Metal-ion-doped lithium iron phosphate material, preparation method therefor, and use thereof

Abstract

A metal-ion-doped lithium iron phosphate material, a preparation method therefor, and a use thereof, relating to the technical field of lithium batteries. The metal-ion-doped lithium iron phosphate material comprises a lithium iron phosphate sheet and metal ions loaded on and doped in the lithium iron phosphate sheet, and the lithium iron phosphate sheet has a porous structure. The method comprises: using an organic metal compound as a deposition raw material, and depositing a carbon layer and metal oxide particles on a surface of a porous Fe2O3 sheet precursor to obtain a composite material; and mixing the composite material, a lithium source, and a phosphorus source according to a stoichiometric ratio, and then drying and sintering to obtain an M-LiFePO4 material. The prepared M-LiFePO4 has good uniformity, is not prone to agglomeration, inherits the two-dimensional sheet-like morphology of the precursor material, has a porous structure, has good capability for rapid charging and discharging, and improves the rate performance of a lithium iron phosphate material by means of doping same with metal ions.

Description

A metal ion-doped lithium iron phosphate material and its preparation method and application Technical Field

[0001] The present disclosure relates to the technical field of lithium batteries, and in particular to a metal ion-doped lithium iron phosphate material, a preparation method thereof, and applications thereof. Background Art

[0002] With the depletion of fossil fuels and the urgent need for renewable energy, people have vigorously developed efficient electrochemical storage systems in recent years. Lithium-ion batteries with high energy density and long cycle life have been widely used in energy storage devices such as large-scale smart grids and portable electronic devices. Lithium iron phosphate (LiFePO4) is a new type of lithium-ion battery cathode material. Due to its excellent properties such as high capacity, stable operating voltage, good cycle performance and good safety, it has become the preferred cathode material for power and energy storage batteries. However, due to its inherent structural limitations, lithium iron phosphate materials have shortcomings such as low electronic / ionic conductivity, low lithium ion diffusion rate and low tap density, which leads to poor rate performance and limits its further practical application. Currently, methods such as material nano-sizing, ion doping, morphology control and carbon layer coating are used to modify lithium iron phosphate to improve the capacity retention and specific capacity of lithium-ion batteries. Doping with metal ions can create lattice defects in lithium iron phosphate, widen the diffusion channels of ions, reduce the band gap width, and thus improve the electronic conductivity of the material; nano-sizing of particles can increase the specific surface area of ​​the material and effectively shorten the diffusion path of lithium ions, thereby improving their diffusion rate; the special morphology and structure can increase the contact between the material and the electrolyte, providing more electrochemically active sites, which is conducive to the rapid insertion and extraction of lithium ions; carbon layer coating can not only improve the conductivity of the material, but also limit the growth of grains and inhibit particle agglomeration. Although modified lithium iron phosphate materials have been prepared using these methods, most of them have defects such as complex processes, high energy consumption, poor particle uniformity and density, low product purity, and limited improvement in material rate performance, making it difficult to meet industrial requirements. Therefore, in order to address the shortcomings of existing technologies, developing a simple and easy-to-operate method to prepare a new lithium iron phosphate cathode material with excellent performance parameters is of great significance for improving the overall electrochemical performance of lithium batteries and promoting their large-scale market application.

[0003] In view of this, the present disclosure is proposed.

[0004] Summary of the Invention

[0005] The purpose of the present disclosure is to provide a metal ion-doped lithium iron phosphate material and a preparation method and application thereof.

[0006] The present disclosure is achieved as follows:

[0007] In a first aspect, the present disclosure provides a metal ion-doped lithium iron phosphate material, comprising: flaky lithium iron phosphate and metal ions loaded and doped on the flaky lithium iron phosphate, wherein the flaky lithium iron phosphate has a porous structure.

[0008] In an optional embodiment, the molar ratio of the doping amount of the iron element to the metal ion in the flaky lithium iron phosphate is 1:(0.03-0.1).

[0009] In an optional embodiment, the thickness of the flaky lithium iron phosphate is 30 nm-60 nm.

[0010] In an optional embodiment, the specific surface area of ​​the sheet-like lithium iron phosphate is 12.5 m 2 / g-14.7m 2 / g.

[0011] In a second aspect, the present disclosure provides a method for preparing a metal ion-doped lithium iron phosphate material, comprising:

[0012] Using organometallic compounds as deposition raw materials, a carbon layer and metal oxide particles are deposited on the surface of a porous Fe2O3 flake precursor to obtain a Fe2O3-C / MO composite material, where M is a divalent transition metal ion Co 2+ 、Ni 2+ 、Mn 2+ One of the following;

[0013] The Fe2O3-C / MO composite material, lithium source and phosphorus source are mixed in a stoichiometric ratio, dried and sintered to obtain M-LiFePO4 material.

[0014] In an alternative embodiment, the organometallic compound includes at least one of bis(cyclopentadienyl)cobalt, cyclododecatriene nickel, and cyclopentadienyl manganese tricarbonyl.

[0015] In an optional embodiment, the molar ratio of the iron element in the porous Fe2O3 flake precursor to the organometallic compound is 1:(0.03-0.1).

[0016] In an alternative embodiment, the depositing comprises chemical vapor deposition.

[0017] In an optional embodiment, the reaction temperature of the chemical vapor deposition is 450° C. to 550° C., and the reaction time is 1 hour to 2 hours.

[0018] In an optional embodiment, the chemical vapor deposition is performed under a protective atmosphere.

[0019] In an optional embodiment, the method for preparing the porous Fe2O3 flake precursor includes: heating a mixture of a trivalent iron salt, urea and water to reflux to prepare ferric hydroxide carbonate; and calcining the ferric hydroxide carbonate to obtain the porous Fe2O3 flake precursor.

[0020] In an optional embodiment, the molar ratio of the trivalent iron salt to the urea is 1:(10-15).

[0021] In an optional embodiment, the temperature during the heating reflux reaction is 90°C to 110°C, the reflux time is 12h to 16h, and the reaction is allowed to stand at 85°C to 95°C for 5h to 8h. After the reaction is completed, the ferric carbonate hydroxide is collected by centrifugation, washed and dried.

[0022] In an optional embodiment, the washing and drying comprises washing with deionized water for several times, then washing with anhydrous ethanol for several times, and then drying in a vacuum oven at 70°C to 90°C.

[0023] In an optional embodiment, the calcination includes placing the ferric hydroxide carbonate in a muffle furnace, heating it to 500° C. to 600° C., and calcining it in an air atmosphere for 1 hour to 2 hours to pyrolyze CO 2 and H 2 O in the escaped products.

[0024] In an optional embodiment, the heating rate in the muffle furnace is 3-10° C. / min.

[0025] In an optional embodiment, the ferric iron salt is at least one of ferric nitrate, ferric chloride and ferric sulfate.

[0026] In an optional embodiment, the molar ratio of the Fe2O3-C / MO composite material, the lithium source and the phosphorus source is 1:(0.98-1.03):1.

[0027] In an optional embodiment, the mixing includes dispersing the Fe2O3-C / MO composite material, the lithium source and the phosphorus source in anhydrous ethanol, and mixing them by ball milling for 2 hours to 5 hours, and the rotation speed of the ball mill is 2000 rpm to 4000 rpm.

[0028] In an optional embodiment, the sintering further includes pre-firing, the pre-firing temperature is 400-550° C., and the reaction time is 2-5 hours.

[0029] In an optional embodiment, the sintering temperature is 650-750° C., and the reaction time is 6-10 hours.

[0030] In an optional embodiment, the lithium source includes at least one of lithium carbonate, lithium hydroxide and lithium acetate.

[0031] In an optional embodiment, the phosphorus source includes at least one of ammonium dihydrogen phosphate, ammonium hydrogen phosphate and sodium hydrogen phosphate.

[0032] In a third aspect, the present disclosure provides the use of the metal ion-doped lithium iron phosphate material as described in the aforementioned embodiment or the metal ion-doped lithium iron phosphate material obtained by the preparation method of the metal ion-doped lithium iron phosphate material as described in the aforementioned embodiment as a positive electrode material in the preparation of lithium-ion batteries.

[0033] In a fourth aspect, the present disclosure provides a lithium-ion battery, which includes the metal ion-doped lithium iron phosphate material as described in the aforementioned embodiment or the metal ion-doped lithium iron phosphate material prepared by the preparation method of the metal ion-doped lithium iron phosphate material as described in the aforementioned embodiment.

[0034] In a fifth aspect, the present disclosure provides the use of the lithium-ion battery described in the aforementioned embodiment in the preparation of a smart grid or a portable electronic device.

[0035] The present disclosure has the following beneficial effects:

[0036] The metal ion-doped lithium iron phosphate material provided by the present disclosure has a two-dimensional sheet-like porous morphology and is doped with metal ions. Compared with the irregular lithium iron phosphate bulk material, the two-dimensional structured material has a larger specific surface area and abundant electrochemical reaction active sites, which is conducive to sufficient contact between the electrode and the electrolyte and accelerates the deintercalation / embedding rate of lithium ions. In addition, the presence of the pore structure provides an ion channel for the diffusion of electrolyte ions in the vertical direction of the two-dimensional nanosheet layer, greatly reducing the charge transmission resistance, shortening the transmission path and diffusion time of lithium ions and electrons, and facilitating the improvement of the ability of the positive electrode material to charge and discharge rapidly at a large specific current. The metal ions doped on the lithium iron phosphate material can cause internal lattice defects in the lithium iron phosphate, which is conducive to improving the rate performance of the lithium iron phosphate material. In addition, the preparation method of the metal ion-doped lithium iron phosphate material provided by the present disclosure uses Fe2O3 flakes as a precursor material and an organometallic compound as a carbon source and a doping metal ion source. The prepared metal ion-doped lithium iron phosphate material inherits the two-dimensional porous structure of the precursor material, and both the carbon source and the metal ion source can improve the electronic conductivity of the material. Furthermore, the metal ion source introduced by the organometallic compound not only causes internal lattice defects in the lithium iron phosphate, but also reduces the obstacles encountered when lithium ions are inserted and deintercalated in the layered crystal structure, facilitating the stable diffusion of lithium ions into the material lattice, thereby greatly improving the rate performance of the lithium iron phosphate material. The lithium iron phosphate flakes synthesized by the present disclosure have good uniformity and are not easy to agglomerate. The process flow is simple, the operation is easy, and the energy consumption is low, which has good prospects for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] 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.

[0038] FIG1 is a preparation flow chart of a method for preparing a metal ion-doped lithium iron phosphate material provided by the present disclosure;

[0039] FIG2 is a scanning electron microscope image of the metal ion-doped lithium iron phosphate material provided in Example 1 of the present disclosure;

[0040] FIG3 is an XRD diagram of the metal ion-doped lithium iron phosphate material provided in Example 1 of the present disclosure. DETAILED DESCRIPTION

[0041] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer were followed. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0042] The present disclosure provides a metal ion doped lithium iron phosphate material, which includes: a sheet of lithium iron phosphate and a metal ion loaded on the sheet of lithium iron phosphate, wherein the sheet of lithium iron phosphate has a porous structure. The molar ratio of the iron element to the metal ion doping amount in the sheet of lithium iron phosphate is 1: (0.03 to 0.1). The thickness of the sheet of lithium iron phosphate is 30nm-60nm. The specific surface area of ​​the sheet of lithium iron phosphate is 12.5m 2 / g-14.7m 2 / g.

[0043] The present disclosure provides a method for preparing a metal ion-doped lithium iron phosphate material, which comprises the following steps:

[0044] Using organometallic compounds as deposition raw materials, a carbon layer and metal oxide particles are deposited on the surface of the porous Fe2O3 flake precursor to obtain Fe2O3-C / MO composite materials, where M is a divalent transition metal ion Co 2+ 、Ni 2+ 、Mn 2+A method of preparing an M-LiFePO4 material comprises mixing an Fe2O3-C / MO composite material, a lithium source, and a phosphorus source in a stoichiometric ratio, drying, and sintering the mixture to obtain an M-LiFePO4 material. It should be noted that the Fe2O3-C / MO composite material refers to a Fe2O3 flake precursor having a carbon layer (C) and metal oxide particles (MO) deposited on the surface. The symbol "-" indicates that the Fe2O3 and C / MO form a layered structure, and the carbon layer (C) and metal oxide particles (MO) are directly deposited on the surface of the Fe2O3 flake precursor. The symbol " / " indicates that the carbon layer (C) and metal oxide particles (MO) are juxtaposed, with the carbon layer (C) and metal oxide particles (MO) being deposited partially, partially, or simultaneously on the surface of the Fe2O3 flake precursor. The symbol "-" in the product M-LiFePO4 indicates that the LiFePO4 is doped with metal ions M. The location of doping is not limited, as long as doping is achieved.

[0045] In the present disclosure, a porous Fe2O3 flake precursor is used as a matrix, and an organic metal compound is used as a deposition raw material. The organic metal compound contains both carbon and doped metals, so it can serve as a carbon source and a doped metal source. A Fe2O3-C / MO composite material is obtained by depositing a carbon layer and metal oxide particles on the surface of the porous Fe2O3 flake precursor. The Fe2O3-C / MO composite material is mixed with a lithium source and a phosphorus source and then calcined at a high temperature to obtain a lithium iron phosphate sheet with a two-dimensional porous structure and doped with metal ions, thereby achieving the purpose of increasing the electronic conductivity of the material, promoting the rapid diffusion of lithium ions, and improving the electrochemical properties of the material.

[0046] Specifically, referring to FIG1 , the preparation method of the metal ion-doped lithium iron phosphate material provided in the present disclosure includes the following steps:

[0047] S1. Preparation of porous Fe2O3 flake precursor.

[0048] The mixed solution of trivalent iron salt, urea and water is subjected to heating reflux reaction to prepare ferric hydroxide carbonate; and the ferric hydroxide carbonate is obtained by calcining the ferric hydroxide carbonate.

[0049] The ferric salt is at least one of ferric nitrate, ferric chloride, and ferric sulfate. The molar ratio of the ferric salt to urea is 1:(10-15). The temperature during the heating reflux reaction is 90°C to 110°C, the reflux time is 12h to 16h, and the mixture is allowed to stand at 85°C to 95°C for 5h to 8h. After the reaction is completed, the ferric carbonate hydroxide is collected by centrifugation and washed and dried. Washing and drying include washing with deionized water several times, then washing with anhydrous ethanol several times, and then drying in a vacuum oven at 70°C to 90°C.

[0050] In the present disclosure, since ferric hydroxide carbonate is prepared by a heating reflux reaction, the ferric hydroxide carbonate will be pyrolyzed at high temperature to generate gas during the subsequent calcination process, thereby forming a porous Fe2O3 flake precursor.

[0051] In some typical embodiments, the molar ratio of the trivalent iron salt to the urea can be, for example, any one of 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, or a range between any two thereof. The temperature during the heating reflux reaction can be, for example, any one of 90°C, 95°C, 100°C, 105°C, 110°C, or a range between any two thereof. The reflux time can be, for example, any one of 12h, 13h, 14h, 15h, 16h, or a range between any two thereof. The standing temperature can be, for example, any one of 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, or a range between any two thereof. The standing time can be, for example, any one of 5h, 6h, 7h, 8h, or a range between any two thereof. The drying temperature of the vacuum oven may be, for example, any one of 70° C., 75° C., 80° C., 85° C., and 90° C., or a value in a range between any two of them.

[0052] The calcination process includes placing the ferric carbonate hydroxide in a muffle furnace, heating the temperature to 500° C. to 600° C. at a heating rate of 3° C. / min to 10° C. / min, and calcining the mixture in an air atmosphere for 1 to 2 hours to pyrolyze CO2 and H2O in the released product.

[0053] In some typical embodiments, the heating rate may be, for example, any one of 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, and 10°C / min, or a range between any two thereof. The calcination temperature may be, for example, any one of 500°C, 530°C, 550°C, 580°C, and 600°C, or a range between any two thereof. The calcination time may be, for example, any one of 1 hour, 1.5 hours, and 2 hours, or a range between any two thereof.

[0054] In the present disclosure, a process of heating reflux and calcination is used to prepare a porous Fe2O3 flake precursor. The porous Fe2O3 flake precursor has a two-dimensional porous structure and a larger specific surface area, which is conducive to subsequent contact with an organic metal compound.

[0055] Preparation of S2, Fe2O3-C / MO composite materials.

[0056] An Fe2O3-C / MO composite material is obtained by depositing a carbon layer and metal oxide particles on the surface of a porous Fe2O3 flake precursor using an organometallic compound as a deposition raw material. The molar ratio of iron to the organometallic compound in the porous Fe2O3 flake precursor is 1:(0.03-0.1). In some typical embodiments, the molar ratio of iron to the organometallic compound in the porous Fe2O3 flake precursor can be, for example, any one of 1:0.03, 1:0.05, 1:0.08, 1:0.1, or a range between any two of these.

[0057] The organometallic compound includes at least one of bis(cyclopentadienyl)cobalt, cyclododecatriene nickel, and cyclopentadienyl manganese tricarbonyl. In the present disclosure, the specific organometallic compound is selected as the deposition raw material. Since it contains both carbon and doped metal, it can simultaneously deposit a carbon layer and metal oxide particles on the surface of the porous Fe2O3 sheet precursor. Both the carbon layer and the metal oxide particles can improve the electronic conductivity of the material. In addition, the metal ion source can cause internal lattice defects in the lithium iron phosphate, reducing the obstacles encountered when lithium ions are inserted and deintercalated in the layered crystal structure, facilitating the stable diffusion of lithium ions into the material lattice, and thus greatly improving the rate performance of the lithium iron phosphate material.

[0058] The deposition includes chemical vapor deposition, the reaction temperature of chemical vapor deposition is 450°C to 550°C, the reaction time is 1h to 2h, and the chemical vapor deposition is carried out under a protective atmosphere. The above-mentioned organometallic compound can decompose into volatile substances at 450°C to 550°C, thereby producing chemical reactions and transport reactions on the solid porous Fe2O3 sheet precursor through chemical vapor deposition and producing solid deposits, thereby depositing a carbon layer and metal oxide particles. This method is simple to operate and can evenly distribute the carbon layer and metal oxide particles on the porous Fe2O3 sheet precursor. In some typical embodiments, the reaction temperature of chemical vapor deposition can be, for example, any one of 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, or a range between any two of them.

[0059] Preparation of S3, M-LiFePO4 materials.

[0060] The Fe2O3-C / MO composite material, a lithium source, and a phosphorus source are mixed in a molar ratio of 1:(0.98-1.03):1. The Fe2O3-C / MO composite material, the lithium source, and the phosphorus source are then dispersed in anhydrous ethanol and ball-milled for 2-5 hours at a speed of 2000-4000 rpm. The material is then dried, pre-calcined at 400-550°C for 2-5 hours, and sintered at 650-750°C for 6-10 hours to obtain the M-LiFePO4 material. The lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium acetate. The phosphorus source includes at least one of ammonium dihydrogen phosphate, ammonium hydrogen phosphate, and sodium hydrogen phosphate.

[0061] In some typical embodiments, the molar ratio of the Fe2O3-C / MO composite material, the lithium source, and the phosphorus source can be, for example, any one of 1:0.98:1, 1:0.99:1, 1:1:1, 1:1.01:1, 1:1.02:1, 1:1.03:1, or a range between any two thereof. The mixing time of the ball mill can be, for example, any one of 2 hours, 3 hours, 4 hours, or 5 hours, or a range between any two thereof. The rotation speed of the ball mill can be, for example, any one of 2000 rpm, 2500 rpm, 3000 rpm, 3500 rpm, or 4000 rpm, or a range between any two thereof. The pre-calcination temperature can be, for example, any one of 400°C, 430°C, 450°C, 500°C, 520°C, or 550°C, or a range between any two thereof. The pre-calcination time can be, for example, any one of 2 hours, 3 hours, 4 hours, or 5 hours, or a range between any two thereof. The sintering temperature may be, for example, any one of 650° C., 680° C., 700° C., 720° C., 740° C., and 750° C., or a range thereof. The sintering time may be, for example, any one of 6 h, 7 h, 8 h, 9 h, and 10 h, or a range thereof.

[0062] In the present disclosure, Fe2O3-C / MO composite material, lithium source, and phosphorus source are directly mixed and ground, and then dried and calcined to prepare M-LiFePO4 material, wherein the Fe2O3-C / MO composite material contains iron, carbon, and metal doping elements, Fe2O3 is used to provide a porous sheet structure, and the M-LiFePO4 material inherits the two-dimensional flaky porous morphology of the precursor material. The high-temperature pyrolysis of ferric hydroxide carbonate will release water vapor and carbon dioxide, thereby making the Fe2O3 two-dimensional thin sheet produce a porous structure. Furthermore, during the high-temperature calcination process under a protective atmosphere, Fe2O3 and the carbon atoms in the carbon layer deposited on its surface undergo an oxidation-reduction reaction, consuming carbon atoms, thereby achieving the purpose of etching the carbon layer, and to a certain extent, a pore structure can also be produced. Therefore, the two work together to produce a porous structure, increasing the surface area. Compared with irregular lithium iron phosphate bulk materials, this two-dimensional structured material has a larger specific surface area and abundant electrochemical reaction active sites, which is conducive to sufficient contact between the electrode and the electrolyte and accelerates the deintercalation / intercalation rate of lithium ions. In addition, the presence of the pore structure provides an ion channel for the diffusion of electrolyte ions in the vertical direction of the two-dimensional nanosheet layer, greatly reducing the charge transmission resistance, shortening the transmission path and diffusion time of lithium ions and electrons, and facilitating the rapid charge and discharge capability of the positive electrode material at a high specific current. In addition, the metal ion source can cause internal lattice defects in lithium iron phosphate, reducing the obstacles encountered by lithium ions when inserting and deintercalating in the layered crystal structure, facilitating the stable diffusion of lithium ions into the material lattice, and thus greatly improving the rate performance of the lithium iron phosphate material.

[0063] The metal ion-doped lithium iron phosphate material can be widely used in the preparation of lithium-ion batteries as a positive electrode material.

[0064] Specifically, the present disclosure further provides a lithium-ion battery comprising the metal ion-doped lithium iron phosphate material. The prepared lithium-ion battery can be widely used in the preparation of smart grids or portable electronic devices.

[0065] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0066] Example 1:

[0067] A preparation method and application of a metal ion-doped lithium iron phosphate material, comprising:

[0068] (1) Dissolve 0.02 mol ferric nitrate and 0.3 mol urea in 100 mL deionized water, stir evenly, and transfer the mixture to a reflux reactor and heat. Stir and reflux at 100 ° C for 12 hours, and let it stand at 90 ° C for 5 hours. After the reaction is completed, the ferric carbonate hydroxide product is collected by centrifugation, washed several times with deionized water and anhydrous ethanol, and dried in a vacuum oven at 80 ° C. Subsequently, the product ferric carbonate hydroxide is placed in a muffle furnace, heated to 500 ° C at a heating rate of 5 ° C / min, and calcined in an air atmosphere for 2 hours to obtain a porous Fe2O3 flake material, which is then ground for use.

[0069] (2) The porous Fe2O3 flake precursor powder prepared in step (1) was placed in a chemical vapor deposition system reaction chamber, and 0.001 mol of bis(cyclopentadienyl)cobalt was used as a deposition raw material. A thin layer of carbon and CoO was deposited on the surface of the Fe2O3 flakes at 500°C in a nitrogen atmosphere (N2: 99%; O2: 0.2% to 1%) for 1.5 hours to obtain a Fe2O3-C / CoO composite material (the molar ratio of iron element to organometallic compound was 1:0.05).

[0070] (3) Fe2O3-C / CoO, lithium carbonate, and ammonium dihydrogen phosphate were dispersed in anhydrous ethanol at a molar ratio of 1:1.02:1 for the iron source composite material, lithium source, and phosphorus source. The mixture was ball-milled for 3 h until uniformly mixed at a speed of 3000 rpm, and then spray-dried to obtain a precursor powder. Subsequently, the precursor powder was heated to 400°C at a rate of 5°C / min in a high-purity argon atmosphere for 3 h, and then heated to 700°C for 8 h to obtain a cobalt-doped Co-LiFePO4 cathode material.

[0071] Please refer to Figure 2 for the scanning electron microscope image of the Co-LiFePO4 positive electrode material provided in this embodiment, and Figure 3 for the XRD pattern. As can be seen from Figure 2, it has a two-dimensional flake morphology and a porous structure, and has good uniformity and is not easy to agglomerate. As can be seen from Figure 3, the XRD pattern of Example 1 has the same characteristic peaks as the LiFePO4 standard card, and there are no other impurity diffraction peaks, indicating that the cobalt metal ions are doped into the interior of the lithium iron phosphate crystal structure and form a continuous solid solution, without affecting the crystal structure of the lithium iron phosphate.

[0072] Example 2:

[0073] A preparation method and application of a metal ion-doped lithium iron phosphate material, comprising:

[0074] (1) Dissolve 0.02 mol ferric nitrate and 0.3 mol urea in 100 mL deionized water, stir evenly, and transfer the mixture to a reflux reactor and heat. Stir and reflux at 100 ° C for 14 h, and let it stand at 90 ° C for 7 h. After the reaction is completed, the ferric carbonate hydroxide product is collected by centrifugation, washed several times with deionized water and anhydrous ethanol, and dried in a vacuum oven at 80 ° C. Subsequently, the product ferric carbonate hydroxide is placed in a muffle furnace, heated to 550 ° C at a heating rate of 5 ° C / min, and calcined in an air atmosphere for 2 h to obtain a porous Fe2O3 flake precursor, which is then ground for use.

[0075] (2) The same as step (2) of Example 1, except that the amount of bis(cyclopentadienyl)cobalt was changed from 0.001 mol to 0.0014 mol. (The molar ratio of iron element to organometallic compound was 1:0.07).

[0076] (3) The same as step (3) of Example 1.

[0077] Example 3:

[0078] A preparation method and application of a metal ion-doped lithium iron phosphate material, comprising:

[0079] (1) Dissolve 0.03 mol ferric nitrate and 0.45 mol urea in 100 mL deionized water, stir evenly, and transfer the mixture to a reflux reactor and heat. Stir and reflux at 100 ° C for 14 h, and let it stand at 90 ° C for 7 h. After the reaction is completed, the ferric carbonate hydroxide product is collected by centrifugation, washed several times with deionized water and anhydrous ethanol, and dried in a vacuum oven at 80 ° C. Subsequently, the product ferric carbonate hydroxide is placed in a muffle furnace, heated to 550 ° C at a heating rate of 5 ° C / min, and calcined in an air atmosphere for 2 h to obtain a porous Fe2O3 flake precursor, which is then ground for use.

[0080] (2) The same as step (2) of Example 1, except that the amount of bis(cyclopentadienyl)cobalt was changed from 0.001 mol to 0.0015 mol. (The molar ratio of iron element to organometallic compound was 1:0.05).

[0081] (3) The same as step (3) of Example 1.

[0082] Example 4:

[0083] A preparation method and application of a metal ion-doped lithium iron phosphate material, comprising:

[0084] (1) Dissolve 0.03 mol ferric nitrate and 0.45 mol urea in 100 mL deionized water, stir evenly, and transfer the mixture to a reflux reactor and heat. Stir and reflux at 100 ° C for 16 hours, and let it stand at 90 ° C for 8 hours. After the reaction is completed, the ferric carbonate hydroxide product is collected by centrifugation, washed several times with deionized water and anhydrous ethanol, and dried in a vacuum oven at 80 ° C. Subsequently, the product ferric carbonate hydroxide is placed in a muffle furnace, heated to 600 ° C at a heating rate of 5 ° C / min, and calcined in an air atmosphere for 2 hours to obtain a porous Fe2O3 flake precursor, which is then ground for use.

[0085] (2) The same as step (2) of Example 3, except that the amount of bis(cyclopentadienyl)cobalt was changed from 0.0015 mol to 0.0024 mol. (The molar ratio of iron element to organometallic compound was 1:0.08).

[0086] (3) The same as step (3) of Example 1.

[0087] Example 5:

[0088] A preparation method and application of a metal ion-doped lithium iron phosphate material, comprising:

[0089] (1) The same as step (1) of Example 1, except that the molar amount of ferric nitrate is 0.01 moL and the molar amount of urea is 0.15 moL.

[0090] (2) The same as step (2) of Example 1, except that the amount of bis(cyclopentadienyl)cobalt was changed from 0.001 mol to 0.0006 mol. (The molar ratio of iron element to organometallic compound was 1:0.03).

[0091] (3) Fe2O3-C / CoO, lithium carbonate, and ammonium dihydrogen phosphate were dispersed in anhydrous ethanol at a molar ratio of 1:0.98:1 for the iron source composite material, lithium source, and phosphorus source. The mixture was ball-milled for 2 h until uniformly mixed at a speed of 4000 rpm, and then spray-dried to obtain a precursor powder. Subsequently, the precursor powder was heated to 500°C at a rate of 5°C / min under a high-purity argon atmosphere for 4 h, and then heated to 650°C and calcined for 10 h to obtain a cobalt-doped Co-LiFePO4 cathode material.

[0092] Example 6:

[0093] A preparation method and application of a metal ion-doped lithium iron phosphate material, comprising:

[0094] (1) The same as step (1) of Example 1, except that the molar amount of ferric nitrate is 0.04 moL and the molar amount of urea is 0.6 moL.

[0095] (2) The same as step (2) of Example 1, except that the amount of bis(cyclopentadienyl)cobalt was changed from 0.001 mol to 0.004 mol. (The molar ratio of iron element to organometallic compound was 1:0.1).

[0096] (3) Fe2O3-C / CoO, lithium carbonate, and ammonium dihydrogen phosphate were dispersed in anhydrous ethanol at a molar ratio of 1:1:1 for the iron source composite material, lithium source, and phosphorus source. The mixture was ball-milled for 5 h until uniformly mixed at a speed of 2000 rpm, and then spray-dried to obtain a precursor powder. Subsequently, the precursor powder was heated to 550°C at a rate of 5°C / min under a high-purity argon atmosphere for 2 h, and then heated to 750°C for 6 h to obtain a cobalt-doped Co-LiFePO4 cathode material.

[0097] Comparative Example 1 (Compared with Example 1, no precursor material was prepared, and a lithium iron phosphate material without metal ion doping was synthesized by a high-temperature solid-phase method)

[0098] According to the stoichiometric ratio of 1:1.02:1:0.1 for the ferric iron source, lithium source, phosphorus source, and carbon source, 0.02 mol of ferric oxide particles, 0.0204 mol of lithium carbonate, 0.02 mol of ammonium dihydrogen phosphate, and 0.002 mol of glucose were dispersed in 50 mL of anhydrous ethanol, ball-milled for 3 hours until uniformly mixed at a speed of 3000 rpm, and then spray-dried to obtain a precursor powder. Subsequently, the precursor powder was heated to 400 ° C at a rate of 8 ° C / min in a high-purity argon atmosphere for 1.5 hours, and then heated to 700 ° C and calcined at high temperature for 8 hours to obtain the LiFePO4 positive electrode material.

[0099] Comparative Example 2 (Compared with Example 1, no precursor material was prepared, and cobalt ion-doped lithium iron phosphate material was synthesized by high-temperature solid-phase method)

[0100] According to the stoichiometric ratio of 1:0.05:1.02:1:0.1 for the trivalent iron source, metal ion source, lithium source, phosphorus source and carbon source, 0.02moL ferric oxide particles, 0.001moL bis(cyclopentadiene)cobalt, 0.0204moL lithium carbonate, 0.02moL ammonium dihydrogen phosphate and 0.002moL glucose were dispersed in 50mL of anhydrous ethanol, ball milled for 3h until uniformly mixed, with a speed of 3000rpm, and then spray dried to obtain a precursor powder. Subsequently, the precursor powder was heated to 400℃ at a heating rate of 8℃ / min under a high-purity argon atmosphere for 1.5h, and then heated to 700℃ and calcined at high temperature for 8h to obtain Co 2+ Doped Co-LiFePO4 positive electrode material.

[0101] Comparative Example 3 (Compared with Example 1, preparation of two-dimensional Fe2O3 sheet precursor, and synthesis of lithium iron phosphate material without metal ion doping by high-temperature solid-phase method)

[0102] (1) The same as step (1) of Example 1.

[0103] (2) Fe2O3 flakes, lithium carbonate, ammonium dihydrogen phosphate, and glucose were dispersed in 50 mL of anhydrous ethanol at a molar ratio of 1:1.02:1:0.1 for the iron source, lithium source, phosphorus source, and carbon source. The mixture was ball-milled for 3 h until uniformly mixed at 3000 rpm, and then spray-dried to obtain a precursor powder. Subsequently, the precursor powder was heated to 400°C at a rate of 8°C / min in a high-purity argon atmosphere for 1.5 h, and then heated to 700°C for 8 h to obtain the LiFePO4 positive electrode material.

[0104] Comparative Example 4:

[0105] This comparative example is essentially the same as Example 1, except that the amount of bis(cyclopentadienyl)cobalt in step (2) is changed from 0.001 mol to 0.004 mol (the molar ratio of iron to organometallic compound is 1:0.2).

[0106] Experimental example:

[0107] The lithium iron phosphate cathode material obtained above was prepared into a button cell for lithium-ion battery electrochemical performance testing (the charge and discharge voltage was controlled between 2.5-4.5V). The results are shown in the following table:

[0108] As can be seen from the above table, the electrochemical properties of the lithium iron phosphate products prepared in Examples 1-6 are significantly better than those in the comparative examples, especially Example 4. Among them, the discharge specific capacity and the first charge and discharge efficiency of the random lithium iron phosphate block prepared in Comparative Example 1 are significantly lower than those in Examples 1-6 and other comparative examples. Although the discharge specific capacity and the first charge and discharge efficiency of the cobalt ion-doped random lithium iron phosphate block prepared in Comparative Example 2 are slightly improved compared with those in Comparative Example 1, they are still significantly worse than those in Examples 1-6. Although the discharge specific capacity and the first charge and discharge efficiency of the metal-free lithium iron phosphate sheet prepared in Comparative Example 3 are slightly improved compared with those in Comparative Example 1, they are still significantly worse than those in Examples 1-6. The molar ratio of iron element to organometallic compound in the porous Fe2O3 sheet precursor in Comparative Example 4 is not within the scope of this application. When there are too many organometallic compounds, the content of doped metal elements will be too much, which will have a certain hindering effect on the deintercalation / embedding of lithium ions, thereby affecting the electrical properties of the electrode material. The lithium iron phosphate prepared in Examples 1-6 of the present disclosure has a two-dimensional porous thin sheet structure and is doped with metal ions. The material of this structure has a large specific surface area and high conductivity, the contact area between the electrolyte and the positive electrode material is large, the diffusion path of lithium ions is shortened, and the deintercalation speed is fast, thereby improving the rate performance of the lithium battery.

[0109] In summary, the metal ion-doped lithium iron phosphate material provided by the present disclosure has a two-dimensional sheet-like porous morphology and is doped with metal ions. Compared with the irregular lithium iron phosphate bulk material, the material of the two-dimensional structure has a larger specific surface area and abundant electrochemical reaction active sites, which is conducive to the full contact between the electrode and the electrolyte and accelerates the lithium ion extraction / insertion rate; in addition, the presence of the pore structure provides an ion channel for the diffusion of electrolyte ions in the vertical direction of the two-dimensional nanosheet layer, greatly reducing the charge transfer resistance, shortening the transmission path and diffusion time of lithium ions and electrons, and is conducive to improving the ability of the positive electrode material to charge and discharge rapidly at a large specific current. The metal ions doped on the lithium iron phosphate material can cause internal lattice defects in the lithium iron phosphate, which is conducive to improving the rate performance of the lithium iron phosphate material. In addition, the preparation method of the metal ion-doped lithium iron phosphate material provided by the present disclosure uses Fe2O3 flakes as a precursor material and an organometallic compound as a carbon source and a doping metal ion source. The prepared metal ion-doped lithium iron phosphate material inherits the two-dimensional porous structure of the precursor material, and both the carbon source and the metal ion source can improve the electronic conductivity of the material. Furthermore, the metal ion source introduced by the organometallic compound not only causes internal lattice defects in the lithium iron phosphate, but also reduces the obstacles encountered when lithium ions are inserted and deintercalated in the layered crystal structure, facilitating the stable diffusion of lithium ions into the material lattice, thereby greatly improving the rate performance of the lithium iron phosphate material. The lithium iron phosphate flakes synthesized by the present disclosure have good uniformity and are not easy to agglomerate. The process flow is simple, the operation is easy, and the energy consumption is low, which has good prospects for industrial application.

[0110] The above describes in detail the optional embodiments of the present disclosure, but the present disclosure is not limited thereto. Within the technical concept of the present disclosure, various simple variations of the technical solution of the present disclosure can be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as the contents disclosed by the present disclosure and fall within the scope of protection of the present disclosure. Industrial Applicability

[0111] The metal ion-doped lithium iron phosphate material provided by the present disclosure has a two-dimensional sheet-like porous morphology and is doped with metal ions. Compared with the irregular lithium iron phosphate bulk material, the two-dimensional structured material has a larger specific surface area and abundant electrochemical reaction active sites, which is conducive to sufficient contact between the electrode and the electrolyte and accelerates the deintercalation / embedding rate of lithium ions. In addition, the presence of the pore structure provides an ion channel for the diffusion of electrolyte ions in the vertical direction of the two-dimensional nanosheet layer, greatly reducing the charge transmission resistance, shortening the transmission path and diffusion time of lithium ions and electrons, and facilitating the improvement of the ability of the positive electrode material to charge and discharge rapidly at a large specific current. The metal ions doped on the lithium iron phosphate material can cause internal lattice defects in the lithium iron phosphate, which is conducive to improving the rate performance of the lithium iron phosphate material. In addition, the preparation method of the metal ion-doped lithium iron phosphate material provided by the present disclosure uses Fe2O3 flakes as a precursor material and an organometallic compound as a carbon source and a doping metal ion source. The prepared metal ion-doped lithium iron phosphate material inherits the two-dimensional porous structure of the precursor material, and both the carbon source and the metal ion source can improve the electronic conductivity of the material. Furthermore, the metal ion source introduced by the organometallic compound not only causes internal lattice defects in the lithium iron phosphate, but also reduces the obstacles encountered when lithium ions are inserted and deintercalated in the layered crystal structure, facilitating the stable diffusion of lithium ions into the material lattice, thereby greatly improving the rate performance of the lithium iron phosphate material. The lithium iron phosphate flakes synthesized by the present disclosure have good uniformity and are not easy to agglomerate. The process flow is simple, the operation is easy, and the energy consumption is low, which has good prospects for industrial application.

Claims

1. A lithium iron phosphate material doped with metal ions, characterized in that, It includes: Flaky lithium iron phosphate and metal ions doped and supported on the flaky lithium iron phosphate, and the flaky lithium iron phosphate has a porous structure.

2. The lithium iron phosphate material doped with metal ions according to claim 1, wherein The molar ratio of iron element to the doping amount of the metal ions in the flaky lithium iron phosphate is 1:(0.03 - 0.1).

3. The lithium iron phosphate material doped with metal ions according to any one of claims 1-2, characterized in that, The thickness of the flaky lithium iron phosphate is 30nm - 60nm.

4. The lithium iron phosphate material doped with metal ions according to any one of claims 1-3, characterized in that, The specific surface area of the flaky lithium iron phosphate is 12.5 m 2 / g - 14.7 m 2 / g.

5. A preparation method of a metal ion-doped lithium iron phosphate material, characterized in that, It includes: Using an organometallic compound as a deposition raw material, a carbon layer and metal oxide particles are deposited on the surface of a porous Fe2O3 flake precursor to obtain an Fe2O3-C / MO composite material, where M is a divalent transition metal ion Co 2+ , Ni 2+ , Mn 2+ ; one of them After mixing the Fe2O3-C / MO composite material, lithium source, and phosphorus source according to the stoichiometric ratio, the M-LiFePO4 material is obtained through drying and sintering.

6. The preparation method of the lithium iron phosphate material doped with metal ions according to claim 5, characterized in that, The organometallic compound includes at least one of bis(cyclopentadienyl)cobalt, cyclododecatriene nickel, and cyclopentadienyltricarbonylmanganese.

7. The preparation method of the metal ion-doped lithium iron phosphate material according to any one of claims 5-6, characterized in that, The molar ratio of iron element to the organometallic compound in the porous Fe2O3 flaky precursor is 1:(0.03 - 0.1).

8. The preparation method of the metal ion-doped lithium iron phosphate material according to any one of claims 5-7, characterized in that, The deposition includes chemical vapor deposition.

9. The preparation method of the metal ion-doped lithium iron phosphate material according to claim 8, characterized in that, The reaction temperature of the chemical vapor deposition is 450°C - 550°C, and the reaction time is 1h - 2h.

10. The preparation method of the metal ion-doped lithium iron phosphate material according to any one of claims 8-9, characterized in that, The chemical vapor deposition is carried out under a protective atmosphere.

11. The preparation method of the metal ion-doped lithium iron phosphate material according to any one of claims 5-10, characterized in that, The preparation method of the porous Fe2O3 flaky precursor includes: preparing iron carbonate hydroxide by heating and refluxing the mixed solution of ferric salt, urea, and water; obtaining it after calcining the iron carbonate hydroxide.

12. The preparation method of the metal ion-doped lithium iron phosphate material according to claim 11, characterized in that, The molar ratio of the ferric salt to the urea is 1:(10 - 15).

13. The preparation method of the metal ion-doped lithium iron phosphate material according to any one of claims 11-12, characterized in that, When carrying out the heating and refluxing reaction, the temperature is 90°C - 110°C, the reflux time is 12h - 16h, standing at 85°C - 95°C for 5h - 8h. After the reaction ends, centrifuge to collect the iron carbonate hydroxide, and wash and dry it.

14. The preparation method of the metal ion-doped lithium iron phosphate material according to claim 13, wherein, The washing and drying include washing several times with deionized water first, then washing several times with absolute ethanol, and then drying in a vacuum oven at 70°C - 90°C.

15. The preparation method of the metal ion-doped lithium iron phosphate material according to any one of claims 11-14, characterized in that, The calcination includes placing the iron carbonate hydroxide in a muffle furnace, heating to 500°C - 600°C, and calcining in an air atmosphere for 1h - 2h to thermally decompose and escape CO2 and H2O in the product.

16. The preparation method of the metal ion-doped lithium iron phosphate material according to claim 15, wherein, The heating rate in the muffle furnace is 3 - 10°C / min.

17. The preparation method of the metal ion-doped lithium iron phosphate material according to any one of claims 11-16, characterized in that, The ferric salt is at least one of ferric nitrate, ferric chloride, and ferric sulfate.

18. The preparation method of the metal ion-doped lithium iron phosphate material according to any one of claims 5-17, characterized in that, The molar ratio of the Fe2O3-C / MO composite material, the lithium source, and the phosphorus source is 1:(0.98 - 1.03):

1.

19. The preparation method of the lithium iron phosphate material doped with metal ions according to any one of claims 5-18, characterized in that, The mixing includes dispersing the Fe2O3-C / MO composite material, the lithium source, and the phosphorus source in absolute ethanol, and ball-milling and mixing for 2h - 5h, and the rotation speed of the ball-milling is 2000rpm - 4000rpm.

20. The preparation method of the metal ion-doped lithium iron phosphate material according to any one of claims 5-19, characterized in that, Before the sintering, there is also a pre-sintering, and the temperature of the pre-sintering is 400 - 550°C, and the reaction time is 2 - 5h.

21. The preparation method of the metal ion-doped lithium iron phosphate material according to any one of claims 5-20, characterized in that, The temperature of the sintering is 650 - 750°C, and the reaction time is 6 - 10h.

22. The preparation method of the metal ion-doped lithium iron phosphate material according to any one of claims 5-21, characterized in that, The lithium source includes at least one of lithium carbonate, lithium hydroxide, and lithium acetate.

23. The preparation method of the metal ion-doped lithium iron phosphate material according to any one of claims 5-22, characterized in that, The phosphorus source includes at least one of ammonium dihydrogen phosphate, ammonium hydrogen phosphate, and sodium hydrogen phosphate.

24. The application of the metal ion-doped lithium iron phosphate material described in any one of claims 1 - 4 or the metal ion-doped lithium iron phosphate material prepared by the preparation method of the metal ion-doped lithium iron phosphate material described in any one of claims 5 - 23 as a cathode material in the preparation of lithium-ion batteries.

25. A lithium-ion battery, characterized in that, It includes a lithium iron phosphate material doped with metal ions obtained by using the lithium iron phosphate material doped with metal ions according to any one of claims 1-4 or the preparation method of the lithium iron phosphate material doped with metal ions according to any one of claims 5-23.

26. Use of the lithium ion battery according to claim 25 in the preparation of a smart grid or a portable electronic device.

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