CN103606649B - A kind of electrolytic preparation method of sulphur/carbon composite - Google Patents

Abstract

The invention discloses an electrolytic preparation method of a sulfur/carbon composite material. The sulfur/carbon composite material is prepared according to the following steps: (1) preparing an electrolyte solution according to a formula; (2) using a graphite rod as an anode and a carbon source at the same time , the platinum sheet is used as the cathode, and the electrolysis reaction is carried out under direct current; (3) the precipitate formed by the electrolysis reaction is filtered by suction to take the filter cake, washed with water and dried to obtain a sulfur/carbon composite material; the sulfur/carbon composite material prepared by the method of the present invention The composite material has good cycle stability and rate performance, and can be used as a cathode material for lithium-sulfur batteries, and is widely used in the field of high-performance lithium-sulfur secondary batteries.

Description

A kind of electrolytic preparation method of sulfur/carbon composite material

(1) Technical field

The invention relates to a preparation method of a sulfur/carbon composite material, in particular to an electrolytic preparation method of a sulfur/carbon composite material.

(2) Background technology

The valence state of sulfur element is rich and can vary from -2 to +7. Using the reversible change between Li2S and S, the lithium-sulfur secondary battery uses metal lithium as the negative electrode and elemental sulfur or sulfur-based composite materials as the positive electrode. With a high theoretical energy density (2600Wh/kg), it is considered to be a new high-capacity reserve battery system with the most development potential. In addition, lithium-sulfur batteries also have the advantages of abundant raw material sources, cheap prices, environmental friendliness, and good battery safety, and have clear and broad market application prospects.

Nevertheless, the sulfur cathode material, which is the key material of lithium-sulfur secondary batteries, still has the following problems: (1) elemental sulfur has poor conductivity at room temperature, and a large amount of conductive agent needs to be added, resulting in a decrease in the energy density of the system; (2) elemental sulfur Sulfur will be reduced to polysulfides that are easily soluble in the electrolyte during the discharge process, resulting in the loss of active materials and a huge change in the morphology of the sulfur electrode material; (3) polysulfides soluble in the electrolyte will increase the viscosity of the electrolyte increase, and at the same time, it will also shuttle to the lithium metal sheet of the counter electrode, and a self-discharge reaction will occur. These problems severely restrict the practical application of lithium-sulfur secondary batteries.

At present, positive progress has been made in sulfur/carbon composite materials at home and abroad, and it is found that filling elemental sulfur into some porous carbon materials (such as mesoporous carbon, activated carbon, graphene, carbon nanotubes, etc.) Problems such as loss of active material and fast capacity fading occur during charge and discharge. The main method of synthesizing sulfur/carbon composites is to diffuse and adsorb elemental sulfur into the pores of porous carbon materials by heating sulfur powder to obtain sulfur/carbon composites. For example, Yuegang Zhang et al. (LiwenJi, MuminRao, Haimei Zheng, Liang Zhang, Yuanchang Li, Yuegang Zhang.GrapheneOxideasaSulfurImmobilizerinHighPerformanceLithium/SulfurCells.J.Am.Chem.Soc.2011,133,18522-18525) filled elemental sulfur into graphene oxide to obtain high-performance sulfur-based Materials; U.S. LyndenA.Archer etc. (N.Jayaprakash, J.Shen, SuryaS.Moganty, A.Corona, and L.A.Archer, PorousHollowCarbonSulfurCompositesforHigh-PowerLithium-SulfurBatteries, Angew.Chem.Int.Ed., 2011,50: 1-6) A hollow spherical sulfur/carbon composite material was prepared by injecting sulfur by multiple vapor deposition, which has high cycle stability and rate characteristics. The present invention adopts a simple electrolysis method for the first time, using graphite rods as anode and carbon source at the same time, to carry out continuous electrolysis reaction in sulfuric acid electrolyte solution containing thiourea as sulfur source, graphite electrolytically deposits elemental sulfur while electrolytic stripping occurs , and sulfur/carbon composites can be prepared by one-step in situ electrolysis.

(3) Contents of the invention

The purpose of the present invention is to provide an electrolytic preparation method of sulfur/carbon composite material with simple operation and low cost.

To achieve the above object, the technical solution adopted in the present invention is:

A kind of electrolytic preparation method of sulfur/carbon composite material, described preparation method is carried out as follows:

(1) Configure the electrolyte, which is mixed with the following raw materials in weight percentage:

(2) Use the graphite rod as the anode and the platinum sheet as the cathode, and conduct the electrolysis reaction at a direct current of 1-100V for 0.1-10 hours;

(3) The precipitate produced by the electrolysis reaction is filtered by suction to extract the filter cake, washed with water and dried to obtain the sulfur/carbon composite material.

In the step (1) of the electrolytic preparation method of the sulfur/carbon composite material of the present invention, the purity of the sulfuric acid, thiourea and potassium hydroxide is preferably chemically pure or higher; and the water is preferably deionized water.

In the step (1) of the present invention, it is preferred that the electrolyte is mixed with the following raw materials in weight percentage:

In the step (1) of the present invention, the preparation method of the electrolyte solution is as follows: take the sulfuric acid and water of the formulation amount to prepare the sulfuric acid aqueous solution, then add the thiourea and potassium hydroxide of the formulation amount into the prepared sulfuric acid aqueous solution, mix Evenly get the electrolyte.

In the step (2) of the electrolytic preparation method of the sulfur/carbon composite material of the present invention, the graphite rod is selected from natural graphite rods, artificial graphite rods or high-purity graphite rods, and the purity of the graphite rods is preferably chemically pure or higher than chemically pure .

In the step (2) of the present invention, the direct current is preferably 3-15V direct current, and the electrolysis reaction time is preferably 0.5-5 hours.

The present invention specifically recommends that the described sulfur/carbon composite material be prepared according to the following steps:

(1) Configure the electrolyte, which is mixed with the following raw materials in weight percentage:

The purity of the sulfuric acid, thiourea and potassium hydroxide is chemically pure or higher than chemically pure;

The preparation method of the electrolyte is as follows: take the sulfuric acid and water in the formulated amount to prepare a sulfuric acid aqueous solution, then add the formulated amount of thiourea and potassium hydroxide into the prepared sulfuric acid aqueous solution, and mix well to obtain the electrolyte;

(2) The graphite rod is used as the anode, the platinum sheet is used as the cathode, and the electrolysis reaction is carried out under 3-15V direct current for 0.5-5 hours; the purity of the graphite rod is chemically pure or higher;

(3) The precipitate produced by the electrolysis reaction is filtered by suction to extract the filter cake, washed with water and dried to obtain the sulfur/carbon composite material.

The form of the sulfur/carbon composite material in the present invention is powder, chip and particle.

The sulfur/carbon composite material prepared by the preparation method provided by the invention can be applied to the positive electrode material of the lithium-sulfur battery, and the lithium-sulfur battery can be prepared by a conventional method.

Compared with the prior art, the method of the present invention is simple, easy to control, low in cost, and easy to realize industrialization; the obtained sulfur/carbon composite material has good cycle stability and rate performance, and can be used as the positive electrode material of lithium-sulfur batteries, widely used It is used in the field of high-performance lithium-sulfur secondary batteries.

(4) Description of drawings

FIG. 1 is an SEM image of the sulfur/carbon composite material prepared in Example 1.

FIG. 2 is a low magnification SEM image of the sulfur/carbon composite material prepared in Example 1.

FIG. 3 is an XRD pattern of the sulfur/carbon composite material prepared in Example 1.

Fig. 4 is the first three discharge curves of the simulated battery prepared in Example 1.

Fig. 5 is the cyclic voltammetry graph of the simulated battery prepared in embodiment 1

FIG. 6 is a graph showing the cycle performance of the simulated battery prepared in Example 1.

(5) Specific implementation methods

The technical solutions of the present invention will be further described below with specific examples, but the protection scope of the present invention is not limited thereto.

Example 1

First, dissolve 4.8g of concentrated sulfuric acid into 100mL of deionized water, then add 10mL of potassium hydroxide solution with a mass fraction of 30%, and then add a certain amount of thiourea to make the concentration of thiourea in the solution 0.5mol/L. The prepared solution was transferred to the electrolytic cell, and the natural graphite rod was used as the anode, and the platinum sheet was used as the cathode, and electrolyzed at a DC voltage of 4.5V for 5 hours, and the precipitate was filtered, washed and dried to obtain a sulfur/carbon composite material . Fig. 1, Fig. 2, Fig. 3 are the SEM spectrum, the low power SEM spectrum and the XRD spectrum of the obtained sulfur/carbon composite material respectively, it can be seen that after the electrolytic reaction, the sulfur/carbon composite material can be obtained in one step, and its morphology It is granular.

The sulfur/carbon composite material obtained in Example 1 was used to make electrodes in the following manner.

Weigh the sulfur/carbon composite material, acetylene black and polyvinylidene fluoride at a mass ratio of 70:15:15, grind them evenly, and coat them on an aluminum foil to make an electrode. A metal lithium sheet is used as the negative electrode, and the electrolyte is 1mol /L1,3-dioxolane (DOL)/ethylene glycol dimethyl ether (DME) based lithium bis(trifluoromethylsulfonate)imide (LiTFSI) (volume ratio 1:1), polypropylene micro The porous film is a separator (Celgard2300), which is assembled into a simulated battery. Figure 4 is the discharge curve of the battery at a current density of 0.1Ag ^-1 and a voltage range of 1.5-3.0V. It can be found that the composite electrode material has a high initial discharge capacity of 1150mAhg ^-1 . Figure 5 is the cyclic voltammetry curve of the corresponding battery at a scan rate of 0.1 mVs ^-1 , where the two reduction peak potentials correspond to the discharge plateau of the corresponding battery, respectively. Figure 6 is the cycle performance graph of the corresponding battery. It can be found that the composite electrode material has excellent cycle stability. After 35 cycles, the specific capacity can still be maintained at 700mAhg ^-1 , and the Coulombic efficiency can reach about 93%.

Example 2

First, dissolve 4.8g of concentrated sulfuric acid into 100mL of deionized water, then add 10mL of potassium hydroxide solution with a mass fraction of 30%, and then add a certain amount of thiourea to make the concentration of thiourea in the solution 1mol/L. The prepared solution was transferred to an electrolytic cell, and a high-purity graphite rod was used as an anode, and a platinum sheet was used as a cathode, and electrolyzed at a DC voltage of 15V for 1 hour, and the precipitate was suction filtered, washed and dried to obtain a sulfur/carbon composite Material.

The sulfur/carbon composite material obtained in Example 2 was used to make an electrode as follows.

Weigh sulfur/carbon composite material, acetylene black and polyvinylidene fluoride at a mass ratio of 70:20:10, grind them evenly and coat them on an aluminum foil to make an electrode, use a lithium metal sheet as the negative electrode, and use 1mol of the electrolyte /L1,3-dioxolane (DOL)/ethylene glycol dimethyl ether (DME)-based lithium bis(trifluoromethylsulfonate)imide (LiTFSI) (volume ratio 1:1), polypropylene micro The porous film is a separator (Celgard2300), which is assembled into a simulated battery. At a current density of 0.1Ag ^-1 and a voltage range of 1.5-3.0V, the first discharge capacity of the composite electrode material reaches 1000mAhg ^-1 , and the specific capacity is still higher than 620mAhg ^-1 after 35 cycles.

Example 3

First, dissolve 4.8g of concentrated sulfuric acid into 100mL of deionized water, then add 10mL of potassium hydroxide solution with a mass fraction of 30%, and then add a certain amount of thiourea to make the concentration of thiourea in the solution 0.8mol/L. The prepared solution was transferred to the electrolytic cell, and the artificial graphite rod was used as the anode, and the platinum sheet was used as the cathode, and electrolyzed at a DC voltage of 7.5V for 2 hours, and the precipitate was suction filtered, washed and dried to obtain a sulfur/carbon composite Material.

The sulfur/carbon composite material obtained in Example 3 was used to make an electrode as follows.

Weigh the sulfur/carbon composite material, acetylene black and polyvinylidene fluoride at a mass ratio of 80:10:10, grind them evenly, and coat them on aluminum foil to make an electrode. A metal lithium sheet is used as the negative electrode, and the electrolyte is 1mol /L1,3-dioxolane (DOL)/ethylene glycol dimethyl ether (DME)-based lithium bis(trifluoromethylsulfonate)imide (LiTFSI) (volume ratio 1:1), polypropylene micro The porous film is a separator (Celgard2300), which is assembled into a simulated battery. At a current density of 0.1Ag ^-1 and a voltage range of 1.5-3.0V, the first discharge capacity of the composite electrode material reaches 1050mAhg ^-1 , and the specific capacity is still higher than 630mAhg ^-1 after 35 cycles.

Example 4

First, dissolve 4.8g of concentrated sulfuric acid into 100mL of deionized water, then add 10mL of potassium hydroxide solution with a mass fraction of 30%, and then add a certain amount of thiourea to make the concentration of thiourea in the solution 0.4mol/L. The prepared solution was transferred to the electrolytic cell, and the natural modified graphite rod was used as the anode, and the platinum sheet was used as the cathode, and electrolyzed at a DC voltage of 3V for 4 hours, and the precipitate was suction filtered, washed and dried to obtain sulfur/carbon composite material.

The sulfur/carbon composite material obtained in Example 4 was used to make electrodes in the following manner.

Weigh the sulfur/carbon composite material, acetylene black and polyvinylidene fluoride at a mass ratio of 80:5:15, grind them evenly, and coat them on aluminum foil to make an electrode. Use a metal lithium sheet as the negative electrode, and the electrolyte is 1mol /L1,3-dioxolane (DOL)/ethylene glycol dimethyl ether (DME)-based lithium bis(trifluoromethylsulfonate)imide (LiTFSI) (volume ratio 1:1), polypropylene micro The porous film is a separator (Celgard2300), which is assembled into a simulated battery. At a current density of 0.1Ag ^-1 and a voltage range of 1.5-3.0V, the first discharge capacity of the composite electrode material reaches 900mAhg ^-1 , and the specific capacity is still higher than 600mAhg ^-1 after 35 cycles.

Example 5

Firstly, the commercial carbon material and sublimed sulfur were uniformly mixed in a mortar at a mass ratio of 1:3, and then pressed into a block in a mold. The prepared module was placed in an oven, and after thermal diffusion at 155°C for 24 hours, it was ground into powder to become a spare sulfur/carbon composite material.

The sulfur/carbon composite material obtained in this example was used to make an electrode as follows.

Weigh the sulfur/carbon composite material, acetylene black and polyvinylidene fluoride at a mass ratio of 80:5:15, grind them evenly, and coat them on aluminum foil to make an electrode. Use a metal lithium sheet as the negative electrode, and the electrolyte is 1mol /L1,3-dioxolane (DOL)/ethylene glycol dimethyl ether (DME)-based lithium bis(trifluoromethylsulfonate)imide (LiTFSI) (volume ratio 1:1), polypropylene micro The porous film is a separator (Celgard2300), which is assembled into a simulated battery. Under the current density of 0.1Ag ^-1 and the voltage range of 1.5-3.0V, the first discharge capacity of the composite electrode material is 600mAhg ^-1 , and the specific capacity drops to 300mAhg ^-1 after 35 cycles.

Comparing Example 4 and Example 5, the sulfur/carbon composite material prepared by the present invention has relatively good electrochemical cycle performance. The thermal diffusion process in Example 5 not only consumes a large amount of energy but also requires a long experiment period, while the present invention synthesizes the sulfur/carbon composite material in one step, which is simple to operate, more environmentally friendly, and more energy-saving.

The sulfur/carbon composite material prepared by the invention has good electrochemical performance, short preparation period, environmental protection and energy saving, and has good industrial application prospect.

Claims (7)

1. an electrolytic preparation method of sulfur/carbon composite material, characterized in that said preparation method is: (1) Electrolyte is configured, and the electrolyte is mixed by the following raw materials in weight percentage: (2) With the graphite rod as the anode and the platinum sheet as the cathode, the electrolysis reaction is carried out under a direct current of 3-15V for 0.5-5 hours; (3) The precipitate produced by the electrolysis reaction is filtered by suction to take the filter cake, washed with water and dried to obtain the sulfur/carbon composite material. 2. the electrolytic preparation method of sulfur/carbon composite material as claimed in claim 1 is characterized in that in step (1), the purity of described sulfuric acid, thiourea and potassium hydroxide is chemically pure or higher than chemically pure; Said water is deionized water. 3. the electrolytic preparation method of sulfur/carbon composite material as claimed in claim 1 is characterized in that in step (1), described electrolytic solution is mixed by the raw material of following weight percent: 4. The electrolytic preparation method of sulfur/carbon composite material as claimed in claim 1, characterized in that in step (2), the graphite rod is a natural graphite rod or an artificial graphite rod. 5. The electrolytic preparation method of sulfur/carbon composite material as claimed in claim 1, characterized in that in step (2), the purity of the graphite rod is chemically pure or higher than chemically pure. 6. The electrolytic preparation method of sulfur/carbon composite material as claimed in any one of claims 1 to 5, characterized in that in step (1), the electrolyte is prepared as follows: take the sulfuric acid and water of the formulation amount to prepare Sulfuric acid aqueous solution, and then add the formulated amount of thiourea and potassium hydroxide into the prepared sulfuric acid aqueous solution, and mix well to obtain the electrolyte solution. 7. the electrolytic preparation method of sulfur/carbon composite material as claimed in claim 1, is characterized in that described preparation method is: (1) Electrolyte is configured, and the electrolyte is mixed by the following raw materials in weight percentage: The purity of the sulfuric acid, thiourea and potassium hydroxide is chemically pure or higher than chemically pure; The preparation method of the electrolyte is as follows: take the sulfuric acid and water in the formulated amount to prepare a sulfuric acid aqueous solution, then add the formulated amount of thiourea and potassium hydroxide into the prepared sulfuric acid aqueous solution, and mix well to obtain the electrolyte; (2) With the graphite rod as the anode and the platinum sheet as the cathode, the electrolysis reaction is carried out under 3-15V direct current for 0.5-5 hours; the purity of the graphite rod is chemically pure or higher than chemically pure; (3) The precipitate produced by the electrolysis reaction is filtered by suction to take the filter cake, washed with water and dried to obtain the sulfur/carbon composite material.