Sulfur-selenium co-doped carbon fluoride material as well as preparation method and application thereof

Abstract

The invention discloses a sulfur-selenium co-doped carbon fluoride material, a preparation method and application thereof, and belongs to the field of carbon fluoride materials, the sulfur-selenium co-doped carbon fluoride material comprises carbon fluoride, the surface of the carbon fluoride is doped with a sulfur-selenium compound, and the mass fraction of the sulfur-selenium compound is 9.99%-30%. According to the sulfur-selenium co-doped carbon fluoride material, the preparation method and the application thereof, the sulfur-selenium co-doped carbon fluoride material is synthesized through simple heating treatment, and the discharge voltage and the rate capability of the carbon fluoride material under high rate can be improved.

Description

[0001] Case Analysis This application is a divisional application of Chinese application filed on May 8, 2024, with application number 2024105632459, entitled "A sulfur-selenium co-doped fluorinated carbon material, preparation method and application thereof". Technical Field

[0002] This invention belongs to the field of fluorinated carbon materials, and particularly relates to a sulfur-selenium co-doped fluorinated carbon material, its preparation method and its application. Background Technology

[0003] Fluorocarbon is an interlayer covalent compound composed of carbon and fluorine elements, with the chemical formula CFx. As the positive electrode of lithium-ion primary batteries, fluorocarbon currently boasts the highest theoretical energy density among lithium-ion primary battery positive electrode materials. It features high safety, stable discharge voltage, low self-discharge rate, and environmental friendliness, and is widely used as an important energy storage component in fields such as medicine, weaponry, aerospace, and shipbuilding.

[0004] Fluorocarbon materials have poor electrical conductivity (10) -10 -10 -11 S cm -1 Lithium ions suffer from slow diffusion and severe polarization, resulting in low discharge voltage and energy density at high rates, thus limiting their applications. To address these issues, extensive research has been conducted, with doping fluorinated carbon with other cathode materials being a simple and effective method to improve its performance. Elemental sulfur has attracted attention due to its low cost, high specific capacity (1672 mAh / g), and high specific energy (2600 Wh / kg); however, its poor conductivity (5*10⁻⁶) limits its application. -30 S cm -1 This results in a low discharge voltage for fluorinated carbon / sulfur composite materials.

[0005] Patent (CN 109742354 A) discloses a composite material made of fluorinated graphite, Ketjen black, and selenium powder. The presence of selenium improves the material's conductivity and rate performance; however, the low specific capacity of selenium leads to a decrease in the composite material's specific capacity. Patent (CN 108039469 A) discloses a method for preparing a fluorinated graphite-sulfur composite material. Because the sulfur mass ratio in the synthesized composite material is much higher than that of the fluorinated carbon material, the material's conductivity and rate performance are poor. Patent (CN 117691038 A) discloses a method for preparing a sulfur-doped fluorinated graphene material. This method involves doping graphene oxide with sulfur atoms and then fluorinating it to obtain a sulfur-doped fluorinated carbon material. This type of method requires the preparation and fluorination of carbon materials, making the material synthesis process complex and unsuitable for widespread application. Patent (CN113903897 A) discloses a method for preparing a composite material of metal fluoride and sulfur-coated fluorinated carbon. The mass ratio of metal fluoride to sulfur in the composite material synthesized by this method is much greater than that of fluorinated carbon material, so its discharge platform is significantly lower than that of fluorinated carbon material. Summary of the Invention

[0006] The purpose of this invention is to provide a sulfur-selenium co-doped fluorinated carbon material, its preparation method, and its application, so as to overcome at least one of the above-mentioned defects in the prior art.

[0007] To achieve this objective, the present invention adopts the following technical solution: The present invention provides a sulfur-selenium co-doped fluorinated carbon material, comprising fluorinated carbon, wherein the surface of the fluorinated carbon is doped with sulfur-selenium compounds, and the mass fraction of the sulfur-selenium compounds is 9.99%-30%.

[0008] Preferably, the surface of the fluorinated carbon is also doped with elemental selenium, with a mass fraction of elemental selenium of 4.36%-5.51%.

[0009] Preferably, elemental selenium is located between sulfur-selenium compounds and fluorinated carbon.

[0010] Preferably, the fluorinated carbon is porous fluorinated carbon with a porous structure, and the sulfur-selenium compound is selenium disulfide or selenium sulfide.

[0011] This invention also provides a method for preparing sulfur-selenium co-doped fluorinated carbon material, which includes the following steps: S1: Weigh fluorinated carbon and selenium powder, with a mass ratio of fluorinated carbon to selenium powder of 7-24:1. Grind the fluorinated carbon and selenium powder evenly and transfer them to an inert atmosphere. Heat at 250℃-270℃ for 11-13 h to obtain selenium-doped fluorinated carbon material. S2: Weigh sulfur powder according to the mass of the selenium-doped fluorinated carbon material obtained in step S1, with a mass ratio of selenium-doped fluorinated carbon material to sulfur powder of 4-26:1. Grind the selenium-doped fluorinated carbon material and sulfur powder evenly and heat at 150℃-160℃ under an inert atmosphere for 11-13 h to obtain sulfur-selenium co-doped fluorinated carbon material.

[0012] Preferably, the inert atmosphere is argon, nitrogen, or helium.

[0013] Preferably, in step S1, the temperature is 4℃-6℃ min. -1 The heating rate is increased to 250℃-270℃.

[0014] Preferably, in step S2, the temperature is 4℃-6℃ min. -1 The heating rate is increased to 150℃-160℃.

[0015] Preferably, the fluorinated carbon and selenium powder in step S1, and the selenium-doped fluorinated carbon material and sulfur powder in step S2 are all reacted in a tube furnace.

[0016] The present invention also provides the application of the sulfur-selenium co-doped fluorinated carbon material or the sulfur-selenium co-doped fluorinated carbon material prepared by the above-mentioned method in the preparation of lithium primary batteries.

[0017] Preferably, the positive electrode of the lithium primary battery comprises sulfur-selenium co-doped fluorinated carbon material, conductive carbon, and binder, wherein the mass ratio of sulfur-selenium co-doped fluorinated carbon material, conductive carbon, and binder is 8:1:1.

[0018] The beneficial effects of this invention are as follows: 1. A sulfur-selenium co-doped fluorinated carbon material was synthesized through simple heat treatment, which can improve the discharge voltage and rate performance of fluorinated carbon materials at high rates.

[0019] 2. In a preferred embodiment of the present invention, the sulfur-selenium co-doped fluorinated carbon material is also doped with elemental selenium, which is located between the sulfur-selenium compound and the fluorinated carbon. As a semiconductor, selenium has a significant increase in conductivity when the temperature rises. Lithium / fluorinated carbon batteries generate a certain amount of heat during discharge, especially at high rates, where the heat release is significant. The heat generated can be transferred to selenium, which is more conducive to improving the conductivity and rate performance of the composite material.

[0020] 3. The porous structure of porous fluorocarbon materials can provide stronger adsorption and higher loading capacity for sulfur and selenium. Attached Figure Description

[0021] Figure 1 This is a specific capacity-voltage curve of the lithium fluoride carbon battery prepared in Example 1 and Comparative Example 1 of the present invention at a rate of 0.01 C.

[0022] Figure 2 This is a specific capacity-voltage curve of the lithium fluoride carbon battery prepared in Example 1 and Comparative Example 1 of the present invention at a rate of 5 C.

[0023] Figure 3 This is a specific capacity-voltage curve of the lithium fluoride carbon battery prepared in Example 1 and Comparative Example 1 of the present invention at a rate of 10 C.

[0024] Figure 4 This is a specific capacity-voltage curve of the lithium fluoride carbon battery prepared in Example 1 and Comparative Example 1 of the present invention at a rate of 20 C.

[0025] Figure 5 This is a specific capacity-voltage curve of the lithium fluoride carbon battery prepared in Example 1 and Comparative Example 1 of the present invention at a rate of 40 C.

[0026] Figure 6 These are the XRD spectra obtained from Examples 1, 2 and Comparative Example 1 of this invention.

[0027] Figure 7 This is the C1s spectrum of the XPS spectrum obtained in Example 1 of this invention.

[0028] Figure 8 This is the Se3d spectrum of the XPS spectrum obtained in Example 1 of this invention.

[0029] Figure 9 This is the total spectrum of the XPS spectrum obtained in Example 1 of the present invention.

[0030] Figure 10 This is the SEM image obtained in Example 1 of the present invention.

[0031] Figure 11 This is the TEM image obtained in Example 1 of the present invention.

[0032] Figure 12 This is a high-resolution TEM image obtained in Example 1 of the present invention.

[0033] Figure 13 This is the elemental distribution map of the TEM image obtained in Example 1 of this invention.

[0034] Figure 14 These are thermogravimetric curves of Examples 1, 2, and Comparative Example 1 of the present invention.

[0035] Figure 15 These are nitrogen adsorption-desorption curves obtained from Examples 1, 2 and Comparative Example 1 of this invention.

[0036] Figure 16 These are aperture distribution diagrams obtained from Examples 1, 2, and Comparative Example 1 of the present invention. Detailed Implementation

[0037] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments.

[0038] Example 1: This embodiment provides a sulfur-selenium co-doped fluorinated carbon material, comprising porous fluorinated carbon with a porous structure. The surface of the fluorinated carbon is doped with a sulfur-selenium compound and elemental selenium, with the elemental selenium located between the sulfur-selenium compound and the fluorinated carbon, forming a three-layer structure. Thus, the elemental selenium is in direct contact with the fluorinated carbon, and the exothermic reaction of the fluorinated carbon is directly conducted to the elemental selenium, improving electrical conductivity. The sulfur-selenium compound is selenium disulfide, with a mass fraction of 15.64%, the elemental selenium mass fraction is 4.36%, and the fluorinated carbon mass fraction is 80%.

[0039] This example also provides a method for preparing sulfur-selenium co-doped fluorinated carbon materials, which includes the following steps: S1: Weigh out fluorinated carbon and selenium powder in a mass ratio of 8:1. Grind the fluorinated carbon and selenium powder evenly and transfer them to a tube furnace under an argon atmosphere. Heat at 5°C for 1 minute. -1 The temperature was increased to 260℃ and heated for 12 h at a heating rate to obtain selenium-doped fluorinated carbon material.

[0040] S2: Weigh sulfur powder according to the mass of the selenium-doped fluorinated carbon material obtained in step S1. The mass ratio of selenium-doped fluorinated carbon material to sulfur powder is 9:1. Grind the selenium-doped fluorinated carbon material and sulfur powder evenly, and then heat them at 5℃ for 1 minute under an argon atmosphere. -1 The temperature was increased to 155℃ at a certain rate and held for 12 h to obtain sulfur-selenium co-doped fluorinated carbon material.

[0041] This invention provides a two-step process for obtaining sulfur-selenium co-doped fluorinated carbon materials. The first step involves heating selenium to a molten state, promoting the doping of selenium with fluorinated carbon. The second step involves heating sulfur to a molten state, promoting the doping of sulfur with fluorinated carbon. The synthesis can be achieved through simple heat treatment, without the need for complex processes.

[0042] This example also provides the application of the sulfur-selenium co-doped fluorinated carbon material described above, or the sulfur-selenium co-doped fluorinated carbon material prepared by the above-described method, in the preparation of lithium primary batteries.

[0043] The positive electrode of the lithium primary battery comprises sulfur-selenium co-doped fluorinated carbon material, conductive carbon, and a binder (PVDF), with a mass ratio of 8:1:1. The electrochemical performance of the prepared lithium fluorinated carbon battery was tested.

[0044] Comparative Example 1: Commercially available, undoped fluorocarbon material was selected. Lithium-fluorinated carbon batteries were fabricated under the same conditions as in Example 1, i.e., batteries were made with an active material: conductive carbon: binder (PVDF) ratio of 8:1:1, and their electrochemical performance was tested.

[0045] Example 2: The difference between this example and Example 1 is that the mass ratio of fluorinated carbon: selenium powder: sulfur powder is 7:1:2.

[0046] Example 3: The difference between this example and Example 1 is that the mass ratio of fluorinated carbon: selenium powder: sulfur powder is 24:2:1.

[0047] Example 4: The difference between this example and Example 1 is that the mass ratio of fluorinated carbon: selenium powder: sulfur powder is 24:1:2.

[0048] Comparative Example 2: The difference between this comparative example and Example 1 is that it is only doped with selenium, and the mass ratio of fluorinated carbon to selenium powder is 9:1.

[0049] Comparative Example 3: The difference between this comparative example and Example 1 is that it is only doped with selenium, and the mass ratio of fluorinated carbon to selenium powder is 8:2.

[0050] Comparative Example 4: The difference between this comparative example and Example 1 is that it is only doped with sulfur, and the mass ratio of fluorinated carbon to sulfur powder is 9:1.

[0051] Comparative Example 5: The difference in Comparative Example 1 is that only sulfur is added, and the mass ratio of fluorinated carbon to sulfur powder is 8:2.

[0052] The XRD spectra of the three groups of materials, namely Example 1, Example 2, and Comparative Example 1, are as follows: Figure 6As shown, diffraction peaks were observed at 14.2° and 41.5° in all three samples, corresponding to the (001) and (100) crystal planes of fluorinated carbon, respectively, indicating that the composite of sulfur and selenium did not damage the structure of fluorinated carbon. In the materials of Examples 1 and 2, a peak at 23.8° corresponds to the characteristic peaks of elemental selenium and selenium disulfide. In Example 1, a characteristic peak corresponding to selenium was observed at 27.9°, while the intensity of this peak was weakened in Example 2. This indicates that both composite materials contain selenium, and with the increase of sulfur, more sulfur-selenium compounds are generated, leading to a decrease in the content of elemental selenium. Figure 7 The image shows seven peaks in the C1s spectrum of the sulfur-selenium co-doped fluorinated carbon material in Example 1: CC (284.8 eV), C=O (285.7 eV), C=C (287.8 eV), half-ionic CF (290.0 eV), covalent C-F (290.2 eV), CF2 (290.7 eV), and CF3 / C-Se (292.0 eV). The content of each bond is as follows: covalent CF 16.23%; CF3 / C-Se 11.80%; half-ionic CF 4.72%; C=C 4.59%; CC 3.43%; C=O 2.61%; CF2 1.73%. Figure 8 The example shown in Figure 1, a sulfur-selenium co-doped fluorinated carbon material, has four peaks in its Se3d spectrum, which are Se3d... 3 / 2 (56.8 eV); S-Se (55.6 eV); Se3d 5 / 2 (54.4 eV); C-Se (55.4 eV). The content of each bond is Se3d. 3 / 2 The content was 0.34%; C-Se content was 0.05%; S-Se content was 0.03%; Se3d 5 / 2 The content is 0.02%. Figure 9 The XPS total spectrum of the sulfur-selenium co-doped fluorinated carbon material shown in Example 1 is as follows: the content of Se is 0.48%, while the content of elemental S is so low that it cannot be detected by XPS. Figure 10 The image shows a SEM image of Example 1, which reveals the porous structure of the material itself. Figure 11 TEM images and Figure 13 The elemental distribution diagram shows that the material in Example 1 is a fluorinated porous carbon material coated with elemental selenium and sulfur-selenium compounds. Figure 12The high-resolution TEM image for Example 1 shows obvious lattice fringes. The lattice spacing measured in the left image is 0.377 nm, which corresponds to the 0.377 nm interplanar spacing of the (130) crystal plane of selenium disulfide. The lattice spacing measured in the right image is 0.301 nm, which corresponds to the 0.301 nm interplanar spacing of the (101) crystal plane of elemental Se. Therefore, it can be inferred that elemental selenium and selenium disulfide exist on the surface of the fluorinated carbon material. Figure 15 and Figure 16 The figures show the nitrogen adsorption-desorption curves and pore size distribution diagrams for Examples 1, 2, and Comparative Example 1, respectively. The adsorption-desorption curves of Examples 1 and 2 have the same shape as those of Comparative Example 1, indicating that the doping of sulfur and selenium did not affect the pore structure of the porous fluorinated carbon. Figure 16 The pore size distribution diagram also shows that the pore size distribution has not changed, only the number of pores has decreased, indicating that sulfur and selenium have entered the porous structure.

[0053] The specific surface areas of Examples 1 and 2 and Comparative Example 1 are shown in Table 1: Table 1. Specific surface area of ​​Examples 1 and 2 compared to Comparative Example 1

[0054] As can be seen from Table 1, the surface area decreases with the increase of sulfur-selenium doping ratio, which also indicates that sulfur-selenium doping enters the porous structure of the material during the doping process.

[0055] The elemental analysis results for Examples 1-4 are shown in Table 2. Table 2 Elemental analysis of Examples 1-4

[0056] Figure 14 The thermogravimetric curves for Examples 1, 2, and Comparative Example 1, combined with the elemental analysis table in Table 2, show that in Example 1, the fluorinated carbon content is 80%, the ratio of sulfur-selenium compounds to elemental selenium is 20%, the sulfur content is 7%, and the calculated selenium disulfide content is 15.64%, while the elemental selenium content is 4.36%. In Example 2, the fluorinated carbon content is 70%, the ratio of sulfur-selenium compounds to elemental selenium is 30%, the sulfur content is 15.7%, and the selenium content is 14.3%, with the calculated selenium disulfide mass percentage being approximately 30%. In Example 3, the fluorinated carbon content is 80%, the ratio of sulfur-selenium compounds to elemental selenium is 20%, the sulfur content is 9%, and the calculated selenium disulfide content is 9.99%, while the elemental selenium content is 5.51%. In Example 4, the fluorinated carbon content is 80%, and the ratio of sulfur-selenium compounds is 20%.

[0057] Table 3 shows the specific capacity and specific energy of each example discharged at a rate of 0.01 C to 1.5V: Table 3. Specific capacity and specific energy of each example discharged at a rate of 0.01 C to 1.5V.

[0058] Table 4 shows the specific capacity and specific energy of each example at a 5C rate discharge to 1.5V: Table 4. Specific capacity and specific energy of each example at 5C rate discharge to 1.5V.

[0059] Table 5 shows the specific capacity and specific energy of each example discharged at 10 C to 1.5V: Table 5. Specific capacity and specific energy of each example discharged at 10C to 1.5V.

[0060] Table 6 shows the specific capacity and specific energy of each example discharged at 20 C to 1.5V: Table 6. Specific capacity and specific energy of each example discharged at 20 C to 1.5V.

[0061] The specific capacity and specific energy of each example discharged at 40 C to 1.5V are shown in Table 7: Table 7. Specific capacity and specific energy of each example discharged at 40 C to 1.5V.

[0062] From Tables 2-7, combined with Figure 1-5 As can be seen, the lithium-carbon fluoride battery prepared in Example 1, when discharged at a rate of 0.01 C to 1.5 V, has a specific capacity of 938 mAh / g and a specific energy of 2314 Wh / kg, respectively; when discharged at a rate of 5 C to 1.5 V, the specific capacity and specific energy are 776 mAh / g and 1689 Wh / kg, respectively; when discharged at a rate of 10 C to 1.5 V, the specific capacity and specific energy are 727 mAh / g and 1564 Wh / kg, respectively; when discharged at a rate of 20 C to 1.5 V, the specific capacity and specific energy are 698 mAh / g and 1380 Wh / kg, respectively; and when discharged at a rate of 40 C to 1.5 V, the specific capacity and specific energy are 560 mAh / g and 983 Wh / kg, respectively.

[0063] Comparative Example 1, discharged at a rate of 0.01 C to 1.5 V, exhibited a specific capacity of 896 mAh / g and a specific energy of 2279 Wh / kg. Discharged at a rate of 5 C to 1.5 V, it achieved a specific capacity of 721 mAh / g and a specific energy of 1479 Wh / kg. Discharged at a rate of 10 C to 1.5 V, it achieved a specific capacity of 678 mAh / g and a specific energy of 1340 Wh / kg. Discharged at a rate of 20 C to 1.5 V, it achieved a specific capacity of 573 mAh / g and a specific energy of 1082 Wh / kg. It could not discharge at a rate of 40 C.

[0064] It is evident that this invention synthesizes a sulfur-selenium co-doped fluorinated carbon material through simple heat treatment, which can improve the discharge voltage and rate performance of fluorinated carbon materials at high rates. The obtained sulfur-selenium co-doped fluorinated carbon material exhibits essentially unchanged specific capacity and specific energy at a rate of 0.01 C, but demonstrates higher discharge voltage, specific capacity, and specific energy at rates above 4 C, and also improves electrochemical performance at a high rate of 40 C. Selenium, as a group element of sulfur, has similar chemical properties to sulfur; however, it possesses a higher electrical conductivity (10⁻⁶ Ω·cm). -3 S cm -1 This method effectively alleviates the problems of poor conductivity and low discharge voltage of composite materials caused by sulfur and fluorinated carbon doping. Furthermore, selenium, as a semiconductor, exhibits a significant increase in conductivity with increasing temperature. Lithium / fluorinated carbon batteries generate heat during discharge, especially at high rates, and this heat can be transferred to selenium, further enhancing the conductivity and rate performance of the composite material. The porous structure of porous fluorinated carbon materials provides stronger adsorption and higher loading capacity for sulfur and selenium. Compared to sulfur-selenium co-doped fluorinated carbon materials where only sulfur-selenium compounds are doped on the surface, sulfur-selenium co-doped fluorinated carbon materials doped with both sulfur-selenium compounds and elemental selenium exhibit better conductivity and rate performance.

[0065] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sulfur-selenium co-doped fluorinated carbon material, comprising fluorinated carbon, characterized in that: The fluorinated carbon surface is doped with a sulfur-selenium compound, the mass fraction of which is 9.99%-30%.

2. The sulfur-selenium co-doped fluorinated carbon material according to claim 1, characterized in that: The fluorinated carbon surface is also doped with elemental selenium, with a mass fraction of 4.36%-5.51%.

3. The sulfur-selenium co-doped fluorinated carbon material according to claim 2, characterized in that: The elemental selenium is located between the sulfur-selenium compound and the fluorinated carbon.

4. The sulfur-selenium co-doped fluorinated carbon material according to claim 1, characterized in that: The fluorinated carbon is porous fluorinated carbon; The sulfur-selenium compound is selenium disulfide or selenium sulfide.

5. A method for preparing a sulfur-selenium co-doped fluorinated carbon material, characterized in that, The method for preparing the sulfur-selenium co-doped fluorinated carbon material according to any one of claims 1-4 comprises the following steps: S1: Weigh fluorinated carbon and selenium powder, with a mass ratio of fluorinated carbon to selenium powder of 7-24:

1. Grind the fluorinated carbon and selenium powder evenly and transfer them to an inert atmosphere. Heat at 250℃-270℃ for 11-13 h to obtain selenium-doped fluorinated carbon material. S2: Weigh sulfur powder according to the mass of the selenium-doped fluorinated carbon material obtained in step S1. The mass ratio of selenium-doped fluorinated carbon material to sulfur powder is 4-26:

1. Grind the selenium-doped fluorinated carbon material and sulfur powder evenly, and then heat them to 150℃-160℃ under an inert atmosphere and keep them at that temperature for 11-13 h to obtain sulfur-selenium co-doped fluorinated carbon material.

6. The method for preparing sulfur-selenium co-doped fluorinated carbon material according to claim 5, characterized in that: The inert atmosphere is argon, nitrogen, or helium.

7. The method for preparing sulfur-selenium co-doped fluorinated carbon material according to claim 5, characterized in that: In step S1, the temperature is 4℃-6℃ min. -1 The heating rate is increased to 250℃-270℃; In step S2, the temperature is 4℃-6℃ min. -1 The heating rate is increased to 150℃-160℃.

8. The method for preparing sulfur-selenium co-doped fluorinated carbon material according to claim 5, characterized in that: The fluorinated carbon and selenium powder in step S1, and the selenium-doped fluorinated carbon material and sulfur powder in step S2, are all reacted in a tube furnace.

9. The application of the sulfur-selenium co-doped fluorinated carbon material according to any one of claims 1-4 or the sulfur-selenium co-doped fluorinated carbon material prepared by the preparation method according to any one of claims 5-8 in the preparation of lithium primary batteries.

10. The application according to claim 9, characterized in that: The positive electrode of the lithium primary battery comprises sulfur-selenium co-doped fluorinated carbon material, conductive carbon, and binder, wherein the mass ratio of the sulfur-selenium co-doped fluorinated carbon material, conductive carbon, and binder is 8:1:1.

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