Method for recovering and repairing waste lithium iron phosphate positive electrode material and lithium iron phosphate finished product

Abstract

The invention belongs to the technical field of lithium ion battery positive electrode materials, and particularly relates to a waste lithium iron phosphate positive electrode material recycling and repairing method. Comprising the following steps: (1) sintering the waste lithium iron phosphate positive plate, pulverizing and sieving to obtain red powder; (2) measuring the molar ratio of each element in the red powder, premixing the red powder, a carbon source, an organic acid and a supplementary lithium source in an aqueous solution, and sanding; and (3) carrying out spray drying on the sanded material, calcining at high temperature, cooling and sieving to obtain a lithium iron phosphate finished product. According to the method disclosed by the invention, the surface layer of the red powder can be etched by using the organic acid, and secondary uniform distribution of surface layer elements after leaching is promoted, so that a melting assisting effect is realized, the specific surface and morphology of the material are optimized, and the obtained lithium iron phosphate finished product has relatively high specific discharge capacity and excellent rate capability. In addition, the recycling and repairing process is simple in technology, high in operability, green and free of pollution in the whole process and high in economic and environment-friendly value.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium-ion battery positive electrode materials, and specifically relates to a method for recovering and repairing waste lithium iron phosphate positive electrode materials and a lithium iron phosphate finished product. Background Art

[0002] In recent years, the world has vigorously developed new energy, and batteries, as carriers of energy storage, play a vital role. As the core component of lithium secondary batteries, lithium iron phosphate cathode materials have become the first choice for lithium-ion battery cathode materials due to their ultra-long life, sufficient safety, fast charging and discharging, and low cost.

[0003] However, with the extensive use of lithium-ion batteries, the batteries used in the early stage have gradually retired. Due to the large accumulation of waste lithium-ion batteries, it is urgent to find a suitable treatment method to recycle them while avoiding damage to the environment.

[0004] Patent CN106976852A discloses a green repair and regeneration technology for lithium iron phosphate materials in waste batteries. In the material regeneration stage, the proportion of elements in waste lithium iron phosphate is adjusted by adding appropriate lithium sources, iron sources and phosphorus sources. However, due to the uneven distribution of elements inside waste lithium iron phosphate particles, especially lithium elements, this method cannot effectively achieve secondary uniform distribution of elements, affecting the material's gram capacity and rate performance. Patent CN112142029A proposes a repair and regeneration method for waste lithium iron phosphate battery positive electrode materials. In this method, only a certain amount of lithium source and carbon source are added to the recycled lithium iron phosphate powder, which also fails to effectively achieve secondary uniform distribution of elements, and there is no surface etching, and there is no melting effect during the sintering process. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and to provide a method for recycling and repairing waste lithium iron phosphate positive electrode materials and a lithium iron phosphate finished product. The surface of the red powder material is etched with an organic acid to promote the secondary uniform distribution of the surface elements after leaching, thereby achieving a melting effect and preparing a low specific surface area lithium iron phosphate finished material with good processing performance and excellent electrochemical performance.

[0006] The object of the present invention is achieved by: a method for recovering and repairing waste lithium iron phosphate positive electrode materials, comprising the following steps: Step 1, sintering the waste lithium iron phosphate positive electrode sheet, grinding it into powder and sieving it to obtain red powder material; Step 2, determining the molar ratio of each element in the red powder material, premixing the red powder material, carbon source, organic acid and supplementary lithium source in an aqueous solution and then performing sand milling; Step 3: spray granulate the sand-milled material, calcine it at high temperature, and sieve it after cooling to obtain the target product.

[0007] Furthermore, in step 1, the sintering temperature of the waste lithium iron phosphate positive electrode sheet is 400-800° C., the sintering time is 4-10 hours, and the sintering atmosphere is air.

[0008] Furthermore, the red powder material obtained in step 1 is Fe2O3 and Li3Fe2(PO4)3.

[0009] Furthermore, the carbon source in step 2 is one or more of polyethylene glycol, glucose and sucrose, and the amount of the carbon source is 3wt% to 15wt% of the red powder.

[0010] Furthermore, the organic acid in step 2 is one or more of oxalic acid, citric acid, tartaric acid, acetic acid, and malic acid, wherein the amount of the organic acid is 1wt% to 5wt% of the red powder.

[0011] Furthermore, the supplementary lithium source in step 2 is one or both of lithium carbonate and lithium hydroxide. After the lithium source is supplemented, the molar ratio of lithium element to phosphorus element in the whole material is (1.0-1.1):1.

[0012] Furthermore, in the step 2, the solid content of each raw material premixed in the aqueous solution is 30% to 70%, the sand-milled particle size D50 is 0.2 to 1 μm, and the powder is obtained by spray granulation after sand-milling.

[0013] Furthermore, in step 3, the powder obtained by spray granulation is calcined at a high temperature, with a sintering temperature of 600-800° C. and a sintering time of 2-10 hours. After cooling, the powder is sieved to obtain the target product.

[0014] A lithium iron phosphate positive electrode product is prepared by the waste lithium iron phosphate positive electrode material recovery and repair method.

[0015] The beneficial effects of the present invention are: (1) The innovative use of organic acid as an additive can etch the surface of the red powder material, promote the secondary uniform distribution of surface elements after leaching, and have a melting effect, thereby optimizing the material surface area and morphology and improving the electrochemical performance of the material; (2) The recycling and repair process is simple, highly operable, green and pollution-free throughout, and has high economic and environmental value. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0017] Figure 1 This is a SEM image of the lithium iron phosphate sintered material obtained in Example 1 of the present invention.

[0018] Figure 2 This is a SEM image of the lithium iron phosphate sintered material obtained in Example 6 of the present invention. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with the accompanying drawings.

[0020] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in 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.

[0022] A method for recycling and repairing waste lithium iron phosphate positive electrode materials of the present invention comprises the following steps: Step 1, sintering the waste lithium iron phosphate positive electrode sheet, grinding it into powder and sieving it to obtain red powder material; Step 2, determining the molar ratio of each element in the red powder material, premixing the red powder material, carbon source, organic acid and supplementary lithium source in an aqueous solution and then performing sand milling; Step 3: spray granulate the sand-milled material, calcine it at high temperature, and sieve it after cooling to obtain the target product.

[0023] Furthermore, in one embodiment, the sintering temperature of the waste lithium iron phosphate positive electrode sheet in step 1 is 400-800° C., the sintering time is 4-10 hours, and the sintering atmosphere is air.

[0024] Furthermore, in one embodiment, the red powder material obtained in step 1 is Fe2O3 and Li3Fe2(PO4)3.

[0025] Furthermore, in one embodiment, the carbon source in step 2 is one or more of polyethylene glycol, glucose and sucrose, and the amount of the carbon source is 3wt% to 15wt% of the red powder.

[0026] Furthermore, in one embodiment, the organic acid in step 2 is one or more of oxalic acid, citric acid, tartaric acid, acetic acid, and malic acid, wherein the amount of the organic acid is 1wt% to 5wt% of the red powder.

[0027] Furthermore, in one embodiment, the supplementary lithium source in step 2 is one or both of lithium carbonate and lithium hydroxide. After the supplementary lithium source, the molar ratio of lithium element to phosphorus element in the whole material is (1.0-1.1):1.

[0028] Furthermore, in one embodiment, the solid content of the raw materials premixed in the aqueous solution in step 2 is 30% to 70%, the sand-milled particle size D50 is 0.2 to 0.5 μm, and the powder is obtained by spray granulation after sand-milling.

[0029] Furthermore, in one embodiment, the powder obtained by spray granulation in step 3 is calcined at a high temperature, with a sintering temperature of 600-800° C. and a sintering time of 2-10 hours, and then sieved after cooling to obtain the target product.

[0030] A lithium iron phosphate positive electrode product is prepared by the waste lithium iron phosphate positive electrode material recovery and repair method.

[0031] The following are specific embodiments. Example

[0032] (1) The waste lithium iron phosphate positive electrode sheet obtained from the dismantling of the battery is sintered at 500°C in air for 7 hours. After cooling, the red powder material falling off the aluminum foil is put into a wall breaking machine for powdering, and then passed through a 100-mesh sieve to obtain the red powder material; (2) Determine the molar ratio of each element in the red powder material, take the red powder material, 5wt% polyethylene glycol, 6wt% glucose, 2wt% oxalic acid and supplement lithium carbonate: after supplementing lithium carbonate, the molar ratio of lithium element to phosphorus element in the whole material is Li:P=1.03, add it into pure water, prepare a mixed solution with a solid content of 40%, stir for 30 minutes and then sand grind it until the slurry particle size D50 is 0.3μm; (3) The sand-milled slurry was transferred to a spray dryer for spray granulation. The powder obtained by spraying was transferred to a box furnace and sintered at 700°C for 5 h under nitrogen protection. After cooling, the material was crushed to a particle size D50 of 1 μm using a jet crusher, and the target product was obtained by passing through a 150-mesh sieve. Example

[0033] The only difference from Example 1 is that the amount of oxalic acid added is reduced to 1 wt %. Example

[0034] The only difference from Example 1 is that the amount of oxalic acid added is increased to 5 wt %. Example

[0035] The only difference from Example 1 is that oxalic acid is replaced by citric acid. Example

[0036] The only difference from Example 1 is that oxalic acid is replaced by inorganic hydrochloric acid, and the hydrogen ion is equivalent to 2 wt % oxalic acid. Example

[0037] The only difference from Example 1 is that no acid is added.

[0038] The positive electrode material prepared in the example was used as the positive electrode, the metal lithium sheet was used as the negative electrode, and a button cell was assembled to conduct an electrochemical performance test (test voltage range 2.0-3.75V, ambient temperature 25°C). In addition, the lithium iron phosphate finished material obtained in the example was subjected to a comparative table test, and the test results are shown in Table 1.

[0039] Table 1 shows the electrochemical properties of the positive electrode materials prepared in the examples. Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Specific surface area (m2 / g) 11.5 16.3 9.7 10.7 18.3 22.2 0.1C discharge specific capacity (mAh / g) 161.4 157.6 155.0 160.9 138.6 144.8 0.5C discharge specific capacity (mAh / g) 155.1 151.3 153.1 154.8 128.0 134.3 1C discharge specific capacity (mAh / g) 145.0 141.1 141.9 144.5 119.7 126.3 As can be seen from Table 1, in the case of using oxalic acid in Example 1 of the present invention, the lithium iron phosphate finished material obtained has a smaller specific surface area, which is more conducive to improving its processing performance; secondly, the specific capacity of the charge-off is higher, and even at a large rate of 1C, it can still exert a higher specific discharge capacity. In Examples 2 and 3, when too little or too much oxalic acid is used, the specific surface area and charge-off performance of the lithium iron phosphate finished material obtained are improved compared to Example 6 without using any acid, but the effect is discounted. In Example 4, when oxalic acid is adjusted to citric acid, the specific surface area and charge-off performance of the lithium iron phosphate finished material obtained are also significantly improved. . However, in Example 5, after adjusting oxalic acid to inorganic hydrochloric acid, the lithium iron phosphate finished material obtained has a weak improvement in the specific surface area, and the charge-off performance is significantly worse. Secondly, it can be seen from the electron microscope that the material obtained in Example 6 without adding any acid cannot promote the fusion growth between particles, and the primary particles are finer and smaller. Therefore, it can be explained that in the process of repairing waste lithium iron phosphate, the use of organic acid additives such as oxalic acid or citric acid can etch the surface of the red powder material, achieve a melting effect, and make the repaired lithium iron phosphate product smaller than the surface. Secondly, the secondary uniform distribution of surface elements effectively improves the electrochemical performance of the material.

[0040] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0041] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for recycling and repairing waste lithium iron phosphate positive electrode materials, characterized in that: The following steps are involved: Step 1, sintering the waste lithium iron phosphate positive electrode sheet, grinding it into powder and sieving it to obtain red powder material; Step 2, determining the molar ratio of each element in the red powder material, premixing the red powder material, carbon source, organic acid and supplementary lithium source in an aqueous solution and then performing sand milling; Step 3: spray granulate the sand-milled material, calcine it at high temperature, and sieve it after cooling to obtain the target product.

2. A method for recycling and repairing waste lithium iron phosphate positive electrode materials as claimed in claim 1, characterized in that: In the step 1, the sintering temperature of the waste lithium iron phosphate positive electrode sheet is 400-800° C., the sintering time is 4-10 hours, and the sintering atmosphere is air.

3. A method for recycling and repairing waste lithium iron phosphate positive electrode materials as claimed in claim 1, characterized in that: The red powder material obtained in step 1 is Fe2O3 and Li3Fe2(PO4)3.

4. A method for recycling and repairing waste lithium iron phosphate positive electrode materials as claimed in claim 1, characterized in that: The carbon source in step 2 is one or more of polyethylene glycol, glucose and sucrose, and the amount of the carbon source is 3wt% to 15wt% of the red powder.

5. A method for recycling and repairing waste lithium iron phosphate positive electrode materials as claimed in claim 1, characterized in that: The organic acid in step 2 is one or more of oxalic acid, citric acid, tartaric acid, acetic acid and malic acid, wherein the amount of the organic acid is 1wt% to 5wt% of the red powder.

6. A method for recycling and repairing waste lithium iron phosphate positive electrode materials as claimed in claim 1, characterized in that: The supplementary lithium source in step 2 is one or both of lithium carbonate and lithium hydroxide. After the lithium source is supplemented, the molar ratio of lithium element to phosphorus element in the whole material is (1.0-1.1):

1.

7. A method for recycling and repairing waste lithium iron phosphate positive electrode materials as claimed in claim 1, characterized in that: In the step 2, the solid content of each raw material premixed in the aqueous solution is 30% to 70%, the sand-milled particle size D50 is 0.2 to 0.5 μm, and the powder is obtained by spray granulation after sand-milling.

8. A method for recycling and repairing waste lithium iron phosphate positive electrode materials as claimed in claim 1, characterized in that: In the step 3, the powder obtained by spray granulation is calcined at a high temperature, the sintering temperature is 600-800° C., the sintering time is 2-10 hours, and after cooling, the powder is sieved to obtain the target product.

9. A finished lithium iron phosphate positive electrode product, which is prepared by the method for recycling and repairing waste lithium iron phosphate positive electrode materials according to any one of claims 1 to 8.

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