CN106033815A - Lithium-sulfur battery positive electrode, its preparation method and application - Google Patents

Abstract

The invention discloses a lithium-sulfur battery positive electrode, which comprises: a porous metal material adopted as the skeleton and the main electric conduction network; a positive electrode material filled in the skeleton, wherein the positive electrode material comprises sulfur, nitrogen-doped graphene, and a carbon material; and a secondary electric conduction network mainly formed by an electric conduction agent doped inside the positive electrode material. The invention further discloses a preparation method and applications of the lithium-sulfur battery positive electrode. According to the present invention, the foamed nickel is adopted as the positive electrode skeleton of the lithium-sulfur battery positive electrode, and the nitrogen-doped graphene is introduced, such that the electric conductivity and the sulfur loading amount of the positive electrode can be effectively improved so as to effectively optimize the battery performance. In addition, the lithium-sulfur battery positive electrode process is simple and controllable, and the large-scale production is easily achieved.

Description

Lithium-sulfur battery positive electrode, its preparation method and application

technical field

The invention relates to a lithium-sulfur battery, in particular to a lithium-sulfur battery positive electrode, a preparation method and application thereof.

Background technique

With the development of science and technology and the continuous improvement of people's living standards, people's demand for resources is also getting higher and higher. At the end of 2012, the data released by the National Bureau of Statistics showed that the per capita energy consumption was 293.8kg standard coal, and the per capita electricity consumption was 460.4KWh, of which electricity consumption accounted for 80% of the total energy consumption.

Lithium-sulfur batteries use metal lithium as the negative electrode and elemental sulfur as the positive electrode. Its theoretical energy density is as high as 2600Whkg ^-1 , which is more than five times that of traditional lithium-ion batteries. At the same time, sulfur, which is used as the active material of the positive electrode, is not only low in cost, non-toxic, but also contains Rich. Therefore, it is considered to be one of the most attractive power battery systems at present. However, due to the problems of low utilization rate of active sulfur, low Coulombic efficiency, and serious reversible capacity fading in lithium-sulfur batteries, the actual energy density that can be achieved is 400Whkg ^-1 . When charging and discharging greater than 0.2C, the capacity loss is relatively large.

Current research mainly focuses on the modification and modification of electrode materials and separators. The electrode material restricts the polysulfides to a fixed range through coating, porous materials, etc., preventing dissolved Li ₂ S _n from escaping from the positive electrode, thereby preventing the "shuttle" phenomenon. The diaphragm prevents the diffusion of polysulfide ions by regulating the size of the diaphragm pore size, surface modification, etc., and blocks the polysulfide ions on the positive side, thereby preventing the "shuttle" phenomenon. In addition to the influence of the "shuttle" phenomenon on the performance of lithium-sulfur batteries, the conductivity of the electrodes is also the main reason. In order to improve the conductivity of the pole piece, the conductivity of the pole piece is usually improved by adding a conductive agent, but the effect is limited. For example, the electrode materials of existing lithium-sulfur batteries have good performance when the sulfur loading is lower than 4mg/cm ² , and when the sulfur loading is greater than 4mg/cm ² , or even greater than 100mg/cm ² , the performance will become very poor. Poor, magnification performance is not good.

Contents of the invention

The main purpose of the present invention is to provide a novel lithium-sulfur battery positive electrode, which has good electrical conductivity and high sulfur loading capacity, and can effectively improve battery performance, thereby overcoming the deficiencies in the prior art.

Another object of the present invention is to provide a method for preparing the positive electrode of the lithium-sulfur battery.

Another object of the present invention is to provide the application of the positive electrode of the lithium-sulfur battery.

In order to realize the aforementioned object of the invention, the technical solutions adopted in the present invention include:

A lithium-sulfur battery positive electrode comprising:

Porous metal material as the skeleton and the main conductive network;

A positive electrode material filled in the framework, the positive electrode material includes sulfur, nitrogen-doped graphene, and carbon materials other than nitrogen-doped graphene;

And, a secondary conductive network mainly formed by the conductive agent doped in the positive electrode material.

Further, the sulfur loading capacity of the positive electrode sheet is 4-200 mg/cm ² .

Further, the porous metal material is particularly preferably nickel foam.

A method for preparing a positive electrode of a lithium-sulfur battery, comprising:

Mix sulfur, nitrogen-doped graphene, and carbon materials other than nitrogen-doped graphene at a mass ratio of 40-95:5-10:0-50, and react in a sealed reactor at 150-300°C for more than 12 hours , forming the positive electrode material;

Take the positive electrode material, conductive agent and binder and mix uniformly according to the mass ratio of 60-95:0-30:1-10 to form a slurry, and then put the slurry on the pretreated nickel foam to make the slurry evenly distributed in nickel foam with a sulfur load of 4-200 mg/cm ² , then dry at 50-100° C., and then dry at 50-100° C. for more than 24 hours under vacuum.

Further, the carbon material includes any one or a combination of two or more of carbon black, acetylene black, activated carbon, single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene, but is not limited thereto.

Further, the conductive agent includes any one or a combination of two or more of carbon black, acetylene black, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene and nitrogen-doped graphene, but is not limited thereto .

Further, the binder includes PVDF (polyvinylidene fluoride), SBR (styrene-butadiene rubber)+CMC (carboxymethyl cellulose), PVA (polyvinyl alcohol), PEO (polyethylene oxide), LA132 polyacrylic acid Any one or a combination of two or more, but not limited thereto.

Further, the pretreated nickel foam is nickel foam after hydrogen reduction and acetone cleaning.

A lithium-sulfur battery positive electrode prepared by any of the aforementioned methods.

A lithium-sulfur battery, comprising the aforementioned positive electrode of the lithium-sulfur battery.

Further, the lithium-sulfur battery further includes a negative electrode and an electrolyte.

Wherein, the negative electrode includes a lithium sheet.

Wherein, the electrolytic solution includes an electrolyte and a solvent.

Further, the electrolyte includes lithium bistrifluoromethanesulfonylimide, lithium nitrate, Li ₂ Sx, lithium bis(trifluoromethylsulfonyl)imide or lithium trifluoromethanesulfonate, lithium hexafluorophosphate, and is not limited to this.

Further, the solvent includes a combination of any two or more of tetrahydrofuran, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and 1,3-dioxolane, but is not limited thereto.

Further, the lithium-sulfur battery is a button, pouch or cylindrical battery.

Compared with the prior art, the advantages of the present invention include: the positive electrode of the lithium-sulfur battery adopts foamed nickel as the positive electrode framework, abandons the traditional current collectors such as aluminum foil, and fills the positive electrode material inside the foamed nickel, because the foamed nickel has good conductivity , has a certain catalytic effect, and is filled in the entire positive electrode, which can form a conductive network and effectively improve the conductivity inside the positive electrode. In addition, nitrogen-doped graphene is added to the positive electrode material, which not only has excellent electrical conductivity, but also reflects A certain sulfur fixation effect can greatly improve the overall performance of the electrode, thereby effectively optimizing the performance of the battery. In addition, the preparation process of the positive electrode of the lithium-sulfur battery is simple and controllable, which is conducive to large-scale production.

detailed description

In view of many deficiencies in the prior art, the inventor of this case was able to propose the technical solution of the present invention after long-term research and practice, which mainly improves the performance of the battery by increasing the sulfur loading capacity, so as to achieve the purpose of practical application.

Generally speaking, the present invention uses nickel foam as the main conductive network, conductive agent as the secondary conductive network, and nitrogen-doped graphene is added to improve the conductivity of the electrode and finally improve the performance of the entire battery.

In a more specific embodiment of the present invention, the preparation process of the positive electrode of the lithium-sulfur battery of the present invention may include:

Sulfur, nitrogen-doped graphene and carbon materials (one or more of carbon black, acetylene black, activated carbon, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene and others) are pressed (40-95): (5-10): (0-50) are mixed in a mass ratio, reacted in a sealed reactor at 150-300° C. for 12 hours to form a positive electrode material. Take a certain amount of positive electrode material and add conductive agent (one or more of carbon black, acetylene black, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene and nitrogen-doped graphene) and binder (PVDF , SBR+CMC, PVA, PEO, LA132 polyacrylic acid), the mass ratio is 60-95:0-30:1-10. Stir to form a slurry, and apply it on the treated foamed nickel (hydrogen reduction, acetone cleaning), so that the slurry is evenly distributed in the foamed nickel, and the sulfur loading is 4-200mg/cm ² . Dry at 50-100°C, dry in vacuum at 50-100°C for 24 hours, and die-cut pole pieces.

Further, the process of assembling the lithium-sulfur battery using the positive electrode of the lithium-sulfur battery may include: immersing the aforementioned pole piece in the electrolyte solution for 1-24 hours, and assembling the battery. Among them, the negative electrode is a lithium sheet, and the electrolyte in the electrolyte is lithium bis(trifluoromethanesulfonyl)imide, lithium nitrate, Li ₂ Sx (x=3～9), lithium bis(trifluoromethylsulfonyl)imide [LiN (CF ₃ SO ₂ ) ₂ ] or lithium triflate (CF ₃ SO ₃ Li), lithium hexafluorophosphate. The solvent is a mixture of two or more of tetrahydrofuran, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and 1,3-dioxolane, and is assembled into a button, a soft pack and a column battery respectively.

The technical solution of the present invention will be further explained below in conjunction with several embodiments.

Example 1

800mg of sulfur, 100mg of nitrogen-doped graphene and 100mg of carbon black were reacted in a sealed reactor at 150°C for 12 hours to form the positive electrode material. Take 900mg of the above positive electrode material, add 50mg of acetylene black conductive agent and 50mg of PVDF binder, add the solvent NMP, stir to form a slurry, and apply it on the nickel foam that has been reduced by hydrogen at 750°C for 30 minutes, so that the slurry is evenly distributed in the nickel foam. Dry at 50°C, dry in vacuum at 50°C for 24 hours, and die-cut pole pieces. Soak the pole pieces in the electrolyte for 24 hours to assemble the battery. Negative pole lithium sheet, 1,3-dioxane/ethylene glycol dimethyl ether (volume ratio 1:1) of 1M bistrifluoromethanesulfonylimide lithium contains 1wt% lithium nitrate and Li ₂ Sx (1M ) is the electrolyte, which are assembled into button, soft pack and columnar batteries respectively. Electrochemical tests are carried out, the charge and discharge voltage range is 1.7-2.8V, and the specific capacity is calculated based on the mass of active sulfur. The sulfur loading capacity is 170mg/cm ² , and the discharge specific capacities are 1010mAhg ^-1 , 1000mAhg ^-1 , and 950mAhg ^-1 , respectively.

Example 2

500mg of sulfur, 100mg of nitrogen-doped graphene and 400mg of multi-walled carbon nanotubes were reacted in a sealed reactor at 300°C for 12 hours to form the positive electrode material. Take 900mg of the above-mentioned positive electrode material, add 50mg of graphene conductive agent and 50mg of PVA binder, add solvent water, stir to form a slurry, and apply it on the nickel foam reduced by hydrogen at 750°C for 30 minutes, so that the slurry is evenly distributed in the nickel foam. Dry at 90°C, dry in vacuum at 100°C for 12 hours, and die-cut pole pieces. Soak the pole pieces in the electrolyte for 12 hours to assemble the battery. Negative pole lithium sheet, 1,3-dioxane/ethylene glycol dimethyl ether (volume ratio 1:1) of 1M bistrifluoromethanesulfonylimide lithium contains 1wt% lithium nitrate and Li ₂ Sx (1M ) is the electrolyte, which are assembled into button, soft pack and columnar batteries respectively. Electrochemical tests are carried out, the charge and discharge voltage range is 1.7-2.8V, and the specific capacity is calculated based on the mass of active sulfur. The sulfur loading capacity is 50mg/cm ² , and the discharge specific capacity is 1100mAhg ^-1 , 1080mAhg ^-1 , 1020mAhg ^-1 .

Example 3

800mg of sulfur, 100mg of nitrogen-doped graphene and 100mg of carbon black were reacted in a sealed reactor at 250°C for 12 hours to form the positive electrode material. Take 900mg of the above-mentioned positive electrode material, add 50mg of acetylene black conductive agent and 50mg of LA132 binder, add solvent water, stir to form a slurry, and apply it on the nickel foam reduced by hydrogen at 750°C for 60 minutes, so that the slurry is evenly distributed in the nickel foam. Dry at 90°C, dry in vacuum at 100°C for 12 hours, and die-cut pole pieces. Soak the pole pieces in the electrolyte for 2 hours and assemble the battery. The negative electrode is a lithium sheet, and 1M bistrifluoromethanesulfonimide lithium 1,3-dioxane/ethylene glycol dimethyl ether (volume ratio 1:1) is used as the electrolyte, which are respectively assembled into buttons, soft pack and cylindrical batteries. Electrochemical tests are carried out, the charge and discharge voltage range is 1.7-2.8V, and the specific capacity is calculated based on the mass of active sulfur. The sulfur load is 10mg/cm ² , and the discharge specific capacity is 1200mAhg ^-1 , 1210mAhg ^-1 , 1180mAhg ^-1 .

Example 4

800mg of sulfur, 100mg of nitrogen-doped graphene and 100mg of carbon black were reacted in a sealed reactor at 200°C for 12 hours to form the positive electrode material. Take 900mg of the above positive electrode material, add 50mg of acetylene black conductive agent and 50mg of PVDF binder, add solvent NMP, stir to form a slurry, and apply it on the foamed nickel after cleaning with acetone, so that the slurry is evenly distributed in the foamed nickel. Dry at 50°C, dry in vacuum at 70°C for 12 hours, and die-cut pole pieces. Soak the pole pieces in the electrolyte for 12 hours to assemble the battery. The negative electrode is a lithium sheet, and 1M lithium trifluoromethanesulfonate 1,3-dioxane/ethylene glycol dimethyl ether (volume ratio 1:1) is used as the electrolyte, which are assembled into buttons, soft bags and Cylindrical battery. Electrochemical tests are carried out, the charge and discharge voltage range is 1.7-2.8V, and the specific capacity is calculated based on the mass of active sulfur. The sulfur load is 10mg/cm ² , and the discharge specific capacity is 1200mAhg ^-1 , 1210mAhg ^-1 , 1180mAhg ^-1 .

Example 5

800mg of sulfur, 100mg of nitrogen-doped graphene and 100mg of carbon black were reacted in a sealed reactor at 280°C for 12 hours to form the positive electrode material. Take 900mg of the above positive electrode material, add 50mg of acetylene black conductive agent and 50mg of PVDF binder, add solvent NMP, stir to form a slurry, and apply it on the foamed nickel after cleaning with acetone, so that the slurry is evenly distributed in the foamed nickel. Dry at 50°C, dry in vacuum at 70°C for 12 hours, and die-cut pole pieces. Soak the pole pieces in the electrolyte for 12 hours to assemble the battery. The negative electrode is a lithium sheet, and ethylene glycol dimethyl ether and tetrahydrofuran (volume ratio 1:1) of 1M lithium hexafluorophosphate are used as electrolytes, which are assembled into button, soft pack and cylindrical batteries respectively. Electrochemical tests are carried out, the charge and discharge voltage range is 1.7-2.8V, and the specific capacity is calculated based on the mass of active sulfur. The sulfur load is 10mg/cm ² , and the specific discharge capacity is 900mAhg ^-1 , 92mAhg ^-1 , 870mAhg ^-1 .

It should be understood that the above-mentioned embodiments are only to illustrate the technical concept and features of the present invention, the purpose of which is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and not to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention shall fall within the protection scope of the present invention.

Claims (10)

1. a lithium-sulphur cell positive electrode, it is characterised in that comprise:

As skeleton and the porous metal material of leading electric network, described porous metal material includes nickel foam；

Being filled in described intraskeletal positive electrode, described positive electrode comprises element sulphur, nitrogen-doped graphene and denitrogenates doping Material with carbon element outside Graphene；

And, the secondary conductive network mainly formed by the conductive agent mixed in positive electrode.

Lithium-sulphur cell positive electrode the most according to claim 1, it is characterised in that:

Described material with carbon element includes appointing in carbon black, acetylene black, activated carbon, SWCN, multi-walled carbon nano-tubes, Graphene One or more combination,

Described conductive agent includes carbon black, acetylene black, SWCN, multi-walled carbon nano-tubes, Graphene and nitrogen-doped graphene In the combination of any one or more.

Lithium-sulphur cell positive electrode the most according to claim 1 and 2, it is characterised in that the load sulfur content of described positive pole is 4-200mg/cm²。

4. the preparation method of a lithium-sulphur cell positive electrode, it is characterised in that including:

By sulfur, nitrogen-doped graphene, denitrogenate the material with carbon element outside doped graphene and mix by the mass ratio of 40～95:5-10:0～50, In sealed reactor, react more than 12h in 150-300 DEG C, form positive electrode；

Take described positive electrode, conductive agent and binding agent and be uniformly mixed to form slurry by the mass ratio of 60-95:0-30:1-10, then By in pretreated for slurry nickel foam, make slurry be uniformly distributed in nickel foam, and make the load sulfur content of described nickel foam be 4-200mg/cm², then at 50-100 DEG C of drying, the most under vacuum in 50-100 DEG C of dry more than 24h.

The preparation method of lithium-sulphur cell positive electrode the most according to claim 4, it is characterised in that:

Described material with carbon element includes appointing in carbon black, acetylene black, activated carbon, SWCN, multi-walled carbon nano-tubes, Graphene One or more combination,

Described conductive agent includes carbon black, acetylene black, SWCN, multi-walled carbon nano-tubes, Graphene and nitrogen-doped graphene In the combination of any one or more,

Described binding agent include in PVDF, SBR+CMC, PVA, PEO, LA132 polyacrylic acid any one or two kinds of with On combination.

The preparation method of lithium-sulphur cell positive electrode the most according to claim 4, it is characterised in that described pretreated nickel foam For the nickel foam after hydrogen reducing and/or acetone clean.

7. the lithium-sulphur cell positive electrode prepared by method according to any one of claim 4-6.

8. a lithium-sulfur cell, it is characterised in that comprise claim 1-3, lithium-sulphur cell positive electrode according to any one of 7.

9. lithium-sulfur cell as claimed in claim 8, it is characterised in that also comprising negative pole and electrolyte, wherein said negative pole includes Lithium sheet, described electrolyte comprises electrolyte and solvent, and described electrolyte comprises double trifluoromethanesulfonimide lithium, lithium nitrate, Li₂Sx、 Two (trimethyl fluoride sulfonyl) imine lithiums or trifluoromethyl sulfonic acid lithium, lithium hexafluoro phosphate, described solvent includes oxolane, ethylene glycol The most two or more combination in dimethyl ether, tetraethyleneglycol dimethyl ether and 1,3-dioxolanes.

10. the lithium-sulfur cell as according to any one of claim 8-9, it is characterised in that it is button, Soft Roll or prismatic battery.