CN103515646A - Lithium-sulfur battery with conductive adsorption layer, and application of conductive polymer film - Google Patents

Abstract

The invention discloses a lithium-sulfur battery with a conductive adsorption layer, and an application of a conductive polymer film. The lithium-sulfur battery comprises a sulfur-containing positive electrode sheet, a separation film, and a lithium negative-electrode sheet. A conductive absorption layer is arranged between the sulfur-containing positive electrode sheet and the separation film. The application comprises that the conductive polymer film prepared from a conductive polymer, a conductive agent, and an adhesive is arranged as a conductive absorption layer between the sulfur-containing positive electrode sheet and the separation film of the lithium-sulfur battery, such that the lithium-sulfur battery is prepared. The prepared lithium-sulfur battery has the characteristics of high specific capacity, high coulombic efficiency, and long service life. The conductive polymer film has the advantages of low raw material cost, simple preparation method, and suitability for industrialized productions.

Description

Application of a lithium-sulfur battery with a conductive adsorption layer and a conductive polymer film

technical field

The invention relates to a lithium-sulfur battery with a conductive adsorption layer and the application of a conductive polymer film, and belongs to the technical field of lithium-sulfur battery systems.

Background technique

Sulfur was first proposed in 1962 as a positive electrode material for batteries, and then the earliest Li-S batteries appeared. When applied to a secondary lithium battery, assuming that Li ₂ S is completely generated during the discharge process, the theoretical specific capacity of sulfur is 1672mAh g ^-1 , the theoretical discharge voltage is 2.287V, and the theoretical energy density of the electrode of the secondary lithium-sulfur battery is 2600Wh kg ^-1 , is currently known as the secondary lithium battery system with the highest energy density except lithium oxygen.

There are two discharge plateaus in the discharge process of a typical secondary lithium-sulfur battery. The first discharge platform is 2.4～2.1V, during which elemental sulfur is transformed into high-valence polysulfide ion S _n ^2- (5≤n≤8); the second discharge platform is 2.1～1.5V, during this process The middle and high valence state polysulfide ions are continuously reduced to low valence state polysulfide ions S _n ^2- (2≤n≤4) and Li ₂ S. The research results show that the intermediate polysulfide ions produced during the charge and discharge process, especially the high-valent polysulfide ions, are easily soluble in the organic electrolyte. When they diffuse to the lithium negative electrode and produce irreversible lithium sulfide, they will seriously affect the secondary lithium. Cycle performance of sulfur batteries. If the intermediate product polysulfide ion migrates to the negative electrode to react with metal lithium for self-discharge, and then migrates to the positive electrode, the internal circulation of the secondary lithium-sulfur battery will occur, the so-called "shuttle" phenomenon, which will make the battery Coulombic efficiency decreases. In addition, the insulating properties of elemental sulfur and its discharge products will lead to low utilization of active materials in electrodes. Due to the difference in density between sulfur and lithium polysulfide, the volume of the electrode active material changes greatly during the charging and discharging process, which easily causes problems such as deterioration of the electrode structure. These problems restrict the performance improvement of secondary lithium-sulfur batteries.

In recent years, in order to solve these problems of sulfur electrodes, people have carried out many useful explorations to solve these problems from the perspectives of preparing carbon-sulfur composite materials and improving electrode structure design.

At present, elemental sulfur is usually loaded (loaded, attached, mixed, epitaxially grown, coated, etc.) into various carbon materials with high specific surface area, high porosity and good electrical conductivity to form composite materials to limit During the cycle, polysulfides dissolve into the electrolyte and various negative effects caused by it. For example, composite materials of sulfur/hollow carbon spheres (Angew.Chem.Int.Ed., 2011,50,5904-5908.), composite materials of sulfur/carbon nanotubes (Nano Letter, 2011,11,4288-4294. ), composites of sulfur/mesoporous spheres (Angew.Chem.Int.Ed.2012,51,3591–3595), composites of sulfur/graphene oxide (J.Am.Chem.Soc.2011,133,18522 –18525.) and other carbon-sulfur composite materials, which greatly improve the electrochemical performance of lithium-sulfur batteries. However, limited by the conductivity, pore volume, and specific surface area of carbon materials, there are generally problems such as low coulombic efficiency, high side reactions, and short cycle life; and there are problems of relatively complicated fabrication and high cost, making lithium-sulfur secondary batteries Difficult to realize industrialized production.

Contents of the invention

The present invention aims at the problems of low coulombic efficiency, short cycle life due to side reactions, and high cost of use in lithium-sulfur batteries with sulfur-containing positive electrodes in the prior art. A lithium-sulfur battery with the characteristics of long length and low cost. The battery is simple to manufacture, low in cost, and can be produced on a large scale.

Another object of the present invention is to provide the application of conductive polymer film, the lithium-sulfur battery that the conductive polymer film is arranged between the sulfur-containing positive plate of lithium-sulfur battery and separator as conductive adsorption layer has high specific capacity, High coulombic efficiency and long cycle life, and low cost of use.

The invention provides a lithium-sulfur battery with a conductive adsorption layer, comprising a sulfur-containing positive electrode sheet, a separator, and a lithium negative electrode sheet, and a conductive adsorption layer is arranged between the sulfur-containing positive electrode sheet and the separator; the conductive adsorption layer is A conductive polymer film with a thickness of 0.1-2.0mm is prepared by conducting the polymer, the conductive agent and the adhesive according to the mass ratio of 5-8:1-4:1-4.

The conductive polymer film is prepared by the following method: the conductive polymer, the conductive agent and the adhesive are mixed in a solvent to form a slurry with a solid content of 20-80%. ℃ vacuum drying 10 ~ 20h, that is.

The conductive polymer is one or more of polyaniline, polypyrrole, polythiophene, polyacene, polyparaphenylene vinylene, polyacetylene and polyparaphenylene vinylene.

The conductive agent is one or more of conductive carbon black, carbon nanotubes, carbon fibers, graphite, and graphene.

The adhesive is one or more of polytetrafluoroethylene, polyacrylic acid, polyvinylidene fluoride and sodium alginate.

The present invention also provides an application of a conductive adsorption polymer film, the application is that the conductive polymer film made of a conductive polymer, a conductive agent and an adhesive is arranged between the sulfur-containing positive electrode sheet and the diaphragm of a lithium-sulfur battery It is used as a conductive adsorption layer in the preparation of lithium-sulfur batteries.

The mass ratio of the conductive polymer, conductive agent and adhesive is 5-8:1-4:1-4.

The conductive polymer is one or more of polyaniline, polypyrrole, polythiophene, polyacene, polyparaphenylene vinylene, polyacetylene, polyparaphenylene vinylene; the conductive agent is conductive carbon black , one or more of carbon nanotubes, carbon fibers, graphite, and graphene; the adhesive is one or more of polytetrafluoroethylene, polyacrylic acid, polyvinylidene fluoride, and sodium alginate.

The thickness of the conductive polymer film is 0.1-2.0mm.

The conductive polymer film is prepared by the following method: the conductive polymer, the conductive agent and the adhesive are mixed in a solvent to form a slurry with a solid content of 20-80%. ℃ vacuum drying 10 ~ 20h, that is.

The solvent is one or more of deionized water, ethanol, and NMP.

The electrolyte that can be used in the lithium-sulfur battery of the present invention is a non-aqueous electrolyte, and the solvent of the electrolyte is a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, or dioxolane and tetraethylene glycol Methyl ether mixed solvent, electrolyte solute is lithium hexafluorophosphate or lithium trifluoromethanesulfonate.

The diaphragm is a porous diaphragm made of a material selected from polytetrafluoroethylene, polypropylene, polyethylene and polyvinylidene fluoride.

The mass percent content of active material sulfur in the sulfur-containing positive electrode sheet is 10%-90%.

The preparation method of the lithium-sulfur battery with conductive adsorption layer of the present invention comprises the following steps:

(1) Preparation of conductive polymer film: Mix the conductive polymer, conductive agent and adhesive in the solvent at a mass ratio of 5 to 8:1 to 4:1 to 4, add a small amount of deionized water and ethanol, Heat and stir in a water bath for 1-5 hours to form a slurry with a solid content of 20-80%, and then repeatedly roll the slurry on a double-roll machine to form a film with a thickness of 0.1-2.0mm, and place it in a vacuum drying oven at 50- Dry at 100°C for 10-20 hours to obtain a conductive polymer film;

(2) Preparation of lithium-sulfur battery: Place the conductive polymer film, separator, lithium negative electrode and foamed nickel mesh obtained in step (1) on the sulfur-containing positive electrode in sequence, inject the electrolyte, and then press it into one body. After sealing, A lithium-sulfur battery is obtained.

Beneficial effects of the present invention: In the present invention, for the first time, a conductive polymer film made by mixing a conductive polymer, a conductive agent and an adhesive is placed between the sulfur-containing positive electrode sheet and the diaphragm of a lithium-sulfur battery as a conductive adsorption layer. The obtained lithium-sulfur battery has high specific capacity, excellent coulombic efficiency and cycle stability. In the research of lithium-sulfur batteries, the present invention unexpectedly finds that: the conductive polymer film prepared by a certain mass ratio of conductive polymer, conductive agent and binder is arranged between the sulfur-containing positive electrode sheet and the diaphragm, and the conductive polymer film On the one hand, it plays an auxiliary role in the conductivity of the sulfur-containing cathode, greatly increasing the conductivity of the sulfur cathode; on the other hand, it can well absorb polysulfides dissolved in the electrolyte and inhibit the "shuttle effect"; at the same time, the conductivity The polymer film has good elasticity and flexibility, which can buffer the volume expansion of the sulfur cathode during charging and discharging, thus effectively improving the Coulombic efficiency and cycle performance of the sulfur-lithium battery. Research shows that: under the current density of 0.2C (335mA/g), the lithium-sulfur battery of the present invention has a discharge specific capacity of 1350-1560mAh/g for the first time, and a discharge specific capacity of 860-960mAh/g after 100 cycles. between, and the Coulombic efficiency is nearly 100%. In addition, the raw material of the conductive polymer film is cheap, the preparation method is simple, and it can be produced industrially.

Description of drawings

[Fig. 1] is the SEM figure of the conductive polymer polyaniline (PANI) adsorption layer that embodiment 1 obtains.

[ Fig. 2 ] is a schematic diagram of the structure of the lithium-sulfur battery obtained in Example 1.

[Figure 3] It is a comparison chart of the 100-cycle cycle performance of the lithium-sulfur battery obtained in Example 1 and the lithium-sulfur battery without a conductive adsorption layer at a current density of 0.2C (335mA/g).

[ FIG. 4 ] is a rate performance diagram of the lithium-sulfur battery obtained in Example 1.

Detailed ways

The following examples are intended to further illustrate the present invention, but not to limit the protection scope of the present invention.

Example 1

Preparation of conductive polymer polyaniline (PANI) adsorption layer:

Conductive polymer PANI, conductive carbon black and polytetrafluoroethylene (PTFE) were mixed uniformly in deionized water at a mass ratio of 8:1:1, heated and stirred in a water bath for 2 hours to form a slurry with a solid content of 80%, and then The slurry was rolled repeatedly on a roller machine to form a film with a thickness of 0.5mm, dried in a vacuum oven at 70°C for 12h, and then cut into small discs with a diameter of 1.0cm to obtain a conductive polymer PANI adsorption layer. The SEM image of the conductive polymer PANI adsorption layer is shown in Figure 1.

Preparation of lithium-sulfur battery:

Mix elemental sulfur, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) solvent at a mass ratio of 8:1:1 to form a slurry with a solid content of 30% as The positive electrode material is coated on the aluminum foil positive current collector, dried at 60°C in a vacuum oven for 12 hours, and then pressed into a positive electrode sheet with a diameter of 1.0 cm; the conductive polymer PANI adsorption layer is placed on the positive electrode sheet and the porous diaphragm In between, a lithium sheet as the negative electrode was placed on the other side of the porous diaphragm, and pressed into one body to prepare a CR2025 lithium-sulfur secondary button battery with a conductive adsorption layer. The internal structure of the battery is shown in Figure 2. After the battery is made, it is tested. The battery charge and discharge cut-off voltage is 1.5~3.0V (vs. Li/Li ⁺ ), and the charge and discharge specific capacity is calculated based on the elemental sulfur active material. The current density is 0.2C (335mA/g). Doing the charge-discharge cycle test, the specific capacity of the first discharge is 1560mAh/g, the specific capacity after 100 cycles is 950mAh/g, and the Coulombic efficiency is nearly 100%, which reflects a very good cycle performance. The 100-cycle cycle performance comparison diagram of the lithium-sulfur battery with the PANI adsorption layer is shown in Figure 3. In addition, the rate performance test was carried out on it, as shown in Figure 4, it can be found from the figure that its rate performance is also very excellent.

Example 2

Preparation of conductive polymer polypyrrole (PPy) adsorption layer:

Mix conductive polymer PPy, carbon nanotubes and PVDF in NMP at a mass ratio of 5:4:1, heat and stir in a water bath for 1 hour to form a slurry with a solid content of 50%, and then repeatedly place the slurry on a double-roll machine Rolled into a film with a thickness of 0.1mm, dried in a vacuum oven at 60°C for 20h, and then cut into small discs with a diameter of 1.2cm to obtain the conductive polymer PPy adsorption layer.

Preparation of lithium-sulfur battery:

Mix elemental sulfur, SP, and PVDF in NMP solvent at a mass ratio of 7:2:1 to form a slurry with a solid content of 30% as the positive electrode material, which is coated on the aluminum foil positive electrode current collector, and placed in a vacuum drying oven for 60 After drying at ℃ for 12 hours, it was pressed into a positive electrode piece with a diameter of 1.0 cm; the conductive polymer PPy adsorption layer was placed between the positive electrode piece and the porous diaphragm, and a lithium sheet as the negative electrode was placed on the other side of the porous diaphragm, and pressed into one , to prepare a CR2025 lithium-sulfur secondary button battery with a conductive adsorption layer. After the battery is made, it is tested. The battery charge and discharge cut-off voltage is 1.5~3.0V (vs. Li/Li ⁺ ), and the charge and discharge specific capacity is calculated based on the elemental sulfur active material. The current density is 0.2C (335mA/g). In the charge-discharge cycle test, the specific capacity of the first discharge is 1450mAh/g, and the specific capacity after 100 cycles is 900mAh/g, and the Coulombic efficiency is nearly 100%, reflecting very good cycle performance.

Example 3

Preparation of conductive polymer poly(paraphenylene vinylene) (PEDOT) adsorption layer:

Mix conductive polymer PEDOT, carbon fiber and PAA in deionized water at a mass ratio of 5:1:4, heat and stir in a water bath for 5 hours to form a slurry with a solid content of 60%, and then repeatedly grind the slurry on a double-roll machine Press it into a film with a thickness of 1.5mm, dry it in a vacuum oven at 100°C for 10h, and then cut it into small discs with a diameter of 1.5cm to obtain the conductive polymer PEDOT adsorption layer.

Preparation of lithium-sulfur battery:

Mix elemental sulfur, SP, and PVDF in NMP solvent at a mass ratio of 6:2:2 to form a slurry with a solid content of 30% as the positive electrode material, which is coated on the aluminum foil positive electrode current collector, and placed in a vacuum drying oven for 60 After drying at ℃ for 12 hours, it was pressed into a positive electrode sheet with a diameter of 1.0 cm; the conductive polymer PEDOT adsorption layer was placed between the positive electrode sheet and the porous diaphragm, and a lithium sheet as the negative electrode was placed on the other side of the porous diaphragm, and pressed into one , to prepare a CR2025 lithium-sulfur secondary button battery with a conductive adsorption layer. After the battery is made, it is tested. The battery charge and discharge cut-off voltage is 1.5~3.0V (vs. Li/Li ⁺ ), and the charge and discharge specific capacity is calculated based on the elemental sulfur active material. The current density is 0.2C (335mA/g). In the charge-discharge cycle test, the specific capacity of the first discharge is 1510mAh/g, the specific capacity after 100 cycles is 920mAh/g, and the Coulombic efficiency is nearly 100%, reflecting very good cycle performance.

Example 4

Preparation of conductive polymer poly(p-phenylene vinylene) (PPv) adsorption layer:

Mix the conductive polymer PPv, graphite and sodium alginate uniformly in a de-alcoholized medium at a mass ratio of 7:2:1, heat and stir in a water bath for 2 hours to form a slurry with a solid content of 70%, and then put the slurry on a roller machine Repeated rolling into a film with a thickness of 0.5mm, dried in a vacuum oven at 50°C for 15h, and then cut into small discs with a diameter of 1.3cm to obtain the conductive polymer PPv adsorption layer.

Preparation of lithium-sulfur battery:

Mix elemental sulfur, SP, and PVDF uniformly in NMP solvent at a mass ratio of 5:3:2 to form a slurry with a solid content of 30% as the positive electrode material, which is coated on the aluminum foil positive electrode current collector, and placed in a vacuum drying oven for 60 After drying at ℃ for 12 hours, it was pressed into a positive electrode piece with a diameter of 1.0 cm; the conductive polymer PPv adsorption layer was placed between the positive electrode piece and the porous diaphragm, and a lithium sheet as the negative electrode was placed on the other side of the porous diaphragm, and pressed into one , to prepare a CR2025 lithium-sulfur secondary button battery with a conductive adsorption layer. After the battery is made, it is tested. The battery charge and discharge cut-off voltage is 1.5~3.0V (vs. Li/Li ⁺ ), and the charge and discharge specific capacity is calculated based on the elemental sulfur active material. The current density is 0.2C (335mA/g). Doing the charge-discharge cycle test, the specific capacity of the first discharge is 1480mAh/g, the specific capacity after 100 cycles is 880mAh/g, and the Coulombic efficiency is nearly 100%, which reflects a very good cycle performance.

Example 5

Preparation of conductive polymer polyacetylene (PAC) adsorption layer:

Mix conductive polymer PAC, graphene and PAA in NMP at a mass ratio of 6:2:2, heat and stir in a water bath for 3 hours to form a slurry with a solid content of 20%, and then repeatedly grind the slurry on a pair of rollers Press it into a film with a thickness of 1.0 mm, dry it in a vacuum oven at 80°C for 12 hours, and then cut it into small discs with a diameter of 1.4 cm to obtain a conductive polymer PAC adsorption layer.

Preparation of lithium-sulfur battery:

Mix elemental sulfur, SP, and PVDF in NMP solvent at a mass ratio of 6:3:1 to form a slurry with a solid content of 30% as the positive electrode material, which is coated on the aluminum foil positive electrode current collector, and placed in a vacuum drying oven for 60 After drying at ℃ for 12 hours, it was pressed into a positive electrode piece with a diameter of 1.0 cm; the conductive polymer PAC adsorption layer was placed between the positive electrode piece and the porous diaphragm, and a lithium sheet as the negative electrode was placed on the other side of the porous diaphragm, and pressed into one , to prepare a CR2025 lithium-sulfur secondary button battery with a conductive adsorption layer. After the battery is made, it is tested. The battery charge and discharge cut-off voltage is 1.5~3.0V (vs. Li/Li ⁺ ), and the charge and discharge specific capacity is calculated based on the elemental sulfur active material. The current density is 0.2C (335mA/g). Doing the charge-discharge cycle test, the specific capacity of the first discharge is 1350mAh/g, the specific capacity after 100 cycles is 860mAh/g, and the Coulombic efficiency is nearly 100%, which reflects a very good cycle performance.

Example 6

Preparation of conductive polymer polythiophene (Pth) adsorption layer:

Mix conductive polymer Pth, graphene and PTFE in deionized water at a mass ratio of 7:1:2, heat and stir in a water bath for 4 hours to form a slurry with a solid content of 40%, and then repeatedly place the slurry on a roller machine Rolled into a film with a thickness of 0.8mm, dried in a vacuum oven at 90°C for 16h, and then cut into small discs with a diameter of 1.5cm to obtain a conductive polymer Pth adsorption layer.

Preparation of lithium-sulfur battery:

Mix elemental sulfur, SP, and PVDF in NMP solvent at a mass ratio of 8:1:1 to form a slurry with a solid content of 30% as the positive electrode material, which is coated on the aluminum foil positive electrode current collector, and placed in a vacuum drying oven for 60 After drying at ℃ for 12 hours, it was pressed into a positive electrode sheet with a diameter of 1.0 cm; the conductive polymer Pth adsorption layer was placed between the positive electrode sheet and the porous diaphragm, and a lithium sheet as the negative electrode was placed on the other side of the porous diaphragm, and pressed into one , to prepare a CR2025 lithium-sulfur secondary button battery with a conductive adsorption layer. After the battery is made, it is tested. The battery charge and discharge cut-off voltage is 1.5~3.0V (vs. Li/Li ⁺ ), and the charge and discharge specific capacity is calculated based on the elemental sulfur active material. The current density is 0.2C (335mA/g). In the charge-discharge cycle test, the specific capacity of the first discharge is 1510mAh/g, the specific capacity after 100 cycles is 920mAh/g, and the Coulombic efficiency is nearly 100%, reflecting very good cycle performance.

Claims (10)

1. a lithium-sulfur cell with conduction adsorption layer, comprises sulfur-bearing positive plate, barrier film, cathode of lithium sheet, it is characterized in that, is provided with conduction adsorption layer between sulfur-bearing positive plate and barrier film; The conducting polymer thin film that described conduction adsorption layer is is 0.1～2.0mm by conducting polymer, conductive agent and the bonding agent thickness that make 5～8:1～4:1～4 in mass ratio.

2. lithium-sulfur cell as claimed in claim 1, it is characterized in that, described conducting polymer thin film prepares by the following method: it is 20～80% slurry that conducting polymer, conductive agent and bonding agent are mixed to form to solid content in solvent, roll after film forming, at 50～100 ℃ of vacuumize 10～20h, obtain.

3. lithium-sulfur cell as claimed in claim 2, is characterized in that, described conducting polymer is polyaniline, polypyrrole, polythiophene, coalescence benzene, p-phenylene vinylene, polyacetylene, gathers one or more during styrene is supportted.

4. lithium-sulfur cell as claimed in claim 2, is characterized in that, described conductive agent is one or more in conductive black, carbon nano-tube, carbon fiber, graphite, Graphene.

5. lithium-sulfur cell as claimed in claim 2, is characterized in that, described bonding agent is one or more in polytetrafluoroethylene, polyacrylic acid, polyvinylidene fluoride, sodium alginate.

6. an application for conducting polymer thin film, is characterized in that, the conducting polymer thin film that conducting polymer, conductive agent and bonding agent are made is arranged on the preparation that is applied to lithium-sulfur cell between the sulfur-bearing positive plate of lithium-sulfur cell and barrier film as conduction adsorption layer.

7. application as claimed in claim 6, is characterized in that, described conducting polymer, conductive agent and bonding agent mass ratio are 5～8:1～4:1～4.

8. application as claimed in claim 7, is characterized in that, described conducting polymer is polyaniline, polypyrrole, polythiophene, coalescence benzene, p-phenylene vinylene, polyacetylene, gathers one or more during styrene is supportted; Described conductive agent is one or more in conductive black, carbon nano-tube, carbon fiber, graphite, Graphene; Described bonding agent is one or more in polytetrafluoroethylene, polyacrylic acid, polyvinylidene fluoride, sodium alginate.

9. application as claimed in claim 6, is characterized in that, described conducting polymer thin film thickness is 0.1～2.0mm.

10. the application as described in claim 6～9 any one, it is characterized in that, described conducting polymer thin film prepares by the following method: it is 20～80% slurry that conducting polymer, conductive agent and bonding agent are mixed to form to solid content in solvent, roll after film forming, at 50～100 ℃ of vacuumize 10～20h, obtain.

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