High-performance lithium iron phosphate composite material and preparation method thereof

Abstract

The application discloses a high-performance lithium iron phosphate composite material and a preparation method thereof, and belongs to the technical field of battery materials. Modified lithium iron phosphate, modified carbon nanotubes, benzoin dimethyl ether and chloroform are stirred, irradiated under a 365nm ultraviolet lamp for 15min, dried to obtain a premix; the premix, glacial acetic acid, polyethylene glycol and DMF are mixed, stirred at 70-80 DEG C for 4-6h, cooled, filtered, washed, immersed in a zinc acetate solution, placed, filtered, washed, dried to obtain the high-performance lithium iron phosphate composite material. The active substance, modified lithium iron phosphate, and the conductive agent, modified carbon nanotubes, have a chemical action, and the premix after the reaction of the two contains hydroxyl groups and a benzotriazole structure, so that the hydrogen bond interaction exists between the premix and the binder, and the adhesion between the premix and the aluminum foil current collector is excellent, therefore, the finished battery prepared from the lithium iron phosphate composite material has excellent and stable electrochemical performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and particularly relates to a high-performance lithium iron phosphate composite material and a preparation method thereof. BACKGROUND

[0002] With the increasingly prominent energy crisis and environmental pollution problems, developing new energy and solving storage problems have become the main task at present. High-performance energy storage equipment is an important carrier for new energy utilization. Green and environmentally friendly lithium ion batteries are widely welcomed due to their suitable working voltage, long cycle life, large energy density, small self-discharge and other advantages. As one of the key materials of lithium ion batteries, the positive electrode material plays a decisive role in the capacity of the entire lithium ion battery and has become the focus of research and development, industrialization and large-scale application in the field of new energy materials in various countries. Lithium iron phosphate, compared with other materials, has the advantages of good thermal stability, high safety performance, low price, environmental friendliness and the like, and has become one of the most potential positive electrode materials.

[0003] The prior art often uses a PVDF binder to bond conductive carbon black and lithium iron phosphate as a positive electrode material. The adhesion between this type of positive electrode material and aluminum foil is poor, thereby causing problems such as material dropping, powder falling off, poor overall flexibility of the positive electrode sheet, and reduction of the unit volume energy density of the electrode sheet, which are all not conducive to the performance of the final product battery. At the same time, the bonding strength between the conductive agent and the conductive active material is insufficient, and the electrode particles are easily detached due to vibration, thereby causing capacity attenuation. SUMMARY

[0004] The purpose of the present application is to overcome the defects of the prior art and provide a high-performance lithium iron phosphate composite material and a preparation method thereof.

[0005] The purpose of the present application can be achieved by the following technical solutions.

[0006] A preparation method of a high-performance lithium iron phosphate composite material, comprising the following steps:

[0007] (1) Under room temperature and nitrogen protection, the modified lithium iron phosphate, the modified carbon nanotube, the benzyldimethyl ether and the chloroform are fully stirred until they are uniformly mixed, then they are irradiated under a 365nm ultraviolet lamp for 15min, and finally they are dried to obtain a premix;

[0008] (2) The premix, the glacial acetic acid, the polyethylene glycol and the DMF (N,N-dimethylformamide) are uniformly mixed, then they are heated to 70-80℃ and stirred for 4-6h, after the reaction is completed, they are cooled to room temperature, then they are filtered, washed with anhydrous ethanol for 3-5 times, immersed in a zinc acetate solution, statically placed for 20h, then they are filtered, washed with anhydrous ethanol for 3-5 times, and finally they are vacuum dried at 80℃ for 8h to obtain the high-performance lithium iron phosphate composite material.

[0009] Further, the modified lithium iron phosphate in step (1) is prepared by the following steps:

[0010] S1, a dry three-necked flask is blown by nitrogen to discharge the air and moisture in the flask, then benzotriazole and chloroform are added, after stirring, the temperature is raised to 65℃, then KH560 (3-glycidyl ether oxypropyl trimethoxysilane) is slowly added, after the addition is completed, the reaction is stirred at 65℃ for 5h, after the reaction is completed, the temperature is cooled to room temperature, and the vacuum distillation is performed to obtain intermediate 1; the amount ratio of benzotriazole, KH560 and chloroform is 13.7g:19.9mL:110mL;

[0011] Under the heating condition, the molar ratio of benzotriazole and KH560 is controlled to be 1.2-1.3:1, then the -NH- of benzotriazole and the epoxy group of KH560 react, and the reaction process is as shown in the following formula:

[0012]

[0013] S2, a dry three-necked flask is blown by nitrogen to discharge the air and moisture in the flask, then intermediate 1, 10% sodium hydroxide solution and benzene are added, after stirring, the temperature is raised to 60℃, then butylene oxide is slowly added, after the addition is completed, the reaction is stirred at 60℃ for 5h, after the reaction is completed, the temperature is cooled to room temperature, and the vacuum distillation is performed to obtain intermediate 2; the amount ratio of intermediate 1 and butylene oxide is 30.2g:5.4mL;

[0014] Under the heating and alkali catalysis condition, the -OH of intermediate 1 and the epoxy group of butylene oxide react, and the reaction process is as shown in the following formula:

[0015]

[0016] S3, lithium carbonate, ferrous oxalate dihydrate and ammonium dihydrogen phosphate are mixed uniformly to obtain a reactant, which is used for stirring with polyethylene glycol and deionized water for 12h, then filtered, vacuum dried for 12h, and finally calcined at 700℃ for 10h under the protection of nitrogen, and naturally cooled to room temperature to obtain lithium iron phosphate; the lithium iron phosphate and deionized water are added into a dry three-necked flask, stirred uniformly, then slowly added with concentrated hydrochloric acid to adjust the pH value of the system to 5, then the temperature is raised to 65℃, and a mixed solution of DMF and intermediate 2 is added, and the reaction is stirred at 65℃ for 10h, and finally cooled to room temperature, filtered, washed with anhydrous ethanol for 5 times, and dried at 80℃ for 12h to obtain modified lithium iron phosphate; the amount ratio of lithium carbonate, ferrous oxalate dihydrate and ammonium dihydrogen phosphate is 7.4g:17.8g:11.5g; the amount ratio of the reactant, polyethylene glycol and deionized water is 36g:7.2g:220mL; and the amount ratio of lithium iron phosphate and intermediate 2 is 20:1.

[0017] The oil-containing siloxyl group in intermediate 2 can be hydrolyzed and condensed to form Si-O-Si and Si-OH, and the Si-OH can be crosslinked with the hydroxyl groups on the surface of the modified lithium iron phosphate to form the modified lithium iron phosphate, so that the dispersion of the modified lithium iron phosphate is greatly improved, and the modified lithium iron phosphate can fully play a role.

[0018] The surface of the modified lithium iron phosphate further has a carbon-carbon double bond, a hydroxyl group and a benzotriazole structure. The hydroxyl group can interact with the hydroxyl group in the polyethylene glycol adhesive through hydrogen bonding, so that the adhesion of the lithium iron phosphate composite is good and the lithium iron phosphate composite is not easy to fall off. Meanwhile, the three nitrogen atoms in the benzotriazole structure are adjacent to the benzene ring, and have strong coordination ability, so that a stable complex can be formed through coordination bonding between the aluminum on the aluminum foil current collector and the aluminum, so that the lithium iron phosphate composite can be adhered to the aluminum foil for a long time and is not easy to fall off, thereby playing a role.

[0019] Further, the modified carbon nanotube in step (1) is prepared by the following steps:

[0020] The carbon nanotube and deionized water are added to a dry three-necked flask, stirred uniformly, then concentrated hydrochloric acid is slowly added to adjust the pH value of the system to 5, then the temperature is raised to 65 DEG C, a mixed solution of anhydrous ethanol and gamma-mercaptopropyl trimethoxysilane is added, stirring is continued at 65 DEG C for 10 hours, finally the temperature is cooled to room temperature, suction filtration is performed, washing with anhydrous ethanol is performed 5 times, and drying is performed at 80 DEG C for 12 hours to obtain the modified carbon nanotube; the amount ratio of the carbon nanotube to gamma-mercaptopropyl trimethoxysilane is 10:1.

[0021] The carbon nanotube can form a linear contact type conductive network between active substances, greatly increase the contact between electrode particles, thereby significantly reducing the battery interface impedance, improving the conductivity, and the amount is small. The surface of the carbon nanotube is treated with gamma-mercaptopropyl trimethoxysilane, so that the carbon nanotube surface contains mercapto groups.

[0022] The carbon-carbon double bond on the modified lithium iron phosphate and the mercapto group on the modified carbon nanotube undergo a click reaction under the action of benzoin dimethyl ether, so that the modified lithium iron phosphate and the modified carbon nanotube can be well adhered together, and the benzotriazole structure on the modified lithium iron phosphate makes the lithium iron phosphate composite adhere to the aluminum foil for a long time and not easy to fall off, thereby the electrochemical performance of the composite material of the present application is more excellent and stable after the composite material is made into a corresponding battery.

[0023] Further, the amount ratio of the modified lithium iron phosphate, the modified carbon nanotube, benzoin dimethyl ether and chloroform in step (1) is 42g:(11-13)g:(0.02-0.05)g:240mL.

[0024] Further, the mass ratio of the premix, glacial acetic acid, polyethylene glycol and DMF in step (2) is 40:(1-2):(1-2):(25-35).

[0025] Further, the zinc acetate solution in step (2) is obtained by mixing zinc acetate and DMF in a mass ratio of 1: (20-30).

[0026] The application further discloses a high-performance lithium iron phosphate composite material prepared according to the preparation method of the high-performance lithium iron phosphate composite material.

[0027] The application has the following beneficial effects: the active substance, modified lithium iron phosphate, and the conductive agent, modified carbon nanotube, have a chemical interaction, and the premix after the reaction contains hydroxyl groups and benzotriazole structures, so that the hydrogen bond interaction between the premix and the binder and the excellent adhesion between the premix and the aluminum foil current collector are achieved, and therefore, the finished battery prepared from the lithium iron phosphate composite material has excellent and stable electrochemical performance. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the application.

[0029] Embodiment 1

[0030] The modified lithium iron phosphate is prepared according to the following specific steps:

[0031] S1, a dry three-necked flask is blown by nitrogen to discharge the air and moisture in the flask, then 13.7 g of benzotriazole and 110 mL of chloroform are added, and after uniform stirring, the temperature is increased to 65 DEG C, and then 19.9 mL of KH560 is slowly added, after the addition is completed, the reaction is stirred at 65 DEG C for 5 h, and after the reaction is completed, the temperature is cooled to room temperature, and the pressure is reduced to distill, to obtain intermediate 1;

[0032] S2, a dry three-necked flask is blown by nitrogen to discharge the air and moisture in the flask, then 30.2 g of intermediate 1, 24 mL of 10% sodium hydroxide solution and 180 mL of benzene are added, and after uniform stirring, the temperature is increased to 60 DEG C, and then 5.4 mL of epoxy butene is slowly added, after the addition is completed, the reaction is stirred at 60 DEG C for 5 h, and after the reaction is completed, the temperature is cooled to room temperature, and the pressure is reduced to distill, to obtain intermediate 2;

[0033] S3, 7.4 g of lithium carbonate, 17.8 g of ferrous acetate dihydrate, 11.5 g of ammonium dihydrogen phosphate were mixed uniformly to obtain a reactant, which was prepared for use. Then, 36 g of the reactant, 7.2 g of polyethylene glycol and 220 mL of deionized water were stirred for 12 h, followed by filtration, vacuum drying for 12 h, and finally calcination at 700°C for 10 h under nitrogen protection, and natural cooling to room temperature to obtain lithium iron phosphate; 40 g of lithium iron phosphate and 300 mL of deionized water were added to a 500 mL dry three-necked flask, and after being stirred uniformly, concentrated hydrochloric acid was slowly added to adjust the pH value of the system to 5, then the temperature was increased to 65°C, and 10 mL of a mixed solution of DMF and 2 g of intermediate 2 was added, and the reaction was stirred at 65°C for 10 h, and finally cooled to room temperature, filtered, washed with anhydrous ethanol 5 times, and dried at 80°C for 12 h to obtain modified lithium iron phosphate.

[0034] Example 2

[0035] The modified carbon nanotubes were prepared by the following specific steps:

[0036] 11 g of carbon nanotubes and 200 mL of deionized water were added to a 500 mL dry three-necked flask, stirred uniformly, and then concentrated hydrochloric acid was slowly added to adjust the pH value of the system to 5, then the temperature was increased to 65°C, and 10 mL of a mixed solution of anhydrous ethanol and 1.1 g of γ-mercaptopropyl trimethoxysilane was added, and the reaction was continued at 65°C for 10 h, and finally cooled to room temperature, filtered, washed with anhydrous ethanol 5 times, and dried at 80°C for 12 h to obtain modified carbon nanotubes.

[0037] Example 3

[0038] The lithium iron phosphate composite material was prepared by the following specific steps:

[0039] (1) 42 g of modified lithium iron phosphate, 12 g of modified carbon nanotubes, 0.03 g of benzoin dimethyl ether and 240 mL of chloroform were fully stirred under nitrogen protection at room temperature until they were mixed uniformly, and then irradiated under a 365 nm ultraviolet lamp for 15 min, and finally dried to obtain a premix;

[0040] (2) The premix, glacial acetic acid, polyethylene glycol and DMF were mixed uniformly, and the mass ratio of the premix, glacial acetic acid, polyethylene glycol and DMF was 40:1:1:30, and then the temperature was increased to 75°C and the reaction was stirred for 5 h, and after the reaction was completed, the temperature was cooled to room temperature, filtered, washed with anhydrous ethanol 4 times, immersed in a zinc acetate solution, and the mass ratio of zinc acetate and DMF was 1:25, and then placed for 20 h, filtered, washed with anhydrous ethanol 4 times, and dried at 80°C for 8 h under vacuum to obtain a high-performance lithium iron phosphate composite material.

[0041] Example 4

[0042] The lithium iron phosphate composite material was prepared by the following specific steps:

[0043] (1) 42 g of modified lithium iron phosphate, 11 g of modified carbon nanotubes, 0.02 g of benzo pinacol and 240 mL of chloroform were fully stirred to be mixed uniformly under room temperature and nitrogen protection, then irradiated under a 365 nm ultraviolet lamp for 15 min, and finally dried to obtain a premix;

[0044] (2) The premix, glacial acetic acid, polyethylene glycol and DMF were mixed uniformly, wherein the mass ratio of the premix, glacial acetic acid, polyethylene glycol and DMF was 40:2:2:30, then the temperature was raised to 80°C for stirring reaction for 6 h, after the reaction was completed, the temperature was cooled to room temperature, filtered, washed with anhydrous ethanol for 5 times, immersed in a zinc acetate solution, wherein the mass ratio of zinc acetate and DMF was 1:30, and then placed for 20 h, filtered, washed with anhydrous ethanol for 5 times, and vacuum dried at 80°C for 8 h to obtain the high-performance lithium iron phosphate composite material.

[0045] Example 5

[0046] The lithium iron phosphate composite material was prepared by the following specific steps:

[0047] (1) 42 g of modified lithium iron phosphate, 11 g of modified carbon nanotubes, 0.02 g of benzo pinacol and 240 mL of chloroform were fully stirred to be mixed uniformly under room temperature and nitrogen protection, then irradiated under a 365 nm ultraviolet lamp for 15 min, and finally dried to obtain a premix;

[0048] (2) The premix, glacial acetic acid, polyethylene glycol and DMF were mixed uniformly, wherein the mass ratio of the premix, glacial acetic acid, polyethylene glycol and DMF was 40:2:2:30, then the temperature was raised to 80°C for stirring reaction for 6 h, after the reaction was completed, the temperature was cooled to room temperature, filtered, washed with anhydrous ethanol for 5 times, immersed in a zinc acetate solution, wherein the mass ratio of zinc acetate and DMF was 1:30, and then placed for 20 h, filtered, washed with anhydrous ethanol for 5 times, and vacuum dried at 80°C for 8 h to obtain the high-performance lithium iron phosphate composite material.

[0049] Comparative Example 1

[0050] The lithium iron phosphate composite material was prepared by the following specific steps:

[0051] The remaining steps were unchanged, only the modified lithium iron phosphate in step (1) of Example 3 was replaced by lithium carbonate without any treatment, thereby obtaining the lithium iron phosphate composite material.

[0052] Comparative Example 2

[0053] The lithium iron phosphate composite material was prepared by the following specific steps:

[0054] The remaining steps were unchanged, only the modified carbon nanotubes in step (1) of Example 3 were replaced by carbon nanotubes without any treatment, thereby obtaining the lithium iron phosphate composite material.

[0055] Comparative Example 3

[0056] The lithium iron phosphate composite material was prepared according to the following specific steps:

[0057] The remaining steps were unchanged, and only the modified lithium iron phosphate in step (1) of Example 3 was replaced with untreated lithium carbonate, and the modified carbon nanotube was replaced with untreated carbon nanotube, so as to prepare the lithium iron phosphate composite material.

[0058] Performance test

[0059] Preparation of positive electrode sheet: Place the aluminum foil current collector at the bottom of the inner diameter 14 mm cylindrical mold, then place the lithium iron phosphate composite material prepared in Examples 3-5 and Comparative Examples 1-3, dry at 95°C for 35 min, mold at 240°C under nitrogen atmosphere, 1.4 MPa mold pressure for 25 min, then heat to 520°C at a rate of 4°C / min and stand for 1-2 h, keep the mold pressure unchanged and cool to room temperature to take out the positive electrode sheet of the button cell;

[0060] Preparation of button cell: Mix lithium hexafluorophosphate, ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate in a mass ratio of 1:2:2:2 to prepare an electrolyte, assemble and fill the electrolyte in the order of positive electrode shell, positive electrode sheet, Celgard2400 separator, lithium sheet, nickel mesh, and negative electrode shell, seal, and assemble into a button cell.

[0061] The positive electrode sheet prepared in Examples 3-5 and Comparative Examples 1-3 was cut into small pieces of 4*10 cm, and then peel strength test was performed on a peel strength machine, and the test results are shown in Table 1 below:

[0062] Table 1

[0063]

[0064] The lithium iron phosphate composite materials prepared in Examples 3-5 and Comparative Example 1 were made into button cells, and the following performance tests were performed:

[0065] (1) Safety performance test of lithium iron phosphate battery: overcharge, overdischarge and needle test were performed according to GB / T 31485-2015 standard, and all were qualified;

[0066] (2) Cycle performance test of lithium iron phosphate battery was performed according to GB / T 31484-2015 standard;

[0067] (3) Charge-discharge experiment was performed at 25°C and 1C current density, and the initial discharge capacity was tested by Neware battery test system BTS-3000 to evaluate the electrical performance;

[0068] (4) The anti-vibration performance was evaluated by recording the vibration damage rate = (1 - discharge capacity after vibration / initial discharge capacity) x 100% under the condition of 1C current density at 25°C after 50h of vibration at 30 kHz.

[0069] The test results of all items are shown in Table 2 below:

[0070] Table 2

[0071]

[0072] In the description of the specification, the description of the terms "one embodiment", "an example", "a specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Also, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0073] The above is only an example and illustration of the present application, and those skilled in the art can make various modifications or supplements to the described specific embodiments or replace them with similar ways, as long as they do not deviate from the invention or exceed the scope defined by the present claims.

Claims

1. A method for preparing a high-performance lithium iron phosphate composite material, characterized in that: The following steps are involved: (1) Modified lithium iron phosphate, modified carbon nanotubes, dimethyl benzoate, and chloroform were stirred at room temperature under nitrogen protection, irradiated under a 365 nm ultraviolet lamp for 15 minutes, and dried to obtain a premix; (2) mixing the premix, glacial acetic acid, polyethylene glycol, and DMF, heating to 70-80° C. and stirring for 4-6 hours, cooling, filtering, washing, immersing in a zinc acetate solution, allowing to stand, filtering, washing, and drying to obtain a high-performance lithium iron phosphate composite material; Wherein, the modified lithium iron phosphate in step (1) is prepared by the following steps: S1. After nitrogen was purged into the flask, benzotriazole and chloroform were added, the temperature was raised to 65°C with stirring, KH560 was added, the reaction was carried out at 65°C for 5 hours, the reaction was cooled, and the reaction was evaporated under reduced pressure to obtain intermediate 1; S2. After nitrogen purging the flask, add intermediate 1, 10% sodium hydroxide solution and benzene, stir and heat to 60°C, add epoxybutene, react at 60°C for 5h, cool, and distill under reduced pressure to obtain intermediate 2; S3. Mix lithium carbonate, ferrous oxalate dihydrate, and ammonium dihydrogen phosphate to obtain a reactant; stir the reactant, polyethylene glycol, and deionized water, filter, dry, calcine at 700° C. for 10 h, and cool to obtain lithium iron phosphate; add lithium iron phosphate and deionized water to a flask, adjust the pH, heat to 65° C., add DMF and intermediate 2, react for 10 h, cool, filter, wash, and dry to obtain modified lithium iron phosphate; The modified carbon nanotubes in step (1) are prepared by the following steps: Add carbon nanotubes and deionized water to a flask, stir and adjust the pH value of the system to 5, heat to 65°C, add anhydrous ethanol and γ-mercaptopropyltrimethoxysilane, stir at 65°C for 10 hours, cool, filter, wash and dry to obtain modified carbon nanotubes.

2. The method for preparing a high-performance lithium iron phosphate composite material according to claim 1, characterized in that: The usage ratio of benzotriazole, KH560 and chloroform in step S1 is 13.7 g:19.9 mL:110 mL.

3. The method for preparing a high-performance lithium iron phosphate composite material according to claim 1, characterized in that: The usage ratio of intermediate 1 and epoxybutene in step S2 is 30.2 g:5.4 mL.

4. The method for preparing a high-performance lithium iron phosphate composite material according to claim 1, characterized in that: The amount ratio of lithium carbonate, ferrous oxalate dihydrate, and ammonium dihydrogen phosphate in step S3 is 7.4g:17.8g:11.5g; the amount ratio of reactants, polyethylene glycol, and deionized water is 36g:7.2g:220mL; and the amount ratio of lithium iron phosphate to intermediate 2 is 20:

1.

5. The method for preparing a high-performance lithium iron phosphate composite material according to claim 1, characterized in that: The usage ratio of carbon nanotubes to γ-mercaptopropyltrimethoxysilane is 10:

1.

6. The method for preparing a high-performance lithium iron phosphate composite material according to claim 1, characterized in that: In the step (1), the usage ratio of modified lithium iron phosphate, modified carbon nanotubes, benzoin dimethyl ether and chloroform is 42 g: (11-13) g: (0.02-0.05) g: 240 mL.

7. The method for preparing a high-performance lithium iron phosphate composite material according to claim 1, characterized in that: The mass ratio of the premix, glacial acetic acid, polyethylene glycol and DMF in step (2) is 40:(1-2):(1-2):(25-35).

8. The method for preparing a high-performance lithium iron phosphate composite material according to claim 1, characterized in that: The zinc acetate solution in step (2) is obtained by mixing zinc acetate and DMF in a mass ratio of 1:(20-30).

9. A high-performance lithium iron phosphate composite material, characterized in that: It is prepared according to the preparation method of a high-performance lithium iron phosphate composite material according to any one of claims 1-8.

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