A kind of ultra-high capacity lithium iron phosphate material and preparation method thereof

Abstract

The present invention discloses an ultra-high capacity lithium iron phosphate material and a preparation method thereof, and relates to the field of material technology. The present invention first prepares a porous template condensation polymer material, and then mixes lithium iron phosphate with the porous template condensation polymer material to prepare a premixed precursor; finally, a ultra-high capacity lithium iron phosphate material is prepared through high temperature calcination. The porous template condensation polymer material of the present invention can provide more synthesis reaction sites during the preparation process, and can also serve as a coating source for lithium iron phosphate, thereby making the prepared lithium iron phosphate material have a very high capacitance.

Description

Technical Field

[0001] The present invention belongs to the field of material technology, and in particular relates to an ultra-high capacity lithium iron phosphate material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have been widely used in portable electronic products and other fields due to their advantages such as high energy density, high power and long cycle life, and are constantly expanding into fields such as electric vehicles and energy storage. Lithium iron phosphate is the safest cathode material currently used, and is widely used in lithium-ion batteries in scenarios such as electric vehicles and energy storage. However, the theoretical capacity of this material is only 170mAh / g, which is low, and its conductivity is poor, so the rate discharge performance is poor. In response to this problem, a lot of research and development work is devoted to the development of high-capacity and high-conductivity lithium iron phosphate materials, but the actual capacity of lithium iron phosphate materials currently used commercially is only about 160mAh / g, which cannot meet the high energy density requirements of long-range electric vehicles. It is of great significance to develop lithium iron phosphate materials with high capacity, even exceeding the theoretical capacity and high conductivity.

[0003] At present, the papers Nature communications 2013(4):1687 and Nano Energy 2017(34):408-420 reported ultra-high capacity lithium iron phosphate materials exceeding the theoretical capacity of 208 mAh / g and 192 mAh / g, respectively. Among them, Nature communications 2013(4):1687 reported a method of preparing lithium iron phosphate with a capacity of 208 mAh / g by coating lithium iron phosphate with graphene, which involved a complex process of electrochemically exfoliating graphite to obtain graphene, and the obtained graphene was prone to defects, and the process was complex and difficult to control, and it was also difficult to achieve mass production. Nano Energy 2017(34):408-420 A glucose-derived carbon encapsulated (GC) internal carbon layer (IC) lithium iron phosphate (LFP) composite material was synthesized by using phytic acid (PhyA) as a special phosphorus source and as a structural regulator, chelating agent and antioxidant. The obtained material capacity reached 192 mA·h / g. The synthesis process of lithium iron phosphate with internal carbon layer involves a high temperature solvent process at 200°C. The selection of phosphorus source acting as a structural regulator, chelating agent and antioxidant is extremely limited and harsh. The process is complicated and difficult to scale up. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides an ultra-high capacity lithium iron phosphate material and a preparation method thereof. The present invention is implemented by adopting the following technical solutions:

[0005] A method for preparing an ultra-high capacity lithium iron phosphate material comprises the following steps:

[0006] Step 1: Preparation of porous template polycondensation polymer material

[0007] Step 1-1, after melting phenol, adding a sodium hydroxide aqueous solution with a mass concentration of 20%, wherein the mass ratio of phenol to sodium hydroxide solid is 1:1, stirring to obtain a mixed solution;

[0008] Step 1-2: weighing a formaldehyde solution with a mass concentration of 30% to 40%, wherein the mass ratio of the formaldehyde solution to phenol is 1.3 to 1.4:1;

[0009] Step 1-3, adding the formaldehyde solution to the mixed solution in step 1-1 at 45°C to 50°C while stirring, and after the addition, heating to 68°C to 78°C and stirring continuously for 1h to 3h;

[0010] Step 1-4, cooling to room temperature, adding an acid-base reagent to adjust the pH value to neutral, and vacuum drying to obtain a porous template polycondensation polymer material;

[0011] Step 2: Preparation of premixed precursor

[0012] Step 2-1, dissolving the porous template polycondensate polymer material in an organic solvent to obtain a porous template polycondensate solution for standby use;

[0013] Step 2-2, weighing or preparing lithium iron phosphate, wherein the mass ratio of lithium iron phosphate to the porous template condensation polymer material is 230-240:1;

[0014] Step 2-3, adding the lithium iron phosphate described in step S2-2 to the porous template polycondensate solution described in step S2-1, stirring and drying the mixture to remove the organic solvent, thereby obtaining a premixed precursor;

[0015] Step 3: Calcination

[0016] The premixed precursor is heated to 700° C. to 750° C. in an inert atmosphere, kept at this temperature for 8 h to 12 h, and then naturally cooled to room temperature to obtain the ultra-high capacity lithium iron phosphate material.

[0017] Preferably, the stirring time in step 1-1 is 10 min to 30 min, and the stirring speed is 120 rpm to 500 rpm.

[0018] Preferably, the stirring speed in steps 1-3 is 120 rpm.

[0019] Preferably, the acid-base reagent in steps 1-3 is a hydrochloric acid solution.

[0020] Preferably, the organic solvent in step 2-1 is ethanol.

[0021] Preferably, the stirring time in step 2-3 is 10 min to 120 min.

[0022] Preferably, the drying temperature in step 2-3 is 50°C

[0023] Preferably, the heating rate in step 3 is 3°C to 5°C / min.

[0024] Preferably, the inert gas in step 3 is nitrogen or argon.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention provides an ultra-high capacity lithium iron phosphate material and a preparation method thereof. The raw material source of the lithium iron phosphate material prepared by the method is wide and the cost is low, and the capacity of the lithium iron phosphate material is significantly improved, so that the lithium battery prepared by the method has a high energy density.

[0027] The porous template polycondensate polymer material of the present invention can provide more synthesis reaction sites during the preparation process and can also serve as a coating source for lithium iron phosphate. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a process flow chart of the present invention;

[0029] Figure 2 This is the XRD pattern of the product obtained in Example 1;

[0030] Figure 3 This is a TEM image of the product obtained using Example 1;

[0031] Figure 4 The charge and discharge curves are obtained by charging and discharging the product obtained in Example 1 at a current density of 17 mA / g;

[0032] Figure 5 The charge and discharge rate performance of the product obtained in Example 1 is shown. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with specific embodiments.

[0034] Example 1

[0035] Weigh 7.6 parts by weight of phenol, add 7.6 parts by weight of sodium hydroxide to a sodium hydroxide solution with a mass concentration of 20% to the phenol while the mixture is melted and stirred continuously, and stir the mixture at 150 rpm for 15 minutes to obtain a mixed solution;

[0036] Weigh 10 parts by weight of formaldehyde solution (mass concentration of 36%), add it to the above mixed solution at 50°C and 150 rpm with stirring. After the formaldehyde solution is completely added, heat it to 70°C, keep it warm and continue stirring for 2 hours. After cooling to room temperature, adjust the pH value to 7.0 with hydrochloric acid solution, and vacuum dry it to obtain a porous template condensation polymer material.

[0037] The lithium iron phosphate and porous template condensation polymer material are weighed at a weight ratio of 237:1, and the weighed porous template condensation polymer material is dissolved in ethanol to obtain a porous template condensation polymer solution with a mass concentration of 20%, and lithium iron phosphate is added to the obtained porous template condensation polymer solution, and the solution is continuously stirred at 200 rpm for 10 minutes at room temperature, and then vacuum dried to remove ethanol to obtain a premixed precursor. The obtained premixed precursor is placed in a high-purity Ar atmosphere, heated to 700°C at a heating rate of 4°C / min, and calcined at a constant temperature for 6 hours, and naturally cooled to obtain an ultra-high capacity lithium iron phosphate material product.

[0038] Example 2

[0039] Weigh 8 parts by weight of phenol, add 8 parts by weight of sodium hydroxide to a sodium hydroxide solution with a mass concentration of 20% to the phenol while the mixture is melted and continuously stirred, and stir at a speed of 120 rpm for 15 minutes to obtain a mixed solution;

[0040] Weigh 10.5 parts by weight of formaldehyde solution (mass concentration is 36%), add it to the above mixed solution at 50°C and 120 rpm with stirring. After the formaldehyde solution is completely added, heat to 70°C, keep warm and continue stirring for 2 hours. After cooling to room temperature, adjust the pH value to 7.0 with hydrochloric acid solution, and vacuum dry to obtain a porous template condensation polymer material.

[0041] The lithium iron phosphate and porous template condensation polymer material are weighed at a weight ratio of 237:1, and the weighed porous template condensation polymer material is dissolved in ethanol to obtain a porous template condensation polymer solution with a mass concentration of 20%, and lithium iron phosphate is added to the obtained porous template condensation polymer solution, and the ethanol is removed by vacuum drying at room temperature at a speed of 150 rpm for 120 minutes to obtain a premixed precursor. The obtained premixed precursor is placed in a high-purity Ar atmosphere, heated to 450°C at a heating rate of 4°C / min and calcined at a constant temperature for 4 hours, and then heated to 700°C at a heating rate of 4°C / min and calcined at a constant temperature for 10 hours, and naturally cooled to obtain an ultra-high capacity lithium iron phosphate material product.

[0042] It should be noted that the above are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and other variations are possible. All variations directly or indirectly derived from the disclosure of the present invention by those skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A method for preparing an ultra-high capacity lithium iron phosphate material, characterized in that: The following steps are involved: Step 1: Preparation of porous template polycondensation polymer material Step 1-1, after melting phenol, adding a sodium hydroxide aqueous solution with a mass concentration of 20%, wherein the mass ratio of phenol to sodium hydroxide solid is 1:1, stirring to obtain a mixed solution; Step 1-2: weighing a formaldehyde solution with a mass concentration of 30% to 40%, wherein the mass ratio of the formaldehyde solution to phenol is 1.3 to 1.4:1; Step 1-3, adding the formaldehyde solution to the mixed solution in step 1-1 at 45°C to 50°C while stirring, and after the addition, heating to 68°C to 78°C and stirring continuously for 1h to 3h; Step 1-4, cooling to room temperature, adding an acid-base reagent to adjust the pH value to neutral, and vacuum drying to obtain a porous template polycondensation polymer material; Step 2: Preparation of premixed precursor Step 2-1, dissolving the porous template polycondensate polymer material in an organic solvent to obtain a porous template polycondensate solution for standby use; Step 2-2, weighing lithium iron phosphate, wherein the mass ratio of lithium iron phosphate to the porous template condensation polymer material is 230-240:1; Step 2-3, adding the lithium iron phosphate described in step S2-2 to the porous template polycondensate solution described in step S2-1, stirring and drying the mixture to remove the organic solvent, thereby obtaining a premixed precursor; Step 3: Calcination The premixed precursor is heated to 700° C. to 750° C. in an inert atmosphere, kept at this temperature for 8 h to 12 h, and then naturally cooled to room temperature to obtain the ultra-high capacity lithium iron phosphate material.

2. The method for preparing the ultra-high capacity lithium iron phosphate material according to claim 1, characterized in that: The stirring time of step 1-1 is 10 min to 30 min, and the stirring speed is 120 rpm to 500 rpm.

3. The method for preparing the ultra-high capacity lithium iron phosphate material according to claim 1, characterized in that: The stirring speed in steps 1-3 is 120 rpm.

4. The method for preparing the ultra-high capacity lithium iron phosphate material according to claim 1, characterized in that: The acid-base reagent in step 1-3 is a hydrochloric acid solution.

5. The method for preparing the ultra-high capacity lithium iron phosphate material according to claim 1, characterized in that: The organic solvent in step 2-1 is ethanol.

6. The method for preparing the ultra-high capacity lithium iron phosphate material according to claim 1, characterized in that: The stirring time in step 2-3 is 10 min to 120 min.

7. The method for preparing the ultra-high capacity lithium iron phosphate material according to claim 1, characterized in that: The drying temperature in step 2-3 is 50°C.

8. The method for preparing the ultra-high capacity lithium iron phosphate material according to claim 1, characterized in that: The heating rate in step 3 is 3°C to 5°C / min.

9. The method for preparing the ultra-high capacity lithium iron phosphate material according to claim 1, characterized in that: In step 3, the inert gas is nitrogen or argon.

10. An ultra-high capacity lithium iron phosphate material, characterized in that: Prepared by any one of the methods of claims 1 to 9.

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