Hollow iron phosphate, preparation method therefor, and use thereof

Abstract

The present disclosure relates to the field of battery material preparation, and provides hollow iron phosphate, a preparation method therefor, and a use thereof. According to the preparation method, a specific iron source precursor, namely spherical ferrous glycerate, is mixed with a phosphorus source for an anion exchange reaction to continuously form iron phosphate having a hollow structure. The preparation method is a template-free method in which a specific iron source precursor is used as a consumable template, rather than incorporating an additional template agent; and the obtained hollow iron phosphate can further be prepared into a lithium iron phosphate material having a hollow structure, thereby facilitating the shortening of the diffusion path of lithium ions, and the improvement of the electrochemical performance of positive electrode materials.

Description

A hollow iron phosphate and its preparation method and use Technical Field

[0001] The present disclosure belongs to the field of battery material preparation and relates to a hollow iron phosphate and a preparation method and use thereof. Background Art

[0002] With energy and environmental issues becoming increasingly serious, the new generation of lithium-ion batteries has been widely used in various fields. Since Goodenough's team first reported olivine-structured lithium iron phosphate (LiFePO4) in 1997, LiFePO4 has been considered one of the most promising cathode materials for lithium-ion batteries due to its high theoretical capacity (170 mAh / g), low cost, environmental compatibility, and inherent thermal safety.

[0003] However, lithium iron phosphate suffers from poor electronic conductivity and low lithium ion diffusion rate, which greatly affect its rate performance. Iron phosphate (FePO4) is an important precursor material for the synthesis of lithium iron phosphate. Currently, in order to overcome the problems of LiFePO4, in addition to modifying it through methods such as doping, coating, and reducing its particle size, preparing high-quality iron phosphate with excellent performance indicators is also an important strategy for researchers to improve the electrochemical performance of lithium iron phosphate cathode materials.

[0004] Related research has shown that hollow nanospheres have a unique internal cavity structure. Compared to similar solid materials, they have advantages such as large specific surface area, low density, high stability, good surface permeability, and high porosity. Therefore, they have attracted considerable attention in the field of electrode materials. Hollow lithium iron phosphate made from hollow iron phosphate materials not only shortens the transmission path of lithium ions and electrons within them, but also exposes more electrochemically active sites, which is of great significance for improving the electrical performance of lithium iron phosphate.

[0005] At present, in the reported studies, most of the hollow iron phosphate structures are prepared by soft template or hard template method. For example, CN106082157A first prepares iron phosphate with a silica core as a template, and then introduces an alkaline solution to consume the silica inside to remove the template, thereby obtaining nano-scale highly active hollow iron phosphate microspheres; CN103887498A uses a polystyrene emulsion as a template, and then introduces a chelating agent and a precipitant to prepare iron phosphate, and obtains nano-iron phosphate hollow microspheres after high-temperature sintering. Although the hollow iron phosphate precursors prepared by these methods improve the electrochemical properties of the resulting lithium iron phosphate to a certain extent, they usually require a cumbersome template removal process, and toxic reagents, strong acids and alkalis, or high-temperature calcination are required to remove the template, which not only increases the process time and preparation cost, but also pollutes the environment.

[0006] Therefore, it is still necessary to develop a simple, economical and environmentally friendly method for preparing hollow structure iron phosphate, which is of great significance for realizing its industrial-scale production.

[0007] Summary of the Invention

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0009] In view of the problems existing in the prior art, the purpose of the present disclosure is to provide a hollow iron phosphate and its preparation method and use. The preparation method uses a specific iron source precursor, namely spherical ferrous glycerate, which is mixed with a phosphorus source to undergo an anion exchange reaction to continuously form a hollow iron phosphate. The preparation method is a template-free method that does not require the introduction of an additional template agent. Instead, a specific iron source precursor is used as a consumable template. The resulting hollow iron phosphate can be further used to prepare a hollow lithium iron phosphate material, which is beneficial for shortening the diffusion path of lithium ions and improving the electrochemical performance of the positive electrode material.

[0010] To achieve this goal, the present disclosure adopts the following technical solutions:

[0011] In a first aspect, the present disclosure provides a method for preparing hollow ferric phosphate, the preparation method comprising:

[0012] Ferrous glycerate (Fe(II)-glycerate) microspheres are mixed with a phosphorus source and reacted to obtain hollow iron phosphate.

[0013] The following are optional technical solutions of the present disclosure, but are not intended to limit the technical solutions provided by the present disclosure. Through the following technical solutions, the technical objectives and beneficial effects of the present disclosure can be better achieved and realized.

[0014] As an optional technical solution of the present disclosure, the method for preparing the ferrous glycerate microspheres includes:

[0015] Ferrous salt, polyvinylpyrrolidone (PVP), glycerol and a solvent are mixed and heated to obtain ferrous glycerate microspheres.

[0016] In one embodiment, the amount of polyvinyl pyrrolidone is 15wt% to 20wt% of the mass of the ferrous salt, for example, 15wt%, 16wt%, 17wt%, 18wt%, 19wt% or 20wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0017] The present disclosure uses polyvinyl pyrrolidone as a specific structure-directing agent or surfactant to control the morphology and consistency of the product and to inhibit product agglomeration. Therefore, its amount affects the size and morphology of the product.

[0018] In one embodiment, the amount of glycerol used is 0.8 to 1.2 mL per millimole of ferrous salt, for example, 0.8 mL, 0.85 mL, 0.9 mL, 0.95 mL, 1 mL, 1.05 mL, 1.1 mL, 1.15 mL or 1.2 mL, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0019] The present disclosure uses glycerol in combination with ferrous salt to generate a specific metal alkoxide precursor, and the amount of glycerol used will affect the particle size of the product.

[0020] In one embodiment, the temperature of the heat treatment is 160-200°C, for example, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C or 200°C, and the time is 8-12h, for example, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h or 12h, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0021] The temperature of the heating treatment will affect the crystal structure and morphology of the nanomaterial, so changes in temperature and heating time will cause changes in the particle size of the nanomaterial.

[0022] In one embodiment, the ferrous salt includes at least one of ferrous nitrate, ferrous sulfate or ferrous oxalate, for example, typical but non-limiting combinations include a combination of ferrous nitrate and ferrous sulfate, a combination of ferrous sulfate and ferrous oxalate, or a combination of ferrous nitrate and ferrous oxalate.

[0023] As an optional technical solution of the present disclosure, the method for preparing the ferrous glycerate microspheres further includes preparing ferrous salt into solution A, preparing polyvinyl pyrrolidone into solution B, adding solution A to solution B, and then adding glycerol to mix.

[0024] In one embodiment, the solvent of solution A comprises water.

[0025] In one embodiment, the concentration of the ferrous salt in the solution A is 0.1 to 0.2 mmol / mL, for example, 0.1 mmol / mL, 0.11 mmol / mL, 0.12 mmol / mL, 0.13 mmol / mL, 0.14 mmol / mL, 0.15 mmol / mL, 0.16 mmol / mL, 0.17 mmol / mL, 0.18 mmol / mL, 0.19 mmol / mL or 0.2 mmol / mL, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0026] In one embodiment, the solvent of solution B comprises isopropyl alcohol.

[0027] As an optional technical solution of the present disclosure, the preparation method further uses an oxidant.

[0028] In one embodiment, the oxidizing agent comprises hydrogen peroxide.

[0029] In one embodiment, the amount of the ferrous glycerate microspheres and the oxidant is controlled according to a molar ratio of iron to oxidant of 1: (1.2 to 1.5), for example, 1:1.2, 1:1.25, 1:1.3, 1:1.35, 1:1.4, 1:1.45 or 1:1.5, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0030] In one embodiment, the amount of the ferrous glycerate microspheres and the phosphorus source is controlled according to a molar ratio of iron to phosphorus of 1: (1 to 1.02), for example, 1:1, 1:1.01, 1:1.015 or 1:1.02, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0031] In one embodiment, the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, ammonium hydrogen phosphate or sodium hydrogen phosphate. For example, typical but non-limiting combinations include a combination of phosphoric acid and ammonium dihydrogen phosphate, a combination of phosphoric acid and ammonium hydrogen phosphate, a combination of phosphoric acid and sodium hydrogen phosphate, etc.

[0032] In one embodiment, the preparation method further comprises preparing ferrous glycerate microspheres into dispersion C, preparing a phosphorus source and an oxidant into dispersion D, adding dispersion C into dispersion D, reacting to obtain hollow ferric phosphate.

[0033] As an optional technical solution of the present disclosure, the pH condition of the reaction is 1.8 to 2.2, such as 1.8, 1.9, 2, 2.1 or 2.2, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0034] In one embodiment, the pH is adjusted using an alkaline substance.

[0035] In one embodiment, the alkaline substance is aqueous ammonia and / or sodium hydroxide.

[0036] In one embodiment, the reaction is carried out under heating under reflux.

[0037] In one embodiment, the reaction temperature is 85-95°C, for example, 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, 94°C or 95°C, and the reaction time is 6-12h, for example, 6h, 7h, 8h, 9h, 10h, 11h or 12h, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0038] The reaction temperature and reaction time will affect the particle size of the product and should be reasonably adjusted within the above range.

[0039] In one embodiment, the reaction is aged for 3 to 5 hours, such as 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, etc., but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0040] The role of aging is to gradually transform amorphous iron phosphate into crystalline iron phosphate, improve the crystallinity and purity of the material, optimize its crystal structure, and promote the formation of more uniform and dense particles.

[0041] In one embodiment, the preparation method further comprises subjecting the obtained hollow ferric phosphate to heat treatment to remove crystal water.

[0042] Before the heat treatment is performed, the hollow iron phosphate obtained by the preparation method disclosed in the present invention is a FePO4·2H2O material, and after the heat treatment, a hollow anhydrous FePO4 material can be obtained.

[0043] In one embodiment, the heat treatment temperature is 500-750°C, for example, 500°C, 520°C, 540°C, 550°C, 580°C, 600°C, 630°C, 650°C, 680°C, 700°C, 720°C or 750°C, and the time is 4-10h, for example, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h or 10h, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0044] Generally, the higher the heat treatment temperature, the more thorough the removal of crystal water, and it can be reasonably adjusted according to actual needs.

[0045] In a second aspect, the present disclosure provides a hollow iron phosphate, which is obtained by the preparation method described in the first aspect.

[0046] In a third aspect, the present disclosure provides a method for preparing a lithium iron phosphate material, the method comprising:

[0047] The lithium source, the carbon source and the hollow iron phosphate described in the second aspect are mixed and sintered to obtain a lithium iron phosphate positive electrode material.

[0048] When synthesizing lithium iron phosphate, except for limiting the iron source to the hollow iron phosphate provided by the present disclosure, the present disclosure does not restrict the use of other raw materials. The lithium source and carbon source that can be used in the prior art are all applicable to the present disclosure.

[0049] Exemplarily, the lithium source includes at least one of lithium carbonate, lithium hydroxide or lithium acetate. For example, typical but non-limiting combinations include a combination of lithium carbonate and lithium hydroxide, a combination of lithium carbonate and lithium acetate, or a combination of lithium hydroxide and lithium acetate.

[0050] Exemplarily, the carbon source comprises at least one of glucose, sucrose, starch or cellulose, for example, typical but non-limiting combinations include a combination of glucose and sucrose, a combination of glucose and starch, a combination of glucose and cellulose, a combination of sucrose and starch, a combination of sucrose and cellulose, or a combination of starch and cellulose.

[0051] In one embodiment, the molar ratio of the lithium source, the carbon source and the hollow iron phosphate is 1:(0.1-0.15):(1-1.1), for example, 1:0.1:1, 1:0.1:1.05, 1:0.1:1.1, 1:0.11:1, 1:0.11:1.05, 1:0.11:1.1, 1:0.12:1, 1:0.12:1.05, 1:0.12:1.1, 1:0.13:1, 1:0.13:1.05, 1:0.13:1.1, 1:0.14:1, 1:0.14:1.05, 1:0.14:1.1, 1:0.15:1, 1:0.15:1.05 or 1:0.15:1.1, etc., but are not limited to the listed values, other values ​​not listed within the above numerical range are also applicable.

[0052] In one embodiment, the mixing method comprises liquid phase ball milling.

[0053] In one embodiment, the grinding medium used in the liquid phase ball milling comprises ethanol.

[0054] In one embodiment, the liquid phase ball milling time is 2 to 5 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, etc., but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0055] In one embodiment, the sintering temperature is 650-750°C, for example, 650°C, 655°C, 660°C, 665°C, 670°C, 675°C, 680°C, 685°C, 690°C, 695°C, 700°C, 705°C, 710°C, 715°C, 720°C, 725°C, 730°C, 735°C, 740°C, 745°C or 750°C, and the sintering time is 6-10h, for example, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h or 10h, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0056] Exemplarily, the method for preparing the lithium iron phosphate material includes:

[0057] (1) Preparation of ferrous glycerate microspheres:

[0058] 2-4 mmol of ferrous salt is dissolved in 20 mL of deionized water, wherein the ferrous salt includes at least one of ferrous nitrate, ferrous sulfate, and ferrous oxalate to obtain solution A; 15 wt% to 20 wt% of polyvinyl pyrrolidone (based on the mass of the ferrous salt) is dissolved in 40 mL of isopropyl alcohol, and the mixture is stirred to obtain solution B; solution A is poured into solution B, and the mixture is continuously stirred, and 8-10 mL of glycerol is dropwise added to the mixture. After stirring for a period of time, the mixture is transferred to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and heated in an oven at 160-200° C. for 8-12 hours; after cooling to room temperature, the ferrous glycerate microsphere product is collected by centrifugation, washed, and dried;

[0059] (2) Preparation of hollow iron phosphate:

[0060] Ultrasonic dispersion of the ferrous glycerate microsphere powder of step (1) in anhydrous ethanol to obtain dispersion C; ultrasonic dispersion of 2-4 mmol of phosphate in anhydrous ethanol, the phosphate comprising at least one of phosphoric acid, diammonium phosphate, ammonium hydrogen phosphate, and sodium hydrogen phosphate, the amount of the ferrous glycerate microsphere and the phosphate being controlled according to a molar ratio of iron to phosphorus of 1:(1-1.02), then dropwise addition of 10% hydrogen peroxide, the amount of the ferrous glycerate microsphere and the hydrogen peroxide being controlled according to a molar ratio of iron to hydrogen peroxide of 1:(1.2-1.5), and stirring to obtain dispersion D; and pouring dispersion C into dispersion D. , stirring at room temperature and adding alkaline substances dropwise into the mixed solution, the alkaline substances including ammonia water and / or sodium hydroxide, controlling the pH of the solution at 1.8-2.2, then transferring the mixed solution to a reflux reaction device and heating, reflux at 85-95° C. for 6-12 hours to react, aging for 3-5 hours after the reaction, filtering, washing, and vacuum drying the product to obtain a hollow FePO4·2H2O material; placing the FePO4·2H2O material in a muffle furnace, heating to 500-750° C. for heat treatment, keeping the temperature for 4-10 hours to remove crystal water, thereby obtaining a hollow anhydrous FePO4 material, which is ground and set aside.

[0061] (3) Preparation of lithium iron phosphate material:

[0062] Under a protective atmosphere, the protective atmosphere includes nitrogen and / or argon, the hollow anhydrous FePO4 material of step (2) is mixed with a lithium source and a carbon source as a precursor, and ball milled for 2 to 5 hours with ethanol as a grinding medium, the lithium source includes at least one of lithium carbonate, lithium hydroxide or lithium acetate, and the carbon source includes at least one of glucose, sucrose, starch or cellulose, and the molar ratio of the lithium source, carbon source and hollow iron phosphate is controlled to be 1: (0.1 to 0.15): (1 to 1.1). After drying, it is sintered at 650 to 750 ° C for 6 to 10 hours to obtain LiFePO4 / C material.

[0063] In a fourth aspect, the present disclosure provides a lithium iron phosphate material, which is prepared by the method described in the third aspect, and the obtained lithium iron phosphate material is a LiFePO4 / C material. The obtained lithium iron phosphate material inherits the hollow structure of the hollow iron phosphate.

[0064] In a fifth aspect, the present disclosure provides a battery comprising the lithium iron phosphate material described in the fourth aspect.

[0065] Compared with the existing technical solutions, the present disclosure has at least the following beneficial effects:

[0066] (1) The preparation method of hollow ferric phosphate disclosed in the present invention does not introduce additional templates, but uses a self-template method, that is, ferrous glycerate microspheres are used as both an iron source and a template material to participate in the formation of the hollow nanostructure shell of ferric phosphate, so that the template material is directly converted into the target product shell and the hollow structure is left. The principle of this method is to use Fe 3+ and PO4 3- Diffusion rate difference (v(Fe 3+ )>v(PO4 3- )), Fe migrates faster outward from the template 3+ and PO4 that migrates from outside to inside the template 3- Upon encounter, they react to form an FePO4 shell. The potential energy difference generated by the diffusion of the two ions in and out causes defects within the template, gradually transforming it into a hollow structure. Furthermore, this self-involved approach allows for excellent control of the uniformity of the product particles, without the need for auxiliary template removal, simplifying the synthesis process, reducing production costs, and being environmentally friendly, making it suitable for industrial-scale production.

[0067] (2) In the method for preparing ferrous glycerate microspheres disclosed herein, the PVP used can not only serve as a structure-directing agent for forming the ferrous glycerate microspheres, but also, by controlling the number of subsequent washings of the obtained ferrous glycerate microspheres, a portion of the PVP can be retained in the formed ferrous glycerate microspheres. When reacting with a phosphorus source, hollow iron phosphate coated with a nitrogen-doped carbon layer can be formed, which is beneficial for improving the electrical conductivity;

[0068] (3) The iron phosphate prepared in the present invention is a microsphere with a hollow structure. Compared with the solid iron phosphate material, the iron phosphate with this structure has a large specific surface area and a high porosity. When synthesizing lithium iron phosphate, the lithium source and the carbon source are more able to penetrate into the interior, shortening the transmission distance between particles and reducing polarization. Accordingly, the specific surface area of ​​the lithium iron phosphate prepared from the hollow iron phosphate will also increase, the contact area between the positive electrode material and the electrolyte will increase, the migration path of the lithium ions will be shortened, and the deintercalation rate will be accelerated, which is beneficial to improving the rate performance of the lithium iron phosphate battery.

[0069] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0071] FIG1 is a SEM image of ferrous glycerate microspheres in Example 1;

[0072] FIG2 is a SEM image of the hollow anhydrous FePO4 material in Example 1;

[0073] FIG3 is a schematic diagram showing the principle of synthesizing hollow iron phosphate according to the preparation method described in Example 1. DETAILED DESCRIPTION

[0074] The technical solution of the present disclosure is further illustrated below through specific implementation methods.

[0075] It should be apparent to those skilled in the art that the embodiments are only intended to help understand the present disclosure and should not be considered as specific limitations of the present disclosure.

[0076] Example 1

[0077] This embodiment provides a method for preparing hollow ferric phosphate, the preparation method comprising:

[0078] (1) Dissolve 2.5 mmol of ferrous salt FeSO4·7H2O in 20 mL of deionized water and ultrasonically treat for 10 minutes to obtain solution A; dissolve 18 wt% of polyvinyl pyrrolidone in 40 mL of isopropanol and stir to obtain solution B; pour solution A into solution B, stir continuously and add 8.5 mL of glycerol to the mixture. After stirring for 30 minutes, transfer the mixture to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and heat it in an oven at 180°C for 10 hours. After cooling to room temperature, collect the ferrous glycerate microspheres by centrifugation and wash them repeatedly with deionized water and anhydrous ethanol. Subsequently, dry the sample in vacuum at 100°C for 12 hours.

[0079] (2) The ferrous glycerate microsphere powder prepared in step (1) was dispersed in 40 mL of anhydrous ethanol and ultrasonically treated for 15 min to obtain dispersion C; 2.5 mmol of ammonium hydrogen phosphate was ultrasonically dispersed in 40 mL of anhydrous ethanol, and then 1.5 mL of 10% hydrogen peroxide was added dropwise and stirred to obtain dispersion D; dispersion C was poured into dispersion D, stirred at room temperature for 20 min, and 25% ammonia water was added dropwise to the mixture to control the pH of the solution at 2. The mixed solution was then transferred to a reflux reaction device and heated, refluxed at 95°C for 10 hours, and then allowed to stand for 4 hours. The precipitate was collected and washed several times with deionized water, and then dried in a vacuum oven at 100°C for 12 hours to obtain hollow FePO4·2H2O. The hollow FePO4·2H2O prepared above was then placed in a muffle furnace, heated to 650°C at a heating rate of 5°C / min, and kept warm for 8 hours to obtain a hollow anhydrous FePO4 material.

[0080] Figure 3 is a schematic diagram of the principle of synthesizing hollow ferric phosphate according to the preparation method of Example 1. Figure 1 is a SEM test image of ferrous glycerate microspheres obtained in Example 1. Figure 2 is a SEM test image of hollow anhydrous ferric phosphate obtained in Example 1. It can be seen from the figure that the synthesized ferrous glycerate is in the form of microspheres. When it is mixed with a phosphorus source and an oxidant, hydrogen peroxide, to generate ferric phosphate, due to the Fe 3+ The diffusion rate is greater than that of PO4 3- The diffusion rate of Fe in ferrous glycerate microspheres 3+ Migrate outward faster, PO4 outside the ferrous glycerate microspheres 3- Fe migrates slowly inwards but quickly outwards 3+ With PO4 3- After meeting, they will react to form a FePO4 shell, and the potential energy difference generated by the diffusion process of the two ions in and out will cause defects inside the ferrous glycerate microspheres and gradually transform them into a hollow structure, eventually forming a hollow structure of iron phosphate.

[0081] Example 2

[0082] This embodiment provides a method for preparing hollow ferric phosphate, the preparation method comprising:

[0083] (1) Dissolve 2mmoL of ferrous salt FeSO4·7H2O in 20mL of deionized water and ultrasonically treat for 10min to obtain solution A; dissolve 15wt% of polyvinyl pyrrolidone in 40mL of isopropanol and stir to obtain solution B; pour solution A into solution B, stir continuously and add 8mL of glycerol to the mixture. After stirring for 30min, transfer the mixture to a 100mL polytetrafluoroethylene-lined stainless steel autoclave and heat it in an oven at 180℃ for 8h. After cooling to room temperature, collect the ferrous glycerate microspheres by centrifugation and wash them repeatedly with deionized water and anhydrous ethanol. Subsequently, dry the sample in vacuum at 100℃ for 12h.

[0084] (2) The ferrous glycerate microsphere powder prepared in step (1) was dispersed in 40 mL of anhydrous ethanol and ultrasonically treated for 15 min to obtain dispersion C; 2 mmol of ammonium hydrogen phosphate was ultrasonically dispersed in 40 mL of anhydrous ethanol, and then 1 mL of 10% hydrogen peroxide was added dropwise and stirred to obtain dispersion D; dispersion C was poured into dispersion D, stirred at room temperature for 20 min, and 25% ammonia water was added dropwise to the mixture to control the pH of the solution at 1.8. The mixed solution was transferred to a reflux reaction device and heated, refluxed at 85°C for 8 hours, and then allowed to stand for 3 hours. The precipitate was collected and washed with deionized water for several times, and then dried in a vacuum oven at 100°C for 12 hours to obtain hollow FePO4·2H2O. The hollow FePO4·2H2O prepared above was then placed in a muffle furnace, heated to 600°C at a heating rate of 5°C / min, and kept warm for 8 hours to obtain a hollow anhydrous FePO4 material.

[0085] Example 3

[0086] This embodiment provides a method for preparing hollow ferric phosphate, the preparation method comprising:

[0087] (1) Dissolve 2.5 mmol of ferrous salt FeSO4·7H2O in 20 mL of deionized water and ultrasonically treat for 10 min to obtain solution A; dissolve 18 wt% of polyvinyl pyrrolidone in 40 mL of isopropanol and stir to obtain solution B; pour solution A into solution B, stir continuously and add 8 mL of glycerol to the mixture. After stirring for 30 min, transfer the mixture to a 100 mL polytetrafluoroethylene-lined stainless steel autoclave and heat it in an oven at 180°C for 8 h. After cooling to room temperature, collect the ferrous glycerate microspheres by centrifugation and wash them repeatedly with deionized water and anhydrous ethanol. Subsequently, dry the sample in vacuum at 100°C for 12 h.

[0088] (2) The ferrous glycerate microsphere powder prepared in step (1) was dispersed in 40 mL of anhydrous ethanol and ultrasonically treated for 15 min to obtain dispersion C; 2.5 mmol of ammonium hydrogen phosphate was ultrasonically dispersed in 40 mL of anhydrous ethanol, and then 1.5 mL of 10% hydrogen peroxide was added dropwise, and the mixture was stirred evenly to obtain dispersion D; dispersion C was poured into dispersion D, and stirred at room temperature for 2 min. 25% ammonia water was added dropwise to the mixture to control the pH of the solution at 2, and then the mixture was transferred to a reflux reaction device and heated, refluxed at 90° C. for 10 h, and then allowed to stand for 4 h after the end. The precipitate was collected and washed with deionized water several times, and then placed at 100° C. The prepared hollow FePO4·2H2O was placed in a muffle furnace and heated to 650°C at a heating rate of 5°C / min for heat treatment, and kept warm for 8 hours to obtain a hollow anhydrous FePO4 material.

[0089] Example 4

[0090] This embodiment provides a method for preparing hollow ferric phosphate. In the preparation method, in step (1), the amount of polyvinyl pyrrolidone is adjusted from 18 wt% to 15 wt% of the mass of ferrous salt. Except for the above, other conditions are exactly the same as those in Example 1.

[0091] Example 5

[0092] This embodiment provides a method for preparing hollow ferric phosphate. In the preparation method, in step (1), the amount of polyvinyl pyrrolidone is adjusted from 18 wt% to 20 wt% of the mass of ferrous salt. Except for the above, other conditions are exactly the same as those in Example 1.

[0093] Example 6

[0094] This embodiment provides a method for preparing hollow iron phosphate. In the preparation method, the temperature of the heating treatment is adjusted from 180° C. to 160° C. in step (1). Except for the above, other conditions are exactly the same as those in Example 1.

[0095] Example 7

[0096] This embodiment provides a method for preparing hollow iron phosphate. In the preparation method, in step (1), the temperature of the heating treatment is adjusted from 180° C. to 200° C. Except for the above, other conditions are exactly the same as those in Example 1.

[0097] Example 8

[0098] This embodiment provides a method for preparing hollow ferric phosphate. In the preparation method, in step (1), the molar amount of ferrous salt is adjusted from 2.5 mmol to 3 mmol. Except for the above, other conditions are exactly the same as those in Example 1.

[0099] Example 9

[0100] This embodiment provides a method for preparing hollow ferric phosphate. In the preparation method, in step (1), the molar amount of ferrous salt is adjusted from 2.5 mmol to 3.5 mmol. Except for the above, other conditions are exactly the same as those in Example 1.

[0101] Example 10

[0102] This embodiment provides a method for preparing hollow ferric phosphate. In the preparation method, the pH is adjusted from 1.8 to 2 in step (2). Except for the above, other conditions are exactly the same as those in Example 1.

[0103] Example 11

[0104] This embodiment provides a method for preparing hollow ferric phosphate. In the preparation method, the pH is adjusted from 1.8 to 2.2 in step (2). Except for the above, other conditions are exactly the same as those in Example 1.

[0105] Comparative Example 1

[0106] This comparative example provides a method for preparing ferric phosphate. The method does not use ferrous glycerate microspheres, but directly replaces the ferrous glycerate microspheres used in step (2) with ferrous salt in step (1) to prepare dispersion C. Except for the above, other conditions are exactly the same as those in Example 1.

[0107] Comparative Example 2

[0108] This comparative example provides a method for preparing ferric phosphate, in which PVP is not used in step (1). Except for the above, other conditions are exactly the same as those in Example 1.

[0109] The iron phosphate obtained in the Examples and Comparative Examples was ground and used as a precursor for preparing lithium iron phosphate. Lithium carbonate, glucose, and iron phosphate were dispersed in anhydrous ethanol at a stoichiometric ratio of 1:0.11:1.02 for lithium source, carbon source, and iron phosphate. The mixture was ball-milled for 3 hours until uniformly mixed at a speed of 3000 rpm, and then spray-dried to obtain a precursor powder. The precursor powder was then heated to 400°C under a nitrogen atmosphere at a heating rate of 8°C / min for 1.5 hours, then heated to 700°C and sintered for 8 hours to obtain a LiFePO4 / C positive electrode material. The LiFePO4 / C positive electrode material obtained above was then assembled into a button cell for lithium-ion battery electrochemical performance testing (controlling the charge and discharge voltage between 2.5 and 4.5 V). The results are recorded in Table 1.

[0110] Table 1

[0111] As can be seen from Table 1, from Examples 1-11, the 0.1C discharge specific capacity of the lithium iron phosphate battery made from the hollow iron phosphate precursor described in the present disclosure can reach more than 157.1 mAh / g, the 0.5C discharge specific capacity can reach more than 151.4 mAh / g, and the first charge and discharge efficiency can reach more than 98.23%.

[0112] By comparing Example 1 and Examples 2-11, it can be seen that factors such as the amount of ferrous salt and polyvinylpyrrolidone (PVP), the synthesis temperature of the microsphere precursor, and the precipitation pH value all have an impact on the electrical properties of the lithium-ion battery. This may be because in the process of synthesizing the hollow structure iron phosphate material, the change of these parameters affects the morphology and size of the iron phosphate product.

[0113] Compared to the solid, irregular iron phosphate blocks prepared in Comparative Example 1, the iron phosphate prepared in Example 1 exhibits a hollow, nano-spherical structure. This structure increases the specific surface area of ​​the lithium iron phosphate material prepared using this as a precursor, shortens the lithium ion diffusion path, and accelerates the rate, thereby improving the electrochemical performance of the lithium-ion battery. Compared to Example 1, Comparative Example 2 does not add the surfactant PVP when preparing the ferrous glycerate precursor. This may cause the precursor product to agglomerate, leading to a decrease in the electrical performance of the subsequently prepared lithium iron phosphate cathode material.

Claims

1. A method for preparing hollow iron phosphate, comprising: Mixing ferrous glycerate microspheres with a phosphorus source and reacting to obtain hollow iron phosphate.

2. The preparation method according to claim 1, wherein, The method for preparing the ferrous glycerate microspheres comprises: Mixing a ferrous salt, polyvinylpyrrolidone, glycerol and a solvent, and performing a heat treatment to obtain ferrous glycerate microspheres.

3. The preparation method according to claim 2, wherein, The dosage of the polyvinylpyrrolidone is 15wt% - 20wt% of the mass of the ferrous salt.

4. The preparation method according to claim 2 or 3, wherein The dosage of the glycerol is 0.8 - 1.2 mL per millimole of the ferrous salt.

5. The preparation method according to any one of claims 2-4, wherein, The temperature of the heat treatment is 160 - 200 °C, and the time is 8 - 12 h.

6. The preparation method according to any one of claims 2-5, wherein, The method for preparing the ferrous glycerate microspheres further comprises preparing a solution A of the ferrous salt, preparing a solution B of the polyvinylpyrrolidone, adding the solution A to the solution B, and then adding glycerol and mixing.

7. The preparation method according to claim 6, wherein The concentration of the ferrous salt in the solution A is 0.1 - 0.2 mmol / mL.

8. The preparation method according to any one of claims 1-7, wherein, An oxidant is also used in the preparation method.

9. According to the preparation method described in claim 8, wherein The oxidant includes hydrogen peroxide.

10. The preparation method according to claim 8 or 9, wherein, The dosages of the ferrous glycerate microspheres and the oxidant are controlled according to the molar ratio of iron element to the oxidant of 1:(1.2 - 1.5).

11. The preparation method according to any one of claims 8-10, wherein, The preparation method further comprises preparing a dispersion liquid C of the ferrous glycerate microspheres, preparing a dispersion liquid D of the phosphorus source and the oxidant, adding the dispersion liquid C to the dispersion liquid D, and reacting to obtain hollow iron phosphate.

12. The preparation method according to any one of claims 1-11, wherein, The pH condition of the reaction is 1.8 - 2.

2.

13. The preparation method according to any one of claims 1-12, wherein, The temperature of the reaction is 85 - 95 °C, and the time is 6 - 12 h.

14. The preparation method according to any one of claims 1-13, wherein, After the reaction, aging is carried out for 3 - 5 h.

15. The preparation method according to any one of claims 1-14, wherein, The preparation method further comprises performing a heat treatment on the obtained hollow iron phosphate to remove crystal water; Optionally, the temperature of the heat treatment is 500 - 750 °C, and the time is 4 - 10 h.

16. A hollow iron phosphate obtained by the preparation method according to any one of claims 1 - 15.

17. A method for preparing a lithium iron phosphate material, comprising: Mixing a lithium source, a carbon source and the hollow iron phosphate according to claim 16 and sintering to obtain a lithium iron phosphate cathode material.

18. The method for preparing lithium iron phosphate material according to claim 17, wherein, The molar ratio of the lithium source, the carbon source and the hollow iron phosphate is 1:(0.1 - 0.15):(1 - 1.1); Optionally, the temperature of the sintering is 650 - 750 °C, and the time is 6 - 10 h.

19. A lithium iron phosphate material obtained by the method according to claim 17 or 18.

20. A battery containing the lithium iron phosphate material according to claim 19.

Images