Sulfur-carbon composite electrode, preparation method thereof and battery system

Abstract

The invention discloses a sulfur-carbon composite electrode, a preparation method thereof and a battery system, the sulfur-carbon composite electrode comprises a porous electrode substrate and sulfur attached to the porous electrode substrate, and the specific surface area of the porous electrode substrate is 1500m < 2 > / g to 2200m < 2 > / g, 0lt; the aperture is less than or equal to 200nm. Sulfur is attached to the porous electrode substrate, the raw materials are easy to obtain, the preparation process is simple, the cost is low, and the safety is high; and the porous electrode substrate can provide more space for sulfur attachment, so that the sulfur loading capacity is increased, and the energy density and the cycling stability of the battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a sulfur-carbon composite electrode and a preparation method thereof, and a battery system. Background Art

[0002] With the development of microelectronics technology, miniaturized devices are increasing, which puts higher requirements on energy storage devices. Lithium batteries have also entered the large-scale practical stage.

[0003] However, the chemical properties of lithium metal are very active, and the environmental requirements during production, storage and use are very high, otherwise safety problems are likely to occur; and the price of lithium battery positive electrode materials such as LiCoO2 is very expensive, and the cost of positive electrode materials accounts for about 40% of the overall cost of lithium batteries. Therefore, the overall cost of lithium batteries is relatively high; lithium batteries have relatively complex technical requirements during the production process, which further increases the production cost of lithium batteries and limits their use; therefore, there is an urgent need to provide a new electrode material to reduce the production cost of batteries and improve their safety. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a sulfur-carbon composite electrode to solve the problems of high production cost and poor safety of existing electrode materials.

[0005] Another object of the present invention is to provide a battery system using the above sulfur-carbon composite electrode as a positive electrode.

[0006] The present invention also aims to provide a method for preparing the sulfur-carbon composite electrode.

[0007] In order to achieve the above object, the first technical solution of the present invention is implemented as follows: a sulfur-carbon composite electrode comprises a porous electrode substrate and sulfur attached to the porous electrode substrate, wherein the specific surface area of ​​the porous electrode substrate is 1500m 2 / g-2200m 2 / g, 0<pore size≤200nm.

[0008] Furthermore, the porous electrode substrate is a porous carbon material, wherein micropores account for 35%-40% of the volume of the porous carbon material, mesopores account for 20%-40% of the volume of the porous carbon material, and macropores account for 10%-15% of the volume of the porous carbon material.

[0009] Furthermore, the distribution density of the sulfur in the porous electrode substrate is 0.3 g / cm 3 -1.0g / cm 3 .

[0010] The second technical solution of the present invention is achieved as follows: a battery system, which includes a negative electrode, an electrolyte and a sulfur-carbon composite electrode as a positive electrode, wherein the negative electrode is a sodium electrode or a potassium electrode.

[0011] Furthermore, the electrolyte is prepared by mixing a mixed solvent and a sodium salt in a mass ratio of (2-5):1; or

[0012] The electrolyte is prepared by mixing a mixed solvent and potassium salt in a mass ratio of (2-5):1.

[0013] Furthermore, the mixed solvent is formed by mixing the ionic liquid and the solvent in a volume ratio of 1:(1-8).

[0014] Furthermore, the solvent is at least one of fluoroethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, diethyl carbonate, trimethylene carbonate, ethylene glycol dimethyl ether, and dioxolane.

[0015] Furthermore, the ionic liquid is EMIM-TFSI, Pyr 14 TFSI、PP 14 At least one of the TFSIs.

[0016] Furthermore, the sodium salt is at least one of NaPF6, NaClO4, NaBF4, NaFSI, and NaTFSI;

[0017] The potassium salt is at least one of KFSI, KPF6, and KTFSI.

[0018] The third technical solution of the present invention is achieved as follows: A method for preparing a sulfur-carbon composite electrode comprises the following steps:

[0019] S1. Completely dissolving elemental sulfur in potassium sulfide to obtain a mixed solution;

[0020] S2. Dispersing the porous electrode substrate in deionized water to obtain a dispersion liquid, then slowly adding the mixed solution obtained in S1 to the dispersion liquid, and adding a dispersant and stirring to disperse uniformly to obtain a dispersed mixed solution;

[0021] S3. Adding formic acid to the dispersed mixed solution obtained in S2 to precipitate the sulfur therein and evenly distribute it in the porous electrode substrate to obtain the sulfur-carbon composite electrode.

[0022] Compared with the existing technology, the present invention has the following beneficial effects: the present invention attaches sulfur to a porous electrode substrate to prepare a sulfur-carbon composite electrode. The raw materials used are easily available, the preparation process is simple, the cost is low, and the safety is high; and the porous electrode substrate can provide more space for the attachment of sulfur, increase the sulfur loading capacity, and improve the energy density and cycle stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a microstructure diagram of the sulfur-carbon composite electrode according to an embodiment of the present invention;

[0024] Figure 2 These are the performance test results of the battery system described in the embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0026] In the description of the present invention, it should be clarified that the terms "vertical", "transverse", "longitudinal", "front", "rear", "left", "right", "up", "down", "horizontal", etc. indicating orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, which are only for the convenience of describing the present invention, and do not mean that the device or element referred to must have a specific orientation or position, and therefore cannot be understood as a limitation on the present invention. In the description of the present invention, it should be noted that, unless otherwise clearly stipulated and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] The sulfur-carbon composite electrode provided in this application comprises a porous electrode substrate and sulfur attached to the porous electrode substrate, wherein the specific surface area of ​​the porous electrode substrate is 1500 m 2 / g-2200m 2 / g, 0<pore size≤200nm.

[0028] Specifically, the porous electrode substrate is a porous carbon material, which contains micropores, mesopores and macropores. The micropores can provide anchoring sites for sulfur, the mesopores are used to construct ion transmission channels during battery charging and discharging, and the macropores can alleviate volume changes during charging and discharging; the micropores account for 35%-40% of the volume of the porous carbon material, the mesopores account for 20%-40% of the volume of the porous carbon material, and the macropores account for 10%-15% of the volume of the porous carbon material.

[0029] The distribution density of sulfur in the porous carbon material is 0.3 g / cm 3 -1.0g / cm 3 .

[0030] Porous carbon materials have a high specific surface area, which can provide more space for loading sulfur, increase the sulfur loading capacity, improve the energy density of the battery when used as an electrode, and effectively alleviate the volume change of sulfur during charging and discharging, promoting electron transmission; the porous structure of porous carbon materials can also inhibit the dissolution and diffusion of polysulfides produced during sulfur charging and discharging, reduce the shuttle effect, and improve the cycle stability when used as a battery.

[0031] The preparation method of the sulfur-carbon composite electrode is as follows:

[0032] S1, completely dissolving elemental sulfur in potassium sulfide to obtain a mixed solution;

[0033] Specifically, elemental sulfur is added to a potassium sulfide solution with a mass concentration of 0.1 g / mL-0.2 g / mL, and stirred at room temperature until the elemental sulfur is completely dissolved. By controlling the amount of dissolved elemental sulfur, the sulfur content in the polybasic potassium sulfide can be controlled;

[0034] S2, preparing a porous electrode substrate, dispersing the porous electrode substrate in deionized water to obtain a dispersion, then slowly adding the mixed solution obtained in S1 to the dispersion, and adding a dispersant to stir and disperse the mixture to obtain a dispersed mixed solution;

[0035] S3, adding formic acid to the dispersed mixed solution to precipitate the sulfur therein and evenly distribute it in the porous carbon material to obtain the sulfur-carbon composite electrode.

[0036] The dispersant includes N-methylpyrrolidone (NMP), polyvinylpyrrolidone (PVP) or polyacrylamide (PAM).

[0037] Specifically, the porous carbon material is prepared using a biomass low-temperature hydrothermal or low-temperature carbonization process, a metal alkoxide pyrolysis process, or a chemical synthesis method combined with a template method;

[0038] The porous carbon material is dispersed in deionized water to obtain a dispersion, the mixed solution is added to the dispersion at a rate of 3mL / min-8mL / min, and a dispersant is added to uniformly disperse the polysulfide to prevent particle aggregation and accumulation. Then, formic acid is used to precipitate the sulfur in the mixed solution in the pores of the porous carbon material to form a sulfur-carbon composite electrode.

[0039] The sulfur-carbon composite electrode is used as the positive electrode of a battery system, which also includes a negative electrode and an electrolyte. The negative electrode is a sodium electrode or a potassium electrode, and the electrolyte is formed by mixing a mixed solvent and a sodium salt in a mass ratio of (2-5):1; or the electrolyte is formed by mixing a mixed solvent and a potassium salt in a mass ratio of (2-5):1.

[0040] The mixed solvent is prepared by mixing an ionic liquid and a solvent in a volume ratio of 1:(1-8), wherein the solvent is at least one of fluoroethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, diethyl carbonate, trimethylene carbonate, ethylene glycol dimethyl ether, and dioxolane, and the ionic liquid is at least one of EMIM-TFSI, Pyr 14 TFSI、PP 14 At least one of the TFSIs.

[0041] Ionic liquids have good electrical conductivity. When mixed with solvents, they can increase the ionic conductivity of the electrolyte, improve the charge and discharge efficiency of the battery, and provide a stable environment for the chemical reactions involved in the charge and discharge process.

[0042] The sodium salt is at least one of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium fluoroborate (NaBF4), sodium bis(fluorosulfonyl)imide (NaFSI), and sodium bis(trifluoromethylsulfonyl)imide (NaTFSI); the potassium salt is at least one of potassium bis(fluorosulfonyl)imide (KFSI), potassium hexafluorophosphate (KPF6), and potassium bis(trifluoromethylsulfonyl)imide (KTFSI).

[0043] Example 1

[0044] This embodiment provides a battery system, including a negative electrode, a positive electrode and an electrolyte, wherein the positive electrode is composed of a porous carbon material and sulfur attached therein, and the specific surface area of ​​the porous carbon material is 1500m 2 / g, which contains 35% micropores, 20% mesopores and 10% macropores by volume. The distribution density of sulfur in the porous carbon material is 0.3g / cm 3 .

[0045] The negative electrode is a sodium electrode, the electrolyte is formed by mixing a mixed solvent and a sodium salt in a mass ratio of 2:1, the mixed solvent is formed by mixing fluoroethylene carbonate and EMIM-TFSI in a volume ratio of 1:1, and the sodium salt is NaPF6.

[0046] Example 2

[0047] This embodiment provides a battery system, including a negative electrode, a positive electrode and an electrolyte. The positive electrode is composed of a porous carbon material and sulfur attached therein. The specific surface area of ​​the porous carbon material is 1600m2 / g, which contains 36% micropores, 23% mesopores and 11% macropores by volume. The distribution density of sulfur in the porous carbon material is 0.4g / cm 3 .

[0048] The negative electrode is a sodium electrode, the electrolyte is a mixture of a mixed solvent and a sodium salt in a mass ratio of 3:1, and the mixed solvent is a mixture of ethylene carbonate and Pyr 14 TFSI is mixed in a volume ratio of 2:1, and the sodium salt is NaClO4.

[0049] Example 3

[0050] This embodiment provides a battery system, including a negative electrode, a positive electrode and an electrolyte. The positive electrode is composed of a porous carbon material and sulfur attached therein. The specific surface area of ​​the porous carbon material is 1700m 2 / g, which contains micropores accounting for 37% by volume, mesopores accounting for 25% by volume, and macropores accounting for 12% by volume. The distribution density of sulfur in the porous carbon material is 0.5g / cm 3 .

[0051] The negative electrode is a sodium electrode, the electrolyte is a mixture of a mixed solvent and a sodium salt in a mass ratio of 4:1, and the mixed solvent is ethyl methyl carbonate and PP 14 TFSI is mixed in a volume ratio of 3:1, and the sodium salt is NaTFSI.

[0052] Example 4

[0053] This embodiment provides a battery system, including a negative electrode, a positive electrode and an electrolyte. The positive electrode is composed of a porous carbon material and sulfur attached therein. The specific surface area of ​​the porous carbon material is 1800m 2 / g, which contains 38% micropores, 28% mesopores and 13% macropores by volume. The distribution density of sulfur in the porous carbon material is 0.6g / cm 3 .

[0054] The negative electrode is a sodium electrode, the electrolyte is formed by mixing a mixed solvent and a sodium salt in a mass ratio of 5:1, the mixed solvent is formed by mixing dioxolane and EMIM-TFSI in a volume ratio of 4:1, and the sodium salt is NaTFSI.

[0055] Example 5

[0056] This embodiment provides a battery system, including a negative electrode, a positive electrode and an electrolyte. The positive electrode is composed of a porous carbon material and sulfur attached therein. The specific surface area of ​​the porous carbon material is 1900 m 2 / g, which contains 39% micropores, 30% mesopores and 14% macropores by volume. The distribution density of sulfur in the porous carbon material is 0.7g / cm 3 .

[0057] The negative electrode is a sodium electrode, the electrolyte is formed by mixing a mixed solvent and a sodium salt in a mass ratio of 3:1, the mixed solvent is formed by mixing fluoroethylene carbonate and EMIM-TFSI in a volume ratio of 6:1, and the sodium salt is NaPF6.

[0058] Example 6

[0059] This embodiment provides a battery system, including a negative electrode, a positive electrode and an electrolyte, wherein the positive electrode is composed of a porous carbon material and sulfur attached therein, and the specific surface area of ​​the porous carbon material is 2000m 2 / g, which contains 40% micropores, 33% mesopores and 15% macropores by volume. The distribution density of sulfur in the porous carbon material is 1.0g / cm 3 .

[0060] The negative electrode is a sodium electrode, the electrolyte is formed by mixing a mixed solvent and a sodium salt in a mass ratio of 3:1, the mixed solvent is formed by mixing fluoroethylene carbonate and EMIM-TFSI in a volume ratio of 7:1, and the sodium salt is NaPF6.

[0061] Example 7

[0062] This embodiment provides a battery system, including a negative electrode, a positive electrode and an electrolyte. The positive electrode is composed of a porous carbon material and sulfur attached thereto. The specific surface area of ​​the porous carbon material is 2200 m 2 / g, which contains 40% micropores, 36% mesopores and 15% macropores by volume. The distribution density of sulfur in the porous carbon material is 0.5g / cm 3 .

[0063] The negative electrode is a sodium electrode, the electrolyte is formed by mixing a mixed solvent and a potassium salt in a mass ratio of 3:1, the mixed solvent is formed by mixing fluoroethylene carbonate and EMIM-TFSI in a volume ratio of 7:1, and the potassium salt is KFSI.

[0064] Example 8

[0065] This embodiment provides a battery system, including a negative electrode, a positive electrode and an electrolyte. The positive electrode is composed of a porous carbon material and sulfur attached thereto. The specific surface area of ​​the porous carbon material is 2200 m 2 / g, which contains 40% micropores, 40% mesopores and 15% macropores by volume. The distribution density of sulfur in the porous carbon material is 0.5g / cm 3 .

[0066] The negative electrode is a sodium electrode, the electrolyte is formed by mixing a mixed solvent and a potassium salt in a mass ratio of 3:1, the mixed solvent is formed by mixing fluoroethylene carbonate and EMIM-TFSI in a volume ratio of 7:1, and the potassium salt is KPF6.

[0067] Test results:

[0068] 1) The microstructure of the sulfur-carbon composite electrode described in Example 4 was observed using a transmission electron microscope (TEM). Figure 1 As shown, the material contains micropores, mesopores and macropores, and the pores are evenly distributed, which can provide more space for the attachment of sulfur.

[0069] 2) Detecting the performance parameters of the battery systems described in Examples 1-8, as shown in Tables 1 and Figure 2 As shown:

[0070] Table 1 Performance parameters of battery system

[0071]

[0072] Among them, the charge and discharge efficiency refers to the ratio of the actual output capacity to the theoretical input capacity of the battery during the charge and discharge process; the energy efficiency refers to the ability of the battery to convert stored chemical energy into electrical energy, expressed as the ratio of output electrical energy to input electrical energy; the battery capacity is the amount of electricity in the battery system; the capacity retention rate is the ratio of the actual capacity of the battery to the original capacity after 100 cycles of charge and discharge.

[0073] From the above test results, it can be seen that the sulfur-carbon composite electrode provided by the present invention achieves effective sulfur loading through a three-dimensional porous network structure, and can be used as a battery to significantly improve its capacity, which is about 30% higher than that of similar sulfur-carbon materials. In addition, the battery system has a low DC internal resistance, low losses during use, improved energy conversion efficiency, and is also beneficial to maintaining the stability of the battery output voltage and improving the safety performance of the battery system.

[0074] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A sulfur-carbon composite electrode, characterized in that: The invention comprises a porous electrode substrate and sulfur attached to the porous electrode substrate, wherein the specific surface area of ​​the porous electrode substrate is 1500m 2 / g-2200m 2 / g, 0<pore size≤200nm.

2. The sulfur-carbon composite electrode according to claim 1, characterized in that The porous electrode substrate is a porous carbon material, wherein micropores account for 35%-40% of the volume of the porous carbon material, mesopores account for 20%-40% of the volume of the porous carbon material, and macropores account for 10%-15% of the volume of the porous carbon material.

3. The sulfur-carbon composite electrode according to claim 1 or 2, characterized in that: The distribution density of sulfur in the porous electrode substrate is 0.3 g / cm 3 -1.0g / cm 3 .

4. A battery system, characterized in that: The battery system comprises a negative electrode, an electrolyte, and the sulfur-carbon composite electrode according to any one of claims 1 to 3 as a positive electrode, wherein the negative electrode is a sodium electrode or a potassium electrode.

5. The battery system according to claim 4, characterized in that The electrolyte is prepared by mixing a mixed solvent and a sodium salt in a mass ratio of (2-5):1; or The electrolyte is prepared by mixing a mixed solvent and potassium salt in a mass ratio of (2-5):

1.

6. The battery system according to claim 5, characterized in that The mixed solvent is prepared by mixing the ionic liquid and the solvent in a volume ratio of 1:(1-8).

7. The battery system according to claim 6, characterized in that The solvent is at least one of fluoroethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, diethyl carbonate, trimethylene carbonate, ethylene glycol dimethyl ether, and dioxolane.

8. The battery system according to claim 6 or 7, characterized in that: The ionic liquid is EMIM-TFSI, Pyr 14 TFSI、PP 14 At least one of the TFSIs.

9. The battery system according to claim 8, characterized in that The sodium salt is at least one of NaPF6, NaClO4, NaBF4, NaFSI, and NaTFSI; The potassium salt is at least one of KFSI, KPF6, and KTFSI.

10. The method for preparing a sulfur-carbon composite electrode according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. Completely dissolving elemental sulfur in potassium sulfide to obtain a mixed solution; S2. Dispersing the porous electrode substrate in deionized water to obtain a dispersion liquid, then slowly adding the mixed solution obtained in S1 to the dispersion liquid, and adding a dispersant and stirring to disperse uniformly to obtain a dispersed mixed solution; S3. Adding formic acid to the dispersed mixed solution obtained in S2 to precipitate the sulfur therein and evenly distribute it in the porous electrode substrate to obtain the sulfur-carbon composite electrode.

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