Iron phosphate as well as preparation method and application thereof
By preparing monoclinic anhydrous iron phosphate with specific grain size and lattice structure, the problem of insufficient electrochemical performance of iron phosphate cathode materials was solved, the cycle stability and rate performance were improved, and the production cost was reduced.
Patent Information
- Application Number
- CN202511588342.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-31
- Publication Date
- 2026-01-02
AI Technical Summary
The electrochemical performance of existing cathode materials made from iron phosphate, such as energy density, cycle life, and charge/discharge efficiency, needs further improvement.
By using monoclinic anhydrous iron phosphate with specific grain size and lattice structure, and by controlling the characteristic peak intensity ratio and half-peak width of iron phosphate XRD pattern, combined with appropriate iron-phosphorus ratio and oxidant treatment, high-density iron phosphate materials were prepared.
It improves the cycle stability and rate performance of iron phosphate cathode materials, making them suitable for high-rate charge and discharge scenarios and reducing production costs.
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Figure CN121247752A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium-ion battery technology, specifically to an iron phosphate compound, its preparation method, and its application. Background Technology
[0002] Lithium iron phosphate (LFP) boasts advantages such as high energy density, long cycle life, and good safety performance, making it the mainstream cathode material in the market. Among various routes for preparing LFP, the production process using iron phosphate as a precursor, compared to the ferrous oxalate and iron oxide processes, offers advantages such as simpler production, lower cost, superior electrochemical performance, and higher compaction density, and has become the mainstream LFP production process. Specifically, the iron method, as the current mainstream process for LFP preparation, is simpler and more environmentally friendly compared to the ammonia and sodium methods, and has thus become the dominant LFP production process. However, the electrochemical performance of cathode materials prepared from iron phosphate, including energy density, cycle life, and charge / discharge efficiency, still needs further improvement and optimization. Summary of the Invention
[0003] The purpose of this invention is to provide an iron phosphate cathode material that has high compaction density and excellent cycle stability and rate performance.
[0004] To achieve the above objectives, a first aspect of the present invention provides an iron phosphate, wherein the iron phosphate is a monoclinic anhydrous iron phosphate, and the XRD pattern of the iron phosphate includes a diffraction peak α1 corresponding to a diffraction angle 2θ of 15°-17°, wherein the grain size of the crystal plane corresponding to the diffraction peak α1 is 155-200 Å.
[0005] In some embodiments, the iron phosphate satisfies at least one of the following conditions: (1) The full width at half maximum (FWHM) of the diffraction peak α1 is 0.38°-0.6°; (2) The XRD pattern of the iron phosphate includes the diffraction peak β1 corresponding to the diffraction angle 2θ at 18°-19°; optionally, the half width of the diffraction peak β1 is 0.4°-0.6°. (3) The XRD pattern of the iron phosphate includes a diffraction peak γ1 corresponding to a diffraction angle 2θ of 19.5°-20.7°; optionally, the half width of the diffraction peak γ1 is 0.58°-1.0°; (4) The XRD pattern of the iron phosphate includes the diffraction peak δ1 corresponding to the diffraction angle 2θ at 21°-23°; optionally, the half width of the diffraction peak δ1 is 0.58°-0.95°; (5) The XRD pattern of the iron phosphate includes the diffraction peak ε1 corresponding to the diffraction angle 2θ between 24.5° and 26°; optionally, the half width of the diffraction peak ε1 is 0.39° to 0.49°.
[0006] In some embodiments, the iron phosphate satisfies at least one of the following conditions: a. The peak intensity ratio of the characteristic peaks of the iron phosphate satisfies: diffraction peak α1: diffraction peak γ1 = 5%-70%; b. The peak intensity ratio of the characteristic peaks of the iron phosphate satisfies: diffraction peak β1: diffraction peak γ1 = 7%-80%.
[0007] In some implementations, ferric phosphate satisfies at least one of the following conditions: ① The general chemical formula of the iron phosphate is Fe. x M y PO4, 0.96≤x≤1.00, 0≤y≤0.04; M is selected from one or more of Mn, V, Ti, Mg, Ca, Zn, Cu, Co, Ni, Al, Ga, In, La, Cr, and W; ② The molar ratio of iron to phosphorus in the iron phosphate, Fe / P, is 0.960-0.985:1; ③ The tap density TD of the iron phosphate is ≥ 0.5 g / cm³. 3 ; ④ The specific surface area of the iron phosphate is BET > 20m². 2 / g.
[0008] A second aspect of the present invention provides a method for preparing ferric phosphate, the method comprising: The iron source is mixed with phosphoric acid to carry out the first reaction, resulting in a ferrous dihydrogen phosphate solution, wherein the molar ratio of phosphorus to iron in the ferrous dihydrogen phosphate solution is 2.3-3.3:1. An oxidant is added to the ferrous dihydrogen phosphate solution to carry out a second reaction to obtain a slurry. The slurry is then aged to obtain ferric phosphate dihydrate. The temperature of the ferrous dihydrogen phosphate solution is 50-65℃. The iron phosphate dihydrate is heat-treated to obtain the iron phosphate; the heat treatment temperature is 200-700℃.
[0009] In some implementations, the method satisfies at least one of the following conditions: A. The iron source is an elemental iron source; optionally, the purity of the iron in the elemental iron source is >99.90 wt%. B. The concentration of the phosphoric acid is 15-40 wt%; C. The pH value of the ferrous dihydrogen phosphate solution is 1-2; D. The temperature of the first reaction is 65-95℃, and the time is 6-14h; E. Before adding the oxidant to the ferrous dihydrogen phosphate solution, the Fe ion concentration in the ferrous dihydrogen phosphate solution is adjusted to 27.9-67.1 g / L; F. The oxidant is selected from at least one of hydrogen peroxide, ozone-containing atmosphere, and oxygen-containing atmosphere; G. The aging time is 5-15 minutes; H. The aging time is 1-6 hours, and the aging temperature is 90-100℃; I. The heat treatment temperature is 200-700℃, and the time is 1-8h; J. The method further includes: aging and maturing the slurry, followed by sequential filtration, washing, and drying to obtain the ferric phosphate dihydrate.
[0010] In some implementations, the method satisfies at least one of the following conditions: 1-1. The method for preparing ferric phosphate further includes: mixing source M with the ferrous dihydrogen phosphate solution before adding the oxidant; or mixing the oxidant with source M and then adding the ferrous dihydrogen phosphate solution to carry out a second reaction to obtain a slurry; Optionally, the metal element in the M source includes at least one of Mn, V, Ti, Mg, Ca, Zn, Cu, Co, Ni, Al, Ga, In, La, Cr, and W; Optionally, the M source includes at least one of the following: hydrochloride, sulfate, nitrate, oxide, and hydrated oxide of a metal element; 1-2. The oxidizing agent is hydrogen peroxide; Optionally, the concentration of the hydrogen peroxide is 20-30 wt%. Optionally, the molar ratio of hydrogen peroxide to Fe in the ferrous dihydrogen phosphate solution is 0.5-0.7:1; Optionally, the hydrogen peroxide is added over a period of 30-80 minutes. 1-3. The oxidant is an ozone-containing atmosphere; Optionally, the ozone volume content in the ozone-containing atmosphere is 2-3%; the molar ratio of ozone in the ozone-containing atmosphere to Fe in the ferrous dihydrogen phosphate solution is 0.5-2:1; and the introduction rate of the ozone-containing atmosphere is 100-400 L / min. 1-4. The oxidant is an oxygen-containing atmosphere; Optionally, the volume content of oxygen in the oxygen-containing atmosphere is 98-100%; the molar ratio of oxygen in the oxygen-containing atmosphere to Fe in the ferrous dihydrogen phosphate solution is 0.25-4:1; and the introduction rate of the oxygen-containing atmosphere is 25-100 L / min.
[0011] A third aspect of the present invention provides a lithium iron phosphate cathode material, wherein the raw materials for the lithium iron phosphate cathode material include iron phosphate as described in the first aspect or iron phosphate prepared by the method for preparing iron phosphate as described in the second aspect.
[0012] A fourth aspect of the present invention provides a lithium-ion battery comprising the lithium iron phosphate cathode material as described in the third aspect.
[0013] A fifth aspect of the present invention provides an electrical device comprising a lithium-ion battery as described in the fourth aspect.
[0014] The iron phosphate provided by this invention has a high rate performance with a grain size within a specific range. The monoclinic anhydrous iron phosphate is more suitable for the Li insertion / extraction path. Compared with iron phosphate materials with smaller grain sizes (such as <100Å), this size avoids the diffusion path being too short due to "excessive nano-sizing" (which may increase the electronic conduction resistance due to too many grain boundaries), and accelerates the lithium-ion insertion and extraction more efficiently than large grain sizes. It is especially suitable for high-rate charge and discharge scenarios (such as the fast charging requirements of power batteries).
[0015] The iron phosphate provided by this invention forms a unique "oblique" lattice channel with lower symmetry than the hexagonal crystal system, but is more suitable for the insertion / extraction path of Li: the oblique lattice can buffer the volume change during ion migration, reduce stress accumulation, and improve cycle stability.
[0016] The method for preparing ferric phosphate provided by this invention can reduce the dehydration and crystallization temperature of anhydrous ferric phosphate, which is beneficial for controlling production costs. Attached Figure Description
[0017] Figure 1 This is the XRD pattern of anhydrous ferric phosphate in Example 2. Detailed Implementation
[0018] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.
[0019] It should be noted that, in all aspects of the present invention, the same components or terms in each aspect are described only once in one aspect and not repeatedly, and those skilled in the art should not understand this as a limitation of the present invention.
[0020] It should be noted that the "half-peak width", "peak intensity ratio" of the diffraction peak corresponding to a certain crystal plane in the XRD pattern described in this invention, as well as the "grain size" calculated from the data in the XRD pattern, are all well-known in the art.
[0021] It should be noted that the half-width at half-maximum (WHM) of a diffraction peak in an iron phosphate XRD pattern represents the width of the diffraction peak at half its peak height, expressed in degrees (°). Å It can be calculated using the Scherrer formula D=Kλ / (Fcosθ), where K is the Scherrer constant, λ is the wavelength of the copper target X-ray, F is the half-width of the diffraction peak corresponding to the crystal plane, and θ is the diffraction angle of the crystal plane.
[0022] For example, the grain size data of iron phosphate in Embodiment 1 of the present invention can be obtained by refining the XRD data obtained from the test using the Rigaku XRD analysis software package and then calculating it using the Scherrer formula; alternatively, it can be calculated directly from the XRD test data using the Scherrer formula. In the above Scherrer formula, K=0.943 is selected, and the X-ray wavelength λ is... 1.54Å The full width at half maximum (F) of diffraction peak α1 is converted to radians as [(F÷180)×π].
[0023] In this invention, angles are all converted to radians during calculation.
[0024] As previously stated, a first aspect of the present invention provides an iron phosphate, wherein the iron phosphate is a monoclinic anhydrous iron phosphate, and the XRD pattern of the iron phosphate includes a diffraction peak α1 corresponding to a diffraction angle 2θ of 15°-17°, wherein the grain size of the crystal plane corresponding to the diffraction peak α1 is 155-200 Å; for example, it can be any value between 155 Å, 160 Å, 170 Å, 180 Å, 190 Å, 200 Å or 155-200 Å; it can be any value between 160-200 Å.
[0025] The iron phosphate provided by this invention is monoclinic, which is more suitable for the Li insertion / extraction path, can buffer the volume change during ion migration, reduce stress accumulation, and improve cycle stability. The diffraction peak α1 of the iron phosphate of this invention corresponds to a crystallite size within a specific range, which avoids the excessively short diffusion path caused by "excessive nano-sizing" and the resulting increase in electron conduction resistance, while accelerating lithium ion insertion and extraction more efficiently than large-grain-size phosphate, resulting in higher rate performance.
[0026] In some embodiments, the full width at half maximum (FWHM) of the diffraction peak α1 is 0.38°–0.6°; for example, it can be any value between 0.38°, 0.4°, 0.42°, 0.44°, 0.46°, 0.48°, 0.5°, 0.52°, 0.54°, 0.56°, 0.58°, 0.6°, or 0.4°–0.6°.
[0027] In some embodiments, the XRD pattern of the iron phosphate includes a diffraction peak β1 corresponding to a diffraction angle 2θ of 18°–19°. Optionally, the full width at half maximum (FWHM) of the diffraction peak β1 is 0.4°–0.6°; for example, it can be any value between 0.4°, 0.42°, 0.44°, 0.46°, 0.48°, 0.5°, 0.52°, 0.54°, 0.56°, 0.58°, 0.6°, or 0.4°–0.6°.
[0028] In some embodiments, the XRD pattern of the iron phosphate includes a diffraction peak γ1 corresponding to a diffraction angle 2θ of 19.5°–20.7°. Optionally, the full width at half maximum (FWHM) of the diffraction peak γ1 is 0.58°–1.0°; for example, it can be any value between 0.58°, 0.6°, 0.65°, 0.7°, 0.75°, 0.8°, 0.85°, 0.9°, 0.95°, 1.0°, or 0.58°–1.0°.
[0029] In some embodiments, the XRD pattern of the iron phosphate includes a diffraction peak δ1 corresponding to a diffraction angle 2θ between 21° and 23°; optionally, the half-width at half maximum (FWHM) of the diffraction peak δ1 is 0.58°–0.95°; for example, it can be any value between 0.58°, 0.6°, 0.65°, 0.7°, 0.75°, 0.8°, 0.85°, 0.9°, 0.95° or 0.58°–0.95°.
[0030] In some embodiments, the XRD pattern of the iron phosphate includes a diffraction peak ε1 corresponding to a diffraction angle 2θ between 24.5° and 26°; optionally, the half-width at half maximum (FWHM) of the diffraction peak ε1 is 0.39° to 0.49°; for example, it can be any value between 0.39°, 0.4°, 0.41°, 0.42°, 0.43°, 0.44°, 0.45°, 0.46°, 0.47°, 0.48°, 0.49°, or 0.39° to 0.49°.
[0031] In some embodiments, the peak intensity ratio of the characteristic peaks of the iron phosphate satisfies: diffraction peak α1: diffraction peak γ1 = 5%-70%; for example, it can be any value between 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or 5%-70%.
[0032] In some embodiments, the peak intensity ratio of the characteristic peaks of the iron phosphate satisfies: diffraction peak β1: diffraction peak γ1 = 7%-80%; for example, it can be any value between 7%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 7%-80%.
[0033] In this invention, the peak intensity ratio of the characteristic peaks refers to the peak area ratio in the XRD pattern. The characteristic peaks of the XRD pattern of iron phosphate in this invention meet the aforementioned requirements, and the cycle stability of the prepared cathode material can be further improved.
[0034] In some embodiments, the general chemical formula of the iron phosphate is Fe. x M y PO4, 0.96≤x≤1.00, 0≤y≤0.04; M is selected from one or more of Mn, V, Ti, Mg, Ca, Zn, Cu, Co, Ni, Al, Ga, In, La, Cr, and W.
[0035] In some implementations, M is selected from one or more of Mn, Ti, Mg, Co, Ni, and Al.
[0036] In some embodiments, the molar ratio of iron to phosphorus in the iron phosphate (Fe / P) is 0.960-0.985:1; for example, it can be any ratio between 0.960:1, 0.965:1, 0.970:1, 0.975:1, 0.980:1, 0.985:1, or 0.960-0.985:1. The specific grain size combined with the appropriate Fe / P ratio of this invention effectively ensures product capacity and further optimizes rate performance; the precise controllability of the iron-phosphorus ratio not only effectively ensures that the specific capacity of the product meets the standard, but also facilitates further optimization of rate performance, providing a stable and reliable material basis for downstream applications.
[0037] In some embodiments, the tap density TD of the iron phosphate is ≥0.5 g / cm³. 3 For example, it can be ≥0.51 g / cm³. 3 ≥0.52 g / cm 3 ≥0.53 g / cm 3 ≥0.54 g / cm 3 ≥0.55 g / cm 3 ≥0.56 g / cm 3 ≥0.57 g / cm 3 ≥0.58 g / cm 3 ≥0.59 g / cm 3 ≥0.60 g / cm 3 The concentration can be selected as 0.5-0.6 g / cm³. 3 Any value between [a certain value]. The high tap density of iron phosphate provided by this invention can significantly improve the volumetric energy density of the battery. It also improves the processing performance of the electrode, resulting in better thickness uniformity and less susceptibility to cracking; optimizes the tap density of the electrode, shortening the ion and electron transport paths, which is beneficial for rate performance. The electrode structure is more compact, resulting in better mechanical strength.
[0038] In some embodiments, the specific surface area (BET) of the iron phosphate is greater than 20 m². 2 / g; for example, it can be >25 m 2 / g、>30 m 2 / g、>35 m 2 / g、>40 m 2 / g、>45 m 2 / g、>50 m 2 / g, or 25-50 m 2 Any value between / g, selectable from 35-50 m 2 / g.
[0039] A second aspect of the present invention provides a method for preparing ferric phosphate, the method comprising: An iron source is mixed with phosphoric acid to carry out a first reaction, yielding a ferrous dihydrogen phosphate solution. The molar ratio of phosphorus to iron in the ferrous dihydrogen phosphate solution is 2.3-3.3:1; for example, it can be 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3:1, 3.1:1, 3.2:1, 3.3:1, or any ratio between 2.3 and 3.3:1. Under these conditions, the ferrous dihydrogen phosphate solution remains stable, providing a stable and sufficient source of phosphorus and iron for subsequent reactions. An oxidant is added to the ferrous dihydrogen phosphate solution to carry out a second reaction to obtain a slurry. The slurry is then aged to obtain ferric phosphate dihydrate. The temperature of the ferrous dihydrogen phosphate solution is 50-65℃; for example, it can be any value between 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, or 60-65℃. Under these conditions, ferrous iron can be completely oxidized, resulting in complete precipitation. The ferric phosphate dihydrate is heat-treated to obtain the ferric phosphate; the heat treatment temperature is 200-700℃; for example, it can be any value between 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, or 200-700℃. Under this condition, free water and water of crystallization can be removed, increasing crystallinity and forming stable anhydrous ferric phosphate with a regular crystal structure.
[0040] In some embodiments, the iron source is an elemental iron source.
[0041] In some embodiments, the iron purity of the iron source is >99.90 wt%; for example, it can be >99.91 wt%, >99.92 wt%, >99.93 wt%, >99.94 wt%, >99.95 wt%, >99.96 wt%, >99.97 wt%, >99.98 wt%, or >99.99 wt%.
[0042] The present invention does not impose any particular limitation on the specific form of the iron element source. For example, it can be iron powder, iron rod, iron block, or any other arbitrary shape. The present invention will not be described in detail here, and those skilled in the art should not understand it as a limitation of the present invention.
[0043] In some embodiments, the concentration of phosphoric acid is 15-40 wt%; for example, it can be any value between 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, or 15-40 wt%.
[0044] In some embodiments, the pH of the ferrous dihydrogen phosphate solution is 1-2; for example, it can be any value between 1, 1.2, 1.4, 1.6, 1.8, 2, or 1-2. Under these conditions, the ferrous dihydrogen phosphate solution can remain stable, reducing the occurrence of hydrolysis reactions.
[0045] In some embodiments, the temperature of the first reaction is 65-95°C, for example, it can be any value between 65°C, 68°C, 70°C, 72°C, 75°C, 77°C, 80°C, 82°C, 85°C, 88°C, 90°C, 92°C, 95°C or 65-95°C; the time is 6-14h, for example, it can be any value between 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h or 6-14h.
[0046] In some embodiments, before adding the oxidant to the ferrous dihydrogen phosphate solution, the Fe ion concentration in the ferrous dihydrogen phosphate solution is further adjusted to 27.9-67.1 g / L; for example, it can be any value between 27.9 g / L, 30 g / L, 35 g / L, 40 g / L, 45 g / L, 50 g / L, 55 g / L, 60 g / L, 65 g / L, 67.1 g / L, or 27.9-67.1 g / L.
[0047] In some embodiments, the oxidant is selected from at least one of hydrogen peroxide, an ozone-containing atmosphere, and an oxygen-containing atmosphere.
[0048] In some implementations, the aging time is 5-15 minutes; for example, it can be any value between 5 minutes, 8 minutes, 10 minutes, 12 minutes, 14 minutes, 15 minutes, or 5-15 minutes.
[0049] In some embodiments, the aging time is 1-6 hours, for example, it can be any value between 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours or 1-6 hours; the aging temperature is 90-100°C, for example, it can be any value between 90°C, 91°C, 92°C, 93°C, 94°C, 95°C, 96°C, 97°C, 98°C, 99°C, 100°C or 90-100°C.
[0050] In some embodiments, the temperature of the heat treatment is 200-700°C, for example, it can be any value between 200°C, 300°C, 400°C, 500°C, 600°C, 700°C or 200-700°C; the time is 1-8h, for example, it can be any value between 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h or 1-8h.
[0051] In some embodiments, the method further includes: aging and maturing the slurry, followed by sequential filtration, washing, and drying to obtain the ferric phosphate dihydrate.
[0052] Optionally, the drying temperature is 80-160℃, for example, it can be 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃ or any value between 80-160℃; the time is 2-16h, for example, it can be 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h or any value between 2-16h.
[0053] In some embodiments, the method for preparing ferric phosphate further includes: mixing source M with the ferrous dihydrogen phosphate solution before adding the oxidant; or mixing the oxidant with source M and then adding the ferrous dihydrogen phosphate solution to perform a second reaction to obtain a slurry.
[0054] Optionally, the metal element in the M source includes at least one of Mn, V, Ti, Mg, Ca, Zn, Cu, Co, Ni, Al, Ga, In, La, Cr, and W.
[0055] Optionally, the M source includes at least one of the following: hydrochloride, sulfate, nitrate, oxide, and hydrated oxide of a metal element.
[0056] According to a specific embodiment 1 of the present invention: the oxidant is hydrogen peroxide; Optionally, the concentration of the hydrogen peroxide is 20-30 wt%; for example, it can be any value between 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, 30 wt%, or 20-30 wt%.
[0057] Optionally, the molar ratio of hydrogen peroxide to Fe in the ferrous dihydrogen phosphate solution is 0.5-0.7:1; for example, it can be any ratio between 0.5:1, 0.55:1, 0.6:1, 0.65:1, 0.7:1 or 0.5-0.7:1.
[0058] Optionally, the hydrogen peroxide feeding time is 30-80 minutes; for example, it can be any value between 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, 65 minutes, 70 minutes, 75 minutes, 80 minutes or 30-80 minutes.
[0059] According to a specific embodiment 2 of the present invention: the oxidant is an ozone-containing atmosphere; optionally, the volume content of ozone in the ozone-containing atmosphere is 2-3%; for example, it can be any value between 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0% or 2-3%.
[0060] Optionally, the molar ratio of ozone in the ozone-containing atmosphere to Fe in the ferrous dihydrogen phosphate solution is 0.5-2:1; for example, it can be any ratio between 0.5:1, 0.8:1, 1.0:1, 1.2:1, 1.5:1, 1.8:1, 2.0:1 or 0.5-2:1.
[0061] Optionally, the rate at which the ozone-containing atmosphere is introduced is 100-400 L / min; for example, it can be any value between 100 L / min, 150 L / min, 200 L / min, 250 L / min, 300 L / min, 350 L / min, 400 L / min or 100-400 L / min.
[0062] According to a specific embodiment 3 of the present invention: the oxidant is an oxygen-containing atmosphere.
[0063] Optionally, the volume content of oxygen in the oxygen-containing atmosphere is 98-100%; for example, it can be any value between 98.0%, 98.5%, 99.0%, 99.5%, 100%, or 98-100%.
[0064] Optionally, the molar ratio of oxygen in the oxygen-containing atmosphere to Fe in the ferrous dihydrogen phosphate solution is 0.25-4:1; for example, it can be any ratio between 0.25:1, 0.28:1, 0.3:1, 0.32:1, 0.34:1, 0.36:1, 0.38:1, 0.40:1 or 0.25-4:1.
[0065] Optionally, the oxygen-containing atmosphere is introduced at a rate of 25-100 L / min, for example, at any value between 25 L / min, 30 L / min, 35 L / min, 40 L / min, 45 L / min, 50 L / min, 55 L / min, 60 L / min, 65 L / min, 70 L / min, 75 L / min, 80 L / min, 85 L / min, 90 L / min, 95 L / min, 100 L / min, or 25-100 L / min.
[0066] The method for preparing anhydrous monoclinic iron phosphate provided by this invention produces a product with a grain size within a specific range and an iron-to-phosphorus ratio that can be precisely controlled.
[0067] A third aspect of the present invention provides a lithium iron phosphate cathode material, wherein the raw materials for the lithium iron phosphate cathode material include iron phosphate as described in the first aspect or iron phosphate prepared by the method for preparing iron phosphate as described in the second aspect.
[0068] A fourth aspect of the present invention provides a lithium-ion battery comprising the lithium iron phosphate cathode material as described in the third aspect.
[0069] A fifth aspect of the present invention provides an electrical device comprising a lithium-ion battery as described in the fourth aspect.
[0070] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, all raw materials used are commercially available products.
[0071] Example 1 1) Iron powder with a purity greater than 99.90% and dilute phosphoric acid with a concentration of 20wt% were reacted continuously at 90℃ for 8 hours to generate ferrous dihydrogen phosphate solution. The phosphorus-to-iron ratio of the ferrous dihydrogen phosphate solution was 2.6:1 and the pH was 1.75. 2) Adjust the iron concentration in the ferrous dihydrogen phosphate solution to 33.5 g / L by adding water, raise the temperature to 60°C, add 30 wt% hydrogen peroxide, and the molar ratio of hydrogen peroxide to Fe in the ferrous dihydrogen phosphate solution is 0.65:1. Add the hydrogen peroxide within 60 min, after the feeding is completed, age for 10 min, raise the temperature to 95°C, and keep it at that temperature for 4 h to obtain ferric phosphate dihydrate slurry; 3) The ferric phosphate dihydrate slurry is filtered, washed, and dried to obtain ferric phosphate dihydrate filter cake, wherein the conductivity at the washing endpoint is 1200 μs / cm and the drying temperature is 120℃.
[0072] 4) The above-mentioned dihydrate ferric phosphate was heat-treated at 550℃ for 6 hours, then pulverized and ground to obtain anhydrous ferric phosphate. The specific surface area of this anhydrous ferric phosphate was 44.64 m². 2 / g, anhydrous ferric phosphate is anhydrous monoclinic phase. The peak intensity ratio of diffraction peak α1 to diffraction peak γ1 is 15.9%; the peak intensity ratio of diffraction peak β1 to diffraction peak γ1 is 20.9%.
[0073] Example 2 1) Iron powder with a purity greater than 99.90% and dilute phosphoric acid with a concentration of 30wt% were continuously reacted at 80℃ for 8 hours to generate ferrous dihydrogen phosphate solution. The phosphorus-to-iron ratio of the ferrous dihydrogen phosphate solution was 2.7:1 and the pH was 1.65. 2) Adjust the iron concentration of the ferrous dihydrogen phosphate solution to 33.5 g / L by adding water, raise the temperature to 65°C, add 30 wt% hydrogen peroxide, and the molar ratio of hydrogen peroxide to Fe in the ferrous dihydrogen phosphate solution is 0.65:1. Add the hydrogen peroxide within 60 min, after the feeding is completed, age for 10 min, raise the temperature to 95°C, and keep it at that temperature for 4 h to obtain ferric phosphate dihydrate slurry; 3) The ferric phosphate dihydrate slurry is filtered, washed, and dried to obtain ferric phosphate dihydrate filter cake, wherein the conductivity at the washing endpoint is 1200 μs / cm and the drying temperature is 120℃.
[0074] 4) The above-mentioned dihydrate ferric phosphate was heat-treated at 550℃ for 6 hours, then pulverized and ground to obtain anhydrous ferric phosphate. The specific surface area of this anhydrous ferric phosphate was 42.83 m². 2 / g, XRD as Figure 1 As shown, XRD results indicate that anhydrous ferric phosphate is an anhydrous monoclinic phase. The peak intensity ratio of diffraction peak α1 to diffraction peak γ1 is 65.7%; the peak intensity ratio of diffraction peak β1 to diffraction peak γ1 is 69.7%.
[0075] Example 3 1) Iron powder with a purity greater than 99.90% and dilute phosphoric acid with a concentration of 40wt% were reacted continuously at 70℃ for 8 hours to generate ferrous dihydrogen phosphate solution. The phosphorus-to-iron ratio of the ferrous dihydrogen phosphate solution was 2.8:1, and the pH was 1.55. 2) Adjust the iron concentration of the ferrous dihydrogen phosphate solution to 33.5 g / L by adding water, raise the temperature to 65°C, add 30 wt% hydrogen peroxide, and the molar ratio of hydrogen peroxide to Fe in the ferrous dihydrogen phosphate solution is 0.65:1. Add the hydrogen peroxide within 60 min, after the feeding is completed, age for 10 min, raise the temperature to 95°C, and keep it at that temperature for 4 h to obtain ferric phosphate dihydrate slurry; 3) The ferric phosphate dihydrate slurry is filtered, washed, and dried to obtain ferric phosphate dihydrate filter cake, wherein the conductivity at the washing endpoint is 1200 μs / cm and the drying temperature is 120℃.
[0076] 4) The above-mentioned dihydrate ferric phosphate was heat-treated at 550℃ for 6 hours, then pulverized and ground to obtain anhydrous ferric phosphate. The specific surface area of this anhydrous ferric phosphate was 41.42 m². 2 / g, anhydrous ferric phosphate is a monoclinic phase. The peak intensity ratio of diffraction peak α1 to diffraction peak γ1 is 19.6%; the peak intensity ratio of diffraction peak β1 to diffraction peak γ1 is 23%.
[0077] Example 4 1) Iron powder with a purity greater than 99.90% and dilute phosphoric acid with a concentration of 30wt% were continuously reacted at 80℃ for 8 hours to generate ferrous dihydrogen phosphate solution. The phosphorus-to-iron ratio of the ferrous dihydrogen phosphate solution was 2.7:1 and the pH was 1.65. 2) Adjust the iron concentration of the ferrous dihydrogen phosphate solution to 50 g / L by adding water, raise the temperature to 65°C, add 30 wt% hydrogen peroxide, and the molar ratio of hydrogen peroxide to Fe in the ferrous dihydrogen phosphate solution is 0.65:1. Add the hydrogen peroxide within 60 min, after the feeding is completed, age for 10 min, raise the temperature to 95°C, and keep it at that temperature for 4 h to obtain ferric phosphate dihydrate slurry; 3) The ferric phosphate dihydrate slurry is filtered, washed, and dried to obtain ferric phosphate dihydrate filter cake, wherein the conductivity at the washing endpoint is 1200 μs / cm and the drying temperature is 120℃.
[0078] 4) The above-mentioned dihydrate ferric phosphate was heat-treated at 550℃ for 6 hours, then pulverized and ground to obtain anhydrous ferric phosphate. The specific surface area of this anhydrous ferric phosphate was 39.96 m². 2 / g, anhydrous ferric phosphate is a monoclinic phase. The peak intensity ratio of diffraction peak α1 to diffraction peak γ1 is 61.5%; the peak intensity ratio of diffraction peak β1 to diffraction peak γ1 is 68%.
[0079] Example 5 1) Iron powder with a purity greater than 99.90% and dilute phosphoric acid with a concentration of 30wt% were reacted continuously at 80℃ for 8 hours to generate ferrous dihydrogen phosphate solution. The phosphorus-to-iron ratio of the ferrous dihydrogen phosphate solution was 2.6:1 and the pH was 1.75. 2) Add 4000 ppm (relative to the theoretical mass of anhydrous ferric phosphate) of titanium oxysulfate (Ti content) to the ferrous dihydrogen phosphate solution, adjust the iron concentration of the ferrous dihydrogen phosphate solution to 50 g / L with water, raise the temperature to 65℃, add 30 wt% hydrogen peroxide, the molar ratio of hydrogen peroxide to Fe in the ferrous dihydrogen phosphate solution is 0.65:1, add hydrogen peroxide within 60 min, after the feeding is completed, age for 10 min, raise the temperature to 95℃, keep at the temperature for 4 h, and obtain ferric phosphate dihydrate slurry; 3) The ferric phosphate dihydrate slurry is filtered, washed, and dried to obtain ferric phosphate dihydrate filter cake, wherein the conductivity at the washing endpoint is 1200 μs / cm and the drying temperature is 120℃.
[0080] 4) The above-mentioned dihydrate ferric phosphate was heat-treated at 550℃ for 6 hours, then pulverized and ground to obtain anhydrous ferric phosphate. The specific surface area of this anhydrous ferric phosphate was 39.96 m². 2 / g, anhydrous ferric phosphate is a monoclinic phase.
[0081] Comparative Example 1 1) Iron powder with a purity greater than 99.90% and dilute phosphoric acid with a concentration of 30wt% were continuously reacted at 80℃ for 8 hours to generate ferrous dihydrogen phosphate solution. The phosphorus-to-iron ratio of the ferrous dihydrogen phosphate solution was 2.7:1 and the pH was 1.65. 2) Adjust the iron concentration of the ferrous dihydrogen phosphate solution to 50.0 g / L by adding water, raise the temperature to 70°C, add 30 wt% hydrogen peroxide, and the molar ratio of hydrogen peroxide to Fe in the ferrous dihydrogen phosphate solution is 0.65:1. Add the hydrogen peroxide within 60 min, after the feeding is completed, age for 10 min, raise the temperature to 95°C, and keep it at that temperature for 4 h to obtain ferric phosphate dihydrate slurry; 3) The ferric phosphate dihydrate slurry is filtered, washed, and dried to obtain ferric phosphate dihydrate filter cake, wherein the conductivity at the washing endpoint is 1200 μs / cm and the drying temperature is 120℃.
[0082] 4) The above-mentioned dihydrate ferric phosphate was heat-treated at 550℃ for 6 hours, then pulverized and ground to obtain anhydrous ferric phosphate. XRD results of the anhydrous ferric phosphate showed that it was an orthorhombic phase.
[0083] Comparative Example 2 1) Iron powder with a purity greater than 99.90% and dilute phosphoric acid with a concentration of 20wt% were reacted continuously at 90℃ for 8 hours to generate ferrous dihydrogen phosphate solution. The phosphorus-to-iron ratio of the ferrous dihydrogen phosphate solution was 2.6:1 and the pH was 1.75. 2) Adjust the iron concentration of the ferrous dihydrogen phosphate solution to 33.5 g / L by adding water, raise the temperature to 40°C, add 30 wt% hydrogen peroxide, and the molar ratio of hydrogen peroxide to Fe in the ferrous dihydrogen phosphate solution is 0.65:1. Add the hydrogen peroxide within 60 min, after the feeding is completed, age for 10 min, raise the temperature to 95°C, and keep it at that temperature for 4 h to obtain ferric phosphate dihydrate slurry; 3) The ferric phosphate dihydrate slurry is filtered, washed, and dried to obtain ferric phosphate dihydrate filter cake, wherein the conductivity at the washing endpoint is 1200 μs / cm and the drying temperature is 120℃.
[0084] 4) The above-mentioned dihydrate ferric phosphate was heat-treated at 550℃ for 6 hours, and then pulverized and ground to obtain anhydrous ferric phosphate, which is a monoclinic phase.
[0085] Comparative Example 3 1) Using iron powder with a purity greater than 99.90wt% and dilute phosphoric acid with a concentration of 20wt%, the reaction is carried out continuously at 90℃ for 8 hours to generate ferrous dihydrogen phosphate solution. The phosphorus-iron ratio of the ferrous dihydrogen phosphate solution is 2.6:1, and the pH is 1.75. 2) Adjust the iron concentration of the ferrous dihydrogen phosphate solution to 33.5 g / L by adding water, raise the temperature to 45°C, add 30 wt% hydrogen peroxide, and the molar ratio of hydrogen peroxide to Fe in the ferrous dihydrogen phosphate solution is 0.65:1. Add the hydrogen peroxide within 60 min, after the feeding is completed, age for 10 min, raise the temperature to 95°C, and keep it at that temperature for 4 h to obtain ferric phosphate dihydrate slurry; 3) The ferric phosphate dihydrate slurry is filtered, washed, and dried to obtain ferric phosphate dihydrate filter cake, wherein the conductivity at the washing endpoint is 1200 μs / cm and the drying temperature is 120℃.
[0086] 4) The above-mentioned dihydrate ferric phosphate was heat-treated at 550℃ for 6 hours, and then pulverized and ground to obtain anhydrous ferric phosphate, which is a monoclinic phase.
[0087] The anhydrous ferric phosphate prepared in the aforementioned examples and comparative examples was subjected to physicochemical data testing, specifically: 1. The test reference standard for tap density (TD) is GB / T5162-2021, which is the determination of tap density of metal powders. 2. Specific surface area (BET) is determined according to GB / T19587-2017, gas adsorption BET method, for solid substances. 3. XRD was measured using an X-ray diffractometer, specifically the Rigaku Ultima IV X-ray diffractometer from Japan. The test parameters were: Cu target + monochromator, 40 kV / 50 mA, scanning range of 10-60°, step size of 0.02°, and scanning rate of 5° / min.
[0088] The physicochemical data of anhydrous ferric phosphate are shown in Tables 1, 2 and 3.
[0089] Application Example 1 The examples and comparative examples were used to prepare lithium iron phosphate, and the specific operations are as follows: 1) Mix lithium carbonate, iron phosphate, titanium dioxide, glucose, PTT, and PEG in a Li / Fe molar ratio of 1:1, and add deionized water to prepare a slurry with a solid content of 40wt%.
[0090] 2) After mixing and stirring for 30 minutes, the slurry is ground in a sand mill. Grinding D 50 The size should be controlled within 2.4~2.5 μm.
[0091] 3) The slurry with qualified particle size after grinding is then introduced into a spray dryer by a peristaltic pump for drying and molding.
[0092] 4) Transfer the dried powder to a box furnace and sinter it under a nitrogen atmosphere. Control the heating rate to 2℃ / min, hold at 450℃ for 2 h, hold at 780℃ for 10 h, and then let it cool naturally to room temperature to obtain carbon-coated lithium iron phosphate cathode material.
[0093] The above-mentioned LFP / C cathode materials were prepared into cathode slurries with conductive carbon nanotubes, conductive carbon black, polyvinylidene fluoride (PVDF) binder, and N-methylpyrrolidone (N-methylpyrrolidone) solvent. The mass ratio of LFP / C cathode material to conductive carbon nanotubes, conductive carbon black, and PVDF binder was 91.5:1.5:1.0:6.0. The cathode slurry was coated onto aluminum foil, then vacuum baked, stamped, and finally LFP / C cathode sheets were formed. Using LFP / C as the cathode, lithium foil as the anode, and a 1 mol / L LiPF6 EC / DMC / EMC solution as the electrolyte, a button cell was assembled. The battery was then subjected to charge-discharge tests (charge-discharge window of 2.0V to 3.75V) and cycled 500 times at 1C to obtain the electrochemical performance of lithium iron phosphate, as shown in Table 3.
[0094] Table 1 Physicochemical data of anhydrous ferric phosphate
[0095] Table 2. Angles and half-peak widths of diffraction peaks of anhydrous iron phosphate
[0096] Table 3 Electrochemical performance
[0097] The results above show that the iron phosphate grain size provided by this invention, within a specific range, combined with the monoclinic phase characteristics, results in a cathode material with excellent rate capability and cycle stability.
[0098] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.
Claims
1. A type of iron phosphate, characterized in that, The iron phosphate is monoclinic anhydrous iron phosphate, and the XRD pattern of the iron phosphate includes a diffraction peak α1 corresponding to a diffraction angle 2θ between 15° and 17°. The grain size of the crystal plane corresponding to the diffraction peak α1 is 155-200 Å.
2. The iron phosphate according to claim 1, characterized in that, The iron phosphate satisfies at least one of the following conditions: (1) The full width at half maximum (FWHM) of the diffraction peak α1 is 0.38°-0.6°; (2) The XRD pattern of the iron phosphate includes the diffraction peak β1 corresponding to the diffraction angle 2θ at 18°-19°; optionally, the half width of the diffraction peak β1 is 0.4°-0.6°. (3) The XRD pattern of the iron phosphate includes a diffraction peak γ1 corresponding to a diffraction angle 2θ of 19.5°-20.7°; optionally, the half width of the diffraction peak γ1 is 0.58°-1.0°; (4) The XRD pattern of the iron phosphate includes the diffraction peak δ1 corresponding to the diffraction angle 2θ at 21°-23°; optionally, the half width of the diffraction peak δ1 is 0.58°-0.95°; (5) The XRD pattern of the iron phosphate includes the diffraction peak ε1 corresponding to the diffraction angle 2θ between 24.5° and 26°; optionally, the half width of the diffraction peak ε1 is 0.39° to 0.49°.
3. The iron phosphate according to claim 2, characterized in that, The iron phosphate satisfies at least one of the following conditions: a. The peak intensity ratio of the characteristic peaks of the iron phosphate satisfies: diffraction peak α1: diffraction peak γ1 = 5%-70%; b. The peak intensity ratio of the characteristic peaks of the iron phosphate satisfies: diffraction peak β1: diffraction peak γ1 = 7%-80%.
4. The ferric phosphate according to any one of claims 1-3, characterized in that, Ferric phosphate must meet at least one of the following conditions: ① The general chemical formula of the iron phosphate is Fe. x M y PO4, 0.96≤x≤1.00, 0≤y≤0.04; M is selected from one or more of Mn, V, Ti, Mg, Ca, Zn, Cu, Co, Ni, Al, Ga, In, La, Cr, and W; ② The molar ratio of iron to phosphorus in the iron phosphate, Fe / P, is 0.960-0.985:1; ③ The tap density TD of the iron phosphate is ≥ 0.5 g / cm³. 3 ; ④ The specific surface area of the iron phosphate is BET > 20m². 2 / g.
5. A method for preparing ferric phosphate, characterized in that, The method includes: The iron source is mixed with phosphoric acid to carry out the first reaction, resulting in a ferrous dihydrogen phosphate solution, wherein the molar ratio of phosphorus to iron in the ferrous dihydrogen phosphate solution is 2.3-3.3:
1. An oxidant is added to the ferrous dihydrogen phosphate solution to carry out a second reaction to obtain a slurry. The slurry is then aged to obtain ferric phosphate dihydrate. The temperature of the ferrous dihydrogen phosphate solution is 50-65℃. The iron phosphate dihydrate is heat-treated to obtain the iron phosphate; the heat treatment temperature is 200-700℃.
6. The method according to claim 5, characterized in that, The method satisfies at least one of the following conditions: A. The iron source is an elemental iron source; optionally, the purity of the iron in the elemental iron source is >99.90 wt%. B. The concentration of the phosphoric acid is 15-40 wt%; C. The pH value of the ferrous dihydrogen phosphate solution is 1-2; D. The temperature of the first reaction is 65-95℃, and the time is 6-14h; E. Before adding the oxidant to the ferrous dihydrogen phosphate solution, the Fe ion concentration in the ferrous dihydrogen phosphate solution is adjusted to 27.9-67.1 g / L; F. The oxidant is selected from at least one of hydrogen peroxide, ozone-containing atmosphere, and oxygen-containing atmosphere; G. The aging time is 5-15 minutes; H. The aging time is 1-6 hours, and the aging temperature is 90-100℃; I. The heat treatment temperature is 200-700℃, and the time is 1-8h; J. The method further includes: aging and maturing the slurry, followed by sequential filtration, washing, and drying to obtain the ferric phosphate dihydrate.
7. The method according to claim 6, characterized in that, The method satisfies at least one of the following conditions: 1-1. The method for preparing ferric phosphate further includes: mixing source M with the ferrous dihydrogen phosphate solution before adding the oxidant; or mixing the oxidant with source M and then adding the ferrous dihydrogen phosphate solution to carry out a second reaction to obtain a slurry; Optionally, the metal element in the M source includes at least one of Mn, V, Ti, Mg, Ca, Zn, Cu, Co, Ni, Al, Ga, In, La, Cr, and W; Optionally, the M source includes at least one of the following: hydrochloride, sulfate, nitrate, oxide, and hydrated oxide of a metal element; 1-2. The oxidizing agent is hydrogen peroxide; Optionally, the concentration of the hydrogen peroxide is 20-30 wt%. Optionally, the molar ratio of hydrogen peroxide to Fe in the ferrous dihydrogen phosphate solution is 0.5-0.7:1; Optionally, the hydrogen peroxide is added over a period of 30-80 minutes. 1-3. The oxidant is an ozone-containing atmosphere; Optionally, the ozone volume content in the ozone-containing atmosphere is 2-3%; the molar ratio of ozone in the ozone-containing atmosphere to Fe in the ferrous dihydrogen phosphate solution is 0.5-2:1; and the introduction rate of the ozone-containing atmosphere is 100-400 L / min. 1-4. The oxidant is an oxygen-containing atmosphere; Optionally, the volume content of oxygen in the oxygen-containing atmosphere is 98-100%; the molar ratio of oxygen in the oxygen-containing atmosphere to Fe in the ferrous dihydrogen phosphate solution is 0.25-4:1; and the introduction rate of the oxygen-containing atmosphere is 25-100 L / min.
8. A lithium iron phosphate cathode material, characterized in that, The raw materials for the lithium iron phosphate cathode material include iron phosphate as described in any one of claims 1-4 or iron phosphate prepared by the method described in any one of claims 5-7.
9. A lithium-ion battery, characterized in that, Including the lithium iron phosphate cathode material as described in claim 8.
10. An electrical-related device, characterized in that, Including the lithium-ion battery as described in claim 9.