CN113363454B - Lithium-sulfur battery positive pole piece and preparation method and application thereof - Google Patents

Lithium-sulfur battery positive pole piece and preparation method and application thereof Download PDF

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CN113363454B
CN113363454B CN202110619697.0A CN202110619697A CN113363454B CN 113363454 B CN113363454 B CN 113363454B CN 202110619697 A CN202110619697 A CN 202110619697A CN 113363454 B CN113363454 B CN 113363454B
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lithium
sulfur
sulfur battery
positive electrode
pole piece
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CN113363454A (en
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鞠署元
马俊青
刘天雷
周景艳
张诗雪
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Shandong Haike Innovation Research Institute Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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    • Y02E60/10—Energy storage using batteries

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Abstract

The invention provides a positive pole piece of a lithium-sulfur battery and a preparation method and application thereof, belonging to the technical field of lithium-sulfur batteries. The lithium-sulfur battery positive pole piece adopts spherical or sphere-like insoluble sulfur as an active material raw material of the lithium-sulfur battery positive pole piece, wherein the content of a fibrous structure of an insoluble sulfur microstructure is60 wt% -95wt%, and the insoluble sulfur in the fibrous structure can be converted into elemental sulfur through hot pressing treatment. The invention can be applied to the lithium-sulfur battery product.

Description

Lithium-sulfur battery positive pole piece and preparation method and application thereof
Technical Field
The invention belongs to the technical field of lithium-sulfur batteries, and particularly relates to a positive pole piece of a lithium-sulfur battery, and a preparation method and application thereof.
Background
The lithium ion battery has high energy density and cycle performance, is widely applied to the fields of digital products, power energy storage and the like, and currently, lithium cobaltate, ternary materials, lithium iron phosphate and lithium manganate are mainstream anode materials, but the materials generally have low gram capacity, so that the further improvement of the energy density of the battery is seriously limited. The theoretical specific capacity of elemental sulfur is 1672mAh/g, and a lithium-sulfur battery taking sulfur as a positive electrode and lithium metal as a negative electrode is considered to be one of the main choices of the next-generation high-energy-density secondary battery.
Currently, the lithium-sulfur battery mostly uses nano sulfur or a nano sulfur composite material as a positive electrode material of the lithium-sulfur battery. However, agglomeration is easy to occur in the process of slurry combination of the positive electrode, so that the dispersion of the positive electrode material and the conductive agent is not uniform, and difficulties are caused in slurry combination and coating processes. Moreover, the high specific surface area can aggravate the dissolution of polysulfide in electrolyte, so that the shuttle problem of polysulfide is difficult to solve, the irreversible capacity loss of the battery in the charging and discharging process is caused, and the cycle performance of the battery is influenced.
In patent CN109192967A, insoluble sulfur IS used as a positive electrode active substance to solve the problem of shuttle of polysulfide, but the insoluble sulfur in the patent IS oil-extended insoluble sulfur such as IS-HS7020, OT20, IS-HS6033, OT33, IS8010, IS8510, IS6010, IS6005, IS60, IS90, etc., where the oil-extended type IS naphthenic oil, and the presence of naphthenic oil not only reduces the active substance content in the positive electrode, but also the high molecular weight naphthenic oil IS difficult to remove in the drying process of the positive electrode sheet, which affects the conductivity of the sheet. In the discharging process of the battery, especially in the previous discharging processes, the conversion of long-chain insoluble sulfur to elemental sulfur causes a plurality of problems of serious polarization, low discharging voltage, volume expansion and the like of the battery, thereby affecting the overall performance of the battery.
Disclosure of Invention
The invention provides a lithium-sulfur battery positive electrode active substance aiming at the technical problems that slurry is not easy to mix when nano sulfur or a nano sulfur composite material is used as a lithium-sulfur battery positive electrode material and polysulfide is dissolved in electrolyte, the requirements on a slurry mixing process can be reduced, and the prepared battery has excellent cycle performance and rate capability.
In order to achieve the purpose, the invention adopts the technical scheme that:
a spherical or sphere-like insoluble sulfur is used as an active material raw material of the lithium-sulfur battery positive pole piece, wherein the content of a microstructure of the insoluble sulfur in a fibrous structure is 60-95 wt%, and the insoluble sulfur in the fibrous structure can be converted into elemental sulfur through hot pressing.
Preferably, the hot pressing treatment is carried out under the pressure of 4-4.5 kg/cm2And keeping the temperature of the mixture at 80-100 ℃ for 5-60 min.
Preferably, the median particle size of the spherical or spheroidal insoluble sulfur is 0.01-10 μm.
Preferably, the 2 theta angles corresponding to the three strong peaks of the XRD pattern of the spherical or spheroidal insoluble sulfur are 22.3 respectivelyo、21.2o、29.7o。
Preferably, the conductive agent, the adhesive and the current collector are also included; the mass ratio of the active substance raw materials to the conductive agent to the binder is 50-90: 8-40: 3 to 10.
Preferably, the conductive agent is one or more of acetylene black, ketjen black, carbon nanotubes, carbon fibers, and graphene.
Preferably, the binder is one or more of Styrene Butadiene Rubber (SBR), sodium carboxymethylcellulose, lithium carboxymethylcellulose, polyacrylonitrile, polyvinylidene fluoride, polyethylene oxide and polyacrylic acid.
Preferably, the current collector is an aluminum foil or a carbon-coated aluminum foil, and the thickness of the current collector is 6-25 μm.
The invention provides a preparation method of a positive pole piece of a lithium-sulfur battery, which comprises the following steps:
mixing the active substance raw material with a conductive agent or slurry of the conductive agent to obtain a premix;
dissolving a binder in a solvent to obtain a glue solution;
mixing the premix and the glue solution to obtain positive electrode slurry;
coating the positive electrode slurry on a current collector for drying to obtain an untreated positive electrode plate;
and carrying out hot-pressing treatment on the untreated positive pole piece to obtain the positive pole piece of the lithium-sulfur battery.
The invention also provides an application of the positive pole piece of the lithium-sulfur battery in the scheme in preparation of the lithium-sulfur battery.
Compared with the prior art, the invention has the advantages and positive effects that:
the invention adopts spherical or sphere-like insoluble sulfur as the positive active substance of the lithium-sulfur battery, has good dispersibility and fluidity, and is simpler and easier in process compared with simple substance sulfur slurry mixing process. The insoluble sulfur is spherical or quasi-spherical, has small specific surface area, can reduce the dissolution of polysulfide in electrolyte in the charge-discharge process, reduce the loss of the positive electrode capacity and improve the cycle performance of the battery.
Meanwhile, the content of the microstructure of the insoluble sulfur adopted in the invention, which is in a fibrous structure, is60 wt% -95wt%, hot pressing treatment is carried out when the anode plate of the battery is prepared, and after the hot pressing treatment is carried out, the insoluble sulfur in the fibrous structure is converted into elemental sulfur, so that the excellent characteristic of high energy density of the lithium-sulfur battery is ensured, the part which is not converted into the elemental sulfur is still the insoluble sulfur, and the structural characteristics of long chain polymerization of the insoluble sulfur are utilized, so that the dissolution of polysulfide is reduced, the shuttle effect is reduced, and the cycle performance of the battery is further improved.
Drawings
FIG. 1 is an SEM photograph of insoluble sulfur in example 1;
FIG. 2 is an XRD spectrum of the positive electrode sheet obtained in step (3) of example 1 without thermal compression treatment;
FIG. 3 is an XRD (X-ray diffraction) spectrum of the positive electrode plate of the lithium-sulfur battery after the hot pressing treatment in the step (4) in the example 1;
FIG. 4 is an SEM photograph of a lithium-sulfur battery pole piece after hot pressing treatment obtained in the step (4) of example 1;
FIG. 5 is a first charge-discharge curve of a lithium-sulfur battery according to example 1;
FIG. 6 is a graph of the cycle performance of the lithium sulfur battery of example 1;
FIG. 7 is a rate charge and discharge curve of a lithium sulfur battery of example 1;
FIG. 8 is an XRD (X-ray diffraction) spectrum of the positive electrode plate of the lithium-sulfur battery obtained in the step (4) of the example 2 after the hot pressing treatment;
fig. 9 is a first charge and discharge curve of the lithium sulfur battery of comparative example 2.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a lithium-sulfur battery positive pole piece, wherein spherical or sphere-like insoluble sulfur is used as an active material raw material of the lithium-sulfur battery positive pole piece, wherein the content of a microstructure of the insoluble sulfur in a fibrous structure is 60-95 wt%, and the insoluble sulfur in the fibrous structure can be converted into elemental sulfur through hot pressing treatment.
In the invention, the median particle size of the spherical or spheroidal insoluble sulfur is preferably 0.01 to 10 μm, more preferably 0.02 to 5 μm, and most preferably 0.1 to 3 μm. In the invention, the 2 theta angles corresponding to the three strong peaks of the XRD pattern of the spherical or sphere-like insoluble sulfur are 22.3 respectivelyo、21.2o、29.7o。
In the invention, the insoluble sulfur is obtained by heating and gasifying elemental sulfur and then performing dual actions of a stabilizer and an extraction cooling liquid. In the invention, the stabilizer is preferably one or more of phosphorus trichloride, phosphorus pentachloride, butadiene, divinyl, a mixed solution of ferric trichloride and dilute nitric acid, phenols and metal salts; the cold extract is preferably carbon disulphide, carbon tetrachloride, xylene or chlorinated hydrocarbons.
In the invention, the hot pressing treatment is preferably carried out under the pressure of 4-4.5 kg/cm2And keeping the temperature of the mixture at 80-100 ℃ for 5-60 min.
In the invention, insoluble sulfur is used as the positive active substance, and has better dispersibility and fluidity compared with nano elemental sulfur, thereby reducing the difficulty of slurry mixing. Meanwhile, the insoluble sulfur is spherical or quasi-spherical, the specific surface area is small, the dissolution of polysulfide in electrolyte in the charge-discharge process can be reduced, the loss of the capacity of the anode is reduced, and the cycle performance of the battery is improved.
Although insoluble sulfur can be directly used as the positive active material without hot pressing treatment, the prepared battery has the problems of large internal resistance, low gram capacity, low discharge plateau, volume expansion and the like. The content of the microstructure of the insoluble sulfur in the invention is 60-95 wt%, hot pressing treatment is carried out when the insoluble sulfur is prepared into the battery positive pole piece, the insoluble sulfur in the fibrous structure is converted into elemental sulfur after the hot pressing treatment, the excellent characteristic of high energy density of the lithium-sulfur battery is ensured, the part which is not converted into the elemental sulfur is still the insoluble sulfur, and the dissolution of polysulfide is reduced, the shuttle effect is reduced, and the cycle performance of the battery is further improved by utilizing the characteristic of long chain polymerization of the insoluble sulfur.
The positive pole piece of the lithium-sulfur battery provided by the invention preferably further comprises a conductive agent, a binder and a current collector. In the invention, the mass ratio of the positive electrode active material, the conductive agent and the binder is preferably 50-90: 8-40: 3 to 10, more preferably 65 to 85:10 to 25: 8.
In the present invention, the conductive agent is preferably one or more of acetylene black, ketjen black, carbon nanotubes, carbon fibers, and graphene.
In the present invention, the binder is preferably one or more of styrene-butadiene rubber (SBR), sodium carboxymethylcellulose, lithium carboxymethylcellulose, polyacrylonitrile, polyvinylidene fluoride, polyethylene oxide, and polyacrylic acid.
In the invention, the current collector is preferably an aluminum foil or a carbon-coated aluminum foil, and the thickness of the current collector is preferably 6-25 μm.
The sources of the conductive agent, the binder and the current collector are not particularly limited in the present invention, and any commercially available product conventionally used in the art may be used.
The invention provides a preparation method of a positive pole piece of a lithium-sulfur battery, which comprises the following steps:
mixing the active substance raw material with a conductive agent or slurry of the conductive agent to obtain a premix;
dissolving a binder in a solvent to obtain a glue solution;
mixing the premix and the glue solution to obtain positive electrode slurry;
coating the positive electrode slurry on a current collector for drying to obtain an untreated positive electrode plate;
and carrying out hot-pressing treatment on the untreated positive pole piece to obtain the positive pole piece of the lithium-sulfur battery.
The invention mixes the active material raw material with the conductive agent to obtain the premix. In the present invention, when the active material raw material is mixed with the conductive agent, the mixing is preferably performed by ball milling. In the invention, the rotation speed during ball milling is preferably 300-2000 r/min, and the time is preferably 50-70 min. When the active material raw material is mixed with the slurry of the conductive agent, the mixing is preferably performed by stirring.
And dissolving the binder in the solvent to obtain a glue solution. In the present invention, the solvent is preferably one or more of water, N-methylpyrrolidone (NMP), and ethanol. In the invention, the solid content of the glue solution is preferably 3-15% by mass percent.
After the premix and the glue solution are obtained, the premix and the glue solution are mixed to obtain the anode slurry. In the invention, the solid content of the positive electrode slurry is preferably 18-25% by mass. After the positive pole slurry is obtained, the invention coats the positive pole slurry on a current collector for drying, and obtains an untreated positive pole piece. In the present invention, the drying temperature is preferably 30 to 60 ℃.
After obtaining the untreated positive pole piece, the invention carries out hot pressing treatment on the untreated positive pole piece to obtain the positive pole piece of the lithium-sulfur battery. In the invention, the hot pressing treatment is carried out under the pressure of 4-4.5 kg/cm2And keeping the temperature of the mixture at 80-100 ℃ for 5-60 min.
The invention also provides an application of the positive pole piece of the lithium-sulfur battery in the scheme in preparation of the lithium-sulfur battery.
In order to further illustrate the present invention, the following embodiments are described in detail, but they should not be construed as limiting the scope of the present invention.
Example 1
(1) 70g of median particle diameter (D) was weighed50) Insoluble sulfur (SEM image shown in FIG. 1) of 2.8 μm and Ketjen black of 11g in a mass ratio of powder to zirconium beads of 1: 3, adding the mixture into a ball mill, and grinding for 60min at the rotating speed of 300 r/min;
(2) adding 220g of carbon nanotube conductive slurry (the mass fraction of CNT is 5%) and 53.3g of 15% polyacrylonitrile solution (LA 133) into the powder after ball milling, adjusting the solid content of the slurry to 25% by using deionized water, and stirring for 30min in a high-speed stirrer at the rotating speed of 2000r/min to obtain anode slurry;
(3) will be provided withCoating the positive electrode slurry on a carbon-coated aluminum foil with the thickness of 10 mu m, and drying in a 60 ℃ drying oven (controlling the surface density of the coated positive electrode to be 2-2.5 mg/cm)2) After drying, XRD is carried out, and the result is shown in figure 2;
(4) placing the positive pole piece in a temperature control type flat press machine, and setting the pressure to be 4kg/cm2And keeping the temperature at 90 ℃ for 30min to obtain the lithium-sulfur battery pole piece after hot pressing, and performing XRD and SEM, wherein the results are respectively shown in figures 3 and 4, and the comparison between figure 2 and figure 3 shows that the hot pressing can realize the conversion from insoluble sulfur to elemental sulfur.
(5) The pole piece is taken as a positive pole, a lithium piece is taken as a negative pole, a polypropylene microporous membrane with the thickness of 25 mu m is taken as a diaphragm, and 1mol/L LiClO4And (solvent DOL: DME is 1: 1, volume ratio) is used as electrolyte, and a CR2025 type button cell is assembled in a glove box to carry out electrochemical test. The voltage test interval is 1.5-2.7V, the circulating test current is set to be 0.2mA/mg, the multiplying current is set to be 0.5mA/mg, 1mA/mg and 2mA/mg respectively after 100 weeks of circulating test. The first charge-discharge curve of the lithium-sulfur battery is shown in fig. 5, the cycle performance curve is shown in fig. 6, and the rate charge-discharge curve is shown in fig. 7, and the tests show that the lithium-sulfur half-battery prepared in example 1 has excellent electrochemical performance in gram capacity, cycle, rate and other aspects, and the test results are shown in statistical table 1.
(6) And (3) testing the stability of the slurry: 30mL of the slurry prepared in step (3) was taken from a 50mL beaker, 2g of the slurry was taken from the upper layer 1/3 of the slurry and tested for solids content and designated X1(ii) a Sealing the beaker with a preservative film, storing the beaker in an oven at 60 ℃ for 24 hours, testing the solid content by the same operation as the above, and recording the solid content as X2(ii) a Characterization of the slurry stability parameter w, w = (X)1-X2）/X 1100%, the smaller the w value, the better the stability and dispersibility of the slurry.
Example 2
(1) Weighing 70g of insoluble sulfur with the median particle size of 2.8 mu m, 11g of Ketjen black and 11g of carbon nanotube powder, wherein the mass ratio of the powder to the zirconium beads is 1: 3, adding the mixture into a ball mill, and grinding for 60min at the rotating speed of 300 r/min;
(2) adding 53.3g of 15% polyacrylonitrile solution (LA 133) into the powder after ball milling, adjusting the solid content of the slurry to 18% by using deionized water, and stirring for 30min in a high-speed stirrer at the rotating speed of 2000r/min to obtain anode slurry;
(3) coating the positive electrode slurry on a carbon-coated aluminum foil with the thickness of 10 mu m, and drying in a 60 ℃ oven (controlling the surface density of the coated positive electrode to be 2-2.5 mg/cm)2）；
(4) Placing the positive pole piece in a temperature control type flat press machine, and setting the pressure to be 4kg/cm2Keeping the temperature at 100 ℃ for 15min to obtain a lithium-sulfur battery pole piece subjected to hot pressing treatment, and performing XRD (X-ray diffraction), wherein the result is shown in figure 8;
(5) the pole piece is taken as a positive pole, a lithium piece is taken as a negative pole, a polypropylene microporous membrane with the thickness of 25 mu m is taken as a diaphragm, and 1mol/L LiClO4And (solvent DOL: DME is 1: 1, volume ratio) is used as electrolyte, and a CR2025 type button cell is assembled in a glove box to carry out electrochemical test. The voltage test interval is 1.5-2.7V, the circulating test current is set to be 0.2mA/mg, the circulation is carried out for 100 weeks, the multiplying current is respectively set to be 0.2mA/mg, 0.5mA/mg, 1mA/mg and 2mA/mg, and the test result is shown in a statistical table 1.
(6) The slurry stability test method was the same as in example 1.
Example 3
(1) Weighing 80g of insoluble sulfur with the median particle size of 2.8 mu m, 6g of acetylene black and 6g of carbon nano powder tube body, wherein the mass ratio of the powder to the zirconium beads is 1: 3, adding the mixture into a ball mill, and grinding for 60min at the rotating speed of 300 r/min;
(2) adding 53.3g of 15% polyacrylonitrile solution (LA 133) into the powder after ball milling, adjusting the solid content of the slurry to 25% by using deionized water, and stirring for 30min in a high-speed stirrer at the rotating speed of 2000r/min to obtain anode slurry;
(3) coating the anode slurry on an aluminum foil with the thickness of 10 mu m, and drying in a 60 ℃ oven (controlling the surface density of the coated anode to be 2-2.5 mg/cm)2）；
(4) Placing the positive pole piece in a temperature control type flat press machine, and setting the pressure to be 4kg/cm2Keeping the temperature at 90 ℃ for 30min to obtain the lithium-sulfur battery pole subjected to hot pressing treatmentSlicing;
(5) the pole piece is taken as a positive pole, a lithium piece is taken as a negative pole, a polypropylene microporous membrane with the thickness of 25 mu m is taken as a diaphragm, and 1mol/L LiClO4And (solvent DOL: DME is 1: 1, volume ratio) is used as electrolyte, and a CR2025 type button cell is assembled in a glove box to carry out electrochemical test. The voltage test interval is 1.5-2.7V, the circulating test current is set to be 0.2mA/mg, the circulation is carried out for 100 weeks, the multiplying current is respectively set to be 0.2mA/mg, 0.5mA/mg, 1mA/mg and 2mA/mg, and the test result is shown in a statistical table 1.
(6) The slurry stability test method was the same as in example 1.
Example 4
(1) Weighing 70g of insoluble sulfur with the median particle size of 2.8 mu m, 11g of acetylene black and 11g of carbon nanotube powder, wherein the mass ratio of the powder to the zirconium beads is 1: 3, adding the mixture into a ball mill, and grinding for 60min at the rotating speed of 300 r/min;
(2) dissolving 8g of HSV900 type polyvinylidene fluoride in 92g of NMP to prepare a glue solution, adding the powder subjected to ball milling into the glue solution, adjusting the solid content of the slurry to 25% by using NMP, and stirring for 30min in a high-speed stirrer at the rotating speed of 2000r/min to obtain anode slurry;
(3) coating the positive electrode slurry on a carbon-coated aluminum foil with the thickness of 10 mu m, and drying in a 60 ℃ drying oven (controlling the surface density of the coated positive electrode to be 2-2.5 mg/cm)2）；
(4) Placing the positive pole piece in a temperature control type flat press machine, and setting the pressure to be 4kg/cm2Keeping the temperature at 90 ℃ for 30min to obtain the lithium-sulfur battery pole piece subjected to hot pressing treatment;
(5) the pole piece is taken as a positive pole, a lithium piece is taken as a negative pole, a polypropylene microporous membrane with the thickness of 25 mu m is taken as a diaphragm, and 1mol/L LiClO4And (solvent DOL: DME is 1: 1, volume ratio) is used as electrolyte, and a CR2025 type button cell is assembled in a glove box to carry out electrochemical test. The voltage test interval is 1.5-2.7V, the circulating test current is set to be 0.2mA/mg, the circulation is carried out for 100 weeks, the multiplying current is respectively set to be 0.2mA/mg, 0.5mA/mg, 1mA/mg and 2mA/mg, and the test result is shown in a statistical table 1.
(6) The slurry stability test method was the same as in example 1.
Example 5
(1) Weighing 70g of insoluble sulfur with the median particle size of 1.2 mu m, 11g of acetylene black and 11g of carbon nanotube powder, wherein the mass ratio of the powder to the zirconium beads is 1: 3, adding the mixture into a ball mill, and grinding for 60min at the rotating speed of 300 r/min;
(2) adding 53.3g of 15% polyacrylonitrile solution (LA 133) into the powder after ball milling, adjusting the solid content of the slurry to 25% by using deionized water, and stirring for 30min in a high-speed stirrer at the rotating speed of 2000r/min to obtain anode slurry;
(3) coating the positive electrode slurry on a carbon-coated aluminum foil with the thickness of 10 mu m, and drying in a 60 ℃ drying oven (controlling the surface density of the coated positive electrode to be 2-2.5 mg/cm)2）；
(4) Placing the positive pole piece in a temperature control type flat press machine, and setting the pressure to be 4.5kg/cm2Keeping the temperature at 90 ℃ for 30min to obtain the lithium-sulfur battery pole piece subjected to hot pressing treatment;
(5) the pole piece is taken as a positive pole, a lithium piece is taken as a negative pole, a polypropylene microporous membrane with the thickness of 25 mu m is taken as a diaphragm, and 1mol/L LiClO4And (solvent DOL: DME is 1: 1, volume ratio) is used as electrolyte, and a CR2025 type button cell is assembled in a glove box to carry out electrochemical test. The voltage test interval is 1.5-2.7V, the circulating test current is set to be 0.2mA/mg, the circulation is performed for 100 weeks, the multiplying current is respectively set to be 0.5mA/mg, 1mA/mg and 2mA/mg, statistics is carried out according to the ratio of the battery capacity under different currents to the battery capacity under the current of 0.2mA/mg, and the test result is shown in a statistical table 1.
(6) The slurry stability test method was the same as in example 1.
Comparative example 1
The operation was exactly the same as in example 1, except that elemental sulfur having a median particle diameter of 20nm was used as the positive electrode active material.
Comparative example 2
The operation was exactly the same as in example 1 except that the autoclave treatment of step (4) was not conducted. The first charge and discharge curve of the lithium sulfur battery prepared by this comparative example is shown in fig. 9. Comparing the first charge-discharge curve of the lithium-sulfur battery in example 1 in fig. 5, it can be seen that the discharge plateau and the first gram capacity are significantly lower, and the defect is mainly due to the fact that the positive active material of the battery is still insoluble sulfur and needs to be converted into elemental sulfur during discharge.
Item Slurry stability parameter w Discharge median current Press and press Initial gram Capacity (0.2 mA @) mg） Capacity of treatment after 100 weeks Measurement of 100 week capacity maintenance Rate of change 0.5mA/mg capacity retention Rate of change 1mA/mg capacity retention Rate of change 2mA/mg capacity retention Rate of change
Examples 1 3.6% 2.124V 1051mAh/g 701mAh/g 66.7% 85.9% 75.5% 72.7%
Examples 2 4.1% 2.123V 1078mAh/g 652mAh/g 60.5% 82.3% 71.5% 65.6%
Examples 3 8.5% 2.117V 926mAh/g 468mAh/g 50.5% 71.2% 66.0% 63.5%
Examples 4 3.9% 2.121V 1103mAh/g 635mAh/g 56.2% 79.3% 67.9% 64.2%
Examples 5 2.1% 2.125V 1146mAh/g 595mAh/g 51.9% 87.1% 79.5% 76.3%
Comparative example 1 31.9% 2.126V 1178mAh/g 201mAh/g 17.1% 81.7% 73.6% 68.7%
Comparative example 2 3.7% 2.003V 884mAh/g 467mAh/g 52.8% 60.9% 45.5% 37.1%
TABLE 1 Electrical Property data
As can be seen from Table 1, electrochemical performance tests show that the lithium-sulfur battery prepared by the method shows good performances in gram capacity, cycle performance, rate performance and other aspects of the positive active material.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (10)

1. The positive pole piece of the lithium-sulfur battery is characterized in that the positive pole piece is obtained by coating positive slurry on a current collector, drying the current collector to obtain an untreated positive pole piece, and then carrying out hot pressing treatment on the untreated positive pole piece; the active material raw material in the anode slurry is spherical or sphere-like insoluble sulfur, wherein the content of a microstructure of the insoluble sulfur in a fibrous structure is 60-95 wt%; the hot pressing treatment converts insoluble sulfur in a fibrous structure into elemental sulfur.
2. The positive electrode plate of the lithium-sulfur battery as claimed in claim 1, wherein the hot pressing treatment is carried out under a pressure of 4 to 4.5kg/cm2And keeping the temperature of the mixture at 80-100 ℃ for 5-60 min.
3. The positive electrode plate of the lithium-sulfur battery as claimed in claim 1, wherein the median particle size of the spherical or spheroidal insoluble sulfur is 0.01 to 10 μm.
4. The positive electrode sheet of the lithium-sulfur battery according to claim 1, wherein the 2 theta angles corresponding to the three strong peaks of the XRD pattern of the spherical or spheroidal insoluble sulfur are 22.3 respectivelyo、21.2o、29.7o。
5. The positive electrode sheet of the lithium-sulfur battery as claimed in claim 1, further comprising a conductive agent, a binder and a current collector; the mass ratio of the active substance raw materials to the conductive agent to the binder is 50-90: 8-40: 3 to 10.
6. The positive electrode sheet for the lithium-sulfur battery according to claim 5, wherein the conductive agent is one or more of acetylene black, Ketjen black, carbon nanotubes, carbon fibers and graphene.
7. The positive electrode plate of the lithium-sulfur battery as claimed in claim 5, wherein the binder is one or more of styrene-butadiene rubber (SBR), sodium carboxymethylcellulose, lithium carboxymethylcellulose, polyacrylonitrile, polyvinylidene fluoride, polyethylene oxide and polyacrylic acid.
8. The positive electrode plate of the lithium-sulfur battery as claimed in claim 5, wherein the current collector is an aluminum foil or a carbon-coated aluminum foil, and the thickness of the current collector is 6-25 μm.
9. The preparation method of the positive pole piece of the lithium-sulfur battery as claimed in any one of claims 1 to 8, characterized by comprising the following steps:
mixing the active substance raw material with a conductive agent or slurry of the conductive agent to obtain a premix;
dissolving a binder in a solvent to obtain a glue solution;
mixing the premix and the glue solution to obtain positive electrode slurry;
coating the positive electrode slurry on a current collector for drying to obtain an untreated positive electrode plate;
and carrying out hot-pressing treatment on the untreated positive pole piece to obtain the positive pole piece of the lithium-sulfur battery.
10. The use of the positive electrode plate of a lithium-sulfur battery according to any one of claims 1 to 8 in the preparation of a lithium-sulfur battery.
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