Preparation Method and Application of Cobalt-Doped Strontium Titanate Sulfur-Carrying Composite Material

Abstract

The present invention relates to a preparation method of a cobalt-doped strontium titanate sulfur-carrying composite material. The obtained composite material is based on the stable network structure of strontium titanate, and the abundant macropore distribution can provide sufficient active sites for elemental sulfur. The incorporation of cobalt nanodots is used to catalyze the conversion and accelerate the conversion of soluble polysulfide to insoluble polysulfide in the electrochemical system of lithium-sulfur batteries. Moreover, the obtained cobalt-doped strontium titanate sulfur-carrying composite material has a stable microstructure, and the prepared button battery has stable electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the field of cathode materials for lithium-sulfur batteries, and particularly relates to a preparation method of a cobalt-doped strontium titanate sulfur-loaded composite material and its use in lithium-sulfur batteries. Background Art

[0002] Lithium-sulfur batteries belong to one of the branches of lithium-ion batteries, and their working principle is based on the redox reaction of elemental sulfur and lithium ions to generate the final product lithium sulfide. During discharge, lithium ions pass through the separator and react with elemental sulfur in the positive electrode, first forming long-chain polysulfides, and then the long-chain polysulfides are converted into short-chain polysulfides, and finally the solid product lithium sulfide is formed. Among them, in the phase change process of the positive electrode during discharge, solid elemental sulfur is converted into liquid polysulfides, and finally into solid lithium sulfide, and its phase change process is from solid to liquid and then to solid; during charging, the solid lithium sulfide in the positive electrode is oxidized into elemental sulfur, and lithium ions pass through the separator and are embedded in the negative electrode.

[0003] Although lithium-sulfur batteries have advantages such as high theoretical specific capacity, rich sulfur resources, and low cost, problems such as the easy solubility of intermediate polysulfides during the charge and discharge process of lithium-sulfur batteries in the electrolyte and the poor conductivity of the final product lithium sulfide have always restricted the development of lithium-sulfur batteries. Research shows that the compounding of some conductive materials with sulfur can effectively solve the problem of poor conductivity of lithium-sulfur batteries, such as materials like graphene and carbon nanotubes; metal-organic framework materials with high specific surface area and rich pores have also been widely used as sulfur-hosting materials for the positive electrodes of lithium-sulfur batteries. However, their weak adsorption ability to polysulfides leads to rapid capacity decay, and they are not ideal sulfur host materials. Summary of the Invention

[0004] In view of the above problems, the purpose of the present invention is to design a preparation method and application of a cathode material for lithium-sulfur batteries - cobalt-doped strontium titanate sulfur-loaded composite material (Co-SrTiO 3 @S). The cathode material includes the prepared Co-SrTiO 3 and elemental sulfur. The synthesis method of this material is simple, suitable for large-scale production and is applied to lithium-sulfur batteries, and has excellent electrochemical performance.

[0005] The preparation method of the above-mentioned cobalt-doped strontium titanate sulfur-loaded composite material (Co-SrTiO 3 @S) for the cathode of a lithium-sulfur battery includes the following steps:

[0006] (1) Add a strontium source and a cobalt source to deionized water, stir until completely dissolved, and then add an appropriate amount of acid to the solution. After complete dissolution, it is recorded as solution A;

[0007] (2) After mixing tetrabutyl titanate and glacial acetic acid evenly, slowly add a small amount of deionized water and stir evenly. It is recorded as solution B;

[0008] (3) Slowly drop the solution A configured above into solution B. After stirring evenly, add an appropriate amount of polyethylene glycol (such as PEG6000). After continuous stirring, raise the temperature to heat and accelerate the reaction, and then dry and grind to obtain a powder sample.

[0009] (4) First calcine the powder sample prepared in step (3) under a nitrogen atmosphere, and then switch to an oxygen atmosphere to continue calcining to obtain Co-SrTiO 3 ;

[0010] (5) Mix the above-prepared Co-SrTiO 3 and elemental sulfur, grind them, transfer them to a hydrothermal reaction kettle. After replacing with an inert gas, heat at a certain temperature to obtain a cobalt-doped strontium titanate supported sulfur composite material (Co-SrTiO 3 @S).

[0011] Further, the molar ratio of the amount of strontium source used in step (1) to the tetrabutyl titanate in step (2) is 1:1, the molar doping amount of cobalt source is 1% - 5% of strontium titanate, the acid is preferably citric acid, and its dosage is 0.05 - 0.1 mol / L; the sources of strontium source include but are not limited to strontium carbonate, strontium nitrate, etc.; the sources of cobalt nitrate include but are not limited to cobalt nitrate, cobalt chloride, etc.

[0012] Further, the dosage of glacial acetic acid in step (2) is controlled to 1 - 100 ml.

[0013] Further, the mass ratio of the amount of polyethylene glycol (PEG6000) used in step (3) to citric acid is 1:2, the temperature increase is controlled between 65 - 85 °C, the reaction time is 4 - 8 h, and the final drying temperature is controlled at 120 - 150 °C.

[0014] Further, the flow rate of the nitrogen atmosphere in step (4) is controlled at 5 - 10 L / min, the calcination temperature is controlled at 700 - 900 °C, and the calcination time is controlled at 5 - 9 h; then the flow rate of the oxygen atmosphere is 5 - 10 L / min, the calcination temperature is 300 - 500 °C, and the calcination time is controlled at 1 - 5 h; in the synthesized Co-SrTiO 3 , the existing forms of cobalt include but are not limited to cobalt tetroxide, cobalt sesquioxide, cobalt oxide and elemental cobalt, etc.

[0015] Further, the mass ratio of Co-SrTiO 3 and elemental sulfur in step (5) is controlled at 1:(3 - 5); the temperature range of the hydrothermal reaction is 130 - 160 °C, and the reaction time is 10 - 20 h.

[0016] The present invention also relates to a cobalt-doped strontium titanate sulfur-loaded composite material obtained by the preparation method of the above cobalt-doped strontium titanate sulfur-loaded composite material; wherein the molar amount of cobalt source doping is 1% to 5% of strontium titanate, and when the composite material is used in a lithium-sulfur battery, it has excellent performance.

[0017] The present invention also relates to the application of the cobalt-doped strontium titanate sulfur-loaded composite material obtained by the above preparation method or the above cobalt-doped strontium titanate sulfur-loaded composite material in a lithium-sulfur battery positive electrode sheet and a button battery.

[0018] For the above application, the preparation method of the lithium-sulfur battery positive electrode sheet is as follows: After weighing and grinding the cobalt-doped strontium titanate sulfur-loaded composite material prepared above, conductive carbon black, and binder PVDF evenly, a dispersant is added to make a stable slurry; then it is coated on carbon-coated aluminum foil, dried in vacuum, cut into electrode sheets and stored in a glove box for assembling a button battery.

[0019] For the above application, preferably, the cobalt-doped strontium titanate sulfur-loaded composite material, conductive carbon black, and binder PVDF are weighed in a mass ratio of 8:1:1; the dispersant is N-methylpyrrolidone (NMP), and the dosage is 15 ml; the vacuum drying conditions are 12 - 48 h at 50 - 80 °C, more preferably 24 h of vacuum drying at 60 °C; it can be cut into electrode sheets with a diameter of 10 mm and stored in a glove box for assembling a button battery.

[0020] Advantages of the present invention:

[0021] The cobalt-doped strontium titanate sulfur-loaded composite material of the present invention has a stable microstructure, a grid-like surface with a rich macroporous structure, which can effectively anchor elemental sulfur. The cobalt doping forms nanodots on its surface distribution, which can effectively accelerate the conversion of soluble polysulfide lithium to insoluble lithium sulfide, and effectively improve the cycling performance of the battery. Brief Description of the Drawings

[0022] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention in combination with the drawings, wherein,

[0023] Figure 1 is the SEM diagram of Co-SrTiO 3 . Detailed Embodiments

[0024] To facilitate the understanding of the present invention, various exemplary embodiments of the present invention are now described in detail. This detailed description should not be regarded as a specific limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0025] Example 1

[0026] 29.23 g of strontium carbonate (0.2 mol) and 0.125 g of cobalt nitrate were added to 500 ml of deionized water. After stirring until completely dissolved, 230 g of citric acid was added and stirred evenly to obtain solution A. 68.76 g of tetrabutyl titanate (0.2 mol) was mixed with 20 ml of glacial acetic acid, stirred for 3 h, and then 20 ml of deionized water was slowly added and continuously stirred for 1 h to obtain solution B. Solution A was slowly dropped into B, and after stirring for 1 h, 115 g of PEG6000 was added to the solution. After continuously stirring for 1 h, the temperature was raised to 65 °C and kept sealed for 8 h. Then, most of the water was removed by opening, and it was dried at 120 °C and ground to obtain the precursor powder. The above powder was transferred to a crucible and heated in an atmosphere muffle furnace. First, the nitrogen atmosphere flow rate was 6 L / min, and it was heated at 800 °C for 6 h. Then, it was switched to an oxygen atmosphere with a flow rate of 5 / min and heated at 450 °C for 2 h to obtain the cobalt-doped strontium titanate material Co 0.5 -SrTiO 3 (0.5% of the molar amount of Co relative to strontium titanate). After mixing and grinding the cobalt-doped strontium titanate material prepared above and elemental sulfur in a mass ratio of 1:3 evenly, it was transferred to a hydrothermal reaction kettle, replaced with an inert gas in a glove box under an argon atmosphere, and heated at 155 °C for 12 h to obtain Co 0.5 -SrTiO 3 @S material.

[0027] The prepared Co 0.5 -SrTiO 3 @S material, conductive carbon black, and binder PVDF were accurately weighed and ground evenly in a mass ratio of 8:1:1. Then, a certain amount of dispersant NMP was added to make a stable slurry, which was then coated on carbon-coated aluminum foil and vacuum dried at 60 °C for 24 h. It was cut into pole pieces with a diameter of 10 mm and stored in a glove box for assembling coin-type half-cells. Under the conditions of a constant temperature of 25 °C, a voltage of 1.7 - 2.8 V, and 0.2C, charge-discharge tests were carried out.

[0028] Comparative Example 1

[0029] 29.23 g of strontium carbonate (0.2 mol) was added to 500 ml of deionized water. After stirring until completely dissolved, 230 g of citric acid was added and stirred evenly to obtain solution A. 68.76 g of tetrabutyl titanate (0.2 mol) was mixed with 20 ml of glacial acetic acid, stirred for 3 h, and then 20 ml of deionized water was slowly added. After continuous stirring for 1 h, it was designated as solution B. Solution A was slowly dropped into B. After stirring for 1 h, 115 g of PEG6000 was added to the solution. After continuous stirring for 1 h, the temperature was raised to 65 °C and kept sealed for 8 h. Then, most of the water was removed by opening, dried at 120 °C, and ground to obtain the precursor powder. The above powder was transferred to a crucible and heated in an atmosphere muffle furnace. First, the nitrogen atmosphere flow rate was 6 L / min, and it was heated at 800 °C for 6 h. Then, it was switched to an oxygen atmosphere with a flow rate of 5 / min and heated at 450 °C for 2 h to obtain the strontium titanate material SrTiO 3 。The cobalt-doped strontium titanate material prepared above was mixed and ground evenly with elemental sulfur in a mass ratio of 1:3, transferred to a hydrothermal reaction kettle, replaced with an inert gas in a glove box under an argon atmosphere, and heated at 155 °C for 12 h to obtain SrTiO 3 @S material.

[0030] The SrTiO 3 @S material prepared above, conductive carbon black, and binder PVDF were accurately weighed and ground evenly in a mass ratio of 8:1:1. Then, a certain amount of dispersant NMP was added to make a stable slurry, which was then coated on carbon-coated aluminum foil, vacuum dried at 60 °C for 24 h, cut into pole pieces with a diameter of 10 mm, and stored in a glove box for assembling coin-type half-cells. In a constant temperature environment at 25 °C, charge-discharge tests were carried out under the conditions of a voltage of 1.7 - 2.8 V and 0.2 C.

[0031] The coin-type half-cells prepared in Example 1 and Comparative Example 1 were respectively tested, and the test results are shown in Table 1.

[0032] Table 1 Charge-discharge test results

[0033]

[0034] It can be seen that the present invention is based on cobalt doping of reticulated strontium carbonate. Under a nitrogen atmosphere, the incorporated cobalt is reduced to form cobalt nanodots, which can effectively improve the adsorption capacity for elemental sulfur and polysulfide lithium, and catalyze the conversion of long-chain polysulfide lithium to short-chain polysulfide lithium. Compared with the test results of the comparative example, it proves the improvement of its electrochemical performance.

[0035] Example 2

[0036] 29.23 g of strontium carbonate (0.2 mol) and 0.25 g of cobalt nitrate were added to 500 ml of deionized water. After stirring until completely dissolved, 230 g of citric acid was added and stirred evenly to obtain solution A. 68.76 g of tetrabutyl titanate (0.2 mol) was mixed with 20 ml of glacial acetic acid, stirred for 3 h, and then 20 ml of deionized water was slowly added and continuously stirred for 1 h to obtain solution B. Solution A was slowly dropped into B. After stirring for 1 h, 115 g of PEG6000 was added. After continuously stirring for 1 h, the temperature was raised to 65 °C and sealed for 8 h. Then, most of the water was removed by opening, dried at 120 °C, and ground to obtain the precursor powder. The above powder was transferred to a crucible and heated in an atmosphere muffle furnace. First, the nitrogen atmosphere flow rate was 6 L / min, and it was heated at 800 °C for 6 h. Then, it was switched to an oxygen atmosphere with a flow rate of 5 / min and heated at 450 °C for 2 h to obtain the cobalt-doped strontium titanate material Co 1 -SrTiO 3 (The Co content is 1% relative to the molar amount of strontium titanate). For Co 1 -SrTiO 3 The SEM image of the Co Figure 1 sample is shown as follows, with an obvious network structure and rich macropore distribution on the surface.

[0037] The cobalt-doped strontium titanate material prepared above was mixed and ground evenly with elemental sulfur in a mass ratio of 1:3, transferred to a hydrothermal reaction kettle, replaced with an inert gas in a glove box under an argon atmosphere, and heated at 155 °C for 12 h to obtain Co 1 -SrTiO 3 @S material.

[0038] The Co 1 -SrTiO 3 @S material prepared above, conductive carbon black, and binder PVDF were accurately weighed and ground evenly in a mass ratio of 8:1:1. Then, a certain amount of dispersant NMP was added to make a stable slurry, which was then coated on carbon-coated aluminum foil, vacuum dried at 60 °C for 24 h, cut into a pole piece with a diameter of 10 mm, and stored in a glove box for assembling a coin-type half-cell. The charge-discharge test was carried out under the conditions of a constant temperature of 25 °C, a voltage of 1.7 - 2.8 V, and 0.2C.

[0039] Example 3

[0040] 29.23 g of strontium carbonate (0.2 mol) and 0.375 g of cobalt nitrate were added to 500 ml of deionized water. After stirring until completely dissolved, 230 g of citric acid was added and stirred evenly to obtain solution A. 68.76 g of tetrabutyl titanate (0.2 mol) was mixed with 20 ml of glacial acetic acid, stirred for 3 h, and then 20 ml of deionized water was slowly added, and stirring was continued for 1 h to obtain solution B. Solution A was slowly dropped into B. After stirring for 1 h, 115 g of PEG6000 was added to the solution. After continuous stirring for 1 h, the temperature was raised to 65 °C and kept sealed for 8 h. Then, most of the water was removed by opening, and it was dried at 120 °C and ground to obtain the precursor powder. The above powder was transferred to a crucible and heated in an atmosphere muffle furnace. First, the nitrogen atmosphere flow rate was 6 L / min, and it was heated at 800 °C for 6 h. Then, it was switched to an oxygen atmosphere with a flow rate of 5 / min and heated at 450 °C for 2 h to obtain the cobalt-doped strontium titanate material Co 1.5 -SrTiO 3 (The Co content is 1.5% relative to the molar amount of strontium titanate). After mixing and grinding the cobalt-doped strontium titanate material prepared above and elemental sulfur in a mass ratio of 1:3, it was transferred to a hydrothermal reaction kettle and heated at 155 °C for 12 h after being replaced with an inert gas in a glove box under an argon atmosphere to obtain Co 1.5 -SrTiO 3 @S material.

[0041] The Co 1.5 -SrTiO 3 @S material prepared above, conductive carbon black, and binder PVDF were accurately weighed and ground evenly according to a mass ratio of 8:1:1, and then a certain amount of dispersant NMP was added to make a stable slurry. Then, it was coated on carbon-coated aluminum foil and vacuum dried at 60 °C for 24 h, and cut into a pole piece with a diameter of 10 mm and stored in a glove box for assembling a coin-type half cell. Under the conditions of a constant temperature of 25 °C, a voltage of 1.7 - 2.8 V, and 0.2 C, charge-discharge tests were carried out.

[0042] Table 2 is a summary of the electrochemical test data of Example 1, Example 2, and Example 3, and the results are as follows.

[0043] Test results of the three examples in Table 2

[0044]

[0045] It can be seen therefrom that the doping of cobalt element does not always improve the battery capacity. When the cobalt doping amount reaches 1.5% compared with 1%, there is an obvious downward trend. The reason for the capacity decline can be attributed to the fact that excessive cobalt nanodots start to react with the electrolyte, inducing side reactions and thus reducing the capacity. However, in terms of the performance requirements of the coin cell, when the Co content is 1-5% of the molar amount of strontium titanate, compared with the undoped material, it has a good capacity retention rate and can meet the performance requirements of the battery (the most preferred content is 1% of the molar amount of strontium titanate). It can be seen that the introduction of an appropriate amount of cobalt nanodots, with its strong catalytic effect, can effectively improve the cycling performance of the battery, which is also of great significance for the development of lithium-sulfur batteries.

[0046] Obviously, the above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. Preparation method of cobalt-doped strontium titanate sulfur-loaded composite material, characterized in that, it comprises the following steps: (1) Add strontium source and cobalt source into deionized water, stir until completely dissolved, then add acid to the solution, and record it as solution A after complete dissolution; (2) Mix tetrabutyl titanate and glacial acetic acid evenly, then slowly add deionized water, and record it as solution B after stirring evenly; (3) Slowly drop the prepared solution A into solution B, stir evenly, add polyethylene glycol, continue to stir, then raise the temperature to accelerate the reaction, and then dry and grind to obtain a powder sample; (4) The powder sample prepared in step (3) is first calcined in a nitrogen atmosphere and then switched to an oxygen atmosphere for calcination to obtain Co-SrTiO 3 ; (5) Mix the prepared Co-SrTiO 3 with elemental sulfur, grind them, transfer to a hydrothermal reaction kettle, replace with inert gas, and heat to obtain a cobalt-doped strontium titanate supported sulfur composite material (Co-SrTiO 3 @S); Among them, in the step (4), the atmosphere flow rate of nitrogen is controlled at 5-10 L / min, the calcination temperature is controlled at 700-900 °C, and the calcination time is controlled at 5-9 h; then the atmosphere flow rate of oxygen is 5-10 L / min, the calcination temperature is 300-500 °C, and the calcination time is controlled at 1-5 h; in the step (5), the mass ratio of Co-SrTiO 3 to elemental sulfur is controlled at 1:(3-5).

2. The preparation method of the cobalt-doped strontium titanate sulfur-loaded composite material according to claim 1, further, the strontium source in step (1) is strontium carbonate, and the molar ratio with the tetrabutyl titanate in step (2) is 1:1; the cobalt source is cobalt nitrate, and the doping amount is 1% - 5% of the molar amount of strontium titanate; the acid is citric acid, and its dosage is 0.05 - 0.1 mol / L.

3. The preparation method of the cobalt-doped strontium titanate sulfur-loaded composite material according to claim 2, further, the polyethylene glycol in step (3) is PEG6000, and its mass ratio with citric acid is 1:

2.

4. The preparation method of the cobalt-doped strontium titanate sulfur-loaded composite material according to claim 1, further, in step (3), the temperature increase is controlled between 65 - 85 °C, the reaction time is 4 - 8 h, and the final drying temperature is controlled at 120 - 150 °C.

5. The preparation method of the cobalt-doped strontium titanate sulfur-loaded composite material according to claim 1, further, in step (5), the temperature range of the hydrothermal reaction is 130 - 160 °C, and the reaction time is 10 - 20 h.

6. Cobalt-doped strontium titanate sulfur-loaded composite material obtained by the preparation method of the cobalt-doped strontium titanate sulfur-loaded composite material according to any one of claims 1 - 5.

7. Application of the cobalt-doped strontium titanate sulfur-loaded composite material obtained by the preparation method according to any one of claims 1 - 5 or the cobalt-doped strontium titanate sulfur-loaded composite material according to claim 6 in a lithium-sulfur battery positive electrode sheet or a button cell.

8. For the application according to claim 7, the preparation method of the lithium-sulfur battery positive electrode sheet is: weigh and grind evenly the cobalt-doped strontium titanate sulfur-loaded composite material prepared above, conductive carbon black, and binder PVDF, then add a dispersant to make a stable slurry; then coat it on carbon-containing aluminum foil, vacuum dry, cut it into electrode sheets and store them in a glove box for assembling button cells.

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