A method for recycling waste lithium iron phosphate positive electrode material

Abstract

The present invention provides a method for recycling waste lithium iron phosphate positive electrode materials. The recycling method can realize the recycling of all components of waste lithium iron phosphate positive electrode materials, and can also prepare new positive electrode materials from the recycled components, and the process flow is extremely simplified; it can also flexibly control the synthesis reaction conditions, adjust the spray drying and sintering conditions, and prepare positive electrode materials with different micromorphologies and component requirements that meet specific needs; moreover, the entire recycling process achieves a green closed loop, and the effective components therein can be completely recycled and reused, thereby maximally reducing the impact of the recycling method on the environment, and improving the production efficiency of preparing new positive electrode materials using waste lithium iron phosphate positive electrode materials, alleviating the dependence of lithium iron phosphate battery production on the natural resources of lithium salt lakes and lithium ores.

Description

Technical Field

[0001] The invention belongs to the technical field of waste battery recycling and relates to a method for recycling positive electrode materials, and in particular to a method for recycling waste lithium iron phosphate positive electrode materials. Background Art

[0002] Lithium iron phosphate (LiFePO4) is the positive electrode material of lithium-ion batteries. Due to its high safety, good stability, economy and environmental protection, it is widely used in new energy vehicles and energy storage fields, especially in fields with high safety requirements.

[0003] With the explosive growth of power batteries and energy storage batteries, the amount of scrapped batteries has also increased exponentially. If large-scale retired batteries are not properly handled, it will not only bring environmental and safety problems, but also cause waste of resources. Therefore, waste lithium batteries will become the main direction of lithium mine utilization in the future. If they can be fully recycled, the demand for primary minerals can be reduced by more than 60%. Therefore, the utilization of waste lithium batteries is crucial to the continuous and stable supply of lithium resources. The recycling of waste lithium iron phosphate batteries can not only reduce the environmental pressure caused by solid waste, but also bring considerable economic benefits, which is conducive to the sustainable development of the lithium battery industry.

[0004] The existing methods for recycling waste lithium iron phosphate batteries include physical disassembly and separation, leaching, filtration, and lithium extraction to obtain lithium carbonate, but a large amount of phosphorus-iron solid waste will be generated; and in various existing technologies, only lithium in waste lithium iron phosphate is extracted, resulting in a waste of phosphorus and iron resources. For example, the method for recycling lithium elements in waste lithium iron phosphate disclosed in CN115784266A does not properly recycle and reuse iron and phosphorus elements.

[0005] Moreover, the prior art will produce a large amount of saline wastewater in the process of producing lithium carbonate and iron phosphate using waste lithium iron phosphate batteries; for example, CN111924817A discloses a method for comprehensive utilization of waste lithium iron phosphate positive electrode materials, which will produce a large amount of saline wastewater during the comprehensive utilization process. In addition, in the drying and crushing process of battery-grade lithium carbonate, and the production process of sewage iron phosphate, a large amount of electricity and heat source are required, resulting in a large amount of resource waste. The recovered lithium carbonate and iron phosphate need to be prepared through solid phase sintering to obtain lithium iron phosphate positive electrode materials, which not only further increases the preparation cost, but also causes a decrease in the yield of lithium iron phosphate positive electrode materials. Finally, the method for preparing lithium iron phosphate positive electrode materials by using the obtained lithium carbonate and iron phosphate cannot realize the preparation of positive electrode materials such as lithium manganese iron phosphate, and the application surface is relatively narrow.

[0006] In view of the shortcomings of the existing technology, it is necessary to provide a method for recycling waste lithium iron phosphate positive electrode materials that is low-cost, green and closed-loop and can prepare new lithium iron phosphate or lithium manganese iron phosphate. Summary of the invention

[0007] The object of the present invention is to provide a method for recycling waste lithium iron phosphate positive electrode materials. The recycling method can realize the recycling of all components of waste lithium iron phosphate positive electrode materials, and can also prepare new positive electrode materials from the recycled components, and the process flow is simplified; it can also flexibly control the synthesis reaction conditions, adjust the spray drying and sintering conditions, and prepare positive electrode materials with different micromorphologies and component requirements that meet specific needs; moreover, the entire recycling process achieves a green closed loop, and the effective components therein can be completely recycled and reused, thereby maximizing the reduction of the impact of the recycling method on the environment, and improving the production efficiency of preparing new positive electrode materials using waste lithium iron phosphate positive electrode materials, alleviating the dependence of lithium iron phosphate battery production on the natural resources of lithium salt lakes and lithium ores.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for recycling waste lithium iron phosphate positive electrode materials, the recycling method comprising the following steps:

[0010] (1) acid leaching waste lithium iron phosphate positive electrode materials, separating the solid and the liquid, and obtaining an acid leaching solution and an acid leaching residue;

[0011] (2) adjusting the molar ratio and pH value of the metal ions in the acid leaching solution obtained in step (1), then adding a nucleation promoter to react, and performing solid-liquid separation after the reaction to obtain a positive electrode material precursor and a filtrate;

[0012] The nucleation promoter includes seed crystals and / or additives;

[0013] (3) The positive electrode material precursor obtained in step (2) is mixed with an organic carbon source and a doping material to prepare a slurry, and the obtained slurry is spray-dried and sintered in sequence to obtain a positive electrode material product;

[0014] (4) recovering lithium ions in the filtrate obtained in step (2) to obtain a lithium-containing compound and waste brine; the lithium-containing compound is reused to adjust the molar ratio of metal ions in the acid leaching solution;

[0015] Among them, step (3) and step (4) are performed in no particular order.

[0016] The recycling method provided by the present invention can realize the full component recovery of phosphorus, iron and lithium elements in waste lithium iron phosphate positive electrode materials, does not pollute the environment, and is of great economic value; the obtained positive electrode material product is lithium iron phosphate or lithium iron manganese phosphate, and there is no need to first synthesize lithium carbonate and anhydrous iron phosphate, and then mix the complicated process of solid-phase synthesis of lithium iron phosphate, thereby reducing resource waste and reducing the generation and discharge of waste solid and waste liquid; the reaction after adding crystal seeds and additives is a uniform liquid phase reaction, the valence state of each ion participating in the reaction is stable, and no impurity phase is generated in the entire concentration variation range, so that the synthesized positive electrode material product has high stability and purity; moreover, the molar ratio of metal ions in the acid leaching solution, pH value, organic carbon source and specific parameters of doping substances can be appropriately adjusted according to process requirements, so that positive electrode material products with different particle sizes, morphological characteristics and electrochemical activities can be obtained; in addition, the reuse of lithium-containing compounds reduces the operating cost of the entire recycling method.

[0017] In the present invention, the acid leaching residue obtained in step (1) is a black powder, the main component of which includes conductive carbon black. After purification of impurity ions, it can be reused as a regenerated conductive material in the battery manufacturing industry chain.

[0018] Preferably, the acid used for the acid leaching in step (1) comprises an organic acid and / or an inorganic acid.

[0019] Preferably, the inorganic acid comprises any one of hydrochloric acid, nitric acid, sulfuric acid or phosphoric acid, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of hydrochloric acid and nitric acid, a combination of nitric acid and sulfuric acid, a combination of sulfuric acid and phosphoric acid, a combination of hydrochloric acid, nitric acid and sulfuric acid, or a combination of hydrochloric acid, nitric acid and phosphoric acid.

[0020] Preferably, the organic acid comprises any one of citric acid, ascorbic acid or benzoic acid or a combination of at least two thereof, and typical but non-limiting combinations include a combination of citric acid and ascorbic acid, a combination of ascorbic acid and benzoic acid, a combination of citric acid and benzoic acid, or a combination of citric acid, ascorbic acid and benzoic acid.

[0021] Preferably, the amount of acid used for the acid leaching in step (1) is 300%-600% more than the molar amount of lithium element in the waste lithium iron phosphate positive electrode material, calculated according to the molar amount of hydrogen ions in the acid, for example, it can be 300%, 350%, 400%, 450%, 500%, 550% or 600%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] The amount of acid used in the acid leaching of the present invention is 300%-600% more than the molar amount of lithium element in the waste lithium iron phosphate positive electrode material, calculated according to the molar amount of hydrogen ions in the acid; if the acid used is a unit acid such as hydrochloric acid, the amount of hydrochloric acid used is 300%-600% more than the molar amount of lithium element in the waste lithium iron phosphate positive electrode material; if the acid used is a dibasic acid such as sulfuric acid, the amount of sulfuric acid used is 150-300% more than the molar amount of lithium element in the waste lithium iron phosphate positive electrode material; if the acid used is a tribasic acid such as phosphoric acid, the amount of phosphoric acid used is 100-200% more than the molar amount of lithium element in the waste lithium iron phosphate positive electrode material.

[0023] Preferably, the solid-liquid mass ratio of the acid leaching in step (1) is 1:(3-8).

[0024] The present invention does not further limit the concentration of the acid used for acid leaching, as long as the solid-liquid mass ratio of the acid leaching in step (1) is 1:(3-8), for example, it can be 1:3, 1:4, 1:5, 1:6 or 1:8, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 1:(4-5).

[0025] Preferably, the acid leaching in step (1) is carried out at a temperature of 60-95° C. and for a time of 60-240 min.

[0026] In the present invention, the temperature of the acid leaching in step (1) is 60-95°C, for example, it can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C or 95°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0027] If the acid leaching temperature is too low, the dissolution will be slow and incomplete; if the acid leaching temperature is too high, it will lead to increased energy consumption, increase the requirements for the acid leaching equipment, and increase unnecessary costs.

[0028] In the present invention, the acid leaching time in step (1) is 60-240 min, for example, it can be 60 min, 80 min, 100 min, 120 min, 150 min, 180 min, 200 min or 240 min, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 100-200 min.

[0029] Preferably, a reducing agent is also added during acid leaching, and the amount of the reducing agent added is 0.1-2wt% of the waste lithium iron phosphate positive electrode material, for example, it can be 0.1wt%, 0.5wt%, 1wt%, 1.5wt% or 2wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, the reducing agent comprises any one of iron powder, ascorbic acid, sodium sulfide or sodium sulfite or a combination of at least two thereof. Typical but non-limiting combinations include a combination of iron powder and ascorbic acid, a combination of sodium sulfide and sodium sulfite, a combination of iron powder, sodium sulfide and sodium sulfite, or a combination of iron powder, ascorbic acid, sodium sulfide and sodium sulfite.

[0031] Preferably, the pH value in step (2) is 4-7, for example, 4, 5, 6 or 7, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0032] The pH value is adjusted in step (2) of the present invention by using an inorganic acid and / or an inorganic base to adjust the pH value, for example, sodium hydroxide, sulfuric acid, hydrochloric acid or nitric acid is used to adjust the pH value.

[0033] Preferably, the molar ratio of metal ions in the acid leaching solution obtained in the adjustment step (1) refers to adjusting the molar ratio of lithium, phosphorus and iron in the acid leaching solution to (1-3):(0.99-2):1.

[0034] When the molar ratio of lithium, phosphorus and iron in the acid leaching solution is adjusted to (1-3):(0.99-2):1, the molar ratio of lithium to iron is (1-3):1, for example, it can be 1:1, 2:1 or 3:1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] The molar ratio of phosphorus to iron is (0.99-2):1, for example, it can be 0.99:1, 1:1, 1.2:1, 1.5:1, 1.8:1 or 2:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] Or the molar ratio of lithium, phosphorus, iron and manganese in the acid leaching solution is adjusted to (1-3):(0.99-2):(0.05-0.5):(0.5-0.95), wherein the molar ratio of iron to manganese sums to 1, for example, it can be 0.05:0.95, 0.1:0.9, 0.2:0.8, 0.3:0.7, 0.4:0.6 or 0.5:0.5, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0037] Exemplarily, when adjusting the molar ratio of metal ions in the acid leaching solution obtained in step (1), the lithium source used includes any one of lithium phosphate, lithium nitrate, lithium sulfate, lithium hydroxide or lithium chloride, or a combination of at least two of them; the phosphorus source includes any one of phosphoric acid, lithium hydrogen phosphate, lithium dihydrogen phosphate or lithium phosphate, or a combination of at least two of them; the iron source includes any one of lithium ferrous sulfate, ferrous oxalate, ferrous chloride or ferrous citrate, or a combination of at least two of them.

[0038] Preferably, the seed crystals in step (2) include nano-scale seed crystals of lithium iron phosphate or nano-scale seed crystals of lithium iron manganese phosphate.

[0039] The present invention can control the particle size of the positive electrode material precursor within 50-500nm by using a nucleation promoter, wherein the use of nano-scale seed crystals can prevent the particle size of the positive electrode material precursor from being too large; the use of additives alone can also achieve the purpose of controlling the particle size of the positive electrode material precursor.

[0040] Exemplarily, the average particle size of the nanoscale seeds of lithium iron phosphate is 5-20 nm, for example, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm or 20 nm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] Exemplarily, the average particle size of the nanoscale seeds of lithium manganese iron phosphate is 5-20 nm, for example, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, 18 nm or 20 nm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also suitable, preferably 5-10 nm.

[0042] Nanoscale seeds of lithium iron phosphate can be used in the production of lithium iron phosphate or lithium iron manganese phosphate; nanoscale seeds of lithium iron manganese phosphate can be used in the production of lithium iron manganese phosphate or lithium iron phosphate; as a preferred technical solution, nanoscale seeds of lithium iron phosphate are used in the production of lithium iron phosphate, and nanoscale seeds of lithium iron manganese phosphate are used in the production of lithium iron manganese phosphate.

[0043] Exemplarily, the amount of the seed crystal added is 0.05-1wt% of the waste lithium iron phosphate positive electrode material, the purpose of which is to control the particle size of the obtained positive electrode material precursor to 50-500nm. Those skilled in the art can add a suitable weight of seed crystals as needed.

[0044] Preferably, the additive in step (2) includes any one of octylphenyl polyoxyethylene ether (OPPE), dimethylformamide (DMF), ascorbic acid, ethylenediaminetetraacetic acid (EDTA), polyethylene glycol or dodecylbenzene sulfonic acid (DBSA) or a combination of at least two thereof. Typical but non-limiting combinations include a combination of OPPE and DMF, a combination of ascorbic acid and EDTA, a combination of polyethylene glycol and DBSA, a combination of OPPE, DMF and EDTA, a combination of DMF, EDTA and DBSA, or a combination of OPPE, DMF, ascorbic acid, EDTA, polyethylene glycol and DBSA.

[0045] Exemplarily, the additive is added in an amount of 0.05-1 wt % of the waste lithium iron phosphate positive electrode material, the purpose of which is to control the particle size of the obtained positive electrode material precursor to be 50-500 nm. Those skilled in the art can add an appropriate weight of additive as needed.

[0046] The invention adds crystal seeds and / or additives into the acid leaching solution, which can induce crystal formation and regulate crystal nucleation.

[0047] Preferably, the reaction temperature in step (2) is 80-120° C., the reaction time is 4-8 h, and the reaction pressure is 0.1-1 MPa.

[0048] As a preferred technical solution of the present invention, the reaction in step (2) is carried out under specific temperature, time and pressure conditions, which can obtain a positive electrode material precursor with good morphology, which is beneficial to improve its stability and electrochemical activity and facilitate subsequent carbon coating and doping.

[0049] The reaction temperature of step (2) is 80-120°C, for example, 80°C, 90°C, 100°C, 110°C or 120°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0050] The reaction time of step (2) is 4-8 hours, for example, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0051] The reaction pressure in step (2) is 0.1-1 MPa, for example, 0.1 MPa, 0.3 MPa, 0.5 MPa, 0.8 MPa or 1 MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0052] The pressure mentioned refers to the absolute pressure inside the device where the reaction takes place.

[0053] Preferably, the organic carbon source in step (3) comprises any one of glucose, sucrose, starch, polyethylene glycol or ascorbic acid, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of glucose and sucrose, a combination of starch and polyethylene glycol, a combination of sucrose and ascorbic acid, a combination of glucose, sucrose and polyethylene glycol, a combination of starch, polyethylene glycol and ascorbic acid, or a combination of glucose, sucrose, starch, polyethylene glycol and ascorbic acid.

[0054] Preferably, the mass ratio of the positive electrode material precursor to the organic carbon source in step (3) is 1:(0.05-0.2).

[0055] Preferably, the metal element in the doping material in step (3) includes any one of magnesium, calcium, strontium, cobalt, titanium, molybdenum, vanadium, niobium, nickel, scandium, copper, zinc, beryllium, lanthanum, holmium or aluminum, or a combination of at least two of them. Typical but non-limiting combinations include a combination of magnesium and calcium, a combination of strontium and cobalt, a combination of titanium and molybdenum, a combination of vanadium and nickel, a combination of copper and zinc, a combination of lanthanum, holmium and aluminum, or a combination of magnesium, calcium, strontium, cobalt, titanium, molybdenum, vanadium, niobium, nickel, scandium, copper, zinc, beryllium, lanthanum, holmium and aluminum.

[0056] In the present invention, the metal element of the doping element is added by adding any one of the phosphates, hydrogen phosphates, dihydrogen phosphates, carbonates, formates, acetates, glycolates, lactates, tartrates, oxalates, oxides, hydroxides, fluorides, chlorides, nitrates, sulfates or bromides of the drinking metal element or a combination of at least two thereof.

[0057] Preferably, the molar ratio of the metal element in the doping substance in step (3) to the lithium in the positive electrode material precursor is (0.005-0.1):1, for example, it can be 0.005:1, 0.01:1, 0.03:1, 0.05:1, 0.08:1 or 0.1:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0058] Preferably, during the mixing and slurrying in step (3), the mass ratio of the positive electrode material precursor to the solvent water is 1:(1-4), for example, it can be 1:1, 1:2, 1:3 or 1:4, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0059] Exemplarily, the particle size of the product obtained by spray drying of the present invention is 0.5-10 μm, so that the average particle size of the final positive electrode material product is 0.5-5 μm, preferably 1-3 μm.

[0060] Preferably, the sintering in step (3) is carried out in a protective atmosphere, and the gas used in the protective atmosphere includes any one of nitrogen, argon or hydrogen, or a combination of at least two of them. Typical but non-limiting combinations include a combination of nitrogen and argon, a combination of argon and hydrogen, a combination of nitrogen and hydrogen, or a combination of nitrogen, argon and hydrogen.

[0061] Preferably, the sintering temperature in step (3) is 500-900° C. and the sintering time is 1-10 h.

[0062] In the present invention, the sintering temperature in step (3) is 500-900°C, for example, it can be 500°C, 600°C, 700°C, 750°C, 800°C, 850°C or 900°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 700-900°C.

[0063] In the present invention, the sintering time in step (3) is 1-10 h, for example, 1 h, 1.5 h, 2 h, 5 h, 8 h or 10 h, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 1-2 h.

[0064] Preferably, the recovery in step (4) comprises: adjusting the phosphorus-lithium molar ratio and pH value in the filtrate obtained in step (2) for recovery.

[0065] The present invention recovers lithium in the filtrate as much as possible by adjusting the molar ratio of phosphorus to lithium, so that the lithium therein is precipitated close to 100%. If the amount of phosphorus used is small, it will lead to waste of lithium.

[0066] Preferably, the phosphorus-lithium molar ratio is above 1:3, for example, 1:3, 1.1:3, 1.2:3, 1.4:3 or 1.5:3, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0067] Preferably, the pH value during the recovery is 10-12, for example, it can be 10, 11 or 12, but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0068] During the recovery in step (4), the pH value is adjusted using phosphoric acid, lithium hydroxide or sodium hydroxide.

[0069] Preferably, the recovery temperature in step (4) is 45-90°C and the recovery time is 1-3h.

[0070] The recovery temperature in step (4) is 45-90°C, for example, 45°C, 50°C, 60°C, 70°C, 80°C or 90°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0071] The recovery time in step (4) is 1-3 hours, for example, 1 hour, 2 hours or 3 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0072] Preferably, the waste brine in step (4) is recovered by a multiple-effect evaporation method.

[0073] The cations in the waste brine obtained in step (4) of the present invention are mainly sodium ions. The present invention uses a multi-effect evaporation method to concentrate the waste brine, and then dries it after it is concentrated to a sufficient concentration to obtain an inorganic salt solid. The evaporated and condensed water is recycled and reused, and the inorganic salts are recycled and utilized in accordance with the relevant industrial or food-grade product quality standards, and enter the relevant industrial chain for recycling.

[0074] Preferably, the waste lithium iron phosphate positive electrode material in step (1) is obtained by calcining a positive electrode sheet.

[0075] The present invention calcines the waste lithium iron phosphate positive electrode sheet to remove organic components such as a binder in the positive electrode sheet, thereby obtaining a current collector and waste lithium iron phosphate positive electrode material.

[0076] Preferably, the calcination is carried out in an oxygen-free atmosphere at a temperature of 200-600°C, for example, 200°C, 300°C, 400°C, 500°C or 600°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0077] The gas used in the oxygen-free atmosphere includes nitrogen and / or argon.

[0078] Compared with the prior art, the present invention has the following beneficial effects:

[0079] The recycling method provided by the present invention can realize the full component recovery of phosphorus, iron and lithium elements in waste lithium iron phosphate positive electrode materials, does not pollute the environment, and is of great economic value; the obtained positive electrode material product is lithium iron phosphate or lithium iron manganese phosphate, and there is no need to first synthesize lithium carbonate and anhydrous iron phosphate, and then mix the complicated process of solid-phase synthesis of lithium iron phosphate, thereby reducing resource waste and reducing the generation and discharge of waste solid and waste liquid; the reaction after adding crystal seeds and additives is a uniform liquid phase reaction, the valence state of each ion participating in the reaction is stable, and no impurity phase is generated in the entire concentration variation range, so that the synthesized positive electrode material product has high stability and purity; moreover, the molar ratio of metal ions in the acid leaching solution, pH value, organic carbon source and specific parameters of doping substances can be appropriately adjusted according to process requirements, so that positive electrode material products with different particle sizes, morphological characteristics and electrochemical activities can be obtained; in addition, the reuse of lithium-containing compounds reduces the operating cost of the entire recycling method. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Figure 1 A process flow chart of a method for recycling waste lithium iron phosphate positive electrode materials provided in Example 1 of the present invention;

[0081] Figure 2 This is a charge and discharge curve diagram of the lithium iron phosphate obtained in Example 15;

[0082] Figure 3 This is a charge and discharge curve of the lithium manganese iron phosphate obtained in Example 21;

[0083] Figure 4 This is the XRD spectrum of lithium manganese iron phosphate obtained in Example 21;

[0084] Figure 5 This is a SEM image of the lithium manganese iron phosphate obtained in Example 21;

[0085] Figure 6 This is the cycle data diagram of the lithium manganese iron phosphate obtained in Example 21. DETAILED DESCRIPTION

[0086] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0087] The waste lithium iron phosphate positive electrode material in the specific embodiment of the present invention is obtained by calcining the positive electrode sheet, which includes 6wt% carbon and 94wt% lithium iron phosphate powder; in terms of mass percentage, the lithium iron phosphate powder includes 3.24wt% lithium, 34.83wt% iron and 18.33wt% phosphorus. The above description is only for the purpose of making the technical solution clear and is not regarded as a further limitation of the present invention.

[0088] Example 1

[0089] This embodiment provides a Figure 1 The recycling method of waste lithium iron phosphate positive electrode material shown in the figure comprises the following steps:

[0090] (1) acid leaching 88 kg of waste lithium iron phosphate positive electrode material, and performing solid-liquid separation by filter pressing and washing to obtain acid leaching liquid and acid leaching residue;

[0091] The acid used for the acid leaching is sulfuric acid, and the amount of the acid used is 300% more than the molar amount of lithium element in the waste lithium iron phosphate positive electrode material, calculated based on the molar amount of hydrogen ions in the acid;

[0092] The solid-liquid mass ratio of the acid leaching is 1:4, the temperature is 80°C, and the time is 100 minutes;

[0093] The reducing agent is added during the acid leaching, including iron powder and ascorbic acid; the amount of iron powder added is 0.8wt% of the waste lithium iron phosphate positive electrode material, and the amount of ascorbic acid added is 0.2wt% of the waste lithium iron phosphate positive electrode material;

[0094] (2) adding sulfuric acid, sodium hydroxide and 38.58 kg of lithium phosphate to the acid leaching solution to adjust the metal ion molar ratio in the acid leaching solution and adjust the pH value to 5.5; then adding 100 g of lithium iron phosphate seed crystals with an average particle size of 10 nm and 100 g of sodium dodecyl sulfate, sealing and heating to 95 ° C for 6 hours, maintaining the system pressure at 0.1 MPa during the reaction, and cooling naturally to room temperature after the reaction; solid-liquid separation, filter pressing, washing, drying, and crushing to obtain a positive electrode material precursor (LiFePO4) and a filtrate;

[0095] Adjusting the molar ratio of metal ions in the acid leaching solution means adjusting the molar ratio of lithium, phosphorus and iron in the acid leaching solution to 2.675:1.628:1;

[0096] (3) The cathode material precursor obtained in step (2) is mixed with soluble starch (CAS: 9005-84-9) and TiO2 to prepare a slurry, and the obtained slurry is spray-dried and sintered in sequence to obtain a cathode material product;

[0097] During the mixing and slurrying, the mass ratio of the cathode material precursor to the solvent water is 1:1.25; the mass ratio of the cathode material precursor to the soluble starch is 1:0.06; the molar ratio of Ti in TiO2 to lithium in the cathode material precursor is 0.02:1;

[0098] The sintering is carried out in a nitrogen atmosphere at a temperature of 700° C. for 2 h;

[0099] (4) Phosphoric acid and lithium hydroxide are added to the filtrate obtained in step (2) to make its pH value 11 and the molar ratio of phosphorus to lithium in the filtrate 1:3, and the filtrate is recovered at a temperature of 90° C. for 1 hour, cooled, filtered, washed, and dried to obtain solid lithium phosphate and waste brine; the solid lithium phosphate is reused in step (2);

[0100] Waste brine contains a certain concentration of sodium sulfate and a very small amount of phosphate. Multiple-effect evaporation is used to recover the sodium sulfate, and the water collected by evaporation is used for subsequent cycle production.

[0101] Among them, step (3) and step (4) are performed in no particular order.

[0102] Example 2

[0103] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials, except that in the acid leaching described in step (1), the amount of acid used is 200% excess over the molar amount of lithium element in the waste lithium iron phosphate positive electrode material, calculated based on the molar amount of hydrogen ions in the acid, and the rest is the same as Example 1.

[0104] Example 3

[0105] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials, except that in the acid leaching described in step (1), the amount of acid used is 400% excess over the molar amount of lithium element in the waste lithium iron phosphate positive electrode material, calculated based on the molar amount of hydrogen ions in the acid, and the rest is the same as Example 1.

[0106] Example 4

[0107] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials, which is the same as that of Embodiment 1 except that the solid-liquid mass ratio of the acid leaching in step (1) is 1:5.

[0108] Example 5

[0109] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials. Except that the acid leaching temperature in step (1) is 60° C., the rest is the same as that in embodiment 1.

[0110] Example 6

[0111] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials. Except that the acid leaching temperature in step (1) is 95° C., the rest is the same as that in embodiment 1.

[0112] Example 7

[0113] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials, which is the same as that of Embodiment 1 except that the acid leaching temperature in step (1) is 95° C. and the acid leaching time is 200 min.

[0114] Example 8

[0115] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials, which is the same as that of Embodiment 1 except that the pH value of the acid leaching solution is adjusted to 4 in step (2).

[0116] Example 9

[0117] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials. Except for adjusting the pH value of the acid leaching solution to 7 in step (2), the rest is the same as that of embodiment 1.

[0118] Example 10

[0119] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials. Except that the reaction temperature in step (2) is 80° C., the rest is the same as that in embodiment 1.

[0120] Embodiment 11

[0121] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials. Except that the reaction temperature in step (2) is 120° C., the rest is the same as that in embodiment 1.

[0122] Example 12

[0123] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials. Except that the reaction time in step (2) is 4 hours, the rest is the same as that in embodiment 1.

[0124] Embodiment 13

[0125] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials. Except that the reaction time in step (2) is 8 hours, the rest is the same as that in embodiment 1.

[0126] Embodiment 14

[0127] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials, which is the same as that of Embodiment 1 except that the soluble starch and other materials in step (3) are replaced by sucrose.

[0128] Embodiment 15

[0129] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials, which is the same as Example 1 except that the soluble starch in step (3) is replaced by soluble starch and sucrose in a mass ratio of 1:1.

[0130] Example 16

[0131] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials, which is the same as Example 1 except that TiO2 in step (3) is replaced by magnesium acetate and the molar amounts of magnesium and Ti are the same.

[0132] Embodiment 17

[0133] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials. Except that the sintering temperature in step (3) is 800° C., the rest is the same as that of embodiment 1.

[0134] Embodiment 18

[0135] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials. Except that the sintering temperature in step (3) is 900° C., the rest is the same as that in embodiment 1.

[0136] Embodiment 19

[0137] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials, which is the same as that of Embodiment 1 except that the sintering temperature in step (3) is 900° C. and the sintering time is 1 h.

[0138] Embodiment 20

[0139] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials, and the recycling method comprises the following steps:

[0140] (1) acid leaching 18 kg of waste lithium iron phosphate positive electrode material, performing solid-liquid separation by filter pressing and washing to obtain an acid leaching solution and an acid leaching residue;

[0141] The acid used for the acid leaching is sulfuric acid, and the amount of the acid used is 300% more than the molar amount of lithium element in the waste lithium iron phosphate positive electrode material, calculated based on the molar amount of hydrogen ions in the acid;

[0142] The solid-liquid mass ratio of the acid leaching is 1:4, the temperature is 80°C, and the time is 100 minutes;

[0143] The reducing agent is added during the acid leaching, including iron powder and ascorbic acid; the amount of iron powder added is 0.8wt% of the waste lithium iron phosphate positive electrode material, and the amount of ascorbic acid added is 0.2wt% of the waste lithium iron phosphate positive electrode material;

[0144] (2) Phosphoric acid, sodium hydroxide, 38.58 kg of lithium phosphate and manganese sulfate in an amount four times the molar number of the iron element in the acid leaching solution were added to the acid leaching solution to adjust the molar ratio of metal ions in the acid leaching solution and make the pH value 5.5; then 100 g of lithium iron manganese phosphate seed crystals with an average particle size of 10 nm and 100 g of sodium dodecyl sulfate were added, and the mixture was sealed and heated to 95° C. for reaction for 6 h. During the reaction, the system pressure was maintained at 0.1 MPa. After the reaction was completed, the mixture was naturally cooled to room temperature; solid-liquid separation, filter pressing, washing, drying, and crushing were performed to obtain a positive electrode material precursor (LiMn 0.8 Fe 0.2 PO4) and filtrate;

[0145] Adjusting the molar ratio of metal ions in the acid leaching solution means adjusting the molar ratio of lithium, phosphorus, iron and manganese in the acid leaching solution to (1-3):(0.99-2):0.2:0.8;

[0146] (3) The cathode material precursor obtained in step (2) is mixed with soluble starch (CAS: 9005-84-9) and TiO2 to prepare a slurry, and the obtained slurry is spray-dried and sintered in sequence to obtain a cathode material product;

[0147] During the mixing and slurrying, the mass ratio of the positive electrode material precursor to the solvent water is 1:1.25; the mass ratio of the positive electrode material precursor to the soluble starch is 1:0.06; the molar ratio of Ti in TiO2 to lithium in the positive electrode material precursor is 0.02:1; the sintering is carried out in a nitrogen atmosphere at a temperature of 700°C for 2 hours;

[0148] (4) Phosphoric acid and lithium hydroxide are added to the filtrate obtained in step (2) to make its pH value 11 and the molar ratio of phosphorus to lithium in the filtrate 1:3, and the filtrate is recovered at a temperature of 90° C. for 1 hour, cooled, filtered, washed, and dried to obtain solid lithium phosphate and waste brine; the solid lithium phosphate is reused in step (2);

[0149] Waste brine contains a certain concentration of sodium sulfate and a very small amount of phosphate. Multiple-effect evaporation is used to recover the sodium sulfate, and the water collected by evaporation is used for subsequent cycle production.

[0150] Among them, step (3) and step (4) are performed in no particular order.

[0151] Embodiment 21

[0152] This embodiment provides a method for recycling waste lithium iron phosphate positive electrode materials. Except that the reaction temperature in step (2) is 105° C., the rest is the same as Example 20.

[0153] Performance Characterization

[0154] The primary particle size, crystallinity and recovery rate of the positive electrode material precursors obtained in Examples 1-13 and Examples 22-26 were measured, and the results are shown in Table 1.

[0155] Among them, the primary particle size is measured by Malvern 3000 laser particle size analyzer; the crystallinity is measured according to the relative value method of X-ray crystal diffraction intensity; the recovery rate is calculated based on the waste lithium iron phosphate positive electrode material minus 6% of the carbon by mass, and theoretically 82.78 kg of new lithium iron phosphate can be obtained.

[0156] Table 1

[0157]

[0158]

[0159] It can be seen from Examples 1-3 in Table 1 that the amount of leaching affects the recovery quality and recovery rate of the positive electrode material precursor. When the amount of acid used for acid leaching is less than 300% of the molar amount of lithium element in the waste lithium iron phosphate positive electrode material according to the molar amount of hydrogen ions in the acid, the lithium, phosphorus, iron and other elements in the waste lithium iron phosphate positive electrode material cannot be completely leached; when the amount of acid used for acid leaching is sufficient, the recovery rate of the positive electrode material precursor can be above 98.5%; however, excessive acid usage will increase the acidity of the system, which is not conducive to reducing the subsequent alkali neutralization usage.

[0160] From the comparison between Example 1 and Example 4, it can be seen that the solid-liquid mass ratio of acid leaching affects the recovery rate of the positive electrode material precursor. The lower the solid-liquid ratio, the lower the recovery rate. Therefore, it is necessary to control the acid leaching within a suitable solid-liquid ratio range.

[0161] From the comparison of Examples 1, 5, 6 and 7, it can be seen that the higher the acid leaching temperature and the longer the time, the higher the quality of the subsequent positive electrode material precursor or the total element recovery rate in the waste material. After the temperature and time exceed certain values, the benefits obtained by further increasing them basically do not change significantly.

[0162] From the comparison of Examples 1, 8 and 9, it can be seen that the pH value in the solution adjustment is crucial to the recovery rate of the positive electrode material precursor after the reaction. The acidic pH value leads to a higher recovery rate; under neutral conditions, the recovery rate is low and the particle size of the primary particles of the precursor is small. A method for preparing a small-particle positive electrode material at the expense of recovery rate is beneficial to achieving the high-power characteristics of fast charging and discharging of lithium-ion batteries.

[0163] From the comparison of Examples 1, 10, 11, 12 and 13, it can be seen that the reaction temperature and the holding time have a great influence on the size of the primary particle size of the positive electrode material precursor crystal. The higher the reaction temperature and the longer the holding time, the larger the particle size. This is also easy to understand in theory. According to Oswald's crystal ripening theory, in the reaction system, small particles gradually disappear and large particles continue to grow; among them, when the reaction temperature is low, the crystallinity of the precursor crystal structure is weak, and the growth of the crystal needs to exceed a certain reaction temperature.

[0164] The electrochemical properties of the positive electrode material products obtained in Example 1 and Examples 14-19 were measured, and the results are shown in Table 2.

[0165] The electrochemical performance test includes: weighing the positive electrode material product, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1 and dissolving them in N-methylpyrrolidone (NMP) and mixing them evenly; then, applying the slurry on aluminum foil with a coater and drying it in a vacuum drying oven at 80°C for 8 hours; finally, punching the aluminum foil into 1.13 cm 2 The positive electrode sheet was obtained by forming a circular shape; the obtained positive electrode sheet was used as the positive electrode, the lithium metal sheet was used as the counter electrode, and a porous polypropylene membrane (Celgard 2400) was used as a separator to separate the positive electrode and the counter electrode, and the CR 2032 button battery was assembled in an argon glove box. The cycle performance test was carried out using a battery test system (Blue Electric CT2001A) at 0.1C and (2.0-3.8V).

[0166] Table 2

[0167]

[0168]

[0169] From the comparison of Examples 1, 14 and 15, it can be seen that different organic carbon sources have different effects on the charge-discharge capacity and cycle characteristics. Among them, the coating of dual carbon sources has a greater effect on the capacity and cycle characteristics of the product. Figure 2 The charge and discharge curve of Example 15 is shown, and the 0.1C discharge capacity is 162.7 mAh / g.

[0170] From the comparison between Example 1 and Example 16, it can be seen that different metal doping elements have different effects on the electrical properties of the product, among which the capacity and cycle characteristics of magnesium doping are better than those of titanium doping.

[0171] From the comparison of Examples 1, 17, 18 and 19, it can be seen that the higher the sintering temperature and the longer the sintering time, the lower the capacity, but the higher the cycle stability. This may be because the high sintering temperature and long time allow the crystal to grow further, resulting in a longer power transmission path for lithium ions, lower kinetics, and lower capacity; however, the crystal structure is more complete and strong, the stability of lithium insertion and extraction is better, and the cycle life is longer.

[0172] The electrochemical properties of the positive electrode material products obtained in Examples 20-21 were measured, and the results are shown in Table 3.

[0173] The electrochemical performance test includes: weighing the positive electrode material product, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1 and dissolving them in N-methylpyrrolidone (NMP) and mixing them evenly; then, applying the slurry on aluminum foil with a coater and drying it in a vacuum drying oven at 80°C for 8 hours; finally, punching the aluminum foil into 1.13 cm 2 The positive electrode sheet was obtained by forming a circular shape; the obtained positive electrode sheet was used as the positive electrode, the lithium metal sheet was used as the counter electrode, and the porous polypropylene membrane (Celgard 2400) was used as the separator to separate the positive electrode and the counter electrode, and the CR 2032 button battery was assembled in an argon glove box. The cycle performance test was carried out using a battery test system (Blue Electric CT2001A) at 0.1C and 1C under the conditions of 2.0V-4.5V.

[0174] Table 3

[0175]

[0176] It can be seen from Example 20 and Example 21 that the synthesis method of the present invention can prepare a lithium manganese iron phosphate battery positive electrode material with excellent charging performance. Figure 3 The charge and discharge curve of the positive electrode material product obtained in Example 21 at a current of 0.1C is shown.

[0177] The positive electrode material product obtained in Example 21 was characterized by elemental analysis and crystal structure. Figure 4 The XRD spectrum shown in Figure 4 and Figure 5 It can be seen that the obtained positive electrode material product has a pure phase and a complete crystal structure. The chemical formula of Examples 20 and 21 can be expressed as LiMn 0.8 Fe 0.2 PO4.

[0178] By comparing Examples 20 and 21, it can be seen that different reaction temperatures have a crucial effect on the capacity and cycle stability of the final material: when the reaction temperature is high, the charge and discharge capacity will be slightly reduced, but it has a good stabilizing effect on the subsequent charge and discharge cycles. Figure 6 The cycle stability of Example 21 is shown, and it can be maintained above 96% for 100 cycles.

[0179] In summary, the recycling method provided by the present invention can realize the full component recovery of phosphorus, iron and lithium elements in waste lithium iron phosphate positive electrode materials, does not pollute the environment, and is of great economic value; the obtained positive electrode material product is lithium iron phosphate or lithium iron manganese phosphate, and there is no need to first synthesize lithium carbonate and anhydrous iron phosphate, and then mix the complex process of solid-phase synthesis of lithium iron phosphate, which reduces resource waste and also reduces the generation and discharge of waste solid and waste liquid; the reaction after adding seed crystals and additives is a uniform liquid phase reaction, the valence state of each ion participating in the reaction is stable, and no impurities are generated in the entire concentration variation range, so that the synthesized positive electrode material product has high stability and purity; moreover, the molar ratio of metal ions in the acid leaching solution, pH value, organic carbon source and specific parameters of doping substances can be appropriately adjusted according to process requirements, so that positive electrode material products with different particle sizes, morphological characteristics and electrochemical activities can be obtained; in addition, the reuse of lithium-containing compounds reduces the operating cost of the entire recycling method.

[0180] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for recycling waste lithium iron phosphate positive electrode materials, characterized in that: The recycling method comprises the following steps: (1) Acid leaching of waste lithium iron phosphate positive electrode materials, solid-liquid separation, and obtaining acid leaching solution and acid leaching residue; (2) adjusting the molar ratio and pH value of the metal ions in the acid leaching solution obtained in step (1), then adding a nucleation promoter to react, and performing solid-liquid separation after the reaction to obtain a positive electrode material precursor and a filtrate; the pH value is 4-7; The nucleation promoter includes crystal seeds and additives; the crystal seeds include nano-scale crystal seeds of lithium iron phosphate or nano-scale crystal seeds of lithium iron manganese phosphate; the positive electrode material precursor is lithium iron phosphate or lithium iron manganese phosphate with a crystal structure; The reaction temperature is 80-120°C, the reaction time is 4-8h, and the pressure is 0.1-1MPa; (3) The cathode material precursor obtained in step (2) is mixed with an organic carbon source and a doping material to prepare a slurry, and the obtained slurry is spray-dried and sintered in sequence to obtain a cathode material product; (4) recovering lithium ions in the filtrate obtained in step (2) to obtain a lithium-containing compound and waste brine; the lithium-containing compound is recycled to adjust the molar ratio of metal ions in the acid leaching solution; Among them, step (3) and step (4) are performed in no particular order.

2. The recycling method according to claim 1, characterized in that: The acid used for the acid leaching in step (1) includes an inorganic acid.

3. The recycling method according to claim 1, characterized in that: The amount of acid used in the acid leaching in step (1) is 300%-600% more than the molar amount of lithium element in the waste lithium iron phosphate positive electrode material, calculated based on the molar amount of hydrogen ions in the acid.

4. The recycling method according to claim 1, characterized in that: The solid-liquid mass ratio of the acid leaching in step (1) is 1:(3-8).

5. The recycling method according to claim 1, characterized in that: The acid leaching temperature in step (1) is 60-95°C and the time is 60-240 minutes.

6. The recycling method according to claim 1, characterized in that: The molar ratio of metal ions in the acid leaching solution obtained in the adjusting step (1) refers to adjusting the molar ratio of lithium, phosphorus and iron in the acid leaching solution to (1-3):(0.99-2):1; Or, the molar ratio of lithium, phosphorus, iron and manganese in the acid leaching solution is adjusted to (1-3):(0.99-2):(0.05-0.5):(0.5-0.95).

7. The recycling method according to claim 1, characterized in that: The additive in step (2) includes sodium dodecyl sulfate.

8. The recycling method according to claim 1, characterized in that: The organic carbon source in step (3) includes sucrose and / or starch.

9. The recycling method according to claim 1, characterized in that: In step (3), the mass ratio of the positive electrode material precursor to the organic carbon source is 1:(0.05-0.2).

10. The recycling method according to claim 1, characterized in that: The metal element in the doping material in step (3) includes magnesium or titanium.

11. The recycling method according to claim 1, characterized in that: The molar ratio of the metal element in the doping material in step (3) to the lithium in the positive electrode material precursor is (0.005-0.1):

1.

12. The recycling method according to claim 1, characterized in that: During the mixing and slurrying in step (3), the mass ratio of the positive electrode material precursor to the solvent water is 1:(1-4).

13. The recycling method according to claim 1, characterized in that: The sintering in step (3) is carried out in a protective atmosphere, and the gas used in the protective atmosphere includes any one of nitrogen, argon or hydrogen, or a combination of at least two of them.

14. The recycling method according to claim 1, characterized in that: The sintering temperature in step (3) is 500-900°C and the sintering time is 1-10h.

15. The recycling method according to claim 1, characterized in that: The recovery in step (4) includes: adjusting the phosphorus-lithium molar ratio and pH value in the filtrate obtained in step (2) for recovery.

16. The recycling method according to claim 15, characterized in that: The phosphorus-lithium molar ratio is above 1:

3.

17. The recycling method according to claim 15, characterized in that: The pH value during the recovery is 10-12.

18. The recycling method according to claim 1, characterized in that: The recovery temperature in step (4) is 45-90°C and the recovery time is 1-3h.

19. The recycling method according to claim 1, characterized in that: The waste brine in step (4) is recovered by a multiple-effect evaporation method.

20. The recycling method according to claim 1, characterized in that: The waste lithium iron phosphate positive electrode material in step (1) is obtained by calcining a positive electrode sheet.

21. The recycling method according to claim 20, characterized in that: The calcination is carried out in an oxygen-free atmosphere at a temperature of 200-600°C.

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