Method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste and application thereof

Abstract

The embodiment of the application discloses a recovery method and application of lithium iron phosphate in carbon-coated lithium iron phosphate waste, which takes unqualified carbon-coated lithium iron phosphate waste as raw material, carries out two-stage roasting of oxidation and reduction, and then uses an acid leaching agent for leaching, so as to obtain a leaching solution containing Li + , Fe 2+ and / or Fe 3+ , and PO4 3‑ , and realizes recovery of Li elements, Fe elements and P elements in lithium iron phosphate. The recovery method is simple in process, high in recovery rate of valuable components, low in solid waste, and high in content of Li + , Fe 2+ and / or Fe 3+ , and PO4 3‑ in the obtained leaching solution, and can be directly used for production of lithium iron phosphate products in a liquid phase method.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a method and application for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste. Background Technology

[0002] Lithium iron phosphate (LiFePO4) is widely recognized as one of the best cathode materials for lithium-ion batteries, suitable for large automobiles and facilities, due to its high theoretical capacity and energy density, low material cost, non-toxicity, and high reversibility. Currently, commercially available lithium iron phosphate batteries are widely used in electric vehicles and electronic devices. However, with the increasing application of lithium iron phosphate batteries, the amount of lithium iron phosphate waste generated during production and from used lithium-ion batteries is also increasing, making the recycling and disposal of retired lithium iron phosphate batteries extremely urgent.

[0003] Currently, the industry primarily uses wet leaching with inorganic / organic acids for the recovery of phosphate-based cathode materials. Some studies employ a one-step leaching process using sulfuric acid, hydrochloric acid, and hydrogen peroxide. Others use selective leaching with acetic acid and phosphoric acid to first leach lithium, followed by secondary leaching of other elements. The leachate is then treated using chemical precipitation to obtain recovered products such as Li₂CO₃ and FePO₄. These products can be used as raw materials for the solid-phase production of lithium iron phosphate, thus achieving the recovery and utilization of Li, Fe, and P elements. However, these methods have low recovery rates for valuable components such as lithium, iron, and phosphorus, and generate significant amounts of solid waste, requiring further improvement. Summary of the Invention

[0004] Based on this, embodiments of the present invention provide a method and application for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste. This recovery method uses substandard carbon-coated lithium iron phosphate waste as raw material, first subjecting it to two-stage roasting (oxidation and reduction), and then leaching it with an acid leaching agent to obtain lithium iron phosphate containing Li. + Fe 2+ and / or Fe 3+ and PO4 3- The leachate was processed to achieve complete recovery of Li, Fe, and P elements from lithium iron phosphate. This recovery method is simple, has a high recovery rate of valuable components, produces less solid waste, and the resulting leachate contains relatively high levels of Li. + Fe 2+ and / or Fe 3+ and PO4 3- It has a high content and can be directly used in the liquid phase method to produce lithium iron phosphate products.

[0005] In a first aspect, embodiments of the present invention provide a method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste, comprising:

[0006] In an oxygen-containing atmosphere, the carbon-coated lithium iron phosphate waste is oxidized and roasted to remove carbon, resulting in a first powder.

[0007] In a reducing atmosphere, the first powder is reduced and calcined to obtain the second powder;

[0008] The second powder is added to water to make a slurry;

[0009] An acid leaching agent is added to the slurry to react and obtain a solution containing Li. + Fe 2+ and / or Fe 3+ and PO4 3- The raw material solution.

[0010] In this embodiment of the invention, the volume fraction of oxygen in the oxygen-containing atmosphere is 7%-21%.

[0011] In this embodiment of the invention, the oxidative calcination temperature is 400℃-600℃ and the time is 3h-6h.

[0012] In this embodiment of the invention, the reducing atmosphere includes CO or H2.

[0013] In this embodiment of the invention, the reduction calcination temperature is 500℃-900℃ and the time is 2h-6h.

[0014] In this embodiment of the invention, the acid leaching agent comprises acid and water, wherein the acid comprises one or more of hydrochloric acid, phosphoric acid, sulfuric acid, nitric acid, and oxalic acid;

[0015] And / or, the mass fraction of the acid in the acid leaching agent is 30%-60%;

[0016] And / or, the H in the acid leaching agent + The molar ratio of the carbon-coated lithium iron phosphate waste to the carbon-coated lithium iron phosphate waste is (3-4):1.

[0017] In this embodiment of the invention, the acid leaching agent further includes a dispersant;

[0018] And / or, the amount of the dispersant is 0.01%-0.1% of the mass of the second powder;

[0019] And / or, the dispersant comprises one or more of isooctanol polyoxyethylene ether, nonylphenol polyoxyethylene ether, sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, tributyl phosphate, and fatty alcohol polyoxyethylene ether.

[0020] In this embodiment of the invention, the reaction temperature is 25℃-70℃ and the reaction time is 2h-6h;

[0021] And / or, the liquid-to-solid ratio of the slurry is 0.8-1.5.

[0022] In this embodiment of the invention, the recovery rate of Li element in the carbon-coated lithium iron phosphate waste reaches 99.9%, the recovery rate of Fe element reaches 99.9%, and the recovery rate of P element reaches 99.9%.

[0023] And / or, the raw material solution can be directly used for the liquid-phase production of lithium iron phosphate precursors.

[0024] The method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste provided in this invention embodiment is simple, requires low-end equipment, and has high recovery rates for Li, Fe, and P elements, with almost no solid waste generated. The recovered liquid contains high levels of Li. + Fe 2+ and / or Fe 3+ and PO4 3- With a high content, it can be directly used for the liquid-phase production of lithium iron phosphate. Specifically, this recovery method first oxidizes and roasts the carbon-coated lithium iron phosphate waste to remove the carbon coating on the waste surface. Then, it uses a reducing gas for reduction roasting, reducing the ferric oxide produced during oxidation roasting to FeO or elemental iron, thereby increasing the iron leaching rate. Finally, the product obtained from reduction roasting is acid-leached to fully dissolve valuable components such as lithium, iron, and phosphorus in the solution, thus achieving efficient recovery of all components of lithium iron phosphate. Using this recovery method, under optimized conditions, the recovery rate of Li, Fe, and P elements in carbon-coated lithium iron phosphate waste can reach 99.9%, and it can achieve complete dissolution of waste with no solid waste generation.

[0025] Secondly, embodiments of the present invention provide the application of the method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste described in the first aspect in the preparation of lithium iron phosphate products. The lithium iron phosphate recovery liquid obtained using the above recovery method contains Li... + Fe 2+ / Fe 3+ and PO4 3- With a high content, it meets the process requirements for the liquid-phase production of lithium iron phosphate and can be used to prepare lithium iron phosphate precursors that meet production requirements and lithium iron phosphate products with qualified electrochemical performance. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be described below.

[0027] Figure 1 This is a process flow diagram of lithium iron phosphate recovery from carbon-coated lithium iron phosphate waste according to one embodiment of the present invention. Detailed Implementation

[0028] The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0029] In recent years, with the rapid development of new energy vehicles and energy storage, the demand and usage of lithium iron phosphate (LFP) batteries have increased rapidly. However, this has also led to a surge in the production of substandard carbon-coated LFP products and the recovery of treated carbon-coated LFP waste from retired batteries. To avoid the waste of lithium, iron, and phosphorus resources caused by carbon-coated LFP waste, it is necessary to recycle and reuse it. Current recycling methods have low recovery rates for valuable components such as lithium, iron, and phosphorus, and generate a large amount of solid waste, which is environmentally unfriendly and requires further improvement.

[0030] Based on this, embodiments of the present invention provide a method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste, such as... Figure 1 As shown, it includes the following steps:

[0031] S1. In an oxygen-containing atmosphere, carbon-coated lithium iron phosphate waste is oxidized and roasted to remove carbon, resulting in the first powder.

[0032] S2. The first powder is reduced and calcined in a reducing atmosphere to obtain the second powder;

[0033] S3. Add the second powder to water to make a slurry;

[0034] S4. Add an acid leaching agent to the slurry and react to obtain a solution containing Li. + Fe 2+ and / or Fe 3+ and PO4 3- The raw material solution.

[0035] In this invention, the main components of carbon-coated lithium iron phosphate waste are LiFePO4 and C. Specifically, it can be carbon-coated lithium iron phosphate products with substandard electrochemical performance, or carbon-coated lithium iron phosphate cathode materials recovered from waste batteries after impurity removal treatment. The lithium iron phosphate recovery method from carbon-coated lithium iron phosphate waste provided in this invention embodiment is simple, requires low-end equipment, and has high recovery rates for Li, Fe, and P elements, with almost no solid waste generated. The recovered liquid contains Li... + Fe 2+ and / or Fe 3+ and PO4 3-With a high content, it can be directly used in the liquid-phase production of lithium iron phosphate, which is beneficial for the recycling and reuse of carbon-coated lithium iron phosphate waste. Specifically, this recycling method first oxidizes and roasts the carbon-coated lithium iron phosphate waste, oxidizing the carbon coating on the waste surface into carbon dioxide, thereby completely removing the carbon and facilitating the subsequent acid leaching of Li, Fe, and P elements, while reducing the generation of solid waste. Then, a reducing gas is used to reduce and roast the oxidized roasting product, reducing the ferric oxide produced during oxidized roasting to FeO or elemental iron. Ferric oxide is less soluble in acid leaching agents than FeO and elemental iron, so reducing ferric oxide to FeO or elemental iron facilitates the subsequent leaching of iron elements and reduces the generation of solid waste. Finally, the reduced roasting product is acid leached, allowing valuable components such as lithium, iron, and phosphorus to fully dissolve in the solution, thereby achieving efficient recovery of all components of lithium iron phosphate waste. Using this recycling method, under optimized conditions, the recovery rate of Li element can reach 99.9%, the recovery rate of Fe element can reach 99.9%, and the recovery rate of P element can reach 99.9% from carbon-coated lithium iron phosphate waste. Furthermore, it can achieve complete dissolution of waste and generate no solid waste.

[0036] In this embodiment of the invention, the volume fraction of oxygen in the oxygen-containing atmosphere can be 7%-21%, which satisfies the carbon combustion reaction to remove carbon from the carbon-coated lithium iron phosphate waste, and also reduces the generation of byproducts such as ferric oxide. In some embodiments, the volume fraction of oxygen in the oxygen-containing atmosphere can be, for example, 7%, 10%, 12%, 15%, 18%, or 21%.

[0037] In this embodiment of the invention, the oxidative roasting temperature can be 400℃-600℃, and the time can be 3h-6h. This can accelerate the carbon combustion reaction, improve the carbon removal rate and efficiency, and reduce the generation of byproducts such as ferric oxide. In some embodiments, the oxidative roasting temperature can be, for example, 400℃, 420℃, 450℃, 480℃, 500℃, 530℃, 550℃, 580℃, or 600℃; and the oxidative roasting time can be, for example, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, or 6h.

[0038] In this embodiment of the invention, the reducing atmosphere can be CO or H2. Both CO and H2 are gases with strong reducing properties, which can quickly reduce ferric oxide to iron with high reduction efficiency. Moreover, the main reaction products of CO and H2 as reducing agents are CO2 and H2O, which have less pollution to the environment.

[0039] In this embodiment of the invention, the reduction roasting temperature can be 500℃-900℃, and the time can be 2h-6h. The preferred temperature for CO is 500℃-900℃, and the preferred temperature for H2 is 600℃-900℃. This ensures the complete reduction reaction, allowing ferric oxide to be completely reduced to FeO or elemental iron, which is beneficial for subsequent acid leaching, and also avoids waste of energy and resources. In some embodiments, the reduction roasting temperature can be, for example, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, or 900℃; and the reduction roasting time can be, for example, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, or 6h.

[0040] In this embodiment of the invention, the acid leaching agent comprises an acid and water, wherein the acid can be one or more selected from hydrochloric acid, phosphoric acid, sulfuric acid, nitric acid, and oxalic acid. These acids can efficiently convert the valuable components contained in the second powder into water-soluble ionic states, yielding a product containing Li. + Fe 2+ Fe 3+ and PO4 3- The leachate has a fast leaching reaction rate, low energy consumption, and high leaching efficiency.

[0041] In this embodiment of the invention, the mass fraction of acid in the acid leaching agent can be 30%-60%, which can effectively leach Li, Fe, and P elements while avoiding passivation of the reactants. In some embodiments, the mass fraction of acid in the acid leaching agent is, for example, 30%, 35%, 40%, 45%, 50%, 55%, or 60%.

[0042] In this embodiment of the invention, the H in the acid leaching agent + The molar ratio of the acid leaching agent to carbon-coated lithium iron phosphate waste can be (3-4):1. This ensures sufficient leaching of lithium, iron, and phosphorus from the carbon-coated lithium iron phosphate waste while avoiding waste of the acid leaching agent, thus helping to control costs. In some embodiments, the acid leaching agent contains H... + The molar ratio of the second powder to carbon-coated lithium iron phosphate waste can be 3:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, 3.6:1, or 4:1. In this embodiment of the invention, the acid leaching agent further includes a dispersant. The dispersant effectively improves the dispersion of the second powder in the acid leaching agent, prevents the agglomeration of the second powder, reduces the generation of solid waste, and is beneficial to improving the acid leaching reaction rate and leaching yield. In some embodiments, the dispersant includes one or more of isooctanol polyoxyethylene ether (PEH-6), nonylphenol polyoxyethylene ether (NP-40), sodium dodecyl sulfate (SDS), hexadecyltrimethylammonium bromide (CTAB), tributyl phosphate (TBP), and fatty alcohol polyoxyethylene ether (AEO).

[0043] In this embodiment of the invention, the amount of dispersant can be 0.01%-0.1% of the mass of the second powder. This effectively improves the dispersion of the second powder in the acid leaching agent while avoiding waste of the dispersant, thus helping to control costs. In some embodiments, the amount of dispersant can be, for example, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, or 0.1% of the mass of the second powder.

[0044] In this embodiment of the invention, the reaction temperature can be 25℃-70℃, and the reaction time can be 2h-6h. This ensures that the second powder is fully dissolved, achieving the leaching of Li, Fe, and P elements, while avoiding waste of energy and resources. In some embodiments, the reaction temperature can be, for example, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, or 70℃, and the reaction time can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, or 6h.

[0045] In this embodiment of the invention, after the reaction is completed, the acid leaching solution can be filtered to remove solid insoluble matter. If the reaction solution is clear and free of residue, filtration is not required.

[0046] In this embodiment of the invention, the liquid-to-solid ratio of the slurry can be 0.8-1.5. Adding the second powder to water to prepare the slurry and ensuring its uniform suspension facilitates subsequent contact and reaction with the acid leaching agent, promoting the leaching of Li, Fe, and P elements. Controlling the liquid-to-solid ratio of the slurry to 0.8-1.5 improves the dispersion of the second powder in the acid leaching agent without excessively affecting the acid concentration in the reaction system. In some embodiments, the liquid-to-solid ratio of the slurry can be, for example, 0.8, 0.9, 1.0, 1.2, 1.3, 1.4, or 1.5.

[0047] In this embodiment of the invention, the recovery rate of Li element in carbon-coated lithium iron phosphate waste can be 98.1%-99.9%, the recovery rate of Fe element can be 90.5%-99.9%, and the recovery rate of P element can be 97.5%-99.9%. The recovery rates of Li, Fe and P elements obtained by the recovery method provided in this embodiment of the invention are all high, which can achieve efficient recovery of all components of lithium iron phosphate and has high economic benefits. In some embodiments, the Li element recovery rate in carbon-coated lithium iron phosphate waste can be, for example, 98.1%, 98.9%, 99%, 99.1%, 99.3%, 99.4%, 99.5%, 99.7%, or 99%; the Fe element recovery rate can be, for example, 90.5%, 92.1%, 92.2%, 93.3%, 94.4%, 96.2%, 96.3%, 97.3%, 98.1%, 98.3%, 98.5%, 99%, 99.3%, 99.6%, or 99.9%; and the phosphorus element recovery rate can be, for example, 97.5%, 98.5%, 98.6%, 98.7%, 99.1%, 99.2%, 99.3%, 99.5%, 99.6%, or 99.9%. In some embodiments, the recovery rates of Li, Fe, and P elements in carbon-coated lithium iron phosphate waste reached 99.9%.

[0048] In this embodiment of the invention, the raw material solution can be directly used for the liquid-phase production of lithium iron phosphate precursor. The raw material solution provided in this embodiment contains Li... + Fe 2+ and / or Fe 3+ and PO4 3- With a high content and appropriate molar ratio of each ion, it meets the raw material requirements for the production of lithium iron phosphate precursors by the liquid phase method and can be directly used to produce lithium iron phosphate precursors. Furthermore, the lithium iron phosphate precursor can be sintered to prepare qualified lithium iron phosphate products.

[0049] This invention also provides the application of the method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste according to any of the above embodiments in the preparation of lithium iron phosphate products. The lithium iron phosphate recovery liquid obtained using the above recovery method contains Li... + Fe 2+ and / or Fe 3+ and PO4 3- With a high content, it meets the process requirements for the liquid-phase production of lithium iron phosphate and can be used to prepare lithium iron phosphate precursors that meet production requirements and lithium iron phosphate products with qualified electrochemical performance, realizing the full-component recovery and regeneration of carbon-coated lithium iron phosphate waste. Specifically, lithium iron phosphate products can be lithium iron phosphate cathode materials used to prepare lithium-ion battery cathode sheets or oxygen evolution reaction electrocatalysts.

[0050] The technical solution of the present invention will be further described below through specific embodiments and comparative examples.

[0051] Example 1

[0052] A method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste includes the following steps:

[0053] (1) In an oxygen-containing atmosphere with an oxygen volume fraction of 10%, 200g of carbon-coated lithium iron phosphate waste was oxidized and roasted to remove carbon. The oxidation and roasting temperature was 500℃ and the time was 3h to obtain the first powder.

[0054] (2) In a CO atmosphere, the first powder was reduced and roasted at a temperature of 700°C for 3 hours, and then naturally cooled to obtain the second powder.

[0055] (3) Mix 100g of the second powder with water at a liquid-to-solid ratio of 1.2 to obtain a slurry; then mix and stir nitric acid aqueous solution, phosphoric acid aqueous solution and nonylphenol polyoxyethylene ether (NP-40) to prepare an acid leaching agent, so that the H in the acid leaching agent... + The molar ratio of carbon-coated lithium iron phosphate waste to carbon-coated lithium iron phosphate waste is 3.2:1, and in the acid leaching agent, nitric acid and phosphoric acid respectively provide H₂. + The ratio was 2:1.2, the total mass fraction of nitric acid and phosphoric acid was 40%, and the amount of NP-40 added was 0.1% of the mass of the second powder in the slurry. Finally, an acid leaching agent was added to the slurry and mixed to obtain a reaction solution. The reaction solution was reacted at 50°C for 4 hours to obtain a leachate, which contained Li. + Fe 2+ and / or Fe 3+ and PO4 3- The raw material solution.

[0056] The leachate obtained in Example 1 was clear. Using the leachate from Example 1 as raw material, lithium iron phosphate precursor was produced by liquid phase method. The lithium iron phosphate precursor was further sintered to obtain qualified lithium iron phosphate products. The composition analysis of lithium iron phosphate waste and qualified lithium iron phosphate products is shown in Table 1.

[0057] Table 1. Composition analysis of lithium iron phosphate waste and qualified lithium iron phosphate products in Example 1

[0058] Lithium iron phosphate waste 32.86 4.21 18.44 Qualified lithium iron phosphate products 32.89 4.33 18.40

[0059] The recovery rates of each valuable component in Example 1 were tested. The recovery rate of Li was detected using inductively coupled plasma (ICP), the recovery rate of Fe was detected using spectrophotometry, and the recovery rate of P was detected using the quinomolybdate-limonene gravimetric method. The results showed that the recovery rates of Li, Fe, and P in Example 1 reached 99.9%. Lithium iron phosphate cathode material was prepared using the leachate obtained in Example 1, and the cathode material was assembled into coin cells for performance testing. The results showed that at room temperature (25°C) and 0.1C, the initial charge specific capacity of the coin cell in Example 1 was 162.4 mAh / g, and the initial coulombic efficiency was 98.51%; at room temperature (25°C) and 1C, the initial charge specific capacity was 160.2 mAh / g, and the initial coulombic efficiency was 87.93%.

[0060] Example 2

[0061] A method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste includes the following steps:

[0062] (1) In an oxygen-containing atmosphere with an oxygen volume fraction of 21%, 200g of carbon-coated lithium iron phosphate waste was oxidized and roasted to remove carbon. The oxidation and roasting temperature was 400℃ and the time was 4h to obtain the first powder.

[0063] (2) In a CO atmosphere, the first powder was reduced and roasted at a temperature of 700°C for 3 hours, and then naturally cooled to obtain the second powder.

[0064] (3) Mix 100g of the second powder with water at a liquid-to-solid ratio of 1.2 to obtain a slurry; then mix and stir nitric acid aqueous solution, oxalic acid aqueous solution and nonylphenol polyoxyethylene ether (NP-40) to prepare an acid leaching agent, so that the H in the acid leaching agent... + The molar ratio of carbon-coated lithium iron phosphate waste to carbon-coated lithium iron phosphate waste is 3.3:1, and the acid leaching agent provides H+ from nitric acid and oxalic acid, respectively. + The ratio is 2.8:0.5, the total mass fraction of nitric acid and oxalic acid is 40%, and the amount of NP-40 added is 0.1% of the mass of the second powder in the slurry. Finally, acid leaching agent is added to the slurry and mixed and stirred to obtain a reaction solution. The reaction solution is reacted at 50°C for 4 hours to obtain a leachate.

[0065] The leachate obtained in Example 2 was clear. Using the leachate from Example 2 as raw material, lithium iron phosphate precursor was produced by liquid phase method. The lithium iron phosphate precursor was further sintered to obtain qualified lithium iron phosphate products. The composition analysis of lithium iron phosphate waste and qualified lithium iron phosphate products is shown in Table 2.

[0066] Table 2. Composition analysis of lithium iron phosphate waste and qualified lithium iron phosphate products in Example 2.

[0067] Lithium iron phosphate waste 32.86 4.21 18.44 Qualified lithium iron phosphate products 32.96 4.29 18.52

[0068] Testing showed that the recovery rates of Li, Fe, and P elements in Example 2 reached 99.9%. Lithium iron phosphate cathode material was prepared using the leachate obtained in Example 2, and the cathode material was assembled into coin cells for performance testing. The initial charge specific capacity of the coin cell in Example 2 at room temperature (25°C) and 0.1C was 162.5 mAh / g, with an initial coulombic efficiency of 98.59%; at room temperature (25°C) and 1C, the initial charge specific capacity was 160.5 mAh / g, with an initial coulombic efficiency of 88.34%.

[0069] Example 3

[0070] A method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste includes the following steps:

[0071] (1) In an oxygen-containing atmosphere with an oxygen volume fraction of 21%, 200g of carbon-coated lithium iron phosphate waste was oxidized and roasted to remove carbon. The oxidation and roasting temperature was 400℃ and the time was 4h to obtain the first powder.

[0072] (2) The first powder was reduced and roasted in H2 atmosphere at a temperature of 850°C for 4 hours. After natural cooling, the second powder was obtained.

[0073] (3) Mix 100g of the second powder with water at a liquid-to-solid ratio of 1.2 to obtain a slurry; then mix and stir nitric acid aqueous solution, phosphoric acid aqueous solution and nonylphenol polyoxyethylene ether (NP-40) to prepare an acid leaching agent, so that the H in the acid leaching agent... + The molar ratio of carbon-coated lithium iron phosphate waste to carbon-coated lithium iron phosphate waste is 3.2:1, and in the acid leaching agent, nitric acid and phosphoric acid respectively provide H₂. + The ratio is 2:1.2, the total mass fraction of nitric acid and phosphoric acid is 40%, and the amount of NP-40 added is 0.1% of the mass of the second powder in the slurry. Finally, acid leaching agent is added to the slurry and mixed and stirred to obtain a reaction solution. The reaction solution is reacted at 50°C for 4 hours to obtain a leachate.

[0074] The leachate obtained in Example 3 was clear. Using the leachate from Example 3 as raw material, lithium iron phosphate precursor was produced by liquid phase method. The lithium iron phosphate precursor was further sintered to obtain qualified lithium iron phosphate product. The composition analysis of lithium iron phosphate waste and qualified lithium iron phosphate product is shown in Table 3.

[0075] Table 3. Composition analysis of lithium iron phosphate waste and qualified lithium iron phosphate products in Example 3.

[0076] Lithium iron phosphate waste 32.86 4.21 18.44 Qualified lithium iron phosphate products 32.93 4.35 18.55

[0077] Testing showed that the recovery rates of Li, Fe, and P elements in Example 3 reached 99.9%. Lithium iron phosphate cathode material was prepared using the leachate obtained in Example 3, and the cathode material was assembled into coin cells for performance testing. The initial charge specific capacity of the coin cell in Example 3 at room temperature (25°C) and 0.1C was 163.6 mAh / g, with an initial coulombic efficiency of 98.59%; at room temperature (25°C) and 1C, the initial charge specific capacity was 161.5 mAh / g, with an initial coulombic efficiency of 88.28%.

[0078] Example 4

[0079] The difference between the method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste in Example 4 and Example 1 is that the volume fraction of oxygen in the oxygen-containing atmosphere in step (1) is 21%, the reaction time of the reaction solution in step (3) is 6 hours, and the reaction solution is filtered after the reaction to remove residue and obtain filtrate.

[0080] The filtrate from Example 4 can be directly used for the liquid-phase production of lithium iron phosphate precursors. Testing showed that the recovery rates of Li, Fe, and P in Example 4 reached 99%, 90.5%, and 99.5%, with a residue volume of 5%. Comparing Examples 1 and 4, it is evident that at a constant oxidative roasting temperature and time, using an appropriate concentration of oxygen helps to better reduce the formation of ferric oxide, allowing for a more complete leaching reaction, thereby increasing the leaching rate of each element and reducing the amount of residual residue.

[0081] Example 5

[0082] The difference between the method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste in Example 5 and Example 1 is that the reaction temperature of the reaction solution in step (3) is 60°C, the reaction time is 3h, and the reaction solution is filtered after the reaction to remove residue and obtain filtrate.

[0083] The filtrate from Example 5 can be directly used for the liquid-phase production of lithium iron phosphate. Testing showed that the recovery rate of Li in Example 5 reached 99.7%, the recovery rate of Fe reached 96.3%, and the recovery rate of P reached 99.6%, with a residue amount of 2.2%. Comparing Examples 1 and 5, it is evident that extending the leaching reaction time allows for a more complete reaction, thereby increasing the leaching rate of each element and reducing the amount of residual residue.

[0084] Example 6

[0085] The method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste in Example 6 differs from that in Example 1 in that the acid leaching agent in step (3) does not include phosphoric acid, and the H2 provided by nitric acid in the acid leaching agent... + The molar ratio of the reactant to carbon-coated lithium iron phosphate waste was 3:1, and the reaction solution was filtered after the reaction to remove residue, resulting in filtrate.

[0086] The filtrate from Example 6 can be directly used for the liquid-phase production of lithium iron phosphate. Testing showed that the recovery rates of Li, Fe, and P in Example 6 reached 98.1%, 94.4%, and 97.5%, with a residue volume of 4.3%. Comparing Examples 1 and 6, it is evident that for a given amount of carbon-coated lithium iron phosphate waste, using an appropriate amount of acid can make the leaching reaction more complete, thereby increasing the leaching rate of each element and reducing the amount of residual residue.

[0087] Example 7

[0088] The difference between the method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste in Example 7 and Example 2 is that the reduction roasting time in step (2) is 2 hours, and the reaction solution is filtered after the reaction to remove residue and obtain filtrate.

[0089] The filtrate from Example 7 can be directly used for the liquid-phase production of lithium iron phosphate. Testing showed that the recovery rates of Li, Fe, and P in Example 7 reached 99.1%, 93.3%, and 98.6%, with a residue weight of 3.9%. Comparing Examples 2 and 7, it is evident that at a constant reduction roasting temperature, a suitable roasting time facilitates the reduction of ferric oxide, better reduces the ferric oxide content in the second powder, ensures a more complete leaching reaction, improves the leaching rate of each element, and reduces the amount of residual residue.

[0090] Example 8

[0091] The difference between the method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste in Example 8 and Example 2 is that the total mass fraction of nitric acid and oxalic acid in the acid leaching agent in step (3) is 60%, and the reaction solution is filtered after the reaction to remove residue and obtain filtrate.

[0092] The filtrate from Example 8 can be directly used for the liquid-phase production of lithium iron phosphate. Testing showed that the recovery rates of Li, Fe, and P in Example 8 reached 99.3%, 96.2%, and 99.1%, with a residue volume of 2.8%. Comparison of Examples 2 and 8 indicates that using an appropriate concentration of acid leaching agent can make the leaching reaction more complete, increase the leaching rate of each element, and reduce the amount of residual residue.

[0093] Example 9

[0094] The difference between the method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste in Example 9 and Example 2 is that the reduction roasting temperature in step (2) is 600°C, and the reaction solution is filtered after the reaction to remove residue and obtain filtrate.

[0095] The filtrate from Example 9 can be directly used for the liquid-phase production of lithium iron phosphate precursors. Testing showed that the recovery rates of Li, Fe, and P in Example 9 reached 99.0%, 92.1%, and 98.5%, with a residue weight of 3.7%. Comparing Examples 2 and 9, it is evident that, under a fixed reduction roasting time, using a suitable roasting temperature facilitates better reduction of ferric oxide in the second powder, thereby resulting in a more complete leaching reaction, increased leaching rates of each element, and reduced residual residue.

[0096] Example 10

[0097] The difference between the method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste in Example 10 and Example 2 is that sodium dodecyl sulfate (SDS) is used as the dispersant in step (3), and the reaction solution is filtered after the reaction to remove residue and obtain filtrate.

[0098] The filtrate from Example 10 can be directly used for the liquid-phase production of lithium iron phosphate. Testing showed that the recovery rates of Li, Fe, and P in Example 10 reached 99.4%, 98.3%, and 99.3%, with a residue amount of 1.3%. Comparing Examples 2 and 10, it is evident that NP-40 dispersant provides better dispersion than SDS, resulting in a more complete leaching reaction, increased leaching rates of each element, and reduced residual residue.

[0099] Example 11

[0100] The difference between the method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste in Example 11 and Example 2 is that in step (3), the second powder and water are mixed into a slurry at a liquid-solid ratio of 1.5, and the reaction solution is filtered after the reaction to remove residue and obtain filtrate.

[0101] The filtrate from Example 11 cannot be directly used for the liquid-phase production of lithium iron phosphate, but lithium, iron, and phosphorus can be added to the filtrate to meet the process requirements for liquid-phase lithium iron phosphate production. Testing showed that the recovery rates of Li, Fe, and P in Example 11 reached 99.5%, 98.1%, and 99.5%, with a residue weight of 1.7%. Comparing Examples 2 and 11, it is evident that using a slurry with a suitable liquid-to-solid ratio facilitates better leaching reactions, thereby increasing the leaching rate of each element and reducing the amount of residual residue.

[0102] Example 12

[0103] The difference between the method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste in Example 12 and Example 2 is that in step (3), sulfuric acid of equal mass is used to replace oxalic acid to prepare the acid leaching agent, and the reaction solution is filtered after the reaction to remove residue and obtain filtrate.

[0104] The filtrate from Example 12 can be directly used for the liquid-phase production of lithium iron phosphate. Testing showed that the recovery rates of Li, Fe, and P in Example 12 reached 99.1%, 97.3%, and 98.7%, with a residue volume of 1.8%. Comparison of Examples 2 and 12 indicates that the acid leaching agent prepared with nitric acid and oxalic acid has a better leaching effect than that prepared with nitric acid and sulfuric acid.

[0105] Example 13

[0106] The method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste in Example 13 differs from that in Example 1 in that the dispersant NP-40 is not added to the reaction solution in step (3), and the reaction solution is filtered after the reaction to remove residues and obtain filtrate.

[0107] The filtrate from Example 13 can be directly used for the liquid-phase production of lithium iron phosphate. Testing showed that the recovery rates of Li, Fe, and P in Example 13 were 98.9%, 92.2%, and 99.2%, with a residue volume of 3.1%. Comparing Example 1 and Example 13, it is evident that adding a dispersant to the leaching reaction solution can improve the recovery rates of Li, Fe, and P elements and reduce the generation of solid waste.

[0108] Comparative Example 1

[0109] A method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste includes the following steps:

[0110] (1) In an oxygen-containing atmosphere with an oxygen volume fraction of 10%, 200g of carbon-coated lithium iron phosphate waste was oxidized and roasted to remove carbon. The oxidation and roasting temperature was 500℃ and the time was 3h to obtain roasted powder.

[0111] (2) The calcined powder and water were mixed at a liquid-to-solid ratio of 1.2 to form a slurry; then, an acid leaching agent was prepared by mixing and stirring a nitric acid aqueous solution, a phosphoric acid aqueous solution, and nonylphenol polyoxyethylene ether (NP-40) to achieve the desired H+ concentration. + The molar ratio of carbon-coated lithium iron phosphate waste to carbon-coated lithium iron phosphate waste is 3.2:1, and in the acid leaching agent, nitric acid and phosphoric acid respectively provide H₂. +The ratio is 2:1.2, the total mass fraction of nitric acid and phosphoric acid is 40%, and the amount of NP-40 added is 0.1% of the mass of the second powder in the slurry. Finally, acid leaching agent is added to the slurry and mixed and stirred to obtain a reaction solution. The reaction solution is reacted at 50°C for 4 hours. After the reaction is completed, the reaction solution is filtered to remove the residue and obtain the filtrate.

[0112] The filtrate obtained from Comparative Example 1 cannot be directly used for the liquid-phase production of lithium iron phosphate. Testing showed that the recovery rates of Li, Fe, and P in Comparative Example 1 were 90.8%, 73.1%, and 87.1%, with a residue volume of 30.7%. Compared to Example 1, the recovery rates of Li, Fe, and P in Comparative Example 1 were all lower, and a large amount of residue was generated. This is mainly because the carbon-coated lithium iron phosphate waste in Comparative Example 1 only underwent oxidative roasting and not reductive roasting. In this case, the roasted powder contained a large amount of ferric oxide, which is insoluble in nitric acid and phosphoric acid, resulting in a low Fe recovery rate. Furthermore, the insoluble ferric oxide may have coated the surface of the roasted powder, preventing the effective dissolution of Li and P, thus reducing their recovery rates.

[0113] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste, characterized in that, include: In an oxygen-containing atmosphere, the carbon-coated lithium iron phosphate waste is oxidized and roasted to remove carbon, resulting in a first powder. The volume fraction of oxygen in the oxygen-containing atmosphere is 7%-21%; In a reducing atmosphere, the first powder is reduced and calcined to obtain the second powder; The second powder is added to water to make a slurry; An acid leaching agent is added to the slurry to react and obtain a solution containing Li. + Fe 2+ and / or Fe 3+ and PO4 3- The raw material solution; the acid leaching agent contains H + The molar ratio of the carbon-coated lithium iron phosphate waste to the carbon-coated lithium iron phosphate waste is (3-4):1; The recovery rates of Li, Fe, and P in the carbon-coated lithium iron phosphate waste are 98.1%-99.9%, 90.5%-99.9%, and 97.5%-99.9%, respectively.

2. The method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste as described in claim 1, characterized in that, The oxidation calcination temperature is 400℃-600℃, and the time is 3h-6h.

3. The method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste as described in claim 1, characterized in that, The reducing atmosphere includes CO or H2.

4. The method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste as described in claim 1, characterized in that, The reduction calcination temperature is 500℃-900℃, and the time is 2h-6h.

5. The method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste as described in claim 1, characterized in that, The acid leaching agent comprises acid and water, wherein the acid comprises one or more of hydrochloric acid, phosphoric acid, sulfuric acid, nitric acid, and oxalic acid, and the mass fraction of the acid in the acid leaching agent is 30%-60%. And / or, the acid leaching agent may also include a dispersant.

6. The method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste as described in claim 5, characterized in that, The amount of the dispersant used is 0.01%-0.1% of the mass of the second powder; And / or, the dispersant comprises one or more of isooctanol polyoxyethylene ether, nonylphenol polyoxyethylene ether, sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, tributyl phosphate, and fatty alcohol polyoxyethylene ether.

7. The method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste as described in claim 1, characterized in that, The reaction temperature is 25°C. o C-70 o C, the time is 2h-6h; And / or, the liquid-to-solid ratio of the slurry is 0.8-1.

5.

8. The method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste as described in any one of claims 1-7, characterized in that, The recovery rates of Li, Fe, and P elements in the carbon-coated lithium iron phosphate waste reached 99.9%. And / or, the raw material solution is used directly for the liquid-phase production of lithium iron phosphate precursors.

9. The application of the method for recovering lithium iron phosphate from carbon-coated lithium iron phosphate waste as described in any one of claims 1-8 in the preparation of lithium iron phosphate products.

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