CN-115868061-B - Electrolyte for lithium-sulfur battery and lithium-sulfur battery comprising same

Abstract

The present invention relates to an electrolyte for a lithium-sulfur battery, and a lithium-sulfur battery comprising the same, wherein the electrolyte comprises a first solvent comprising a heterocyclic compound comprising at least one double bond and simultaneously comprising an oxygen atom or a sulfur atom, a second solvent comprising at least one of an ether-based compound, an ester-based compound, an amide-based compound and a carbonate-based compound, a lithium salt, lithium nitrate, and a borate-based lithium salt.

Inventors

• Pu Chengxiao
• JIN XIANZHEN
• PU CHANGXUN

Assignees

• 株式会社LG新能源

Dates

Publication Date

20260512

Application Date

20220106

Priority Date

20210107

Claims (6)

1. 1. An electrolyte for a lithium-sulfur battery, comprising: a first solvent which is 2-methylfuran; A second solvent which is dimethoxyethane; a lithium salt, which is (SO 2 F) 2 NLi; lithium nitrate, and The borate salt is a lithium salt of the type, Wherein the volume ratio of the first solvent to the second solvent is 1:4.5 to 1:5.5, Wherein the borate-based lithium salt is contained in an amount of 0.01 to 5.0 wt% relative to the total weight of the electrolyte for lithium-sulfur batteries, and Wherein the borate-based lithium salt is at least one selected from the group consisting of lithium bis (oxalato) borate, lithium difluoro (oxalato) borate, and lithium bis (2-methyl-2-fluoro-malonic acid) borate.
2. 2. The electrolyte for lithium-sulfur battery according to claim 1, wherein a weight ratio of the borate-based lithium salt to the lithium nitrate is 1:1 to 1:30.
3. 3. The electrolyte for a lithium-sulfur battery according to claim 1, wherein the concentration of the lithium salt is 0.2 to 2.0M.
4. 4. The electrolyte for a lithium sulfur battery according to claim 1, wherein the electrolyte for a lithium sulfur battery further comprises at least one selected from the group consisting of lanthanum nitrate, potassium nitrate, cesium nitrate, magnesium nitrate, barium nitrate, lithium nitrite, potassium nitrite, and cesium nitrite.
5. 5. The electrolyte for a lithium-sulfur battery according to claim 1, wherein the electrolyte for a lithium-sulfur battery comprises 2-methylfuran as a first solvent, dimethoxyethane as a second solvent, and (SO 2 F) 2 NLi as a lithium salt, lithium difluorooxalato borate as a borate-based lithium salt, and lithium nitrate.
6. 6. A lithium sulfur battery comprises A positive electrode; A negative electrode; A separator interposed between the positive electrode and the negative electrode, and The electrolyte for a lithium-sulfur battery according to claim 1.

Description

Electrolyte for lithium-sulfur battery and lithium-sulfur battery comprising same Technical Field The present invention relates to an electrolyte for a lithium-sulfur battery and a lithium-sulfur battery including the same, and more particularly, to an electrolyte for a lithium-sulfur battery capable of improving life characteristics and lithium cycle efficiency of a lithium-sulfur battery by appropriately combining a solvent, a lithium salt, and an additive contained in the electrolyte for a lithium-sulfur battery, and a lithium-sulfur battery including the same. The present application claims priority based on korean patent application No. 10-2021-0001823 filed on 1 month 7 of 2021, the entire contents of which are incorporated herein by reference. Background As the field of application of secondary batteries expands to Electric Vehicles (EV) or energy storage devices (ESS), lithium ion secondary batteries having a relatively low gravimetric energy storage density (250 Wh/kg) face limitations in the application of such products. In contrast, lithium-sulfur secondary batteries are attracting attention as next-generation secondary battery technologies because they can achieve a theoretically high gravimetric energy storage density (2,600 wh/kg). A lithium-sulfur battery refers to a battery system using a sulfur-based material having an S-S bond (sulfur-sulfur bond) as a positive electrode active material, and using lithium metal as a negative electrode active material. Sulfur, which is a main material of the positive electrode active material, has advantages of very abundant worldwide resources, no toxicity, and low atomic weight. In a lithium-sulfur secondary battery, when the battery is discharged, lithium as a negative electrode active material is oxidized while releasing electrons to be ionized, and a sulfur-based material as a positive electrode active material is reduced while accepting electrons. In this case, the oxidation reaction of lithium is a process in which lithium metal releases electrons and converts into a lithium cation form. In addition, the reduction reaction of sulfur is a process in which the S-S bond accepts two electrons and converts to the sulfide anion form. Lithium cations generated by the oxidation reaction of lithium are transferred to the positive electrode (positive electrode) through the electrolyte and combined with sulfur anions generated by the reduction reaction of sulfur to form a salt. Specifically, sulfur before discharge has a ring-shaped S 8 structure, which is converted into lithium polysulfide (LiS x) by a reduction reaction. When the lithium polysulfide is fully reduced, lithium sulfide (Li 2 S) is produced. Sulfur as a positive electrode active material is difficult to ensure reactivity with electrons and lithium ions in a solid state due to its low conductivity characteristics. In the existing lithium sulfur secondary battery, in order to improve the reactivity of sulfur, intermediate polysulfide in the form of Li 2Sx is generated to induce a liquid phase reaction and improve the reactivity. In this case, an ether solvent such as dioxolane or dimethoxyethane having high solubility in lithium polysulfide is used as the solvent for the electrolyte. However, when such an ether-based solvent is used, there is a problem in that life characteristics of the lithium-sulfur battery deteriorate due to various reasons. For example, life characteristics of lithium-sulfur batteries may be deteriorated by leaching of lithium polysulfide from the positive electrode, occurrence of short circuits due to growth of dendrites on the lithium negative electrode, accumulation of byproducts from decomposition of the electrolyte, and the like. In particular, when such an ether-based solvent is used, it is capable of dissolving a large amount of lithium polysulfide, and thus the reactivity is high. However, due to the nature of lithium polysulfide that is soluble in the electrolyte, the reactivity and lifetime characteristics of sulfur are affected by the electrolyte content. In recent years, in order to develop lithium sulfur secondary batteries of 500Wh/kg or more high energy density required for aircrafts and next-generation electric vehicles, it is required that the amount of sulfur loading in the electrode is large and the content of the electrolyte is minimized. However, due to the characteristics of the ether solvent, there is a problem in that as the content of the electrolyte decreases, viscosity rapidly increases during charge and discharge, and thus overvoltage may occur and the battery may deteriorate. Therefore, in order to prevent decomposition of the electrolyte and ensure excellent life characteristics, research is being conducted on adding a separate additive to the electrolyte. However, the composition and composition of the electrolyte capable of improving life characteristics and lithium cycle efficiency have not been clearly determined. [ Prior art document ] [ Pate