Self-supporting sulfur-carbon electrode sheet and method for manufacturing the same

Abstract

The application discloses a preparation method of a self-supporting sulfur-carbon electrode sheet, and comprises the following steps: preparing expanded graphite, nitrogen doping, pore forming, vapor deposition of sulfur elements, and mold forming. The micro two-dimensional sheet structure of the expanded graphite is overlapped under the action of pressure, the combination of sulfur and carbon materials and the construction of the self-supporting electrode sheet are completed in one step, a three-dimensional body phase composite structure with certain elasticity is formed, the structure can remain stable in the repeated expansion process of the sulfur volume caused by the charging and discharging of the battery, the doping of the nitrogen elements can effectively adsorb polysulfides and relieve the shuttle effect, and the cycle stability of the lithium-sulfur battery can be increased; the porous structure on the expanded graphite sheet can provide a channel for ion transmission, and the electrode sheet itself has an excellent conductive network construction, the rate performance of the lithium-sulfur battery can be improved, and a relatively thick electrode sheet thickness (up to 1-2 mm) can be realized. The preparation process of the self-supporting sulfur-carbon electrode sheet does not need a binder, a conductive agent and a metal current collector, the loading capacity of sulfur is high, and the highest loading capacity can reach 65%.

Description

Technical Field

[0001] This invention relates to the field of lithium-sulfur battery electrode materials, and in particular to a self-supporting sulfur-carbon electrode sheet and its preparation method. Background Technology

[0002] Lithium-ion batteries, with their advantages of high specific energy, high operating voltage, low self-discharge rate, small size, and light weight, have revolutionized the energy storage field since their inception and are widely used in various portable electronic devices and electric vehicles. However, with the improvement of people's living standards, higher user experience demands have placed higher requirements on lithium-ion batteries: lighter weight, longer service life, etc. To solve these problems, it is necessary to find new electrode materials with superior performance.

[0003] Lithium-sulfur batteries possess extremely high theoretical energy density (more than five times that of lithium-ion batteries), and sulfur raw materials are abundant, inexpensive, and environmentally friendly. Their lightweight characteristics make them particularly suitable for weight-sensitive new energy devices and electric vehicles. However, lithium-sulfur batteries currently face challenges such as the low conductivity of sulfur and its discharge products limiting high-rate performance, the volume expansion of sulfur during battery cycling (approximately 80%) leading to structural damage, and the "shuttle effect" caused by the dissolution of intermediate polysulfides, resulting in loss of active material and capacity decay.

[0004] Existing methods mostly employ composite electrode materials to improve the electrode performance of lithium-sulfur batteries. For example, composite materials are prepared using carbon and sulfur, and then the electrode material is coated onto the current collector using binders and conductive agents. While such methods can effectively improve electrode performance, they have limited sulfur loading, making it difficult to cope with the volume expansion of sulfur materials during charge and discharge, and they cannot effectively mitigate the shuttle effect of polysulfides, resulting in low battery life. Furthermore, the poor conductive network construction of the electrode due to the coating slurry process also limits the rate performance of lithium-sulfur batteries. Therefore, it is necessary to propose a new approach to address these issues. Summary of the Invention

[0005] In view of this, the present invention addresses the deficiencies of the prior art, and its main objective is to provide a self-supporting sulfur-carbon electrode sheet and its preparation method. This invention can effectively solve the problems of limited sulfur loading in existing sulfur-carbon electrodes, difficulty in coping with the volume expansion of sulfur materials during charging and discharging, inability to effectively alleviate the shuttle effect of polysulfides leading to low battery life, and the limited rate performance of lithium-sulfur batteries due to the poor conductive network of the electrode sheet caused by the design of coating on the current collector.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a self-supporting sulfur-carbon electrode sheet includes the following steps:

[0008] (1) Mix natural graphite with a certain amount of oxidant and intercalating agent. The mass ratio of natural graphite to intercalating agent and oxidant is 1:(1-15):(0.05-0.5). Let it stand at 40℃ for 30 minutes, filter, wash and obtain expandable graphite.

[0009] (2) The expandable graphite obtained in step (1) is placed in an inert gas atmosphere and heated to 1000°C to obtain expanded graphite;

[0010] (3) Place the expanded graphite obtained in step (2) in a mixed gas atmosphere, which consists of an inert gas and a nitrogen-containing gas, and the volume ratio of the inert gas to the nitrogen-containing gas is (30-90): (10-70). Heat to 1000℃ and keep warm for 30 minutes to obtain nitrogen-doped porous expanded graphite.

[0011] (4) Take a portion of the nitrogen-doped porous expanded graphite obtained in step (3) and place it in a reactor. Inert gas is introduced to replace the air inside the reactor, so that an oxygen-free environment is formed inside the reactor. Heat it to 170-230℃ and keep it at that temperature for 3-5 hours. Then, gaseous sulfur is introduced to carry out a chemical vapor deposition reaction to obtain a sulfur-carbon composite material.

[0012] (5) Take the nitrogen-doped porous expanded graphite obtained in step (3) and the sulfur-carbon composite material obtained in step (4) and mix them. The mass ratio of nitrogen-doped porous expanded graphite to sulfur-carbon composite material is 1:(0.2-20). After mixing evenly, the mixture is spread out and molded to obtain a self-supporting sulfur-carbon electrode sheet.

[0013] As a preferred embodiment, in step (1), the natural graphite is natural flake graphite.

[0014] As a preferred embodiment, in step (3), the inert gas is argon and the nitrogen-containing gas is ammonia.

[0015] As a preferred embodiment, in step (4), the inert gas is argon.

[0016] As a preferred embodiment, in step (5), the density of the self-supporting sulfur-carbon electrode sheet is 0.3-0.8 g / cm³. 3 Its sulfur content ranges from 10% to 65% by mass.

[0017] As a preferred embodiment, in step (1), the oxidant is one of hydrogen peroxide, potassium permanganate, and potassium dichromate, and the intercalating agent is one of concentrated sulfuric acid, concentrated nitric acid, perchloric acid, and concentrated phosphoric acid.

[0018] A method for preparing a self-supporting sulfur-carbon electrode sheet, which is obtained by the aforementioned method for preparing a self-supporting sulfur-carbon electrode sheet.

[0019] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, as can be seen from the above technical solution:

[0020] By utilizing the microscopic two-dimensional sheet structure of expanded graphite, which overlaps under pressure, the composite of sulfur and carbon materials and the construction of a self-supporting electrode are completed in one step, forming a three-dimensional bulk composite structure with a certain degree of elasticity. This structure can remain stable during the repeated expansion of sulfur volume caused by battery charging and discharging. Nitrogen doping can effectively adsorb polysulfides, alleviate the shuttle effect, and increase the cycle stability of lithium-sulfur batteries. The porous structure on the expanded graphite sheets can provide channels for ion transport, and the electrode itself has an excellent conductive network structure, which can improve the rate performance of lithium-sulfur batteries and achieve a relatively thick electrode (up to 1-2 mm). The preparation process of the self-supporting sulfur-carbon electrode sheet does not require binders, conductive agents, or metal current collectors, and the sulfur loading is high, up to 65%.

[0021] To more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the self-supporting sulfur-carbon electrode sheet obtained by the present invention. Detailed Implementation

[0023] This invention discloses a method for preparing a self-supporting sulfur-carbon electrode sheet, which includes the following steps:

[0024] (1) Mix natural graphite with a certain amount of oxidant and intercalating agent. The mass ratio of natural graphite to intercalating agent and oxidant is 1:(1-15):(0.05-0.5). Let it stand at 40℃ for 30 minutes, filter, and wash to obtain expandable graphite. The natural graphite is natural flake graphite, the oxidant is one of hydrogen peroxide, potassium permanganate, and potassium dichromate, and the intercalating agent is one of concentrated sulfuric acid, concentrated nitric acid, perchloric acid, and concentrated phosphoric acid.

[0025] (2) The expandable graphite obtained in step (1) is placed in an inert gas atmosphere and heated to 1000°C to obtain expanded graphite;

[0026] (3) The expanded graphite obtained in step (2) is placed in a mixed gas atmosphere, which consists of an inert gas and a nitrogen-containing gas, and the volume ratio of the inert gas to the nitrogen-containing gas is (30-90): (10-70). After heating to 1000℃, it is kept at the temperature for 30 minutes to obtain nitrogen-doped porous expanded graphite. The inert gas is argon and the nitrogen-containing gas is ammonia.

[0027] (4) Take a portion of the nitrogen-doped porous expanded graphite obtained in step (3) and place it in a reactor. Inert gas is introduced to replace the air inside the reactor, so that an oxygen-free environment is formed inside the reactor. Heat it to 170-230℃ and keep it at that temperature for 3-5 hours. Then, gaseous sulfur is introduced to carry out a chemical vapor deposition reaction to obtain a sulfur-carbon composite material. The inert gas is argon.

[0028] (5) Take the nitrogen-doped porous expanded graphite obtained in step (3) and the sulfur-carbon composite material obtained in step (4), and mix them. The mass ratio of nitrogen-doped porous expanded graphite to sulfur-carbon composite material is 1:(0.2-20). After mixing evenly, the mixture is spread out and molded to obtain a self-supporting sulfur-carbon electrode sheet. The density of the self-supporting sulfur-carbon electrode sheet is 0.3-0.8 g / cm³. 3 The mass percentage of sulfur in the mold is 10%-65%. It should be noted that this invention application specifies the pressure and pressing time of the molding process. Since the bottom area of ​​the molding cavity is fixed, the pressing area is also fixed. A certain amount of material is placed in the molding cavity of the mold, and the electrode sheet is pressed to a certain thickness through appropriate pressure and pressing time, so that the electrode sheet reaches the target density.

[0029] The present invention also discloses a method for preparing a self-supporting sulfur-carbon electrode sheet, which is obtained by the aforementioned method for preparing a self-supporting sulfur-carbon electrode sheet.

[0030] The following detailed description is based on specific embodiments.

[0031] Example 1

[0032] (1) Mix natural graphite with a certain amount of oxidant and intercalating agent. The mass ratio of natural graphite to intercalating agent and oxidant is 1:15:0.2. Let it stand at 40°C for 30 minutes, filter, and wash to obtain expandable graphite. The natural graphite is natural flake graphite, the oxidant is hydrogen peroxide, and the intercalating agent is concentrated sulfuric acid.

[0033] (2) The expandable graphite obtained in step (1) is placed in an inert gas atmosphere and heated to 1000°C to obtain expanded graphite.

[0034] (3) The expanded graphite obtained in step (2) is placed in a mixed gas atmosphere, which consists of an inert gas and a nitrogen-containing gas, and the volume ratio of the inert gas to the nitrogen-containing gas is 70:30. After heating to 1000℃, it is kept at the temperature for 30 minutes to obtain nitrogen-doped porous expanded graphite. The inert gas is argon and the nitrogen-containing gas is ammonia.

[0035] (4) Take a portion of the nitrogen-doped porous expanded graphite obtained in step (3) and place it in a reactor. Inert gas is introduced to replace the air inside the reactor, so that an oxygen-free environment is formed inside the reactor. Heat it to 200°C and keep it at that temperature for 4 hours. Then, gaseous sulfur is introduced to carry out a chemical vapor deposition reaction to obtain a sulfur-carbon composite material. The inert gas is argon.

[0036] (5) Take the nitrogen-doped porous expanded graphite obtained in step (3) and the sulfur-carbon composite material obtained in step (4) and mix them. The mass ratio of nitrogen-doped porous expanded graphite to sulfur-carbon composite material is 1:9. After mixing evenly, the mixture is spread out and molded to obtain a self-supporting sulfur-carbon electrode sheet.

[0037] Example 2

[0038] (1) Mix natural graphite with a certain amount of oxidant and intercalating agent. The mass ratio of natural graphite to intercalating agent and oxidant is 1:3:0.05. Let it stand at 40°C for 30 minutes, filter, and wash to obtain expandable graphite. The natural graphite is natural flake graphite, the oxidant is potassium permanganate, and the intercalating agent is perchloric acid.

[0039] (2) The expandable graphite obtained in step (1) is placed in an inert gas atmosphere and heated to 1000°C to obtain expanded graphite;

[0040] (3) The expanded graphite obtained in step (2) is placed in a mixed gas atmosphere, which consists of an inert gas and a nitrogen-containing gas, and the volume ratio of the inert gas to the nitrogen-containing gas is 90:10. After heating to 1000°C, it is kept at the temperature for 30 minutes to obtain nitrogen-doped porous expanded graphite. The inert gas is argon and the nitrogen-containing gas is ammonia.

[0041] (4) Take a portion of the nitrogen-doped porous expanded graphite obtained in step (3) and place it in a reactor. Inert gas is introduced to replace the air inside the reactor, so that an oxygen-free environment is formed inside the reactor. Heat it to 210°C and keep it at that temperature for 3 hours. Then, gaseous sulfur is introduced to carry out a chemical vapor deposition reaction to obtain a sulfur-carbon composite material. The inert gas is argon.

[0042] (5) Take the nitrogen-doped porous expanded graphite obtained in step (3) and the sulfur-carbon composite material obtained in step (4) and mix them. The mass ratio of nitrogen-doped porous expanded graphite to sulfur-carbon composite material is 1:9. After mixing evenly, the mixture is spread out and molded to obtain a self-supporting sulfur-carbon electrode sheet.

[0043] Example 3

[0044] (1) Mix natural graphite with a certain amount of oxidant and intercalating agent. The mass ratio of natural graphite to intercalating agent and oxidant is 1:15:0.5. Let it stand at 40°C for 30 minutes, filter, and wash to obtain expandable graphite. The natural graphite is natural flake graphite, the oxidant is hydrogen peroxide, and the intercalating agent is concentrated phosphoric acid.

[0045] (2) The expandable graphite obtained in step (1) is placed in an inert gas atmosphere and heated to 1000°C to obtain expanded graphite;

[0046] (3) The expanded graphite obtained in step (2) is placed in a mixed gas atmosphere, which consists of an inert gas and a nitrogen-containing gas, and the volume ratio of the inert gas to the nitrogen-containing gas is 80:20. After heating to 1000℃, it is kept at the temperature for 30 minutes to obtain nitrogen-doped porous expanded graphite. The inert gas is argon and the nitrogen-containing gas is ammonia.

[0047] (4) Take a portion of the nitrogen-doped porous expanded graphite obtained in step (3) and place it in a reactor. Inert gas is introduced to replace the air inside the reactor, so that an oxygen-free environment is formed inside the reactor. Heat it to 170°C and keep it at that temperature for 5 hours. Then, gaseous sulfur is introduced to carry out a chemical vapor deposition reaction to obtain a sulfur-carbon composite material. The inert gas is argon.

[0048] (5) Take the nitrogen-doped porous expanded graphite obtained in step (3) and the sulfur-carbon composite material obtained in step (4) and mix them. The mass ratio of nitrogen-doped porous expanded graphite to sulfur-carbon composite material is 1:4. After mixing evenly, the mixture is spread out and molded to obtain a self-supporting sulfur-carbon electrode sheet.

[0049] Example 4

[0050] (1) Mix natural graphite with a certain amount of oxidant and intercalating agent. The mass ratio of natural graphite to intercalating agent and oxidant is 1:3:0.05. Let it stand at 40°C for 30 minutes, filter, and wash to obtain expandable graphite. The natural graphite is natural flake graphite, the oxidant is potassium dichromate, and the intercalating agent is concentrated sulfuric acid.

[0051] (2) The expandable graphite obtained in step (1) is placed in an inert gas atmosphere and heated to 1000°C to obtain expanded graphite.

[0052] (3) The expanded graphite obtained in step (2) is placed in a mixed gas atmosphere, which consists of an inert gas and a nitrogen-containing gas, and the volume ratio of the inert gas to the nitrogen-containing gas is 60:40. After heating to 1000℃, it is kept at the temperature for 30 minutes to obtain nitrogen-doped porous expanded graphite. The inert gas is argon and the nitrogen-containing gas is ammonia.

[0053] (4) Take a portion of the nitrogen-doped porous expanded graphite obtained in step (3) and place it in a reactor. Inert gas is introduced to replace the air inside the reactor, so that an oxygen-free environment is formed inside the reactor. Heat it to 170°C and keep it at that temperature for 3.5 hours. Then, gaseous sulfur is introduced to carry out a chemical vapor deposition reaction to obtain a sulfur-carbon composite material. The inert gas is argon.

[0054] (5) Take the nitrogen-doped porous expanded graphite obtained in step (3) and the sulfur-carbon composite material obtained in step (4) and mix them. The mass ratio of nitrogen-doped porous expanded graphite to sulfur-carbon composite material is 1:1. After mixing evenly, the mixture is spread out and molded to obtain a self-supporting sulfur-carbon electrode sheet.

[0055] Example 5

[0056] (1) Mix natural graphite with a certain amount of oxidant and intercalating agent. The mass ratio of natural graphite to intercalating agent and oxidant is 1:1:0.1. Let it stand at 40°C for 30 minutes, filter, and wash to obtain expandable graphite. The natural graphite is natural flake graphite, the oxidant is hydrogen peroxide, and the intercalating agent is perchloric acid.

[0057] (2) The expandable graphite obtained in step (1) is placed in an inert gas atmosphere and heated to 1000°C to obtain expanded graphite;

[0058] (3) The expanded graphite obtained in step (2) is placed in a mixed gas atmosphere, which consists of an inert gas and a nitrogen-containing gas, and the volume ratio of the inert gas to the nitrogen-containing gas is 50:50. After heating to 1000℃, it is kept at the temperature for 30 minutes to obtain nitrogen-doped porous expanded graphite. The inert gas is argon and the nitrogen-containing gas is ammonia.

[0059] (4) Take a portion of the nitrogen-doped porous expanded graphite obtained in step (3) and place it in a reactor. Inert gas is introduced to replace the air inside the reactor, so that an oxygen-free environment is formed inside the reactor. Heat it to 180°C and keep it at that temperature for 5 hours. Then, gaseous sulfur is introduced to carry out a chemical vapor deposition reaction to obtain a sulfur-carbon composite material. The inert gas is argon.

[0060] (5) Take the nitrogen-doped porous expanded graphite obtained in step (3) and the sulfur-carbon composite material obtained in step (4) and mix them. The mass ratio of nitrogen-doped porous expanded graphite to sulfur-carbon composite material is 1:19. After mixing evenly, the mixture is spread out and molded to obtain a self-supporting sulfur-carbon electrode sheet.

[0061] Example 6

[0062] (1) Mix natural graphite with a certain amount of oxidant and intercalating agent. The mass ratio of natural graphite to intercalating agent and oxidant is 1:10:0.2. Let it stand at 40°C for 30 minutes, filter, and wash to obtain expandable graphite. The natural graphite is natural flake graphite, the oxidant is potassium permanganate, and the intercalating agent is concentrated nitric acid.

[0063] (2) The expandable graphite obtained in step (1) is placed in an inert gas atmosphere and heated to 1000°C to obtain expanded graphite;

[0064] (3) The expanded graphite obtained in step (2) is placed in a mixed gas atmosphere, which consists of an inert gas and a nitrogen-containing gas, and the volume ratio of the inert gas to the nitrogen-containing gas is 40:60. After heating to 1000℃, it is kept at the temperature for 30 minutes to obtain nitrogen-doped porous expanded graphite. The inert gas is argon and the nitrogen-containing gas is ammonia.

[0065] (4) Take a portion of the nitrogen-doped porous expanded graphite obtained in step (3) and place it in a reactor. Inert gas is introduced to replace the air inside the reactor, so that an oxygen-free environment is formed inside the reactor. Heat it to 230°C and keep it at that temperature for 5 hours. Then, gaseous sulfur is introduced to carry out a chemical vapor deposition reaction to obtain a sulfur-carbon composite material. The inert gas is argon.

[0066] (5) Take the nitrogen-doped porous expanded graphite obtained in step (3) and the sulfur-carbon composite material obtained in step (4) and mix them. The mass ratio of nitrogen-doped porous expanded graphite to sulfur-carbon composite material is 1:0.4. After mixing evenly, the mixture is spread out and molded to obtain a self-supporting sulfur-carbon electrode sheet.

[0067] Performance tests were conducted on the above embodiments, and the test results are shown in Table 1. The reversible specific capacity was tested using a half-coin cell, and the value was calculated based on the mass of the electrode.

[0068]

[0069] Table 1

[0070] Based on the experimental observations and the data above, it is clear that the higher the proportion of sulfur-carbon composite material, the greater the amount of active material loaded on the electrode; the higher the proportion of nitrogen-doped porous expanded graphite, the easier the electrode is to form, the higher the structural strength, and the richer the conductive network. Moreover, the pores created by expanded graphite can serve as transport channels for ions between graphite layers, improving the lithium insertion and extraction performance of the electrode. Therefore, the higher the proportion of nitrogen-doped porous expanded graphite in the electrode, the higher its cycle retention rate.

[0071] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a self-supporting sulfur-carbon electrode sheet, characterized in that: It includes the following steps: (1) Mix natural graphite with a certain amount of oxidant and intercalating agent. The mass ratio of natural graphite to intercalating agent and oxidant is 1:(1-15):(0.05-0.5). Let it stand at 40℃ for 30 min, filter, wash and obtain expandable graphite. (2) The expandable graphite obtained in step (1) is placed in an inert gas atmosphere and heated to 1000°C to obtain expanded graphite; (3) Place the expanded graphite obtained in step (2) in a mixed gas atmosphere, which consists of an inert gas and a nitrogen-containing gas, and the volume ratio of the inert gas to the nitrogen-containing gas is (30-90): (10-70). Heat to 1000℃ and keep warm for 30 minutes to obtain nitrogen-doped porous expanded graphite. (4) Take a portion of the nitrogen-doped porous expanded graphite obtained in step (3) and place it in a reactor. Inert gas is introduced to replace the air inside the reactor, so that an oxygen-free environment is formed inside the reactor. Heat it to 170-230℃ and keep it at that temperature for 3-5 hours. Then, gaseous sulfur is introduced to carry out a chemical vapor deposition reaction to obtain a sulfur-carbon composite material. (5) Take the nitrogen-doped porous expanded graphite obtained in step (3) and the sulfur-carbon composite material obtained in step (4) and mix them. The mass ratio of nitrogen-doped porous expanded graphite to sulfur-carbon composite material is 1: (0.2-20). After mixing evenly, the mixture is spread out and molded to obtain a self-supporting sulfur-carbon electrode sheet.

2. The method for preparing a self-supporting sulfur-carbon electrode sheet according to claim 1, characterized in that: In step (1), the natural graphite is natural flake graphite.

3. The method for preparing a self-supporting sulfur-carbon electrode sheet according to claim 1, characterized in that: In step (3), the inert gas is argon and the nitrogen-containing gas is ammonia.

4. The method for preparing a self-supporting sulfur-carbon electrode sheet according to claim 1, characterized in that: In step (4), the inert gas is argon.

5. The method for preparing a self-supporting sulfur-carbon electrode sheet according to claim 1, characterized in that: In step (5), the density of the self-supporting sulfur-carbon electrode sheet is 0.3-0.8 g / cm³. 3 Its sulfur content ranges from 10% to 65% by mass.

6. The method for preparing a self-supporting sulfur-carbon electrode sheet according to claim 1, characterized in that: In step (1), the oxidant is one of hydrogen peroxide, potassium permanganate, and potassium dichromate, and the intercalating agent is one of concentrated sulfuric acid, concentrated nitric acid, perchloric acid, and concentrated phosphoric acid.

7. A self-supporting sulfur-carbon electrode sheet, characterized in that: It is prepared by the method of any one of claims 1-6 for preparing a self-supporting sulfur-carbon electrode sheet.

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