A method for recycling waste lithium iron phosphate positive electrode material

Abstract

The present invention relates to the technical field of battery recycling, and in particular to a method for recycling waste lithium iron phosphate positive electrode materials, comprising: A) sintering the waste lithium iron phosphate positive electrode materials at high temperature in an atmosphere where carbon dioxide and oxidizing gas coexist to obtain a first mixture; B) keeping the first mixture warm under low temperature conditions in an atmosphere where water vapor and carbon dioxide coexist to obtain a second mixture; C) mixing the second mixture with water, and then performing solid-liquid separation to obtain a lithium-containing solution. The recycling method provided by the present invention does not add any acid or alkali reagents, directly recovers lithium iron phosphate by a solid phase method to obtain an iron phosphate product, realizes effective conversion of lithium iron phosphate positive electrode materials by a solid phase sintering process, realizes refining of iron phosphate, and realizes effective recovery of phosphorus and iron elements. Subsequent lithium carbonate lattice transformation realizes refining of lithium products, thereby improving product purity. The entire process does not involve acid or alkali reagents, has few water treatment links, and has high lithium recovery efficiency.

Description

Technical Field

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

[0002] The recycling methods for waste lithium iron phosphate lithium-ion battery positive electrode materials are mainly divided into oxidation lithium extraction method and direct dissolution method. Oxidation lithium extraction generally uses oxidants to destroy the structure of lithium iron phosphate positive electrode materials to remove lithium, while the direct dissolution method generally uses strong acidic solvents to directly dissolve all lithium iron phosphate positive electrode materials. The direct dissolution method has multiple water treatment links, low lithium recovery efficiency, loss of valuable elements, and a large amount of acid and alkali consumption, which increases production costs. In comparison, the oxidation lithium extraction method has the advantages of short process and high efficiency, and is more suitable for recycling.

[0003] Patent CN115340080A discloses a method for regenerating waste lithium iron phosphate powder, which adopts the lithium oxidation extraction method. After high-temperature sintering, hydrogen peroxide is used to adjust the valence state of the iron element so that the lithium element can be removed from the lithium iron phosphate positive electrode material structure. However, inorganic acid is also required, resulting in acid and alkali consumption and increasing costs.

[0004] Moreover, in the existing recycling of waste lithium iron phosphate positive electrode materials, only the lithium recovery link is described in detail, and the refining process of iron phosphate in the residue left after lithium extraction has never been mentioned. Obviously, the existing technology does not carry out valuable recovery of iron phosphate, but only recovers the lithium element in the waste, resulting in a waste of resources. Patent CN113314778A discloses a recycling method for waste lithium-ion battery positive electrode materials, which also adopts the oxidation lithium extraction method. Although the recycling method is simple, it is designed with multiple water treatments, and does not carry out valuable recovery of iron phosphate, which also causes a waste of resources. Summary of the invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a method for recycling waste lithium iron phosphate positive electrode materials, which avoids the traditional wet leaching recovery route of positive electrode materials and directly recovers lithium iron phosphate through a solid phase method. There is no consumption of acid and alkali reagents in the intermediate process, there are fewer water treatment steps, the lithium recovery efficiency is high, and iron phosphate products can also be produced.

[0006] The present invention provides a method for recycling waste lithium iron phosphate positive electrode materials, comprising the following steps:

[0007] A) sintering the waste lithium iron phosphate positive electrode material at a temperature of 300 to 800° C. in an atmosphere where carbon dioxide and an oxidizing gas coexist to obtain a first mixture;

[0008] B) in an atmosphere where water vapor and carbon dioxide coexist, keeping the first mixture at 0 to 300° C. to obtain a second mixture;

[0009] C) mixing the second mixture with water, and then performing solid-liquid separation to obtain a lithium-containing solution.

[0010] Preferably, in step A), during the high-temperature sintering process, the flow rate of carbon dioxide is 0.1 to 3 L / min, and the flow rate of the oxidizing gas is 0.1 to 3 L / min.

[0011] Preferably, in step A), the oxidizing gas comprises oxygen or ozone.

[0012] Preferably, in step A), before high-temperature sintering the waste lithium-ion battery, the process further comprises: heating the waste lithium iron phosphate positive electrode material to a high-temperature sintering temperature;

[0013] The heating rate is 3-7°C / min;

[0014] The high temperature sintering time is 2 to 8 hours.

[0015] Preferably, in step A), the mass content of lithium in the waste lithium iron phosphate positive electrode material is 3% to 4.5%, the mass content of iron is 30% to 40%, the mass content of phosphorus is 15% to 22%, the mass content of oxygen is 25% to 33%, and the mass content of aluminum is 0.1% to 0.4%.

[0016] Preferably, in step B), during the heat preservation process under low temperature conditions, the flow rate of carbon dioxide is 0.1 to 3 L / min, and the flow rate of water vapor is 0.1 to 3 L / min.

[0017] Preferably, in step B), before keeping the first mixture warm under low temperature conditions, the step further includes: cooling the first mixture to a temperature under low temperature conditions;

[0018] The cooling rate is 3-7°C / min;

[0019] The insulation time under the low temperature condition is 2 to 24 hours.

[0020] Preferably, in step C), the dosage ratio of the second mixture to water is 1 g: 1 to 100 mL.

[0021] Preferably, step C) further comprises: decomposing the lithium-containing solution by heating to obtain lithium carbonate.

[0022] Preferably, the temperature of the thermal decomposition is 40-90°C.

[0023] The present invention provides a method for recovering waste lithium iron phosphate positive electrode materials, comprising the following steps: A) in an atmosphere where carbon dioxide and an oxidizing gas coexist, high-temperature sintering the waste lithium iron phosphate positive electrode materials to obtain a first mixture; B) in an atmosphere where water vapor and carbon dioxide coexist, keeping the first mixture warm under low temperature conditions to obtain a second mixture; C) mixing the second mixture with water, and then performing solid-liquid separation to obtain a lithium-containing solution. The present invention recovers lithium iron phosphate by a solid-phase sintering method. In a high-temperature solid-phase environment, the oxidizing properties of the oxidizing gas are used to increase the valence of iron, thereby allowing lithium to be released from the lattice of lithium iron phosphate and to form lithium carbonate with carbon dioxide, while the iron element is combined with phosphate ions in a trivalent form to obtain iron phosphate. Subsequently, the lithium carbonate is converted at low temperature to form lithium bicarbonate that can be dissolved in water to achieve separation of iron and lithium elements, and finally the lithium bicarbonate solution is subjected to a thermal decomposition reaction to obtain a lithium carbonate product.

[0024] Compared with the prior art, the recovery method provided by the present invention does not add any acid or alkali reagents, directly recovers lithium iron phosphate by solid phase method to obtain iron phosphate products, realizes effective conversion of lithium iron phosphate positive electrode materials by solid phase sintering process, and realizes the refining of iron phosphate (removing a large amount of impurities during high temperature process), and realizes effective recovery of phosphorus and iron elements. Subsequent lithium carbonate lattice transformation realizes lithium product refining and improves product purity. The entire process does not involve acid or alkali reagents, has few water treatment links, and has high lithium recovery efficiency.

[0025] Experimental results show that the recovery method provided by the present invention has a high leaching rate for Li in waste lithium iron phosphate positive electrode materials, with the highest leaching rate exceeding 99%; the leaching rates for other components in waste lithium iron phosphate positive electrode materials are relatively low, specifically, the leaching rate of Fe is less than 1.3%, and the leaching rate of P is less than 2.2%; the yield of iron phosphate is greater than 91%. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The present invention provides a method for recycling waste lithium iron phosphate positive electrode materials, comprising the following steps:

[0028] A) sintering the waste lithium iron phosphate positive electrode material at high temperature in an atmosphere where carbon dioxide and an oxidizing gas coexist to obtain a first mixture;

[0029] B) in an atmosphere where water vapor and carbon dioxide coexist, keeping the first mixture warm under low temperature conditions to obtain a second mixture;

[0030] C) mixing the second mixture with water, and then performing solid-liquid separation to obtain a lithium-containing solution.

[0031] In step A):

[0032] In an atmosphere where carbon dioxide and an oxidizing gas coexist, waste lithium iron phosphate positive electrode materials are sintered at high temperature to obtain a first mixture.

[0033] In certain embodiments of the present invention, the mass content of lithium in the waste lithium iron phosphate positive electrode material is 3% to 4.5%, the mass content of iron is 30% to 40%, the mass content of phosphorus is 15% to 22%, the mass content of oxygen is 25% to 33%, and the mass content of aluminum is 0.1% to 0.4%. In certain embodiments, the mass content of lithium in the waste lithium iron phosphate positive electrode material is 4.39%, the mass content of iron is 37.5%, the mass content of phosphorus is 20.13%, the mass content of oxygen is 28.45%, and the mass content of aluminum is 0.289%.

[0034] In some embodiments of the present invention, before using the waste lithium iron phosphate positive electrode material, the process further includes: preparing the waste lithium iron phosphate positive electrode material into powder. The particle size of the powder may be 50 to 300 meshes, specifically 50 to 100 meshes.

[0035] In certain embodiments of the present invention, the high temperature sintering temperature is 300-800° C., specifically 600° C., 800° C., 650° C. or 625° C., and the sintering time is 2-8 hours, specifically 4 hours or 8 hours.

[0036] In some embodiments of the present invention, before high-temperature sintering the waste lithium-ion battery, the process further includes: heating the waste lithium iron phosphate positive electrode material to a high-temperature sintering temperature at a heating rate of 3 to 7°C / min, specifically 5°C / min.

[0037] In certain embodiments of the present invention, during the high temperature sintering process, the flow rate of carbon dioxide is 0.1 to 3 L / min, specifically 0.5 L / min or 1.5 L / min; the flow rate of the oxidizing gas is 0.1 to 3 L / min, specifically 0.5 L / min or 1.5 L / min. The high temperature sintering is performed in a tubular furnace.

[0038] In certain embodiments of the present invention, the oxidizing gas comprises oxygen or ozone.

[0039] In the present invention, during the high temperature sintering process, the chemical equation involved is as shown in formula (1);

[0040] 4LiFePO4+2CO2+O2→4FePO4+2Li2CO3 (1).

[0041] After high-temperature sintering, the obtained first mixture includes iron phosphate and lithium carbonate.

[0042] During the high-temperature process, not only is lithium iron phosphate converted into lithium carbonate and iron phosphate, but impurities originally contained in the raw materials (such as organic matter, binders, residual electrolyte, etc.) are also removed in this process, thus achieving the refining of iron phosphate.

[0043] In step B):

[0044] In an atmosphere where water vapor and carbon dioxide coexist, the first mixture is kept warm under low temperature conditions to obtain a second mixture.

[0045] In certain embodiments of the present invention, the temperature of the low temperature condition is 0-300°C, specifically 100°C, 200°C, 80°C or 85°C; the insulation time is 2-24h, specifically 12h or 8h. The insulation under the low temperature condition is carried out in a tube furnace.

[0046] In certain embodiments of the present invention, before keeping the first mixture warm under low temperature conditions, the process further comprises: cooling the first mixture to a temperature under low temperature conditions. The cooling rate is 3-7°C / min, specifically 5°C / min.

[0047] In certain embodiments of the present invention, during the insulation process under low temperature conditions, the flow rate of carbon dioxide is 0.1 to 3 L / min, specifically 0.5 L / min or 1.5 L / min; the flow rate of water vapor is 0.1 to 3 L / min, specifically 0.5 L / min or 1.5 L / min.

[0048] In the present invention, during the heat preservation process under low temperature conditions, the chemical equation involved is as shown in formula (2);

[0049] Li2CO3+CO2+H2O→2LiHCO3 (2).

[0050] After heat preservation under low temperature conditions, the obtained second mixture includes lithium bicarbonate and iron phosphate.

[0051] In step C):

[0052] After the second mixture is mixed with water, solid-liquid separation is performed to obtain a lithium-containing solution.

[0053] The lithium-containing solution is heated and decomposed to obtain lithium carbonate.

[0054] In certain embodiments of the present invention, the dosage ratio of the second mixture to water is 1 g: 1-100 mL; specifically 1 g: 10 mL.

[0055] The mixing is stirring and mixing.

[0056] In certain embodiments of the present invention, the solid-liquid separation method is filtration.

[0057] After the second mixture is mixed with water, lithium bicarbonate dissolves in water, while iron phosphate does not dissolve in water, so that lithium bicarbonate and iron phosphate are separated. After solid-liquid separation, a lithium bicarbonate solution and solid iron phosphate are obtained.

[0058] The lithium bicarbonate solution is heated and decomposed to obtain lithium carbonate.

[0059] In certain embodiments of the present invention, the temperature of the thermal decomposition is 40-90° C., specifically 85° C., 60° C. or 65° C. The thermal decomposition is preferably stopped after the white precipitate no longer increases. The thermal decomposition method can cause the lithium carbonate in the lithium-containing solution to be superheated and saturated and precipitated.

[0060] The present invention has no particular limitation on the sources of the raw materials used above, and they can be generally commercially available.

[0061] The recovery method provided by the present invention realizes the effective conversion of lithium iron phosphate, and realizes the refining of iron phosphate (removing a large amount of impurities during the high temperature process), realizes the separation of lithium elements during the water leaching process, and obtains lithium products during the thermal decomposition process. Among them, there is only one water treatment link, which improves the lithium recovery efficiency. No additional reagents are added in the whole link, which reduces the consumption of acid and alkali reagents and improves the product purity.

[0062] In the present invention, the solid phase method is used to recover the lithium iron phosphate positive electrode material, and the conversion and refining of the iron phosphate are achieved in one step;

[0063] The entire iron phosphate preparation process is in a high-temperature stage, and iron phosphate is insoluble in water, so there is no loss in the subsequent separation process. The recovery efficiency of iron phosphate is high, which improves the overall recovery value;

[0064] No acid or alkali consumption and no introduction of cation or cation impurity ions, the lithium product is of high purity;

[0065] Carbon dioxide is not only a reactant for converting lithium iron phosphate into iron phosphate, but also plays a role in the lattice transformation of lithium carbonate. At the same time, carbon dioxide as a reactant can be recycled.

[0066] Only one water treatment process is needed to reduce lithium loss, with a short process and simple technology;

[0067] The leaching environment only requires a neutral environment with weak corrosion ability and low requirements for equipment materials, which is convenient for industrial production.

[0068] In order to further illustrate the present invention, a method for recycling waste lithium iron phosphate positive electrode materials provided by the present invention is described in detail below in combination with embodiments, but it should not be understood as limiting the scope of protection of the present invention.

[0069] Example 1

[0070] In the waste lithium iron phosphate positive electrode material, the mass content of lithium is 4.39%, the mass content of iron is 37.5%, the mass content of phosphorus is 20.13%, the mass content of oxygen is 28.45%, and the mass content of aluminum is 0.289%.

[0071] 50g of waste lithium iron phosphate positive electrode material powder (particle size of 50-100 mesh) is put into a tubular furnace, heated to 600°C at a heating rate of 5°C / min, and sintered for 4h. Carbon dioxide and oxygen are introduced during the sintering process, and the rates of carbon dioxide and oxygen are maintained at 0.5L / min; after the sintering is completed, the oxygen is stopped, and carbon dioxide is continued to be introduced at 0.5L / min, and the temperature is lowered to 100°C at 5°C / min, and then 0.5L / min of water vapor is introduced, and the mixture is kept at 100°C for 12h; the mixture is taken out and added to a beaker, and deionized water is added at a solid-liquid ratio of 1g:10mL. After being fully stirred, it is filtered to obtain a lithium-containing solution, and the lithium-containing solution is heated to 85°C, and heated to decompose to obtain lithium carbonate; the solid matter after filtration is iron phosphate, and the yield of iron phosphate is 94.34%.

[0072] ICP detection was performed on the lithium-containing solution, and the lithium content in the lithium-containing solution was 2.118g; the Fe content was 0.1575g, and the P content was 0.2195g.

[0073] It can be seen that in the recovery method provided in this embodiment, the leaching rate of Li is 96.45%, the leaching rate of Fe is 0.84%, and the leaching rate of P is 2.18%.

[0074] Example 2

[0075] In the waste lithium iron phosphate positive electrode material, the mass content of lithium is 4.39%, the mass content of iron is 37.5%, the mass content of phosphorus is 20.13%, the mass content of oxygen is 28.45%, and the mass content of aluminum is 0.289%.

[0076] 50g of waste lithium iron phosphate positive electrode material powder (particle size of 50-100 mesh) is put into a tubular furnace, heated to 800°C at a heating rate of 5°C / min, and sintered for 4h. Carbon dioxide and oxygen are introduced during the sintering process, and the rates of carbon dioxide and oxygen are maintained at 1.5L / min; after the sintering is completed, the oxygen is stopped, and carbon dioxide is continued to be introduced at 1.5L / min, and the temperature is lowered to 200°C at 5°C / min, and then 1.5L / min of water vapor is introduced, and the mixture is kept at 200°C for 8h; the mixture is taken out and added to a beaker, and deionized water is added at a solid-liquid ratio of 1g:10mL. After being fully stirred, it is filtered to obtain a lithium-containing solution, and the lithium-containing solution is heated to 60°C, and heated to decompose to obtain lithium carbonate; the solid matter after filtration is iron phosphate, and the yield of iron phosphate is 93.28%.

[0077] ICP detection was performed on the lithium-containing solution, and the lithium content in the lithium-containing solution was 2.053g; the Fe content was 0.227g, and the P content was 0.167g.

[0078] It can be seen that in the recovery method provided in this embodiment, the leaching rate of Li is 93.55%, the leaching rate of Fe is 1.21%, and the leaching rate of P is 1.66%.

[0079] Example 3

[0080] In the waste lithium iron phosphate positive electrode material, the mass content of lithium is 4.39%, the mass content of iron is 37.5%, the mass content of phosphorus is 20.13%, the mass content of oxygen is 28.45%, and the mass content of aluminum is 0.289%.

[0081] 50g of waste lithium iron phosphate positive electrode material powder (particle size of 50-100 mesh) is put into a tubular furnace, heated to 600°C at a heating rate of 5°C / min, and sintered for 4h. Carbon dioxide and oxygen are introduced during the sintering process, and the rates of carbon dioxide and oxygen are maintained at 1.5L / min; after the sintering is completed, the oxygen is stopped, and carbon dioxide is continued to be introduced at 1.5L / min, and the temperature is lowered to 200°C at 5°C / min, and then 1.5L / min of water vapor is introduced, and the mixture is kept at 200°C for 8h; the mixture is taken out and added to a beaker, and deionized water is added at a solid-liquid ratio of 1g:10mL. After being fully stirred, it is filtered to obtain a lithium-containing solution, and the lithium-containing solution is heated to 60°C, and heated to decompose to obtain lithium carbonate; the solid matter after filtration is iron phosphate, and the yield of iron phosphate is 91.15%.

[0082] ICP detection was performed on the lithium-containing solution, and the lithium content in the lithium-containing solution was 2.095g; the Fe content was 0.200g, and the P content was 0.190g.

[0083] It can be seen that in the recovery method provided in this embodiment, the leaching rate of Li is 95.45%, the leaching rate of Fe is 1.07%, and the leaching rate of P is 1.89%.

[0084] Example 4

[0085] In the waste lithium iron phosphate positive electrode material, the mass content of lithium is 4.39%, the mass content of iron is 37.5%, the mass content of phosphorus is 20.13%, the mass content of oxygen is 28.45%, and the mass content of aluminum is 0.289%.

[0086] 50g of waste lithium iron phosphate positive electrode material powder (particle size of 50-100 mesh) is placed in a tubular furnace, heated to 650°C at a heating rate of 5°C / min, and sintered for 8h. During the sintering process, carbon dioxide and oxygen are introduced, and the rates of carbon dioxide and oxygen are maintained at 1.5L / min; after the sintering is completed, the oxygen is stopped, and carbon dioxide is continued to be introduced at 1.5L / min, and the temperature is lowered to 80°C at 5°C / min, and then 1.5L / min of water vapor is introduced, and the temperature is kept at 80°C for 8h; the mixture is taken out and added to a beaker, and deionized water is added at a solid-liquid ratio of 1g:10mL. After being fully stirred, it is filtered to obtain a lithium-containing solution, and the lithium-containing solution is heated to 60°C, and heated to decompose to obtain lithium carbonate; the solid matter after filtration is iron phosphate, and the yield of iron phosphate is 93.46%.

[0087] ICP detection was performed on the lithium-containing solution, and the lithium content in the lithium-containing solution was 2.1807g; the Fe content was 0.0244g, and the P content was 0.1218g.

[0088] It can be seen that in the recovery method provided in this embodiment, the leaching rate of Li is 99.35%, the leaching rate of Fe is 0.13%, and the leaching rate of P is 1.21%.

[0089] Example 5

[0090] In the waste lithium iron phosphate positive electrode material, the mass content of lithium is 4.39%, the mass content of iron is 37.5%, the mass content of phosphorus is 20.13%, the mass content of oxygen is 28.45%, and the mass content of aluminum is 0.289%.

[0091] 50g of waste lithium iron phosphate positive electrode material powder (particle size of 50-100 mesh) is placed in a tubular furnace, heated to 625°C at a heating rate of 5°C / min, and sintered for 8h. During the sintering process, carbon dioxide and oxygen are introduced, and the rates of carbon dioxide and oxygen are maintained at 1.5L / min; after the sintering is completed, the oxygen is stopped, and carbon dioxide is continued to be introduced at 1.5L / min, and the temperature is lowered to 85°C at 5°C / min, and then 1.5L / min of water vapor is introduced, and the mixture is kept at 85°C for 8h; the mixture is taken out and added to a beaker, and deionized water is added at a solid-liquid ratio of 1g:10mL. After being fully stirred, it is filtered to obtain a lithium-containing solution, and the lithium-containing solution is heated to 65°C, and heated to decompose to obtain lithium carbonate; the solid matter after filtration is iron phosphate, and the yield of iron phosphate is 97.34%.

[0092] ICP detection was performed on the lithium-containing solution, and the lithium content in the lithium-containing solution was 2.1822g; the Fe content was 0.0431g, and the P content was 0.0372g.

[0093] It can be seen that in the recovery method provided in this embodiment, the leaching rate of Li is 99.42%, the leaching rate of Fe is 0.23%, and the leaching rate of P is 0.37%.

[0094] Example 6

[0095] The difference from Example 2 is that the oxidizing gas oxygen is replaced by ozone.

[0096] The solid matter after filtration was ferric phosphate, and the yield of ferric phosphate was 92.41%.

[0097] ICP detection was performed on the lithium-containing solution, and the lithium content in the lithium-containing solution was 1.996g; the Fe content was 0.247g, and the P content was 0.187g.

[0098] It can be seen that in the recovery method provided in this embodiment, the leaching rate of Li is 90.95%, the leaching rate of Fe is 1.31%, and the leaching rate of P is 1.86%.

[0099] Comparative Example 1

[0100] The difference from Example 1 is that carbon dioxide gas is not introduced into the high temperature step, specifically, including:

[0101] In the waste lithium iron phosphate positive electrode material, the mass content of lithium is 4.39%, the mass content of iron is 37.5%, the mass content of phosphorus is 20.13%, the mass content of oxygen is 28.45%, and the mass content of aluminum is 0.289%.

[0102] 50g of waste lithium iron phosphate positive electrode material powder (particle size of 50-100 mesh) is put into a tubular furnace, heated to 600°C at a heating rate of 5°C / min, and sintered for 4h. Oxygen is introduced during the sintering process, and the oxygen rate is maintained at 0.5L / min; after the sintering is completed, the oxygen is stopped, the temperature is lowered to 100°C at 5°C / min, water vapor and carbon dioxide are introduced, and the water vapor and carbon dioxide rates are maintained at 0.5L / min, and the mixture is kept at 100°C for 12h; the mixture is taken out and added to a beaker, deionized water is added at a solid-liquid ratio of 1g:10mL, and after being fully stirred, it is filtered to obtain a filtrate and a reddish-brown solid powder, wherein the solid powder is iron oxide and Li3Fe2(PO4)3.

[0103] The filtrate was subjected to ICP detection, and the lithium content in the filtrate was 0.0108g; the Fe content was 0.0148g, and the phosphorus content was 0.0148g.

[0104] Lithium leaching rate: 0.49%; Iron leaching rate: 0.08%; Phosphorus leaching rate: 0.15%.

[0105] This shows that without the involvement of carbon dioxide in the high-temperature stage, lithium iron phosphate cannot be effectively recovered.

[0106] Comparative Example 2

[0107] The difference from Example 1 is that oxygen gas is not introduced into the high temperature section, specifically, including:

[0108] In the waste lithium iron phosphate positive electrode material, the mass content of lithium is 4.39%, the mass content of iron is 37.5%, the mass content of phosphorus is 20.13%, the mass content of oxygen is 28.45%, and the mass content of aluminum is 0.289%.

[0109] 50g of waste lithium iron phosphate positive electrode material powder (particle size of 50-100 mesh) was placed in a tube furnace, heated to 600℃ at a heating rate of 5℃ / min, and sintered for 4h. Carbon dioxide was introduced during the sintering process, and the rate of carbon dioxide was maintained at 0.5L / min; after the sintering was completed, carbon dioxide was continued to be introduced at 0.5L / min, and the temperature was lowered to 100℃ at 5℃ / min, and then 0.5L / min of water vapor was introduced, and the temperature was kept at 100℃ for 12h; the mixture was taken out and added to a beaker, and deionized water was added at a solid-liquid ratio of 1g:10mL. After fully stirring, it was filtered to obtain a filtrate and a solid substance, and the solid substance was lithium iron phosphate. Obviously, the reaction did not occur when there was no oxygen atmosphere at the high temperature stage.

[0110] Comparative Example 3

[0111] The difference from Example 1 is that carbon dioxide is not introduced into the heat preservation step under low temperature conditions. Specifically, the steps include:

[0112] In the waste lithium iron phosphate positive electrode material, the mass content of lithium is 4.39%, the mass content of iron is 37.5%, the mass content of phosphorus is 20.13%, the mass content of oxygen is 28.45%, and the mass content of aluminum is 0.289%.

[0113] 50g of waste lithium iron phosphate positive electrode material powder (particle size of 50-100 mesh) was put into a tubular furnace, heated to 600°C at a heating rate of 5°C / min, and sintered for 4h. Carbon dioxide and oxygen were introduced during the sintering process, and the rates of carbon dioxide and oxygen were maintained at 0.5L / min; after the sintering was completed, the oxygen and carbon dioxide were stopped, the temperature was lowered to 100°C at 5°C / min, 0.5L / min of water vapor was introduced, and the mixture was kept at 100°C for 12h; the mixture was taken out and added to a beaker, deionized water was added at a solid-liquid ratio of 1g:10mL, and after being fully stirred, it was filtered to obtain a filtrate and a solid substance. The filtrate contained part of the lithium element, and the solid substance after filtration was lithium carbonate and iron phosphate.

[0114] ICP detection was performed on the lithium-containing solution, and the lithium content in the lithium-containing solution was 0.0522g; the Fe content was 0.1631g, and the P content was 0.1469g.

[0115] It can be seen that in the recovery method provided in this comparative example, the leaching rate of Li is 2.38%, the leaching rate of Fe is 0.87%, and the leaching rate of P is 1.46%.

[0116] Comparative Example 4

[0117] The difference from Example 1 is that water vapor is not introduced into the heat preservation step under low temperature conditions, specifically, including:

[0118] In the waste lithium iron phosphate positive electrode material, the mass content of lithium is 4.39%, the mass content of iron is 37.5%, the mass content of phosphorus is 20.13%, the mass content of oxygen is 28.45%, and the mass content of aluminum is 0.289%.

[0119] 50g of waste lithium iron phosphate positive electrode material powder (particle size of 50-100 mesh) was put into a tubular furnace, heated to 600°C at a heating rate of 5°C / min, and sintered for 4h. Carbon dioxide and oxygen were introduced during the sintering process, and the rates of carbon dioxide and oxygen were maintained at 0.5L / min; after the sintering was completed, the oxygen was stopped, and carbon dioxide was continued to be introduced at 0.5L / min, and the temperature was lowered to 100°C at 5°C / min, and kept at 100°C for 12h; the mixture was taken out and added to a beaker, and deionized water was added at a solid-liquid ratio of 1g:10mL. After fully stirring, it was filtered to obtain a filtrate and a solid substance. The filtrate contained part of the lithium element, and the solid substance after filtration was lithium carbonate and iron phosphate.

[0120] ICP detection was performed on the lithium-containing solution, and the lithium content in the lithium-containing solution was 0.0338g; the Fe content was 0.4613g, and the P content was 0.1751g.

[0121] It can be seen that in the recovery method provided in this comparative example, the leaching rate of Li is 1.54%, the leaching rate of Fe is 2.46%, and the leaching rate of P is 1.74%.

[0122] Comparative Example 5

[0123] The difference from Example 2 is that the sintering temperature is replaced with 25° C. Specifically, it includes:

[0124] In the waste lithium iron phosphate positive electrode material, the mass content of lithium is 4.39%, the mass content of iron is 37.5%, the mass content of phosphorus is 20.13%, the mass content of oxygen is 28.45%, and the mass content of aluminum is 0.289%.

[0125] 50g of waste lithium iron phosphate positive electrode material powder (particle size of 50-100 mesh) was put into a tubular furnace and kept at 25°C for 4h. Carbon dioxide and oxygen were introduced during the insulation process, and the rates of carbon dioxide and oxygen were maintained at 1.5L / min; after the insulation was completed, the oxygen was stopped, and carbon dioxide was continued to be introduced at 1.5L / min, the temperature was lowered to 200°C at 5°C / min, and then 1.5L / min of water vapor was introduced, and the mixture was kept at 200°C for 8h; the mixture was taken out and added to a beaker, and deionized water was added at a solid-liquid ratio of 1g:10mL. After fully stirring, it was filtered to obtain a filtrate and a solid substance. The solid substance was lithium iron phosphate. Obviously, when the high-temperature sintering temperature was changed to 25°C, the reaction did not occur.

[0126] Experimental results show that the recovery method provided by the present invention has a high leaching rate for Li in waste lithium iron phosphate positive electrode materials, with the highest leaching rate exceeding 99%; the leaching rates for other components in waste lithium iron phosphate positive electrode materials are relatively low, specifically, the leaching rate of Fe is less than 1.35%, and the leaching rate of P is less than 2.2%; the yield of iron phosphate is greater than 91%.

[0127] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for recycling waste lithium iron phosphate positive electrode materials, comprising the following steps: A) sintering the waste lithium iron phosphate positive electrode material at a temperature of 300-800° C. in an atmosphere where carbon dioxide and an oxidizing gas coexist to obtain a first mixture; The oxidizing gas is oxygen or ozone; B) in an atmosphere where water vapor and carbon dioxide coexist, keeping the first mixture warm under low temperature conditions to obtain a second mixture; the low temperature conditions are 0 to 300° C.; C) mixing the second mixture with water and performing solid-liquid separation to obtain a lithium-containing solution; No acid or alkali reagent is added in the recovery method; The recycling method has only one water treatment process.

2. The recycling method according to claim 1, characterized in that: In step A), during the high temperature sintering process, the flow rate of carbon dioxide is 0.1-3 L / min, and the flow rate of the oxidizing gas is 0.1-3 L / min.

3. The recycling method according to claim 1, characterized in that: In step A), before high-temperature sintering the waste lithium-ion battery, the method further includes: heating the waste lithium iron phosphate positive electrode material to a high-temperature sintering temperature; The heating rate is 3-7°C / min; The high temperature sintering time is 2 to 8 h.

4. The recycling method according to claim 1, characterized in that: In step A), the waste lithium iron phosphate positive electrode material has a lithium content of 3% to 4.5%, an iron content of 30% to 40%, a phosphorus content of 15% to 22%, an oxygen content of 25% to 33%, and an aluminum content of 0.1% to 0.4%.

5. The recycling method according to claim 1, characterized in that: In step B), during the heat preservation process under low temperature conditions, the flow rate of carbon dioxide is 0.1~3L / min, and the flow rate of water vapor is 0.1~3L / min.

6. The recycling method according to claim 1, characterized in that: In step B), before keeping the first mixture warm under low temperature conditions, the process further comprises: cooling the first mixture to a temperature under low temperature conditions; The cooling rate is 3-7°C / min; The insulation time under the low temperature condition is 2 to 24 hours.

7. The recycling method according to claim 1, characterized in that: In step C), the dosage ratio of the second mixture to water is 1 g: 1-100 mL.

8. The recycling method according to claim 1, characterized in that: Step C) further comprises: heating and decomposing the lithium-containing solution to obtain lithium carbonate.

9. The recycling method according to claim 8, characterized in that: The temperature of the heating decomposition is 40-90°C.