Method for manufacturing a positive electrode for a lithium-sulfur battery

Abstract

The present invention relates to a method for manufacturing a positive electrode for a lithium-sulfur battery, the method comprising: (1) a step of mixing a sulfur-carbon composite material and a binder to prepare a slurry for a positive electrode active material; (2) a step of coating the slurry for the positive electrode active material onto one surface of a current collector; (3) a first drying step of drying the current collector coated with the slurry using hot air and medium-wave infrared radiation; and (4) a second drying step of further drying using a laser heat source after the first drying step.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a positive electrode for a lithium-sulfur battery, and more particularly, to a method for manufacturing a positive electrode for a lithium-sulfur battery comprising a drying step using a laser heat source.

[0002] This application claims priority to Korean Patent Application No. 10-2020-0160370 filed on November 25, 2020, which is incorporated herein by reference in its entirety. Background Art

[0003] As the application range of secondary batteries expands from small portable electronic devices to medium and large electric vehicles (EVs), energy storage systems (ESS), electric ships, etc., the demand for lithium secondary batteries with high capacity, high energy density and long life is rapidly increasing.

[0004] Among them, lithium-sulfur battery means a battery system that uses a sulfur-based material with a "sulfur-sulfur bond (SS bond)" as a positive electrode active material and lithium metal as a negative electrode active material. Sulfur, which is the main material of the positive electrode active material, has the following properties: sulfur has a low atomic weight, is easy to supply and receive due to its abundant resources, and is inexpensive, thereby reducing the manufacturing cost of the battery, and sulfur is non-toxic and therefore environmentally friendly.

[0005] In particular, the theoretical discharge capacity of lithium-sulfur batteries is 1675 mAh / g sulfur, which is theoretically capable of achieving a high energy storage density of 2600 Wh / kg compared to its weight. Therefore, due to the high energy storage density compared to other battery systems (Ni-MH battery: 450 Wh / kg, Li-FeS battery: 480 Wh / kg, Li-MnO 2 Compared with the theoretical energy density of lithium-sulfur batteries (1000Wh / kg, Na-S batteries: 800Wh / kg) and the lithium-ion batteries currently under research (250Wh / kg), lithium-sulfur batteries have a very high value, so lithium-sulfur batteries have received a lot of attention in the developing market for medium and large secondary batteries.

[0006] A lithium-sulfur battery has a positive electrode, a negative electrode, a separator, and an electrolyte as basic components, wherein the positive electrode corresponds to a main component of the lithium-sulfur battery because the positive electrode active material can have a great influence on the performance of the battery. The positive electrode can be prepared by first adding a binder and a solvent to the positive electrode active material to prepare a slurry for the positive electrode active material in a fluid form, and then coating the slurry on a current collector and drying it.

[0007] Regarding the manufacturing method of lithium-sulfur batteries, there is a problem regarding the stability of lithium-sulfur batteries. This is because highly reactive lithium metal is used as the negative electrode. If the moisture in the electrode is not sufficiently removed, a side reaction between the negative electrode and the electrolyte may occur, thereby accelerating the deterioration of the battery and causing gas to be generated in the battery.

[0008] To solve this problem, various attempts have been made to remove moisture contained in the positive electrode of a lithium-sulfur battery.

[0009] For example, an attempt was made to apply vacuum drying used in lithium-ion batteries as is, but in this case, the loss rate of sulfur as an active material is large, and when the temperature or vacuum degree is reduced to prevent this problem, it is difficult to sufficiently remove moisture from the electrode. In addition, in the case of a high-temperature drying method, since sulfur has a low melting point and a low volatility point, the active material is easily lost or melted, causing a problem of deformation of the shape of the electrode itself.

[0010] In the conventional case of drying using medium wave infrared radiation, sulfur loss is not effectively prevented and a long drying time of several minutes is required. In order to improve this problem, it is necessary to increase the drying section and the operating speed. However, it has been pointed out that in order to increase the drying section, there are limitations that must be considered for additional space constraints.

[0011] Therefore, it is necessary to study and develop a method for manufacturing a positive electrode for a lithium-sulfur battery, which is improved in terms of a drying method so that the loss of sulfur contained in the positive electrode active material can be minimized, and even heat can be uniformly transferred into the positive electrode and irradiated at once to a large area, thereby having an excellent effect of reducing the moisture content, and increasing the production speed of the positive electrode by shortening the drying time.

[0012] [Prior art literature]

[0013] [Patent Document]

[0014] (Patent Document 1) Korean Patent Publication No. 10-2018-0010862 (January 31, 2018), “A method of preparing electrodes for lithium-sulfur battery” Summary of the invention

[0015] Technical issues

[0016] An object of the present invention is to provide a method for manufacturing a positive electrode for a lithium-sulfur battery including a drying method capable of effectively removing moisture contained in the positive electrode and shortening the drying time even while minimizing the loss of sulfur contained in the positive electrode active material.

[0017] Technical Solution

[0018] According to a first aspect of the present invention, the present invention provides a method for manufacturing a positive electrode for a lithium-sulfur battery, the method comprising:

[0019] (1) a step of mixing a sulfur-carbon composite material and a binder to prepare a slurry for a positive electrode active material;

[0020] (2) applying the positive electrode active material slurry to one surface of a current collector;

[0021] (3) a first drying step of drying the current collector coated with the slurry using hot air and medium-wave infrared radiation; and

[0022] (4) A second drying step of further performing drying using a laser heat source after the first drying step.

[0023] In one embodiment of the present invention, the above step (4) may be a step of drying by irradiating a surface-emitting laser heat source.

[0024] In one embodiment of the present invention, step (4) may be a step of drying by irradiating a surface emitting laser heat source having a size of 5 to 20 cm in width and 3 to 10 cm in length.

[0025] In one embodiment of the present invention, step (4) may be a step of irradiating a laser heat source having an output of 160 to 750W.

[0026] In one embodiment of the present invention, step (4) may be a step of irradiating the laser heat source for 0.1 to 2 seconds.

[0027] In one embodiment of the present invention, step (4) may be a step of irradiating a laser heat source having a wavelength of 950 to 1000 nm.

[0028] In one embodiment of the present invention, step (4) may be performed with an irradiation cumulative energy density of 3 to 6 J / cm 2 The steps of the laser heat source.

[0029] In one embodiment of the present invention, the sulfur loss rate of the positive electrode for a lithium-sulfur battery that has completed the second drying step of step (4) can be 0.1 to 1.1 weight % compared to the positive electrode for a lithium-sulfur battery that has completed the first drying step of step (3).

[0030] Beneficial Effects

[0031] The method for manufacturing a positive electrode for a lithium-sulfur battery according to the present invention has the effect of increasing the speed of the positive electrode manufacturing process by shortening the drying time by using a surface-emitting laser heat source capable of uniformly irradiating a large area.

[0032] In addition, the method for manufacturing a positive electrode for a lithium-sulfur battery according to the present invention has the advantage of achieving an excellent moisture removal effect in the positive electrode even in a short drying time while minimizing the loss of sulfur contained in the positive electrode active material. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic diagram showing a drying device including a surface emitting laser used in the second drying of the positive electrode for a lithium-sulfur battery according to an embodiment of the present invention.

[0034] Figure 2 : is a graph showing the moisture content in the positive electrode manufactured by the method of manufacturing a positive electrode for a lithium-sulfur battery according to the example of the present invention and the comparative example.

[0035] Figure 3 , Figure 4 and Figure 5 : is a graph showing the sulfur content in the positive electrode manufactured by the method of manufacturing a positive electrode for a lithium-sulfur battery according to the example of the present invention and the comparative example. DETAILED DESCRIPTION

[0036] The embodiments provided according to the present invention can be realized by the following description. It should be understood that the following description describes the preferred embodiments of the present invention, and it should be understood that the present invention is not necessarily limited thereto.

[0037] As a result of experiments by the inventors of the present invention, the conventional method for manufacturing a positive electrode for a lithium-sulfur battery is ineffective in removing moisture contained in the electrode, and thus has the following limitations: battery deterioration is easily accelerated due to the reaction between the residual moisture and the lithium metal used as the negative electrode, the positive electrode production process is not efficient due to a long drying process, and sulfur loss is accompanied during drying.

[0038] In order to solve the above problems, the inventors of the present invention have invented a method for manufacturing a positive electrode for a lithium-sulfur battery, which can effectively remove moisture in the positive electrode in a short time by using a laser heat source for secondary drying after the first drying, and even reduce the loss of sulfur as an active material at the same time.

[0039] The method for manufacturing a positive electrode for a lithium-sulfur battery according to the present invention comprises: (1) a step of mixing a sulfur-carbon composite material and a binder to prepare a slurry for a positive electrode active material; (2) a step of coating the slurry for the positive electrode active material on one surface of a current collector; (3) a first drying step of drying the current collector coated with the slurry using hot air and medium-wave infrared radiation; and (4) a second drying step of further drying using a laser heat source after the first drying step.

[0040] (1) Step of preparing slurry for positive electrode active material

[0041] The method for manufacturing a positive electrode for a lithium-sulfur battery includes the step of (1) mixing a sulfur-carbon composite material and a binder to prepare a slurry for a positive electrode active material.

[0042] In the case of sulfur contained in the sulfur-carbon composite material, since sulfur itself has no conductivity, sulfur may be used in combination with a conductive material such as a carbon material, and thus sulfur may be contained in the form of the sulfur-carbon composite material.

[0043] The sulfur loading capacity of the positive electrode can be 1 mAh / cm 2 Above, 2mAh / cm 2 Above or 3mAh / cm 2 Above, and 10mAh / cm 2 Below, 9mAh / cm 2 Below or 8mAh / cm 2 the following.

[0044] The carbon contained in the sulfur-carbon composite material is a porous carbon material, and provides a framework capable of uniformly and stably fixing sulfur, and compensates for the low conductivity of sulfur, so that the electrochemical reaction can proceed smoothly. The porous carbon material can generally be prepared by carbonizing various carbonaceous precursors, and non-uniform pores may be included in the porous carbon material.

[0045] The shape of the porous carbon material may be spherical, rod-shaped, needle-shaped, plate-shaped, tubular or block-shaped, and may be used without restriction as long as it is commonly used in lithium-sulfur batteries. The porous carbon material may have a porous structure or a high specific surface area, and may be any of those conventionally used in the art. For example, the porous carbon material may be, but is not limited to, at least one of the following: graphite; graphene; carbon black, such as denka black, acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black; carbon nanotubes (CNTs), such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs); carbon fibers, such as graphite nanofibers (GNFs), carbon nanofibers (CNFs) and activated carbon fibers (ACFs); and graphites, such as natural graphite, artificial graphite and expanded graphite; and activated carbon.

[0046] The preparation method of the sulfur-carbon composite material is not particularly limited in the present invention, and a method commonly used in the art may be used.

[0047] In step (1), the amount of the sulfur-carbon composite material, relative to the total weight of the slurry for positive electrode active material, may be 85 wt % or more, 86 wt % or more, 87 wt % or more, 88 wt % or more, 89 wt % or more, or 90 wt % or more, 91 wt % or more, 92 wt % or more and 98 wt % or less, 97 wt % or less, or 96 wt % or less.

[0048] The binder holds the positive electrode active material in the current collector and organically connects the positive electrode active materials to increase the binding force therebetween, and any binder known in the art may be used.

[0049] For example, the binder may be any one selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyvinyl pyrrolidone, styrene butadiene rubber, acrylonitrile butadiene rubber, styrene isoprene rubber, carboxymethyl cellulose, lithium polyacrylate, and combinations thereof.

[0050] In step (1), the amount of the binder may be 2 wt % or more, 2.5 wt % or more, 3 wt % or more, or 3.5 wt % or more and 6 wt % or less, 5.5 wt % or less, 5 wt % or less, or 4.5 wt % or less, relative to the total weight of the slurry for the positive electrode active material.

[0051] The positive electrode active material slurry may further include a conductive material.

[0052] The conductive material is a material that electrically connects the electrolyte to the positive electrode active material and serves as a path for electrons to move from the current collector to the positive electrode active material, and is not particularly limited as long as it has conductivity.

[0053] For example, as the conductive material, the following can be used alone or in combination: graphite, such as natural graphite or artificial graphite; carbon black, such as Super-P, Denka black, acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; carbon derivatives, such as carbon nanotubes and fullerenes; conductive fibers, such as carbon fibers and metal fibers; carbon fluoride; metal powders, such as aluminum powder and nickel powder; or conductive polymers, such as polyaniline, polythiophene, polyacetylene and polypyrrole.

[0054] The positive electrode active material slurry may further include a solvent.

[0055] The solvent may be a solvent capable of uniformly dispersing the sulfur-carbon composite material and the adhesive. The solvent is an aqueous solvent, most preferably water, in which case the water may be distilled water or deionized water. However, the present invention is not necessarily limited thereto, and if necessary, a lower alcohol that is easily miscible with water may be used. The lower alcohol may be methanol, ethanol, propanol, isopropanol and butanol, and preferably, these lower alcohols may be used as a mixture with water.

[0056] (2) Step of applying a slurry of a positive electrode active material to one surface of a current collector

[0057] The method for manufacturing a positive electrode for a lithium-sulfur battery includes the step of coating the positive electrode active material slurry on one surface of a current collector.

[0058] The positive electrode active material slurry prepared through step (1) may be coated on one surface of the current collector.

[0059] The current collector is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery, for example, stainless steel; aluminum; nickel; titanium; calcined carbon; or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In addition, the thickness of the positive electrode current collector can generally be 3 to 500 μm, and the current collector can enhance the binding force with the positive electrode active material by having fine concave-convex on its surface. The current collector can be formed into various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0060] The coating thickness of the positive electrode active material slurry may be 50 to 300 μm, preferably 100 to 250 μm, more preferably 150 to 200 μm, and it is preferred that the positive electrode active material slurry is coated on a current collector by a method using a comma coater.

[0061] (3) First Drying Step

[0062] The method for manufacturing a positive electrode for a lithium-sulfur battery includes (3) a first drying step of drying the current collector coated with the slurry using hot air and medium-wave infrared radiation.

[0063] When manufacturing the positive electrode for a lithium-sulfur battery, in order to remove moisture from the slurry coated on the current collector, a drying process may be performed using hot air and medium-wave infrared radiation simultaneously in the first drying step.

[0064] Hot air drying is a drying method that uses convection drying to remove moisture, which can be performed by irradiating hot air in a closed drying space or supplying heated air into the drying space to transfer heat to heat the air medium.

[0065] In order to effectively remove moisture from the slurry by hot air drying, the temperature of the hot air drying device may be 70 to 100° C., preferably 80 to 90° C., and the air volume may be 3 to 10 m 3 / min, preferably 4 to 6m 3 / min.

[0066] Drying by medium-wave infrared radiation is effective because the moisture content in the electrode can be removed by evaporating not only the moisture on the surface of the slurry but also the moisture contained inside.

[0067] The drying process by medium-wave infrared radiation can use a drying device in the form of a heater, and can be performed by irradiating medium-wave infrared radiation with a wavelength of 1 to 5 μm, preferably 1 to 3 μm, at a temperature of 70 to 100° C., preferably 80 to 90° C. for 1 to 6 minutes.

[0068] The step (3) may further include a step of pressing 'the first dried current collector after coating with the slurry for the positive electrode active material'.

[0069] In the pressing step, the first dried current collector after coating the positive electrode active material slurry may be put into a roller press and compressed with a roller to have a constant thickness. In addition, the porosity of the positive electrode can be controlled by adjusting the roller gap.

[0070] In addition, before the pressing step, a release film may be placed on the first dried current collector after the positive active material slurry is applied. If compression is performed after placing the release film, the positive active material can be prevented from sticking to the roller of the roller press and not being separated from the roller.

[0071] (4) Second Drying Step

[0072] The method for manufacturing a positive electrode for a lithium-sulfur battery includes (4) a second drying step of further drying using a laser heat source after the first drying step.

[0073] A certain portion of moisture contained in the slurry may be removed through the first drying by hot air drying, but the remaining moisture may cause unstable battery operation due to a side reaction with lithium metal, and thus an additional second drying process may be required.

[0074] Step (4) may be a step of drying by irradiating a surface-emitting laser heat source. Alternatively, step (4) may be a step of drying by irradiating a surface-emitting laser heat source having a size of 5 to 20 cm wide and 3 to 10 cm long, preferably 10 to 16 cm wide and 4 to 7 cm long.

[0075] Compared with a laser heat source in the form of a line beam or a spot beam, the surface emitting laser has advantages in that it can have a fast drying speed, a uniform drying effect, and a sulfur loss amount reduction effect when drying is performed by uniformly irradiating a large area.

[0076] In particular, in the case of drying electrodes manufactured using roll-to-roll processing, since a large area is uniformly irradiated simultaneously by a surface-emitting laser, the electrode is continuously moved throughout the roll-to-roll process and the entire area of ​​the electrode can be dried with only one row.

[0077] On the other hand, in the case of a line beam or a spot beam, since the beam width is small compared to a surface emission type laser, the area irradiated by the laser at the same time is relatively small, so there may be a disadvantage in the process that after the laser is irradiated in one row and the electrode is moved to the next row, the non-irradiated portion of the electrode must be dried by irradiating the laser. In addition, a form capable of irradiating a large area can be formed by continuously arranging spot beam lasers, but the effect of uniformly transferring heat over the entire area may be reduced compared to a surface emission type laser.

[0078] Step (4) may be a step of irradiating a laser heat source having an output of 160 W or more, 180 W or more, 200 W or more, 220 W or more, 240 W or more, 260 W or more, or 280 W or less, or 750 W or less, 700 W or less, 650 W or less, 600 W or less, 550 W or less, 500 W or less, 450 W or less, 400 W or less, 380 W or less, 360 W or less, 340 W or less, or 320 W or less. In the case where the output is below the range, it may not be sufficient to remove the moisture remaining in the electrode by the laser heat source, and in the case where the output exceeds the above range, sulfur in the positive electrode is melted from the carbon support due to the high output, so the positive electrode may lose uniform conductivity, and sulfur may be lost due to the high output, thereby reducing the performance of the electrode.

[0079] Step (4) may be a step of irradiating the laser heat source for a time of 0.1 second or more, or 0.15 second or more, or 2 seconds or less, 1.8 seconds or less, 1.6 seconds or less, 1.4 seconds or less, 1.2 seconds or less, 1 second or less, 0.9 seconds or less, 0.8 seconds or less, 0.7 seconds or less, or 0.6 seconds or less. In the case of irradiating for less than the above time, it may not be sufficient to remove the moisture remaining in the electrode by the laser heat source, and in the case of irradiating for more than the above time, sulfur in the positive electrode is melted from the carbon support due to high output, so the positive electrode may lose uniform conductivity, and sulfur may be lost due to high output, thereby reducing the performance of the electrode.

[0080] Step (4) may preferably be a step of irradiating a laser heat source having a wavelength of 950 to 1000 nm. In the case of irradiating a laser having a wavelength lower than the wavelength, sulfur in the positive electrode may be melted or lost due to excessive energy, and the function of the electrode may be lost, while in the case of irradiating a laser having a wavelength exceeding the wavelength, it may not be sufficient to remove the moisture remaining in the electrode by the laser heat source.

[0081] Step (4) may be to irradiate with a cumulative energy density of 3.0 J / cm 2 Above, 3.2J / cm 2 Above, 3.4J / cm 2 Above, 3.6J / cm 2 Above, 3.8J / cm 2 Above, 4.0J / cm 2 Above, 4.2J / cm 2 Above, 4.4J / cm 2 Above, 4.6J / cm 2 Above and 6.0J / cm 2 Below, 5.8J / cm 2 Below, 5.6J / cm 2 Below, 5.4J / cm 2 Below, 5.2J / cm 2 In the case of a cumulative energy density below the above, the amount of energy transferred is negligible and the drying effect may be small, while in the case of a cumulative energy density exceeding the above, the laser heat source with excessive energy is irradiated for a short time, so that there may be a problem of sublimation and a large proportion of sulfur loss caused thereby.

[0082] After the above step (4), the water content in the positive electrode for lithium-sulfur batteries may be 10 ppm or more, 20 ppm or more, 30 ppm or more, 40 ppm or more, 50 ppm or more, 60 ppm or more, 70 ppm or more, 80 ppm or more, 90 ppm or more, or 100 ppm or more and 500 ppm or less, 490 ppm or less, 480 ppm or less, 470 ppm or less, or 460 ppm or less. When the above range is met, the possibility of side reactions between the residual water in the positive electrode and lithium metal can be reduced, thereby preventing battery degradation and increasing the stability of the battery during operation.

[0083] Compared to the positive electrode for lithium-sulfur battery that has completed the first drying of step (3), the sulfur loss rate of the positive electrode for lithium-sulfur battery after the second drying of step (4) may be 0.1 wt % or more, 0.2 wt % or more, or 0.3 wt % or more, and 1.1 wt % or less, 1.0 wt % or less, 0.9 wt % or less, 0.8 wt % or less, 0.7 wt % or less, 0.6 wt % or less, or 0.5 wt % or less. If the above range is met, the sulfur loss rate during the drying process is small, and thus a sulfur loading amount sufficient to express the energy required for the lithium-sulfur battery can be exhibited. In this specification, the sulfur loss rate may be defined as the difference in weight % between the sulfur content of the positive electrode before the second drying and the sulfur content of the positive electrode after the second drying.

[0084] Preferred Implementation

[0085] Hereinafter, preferred embodiments are provided to help understand the present invention, but the following embodiments are provided only to make the present invention easier to understand, and the present invention is not limited thereto.

[0086] Example: Manufacturing of positive electrode for lithium-sulfur battery

[0087] [Example 1]

[0088] 96 wt % of a sulfur-carbon composite material (S:C=75:25 (weight ratio)) and 4 wt % of LiPAA (lithium polyacrylate) as a binder were mixed to prepare a slurry for a positive electrode active material.

[0089] After the positive active material slurry was coated on one surface of the aluminum current collector, first drying was performed using hot air at 80° C. and a dryer operating a medium-wave infrared radiation lamp at 90° C. for 6 minutes simultaneously.

[0090] After the first drying was completed, a surface emitting laser heat source having a wavelength of 970 nm and an output of 300 W was irradiated for 0.2 seconds to perform additional second drying, thereby finally preparing a positive electrode for a lithium-sulfur battery.

[0091] [Example 2]

[0092] A positive electrode for a lithium-sulfur battery was manufactured in the same manner as in the above-mentioned Example 1, except that in the manufacturing process of the positive electrode for a lithium-sulfur battery, the laser heat source was irradiated for 0.5 seconds during the second drying period.

[0093] [Comparative Example 1]

[0094] A positive electrode for a lithium-sulfur battery was manufactured in the same manner as in the above-mentioned Example 1, except that in the manufacturing process of the positive electrode for a lithium-sulfur battery, the drying process was performed by performing only the first drying without performing the additional second drying.

[0095] [Comparative Examples 2 to 4]

[0096] A positive electrode for a lithium-sulfur battery was manufactured in the same manner as in Example 1 above, except that in the manufacturing process of the positive electrode for a lithium-sulfur battery, after the first drying, second drying was additionally performed by a dryer operating a medium-wave infrared radiation lamp at 90° C. for a period of time shown in the following Table 1.

[0097] Table 1:

[0098] Type of Secondary Drying Heat Source Second drying time Example 1 Surface emitting laser (300W) 0.2 seconds Example 2 Surface emitting laser (300W) 0.5 seconds Comparative Example 1 - - Comparative Example 2 Medium wave infrared radiation 5 minutes Comparative Example 3 Medium wave infrared radiation 10 minutes Comparative Example 4 Medium wave infrared radiation 30 minutes

[0099] [Comparative Example 5]

[0100] A positive electrode for a lithium-sulfur battery was manufactured in the same manner as in Comparative Example 1 above, except that moisture absorption was performed by storing the positive electrode for a lithium-sulfur battery in a state of being exposed to the outside air for a long time after only the first drying was completed in the same manner as in Comparative Example 1.

[0101] [Example 3]

[0102] A positive electrode for a lithium-sulfur battery was manufactured in the same manner as in Comparative Example 5, except that the second drying was performed by irradiation with a laser heat source having an output of 384 W for 0.2 seconds.

[0103] [Example 4 and Example 5]

[0104] A positive electrode for a lithium-sulfur battery was manufactured in the same manner as in Example 3 above, except that the second drying was performed by a laser heat source by changing the drying time as shown in Table 2 below during the second drying.

[0105] Table 2:

[0106] Type of heat source during the second drying period Second drying time Cumulative energy density Example 3 Surface emitting laser (384W) 0.2 seconds <![CDATA[1.92J / cm 2 ]]> Example 4 Surface emitting laser (384W) 0.5 seconds <![CDATA[4.80J / cm 2 ]]> Example 5 Surface emitting laser (384W) 1.0 sec <![CDATA[9.60J / cm 2 ]]>

[0107] Experimental Example 1: Evaluation of the Moisture Content in the Positive Electrode

[0108] For the positive electrodes for lithium-sulfur batteries manufactured by Example 1 and Example 2 and Comparative Examples 1 to Comparative Examples 4, the moisture content in the electrodes was measured using a moisture content measuring device (Metrom, 831KF Coulometer), and the results are shown in the following Tables 3 and Figure 2 In addition, for Examples 3 to 5 and Comparative Example 5, the moisture content was measured in the same manner, and the results are shown in Table 3.

[0109] Table 3:

[0110] Moisture content in electrode (ppm) Example 1 290.6 Example 2 121.6 Example 3 743.1 Example 4 312.5 Example 5 534.0 Comparative Example 1 310.0 Comparative Example 2 289.8 Comparative Example 3 293.2 Comparative Example 4 199.3 Comparative Example 5 600.0

[0111] As shown in Table 3 above and Figure 2As shown, it was confirmed that in the case of Examples 1 and 2, although the second drying was performed for a short time of 0.2 to 0.5 seconds using a laser heat source, the moisture content was reduced by 19.4 ppm or more compared with Comparative Example 1 in which only the first drying was performed.

[0112] In particular, it was confirmed that in the case of Example 2, the drying effect of removing moisture from the electrode was excellent, so that even after the short second drying time of 0.5 seconds using the laser heat source, the moisture content was reduced to 188.4 ppm compared with Comparative Example 1.

[0113] On the other hand, it was confirmed that in the case of Comparative Examples 2 to 3 using medium-wave infrared radiation, the reduction in moisture content was not significantly different from that in Example 1 in which laser drying was performed for only 0.2 seconds even after drying for 5 minutes and 10 minutes, respectively, while in the case of Comparative Example 4 in which drying was performed for 30 minutes, the drying effect was significantly lower than that in Example 2 in which laser drying was performed for only 0.5 seconds.

[0114] From the above results, it was confirmed that the second drying using the surface emitting laser heat source after the first drying has the effect of uniformly drying a large area in a short time of several seconds.

[0115] In addition, it was confirmed that as the experimental results of Examples 3 to 5 in which the output and drying time were different for the positive electrode such as Comparative Example 5 in which the moisture content in the electrode after the first drying was high, the cumulative energy density was 3 to 6 J / cm 2 Example 4 has an excellent drying effect. In Example 3, it was confirmed that the drying effect was not significant due to the short drying time, but rather rapid reabsorption occurred, while in Example 5, it was confirmed that the cumulative energy density was relatively large, but reabsorption occurred rapidly after drying.

[0116] Experimental Example 2: Evaluation of the loss of sulfur content in the positive electrode

[0117] For the positive electrodes for lithium-sulfur batteries manufactured by Examples 1 to 5 and Comparative Examples 1, 4 and 5, the sulfur content in the electrodes was measured by thermogravimetric analysis (TGA) using a thermogravimetric analyzer (Mettler Toledo, TGA / DSC 2), and the results are shown in the following Tables 4 and 5 and Figure 3 and Figure 4 middle.

[0118] Table 4:

[0119] Sulfur content in electrode (wt%) Example 1 66.5 Example 2 66.7 Example 3 67.04 Example 4 66.22 Example 5 65.09 Comparative Example 1 67.2 Comparative Example 4 66.4 Comparative Example 5 67.21

[0120] As shown in Table 4, it was confirmed that compared with Comparative Example 1 in which no secondary drying was performed, the loss rates of sulfur content in Examples 1 and 2 in which the secondary drying was performed using a laser heat source were 0.7 wt% and 0.5 wt%, respectively, while the loss rate of sulfur content in Comparative Example 4 in which the secondary drying was performed by medium-wave infrared radiation was 0.8 wt%.

[0121] It was confirmed that Comparative Example 4 had a long drying time of 30 minutes and its loss of sulfur content was relatively large compared with the examples, while Examples 1 and 2 were effective drying methods for the positive electrode for a lithium-sulfur battery because even if sulfur loss occurred with the second drying, it showed a relatively small loss of 0.7 wt % or less, and as in Experimental Example 1, an excellent drying effect was shown even at a short drying time of 0.5 seconds or less.

[0122] In addition, it was confirmed that as the experimental results of Examples 3 to 5 in which the output and drying time were different for the positive electrode such as Comparative Example 5 in which the moisture content in the electrode after the first drying was high, the cumulative energy density was 3 to 6 J / cm 2 Example 4 has the effect of effectively reducing the moisture content in a short time of 0.5 seconds, and at the same time has a small sulfur loss rate of less than 1%.

[0123] All simple modifications and variations of the present invention are within the scope of the present invention, and the specific scope of protection of the present invention will become apparent from the appended claims.

Claims

1. A method for manufacturing a positive electrode for a lithium-sulfur battery, the method comprises: (1) A step of mixing a sulfur-carbon composite material and a binder to prepare a slurry for a positive electrode active material; (2) A step of coating the slurry for the positive electrode active material on one surface of a current collector; (3) A first drying step of drying the current collector coated with the slurry using hot air and medium-wave infrared radiation; and (4) A second drying step of further drying using a laser heat source after the first drying step, Among them, step (4) is a step of irradiating a laser heat source with an accumulated energy density of 3 J / cm 2 to 6 J / cm 2 for 0.1 second to 2 seconds.

2. The method for manufacturing a positive electrode for a lithium-sulfur battery according to claim 1, wherein, step (4) is a step of drying by irradiating a laser heat source in a surface emission form.

3. The method for manufacturing a positive electrode for a lithium-sulfur battery according to claim 1, wherein, step (4) is a step of drying by irradiating a surface emission laser heat source having a width of 5 cm to 20 cm and a length of 3 cm to 10 cm.

4. The method for manufacturing a positive electrode for a lithium-sulfur battery according to claim 1, wherein, step (4) is a step of irradiating a laser heat source with an output of 160 W to 750 W.

5. The method for manufacturing a positive electrode for a lithium-sulfur battery according to claim 1, wherein, step (4) is a step of irradiating a laser heat source with a wavelength of 950 nm to 1000 nm.

6. The method for manufacturing a positive electrode for a lithium-sulfur battery according to claim 1, wherein, when compared with the positive electrode for a lithium-sulfur battery after the first drying in step (3), the sulfur loss rate of the positive electrode for a lithium-sulfur battery after the second drying in step (4) is 0.1 wt% to 1.1 wt%.

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