A heterogeneous doped iron phosphate, a method for preparing the same and a heterogeneous doped lithium iron phosphate

Abstract

The present application relates to the field of iron phosphate preparation, in particular to a kind of heterogeneous doping iron phosphate, its preparation method and heterogeneous doping lithium iron phosphate, the preparation method of heterogeneous doping iron phosphate includes the following steps: S1 configuration contains titanium iron source solution and phosphorus source solution;S2 iron source solution, phosphorus source solution and oxidizing agent are mixed to react, and titanium-doped amorphous iron phosphate is prepared;S3 titanium-doped amorphous iron phosphate is aged and crystallized, and titanium-doped dihydrate iron phosphate is prepared;S4 secondary doping aid is uniformly added in titanium-doped dihydrate iron phosphate, and secondary doping dihydrate iron phosphate is formed;Secondary doping aid contains at least one element in titanium, vanadium or niobium;S5 secondary doping dihydrate iron phosphate is dehydrated and dried, and then high-temperature calcination is carried out, and heterogeneous doping iron phosphate is formed.The whole process of the present application is simple and controllable, and the quality is stable, the cost is low, easy to industrialization promotion, and the prepared lithium iron phosphate material has excellent specific capacity and rate performance, and is widely used in various fields.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery-grade iron phosphate preparation, in particular to a heterogeneous doped iron phosphate, a preparation method thereof and a heterogeneous doped lithium iron phosphate. BACKGROUND

[0002] Lithium iron phosphate positive electrode material has the advantages of long service life, high discharge specific capacity, high safety, non-toxicity, and wide raw material sources. With the progress of overall battery technology, the application range of lithium iron phosphate is further expanded. In the field of lithium-ion battery energy storage, lithium iron phosphate has absolute market and influence. In the field of power batteries, lithium iron phosphate has achieved a reverse breakthrough over ternary batteries, with a market share of more than 70%.

[0003] The overall improvement of the performance of the positive electrode material of lithium iron phosphate battery directly promotes the progress of lithium iron phosphate battery technology. The energy density, compaction performance, rate performance, and cycle life of the material have been improved to varying degrees. The existing technology focuses on optimizing and improving the chemical, physical, and electrochemical indicators of lithium iron phosphate positive electrode material. The effect of element doping in the chemical indicators is very obvious.

[0004] Doping certain metal ions in the LiFePO4 lattice can promote the generation of beneficial defects in the material lattice. Doping elements with different electronic structures can improve the migration channel of lithium ions, reduce the resistance of lithium ions along a one-dimensional path, and improve the migration rate of lithium ions inside lithium iron phosphate. This can improve the cycle performance and rate performance of LiFePO4 material.

[0005] The existing technology mainly realizes metal ion doping during the preparation of lithium iron phosphate, i.e., adding doping ions during the mixing and sanding process of iron phosphate and lithium carbonate. The doping ions are mostly in solid phase, and the doping effect needs to be improved due to the influence of solid-solid reaction efficiency.

[0006] Some existing technologies combine the addition of doping ions with the preparation process of iron phosphate to improve the uniformity and effect of doping. The doping ions are prepared into a solution and mixed with the iron source raw material solution or the phosphorus source raw material solution to participate in the reaction of preparing iron phosphate from phosphorus source and iron source. Through liquid-phase doping, the uniformity of doping is ensured, and the doping effect is improved.

[0007] Among them, it is typical to combine titanium doping and the preparation process of iron phosphate, because the preparation process of iron phosphate often uses titanium-containing ferrous sulfate as a raw material source, directly uses titanium-containing ferrous sulfate to participate in the reaction to prepare iron phosphate, simplifies the impurity removal process of ferrous sulfate raw material solution, and introduces titanium doping ions at the same time, which is a more efficient and energy-saving doping method. The Chinese patent with publication number CN117756076 A discloses a titanium-doped anhydrous iron phosphate material and its preparation method and application, titanium-containing ferrous sulfate raw material solution and titanium-free ferrous sulfate raw material solution are mixed, reacted with an oxidizing agent and a phosphorus source, aged, rinsed, dried and sintered to obtain a titanium-doped anhydrous iron phosphate material. However, the titanium-containing ferrous sulfate raw material solution used in this patent is directly obtained by dissolving titanium dioxide by-product, and the impurity ions are not purified, so the impurity ions will enter the iron phosphate, causing the impurity content to increase. The Chinese patent with publication number CN118495494 A discloses a preparation method of a battery-grade titanium-doped iron phosphate, which uses titanium dioxide by-product ferrous sulfate as a raw material, introduces titanium ion dopant after purification treatment, and effectively controls the impurities in ferrous sulfate. However, the existence form of titanium introduced in the titanium dioxide by-product ferrous sulfate is mainly metatitanic acid and titanium dioxide, and these components are difficult to dissolve to form titanium ions, so the substitution of iron in the iron phosphate lattice during the doping process cannot be realized, and therefore the doping uniformity is difficult to control.

[0008] In summary, neither solid-phase doping nor ion-state doping in the prior art can well guarantee the doping effect, and the electrical performance of the lithium iron phosphate positive electrode material prepared finally still has a large improvement space. SUMMARY

[0009] The first object of the present application is to provide a preparation method of a heterogeneous doped iron phosphate, which can prepare a precursor iron phosphate of a lithium iron phosphate positive electrode material with excellent electrical performance.

[0010] The second object of the present application is to provide a heterogeneous doped iron phosphate, and a lithium iron phosphate positive electrode material prepared from the iron phosphate has excellent electrical performance.

[0011] The third object of the present application is to provide a heterogeneous doped lithium iron phosphate, which has excellent electrical performance.

[0012] To achieve the above objects, the present application realizes the following technical solutions:

[0013] A preparation method of a heterogeneous doped iron phosphate, comprising the following steps:

[0014] S1 raw material solution preparation: the iron source is configured into an iron source solution, and the phosphorus source is configured into a phosphorus source solution; a first doping aid containing titanium ions is configured into a solution and added to the iron source solution or the phosphorus source solution, and mixed uniformly for use; wherein the iron source is ferrous sulfate, and the phosphorus source is industrial grade monoammonium phosphate, and the phosphorus source solution prepared from the industrial grade monoammonium phosphate is adjusted to neutral by ammonia water;

[0015] S2 mixing reaction: the titanium ion-containing iron source solution, the phosphorus source solution and the oxidizing agent prepared in step S1, or the titanium ion-containing phosphorus source solution, the iron source solution and the oxidizing agent are added into a reactor in proportion to carry out a rapid reaction; after the reaction is completed, the slurry is filtered and washed to prepare titanium-doped amorphous iron phosphate; wherein the oxidizing agent is selected from oxygen, ozone or hydrogen peroxide; preferably hydrogen peroxide;

[0016] S3 aging and crystallization: the titanium-doped amorphous iron phosphate prepared in step S2 is slurried with water, and a phosphoric acid solution is added to the slurry; the slurry is gradually heated for aging and crystallization, and titanium-doped dihydrate iron phosphate is prepared after the crystallization is completed;

[0017] S4 secondary doping: a secondary doping aid is uniformly added to the titanium-doped dihydrate iron phosphate prepared in step S3 to form secondary-doped dihydrate iron phosphate; the secondary doping aid contains a secondary doping element, and the secondary doping element is selected from at least one of titanium, vanadium or niobium.

[0018] S5 drying and calcination: the secondary-doped dihydrate iron phosphate obtained in step S4 is dehydrated and dried, and then high-temperature calcination is carried out to form a heterogeneous doped iron phosphate.

[0019] When the lithium iron phosphate positive electrode material works, Li + forms an electric current between the positive electrode and the negative electrode, and the Li + motion distance is shortened and the motion is limited due to the unit cell structure of lithium iron phosphate; improving the diffusion channel of Li + by ion doping is a commonly used means. The inventors further study the crystal structure of lithium iron phosphate and find that the more the Li + is to the surface, the more difficult the migration is; based on this, the inventors creatively think of designing the Li + migration channel on the surface of the lithium iron phosphate unit cell to be more than the Li + migration channel inside, so as to achieve the purpose of improving the Li + migration rate and migration speed. And further designs the specific technical scheme of the application.

[0020] Firstly, the titanium element is added in the form of ions in the process of generating iron phosphate, so that titanium and iron are co-precipitated, the titanium element can effectively replace the iron element in the iron phosphate lattice, and the titanium element can be uniformly distributed in the iron phosphate lattice in the form of titanium ions in the liquid phase reaction process, so that the uniformity of titanium doping is ensured.

[0021] Secondly, after the titanium-doped amorphous iron phosphate is converted into titanium-doped dihydrate iron phosphate, the secondary doping aid is uniformly added, so that the secondary doping aid can be physically mixed with the titanium-doped dihydrate iron phosphate and distributed on the surface of the titanium-doped dihydrate iron phosphate.

[0022] Further, after the secondary doping aid is added, the titanium-doped dihydrate iron phosphate is dried and dehydrated, and then high-temperature calcination is performed, so that the secondary doping aid distributed on the surface of the titanium-doped dihydrate iron phosphate realizes particle melting and growth under high-temperature sintering conditions, the secondary doping aid in contact with the surface layer of the iron phosphate is further dispersed to the surface of the iron phosphate particle under the action of high temperature, the content of doping ions in the surface layer of the iron phosphate particle is increased, and a shell-core structure with a higher content of doping ions on the surface than in the interior is formed.

[0023] The secondary doping aid of the present application is selected from titanium-, vanadium- or niobium-containing compounds, which can realize the purpose of replacing iron ions and lithium ions in the structure of lithium iron phosphate by doping titanium-, vanadium- or niobium-containing compounds on the surface of iron phosphate particles after the preparation of lithium iron phosphate, so as to distort the lithium iron phosphate lattice and produce defects, improve the Li + diffusion channel and further improve the electrochemical performance.

[0024] The iron phosphate particles prepared by the above method of the present application are further prepared into lithium iron phosphate material by high-temperature solid-phase method process, the titanium ions are co-precipitated and incorporated into the interior in the form of ions in the process of iron phosphate reaction, so as to ensure the uniform and unobstructed migration channel in the interior; more importantly, the content of doping ions on the surface of the iron phosphate is higher than that in the interior, so as to ensure that the migration channel in the surface layer of the formed lithium iron phosphate unit is more than that in the interior, which can better ensure the migration amount and migration rate of Li + , and effectively improve the electrical performance of the lithium iron phosphate positive electrode material.

[0025] As a preferred, the primary doping aid is one or more of titanyl sulfate, titanium tetrachloride, tetrabutyl titanate and titanium citrate.

[0026] The above titanium-containing compound can form titanium ions in the solution, and the above titanium-containing compound is used as the primary doping aid, so as to ensure that the titanium element is co-precipitated with the iron phosphate in the form of ions in the process of generating iron phosphate, and is uniformly and stably doped in the iron phosphate.

[0027] Further preferably, the amount of the primary doping agent is controlled so that the titanium content of the prepared titanium-doped amorphous iron phosphate is 500-3000 ppm.

[0028] Preferably, the iron source solution in step S1 is prepared by configuring the titanium dioxide by-product ferrous sulfate into a solution, adjusting the pH value to 2.8-5.5 by a pH value regulator to remove impurities, and separating the precipitate after the removal of impurities to obtain the iron source solution.

[0029] To reduce the cost, the titanium dioxide by-product ferrous sulfate is selected as the iron source for the preparation of iron phosphate. Since the titanium dioxide by-product ferrous sulfate contains sulfuric acid and other metal impurities, these impurities are removed before the iron phosphate formation reaction. In this application, the pH value is adjusted to 2.8-5.5 by a pH value regulator to remove the sulfuric acid and other metal impurities contained in the titanium dioxide by-product ferrous sulfate. Preferably, the pH value regulator is one or more of ammonia, sodium hydroxide, sodium carbonate, monoammonium phosphate, diammonium phosphate, iron powder, and iron hydroxide.

[0030] In this application, the metal impurities in the titanium dioxide by-product ferrous sulfate are removed to obtain an iron source solution, and then a primary doping agent containing titanium ions is added to the iron source solution. The purpose is to remove the titanium-containing compounds (which cannot produce titanium ions) contained in the original titanium dioxide by-product ferrous sulfate, and then introduce titanium ions to ensure that the titanium ions are co-precipitated with the iron phosphate, thereby achieving the purpose of replacing the iron elements in the iron phosphate crystal cell with titanium elements to establish more lithium ion migration channels.

[0031] Preferably, the mixing reaction in step S2 is carried out in a micro-channel tube reactor. In the tube reactor, the material is in a turbulent flow state, and the mass transfer and heat transfer efficiency is high, so that the reaction can be quickly carried out, which is conducive to the rapid and uniform combination of titanium, iron and phosphorus.

[0032] Preferably, the molar ratio of the phosphorus source, hydrogen peroxide and iron source added in the micro-channel tube reactor satisfies P:H2O2:Fe = 1.0:0.55-0.8:1.0-1.4. After the reaction, the slurry is first introduced into a homogenization reactor, and a phosphorus source solution is supplemented to the homogenization reactor, so that the final P:Fe ratio in the reaction is 1:0.95-1.05. After the reaction, the slurry is filtered and washed to prepare titanium-doped amorphous iron phosphate.

[0033] The present application controls the iron salt solution and hydrogen peroxide slight excess in the tubular reactor, is favorable to the stable control of the combination of ferric ion and phosphate, avoids the formation of ferrous ion precipitation, and influences the quality of iron phosphate. Further, after the reaction is completed, a homogeneous reaction kettle is used as a further reaction of the outlet material of the reaction, the amount of phosphorus salt is further supplemented in the homogeneous reaction kettle, the unreacted iron salt solution can continue to react, the growth of iron phosphate crystallization is promoted, the particle size of iron phosphate can be effectively controlled, and the subsequent washing efficiency is improved.

[0034] As preferred, in the aging and crystallization of step S3, the titanium-doped amorphous iron phosphate is slurried with water to obtain a slurry with a solid content of 8-15%, 85% phosphoric acid with a solid content of 8-14% is added to the slurry, the slurry is gradually heated and then aged and crystallized, the crystallization temperature is controlled at 90-95°C, and the crystallization time is 1-2h.

[0035] As preferred, the amount of the secondary doping aid is controlled to be 500-3000ppm of the secondary doping element in the final product of heterogeneous doped iron phosphate.

[0036] As preferred, when the secondary doping element is titanium, the secondary doping aid is one or more of titanyl sulfate, titanium tetrachloride, tetrabutyl titanate, titanium citrate, nanometer rutile titanium dioxide, nanometer anatase titanium dioxide, and metatitanic acid; preferably, the secondary doping aid is one or more of nanometer rutile titanium dioxide, nanometer anatase titanium dioxide, and metatitanic acid.

[0037] Since the secondary doping is added after the formation of titanium-doped dihydrate iron phosphate in the aging and crystallization, it can only be added to the surface of the titanium-doped dihydrate iron phosphate particles, therefore, it can be added in the form of ions or in the form of solids, as preferred, one or more of nanometer rutile titanium dioxide, nanometer anatase titanium dioxide, and metatitanic acid is selected to introduce titanium element on the surface of iron phosphate.

[0038] When the secondary doping element is vanadium, the secondary doping aid is one or more of ammonium metavanadate, divanadium pentoxide, and vanadyl sulfate.

[0039] When the secondary doping element is niobium, the secondary doping aid is one or more of niobic acid, divanadium pentoxide, niobium oxalate, and ammonium niobium oxalate.

[0040] Similarly, the above vanadium-containing secondary doping aid and niobium-containing secondary doping aid are selected by comprehensively considering the introduction method and cost of the doping element.

[0041] As preferred, in step S4, when the secondary doping agent is non-water-soluble or has extremely poor solubility in water, the secondary doping agent is added in solid phase and directly added into the slurry containing titanium-doped iron (II) phosphate dihydrate obtained after the end of the crystallization in step S3, and then the slurry is filtered and washed to obtain the secondary-doped iron (II) phosphate dihydrate;

[0042] In step S4, when the secondary doping agent is water-soluble, the secondary doping agent is added in solution. After the slurry containing titanium-doped iron (II) phosphate dihydrate obtained after the end of the crystallization in step S3 is filtered and washed, a solid phase of titanium-doped iron (II) phosphate dihydrate is obtained. The solution containing the secondary doping agent is directly added into the solid phase of titanium-doped iron (II) phosphate dihydrate in atomized form, or the solution containing the secondary doping agent and the solid phase of titanium-doped iron (II) phosphate dihydrate are jointly fed into a dehydration and drying device in atomized form, to obtain the secondary-doped iron (II) phosphate dihydrate.

[0043] In order to ensure that the secondary doping elements can be more uniformly distributed on the surface of the titanium-doped iron (II) phosphate dihydrate, the present application designs:

[0044] When the secondary doping agent is insoluble in water or has extremely poor solubility in water, the secondary doping agent is added in solid phase, such as nano-rutile titanium dioxide, nano-anatase titanium dioxide, metatitanic acid. The secondary doping agent is added into the slurry which has not been filtered and washed after the end of the aging and crystallization in step S3. The solid material can be better dispersed in the slurry, and the solid-phase secondary doping agent can finally enter the iron phosphate and will not be removed by filtration. After the solid-phase secondary doping agent is uniformly mixed, the filtration, washing, drying and calcination processes are performed.

[0045] When the secondary doping agent is easily soluble in water, the secondary doping agent is added in solution, such as ammonium metavanadate, vanadium pentoxide, and vanadyl sulfate. The secondary doping agent is added after the end of the crystallization and filtration and washing in step S3. The secondary doping agent can be directly added into the filter cake in the form of solution spray, or the secondary doping agent and the filter cake can be jointly added into a drying device in the form of solution spray. Preferably, the secondary doping agent and the filter cake are jointly added into a drying device, so as to realize the uniform mixing of the dissolved doping elements in the solution and the iron phosphate particles. If the secondary doping agent which is easily soluble in water is directly added into the slurry after the aging and crystallization, the doping elements may be dissolved in water and then filtered out, so that the doping elements cannot enter the iron phosphate product.

[0046] Specifically, when the secondary doping agent is selected from one or more of ammonium metavanadate, vanadium pentoxide, and vanadyl sulfate, the secondary doping agent is dissolved in desalted water or hydrochloric acid or nitric acid with a molar concentration of 0.01-0.1%, and the concentration of vanadium ions in the secondary doping agent solution is controlled to be 0.1%-5%.

[0047] Similarly, when the secondary doping aid is selected from one or more of niobic acid, niobium pentoxide, niobium oxalate, and ammonium niobium oxalate, desalted water or hydrochloric acid or nitric acid with a molar concentration of 0.01 to 0.1% is used to dissolve the secondary doping aid, and the niobium ion concentration in the secondary doping aid solution is controlled to reach 0.1% to 5%.

[0048] Preferably, in step S5, the dehydration and drying is carried out in a flash evaporation device, the flash evaporation temperature is 120-300° C., and the free water content of the flash dried material is controlled at 0.1-2%.

[0049] Preferably, in step S5, calcination is carried out in a rotary kiln, the calcination temperature of the rotary kiln is 500-800° C., and the calcination time is 0.5-6 h.

[0050] The present invention also provides a heterogeneously doped iron phosphate prepared by the above-mentioned preparation method, wherein the surface doping ion content of the heterogeneously doped iron phosphate is 1.2 to 1.7 times the core doping ion content.

[0051] The present invention also provides a heterogeneously doped lithium iron phosphate, which is prepared from the above-mentioned heterogeneously doped lithium iron phosphate by a high-temperature solid-phase method.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] (1) The present invention adopts the method of adding titanium ions to an iron source solution or a phosphorus source solution to uniformly dope titanium ions into the interior of iron phosphate particles, and by mixing and adding a secondary doping auxiliary agent on the surface of the dihydrate iron phosphate after aging and crystallization and drying and sintering, another layer of doping ions is added to the surface of the iron phosphate particles, thereby forming a shell-core structure of iron phosphate with a high surface doping ion content and a low internal doping ion content. After the formation of lithium iron phosphate, the migration of lithium ions inside and on the surface of the unit cell is easier, and its electrical performance can reach 0.1C discharge gram capacity ≥162mAh / g, 1C discharge gram capacity ≥150mAh / g, and 10C discharge gram capacity ≥135mAh / g, with excellent capacity and rate performance.

[0054] (2) The present invention introduces titanium ions by removing impurities from the ferrous sulfate produced as a by-product of titanium dioxide and then adding a doping aid. This not only reduces costs but also avoids the problem of uneven doping caused by the co-precipitation of non-ionic titanium in the original ferrous sulfate into ferric phosphate, which cannot effectively replace the iron element in the unit cell structure.

[0055] (3) The present invention adopts a microchannel tubular reactor as a reactor, which can achieve rapid and uniform generation of iron phosphate and effectively ensure the uniform replacement of iron by titanium.

[0056] (4) The present application controls the slight excess of ferrous salt solution and hydrogen peroxide in the tubular reactor, which is conducive to the stable control of the combination of ferric ions and phosphate ions, avoids the formation of ferrous ion precipitate, and affects the quality of ferric phosphate. Further, after the reaction is completed, a homogeneous reaction kettle is used as a further reaction of the outlet material of the reaction kettle, and the amount of phosphorus salt is further supplemented in the homogeneous reaction kettle, so that the unreacted ferrous salt solution can continue to react, promote the continuous growth of ferric phosphate crystals, and effectively control the particle size of ferric phosphate, thereby improving the subsequent washing efficiency.

[0057] (5) The non-homogeneous doped ferric phosphate prepared by the present application is prepared by a high-temperature solid-phase method. The secondary doped elements uniformly distributed on the surface of the non-homogeneous doped ferric phosphate particles after calcination are further melted and homogenized in the preparation of lithium phosphate iron, and are better dispersed in the lithium phosphate iron material, thereby ensuring that Li + uniform migration channels.

[0058] (6) The whole process of the present application is simple and controllable, low in energy consumption, stable in quality, low in cost, and easy to be industrialized and applied. BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 SEM of the non-homogeneous doped ferric phosphate used in experimental group 5 in the embodiments of the present application;

[0060] Figure 2 SEM of the lithium phosphate iron prepared by experimental group 5 in the embodiments of the present application. DETAILED DESCRIPTION

[0061] The technical solutions of the present application will be further described in combination with specific embodiments.

[0062] Embodiment 1

[0063] The present embodiment provides a preparation method of non-homogeneous doped ferric phosphate, which specifically comprises the following steps:

[0064] S1: Prepare a ferrous sulfate solution from titanium dioxide by-product, neutralize the residual sulfuric acid in the ferrous sulfate with ammonia, adjust the pH value of the solution to 3.8 to remove impurity ions carried by the ferrous sulfate, and then filter and separate the ferrous sulfate solution. Add titanium tetrachloride to the ferrous sulfate solution after homogenization treatment to obtain a titanium-containing ferrous sulfate solution. The amount of titanium tetrachloride is calculated according to the control of titanium content in amorphous ferric phosphate at 1000 ppm. Prepare a phosphorus source solution from industrial-grade monoammonium phosphate, and adjust the pH of the phosphorus source solution to 7.0 with ammonia.

[0065] S2 mixing reaction: the phosphorus source solution prepared in step S1, hydrogen peroxide and titanium-containing ferrous sulfate solution are heated to 30°C, and are added into a micro-channel tube reactor for rapid reaction at a molar ratio of P:H2O2:Fe = 1.0:0.65:1.1; after the reaction, the slurry is introduced into a homogenization reactor, and the remaining part of the phosphorus source solution is added into the homogenization reactor at a P:Fe element ratio of 1.0:1.0; the reaction temperature is 50°C, and the reaction time is 1 hour; the slurry is filtered and washed to obtain titanium-doped amorphous iron phosphate.

[0066] S3 aging and crystallization: the titanium-doped amorphous iron phosphate prepared in step S2 is slurried with water to obtain a slurry with a solid content of 12%, and 85% phosphoric acid with a solid mass of 10% is added to the slurry; the slurry is gradually heated for aging and crystallization, and the crystallization temperature is controlled at 95°C, and the crystallization time is 2 hours, thereby preparing a slurry containing titanium-doped dihydrate iron phosphate.

[0067] S4 secondary doping: a secondary doping aid, nano-rutile titanium dioxide, is added to the slurry containing titanium-doped dihydrate iron phosphate in step S3 and uniformly mixed; the amount of nano-rutile titanium dioxide is calculated according to the requirement that the titanium content in the heterogeneous doped iron phosphate reaches 3000 ppm, and after the mixing is completed, the slurry is filtered and washed to prepare secondary doped dihydrate iron phosphate.

[0068] S5 drying and calcination: the secondary doped dihydrate iron phosphate prepared in step S4 is flash dried and dehydrated, the flash drying temperature is controlled at 260°C, and the free water content of the flash dried material is controlled at 0.5%; then it is added to a rotary kiln for high-temperature calcination, the rotary kiln calcination temperature is 700°C, and the calcination time is 3.0 hours, thereby promoting the further surface fusion of the secondary doped material and the iron phosphate, and preparing the heterogeneous titanium-doped iron phosphate of the present embodiment.

[0069] Example 2

[0070] The present embodiment provides a preparation method of heterogeneous doped iron phosphate, which is different from example 1 only in that:

[0071] In step S1, titanium sulfate solution is prepared by replacing titanium tetrachloride in example 1 with titanium sulfate.

[0072] Example 3

[0073] The present embodiment provides a preparation method of heterogeneous doped iron phosphate, which is different from example 1 only in that:

[0074] In step S1, titanium sulfate solution is prepared by replacing titanium tetrachloride in example 1 with titanium sulfate.

[0075] Example 4

[0076] The embodiment provides a preparation method of heterogeneous doping iron phosphate, and the difference from the embodiment 1 is only that:

[0077] In step S1, titanium sulfate ferrous sulfate solution preparation is prepared by using titanium citrate instead of titanium tetrachloride in the embodiment 1.

[0078] Embodiment 5

[0079] The embodiment provides a preparation method of heterogeneous doping iron phosphate, and the difference from the embodiment 1 is only that:

[0080] In step S1, the amount of titanium tetrachloride is calculated according to the control of the titanium content of 500 ppm in amorphous iron phosphate;

[0081] In step S4, the amount of nano rutile titanium dioxide is calculated according to the further control of the titanium content of 2500 ppm in the heterogeneous doping iron phosphate.

[0082] Embodiment 6

[0083] The embodiment provides a preparation method of heterogeneous doping iron phosphate, and the difference from the embodiment 1 is only that:

[0084] In step S1, the amount of titanium tetrachloride is calculated according to the control of the titanium content of 3000 ppm in amorphous iron phosphate;

[0085] In step S4, the amount of nano rutile titanium dioxide is calculated according to the further control of the titanium content of 5000 ppm in the heterogeneous doping iron phosphate.

[0086] Embodiment 7

[0087] The embodiment provides a preparation method of heterogeneous doping iron phosphate, and the difference from the embodiment 1 is only that:

[0088] In step S4, the amount of nano rutile titanium dioxide is calculated according to the further control of the titanium content of 1500 ppm in the heterogeneous doping iron phosphate.

[0089] Embodiment 8

[0090] The embodiment provides a preparation method of heterogeneous doping iron phosphate, and the difference from the embodiment 1 is only that:

[0091] In step S4, the amount of nano rutile titanium dioxide is calculated according to the further control of the titanium content of 4000 ppm in the heterogeneous doping iron phosphate.

[0092] Embodiment 9

[0093] The embodiment provides a preparation method of heterogeneous doping iron phosphate, and the difference from the embodiment 1 is only that:

[0094] S1 raw material solution preparation: take titanium dioxide by-product ferrous sulfate heptahydrate to prepare an iron source solution, use ammonia to neutralize the residual sulfuric acid in the ferrous sulfate, adjust the pH value of the solution to 5.5, and remove the impurity ions carried by the ferrous sulfate; after filtration separation, add titanium tetrachloride to the ferrous sulfate solution, and after homogenization treatment, a titanium-containing ferrous sulfate solution can be obtained; the amount of titanium tetrachloride is calculated according to the control of titanium content in amorphous iron phosphate to 1000 ppm; take industrial grade monoammonium phosphate to prepare a phosphorus source solution, and adjust the pH of the phosphorus source solution to 7.0 with ammonia water.

[0095] S2 mixed reaction: heat the phosphorus source solution, hydrogen peroxide and titanium-containing ferrous sulfate solution prepared in step S1 to 30℃, and add them into a micro-channel pipe reactor for rapid reaction according to the molar ratio of P:H2O2:Fe=1.0:0.8:1.4; after reaction, the slurry enters a homogenization reactor, and the remaining part of the phosphorus source solution is added to the homogenization reactor according to the P:Fe element ratio of 1.0:1.05; the reaction temperature is 55℃, and the reaction time is 1.5 hours; the slurry is filtered and washed to obtain titanium-doped amorphous iron phosphate.

[0096] S3 aging and crystallization: the titanium-doped amorphous iron phosphate prepared in step S2 is slurried with water to obtain a slurry with a solid content of 15%, and 85% phosphoric acid with a solid mass of 14% is added to the slurry; the slurry is gradually heated for aging and crystallization, and the crystallization conditions are controlled as follows: crystallization temperature 95℃, crystallization time 1 hour, to prepare a slurry containing titanium-doped dihydrate iron phosphate.

[0097] S4 secondary doping: add secondary doping aid nano anatase titanium dioxide to the slurry containing titanium-doped dihydrate iron phosphate in step S3 and mix uniformly; the amount of nano anatase titanium dioxide is calculated according to the control of titanium content in the heterogeneous doped iron phosphate to further reach 3000 ppm; after mixing, the slurry is filtered and washed to obtain secondary doped dihydrate iron phosphate.

[0098] S5 drying and calcination: the secondary doped dihydrate iron phosphate prepared in step S4 is flash dried and dehydrated, the flash drying temperature is controlled at 120℃, and the free water content of the flash dried material is controlled at 2%; then it is added to a rotary kiln for high temperature calcination, the rotary kiln calcination temperature is 800℃, and the calcination time is 6.0 hours, which promotes the further surface fusion of the secondary doped material and the iron phosphate, to prepare the heterogeneous titanium-doped iron phosphate of the embodiment.

[0099] Example 10

[0100] The embodiment provides a preparation method of heterogeneous doped iron phosphate, which specifically comprises the following steps:

[0101] Preparation of S1 raw material liquid: prepare an iron source solution with ferrous sulfate heptahydrate, a by-product of titanium dioxide, and use ammonia water to neutralize the residual sulfuric acid in the ferrous sulfate, adjust the pH value of the solution to 2.8, and remove the impurity ions carried by the ferrous sulfate; add titanium tetrachloride to the ferrous sulfate solution after filtration and separation, and obtain a titanium-containing ferrous sulfate solution after homogenization. The amount of titanium tetrachloride added is calculated based on controlling the titanium content in the amorphous iron phosphate to 1000 ppm; prepare a phosphorus source solution with industrial-grade monoammonium phosphate, and use ammonia water to adjust the pH value of the phosphorus source solution to 7.0 for standby use.

[0102] S2 mixing reaction: The phosphorus source solution, hydrogen peroxide and titanium-containing ferrous sulfate solution prepared in step S1 are heated to 30°C, and added to a microchannel tubular reactor at a molar ratio of P:H2O2:Fe = 1.0:0.55:1.0 for rapid reaction; after the reaction, the slurry enters a homogenizing reactor, and the remaining part of the phosphorus source solution is added to the homogenizing reactor at a P:Fe element ratio of 1.0:0.95. The reaction temperature is 45°C, the reaction time is 1.5 hours, and the slurry is filtered and washed to obtain titanium-doped amorphous iron phosphate.

[0103] S3 aging and crystallization: The titanium-doped amorphous ferric phosphate prepared in step S2 is added with water to prepare a slurry with a solid content of 8%, and 85% phosphoric acid with a solid content of 8% is added to the slurry; the slurry is gradually heated for aging and crystallization, and the crystallization conditions control the crystallization temperature to 90°C and the crystallization time to 2 hours to prepare a slurry containing titanium-doped ferric phosphate dihydrate.

[0104] S4 secondary doping: adding a secondary doping auxiliary agent, metatitanic acid, to the slurry containing titanium-doped ferric phosphate dihydrate in step S3 and uniformly mixing them. The amount of metatitanic acid added is calculated based on controlling the titanium content in the heterogeneously doped ferric phosphate to further reach 3000 ppm. After the mixing is completed, filtering and washing are performed to prepare secondary doped ferric phosphate dihydrate;

[0105] S5 drying and calcination: The secondary doped ferric phosphate dihydrate prepared in step S4 is flash dried and dehydrated, the flash temperature is controlled at 300°C, and the free water content of the flash dried material is controlled at 0.1%; it is then added to a rotary kiln for high-temperature calcination, the rotary kiln calcination temperature is 500°C, and the calcination time is 4.0 hours to promote further surface fusion of the secondary doping material and the ferric phosphate, and prepare the heterogeneous titanium-doped ferric phosphate of this embodiment.

[0106] Example 11

[0107] This embodiment provides a method for preparing heterogeneously doped iron phosphate, which specifically includes the following steps:

[0108] S1 raw material solution preparation: take the by-product ferrous sulfate heptahydrate of titanium white powder to prepare an iron source solution, use ammonia to neutralize the residual sulfuric acid in the ferrous sulfate, adjust the pH value of the solution to 3.8, and remove the impurity ions carried by the ferrous sulfate; after filtration and separation, add titanium tetrachloride to the ferrous sulfate solution, and after homogenization treatment, a titanium-containing ferrous sulfate solution can be obtained, the amount of titanium tetrachloride is calculated according to the control of titanium content in amorphous iron phosphate of 1000ppm; take industrial grade monoammonium phosphate to prepare a phosphorus source solution, use ammonia to adjust the pH of the phosphorus source solution to 7.0, and reserve.

[0109] S2 mixed reaction: heat the phosphorus source solution prepared in step S1, hydrogen peroxide and titanium-containing ferrous sulfate solution to 30℃, add them into a micro-channel pipe reactor for rapid reaction according to the molar ratio of P:H2O2:Fe=1.0:0.65:1.1; after reaction, the slurry enters the homogenization reactor, and the remaining part of the phosphorus source solution is added to the homogenization reactor according to the P:Fe element ratio of 1.0:1.0, the reaction temperature is 50℃, and the reaction time is 1 hour; filter and wash the slurry to obtain titanium-doped amorphous iron phosphate.

[0110] S3 aging and crystallization: prepare a slurry by adding water to the titanium-doped amorphous iron phosphate prepared in step S2, and the solid content of the slurry is 12%; add 85% phosphoric acid with a solid mass of 10% to the slurry; gradually heat the slurry for aging and crystallization, control the crystallization temperature at 95℃, and the crystallization time is 2 hours; after filtration and washing, titanium-doped dihydrate iron phosphate solid phase is prepared.

[0111] S4 secondary doping: dissolve the secondary doping aid ammonium metavanadate in desalted water to prepare a vanadium-containing solution, and control the vanadium ion concentration to 3%; spray the vanadium-containing solution in the form of atomization into the titanium-doped dihydrate iron phosphate solid phase prepared in step S3 under stirring. The amount of secondary doping aid ammonium metavanadate is controlled to make the vanadium doping amount in the final heterogeneous doped iron phosphate reach 2000ppm.

[0112] S5 drying and calcination: flash dry the secondary doped dihydrate iron phosphate prepared in step S4, control the flash drying temperature at 260℃, and control the free water content of the flash dried material at 0.5%; then add it to a rotary kiln for high temperature calcination, the rotary kiln calcination temperature is 700℃, and the calcination time is 3.0 hours, which promotes the further surface fusion of the secondary doped material and the iron phosphate, and the heterogeneous titanium-doped iron phosphate of the embodiment is prepared.

[0113] Example 12

[0114] The embodiment provides a preparation method of heterogeneous doped iron phosphate, and the difference from example 11 is only that:

[0115] The adding method of the secondary doping assistant vanadium in step S4 is different: in this embodiment, the vanadium-containing solution is added in the form of atomization and the titanium-doped iron phosphate dihydrate solid phase prepared in step S3 is added into the flash device in step S5 at the same time for dehydration and drying.

[0116] Example 13

[0117] This embodiment provides a preparation method of heterogeneous doped iron phosphate, and the difference from example 12 is only that:

[0118] The adding amount of the secondary doping assistant vanadium in step S4 is different: in this embodiment, the adding amount of the secondary doping assistant ammonium metavanadate is controlled to make the vanadium doping amount in the final heterogeneous doped iron phosphate be 500 ppm.

[0119] Example 14

[0120] This embodiment provides a preparation method of heterogeneous doped iron phosphate, and the difference from example 12 is only that:

[0121] The adding amount of the secondary doping assistant vanadium in step S4 is different: in this embodiment, the adding amount of the secondary doping assistant ammonium metavanadate is controlled to make the vanadium doping amount in the final heterogeneous doped iron phosphate be 3000 ppm.

[0122] Example 15

[0123] This embodiment provides a preparation method of heterogeneous doped iron phosphate, and the difference from example 12 is only that:

[0124] The selection of the secondary doping assistant in step S4 is different: in this embodiment, the secondary doping assistant is selected to be vanadium pentoxide instead of ammonium metavanadate in example 12.

[0125] Example 16

[0126] This embodiment provides a preparation method of heterogeneous doped iron phosphate, and the difference from example 12 is only that:

[0127] The selection of the secondary doping assistant in step S4 is different: in this embodiment, the secondary doping assistant is selected to be vanadyl sulfate instead of ammonium metavanadate in example 12.

[0128] Example 17

[0129] This embodiment provides a preparation method of heterogeneous doped iron phosphate, and the difference from example 12 is only that:

[0130] S1 raw material solution preparation: take the by-product ferrous sulfate heptahydrate of titanium white powder to prepare an iron source solution, use ammonia to neutralize the residual sulfuric acid in the ferrous sulfate, adjust the pH value of the solution to 3.8, and remove the impurity ions carried by the ferrous sulfate; after filtration and separation, add titanium tetrachloride to the ferrous sulfate solution, and after homogenization treatment, a titanium-containing ferrous sulfate solution can be obtained, the amount of titanium tetrachloride is calculated according to the control of titanium content in amorphous iron phosphate of 1000ppm; take industrial grade monoammonium phosphate to prepare a phosphorus source solution, adjust the pH of the phosphorus source solution to 7.0 with ammonia water, and reserve.

[0131] S2 mixed reaction: heat the phosphorus source solution prepared in step S1, hydrogen peroxide and titanium-containing ferrous sulfate solution to 30℃, add them into a micro-channel pipe reactor for rapid reaction according to the molar ratio of P:H2O2:Fe=1.0:0.65:1.1; after reaction, the slurry enters the homogenization reactor, and the remaining part of the phosphorus source solution is added to the homogenization reactor according to the P:Fe element ratio of 1.0:1.0, the reaction temperature is 50℃, and the reaction time is 1 hour; filter and wash the slurry to obtain titanium-doped amorphous iron phosphate.

[0132] S3 aging and crystal transformation: prepare a slurry by adding water to the titanium-doped amorphous iron phosphate prepared in step S2, and the solid content of the slurry is 12%; add 85% phosphoric acid with a solid mass of 10% to the slurry; gradually heat the slurry for aging and crystal transformation, control the crystal transformation temperature at 95℃, and the crystal transformation time is 2 hours; after filtration and washing, titanium-doped dihydrate iron phosphate solid phase is prepared.

[0133] S4 secondary doping solution preparation: dissolve the secondary doping aid niobium oxalate in desalted water to prepare a niobium-containing solution, and control the niobium ion concentration to 3%; the amount of secondary doping aid niobium oxalate is controlled to make the final amount of niobium doping in the heterogeneous doped iron phosphate reach 2000ppm.

[0134] S5 drying and calcination: add the secondary doping solution prepared in step S4 to the flash evaporation device in the form of atomization and the titanium-doped dihydrate iron phosphate prepared in step S3 at the same time for flash evaporation drying and dehydration, control the flash evaporation temperature at 260℃, and control the free water content of the flash evaporation dried material at 0.5%; then add it to a rotary kiln for high-temperature calcination, the rotary kiln calcination temperature is 700℃, and the calcination time is 3.0 hours, which promotes the further surface fusion of the secondary doping material and the iron phosphate, and the heterogeneous titanium-doped iron phosphate of the embodiment is prepared.

[0135] Comparative Example 1

[0136] The present comparative example provides a preparation method of doped iron phosphate, which specifically comprises the following steps:

[0137] S1 raw material solution preparation: take the by-product ferrous sulfate heptahydrate of titanium dioxide to prepare an iron source solution, use ammonia to neutralize the residual sulfuric acid in the ferrous sulfate, adjust the pH value of the solution to 3.8, and remove the impurity ions carried by the ferrous sulfate; after filtration and separation, add titanium tetrachloride to the ferrous sulfate solution, and after homogenization treatment, a titanium-containing ferrous sulfate solution can be obtained, and the amount of titanium tetrachloride is calculated according to the control of titanium content in amorphous iron phosphate of 3000ppm; take industrial grade monoammonium phosphate to prepare a phosphorus source solution, and adjust the pH of the phosphorus source solution to 7.0 with ammonia water.

[0138] S2 mixed reaction: heat the phosphorus source solution prepared in step S1, hydrogen peroxide and titanium-containing ferrous sulfate solution to 30℃, and add them into a micro-channel pipe reactor for rapid reaction according to the molar ratio of P:H2O2:Fe=1.0:0.65:1.1; after reaction, the slurry enters the homogenization reactor, and the remaining part of the phosphorus source solution is added to the homogenization reactor according to the P:Fe element ratio of 1.0:1.0, the reaction temperature is 50℃, and the reaction time is 1 hour; filter and wash the slurry to obtain titanium-doped amorphous iron phosphate.

[0139] S3 aging and crystallization: prepare a slurry by adding water to the titanium-doped amorphous iron phosphate prepared in step S2 to obtain a slurry with a solid content of 12%, and add 85% phosphoric acid with a solid mass of 10% to the slurry; gradually heat the slurry for aging and crystallization, control the crystallization temperature at 95℃, and the crystallization time at 2 hours, filter and wash to prepare titanium-doped dihydrate iron phosphate.

[0140] S4 drying and calcination: the titanium-doped dihydrate iron phosphate prepared in step S3 is subjected to flash drying and dehydration, the flash drying temperature is controlled at 260℃, and the free water content of the flash drying material is controlled at 0.5%; then it is added to a rotary kiln for high-temperature calcination, the rotary kiln calcination temperature is 700℃, and the calcination time is 3.0 hours, to prepare the doped iron phosphate of the embodiment.

[0141] Comparative Example 2

[0142] The present comparative example provides a method for preparing iron phosphate, which specifically comprises the following steps:

[0143] S1 raw material solution preparation: take the by-product ferrous sulfate heptahydrate of titanium dioxide to prepare an iron source solution, use ammonia to neutralize the residual sulfuric acid in the ferrous sulfate, adjust the pH value of the solution to 3.8, and remove the impurity ions carried by the ferrous sulfate; take industrial grade monoammonium phosphate to prepare a phosphorus source solution, and adjust the pH of the phosphorus source solution to 7.0 with ammonia water.

[0144] S2 mixing reaction: the phosphorus source solution prepared in step S1, hydrogen peroxide and ferrous sulfate solution are heated to 30°C, and then added into a microchannel tube reactor for rapid reaction at a molar ratio of P:H2O2:Fe = 1.0:0.65:1.1; after the reaction, the slurry is introduced into a homogenization reactor, and the remaining part of the phosphorus source solution is added into the homogenization reactor at a P:Fe element ratio of 1.0:1.0, the reaction temperature is 50°C, and the reaction time is 1 hour; the slurry is filtered and washed to obtain amorphous iron phosphate.

[0145] S3 aging and crystallization: the amorphous iron phosphate prepared in step S2 is slurried with water to obtain a slurry with a solid content of 12%, and 85% phosphoric acid with a solid mass of 10% is added to the slurry; the slurry is gradually heated for aging and crystallization, and the crystallization conditions are controlled at a crystallization temperature of 95°C and a crystallization time of 2 hours to prepare iron phosphate dihydrate.

[0146] S4 drying and calcination: the iron phosphate dihydrate prepared in step S3 is flash dried and dehydrated, the flash drying temperature is controlled at 260°C, and the free water content of the flash dried material is controlled at 0.5%; then it is added into a rotary kiln for high temperature calcination, the rotary kiln calcination temperature is 700°C, and the calcination time is 3.0 hours to prepare the iron phosphate of the present embodiment.

[0147] Experimental example

[0148] The heterogeneous doped iron phosphate prepared in Examples 1-17, the doped iron phosphate prepared in Comparative Example 1 and the iron phosphate prepared in Comparative Example 2 are used to prepare lithium iron phosphate positive electrode materials according to the following method:

[0149] Lithium carbonate and iron phosphate are prepared according to the requirements of Li:Fe:P molar ratio 1.03:1:1.03 to obtain raw materials, the above prepared powder materials and 15% of the total mass of the raw materials of citric acid are dissolved in deionized water to adjust the solid content to 45%, and then wet grinding is carried out to make the slurry product particle size D50 350±10nm; then the slurry is pumped into a spray drying device through a diaphragm pump for drying and granulation; then the dried material is sintered in a kiln, and the sintering temperature is 780°C, and the holding time is about 10 hours to obtain the corresponding lithium iron phosphate positive electrode material.

[0150] Meanwhile, the iron phosphate prepared in Comparative Example 1 and Comparative Example 2 is used to prepare lithium iron phosphate positive electrode materials according to the following method:

[0151] Lithium carbonate, iron phosphate are dosed according to the requirement of Li:Fe:P molar ratio 1.03:1:1.03 to obtain raw materials, 3000ppm of titanium dioxide is added (calculated based on lithium iron phosphate product); the powder material obtained by the above dosing and 15% of the total mass of the raw material of citric acid mixed solution is dissolved in deionized water, the solid content is adjusted to 45%, then wet grinding is carried out, so that the particle size D50 of the slurry finished product is 350±10nm; then the slurry is pumped into a spray drying device by a diaphragm pump, and drying granulation is carried out; then the dried material is sintered in a kiln, wherein the sintering temperature is 780℃, and the holding time is about 10 hours, to obtain the corresponding lithium iron phosphate positive electrode material.

[0152] The lithium iron phosphate positive electrode material prepared above is subjected to 0.1C discharge gram capacity, 1C discharge gram capacity, and 10C discharge gram capacity parameter determination, and the determination results are shown in Table 1 as follows:

[0153] Table 1: Electrical performance data of each sample

[0154]

[0155] From the results in Table 1 above, it can be seen that:

[0156] (1) The experimental group 1 is a lithium iron phosphate positive electrode material without any doping, and its electrical performance is the worst, which confirms the promoting effect of doping modification on improving the electrical performance of lithium iron phosphate positive electrode material.

[0157] (2) The experimental group 2 only co-precipitates titanium ions and iron phosphate once during the preparation of iron phosphate; the experimental group 3 only adds titanium in a solid mixing manner during the preparation of lithium iron phosphate to dope titanium; and the experimental group 5 is the lithium iron phosphate prepared by the twice doping preparation method of the present application. By comparing the data of experimental group 2, experimental group 3 and experimental group 5, it can be seen that under the condition of the same doping element and the same doping amount, the electrical performance of the lithium iron phosphate prepared by the preparation method of the present application is far superior to that of the prior art only once doping or only solid-phase doping during the preparation of lithium iron phosphate, which shows that the prepared iron phosphate by the preparation method of the present application not only can ensure the uniform distribution of titanium ions in the iron phosphate, but also can form more Li + migration channels on the surface of the iron phosphate particles, which better adapts to the restriction that the more difficult the Li + migration migrates to the surface, thereby promoting the good electrical performance of the prepared lithium iron phosphate positive electrode material.

[0158] (3) Experiment Group 4 only co-precipitates titanium ions and iron phosphate once during the preparation of iron phosphate, and further dopes twice by solid-phase doping during the preparation of lithium iron phosphate; Experiment Group 5 only co-precipitates titanium ions and iron phosphate once during the preparation of iron phosphate, and further dopes twice before calcination at the end of the crystal transformation. By comparing the results of Experiment Group 4 and Experiment Group 5, it can be seen that the electrical properties of the lithium iron phosphate anode material of Experiment Group 5 are superior to those of Experiment Group 4, indicating that the method of further doping after the end of the crystal transformation adopted by the present application can enable the iron phosphate precursor itself to form a stable shell-core structure doping structure, and the lithium iron phosphate unit cells formed subsequently can effectively realize Li + migration from the core to the surface in the unit cell structure, and the electrical properties of the entire material are stable and excellent.

[0159] (4) Experiment Groups 5-8 differ in the different doping aids used to prepare iron phosphate. By comparing the data of Experiment Groups 5-8, it can be seen that when different doping aids are selected for doping, the amount of doping ions that can enter the iron phosphate is different, thereby affecting the performance of the final product.

[0160] (5) Experiment Groups 9-12 differ in the amount of two-time doping. By comparing the data of Experiment Groups 9-12, it can be seen that the more doping, the better the electrical properties of the iron phosphate obtained, and the more doping, the more impurities in the lithium iron phosphate, thereby affecting the electrical properties of the lithium iron phosphate; when the amount of one-time doping and two-time doping reaches a certain reasonable ratio, the electrical properties of the iron phosphate obtained are best.

[0161] (6) Experiment Groups 15-20 all use vanadium as the second doping element, and different mixing forms and different doping amounts are used for vanadium doping. The results show that vanadium doping as the second doping element can obtain the same level of electrical properties as titanium doping.

[0162] (7) Experiment Group 21 uses niobium as the second doping element, and the results show that niobium doping as the second doping element can obtain the same level of electrical properties as titanium doping.

[0163] Figure 1 The SEM image of the heterogeneous doped iron phosphate used for Experiment Group 5 (i.e., the heterogeneous doped iron phosphate prepared in Example 1) is shown in FIG. 1. Figure 2 The SEM image of the lithium iron phosphate further prepared from the heterogeneous doped iron phosphate of Experiment Group 5 is shown in FIG. 2. Figure 1It can be concluded that the non-homogeneous doped iron phosphate prepared by the method of the present application presents a sheet-like morphology as a whole, and columnar growths are present on the surface or edge of the sheet-like substrate. The columnar growths are uniformly dispersed on the surface of the iron phosphate grains and partially penetrate into the interior of the surface of the iron phosphate grains, forming a stable shell doping. Further observation Figure 2 It can be seen that, Figure 1 The lithium iron phosphate particles formed by the high-temperature solid phase method in the present application have a smooth surface and uniform particle size distribution, and the doped elements are uniformly dispersed on the surface of the lithium iron phosphate particles Figure 2 The doped iron phosphate is further calcined at high temperature, and the doped elements are completely and uniformly dispersed in the lithium iron phosphate product, forming a microstructure in which the surface migration channels are more than the core migration channels in the unit cell of the lithium iron phosphate, which effectively promotes the uniform improvement of the overall material electrical performance.

Claims

1. A method for preparing heterogeneously doped iron phosphate, characterized in that: The method comprises the following steps: S1: preparing raw material solution: configuring iron source into iron source solution, and configuring phosphorus source into phosphorus source solution; adding a first doping aid containing titanium ions into the iron source solution or the phosphorus source solution, and mixing uniformly for standby; S2: mixing reaction: adding the iron source solution containing titanium ions, the phosphorus source solution, and an oxidizing agent prepared in step S1, or the phosphorus source solution containing titanium ions, the iron source solution, and the oxidizing agent into a reactor in proportion to perform rapid reaction; after the reaction is completed, the slurry is filtered and washed to prepare titanium-doped amorphous iron phosphate; S3: aging and crystallization: preparing the titanium-doped amorphous iron phosphate prepared in step S2 into slurry by adding water, and adding phosphoric acid solution into the slurry; the slurry is gradually heated to perform aging and crystallization, and titanium-doped dihydrate iron phosphate is prepared after the crystallization is completed; S4: secondary doping: uniformly adding a secondary doping aid into the titanium-doped dihydrate iron phosphate prepared in step S3 to form secondary-doped dihydrate iron phosphate; the secondary doping aid contains secondary doping elements selected from at least one of titanium, vanadium, and niobium; S5: drying and calcination: dehydrating and drying the secondary-doped dihydrate iron phosphate prepared in step S4, and then performing high-temperature calcination to form heterogeneous-doped iron phosphate; The content of doping ions in the surface layer of the heterogeneous-doped iron phosphate particles is 1.2-1.7 times that of the doping ions in the core.

2. The method of claim 1, wherein the non-homogeneous doping of iron phosphate is characterized by, The first doping aid is one or more of titanyl sulfate, titanium tetrachloride, tetrabutyl titanate, and titanium citrate.

3. The method of claim 1, wherein the non-homogeneous doping of iron phosphate is characterized by, The amount of the first doping aid is controlled to obtain titanium content of 500-3000 ppm in the titanium-doped amorphous iron phosphate.

4. The method of claim 1, wherein the non-homogeneous doping of iron phosphate is characterized by, In step S1, the preparation method of the iron source solution is as follows: configuring titanium dioxide by-product ferrous sulfate into a solution, adjusting the pH value to 2.8-5.5 by a pH value regulator to perform impurity removal reaction, and separating the precipitate after the impurity removal reaction to obtain the iron source solution.

5. The method for preparing heterogeneously doped ferric phosphate according to claim 1, characterized in that: The mixing reaction in step S2 is performed in a micro-channel pipe reactor.

6. The method of claim 5, wherein the non-homogeneous doping of iron phosphate is prepared by, The molar ratio of the phosphorus source, the oxidizing agent, and the iron source added into the micro-channel pipe reactor satisfies P:oxidizing agent:Fe=1.0:0.55-0.8:1.0-1.4; after the reaction is completed, the slurry is first introduced into a homogenization reactor, and the phosphorus source solution is continuously added into the homogenization reactor to make the final P:Fe ratio in the reaction be 1:0.95-1.05; after the reaction is completed, the slurry is filtered and washed to prepare titanium-doped amorphous iron phosphate.

7. The process for the preparation of a heterogeneous doped iron phosphate according to any one of claims 1 to 6, characterized in that, The amount of the secondary doping aid is controlled to make the content of the secondary doping elements in the final product heterogeneous-doped iron phosphate be 500-3000 ppm.

8. The method of claim 7, wherein the non-homogeneous doping of iron phosphate is prepared by, When the secondary doping element is titanium, the secondary doping aid is one or more of titanyl sulfate, titanium tetrachloride, tetrabutyl titanate, titanium citrate, nano-rutile titanium dioxide, nano-anatase titanium dioxide, and metatitanic acid; When the secondary doping element is vanadium, the secondary doping aid is one or more of ammonium metavanadate, divanadium pentoxide, and vanadyl sulfate; When the secondary doping element is niobium, the secondary doping aid is one or more of niobic acid, divanadium pentoxide, niobium oxalate, and ammonium niobium oxalate.

9. The method of claim 8, wherein the non-homogeneous doping of iron phosphate is prepared by, When the secondary doping element is titanium, the secondary doping assistant is one or more of nano-rutile titanium dioxide, nano-anatase titanium dioxide, metatitanic acid.

10. The method of claim 9, wherein the non-homogeneous doping of iron phosphate is prepared by, In step S4, when the secondary doping assistant is insoluble in water, the secondary doping assistant is added in solid phase, directly added into the slurry containing titanium-doped ferriphosphate dihydrate after the end of the crystal transformation in step S3, and then the slurry is filtered and washed to obtain the secondary titanium-doped ferriphosphate dihydrate. In step S4, when the secondary doping assistant is soluble in water, the secondary doping assistant is added in solution phase, the slurry containing titanium-doped ferriphosphate dihydrate after the end of the crystal transformation in step S3 is filtered and washed to obtain the titanium-doped ferriphosphate dihydrate solid phase; the solution containing the secondary doping assistant is directly added into the titanium-doped ferriphosphate dihydrate solid phase in atomized form, or the solution containing the secondary doping assistant and the titanium-doped ferriphosphate dihydrate solid phase are jointly fed into a dehydration and drying device in atomized form to obtain the secondary titanium-doped ferriphosphate dihydrate.

11. The method for preparing heterogeneously doped ferric phosphate according to claim 10, characterized in that: In step S4, when the secondary doping assistant is soluble in water, the secondary doping assistant is dissolved with desalted water or hydrochloric acid or nitric acid with a molar concentration of 0.01-0.1% to form a solution for addition in solution phase.

12. The method for preparing heterogeneously doped ferric phosphate according to claim 1, wherein: In step S5, the dehydration and drying are performed in a flash device, and the flash temperature is 120-300°C.

13. A heterogeneous doped iron phosphate characterized in that, The non-homogeneous doping ferriphosphate is prepared by the preparation method of any one of claims 1-12.

14. A heterogeneous doped lithium iron phosphate characterized in that, The non-homogeneous doping ferriphosphate is prepared by the preparation method of claim 13.

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