Molybdenum sulfidized polyacrylonitrile positive electrode material for lithium-sulfur battery and preparation method thereof

Abstract

This invention discloses a molybdenum-sulfurized polyacrylonitrile (PABN) cathode material for lithium-sulfur batteries and its preparation process. By using molybdenum polysulfide instead of elemental sulfur as the sulfur source for PABN, molybdenum is incorporated into the bulk structure of PABN via Mo-S bonds, thereby improving the discharge voltage and reaction kinetics of the PABN cathode material. The molybdenum-sulfurized PABN cathode material exhibits high discharge voltage, excellent cycle stability, rate performance, and coulombic efficiency. At a rate of 0.2C, the material has an average discharge voltage of 1.89V, a stable cycle capacity of 650mAh / g, and an average coulombic efficiency greater than 99.9% after 200 cycles. This method significantly promotes the practical application of lithium-sulfur batteries.

Description

Technical Field

[0001] This invention designs a molybdenum-sulfurized polyacrylonitrile cathode material for lithium-sulfur batteries and its preparation method, relating to the field of chemical power sources. Technical Background

[0002] Lithium-sulfur batteries have attracted much attention due to their high theoretical specific energy (2600 Wh / kg), low price, and environmental friendliness. However, the carbon-sulfur composite cathode materials used in traditional lithium-sulfur batteries face a series of problems, such as cycle performance degradation caused by the dissolution of long-chain lithium polysulfides (Li2Sn, 4≤n≤8) in the electrolyte, decreased coulombic efficiency, and safety issues related to lithium dendrite pulverization, which greatly hinder the degradation of lithium-sulfur batteries.

[0003] Sulfurized polyacrylonitrile (SPAC) is considered a promising cathode material for lithium-sulfur batteries due to its high specific capacity, excellent cycle performance, and near-100% coulombic efficiency. SPAC is formed by the cyclization of polyacrylonitrile under certain temperature conditions and its bonding with sulfur. It is generally believed that the sulfur chains (-S) in the SPAC structure... x The length of the -) component does not exceed 4, therefore, the sulfurized polyacrylonitrile cathode material does not generate long-chain lithium polysulfides during cycling, avoiding the solution and shuttle of long-chain lithium polysulfides, thus exhibiting cycle stability comparable to commercial lithium-ion batteries. It is worth noting that sulfurized polyacrylonitrile can cycle stably in carbonate electrolytes, and the process can continue the preparation methods of commercial lithium-ion batteries, which is conducive to promoting its commercialization.

[0004] However, sulfurized polyacrylonitrile (PPI) cathode materials still face two key problems: low discharge voltage and low rate performance. Therefore, lithium-sulfur batteries based on PPI cathodes still need improvement in terms of rate performance and actual specific energy. Currently, literature reports on using various transition metals to improve the discharge voltage and intrinsic conductivity of PPI cathode materials, as well as enhance the overall reaction kinetics during charge and discharge. However, the doping of these transition metals is all done in the form of metal salts, such as transition metal sulfides and transition metal oxides. The content, particle size, and dispersion of these dopants all affect the performance of PPI cathode materials. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a molybdenum-sulfurized polyacrylonitrile cathode material for lithium-sulfur batteries and its preparation method. The method uses molybdenum polysulfide instead of elemental sulfur as the sulfur source in the preparation process of the polyacrylonitrile, allowing molybdenum to enter the bulk structure of the polyacrylonitrile in the form of -Mo-S- bonds, thereby improving the discharge voltage and reaction kinetics of the polyacrylonitrile cathode material.

[0006] A molybdenum-sulfurized polyacrylonitrile cathode material for lithium-sulfur batteries and its preparation method, comprising the following steps:

[0007] (1) Mix molybdenum polysulfide and polyacrylonitrile evenly and seal in an inert atmosphere;

[0008] (2) The above mixture is heated to obtain molybdenum vulcanized polyacrylonitrile cathode material.

[0009] In molybdenum polysulfide, the atomic ratio of molybdenum to sulfur is 1:2 to 18; the molecular weight of polyacrylonitrile is 10,000 to 500,000; the mass ratio of polyacrylonitrile to molybdenum polysulfide is 1:1 to 20; and the inert atmosphere is nitrogen or argon.

[0010] The heat treatment reaction temperature is 200~500℃, and the reaction time is 1~200 hours.

[0011] Molybdenum-sulfurized polyacrylonitrile cathode material is assembled with metallic lithium, lithium alloy, silicon, and graphite to form a secondary battery.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0013] 1. The main chain of the prepared molybdenum-cured polyacrylonitrile cathode material is a nitrogen-containing carbon chain, and the side chain is a sulfur-sulfur chain doped with molybdenum atoms. The doping of molybdenum in the molecular structure can improve the discharge voltage and reaction kinetics of the curing polyacrylonitrile cathode material.

[0014] 2. The chemical raw materials used in this invention are inexpensive, the reaction method is simple, and it is easy to prepare on a large scale, thus having commercial potential. Attached Figure Description

[0015] Figure 1 SEM images of molybdenum vulcanized polyacrylonitrile

[0016] Figure 2 Cyclic performance and coulombic efficiency of molybdenum vulcanized polyacrylonitrile

[0017] Figure 3 SEM images of vulcanized polyacrylonitrile

[0018] Figure 4 Cyclic performance and coulombic efficiency of vulcanized polyacrylonitrile Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0020] Weigh 10g of molybdenum polysulfide and 2g of polyacrylonitrile with a molecular weight of 150,000, grind them evenly, and heat them to 350℃ in an argon-protected tube furnace and hold for 5 hours to obtain molybdenum-sulfurized polyacrylonitrile. Its SEM image is shown below. Figure 1 As shown in the figure. The obtained molybdenum-sulfurized polyacrylonitrile was used as the positive electrode and lithium metal as the negative electrode to assemble a button cell. Electrochemical performance was tested within a voltage range of 1-3V. At a 0.1C rate, the average discharge voltage of the lithium-sulfur battery was 1.89V, the stable cycle capacity of the material was 650 mAh / g, and after 200 cycles, the average coulombic efficiency was greater than 99.9%. (See attached figure). Figure 2 . Example 2

[0021] 16g of molybdenum polysulfide and 2g of polyacrylonitrile with a molecular weight of 150,000 were weighed and ground evenly. The mixture was then heated to 400℃ and held at that temperature for 8 hours in an argon-protected tube furnace to obtain molybdenum-sulfurized polyacrylonitrile. A button cell was assembled using the obtained molybdenum-sulfurized polyacrylonitrile as the positive electrode and lithium metal as the negative electrode. Electrochemical performance tests were conducted within a voltage range of 1-3V. At a 0.2C rate, the average discharge voltage of the lithium-sulfur battery was 1.89V, the stable cycle capacity of the material was greater than 630 mAh / g, and the average coulombic efficiency after 100 cycles was greater than 99.9%. Example 3

[0022] 10g of molybdenum polysulfide and 2g of polyacrylonitrile with a molecular weight of 30,000 were weighed, ground evenly, and then heated to 400℃ and held for 8 hours in a tube furnace under argon protection to obtain molybdenum-sulfurized polyacrylonitrile. The obtained molybdenum-sulfurized polyacrylonitrile was used as the positive electrode and lithium metal as the negative electrode to assemble a button cell. Electrochemical performance tests were conducted within a voltage range of 1-3V. At a 0.2C rate, the average discharge voltage of the lithium-sulfur battery was 1.89V, the stable cycle capacity of the material was greater than 630 mAh / g, and the average coulombic efficiency after 100 cycles was greater than 99.9%. Example 4

[0023] 10g of molybdenum polysulfide and 2g of polyacrylonitrile with a molecular weight of 150,000 were weighed, ground evenly, and then heated to 350℃ and held for 5 hours in an argon-protected tube furnace to obtain molybdenum-sulfurized polyacrylonitrile. The obtained molybdenum-sulfurized polyacrylonitrile was used as the positive electrode and lithium metal as the negative electrode to assemble a button cell. Electrochemical performance tests were conducted within a voltage range of 1-3V. At a 0.2C rate, the average discharge voltage of the lithium-sulfur battery was 1.89V, the stable cycle capacity of the material was 610 mAh / g, and after 100 cycles, the average coulombic efficiency was greater than 99.9%. Example 5

[0024] 10g of molybdenum octasulfide and 2g of polyacrylonitrile with a molecular weight of 150,000 were weighed, ground evenly, and then heated to 350℃ and held for 5 hours in an argon-protected tube furnace to obtain molybdenum-sulfurized polyacrylonitrile. The obtained molybdenum-sulfurized polyacrylonitrile was used as the positive electrode and lithium metal as the negative electrode to assemble a button cell. Electrochemical performance tests were conducted within a voltage range of 1-3V. At a 0.2C rate, the average discharge voltage of the lithium-sulfur battery was 1.88V, the stable cycle capacity of the material was 600 mAh / g, and after 100 cycles, the average coulombic efficiency was greater than 99.9%.

[0025] Comparative Example

[0026] Weigh 10g of elemental sulfur powder and 2g of polyacrylonitrile with a molecular weight of 150,000, grind them evenly, and heat them to 350℃ in an argon-protected tube furnace and hold for 5 hours to obtain vulcanized polyacrylonitrile. Its SEM image is shown below. Figure 3 As shown in the figure. The obtained sulfurized polyacrylonitrile was used as the positive electrode and lithium metal as the negative electrode to assemble a button cell. Electrochemical performance was tested within a voltage range of 1-3V. At a 0.2C rate, the average discharge voltage of the lithium-sulfur battery was 1.81V, the stable cycle capacity of the material was 550 mAh / g, and after 100 cycles, the average coulombic efficiency was 99.7%. (See attached figure). Figure 4 .

Claims

1. A method for preparing a molybdenum-sulfurized polyacrylonitrile cathode material for lithium-sulfur batteries, characterized in that, Includes the following steps: (1) Mix molybdenum polysulfide and polyacrylonitrile evenly and seal in an inert atmosphere; (2) The above mixture is heated to obtain molybdenum vulcanized polyacrylonitrile cathode material.

2. The preparation method according to claim 1, characterized in that: In step (1), the atomic ratio of molybdenum to sulfur in molybdenum polysulfide is 1:2 to 18; the molecular weight of polyacrylonitrile is 10,000 to 500,000; the mass ratio of polyacrylonitrile to molybdenum polysulfide is 1:1 to 20; and the inert atmosphere is nitrogen or argon.

3. The preparation method according to claim 1, characterized in that: In step (2), the reaction temperature of the heat treatment is 200~500℃ and the reaction time is 1~200 hours.

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