KR20160042357A - Manufacturing Methods of Silicon Anode withLTO-Coating in Reduced Environment - Google Patents

Abstract

A manufacturing method of an anode material for a Li secondary battery having an artificial surface protection layer is disclosed. The present invention provides a method of manufacturing a semiconductor device, comprising: mixing an Li source, a Ti source, and an Si source into an organic solvent; Drying and pulverizing the mixed solution; And heat-treating the mixed solution at a temperature of 600 to 650 ° C to synthesize LTO from the Li source and Ti source. According to the present invention, an artificial SEI layer is formed in order to suppress side reactions at the interface between the negative electrode and the electrolyte, thereby making it possible to manufacture a lithium secondary battery capable of ensuring long life and high thermal stability in the occlusion / deactivation cycling.

Description

[0001] Manufacturing Methods of Silicon Anode with LTO-Coating in Reduced Environment [

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an anode material for a lithium secondary battery, and more particularly, to a method for manufacturing an anode material having an artificial surface protection layer.

As electronic devices using batteries are becoming smaller, lighter and larger, there is an increasing interest in high capacity compact batteries, and the use of lithium ion batteries is increasing.

A commercially available lithium secondary battery has a structure in which a polymer separator is added in a liquid electrolyte composed of an organic solvent and a lithium salt. When discharged, Li ⁺ ions migrate from a cathode to an anode, and electrons generated as Li ionizes Moves to the anode, and moves in the opposite direction when charging. The driving force of this Li ⁺ ion movement is generated by the chemical stability depending on the potential difference between the two electrodes. The capacity (capacity, Ah) of the battery is determined by the amount of Li ⁺ ions moving from the cathode to the anode and from the anode to the cathode.

In a lithium ion battery, lithium is added to the active material during a lithium ion-exchange reaction, and lithium ions are removed from the active material during a delithiation reaction. Currently, most of the anodes that are applied to lithium-ion batteries operate by means of lithium intercalation and de-intercalation mechanisms during charging and discharging. Graphite, lithium titanium oxide (LTO) and Si or Si alloys.

Cycling of lithium insertion or lithium elimination causes expansion or reduction of the particle volume, and a new phase due to the reaction of the lithium ion and the negative electrode material can be generated. As a result, particle decomposition, pulverization or cracking occurs, or a spontaneous SEI (Solid Electrolyte Interphase) layer is formed due to a side reaction at the cathode and the electrolyte interface, which may adversely affect the lifetime and thermal stability of the electrode. .

In order to solve the problems of the prior art, it is an object of the present invention to provide a method of forming an artificial SEI layer in order to suppress side reactions at the cathode and the electrolyte interface of a lithium secondary battery.

It is another object of the present invention to provide a method for forming an artificial SEI layer capable of ensuring long life and high thermal stability in an insert / tear-off cycle.

According to an aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: mixing an Li source, a Ti source, and a Si source into an organic solvent; Drying and pulverizing the mixed solution; And heat-treating the mixed solution at a temperature of 600 to 650 ° C to synthesize LTO from the Li source and Ti source.

In the present invention, the LTO preferably includes Li ₄ Ti ₅ O ₁₂ .

In the present invention, the heat treatment step may be performed in an inert atmosphere. At this time, the inert atmosphere is preferably an Ar atmosphere.

In the present invention, the heat treatment step is preferably performed in a reducing atmosphere, and the reducing atmosphere may be a mixed gas atmosphere of hydrogen and Ar.

In the present invention, the LTO-Si negative electrode material may be coated with LTO on the surface of the Si powder.

In the present invention, the Si is preferably porous nano-Si.

According to the present invention, an artificial SEI layer is formed to suppress side reactions at the cathode and the electrolyte interface. This makes it possible to manufacture a lithium secondary battery that can ensure long life and high thermal stability in the occlusion / dehumidification cycling.

1 is a view schematically showing an anode material of the present invention.
FIG. 2 is a schematic diagram illustrating a method of manufacturing the above-described anode material according to an embodiment of the present invention.
3 (a) and 3 (b) are electron micrographs of Si-LTO powder prepared according to Experimental Examples 1 and 2, respectively.
4 is an X-ray diffraction pattern of Si-LTO powder prepared according to Experimental Examples 1 and 2 of the present invention.
5 is a graph showing changes in charge / discharge capacity depending on charge / discharge potentials of a battery sample manufactured according to an embodiment of the present invention.
6 is a graph showing the results of measurement of high-rate characteristics of a sample manufactured according to an embodiment of the present invention.
7 is a graph showing the results of measurement of cycle characteristics of a sample manufactured according to an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the preferred embodiments of the present invention with reference to the drawings.

1 is a view schematically showing an anode material of the present invention.

Referring to FIG. 1, an anode material 100 includes silicon particles 110 and an artificial SEI layer 120 coated on the surface thereof. The SEI layer 120 should have a high lithium ion conductivity and have a relatively high redox potential (~1 V) to prevent electrolyte decomposition reaction.

In the present invention, the SEI layer provides a filling channel for Li ions with a high ion conductivity, so that Li ions are supplied to the core Si smoothly. The SEI layer is implemented with LTO (Litium Titanium Oxide). The LTO has a structure in which changes in crystal structure during charging and discharging are low and reversible, 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 _12, and the like. More preferably, Li ₄ Ti ₅ O ₁₂ having a high ionic conductivity is used in the present invention.

In the present invention, the artificial SEI layer performs the following functions. First, an artificial SEI layer suppresses the formation of by-products due to undesired side reactions of Li ions and Si during charge and discharge. Unintended reaction byproducts cause decomposition, pulverization or cracking of the particles, and may adversely affect the stability of the electrode due to non-uniformity such as composition and thickness of reaction by-products. The artificial SEI layer of the present invention provides a charge / discharge channel with a high ionic conductivity and provides a stable composite layer, thereby preventing the anode material from reacting with Li ions due to side reactions.

FIG. 2 is a schematic diagram illustrating a method of manufacturing the above-described anode material according to an embodiment of the present invention.

Referring to FIG. 2, a Li precursor, a Ti precursor, and a nano Si precursor are mixed with a source of LI, Ti, and Si in an organic solvent to prepare a mixed solution (S110).

As the Li and Ti precursors, any type of metal precursor may be used. For example, the lithium precursor in the present invention includes lithium acetate (CH ₃ COOLi) lithium hydroxide (LiOH) and the like can be used. As the Ti precursor, titanium propoxide (Ti (OCH (CH ₃ ) ₂ ) ₄ ), Titanium butoxide Etc. may be used. The oxygen contained in the Li and / or Ti precursors serves as an oxygen source for LTO synthesis. In the present invention, a metal precursor in the form of a compound is used as a Li and Ti source, but it is also possible to use a metal powder directly in the present invention. As the Si precursor in the present invention, a porous Si powder is used. Preferably, the porous Si powder is a nano-sized powder.

Suitable organic solvents may be used depending on the precursor used in the present invention.

In the present invention, the precursors used in the preparation of the mixed solution can be mixed in various ways. For example, the Li precursor and ethyl alcohol may be mixed and stirred, and then the nano Si powder and the Ti precursor may each be mixed and stirred. Alternatively, Li precursor, Ti precursor and Si nano powder may be mixed and stirred at the same time. The preparation of the mixed solution can be carried out at an appropriate rate, for example, 500 to 2000 rpm, on any stirrer. The mixed solution may be prepared at room temperature.

Subsequently, the mixed solution is dried in a dryer such as a convection oven (S120), and the dried mixed powder is pulverized using induction or the like (S130).

Then, the mixed powder is heat-treated to synthesize an anode material having an LTO layer formed on the surface of Si nanoparticles. An appropriate heat treatment temperature can be selected according to the LTO composition 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.

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

<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, a porous Si powder (Sigma Aldrich) having an average particle diameter of 100 nm was mixed with this solution, and the mixture was stirred at 1000 rpm for 1 hour. Next, Ti (OCH (CH ₃ ) ₂ ) ₄ (Sigma Aldrich) was added to this solution, and the mixture was stirred at a room temperature of 700 rpm for 2 hours. The above mixing and stirring processes were carried out at room temperature. In this experiment, the g numbers of Ti and Si in Li and Ti precursors in the Li precursor were weighed at a ratio of 0.311: 1.083: 0.65.

The prepared mixed solution was dried in a convection oven at 70 캜 for 12 hours. The dried powder was pulverized and mixed with triglyceride. Subsequently, the Si-LTO powder was heat-treated at 610 캜 in an Ar atmosphere for 12 hours.

<Experimental Example 2>

Si-LTO powder was prepared by preparing a mixed solution of Li precursor, Ti precursor and nano Si powder under the same composition and manufacturing conditions as in Example 1, followed by drying and heat treatment. In this embodiment, Si-LTO powder was prepared by heat treatment at 610 ° C in H2 (5%) / Ar atmosphere for 12 hours.

3 (a) and 3 (b) are electron micrographs of Si-LTO powder prepared according to Experimental Examples 1 and 2, respectively.

Referring to FIG. 3, it can be seen that a spherical powder of uniform size having an average particle diameter of 130 to 200 nm is obtained.

4 is an X-ray diffraction pattern of the Si-LTO powder prepared according to Experimental Examples 1 and 2. Fig. FIG. 4 (c) also shows the XRD pattern of the nano Si powder used as the Si precursor.

Referring to FIG. 4, it can be seen that the synthesized Si-LTO is mostly composed of Si, and Li ₄ Ti ₅ O ₁₂ Peak (LTO) is observed. In addition, some TiO ₂ peaks are also observed. No alloy or compound peak of Si such as Ti-Si-O or Si-Li-O was observed. Therefore, at the heat treatment temperature, it can be seen that Ti and Li contained in the raw material powder do not generate a reaction product with Si.

On the other hand, observing EDS mapping data, it was confirmed that LTO was uniformly coated on the surface of Si.

&Lt; Example 1 >

The negative electrode was prepared using the Si-LTO powder prepared in Experimental Example 1 as a negative active material. PAA (Polyacrylic Acid) -CMC (Carboxymethylcellulose Sodium Salt) was used as the binder and SPB (Super P Black) was used as the conductive material.

The slurry was prepared by mixing distilled water as a solvent with an anode material, a binder and a conductive material in a weight ratio of 6: 2: 2, and then slurry was applied to the cross section of the Cu foil used as the current collector. Then, it was dried in an oven at about 100 DEG C for 2 hours. At this time, the thickness of the formed electrode plate was approximately 30 to 35 μm. The prepared Si-LTO anode material was molded into a 14 mm diameter electrode.

A coin cell 2032 was fabricated by laminating a Li metal plate having a diameter of 16 mm, a separation membrane and a Si-LTO electrode, a stainless steel plate and a spring. At this time, a 1M LiPF ₆ electrolyte solution 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 as the electrolyte .

The prepared coin cell sample was used to measure electrochemical properties. (C-rate: 0.05 C (charge / discharge)) and high-rate characteristics (Cut off voltage: 0.01 to 1.2 V, (C-rate: 0.1 C (first cycle / 0.05 C)) and electrode life characteristics (cut off voltage: 0.01 to 1.2 V, C-rate: 0.1 C (charge / discharge)).

The change in electrode thickness before and after charging was measured to calculate the rate of electrode expansion. In the expansion rate measurement, the cut off voltage and the C-rate were set to 0.005 V and 0.05 C, respectively.

&Lt; Example 2 >

A negative electrode and a coin cell sample were prepared and the characteristics thereof were measured in the same manner as in Example 1, except that the Si-LTO powder prepared in Experimental Example 2 was used as a negative electrode active material.

<Comparative Example>

For comparison with the examples, negative electrode and coin cell samples were prepared and measured for their properties, as in Example 1, except that instead of Si-LTO, the Si nanopowder was made of the negative electrode active material.

Table 1 shows the initial charge / discharge capacities and charge / discharge efficiencies of Examples and Comparative Examples, and FIG. 5 is a graph showing changes in charge / discharge capacity according to the charge discharge potential.

division Charging capacity
(mAh / g) Discharge capacity
(mAh / g) efficiency(%) Comparative Example 1938.51 1733.07 89.4 Example 1 1364.64 1251.62 91.7 Example 2 1351.90 1237.51 91.4

It can be seen from Table 1 that the sample of Example 1 (LTO-nano Si) and the sample of Example 2 (R-LRO-nano Si) show higher initial efficiency than the sample of Comparative Example (Ref. Nano-Si) .

6 is a graph showing the results of measurement of the high rate characteristics of the samples of the example and the comparative example.

The high-rate characteristics (10C / 0.2C) were 33.6% and 40.5% higher than those of the comparative example (ref. Nano-Si) in Example 1 (LTO-nano Si) and Example 2 (R-LRO- Respectively. In particular, Example 2 produced by a heat treatment in a reducing atmosphere shows excellent high-rate characteristics as compared with Example 1.

7 is a graph showing the results of measurement of cycle characteristics of the samples of the examples and comparative examples.

From FIG. 7, it can be seen that the electrode lifetime characteristics are most excellent in the case of the sample 2 (R-LTO-nano-Si) subjected to the reduction heat treatment.

Table 2 shows the results of measurement of the rate of electrode expansion before and after charging. Referring to Table 2, the rate of electrode expansion (%) was in the order of Example 2 <Example 1 <Comparative Example. The expansion ratio ((% / mAhg ^-1 )) normalized by the unit charge amount shows such tendency. That is, expansion of the electrode is suppressed by the RTO coating, and in the case of Example 2 synthesized in a reducing atmosphere, it shows improved characteristics as compared with Example 1 synthesized in an inert atmosphere.

Sample Charge amount
(mAh / g) Thickness before filling
(탆) Thickness after filling
(탆) Expansion ratio (%) Expansion ratio
(% / mAhg- ¹ ) Comparative Example 1954 40 91 127.5 0.065 Example 1 1383 45 67 48.9 0.035 Example 2 1378 46 64 39.5 0.028

Claims (8)

Mixing an Li source, a Ti source, and an Si source into an organic solvent;
Drying and pulverizing the mixed solution; And
And heat-treating the mixed solution at a temperature of 600 to 650 ° C to synthesize LTO from the Li source and the Ti source. The method according to claim 1,
Wherein the LTO is Li ₄ Ti ₅ O ₁₂ . The method according to claim 1,
Wherein the heat treatment step is performed in an inert atmosphere. &Lt; RTI ID = 0.0 &gt; 15. &lt; / RTI &gt; 4. The method for producing an LTO-Si-based anode material according to claim 3, wherein the inert atmosphere is an Ar atmosphere. The method according to claim 1,
Wherein the heat treatment step is performed in a reducing atmosphere. The method according to claim 1,
Wherein the reducing atmosphere in the heat treatment step is a mixed gas atmosphere of hydrogen and Ar. The method according to claim 1,
Wherein the LTO-Si negative electrode material is coated with LTO on the surface of the Si powder. The method according to claim 1,
Wherein the Si is porous nano Si. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt;

Images