KR102479063B1 - Porous Silicon Or Silicon Alloy Anode With Coating For Intercalation/ De-intercalation Of Lithium Ions And Manufacturing Methods Thereof - Google Patents

Abstract

A method of manufacturing a porous silicon negative electrode material that is adaptive to lithium insertion and extraction cycles is disclosed. The present invention comprises the steps of preparing a porous Si powder and at least one precursor of a Nb ₂ O ₅ precursor and an LTO precursor; mixing the precursor and the porous Si powder in an organic solvent; drying and pulverizing the mixed solution; and synthesizing an SEI layer having a Nb ₂ O ₅ or LTO composition on the surface of the porous Si powder by heat-treating the mixed solution at a temperature of 600 to 650 °C. According to the present invention, by forming an artificial SEI layer, it is possible to provide a Si or Si alloy anode material that is more adaptive to expansion and contraction due to lithium intercalation and desorption cycles.

Description

Porous Silicon Or Silicon Alloy Anode With Coating For Intercalation/ De-intercalation Of Lithium Ions And Manufacturing Methods Thereof}

The present invention relates to a method for manufacturing a negative electrode material for a lithium secondary battery, and more particularly, to a method for manufacturing a porous silicon negative electrode material that is adaptive to a lithium intercalation and desorption cycle.

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.

In a lithium ion battery, lithium is added to an active material during a lithiation reaction, and lithium ions are removed from the active material during a delithiation reaction. Most of the anodes currently applied to lithium ion batteries operate by lithium intercalation and de-intercalation mechanisms during charging and discharging. graphite, lithium titanium oxide (LTO), and Si or Si alloys.

Si or Si alloys used as negative electrode materials for lithium secondary batteries have the advantages of high theoretical capacity of 4200 mA/g, low reaction potential for positive electrode materials, low toxicity, and low cost. However, the volume of the particle expands or decreases according to cycling of lithium insertion or desorption of lithium, and a new phase may be generated by a reaction between lithium ions and an anode material. As a result, particle decomposition, pulverization, or cracking occurs, or a spontaneous electrically insulating SEI (Solid Electrolyte Interphase) layer is created by a side reaction at the interface between the cathode and the electrolyte, which adversely affects the lifespan and thermal stability of the electrode. can cause

In order to solve the above problems of the prior art, an object of the present invention is to provide a Si or Si alloy anode material that is more adaptive to expansion and contraction due to lithium insertion and extraction cycles.

Another object of the present invention is to provide a Si or Si alloy negative electrode material capable of suppressing the formation of an electrically insulating reactive layer of the Si negative electrode material.

An object of the present invention is to provide a method for forming an artificial SEI layer to suppress a side reaction at an interface between a negative electrode and an electrolyte of a lithium secondary battery.

Another object of the present invention is to provide a method for forming an artificial SEI layer capable of ensuring long lifespan and high thermal stability in insertion/desorption cycling.

In addition, an object of the present invention is to provide a method for producing the above-mentioned Si or Si negative electrode alloy material.

In order to achieve the above technical problem, the present invention comprises the steps of preparing at least one precursor and porous Si powder of a Nb ₂ O ₅ precursor and an LTO precursor; mixing the precursor and the porous Si powder in an organic solvent; drying and pulverizing the mixed solution; and synthesizing an SEI layer having a Nb ₂ O ₅ or LTO composition on the surface of the porous Si powder by heat-treating the mixed solution at a temperature of 600 to 650 °C.

In the present invention, the LTO may be Li ₄ Ti ₅ O ₁₂ .

Also, in the present invention, the heat treatment step may be performed in an inert atmosphere, and the inert atmosphere is preferably an Ar atmosphere. Also, in the present invention, the heat treatment step may be performed in a reducing atmosphere.

In one embodiment of the present invention, preparing the porous Si powder may include preparing a Si precursor; mixing the Si precursor and a reducing agent; and synthesizing a porous Si powder by heat-treating the mixture in a non-oxidizing atmosphere or a reducing atmosphere.

In this case, the Si precursor may include at least one mineral selected from the group consisting of diatomaceous earth, kaolin, bentonite, halosite nanoclay, and montmorillonite.

In one embodiment of the present invention, the reducing agent may be magnesium.

According to the present invention, it is possible to provide a Si or Si alloy negative electrode material that is more adaptable to expansion and contraction due to lithium insertion and extraction cycles. In addition, according to the present invention, it is possible to form an artificial SEI layer for suppressing side reactions at the interface between the negative electrode of a lithium secondary battery and the electrolyte solution while suppressing the formation of an electrical insulating reaction layer of the Si negative electrode material. In addition, according to the present invention, it is possible to form an artificial SEI layer capable of ensuring long lifespan and high thermal stability in insertion/desorption cycling.

1 is a diagram schematically showing a porous Si negative electrode material according to an embodiment of the present invention.
2 is a procedure diagram schematically illustrating a method of manufacturing an anode material made of porous silicon powder according to an embodiment of the present invention.
3 is a procedure diagram schematically illustrating a procedure for forming an LTO SEI layer according to an embodiment of the present invention.
4 is a flowchart illustrating a procedure of forming an SEI layer having a composition of Nb ₂ O ₅ on porous Si powder according to another embodiment of the present invention.
5 is a transmission electron micrograph of the porous Si powder prepared in Example of the present invention.
6 is a view showing an X-ray diffraction pattern of Si-Nb ₂ O ₅ powder prepared according to an embodiment of the present invention.
7 is a transmission electron microscope analysis picture of Si-Nb ₂ O ₅ powder prepared according to an embodiment of the present invention.
8 is a graph showing changes in charge and discharge capacities according to charge and discharge potentials of samples prepared according to an embodiment of the present invention.
9 is a graph showing measurement results of cycle characteristics and high rate characteristics of samples prepared according to an embodiment of the present invention.

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

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 porous Si negative electrode material according to an embodiment of the present invention.

Referring to FIG. 1 , the Si anode material 100 includes porous silicon or silicon alloy particles 110 and an artificial SEI layer 120 coated on the surface thereof. The SEI layer 120 has high lithium ion conductivity and has a relatively high redox potential (~1V) so that an electrolyte decomposition reaction does not occur.

In the present invention, the porous silicon particles 110 may be manufactured in various ways. As an example, the porous silicon particles 110 may be reduced from porous silicon oxide such as diatomite. In addition, in the present invention, the porous silicon particles 110 are kaolin (Kaolin, H ₂ Al ₂ Si ₂ O ₅ H ₂ O), bentonite (Na _0.5 Al ₂ (Si _3.5 Al _0.5 ) O ₁₀ (OH) ₂ n ( H ₂ O)), halosite nanoclay (Al ₂ Si ₂ O ₅ (OH) ₄ 2H ₂ O) or montmorillonite ((Na, Ca) _0.3 (Al, Mg) ₂ Si ₄ O ₁₀ (OH) ₂ n( It may be silicon or silicon alloy particles obtained by reducing H ₂ O)).

In the present invention, the porous silicon particles 110 have a very low electrode expansion rate compared to the nano-silicon negative electrode material. In addition, the porous silicon particles 110 have a high specific surface area and show a higher charging capacity than silicon particles.

In the present invention, the SEI layer provides a charging channel for Li ions with high ionic conductivity so that Li ions can be smoothly supplied to the core Si.

The SEI layer may be implemented such that its composition includes Nb ₂ O ₅ or LTO (Litium Titanium Oxide). The LTO includes Li 0.8 Ti _{2.2 O 4 , Li 8 Ti 4 O 12 , LiTi 2 O 4 , Li 4 Ti 5 O 12 ,} Li ₄ Ti ₅ O with little change _in crystal structure and excellent reversibility during charging and discharging _{. 12} etc. can be used. More preferably, in the present invention, Li ₄ Ti ₅ O ₁₂ having high ionic conductivity is used.

In the present invention, the artificial SEI layer performs the following functions. First, the artificial SEI layer suppresses the generation of by-products caused by unwanted side reactions between Li ions and Si during charging and discharging. Unintended reaction by-products may cause decomposition, pulverization, or cracking of particles, and adversely affect the stability of the electrode due to non-uniformity of the composition and thickness of the reaction by-products. The artificial SEI layer of the present invention provides a charge/discharge channel with high ionic conductivity, and prevents the negative electrode material from reacting with Li ions by side reactions by providing a stable synthetic layer.

In the present invention, the porous silicon or silicon alloy may be manufactured in various ways. In a preferred embodiment of the present invention, porous silicon or silicon alloys can be prepared by reduction from various silicon minerals. An example thereof will be described below.

2 is a procedure diagram schematically illustrating a method of manufacturing an anode material made of porous silicon powder according to an embodiment of the present invention.

Diatomite is prepared as a silicon source (S100) and milled with zirconia balls (S110). A reducing agent is added to the pulverized diatomaceous earth (S120), and heat treatment is performed in a non-oxidizing atmosphere or a reducing atmosphere (S130). For example, magnesium may be used as the reducing agent. Subsequently, impurities are removed by washing the reduced powder with hydrochloric acid or the like (S140). Through this manufacturing process, porous silicon can be obtained.

Hereinafter, a method of forming an SEI coating layer on porous silicon powder will be described with reference to FIGS. 3 and 4 .

3 is a procedure diagram schematically illustrating a procedure for forming an LTO SEI layer on porous silicon powder.

Referring to FIG. 3, a mixed solution is prepared by stirring Li precursor, Ti precursor, and porous Si powder as sources of LI and Ti in an organic solvent (S210).

Any type of metal precursor may be used as the Li and Ti precursors. For example, as the lithium precursor in the present invention, lithium acetate (CH ₃ COOLi), lithium hydroxide (LiOH), etc. may be used. As the Ti precursor, titanium propoxide (Ti(OCH(CH ₃ ) ₂ ) ₄ ), Titanium butoxide etc. can be used. Oxygen contained in the Li and/or Ti precursors serves as an oxygen source for LTO synthesis. In the present invention, a case in which a metal precursor in the form of a compound is used as a source of Li and Ti is exemplified, but it is also possible to directly use metal powder in the present invention. An appropriate organic solvent may be used depending on the precursor used in the present invention.

In the present invention, the raw materials used for preparing the mixed solution may be mixed in various ways. For example, the Li precursor and ethyl alcohol may be mixed and stirred, followed by mixing and stirring the porous Si powder and the Ti precursor, respectively. Of course, otherwise, the Li precursor, the Ti precursor, and the porous Si powder may be simultaneously mixed and stirred. Preparation of the mixed solution may be performed at an appropriate speed, for example, 500 to 2000 rpm in an arbitrary stirrer. The mixed solution may be prepared at room temperature.

Subsequently, the mixed solution is dried in a dryer such as a convection oven (S212), and the dried mixed powder is pulverized using a mortar or the like (S214). Of course, in the present invention, the crushing step may be selectively applied.

Subsequently, the mixed powder is heat-treated to synthesize an anode material in which an LTO layer is formed on the surface of the porous Si particles (S216). An appropriate heat treatment temperature may be selected according to the composition of the LTO to be synthesized in the present invention. For example, in the case of Li ₄ Ti ₅ O ₁₂ , the heat treatment temperature is preferably in the range of 600 to 650°C.

In addition, the LTO layer in the present invention can be synthesized in various atmospheres. For example, the LTO layer may be synthesized in an inert gas atmosphere such as Ar or a reducing atmosphere containing hydrogen. As will be described later, the LTO layer is preferably synthesized in a reducing atmosphere.

4 is a flowchart illustrating a procedure of forming an SEI layer having a composition of Nb ₂ O ₅ on porous Si powder according to another embodiment of the present invention.

As in FIG. 3, a mixed solution is prepared by stirring the Nb precursor and the porous Si powder in an organic solvent (S220). As the Nb precursor, any type of metal precursor may be used. For example, niobium ethoxide may be used as the Nb precursor in the present invention. The mixed solution is dried (S222), pulverized (S224), and heat treated (S226) as in FIG. Even in this embodiment, heat treatment may be performed in a non-oxidizing atmosphere or a reducing atmosphere. For example, heat treatment may be performed at a temperature of 610° C. and in an Ar atmosphere.

Hereinafter, preferred embodiments of the present invention will be described.

<Preparation of porous Si powder>

Diatomaceous earth was pulverized using a zirconia ball. After mixing pulverized diatomaceous earth and magnesium as a reducing agent at a weight ratio of 1:2, heat treatment was performed at 750° C. in an Ar atmosphere for 2 hours. Subsequently, the heat-treated powder was treated with hydrochloric acid to remove impurities and washed with water to prepare a porous Si powder.

5 is a transmission electron micrograph of the porous Si powder prepared in this example. Referring to FIG. 5 , it can be seen that particles having a size of approximately 0.1 micrometer are formed.

<Experimental Example 1>

CH ₃ COOLi (Sigma-Aldrich) was used as a solvent in ethyl alcohol and stirred for 10 minutes with a stirrer at 1000 rpm to prepare a solution. Subsequently, the porous Si powder prepared previously was mixed with this solution and stirred at 1000 rpm for 1 hour. Next, Ti(OCH(CH ₃ ) ₂ ) ₄ (Sigma-Aldrich) was mixed with the solution and stirred at room temperature at 700 rpm for 2 hours. The mixing and stirring process described above was performed at room temperature. In this experiment, the number of grams of Li in the Li precursor, Ti and Si in the Ti precursor were weighed in a ratio of 0.311:1.083:0.65.

The prepared mixed solution was dried in a convection oven at 70°C for 12 hours. The dried powder was ground and mixed in a mortar. Subsequently, heat treatment was performed at 610° C. in an Ar atmosphere for 12 hours to prepare Si—Li ₄ Ti ₅ O ₁₂ powder.

<Experimental Example 2>

Niobium ethoxide (Aldrich Co.) was used as a solvent in ethyl alcohol and stirred for 10 minutes with a stirrer at 1000 rpm to prepare a solution. Subsequently, the porous Si powder prepared previously was mixed with this solution and stirred at 1000 rpm for 1 hour. The mixing and stirring process described above was performed at room temperature. In this experiment, the number of grams of Nb and Si in the Nb precursor was 0.1:0.9 Weighed in the ratio of.

The prepared mixed solution was dried in a convection oven at 110°C for 12 hours. The dried powder was ground and mixed in a mortar. Subsequently, heat treatment was performed at 610° C. in an Ar atmosphere for 12 hours to prepare Si-Nb ₂ O ₅ powder.

6 is a view showing an X-ray diffraction pattern of the Si-Nb ₂ O ₅ powder prepared in Experimental Example 2. Figure 6 (a) is an X-ray diffraction pattern of porous Si powder as a raw material powder, and Figure 6 (b) is an X-ray diffraction pattern of Si-Nb ₂ O ₅ powder. In Figure 6 (b), Nb ₂ An O ₅ peak can be confirmed, and it can be seen that Nb ₂ O ₅ has been synthesized.

7 is a transmission electron microscope analysis photograph of the Si-Nb ₂ O ₅ powder prepared in Experimental Example 2. It can be seen from (a) of FIG. ₇ that Nb is distributed _on the surface of the powder, and from (b) of FIG. corresponds to a constant.

<Example 1>

An anode was prepared using the Si-Nb ₂ O ₅ powder prepared in Experimental Example 2 as an anode active material. PAA (Poly Acrylic Acid)-CMC (Carboxymethylcellulose Sodium Salt) was used as a binder, and SPB (Super P Black) was used as a conductive material.

A slurry was prepared by mixing an anode material, a binder, and a conductive material in a weight ratio of 6:2:2 with distilled water as a solvent, and then the slurry was applied to the end surface of a Cu foil used as a current collector. Then, it was dried in an oven at about 100° C. for 2 hours. At this time, the thickness of the electrode plate made was approximately 30 to 35 um. An electrode was manufactured by molding the prepared Si-Nb ₂ O ₅ negative electrode material into a diameter of 14 mm.

A coin cell 2032 was manufactured by stacking a Li metal plate having a diameter of 16 mm, a separator, a Si-Nb ₂ O ₅ electrode, a stainless steel plate, and a spring. At this time, as the electrolyte, an electrolyte of 1M LiPF ₆ containing a mixture of EC (ethylene carbonate) / DEC (diethyl carbonate) / EMC (ethylmethyl carbonate) in a volume ratio of 3: 5: 2 and 10 wt% FEC was used. .

Electrochemical properties were measured using the prepared coin cell sample. Using Toyo's T-3100, initial charge/discharge characteristics (Cut off voltage: 0.005~2V, C-rate: 0.05C (charge/discharge)), high rate characteristics (Cut off voltage: 0.01~1.2V, C-rate: 0.1C (First cycle/ 0.05C)) and electrode life characteristics (Cut off voltage: 0.01-1.2V, C-rate: 0.1C (charge/discharge)) were measured.

In addition, the electrode expansion rate was calculated by measuring the change in electrode thickness before and after charging. In the expansion rate measurement, the charging conditions were set to a cut off voltage of 0.005V and a C-rate of 0.05C.

<Example 2>

Anode and coin cell samples were prepared and their characteristics were measured in the same manner as in Example 1, except that porous Si powder was used as the anode active material.

8 is a graph showing changes in charge and discharge capacities according to charge and discharge potentials of samples prepared according to Examples 1 and 2.

From FIG. 8 , it can be seen that high charge and discharge capacities are implemented in the Si—Nb ₂ O ₅ negative electrode material sample (Nb ₂ O ₅ -porous Si).

Figure 9 (a) is a graph showing the cycle characteristics of the samples prepared according to Examples 1 and 2, Figure 9 (b) is a graph showing the high rate characteristics measurement results.

From FIG. 9, it can be seen that the Si-Nb ₂ O ₅ anode material sample (Nb ₂ O ₅ -porous Si) is stable at a high rate (7C) compared to the porous Si anode material sample (porous-Si), and the high rate characteristics It can be seen that there is almost no decrease in capacity as the process progresses.

Although preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments. Those of ordinary skill in the art to which the present invention pertains will know that it can be applied not only to silicon or silicon alloy but also to other anode materials without departing from the scope of the technical idea disclosed by the present invention.

100 active materials
110 Porous Si Particles
120 SEI layer

Claims (8)

preparing at least one precursor of a Nb ₂ O ₅ precursor and an LTO precursor and a porous Si powder;
mixing the precursor and the porous Si powder in an organic solvent;
drying and pulverizing the mixed solution; and
Heat-treating the pulverized powder at a temperature of 600 to 650 ° C. to synthesize an SEI layer of Nb2O5 or LTO composition on the surface of the porous Si powder,
The method for producing a porous Si-based negative electrode material, characterized in that the porous Si powder is reduced from porous silicon oxide. According to claim 1,
The LTO is a method for producing a porous Si-based negative electrode material, characterized in that Li ₄ Ti ₅ O ₁₂ . According to claim 1,
The heat treatment step is a method for producing a porous Si-based negative electrode material, characterized in that carried out in an inert atmosphere. The method of claim 3, wherein the inert atmosphere is an Ar atmosphere. According to claim 1,
The heat treatment step is a method for producing a porous Si-based negative electrode material, characterized in that carried out in a reducing atmosphere. According to claim 1,
Preparing the porous Si powder,
preparing porous silicon oxide;
mixing the porous silicon oxide and a reducing agent; and
Method for producing a porous Si-based negative electrode material comprising the step of synthesizing a porous Si powder by heat-treating the mixture in a non-oxidizing atmosphere or a reducing atmosphere. According to claim 6,
The method for producing a porous Si-based negative electrode material, characterized in that the porous silicon oxide comprises at least one mineral selected from the group consisting of diatomaceous earth, kaolin, bentonite, halosite nanoclay and montmorillonite. According to claim 6,
The method for producing a porous Si negative electrode material, characterized in that the reducing agent is magnesium.

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