A nitrogen-rich fibrous gelatin-based separator for lithium-sulfur batteries and a preparation method and application thereof

Abstract

The present application relates to a kind of nitrogen-rich fibrous gelatin-based separator for lithium-sulfur battery and its preparation method and application, comprising the following steps: gelatin and glucose are added to deionized water and trifluoroethanol mixed solvent, while adding hydroxyapatite, after heating and stirring uniformly, spinning solution is obtained, first gelatin fiber film is obtained by electrospinning;The obtained fiber film is subjected to heat crosslinking, high-temperature carbonization treatment to obtain fibrous carbon film;Prepare gelatin spinning solution, and pure second gelatin fiber film is prepared by electrospinning;The fibrous carbon film after carbonization and the second gelatin fiber film are assembled to obtain the nitrogen-rich gelatin-based separator.The present application uses gelatin as the main body of lithium-sulfur battery diaphragm, doped with hydroxyapatite, which has a strong adsorption effect on polysulfide after carbonization, and the fibrous carbon layer with long-range conductivity has a positive effect on the reuse of polysulfide, inhibits the shuttle effect, and improves the cycle performance of battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium-sulfur batteries, and particularly relates to a nitrogen-rich fibrous gelatin-based separator for lithium-sulfur batteries and a preparation method and application thereof. BACKGROUND

[0002] Under the background of the "double carbon" policy, we need to vigorously develop new energy technologies. Lithium-sulfur batteries, as a new type of alternative battery technology for energy storage, have high specific energy, stable working voltage, wide temperature range, and other excellent properties. If it can be used on a large scale, the problem of insufficient battery capacity in electronic devices will be solved. In the commercial development process of lithium-sulfur batteries, some difficult problems have also been encountered, such as positive electrode volume expansion, "shuttle effect" of polysulfides, and lithium metal negative electrode dendrite.

[0003] Gelatin, as a natural polymer material, is obtained by hydrolysis of collagen and widely exists in the skin, skeleton, tendon and other parts of mammals. Gelatin contains a large number of nitrogen-containing functional groups and has a strong adsorption effect on polysulfides. At the same time, it has a guiding effect on the uniform deposition of lithium ions. However, due to the poor conductivity of gelatin, the adsorbed polysulfides cannot be reused. This problem caused by the characteristics of gelatin has made the research on using gelatin as a lithium-sulfur battery separator very slow. SUMMARY

[0004] In order to overcome the above technical problems existing in the prior art, the application provides a nitrogen-rich fibrous gelatin-based separator for lithium-sulfur batteries and a preparation method and application thereof. The preparation method is as follows: gelatin and glucose are added to a mixed solvent of deionized water and trifluoroethanol, and hydroxyapatite is added at the same time. After uniform heating and stirring, a spinning solution is obtained. A first gelatin fiber membrane is obtained by electrospinning. The obtained fiber membrane is subjected to heat crosslinking and high-temperature carbonization treatment to obtain a fibrous carbon membrane. A gelatin spinning solution is prepared, and a pure second gelatin fiber membrane is prepared by electrospinning. The carbonized fibrous carbon membrane and the second gelatin fiber membrane are assembled to obtain the nitrogen-rich gelatin-based separator. The application uses electrospinning technology to prepare gelatin molecules into the required separator material. Glucose is used as a crosslinking agent to realize the maintenance of the micro-fiber structure and the macro-film morphology of the gelatin fiber membrane during the carbonization process. Then, the hydroxyapatite is uniformly attached to the carbon fiber in situ during the carbonization process. The prepared fibrous carbon membrane has uniform morphology, greater porosity and smaller pore size, which can effectively inhibit the shuttle effect of polysulfides, catalyze the conversion of polysulfides, guide the ordered transmission of lithium ions, and control the growth of lithium dendrites. The application in lithium-sulfur batteries can effectively improve the cycle performance of the battery.

[0005] In order to achieve the purpose of the application, the following technical scheme is adopted: a preparation method of a nitrogen-rich gelatin-based separator for lithium-sulfur batteries, comprising the following steps:

[0006] (1) Dissolve gelatin and glucose with water and trifluoroethanol as solvent, and add hydroxyapatite, heat and stir to obtain a uniform suspension;

[0007] (2) Prepare a first gelatin fiber membrane by electrospinning the suspension obtained in step (1);

[0008] (3) Heat crosslink the first gelatin fiber membrane obtained in step (2);

[0009] (4) Carbonize the crosslinked gelatin fiber membrane obtained in step (3) under inert gas conditions to obtain a fibrous carbon membrane;

[0010] (5) Dissolve gelatin with water and trifluoroethanol as solvent, and heat and stir to obtain a uniform transparent solution;

[0011] (6) Prepare a pure second gelatin fiber membrane by electrospinning the uniform transparent solution obtained in step (5);

[0012] (7) Assemble the fibrous carbon membrane obtained in step (4) and the second gelatin fiber membrane obtained in step (6) to obtain the nitrogen-rich gelatin-based separator for lithium-sulfur batteries.

[0013] In a preferred embodiment of the present application, in step (1), the mass concentration of gelatin in the suspension is 10-20 wt%, more preferably 12.5 wt%; glucose is used as a crosslinking agent, and its mass concentration is 3 wt%-5 wt%, preferably 5 wt%; hydroxyapatite is 1-3 wt%; and the mass ratio of alcohol to water in the solvent is 3:7.

[0014] In a preferred embodiment of the present application, in steps (2) and (6), during the electrospinning process, the positive and negative voltages are 12-20 kV, more preferably 14 kV; the injection speed is 0.08-0.2 mm / min, more preferably 0.1 mm / min; the receiving distance is 16-24 cm, more preferably 20 cm; and the spinning temperature is 40-60℃, more preferably 40℃.

[0015] In a preferred embodiment of the present application, in step (3), the heat crosslinking is carried out at 260-300℃ in a muffle furnace, and the crosslinking time is 1-3 h; the heating rate is 1-5℃ / min, preferably 1℃ / min.

[0016] In a preferred embodiment of the present application, in step (4), the carbonization is carried out at 500-1000℃ in a tube furnace, and the holding time is 1-2 h; the heating rate is 3-5℃ / min.

[0017] In a preferred embodiment of the present application, in step (5), the mass fraction of gelatin in the solution is between 10wt%-20wt%, preferably 12.5wt%; and the mass ratio of alcohol to water in the solvent is 3:7.

[0018] In a preferred embodiment of the present application, in step (7), the carbon layer obtained in step (4) faces the positive electrode, and the second gelatin fiber membrane obtained in step (6) faces the negative electrode, and is applied in a lithium-sulfur battery.

[0019] The present application also protects the nitrogen-rich gelatin-based separator prepared by the above preparation method.

[0020] The present application also protects a high-performance lithium-sulfur battery assembled using the nitrogen-rich gelatin-based separator.

[0021] Compared with the prior art, the present application has the following advantages:

[0022] 1. The gelatin is used as the main body of the diaphragm of the lithium-sulfur battery, and the hydroxyapatite is doped and carbonized to obtain an intermediate layer having a strong adsorption effect on polysulfides, and the fibrous carbon layer having long-range conductivity has a positive effect on the reuse of polysulfides, thereby inhibiting the shuttle effect and greatly improving the problem of electrochemical performance degradation during the cycle process of the lithium-sulfur battery.

[0023] 2. The separator material used in the present application is a natural gelatin molecule, which is environmentally friendly and biodegradable, and is conducive to the recycling of waste batteries. The electrospun separator has a pore size that is easy to adjust and various functional groups, and the fiber morphology is uniform and the porosity is large, which provides a selective ion channel for lithium ion diffusion, and the in-situ attached hydroxyapatite strengthens the adsorption of polysulfides, greatly improving the negative effects of the shuttle effect, thereby improving the cycle performance of the lithium-sulfur battery.

[0024] 3. The present application uses glucose as a crosslinking agent to form more crosslinking points during the crosslinking process, thereby avoiding the fusion of fibers into blocks during the crosslinking process of the gelatin membrane, and achieving the preservation of the micro-fiber and macro-morphology of the gelatin during the carbonization process. BRIEF DESCRIPTION OF DRAWINGS

[0025] The present application will be further described with reference to the accompanying drawings.

[0026] Figure 1 The SEM image of the fiber membrane before crosslinking obtained in Example 1 of the present application.

[0027] Figure 2 The SEM image of the fiber membrane after crosslinking obtained in Example 1 of the present application.

[0028] Figure 3 The SEM image of the carbonized fiber membrane obtained in Example 1 of the present application.

[0029] Figure 4 EDS image of the cross section of the carbonized fiber membrane obtained in Example 1 of the present application.

[0030] Figure 5 Adsorption effect of the carbonized fiber membrane obtained in Example 1 of the present application on polysulfides.

[0031] Figure 6 Cycle performance curve of the gelatin-based separator obtained in Example 1 of the present application applied to a lithium-sulfur battery. DETAILED DESCRIPTION

[0032] The present application will be further described in conjunction with specific examples and application examples, but the scope of the present application is not limited thereto, and any form of modification or change made to the present application shall be within the scope of protection of the present application.

[0033] Example 1

[0034] (1) Preparation of fibrous carbon membrane

[0035] Accurately weigh 1.25 g of alkali method cowhide gelatin, 0.5 g of anhydrous glucose, and 0.1 g of hydroxyapatite. Add 2.445 g of trifluoroethanol and 5.705 g of deionized water, first swell at room temperature for 15 min, and then place in a 60℃ water bath for stirring and complete dissolution. Take 10 ml of medical disposable needle tube, add the above prepared suspension liquid into it, use an 18 gauge spinning needle, open the electrospinning machine, set the temperature to 40℃, the positive voltage to 11.00 kV, the negative voltage to -3.00 kV, the stroke to 50 cm, the receiving distance to 20 cm, the injection speed to 0.1 mm / min, and the electrospinning separator is received by the aluminum foil placed on the roller. After about 6 h, the spinning is completed, and the first gelatin fiber membrane is obtained.

[0036] Put the above fiber membrane into a muffle furnace at 270℃ for 1 h, then take it out and place it in a tube furnace at 800℃ in a nitrogen environment for 1 h. Use a scanning electron microscope to observe the microstructure of the prepared gelatin nanofiber membrane before and after crosslinking and after carbonization, as shown in Figure 1 , Figure 2 , Figure 3 From the figures, it can be seen that the obtained fiber membrane has a three-dimensional fiber structure. Figure 4 Energy dispersive X-ray spectrum of the obtained fibrous carbon membrane. Cut the carbonized carbon membrane into a 19 mm diameter disc using a dicing machine.

[0037] (2) Put the above obtained carbonized fibrous carbon membrane into a self-prepared polysulfide solution, and after standing for 24 h of adsorption, use an ultraviolet spectrometer to determine the change of the polysulfide solution before and after adsorption. The results are shown in Figure 5The figure shows that the carbon film prepared has a good adsorption effect on polysulfides.

[0038] (3) Preparation of pure second gelatin fiber film

[0039] Accurately weigh 1.25 g of alkali method cowhide frozen power gelatin, add 2.625 g of trifluoroethanol and 6.125 g of deionized water, first swell at room temperature for 15 min, then place in a 60°C water bath and stir to dissolve completely. Take 10 ml of medical disposable needle tube, add the above prepared solution to it, use an 18 gauge spinning needle, open the electrospinning machine, set the temperature to 60°C, the positive voltage to 11.00 kV, the negative voltage to -3.00 kV, the stroke to 50 cm, the receiving distance to 20 cm, the push injection speed to 0.2 mm / min, and the second gelatin fiber film obtained by electrospinning is received by the aluminum foil placed on the roller, and the spinning is completed after about 3 h. Cut the second gelatin fiber film into a 19 mm diameter disc using a disc cutter.

[0040] Application example

[0041] Assemble the 19 mm diameter discs obtained in steps (1) and (3) together as a separator, with the disc obtained in step (1) facing the positive electrode side and the disc obtained in step (3) facing the negative electrode side, the electrolyte is a traditional lithium-sulfur electrolyte, and the test conditions are 1C. And use the unmodified commercial Gelgard 2325 separator as a blank control. As shown in Figure 6 The result of the cycle performance test is shown in the figure.

[0042] As can be seen from the data in the figure, the lithium-sulfur battery using the gelatin separator prepared by the present application shows a higher initial discharge specific capacity of 959 mAh g -1 , which is much higher than the blank control group of 684.8 mAh g -1 . And after 90 cycles, the capacity retention rate is 97.08%, higher than the blank control of 74.5%, which is due to the good adsorption effect of the gelatin-based separator on polysulfides, and the fibrous carbon layer on the positive electrode side can reuse the adsorbed polysulfides, thereby improving the cycle stability and capacity retention rate of the lithium-sulfur battery, and having good application effect.

[0043] The above specific embodiments further illustrate the purpose, technical solutions and advantages of the present application, and it should be understood that the above are only specific embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A process for the preparation of a nitrogen-rich fibrous gelatin-based separator for lithium-sulfur batteries, characterized by, The gelatin and glucose are added into a mixed solvent of deionized water and trifluoroethanol, and hydroxyapatite is added, and after uniform heating and stirring, a spinning solution is obtained, and a first gelatin fiber membrane is obtained by electrospinning; the obtained fiber membrane is subjected to heat crosslinking and high-temperature carbonization treatment to obtain a fibrous carbon membrane; the gelatin is dissolved in water and trifluoroethanol as a solvent, and a uniform transparent solution is obtained after heating and stirring, and a pure second gelatin fiber membrane is prepared by electrospinning; and the carbonized fibrous carbon membrane and the second gelatin fiber membrane are assembled to obtain the nitrogen-rich fibrous gelatin-based separator.

2. The production method according to claim 1, characterized by, The method comprises the following steps: (1) The gelatin and glucose are dissolved in water and trifluoroethanol as a solvent, and hydroxyapatite is added, and a uniform suspension is obtained after heating and stirring; (2) The suspension obtained in step (1) is electrospun to prepare a first gelatin fiber membrane; (3) The first gelatin fiber membrane obtained in step (2) is subjected to heat crosslinking; (4) The crosslinked gelatin fiber membrane obtained in step (3) is subjected to carbonization under inert gas conditions to obtain a fibrous carbon membrane; (5) The gelatin is dissolved in water and trifluoroethanol as a solvent, and a uniform transparent solution is obtained after heating and stirring; (6) The uniform transparent solution obtained in step (5) is electrospun to prepare a pure second gelatin fiber membrane; (7) The fibrous carbon membrane obtained in step (4) and the second gelatin fiber membrane obtained in step (6) are assembled to obtain the nitrogen-rich fibrous gelatin-based separator for lithium-sulfur batteries.

3. The production method according to claim 2, characterized by, In step (1), the mass concentration of gelatin in the suspension is 10-20 wt%; glucose is used as a crosslinking agent, and the mass concentration is 3 wt%-5 wt%; the hydroxyapatite is 1-3 wt%; and the mass ratio of alcohol to water in the solvent is 3:

7.

4. The production method according to claim 3, characterized by, In step (1), the mass concentration of gelatin in the suspension is 12.5 wt%; glucose is used as a crosslinking agent, and the mass concentration is 5 wt%.

5. The preparation method according to claim 2, characterized in that, In steps (2) and (6), during the electrospinning process, the positive and negative voltages are 12-20 kV; the injection speed is 0.08-0.2 mm / min; the receiving distance is 16-24 cm; and the spinning temperature is 40-60℃.

6. The preparation method according to claim 5, characterized in that, In steps (2) and (6), during the electrospinning process, the positive and negative voltages are 14 kV; the injection speed is 0.1 mm / min; the receiving distance is 20 cm; and the spinning temperature is 40℃.

7. The preparation method according to claim 2, characterized in that, In step (3), the heat crosslinking is carried out at 260-300℃ in a muffle furnace, and the crosslinking time is 1-3 h; and the heating rate is 1-5℃ / min.

8. The preparation method according to claim 7, characterized in that, In step (3), the heating rate is 1℃ / min.

9. The preparation method according to claim 2, characterized in that, In step (4), the carbonization is carried out at 500-1000℃ in a tube furnace, the holding time is 1-2 h, and the heating rate is 3-5℃ / min.

10. The method of claim 2, wherein, In step (5), the mass fraction of gelatin in the solution is between 10 wt% and 20 wt%; and the mass ratio of alcohol to water in the solvent is 3:

7.

11. The method of claim 10, wherein, In step (5), the mass fraction of gelatin in the solution is 12.5 wt%.

12. The method of claim 2, wherein, In step (7), the fibrous carbon film obtained in step (4) and the second gelatin fiber film obtained in step (6) are applied to a lithium-sulfur battery with the second gelatin fiber film facing the negative electrode.

13. A nitrogen-enriched fibrous gelatin-based separator prepared according to the preparation method of any one of claims 1-12.

14. A high performance lithium sulfur battery, characterized by, A lithium-sulfur battery is assembled using the nitrogen-enriched fibrous gelatin-based separator of claim 13.

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