KR102099387B1 - Electrolyte system and lithium metal battery comprising the same - Google Patents

Abstract

The present invention relates to an electrolyte for a lithium metal secondary battery and a lithium metal secondary battery comprising the same. According to the present invention, an electrolyte system for maintaining the energy density of the lithium metal anode-based secondary battery and extending the life of the battery can be provided. Specifically, lithium is stabilized to prevent the internal short circuit and the anode of the lithium metal battery having a high probability of ignition of the battery. It may be provided in a lithium metal battery electrolyte having a stable SEI film capable of suppressing the formation and diffusion of dendrites and a lithium metal secondary battery including the same.

Description

Electrolyte for lithium metal secondary battery and lithium metal secondary battery comprising the same {Electrolyte system and lithium metal battery comprising the same}

The present invention relates to an electrolyte system for a lithium metal secondary battery and a lithium metal secondary battery comprising the same.

The first concept of a lithium ion battery (LiB) was presented in 1962, and a LiB secondary battery was proposed by MS Whittingham of Exxon, leading to the invention of the Li-TiS ₂ battery. However, commercialization of the battery system using lithium metal and TiS ₂ as negative and positive electrodes failed, due to the weak safety of lithium metal batteries (LiM) and the high manufacturing cost of TiS ₂ sensitive to air and water. Afterwards, commercialization of the current LiB was successful by solving these problems by using graphite and anode oxide (developed by Besenhard), which reversibly insert and deintercalate lithium, as cathode and anode, respectively. For the first time in 1991, LiB's commercial products were launched by Sony and Asahi companies, bringing revolutionary momentum to the successful market expansion of portable electronics. Since then, LiB has been used explosively and has met the demand for electrical energy, which is directly related to the constant innovation of everyday electrical devices, especially mobile phones, music players, speakers, drones, automobiles and micro sensors. Many researchers and scientists have been working on new and advanced energy materials, chemistry and physics for stationary or mobile energy storage systems that meet increasing energy demands.

Since the development of commercial LiB technology has recently reached a saturation state where only a gradual improvement in the electrochemical performance of LiB is reported, research and development of new energy storage materials and systems with different shapes and compositions is essential. Therefore, secondary batteries such as lithium-sulfur and lithium-air batteries having a lithium metal negative electrode and a convertible positive electrode have attracted attention as a next-generation battery because they have a high energy density. Sulfur and carbon-based air anodes theoretically have energy densities of ~ 2,600 Wh / kg and ~ 11,400 Wh / kg, respectively, which are almost 10 times the energy density of existing LiB (~ 360 Wh / kg, C / LiCoO ₂ ). It shows a high value. Lithium metal, one of the negative electrode materials, has a very low redox potential (-3.04 V vs. SHE) and a density of 0.59 g / cm ³ with a high theoretical energy density of ~ 3,860 Wh / kg, whereas graphite negative electrode materials It has a theoretical energy density of ~ 372 mAh / g, a slightly higher redox potential and density. Therefore, if the graphite cathode is replaced with a lithium cathode, the energy density per weight of the existing LiB can be greatly increased. If lithium-sulfur and lithium-air batteries are commercialized in the future, lithium metal anodes and convertible anode materials may show a hopeful way to overcome high energy density requirements.

Although it has such good merits, it is necessary to solve some difficult challenges in order to commercialize a battery using lithium metal as a negative electrode. At the center is the reversibility of electrodeposition and dissolution of lithium ions. Lithium's high reactivity and non-uniform electrodeposition cause problems such as thermal runaway, electrolyte decomposition, and lithium loss. Non-uniform electrodeposition of lithium ions during charging causes dendrite growth in the shape of branches, which is due to the growth of SEI (solid electrolyte interface) films, low coulomb efficiency and electrochemical properties of the lithium surface due to side reactions between the electrolyte and the lithium cathode. Causing the problem of sharply lowering. In addition, the short circuit caused by the growth of lithium dendrites causes a lot of heat and sparks, leading to serious safety problems that ignite the flammable organic electrolyte. Therefore, in order to increase the safety, it is necessary to form a stable SEI for the formation of dendrites and severe side reactions with the electrolyte in the lithium cathode, which is possible by appropriately mixing the salts used in the electrolyte to change the constituent materials of the SEI film. . The formation of a thin, strong and high lithium ion conductivity SEI film on the surface of the lithium cathode is important, and the development of an electrolyte system capable of maintaining the desired anode characteristics is the core of lithium metal battery development.

Korean Registered Patent No. 10-1586139 Korean Patent Publication No. 10-2016-0078334 Korean Registered Patent No. 10-1471793 Korean Registered Patent No. 10-15380790 Korean Registered Patent No. 10-10747830 Korean Patent Publication No. 10-2015-0004179 U.S. Patent Publication No. 2014-0127577

During the electrochemical cycle, a large, active lithium metal surface tends to form dendrites during charging due to local current density differences on irregular surfaces. When the dendrite-growing dendrite formation diffuses, the surface area of the lithium cathode rapidly increases, which causes the formation of an SEI film on the surface of the lithium cathode, and the continuous formation of a thick SEI film reduces the electrolyte and lithium ion conductivity of the lithium cathode. The problem of sharply lowering occurs. Lithium tribis (fluorosulfonyl) imide (LiTFSI), lithium bis (fluorosulfonyl) imide (LiFSI), and lithium bis (oxalate) borate in order to suppress unstable SEI formation due to the generation of lithium dendrites (LiBOB), lithium hexafluoro phosphate (LiPF ₆ ), lithium fluoride (LiF) salt dissolved in a solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), 1,2-dimethoxyethane (DME) to fluorine As an electrolyte, Ethylene Carbonate (FEC) and Vinylene Carbonate (VC) are additionally used together, and it is compatible with various positive electrode materials of lithium metal batteries. As a result, by applying the invented electrolyte system, it was possible to increase the cycle life and capacity retention rate of the lithium metal anode-based battery by generating a thin, sturdy and stable SEI on the surface of the lithium cathode and suppressing side reactions with the electrolyte.

One aspect of the present invention is (a) a first salt selected from LiFSI, LiTFSI, and mixtures thereof, (b) a second salt selected from LiBOB, LiDFOB and mixtures thereof, (c) a third salt comprising LiPF ₆ , (d) An electrolyte for a lithium metal secondary battery comprising a solvent composed of a mixture of EC and DMC, (e) further comprising at least one solvent additive selected from FEC and VC, wherein the solvent additive is the entire electrolyte. It relates to a lithium metal secondary battery electrolyte, characterized in that at least one selected from 0.4 to 1.5% by weight of FEC and 0.01 to 3.5% by weight of VC based on weight.

Another aspect of the invention is (a) a first salt selected from LiFSI, LiTFSI, and mixtures thereof, (b) a second salt selected from LiBOB, LiDFOB and mixtures thereof, (c) a third salt comprising LiPF ₆ , (d) An electrolyte for a lithium metal secondary battery comprising a solvent composed of a mixture of EC and DMC, (e) further comprising at least one first solvent additive selected from FEC and VC, and (f) removing TFEC. 2 It is further included as a solvent additive, the first solvent additive is at least one selected from 0.4 to 1.5% by weight of FEC and 0.01 to 3.5% by weight of VC based on the total weight of the electrolyte, the second solvent The concentration of the sex additive relates to an electrolyte for a lithium metal secondary battery, characterized in that it is 2.5 to 4.5% by weight based on the total weight of the electrolyte.

Another aspect of the invention is a third salt comprising (a) a first salt selected from LiFSI, LiTFSI, and mixtures thereof, (b) a second salt selected from LiBOB, LiDFOB and mixtures thereof, and (c) LiPF ₆ An electrolyte for a lithium metal secondary battery comprising a salt, (d) a solvent composed of a mixture of EC and DMC, further comprising (e) at least one first solvent additive selected from FEC and VC, and (f) LiBF ₄ It is further included as a fourth salt, (g) optionally further comprises TFEC as a second solvent additive, the first solvent additive is FEC of 0.4 to 1.5% by weight based on the total weight of the electrolyte and 0.01 to 3.5% by weight of one or more selected from VC, the concentration of the fourth salt is 0.02 to 0.06 M, and if the second solvent additive is included, the concentration of the second solvent additive is the electrolyte 0.8 to 1.2% by weight based on the total weight It relates to a lithium metal secondary battery electrolyte as.

Another aspect of the present invention relates to a lithium metal secondary battery including an electrolyte for a lithium metal secondary battery according to various embodiments of the present invention.

Another aspect of the present invention relates to an electrical device including an electrolyte for a lithium metal secondary battery according to various embodiments of the present invention.

It is an object of the present invention to provide an electrolyte system for maintaining the energy density of the lithium metal anode-based secondary battery and extending the battery life. The ultimate application goal of this technology is to use various anodes such as transition metal oxides, sulfur, and air electrodes used in lithium metal batteries with high energy density, as well as existing lithium ion batteries used in future unmanned electric vehicles and power grid energy storage systems. Lithium metal is used together. It will also contribute to the development of unmanned aerial vehicles such as drones. It is expected that the present invention can secure the global competitiveness of the related secondary battery and electrochemical capacitor industries. In particular, when dealing with high-density materials, safety studies have recently attracted attention as one of the key studies. The reason is that the safety is reduced due to the implementation of a high energy density in commercializing the product. It is inevitable to secure battery safety with high energy density, especially due to the social and technological winds caused by the recent ignition of smartphones. In particular, the upcoming next-generation cells are subject to research and verification on the safety of cells and systems handling the cells, since the energy density of existing lithium-ion batteries is substantially at least 2 to 8 times higher. Accordingly, the present invention provides a technology for a lithium metal battery electrolyte capable of forming a stable SEI film capable of stabilizing the negative electrode of a lithium metal battery with high probability of battery ignition and suppressing the formation and diffusion of lithium dendrites so that internal short circuit does not occur. Is to provide.

1A to 1C show the molecular structures of LiFSI, LiTFSI, LiBOB, LiDFOB, LiPF ₆ , LiF salts and EC, DMC, VC, and FEC solvents constituting the electrolyte according to the present invention.
Figure 2 is a LiFSI, LiTFSI, LiBOB, LiDFOB, LiPF ₆ combination of EC: DMC (4: 6 weight ratio) and DME electrolyte using a coin-type NCM (6/2/2) anode using lithium metal battery characteristics Show.
3 is 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) lithium metal coin using NCM (6/2/2) anode according to FEC addition ratio in the electrolyte system It shows the characteristics of the cell battery.
Figure 4 is a lithium metal coin using NCM (6/2/2) anode according to the ratio of VC in the 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system It shows the characteristics of the cell battery.
5 is a lithium metal coin cell using the NCM (6/2/2) anode according to the FEC addition ratio in the 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system of Figure 3 Shows the characteristics of the battery.
6 is a 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) characteristics of a lithium metal coin cell battery using an NCM (6/2/2) anode according to the VC addition ratio in an electrolyte system Shows
FIG. 7 shows lithium using NCM (6/2/2) anode with FEC and VC added solvent in 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, and 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. It shows the characteristics of a metal coin cell battery.
8 is 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) NCM with 0.5 wt% FEC and 0.5 wt% FEC + 2 wt% VC added solvent in electrolyte system (6/2) / 2) It shows the characteristics of a lithium metal coin cell battery using a positive electrode.
FIG. 9 is a SEM image of the lithium surface after cycling by applying the electrolytes without addition of an additive solvent and an additive solvent other than EC: DMC and the LiTFSI, LiBOB, and LiPF ₆ salts.
FIG. 10 is a spectrum obtained by charging and discharging a cell containing an electrolyte containing the above-described LiTFSI, LiBOB, and LiPF ₆ salts and an additive solvent at 1C for 200 cycles, and then measuring the surface of the lithium cathode with XPS.
11 is a characteristic of a lithium metal coin cell using an NCM (8/1/1) anode according to the FEC addition ratio in the 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system Shows
FIG. 12 shows NCM (8/1 /) according to LiF (0.3-1 M) concentration in 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1 weight% FEC (weight ratio) electrolyte system 1) It shows the characteristics of a lithium metal coin cell battery using a positive electrode.
Figure 13 is a LiFSI, LiTFSI, LiBOB, LiDFOB, LiPF ₆ salt combination EC: DMC (4: 6 weight ratio) and the characteristics of a lithium metal battery using a coin-type NCM (6/2/2) anode using DME electrolyte Show.
FIG. 14 is a lithium metal coin using NCM (6/2/2) anode according to FEC addition ratio in a 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. It shows the characteristics of the cell battery.
FIG. 15 is a lithium metal coin using an NCM (6/2/2) anode according to the ratio of VC in a 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. It shows the characteristics of the cell battery.
FIG. 16 is a lithium metal coin cell using an NCM (6/2/2) anode according to a FEC addition ratio in the 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system of FIG. 3. Shows the characteristics of the battery.
17 is a characteristic of a lithium metal coin cell battery using an NCM (6/2/2) anode according to the VC addition ratio in a 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. Shows
FIG. 18 is a lithium using NCM (6/2/2) anode with FEC and VC additive solvent in a 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. It shows the characteristics of a metal coin cell battery.
Figure 19 is 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) NCM with 0.5 wt% FEC and 0.5 wt% FEC + 2 wt% VC additive solvent in an electrolyte system (6/2) / 2) It shows the characteristics of a lithium metal coin cell battery using a positive electrode.
FIG. 20 is a SEM image of the lithium surface after cycle by applying the electrolytes without the addition of an additive solvent and an additive solvent other than EC: DMC and the LiTFSI, LiBOB, and LiPF ₆ salts.
FIG. 21 is a spectrum obtained by charging and discharging a cell containing an electrolyte containing the above-described LiTFSI, LiBOB, and LiPF ₆ salts and an additive solvent at 1C for 200 cycles, and then measuring the surface of the lithium cathode with XPS.
22 is a characteristic of a lithium metal coin cell using an NCM (8/1/1) anode according to the FEC addition ratio in a 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. Shows
23 is NCM (8/1 /) according to LiF (0.3-1 M) concentration in 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1 weight% FEC (weight ratio) electrolyte system 1) It shows the characteristics of a lithium metal coin cell battery using a positive electrode.
FIG. 24 shows an TFEC-added solvent in an electrolyte in which 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, and 0.05 M LiPF ₆ salts were mixed with EC: DMC (4: 6 weight ratio), 1% by weight FEC, and 3% by weight VC solvent. It is a figure which measured the cycle characteristics of the lithium metal coin cell battery using NCM (8/1/1) positive electrode by adding 0-30 weight% by weight.
Figure 25 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 wt% FEC, 3 wt% VC, 0 wt% TFEC electrolyte After charging and discharging 20 times under the conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown.
Figure 26 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 wt% FEC, 3 wt% VC, 1 wt% TFEC electrolyte After charging and discharging 20 times under the conditions, XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown.
FIG. 27 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 weight% FEC, 3 weight% VC, 3 weight% TFEC electrolyte After charging and discharging under conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown.
FIG. 28 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 wt% FEC, 3 wt% VC, 5 wt% TFEC electrolyte After charging and discharging 20 times under the conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown.
FIG. 29 lists narrow scan XPS spectra of C 1s and F 1s elements of FIGS. 14 to 17 and shows the change of each peak.
Figure 30 is a LiFSI, LiTFSI, LiBOB, LiDFOB, LiPF ₆ salt combination of EC: DMC (4: 6 weight ratio) and the characteristics of a lithium metal battery using a coin-type NCM (6/2/2) anode using DME electrolyte Show.
FIG. 31 is a lithium metal coin using an NCM (6/2/2) anode according to FEC addition ratio in a 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. It shows the characteristics of the cell battery.
FIG. 32 is a lithium metal coin using an NCM (6/2/2) anode according to the ratio of VC in a 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. It shows the characteristics of the cell battery.
33 is a lithium metal coin cell using an NCM (6/2/2) anode according to the FEC addition ratio in the 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system of FIG. 3; Shows the characteristics of the battery.
34 is a characteristic of a lithium metal coin cell battery using an NCM (6/2/2) anode according to the ratio of VC in a 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system Shows
Figure 35 is a lithium using NCM (6/2/2) anode with FEC and VC additive solvent in 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system It shows the characteristics of a metal coin cell battery.
Figure 36 is a 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) NCM with 0.5 wt% FEC and 0.5 wt% FEC + 2 wt% VC additive solvent in an electrolyte system (6/2) / 2) It shows the characteristics of a lithium metal coin cell battery using a positive electrode.
FIG. 37 is a SEM image of the lithium surface after cycling by applying the electrolytes without addition of an additive solvent and an additive solvent other than EC: DMC and the LiTFSI, LiBOB, and LiPF ₆ salts.
FIG. 38 is a spectrum obtained by charging and discharging a cell containing an electrolyte containing the above-described LiTFSI, LiBOB, and LiPF ₆ salts and an additive solvent at 1C for 200 cycles, and then measuring the surface of the lithium cathode with XPS.
39 is a characteristic of a lithium metal coin cell battery using an NCM (8/1/1) anode according to the FEC addition ratio in a 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. Shows
40 is 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1 weight% FEC (weight ratio) NCM according to LiF (0.3 to 1 M) concentration in the electrolyte system (8/1 / 1) It shows the characteristics of a lithium metal coin cell battery using a positive electrode.
FIG. 41 shows an TFEC-added solvent in an electrolyte in which 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, and 0.05 M LiPF ₆ salts were mixed with EC: DMC (4: 6 weight ratio), 1% by weight FEC, and 3% by weight VC solvent. It is a figure which measured the cycle characteristics of the lithium metal coin cell battery using NCM (8/1/1) positive electrode by adding 0-30 weight% by weight.
Figure 42 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 wt% FEC, 3 wt% VC, 0 wt% TFEC electrolyte After charging and discharging 20 times under conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown.
FIG. 43 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 wt% FEC, 3 wt% VC, 1 wt% TFEC electrolyte After charging and discharging 20 times under the conditions, XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown.
FIG. 44 shows EC: DMC (4: 6 weight ratio), 1 weight% FEC, 3 weight% VC, 3 weight% TFEC electrolyte with 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts. After charging and discharging under conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown.
FIG. 45 is 1C using 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts with EC: DMC (4: 6 weight ratio), 1 weight% FEC, 3 weight% VC, 5 weight% TFEC electrolyte. After charging and discharging 20 times under the conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown.
FIG. 46 lists narrow scan XPS spectra of C 1s and F 1s elements of FIGS. 14 to 17 and shows the change of each peak.
FIG. 47 shows the addition of LiBF ₄ to the electrolyte in which 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, and 0.05 M LiPF ₆ salts were mixed with EC: DMC (4: 6 weight ratio), 1 wt% FEC, 3 wt% VC solvent. It is a figure in which the cycle characteristics of a lithium metal coin cell battery using an NCM (8/1/1) positive electrode were measured by adding a concentration of 0 to 0.3 M.
Figure 48 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 weight% FEC, 3 weight% VC, 0 M LiBF ₄ electrolyte After charging and discharging 20 times under the conditions, the cell shows the XPS narrow scan spectra (elements C, O, F, B) of the lithium cathode surface.
FIG. 49 shows EC: DMC (4: 6 weight ratio), 1 weight% FEC, 3 weight% VC, 0.05 M LiBF ₄ electrolyte 1C using 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts After charging and discharging 20 times under the conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown.
FIG. 50 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 wt% FEC, 3 wt% VC, 0.1 M LiBF ₄ electrolyte After charging and discharging 20 times under the conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown.
FIG. 51 shows 1 M using 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts with EC: DMC (4: 6 weight ratio), 1 wt% FEC, 3 wt% VC, 0.2 M LiBF ₄ electrolyte After charging and discharging 20 times under the conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown.
Figure 52 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 wt% FEC, 3 wt% VC, 0.3 M LiBF ₄ electrolyte After charging and discharging 20 times under the conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown.
FIG. 53 shows the peak variation by listing the narrow scan XPS spectra of the C 1s and F 1s elements of FIGS. 20 to 23.
FIG. 54 is an electrolyte in which 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ and 0.05 M LiBF ₄ salts are mixed in EC: DMC (4: 6 weight ratio), 1 weight% FEC, and 3 weight% VC solvent. It is a figure measuring the cycle characteristics of a lithium metal coin cell battery using an NCM (8/1/1) positive electrode by adding 0 to 7 wt% of the concentration of the TFEC-added solvent to the.

Hereinafter, various aspects and various embodiments of the present invention will be described in more detail.

One aspect of the present invention is (a) a first salt selected from LiFSI, LiTFSI, and mixtures thereof, (b) a second salt selected from LiBOB, LiDFOB and mixtures thereof, (c) a third salt comprising LiPF ₆ , (d) An electrolyte for a lithium metal secondary battery comprising a solvent composed of a mixture of EC and DMC, (e) further comprising at least one solvent additive selected from FEC and VC, wherein the solvent additive is the entire electrolyte. It relates to a lithium metal secondary battery electrolyte, characterized in that at least one selected from 0.4 to 1.5% by weight of FEC and 0.01 to 3.5% by weight of VC based on weight.

According to one embodiment, the first salt is composed of 0.2 to 0.4 M of LiFSI and 0.2 to 0.4 M of LiTFSI, or 0.3 to 1 M of LiTFSI, and the concentration of LiPF ₆ is 0.03 to 0.07 M , The mixing weight ratio of the EC and the DMC is 3 to 6: 7 to 4.

According to another embodiment, the first salt is composed of only 0.5 to 0.7 M of LiTFSI, the second salt is composed of only 0.3 to 0.5 M of LiBOB, and the third salt is composed of only 0.4 to 0.5 M of LiF, The concentration of the LiPF ₆ is 0.04 to 0.06 M, and the mixing weight ratio of the EC and the DMC is 3.75 to 5.25: 6.25 to 4.75.

According to another embodiment, at this time, the solvent additive is 0.5 to 1.3% by weight of FEC based on the total weight of the electrolyte, and may optionally include 0.01 to 3.5% by weight of VC.

According to another embodiment, the lithium metal secondary battery electrolyte further comprises a LiF salt.

According to another embodiment, the concentration of the LiF salt is 0.3-0.5 M.

According to another embodiment, the solvent-based additive is FEC of 0.7 to 1.3% by weight based on the total weight of the electrolyte.

According to the most preferred embodiment, (a) a first salt selected from LiTFSI, LiFSI, or mixtures thereof, (b) a second salt composed of a mixture of LiBOB and LiPF ₆ , (c) a solvent composed of a mixture of EC and DMC As an electrolyte for a lithium metal secondary battery comprising a, (d) further comprises at least one solvent additive selected from FEC and VC, the solvent additive is FEC of 0.4 to 1.5% by weight based on the total weight of the electrolyte and In the electrolyte for a lithium metal secondary battery, characterized in that at least one selected from 0.01 to 3.5% by weight of VC, ① the first salt is composed of only 0.5 to 0.7 M LiTFSI, ② the second salt is 0.35 to 0.45 M It consists of only LiBOB, ③ the concentration of the LiPF ₆ is 0.04 to 0.06 M, ④ in particular the mixing weight ratio of the EC and the DMC is 3.75 to 5.25: 6.25 to 4.75, ⑤ adding 0.4 to 0.5 M concentration of LiF salt Lofo In addition, it is very important that ⑥ also contains 0.8 to 1.2% by weight of FEC based on the total weight of the electrolyte as the solvent additive, and optionally 0.01 to 3.5% by weight of VC.

When the above 6 conditions are satisfied, the content of LiF and polycarbonate (CO ₃ ) in SEI is increased through XPS analysis, etc., and the vinyl carbonate bond point is newly formed due to FEC decomposition and the properties of LiF-based SEI It was confirmed that this change. This is one of the characteristics of the SEI containing boron, while maintaining the dense and rigid properties as it is, while changing to an elastic SEI (FIG. 9), improving the electrochemical stability and retention characteristics of the SEI, and maintaining the interfacial resistance constant. It was confirmed.

It was confirmed that the improvement of the above-mentioned effects and the expression of new effects were not observed when any one of the above six conditions was not satisfied. Also, these effects are lithium metal secondary batteries or carbonates using lithium metal itself as a negative electrode. It appears only when the above electrolyte is applied to a lithium-sulfur secondary battery or a lithium-air secondary battery using a series of electrolytes, and this effect is applied to a lithium ion secondary battery used as a negative electrode together with carbon material or silicon. It was confirmed that it was not expressed. This appears to be due to the formation of SEI directly on the surface of the lithium metal, and on the other hand, the above effects are applied to materials of lithium ion secondary batteries having a mechanism for inserting or deintercalating lithium ions, such as graphite, silicon, and metal oxides. Means that is not expressed.

In particular, LiFSI and LiTFSI form a SEI film rich in lithium fluoride (LiF) on the surface of a lithium metal through corrosion, thereby increasing the conductivity of lithium ions. In addition, it is more electrochemically stable than LiPF ₆ and has better thermal stability. LiBOB also forms SEI with components of boron and Li ₂ SO _x through corrosion, thereby forming a thin, robust, and high lithium ion conductivity SEI film. The LiPF ₆ salt contains a polycarbonate component in the SEI on the surface of the lithium cathode, thereby controlling the formation and shape of lithium dendrites to improve the electrochemical stability of the lithium cathode. Through this, it is possible to obtain an effect of forming a stable SEI film on the surface of the lithium cathode to improve the lifespan and energy density retention of the lithium metal battery.

As above, when the solvent is a mixed solvent of EC and DMC and both the concentration of each salt and the weight ratio of the mixed solvent satisfy the above conditions, aluminum corrosion, which is a positive electrode current collector by LiFSI and LiTFSI, is blocked (FIG. 10), and at the same time, den It can be confirmed that the structure of the SEI type having a stable and elastic shape that suppresses the continuous formation of the dry (FIG. 9). In addition to this heterogeneous effect, the effect of homogeneity is also greatly improved. As described above, when the solvent is a mixed solvent of EC and DMC and the concentration of each added solvent and the salt and the weight ratio of the mixed solvent both satisfy the above conditions, the most Stable SEI is formed at the lithium-electrolyte interface to show very good lithium metal battery properties.

On the other hand, if any of the above numerical ranges is out of range, unsuitable amount of LiF is included in SEI due to the changed composition of LiFSI, LiTFSI, LiPF ₆ , LiF salt and FEC, VC additive solvent, and the mechanical and electrochemical properties of SEI. , Which makes the interface resistance of the lithium anode large. In addition, if the concentration of the main salts (LiTFSI, LiBOB) deviates, it exhibits low LiBOB solubility, resulting in an instability of the electrolyte to precipitate in the dissolved lithium salt. The proposed composition serves to greatly improve the stability of the electrolyte as well as the electrochemical properties of the silk metal battery. In particular, it was confirmed that when other salts such as LiDFOB are also included in a small amount and the addition ratio of FEC and VC, which are additional solvents, exceeds the above values, the stability of SEI decreases, the battery life decreases, and the resistance increase of the cathode increases.

Another aspect of the invention is (a) a first salt selected from LiFSI, LiTFSI, and mixtures thereof, (b) a second salt selected from LiBOB, LiDFOB and mixtures thereof, (c) a third salt comprising LiPF ₆ , (d) An electrolyte for a lithium metal secondary battery comprising a solvent composed of a mixture of EC and DMC, (e) further comprising at least one first solvent additive selected from FEC and VC, and (f) removing TFEC. 2 It is further included as a solvent additive, the first solvent additive is at least one selected from 0.4 to 1.5% by weight of FEC and 0.01 to 3.5% by weight of VC based on the total weight of the electrolyte, the second solvent The concentration of the sex additive relates to an electrolyte for a lithium metal secondary battery, characterized in that it is 2.5 to 4.5% by weight based on the total weight of the electrolyte.

According to one embodiment, the first salt is composed of 0.2 to 0.4 M of LiFSI and 0.2 to 0.4 M of LiTFSI, or 0.3 to 1 M of LiTFSI, and the concentration of LiPF ₆ is 0.03 to 0.07 M , The mixing weight ratio of the EC and the DMC is 3 to 6: 7 to 4.

According to another embodiment, the first salt is composed of only 0.5 to 0.7 M of LiTFSI, the second salt is composed of only 0.3 to 0.5 M of LiBOB, the concentration of LiPF ₆ is 0.04 to 0.06 M, and the EC And the mixing weight ratio of the DMC is 3.75 to 5.25: 6.25 to 4.75.

According to another embodiment, the first solvent-based additive is FEC of 0.5 to 1.3% by weight based on the total weight of the electrolyte, and may optionally include 0.01 to 3.5% by weight of VC.

According to another embodiment, the lithium metal secondary battery electrolyte further comprises a LiF salt.

According to another embodiment, the concentration of the LiF salt is 0.3-0.5 M.

According to another embodiment, the first solvent-based additive is FEC of 0.7 to 1.3% by weight based on the total weight of the electrolyte.

According to the most preferred embodiment, (a) a first salt selected from LiTFSI, LiFSI, or mixtures thereof, (b) a second salt composed of a mixture of LiBOB and LiPF ₆ , (c) a solvent composed of a mixture of EC and DMC As an electrolyte for a lithium metal secondary battery comprising a, (d) further comprises at least one first solvent additive selected from FEC and VC, (f) further comprises TFEC as a second solvent additive, the solvent Sex additive is a lithium metal secondary battery electrolyte, characterized in that at least one selected from 0.4 to 1.5% by weight of FEC and 0.01 to 3.5% by weight of VC based on the total weight of the electrolyte, ① the first salt is 0.5 to 0.5 Consisting only of 0.7 M of LiTFSI, ② The second salt is comprised of 0.35 to 0.45 M of LiBOB only, ③ The concentration of LiPF ₆ is 0.04 to 0.06 M, ④ In particular, the mixing weight ratio of the EC and the DMC is 3.75 to 5.25: within 6.25 4.75, ⑤ additionally comprising a LiF salt of 0.3 to 0.5 M concentration, ⑥ also comprises a FEC of 0.8 to 1.2% by weight based on the total weight of the electrolyte as the first solvent additive, and optionally VC 0.01 It is very important that the concentration of the second solvent-based additive is 2.5 to 3.5% by weight based on the total weight of the electrolyte.

When the above 7 conditions are satisfied, peaks for -CF ₂ -CF ₂ and -CF ₂ -CH ₂ are newly formed due to TFEC corrosion through XPS analysis, etc., and the properties of LiF-based SEI are changed. Confirmed. This maintains the compact and rigid properties of one of the properties of SEI with boron, while changing from new bonding points ?? CF ₂ -CF ₂ and -CF ₂ -CH ₂ to a more elastic SEI ( 9), it was confirmed that the electrochemical stability and maintenance characteristics of the SEI were improved, and the interface resistance was kept constant.

It was confirmed that the improvement of the above-mentioned effects and the expression of new effects were not observed when any one of the above 7 conditions was not satisfied. Also, these effects are lithium metal secondary batteries or carbonates using lithium metal itself as a negative electrode. It appears only when the above electrolyte is applied to a lithium-sulfur secondary battery or a lithium-air secondary battery using a series of electrolytes, and this effect is exhibited for lithium ion secondary batteries used as a negative electrode together with carbon materials or silicon. Was confirmed. This appears to be due to the formation of SEI directly on the surface of the lithium metal, and on the other hand, the above effects are applied to materials of lithium ion secondary batteries having a mechanism for inserting or deintercalating lithium ions, such as graphite, silicon, and metal oxides. Means that is not expressed.

In particular, LiFSI, LiTFSI, and TFEC form suitable SEI films of lithium fluoride (LiF) and ?? CF ₂ -CF ₂ and -CF ₂ -CH ₂ on the surface of lithium metal through corrosion, thereby increasing the conductivity of lithium ions. Giving functions. In addition, it is more electrochemically stable than LiPF ₆ and has better thermal stability. LiBOB also forms SEI with components of boron and Li ₂ SO _x through corrosion, thereby forming a thin, robust, and high lithium ion conductivity SEI film. The LiPF ₆ salt contains a polycarbonate component in the SEI on the surface of the lithium cathode, thereby controlling the formation and shape of lithium dendrites to improve the electrochemical stability of the lithium cathode. Through this, it is possible to obtain an effect of forming a stable SEI film on the surface of the lithium cathode to improve the lifespan and energy density retention of the lithium metal battery.

As above, when the solvent is a mixed solvent of EC and DMC and both the concentration of each salt and the weight ratio of the mixed solvent satisfy the above conditions, aluminum corrosion, which is a positive electrode current collector by LiFSI and LiTFSI, is blocked (FIG. 10), and at the same time, den A small amount of dendrites formed while the formation of the dry was suppressed also confirmed a stable and elastic SEI type structure (FIG. 9). In addition to this heterogeneous effect, the effect of homogeneity is also greatly improved. As described above, when the solvent is a mixed solvent of EC and DMC and the concentration of each added solvent and the salt and the weight ratio of the mixed solvent both satisfy the above conditions, the most Stable SEI is formed at the lithium-electrolyte interface to show very good lithium metal battery properties.

On the other hand, if any of the above numerical ranges is out of range, the amount of unsuitable -F binders is included in SEI due to the changed composition of LiFSI, LiTFSI, LiPF ₆ , LiF salt and FEC, VC, and TFEC-added solvent. It deteriorates the properties and electrochemical properties, which makes the interface resistance of the lithium cathode large. In addition, if the concentration of the main salts (LiTFSI, LiBOB) deviates, it exhibits low LiBOB solubility, resulting in an instability of the electrolyte to precipitate in the dissolved lithium salt. The proposed composition serves to greatly improve the stability of the electrolyte as well as the electrochemical properties of the silk metal battery. In particular, it was confirmed that when other salts such as LiDFOB are also included in a small amount and the addition ratio of FEC and VC, which are additional solvents, exceeds the above values, the stability of SEI decreases, the battery life decreases, and the resistance increase of the cathode increases.

One aspect of the present invention is (a) a first salt selected from LiFSI, LiTFSI, and mixtures thereof, (b) a second salt selected from LiBOB, LiDFOB and mixtures thereof, (c) a fourth salt comprising LiPF ₆ , (d) An electrolyte for a lithium metal secondary battery comprising a solvent composed of a mixture of EC and DMC, (e) further comprising at least one first solvent additive selected from FEC and VC, and (f) LiBF ₄ . It is further included as a fourth salt, (g) optionally further comprising TFEC as a second solvent additive, wherein the first solvent additive is 0.4 to 1.5% by weight of FEC and 0.01 based on the total weight of the electrolyte. To 3.5 wt% or more selected from VC, the concentration of the fourth salt is 0.02 to 0.06 M, and if the second solvent additive is included, the concentration of the second solvent additive is the total of the electrolyte. Characterized by 0.8 to 1.2% by weight based on weight It relates to an electrolyte for a lithium metal secondary battery.

According to one embodiment, the first salt is composed of 0.2 to 0.4 M of LiFSI and 0.2 to 0.4 M of LiTFSI, or 0.3 to 1 M of LiTFSI, and the concentration of LiPF ₆ is 0.03 to 0.07 M , The mixing weight ratio of the EC and the DMC is 3 to 6: 7 to 4.

According to another embodiment, the first salt is composed of only 0.5 to 0.7 M of LiTFSI, the second salt is composed of only 0.3 to 0.5 M of LiBOB, the concentration of LiPF ₆ is 0.04 to 0.06 M, and the EC And the mixing weight ratio of the DMC is 3.75 to 5.25: 6.25 to 4.75.

According to another embodiment, the first solvent-based additive is FEC of 0.5 to 1.3% by weight based on the total weight of the electrolyte, and may optionally include 0.01 to 3.5% by weight of VC.

According to another embodiment, the lithium metal secondary battery electrolyte further comprises a LiF salt.

According to another embodiment, the concentration of the LiF salt is 0.3-0.5 M.

According to another embodiment, the first solvent-based additive is FEC of 0.7 to 1.3% by weight based on the total weight of the electrolyte.

According to a preferred embodiment, (a) a first salt selected from LiTFSI, LiFSI, or mixtures thereof, (b) a second salt consisting of a mixture of LiBOB, LiF and LiPF ₆ , (c) consisting of a mixture of EC and DMC An electrolyte for a lithium metal secondary battery comprising a solvent, (d) further comprising at least one first solvent additive selected from FEC and VC, (f) further comprising LiBF ₄ as a fourth salt, and the solvent Sex additive is a lithium metal secondary battery electrolyte, characterized in that at least one selected from 0.4 to 1.5% by weight of FEC and 0.01 to 3.5% by weight of VC based on the total weight of the electrolyte, ① the first salt is 0.5 to 0.5 Consists only of 0.7 M LiTFSI, ② Consists only of the second 0.35 to 0.45 M LiBOB, ③ Concentrations of the LiPF ₆ are 0.04 to 0.06 M, ④ Especially, the mixed weight ratio of the EC and the DMC is 3.75 to 5.25. : 6.25 to 4.75 , ⑤ additionally comprising a LiF salt having a concentration of 0.3 to 0.5 M, and ⑥ also comprising 0.8 to 1.2% by weight of FEC based on the total weight of the electrolyte as the first solvent additive, and optionally VC to 0.01 to 3.5. Weight percent, ⑦ The concentration of the second solvent additive is 0.8 to 1.2% by weight based on the total weight of the electrolyte, ⑧ The LiBF ₄ is further included as a fourth salt to a concentration of 0.04 to 0.06 M, ⑨ Optionally, TFEC is additionally included as a second solvent additive, and if the second solvent additive is included, the concentration of the second solvent additive is 0.8 to 1.2% by weight based on the total weight of the electrolyte. It is very important.

According to a most preferred embodiment, (a) a first salt selected from LiFSI, LiTFSI, and mixtures thereof, (b) a second salt selected from LiBOB, LiDFOB and mixtures thereof, (c) a third comprising LiPF ₆ An electrolyte for a lithium metal secondary battery comprising a salt, (d) a solvent composed of a mixture of EC and DMC, further comprising (e) at least one first solvent additive selected from FEC and VC, and (f) LiBF ₄ It is further included as a fourth salt, (g) optionally further comprises TFEC as a second solvent additive, the first solvent additive is FEC of 0.4 to 1.5% by weight based on the total weight of the electrolyte and In the electrolyte for a lithium metal secondary battery, characterized in that at least one selected from 0.01 to 3.5% by weight of VC, ① the first salt is composed of only 0.5 to 0.7 M LiTFSI, ② the second salt is 0.35 to 0.45 M It consists of only LiBOB, ③ of LiPF ₆ Concentration is 0.04 to 0.06 M, ④ The mixed weight ratio of the EC and the DMC is 3.75 to 5.25: 6.25 to 4.75, ⑤ additionally includes a LiF salt having a concentration of 0.3 to 0.5 M, and ⑥ as the first solvent additive. According to the total weight of the electrolyte, 0.8 to 1.2% by weight of FEC, and optionally 0.01 to 3.5% by weight of VC, ⑦ The method of claim 16, wherein the third salt is composed of only LiPF ₆ , the LiPF The concentration of ₆ is 0.04 to 0.06 M, ⑧ the concentration of the fourth salt is 0.02 to 0.04 M, ⑨ further includes a LiNO ₃ salt of 0.05 to 0.1 M concentration, ⑩ the mixed weight ratio of the EC and the DMC is 0.6 0.8 to 0.2: 0.4, wherein the first solvent-based additive comprises 0.8 to 1.2% by weight of FEC and 0.01 to 3.5% by weight of VC based on the total weight of the electrolyte, and ⑫ based on the total weight of the electrolyte. 2.5 to 3.5% by weight of the second dragon It is very important to include a solvent additive.

When the first 9 conditions above are satisfied or the following 12 conditions are satisfied, the content of LiF and polycarbonate, CF, C = O, CO, and C (O) F components in SEI through XPS analysis, etc. Not only increased, LiBF ₄ decomposition showed CF ₂ , -CF ₃ new binding points (FIG. 25), and it was confirmed that the physical properties of the SEI based on the base were changed. Thus, it was confirmed that in the SEI composition in the electrolyte to which 0.05M LiBF ₄ was added, the lithium cathode stability / preservation rate and lithium ion conductivity were rapidly improved.

However, if none of the above nine conditions or any of the above 12 conditions were met, it was confirmed that the improvement of the above-mentioned effects and the expression of new effects were not observed at all. It appears only when the above electrolyte is applied to a lithium metal secondary battery used as a negative electrode, a lithium-sulfur secondary battery using a carbonate-based electrolyte or a lithium-air secondary battery, and lithium ions used as a negative electrode together with a carbon material or silicon It was confirmed that this effect was not exhibited for the secondary battery. This appears to be due to the formation of SEI directly on the surface of the lithium metal, and on the other hand, the above effects are applied to materials of lithium ion secondary batteries having a mechanism for inserting or deintercalating lithium ions, such as graphite, silicon, and metal oxides. Means that is not expressed.

In particular, LiFSI and LiTFSI form a SEI layer rich in lithium fluoride (LiF) on the surface of the lithium metal through corrosion, thereby increasing the conductivity of lithium ions. In addition, it is more electrochemically stable than LiPF ₆ and has better thermal stability. LiBOB also forms SEI with boron and Li ₂ SO _x components through corrosion, thereby forming a thin, robust, and high lithium ion conductivity SEI layer. The LiPF ₆ salt contains a poly (CO ₃ ) component in the SEI of the lithium cathode surface to control the formation and shape of lithium dendrites, thereby improving the electrochemical stability of the lithium cathode. Through this, it is possible to obtain an effect of forming a stable SEI layer on the surface of the lithium cathode to improve the lifespan and energy density retention of the lithium metal battery.

As above, when the solvent is a mixed solvent of EC and DMC and both the concentration of each salt and the weight ratio of the mixed solvent satisfy the above conditions, aluminum corrosion, which is a positive electrode current collector by LiFSI and LiTFSI, is blocked (FIG. 10), and at the same time, den A small amount of dendrites formed while the formation of the dry was suppressed was also able to confirm a stable and elastic SEI type structure (FIG. 9). In addition to this heterogeneous effect, the effect of homogeneity is also greatly improved. As described above, when the solvent is a mixed solvent of EC and DMC and the concentration of each added solvent and the salt and the weight ratio of the mixed solvent both satisfy the above conditions, the most Stable SEI is formed at the lithium-electrolyte interface to show very good lithium metal battery properties.

On the other hand, if any one of the above numerical ranges is out of range, the amount of LiFSI, LiTFSI, LiPF ₆ , LiF, and LiBF ₄ salts and the changed composition of FEC, VC, and TFEC-added solvents are included in the SEI. It deteriorates the properties and electrochemical properties, which makes the interface resistance of the lithium cathode large. In addition, if the concentration of the main salts (LiTFSI, LiBOB) deviates, it exhibits low LiBOB solubility, resulting in an instability of the electrolyte to precipitate in the dissolved lithium salt. The proposed composition serves to greatly improve the stability of the electrolyte as well as the electrochemical properties of the silk metal battery. In particular, it was confirmed that when other salts such as LiDFOB are also included in a small amount and the addition ratio of FEC and VC, which are additional solvents, exceeds the above values, the stability of SEI decreases, the battery life decreases, and the resistance increase of the cathode increases.

Another aspect of the present invention relates to a lithium metal secondary battery including an electrolyte for a lithium metal secondary battery according to various embodiments of the present invention.

According to one embodiment, the material of the positive electrode in the lithium metal secondary battery is one selected from lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt oxide, and lithium iron phosphate.

According to another embodiment, the material of the positive electrode is lithium nickel cobalt manganese oxide.

Another aspect of the present invention relates to an electrical device including an electrolyte for a lithium metal secondary battery according to various embodiments of the present invention.

According to one embodiment, the electrical device is one selected from a communication device, a transportation device, an energy storage device, and an acoustic device.

Specific examples of these electric devices include, but are not limited to, mobile phones, music players, speakers, drones, automobiles, sensors, and the like.

Hereinafter, the present invention will be described in more detail through examples and the like, but the scope and content of the present invention may be reduced or limited by the examples below. In addition, if it is based on the disclosure of the present invention including the following examples, it is obvious that a person skilled in the art can easily carry out the present invention in which experimental results are not specifically presented, and patents to which such modifications and corrections are attached Naturally, it is within the scope of the claims.

In addition, the experimental results presented below are only representative of experimental results of the examples and comparative examples, and the effects of the various embodiments of the present invention, which are not explicitly presented below, will be described in detail in the corresponding parts.

In the following, examples, comparative examples, and test examples are divided into three groups to help understanding of the present invention.

Example

(1) Examples, comparative examples and test examples of the first group

Comparative Example 1: LiFSI, LiTFSI, LiBOB, LiPF ₆  Electrolyte synthesis using salt and EC: DMC solvent

First, after the EC was dissolved at 60 ° C., DMC and a weight ratio of 4: 6 were mixed in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiBOB salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, LiFSI was dissolved at a concentration of 0.3 M and LiTFSI salt at a concentration of 0.3 M.

The thus prepared (0.3 M LiFSI + 0.3 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in EC: DMC (4: 6 v / v) electrolyte was used in the lithium metal battery.

Comparative Example 2: LiTFSI, LiBOB, LiPF ₆  Electrolyte synthesis using salt and EC: DMC solvent

First, after the EC was dissolved at 60 ° C., DMC and a weight ratio of 4: 6 were mixed in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiBOB salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, the LiTFSI salt was dissolved to a concentration of 0.6 M.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in EC: DMC (4: 6 v / v) electrolyte was used in the lithium metal battery.

Comparative Example 3: LiFSI, LiDFOB, LiPF ₆  Electrolyte synthesis using salt and EC: DMC solvent

First, after the EC was dissolved at 60 ° C., DMC and a weight ratio of 4: 6 were mixed in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiDFOB salt was dissolved in a moisture-free environment for 3 to 6 hours with constant stirring to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, the LiFSI salt was dissolved to a concentration of 0.6 M.

The thus prepared (0.6 M LiFSI + 0.4 M LiDFOB + 0.05 M LiPF ₆ ) in EC: DMC (4: 6 v / v) electrolyte was used in the lithium metal battery.

Comparative Example 4: LiFSI, LiTFSI, LiBOB, LiPF ₆  Electrolyte synthesis using salt and FEC: DMC solvent

FEC was mixed with DMC at a weight ratio of 3: 7 in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiBOB salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, LiFSI was dissolved at a concentration of 0.3 M and LiTFSI salt at a concentration of 0.3 M.

The thus prepared (0.3 M LiFSI + 0.3 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in FEC: DMC (3: 7 v / v) electrolyte was used in the lithium metal battery.

Comparative Example 5a: LiTFSI, LiBOB, LiPF ₆  Electrolyte synthesis using salt and FEC: DMC or VC: 읓 solvent

FEC and DMC or VC and DMC were mixed for 15 to 30 minutes while stirring in a moisture-free environment at a weight ratio of 3: 7 and 3: 7, respectively, to prepare a mixed solvent. In the mixed solvent, the LiBOB salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, the LiTFSI salt was dissolved to a concentration of 0.6 M.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (FEC: DMC (3: 7 v / v) or VC: DMC (3: 7 v / v) electrolyte was used in the lithium metal battery. .

Comparative Example 6: LiPF ₆  Electrolyte synthesis using salt and EC: DMC solvent

First, after the EC was dissolved at 60 ° C., DMC and a weight ratio of 4: 6 were mixed in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiPF ₆ salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 1 M.

The thus prepared (1 M LiPF ₆ ) in EC: DMC (4: 6 v / v) electrolyte was used in a lithium metal battery.

Comparative Examples 7a to 7e: LiTFSI, LiBOB, LiPF ₆ , LiF salt and electrolyte synthesis using EC: DMC solvent

First, after the EC was dissolved at 60 ° C., DMC and a weight ratio of 4: 6 were mixed in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiBOB salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, the LiTFSI salt was dissolved to a concentration of 0.6 M. In addition, LiF salts were further dissolved so that the concentrations were 0.3 M, 0.4 M, 0.5 M, 0.7 M, and 1 M, respectively.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ + 0.3 to 1 M LiF) in EC: DMC (4: 6 v / v) electrolyte was used in a lithium metal battery.

Examples 1a and 1b: electrolyte synthesis with FEC solvent added

To the electrolyte prepared in Comparative Example 1, based on the total weight of the electrolyte, 0.5% by weight and 5% by weight of FEC, respectively, were added, followed by stirring in an environment without moisture for 1 hour.

The thus prepared (0.3 M LiFSI + 0.3 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (EC: DMC (4: 6 v / v) + 0.5 or 5 wt% FEC) electrolyte was used in the lithium metal battery. .

Examples 2a to 2e: Electrolyte synthesis with VC solvent added

0.5% by weight, 1% by weight, 2% by weight, 2% by weight, 3% by weight, and 5% by weight of VC, respectively, based on the total weight of the electrolyte, added to the electrolyte prepared in Comparative Example 1, stirred in an environment free of moisture for 1 hour Was added.

The thus prepared (0.3 M LiFSI + 0.3 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (EC: DMC (4: 6 v / v) + 0.5 to 2 wt% VC) electrolyte was used in the lithium metal battery. .

Example 3: Electrolyte synthesis with FEC + VC solvent added

To the electrolyte prepared in Comparative Example 1, based on the total weight of the electrolyte, 0.5% by weight of FEC and 2% by weight of VC were added, followed by stirring in an environment free of moisture for 1 hour.

(0.3 M LiFSI + 0.3 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) prepared in this way (EC: DMC (4: 6 v / v) + 0.5 wt% FEC + 2 wt% VC) electrolyte lithium metal battery Used for.

Examples 4a to 4i: Electrolyte synthesis with FEC solvent added

Based on the total weight of the electrolyte in the electrolyte prepared in Comparative Example 2, the FEC was 0.3 wt%, 0.5 wt%, 0.7 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt%, 10 wt%, respectively. , 20% by weight was added by stirring in an environment free of moisture for 1 hour.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (EC: DMC (4: 6 v / v) + 0.3 to 20% by weight FEC) electrolyte was used in the lithium metal battery.

Example 5: Electrolyte synthesis with VC solvent added

To the electrolyte prepared in Comparative Example 2, 2% by weight of VC was added based on the total weight of the electrolyte, followed by stirring in an environment free of moisture for 1 hour.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (EC: DMC (4: 6 v / v) + 2 wt% VC) electrolyte was used in a lithium metal battery.

Example 6: Electrolyte synthesis with FEC + VC solvent added

To the electrolyte prepared in Comparative Example 2, based on the total weight of the electrolyte, 0.5% by weight of FEC and 2% by weight of VC were added, followed by stirring in an environment without moisture for 1 hour.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (EC: DMC (4: 6 v / v) + 0.5 wt% FEC + 2 wt% VC) electrolyte was used in the lithium metal battery.

Examples 7a to 7e: LiTFSI, LiBOB, LiPF ₆ , LiF salt and electrolyte synthesis using EC: DMC solvent

LiF salts were further dissolved in the electrolytes prepared in Example 4d such that the concentrations were 0.3 M, 0.4 M, 0.5 M, 0.7 M, and 1 M, respectively.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ + 0.3 to 1 M LiF) in (EC: DMC (4: 6 v / v) + 1 wt% FEC) electrolyte was used in the lithium metal battery. ..

Electrochemical analysis of modified electrolyte lithium metal battery

The electrochemical properties of the lithium metal battery were measured by charging and discharging the electrolytes. In the coin cell measurement, lithium metal (1.5 cm in diameter, 150 μm in thickness), 11 μm thick PP separator (1.8 cm in diameter), NCM (6/2/2) and NCM (8/1/1) anodes (1.2 cm in diameter) , Electrochemical properties were measured using an electrolyte (30 μL), and the applied voltage range was 3 to 4.2 V. When reaching 4.2 V, a constant voltage was used to charge until the current value was 0.05 C. In the first formation cycle of the battery, 1 cycle was performed at 0.1 C, and after that, the battery was continuously charged and discharged at 1 C.

Hereinafter, the analysis results will be described in detail with reference to the drawings.

FIG. 2 shows the characteristics of a coin-type lithium metal battery using an EC: DMC (4: 6 weight ratio) electrolyte containing LiFSI, LiTFSI, LiBOB, LiDFOB, and LiPF ₆ salts. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data and battery life is over at 80 cycles, while 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C and 0.6M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system with a combination shows somewhat stable capacity retention and life characteristics, but an embodiment of the present invention It can be seen that it is considerably less than the electrolyte system according to. The anode used here is NCM (6/2/2).

Figure 3 shows the characteristics of the lithium metal coin cell battery according to the FEC addition ratio in the 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while cell life ends at 80 cycles, while 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 1C coin cell with FEC added to 6 weight ratio) shows somewhat improved life characteristics, and shows the most stable capacity retention rate when FEC is added at 0.5% by weight. This is because an appropriate amount of LiF-based SEI formed from FEC is formed on the lithium anode, and the SEI of the NCM anode also stabilizes. The anode used here is NCM (6/2/2).

Figure 4 shows the characteristics of a lithium metal coin cell battery according to the ratio of VC addition in a 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while cell life ends at 80 cycles, while 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: Coin cell with VC added to 6 weight ratio) shows somewhat improved life characteristics at 1C condition charge / discharge and shows the most stable capacity retention rate when VC is added at 0.5% or 2% by weight. This is because the SEI formed from VC at the lithium anode and the NCM anode inhibits side reactions with the electrolyte and stabilizes the electrochemical surface. The anode used here is NCM (6/2/2).

FIG. 5 shows the characteristics of the lithium metal coin cell battery according to the FEC addition ratio in the 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system of FIG. 3. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while battery life ends at 80 cycles, while 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) FEC-added coin cells show somewhat improved life characteristics under 1C charge / discharge and show the most stable capacity retention rate when FEC is added at 0.5% by weight. This is because an appropriate amount of LiF-based SEI formed from FEC is formed on the lithium anode, and the SEI of the NCM anode also stabilizes. The anode used here is NCM (6/2/2).

Figure 6 shows the characteristics of the lithium metal coin cell battery according to the VC addition ratio in the 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while battery life ends at 80 cycles, while 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) Coin cells added with VC show somewhat improved life characteristics under 1C charge and discharge conditions, and show the most stable capacity retention rate when VC is added at 2% by weight. This is because the SEI formed from VC at the lithium anode and the NCM anode inhibits side reactions with the electrolyte and stabilizes the electrochemical surface. The anode used here is NCM (6/2/2).

FIG. 7 shows the characteristics of a lithium metal coin cell battery using an optimized FEC and VC additive solvent in a 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while cell life ends at 80 cycles, while 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: Optimized for 6 weight ratio), the coin cell using 0.5 wt% FEC and 2 wt% VC additive solvent shows the most stable life characteristics even under 1C charge and discharge conditions, and more stable life characteristics than the electrolyte system without additive solvent. The anode used here is NCM (6/2/2).

8 is 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) lithium metal coin with 0.5 wt% FEC and 0.5 wt% FEC + 2 wt% VC added solvent optimized in the electrolyte system It shows the characteristics of the cell battery. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while the battery life ends at 80 cycles and the electrolyte without added solvents ends at 400 cycles, while 0.6 M LiTFSI, 0.4 M LiBOB, Coin cell with 0.5 wt% FEC and 2 wt% VC optimized for 0.05 M LiPF ₆ EC: DMC (4: 6 wt%) or with solvent added with FEC alone shows stable life characteristics even under 1C charge and discharge conditions. It shows more stable life characteristics than electrolyte system without solvent.

FIG. 9 is a SEM image of the lithium surface after a cycle by applying the above-described LiTFSI, LiBOB, LiPF ₆ salts and electrolytes without addition of EC: DMC and electrolytes with addition of solvents. High cell surface lithium dendrite formation in cell (a) when electrolytes without addition solvents other than EC: DMC and LiTFSI, LiBOB, and LiPF ₆ salts were added to cells after 200 cycles of charging and discharging at 1C were added. It was higher than the electrolyte (b) containing the solvent, and the roughness of the surface was also less rough. This is because a stable and elastic SEI formed due to the proper combination of the above salts and an additive solvent is formed on the surface of the lithium cathode.

FIG. 10 is a spectrum obtained by charging and discharging a cell containing an electrolyte containing the above-described LiTFSI, LiBOB, and LiPF ₆ salts and an additive solvent at 1C for 200 cycles, and then measuring the surface of the lithium cathode with XPS. Al was not detected even after cycling for a long time using an electrolyte system containing LiTFSI, LiBOB, LiPF ₆ salts and an additive solvent, and Li (13.99%), B (3.16%), C in SEI formed from the composition of the main salt (26.81%), N (3.41%), O (34%), F (12.41%), and S (5.41%) were detected. This indicates that Al corrosion was suppressed due to the proper combination of the salts.

Figure 11 shows the characteristics of the lithium metal coin cell battery according to the FEC addition ratio in the 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while battery life ends at 30 cycles, while 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) Coin cells using an optimized 1% by weight FEC additive solvent show the most stable life characteristics even under 1C charge and discharge conditions and more stable life characteristics than electrolyte systems without additive solvents. The anode used here is NCM (8/1/1). Unlike the anode, it is an experiment to find an optimized FEC addition ratio when using a high energy density NCM anode.

12 is a lithium metal coin cell cell according to the concentration of LiF (0.3 to 1 M) in a 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1% by weight FEC (weight ratio) electrolyte system It shows characteristics. 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1% by weight FF (weight ratio) optimized LiF concentration is 0.4 M. Coin cells using a solvent with an optimized LiF salt show the most stable life characteristics even under 1C charge and discharge conditions. The anode used here is NCM (8/1/1). Unlike the positive electrode, it is an experiment to find an optimized LiF addition ratio when using a high energy density NCM positive electrode.

(2) Examples, comparative examples and test examples of the second group

Comparative Example 1: LiFSI, LiTFSI, LiBOB, LiPF ₆  Electrolyte synthesis using salt and EC: DMC solvent

First, after the EC was dissolved at 60 ° C., DMC and a weight ratio of 4: 6 were mixed in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiBOB salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, LiFSI was dissolved at a concentration of 0.3 M and LiTFSI salt at a concentration of 0.3 M.

The thus prepared (0.3 M LiFSI + 0.3 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in EC: DMC (4: 6 w / w) electrolyte was used in the lithium metal battery.

Comparative Example 2: LiTFSI, LiBOB, LiPF ₆  Electrolyte synthesis using salt and EC: DMC solvent

First, after the EC was dissolved at 60 ° C., DMC and a weight ratio of 4: 6 were mixed in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiBOB salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, the LiTFSI salt was dissolved to a concentration of 0.6 M.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in EC: DMC (4: 6 w / w) electrolyte electrolyte was used in a lithium metal battery.

Comparative Example 3: LiFSI, LiDFOB, LiPF ₆  Electrolyte synthesis using salt and EC: DMC solvent

First, after the EC was dissolved at 60 ° C., DMC and a weight ratio of 4: 6 were mixed in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiDFOB salt was dissolved in a moisture-free environment for 3 to 6 hours with constant stirring to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, the LiFSI salt was dissolved to a concentration of 0.6 M.

The thus prepared (0.6 M LiFSI + 0.4 M LiDFOB + 0.05 M LiPF ₆ ) in EC: DMC (4: 6 w / w) electrolyte was used for the lithium metal battery.

Comparative Example 4: LiFSI, LiTFSI, LiBOB, LiPF ₆  Electrolyte synthesis using salt and FEC: DMC solvent

FEC was mixed with DMC at a weight ratio of 3: 7 in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiBOB salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, LiFSI was dissolved at a concentration of 0.3 M and LiTFSI salt at a concentration of 0.3 M.

The thus prepared (0.3 M LiFSI + 0.3 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in FEC: DMC (3: 7 w / w) electrolyte was used in the lithium metal battery.

Comparative Examples 5a and 5b: LiTFSI, LiBOB, LiPF ₆  Electrolyte synthesis using salt and FEC: DMC or VC: DMC solvent

FEC and DMC or VC and DMC were mixed for 15 to 30 minutes while stirring in a moisture-free environment at a weight ratio of 3: 7 and 3: 7, respectively, to prepare a mixed solvent. In the mixed solvent, the LiBOB salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, the LiTFSI salt was dissolved to a concentration of 0.6 M.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (FEC: DMC (3: 7 w / w) or VC: DMC (3: 7 w / w) electrolyte was used in the lithium metal battery. .

Comparative Example 6: LiPF ₆  Electrolyte synthesis using salt and EC: DMC solvent

First, after the EC was dissolved at 60 ° C., DMC and a weight ratio of 4: 6 were mixed in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiPF ₆ salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 1 M.

The thus prepared (1 M LiPF ₆ ) in EC: DMC (4: 6 w / w) electrolyte was used in a lithium metal battery.

Comparative Examples 7a to 7e: LiTFSI, LiBOB, LiPF ₆ , LiF salt and electrolyte synthesis using EC: DMC solvent

First, after the EC was dissolved at 60 ° C., DMC and a weight ratio of 4: 6 were mixed in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiBOB salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, the LiTFSI salt was dissolved to a concentration of 0.6 M. In addition, LiF salts were further dissolved so that the concentrations were 0.3 M, 0.4 M, 0.5 M, 0.7 M, and 1 M, respectively.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ + 0.3 to 1 M LiF) in EC: DMC (4: 6 w / w) electrolyte was used in a lithium metal battery.

Examples 1a and 1b: electrolyte synthesis with FEC solvent added

To the electrolyte prepared in Comparative Example 1, based on the total weight of the electrolyte, 0.5% by weight and 5% by weight of FEC, respectively, were added, followed by stirring in an environment without moisture for 1 hour.

The thus prepared (0.3 M LiFSI + 0.3 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (EC: DMC (4: 6 w / w) + 0.5 or 5 wt% FEC) electrolyte was used in the lithium metal battery. .

Examples 2a to 2e: Electrolyte synthesis with VC solvent added

0.5% by weight, 1% by weight, 2% by weight, 2% by weight, 3% by weight, and 5% by weight of VC, respectively, based on the total weight of the electrolyte, were added to the electrolyte prepared in Comparative Example 1 and stirred in an environment free of moisture for 1 hour. Was added.

The thus prepared (0.3 M LiFSI + 0.3 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (EC: DMC (4: 6 w / w) + 0.5 to 2 wt% VC) electrolyte was used in the lithium metal battery. .

Example 3: Electrolyte synthesis with FEC + VC solvent added

To the electrolyte prepared in Comparative Example 1, based on the total weight of the electrolyte, 0.5% by weight of FEC and 2% by weight of VC were added, followed by stirring in an environment free of moisture for 1 hour.

(0.3 M LiFSI + 0.3 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) prepared in this way (EC: DMC (4: 6 w / w) + 0.5 wt% FEC + 2 wt% VC) Used for.

Examples 4a to 4i: Electrolyte synthesis with FEC solvent added

Based on the total weight of the electrolyte in the electrolyte prepared in Comparative Example 2, the FEC was 0.3 wt%, 0.5 wt%, 0.7 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt%, 10 wt%, respectively. , 20% by weight was added by stirring in an environment free of moisture for 1 hour.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (EC: DMC (4: 6 w / w) + 0.3 to 20 wt% FEC) electrolyte was used in the lithium metal battery.

Example 5: Electrolyte synthesis with VC solvent added

To the electrolyte prepared in Comparative Example 2, 2% by weight of VC was added based on the total weight of the electrolyte, followed by stirring in an environment free of moisture for 1 hour.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (EC: DMC (4: 6 w / w) + 2 wt% VC) electrolyte was used in a lithium metal battery.

Example 6: Electrolyte synthesis with FEC + VC solvent added

To the electrolyte prepared in Comparative Example 2, based on the total weight of the electrolyte, 0.5% by weight of FEC and 2% by weight of VC were added, followed by stirring in an environment without moisture for 1 hour.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (EC: DMC (4: 6 w / w) + 0.5 wt% FEC + 2 wt% VC) electrolyte was used in the lithium metal battery.

Examples 7a to 7e: LiTFSI, LiBOB, LiPF ₆ , LiF salt and electrolyte synthesis using EC: DMC solvent

LiF salts were further dissolved in the electrolytes prepared in Example 4d such that the concentrations were 0.3 M, 0.4 M, 0.5 M, 0.7 M, and 1 M, respectively.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ + 0.3 to 1 M LiF) in (EC: DMC (4: 6 w / w) + 1 wt% FEC) electrolyte was used in the lithium metal battery. .

Example 2-1: LiTFSI, LiBOB, LiF, LiPF ₆  Electrolyte synthesis using salt and EC: DMC solvent

First, after the EC was dissolved at 60 ° C., the mixture was prepared by mixing with DMC and a weight ratio of 4: 6 in a moisture-free environment for 15 to 30 minutes while stirring. In the mixed solvent, the LiBOB salt was dissolved through continuous stirring in a moisture-free environment for 12 to 24 hours to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, the LiTFSI salt was dissolved to a concentration of 0.6 M. In addition, LiF salt was further dissolved to a concentration of 0.4 M. To this, 1% by weight and 3% by weight of FEC and VC, respectively, based on the total weight of the electrolyte were added, followed by stirring in a moisture-free environment for 1 hour.

(0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ + 0.4 M LiF) in (EC: DMC (4: 6 w / w) + 1 wt% FEC + 3 wt% VC) Used for.

Examples 2-2a to 2-2i: LiTFSI, LiBOB, LiF, LiPF ₆  Electrolyte synthesis using salt and EC: DMC solvent

0.5% by weight, 1% by weight, 3% by weight, 5% by weight, 7% by weight, 10% by weight, 15% by weight, 20% by weight, based on the total weight of the electrolyte in the electrolyte prepared in Example 2-1, 30% by weight of TFEC was added and stirred for 2 hours in a moisture-free environment.

Thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ + 0.4 M LiF) in (EC: DMC (4: 6 w / w) + 1 wt% FEC + 3 wt% VC + 0.5 to 30 wt% TFEC) electrolyte was used in lithium metal batteries.

Electrochemical analysis of modified electrolyte lithium metal battery

A constant current charging and discharging test was performed on the coin cell of the lithium metal secondary battery to which the electrolytes prepared above were applied to measure the electrochemical properties of the lithium metal battery. Lithium metal (1.5 cm diameter, 150 μm thick disc), 25 μm thick PP separator (diameter, 1.8 cm), NCM anode (8/1/1 composition 3.8 mAh / cm ² loading, diameter 1.2) cm), the electrochemical properties were measured using the electrolyte of 30 μL, and the applied voltage range was 3 to 4.2 V and charged until the current value was 0.05 C in the constant voltage mode when 4.2 V was reached. The first charging and discharging of the battery proceeded to 0.1 C as a formation process, and thereafter continued charging and discharging at 1 C.

Hereinafter, the analysis results will be described in detail with reference to the drawings.

FIG. 2 shows the characteristics of a coin-type lithium metal battery using an EC: DMC (4: 6 weight ratio) electrolyte containing LiFSI, LiTFSI, LiBOB, LiDFOB, and LiPF ₆ salts. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data and battery life is over at 80 cycles, while 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C and 0.6M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) The electrolyte system with a combination shows somewhat stable capacity retention and life characteristics, but an embodiment of the present invention It can be seen that it is considerably less than the electrolyte system according to. The anode used here is NCM (6/2/2).

Figure 3 shows the characteristics of the lithium metal coin cell battery according to the FEC addition ratio in the 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while cell life ends at 80 cycles, while 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 1C coin cell with FEC added to 6 weight ratio) shows somewhat improved life characteristics, and shows the most stable capacity retention rate when FEC is added at 0.5% by weight. This is because an appropriate amount of LiF-based SEI formed from FEC is formed on the lithium anode, and the SEI of the NCM anode also stabilizes. The anode used here is NCM (6/2/2).

Figure 4 shows the characteristics of a lithium metal coin cell battery according to the ratio of VC addition in a 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while cell life ends at 80 cycles, while 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: Coin cell with VC added to 6 weight ratio) shows somewhat improved life characteristics at 1C condition charge / discharge and shows the most stable capacity retention rate when VC is added at 0.5% or 2% by weight. This is because the SEI formed from VC at the lithium anode and the NCM anode inhibits side reactions with the electrolyte and stabilizes the electrochemical surface. The anode used here is NCM (6/2/2).

FIG. 5 shows the characteristics of the lithium metal coin cell battery according to the FEC addition ratio in the 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system of FIG. 3. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while battery life ends at 80 cycles, while 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) FEC-added coin cells show somewhat improved life characteristics under 1C charge / discharge and show the most stable capacity retention rate when FEC is added at 0.5% by weight. This is because an appropriate amount of LiF-based SEI formed from FEC is formed on the lithium anode, and the SEI of the NCM anode also stabilizes. The anode used here is NCM (6/2/2).

Figure 6 shows the characteristics of the lithium metal coin cell battery according to the VC addition ratio in the 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while battery life ends at 80 cycles, while 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) Coin cells added with VC show somewhat improved life characteristics under 1C charge and discharge conditions, and show the most stable capacity retention rate when VC is added at 2% by weight. This is because the SEI formed from VC at the lithium anode and the NCM anode inhibits side reactions with the electrolyte and stabilizes the electrochemical surface. The anode used here is NCM (6/2/2).

FIG. 7 shows the characteristics of a lithium metal coin cell battery using an optimized FEC and VC additive solvent in a 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while cell life ends at 80 cycles, while 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: Optimized for 6 weight ratio), the coin cell using 0.5 wt% FEC and 2 wt% VC additive solvent shows the most stable life characteristics even under 1C charge and discharge conditions, and more stable life characteristics than the electrolyte system without additive solvent. The anode used here is NCM (6/2/2).

8 is 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) lithium metal coin with 0.5 wt% FEC and 0.5 wt% FEC + 2 wt% VC added solvent optimized in the electrolyte system It shows the characteristics of the cell battery. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while the battery life ends at 80 cycles and the electrolyte without added solvents ends at 400 cycles, while 0.6 M LiTFSI, 0.4 M LiBOB, Coin cell with 0.5 wt% FEC and 2 wt% VC optimized for 0.05 M LiPF ₆ EC: DMC (4: 6 wt%) or with solvent added with FEC alone shows stable life characteristics even under 1C charge and discharge conditions. It shows more stable life characteristics than electrolyte system without solvent.

FIG. 9 is a SEM image of the lithium surface after a cycle by applying the above-described LiTFSI, LiBOB, LiPF ₆ salts and electrolytes without addition of EC: DMC and electrolytes with addition of solvents. High cell surface lithium dendrite formation in cell (a) when electrolytes without addition solvents other than EC: DMC and LiTFSI, LiBOB, and LiPF ₆ salts were added to cells after 200 cycles of charging and discharging at 1C were added. It was higher than the electrolyte (b) containing the solvent, and the roughness of the surface was also less rough. This is because a stable and elastic SEI formed due to the proper combination of the above salts and an additive solvent is formed on the surface of the lithium cathode.

FIG. 10 is a spectrum obtained by charging and discharging a cell containing an electrolyte containing the above-described LiTFSI, LiBOB, and LiPF ₆ salts and an additive solvent at 1C for 200 cycles, and then measuring the surface of the lithium cathode with XPS. Al was not detected even after cycling for a long time using an electrolyte system containing LiTFSI, LiBOB, and LiPF ₆ salts and an additive solvent. (26.81%), N (3.41%), O (34%), F (12.41%), and S (5.41%) were detected. This indicates that Al corrosion was suppressed due to the proper combination of the salts.

Figure 11 shows the characteristics of the lithium metal coin cell battery according to the FEC addition ratio in the 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while battery life ends at 30 cycles, while 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) Coin cells using an optimized 1% by weight FEC additive solvent show the most stable life characteristics even under 1C charge and discharge conditions and more stable life characteristics than electrolyte systems without additive solvents. The anode used here is NCM (8/1/1). Unlike the anode, it is an experiment to find an optimized FEC addition ratio when using a high energy density NCM anode.

12 is a lithium metal coin cell cell according to the concentration of LiF (0.3 to 1 M) in a 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1% by weight FEC (weight ratio) electrolyte system It shows characteristics. 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1% by weight FF (weight ratio) optimized LiF concentration is 0.4 M. Coin cells using a solvent with an optimized LiF salt show the most stable life characteristics even under 1C charge and discharge conditions. The anode used here is NCM (8/1/1). Unlike the positive electrode, it is an experiment to find an optimized LiF addition ratio when using a high energy density NCM positive electrode.

Figure 13 shows the addition of TFEC solvent to the electrolyte in which 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, and 0.05 M LiPF ₆ salts were mixed with EC: DMC (4: 6 weight ratio), 1% by weight FEC, and 3% by weight VC solvent. It is a figure which measured cycle characteristics by adding 0-30 weight% of a weight ratio. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) [Conventional] 1C is comparative data, while the battery life is over at 30 cycles, while 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts Electrolyte systems with EC: DMC (4: 6 weight ratio), 1% by weight FEC, 3% by weight VC, and 3% by weight TFEC formulations show very stable capacity retention and life characteristics. The positive electrode used here is NCM (8/1/1), and it is most preferable to add 3% by weight to 0 to 30% by weight of the TFEC weight ratio.

14 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 weight% FEC, 3 weight% VC, 0 weight% TFEC electrolyte After charging and discharging 20 times under the conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown. The anode used here is NCM (8/1/1).

15 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 wt% FEC, 3 wt% VC, 1 wt% TFEC electrolyte After charging and discharging 20 times under the conditions, XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown. The anode used here is NCM (8/1/1).

FIG. 16 shows 1 M using EC: DMC (4: 6 weight ratio), 1 weight% FEC, 3 weight% VC, 3 weight% TFEC electrolyte with 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts After charging and discharging under conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown. The anode used here is NCM (8/1/1).

FIG. 17 shows EC: DMC (4: 6 weight ratio), 1 weight% FEC, 3 weight% VC, 5 weight% TFEC electrolyte with 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts. After charging and discharging 20 times under the conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown. The anode used here is NCM (8/1/1).

FIG. 18 lists narrow scan XPS spectra of the C 1s and F 1s elements of FIGS. 14 to 17 and shows the change of each peak.

As the weight ratio of TFEC increases, the peak ratio for LiF changes, and peaks for -CF ₂ -CF ₂ and -CF ₂ -CH ₂ are newly formed, and the peak ratio of F 1s containing 3% by weight TFEC is the most. desirable. In addition, in the C 1s peaks, as the weight ratio of TFEC increases, the peaks of [CF, C = 0, C (O) F, CO ₃ ], that is, the combination of F and C elements increase, and C containing 3% by weight TFEC The peak ratio of 1s is most preferred.

The reason for this is that if LiF is produced too much, the proper LiF forms a stable SEI layer, but the ion conductivity is bad, so that the ion conductivity of the SEI layer falls and becomes too hard to degrade physical properties.

On the other hand, since the SEI layer with a suitable combination of [CF, C = 0, C (O) F, CO ₃ ] has some flexibility, the formation of a SEI layer with a proper proportion of C and F bonds results in lithium metal. It contributes greatly to the improvement of the characteristics of the secondary battery.

(3) Examples, comparative examples and test examples of the third group

Comparative Example 1: LiFSI, LiTFSI, LiBOB, LiPF ₆  Electrolyte synthesis using salt and EC: DMC solvent

First, after the EC was dissolved at 60 ° C., DMC and a weight ratio of 4: 6 were mixed in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiBOB salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, LiFSI was dissolved at a concentration of 0.3 M and LiTFSI salt at a concentration of 0.3 M.

The thus prepared (0.3 M LiFSI + 0.3 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in EC: DMC (4: 6 w / w) electrolyte was used in the lithium metal battery.

Comparative Example 2: LiTFSI, LiBOB, LiPF ₆  Electrolyte synthesis using salt and EC: DMC solvent

First, after the EC was dissolved at 60 ° C., DMC and a weight ratio of 4: 6 were mixed in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiBOB salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, the LiTFSI salt was dissolved to a concentration of 0.6 M.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in EC: DMC (4: 6 w / w) electrolyte electrolyte was used in a lithium metal battery.

Comparative Example 3: LiFSI, LiDFOB, LiPF ₆  Electrolyte synthesis using salt and EC: DMC solvent

First, after the EC was dissolved at 60 ° C., DMC and a weight ratio of 4: 6 were mixed in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiDFOB salt was dissolved in a moisture-free environment for 3 to 6 hours with constant stirring to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, the LiFSI salt was dissolved to a concentration of 0.6 M.

The thus prepared (0.6 M LiFSI + 0.4 M LiDFOB + 0.05 M LiPF ₆ ) in EC: DMC (4: 6 w / w) electrolyte was used for the lithium metal battery.

Comparative Example 4: LiFSI, LiTFSI, LiBOB, LiPF ₆  Electrolyte synthesis using salt and FEC: DMC solvent

FEC was mixed with DMC at a weight ratio of 3: 7 in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiBOB salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, LiFSI was dissolved at a concentration of 0.3 M and LiTFSI salt at a concentration of 0.3 M.

The thus prepared (0.3 M LiFSI + 0.3 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in FEC: DMC (3: 7 w / w) electrolyte was used in the lithium metal battery.

Comparative Examples 5a and 5b: LiTFSI, LiBOB, LiPF ₆  Electrolyte synthesis using salt and FEC: DMC or VC: DMC solvent

FEC and DMC or VC and DMC were mixed for 15 to 30 minutes while stirring in a moisture-free environment at a weight ratio of 3: 7 and 3: 7, respectively, to prepare a mixed solvent. In the mixed solvent, the LiBOB salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, the LiTFSI salt was dissolved to a concentration of 0.6 M.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (FEC: DMC (3: 7 w / w) or VC: DMC (3: 7 w / w) electrolyte was used in the lithium metal battery. .

Comparative Example 6: LiPF ₆  Electrolyte synthesis using salt and EC: DMC solvent

First, after the EC was dissolved at 60 ° C., DMC and a weight ratio of 4: 6 were mixed in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiPF ₆ salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 1 M.

The thus prepared (1 M LiPF ₆ ) in EC: DMC (4: 6 w / w) electrolyte was used in a lithium metal battery.

Comparative Examples 7a to 7e: LiTFSI, LiBOB, LiPF ₆ , LiF salt and electrolyte synthesis using EC: DMC solvent

First, after the EC was dissolved at 60 ° C., DMC and a weight ratio of 4: 6 were mixed in a moisture-free environment for 15 to 30 minutes while stirring to prepare a mixed solvent. In the mixed solvent, the LiBOB salt was dissolved while continuously stirring in a moisture-free environment for 12 to 24 hours to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, the LiTFSI salt was dissolved to a concentration of 0.6 M. In addition, LiF salts were further dissolved so that the concentrations were 0.3 M, 0.4 M, 0.5 M, 0.7 M, and 1 M, respectively.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ + 0.3 to 1 M LiF) in EC: DMC (4: 6 w / w) electrolyte was used in a lithium metal battery.

Examples 1a and 1b: electrolyte synthesis with FEC solvent added

To the electrolyte prepared in Comparative Example 1, based on the total weight of the electrolyte, 0.5% by weight and 5% by weight of FEC, respectively, were added, followed by stirring in an environment without moisture for 1 hour.

The thus prepared (0.3 M LiFSI + 0.3 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (EC: DMC (4: 6 w / w) + 0.5 or 5 wt% FEC) electrolyte was used in the lithium metal battery. .

Examples 2a to 2e: Electrolyte synthesis with VC solvent added

0.5% by weight, 1% by weight, 2% by weight, 2% by weight, 3% by weight, and 5% by weight of VC, respectively, based on the total weight of the electrolyte, added to the electrolyte prepared in Comparative Example 1, stirred in an environment free of moisture for 1 hour Was added.

The thus prepared (0.3 M LiFSI + 0.3 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (EC: DMC (4: 6 w / w) + 0.5 to 2 wt% VC) electrolyte was used in the lithium metal battery. .

Example 3: Electrolyte synthesis with FEC + VC solvent added

To the electrolyte prepared in Comparative Example 1, based on the total weight of the electrolyte, 0.5% by weight of FEC and 2% by weight of VC were added, followed by stirring in an environment free of moisture for 1 hour.

(0.3 M LiFSI + 0.3 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) prepared in this way (EC: DMC (4: 6 w / w) + 0.5 wt% FEC + 2 wt% VC) Used for.

Examples 4a to 4i: Electrolyte synthesis with FEC solvent added

Based on the total weight of the electrolyte in the electrolyte prepared in Comparative Example 2, the FEC was 0.3 wt%, 0.5 wt%, 0.7 wt%, 1 wt%, 3 wt%, 5 wt%, 7 wt%, 10 wt%, respectively. , 20% by weight was added by stirring in an environment free of moisture for 1 hour.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (EC: DMC (4: 6 w / w) + 0.3 to 20 wt% FEC) electrolyte was used in the lithium metal battery.

Example 5: Electrolyte synthesis with VC solvent added

To the electrolyte prepared in Comparative Example 2, 2% by weight of VC was added based on the total weight of the electrolyte, followed by stirring in an environment free of moisture for 1 hour.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (EC: DMC (4: 6 w / w) + 2 wt% VC) electrolyte was used in a lithium metal battery.

Example 6: Electrolyte synthesis with FEC + VC solvent added

To the electrolyte prepared in Comparative Example 2, based on the total weight of the electrolyte, 0.5% by weight of FEC and 2% by weight of VC were added, followed by stirring in an environment without moisture for 1 hour.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ ) in (EC: DMC (4: 6 w / w) + 0.5 wt% FEC + 2 wt% VC) electrolyte was used in the lithium metal battery.

Examples 7a to 7e: LiTFSI, LiBOB, LiPF ₆ , LiF salt and electrolyte synthesis using EC: DMC solvent

LiF salts were further dissolved in the electrolytes prepared in Example 4d such that the concentrations were 0.3 M, 0.4 M, 0.5 M, 0.7 M, and 1 M, respectively.

The thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ + 0.3 to 1 M LiF) in (EC: DMC (4: 6 w / w) + 1 wt% FEC) electrolyte was used in the lithium metal battery. .

Example 2-1: LiTFSI, LiBOB, LiF, LiPF ₆  Electrolyte synthesis using salt and EC: DMC solvent

First, after the EC was dissolved at 60 ° C., the mixture was prepared by mixing with DMC and a weight ratio of 4: 6 in a moisture-free environment for 15 to 30 minutes while stirring. In the mixed solvent, the LiBOB salt was dissolved through continuous stirring in a moisture-free environment for 12 to 24 hours to a concentration of 0.4 M. Here, LiPF ₆ salt was dissolved at a concentration of 0.05 M for 6 to 12 hours. Additionally, the LiTFSI salt was dissolved to a concentration of 0.6 M. In addition, LiF salt was further dissolved to a concentration of 0.4 M. To this, 1% by weight and 3% by weight of FEC and VC, respectively, based on the total weight of the electrolyte were added, followed by stirring in a moisture-free environment for 1 hour.

(0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ + 0.4 M LiF) in (EC: DMC (4: 6 w / w) + 1 wt% FEC + 3 wt% VC) Used for.

Examples 2-2a to 2-2i: LiTFSI, LiBOB, LiF, LiPF ₆  Electrolyte synthesis using salt and EC: DMC solvent

0.5% by weight, 1% by weight, 3% by weight, 5% by weight, 7% by weight, 10% by weight, 15% by weight, 20% by weight, based on the total weight of the electrolyte in the electrolyte prepared in Example 2-1, 30% by weight of TFEC was added and stirred for 2 hours in a moisture-free environment.

Thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ + 0.4 M LiF) in (EC: DMC (4: 6 w / w) + 1 wt% FEC + 3 wt% VC + 0.5 to 30 wt% TFEC) electrolyte was used in lithium metal batteries.

Examples 3-1a to 3-1d: LiTFSI, LiBOB, LiF, LiPF ₆  Electrolyte synthesis using salt and EC: DMC solvent

(0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ + 0.4 M LiF) prepared in Example 2-1 in (EC: DMC (4: 6 w / w) + 1 wt% FEC + 3 wt% VC ) LiBF ₄ salt was added to the electrolyte so that the concentrations were 0.05 M, 0.1 M, 0.2 M, and 0.3 M, respectively, and the mixture was stirred for 1 hour in a moisture-free environment.

Thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ + 0.4 M LiF + 0.05 to 0.3 M LiBF ₄ )) in (EC: DMC (4: 6 w / w) + 1 wt% FEC + 3 weight % VC) Electrolyte was used in a lithium metal battery.

Examples 3-2a to 3-2e: Electrolyte synthesis with TFEC added solvent

Prepared in Example 3-a above (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ + 0.4 M LiF + 0.05 M LiBF ₄ )) in (EC: DMC (4: 6 w / w) + 1% by weight FEC + 3% by weight VC) 0.5%, 1%, 3%, 5%, and 7% by weight of TFEC, respectively, based on the total weight of the electrolyte, in an environment free of moisture for 2 hours It was added by stirring.

Thus prepared (0.6 M LiTFSI + 0.4 M LiBOB + 0.05 M LiPF ₆ + 0.4 M LiF + 0.05 M LiBF ₄ )) in (EC: DMC (4: 6 w / w) + 1 wt% FEC + 3 wt% VC + 0.5 to 7% by weight TFEC) electrolyte was used in lithium metal cells.

Electrochemical analysis of modified electrolyte lithium metal battery

A constant current charging and discharging test was performed on the coin cell of the lithium metal secondary battery to which the electrolytes prepared above were applied to measure the electrochemical properties of the lithium metal battery. Lithium metal (1.5 cm diameter, 150 μm thick disc) for producing a coin cell, PP separator with a thickness of 25 μm (1.8 cm diameter), NCM anode (3.8 / ¹ mAh / cm ² loading of 8/1/1 composition, 1.2 cm diameter ), The electrochemical properties were measured using the electrolyte of the present invention (30 μL), and the voltage range applied at this time was 3 to 4.2 V, and when the voltage reached 4.2 V, the current value in the constant voltage mode was 0.05 C. It was charged. The first charging and discharging of the battery proceeded to 0.1 C in the formation process, and thereafter continued charging and discharging at 1 C.

Hereinafter, the analysis results will be described in detail with reference to the drawings.

FIG. 2 shows the characteristics of a coin-type lithium metal battery using an EC: DMC (4: 6 weight ratio) electrolyte containing LiFSI, LiTFSI, LiBOB, LiDFOB, and LiPF ₆ salts. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data and battery life is over at 80 cycles, while 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C and 0.6M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) The electrolyte system with a combination shows somewhat stable capacity retention and life characteristics, but an embodiment of the present invention It can be seen that it is considerably less than the electrolyte system according to. The anode used here is NCM (6/2/2).

Figure 3 shows the characteristics of the lithium metal coin cell battery according to the FEC addition ratio in the 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while cell life ends at 80 cycles, while 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 1C coin cell with FEC added to 6 weight ratio) shows somewhat improved life characteristics, and shows the most stable capacity retention rate when FEC is added at 0.5% by weight. This is because an appropriate amount of LiF-based SEI formed from FEC is formed on the lithium anode, and the SEI of the NCM anode also stabilizes. The anode used here is NCM (6/2/2).

Figure 4 shows the characteristics of a lithium metal coin cell battery according to the ratio of VC addition in a 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while cell life ends at 80 cycles, while 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: Coin cell with VC added to 6 weight ratio) shows somewhat improved life characteristics at 1C condition charge / discharge and shows the most stable capacity retention rate when VC is added at 0.5% or 2% by weight. This is because the SEI formed from VC at the lithium anode and the NCM anode inhibits side reactions with the electrolyte and stabilizes the electrochemical surface. The anode used here is NCM (6/2/2).

FIG. 5 shows the characteristics of the lithium metal coin cell battery according to the FEC addition ratio in the 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system of FIG. 3. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while battery life ends at 80 cycles, while 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) FEC-added coin cells show somewhat improved life characteristics under 1C charge / discharge and show the most stable capacity retention rate when FEC is added at 0.5% by weight. This is because an appropriate amount of LiF-based SEI formed from FEC is formed on the lithium anode, and the SEI of the NCM anode also stabilizes. The anode used here is NCM (6/2/2).

Figure 6 shows the characteristics of the lithium metal coin cell battery according to the VC addition ratio in the 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while battery life ends at 80 cycles, while 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) Coin cells added with VC show somewhat improved life characteristics under 1C charge and discharge conditions, and show the most stable capacity retention rate when VC is added at 2% by weight. This is because the SEI formed from VC at the lithium anode and the NCM anode inhibits side reactions with the electrolyte and stabilizes the electrochemical surface. The anode used here is NCM (6/2/2).

FIG. 7 shows the characteristics of a lithium metal coin cell battery using an optimized FEC and VC addition solvent in an 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while cell life ends at 80 cycles, while 0.3 M LiFSI, 0.3 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: Coin cell using 0.5 wt% FEC and 2 wt% VC additive solvent optimized for 6 wt.%) Shows the most stable life characteristics even under 1C charge and discharge conditions, and more stable life characteristics than the electrolyte system without added solvent. The anode used here is NCM (6/2/2).

FIG. 8 is a lithium metal coin with 0.5 wt% FEC and 0.5 wt% FEC + 2 wt% VC added solvent optimized in an 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. It shows the characteristics of the cell battery. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while the battery life ends at 80 cycles and the electrolyte without added solvents ends at 400 cycles, while 0.6 M LiTFSI, 0.4 M LiBOB, Coin cell with 0.5 wt% FEC and 2 wt% VC optimized for 0.05 M LiPF ₆ EC: DMC (4: 6 wt%) or with solvent added with FEC alone shows stable life characteristics even under 1C charge and discharge conditions. It shows more stable life characteristics than electrolyte system without solvent.

FIG. 9 is a SEM image of the lithium surface after a cycle by applying the above-described LiTFSI, LiBOB, LiPF ₆ salts and electrolytes without addition of EC: DMC and electrolytes with addition of solvents. High cell surface lithium dendrite formation in cell (a) when electrolytes without addition solvents other than EC: DMC and LiTFSI, LiBOB, and LiPF ₆ salts were added to cells after 200 cycles of charging and discharging at 1C were added. It was higher than the electrolyte (b) containing the solvent, and the roughness of the surface was also less rough. This is because the stable and elastic SEI formed due to the proper combination of the above salts and the added solvent is formed on the surface of the lithium cathode.

FIG. 10 is a spectrum obtained by charging and discharging a cell to which an electrolyte containing LiTFSI, LiBOB, and LiPF ₆ salts and an additive solvent are added at 200 cycles at 1C, and then measuring the surface of the lithium cathode with XPS. Al was not detected even after cycling for a long time using an electrolyte system containing LiTFSI, LiBOB, LiPF ₆ salts and an additive solvent, and Li (13.99%), B (3.16%), C in SEI formed from the composition of the main salt (26.81%), N (3.41%), O (34%), F (12.41%), and S (5.41%) were detected. This indicates that Al corrosion was suppressed due to the proper combination of the salts.

Figure 11 shows the characteristics of the lithium metal coin cell battery according to the FEC addition ratio in the 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) electrolyte system. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1C is comparative data, while battery life ends at 30 cycles, while 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) Coin cells using an optimized 1% by weight FEC additive solvent show the most stable life characteristics even under 1C charge and discharge conditions and more stable life characteristics than electrolyte systems without added solvent. The anode used here is NCM (8/1/1). Unlike the anode, it is an experiment to find an optimized FEC addition ratio when using a high energy density NCM anode.

12 is a lithium metal coin cell cell according to the concentration of LiF (0.3 to 1 M) in a 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1% by weight FEC (weight ratio) electrolyte system It shows characteristics. 0.6 M LiTFSI, 0.4 M LiBOB, 0.05 M LiPF ₆ EC: DMC (4: 6 weight ratio) 1% by weight FF (weight ratio) optimized LiF concentration is 0.4 M. Coin cells using a solvent with an optimized LiF salt show the most stable life characteristics even under 1C charge and discharge conditions. The anode used here is NCM (8/1/1). Unlike the positive electrode, it is an experiment to find an optimized LiF addition ratio when using a high energy density NCM positive electrode.

FIG. 13 shows the TFEC-added solvent in an electrolyte in which 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, and 0.05 M LiPF ₆ salts were mixed with EC: DMC (4: 6 weight ratio), 1% by weight FEC, and 3% by weight VC solvent. It is a figure which measured cycle characteristics by adding 0-30 weight% of a weight ratio. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) [Conventional] 1C is comparative data, while the battery life is over at 30 cycles, while 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts Electrolyte systems with EC: DMC (4: 6 weight ratio), 1% by weight FEC, 3% by weight VC, and 3% by weight TFEC formulations show very stable capacity retention and life characteristics. The positive electrode used here is NCM (8/1/1), and it is most preferable to add 3% by weight in 0 to 30% by weight of the TFEC weight ratio.

14 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 weight% FEC, 3 weight% VC, 0 weight% TFEC electrolyte After charging and discharging 20 times under the conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown. The anode used here is NCM (8/1/1).

15 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 wt% FEC, 3 wt% VC, 1 wt% TFEC electrolyte After charging and discharging 20 times under the conditions, XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown. The anode used here is NCM (8/1/1).

FIG. 16 shows 1 M using EC: DMC (4: 6 weight ratio), 1 weight% FEC, 3 weight% VC, 3 weight% TFEC electrolyte with 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts After charging and discharging under conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown. The anode used here is NCM (8/1/1).

FIG. 17 shows EC: DMC (4: 6 weight ratio), 1 weight% FEC, 3 weight% VC, 5 weight% TFEC electrolyte with 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts. After charging and discharging 20 times under the conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown. The anode used here is NCM (8/1/1).

FIG. 18 lists narrow scan XPS spectra of the C 1s and F 1s elements of FIGS. 14 to 17 and shows the change of each peak.

As the weight ratio of TFEC increases, the peak ratio for LiF changes, and peaks for -CF ₂ -CF ₂ and -CF ₂ -CH ₂ are newly formed, and the peak ratio of F 1s containing 3% by weight TFEC is the most. desirable. In addition, in the C 1s peaks, as the weight ratio of TFEC increases, the peaks of [CF, C = 0, C (O) F, CO ₃ ], that is, the combination of F and C elements increase, and C containing 3% by weight TFEC The peak ratio of 1s is most preferred.

The reason for this is that if LiF is produced too much, the proper LiF forms a stable SEI layer, but the ion conductivity is bad, so that the ion conductivity of the SEI layer falls and becomes too hard to degrade physical properties.

On the other hand, since the SEI layer with a suitable combination of [CF, C = 0, C (O) F, CO ₃ ] has some flexibility, the formation of a SEI layer with a proper proportion of C and F bonds results in lithium metal. It contributes greatly to the improvement of the characteristics of the secondary battery.

FIG. 19 shows the addition of LiBF ₄ salt to the electrolyte in which 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, and 0.05 M LiPF ₆ salts were mixed with EC: DMC (4: 6 weight ratio), 1 wt% FEC, 3 wt% VC solvent. It is a figure which measured cycle characteristics by adding 0 to 0.3 M concentration. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) [Conventional] 1C is comparative data, while the battery life is over at 30 cycles, while 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts Electrolyte systems with EC: DMC (4: 6 weight ratio), 1 wt% FEC, 3 wt% VC, 0.05 M LiBF ₄ formulation show very stable capacity retention and life characteristics. The positive electrode used here is NCM (8/1/1), and it is most preferable to add 0.05 M in the 0 to 0.3 M concentration of LiBF ₄ .

FIG. 20 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 weight% FEC, 3 weight% VC, 0 M LiBF ₄ electrolyte After charging and discharging 20 times under the conditions, the cell shows the XPS narrow scan spectra (elements C, O, F, B) of the lithium cathode surface. The anode used here is NCM (8/1/1).

Figure 21 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 weight% FEC, 3 weight% VC, 0.05 M LiBF ₄ electrolyte After charging and discharging 20 times under the conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown. The anode used here is NCM (8/1/1).

Figure 22 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 wt% FEC, 3 wt% VC, 0.1 M LiBF ₄ electrolyte After charging and discharging 20 times under the conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown. The anode used here is NCM (8/1/1).

FIG. 23 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 weight% FEC, 3 weight% VC, 0.2 M LiBF ₄ electrolyte After charging and discharging 20 times under the conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown. The anode used here is NCM (8/1/1).

FIG. 24 shows 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ salts using EC: DMC (4: 6 weight ratio), 1 wt% FEC, 3 wt% VC, 0.3 M LiBF ₄ electrolyte After charging and discharging 20 times under the conditions, the XPS narrow scan spectra (elements C, O, F, and B) of the surface of the lithium cathode separated from the battery is shown. The anode used here is NCM (8/1/1).

25 shows the peak variation by listing the narrow scan XPS spectra of the C 1s and F 1s elements of FIGS. 20 to 23. As the concentration of LiBF ₄ increases, the peak ratio for LiF and -CF ₂ and -CF ₃ varies, and the peak ratio of F 1s containing 0.05 M LiBF ₄ is most preferable. Also, in the C 1s peaks, as the concentration of LiBF ₄ increases, the peaks of [CF, C = 0, C (O) F, CO ₃ ], ie, the combination of F and C elements increase, and the peak of C 1s containing 0.05 M LiBF ₄ The ratio is most preferred. The reason for this is that a suitable LiF forms a stable SEI layer, but deteriorates ion conductivity, so if too much LiF is produced, the ion conductivity of the SEI layer falls and becomes too hard to degrade physical function. In addition, since the SEI layer with a suitable combination of [CF, C = 0, C (O) F, CO ₃ ] has some flexibility, the formation of a SEI layer having a suitable ratio of C and F bonds results in lithium metal. It contributes greatly to the improvement of the characteristics of the secondary battery.

FIG. 26 is an electrolyte in which 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ and 0.05 M LiBF ₄ salts are mixed in EC: DMC (4: 6 weight ratio), 1% by weight FEC, and 3% by weight VC solvent It is a figure which measured the cycle characteristics by adding 0-7 weight% of the concentration of the TFEC-added solvent to the. 1 M LiPF ₆ EC: DMC (4: 6 weight ratio) [Conventional] 1C is comparative data, while the battery life is over at 30 cycles, while 0.6 M LiTFSI, 0.4 M LiBOB, 0.4 M LiF, 0.05 M LiPF ₆ , 0.05 The electrolyte system with M LiBF ₄ salts with EC: DMC (4: 6 weight ratio), 1% by weight FEC, 3% by weight VC, 1% by weight TFEC formulation shows very stable capacity retention and life characteristics. The positive electrode used here is NCM (8/1/1), and it is most preferable to add 1% by weight of 0 to 7% by weight of TFEC in the electrolyte to which 0.05 M LiBF ₄ additive salt is added.

Claims (20)

delete delete delete delete delete delete delete delete delete (a) a first salt consisting only of LiTFSI at a concentration of -0.5 to 0.7 M, (b) a second salt consisting only of LiBOB at a concentration of 0.35 to 0.45 M, and (c) a agent consisting only of LiPF _{6 at a} concentration of 0.04 to 0.06 M. 3 salt, (d) an electrolyte for a lithium metal secondary battery comprising a solvent composed of a mixture of ethylene carbonate and dimethyl carbonate,
(e) further comprising at least one first solvent additive selected from fluoro ethylene carbonate and vinylene carbonate,
(f) further comprising LiBF ₄ at a concentration of 0.03 to 0.04 M as a fourth salt,
(g) 2.5 to 3.5% by weight of trifluoro ethylene carbonate based on the total weight of the electrolyte is further included as a second solvent additive,
The first solvent-based additive comprises 0.8 to 1.2% by weight of fluoro ethylene carbonate and 0.01 to 3.5% by weight of vinylene carbonate based on the total weight of the electrolyte,
The mixing weight ratio of the ethylene carbonate and the dimethyl carbonate is 0.6 to 0.8: 0.2 to 0.4,
An electrolyte for a lithium metal secondary battery, further comprising a LiF salt at a concentration of 0.3 to 0.5 M and a LiNO ₃ salt at a concentration of 0.05 to 0.1 M. delete delete delete delete delete delete delete A lithium metal secondary battery comprising the electrolyte for a lithium metal secondary battery according to claim 10. An electrical device comprising the lithium metal secondary battery according to claim 18. The electrical device according to claim 19, wherein the electrical device is selected from a communication device, a transportation device, an energy storage device, and an acoustic device.

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