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KR-20260066302-A - Cathode material with lithium salt additive for improved performance of thick cathodes and lithium-sulfur batteries operating in lean electrolytes

KR20260066302AKR 20260066302 AKR20260066302 AKR 20260066302AKR-20260066302-A

Abstract

The present invention relates to a cathode material using a lithium salt additive for improving the performance of a thick cathode and a lithium-sulfur battery operating in a dilute electrolyte using the same. By using a lithium-based additive, the wettability of a polyvinylidene fluoride (PVDF) binder and the bending path for ion movement are improved, and additional availability of lithium ions is provided in a limited electrolyte volume, thereby increasing the energy density of the lithium-sulfur battery.

Inventors

  • 정현영
  • 김희준
  • 첸라얀 센틸

Assignees

  • 경상국립대학교산학협력단

Dates

Publication Date
20260512
Application Date
20241104

Claims (14)

  1. A cathode material for a lithium secondary battery characterized by a polyvinylidene fluoride (PVDF) binder lithiated by a lithium salt.
  2. In paragraph 1, The above-mentioned cathode material for a lithium secondary battery is, A cathode material for a lithium secondary battery characterized by being modified by mixing a PVDF binder in an N-methyl-2-pyrrolidone (NMP) solvent in which a lithium salt is dissolved.
  3. In paragraph 2, The above PVDF modified binder is, A cathode material for a lithium secondary battery characterized by comprising 70 to 85 parts by weight of a sulfur/carbon composite, 10 to 15 parts by weight of a conductive material, and 5 to 15 parts by weight of polyvinylidene fluoride (PVDF).
  4. In paragraph 3, The N-methyl-2-pyrrolidone (NMP) solvent in which the above lithium salt is dissolved is, A cathode material for a lithium secondary battery characterized by dissolving 4 to 10 mg of lithium salt in 1 mL of solvent.
  5. In paragraph 4, A cathode material for a lithium secondary battery characterized by selecting one of LiTFSI, LiNO3 , LiOH, or LiF for the lithium salt.
  6. In paragraph 5, The above lithium salt is a cathode material for a lithium secondary battery characterized by having a lithium content of 0.0019 to 0.023 mg/ cm².
  7. In paragraph 3, The PVDF binder modified by the above lithium salt is, A cathode material for a lithium secondary battery characterized by a modified and reduced α phase.
  8. In Paragraph 7, The above PVDF modified binder is, A cathode material for a lithium secondary battery characterized by a 1.5 to 2.4-fold increase in specific capacity compared to using a pure PVDF binder.
  9. A lithium-sulfur battery capable of operating in a dilute electrolyte comprising a cathode material for a lithium secondary battery according to any one of claims 1 to 8.
  10. In Paragraph 9, The above sulfur cathode material is, A lithium-sulfur battery capable of operating in a dilute electrolyte, characterized by having a cathode material thickness of 50 to 200 μm and a sulfur loading amount of 0.8 to 4.0 mg/ cm² .
  11. In Article 9 The above lithium-sulfur battery is, A cathode material for a lithium-sulfur battery characterized by a PVDF-modified binder having a sulfur utilization rate increased by 32–50% compared to a pure PVDF binder.
  12. In Paragraph 9, A lithium-sulfur battery capable of operating in a lean electrolyte, characterized in that the lean electrolyte has an electrolyte/sulfur ratio of 4 to 12 μL/mg.
  13. In Paragraph 9, The above lithium-sulfur battery is, A lithium-sulfur battery capable of operating in a dilute electrolyte, characterized by the ability to continuously emit or donate lithium ions during discharge by a cathode material for a lithium-sulfur battery according to any one of claims 1 to 8 above.
  14. In Paragraph 9, The above lithium-sulfur battery It can be made of pouch cells, A lithium-sulfur battery capable of operating in a lean electrolyte, characterized by the above-described pouch cell exhibiting an energy density of 190 to 253 Wh/kg.

Description

Cathode material with lithium salt additive for improved performance of thick cathodes and lithium-sulfur batteries operating in lean electrolytes using the same The present invention relates to a cathode material using a lithium salt additive for improving the performance of a thick cathode and a lithium-sulfur battery operating in a dilute electrolyte using the same, characterized by improving the wettability of a polyvinylidene fluoride (PVDF) binder and bending paths for ion movement using a lithium-based additive, and increasing the energy density of the lithium-sulfur battery by providing additional availability of lithium ions in a limited electrolyte volume. As the application areas of secondary batteries expand to include electric vehicles (EVs) and energy storage systems (ESS), lithium-ion secondary batteries, which have a relatively low energy storage density relative to weight, 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. However, although lithium-sulfur (Li-S) batteries are energy storage systems with high energy density, having a theoretical energy density of 2567 Wh/kg and a specific capacity of 1675 mAh/g, various cell engineering factors including insulating sulfur, dissolution of polysulfides, unused sulfur, lithium dendrites, loading of high sulfur mass, and the ratio of negative electrode/anode (N/P) and electrolyte/sulfur (E/S) limit overall electrochemical performance, as known in Non-Patent Literature 1, lithium-sulfur (Li-S) batteries may find it difficult to reach an energy density of 500 Wh/kg due to the factors of the various problems described above. As a solution to the above problems, notable improvements to the sulfur anode have focused on the design of sulfide polymers, engineered carbon, and electrocatalysts, which improved sulfur electrochemistry by using an excessive volume of liquid electrolyte. The above limited studies have focused only on controlling the mass loading of sulfur and the E/S volume by adjusting the wettability of the sulfur anode through additives, electrode structures, etc., which resulted in an energy density between 200 and 350 Wh/kg as known in Non-Patent Literature 2. Therefore, to develop high-energy-density lithium-sulfur batteries, high sulfur mass loading and controlled liquid electrolyte volume are required, and considering the electrode components of a sulfur cathode as known in Non-Patent Literature 3, the binder polyvinylidene difluoride (PVDF) plays an important role in the mechanical integrity of the electrode. However, increasing the electrode thickness and the mass loading of sulfur to increase energy density actually reduces electron and ion transport. In particular, in situations with limited liquid electrolyte, the situation is exacerbated by the poor wettability and high bending path of the original PVDF. Although conductive carbon was adopted to overcome electron transport, ion transport during electrochemical cycling increases the ion polarization concentration. Furthermore, due to the strong interaction between PVDF and N-methyl pyrrolidone (NMP), the binder tends to migrate to the propylene membrane. This migration of the binder adversely affects the pore distribution across the carbon-binder interface and electrode depth, particularly in thick electrodes, leading to higher bending. Furthermore, this situation weakens the mechanical integrity of the electrode and its adhesion to the current collector. Increasing the porosity of the electrode can enhance electrolyte penetration and reduce bending, but it may reduce the mass of the active material. Therefore, it is essential to adjust the physical properties of the thick electrode to enable operation under conditions of low E/S volume and high sulfur mass loading. Generally, the binder components PVDF and NMP can be surface-modified under alkaline conditions, which can be used to finely tune the electrode properties. Based on the problems and surface modifications of lithium-sulfur batteries, lithium-based additives adopted in PVDF can increase the energy density of lithium-sulfur batteries by activating the phases of the existing PVDF binder to improve wettability and bending pathways for ion movement, as well as providing additional availability of lithium ions in a limited electrolyte volume. Here is a novel approach to modulating the phase of conventional polyvinylidene fluoride binders through lithium-based additives containing various anions such as TFSI-, NO3-, OH-, and F-. The phase modulation of PVDF imparts wettability and a favorable bending path to the electrode, while the ion donation effect provides additional lithium reactivity to sulfur. In addition, as a technology to increase the energy density of lithium-sulfur (Li-S) batteries, various technologi