Vanadium and titanium composite doped iron phosphate as well as preparation method and application thereof

Abstract

The invention relates to the technical field of electrode materials, in particular to vanadium and titanium composite doped iron phosphate and a preparation method and application thereof.The preparation method comprises the following steps that S1, an iron source and a phosphorus source are weighed and placed in a beaker A and a beaker B respectively, ultrapure water is added into the beaker A, and an iron salt solution is obtained; b, adding ultrapure water, hydrogen peroxide and ammonia water into a beaker to obtain a phosphorus salt solution; s2, adding the ferric salt solution and the phosphorus salt solution into a reaction kettle to obtain yellow slurry A, and then obtaining a yellow filter cake; s3, adding ultrapure water into the yellow filter cake to obtain yellow slurry B, adding phosphoric acid into the yellow slurry B, heating until the system becomes white, and preserving heat; adding a vanadium source and a titanium source into the ferric salt solution prepared in the step S1; or adding a vanadium source and a titanium source into the yellow slurry B prepared in the step S3; or adding the vanadium source and the titanium source after the system in S3 becomes white; and S4, carrying out suction filtration, drying and sintering on the system after heat preservation. And the prepared vanadium and titanium composite doped iron phosphate has excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrode materials, in particular to a vanadium and titanium composite doped iron phosphate and a preparation method and application thereof. BACKGROUND

[0002] Lithium iron phosphate has become one of the most promising positive electrode materials for lithium ion batteries, and iron phosphate, as an important precursor thereof, has also been widely studied and applied. However, the existing conventional lithium iron phosphate material has low electronic conductivity and low compaction density, which greatly limits its commercial application in the fields of energy storage and power lithium ion batteries. In recent years, researchers have developed many improvement strategies, such as ion doping, surface coating, particle size distribution control, and composite material construction, among which metal ion doping has been widely studied because it can improve the conductivity of the material.

[0003] Generally, the doping elements can be introduced in two ways: the first way is to introduce during the solid-phase synthesis of lithium iron phosphate, usually using rutile titanium dioxide which has better reactivity, but this process requires uninterrupted grinding and consumes a large amount of heat energy; the second way is to introduce during the liquid-phase precipitation synthesis of iron phosphate, in which the doping elements are introduced in the form of ions, and there is almost no energy consumption, which is a more ideal doping method. Chinese Patent Application CN111908441A discloses a method for preparing titanium-doped iron phosphate by wet process, which controls the reaction of iron source and phosphorus source at low pH (pH<1) for a long time (3-5h), then filters, adds saturated titanium salt to the obtained clear solution, oxidizes for 0.75-1.25h, adjusts the pH to 1.2-1.8, and reacts at high temperature for 1-4h, and then washes, dries and calcines to obtain titanium-doped iron phosphate material. Although the cost of doping iron phosphate is reduced, the reaction conditions are harsh. Chinese Patent Application CN115818601A discloses a titanium-doped battery-grade iron phosphate and a preparation method thereof, which has the disadvantages of uncontrollable reaction, uneven doping, and uncontrollable doping amount, and the reaction also needs to add additional sodium nitrite catalyst, which increases the water treatment cost. SUMMARY

[0004] In view of the technical problems of unreasonable reaction conditions of existing doped elements and uneven doping, the present application provides a vanadium and titanium composite doped iron phosphate and a preparation method and application thereof.

[0005] The technical scheme of the present application is as follows: In a first aspect, the present application provides a preparation method of a vanadium and titanium composite doped iron phosphate, comprising the following steps: S1, weigh the iron source and the phosphorus source, and respectively put them in two beakers A and B. In the beaker A, add ultrapure water to mix with the iron source uniformly to obtain an iron salt solution. In the beaker B, add ultrapure water and hydrogen peroxide to mix with the phosphorus source uniformly, and then add ammonia water to adjust the pH and the concentration of phosphorus to obtain a phosphorus salt solution. S2, add the iron salt solution and the phosphorus salt solution into a reaction kettle to obtain yellow slurry A, and then obtain yellow filter cake after filtration and washing. S3, add ultrapure water to disperse the yellow filter cake to obtain yellow slurry B, and then add phosphoric acid to the yellow slurry B and heat to white system and keep warm. In the step S1, the iron salt solution is added with vanadium source and titanium source; or, in the step S3, the yellow slurry B is added with vanadium source and titanium source; or, after the system is heated to white, the vanadium source and the titanium source are added. S4, the system after keeping warm is filtered and dried to obtain a vanadium and titanium composite doped iron phosphate hydrate, and the vanadium and titanium composite doped iron phosphate is obtained after sintering.

[0006] Further, in the step S1, the iron source is one or more of FeCl2·4H2O, FeSO4·7H2O and Fe(CH3COO)2, and the phosphorus source is one or more of H3PO4 and NH4H2PO4; the molar ratio of iron to phosphorus is 1:(0.85-1.15).

[0007] Further, in the step S1, the molar ratio of iron to hydrogen peroxide is 1:(0.8-1.2), and the concentration of iron in the iron salt solution is 1.0-1.5 mol / L; the pH of the phosphorus salt solution is 6.0-6.5, and the concentration of phosphorus in the phosphorus salt solution is 1.0-1.5 mol / L.

[0008] Further, in the step S2, the feeding mode of the phosphorus salt solution and the iron salt solution is to add the phosphorus salt solution first, and then add the iron salt solution; or, to add the iron salt solution first, and then add the phosphorus salt solution; or, to add the phosphorus salt solution and the iron salt solution in parallel flow.

[0009] Further, in the step S3, the concentration of iron in the yellow slurry B is 0.6-1.2 mol / L, and the molar ratio of iron to phosphoric acid is 1:(0.4-1.0).

[0010] Further, in the step S3, the heating temperature is 86-90℃, and the keeping warm time is 1-2h.

[0011] Further, in the step S4, the sintering temperature is 550-650℃, and the keeping warm time is 3-5h.

[0012] Further, the vanadium source is one or more of vanadium pentoxide, ammonium metavanadate and vanadyl sulfate, and the titanium source is one or more of titanium sulfate, titanyl sulfate and metatitanic acid.

[0013] In a second aspect, the vanadium and titanium co-doped iron phosphate is prepared by the above preparation method, wherein the doping amount of vanadium is 500-1000 ppm, and the doping amount of titanium is 1000-5000 ppm.

[0014] In a third aspect, the vanadium and titanium co-doped iron phosphate is used for preparing a positive electrode material of a lithium ion battery.

[0015] The present application has the following advantages: The present application provides a preparation method of vanadium and titanium co-doped iron phosphate, which realizes uniform and controllable doping of vanadium and titanium by optimizing the doping process (including when to introduce vanadium source and titanium source together), and has the advantages of simple process, no toxic catalyst, and reduced production cost. 4+ expanding the unit cell to reduce the lithium ion diffusion energy barrier, V 5+ densifying the structure to improve the thermal stability), while refining the particles and improving the dispersibility, and the prepared lithium iron phosphate positive electrode material exhibits high tap density and excellent electrochemical performance, solving the problems of poor conductivity and low tap density of traditional lithium iron phosphate, and having a wide application prospect in the field of power batteries and energy storage. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0017] Figure 1 is the SEM image of the iron phosphate dihydrate prepared in Example 3 of the present application at 5000 times.

[0018] Figure 2 is the SEM image of the iron phosphate dihydrate prepared in Example 3 of the present application at 10000 times.

[0019] Figure 3 is the SEM image of the iron phosphate dihydrate prepared in Example 3 of the present application at 3000 times.

[0020] Figure 4 is the SEM image of the iron phosphate dihydrate prepared in Example 3 of the present application at 10000 times.

[0021] Figure 5 is the distribution map of the titanium element face scanning of the iron phosphate dihydrate prepared in Example 3 of the present application.

[0022] Figure 6 is the distribution map of the vanadium element face scanning of the iron phosphate dihydrate prepared in Example 3 of the present application.

[0023] Figure 7 is the XRD pattern of the iron phosphate dihydrate prepared by the embodiment 3 of the present application.

[0024] Figure 8 is the XRD pattern of the iron phosphate anhydride prepared by the embodiment 3 of the present application.

[0025] Figure 9 is the charge-discharge curve of the lithium iron phosphate prepared by using the iron phosphate prepared by the embodiment 3 of the present application as a precursor. DETAILED DESCRIPTION

[0026] In order to make the person skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by the person skilled in the art without creative labor should belong to the protection scope of the present application.

[0027] Embodiment 1 A preparation method of vanadium and titanium composite doped iron phosphate, comprising the following steps: (1) FeCl2·4H2O and H3PO4 are weighed according to the molar ratio of Fe:P=1:0.85 and placed in two beakers A and B respectively, titanium sulfate and vanadium pentoxide are weighed according to the molar ratio of Fe:Ti=1:0.01 and Fe:V=1:0.27 and added into beaker A, appropriate amount of ultrapure water is added into beaker A, ultrasonic mixing and dissolution are carried out at room temperature, the concentration of iron is adjusted to 1.0 mol / L, and iron salt solution is obtained; H2O2 is weighed according to the molar ratio of Fe:H2O2=1:0.8, added into beaker B together with ultrapure water, ammonia water is added to adjust the pH to 6, the concentration of phosphorus is adjusted to 1.0 mol / L, and phosphorus salt solution is obtained; (2) iron salt solution is first added into a reaction kettle, then phosphorus salt solution is added into the reaction kettle at a flow rate of 1.0 L / h, yellow slurry A is obtained by mixing the iron salt solution, and yellow filter cake is obtained after suction filtration and washing; (3) appropriate amount of ultrapure water is added into the yellow filter cake to disperse it, yellow slurry B is obtained, the concentration of iron is ensured to be 0.6 mol / L, H3PO4 is weighed again according to the molar ratio of Fe:H3PO4=1:1, yellow slurry B is mixed with H3PO4, and then the temperature is increased to 86℃, the mixture is kept white for 1 h, and vanadium and titanium composite doped iron phosphate dihydrate is obtained after suction filtration and drying, vanadium and titanium composite doped iron phosphate anhydride is obtained after sintering in a muffle furnace at 550℃ for 5 h.

[0028] Embodiment 2 A preparation method of vanadium and titanium composite doped iron phosphate, comprising the following steps: (1) FeSO4.7H2O and NH4H2PO4 are weighed according to the molar ratio of Fe:P=1:1, and are respectively placed in A and B beakers, and a proper amount of ultrapure water is added to the A beaker, ultrasonic mixing and dissolution are carried out at room temperature, the concentration of iron is adjusted to 1.25 mol / L, and an iron salt solution is obtained; H2O2 is weighed according to the molar ratio of Fe:H2O2=1:0.8, and is added to the B beaker together with ultrapure water, and ammonia water is added to adjust the pH to 6.5, and the concentration of phosphorus is adjusted to 1.25 mol / L, and a phosphorus salt solution is obtained; (2) The phosphorus salt solution is first added to a reaction kettle, then the iron salt solution is added to the reaction kettle at a flow rate of 1.0 L / h, and yellow slurry A is obtained by mixing the phosphorus salt solution; after filtration and washing, yellow filter cake is obtained; (3) A proper amount of ultrapure water is added to the yellow filter cake, which is dispersed to obtain yellow slurry B, the concentration of iron is ensured to be 0.9 mol / L, phosphoric acid is weighed again according to the molar ratio of Fe:H3PO4=1:0.7, titanium sulfate and ammonium metavanadate are weighed according to the molar ratio of Fe:Ti=1:0.03 and Fe:V=1:0.37, and after being mixed with the yellow slurry B, the temperature is increased to 90℃, and after turning white, the temperature is kept for 2h, and after filtration and drying, vanadium and titanium composite doped iron phosphate dihydrate is obtained, and after sintering in a muffle furnace at 600℃ for 4h, vanadium and titanium composite doped iron phosphate anhydride is obtained.

[0029] Example 3 A preparation method of vanadium and titanium composite doped iron phosphate, comprising the following steps: (1) Fe(CH3COO)2 and NH4H2PO4 are weighed according to the molar ratio of Fe:P=1:1.15, and are respectively placed in A and B beakers, a proper amount of ultrapure water is added to the A beaker, ultrasonic mixing and dissolution are carried out at room temperature, the concentration of iron is adjusted to 1.5 mol / L, and an iron salt solution is obtained; H2O2 is weighed according to the molar ratio of Fe:H2O2=1:1.2, and is added to the B beaker together with ultrapure water, and ammonia water is added to adjust the pH to 6.5, and the concentration of phosphorus is adjusted to 1.5 mol / L, and a phosphorus salt solution is obtained; (2) The iron salt solution and the phosphorus salt solution are added to a reaction kettle in a parallel flow mode, and the flow rates are both 1.0 L / h, yellow slurry A is obtained, and after filtration and washing, yellow filter cake is obtained; The iron salt solution and the phosphorus salt solution are added to the reaction kettle in a parallel flow mode, which can simplify the process flow and reduce the time cost; the two elements are dispersed synchronously, which can achieve more uniform mixing; different elements need to occupy different lattice positions (such as interstitial sites and substitution sites) of the material during the doping process, and the simultaneous addition can reduce the site competition during doping, so that the doping of different sites is more uniform; in addition, in the periodic table, vanadium and titanium are both fourth period transition elements, and they are adjacent elements, titanium is element 22, and vanadium is element 23, their electron configurations are similar, and their properties are also similar, and the element compatibility is good, and harmful side reactions are not easy to occur during dispersion and reaction, so the two elements are added together to promote the coordination effect.

[0030] (3) A proper amount of ultrapure water was added to the yellow filter cake to disperse it, obtaining yellow slurry B, ensuring that the concentration of iron was 1.2 mol / L, and phosphoric acid was weighed again according to the molar ratio of Fe:H3PO4=1:0.4, and the yellow slurry B was mixed well and heated to 90°C to obtain a whitish slurry, and metatitanic acid and vanadyl sulfate were weighed according to the molar ratio of Fe:Ti=1:0.06 and Fe:V=1:0.47 and added to the whitish slurry (added just after the slurry turned whitish), and the mixture was kept at 90°C for 2 hours, then filtered and dried to obtain vanadium and titanium composite doped iron phosphate dihydrate, which was sintered in a muffle furnace at 650°C for 3 hours to obtain vanadium and titanium composite doped iron phosphate anhydride, i.e., vanadium and titanium composite doped iron phosphate.

[0031] Compared with Example 1, the reasons for adding Ti and V after dispersion are as follows: during the synthesis stage of the iron salt raw material, a specific structure may be formed, and direct doping may cause the doped elements to be wrapped or limited in distribution, and adding the elements to be doped after dispersion can avoid these limitations and achieve more uniform dispersion. Moreover, considering that the doping rate of the elements to be doped is not 100%, if Ti and V are directly doped into the iron salt in step (1) and there is a washing operation in step (2), this will inevitably cause loss, and directly adding in the dispersion process in step (3) can perfectly avoid this disadvantage, avoid element loss, and improve the utilization rate of elements.

[0032] Compared with Example 2, the reasons for adding Ti and V after the slurry turns whitish are as follows: at this time, the nucleation process of the iron phosphate has been completed, and the element doping also introduces new impurity ions into the system, regardless of vanadium, titanium or other impurity ions. If introduced before whitening, they will be preferentially adsorbed on certain crystal faces, causing a large change in their morphology, and introduction after whitening can maximize the retention of the morphology.

[0033] Example 4 A preparation method of lithium iron phosphate, the vanadium and titanium composite doped iron phosphate prepared in Example 3 is mixed with water, lithium source (a mixture of Li2CO3 and LiOH·H2O) and carbon source (carbon black), sand milling treatment and spray drying are performed, the particle size of the mixture after sand milling treatment is in the range of 150-250 nm, the dried mixture is placed in a protective gas (a mixture of argon and nitrogen, the volume ratio of argon to nitrogen is 0.7:0.3) for high-temperature calcination (the temperature is 750℃, the time is 10h), and lithium iron phosphate is obtained.

[0034] In the formula, the mass ratio of vanadium and titanium composite doped iron phosphate: Li2CO3: LiOH·H2O: carbon source: water is 200:30:21:11.4:426.

[0035] Example 5 A preparation method of lithium iron phosphate, the vanadium and titanium composite doped iron phosphate prepared in Example 2 is mixed with water, lithium source (a mixture of Li2CO3 and LiOH·H2O) and carbon source (carbon black), sand milling treatment and spray drying are performed, the particle size of the mixture after sand milling treatment is in the range of 150-250 nm, the dried mixture is placed in a protective gas (a mixture of argon and nitrogen, the volume ratio of argon to nitrogen is 0.6:0.4) for high-temperature calcination (the temperature is 850℃, the time is 15h), and lithium iron phosphate is obtained.

[0036] In the formula, the mass ratio of vanadium and titanium composite doped iron phosphate: Li2CO3: LiOH·H2O: carbon source: water is 200:30:21:11.4:426.

[0037] Example 6 A preparation method of lithium iron phosphate, the vanadium and titanium composite doped iron phosphate prepared in Example 3 is mixed with water, lithium source (a mixture of Li2CO3 and LiOH·H2O) and carbon source (carbon black), sand milling treatment and spray drying are performed, the particle size of the mixture after sand milling treatment is in the range of 150-250 nm, the dried mixture is placed in a protective gas (a mixture of argon and nitrogen, the volume ratio of argon to nitrogen is 0.6:0.4) for high-temperature calcination (the temperature is 850℃, the time is 15h), and lithium iron phosphate is obtained.

[0038] In the formula, the mass ratio of vanadium and titanium composite doped iron phosphate: Li2CO3: LiOH·H2O: carbon source: water is 200:30:21:11.4:426.

[0039] Comparative Example 1 A preparation method of iron phosphate, comprising the following steps: (1) FeSO4.7H2O and NH4H2PO4 were weighed according to the molar ratio of Fe:P = 1:1, and were respectively placed in two beakers A and B. Appropriate ultrapure water was added to the beaker A, and the mixture was dissolved under ultrasonic mixing at room temperature. The concentration of iron was adjusted to 1.25 mol / L to obtain an iron salt solution. H2O2 was weighed according to the molar ratio of Fe:H2O2 = 1:0.8, and was added to the beaker B together with ultrapure water. Ammonia was added to adjust the pH to 6.5, and the concentration of phosphorus was adjusted to 1.25 mol / L to obtain a phosphorus salt solution; (2) The iron salt solution and the phosphorus salt solution were added to a reaction kettle in a parallel flow manner, and the flow rate was 1.0 L / h to obtain yellow slurry A. After filtration and washing, yellow filter cake was obtained; (3) Appropriate ultrapure water was added to the yellow filter cake to disperse it, and yellow slurry B was obtained. The concentration of iron was adjusted to 1.2 mol / L. Phosphoric acid was weighed according to the molar ratio of Fe:H3PO4 = 1:0.4, and was mixed with the yellow slurry B. After being heated to 95℃, the mixture turned white, and was kept for 2 h. After filtration and drying, iron phosphate dihydrate was obtained. After being sintered in a muffle furnace at 600℃ for 4 h, iron phosphate anhydride was obtained, i.e. iron phosphate.

[0040] Comparative Example 2 A preparation method of titanium-doped iron phosphate, comprising the following steps: (1) FeSO4.7H2O and NH4H2PO4 were weighed according to the molar ratio of Fe:P = 1:1, and were respectively placed in two beakers A and B. Titanium sulfate was weighed according to the molar ratio of Fe:Ti = 1:0.01, and was added to the beaker A. Appropriate ultrapure water was added to the beaker A, and the mixture was dissolved under ultrasonic mixing at room temperature. The concentration of iron was adjusted to 1.25 mol / L to obtain an iron salt solution. H2O2 was weighed according to the molar ratio of Fe:H2O2 = 1:0.8, and was added to the beaker B together with ultrapure water. Ammonia was added to adjust the pH to 6.5, and the concentration of phosphorus was adjusted to 1.25 mol / L to obtain a phosphorus salt solution; (2) The iron salt solution and the phosphorus salt solution were added to a reaction kettle in a parallel flow manner, and the flow rate was 1.0 L / h to obtain yellow slurry A. After filtration and washing, yellow filter cake was obtained; (3) Appropriate ultrapure water was added to the yellow filter cake to disperse it, and yellow slurry B was obtained. The concentration of iron was adjusted to 1.2 mol / L. Phosphoric acid was weighed according to the molar ratio of Fe:H3PO4 = 1:0.4, and was mixed with the yellow slurry B. After being heated to 95℃, the mixture turned white, and was kept for 2 h. After filtration and drying, titanium-doped iron phosphate dihydrate was obtained. After being sintered in a muffle furnace at 600℃ for 4 h, titanium-doped iron phosphate anhydride was obtained, i.e. titanium-doped iron phosphate.

[0041] Comparative Example 3 A preparation method of vanadium-doped iron phosphate, comprising the following steps: (1) FeSO4·7H2O and NH4H2PO4 were weighed according to the molar ratio of Fe:P = 1:1 and placed in two beakers A and B respectively, and vanadic oxide was weighed according to the molar ratio of Fe:V = 1:0.27 and added to the beaker A, and then a proper amount of ultrapure water was added to the beaker A, and the mixture was dissolved under ultrasonic mixing at room temperature, and the concentration of iron was adjusted to 1.25 mol / L to obtain an iron salt solution; H2O2 was weighed according to the molar ratio of Fe:H2O2 = 1:0.8, and added to the beaker B together with ultrapure water, and ammonia water was added to adjust the pH to 6.5, and the concentration of phosphorus was adjusted to 1.25 mol / L to obtain a phosphorus salt solution; (2) The iron salt solution and the phosphorus salt solution were added to a reaction kettle in a parallel flow mode, and the flow rate was 1.0 L / h to obtain yellow slurry A, and yellow filter cake was obtained after filtration and washing; (3) A proper amount of ultrapure water was added to the yellow filter cake to disperse it to obtain yellow slurry B, and the concentration of iron was ensured to be 1.2 mol / L, and phosphoric acid was weighed again according to the molar ratio of Fe:H3PO4 = 1:0.4, and the yellow slurry B was mixed with the phosphoric acid, and then the temperature was raised to 95℃, and the mixture was kept white for 2 h, and then filtration and drying were performed to obtain vanadium-doped iron phosphate dihydrate, and the vanadium-doped iron phosphate dihydrate was sintered in a muffle furnace at 600℃ for 4 h to obtain vanadium-doped iron phosphate anhydride, i.e., vanadium-doped iron phosphate.

[0042] Comparative Example 4 A preparation method of vanadium and titanium composite-doped iron phosphate, comprising the following steps: (1) FeSO4·7H2O and NH4H2PO4 were weighed according to the molar ratio of Fe:P = 1:1 and placed in two beakers A and B respectively, and a proper amount of ultrapure water was added to the beaker A, and titanium sulfate was weighed according to the molar ratio of Fe:Ti = 1:0.01 and added to the beaker A, and then the mixture was dissolved under ultrasonic mixing at room temperature, and the concentration of iron was adjusted to 1.25 mol / L to obtain an iron salt solution; H2O2 was weighed according to the molar ratio of Fe:H2O2 = 1:0.8, and added to the beaker B together with ultrapure water, and ammonia water was added to adjust the pH to 6.5, and the concentration of phosphorus was adjusted to 1.25 mol / L to obtain a phosphorus salt solution; (2) The iron salt solution and the phosphorus salt solution were added to a reaction kettle in a parallel flow mode, and the flow rate was 1.0 L / h to obtain yellow slurry A, and yellow filter cake was obtained after filtration and washing; (3) A proper amount of ultrapure water was added to the yellow filter cake to disperse it to obtain yellow slurry B, and the concentration of iron was ensured to be 1.2 mol / L, and phosphoric acid was weighed again according to the molar ratio of Fe:H3PO4 = 1:0.4, and the yellow slurry B was mixed with the phosphoric acid, and then the temperature was raised to 95℃, and the mixture was kept white for 2 h, and then filtration and drying were performed to obtain vanadium and titanium composite-doped iron phosphate dihydrate, and the vanadium and titanium composite-doped iron phosphate dihydrate was sintered in a muffle furnace at 600℃ for 4 h to obtain vanadium and titanium composite-doped iron phosphate anhydride, i.e., vanadium and titanium composite-doped iron phosphate.

[0043] Comparative Example 5 A preparation method of vanadium and titanium composite doped iron phosphate, comprising the following steps: (1) FeSO4·7H2O and NH4H2PO4 are weighed according to the molar ratio of Fe:P=1:1 and placed in two beakers A and B respectively, an appropriate amount of ultrapure water is added to the beaker A, titanium sulfate is weighed according to the molar ratio of Fe:Ti=1:0.01 and added to the beaker A, an appropriate amount of ultrapure water is added to the beaker A, and the mixture is dissolved under ultrasonic mixing at room temperature, the concentration of iron is adjusted to 1.25 mol / L to obtain an iron salt solution; H2O2 is weighed according to the molar ratio of Fe:H2O2=1:0.8, added to the beaker B together with ultrapure water, and ammonia water is added to adjust the pH to 6.5, and the concentration of phosphorus is adjusted to 1.25 mol / L to obtain a phosphorus salt solution; (2) The iron salt solution and the phosphorus salt solution are added to a reaction kettle in a parallel flow manner, and the flow rate is 1.0 L / h, to obtain yellow slurry A, and yellow filter cake can be obtained after suction filtration and washing; (3) An appropriate amount of ultrapure water is added to the yellow filter cake to disperse it to obtain yellow slurry B, the concentration of iron is ensured to be 1.2 mol / L, phosphoric acid is weighed according to the molar ratio of Fe:H3PO4=1:0.4, and the yellow slurry B is mixed with the phosphoric acid and then heated to 95°C to obtain whitened slurry, ammonium metavanadate is weighed according to the molar ratio of Fe:V=1:0.27 and added to the whitened slurry (added after the slurry just turns white), and the mixture is kept for 2 h, suction filtration and drying are performed to obtain vanadium and titanium composite doped iron phosphate dihydrate, and after sintering at 600°C in a muffle furnace for 4 h, vanadium and titanium composite doped iron phosphate anhydride is obtained, i.e., vanadium and titanium composite doped iron phosphate.

[0044] Comparative Example 6 A preparation method of vanadium and titanium composite doped iron phosphate, comprising the following steps: (1) FeSO4·7H2O and NH4H2PO4 are weighed according to the molar ratio of Fe:P=1:1 and placed in two beakers A and B respectively, an appropriate amount of ultrapure water is added to the beaker A, ammonium metavanadate is weighed according to the molar ratio of Fe:V=1:0.27 and added to the beaker A, an appropriate amount of ultrapure water is added to the beaker A, and the mixture is dissolved under ultrasonic mixing at room temperature, the concentration of iron is adjusted to 1.25 mol / L to obtain an iron salt solution; H2O2 is weighed according to the molar ratio of Fe:H2O2=1:0.8, added to the beaker B together with ultrapure water, and ammonia water is added to adjust the pH to 6.5, and the concentration of phosphorus is adjusted to 1.25 mol / L to obtain a phosphorus salt solution; (2) The iron salt solution and the phosphorus salt solution are added to a reaction kettle in a parallel flow manner, and the flow rate is 1.0 L / h, to obtain yellow slurry A, and yellow filter cake can be obtained after suction filtration and washing; (3) adding appropriate amount of ultrapure water to the yellow filter cake, dispersing it to obtain yellow slurry B, ensuring the concentration of iron to be 1.2 mol / L, re-weighing phosphoric acid according to the molar ratio of Fe:H3PO4=1:0.4, weighing titanium sulfate according to the molar ratio of Fe:Ti=1:0.01, and mixing it with the yellow slurry B, then heating to 95℃, turning white, and keeping the temperature for 2h, then filtering and drying to obtain vanadium and titanium composite doped iron phosphate dihydrate, sintering in a muffle furnace at 600℃ for 4h to obtain vanadium and titanium composite doped iron phosphate anhydride, and vanadium and titanium composite doped iron phosphate.

[0045] Comparative Example 7 A preparation method of vanadium and titanium composite doped iron phosphate, comprising the following steps: (1) weighing FeSO4·7H2O and NH4H2PO4 according to the molar ratio of Fe:P=1:1, respectively placing them in A and B beakers, adding appropriate amount of ultrapure water in the A beaker, ultrasonic mixing and dissolving at room temperature, adjusting the concentration of iron to 1.25 mol / L to obtain an iron salt solution; weighing H2O2 according to the molar ratio of Fe:H2O2=1:0.8, adding it into the B beaker together with ultrapure water, and adding ammonia water to adjust the pH to 6.5, and adjusting the concentration of phosphorus to 1.25 mol / L to obtain a phosphorus salt solution; (2) adding the iron salt solution and the phosphorus salt solution into a reaction kettle in a parallel flow manner, and the flow rate is 1.0 L / h to obtain yellow slurry A, which can be obtained as a yellow filter cake after filtration and washing; (3) adding appropriate amount of ultrapure water to the yellow filter cake, dispersing it to obtain yellow slurry B, ensuring the concentration of iron to be 1.2 mol / L, re-weighing phosphoric acid according to the molar ratio of Fe:H3PO4=1:0.4, weighing titanium sulfate according to the molar ratio of Fe:Ti=1:0.01, and mixing it with the yellow slurry B, then heating to 95℃ to obtain a white slurry, weighing ammonium metavanadate according to the molar ratio of Fe:V=1:0.27, adding it to the white slurry (adding it just after the slurry turns white), keeping the temperature for 2h, filtering and drying to obtain vanadium and titanium composite doped iron phosphate dihydrate, sintering in a muffle furnace at 600℃ for 4h to obtain vanadium and titanium composite doped iron phosphate anhydride, and vanadium and titanium composite doped iron phosphate.

[0046] Comparative Example 8 A preparation method of vanadium and titanium composite doped iron phosphate, comprising the following steps: (1) FeSO4.7H2O and NH4H2PO4 were weighed according to the molar ratio of Fe:P = 1:1, and were respectively placed in two beakers A and B. Appropriate ultrapure water was added to the beaker A, and the mixture was dissolved under ultrasonic mixing at room temperature. The concentration of iron was adjusted to 1.25 mol / L to obtain an iron salt solution. H2O2 was weighed according to the molar ratio of Fe:H2O2 = 1:0.8, and was added to the beaker B together with ultrapure water. Ammonia water was added to adjust the pH to 6.5, and the concentration of phosphorus was adjusted to 1.25 mol / L to obtain a phosphorus salt solution; (2) The iron salt solution and the phosphorus salt solution were added to a reaction kettle in a parallel flow manner, and the flow rate was 1.0 L / h to obtain yellow slurry A. After filtration and washing, yellow filter cake was obtained; (3) Appropriate ultrapure water was added to the yellow filter cake to disperse it to obtain yellow slurry B. The concentration of iron was adjusted to 1.2 mol / L. Phosphoric acid was weighed according to the molar ratio of Fe:H3PO4 = 1:0.4. Titanium sulfate was weighed according to the molar ratio of Fe:Ti = 1:0.01. After being mixed with the yellow slurry B, the mixture was heated to 95℃ to obtain whitened slurry. Ammonium metavanadate was weighed according to the molar ratio of Fe:V = 1:0.27, and was added to the whitened slurry (added after the slurry just turned white). The mixture was kept for 2 h, and then was filtered and dried to obtain vanadium and titanium composite doped iron phosphate ferric phosphate dihydrate. After being sintered in a muffle furnace at 600℃ for 4 h, vanadium and titanium composite doped iron phosphate ferric phosphate anhydride was obtained, i.e., vanadium and titanium composite doped iron phosphate ferric phosphate.

[0047] Comparative Example 9 A preparation method of vanadium and titanium composite doped iron phosphate ferric phosphate includes the following steps: (1) FeSO4.7H2O and NH4H2PO4 were weighed according to the molar ratio of Fe:P = 1:1, and were respectively placed in two beakers A and B. Appropriate ultrapure water was added to the beaker A, and the mixture was dissolved under ultrasonic mixing at room temperature. The concentration of iron was adjusted to 1.25 mol / L to obtain an iron salt solution. H2O2 was weighed according to the molar ratio of Fe:H2O2 = 1:0.8, and was added to the beaker B together with ultrapure water. Ammonia water was added to adjust the pH to 6.5, and the concentration of phosphorus was adjusted to 1.25 mol / L to obtain a phosphorus salt solution; (2) The iron salt solution and the phosphorus salt solution were added to a reaction kettle in a parallel flow manner, and the flow rate was 1.0 L / h to obtain yellow slurry A. After filtration and washing, yellow filter cake was obtained; (3) adding an appropriate amount of ultrapure water to the yellow filter cake, dispersing the same to obtain yellow slurry B, ensuring that the concentration of iron is 1.2 mol / L, re-weighing phosphoric acid according to a molar ratio of Fe:H3PO4=1:0.4, weighing ammonium metavanadate according to a molar ratio of Fe:V=1:0.27, mixing the yellow slurry B with the ammonium metavanadate, and then heating to 95°C to obtain whitened slurry, weighing titanium sulfate according to a molar ratio of Fe:Ti=1:0.01, adding the titanium sulfate to the whitened slurry (the titanium sulfate is added immediately after the slurry turns white), and keeping the temperature for 2 h, and then performing suction filtration and drying to obtain vanadium and titanium composite-doped iron phosphate dihydrate, and then sintering the vanadium and titanium composite-doped iron phosphate dihydrate in a muffle furnace at 600°C for 4 h to obtain vanadium and titanium composite-doped iron phosphate anhydride, i.e., vanadium and titanium composite-doped iron phosphate.

[0048] Comparative Example 10 According to the preparation method of Example 4, lithium iron phosphate was prepared, except that the vanadium and titanium composite-doped iron phosphate of Example 3 was replaced by one of the different types of iron phosphate of Comparative Examples 1-9, respectively, to obtain 9 different types of lithium iron phosphate.

[0049] Test Example 1 Microscopic Test 1. Scanning Electron Microscope Test The vanadium and titanium composite-doped iron phosphate dihydrate and the iron phosphate anhydride prepared in Examples 1-3 were subjected to scanning electron microscope (SEM) test. The SEM images of the iron phosphate dihydrate of Example 3 at different magnifications are shown in FIG. 1, the SEM images of the iron phosphate anhydride at different magnifications are shown in FIG. 2, and the surface scanning of titanium and vanadium element distribution is shown in FIG. 3. Similar results were obtained for other examples (no figures are attached). Figures 1-2 Figures 3-4 Figures 5-6

[0050] 2. X-ray Diffraction Test The vanadium and titanium composite-doped iron phosphate dihydrate and the iron phosphate anhydride prepared in Examples 1-3 were subjected to X-ray diffraction (XRD) test. The test results of the iron phosphate dihydrate and the iron phosphate anhydride of Example 3 are shown in FIG. 4. Similar results were obtained for other examples. Figures 7-8

[0051] 3. Iron and Phosphorus Content Test The vanadium and titanium composite-doped iron phosphate of Examples 1-3 and Comparative Examples 1-3 was subjected to iron and phosphorus content test, and the results are shown in Table 1.

[0052] Table 1 Iron and Phosphorus Content Test Results

[0053] As shown in Table 1, the iron and phosphorus ratio values of Examples 1-3 and Comparative Examples 1-3 are similar, both of which are above 0.95, indicating that the V and Ti doping contents are not high. Comparative Examples 4-9 were also subjected to the same test, and the data were similar.

[0054] ​​​​4. Impurity content detection The different kinds of iron phosphate prepared in Examples 1-3 and Comparative Examples 1-9 were subjected to impurity content detection by ICP (inductively coupled plasma), and the results are shown in Table 2.

[0055] Table 2. Impurity content detection results (ppm)

[0056] 5. Performance detection Twelve kinds of lithium iron phosphate prepared in the above Examples 4-6 and Comparative Example 10 (numbered 1-12 in turn) were subjected to compactness density and electrical performance tests, and the specific methods were as follows: Compactness density test method: a Sansi Zongheng UTM7305 microcomputer-controlled electronic compactness density tester was used, and the specific test process was as follows: 1 g of the positive electrode material (lithium iron phosphate) was weighed on a balance and placed in a clean mold, the radius of the hole in the mold was 6.5 mm, then the mold was placed on the equipment pressure plate, and a test pressure of 3T was selected for testing; Electrochemical performance test method: a Mico Super (1220 / 750 / 900) glove box and a Land battery test system CT3004A were used, and the specific test process was as follows: the battery was assembled in the glove box, then the battery was connected to the Land system, the parameters were set, the voltage window was 2.5-4.0V, and the temperature was 25°C constant temperature.

[0057] Table 3. Compactness density and electrical performance test results

[0058] As can be seen from the compactness density and electrical performance test data results shown in Table 3, compared with Comparative Examples 1-9, the lithium iron phosphate prepared from the vanadium and titanium composite doped iron phosphate of Examples 1-3 has high compactness density and good electrical performance when tested as a positive electrode material, especially the lithium iron phosphate prepared from the vanadium and titanium composite doped iron phosphate of Example 3. The reason for this is that the composite doping of vanadium and titanium at the appropriate time in Examples 1-3 can adjust the unit cell parameters of the iron phosphate, wherein the ionic radius of Ti 4+ is larger than that of Fe 3+ , so that the doping of titanium increases the unit cell volume, reduces the lattice distortion, and reduces the lithium ion diffusion energy barrier; vanadium doping may reduce the unit cell volume and form a more compact structure, thereby increasing the compactness and improving the compactness density of the lithium iron phosphate; when both are doped, the coordination effect can stabilize the structure, inhibit abnormal grain growth during high-temperature calcination, and improve the thermal stability of the material. In addition, vanadium doping can refine the primary particles of the iron phosphate and reduce agglomeration, and titanium doping can promote particle dispersion and form a more uniform microstructure, which is beneficial to improving the compactness density of the lithium iron phosphate. After the composite doping of vanadium and titanium at the appropriate time, cation vacancies and mixed valence (Ti4+ , V 5+ , Fe 3+ ), can significantly improve the electronic conductivity of the material; co-doping optimizes the lithium ion transmission channel, reduces the lithium ion migration resistance, which is conducive to improving the rate performance of lithium iron phosphate.

[0059] Although the present application has been described in detail with reference to the preferred embodiments, it should be understood that the application is not limited to those preferred embodiments. Without departing from the spirit and essential characteristics of the application, one of ordinary skill in the art can make other variations and modifications of the application and all should be considered within the scope of the application. Any variations or modifications based on the technical range disclosed in the present application should be considered within the protection scope of the present application.

Claims

1. A method for preparing vanadium and titanium composite doped iron phosphate, characterized in that: The following steps are involved: S1. Weigh an iron source and a phosphorus source, place them in beakers A and B, respectively, add ultrapure water to beaker A, and mix evenly with the iron source to obtain an iron salt solution; add ultrapure water and hydrogen peroxide to beaker B, mix evenly with the phosphorus source, and then add ammonia water to adjust the pH and phosphorus concentration to obtain a phosphate salt solution; S2, adding the iron salt solution and the phosphate salt solution into the reactor to obtain yellow slurry A, and filtering and washing to obtain a yellow filter cake; S3. Add ultrapure water to the yellow filter cake to disperse it to obtain yellow slurry B. Add phosphoric acid to the yellow slurry B, heat until the system turns white, and then keep warm; Wherein, the vanadium source and the titanium source are added to the iron salt solution prepared in S1; or, the vanadium source and the titanium source are added to the yellow slurry B prepared in S3; or, the vanadium source and the titanium source are added after the S3 system turns white; S4. The system after heat preservation is filtered and dried to obtain a hydrate of vanadium and titanium composite doped iron phosphate, and the vanadium and titanium composite doped iron phosphate is obtained after sintering.

2. The method for preparing vanadium-titanium composite doped ferric phosphate according to claim 1, characterized in that: In step S1, the iron source is one or more of FeCl2·4H2O, FeSO4·7H2O and Fe(CH3COO)2, and the phosphorus source is one or more of H3PO4 and NH4H2PO4; the molar ratio of iron to phosphorus is 1:(0.85-1.15).

3. The method for preparing vanadium-titanium composite-doped ferric phosphate according to claim 1, wherein: In step S1, the molar ratio of iron to hydrogen peroxide is 1:(0.8-1.2), the concentration of iron in the iron salt solution is 1.0-1.5 mol / L; the pH of the phosphate salt solution is 6.0-6.5, and the concentration of phosphorus in the phosphate salt solution is 1.0-1.5 mol / L.

4. The method for preparing vanadium-titanium composite doped ferric phosphate according to claim 1, wherein: In step S2, the phosphate salt solution and the iron salt solution are added by first adding the phosphate salt solution and then adding the iron salt solution; or, first adding the iron salt solution and then adding the phosphate salt solution; or, adding the phosphate salt solution and the iron salt solution in parallel.

5. The method for preparing vanadium-titanium composite-doped ferric phosphate according to claim 1, wherein: In step S3, the concentration of iron in the yellow slurry B is 0.6-1.2 mol / L, and the molar ratio of iron to phosphoric acid is 1:(0.4-1.0).

6. The method for preparing vanadium-titanium composite-doped ferric phosphate according to claim 1, characterized in that: In step S3, the heating temperature is 86-90° C. and the holding time is 1-2 h.

7. The method for preparing vanadium-titanium composite-doped ferric phosphate according to claim 1, characterized in that: In step S4, the sintering temperature is 550-650° C., and the holding time is 3-5 hours.

8. The method for preparing vanadium-titanium composite-doped ferric phosphate according to claim 1, characterized in that: The vanadium source is one or more of vanadium pentoxide, ammonium metavanadate, and vanadyl sulfate; the titanium source is one or more of titanium sulfate, titanyl sulfate, and metatitanic acid.

9. A vanadium and titanium composite doped iron phosphate, characterized in that: The vanadium-doped quartz crystal is prepared by the preparation method according to any one of claims 1 to 8, wherein the doping amount of vanadium is 500-1000 ppm; and the doping amount of titanium is 1000-5000 ppm.

10. Use of the vanadium and titanium composite doped iron phosphate as claimed in claim 9 in preparing a positive electrode material for lithium ion batteries.

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