Lithium manganese iron phosphate positive electrode material synthesized by Joule heat flash and preparation method of lithium manganese iron phosphate positive electrode material

Abstract

The invention discloses a Joule heat flash synthesized lithium manganese iron phosphate positive electrode material and a preparation method thereof, and belongs to the technical field of lithium ion battery positive electrode materials, the preparation method comprises the following steps: S1, adding an iron source, a manganese source and a phosphorus source into deionized water, and uniformly stirring at room temperature to obtain mixed slurry; s2, carrying out mechanical sanding on the mixed slurry prepared in S1, then carrying out spray drying, and then heating in a vacuum box in an inert gas atmosphere in a Joule thermal shock instrument; s3, adding a lithium source, a carbon source, an additive and the iron manganese phosphate precursor into deionized water to be mixed and stirred to form a primary mixed phase, then carrying out secondary mechanical sanding, carrying out spray drying on the sanded slurry, then rapidly heating in a Joule thermal shock instrument in an inert gas atmosphere, and then carrying out air jet pulverization and sieving to obtain the lithium-manganese-iron phosphate composite material. And obtaining the lithium manganese iron phosphate positive electrode material synthesized by Joule heat flash. The lithium manganese iron phosphate positive electrode material prepared by the invention has excellent discharge stability and conductivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials for lithium-ion batteries, and particularly relates to a lithium iron manganese phosphate cathode material synthesized by Joule heat flash and a preparation method thereof. Background Art

[0002] Lithium iron phosphate cathode materials have been widely used due to their high theoretical specific capacity (170 mAh / g), stable structure, and low cost. However, due to the needs of social development, its low voltage platform (3.4 V) can no longer meet the current society's demand for high-density energy batteries. Therefore, there is an urgent need to find a material that can both improve the energy density of lithium iron phosphate and have good safety performance. Among them, lithium iron manganese phosphate, as a cathode material for batteries that has been widely studied in recent years, combines the advantages of lithium iron phosphate and lithium manganese phosphate, has a higher voltage platform (3.4 V - 4.1 V), and increases the energy density by 10 - 21% based on the lithium iron phosphate material. At the same time, lithium iron manganese phosphate also inherits the excellent thermal stability and safety of lithium iron phosphate, with a low risk of thermal runaway. Therefore, it can be applied on a large scale in power batteries and energy storage fields, which can better improve people's quality of life.

[0003] Currently, the synthesis method of lithium iron manganese phosphate mainly follows the production process of lithium iron phosphate, mixing iron source, manganese source, lithium source, phosphorus source, carbon source, additives, etc. through mechanical stirring, and then obtaining the final material through steps such as sanding, spray drying, and solid-phase sintering. However, on the one hand, in the preparation process of this method, the distribution of manganese and iron elements is uneven, resulting in the inability to synthesize a completely homogeneous manganese-iron melt, which will cause a series of defects such as poor cycle performance and poor discharge voltage consistency of the lithium iron manganese phosphate material; on the other hand, due to the excessive growth of manganese in the thermal reaction stage, if the heat preservation time is too long, it is not conducive to the stability of the material structure. In addition, due to the poor intrinsic conductivity of the lithium iron manganese phosphate material, its electrochemical performance is relatively low. The stability of the material structure and excellent electrical properties have become the current mainstream research directions, and many researchers have begun to focus on synthesizing manganese iron phosphate as a precursor for lithium iron manganese phosphate. Coprecipitation is a relatively common method for synthesizing manganese iron phosphate. The manganese iron phosphate synthesized by this method has a uniform element distribution and good consistency. However, due to the large difference in Ksp between iron and manganese elements, it is very difficult to synthesize manganese iron phosphate in a conventional liquid-phase reaction system, and the tap density of the material also lags behind the current requirements; at the same time, a large amount of wastewater is discharged during the production process of this process, resulting in great pressure on environmental protection, and it is difficult to achieve large-scale mass production.

[0004] Therefore, it has become an urgent problem to study a new synthesis process to solve the above problems. Based on the above process, the present invention changes the preparation strategy of manganese iron phosphate, synthesizes lithium manganese iron phosphate material by a two-step method, uses Joule heat to achieve rapid thermal shock, generates defective carbon carriers to anchor lithium manganese iron phosphate nanoparticles, significantly improving the electrical conductivity of the material. Compared with other manganese iron phosphate synthesis processes, a large amount of waste emissions is avoided. Summary of the Invention

[0005] (1) Technical Problems to be Solved

[0006] In view of the deficiencies of the prior art, the present invention provides a lithium manganese iron phosphate cathode material synthesized by Joule heat flash and a preparation method thereof. The lithium manganese iron phosphate material is synthesized by a two-step method. Joule heat is used to achieve rapid thermal shock, generating defective carbon carriers to anchor lithium manganese iron phosphate nanoparticles, significantly improving the electrical conductivity of the material. Compared with other manganese iron phosphate synthesis processes, a large amount of waste emissions is avoided.

[0007] (2) Technical Solutions

[0008] To achieve the above objectives, the present invention is realized through the following technical solutions:

[0009] A preparation method of a lithium manganese iron phosphate cathode material synthesized by Joule heat flash includes the following steps:

[0010] S1: Add an iron source, a manganese source, and a phosphorus source to 600 ml of deionized water, stir evenly at room temperature to obtain a mixed slurry, where the molar ratio of (Fe + Mn):P is 0.96 - 1.02, the molar ratio of Fe:Mn is (2 - 4):(8 - 6), the stirring speed is 600 - 1500 rpm, and the stirring time is 0.5 - 1 h;

[0011] S2: Mechanically grind the mixed slurry prepared in S1, then perform spray drying, and then heat it to 600 °C in a Joule heat shock instrument in an inert gas atmosphere in a vacuum box and hold for 120 s to obtain a manganese iron phosphate precursor;

[0012] S3: Add a lithium source, a carbon source, an additive, and the manganese iron phosphate precursor prepared in step S2 to deionized water to form a preliminary mixed phase by mixing and stirring, then perform secondary mechanical grinding. After the ground slurry is spray-dried, it is rapidly heated to 760 °C in a Joule heat shock instrument in an inert gas atmosphere, and then subjected to air flow pulverization and sieving to obtain a lithium manganese iron phosphate cathode material synthesized by Joule heat flash.

[0013] Further, the chemical general formula of the manganese iron phosphate is Mn x Fe 1-x PO4, and the chemical general formula of the lithium manganese iron phosphate is LiMnx Fe 1-x PO4, where 0.5 < x < 0.8.

[0014] Furthermore, the iron source in S1 is one or more of iron nitrate, iron(III) oxide, iron phosphate, iron chloride, ferrous oxalate, ferrous chloride, ferrous sulfate; the manganese source is one or more of manganese dioxide, manganese(III) oxide, manganese(II,III) oxide, manganese sulfate, manganese acetate, manganese phosphate, manganese nitrate, manganese carbonate; and the phosphorus source is one or more of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate.

[0015] Furthermore, the mechanical sanding speed in both S2 and S3 is 1000 - 2500 rpm, and the sanding time is 1 - 3 h. The mechanical sanding includes primary sanding and secondary sanding. The primary sanding is rough grinding with a time of 0.5 - 1 h, and the slurry particle size is controlled at 600 - 800 nm. The secondary sanding is fine grinding with a time of 1 - 2 h, and the slurry particle size is controlled at 300 - 400 nm.

[0016] Furthermore, the lithium source in S3 is any one of lithium carbonate, lithium hydroxide, lithium acetate, lithium dihydrogen phosphate, and the carbon source is one or more of glucose, polyethylene glycol, sucrose, β - cyclodextrin, polyacrylonitrile.

[0017] Furthermore, the additive in S3 is one or more of magnesium sulfate, magnesium oxide, titanium dioxide, tetrabutyl titanate, niobium pentoxide.

[0018] Furthermore, the additive is 0 - 0.5 wt% of the mass of the lithium iron manganese phosphate precursor prepared in S2.

[0019] Furthermore, the mass of the lithium source in S3 is 25 - 26% of the mass of the lithium iron manganese phosphate, the mass ratio of Li:M in S3 is 1.035:1, and the residual carbon content in the lithium iron manganese phosphate cathode material synthesized by Joule - heat flash synthesis is 1.5 - 2.5 wt% of the carbon mass in the carbon source.

[0020] A lithium iron manganese phosphate cathode material synthesized by Joule - heat flash synthesis, which is obtained by the preparation method of the above - mentioned lithium iron manganese phosphate cathode material synthesized by Joule - heat flash synthesis.

[0021] After adopting the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The preparation method of the present invention prepares the lithium iron manganese phosphate cathode material by a two - step method. In the first step, a nanoscale lithium iron manganese phosphate precursor, i.e., lithium iron manganese phosphate, is synthesized. The preparation process is simple and easy to control, the distribution of manganese and iron elements is uniform, the ratio is accurate, and no redundant impurities are generated. Then, using this as a raw material, the second step is carried out to synthesize lithium iron manganese phosphate, so that the cathode material has excellent electrochemical performance and physical and chemical indexes.

[0023] 2. The rapid thermal shock method of Joule heating according to the present invention can achieve rapid temperature rise in an extremely short time, effectively prevent the migration of metal elements and the aggregation of nanoparticles, and retain the element concentration gradient structure to a great extent, improving the consistency of the discharge voltage of the material. More importantly, the defective carbon carriers generated under the condition of rapid temperature rise can greatly improve the electrical conductivity of the material, compensating for the disadvantage of the low intrinsic conductivity of lithium iron phosphate manganese.

[0024] 3. The synthesis process of the present invention can effectively reduce the production input cost and cycle, and avoid a large amount of wastewater discharged by the traditional liquid-phase method for synthesizing lithium iron phosphate manganese. Description of the Drawings

[0025] Figure 1 XRD pattern of the lithium iron phosphate manganese precursor;

[0026] Figure 2 XRD pattern of the lithium iron phosphate manganese cathode material;

[0027] Figure 3 Raman spectrum comparison diagram of the samples obtained by different heating methods in Example and Comparative Example 1;

[0028] Figure 4 SEM image of the lithium iron phosphate manganese precursor prepared in the example;

[0029] Figure 5 SEM image of the lithium iron phosphate manganese cathode material prepared in the example. Detailed Description of the Invention

[0030] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way restrictive of the present invention and its application or use. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts belong to the scope of protection of the present invention.

[0031] Example 1

[0032] A preparation method of a lithium iron phosphate manganese cathode material by Joule heat flash synthesis, comprising the following steps:

[0033] S1: Add iron phosphate, manganese carbonate, and ammonium dihydrogen phosphate to 600 ml of deionized water according to a mass ratio of 1:1.14:1.03, and stir at room temperature until the slurry is completely dissolved to obtain a mixed slurry, where the molar ratio of (Fe + Mn):P is 0.97, the stirring speed is 600 rpm, and the stirring time is 0.5 h;

[0034] S2: Transfer the mixed slurry prepared in S1 to a horizontal sand mill and grind it at a speed of 1500 rpm for 1 h. After the particle size of the slurry reaches D50 < 1 μm, perform spray drying to obtain spray-dried powder. Then place the powder obtained by spray drying in a vacuum chamber

[0035] and set the heating rate of the joule heat shock instrument to 300 °C / 100 ms, the target temperature to 600 °C, and maintain it for 120 s to obtain a manganese iron phosphate precursor (Fe 0.4 Mn 0.6 PO4), and its XRD pattern is as Figure 1 shown. The contents of iron, manganese, and phosphorus in the manganese iron phosphate precursor are 14.21%, 20.36%, and 35.87% respectively;

[0036] S3: Add 100 g of iron manganese phosphate, 25.09 g of lithium carbonate (purity 99.7%), 8.27 g of glucose, 0.9 g of PEG-400, 0.4 g of magnesium oxide, and 0.33 g of titanium dioxide to deionized water to form a preliminary mixed phase by mixing and stirring. Transfer it to a horizontal sand mill and grind it at a speed of 1500 rpm for 1 h. After the particle size of the slurry reaches 320 nm, perform spray drying. The dried powder is subjected to the heat shock step again, with the target temperature being 760 °C. Classify and crush the obtained material and screen it to obtain a lithium iron manganese phosphate cathode material (LiFe 0.4 Mn 0.6 PO4 / C), and its XRD pattern is as Figure 2 shown.

[0037] Observe the morphology of the prepared Fe 0.4 Mn 0.6 PO4 and LiFe 0.4 Mn 0.6 PO4 / C materials using a scanning electron microscope, and the results are as Figure 4 and 5 shown.

[0038] Comparative Example 1

[0039] The difference from Example 1 is only that joule heating is not performed in steps S2 and S3.

[0040] A preparation method of a lithium iron manganese phosphate cathode material synthesized by joule heat flash includes the following steps:

[0041] S1: Add iron phosphate, manganese carbonate, and ammonium dihydrogen phosphate to 600 ml of deionized water according to a mass ratio of 1:1.14:1.03, and stir at room temperature until the slurry is completely dissolved to obtain a mixed slurry, where the molar ratio of (Fe + Mn):P is 0.97, the stirring speed is 600 rpm, and the stirring time is 0.5 h;

[0042] S2: Transfer the mixed slurry prepared in S1 to a horizontal sand mill and grind it at a speed of 1500 rpm for 1 h. After the particle size of the slurry reaches D50 < 1 μm, perform spray drying to obtain spray-dried powder. Place the dried powder in a tubular furnace and keep it at 600 °C for 5 h to obtain a manganese iron phosphate precursor (Fe 0.4 Mn 0.6 PO4):

[0043] S3: Add 100 g of manganese iron phosphate, 25.09 g of lithium carbonate (purity 99.7%), 8.27 g of glucose, 0.9 g of PEG-400, 0.4 g of magnesium oxide, and 0.33 g of titanium dioxide to deionized water and mix and stir to form a preliminary mixed phase. Transfer it to a horizontal sand mill and grind it at a speed of 1500 rpm for 1 h. After the particle size of the slurry reaches 320 nm, perform spray drying. Place the dried powder in a tubular furnace and keep it at 760 °C for 8 h. Classify and crush the sintered material and screen it to obtain a lithium manganese iron phosphate cathode material (LiFe 0.4 Mn 0.6 PO4 / C). The Raman spectrum comparison diagram of the samples of the lithium manganese iron phosphate cathode material prepared and the samples of the lithium manganese iron phosphate cathode material prepared in Example 1 is as shown in Figure 3 shown.

[0044] Comparative Example 2

[0045] The difference from Example 1 is that the lithium manganese iron phosphate precursor was not prepared.

[0046] A preparation method of a lithium manganese iron phosphate cathode material by Joule heat flash synthesis, comprising the following steps:

[0047] S3: Add 100 g of iron phosphate, 116.72 g of manganese carbonate, 64 g of lithium carbonate (purity 99.7%), 105.4 g of ammonium dihydrogen phosphate, 18.75 g of glucose, 2.2 g of PEG-400, 0.62 g of magnesium oxide, and 0.58 g of titanium dioxide to deionized water and stir evenly. Then transfer it to a horizontal sand mill and grind it at a speed of 1500 rpm for 1 h. After the particle size of the slurry reaches 320 nm, perform spray drying. Place the powder obtained by spray drying in a vacuum box, set the heating rate of the Joule heat shock instrument to 300 °C / 100 ms, the target temperature to 760 °C, and keep it for 120 s. Classify and crush the obtained material and screen it to obtain a lithium manganese iron phosphate cathode material by Joule heat flash synthesis (LiFe 0.4 Mn 0.6 PO4 / C).

[0048] Comparative Example 3

[0049] The only difference from Example 1 is that the heat shock target temperature of the Joule heat in step S3 is different

[0050] A preparation method of a lithium iron manganese phosphate cathode material synthesized by Joule heat flash includes the following steps:

[0051] S1: Add iron phosphate, manganese tetraoxide, and ammonium dihydrogen phosphate in a mass ratio of 1:1.14:1.03 to 600 ml of deionized water, stir at room temperature until the slurry is completely dissolved to obtain a mixed slurry, where the molar ratio of (Fe + Mn):P is 0.97, the stirring speed is 600 rpm, and the stirring time is 0.5 h;

[0052] S2: Transfer the mixed slurry prepared in S1 to a horizontal sand mill and grind it at a speed of 1500 rpm for 1 h. After the particle size of the slurry reaches D50 < 1 μm, perform spray drying to obtain a spray-dried powder. Then place the powder obtained by spray drying in a vacuum box, set the heating rate of the Joule heat shock instrument to 300 °C / 100 ms, the target temperature to 600 °C, and keep it for 120 s to obtain a lithium iron manganese phosphate precursor (Fe 0.4 Mn 0.6 PO4);

[0053] S3: Add 100 g of lithium iron manganese phosphate, 25.09 g of lithium carbonate (purity 99.7%), 8.27 g of glucose, 0.9 g of PEG-400, 0.4 g of magnesium oxide, and 0.33 g of titanium dioxide to deionized water for mixing and stirring to form a preliminary mixed phase. Transfer it to a horizontal sand mill and grind it at a speed of 1500 rpm for 1 h. After the particle size of the slurry reaches 350 nm, perform spray drying. Repeat the heat shock step for the dried powder, with the target temperature being 700 °C. Classify and crush the obtained material and sieve it to obtain a lithium iron manganese phosphate cathode material (LiFe 0.4 Mn 0.6 PO4 / C) anchored by a defective carbon carrier.

[0054] Using the prepared LiFe 0.4 Mn 0.6 PO4 / C composite material as the cathode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to make an electrode sheet. Using a lithium metal sheet as the anode, assemble a button cell. Test it under different charge-discharge current conditions at 2.3 - 4.5 V and 25 °C. The results are shown in Table 1.

[0055] Table 1

[0056]

[0057] As can be seen from Example 1, the lithium iron manganese phosphate cathode material synthesized by Joule heat flash prepared in the present invention has excellent conductivity and discharge stability.

[0058] According to Comparative Examples 1-2, Example 1 and the data in Table 1, in the technical solution of the present invention, if neither the preparation of the lithium iron manganese phosphate precursor nor the preparation of the target product lithium iron manganese phosphate cathode material uses the rapid thermal shock method of Joule heating for pyrolysis during the preparation of the lithium iron manganese phosphate cathode material, the conductivity and discharge stability of the finally prepared lithium iron manganese phosphate cathode material will be greatly reduced. If the preparation of the lithium iron manganese phosphate precursor is not carried out during the preparation of the lithium iron manganese phosphate cathode material, the discharge stability and conductivity of the finally prepared lithium iron manganese phosphate cathode material will be significantly reduced.

[0059] According to Example 1, Comparative Example 3 and the data in Table 1, it can be seen that if the target temperature of the Joule thermal shock in Step S3 during the preparation of the lithium iron manganese phosphate cathode material is slightly lower than 760 °C, the conductivity and discharge stability of the prepared lithium iron manganese phosphate cathode material will be reduced.

[0060] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A preparation method of a lithium iron manganese phosphate cathode material synthesized by Joule heat flash, characterized in that, It includes the following steps: S1: Add iron source, manganese source, and phosphorus source into 600 ml of deionized water, stir evenly at room temperature to obtain a mixed slurry, where the molar ratio of (Fe + Mn):P is 0.96 - 1.02, the molar ratio of Fe:Mn is (2 - 4):(8 - 6), the stirring speed is 600 - 1500 rpm, and the stirring time is 0.5 - 1 h; S2: Mechanically sand the mixed slurry prepared in S1, then perform spray drying, and then heat it to 600 °C in a Joule heat shock instrument in an inert gas atmosphere in a vacuum chamber, and hold for 120 s to obtain a manganese iron phosphate precursor, and the particle size of the manganese iron phosphate precursor is D 50 <1 μm; S3: Add the lithium source, carbon source, additive, and the lithium iron manganese phosphate precursor prepared in step S2 to deionized water for mixing and stirring to form a preliminary mixed phase, then perform secondary mechanical sanding. The sanded slurry is spray-dried and then rapidly heated to 760 °C in a Joule heat shock instrument under an inert gas atmosphere, and then subjected to air flow pulverization and sieving to obtain the lithium iron manganese phosphate cathode material synthesized by Joule heat flash. The particle size of the sanded particles is D 50 <350 nm.

2. The preparation method of the lithium iron manganese phosphate cathode material synthesized by Joule heat flash according to claim 1, characterized in that: The chemical general formula of the manganese iron phosphate is Mn x Fe 1-x PO4, and the chemical general formula of the lithium manganese iron phosphate is LiMn x Fe 1-x PO4, where 0.5 ≤ x ≤ 0.

8.

3. The preparation method of the lithium iron manganese phosphate cathode material synthesized by Joule heat flash according to claim 1, characterized in that: In S1, the iron source is one or more of ferric nitrate, ferric oxide, iron phosphate, ferric chloride, ferrous oxalate, ferrous chloride, ferrous sulfate; the manganese source is one or more of manganese dioxide, manganese trioxide, manganese tetroxide, manganese sulfate, manganese acetate, manganese phosphate, manganese nitrate, manganese carbonate; the phosphorus source is one or more of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate.

4. The preparation method of the lithium iron manganese phosphate cathode material synthesized by Joule heat flash according to claim 1, characterized in that: In S2 and S3, the mechanical sanding speed is 1000 - 2500 rpm, and the sanding time is 1 - 3 h. The mechanical sanding includes primary sanding and secondary sanding. The primary sanding is rough grinding, the rough grinding time is 0.5 - 1 h, and the particle size of the slurry is controlled at 600 - 800 nm. The secondary sanding is fine grinding, the fine grinding time is 1 - 2 h, and the particle size of the slurry is controlled at 300 - 400 nm.

5. The preparation method of the lithium iron manganese phosphate cathode material synthesized by Joule heat flash according to claim 1, wherein: In S3, the lithium source is any one of lithium carbonate, lithium hydroxide, lithium acetate, lithium dihydrogen phosphate, and the carbon source is one or more of glucose, polyethylene glycol, sucrose, β - cyclodextrin, polyacrylonitrile.

6. The preparation method of the lithium iron manganese phosphate cathode material synthesized by Joule heat flash according to claim 1, characterized in that: In S3, the additive is one or more of magnesium sulfate, magnesium oxide, titanium dioxide, tetrabutyl titanate, niobium pentoxide.

7. The preparation method of the lithium iron manganese phosphate cathode material synthesized by Joule heat flash according to claim 1, wherein: The additive is 0 - 0.5 wt% of the mass of the manganese iron phosphate precursor prepared in S2.

8. The preparation method of the lithium iron manganese phosphate cathode material synthesized by Joule heat flash according to claim 1, characterized in that: In S3, the mass of the lithium source is 25 - 26% of the mass of lithium iron manganese phosphate. In S3, the mass ratio of Li:M is 1.035:

1. The residual carbon content in the lithium iron manganese phosphate cathode material synthesized by Joule heat flash is 1.5 - 2.5 wt% of the carbon mass in the carbon source.

9. A lithium iron manganese phosphate cathode material synthesized by Joule heat flash, characterized in that: It is prepared by the preparation method of the lithium iron manganese phosphate cathode material synthesized by Joule heat flash according to any one of claims 1 - 8.

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