Titanium-doped anhydrous iron phosphate material, preparation method therefor and use thereof

Abstract

The present application belongs to the technical field of iron phosphate material preparation, and provides a titanium-doped anhydrous iron phosphate material, a preparation method therefor, and a use thereof. The preparation method of the titanium-doped anhydrous iron phosphate material comprises the steps: providing a titanium-containing ferrous sulfate raw material liquid and a titanium-free ferrous sulfate raw material liquid; mixing the titanium-containing ferrous sulfate raw material liquid and the titanium-free ferrous sulfate raw material liquid, to obtain a mixed solution; mixing the mixed solution with an oxidant and a phosphorus source, to obtain a slurry containing iron phosphate and titanium phosphate; sequentially subjecting the slurry to aging, rinsing, drying and sintering, to obtain a titanium-doped anhydrous iron phosphate material. The present application can achieve doping control of elemental titanium in the titanium-doped anhydrous iron phosphate material by means of adjusting the mixing ratio of the titanium-containing ferrous sulfate raw material liquid and the titanium-free ferrous sulfate raw material liquid, so that the elemental titanium content in the final product is stable and controllable; the titanium-doped anhydrous iron phosphate material has a uniform nanoscale particle stacking morphology, which is beneficial for use in preparing battery materials.

Description

Titanium-doped anhydrous ferric phosphate material and its preparation method and application

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on December 22, 2023, with application number 2023117858803 and application name “Titanium-doped anhydrous ferric phosphate material, preparation method and application thereof”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the technical field of preparation of iron phosphate materials, and in particular to a titanium-doped anhydrous iron phosphate material, a preparation method and application thereof, mainly a method for preparing titanium-doped anhydrous iron phosphate with controllable titanium content by utilizing waste titanium elements in titanium dioxide by-products, which is beneficial for the preparation of battery materials. Background Art

[0004] Anhydrous iron phosphate is a precursor to lithium iron phosphate, one of the most popular battery cathode materials. The solid-phase preparation process for lithium iron phosphate is shown in Figure 1 and generally includes mixing, spray drying, sintering, pulverization, mixing and grading, and baking. Figure 2 illustrates the conventional preparation process for iron phosphate, which primarily utilizes an iron solution, a phosphorus solution, and an oxidant for oxidation synthesis. High-temperature crystallization, drying, and calcination yield anhydrous iron phosphate. In research on the modification of iron phosphate battery materials, titanium and iron both have a d2sp3 hybridization pattern. Although the stable phase structures of titanium phosphate and iron phosphate differ, adding titanium (Ti) as a dopant to iron phosphate can cause the crystals to arrange themselves in the same pattern as iron. It is generally believed that the effects of titanium doping on iron phosphate / lithium iron phosphate modification include: ① Under the same unit cell parameters, the smaller radius of titanium results in a wider electron migration channel; ② The introduction of the heterogeneous element hinders crystal growth after nucleation, effectively reducing primary particles. This is reflected in the resulting battery's electrical properties, resulting in significantly improved high-rate performance and significantly reduced impedance.

[0005] Titanium doping can be divided into two categories: 1. Introduced during the lithium iron phosphate solid-phase process; 2. Introduced during the iron phosphate process. The first method typically uses rutile titanium dioxide, a more reactive material, in a high-temperature solid-phase reaction with other materials. However, this reaction requires a large amount of heat energy and continuous mechanical grinding.

[0006] Titanium is used as an alternative doping element to iron and is introduced in the form of ions during the preparation of the second type of iron phosphate. There is almost no increase in energy consumption during the production process, which is a more ideal doping method, but there are many influencing factors. In the preparation of iron phosphate compounds, ferrous sulfate heptahydrate, a by-product of titanium dioxide, is generally used as the source of iron. Since this by-product is crystallized from the acid hydrolysis solution of ilmenite, it will have a certain amount of titanium attached to it. Most companies that use this route to produce iron phosphate will remove this part of the titanium element by raising the pH (adding alkali or reacting elemental iron with acid) when preparing the iron source solution. Under this route, it is necessary to further add titanium-containing materials to prepare titanium-doped iron phosphate products, and the quality of the product needs to be further improved.

[0007] Summary of the Invention

[0008] In view of the technical problems existing in the background technology, the present application provides a titanium-doped anhydrous iron phosphate material and its preparation method and application. The titanium-doped anhydrous iron phosphate material provided in the present application has good performance quality, is easy to prepare, and is conducive to application in battery materials.

[0009] In a first aspect, an embodiment of the present application provides a method for preparing a titanium-doped anhydrous ferric phosphate material, which comprises the following steps:

[0010] Provide titanium-containing ferrous sulfate raw material solution and titanium-free ferrous sulfate raw material solution;

[0011] Mixing the titanium-containing ferrous sulfate raw material liquid and the titanium-free ferrous sulfate raw material liquid to obtain a mixed solution;

[0012] mixing the mixed solution with an oxidant and a phosphorus source to obtain a slurry containing iron phosphate and titanium phosphate;

[0013] The slurry is sequentially aged, rinsed, dried and sintered to obtain a titanium-doped anhydrous ferric phosphate material.

[0014] In the technical solution of the embodiment of the present application, the titanium-containing ferrous sulfate raw material liquid is mixed with the titanium-free ferrous sulfate raw material liquid to obtain the mixed solution, and then the obtained mixed solution and the phosphorus source are oxidized to obtain a slurry containing iron phosphate and titanium phosphate, and then the slurry is aged, rinsed, dried, and sintered in sequence to obtain the titanium-doped anhydrous ferric phosphate material. Among them, by mixing the titanium-containing ferrous sulfate raw material liquid and the titanium-free ferrous sulfate raw material liquid in a certain proportion, the doping control of the titanium element in the final doped ferric phosphate product can be achieved by adjusting the proportion, so that the titanium content in the prepared titanium-doped anhydrous ferric phosphate material is stable and controllable, thereby solving the problem of uncontrollable titanium content in anhydrous ferric phosphate caused by uneven quality of ferrous sulfate heptahydrate; at the same time, the titanium-doped anhydrous ferric phosphate prepared in the embodiment of the present application has a uniform nano-scale particle stacking morphology, which is conducive to application.

[0015] In some embodiments, the raw materials for preparing the titanium-containing ferrous sulfate raw material solution and the titanium-free ferrous sulfate raw material solution include titanium dioxide by-product, and the mass fraction of titanium in the titanium dioxide by-product is 600-4200 ppm.

[0016] In this embodiment, the titanium dioxide by-product is used when selecting the source of titanium element introduction. The main component of the titanium dioxide by-product is ferrous sulfate heptahydrate, and titanium is attached to it, so no additional titanium needs to be added. At the same time, in the titanium dioxide by-product, the titanium element exists stably in the form of ions, which is beneficial to improving the quality of the prepared titanium-doped anhydrous ferric phosphate and also realizes waste utilization.

[0017] In addition, the titanium dioxide by-products having a titanium mass fraction within the range of 600-4200 ppm can be used as raw materials for the preparation of the titanium-doped anhydrous ferric phosphate material. In this embodiment, there are no excessive restrictions on the source of the titanium dioxide by-products.

[0018] In some embodiments, the steps of preparing the titanium-containing ferrous sulfate raw material solution include:

[0019] Dissolving the titanium dioxide by-product in an acidic aqueous solution, and obtaining the titanium-containing ferrous sulfate raw material liquid after solid-liquid separation;

[0020] And / or, the steps of preparing the titanium-free ferrous sulfate raw material solution include:

[0021] Mixing the titanium dioxide by-product with a phosphorus-containing solution, and performing solid-liquid separation to obtain the titanium-free ferrous sulfate raw material solution;

[0022] The phosphorus-containing solution includes at least one of phosphoric acid or phosphate; the mass fraction of phosphorus element in the phosphorus-containing solution is 1000-3000 ppm.

[0023] In this embodiment, during the preparation of the titanium-containing ferrous sulfate raw material liquid, an acidic aqueous solution is used to dissolve the titanium dioxide by-product, and the acidic environment can prevent the titanium element from being hydrolyzed. During the preparation of the titanium-free ferrous sulfate raw material liquid, a phosphorus-containing solution is used to dissolve the titanium dioxide by-product to hydrolyze the titanium element.

[0024] In some embodiments, the pH values ​​of the titanium-containing ferrous sulfate raw material solution and the titanium-free ferrous sulfate raw material solution are 0.8-1.8, respectively.

[0025] In this embodiment, by controlling the pH values ​​of the titanium-containing ferrous sulfate raw material solution and the titanium-free ferrous sulfate raw material solution to be between 0.8 and 1.8, it is advantageous to obtain a slurry containing iron phosphate and titanium phosphate through the reaction.

[0026] In some embodiments, in the step of obtaining the slurry containing iron phosphate and titanium phosphate, the mixed solution is mixed with the oxidant and the phosphorus source according to a molar ratio of iron element, phosphorus element and oxidant of 1:1.01-1.05:0.55-0.65.

[0027] In this embodiment, the mixed oxidation is sufficient by adopting this ratio, and the content of active substances in the prepared slurry containing iron phosphate and titanium phosphate is high.

[0028] In some embodiments, the steps of sequentially aging, rinsing, drying, and sintering the slurry include:

[0029] The slurry is heated to 80-98° C. and kept warm for 1-4 hours, and then rinsed with water to obtain a phosphorus-containing rinse liquid and a filter cake;

[0030] The filter cake is dried and then sintered at 550-750° C. for 1-4 hours to obtain the titanium-doped anhydrous ferric phosphate material.

[0031] In this embodiment, the phosphorus-containing rinse liquid can be used to prepare titanium-free ferrous sulfate raw material liquid. On the one hand, the waste liquid is recycled and the cost of alkaline reagents is saved. The ferrous solution not consumed in the preparation process of titanium-doped anhydrous ferric phosphate can also be used for the preparation of conventional ferric phosphate without waste. On the other hand, impurities can be removed under the required low pH conditions, which is different from the increase in pH value caused by alkaline reagents.

[0032] In the second aspect, an embodiment of the present application provides a titanium-doped anhydrous iron phosphate material, which is prepared by the preparation method described above; the titanium-doped anhydrous iron phosphate material has an anhydrous iron phosphate crystal structure and a nano-scale particle stacking morphology, wherein the Ti doping amount of the titanium-doped anhydrous iron phosphate material is less than or equal to 2wt%.

[0033] In the technical solution of the embodiment of the present application, the titanium content in the prepared titanium-doped anhydrous ferric phosphate material is stable, and its crystal structure is consistent with that of anhydrous ferric phosphate. The Fe / P molar ratio of the titanium-doped anhydrous ferric phosphate material is 0.96~1.01, and it has a nano-scale particle stacking morphology and a uniform material morphology, which is convenient for subsequent product applications.

[0034] In some embodiments, the Ti doping amount of the titanium-doped anhydrous ferric phosphate material is less than or equal to 1 wt %; in some embodiments, the Fe / P molar ratio of the titanium-doped anhydrous ferric phosphate material is 0.96-1.01, and the specific surface area can be 8-10 m 2 / g, the material properties are more conducive to subsequent applications.

[0035] In a third aspect, an embodiment of the present application provides a positive electrode plate, in which the active material is titanium-doped lithium iron phosphate prepared from the titanium-doped anhydrous iron phosphate material described above.

[0036] In this embodiment, the titanium-doped anhydrous ferric phosphate material can be used as a precursor to prepare an iron phosphate-based positive electrode material. The positive electrode material is prepared from the titanium-doped anhydrous ferric phosphate and an ion battery source, specifically a titanium-doped lithium iron phosphate active material, and thus has advantages such as stable quality and excellent performance. Using the positive electrode battery material of this embodiment, battery electrodes and devices with corresponding excellent performance are assembled.

[0037] In a fourth aspect, an embodiment of the present application provides a secondary battery comprising the positive electrode sheet described above.

[0038] In this embodiment, the secondary battery includes the above-mentioned positive electrode sheet, and thus has the advantages of stable quality and good performance.

[0039] In a fifth aspect, an embodiment of the present application provides an electrical device comprising the secondary battery described above.

[0040] In this embodiment, the electrical device includes the secondary battery, and thus has the advantages of stable quality and good performance.

[0041] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only part of the embodiments or some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0043] FIG1 is a process for preparing lithium iron phosphate by a conventional solid phase method;

[0044] FIG2 is a conventional preparation process of ferric phosphate;

[0045] FIG3 is a schematic diagram of a process for preparing titanium-doped anhydrous ferric phosphate materials according to some embodiments of the present application;

[0046] FIG4 is an XRD pattern of the final product sample of Example 1 of the present application;

[0047] FIG5 is a SEM image of the final product sample of Example 1 of the present application. DETAILED DESCRIPTION

[0048] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0050] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0051] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0052] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0053] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0054] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0055] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0056] Currently, there are two main approaches to doping titanium: 1. Exogenous introduction through the addition of titanium-containing materials; 2. During the production of ferric phosphate, the iron source is often ferrous sulfate heptahydrate, a byproduct of titanium dioxide. This iron source carries residual ilmenite extract from crystallization and separation, which can be introduced into the anhydrous ferric phosphate. The first approach requires an additional raw material and a raw material addition step. Furthermore, because the designed titanium content in the final product is often less than 1%, titanium is difficult to stably exist in aqueous solution. If hydrolysis occurs, it is difficult to reverse. Subsequent doping also shifts from iron substitution to solid-phase mixing, making the dosing method more difficult to design. For example, CN111908441A uses a mixed solution of ferrous sulfate, iron filings, and phosphoric acid as the base solution. A titanium salt solution is then introduced exogenously to form titanium phosphate. Hydrogen peroxide and alkali are then added dropwise to precipitate the iron phosphate and coat the titanium phosphate.

[0057] The second route requires no new raw materials, offers cost advantages, and reduces the amount of waste residue generated during the production of iron salts, effectively turning waste into valuable resources and better aligning with the principles of energy conservation and emission reduction. However, it also suffers from the drawback of unstable content. This is because different titanium dioxide manufacturers have different methods and limits for handling byproducts, resulting in variations in the pH, titanium content, and main content of their solid ferrous sulfate heptahydrate. Because titanium is amphoteric and readily forms metatitanic acid, retaining all soluble titanium in solid ferrous sulfate is often necessary. Furthermore, since ferric phosphate is produced by a liquid-phase precipitation process, insoluble titanium precipitates must be filtered out during the production of the iron salts. These factors result in the titanium doped into anhydrous ferric phosphate being completely affected by the ferrous sulfate heptahydrate. Therefore, manufacturers currently producing titanium-containing ferrous phosphate using this method exclusively use solid ferrous sulfate supplied by a single titanium dioxide manufacturer to ensure a stable titanium content in the anhydrous ferric phosphate.

[0058] In order to solve the technical problems of the prior art in the preparation of titanium-containing materials or high energy consumption, and the need to improve product quality, the present application first provides a method for preparing titanium-doped anhydrous ferric phosphate material, which comprises the following steps:

[0059] S1. Providing titanium-containing ferrous sulfate raw material solution and titanium-free ferrous sulfate raw material solution;

[0060] S2, mixing the titanium-containing ferrous sulfate raw material liquid and the titanium-free ferrous sulfate raw material liquid to obtain a mixed solution;

[0061] S3, mixing the mixed solution with an oxidant and a phosphorus source to obtain a slurry containing iron phosphate and titanium phosphate;

[0062] S4. The slurry is aged, rinsed, dried and sintered in sequence to obtain a titanium-doped anhydrous ferric phosphate material.

[0063] Specifically, in step S1, a titanium-containing ferrous sulfate raw material liquid (hereinafter referred to as the first ferrous solution) and a titanium-free ferrous sulfate raw material liquid (hereinafter referred to as the second ferrous solution) are required, wherein the first ferrous solution is obtained by dissolving the titanium dioxide by-product in an acidic aqueous solution and performing solid-liquid separation; the second ferrous solution is obtained by mixing the titanium dioxide by-product with a phosphorus-containing solution and performing solid-liquid separation, and the phosphorus-containing solution includes at least one of phosphoric acid or phosphate.

[0064] The raw materials for preparing the first and second ferrous solutions are preferably titanium dioxide byproducts, whose primary component is ferrous sulfate heptahydrate and also contains a small amount of titanium, typically in the form of a solid powder or solid. The titanium dioxide byproduct can be any commercially available material, with a titanium content of 600-4200 ppm (parts per million by mass) being preferred, and 2000-4000 ppm being more preferred. It should be noted that titanium dioxide byproducts typically also contain minor amounts of metallic impurities such as aluminum, potassium, magnesium, and manganese. For example, the titanium dioxide byproduct has a primary content (calculated as ferrous sulfate heptahydrate) of ≥80%, preferably ≥85%, a pH (10 g solid dissolved in 100 g water) of 2.5-3.25, and cationic impurity indicators of lead (Pb) <20 ppm, nickel (Ni) <100 ppm, chromium (Cr) <65 ppm, copper (Cu) <20 ppm, and zinc (Zn) <100 ppm.

[0065] Furthermore, in this embodiment, the titanium dioxide by-product is dissolved in an acidic aqueous solution, and after solid-liquid separation, a first ferrous solution is obtained. For example, concentrated sulfuric acid can be diluted with water to a dilute sulfuric acid solution, stirred for 5-10 minutes to ensure uniformity, and then the titanium dioxide by-product is added and stirred for 10-15 minutes to disperse and dissolve evenly. The weight ratio of the titanium dioxide by-product to water can be 1:1.0-2.0; the molar ratio of the titanium dioxide by-product to the added sulfuric acid can be 32-40:1. The pH value of the obtained first ferrous solution should be between 0.8 and 1.8. Preferably, a filter press is used for solid-liquid separation to separate foreign matter such as dust, sediment, plastic film, and insoluble compounds (mainly titanate) carried in the solid ferrous iron. The filtered first ferrous solution contains titanium ions, sulfate ions, ferrous ions, etc.

[0066] Furthermore, in this embodiment, the titanium dioxide by-product is mixed with a phosphorus-containing solution, and after solid-liquid separation, a second ferrous solution is obtained. The components of the phosphorus-containing solution include one or more of phosphoric acid and phosphates. Preferably, a phosphorus-containing rinse liquid (or phosphoric acid, ammonium phosphate, sodium phosphate, etc.) is mixed with water to prepare a phosphorus-containing solution with a phosphorus mass fraction of 1000ppm-3000ppm. Specifically, in this embodiment of the application, the phosphorus-containing solution is added to the reactor, and after stirring, the titanium dioxide by-product powder is added to the reactor. The mass ratio of the titanium dioxide by-product to the phosphorus-containing solution is 1:1.0-2.0; after the addition is completed, it can be stirred for 10-15 minutes to react evenly, involving the reaction: 3Ti 4+ +4PO4 3- →Ti3(PO4)4; the pH value of the obtained second ferrous solution should be between 0.8 and 1.8. After the reaction is completed, solid-liquid separation is performed to obtain a ferrous solution free of titanium, namely the second ferrous solution.

[0067] During the preparation of the above-mentioned first ferrous solution, the acidic environment can prevent the titanium element from hydrolyzing; during the preparation of the second ferrous solution, it is preferred to use the phosphorus-containing rinse liquid and pure water in the preparation process of ferric phosphate to prepare the dissolving solution, which not only recycles the waste liquid, but also ensures a lower pH value of the ferrous solution after impurities are removed, and can avoid the risk of hydrolysis of the titanium element during subsequent mixing to prepare the second ferrous solution.

[0068] In step S2, the first ferrous solution and the second ferrous solution are mixed to obtain a mixed solution. In this embodiment, by adjusting the mixing ratio of the first ferrous solution and the second ferrous solution, a controllable design of the titanium content in the final product within the range of 0-2% can be achieved, which facilitates solving the problem of uncontrollable titanium content in anhydrous ferric phosphate caused by uneven quality of ferrous sulfate heptahydrate. For example, the first ferrous solution and the second ferrous solution can be mixed in a mass ratio of 4:1 or 1:4.

[0069] Specifically, in step S3, the mixed solution is mixed with an oxidant and a phosphorus source to obtain a slurry containing iron phosphate and titanium phosphate. In this embodiment, a phosphorus source is also prepared by mixing a phosphorus-containing material with water to form a solution having a phosphorus mass fraction of 6-18%. The phosphorus-containing material includes, but is not limited to, phosphoric acid, ammonium phosphate, sodium phosphate, etc.

[0070] In step S3, in the present embodiment, stirring can be turned on during the process of mixing the mixed solution with the oxidant and the phosphorus source. The stirring frequency is related to the stirring equipment and the reaction volume, and it is sufficient to meet the principle of sufficient dispersion and no splashing out of the reaction container. For example, the oxidant (commonly used hydrogen peroxide) and the phosphorus source are added dropwise to the mixed solution at the same time, and the addition time is controlled to be 20-60 minutes. The proportion of each material here is calculated according to the amount of substance, and the molar ratio is preferably n iron element: n phosphorus element (P): n hydrogen peroxide (H2O2) = 1: 1.01-1.05: 0.55-0.65; this reaction method can ensure that the titanium element is evenly dispersed in the slurry. After the addition is completed, the present embodiment can obtain a yellow slurry, which contains the generated iron phosphate and titanium phosphate.

[0071] Reactions include:

[0072] 2Fe 2+ +H2O2+HPO4 2- +H2PO4 - →2FePO4↓+2H2O+H + ;

[0073] 3Ti 4+ +4PO4 3- →Ti3(PO4)4.

[0074] Specifically, in step S4, the slurry is aged, rinsed, dried and sintered in sequence; wherein, in this embodiment, the aging can be carried out under stirring conditions to achieve crystal transformation. The obtained slurry is preferably heated to 80-98°C (more preferably 92-95°C) in a kettle and kept warm for 1h-4h to achieve high-temperature crystal transformation, and filtered after the insulation is completed.

[0075] In step S4, 10-30% of the amount of phosphoric acid of the iron phosphate substance can be added during the aging process to speed up the conversion rate. After aging, rinsing is also included to remove impurities in the slurry precipitate by washing with water, filtering to obtain a precipitate and a phosphorus-containing rinsing liquid (which can be rinsed until the conductivity of the newly filtered rinsing water is not higher than 200μs / cm); the phosphorus-containing rinsing liquid is used to provide a titanium-free ferrous sulfate raw material liquid, that is, it can be recovered and used for the preparation of a phosphorus-containing solution. The embodiment of the present application can use the phosphorus-containing rinsing liquid to prepare the above-mentioned second ferrous solution, which can not only maintain a low pH value of the solution, but also realize the secondary utilization of the waste liquid.

[0076] In step S4, the filter cake is dried, and the drying is preferably carried out by oven drying, that is, the rinsed filter cake is dried and water-controlled, and sintered at 550-750°C for 1-4h, and the heating rate can be controlled to be 3-5°C / min. After the sintering is completed, the product titanium-doped anhydrous ferric phosphate material is obtained.

[0077] Furthermore, in conjunction with the flow diagram for preparing the titanium-doped anhydrous ferric phosphate material shown in Figure 3, in the present embodiment, ferrous sulfate heptahydrate, sulfuric acid, and water are first prepared to form a first ferrous solution, and ferrous sulfate heptahydrate and a phosphorus-containing solution are separately prepared to form a second ferrous solution. Next, the first and second ferrous solutions are mixed to obtain a mixed solution. The mixed solution is then mixed with an oxidant and a phosphorus source to obtain a slurry containing ferric phosphate and titanium phosphate. Finally, the resulting slurry is sequentially aged and rinsed to obtain a filter cake and a phosphorus-containing rinse solution. The filter cake is then dried and sintered to prepare the titanium-doped anhydrous ferric phosphate material. The phosphorus-containing rinse solution is then mixed with water to prepare a phosphorus-containing solution, which is then reused as an ingredient in the second ferrous solution. The yield of the titanium-doped ferric phosphate prepared in the present embodiment is over 99%. Furthermore, the titanium element in the ferrous sulfate heptahydrate, a byproduct of titanium dioxide, can be recycled, thereby reducing waste and raw materials, effectively turning waste into valuable resources. The method of the present application can obtain anhydrous ferric phosphate doped with titanium element, which has good performance and quality and low preparation energy consumption.

[0078] Secondly, an embodiment of the present application provides a titanium-doped anhydrous iron phosphate material, which is prepared by the preparation method described above, has an anhydrous iron phosphate crystal structure, and has a nano-scale particle stacking morphology. The Fe / P molar ratio of the titanium-doped anhydrous iron phosphate material is 0.96~1.01, and the Ti doping amount is less than or equal to 2wt%.

[0079] In some embodiments of the present application, the Ti doping amount of the titanium-doped anhydrous ferric phosphate material is less than or equal to 1 wt%, and can be prepared by the preparation method described above. In addition, the specific surface area of ​​the titanium-doped anhydrous ferric phosphate material can be 8 to 10 m 2 / g.

[0080] The titanium content in the finished product of the titanium-doped anhydrous ferric phosphate material described in the embodiment of the present application is stable, its crystal structure is consistent with that of anhydrous ferric phosphate (according to X-ray diffraction pattern analysis), and it has a nano-scale particle stacking morphology (according to scanning electron microscope image analysis). The sample material has a uniform morphology, which is convenient for subsequent product applications.

[0081] Furthermore, the embodiments of the present application also provide the application of the titanium-doped anhydrous iron phosphate material described above in the preparation of electrode materials and batteries, specifically positive electrode sheets, secondary batteries and electrical devices. The titanium-doped anhydrous iron phosphate material can be used as a precursor to prepare iron phosphate-based positive electrode materials, and the positive electrode material is prepared from the above-mentioned titanium-doped anhydrous iron phosphate and an ion battery source (such as lithium salt). The positive electrode battery material of this embodiment is used to assemble and prepare the corresponding battery electrodes and their devices and apparatus. The preparation of the electrode materials and batteries described in the embodiments of the present application is a conventional preparation method in the field. Through the preparation of the precursor material, the technical effect of stable quality can be achieved, and the performance of the positive electrode sheets, secondary batteries and electrical devices can also be improved.

[0082] In some embodiments of the present application, the secondary battery can serve as an operating power source, driving power source, or other means for powering electrical devices. The secondary battery may include multiple battery cells, which may be connected in series, parallel, or in a hybrid configuration. The battery cells may be cylindrical, flat, rectangular, or in other shapes. The secondary battery may also include a busbar for electrically connecting the multiple battery cells.

[0083] The electrical devices provided in the embodiments of the present application may be, but are not limited to, mobile phones, tablets, laptop computers, electric toys, electric tools, battery-powered vehicles, electric cars, ships, spacecraft, etc. The electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, and the spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0084] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used without manufacturer's indication are all commercially available conventional products.

[0085] Example 1

[0086] 1. Preparation of the First Ferrous Solution: Add 7 kg of pure water to a reactor, dilute with 50 g of concentrated sulfuric acid (75 wt%), and stir for 10 minutes. Add 3.5 kg of ferrous sulfate heptahydrate and stir for 15 minutes. Ferrous sulfate heptahydrate is a byproduct of titanium dioxide sold by Longmang Group (see the table below for its composition). After dispersibility and dissolution, the pH of the solution was measured to be 1.707. Filter the solution to obtain the First Ferrous Solution.

[0087] Table 1 Titanium dioxide by-product detection results

[0088] 2. Preparation of the Phosphorus Solution and the Second Ferrous Solution: Mix 20 kg of phosphorus-containing rinse liquid collected from the workshop of a Hubei iron phosphate company with 10 kg of pure water to prepare a phosphorus solution. Add 7 kg of the phosphorus solution to a reactor and stir. Then, add 3.5 g of ferrous sulfate heptahydrate (a byproduct of titanium dioxide sold by Longmang Group) to the reactor. Stir and react for 10-15 minutes. The pH value was measured to be 1.401. Filter to obtain the second ferrous solution.

[0089] 3. Preparation of phosphorus source: Dissolve 5 kg of ammonium dihydrogen phosphate in 16 kg of pure water, add 3 kg of ammonia water and stir thoroughly to obtain a phosphorus source. (In steps 1, 2, and 3, the materials used in the preparation are all in excess and are used for the other examples and comparative examples)

[0090] 4. Preparation of mixed solution: Mix the first ferrous solution and the second ferrous solution in a mass ratio of 4:1 and stir for 10 minutes to obtain 750g of mixed solution.

[0091] 5. Preparation of titanium-doped ferric phosphate: 60 g of hydrogen peroxide and 355.96 g of phosphorus-containing solution A were simultaneously added dropwise to 750 g of the mixed solution. The addition time was controlled within 40 min. After the addition was completed, a yellow slurry was obtained.

[0092] 6. Crystal transformation (aging): While stirring, add 10 g of 86 wt% phosphoric acid to the slurry, heat to 95° C. and keep warm for 2 h. After the end of the insulation, a white slurry is obtained.

[0093] 7. Rinsing and impurity removal: Remove impurities in the slurry precipitate by water washing, and rinse until the conductivity of the newly filtered rinsing water is no more than 200μs / cm to obtain phosphorus-containing rinsing liquid and filter cake.

[0094] 8. Drying and sintering: The rinsed filter cake was dried at 98°C for 6 hours and then sintered in a muffle furnace at 700°C for 2 hours at a heating rate of 4°C / min. After sintering, 114.87 g of anhydrous iron phosphate was obtained.

[0095] Figures 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. Comparing the diffraction peak angles in the XRD pattern with those of standard card 29-0715 confirms that the sample's crystal structure is consistent with anhydrous ferric phosphate. The SEM image shows that the sample of Example 1 of the present application is composed of melt-stacked nanoscale particles.

[0096] Example 2

[0097] The first ferrous solution and the second ferrous solution in Example 1 are still used, but the mixing ratio of the two ferrous solutions in step 3 is adjusted to 1:4. The remaining steps are exactly the same.

[0098] Example 3

[0099] The source of ferrous sulfate heptahydrate in step 1 was changed from that sold by Lomon Group to titanium dioxide byproduct sold by Billions Group to prepare the first ferrous solution. The subsequent steps were the same as in Example 1. The second ferrous solution was prepared using titanium dioxide byproduct sold by Lomon Group as a raw material.

[0100] Example 4

[0101] The source of ferrous sulfate heptahydrate in step 2 was changed to the titanium dioxide byproduct sold by Billions Group to prepare the second ferrous solution. The other steps were the same as in Example 1. The raw material for preparing the first ferrous solution was still the titanium dioxide byproduct sold by Lomon Group.

[0102] Table 2 Detection results of titanium dioxide by-products in Example 4

[0103] Comparative Example 1

[0104] The first ferrous solution in Example 1 is still used, but the mixed solution in step 3 is changed to use the first ferrous solution entirely.

[0105] Comparative Example 2

[0106] When preparing the first ferrous solution in step 1, sulfuric acid is not added for dilution, and the other steps are the same as those in Example 1.

[0107] Comparative Example 3

[0108] In step 2, when preparing the second ferrous solution, the method for preparing the phosphorus-containing solution B was not used. Instead, 1 kg of ferrous sulfate heptahydrate was dissolved in 2 kg of water, and sodium hydroxide was used to adjust the pH to 3. The other steps were the same as in Example 1.

[0109] Samples obtained from each example and comparative example were characterized using the following equipment and methods: 1. BET (Between-Emitting Dioxide) analysis using a Tristar II 3020 surface area analyzer; 2. Metal element content using a 5110 ICP-OES spectrometer; 3. Iron content using the GB / T 6730.66-2009 method; and 4. Phosphorus content using the quinoline gravimetric method. The BET and Fe / P content data are shown in Table 3, and the restricted metal element content of battery-grade iron phosphate is shown in Table 4.

[0110] Table 3 BET and Fe / P contents of samples obtained from examples and comparative examples

[0111] Table 4 Restricted metal element content of battery-grade iron phosphate

[0112] Comparing the data in Table 3: Since the amount of titanium doping is relatively small, there is no significant change in the specific surface area, and there is a slight effect on the molar ratio of iron to phosphorus. The more titanium is added, the lower the ratio is, because titanium will replace the position of iron.

[0113] Compare the mass fractions of metal element impurities in Table 4:

[0114] ① Compared with Comparative Example 1, Example 1 is prepared by changing the ratio of the first ferrous solution and the second ferrous solution, so the titanium content in the sample also changes accordingly. When the mixing ratio is 4:1, the titanium content is 2356.04ppm, and when the ratio is 5:0, it is 2898.26ppm. Compared with Example 2, the mixing ratio of Example 2 is 4:1, and the titanium content in the sample is 603.8ppm. Comprehensive comparison shows that the maximum titanium content of the ferric phosphate produced by dissolving the ferrous sulfate heptahydrate and pure water in a ratio of 1:2 is about 2898ppm. When the first ferrous solution and the second ferrous solution are mixed in different ratios, anhydrous ferric phosphate samples with corresponding titanium contents can be obtained.

[0115] ② Comparing Example 1 with Example 3, the source of the titanium dioxide byproduct used in preparing the first ferrous solution was changed, and the titanium content in the sample also changed. The titanium content of the sample in Example 3 was 4189.46 ppm, indicating that the maximum titanium content in this application is related to the source of the raw materials for the first ferrous solution. This is because the source of titanium in this application is the attached titanium of ferrous sulfate heptahydrate in the first ferrous solution, which affects the maximum titanium content.

[0116] ③ Comparing Example 1 with Example 4, the source of the titanium dioxide byproduct used in preparing the second ferrous solution was changed. The final samples showed no difference. This is because the use of phosphorus-containing solution B removes impurities from the second ferrous solution, thus having no effect on the sample composition. The second ferrous solution only regulates the titanium content and is not affected by the source of the raw materials.

[0117] ④ In Comparative Example 2, sulfuric acid was not added to control the pH when preparing the first ferrous solution. Compared with Example 1, the titanium content in the final sample decreased. This is because the pH of pure water used to dissolve the first ferrous solution was higher (the measured data was 2.1), which caused some titanium ions to hydrolyze to form colloids, which were intercepted during filtration.

[0118] ⑤ In Comparative Example 3, the second ferrous solution was prepared using pure water and the pH was adjusted to control impurities. In both tests, the aluminum impurity content was less than 20% of that in the other samples, but the detected titanium content was uneven, indicating that the titanium distribution in the samples was not uniform. This is because when the first and second ferrous solutions were mixed, the increase in pH caused some titanium ions to hydrolyze. Although this hydrolysis step does not reduce the amount of titanium, the resulting colloid does not disperse the titanium sufficiently. This titanium, after the sintering step, ultimately exists only as amorphous titanate or titanium dioxide.

[0119] As can be seen from the above embodiments, the present application adopts a titanium-containing ferrous sulfate raw material liquid (preferably prepared from a titanium dioxide by-product), and carries out a batching step with a titanium-free ferrous sulfate raw material liquid, and then oxidizes the obtained mixed solution and a phosphorus source to obtain a slurry containing iron phosphate and titanium phosphate, which is then aged, rinsed, dried, and sintered in sequence to obtain a titanium-doped anhydrous ferric phosphate material. The present application mainly adjusts the ingredients of the ferrous solution to be added into two sections, and the doping control of the titanium element in the final doped ferric phosphate product can be achieved by adjusting the proportion, thereby making the titanium content in the finished product stable and controllable; at the same time, the titanium-doped anhydrous ferric phosphate product has a uniform nano-scale particle stacking morphology, which is beneficial for the preparation of battery materials. In addition, the present application is simple to prepare and has low energy consumption. It can use titanium attached to the titanium dioxide by-product ferrous sulfate heptahydrate itself. Before the reaction, the titanium element is stably present in the form of ions, which not only improves the quality of the finished product, but also realizes waste utilization.

[0120] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing titanium-doped anhydrous ferric phosphate material, characterized in that: Includes steps: Providing titanium-containing ferrous sulfate raw material liquid and titanium-free ferrous sulfate raw material liquid; Mixing the titanium-containing ferrous sulfate raw material liquid and the titanium-free ferrous sulfate raw material liquid to obtain a mixed solution; The mixed solution is mixed with an oxidant and a phosphorus source to obtain a slurry containing iron phosphate and titanium phosphate; The slurry is aged, rinsed, dried and sintered in sequence to obtain a titanium-doped anhydrous iron phosphate material.

2. The preparation method according to claim 1, characterized in that: The raw materials for preparing the titanium-containing ferrous sulfate raw material solution and the titanium-free ferrous sulfate raw material solution include titanium dioxide by-product, and the mass fraction of titanium in the titanium dioxide by-product is 600-4200 ppm.

3. The preparation method according to claim 2, characterized in that: The steps for preparing the titanium-containing ferrous sulfate raw material solution include: Dissolving the titanium dioxide byproduct in an acidic aqueous solution, and obtaining the titanium-containing ferrous sulfate raw material liquid after solid-liquid separation; And / or, the steps of preparing the titanium-free ferrous sulfate raw material solution include: The titanium dioxide byproduct is mixed with a phosphorus-containing solution, and after solid-liquid separation, the titanium-free ferrous sulfate raw material solution is obtained; Wherein, the phosphorus-containing solution includes at least one of phosphoric acid or phosphate; the mass fraction of phosphorus element in the phosphorus-containing solution is 1000-3000 ppm.

4. The preparation method according to claim 3, characterized in that: The pH values ​​of the titanium-containing ferrous sulfate raw material solution and the titanium-free ferrous sulfate raw material solution are both 0.8-1.

8.

5. The preparation method according to claim 3, characterized in that: The mass ratio of the titanium dioxide by-product to the phosphorus-containing solution is 1:1.0-2.

0.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In the step of obtaining the slurry containing iron phosphate and titanium phosphate, the mixed solution is mixed with the oxidant and the phosphorus source according to a molar ratio of iron element, phosphorus element and oxidant of 1:1.01-1.05:0.55-0.

65.

7. The preparation method according to any one of claims 1 to 5, characterized in that: The steps of sequentially aging, rinsing, drying and sintering the slurry include: The slurry is heated to 80-98° C. and kept warm for 1-4 hours, and then rinsed with water to obtain a phosphorus-containing rinse liquid and a filter cake; The filter cake is dried and then sintered at 550-750° C. for 1-4 hours to obtain the titanium-doped anhydrous ferric phosphate material.

8. The preparation method according to claim 7, characterized in that: The aging process includes adding 10-30% of the amount of the iron phosphate material with phosphoric acid.

9. A titanium-doped anhydrous ferric phosphate material, characterized in that: Prepared by the preparation method described in any one of claims 1-8; the titanium-doped anhydrous iron phosphate material has an anhydrous iron phosphate crystal structure and a nano-scale particle stacking morphology, wherein the Ti doping amount of the titanium-doped anhydrous iron phosphate material is less than or equal to 2wt%.

10. The titanium-doped anhydrous ferric phosphate material according to claim 9, characterized in that: The Ti doping amount of the titanium-doped anhydrous ferric phosphate material is less than or equal to 1 wt %.

11. The titanium-doped anhydrous ferric phosphate material according to claim 9, characterized in that: The Fe / P molar ratio of the titanium-doped anhydrous ferric phosphate material is 0.96-1.01, and the specific surface area of ​​the titanium-doped anhydrous ferric phosphate material is 8-10 m 2 / g.

12. A positive electrode sheet, characterized in that: The titanium-doped lithium iron phosphate prepared from the titanium-doped anhydrous iron phosphate material according to any one of claims 9 to 11 is used as the active material.

13. A secondary battery, characterized in that: Including the positive electrode sheet as described in claim 12.

14. An electrical device, characterized in that: Includes the secondary battery as claimed in claim 13.

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