Supercritical preparation method of spherical high-density lithium iron manganese phosphate

Abstract

The application belongs to the technical field of lithium ion batteries, and particularly relates to a supercritical preparation method of spherical high-compaction lithium manganese iron phosphate. The application comprises the following steps: lithium source, iron source, manganese source, phosphorus source, carbon source and two kinds of metal ion additives with different contents are respectively dissolved in organic solutions, and are respectively named as solution A and solution B; solution A is a low-content metal ion additive solution, and solution B is a high-content metal ion additive solution; two kinds of precursors A and B are generated by reaction in a high-pressure reaction kettle; the two kinds of precursors A and B are mixed in a certain proportion, dried in a vacuum drying box, and then sintered under an inert atmosphere to obtain carbon-coated spherical high-compaction lithium manganese iron phosphate material. The application utilizes the characteristic that different particle sizes of lithium manganese iron phosphate precursors can be prepared by using different metal ion doping amounts, mixes in a certain proportion, and calcines to improve the compaction density of lithium manganese iron phosphate and the energy density thereof.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a supercritical preparation method of spherical high-compaction lithium iron manganese phosphate. BACKGROUND

[0002] Among a large number of positive electrode materials, olivine-type phosphate is considered to be the most promising positive electrode material for lithium ion power batteries. Among them, lithium iron phosphate has been widely used in lithium batteries due to its excellent cycle performance, structural stability, safety and low cost. However, the low working voltage (3.4 V) and energy density (580 Wh / kg) of lithium iron phosphate seriously limit the further development of power batteries.

[0003] Compared with lithium iron phosphate, lithium manganese iron phosphate has a higher working voltage and a higher energy density, which can increase the specific energy of the battery by 10-15%, and is a new generation of positive electrode material. Limited by the inherent defects of olivine-type structure material, lithium manganese iron phosphate has problems such as poor electrical conductivity, small Li + transport rate, and the Jahn-Teller effect of manganese element in the charging and discharging process has a great impact on the structural stability of the material. By reasonably adjusting the iron-manganese ratio, using metal ion doping and carbon coating strategies, the electrical conductivity of the material can be effectively improved, the Jahn-Teller effect can be reduced, and the Li + transport rate can be improved, so as to obtain a material with higher energy density.

[0004] Excessive metal ion doping can increase the specific surface area of lithium manganese iron phosphate and make the particles smaller, that is, the compaction density is reduced. This may be due to the lattice distortion caused by the generation of metal ion doping. The generation of lattice distortion can effectively inhibit the growth of crystal grains. By using this characteristic, high-compaction lithium manganese iron phosphate material can be prepared by one-step calcination method. Similarly, it has important reference significance for lithium iron phosphate material. SUMMARY

[0005] In view of the deficiencies of the prior art, the application provides a supercritical preparation method of spherical high-compaction lithium manganese iron phosphate, which solves the problems of low compaction of existing lithium manganese iron phosphate particles, poor electrical conductivity and improvement of Jahn-Teller effect.

[0006] The application is achieved by the following technical solutions:

[0007] The supercritical preparation method of spherical high-compaction lithium manganese iron phosphate of the application comprises the following steps:

[0008] (1) Dissolve the lithium source, iron source, manganese source, phosphorus source, carbon source and two different content metal ion additives in organic solution respectively, and name them as solution A and solution B respectively, and stir for 0.5-2 h, wherein solution A is a low content metal ion additive solution, and solution B is a high content metal ion additive solution;

[0009] (2) Transfer the two slurries after stirring in step (1) into a high-pressure reaction kettle respectively, introduce inert atmosphere gas to discharge the air in the kettle, and carry out reaction under the condition of 200-350 DEG C, the pressure in the kettle is kept at 20-30 MPa, and the reaction time is 1-7 h, to generate two precursors A and B;

[0010] (3) After the above reaction is completed, mix the two precursors A and B according to a certain proportion, filter and wash until no free metal ion is left, and dry the obtained filtered product in a vacuum drying box;

[0011] (4) Sinter the material after drying in step (3) under inert atmosphere, the sintering process is 700-1000 DEG C, and the sintering time is 3-10 h, to obtain a carbon-coated spherical high-density manganese iron lithium phosphate material.

[0012] According to the supercritical preparation method of the spherical high-density manganese iron lithium phosphate, the iron source in step (1) is selected from one or more of ferrous chloride, ferrous sulfate, ferrous oxalate, ferric chloride, ferric nitrate, ferric acetate and diiron trioxide; the phosphorus source is one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and red phosphorus; the lithium source is selected from one or more of lithium carbonate, lithium hydroxide and lithium acetate; the manganese source is selected from one or more of manganese carbonate, manganese acetate, manganese chloride, manganese nitrate and manganese sulfate; the carbon source is selected from one or more of glucose, polyethylene glycol, polyvinylpyrrolidone, polyacrylonitrile, polydopamine, tannic acid and cetyltrimethylammonium bromide; and the additive is at least one or more of titanium ion, nickel ion, magnesium ion, vanadium ion and niobium ion.

[0013] According to the supercritical preparation method of the spherical high-density manganese iron lithium phosphate, the molar ratio of the additive metal element to iron element in step (1) is 0.003-0.03:1.

[0014] According to the supercritical preparation method of the spherical high-density manganese iron lithium phosphate, the organic solvent in step (1) is selected from one or more of anhydrous ethanol, isopropyl alcohol, ethylene glycol, glycerol, N,N-dimethylformamide, oleylamine and toluene.

[0015] According to the supercritical preparation method of the spherical high-density manganese iron lithium phosphate, the molar ratio of lithium, iron, manganese and phosphorus in step (1) is 1:x:1-x:1, and 0

[0016] According to the supercritical preparation method of spherical high-pressure lithium manganese iron phosphate, in step (1), the solution occupies 50%-75% of the reactor volume.

[0017] According to the supercritical preparation method of spherical high-pressure lithium manganese iron phosphate, the inert atmosphere gas introduced in step (2) is selected from nitrogen, argon, or a mixture of nitrogen and argon.

[0018] According to the supercritical preparation method of spherical high-density lithium manganese iron phosphate, the vacuum drying temperature in step (3) is 60-100℃ and the drying time is 1-10 h.

[0019] According to the supercritical preparation method of spherical high-pressure lithium manganese iron phosphate, the ratio of precursor A to B in step (3) is 1-5:1.

[0020] According to the supercritical preparation method of spherical high-pressure lithium manganese iron phosphate, the inert atmosphere gas introduced in step (4) is selected from nitrogen, argon, or a mixture of nitrogen and argon; the heating rate is 1-10℃ / min.

[0021] Compared with existing technologies, the present invention has the following technical effects:

[0022] (1) The sample obtained by the supercritical method adopts the in-situ growth strategy. By controlling the preparation process, the particle size of the product is controllable and the particle size distribution is uniform, thus avoiding the agglomeration of the material.

[0023] (2) By taking advantage of the fact that different particle sizes of lithium manganese iron phosphate precursors can be prepared by different metal ion doping amounts, and by combining the doping of large and small particles and mixing them in a certain proportion, the compaction density of lithium manganese iron phosphate can be increased by one-step calcination, thereby further improving its energy density.

[0024] (3) Supercritical in-situ carbon coating can obtain a thinner and more uniform carbon layer structure, effectively reducing the Jahn-Teller effect. The addition of high molecular carbon compounds forms a uniformly coated thin carbon shell on the material surface, forming 2D and 3D mass transfer networks, improving the conductivity and rate performance of the material. Attached Figure Description

[0025] Figure 1 This is a process flow diagram of the supercritical preparation method of high-pressure lithium manganese iron phosphate.

[0026] Figure 2 This is a schematic diagram of lithium manganese iron phosphate. Implementation

[0027] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Example

[0028] (1) Lithium carbonate, ferrous sulfate, manganese sulfate, ammonium dihydrogen phosphate and vanadium pentoxide were dissolved in anhydrous ethanol at molar ratios of 1:0.4:0.6:1:0.0012 and 1:0.4:0.6:1:0.012, respectively. The solid content of the mixture was kept at 40%, and nitrogen gas was passed through and stirred for 1 hour to prepare solutions A and B.

[0029] (2) Add PVP to the mixed solution in step (1). The amount of PVP added is 9% of the solid mass in the slurry. After stirring and dispersing, transfer it to a high-pressure reactor, seal the high-pressure reactor, purge the air in the reactor with nitrogen for 20-30 minutes, heat the high-pressure reactor to 250°C, control the pressure inside the reactor to 25 MPa, and react for 3 hours.

[0030] (3) After the above reaction is completed, after the high-pressure reactor cools to room temperature, take out materials A and B, mix, wash and filter them in a 1:1 ratio. Place the washed materials in a vacuum drying oven and dry at 90°C for 3 hours.

[0031] (4) The dried material in step (3) is placed in a sagger and nitrogen is used as a protective gas. The material is kept at 750°C for 5 hours in a sintering furnace. After the sintering furnace is naturally cooled to room temperature, a spherical high-compact material with a thin carbon shell is obtained. Example

[0032] (1) Lithium hydroxide, ferrous chloride, manganese acetate, ammonium dihydrogen phosphate, and titanium dioxide were dissolved in a mixed solution of anhydrous ethanol / isopropanol / ethylene glycol at molar ratios of 1:0.4:0.6:1:0.0012 and 1:0.4:0.6:1:0.012 (mass ratio of anhydrous ethanol / isopropanol / ethylene glycol is 5:3:2). The solid content of the mixture was kept at 40%, and the mixture was stirred and dispersed under nitrogen for 1 hour to prepare solutions A and B.

[0033] (2) Add polydopamine to the mixed solution in step (1). The amount of polydopamine added is 10% of the solid mass in the slurry. After stirring and dispersing, transfer it to a high-pressure reactor, seal the high-pressure reactor, purge the air in the reactor with nitrogen for 20-30 minutes, heat the high-pressure reactor to 275°C, control the pressure inside the reactor to 30 MPa, and react for 1.5 hours.

[0034] (3) After the above reaction is completed, after the high-pressure reactor cools to room temperature, take out materials A and B, mix, wash and filter them in a 1:2 ratio. Place the washed materials in a vacuum drying oven and dry at 100°C for 2 hours.

[0035] (4) The dried material in step (3) is placed in a sagger and nitrogen is used as a protective gas. The material is kept at 740°C for 6 hours in a sintering furnace. After the sintering furnace is naturally cooled to room temperature, a spherical high-compact material with a thin carbon shell is obtained. Example

[0036] (1) Lithium hydroxide, ferrous chloride, manganese nitrate, diammonium hydrogen phosphate and niobium pentoxide were dissolved in anhydrous ethanol solution in molar ratios of 1:0.4:0.6:1:0.0012 and 1:0.4:0.6:1:0.012, respectively, and the solid content of the mixture was kept at 40%. Nitrogen gas was passed through and the mixture was stirred and dispersed for 1 h.

[0037] (2) Add polyethylene glycol / carbon nanotubes to the mixed solution in step (1) (the mass ratio of polyethylene glycol to carbon nanotubes is 10:1). The amount of carbon-containing compound added is 10% of the solid mass in the slurry. After stirring and dispersing, transfer it to a high-pressure reactor, seal the high-pressure reactor, purge the air in the reactor with nitrogen for 20-30 minutes, heat the high-pressure reactor to 260°C, control the pressure inside the reactor to 27 MPa, and react for 4 hours.

[0038] (3) After the above reaction is completed, after the high-pressure reactor cools to room temperature, take out materials A and B, mix, wash and filter them in a 1:3 ratio. Place the washed materials in a vacuum drying oven and dry at 90°C for 4 hours.

[0039] (4) The dried material in step (3) is placed in a sagger and nitrogen is used as a protective gas. The material is kept at 760°C for 4 hours in a sintering furnace. After the sintering furnace is naturally cooled to room temperature, a three-dimensional conductive network nanomaterial is obtained. The carbonized polyethylene glycol can be used as a carbon layer to coat the surface of the material particles.

[0040] Comparative Example 1

[0041] (1) Lithium carbonate, ferrous chloride, manganese sulfate and ammonium dihydrogen phosphate were dissolved in anhydrous ethanol at a molar ratio of 1:0.4:0.6:1, and the solid content of the mixture was kept at 40%. Nitrogen gas was passed through and the mixture was stirred and dispersed for 1 hour.

[0042] (2) Add PVP to the mixed solution in step (1). The amount of PVP added is 9% of the solid mass in the slurry. After stirring and dispersing, transfer it to a high-pressure reactor, seal the high-pressure reactor, purge the air in the reactor with nitrogen for 20-30 minutes, heat the high-pressure reactor to 255°C, control the pressure inside the reactor to 25 MPa, and react for 2 hours.

[0043] (3) After the above reaction is completed, wait for the high-pressure reactor to cool to room temperature, then take out the material and wash and filter it. Place the washed material in a vacuum drying oven and dry it at 90°C for 2 hours.

[0044] (4) The dried material in step (3) is placed in a sagger and kept at 750°C for 5 hours in a sintering furnace with nitrogen as a protective gas. After the sintering furnace is naturally cooled to room temperature, a thin carbon shell coating material is obtained.

[0045] Comparative Example 2

[0046] (1) Lithium hydroxide, ferrous sulfate, manganese nitrate, ammonium dihydrogen phosphate and nickel nitrate were dissolved in anhydrous ethanol solution in a molar ratio of 1:0.4:0.6:1:0.0012, and the solid content of the mixture was kept at 40%. Nitrogen gas was passed through and the mixture was stirred and dispersed for 1 h.

[0047] (2) Add PVP / tannic acid to the mixed solution in step (1) (the ratio of PVP to tannic acid is 9:1). The amount of carbon-containing compound added is 10% of the solid mass in the slurry. After stirring and dispersing, transfer it to a high-pressure reactor, seal the high-pressure reactor, purge the air in the reactor with nitrogen for 20-30 minutes, heat the high-pressure reactor to 260°C, control the pressure inside the reactor to 28 MPa, and react for 5 hours.

[0048] (3) After the above reaction is completed, after the high-pressure reactor is cooled to room temperature, the material is taken out, washed and filtered, and the washed material is placed in a vacuum drying oven at 100°C for 2 hours.

[0049] (4) The dried material in step (3) is placed in a sagger and nitrogen is used as a protective gas. The material is kept at 740°C for 5 hours in a sintering furnace. After the sintering furnace is naturally cooled to room temperature, a spherical material with a three-dimensional conductive network is obtained.

[0050] Comparative Example 3

[0051] (1) Lithium hydroxide, ferrous sulfate, manganese chloride, ammonium dihydrogen phosphate and magnesium sulfate were dissolved in anhydrous ethanol solution in a molar ratio of 1:0.4:0.6:1:0.012, and the solid content of the mixture was kept at 40%. Nitrogen gas was passed through and the mixture was stirred and dispersed for 1 h.

[0052] (2) Add glucose / carbon nanotubes to the mixed solution in step (1) (the ratio of glucose to carbon nanotubes is 10:1). The amount of carbon-containing compound added is 9% of the solid mass in the slurry. After stirring and dispersing, transfer it to a high-pressure reactor, seal the high-pressure reactor, purge the air in the reactor with nitrogen for 20-30 minutes, heat the high-pressure reactor to 270°C, control the pressure inside the reactor to 28 MPa, and react for 3 hours.

[0053] (3) After the above reaction is completed, after the high-pressure reactor is cooled to room temperature, the material is taken out, washed and filtered, and the washed material is placed in a vacuum drying oven at 80°C for 4 hours.

[0054] (4) The dried material in step (3) is placed in a sagger and nitrogen is used as a protective gas. The material is kept at 730°C for 8 hours in a sintering furnace. After the sintering furnace is naturally cooled to room temperature, carbon-coated material is obtained.

[0055] The discharge capacity and compaction density of the examples and comparative examples were tested, and the final material properties are as follows:

[0056] Table 1

[0057] 1C discharge capacity (mAh / g) Powder compaction density (g / cm3) Example 1 141 2.60 Example 2 143 2.57 Example 3 147 2.53 Comparative Example 1 131 2.58 Comparative Example 2 138 2.54 Comparative Example 3 150 2.40

[0058] As can be seen from the table, the characteristic that different particle sizes of lithium manganese iron phosphate precursors can be prepared by utilizing different amounts of metal ion doping, combined with the doping of large and small particles, mixed in a certain proportion, and then calcined, can improve the compaction density of lithium manganese iron phosphate and further improve its energy density.

[0059] This invention utilizes supercritical in-situ carbon coating to obtain a thinner and more uniform carbon layer structure, effectively reducing the Jahn-Teller effect. The addition of carbon-containing polymers forms a uniformly coated thin carbon shell on the material surface, creating 2D and 3D mass transfer networks, thereby improving the material's conductivity and rate performance.

Claims

1. A supercritical preparation method for spherical high-pressure lithium manganese iron phosphate, characterized in that, Includes the following steps: (1) Dissolve lithium source, iron source, manganese source, phosphorus source, carbon source and two metal ion additives with different contents in organic solvents respectively, and name them solution A and solution B respectively. Stir for 0.5-2h. Solution A is a solution with low metal ion additive content and solution B is a solution with high metal ion additive content. The organic solvent is selected from one or more of anhydrous ethanol, isopropanol, ethylene glycol, glycerol, N,N-dimethylformamide, oleylamine and toluene. (2) Transfer the two slurries after stirring in step (1) to a high-pressure reactor, introduce an inert atmosphere gas to remove the air in the reactor, and carry out the reaction at 200-350℃, with the pressure inside the reactor maintained at 20-30MPa and the reaction time being 1-7h, to generate two precursors A and B. (3) After the above reaction is completed, the two precursors A and B are mixed, filtered and washed in a certain proportion until no free metal ions are found. The filtered product is then placed in a vacuum drying oven to dry. (4) The material dried in step (3) is placed in an inert atmosphere for sintering. The sintering process is 700-1000℃ and the sintering time is 3-10h to obtain carbon-coated spherical high-pressure lithium manganese iron phosphate material.

2. The supercritical preparation method of spherical high-pressure lithium manganese iron phosphate according to claim 1, characterized in that, In step (1), the iron source is selected from one or more of ferrous chloride, ferrous sulfate, ferrous oxalate, ferric chloride, ferric nitrate, ferric acetate, and ferric oxide; the phosphorus source is one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and red phosphorus; the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, and lithium acetate; the manganese source is selected from one or more of manganese carbonate, manganese acetate, manganese chloride, manganese nitrate, and manganese sulfate; the carbon source is selected from one or more of glucose, polyethylene glycol, polyvinylpyrrolidone, polyacrylonitrile, polydopamine, tannic acid, and hexadecyltrimethylammonium bromide; and the metal ion additive is one or more of titanium ions, nickel ions, magnesium ions, vanadium ions, and niobium ions.

3. The supercritical preparation method of spherical high-pressure lithium manganese iron phosphate according to claim 1, characterized in that, In step (1), the molar ratio of the metal element to the iron element in the solution additive is 0.003-0.03:

1.

4. The supercritical preparation method of spherical high-pressure lithium manganese iron phosphate according to claim 1, characterized in that, In step (1), the molar ratio of lithium, iron, manganese, and phosphorus is 1:x:1-x:1, 0 <x<1。 5. The supercritical preparation method of spherical high-pressure lithium manganese iron phosphate according to claim 1, characterized in that, In step (1), the solution occupies 50%-75% of the reactor volume.

6. The supercritical preparation method of spherical high-pressure lithium manganese iron phosphate according to claim 1, characterized in that, In step (2), the inert atmosphere gas introduced is selected from nitrogen, argon, or a mixture of nitrogen and argon.

7. The supercritical preparation method of spherical high-pressure lithium manganese iron phosphate according to claim 1, characterized in that, In step (3), the vacuum drying temperature is 60-100℃ and the drying time is 1-10h.

8. The supercritical preparation method of spherical high-pressure lithium manganese iron phosphate according to claim 1, characterized in that, In step (3), the ratio of precursors A and B is 1-5:

1.

9. The supercritical preparation method of spherical high-pressure lithium manganese iron phosphate according to claim 1, characterized in that, In step (4), the inert atmosphere gas introduced is selected from nitrogen, argon, or a mixture of nitrogen and argon; the heating rate is 1-10℃ / min.

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