WO2019221584A9

WO2019221584A9 - Layered ge, manufacturing method therefor, ge nanosheet peeled therefrom, and electrode comprising same for lithium ion battery

Info

Publication number: WO2019221584A9
Application number: PCT/KR2019/008903
Authority: WO
Inventors: 심우영; 김혜수; 이수운; 김민정
Original assignee: 연세대학교 산학협력단
Priority date: 2018-05-18
Filing date: 2019-07-18
Publication date: 2020-02-27
Also published as: WO2019221584A3; KR102080829B1; KR20190132150A; WO2019221584A2

Abstract

The present invention relates to layered Ge, a manufacturing method therefor, and a Ge nanosheet released therefrom and, more specifically, to layered Ge, which has a two-dimensional crystalline structure unlike conventional bulky Ge, is easy to release in the form of a nanosheet due to excellent releasability thereof, and has a large surface area and excellent ion capacity, to a manufacturing method therefor, to a GE nanosheet released therefrom, and to an electrode comprising same for a lithium ion battery.

Description

Layered GE, a method of manufacturing the same, GE nanosheets peeled from the same, and an electrode for a lithium ion battery comprising the same

The present invention relates to a layered Ge, a method for preparing the same, and a Ge nanosheet peeled from the same. More specifically, the present invention relates to a layered Ge, and, more particularly, has a two-dimensional crystal structure unlike a conventional bulk Ge, and has excellent peelability. The present invention relates to a layered Ge having a wide surface area and excellent ion capacity, a method for preparing the same, a Ge nanosheet peeled from the same, and an electrode for a lithium ion battery including the same.

Graphene and other ultra-thin two-dimensional (2D) materials are being actively studied in various fields based on new physical, chemical, mechanical and optical properties. This low-dimensional material is expected to be a breakthrough new function that the existing bulk material does not have and is very likely as a next-generation future material to replace the existing material.

Research on existing 2D materials is based on top-down method for separating van der Waals bonds with weak interlayer bondability by physical and chemical methods, and bottom-up method for growing large-area thin films based on vapor deposition. It is becoming. In particular, in the top-down method, since the pristine of the material to be exfoliated must have a two-dimensional layered crystal structure, graphene without band gap, layered metal oxide / nitride with low charge mobility, electron mobility / Research subjects such as transition metal chalcogenides with low electrical conductivity have very limited problems.

Due to the limitations of the previous research methods, 2D materials have been very limitedly studied for materials such as graphene and transition metal chalcogenides. It is limited in that it is not suitable for the development of low-dimensional future materials of a myriad of 3D bulk materials that are not layered.

On the other hand, lithium ion batteries have high energy density and are widely used as a power supply device for complex applications such as portable electronic devices and electric vehicles.In order to improve the performance of lithium ion batteries, lithium ions must be easily moved and charged. As the discharge is repeated, structural stability of the electrode should be ensured.

When Ge is used as an electrode material, it has the advantage of having a high theoretical capacity of 1,384 mAh / g, but has a problem of rapidly decreasing ion storage capacity due to a volume change of 300 to 400% during the insertion and desorption of lithium ions. . Accordingly, when the Ge material is manufactured in a low dimensional structure, structural stability may be improved to minimize the reduction of the ion storage capacity.

The present invention has been made in view of the above, and unlike the conventional 3D bulk Ge, it has a two-dimensional crystal structure, has excellent peelability and is easy to peel in the form of a nanosheet, and has a large surface area and excellent ion capacity. It is an object to provide a layered Ge having, a method for producing the same, and a Ge nanosheet peeled therefrom.

Another object of the present invention is to provide an electrode for a lithium ion battery having excellent ion storage capacity and minimizing capacity loss, including the layered Ge or Ge nanosheets according to the present invention.

In order to solve the above problems, the present invention (1) a trigonal crystal having a space group of Rm-3m by cooling a mixture containing Ca powder and Ge powder and cooling at a predetermined temperature reduction rate. Preparing a layered compound represented by the formula CaGe ₂ having a structure, and (2) a mixture comprising a salt capable of selectively removing Ca ions contained in the layered compound and a solvent capable of dissolving the salt. It provides a method for producing a layered Ge comprising treating the layered compound with a solution to prepare a layered Ge having a trigonal crystal structure of amorphous, space group (Rm-3m). .

According to one embodiment of the present invention, the salt is a method of producing a layered Ge represented by the following formula (1):

MX _a (1≤a≤3)

In Formula 1, M is any one selected from Sn, Al, and Ga, and X is any one selected from Cl, F, and I.

In addition, according to an embodiment of the present invention, the solvent may be at least one selected from ethanol, water, acetone and isopropanol.

In addition, according to an embodiment of the present invention, the heat treatment may be performed for 5 to 10 days at 730 ~ 830 ℃ or 2 to 24 hours at 830 ~ 1000 ℃.

In addition, according to one embodiment of the present invention, the cooling may be performed at a temperature reduction rate of 3 ~ 20 ℃ / hour.

In addition, according to an embodiment of the present invention, the step (2) is carried out at -40 ~ 0 ℃ to produce a layered Ge having a trigonal crystal structure with a space group (Rm-3m). Can be.

In addition, according to an embodiment of the present invention, step (2) may be carried out at 15 ~ 60 ℃ to produce a layered Ge having an amorphous crystal structure.

The present invention also provides a layered Ge having a trigonal crystal structure having an amorphous or space group of Rm-3m.

According to one embodiment of the present invention, the layered Ge having a trigonal crystal structure having the space group of Rm-3m has an X-ray diffraction diagram obtained by a powder X-ray diffraction method using Cu-Kα rays. With peaks at 2θ values of 15.5 ± 0.2, 26.4 ± 0.2, 35.6 ± 0.2, 45.7 ± 0.2, 48.5 ± 0.2 and 53.6 ± 0.2, of 27.4 ± 0.2, 45.6 ± 0.2, 54.0 ± 0.2 and 66.4 ± 0.2 It may not have a peak at 2θ.

The present invention also provides a Ge nanosheet exfoliated from the layered Ge according to the present invention and having an amorphous or triangular symmetric crystal structure.

According to an embodiment of the present invention, the thickness of the Ge nanosheets may be 100 nm or less.

In addition, the present invention (1) the layered CaGe ₂ and space group having a trigonal crystal structure having a trigonal crystal structure of the space group (Rm-3m) after quenching the mixture containing the Ca powder and Ge powder Preparing a compound comprising Ge having a cubic crystal structure of Fd-3m, and (2) a salt capable of selectively removing Ca ions contained in the layered CaGe ₂ and dissolving the salt. Treating the layered compound with a mixed solution containing a solvent which can be used to form a Ge nanosheet having a trigonal crystal structure of amorphous or space group (Rm-3m), and the space group is Fd-3m It provides a method for producing a Ge nanosheet comprising the step of producing a Ge nanosheet having a monoclinic (cubic) crystal structure.

According to one embodiment of the present invention, the heat treatment may be performed for 2 to 24 hours at 830 ~ 1,000 ℃.

In addition, according to an embodiment of the present invention, the quenching of step (1) may be performed at 10 ~ 40 ℃.

The present invention also provides a layered Ge having a trigonal crystal structure having an amorphous or space group of Rm-3m, a Ge nanosheet having an amorphous or triangular symmetric crystal structure, and an amorphous or triangular symmetric crystal structure. Provided is an electrode for a lithium ion battery including at least one selected from a Ge nanosheet having a Ge nanosheet including a Ge nanosheet having a monoclinic (cubic) crystal structure having a space group of Fd-3m.

Unlike the conventional bulk Ge, the layered Ge according to the present invention has a two-dimensional crystal structure, has excellent peelability and is easily peeled off in the form of a nanosheet, and has a large surface area and excellent ion capacity. It is included to implement a lithium ion battery with excellent ion storage capacity and minimized capacity loss.

1 is a schematic view of a layered Ge manufacturing method according to an embodiment of the present invention.

Figure 2 is a photograph of the samples prepared in Ge, Preparation Example 1, Example 1 of Comparative Example 1.

3 is a graph showing the XRD analysis results of the samples prepared in Ge of Preparation Example 1, Preparation Example 1, Example 1 and Example 2.

Figure 4 is a graph showing the Raman spectrum analysis results for the samples prepared in 3D Ge, Preparation Example 1 and Example 1 of Comparative Example 1.

5A is an SEM image of a conventional 3D bulk Ge.

5B is an SEM image of the layered CaGe ₂ according to an embodiment of the present invention.

5C is an SEM image of a layered Ge in accordance with one embodiment of the present invention.

5D is an SEM image of the sample prepared in Example 1. FIG.

6A is a TEM image of a sample prepared in Example 1. FIG.

6B is a TEM image of a sample prepared in 3D Ge, Preparation Example 1, and Example 1 of Comparative Example 1. FIG.

6C is a TEM image of layered Ge according to Example 1 and Example 2. FIG.

6D is a TEM image of a Ge nanosheet according to Example 4. FIG.

[Revision 23.09.2019 under Rule 91]
7A is an EDS image of layered CaGe ₂ according to Preparation Example 2. FIG.

[Revision 23.09.2019 under Rule 91]
7B is an EDS image for the layered Ge according to Example 1. FIG.

[Revision 23.09.2019 under Rule 91]
8 is a graph showing the AFM image and analysis results of the Ge nanosheets according to an embodiment of the present invention.

[Revision 23.09.2019 under Rule 91]
9A is a graph showing charge and discharge curves of the lithium ion battery of Preparation Example 1. FIG.

[Revision 23.09.2019 under Rule 91]
9B is a graph showing discharge capacity according to cycles of the lithium ion battery prepared in Preparation Example 1 and Comparative Preparation Example 1. FIG.

[Revision 23.09.2019 under Rule 91]
FIG. 9C is a graph showing capacity characteristics according to discharge rates of the lithium ion batteries prepared in Preparation Example 1 and Comparative Preparation Example 1. FIG.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

The method of manufacturing a layered Ge according to the present invention can produce a bulk Ge of a conventional 3D structure in a two-dimensional structure, and unlike the existing bulk Ge, it is easy to peel, manufacturing a layered Ge having a wide surface area and excellent ion capacity. can do.

First, as step (1), the mixture including Ca powder and Ge powder is heat-treated and then cooled to have a trigonal crystal structure having a space group of Rm-3m and a layer type represented by the formula CaGe ₂ . Obtain the compound.

The mixture may be heat treated after being encapsulated in a reaction vessel, and the inside of the reaction vessel may be maintained in an inert gas atmosphere or a vacuum atmosphere.

In addition, the material of the reaction vessel may be, for example, alumina, molybdenum, tungsten or quartz, but any material that does not react with the sample and does not break at a high temperature may be used without limitation.

As shown in FIG. 1, CaGe ₂ prepared through step (1) has a 2D crystal structure different from Ge of a 3D crystal structure, and in step (2) described later, a layer is formed by selectively removing Ca ions of CaGe ₂ . Pictographic Ge can be prepared.

According to one embodiment of the invention, the heat treatment may be performed for 6 to 24 hours at 830 ~ 1,000 ℃ or for 5 to 10 days at 730 ~ 830 ℃.

When the heat treatment temperature is 830 ~ 1,000 ° C, CaGe ₂ may have a layered structure. When the heat treatment temperature is 730 ~ 830 ° C, the layered CaGe ₂ may be formed of polycrystal. When the layered CaGe ₂ is a single crystal, the layered CaGe ₂ may have better charge mobility than the polycrystal.

If the heat treatment is performed at less than 730 ° C., the sintering reaction of the mixture may not be completed, and thus unreacted raw materials may remain, resulting in lowered yield of the layered compound prepared. have. In addition, when the heat treatment is carried out in excess of 1,000 ℃, there may be a problem such as the reaction vessel used in the sintering reaction by the vaporization of Ca ions, or the yield of the layered compound produced is lowered.

In addition, when the heat treatment temperature is 830 ~ 1,000 ℃, when the heat treatment is carried out in less than 2 hours, the sintering reaction of the mixture is not completed, the unreacted raw material may remain, the layered compound prepared accordingly There may be a problem such as a decrease in yield. In addition, when the heat treatment is performed for more than 24 hours, there is a fear that the manufacturing process time unnecessarily increases.

In addition, when the heat treatment temperature is 730 ~ 830 ℃, if the heat treatment is performed less than 5 days, the sintering reaction of the mixture is not completed, the unreacted raw material may remain, the yield of the layered compound prepared accordingly There may be a problem such as deterioration. In addition, when the heat treatment is performed for more than 10 days, there is a fear that the manufacturing process time unnecessarily increases.

After the heat treatment in step (1), the cooling process may vary depending on the temperature of the heat treatment. When the heat treatment is performed at 730 ~ 830 ℃ the cooling may be natural cooling.

When the heat treatment is performed at 830 ~ 1,000 ℃, the cooling may be carried out at a temperature reduction rate of 3 ~ 20 ℃ / hour, through which the heat-treated layered compound can be single crystallized. Cooling at the temperature reduction rate may increase the size of the single crystal of the layered compound prepared. As the size of the single crystal of the layered compound increases, grain boundaries of the particles may decrease, thereby increasing charge mobility, and the aspect ratio of the nanosheet peeled off when the layered compound is peeled off may increase.

If the temperature reduction rate is less than 3 ℃ / hour, a change in the composition of the material produced due to the vaporization of Ca ions may occur, and when the temperature reduction rate exceeds 20 ℃ / hour, the layered compound prepared is polycrystalline Can be.

Next, as step (2), the layered compound prepared in step (1) is mixed with a salt capable of selectively removing Ca ions contained in the layered compound and a solvent capable of dissolving the salt. Treated with solution to produce layered Ge.

The salt may include an anion having a high electronegativity and a cation having an electronegativity value between the alkaline earth metal ion and the Ge ion in order to easily react with the alkaline earth metal ion (Ca ion) included in the layered compound. have

According to an embodiment of the present invention, the salt may be represented by the following Chemical Formula 1, wherein the salt is a cation having an electronegativity value between the alkaline earth metal ions and Ge ions, and M and Cl ions having high electronegativity. It consists of.

MX _a (1≤a≤3)

In Formula 1, M may be any one selected from Sn, Al, and Ga, and X may be any one selected from Cl, F, and I.

In addition, the solvent may include at least one selected from ethanol, water, acetone and isopropanol, and the composition of the solvent may vary depending on the temperature at which step (2) is performed.

The salt may be used in an amount sufficient to remove alkaline earth metal ions of the layered compound, but preferably, the layered compound and the salt in the mixed solution may be included in a molar ratio of 1: 1 to 1: 3. If the molar ratio of the layered compound and salt is less than 1: 1, alkaline earth metal ions of the layered compound may not be removed to the desired level, and if the molar ratio exceeds 1: 3, the salt There may be a problem such as a precipitate is not dissolved in the mixed solution.

In addition, the crystal structure of the layered Ge may be changed depending on the temperature at which step (2) is performed. When the step (2) is performed at -40 to 0 ° C., the layered Ge may have a trigonal crystal structure having a space group of Rm-3m, and the step (2) may be 15 to 60 ° C. The layered Ge prepared when carried out at ° C. may have an amorphous crystal structure.

In the preparation of layered Ge having a trigonal crystal structure, if step (2) is performed at less than -40 ° C, the crystallinity of the layered Ge to be produced is increased, but the reaction time for removing alkaline earth metal ions is excessive. It may increase, and if the crystallinity of the layered Ge produced is not expressed to the desired level when it exceeds 0 ° C., or the layered Ge produced may have an amorphous crystal structure.

In preparing a layered Ge having an amorphous crystal structure, if step (2) is performed at less than 15 ° C., the crystallinity of the layered Ge to be produced may be increased and the reaction time for removing alkaline earth metal ions may be increased. When the reaction time exceeds 60 ° C, the reaction time for removing the alkaline earth metal ions may decrease, but the layered structure of the layered Ge may be disrupted.

In addition, the step (2) may be performed a plurality of times depending on the composition of the mixed solution and the removal rate of Ca ions, but is preferably performed once to maintain the layered structure of the layered Ge.

In addition, after performing step (2), there may be a reactant formed by reacting alkaline earth metal ions with a salt in addition to the layered Ge. To remove this, the powder obtained through step (2) may be washed with a solvent. Can be.

The solvent for removing the reactant may be at least one selected from water, deionized water, methanol and ethanol.

Next, the layered Ge of this invention is demonstrated.

The layered Ge according to the present invention has a trigonal crystal structure having an amorphous or space group of Rm-3m, which is different from the existing 3D bulk Ge, and has excellent peelability and has a form of nanosheets. It is easy to peel off, and has a large surface area and excellent ion capacity.

According to an embodiment of the present invention, in the X-ray diffractogram obtained by powder X-ray diffraction using Cu-Kα rays, the space group has a trigonal crystal structure of Rm-3m. Phase Ge is 2θ of 15.5 ± 0.2, 26.4 ± 0.2, 35.6 ± 0.2, 45.7 ± 0.2, 48.5 ± 0.2 and 53.6 ± 0.2 in the X-ray diffractogram obtained by powder X-ray diffraction using Cu-Kα rays. It may have a peak at the value and may not have a peak at 2θ values of 27.4 ± 0.2, 45.6 ± 0.2, 54.0 ± 0.2 and 66.4 ± 0.2.

Next, the Ge nanosheet of this invention is demonstrated.

The Ge nanosheets according to the present invention can be obtained by peeling from the layered Ge according to the present invention and have an amorphous or triangular symmetric crystal structure.

According to an embodiment of the present invention, the Ge nanosheets may have a thickness of 100 nm or less, and if the thickness exceeds 100 nm, the surface area of the Ge nanosheets may be lowered to decrease ion storage capacity or the Ge nanosheets. May be difficult to stack.

As the method of peeling the layered Ge, a method of peeling a layered material known in the art may be used, and for example, a method of peeling with energy by ultrasonic waves, a peeling method by invasion of a solvent, a peeling method using a tape, and adhesion Any of the methods of stripping using a substance having a surface may be used.

Next, the Ge nanosheet manufacturing method of this invention is demonstrated.

First, in step (1), the mixture comprising Ca powder and Ge powder is heat-treated and then quenched so that the layered CaGe ₂ and space group having a trigonal crystal structure having a space group of Rm-3m are formed. A compound containing Ge having a cubic crystal structure of Fd-3m is prepared.

The heat treatment may be performed for 6 to 24 hours at 830 ~ 1,000 ℃, quenching the heat-treated mixture to form a layered CaGe ₂ and trigonal (trigonal) crystal structure of the space group (space group) Rm-3m A compound having a lamella structure including Ge having a cubic crystal structure in which the group is Fd-3m can be prepared. Such a lamellar structure is formed only when the molten mixture is quenched, and Ge nanosheets may be prepared from the lamellar structure in step (2) described later.

The quench may be performed at 10 ~ 40 ℃.

As shown in FIG. X, the lamellar structure may be formed by alternately stacking a first layer including the layered CaGe ₂ and a second layer including the Ge, and the layered type in step (2) described later. When the Ca ions contained in CaGe ₂ are removed, the first layer is formed of Ge nanosheets having an amorphous or triangular symmetric crystal structure, and the second layer has a cubic crystal structure having a space group of Fd-3m. It can be formed of a Ge nanosheet having.

Next, step (2) is performed by treating the layered compound with a mixed solution containing a salt capable of selectively removing Ca ions contained in the layered CaGe ₂ and a solvent capable of dissolving the salt. Ge nanosheets having a trigonal crystal structure having a space group of Rm-3m and Ge nanosheets having a cubic crystal structure having a space group of Fd-3m are prepared.

The composition of the mixed solution for removing Ca ions, the temperature condition of step (2) and the crystal structure of the Ge nanosheets prepared from the layered CaGe ₂ are the same as described above in the manufacturing method of the layered Ge. Detailed description thereof will be omitted.

In the process of removing Ca ions contained in the layered CaGe ₂ , the Ge nanosheets having a trigonal crystal structure and the Ge nanosheets having a monoclinic crystal structure may be peeled off without a separate peeling process.

Ge nanosheets prepared by the method of manufacturing Ge nanosheets of the present invention include Ge nanosheets having an amorphous or triangular symmetric crystal structure and Ge nanosheets having a cubic crystal structure having a space group of Fd-3m. .

Meanwhile, since the layered Ge and Ge nanosheets according to the present invention have a wide surface area and excellent ion capacity, when used as an electrode for a lithium ion battery, it is possible to implement a lithium ion battery with a minimum capacity loss.

In detail, the lithium ion battery may include an electrode, a counter electrode, an separator provided between the electrode and the counter electrode, and an electrolyte. When the electrode includes the layered Ge or Ge nanosheets according to the present invention, capacity loss due to volume expansion of the electrode generated during charging and discharging may be minimized, and thus life of a lithium ion battery may be improved. The counter electrode, the separator, and the electrolyte included in the lithium ion battery may adopt a well-known configuration in the field of lithium ion batteries, and thus the present invention will not be described in detail.

Although one embodiment of the present invention has been described above, the spirit of the present invention is not limited to the embodiments set forth herein, and those skilled in the art who understand the spirit of the present invention may add components within the scope of the same idea. Other embodiments may be easily proposed by changing, deleting, adding, etc., but this will also fall within the spirit of the present invention.

Preparation Example 1 Layered CaGe ₂ Preparation

For the synthesis of layered CaGe ₂ , Ca powder and Ge powder were mixed and then heat treated at 800 ° C. for 7 days and cooled to give a layered trigonal crystal structure with a space group of Rm-3m. CaGe ₂ was obtained.

(Preparation Example 2) Preparation of lamellae compound in which layered CaGe ₂ and Ge were alternately laminated

After mixing Ca powder and Ge powder, heat treatment at 900 ℃ for 12 hours, and then quenched at room temperature to prepare a lamellae compound.

Example 1 Manufacture of Layered Ge

After mixing the layered CaGe ₂ prepared in Preparation Example 1 with ethanol and SnCl ₂ and removed the Ca ions from the layered CaGe ₂ at -20 ℃, through which the trigonal system (space group) Rm-3m A layered Ge having a (trigonal) crystal structure was obtained.

Example 2 Manufacture of Layered Ge

In the same manner as in Example 1, Ca ions were removed at room temperature to obtain a layered Ge.

Example 3 Ge Nanosheet Preparation

The layered Ge prepared in Example 1 was peeled off with Scotch tape (3M) to prepare Ge nanosheets.

Example 4 Ge Nanosheet Preparation

The Lamellar structure prepared in Preparation Example 2 was mixed with ethanol and SnCl ₂ at -20 ° C to remove Ca ions, thereby preparing Ge nanosheets.

Comparative Example 1 3D Bulk Ge

A commercial 3D bulk Ge (Sigma Aldrich, product no .: 203351) was prepared.

(Manufacture example 1) The electrode for lithium ion batteries containing layered Ge

The layered Ge (0.08 g) prepared in Example 1 was mixed with Super P (0.01 g) and PVDF (0.01 g). After mixing with NMP solvent to prepare a slurry for the electrode, this was applied to the copper thin film by a doctor blade method 2 ㎛ and then heat-treated to prepare a Ge electrode.

The Ge electrode was laminated with a lithium metal electrode, a separator was inserted between the two electrodes, and an electrolyte solution containing LiPF ₆ (1.0 M) dissolved in an organic solvent in which EC and DEC were mixed at a volume ratio of 1: 1 was injected. A coin-type half cell was assembled to fabricate a lithium ion battery.

Comparative Production Example 1 Lithium-ion Battery Electrode Containing 3D Bulk Ge

Prepared in the same manner as in Preparation Example 1, instead of the layered Ge prepared in Example 1 using the Ge of Comparative Example 1 to prepare a Ge electrode and to produce a lithium ion battery comprising the same.

Experimental Example 1 XRD Analysis

XRD analysis was performed on the samples prepared in Ge of Preparation Example 1, Preparation Example 1, Example 1, and Example 2, and the results are shown in FIG. 3.

Referring to FIG. 3, it can be seen that the crystal structure of the layered CaGe ₂ (preparation example 1) is a trigonal having a space group of Rm-3m, and the layered types of Examples 1 and 2 It can be confirmed that Ge has a crystal structure different from the bulk Ge of the existing 3D crystal structure.

In addition, it can be confirmed that the layered Ge of Example 1 has a higher crystallinity than the layered Ge of Example 2.

Experimental Example 2 Raman Spectrum Analysis

Raman spectrum analysis was performed on the samples prepared in 3D Ge, Preparation Example 1 and Example 1 of Comparative Example 1, and the results are shown in FIG.

Referring to FIG. 4, it can be seen that the layered Ge (Example 1) has a stronger Ge-Ge in-plane strain than 3D Ge (Comparative Example 1), which is a buckle angle of Ge. Means increased.

Experimental Example 3 SEM Analysis

SEM images of the samples prepared in Comparative Example 1 and Examples 1 and 2 were taken, and the results are shown in FIGS. 5A to 5D.

5B and 5C, it can be seen that Ge prepared from layered CaGe ₂ is layered. It can be seen that this has a significantly different structure compared to the 3D bulk Ge shown in FIG. 5A. 5D shows an SEM image of the layered structure of Example 1 at different magnifications, and the layered structure of the layered Ge according to Example 1 can be clearly seen.

Experimental Example 4 TEM Analysis

TEM analysis was performed on the samples prepared in Comparative Example 1, 3D Ge, Preparation Example 1 and Example 1, and the results are shown in FIGS. 6A to 6D.

Referring to FIG. 6B, it can be seen that the crystal structures of 3D bulk Ge and layered CaGe ₂ are different. Referring to FIG. 6C, the layered Ge (Example 1) having Ca ions removed at −20 ° C. has higher crystallinity and has a trigonal crystal structure than the layered Ge having removed Ca ions at room temperature (Example 2). You can check it.

Experimental Example 5 EDS Analysis

EDS analysis was performed on the samples prepared in Preparation Example 2 and Example 1, and the results are shown in FIGS. 7A and 7B.

Referring to FIG. 7A, it can be seen that lamellar structures in which layered CaGe ₂ and Ge are alternately stacked.

Referring to FIG. 7B, after removing Ca ions of the layered CaGe 2, it is confirmed that the Ca element content of the layered Ge (Example 1) is significantly reduced.

Experimental Example 6 AFM Analysis

AFM analysis was performed on the Ge nanosheets according to Example 3, and the results are shown in FIG. 8. Referring to Figure 8, it can be seen that the thickness of the Ge nanosheets are 9nm, 29nm.

Experimental Example 7 Evaluation of Discharge Capacity and Charge / Discharge Characteristics

Discharge capacity and charge / discharge characteristics of the lithium ion battery prepared in Preparation Example 1 and Comparative Preparation Example 1 were evaluated, and the results are shown in FIGS. 9A to 9C.

9A is a graph showing charge and discharge curves of a lithium ion battery (manufacture example 1) including a layered Ge. Referring to FIG. 9A, it can be seen that the lithium ion battery of Preparation Example 1 has stable charge and discharge characteristics. .

Figure 9b is a discharge capacity graph according to the cycle, the lithium ion battery according to Preparation Example 1 shows that the first cycle efficiency of about 80% performance, but from the second cycle it can be seen that the cycle efficiency increased to about 96%. In addition, when the charge-discharge experiment was conducted in the region of 0 V (at discharge) and 2.5 V (at charge) at a current of 100 mA / g, the discharge capacity was measured in the first cycle. About 1,230 mAh / g, Comparative Preparation Example 1 had a capacity of about 1,396 mAh / g, but after 50 cycles Preparation Example 1 shows a capacity of about 163 mAh / g, while Comparative Production Example 1 has a capacity of about 46 mAh Had Through this, it can be seen that when using the layered Ge electrode according to the present invention, capacity loss due to volume expansion of the electrode can be minimized.

Claims

(1) a layer represented by the formula CaGe 2 having a trigonal crystal structure having a space group of Rm-3m by cooling the mixture including Ca powder and Ge powder at a predetermined temperature reduction rate Preparing a phase compound; And

(2) an amorphous, space group by treating the layered compound with a mixed solution comprising a salt capable of selectively removing Ca ions contained in the layered compound and a solvent capable of dissolving the salt. Preparing a layered Ge having a trigonal crystal structure of Rm-3m;

Method for producing a layered Ge comprising a.
The method of claim 1,

The salt is a method for producing a layered Ge represented by the following formula (1):

<Formula 1>

MX a (1≤a≤3)

In Formula 1, M is any one selected from Sn, Al, and Ga, and X is any one selected from Cl, F, and I.
The method of claim 1,

The solvent is a method of producing a layered Ge is at least one selected from ethanol, water, acetone and isopropanol.
The method of claim 1,

The heat treatment is a method of producing a layered Ge is performed for 5 to 10 days at 730 ~ 830 ℃ or 2 ~ 24 hours at 830 ~ 1,000 ℃.
The method of claim 1,

The cooling method of manufacturing a layered Ge is carried out at a temperature reduction rate of 3 ~ 20 ℃ / hour.
The method of claim 1,

Step (2) is carried out at -40 ~ 0 ℃ to produce a layered Ge having a trigonal (trigonal) crystal structure of the group (space group (Rm-3m) layered Ge manufacturing method.
The method of claim 1,

Step (2) is carried out at 15 ~ 60 ℃ to produce a layered Ge having an amorphous crystal structure layered Ge manufacturing method.
Layered Ge having a trigonal crystal structure with an amorphous or space group of Rm-3m.
The method of claim 8,

In the X-ray diffractogram obtained by the powder X-ray diffraction method using a Cu-Kα ray, the layered Ge having a trigonal crystal structure having the space group of Rm-3m is 15.5 ± 0.2, 26.4 ±. Layered, with peaks at 2θ values of 0.2, 35.6 ± 0.2, 45.7 ± 0.2, 48.5 ± 0.2 and 53.6 ± 0.2, and no peaks at 2θ values of 27.4 ± 0.2, 45.6 ± 0.2, 54.0 ± 0.2 and 66.4 ± 0.2 Ge.
A Ge nanosheet exfoliated from the layered Ge according to claim 8 and having an amorphous or triangular symmetric crystal structure.
The method of claim 10,

The Ge nanosheets have a thickness of 100 nm or less.
(1) After heat-treating the mixture containing Ca powder and Ge powder, it is quenched to form a layered CaGe2 having a trigonal crystal structure having a space group of Rm-3m and a single yarn having a space group of Fd-3m Preparing a compound comprising Ge having a cubic crystal structure; And

(2) an amorphous or space group by treating the layered CaGe 2 with a mixed solution containing a salt capable of selectively removing Ca ions contained in the layered CaGe2 and a solvent capable of dissolving the salt. Preparing a Ge nanosheet having a trigonal crystal structure having Rm-3m and a cubic crystal structure having a space group of Fd-3m;

Method of producing a Ge nanosheet comprising a.
The method of claim 12,

The heat treatment is a method of producing a Ge nanosheet is carried out for 2 to 24 hours at 830 ~ 1,000 ℃.
The method of claim 12,

The quenching of step (1) is a method for producing a Ge nanosheets is carried out at 10 ~ 40 ℃.
A Ge nanosheet comprising a Ge nanosheet having an amorphous or triangular symmetric crystal structure and a Ge nanosheet having a cubic crystal structure having a space group of Fd-3m.
A lithium ion battery electrode comprising at least one selected from the layered Ge according to claim 8, the Ge nanosheets according to claim 10, and the Ge nanosheets according to claim 15.