, high-temperature calcination releases large amounts of harmful gases and solid waste, which is also environmentally unfriendly.

[0004] While lithium iron phosphate (LFP) recycling technology is becoming increasingly mature, the recycling and reuse of lithium iron manganese phosphate (LMP) is also gradually underway. This primarily involves acid leaching, followed by filtration to obtain a lithium-rich solution and iron-manganese slag. The iron-manganese slag is then roasted with sodium hydroxide to obtain iron phosphate and manganese oxide products, achieving the recovery of individual iron and manganese compounds. However, this process is complex, environmentally unfriendly, and energy-intensive, making it unsuitable for industrial applications. Therefore, Chinese patent CN118198571A proposes a more environmentally friendly process that eliminates the need for roasting. Instead, it involves alkaline washing followed by acid leaching with the addition of an oxidant, achieving full-element leaching. Simultaneously, it enables the recovery of lithium carbonate, manganese tetroxide, and iron phosphate in Li / Fe / Mn / P ratios. However, this process uses a large number of chemicals and is also complex. Iron and manganese can only be recovered sequentially as iron phosphate and manganese tetroxide, and cannot simultaneously recover Fe and Mn elements. In other words, Fe / Mn cannot form iron-manganese precursors in the form of co-precipitation (the Ksp values ​​of iron-manganese precursors differ greatly, making it difficult for iron and manganese to co-precipitate). This limits the in-depth application of iron-manganese precursors in the preparation of lithium iron manganese phosphate materials. Therefore, it is very necessary to explore how to utilize lithium iron manganese phosphate recovery to prepare iron and manganese coprecipitation precursors. Summary of the Invention

[0005] This invention addresses the problems of existing waste phosphate cathode material recycling technologies, such as environmental unfriendliness, high impurity content, limited recovery of single elements (Li, Fe, Mn), inability to simultaneously co-precipitate and recycle Fe / Mn / P elements, and low initial discharge specific capacity of the recovered precursor. It provides a more environmentally friendly method for regenerating waste phosphate cathode materials to prepare lithium iron manganese phosphate precursors, which recovers more elements and achieves higher comprehensive element utilization, and its application in the preparation of lithium iron phosphate manganese / carbon composite materials.

[0006] Terminology Explanation: Unless otherwise defined, all technical terms in this document have the same meanings as commonly understood by one of ordinary skill in the art to which the subject matter of the claims pertains. Unless otherwise stated, all patents, patent inventions, and publications cited in this document are incorporated herein by reference in their entirety. If multiple definitions exist for terms in this document, the definitions in this chapter shall prevail.

[0007] It should be understood that the above brief description and the following detailed description are exemplary and for illustrative purposes only, and do not limit the subject matter of the invention in any way. In this invention, the singular is used in conjunction with the plural unless otherwise specifically stated. It should also be noted that, unless otherwise stated, the use of “or” or “or” means “and / or”. Furthermore, the use of the term “comprising” and other forms such as “including,” “containing,” and “contains” are not limiting.

[0008] The definition of the standard chemical term can be found in the reference "Fine Phosphorus Chemical Technology", Chemical Industry Press, Ran Longwen (chief editor), 2009.

[0009] Unless specifically defined herein, the use of all commercially available products herein employs standard techniques. For example, it may be carried out using the manufacturer's instructions for use with the kit, or in accordance with methods known in the art or the description of this invention. The techniques and methods described herein can generally be implemented according to conventional methods well known in the art, based on the descriptions in the various summary and more specific documents cited and discussed in this specification.

[0010] In a first aspect, the present invention provides a method for synthesizing iron-manganese phosphate precursors by recycling waste phosphate cathode materials, comprising the following steps: S1. Disperse the waste phosphate cathode material powder in a phosphoric acid solution for reaction. After the reaction is completed, filter to obtain filter residue 1 and filtrate 1. S2. Add the metal source to filtrate 1 to carry out the reaction, continue heating, and after the reaction is completed, filter to obtain residue 2 and filtrate 2; S3. Dry the filter residue 2 to obtain the iron-manganese phosphate precursor; The ratio of the total molar amount of metal source added in S2 and the total molar amount of metal elements in filtrate 1 to the molar amount of phosphorus in the phosphoric acid solution is 1:1.8-2.2. Other specific point values ​​within the above range can be selected, and all can achieve the technical effect of the present invention.

[0011] Preferably, the waste phosphate cathode material is selected from at least one of waste lithium iron phosphate and lithium manganese phosphate, waste lithium iron manganese phosphate, waste lithium iron manganese phosphate and waste lithium iron phosphate, and a combination of waste lithium iron manganese phosphate and lithium manganese phosphate, and the molar ratio of metal elements Mn:Fe in the waste lithium iron manganese phosphate is 6-8:2-4; other specific values ​​within the above range can be selected, and all can achieve the technical effects of the present invention.

[0012] More preferably, the molar ratio of metal elements Mn:Fe in waste lithium iron manganese phosphate is 6:4.

[0013] Preferably, the mass concentration of the phosphoric acid solution in S1 is 20-40%; other specific values ​​within the above range can be selected, all of which can achieve the technical effect of the present invention, including but not limited to 20%, 25%, 30%, and 40%.

[0014] More preferably, the phosphoric acid solution in S1 has a mass concentration of 30%.

[0015] Preferably, the molar ratio of the metal source to phosphorus in the phosphoric acid in the waste phosphate cathode material in S1 is 1:5-10.

[0016] More preferably, the molar ratio of the metal source to the phosphorus in the phosphoric acid in the waste phosphate cathode material in S1 is 1:6. Preferably, the reaction temperature in S1 is 90-100℃, and the reaction time is 6-10h; other specific values ​​within the above range can also be selected, all of which can achieve the technical effects of the present invention. For example, the time includes, but is not limited to, 6h, 7h, 8h, 9h, and 10h.

[0017] More preferably, the reaction temperature in S1 is 95°C and the reaction time is 6 hours.

[0018] Preferably, the metal source in S2 is selected from one or more of iron powder, iron sheets, iron ingots, manganese powder, and electrolytic manganese sheets; more preferably, it is iron powder and manganese sheets.

[0019] Preferably, the metal source described in S2 is added to filtrate 1 and reacted at 50-65°C for 2-3 hours, and then heated to 90-100°C for 3-4 hours.

[0020] Preferably, the metal element molar ratio Mn / (Mn+Fe) of the iron-manganese phosphate precursor in S3 is 0.5-0.9; other specific values ​​within the above range can be selected, and all can achieve the technical effects of the present invention.

[0021] A second aspect of the present invention provides the application of the iron-manganese phosphate precursor prepared by the above method in the preparation of lithium iron-manganese phosphate / carbon composite materials.

[0022] Preferably, the preparation method of the lithium iron phosphate / carbon composite material includes the following steps; (1) The lithium source, the above-mentioned iron manganese phosphate precursor, the phosphorus source, and the additives are coarsely ground and finely ground in an ethanol or deionized water system to obtain slurry 1; the obtained slurry 1 is dried, and the dried powder is sintered in an inert atmosphere to obtain a pre-lithiated lithium iron manganese phosphate precursor. (2) The pre-lithiated lithium iron manganese phosphate precursor and organic carbon source obtained in step (1) are coarsely ground and finely ground in ethanol or deionized water system to obtain slurry 2. The slurry 2 is dried, and the dried powder is sintered in an inert atmosphere and sieved to obtain lithium iron manganese phosphate / carbon composite material.

[0023] Preferably, in step (1), the molar ratio of each element in the raw material feed lithium source, iron-manganese phosphate precursor, and phosphorus source is Li:Fe+Mn:P=(1.0-1.1):1:(1.0-1.1); Preferably, the lithium source in step (1) is one or more of lithium carbonate, lithium acetate, lithium phosphate, and lithium dihydrogen phosphate; Preferably, the phosphorus source in step (1) is one or more of ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid.

[0024] Preferably, the mass of the additive in step (1) is 0.1-1% of the mass of the iron manganese phosphate precursor.

[0025] Preferably, the additive in step (1) is selected from one or more of magnesium oxide, magnesium hydroxide, magnesium carbonate, magnesium acetate, niobium pentoxide, niobium hydroxide, zirconium dioxide, zirconium hydroxide, vanadium pentoxide, ammonium vanadate, nickel acetate, nickel hydroxide, and nickel carbonate; Preferably, the organic carbon source in step (2) is selected from at least one of glucose, sucrose, citric acid, polyethylene glycol, fructose, cyclodextrin, polyvinyl alcohol, polyacrylonitrile, starch, cellulose, and fructose; and the amount of carbon source added is 5-20% of the mass of the pre-lithiated lithium iron manganese phosphate precursor.

[0026] Preferably, the coarse grinding in steps (1) and (2) refers to grinding to a particle size of 1-2 μm using a basket mill, and the fine grinding refers to grinding to a particle size of 250-400 nm using a sand mill; other specific values ​​within the above range can be selected, and all can achieve the technical effect of the present invention.

[0027] Preferably, the drying in steps (1) and (2) refers to spray drying, and the inert atmosphere is selected from one or more of nitrogen, argon, and helium. In step (2), the sintering temperature is 500-750℃ and the sintering time is 3-6h; in step (2), the sintering temperature is 650-750℃ and the sintering time is 6-12h. Other specific values ​​within the above range can be selected, and all can achieve the technical effect of the present invention.

[0028] Preferably, the mesh size of the sieve in step (2) is 180-220 mesh, more preferably 200 mesh.

[0029] A third aspect of the present invention provides an application of the above-mentioned lithium iron manganese phosphate / carbon composite material in the preparation of lithium-ion batteries.

[0030] Embodiments 1-6 of this invention at least support the protection scope of claim 1.

[0031] The technical feature “the ratio of the sum of the total molar amount of the metal source added in S2 and the total molar amount of the metal elements in filtrate 1 to the molar amount of phosphorus in the phosphoric acid solution is 1:1.8-2.2” is derived from the foregoing explanation and / or the corresponding technical features 1:1.8, 1:2, 1:2.2, etc. in Examples 1-6, summarized by the common feature “1:1.8-2.2”. Therefore, those skilled in the art can reasonably infer that any point value within the range of technical feature 1:1.8-2.2 should fall within the protection scope of claim 1. For example, replacing 1:2 with 1:1.9, etc., while keeping other technical features unchanged, still falls within the protection scope of claim 1 of this invention.

[0032] The present invention has the following beneficial effects: 1. This invention uses a specific amount of phosphoric acid to dissolve waste phosphate cathode materials, achieving a dissolution rate of over 98%. In the dissolution process, it avoids the problems of traditional phosphate cathode material recycling processes, such as high-temperature roasting, the use of large amounts of strong alkalis, strong acids, and oxidants, which are not environmentally friendly and introduce impurities. At the same time, excess phosphoric acid solution can be repeatedly recycled, resulting in better environmental performance and lower costs.

[0033] 2. In the preparation of the divalent iron-manganese phosphate precursor, this invention avoids the reuse of the oxidant. Simultaneously, by adding a metal source a second time, it can reduce impurity element ions with lower metal reactivity than iron and manganese to their elemental form for removal (such as Cu). 2+This reduces the impurity content in the precursor and allows for the control of the Fe / Mn ratio in the later-stage iron-manganese phosphate precursor. The designed Fe / Mn value is close to the actual ratio. Through heating and co-precipitation reaction, Fe, Mn, and P can be recovered and utilized simultaneously, avoiding the limitation of traditional iron-manganese phosphate salt recovery which can only recover Fe / Mn elements separately. This further expands the application range of the prepared iron-manganese phosphate precursor in the later-stage lithium iron-manganese phosphate preparation process.

[0034] 3. The lithium iron manganese phosphate precursor prepared by this invention has a red phosphorus manganese ore type and rod-shaped structure with a small specific surface area, which is beneficial for washing and reduces the generation of wastewater.

[0035] 4. The iron-manganese phosphate precursor prepared by this invention can be used to prepare lithium iron phosphate manganese / carbon composite materials with excellent electrochemical performance.

[0036] 5. The iron-manganese phosphate precursor prepared by this invention has a lower impurity content. Attached Figure Description

[0037] Figure 1 This is a 20,000x SEM image of the lithium iron manganese phosphate precursor prepared in Example 1.

[0038] Figure 2 The image shows the XRD pattern of the lithium iron manganese phosphate precursor prepared in Example 1.

[0039] Figure 3 The electrochemical performance of the lithium iron phosphate manganese / carbon composite material prepared in Example 1 is shown. Detailed Implementation

[0040] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way. The following content is merely an exemplary description of the scope of protection claimed by the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, and such changes should also fall within the scope of protection claimed by the present invention.

[0041] The present invention will be further described below by way of specific embodiments. Unless otherwise specified, all instruments, devices, equipment, reagents, products, etc., used in the embodiments of the present invention are obtained through conventional commercial means.

[0042] Example 1 The waste phosphate cathode material used in this embodiment is lithium iron manganese phosphate powder 1. According to ICP analysis, its Mn / Fe ratio is 6:4, and its impurity element content is shown in Table 1.

[0043] A method for synthesizing a precursor of iron-manganese phosphate (designed with a manganese-iron element ratio of Mn:Fe = 6:4) from recycled waste phosphate cathode material includes the following steps: S1. Weigh 110.0g of waste lithium iron phosphate and lithium manganese powder and slowly add it to a 5L three-necked flask containing 1614.0g of phosphoric acid solution with a mass concentration of 30%. Stirring is started at the same time. After the powder is added, heat to 95℃ and react for 6 hours. After the reaction is completed, filter and wash with a small amount of water to obtain filtrate 1 and filter residue 1. Filter residue 1 is dried and weighed. Its mass is 1.8g, which shows that the phosphoric acid solution dissolution and leaching rate is as high as 98.36%. Filter residue 1 can be redissolved in phosphoric acid solution and reused.

[0044] S2. Add 47.5g of electrolytic manganese flakes and 32.2g of iron powder to filtrate 1. At this time, the ratio of the total molar amount of the metal source and the total molar amount of metal elements in filtrate 1 to the molar amount of phosphorus in the phosphoric acid solution is 1:2. After reacting at 60℃ for 3 hours, the temperature is increased to 90℃ and reacted for another 3 hours at 90℃. After the reaction is completed, the reactants are passed through a 300-mesh sieve to remove unreacted iron powder, manganese flakes, carbon or metal impurities. Then, the reactants that have passed through the sieve are filtered and washed until the conductivity of the filtrate is <300us / cm, resulting in a reactant filter cake and filtrate 2. Filtrate 2 can be reused to dissolve waste phosphate cathode materials.

[0045] S3. The filter cake was dried in a 100℃ forced-air drying oven for 12 hours to obtain 164.0 g of a yellowish-brown precursor. Analysis showed that its specific surface area was 2.32 m². 2 / g, Fe content is 12.96%, Mn content is 22.02%, P content is 16.44%, Mn / (Fe+Mn)=0.633, Fe+Mn / P=1.192.

[0046] The prepared precursor was observed by scanning electron microscopy (SEM), and the results are as follows: Figure 1 As shown. From Figure 1 As can be seen from the data, the prepared precursor has a rod-like structure, with the length of the primary particle rods ranging from 2 to 8 μm and the width ranging from 0.2 to 1 μm.

[0047] XRD analysis was performed on the prepared iron-manganese phosphate precursor, and the results are as follows: Figure 2 As shown. From Figure 2 As can be seen from the data, the XRD pattern of the prepared iron-manganese phosphate precursor is completely consistent with the pattern of the substance Mn5(PO4)2[PO3(OH)]2·4H2O (PDF card number #71-1545), which indicates that the precursor prepared by this method is an iron-manganese phosphate precursor, and that Fe and Mn elements exist in the form of co-precipitation.

[0048] Preparation of lithium iron manganese phosphate / carbon composite materials: (1) The raw materials were fed according to the molar ratio of each element in the lithium source, iron-manganese phosphate precursor, and phosphorus source, Li:Fe+Mn:P=1.06:1:1.03. 160.0g of iron-manganese phosphate precursor, 40.89g of lithium carbonate (99.5%), 25.65g of ammonium dihydrogen phosphate (99%), and 1.25g of magnesium hydroxide were added sequentially to a 2L measuring cup containing 800mL of pure water. The mixture was then placed in a basket mill and ground at 2000r / min for 40min. After the slurry particle size reached 1-2μm, the slurry was fed into a sand mill for fine grinding. After the slurry particle size reached 300nm, the slurry was spray-dried. After spray drying, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at 650℃ for 4 hours. After the tubular furnace naturally cooled to 80°C, the sintered material was crushed to obtain 150.12g of pre-lithiated lithium iron manganese phosphate precursor.

[0049] (2) 150.00g of pre-lithiated lithium iron manganese phosphate precursor, 12.00g of glucose, and 12.00g of polyethylene glycol 8000 were added sequentially to a 2L measuring cup containing 800mL of pure water. The mixture was then placed in a basket mill and ground at 2000r / min for 40min. After the slurry particle size reached 1-2μm, it was fed into a sand mill for fine grinding. After the slurry particle size reached 300nm, it was spray-dried. After spray drying, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 8 hours. After the tube furnace cooled naturally to 80℃, the sintered material was graded and crushed to obtain LiFe with a carbon content of 1.38%. 0.367 Mn 0.633 PO4 / C composite material.

[0050] Prepared LiFe 0.367 Mn 0.633 A PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. Lithium metal was used as the negative electrode, and the cells were assembled into a coin cell. Tests were conducted under different charge-discharge current conditions at 2-4.3V and 25℃. The discharge curve results are shown below. Figure 3 The initial reversible capacity at 0.1C charge-discharge is 156.2 mAh / g, the initial reversible capacity at 0.2C charge-discharge is 152.6 mAh / g, the initial reversible capacity at 1C charge-discharge is 146.2 mAh / g, and the capacity retention rate is 97.5% after 100 cycles at 1C.

[0051] Example 2 The waste phosphate cathode material used in this embodiment is lithium iron manganese phosphate powder 1. According to ICP analysis, its Mn / Fe ratio is 6:4, and its impurity element content is shown in Table 1.

[0052] A method for synthesizing lithium iron manganese lithium precursors (with a designed manganese-iron element ratio of Mn:Fe = 6:4) from recycled waste phosphate cathode materials includes the following steps: S1. Weigh 110.0g of waste lithium iron phosphate and lithium manganese powder and slowly add it to a 5L three-necked flask containing 1614.0g of phosphoric acid solution with a mass concentration of 30%. Stirring is started at the same time. After the powder is added, heat to 95℃ and react for 6 hours. After the reaction is completed, filter and wash with a small amount of water to obtain filtrate 1 and filter residue 1. Filter residue 1 is dried and weighed. Its mass is 1.75g, which shows that the dissolution and leaching rate of phosphoric acid solution is as high as 98.41%. Filter residue 1 can be redissolved in phosphoric acid solution and reused.

[0053] S2. Add 53.8g of electrolytic manganese flakes and 36.5g of iron powder to filtrate 1. At this point, the ratio of the total molar amount of the metal source and the total molar amount of metal elements in filtrate 1 to the molar amount of phosphorus in the phosphoric acid solution is 1:1.8. After reacting at 60℃ for 3 hours, the temperature is increased to 90℃ and reacted for another 3 hours at 90℃. After the reaction is completed, the reactants are passed through a 300-mesh sieve to remove unreacted iron powder, manganese flakes, carbon, or metal impurities. Then, the reactants that have passed through the sieve are filtered and washed until the conductivity of the filtrate is <300us / cm, resulting in a reactant filter cake and filtrate 2. Filtrate 2 can be reused to dissolve waste phosphate cathode materials.

[0054] S3. The filter cake was dried in a 100℃ forced-air drying oven for 12 hours to obtain 151.8 g of iron-manganese phosphate precursor. Analysis showed its specific surface area was 3.58 m². 2 / g, Fe content is 12.89%, Mn content is 21.92%, P content is 16.43%, Mn / (Fe+Mn)=0.633, Fe+Mn / P=1.187. Preparation of lithium iron manganese phosphate / carbon composite materials: (1) The raw materials were fed according to the molar ratio of each element in the lithium source, iron-manganese phosphate precursor, and phosphorus source, Li:Fe+Mn:P=1.06:1:1.03. 150.0g of iron-manganese phosphate precursor, 37.18g of lithium carbonate (99.5%), 20.61g of ammonium dihydrogen phosphate (99%), 0.6g of niobium pentoxide, and 0.7g of magnesium oxide were added sequentially to a 2L measuring cup containing 800mL of pure water. The mixture was then placed in a basket mill and ground at 2000r / min for 40min. After the slurry particle size reached 1-2μm, the slurry was fed into a sand mill for fine grinding. After the slurry particle size reached 320nm, the slurry was spray-dried. After spray drying, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at 600℃ for 4 hours. After the tubular furnace naturally cooled to 80°C, the sintered material was crushed to obtain 136.8g of pre-lithiated lithium iron manganese phosphate precursor.

[0055] (2) 135g of pre-lithiated lithium iron manganese phosphate precursor, 10.00g of glucose, and 3g of sucrose were added sequentially to a 2L measuring cup containing 800mL of pure water. The mixture was then placed in a basket mill and ground at 2000r / min for 40min. After the slurry particle size reached 1-2μm, it was fed into a sand mill for fine grinding. After the slurry particle size reached 300nm, it was spray-dried. After spray drying, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 8 hours. After the tube furnace cooled naturally to 80℃, the sintered material was graded and crushed to obtain LiFe with a carbon content of 1.35%. 0.367 Mn 0.633 PO4 / C composite material.

[0056] Prepared LiFe 0.367 Mn 0.633 A PO4 / C composite material is used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. Lithium metal is used as the negative electrode, and the cells are assembled into a coin cell. Tests were conducted at 2-4.3V and 25℃ under different charge / discharge current conditions. The initial reversible capacity was 156.0 mAh / g at 0.1C, 153.5 mAh / g at 0.2C, and 146.5 mAh / g at 1C. After 100 cycles at 1C, the capacity retention was 97.8%.

[0057] Example 3 The waste phosphate cathode material used in this embodiment is lithium iron manganese phosphate powder 1. According to ICP analysis, its Mn / Fe ratio is 6:4, and its impurity element content is shown in Table 1.

[0058] A method for synthesizing lithium iron manganese lithium precursors (with a designed manganese-iron element ratio of Mn:Fe = 6:4) from recycled waste phosphate cathode materials includes the following steps: S1. Weigh 110.0g of waste lithium iron phosphate and lithium manganese powder and slowly add it to a 5L three-necked flask containing 1614.0g of 30% phosphoric acid solution. Stirring is started at the same time. After the powder is added, heat to 95℃ and react for 6 hours. After the reaction is completed, filter and wash with a small amount of water to obtain filtrate 1 and filter residue 1. Filter residue 1 is dried and weighed. Its mass is 1.9g, which shows that the leaching rate of phosphoric acid solution is as high as 98.22%. Filter residue 1 can be redissolved in phosphoric acid solution and reused.

[0059] S2. Add 39.8g of electrolytic manganese flakes and 27.0g of iron powder to filtrate 1. At this time, the ratio of the total molar amount of the metal source and the total molar amount of metal elements in filtrate 1 to the molar amount of phosphorus in the phosphoric acid solution is 1:2.2. After reacting at 50℃ for 3 hours, the temperature is increased to 90℃ and reacted for another 3 hours at 90℃. After the reaction is completed, the reactants are passed through a 300-mesh sieve to remove unreacted iron powder, manganese flakes, carbon or metal impurities. Then, the reactants that have passed through the sieve are filtered and washed until the conductivity of the filtrate is <300us / cm, resulting in a reactant filter cake and filtrate 2. Filtrate 2 can be reused to dissolve waste phosphate cathode materials.

[0060] S3. The filter cake was dried in a 100℃ forced-air drying oven for 12 hours to obtain 120.5 g of iron-manganese phosphate precursor. Analysis showed that its specific surface area was 4.68 m². 2 / g, Fe content is 13.04%, Mn content is 21.53%, P content is 16.34%, Mn / (Fe+Mn)=0.627, Fe+Mn / P=1.185.

[0061] Preparation of lithium iron manganese phosphate / carbon composite materials: (1) The raw materials were fed according to the molar ratio of each element in the lithium source, iron-manganese phosphate precursor, and phosphorus source, Li:Fe+Mn:P=1.06:1:1.03. 115.0g of iron-manganese phosphate precursor, 28.30g of lithium carbonate (99.5%), 15.58g of ammonium dihydrogen phosphate (99%), and 0.8g of magnesium oxide were added sequentially to a 2L measuring cup containing 800mL of pure water. The mixture was then placed in a basket mill and ground at 2000r / min for 40min. After the slurry particle size reached 1-2μm, the slurry was fed into a sand mill for fine grinding. After the slurry particle size reached 350nm, the slurry was spray-dried. After spray drying, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at 600℃ for 4 hours. After the tubular furnace cools down naturally to 80°C, the sintered material is crushed to obtain 100g of pre-lithiated lithium iron manganese phosphate precursor.

[0062] (2) 100g of pre-lithiated lithium iron manganese phosphate precursor, 6g of rock sugar, and 2g of starch were added sequentially to a 2L measuring cup containing 800mL of pure water. The mixture was then placed in a basket mill and ground at 2000r / min for 40min. After the slurry particle size reached 1-2μm, the slurry was fed into a sand mill for fine grinding. After the slurry particle size reached 300nm, the slurry was spray-dried. After spray drying, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 8 hours. After the tube furnace cooled naturally to 80℃, the sintered material was graded and crushed to obtain LiFe with a carbon content of 1.40%. 0..353 Mn 0.627 PO4 / C composite material.

[0063] Prepared LiFe 0.353 Mn 0.627 A PO4 / C composite material is used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. Lithium metal is used as the negative electrode, and the cells are assembled into a coin cell. Tests were conducted at 2-4.3V and 25℃ using different charge-discharge current conditions. The initial reversible capacity was 156.3 mAh / g at 0.1C, 154.7 mAh / g at 0.2C, and 146.2 mAh / g at 1C. After 100 cycles at 1C, the capacity retention was 97.2%.

[0064] Example 4 The waste phosphate cathode material used in this embodiment is lithium iron manganese phosphate powder 2. According to ICP analysis, its Mn / Fe ratio is 7:3, and its impurity element content is shown in Table 1.

[0065] A method for synthesizing lithium iron manganese lithium precursors (with a designed manganese-iron element ratio of Mn:Fe = 7:3) from recycled waste phosphate cathode materials includes the following steps: S1. Weigh 110.0g of waste lithium iron phosphate and lithium manganese powder and slowly add it to a 5L three-necked flask containing 1614.0g of phosphoric acid solution with a mass concentration of 30%. Stirring is started at the same time. After the powder is added, heat to 95℃ and react for 6 hours. After the reaction is completed, filter and wash with a small amount of water to obtain filtrate 1 and filter residue 1. Filter residue 1 is dried and weighed. Its mass is 1.8g, which shows that the phosphoric acid solution dissolution and leaching rate is as high as 98.36%. Filter residue 1 can be redissolved in phosphoric acid solution and reused.

[0066] S2. Add 55.4g of electrolytic manganese flakes and 24.2g of iron powder to filtrate 1. At this point, the ratio of the total molar amount of the metal source and the total molar amount of metal elements in filtrate 1 to the molar amount of phosphorus in the phosphoric acid solution is 1:2. After reacting at 60℃ for 3 hours, the temperature is increased to 90℃ and reacted for another 3 hours at 90℃. After the reaction is completed, the reactants are passed through a 300-mesh sieve to remove unreacted iron powder, manganese flakes, carbon, or metal impurities. Then, the reactants that have passed through the sieve are filtered and washed until the conductivity of the filtrate is <300us / cm, resulting in a reactant filter cake and filtrate 2. Filtrate 2 can be reused to dissolve waste phosphate cathode materials.

[0067] S3. The filter cake was dried in a 100℃ forced-air drying oven for 12 hours to obtain 165.1 g of lithium iron manganese phosphate precursor. Analysis showed that its specific surface area was 4.52 m². 2 / g, Fe content is 10.03%, Mn content is 25.68%, P content is 16.44%, Mn / (Fe+Mn)=0.722, Fe+Mn / P=1.208.

[0068] Preparation of lithium iron manganese phosphate / carbon composite materials (1) The raw materials were fed according to the molar ratio of each element in the lithium source, iron-manganese phosphate precursor, and phosphorus source, Li:Fe+Mn:P=1.08:1:1.03. 160.0g of iron-manganese phosphate precursor, 41.52g of lithium carbonate (99.5%), 25.22g of ammonium dihydrogen phosphate (99%), and 1.25g of magnesium oxide were added sequentially to a 2L measuring cup containing 800mL of pure water. The mixture was then placed in a basket mill and ground at 2000r / min for 40min. After the slurry particle size reached 1-2μm, the slurry was fed into a sand mill for fine grinding. After the slurry particle size reached 300nm, the slurry was spray-dried. After spray drying, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at 600℃ for 4 hours. After the tubular furnace cools down naturally to 80°C, the sintered material is crushed to obtain 150g of pre-lithiated lithium iron manganese phosphate precursor.

[0069] (2) 150g of pre-lithiated lithium iron manganese phosphate precursor, 12g of starch, and 20000 polyethylene glycol were added sequentially to a 2L measuring cup containing 800mL of pure water. The mixture was then placed in a basket mill and ground at 2000r / min for 40min. After the slurry particle size reached 1-2μm, it was fed into a sand mill for fine grinding. After the slurry particle size reached 300nm, it was spray-dried. After spray drying, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 6 hours. After the tube furnace cooled naturally to 80℃, the sintered material was graded and crushed to obtain LiFe with a carbon content of 1.40%. 0..278 Mn 0.722 PO4 / C composite material.

[0070] Prepared LiFe 0.278 Mn 0.722 A PO4 / C composite material is used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. Lithium metal is used as the negative electrode, and the cells are assembled into a coin cell. Tests were conducted at 2-4.3V and 25℃ under different charge-discharge current conditions. The initial reversible capacity was 154.9 mAh / g at 0.1C, 152.1 mAh / g at 0.2C, and 145.2 mAh / g at 1C. After 100 cycles at 1C, the capacity retention was 97.6%.

[0071] Example 5 The waste phosphate cathode material used in this embodiment is lithium iron manganese phosphate powder 3. According to ICP analysis, its Mn / Fe ratio is 8:2, and its impurity element content is shown in Table 1.

[0072] A method for synthesizing lithium iron manganese lithium precursors (with a designed manganese-iron element ratio of Mn:Fe = 8:2) from recycled waste phosphate cathode materials includes the following steps: S1. Weigh 110.0g of waste lithium iron phosphate and lithium manganese powder and slowly add it to a 5L three-necked flask containing 1614.0g of phosphoric acid solution with a mass concentration of 30%. Stirring is started at the same time. After the powder is added, heat to 95℃ and react for 6 hours. After the reaction is completed, filter and wash with a small amount of water to obtain filtrate 1 and filter residue 1. Filter residue 1 is dried and weighed. Its mass is 1.9g, which shows that the phosphoric acid solution dissolution and leaching rate is as high as 98.3%. Filter residue 1 can be redissolved in phosphoric acid solution and reused.

[0073] S2. Add 63.4g of electrolytic manganese flakes and 16.1g of iron powder to filtrate 1. At this time, the ratio of the total molar amount of the metal source and the total molar amount of metal elements in filtrate 1 to the molar amount of phosphorus in the phosphoric acid solution is 1:2. After reacting at 60℃ for 3 hours, the temperature is increased to 90℃ and reacted for another 3 hours at 90℃. After the reaction is completed, the reactants are passed through a 300-mesh sieve to remove unreacted iron powder, manganese flakes, carbon or metal impurities. Then, the reactants that have passed through the sieve are filtered and washed until the conductivity of the filtrate is <300us / cm, resulting in a reactant filter cake and filtrate 2. Filtrate 2 can be reused to dissolve waste phosphate cathode materials.

[0074] S3. The filter cake was dried in a 100℃ forced-air drying oven for 12 hours to obtain 161.0 g of lithium iron manganese phosphate precursor. Analysis showed that its specific surface area was 5.62 m². 2 / g, Fe content is 8.46%, Mn content is 28.99%, P content is 16.68%, molar ratio Mn / (Fe+Mn) = 0.777, molar ratio (Fe+Mn) / P = 1.261.

[0075] Preparation of lithium iron manganese phosphate / carbon composite materials: (1) The raw materials were fed according to the molar ratio of each element in the lithium source, iron-manganese phosphate precursor, and phosphorus source, Li:Fe+Mn:P=1.08:1:1.03. 155.0g of iron-manganese phosphate precursor, 42.21g of lithium carbonate (99.5%), 29.00g of ammonium dihydrogen phosphate (99%), 0.6g of magnesium oxide, and 0.5g of nickel acetate were added sequentially to a 2L measuring cup containing 800mL of pure water. The mixture was then placed in a basket mill and ground at 2000r / min for 40min. After the slurry particle size reached 1-2μm, the slurry was fed into a sand mill for fine grinding. After the slurry particle size reached 300nm, the slurry was spray-dried. After spray drying, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at 600℃ for 4 hours. After the tubular furnace cools down naturally to 80°C, the sintered material is crushed to obtain 150g of pre-lithiated lithium iron manganese phosphate precursor.

[0076] (2) 150g of pre-lithiated lithium iron manganese phosphate precursor, 12g of starch, and 12g of polyethylene glycol 20000 were added sequentially to a 2L measuring cup containing 800mL of pure water. The mixture was then placed in a basket mill and ground at 2000r / min for 40min. After the slurry particle size reached 1-2μm, it was fed into a sand mill for fine grinding. After the slurry particle size reached 300nm, it was spray-dried. After spray drying, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 6 hours. After the tube furnace cooled naturally to 80℃, the sintered material was graded and crushed to obtain LiFe with a carbon content of 1.40%. 0..278 Mn 0.722 PO4 / C composite material.

[0077] Prepared LiFe 0.278 Mn 0.722 A PO4 / C composite material is used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. Lithium metal is used as the negative electrode, and the cells are assembled into a coin cell. Tests were conducted at 2-4.3V and 25℃ under different charge-discharge current conditions. The initial reversible capacity was 154.9 mAh / g at 0.1C, 152.1 mAh / g at 0.2C, and 145.2 mAh / g at 1C. After 100 cycles at 1C, the capacity retention was 97.6%.

[0078] Example 6 The waste phosphate cathode material used in this embodiment is lithium iron manganese phosphate 2 and lithium iron phosphate powder. According to ICP analysis, the Mn / Fe ratio of the lithium iron manganese phosphate material is 7:3, and the content of its impurity elements is shown in Table 1.

[0079] A method for synthesizing lithium iron manganese lithium precursors (with a designed manganese-iron element ratio of Mn:Fe = 6:4) from recycled waste phosphate cathode materials includes the following steps: S1. Weigh 94.3g of waste lithium iron phosphate and lithium manganese and 15.7g of lithium iron phosphate powder in sequence, and slowly add them to a 5L three-necked flask containing 1614.0g of phosphoric acid solution with a mass concentration of 30%. Stirring is started at the same time. After the powder is added, heat to 95℃ and react for 6 hours. After the reaction is completed, filter and wash with a small amount of water to obtain filtrate 1 and filter residue 1. Filter residue 1 is dried and weighed. Its mass is 1.6g, which shows that the leaching rate of phosphoric acid solution is as high as 98.54%. Filter residue 1 can be redissolved in phosphoric acid solution and reused.

[0080] S2. Add 47.5g of electrolytic manganese flakes and 32.2g of iron powder to filtrate 1. At this time, the ratio of the total molar amount of the metal source and the total molar amount of metal elements in filtrate 1 to the molar amount of phosphorus in the phosphoric acid solution is 1:2. After reacting at 60℃ for 3 hours, the temperature is increased to 90℃ and reacted for another 3 hours at 90℃. After the reaction is completed, the reactants are passed through a 300-mesh sieve to remove unreacted iron powder, manganese flakes, carbon or metal impurities. Then, the reactants that have passed through the sieve are filtered and washed until the conductivity of the filtrate is <300us / cm, resulting in a reactant filter cake and filtrate 2. Filtrate 2 can be reused to dissolve waste phosphate cathode materials.

[0081] S3. The filter cake was dried in a 100℃ forced-air drying oven for 12 hours to obtain 164.8 g of lithium iron manganese phosphate precursor. Analysis showed that its specific surface area was 3.52 m². 2 / g, Fe content is 13.06%, Mn content is 22.13%, P content is 16.48%, molar ratio Mn / (Fe+Mn)=0.633, molar ratio (Fe+Mn) / P=1.196.

[0082] Preparation of lithium iron manganese phosphate / carbon composite materials: (1) The raw materials were fed according to the molar ratio of each element in the lithium source, iron-manganese phosphate precursor, and phosphorus source, Li:Fe+Mn:P=1.06:1:1.03. 160.0g of iron-manganese phosphate precursor, 40.10g of lithium carbonate (99.5%), 22.99g of ammonium dihydrogen phosphate (99%), 0.6g of magnesium oxide, and 0.5g of zirconium oxide were added sequentially to a 2L measuring cup containing 800mL of pure water. The mixture was then placed in a basket mill and ground at 2000r / min for 40min. After the slurry particle size reached 1-2μm, the slurry was fed into a sand mill for fine grinding. After the slurry particle size reached 300nm, the slurry was spray-dried. After spray drying, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at 650℃ for 4 hours. After the tubular furnace cools down naturally to 80°C, the sintered material is crushed to obtain 150g of pre-lithiated lithium iron manganese phosphate precursor.

[0083] (2) 150g of pre-lithiated lithium iron manganese phosphate precursor, 12g of starch, and 12g of polyethylene glycol 20000 were added sequentially to a 2L measuring cup containing 800mL of pure water. The mixture was then placed in a basket mill and ground at 2000r / min for 40min. After the slurry particle size reached 1-2μm, it was fed into a sand mill for fine grinding. After the slurry particle size reached 300nm, the slurry was spray-dried. After spray drying, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 6 hours. After the tube furnace cooled naturally to 80℃, the sintered material was graded and crushed to obtain LiFe with a carbon content of 1.36%. 0..278 Mn 0.633 PO4 / C composite material.

[0084] Prepared LiFe 0.278 Mn 0.633 A PO4 / C composite material is used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. Lithium metal is used as the negative electrode, and the cells are assembled into a coin cell. Tests were conducted at 2-4.3V and 25℃ under different charge-discharge current conditions. The initial reversible capacity was 156.2 mAh / g at 0.1C, 154.1 mAh / g at 0.2C, and 146.7 mAh / g at 1C. After 100 cycles at 1C, the capacity retention was 97.8%.

[0085] Comparative Example 1 Unlike Example 1, the ratio of the total molar amount of the added metal source and the total molar amount of metal elements in filtrate 1 to the molar amount of phosphorus in the phosphoric acid solution is 1:2.4.

[0086] The waste phosphate cathode material used in this embodiment is lithium iron manganese phosphate powder 1. According to ICP analysis, its Mn / Fe ratio is 6:4, and its impurity element content is shown in Table 1.

[0087] A method for synthesizing lithium iron manganese lithium precursors (with a designed manganese:iron element ratio of Mn:Fe = 6:4) from recycled waste phosphate cathode materials includes the following steps: S1. Weigh 110.0g of waste lithium iron phosphate and lithium manganese powder and slowly add it to a 5L three-necked flask containing 1614.0g of phosphoric acid solution with a mass concentration of 30%. Stirring is started at the same time. After the powder is added, heat to 95℃ and react for 6 hours. After the reaction is completed, filter and wash with a small amount of water to obtain filtrate 1 and filter residue 1. Filter residue 1 is dried and weighed. Its mass is 1.7g, which shows that the phosphoric acid solution dissolution and leaching rate is as high as 98.45%. Filter residue 1 can be redissolved in phosphoric acid solution and reused.

[0088] S2. Add 34.6g of electrolytic manganese flakes and 23.4g of iron powder to filtrate 1. The ratio of the total molar amount of the metal source and the total molar amount of metal elements in filtrate 1 to the molar amount of phosphorus in the phosphoric acid solution is 1:2.4. After reacting at 60℃ for 3 hours, the temperature is increased to 90℃ and reacted for another 3 hours at 90℃. After the reaction is completed, the reactants are passed through a 300-mesh sieve to remove unreacted iron powder, manganese flakes, carbon or metal impurities. Then, the reactants that have passed through the sieve are filtered and washed until the conductivity of the filtrate is <300us / cm, resulting in a reactant filter cake and filtrate 2. Filtrate 2 can be reused to dissolve waste phosphate cathode materials.

[0089] S3. The filter cake was dried in a 100°C forced-air drying oven for 12 hours to obtain 108.9 g of a light yellow lithium iron manganese phosphate precursor (the product mass was lower than that in Example 1). Analysis showed that its specific surface area was 4.32 m². 2 / g, Fe content is 15.01%, Mn content is 18.72%, P content is 16.20%, Mn / (Fe+Mn)=0.559 (lower than the design ratio of 0.6), Fe+Mn / P=1.165.

[0090] Preparation of lithium iron manganese phosphate / carbon composite materials: (1) The raw materials were fed according to the molar ratio of each element in the lithium source, iron-manganese phosphate precursor, and phosphorus source, Li:Fe+Mn:P=1.06:1:1.03. 105.0g of iron-manganese phosphate precursor, 25.19g of lithium carbonate (99.5%), 12.78g of ammonium dihydrogen phosphate (99%), and 0.76g of magnesium hydroxide were added sequentially to a 2L measuring cup containing 800mL of pure water. The mixture was then placed in a basket mill and ground at 2000r / min for 40min. After the slurry particle size reached 1-2μm, the slurry was fed into a sand mill for fine grinding. After the slurry particle size reached 300nm, the slurry was spray-dried. After spray drying, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at 650℃ for 4 hours. After the tubular furnace naturally cooled to 80°C, the sintered material was crushed to obtain 95.04g of pre-lithiated lithium iron manganese phosphate precursor.

[0091] (2) 90g of pre-lithiated lithium iron manganese phosphate precursor, 7.2g of glucose, and 7.2g of polyethylene glycol 8000 were added sequentially to a 2L measuring cup containing 800mL of pure water. The mixture was then placed in a basket mill and ground at 2000r / min for 40min. After the slurry particle size reached 1-2μm, it was fed into a sand mill for fine grinding. After the slurry particle size reached 300nm, the slurry was spray-dried. After spray drying, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 8 hours. After the tube furnace cooled naturally to 80℃, the sintered material was graded and crushed to obtain LiFe with a carbon content of 1.40%. 0.441 Mn 0.559 PO4 / C composite material.

[0092] Prepared LiFe 0.367 Mn 0.633 A PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. Lithium metal was used as the negative electrode, and the cells were assembled into a coin cell. Tests were conducted at 2-4.3V and 25℃ under different charge-discharge current conditions. The initial reversible capacity was 151.2 mAh / g at 0.1C, 146.8 mAh / g at 0.2C, and 137.8 mAh / g at 1C. After 100 cycles at 1C, the capacity retention was 89.7%.

[0093] The experimental results from Examples 1-6 and Comparative Example 1 show that when the ratio of the total molar amount of the metal source and the total molar amount of metal elements in filtrate 1 to the molar amount of phosphorus in the phosphoric acid solution is 1:2.4 (exceeding Example 1: 1.8-2.2), the quality of the iron-manganese precursor is low, and the Mn / (Fe+Mn) ratio (0.533) is lower than the theoretical design value (0.60). At the same time, the electrochemical performance of the precursor prepared under this condition is also poor. Comparative Example 2 The difference from Example 1 is that no additives are introduced during the preparation of the pre-lithiated lithium iron manganese phosphate precursor, i.e., no doping is performed. The waste phosphate cathode material used in this embodiment is lithium iron manganese phosphate powder 1. According to ICP analysis, its Mn / Fe ratio is 6:4, and its impurity element content is shown in Table 1.

[0094] A method for synthesizing lithium iron manganese precursor by recycling waste phosphate cathode materials includes the following steps: S1. Weigh 110.0g of waste lithium iron phosphate and lithium manganese powder and slowly add it to a 5L three-necked flask containing 1614.0g of phosphoric acid solution with a mass concentration of 30%. Stirring is started at the same time. After the powder is added, heat to 95℃ and react for 6 hours. After the reaction is completed, filter and wash with a small amount of water to obtain filtrate 1 and filter residue 1. Filter residue 1 is dried and weighed. Its mass is 1.7g, which shows that the phosphoric acid solution dissolution and leaching rate is as high as 98.45%. Filter residue 1 can be redissolved in phosphoric acid solution and reused.

[0095] S2. Add 47.3g of electrolytic manganese flakes and 32.1g of iron powder to filtrate 1. At this time, the ratio of the total molar amount of the metal source and the total molar amount of metal elements in filtrate 1 to the molar amount of phosphorus in the phosphoric acid solution is 1:2. After reacting at 60℃ for 3 hours, the temperature is increased to 90℃ and reacted for another 3 hours at 90℃. After the reaction is completed, the reactants are passed through a 300-mesh sieve to remove unreacted iron powder, manganese flakes, carbon or metal impurities. Then, the reactants that have passed through the sieve are filtered and washed until the conductivity of the filtrate is <300us / cm, resulting in a reactant filter cake and filtrate 2. Filtrate 2 can be reused to dissolve waste phosphate cathode materials.

[0096] S3. The filter cake was dried in a 100℃ forced-air drying oven for 12 hours to obtain 166.0 g of iron-manganese phosphate precursor. Analysis showed its specific surface area was 2.48 m². 2 / g, Fe content is 13.00%, Mn content is 21.89%, P content is 16.42%, Mn / (Fe+Mn)=0.631, Fe+Mn / P=1.190.

[0097] Preparation of lithium iron manganese phosphate / carbon composite materials: (1) The raw materials were fed according to the molar ratio of each element in the lithium source, iron-manganese phosphate precursor, and phosphorus source, Li:Fe+Mn:P=1.06:1:1.03. 160.0g of iron-manganese phosphate precursor, 39.75g of lithium carbonate (99.5%), and 22.32g of ammonium dihydrogen phosphate (99%) were added sequentially to a 2L measuring cup containing 800mL of pure water. The mixture was then placed in a basket mill and ground at 2000r / min for 40min. After the slurry particle size reached 1-2μm, the slurry was fed into a sand mill for fine grinding. After the slurry particle size reached 300nm, the slurry was spray-dried. After spray drying, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at 650℃ for 4 hours. After the tubular furnace naturally cooled to 80°C, the sintered material was crushed to obtain 151.23g of pre-lithiated lithium iron manganese phosphate precursor.

[0098] (2) 150.00g of pre-lithiated lithium iron manganese phosphate precursor, 12.00g of glucose, and 12.00g of polyethylene glycol 8000 were added sequentially to a 2L measuring cup containing 800mL of pure water. The mixture was then placed in a basket mill and ground at 2000r / min for 40min. After the slurry particle size reached 1-2μm, it was fed into a sand mill for fine grinding. After the slurry particle size reached 300nm, the slurry was spray-dried. After spray drying, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at 700℃ for 8 hours. After the tube furnace cooled naturally to 80℃, the sintered material was graded and crushed to obtain LiFe with a carbon content of 1.38%. 0.369 Mn 0.631 PO4 / C composite material.

[0099] Prepared LiFe 0.369 Mn 0.631 A PO4 / C composite material was used as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to form the electrode sheet. Lithium metal was used as the negative electrode, and the cells were assembled into a coin cell. Tests were conducted at 2-4.3V and 25℃ under different charge-discharge current conditions. The initial reversible capacity was 148.1 mAh / g at 0.1C, 140.2 mAh / g at 0.2C, and 130.1 mAh / g at 1C. After 100 cycles at 1C, the capacity retention was 78.2%.

[0100] The experimental data from Example 1 and Comparative Example 2 show that, under the same conditions, whether or not additives are added during the subsequent preparation of lithium iron phosphate from the iron manganese phosphate precursor has a significant impact on the performance of the prepared lithium iron manganese phosphate. Compared with Comparative Example 2, Example 1, which added magnesium hydroxide, showed a significant improvement in discharge capacity and cycle performance. This is mainly because the doping of Mg element is beneficial to improving the conductivity and structural stability of lithium manganese phosphate, thereby further improving the discharge capacity and cycle performance of lithium iron manganese phosphate material.

[0101] Detection Example 1 Impurity content testing performance test: 1. The impurity content of the iron-manganese phosphate precursor before and after regeneration of the waste phosphate cathode materials in Examples 1-6 and Comparative Examples 1-2 was compared by ICP measurement. The results are shown in Table 1.

[0102] Test Results Table 1

[0103] As can be seen from the data in Table 1, compared with the impurity content of the phosphate raw material before regeneration, the impurity content of the regenerated iron-manganese phosphate precursor in the examples is better than that of the raw material of the phosphate before regeneration. The impurity content is lower, especially Cu and Co elements. This is mainly because iron powder and manganese flakes are added to reduce the ionic Cu and Co elements to elemental Cu / Co, which are then removed by filtration.

[0104] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for synthesizing iron-manganese phosphate precursor by recycling waste phosphate cathode materials, characterized in that, Includes the following steps: S1. Disperse the waste phosphate cathode material powder in a phosphoric acid solution for reaction. After the reaction is completed, filter to obtain filter residue 1 and filtrate 1. S2. Add the metal source to filtrate 1 to carry out the reaction, continue heating, and after the reaction is completed, filter to obtain residue 2 and filtrate 2; S3. Dry the filter residue 2 to obtain the iron-manganese phosphate precursor; The ratio of the total molar amount of metal source added to S2 and the total molar amount of metal elements in filtrate 1 to the molar amount of phosphorus in the phosphoric acid solution is 1:1.8-2.

2.

2. The method according to claim 1, characterized in that, The waste phosphate cathode material is selected from at least one of the following: waste lithium iron phosphate and lithium manganese phosphate, waste lithium iron phosphate, waste lithium iron phosphate and waste lithium iron phosphate, and a combination of waste lithium iron phosphate and lithium manganese phosphate, and the molar ratio of metal elements in the waste lithium iron phosphate is Mn:Fe = 6-8:2-4.

3. The method according to claim 1, characterized in that, The metal source mentioned in S2 is selected from one or more of iron powder, iron sheet, iron ingot, manganese powder, and electrolytic manganese sheet.

4. The application of the iron-manganese phosphate precursor prepared by the method according to any one of claims 1-3 in the preparation of lithium iron-manganese phosphate / carbon composite materials.

5. A method for preparing a lithium iron manganese phosphate / carbon composite material, characterized in that, Includes the following steps; (1) The lithium source, the iron manganese phosphate precursor obtained by the method of any one of claims 1-3, the phosphorus source, and the additives are coarsely ground and finely ground in an ethanol or deionized water system to obtain slurry 1. The obtained slurry 1 is dried, and the dried powder is sintered in an inert atmosphere to obtain a pre-lithiated lithium iron manganese phosphate precursor. (2) The pre-lithiated lithium iron manganese phosphate precursor and organic carbon source obtained in step (1) are coarsely ground and finely ground in ethanol or deionized water system to obtain slurry 2; the slurry 2 is dried and the dried powder is sintered in an inert atmosphere and sieved to obtain lithium iron manganese phosphate / carbon composite material.

6. The preparation method according to claim 5, characterized in that, In step (1), the molar ratio of each element in the raw material feed lithium source, iron-manganese phosphate precursor and phosphorus source is Li:Fe+Mn:P=1.0-1.1:1:1.0-1.

1.

7. The preparation method according to claim 5, characterized in that, The lithium source in step (1) is one or more of lithium carbonate, lithium acetate, lithium phosphate, and lithium dihydrogen phosphate; the phosphorus source is one or more of ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid; the additive is selected from one or more of magnesium oxide, magnesium hydroxide, magnesium carbonate, magnesium acetate, niobium pentoxide, niobium hydroxide, zirconium dioxide, zirconium hydroxide, vanadium pentoxide, ammonium vanadate, nickel acetate, nickel hydroxide, and nickel carbonate.

8. The preparation method according to claim 5, characterized in that, In step (1), the amount of additive added is 0.1-1% of the mass of the iron manganese phosphate precursor.

9. The preparation method according to claim 5, characterized in that, The organic carbon source mentioned in step (2) is selected from at least one of glucose, sucrose, citric acid, polyethylene glycol, fructose, cyclodextrin, polyvinyl alcohol, polyacrylonitrile, starch, cellulose, and fructose; and the amount of carbon source added is 5-20% of the mass of the pre-lithiated lithium iron manganese phosphate precursor.

10. The application of the lithium iron manganese phosphate / carbon composite material prepared by the preparation method according to any one of claims 5-9 in the preparation of lithium-ion batteries.

Images