Lithium manganese iron phosphate precursor and preparation method and application thereof

Abstract

The invention discloses a lithium iron manganese phosphate precursor and a preparation method and application thereof, belonging to the technical field of lithium iron manganese phosphate precursors, and comprising 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. subjecting the first solution to a hydrothermal reaction, adding a MOF mixture to obtain a second solution, subjecting the second solution to a secondary hydrothermal reaction to obtain a lithium iron manganese phosphate precursor; the MOF mixture comprises an iron-based MOF, a zinc-based MOF and sodium poly(p-styrene sulfonate). The invention prepares a micron-sized lithium iron manganese phosphate precursor with a high tap density by a hydrothermal reaction.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium iron manganese phosphate precursors, and in particular relates to a lithium iron manganese phosphate precursor and a preparation method and application thereof. Background Art

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

[0003] As a traditional synthesis process, the high-temperature solid-phase method is widely used and produced because of its simple process. However, the manganese phosphate products obtained by this method have problems such as uneven distribution and uncontrollable morphology, which directly affect the overall consistency and quality of the product. In contrast, the liquid phase method has obvious advantages because of its good product consistency and relatively high quality. However, for example, the particle size of lithium manganese iron phosphate prepared by hydrothermal reaction is mostly nanometer-sized, resulting in a low tap density and an insufficiently dense crystal structure, so calcination is usually required to improve the tap density and electrical properties. Summary of the invention

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

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

[0006] The present invention discloses a method for preparing a lithium iron manganese phosphate precursor, comprising the following steps:

[0007] 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;

[0008] S2. The first solution is subjected to a hydrothermal reaction, and then the MOF mixture is 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;

[0009] The MOF mixture includes an iron-based MOF, a zinc-based MOF and poly (sodium p-styrene sulfonate) (PSS).

[0010] In the present invention, the addition of MOF material can effectively control the particle size of lithium manganese iron phosphate, and in order to effectively combine lithium manganese iron phosphate and MOF material, sodium poly(p-styrene sulfonate) is introduced.

[0011] PSS is an anionic copolymer with good water solubility and is often used as a polyelectrolyte material. In the present invention, it can improve the binding property of lithium manganese iron phosphate and MOF material and form a MOF-coated lithium manganese iron phosphate precursor.

[0012] In S1, the concentration of the lithium hydroxide solution is 0.8-1.0 mol / L.

[0013] In S1, the concentration of concentrated phosphoric acid in the phosphoric acid solution is 4-7 V / V%.

[0014] In S1, the concentration of the manganese sulfate solution is 0.4-0.5 mol / L.

[0015] In S1, the concentration of the ferrous sulfate solution is 0.4-0.5 mol / L.

[0016] In S1, the molar ratio of Fe:Mn in the first solution is x:1-x, wherein x=0.4~0.6.

[0017] In S1, ascorbic acid in an amount equimolar to ferrous sulfate is added to the first solution.

[0018] In S1, the solvent in the first solution is water and the co-solvent is polyethylene glycol.

[0019] In S1, 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.

[0020] In S1, the molar ratio of Fe:Mn in the first solution is x:1-x, wherein x=0.4~0.6.

[0021] In S2, the MOF mixture includes 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) by mass;

[0022] Preferably, the MOF mixture comprises 10 parts of iron-based MOF, 5 to 8 parts of zinc-based MOF, and 0.7 to 1.2 parts of sodium poly(p-styrene sulfonate) by mass.

[0023] In S2, the MOF mixture consists of 10 parts of iron-based MOF, 5 to 8 parts of zinc-based MOF, 0.6 to 1.5 parts of sodium poly(p-styrene sulfonate) and 50 parts of water, in parts by mass.

[0024] In the present invention, the volume ratio of the first solution to the MOF mixture is 100:15-30, preferably 100:18-25.

[0025] In S2, the iron-based MOF is Fe-NH2-MIL-101 or MIL-101(Fe).

[0026] In S2, the pore volume of the iron-based MOF is 1.5~2.0cm 3 / g, for example 1.8cm 3 / g. The iron-based MOF in the present invention has a large pore volume, which is helpful for coating and promoting the growth of lithium iron manganese phosphate, and finally obtaining a lithium iron manganese phosphate precursor.

[0027] In S2, the zinc-based MOF is ZIF-70 (Zn).

[0028] Further in S2, the ligand of the Fe-NH2-MIL-101 is 2-aminoterephthalic acid (CAS: 10312-55-7).

[0029] Further in S2, the ligand of the MIL-101(Fe) is terephthalic acid (CAS: 100-21-0).

[0030] Further in S2, the ligands of the ZIF-70 are imidazole (CAS: 288-32-4) and 2-nitroimidazole (CAS: 527-73-1).

[0031] In S2, the average Mw of the sodium poly(p-styrene sulfonate) is 70,000 to 80,000.

[0032] In S2, the temperature of the hydrothermal reaction is 170-200°C, preferably 180°C.

[0033] In S2, the hydrothermal reaction time is 5 to 8 hours.

[0034] In S2, the temperature of the secondary hydrothermal reaction is 150-170° C., preferably 150-160° C. Among them, the hydrothermal reaction temperature after adding the MOF mixture should not be too high. The lithium manganese iron phosphate precursor formed at a lower temperature has a better crystal form and a larger tap density.

[0035] In S2, the secondary hydrothermal reaction time is 5 to 8 hours.

[0036] In S2, the hydrothermal reaction and the secondary hydrothermal reaction both use a hydrothermal reaction kettle.

[0037] In S2, after the first hydrothermal reaction is completed, the MOF mixture is added after cooling.

[0038] In S2, after the secondary hydrothermal reaction is completed, solid-liquid separation, water washing, MOF stripping treatment, alcohol washing, and vacuum drying are required;

[0039] The MOF exfoliation treatment is carried out by ultrasonic treatment in an ionic liquid;

[0040] The ionic liquid includes 5 parts of 1-octyl-3-methylimidazolium chloride and 3 to 5 parts of deionized water by mass.

[0041] Further in S2, the alcohol washing is performed with an aqueous solution of 80-95 V / V % ethanol for 2-3 times.

[0042] Further in S2, the ultrasonic time is 1-3 hours, and the ultrasonic power is 150-180W.

[0043] Further in S2, the washing is performed with deionized water for 2 to 3 times.

[0044] Further in S2, the vacuum drying temperature is 120-170°C, and the vacuum drying pressure is 10-30Pa.

[0045] Further in S2, the vacuum drying time is 3 to 5 hours.

[0046] The present invention also provides a lithium iron manganese phosphate precursor prepared by the above-mentioned method for preparing the lithium iron manganese phosphate precursor.

[0047] In the present invention, the D50 of the lithium manganese iron phosphate precursor is 300-800 nm, preferably 523-738 nm.

[0048] In the present invention, the tap density of the lithium manganese iron phosphate precursor is 0.5-1.0 g / cm 3 , preferably 0.77~0.97 g / cm 3 .

[0049] In the present invention, the specific surface area of ​​the lithium manganese iron phosphate precursor is less than 4 m 2 / g, preferably 2.3~3.4 m 2 / g.

[0050] For example, the aforementioned application of lithium iron manganese phosphate precursor in lithium battery positive electrode materials.

[0051] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] The present invention prepares the lithium iron manganese phosphate precursor by hydrothermal reaction and uses MOF material for coating, thereby effectively controlling the crystal form and density of the lithium iron manganese phosphate. In this process, an anionic copolymer PSS is also added to the MOF mixture. This polyelectrolyte polymer has good water solubility and can efficiently combine the lithium iron manganese phosphate with MOF.

[0054] In addition, PSS can also effectively prevent the agglomeration of the lithium iron manganese phosphate precursor, thereby obtaining a uniform high-quality lithium iron manganese phosphate precursor. Therefore, the present invention can obtain a lithium iron manganese phosphate precursor with a larger particle size and a higher tap density only after the hydrothermal reaction, while ensuring a good crystallinity. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 This is the SEM image of the lithium manganese iron phosphate precursor prepared in Example 1.

[0056] Figure 2 This is the SEM image of the lithium manganese iron phosphate precursor prepared in Comparative Example 1.

[0057] Figure 3 This is the SEM image of the lithium manganese iron phosphate precursor prepared in Comparative Example 2.

[0058] Figure 4 This is the SEM image of the lithium manganese iron phosphate precursor prepared in Comparative Example 3. DETAILED DESCRIPTION

[0059] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and carefully in combination with preferred embodiments below, but the protection scope of the present invention is not limited to the following specific embodiments.

[0060] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0061] The "range" disclosed in the present invention is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and 80-110 is listed for a specific parameter, it is understood that the range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present invention, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" represents that all real numbers between "0-5" have been fully listed herein, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0062] If not otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form a new technical solution.

[0063] Unless otherwise specified, all technical features and optional technical features of the present invention can be combined with each other to form a new technical solution.

[0064] If not 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), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0065] If there is no special explanation, the "include" and "comprising" mentioned in the present invention represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0066] If not specifically stated, in the present invention, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": 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).

[0067] The raw material information used in the following examples and comparative examples is shown in Table 1.

[0068]

[0069]

Preparation method of lithium manganese iron phosphate precursor

[0070] Example 1

[0071] The method for preparing the lithium manganese iron phosphate precursor of this embodiment comprises the following steps:

[0072] S1. To a 1.0 mol / L aqueous lithium hydroxide solution, a 5 V / V% concentrated phosphoric acid solution was added to a pH of 11.0, and then a 0.5 mol / L aqueous solution of manganese sulfate and a 0.5 mol / L aqueous solution of ferrous sulfate were added to a pH of 6.8 to obtain a first solution; the molar ratio of manganese sulfate to ferrous sulfate was 0.5:0.5;

[0073] In this embodiment, PEG400 accounting for 25% of the total volume of the first solution needs to be added to the first solution;

[0074] In this embodiment, ascorbic acid in an amount equimolar to ferrous sulfate is also added to the first solution.

[0075] S2. The first solution was subjected to a hydrothermal reaction in a hydrothermal reactor at 180°C for 7 hours and then cooled, and then the MOF mixture was added to obtain a second solution, and the second solution was subjected to a secondary hydrothermal reaction at 160°C for 6 hours;

[0076] In this embodiment, the MOF mixture includes 10 parts of iron-based MOF, 8 parts of zinc-based MOF, 1.2 parts of PSS and 50 parts of water, by mass;

[0077] The iron-based MOF is Fe-NH2-MIL-101, and the zinc-based MOF is ZIF-70(Zn);

[0078] In this embodiment, the volume ratio of the first solution:MOF mixture is 100:25;

[0079] After the secondary hydrothermal reaction, the solid was separated by solid-liquid separation, and the solid was washed with deionized water for 3 times, and then subjected to MOF exfoliation treatment in an ionic liquid for 3 h. After washing with 95 V / V % ethanol for 3 times, the solid was vacuum dried at 150 ° C and 20-30 Pa for 4 h to obtain a lithium manganese iron phosphate precursor.

[0080] The ultrasound was performed using an ultrasonic cell crusher with an ultrasonic power of 150W; the ionic liquid consisted of 5 parts of 1-octyl-3-methylimidazolium chloride and 5 parts of deionized water by weight;

[0081] The SEM image of the lithium manganese iron phosphate precursor prepared in this example is shown in Figure 1 .

[0082] Example 2

[0083] The difference between this embodiment and embodiment 1 is that:

[0084] The iron-based MOF of this embodiment is MIL-101(Fe).

[0085] Example 3

[0086] The difference between this embodiment and embodiment 1 is that:

[0087] The MOF mixture described in this embodiment includes 10 parts of iron-based MOF, 5 parts of zinc-based MOF, 1.2 parts of PSS and 50 parts of water. The MOF mixture of this embodiment and Example 1 is different only in the ratio, and the other steps and parameters are the same as Example 1.

[0088] Example 4

[0089] The difference between this embodiment and embodiment 1 is that:

[0090] In parts by mass, the MOF mixture described in this embodiment includes 10 parts of iron-based MOF, 7 parts of zinc-based MOF, 1.2 parts of PSS and 50 parts of water. The MOF mixture of this embodiment and Example 1 differs only in the ratio, and the other steps and parameters are the same as Example 1.

[0091] Example 5

[0092] The difference between this embodiment and embodiment 1 is that:

[0093] The temperature of the secondary hydrothermal reaction in this embodiment is 150° C. The only difference between this embodiment and embodiment 1 is the temperature of the secondary hydrothermal reaction. The other steps and parameters are the same as those in embodiment 1.

[0094] Comparative Example 1

[0095] The difference between this comparative example and Example 1 is:

[0096] In parts by mass, the MOF mixture in this comparative example includes 10 parts of iron-based MOF, 8 parts of zinc-based MOF and 50 parts of water. The MOF mixture in this comparative example differs from that in Example 1 only in the proportion. The MOF mixture in this comparative example does not contain PSS. Other steps and parameters are the same as those in Example 1.

[0097] The SEM image of the lithium manganese iron phosphate precursor prepared in this comparative example is shown in Figure 2 .

[0098] Comparative Example 2

[0099] The difference between this comparative example and Example 1 is:

[0100] In parts by mass, the MOF mixture includes 10 parts of zinc-based MOF, 1.2 parts of PSS and 50 parts of water. The solution of this comparative example and Example 1 differs only in the ratio. The MOF mixture of this comparative example does not contain iron-based MOF. Other steps and parameters are the same as those of Example 1.

[0101] The SEM image of the lithium manganese iron phosphate precursor prepared in this comparative example is shown in Figure 3 .

[0102] Comparative Example 3

[0103] The difference between this comparative example and Example 1 is:

[0104] The temperature of the secondary hydrothermal reaction in this comparative example is 180° C. This comparative example is different from Example 1 only in the secondary hydrothermal temperature, and the other steps and parameters are the same as Example 1.

[0105] The SEM image of the lithium manganese iron phosphate precursor prepared in this comparative example is shown in Figure 4 .

[0106] Effect example

[0107] The parameters of the lithium manganese iron phosphate precursors of the above examples and comparative examples are shown in Table 2.

[0108]

[0109] The data in Table 2 of the comparative examples of the above embodiments can be seen in combination with the accompanying drawings:

[0110] In Comparative Example 1, since PSS is not added, the binding property between MOF and lithium iron manganese phosphate is poor, and the particle size of the lithium iron manganese phosphate precursor finally obtained is smaller and the uniformity is not as good as that of the lithium iron manganese phosphate precursor in Example 1.

[0111] In Comparative Example 2, since no iron-based MOF with a large specific volume and a large BET surface is added, the lithium manganese iron phosphate loses its crystallization support point during the hydrothermal process. Therefore, compared with Example 1, the particle size of the lithium manganese iron phosphate precursor in Comparative Example 2 is smaller.

[0112] In Comparative Example 3, the temperature of the secondary hydrothermal reaction is relatively high, which may cause the MOF material to be more easily destroyed during the hydrothermal process. Compared with Example 1, the lithium manganese iron phosphate precursor prepared in this comparative example will agglomerate, and its performance is poor in subsequent electrical performance tests.

[0113] Application Examples

[0114] The lithium manganese iron phosphate precursors prepared in the above examples and comparative examples are prepared into button-type half-cells, and the preparation steps are as follows:

[0115] (1) Adding N-methylpyrrolidone (NMP) as solvent to lithium manganese iron phosphate precursor: acetylene black: polyvinylidene fluoride in a mass ratio of 8:1:1 to adjust the viscosity to 4000-8000 mPa·s to prepare a positive electrode slurry;

[0116] (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, and then rolled and sheared to obtain a positive electrode sheet containing a positive electrode film layer.

[0117] (3) Using lithium hexafluorophosphate-ethyl methyl carbonate as the electrolyte and polypropylene as the isolation membrane, the prepared positive electrode sheet and negative lithium sheet are combined to make a button half-cell.

[0118] The button half-cell was tested in a voltage range of 2.0V to 4.35V using a Blue Electric device, including a 1.0C discharge capacity (measured at 20°C). The test results are shown in Table 3 below.

[0119]

[0120] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods. The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present 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); The temperature of the secondary hydrothermal reaction is 150-170°C.

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 ①~③: ① The temperature of the hydrothermal reaction is 170-200°C; ② The hydrothermal reaction time is 5 to 8 hours; ③The 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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