CN106169561B - A kind of sulphur system anode composite pole piece includes its battery and preparation method thereof - Google Patents

Abstract

The invention discloses a sulfur-based composite positive electrode, a battery containing the same and a preparation method thereof. The sulfur-based composite electrode provided by the present invention is a binder-free positive electrode, and its preparation process is as follows: the lamellar carbon is dispersed in a solvent to form a dispersion, and then the sulfur-based material, carbon fluoride and polyacrylonitrile are added to the The dispersion liquid is mixed evenly to prepare a positive electrode active material slurry, which is coated on the aluminum foil of the current collector, and dried to prepare a composite positive electrode piece for a sulfur-based battery. The advantages of the binder-free sulfur-based composite positive electrode provided by the present invention are: the lamellar carbon material is coated on the surface of the sulfur-based material and carbon fluoride to form a buffer layer; polyacrylonitrile builds a stable structure in the positive electrode, ( 1) It can buffer the expansion and contraction of electrode materials; (2) It can limit the effective active material of the positive electrode; (3) The active ratio of the positive electrode is high; (4) The cost of raw materials is low, and it can be mass-produced.

Description

A sulfur-based composite positive electrode, a battery containing the same, and a preparation method thereof

technical field

The invention belongs to the technical field of chemical power sources, and particularly relates to a binder-free sulfur-based positive electrode piece, a preparation method thereof, and a battery to which it is applied.

Background technique

Since its industrialization in the 1990s, lithium-ion batteries have become the most practical chemical power source, and there is a trend to further expand the scope of application in power batteries and energy storage batteries. However, the lithium-ion battery is limited by the low lithium storage capacity of the existing electrodes, especially the positive electrode (the actual capacity of lithium cobalt oxide is about 140mAh/g, and the theoretical capacity of graphite carbon negative electrode is 372mAh/g), and there is limited space for further improving the energy density. With the development of a new generation of electric vehicles, unmanned aerial vehicles, electronic products, military aerospace vehicles and other fields, the demand for high specific energy energy storage batteries in military and civilian industries is becoming more and more urgent.

Sulfur is a solid-state cathode material with a higher theoretical specific capacity, and when matched with a higher-capacity light metal anode, a higher theoretical specific energy of the battery can be obtained. For example, lithium and sulfur are combined to form a lithium-sulfur battery, and the theoretical specific energy reaches ~2600Wh/kg, which is one of the secondary battery systems with the highest specific energy solid-state electrode. By using other light metals in combination with sulfur, higher theoretical specific energy can also be obtained. As a positive electrode material, carbon fluoride has high specific capacity, stable discharge platform, long storage life and wide operating temperature range. The lithium primary battery using it as a positive electrode material is the first solid positive lithium battery as a commercial product. The application in sodium batteries has greatly broadened the application range of carbon fluoride materials.

These two materials, although both have high specific capacity, have a common problem, the active material is easily diffused into the liquid electrolyte during the cycle. For the sulfur-based positive electrode, the use of liquid electrolyte will cause the sulfur discharge product lithium polysulfide to dissolve in the electrolyte and diffuse into the negative electrode to react with it, resulting in a shuttle effect during charging, resulting in low charging efficiency and large self-discharge. At the same time, a layer of insulator will be deposited on the surface of the negative electrode, which will deteriorate the battery performance, especially the rapid capacity decay. For the carbon fluoride cathode, when it is cycled in a sodium battery, some active fluorine will dissolve in the electrolyte, resulting in rapid capacity decay. If an electrode is constructed, the advantages of high specific capacity of sulfur-based cathode and carbon fluoride cathode can be used at the same time, and the effective active material generated during the cycle can be confined, the cycle stability of this type of battery can be effectively improved, and there is potential space for development. huge.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the problems that polysulfides are dissolved in the electrolyte during the cycle process of the existing sulfur-based positive electrode, resulting in the formation of the flying shuttle effect and the low Coulomb efficiency, and the problem that the active material of the carbon fluoride positive electrode is dissolved in the sodium battery, Provided are a preparation method of a binder-free sulfur-based composite positive electrode sheet, and a battery related thereto.

In order to achieve the above purpose, the present invention provides a method for preparing a sulfur-based composite positive electrode piece: first, disperse the lamellar carbon material in a solvent to form a lamellar carbon dispersion; then mix the sulfur-based material, fluorocarbon , polyacrylonitrile is added to the lamellar carbon dispersion to prepare a positive electrode slurry; finally, the above slurry is coated on the surface of the current collector and dried to obtain a sulfur-based composite positive electrode plate. The sheet-like carbon material is coated on the surface of sulfur-based materials and carbon fluoride to form a buffer layer, which can buffer the expansion and contraction of electrode materials; polyacrylonitrile builds a stable structure in the positive electrode, which can limit the effective active material of the positive electrode . The lamellar carbon in the positive electrode is coated on the surface of the positive electrode active material to form a "sandwich"-like structure, while the polyacrylonitrile effectively "glues" the components in the positive electrode together, and the two have a synergistic effect. .

Preferably, the lamellar carbon material is selected from one of graphene (GNS), graphene oxide (GO), nitrogen-doped graphene, sulfur-doped graphene, or phosphorous-sulfur-doped graphene or the like or variety.

Preferably, the mass fraction of carbon in the lamellar carbon dispersion liquid is 3-6%.

Preferably, the solvent is one of dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), dimethylsulfoxide (DMSO), N-methylpyrrolidone (NMP), etc. A sort of.

Preferably, the sulfur-based material in the positive electrode active material is selected from one or more of elemental sulfur and its sulfur-carbon composite materials, organic sulfides, inorganic sulfides, etc. In the positive electrode, its mass fraction is 30-80%.

Preferably, the fluorinated carbon material of the positive electrode active material is one or more of fluorinated graphite, fluorinated carbon nanotubes, fluorinated graphene, fluorinated carbon fibers, fluorinated carbon nanodiscs, fluorinated coke, etc., The fluorocarbon molar ratio is 0.33~1.2, and in the positive electrode, its mass ratio is 30~80%.

Preferably, the polyacrylonitrile (PAN) has a particle size of 20 nm to 40 μm and a mass fraction of 3 to 5%.

Preferably, the prepared sulfur-based composite positive electrode is vacuum-dried at 70-90° C. for 12-24 hours.

The present invention also provides a battery assembled with the sulfur-based composite positive electrode prepared by the method provided by the present invention, comprising:

Negative electrode: selected from Group IA, Group IIA, aluminum and its alloys or intermetallic compounds of the periodic table of elements.

Electrolyte: The electrolyte contains an organic solvent and an electrolyte salt. The organic solvent is selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), methyl acetate (MA), diethylene glycol Dimethyl ether, triglyme, tetraglyme, propylene carbonate (PC), ethylene carbonate (EC), acetonitrile, dimethyl sulfoxide, dimethylformamide, dimethicone Methylacetamide, gamma-butyrolactone (GBL), N-methyl-pyrrolidone (NMP), ethyl methyl carbonate, vinylene carbonate, dioxolane, dioxane, dimethoxyethane , or a mixture thereof. The electrolyte salt is selected from salts of _MM'F6 or _MM'F4 , wherein M is the same metal as at least one metal in the negative electrode, and M' is an element selected from trivalent phosphorus, arsenic, antimony and boron , such as lithium salts LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiClO ₄ , LiAlCl ₄ , LiGaCl ₄ , LiC(SO ₂ CF ₃ ) ₃ , LiB(C ₆ H ₄ O ₂ ) ₂ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiB(C ₂ O ₄ ) ₂ , Li(SO ₃ CF ₃ ) and salts of their mixtures, other batteries and so on. The concentration of the salt in the organic solvent is 0.3~2M.

Diaphragm: one of polypropylene, polyethylene, polyamide, polyvinylidene chloride (PVC), polyvinylidene fluoride (PVDF), glass fiber, non-woven fabric, etc.

The beneficial effects of the present invention include: (1) preparing a binder-free pole piece, improving the energy density of the battery, (2) being able to be used as a positive electrode material for different metal-based batteries, (3) using lamellar carbon materials and polymer Acrylonitrile, in the process of charging and discharging, can alleviate the shuttle effect during the cycle due to the firm "adhesive" effect of polyacrylonitrile and the coating effect of the lamellar carbon material on the sulfur-based positive electrode material, which can improve the cycle of the battery. Performance (4) Low cost of raw materials.

Description of drawings

FIG. 1 is a flow chart of the preparation process of the sulfur-based composite positive electrode piece of the present invention.

FIG. 2 is a microscopic topography diagram of the sulfur-based composite positive electrode piece of the present invention.

3 is a discharge curve of the sulfur-based composite positive electrode/lithium battery of the present invention.

Detailed ways

The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments. The embodiments of the present invention are for the purpose of further illustrating the present invention, rather than limiting the protection scope of the claims of the present invention.

As shown in Figure 1, the preparation process of the sulfur-based composite positive electrode plate of the present invention includes:

Step 1, dispersing the lamellar carbon material in a solvent to form a lamellar carbon dispersion;

Step 2, adding sulfur-based material, carbon fluoride, and polyacrylonitrile into the lamellar carbon-like dispersion to prepare a positive electrode slurry;

Step 3, coating the positive electrode slurry on the surface of the current collector, and vacuum drying at 70-90° C. for 12-24 hours to obtain a sulfur-based composite positive electrode sheet.

Example 1

Preparation of sulfur-based composite cathode electrode: Weigh 50 mg of GO, disperse it in 40 ml of NMP, stir for 1 h, and then ultrasonicate for 1 h to form a uniform dispersion. 460 mg of fluorinated graphite (with a fluorocarbon ratio of 0.8), 30 mg of PAN, and 460 mg of elemental sulfur were sequentially added, and stirred for 8 h to form a sulfur-based composite cathode slurry. The slurry was coated on the aluminum foil current collector with a scraper, and dried at 70 °C for 2 h until the NMP solvent was completely volatilized to obtain a sulfur-based composite cathode. The microscopic morphology is shown in Figure 2.

Preparation of metal-based battery: The prepared sulfur-based composite positive electrode was punched into circular pole pieces of Φ14 mm, and dried in a vacuum drying oven at 85 °C for 12 h. Under the condition of dry air or inert atmosphere, metal lithium sheet is used as negative electrode, Celgard 2325 is used as separator, 1mol/L lithium bis(trifluoromethylsulfonyl)imide (LiTFSI)/dioxolane (DOL)+1 , 2-dimethoxyethane (DME) (volume ratio of 1:1) was used as the electrolyte, and a CR2016 button battery was assembled. The battery was discharged at a current density of 50 mA/g. After calculation, the specific discharge capacity of the sulfur-based composite positive electrode was 853 mAh/g.

Example 2

Preparation of sulfur-based composite cathode electrode: Weigh 30 mg of GO and 20 mg of GNS, disperse them in 40 ml of DMF, stir for 1 h, and then ultrasonicate for 1 h to form a uniform dispersion. Add 300 mg of graphite fluoride (fluorine to carbon ratio is 1.0), 50 mg of PAN, and 600 mg of sulfur-carbon composite material in sequence, and stir for 8 hours to form sulfur-based composite cathode slurry. The slurry was coated on the aluminum foil current collector with a doctor blade, and dried at 70 °C for 2 h until the NMP solvent was completely evaporated.

Preparation of metal-based battery: The prepared sulfur-based composite positive electrode was punched into circular pole pieces of Φ14 mm, and dried in a vacuum drying oven at 85 °C for 24 h. Under the condition of dry air or inert atmosphere, metal lithium sheet is used as negative electrode, Celgard 2325 is used as separator, 1mol/L lithium bis(trifluoromethylsulfonyl)imide (LiTFSI)/dioxolane (DOL)+1 , 2-dimethoxyethane (DME) (volume ratio of 1:1) was used as the electrolyte, and a CR2016 button battery was assembled. The battery was charged and discharged at a current density of 50 mA/g, and the first discharge curve is shown in Figure 3. After calculation, the specific discharge capacity of the sulfur-based composite cathode is 947mAh/g. After 10 cycles, the capacity is 557mAh/g due to the irreversible cycle of the carbon fluoride cathode in the lithium battery.

Example 3

Preparation of sulfur-based composite cathode electrode: Weigh 60 mg of N-GNS, disperse it in 40 ml of NMP, stir for 1 h, and then ultrasonicate for 1 h to form a uniform dispersion. Add 400 mg of fluorinated graphite (fluorine to carbon ratio is 1.0), 40 mg of PAN, and 500 mg of sulfur-carbon composite material in sequence, and stir for 8 hours to form sulfur-based composite cathode slurry. The slurry was coated on the aluminum foil current collector with a doctor blade, and dried at 70 °C for 2 h until the NMP solvent was completely evaporated.

Preparation of metal-based battery: The prepared carbon fluoride positive electrode was punched into circular pole pieces of Φ14 mm, and dried in a vacuum drying oven at 85 °C for 24 h. Under the condition of dry air or inert atmosphere, metal sodium sheet is used as negative electrode, Glass Fiber is used as separator, and 0.5mol/L sodium hexafluorophosphate (NaPF ₆ )/1,2-dimethoxyethane (DME) is used as electrolyte , assembled into a CR2016 button battery. The battery was cycled at a current density of 50 mA/g, and the first discharge specific capacity was 907 mAh/g. After 10 cycles, the discharge specific capacity was 865 mAh/g, and the cycle stability was good.

The positive electrode sheet provided by the present invention can be assembled into a battery by using metal lithium, sodium, etc. as the negative electrode. When lithium is used as the negative electrode, because it contains carbon fluoride, which is the material of the primary battery, the cycle performance is not good relative to the first discharge capacity. In Example 3, metal sodium is used as the negative electrode, and the carbon fluoride is secondary reversible at this time, which shows that the cycle performance is better.

To sum up, the sulfur-based composite positive electrode plate provided by the present invention does not need a binder, can improve the energy density of the battery, and has good cycle performance.

While the content of the present invention has been described in detail by way of the above preferred embodiments, it should be appreciated that the above description should not be construed as limiting the present invention. Various modifications and alternatives to the present invention will be apparent to those skilled in the art upon reading the foregoing. Accordingly, the scope of protection of the present invention should be defined by the appended claims.

Claims (6)

1. a preparation method of a sulfur-based composite positive pole piece, is characterized in that, the method comprises: Step 1: Disperse the lamellar carbon material in a solvent to form a lamellar carbon dispersion; the lamellar carbon material is selected from graphene, graphene oxide, nitrogen-doped graphene, sulfur-doped graphene, Or any one or more in phosphorus-sulfur-doped graphene; Described solvent selects at least one in DMF, DMAC, DMSO, NMP; Step 2, adding sulfur-based material, carbon fluoride, and polyacrylonitrile into the lamellar carbon-like dispersion to prepare a positive electrode slurry; Step 3, coating the positive electrode slurry on the surface of the current collector and drying to obtain a sulfur-based composite positive electrode plate; Wherein, the mass fraction of carbon in the lamellar carbon dispersion liquid is 3-6%; the particle size of the polyacrylonitrile is 20 nm-40 μm, and the mass fraction is 3-5%. 2. The preparation method of the sulfur-based composite positive pole piece according to claim 1, wherein the sulfur-based material selects any one of elemental sulfur, sulfur-carbon composite material, organic sulfide, and inorganic sulfide Or more, in the positive electrode, its mass fraction is 30-80%. 3. The preparation method of the sulfur-based composite positive pole piece according to claim 1, wherein the carbon fluoride selects fluorinated graphite, fluorinated carbon nanotube, fluorinated graphene, fluorinated carbon fiber, fluorine Any one or more of the carbonized carbon nano-disc and the fluorinated coke, the fluorocarbon molar ratio is 0.33-1.2, and in the positive electrode, the mass ratio is 30-80%. 4. A sulfur-based composite positive electrode pole piece prepared by the method according to any one of claims 1-3. 5 . A battery comprising the sulfur-based composite positive electrode plate of claim 4 , wherein the battery comprises the sulfur-based composite positive electrode, a negative electrode, an electrolyte, and a separator. 6 . 6. The battery of claim 5, wherein the negative electrode is a lithium sheet or a sodium sheet.