A kind of flaky iron phosphate and its preparation method and application

Abstract

The present application discloses a flaky iron phosphate and its preparation method and application, relating to the technical field of lithium-ion positive electrode materials. The preparation method of the flaky iron phosphate comprises the following steps: uniformly mixing oleyl alcohol and a lower alcohol having 1-4 carbon atoms, sequentially adding a trivalent iron salt solution and a solution containing phosphate to obtain a first solution; subjecting the first solution to a hydrothermal reaction, and after completion of the reaction, filtering, washing, drying, and calcining the product to obtain the flaky iron phosphate. The lithium iron phosphate obtained by the flaky iron phosphate prepared by the method disclosed herein has good charge and discharge performance as a positive electrode material for batteries.

Description

Technical Field

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

[0002] Lithium iron phosphate (LiFePO4) is the mainstream of lithium-ion batteries and is widely used in various industries. As a lithium battery, it not only has excellent cycle performance but also high safety. The excellent cycle performance is due to its stable olivine structure, which allows lithium ions to be repeatedly intercalated and deintercalated for a long time and multiple cycles of charge and discharge without structural collapse. However, this structure makes lithium ions (Li + ) can only diffuse along the one-dimensional channel (010) crystal plane, resulting in a low lithium ion diffusion rate, which fundamentally affects its electrical performance. Industrially, lithium iron phosphate is prepared by sintering iron phosphate (LFP) and a lithium source at high temperatures. Iron phosphate and lithium iron phosphate have similar olivine structures, so any changes to the structure or morphology of iron phosphate will directly affect the performance of the lithium iron phosphate cathode material.

[0003] At present, the morphology of iron phosphate is mainly spherical, such as core-shell structure or hollow sphere structure. Studies have shown that due to Li + Due to the one-dimensional diffusion characteristics along the (010) direction in LFP, iron phosphate nanosheets or nanorods with (010) plane orientation can be prepared. Compared with the irregular or spherical structure, the sheet-like structure or the rod-like structure can greatly shorten the Li + Diffusion distance in the bulk phase increases Li + Deintercalation sites, making Li in LFP + More fully participate in the electrochemical reaction, thereby improving the reversible capacity and rate performance of lithium iron phosphate materials. Therefore, how to prepare flake iron phosphate is of great significance to the field of lithium-ion battery technology. Summary of the Invention

[0004] The purpose of the present disclosure is to overcome the deficiencies of the prior art and to provide a flaky iron phosphate and a preparation method and application thereof.

[0005] To achieve the above objectives, the technical solution adopted by the present disclosure is as follows: In a first aspect, a method for preparing flaky iron phosphate is provided, comprising the following steps:

[0006] Mixing oleyl alcohol and a lower alcohol having 1 to 4 carbon atoms uniformly, and sequentially adding a trivalent iron salt solution and a solution containing phosphate to obtain a first solution;

[0007] The first solution is subjected to a hydrothermal reaction, and after the reaction is completed, the product is filtered, washed, dried, and calcined to obtain flaky iron phosphate;

[0008] The mass ratio of the oleyl alcohol to the lower alcohol is 1:(0.7-1.3); the molar ratio of the oleyl alcohol to the trivalent iron salt is 1:(0.05-0.30);

[0009] The molar ratio of the ferric salt to the phosphate is (0.95-1.1):1, wherein the molar amount of the ferric salt is calculated as iron ions. In one embodiment, the molar ratio of the oleyl alcohol to the ferric salt is 1:(0.1-0.25).

[0010] In one embodiment, the mass ratio of oleyl alcohol to lower alcohol is 1:(0.8-1.2).

[0011] In one embodiment, the ferric salt is at least one of ferric chloride, ferric perchlorate, and ferric nitrate.

[0012] In one embodiment, the phosphate radical is provided by at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

[0013] In one embodiment, the lower alcohol is at least one of ethanol, methanol, and ethylene glycol.

[0014] In one embodiment, the temperature of the hydrothermal reaction is 80-180° C., and the time of the hydrothermal reaction is 4-18 hours.

[0015] In one embodiment, the calcination temperature is 450-750° C., and the calcination time is 2-8 hours.

[0016] In one embodiment, the drying temperature is 60-80° C., and the drying time is 4-10 h.

[0017] In one embodiment, the solution containing phosphate is added dropwise at a rate of 1 to 10 mL / min.

[0018] In a second aspect, a flake iron phosphate is provided, which is prepared by the flake iron phosphate preparation method.

[0019] In a third aspect, a lithium iron phosphate is provided. The lithium iron phosphate is obtained by mixing the flaky iron phosphate as a raw material with a lithium source and a carbon source, and then ball milling and sintering.

[0020] In one embodiment, the molar ratio of the flaky iron phosphate to the lithium source is 1:(1-1.03), wherein the molar amount of the flaky iron phosphate is calculated as iron ions, and the molar amount of the lithium source is calculated as lithium element.

[0021] In one embodiment, the mass of the carbon source is 2-10% of the total mass of the flaky iron phosphate and the lithium source.

[0022] In one embodiment, the lithium source is at least one of lithium carbonate, lithium hydroxide, and lithium acetate.

[0023] In one embodiment, the carbon source is at least one of glucose, sucrose, starch, dextrin, citric acid, and cellulose.

[0024] In one embodiment, the sintering temperature is 400-850° C., and the sintering time is 6.5-20 hours.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The present invention uses oleyl alcohol and a lower alcohol having 1 to 4 carbon atoms as reaction solvents. In the hydrothermal reaction, oleyl alcohol acts as a soft template with the assistance of the lower alcohol. Under the action of the lower alcohol having 1 to 4 carbon atoms, bilayer micelles are spontaneously formed, thereby promoting the formation of sheet iron phosphate and making the exposed surface of the sheet iron phosphate a (010) crystal plane, which is beneficial for the subsequent synthesis of lithium iron phosphate in which lithium ions move along the one-dimensional direction of the (010) crystal plane, thereby improving the electrochemical performance of the LiFePO4 positive electrode material.

[0027] (2) Oleyl alcohol is a simple ingredient containing only carbon, hydrogen and oxygen elements. No other elements will be introduced during the synthesis process, and no additional removal is required, which reduces the appearance of impurities during the synthesis of iron phosphate. It can be used as a supplementary carbon source for in-situ coating on iron phosphate, thereby improving the conductivity of iron phosphate and further improving the electrical properties of lithium iron phosphate. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a scanning electron microscope image of the anhydrous ferric phosphate obtained in Example 1 of the present disclosure. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present disclosure, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present disclosure without making any creative efforts are within the scope of protection of the present disclosure.

[0030] In the present disclosure, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0031] In this disclosure, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0032] In the present disclosure, there is no particular limitation on the specific dispersion and stirring treatment methods.

[0033] The reagents and instruments used in this disclosure without manufacturer indication are all conventional products that can be purchased commercially.

[0034] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0035] In a first aspect, the present disclosure provides a method for preparing flaky iron phosphate, comprising the following steps:

[0036] Mixing oleyl alcohol and a lower alcohol having 1 to 4 carbon atoms uniformly, and sequentially adding a trivalent iron salt solution and a solution containing phosphate to obtain a first solution;

[0037] The first solution is subjected to a hydrothermal reaction, and after the reaction is completed, the product is filtered, washed, dried, and calcined to obtain flaky iron phosphate;

[0038] The mass ratio of the oleyl alcohol to the lower alcohol is 1:(0.7-1.3); the molar ratio of the oleyl alcohol to the trivalent iron salt is 1:(0.05-0.30);

[0039] The molar ratio of the ferric salt to the phosphate radical is (0.95-1.1):1, wherein the molar amount of the ferric salt is calculated based on iron ions.

[0040] The present invention uses oleyl alcohol and a lower alcohol having 1 to 4 carbon atoms as solvents for a hydrothermal reaction. With the assistance of the lower alcohol, oleyl alcohol spontaneously forms a double-layer micelle, with the hydrophobic group facing the inside of the micelle and the hydroxyl group facing the outside of the micelle, which can serve as a soft template. The hydroxyl group on the outside of the micelle has a guiding effect, attracting trivalent iron ions to be fixed on the hydroxyl surface. After adding a phosphorus source solution, the phosphate ions are combined with the trivalent iron and fixed together on the outside of the double-layer micelle, and a hydrothermal reaction is performed to generate a sheet of iron phosphate. The crystal structure of the sheet of iron phosphate disclosed in the present invention has a shorter b-axis, and its main exposed crystal plane is the (010) crystal plane, which is beneficial in the subsequent synthesis of lithium iron phosphate. It promotes the movement of lithium ions along the (010) crystal plane in a one-dimensional direction, thereby improving the electrochemical performance of the LiFePO4 positive electrode material.

[0041] In the present disclosure, oleyl alcohol contains only carbon, hydrogen and oxygen elements and has a simple composition. No other elements will be introduced during the preparation of iron phosphate, and no additional removal is required, thereby reducing the appearance of impurities during the synthesis of iron phosphate. During the calcination process, it can be used as a supplementary carbon source for in-situ coating on the iron phosphate to improve the conductivity of the iron phosphate, thereby further improving the electrical properties of lithium iron phosphate.

[0042] In the present disclosure, the mass ratio of oleyl alcohol to lower alcohol may be 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, or 1:1.3, but the present disclosure is not limited thereto; preferably, it is 1:(0.8-1.2).

[0043] In the present disclosure, the mass ratio of oleyl alcohol to lower alcohol affects the morphology of ferric phosphate. If the content of oleyl alcohol is too low, the shape of the micelles will change and the ferric phosphate will become spherical. If the content of oleyl alcohol is too high, the size of the flaky ferric phosphate will be uneven.

[0044] In the present disclosure, the molar ratio of oleyl alcohol to trivalent iron salt can be 1:0.05, 1:0.08, 1:0.1, 1:0.12, 1:0.15, 1:0.17, 1:0.20, 1:0.23, 1:0.25, 1:0.28, 1:0.30, but the present disclosure is not limited thereto; preferably, it is 1:(0.1-0.25).

[0045] In the present disclosure, the inventors further explored the effect of the molar ratio of oleyl alcohol and ferric salt on the morphology of iron phosphate, and found that when the molar ratio of oleyl alcohol and ferric salt is controlled in the range of 1: (0.05-0.30), flaky iron phosphate can be obtained. If the content of ferric salt is too little, the micelles will not be able to adsorb enough ferric ions, and the flaky iron phosphate will have an irregular morphology; if the content of ferric salt is too much, the thickness of the flaky iron phosphate will increase, and it will transform into a block-like or rod-like morphology of iron phosphate.

[0046] In the present disclosure, the molar ratio of the ferric salt to the phosphate can be 0.95:1, 0.96:1, 0.97:1, 0.98:1, 0.99:1, 1:1, 1.02:1, 1.04:1, 1.06:1, 1.08:1, 1.1:1, wherein the molar amount of the ferric salt is calculated based on iron ions, but the present disclosure is not limited thereto.

[0047] In the present disclosure, there is no particular limitation on the concentration of the ferric salt solution. Specifically, in the ferric salt solution, the concentration of the ferric salt is 0.6-2 mol / L, more specifically, the concentration of the ferric salt is 0.8-1.5 mol / L.

[0048] In the present disclosure, the ferric iron salt may be an existing ferric iron salt that can be used to prepare ferric phosphate. Specifically, the ferric iron salt is at least one of ferric chloride, ferric perchlorate, and ferric nitrate.

[0049] In the present disclosure, there is no particular limitation on the concentration of the solution containing phosphate. Specifically, in the solution containing phosphate, the concentration of phosphate is 0.6-2 mol / L. More specifically, the concentration of trivalent iron salt is 0.8-1.5 mol / L.

[0050] In the present disclosure, the phosphate radical may be provided by a soluble substance containing a phosphate radical, for example, the phosphate radical is provided by at least one of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0051] In the present disclosure, there is no particular limitation on the manner of adding the ferric salt solution and the phosphate-containing solution, and various methods commonly used in the art may be used, such as dropwise addition. More specifically, the rate of addition is 1 to 10 mL / min.

[0052] In the present disclosure, the lower alcohol is at least one of ethanol, methanol, and ethylene glycol.

[0053] In the present disclosure, the temperature of the hydrothermal reaction is 80-180°C, for example, it can be 80°C, 85°C, 90°C, 95°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C or a range consisting of any two of them, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0054] In the present disclosure, the time of the hydrothermal reaction is 4-18 h, for example, it can be 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 12 h, 14 h, 16 h, 18 h or a range consisting of any two of them, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0055] Reacting at the above temperature and time can further ensure that the morphology of the iron phosphate is flaky.

[0056] In the present disclosure, the washing process refers to washing the filtered medium alternately with deionized water and ethanol until the upper centrifuged liquid is colorless and clear.

[0057] In the present disclosure, there is no particular limitation on the drying method, and various methods commonly used in the art may be used, such as vacuum drying and hot air drying. Specifically, the drying temperature is 60-80° C., and the drying time is 4-10 h.

[0058] In the present disclosure, the calcination temperature is 450-750° C., the calcination time is 2-8 hours, and the calcination process can be carried out in a muffle furnace, a rotary kiln, or other equipment.

[0059] In one embodiment, the phosphorus source solution is added dropwise at a rate of 1 to 10 mL / min.

[0060] In a second aspect, a flake iron phosphate is provided, which is prepared by the flake iron phosphate preparation method.

[0061] In the present disclosure, there is no particular limitation on the specific method for preparing lithium iron phosphate, which can be various methods commonly used in the art, for example, the flaky iron phosphate is used as a raw material, mixed with a lithium source and a carbon source, and then ball milled and sintered.

[0062] In one embodiment, the molar ratio of the flaky iron phosphate to the lithium source is 1:(1-1.03), wherein the molar amount of the flaky iron phosphate is calculated as iron ions, and the molar amount of the lithium source is calculated as lithium element.

[0063] In one embodiment, the mass of the carbon source is 2-10% of the total mass of the flaky iron phosphate and the lithium source.

[0064] In the present disclosure, the lithium source and carbon source can be various lithium sources and carbon sources commonly used in the art. For example, the lithium source can be at least one of lithium carbonate, lithium hydroxide, and lithium acetate; the carbon source can be at least one of glucose, sucrose, starch, dextrin, citric acid, and cellulose.

[0065] In one embodiment, the sintering temperature is 400-850° C., and the sintering time is 6.5-20 hours.

[0066] Specifically, the sintering is divided into two steps. The first step is sintering at a temperature of 400-500° C. for 0.5-2 hours. The second step is sintering at a temperature of 500-850° C. for 6-18 hours.

[0067] Specifically, the sintering is performed under a protective atmosphere, more specifically, the protective atmosphere is an inert gas, such as nitrogen or argon.

[0068] In one embodiment, the ball mill has a rotation speed of 400-1200 r / min.

[0069] The present disclosure will be described in detail below through examples.

[0070] Example 1

[0071] This embodiment provides a method for preparing flaky iron phosphate, comprising the following steps:

[0072] After mixing oleyl alcohol and ethanol for 30 minutes, 1 mol / L ferric chloride solution was added at a rate of 5 mL / min, and after mixing evenly, 1 mol / L ammonium dihydrogen phosphate solution was added at a rate of 5 mL / min and stirred evenly to obtain a first solution; wherein the mass ratio of oleyl alcohol to ethanol is 1:1, the molar ratio of oleyl alcohol to ferric chloride is 1:0.08, and Fe 3+ :PO4 3- The molar ratio is 1:1;

[0073] The obtained first solution was transferred to a reactor and reacted at 100°C for 6 hours. The obtained product was filtered, and the obtained filter material was washed alternately with deionized water and ethanol until the upper centrifuged liquid was colorless and clear. The obtained precipitate was placed in a vacuum drying oven and dried at 60°C for 4 hours to obtain FePO4·xH2O;

[0074] The obtained FePO4·xH2O was placed in a muffle furnace, heated to 600°C at a rate of 4°C / min and kept at this temperature for 6 hours to obtain anhydrous iron phosphate.

[0075] The anhydrous ferric phosphate of this embodiment was characterized by SEM. The results are as follows Figure 1 As shown, from Figure 1 It can be seen that the prepared anhydrous iron phosphate shows a flake-like morphology.

[0076] This embodiment also provides a method for preparing lithium iron phosphate, comprising the following steps:

[0077] Anhydrous ferric phosphate, lithium carbonate, and glucose of this example were added to water at a molar ratio of Fe:Li:C of 1:1.02:0.05 and mixed evenly. The resulting mixture was ball-milled at a speed of 700 r / min for 5 h, and the ball-milled product was spray-dried to obtain a precursor powder.

[0078] The precursor powder was kept at 350°C for 2 h at a heating rate of 3°C / min under a nitrogen atmosphere, and then heated to 750°C and calcined at high temperature for 6 h to obtain LiFePO4 / C positive electrode material.

[0079] Example 2

[0080] This embodiment provides a method for preparing flaky iron phosphate, comprising the following steps:

[0081] After mixing oleyl alcohol and methanol for 30 minutes, 1 mol / L ferric nitrate solution was added at a rate of 10 mL / min, and after mixing evenly, 1 mol / L ammonium dihydrogen phosphate solution was added at a rate of 10 mL / min and stirred evenly to obtain a first solution; wherein the mass ratio of oleyl alcohol to methanol is 1:1, the molar ratio of oleyl alcohol to ferric nitrate is 1:0.08, and Fe 3+ :PO4 3- The molar ratio is 1.1:1;

[0082] The obtained first solution was transferred to a reactor and reacted at 180°C for 4 hours. The obtained product was filtered, and the obtained filter material was washed alternately with deionized water and ethanol until the upper centrifuged liquid was colorless and clear. The obtained precipitate was placed in a vacuum drying oven and dried at 60°C for 4 hours to obtain FePO4·xH2O;

[0083] The obtained FePO4·xH2O was placed in a muffle furnace, heated to 750°C at a rate of 4°C / min and kept at this temperature for 2 hours to obtain anhydrous iron phosphate.

[0084] This embodiment further provides a method for preparing lithium iron phosphate. The only difference between the method for preparing lithium iron phosphate in this embodiment and that in Example 1 is that the anhydrous iron phosphate in Example 1 is replaced by the anhydrous iron phosphate in this embodiment.

[0085] Example 3

[0086] This embodiment provides a method for preparing flaky iron phosphate, comprising the following steps:

[0087] After mixing oleyl alcohol and ethylene glycol for 60 minutes, 1 mol / L ferric perchlorate solution was added at a rate of 1 mL / min, and after mixing evenly, 1 mol / L diammonium hydrogen phosphate solution was added at a rate of 1 mL / min and stirred evenly to obtain a first solution; wherein the mass ratio of oleyl alcohol to ethylene glycol was 1:1, the molar ratio of oleyl alcohol to ferric perchlorate was 1:0.08, and Fe 3+ :PO4 3- The molar ratio is 0.95:1;

[0088] The obtained first solution was transferred to a reactor and reacted at 80°C for 18 hours. The obtained product was filtered, and the obtained filter material was washed alternately with deionized water and ethanol until the upper centrifuged liquid was colorless and clear. The obtained precipitate was placed in a vacuum drying oven and dried at 80°C for 10 hours to obtain FePO4·xH2O;

[0089] The obtained FePO4·xH2O was placed in a muffle furnace, heated to 450°C at a rate of 4°C / min and kept at that temperature for 8 hours to obtain anhydrous iron phosphate.

[0090] This embodiment further provides a method for preparing lithium iron phosphate. The only difference between the method for preparing lithium iron phosphate in this embodiment and that in Example 1 is that the anhydrous iron phosphate in Example 1 is replaced by the anhydrous iron phosphate in this embodiment.

[0091] Example 4

[0092] This embodiment provides a method for preparing flaky iron phosphate. The only difference between the method for preparing flaky iron phosphate in this embodiment and that in Example 1 is that the mass ratio of oleyl alcohol to ethanol is 1:1.2.

[0093] This embodiment further provides a method for preparing lithium iron phosphate. The only difference between the method for preparing lithium iron phosphate in this embodiment and that in Example 1 is that the anhydrous iron phosphate in Example 1 is replaced by the anhydrous iron phosphate in this embodiment.

[0094] Example 5

[0095] This embodiment provides a method for preparing flaky iron phosphate. The only difference between the method for preparing flaky iron phosphate in this embodiment and that in Example 1 is that the mass ratio of oleyl alcohol to ethanol is 1:0.8.

[0096] This embodiment further provides a method for preparing lithium iron phosphate. The only difference between the method for preparing lithium iron phosphate in this embodiment and that in Example 1 is that the anhydrous iron phosphate in Example 1 is replaced by the anhydrous iron phosphate in this embodiment.

[0097] Example 6

[0098] This embodiment provides a method for preparing flaky iron phosphate. The only difference between the method for preparing flaky iron phosphate in this embodiment and that in Example 1 is that the mass ratio of oleyl alcohol to ethanol is 1:0.7.

[0099] This embodiment further provides a method for preparing lithium iron phosphate. The only difference between the method for preparing lithium iron phosphate in this embodiment and that in Example 1 is that the anhydrous iron phosphate in Example 1 is replaced by the anhydrous iron phosphate in this embodiment.

[0100] Example 7

[0101] This embodiment provides a method for preparing flaky iron phosphate. The only difference between the method for preparing flaky iron phosphate in this embodiment and that in Example 1 is that the mass ratio of oleyl alcohol to ethanol is 1:1.3.

[0102] This embodiment further provides a method for preparing lithium iron phosphate. The only difference between the method for preparing lithium iron phosphate in this embodiment and that in Example 1 is that the anhydrous iron phosphate in Example 1 is replaced by the anhydrous iron phosphate in this embodiment.

[0103] Example 8

[0104] This embodiment provides a method for preparing flaky iron phosphate. The only difference between the method for preparing flaky iron phosphate in this embodiment and that in Example 1 is that the molar ratio of oleyl alcohol to ferric chloride is 1:0.1.

[0105] This embodiment further provides a method for preparing lithium iron phosphate. The only difference between the method for preparing lithium iron phosphate in this embodiment and that in Example 1 is that the anhydrous iron phosphate in Example 1 is replaced by the anhydrous iron phosphate in this embodiment.

[0106] Example 9

[0107] This embodiment provides a method for preparing flaky iron phosphate. The only difference between the method for preparing flaky iron phosphate in this embodiment and that in Example 1 is that the molar ratio of oleyl alcohol to ferric chloride is 1:0.25.

[0108] This embodiment further provides a method for preparing lithium iron phosphate. The only difference between the method for preparing lithium iron phosphate in this embodiment and that in Example 1 is that the anhydrous iron phosphate in Example 1 is replaced by the anhydrous iron phosphate in this embodiment.

[0109] Example 10

[0110] This embodiment provides a method for preparing flaky iron phosphate. The only difference between the method for preparing flaky iron phosphate in this embodiment and that in Example 1 is that the molar ratio of oleyl alcohol to ferric chloride is 1:0.05.

[0111] This embodiment further provides a method for preparing lithium iron phosphate. The only difference between the method for preparing lithium iron phosphate in this embodiment and that in Example 1 is that the anhydrous iron phosphate in Example 1 is replaced by the anhydrous iron phosphate in this embodiment.

[0112] Example 11

[0113] This embodiment provides a method for preparing flaky iron phosphate. The only difference between the method for preparing flaky iron phosphate in this embodiment and that in Example 1 is that the molar ratio of oleyl alcohol to ferric chloride is 1:0.3.

[0114] This embodiment further provides a method for preparing lithium iron phosphate. The only difference between the method for preparing lithium iron phosphate in this embodiment and that in Example 1 is that the anhydrous iron phosphate in Example 1 is replaced by the anhydrous iron phosphate in this embodiment.

[0115] Comparative Example 1

[0116] This comparative example provides a method for preparing flaky iron phosphate, comprising the following steps:

[0117] 1 mol / L ferric chloride solution and 1 mol / L ammonium dihydrogen phosphate solution were stirred evenly to obtain a first solution; wherein, Fe 3+ :PO4 3- The molar ratio is 1:1;

[0118] The obtained first solution was transferred to a reactor and reacted at 100°C for 6 hours. The obtained product was filtered, and the obtained filter material was washed alternately with deionized water and ethanol until the upper centrifuged liquid was colorless and clear. The obtained precipitate was placed in a vacuum drying oven and dried at 60°C for 4 hours to obtain FePO4·xH2O;

[0119] The obtained FePO4·xH2O was placed in a muffle furnace, heated to 600°C at a rate of 4°C / min and kept at this temperature for 6 hours to obtain anhydrous iron phosphate.

[0120] This comparative example also provides a method for preparing lithium iron phosphate. The only difference between the method for preparing lithium iron phosphate in this comparative example and that in Example 1 is that the anhydrous iron phosphate in Example 1 is replaced by the anhydrous iron phosphate in this comparative example.

[0121] Test Case

[0122] Prepare a positive electrode slurry: add N-methylpyrrolidone to the lithium iron phosphate, acetylene black and polyvinylidene fluoride prepared above at a mass ratio of 90:5:5, mix well, and obtain a positive electrode slurry;

[0123] Preparation of a lithium-ion battery: The positive electrode slurry was evenly coated on aluminum foil, then dried at 100°C, roll-pressed, and cut to produce a 14mm circular positive electrode sheet. A metallic lithium sheet was used as the negative electrode. The positive electrode, polypropylene porous membrane, and negative electrode were assembled into a circular button cell. The electrolyte was LiPF6, dissolved at a concentration of 1 mol / L in a 1:1 (volume ratio) mixed solvent to form a non-aqueous electrolyte.

[0124] Charge and Discharge Performance Testing: The button-type lithium-ion batteries prepared above were tested at a constant temperature of 25°C. The specific charging conditions were: first, constant current charging with currents of 0.1C, 1C, 3C, and 5C, with a charge cutoff voltage of 4.5V, followed by a 2-minute constant voltage hold. Discharge conditions: constant current discharging with currents of 0.1C, 1C, 3C, and 5C, with a discharge cutoff voltage of 2.5V. The test results are shown in Table 1.

[0125] Table 1

[0126]

[0127] It can be seen from the experimental data in Table 1 that the lithium iron phosphate obtained by the flaky iron phosphate prepared by the method disclosed in the present invention has good charge and discharge performance as a positive electrode material for a battery.

[0128] From the comparison between Example 1 and Examples 4-7, it can be seen that when the mass ratio of oleyl alcohol to ethanol is 1:(0.8-1.2), the obtained battery has better electrochemical performance.

[0129] From the comparison between Example 1 and Examples 8-11, it can be seen that when the molar ratio of oleyl alcohol to trivalent iron salt is 1:(0.1-0.25), the electrochemical performance of the obtained battery is better.

[0130] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present disclosure rather than to limit the scope of protection of the present disclosure. Although the present disclosure has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present disclosure may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present disclosure.

Claims

1. A method for preparing flaky iron phosphate, characterized in that: The following steps are involved: Mixing oleyl alcohol and a lower alcohol having 1 to 4 carbon atoms uniformly, and sequentially adding a trivalent iron salt solution and a solution containing phosphate to obtain a first solution; The first solution is subjected to a hydrothermal reaction, and after the reaction is completed, the product is filtered, washed, dried, and calcined to obtain flaky iron phosphate; The mass ratio of the oleyl alcohol to the lower alcohol is 1:(0.7-1.3); the molar ratio of the oleyl alcohol to the trivalent iron salt is 1:(0.05-0.30); The molar ratio of the ferric salt to the phosphate is (0.95-1.1):1, wherein the molar amount of the ferric salt is calculated as iron ions; The temperature of the hydrothermal reaction is 80-180° C., and the time of the hydrothermal reaction is 4-18 hours.

2. The preparation method according to claim 1, wherein The molar ratio of the oleyl alcohol to the trivalent iron salt is 1:(0.1-0.25).

3. The preparation method according to claim 1, wherein The mass ratio of the oleyl alcohol to the lower alcohol is 1:(0.8-1.2).

4. The preparation method according to claim 1, wherein The trivalent iron salt is at least one of ferric chloride, ferric perchlorate and ferric nitrate.

5. The preparation method according to claim 1, wherein The phosphate radical is provided by at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

6. The preparation method according to claim 1, wherein The lower alcohol is at least one of ethanol, methanol and ethylene glycol.

7. The preparation method according to claim 1, wherein The calcination temperature is 450-750° C., and the calcination time is 2-8 hours.

8. The preparation method according to claim 1, wherein The drying temperature is 60-80° C., and the drying time is 4-10 hours.

9. The preparation method according to claim 1, wherein The phosphate-containing solution is added dropwise at a rate of 1 to 10 mL / min.

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