CN106058173A - Graphene-like carbon material/sulphur composite cathode material for lithium-sulphur battery, and preparation method and application thereof - Google Patents

Abstract

The invention discloses a graphene-like carbon material/sulfur composite positive electrode material for lithium-sulfur batteries and a preparation method and application thereof. The positive electrode material is composed of a three-dimensional porous graphene-like carbon material with a micro-nano structure and simple sulfur. The invention has simple operation and low cost, and the prepared lithium-sulfur battery composite cathode material has a high sulfur utilization rate, and greatly improves the cycle performance of the lithium-sulfur battery.

Description

A graphene-like carbon material/sulfur composite cathode material for lithium-sulfur batteries and its preparation Methods and Applications

technical field

The invention relates to the field of preparation of positive electrode materials for lithium-sulfur batteries, in particular to a graphene-like carbon material/sulfur composite positive electrode material for lithium-sulfur batteries and its preparation method and application.

Background technique

With the widespread application of lithium-ion batteries in portable electronics, electric vehicles, and plug-in hybrid electric vehicles, there is an urgent need to develop batteries with higher energy density. As the specific capacity of lithium-ion battery cathode materials is limited, it is difficult to further increase the energy density of lithium-ion batteries. At the same time, increasing the energy density by increasing the voltage platform of the cathode material will bring safety problems. Changing the cathode material from the "deintercalation mechanism" to the "conversion reaction chemical mechanism" is expected to obtain materials with high specific capacity and specific energy. Elemental sulfur is one of the most promising positive electrode materials. Sulfur reacts completely with lithium metal to generate Li ₂ S. The battery reaction is S+2Li=Li ₂ S, which is a two-electron reaction process and does not involve the deintercalation reaction of lithium ions. Due to the low molecular weight of sulfur, the theoretical specific capacity of sulfur is as high as 1675mAh/g (almost 10 times that of LiFePO ₄ ), and the theoretical specific energy is as high as 2600Wh/Kg. In addition, elemental sulfur is abundant in nature, has low toxicity, and is inexpensive, so elemental sulfur is a very attractive cathode material.

However, lithium-sulfur batteries have problems such as low utilization of active materials, poor cycle performance, and rate performance needs to be further improved. In lithium-sulfur batteries, the active material sulfur material itself and the final discharge product Li ₂ S are insulators of electrons and ions, and the intermediate product polysulfides in the discharge process are easily dissolved in the electrolyte, which will cause irreversible loss of active materials and capacity. attenuation. For this reason, how to suppress the diffusion of polysulfides, improve the distribution of sulfur, and improve the conductivity of sulfur cathodes during cycling is the focus of research on sulfur-based cathode materials.

In order to solve these problems of lithium-sulfur batteries, elemental sulfur is usually loaded (loaded, attached, mixed, epitaxially grown, coated, etc.) into carbon materials with high specific surface area, high porosity and good electrical conductivity. , to form a composite positive electrode material to limit the dissolution of polysulfides into the electrolyte during the cycle and the various negative effects caused by it. Among them, three-dimensional porous graphene has the advantages of good electrical conductivity and large specific surface area, and can bridge between them to form a natural conductive network, which is conducive to electron conduction and lithium ion diffusion. In addition, the three-dimensional porous graphene has a large spatial gap, which has positive significance for stabilizing the electrode structure. However, the traditional three-dimensional structure graphene carbon material generally has a small specific surface area and limited sulfur loading capacity, resulting in low sulfur content and uneven distribution in the prepared composite positive electrode material. After being assembled into a battery for several cycles, there are still a lot of active substances Sulfur will dissolve from the surface of three-dimensional graphene, resulting in the loss of active materials, and it is difficult to further increase the energy density of lithium-sulfur batteries. If the sulfur content in the composite positive electrode material is further increased, a large amount of sulfur is distributed on the outer surface of the three-dimensional porous graphene, which will lead to a decrease in the conductivity of the electrode on the one hand; on the other hand, the polysulfides generated by this part of sulfur after the electrode reaction are easy to diffuse and shuttle. The irreversible loss of the active material is caused, and the electrochemical performance of the material cannot be well exerted.

Contents of the invention

The present invention aims at the common problems of low sulfur loading, low specific capacity of sulfur electrodes, low energy density and poor cycle performance of the three-dimensional graphene/sulfur composite cathode materials in the prior art, and provides a high sulfur loading, The active material sulfur utilization rate is high, the energy density is high, and the cycle performance is greatly improved when used in lithium-sulfur batteries. The graphene-like carbon material/sulfur composite cathode material for lithium-sulfur batteries.

Another object of the present invention is to provide a method for preparing a graphene-like carbon material/sulfur composite positive electrode material for lithium-sulfur batteries, which is simple in operation, low in cost and suitable for industrial production.

Another object of the present invention is to provide an application of the graphene-like carbon material/sulfur composite positive electrode material, and apply the graphene-like carbon material/sulfur composite positive electrode material as a lithium-sulfur battery positive electrode material to improve the cycle performance of lithium-sulfur batteries , improve energy density and active material sulfur utilization.

Technical scheme of the present invention:

A graphene-like carbon material/sulfur composite positive electrode material for a lithium-sulfur battery, the positive electrode material is composed of a three-dimensional porous graphene-like carbon material with a micro-nano structure and simple sulfur; the three-dimensional porous graphene-like carbon material with a micro-nano structure Graphene-like carbon material is obtained by mixing waste ion exchange resin with alkaline solution and then carbonizing at 500-1200°C;

The specific surface area of the three-dimensional porous graphene-like carbon material with micro-nano structure is 1500-3200m ² /g;

In the three-dimensional porous graphene-like carbon material with a micro-nano structure, the diameter of the micropores is ≤2nm, and the micropores account for 50%-80% of the entire pore structure.

The three-dimensional porous graphene-like carbon material with a micro-nano structure has a three-dimensional carbon skeleton, and the three-dimensional carbon skeleton has a micro-nano porous structure.

The porous carbon structure is dominated by micropores and the pore structures are interconnected, so that the porous graphene-like carbon material has a higher porosity and a larger specific surface area, which greatly increases the loading capacity of elemental sulfur (weight content reach 70-85%) and the contact area of elemental sulfur, which improves the electron transport rate and reaction area; at the same time, the entire three-dimensional carbon skeleton maintains the ion transport capacity and conductivity of the carbon material, and provides an effective conductive network and lithium ions for the entire positive electrode. Migration channels; at the same time, there are a large number of micropores on the three-dimensional carbon skeleton, and the nanoscale micropores reach 50-80% of the pore structure. The nanoscale network channels effectively inhibit the dissolution and diffusion loss of lithium polysulfide, greatly improving the activity of the positive electrode material The utilization efficiency of the material sulfur is conducive to the improvement of the cycle stability of the lithium-sulfur battery.

The present invention further includes the following preferred technical solutions:

In a preferred solution, the mass ratio of the waste ion exchange resin to the alkaline substance is 1:2˜1:10.

The alkaline substance is an alkaline substance in an alkaline solution.

In a preferred solution, the waste ion exchange resin is a macroporous anion exchange resin.

In a preferred solution, the alkaline solution is one or more of KOH, NaOH, K ₂ CO ₃ , Na ₂ CO ₃ , K ₃ PO ₄ or Na ₃ PO ₄ aqueous solution.

In a preferred solution, the concentration of the alkaline solution is 0.5-10 g/L.

The preparation method of the above-mentioned composite positive electrode material, the preparation process of the three-dimensional porous graphene-like carbon material with a micro-nano structure is: dispersing the waste ion exchange resin in an alkaline solution, stirring, reacting, and heating to 500-1200°C, the obtained three-dimensional porous graphene-like carbon material with micro-nano structure is compounded with elemental sulfur to obtain a composite positive electrode material.

In a preferred scheme, heat to 500-1200° C. for 5-20 hours.

In a preferred solution, the temperature is heated to 500-1200° C. at a heating rate of 5-15° C./min.

In a preferred scheme, the waste ion exchange resin is dispersed in the alkaline solution, stirred, and reacted for 1-5 hours.

In a preferred solution, the three-dimensional porous graphene-like carbon material with micro-nano structure is compounded with elemental sulfur by ball milling, high-temperature thermal melting, in-situ liquid deposition or liquid infiltration.

The present invention also relates to the application of the composite positive electrode material, and the graphene-like carbon material/sulfur composite positive electrode material is used as the positive electrode material for lithium-sulfur batteries.

Beneficial effects of the present invention:

For the first time, the present invention uses waste ion exchange resin combined with high-temperature carbonization to prepare a three-dimensional porous graphene-like carbon material with a micro-nano structure. The material is compounded with elemental sulfur to obtain a large sulfur-loading capacity that can effectively inhibit polysulfides from electrolysis. Graphene/sulfur composite cathode material with high sulfur utilization rate as active material.

When the obtained three-dimensional porous graphene-like carbon material with a micro-nano structure is compounded with elemental sulfur and used as a cathode material for a lithium-sulfur battery, the cycle stability of the lithium-sulfur battery can be greatly improved.

The present invention not only achieves the reuse of waste ion exchange resins, but also obtains an unexpected three-dimensional porous graphene-like carbon material with micro-nano structure through a simple reaction, and the composite application of this material and elemental sulfur as a lithium-sulfur battery When used as a positive electrode material, very good results have been obtained. The actual sulfur content is as high as 76.6wt.% through thermogravimetric testing, and it has very good cycle stability.

The invention provides a graphene-like carbon material/sulfur composite positive electrode material for a lithium-sulfur battery with high sulfur loading, high sulfur utilization rate as an active material, high energy density, and greatly improved cycle performance when used in a lithium-sulfur battery.

The raw materials used in the invention have wide sources and are cheap, and the preparation method is simple in operation and low in cost, and is suitable for industrialized production.

Description of drawings

[Fig. 1] is the SEM figure of the graphene-like carbon material/sulfur composite cathode material obtained in Example 1. It can be seen from the figure that sulfur is uniformly distributed throughout the composite cathode material.

[Fig. 2] is the first discharge curve of the graphene-like carbon material/sulfur composite cathode material obtained in Example 1.

[Fig. 3] is the 100-cycle cycle performance diagram of the graphene-like carbon material/sulfur composite positive electrode material obtained in Example 1 at a current density of 0.5C.

[Fig. 4] is the first discharge curve of the graphene-like carbon material/sulfur composite cathode material obtained in Example 2.

[ Fig. 5 ] is the 100-cycle cycle performance diagram of the graphene-like carbon material/sulfur composite positive electrode material obtained in Example 2 at a current density of 0.5C.

[Fig. 6] is the first discharge curve of the graphene-like carbon material/sulfur composite positive electrode material obtained in Example 3.

[ FIG. 7 ] is a 100-cycle cycle performance diagram of the graphene-like carbon material/sulfur composite positive electrode material obtained in Example 3 at a current density of 0.5C.

[ FIG. 8 ] is the first discharge curve of the graphene-like carbon material/sulfur composite positive electrode material obtained in Example 4.

[ FIG. 9 ] is a 100-cycle cycle performance diagram of the graphene-like carbon material/sulfur composite positive electrode material obtained in Example 4 at a current density of 0.5C.

[Fig. 10] Fig. 10 is the pore size distribution curve of the graphene-like carbon material/sulfur composite positive electrode material obtained in Example 1. It can be seen from the figure that the pore size of the sample is concentrated in the range of 0-2nm. The pore size distribution rate is about 78% in the range of 0-2nm.

detailed description

Below in conjunction with embodiment, the present invention will be described in further detail, but not limited to the scope of protection of the invention.

Example 1

Add 2.0 g of macroporous anion exchange resin into 2 L of KOH solution with a concentration of 3 g/L, and react with mechanical stirring at room temperature for 10 h. After filtering, it was transferred to a tube furnace, and under the protection of nitrogen, it was heated to 800°C at a heating rate of 10°C/min, and kept for 6 hours. After carbonization, a three-dimensional porous graphene-like carbon material with micro-nano structure was obtained. It is found by BET test that its specific surface area is 3002m ² /g, the diameter of micropores is ≤2nm, and the ratio of micropores to the whole pore structure is 70%. The three-dimensional porous graphene-like carbon material with micro-nano structure and sulfur powder were mixed by high-speed ball milling at a mass ratio of 2:8 for 2 hours, and then under the protection of argon, the temperature was raised to 155°C and kept for 24 hours to obtain a graphene-like carbon material /sulfur composite positive electrode material, its actual sulfur content is 72.5wt.% through thermogravimetric test.

The composite cathode material obtained in Example 1, conductive carbon black, and polyvinylidene fluoride (PVDF) were uniformly mixed according to a mass ratio of 8:1:1, and dispersed in a certain quality of NMP to make a slurry (solid content was 80wt %), and then coated on the aluminum foil current collector, and dried in vacuum at 60°C to obtain a lithium-sulfur battery positive electrode sheet.

The battery assembly and testing are as follows: the positive electrode sheet is punched into an electrode sheet with a diameter of 10mm, the metal lithium sheet is used as the negative electrode, and the electrolyte is 1M LiTFSI/DOL:DME (1:1), assembled in a glove box filled with argon. CR2025 button battery. Carry out constant current charge and discharge test at room temperature (25°C) with a current density of 0.5C (837mA/g), and the charge and discharge cut-off voltage is 1.5-3.0V. As shown in Figure 2 and Figure 3, the specific capacity of the first discharge is 1080mAh/g, and the specific capacity after 100 cycles is maintained at 710mAh/g, respectively maintaining a capacity retention rate of 65.7%.

It can be seen that the graphene-like carbon material/sulfur composite cathode material improves the cycle stability and active material utilization of lithium-sulfur batteries.

Example 2

Add 2.0 g of macroporous anion exchange resin into 2 L of NaOH solution with a concentration of 4 g/L, and react with mechanical stirring at room temperature for 10 h. After filtering, it was transferred to a tube furnace, and under the protection of nitrogen, it was heated to 900°C at a heating rate of 5°C/min, and kept for 8 hours. After carbonization, a three-dimensional porous graphene-like carbon material with a micro-nano structure was obtained. It is found by BET test that its specific surface area is 1870m ² /g, the pore diameter of micropores is ≤2nm, and the proportion of micropores to the whole pore structure is 50%. The three-dimensional porous graphene-like carbon material with micro-nano structure and sulfur powder were mixed by high-speed ball milling at a mass ratio of 2:8 for 2 hours, and then under the protection of argon, the temperature was raised to 155°C and kept for 24 hours to obtain a graphene-like carbon material /sulfur composite cathode material, the actual sulfur content is 70.9wt.% through thermogravimetric test. As shown in Figure 4 and Figure 5, the specific capacity of the first discharge is 955mAh/g, and the specific capacity after 100 cycles is maintained at 628mAh/g, respectively maintaining a capacity retention rate of 65.8%.

Example 3

Add 2.0 g of macroporous anion exchange resin into 3 L of Na ₂ CO ₃ solution with a concentration of 1.8 g/L, and react with mechanical stirring at room temperature for 24 h. After filtration, it was transferred to a tube furnace, and under the protection of nitrogen, it was heated to 1100°C at a heating rate of 15°C/min, and kept for 7 hours. After carbonization, a three-dimensional porous graphene-like carbon material with a micro-nano structure was obtained. It is found by BET test that the specific surface area of the material is 1666m ² /g, the pore diameter of the micropores is ≤2nm, and the micropores account for 60% of the whole pore structure. The three-dimensional porous graphene-like carbon material with micro-nano structure and sulfur powder are mixed by high-speed ball milling at a mass ratio of 2:8 for 2 hours, then heated to 155 °C under the protection of argon, and kept for 24 hours to obtain a graphene-like carbon material/ The actual sulfur content of the sulfur composite cathode material is 76.6wt.% through thermogravimetric testing. As shown in Figure 6 and Figure 7, the specific capacity of the first discharge is 1120mAh/g, and the specific capacity after 100 cycles is maintained at 710mAh/g, respectively maintaining a capacity retention rate of 63.4%.

Example 4

Add 2.0 g of macroporous anion exchange resin into 200 mL of KOH solution with a concentration of 0.2 g/L, and react with mechanical stirring at room temperature for 10 h. After filtering, it was transferred to a tube furnace, and under the protection of nitrogen, it was heated to 800°C at a heating rate of 10°C/min, and kept for 9 hours. After carbonization, a three-dimensional porous graphene-like carbon material with a micro-nano structure was obtained. It is found by BET test that the specific surface area of the material is 3002m ² /g, the pore diameter of the micropores is ≤2nm, and the micropores account for 70% of the whole pore structure. The three-dimensional porous graphene-like carbon material with micro-nano structure is dispersed in 200mL Na ₂ S solution with a mass concentration of 20%, and 200mL Na ₂ SO ₃ solution with a concentration of 10% is slowly added dropwise. The product separated by suction filtration after continuous stirring for 24 hours was placed in an oven at 80°C for 12 hours to obtain a graphene-like carbon material/sulfur composite positive electrode material. The actual sulfur content was 75.8wt.% by thermogravimetric test. As shown in Figure 8 and Figure 9, the specific capacity of the first discharge is 818mAh/g, and the specific capacity after 100 cycles is maintained at 652mAh/g, respectively maintaining a capacity retention rate of 79.7%.

Claims (10)

1. lithium-sulfur cell class graphene carbon material/sulfur composite positive pole, it is characterised in that this positive electrode is by having The three-dimensional porous class graphene carbon material of micro nano structure is composited with elemental sulfur；The described three-dimensional with micro nano structure Porous class graphene carbon material is obtained in 500-1200 DEG C of carbonization after being mixed with alkaline solution by discarded ion exchange resin；

The specific surface area of the described three-dimensional porous class graphene carbon material with micro nano structure is 1500～3200m²/g；

In the described three-dimensional porous class graphene carbon material with micro nano structure, the aperture≤2nm of micropore, micropore accounts for whole hole The 50%～80% of structure.

Composite positive pole the most according to claim 1, it is characterised in that described discarded ion exchange resin and basic species The mass ratio of matter is 1:2～1:10.

Composite positive pole the most according to claim 1 and 2, it is characterised in that described discarded ion exchange resin is big Pass anion exchange resin.

Composite positive pole the most according to claim 1, it is characterised in that described alkaline solution is KOH, NaOH, K₂CO₃、 Na₂CO₃、K₃PO₄Or Na₃PO₄One or more in aqueous solution.

5. according to the composite positive pole described in claim 1 or 4, it is characterised in that the concentration of described alkaline solution be 0.5～ 10g/L。

6. according to the preparation method of the composite positive pole described in any one of claim 1-5, it is characterised in that described in have micro- The preparation process of the three-dimensional porous class graphene carbon material of nanostructured is: discarded ion exchange resin is scattered in alkaline solution In, stirring, reaction, under an inert atmosphere, it is heated to 500～1200 DEG C of reactions, the three-dimensional with micro nano structure obtained is many Hole class graphene carbon material is combined with elemental sulfur again, obtains composite positive pole.

Preparation method the most according to claim 6, it is characterised in that with the heating rate of 5～15 DEG C/min, be heated to 500～1200 DEG C.

8. according to the preparation method described in claim 6 or 7, it is characterised in that discarded ion exchange resin is scattered in alkalescence In solution, stirring, react 1-5h.

Preparation method the most according to claim 6, it is characterised in that described in there is the three-dimensional porous class stone of micro nano structure Ink olefinic carbon material and elemental sulfur are melted by ball-milling method, high-temperature hot, liquid phase deposition or liquid infiltration method are combined in situ.

10. the application of the composite positive pole described in any one of claim 1-5, it is characterised in that by described class graphene carbon Material/sulfur composite positive pole is applied as lithium sulfur battery anode material.