Patent Application
20120181477
The present invention relates to SiOx that can be suitably used as a vapor deposition material for a barrier film and a negative electrode active material for a lithium-ion secondary battery, and a vapor deposition material for a barrier film and a negative electrode active material for a lithium-ion secondary battery each using the same.
Usually, in the case where foods and the like are packaged in the food processing field, in order to prevent degradation of fats and oils, proteins, and the like, so-called gas barrier properties are demanded for the packaging materials, so that oxygen, moisture and the like do not permeate the packaging materials. Furthermore, in the field in which medical products and medicinal products are treated, a rigorously high standard to the deterioration or degradation is set with respect to the medical products and medicinal products, and the packaging materials having high gas barrier properties are demanded.
In recent years, attention is being paid to packaging materials comprising an SiO vapor-deposited film having high gas barrier properties and excellent transparency. Examples include a material obtained by forming a SiO vapor-deposited film on a polymer film. As used herein, the SiO vapor-deposited film means a silica type vapor-deposited film, and when the composition is represented by SiOx, the value of x is in the range of 1<x<2. When the SiO vapor-deposited film is used as a packaging barrier film, the value of x is preferably set in the range of 1.4<x<1.8. Incidentally, excellent transparency is necessary to observe packaged contents by appearance and check deterioration or degradation thereof, and can be said as an essential property, particularly for the packaging material that packages foods and the like.
The vapor deposition material which can form the SiO vapor-deposited film having high gas-barrier properties is produced by heating a mixture of Si and SiO2, precipitating the sublimated SiO gas on a precipitation substrate, and processing the resulting precipitated SiO by pulverization, grinding or the like. However, when forming a SiO vapor-deposited film on a polymer film using this SiO vapor deposition material, splashing happens to occur. Splashing is a phenomenon in which high-temperature fine particles that are not sublimated scatter together with the sublimated SiO gas, and when the fine particles adhere to the SiO vapor-deposited film on a polymer film, pinholes and other defects are generated, and result in deteriorating gas-barrier properties.
Therefore, in order to suppress the number of generation of splashing, various improvements have been attempted in the past, for example, a SiO vapor deposition material having a low hydrogen gas content is proposed in Patent Literature 1. The said literature shows a relationship between a hydrogen gas content in a SiO vapor deposition material and the number of generation of splashing and describes that the number of generation of splashing can be significantly reduced by setting the hydrogen gas content to 50 ppm or less. However, expected effect on reducing splashing is not necessarily obtained. In addition, since it is necessary to remove hydrogen gas that is contained in silicon and silicon dioxide to be used in producing a SiO vapor deposition material, there arise problems that productivity is low, and the production cost of SiO increases.
In Patent Literature 2 and Patent Literature 3, highly active silicon oxide powder is proposed. Since being highly active enables a reaction with other elements to be efficient and easy, the highly active silicon oxide powder can be expected as a raw material for producing a silicon compound. It is described in Example of Patent Literature 3 that silicon nitride is obtained with a high reaction rate using this silicon oxide powder as a raw material. However, the improvement of physical properties thereof for utilizing as a vapor deposition material is not made, and it is considered to be difficult to obtain an effect on reducing splashing when forming a film using the silicon oxide powder described in these patent literatures. In addition, the silicon oxide powder described in these patent literatures is liable to promote surface oxidation and nitridation under an atmosphere due to its high activity, and is poor in handling characteristic.
On the other hand, in accordance with recent noticeable developments in portable electronic equipments, communication equipments and the like, development of secondary batteries with high energy density is strongly requested from the viewpoint of economic aspect and miniaturization and weight reduction of equipment, and the demand for a lithium-ion secondary battery is strongly growing in the power source market because of its enhanced life and capacity.
The lithium-ion secondary battery comprises a positive electrode, a negative electrode, and a separator impregnated with electrolyte between these opposite electrodes, and is configured such that lithium ions move back and forth between the positive electrode and the negative electrode through the electrolyte on the occasion of charging and discharging.
The negative electrode uses an active material capable of occluding and releasing lithium ions (negative electrode active material), and it is attempted to use a silicon oxide such as SiO, as the negative electrode active material. Since the silicon oxide is low (less noble) in electrode potential to lithium and has no deterioration such as collapse of crystal structure or generation of an irreversible substance, which results from the occlusion and release of lithium ions during charging and discharging, the silicon oxide can be expected, by using it as the negative electrode active material, to provide a lithium-ion secondary battery high in voltage and energy density and also excellent in cycle characteristic (maintainability of discharge capacity in repeating charging and discharging) and initial efficiency.
The initial efficiency refers to the ratio of initial discharge capacity to initial charge capacity and is one of important battery design factors. Law initial efficiency means that lithium ions implanted to a negative electrode by the initial charge is not sufficiently discharged at the initial discharge, and it is difficult to use a silicon oxide displaying lower initial efficiency as a negative electrode active material for a lithium-ion secondary battery. While a SiO vapor deposition material and silicon oxide having various properties are suggested in Patent Literatures 1 to 3 describe above, an improvement for an increase in initial efficiency has not been accomplished in any of them.
An object of the present invention is to provide SiOx that can form a vapor-deposited film having excellent gas barrier properties, in which the generation of splashing is suppressed, and pinholes and other defects are not generated, when forming a SiO vapor-deposited film on a polymer film using a SiO vapor deposition material, and that can maintain the initial efficiency (the ratio of initial discharge capacity to initial charge capacity, i.e., discharge-to-charge ratio) at high level in a case of being used as a negative electrode active material for a lithium-ion secondary battery, and to provide a vapor deposition material for a barrier film and a negative electrode active material for a lithium-ion secondary battery each using this SiOx.
The present inventors studied in order to solve the above-mentioned problems and it turned out that, the more the amount of the generated H2O gas detected in a temperature range of 200 to 800° C. when performing temperature-programmed desorption gas analysis is, the more the splashing is generated when forming a SiOx vapor-deposited film on a polymer film, and in addition, the initial efficiency becomes lower when using SiOx as a negative electrode active material for a lithium-ion secondary battery.
The amount of the generated H2O gas detected from SiOx in a temperature range of 200 to 800° C. in temperature-programmed desorption gas analysis depends on the number of silanol groups contained in SiOx. A silanol group (Si—OH) is a group formed by covalent bonding between Si and a hydroxyl group. A silanol group causes a reaction of the following chemical formula (1) at 200 to 800° C., to form a siloxane bond (Si—O—Si) and also generate H2O gas.
Si—OH+HO—Si→—Si—O—Si—+H2O↑ (1)
The present invention is achieved based on the above-mentioned findings, and the summaries thereof lies in SiOx of the (1) below, a vapor deposition material for a barrier film of the (2) below, and a negative electrode active material for a lithium-ion secondary battery of the (3) below.
(1) SiOx, characterized in that the amount of generated H2O gas detected in a temperature range of 200 to 800° C. in a temperature-programmed desorption gas analysis is 680 ppm or less.
In the SiOx of (1), an embodiment in which the amount of the generated H2O gas detected in a temperature range of 200 to 800° C. in a temperature-programmed desorption gas analysis is 420 ppm or less can be adopted.
In addition, in the SiOx of (1), when transforming a graph of raw data obtained by X-ray diffraction into a moving average approximation curve by use of a fixed subset size of 49, the relationship between a peak intensity P1 at a Si peak point generated near 2θ=28° on the curve and a base intensity P2 at a peak point expected from the average gradient before and after the peak point satisfies (P1−P2)/P2≦0.2, which can be, deemed as a preferred mode of an embodiment.
(2) A vapor deposition material for a barrier film, which uses the SiOx of the (1) above.
(3) A negative electrode active material for a lithium-ion secondary battery, which uses the SiOx of the (1) above.
When the SiOx of the present invention is used as a vapor deposition material for a barrier film (packaging material) used in the field of food processing, medical products and medicinal products and the like, the generation of splashing can be suppressed in forming a SiOx vapor-deposited film, and a vapor-deposited film having excellent gas barrier properties, without pinholes and other defects, can be formed. In addition, in case of being used as a negative electrode active material for a lithium-ion secondary battery, high initial efficiency (ratio of initial discharge capacity to initial charge capacity) of the secondary battery can be maintained. The SiOx of the present invention is low in activity, and thus surface oxidation and/or nitridation do not develop under open air and is also excellent in handling characteristic.
In addition, using the vapor deposition material for a barrier film of the present invention permits a vapor-deposited film having excellent gas barrier properties to be formed, and using the negative electrode active material for a lithium-ion secondary battery of the present invention enables high initial efficiency of a lithium-ion secondary battery to be maintained.
As described above, SiOx of the present invention is the SiOx being characterized in that the amount of the generated H2O gas detected in a temperature range of 200 to 800° C. in a temperature-programmed desorption gas analysis is 680 ppm or less.
In SiOx of the present invention, the reason for specifying the amount of the generated H2O gas detected in a temperature range of 200 to 800° C. in a temperature-programmed desorption gas analysis at 680 ppm or less is, for example, to eliminate the generation of splashing when forming a SiOx vapor-deposited film on a polymer film using the SiOx of the present invention, and to maintain high initial efficiency of the secondary battery constituted using the SiOx of the present invention as a negative electrode active material for a lithium-ion secondary battery, while retarding a decrease thereof. The amount of the generated H2O gas detected in a temperature range of 200 to 800° C. in a temperature-programmed desorption gas analysis is preferably 420 ppm or less from the viewpoint of further reducing the generation of splashing and maintaining further high initial efficiency of a lithium-ion secondary battery.
When the amount of the generated H2O gas detected from SiOx in a temperature range of 200 to 800° C. in a temperature-programmed desorption gas analysis is 680 ppm or more, splashing is generated in forming a film, and initial efficiency of a lithium-ion secondary battery decreases.
The amount of the generated H2O gas detected from SiOx in a temperature range of 200 to 800° C. in a temperature-programmed desorption gas analysis is measured using a temperature-programmed desorption gas analysis apparatus (TDS) by a mass fragment method. A sample is heated from room temperature at a heating rate of 0.5° C./s. The mass fragment method is a method such that a spectrum with temperatures being on the axis of abscissa and ion intensities of a specific mass number being on the axis of ordinate is obtained, and an area of this spectrum is used to perform a quantitative analysis.
In SiOx of the present invention, the range of x is desirably 0.5≦x≦1.5. This is because, when the SiOx is used as a vapor deposition material for a barrier film, the SiOx wherein x is more than 1 is usually desirable, and when the SiOx is used as a negative electrode active material for a lithium-ion secondary battery, the SiOx wherein x is less than 1 is generally used.
In SiOx of the present invention, an embodiment that, when transforming a graph of the raw data obtained by X-ray diffraction into a moving average approximation curve by use of a fixed subset size of 49 (49 data in a subset being averaged, in succession), the relationship between the peak intensity P1 at a Si peak point exhibited near 2θ=28° on the curve and the base intensity P2 at the peak point, which is interpolated from the gradient of average intensities in the fore and aft positions near the peak point, satisfies (P1−P2)/P2≦0.2 can be adopted.
The SiOx is obtained by precipitating the sublimated SiOx on the inner periphery of the heated precipitation substrate as set forth below. Si happens to be mixed in this SiOx, and when this is used as a vapor deposition material, the mixed Si is evaporated and scattered, and this also causes splashing. The present inventors have found that: this mixed Si is precipitated on the precipitation substrate after thermal cracking of SiOx; as (P1−P2)/P2 is smaller, splashing by the precipitated Si gets fewer, so that splashing is practically sufficiently reduced when (P1−P2)/P2≦0.2 is satisfied; and the lower the temperature of the inner periphery of the precipitation substrate is, (P1−P2)/P2 becomes smaller. As used herein, the method of obtaining P1 and P2 will be described using
More specifically, as the fore and alt regions near the peak, except for the peak region, regions of 24 to 26° and 30 to 32° are selected, respectively. In the regions, the average intensities P3 and P4 are obtained, respectively. The average intensities P3 and P4 are regarded as the intensities at 25° and 31°, respectively, and a straight line is drawn connecting respective points. This is used as the base line. The intensity of the intersection between a perpendicular erected at the peak point 20 and the base line is used as the base intensity P2.
The base intensity P2 at the peak point is interpolated in this way, then (P1−P2)/P2 can be calculated. (P1−P2)/P2 is 0.10 in
The SiOx of the present invention can be produced through the steps shown in the following (1) to (4).
(1) A mixed pelletized raw material that is obtained by blending and pelletizing Si powder and SiO2 powder is heated to 1100 to 1350° C. In this case, as described in afore-mentioned Patent Literature 1, it is desirable to use a raw material having a low hydrogen gas content for reducing the number of generation of splashing.
In the case where SiOx is for use in a vapor deposition material for a barrier film, the SiOx wherein x is more than 1 is usually used, and when used as a negative electrode active material for a lithium-ion secondary battery, the SiOx wherein x is less than 1 is generally used. When SiOx powder is produced by pulverizing the SiOx film that is prepared, for example, by a binary deposition method that independently heats two types of raw materials, Si and SiO2, with an individual heating source to deposit, the value of this x can be adjusted by adjusting each deposition rate of Si and SiO2 when preparing a SiOx film.
(2) The sublimated SiOx is precipitated on a precipitation portion (the inner periphery of a precipitation substrate) at 500 to 600° C.
(3) The precipitation substrate on which SiOx is precipitated is cooled in an Ar atmosphere, and SiOx is collected and pulverized.
(4) The collected SiOx and an appropriate amount of ethanol are put into in an autoclave and then treated at a pressure of 0.1 to 1 MPa and a temperature of 80 to 150° C.
The treatment of the (4) above (hereinafter, referred to as “treatment after collection”) is an important treatment for producing the SiOx of the present invention. The treatment after collection is performed, whereby part with a silanol group being present can be repaired in a state maintaining the original structure of SiOx, to form a stable siloxane bond (Si—O—Si). As a result, the SiOx of the present invention, wherein the amount of the generated H2O gas detected in a temperature range of 200 to 800° C. in a temperature-programmed desorption gas analysis is 680 ppm or less, can be produced.
In the treatment after collection, a treatment pressure at 0.3 to 1 MPa and a treatment temperature of 105 to 150° C. are desirable. This is due to the fact that the SiOx of the present invention, wherein the amount of the generated H2O gas detected in a temperature range of 200 to 800° C. in a temperature-programmed desorption gas analysis is 420 ppm or less, can be produced thereby. Also, this is due to the fact that it maintains the original structure of SiOx and simplifies the post-treatment.
This treatment after collection can be relatively easily performed, for example, by storing the collected SiOx and an appropriate amount of ethanol in an autoclave and heating at a given temperature. The reason for charging ethanol into the autoclave at the same time is to gasify ethanol to adjust the pressure in the autoclave to a given pressure.
The SiOx of the present invention described above can suppress the generation of splashing in forming a SiOx vapor-deposited film, and a vapor-deposited film having excellent gas barrier properties can be formed. In addition, in case of being used as a negative electrode active material for a lithium-ion secondary battery, high initial efficiency of the secondary battery can be maintained. This SiOx is low in activity, thus surface oxidation and/or nitridation do not develop and is also excellent in handling characteristic.
The vapor deposition material for a barrier film of the present invention uses the SiOx of the present invention, and the SiOx vapor-deposited film formed using the SiOx is excellent in gas barrier properties. In addition, the negative electrode active material for a lithium-ion secondary battery of the present invention uses the SiOx of the present invention, and the lithium-ion secondary battery using the SiOx can maintain high initial efficiency.
A mixed pelletized raw material obtained by blending Si powder and SiO2 powder having a hydrogen gas content of 35 ppm and pelletizing was heated at 1100 to 1350° C., and the generated gaseous SiOx was precipitated on the inner periphery of the precipitation substrate and cooled in an Ar atmosphere until the temperature of the precipitation substrate reached to room temperature, thereafter released to open air, to collect and pulverize SiOx. Subsequently, the collected SiOx and a given amount of ethanol (special grade chemical) were put into an autoclave and subjected to treatment after collection for 5 hours, and then filtered and dried to produce SiOx. Table 1 shows the temperature of the inner periphery of the precipitation substrate (precipitation portion) and the pressure and temperature conditions of treatment after collection. In comparative examples shown in Table 1, the treatment after collection was not performed. The inventive examples each, shown in Table 1, is the one in which the amount of the generated H2O gas detected in a temperature range of 200 to 800° C. in a temperature-programmed desorption gas analysis satisfies the conditions specified in the present invention and comparative examples each is the one that does not satisfy the conditions.
The amount of the generated H2O gas detected in a temperature range of 200 to 800° C. in a temperature-programmed desorption gas analysis, the value x of SiOx, and Si peak intensity by X-ray diffraction for each of SiOx was investigated. Furthermore, the number of splashing generation when the SiOx was used as a vapor deposition material for a barrier film, and the initial efficiency of a secondary battery when used as a negative electrode active material for a lithium-ion secondary battery were investigated. Incidentally, for the purpose of comparison, the same investigation was performed for the SiOx in which the treatment after collection was not performed.
The investigation method is as described below.
Amount of generated H2O gas detected in a temperature range of 200 to 800° C. in a temperature-programmed desorption gas analysis:
SiO was heated from room temperature at a heating rate of 0.5° C./s using a temperature-programmed desorption gas analysis apparatus, and the amount was measured by mass fragment method.
Value x of SiOx:
The amount of O (oxygen) of SiOx was determined by an oxygen-in-ceramic analysis apparatus (fusion method under inert gas flow), and SiOx was dissolved, thereafter, the amount of Si of SiOx was determined by ICP emission spectrochemical analysis (inductively-coupled high-frequency plasma emission spectrometry), and the value x of SiOx was calculated from the above two determined values.
Si Peak Intensity by X-Ray Diffraction:
The relationship between the incidence angle and diffraction intensity of X-ray was investigated using powder X-ray diffractometer. The SiOx prepared by the above method was pulverized to an average particle size of 20 μm and used as a sample. The deteimination conditions of X-ray diffraction shown in Table 2 were used. Moreover, the ratio of the value of P1−P2, which is obtained by subtracting the base intensity P2 from the peak intensity P1 at a Si peak point, to the base intensity P2 (intensity ratio (P1−P2)/P2) was obtained. The method of obtaining this intensity ratio is as being afore-mentiond.
Number of Splashing Generation
Using an ion plating apparatus, the number of splashing generated in a case where electron beam was emitted with an output of 300 W and an initial pressure of 4×10−4 Pa for 60 seconds when the sublimated SiO was deposited on a precipitation substrate.
Initial Efficiency of Lithium-Ion Secondary Battery
A lithium-ion secondary battery using SiOx as a negative electrode active material was prepared, and then charged and discharged with a specific electric current, to obtain an initial efficiency.
Table 1 described above collectively shows the physical properties of the resulting SiOx and the effect in a case where this SiOx is used as a vapor deposition material for a barrier film or negative electrode active material for a lithium-ion secondary battery (the number of splashing generation and the initial efficiency), together with the production conditions of SiOx.
As shown in the above-mentioned Table 1, the generation of splashing was hardly found in any of the SiOx of Inventive Examples 1 to 4 that satisfy the conditions specified in the present invention, and the initial efficiency was also good as 60% or more.
On the other hand, the generation of splashing was found in the SiO of Comparative Examples 1 and 2 that were out of the conditions specified in the present invention regarding the amount of the generated H2O gas detected in a temperature range of 200 to 800° C. in a temperature-programmed desorption gas analysis and in which the treatment after collection during production is not performed, and the initial efficiency was also low.
When the SiOx of the present invention is used as a vapor deposition material for a barrier film, the generation of splashing can be suppressed in forming a SiOx vapor-deposited film, and a vapor-deposited film having excellent gas barrier properties, without pinholes and other defects, can be formed. In addition, in case of being used as a negative electrode active material for a lithium-ion secondary battery, high initial efficiency of the secondary battery can be maintained. Accordingly, the SiOx of the present invention can be suitably utilized in various industrial fields such as food processing, medicinal product production, and further, production of a lithium-ion secondary battery.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-235365 | Oct 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/005927 | 10/4/2010 | WO | 00 | 3/28/2012 |
