Spherical sodium ion battery positive electrode material and preparation process thereof

Abstract

The invention discloses a spherical sodium-ion battery positive electrode material and a preparation process thereof, and belongs to the technical field of sodium-ion batteries. According to the technical scheme, the preparation method comprises the following steps: S1, mixing MnF2 and NaF, and dispersing the mixture in an organic solvent to obtain a dispersion liquid; s2, carrying out vacuum drying on the dispersion liquid to obtain a mixed dispersion of MnF2 and NaF; s3, carrying out ball milling on the mixed dispersion until the particle size is 0.1-0.2 mu m, so as to obtain NaMnF3; and S4, carrying out hydrothermal reaction on the NaMnF3 and the fluorinated carbon fiber to synthesize the spherical sodium ion battery positive electrode material. According to the invention, the NaMnF3 positive electrode material is coated with the fluorinated carbon fiber, so that the reversibility and the capacity retention rate of the NaMnF3 positive electrode material during charging and discharging are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and particularly to a spherical sodium-ion battery cathode material and a preparation process thereof. Background Art

[0002] As the source of active sodium ions in sodium-ion batteries, the cathode material plays a crucial role in the performance of battery capacity. With the increasing social attention to sodium-ion batteries, it is urgent to find a cathode material with high specific energy and low cost. When NaMnF3 is used as the cathode material, due to the high electronegativity of F, the F-Mn structure has strong stability, so NaMnF3 has good stability in the electrochemical reaction. However, the reversibility and conductivity of the NaMnF3 cathode material are poor, resulting in a low capacity retention rate. Therefore, a preparation process is needed to improve the reversibility and capacity retention rate of the NaMnF3 material during charge and discharge. Summary of the Invention

[0003] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art and provide a spherical sodium-ion battery cathode material and a preparation process thereof. By coating the NaMnF3 cathode material with fluorinated carbon fiber, its reversibility and capacity retention rate during charge and discharge are improved.

[0004] The technical solution of the present invention is as follows:

[0005] On the one hand, the present invention provides a preparation process of a spherical sodium-ion battery cathode material, including the following steps:

[0006] S1 Mix MnF2 and NaF and disperse them in an organic solvent to obtain a dispersion;

[0007] S2 Vacuum-dry the dispersion to obtain a mixed dispersion of MnF2 and NaF;

[0008] S3 Ball-mill the mixed dispersion to a particle size of 0.1 - 0.2 μm to obtain NaMnF3;

[0009] S4 Perform a hydrothermal reaction on NaMnF3 and fluorinated carbon fiber to synthesize a spherical sodium-ion battery cathode material.

[0010] Preferably, in step S1, the molar ratio of MnF2 to NaF is 1:(1 - 1.5), and the solid-liquid ratio of the dispersion is 1:(2 - 3).

[0011] Preferably, in step S1, after mixing MnF2 and NaF, add them to an organic solvent and perform ultrasonic dispersion, with an ultrasonic power of 120 - 420 W.

[0012] Preferably, in step S1, the organic solvent is N-methylpyrrolidone (NMP) or ethylene glycol.

[0013] Preferably, in step S2, the temperature of the vacuum drying is 70-90 °C.

[0014] Preferably, in step S3, a planetary ball mill is used to perform dry ball milling on the mixed dispersion, agate balls are used as grinding balls, the ball-to-material ratio is (10-12):1, the ball milling speed is 300-350 rpm, and the ball milling time is 8-12 h.

[0015] Preferably, in step S4, the mass ratio of the fluorinated carbon fiber to NaMnF3 is 1:(5-8).

[0016] Preferably, in step S4, the temperature of the hydrothermal reaction is 300-500 °C, the heating rate is 1-3 °C / min, and the heat preservation time is 6-10 h.

[0017] On the other hand, the present invention also provides a spherical sodium-ion battery cathode material, which is prepared by the above-mentioned preparation process of the spherical sodium-ion battery cathode material, and the molecular formula is NaMnCF 3.5 .

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] In the preparation process of the present invention, a hydrothermal method is used to prepare a NaMnF3 cathode material coated with fluorinated carbon fiber, which has good dispersion, more sufficient electrochemical reactions, and a greatly improved capacity retention rate, providing the possibility for further preparing a sodium-ion battery with a high cycle life. Description of the Drawings

[0020] Figure 1 is the SEM image of the cathode material NaMnCF prepared in Example 1 of the present invention 3.5 .

[0021] Figure 2 is the SEM image of the cathode material NaMnCF prepared in Comparative Example 1 of the present invention 3.5 .

[0022] Figure 3 is the SEM image of the cathode material NaMnCF prepared in Comparative Example 2 of the present invention 3.5 . Detailed Embodiments

[0023] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention.

[0024] Example 1

[0025] The preparation process of the spherical sodium-ion battery cathode material in this embodiment includes the following steps:

[0026] S1 Mix MnF2 and NaF in a molar ratio of 1:1, then add the organic solvent NMP and perform ultrasonic dispersion to make MnF2 and NaF evenly dispersed. The ultrasonic power is 120 W to obtain a dispersion, and the solid-liquid ratio of the dispersion is 1:2;

[0027] S2 Vacuum-dry the dispersion at 70 °C to obtain a mixed dispersion of MnF2 and NaF;

[0028] S3 Use a planetary ball mill to perform dry ball milling on the mixed dispersion until the particle size reaches 0.2 μm. Use agate balls as grinding balls, the ball-to-material ratio is 10:1, the ball milling speed is 320 rpm, and the ball milling time is 8 h to obtain NaMnF3;

[0029] S4 Put NaMnF3 into a hydrothermal autoclave, add fluorinated carbon fiber CF 0.5 , and make its mass ratio to NaMnF3 1:5. Perform synthesis by the hydrothermal method. The hydrothermal reaction temperature is 300 °C, the heating rate is 1 °C / min, and the holding time is 10 h.

[0030] Example 2

[0031] The preparation process of the spherical sodium-ion battery cathode material in this embodiment includes the following steps:

[0032] S1 Mix MnF2 and NaF in a molar ratio of 1:1.1, then add the organic solvent ethylene glycol and perform ultrasonic dispersion to make MnF2 and NaF evenly dispersed. The ultrasonic power is 180 W to obtain a dispersion, and the solid-liquid ratio of the dispersion is 1:2.2;

[0033] S2 Vacuum-dry the dispersion at 75 °C to obtain a mixed dispersion of MnF2 and NaF;

[0034] S3 Use a planetary ball mill to perform dry ball milling on the mixed dispersion until the particle size reaches 0.2 μm. Use agate balls as grinding balls, the ball-to-material ratio is 10:1, the ball milling speed is 300 rpm, and the ball milling time is 12 h to obtain NaMnF3;

[0035] S4 Put NaMnF3 into a hydrothermal autoclave, add fluorinated carbon fiber CF 0.5 , and make its mass ratio to NaMnF3 1:6. Perform synthesis by the hydrothermal method. The hydrothermal reaction temperature is 350 °C, the heating rate is 1 °C / min, and the holding time is 8 h.

[0036] Example 3

[0037] The preparation process of the spherical sodium-ion battery cathode material in this embodiment includes the following steps:

[0038] S1 Mix MnF2 and NaF in a molar ratio of 1:1.2, then add the organic solvent NMP and perform ultrasonic dispersion to make MnF2 and NaF evenly dispersed. The ultrasonic power is 240 W to obtain a dispersion, and the solid-liquid ratio of the dispersion is 1:2.4;

[0039] S2 Vacuum-dry the dispersion at 75 °C to obtain a mixed dispersion of MnF2 and NaF;

[0040] S3 Use a planetary ball mill to perform dry ball milling on the mixed dispersion until the particle size reaches 0.2 μm. Use agate balls as the grinding balls, the ball-to-material ratio is 11:1, the ball milling speed is 300 rpm, and the ball milling time is 10 h to obtain NaMnF3;

[0041] S4 Put NaMnF3 into a hydrothermal autoclave, add carbon fiber fluoride CF 0.5 , so that its mass ratio to NaMnF3 is 1:7, and perform synthesis by the hydrothermal method. The hydrothermal reaction temperature is 400 °C, the heating rate is 2 °C / min, and the holding time is 8 h.

[0042] Example 4

[0043] The preparation process of the spherical sodium-ion battery cathode material in this embodiment includes the following steps:

[0044] S1 Mix MnF2 and NaF in a molar ratio of 1:1.3, then add the organic solvent ethylene glycol and perform ultrasonic dispersion to make MnF2 and NaF evenly dispersed. The ultrasonic power is 300 W to obtain a dispersion, and the solid-liquid ratio of the dispersion is 1:2.6;

[0045] S2 Vacuum-dry the dispersion at 80 °C to obtain a mixed dispersion of MnF2 and NaF;

[0046] S3 Use a planetary ball mill to perform dry ball milling on the mixed dispersion until the particle size reaches 0.15 μm. Use agate balls as the grinding balls, the ball-to-material ratio is 12:1, the ball milling speed is 320 rpm, and the ball milling time is 12 h to obtain NaMnF3;

[0047] S4 Put NaMnF3 into a hydrothermal autoclave, add carbon fiber fluoride CF 0.5 , so that its mass ratio to NaMnF3 is 1:8, and perform synthesis by the hydrothermal method. The hydrothermal reaction temperature is 400 °C, the heating rate is 2 °C / min, and the holding time is 8 h.

[0048] Example 5

[0049] The preparation process of the spherical sodium-ion battery cathode material in this embodiment includes the following steps:

[0050] S1 Mix MnF2 and NaF in a molar ratio of 1:1.4, then add the organic solvent NMP and perform ultrasonic dispersion to uniformly disperse MnF2 and NaF. The ultrasonic power is 360 W to obtain a dispersion liquid, and the solid-liquid ratio of the dispersion liquid is 1:2.8;

[0051] S2 Vacuum-dry the dispersion liquid at 85 °C to obtain a mixed dispersion of MnF2 and NaF;

[0052] S3 Use a planetary ball mill to perform dry ball milling on the mixed dispersion until the particle size reaches 0.1 μm. Use agate balls as grinding balls, the ball-to-material ratio is 12:1, the ball milling speed is 350 rpm, and the ball milling time is 8 h to obtain NaMnF3;

[0053] S4 Put NaMnF3 into a hydrothermal autoclave, add carbon fiber fluoride CF 0.5 , such that its mass ratio to NaMnF3 is 1:5, and perform synthesis using the hydrothermal method. The hydrothermal reaction temperature is 450 °C, the heating rate is 3 °C / min, and the heat preservation time is 6 h.

[0054] Example 6

[0055] The preparation process of the spherical sodium-ion battery cathode material in this embodiment includes the following steps:

[0056] S1 Mix MnF2 and NaF in a molar ratio of 1:1.5, then add the organic solvent NMP and perform ultrasonic dispersion to uniformly disperse MnF2 and NaF. The ultrasonic power is 420 W to obtain a dispersion liquid, and the solid-liquid ratio of the dispersion liquid is 1:3;

[0057] S2 Vacuum-dry the dispersion liquid at 90 °C to obtain a mixed dispersion of MnF2 and NaF;

[0058] S3 Use a planetary ball mill to perform dry ball milling on the mixed dispersion until the particle size reaches 0.1 μm. Use agate balls as grinding balls, the ball-to-material ratio is 10:1, the ball milling speed is 350 rpm, and the ball milling time is 12 h to obtain NaMnF3;

[0059] S4 Put NaMnF3 into a hydrothermal autoclave, add carbon fiber fluoride CF 0.5 , such that its mass ratio to NaMnF3 is 1:8, and perform synthesis using the hydrothermal method. The hydrothermal reaction temperature is 500 °C, the heating rate is 3 °C / min, and the heat preservation time is 10 h.

[0060] Comparative Example 1

[0061] The difference from Example 1 is that in step S4, the hydrothermal reaction temperature is 280 °C and the heat preservation time is 10 h.

[0062] The SEM image of the positive electrode material NaMnCF prepared in Comparative Example 1 3.5 is as shown in Figure 2 As shown, compared with Figure 1 the SEM image of the positive electrode material NaMnCF prepared in Example 1 as shown in 3.5 it is found that when the hydrothermal reaction temperature is too low, it is difficult for carbon fluoride fibers to coat NaMnF3, resulting in serious agglomeration.

[0063] Comparative Example 2

[0064] The difference from Example 1 is that in step S4, the hydrothermal reaction temperature is 550 °C and the heat preservation time is 10 h.

[0065] The SEM image of the positive electrode material NaMnCF prepared in Comparative Example 2 3.5 is as shown in Figure 3 As shown, compared with Figure 1 the SEM image of the positive electrode material NaMnCF prepared in Example 1 as shown in 3.5 it is found that when the hydrothermal reaction temperature is too high, it is not conducive to the synthesis of the material morphology.

[0066] Comparative Example 3

[0067] The difference from Example 2 is that step S4 is not performed.

[0068] Comparative Example 4

[0069] The difference from Example 3 is that in step S3, a planetary ball mill is used to perform dry ball milling on the mixed dispersion until the particle size reaches 0.05 μm. Agate balls are used as grinding balls, the ball-to-material ratio is 10:1, the ball milling speed is 500 rpm, and the ball milling time is 16 h to obtain NaMnF3.

[0070] Comparative Example 5

[0071] The difference from Example 3 is that in step S3, a planetary ball mill is used to perform dry ball milling on the mixed dispersion until the particle size reaches 0.3 μm. Agate balls are used as grinding balls, the ball-to-material ratio is 10:1, the ball milling speed is 200 rpm, and the ball milling time is 8 h to obtain NaMnF3.

[0072] Comparative Example 6

[0073] The difference from Example 4 is that in step S1, the molar ratio of MnF2 to NaF is 1:2.

[0074] Comparative Example 7

[0075] The difference from Example 4 is that in step S1, the molar ratio of MnF2 to NaF is 1:0.8.

[0076] Comparative Example 8

[0077] The difference from Example 5 is that in step S4, the mass ratio of fluorinated carbon fiber to NaMnF3 is 1:10.

[0078] Comparative Example 9

[0079] The difference from Example 5 is that in step S4, the mass ratio of fluorinated carbon fiber to NaMnF3 is 1:3.

[0080] Comparative Example 10

[0081] The difference from Example 6 is that in step S4, carbon fiber is used to replace fluorinated carbon fiber.

[0082] Using the positive electrode materials NaMnCF prepared in Examples 1-6 and Comparative Examples 1-10 3.5 as the positive electrode and hard carbon as the negative electrode, 95mm×80mm electrode sheets were prepared respectively. The electrolyte in the electrolyte was 1M NaPF6, the organic solvent was EC and DEC with a volume ratio of 1:1, and the additive was FEC with a volume concentration of 5%. A soft-pack battery was assembled and designed with a theoretical capacity of 3700 mAh for performance testing. The test results are shown in Table 1:

[0083] Table 1 Performance test results of the positive electrode material NaMnCF in Examples 1-6 and Comparative Examples 1-10 3.5 Performance test results of the assembled batteries

[0084]

[0085]

[0086] As can be seen from Table 1, compared with Example 1, the capacity retention rates of Comparative Examples 1-2 decreased. This is because too low a hydrothermal reaction temperature will cause serious agglomeration of NaMnCF, resulting in a decrease in its efficiency in the electrochemical reaction; while too high a hydrothermal reaction temperature will damage the morphology of NaMnCF, which is also not conducive to improving the efficiency of the electrochemical reaction. 3.5 Agglomeration is serious, resulting in a decrease in its efficiency in the electrochemical reaction; while too high a hydrothermal reaction temperature will damage the morphology of NaMnCF 3.5 Morphology, which is also not conducive to improving the efficiency of the electrochemical reaction.

[0087] Compared with Example 2, after 30 cycles, the capacity retention rate of Comparative Example 3 decreased. This is because NaMnF3 itself has poor conductivity, and the carbon-containing substance plays a role in transporting electrons in the electrochemical reaction. Coating with fluorinated carbon fiber can improve the conduction efficiency of Na + And electrons.

[0088] Compared with Example 3, after 30 cycles, the capacity retention rate of Comparative Examples 4-5 decreased. It can be seen that the particle size of the material after ball milling has an impact on the material properties, thereby affecting the battery cycle life.

[0089] Compared with Example 4, after 30 cycles, the capacity retention rate of Comparative Examples 6-7 decreased. It can be seen that too high or too low molar ratio of Na and Mn will affect the battery cycle performance.

[0090] Compared with Example 5, after 30 cycles, the capacity retention rate of Comparative Examples 8-9 decreased. This shows that the addition ratio of fluorinated carbon fiber CF 0.5 and NaMnF3 should be appropriate. Too much or too little is not conducive to the electrochemical reaction.

[0091] Compared with Example 6, after 30 cycles, the capacity retention rate of Comparative Example 10 decreased. It can be seen that fluorinated carbon fiber is better than carbon fiber in the charge-discharge cycle performance of the battery. This is because the F-C bonding is more stable than the C-C bond, resulting in that fluorinated carbon fiber is not easy to react with other substances in the electrochemical reaction, thus being conducive to the charge-discharge cycle.

Claims

1. Preparation process of spherical sodium ion battery cathode material, characterized in that, It includes the following steps: S1: Mix MnF2 and NaF and disperse them in an organic solvent to obtain a dispersion; S2: Vacuum-dry the dispersion to obtain a mixed dispersion of MnF2 and NaF; S3: Ball-mill the mixed dispersion until the particle size reaches 0.1 - 0.2 μm to obtain NaMnF3; S4: Carry out a hydrothermal reaction on NaMnF3 and fluorinated carbon fiber to synthesize a spherical cathode material for sodium-ion batteries.

2. The preparation process of the spherical sodium ion battery cathode material according to claim 1, characterized in that, In step S1, the molar ratio of MnF2 to NaF is 1:(1 - 1.5), and the solid-liquid ratio of the dispersion is 1:(2 - 3).

3. The preparation process of the spherical sodium ion battery cathode material according to claim 1, characterized in that, In step S1, after mixing MnF2 and NaF, add them to the organic solvent and carry out ultrasonic dispersion with an ultrasonic power of 120 - 420 W.

4. The preparation process of the spherical sodium ion battery cathode material according to claim 1, characterized in that, In step S1, the organic solvent is N-methylpyrrolidone or ethylene glycol.

5. The preparation process of the spherical sodium ion battery cathode material according to claim 1, characterized in that, In step S2, the temperature of vacuum drying is 70 - 90 °C.

6. The preparation process of the spherical sodium-ion battery cathode material according to claim 1, characterized in that, In step S3, use a planetary ball mill to carry out dry ball-milling on the mixed dispersion, use agate balls as grinding balls, the ball-to-material ratio is (10 - 12):1, the ball-milling speed is 300 - 350 rpm, and the ball-milling time is 8 - 12 h.

7. The preparation process of the spherical sodium ion battery cathode material according to claim 1, characterized in that, In step S4, the mass ratio of fluorinated carbon fiber to NaMnF3 is 1:(5 - 8).

8. The preparation process of the spherical sodium-ion battery cathode material according to claim 1, characterized in that, In step S4, the temperature of the hydrothermal reaction is 300 - 500 °C, the heating rate is 1 - 3 °C / min, and the heat preservation time is 6 - 10 h.

9. Spherical sodium-ion battery cathode material, characterized in that, It is prepared by the preparation process of the spherical cathode material for sodium-ion batteries according to any one of claims 1 - 8.

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