A long-lasting lithium battery

Abstract

The application discloses a long-lasting lithium battery, which comprises a positive electrode sheet, a negative electrode sheet, a battery diaphragm and an electrolyte; the positive electrode sheet is obtained by film forming of mixed paste of sulfur / carbon nanotube composite, carbon black and a binder; the negative electrode sheet is a lithium metal foil; the electrolyte is a lithium-sulfur electrolyte; the diaphragm comprises a functional layer and a base film layer; the functional layer is obtained by coating paste of vermiculite loaded titanium dioxide / carbon material on a polyolefin diaphragm layer; the diaphragm can adsorb polysulfides generated in the charging and discharging process of the lithium-sulfur battery through physical or chemical action, inhibit the occurrence of the shuttle effect, improve the utilization rate and cycle stability of the sulfur active material, and solve the problem of shortening of the battery life caused by loss of polysulfides; the battery comprising the lithium-sulfur battery diaphragm has good charging and discharging cycle stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium batteries, and particularly relates to a long-lasting lithium battery. BACKGROUND

[0002] Lithium ion batteries, as a kind of energy storage components for realizing free conversion between chemical energy and electrical energy, are widely applied to various electronic devices and new energy fields due to their high energy density, long cycle life and no memory effect. Lithium ion batteries mainly include positive electrode materials, negative electrode materials, separators and electrolytes. At present, the positive electrode materials of lithium ion batteries on the market are mainly lithium iron phosphate, lithium cobaltate and ternary lithium nickel cobaltate. However, these materials generally have the problem of low specific capacity, which limits the lithium ion batteries to meet the market demand in various fields. In addition, as the positive electrode material, lithium iron phosphate has the problems of low conductivity, expensive lithium cobaltate and poor cycle performance of ternary lithium nickel cobaltate. Sulfur is widely studied as a positive electrode material of lithium batteries due to its high theoretical specific capacity and theoretical energy density. In addition, the active material sulfur has the advantages of abundant resources, low price and environmental friendliness, which will further improve the application value of lithium-sulfur batteries in the field of new energy. However, during the charging and discharging process of the lithium-sulfur battery, the intermediate product lithium polysulfide is easily dissolved in the electrolyte and diffused to the negative electrode, causing serious "shuttle effect". This leads to irreversible loss of active material, poor cycle performance and low coulombic efficiency. The actual energy density of the battery is far lower than its theoretical energy density, and the cycle stability and service life are poor, which limits the commercial application of lithium-sulfur batteries. SUMMARY

[0003] In view of the deficiencies of the prior art, the application first provides a lithium-sulfur battery separator. The lithium-sulfur battery separator can adsorb polysulfides generated during the charging and discharging process of the lithium-sulfur battery through physical or chemical action, thereby inhibiting the occurrence of "shuttle effect", improving the utilization rate and cycle stability of sulfur active material, and solving the problem of battery life shortening caused by the reduction of polysulfides. The application of the lithium-sulfur battery separator to the lithium-sulfur battery will be beneficial to improving the service life of the lithium-sulfur battery.

[0004] To achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows:

[0005] A lithium-sulfur battery separator, wherein the separator comprises a functional layer and a base film layer; the functional layer is obtained by coating a vermiculite loaded titanium dioxide / carbon material slurry on the base film layer; and the base film layer is a polyolefin separator.

[0006] Preferably, the polyolefin separator is one or both of a polypropylene separator and a polyethylene separator.

[0007] Preferably, the preparation method of the lithium-sulfur battery separator is as follows:

[0008] (1) the activated vermiculite is dipped in a TiOSO4 solution, citric acid and thiourea are added and uniformly dispersed by ultrasonic to obtain a mixed dispersion liquid, and the mixed dispersion liquid is calcined to obtain the vermiculite loaded titanium dioxide / carbon material;

[0009] (2) the vermiculite loaded titanium dioxide / carbon material is dispersed in an ethanol solution to obtain a dispersion liquid, polyvinyl alcohol is added to the dispersion liquid and stirred to obtain a mixed slurry, and the mixed slurry is uniformly coated on a base film to obtain the lithium-sulfur battery separator after solidification;

[0010] Preferably, the mass-volume ratio of the vermiculite to the TiOSO4 solution is 1g:(2-4)mL; the concentration of the TiOSO4 solution is 1-3mol / L; and the molar ratio of the citric acid, the thiourea and the TiOSO4 is 5:2:1.

[0011] Preferably, the particle size of the vermiculite is 300 mesh; and the pretreatment of the vermiculite is to place the vermiculite in an acid solution and treat by ultrasonic to obtain the surface-activated vermiculite.

[0012] Preferably, the calcination conditions are as follows: placed in a tube furnace and calcined at 130-180℃ for 20-30min, then calcined at 400-500℃ for 30-60min, and finally calcined at 800-1000℃ for 60-80min.

[0013] Preferably, the viscosity of the mixed slurry is 800-1000mPa.s.

[0014] The application further provides a long-lasting lithium-sulfur battery, which comprises the lithium-sulfur battery separator described above, and further comprises a positive electrode sheet, a negative electrode sheet and an electrolyte; and the functional layer of the lithium-sulfur battery separator is arranged close to the positive electrode sheet. The arrangement of the lithium-sulfur battery separator in the application improves the cycle stability of the lithium-sulfur battery, and thus the service life of the lithium-sulfur battery can be significantly improved.

[0015] In the preparation process of the vermiculite loaded titanium dioxide / carbon material of the application, the vermiculite expands to form a lamellar structure under high temperature conditions, which provides sufficient loading space for the loading of titanium dioxide and carbon materials, and the formation process of the lamellar structure of the vermiculite is synchronous with the formation process of titanium dioxide and carbon materials, which significantly improves the uniformity of the loading.

[0016] Advantages

[0017] The vermiculite loaded titanium dioxide / carbon material of the present application comprises a vermiculite loaded nitrogen-sulfur co-doped titanium dioxide / nitrogen-sulfur co-doped carbon material, a vermiculite loaded titanium dioxide / nitrogen-sulfur co-doped carbon material, and a vermiculite loaded nitrogen-sulfur co-doped titanium dioxide / carbon material. The vermiculite loaded titanium dioxide / carbon material is coated on the surface of a polyolefin separator as a functional layer to obtain a composite functional lithium-sulfur battery separator. The composite functional lithium-sulfur battery separator not only overcomes the problems of poor heat resistance, easy shrinkage, and poor wettability of electrolyte of a pure polyolefin separator, but also can adsorb polysulfides generated in the charging and discharging process of a lithium-sulfur battery through physical or chemical action to inhibit the "shuttle effect". The utilization rate and cycle stability of the positive active material in the lithium-sulfur battery are improved, and the service life of the lithium-sulfur battery is improved.

[0018] The functional lithium-sulfur battery separator of the present application is simple to prepare, and the performance of the lithium-sulfur battery to which the obtained separator is applied is significantly improved. Thus, the present application provides a long-lasting lithium battery. DETAILED DESCRIPTION

[0019] The technical solutions of the present application will be described in detail below in conjunction with specific examples. It should be noted that the raw materials of the present application can be obtained from the market unless otherwise specified. The methods are conventional unless otherwise specified.

[0020] Raw material preparation

[0021] Preparation of activated vermiculite

[0022] After the 300-mesh vermiculite powder is ultrasonically immersed in a 0.5 mol / L sulfuric acid solution for 24-48 hours, it is filtered and washed until the washing liquid is neutral, and then dried to obtain activated vermiculite.

[0023] Example 1

[0024] A lithium-sulfur battery separator comprises a functional layer and a base film layer. The functional layer is a vermiculite loaded titanium dioxide / carbon material slurry coated on the base film layer. The base film is a polyethylene separator. The preparation method is as follows:

[0025] (1) 500 g of activated vermiculite is immersed in 1 L of 1 mol / L TiOSO4 solution, and then citric acid solution and thiourea solution are added and ultrasonically dispersed to obtain a mixed dispersion liquid. The mixed dispersion liquid is calcined in a tube furnace to obtain a vermiculite loaded titanium dioxide / carbon material. The molar ratio of citric acid, thiourea, and TiOSO4 is 5:2:1.

[0026] (2) The vermiculite loaded titanium dioxide / carbon material is dispersed in an ethanol solution to obtain a dispersion liquid. Polyvinyl alcohol is added to the dispersion liquid and stirred uniformly to obtain a mixed slurry. The mixed slurry is uniformly coated on the base film and solidified to obtain a lithium-sulfur battery separator.

[0027] The calcination condition in step (1) is: placed in a tube furnace, calcined at 130-180℃ for 20-30min, then calcined at 400-500℃ for 30-60min, and finally calcined at 800-1000℃ for 60-80min.

[0028] The viscosity of the slurry in step (2) is 800-1000mPa.s.

[0029] The thickness of the lithium-sulfur battery diaphragm prepared is 50μm.

[0030] Example 2

[0031] A lithium-sulfur battery diaphragm, the diaphragm comprises a functional layer and a base film layer; the functional layer is a vermiculite loaded titanium dioxide / carbon material slurry coated on the base film layer; the base film layer is a polyethylene diaphragm; and the preparation method is specifically:

[0032] (1) 500g of activated vermiculite is immersed in 1L of 2mol / L TiOSO4 solution, then citric acid solution and thiourea solution are added and uniformly dispersed by ultrasonic to obtain a mixed dispersion liquid, and the mixed dispersion liquid is placed in a tube furnace to obtain vermiculite loaded titanium dioxide / carbon material; the molar ratio of citric acid, thiourea and TiOSO4 is 5:2:1;

[0033] (2) the vermiculite loaded titanium dioxide / carbon material is dispersed in an ethanol solution to obtain a dispersion liquid, polyvinyl alcohol is added to the dispersion liquid and stirred uniformly to obtain a mixed slurry; the mixed slurry is uniformly coated on the base film and solidified to obtain a lithium-sulfur battery diaphragm;

[0034] The calcination condition in step (1) is: placed in a tube furnace, calcined at 130-180℃ for 20-30min, then calcined at 400-500℃ for 30-60min, and finally calcined at 800-1000℃ for 60-80min.

[0035] The viscosity of the mixed slurry in step (2) is: 800-1000mPa.s.

[0036] The thickness of the lithium-sulfur battery diaphragm prepared is 50μm.

[0037] Example 3

[0038] A lithium-sulfur battery diaphragm, the diaphragm comprises a functional layer and a base film layer; the functional layer is a vermiculite loaded titanium dioxide / carbon material slurry coated on the base film layer; the base film is a polyethylene diaphragm; and the preparation method is specifically:

[0039] (1) 500 g of activated vermiculite is immersed in 1 L of 3 mol / L TiOSO4 solution, and then citric acid solution and thiourea solution are added and uniformly dispersed by ultrasonic to obtain a mixed dispersion liquid. The mixed dispersion liquid is placed in a tube furnace to obtain a vermiculite loaded titanium dioxide / carbon material by calcination; wherein the molar ratio of citric acid, thiourea and titanyl sulfate is 5:2:1;

[0040] (2) The vermiculite loaded titanium dioxide / carbon material is dispersed in an ethanol solution to obtain a dispersion liquid, and polyvinyl alcohol is added to the dispersion liquid and stirred uniformly to obtain a mixed slurry. The mixed slurry is uniformly coated on a base film and solidified to obtain a lithium-sulfur battery separator;

[0041] In step (1), the calcination conditions are as follows: placed in a tube furnace and calcined at 130-180°C for 20-30 min, then calcined at 400-500°C for 30-60 min, and finally calcined at 800-1000°C for 60-80 min;

[0042] The viscosity of the mixed slurry in step (2) is 800-1000 mPa.s;

[0043] The thickness of the lithium-sulfur battery separator prepared is 50 μm.

[0044] Example 4

[0045] A long-lasting lithium battery, which comprises the separator prepared in any of the above examples, a positive electrode sheet, a negative electrode sheet and an electrolyte. The assembly method is as follows: the positive electrode sheet, the separator and the negative electrode sheet are sequentially inserted into a battery shell, the electrolyte is added to the battery shell, and then the battery shell is packaged to obtain the lithium battery.

[0046] The positive electrode sheet is obtained by film forming a mixed slurry of sulfur / carbon nanotube composite, carbon black and binder; the negative electrode sheet is a lithium metal foil; and the electrolyte is a lithium-sulfur electrolyte.

[0047] Comparative Example 1

[0048] A lithium-sulfur battery separator, and the preparation method is as follows:

[0049] (1) The mixed solutions of activated vermiculite, TiOSO4 solution, citric acid solution and thiourea solution are placed in a tube furnace to obtain expanded vermiculite powder, titanium dioxide powder and carbon material powder by calcination, respectively;

[0050] (2) The expanded vermiculite powder, titanium dioxide powder and carbon material powder obtained in step (1) are dispersed in an ethanol solution to obtain a dispersion liquid, and polyvinyl alcohol is added to the dispersion liquid and stirred uniformly to obtain a mixed slurry. The mixed slurry is uniformly coated on a polyethylene separator and solidified to obtain a lithium-sulfur battery separator;

[0051] The calcination condition in step (1) is as follows: placed in a tube furnace and calcined at 130-180°C for 20-30 min; then calcined at 400-500°C for 30-60 min; finally calcined at 800-1000°C for 60-80 min.

[0052] The viscosity of the mixed slurry in step (2) is 800-1000 mPa.s.

[0053] The thickness of the prepared lithium-sulfur battery separator is 50 μm.

[0054] Comparative Example 2

[0055] A lithium-sulfur battery separator is prepared by the following method:

[0056] (1) 500 g of activated vermiculite is immersed in a citric acid solution and a thiourea solution, and uniformly dispersed by ultrasonic treatment to obtain a mixed dispersion liquid. The mixed dispersion liquid is placed in a tube furnace and calcined to obtain a vermiculite-loaded carbon material; the molar ratio of citric acid to thiourea is 5:2.

[0057] (2) The vermiculite-loaded carbon material obtained in step (1) is dispersed in an ethanol solution to obtain a dispersion liquid. Polyvinyl alcohol is added to the dispersion liquid and stirred uniformly to obtain a mixed slurry. The mixed slurry is uniformly coated on a polyethylene separator and solidified to obtain a lithium-sulfur battery separator.

[0058] The calcination condition in step (1) is as follows: placed in a tube furnace and calcined at 130-180°C for 20-30 min; then calcined at 400-500°C for 30-60 min; finally calcined at 800-1000°C for 60-80 min.

[0059] The viscosity of the mixed slurry in step (2) is 800-1000 mPa.s.

[0060] The thickness of the prepared lithium-sulfur battery separator is 50 μm.

[0061] Comparative Example 3

[0062] (1) 500 g of activated vermiculite is immersed in 1 L of a 2 mol / L TiOSO4 solution, and uniformly dispersed by ultrasonic treatment to obtain a mixed dispersion liquid. The mixed dispersion liquid is placed in a tube furnace and calcined to obtain a vermiculite-loaded titanium dioxide material.

[0063] (2) The vermiculite-loaded titanium dioxide material is dispersed in an ethanol solution to obtain a dispersion liquid. Polyvinyl alcohol is added to the dispersion liquid and stirred uniformly to obtain a mixed slurry. The mixed slurry is uniformly coated on a polyethylene separator and solidified to obtain a lithium-sulfur battery separator.

[0064] The roasting condition in step (1) is: placed in a tube furnace and roasted at 130-180℃ for 20-30min; then roasted at 400-500℃ for 30-60min; finally roasted at 800-1000℃ for 60-80min.

[0065] The viscosity of the mixed slurry in step (2) is: 800-1000mPa.s.

[0066] The thickness of the lithium-sulfur battery diaphragm is 50μm.

[0067] Comparative Example 4

[0068] A lithium-sulfur battery diaphragm is prepared by the following method:

[0069] (1) Take 1L 2mol / L TiOSO4solution, then add citric acid solution and thiourea solution to it and ultrasonically disperse to obtain a mixed dispersion, and then place the mixed dispersion in a tube furnace to obtain a carbon material / titanium dioxide composite by roasting; wherein the molar ratio of citric acid, thiourea and titanyl sulfate is 5:2:1;

[0070] (2) Disperse the carbon material / titanium dioxide composite in an ethanol solution to obtain a dispersion, add polyvinyl alcohol to the dispersion and stir to obtain a mixed slurry; coat the mixed slurry on a polyethylene diaphragm and solidify to obtain a lithium-sulfur battery diaphragm;

[0071] The roasting condition in step (1) is: placed in a tube furnace and roasted at 130-180℃ for 20-30min; then roasted at 400-500℃ for 30-60min; finally roasted at 800-1000℃ for 60-80min.

[0072] The viscosity of the mixed slurry in step (2) is: 800-1000mPa.s.

[0073] The thickness of the lithium-sulfur battery diaphragm is 50μm.

[0074] Thermal stability test

[0075] Cut the polyethylene diaphragm of Examples 1-3 and commercially available polyethylene diaphragm (PE) into a certain size, place them in an oven at 120℃ for 2h, take out the diaphragm samples and observe the shape change; the results are recorded in Table 1.

[0076] Table 1: Thermal stability test results

[0077] Sample grouping Sample shape Example 1 No shrinkage Example 2 No shrinkage Example 3 No shrinkage PE Melted

[0078] Battery cycle performance test

[0079] The lithium-sulfur battery separator, the positive electrode sheet, and the negative electrode sheet prepared by the lithium-sulfur battery of the present application embodiments 1-3 and the comparative examples 1-4 were inserted into a battery shell, and after adding an electrolyte, the battery shell was packaged to prepare a lithium-sulfur battery.

[0080] In order to evaluate the service life of the lithium-sulfur battery, the charge-discharge cycle performance of the lithium-sulfur battery prepared above was tested, and the charge-discharge cycle performance test was carried out at a current density of 0.5C, and the results are recorded in Table 2.

[0081] Table 2: Charge-discharge cycle performance test results

[0082]

[0083] As can be seen from the data in Table 2, the first charge-discharge coulombic efficiency of the lithium-sulfur battery assembled by the lithium-sulfur battery separator prepared by the present application embodiments 1-3 reached more than 90%; and after 100 cycles, the capacity retention rate reached more than 85%; which shows that the lithium-sulfur battery separator prepared by the present application embodiments can significantly improve the cycle stability of the lithium-sulfur battery; and compared with example 2, the first charge-discharge coulombic efficiency of the lithium-sulfur battery assembled by the separator prepared by comparative examples 1-4 is reduced, and the capacity retention rate is significantly reduced after 100 cycles; which shows that the present application uses vermiculite in situ loaded titanium dioxide / carbon material coated on the surface of the polyethylene separator to have adsorption and conversion effect on the polysulfides generated during the charge-discharge process of the battery, thereby reducing the loss of active material sulfur, and can significantly improve the cycle stability of the lithium-sulfur battery;

[0084] Compared with example 2, the composite separator in comparative example 2 is applied to the lithium-sulfur battery, and the capacity retention rate of the lithium-sulfur battery after 100 charge-discharge cycles is significantly reduced; which shows that the three materials of expanded vermiculite, titanium dioxide and carbon material have a synergistic effect in adsorbing and converting polysulfides generated during the charge-discharge process of the battery; and at the same time, the composite separator obtained by coating the mechanical mixture of expanded vermiculite, titanium dioxide and carbon material on the polyethylene separator is applied to the lithium-sulfur battery in comparative example 1, and the capacity retention rate of the lithium-sulfur battery after 100 charge-discharge cycles is still significantly reduced; the reason for the analysis may be that the present application uses vermiculite in situ loaded titanium dioxide and carbon material to obtain a composite material coated on the surface of the polyethylene separator to obtain a composite separator; on the one hand, it improves the loading amount of titanium dioxide and carbon material on the surface of vermiculite and the uniformity of coating on the surface of the polyethylene separator; at the same time, it avoids the coating particles from falling off the surface of the polyethylene separator to improve the stability of the functional layer and facilitate its function; on the other hand, it improves the contact area of the functional particles in the functional layer with the electrolyte and improves the adsorption and conversion effect of polysulfides.

[0085] The above embodiments are only the preferred embodiments of the present application, and the protection scope of the present application is not limited thereto, and any simple change or equivalent replacement of the technical solutions within the technical range disclosed by the present application can fall within the protection scope of the present application.

Claims

1. A method of preparing a lithium-sulfur battery separator, characterized by, Specifically: (1) the activated vermiculite is immersed in a TiOSO4 solution, and then citric acid and thiourea are added and uniformly dispersed by ultrasonic treatment to obtain a mixed dispersion liquid, and the mixed dispersion liquid is calcined to obtain a vermiculite loaded titanium dioxide / carbon material; (2) the vermiculite loaded titanium dioxide / carbon material is dispersed in an ethanol solution to obtain a dispersion liquid, and polyvinyl alcohol is added to the dispersion liquid and stirred to obtain a mixed slurry; the mixed slurry is uniformly coated on a base film and solidified to obtain a lithium-sulfur battery separator.

2. The method for preparing a lithium-sulfur battery separator according to claim 1, wherein, The mass-volume ratio of the activated vermiculite to the TiOSO4 solution is 1 g:(2-4) mL; the concentration of the TiOSO4 solution is 1-3 mol / L; and the molar ratio of citric acid, thiourea and TiOSO4 is 5:2:

1.

3. The method of producing a lithium-sulfur battery separator according to claim 1, wherein The particle size of the vermiculite is 300 mesh.

4. The method of producing a lithium-sulfur battery separator according to claim 1, wherein The activated vermiculite is obtained by ultrasonic treatment of vermiculite in an acidic solution.

5. The method of producing a lithium-sulfur battery separator according to claim 1, wherein The calcination conditions in step (1) are as follows: the mixture is placed in a tube furnace and calcined at 130-180°C for 20-30 min, then calcined at 400-500°C for 30-60 min, and finally calcined at 800-1000°C for 60-80 min.

6. The method of producing a lithium-sulfur battery separator according to claim 1, wherein The viscosity of the mixed slurry is 800-1000 mPa.s.

7. The lithium-sulfur battery separator prepared by the method of any one of claims 1-6, characterized in that, The separator comprises a functional layer and a base film layer; the functional layer is obtained by coating the vermiculite loaded titanium dioxide / carbon material slurry on the base film layer; and the base film layer is a polyolefin separator.

8. The lithium-sulfur battery separator of claim 7, wherein, The polyolefin separator is one or both of a polypropylene separator and a polyethylene separator.

9. A long-life lithium battery, characterized by, The lithium-sulfur battery separator of claim 8. The lithium-sulfur battery separator of claim 8.

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