Secondary coated Na2Fe (SO4) 2-PbO / C sodium ion battery positive electrode material and preparation method thereof

Abstract

The invention relates to a preparation method of a secondary coated Na2Fe (SO4) 2-PbO / C sodium ion battery positive electrode material. The sodium ion battery positive electrode material Na2Fe (SO4) 2-PbO / C with a secondary coating structure is formed by Na2Fe (SO4) 2 coated PbO and a carbon material; the preparation method comprises the following steps: (1) mixing sodium sulfate and ferrous sulfate dihydrate in a molar ratio of 1: (0.5-1.5), putting the mixture into a ball milling tank, and carrying out ball milling at the frequency of 10-50Hz for 1-10 hours to obtain mixed solid powder; (2) mixing the mixed solid powder, lead acetate and acetone according to the mass ratio of 1: (0.03-0.2): (0.1-1.2), putting the mixture into a ball milling tank, and performing ball milling at the frequency of 10-50Hz for 0.1-3h to obtain solid slurry; (3) putting the solid slurry and Super P in a mass ratio of 1: (0.005-0.015) into a ball milling tank, and carrying out ball milling for 1-10 hours at the frequency of 10-50 Hz to obtain a black precursor; and (4) carrying out heat treatment on the black precursor in protective gas N2 to obtain the secondary coated Na2Fe (SO4) 2-PbO / C sodium ion battery positive electrode material. The heat treatment is two-stage heat treatment, and the temperature of the two-stage heat treatment is 150-200 DEG C and 300-400 DEG C respectively; the treatment time is 1-3 hours and 10-15 hours respectively.

Description

TECHNICAL FIELD

[0001] The application relates to the field of sodium ion battery positive electrode materials, in particular to a secondary coated Na2Fe(SO4)2-PbO / C sodium ion battery positive electrode material and a preparation method thereof. BACKGROUND

[0002] Sodium ion battery positive electrode materials mainly include layered oxides, polyanions and prussian blue. Iron and sodium are abundant and low-cost metal elements, which are the preferred elements for power batteries and energy storage batteries. The widely studied layered oxide NaFeO2 has low cost and excellent stability, but the voltage platform is too low, which limits its application range. In contrast, the polyanion type iron sodium positive electrode material has a higher working voltage. For example, the currently mass-produced Na2Fe(SO4)2 battery has a working voltage of about 3.6V, has the advantages of low cost and simple preparation process, but the electronic conductivity and structural stability are low, so it is particularly important to improve the electronic conductivity and structural stability of the Na2Fe(SO4)2 positive electrode material.

[0003] Carbon coating is a common means to improve the electronic conductivity of sodium iron sulfate, but the in-situ carbon coating reaction temperature needs to reach more than 500 DEG C, which will cause the decomposition of sulfate, so the traditional carbon coating cannot improve the electronic conductivity of sodium iron sulfate. SUMMARY

[0004] The application is to solve the problem of low electronic conductivity of existing sodium iron sulfate batteries, and provides a preparation method of a secondary coated Na2Fe(SO4)2-PbO / C sodium ion battery positive electrode material to solve the problem of sulfate decomposition caused by too high carbon coating temperature and realize low-cost improvement of electronic conductivity of sodium iron sulfate. The prepared secondary coated Na2Fe(SO4)2-PbO / C sodium ion battery positive electrode material has the characteristics of high specific capacity and good charge-discharge cycle performance.

[0005] A preparation method of 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 and placed in a ball mill jar, and ball milling is carried out at a frequency of 10-50 Hz for 1-10 h to obtain a mixed solid powder; (2) The mixed solid powder, lead acetate and acetone with a mass ratio of 1: (0.03-0.2): (0.1-1.2) are mixed and placed in a ball mill jar, and ball milling is carried out at a frequency of 10-50 Hz for 0.1-3 h to obtain a solid slurry; (3) the solid slurry with a mass ratio of 1: (0.005-0.015) is placed in a ball mill tank with Super P, and ball milling is carried out at a frequency of 10-50 Hz for 1-10 h 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 positive electrode material; the heat treatment is secondary heat treatment, and the temperatures are 150-200 DEG C and 300-400 DEG C respectively; and the heat treatment times are 1-3 h and 10-15 h respectively.

[0006] The further design of the application is that the molar ratio of sodium sulfate and ferrous sulfate dihydrate in step (1) is 1: (0.7-1.2).

[0007] The further design of the application is that the ball-to-material ratio of ball milling in step (1) is 10-20:1, and the ball milling time is 1-3 h.

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

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

[0010] The further design of the application is that the mass ratio of solid slurry to Super P in step (3) is 1:0.001-0.012.

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

[0012] The further design of the application is that the secondary heat treatment in step (4) has temperatures of 175-185 DEG C and 335-375 DEG C respectively, and heat treatment times of 1.5-3 h and 10-12 h respectively; and the heating rates are 2-5 DEG C / min and 3-6 DEG C / min respectively.

[0013] The effect of the present application is that: in the preparation of the positive electrode material, PbO as the primary coating material can inhibit the decomposition of sulfate due to high temperature in the carbon coating process, which is conducive to ensuring the structural stability of the material; as the positive electrode material, Na2Fe(SO4)2 will produce a certain degree of water absorption during use, and PbO plays a role in improving the stability of the positive electrode material, which is conducive to improving the cycle stability of the sodium ion battery positive electrode material; the core-shell structure composite material obtained by adopting SuperP outer coating of Na2Fe(SO4)2-PbO / C makes the positive electrode material have higher electronic conductivity and cycle stability, which can ensure that the positive electrode material still has a high specific capacity retention rate after multiple cycles. BRIEF DESCRIPTION OF DRAWINGS

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

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

[0016] Figure 3 is the discharge cycle diagram of the Na2Fe(SO4)2-PbO / C, Na2Fe(SO4)2, Na2Fe(SO4)2-PbO, Na2Fe(SO4)2 / C sodium ion battery positive electrode materials prepared in Example 2 and Comparative Examples 1-3 at 1C rate.

[0017] Figure 4 is the electrochemical performance table of the positive electrode materials prepared in Examples 1-3 and Comparative Examples 1-3 of the present application.

[0018] Figure 5 is a structural schematic diagram of the secondary coated Na2Fe(SO4)2-PbO / C sodium ion battery positive electrode material of the present application. DETAILED DESCRIPTION

[0019] The following examples are intended to further illustrate the present application, and the scope of protection of the claims of the present application is not limited by the examples. EXAMPLE

[0020] (1) 14.2g of sodium sulfate and 17g of ferrous sulfate were ball milled for 2h at a ball milling frequency of 50Hz to obtain a mixed solid powder; (2) The mixed solid powder was ball milled with 1.9g of lead acetate and 10g of acetone for 0.5h at a ball milling frequency of 50Hz to obtain a solid slurry; (3) The solid slurry was ball-milled with 0.5 g Super P for 1 h at a ball-milling frequency of 50 Hz to obtain a black precursor; (4) The black precursor was sintered at 180 °C for 2 h under N2protection at a heating rate of 3 °C / min, and then sintered at 350 °C for 10 h at a heating rate of 5 °C / min to obtain Na2Fe(S04)2-PbO / C. Example

[0021] (1) 14.2 g of sodium sulfate and 15 g of ferrous sulfate were ball-milled for 2 h at a ball-milling frequency of 30 Hz to obtain a mixed solid powder; (2) The mixed solid powder was ball-milled with 2.9 g of lead acetate and 15 g of acetone for 0.5 h at a ball-milling frequency of 30 Hz to obtain a solid slurry; (3) The solid slurry was ball-milled with 0.3 g of Super P for 1 h at a ball-milling frequency of 30 Hz to obtain a black precursor; (4) The black precursor was sintered at 180 °C for 2 h under N2protection at a heating rate of 3 °C / min, and then sintered at 350 °C for 12 h at a heating rate of 5 °C / min to obtain Na2Fe(S04)2-PbO / C. Example

[0022] (1) 14.2 g of sodium sulfate and 15 g of ferrous sulfate were ball-milled for 2 h at a ball-milling frequency of 30 Hz to obtain a mixed solid powder; (2) The mixed solid powder was ball-milled with 2.9 g of lead acetate and 15 g of acetone for 0.5 h at a ball-milling frequency of 30 Hz to obtain a solid slurry; (3) The solid slurry was ball-milled with 0.3 g of Super P for 1 h at a ball-milling frequency of 30 Hz to obtain a black precursor; (4) The black precursor was sintered at 180 °C for 2 h under N2protection at a heating rate of 3 °C / min, and then sintered at 350 °C for 12 h at a heating rate of 5 °C / min to obtain Na2Fe(S04)2-PbO / C.

[0023] Comparative Example 1 (1) 14.2 g of sodium sulfate and 15 g of ferrous sulfate were ball-milled for 2 h at a ball-milling frequency of 30 Hz to obtain a mixed solid powder; (2) The mixed solid powder was sintered at 180 °C for 2 h under N2protection at a heating rate of 3 °C / min, and then sintered at 350 °C for 12 h at a heating rate of 5 °C / min to obtain Na2Fe(S04)2.

[0024] Comparative Example 2 (1) 14.2 g of sodium sulfate and 15 g of ferrous sulfate were ball-milled for 2 h at a ball-milling frequency of 30 Hz to obtain a mixed solid powder; (2) The mixed solid powder was ball-milled with 2.9 g of lead acetate and 15 g of acetone for 0.5 h at a ball-milling frequency of 30 Hz to obtain a solid slurry; (3) The solid slurry was sintered at 180 °C for 2 h under N2protection at a temperature increasing rate of 3 °C / min, and then sintered at 350 °C for 12 h at a temperature increasing rate of 5 °C / min to obtain Na2Fe(SO4)2-PbO.

[0025] Comparative Example 3 (1) 14.2 g of sodium sulfate and 15 g of ferrous sulfate were ball-milled for 2 h at a ball-milling frequency of 30 Hz to obtain a mixed solid powder; (2) The solid slurry was ball-milled with 0.3 g of Super P for 1 h at a ball-milling frequency of 30 Hz to obtain a black precursor; (3) The black precursor was sintered at 180 °C for 2 h under N2protection at a temperature increasing rate of 3 °C / min, and then sintered at 350 °C for 12 h at a temperature increasing rate of 5 °C / min to obtain Na2Fe(SO4)2 / C.

[0026] The test results of the examples and comparative examples are shown in Table 1. 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 formed by coating PbO and carbon material with Na2Fe(SO4)2; the preparation method comprises the following steps: (1) mixing sodium sulfate and ferrous sulfate heptahydrate in a molar ratio of 1:(0.5-1.5) in a ball mill jar, and ball milling at a frequency of 10-50 Hz for 1-10 h to obtain a mixed solid powder; (2) mixing the mixed solid powder, lead acetate and acetone in a mass ratio of 1:(0.03-0.2):(0.1-1.2) in a ball mill jar, and ball milling at a frequency of 10-50 Hz for 0.1-3 h to obtain a solid slurry; (3) mixing the solid slurry and Super P in a mass ratio of 1:(0.005-0.015) in a ball mill jar, and ball milling at a frequency of 10-50 Hz for 1-10 h to obtain a black precursor; (4) heat treating the black precursor in a protective gas N2 to obtain a secondary coated Na2Fe(SO4)2-PbO / C sodium-ion battery cathode material; the heat treatment is two-stage heat treatment, and the temperatures of the two-stage heat treatment are 150-200 ℃ and 300-400 ℃, respectively; and the treatment times are 1-3 h and 10-15 h, 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 to ferrous sulfate heptahydrate 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 heptahydrate is obtained by heat treating ferrous sulfate heptahydrate under Ar2 protection conditions; the specific heat treatment conditions are: 5 ℃ / min to 150 ℃, then maintaining at 150 ℃ for 2 h, and finally reducing to room temperature for 30 min.

4. 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 ball-to-material ratio of ball milling is 10-20:1; and the ball milling time is 1-3 h.

5. 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 (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(S04)2-PbO / C sodium-ion battery cathode material of claim 1, characterized in that In step (2), the ball-to-material ratio of ball milling is 10-20:1; the ball milling frequency is 35-50 Hz; and the ball milling time is 0.5-1 h.

7. 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 (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(S04)2-PbO / C sodium-ion battery cathode material of claim 1, characterized in that In step (3), the ball-to-material ratio of ball milling is 10-20:1; the ball milling frequency is 30-50 Hz; and the ball milling time is 1-3 h.

9. 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 (4), the heat treatment is two-stage heat treatment, and the temperatures are 175-185 ℃ and 335-375 ℃, respectively; the heat treatment times are 1.5-3 h and 10-12 h, respectively; and the heating rates are 2-5 ℃ / min and 3-6 ℃ / min, respectively.

10. A secondary coated Na2Fe(S04)2-PbO / C sodium-ion battery cathode material characterized by, The sodium-ion battery cathode material is prepared by the preparation method of any one of claims 1-9.

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