Iron phosphate precursor and method for manufacturing the same

Abstract

The application belongs to the technical field of composite materials and relates to a kind of iron phosphate precursor, and the composition thereof is FePO4·L X Wherein, L is an organic matter containing a plurality of groups capable of being combined with iron ions, and X≤1; the application further discloses a preparation method of the precursor, which comprises mixing an iron source, a phosphorus source and an organic matter in water, stirring uniformly, reacting at a temperature of 50-100 DEG C, keeping warm for 0.5-1.5 hours, then filtering, washing and drying the product, and obtaining the product. The iron phosphate precursor is mixed with lithium salt to prepare an olivine-type lithium iron phosphate anode material by carbon thermal reduction method. The application utilizes the particularity of the molecular structure of the organic matter to form a microporous structure inside or on the surface of the iron phosphate, improves the diffusion capacity of lithium ions, and utilizes the residual carbon after pyrolysis to improve the electronic conductivity of the lithium iron phosphate, thereby obtaining a lithium iron phosphate anode material with excellent performance in all aspects.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, and relates to lithium battery materials, particularly to an iron phosphate precursor and its manufacturing method. Background Technology

[0002] Lithium iron phosphate (LFP) is a crucial material in lithium-ion batteries, and its composition and structure significantly influence its physical, chemical, and electrochemical properties. Researchers have attempted to modify and control the size, shape, and composition of LFP particles to obtain high-performance LFP cathode materials, such as through nano-sizing, doping, and coating. Despite these efforts, the desired results have not yet been achieved.

[0003] In the preparation of lithium iron phosphate (LFP), iron phosphate is an important precursor, and its microstructure and microstructure greatly affect the performance of LFP. Therefore, through continuous adjustment of the microstructure of iron phosphate in experiments, it was found that the micropores of iron phosphate alter the performance of LFP. Based on this finding, this invention discloses a pore-forming method for iron phosphate to improve the performance of LFP. Summary of the Invention

[0004] In view of the shortcomings of the prior art, one of the objectives of this invention is to provide an organic compound that can be combined with iron phosphate; another objective of this invention is to utilize the special molecular structure of organic compound to form a microporous structure in iron phosphate, thereby improving the diffusion capacity of lithium ions.

[0005] Technical solution

[0006] A ferric phosphate precursor with the composition FePO4·L X Where L is an organic compound containing multiple groups that can bind to iron ions, and X≤1.

[0007] Furthermore, the organic compound L containing multiple groups is bonded to iron phosphate by physical or chemical means, preferably by chemical means.

[0008] Furthermore, the organic compound L containing multiple groups capable of binding with iron ions is a polyhydroxy organic compound, such as citric acid, tannic acid, 3,6,8-trihydroxy-2-(3,4,5-trihydroxyphenyl)chromone-4-one, etc.; preferably 3,6,8-trihydroxy-2-(3,4,5-trihydroxyphenyl)chromone-4-one, with the structural formula […].

[0009]

[0010] Furthermore, the range of X is 0.1 ≤ X ≤ 0.5.

[0011] The second objective of this invention is to disclose a method for manufacturing the aforementioned iron phosphate precursor.

[0012] A method for manufacturing an iron phosphate precursor includes mixing an iron source, a phosphorus source, and an organic compound in water and stirring until homogeneous; reacting at 50–100°C for 0.5–1.5 h; then filtering, washing, and drying the product to obtain the iron phosphate precursor. The reaction equation is Fe… 3+ +PO4 3- +XL→FePO4·L x .

[0013] In a preferred embodiment of the present invention, the temperature is 85°C and the holding time is 1.0 h.

[0014] Furthermore, the iron source is a ferric salt or an oxidized elemental iron or ferrous salt to ferric iron, preferably ferric nitrate or ferric chloride.

[0015] Furthermore, the phosphorus source is ammonium dihydrogen phosphate.

[0016] Furthermore, the organic compound is a polyhydroxy organic compound, preferably 3,6,8-trihydroxy-2-(3,4,5-trihydroxyphenyl)chromene-4-one.

[0017] The third objective of this invention is to disclose a method for preparing porous iron phosphate, which involves heating the aforementioned iron phosphate precursor to 150–700°C for 8–12 hours and then allowing it to cool naturally; wherein the preferred heating temperature is 450–700°C, and the optimal temperature is 650°C.

[0018] The ferric phosphate precursor disclosed in this invention is a composition containing special organic compounds. While some organic compounds possess certain properties of binding with ferric phosphate and creating pores, substances containing specific functional groups are consistently found to exhibit superior pore-forming and pore-creating properties. These special organic compounds can bind with ferric phosphate, enabling it to form a porous structure during subsequent pyrolysis, and can also form SP on the surface of the ferric phosphate. 2 Hybridized, highly conductive, high-carbon composition.

[0019] This invention discloses a composition comprising a highly efficient and long-lasting formulation for preparing porous lithium iron phosphate. The organic compound L is a polyhydroxy organic compound, not excessively restricted, provided that it contains the organic component. In some embodiments, the organic compound is incorporated within or on the surface of the lithium iron phosphate, thereby improving the physical, chemical, and electrochemical properties of lithium iron phosphate.

[0020] This invention utilizes the combination of organic matter and ferric phosphate, followed by thermal decomposition to create pores. Specifically, it employs the molecular structure characteristics of polyhydroxy organic compounds to link organic matter to ferric phosphate in a composition.

[0021] Beneficial effects

[0022] This invention modifies the performance of lithium iron phosphate by adjusting the microstructure of iron phosphate. It provides a lithium iron phosphate cathode material that can combine with organic matter, utilizing the unique molecular structure of the organic matter to form a microporous structure inside or on the surface of the iron phosphate, thereby improving the diffusion capacity of lithium ions. Furthermore, it utilizes the residual carbon after pyrolysis to enhance the electronic conductivity of lithium iron phosphate, thus obtaining a lithium iron phosphate cathode material with excellent performance in all aspects. Attached Figure Description

[0023] Figure 1 X-ray diffraction pattern (XRD);

[0024] Figure 2 Raman spectrum;

[0025] Figure 3 Electrochemical test results;

[0026] Figure 4 SEM images of ferric phosphate before (A) and after (B) pore formation. Detailed Implementation

[0027] The present invention will be described in detail below with reference to embodiments, so that those skilled in the art can better understand the present invention, but the present invention is not limited to the following embodiments.

[0028] 1)FePO4·L x preparation

[0029] First, select molecules with a molecular weight and an organic content (X) between 0.1 and 0.9. Take 404 g of ferric nitrate and 15 g of 3,6,8-trihydroxy-2-(3,4,5-trihydroxyphenyl)chromone-4-one and add them to a three-necked flask with cooling water. After dissolving, add ammonium dihydrogen phosphate, heat to 80°C, and maintain the temperature for 0.5-1.5 hours. The resulting crystal structure is as follows. Figure 1 As shown in the figure. It can be seen from the figure that the prepared FePO4·L x Corresponding to standard PDF#72-0464, the main characteristic peak near 20° has a relatively wide half-width at half-maximum (HWHM), indicating poor crystallinity of the sample. The absence of impurity peaks indicates high product purity via XRD. Figure 2 The Raman spectrum shows that the peak at 1336.73 cm⁻¹ is an amorphous peak, and the peak at 1583.09 cm⁻¹ is... -1 The graphitization peak is significant. Compared with the graphite peak of general organic compounds, the addition of organic compound L significantly increases the amount of graphitized carbon in iron phosphate, indicating that this method is feasible and effective in increasing the amount of graphitized carbon.

[0030] 2)FePO4·L x Preparation of porous iron phosphate after pyrolysis

[0031] In the reactor described above, the product was removed, dried, placed in a quartz tube, and heated to decompose. The temperature was raised from room temperature to 700℃ and held for 10 hours. After being assembled into a battery, X was set to a value of 0.1-0.9. The electrochemical test results are as follows: Figure 3 As shown.

[0032] Figure 4 The SEM images show the morphology of iron phosphate before and after pore creation. As can be seen from the images, there were no pores before pore creation, and the morphology after pore creation is a porous structure.

[0033] Preparation method of porous lithium iron phosphate: Li2CO3 and FePO4·Lx were weighed in a ratio of 1.02:2 and added to a stirred tank for stirring at a speed of 450 r / min. After stirring evenly, the mixture was transferred to a rotary kiln for drying at a temperature of 700℃ for 3 hours, and then tested.

[0034] Olivine-type lithium iron phosphate cathode material was prepared by carbothermal reduction. Solid-phase wet ball milling was used when mixing the samples. The specific procedures are as follows:

[0035] ① Weigh Li₂CO₃ and FePO₄·Lx according to a stoichiometric ratio of 1.02:2, use deionized water as the dispersant / medium, and pulverize and mix them in a conventional planetary ball mill with a ball-to-material ratio of 20:1.

[0036] Ball milling at 400 r / min for 10 h;

[0037] ② Place the ball-milled mixture into a standard electric heating drying oven and set the temperature to 70℃.

[0038] Dry for 10 hours;

[0039] ③ Take out the dried sample, grind it and pass it through a 200-mesh sieve to obtain a precursor with a smaller particle size. Sinter it in a vacuum tube sintering furnace under an argon atmosphere. The sintering process is to hold it at 550℃ for 6 hours and at 750℃ for 18 hours.

[0040] ④ Cooling: Remove the sample at a temperature below 80℃ and perform appropriate characterization.

[0041] ⑤ It was made into a positive electrode material, and the battery was assembled in a glove box to test its electrochemical performance.

[0042] The cathode material is carbon-coated lithium iron phosphate, the conductive agent is acetylene black, the binder is polyvinylidene fluoride (PVDF), the solvent is N-methylpyrrolidone (NMP), the current collector is aluminum foil, and the anode is lithium metal sheet. The specific operation process is as follows:

[0043] 1. Separately bake and dry the sintered lithium iron phosphate, conductive agent, and binder to remove the adsorbed moisture;

[0044] 2. Weigh out lithium iron phosphate, acetylene black, and PVDF in a mass ratio of 8:1:1;

[0045] 3. In a weighing bottle, first dissolve PVDF in an appropriate amount of N-methylpyrrolidone, then add lithium iron phosphate, acetylene black and a stir bar, and then add NMP dropwise while stirring and dispersing until the mixture reaches a suitable viscosity. Continue stirring and dispersing for 4 hours.

[0046] 4. Apply a slurry of a certain viscosity onto aluminum foil using an automatic coating machine, and dry it in an oven at 70°C for 6 hours.

[0047] 5. The dried electrode sheets are punched into small round sheets with a diameter of 14mm using a punching machine, which are the positive electrode sheets;

[0048] 6. After completely removing moisture from the positive electrode sheet in a vacuum drying oven, transfer it to a glove box and follow the steps outlined for the negative electrode shell.

[0049] The battery is assembled in the following order: spring sheet—pad—lithium sheet—electrolyte—separator—electrolyte—positive electrode sheet—pad—positive electrode shell;

[0050] 7. After the assembled battery has been left to stand for 24 hours to allow the electrolyte to fully wet the separator, the electrochemical performance of the battery can be tested.

[0051] Example 1

[0052] A precursor of iron phosphate, FePO4·L X Where L is tannic acid, X ranges from 0.1 to 0.9, and the iron source is Fe(NO3)3.

[0053] Preparation of iron phosphate precursor FePO4·L X Method: Take 404g Fe(NO3)3 and 170.12g tannic acid and add them to a three-necked flask with cooling water. After they dissolve, add 115g ammonium dihydrogen phosphate, heat to 90℃, and keep warm for 1-2 hours.

[0054] Preparation method of porous lithium iron phosphate: Li2CO3 and FePO4·Lx are weighed sequentially according to a stoichiometric ratio of 1:2, and then added to a stirred tank and stirred at a speed of 550 r / min. After stirring evenly, the mixture is transferred to a rotary kiln for drying, and the temperature is maintained at 750℃ for 3 h.

[0055] Batteries are prepared according to the aforementioned method.

[0056] Example 2

[0057] A precursor of iron phosphate, FePO4·L X Where L is tannic acid, X ranges from 0.1 to 0.9, and FeCl3 is chosen as the iron source.

[0058] Preparation of iron phosphate precursor FePO4·L X The method involves adding 162g of FeCl3 and 170.12g of tannic acid to a three-necked flask containing cooling water. After they dissolve, 115g of ammonium dihydrogen phosphate is added, and the mixture is heated to 90℃ and kept warm for 1–2 hours.

[0059] Preparation method of porous lithium iron phosphate: Li2CO3 and FePO4·Lx are weighed sequentially according to a stoichiometric ratio of 1:2, and then added to a stirred tank and stirred at a speed of 550 r / min. After stirring evenly, the mixture is transferred to a rotary kiln for drying, and the temperature is maintained at 750℃ for 3 h.

[0060] Batteries are prepared according to the aforementioned method.

[0061] Example 3

[0062] A precursor of iron phosphate, FePO4·L X Where L is tannic acid, X ranges from 0.1 to 0.9, and FeSO4 is chosen as the iron source.

[0063] Iron phosphate precursor FePO4·L X The preparation method involves taking 278g of FeSO4 and 170.12g of tannic acid and adding them to a three-necked flask with cooling water. After they dissolve, an appropriate amount of hydrogen peroxide is added for oxidation. After complete oxidation, 115g of ammonium dihydrogen phosphate is added, and the mixture is heated to 90℃ and kept warm for 1-2 hours.

[0064] Preparation method of porous lithium iron phosphate: Weigh Li₂CO₃ and FePO₄·L⁻¹ sequentially according to a stoichiometric ratio of 1:2. X Weigh them sequentially, then add them to a mixing tank and stir at a speed of 550 r / min. After stirring evenly, transfer them to a rotary kiln for drying, maintaining a temperature of 750℃ for 3 hours.

[0065] Batteries are prepared according to the aforementioned method.

[0066] Example 4

[0067] A precursor of iron phosphate, FePO4·L X Where L is tannic acid, X ranges from 0.1 to 0.9, and the iron source is Fe(AC)2.

[0068] Iron phosphate precursor FePO4·L X The preparation method involves taking 174g of Fe(AC)2 and 170.12g of tannic acid and adding them to a three-necked flask with cooling water. After they dissolve, an appropriate amount of hydrogen peroxide is added for oxidation. After complete oxidation, 115g of ammonium dihydrogen phosphate is added, and the mixture is heated to 90℃ and kept warm for 1-2 hours.

[0069] Preparation method of porous lithium iron phosphate: Li2CO3 and FePO4 are weighed sequentially according to a stoichiometric ratio of 1:2, and then added to a stirred tank and stirred at a speed of 550 r / min. After stirring evenly, the mixture is transferred to a rotary kiln for drying at a temperature of 750℃ for 3 h.

[0070] Batteries are prepared according to the aforementioned method.

[0071] Example 5

[0072] A precursor of iron phosphate, FePO4·L X Where L is tannic acid and X ranges from 0.1 to 0.9. The iron source is Fe powder.

[0073] Iron phosphate precursor FePO4·L X The preparation method involves taking 56g of Fe powder and 170.12g of tannic acid and adding them to a three-necked flask with cooling water. After they dissolve, an appropriate amount of hydrogen peroxide is added for oxidation. After complete oxidation, 115g of ammonium dihydrogen phosphate is added, and the mixture is heated to 90℃ and kept warm for 1-2 hours.

[0074] Preparation method of porous lithium iron phosphate: Li2CO3 and FePO4 are weighed sequentially according to a stoichiometric ratio of 1:2, and then added to a stirred tank and stirred at a speed of 550 r / min. After stirring evenly, the mixture is transferred to a rotary kiln for drying at a temperature of 750℃ for 3 h.

[0075] Batteries are prepared according to the aforementioned method.

[0076] Examples 6-10

[0077] A precursor of iron phosphate, FePO4·L X Where L is citric acid, X ranges from 0.1 to 0.9, and the iron source is Fe(NO3)3.

[0078] Iron phosphate precursor FePO4·L X The preparation method involves taking 404g of Fe(NO3)3 and 19.2g of citric acid and adding them to a three-necked flask with cooling water. After they dissolve, 115g of ammonium dihydrogen phosphate is added, and the mixture is heated to Z℃ (Z = 70, 80, 90, 100℃) and kept at that temperature for 1-2 hours.

[0079] Preparation method of porous lithium iron phosphate: Li2CO3 and FePO4 are weighed sequentially according to a stoichiometric ratio of 1:2, and then added to a stirred tank and stirred at a speed of 550 r / min. After stirring evenly, the mixture is transferred to a rotary kiln for drying at a temperature of 750℃ for 3 h.

[0080] Batteries are prepared according to the aforementioned method.

[0081] Examples 11-14

[0082] A precursor of iron phosphate, FePO4·L X Where L is citric acid, X ranges from 0.1 to 0.9, and the iron source is Fe(NO3)3.

[0083] Iron phosphate precursor FePO4·L X The preparation method involves adding 404g of Fe(NO3)3 and 19.2g of citric acid to a three-necked flask with cooling water. After they dissolve, 115g of ammonium dihydrogen phosphate is added, and the mixture is heated to 80℃ and kept at that temperature for Y h (Y = 0.2~1, 0.5~1.5, 0.8~1.8, 1~2h).

[0084] Preparation method of porous lithium iron phosphate: Li2CO3 and FePO4 are weighed sequentially according to a stoichiometric ratio of 1:2, and then added to a stirred tank and stirred at a speed of 550 r / min. After stirring evenly, the mixture is transferred to a rotary kiln for drying at a temperature of 750℃ for 3 h.

[0085] The battery was prepared according to the aforementioned method.

[0086] Examples 15-18

[0087] A precursor of iron phosphate, FePO4·L X Where L is citric acid, X ranges from 0.1 to 0.9, and the iron source is Fe(NO3)3.

[0088] Iron phosphate precursor FePO4·L X The preparation method involves taking 404g of Fe(NO3)3 and 19.2g of citric acid and adding them to a three-necked flask with cooling water. After they dissolve, 115g of ammonium dihydrogen phosphate is added, and the mixture is heated to 80℃ and kept at that temperature for 0.5 to 1.5 hours.

[0089] Preparation method of porous lithium iron phosphate: Li₂CO₃ and FePO₄ are weighed sequentially according to stoichiometric ratios A:B (A:B = 1:2, 1.01:2, 1.02:2, 1.03:2), and then added to a stirred tank and stirred at a speed of 550 r / min. After stirring until homogeneous, the mixture is transferred to a rotary kiln for drying at 750℃ for 3 h. Batteries are then prepared according to the aforementioned method.

[0090] Examples 19-23

[0091] A precursor of iron phosphate, FePO4·L XWhere L is citric acid, X ranges from 0.1 to 0.9, and the iron source is Fe(NO3)3.

[0092] Iron phosphate precursor FePO4·L X The preparation method involves taking 404g of Fe(NO3)3 and 19.2g of citric acid and adding them to a three-necked flask with cooling water. After they dissolve, 115g of ammonium dihydrogen phosphate is added, and the mixture is heated to 80℃ and kept at that temperature for 0.5 to 1.5 hours.

[0093] Preparation method of porous lithium iron phosphate: Li2CO3 and FePO4 are weighed sequentially according to a stoichiometric ratio of 1.02:2, and then added to a stirred tank for stirring at a rate of Cr / min (C = 350, 450, 550, 650). After stirring evenly, the mixture is transferred to a rotary kiln for drying at a temperature of 750℃ for 7 hours.

[0094] The battery was prepared according to the aforementioned method.

[0095] Examples 24-27

[0096] A precursor of iron phosphate, FePO4·L X Where L is 3,6,8-trihydroxy-2-(3,4,5-trihydroxyphenyl)chromene-4-one, X ranges from 0.1 to 0.9, and the iron source is Fe(NO3)3.

[0097] The preparation method of the iron phosphate precursor FePO4 involves taking 404g of Fe(NO3)3 and 31.8g of 3,6,8-trihydroxy-2-(3,4,5-trihydroxyphenyl)chromene-4-one and adding them to a three-necked flask with cooling water. After they dissolve, 115g of ammonium dihydrogen phosphate is added, and the mixture is heated to 80℃ and kept at that temperature for 0.5 to 1.5 hours.

[0098] Preparation method of porous lithium iron phosphate: Li2CO3 and FePO4 are weighed sequentially according to a stoichiometric ratio of 1.02:2, and then added to a stirred tank and stirred at a speed of 450 r / min. After stirring evenly, the mixture is transferred to a rotary kiln for drying, and the temperature is maintained at D℃ (D=650, 700, 750, 800) for 7 h.

[0099] The battery was prepared according to the aforementioned method.

[0100] Examples 28-30

[0101] A precursor of iron phosphate, FePO4·L XWhere L is an organic compound containing multiple groups (L = citric acid, tannic acid, 3,6,8-trihydroxy-2-(3,4,5-trihydroxyphenyl)chromene-4-one), and the value of X ranges from 0.1 to 0.9.

[0102] Iron phosphate precursor FePO4·L X The preparation method involves taking 404g of Fe(NO3)3 and different mass amounts of L and adding them to a three-necked flask with cooling water. After they dissolve, 115g of ammonium dihydrogen phosphate is added, and the mixture is heated to 80℃ and kept at that temperature for 0.5 to 1.5 hours.

[0103] Preparation method of porous lithium iron phosphate: Li2CO3 and FePO4 are weighed sequentially according to a stoichiometric ratio of 1.02:2, and then added to a stirred tank and stirred at a speed of 450 r / min. After stirring evenly, the mixture is transferred to a rotary kiln for drying at a temperature of 700℃ for 3 h.

[0104] The battery was prepared according to the aforementioned method.

[0105] Examples 31-38

[0106] In the following embodiments, the sintering process and battery preparation method are the same, the difference being FePO4·L X In the structural formula (L = 3,6,8-trihydroxy-2-(3,4,5-trihydroxyphenyl)chromen-4-one), different values ​​of X are obtained by drying FePO4·L with different X values. x The components were combined with lithium carbonate to form a battery, and then the experiment was carried out. The test included electrochemical performance and the graphitization, amorphous carbon and their ratio. The graphitization and amorphous carbon were calculated based on the Raman spectral peak area.

[0107] This set of examples includes a base sample of the composition, and a series of examples identical to the base composition, except that they are each assigned a different value for X.

[0108] Examples 31-38 are summarized in Table 1 below:

[0109] Table 1 Summary of Test Results for Examples 31-38

[0110]

[0111] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. An iron phosphate precursor having a composition of FePO4-L X characterized in that: L is an organic compound containing multi-groups capable of combining with iron ions, X≤1, and the L is 3,6,8-trihydroxy-2-(3,4,5-trihydroxyphenyl)chromen-4-one, with a structural formula of 。 2. The iron phosphate precursor of claim 1, wherein: The value range of X is 0.1≤X≤0.

5.

3. A method of preparing the iron phosphate precursor according to claim 1 or 2, characterized in that: The method comprises the following steps: mixing an iron source, a phosphorus source and an organic matter in water, stirring uniformly, reaction temperature 50-100 DEG C, keeping warm 0.5-1.5h, then filtering, washing and drying the product, and the iron phosphate precursor can be obtained, the reaction equation is Fe 3+ +PO4 3- +XL→FePO4·L x , the organic matter L is 3,6,8-trihydroxy-2-(3,4,5-trihydroxyphenyl) chromen-4-ketone, and X≤1.

4. The method of claim 3, wherein: The temperature is 85℃, and the incubation time is 1.0h.

5. The method of claim 3, wherein: The iron source is a trivalent iron salt.

6. The method of claim 5, wherein: The trivalent iron salt is ferric nitrate or ferric chloride.

7. The method for preparing the iron phosphate precursor according to claim 3, characterized in that: The phosphorus source is ammonium dihydrogen phosphate.

8. A method of preparing porous iron phosphate, characterized by: The iron phosphate precursor of claim 1 or 2 is heated to 150-700℃ for 8-12h, and the product is obtained after natural cooling.

9. The method of claim 8, wherein: The temperature is 450-700℃.

10. The method of claim 8, wherein: The temperature is 650℃.

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