A method for preparing lithium manganese iron phosphate by solid phase method from recycled lithium iron phosphate
The solid-state method for preparing lithium iron phosphate solves the problem of recycling and reusing lithium iron phosphate, and produces a high-performance lithium iron phosphate cathode material suitable for lithium-ion batteries, exhibiting good electrochemical performance and stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- TIANJIN RONBAY SKYLAND TECHNOLOGY CO LTD
- Filing Date
- 2023-12-29
- Publication Date
- 2026-07-31
AI Technical Summary
How to effectively utilize recycled lithium iron phosphate to prepare high-performance lithium manganese iron phosphate cathode materials, thus solving the problem of material reuse after lithium-ion batteries are decommissioned.
Lithium manganese iron phosphate was prepared by solid-state method. The process involved mixing LixMnyFezPO4 lithium manganese iron phosphate precursor, recycled lithium iron phosphate and carbon source, ball milling to a specific particle size, and then sintering under an inert atmosphere. The sintering temperature and heating rate were controlled to prepare high-performance lithium manganese iron phosphate.
It achieves efficient reuse of lithium manganese iron phosphate, improves lithium-ion diffusion rate, conductivity and cycle stability, reduces processing difficulty, and is suitable for industrial production.
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Abstract
Description
Technical Field
[0001] This invention relates to a method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method, belonging to the field of waste recycling technology for waste lithium iron phosphate cathode materials. Background Technology
[0002] With the rapid development of electric vehicles and clean energy storage, the demand for high-performance lithium-ion batteries is increasing. The electrochemical performance of lithium-ion batteries, including energy density, cost, and safety, largely depends on the cathode material used. Compared to other cathode materials, lithium iron phosphate (LFP) has been widely used in lithium-ion batteries due to its superior safety performance. However, since the lifespan of lithium-ion batteries is generally only 5-8 years, and some even shorter, the large amount of recycled LFP material faces the challenge of how to reuse it as a large number of lithium iron phosphate batteries are retired.
[0003] Compared to lithium iron phosphate, lithium manganese iron phosphate has a higher operating voltage; compared to layered oxide cathode materials, lithium manganese iron phosphate has advantages such as higher cost-effectiveness, high safety performance, high thermal stability, no spontaneous combustion during needle penetration and overcharging, long lifespan, and no risk of explosion. These advantages make lithium manganese iron phosphate a promising cathode material.
[0004] Therefore, how to prepare lithium manganese iron phosphate from recycled lithium iron phosphate has become a hot topic in the field. Summary of the Invention
[0005] This invention provides a method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method. This method is simple to operate and provides a new approach for the reuse of recycled lithium iron phosphate.
[0006] This invention provides a method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method, comprising the following steps:
[0007] 1) Li x Mn y Fe z The PO4 lithium manganese iron phosphate precursor, recycled lithium iron phosphate, first carbon source, and deionized water were mixed and then ball-milled until the particle size D50 was 0.35-0.40μm to obtain the first material; wherein, 1.0≤x≤1.05, 0.2≤y≤0.8, 0.2≤z≤0.8, and y+z=1;
[0008] 2) Under an inert atmosphere, the first material is subjected to a first sintering treatment to obtain the lithium manganese iron phosphate.
[0009] In the method described above, the temperature of the first sintering treatment is 720-770°C.
[0010] In the method described above, the heating rate of the first sintering treatment is 3-5°C / min.
[0011] In the method described above, the first carbon source includes at least one of sucrose, glucose, and polyethylene glycol.
[0012] The method described above, wherein the lithium manganese iron phosphate precursor is prepared by at least the following steps:
[0013] 1) After mixing lithium source, manganese source, iron source, phosphorus source, second carbon source and deionized water, the mixture is ball-milled until the particle size D50 is 0.6-0.65μm. After drying, the second material is obtained.
[0014] 2) The second material is subjected to a second sintering treatment to obtain the lithium manganese iron phosphate precursor;
[0015] The molar ratio of the lithium source, manganese source, iron source, and phosphorus source is 1.0-1.05:0.7:0.3:1.0.
[0016] In the method described above, the temperature of the second sintering treatment is 450-500°C.
[0017] In the method described above, the heating rate of the second sintering treatment is 3-5°C / min.
[0018] In the method described above, the lithium source is a mixture of lithium carbonate and lithium dihydrogen phosphate; and / or, the manganese source is at least one of manganese tetroxide, manganese acetate, and manganese oxalate; and / or, the iron source is iron phosphate; and / or, the phosphorus source is at least one of lithium dihydrogen phosphate and iron phosphate; and / or, the second carbon source includes at least one of sucrose and glucose.
[0019] The method described above, wherein the drying in step 1) is spray drying, wherein the conditions for spray drying are: inlet temperature 180-250℃, outlet temperature 70-90℃.
[0020] The method described above involves obtaining the elemental content of the lithium manganese iron phosphate precursor and the recovered lithium iron phosphate, respectively.
[0021] The molar ratio of the lithium manganese iron phosphate precursor to the recovered lithium iron phosphate is determined based on the elemental content in the lithium manganese iron phosphate precursor and the recovered lithium iron phosphate, as well as the target elemental content of the lithium manganese iron phosphate.
[0022] The present invention provides a method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method, by using Li x Mn y Fe zThe precursor of lithium manganese iron phosphate (LFP) (PO4), recycled lithium iron phosphate, a primary carbon source, and deionized water are mixed and ball-milled until the particle size D50 is 0.35-0.40 μm. Then, under an inert atmosphere, sintering is performed to obtain lithium manganese iron phosphate. The formula is: 1.0 ≤ x ≤ 1.05, 0.2 ≤ y ≤ 0.8, 0.2 ≤ z ≤ 0.8, and y + z = 1. This method is simple to operate and provides a new approach for the reuse of recycled lithium iron phosphate. Detailed Implementation
[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.
[0024] This invention provides a method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method, comprising the following steps:
[0025] 1) Li x Mn y Fe z The PO4 lithium manganese iron phosphate precursor, recycled lithium iron phosphate, first carbon source, and deionized water were mixed and then ball-milled until the particle size D50 was 0.35-0.40μm to obtain the first material; wherein, 1.0≤x≤1.05, 0.2≤y≤0.8, 0.2≤z≤0.8, and y+z=1;
[0026] 2) Under an inert atmosphere, the first material is subjected to a first sintering treatment to obtain lithium manganese iron phosphate.
[0027] The chemical composition of the above-mentioned lithium manganese iron phosphate precursor is Li x Mn y Fe z PO4, where 1.0≤x≤1.05, 0.2≤y≤0.8, 0.2≤z≤0.8, and y+z=1.
[0028] This invention has universal applicability to the recycling of lithium iron phosphate, and does not limit the recycling method or composition of lithium iron phosphate. In one specific embodiment, the chemical composition of the recycled lithium iron phosphate is LiFePO4.
[0029] The aforementioned first carbon source can coat at least part of the surface of the first material, which is beneficial to improving the conductivity of the product and can also prevent the leaching of manganese.
[0030] Deionized water, used as a solvent, provides a liquid environment for ball milling, which is beneficial for Lix Mn y Fe z The PO4 lithium manganese iron phosphate precursor, recycled lithium iron phosphate, and the first carbon source are thoroughly mixed during the ball milling process to improve the uniformity of the reaction.
[0031] To further improve the ball milling effect, the amount of deionized water added can be controlled to make the solid content in the first material 30%-40%, which is beneficial to improving the ball milling effect.
[0032] When the particle size D50 of the first material after grinding is 0.35-0.40 μm, the reaction of the lithium manganese iron phosphate precursor, recycled lithium iron phosphate, and the first carbon source is more complete, which is beneficial to improving the energy density, rate performance, and cycle performance of the lithium manganese iron phosphate product. The inventors speculate that this may be because the morphological framework of the recycled lithium iron phosphate in the first material with this particle size is more stable, and it can better integrate with the lithium manganese iron phosphate precursor, so that the prepared lithium manganese iron phosphate has a suitable specific surface area. This avoids the chemical and structural properties changes caused by coating, rolling, and other processes during the processing of the positive electrode sheet due to the excessively high specific surface area of the lithium manganese iron phosphate, which would reduce the processing performance. At the same time, the prepared lithium manganese iron phosphate can provide sufficient contact area to fully contact the electrolyte, thereby increasing the lithium ion diffusion rate. In addition, the coating effect of the first carbon layer in the first material with this particle size is better, which is beneficial to improving the conductivity of the product and preventing the dissolution of manganese. Moreover, the first material with the above-mentioned particle size also helps to increase the compaction density of the lithium manganese iron phosphate, thereby significantly improving the rate performance, cycle stability, and energy density of the product.
[0033] In some embodiments, the lithium manganese iron phosphate obtained by the above method has a particle size between 1.1 and 1.5 μm and a specific surface area between 20.10 and 20.87 m². 2 / g.
[0034] The purpose of limiting the inert atmosphere in step 2) is to avoid air interfering with the first sintering process. For example, the first carbon source can react with oxygen in the air to generate carbon dioxide and be lost, thereby reducing the electrochemical performance of lithium manganese iron phosphate.
[0035] This invention does not limit the temperature, heating rate, and time of the first sintering treatment described above. Conventional sintering temperatures in the art can be used, such as 400-800℃, 1.5-5℃ / min, and 6-12h, as long as Li... x Mn y Fe z The process involves reacting PO4 (lithium iron phosphate precursor), recycled lithium iron phosphate, and the first carbon source.
[0036] In one specific embodiment, the first sintering process described above uses a tube furnace.
[0037] The above-mentioned method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method is simple to operate and suitable for large-scale industrial production, providing a new approach for the preparation of lithium manganese iron phosphate and the reuse of recycled lithium iron phosphate.
[0038] In one specific embodiment, the temperature of the first sintering treatment is 720-770℃, which is beneficial to improving the lithium-ion diffusion rate of the lithium manganese iron phosphate product. The inventors speculate that by controlling the sintering temperature within the above range, the lithium-ion diffusion rate of the product can be improved. x Mn y Fe z The reaction rate of PO4 lithium manganese iron phosphate precursor, recovered lithium iron phosphate, and the first carbon source is suitable. At this reaction rate, the lithium manganese iron phosphate precursor and the lithium manganese iron phosphate in the recovered lithium iron phosphate have suitable occupancy during the formation of lithium manganese iron phosphate, which is conducive to providing more channels for lithium ion diffusion.
[0039] Furthermore, by controlling the heating rate of the first sintering process to 3-5℃ / min, a suitable temperature gradient can be maintained inside the first material, thereby generating lithium manganese iron phosphate with high performance consistency.
[0040] In one specific embodiment, the first carbon source includes at least one of sucrose, glucose, and polyethylene glycol. These raw materials are inexpensive and readily available, which is beneficial for improving the electrochemical performance of lithium manganese iron phosphate.
[0041] In one specific embodiment, the above-mentioned lithium manganese iron phosphate precursor is prepared by a method including at least the following steps:
[0042] 1) After mixing lithium source, manganese source, iron source, phosphorus source, second carbon source and deionized water, the mixture is ball-milled until the particle size D50 is 0.6-0.65μm. After drying, the second material is obtained.
[0043] 2) The second material is subjected to a second sintering treatment to obtain lithium manganese iron phosphate precursor;
[0044] The molar ratio of lithium source, manganese source, iron source and phosphorus source is 1.0-1.05:0.7:0.3:1.0.
[0045] The present invention does not limit the types of lithium source, manganese source, iron source, phosphorus source and second carbon source mentioned above, and can select from the types commonly used in the art.
[0046] The aforementioned restrictions on the molar ratios of lithium, manganese, iron, and phosphorus sources are beneficial for obtaining the lithium manganese iron phosphate precursor with the aforementioned chemical composition.
[0047] Understandably, deionized water acts as a ball milling solvent in step 1), which helps improve the ball milling effect and ensures thorough mixing of the lithium, manganese, iron, phosphorus, and second carbon sources. To further improve the ball milling effect, the amount of deionized water added can be controlled to limit the solid content in the second material to 30%-40%, thus improving the ball milling effect.
[0048] The second carbon source can coat part of the surface of the lithium manganese iron phosphate precursor core, which helps to improve conductivity and prevents the leaching of manganese.
[0049] The aforementioned limitation on particle size range helps to make the reaction between the lithium source, manganese source, iron source, phosphorus source, and second carbon source more complete.
[0050] The present invention does not limit the temperature, heating rate and time of the second sintering treatment. Conventional sintering temperatures in the art can be used, such as 400-800℃, 1.5-5℃ / min, 4-8h, as long as the lithium source, manganese source, iron source, phosphorus source and second carbon source can react fully.
[0051] Generally, the above-mentioned second sintering treatment can be carried out in a muffle furnace.
[0052] After the second sintering process is completed, the material can be allowed to cool naturally.
[0053] The lithium manganese iron phosphate precursor prepared by the method including the above steps can be reacted with recycled lithium manganese iron to prepare lithium manganese iron phosphate.
[0054] It is understandable that the first and second carbon sources mentioned above can be their aqueous solutions or dry substances. When using their aqueous solutions, it helps to improve the coating effect. When calculating the amount of raw materials used, the water content in their aqueous solutions should be included in the content of deionized water.
[0055] In one specific embodiment, the mass ratio of the first carbon source to the lithium manganese iron phosphate precursor and the recovered lithium iron phosphate is 0.8-1:10, and the mass ratio of the second carbon source to the lithium source, manganese source, iron source and phosphorus source is 0.8-1:10.
[0056] In one specific embodiment, the temperature of the second sintering treatment is 450-500℃. The inventors speculate that this temperature is beneficial for controlling the reaction rate between the lithium source, manganese source, iron source, phosphorus source, and second carbon source, making the manganese element occupancy more stable, which helps to avoid the dissolution of manganese element in lithium manganese iron phosphate and improves the cycle performance of the battery.
[0057] Furthermore, the heating rate of the second sintering treatment is 3-5℃ / min, which maintains a suitable temperature gradient inside the second material, thereby forming a lithium manganese iron phosphate precursor with high performance consistency.
[0058] The lithium source is a mixture of lithium carbonate and lithium dihydrogen phosphate; and / or, the manganese source is at least one of manganese tetroxide, manganese acetate, and manganese oxalate; and / or, the iron source is iron phosphate; and / or, the phosphorus source is at least one of lithium dihydrogen phosphate and iron phosphate; and / or, the second carbon source includes at least one of sucrose and glucose. The above materials are readily available and can be used to prepare lithium manganese iron phosphate of the present invention. Furthermore, the combined use of the above materials is beneficial to improving the electrochemical performance of lithium manganese iron phosphate.
[0059] In one specific embodiment, the mixing steps of the above raw materials are as follows: first, lithium carbonate is dissolved in water, then lithium dihydrogen phosphate is added, and finally, iron source, manganese source and carbon source are added to the system.
[0060] When the drying in step 1) above is spray drying, and the spray drying conditions are an inlet temperature of 180-250℃ and an outlet temperature of 70-90℃, it is beneficial to control the second material to maintain uniform particle size and high consistency in crystal structure and grain size.
[0061] This invention can prepare lithium manganese iron phosphate with a specific manganese-iron ratio, which can be achieved by a method including at least the following processes:
[0062] The elemental contents of lithium manganese iron phosphate precursor and recovered lithium iron phosphate were obtained separately.
[0063] The molar ratio of lithium manganese iron phosphate precursor to recovered iron phosphate is determined based on the elemental content in lithium manganese iron phosphate precursor and recovered iron phosphate, as well as the target elemental content of lithium manganese iron phosphate.
[0064] The above operations help to obtain lithium manganese iron phosphate with a specific manganese-iron ratio, which has high practical value.
[0065] For example, the contents of manganese and iron in the lithium iron phosphate precursor and the iron content in the recovered lithium iron phosphate can be detected by inductively coupled plasma spectrometry (ICP). Then, combined with the target manganese and iron contents of the lithium iron phosphate, the molar ratio of the lithium iron phosphate precursor and the recovered iron phosphate can be determined by calculation according to the principle of conservation of element quantity. The lithium iron phosphate precursor and the recovered iron phosphate with this molar ratio can be used to prepare lithium iron phosphate with the above-mentioned target manganese and iron contents by the method of the present invention.
[0066] The present invention will be further described below through specific embodiments and comparative examples.
[0067] Example 1
[0068] This embodiment provides a method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method, including the following steps:
[0069] 1) After dissolving lithium carbonate in deionized water, lithium dihydrogen phosphate is added and reacted fully. Then, manganese tetroxide and ferric phosphate are added, along with glucose. The mass ratio of glucose to the sum of the masses of lithium carbonate, lithium dihydrogen phosphate, manganese tetroxide, and ferric phosphate is 1:10. The solid content of the system is adjusted to 35% with deionized water. The mixture is then ball-milled until the particle size D50 is 0.6-0.65 μm. Finally, it is spray-dried. The molar ratio of lithium carbonate, lithium dihydrogen phosphate, manganese tetroxide, and ferric phosphate is 0.150:0.700:0.233:0.300. The spray-drying conditions are an inlet temperature of 180℃ and an outlet temperature of 70-90℃ to obtain the second material.
[0070] 2) The second material is transferred into a muffle furnace for a second sintering treatment. The temperature of the second sintering treatment is 500℃, the heating rate is 5℃ / min, and the time is 4h. After natural cooling, lithium manganese iron phosphate precursor is obtained.
[0071] 3) Using inductively coupled plasma atomic spectroscopy (ICP), and combining the mass of the lithium manganese iron phosphate precursor and the relative atomic masses of each element, as well as the mass of the recovered lithium iron phosphate and the relative atomic masses of each element, the molar percentage content of elements in the lithium manganese iron phosphate precursor and the recovered lithium iron phosphate was calculated. Based on the molar percentage content of each element, the relative proportions between them were determined, thus confirming the molecular formula of the lithium manganese iron phosphate precursor as LiMn. 0.7 Fe 0.3 PO4, the molecular formula of recovered lithium iron phosphate is LiFePO4;
[0072] 4) After mixing the above-mentioned lithium manganese iron phosphate precursor and recycled lithium iron phosphate, glucose and polyethylene glycol are added, wherein the mass ratio of glucose, polyethylene glycol, lithium manganese iron phosphate precursor and recycled lithium iron phosphate mixture is 0.6:0.2:10. The solid content of the system is adjusted to 35% with deionized water, and ball milling is performed until the particle size D50 is 0.35-0.40μm. The molar ratio of the above-mentioned lithium manganese iron phosphate precursor and recycled lithium iron phosphate is 0.571:0.429, to obtain the first material;
[0073] 5) Using a tube furnace, the first material is subjected to a first sintering treatment under a nitrogen atmosphere. The temperature of the first sintering treatment is 740℃, the heating rate is 3℃ / min, and the time is 6h. After natural cooling, lithium manganese iron phosphate is obtained.
[0074] Example 2
[0075] The method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method provided in this embodiment is basically the same as that in Example 1, except that...
[0076] In step 4), the molar ratio of lithium manganese iron phosphate precursor to recycled lithium iron phosphate is 0.714:0.286.
[0077] Example 3
[0078] The method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method provided in this embodiment is basically the same as that in Example 1, except that...
[0079] In step 4), the molar ratio of lithium manganese iron phosphate precursor to recycled lithium iron phosphate is 0.857:0.143.
[0080] Example 4
[0081] The method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method provided in this embodiment is basically the same as that in Example 2, except that...
[0082] The temperature of the first sintering treatment is 720℃, and the heating rate is 5℃ / min.
[0083] Example 5
[0084] The method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method provided in this embodiment is basically the same as that in Example 2, except that...
[0085] The second sintering temperature is 450℃, and the heating rate is 3℃ / min.
[0086] Example 6
[0087] The method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method provided in this embodiment is basically the same as that in Example 1, except that...
[0088] The first sintering temperature is 700℃.
[0089] Example 7
[0090] The method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method provided in this embodiment is basically the same as that in Example 1, except that...
[0091] The first sintering temperature is 790℃.
[0092] Example 8
[0093] The method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method provided in this embodiment is basically the same as that in Example 1, except that...
[0094] The heating rate for the first sintering is 1℃ / min.
[0095] Example 9
[0096] The method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method provided in this embodiment is basically the same as that in Example 1, except that...
[0097] The heating rate for the first sintering is 8℃ / min.
[0098] Example 10
[0099] The method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method provided in this embodiment is basically the same as that in Example 1, except that...
[0100] The second sintering temperature is 400℃.
[0101] Example 11
[0102] The method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method provided in this embodiment is basically the same as that in Example 1, except that...
[0103] The second sintering temperature is 550℃.
[0104] Example 12
[0105] The method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method provided in this embodiment is basically the same as that in Example 1, except that...
[0106] The heating rate for the second sintering is 1℃ / min.
[0107] Example 13
[0108] The method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method provided in this embodiment is basically the same as that in Example 1, except that...
[0109] The heating rate for the second sintering is 8℃ / min.
[0110] Comparative Example 1
[0111] The method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method provided in this embodiment is basically the same as that in Example 2, except that...
[0112] In step 1), the molar ratio of lithium carbonate, lithium dihydrogen phosphate, manganese tetroxide, and iron phosphate is 0.250:0.500:0.167:0.500.
[0113] No recycled lithium iron phosphate is added in step 4).
[0114] Comparative Example 2
[0115] The method for preparing lithium manganese iron phosphate from recycled lithium iron phosphate using a solid-phase method provided in this comparative example includes the following steps:
[0116] 1) Lithium carbonate, lithium dihydrogen phosphate, manganese tetroxide, iron phosphate, recovered lithium iron phosphate, glucose, and polyethylene glycol were prepared according to the molar ratio in Example 1. An appropriate amount of deionized water was added and the mixture was ball-milled in a sand mill. The diameter of the zirconia balls was 0.5 mm, the ball milling time was 3 h, and the particle size of the material after ball milling was measured to be 270 nm. Then, the material was spray-dried at a temperature of 160 °C.
[0117] 2) The ball-milled and dried material was sintered at 720℃ for 16 hours under a nitrogen atmosphere, and finally crushed and sieved to obtain lithium manganese iron phosphate.
[0118] Experimental Example 1
[0119] 1) The elemental content of lithium manganese iron phosphate in the above examples and comparative examples was detected using an inductively coupled plasma spectrometer (ICP). The molar percentage of each element in lithium manganese iron phosphate was determined by calculation based on the mass of lithium manganese iron phosphate and the relative atomic mass of each element. The relative proportions between each element in lithium manganese iron phosphate were determined based on the molar percentage of each element in lithium manganese iron phosphate, thereby determining its molecular formula. The relevant data are shown in Table 1.
[0120] 2) The specific surface area of lithium manganese iron phosphate in the above examples and comparative examples was measured by BET method using a specific surface area analyzer. The relevant data are shown in Table 2.
[0121] 3) The particle size of lithium manganese iron phosphate in the above examples and comparative examples was obtained by laser particle size analyzer. The relevant data are shown in Table 2.
[0122] Experimental Example 2
[0123] After the lithium manganese iron phosphate obtained in all the examples and comparative examples was used as the positive electrode, it was assembled with the negative electrode, electrolyte, and separator according to the following method to obtain a coin cell. The method includes:
[0124] Lithium manganese iron phosphate from the examples and comparative examples was mixed with conductive carbon black (SP) and PVDF at a weight ratio of 0.95:0.03:0.02, and dispersed to obtain a positive electrode slurry. This slurry was coated onto an aluminum foil current collector and rolled to prepare a positive electrode sheet. The positive electrode sheet was then punched into small discs with a diameter of 12 mm using a die-cutting tool. After drying and weighing, the discs were assembled into coin cells in a glove box under an Ar protective atmosphere using a 2025 coin cell casing, with a Li metal disc as the negative electrode and conventional high-voltage lithium cobalt oxide electrolyte.
[0125] After each coin cell was left to stand for 4 hours under normal conditions, its rate performance was tested according to the following steps:
[0126] 1. Charge to 4.35V at 0.2C, then charge at a constant voltage to 0.02C and let stand for 3 minutes. Then discharge to 2.0V at 0.2C. Repeat this charge and discharge cycle twice. Calculate the charge and discharge capacity at 4.35V / 0.2C based on the optimal charge and discharge capacity from the two discharge cycles.
[0127] 2. Charge to 4.35V at 1C, then charge at constant voltage to 0.02C and let stand for 3 minutes. Then discharge to 2.0V at 1C. Repeat this charge and discharge cycle twice. Calculate the charge and discharge capacity of 4.35V / 1C based on the optimal charge and discharge capacity from the two discharge cycles.
[0128] The ratio of the discharge capacity at 1C to the discharge capacity at 0.2C was calculated and expressed as C1.0 / C0.2. The relevant data are shown in Table 2.
[0129] Experimental Example 3
[0130] After the lithium manganese iron phosphate used in all the examples and comparative examples was fabricated as the positive electrode, it was assembled with the negative electrode, electrolyte, and separator according to the following method to obtain a lithium-ion battery. The method includes:
[0131] 1) The positive electrode active materials from the examples and comparative examples were mixed with conductive carbon black and PVDF at a weight ratio of 95%:3%:2%, respectively, and dispersed to obtain a positive electrode slurry. This slurry was then coated onto an aluminum foil current collector, with a positive electrode areal density of 150 g / cm³. 3 The positive electrode sheet is prepared by rolling.
[0132] 2) Artificial graphite, styrene-diene rubber (SBR), sodium carboxymethyl cellulose, and conductive carbon black are mixed in a weight ratio of 95%:2%:2%:1%. The mixture is dispersed in water and then mixed using a double planetary mixer to obtain a negative electrode slurry. This slurry is coated onto a copper current collector, followed by rolling and drying to obtain the negative electrode sheet.
[0133] 3) Assemble the positive electrode, negative electrode, and separator into a lithium-ion battery and inject a non-aqueous electrolyte. The electrolyte is prepared by mixing ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC) in a mass ratio of 2:5:3. Then, add 5% fluoroethylene carbonate (FEC) and 13% lithium hexafluorophosphate (LiPF6) by mass of the total electrolyte.
[0134] After each lithium-ion battery was left to stand for 4 hours under normal conditions, its rate performance was tested according to the following steps:
[0135] 1. Charge to 4.3V at 0.2C, then charge at a constant voltage to 0.05C and let stand for 3 minutes. Then discharge to 2V at 0.2C. Repeat this charge and discharge cycle twice. Calculate the charge and discharge capacity at 4.3V / 0.2C based on the optimal charge and discharge capacity from the two discharge cycles.
[0136] 2. Charge to 4.3V at 1C, then charge at constant voltage to 0.05C and let stand for 3 minutes. Then discharge to 2V at 1C. Repeat this charge and discharge cycle twice. Calculate the charge and discharge capacity of 4.3V / 1C based on the optimal charge and discharge capacity from the two discharge cycles.
[0137] The ratio of the discharge capacity at 1C to the discharge capacity at 0.2C was calculated and expressed as C1.0 / C0.2. The relevant data are shown in Table 3.
[0138] Test results
[0139] Table 1. Elemental content and molecular formula of lithium manganese iron phosphate
[0140] Example 1 4.45 13.72 19.63 19.37 <![CDATA[LiMn 0.4 Fe 0.6 PO4]]> Example 2 4.40 16.42 17.39 19.31 <![CDATA[LiMn 0.5 Fe 0.5 PO4]]> Example 3 4.34 19.63 13.51 19.32 <![CDATA[LiMn 0.6 Fe 0.4 PO4]]> Example 4 4.50 16.42 17.30 19.33 <![CDATA[LiMn 0.5 Fe 0.5 PO4]]> Example 5 4.43 16.95 16.26 19.43 <![CDATA[LiMn 0.5 Fe 0.5 PO4]]> Example 6 4.46 13.76 19.70 19.36 <![CDATA[LiMn 0.4 Fe 0.6 PO4]]> Example 7 4.45 13.77 19.91 19.35 <![CDATA[LiMn 0.4 Fe 0.6 PO4]]> Example 8 4.45 13.86 19.98 19.42 <![CDATA[LiMn 0.4 Fe 0.6 PO4]]> Example 9 4.44 13.83 19.96 19.37 <![CDATA[LiMn 0.4 Fe 0.6 PO4]]> Example 10 4.43 13.72 19.83 19.38 <![CDATA[LiMn 0.4 Fe 0.6 PO4]]> Example 11 4.42 13.72 19.79 19.40 <![CDATA[LiMn 0.4 Fe 0.6 PO4]]> Example 12 4.43 13.88 19.95 19.45 <![CDATA[LiMn 0.4 Fe 0.6 PO4]]> Example 13 4.45 13.72 19.63 19.37 <![CDATA[LiMn 0.4 Fe 0.6 PO4]]> Comparative Example 1 4.40 16.11 16.43 19.44 <![CDATA[LiMn 0.5 Fe 0.5 PO4]]> Comparative Example 2 4.45 14.81 19.97 19.40 <![CDATA[LiMn 0.4 Fe 0.6 PO4]]>
[0141] As shown in Table 1, by controlling the molar ratio of lithium manganese iron phosphate precursor and recycled lithium iron phosphate, lithium manganese iron phosphate with a specific manganese-iron ratio can be obtained using the preparation method of the present invention.
[0142] Table 2 Test results of lithium manganese iron phosphate and coin cells
[0143]
[0144] As shown in Table 2, compared with Comparative Example 1, the specific surface area of lithium manganese iron phosphate in Examples 2, 4, and 5 is reduced, which helps to improve the processing performance of lithium manganese iron phosphate in the process of processing into positive electrode sheets; compared with Comparative Example 2, the specific capacity of Examples 1 and 6-13 is higher, proving that the lithium manganese iron phosphate prepared by the method of the present invention has a higher specific capacity.
[0145] Table 3 Test results of lithium-ion batteries
[0146]
[0147]
[0148] As shown in Table 3, the lithium manganese iron phosphate prepared by the method of the present invention has a high specific capacity.
[0149] The preferred embodiments and experimental verifications of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.
Claims
1. A method of preparing lithium manganese iron phosphate by solid phase method from recycled lithium iron phosphate, characterized by, Includes the following steps: 1) Li x Mn y Fe z The PO4 lithium manganese iron phosphate precursor, recycled lithium iron phosphate, first carbon source, and deionized water were mixed and then ball-milled until the particle size D50 was 0.35-0.40μm to obtain the first material; wherein, 1.0≤x≤1.05, 0.2≤y≤0.8, 0.2≤z≤0.8, and y+z=1; 2) Under an inert atmosphere, the first material is subjected to a first sintering treatment to obtain the lithium manganese iron phosphate; the temperature of the first sintering treatment is 720-770℃. The lithium manganese iron phosphate precursor is prepared by a method including at least the following steps: 1) After mixing lithium source, manganese source, iron source, phosphorus source, second carbon source and deionized water, the mixture is ball-milled until the particle size D50 is 0.6-0.65μm. After drying, the second material is obtained. 2) The second material is subjected to a second sintering treatment to obtain the lithium manganese iron phosphate precursor; the temperature of the second sintering treatment is 450-500℃.
2. The method of claim 1, wherein, The heating rate of the first sintering treatment is 3-5℃ / min.
3. The method according to any of claims 1-2, characterized in that, The first carbon source includes at least one of sucrose, glucose, and polyethylene glycol.
4. The method according to any one of claims 3, characterized in that, wherein The molar ratio of the lithium source, manganese source, iron source, and phosphorus source is 1.0-1.05:0.7:0.3:1.
0.
5. The method of claim 1, wherein, The heating rate for the second sintering treatment is 3-5℃ / min.
6. The method according to any one of claims 1-2, 4-5, characterized in that, The lithium source is a mixture of lithium carbonate and lithium dihydrogen phosphate; and / or, the manganese source is at least one of manganese tetroxide, manganese acetate, and manganese oxalate; and / or, the iron source is iron phosphate; and / or, the phosphorus source is at least one of lithium dihydrogen phosphate and iron phosphate; and / or, the second carbon source includes at least one of sucrose and glucose.
7. The method according to any one of claims 4-5, characterized in that, The drying in step 1) is spray drying, and the conditions for spray drying are: inlet temperature 180-250℃ and outlet temperature 70-90℃.
8. The method of any one of claims 1-2, 4-5, wherein, The elemental contents of the lithium manganese iron phosphate precursor and the recovered lithium iron phosphate were obtained respectively. The molar ratio of the lithium manganese iron phosphate precursor to the recovered lithium iron phosphate is determined based on the elemental content in the lithium manganese iron phosphate precursor and the recovered lithium iron phosphate, as well as the target elemental content of the lithium manganese iron phosphate.