Aluminum removal method of lithium iron phosphate pole piece and preparation method and application of regenerated lithium iron phosphate material

Abstract

The invention discloses an aluminum removal method of a lithium iron phosphate pole piece and a preparation method and application of a regenerated lithium iron phosphate material. The aluminum removal method of the lithium iron phosphate material comprises the following steps: S1, stirring and washing a lithium iron phosphate pole piece in hot water to obtain a product I; the temperature of the hot water is 80-95 DEG C; s2, reacting a mixture containing the product I, inorganic salt and water to obtain a dealuminated lithium iron phosphate material; the inorganic salt is ferric sulfate and / or ferric nitrate; the liquid-solid ratio of the mixture is (2.5-6): 1; the molar ratio of the inorganic salt to the aluminum is (3.2-5): 1. The aluminum removal method provided by the invention is high in aluminum impurity removal rate, low in lithium element and iron element loss rate, simple and environment-friendly.

Description

TECHNICAL FIELD

[0001] The application relates to a method for removing aluminum from a lithium iron phosphate pole piece and a preparation method and application of regenerated lithium iron phosphate material. BACKGROUND

[0002] At present, the lithium iron phosphate positive electrode material has been widely applied, such as in electric buses, electric bicycles, electric buses, large-scale energy storage and other fields. The main reason is that the lithium iron phosphate positive electrode material has a theoretical specific capacity of 170 mAh / g, the lithium charging platform reaches 3.5 V, and compared with traditional lithium battery materials, the raw material source of lithium iron phosphate is very extensive, the safety performance is relatively outstanding, the cost is low, the thermal stability is good, the cycle performance is good, and it is green and environmentally friendly, which is an ideal power positive electrode material. At the same time, in recent years, with the increasing reduction of subsidies for new energy vehicles, and the frequent reports of vehicle accidents caused by ternary batteries, the lithium iron phosphate which has low cost and good safety is more popular.

[0003] However, with the continuous use of power batteries, their service life is limited. Generally speaking, the service life of power batteries is 3-5 years, and the batteries matched with pure electric buses are almost all lithium iron phosphate. In the early stage of the industry, lithium iron phosphate is the most popular power battery matching system. At present, the retired power batteries have increased sharply, and in the next few years, there will be an explosive wave of lithium iron phosphate battery retirement. Therefore, the recycling of lithium iron phosphate power batteries will become the focus of the battery recycling industry. At present, there are two methods for recycling lithium iron phosphate batteries: repair and hydrometallurgical recycling. The latter is the method currently used. This is mainly because the impurity content in the positive material repair process exceeds the standard, resulting in poor electrochemical performance after high-temperature repair, which cannot meet the actual demand. The target products of hydrometallurgical recycling of lithium iron phosphate batteries are mainly lithium carbonate, iron phosphate and the like. The above products are still used to prepare positive electrode materials, and the aluminum impurity index is very high. Therefore, how to reduce the aluminum impurity content in the waste lithium battery positive electrode material is crucial for subsequent hydrometallurgical or repair resource treatment.

[0004] In the prior art, Chinese patent CN105263872B discloses producing a phosphate compound from a material containing phosphorus and at least one of iron and aluminum. The patent can effectively recover aluminum by applying phosphate to the aluminum removal process. However, the method of the patent is complicated and involves many process steps, which is not conducive to industrial application. This is because the composition of the sludge ash raw material itself is relatively complex, and the compositions of various recyclable materials are different, leading to recycling difficulties.

[0005] Chinese patent CN109573974A discloses a method for removing aluminum from acidic leaching solution in the recycling of waste lithium iron phosphate batteries. The method can effectively remove aluminum in the leaching solution by adding an alkaline precipitate after heating the acidic leaching solution of the waste lithium iron phosphate battery. However, the addition of alkali will greatly reduce the content of iron, causing the iron to precipitate as red-brown iron hydroxide, resulting in heavy iron loss, which is not conducive to the recycling of lithium iron phosphate positive materials.

[0006] Chinese patent CN110112481B discloses a method for preparing lithium iron phosphate positive materials from waste lithium iron phosphate batteries. The method mainly removes aluminum by adjusting the pH to 3-5 by adding an alkaline substance to the acid leaching solution. The addition of alkali will also greatly reduce the content of iron, causing the iron to precipitate as red-brown iron hydroxide, resulting in heavy iron loss, which is not conducive to the recycling of lithium iron phosphate positive materials.

[0007] Chinese patent CN106848473A discloses a selective recovery method for lithium in waste lithium iron phosphate batteries. The method mainly uses an alkaline solution to dissolve aluminum and its oxides. This method is similar to the above two patents. The addition of alkali will also greatly reduce the content of iron, causing the iron to precipitate as red-brown iron hydroxide, resulting in heavy iron loss, which is not conducive to the recycling of lithium iron phosphate positive materials.

[0008] Based on the current research, the treatment of aluminum mainly focuses on the early stage of battery processing, such as high-temperature treatment, organic soaking, or alkali leaching. High-temperature treatment has good results, but requires high energy, increasing the cost of processing. Organic soaking is simple and easy to implement, but the organic solution required is expensive and difficult to control the cost, and it causes serious environmental pollution and greater harm to the human body. Alkali leaching can remove most of the aluminum, but also removes most of the iron, which needs to be supplemented later. In addition, the removal of aluminum is not complete enough to meet the industry standard for aluminum content in commercially available battery-grade iron phosphate. Therefore, it is urgent to develop a simple and efficient aluminum removal process to achieve the goal of meeting the industry standard for aluminum content in waste lithium iron phosphate battery positive materials. SUMMARY

[0009] The present application mainly overcomes the defects of the prior art, such as complex process, high cost, poor removal effect, and high loss of lithium and iron, in the recycling of lithium iron phosphate batteries. The present application provides a method for removing aluminum from lithium iron phosphate electrode sheets, a method for preparing regenerated lithium iron phosphate materials, and applications. The aluminum removal method provided by the present application has high removal rate of aluminum impurities, low loss rate of lithium and iron elements, and is simple and environmentally friendly.

[0010] The present application provides a method for removing aluminum from lithium iron phosphate electrode sheets, which comprises the following steps:

[0011] S1. Stir-washing the lithium iron phosphate material pole piece in hot water to obtain product I; the temperature of the hot water is 80-95 DEG C;

[0012] S2. Reacting a mixture containing the product I, inorganic salt and water to obtain a delaminated lithium iron phosphate material; the inorganic salt is iron sulfate and / or iron nitrate; the liquid-solid ratio of the mixture is (2.5-6):1; the molar ratio of the inorganic salt to aluminum is (3.2-5):1.

[0013] In the present application, the liquid-solid ratio refers to the mass ratio of solid to liquid in the mixture, the solid including the product I and the inorganic salt; the liquid including water.

[0014] In the present application, the lithium iron phosphate pole piece is derived from the conventional waste lithium iron phosphate battery in the art, the lithium iron phosphate pole piece contains a current collector and a positive electrode material layer, the current collector is an aluminum foil, and the positive electrode material layer includes a lithium iron phosphate material, a binder and a conductive agent.

[0015] Optionally, the binder is polyvinylidene fluoride (PVDF).

[0016] Optionally, the conductive agent is one or more of carbon black, acetylene black and graphene.

[0017] Optionally, in the positive electrode material layer, the content of the lithium iron phosphate material is 65-70%, which refers to the mass percentage of the lithium iron phosphate material in the mass of the positive electrode material layer.

[0018] Optionally, in the positive electrode material layer, the content of the binder is 2-2.5%, which refers to the mass percentage of the binder in the mass of the positive electrode material layer.

[0019] Optionally, in the positive electrode material layer, the content of the conductive agent is 5-5.5%, which refers to the mass percentage of the conductive agent in the mass of the positive electrode material layer.

[0020] Optionally, in the lithium iron phosphate pole piece, the content of aluminum element is 20-25%, which refers to the mass percentage of the aluminum element in the mass of the lithium iron phosphate pole piece.

[0021] Optionally, in the lithium iron phosphate pole piece, the content of iron element is 22-26%, which refers to the mass percentage of the iron element in the mass of the lithium iron phosphate pole piece.

[0022] Optionally, in the lithium iron phosphate pole piece, the content of lithium element is 2-4%, which refers to the mass percentage of the lithium element in the mass of the lithium iron phosphate pole piece.

[0023] In step S1, the temperature of the hot water can be 80-90℃, for example 80℃, 85℃ or 90℃.

[0024] In step S1, the time of the stirring can be 3h-4h, for example 3h, 3.5h or 4h.

[0025] In step S1, the stirring speed can be 300 r / min -400r / min, for example 300 r / min, 350 r / min or 400 r / min.

[0026] In step S1, after the stirring, a first screening is further performed to obtain a first screening overfall and a first screening underfall.

[0027] In the first screening, the mesh number of the screen used is preferably 10-30, for example 20.

[0028] In the first screening, a drying is preferably further performed, and the temperature of the drying is 80-105℃, for example 105℃.

[0029] Preferably, after the first screening, a crushing of the first screening overfall and the first screening underfall is further included.

[0030] In the crushing, the mode is preferably one or more of mechanical grinding, grinding, ball milling and sand milling.

[0031] In the first screening, the first screening overfall is preferably an aluminum foil containing part of lithium iron phosphate material; and the first screening underfall is a lithium iron phosphate material containing part of aluminum foil particles.

[0032] In some embodiments, the first screening underfall is crushed by grinding.

[0033] In some embodiments, the first screening overfall is crushed by mechanical grinding.

[0034] In some embodiments, the crushed material of the first screening overfall and the first screening underfall is further subjected to a second screening to obtain a second screening overfall and a second screening underfall, wherein the second screening underfall is taken as product I.

[0035] In the second screening, the mesh number of the screen used is preferably 80-150, for example 100.

[0036] In the second screening, the mode is preferably mode one or mode two:

[0037] Mode one, the crushed material of the first screening overfall and the first screening underfall is respectively subjected to a second screening, and then the two parts of the screening underfall are mixed as the second screening underfall, which is taken as product I.

[0038] Method two, the first sieve and the first sieve under the material are broken respectively, and then the obtained materials are mixed, and then second screening is carried out to obtain second sieve under, which is recorded as product I.

[0039] In the present application, the molar ratio of the inorganic salt to aluminum can be (3.5-4.5):1, preferably (3.4-4.8):1, for example 3.5:1, 4:1 or 4.5:1.

[0040] In the present application, the liquid-solid ratio of the mixture can be (3-5):1, for example 3:1, 4:1 or 5:1.

[0041] In step S2, the reaction time can be 30min-60min, for example 30min or 60min.

[0042] In step S2, the reaction temperature can be room temperature. The room temperature is understood to be 15℃-35℃.

[0043] In step S2, after the reaction, filtration, washing and drying are generally performed.

[0044] The number of washing is preferably 2-3 times.

[0045] The water after washing is preferably reused as the water in the mixture.

[0046] The present application also provides a preparation method of a regenerated lithium iron phosphate material, which comprises the following steps:

[0047] (1) removing aluminum from the lithium iron phosphate pole piece by using the aluminum removal method comprising the lithium iron phosphate pole piece as described above, to obtain a deluminized lithium iron phosphate material;

[0048] (2) calcining a mixture comprising the deluminized lithium iron phosphate material, a lithium source, an iron source and a carbon source to obtain a regenerated lithium iron phosphate material.

[0049] In the present application, the lithium source can be a conventional lithium-containing compound in the art, preferably a lithium salt and / or lithium hydroxide, and the lithium salt is preferably one or more of lithium carbonate, lithium nitrate and lithium chloride.

[0050] In the present application, the iron source can be a conventional iron-containing compound in the art, preferably an iron salt, for example iron oxalate and / or iron phosphate.

[0051] In this invention, the carbon source may be one or more of sugars, organic acids, and polymers; the sugars are preferably one or more of glucose, sucrose, lactose, and maltose, such as glucose; the organic acids are preferably one or more of citric acid, malic acid, and tartaric acid; and the polymers are preferably one or more of polyethylene, polyethylene glycol, polyvinyl alcohol, polyvinyl alcohol derivatives, polyacrylic acid, and polyacrylic acid derivatives.

[0052] In this invention, the molar ratio of lithium provided by the lithium source, iron provided by the iron source, and carbon provided by the carbon source can be 1:1:x / 2, where 0 < x < 1, for example, x = 0.5.

[0053] In step (2), the calcination temperature can be 600℃-650℃, for example 600℃, 625℃ or 650℃.

[0054] In step (2), the calcination time can be 6 h - 7 h, for example 6 h, 6.5 h or 7 h.

[0055] In step (2), the calcination can be carried out in equipment conventionally used in the art, such as a tube furnace.

[0056] In step (2), after calcination, mechanical crushing and sieving are performed. The mechanical crushing method is preferably grinding, sand milling or ball milling. The mesh size of the sieve used for sieving is preferably 200 mesh.

[0057] This invention also provides the application of the aluminum removal method for lithium iron phosphate materials as described above or the preparation method for recycled lithium iron phosphate materials as described above in the field of battery recycling.

[0058] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0059] The reagents and raw materials used in this invention are all commercially available.

[0060] The positive and progressive effects of this invention are as follows:

[0061] (1) The present invention uses hot water to wash the battery electrode sheet and the electrode powder to achieve effective separation. The electrode powder recovery rate can reach more than 99%. Compared with the use of organic solvents or pyrolysis, it is more environmentally friendly and simple.

[0062] (2) The process of removing aluminum using inorganic salts is simple to operate, safe and environmentally friendly, and has a good aluminum removal effect. The aluminum removal rate can reach more than 98%, and the loss of lithium and iron is less. The loss rate of lithium and iron is less than 2%, and the dissolution of lithium iron phosphate powder is less. The loss rate of the dealuminized lithium iron phosphate powder is less than 1%.

[0063] (3) The recycled lithium iron phosphate material obtained by the present invention has a high purity, up to 99.9% or more. When it is applied to a battery, the first discharge specific capacity under the 0.1C charge-discharge rate condition is greater than 170mAh / g. Attached Figure Description

[0064] Figure 1 This is a process flow diagram of the preparation method of the recycled lithium iron phosphate material in the embodiment. Detailed Implementation

[0065] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0066] The sources of the lithium iron phosphate electrodes used in the following examples and comparative examples are as follows:

[0067] Before removing aluminum, the content of each element was tested: the positive electrode contained 66% lithium iron phosphate, 24% aluminum, 23% iron, and 2.9% lithium.

[0068] Examples 1-3 and Comparative Examples 1-6 all used the above-mentioned electrode sheets for subsequent preparation processes.

[0069] Example 1

[0070] (1) Removal of aluminum from lithium iron phosphate electrodes

[0071] S1. Preparation of Product I

[0072] S1-1. Place 50g of lithium iron phosphate electrode sheet into a beaker, add 250mL of deionized water at 90℃ to submerge the electrode sheet, place the beaker in a water bath, control the water bath temperature at 90℃, insert a stirrer into the beaker, stir for 4 hours at a stirring speed of 400r / min.

[0073] S1-2. The material obtained in S-11 is first screened using a 20-mesh sieve to obtain aluminum foil containing some lithium iron phosphate cathode powder as the material on the first sieve and lithium iron phosphate cathode powder containing some aluminum foil particles as the material below the first sieve.

[0074] S1-3. Place the first sieve oversize and the first sieve undersize obtained in S1-2 into a muffle furnace for drying at a temperature of 105℃.

[0075] S1-4. Grind the first sieve material dried in step S1-3 using a mortar and pestle, and then pass it through a 100-mesh sieve for a second sieve separation. Crush the first sieve material dried in S1-3 using a mechanical mill, and then pass it through a 100-mesh sieve for a second sieve separation. Mix the two portions of the second sieve material to obtain product I.

[0076] S2. Aluminum Removal

[0077] S2-1. According to the ratio of inorganic salt to aluminum (molar ratio) 4.5:1 and liquid-solid ratio 5:1, add inorganic salt and deionized water to product I obtained from S1, wherein the inorganic salt is ferric sulfate, the reaction time is 60 min, and the reaction temperature is room temperature.

[0078] S2-2. Filter the mixture obtained in S2-1 and wash the solid with deionized water three times. The water after washing can be reused in step S2-1. Dry the solid to obtain the dealuminated lithium iron phosphate material.

[0079] (2) Preparation of recycled lithium iron phosphate materials

[0080] Lithium chloride, iron phosphate, and glucose were added to the dealuded lithium iron phosphate material obtained in step (1), ensuring that the molar ratio of lithium, iron, and carbon was 1:1:0.25. After mixing and grinding, the mixture was placed in a tube furnace for high-temperature calcination at 650°C for 7 hours. After calcination, the powder was ground and passed through a 200-mesh sieve to obtain recycled lithium iron phosphate material.

[0081] Example 2

[0082] (1) Removal of aluminum from lithium iron phosphate electrodes

[0083] S1. Preparation of Product I

[0084] S1-1. Place 50g of lithium iron phosphate electrode sheet into a beaker, add 250mL of deionized water at 85℃ to submerge the electrode sheet, place the beaker in a water bath, control the water bath temperature at 85℃, insert a stirrer into the beaker, stir for 3.5h at a stirring speed of 350r / min.

[0085] S1-2. The material obtained in S1-1 is first screened using a 20-mesh sieve to obtain aluminum foil containing some lithium iron phosphate cathode powder as the material on the first sieve and lithium iron phosphate cathode powder containing some aluminum foil particles as the material below the first sieve.

[0086] S1-3. Place the first sieve oversize and the first sieve undersize obtained in S1-2 into a muffle furnace for drying at a temperature of 95°C.

[0087] S1-4. Grind the first sieve material dried in step S1-3 using a mortar and pestle, and then pass it through a 100-mesh sieve for a second sieve separation. Crush the first sieve material dried in S1-3 using a mechanical mill, and then pass it through a 100-mesh sieve for a second sieve separation. Mix the two portions of the second sieve material to obtain product I.

[0088] S2. Aluminum Removal

[0089] S2-1. According to the ratio of inorganic salt to aluminum (molar ratio) 4:1 and liquid-solid ratio 4:1, add inorganic salt and deionized water to product I obtained from S1, wherein the inorganic salt is ferric nitrate, the stirring reaction time is 45 min, and the reaction temperature is room temperature;

[0090] S2-2. Filter the mixture obtained in S2-1, wash the solid three times with deionized water, and dry the solid to obtain the dealuminated lithium iron phosphate material;

[0091] (2) Preparation of recycled lithium iron phosphate materials

[0092] Lithium hydroxide, iron oxalate, and sucrose were added to the dealuded lithium iron phosphate material obtained in step (1), ensuring that the molar ratio of lithium, iron, and carbon was 1:1:0.25. After mixing and grinding, the mixture was placed in a tube furnace for high-temperature calcination at 625°C for 6.5 hours. After calcination, the powder was ground and passed through a 200-mesh sieve to obtain recycled lithium iron phosphate material.

[0093] Example 3

[0094] (1) Removal of aluminum from lithium iron phosphate electrodes

[0095] S1. Preparation of Product I

[0096] S1-1. Place 50g of lithium iron phosphate electrode sheet into a beaker, add 250mL of deionized water at 80℃ to submerge the electrode sheet, place the beaker in a water bath, control the water bath temperature at 80℃, insert a stirrer into the beaker, stir for 3h at a stirring speed of 300r / min.

[0097] S1-2. The material obtained in S1-1 is first screened using a 20-mesh sieve to obtain aluminum foil containing some lithium iron phosphate cathode powder as the material on the first sieve and lithium iron phosphate cathode powder containing some aluminum foil particles as the material below the first sieve.

[0098] S1-3. Place the first sieve oversize and the first sieve undersize obtained in S1-2 into a muffle furnace for drying at a temperature of 80°C.

[0099] S1-4. Grind the first sieve material dried in step S1-3 using a mortar and pestle, and then pass it through a 100-mesh sieve for a second sieve separation. Crush the first sieve material dried in S1-3 using a mechanical mill, and then pass it through a 100-mesh sieve for a second sieve separation. Mix the two portions of the second sieve material to obtain product I.

[0100] S2. Aluminum Removal

[0101] S2-1. According to the ratio of inorganic salt to aluminum (molar ratio) 3.5:1 and liquid-solid ratio 3:1, add inorganic salt and deionized water to product I obtained from S1, wherein the inorganic salt is ferric sulfate, stir for 30 min, and react at room temperature.

[0102] S2-2. Filter the mixture obtained in S2-1, wash the solid twice with deionized water, and dry the solid to obtain the dealuminated lithium iron phosphate material;

[0103] (2) Preparation of recycled lithium iron phosphate materials

[0104] Lithium carbonate, iron oxalate, and glucose were added to the dealuded lithium iron phosphate material obtained in step (1), ensuring that the molar ratio of lithium, iron, and carbon was 1:1:0.25. After mixing and grinding, the mixture was placed in a tube furnace for high-temperature calcination at 600°C for 6 hours. After calcination, the powder was ground and passed through a 200-mesh sieve to obtain recycled lithium iron phosphate material.

[0105] Comparative Example 1

[0106] (1) Removal of aluminum from lithium iron phosphate electrodes

[0107] S1. Preparation of Product I:

[0108] S1-1. Place 50g of lithium iron phosphate electrode sheet into a beaker, add 250mL of deionized water at 80℃ to submerge the electrode sheet, place the beaker in a water bath, control the water bath temperature at 80℃, insert a stirrer into the beaker, stir for 3h at a stirring speed of 300r / min.

[0109] S1-2. The material obtained in S1-1 is first screened using a 20-mesh sieve to obtain aluminum foil containing some lithium iron phosphate cathode powder as the material on the first sieve and lithium iron phosphate cathode powder containing some aluminum foil particles as the material below the first sieve.

[0110] S1-3. Place the first sieve oversize and the first sieve undersize obtained in S1-2 into a muffle furnace for drying at a temperature of 80°C.

[0111] S1-4. Grind the first sieve material dried in step S1-3 using a mortar and pestle, and then pass it through a 100-mesh sieve for a second sieve separation. Crush the first sieve material dried in S1-3 using a mechanical mill, and then pass it through a 100-mesh sieve for a second sieve separation. Mix the two portions of the second sieve material to obtain product I.

[0112] S2. Aluminum removal:

[0113] S2-1. According to the ratio of inorganic salt to aluminum (molar ratio) 3.5:1 and liquid-solid ratio 3:1, add inorganic salt and deionized water to product I obtained from S1, wherein the inorganic salt is ferric chloride, the stirring reaction time is 30 min, and the reaction temperature is room temperature;

[0114] S2-2. Filter the mixture obtained in S2-1, wash the solid twice with deionized water, and dry the solid to obtain the dealuminated lithium iron phosphate material;

[0115] (2) Preparation of recycled lithium iron phosphate materials

[0116] Lithium chloride, iron phosphate, and glucose were added to the dealuded lithium iron phosphate material obtained in step (1), ensuring that the molar ratio of lithium, iron, and carbon was 1:1:0.25. After mixing and grinding, the mixture was placed in a tube furnace for high-temperature calcination at 600°C for 6 hours. After calcination, the powder was ground and passed through a 200-mesh sieve to obtain recycled lithium iron phosphate material.

[0117] Comparative Example 2

[0118] (1) Removal of aluminum from lithium iron phosphate electrodes

[0119] S1. Preparation of Product I:

[0120] S1-1. Place 50g of lithium iron phosphate electrode sheet into a beaker, add 250mL of deionized water at 80℃ to submerge the electrode sheet, place the beaker in a water bath, control the water bath temperature at 80℃, insert a stirrer into the beaker, stir for 3h at a stirring speed of 300r / min.

[0121] S1-2. The material obtained in S1-1 is first screened using a 20-mesh sieve to obtain aluminum foil containing some lithium iron phosphate cathode powder as the material on the first sieve and lithium iron phosphate cathode powder containing some aluminum foil particles as the material below the first sieve.

[0122] S1-3. Place the first sieve oversize and the first sieve undersize obtained in S1-2 into a muffle furnace for drying at a temperature of 80°C.

[0123] S1-4. Grind the first sieve material dried in step S1-3 using a mortar and pestle, and then pass it through a 100-mesh sieve for a second sieve separation. Crush the first sieve material dried in S1-3 using a mechanical mill, and then pass it through a 100-mesh sieve for a second sieve separation. Mix the two portions of the second sieve material to obtain product I.

[0124] S2. Aluminum removal:

[0125] S2-1. According to the ratio of inorganic salt to aluminum (molar ratio) 3:1 and liquid-solid ratio 3:1, add inorganic salt and deionized water to product I obtained from S1, wherein the inorganic salt is ferric sulfate, stir for 30 min, and react at room temperature.

[0126] S2-2. Filter the mixture obtained in S2-1, wash the solid twice with deionized water, and dry the solid to obtain the dealuminated lithium iron phosphate material;

[0127] (2) Preparation of recycled lithium iron phosphate materials

[0128] Lithium chloride, iron phosphate, and glucose were added to the dealuded lithium iron phosphate material obtained in step (1), ensuring that the molar ratio of lithium, iron, and carbon was 1:1:0.25. After mixing and grinding, the mixture was placed in a tube furnace for high-temperature calcination at 600°C for 6 hours. After calcination, the powder was ground and passed through a 200-mesh sieve to obtain recycled lithium iron phosphate material.

[0129] Comparative Example 3

[0130] (1) Removal of aluminum from lithium iron phosphate electrodes

[0131] S1. Preparation of Product I:

[0132] S1-1. Place 50g of lithium iron phosphate electrode sheet into a beaker, add 250mL of deionized water at 80℃ to submerge the electrode sheet, place the beaker in a water bath, control the water bath temperature at 80℃, insert a stirrer into the beaker, stir for 3h at a stirring speed of 300r / min.

[0133] S1-2. The material obtained in S1-1 is first screened using a 20-mesh sieve to obtain aluminum foil containing some lithium iron phosphate cathode powder as the material on the first sieve and lithium iron phosphate cathode powder containing some aluminum foil particles as the material below the first sieve.

[0134] S1-3. Place the first sieve oversize and the first sieve undersize obtained in S1-2 into a muffle furnace for drying at a temperature of 80°C.

[0135] S1-4. Grind the first sieve material dried in step S1-3 using a mortar and pestle, and then pass it through a 100-mesh sieve for a second sieve separation. Crush the first sieve material dried in S1-3 using a mechanical mill, and then pass it through a 100-mesh sieve for a second sieve separation. Mix the two portions of the second sieve material to obtain product I.

[0136] S2. Aluminum removal:

[0137] S2-1. According to the ratio of inorganic salt to aluminum (molar ratio) 3.5:1 and liquid-solid ratio 2:1, add inorganic salt and deionized water to product I obtained from S1, wherein the inorganic salt is ferric chloride, the reaction time is 30 min, and the reaction temperature is room temperature.

[0138] S2-2. Filter the mixture obtained in S2-1, wash the solid twice with deionized water, and dry the solid to obtain the dealuminated lithium iron phosphate material;

[0139] (2) Preparation of recycled lithium iron phosphate materials

[0140] Lithium chloride, iron phosphate, and glucose were added to the dealuded lithium iron phosphate material obtained in step (1), ensuring that the molar ratio of lithium, iron, and carbon was 1:1:0.25. After mixing and grinding, the mixture was placed in a tube furnace for high-temperature calcination at 600°C for 6 hours. After calcination, the powder was ground and passed through a 200-mesh sieve to obtain recycled lithium iron phosphate material.

[0141] Comparative Example 4

[0142] (1) Removal of aluminum from lithium iron phosphate electrodes

[0143] S1. Preparation of Product I:

[0144] S1-1. Place 50g of lithium iron phosphate electrode sheet into a beaker, add 250mL of deionized water at 80℃ to submerge the electrode sheet, place the beaker in a water bath, control the water bath temperature at 80℃, insert a stirrer into the beaker, stir for 3h at a stirring speed of 300r / min.

[0145] S1-2. The material obtained in S1-1 is first screened using a 20-mesh sieve to obtain aluminum foil containing some lithium iron phosphate cathode powder as the material on the first sieve and lithium iron phosphate cathode powder containing some aluminum foil particles as the material below the first sieve.

[0146] S1-3. Place the first sieve oversize and the first sieve undersize obtained in S1-2 into a muffle furnace for drying at a temperature of 80°C.

[0147] S1-4. Grind the first sieve material dried in step S1-3 using a mortar and pestle, and then pass it through a 100-mesh sieve for a second sieve separation. Crush the first sieve material dried in S1-3 using a mechanical mill, and then pass it through a 100-mesh sieve for a second sieve separation. Mix the two portions of the second sieve material to obtain product I.

[0148] S2. Aluminum removal:

[0149] S2-1. According to the ratio of inorganic salt to aluminum (molar ratio) 3.5:1 and liquid-solid ratio 3:1, add inorganic salt and deionized water to product I obtained from S1, wherein the inorganic salt is copper chloride, the stirring reaction time is 30 min, and the reaction temperature is room temperature;

[0150] S2-2. Filter the mixture obtained in S2-1, wash the solid twice with deionized water, and dry the solid to obtain the dealuminated lithium iron phosphate material;

[0151] (2) Preparation of recycled lithium iron phosphate materials

[0152] Lithium chloride, iron phosphate, and glucose were added to the dealuded lithium iron phosphate material obtained in step (1), ensuring that the molar ratio of lithium, iron, and carbon was 1:1:0.25. After mixing and grinding, the mixture was placed in a tube furnace for high-temperature calcination at 600°C for 6 hours. After calcination, the powder was ground and passed through a 200-mesh sieve to obtain recycled lithium iron phosphate material.

[0153] Comparative Example 5

[0154] (1) Removal of aluminum from lithium iron phosphate electrodes

[0155] S1. Preparation of Product I

[0156] S1-1. Place 50g of lithium iron phosphate electrode sheet into a beaker, add 250mL of deionized water at 70℃ to submerge the electrode sheet, place the beaker in a water bath, control the water bath temperature at 70℃, insert a stirrer into the beaker, stir for 4 hours at a stirring speed of 400r / min.

[0157] S1-2. The material obtained in S1-1 is first screened using a 20-mesh sieve to obtain aluminum foil containing some lithium iron phosphate cathode powder as the material on the first sieve and lithium iron phosphate cathode powder containing some aluminum foil particles as the material below the first sieve.

[0158] S1-3. Place the first sieve oversize and the first sieve undersize obtained in S1-2 into a muffle furnace for drying at a temperature of 105℃.

[0159] S1-4. Grind the first sieve material dried in step S1-3 using a mortar and pestle, and then pass it through a 100-mesh sieve for a second sieve separation. Crush the first sieve material dried in S1-3 using a mechanical mill, and then pass it through a 100-mesh sieve for a second sieve separation. Mix the two portions of the second sieve material to obtain product I.

[0160] S2. Aluminum Removal

[0161] S2-1. According to the ratio of inorganic salt to aluminum (molar ratio) of 4.5:1 and liquid-solid ratio of 5:1, add inorganic salt and deionized water to product I obtained from S1, wherein the inorganic salt is ferric sulfate, stir for 60 min, and react at room temperature.

[0162] S2-2. Filter the mixture obtained in S2-1, wash the solid three times with deionized water, and dry the solid to obtain the dealuminated lithium iron phosphate material;

[0163] (2) Preparation of recycled lithium iron phosphate materials

[0164] Lithium chloride, iron phosphate, and glucose were added to the dealuded lithium iron phosphate material obtained in step (1), ensuring that the molar ratio of lithium, iron, and carbon was 1:1:0.25. After mixing and grinding, the mixture was placed in a tube furnace for high-temperature calcination at 650°C for 7 hours. After calcination, the powder was ground and passed through a 200-mesh sieve to obtain recycled lithium iron phosphate material.

[0165] Comparative Example 6

[0166] (1) Removal of aluminum from lithium iron phosphate electrodes

[0167] S1. Preparation of Product I

[0168] S1-1. Place 50g of lithium iron phosphate electrode sheet into a beaker, add 250mL of deionized water at 90℃ to submerge the electrode sheet, place the beaker in a water bath, control the water bath temperature at 90℃, insert a stirrer into the beaker, stir for 4 hours at a stirring speed of 400r / min.

[0169] S1-2. The material obtained in S1-1 is first screened using a 20-mesh sieve to obtain aluminum foil containing some lithium iron phosphate cathode powder as the material on the first sieve and lithium iron phosphate cathode powder containing some aluminum foil particles as the material below the first sieve.

[0170] S1-3. Place the first sieve oversize and the first sieve undersize obtained in S1-2 into a muffle furnace for drying at a temperature of 105℃.

[0171] S1-4. Grind the first sieve material dried in step S1-3 using a mortar and pestle, and then pass it through a 100-mesh sieve for a second sieve separation. Crush the first sieve material dried in S1-3 using a mechanical mill, and then pass it through a 100-mesh sieve for a second sieve separation. Mix the two portions of the second sieve material to obtain product I.

[0172] S2. Aluminum Removal

[0173] S2-1. According to the ratio of inorganic salt to aluminum (molar ratio) 4.5:1 and liquid-solid ratio 2:1, add inorganic salt and deionized water to product I obtained from S1, wherein the inorganic salt is ferric sulfate, the reaction time is 60 min, and the reaction temperature is room temperature.

[0174] S2-2. Filter the mixture obtained in S2-1, wash the solid three times with deionized water, and dry the solid to obtain the dealuminated lithium iron phosphate material;

[0175] (2) Preparation of recycled lithium iron phosphate materials

[0176] Lithium chloride, iron phosphate, and glucose were added to the dealuded lithium iron phosphate material obtained in step (1), ensuring that the molar ratio of lithium, iron, and carbon was 1:1:0.25. After mixing and grinding, the mixture was placed in a tube furnace for high-temperature calcination at 650°C for 7 hours. After calcination, the powder was ground and passed through a 200-mesh sieve to obtain recycled lithium iron phosphate material.

[0177] Example 1

[0178] (1) Aluminum removal rate

[0179] The aluminum content (referred to as initial aluminum content) in product I of Examples 1-3 and Comparative Examples 1-6 and the aluminum content (referred to as final aluminum content) in the lithium iron phosphate material after aluminum removal were determined according to GB / T 11064.16-2023. The aluminum removal rate was then calculated using the following method, and the calculation results are recorded in Table 1:

[0180] Aluminum removal rate = (initial aluminum content - final aluminum content) / initial aluminum content × 100%.

[0181] (2) Lithium loss rate

[0182] The lithium content (referred to as initial lithium content) in product I of Examples 1-3 and Comparative Examples 1-6 and the lithium iron phosphate material after aluminum removal (referred to as final lithium content) were determined according to GB / T 11064.1-2024. The lithium loss rate was then calculated using the following method, and the calculation results are recorded in Table 1:

[0183] Lithium loss rate = (initial lithium content - final lithium content) / initial lithium content × 100%.

[0184] (3) Iron loss rate

[0185] According to GB / T 11064.7-2013, the iron content (referred to as initial iron content) in product I of Examples 1-3 and Comparative Examples 1-6 and the iron content (referred to as final iron content) in lithium iron phosphate material after aluminum removal were determined respectively. The iron loss rate was then calculated in the following manner, and the calculation results are recorded in Table 1:

[0186] Iron loss rate = (initial iron content - final iron content) / initial iron content × 100%.

[0187] (4) Loss rate of lithium iron phosphate powder after aluminum removal

[0188] The loss rate of lithium iron phosphate powder after aluminum removal was calculated using the following method, and the results are recorded in Table 1:

[0189] Loss rate of lithium iron phosphate powder after aluminum removal = (mass of product I - mass of dealuminated lithium iron phosphate material) / mass of product I × 100%.

[0190] (5) Purity of lithium iron phosphate powder

[0191] The purity of the lithium iron phosphate materials after aluminum removal in Examples 1-3 and Comparative Examples 1-6 was determined according to YS / T1027-2015, and the results are recorded in Table 1.

[0192] Example 2

[0193] The initial discharge specific capacity of the regenerated lithium iron phosphate materials in Examples 1-3 and Comparative Examples 1-6 was determined according to GB / T 23365, and the results are recorded in Table 1.

[0194] Table 1

[0195] Aluminum removal rate Lithium element loss rate Iron element loss rate Loss rate of lithium iron phosphate powder after aluminum removal Purity of lithium iron phosphate powder Initial discharge specific capacity / mAh / g Example 1 99% 1% 1% 0.3% 99.95% 175 Example 2 98.8% 1.2% 1.1% 0.5% 99.92% 172 Example 3 98.9% 1.4% 1.2% 0.6% 99.93% 172 Comparative Example 1 98.5% 1.5% 1.3% 0.8% 99.91% 171 Comparative Example 2 92% 1.4% 1.3% 0.8% 99.92% 170 Comparative Example 3 93% 1.5% 1.3% 0.7% 99.92% 168 Comparative Example 4 98.4% 1.6% 1.4% 0.9% 95.8% 167 Comparative Example 5 97.5% 2.8% 2.6% 1.5% 99.91% 170 Comparative Example 6 93% 1.5% 1.3% 0.7% 99.92% 168

[0196] The process flow of the method for removing aluminum from lithium iron phosphate materials and the method for preparing recycled lithium iron phosphate materials of the present invention is as follows: Figure 1 As shown, the process is simple to operate and safe and environmentally friendly. According to the data in Table 1, the aluminum removal method for lithium iron phosphate materials provided by this invention has a high aluminum removal rate of over 98.5%, a lithium element loss rate of less than 1.5%, and an iron element loss rate of less than 1.2%. The loss rate of lithium iron phosphate powder after aluminum removal is 0.6% or lower, and the purity is over 99.9%. The repaired lithium iron phosphate material also exhibits good electrical performance when used in batteries, with an initial discharge specific capacity of 170 mAh / g.

[0197] Comparative Example 1 uses ferric chloride to react with aluminum to remove aluminum. Although it is a lithium salt like ferric sulfate and ferric nitrate, the loss rates of lithium and iron are relatively high.

[0198] In Comparative Example 2, the molar ratio of inorganic salt to aluminum was smaller than that in the Example, indicating a significant loss rate of aluminum. Additionally, the loss rates of lithium, iron, and lithium iron phosphate powder after aluminum removal were also relatively high.

[0199] In Comparative Example 3, aluminum was removed by reacting ferric chloride with aluminum and a relatively small liquid-solid ratio was used. It can be seen that the aluminum loss rate was very large, and the loss rates of lithium and iron were also relatively high.

[0200] In Comparative Example 4, aluminum was removed by reacting ferric chloride with aluminum. Although the aluminum removal rate was comparable to that of some examples, the lithium loss rate was high and the purity of the resulting lithium iron phosphate powder was low.

[0201] In Comparative Example 5, hot water at 70°C was used for washing, which significantly worsened the aluminum removal rate, lithium and iron loss rates, and the loss rate of lithium iron phosphate powder after aluminum removal.

[0202] Comparative Example 6 uses a smaller liquid-to-solid ratio, which shows that the loss rate of aluminum is very large, and the loss rates of lithium and iron are also relatively high.

[0203] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for removing aluminum from lithium iron phosphate electrodes, characterized in that, It includes the following steps: S1. The lithium iron phosphate electrode is washed in hot water to obtain product I; the temperature of the hot water is 80℃-95℃; S2. React the mixture containing product I, inorganic salt and water to obtain dealuminated lithium iron phosphate material; the inorganic salt is ferric sulfate and / or ferric nitrate; the liquid-to-solid ratio of the mixture is (2.5-6):1; the molar ratio of the inorganic salt to aluminum is (3.2-5):

1.

2. The method for removing aluminum from lithium iron phosphate electrodes according to claim 1, characterized in that, In step S1, the temperature of the hot water is 80-90℃, for example, 80℃, 85℃ or 90℃; And / or, in step S1, the agitation time is 3h-4h, for example 3h, 3.5h or 4h; And / or, in step S1, the stirring speed is 300 r / min - 400 r / min, for example 300 r / min, 350 r / min or 400 r / min.

3. The method for removing aluminum from lithium iron phosphate electrodes according to claim 1, characterized in that, The liquid-to-solid ratio of the mixture is (3-5):1, for example 3:1, 4:1 or 5:1; And / or, the molar ratio of the inorganic salt to aluminum is (3.5-4.5):1, preferably (3.4-4.8):1, for example 3.5:1, 4:1 or 4.5:

1.

4. The method for removing aluminum from lithium iron phosphate electrodes according to claim 1, characterized in that, In step S1, after the agitation and washing, a first sieving is performed to obtain the first sieve oversize and the first sieve undersize. Preferably, the sieve used for the first screening is 10-30 mesh, for example, 20 mesh; Preferably, after the first screening, the material is dried at a temperature preferably between 80 and 105°C, for example, 105°C.

5. The method for removing aluminum from lithium iron phosphate electrodes according to claim 4, characterized in that, In step S1, after the first screening, the material above the first screen and the material below the first screen are crushed respectively. The crushing method is preferably one or more of mechanical grinding, grinding, ball milling and sand milling; the first undersize material is preferably crushed by grinding; the first oversize material is preferably crushed by mechanical grinding. Preferably, the material obtained from crushing the first oversize and the first undersize is further subjected to a second screening to obtain a second oversize and a second undersize, wherein the second undersize is denoted as product I; wherein the mesh size of the sieve used for the second screening is preferably 80-150 mesh, for example 100 mesh; The second screening method is preferably method one or method two: Method 1: The materials obtained from crushing the material above the first screen and the material below the first screen are subjected to a second screening, and then the two parts of the material below the screen are mixed together as the second material below the screen, which is denoted as Product I; Method 2: Mix the materials obtained from crushing the material above the first sieve and the material below the first sieve, and then perform a second sieve separation to obtain the material below the second sieve, which is denoted as Product I.

6. The method for removing aluminum from lithium iron phosphate electrodes according to claim 1, characterized in that, In step S2, the reaction time is 30 min to 60 min, for example, 30 min or 60 min; And / or, in step S2, the reaction temperature is room temperature; And / or, in step S2, after the reaction, filtration, washing and drying are also performed; the number of washings is preferably 2-3 times; the water after washing is preferably reused as water in the mixture.

7. A method for preparing recycled lithium iron phosphate material, characterized in that, It includes the following steps: (1) The lithium iron phosphate electrode is dealuminized using the method comprising the lithium iron phosphate electrode as described in any one of claims 1-6 to obtain dealuminized lithium iron phosphate material; (2) The mixture containing the dealuated lithium iron phosphate material, lithium source, iron source and carbon source is calcined to obtain regenerated lithium iron phosphate material.

8. The method for preparing recycled lithium iron phosphate material according to claim 7, characterized in that, The lithium source is a lithium salt and / or lithium hydroxide, and the lithium salt is preferably one or more of lithium carbonate, lithium nitrate and lithium chloride; And / or, the iron source is an iron salt, preferably ferric oxalate and / or ferric phosphate; And / or, the carbon source is one or more of sugars, organic acids, and polymers; the sugar is preferably one or more of glucose, sucrose, lactose, and maltose, such as glucose; the organic acid is preferably one or more of citric acid, malic acid, and tartaric acid; and the polymer is preferably one or more of polyethylene, polyethylene glycol, polyvinyl alcohol, polyvinyl alcohol derivatives, polyacrylic acid, and polyacrylic acid derivatives.

9. The method for preparing recycled lithium iron phosphate material according to claim 7, characterized in that, The molar ratio of lithium provided by the lithium source, iron provided by the iron source, and carbon provided by the carbon source is 1:1:x / 2, where 0 < x < 1, for example, x = 0.5; And / or, in step (2), the calcination temperature is 600℃-650℃, for example 600℃, 625℃ or 650℃; And / or, in step (2), the calcination time is 6 h - 7 h, for example 6 h, 6.5 h or 7 h; And / or, in step (2), the calcination equipment is a tube furnace; And / or, in step (2), after calcination, mechanical crushing and sieving are also performed, wherein the mechanical crushing method is preferably grinding, sand milling or ball milling; and the mesh size of the sieve used for sieving is preferably 200 mesh.

10. The application of a method for aluminum removal in lithium iron phosphate recycling as described in any one of claims 1-6 or a method for preparing recycled lithium iron phosphate material as described in any one of claims 7-9 in the field of battery recycling.

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