Regenerated lithium iron phosphate and a preparation method thereof
By heating, stirring, filtering, evaporating, crystallizing, and sintering waste lithium iron phosphate, porous regenerated lithium iron phosphate with low sulfur content was prepared, which solved the problem of sulfur residue affecting battery performance and improved the electrochemical performance of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- WELNENG ENVIRONMENTAL TECH (SUZHOU) CO LTD
- Filing Date
- 2026-06-15
- Publication Date
- 2026-07-14
Smart Images
Figure CN122393290A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the technical field of recycled lithium iron phosphate, specifically to a recycled lithium iron phosphate and its preparation method. Background Technology
[0002] Waste lithium iron phosphate cathode materials are crushed and screened to obtain waste lithium iron phosphate material. Subsequently, sulfuric acid is used to leach the waste lithium iron phosphate material, causing valuable metals such as lithium and iron to enter the solution as sulfates. Then, lithium iron phosphate material is resynthesized through precipitation and calcination. However, the lithium iron phosphate product regenerated by this process has a high residual sulfur content. Summary of the Invention
[0003] In a first aspect, this application provides a recycled lithium iron phosphate, which has a porous structure and a sulfur content of less than 300 ppm. The initial discharge specific capacity of regenerated lithium iron phosphate at 0.1C charge-discharge is no less than 150mAh / g.
[0004] In some optional embodiments of the first aspect of this application, the pore size distribution of the regenerated lithium iron phosphate exhibits a single main peak, and the most probable pore size corresponding to the main peak is located in the range of 25nm~46nm.
[0005] In some optional embodiments of the first aspect of this application, the average pore size of the regenerated lithium iron phosphate is 25 nm to 46 nm.
[0006] The second aspect of this application provides a method for preparing recycled lithium iron phosphate, which is used to prepare the above-mentioned recycled lithium iron phosphate. The preparation method includes the following steps: Waste lithium iron phosphate material is mixed with an acid solution, heated and stirred to dissolve, and filtered to obtain a first leachate; impurity metal ions are removed from the first leachate to obtain a second leachate; The second leachate was evaporated, crystallized, and dehydrated to obtain powder. The powder, lithium source, and phosphorus source were mixed in a molar ratio of Li:Fe:P = (1~1.05):(0.96~1):1 to obtain dry powder. The dried powder is sintered in an oxygen atmosphere to obtain intermediate powder. The intermediate powder is mixed with a carbon source, ground, spray-dried, sintered in an inert atmosphere, and then pulverized by airflow to obtain regenerated lithium iron phosphate.
[0007] In some optional embodiments of the second aspect of this application, evaporating and crystallizing the second leachate to obtain powder includes: The second leachate was evaporated and crystallized to obtain a cake-like substance, which was then dehydrated in air at 400℃~600℃ to obtain a powder.
[0008] In some optional embodiments of the second aspect of this application, the dried powder is sintered in an oxygen atmosphere at a temperature of 500°C to 950°C for a duration of 1 hour to 4 hours.
[0009] In some optional embodiments of the second aspect of this application, mixing the intermediate powder and the carbon source for grinding includes: The intermediate powder and carbon source are mixed to obtain a mixture, and the mixture is ground until the D50 particle size of the mixture is 250nm~500nm; wherein the grinding medium is selected from at least one of deionized water, ethanol and methanol.
[0010] In some optional embodiments of the second aspect of this application, the sintering temperature in an inert atmosphere is 650°C to 850°C, and the duration is 6h to 12h.
[0011] In some optional embodiments of the second aspect of this application, the acid solution is selected from sulfuric acid solution, and the mass fraction of sulfuric acid in the acid solution is 10% to 30%; Mixing waste lithium iron phosphate material with an acid solution includes: mixing waste lithium iron phosphate with a sulfuric acid solution, wherein the molar ratio between sulfate ions in the sulfuric acid solution and iron ions in the waste lithium iron phosphate is (0.5~2):1.
[0012] In some optional embodiments of the second aspect of this application, the temperature at which the waste lithium iron phosphate material is mixed with the acid solution and heated and stirred to dissolve is 40°C to 90°C.
[0013] Beneficial effects: The recycled lithium iron phosphate provided in the first aspect of this application has a porous structure and a sulfur content of less than 300 ppm. The porous structure of the recycled lithium iron phosphate provides an effective microscopic channel basis for electrolyte wetting and lithium-ion transport, thereby improving the electrochemical performance of the battery assembled from the recycled lithium iron phosphate.
[0014] The method for preparing recycled lithium iron phosphate provided in the second aspect of this application involves mixing waste lithium iron phosphate with an acid solution, heating and stirring to dissolve it, filtering to obtain a first leachate, removing impurity metal ions from the first leachate to obtain a second leachate, evaporating and crystallizing the second leachate to obtain powder, and then sintering it in an aerobic atmosphere to obtain an intermediate powder. During sintering in an aerobic atmosphere, impurities such as sulfur and carbon in the powder are sintered in a high-temperature oxidizing atmosphere, generating corresponding gases. The escape of these gases results in a rich porous structure in the obtained intermediate powder. A carbon source is added to the intermediate powder, and it is sintered in an inert gas atmosphere, followed by airflow pulverization to obtain recycled lithium iron phosphate. This recycling method has a short process flow, does not produce byproducts such as sodium sulfate and ammonium sulfate, and is low in cost. Attached Figure Description
[0015] Figure 1This is a scanning electron microscope image of the regenerated lithium iron phosphate obtained in Example 1; Figure 2 The diagram shows the pore size distribution of the regenerated lithium iron phosphate obtained in Examples 1 to 4. Detailed Implementation
[0016] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the present application and are not intended to limit the present application.
[0017] This embodiment provides a recycled lithium iron phosphate, which has a porous structure and a sulfur content of less than 300 ppm. The initial discharge specific capacity of regenerated lithium iron phosphate at 0.1C charge-discharge is no less than 150mAh / g.
[0018] In one embodiment, the pore size distribution of the regenerated lithium iron phosphate exhibits a single main peak, with the most probable pore size corresponding to the main peak located in the range of 25 nm to 46 nm.
[0019] In one embodiment, the average pore size of the regenerated lithium iron phosphate is 25 nm to 46 nm.
[0020] Another embodiment provides a method for preparing recycled lithium iron phosphate, which includes the following steps: Waste lithium iron phosphate material is mixed with an acid solution, heated and stirred to dissolve, and filtered to obtain a first leachate; impurity metal ions are removed from the first leachate to obtain a second leachate; The second leachate was evaporated, crystallized, and dehydrated to obtain powder. The powder, lithium source, and phosphorus source were mixed in a molar ratio of Li:Fe:P = (1~1.05):(0.96~1):1 to obtain dry powder. The dried powder is sintered in an oxygen atmosphere to obtain intermediate powder. The intermediate powder is mixed with a carbon source, ground, spray-dried, sintered in an inert atmosphere, and then pulverized by airflow to obtain regenerated lithium iron phosphate.
[0021] In the above scheme, the waste lithium iron phosphate material is prepared by dismantling, crushing and screening (while removing aluminum foil) retired lithium iron phosphate batteries. The retired lithium iron phosphate batteries include batteries scrapped from electric vehicles, energy storage power stations and power tools.
[0022] In this embodiment, waste lithium iron phosphate is mixed with an acid solution, heated and stirred to dissolve it. After dissolution, the mixture is filtered to obtain a first leachate. The first leachate mainly contains lithium ions, ferrous ions, ferric ions, impurity metal ions (such as copper ions), and acid radical ions. Impurity metal ions in the first leachate are removed, for example, by adding pure iron flakes to the first leachate to displace elemental copper, followed by filtration to obtain a second leachate; or by using other known methods for removing impurity metal ions from the first leachate, which will not be elaborated here.
[0023] The second leachate is evaporated and crystallized to obtain a cake-like substance, which is then dehydrated to obtain powder. At this stage, the powder contains a large amount of impurities such as sulfur and carbon. Lithium and phosphorus sources are added to the powder, followed by sintering in an aerobic atmosphere to obtain intermediate powder. During sintering in an aerobic atmosphere, the sulfur and carbon impurities in the powder are sintered in a high-temperature oxidizing atmosphere, generating corresponding gases. The escape of these gases results in a rich porous structure in the obtained intermediate powder. A carbon source is then added to the intermediate powder, and it is sintered in an inert gas atmosphere followed by air jet milling to obtain regenerated lithium iron phosphate. The resulting regenerated lithium iron phosphate exhibits a porous structure and low sulfur content. This porous structure provides an effective microscopic channel basis for electrolyte wetting and lithium-ion transport, improving the electrochemical performance of batteries assembled from this regenerated lithium iron phosphate.
[0024] In one embodiment, evaporating and crystallizing the second leachate to obtain a powder includes: The second leachate was evaporated and crystallized to obtain a cake-like substance, which was then dehydrated in air at 400℃~600℃ to obtain a powder.
[0025] In one embodiment, the dried powder is sintered in an aerobic atmosphere at a temperature of 500°C to 950°C for 1 to 4 hours. Within this temperature range, sulfur in the dried powder volatilizes and escapes in the form of oxides, thereby effectively removing sulfur impurities.
[0026] In one embodiment, mixing the intermediate powder and the carbon source for grinding includes: The intermediate powder and carbon source are mixed to obtain a mixture, and the mixture is ground until the D50 particle size of the mixture is 250nm~500nm; wherein the grinding medium is selected from at least one of deionized water, ethanol and methanol.
[0027] In one embodiment, the sintering temperature in an inert atmosphere is 650°C to 850°C, and the duration is 6 hours to 12 hours.
[0028] In one embodiment, the acid solution is selected from sulfuric acid solution, and the mass fraction of sulfuric acid in the acid solution is 10% to 30%. Mixing waste lithium iron phosphate material with an acid solution includes: mixing waste lithium iron phosphate with a sulfuric acid solution, wherein the molar ratio between sulfate ions in the sulfuric acid solution and iron ions in the waste lithium iron phosphate is (0.5~2):1.
[0029] In one embodiment, the temperature at which the waste lithium iron phosphate material is mixed with the acid solution and heated and stirred to dissolve is 40°C to 90°C.
[0030] The present application is further illustrated below with reference to embodiments and comparative examples. Unless otherwise specified, the raw materials, reagents, materials and equipment used in this application are all commercially available products conventionally used in the art.
[0031]
Example 1
[0032]
Example 2
[0033]
Example 3
[0034]
Example 4
[0035] Comparative Example 1 S1. Mix waste lithium iron phosphate material with a 15% sulfuric acid solution, controlling the molar ratio between sulfate and iron in the waste lithium iron phosphate material to be 1.2:1, and the solid content to be 20%. Stir and dissolve at 60°C, keeping the container covered during the dissolution process. After dissolution, filter to obtain the first leachate. Add pure iron flakes to the first leachate to remove copper ions. Once the copper ion content in the first leachate reaches below 5 ppm, transfer it to another container to obtain the second leachate. S2. The second leachate is evaporated and crystallized to obtain a viscous cake. The cake is dehydrated in air at 500°C to obtain powder. The content of lithium, iron and phosphorus in the powder is tested. The powder, lithium carbonate and lithium dihydrogen phosphate are mixed in a molar ratio of Li:Fe:P=1.05:1:1.05 to obtain dry powder, that is, the molar ratio of Li:Fe:P in the dry powder is 1.05:1:1.05. S3. Add 3.5% glucose monohydrate (calculated as iron) to the dry powder to obtain a mixture. Grind the mixture in a sand mill (grinding medium is deionized water) to a D50 particle size of 350 nm. Then spray dry and sinter at 800 degrees Celsius for 8 hours under a nitrogen atmosphere. After that, air jet milling is performed to obtain regenerated lithium iron phosphate.
[0036] [Performance Testing] Sulfur content determination: Sulfur content was determined using a high-frequency infrared carbon-sulfur analyzer. The specific steps are as follows: Take an appropriate amount of regenerated lithium iron phosphate sample, accurately weigh it, and place it in a carbon-sulfur-specific crucible that has been ignited. Add an appropriate amount of tungsten flux (carbon content ≤ 0.0008%) to promote complete combustion of the sample. Place the crucible containing the sample into the combustion chamber of a high-frequency furnace, close the furnace door, and start the analysis program. Under high-frequency induction heating (temperature 1200℃), the instrument introduces high-purity oxygen to ensure complete combustion of the sample, converting the sulfur element in the sample into sulfur dioxide gas. The generated gas is then treated by dust removal and water removal before entering the infrared detector. By measuring the absorption intensity of sulfur dioxide gas in a specific infrared band, the computer automatically calculates and outputs the mass fraction of sulfur element. Each sample is measured in triplicate, and the average value is taken as the final test result. The test results are shown in Table 1.
[0037] Average pore size determination: The average pore size was determined using nitrogen adsorption combined with the BET / BJH model. The specific steps are as follows: First, take an appropriate amount of regenerated lithium iron phosphate sample, place it in a special sample tube, and put it in a degassing station for pretreatment: under vacuum conditions (vacuum degree < 10). -3The sample was heated to 200℃ for 4 hours to completely remove moisture, gas, and other impurities adsorbed on the surface of the regenerated lithium iron phosphate sample. After degassing, the sample was cooled to room temperature, sealed in an inert atmosphere, and accurately weighed. The sample tube was then installed in the analysis station of a fully automated specific surface area and porosity analyzer (such as the Micromeritics ASAP2020), with high-purity nitrogen (≥99.999%) as the adsorbate and liquid nitrogen (77K) as the cooling bath medium. The instrument automatically collected nitrogen adsorption-desorption isotherm data at multiple preset pressure points within a relative pressure (P / P0) range of 0.01 to 0.99. After the tests were completed, the linear region of the isotherm (typically P / P0 = 0.05~0.30) was fitted using the BET (Brunauer-Emmett-Teller) equation to calculate the specific surface area of the sample. Simultaneously, pore size distribution analysis was performed on the desorption branch data based on the BJH (Barrett-Joyner-Halenda) model, and the average pore size (defined as 4 times the total pore volume divided by the BET specific surface area) was automatically calculated using software integration. Each sample was tested in triplicate to ensure data reproducibility, and the final result was the average. The test results are shown in Table 1.
[0038] Electrochemical performance testing: The recycled lithium iron phosphate materials obtained in Examples 1 to 4 and Comparative Example 1 were assembled into CR2032 coin cells for electrochemical performance testing. The test results are shown in Table 1. The test methods are as follows: First, an electrode slurry was prepared according to a mass ratio of recycled lithium iron phosphate: conductive carbon black: polyvinylidene fluoride = 80:10:10. Polyvinylidene fluoride was dissolved in N-methylpyrrolidone and magnetically stirred until transparent. Conductive carbon black was added and ultrasonically dispersed for 30 minutes. Then, recycled lithium iron phosphate powder was added and stirring continued for 6 hours to obtain a uniform slurry with a solid content of approximately 35%. The slurry was then coated on one side of a clean aluminum foil, with a wet film thickness controlled at 100 μm. After pre-baking at 80°C for 2 hours and vacuum drying at 120°C for 12 hours, it was rolled to a compacted density of 2.2 g / cm³. 3 It is then cut into φ14mm round pieces, and then vacuum dried at 100℃ for 2 hours before being transferred to an argon glove box for later use.
[0039] Assemble the CR2032 button cell battery inside the glove box. The assembly sequence from bottom to top is as follows: positive electrode shell, positive electrode sheet (active side up), add 40μL of electrolyte for wetting, φ19mm separator, add another 40μL of electrolyte, φ16mm lithium sheet (bright side down), stainless steel gasket, and finally cover with the negative electrode shell and seal it with a sealing machine at 800psi. Let it stand for 4 hours to allow the electrolyte to fully wet the battery.
[0040] The electrochemical performance of the battery was tested using the Blue Electric testing system at a constant temperature of 25°C, with a voltage window of 2.0V~3.75V (vs. Li / Li). + The 0.1C initial charge specific capacity and 0.1C initial discharge specific capacity were determined through the first week of activation: after a 4-hour rest period, the battery was charged at a constant current rate of 0.1C to 3.75V, then switched to constant voltage charging until the current dropped to 0.02C; after a 3-minute rest period, it was discharged at a constant current rate of 0.1C to 2.0V. The test system recorded the total charge / discharge capacity (mAh) during the charging / discharging process, which was divided by the mass (g) of the lithium iron phosphate active material in the corresponding electrode to obtain the 0.1C initial charge specific capacity and 0.1C initial discharge specific capacity in mAh / g. The 1C discharge specific capacity was obtained in the second week of testing: the battery was first charged at a constant current-constant voltage rate of 1C (with the same cutoff conditions), then discharged at a constant current rate of 1C to 2.0V after a 3-minute rest period. The resulting discharge capacity was normalized to the mass of the active material to obtain the 1C discharge specific capacity (mAh / g). All specific capacity data were calibrated based on the theoretical capacity of lithium iron phosphate, 170mAh / g, to ensure the accuracy and comparability of the results.
[0041] Table 1
[0042] As shown in Table 1, the sulfur content of Examples 1 to 4 ranges from 189 ppm to 265 ppm, all of which are controlled below 300 ppm. In contrast, the sulfur content of Comparative Example 1 is as high as 21342 ppm, which indicates that this application can effectively remove sulfur impurities introduced during the sulfuric acid dissolution process.
[0043] The average pore size distribution of Examples 1 to 4 is in the range of 25nm to 46nm; in Comparative Example 1, due to the failure to effectively remove sulfur impurities, the regenerated lithium iron phosphate material has basically no pore structure and cannot meet the testing requirements of the nitrogen adsorption method, so the average pore size data is missing.
[0044] The specific capacity of the first charge at 0.1C in Examples 1 to 4 is 160.5 mAh / g to 162.2 mAh / g, the specific capacity of the first discharge at 0.1C is 157.2 mAh / g to 162.0 mAh / g, and the specific capacity of the discharge at 1C rate is 138.1 mAh / g to 146.2 mAh / g, all of which are higher than that of Comparative Example 1.
[0045] The specific capacity of Comparative Example 1 at 0.1C initial charge was 141.1 mAh / g, the specific capacity at 0.1C initial discharge was 137.1 mAh / g, and the specific capacity at 1C discharge was 100.1 mAh / g, which was lower than that of the other examples. The high sulfur residue in Comparative Example 1 reduced the performance of the regenerated lithium iron phosphate.
[0046] Examples 3 and 4 have smaller average pore sizes (25 nm and 29 nm) and relatively higher 1C discharge specific capacities (146.2 mAh / g and 145.1 mAh / g), indicating that smaller mesopores are beneficial for shortening the lithium-ion diffusion path and improving rate performance.
[0047] Example 1 has a larger average pore size (46 nm) and a relatively lower 1C discharge specific capacity (138.1 mAh / g), but it is still better than Comparative Example 1, indicating that even under the condition of larger pore size, low sulfur content can still ensure the basic electrochemical performance of regenerated lithium iron phosphate materials.
[0048] Depend on Figure 1 It can be seen that the regenerated lithium iron phosphate obtained in Example 1 has a connected pore structure.
[0049] Depend on Figure 2 It can be seen that the peak pore size distribution values of Examples 1 to 4 are 46nm, 38nm, 25nm, and 29nm, respectively; the pore size of the regenerated lithium iron phosphate obtained in each example falls within the mesoporous range of 2nm to 50nm, which is consistent with the basic characteristics of porous materials; the mesoporous structure of the regenerated lithium iron phosphate provides an effective microscopic channel basis for electrolyte wetting and lithium-ion transport.
[0050] Examples 1 to 4 all exhibit a clear single-peak distribution characteristic, indicating that the pore size distribution is concentrated and there are no obvious stray pores. The peak shape of Example 3 is sharper, indicating that its pore size uniformity is better and its microstructure is highly regular. The narrow distribution characteristic is conducive to the formation of a consistent ion transport path and reduces the difference in diffusion resistance.
[0051] The curves obtained in Examples 1 to 4 showed no abnormally broad peaks or impurities within the test range (10nm~200nm), indicating that the internal pore structure of the regenerated lithium iron phosphate was intact.
[0052] It should be noted that, in this document, "comprising," "including," or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.
[0053] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.
[0054] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the principles of this application should be included within the scope of protection of this application.
Claims
1. A regenerated lithium iron phosphate, characterized in that, The recycled lithium iron phosphate has a porous structure and a sulfur content of less than 300 ppm. The regenerated lithium iron phosphate has an initial discharge specific capacity of not less than 150 mAh / g under 0.1C charge-discharge conditions.
2. The regenerated lithium iron phosphate as described in claim 1, characterized in that, The pore size distribution of the regenerated lithium iron phosphate exhibits a single main peak, and the most probable pore size corresponding to the main peak is located in the range of 25nm~46nm.
3. The regenerated lithium iron phosphate as described in claim 2, characterized in that, The average pore size of the recycled lithium iron phosphate is 25nm~46nm.
4. A method for preparing recycled lithium iron phosphate, characterized in that, The method for preparing the recycled lithium iron phosphate according to any one of claims 1 to 3 comprises the following steps: Waste lithium iron phosphate material is mixed with an acid solution, heated and stirred to dissolve, and filtered to obtain a first leachate; impurity metal ions are removed from the first leachate to obtain a second leachate; The second leachate is evaporated, crystallized, and dehydrated to obtain powder. The powder, lithium source, and phosphorus source are mixed in a molar ratio of Li:Fe:P = (1~1.05):(0.96~1):1 to obtain dry powder. The dried powder is sintered in an oxygen atmosphere to obtain an intermediate powder. The intermediate powder is mixed with a carbon source, ground, spray-dried, sintered in an inert atmosphere, and then pulverized by airflow to obtain regenerated lithium iron phosphate.
5. The method for preparing recycled lithium iron phosphate as described in claim 4, characterized in that, The step of evaporating, crystallizing, and dehydrating the second leachate to obtain powder includes: The second leachate is evaporated and crystallized to obtain a cake-like substance, which is then dehydrated in air at 400°C to 600°C to obtain the powder.
6. The method for preparing recycled lithium iron phosphate as described in claim 4, characterized in that, The sintering temperature of the dried powder in an oxygen atmosphere is 500℃~950℃, and the time is 1h~4h.
7. The method for preparing recycled lithium iron phosphate as described in claim 4, characterized in that, The step of mixing and grinding the intermediate powder and carbon source includes: The intermediate powder and carbon source are mixed to obtain a mixture, and the mixture is ground until the D50 particle size of the mixture is 250nm~500nm; wherein the grinding medium is selected from at least one of deionized water, ethanol and methanol.
8. The method for preparing recycled lithium iron phosphate as described in claim 4, characterized in that, The sintering temperature under an inert atmosphere is 650℃~850℃, and the duration is 6h~12h.
9. The method for preparing recycled lithium iron phosphate as described in claim 4, characterized in that, The acid solution is selected from sulfuric acid solution, and the mass fraction of sulfuric acid in the acid solution is 10%~30%; The process of mixing waste lithium iron phosphate material with an acid solution includes: mixing the waste lithium iron phosphate with a sulfuric acid solution, wherein the molar ratio between sulfate ions in the sulfuric acid solution and iron ions in the waste lithium iron phosphate is (0.5~2):
1.
10. The method for preparing recycled lithium iron phosphate as described in claim 4, characterized in that, The temperature at which the waste lithium iron phosphate material is mixed with the acid solution and heated and stirred to dissolve it is 40℃~90℃.