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KR-102962583-B1 - ELECTROLYTE FOR LITHIUM SECONDARY BATTERY AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME

KR102962583B1KR 102962583 B1KR102962583 B1KR 102962583B1KR-102962583-B1

Abstract

The present invention relates to an electrolyte for a lithium secondary battery comprising: a first solvent comprising a heterocyclic compound comprising one or more double bonds and simultaneously comprising one of an oxygen atom and a sulfur atom; a second solvent comprising one or more of an ether-based compound, an ester-based compound, an amide-based compound and a carbonate-based compound; a lithium salt; lithium nitrate; and an additive for ORM; and a lithium-sulfur secondary battery comprising the same.

Inventors

  • 김현진
  • 박성효
  • 신동석

Assignees

  • 주식회사 엘지에너지솔루션

Dates

Publication Date
20260507
Application Date
20210129

Claims (15)

  1. A first solvent comprising a heterocyclic compound comprising one or more double bonds and simultaneously comprising either an oxygen atom or a sulfur atom; A second solvent comprising one or more of ether-based compounds, ester-based compounds, amide-based compounds, and carbonate-based compounds; Lithium salt; Lithium nitrate; and Additives for ORM (Organic redox mediator); including, The above additive for the ORM (Organic redox mediator) is a cyanoquinone-based additive, an electrolyte for a lithium-sulfur secondary battery.
  2. In paragraph 1, An electrolyte for a lithium-sulfur secondary battery comprising one or more selected from the group consisting of the above cyanoquinone-based additive being 7,7,8,8-tetracyanoquinodimethane (TCNQ).
  3. delete
  4. delete
  5. In paragraph 1, A lithium-sulfur secondary battery electrolyte having a content of the above-mentioned ORM additive of 0.01% to 0.8% by weight relative to the total weight of the above-mentioned lithium-sulfur secondary battery electrolyte.
  6. In paragraph 1, Electrolyte for a lithium-sulfur secondary battery, wherein the volume ratio of the first solvent and the second solvent is 1:0.5 to 1:6.
  7. In paragraph 1, An electrolyte for a lithium-sulfur secondary battery, wherein the lithium salt is one or more selected from the group consisting of LiCl, LiBr, LiI , LiClO₄ , LiBF₄ , LiB₁₀Cl₁₀ , LiPF₆ , LiCF₃SO₃ , LiCF₃CO₂ , LiC₄BO₅ , LiAsF₆ , LiSbF₆ , LiAlCl₄ , CH₃SO₃Li , CF₃SO₃Li , ( C₂F₅SO₂ ) ₂NLi , LiFSI((SO₂F)₂NLi ) , ( CF₃SO₂ ) ₃CLi , lithium chloroborane, lithium lower aliphatic carboxylate having 4 or fewer carbon atoms, lithium 4-phenylborate, and lithium imide.
  8. In paragraph 1, Electrolyte for a lithium-sulfur secondary battery, characterized in that the concentration of the lithium salt is 0.2 to 2.0 M.
  9. In paragraph 1, An electrolyte for a lithium-sulfur secondary battery, wherein the above heterocyclic compound is a heterocyclic compound of 3 to 15 members substituted or unsubstituted with one or more selected from the group consisting of an alkyl group having 1 to 4 carbon atoms, a cyclic alkyl group having 3 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, a halogen group, a nitro group, an amine group, and a sulfonyl group, or a polycyclic compound of a heterocyclic compound and one or more of a cyclic alkyl group having 3 to 8 carbon atoms and an aryl group having 6 to 10 carbon atoms.
  10. In paragraph 1, An electrolyte for a lithium-sulfur secondary battery, wherein the above heterocyclic compound is selected from the group consisting of furan, 2-methylfuran, 3-methylfuran, 2-ethylfuran, 2-propylfuran, 2-butylfuran, 2,3-dimethylfuran, 2,4-dimethylfuran, 2,5-dimethylfuran, pyran, 2-methylpyran, 3-methylpyran, 4-methylpyran, benzofuran, 2-(2-nitrovinyl)furan, thiophene, 2-methylthiophene, 2-ethylthiophene, 2-propylthiophene, 2-butylthiophene, 2,3-dimethylthiophene, 2,4-dimethylthiophene, and 2,5-dimethylthiophene.
  11. In paragraph 1, An electrolyte for a lithium-sulfur secondary battery, wherein the ether-based compound of the second solvent is one or more selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 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.
  12. In paragraph 1, The above electrolyte for a lithium-sulfur secondary battery further comprises one or more selected from the group consisting of lanthanum nitrate, potassium nitrate, cesium nitrate, magnesium nitrate, barium nitrate, lithium nitrite, potassium nitrite, and cesium nitrite.
  13. In paragraph 1, The above electrolyte for a lithium-sulfur secondary battery comprises 2-methylfuran as a first solvent, dimethoxyethane as a second solvent, LiFSI (( SO₂F ) ₂NLi ) as a lithium salt, lithium 7,7,8,8-tetracyanoquinodimethane (TCNQ) as a cyanoquinone-based additive, and lithium nitrate.
  14. anode; cathode; A separator interposed between the anode and the cathode; and A lithium-sulfur secondary battery comprising an electrolyte for a lithium-sulfur secondary battery according to claim 1.
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Description

Electrolyte for lithium secondary battery and lithium secondary battery comprising the same The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery containing the same, and more specifically, to an electrolyte for a lithium secondary battery and a lithium secondary battery containing the same, which can improve the lifespan characteristics and lithium cycle efficiency of a lithium secondary battery by appropriately combining a solvent, a lithium salt, and an additive included in the electrolyte of the lithium secondary battery. 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. Due to the low electrical conductivity of sulfur, the cathode active material, it is difficult to ensure reactivity with electrons and lithium ions in its solid form. To improve the reactivity of sulfur, conventional lithium-sulfur secondary batteries generate intermediate polysulfides of theLi₂Sx type to induce a liquid-phase reaction and enhance reactivity. In this case, ether-based solvents such as dioxolane and dimethoxyethane, which have high solubility for lithium polysulfides, are used as the solvent for the electrolyte. However, when using such ether-based solvents, there is a problem in that the lifespan characteristics of the lithium-sulfur secondary battery are degraded due to various causes. For example, the lifespan characteristics of the lithium-sulfur secondary battery may be degraded due to the leaching of lithium polysulfide from the anode, the occurrence of a short circuit caused by the growth of dendrites on the lithium anode, and the deposition of by-products due to the decomposition of the electrolyte. In particular, when using such ether-based solvents, a large amount of lithium polysulfide can be dissolved, resulting in high reactivity; however, due to the characteristics of lithium polysulfide dissolved in the electrolyte, the reactivity and lifespan characteristics of sulfur are affected by the electrolyte content. In order to develop high-energy density lithium-sulfur secondary batteries with a capacity of 500 Wh/kg or more, which are required for aircraft and next-generation electric vehicles, it is required that the loading amount of sulfur in the electrode be large and the electrolyte content be minimized. However, due to the characteristics of the above ether-based solvent, as the electrolyte content decreases, the viscosity increases rapidly during charging and discharging, and as a result, there is a problem that overvoltage may occur and degradation may occur. Accordingly, research on adding separate additives to the electrolyte is continuously being conducted to prevent electrolyte decomposition and ensure excellent lifespan characteristics. Nevertheless, the components and composition of the electrolyte capable of improving lifespan characteristics and lithium cycle efficiency have not been clearly identified. FIG. 1 is a graph showing the high-rate discharge characteristics of a lithium-sulfur secondary battery manufactured according to Examples 1 to 3 and Comparative Example 1 of the pr