Ferric phosphate, lithium ferric phosphate positive electrode material, preparation methods therefor, and use thereof

Abstract

The present disclosure belongs to the technical field of lithium batteries, and particularly relates to ferric phosphate, a lithium ferric phosphate positive electrode material, preparation methods therefor, and the use thereof. The present disclosure uses a ferrous iron source and copperas together as iron sources, and controls the dosages of the two components to enable copperas to serve as not only an iron source but also a dopant, so that impurity elements, such as Ti, Mn and Mg, contained in copperas are introduced into ferric phosphate as beneficial doping elements and are further introduced into the lithium ferric phosphate positive electrode material. During a reaction process, a polymer monomer is polymerized in situ onto the surface of ferric phosphate, so as to limit the particle size of the material, thereby obtaining precursor particles having more uniform particle size and appearance. Thus, uniform coating and doping means can remarkably improve the electrochemical properties of lithium ferric phosphate. In addition, the preparation method for ferric phosphate provided by the present disclosure achieves high-added-value resource utilization on copperas without the need of impurity removal, thereby achieving the effects of reducing the cost and improving the efficiency.

Description

A kind of iron phosphate, lithium iron phosphate positive electrode material and its preparation method and application Technical Field

[0001] The present disclosure belongs to the technical field of lithium batteries, and in particular relates to an iron phosphate, lithium iron phosphate positive electrode material, and a preparation method and application thereof. Background Art

[0002] Lithium iron phosphate (LiFePO4) is a cathode material for lithium-ion batteries. Its chemical formula is LiFePO4, and it is primarily used in various lithium-ion batteries. It has attracted considerable attention for its low cost, excellent cycle performance, and safety and environmental friendliness. During charge and discharge, LiFePO4 undergoes a phase transition between lithium iron phosphate and iron phosphate, with minimal volume difference. Iron phosphate is also a precursor for preparing LiFePO4 cathode materials, and its morphology, particle size, and structure are closely related to the performance and properties of LiFePO4.

[0003] Currently, ferric phosphate is primarily prepared through coprecipitation, with analytically pure divalent iron salts typically being used as the iron source. To enhance the conductivity of the target product, methods such as doping and coating are often employed, which can improve the electrochemical performance of lithium iron phosphate to a certain extent.

[0004] However, the lithium iron phosphate prepared by the current preparation method still has the problem of low gram capacity, and its electrochemical performance needs to be further improved.

[0005] In view of this, the present disclosure is proposed.

[0006] Summary of the Invention

[0007] The purpose of the present disclosure includes providing an iron phosphate, lithium iron phosphate positive electrode material and its preparation method and application, aiming to provide a lower-cost preparation method and improve the electrochemical performance of lithium iron phosphate.

[0008] In order to achieve the above-mentioned purpose of the present disclosure, the following technical solutions can be adopted:

[0009] The solution provided by the present disclosure includes a method for preparing ferric phosphate, comprising: reacting a phosphorus source solution and an iron source solution in the presence of an oxidant and a polymer monomer;

[0010] The iron source in the iron source solution includes a divalent iron source and green vitriol, and the molar ratio of the iron element in the green vitriol to the iron element in the divalent iron source is 1:(6-12);

[0011] Green vitriol contains doping elements, and the doping elements include at least one of Ti, Mn and Mg.

[0012] In some embodiments of the present disclosure, the molar ratio of the iron element in the green vitriol to the iron element in the ferrous iron source is 1:(8-10).

[0013] In some embodiments of the present disclosure, green vitriol is a titanium dioxide waste byproduct.

[0014] In some embodiments of the present disclosure, the polymer monomer is selected from at least one of pyrrole, thiophene, carbazole, and aniline.

[0015] In some embodiments of the present disclosure, the amount of polymer monomer used per gram of total iron source is 0.16 g to 0.35 g.

[0016] In some embodiments of the present disclosure, the molar ratio of the oxidant to the total amount of the iron source is (1-2):1.

[0017] In some embodiments of the present disclosure, an interface morphology regulator is added during the reaction of the phosphorus source solution and the iron source solution. The interface morphology regulator is selected from at least one of polyvinyl alcohol, polyvinyl pyrrolidone, dodecyltrimethylammonium bromide and sodium lauryl sulfate.

[0018] In some embodiments of the present disclosure, the mass ratio of the interface morphology modifier to the total amount of the iron source is (1-2):100.

[0019] In some embodiments of the present disclosure, the phosphorus source solution contains a phosphoric acid compound and an ammonium phosphate salt, and the molar ratio of the phosphate radical in the phosphoric acid compound to the phosphate radical in the ammonium phosphate salt is 1:(0.8-1.2).

[0020] In some embodiments of the present disclosure, the total amount of the phosphoric acid compound and the ammonium phosphate salt is controlled to make the iron-to-phosphorus molar ratio 1:(1.0-1.5).

[0021] In some embodiments of the present disclosure, the reaction temperature is 80° C.-95° C., and the reaction time is 2 h-6 h.

[0022] In some embodiments of the present disclosure, after the phosphorus source solution and the iron source solution have reacted, they are aged, and then the solid material is separated and spray-dried and calcined at high temperature.

[0023] In some embodiments of the present disclosure, the separated solid material is mixed with water and spray-dried, and the mass ratio of the solid material to water is (35-38):(62-65).

[0024] In some embodiments of the present disclosure, the inlet air temperature of the spray drying is controlled to be 250° C.-350° C., the outlet air temperature is controlled to be 80° C.-120° C., and the feeding frequency is controlled to be 15 Hz-25 Hz.

[0025] The solution provided by the present disclosure also includes iron phosphate, which is prepared by the preparation method in any of the above embodiments.

[0026] In some embodiments of the present disclosure, the iron phosphate includes an iron phosphate matrix, a polymer layer is coated on the iron phosphate matrix, and the iron phosphate matrix contains a doping element.

[0027] The solution provided by the present disclosure also includes a method for preparing a lithium iron phosphate positive electrode material, comprising: utilizing the iron phosphate in any of the above embodiments to react with a lithium salt.

[0028] In some embodiments of the present disclosure, the process includes mixing iron phosphate with a carbon source and a lithium salt and sintering the mixture, controlling the sintering temperature to be 600° C.-800° C., and the sintering time to be 10 h-12 h.

[0029] In some embodiments of the present disclosure, the molar ratio of the carbon source to the ferric phosphate is (0.03-0.04):1.

[0030] The solution provided by the present disclosure also includes a lithium iron phosphate positive electrode material prepared by the preparation method in any of the above embodiments.

[0031] The solution provided by the present disclosure also includes a positive electrode plate, including the lithium iron phosphate positive electrode material in the above embodiment.

[0032] The solution provided by the present disclosure also includes a lithium battery, including the positive electrode plate in the above embodiment.

[0033] The solution provided by the present disclosure also includes an electrical device, including the lithium battery in the above embodiment.

[0034] Utilize divalent iron source and green vitriol together as iron source, by controlling the dosage of the two so that green vitriol can be used as both iron source and dopant, so that the impurity elements such as Ti, Mn, Mg contained in green vitriol are introduced into iron phosphate as beneficial doping elements, and then introduced into lithium iron phosphate positive electrode material; in the reaction process of phosphorus source solution and iron source solution, divalent iron generates trivalent iron under the action of oxidant, and trivalent iron ion acts as initiator to make polymer monomer in situ polymerize on the surface of iron phosphate, limit the particle size of the material, and obtain precursor particles with more uniform particle size and morphology. The electrochemical performance of lithium iron phosphate can be significantly improved by means of uniform coating and doping. In addition, the preparation method of iron phosphate provided by the present disclosure enables green vitriol to be utilized as a resource with high added value without the need for impurity removal, thereby playing a role in reducing costs and increasing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0036] FIG1 is a process flow chart of the preparation method provided by the present disclosure;

[0037] FIG2 is a diagram showing the first charge and discharge of lithium iron phosphate prepared from the iron phosphate of the embodiment and the comparative example. DETAILED DESCRIPTION

[0038] The embodiments of the present disclosure will be described in detail below with reference to the examples. However, those skilled in the art will appreciate that the following examples are intended only to illustrate the present disclosure and should not be construed as limiting the scope of the present disclosure. Where specific conditions are not specified in the examples, the experiments were performed under conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, all are commercially available conventional products.

[0039] The endpoints of the ranges and any values ​​disclosed in this disclosure are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0040] The present disclosure provides a method for preparing iron phosphate, which includes the following steps, referring to FIG1 :

[0041] S1. Prepare iron source solution

[0042] A divalent iron source and a green vitriol are used as an iron source, and the two are dissolved in water and mixed uniformly to obtain an iron source solution. The molar ratio of the iron element in the green vitriol to the iron element in the divalent iron source is controlled to be 1: (6-12), preferably 1: (8-10). By controlling the molar ratio of the green vitriol and the divalent iron source, the green vitriol is used as both an iron source and a dopant, so that the impurity elements such as Ti, Mn, and Mg contained in the green vitriol are introduced into the iron phosphate as beneficial doping elements, and are doped into the lithium iron phosphate positive electrode material during the lithiation reaction, thereby improving the electrical conductivity of the material.

[0043] Specifically, the molar ratio of the iron element in the green vitriol to the iron element in the ferrous iron source can be 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, etc. If the amount of green vitriol used is too small, it will not have a significant effect on the performance of the lithium iron phosphate; if the amount of green vitriol used is too large, it will have a negative effect and reduce the electrochemical performance of the lithium iron phosphate.

[0044] In some embodiments of the present disclosure, green vitriol can be a titanium dioxide waste byproduct, and the doping elements contained in the green vitriol include at least one of Ti, Mn, and Mg, and at least one or more of the above. The method provided by the present disclosure can directly utilize the titanium dioxide waste byproduct for high added value without the need for impurity removal, significantly reducing process costs.

[0045] In some embodiments of the present disclosure, the ferrous iron source is selected from at least one of ferrous sulfate, ferrous chloride and ferrous nitrate, and may be any one or more of the above.

[0046] In some embodiments of the present disclosure, the amount of water added when preparing the iron source solution is not limited, and the concentration of the iron source can be controlled to be 0.1 mol / L-1 mol / L.

[0047] S2. Prepare phosphorus source solution

[0048] The phosphorus source solution is obtained by mixing a phosphorus source and water. The phosphorus source can be a commonly used raw material and is not limited here.

[0049] In some embodiments of the present disclosure, the phosphorus source includes a phosphoric acid compound and an ammonium phosphate salt, and the molar ratio of the phosphate radical in the phosphoric acid compound to the phosphate radical in the ammonium phosphate salt is 1:(0.8-1.2). By controlling the amount of the phosphate radical and the ammonium phosphate salt, the ammonium phosphate salt can be used as both a phosphorus source and a pore-forming regulator. 4+ It can be complexed to the surface of iron phosphate, and when calcined and dehydrated at high temperature, it will release NH3 to form holes, and lithium iron phosphate can enhance the Li + The migration rate of the electrodes can be increased, thus improving their electrochemical performance.

[0050] Specifically, the molar ratio of the phosphate in the phosphoric acid compound to the phosphate in the ammonium phosphate salt can be 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, etc.

[0051] In some embodiments of the present disclosure, the phosphate compound is selected from at least one of phosphoric acid, sodium dihydrogen phosphate and disodium hydrogen phosphate, and may be any one or more of the above; the ammonium phosphate salt is selected from at least one of monoammonium phosphate and diammonium phosphate, and may be any one or more of the above.

[0052] S3. Precipitation reaction

[0053] The phosphorus source solution and the iron source solution are reacted in the presence of an oxidant and polymer monomers at a temperature of 80°C-95°C for 2-6 hours. By controlling the reaction temperature and time, the divalent iron is converted to trivalent iron under the action of the oxidant during the reaction. The trivalent iron ions act as an initiator to cause the polymer monomers to polymerize in situ on the surface of the iron phosphate. The polymer can be coated on the surface of the iron phosphate, reducing the particle size of the iron phosphate. During the lithiation reaction, the polymer is carbonized to form carbon, which coats the surface of the lithium iron phosphate and improves its conductivity.

[0054] Specifically, the reaction temperature can be 80°C, 85°C, 90°C, 95°C, etc., and the reaction time can be 2h, 3h, 4h, 5h, 6h, etc.

[0055] In some embodiments of the present disclosure, by controlling the phosphorus source solution and the iron source solution, the iron-phosphorus molar ratio is 1:(1.0-1.5), such as 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, etc., so that phosphorus is in a slightly excess state and the reaction is fully carried out.

[0056] In some embodiments of the present disclosure, the oxidant is selected from at least one of hydrogen peroxide and oxygen, and may be any one or more of the above. Hydrogen peroxide may be selected based on cost considerations. The molar ratio of the oxidant to the total amount of the iron source is (1-2):1 to ensure sufficient reaction.

[0057] In some embodiments of the present disclosure, the polymer monomer is selected from at least one of pyrrole, thiophene, carbazole and aniline, and can be any one or more of the above; the amount of polymer monomer corresponding to each gram of the total iron source is 0.16g-0.35g, and the electrochemical performance of the positive electrode material is improved by controlling the amount of monomer and thus the amount of polymer coating within an appropriate range.

[0058] In some embodiments of the present disclosure, an interface morphology modifier is added during the reaction between the phosphorus source solution and the iron source solution to better control the morphology of the iron phosphate primary particles and obtain a precursor with a uniform morphology. The interface morphology modifier is selected from at least one of polyvinyl alcohol, polyvinyl pyrrolidone, dodecyltrimethylammonium bromide, and sodium lauryl sulfate, and can be any one or more of the above. All of the above interface morphology modifiers are conducive to obtaining a precursor with a uniform morphology.

[0059] Furthermore, the mass ratio of the interface morphology modifier to the total amount of the iron source is (1-2):100, and the morphology of the particles can be better controlled by adjusting the amount of the interface morphology modifier. Specifically, the mass ratio of the interface morphology modifier to the total amount of the iron source can be 1.0:100, 1.5:100, 2.0:100, etc.

[0060] S4. Post-processing

[0061] After the reaction of the phosphorus source solution and the iron source solution is completed, aging is carried out, and then the solid material is separated and spray-dried and high-temperature calcined. The aging makes the crystal form more uniform. The secondary particle morphology is regulated by spray drying to obtain polymer-coated dihydrate iron phosphate powder, and then high-temperature calcination is performed to obtain polymer-coated anhydrous iron phosphate.

[0062] In some embodiments of the present disclosure, after the phosphorus source solution and the iron source solution are reacted, they are aged for 3 h to 8 h (e.g., 3 h, 5 h, 8 h, etc.), and then washed and solid-liquid separated to obtain a solid material. The solvent used in the washing process can be distilled water and anhydrous ethanol, and the washing can be multiple times. After washing, the filter cake can be obtained by filtration.

[0063] In some embodiments of the present disclosure, water may be introduced during the spray drying process, and the separated solid material may be mixed with water before spray drying. The amount of water may be adjusted to achieve a mass ratio of solid material to water of (35-38):(62-65), such as 35:62, 36:63, 37:64, 38:65, and the like.

[0064] Furthermore, by controlling the spray drying air inlet temperature to 250°C-350°C, the air outlet temperature to 80°C-120°C, and the feed frequency to 15Hz-25Hz, the spray drying process can be completed quickly, yielding iron phosphate particles with uniform morphology. Specifically, the spray drying air inlet temperature can be 250°C, 300°C, 350°C, etc., and the air outlet temperature can be 80°C, 100°C, 120°C, etc.

[0065] In some embodiments of the present disclosure, during high-temperature calcination, the heating rate is controlled to be 4°C / min-6°C / min, the calcination temperature is 400°C-600°C, and the calcination time is 3 hours-8 hours, so that ferric phosphate dihydrate is fully converted into anhydrous ferric phosphate. Specifically, the calcination temperature can be 400°C, 450°C, 500°C, 550°C, 600°C, etc., and the calcination time can be 3 hours, 5 hours, 8 hours, etc.

[0066] The present disclosure also provides an iron phosphate prepared by the above-described preparation method, which has low production cost and uniform morphology. The prepared iron phosphate can be subjected to a lithiation reaction to obtain lithium iron phosphate with improved electrochemical performance. Specifically, the iron phosphate includes an iron phosphate matrix coated with a polymer layer, and the iron phosphate matrix contains doping elements such as Ti, Mn, and Mg.

[0067] The disclosed embodiment also provides a method for preparing a lithium iron phosphate positive electrode material, comprising: utilizing the above-mentioned iron phosphate to react with a lithium salt. Since the precursor has a relatively uniform morphology and contains beneficial doping elements, the electrochemical performance of the prepared lithium iron phosphate positive electrode material can be improved.

[0068] In actual operation, the preparation process of lithium iron phosphate positive electrode material includes: mixing iron phosphate with a carbon source and a lithium salt and sintering them, controlling the sintering temperature to 600℃-800℃ and the sintering time to 10h-12h, so as to fully react and obtain a uniform lithium iron phosphate product. By adding an external carbon source, the trivalent iron in the iron phosphate can be reduced to divalent iron, and at the same time, it is coated on the surface of the lithium iron phosphate to improve the conductive properties of the material. Specifically, the sintering temperature can be 600℃, 700℃, 800℃, etc., and the sintering time can be 10h, 11h, 12h, etc.

[0069] In some embodiments of the present disclosure, the carbon source is selected from at least one of cyclodextrin, starch, glucose, sucrose, polyvinyl alcohol, and cellulose, and may be any one or more of the above, or may be other inorganic carbon sources, organic carbon sources, or conductive polymers. The molar ratio of the carbon source to the ferric phosphate is (0.03-0.04):1. It is preferable to control the amount of the carbon source within the above range to further improve the electrochemical performance of the material.

[0070] The disclosed embodiments also provide a lithium iron phosphate positive electrode material, which is prepared by the above-mentioned preparation method and has excellent electrochemical properties and low preparation cost.

[0071] The embodiments of the present disclosure further provide a positive electrode plate, comprising the lithium iron phosphate positive electrode material in the above embodiment, and may further comprise a positive electrode current collector, wherein the lithium iron phosphate positive electrode material serves as an active coating on the positive electrode current collector.

[0072] The present disclosure also provides a lithium battery comprising the positive electrode sheet described in the above embodiment, and further comprising a negative electrode sheet, an electrolyte, a separator, and the like to form a complete lithium battery structure. Improvements to the lithium iron phosphate positive electrode material can improve the electrochemical performance of the positive electrode sheet, thereby improving the electrochemical performance of the lithium battery.

[0073] The embodiments of the present disclosure further provide an electrical device, including the lithium battery in the above embodiment, and may also include electrical appliances, etc. The lithium battery is used to power the electrical appliances, and the specific types of the electrical appliances are not limited.

[0074] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0075] It should be noted that the composition of the green vitriol used in the following examples is shown in Table 1:

[0076] Table 1 Composition of the green vitriol used in the embodiment

[0077] Example 1

[0078] This embodiment provides a method for preparing iron phosphate, comprising the following steps:

[0079] (1) Mix green vitriol and analytically pure ferrous sulfate in a molar ratio of 1:9 for the iron element, add water to dissolve, filter, and obtain an iron source solution for standby use. The concentration of iron in the iron source solution is 0.5 mol / L.

[0080] (2) Phosphoric acid and ammonium monohydrogen phosphate are mixed at a phosphate molar ratio of 1:1, and water is added to dissolve the mixture to obtain a phosphorus source solution. The concentration of the phosphate in the phosphorus source solution is 0.5 mol / L.

[0081] (3) Add the iron source solution and the phosphorus source solution to the reactor, controlling the iron-to-phosphorus ratio to be 1:1. After stirring evenly, add the interface morphology modifier polyvinyl alcohol, hydrogen peroxide, and pyrrole (polymer monomer), and react at 90°C for 4 hours to obtain a black polymer-coated iron phosphate solution. The mass ratio of the interface morphology modifier to the total amount of the iron source is 1.5:100, the molar ratio of the hydrogen peroxide to the iron source is 1.5:1, and the amount of polymer monomer used per gram of the total amount of the iron source is 0.16g.

[0082] (4) After the reaction is completed, the mixture is aged for 5 hours, washed with distilled water and anhydrous ethanol, and filtered to obtain a filter cake. The filter cake and distilled water are mixed in a mass ratio of 35:65, spray-dried to obtain polymer-coated dihydrate iron phosphate powder, and then calcined at high temperature to obtain polymer-coated anhydrous iron phosphate. The inlet air temperature of the spray drying is controlled to be 300°C, the outlet air temperature is controlled to be 100°C, and the feed frequency is controlled to be 20Hz; during the high-temperature calcination process, the heating rate is controlled to be 5°C / min, the calcination temperature is controlled to be 500°C, and the calcination time is controlled to be 5h.

[0083] This embodiment also provides a method for preparing a lithium iron phosphate positive electrode material, comprising the following steps: mixing the iron phosphate prepared in this embodiment with a carbon source and lithium carbonate and sintering them, controlling the sintering temperature to 800°C, the sintering time to 10 hours, the carbon source to be glucose, the molar ratio of the carbon source to the iron phosphate to be 0.03:1, and controlling the amount of lithium carbonate to achieve a molar ratio of lithium to iron elements of 1:1.01.

[0084] Example 2

[0085] This embodiment provides a method for preparing iron phosphate, comprising the following steps:

[0086] (1) Mix green vitriol and analytically pure ferrous chloride in a molar ratio of 1:9 for the iron element, add water to dissolve, filter, and obtain an iron source solution for standby use. The concentration of iron in the iron source solution is 0.5 mol / L.

[0087] (2) Phosphoric acid and ammonium dihydrogen phosphate are mixed at a phosphate molar ratio of 1:1, and water is added to dissolve the mixture to obtain a phosphorus source solution. The concentration of the phosphate in the phosphorus source solution is 0.5 mol / L.

[0088] (3) Add the iron source solution and the phosphorus source solution to the reactor, controlling the iron-to-phosphorus ratio to be 1:1. After stirring evenly, add the interface morphology modifier hexadecyltrimethylammonium bromide, hydrogen peroxide, and aniline (polymer monomer), and react at 90°C for 4 hours to obtain a black polymer-coated iron phosphate solution. The mass ratio of the interface morphology modifier to the total amount of the iron source is 1.5:100, the molar ratio of the hydrogen peroxide to the iron source is 1.5:1, and the amount of polymer monomer used per gram of the total amount of the iron source is 0.35g.

[0089] (4) After the reaction is completed, the mixture is aged for 5 hours, washed with distilled water and anhydrous ethanol, and filtered to obtain a filter cake. The filter cake and distilled water are mixed in a mass ratio of 35:65, spray-dried to obtain polymer-coated dihydrate iron phosphate powder, and then calcined at high temperature to obtain polymer-coated anhydrous iron phosphate. The inlet air temperature of the spray drying is controlled to be 300°C, the outlet air temperature is controlled to be 100°C, and the feed frequency is controlled to be 20Hz; during the high-temperature calcination process, the heating rate is controlled to be 5°C / min, the calcination temperature is controlled to be 500°C, and the calcination time is controlled to be 5h.

[0090] This embodiment also provides a method for preparing a lithium iron phosphate positive electrode material, which is prepared using the iron phosphate prepared in this embodiment. The specific steps are as described in Example 1.

[0091] Example 3

[0092] This embodiment provides a method for preparing iron phosphate, comprising the following steps:

[0093] (1) Mix green vitriol and analytically pure ferrous nitrate in a molar ratio of 1:9 for the iron element, add water to dissolve, filter, and obtain an iron source solution for standby use. The concentration of iron in the iron source solution is 0.5 mol / L.

[0094] (2) Phosphoric acid and ammonium dihydrogen phosphate are mixed at a phosphate molar ratio of 1:1, and water is added to dissolve the mixture to obtain a phosphorus source solution. The concentration of the phosphate in the phosphorus source solution is 0.5 mol / L.

[0095] (3) Add the iron source solution and the phosphorus source solution to the reactor, controlling the iron-phosphorus ratio to be 1:1. After stirring evenly, add the interface morphology modifier polyvinyl pyrrolidone, hydrogen peroxide, and thiophene (polymer monomer), and react at a constant temperature of 90°C for 4 hours to obtain a black polymer-coated iron phosphate solution. The mass ratio of the added interface morphology modifier to the total amount of the iron source is 1.5:100, the molar ratio of the added amount of hydrogen peroxide to the iron source is 1.5:1, and the amount of polymer monomer used per gram of the total amount of the iron source is 0.3g.

[0096] (4) After the reaction is completed, the mixture is aged for 5 hours, washed with distilled water and anhydrous ethanol, and filtered to obtain a filter cake. The filter cake and distilled water are mixed in a mass ratio of 35:65, spray-dried to obtain polymer-coated dihydrate iron phosphate powder, and then calcined at high temperature to obtain polymer-coated anhydrous iron phosphate. The inlet air temperature of the spray drying is controlled to be 300°C, the outlet air temperature is controlled to be 100°C, and the feed frequency is controlled to be 20Hz; during the high-temperature calcination process, the heating rate is controlled to be 5°C / min, the calcination temperature is controlled to be 500°C, and the calcination time is controlled to be 5h.

[0097] This embodiment also provides a method for preparing a lithium iron phosphate positive electrode material, which is prepared using the iron phosphate prepared in this embodiment. The specific steps are as described in Example 1.

[0098] Comparative Example 1

[0099] This comparative example provides a method for preparing ferric phosphate, which differs from Example 1 only in that no green vitriol is added and green vitriol is replaced by an equimolar amount of ferrous sulfate (calculated as the molar amount of the iron element).

[0100] This comparative example also provides a method for preparing a lithium iron phosphate positive electrode material, which is prepared using the iron phosphate prepared in this comparative example. The specific steps refer to Example 1.

[0101] Comparative Example 2

[0102] This comparative example provides a method for preparing ferric phosphate, which differs from Example 1 only in that: green vitriol and analytically pure ferrous sulfate are mixed in a molar ratio of 0.5:0.95 for the iron element.

[0103] This comparative example also provides a method for preparing a lithium iron phosphate positive electrode material, which is prepared using the iron phosphate prepared in this comparative example. The specific steps refer to Example 1.

[0104] Comparative Example 3

[0105] This comparative example provides a method for preparing ferric phosphate, which differs from Example 1 only in that: green vitriol and analytically pure ferrous sulfate are mixed in a molar ratio of 2:8 for the iron element.

[0106] This comparative example also provides a method for preparing a lithium iron phosphate positive electrode material, which is prepared using the iron phosphate prepared in this comparative example. The specific steps refer to Example 1.

[0107] Comparative Example 4

[0108] This comparative example provides a method for preparing a lithium iron phosphate cathode material. The method differs from Example 3 only in that, in Example 4, no monomer is added during the iron phosphate generation step, and lithium iron phosphate is generated after a lithiation reaction. Lithium iron phosphate powder, hydrogen peroxide, and thiophene are then mixed (the amounts of hydrogen peroxide and thiophene used are the same as in Example 3). The resulting suspension is stirred and polymerized for 5 hours. The polymer is then washed, centrifuged, and vacuum-dried to obtain a polymer-coated lithium iron phosphate cathode material.

[0109] Test Example 1

[0110] The electrochemical properties of the lithium iron phosphate cathode materials prepared in the comparative example and the example were tested, and the results are shown in Table 2 and Figure 2.

[0111] Test method: (1) Battery assembly: negative electrode shell - lithium sheet - LiPF6 electrolyte - celgard2500 diaphragm - LiPF6 electrolyte - positive electrode sheet - gasket - spring - positive electrode shell (2) Test conditions: The assembled button battery was placed in a constant temperature box at 25℃ for 10 hours. After the standing time, the electrochemical performance test was carried out using the LAND battery test system. The voltage range was: 1.5-4.2V.

[0112] Table 2 Discharge specific capacity of the embodiments and comparative examples

[0113] Comparison of the comparative examples with the examples reveals that the electrochemical performance of the materials prepared in Comparative Examples 1-3 using green vitriol as a dopant and an iron source in lithium iron phosphate is inferior to that of the examples. The electrochemical performance of lithium iron phosphate without the addition of a dopant is relatively low, and a low doping level has little effect on the electrochemical performance of lithium iron phosphate. However, a high doping level can affect the purity of the lithium iron phosphate, thereby reducing the electrochemical performance.

[0114] The electrochemical performance of the polymer-coated lithium iron phosphate material presented in Comparative Example 4 is inferior to that of the material prepared by in-situ polymerization of polymer monomers on the iron phosphate surface. This may be because: the iron phosphate formation and monomer polymerization processes occur simultaneously, allowing for uniform coating; calcination during the lithiation reaction produces a uniform coating of carbon; whereas in the comparative example, the polymerization of lithium iron phosphate powder and monomers results in the polymer not being coated on the lithium iron phosphate surface, but rather precipitating as a polymer. Industrial Applicability

[0115] The present invention utilizes a divalent iron source and alum as an iron source, and controls the dosage of the two so that the alum serves as both an iron source and a dopant, so that the impurity elements such as Ti, Mn, Mg contained in the alum are introduced into the iron phosphate as beneficial doping elements, and then introduced into the lithium iron phosphate positive electrode material, so that the alum can be utilized as a resource with high added value without the need for impurity removal, thereby reducing costs and increasing efficiency, and having very good market application value.

Claims

1. A method for preparing ferric phosphate, characterized in that: include: reacting a phosphorus source solution and an iron source solution in the presence of an oxidant and a polymer monomer; Wherein, the iron source in the iron source solution includes a divalent iron source and green vitriol, and the molar ratio of the iron element in the green vitriol to the iron element in the divalent iron source is 1:(6-12); The green vitriol contains doping elements, and the doping elements include at least one of Ti, Mn and Mg.

2. The preparation method according to claim 1, characterized in that: The molar ratio of the iron element in the green vitriol to the iron element in the divalent iron source is 1:(8-10).

3. The preparation method according to any one of claims 1-2, characterized in that The green vitriol is a waste by-product of titanium dioxide.

4. The preparation method according to any one of claims 1 to 3, characterized in that The polymer monomer is selected from at least one of pyrrole, thiophene, carbazole and aniline.

5. The preparation method according to claim 4, characterized in that: The amount of the polymer monomer corresponding to each gram of the total amount of the iron source is 0.16g-0.35g.

6. The preparation method according to claim 5, characterized in that: The molar ratio of the oxidant to the total amount of the iron source is (1-2):

1.

7. The preparation method according to any one of claims 1 to 6, characterized in that During the reaction of the phosphorus source solution and the iron source solution, an interface morphology regulator is added, and the interface morphology regulator is selected from at least one of polyvinyl alcohol, polyvinyl pyrrolidone, dodecyltrimethylammonium bromide and sodium dodecyl sulfate.

8. The preparation method according to claim 7, characterized in that: The mass ratio of the interface morphology regulator to the total amount of the iron source is (1-2):

100.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The phosphorus source solution contains a phosphoric acid compound and an ammonium phosphate salt, and the molar ratio of the phosphate radical in the phosphoric acid compound to the phosphate radical in the ammonium phosphate salt is 1:(0.8-1.2).

10. The preparation method according to claim 9, characterized in that: By controlling the total amount of the phosphoric acid compound and the ammonium phosphate salt, the iron-phosphorus molar ratio is 1:(1.0-1.5).

11. The preparation method according to any one of claims 1 to 10, characterized in that: The reaction temperature is 80°C-95°C, and the reaction time is 2h-6h.

12. The preparation method according to any one of claims 1 to 11, characterized in that: After the phosphorus source solution and the iron source solution have reacted, they are aged, and then the solid material is separated, spray-dried and calcined at high temperature.

13. The preparation method according to claim 12, characterized in that: The separated solid material is mixed with water and spray-dried, and the mass ratio of the solid material to water is (35-38):(62-65).

14. The preparation method according to claim 12 or 13, characterized in that: The inlet air temperature of the spray drying is controlled to be 250℃-350℃, the outlet air temperature is 80℃-120℃, and the feed frequency is 15-25Hz.

15. An iron phosphate, characterized in that: It is prepared by the preparation method described in any one of claims 1 to 14.

16. The iron phosphate according to claim 15, characterized in that It comprises an iron phosphate matrix, a polymer layer is coated on the iron phosphate matrix, and the iron phosphate matrix contains the doping element.

17. A method for preparing a lithium iron phosphate positive electrode material, characterized in that: Comprising: utilizing the iron phosphate described in claim 15 or 16 to react with a lithium salt.

18. The preparation method according to claim 17, characterized in that: The method comprises: mixing the iron phosphate with a carbon source and a lithium salt and sintering the mixture, controlling the sintering temperature to be 600° C.-800° C., and the sintering time to be 10 h-12 h.

19. The preparation method according to claim 18, characterized in that: The molar ratio of the carbon source to iron phosphate is (0.03-0.04):

1.

20. A lithium iron phosphate positive electrode material, characterized in that: It is prepared by the preparation method described in any one of claims 17 to 19.

21. A positive electrode sheet, characterized in that: Including the lithium iron phosphate positive electrode material as described in claim 20.

22. A lithium battery, characterized in that: Including the positive electrode sheet as described in claim 21.

23. An electrical device, characterized in that: Including the lithium battery as described in claim 22.

Images