WO2012036354A1

WO2012036354A1 - SiO-C COMPOSITE POWDER FOR LITHIUM SECONDARY BATTERIES AND PREPARATION METHOD THEREOF

Info

Publication number: WO2012036354A1
Application number: PCT/KR2011/000299
Authority: WO
Inventors: Yun-Kyu Kang; Chul Lee
Original assignee: Yeil Electronics Co., Ltd.
Priority date: 2010-09-13
Filing date: 2011-01-14
Publication date: 2012-03-22
Also published as: KR101036288B1

Abstract

Provided is a negative active material which is used as a negative electrode material for lithium secondary batteries. More specifically, provided is SiO-C composite powder for lithium secondary batteries, wherein SiO particles are coated with carbon (C), as well as a method for preparing the same. The negative active material exhibits excellent battery efficiency, does not significantly change in volume and thus has a long cycle life.

Description

[DESCRIPTION]

[Invention Title]

SiO-C COMPOSITE POWDER FOR LITHIUM SECONDARY BATTERIES AND PREPARATION METHOD THEREOF

[Technical Field]

The present invention relates to a negative electrode material for lithium secondary batteries, and more particularly, to a negative active material for lithium secondary batteries, which has large capacity and a long cycle life, and a preparation method thereof.

[Background Art]

Since the 21st century began, the field of the IT industry has developed rapidly, as compared to other scientific/technical fields. With respect to mobile devices, including notebook computers, mobile phones and PDAs, many products have been developed. In recent years, ubiquitous networks have rapidly progressed, which diversify the performance of mobile devices and connect homes, work places and communities to each other.

Particularly, as concerns about environmental and energy problems have increased and research into solving such problems have been conducted, technologies relating to lithium secondary batteries for electric vehicles and lithium secondary batteries for energy storage have been competitively developed worldwide, and studies thereon have been actively conducted.

In lithium secondary batteries, technology for negative electrode materials is particularly important. As a negative active material for lithium secondary batteries, graphite has been continuously used, and to satisfy the demand for an increase in capacity, other carbonaceous materials or lithium metal compounds have been studied. However, negative electrode materials which have been studied have problems in that they have initial irreversible capacity, the volume thereof seriously changes, and the cycle-life characteristics thereof are significantly poor. Due to these problems, it is difficult to find a material which can be commercially used as a substitute for graphite.

Recently, metal Si nanowires were developed for use as a negative active material for lithium secondary batteries; however, they are relatively expensive, and thus disadvantageous in terms of price competitiveness. Also, technology for manufacturing combination electrodes using other metals or metal oxides has been suggested, but the added metals or metal oxides do not exhibit sufficient capacity, and they show low energy density.

Meanwhile, technology of preparing an SiO-C composite for use as a negative active material has been suggested, but it has technical disadvantages in that SiO, which is the precursor of the SiO-C composite, needs to be heat-treated at a high temperature (about 700-1000 ^°C) and should be mechanically or physically crushed to reduce the particle size thereof.

Accordingly, there is an urgent need for a negative active material that shows excellent battery efficiency and can be used for a long period of time. Also, there is a need for a method that can prepare such a negative active material in an economical and easy manner.

[Disclosure]

[Technical Problem]

An aspect of the present invention provides Si0^~C composite powder for lithium secondary batteries, which exhibits excellent battery efficiency, does not significantly change in volume and thus has a long cycle life, and a method capable of manufacturing the same in an easy manner.

[Technical Solution]

According to an aspect of the present invention, there is provided Si0-C composite powder for lithium secondary batteries, wherein SiO particles are coated with carbon (C). According to another aspect of the present invention, there is provided a method for preparing Si0-C composite powder for lithium secondary batteries, the method including: (a) mixing silicon tetrachloride (SiC14) with a hydrochloric acid solution; (b) adding to and mixing with the mixed solution of step (a) a sol obtained by mixing graphite with distilled water; and (c) drying the mixture resulting from step (b).

[Advantageous Effects]

The Si0-C composite powder according to the present invention may be applied to information electronic devices, which can be applied to next -generation semiconductor devices, nano-sized semiconductor devices, terabit information storage devices, ultra-high-speed devices for optical communication, and the like. Also, it may be used in medical and biotechnical applications, including drug delivery systems, biotechnical devices such as biosensors, and the like.

In addition, the Si0-C composite powder of the present invention may also be used in energy and environmental applications, including solar cells, hydrogen storage materials, lithium ion storage materials, nanosized catalysts, high-sensitivity biosensors for the measurement of environmental pollution, etc.

[Description of Drawings] The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which^'.

FIG. 1 is a schematic view showing SiOC composite powder of the present invention;

FIG. 2 is a cross-sectional view showing an apparatus for preparing the SiO-C composite powder of the present invention;

FIG. 3 shows the results of X-ray diffraction analysis of an inventive material and a comparative material;

FIGS. 4(a) and 4(b) are SEM photographs of a comparative material and an inventive material, respectively; and

FIG. 5 is a graphic diagram showing the change in capacity according to the number of cycles of an inventive material and a comparative material .

[Best Mode]

Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Like reference numerals in the drawings denote like elements, and thus their description will be omitted.

Hereinafter, the SiO-C composite powder of the present invention will be described in detail.

The SiO-C composite powder of the present invention is prepared using the method described below. As shown in FIG. 1, the SiO-C composite powder of the present invention has a configuration in which SiO particles are coated with carbon (C).

The SiO-C composite powder has an average particle size of 3~10 /m. If the average particle size is less than 3 μιη, the composite powder particles will agglomerate to reduce the surface reactivity thereof. On the other hand, if the average particle size is more than 10 (m, the reaction area of the particles will decrease to reduce the reaction efficiency thereof. For this reason, the upper limit of the average particle size is preferably 10 im.

Hereinafter, the preparation method of the present invention will be described in detai 1.

In order to prepare the SiO-C composite powder of the present invention, silicon tetrachloride (SiC14) is first added to and mixed with hydrochloric acid (HC1) solution in an inert gas atmosphere to prepare SiO powder. The silicon tetrachloride (SiCl₄) and the hydrochloric acid are ion-exchanged to produce silicon oxide (SiO) and HC1 gas.

The hydrochloric acid solution is preferably used at a concentration of 0.5 M.

The mixing of the silicon tetrachloride (SiCl₄) with the hydrochloric acid solution is preferably carried out using a ball milling process, in which the ball milling process is preferably carried out at a speed of 100-300 rpm for 2-6 hours, and more preferably, at a speed of 150 rpm for 4 hours.

If the ball milling speed is lower than 100 rpm, uniform mixing will not occur, and thus uniform SiO precipitates will not be produced, ^"and if the ball milling speed is higher than 300 rpm, the reaction product HC1 gas will be mixed at high pressure to cause gas expansion.

If the ball milling time is shorter than 2 hours, it will not be easy to obtain the reaction product, and if the ball milling time is longer than 6 hours, the expansion of HC1 can occur. For this reason, the ball milling time is preferably limited to 6 hours or less.

The inert gas atmosphere is applied in order to suppress the growth of SiO formed during the reaction. The inert gas used herein is not specifically limited, but one preferred example thereof may be argon (Ar) gas.

Next, a sol obtained by mixing graphite with distilled water is added to the above reaction product. The mixing ratio of graphite to distilled water in the sol is preferably 7-13:1 (graphite: distilled water). If the mixing ratio is less than 7:1, drying will not be easy due to a lack of carbon particles and an excessive addition of water, and it will be impossible to obtain an effective coating with carbon particles, due to lack of the carbon particles. On the other hand, if the mixing ratio is more than 13:1, it will not be easy to mix graphite with distilled water, and graphite will be likely to agglomerate.

After adding the sol mixture of graphite and distilled water, a mixing process is preferably carried out using a ball milling process. Herein, the ball milling process is preferably carried out at a speed of 100-300 rpm for 1-3 hours. If the ball milling time is shorter than 1 hour, the particles will not be mixed with each other due to insufficient coating time and will remain in the original state, and if the ball milling time is longer than 3 hours, the carbon powder particles will not be uniformly coated on the SiO surface in a semi- stable state and will agglomerate with each other, such that a uniform coating of the particles will not be formed. For this reason, the ball coating process is preferably carried out for 3 hours or less.

The mixing process is carried out in an inert gas atmosphere, in which the inert gas is preferably argon (Ar) gas.

Next, a drying process is carried out to prepare SiO-C as a final product. The drying process is preferably carried out using a circulation process of injecting and discharging carbon dioxide ((CO2) at 40-50 ^°C.

Hereinafter, the apparatus which is used for the preparation of the SiO-C composite powder according to the present invention will be described in detail with reference to FIG. 2.

The present invention is not limited to the embodiment of FIG. 2 and may be embodied in other various forms. The embodiment of FIG. 2 is provided to complete the disclosure of the present invention and to allow those having ordinary skill in the art to understand the scope of the present invention.

As shown in FIG. 2, an apparatus 10 according to the present invention comprises a housing 11 made of ceramic material. A gas inlet 14 for inert gas for forming an inert gas atmosphere is provided through the lid portion of the housing, and an inlet 12 and an outlet 13 for drying gas are also provided through the lid portion, such that a circulation drying process can be applied. The outlet 13 also serves as a passage for discharging HCI gas formed during a reaction.

Meanwhile, at the lower portion of the housing 11, a liquid outlet 16 is preferably provided such that water (H2O) formed during a reaction can be discharged through the outlet 16.

In addition, the apparatus 10 comprises the lid portion and an 0-ring 15, such that it can be sealed.

The preparation of SiO-C composite powder using the apparatus 10 has advantages in that the SiO-C composite powder can be prepared using one apparatus in a convenient and simple manner and thus can be prepared in a large amount at one time.

Hereinafter, the present invention will be described in detail with reference to examples. It is to be understood, however, that these examples are for illustrative purposes only and are not to be construed as limiting the scope of the present invention.

Examples

Silicon tetrachloride (S1CI4) was mixed with 0.5M hydrochloric acid (HCI), and the mixture was charged into the apparatus of FIG. 2. Then, the mixture was ball-milled in the apparatus at 150 rpm for about 4 hours while injecting argon gas into the apparatus. After the mixing process, while the ball-milled mixture was caused to remain in the apparatus, a sol obtained by mixing graphite with distilled water was charged into the apparatus. Then, the content in the apparatus was ball-milled at 200 rpm for 2 hours while injecting argon into the apparatus, followed by drying. The drying was carried out using a process of circulating carbon dioxide at 50 ^"C , thereby preparing SiO- C composite powder as an inventive material.

For comparison with the inventive material, a comparative material was prepared according to a conventional method.

In order to examine the characteristics of the inventive material and the comparative material, X-ray diffraction analysis was performed, and the results of the analysis are shown in FIG. 3. As can be seen from the results in FIG. 3, the inventive material had a very stable structure as compared to the comparative material. An SiC peak indicating the formation of an uniform composite was observed in the invent ive material .

Moreover, the microstructures of the comparative material and the invention material were observed using a scanning electron microscope (SEM), and the results of the observation are shown in FIGS. 4(a) and 4(b), respectively. As can be seen therein, in the inventive material (FIG. 4(b)), fine and uniform particles having a size of about 3-10 p were distributed, unlike the comparative material (FIG. 4(a)). On the contrary, the particles in the comparative material (FIG. 4(a)) were non-uniform and agglomerated.

The cycle-life characteristics of the inventive material and the comparative material were evaluated, and the results of the evaluation are shown in FIG. 5. As can be seen therein, the inventive material allowed a high capacity of about 675 mAh/g to be constantly supplied even at 200 cycles or more, suggesting that the inventive material had excellent cycle-life characteristics, like the comparative material, the capacity of which rapidly decreased as the number of cycles increased.

While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

[CLAIMS]

[Claim 1]

SiO-C composite powder for lithium secondary batteries, wherein SiO particles are coated with carbon (C).

[Claim 2]

The SiO-C composite powder of claim 1, wherein the composite powder has an average particle size of 3-10 μχα.

[Claim 3]

A method for preparing SiO-C composite powder for lithium secondary batteries, the method comprising:

(a) mixing silicon tetrachloride (SiC14) with a hydrochloric acid solut ion;

(b) adding to and mixing with the mixed solution of step (a) a sol, obtained by mixing graphite with distilled water; and

(c) drying the mixture resulting from step (b) .

[Claim 4]

The method of claim 3, wherein the mixing of the silicon tetrachloride (SiC14) with the hydrochloric acid solution is carried out in an inert gas atmosphere.

[Claim 5]

The method of claim 3, wherein the mixing of the silicon tetrachloride (SiC14) with the hydrochloric acid solution is carried out using a ball milling process.

[Claim 6] The method of claim 5, wherein the mixing is carried out at a speed of 100-300 rpm for 2-6 hours.

[Claim 7]

The method of claim 3, wherein the mixing ratio of graphite to distilled water in the sol is 7-13:1 (graphite: distilled water).

[Claim 8]

The method of claim 3, wherein step (b) is carried out using a ball milling process at a speed of 100-300 rpm for 1-3 hours.

[Claim 9]

The method of claim 3, wherein the drying step is carried out using a circulation process of injecting and discharging carbon dioxide at 40-50 ^°C.