Specification
Title of Invention: Electrolyte for lithium metal secondary battery
technical field
[One]
Cross-Citation with Related Application(s)
[2]
This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0170942 on December 19, 2019 and Korean Patent Application No. 10-2020-0141979 on October 29, 2020, All content disclosed in the literature is incorporated as a part of this specification.
[3]
The present invention relates to an electrolyte for a lithium metal secondary battery that can be applied to a lithium metal secondary battery containing lithium metal as an anode active material to improve the lifespan characteristics of the battery.
[4]
background
[5]
With the rapid development of electronics, telecommunication, and computer industries, the field of application of energy storage technology is expanding to camcorders, mobile phones, laptops, PCs, and even electric vehicles. Accordingly, the development of high-performance, lightweight, long-lasting, and reliable secondary batteries is in progress.
[6]
Among the currently applied secondary batteries, lithium secondary batteries developed in the early 1990s are in the spotlight because of their high operating voltage and significantly higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries that use aqueous electrolyte solutions. are receiving
[7]
As an anode active material for a lithium secondary battery, lithium metal, a carbon-based material, silicon, etc. are used. Among them, lithium metal has the advantage of obtaining the highest energy density, and thus continuous research is being conducted.
[8]
A lithium electrode using lithium metal as an active material is typically manufactured by using a flat copper or nickel foil as a current collector and attaching a lithium foil thereon. Alternatively, a method of using a lithium foil itself as a lithium electrode without a separate current collector, or assembling a battery using only a current collector without a lithium foil, and then forming a lithium metal layer by charging and discharging the battery to use it as a negative electrode, etc. are known. .
[9]
However, a lithium secondary battery including a lithium metal electrode is stable between the electrolyte and the lithium metal electrode due to the high reactivity of the lithium metal and the surface non-uniformity phenomenon that occurs during the electrodeposition and peeling of the lithium metal on the electrode during battery charging and discharging. There is a problem in that the interface is not formed and a continuous electrolyte decomposition reaction occurs. This electrolyte side reaction not only rapidly increases the battery resistance, but also depletes the electrolyte and available lithium in the battery, which is the main cause of deterioration of the battery life.
[10]
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[11]
In order to solve the above problems, an object of the present invention is to provide a non-aqueous electrolyte having excellent stability with respect to lithium metal.
[12]
means of solving the problem
[13]
Accordingly, according to one embodiment of the present invention,
[14]
An electrolyte for a lithium metal secondary battery comprising a lithium salt and a non-aqueous solvent, wherein the concentration of the lithium salt is greater than 2.0 M to 4.0 M or less,
[15]
The lithium salt includes lithium bis(fluorosulfonyl)imide,
[16]
The non-aqueous solvent is 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether; cyclic fluorinated carbonate-based solvents; and one or more solvents selected from the group consisting of chain carbonates, chain esters, and chain ether solvents;
[17]
The 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether is included in an amount of 32% by volume or less with respect to 100% by volume of the total non-aqueous solvent, an electrolyte for a lithium metal secondary battery is provided do.
[18]
In one embodiment, the 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether may be included in an amount of 10% by volume to 30% by volume based on 100% by volume of the total non-aqueous solvent. have.
[19]
In one embodiment, the cyclic fluorinated carbonate-based solvent may be included in an amount of 5 to 30% by volume based on 100% by volume of the total non-aqueous solvent.
[20]
In one embodiment, the cyclic fluorinated carbonate-based solvent may be at least one selected from the group consisting of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate.
[21]
In one embodiment, the chain carbonate may be at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.
[22]
In one embodiment, the chain ester may be at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.
[23]
In one embodiment, the chain ether may be at least one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether.
[24]
In one embodiment, the at least one solvent selected from the group consisting of the chain carbonate, the chain ester, and the chain ether solvent is dimethyl carbonate, diethyl carbonate, methyl propionate, ethyl propionate, dimethyl ether, and It may be at least one selected from the group consisting of diethyl ether.
[25]
In one embodiment, the electrolyte may include lithium bis(fluorosulfonyl)imide in an amount of 20 to 50% by weight of the total weight of the electrolyte.
[26]
In one embodiment, the electrolyte may have a lithium salt concentration of 2.1 M to 3.0 M.
[27]
In addition, according to another embodiment of the present invention, a lithium metal secondary battery including the electrolyte is provided.
[28]
Specifically, the lithium metal secondary battery includes a positive electrode; lithium metal negative electrode; a separator interposed between the anode and the cathode; and the electrolyte solution of the present invention described above.
[29]
Effects of the Invention
[30]
The electrolyte solution for a lithium metal secondary battery of the present invention has excellent stability to lithium metal and thus has few electrolyte side reactions. Accordingly, it can be applied to a lithium metal secondary battery to improve the lifespan characteristics and high rate charging performance of the battery.
[31]
Brief description of the drawing
[32]
1 is a result of measuring the capacity retention rate at 25 ℃ for each battery of Examples 1, 2, and Comparative Examples 1-3.
[33]
2 is a result of measuring the capacity retention rate at 45 ℃ for each battery of Example 2 and Comparative Example 1.
[34]
Modes for carrying out the invention
[35]
The terminology used herein is used to describe exemplary embodiments only, and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In this specification, terms such as "comprises", "comprising" or "have" are intended to designate the presence of an embodied feature, step, element, or a combination thereof, but one or more other features or steps; It should be understood that the possibility of the presence or addition of components, or combinations thereof, is not precluded in advance.
[36]
Since the present invention may have various modifications and various forms, specific embodiments will be illustrated and described in detail below. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.
[37]
Hereinafter, the present invention will be described in detail.
[38]
[39]
Electrolyte for lithium metal secondary battery
[40]
The electrolyte solution for a lithium metal secondary battery according to an embodiment of the present invention includes a lithium salt and a non-aqueous solvent, the concentration of the lithium salt is greater than 2.0 M to 4.0 M or less, and the lithium salt is lithium bis(fluorosulfonyl)imide (LiFSI), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE) as a non-aqueous solvent; cyclic fluorinated carbonate-based solvents; and one or more solvents selected from the group consisting of chain carbonates, chain esters, and chain ether solvents. In this case, the OTE is included in an amount of 32% by volume or less based on 100% by volume of the total non-aqueous solvent.
[41]
The present inventors have repeatedly studied the composition of a non-aqueous electrolyte suitable for use in a lithium metal battery containing lithium metal as an anode active material. As a result, when the electrolyte satisfying the composition of the present invention is applied to a lithium metal battery, the conventional electrolyte solution The present invention was completed by confirming that it exhibits significantly improved stability compared to , and greatly improves battery life and high-rate charging performance. Such an effect of the present invention can be secured only when the combination of the lithium salt and the solvent is satisfied, and it is difficult to achieve when any one of the above components is insufficient.
[42]
The 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE) is a material having the following structural formula and is used as a solvent in the non-aqueous electrolyte of the present invention.
[43]

[44]
OTE has the effect of improving the battery life characteristics by suppressing the side reaction between the lithium metal and the electrolyte, and reducing the viscosity of the high-concentration electrolyte with high viscosity to improve the impregnation of the electrode and the separator.
[45]
However, as a result of the experiments of the present inventors, when the content of OTE exceeds 32% by volume based on 100% by volume of the total non-aqueous solvent used in the electrolyte, the life improvement effect is somewhat reduced. In addition, even when the OTE content is too small, less than 5% by volume based on the total volume of the non-aqueous solvent, the above effect cannot be ensured. Therefore, in order to secure the effect of improving the stability of the electrolyte and improving the battery life characteristics, OTE is 5% by volume or more, 10% by volume or more, or 20% by volume or more, and 30% by volume or less with respect to 100% by volume of the total non-aqueous solvent , 25% by volume or less, or 24% by volume or less is preferably included.

Claims
[Claim 1]
An electrolyte for a lithium metal secondary battery comprising a lithium salt and a non-aqueous solvent, wherein the lithium salt concentration is greater than 2.0 M to 4.0 M or less, wherein the lithium salt includes lithium bis (fluorosulfonyl) imide, and the non-aqueous solvent is 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether; cyclic fluorinated carbonate-based solvents; and one or more solvents selected from the group consisting of chain carbonates, chain esters, and chain ether solvents, wherein the 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoro Roethyl ether is included in an amount of 32% by volume or less with respect to 100% by volume of the total non-aqueous solvent, an electrolyte for a lithium metal secondary battery.
[Claim 2]
The method according to claim 1, wherein the 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether is included in an amount of 10% by volume to 30% by volume based on 100% by volume of the total non-aqueous solvent. An electrolyte for a lithium metal secondary battery.
[Claim 3]
The electrolyte solution for a lithium metal secondary battery according to claim 1, wherein the cyclic fluorinated carbonate-based solvent is included in an amount of 5 to 30% by volume based on 100% by volume of the total non-aqueous solvent.
[Claim 4]
The electrolyte solution for a lithium metal secondary battery according to claim 1, wherein the cyclic fluorinated carbonate-based solvent is at least one selected from the group consisting of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate.
[Claim 5]
According to claim 1, wherein the chain carbonate is dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and at least one selected from the group consisting of ethyl propyl carbonate, lithium metal electrolyte for a secondary battery.
[Claim 6]
The electrolyte for a lithium metal secondary battery according to claim 1, wherein the chain ester is at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.
[Claim 7]
The electrolyte solution for a lithium metal secondary battery according to claim 1, wherein the chain ether is at least one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether.
[Claim 8]
According to claim 1, wherein at least one solvent selected from the group consisting of chain carbonate, chain ester, and chain ether solvent is dimethyl carbonate, diethyl carbonate, methyl propionate, ethyl propionate, dimethyl ether, and at least one electrolyte solution for a lithium metal secondary battery selected from the group consisting of diethyl ether.
[Claim 9]
The electrolyte solution for a lithium metal secondary battery according to claim 1, wherein the lithium bis(fluorosulfonyl)imide is contained in an amount of 20 to 50% by weight of the total weight of the electrolyte.
[Claim 10]
The electrolyte for a lithium metal secondary battery according to claim 1, wherein the lithium salt concentration is 2.1 M to 3.0 M.
[Claim 11]
anode; lithium metal negative electrode; a separator interposed between the anode and the cathode; and a lithium metal secondary battery comprising the electrolyte of any one of claims 1 to 10.