Lithium manganese iron phosphate precursor as well as preparation method and application thereof

Abstract

The invention discloses a lithium iron manganese phosphate precursor and a preparation method and application thereof, and belongs to the technical field of lithium iron manganese phosphate precursors, and the preparation method comprises the following steps: S1, mixing a lithium hydroxide solution, a phosphoric acid solution, a manganese sulfate solution and a ferrous sulfate solution to obtain a first solution; s2, carrying out a hydrothermal reaction on the first solution, adding an MOF mixture to obtain a second solution, and carrying out a secondary hydrothermal reaction on the second solution to obtain a lithium manganese iron phosphate precursor; the MOF mixture comprises an iron-based MOF, a zinc-based MOF and sodium poly (p-styrenesulfonate). According to the preparation method, the micron-sized lithium manganese iron phosphate precursor with relatively high tap density is prepared through the hydrothermal reaction.

Description

Technical Field

[0001] This invention belongs to the field of lithium manganese iron phosphate precursor technology, specifically lithium manganese iron phosphate precursor, its preparation method and application. Background Technology

[0002] Lithium manganese iron phosphate (LiMn) 1-x Fe x Lithium iron phosphate (LiFePO4) is a material formed by doping a certain proportion of manganese (Mn) onto lithium iron phosphate (LiFePO4). By doping with manganese, the electrical conductivity of the material can be improved, and the energy density and cycle life of the battery can be increased.

[0003] High-temperature solid-state synthesis is a traditional process widely used and produced due to its simplicity. However, the uneven distribution and uncontrollable morphology of manganese phosphate products obtained by this method directly affect the overall consistency and quality of the product. In contrast, liquid-phase synthesis yields products with better consistency and relatively higher quality, thus possessing a clear advantage. However, for example, lithium manganese iron phosphate prepared by hydrothermal reaction often has nanoscale particle sizes, resulting in low tap density and insufficient crystal density. Therefore, calcination is usually required to improve tap density and electrical properties. Summary of the Invention

[0004] This invention overcomes the above-mentioned technical problems and thus provides a lithium manganese iron phosphate precursor, its preparation method and application. This invention prepares a micron-sized lithium manganese iron phosphate precursor with high tap density through hydrothermal reaction.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0006] This invention discloses a method for preparing lithium manganese iron phosphate precursor, comprising the following steps: S1. The first solution is obtained by mixing lithium hydroxide solution, phosphoric acid solution, manganese sulfate solution and ferrous sulfate solution; S2. The first solution is subjected to a hydrothermal reaction, and then a MOF mixture is added to obtain a second solution. The second solution is subjected to a second hydrothermal reaction to obtain the lithium manganese iron phosphate precursor. The MOF mixture includes iron-based MOF, zinc-based MOF, and sodium poly(p-styrene sulfonate) (PSS).

[0007] In this invention, the addition of MOF material can effectively control the particle size of lithium manganese iron phosphate, and sodium poly(p-styrene sulfonate) is introduced in order to effectively combine lithium manganese iron phosphate and MOF material.

[0008] PSS is an anionic copolymer with good water solubility and is often used as a polyelectrolyte material. In this invention, it can improve the binding between lithium manganese iron phosphate and MOF material and form a MOF-coated lithium manganese iron phosphate precursor.

[0009] In S1, the concentration of the lithium hydroxide solution is 0.8~1.0 mol / L.

[0010] In S1, the concentration of concentrated phosphoric acid in the phosphoric acid solution is 4~7 V / V.

[0011] In S1, the concentration of the manganese sulfate solution is 0.4~0.5 mol / L.

[0012] In S1, the concentration of the ferrous sulfate solution is 0.4~0.5 mol / L.

[0013] In S1, the molar ratio of Fe to Mn in the first solution is x:1-x, where x = 0.4~0.6.

[0014] In S1, ascorbic acid in an amount equal to ferrous sulfate is also added to the first solution.

[0015] In S1, the solvent in the first solution is water and the co-solvent is polyethylene glycol.

[0016] In S1, the mixing process involves adding phosphoric acid solution to lithium hydroxide solution to bring the pH to 10.0-11.5, and then adding manganese sulfate solution and ferrous sulfate solution to bring the pH to 6.5-7.5.

[0017] In S1, the molar ratio of Fe to Mn in the first solution is x:1-x, where x = 0.4~0.6.

[0018] In S2, by mass, the MOF mixture comprises 10 parts iron-based MOF, 4 to 10 parts zinc-based MOF, and 0.6 to 1.5 parts sodium poly(p-styrene sulfonate). Preferably, the MOF mixture comprises, by weight, 10 parts iron-based MOF, 5-8 parts zinc-based MOF, and 0.7-1.2 parts sodium poly(p-styrene sulfonate).

[0019] In S2, the MOF mixture, by mass, consists of 10 parts iron-based MOF, 5-8 parts zinc-based MOF, 0.6-1.5 parts sodium poly(p-styrene sulfonate), and 50 parts water.

[0020] In this invention, the volume ratio of the first solution to the MOF mixture is 100:15~30, preferably 100:18~25.

[0021] In S2, the iron-based MOF is Fe-NH2-MIL-101 or MIL-101(Fe).

[0022] In S2, the pore volume of the iron-based MOF is 1.5~2.0 cm³. 3 / g, for example, 1.8cm3 / g. The iron-based MOF in this invention has a large pore volume, which helps to coat and promote the growth of lithium manganese iron phosphate, ultimately yielding the lithium manganese iron phosphate precursor.

[0023] In S2, the zinc-based MOF is ZIF-70 (Zn).

[0024] In further S2, the ligand of Fe-NH2-MIL-101 is 2-aminoterephthalic acid (CAS: 10312-55-7).

[0025] In further step S2, the ligand of MIL-101(Fe) is terephthalic acid (CAS: 100-21-0).

[0026] In further S2, the ligands of ZIF-70 are imidazole (CAS: 288-32-4) and 2-nitroimidazole (CAS: 527-73-1).

[0027] In S2, the average Mw of the sodium poly(p-styrene sulfonate) is 70,000 to 80,000.

[0028] In S2, the temperature of the hydrothermal reaction is 170~200℃, preferably 180℃.

[0029] In S2, the hydrothermal reaction time is 5-8 hours.

[0030] In S2, the temperature of the secondary hydrothermal reaction is 150~170℃, preferably 150~160℃. The hydrothermal reaction temperature should not be too high after adding the MOF mixture; lithium manganese iron phosphate precursors formed at lower temperatures have better crystal structures and higher tap densities.

[0031] In S2, the secondary hydrothermal reaction takes 5 to 8 hours.

[0032] In S2, both the hydrothermal reaction and the secondary hydrothermal reaction are carried out in a hydrothermal reactor.

[0033] In S2, the MOF mixture needs to be added after the first hydrothermal reaction is completed and then cooled.

[0034] In S2, after the secondary hydrothermal reaction is completed, solid-liquid separation, water washing, MOF stripping treatment, alcohol washing, and vacuum drying are required. The MOF stripping process involves ultrasonic treatment in an ionic liquid. The ionic liquid comprises 5 parts by weight of 1-octyl-3-methylimidazolium chloride and 3 to 5 parts of deionized water.

[0035] In further step S2, the alcohol washing is performed 2-3 times using an aqueous solution of 80-95% ethanol.

[0036] In further step S2, the ultrasound duration is 1-3 hours and the ultrasound power is 150-180W.

[0037] In step S2, the water washing is performed using deionized water 2-3 times.

[0038] In further step S2, the temperature of the vacuum drying is 120~170℃, and the pressure of the vacuum drying is 10~30Pa.

[0039] In further step S2, the vacuum drying time is 3-5 hours.

[0040] The present invention also provides a lithium manganese iron phosphate precursor prepared by the aforementioned method for preparing lithium manganese iron phosphate precursor.

[0041] In this invention, the D50 of the lithium manganese iron phosphate precursor is 300~800 nm, preferably 523~738 nm.

[0042] In this invention, the tap density of the lithium manganese iron phosphate precursor is 0.5~1.0 g / cm³. 3 The preferred value is 0.77~0.97 g / cm³. 3 .

[0043] In this invention, the specific surface area of ​​the lithium manganese iron phosphate precursor is <4 m². 2 / g, preferably 2.3~3.4 m 2 / g.

[0044] As mentioned above, lithium manganese iron phosphate precursors are used in lithium battery cathode materials.

[0045] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0046] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention prepares lithium manganese iron phosphate precursors via a hydrothermal reaction and uses MOF (Metal-Oxide-Factory) material for coating, effectively controlling the crystal form and density of lithium manganese iron phosphate. During this process, anionic copolymer PSS is also added to the MOF mixture. This polyelectrolyte polymer has good water solubility and can efficiently bind lithium manganese iron phosphate to the MOF.

[0047] Furthermore, PSS can effectively prevent the agglomeration of lithium manganese iron phosphate precursor, thereby obtaining a uniform, high-quality lithium manganese iron phosphate precursor. Therefore, this invention can obtain lithium manganese iron phosphate precursors with larger particle size and higher tap density after only a hydrothermal reaction, while ensuring good crystallinity. Attached Figure Description

[0048] Figure 1 The image shows a SEM image of the lithium manganese iron phosphate precursor prepared in Example 1.

[0049] Figure 2 The image shows the SEM image of the lithium manganese iron phosphate precursor prepared in Comparative Example 1.

[0050] Figure 3 The image shows the SEM image of the lithium manganese iron phosphate precursor prepared in Comparative Example 2.

[0051] Figure 4 The image shows the SEM image of the lithium manganese iron phosphate precursor prepared in Comparative Example 3. Detailed Implementation

[0052] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0053] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0054] The "range" disclosed in this invention is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for specific parameters, it is understood that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this invention, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein; "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer greater than or equal to 2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0055] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0056] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0057] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0058] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0059] Unless otherwise specified, the term "or" is inclusive in this invention. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0060] The raw material information used in the following examples and comparative examples is shown in Table 1.

[0061]

[0062] Preparation method of lithium manganese iron phosphate precursor Example 1 The method for preparing lithium manganese iron phosphate precursor in this embodiment includes the following steps: S1. Add 5 V / V % concentrated phosphoric acid aqueous solution to a 1.0 mol / L lithium hydroxide aqueous solution to adjust the pH to 11.0, then add 0.5 mol / L manganese sulfate aqueous solution and 0.5 mol / L ferrous sulfate aqueous solution to adjust the pH to 6.8 to obtain the first solution; the molar ratio of manganese sulfate to ferrous sulfate is 0.5:0.5; In this embodiment, PEG400, accounting for 25% of the total volume of the first solution, also needs to be added to the first solution. In this embodiment, ascorbic acid in an amount equal to ferrous sulfate is also added to the first solution.

[0063] S2. The first solution is subjected to a hydrothermal reaction at 180°C in a hydrothermal reactor. After the hydrothermal reaction is carried out for 7 hours, it is cooled, and then MOF mixture is added to obtain the second solution. The second solution is subjected to a second hydrothermal reaction at 160°C for 6 hours. In this embodiment, the MOF mixture comprises 10 parts by weight of iron-based MOF, 8 parts by weight of zinc-based MOF, 1.2 parts by weight of PSS and 50 parts by weight of water. The iron-based MOF is Fe-NH2-MIL-101, and the zinc-based MOF is ZIF-70(Zn). In this embodiment, the volume ratio of the first solution to the MOF mixture is 100:25; After the second hydrothermal reaction, solid and liquid were separated. The solid was washed three times with deionized water, then sonicated in ionic liquid for 3 hours for MOF stripping treatment. After washing three times with 95 V / V % ethanol, it was vacuum dried at 150℃ and 20~30Pa for 4 hours to obtain lithium manganese iron phosphate precursor. The ultrasound process uses an ultrasonic cell disruptor with an ultrasonic power of 150W; the ionic liquid consists of 5 parts by mass of 1-octyl-3-methylimidazolium chloride and 5 parts by mass of deionized water. SEM images of the lithium manganese iron phosphate precursor prepared in this embodiment are shown below. Figure 1 .

[0064] Example 2 The difference between this embodiment and Embodiment 1 is as follows: The iron-based MOF in this embodiment is MIL-101(Fe).

[0065] Example 3 The difference between this embodiment and Embodiment 1 is as follows: The MOF mixture described in this embodiment includes 10 parts iron-based MOF, 5 parts zinc-based MOF, 1.2 parts PSS and 50 parts water. The MOF mixture in this embodiment differs from that in Embodiment 1 only in the proportions; all other steps and parameters are the same as in Embodiment 1.

[0066] Example 4 The difference between this embodiment and Embodiment 1 is as follows: By mass, the MOF mixture in this embodiment includes 10 parts iron-based MOF, 7 parts zinc-based MOF, 1.2 parts PSS and 50 parts water. The MOF mixture in this embodiment and that in Example 1 are different only in the proportions; the other steps and parameters are the same as in Example 1.

[0067] Example 5 The difference between this embodiment and Embodiment 1 is as follows: In this embodiment, the temperature of the secondary hydrothermal reaction is 150°C. This embodiment differs from Embodiment 1 only in the temperature of the secondary hydrothermal reaction; all other steps and parameters are the same as in Embodiment 1.

[0068] Comparative Example 1 The difference between this comparative example and Example 1 is as follows: By mass, the MOF mixture described in this comparative example comprises 10 parts iron-based MOF, 8 parts zinc-based MOF, and 50 parts water. The MOF mixture in this comparative example differs from that in Example 1 only in the proportions. The MOF mixture in this comparative example does not contain PSS, and all other steps and parameters are the same as in Example 1.

[0069] SEM images of the lithium manganese iron phosphate precursor prepared in this comparative example are shown below. Figure 2 .

[0070] Comparative Example 2 The difference between this comparative example and Example 1 is as follows: The MOF mixture comprises 10 parts zinc-based MOF, 1.2 parts PSS and 50 parts water by mass. The only difference between the comparative example and the solution in Example 1 is the ratio. The MOF mixture in this comparative example does not contain iron-based MOF. All other steps and parameters are the same as in Example 1.

[0071] SEM images of the lithium manganese iron phosphate precursor prepared in this comparative example are shown below. Figure 3 .

[0072] Comparative Example 3 The difference between this comparative example and Example 1 is as follows: In this comparative example, the temperature of the secondary hydrothermal reaction is 180°C. This comparative example and Example 1 differ only in the secondary hydrothermal temperature; all other steps and parameters are the same as in Example 1.

[0073] SEM images of the lithium manganese iron phosphate precursor prepared in this comparative example are shown below. Figure 4 .

[0074] Example of effect The parameters of the lithium manganese iron phosphate precursors in the above embodiments and comparative examples are shown in Table 2.

[0075]

[0076] As can be seen from the data in Table 2 of the above comparative embodiments, combined with the accompanying drawings: In Comparative Example 1, the lack of PSS resulted in poor binding between MOF and lithium manganese iron phosphate, and the final lithium manganese iron phosphate precursor had a smaller particle size and lower uniformity than the lithium manganese iron phosphate precursor in Example 1.

[0077] In Comparative Example 2, since no iron-based MOF with a large specific volume and large BET surface was added, lithium manganese iron phosphate lost its crystallization support points during the hydrothermal process. Therefore, compared with Example 1, the lithium manganese iron phosphate precursor of Comparative Example 2 has a smaller particle size.

[0078] In Comparative Example 3, the temperature of the secondary hydrothermal reaction was higher, which may have made the MOF material more susceptible to damage during the hydrothermal process. Compared with Example 1, the lithium manganese iron phosphate precursor prepared in this comparative example exhibited agglomeration and performed poorly in subsequent electrical performance tests.

[0079] Application examples The lithium manganese iron phosphate precursors obtained in the above examples and comparative examples were used to prepare coin cells. The preparation steps are as follows: (1) The positive electrode slurry was prepared by adding N-methylpyrrolidone (NMP) solvent to adjust the viscosity to 4000~8000 mPa·s by mixing lithium manganese iron phosphate precursor, acetylene black and polyvinylidene fluoride in a mass ratio of 8:1:1. (2) The positive electrode slurry is evenly coated on one surface (perpendicular to the thickness direction) of the aluminum foil (positive electrode current collector) and dried. Then, it is rolled and sheared to obtain a positive electrode sheet containing a positive electrode film.

[0080] (3) Using lithium hexafluorophosphate-ethyl methyl carbonate as electrolyte and polypropylene as separator, a button cell is made by combining the prepared positive electrode and negative lithium electrode.

[0081] The fabricated button cells were tested using Blue Electric equipment, including the 1.0C discharge specific capacity (measured at 20℃) within a voltage range of 2.0V to 4.35V. The test results are shown in Table 3 below.

[0082]

[0083] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this invention. It should be understood that the above descriptions are merely specific embodiments of this invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing a lithium manganese iron phosphate precursor, characterized in that: The following steps are involved: S1. The lithium hydroxide solution, the phosphoric acid solution, the manganese sulfate solution and the ferrous sulfate solution are mixed to obtain a first solution; S2. The first solution is subjected to a hydrothermal reaction; the MOF mixture is then added to obtain a second solution, and the second solution is subjected to a secondary hydrothermal reaction to obtain a lithium manganese iron phosphate precursor; The MOF mixture includes iron-based MOF, zinc-based MOF and sodium poly(p-styrene sulfonate).

2. The method for preparing a lithium iron manganese phosphate precursor according to claim 1, characterized in that: The molar ratio of Fe:Mn in the first solution is x:1-x, wherein x=0.4-0.6; And / or, the MOF mixture comprises, by mass, 10 parts of iron-based MOF, 4 to 10 parts of zinc-based MOF, and 0.6 to 1.5 parts of sodium poly(p-styrene sulfonate); And / or, the volume ratio of the first solution: the MOF mixture is 100:15-30.

3. The method for preparing a lithium iron manganese phosphate precursor according to claim 1, characterized in that: The mixing process is to add phosphoric acid solution to lithium hydroxide solution to adjust the pH to 10.0-11.5, and then add manganese sulfate solution and ferrous sulfate solution to adjust the pH to 6.5-7.

5.

4. The method for preparing a lithium iron manganese phosphate precursor according to claim 1, characterized in that: Meet at least one of the following conditions ①~④: ① The iron-based MOF is Fe-NH2-MIL-101 or MIL-101; ② The zinc-based MOF is ZIF-70; ③The pore volume of the iron-based MOF is 1.5~2.0cm 3 / g; ④ The average Mw of the sodium poly(p-styrene sulfonate) is 70,000 to 80,000.

5. The method for preparing a lithium iron manganese phosphate precursor according to claim 1, characterized in that: After the secondary hydrothermal reaction is completed, solid-liquid separation, water washing, MOF stripping treatment, alcohol washing, and vacuum drying are required; The MOF exfoliation treatment is carried out by ultrasonic treatment in an ionic liquid; The ionic liquid includes 5 parts of 1-octyl-3-methylimidazolium chloride and 3 to 5 parts of deionized water by mass.

6. The method for preparing a lithium iron manganese phosphate precursor according to claim 5, characterized in that: Meet at least one of the following conditions ①~②: ① The alcohol washing adopts 80~95 V / V% ethanol aqueous solution to wash 2~3 times; ② The ultrasonic time is 1-3 hours, and the ultrasonic power is 150-180W.

7. The method for preparing a lithium iron manganese phosphate precursor according to claim 1, characterized in that: Meet at least one of the following conditions ①~④: ① The temperature of the hydrothermal reaction is 170-200°C; ② The hydrothermal reaction time is 5 to 8 hours; ③ The temperature of the secondary hydrothermal reaction is 150~170℃; ④ The time of the secondary hydrothermal reaction is 5 to 8 hours.

8. The lithium iron manganese phosphate precursor prepared by the method for preparing a lithium iron manganese phosphate precursor according to any one of claims 1 to 7.

9. The lithium iron manganese phosphate precursor according to claim 8, characterized in that Meet at least one of the following conditions ①~③: ① The D50 of the lithium manganese iron phosphate precursor is 300-800nm; ② The tap density of the lithium manganese iron phosphate precursor is 0.5~1.0g / cm 3 ; ③ The specific surface area of ​​the lithium manganese iron phosphate precursor is <4 m 2 / g.

10. Use of the lithium iron manganese phosphate precursor according to any one of claims 8 to 9 in positive electrode materials.

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