Secondary coated Na2Fe(SO4)2-PbO / C sodium-ion battery cathode material and its preparation method

Abstract

This invention relates to a method for preparing a secondary coated Na2Fe(SO4)2-PbO / C sodium-ion battery cathode material, wherein the sodium-ion battery cathode material Na2Fe(SO4)2-PbO / C is formed by coating PbO and carbon materials with Na2Fe(SO4)2 and having a secondary coated structure; the preparation method includes the following steps: (1) mixing sodium sulfate and ferrous sulfate dihydrate in a molar ratio of 1:(0.5~1.5) and placing them in a ball mill jar, and ball milling at a frequency of 10~50Hz for 1~10h to obtain a mixed solid powder; (2) mixing the mixed solid powder in a mass ratio of 1:(0.03~0.2):(0.1~1.2), lead acetate and acetone in a ball mill jar, and ball milling at a frequency of 10~50Hz for 0.1~3h to obtain a solid slurry; (3) mixing the solid slurry in a mass ratio of 1:(0.005~0.015) with Super P is placed in a ball mill jar and ball milled at a frequency of 10~50Hz for 1~10h to obtain a black precursor; (4) the black precursor is heat-treated in a protective gas N2 to obtain a secondary coated Na2Fe(SO4)2-PbO / C sodium ion battery cathode material; the heat treatment is a two-stage heat treatment, the temperatures of the two stages are 150~200℃ and 300~400℃ respectively; the treatment times are 1~3h and 10~15h respectively.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery cathode materials, specifically to a secondary coated Na2Fe(SO4)2-PbO / C sodium-ion battery cathode material and its preparation method. Background Technology

[0002] Sodium-ion battery cathode materials mainly include layered oxide, polyanionic, and Prussian blue types. Iron and sodium, as abundant and inexpensive metallic elements, are the preferred elements for power and energy storage batteries. The widely studied layered oxide NaFeO2 possesses low cost and excellent stability, but its low voltage plateau limits its application. In contrast, polyanionic iron-sodium cathode materials have higher operating voltages; for example, the currently mass-produced Na2Fe(SO4)2 battery operates at around 3.6V, offering advantages such as low cost and simple manufacturing processes. However, its electronic conductivity and structural stability are relatively low. Therefore, improving the electronic conductivity and structural stability of Na2Fe(SO4)2 cathode materials is particularly important.

[0003] Carbon coating is a common method to improve the electronic conductivity of sodium ferric sulfate, but the reaction temperature for in-situ carbon coating needs to reach above 500℃, which will lead to the decomposition of sulfate ions. Therefore, traditional carbon coating cannot improve the electronic conductivity of sodium ferric sulfate. Summary of the Invention

[0004] This invention addresses the problem of low electronic conductivity in existing sodium iron sulfate batteries by providing a method for preparing a secondary-coated Na2Fe(SO4)2-PbO / C sodium-ion battery cathode material. This method solves the problem of sulfate decomposition caused by excessively high carbon coating temperatures, thus achieving a low-cost improvement in the electronic conductivity of sodium iron sulfate. The prepared secondary-coated Na2Fe(SO4)2-PbO / C sodium-ion battery cathode material exhibits high specific capacity and good charge-discharge cycle performance.

[0005] A method for preparing a secondary coated Na2Fe(SO4)2-PbO / C composite material is carried out according to the following steps: (1) Sodium sulfate and ferrous sulfate dihydrate with a molar ratio of 1:(0.5~1.5) are mixed in a ball mill jar and ball milled at a frequency of 10~50Hz for 1~10h to obtain a mixed solid powder; (2) Mix solid powder with a mass ratio of 1:(0.03~0.2):(0.1~1.2), lead acetate and acetone in a ball mill jar and ball mill at a frequency of 10~50Hz for 0.1~3h to obtain solid slurry; (3) Place the solid slurry with a mass ratio of 1:(0.005~0.015) and Super P in a ball mill jar and ball mill at a frequency of 10~50Hz for 1~10h to obtain a black precursor; (4) The black precursor was heat-treated in protective gas N2 to obtain secondary coated Na2Fe(SO4)2-PbO / C sodium ion battery cathode material; the heat treatment was a two-stage heat treatment with temperatures of 150~200℃ and 300~400℃ respectively; the heat treatment time was 1~3h and 10~15h respectively.

[0006] A further design of the present invention is that the molar ratio of sodium sulfate and ferrous sulfate dihydrate in step (1) is 1:(0.7~1.2).

[0007] A further design of the present invention is that the ball-to-material ratio in step (1) is 10-20:1 and the ball-milling time is 1-3 hours.

[0008] A further design of the present invention is that the mass ratio of the mixed solid powder, lead acetate and acetone in step (2) is 1:(0.05~0.13):(0.3~0.8).

[0009] A further design of the present invention is that, in step (2), the ball-to-material ratio of the ball mill is 10~20:1; the ball milling frequency is 35~50Hz; and the ball milling time is 0.5~1h.

[0010] A further design of the present invention is that the mass ratio of solid slurry to Super P in step (3) is 1:0.001~0.012.

[0011] A further design of the present invention is that, in step (3), the ball-to-material ratio of the ball mill is 10~20:1; the ball milling frequency is 30~50Hz; and the ball milling time is 1~3h.

[0012] A further design of the present invention is that, in step (4), the secondary heat treatment temperatures are 175~185℃ and 335~375℃, respectively; the heat treatment times are 1.5~3h and 10~12h, respectively; and the heating rates are 2~5℃ / min and 3~6℃ / min, respectively.

[0013] The advantages of this invention are: when preparing cathode materials, PbO, as a primary coating material, can suppress sulfate decomposition caused by high temperature during carbon coating, which is beneficial to ensuring the structural stability of the material; as a cathode material, Na2Fe(SO4)2 will absorb water to a certain extent during use, and PbO plays a role in improving the stability of the cathode material, which is beneficial to improving the cycle stability of sodium-ion battery cathode materials; the core-shell structure composite material obtained by using SuperP outer coating for Na2Fe(SO4)2-PbO / C gives the cathode material higher electronic conductivity and cycle stability, which can ensure that the cathode material still has a high specific capacity retention rate after multiple cycles. Attached Figure Description

[0014] Figure 1 The image shows the XRD pattern of the secondary coated Na2Fe(SO4)2-PbO / C sodium-ion battery cathode material prepared in Example 2.

[0015] Figure 2 This is the first charge-discharge curve of the secondary coated Na2Fe(SO4)2-PbO / C sodium-ion battery cathode material prepared in Example 2 at a rate of 0.1C.

[0016] Figure 3 The figures show the discharge cycle diagrams at 1C rate for the Na2Fe(SO4)2-PbO / C, Na2Fe(SO4)2, Na2Fe(SO4)2-PbO, and Na2Fe(SO4)2 / C sodium-ion battery cathode materials prepared using Examples 2 and Comparative Examples 1-3.

[0017] Figure 4 This is a table showing the electrochemical performance of the cathode materials prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention.

[0018] Figure 5 This is a schematic diagram of the structure of the secondary coated Na2Fe(SO4)2-PbO / C sodium-ion battery cathode material of the present invention. Detailed Implementation

[0019] The following embodiments are intended to further illustrate the content of the present invention, but the scope of protection of the claims of the present invention is not limited by the embodiments. Example

[0020] (1) 14.2g sodium sulfate and 17g ferrous sulfate were ball-milled for 2 hours at a frequency of 50Hz to obtain a mixed solid powder; (2) The mixed solid powder was ball-milled with 1.9g lead acetate and 10g acetone for 0.5h at a ball-milling frequency of 50Hz to obtain a solid slurry; (3) The solid slurry was ball-milled with 0.5g SuperP for 1h at a frequency of 50Hz to obtain a black precursor; (4) The black precursor was sintered at 180°C for 2 hours under N2 protective gas at a heating rate of 3°C / min. Then, it was sintered at 350°C for 10 hours at a heating rate of 5°C / min to obtain Na2Fe(SO4)2-PbO / C. Example

[0021] (1) 14.2g sodium sulfate and 15g ferrous sulfate were ball-milled for 2 hours at a frequency of 30Hz to obtain a mixed solid powder; (2) The mixed solid powder was ball-milled with 2.9g lead acetate and 15g acetone for 0.5h at a ball-milling frequency of 30Hz to obtain a solid slurry; (3) The solid slurry was ball-milled with 0.3g SuperP for 1h at a frequency of 30Hz to obtain a black precursor; (4) The black precursor was sintered at 180°C for 2 hours under N2 protective gas at a heating rate of 3°C / min. Then, it was sintered at 350°C for 12 hours at a heating rate of 5°C / min to obtain Na2Fe(SO4)2-PbO / C. Example

[0022] (1) 14.2g sodium sulfate and 13g ferrous sulfate were ball-milled for 1 hour at a frequency of 30Hz to obtain a mixed solid powder; (2) The mixed solid powder was ball-milled with 3.5g lead acetate and 20g acetone for 1h at a ball-milling frequency of 30Hz to obtain a solid slurry; (3) The solid slurry was ball-milled with 0.1g SuperP for 1h at a frequency of 30Hz to obtain a black precursor; (4) The black precursor was sintered at 180°C for 1 h under N2 protective gas at a heating rate of 3°C / min. Then, it was sintered at 350°C for 10 h at a heating rate of 5°C / min to obtain Na2Fe(SO4)2-PbO / C.

[0023] Comparative Example 1 (1) 14.2g sodium sulfate and 15g ferrous sulfate were ball-milled for 2 hours at a frequency of 30Hz to obtain a mixed solid powder; (2) The mixed solid powder was sintered at 180°C for 2 hours under N2 protective gas at a heating rate of 3°C / min. Then, it was sintered at 350°C for 12 hours at a heating rate of 5°C / min to obtain Na2Fe(SO4)2.

[0024] Comparative Example 2 (1) 14.2g sodium sulfate and 15g ferrous sulfate were ball-milled for 2 hours at a frequency of 30Hz to obtain a mixed solid powder; (2) The mixed solid powder was ball-milled with 2.9g lead acetate and 15g acetone for 0.5h at a ball-milling frequency of 30Hz to obtain a solid slurry; (3) The solid slurry was sintered at 180°C for 2 hours under N2 protective gas at a heating rate of 3°C / min. Then, it was sintered at 350°C for 12 hours at a heating rate of 5°C / min to obtain Na2Fe(SO4)2-PbO.

[0025] Comparative Example 3 (1) 14.2g sodium sulfate and 15g ferrous sulfate were ball-milled for 2 hours at a frequency of 30Hz to obtain a mixed solid powder; (2) The solid slurry was ball-milled with 0.3g SuperP for 1h at a frequency of 30Hz to obtain a black precursor; (3) The black precursor was sintered at 180°C for 2 hours under N2 protective gas at a heating rate of 3°C / min. Then, it was sintered at 350°C for 12 hours at a heating rate of 5°C / min to obtain Na2Fe(SO4)2 / C.

[0026] The test results of the examples and comparative examples are as follows: Figure 4 .

Claims

1. A method for preparing a secondary coated Na2Fe(SO4)2-PbO / C sodium-ion battery cathode material, characterized in that: A sodium-ion battery cathode material, Na2Fe(SO4)2-PbO / C, with a secondary coating structure, is formed by coating PbO and carbon materials with Na2Fe(SO4)2. The preparation method includes the following steps: (1) Sodium sulfate and ferrous sulfate dihydrate with a molar ratio of 1:(0.5~1.5) are mixed in a ball mill jar and ball milled at a frequency of 10~50Hz for 1~10h to obtain a mixed solid powder; (2) Mix solid powder with a mass ratio of 1:(0.03~0.2):(0.1~1.2), lead acetate and acetone in a ball mill jar and ball mill at a frequency of 10~50Hz for 0.1~3h to obtain solid slurry; (3) Place the solid slurry with a mass ratio of 1:(0.005~0.015) and Super P in a ball mill jar and ball mill at a frequency of 10~50Hz for 1~10h to obtain a black precursor; (4) The black precursor was heat-treated in protective gas N2 to obtain secondary coated Na2Fe(SO4)2-PbO / C sodium ion battery cathode material; the heat treatment was a two-stage heat treatment, with the temperatures of the two stages being 150~200℃ and 300~400℃, respectively; and the treatment times being 1~3h and 10~15h, respectively.

2. The method for preparing the secondary coated Na2Fe(S04)2-PbO / C sodium-ion battery cathode material according to claim 1, characterized in that In step (1), the molar ratio of sodium sulfate and ferrous sulfate dihydrate is 1:(0.7~1.2).

3. The method for preparing the secondary coated Na2Fe(S04)2-PbO / C sodium-ion battery cathode material of claim 1, characterized in that In step (1), the ferrous sulfate dihydrate is obtained by heat treatment of ferrous sulfate heptahydrate under Ar2 protection conditions; the heat treatment conditions are to heat up to 150°C at 5°C / min, then keep at 150°C for 2 hours, and finally cool to room temperature for 30 minutes.

4. The method for preparing the secondary coated Na2Fe(SO4)2-PbO / C sodium-ion battery cathode material according to claim 1, characterized in that... In step (1), the ball-to-material ratio of the ball mill is 10-20:1; the ball milling time is 1-3 hours.

5. The method for preparing the secondary coated Na2Fe(SO4)2-PbO / C sodium-ion battery cathode material according to claim 1, characterized in that... In step (2), the mass ratio of the mixed solid powder, lead acetate and acetone is 1:(0.05~0.13):(0.3~0.8).

6. The method for preparing the secondary coated Na2Fe(SO4)2-PbO / C sodium-ion battery cathode material according to claim 1, characterized in that... In step (2), the ball-to-material ratio of the ball mill is 10~20:1; the ball milling frequency is 35~50Hz; and the ball milling time is 0.5~1h.

7. The method for preparing the secondary coated Na2Fe(SO4)2-PbO / C sodium-ion battery cathode material according to claim 1, characterized in that... In step (3), the mass ratio of the solid slurry to Super P is 1:0.001~0.

012.

8. The method for preparing the secondary coated Na2Fe(SO4)2-PbO / C sodium-ion battery cathode material according to claim 1, characterized in that... In step (3), the ball-to-material ratio of the ball mill is 10~20:1; the ball milling frequency is 30~50Hz; and the ball milling time is 1~3h.

9. The method for preparing the secondary coated Na2Fe(SO4)2-PbO / C sodium-ion battery cathode material according to claim 1, characterized in that... In step (4), the heat treatment is a two-stage heat treatment with temperatures of 175~185℃ and 335~375℃, respectively; heat treatment times of 1.5~3h and 10~12h, respectively; and heating rates of 2~5℃ / min and 3~6℃ / min, respectively.

10. A secondary coated Na2Fe(SO4)2-PbO / C sodium-ion battery cathode material, characterized in that, The sodium-ion battery cathode material is prepared by the preparation method described in any one of claims 1 to 9.

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