CN104600251A - Lithium-sulfur battery positive electrode and preparation method thereof - Google Patents

Abstract

The invention discloses a positive electrode of a lithium-sulfur battery and a preparation method thereof. The preparation method is to uniformly mix the active material of the positive electrode, a conductive agent, and a binder as an active material layer and coat it on a current collector, and obtain a positive electrode matrix after drying; Conductive agent, binder and dispersant uniformly mixed conductive paste prepared as a protective layer coated on the outer surface of the positive electrode base, after drying to obtain a lithium-sulfur battery positive electrode. The preparation method is simple and easy to operate, easy to control, and suitable for industrial production; in the positive electrode of the lithium-sulfur battery prepared by it, the protective layer can play the role of conducting electricity, intercepting sulfur and stabilizing the electrode structure, thereby effectively improving the capacity of the lithium-sulfur battery , rate and cycle stability, and the thickness of the protective layer is easy to control, which can minimize the impact on the sulfur content of the positive electrode.

Description

A kind of positive electrode of lithium-sulfur battery and preparation method thereof

technical field

The invention relates to the technical field of lithium-sulfur batteries, in particular to a lithium-sulfur battery positive electrode and a preparation method thereof.

Background technique

With the growth of population and economy and the improvement of people's living standards, the demand for energy is increasing year by year, and the environmental pollution caused by the use of fossil energy is also becoming more and more serious. In order to reduce dependence on fossil energy, new energy technologies based on renewable energy are rapidly developed and applied. As a cheap and rechargeable battery with high energy density (the theoretical energy density of lithium-sulfur battery is as high as 2600W h kg ^-1 ), lithium-sulfur battery is considered to be one of the most attractive battery systems in the future. However, lithium-sulfur battery technology also faces many problems from materials and systems: first, the active material sulfur has a high resistivity (5×10 ^-30 S cm ^-1 , 25°C); Volume expansion will occur in the process, leading to the destruction of the structure of the sulfur electrode; again, the polysulfides formed during the cycle are easy to dissolve in the electrolyte, the electrode active material gradually decreases, and the specific capacity decreases. These problems directly lead to lower utilization of active materials, lower cycle life, and lower capacity.

In order to solve the above problems, many scientific and technological workers have conducted a lot of research in recent years, and have successively published many patents on lithium-sulfur batteries. Some of these methods focus on the development of sulfur composite materials with nanostructure and good performance to improve discharge capacity, cycle life and current efficiency, but most of the sulfur content in the composite materials will be significantly reduced. Other methods improve the utilization of active materials by designing new battery configurations, for example, Arumugam Manthiram et al [Su Y S, Manthiram A. Lithium–sulfur batteries with a microporous carbon paper as a bifunctional interlayer. [J] Nature Communications , 2012, 3: 1166.] A porous conductive interlayer is added between the pole piece and the diaphragm to prevent the shuttle of polysulfide compounds and achieve the purpose of improving the electrochemical performance of lithium-sulfur batteries. However, the addition of the interlayer will increase the quality of the positive electrode. resulting in low energy density, and the manufacturing process of the interlayer is complicated, which is not conducive to industrial production; the Chinese patent application "a lithium-sulfur battery with an adsorption layer" (application number: 201110092817.2) proposed by Tu Muchun et al. A layer of adsorption layer is coated on the separator to achieve the purpose of adsorbing polysulfides and improving the electrochemical performance of the lithium-sulfur battery. However, the method of coating the adsorption layer on the separator is difficult and may cause a short circuit of the battery. In addition, the Chinese patent application "a multi-layer structure composite positive electrode for lithium-sulfur secondary battery and its preparation method" (application number: 201210538945.X) proposed by Zhang Kai et al. sputters a layer of The purpose of the conductive film is to conduct electricity and intercept sulfur, but this method is complicated and the cost is high.

Contents of the invention

The technical problem to be solved in the present invention is to overcome the deficiencies in the prior art, and provide a lithium-sulfur battery positive electrode and a preparation method thereof. The lithium-sulfur battery positive electrode can effectively improve the capacity, rate and cycle stability of the lithium-sulfur battery. The method is simple and easy to operate, easy to control and suitable for industrial production.

In order to solve the problems of the technologies described above, the present invention adopts the following technical solutions:

A method for preparing a positive electrode of a lithium-sulfur battery, comprising uniformly mixing a positive electrode active material, a conductive agent, and a binder in a dispersant as an active material layer, coating it on a current collector, and obtaining a positive electrode matrix after drying; The conductive paste prepared by uniformly mixing the additive and the dispersant is used as a protective layer and coated on the outer surface of the positive electrode substrate, and the positive electrode of the lithium-sulfur battery is obtained after drying. The active material layer is preferably coated on the current collector by scraping or spraying.

In the above preparation method, preferably, the protective layer has a thickness of 150 nm to 150 μm.

In the above preparation method, preferably, the mass of the conductive agent in the conductive paste is 10-90% of the total mass of the conductive agent and the binder, and the mass of the dispersant is 45-95% of the total mass of the conductive paste.

In the above preparation method, preferably, the conductive agent is one or more of conductive carbon black, acetylene black, graphite powder, porous carbon spheres, carbon nanotubes, carbon fibers, graphene, and biomass carbon; The agent is one or more of polyvinyl alcohol, polytetrafluoroethylene, polyacrylic acid, carboxymethyl fiber, polyolefin, polyvinylidene fluoride, polyurethane, SBR rubber, fluorinated rubber, and polyvinylidene fluoride; The dispersant is one or more of water, methanol, ethanol, isopropanol, tetrahydrofuran, acetonitrile, dimethylformamide, dimethylacetamide, and N-methylpyrrolidone.

In the above preparation method, preferably, the conductive agent, binder and dispersant are uniformly mixed by one or more methods of physical grinding, mechanical ball milling and mechanical stirring to prepare conductive paste.

The above-mentioned preparation method, preferably, the method for coating the outer surface of the positive electrode substrate with the conductive paste is scraping, brushing, spraying, screen printing, roll coating, gravure printing and laser printing. kind of.

In the above preparation method, preferably, the current collector is one of aluminum foil, carbon film, aluminum mesh and nickel mesh. The aforementioned aluminum foil is preferably corroded aluminum foil or carbon-coated aluminum foil.

In the above preparation method, preferably, the active material layer comprises 50-90% of the positive active material, 5-30% of the conductive agent and 5-20% of the binder by weight percentage; the positive active material is a simple One or more of sulfur, sulfide, and sulfur-containing compounds.

In the above preparation method, preferably, the sulfide is one or more of inorganic sulfides, organic sulfides, and sulfur-containing complexes; the sulfur-containing compound is a sulfur-carbon composite material, a sulfur polymer composite material, One or more of organic sulfides, metal sulfides and their composite materials, and the mass percentage of sulfur in the sulfur-containing composite is 5% to 100%, wherein the carbon in the sulfur-carbon composite material is porous carbon , carbon nanotubes, graphene or carbon fiber, the polymer in the sulfur-polymer composite material is one or more of polyaniline, polypyrrole, polythiophene, polydopamine, polyethylene oxide, and the metal sulfide is iron sulfide, One or more of nickel sulfide, cobalt sulfide, tin sulfide, copper sulfide, titanium sulfide. The mass percent content of sulfur in the above-mentioned sulfur composite is preferably 5% to 95%; the sulfur-carbon composite material is preferably a porous carbon-sulfur composite, a carbon nanotube-sulfur composite, a graphene-sulfur composite or a carbon fiber-sulfur composite Composite; Sulfur polymer composites are preferably polyaniline-sulfur composites, polypyrrole-sulfur composites, polythiophene-sulfur composites.

The present invention also provides a lithium-sulfur battery cathode prepared by the above-mentioned preparation method.

Compared with the prior art, the present invention has the advantages that: the present invention coats a layer of conductive paste containing conductive agent, binder and dispersant on the positive electrode sheet of the traditional lithium-sulfur battery, and forms a protective layer after the conductive paste is dried. , the protective layer containing the conductive agent plays the role of conducting electricity and intercepting sulfur, which not only further increases the conductivity of the electrode, but also prevents polysulfide compounds from dissolving in the electrolyte during the cycle, which can significantly inhibit the "shuttle effect"; at the same time, The cohesiveness of the adhesive in the protective layer can also play a role in stabilizing the electrode structure; in addition, the protective layer formed after the conductive paste is dried has a porous structure, which is conducive to the infiltration of the electrolyte. The protective layer is formed by coating, which is simple, easy to operate, has the characteristics of controllable coating thickness, less material, and basically does not change the quality of the pole piece, so that the total sulfur content can be increased as much as possible. The battery assembled by using the positive electrode of the lithium-sulfur battery of the invention has the advantages of high capacity, good rate and cycle stability, and the like.

In summary, the present invention is a method for preparing a positive electrode of a lithium-sulfur battery with good electrochemical performance, which is simple in operation, easy to implement, and easy to control. The lithium-sulfur battery cathode prepared by the method can significantly improve the discharge specific capacity, rate performance and cycle stability of the lithium-sulfur battery.

Description of drawings

FIG. 1 is a schematic diagram of the structure of the positive electrode of the lithium-sulfur battery of the present invention.

FIG. 2 is a graph showing cycle performance curves of lithium-sulfur battery cathodes obtained in Example 1 and Comparative Example.

illustration:

1. Current collector; 2. Active material layer; 3. Protective layer.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

Comparative example:

Disperse elemental sulfur, conductive carbon black and polyvinylidene fluoride in N-methylpyrrolidone (NMP) at a mass ratio of 7:2:1, and then scrape-coat it on the aluminum foil current collector after sufficient mechanical stirring. Vacuum-dried at 60°C for 24h, and directly pressed into an electrode sheet with a diameter of 10mm.

Using the above-prepared electrode sheet as the positive electrode and the lithium sheet as the negative electrode, assemble it into a CR2025 button cell in an argon-filled glove box. Electrochemical performance tests were carried out under the conditions. The test results are shown in the lower curve in Figure 2. It can be seen that the specific capacity of the battery at the first discharge is 790mAh/g, and the specific capacity after 100 cycles is 424mAh/g.

Example 1:

Disperse elemental sulfur, conductive carbon black and polyvinylidene fluoride in N-methylpyrrolidone (NMP) at a mass ratio of 7:2:1, and after sufficient mechanical stirring, scrape-coat it on the aluminum foil current collector 1 , and vacuum-dried at a temperature of 60° C. for 24 hours to prepare a positive electrode substrate with an active material layer 2 .

Disperse conductive carbon black and polyvinylidene fluoride in N-methylpyrrolidone (NMP) at a mass ratio of 8:2, use mechanical stirring to mix evenly to obtain a conductive paste, and gently brush the conductive paste on the surface with a brush. A protective layer 3 is formed on the positive electrode substrate with an active material layer 2, and after vacuum drying at a temperature of 60° C., a lithium-sulfur battery positive electrode is obtained. The structure is shown in FIG. 1 , and the thickness of the protective layer 3 is 35 μm. Then press it into an electrode sheet with a diameter of 10mm.

Using the electrode sheet prepared above as the positive electrode and the lithium sheet as the negative electrode, assemble it into a CR2025 button cell in an argon-filled glove box. The electrochemical performance test was carried out under the condition of C. The test results are shown in the upper curve in Figure 2. It can be seen that the specific capacity of the battery for the first discharge is 1255mAh/g, and the specific capacity after 100 cycles is 811mAh/g. Compared with the comparative example, the lithium-sulfur After the positive electrode of the battery, the discharge specific capacity, rate performance and cycle stability of the lithium-sulfur battery are significantly improved.

Example 2:

Mix elemental sulfur, conductive carbon black, and polyvinyl alcohol evenly in a mass ratio of 6:3:1, and after sufficient mechanical stirring, scrape-coat it on the aluminum foil current collector 1, and dry it in vacuum at 70°C for 24 hours , to prepare a positive electrode substrate with an active material layer 2 .

Disperse conductive carbon black and polyvinylidene fluoride in N-methylpyrrolidone (NMP) at a mass ratio of 7:3, grind them by hand until uniformly mixed to obtain a protective layer slurry, and gently scrape the protective layer slurry A protective layer 3 is formed on the positive electrode substrate with an active material layer 2, and after vacuum drying at a temperature of 80°C, a lithium-sulfur battery positive electrode is obtained, wherein the thickness of the protective layer 3 is 20 μm, and then pressed into an electrode sheet with a diameter of 10 mm .

With the electrode sheet prepared above as the positive electrode and the lithium sheet as the negative electrode, the electrochemical performance test was carried out by the method in Example 1. The first discharge specific capacity of the battery was measured to be 1231mAh/g, and the specific capacity after 100 cycles was 783mAh/g .

Example 3:

Disperse the carbon nanotube-sulfur composite material, conductive carbon black and polyacrylic acid in water at a mass ratio of 8:1:1, grind them by hand until they are evenly mixed, and scrape-coat them on the aluminum foil current collector 1. vacuum drying at high temperature for 24 hours to prepare a positive electrode substrate with an active material layer 2 .

Disperse carbon nanotubes and polyvinylidene fluoride in N-methylpyrrolidone (NMP) at a mass ratio of 6:4, grind them manually until uniformly mixed to obtain a protective layer slurry, and spray the protective layer slurry Gently spray the material on the positive electrode substrate with the active material layer 2 to form a protective layer 3, and after vacuum drying at a temperature of 50°C, a lithium-sulfur battery positive electrode is obtained, wherein the thickness of the protective layer 3 is 15 μm, and then pressed into a diameter of 10mm electrode pads.

With the electrode sheet prepared above as the positive electrode and the lithium sheet as the negative electrode, the electrochemical performance test was carried out by the method in Example 1. The first discharge specific capacity of the battery was measured to be 1121mAh/g, and the specific capacity after 100 cycles was 763mAh/g .

Example 4:

Disperse the sulfur-polyaniline composite material, cassava carbon and polyvinylidene fluoride in N-methylpyrrolidone (NMP) at a mass ratio of 5:3:2, and after sufficient mechanical stirring, scrape-coat on the carbon film The current collector 1 was vacuum dried at a temperature of 70° C. for 24 hours to prepare a positive electrode substrate with an active material layer 2 .

Disperse carbon nanotubes and polyacrylic acid in N-methylpyrrolidone (NMP) at a mass ratio of 8:2, grind them manually until they are evenly mixed to obtain a protective layer slurry, and gently scrape the protective layer slurry on an active A protective layer 3 is formed on the positive electrode substrate of the material layer 2, and after vacuum drying at a temperature of 60° C., the positive electrode of a lithium-sulfur battery is obtained, wherein the thickness of the protective layer 3 is 80 μm, and then pressed into an electrode sheet with a diameter of 10 mm.

The electrode sheet prepared above was used as the positive electrode, and the lithium sheet was used as the negative electrode. The electrochemical performance test was carried out by the method in Example 1. The specific capacity of the battery was 1220mAh/g for the first discharge, and the specific capacity after 100 cycles was 781mAh/g.

Claims (10)

1. a preparation method for lithium-sulphur cell positive electrode, is characterized in that: positive active material, conductive agent, binding agent are mixed in dispersant as active material layer coating on a current collector, obtain positive electrode substrate after drying; The electrocondution slurry be made up of conductive agent, binding agent and dispersant Homogeneous phase mixing is coated in the outer surface of positive electrode substrate as protective layer, after drying, obtains lithium-sulphur cell positive electrode.

2. the preparation method of lithium-sulphur cell positive electrode according to claim 1, is characterized in that: the thickness of described protective layer is 150 nm ~ 150 μm.

3. the preparation method of lithium-sulphur cell positive electrode according to claim 1, is characterized in that: in described electrocondution slurry, the quality of conductive agent is 10 ~ 90% of conductive agent and binding agent gross mass, and the quality of dispersant is 45 ~ 95% of electrocondution slurry gross mass.

4. the preparation method of lithium-sulphur cell positive electrode according to claim 1, is characterized in that: described conductive agent is one or more in conductive carbon black, acetylene black, graphite powder, porous charcoal ball, carbon nano-tube, carbon fiber, Graphene, biomass carbon; Described binding agent is one or more in polyvinyl alcohol, polytetrafluoroethylene, polyacrylic acid, carboxymethyl cellulose, TPO, polyvinylidene fluoride, Polyurethane, SBR rubber, Viton, Kynoar; Described dispersant is one or more in water, methyl alcohol, ethanol, isopropyl alcohol, oxolane, acetonitrile, dimethyl formamide, dimethylacetylamide, 1-METHYLPYRROLIDONE.

5. the preparation method of lithium-sulphur cell positive electrode according to claim 1, is characterized in that: described conductive agent, binding agent and dispersant make electrocondution slurry by one or more the mode Homogeneous phase mixing in physical grinding, mechanical ball milling, mechanical agitation.

6. the preparation method of lithium-sulphur cell positive electrode according to claim 1, is characterized in that: the method that described electrocondution slurry is coated in the outer surface of positive electrode substrate is the one in knife coating, spread coating, spraying process, silk screen print method, rolling method, intaglio printing and laser printing method.

7. the preparation method of lithium-sulphur cell positive electrode according to claim 1, is characterized in that: described collector is the one in aluminium foil, carbon film, aluminium net and nickel screen.

8. the preparation method of lithium-sulphur cell positive electrode according to claim 1, is characterized in that: by weight percentage described active material layer comprise the positive active material of 50 ~ 90%, the conductive agent of 5 ~ 30% and 5 ~ 20% binding agent; Described positive active material be elemental sulfur, sulfide, containing one or more in sulfur compound.

9. the preparation method of lithium-sulphur cell positive electrode according to claim 8, is characterized in that: described sulfide is one or more in inorganic sulphide, organic sulfur compound, sulfur-bearing complex, described is sulphur carbon composite containing sulfur compound, sulphur polymer composites, organic sulfur compound, one or more in metal sulfide and composite material thereof, and be 5% ~ 100% containing the mass percentage of sulphur in sulfur compound, wherein, carbon in sulphur carbon composite is porous carbon, carbon nano-tube, Graphene or carbon fiber, polymer in sulphur polymer composites is polyaniline, polypyrrole, polythiophene, poly-dopamine, one or more in polyethylene glycol oxide, metal sulfide is iron sulfide, nickel sulfide, cobalt sulfide, artificial gold, copper sulfide, one or more in titanium sulfide.

10. the lithium-sulphur cell positive electrode that the preparation method according to any one of a claim 1 to 9 obtains.