Titanium-sulfurized polyacrylonitrile cathode material with high rate performance and preparation method thereof

Abstract

This invention discloses a high-rate-performance titanium-sulfurized polyacrylonitrile (TSU) cathode material and its preparation method. Amorphous titanium polysulfide replaces elemental sulfur as the sulfur source for TSU. A portion of the titanium enters the bulk structure of the TSU via Ti-S bonds, while the remaining portion is in situ coated on the surface of the TSU cathode material as titanium disulfide, thereby improving the rate performance of the cathode material. The titanium disulfide@TISU cathode material exhibits excellent cycle stability, rate performance, and coulombic efficiency. At 1C, the material maintains a stable cycle capacity of 700 mAh / g, with an average coulombic efficiency greater than 99.9% after 300 cycles. Even at 30C, the material still maintains a cycle capacity of 430 mAh / g. This method significantly promotes the practical application of lithium-sulfur batteries.

Description

Technical Field

[0001] This invention designs a high-rate performance titanium-sulfurized polyacrylonitrile cathode material and its preparation method, relating to the field of chemical power sources. Background Technology

[0002] Lithium-sulfur batteries have attracted much attention due to their high theoretical specific energy (2600 Wh / kg), low price, and environmental friendliness. Traditional carbon-sulfur composite cathode materials suffer from a series of problems, such as cycle performance degradation, coulombic efficiency reduction, and lithium dendrite pulverization caused by the shuttle phenomenon, which greatly hinder the practicality of lithium-sulfur batteries.

[0003] Vulcanized polyacrylonitrile (PVC) is considered a novel sulfur-containing cathode material, and due to its excellent cycle performance and near-100% coulombic efficiency, it is regarded as a more practical lithium-sulfur battery cathode material. It is generally believed that PVC is formed by the cyclization of polyacrylonitrile under certain temperature conditions, with sulfur replacing hydrogen in the polymer backbone. There is no shuttle phenomenon during cycling. However, precisely because of the poor conductivity of the polymer backbone, PVC cathode materials still face the problem of low rate performance. Currently, the common solution to improve the rate performance of PVC cathode materials is to blend PVC with a conductive agent (usually conductive carbon). However, the added conductive agent only solves the electronic conductivity problem of PVC cathode; how to improve the ionic conductivity of PVC cathode remains largely unexplored. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a high-rate performance titanium-sulfurized polyacrylonitrile cathode material and its preparation method. Amorphous titanium polysulfide replaces elemental sulfur as the sulfur source in the preparation process of titanium-sulfurized polyacrylonitrile. A portion of this titanium polysulfide is incorporated into the bulk structure of the titanium-sulfurized polyacrylonitrile as a -Ti-S- bond, while the other portion is in situ coated onto the surface of the titanium-sulfurized polyacrylonitrile cathode material as titanium disulfide. During charge and discharge, the Li2S formed reacts with TiS2, resulting in Li2S + 2πε₀ ... x TiS2→Li2Ti x S 2x+1 Solid electrolyte with an ionic conductivity of 10 -3 With an S / cm or higher, the ionic conductivity of the cathode material is increased, thereby improving the rate performance of the battery.

[0005] In a first aspect, the present invention provides a method for preparing a high-rate performance titanium-sulfurized polyacrylonitrile cathode material, comprising the following steps:

[0006] (1) Mix amorphous titanium polysulfide and polyacrylonitrile evenly and seal in an inert atmosphere;

[0007] (2) The above mixture is heated to obtain titanium disulfide@titanium sulfide polyacrylonitrile cathode material.

[0008] According to a further improvement of the present invention, in step (1), the atomic ratio of titanium to sulfur in amorphous titanium polysulfide is 1:3~8; the molecular weight of polyacrylonitrile is 10000~500000; the mass ratio of polyacrylonitrile to titanium polysulfide is 1:2~100; and the inert atmosphere is nitrogen or argon.

[0009] According to a further improvement of the present invention, in step (2), the reaction temperature of the heat treatment is 200~500℃ and the reaction time is 1~20 hours.

[0010] Secondly, the present invention provides a high-rate performance titanium-sulfurized polyacrylonitrile cathode material, wherein the titanium-sulfurized polyacrylonitrile cathode material is assembled with lithium metal, lithium alloy, silicon, and graphite to form a secondary battery.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0012] 1. The prepared titanium disulfide@titanium sulfide polyacrylonitrile cathode material has a titanium disulfide coating that forms Li2Ti during charge and discharge. x S 2x+1 Solid electrolyte with an ionic conductivity of 10 -3 A value above S / cm can improve the ionic conductivity of vulcanized polyacrylonitrile cathode materials.

[0013] 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

[0014] Figure 1 SEM image of titanium disulfide@titanium-sulfurized polyacrylonitrile;

[0015] Figure 2 Cyclic performance and coulombic efficiency of titanium disulfide@titanium-sulfurized polyacrylonitrile.

[0016] Figure 3 Rate performance of titanium disulfide@titanium vulcanized polyacrylonitrile;

[0017] Figure 4 Rate performance of vulcanized polyacrylonitrile. Detailed Implementation

[0018] 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.

[0019] Example 1

[0020] 10g of amorphous titanium 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 titanium disulfide@titanium sulfide polyacrylonitrile. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images are shown below. Figure 1 As shown in the figure. Using titanium disulfide@titanium sulfide polyacrylonitrile as the positive electrode and lithium metal as the negative electrode, a button cell was assembled. Electrochemical performance was tested within a voltage range of 1-3V. At 1C rate, the average discharge voltage of the lithium-sulfur battery was 1.85V, the stable cycle capacity of the material was 0 mAh / g, and after 300 cycles, the average coulombic efficiency was greater than 99.9%. (See attached figure). Figure 2 .

[0021] Example 2

[0022] 16g of amorphous titanium 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 titanium disulfide@titanium-sulfurized polyacrylonitrile. A button cell was assembled using the obtained titanium disulfide@titanium-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 2C rate, the average discharge voltage of the lithium-sulfur battery was 1.80V, the stable cycle capacity of the material was greater than 600mAh / g, and after 200 cycles, the average coulombic efficiency was greater than 99.9%.

[0023] Example 3

[0024] 10g of amorphous titanium polysulfide and 2g of polyacrylonitrile with a molecular weight of 30,000 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 titanium disulfide@titanium-sulfurized polyacrylonitrile. A button cell was assembled using the obtained titanium disulfide@titanium-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 2C rate, the average discharge voltage of the lithium-sulfur battery was 1.78V, the stable cycle capacity of the material was greater than 580mAh / g, and after 200 cycles, the average coulombic efficiency was greater than 99.9%.

[0025] Example 4

[0026] 10g of amorphous titanium polysulfide and 2g of polyacrylonitrile with a molecular weight of 150,000 were weighed and ground evenly. The mixture was then heated to 350℃ and held at this temperature for 5 hours in an argon-protected tube furnace to obtain titanium disulfide@titanium-sulfurized polyacrylonitrile. A button cell was assembled using the obtained titanium disulfide@titanium-sulfurized polyacrylonitrile as the positive electrode and lithium metal as the negative electrode. Electrochemical performance was tested at a rate within a voltage range of 1-3V. At a 30C rate, the cycle capacity still reached 430 mAh / g (see attached figure). Figure 3 .

[0027] Comparative Example

[0028] 10g of elemental sulfur powder and 2g of polyacrylonitrile with a molecular weight of 150,000 were weighed and ground evenly. The mixture was then heated to 350℃ and held at that temperature for 5 hours in an argon-protected tube furnace to obtain sulfurized polyacrylonitrile. A button cell was assembled using the obtained sulfurized polyacrylonitrile as the positive electrode and lithium metal as the negative electrode. Electrochemical performance was tested at a rate within a voltage range of 1-3V. The cycle capacity at 30C was only 150 mAh / g (see attached figure). Figure 4 .

[0029] As described above, although the invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method for preparing a high-rate performance titanium disulfide@titanium sulfide polyacrylonitrile cathode material, characterized in that, Includes the following steps: (1) Mix amorphous titanium polysulfide and polyacrylonitrile evenly to obtain a mixture, and seal it in an inert atmosphere; (2) The above mixture is heated to obtain titanium disulfide@titanium sulfide polyacrylonitrile cathode material.

2. The preparation method according to claim 1, characterized in that: In step (1), the atomic ratio of titanium to sulfur in amorphous titanium polysulfide is 1:3~8; the molecular weight of polyacrylonitrile is 10000~500000; the mass ratio of polyacrylonitrile to titanium polysulfide is 1:2~100; 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 1~20 hours.

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