A method for regenerating FePO4.2H2O from waste lithium iron phosphate

Abstract

The application discloses a method for regenerating FePO4.2H2O from waste lithium iron phosphate, and belongs to the field of recycling of lithium battery materials, and comprises the following steps: 1) discharging, disassembling, peeling off active material and crushing a waste lithium iron phosphate battery to obtain waste lithium iron phosphate powder, mixing the waste lithium iron phosphate powder with an acid solution to perform leaching reaction, and filtering to obtain a leaching solution; 2) adding an oxidizing agent to the leaching solution obtained in the step 1) to perform oxidation reaction; 3) heating the product obtained in the step 2) to perform crystallization reaction, and after the reaction is completed, filtering out the solid product to perform washing and drying, thereby obtaining FePO4.2H2O; the application is directed to leaching of all components of the waste lithium iron phosphate, and a high-performance FePO4.2H2O is directly regenerated and prepared by abandoning a traditional pH regulating step and starting from a strong-acid whole leaching solution; the prepared FePO4.2H2O has a nanosheet morphology of agglomeration into a spherical shape, and the washing and filtering speed is fast, which is beneficial to preparation of a LiFePO4 / C material with excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium battery recycling, and particularly relates to a method for regenerating FePO4·2H2O from waste lithium iron phosphate. BACKGROUND

[0002] In recent years, lithium iron phosphate batteries have occupied a considerable share in the lithium-ion power battery and energy storage market due to their low cost, high safety, excellent thermal stability, and excellent cycle performance, and have developed rapidly. With the increasing demand for lithium iron phosphate batteries, the number of waste lithium iron phosphate batteries has also increased rapidly. Recycling and processing waste lithium iron phosphate batteries not only can avoid environmental pollution caused by toxic substances and metal ions in the batteries, but also can recycle and utilize lithium, iron, phosphorus and other elements in the batteries, thus having good economic benefits. Therefore, it is of great significance to develop an efficient recycling and resource regeneration method for waste lithium iron phosphate cathode materials.

[0003] At present, the main process for recycling waste lithium iron phosphate cathode materials is hydrometallurgical separation process. The target elements are transferred to the solution by leaching agent (such as strong acid), and then separated and recovered by liquid phase precipitation method or extraction method. According to the different target elements, the leaching process can be divided into selective leaching of only Li element and full element component leaching of Li, Fe, P and O elements. The selective leaching process can selectively leach the lithium element with relatively high economic value under weak acid or even no acid conditions by adding an oxidizing agent, which is the mainstream idea for industrial recycling of waste lithium iron phosphate materials in recent years. However, this process will produce FePO4 / C residues which are difficult to recycle. The full component leaching process can dissolve Li, Fe, P and O elements in waste lithium iron phosphate materials in a strong acid environment, and then introduce an oxidizing agent and adjust the pH value to realize the step-by-step separation of each element. Although the process flow is relatively complex, it can realize the full component recovery and efficient resource regeneration of valuable elements, and is a relatively complete method for recycling waste lithium phosphate iron.

[0004] In the full component leaching process, in order to ensure the high leaching efficiency of Li and Fe elements, an excess of acid is introduced, and then a strong acidity (pH<1) leaching solution is obtained. Then a large amount of alkaline precipitant (such as NH3·H2O or NaOH) is added to the leaching solution to adjust the system pH≈2 (referred to as H-pH) to ensure a high iron and phosphorus precipitation rate. Finally, the obtained slurry is filtered, washed, beaten, the iron and phosphorus ratio is adjusted, and the temperature is crystallized to obtain FePO4·2H2O. This process flow is not only complex, but also introduces additional NH4 + and Na +, which increases the difficulty of subsequent separation and purification steps of FePO4·2H2O and Li elements, and affects the purity of the product. SUMMARY

[0005] The present application aims to provide a method for recycling FePO4·2H2O from waste lithium iron phosphate, which solves the problems of complex process flow, high difficulty of subsequent separation and purification, etc.

[0006] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0007] A method for recycling FePO4·2H2O from waste lithium iron phosphate, comprising the following steps:

[0008] 1) Discharge, disassemble, peel off the active material, and crush the waste lithium iron phosphate battery to obtain waste lithium iron phosphate powder, then mix the waste lithium iron phosphate powder with an acid solution to perform leaching reaction, and filter to obtain a leaching solution;

[0009] 2) Add an oxidizing agent to the leaching solution obtained in step 1) to oxidize divalent iron in the leaching solution to trivalent iron;

[0010] 3) Heat the product obtained in step 2) to perform crystallization reaction, after the reaction is completed, filter out the solid product to perform washing and drying, thereby obtaining FePO4·2H2O.

[0011] Preferably, the acid solution in step 1) is one or both of H2SO4 or H3PO4, the liquid-solid mass ratio of the acid solution to the waste lithium iron phosphate powder is 4-8:1, and the molar ratio of H + to Fe element in the waste lithium iron phosphate powder is 2-2.3:1.

[0012] Preferably, the leaching reaction temperature in step 1) is 25-70℃, the time is 60-180min, and the stirring rate is 0-1000r / min.

[0013] Preferably, the oxidizing agent in step 2) is one or more of oxygen, ozone, hydroxyl radical, or H2O2.

[0014] Preferably, step 2) further comprises a step of adding one or both of amorphous iron phosphate or FePO4·2H2O to the solution after the oxidation reaction, wherein the amorphous iron phosphate is uncrystallized iron phosphate prepared under the condition that the pH is 1.5-2.5.

[0015] Further preferably, the amount of amorphous iron phosphate or FePO4·2H2O and the solid-liquid mass ratio of the solution after the oxidation reaction is 1-200g:1000g.

[0016] Preferably, the oxidation reaction temperature in step 2) is 10-50℃, and the stirring rate is 0-1000r / min.

[0017] Preferably, the crystallization reaction temperature in step 3) is 80-95℃, the stirring rate is 0-1000r / min, and the reaction is ended after the reaction material changes from yellow brown to powder white.

[0018] Preferably, the drying temperature in step 3) is 60-80℃, and the drying time is 10-24h.

[0019] Preferably, step 3) further comprises that the crystallization product after the crystallization reaction is kept for 0.5-3h before filtration.

[0020] The present application has the following beneficial effects:

[0021] 1. The present application provides a method for regenerating FePO4·2H2O from waste lithium iron phosphate, which can directly regenerate FePO4·2H2O from the acid leaching solution of waste lithium iron phosphate through acid leaching, oxidation and temperature crystallization, without the traditional pH control step, avoiding the introduction of additional impurity ions, reducing the washing and impurity removal pressure in the subsequent separation and purification process, and the process is simple and easy to operate.

[0022] 2. The present application can significantly accelerate the crystallization process by introducing amorphous iron phosphate or FePO4·2H2O into the solution before crystallization; wherein the amorphous iron phosphate can continuously dissolve and expose new surfaces during the crystallization process, thereby providing a large number of nucleation sites for the crystallization process; and FePO4·2H2O can provide a large number of homologous nucleation sites with better affinity and lower nucleation energy, thereby accelerating the crystallization process.

[0023] 3. The present application regenerates FePO4·2H2O in a low pH system, so that the primary particle size of the prepared FePO4·2H2O is smaller than that of the FePO4·2H2O prepared in the traditional high pH system, and the tap density of the FePO4 prepared by using the FePO4·2H2O is also larger.

[0024] 4. The FePO4·2H2O prepared by the present application has a nanosheet morphology of agglomeration into spherical shape, good quality, high purity, small primary particle size, fast washing and filtering speed, and the LiFePO4 / C material prepared by using the FePO4·2H2O has small primary particle size, good wettability with electrolyte, many electrochemical reaction active sites, short diffusion distance of Li + and electron, high electrochemical rate and cycle performance. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1XRD patterns of the products at different time during the crystallization process in Example 1, Example 2, Example 3, Comparative Example 1;

[0026] Figure 2 pH values of the system and mass fractions of Fe element during the crystallization process in Example 1, Example 2, Example 3, and pH values of the system and precipitation rates of Fe element during the crystallization process in Comparative Example 1;

[0027] Figure 3 SEM images of the products at the end of the crystallization process in Example 1, Example 2, Example 3, Comparative Example 1;

[0028] Figure 4 High-resolution SEM image of FePO4·2H2O prepared in Example 1;

[0029] Figure 5 SEM images of FePO4 further prepared from the products of Example 1, Example 2, Example 3, Comparative Example 1;

[0030] Figure 6 SEM images of LiFePO4 / C finally prepared from the products of Example 1, Example 2, Example 3, Comparative Example 1;

[0031] Figure 7 Rate performance of LiFePO4 / C materials finally prepared from the products of Example 1, Example 2, Example 3, Comparative Example 1;

[0032] Figure 8 Cycle performance and corresponding Coulombic efficiency of LiFePO4 / C materials finally prepared from the products of Example 1, Example 2, Example 3, Comparative Example 1. DETAILED DESCRIPTION

[0033] It is necessary to point out that the following examples are only used to further illustrate the present application and cannot be understood as limiting the scope of the present application, and those skilled in the art can make some non-essential improvements and adjustments to the present application according to the above content of the present application. In the following examples, reagents and instruments not specifically mentioned can be commercially available, and experimental operations not specifically mentioned are implemented according to the manufacturer's instructions or conventional techniques in the art, unless otherwise defined, all professional and scientific terms used herein have the same meaning as familiar to those skilled in the art. In addition, any method and material similar or equivalent to the described content can be applied in the present application.

[0034] The present application provides a method for regenerating FePO4·2H2O from waste lithium iron phosphate, comprising the following steps:

[0035] 1) discharging, disassembling, stripping active material and crushing the waste lithium iron phosphate battery to obtain waste lithium iron phosphate powder, and then mixing the waste lithium iron phosphate powder with an acid solution to perform leaching reaction, and filtering to obtain leaching liquor;

[0036] 2) adding an oxidizing agent to the leaching liquor obtained in step 1) to perform oxidation reaction, and oxidizing divalent iron in the leaching liquor into trivalent iron;

[0037] 3) heating the product obtained in step 2) to perform crystallization reaction, and ending the reaction after the reaction substance changes from yellow brown to powder white, filtering out the solid product to perform washing and drying, thereby obtaining FePO4·2H2O.

[0038] In some preferred embodiments of the present application, the acid solution in step 1) is H2SO4 or H3PO4, the liquid-solid mass ratio of the acid solution to the waste lithium iron phosphate powder is 4-8:1, and the molar ratio of H + to Fe element in the waste lithium iron phosphate powder is 2-2.3:1. Among them, the molar ratio of H + to Fe element in the waste lithium iron phosphate powder can also be 2.1:1, 2.2:1, and the liquid-solid mass ratio of the acid solution to the waste lithium iron phosphate powder can also be 5:1, 6:1, 7:1.

[0039] In some preferred embodiments of the present application, the leaching reaction temperature in step 1) is 25-70℃, the reaction time is 60-180min, and the stirring rate is 0-1000r / min. The leaching reaction temperature can also be 40℃, 55℃, the reaction time can also be 70min, 80min, 90min, 100min, 110min, 120min, 130min, 140min, 150min, 160min, 170min, and the stirring rate can also be 100r / min, 200r / min, 300r / min, 400r / min, 500r / min, 600r / min, 700r / min, 800r / min, 900r / min.

[0040] In some preferred embodiments of the present application, step 2) further comprises a step of adding one or both of amorphous iron phosphate or FePO4·2H2O to the solution after the oxidation reaction, wherein the amorphous iron phosphate is iron phosphate that has not been crystallized and is prepared under the condition that the pH is 1.5-2.5.

[0041] In some preferred embodiments of the present application, the oxidizing agent in step 2) is one or more of oxygen, ozone, hydroxyl radical or H2O2, preferably H2O2 solution. The molar ratio of H2O2 in the H2O2 solution to Fe in the leaching solution is 0.5-1.5:1. The molar ratio of H2O2 in the H2O2 solution to Fe in the leaching solution can also be 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1.

[0042] In some preferred embodiments of the present application, the oxidation reaction temperature in step 2) is 10-50°C, and the stirring rate is 0-1000 r / min. The oxidation reaction temperature can also be 20°C, 30°C, 40°C. The stirring rate when adding can also be 100 r / min, 200 r / min, 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min, 900 r / min.

[0043] In some preferred embodiments of the present application, the crystallization reaction temperature in step 3) is 80-95°C, the stirring rate is 0-1000 r / min, the drying temperature is 60-80°C, and the drying time is 10-24 h. The crystallization reaction temperature can also be 85°C, 90°C. The stirring rate can also be 100 r / min, 200 r / min, 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min, 900 r / min. The holding time can also be 1 h, 1.5 h, 2 h, 2.5 h. The drying temperature can also be 65°C, 70°C, 75°C. The drying time can also be 12 h, 14 h, 16 h, 18 h, 20 h, 22 h.

[0044] In some preferred embodiments of the present application, step 3) further comprises holding the crystallization product after the crystallization reaction is completed for 0.5-3 h before filtering. The holding time can also be 1 h, 1.5 h, 2 h, 2.5 h. The benefit of holding is to make the reaction more complete, because as the concentration of Fe 3+ , PO4 3- in the solution decreases, the generation rate of FePO4·2H2O will decrease, so when the crystallization process is basically completed (the slurry changes from yellow brown to uniform white powder), there is still a small amount of Fe 3+ , PO4 3- unreacted in the system. The purpose of holding is to make the reaction as complete as possible and make the precipitation rate of Fe element approach the limit as much as possible.

[0045] The following are specific embodiments:

[0046] Example 1

[0047] 1) First, the waste lithium iron phosphate battery is discharged, the waste lithium iron phosphate positive plate is disassembled, the aluminum foil is further peeled off, and the waste lithium iron phosphate powder is obtained by crushing.

[0048] 2) The waste lithium iron phosphate powder is mixed with H2SO4 solution according to nH + : nFe = 2.2:1, the liquid-solid mass ratio is 6:1, the stirring speed is 600r / min, the reaction time is 120min, and the leaching solution is obtained by filtering;

[0049] 3) Under the condition of temperature 30℃, the stirring speed is 600r / min, H2O2 is added to the leaching solution obtained in step 1), and the molar ratio of H2O2 in H2O2 solution to Fe in leaching solution is 0.7:1;

[0050] 4) The product obtained in step 2) is subjected to temperature crystallization reaction under the condition of temperature 95℃ and stirring speed 600r / min. After the slurry changes from yellow brown to powder white, it is kept for 1h, filtered, washed, and dried in a 60℃ air drying oven for 24h to obtain the target product FePO4·2H2O, which is marked as L1-FePO4·2H2O.

[0051] Example 2

[0052] 1) First, the waste lithium iron phosphate battery is discharged, the waste lithium iron phosphate positive plate is disassembled, the aluminum foil is further peeled off, and the waste lithium iron phosphate powder is obtained by crushing.

[0053] 2) The waste lithium iron phosphate powder is mixed with H2SO4 solution according to nH + : nFe = 2.2:1, the liquid-solid mass ratio is 6:1, the stirring speed is 600r / min, the reaction time is 120min, and the leaching solution is obtained by filtering;

[0054] 3) Under the condition of temperature 30℃, the stirring speed is 600r / min, H2O2 is added to the leaching solution obtained in step 1), and the molar ratio of H2O2 in H2O2 solution to Fe in leaching solution is 0.7:1;

[0055] 4) The product obtained in step 2) is subjected to a temperature crystallization reaction at a temperature of 95 DEG C and a stirring rate of 600 r / min. After the slurry changes from yellow brown to powder white, it is kept for 1 h, filtered, washed, and placed in a 60 DEG C air drying oven for drying for 24 h to obtain the target product FePO4.2H2O, which is marked as L2-FePO4.2H2O.

[0056] Example 3

[0057] 1) First, the waste lithium iron phosphate battery is discharged, and the waste lithium iron phosphate positive plate is disassembled. The aluminum foil is further peeled off, and the waste lithium iron phosphate powder is obtained by crushing.

[0058] 2) The waste lithium iron phosphate powder is mixed with an H2SO4 solution in a nH + : nFe = 2.2:1, and a liquid-solid mass ratio of 6:1. The mixture is stirred at a temperature of 25 DEG C and a stirring rate of 600 r / min for 120 min, and the leaching solution is obtained by filtration.

[0059] 3) At a temperature of 30 DEG C and a stirring rate of 600 r / min, H2O2 is added to the leaching solution obtained in step 1). After the oxidation reaction is completed, amorphous iron phosphate is added to the solution in a solid-liquid mass ratio of 100 g / 1000 g, and the molar ratio of H2O2 in the H2O2 solution to Fe in the leaching solution is 0.7:1.

[0060] 4) The product obtained in step 2) is subjected to a temperature crystallization reaction at a temperature of 95 DEG C and a stirring rate of 600 r / min. After the slurry changes from yellow brown to powder white, it is kept for 1 h, filtered, washed, and placed in a 60 DEG C air drying oven for drying for 24 h to obtain the target product FePO4.2H2O, which is marked as L3-FePO4.2H2O.

[0061] Comparative Example 1

[0062] 1) First, the waste lithium iron phosphate battery is discharged, and the waste lithium iron phosphate positive plate is disassembled. The aluminum foil is further peeled off, and the waste lithium iron phosphate powder is obtained by crushing.

[0063] 2) The waste lithium iron phosphate powder is mixed with an H2SO4 solution in a nH + : nFe = 2.2:1, and a liquid-solid mass ratio of 6:1. The mixture is stirred at a temperature of 25 DEG C and a stirring rate of 600 r / min for 120 min, and the leaching solution is obtained by filtration.

[0064] 3) At a temperature of 30℃, add H2O2 to the leachate obtained in step 1) at a stirring rate of 600r / min, wherein the molar ratio of H2O2 in the H2O2 solution to Fe in the leachate is 0.7:1;

[0065] 4) Add NH3·H2O or NaOH solution to the solution obtained in step 2) while stirring at a stirring rate of 600 r / min to adjust the pH of the system to 2. After the pH of the system stabilizes, filter, wash, and then mix the filter cake with an appropriate amount of deionized water to obtain a certain amount of amorphous iron phosphate mixed slurry.

[0066] 5) The mixed slurry obtained in step 3) is subjected to a crystallization reaction at a temperature of 95℃ and a stirring rate of 600r / min. After the slurry changes from yellow-brown to pinkish-white, it is kept at this temperature for 1 hour, filtered, washed, and dried in a 60℃ forced-air drying oven for 24 hours to obtain the target product FePO4·2H2O, which is labeled as H1-FePO4·2H2O.

[0067] It should be noted that the mass fraction of Fe in the pre-crystallization mixture systems of Examples 1, 2, 3, and Comparative Example 1 was 3.75%.

[0068] Experimental Example 1

[0069] X-ray powder diffraction was performed on the products from different crystallization times of Examples 1, 2, 3, and Comparative Example 1. The results are as follows: Figure 1 As shown, the moment marked by the five-pointed star pattern is the moment when the reaction slurry completely changes from brownish-yellow to uniform pinkish-white, which is the moment when the crystallization reaction is basically over.

[0070] Depend on Figure 1 Analysis shows that: a. The XRD patterns of the final products of Examples 1, 2, and 3 after heat preservation for 1 hour all correspond well with FePO4·2H2O (PDF#72-0471) and there are no impurity peaks, indicating that the preparation method of the present invention can obtain high-quality FePO4·2H2O.

[0071] b. The crystallization process in Example 1 basically ended in 110 min, while the crystallization processes in Examples 2 and 3 were shortened to 60 min and 70 min respectively, indicating that introducing a certain amount of amorphous iron phosphate or FePO4·2H2O into the solution before crystallization can significantly accelerate the crystallization process.

[0072] Experiment Example 2

[0073] The filtrates from Examples 1, 2, 3, and Comparative Example 1 at different times during crystallization were taken, and their pH values ​​and the mass fraction of Fe were measured. Simultaneously, the precipitation rate of Fe in Comparative Example 1 was calculated based on the mass fraction of Fe. The results are as follows: Figure 2 As shown.

[0074] Depend on Figure 2 Analysis shows that the pH value and the mass fraction of Fe in the systems of Examples 1, 2, and 3 reached their lowest levels at 110 min, 60 min, and 70 min, respectively. Figure 1 The results from the XRD further demonstrate that introducing a certain amount of amorphous iron phosphate or FePO4·2H2O into the system can significantly accelerate the crystallization process. Furthermore, the pH value and the mass fraction of Fe in the systems of Examples 1, 2, and 3 are similar at the same stage, indicating that the addition of amorphous iron phosphate or FePO4·2H2O does not affect the system environment during the FePO4·2H2O formation process, nor does it reduce the originally high precipitation rate of Fe in the system.

[0075] In Comparative Example 1, due to the relatively high pH, ​​the solubility of both amorphous iron phosphate and FePO4·2H2O is very low. Figure 2 It is evident that the precipitation rate of Fe in the filtrate of Comparative Example 1 remained at a very high level.

[0076] Experimental Example 3

[0077] Scanning electron microscopy (SEM) was performed on the products obtained in Examples 1, 2, 3, and Comparative Example 1 at the point where the crystallization process was essentially complete. The results are shown in Figure 3. High-resolution SEM was performed on the FePO4·2H2O prepared in Example 1. The test results are shown in Figure 3. Figure 4 As shown.

[0078] Depend on Figure 3 Analysis shows that the FePO4·2H2O obtained in Examples 1, 2, and 3 have similar morphologies, all agglomerated into spherical nanosheets with similar sizes. This indicates that introducing an appropriate amount of amorphous iron phosphate or FePO4·2H2O into the system does not affect the morphology of the final product. However, the FePO4·2H2O obtained in Comparative Example 1 has a dispersed nanosheet morphology. The main reason for the above morphological differences is the different pH values ​​of the systems, which cause different morphologies of amorphous iron phosphate in the systems, ultimately resulting in different morphologies of FePO4·2H2O that grows from it.

[0079] Depend on Figure 4The analysis shows that the primary particles of L1-FePO4·2H2O are small particles with a particle size of about 30-50 nm, which further form nanosheet with a length of 100-200 nm and a width of 30-50 nm, and the nanosheet is stacked and crosslinked to form the final agglomerated spherical morphology; it is shown that the primary particle size of FePO4·2H2O obtained by direct regeneration in the low-pH system proposed in the application is very small, which will be beneficial to improve the performance of the LiFePO4 / C material finally prepared.

[0080] Experimental Example 4

[0081] The FePO4·2H2O obtained in Example 1, Example 2, Example 3 and Comparative Example 1 is placed in a 600°C muffle furnace for calcination for 2h to obtain the product FePO4, which is marked as L1-FePO4, L2-FePO4, L3-FePO4 and H1-FePO4 respectively, and the obtained product is subjected to scanning electron microscope test, as shown in FIG. 1. Figure 5

[0082] It is shown from the analysis of FIG. 1 that the morphology of the product obtained by removing the crystal water from Example 1, Example 2 and Example 3 does not change obviously, i.e. L1-FePO4, L2-FePO4 and L3-FePO4 still show the morphology of agglomerated nanosheet-like spherical shape, while the product H1-FePO4 obtained in Comparative Example 1 shows the morphology of dispersed nanosheet, and compared with H1-FePO4, the size of the nanosheet of L1-FePO4, L2-FePO4 and L3-FePO4 is smaller, which shows that the primary particle size of FePO4·2H2O prepared in the low-pH system according to the application is smaller, which will be beneficial to the subsequent preparation of LiFePO4 / C material with smaller primary particle size.

[0083] Experimental Example 5

[0084] The L1-FePO4, L2-FePO4, L3-FePO4 and H1-FePO4 prepared in Experimental Example 4 are placed in a tap density tester for tap density test, and the results are shown in Table 1 below.

[0085] It is shown from Table 1 that the tap densities of L1-FePO4, L2-FePO4, L3-FePO4 and H1-FePO4 are 0.83, 1.101, 0.935 and 0.541 g·cm -3 ​Compared to FePO4 prepared under the traditional high-pH process (pH≈2), the FePO4 prepared under the low-pH process provided by this invention has a higher tap density, indicating that the product prepared according to the preparation method proposed in this invention has better performance. At the same time, compared to L1-FePO4, L2-FePO4 and L3-FePO4 have higher tap densities, which indicates that the addition of amorphous iron phosphate or FePO4·2H2O can increase the tap density of the subsequent FePO4 product. In Example 2, FePO4·2H2O will further grow on the surface and in the gaps of the spherical FePO4·2H2O introduced, resulting in an increased degree of aggregation of the final product and thus an increased tap density. In Example 3, the density of amorphous iron phosphate during crystallization was increased, which also improved the density of FePO4·2H2O formed by it.

[0086] Experimental Example 6

[0087] The L1-FePO4, L2-FePO4, L3-FePO4, and H1-FePO4 prepared in Experimental Example 4 above were reacted with a certain amount of Li2CO3 and C6H4, respectively. 12 O6 was milled in a sand mill for 4 hours (Li excess 2%, theoretical carbon content of the final product is 2%), then spray-dried, and the resulting dry material was placed in a tube furnace and calcined at 700℃ for 8 hours in an Ar atmosphere. After cooling, the target LiFePO4 / C materials were obtained, labeled as L1-LiFePO4 / C, L2-LiFePO4 / C, L3-LiFePO4 / C, and H1-LiFePO4 / C, respectively. Scanning electron microscopy (SEM) was performed on each material, and the results are as follows: Figure 6 As shown.

[0088] Depend on Figure 6 Analysis shows that the primary particle sizes of L1-LiFePO4 / C, L2-LiFePO4 / C, and L3-LiFePO4 / C materials are similar, roughly in the range of 200-400 nm, while the primary particle size of H1-LiFePO4 / C material is significantly larger, roughly in the range of 400-600 nm. This indicates that compared to the traditional high-pH process, the process provided by this invention for directly regenerating FePO4·2H2O from the strongly acidic waste lithium iron phosphate full-component leachate is more conducive to preparing LiFePO4 / C materials with smaller primary particles.

[0089] Experimental Example 7

[0090] The L1-LiFePO4 / C, L2-LiFePO4 / C, L3-LiFePO4 / C, and H1-LiFePO4 / C prepared in Experimental Example 6 were assembled into 2032 coin cells, and the performance of the cells was tested.

[0091] 1. Fabrication of 2032 coin cells:

[0092] The above-mentioned LiFePO4 / C material was used as the active material, acetylene black as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder. The active material, conductive agent, and binder were placed in a 5 mL vial at a mass ratio of 8:1:1. Then, 0.5 mL of N-methylpyrrolidone (NMP) was added dropwise and stirred for 4 hours to form a slurry. The slurry was evenly coated onto carbon-coated aluminum foil and then placed in a constant temperature drying oven at 80°C for 12 hours. After drying to constant weight, a small disc with a diameter of 12 mm was punched out using a punching machine, which became the positive electrode. Under the condition of ensuring no water, the small disc was placed in a glove box filled with argon gas. Lithium foil was used as the counter electrode and reference electrode, polypropylene film was used as the separator, and the electrolyte was 1M LiPF6 / EC+EMC+DMC (volume ratio 1:1:1). Finally, the CR2032 coin cell was assembled in the glove box.

[0093] The corresponding batteries for Example 1, Example 2, Example 3, and Comparative Example 1 are L1-LFP, L2-LFP, L3-LFP, and H1-LFP, respectively.

[0094] 2. Performance Testing and Results:

[0095] (1) L1-LFP, L2-LFP, L3-LFP, and H1-LFP were subjected to constant current charge-discharge tests at room temperature with current densities of 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, and 10C, respectively. The results are as follows: Figure 7 As shown.

[0096] Depend on Figure 7 Analysis shows that, compared to H1-LFP, L1-LFP, L2-LFP, and L3-LFP exhibit superior rate performance, achieving current densities of 115.6, 117.2, and 114.8 mAh·g, respectively, at 10C. -1 The discharge specific capacity is higher, while the discharge capacity of H1-LFP at a current density of 10C is only 103.8 mAh·g. -1 This indicates that, compared to the traditional high-pH process, the LiFePO4 / C material prepared by the low-pH process provided by this invention has superior rate performance.

[0097] (2) L1-LFP, L2-LFP, L3-LFP, and H1-LFP were first activated by performing 3 cycles of constant current charge-discharge test at a current density of 0.1C at room temperature. Then, they were subjected to 300 cycles of constant current charge-discharge test at a current density of 2C. The results are as follows. Figure 8 As shown.

[0098] By Figure 8 Analysis shows that after 300 cycles at a current density of 2C, L1, L2, L3-LFP can still release 138.8, 137.2 and 134.5 mAh·g -1 respectively, and the corresponding capacity retention rates are 96.5%, 95.2% and 95.3% respectively; while H1-LFP can only maintain a discharge specific capacity of 118.5 mAh·g -1 after 300 cycles at a current density of 2C, and the corresponding capacity retention rate is only 87.4%. It shows that compared with the traditional high-pH process, the LiFePO4 / C material prepared by the low-pH process provided by the application has better cycle performance.

[0099] In summary, compared with the traditional high-pH process, the LiFePO4 / C product prepared by the method for directly regenerating FePO4·2H2O from the strong acid waste lithium iron phosphate full-component leaching solution provided by the application has better electrochemical rate and cycle performance; the main reason is that the primary particle size of FePO4·2H2O that can exist stably in a low-pH system (pH<1) is smaller, so that the primary particle size of the subsequently prepared LiFePO4 / C is smaller, which makes the material have better wettability with electrolyte, more electrochemical reaction active sites, shorter diffusion distance of Li + and electrons, and finally better electrochemical performance of the material.

[0100] Table 1 Related parameters of Example 1, Example 2, Example 3, Comparative Example 1

[0101]

[0102] It should be noted that the above only describes the preferred embodiments of the application, and does not limit the application too much. Although the application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still make some simple deductions, substitutions or equivalent replacements of part of the technical features of the foregoing embodiments without departing from the concept of the application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the application should be included in the protection scope of the application.

Claims

1. A method for regenerating FeP04-2H20 from spent lithium iron phosphate, characterized by, The method comprises the following steps: 1) discharging, disassembling, stripping active material and crushing the waste lithium iron phosphate battery to obtain waste lithium iron phosphate powder, mixing the waste lithium iron phosphate powder with an acid solution to perform leaching reaction, and filtering to obtain a leaching solution; 2) adding an oxidizing agent to the leaching solution obtained in step 1) to perform oxidation reaction, so that the divalent iron in the leaching solution is oxidized into trivalent iron, and then adding amorphous iron phosphate to the solution after the oxidation reaction, the amorphous iron phosphate being uncrystallized iron phosphate prepared under the condition that the pH is 1.5-2.5; 3) heating the product obtained in step 2) to perform crystallization reaction, filtering the solid product after the reaction to perform washing and drying, thereby obtaining FePO4·2H2O.

2. The method for regenerating FeP04-2H20 from waste lithium iron phosphate according to claim 1, characterized in that: The acid solution in the step 1) is one or both of H2SO4 or H3PO4, the liquid-solid mass ratio of the acid solution to the waste lithium iron phosphate powder is 4-8:1, and the H + The molar ratio of the acid solution to the Fe element in the waste lithium iron phosphate powder is 2-2.3:

1.

3. The method of regenerating FeP04-2H20 from spent lithium iron phosphate according to claim 1, characterized in that: The leaching reaction in step 1) is performed at a temperature of 25-70℃ for 60-180 min at a stirring rate of 0-1000 r / min.

4. The method for regenerating FeP04-2H20 from waste lithium iron phosphate according to claim 1, characterized in that: The oxidizing agent in step 2) is one or more of oxygen, ozone, hydroxyl radical and H2O2.

5. The method of regenerating FeP04-2H20 from spent lithium iron phosphate according to claim 1, characterized in that: The amount of the amorphous iron phosphate and the solid-liquid mass ratio of the solution after the oxidation reaction is 1-200 g:1000 g.

6. The method of regenerating FeP04-2H20 from spent lithium iron phosphate according to claim 1, characterized in that: The oxidation reaction in step 2) is performed at a temperature of 10-50℃ at a stirring rate of 0-1000 r / min.

7. The method of regenerating FeP04-2H20 from spent lithium iron phosphate according to claim 1, characterized in that: The crystallization reaction in step 3) is performed at a temperature of 80-95℃ at a stirring rate of 0-1000 r / min, and the reaction is ended after the reaction substance changes from yellow brown to powder white.

8. The method for regenerating FeP04-2H20 from waste lithium iron phosphate according to claim 1, characterized in that: The drying temperature in step 3) is 60-80℃, and the drying time is 10-24 h.

9. The method for regenerating FePO4-2H2O from waste lithium iron phosphate according to claim 1, characterized in that: Step 3) further comprises that the crystallization product after the crystallization reaction is kept for 0.5-3 h before being filtered. The method comprises the following steps: 1) discharging, disassembling, stripping active material and crushing the waste lithium iron phosphate battery to obtain waste lithium iron phosphate powder, mixing the waste lithium iron phosphate powder with an acid solution to perform leaching reaction, and filtering to obtain a leaching solution; 2) adding an oxidizing agent to the leaching solution obtained in step 1) to perform oxidation reaction, so that the divalent iron in the leaching solution is oxidized into trivalent iron, and then adding amorphous iron phosphate to the solution after the oxidation reaction, the amorphous iron phosphate being uncrystallized iron phosphate prepared under the condition that the pH is 1.5-2.5; 3) heating the product obtained in step 2) to perform crystallization reaction, filtering the solid product after the reaction to perform washing and drying, thereby obtaining FePO4·2H2O. The leaching reaction in step 1) is performed at a temperature of 25-70℃ for 60-180 min at a stirring rate of 0-1000 r / min. The oxidizing agent in step 2) is one or more of oxygen, ozone, hydroxyl radical and H2O2. The amount of the amorphous iron phosphate and the solid-liquid mass ratio of the solution after the oxidation reaction is 1-200 g:1000 g. The oxidation reaction in step 2) is performed at a temperature of 10-50℃ at a stirring rate of 0-1000 r / min. The crystallization reaction in step 3) is performed at a temperature of 80-95℃ at a stirring rate of 0-1000 r / min, and the reaction is ended after the reaction substance changes from yellow brown to powder white. The drying temperature in step 3) is 60-80℃, and the drying time is 10-24 h. Step 3) further comprises that the crystallization product after the crystallization reaction is kept for 0.5-3 h before being filtered.

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