Method for in-situ growth of lithium iron phosphate on three-dimensional graphene and use of lithium iron phosphate

Abstract

Disclosed in the present invention are a method for in-situ growth of lithium iron phosphate on three-dimensional graphene and a use of the lithium iron phosphate. The method comprises: dissolving an iron source and a phosphorus source in water, mixing to obtain a reaction solution, adding a lithium source, adding a doping element source for the first time, and carrying out primary grinding and mixing; adding three-dimensional graphene, and carrying out secondary grinding and mixing; and carrying out a hydrothermal reaction and tertiary grinding and mixing; adding the doping element source for the second time to obtain a mixed slurry, carrying out spray granulation, sintering particles in an inert gas atmosphere, and crushing and sieving a sintered product to obtain the lithium iron phosphate grown in situ on the three-dimensional graphene. According to the method of the present invention, growing in situ a lithium iron phosphate material within pores of three-dimensional graphene greatly improves the electrical conductivity of the growth material, thereby greatly increasing the power density of the growth material, and significantly improving the cycle performance and low-temperature performance of the growth material.

Description

A method for in-situ growth of lithium iron phosphate on three-dimensional graphene and its application Technical Field

[0001] The present invention relates to the field of energy storage material production, and in particular to a method for in-situ growth of lithium iron phosphate on three-dimensional graphene and applications thereof. Background Art

[0002] Research indicates that lithium iron phosphate (LiFePO4) batteries have become one of the most promising cathode materials for lithium-ion batteries due to their low cost, long cycle life, and excellent safety. However, the material's low electrical conductivity hinders its performance at high power and low temperatures, limiting its wider application.

[0003] Therefore, it is necessary to modify the lithium iron phosphate material to increase its electrical conductivity and power density, and improve its cycle performance and low-temperature performance. Technical issues

[0004] To solve the problems existing in the prior art, the present invention provides a method for in-situ growth of lithium iron phosphate using three-dimensional graphene. By utilizing the properties of graphene, the electrical conductivity of the lithium iron phosphate growth material is greatly improved, thereby significantly increasing its power density and significantly improving its cycle performance and low-temperature performance.

[0005] Another object of the present invention is to provide an application of the three-dimensional graphene in-situ growth of lithium iron phosphate. Technical Solutions

[0006] In order to achieve the above object of the invention, the present invention adopts the following technical solutions:

[0007] A method for in-situ growth of lithium iron phosphate on three-dimensional graphene comprises the following steps:

[0008] S1. Dissolve an iron source and a phosphorus source in water, mix to obtain a reaction solution, add a lithium source and a doping element source once to the reaction solution, and grind and mix again;

[0009] S2, adding three-dimensional graphene to the first-grinded mixture of S1, and grinding and mixing again;

[0010] S3, subjecting the twice-ground mixture of S2 to a hydrothermal reaction, and subjecting the reaction product to a third grinding and mixing;

[0011] S4, adding a doping element source to the thrice-milled mixture of S3 for a second time to obtain a mixed slurry;

[0012] S5. Spray granulate the mixed slurry obtained in S4, sinter the obtained particles under an inert gas protection atmosphere, crush and sieve the sintered material to obtain the three-dimensional graphene in-situ grown lithium iron phosphate.

[0013] In a specific embodiment, the iron source in step S1 is selected from any one of ferrous oxalate, ferric phosphate, ferric oxide or iron powder, or a combination of two or more thereof; the phosphorus source is selected from any one of phosphoric acid, ammonium monohydrogen phosphate or ammonium dihydrogen phosphate, or a combination of two or more thereof.

[0014] In a specific embodiment, the lithium source in step S1 is one or a combination of two or more of lithium carbonate or lithium hydroxide; the primary added doping element source is a metal element selected from at least any one of Mn, Mg, Al, Zn, Ni, Co, Ca, and Cu.

[0015] In a specific embodiment, the total molar number of the iron source and the doping element source added once in step S1 is the same as the molar number of the phosphorus source; and the molar ratio of the lithium source to the phosphorus source is (1-1.1):1.

[0016] In a specific embodiment, the primary particle size D90 of the solid particles obtained by the primary grinding and mixing in step S1 is 10 to 300 nm.

[0017] In a specific embodiment, the amount of three-dimensional graphene added in step S2 is 0.5% to 8% of the mass of the first grinding mixture; preferably, the three-dimensional graphene has a specific surface area of ​​500-2500m 2 / g, and a three-dimensional structure with pore size of 10nm-2μm.

[0018] In a specific embodiment, the temperature of the hydrothermal reaction in step S3 is 100-300° C., the reaction pressure is 0.1-2.0 MPa, the reaction time is 1-36 h, and the solid content of the hydrothermal reaction material is 10-80%.

[0019] In a specific embodiment, the primary particle size of the solid particles in the reaction solution after the hydrothermal reaction in step S3 is 200-2000 nm; preferably, the primary particle size of the solid particles in the reaction solution after three grindings is 50-500 nm.

[0020] In a specific embodiment, the secondary added doping element source in step S4 is a carbon source, selected from any one of lactose, glucose, sucrose, polyethylene glycol, or a combination of two or more thereof.

[0021] In a specific embodiment, the sintering temperature in step S5 is 650-950° C., and the sintering time is 6-36 hours.

[0022] Another aspect of the present invention is the use of in-situ grown lithium iron phosphate of three-dimensional graphene prepared by the above method in lithium batteries. Beneficial effects

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] The method of the present invention in situ grows lithium iron phosphate material in the pores of three-dimensional graphene. Since the three-dimensional graphene structure has ultra-high electrical conductivity, it can serve as a carrier to greatly improve the electrical conductivity of the grown material, greatly increase its power density, and significantly improve its cycle performance and low-temperature performance. At the same time, the porosity of three-dimensional graphene gives it excellent adsorption capacity and can well load other materials, providing a basis for in situ growth. The high specific surface area of ​​three-dimensional graphene can form a double layer reaction in the ungrown pores, thereby greatly improving the pulse performance of the material and increasing the response speed of the device. Best Mode for Carrying Out the Invention

[0025] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0026] A method for in-situ growth of lithium iron phosphate on three-dimensional graphene comprises the following steps:

[0027] S1. Dissolve an iron source and a phosphorus source in water, mix to obtain a reaction solution, add a lithium source and a doping element source once to the reaction solution, and grind and mix again;

[0028] S2, adding three-dimensional graphene to the first-grinded mixture of S1, and grinding and mixing again;

[0029] S3, subjecting the twice-ground mixture of S2 to a hydrothermal reaction, and subjecting the reaction product to a third grinding and mixing;

[0030] S4, adding a doping element source to the thrice-milled mixture of S3 for a second time to obtain a mixed slurry;

[0031] S5. Spray granulate the mixed slurry obtained in S4, sinter the obtained particles under an inert gas protection atmosphere, crush and sieve the sintered material to obtain the three-dimensional graphene in-situ grown lithium iron phosphate.

[0032] In step S1, the iron source is selected from any one of ferrous oxalate, ferric phosphate, iron oxide or iron powder, or a combination of two or more thereof, preferably ferric oxalate; the phosphorus source is selected from any one of phosphoric acid, ammonium monohydrogen phosphate or ammonium dihydrogen phosphate, or a combination of two or more thereof, preferably ammonium dihydrogen phosphate. The lithium source is one of lithium carbonate or lithium hydroxide, or a combination of two or more thereof, preferably lithium carbonate; the primary added doping element source is a metal element, selected from any one of Mn, Mg, Al, Zn, Ni, Co, Ca, Cu, or preferably Al or Mn. The total molar number of the iron source and the primary added doping element source is the same as the molar number of the phosphorus source; the molar ratio of the lithium source to the phosphorus source is (1-1.1):1, for example, 1; 1, 1.05:1, 1.1:1, etc., all calculated based on the molar number of the corresponding elements.

[0033] The above-mentioned iron source, phosphorus source, lithium source and primary doping element source are added together and then wet ball milled. There is no particular restriction on the ball milling speed, for example, 200-2000 rpm, preferably 500-1000 rpm, and there is no particular restriction on the ball milling time, for example, 2-6 h. The solid particles obtained by the primary grinding and mixing have a primary particle size D90 of 10 to 300 nm, for example, 30 nm, 50 nm, 75 nm, 100 nm, 150 nm, 200 nm, 250 nm, etc.

[0034] In step S2, after the first grinding and mixing, the raw materials are fully mixed, and then three-dimensional graphene is added thereto, and the amount of the three-dimensional graphene added is 0.5% to 8% of the mass of the first grinding mixture, for example, including but not limited to 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%; and ball milling is performed again to fully mix the graphene and the raw materials. There is no special restriction on the speed of the second ball milling, for example, 200-2000rpm, preferably 500-1000rpm, and there is no special restriction on the ball milling time, for example, 0.5-4h, mainly to fully mix and contact the graphene with the raw materials of the next hydrothermal reaction. Wherein, the three-dimensional graphene has a specific surface area of ​​500-2500m 2 / g, and a three-dimensional structure with pore size of 10nm-2μm. Its porous properties provide good adsorption and a place for in-situ growth of hydrothermal reactions.

[0035] In step S3, the hydrothermal reaction can be carried out in a hydrothermal reactor, for example, the temperature of the hydrothermal reaction is 100-300°C, for example, 100°C, 150°C, 200°C, 250°C, 300°C, etc., the reaction pressure is 0.1-2.0 MPa, for example, 0.1 MPa, 0.5 MPa, 1.0 MPa, 1.5 MPa, 2.0 MPa, etc., the reaction time is 1-36h, for example, 2h, 5h, 8h, 10h, 15h, 20h, 25h, 30h, 35h, etc., and the solid content in the hydrothermal reaction material is 10-80%, for example, 15%, 20%, 30%, 40%, 50%, 60%, 70%, etc. After the hydrothermal reaction, the primary particle size of the solid particles in the reaction liquid is about 200 to 2000 nm, for example, 500 nm, 800 nm, 1000 nm, 1500 nm, 2000 nm, etc., and then further homogenized by three grindings. After the three grindings, the primary particle size of the solid particles in the reaction liquid is 50 to 500 nm, for example, 50 nm, 80 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, etc.

[0036] In step S4, a doping element source is added a second time to the tertiary-milled mixture to obtain a mixed slurry. The secondary doping element source is a carbon source, such as one or a combination of two or more selected from lactose, glucose, sucrose, and polyethylene glycol, preferably glucose. The carbon source is added in an amount of 1-5% of the mass of the tertiary-milled mixture to obtain a mixed slurry having a solids content of 20-50%.

[0037] In step S5, the mixed slurry is spray-granulated, and the particle size is usually 1-5 μm. The obtained particles are sintered under an inert gas (e.g., nitrogen) protective atmosphere, and the sintering temperature is 650-950°C, for example, 700°C, 750°C, 800°C, 850°C, 900°C, etc., and the sintering time is 6-36h, for example, 8h, 10h, 15h, 20h, 25h, 30h, 35h, etc. The sintered material is crushed and passed through a 200-mesh sieve to obtain the three-dimensional graphene in situ grown lithium iron phosphate.

[0038] The three-dimensional graphene in-situ grown lithium iron phosphate prepared by the above method can be used as a positive electrode material and applied in lithium batteries.

[0039] The present invention is further explained below by more specific examples, but does not constitute any limitation. Example 1

[0040] The three-dimensional graphene in situ growth of lithium iron phosphate is prepared by the following steps:

[0041] S1, 14.4g of ferrous oxalate and 13.2g of ammonium monohydrogen phosphate were dissolved in 100mL of water, and the mixture was mixed to obtain a reaction solution. 37g of lithium carbonate and 2000ppm of Al were added to the reaction solution, and the mixture was ground and mixed again. The ball mill was milled at a speed of 1000rpm for about 3h until the primary particle size D90 of the solid particles was 150nm.

[0042] S2. Add 1.6 g of three-dimensional graphene (Xianfeng Nano) to the first-milled mixture of S1, and then mill again at a ball mill speed of 500 rpm for 2 h.

[0043] S3, the second grinding mixture of S2 was subjected to hydrothermal reaction at 200°C and 1.0 MPa for 15 h, and the reaction product was ground and mixed three times, and ground at a ball mill speed of 2000 rpm for about 1 h until the primary particle size D90 of the solid particles was 100 nm;

[0044] S4, adding 3 g of polyethylene glycol a second time to the thrice-ground mixture of S3 to obtain a mixed slurry;

[0045] S5. Spray granulate the mixed slurry obtained in S4 to obtain 4 μm particles, sinter them under a nitrogen gas protection atmosphere at a sintering temperature of 800° C. and a sintering time of 20 h. The sintered material is crushed and passed through a 200-mesh sieve to obtain the three-dimensional graphene in situ grown lithium iron phosphate. Example 2

[0046] The three-dimensional graphene in situ growth of lithium iron phosphate is prepared by the following steps:

[0047] S1, 14.4g of ferrous oxalate and 13.2g of ammonium monohydrogen phosphate were dissolved in 100mL of water, and the mixture was mixed to obtain a reaction solution. 37g of lithium carbonate and 3000ppm of Al were added to the reaction solution, and the mixture was ground and mixed again. The ball mill was milled at a speed of 500rpm for about 5h until the primary particle size D90 of the solid particles was 300nm.

[0048] S2. Add 5 g of three-dimensional graphene (Xianfeng Nano) to the first-milled mixture of S1, and then grind again at a ball mill speed of 1500 rpm for 4 h.

[0049] S3, the second grinding mixture of S2 was subjected to hydrothermal reaction at 300°C and 1.8 MPa for 30 h, and the reaction product was ground and mixed three times, and ground at a ball mill speed of 1000 rpm for about 3.5 h until the primary particle size D90 of the solid particles was 200 nm;

[0050] S4, adding 2 g of glucose a second time to the thrice-milled mixture of S3 to obtain a mixed slurry;

[0051] S5. The mixed slurry obtained in S4 is spray-granulated to obtain 3 μm particles, which are sintered under a nitrogen gas protection atmosphere at a sintering temperature of 700° C. and a sintering time of 30 h. The sintered material is crushed and passed through a 200-mesh sieve to obtain the three-dimensional graphene in-situ grown lithium iron phosphate. Example 3

[0052] The three-dimensional graphene in situ growth of lithium iron phosphate is prepared by the following steps:

[0053] S1, 14.4g of ferrous oxalate and 13.2g of ammonium monohydrogen phosphate were dissolved in 100mL of water, and the mixture was mixed to obtain a reaction solution. 37g of lithium carbonate and 1000ppm of Mn were added to the reaction solution, and the mixture was ground and mixed again. The ball mill was milled at a speed of 1000rpm for about 3h until the primary particle size D90 of the solid particles was 150nm.

[0054] S2. Add 1.6 g of three-dimensional graphene (Xianfeng Nano) to the first-milled mixture of S1, and then mill again at a ball mill speed of 500 rpm for 2 h.

[0055] S3, the second grinding mixture of S2 was subjected to hydrothermal reaction at 200°C and 1.0 MPa for 15 h, and the reaction product was ground and mixed three times, and ground at a ball mill speed of 2000 rpm for about 4 h until the primary particle size D90 of the solid particles was 100 nm;

[0056] S4, adding 3 g of polyethylene glycol a second time to the thrice-ground mixture of S3 to obtain a mixed slurry;

[0057] S5. Spray granulate the mixed slurry obtained in S4 to obtain 4 μm particles, sinter them under a nitrogen gas protection atmosphere at a sintering temperature of 800° C. and a sintering time of 20 h. The sintered material is crushed and passed through a 200-mesh sieve to obtain the three-dimensional graphene in situ grown lithium iron phosphate. Application Examples

[0058] The positive electrode uses conductive carbon black as the conductive agent, PVDF as the binder, and NMP as the solvent. The slurry is prepared according to the mass ratio of lithium iron phosphate: conductive agent: binder for the in-situ growth of three-dimensional graphene at a ratio of 94:3:3. The slurry has a solid content of 48% and is coated on a 12um aluminum foil. It is then dried, rolled, and cut into pieces to make the positive electrode.

[0059] The negative electrode uses hard carbon as the active material, conductive carbon black as the conductive agent, SBR emulsion binder 1, CMC as binder 2, and pure water as the solvent. The slurry is prepared in a mass ratio of artificial graphite, conductive agent, binder 1, and binder 2 of 95.5:2:2:1.5, with a solid content of 50%. The slurry is coated on 8um copper foil, dried, rolled, and slit to form a negative electrode.

[0060] The positive and negative electrodes of the above three embodiments are respectively used through die-cutting, lamination, packaging, and liquid injection processes to prepare soft-pack battery cells. Performance testing:

[0061] The average capacity of the soft-pack battery cell made of the positive electrode of lithium iron phosphate grown by in-situ three-dimensional graphene in Example 1 is 2.258Ah;

[0062] The power characteristics are shown in the following table:

[0063] ,

[0064] The soft-pack battery cell has a capacity retention rate of 89.2% after 8000 cycles at a charge and discharge current of 5C and 100% SOC, showing good cycle performance.

[0065] The temperature performance of the soft-pack battery is as follows (5C rate discharge):

[0066] , Comparative Example 1

[0067] Compared with Example 1, only the three-dimensional graphene is not added, and other conditions are exactly the same. Comparative Example 2

[0068] Compared with Example 1, activated carbon was used instead of three-dimensional graphene, and other conditions were exactly the same. Comparative Example 3

[0069] Compared with Example 1, lithium iron phosphate and three-dimensional graphene are directly ball-milled and mixed without going through the in-situ growth step.

[0070] The lithium iron phosphate materials prepared in the above embodiments and comparative examples were made into soft-pack batteries with the same electrode surface density, the same die-cutting size, and the same number of electrode sheets. The first-cycle capacity, cycle performance, power performance, and low-temperature performance were mainly tested. The test results are shown in the following table.

[0071] Performance test data of the examples and comparative examples

[0072] ,

[0073] As can be seen from the above table, the lithium iron phosphate prepared by the present invention has excellent cycle performance, power characteristics and low-temperature performance, and can well solve the defects of the existing use of lithium iron phosphate.

[0074] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

[0075] The present invention discloses a method for in-situ growth of lithium iron phosphate on three-dimensional graphene and its application, comprising dissolving an iron source and a phosphorus source in water, mixing to obtain a reaction solution, adding a lithium source and a doping element source, grinding and mixing once; then adding the three-dimensional graphene, grinding and mixing again; performing a hydrothermal reaction, grinding and mixing a third time; adding the doping element source a second time to obtain a mixed slurry, spray-granulating the slurry, sintering the particles under an inert gas atmosphere, crushing and sieving the sintered material, and obtaining the in-situ growth of lithium iron phosphate on three-dimensional graphene. The method of the present invention in-situ grows lithium iron phosphate material in the pores of the three-dimensional graphene, significantly improving the conductivity of the grown material, significantly increasing its power density, and significantly improving its cycle performance and low-temperature performance.

Claims

1. A method for in-situ growth of three-dimensional graphene on lithium iron phosphate, characterized in that: The following steps are involved: S1. Dissolve an iron source and a phosphorus source in water, mix to obtain a reaction solution, add a lithium source and a doping element source once to the reaction solution, and grind and mix again; S2, adding three-dimensional graphene to the first-grinded mixture of S1, and grinding and mixing again; S3, subjecting the twice-ground mixture of S2 to a hydrothermal reaction, and subjecting the reaction product to a third grinding and mixing; S4, adding a doping element source to the thrice-milled mixture of S3 for a second time to obtain a mixed slurry; S5. Spray granulate the mixed slurry obtained in S4, sinter the obtained particles under an inert gas protection atmosphere, crush and sieve the sintered material to obtain the three-dimensional graphene in-situ grown lithium iron phosphate.

2. The method according to claim 1, characterized in that In step S1, the iron source is selected from any one of ferrous oxalate, ferric phosphate, ferric oxide or iron powder, or a combination of two or more thereof; the phosphorus source is selected from any one of phosphoric acid, ammonium monohydrogen phosphate or ammonium dihydrogen phosphate, or a combination of two or more thereof.

3. The method according to claim 1 or 2, characterized in that The lithium source in step S1 is one or a combination of two or more of lithium carbonate or lithium hydroxide; the primary added doping element source is a metal element selected from at least any one of Mn, Mg, Al, Zn, Ni, Co, Ca, and Cu.

4. The method according to claim 3, characterized in that In step S1, the total molar number of the iron source and the doping element source added once is the same as the molar number of the phosphorus source; and the molar ratio of the lithium source to the phosphorus source is (1-1.1):

1.

5. The method according to claim 1, wherein The primary particle size D90 of the solid particles obtained by the primary grinding and mixing in step S1 is 10 to 300 nm.

6. The method according to claim 1, characterized in that The amount of three-dimensional graphene added in step S2 is 0.5% to 8% of the mass of the first grinding mixture; preferably, the three-dimensional graphene has a specific surface area of ​​500-2500m 2 / g, and a three-dimensional structure with pore size of 10nm-2μm.

7. The method according to claim 1, characterized in that The temperature of the hydrothermal reaction in step S3 is 100-300° C., the reaction pressure is 0.1-2.0 MPa, the reaction time is 1-36 h, and the solid content of the hydrothermal reaction material is 10-80%.

8. The method according to claim 1 or 7, characterized in that After the hydrothermal reaction in step S3 is completed, the primary particle size of the solid particles in the reaction solution is 200-2000 nm; preferably, after three grindings, the primary particle size of the solid particles in the reaction solution is 50-500 nm.

9. The method according to claim 1, characterized in that The secondary added doping element source in step S4 is a carbon source, selected from any one of lactose, glucose, sucrose, and polyethylene glycol, or a combination of two or more thereof.

10. The method according to claim 1, characterized in that In step S5, the sintering temperature is 650-950° C., and the sintering time is 6-36 hours.

11. Use of lithium iron phosphate grown on three-dimensional graphene prepared by the method according to any one of claims 1 to 10 in lithium batteries.

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