KR102465961B1 - Anode Active Materails With Long Life Cycle For Li Secondary Battery And Manufacturing Methods Thereof - Google Patents

Abstract

An anode material having a longer lifespan is disclosed. The present invention comprises the steps of disproportionating the SiO _x powder; Stirring the disproportionated SiO _x powder into an organic solvent; mixing the disproportionated SiO _x powder and the Ti precursor solution; drying the mixed solution to obtain a solid content; And it provides a method for manufacturing a negative electrode material for a lithium secondary battery comprising the step of heat-treating the solid content. According to the present invention, it is possible to provide an anode material for a SiOx-based lithium secondary battery capable of expressing high capacity, including nano-silicon. In addition, according to the present invention, it is possible to provide an anode material that provides a wide specific surface area upon lithium insertion and provides three-dimensional pores that serve as a buffer against deterioration due to volume expansion during lithium insertion. In addition, according to the present invention, it is possible to provide an anode material having a stable solid electrolyte interface that suppresses a direct reaction between the electrolyte and the anode material.

Description

Anode Active Materials With Long Life Cycle For Li Secondary Battery And Manufacturing Methods Thereof

The present invention relates to a negative electrode active material for a lithium secondary battery, and more particularly, to a negative electrode material having a long lifespan.

BACKGROUND As electronic devices using batteries have been miniaturized, lightened, and increased in capacity, interest in high-capacity compact batteries has increased, and lithium ion batteries have been increasingly used.

Commonly commercialized lithium secondary batteries have a structure in which a polymer separator is added to a liquid electrolyte composed of an organic solvent ^and lithium salt. It moves to the positive pole, and moves in the opposite direction when charging. The driving force for such Li ⁺ ion movement is generated by chemical stability according to the potential difference between the two electrodes. The capacity (Ah) of a battery is determined by the amount of Li ⁺ ions moving from the negative electrode to the positive electrode and from the positive electrode to the negative electrode.

As science and technology develop, various devices are developed, and demand for a variety of energy supply sources used in portable devices is increasing. Accordingly, in order to facilitate mobility, wireless energy supply sources are being actively developed, and lithium secondary batteries have been studied the most. However, carbon-based active materials, which are most often used as negative electrodes in lithium secondary batteries, require high-capacity batteries to drive devices that evolve into multifunctional complex devices due to their limited capacity, and for this, a large amount of active material is required. It is a state in which the size of the battery that is being used is bound to increase.

On the other hand, silicon material as an active material has been widely discussed as an anode material, but due to the problem of volume expansion during intercalation and desorption of lithium, it is difficult to guarantee lifespan due to decrease in adhesion and conductivity in the electrode, so it is not currently commercialized. In addition, due to the reaction with the electrolyte on the surface of the electrode during charging and discharging, the decomposition reaction of the electrolyte proceeds rapidly, resulting in a significant decrease in the performance of the battery.

In order to solve the problems of the prior art, it is an object of the present invention to provide a method of manufacturing a negative electrode material for a SiOx-based lithium secondary battery capable of expressing high capacity, including crystalline nano-silicon.

Furthermore, an object of the present invention is to provide a method for manufacturing an anode material that provides a wide specific surface area during lithium insertion and provides a three-dimensional pore that serves as a buffer against deterioration due to volume expansion during lithium insertion.

In addition, an object of the present invention is to provide a method for manufacturing an anode material capable of providing a stable solid electrolyte interface that suppresses a direct reaction between the electrolyte and the anode material.

In addition, an object of the present invention is to provide a negative electrode material prepared by the above-described method and a lithium secondary battery including the same.

The present invention in order to achieve the above technical problem disproportionate the SiO _x powder; Stirring the disproportionated SiO _x powder into an organic solvent; mixing the disproportionated SiO _x powder and the Ti precursor solution; drying the mixed solution to obtain a solid content; And it provides a method for manufacturing a negative electrode material for a lithium secondary battery comprising the step of heat-treating the solid content.

In the present invention, the Ti precursor may include Ti(OCH(CH ₃ ) ₂ ) ₄ or Ti(OCH ₂ CH ₂ CH ₂ CH ₃ ) ₄ .

In addition, in the heat treatment step, a crystalline TiO ₂ - _x (x>0) coating layer is formed on the surface of the SiO _x powder.

In addition, the present invention may further include the step of porous treatment of the SiOx powder.

In order to achieve the above other technical problem, the present invention, the disproportionated SiO _x core; and a TiO _{2- x} coating layer (where x>0) surrounding the SiO _x core.

In the present invention, pores may be formed on the surface of the negative electrode material powder.

In addition, in the present invention, the TiO _{2- x} coating layer preferably has higher electrical conductivity than the SiO _x core. In the present invention, the TiO ₂ - _x coating layer may include an anatase phase.

In order to achieve the above another technical problem, the present invention, in a lithium secondary battery including a negative electrode, a positive electrode and an electrolyte, the negative electrode is a disproportionated SiO _x core and a TiO _{2- x} coating layer surrounding the SiO _x core ( Here, an anode material including powder for a lithium secondary battery including x>0) may be included, and the coating layer may further include a TiOF ₂ and/or LiTiOF ₂ phase. The TiOF ₂ and/or LiTiOF ₂ phase may be formed outside the coating layer. At this time, the TiOF ₂ /LiTiOF ₂ phase is preferably amorphous.

According to the present invention, it is possible to provide an anode material for a SiOx-based lithium secondary battery capable of expressing high capacity, including crystalline nano-silicon. In addition, according to the present invention, it is possible to provide an anode material that provides a wide specific surface area upon lithium insertion and provides three-dimensional pores that serve as a buffer against deterioration due to volume expansion during lithium insertion. In addition, according to the present invention, it is possible to provide an anode material having a stable solid electrolyte interface that suppresses a direct reaction between the electrolyte and the anode material.

1 is a diagram schematically showing a manufacturing process of an anode material according to an embodiment of the present invention.
2 is a diagram schematically illustrating a method for manufacturing an anode active material according to another embodiment of the present invention.
3 is a transmission electron microscope image of SiOx powder prepared according to an embodiment of the present invention.
FIG. 4 is a photograph showing the results of EDS analysis of the inside of the powder and the boundary of the coating layer in the powder of FIG. 3 .
5 is a scanning electron microscope photograph of TiO ₂ coated porous SiO _x powder prepared according to an embodiment of the present invention.
6 is a graph showing electrical characteristics measurement results of battery samples prepared in Example of the present invention.
7 is a graph showing the results of measuring the battery characteristics according to the cycle of the battery using each electrode sample.
8 is a schematic diagram for explaining the surface reaction mechanism by the TIO _{2- x} coating layer according to the present invention.
9 is a scanning electron microscope photograph of the shape of an electrode powder in a lithiation and delithiation step during charging and discharging.
10 is a graph showing XPS analysis results of electrode powder in lithiation and delithiation steps during charging and discharging.

The present invention will be described in detail by describing preferred embodiments of the present invention with reference to the following drawings.

1 is a diagram schematically showing a manufacturing process of an anode material according to an embodiment of the present invention.

1 is a diagram schematically illustrating a method for manufacturing an anode active material according to an embodiment of the present invention.

First, the SiO _x powder is disproportionated by heat treatment at 1050 to 1150 ° C (S110).

The SiO _x (where 0.5≤x≤1.2) material is composed of amorphous Si and silicon oxide of various valences. The SiO _x material is thermodynamically unstable and can be disproportionated into Si and SiO ₂ . In the present invention, the SiOx powder is heat-treated at a high temperature of 1050 to 1150° C. to disproportionate into crystalline Si and SiO ₂ . In this disproportionation process, the particle size of Si grows while forming a crystalline state. In the present invention, Si subjected to the disproportionation process may exhibit a higher reversible capacity than silicon in an amorphous state.

Then, the disproportionated SiO _x powder is stirred in an appropriate organic solvent such as ethanol (S120).

Next, a Ti precursor solution is added to the stirred solution and stirred for about 1 hour (S130). At this time, Ti precursors include, for example, Ti(OCH(CH ₃ ) ₂ ) ₄ , Ti(OCH ₂ CH ₂ CH ₂ CH ₃ ) ₄ etc. can be used. In addition, NH ₄ OH, CH ₃ CN, CH ₃ CH ₂ OH, etc. may be used as a solvent for dissolving the precursor.

The mixed solution after stirring is centrifuged and washed (S140) and dried (S150). At this time, heavy water may be used as the cleaning solution. Drying the mixed solution is preferably performed in a vacuum oven.

Finally, heat treatment is performed for 12 hours at a temperature suitable for crystallization of the Ti precursor coated on the SiOx surface, such as 550 to 650 ° C, to form a non-stoichiometric TiO ₂ TiO _{2 -x} (x>0) coating layer (S160 ). Here, the degree of oxygen deficiency (x) of the TiO ₂ - _x (x>0) coating layer may change depending on heat treatment conditions. For example, oxygen deficiency may be appropriately adjusted in the range of 0<x<0.25, preferably 0.1<x<0.25. Of course, a higher value of oxygen deficiency is also possible.

At this time, in order to form a TiO _{2- x} coating layer having non-stoichiometry (x>0), the heat treatment is preferably performed in an inert atmosphere or a reducing atmosphere such as Ar or N ₂ atmosphere. Conversely, TiO ₂ with stoichiometry can be obtained in an oxidizing atmosphere. In the present invention, the TiO _2-x (x>0) coating layer is preferably crystalline.

2 is a diagram schematically illustrating a method of manufacturing an anode active material according to another embodiment of the present invention.

In this embodiment, the SiO _x powder is subjected to a porous treatment process to form pores or voids in a three-dimensional shape extending from the surface of the powder or into the inside of the powder.

Illustratively, the porosity treatment of the SiO _x powder in the present invention may be performed as follows. First, Ag is coated on the surface of the disproportionated SiOx powder (S210). Ag coating can be achieved by stirring SiO _x powder in a hydrofluoric acid (HF) solution in which silver nitrate (AgNO ₃ ) is dissolved. The stirred solution is washed with deuterated water to remove remaining Ag ⁺ ions and NO ^3- ions.

Next, porous SiO _x is prepared by chemical etching the Ag-coated SiOx powder (S220). This process may be performed by introducing Ag-coated SiO _x powder into a mixed solution of hydrofluoric acid and hydrogen peroxide and mixing them. After the treated powder is washed with heavy water, it is dried in a vacuum oven.

Subsequently, Ag coated on the surface of the powder is removed (S230). Removal of Ag can be achieved by mixing the coating powder in a nitric acid solution heated to approximately 50°C. Subsequently, porous SiO _x powder can be obtained through washing in heavy water and drying in a vacuum oven.

The porous SiO _x powder thus obtained is disproportionated by going through steps 110 to S160 described with reference to FIG. 1, and TiO ₂ - _x coated SiO _x powder can be obtained on the surface.

<Experimental Example 1>

The SiOx powder was heat treated at 1100 °C for 6 hours in an Ar atmosphere. Then, 10 g of the disproportionated SiOx powder was dissolved in ethanol and stirred. After dissolving Ti(OCH(CH ₃ ) ₂ ) ₄ in acetonitrile, an NH ₄ OH solution was added and stirred for 1 hour. Subsequently, Ti(OCH(CH ₃ ) ₂ ) ₄ was added to the mixed solution of SiOx stirred in ethanol. The solution was slowly added dropwise to react, centrifuged, washed with heavy water, and dried in a vacuum oven. The dried specimens were heat-treated for 12 hours at a temperature of 500 °C and in an Ar atmosphere.

<Experimental Example 2>

The SiOx powder was added to a hydrofluoric acid (HF) solution in which silver nitrate (AgNO ₃ ) was dissolved, stirred, and washed with heavy water to remove remaining Ag ⁺ ions and NO ^3- ions. Then, the Ag-coated SiOx powder was chemically etched _by adding the Ag-coated SiOx powder to a solution in which hydrofluoric acid and hydrogen peroxide were mixed. The etched powder was washed with heavy water and then dried in a vacuum oven. Subsequently, the coating powder was mixed in a nitric acid solution heated to about 50° C. to remove Ag, and the coating powder was washed in heavy water and dried in a vacuum oven to obtain a porous SiO _x powder. Then, the obtained powder was subjected to disproportionation treatment.

TiO _2-x was coated on the surface of the porous SiO _x powder thus obtained in the same manner as in Experimental Example 1.

3 is a transmission electron microscope photograph of the SiOx powder prepared in Experimental Example 1;

In FIG. 3, (a) is the SiOx powder before the disproportionation treatment, (b) is the SiOx powder after the disproportionation treatment, and (c) is a transmission electron microscope image of the SiOx powder after the TiO _2-x coating.

Referring to (b) of FIG. 3 , it can be seen that the inside of the powder has a microstructure in which the Si phase is dispersed on the SiO2 matrix by the disproportionation treatment compared to before the disproportionation treatment. In addition, as can be seen in (c) of FIG. 3, it can be seen that a TiO ₂ coating on anatase is formed on the surface of the powder.

FIG. 4 is a photograph showing the results of EDS analysis of the inside of the powder and the boundary of the coating layer in the powder of FIG. 3 . It can be seen that the TiO ₂ coating layer is coated at a level of 30 to 40 nm, and it can be seen that it is coated at a molar ratio of about 6.2%.

5 is a scanning electron microscope photograph of TiO ₂ coated porous SiOx (p-SiOx) powder prepared in Experimental Example 2; It can be seen from FIG. 2 that a plurality of pores are formed on the surface of the powder and a TiO ₂ coating layer is formed on the surface.

Table 1 below is a table showing the results of measuring the electrical properties of the powders of each step prepared in Experimental Examples 1 and 2.

division resistance
(x10 ² Ω) volume resistance
(x10 ² Ω cm) electrical conductivity
(S/cm) SiOx 4.22 0.22 4.65 p-SiOx 2.50 0.13 7.84 p-SiO _{x (} 1100 ℃ ₎ 3.89 0.20 5.04 TiO ₂ @p-SiO _x 1.75 0.09 11.19

In the table above, SiOx is a disproportionated SiOx powder, p-SiOx is a porous treated SiOx powder, p-SiOx (1100 ℃) is a powder heat treated at 1100 ℃ with TiO2 coating condition, TiO ₂ @p -SiO _x refers to surface coated p-SiOx powder. From the above table, it can be observed that the electrical conductivity of the powder is increased by the coating of TiO ₂ . In general, TiO ₂ powder has electrical insulating properties. The TiO 2 powder prepared in this experimental example is a non-stoichiometric TiO ₂ powder TiO _{2 -x} (x>0) powder, which can contribute to improving the electrical conductivity of the SiOx powder. be able to

<Example>

Secondary batteries were manufactured using the powders obtained in Experimental Examples 1 and 2. As the electrode powder, disproportionated SiO _x powder (SiO _x ), porous treated SiO _x (p-SiOx) powder, and TiO _2-x coated p-SiO _x powder (TiO _2-x @p-SiO _x ) were used, respectively.

After mixing electrode powder: PAA (polyacrylic acid) binder: CMC: SPB at a ratio of 70: 10: 10: 10, put NMP (N-methyl pyrrolidinone) as a solvent in a container and use a Thinker mixer for 20 minutes mixed. The prepared homogeneous slurry was applied on a Cu current collector and then dried in air at 100° C. for 20 minutes. As the electrolyte, LiPF ₆ electrolyte salt with a concentration of 1.3 M was used in a mixture containing EC (ethylene carbonate)/DEC (diethyl carbonate) in a volume ratio of 3:7 and 10 wt% FEC (fluoroethylene carbonate). Li metal was used as a counter electrode, and Celgard 2325 was used as a separator.

Electrochemical properties were measured using the prepared electrode cell and electrolyte solution. Using Toyo's T-3100, charge and discharge capacity and cycle characteristics were measured. The cycle was charged/discharged at a 0.5C-rate in the voltage range of 0.005 to 1.2 V in a constant current-constant voltage method (CC-CV).

6 is a graph showing electrical characteristics measurement results of battery samples prepared in Examples, and Table 2 below is a table summarizing battery characteristics.

electrode division L/L
(mg/cm ² ) Density
(g/cc) Charge
(mAh/g) Discharge
(mAh/g) CE
(%) SiOx 1.19 0.77 1451.33 2262.77 64.14 p-SiOx 0.99 0.71 1523.51 2257.91 67.47 TiO2-x@p-SiOx 1.24 0.89 1507.33 2099.12 71.81

Referring to FIG. 6 and Table 7, it can be seen that the battery using the TiO _2-x @p-SiO _x electrode sample exhibits high initial efficiency.

7 is a graph showing the results of measuring the battery characteristics according to the cycle of the battery using each electrode sample.

Referring to FIG. 7 , it can be seen that the battery using the TiO _2-x @p-SiO _x electrode sample exhibits a high capacity retention rate. This is because the TiO ₂ - _x coating suppresses the direct reaction of the SiO _x material, thereby reducing electrolyte decomposition.

8 is a schematic diagram for explaining the surface reaction mechanism by the TIO _{2- x} coating layer according to the present invention.

In a conventional lithium secondary battery, the LiPF ₆ salt electrolyte generates HF, which causes a chemical reaction between the electrode surface and the electrolyte, and decomposes the electrolyte to shorten battery life. However, in the present invention, the TiO _{2- x} coating layer forms an amorphous LiTiOF ₂ SEI layer capable of intercalating and detaching lithium on the surface to suppress electrolyte decomposition, thereby enabling high capacity and long life due to capacity development.

9 is a scanning electron microscope photograph of the shape of an electrode powder in a lithiation and delithiation step during charging and discharging.

Referring to FIG. 9, in the case of SiO _x electrode powder (SiO _x ) and SiO _x electrode powder (SiO _x @ 1100 ° C) heat-treated at 1100 ° C, an irreversible SEI layer is formed and an electrolyte decomposition reaction occurs, so that the volume of SIO _x It can be seen that the separation between the SEI layer and the core material due to the expansion is intensified. However, in the case of TiO ₂ coated electrode powder (TiO _2-x @SiO _x ) according to an embodiment of the present invention, it can be seen that this separation phenomenon is suppressed.

10 shows SiO _x electrode powder (marked as SiO _x ) and SiO _x electrode powder heat-treated at 1100 ° C (marked as 1100 ° C@ SiO _x ) in the lithiation and delithiation steps during charging and discharging. , A graph showing the results of XPS analysis of TiO _{2 -x} coated electrode powder (TiO ₂ @1100°C@ SiO _x ).

Referring to FIG. 10, it can be seen that a LiTiOF ₂ phase is observed during lithium substitution by the TiO _{2- x} coating layer, and this SEI layer acts as a protective layer involved in capacity.

Above, the embodiments disclosed in this specification and drawings are only presented as specific examples to aid understanding, and are not intended to limit the scope of the present invention. In addition to the embodiments disclosed herein, it is obvious to those skilled in the art that other modifications based on the technical idea of the present invention can be implemented.

Claims (10)

disproportionating SiO _x (where 0.5≤x≤1.2) powder;
Stirring the disproportionated SiO _x powder into an organic solvent;
mixing the disproportionated SiO _x powder and the Ti precursor solution;
drying the mixed solution to obtain a solid content; and
Including the step of heat-treating the solid content,
The heat treatment step forms a crystalline TiO _2-y (0.1 <y <0.25) coating layer having a higher electrical conductivity than the SiO _x core on the surface of the SiO _x powder. Manufacturing method of negative electrode material for a lithium secondary battery. According to claim 1,
The Ti precursor is a method for producing a negative electrode material for a lithium secondary battery, characterized in that it comprises Ti(OCH(CH ₃ ) ₂ ) ₄ or Ti(OCH ₂ CH ₂ CH ₂ CH ₃ ) ₄ . delete According to claim 1,
Method for producing a negative electrode material for a lithium secondary battery, further comprising the step of porous processing the SiO _x powder. disproportionated SiO _x (where 0.5≤x≤1.2) core; and
A TiO _2-y coating layer (here, 0.1<y<0.25) surrounding the SiO _x core,
The anode material powder for a lithium secondary battery, characterized in that the TiO _2-y coating layer has a higher electrical conductivity than the SiO _x core. According to claim 5,
The negative electrode material powder for a lithium secondary battery, characterized in that the surface of the negative electrode material powder is formed with pores. delete According to claim 5,
The negative electrode material powder for a lithium secondary battery, characterized in that the TiO _2-y coating layer contains an anatase phase. In the lithium secondary battery including a negative electrode, a positive electrode and an electrolyte,
The cathode includes a disproportionated SiO _x core (where 0.5≤x≤1.2) and a TiO _2-y coating layer (where 0.1<y<0.25) surrounding the SiO _x core and having a higher electrical conductivity than the SiO _x core. Including a negative electrode material containing a powder for a lithium secondary battery containing,
The lithium secondary battery, characterized in that the coating layer further comprises a TiOF ₂ or LiTiOF ₂ phase. According to claim 9,
The TiOF ₂ or LiTiOF ₂ phase is a lithium secondary battery, characterized in that amorphous.

Images