Process for the preparation of vanadium-doped iron phosphate and lithium iron phosphate

Abstract

The application discloses a preparation method of vanadium-doped iron phosphate and lithium iron phosphate, and relates to the technical field of preparation of iron phosphate and lithium iron phosphate. The preparation method of the vanadium-doped iron phosphate comprises the following steps: S1, weighing iron source, phosphorus source and vanadium source, mixing and grinding, then adding hydrogen peroxide after drying to obtain a mixed solution; S2, filtering the mixed solution to obtain a solid sample, drying the solid sample, and then sintering to obtain the vanadium-doped iron phosphate. The vanadium compound is treated separately with the iron phosphate, so that the vanadium doping is more uniform. In the preparation process of the iron phosphate, the vanadium compound is added, and the vanadium element is directly embedded into the crystal lattice of the iron phosphate, so that the charging performance is improved. The doping of the iron position is better than that of the lithium position, so the vanadium doping is performed on the iron phosphate, and the vanadium partially replaces the iron position. The doping improves the conductivity of the material, reduces the polarization value in the charging and discharging process, and improves the capacity in the charging and discharging range.

Description

Technical Field

[0001] This invention relates to the field of iron phosphate and lithium iron phosphate preparation technology, and specifically to a method for preparing vanadium-doped iron phosphate and lithium iron phosphate. Background Technology

[0002] Lithium iron phosphate (LiFePO4) is a cathode material for lithium-ion batteries, possessing excellent electrochemical performance and widely used in electric vehicles, energy storage systems, and portable electronic devices. LiFePO4 batteries are widely used in vehicles such as electric cars and electric bicycles due to their high safety, long lifespan, and high-temperature stability. They exhibit better high-temperature resistance compared to other lithium-ion battery types. They are also used in energy storage systems, such as solar and wind power storage systems, primarily due to their long cycle life and high charge / discharge efficiency. Because of their relatively high energy density and low cost, LiFePO4 batteries are widely used in portable electronic devices such as laptops, smartphones, and tablets. LiFePO4 batteries are also used in emergency power and backup power systems to ensure reliable power supply during power outages or grid failures.

[0003] To improve the conductivity and cycle life of lithium iron phosphate batteries, vanadium is typically doped into the cathode material during the manufacturing process. Vanadium doping improves the conductivity of the cathode material. Conductivity refers to a material's ability to conduct electricity; increasing conductivity helps to conduct lithium ions more quickly, thereby improving the battery's charge / discharge rate and performance. It also slows down structural changes in the cathode material during cycling, reducing the material's polarization and extending the battery's cycle life. Battery cycle life refers to the number of charge / discharge cycles a battery can undergo while maintaining relatively stable performance.

[0004] However, in existing doping processes, vanadium is usually doped by ball milling it together with other materials during the preparation of lithium iron phosphate, followed by sintering. In this doping method, vanadium largely replaces lithium sites, resulting in a minimal improvement in the conductivity of lithium iron phosphate batteries.

[0005] In view of the above, this application is hereby submitted. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method for preparing vanadium-doped iron phosphate and lithium iron phosphate. The method involves preparing the vanadium-doped iron phosphate separately using an iron source, a phosphorus source, and a vanadium source, thereby solving the problem that the conductivity improvement of vanadium-doped lithium iron phosphate batteries in the prior art is not significant.

[0007] This invention provides a method for preparing vanadium-doped iron phosphate, comprising the following steps:

[0008] S1: Weigh out the iron source, phosphorus source and vanadium source, mix and grind them, then dry them and add hydrogen peroxide to stir to obtain a mixed solution;

[0009] S2: After filtering the mixture, a solid sample is obtained. The solid sample is dried and then sintered to obtain vanadium-doped iron phosphate.

[0010] Preferably, the iron source is ferrous sulfate, the phosphorus source is one or a mixture of several of ammonium phosphate, ammonium monohydrogen phosphate and ammonium dihydrogen phosphate, and the vanadium source is one or a mixture of several of vanadium pentoxide, vanadium oxalate, vanadium oxalate and ammonium metavanadate.

[0011] Preferably, the molar ratio of elements Fe, P, and V in the mixture is 2:1:0.05 to 0.1.

[0012] Preferably, the concentration of the hydrogen peroxide is 10 wt%.

[0013] Preferably, the sintering temperature in S2 is 700–800°C, and the sintering time is 10–14 hours.

[0014] To achieve the above objectives, embodiments of the present invention also provide a method for preparing vanadium-doped lithium iron phosphate, which is prepared from the vanadium-doped lithium iron phosphate obtained by the above preparation method, and includes the following steps:

[0015] S01: Weigh the vanadium-doped iron phosphate, lithium source, carbon source and vanadium source, mix and grind them, and then dry them to obtain the pre-calcined material;

[0016] S02: The above pre-calcined material is subjected to a first calcination and a second calcination in sequence to obtain lithium iron phosphate cathode material.

[0017] Preferably, the carbon source in S01 is PEG1500 or glucose, and the amount of the carbon source is 3-10%.

[0018] Preferably, the lithium source is lithium carbonate.

[0019] Preferably, the temperature of the first calcination is 250–600°C, and the calcination time is 3–6 hours.

[0020] Preferably, the temperature of the second calcination is 600–750°C, and the calcination time is 5–8 hours.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] (1) In this embodiment of the invention, vanadium compounds are treated separately and together with iron phosphate to make the vanadium doping more uniform. Adding vanadium compounds during the preparation of iron phosphate allows vanadium to be directly embedded into the lattice of iron phosphate, creating more and more uniform migration channels, thereby improving the charging performance. Iron doping is better than lithium doping because the stable high-valence dopant position in the lithium-ion transport channel hinders lithium-ion diffusion, while iron doping does not have this problem. Therefore, when vanadium is doped into iron phosphate, vanadium partially replaces the iron position. Vanadium ions enter the iron phosphate and replace the iron position, causing lattice distortion and improving the diffusion path of ions in the crystal. Doping improves the conductivity of the material, reduces the polarization value during charging and discharging, and increases the capacity within the charging and discharging range. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0024] Figure 1 The image shows a performance test diagram of a battery made from the vanadium-doped lithium iron phosphate cathode material of this invention.

[0025] Figure 2 This is a diagram illustrating the sampling process in this invention;

[0026] Figure 3 This is a diagram showing the ICP test results in this invention;

[0027] Figure 4 The image shows a SEM scan of the vanadium-doped lithium iron phosphate cathode material prepared in Example 1 of this invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0029] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0030] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0031] This invention provides a method for preparing vanadium-doped iron phosphate, comprising the following steps:

[0032] S1: Weigh out an iron source, a phosphorus source, and a vanadium source, mix and grind them, then dry them and add hydrogen peroxide to stir to obtain a mixed solution; wherein, the iron source is ferrous sulfate, the phosphorus source is one or a mixture of several of ammonium phosphate, ammonium monohydrogen phosphate, and ammonium dihydrogen phosphate, the vanadium source is one or a mixture of several of vanadium pentoxide, vanadium oxalate, vanadium oxyoxalate, and ammonium metavanadate, and the molar ratio of Fe, P, and V in the mixed solution is 2:1:0.05-0.1, and the concentration of hydrogen peroxide is 10wt%.

[0033] S2: After filtering the mixture, a solid sample is obtained. The solid sample is dried and then sintered to obtain vanadium-doped iron phosphate. The sintering temperature is 700-800℃ and the sintering time is 10-14 hours.

[0034] This invention also provides a method for preparing vanadium-doped lithium iron phosphate, which is prepared from the vanadium-doped lithium iron phosphate obtained by the above preparation method, and includes the following steps:

[0035] S01: Weigh the vanadium-doped iron phosphate, lithium source, carbon source, and vanadium source, mix and grind them, and then dry them to obtain a pre-calcined material; wherein, the carbon source is PEG1500 and glucose, the amount of the carbon source is 3-10%, and the lithium source is lithium carbonate.

[0036] S02: The above pre-calcined material is subjected to a first calcination and a second calcination in sequence to obtain lithium iron phosphate cathode material. The temperature of the first calcination is 250-600℃ and the calcination time is 3-6h. The temperature of the second calcination is 600-750℃ and the calcination time is 5-8h.

[0037] Example 1

[0038] This invention provides a method for preparing vanadium-doped lithium iron phosphate, comprising the following steps:

[0039] Weigh 304g of ferrous sulfate, 149g of ammonium phosphate and 14.56g of V2O5, grind them together in a mortar for half an hour, place them in a constant temperature oven at 80℃ for 12 hours, take them out, let them cool to room temperature, add 10% hydrogen peroxide, stir for half an hour, filter, place the filtered sample in a drying oven to dry for 2 hours, put the dried sample into a muffle furnace, sinter at 750℃ for 12 hours, and obtain vanadium-doped iron phosphate material.

[0040] Weigh 200g of vanadium-doped iron phosphate, 51.4g of lithium carbonate, 6g of PEG1500, and 12g of glucose prepared by the above method and mix them in a ball mill for 2 hours. The mixture is then spray-dried and calcined at 400°C for 4 hours under a nitrogen atmosphere. Finally, the temperature is raised to 780°C and calcined for 6 hours to obtain the lithium iron phosphate cathode material.

[0041] Example 2

[0042] This invention provides a method for preparing vanadium-doped lithium iron phosphate, comprising the following steps:

[0043] Weigh 304g of ferrous sulfate, 149g of ammonium phosphate, and 14.56g of vanadium oxalate, and grind them together in a mortar. After grinding for half an hour, place the mortar in a constant temperature oven at 80℃ for 12 hours. Remove the mortar, allow it to cool to room temperature, add 10% hydrogen peroxide, stir for half an hour, filter, and dry the filtered sample in a drying oven for 2 hours. Place the dried sample in a muffle furnace and sinter at 750℃ for 12 hours to obtain vanadium-doped iron phosphate material.

[0044] Weigh 200g of vanadium-doped iron phosphate, 51.4g of lithium carbonate, 6g of PEG1500, and 12g of glucose prepared by the above method and mix them in a ball mill for 2 hours. The mixture is then spray-dried and calcined at 400°C for 4 hours under a nitrogen atmosphere, and then heated to 780°C for 6 hours to obtain lithium iron phosphate cathode material.

[0045] Example 3

[0046] This invention provides a method for preparing vanadium-doped lithium iron phosphate, comprising the following steps:

[0047] Weigh 304g of ferrous sulfate, 149g of ammonium phosphate, and 20.02g of vanadium oxalate, and grind them together in a mortar. After grinding for half an hour, place the mortar in a constant temperature oven at 80℃ for 12 hours. Remove the mortar, allow it to cool to room temperature, add 10% hydrogen peroxide, stir for half an hour, filter, and dry the filtered sample in a drying oven for 2 hours. Place the dried sample in a muffle furnace and sinter at 750℃ for 12 hours to obtain vanadium-doped iron phosphate material.

[0048] Weigh 200g of vanadium-doped iron phosphate, 51.4g of lithium carbonate, 6g of PEG1500, and 12g of glucose prepared by the above method and mix them in a ball mill for 2 hours. The mixture is then spray-dried and calcined at 400°C for 4 hours under a nitrogen atmosphere, and then heated to 780°C for 6 hours to obtain lithium iron phosphate cathode material.

[0049] Example 4

[0050] This invention provides a method for preparing vanadium-doped lithium iron phosphate, comprising the following steps:

[0051] Weigh 304g of ferrous sulfate, 149g of ammonium phosphate, and 7.28g of vanadium oxalate, and grind them together in a mortar. After grinding for half an hour, place the mortar in a constant temperature oven at 80℃ for 12 hours. Remove the mortar, allow it to cool to room temperature, add 10% hydrogen peroxide, stir for half an hour, filter, and dry the filtered sample in a drying oven for 2 hours. Place the dried sample in a muffle furnace and sinter at 750℃ for 12 hours to obtain vanadium-doped iron phosphate material.

[0052] Weigh 200g of vanadium-doped iron phosphate, 51.4g of lithium carbonate, 6g of PEG1500, and 12g of glucose prepared by the above method and mix them in a ball mill for 2 hours. The mixture is then spray-dried and calcined at 400°C for 4 hours under a nitrogen atmosphere, and then heated to 780°C for 6 hours to obtain lithium iron phosphate cathode material.

[0053] Example 5

[0054] This invention provides a method for preparing vanadium-doped lithium iron phosphate, comprising the following steps:

[0055] Weigh 304g of ferrous sulfate, 149g of ammonium phosphate, and 9.1g of vanadium oxalate, and grind them together in a mortar. After grinding for half an hour, place the mortar in a constant temperature oven at 80℃ for 12 hours. Remove the mortar, allow it to cool to room temperature, add 10% hydrogen peroxide, stir for half an hour, filter, and dry the filtered sample in a drying oven for 2 hours. Place the dried sample in a muffle furnace and sinter at 750℃ for 12 hours to obtain vanadium-doped iron phosphate material.

[0056] Weigh 200g of vanadium-doped iron phosphate, 51.4g of lithium carbonate, 6g of PEG1500, and 12g of glucose prepared by the above method and mix them in a ball mill for 2 hours. The mixture is then spray-dried and calcined at 400°C for 4 hours under a nitrogen atmosphere, and then heated to 780°C for 6 hours to obtain lithium iron phosphate cathode material.

[0057] Example 6

[0058] This invention provides a method for preparing vanadium-doped lithium iron phosphate, comprising the following steps:

[0059] Weigh 304g of ferrous sulfate, 149g of ammonium phosphate, and 18.2g of vanadium oxalate, and grind them together in a mortar. After grinding for half an hour, place the mortar in a constant temperature oven at 80℃ for 12 hours. Remove the mortar, allow it to cool to room temperature, add 10% hydrogen peroxide, stir for half an hour, filter, and dry the filtered sample in a drying oven for 2 hours. Place the dried sample in a muffle furnace and sinter at 750℃ for 12 hours to obtain vanadium-doped iron phosphate material.

[0060] Weigh 200g of vanadium-doped iron phosphate, 51.4g of lithium carbonate, 6g of PEG1500, and 12g of glucose prepared by the above method and mix them in a ball mill for 2 hours. The mixture is then spray-dried and calcined at 400°C for 4 hours under a nitrogen atmosphere, and then heated to 780°C for 6 hours to obtain lithium iron phosphate cathode material.

[0061] Example 7

[0062] This invention provides a method for preparing vanadium-doped lithium iron phosphate, which differs from Example 6 in that the phosphorus source in this example is ammonium hydrogen phosphate, and includes the following steps:

[0063] Weigh 304g of ferrous sulfate, 149g of ammonium hydrogen phosphate, and 18.2g of vanadium oxalate, and grind them together in a mortar. After grinding for half an hour, place the mortar in a constant temperature oven at 80℃ for 12 hours. Remove the mortar, allow it to cool to room temperature, add 10% hydrogen peroxide, stir for half an hour, filter, and dry the filtered sample in a drying oven for 2 hours. Place the dried sample in a muffle furnace and sinter at 750℃ for 12 hours to obtain vanadium-doped iron phosphate material.

[0064] Weigh 200g of vanadium-doped iron phosphate, 51.4g of lithium carbonate, 6g of PEG1500, and 12g of glucose prepared by the above method and mix them in a ball mill for 2 hours. The mixture is then spray-dried and calcined at 400°C for 4 hours under a nitrogen atmosphere, and then heated to 780°C for 6 hours to obtain lithium iron phosphate cathode material.

[0065] Comparative Example 1

[0066] A method for preparing lithium iron phosphate is provided, comprising the following steps:

[0067] Weigh 200g of iron phosphate (without vanadium doping), 51.4g of lithium carbonate, 6g of PEG1500, 12g of glucose and 2g of V2O5 and mix them in a ball mill for 2 hours. The mixture is then spray-dried and calcined at 400°C for 4 hours under a nitrogen atmosphere. The temperature is then raised to 780°C and calcined for 6 hours to obtain vanadium-doped lithium iron phosphate cathode material.

[0068] Comparative Example 2

[0069] A method for preparing lithium iron phosphate is provided, comprising the following steps:

[0070] Weigh 200g of iron phosphate (without vanadium doping), 51.4g of lithium carbonate, 6g of PEG1500, 12g of glucose and 2g of vanadium oxalate and mix them in a ball mill for 2 hours. The mixture is then spray-dried and calcined at 400°C for 4 hours under a nitrogen atmosphere. The temperature is then raised to 780°C and calcined for 6 hours to obtain vanadium-doped lithium iron phosphate cathode material.

[0071] Test results

[0072] The vanadium-doped lithium iron phosphate cathode materials prepared by the methods in Examples 1-6 and Comparative Examples 1-2 were used to prepare batteries, and performance tests were conducted. The performance test results are shown in Table 1 and Table 2. Figure 1 As shown, the battery manufacturing process is as follows:

[0073] This experiment required configuring the positive electrode material into a button cell for testing. The specific procedures were as follows: the prepared material was used as the positive electrode, and a lithium sheet was used as the negative electrode for battery assembly. A 1 mol / L LiPF6 / EC (ethylene carbonate) / DMC (diethyl carbonate) electrolyte (EC and DMC volume ratio 1:1) was used as the electrolyte, and a polypropylene microporous membrane was used as the separator. A two-electrode battery testing module was used for battery performance testing. The charge-discharge performance of the positive electrode material was tested on a battery testing system. A constant current charge-discharge regime was adopted, with a charge-discharge voltage range of 2.0-4.2V. A 1-minute resting period was set before each constant current process. Battery assembly was carried out in a glove box under a high-purity argon atmosphere.

[0074] Table 1

[0075]

[0076]

[0077] As can be seen from the comparison of Comparative Examples 1-2 and Examples 1-7 in Table 1, the addition of vanadium compounds during the preparation of iron phosphate in the embodiments of the present invention, through pre-doping, results in vanadium-doped lithium iron phosphate cathode materials with higher conductivity compared to those prepared by co-doping in the prior art. Furthermore, it reduces the polarization value during charge and discharge processes and improves the capacity within the charge and discharge range. Moreover, a comparison between Example 4 and other examples shows that a molar ratio of Fe, P, and V within the range of 2:1:0.05 to 0.1 is more advantageous during the iron phosphate doping process.

[0078] The vanadium-doped lithium iron phosphate cathode materials prepared by the methods in Examples 1-6 and Comparative Examples 1-2 were subjected to ICP testing. The testing method included the following steps:

[0079] 1. Weighing: Accurately weigh 0.1g of vanadium-doped lithium iron phosphate cathode material into a 50mL polytetrafluoroethylene digestion tube. Record its mass as m1, m2, m3…

[0080] 2. Add appropriate amounts of inorganic acid (5 mL concentrated nitric acid / 1 mL hydrochloric acid) to the weighed sample digestion tubes. Cover the tubes and place them in a stainless steel reaction vessel. Heat the vessel in an oven at 190 degrees Celsius for approximately 10 hours, then stop heating and allow it to cool.

[0081] 3. Transfer the cooled solution to a 25ml plastic volumetric flask, and finally dilute to volume with deionized water.

[0082] 4. Prepare standard test solutions. The standard solutions are national standard reference materials, and the concentration points of the curve are 0, 0.5, 1.0, 2.0, and 5.0 mg / L.

[0083] 5. Instrument Testing: First, establish a standard solution calibration curve using the instrument's ICP. Input the sample mass and volume, then test the digested solutions sequentially. Solutions exceeding the curve range should be diluted before testing. Finally, determine the final content of each element in each sample using spectral analysis. The test results are shown in Table 2 below. Figure 3 As shown, the sampling situation is as follows: Figure 2 As shown, the vanadium-doped lithium iron phosphate cathode material prepared in Example 1 was also subjected to SEM scanning, and the results are as follows. Figure 4 As shown:

[0084]

[0085]

[0086] The ICP test results and SEM scan results show that the vanadium-doped lithium iron phosphate cathode material prepared in the embodiments of the present invention has a higher uniformity of vanadium doping.

[0087] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing vanadium-doped lithium iron phosphate, comprising preparing vanadium-doped iron phosphate, characterized in that, Includes the following steps: S01: Weigh vanadium-doped iron phosphate, lithium source, carbon source and vanadium source, mix, grind and dry to obtain pre-calcined material; S02: The above pre-calcined material is subjected to a first calcination and a second calcination in sequence to obtain lithium iron phosphate cathode material; The method for preparing the vanadium-doped iron phosphate includes the following steps: S1: Weigh out iron source, phosphorus source and vanadium source, mix and grind them, then dry them and add hydrogen peroxide to stir to obtain a mixed solution; in the mixed solution, the molar ratio of elements Fe, P and V is 2:1:0.05~0.1; S2: After filtering the mixture, a solid sample is obtained. The solid sample is dried and then sintered to obtain vanadium-doped iron phosphate.

2. The method for preparing vanadium-doped lithium iron phosphate according to claim 1, characterized in that, The carbon source described in S01 is PEG1500 and glucose, and the amount of the carbon source is 3-10%.

3. The method for preparing vanadium-doped lithium iron phosphate according to claim 1, characterized in that, The lithium source is lithium carbonate.

4. The method for preparing vanadium-doped lithium iron phosphate according to claim 1, characterized in that, The temperature of the first calcination is 250~600℃, and the calcination time is 3~6h.

5. The method for preparing vanadium-doped lithium iron phosphate according to claim 1, characterized in that, The second calcination temperature is 600~750℃, and the calcination time is 5~8h.

6. The method for preparing vanadium-doped lithium iron phosphate according to claim 1, characterized in that, The iron source is ferrous sulfate, the phosphorus source is one or a mixture of several of ammonium phosphate, ammonium monohydrogen phosphate and ammonium dihydrogen phosphate, and the vanadium source is one or a mixture of several of vanadium pentoxide, vanadium oxalate, vanadium oxalate and ammonium metavanadate.

7. The method for preparing vanadium-doped lithium iron phosphate according to claim 1, characterized in that, The concentration of the hydrogen peroxide is 10 wt%.

8. The method for preparing vanadium-doped lithium iron phosphate according to claim 1, characterized in that, The sintering temperature in S2 is 700~800℃, and the sintering time is 10~14 hours.

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