Titanium-doped anhydrous iron phosphate material, its manufacturing method and use

Abstract

This application provides a titanium-doped anhydrous iron phosphate material, its preparation method, and use, which belong to the technical field of producing iron phosphate-based materials. The method for preparing the titanium-doped anhydrous iron phosphate material includes the steps of providing a titanium-containing ferrous sulfate raw material solution and a titanium-free ferrous sulfate raw material solution, mixing the titanium-containing ferrous sulfate raw material solution with the titanium-free ferrous sulfate raw material solution to obtain a mixed solution, mixing the mixed solution with an oxidizing agent and a phosphorus source to obtain a slurry containing iron phosphate and titanium phosphate, and sequentially aging, rinsing, drying, and sintering the slurry to obtain the titanium-doped anhydrous iron phosphate material. In this application, the doping of titanium in the titanium-doped anhydrous iron phosphate material is controlled by adjusting the mixing ratio of the titanium-containing ferrous sulfate raw material solution and the titanium-free ferrous sulfate raw material solution, thereby enabling stable and controllable titanium content in the final product. The titanium-doped anhydrous iron phosphate material has a uniform nanoscale particle stacking morphology, making it suitable for use in the production of battery materials.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to a Chinese patent application bearing application number 2023117858803 and entitled "Titanium-doped anhydrous iron phosphate material, its manufacturing method and use" filed with the China Patent Office on December 22, 2023, the entire contents of which are incorporated herein by reference.

[0002] Technical Field The present application relates to the technical field of iron phosphate material production, and in particular to a titanium-doped anhydrous iron phosphate material that is advantageous for use in the production of battery materials, its production method and use, and mainly to a method for producing titanium-doped anhydrous iron phosphate with a controllable titanium content by utilizing waste titanium element in titanium white by-products. [Background technology]

[0003] Anhydrous iron phosphate is a precursor material for lithium iron phosphate, one of the mainstream battery cathode materials. The solid-state manufacturing process for lithium iron phosphate is shown in Figure 1 and generally includes mixing, spray drying, sintering, grinding, mixing and classification, and roasting. Figure 2 shows the conventional iron phosphate manufacturing process, which primarily involves oxidation synthesis using iron solution, phosphorus solution, and oxidant, followed by high-temperature crystal transformation, drying, and calcination to obtain anhydrous iron phosphate. Research into the modification of iron phosphate-based battery materials has shown that titanium and iron both share the d2sp3 hybridization scheme. Although the stable phase structures of titanium phosphate and iron phosphate are different, adding titanium (Ti) to iron phosphate as a dopant allows the titanium (Ti) to be arranged in the crystal according to the same rules as iron. Currently, the modifying effects of titanium doping on iron phosphate / lithium iron phosphate are generally believed to include the following: (1) Under the same unit cell parameters, a smaller radius of titanium results in a wider electron transfer channel. (2) The introduction of foreign elements can hinder the growth of crystals after nucleation and effectively reduce the primary particles, which results in a significant improvement in the high-rate performance and a significant reduction in impedance of the fabricated batteries.

[0004] Among them, the doping time of titanium element can be divided into the following: (1) It is introduced during the production of lithium iron phosphate by the solid-state method. (2) It is introduced during the production of iron phosphate. Type (1) is generally introduced by using rutile titanium dioxide, which has better reaction activity, and carrying out a high-temperature solid-state reaction with other materials, but this reaction process requires a large amount of thermal energy and continuous mechanical polishing.

[0005] Titanium is introduced in the form of ions as an iron-site substitution doping element during the production of type II iron phosphate. This is a more ideal doping method because it consumes very little energy during the production process. However, there are many influencing factors. In the production of iron phosphate compounds, ferrous sulfate heptahydrate, a titanium dioxide by-product, is commonly used as the iron source. This by-product is crystallized from the acid decomposition solution of ilmenite, so it contains a certain amount of titanium. Most companies that use this route to produce iron phosphate remove this portion of the titanium element by increasing the pH (by adding alkali or reacting elemental iron with acid) when preparing the iron source solution. This route requires the addition of additional titanium-containing materials to produce titanium-doped iron phosphate products, further improving product quality. Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the technical problems existing in the background art, the present application provides a titanium-doped anhydrous iron phosphate material, its preparation method and use, which has high performance and quality, is simple and convenient to prepare, and is advantageous for use as a battery material. [Means for solving the problem]

[0007] In a first aspect, the present embodiment comprises: providing a titanium-containing ferrous sulfate source liquid and a titanium-free ferrous sulfate source liquid; mixing the titanium-containing ferrous sulfate raw material liquid with the titanium-free ferrous sulfate raw material liquid to obtain a mixed solution; mixing the mixed solution with an oxidizing agent and a phosphorus source to obtain a slurry containing iron phosphate and titanium phosphate; and sequentially subjecting the slurry to aging, rinsing, drying, and sintering to obtain a titanium-doped anhydrous iron phosphate material.

[0008] In the technical solution of the present embodiment, the titanium-containing ferrous sulfate raw material solution and the titanium-free ferrous sulfate raw material solution are mixed to obtain the mixed solution, and then the resulting mixed solution and a phosphorus source are oxidized to obtain a slurry containing iron phosphate and titanium phosphate. The slurry is then aged, rinsed, dried, and sintered to obtain the titanium-doped anhydrous iron phosphate material. The titanium-containing ferrous sulfate raw material solution and the titanium-free ferrous sulfate raw material solution are mixed in a predetermined ratio, and by adjusting this ratio, the doping of titanium in the final doped iron phosphate product is controlled, thereby ensuring a stable and controllable titanium content in the produced titanium-doped anhydrous iron phosphate material and solving the problem of uncontrollable titanium content in anhydrous iron phosphate due to uneven quality of ferrous sulfate heptahydrate. At the same time, the titanium-doped anhydrous iron phosphate produced in the present embodiment has a uniform nanoscale particle stacking shape, making it convenient for use.

[0009] In some embodiments, the raw materials for preparing the titanium-containing ferrous sulfate raw material liquid and the titanium-free ferrous sulfate raw material liquid contain a titanium white by-product, and the mass fraction of titanium in the titanium white by-product is 600 to 4200 ppm.

[0010] In this embodiment, the titanium white by-product is used as the titanium introduction source. The titanium white by-product is mainly composed of ferrous sulfate heptahydrate, and titanium is attached to the titanium white by-product itself. Therefore, there is no need to add titanium separately. In addition, titanium element exists stably in the form of ions in the titanium white by-product, which is advantageous for improving the quality of the produced titanium-doped anhydrous iron phosphate and also realizes the recycling of waste materials.

[0011] Furthermore, as long as the mass fraction of titanium in the titanium white by-product falls within the range of 600 to 4200 ppm, the titanium white by-product can be used as a raw material for producing the titanium-doped anhydrous iron phosphate material. In this embodiment, the origin of the titanium white by-product is not particularly limited.

[0012] In some embodiments, the manufacturing steps for providing the titanium-containing ferrous sulfate source solution include: the titanium white by-product is dissolved in an acidic aqueous solution, followed by solid-liquid separation to obtain the titanium-containing ferrous sulfate raw material solution; And / or, the manufacturing step for providing the titanium-free ferrous sulfate raw material solution includes: mixing the titanium white by-product with a phosphorus-containing solution and performing solid-liquid separation to obtain the titanium-free ferrous sulfate raw material solution; However, the phosphorus-containing solution contains at least one of phosphoric acid and phosphates, and the mass fraction of elemental phosphorus in the phosphorus-containing solution is 1000 to 3000 ppm.

[0013] In this embodiment, in the process for producing the titanium-containing ferrous sulfate raw material solution, an acidic aqueous solution is used to dissolve the titanium white by-product, ensuring that the titanium element is not hydrolyzed in the acidic environment, while in the process for producing the titanium-free ferrous sulfate raw material solution, a phosphorus-containing solution is used to dissolve the titanium white by-product, resulting in the hydrolysis of the titanium element.

[0014] In some embodiments, the titanium-containing ferrous sulfate raw material solution and the titanium-free ferrous sulfate raw material solution each have a pH value of 0.8 to 1.8.

[0015] In this example, the pH values ​​of the titanium-containing ferrous sulfate raw material liquid and the titanium-free ferrous sulfate raw material liquid are controlled to 0.8 to 1.8, which is advantageous for obtaining a slurry containing iron phosphate and titanium phosphate through the reaction.

[0016] In some embodiments, in the step of obtaining a slurry containing iron phosphate and titanium phosphate, the mixed solution is mixed with the oxidizing agent and the phosphorus source such that the molar ratio of elemental iron, elemental phosphorus, and oxidizing agent is 1:1.01-1.05:0.55-0.65.

[0017] In this example, this ratio ensures sufficient mixing and oxidation, resulting in a high content of active material in the produced slurry containing iron phosphate and titanium phosphate.

[0018] In some embodiments, the step of sequentially aging, rinsing, drying, and sintering the slurry comprises: heating the slurry to 80-98°C and keeping the temperature for 1-4 hours, and then rinsing with water to obtain a phosphorus-containing rinse solution and a filter cake; and drying the filter cake and then sintering it at 550-750°C for 1-4 hours to obtain the titanium-doped anhydrous iron phosphate material.

[0019] In this embodiment, the phosphorus-containing rinse solution can be used to produce a titanium-free ferrous sulfate raw material solution, which, on the one hand, recycles the waste solution and reduces the cost of alkaline reagents, and the ferrous solution not consumed in the titanium-doped anhydrous iron phosphate production process can be used again in the normal production of iron phosphate, avoiding waste. On the other hand, it can remove impurities under conditions requiring a low pH, which is different from raising the pH value with an alkaline reagent.

[0020] In a second aspect, an embodiment of the present application provides a titanium-doped anhydrous iron phosphate material, which is produced by the above-described production method, and which has an anhydrous iron phosphate crystal structure and a nanoscale particle stacking morphology, with the proviso that the Ti doping amount of the titanium-doped anhydrous iron phosphate material is 2 wt% or less.

[0021] In the technical solutions of the embodiments of the present application, the titanium-doped anhydrous iron phosphate material prepared has a stable titanium element content, a crystal structure consistent with that of anhydrous iron phosphate, an Fe / P molar ratio of 0.96-1.01, and a nano-scale particle stacking shape, with a uniform material shape, which is advantageous for subsequent use in products.

[0022] In some embodiments, the titanium-doped anhydrous iron phosphate material has a Ti doping amount of 1 wt % or less. In some embodiments, the titanium-doped anhydrous iron phosphate material has an Fe / P molar ratio of 0.96 to 1.01 and a specific surface area of ​​8 to 10 m 2 / g, and the performance of the material is more favorable for subsequent use.

[0023] In a third aspect, the present invention provides a positive electrode sheet using titanium-doped lithium iron phosphate as an active material, which is manufactured using the titanium-doped anhydrous iron phosphate material.

[0024] In this embodiment, the titanium-doped anhydrous iron phosphate material can be used as a precursor to prepare an iron phosphate-based positive electrode material. The positive electrode material is prepared using the titanium-doped anhydrous iron phosphate and an ion battery source, specifically, functions as a titanium-doped lithium iron phosphate active material, which has the advantages of stable quality and good performance. By combining the positive electrode battery material of this embodiment, a battery electrode sheet and a device using the same can be obtained with good performance.

[0025] In a fourth aspect, an embodiment of the present application provides a secondary battery including the positive electrode sheet described above.

[0026] In this embodiment, the secondary battery includes the above-mentioned positive electrode sheet, and therefore has the advantages of stable quality and good performance.

[0027] In a fifth aspect, embodiments of the present application provide an electrical device including the secondary battery described above.

[0028] In this embodiment, the electrical device includes the secondary battery, and therefore has the advantages of stable quality and good performance.

[0029] The above description is merely an outline of the technical solution of the present application. In order to make the technical means of the present application more clearly understood and to be able to implement the present application in accordance with the content of the specification, and to make the above and other objectives, features and advantages of the present application more apparent and comprehensible, specific embodiments of the present application are specifically set forth below. [Brief explanation of the drawings]

[0030] In order to more clearly explain the technical solution of the present application, the following briefly introduces drawings that may be used in the examples or the description of the prior art. However, the drawings in the following description are only some examples or some embodiments of the present application, and it is obvious that those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0031] [Figure 1] This is the flow of manufacturing lithium iron phosphate using the conventional solid-phase method. [Figure 2] This is the normal manufacturing process for iron phosphate. [Figure 3] 1 is a schematic diagram of a manufacturing flow of titanium-doped anhydrous iron phosphate material according to some embodiments of the present application. [Figure 4] 1 is an XRD pattern of a final product sample of Example 1 of the present application. [Figure 5] 1 is an SEM image of a final product sample of Example 1 of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, the embodiments of the technical solution of the present application will be described in detail with reference to the drawings. The following embodiments are only used to more clearly explain the technical solution of the present application, and are therefore used as examples only, and do not limit the scope of protection of the present application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. The terms used herein are used only to describe specific embodiments and are not intended to limit the present application. The terms "comprises" and "has" and variations thereof in the present specification, claims, and above description of the drawings are intended to cover a non-exclusive inclusion.

[0034] In the description of the embodiments of the present application, the technical terms "first," "second," etc. are used only to distinguish between different objects, and are not understood to indicate or imply relative importance, or to imply the number, specific order, or primary or secondary relationship of the technical features shown. In the description of the embodiments of the present application, "plurality" means two or more, unless otherwise clearly and specifically limited.

[0035] References herein to an "embodiment" mean that a particular feature, structure, or characteristic described with reference to the embodiment may be included in at least one embodiment of the present application. The appearance of such phrases in various places throughout the specification does not necessarily refer to the same embodiment, nor does it refer to separate or alternative embodiments that are mutually exclusive of other embodiments. As one skilled in the art will understand, either explicitly or implicitly, the embodiments described herein may be combined with other embodiments.

[0036] In the description of the embodiments of the present application, the term "and / or" is merely one relation describing related objects, and indicates that three relations may exist. For example, in the case of A and / or B, it can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, in this specification, the symbol " / " generally indicates that the related objects before and after it are in a kind of "or" relationship.

[0037] In describing the examples of the present application, the term "plurality" means two or more (including two); similarly, "multiple groups" means two or more (including two groups), and "multiple sheets" means two or more (including two).

[0038] In describing the embodiments of the present application, the orientations or positional relationships indicated by technical terms such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial direction," "radial direction," and "circumferential direction" are based on the orientations or positional relationships shown in the drawings, and are merely for the convenience and simplification of the description of the embodiments of the present application. They do not indicate or imply that the devices or elements referred to must have a specific orientation, or be configured or operate in a specific orientation, and therefore are not to be construed as limiting the embodiments of the present application.

[0039] In describing the embodiments of the present application, unless otherwise clearly specified and limited, the technical terms "attach," "couple," "connect," "fixed," etc. should be understood in a broad sense, and may refer to, for example, a fixed connection, a detachable connection, or an integral connection; a mechanical connection, or an electrical connection; a direct connection, an indirect connection via an intermediate medium, an internal communication between two components, or an interactive relationship between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application according to specific circumstances.

[0040] Currently, there are two main routes for titanium doping: (1) external introduction, i.e., the addition of titanium-containing materials; (2) in the production of iron phosphate, the iron source is often ferrous sulfate heptahydrate, a titanium white by-product. This contains residual ilmenite extract from crystallization and separation, allowing this portion of elemental titanium to be incorporated into the anhydrous iron phosphate. Route 1 requires the addition of new raw materials and a raw material doping step. Furthermore, the titanium content in the final product is often designed to be less than 1%. Furthermore, titanium is difficult to stably exist in aqueous solution, and once hydrolysis occurs, it is difficult to reverse the process. The subsequent doping process also changes from iron site substitution to solid-phase mixing, making the material supply design difficult. For example, in CN111908441A, a mixed solution of ferrous sulfate and iron scrap phosphoric acid is used as the base solution. An external titanium salt solution is introduced. After titanium phosphate is formed, hydrogen peroxide and alkali are added dropwise to precipitate iron phosphate, forming a coating on the titanium phosphate.

[0041] The second route has cost advantages because it does not require the addition of new raw materials. It also reduces the amount of waste generated from iron salts during production and allows waste to be recycled, which is more consistent with the concepts of energy conservation and emission reduction. However, it also has the disadvantage of unstable content. This is because different by-product processing methods and limits vary among titanium white manufacturers, leading to variations in the pH, titanium content, and main component content of solid ferrous sulfate heptahydrate. Because titanium is amphoteric and highly susceptible to metatitanic acid formation, preserving titanium in solid ferrous sulfate often requires preserving all soluble titanium. Furthermore, because iron phosphate is produced by liquid-phase precipitation, insoluble titanium precipitates must be filtered out during iron salt production. For these reasons, the titanium doped in anhydrous iron phosphate is completely affected by the ferrous sulfate heptahydrate. Therefore, all manufacturers currently using this method to produce titanium-containing iron phosphate use solid ferrous iron supplied by the same titanium white plant to stabilize the titanium content in the anhydrous iron phosphate.

[0042] To solve the technical problems of the prior art, which require adding titanium externally to produce titanium-containing materials or consume high energy, and also require improving the quality of the products, the present application provides a method for producing titanium-doped anhydrous iron phosphate material, which includes the following steps: S1: Provide a titanium-containing ferrous sulfate raw material solution and a titanium-free ferrous sulfate raw material solution. S2: The titanium-containing ferrous sulfate raw material liquid and the titanium-free ferrous sulfate raw material liquid are mixed to obtain a mixed solution. S3: The mixed solution is mixed with an oxidizer and a phosphorus source to obtain a slurry containing iron phosphate and titanium phosphate. S4: The slurry is sequentially subjected to aging, rinsing, drying, and sintering to obtain a titanium-doped anhydrous iron phosphate material.

[0043] Specifically, in step S1, a titanium-containing ferrous sulfate raw material liquid (hereinafter, simply referred to as the ferrous solution) and a titanium-free ferrous sulfate raw material liquid (hereinafter, simply referred to as the ferrous solution) must be provided. The ferrous solution is obtained by dissolving a titanium white by-product in an acidic aqueous solution and performing solid-liquid separation. The ferrous solution is obtained by mixing the titanium white by-product with a phosphorus-containing solution and performing solid-liquid separation. The phosphorus-containing solution contains at least one of phosphoric acid and a phosphate.

[0044] The raw material for preparing the ferrous iron solution and the ferrous iron solution is preferably a titanium white by-product. The titanium white by-product contains ferrous sulfate heptahydrate as a main component and a small amount of elemental titanium, and is generally in the form of a solid powder or powder. The titanium white by-product may be a commercially available product, and the titanium content ranges preferably from 600 to 4200 ppm (mass fraction, parts per million), more preferably from 2000 to 4000 ppm. The titanium white by-product also typically contains extremely small amounts of metal element impurities such as aluminum, potassium, magnesium, and manganese. For example, the titanium white by-product has a main component content (calculated as ferrous sulfate heptahydrate) of 80% or more, preferably 85% or more, a pH value (calculated by dissolving 10 g of solid in 100 g of water) of 2.5 to 3.25, and cationic impurity indices of lead (Pb) < 20 ppm, nickel (Ni) < 100 ppm, chromium (Cr) < 65 ppm, copper (Cu) < 20 ppm, and zinc (Zn) < 100 ppm.

[0045] In this example, the titanium white by-product is dissolved in an acidic aqueous solution and subjected to solid-liquid separation to obtain a ferrous solution. For example, concentrated sulfuric acid is diluted with water to obtain a dilute sulfuric acid solution, which is stirred for 5-10 minutes to ensure uniformity. The titanium white by-product is then added and stirred for 10-15 minutes to dissolve and dissolve uniformly. The weight ratio of the titanium white by-product to water may be 1:1.0-2.0, and the molar ratio of the titanium white by-product to added sulfuric acid may be 32-40:1. The pH of the resulting ferrous solution should be 0.8-1.8. Preferably, solid-liquid separation is performed using a filter press to separate foreign matter, such as dust, soil, and plastic film, and insoluble compounds (mainly titanates) contained in the solid ferrous solution. The filtered ferrous solution contains titanium ions, sulfate ions, and ferrous ions.

[0046] Furthermore, in this example, the titanium white by-product and the phosphorus-containing solution are mixed and subjected to solid-liquid separation to obtain a ferrous iron solution. The components of the phosphorus-containing solution include one or more of phosphoric acid and phosphates. Preferably, a phosphorus-containing rinse (or phosphoric acid, ammonium phosphate, sodium phosphate, etc.) is mixed with water to prepare a phosphorus-containing solution with a mass fraction of elemental phosphorus of 1000 ppm to 3000 ppm. Specifically, in this example, the phosphorus-containing solution is added to a reactor, stirring is initiated, and then titanium white by-product powder is added to the reactor, with the mass ratio of titanium white by-product to phosphorus-containing solution being 1:1.0 to 2.0. After the addition is complete, stirring is continued for 10 to 15 minutes to allow the reaction to proceed uniformly. The reaction involved is 3Ti 4+ +4PO4 3- →Ti3(PO4)4. The pH value of the obtained ferrous solution is 0.8 to 1.8. After the reaction is completed, solid-liquid separation is carried out to obtain a ferrous solution that does not contain titanium element.

[0047] In the preparation process of the above-mentioned first ferrous solution, the acidic environment ensures that elemental titanium is not hydrolyzed. In the preparation process of the second ferrous solution, the phosphorus-containing rinse solution from the iron phosphate production process and pure water are preferably used to prepare the dissolving solution, thereby recycling the waste liquid and ensuring a low pH value for the ferrous solution after impurities have been removed, thereby avoiding the risk of elemental titanium being hydrolyzed during subsequent mixing and enabling the production of the second ferrous solution.

[0048] In step S2, the ferrous iron solution and the ferrous iron solution are mixed to obtain a mixed solution. In this embodiment, by adjusting the mixing ratio of the ferrous iron solution and the ferrous iron solution, a controllable design can be achieved in which the titanium content in the final product is within the range of 0-2%, which is convenient for solving the problem of uncontrollable titanium content in anhydrous iron phosphate due to uneven quality of ferrous sulfate heptahydrate. For example, the ferrous iron solution and the ferrous iron solution may be mixed at a mass ratio of 4:1 or 1:4.

[0049] Specifically, in step S3, the mixed solution is mixed with an oxidizing agent and a phosphorus source to obtain a slurry containing iron phosphate and titanium phosphate. In this embodiment, the phosphorus source is also prepared by mixing a phosphorus-containing material and water to prepare a solution with a phosphorus mass fraction of 6 to 18%. The phosphorus-containing material includes, but is not limited to, phosphoric acid, ammonium phosphate, sodium phosphate, etc.

[0050] In step S3, in this embodiment, stirring may be turned on during the process of mixing the mixed solution with the oxidizing agent and phosphorus source. The frequency and stirring device are related to the volume of the reactants and are sufficient to ensure sufficient dispersion without spillage from the reaction vessel. For example, the oxidizing agent (typically hydrogen peroxide solution) and the phosphorus source are simultaneously added dropwise to the mixed solution, and the addition time is controlled to 20 to 60 minutes. Here, the ratio of each material is calculated based on the amount of substance, and the molar ratio is preferably n iron element:n phosphorus element (P):n hydrogen peroxide solution (H2O2) = 1:1.01 to 1.05:0.55 to 0.65. This reaction method allows titanium element to be uniformly dispersed in the slurry. After the addition is completed, in this embodiment, a yellow slurry containing the produced iron phosphate and titanium phosphate is obtained.

[0051] The reactions involved include: 2Fe 2+ +H2O2+HPO4 2- +H2PO4 - →2FePO4↓+2H2O+H + 3Ti 4+ +4PO4 3- →Ti3(PO4)4

[0052] Specifically, in step S4, the slurry is sequentially subjected to aging, rinsing, drying, and sintering. In this embodiment, aging may be performed while stirring to achieve crystal transformation. Preferably, the resulting slurry is heated to 80 to 98°C (more preferably 92 to 95°C) in a kettle and kept at this temperature for 1 to 4 hours to achieve high-temperature induced crystal transformation. After the temperature is maintained, the slurry is filtered.

[0053] In step S4, phosphoric acid may be added in an amount of 10 to 30% relative to the amount of iron phosphate during the aging process to accelerate the conversion rate. After aging, rinsing is also performed. Impurities in the slurry precipitate are removed by water washing, followed by filtration to obtain a precipitate and a phosphorus-containing rinse solution (rinsing may be performed until the conductivity of the rinse water obtained by filtration no longer exceeds 200 μs / cm). The phosphorus-containing rinse solution provides a titanium-free ferrous sulfate raw material solution; that is, it can be recovered and used to prepare a phosphorus-containing solution. In the present embodiment, the phosphorus-containing rinse solution can be used to produce the ferrous iron solution. This allows the pH value of the solution to be maintained low and allows for the reuse of waste liquid.

[0054] In step S4, the filter cake is dried, preferably by baking, i.e., the rinsed filter cake is baked to control the moisture content, and then sintered at 550-750°C for 1-4 hours. The heating rate may be controlled at 3-5°C / min. After sintering is complete, the titanium-doped anhydrous iron phosphate material is obtained as the product.

[0055] Furthermore, referring to the schematic diagram of the production flow of titanium-doped anhydrous iron phosphate material shown in Figure 3, in this example, first, a first ferrous solution is prepared using ferrous sulfate heptahydrate, sulfuric acid, and water, and then a second ferrous solution is prepared using ferrous sulfate heptahydrate and a phosphorus-containing solution. The first ferrous solution and the second ferrous solution are then mixed to obtain a mixed solution. The mixed solution is then mixed with an oxidizing agent and a phosphorus source to obtain a slurry containing iron phosphate and titanium phosphate. The resulting slurry is then subjected to aging and rinsing, and after rinsing, a filter cake and a phosphorus-containing rinse are obtained, respectively. The resulting filter cake is then dried and sintered to produce the titanium-doped anhydrous iron phosphate material. Meanwhile, a phosphorus-containing solution is prepared using the phosphorus-containing rinse and water, and reused to prepare the second ferrous solution. The titanium-doped iron phosphate produced in the examples of the present application has a yield of 99% or more, and the titanium element in the titanium white by-product, ferrous sulfate heptahydrate, can be recovered and reused, thereby reducing waste and raw materials and recycling waste.The method of the present application provides titanium-doped anhydrous iron phosphate with good performance and quality and with low energy consumption for production.

[0056] Next, in the embodiments of the present application, there is provided a titanium-doped anhydrous iron phosphate material produced by the above-mentioned production method, which has an anhydrous iron phosphate crystal structure and a nanoscale particle stacking morphology, with an Fe / P molar ratio of 0.96 to 1.01, and a Ti doping amount of 2 wt% or less.

[0057] In some embodiments of the present application, the titanium-doped anhydrous iron phosphate material has a Ti doping amount of 1 wt% or less and can be produced by the above-mentioned production method. In addition, the specific surface area of ​​the titanium-doped anhydrous iron phosphate material is 8-10 m 2 / g.

[0058] The titanium-doped anhydrous iron phosphate material product described in the examples of this application has a stable titanium element content, and its crystal structure is consistent with that of anhydrous iron phosphate (as determined by X-ray diffraction pattern analysis). Furthermore, it has a nanoscale particle stacking shape (as determined by scanning electron microscope image analysis). The sample material has a uniform shape, which is advantageous for subsequent use in products.

[0059] Furthermore, the present application also provides examples of the use of the titanium-doped anhydrous iron phosphate material in the manufacture of electrode materials and batteries, specifically, cathode sheets, secondary batteries, and electrical devices. The titanium-doped anhydrous iron phosphate material can be used as a precursor to manufacture iron phosphate-based cathode materials, and the cathode materials are manufactured using the titanium-doped anhydrous iron phosphate and an ionic battery source (e.g., lithium salt). The cathode battery material of the present application is assembled to manufacture corresponding battery electrode sheets and their devices and apparatuses. In the present application, the electrode material and batteries are manufactured using conventional manufacturing methods in the art. Manufacturing the precursor material has the technical effect of stabilizing the quality, thereby improving the performance of the cathode sheets, secondary batteries, and electrical devices.

[0060] In some embodiments of the present application, the secondary battery is useful as a power source for operating or driving an electrical device, and may include a plurality of battery cells, which may be connected in series, parallel, or series-parallel. The battery cells may have a cylindrical, flat, rectangular, or other shape. The secondary battery may further include a bus component for electrically connecting the plurality of battery cells.

[0061] The electric device according to the embodiment of the present application may be, but is not limited to, a mobile phone, a tablet, a laptop, an electric toy, an electric tool, a battery car, an electric vehicle, a boat, a spaceship, etc. Among these, the electric toy may include a game console, an electric toy vehicle, an electric toy boat, an electric toy airplane, or other stationary or mobile electric toy, and the spaceship may include an airplane, a rocket, a space shuttle, a spaceship, etc.

[0062] Some specific examples are listed below, but the examples described below are illustrative and are used only to explain the present application and are not to be understood as limiting the present application. If specific techniques or conditions are not specified in the examples, the techniques, conditions, or product instructions described in the literature of the field should be followed. If the manufacturers of the reagents and equipment used are not listed, commercially available conventional products should be used.

[0063] Example 1 1. Preparation of ferrous iron solution: 7 kg of pure water was added to a reactor, followed by dilution with 50 g of concentrated sulfuric acid (75 wt%) and stirring for 10 minutes. 3.5 kg of ferrous sulfate heptahydrate was added and stirred for 15 minutes. The ferrous sulfate heptahydrate used here was a titanium white by-product sold by the Longman Group (composition listed in the table below). The pH of the dispersed and dissolved solution was measured and found to be 1.707. The solution obtained by filtration was the ferrous iron solution. [Table 1]

[0064] 2. Preparation of phosphorus-containing solution and ferrous iron solution: 20 kg of phosphorus-containing rinse solution collected from the workshop of an iron phosphate manufacturer in Hubei Province was mixed with 10 kg of pure water to prepare a phosphorus-containing solution. 7 kg of the phosphorus-containing solution was added to the reactor, stirring began, and then 3.5 g of ferrous sulfate heptahydrate was added to the reactor. The ferrous sulfate heptahydrate used here is a titanium dioxide by-product sold by the Longman Group. After 10-15 minutes of stirring and reaction, the pH was measured and found to be 1.401. The resulting solution was filtered to obtain a ferrous iron solution.

[0065] 3. Preparation of phosphorus source: 5 kg of ammonium dihydrogen phosphate was dissolved in 16 kg of pure water, 3 kg of aqueous ammonia was added, and the mixture was thoroughly stirred to obtain a phosphorus source (in each of steps 1, 2, and 3, materials were produced in excess for use in other examples and comparative examples).

[0066] 4. Preparation of mixed solution: The ferrous iron solution and the ferric iron solution were mixed in a mass ratio of 4:1 and stirred for 10 minutes to obtain 750 g of a mixed solution.

[0067] 5. Preparation of titanium-doped iron phosphate: 60 g of hydrogen peroxide solution and 355.96 g of phosphorus-containing solution A were simultaneously added dropwise to 750 g of the mixed solution, and the addition time was controlled to 40 minutes. Upon completion of the addition, a yellow slurry was obtained.

[0068] 6. Crystalline form conversion (aging): While stirring, 10 g of 86 wt % phosphoric acid was added to the slurry, which was then heated to 95°C and kept at that temperature for 2 hours. Upon completion of the keeping, a white slurry was obtained.

[0069] 7. Rinsing and impurity removal: Impurities in the slurry precipitate were removed by washing with water, and the slurry was rinsed until the conductivity of the rinse water obtained by filtration did not exceed 200 μs / cm, to obtain a phosphorus-containing rinse solution and a filter cake.

[0070] 8. Drying and sintering: The rinsed filter cake was baked at 98°C for 6 hours, and then sintered in a muffle furnace at 700°C for 2 hours, with the heating rate controlled at 4°C / min. Upon completion of sintering, 114.87g of the product, anhydrous iron phosphate, was obtained.

[0071] 4 and 5 show the X-ray diffraction (XRD) pattern and scanning electron microscope (SEM) image of the final product sample of Example 1 of the present application. A comparison of the diffraction peak angles in the XRD pattern with those of standard card 29-0715 confirmed that the crystalline structure of the sample was consistent with that of anhydrous iron phosphate. The SEM image revealed that the sample of Example 1 of the present application was composed of melted and stacked nanoscale particles.

[0072] Example 2 The ferrous iron and ferrous iron solutions of Example 1 were used, but the mixing ratio of the two ferrous iron solutions was adjusted to 1:4 in step 3. The remaining steps were completely similar.

[0073] Example 3 The remaining steps were the same as in Example 1, except that the source of ferrous sulfate heptahydrate in step 1 was changed from that commercially available from Longpan Group to a titanium white by-product commercially available from Baililian Group to prepare the first ferrous solution. The titanium white by-product commercially available from Longpan Group was still used as the raw material for preparing the second ferrous solution.

[0074] Example 4 The source of ferrous sulfate heptahydrate in step 2 was changed to titanium white by-product commercially available from the Baili Lian Group to prepare the ferrous iron solution, and the remaining steps were the same as in Example 1. The titanium white by-product commercially available from the Longhan Group was still used as the raw material for preparing the ferrous iron solution.

[0075] [Table 2]

[0076] Comparative Example 1 The ferrous iron solution of Example 1 was used, but the mixed solution in Step 3 was changed entirely to ferrous iron solution.

[0077] Comparative Example 2 The remaining steps were the same as in Example 1, except that in step 1, no dilution with sulfuric acid was added to prepare the ferrous iron solution.

[0078] Comparative Example 3 When preparing the ferrous iron solution in step 2, instead of the method for preparing phosphorus-containing solution B, 1 kg of ferrous sulfate heptahydrate was dissolved in 2 kg of water and the pH was adjusted to 3 with sodium hydride. The remaining steps were the same as in Example 1.

[0079] The devices and methods used to detect and characterize the samples obtained in each example and comparative example include: 1. BET (Bright Energy Transfer Emission Test) detection: Tristar II 3020 specific surface area detector; 2. Metal element content: 5110 ICP-OES spectrometer; 3. Iron element: GB / T6730.66-2009; 4. Phosphorus element: Quinoline-molybdate-citric acid-acetone gravimetric method. The BET detection data and Fe / P content are shown in Table 3, and the metal element content limited to battery-grade iron phosphate is shown in Table 4.

[0080] [Table 3] [Table 4]

[0081] Comparing the data in Table 3, the doping amount of titanium element is small, so it does not bring about obvious changes in the specific surface area, but has a slight effect on the iron-phosphorus moles. The more titanium element, the lower this ratio becomes, because titanium element replaces the position of iron element.

[0082] As a result of comparing the mass fractions of metal element impurities listed in Table 4, (1) Comparing Example 1 and Comparative Example 1, the ratio of ferrous iron solution to ferrous iron solution during production was changed, and the titanium content in the sample also changed accordingly. When the mixing ratio was 4:1, the titanium content was 2356.04 ppm, and when the mixing ratio was 5:0, the titanium content was 2898.26 ppm. Comparing Example 1 and Example 2, the mixing ratio was 4:1, and the titanium content in the sample was 603.8 ppm. Overall, in this batch, the iron phosphate produced by dissolving ferrous sulfate heptahydrate and pure water in a 1:2 ratio had a maximum titanium doping level of approximately 2898 ppm. By mixing the ferrous iron solution and ferrous iron solution in different ratios, anhydrous iron phosphate samples with various titanium contents could be obtained.

[0083] (2) A comparison between Examples 1 and 3 shows that the origin of the titanium white by-product in the raw material used to prepare the ferrous iron solution changed, and therefore the titanium content in the sample also changed. In Example 3, the titanium content of the sample was 4189.46 ppm, and therefore the maximum titanium content in this application is related to the origin of the raw material for the ferrous iron solution. This is because the titanium element in this application originates from titanium attached to ferrous sulfate heptahydrate in the ferrous iron solution, and the maximum titanium content is affected by this attached titanium.

[0084] (3) Comparing Examples 1 and 4, although the origin of the titanium white by-product used to prepare the ferrous iron solution was different, no difference was observed in the final sample. This is because the phosphorus-containing solution B acts to remove impurities from the ferrous iron solution and does not affect the sample components. The ferrous iron solution only functions to adjust the titanium content and is not affected by the origin of the raw materials.

[0085] (4) In Comparative Example 2, sulfuric acid was replenished and pH was not controlled when the ferrous iron solution was prepared, and therefore the titanium content in the final sample was lower than in Example 1. This is because the ferrous iron solution was prepared by dissolving it in pure water, resulting in a high pH (measured data: 2.1), and as a result, some of the titanium ions were hydrolyzed to form colloids, which were then filtered out.

[0086] (5) In Comparative Example 3, the preparation method for the ferrous iron solution was modified by dissolving it in pure water and increasing the pH to suppress impurities. In both detection runs, the aluminum impurity content was less than 20% of that of the other samples, but the detected titanium content was not consistent, indicating that the distribution of titanium in the samples was not sufficiently uniform. When the ferrous iron solution and the ferrous iron solution were mixed, some of the titanium ions were hydrolyzed due to the increase in pH. Although the titanium content was not reduced by the hydrolysis in this step, the colloid formed by the hydrolysis resulted in insufficient dispersion of the titanium. After the sintering step, this portion of the titanium was ultimately present only in the form of amorphous titanate or titanium dioxide.

[0087] As can be seen from the above examples, the present invention involves blending a titanium-containing ferrous sulfate raw material solution (preferably produced from a titanium white by-product) with a titanium-free ferrous sulfate raw material solution. The resulting mixed solution is then oxidized with a phosphorus source to obtain a slurry containing iron phosphate and titanium phosphate. This slurry is then aged, rinsed, dried, and sintered to obtain a titanium-doped anhydrous iron phosphate material. The present invention primarily involves blending the ferrous solution in two stages, thereby controlling the ratio to control the titanium content in the final doped iron phosphate product and ensuring stable and controllable titanium content. Furthermore, the titanium-doped anhydrous iron phosphate product has a uniform nanoscale particle stacking morphology, making it suitable for use in the manufacture of battery materials. Furthermore, the present invention is simple and convenient to produce, consumes little energy, and uses titanium attached to the titanium white by-product, ferrous sulfate heptahydrate, itself. Before the reaction, the titanium element exists stably in the form of ions, thereby improving product quality and enabling waste to be recycled.

[0088] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiment that has substantially the same configuration as the technical idea and exhibits the same effects within the scope of the technical solution of the present application is included within the technical scope of the present application. It should be noted that various modifications that a person skilled in the art may make to the embodiments or other forms constructed by combining some of the components of the embodiments are also included within the scope of the present application, as long as they do not deviate from the spirit of the present application.

Claims

1. providing a titanium-containing ferrous sulfate source liquid and a titanium-free ferrous sulfate source liquid; mixing the titanium-containing ferrous sulfate raw material liquid with the titanium-free ferrous sulfate raw material liquid to obtain a mixed solution; mixing the mixed solution with an oxidizing agent and a phosphorus source to obtain a slurry containing iron phosphate and titanium phosphate; and sequentially subjecting the slurry to aging, rinsing, drying, and sintering to obtain a titanium-doped anhydrous iron phosphate material.

2. 2. The production method according to claim 1, wherein raw materials for preparing the titanium-containing ferrous sulfate raw material liquid and the titanium-free ferrous sulfate raw material liquid contain a titanium white by-product, and the titanium white by-product has a mass fraction of titanium of 600 ppm to 4200 ppm.

3. The manufacturing step for providing the titanium-containing ferrous sulfate raw material solution includes: the titanium white by-product is dissolved in an acidic aqueous solution, and solid-liquid separation is performed to obtain the titanium-containing ferrous sulfate raw material solution; And / or, the manufacturing step for providing the titanium-free ferrous sulfate raw material solution includes: mixing the titanium white by-product with a phosphorus-containing solution and performing solid-liquid separation to obtain the titanium-free ferrous sulfate raw material solution; The manufacturing method according to claim 2, wherein the phosphorus-containing solution contains at least one of phosphoric acid and a phosphate, and a mass fraction of elemental phosphorus in the phosphorus-containing solution is 1000 ppm to 3000 ppm.

4. 4. The method according to claim 3, wherein the titanium-containing ferrous sulfate raw material solution and the titanium-free ferrous sulfate raw material solution each have a pH value of 0.8 to 1.

8.

5. 4. The method according to claim 3, wherein the mass ratio of the titanium white by-product to the phosphorus-containing solution is 1:1.0-2.

0.

6. 6. The method according to claim 1, wherein in the step of obtaining a slurry containing iron phosphate and titanium phosphate, the mixed solution is mixed with the oxidizing agent and the phosphorus source so that a molar ratio of iron element, phosphorus element, and oxidizing agent is 1:1.01-1.05:0.55-0.

65.

7. The step of sequentially aging, rinsing, drying, and sintering the slurry includes: heating the slurry to 80-98°C and keeping it at that temperature for 1-4 hours, and then rinsing it with water to obtain a phosphorus-containing rinse solution and a filter cake; and drying the filter cake and then sintering it at 550°C-750°C for 1h-4h to obtain the titanium-doped anhydrous iron phosphate material.

8. 8. The method of claim 7, wherein the aging process includes adding 10% to 30% of phosphoric acid to the iron phosphate.

9. 1. A titanium-doped anhydrous iron phosphate material, comprising: Produced by the production method according to any one of claims 1 to 8, The titanium-doped anhydrous iron phosphate material has an anhydrous iron phosphate crystal structure and a nano-scale particle stacking shape, and the Ti doping amount is 2 wt% or less.

10. 10. The titanium-doped anhydrous iron phosphate material according to claim 9, wherein the Ti-doping amount of the titanium-doped anhydrous iron phosphate material is 1 wt% or less.

11. The titanium-doped anhydrous iron phosphate material has an Fe / P molar ratio of 0.96 to 1.01, and a specific surface area of ​​the titanium-doped anhydrous iron phosphate material of 8 m ２ / g to 10m ２ 10. The titanium-doped anhydrous iron phosphate material of claim 9, wherein the average molecular weight of the material is 1000 or more.

12. A positive electrode sheet, characterized in that the active material is titanium-doped lithium iron phosphate produced using the titanium-doped anhydrous iron phosphate material according to any one of claims 9 to 11.

13. A secondary battery comprising the positive electrode sheet according to claim 12.

14. An electrical device comprising the secondary battery of claim 13.

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