Ferrous fluoride positive electrode pre-lithiation method and application in lithium ion battery

Abstract

The invention discloses a ferrous fluoride pre-lithiation method which comprises the following steps: (1) reacting reduced iron powder with a fluosilicic acid solution to obtain a precursor solution, and diluting, drying and calcining the precursor solution to obtain ferrous fluoride powder; (2) mixing ferrous fluoride, conductive carbon and a binder to obtain a slurry, and coating the slurry on an aluminum foil to prepare a pole piece; (3) immersing the prepared pole piece in an n-butyllithium solution to react for different times; and (4) cleaning the reacted pole piece with n-hexane to obtain a product. Through pre-lithiation of ferrous fluoride, the performance of the lithium ion battery is remarkably improved, and matching with a limited lithium negative electrode is completed.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery positive electrode material modification, and in particular relates to a method for pre-lithiation of a ferrous fluoride positive electrode. Background Art

[0002] Compared with traditional intercalation cathode materials, iron-based fluorides have been widely studied for their high theoretical capacity density and environmental friendliness. However, some inherent defects of metal fluorides have hindered their commercialization. Among them, compared with traditional commercial lithium-containing cathodes, iron-based fluorides do not contain lithium sources and are difficult to match with negative electrodes such as graphite. Therefore, the study of pre-lithiation of iron-based fluoride cathodes is particularly important. Summary of the invention

[0003] The purpose of the present invention is to provide a method for pre-lithiation of ferrous fluoride positive electrode, which has a simple process, significantly improves the cycle performance of lithium ion batteries, and provides a new idea for the application of metal fluoride positive electrodes in lithium ion batteries.

[0004] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0005] (1) reacting elemental iron with a fluorosilicic acid solution to obtain respective precursor solutions, adding deionized water to the precursor solution to uniformly dilute it, and drying it to obtain a solid powder.

[0006] (2) Under a protective atmosphere, the solid powder is calcined at 220-280°C to obtain FeF2.

[0007] (3) FeF2, conductive carbon Super P and binder PVDF were mixed evenly in proportion and added into N-methylpyrrolidone and stirred at 300 r / min to form a slurry.

[0008] (4) The stirred slurry is evenly coated on aluminum foil, and the FeF2 positive electrode is obtained after vacuum drying, and the FeF2 electrode is obtained after punching.

[0009] (5) Immerse the FeF2 electrode in n-butyl lithium solution for different immersion reaction times.

[0010] (6) After the reaction is completed, the electrode is washed and dried in n-hexane to obtain a pre-lithiated FeF2 positive electrode.

[0011] Furthermore, in step (1), the reaction time is 12 to 24 hours.

[0012] Furthermore, in step (1), the mass fraction of the fluorosilicic acid solution is 30 to 32 wt%.

[0013] Furthermore, in step (1), the dilution multiple of deionized water is 3 to 10 times.

[0014] Furthermore, in step (2), the calcination heating rate is 2 to 5°C / min, and the holding time is 4 to 8h.

[0015] Furthermore, in step (3), the ratio of FeF2, Super P and PVDF is 7:2:1.

[0016] Furthermore, in step (3), the slurry stirring time is 12 to 24 hours.

[0017] Furthermore, in step (4), the vacuum drying temperature is 80° C. and the time is 10 to 12 hours.

[0018] Furthermore, in step (4), the FeF2 pole piece punching diameter is 12 mm.

[0019] Furthermore, in step (5), the concentration of the n-butyllithium solution is 1.6M to 2.4M.

[0020] Furthermore, in step (5), the reaction time is 1 to 5 hours.

[0021] Furthermore, in step (6), the n-hexane washing time is 10 to 30 minutes.

[0022] Furthermore, in step (6), the drying time is 6 to 8 hours.

[0023] The advantages of the present invention are:

[0024] The pre-lithiation method of the ferrous fluoride positive electrode of the present invention has a simple process. The ferrous fluoride positive electrode forms iron and lithium fluoride in situ in an n-butyl lithium solution, so that the ferrous fluoride contains a lithium source, which effectively improves the cycle life of the ferrous fluoride positive electrode and provides a new idea for the commercialization of fluoride positive electrodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 1 is the XRD diagram of the pre-lithiation and original ferrous fluoride obtained in Examples 1-3 and Comparative Example 1.

[0026] Figure 2 This is the TEM image of ferrous fluoride prepared in Example 1 after pre-lithiation for 30 minutes.

[0027] Figure 3 This is the TEM image of pre-lithiated 1h ferrous fluoride obtained in Example 2.

[0028] Figure 4 This is the TEM image of pre-lithiated 5h ferrous fluoride obtained in Example 3.

[0029] Figure 5The cycle diagram of the button batteries assembled for Examples 1-3 and Comparative Example 1 at room temperature, 1-4V voltage range, and 0.2C rate. DETAILED DESCRIPTION

[0030] The present invention will be described in more detail below in conjunction with the accompanying drawings and embodiments. The embodiments described below are part of the embodiments of the present invention, and the protection scope of the present invention is not limited to the following embodiments.

[0031] Example 1

[0032] 1.4 g of iron powder was reacted with 10 g of 30-32% fluorosilicic acid to obtain a precursor solution. The precursor solution was diluted 5 times with deionized water. The diluted solution was placed on a heating table and dried at 60°C for 72 h. The dried sample was placed in a tubular furnace in an argon atmosphere and heated to 250°C at a heating rate of 3°C / min and kept warm for 8 h to obtain FeF2.

[0033] The FeF2 sample synthesized above is made into a circular electrode.

[0034] The specific operation of the above process is as follows: FeF2, Super P, and PVDF are weighed respectively in a mass ratio of 7:2:1, placed in a mortar and ground for 30 minutes to fully mix them, and then an appropriate amount of NMP is added, placed on a stirring table at 300r / min, and stirred for 12 hours to obtain a mixed slurry, and then it is evenly coated on aluminum foil through a coater, placed in a vacuum drying oven at 80°C and dried for 12 hours, and cut into small circular electrodes with a diameter of 12mm and a mass of about 7.5mg by a cutting machine.

[0035] Immerse 15 FeF2 electrodes in 6 ml of 1.6 M n-butyl lithium solution and react for 30 minutes.

[0036] After the reaction was completed, the sample was soaked and washed with 10 ml of n-hexane for 30 min and then dried naturally for 6 h. The entire reaction and washing process was carried out in a vacuum glove box filled with argon.

[0037] The button cell was assembled in a vacuum glove box filled with argon gas, and after being left to stand for 12 hours, the electrochemical performance test was performed.

[0038] Example 2

[0039] 1.4 g of iron powder was reacted with 10 g of 30-32% fluorosilicic acid to obtain a precursor solution. The precursor solution was diluted 5 times with deionized water. The diluted solution was placed on a heating table and dried at 60°C for 72 h. The dried sample was placed in a tubular furnace in an argon atmosphere and heated to 250°C at a heating rate of 3°C / min and kept warm for 8 h to obtain FeF2.

[0040] The FeF2 sample synthesized above is made into a circular electrode.

[0041] The specific operation of the above process is as follows: FeF2, Super P, and PVDF are weighed respectively in a mass ratio of 7:2:1, placed in a mortar and ground for 30 minutes to fully mix them, and then an appropriate amount of NMP is added, placed on a stirring table at 300r / min, and stirred for 12 hours to obtain a mixed slurry, and then it is evenly coated on aluminum foil through a coater, placed in a vacuum drying oven at 80°C and dried for 12 hours, and cut into small circular electrodes with a diameter of 12mm and a mass of about 7.5mg by a cutting machine.

[0042] Immerse 15 FeF2 electrodes in 6 ml of 1.6 M n-butyl lithium solution and react for 1 hour.

[0043] After the reaction was completed, the sample was soaked and washed with 10 ml of n-hexane for 1 hour and then dried naturally for 6 hours. The entire reaction and washing process was carried out in a vacuum glove box filled with argon.

[0044] The button cell was assembled in a vacuum glove box filled with argon gas, and after being left to stand for 12 hours, the electrochemical performance test was performed.

[0045] Example 3

[0046] 1.4 g of iron powder was reacted with 10 g of 30-32% fluorosilicic acid to obtain a precursor solution. The precursor solution was diluted 5 times with deionized water. The diluted solution was placed on a heating table and dried at 60°C for 72 h. The dried sample was placed in a tubular furnace in an argon atmosphere and heated to 250°C at a heating rate of 3°C / min and kept warm for 8 h to obtain FeF2.

[0047] The FeF2 sample synthesized above is made into a circular electrode.

[0048] The specific operation of the above process is as follows: FeF2, Super P, and PVDF are weighed respectively in a mass ratio of 7:2:1, placed in a mortar and ground for 30 minutes to fully mix them, and then an appropriate amount of NMP is added, placed on a stirring table at 300r / min, and stirred for 12 hours to obtain a mixed slurry, and then it is evenly coated on aluminum foil through a coater, placed in a vacuum drying oven at 80°C and dried for 12 hours, and cut into small circular electrodes with a diameter of 12mm and a mass of about 7.5mg by a cutting machine.

[0049] Immerse 15 FeF2 electrodes in 6 ml of 1.6 M n-butyl lithium solution and react for 5 hours.

[0050] After the reaction was completed, the sample was soaked and washed with 10 ml of n-hexane for 5 h and then dried naturally for 6 h. The entire reaction and washing process was carried out in a vacuum glove box filled with argon.

[0051] The button cell was assembled in a vacuum glove box filled with argon gas, and after being left to stand for 12 hours, the electrochemical performance test was performed.

[0052] Comparative Example 1

[0053] 1.4 g of iron powder was reacted with 10 g of 30-32% fluorosilicic acid to obtain a precursor solution. The precursor solution was diluted 5 times with deionized water. The diluted solution was placed on a heating table and dried at 60°C for 72 h. The dried sample was placed in a tubular furnace in an argon atmosphere and heated to 250°C at a heating rate of 3°C / min and kept warm for 8 h to obtain FeF2.

[0054] The FeF2 sample synthesized above is made into a circular electrode.

[0055] The specific operation of the above process is as follows: FeF2, Super P, and PVDF are weighed respectively in a mass ratio of 7:2:1, placed in a mortar and ground for 30 minutes to fully mix them, and then an appropriate amount of NMP is added, placed on a stirring table at 300r / min, and stirred for 12 hours to obtain a mixed slurry, and then it is evenly coated on aluminum foil through a coater, placed in a vacuum drying oven at 80°C and dried for 12 hours, and cut into small circular electrodes with a diameter of 12mm and a mass of about 7.5mg by a cutting machine.

[0056] The button cell was assembled in a vacuum glove box filled with argon gas, and after being left to stand for 12 hours, the electrochemical performance test was performed.

[0057] Among them, PVDF is polyvinylidene fluoride, and NMP is N-methylpyrrolidone.

Claims

1. A method for pre-lithiation of ferrous fluoride positive electrode in a lithium ion battery, characterized in that: The steps include: (1) Reduced iron powder is reacted with a fluorosilicic acid solution to obtain a precursor solution, the precursor solution is diluted with deionized water, and a solid powder is obtained after drying, and the solid powder is calcined at 250° C. under argon to obtain ferrous fluoride. (2) The prepared ferrous fluoride, conductive carbon Super P and binder PVDF are evenly ground in a certain proportion, added into N-methylpyrrolidone and stirred to form a slurry. (3) The slurry is coated on an aluminum foil current collector, and after vacuum drying, it is cut to obtain ferrous fluoride electrodes. (4) Immerse the ferrous fluoride electrode in an n-butyl lithium solution and control the degree of reaction by controlling the immersion time. (5) The ferrous fluoride positive electrode sheet after the reaction is immersed in n-hexane for cleaning, and after drying, a ferrous fluoride positive electrode with different degrees of pre-lithiation is obtained.

2. The method for pre-lithiation of ferrous fluoride according to claim 1, characterized in that: In step (1), the reaction time is 12 to 24 hours.

3. The method for pre-lithiation of ferrous fluoride according to claim 1, characterized in that: In step (1), the mass fraction of the fluorosilicic acid solution is 30 to 32 wt %.

4. The method for pre-lithiation of ferrous fluoride according to claim 1, characterized in that: In step (1), the dilution multiple of deionized water is 3 to 10 times.

5. The method for pre-lithiation of ferrous fluoride according to claim 1, characterized in that: In step (1), the heating rate of the calcination process is 2 to 5°C / min, and the holding time is 4 to 8h.

6. The method for pre-lithiation of ferrous fluoride according to claim 1, characterized in that: In step (2), the ratio of ferrous fluoride, Super P and PVDF is 7:2:

1.

7. The method for pre-lithiation of ferrous fluoride according to claim 1, characterized in that: In step (2), the slurry is stirred for 12 h to 24 h.

8. The method for pre-lithiation of ferrous fluoride according to claim 1, characterized in that: In step (3), the cutting diameter is 12 mm.

9. The method for pre-lithiation of ferrous fluoride according to claim 1, characterized in that: In step (4), the immersion time is controlled to 30 min, 1 h, and 5 h.

10. The method for pre-lithiation of ferrous fluoride according to claim 1, characterized in that: In step (5), the cleaning time is 30 minutes.

11. The method for pre-lithiation of ferrous fluoride according to claim 1, characterized in that: In step (5), the drying time is 6 hours.

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