WO2020009313A1 - Secondary battery system comprising molybdenum sulfide electrode with electrochemical property enhanced through co-insertion of lithium-electrolyte solvent - Google Patents

Abstract

The present invention relates to a lithium secondary battery system comprising a molybdenum sulfide (MoS₂) electrode and, more specifically, to a lithium secondary battery system having electrochemical properties enhanced by the control of charge/discharge voltages and the co-insertion of lithium-electrolyte through solvent electrolyte control. In the secondary battery system according to the present invention, an ether-based solvent able to be co-inserted, together with lithium ions, into the interlayer of MoS₂ is employed as an electrolyte solvent and the charge/discharge voltage condition is controlled to 1.0-3.0 V, thereby enhancing electrochemical properties of the battery, such as the battery's rate, lifespan, and so forth.

Description

Secondary battery system including molybdenum sulfide electrode with improved electrochemical properties through co-insertion of lithium-electrolyte solvent

The present invention relates to a lithium ion secondary battery system including a molybdenum sulfide (MoS ₂ ) electrode, and more particularly lithium ion with improved electrochemical characteristics through co-insertion of a lithium-electrolyte solvent through charge and discharge voltage and electrolyte control It relates to a secondary battery system.

Recently, with the rapid development of electronics, telecommunications, and computer industry, camcorders, mobile phones, notebook PCs, etc. have emerged and are developing remarkably, and the demand for lithium ion secondary battery as a power source to drive these portable electronic information communication devices is increasing day by day It is increasing. In particular, research on power sources for electric vehicles by hybridizing internal combustion engines and lithium secondary batteries has been actively conducted in the US, Japan, and Europe.

Commercially available small lithium ion _secondary batteries use LiCoO ₂ for the positive electrode and carbon for the negative electrode. In the case of the carbon anode which is most used at present, it shows a voltage flat area close to 0V compared to the lithium reduction potential. In addition, a cathode material having an alloying and conversion reaction mechanism, in which much research is being conducted, also reacts to 0.1V or 0.01V relative to the lithium reduction potential. However, when the negative electrode is charged near 0V, lithium metal precipitates, which is a problem in stability. In order to solve this problem, research on Ti-based anode materials such as Li ₄ Ti ₅ O ₁₂ or TiO ₂ has been made. However, these Ti-based negative electrode materials have limitations such as low electronic conductivity and relatively low theoretical capacity (200 mAh / g or less). Therefore, there is a need for research on a new material having appropriate theoretical capacity, rapid charging characteristics and stability at the same time.

Accordingly, bicomponent sulfides are being studied as new materials that can replace carbon anodes and Ti-based anode materials. In particular, MoS ₂ is attracting attention as a cathode material to replace carbon cathodes with high theoretical capacity.

The molybdenum sulfide (MoS ₂ ) is one of the sulfide-based materials having a layered structure, as shown below, during the charging process, lithium ions are inserted between the MoS ₂ layers, after which lithium is combined with sulfur to form Li _It has a reaction mechanism to form ₂ S, the theoretical capacity is 670 mAh / g, has a high discharge capacity, is stable at room temperature, and does not use heavy metals, has an environmentally friendly advantage.

First process: xLi + MoS ₂ → Li _x MoS ₂ (Insertion reaction)

Second process: Li _x MoS ₂ + (4-x) Li → Mo + 2Li ₂ S (conversion reaction)

According to some report, because it affects the Mo + 2Li ₂ S is said to be the MoS ₂ is formed again by the discharge process, but large volume expansion for a conversion reaction involves the structure formed by the theoretical charging process of MoS ₂ It is reported that the reaction of Li + S ↔ Li ₂ S occurs rather than formation. In the case of sulfur (S) formed in this reaction mechanism, the insulator properties and the shuttle effect of polysulfide lead to slow kinetic and low lifespan characteristics. Therefore, when charged to 0.01V or 0.1V, the battery composed of the MoS ₂ negative electrode becomes unstable due to the formation of lithium dendrite and the aforementioned characteristics of sulfur. In addition, the rate characteristic of MoS ₂ is not high.

As such, MoS ₂ is difficult to be commercialized due to the decomposition of Mo and S in the process of low electrical conductivity and charging and discharging, resulting in a change in volume.

Therefore, there is an urgent need for research and development on a method for improving the electrochemical characteristics of a lithium ion secondary battery capable of alleviating the reduction of capacity by suppressing the decomposition of MoS ₂ .

Accordingly, the present inventors were studying a method of controlling only insertion reaction of lithium ions to suppress the decomposition of MoS ₂ , while controlling the charge and discharge voltage to 1.0 to 3.0V, and adjusting the solvent conditions of the electrolyte, ether As the charge / discharge cycle progresses when using the solvent, Li ions form a complex with the ether solvent and the electrochemical characteristics of the battery are improved by the co-intercalation effect of intercalating MoS ₂ into the interlayer. The present invention has been completed.

The present invention is to solve the above problems, an object of the present invention is to provide a secondary battery system comprising a molybdenum sulfide electrode, the electrochemical properties improved.

In order to achieve the above object, the present invention provides a lithium ion secondary battery comprising a MoS ₂ electrode, a counter electrode material, a separator located between the MoS ₂ electrode and the counter electrode material, and an electrolyte, and charge and discharge of the lithium ion secondary battery A secondary battery system including a charge / discharge control unit controlled by voltage, wherein the electrolyte is a solution in which lithium salt is dissolved in an ether solvent, and the charge / discharge control unit controls the charge / discharge voltage to 1.0 to 3.0V. Provided is a secondary battery system.

Also preferably, when the charge and discharge voltage is controlled to 1.0 to 3.0V in the secondary battery system, lithium ions in the electrolyte may be co-intercalated into the MoS ₂ electrode by forming a complex with the ether solvent. have.

Also preferably, the ether solvent is one or more selected from the group consisting of dimethyl ether (DME), diethylene glycol monomethyl ether (DGM) and triethylene glycol monomethyl ether (TGM), or a mixture thereof Can be everyday.

Also preferably, the ether solvent may be a mixed solvent of dimethyl ether (DME) and triethylene glycol monomethyl ether (TGM).

Also preferably, the mixing ratio of the mixed solvent of dimethyl ether (DME) and triethylene glycol monomethyl ether (TGM) may be 1: 9 to 9: 1 by volume ratio.

Also preferably, the lithium salt may be at least one selected from the group consisting of LiPF ₆ , LiClO ₄ , LiTFSI, and LiCF ₃ SO ₃ , or a mixture thereof.

Also preferably, the concentration of the lithium salt may be 0.6 to 3 mol / L.

Also preferably, the MoS ₂ electrode may include a MoS ₂ active material, a conductive material and a binder.

Also preferably, the conductive material may be at least one carbon material selected from the group consisting of carbon nanofibers, carbon nanotubes, conductive graphite, acetylene black, Super P, KS6, and Vulcan XC-72, or a mixture thereof. have.

Also preferably, the binder may be carboxymethyl cellulose sodium salt (NaCMC) or poly (vinylidene fluoride) (PVDF).

Also preferably, the MoS ₂ electrode may be made of 5-15 wt% of the conductive material, 5-10 wt% of the binder, and the remainder of the MoS ₂ active material.

Also preferably, the binder may be used by dissolving in a solvent. The solvent may be distilled water for NaCMC and N-methyl pyrrolidone (NMP) for PVdF.

Also preferably, the counter electrode material may be selected from the group consisting of Li, a metal of Na, or a mixture thereof.

Also preferably, the separator may be at least one microporous membrane selected from glass fibers, polyethylene (PE) and polypropylene (PP).

The secondary battery system according to the present invention uses an ether solvent which can be co-inserted with lithium ions between MoS ₂ layers as an electrolyte solvent, and controls the charging and discharging voltage conditions at 1.0 to 3.0 V, thereby controlling the rate-of-charge characteristics and lifetime of the battery. Electrochemical characteristics, such as a characteristic, can be improved.

1 is an X-ray diffraction (XRD) graph of MoS ₂ synthesized for the production of a Li / MoS ₂ secondary battery according to an embodiment of the present invention.

2 is a scanning electron microscope (SEM) photograph of MoS ₂ synthesized for the production of a Li / MoS ₂ secondary battery according to an embodiment of the present invention.

Figure 3 is a (a) transmission electron microscope (TEM) and (b) high magnification transmission electron microscope (HRTEM) of MoS ₂ synthesized for the production of Li / MoS ₂ secondary battery according to an embodiment of the present invention.

4 is a graph showing the life characteristics of a secondary battery when charging and discharging at a voltage range of 1.0 to 3.0 V in a Li / MoS ₂ secondary battery including a 1M LiTFSI electrolyte in a DME according to an embodiment of the present invention (current density = 100 mA / g)

FIG. 5 is a graph showing the rate characteristic of a secondary battery during charge / discharge at a voltage range of 1.0 to 3.0 V in a Li / MoS ₂ secondary battery including a 1 M LiTFSI electrolyte in TGM according to an embodiment of the present invention.

FIG. 6 is a secondary battery in charge / discharge of a voltage range of 1.0 to 3.0 V in a Li / MoS ₂ secondary battery including a 1 M LiTFSI electrolyte in DME / TGM (v / v = 1: 1) according to an embodiment of the present invention. It is a graph of the life characteristics of the battery (current density = 100 mA / g).

FIG. 7 is a secondary battery for charging and discharging at a voltage range of 1.0 to 3.0 V in a Li / MoS ₂ secondary battery including a 1M LiTFSI electrolyte in DME / TGM (v / v = 1: 1) according to an embodiment of the present invention. It is a rate characteristic graph of a battery.

8 is a secondary battery when charging and discharging at a voltage range of 1.0 to 3.0 V in a Li / MoS ₂ secondary battery including a 1M LiTFSI electrolyte in DME / TGM (v / v = 9: 1) according to an embodiment of the present invention. It is a graph of the life characteristics of the battery (current density = 100 mA / g).

9 is a secondary battery when charging and discharging at a voltage range of 1.0 to 3.0 V in a Li / MoS ₂ secondary battery including a 1M LiTFSI electrolyte in DME / TGM (v / v = 9: 1) according to an embodiment of the present invention. It is a rate characteristic graph of a battery.

10 is a secondary battery when charging and discharging at a voltage range of 1.0 to 3.0 V in a Li / MoS ₂ secondary battery including a 1M LiTFSI electrolyte in DME / TGM (v / v = 3: 1) according to an embodiment of the present invention. It is a graph of the life characteristics of the battery (current density = 100 mA / g).

11 is a secondary battery when charging and discharging at a voltage range of 1.0 to 3.0 V in a Li / MoS ₂ secondary battery including a 1M LiTFSI electrolyte in DME / TGM (v / v = 3: 1) according to an embodiment of the present invention. It is a graph of the life characteristics of the battery (current density = 1A / g).

12 is a secondary battery when charging and discharging at a voltage range of 1.0 to 3.0 V in a Li / MoS ₂ secondary battery including a 1M LiTFSI electrolyte in DME / TGM (v / v = 3: 1) according to an embodiment of the present invention. It is a rate characteristic graph and a charge / discharge graph of a battery.

13 is a Li / MoS ₂ secondary battery including a 1M LiTFSI electrolyte in DME / TGM (v / v = 3: 1) according to an embodiment of the present invention, an electrolyte solvent, a MoS ₂ electrode discharged to 1.0 V, and The FT-IR spectrum of the MoS ₂ electrode charged up to 3.0 V is shown.

FIG. 14 is a cycle of charging and discharging at a voltage range of 1.0 to 3.0 V in a Li / MoS ₂ secondary battery including a 1 M LiTFSI electrolyte in DME / TGM (v / v = 3: 1) according to an embodiment of the present invention. High magnification transmission electron micrographs and interlayer spacing data of stars MoS ₂ are shown.

FIG. 15 illustrates a MoS during charge / discharge at a voltage range of 1.0 to 3.0 V in a Li / MoS ₂ secondary battery including 1M LiTFSI electrolyte in DME / TGM (v / v = 3: 1) according to an embodiment of the present invention. a _second electrode (a) the scan speed by cyclic voltammetry (CV) graph, (b) log i for log v graphs, (c) similar to the capacitive (Pseudocapacitive) histogram and (d) represents the ratio of the behavior similar capacity A cyclic voltammetry (CV) graph showing the pseudocapacitive behavior is shown.

FIG. 16 is a secondary battery in charge / discharge at a voltage range of 0.1 to 3.0 V in a Li / MoS ₂ secondary battery including a 1M LiTFSI electrolyte in DME / TGM (v / v = 1: 1) according to a comparative example of the present invention. Graph of battery life characteristics (current density = 100 mA / g)

FIG. 17 illustrates a voltage range of 0.7 to 3.0 V in a Li / MoS ₂ secondary battery including an electrolyte in which 1 M LiCF ₃ SO ₃ lithium salt is dissolved in tetraglycol dimethyl ether (TEGDME) electrolyte according to a comparative example of the present invention. This is a graph of the life characteristics of secondary batteries during charge and discharge (current density = 50 mA / g).

18 is a secondary battery in charge / discharge at a voltage range of 1.0 to 3.0 V in a Li / MoS ₂ secondary battery including a 1M LiTFSI electrolyte in EC / DEC (v / v = 1: 1) according to a comparative example of the present invention. It is a graph of the life characteristics of the battery (current density = 100 mA / g).

19 is a secondary battery at the time of charging and discharging at a voltage range of 1.0 to 3.0 V in a Li / MoS ₂ secondary battery including a 1 M LiTFSI electrolyte in EC / DEC (v / v = 1: 1) according to a comparative example of the present invention. It is a rate characteristic graph of a battery.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

While the invention allows for various modifications and variations, specific embodiments thereof are illustrated by way of example in the drawings and will be described in detail below. However, it is not intended to be exhaustive or to limit the invention to the precise forms disclosed, but rather the invention includes all modifications, equivalents, and alternatives consistent with the spirit of the invention as defined by the claims.

The present invention provides a secondary battery system including a lithium ion secondary battery including a MoS ₂ electrode, and a charge and discharge control unit for controlling charge and discharge of the lithium ion secondary battery by voltage.

A secondary battery system according to the present invention specifically includes a lithium ion secondary battery including a MoS ₂ electrode, a counter electrode material, a separator positioned between the MoS ₂ electrode and the counter electrode material, and an electrolyte, and charge and discharge of the lithium ion secondary battery. It includes a charge and discharge control unit controlled by the voltage.

In the molybdenum sulfide (MoS ₂ ) electrode, MoS ₂ is one of the sulfide-based materials having a layered structure, as described below, during the charging process, lithium ions are inserted between the MoS ₂ layers and thereafter. Lithium has a reaction mechanism that combines with sulfur to form Li ₂ S, and has a high discharge capacity with a theoretical capacity of 670 mAh / g.

First process: xLi + MoS ₂ → Li _x MoS ₂ (Insertion reaction)

Second process: Li _x MoS ₂ + (4-x) Li → Mo + 2Li ₂ S (conversion reaction)

In the case of sulfur (S) formed in this reaction mechanism, the insulator properties and the shuttle effect of polysulfide lead to slow kinetic and low lifespan characteristics. Therefore, when charged to 0.01V or 0.1V, the battery composed of the MoS ₂ negative electrode becomes unstable due to the formation of lithium dendrite and the aforementioned characteristics of sulfur. In addition, the rate characteristic of MoS ₂ is not high.

Therefore, in order to improve the electrochemical characteristics of the secondary battery including the MoS ₂ electrode, it is important to control only the insertion reaction of lithium ions without the conversion reaction, which is a side reaction of the battery.

Thus, the present inventors found that by controlling the voltage range of charge and discharge in the range of 1.0 to 3.0 V, only the insertion reaction of lithium ions can be controlled in the secondary battery including the MoS ₂ electrode (Experimental Example 1 Reference).

In addition, the inventors have found that the electrochemical properties of MoS ₂ materials vary depending on the solvent conditions of the electrolyte when the charge and discharge voltage is controlled to 1.0 to 3.0V in the secondary battery system. Specifically, since the conventional case, which typically use a carbonate-based solvent is used as is size is less Li ions only and inserted in the interlayer of MoS ₂ as the solvent of the electrolyte is not greater the difference between the inter-layer spacing of MoS ₂ in accordance with the cycles, capacity and The rate property also shows a low value, but when using an ether solvent, as the charge and discharge cycle proceeds, the interlayer spacing of MoS ₂ increases and it is confirmed that the electrochemical properties such as the capacity and the rate property are improved (see Experimental Example 2). . From this, it can be seen that in the case of the ether solvent, Li ions are complexed with the ether solvent to be inserted into the interlayer of MoS ₂ together, and the electrochemical characteristics of the battery are improved by such co-intercalation. It was confirmed.

Accordingly, the present invention is controlled to a voltage range of 1.0 ~ 3.0V showing only the insertion reaction of lithium ions in the secondary battery system including the MoS ₂ electrode, and the lithium ion by using an ether solvent as the electrolyte solvent in the voltage range It is characterized by improving the electrochemical characteristics of the battery due to co-intercalation into the MoS ₂ electrode by complexing with an ether solvent.

In the secondary battery system according to the present invention, the electrolyte may be a solution in which lithium salt is dissolved in an ether solvent as an electrolyte solvent.

In this case, the ether solvent may be at least one selected from the group consisting of dimethyl ether (DME), diethylene glycol monomethyl ether (DGM) and triethylene glycol monomethyl ether (TGM), or a mixed solvent thereof. have.

Preferably, the ether solvent may be a mixed solvent of dimethyl ether (DME) and triethylene glycol monomethyl ether (TGM). The DME is excellent for improving battery life, and the TGM has been shown to be excellent for improving the rate characteristic of the battery, and the mixed solvent of the two may improve both the life and rate characteristic of the battery.

The mixing ratio of the mixed solvent of dimethyl ether (DME) and triethylene glycol monomethyl ether (TGM) may be 1: 9 to 9: 1 by volume ratio.

The lithium salt may be used a lithium salt commonly used in the art, for example, at least one selected from the group consisting of LiPF ₆ , LiClO ₄ , LiTFSI and LiCF ₃ SO ₃ , or a mixture thereof. have.

The concentration of the lithium salt is preferably in the range of 0.6 to 3 mol / L. When the lithium salt is out of the concentration range, there is a problem in that the electrochemical characteristic is not sufficiently expressed.

In the secondary battery system according to the present invention, the MoS ₂ electrode may include a MoS ₂ active material, a conductive material and a binder.

The conductive material and the binder may be used commonly used in the art.

For example, the conductive material may be at least one carbon material selected from the group consisting of carbon nanofibers, carbon nanotubes, conductive graphite, acetylene black, Super P, KS6, and Vulcan XC-72, or a mixture thereof. .

The binder may be carboxymethyl cellulose sodium salt (NaCMC) or poly (vinylidene fluoride) (PVDF).

The binder may be dissolved in a solvent, and the solvent may be distilled water for NaCMC, and N-methyl pyrrolidone (NMP) for PVdF.

The MoS ₂ electrode may be made of 5 to 15 wt% of the conductive material, 5 to 10 wt% of the binder, and the remainder of the MoS ₂ active material, but is not limited thereto.

The MoS ₂ electrode may be prepared by mixing a MoS ₂ active material, a conductive material, and a binder with a solvent to prepare a slurry, and then applying and drying the slurry on a current collector.

In the secondary battery system according to the present invention, the counter electrode material may be conventionally used in the art, and may be specifically selected from the group consisting of a metal of Li, Na, or a mixture thereof.

In the secondary battery system according to the present invention, the separator may be one commonly used in the art, and may be one or more microporous membranes selected from glass fiber, polyethylene (PE) and polypropylene (PP).

In addition, it is also possible to use a laminated separator in which a heat-resistant layer containing heat-resistant inorganic fillers such as silica, alumina and boehmite is formed on one or both surfaces of the microporous membrane.

In the lithium ion secondary battery of the present invention, after the above-mentioned MoS ₂ electrode and the counter electrode are stacked with the separator, the laminated electrode body is loaded into the exterior body, and the electrolyte is injected into the exterior body to immerse the electrode body in the electrolyte. It can be produced by sealing the opening of the exterior body.

As the exterior body, an exterior can made of steel, aluminum or aluminum alloy tubular can (eg, cylindrical or cylindrical), or an outer body composed of a laminated film on which metal is deposited can be used.

The lithium ion secondary battery of the present invention is used in a battery system having a charge and discharge control unit for controlling the charge and discharge of the battery by the voltage, wherein the rate-of-rate characteristics of the battery by controlling the charge and discharge voltage conditions to 1.0 ~ 3.0V, Electrochemical characteristics, such as a lifetime characteristic, can be improved.

That is, the battery system of the present invention includes the lithium ion secondary battery of the present invention and the charge / discharge control unit. For other configurations and structures, the battery system of the present invention may be configured by various conventionally known battery systems. Applicable Specifically, the battery system may include, for example, a battery, a rack for fixing a battery pack or a battery module described later, a cooling fan, and the like. In addition, the same thing as the charge / discharge control part for lithium ion secondary batteries employ | adopted for the battery system known conventionally can be applied also to the said charge / discharge control part.

In addition, the battery system of the present invention may have one or two or more lithium ion secondary batteries of the present invention, the lithium ion secondary battery used in the secondary battery system of the present invention is a battery pack packaged in a plurality of In addition, the battery pack may be in the form of a battery module having a plurality of such battery packs.

Hereinafter, preferred examples are provided to aid the understanding of the present invention. However, the following preparation examples are only to aid the understanding of the present invention, the present invention is not limited by the following preparation examples.

Preparation Example 1 Synthesis of MoS ₂

0.2-0.4 g of NaMoO ₄ .2H ₂ O and 0.3-0.5 g CS (NH ₂ ) ₂ were dissolved in 20-40 mL of distilled water to prepare a mixed solution. Next, 0.5-1.5 mL of hydrochloric acid solution (30.0-37.0%) was added to the mixed solution, followed by stirring for 0.5-1 hour to prepare a blue solution. Thereafter, the blue solution was placed in a 50 mL Teflon-lined stainless-steel autoclave and heated at 160-200 ° C. for 12-48 hours. After the reaction, the mixture was cooled to room temperature, washed with distilled water and ethanol, and centrifuged to obtain a product, and dried at 40 to 80 ° C. in a vacuum oven. Thereafter, the dried powder was heat-treated at 600-800 ° C. for 2-6 hours in an argon atmosphere furnace to obtain a final product.

The prepared product was shown in FIG. 1 by X-ray diffraction (XRD).

As shown in FIG. 1, the pattern of all peaks of the product was consistent with the literature value of MoS ₂ (JCPDS no. 37-1492). The peak seen at 14.2 ° is a peak corresponding to the (002) crystal plane and shows the layer structure characteristic, and no peak other than MoS ₂ was found.

Thus, the prepared material was confirmed to be MoS ₂ .

In addition, the product was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and shown in Figures 2 and 3, respectively.

2 is a photo scanning electron microscopy of the resulting MoS ₂ (SEM), Figure 3 (a) is a general transmission electron microscope (TEM) photograph of the resulting MoS _2, 3 (b) is a high magnification of the resulting MoS ₂ Transmission electron microscope (HRTEM) photographs.

As shown in Figure 2 and 3 (a), the prepared MoS ₂ exhibited the appearance of the corrugated nanoplates assembled. In addition, in the high magnification transmission electron microscope image of FIG. 3 (b), the sheets of the layered structure can be confirmed, and the interlayer spacing was analyzed to be 0.64 nm.

Preparation Example 2 Preparation of MoS ₂ Electrode

A slurry was prepared by mixing 80 wt% MoS ₂ powder, 10 wt% Super P conductive material and 10 wt% PVdF binder in N-methyl pyrrolidone (NMP) solvent. The slurry was uniformly coated on Cu foil and then vacuum dried at 110 ° C. for 12 hours to form a MoS ₂ electrode. The MoS ₂ electrode material had a density of 2.0 mg / cm ² and was cut into 10 mm diameter circles.

Preparation Example 3 Fabrication of a Lithium Secondary Battery Comprising a MoS ₂ Electrode and an Ether Electrolyte Solvent (DME)

A battery was manufactured with a 2032 type coin cell. Specifically, lithium metal was prepared in a circular shape of 16 mm and used as a counter electrode and a reference electrode, and a MoS ₂ electrode of Preparation Example 2 was used as a cathode, glass fiber was used as a separator, and 1M of A solution in which LiTFSI electrolyte salt was dissolved in a DME solvent was used as an electrolyte. This process was carried out in a glove box filled with argon.

The prepared battery was charged and discharged in the voltage range of 1.0 ~ 3.0V, and measured the life characteristics of the battery is shown in Figure 4.

As shown in FIG. 4, the Li / MoS ₂ secondary battery including DME, an ether solvent, as an electrolyte solvent, was charged and discharged in a voltage range of 1.0 to 3.0 V, and the first discharge capacity was 228 mAh / g, and 160 after 40 cycles. It has been shown to remain constant at a capacity of mAh / g.

Preparation Example 4 Preparation of a Lithium Secondary Battery Comprising a MoS ₂ Electrode and an Ether Electrolyte Solvent (TGM)

A lithium ion secondary battery was prepared in the same manner as in Preparation Example 3, except that a solution in which 1 M LiTFSI electrolyte salt was dissolved in a TGM solvent was used as an electrolyte.

The manufactured battery was charged and discharged in the voltage range of 1.0 ~ 3.0V, it is shown in Figure 5 by measuring the rate characteristic.

As shown in FIG. 5, the Li / MoS ₂ secondary battery including TGM, which is an ether solvent, as an electrolyte solvent has a current density of 0.05 to 0.1, 0.2, 0.5 A / g when charged and discharged in a voltage range of 1.0 to 3.0 V. As it increased, the discharge capacity was measured at 251, 232, 218, 205 mAh / g, and increased to 1, 2, 5 A / g, and 189, 162, 102 mAh / g. Accordingly, the Li / MoS ₂ secondary battery according to the present invention includes an ether solvent as an electrolyte solvent, and the charge / discharge voltage range is limited to 1.0 to 3.0 V, thereby rapidly reducing the discharge capacity even when the current density increases by 1 A / g or more. It can be seen that it shows excellent rate property.

Preparation Example 5 Preparation of a Lithium Secondary Battery Comprising a MoS ₂ Electrode and an Ether-Based Electrolyte Solvent (DME / TGM = 1: 1)

A lithium ion secondary battery was manufactured in the same manner as in Preparation Example 3, except that a solution in which 1 M LiTFSI electrolyte salt was dissolved in a DME / TGM (v / v = 1: 1) solvent was used as an electrolyte.

The manufactured battery was charged and discharged in the voltage range of 1.0 ~ 3.0V, measured the life characteristics of the battery is shown in Figure 6, the rate characteristic is shown in Figure 7 measured.

As shown in FIG. 6, the Li / MoS ₂ secondary battery using a mixed solvent (v / v = 1: 1) of an ether solvent DME and TGM as an electrolyte solvent was charged and discharged in a voltage range of 1.0 to 3.0 V. The first discharge capacity was 232 mAh / g, and after 40 cycles, the capacity was 242 mAh / g, which showed the effect of improving the life characteristics than the DME solvent alone.

As shown in FIG. 7, Li / MoS ₂ secondary batteries using a mixed solvent of DME and TGM, which are ether solvents, as an electrolyte solvent, have a current density of 0.05 to 0.1 when charging and discharging in a voltage range of 1.0 to 3.0V. The discharge capacities were increased to 253, 246, 236, 226, 214 mAh / g with increasing 0.2, 0.5, 1 A / g and at current densities of 2, 5, 10, 20, and 50 A / g. The capacity of 194, 156, 128, 117, and 63 mAh / g shows excellent rate-rate characteristics because the discharge capacity does not drop rapidly even when the current density increases by 1 A / g or more, which is an improvement over TGM solvent alone. Indicated.

Preparation Example 6 Preparation of a Lithium Secondary Battery Comprising a MoS ₂ Electrode and an Ether Electrolyte Solvent (DME / TGM = 9: 1)

In the same manner as in Preparation Example 3, except that a solution of 1 M LiTFSI electrolyte salt dissolved in dimethyl ether (DME) / triethylene glycol monomethyl ether (TGM) (v / v = 9: 1) solvent was used as the electrolyte. A lithium secondary battery was prepared.

The prepared battery was charged and discharged in the voltage range of 1.0 ~ 3.0V, and measured in the life characteristics of the battery is shown in Figure 8, it is shown in Figure 9 by measuring the rate characteristic.

As shown in FIG. 8, a Li / MoS ₂ secondary battery using a mixed solvent (v / v = 9: 1) of dimethyl ether and triethylene glycol monomethyl ether, which are ether solvents, as an electrolyte solvent, has a voltage of 1.0 to 3.0 V. In the range of charging and discharging, the discharge capacity was 221 mAh / g in the first cycle and 185 mAh / g after 40 cycles, thereby improving the lifespan characteristics than the dimethyl ether (DME) solvent alone.

As shown in FIG. 9, the Li / MoS ₂ secondary battery using a mixed solvent (v / v = 9: 1) of dimethyl ether and triethylene glycol monomethyl ether, which are ether solvents, as the electrolyte solvent is 1.0 to 3.0 V. When charging and discharging in the voltage range of, the current density was increased from 0.05 to 0.1, 0.2, 0.5, 1 A / g, and the discharge capacity was measured at 236, 226, 221, 219, 214 mAh / g, 2, Capacities of 196, 170, 120, 100, and 40 mAh / g at current densities of 5, 10, 20, and 50 A / g ensure that the discharge capacity does not drop rapidly even when the current density increases by 1 A / g or more. Therefore, it exhibited excellent rate-of-velocity properties, which showed an improved value over triethylene glycol monomethyl ether (TGM) solvent alone.

Preparation Example 7 Preparation of a Lithium Secondary Battery Comprising a MoS ₂ Electrode and an Ether Electrolyte Solvent (DME / TGM = 3: 1)

In the same manner as in Preparation Example 3, except that 1M LiTFSI electrolyte salt was dissolved in dimethyl ether (DME) / triethylene glycol monomethyl ether (TGM) (v / v = 3: 1) solvent. A lithium secondary battery was prepared.

The manufactured battery was charged and discharged in the voltage range of 1.0 ~ 3.0V.

<Analysis>

(1) battery life characteristics

The lifetime characteristics of the Li / MoS ₂ secondary battery charged and discharged at a voltage range of 1.0 to 3.0 V and a current density of 100 mA / g are measured and shown in FIG. 10.

As shown in FIG. 10, the first discharge capacity of a Li / MoS ₂ secondary battery using a mixed solvent (v / v = 3: 1) of an ether solvent DME and TGM as an electrolyte solvent according to the present invention is 228 mAh / g. It can be seen that excellent cycle characteristics are shown by maintaining a capacity of 218 mAh / g after 40 cycles.

Subsequently, the Li / MoS ₂ secondary battery was shown in FIG. 11 by measuring the discharge capacity while performing 2000 cycles under the condition of a current density of 1 A / g.

As shown in FIG. 11, a Li / MoS ₂ secondary battery using a mixed solvent (v / v = 3: 1) of an ether solvent, DME and TGM, as an electrolyte solvent according to the present invention has a voltage range of 1.0 to 3.0 V. During charging and discharging, it showed a capacity of 193.1 mAh / g even after 2000 cycles under a current density of 1 A / g, which shows an excellent lifespan characteristic by showing a retention rate of 103.7% compared to the capacity of the second cycle.

(2) rate characteristics

The rate characteristics of the Li / MoS ₂ secondary battery charged and discharged in the voltage range of 1.0 to 3.0V were measured and shown in FIG. 12.

As shown in FIG. 12, the Li / MoS ₂ secondary battery according to the present invention discharges as the current density increases from 0.05 to 0.1, 0.2, 0.5, 1 A / g during charge and discharge in a voltage range of 1.0 to 3.0 V. The capacity ranged from 243 to 233, 223, 218, 213 mAh / g, and the discharge capacity increased to 206, 187, 165, 134, 77 as the current density increased to 2, 5, 10, 20, 50 A / g. mAh / g. Therefore, the Li / MoS ₂ secondary battery according to the present invention exhibits excellent rate-rate characteristics because the discharge capacity does not drop rapidly even when the current density increases by more than 1 A / g by limiting the charge / discharge voltage range to 1.0 to 3.0 V. have.

(3) FT-IR analysis of MoS ₂ electrode

For a MoS ₂ electrode of a Li / MoS ₂ secondary battery charged and discharged in a voltage range of 1.0 to 3.0 V, a lithium salt electrolyte dissolved in a DME / TGM solvent, a MoS ₂ electrode discharged to 1.0 V in the electrolyte, and 3.0 FT-IR analysis of the MoS2 electrode charged to V was performed and the results are shown in FIG. 13.

As shown in Figure 13, DME / a peak of CO bonding appears in TGM solvent, MoS ₂ and the electrode discharge to 1.0V, MoS discharge to be viewed, appear to 1.0V MoS ₂ electrode was charged up to 3.0V ₂ It was confirmed that the insertion of the DME / TGM solvent occurred in both the electrode and the MoS ₂ electrode charged up to 3.0V.

(4) High magnification transmission electron microscope (HRTEM) of MoS ₂ electrode

In order to confirm that the electrolyte solvent is inserted into the MoS ₂ electrode during charging and discharging, the state of the MoS ₂ electrode of the Li / MoS ₂ secondary battery charged / discharged at a voltage range of 1.0 to 3.0 V is determined by a high magnification transmission electron microscope for each cycle. Observations were made, and the interlayer spacing of the MoS ₂ electrodes was measured and the results are shown in FIG. 14.

As shown in FIG. 14, in the case of MoS ₂ charged and discharged in a lithium salt electrolyte dissolved in a DME / TGM (v / v = 3: 1) solvent, the interlayer spacing gradually increased. Specifically, the interlayer spacing measured after 100 cycles increased to 1 nm or more. From this, it was confirmed that the DME / TGM (v / v = 3: 1) solvent was inserted together with the lithium salt inserted between the MoS ₂ layers, and the change in the interlayer spacing reduced the number of layers of the entire MoS ₂ so that Induce to increase.

(5) Cyclic Voltammetry (CV)

Cyclic voltammetry was performed on the MoS ₂ electrode of the Li / MoS ₂ secondary battery charged and discharged in the voltage range of 1.0 to 3.0 V, and the results are shown in FIG. 15.

In FIG. 15, (a) is a CV curve for various scanning speeds of the MoS ₂ electrode, and (b) is a graph showing log i (current) vs. log V (voltage). In addition, (c) is a bar graph showing the ratio of pseudocapacitive behavior, and (d) is a CV graph showing pseudocapacitive behavior.

As shown in FIG. 15 (a), in the case of MoS ₂ charged and discharged in a lithium salt electrolyte dissolved in a DME / TGM (v / v = 3: 1) solvent, the result of CV evaluation showed that one reduction peak and two oxidations were performed. Peaks were observed.

The relationship between the current i and the scanning speed v is shown in Equations 1 and 2 below.

[Equation 1]

i = a v ^b

[Equation 2]

log ( i ) = b × long ( v ) + a

In the above equations, a and b are adjustable variables. If b is 1, the electrochemical reaction follows pseudocapacitive behavior, and if b is 0.5, the electrochemical reaction results in ionic diffusion. Follow.

FIG. 15 (b) shows a log ( i ) vs. log ( v ) curve for each peak obtained from the CV graph of FIG. 15 (a), wherein the values of peaks 1, 2, and 3 are 0.79 and 0.84, respectively. And 0.84.

According to this, in the case of MoS ₂ charged and discharged in a lithium salt electrolyte dissolved in a DME / TGM (v / v = 3: 1) solvent, the reaction is performed by mixing the similar capacitive behavior and the co-insertion reaction behavior. Therefore, the high capacity of the battery and the high rate characteristics of the capacitor are both seen.

Specific pseudocapacitive behavior was calculated by the following equations (3) and (4).

[Equation 3]

i = k ₁ v + k ₂ v ^0.5

[Equation 4]

In Equation (3) from k ₁ and k ₂ v v ^{0 .5} is the expression (4) represents the contribution of similar capacity and ion diffusion in each of the electrochemical reaction, k ₁ represents the gradient of v ^0.5.

As shown in FIG. 15 (c), the pseudocapacitive contributions at 0.1, 0.2, 0.3, 0.5, 0.8, 1, 1.5, and 2 mV / s through the above equations are 47.6%, 48.2%, and 51.7%, respectively. , 55.3%, 59.3%, 63.3%, 68.7%, and 75.2%.

15 (d) shows the CV curve and pseudocapacitive ratio.

High rate-rate characteristics during charging and discharging at a voltage range of 1.0 to 3.0 V of a Li / MoS ₂ secondary battery using a mixed solvent (v / v = 3: 1) of an ether solvent DME and TGM as an electrolyte solvent according to the present invention. The overlife characteristics can be summarized based on the following factors.

First, MoS ₂ shows the ion storage mechanism by co-intercalation reaction under the electrolyte condition of 1.0 ~ 3.0V. This reaction mechanism inhibits the formation of LiS, and in particular, it is possible to prevent the formation of S due to repetitive charging and discharging, thereby preventing the deterioration of the rate characteristic and the degradation of the material. In addition, the co-insertion reaction controls the formation of the SEI layer, thus contributing to increasing the rate property.

Secondly, since the reaction mechanism of the secondary battery exhibits both quasi-capacitive behavior, which is a characteristic of a capacitor, and ion diffusion behavior, which is a characteristic of a battery, it may exhibit high rate-rate characteristics and lifetime characteristics.

Comparative Example 1 A lithium secondary battery including a MoS ₂ electrode by a conventional method

A lithium ion secondary battery including a MoS2 electrode was manufactured by the method of Example 1 of Korean Patent Laid-Open Publication No. 10-2009-0092070.

Specifically, MoS ₂ powder was ball milled with a zirconia ball for 3 hours to reduce powder particle size. The weight ratio of the ball and the powder was set to 20: 1. N-methylpyrrolidone (NMP), which is a dispersion solvent, is added to a mixture of MoS ₂ powder, which is the active material, acetylene carbon black, and binder PVdF-co-HFP, in a 60:20:20 weight ratio. Then, ball milling with a zirconia ball (zirconia ball) for 3 hours to prepare a uniform slurry. A predetermined amount of the prepared slurry was cast on a glass plate to remove the solvent at room temperature, dried at 60 ° C. for 24 hours to prepare a MoS ₂ electrode, and then stored in an argon atmosphere glove box.

The MoS ₂ positive electrode prepared above and 1M LiCF ₃ SO ₃ lithium salt were used as a liquid electrolyte dissolved in a tetraglycol dimethyl ether (TEGDME) electrolyte solution, and a model number 2400 of celgard was used as a polarizing plate. A lithium molybdenum sulfide (Li / MoS ₂ ) battery was prepared by laminating in a glove box using lithium foil as a negative electrode.

The prepared Li / MoS ₂ batteries were charged / discharged at room temperature after 2 hours of rest at room temperature. The current density during charging / discharging was 50 mA / g-MoS ₂ , the charging end voltage was 3.0V, and the discharge end voltage was 0.7V. The pause between charge and discharge gave 10 minutes.

Experimental Example 1 Effect of Charge and Discharge Voltage Range on Electrochemical Characteristics in Lithium Secondary Battery with MoS ₂ Electrode

In order to determine the effect of the charge and discharge voltage range on the electrochemical characteristics in the lithium ion secondary battery including the MoS ₂ electrode according to the present invention, having a lithium ion secondary battery prepared in Preparation Example 5, the voltage range is 1.0 ~ 3.0 Cyclic characteristics in the case of adjusting to V and adjusting to 0.1 to 3.0 V were measured and shown in FIGS. 6 and 16, respectively.

In addition, the cycle characteristics when the voltage range is adjusted to 0.7 to 3 V with the lithium ion secondary battery prepared in Comparative Example 1 is shown in FIG. 17.

As shown in FIG. 6, when the charge / discharge voltage range of the secondary battery of the present invention was adjusted to 1.0 to 3.0 V, the battery was maintained at a constant capacity of about 200 mAh / g even after 40 cycles, as shown in FIG. 16. In the case of the expansion to -3.0V, the discharge capacity was 1148 mAh / g in the first cycle, but after 30 cycles, the capacity began to decrease rapidly, and after 50 cycles, the capacity value was 93 mAh / g. . This can be understood as a result of the material deterioration due to the conversion reaction of Li-S.

In addition, in the lithium ion secondary battery prepared in Comparative Example 1, as shown in Figure 17, when the voltage range is adjusted to 0.7 ~ 3.0V, the capacity of the first cycle is high, but the capacity is reduced by almost half from subsequent cycles After 10 cycles, the capacity value was less than 100 mAh / g. This is also the result of the irreversible capacity that occurs when the conversion reaction occurs.

As such, it can be seen that the lithium ion secondary battery including the MoS ₂ electrode is sensitively affected by the charge / discharge voltage range, and the voltage condition is preferably adjusted to 1.0V to 3.0V so that the conversion reaction does not occur. Able to know.

Comparative Example 2 Fabrication of Lithium Secondary Battery Comprising MoS ₂ Electrode and Carbonate Electrolyte Solvent (EC / DEC)

A lithium ion secondary battery was manufactured in the same manner as in Preparation Example 3, except that a solution in which 1 M LiTFSI electrolyte salt was dissolved in an ethyl carbonate (EC) / diethyl carbonate (DEC) solvent was used as an electrolyte.

The manufactured battery was charged and discharged in the voltage range of 1.0 ~ 3.0V.

The manufactured battery was charged and discharged in the voltage range of 1.0 ~ 3.0V, measured the life characteristics of the battery is shown in Figure 18, and the rate characteristic is shown in Figure 19.

As shown in FIG. 18, a Li / MoS ₂ secondary battery using a mixed solvent (v / v = 1: 1) of carbonate-based solvent, ethyl carbonate and diethyl carbonate, as an electrolyte solvent is charged in a voltage range of 1.0 to 3.0 V. At the time of discharge, the discharge capacity was 177 mAh / g in the first cycle and 162 mAh / g after 40 cycles, thereby showing lower life characteristics than when using an ether solvent.

As shown in FIG. 19, the Li / MoS ₂ secondary battery using a mixed solvent (v / v = 1: 1) of ethyl carbonate and diethyl carbonate, which are carbonate solvents, as an electrolyte solvent is 1.0 to 3.0 V. When charging and discharging in the voltage range of, the current density was increased from 0.05 to 0.1, 0.2, 0.5 A / g, and the discharge capacity was measured at 181, 158, 140, 113 mAh / g, and 1, 2, 5, At current densities of 10, 20, and 50 A / g, the capacities of 89, 66, 35, 28, 17, and 5 mAh / g were significantly lower than when using ether solvents.

Experimental Example 2 Effect of Electrolyte Solvent on MoS ₂ Interlayer Insertion in Lithium Secondary Battery with MoS ₂ Electrode

In order to examine the effect of the electrolyte solvent on the MoS ₂ interlayer insertion in the lithium secondary battery including the MoS ₂ electrode according to the present invention, the secondary batteries prepared in Preparation Examples 4 and 5 and the secondary batteries prepared in Comparative Example 2 The interlayer spacing of MoS ₂ for each cycle during charging and discharging at 1.0 to 3.0 V was measured and shown in Table 1 below.

cycle	Interlayer spacing of MoS 2 (nm)
	Preparation Example 4 (TGM)	Preparation Example 5 (DME / TGM)	Comparative Example 2 (EC / DEC)
After 1 cycle	0.82	0.64	0.64
After 10 cycles	0.85	0.66	0.65
After 50 cycles	> 1.0	0.69	0.68
After 100 cycles	> 1.0	0.96	0.71
After 200 cycles		> 1.0

As shown in Table 1, as an electrolyte solvent when using a carbonate-based solvent of Comparative Example 2, since the size is smaller Li ion only and inserted in the interlayer of MoS _2, but the difference in inter-layer spacing of MoS ₂ of the cycle larger, the present invention In the case of using the ether solvents of Preparation Example 4 and Preparation Example 5 according to the charging and discharging cycle was progressed, the interlayer spacing of MoS ₂ was increased to finally open more than 1.0 nm interlayer spacing. From this, it can be seen that in the case of an ether solvent, Li ions form an ether-based solvated complex to be intercalated with MoS ₂ , and the co-intercalation improves the electrochemical characteristics of the battery. Can be.

Therefore, the secondary battery system according to the present invention uses an ether solvent that can be co-inserted between the layers of MoS ₂ as the electrolyte solvent and by controlling the charging and discharging voltage conditions to 1.0 ~ 3.0V, such as the rate characteristics, life characteristics, etc. of the battery It is possible to improve the electrochemical properties of.

While the present invention has been described with reference to preferred embodiments, it is to be understood that the present invention is not limited to the above embodiments. The present invention can be variously modified and modified within the scope of the following claims, which are all within the scope of the invention. Accordingly, the invention is limited only by the claims and the equivalents thereof.

Claims (14)

1. A lithium ion secondary battery comprising a MoS ₂ electrode, a counter electrode material, a separator positioned between the MoS ₂ electrode and the counter electrode material, and an electrolyte,

   A secondary battery system including a charge and discharge control unit for controlling the charge and discharge of the lithium ion secondary battery by the voltage,

   The electrolyte is a solution in which a lithium salt is dissolved in an ether solvent,

   The charge and discharge controller is a secondary battery system, characterized in that for controlling the charge and discharge voltage to 1.0 ~ 3.0V.
2. The method of claim 1,

   When the charge and discharge voltage is controlled to 1.0 ~ 3.0V in the secondary battery system, the lithium ion in the electrolyte is complexed with the ether solvent, the secondary battery characterized in that the co-intercalation into the MoS ₂ electrode system.
3. The method of claim 1,

   The ether solvent is at least one selected from the group consisting of dimethyl ether (DME), diethylene glycol monomethyl ether (DGM) and triethylene glycol monomethyl ether (TGM), or a mixed solvent thereof. Secondary Battery System.
4. The method of claim 3,

   The ether solvent is a secondary battery system, characterized in that the mixed solvent of dimethyl ether (DME) and triethylene glycol monomethyl ether (TGM).
5. The method of claim 4, wherein

   The mixing ratio of the mixed solvent of the dimethyl ether (DME) and triethylene glycol monomethyl ether (TGM) is 1: 9 ~ 9: 1 by volume ratio.
6. The method of claim 1,

   The lithium salt is at least one selected from the group consisting of LiPF ₆ , LiClO ₄ , LiTFSI and LiCF ₃ SO ₃ , or a mixture thereof.
7. The method of claim 1,

   The concentration of the lithium salt is a secondary battery system, characterized in that 0.6 ~ 3 mol / L.
8. The method of claim 1,

   The MoS ₂ electrode is a secondary battery system comprising a MoS ₂ active material, a conductive material and a binder.
9. The method of claim 8,

   The conductive material is at least one carbon material selected from the group consisting of carbon nanofibers, carbon nanotubes, conductive graphite, acetylene black, Super P, KS6, and Vulcan XC-72, or a mixture thereof. system.
10. The method of claim 8,

    The binder is a secondary battery system, characterized in that the carboxymethyl cellulose sodium salt (NaCMC) or poly (vinylidene fluoride) (PVDF).
11. The method of claim 8,

    The MoS ₂ electrode is a secondary battery system, characterized in that 5 to 15% by weight of the conductive material, 5 to 10% by weight of the binder and the rest of the MoS ₂ active material.
12. The method of claim 10,

    The binder is dissolved in a solvent, the solvent is distilled water in the case of NaCMC, N-methyl pyrrolidone (NMP) in the case of PVdF, characterized in that the secondary battery system.
13. The method of claim 1,

    The counter electrode material is a secondary battery system, characterized in that selected from the group consisting of a metal of Li, Na, or a mixture thereof.
14. The method of claim 1,

    The separator is a secondary battery system, characterized in that at least one microporous membrane selected from glass fiber, polyethylene (PE) and polypropylene (PP).

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