Preparation method of vanadium and titanium co-doped high-compaction lithium iron phosphate positive electrode material

Abstract

The invention discloses a vanadium and titanium co-doped high-compaction lithium iron phosphate positive electrode material preparation method, which comprises: S1, filtering rutile mother liquor to remove impurities, adjusting the content of solution elements to obtain a ferrous sulfate acidic solution containing a titanium source, and recording the ferrous sulfate acidic solution as a solution A; preparing a phosphoric acid solution containing a vanadium source, and recording the phosphoric acid solution as a solution B; s2, adding an oxidizing agent and a phosphorus salt solution into the solution A in a parallel flow manner, adjusting the pH value through alkali liquor, and performing a synthetic reaction to obtain yellow slurry C; s3, filtering, washing and pulping the yellow slurry C to obtain yellow slurry D; s4, adding the solution B into the yellow slurry D, aging, washing, flashing and calcining to obtain yellow white dry powder E; and S5, uniformly premixing the yellowish-white dry powder E, a lithium source, a carbon source and water, and performing graded grinding, spraying, sintering, crushing and packaging to obtain the high-compaction lithium iron phosphate. The method provided by the invention has the characteristics of simple synthesis process, uniform material mixing and the like, and can realize large-scale production of a production line.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to a method for preparing a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material. Background Art

[0002] Lithium iron phosphate cathode materials are widely used in the new energy vehicle market and energy storage field due to their safety, environmental protection, low raw material prices, stable discharge platform, and high energy density. + The diffusion coefficient and low electrical conductivity limit the use of lithium iron phosphate materials for high-rate discharge.

[0003] Therefore, people have adopted a variety of strategies to improve the electrochemical performance of lithium iron phosphate cathode materials. They mainly include particle size adjustment, carbon coating and ion doping. For example, reducing the size of lithium iron phosphate particles helps to shorten the diffusion distance of lithium ions, thereby improving rate performance and cycle stability. Carbon coating can improve the conductivity of lithium iron phosphate cathode materials and further optimize the electrochemical properties of lithium iron phosphate materials. At the same time, during the carbon thermal reduction process, the carbon source will inhibit the growth of lithium iron phosphate primary particles. In addition, ion doping can also improve the conductivity of lithium iron phosphate cathode materials.

[0004] High-valent metal cations can effectively improve the conductivity of materials, thereby improving the rate performance of lithium iron phosphate positive electrode materials. High-valent elements such as metal vanadium, titanium, and niobium are widely used in the doping preparation of lithium iron phosphate. In the existing lithium iron phosphate preparation process, most of the doping processes are introduced through sand grinding and subsequent sintering. This may cause uneven distribution of doping elements and local enrichment, thereby forming impurities, making it difficult to effectively improve the electrochemical performance of the material.

[0005] Chinese patents CN118125410A and CN118495494A respectively doped vanadium and titanium in the process of preparing iron phosphate, but it is difficult to effectively improve the performance of the material by doping with a single element; Chinese patent CN118811788A respectively prepared vanadium and titanium doped iron phosphate by hydrothermal method, and then mixed them at the lithium iron phosphate end, but this is still a single element doping. Chinese patent CN 118270753 A discloses a method for preparing vanadium-titanium ion co-doped lithium iron phosphate material with vanadium extraction tailings, pre-treating the vanadium extraction tailings by alkali roasting-water leaching process; then adding iron source, phosphorus source and lithium source to the high-concentration vanadium-titanium separation liquid for hydrothermal reaction to obtain vanadium-titanium co-doped lithium iron phosphate crystals, but this method still requires hydrothermal reaction, which has high energy consumption and is difficult to be applied industrially. Summary of the invention

[0006] One of the purposes of the present invention is to provide a method for preparing a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material, so as to solve the problems of uneven distribution of doping elements, low electronic conductivity and poor rate performance of lithium iron phosphate positive electrode materials in the prior art; In order to achieve the above object, the present invention adopts the following technical solution.

[0007] A vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material and a preparation method thereof, comprising the following preparation steps: S1, filtering and removing impurities from the rutile mother liquor, adjusting the element content of the solution (adjusting the titanium content in the solution by adding titanium dioxide or titanyl sulfate) to obtain an acidic ferrous sulfate solution containing a titanium source, which is recorded as solution A; preparing a phosphoric acid mixed solution containing a vanadium source, which is recorded as solution B; S2, adding the oxidant and the phosphate solution to the solution A in parallel, adjusting the pH with an alkali solution, and obtaining a yellow slurry C through a synthesis reaction; S3, filtering, washing and beating the yellow slurry C to obtain yellow slurry D; S4, adding solution B to yellow slurry D, and obtaining yellow-white dry powder E after aging, washing, flash evaporation and calcination; S5. Add water to the yellow-white dry powder E, lithium source and carbon source and premix them evenly, then grind and spray them, sinter them, and crush them to obtain a high-density lithium iron phosphate product.

[0008] Preferably, in step S1, the pH of solution A is between 1.0 and 2.2, and the concentration of ferrous iron is 50-120 g / L; and the vanadium source is one or more of ammonium metavanadate, vanadium pentoxide, and vanadyl sulfate.

[0009] Preferably, in step S2, the oxidant is one or more of hydrogen peroxide, oxygen, and ozone, and the phosphate salt is one or more of ammonium phosphate, phosphoric acid, and sodium hydrogen phosphate; the molar ratio of the oxidant to ferrous sulfate is 1.0-1.5:1; the molar ratio of ferrous sulfate to phosphate salt is 1:1.01-1.08; the temperature in the synthesis reaction is 45-70°C, the insulation time is 30-120min, and the reaction pH is 1.5-2.2.

[0010] Preferably, in step S3, the conductivity of the solution after washing is less than 2000 us / cm; and the solid content after pulping is 10-18%.

[0011] Preferably, in step S4, the aging pH is 1.2-1.8, the aging time is 90-300 min, and the aging temperature is 84-97°C; the conductivity of the washed solution is <500 us / cm; the calcination temperature is 500-700°C, and the calcination time is 30-240 min.

[0012] Preferably, in step S5: the lithium source is one or more of lithium carbonate, lithium hydroxide, and lithium acetate; the carbon source is one or more of glucose, sucrose, polyethylene glycol, soluble starch and carbon black, and the amount of carbon source added is 5%-18% of the mass of the iron phosphate raw material; the molar ratio of lithium, iron and phosphorus is (0.99-1.01): (0.955-0.975): 1.

[0013] Preferably, in step S5, the grinding particle size D50 is 0.30-0.50 μm; the sintering temperature is 750-820° C., and the holding time is 510-600 min.

[0014] A lithium iron phosphate battery prepared from a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material.

[0015] Compared with the existing technology, the present invention has the following beneficial effects: the present invention realizes the preparation of high-density lithium iron phosphate by in-situ doping. Titanium and vanadium are doped at the synthesis and aging ends of the iron phosphate respectively, which can effectively enter the iron phosphate lattice, not only realizing the uniform distribution of titanium and vanadium in the lithium iron phosphate material, avoiding the possibility of local enrichment to form impurities; but also effectively improving the conductivity and ion migration rate of the lithium iron phosphate positive electrode material, thereby improving the electrochemical performance of the material.

[0016] In the present invention, the doping amount of vanadium and titanium elements can be adjusted according to the content of vanadium and titanium sources in the solution. Theoretically, the doping amount of vanadium and titanium in the finished product can be adjusted within the range of 0-5000ppm, which has a wide range of applications. The preparation method of this patent has the characteristics of simple synthesis process and uniform mixing, and can realize large-scale production of production lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The XRD patterns of Example 1 and Comparative Example 1 are shown below; Figure 2 This is the SEM image of Example 1, with a magnification of 10,000 times; Figure 3 This is the SEM image of Example 1, with a magnification of 30,000 times; Figure 4 is the EDS element distribution diagram of Example 1; Figure 5 This is the 0.1C charge and discharge curve of Example 1. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0019] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0020] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "inner", "outer", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the product of the invention is usually placed when in use. This is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, if the terms "first", "second", etc. appear in the description of the present invention, they are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0021] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "setting" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] <Example 1> A method for preparing a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material comprises the following steps: S1): After filtering and removing impurities from the rutile mother liquor, prepare a 2.2L solution with a ferrous iron concentration of 80g / L, add 2.75g of titanium dioxide and stir evenly, record it as solution A for later use; add 1.2g of ammonium metavanadate into the phosphoric acid solution to prepare a phosphoric acid mixed solution, record it as solution B.

[0023] S2): After adding hydrogen peroxide with a molar amount of 1.3 times that of ferrous sulfate and phosphate solution with a molar amount of 1.04 times that of ferrous sulfate to solution A in parallel, the pH value was adjusted to 1.9, and the mixture was heated to 55° C. and stirred for 90 minutes to obtain a yellow slurry.

[0024] S3): The yellow slurry is filtered and washed until the conductivity is 1500 us / cm, and a slurry with a solid content of 16% is obtained after beating.

[0025] S4): Add a mixed solution of phosphoric acid containing a vanadium source to the slurry, heat to 95°C, keep warm for 120 minutes, filter and wash until the conductivity is 500us / cm, flash dry, and sinter at 550°C for 120 minutes to obtain a yellow-white dry powder.

[0026] S5): The amount of lithium carbonate and iron-phosphorus substances in the yellow-white dry powder is 1.005:0.962:1, and the materials are sand-ground to a particle size of D50 = 0.45 μm, and then spray-dried. After being kept at 780°C for 540 minutes, they are crushed to obtain a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material.

[0027] <Example 2> A method for preparing a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material comprises the following steps: S1): After filtering and removing impurities from the rutile mother liquor, prepare a 2.2L solution with a ferrous iron concentration of 80g / L, add 5.5g of titanyl sulfate and stir evenly, record it as solution A for later use; add 1.2g of ammonium metavanadate to the phosphoric acid solution to prepare a phosphoric acid mixed solution, record it as solution B.

[0028] S2): After adding hydrogen peroxide with a molar amount of 1.3 times that of ferrous sulfate and phosphate solution with a molar amount of 1.04 times that of ferrous sulfate to solution A in parallel, the pH value was adjusted to 1.9, and the mixture was heated to 55° C. and stirred for 90 minutes to obtain a yellow slurry.

[0029] S3): The yellow slurry is filtered and washed until the conductivity is 1500 us / cm, and a slurry with a solid content of 16% is obtained after beating.

[0030] S4): Add a mixed solution of phosphoric acid containing a vanadium source to the slurry, heat to 95°C, keep warm for 120 minutes, filter and wash until the conductivity is 500us / cm, flash dry, and sinter at 550°C for 120 minutes to obtain a yellow-white dry powder.

[0031] S5): The amount of lithium carbonate and iron-phosphorus substances in yellow-white dry powder is 1.005:0.962:1, and the materials are sand-ground to a particle size of D50 = 0.45 μm, and then sprayed. After being kept at 780°C for 540 minutes, they are crushed to obtain a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material.

[0032] <Example 3> A method for preparing a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material comprises the following steps: S1): After filtering and removing impurities from the rutile mother liquor, prepare a 2.2L solution with a ferrous iron concentration of 80g / L, add 2.58g of titanium dioxide and stir evenly, record it as solution A for standby use; add 1.4g of ammonium metavanadate to the phosphoric acid solution to prepare a phosphoric acid mixed solution, record it as solution B; S2): After adding hydrogen peroxide with a molar amount of 1.3 times that of ferrous sulfate and phosphate solution with a molar amount of 1.04 times that of ferrous sulfate to solution A in parallel, the pH was adjusted to 1.9, heated to 55°C, and stirred for 90 minutes to obtain a yellow slurry.

[0033] S3): The yellow slurry is filtered and washed until the conductivity is 1500 us / cm, and a slurry with a solid content of 16% is obtained after beating.

[0034] S4): Add a mixed solution of phosphoric acid containing a vanadium source to the slurry, heat to 95°C, keep warm for 120 minutes, filter and wash until the conductivity is 500us / cm, flash dry, and sinter at 550°C for 120 minutes to obtain a yellow-white dry powder.

[0035] S5): The amount of lithium carbonate and iron-phosphorus substances in yellow-white dry powder is 1.005:0.962:1, and the materials are sand-ground to a particle size of D50 = 0.45 μm, and then sprayed. After being kept at 780°C for 540 minutes, they are crushed to obtain a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material.

[0036] <Comparative Example 1> Compared with Example 1, the only difference is that in step S1, no titanium or vanadium source is added to obtain the lithium iron phosphate positive electrode material (the solution obtained by filtering and removing impurities from the rutile mother liquor is used).

[0037] <Performance Test> The vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material prepared in the embodiment and the lithium iron phosphate positive electrode material of comparative example 1 were dispersed in NMP with PVDF and Super-p at a mass ratio of 94:3:3 for homogenization, and then coated, dried and punched to obtain circular pole pieces. Finally, the circular pole pieces, diaphragms, lithium sheets, gaskets and springs were assembled into CR2032 button batteries in a glove box for testing. The button battery was charged and discharged in the voltage range of 2.0~3.75 V. First, the electrochemical performance was tested at 0.2C / 0.5C and 0.2C / 1C rates after two cycles at 0.1C.

[0038] Compaction density test: measured under 3 tons of pressure using Sansi vertical and horizontal compaction density meter.

[0039] Scanning electron microscope test: The test was carried out using JSM-IT800 instrument from Japan Electronics.

[0040] Table 1: Electrochemical properties, compaction density and ICP test vanadium and titanium content of lithium iron phosphate samples

[0041] Table 2: Cell parameters of samples in Example 1 and Comparative Example 1

[0042] Depend on Figure 1 It can be seen that when the vanadium and titanium contents are constant, the main diffraction peaks of the vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material in Example 1 are consistent with the diffraction peaks of the lithium iron phosphate standard card, and there are no other impurity peaks. The synthesized samples all have a complete olivine structure, indicating that vanadium and titanium are not simply physically mixed in the lithium iron phosphate positive electrode material, but enter the lithium iron phosphate lattice, so it does not affect the crystal structure of LiFePO4. No diffraction peaks of carbon were observed in the XRD spectrum, indicating that the carbon after pyrolysis of the carbon source exists in an amorphous form. Table 2 Electrochemical tests show that when the compaction density is close, the electrochemical performance of the embodiments is better than that of the comparative examples, indicating that the doping of vanadium and titanium elements reduces the particle size of the lithium iron phosphate positive electrode material and reduces Li + The migration distance of the lithium iron phosphate cathode material is increased, and the electronic conductivity of the lithium iron phosphate cathode material is improved, so that the electrochemical performance is improved. Table 2 lists the unit cell parameters of the samples of Example 1 and Comparative Example 1 calculated by Jade 6.0 software. The decrease in the unit cell parameters of Example 1 may be due to the fact that V 5+ 、Ti 4+ Fe 2+ bit, and V 5+ 、Ti 4+ The radius is smaller than Fe 2+ (0.078 nm) ionic radius. Figure 2 , 3 It can be seen that the prepared lithium iron phosphate spherical particles have a particle size distribution of 200~600nm. Figure 4 It can be seen that in addition to the uniform distribution of Fe, O, and P elements in the lithium iron phosphate particles, Ti, V, and C are also uniformly distributed in the particles. This not only shows that a uniform carbon coating layer is formed on the surface of the LiFePO4 material after high-temperature calcination of the carbon source, but also proves that the co-doping of Ti and V elements has been achieved.

[0043] The above implementation cases are only for illustrating the technical solutions and features of the present invention, and their purpose is to enable people familiar with the technology to implement them better. They cannot be used to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention are within the protection scope of the present invention, and those not described in detail are prior art.

Claims

1. A method for preparing a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material, characterized in that: The following steps are involved: S1, filtering and removing impurities from the rutile mother liquor, adjusting the element content of the solution to obtain an acidic ferrous sulfate solution containing a titanium source, recorded as solution A; A phosphoric acid mixed solution containing a vanadium source is prepared, which is referred to as solution B; S2, adding the oxidant and the phosphate solution to the solution A in parallel, adjusting the pH with an alkali solution, and obtaining a yellow slurry C through a synthesis reaction; S3, filtering, washing and beating the yellow slurry C to obtain yellow slurry D; S4, adding solution B to yellow slurry D, and obtaining yellow-white dry powder E after aging, washing, flash evaporation and calcination; S5. Add water to the yellow-white dry powder E, the lithium source and the carbon source, premix them evenly, and then grind them by graded grinding, spraying, sintering and crushing to obtain the vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material.

2. The method for preparing a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material according to claim 1, characterized in that: The pH of solution A in S1 is between 1.0 and 2.2, and the concentration of ferrous ions is 50-120 g / L; the vanadium source is a mixture of one or more of ammonium metavanadate, vanadium pentoxide, and vanadyl sulfate.

3. The method for preparing a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material according to claim 1, characterized in that: The oxidant in S2 is a mixture of one or more of hydrogen peroxide, oxygen, and ozone; the phosphate salt is a mixture of one or more of ammonium phosphate, phosphoric acid, and sodium hydrogen phosphate.

4. The method for preparing a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material according to claim 3, characterized in that: The molar ratio of the oxidant to ferrous sulfate in S2 is (1.0-1.5):1; the molar ratio of ferrous sulfate to phosphate is 1:(1.01-1.08); the synthesis reaction temperature is 45-70°C, the reaction time is 30-120min, and the reaction pH is controlled between 1.5-2.

2.

5. The method for preparing a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material according to claim 1, characterized in that: The conductivity of the solution after washing in S3 is <2000us / cm; the solid content after pulping is 10%-18%.

6. The method for preparing a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material according to claim 1, characterized in that: In S4, the aging pH is controlled between 1.2-1.8, the aging time is 90-300 minutes, and the aging temperature is 84-97°C; the conductivity of the solution after washing is <500 us / cm, the calcination temperature is 500-700°C, and the calcination time is 30-240 minutes.

7. The method for preparing a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material according to claim 1, characterized in that: In S5, the lithium source is a mixture of one or more of lithium carbonate, lithium hydroxide, and lithium acetate; the carbon source is a mixture of one or more of glucose, sucrose, polyethylene glycol, soluble starch, and carbon black.

8. The method for preparing a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material according to claim 7, characterized in that: The amount of carbon source added in S5 is 5%-18% of the mass of the iron phosphate raw material; the molar ratio of lithium, iron and phosphorus is (0.99-1.01): (0.955-0.975):

1.

9. The method for preparing a vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material according to claim 1, characterized in that: The grinding particle size D50 in S5 is 0.30-0.50 μm; the sintering temperature is 750-820°C, and the holding time is 510-600 min.

10. A lithium iron phosphate battery prepared from the vanadium and titanium co-doped high-density lithium iron phosphate positive electrode material according to claims 1-9.

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