Preparation method of lithium-sulfur battery positive electrode sheet and lithium-sulfur battery

Abstract

The present invention belongs to the technical field of lithium-sulfur batteries, and specifically discloses a method for preparing a positive electrode sheet of a lithium-sulfur battery with a sulfur gradient distribution, wherein carbon material and sulfur powder are uniformly mixed to obtain sulfur-carbon powder; the sulfur-carbon powder is heated to obtain a sulfur-carbon composite material; the sulfur-carbon composite material is mixed with a conductive agent, a binder, and a solvent to obtain a slurry; the slurry is coated on a current collector, and a positive electrode sheet is formed after heating; the positive electrode sheet obtained in step S3 is placed in a heating device with the current collector on top and the coated slurry on the bottom for heating, so as to obtain a positive electrode sheet of a lithium-sulfur battery with a sulfur gradient distribution. The present invention constructs a lithium-sulfur positive electrode sheet with a sulfur gradient distribution only by controlling the heating method of the positive electrode sheet of the lithium-sulfur battery. The method is simple, efficient, and environmentally friendly in the processing process, and is suitable for large-scale industrial production. The present invention further discloses the application of the positive electrode sheet prepared by the above preparation method in a lithium-sulfur battery.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium-sulfur batteries, and in particular relates to a method for preparing a positive electrode sheet of a lithium-sulfur battery. Background Art

[0002] Energy crisis and environmental pollution have greatly promoted the development of clean energy storage industry. At the same time, the continuous improvement of people's living standards has made people more pursuing some high-power and high-energy-consuming electronic products, such as electric vehicles and digital products. Today's mainstream positive electrode materials, such as lithium iron phosphate, lithium cobalt oxide and high-nickel ternary positive electrode materials, have relatively limited specific capacity. The development of positive electrode materials with high specific capacity has become the top priority of scientific researchers.

[0003] Elemental sulfur is a lightweight, multi-electron reactive cathode material with a large specific capacity (1675 mAh g -1 ), environmentally friendly, abundant reserves, low price and other advantages. However, as the next generation of high-energy-density batteries, the dissolution and shuttle effect of the intermediate polysulfide seriously deteriorates the positive and negative electrode transmission interface and cycle stability. Summary of the invention

[0004] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for preparing a lithium-sulfur battery positive electrode sheet with a sulfur gradient distribution. Starting from the lithium-sulfur battery positive electrode sheet itself, a lithium-sulfur battery positive electrode sheet with a sulfur gradient distribution is constructed. The sulfur gradient distribution structure can greatly inhibit polysulfide dissolution and reduce the shuttle effect, thereby greatly improving the performance of the battery and extending the battery life.

[0005] To achieve the above objectives, the present invention provides the following specific technical solutions.

[0006] A method for preparing a lithium-sulfur battery positive electrode sheet with a sulfur gradient distribution comprises the following steps:

[0007] Step S1, mixing the carbon material and sulfur powder evenly to obtain sulfur-carbon powder;

[0008] Step S2, heating the sulfur-carbon powder to obtain a sulfur-carbon composite material;

[0009] Step S3, mixing the sulfur-carbon composite material with a conductive agent, a binder, and a solvent to obtain a slurry; coating the slurry on a current collector, and heating to form a positive electrode sheet;

[0010] Step S4, placing the positive electrode sheet obtained in step S3 in a heating device with the current collector on top and the coating slurry on the bottom for heating, so as to obtain a lithium-sulfur battery positive electrode sheet with a sulfur gradient distribution.

[0011] Furthermore, in some preferred embodiments of the present invention, the carbon material is one or more of Ketjen black, acetylene black, graphite, graphene, and porous carbon spheres; and the sulfur powder is sublimated sulfur powder.

[0012] Furthermore, in some preferred embodiments of the present invention, the mixing mass ratio of the carbon material to the sulfur powder is 1:(0.4-0.8).

[0013] Furthermore, in some preferred embodiments of the present invention, the heating temperature in step S2 is 100-160° C., and the heating time is 4-20 hours.

[0014] Furthermore, in some preferred embodiments of the present invention, the conductive agent is at least one of acetylene black and Super P; and the binder is an oil-based binder PVDF or a water-based binder CMC.

[0015] Further, in some preferred embodiments of the present invention, the solvent is one of NMP, anhydrous ethanol and deionized water.

[0016] Furthermore, in some preferred embodiments of the present invention, in the slurry, the mass ratio of the sulfur-carbon composite material, the conductive agent and the binder is 7~9:2~0.5:1~0.5.

[0017] Furthermore, in some preferred embodiments of the present invention, the heating temperature in step S3 is 40-70° C., and the heating time is 6-24 hours.

[0018] Further, in some preferred embodiments of the present invention, the heating device is selected from a hot table, an oven or an alcohol lamp.

[0019] Furthermore, in some preferred embodiments of the present invention, the heating temperature in step S4 is 60-120° C., and the heating time is 5-120 min.

[0020] The present invention directly starts with the pole piece. The positive pole piece of the lithium-sulfur battery only includes aluminum foil and a slurry mixed with a sulfur-carbon composite material, a conductive agent, a binder, and a solvent coated on the aluminum foil. There is no need to add other substances or perform other coating treatments on the pole piece. The heating method of directly using the current collector on the top and the coating slurry on the bottom is used so that the current collector (aluminum foil) blocks the escape of sulfur during the heating process, thereby constructing a lithium-sulfur battery positive pole piece with a sulfur gradient distribution in which the sulfur content is high on the current collector side and the sulfur content is lower the farther away from the current collector.

[0021] Based on the same inventive concept, the present invention also provides a lithium-sulfur battery, including a lithium-sulfur battery positive electrode sheet with sulfur gradient distribution prepared by the above preparation method.

[0022] Compared with the prior art, the present invention has the following obvious beneficial technical effects:

[0023] The present invention constructs a lithium-sulfur positive electrode sheet with a sulfur gradient distribution by only controlling the heating method of the lithium-sulfur battery positive electrode sheet. The method is simple, efficient, and environmentally friendly during the treatment process, and is suitable for large-scale industrial production.

[0024] The lithium-sulfur battery positive electrode with sulfur gradient distribution greatly inhibits the shuttling of polysulfides, improves the electrochemical performance of the lithium-sulfur battery, extends the battery life, and has strong commercial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the S trend of the lithium-sulfur positive electrode during the heating process.

[0026] Figure 2 Electrochemical performance diagram of the batteries assembled in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0027] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0028] Unless otherwise defined, all the professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0029] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0030] Example 1

[0031] This embodiment includes the following steps:

[0032] (1) Grind 0.8 g of Ketjen black and 1.2 g of sublimated sulfur powder in a mortar and mix well to obtain sulfur-carbon powder;

[0033] (2) The sulfur-carbon powder mixed in step (1) is sealed in a glass bottle, and placed in a 150° C. forced air oven for heating for 15 h to obtain a sulfur-carbon composite material;

[0034] (3) Grinding and mixing the sulfur-carbon composite material obtained in step (2) with acetylene black and PVDF in a mass ratio of 8:1:1, adding an appropriate amount of NMP solvent to prepare a slurry after the slurry is evenly ground, and coating the slurry on a current collector aluminum foil after the slurry has a moderate viscosity, and then placing the electrode in a 40° C. forced air oven for drying to obtain a lithium-sulfur positive electrode;

[0035] (4) If Figure 1 As shown, the lithium-sulfur positive electrode sheet obtained by S3 is placed on a hot plate at 80° C. with the substrate on top and the material on the bottom, and heated for 30 minutes, and then cooled naturally to obtain a lithium-sulfur positive electrode sheet with a sulfur gradient distribution.

[0036] During the heating process, the sulfur in the lithium-sulfur positive electrode sheet, which was originally evenly distributed, continues to sublime under the action of heat and runs to the side of the current collector, forming a lithium-sulfur positive electrode sheet with a sulfur gradient distribution.

[0037] Comparative Example 1

[0038] The only difference between Comparative Example 1 and Example 1 is that there is no step (4).

[0039] The lithium-sulfur positive electrode sheet with sulfur gradient distribution obtained in Example 1 and the lithium-sulfur positive electrode sheet obtained in Comparative Example 1 were respectively assembled into button cells with metal lithium negative electrode and commercial lithium-sulfur electrolyte (1 M LiTFSI in DOL:DME=1:1Vol% with 2% LiNO3) to test the electrochemical performance of the battery. The results are as follows: Figure 2 shown.

[0040] pass Figure 2 It can be seen that the battery with the sulfur gradient distribution lithium sulfur cathode plate as the positive electrode is cycled 300 times at a rate of 1C, and the discharge capacity remains at 581.5 mAh g -1 The capacity decays by 0.047% per cycle, the cycle stability is good, and the coulomb efficiency is always stable above 98%. The capacity of comparative example 1 is only 295.7 mAh g after 300 cycles. -1 The capacity decay per cycle is as high as 0.18%. The lithium-sulfur positive electrode sheet with gradient sulfur distribution prepared in Example 1 has excellent performance as a positive electrode for lithium-sulfur batteries and shows good commercial prospects.

[0041] Example 2

[0042] This embodiment includes the following steps:

[0043] (1) Grind 5 g of graphite and 2.5 g of sublimated sulfur powder in a mortar and mix well to obtain sulfur-carbon powder;

[0044] (2) The sulfur-carbon powder mixed in step (1) is sealed in a glass bottle, and placed in a 120° C. forced air oven for heating for 18 h to obtain a sulfur-carbon composite material;

[0045] (3) Grinding and mixing the sulfur-carbon composite material obtained in step (2) with acetylene black and CMC in a mass ratio of 7:2:1, adding an appropriate amount of deionized water solvent to prepare a slurry after the slurry is evenly ground, and coating the slurry on a current collector aluminum foil after the slurry has a moderate viscosity, and then placing the electrode in a 60° C. forced air oven for drying to obtain a lithium-sulfur positive electrode;

[0046] (4) The lithium-sulfur positive electrode sheet obtained by S3 is placed on a hot plate at 100°C with the substrate on top and the material on the bottom for 20 minutes, and then cooled naturally to obtain a lithium-sulfur positive electrode sheet with a sulfur gradient distribution.

[0047] Example 3

[0048] This embodiment includes the following steps:

[0049] (1) Grind 4 g of porous carbon spheres and 3.2 g of sublimated sulfur powder in a mortar and mix well to obtain sulfur-carbon powder;

[0050] (2) The sulfur-carbon powder mixed in step (1) is sealed in a glass bottle, and placed in a 150° C. forced air oven for heating for 10 h to obtain a sulfur-carbon composite material;

[0051] (3) Grind and mix the sulfur-carbon composite material obtained in step (2) with Super P and CMC in a mass ratio of 9:0.5:0.1, add an appropriate amount of ethanol solvent to mix the slurry after grinding evenly, and apply the slurry on the current collector aluminum foil after the slurry has a moderate viscosity, and then place the electrode in a 70°C forced air oven for drying to obtain a lithium-sulfur positive electrode;

[0052] (4) The lithium-sulfur positive electrode sheet obtained by S3 is placed on a hot plate at 120°C with the substrate on top and the material on the bottom for 100 min, and then cooled naturally to obtain a lithium-sulfur positive electrode sheet with a sulfur gradient distribution.

[0053] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a lithium-sulfur battery positive electrode sheet with a sulfur gradient distribution, characterized in that: The following steps are involved: Step S1, mixing the carbon material and sulfur powder evenly to obtain sulfur-carbon powder; Step S2, heating the sulfur-carbon powder to obtain a sulfur-carbon composite material; Step S3, mixing the sulfur-carbon composite material with a conductive agent, a binder, and a solvent to obtain a slurry; coating the slurry on a current collector, and heating to form a positive electrode sheet; Step S4, placing the positive electrode sheet obtained in step S3 in a heating device with the current collector on top and the coating slurry on the bottom for heating, so as to obtain a lithium-sulfur battery positive electrode sheet with a sulfur gradient distribution.

2. The preparation method according to claim 1, characterized in that The carbon material is one or more of Ketjen black, acetylene black, graphite, graphene, and porous carbon balls; and the sulfur powder is sublimated sulfur powder.

3. The preparation method according to claim 2, characterized in that: The mixing mass ratio of the carbon material to the sulfur powder is 1:(0.4-0.8).

4. The preparation method according to claim 1, characterized in that: The heating temperature in step S2 is 100-160° C., and the heating time is 4-20 hours.

5. The preparation method according to claim 1, characterized in that: The conductive agent is at least one of acetylene black and Super P; the binder is an oil-based binder PVDF or a water-based binder CMC.

6. The preparation method according to claim 1, characterized in that: The solvent is one of NMP, anhydrous ethanol and deionized water.

7. The preparation method according to claim 5 or 6, characterized in that: In the slurry, the mass ratio of the sulfur-carbon composite material, the conductive agent and the binder is 7-9:2-0.5:1-0.

5.

8. The preparation method according to claim 1, characterized in that: The heating temperature in step S3 is 40-70° C. and the heating time is 6-24 hours.

9. The preparation method according to claim 1, characterized in that: The heating temperature in step S4 is 60-120° C. and the heating time is 5-120 min.

10. A lithium-sulfur battery, characterized in that: A lithium-sulfur battery positive electrode sheet with a sulfur gradient distribution prepared by the preparation method according to any one of claims 1 to 9.

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