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KR-102962581-B1 - METHOD OF MANUFACTURING PATTERNED POSITIVE ELECTRODE FOR LITHIUM-SULFUR SECONDARY BATTERY AND METHOD OF MANUFACTURING LITHIUM-SULFUR SECONDARY BATTERY COMPRISING THE SAME

KR102962581B1KR 102962581 B1KR102962581 B1KR 102962581B1KR-102962581-B1

Abstract

A method for manufacturing a positive electrode for a lithium-sulfur secondary battery is provided, comprising the steps of: (1) applying a slurry for forming a positive electrode active material onto a current collector to form a positive electrode active material layer before rolling; (2) rolling the positive electrode active material layer before rolling to form a positive electrode active material layer after rolling having a porosity of 50 to 65%; and (3) irradiating a laser onto the surface of the positive electrode active material layer after rolling to form a positive electrode active material layer with an intaglio pattern. The positive electrode manufactured by the method for manufacturing a positive electrode for a lithium-sulfur secondary battery can significantly improve the energy density per unit volume when applied to a lithium-sulfur secondary battery.

Inventors

  • 이승호
  • 박기수
  • 김봉수

Assignees

  • 주식회사 엘지에너지솔루션

Dates

Publication Date
20260507
Application Date
20190924

Claims (15)

  1. (1) A step of forming a positive active material layer before rolling by applying a slurry for forming a positive active material onto a current collector; (2) A step of rolling the positive active material layer before rolling to form a positive active material layer after rolling; and (3) A step of forming an anode active material layer with an intaglio pattern by irradiating a laser onto the surface of the anode active material layer after the above rolling, and The anode active material layer after rolling has a porosity of 50 to 65%, and The positive active material layer after the above rolling and the positive active material layer with an intaglio pattern formed thereon have the same porosity, and The slurry for forming the positive electrode active material in step (1) above comprises a positive electrode active material comprising a sulfur-carbon composite, and The intaglio pattern formed by the above step (3) has a width of 30 to 100 μm, and A method for manufacturing a positive electrode for a lithium-sulfur secondary battery, characterized in that the intaglio pattern formed by the above step (3) has a depth of 30 to 99% based on the thickness of the positive electrode active material layer.
  2. In claim 1, A method for manufacturing a positive electrode for a lithium-sulfur secondary battery, characterized in that the positive electrode active material layer before rolling in step (1) above has a porosity of 60 to 80%.
  3. In claim 1, A method for manufacturing a positive electrode for a lithium-sulfur secondary battery, characterized in that the slurry for forming the positive electrode active material in step (1) above further comprises a conductive material and a binder.
  4. In claim 1, A method for manufacturing a positive electrode for a lithium-sulfur secondary battery, characterized in that the above sulfur-carbon composite comprises 60 to 90 parts by weight of sulfur based on 100 parts by weight of the sulfur-carbon composite.
  5. In claim 1, A method for manufacturing a positive electrode for a lithium-sulfur secondary battery, characterized in that the rolling of step (2) above is carried out through a roll press process.
  6. In claim 5, A method for manufacturing a positive electrode for a lithium-sulfur secondary battery, characterized in that the pressure applied in the above roll press process is 300 to 1000 KgF.
  7. In claim 1, A method for manufacturing a positive electrode for a lithium-sulfur secondary battery, characterized in that the thickness of the positive electrode active material layer after rolling in step (2) above is 70 to 90% of the thickness of the positive electrode active material layer before rolling in step (1) above.
  8. In claim 1, A method for manufacturing a positive electrode for a lithium-sulfur secondary battery, characterized in that the laser in step (3) above has a wavelength range of 300 to 2000 nm and a frequency of 10 to 1000 kHz.
  9. In claim 1, A method for manufacturing a positive electrode for a lithium-sulfur secondary battery, characterized in that the loading loss rate of the positive electrode active material in step (3) above is 2.5 to 20%.
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  12. In claim 1, A method for manufacturing a positive electrode for a lithium-sulfur secondary battery, characterized in that the intaglio pattern formed by the above (3) step has a plurality of straight lines or dashed lines that are horizontal or orthogonal to each other.
  13. In claim 1, A method for manufacturing a positive electrode for a lithium-sulfur secondary battery, characterized in that the intaglio pattern formed by the above step (3) is located within 200 μm of a predetermined point located on the surface of the rolled positive electrode active material layer.
  14. A positive electrode for a lithium-sulfur secondary battery manufactured by the method for manufacturing a positive electrode described in claim 1.
  15. A lithium-sulfur secondary battery comprising a positive electrode for a lithium-sulfur secondary battery as described in claim 14.

Description

Method of manufacturing a patterned positive electrode for a lithium-sulfur secondary battery and method of manufacturing a lithium-sulfur secondary battery comprising the same The present invention relates to a positive electrode for a lithium-sulfur secondary battery and a lithium-sulfur secondary battery including the same. As the application areas of secondary batteries expand to electric vehicles (EVs) and energy storage systems (ESS), lithium-ion secondary batteries, which have a relatively low energy storage density relative to weight (~250 Wh/kg), have limitations in their application to these products. In contrast, lithium-sulfur secondary batteries are gaining attention as a next-generation secondary battery technology because they can theoretically achieve a high energy storage density relative to weight (~2,600 Wh/kg). A lithium-sulfur secondary battery refers to a battery system that uses a sulfur-based material with an S-S (sulfur-sulfur) bond as the positive electrode active material and lithium metal as the negative electrode active material. Sulfur, the main material of the aforementioned positive electrode active material, has the advantages of being abundant globally, non-toxic, and having a low weight per atom. In a lithium-sulfur secondary battery, during discharge, lithium, the negative electrode active material, releases electrons and becomes ionized, undergoing oxidation, while sulfur-based materials, the positive electrode active material, accept electrons and undergo reduction. Here, the oxidation reaction of lithium is a process in which lithium metal releases electrons and is converted into a lithium cation. Additionally, the reduction reaction of sulfur is a process in which the SS bond accepts two electrons and is converted into a sulfur anion. The lithium cations generated by the oxidation reaction of lithium are transferred to the positive electrode through the electrolyte and combine with the sulfur anions generated by the reduction reaction of sulfur to form a salt. Specifically, sulfur prior to discharge has a cyclic S8 structure, which is converted into lithium polysulfide (LiS x ⇌ ) through a reduction reaction. When lithium polysulfide is completely reduced, lithium sulfide ( Li₂S ) is produced. In lithium-sulfur rechargeable batteries, the repeated dissolution and adsorption of polysulfides during charging and discharging significantly impacts performance, as the movement of polysulfides with larger molecular weights, in addition to lithium ions within the electrolyte, has a major influence. Furthermore, electrolytes containing large amounts of dissolved polysulfides exhibit high viscosity and slow down the diffusion rate of lithium ions. Since battery performance varies significantly depending on mass transport characteristics, the technology field has introduced cathodes containing a large number of internal pores using porous carbon materials to enhance mass transport properties. However, while increasing the porosity of the anode can raise energy density, it leads to a problem where the energy density per unit volume decreases because the volume occupied by the pores increases the anode's volume. To miniaturize batteries, the relevant technology field requires measures to improve energy density per unit volume. Meanwhile, in lithium secondary batteries using lithium-based oxides such as LiCoO2 , LiMn2O4 , LiNiO2 , and LiMnO2 as positive electrode active materials, the porosity within the electrode does not significantly affect the performance of the battery because there is no movement of large molecular weight materials such as polysulfides. Therefore, the positive electrode of the above lithium secondary battery generally has a much lower porosity than that of a lithium-sulfur secondary battery, and such a positive electrode with low porosity typically has a problem with wettability with the electrolyte at its surface. Accordingly, Korean Patent Publication No. 10-2015-0082958 solved this problem by increasing the specific surface area of the positive electrode by laser patterning the positive electrode to improve the problem of wettability with the electrolyte at the surface of the positive electrode. In contrast, lithium-sulfur secondary batteries contain many pores within the cathode, facilitating the penetration of the electrolyte; therefore, since the wettability between the electrolyte and the cathode is not an issue in the first place, there was typically no need to utilize the aforementioned laser patterning technology in lithium-sulfur secondary batteries. The inventors realized that, rather than improving the wettability of the electrolyte and the cathode in a lithium-sulfur secondary battery, the energy density per unit volume of the lithium-sulfur secondary battery can be enhanced by utilizing laser patterning technology on the cathode of a low-porosity lithium-sulfur secondary battery to process its surface into a uniform pattern, thereby modifying t