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KR-102962592-B1 - Lithium-sulfur battery with improved lifespan performance

KR102962592B1KR 102962592 B1KR102962592 B1KR 102962592B1KR-102962592-B1

Abstract

A lithium-sulfur battery with improved lifespan performance is disclosed, which can utilize more than 80% of the theoretical discharge capacity (1,675 mAh/g) of sulfur and enable long-life operation by using a sparingly solvating electrolyte (SSE) system (discharge capacity ~1,600 mAh/gs) excluding nitrile-based solvents and applying a carbon material with a high specific surface area to the cathode. The lithium-sulfur battery comprises: an electrolyte comprising a first solvent containing a fluorine-based ether compound, a second solvent containing a glycine-based compound, and a lithium salt containing lithium bis(pentafluoroethanesulfonyl)imide; and a cathode comprising sulfur and a carbon material as active materials.

Inventors

  • 박성효
  • 이창훈
  • 박인태
  • 최란
  • 이현수
  • 김용휘
  • 송명준

Assignees

  • 주식회사 엘지에너지솔루션

Dates

Publication Date
20260507
Application Date
20220118

Claims (13)

  1. An electrolyte comprising a first solvent comprising a fluorinated ether compound, a second solvent comprising a glycine compound, and a lithium salt comprising lithium bis(pentafluoroethanesulfonyl)imide; and A cathode comprising sulfur and carbon material as active material; and A lithium-sulfur battery in which the molar ratio of the lithium salt, the second solvent, and the first solvent included in the electrolyte is 1 : 1.5 ~ 2.7 : 2.8 ~ 5.
  2. delete
  3. A lithium-sulfur battery according to claim 1, characterized in that the concentration of the lithium salt is 1 M to 1.8 M.
  4. A lithium-sulfur battery according to claim 1, wherein the fluorinated ether compound comprises one or more selected from the group consisting of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), bis(fluoromethyl) ether, 2-fluoromethyl ether, bis(2,2,2-trifluoroethyl) ether, propyl 1,1,2,2-tetrafluoroethyl ether, isopropyl 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl isobutyl ether, 1,1,2,3,3,3-hexafluoropropylethyl ether, 1H,1H,2'H,3H-decafluorodipropyl ether, and 1H,1H,2'H-perfluorodipropyl ether.
  5. A lithium-sulfur battery according to claim 1, wherein the glycine-based compound comprises one or more selected from the group consisting of dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether, and polyethylene glycol methyl ether.
  6. A lithium-sulfur battery according to claim 1, characterized in that the electrolyte does not contain a nitrile-based solvent.
  7. A lithium-sulfur battery according to claim 1, characterized in that the sulfur is included in an amount of 60 to 80 weight% with respect to the total weight of the anode.
  8. A lithium-sulfur battery according to claim 1, characterized in that the pore volume of the carbon material is 0.7 to 3 cm³ /g and the specific surface area is 1,700 m² /g or more.
  9. A lithium-sulfur battery according to claim 1, characterized in that the positive electrode active material included in the positive electrode comprises a sulfur-carbon composite.
  10. A lithium-sulfur battery according to claim 1, characterized in that the sulfur utilization rate included in the anode is 80% or more of the theoretical discharge capacity.
  11. A lithium-sulfur battery according to claim 1, characterized in that the energy density of the lithium-sulfur battery is 400 Wh/kg or more or 600 Wh/L or more.
  12. A lithium-sulfur battery according to claim 1, wherein the first solvent is 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), the second solvent is dimethoxyethane (DME), and the lithium salt is lithium bis(pentafluoroethanesulfonyl)imide (LiBETI).
  13. A lithium-sulfur battery according to claim 12, characterized in that the molar ratio of the lithium salt, the second solvent, and the first solvent is 1:1.9 to 2.4:3.1 to 3.6.

Description

Lithium-sulfur battery with improved lifespan performance The present invention relates to a lithium-sulfur battery with excellent lifespan performance, and more specifically, to a lithium-sulfur battery with improved lifespan performance that can utilize more than 80% of the theoretical discharge capacity (1,675 mAh/g) of sulfur and can operate for a long life by using a sparingly solvating electrolyte (SSE) electrolyte system (discharge capacity ~1,600 mAh/gs) excluding nitrile-based solvents and applying a carbon material with a high specific surface area to the cathode. As interest in energy storage technology continues to grow, research and development in electrochemical devices are steadily increasing as application fields expand to include mobile phones, tablets, laptops, camcorders, and even electric vehicles (EVs) and hybrid electric vehicles (HEVs). Electrochemical devices are receiving the most attention in this regard, and among them, the development of rechargeable secondary batteries, such as rechargeable lithium-sulfur batteries, is a focal point of interest. Recently, research and development in developing such batteries has led to the design of new electrodes and batteries to improve capacity density and specific energy. Such electrochemical devices, among which lithium-sulfur batteries (Li-S batteries), have high energy density (theoretical capacity) and are attracting attention as next-generation rechargeable batteries that can replace lithium-ion batteries. In such lithium-sulfur batteries, a reduction reaction of sulfur and an oxidation reaction of lithium metal occur during discharge, and at this time, sulfur forms a linear structure of lithium polysulfide (LiPS) from a cyclic structure of S8 . Such lithium-sulfur batteries are characterized by exhibiting stepwise discharge voltages until the polysulfide is completely reduced to Li2S . However, the biggest obstacle to the commercialization of lithium-sulfur batteries is their lifespan, as the charge/discharge efficiency decreases during the charge/discharge process, causing the battery's lifespan to degrade. The causes of this degradation in the lifespan of lithium-sulfur batteries are diverse, including side reactions of the electrolyte (deposition of byproducts due to the decomposition of the electrolyte), instability of lithium metal (short circuits caused by the growth of dendrites on the lithium anode), and deposition of cathode byproducts (leaching of lithium polysulfide from the cathode). In other words, in batteries using sulfur-based compounds as the positive electrode active material and alkali metals such as lithium as the negative electrode active material, the leaching and shuttle phenomenon of lithium polysulfides occur during charging and discharging. As lithium polysulfides are transferred to the negative electrode, the capacity of the lithium-sulfur battery decreases, leading to significant problems such as reduced lifespan and decreased reactivity. Specifically, since polysulfides leached from the positive electrode have high solubility in organic electrolytes, unwanted migration (PS shuttling) to the negative electrode through the electrolyte can occur. Consequently, this results in a decrease in capacity due to the irreversible loss of the positive electrode active material and a reduction in battery lifespan caused by the deposition of sulfur particles on the lithium metal surface due to side reactions. Meanwhile, the behavior of such lithium-sulfur batteries can vary significantly depending on the electrolyte. An electrolyte in which sulfur from the cathode leaches out into the electrolyte in the form of lithium polysulfide (LiPS) is called a catholyte, and an electrolyte in which sulfur is hardly leached out in the form of lithium polysulfide is called a sparingly solvating electrolyte (SSE). Lithium-sulfur batteries utilizing the existing catholyte system rely on a liquid phase reaction (catholyte type) through the formation of an intermediate product (intermediate polysulfide) having the form of Li₂Sx . Consequently, they cannot fully utilize the high theoretical discharge capacity (1,675 mAh/g) of sulfur, and instead suffer from the problem of rapidly decreasing battery life due to degradation caused by the leaching of polysulfide. On the other hand, recently, SSE (sparing solvating electrolyte) electrolyte systems capable of suppressing polysulfide leaching have been developed, allowing for the utilization of more than 80% of the theoretical discharge capacity of sulfur. However, most SSE electrolyte systems rely on nitrile-based solvents, and in this case, there are fatal disadvantages to the battery's lifespan, such as the degradation of the lithium anode due to reaction with the lithium anode and the generation of gas inside the lithium-sulfur battery. Accordingly, the industry is conducting various studies on lithium-sulfur batteries in which sulfur, the cathode active material, does not leach into the el