WO2017110040A1

WO2017110040A1 - Negative electrode active material, negative electrode, lithium ion secondary battery, manufacturing method for negative electrode active material, and manufacturing method for lithium ion secondary battery

Info

Publication number: WO2017110040A1
Application number: PCT/JP2016/004972
Authority: WO
Inventors: 貴一廣瀬; 博道加茂; 拓史松野; 玲子酒井
Original assignee: 信越化学工業株式会社
Priority date: 2015-12-24
Filing date: 2016-11-28
Publication date: 2017-06-29
Also published as: JP6680531B2; TW201740600A; JP2017117656A

Abstract

The present invention is a negative electrode active material including negative electrode active material particles, characterized in that: the negative electrode active material particles contain a silicon compound represented by SiO_x (0.5≤x≤1.6); when the negative electrode active material including the negative electrode active material particles is used for the negative electrode of a secondary battery including metal lithium as the counter electrode, in a state where a cycle of 0-V constant-current constant-voltage charging and 1.2-V constant-current discharging of the secondary battery is repeated X times (X>0), and subsequently, 0-V constant-current constant-voltage charging of the secondary battery (wherein, the charging is terminated after elapse of 60 hours since 0 V is reached) is further performed, the negative electrode active material after the charging termination has peaks within a range of 25-55 ppm and a range of 0-3 ppm, in terms of a chemical shift value, obtained from a ⁷Li-MAS-NMR spectrum. Thus, provided is a negative electrode active material which can, when being used as a negative electrode active material for a secondary battery, increase the battery capacity and improve the cycle characteristics.

Description

Negative electrode active material, negative electrode, lithium ion secondary battery, method for producing negative electrode active material, and method for producing lithium ion secondary battery

The present invention relates to a negative electrode active material, a negative electrode, a lithium ion secondary battery, a method for producing a negative electrode active material, and a method for producing a lithium ion secondary battery.

In recent years, small electronic devices such as mobile terminals have become widespread, and further downsizing, weight reduction, and long life have been strongly demanded. In response to such market demands, development of secondary batteries capable of obtaining a high energy density, in particular, being small and light is underway. This secondary battery is not limited to a small electronic device, but is also considered to be applied to a large-sized electronic device represented by an automobile or the like, or an electric power storage system represented by a house.

Among them, lithium ion secondary batteries are highly expected because they are small in size and easy to increase in capacity, and can obtain higher energy density than lead batteries and nickel cadmium batteries.

The above lithium ion secondary battery includes a positive electrode, a negative electrode, and a separator together with an electrolyte, and the negative electrode includes a negative electrode active material involved in a charge / discharge reaction.

As this negative electrode active material, while a carbon-based active material is widely used, further improvement in battery capacity is required due to recent market demand. In order to improve battery capacity, use of silicon as a negative electrode active material has been studied. This is because the theoretical capacity of silicon (4199 mAh / g) is 10 times or more larger than the theoretical capacity of graphite (372 mAh / g), so that significant improvement in battery capacity can be expected. The development of a siliceous material as a negative electrode active material has been examined not only for silicon itself but also for compounds represented by alloys and oxides. In addition, the active material shape has been studied from a standard coating type in a carbon-based active material to an integrated type directly deposited on a current collector.

However, when silicon is used as the negative electrode active material as the main raw material, the negative electrode active material expands and contracts during charge / discharge, and therefore, it tends to break mainly near the surface of the negative electrode active material. Further, an ionic material is generated inside the active material, and the negative electrode active material is easily broken. When the negative electrode active material surface layer is cracked, a new surface is generated thereby increasing the reaction area of the active material. At this time, a decomposition reaction of the electrolytic solution occurs on the new surface, and a coating that is a decomposition product of the electrolytic solution is formed on the new surface, so that the electrolytic solution is consumed. For this reason, the cycle characteristics are likely to deteriorate.

So far, in order to improve the initial efficiency and cycle characteristics of the battery, various studies have been made on the negative electrode material for lithium ion secondary batteries mainly composed of a siliceous material and the electrode configuration.

Specifically, for the purpose of obtaining good cycle characteristics and high safety, silicon and amorphous silicon dioxide are simultaneously deposited using a vapor phase method (see, for example, Patent Document 1). Further, in order to obtain a high battery capacity and safety, a carbon material (electron conductive material) is provided on the surface layer of the silicon oxide particles (see, for example, Patent Document 2). Furthermore, in order to improve cycle characteristics and obtain high input / output characteristics, an active material containing silicon and oxygen is produced, and an active material layer having a high oxygen ratio in the vicinity of the current collector is formed ( For example, see Patent Document 3). Further, in order to improve the cycle characteristics, oxygen is contained in the silicon active material, the average oxygen content is 40 at% or less, and the oxygen content is increased at a location close to the current collector. (For example, refer to Patent Document 4).

Further, Si phase, (for example, see Patent Document 5) by using a nanocomposite containing SiO 2, _M y _O metal oxide in order to improve the initial charge and discharge efficiency. In order to improve cycle characteristics, SiO _x (0.8 ≦ x ≦ 1.5, particle size range = 1 μm to 50 μm) and a carbon material are mixed and fired at a high temperature (see, for example, Patent Document 6). In order to improve cycle characteristics, the molar ratio of oxygen to silicon in the negative electrode active material is set to 0.1 to 1.2, and the difference between the maximum and minimum molar ratios in the vicinity of the active material and current collector interface The active material is controlled within a range of 0.4 or less (see, for example, Patent Document 7). Further, in order to improve battery load characteristics, a metal oxide containing lithium is used (see, for example, Patent Document 8). Further, in order to improve cycle characteristics, a hydrophobic layer such as a silane compound is formed on the surface layer of the siliceous material (see, for example, Patent Document 9). Further, in order to improve cycle characteristics, conductivity is imparted by using silicon oxide and forming a graphite film on the surface layer (see, for example, Patent Document 10). In Patent Document 10, with respect to the shift value obtained from the RAMAN spectrum for graphite coating, with broad peaks appearing at 1330 cm ^-1 and 1580 cm ^-1, their intensity ratio _I 1330 _{/ I 1580} is _{1.5 <I 1330} / _I ₁₅₈₀ has become a <3. In addition, particles having a silicon microcrystalline phase dispersed in silicon dioxide are used in order to improve high battery capacity and cycle characteristics (see, for example, Patent Document 11). Further, in order to improve overcharge and overdischarge characteristics, silicon oxide in which the atomic ratio of silicon and oxygen is controlled to 1: y (0 <y <2) is used (see, for example, Patent Document 12).

JP 2001-185127 A JP 2002-042806 A JP 2006-164955 A JP 2006-114454 A JP 2009-070825 A JP 2008-282819 A JP 2008-251369 A JP 2008-177346 A JP 2007-234255 A JP 2009-212074 A JP 2009-205950 A Japanese Patent No. 2,997,741

As described above, in recent years, small mobile devices typified by electronic devices have been improved in performance and multifunction, and lithium ion secondary batteries, which are the main power sources, are required to have an increased battery capacity. Yes. As one method for solving this problem, development of a lithium ion secondary battery composed of a negative electrode using a siliceous material as a main material is desired. Moreover, the lithium ion secondary battery using a siliceous material is desired to have cycle characteristics similar to those of a lithium ion secondary battery using a carbon-based active material. However, a negative electrode active material that exhibits the same cycle stability as a lithium ion secondary battery using a carbon-based active material has not been proposed.

The present invention has been made in view of the above problems, and when used as a negative electrode active material for a secondary battery, the negative electrode active material capable of increasing battery capacity and improving cycle characteristics, An object is to provide a negative electrode having a negative electrode active material layer including a negative electrode active material, and a lithium ion secondary battery using the negative electrode. Moreover, it aims at providing the manufacturing method of the negative electrode active material which can increase battery capacity and can improve cycling characteristics. Moreover, it aims at providing the manufacturing method of the lithium ion secondary battery using such a negative electrode active material.

In order to achieve the above object, the present invention provides a negative electrode active material including negative electrode active material particles, wherein the negative electrode active material particles are silicon represented by SiO _x (0.5 ≦ x ≦ 1.6). Containing a compound,
The negative electrode active material containing the negative electrode active material particles is used for a negative electrode of a secondary battery having metallic lithium as a counter electrode, and a cycle of 0 V constant current constant voltage charging and 1.2 V constant current discharge of the secondary battery is performed X times ( After repeating X ≧ 0), in the state where the secondary battery was further charged with 0V constant current and constant voltage (however, after 60 hours from 0V, the charge was stopped), the negative electrode active material after the end of charge was ⁷ Disclosed is a negative electrode active material characterized by having a peak in the range of 25 to 55 ppm and the range of 0 to 3 ppm as a chemical shift value obtained from a Li-MAS-NMR spectrum.

Thus, the negative electrode active material includes negative electrode active material particles containing a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6, hereinafter also referred to as silicon oxide), and the above-mentioned As long as it has the above two types of peaks after the end of charging, when this negative electrode active material is used as the negative electrode active material of a lithium ion secondary battery, it has a high battery capacity and good cycle characteristics. It is done.

Further, it is preferable that the peak in the range of 25 to 55 ppm appears within 49 times of the X.

With such a negative electrode active material, when this negative electrode active material is used as the negative electrode active material of a lithium ion secondary battery, the time (number of cycles) until the secondary battery is stabilized should be reduced. Can do.

Further, it is preferable that the peak in the range of 0 to 3 ppm appears within 9 times of the X.

With such a negative electrode active material, when this negative electrode active material is used as the negative electrode active material of a lithium ion secondary battery, the time until the stable Li compound is generated inside the negative electrode active material particles (number of cycles) ) Can be reduced.

Further, it is preferable that the peak in the range of 25 to 55 ppm and the peak in the range of 0 to 3 ppm appear when the X is 0 times.

With such a negative electrode active material, when this negative electrode active material is used as the negative electrode active material of a lithium ion secondary battery, the time until the secondary battery stabilizes and the inside of the negative electrode active material particles are stabilized. The time until the Li compound is produced can be further reduced.

In addition, it is preferable that the peak in the range of 25 to 55 ppm is reduced while repeating the cycle of 0V constant current constant voltage charging and 1.2V constant current discharge within 49 times.

Such a negative electrode active material stabilizes the bulk state of silicon oxide by repeating Li insertion and desorption.

The negative electrode active material has a half-value width (2θ) of a diffraction peak caused by an Si (111) crystal plane obtained by X-ray diffraction of 1.2 ° or more and a crystallite size corresponding to the crystal plane. Is preferably 7.5 nm or less.

When the negative electrode active material contains a silicon oxide having the crystallinity of the Si crystallite as described above, when such a negative electrode active material is used as the negative electrode active material of a lithium ion secondary battery, better cycle characteristics In addition, initial charge / discharge characteristics can be obtained.

The median diameter of the negative electrode active material particles is preferably 0.5 μm or more and 20 μm or less.

When the median diameter of the negative electrode active material particles is within the above range, better cycle characteristics can be obtained when a negative electrode active material containing such negative electrode active material particles is used as the negative electrode active material of a lithium ion secondary battery. In addition, initial charge / discharge characteristics can be obtained.

The negative electrode active material particles preferably include a carbon material in the surface layer portion.

As described above, since the negative electrode active material particles include a carbon material in the surface layer portion, conductivity can be improved. Therefore, the negative electrode active material including such negative electrode active material particles is used as a negative electrode active material for a lithium ion secondary battery. When used as a substance, battery characteristics can be improved.

The average thickness of the carbon material is preferably 1 nm or more and 5000 nm or less.

If the average thickness of the carbon material to be coated is 1 nm or more, improved conductivity is obtained. If the average thickness of the carbon material to be coated is 5000 nm or less, the negative electrode active material containing such negative electrode active material particles is lithium. When used as a negative electrode active material for an ion secondary battery, a decrease in battery capacity can be suppressed.

Furthermore, the present invention provides a negative electrode comprising the negative electrode active material of the present invention.

With such a negative electrode, when this negative electrode is used as a negative electrode of a lithium ion secondary battery, it has a high battery capacity and good cycle characteristics.

The negative electrode includes a negative electrode active material layer containing the negative electrode active material,
A negative electrode current collector,
The negative electrode active material layer is formed on the negative electrode current collector,
The negative electrode current collector preferably contains carbon and sulfur, and the content of both is 100 mass ppm or less.

Thus, the negative electrode current collector constituting the negative electrode includes carbon and sulfur as described above, so that deformation of the negative electrode during charging can be suppressed.

Furthermore, the present invention provides a lithium ion secondary battery using the negative electrode of the present invention as the negative electrode.

A lithium ion secondary battery using such a negative electrode has a high capacity and good cycle characteristics.

Furthermore, in the present invention, a method for producing a negative electrode active material containing negative electrode active material particles,
Preparing negative electrode active material particles containing a silicon compound represented by the general formula SiO _x (0.5 ≦ x ≦ 1.6);
Producing a secondary battery having a negative electrode containing a negative electrode active material containing the negative electrode active material particles and a counter electrode made of metallic lithium;
After repeating the cycle of 0V constant current and constant voltage charge and 1.2V constant current discharge of the secondary battery X times (X ≧ 0), the secondary battery is further charged with 0V constant current and constant voltage (however, it becomes 0V). A process of stopping charging after 60 hours),
Measuring the negative electrode active material by ⁷ Li-MAS-NMR in the state of charge termination;
And a step of selecting a negative electrode active material obtained from the ⁷ Li-MAS-NMR spectrum, having a chemical shift value in the range of 25 to 55 ppm and a peak in the range of 0 to 3 ppm. A manufacturing method is provided.

By selecting the negative electrode active material in this way and producing the negative electrode active material, when used as the negative electrode active material of the lithium ion secondary battery, the negative electrode active material having high capacity and good cycle characteristics is obtained. Can be manufactured.

Furthermore, in the present invention, a negative electrode is produced using the negative electrode active material produced by the method for producing a negative electrode active material of the present invention, and a lithium ion secondary battery is produced using the produced negative electrode. A method for manufacturing an ion secondary battery is provided.

This manufacturing method can manufacture a lithium ion secondary battery having high capacity and good cycle characteristics by using the negative electrode active material selected as described above.

As described above, when the negative electrode active material of the present invention is used as the negative electrode active material of a lithium ion secondary battery, high capacity and good cycle characteristics can be obtained. Moreover, if it is the manufacturing method of the negative electrode active material of this invention, the negative electrode active material for lithium ion secondary batteries which has favorable cycling characteristics can be manufactured.

⁷ is a ⁷ Li-MAS-NMR spectrum measured in Example 1-3 of the present invention. It is sectional drawing which shows an example of a structure of the negative electrode of this invention. It is an exploded view which shows an example of a structure of the lithium ion secondary battery (laminate film type) of this invention. ⁷ is a ⁷ Li-MAS-NMR spectrum measured using a general silicon simple substance negative electrode containing silicon simple substance as a negative electrode active material.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited thereto.

As described above, as one method for increasing the battery capacity of a lithium ion secondary battery, it has been studied to use a negative electrode using a siliceous material as a main material as a negative electrode of a lithium ion secondary battery. The lithium ion secondary battery using this siliceous material is expected to have cycle characteristics similar to those of a lithium ion secondary battery using a carbon-based active material. However, a lithium-ion secondary battery using a carbon-based active material is desired. Has not yet been proposed for a negative electrode active material exhibiting the same cycle characteristics.

Accordingly, the present inventors have made extensive studies on a negative electrode active material that can provide good cycle characteristics when used as a negative electrode of a lithium ion secondary battery. As a result, the negative electrode active material includes negative electrode active material particles, and the negative electrode active material particles contain a silicon compound represented by SiO _x (0.5 ≦ x ≦ 1.6). A negative electrode active material containing particles is used for a negative electrode of a secondary battery having metallic lithium as a counter electrode, and a cycle of 0 V constant current constant voltage charge and 1.2 V constant current discharge of the secondary battery is X times (X ≧ 0). After the repetition, in the state where the secondary battery was further charged with 0V constant current and constant voltage (however, the charging was terminated 60 hours after the voltage became 0V), the negative electrode active material after the termination of charging was ⁷ Li-MAS-NMR. High battery capacity and good cycle characteristics can be obtained when a negative electrode active material characterized by having a peak in the range of 25 to 55 ppm and 0 to 3 ppm as the chemical shift value obtained from the spectrum is obtained. Heading the door, the present invention has been accomplished.

<Negative electrode>
First, the negative electrode (negative electrode for nonaqueous electrolyte secondary battery) will be described. FIG. 2 is a cross-sectional view showing an example of the configuration of the negative electrode (hereinafter also referred to as negative electrode) of the present invention.

[Configuration of negative electrode]
As shown in FIG. 2, the negative electrode 10 is configured to have a negative electrode active material layer 12 on a negative electrode current collector 11. Further, the negative electrode active material layer 12 may be provided on both surfaces or only one surface of the negative electrode current collector 11. Furthermore, the negative electrode current collector 11 may be omitted as long as the negative electrode active material of the present invention is used.

[Negative electrode current collector]
The negative electrode current collector 11 is an excellent conductive material and is made of a material that is excellent in mechanical strength. Examples of the conductive material that can be used for the negative electrode current collector 11 include copper (Cu) and nickel (Ni). The conductive material is preferably a material that does not form an intermetallic compound with lithium (Li).

The negative electrode current collector 11 preferably contains carbon (C) or sulfur (S) in addition to the main element. This is because the physical strength of the negative electrode current collector 11 is improved. In particular, when the negative electrode has an active material layer that expands during charging, if the current collector contains the above-described element, there is an effect of suppressing electrode deformation including the current collector. The content of each of the above contained elements is not particularly limited, but is preferably 100 ppm by mass or less. This is because a higher deformation suppressing effect can be obtained. Such a deformation suppressing effect can further improve the cycle characteristics.

Further, the surface of the negative electrode current collector 11 may be roughened or may not be roughened. The roughened negative electrode current collector is, for example, a metal foil subjected to electrolytic treatment, embossing treatment, or chemical etching treatment. The non-roughened negative electrode current collector is, for example, a rolled metal foil.

[Negative electrode active material layer]
The negative electrode active material layer 12 contains the negative electrode active material of the present invention capable of occluding and releasing lithium ions, and from the viewpoint of battery design, further, other materials such as a negative electrode binder (binder) and a conductive aid. May be included.

The negative electrode active material of the present invention includes negative electrode active material particles. The negative electrode active material particles have a core part capable of inserting and extracting lithium ions. When the negative electrode active material particles include a carbon material in the surface layer portion, the negative electrode active material particles further have a carbon coating portion from which electrical conductivity is obtained.

The negative electrode active material particles contain a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6). The composition of the silicon compound is preferably such that x is close to 1. This is because stable battery characteristics can be obtained. Note that the composition of the silicon compound in the present invention does not necessarily mean a purity of 100%, and may contain a trace amount of impurity elements.

The negative electrode active material of the present invention uses the negative electrode active material for a negative electrode of a secondary battery having metallic lithium as a counter electrode, and a cycle of 0 V constant current constant voltage charging and 1.2 V constant current discharge of the secondary battery (hereinafter, 0V-1.2V cycle) is repeated X times (X ≧ 0), and then the secondary battery is charged with 0V constant current and constant voltage (however, after 60 hours from 0V, the charging is terminated) (hereinafter, 60V The negative electrode active material after charge termination has peaks in the range of 25 to 55 ppm and in the range of 0 to 3 ppm as chemical shift values obtained from the ⁷ Li-MAS-NMR spectrum. It is characterized by. Hereinafter, the period from 0V-1.2V cycle to 60-hour charging is also referred to as charging condition A.

First, the details of the charging condition A will be described. First, 0V constant current / constant voltage charging (0VCCCV) is a method of manufacturing a secondary battery using lithium as a counter electrode, and then charging in a constant current (current density: 0.5 mA / cm ² ) mode up to 0V. It means that charging is terminated after the voltage mode is reached and the current density reaches 0.1 mA / cm ² . Next, 1.2V constant current discharge means discharging in a constant current (current density: 0.5 mA / cm ² ) mode, and stopping the discharge after the potential reaches 1.2V. Next, 60-hour charging means charging in a constant current (current density: 0.5 mA / cm ² ) mode to 0 V, switching from 0 V to a constant voltage mode, and stopping charging after 60 hours have elapsed since becoming 0 V. Means.

As described above, the negative electrode active material of the present invention is an active material from which the above two types of peaks can be obtained when charging is performed under the above charging condition A. As described above, if the negative electrode active material includes negative electrode active material particles containing a silicon compound and has the above two types of peaks after the termination of the charge, the negative electrode active material Is used as a negative electrode active material of a lithium ion secondary battery, it has a high battery capacity and good cycle characteristics.

Here, it is assumed that the peak in the range of 25 to 55 ppm represents the presence of Li—Si bond. The negative electrode active material from which this peak is obtained tends to stabilize the bulk state of silicon oxide by repeating Li insertion and desorption. Therefore, when the negative electrode active material from which this peak is obtained is used as the negative electrode active material of a lithium ion secondary battery, stable battery characteristics, particularly stable cycle characteristics can be obtained.

On the other hand, the peak in the range of 0 to 3 ppm is presumed to indicate the presence of a Li silicate layer (Li—O bond). The negative electrode active material from which this peak is obtained tends to generate a stable Li compound inside the negative electrode active material particles by repeating Li insertion and desorption. Therefore, in the negative electrode active material from which this peak is obtained, Li easily diffuses in the bulk of the silicon oxide. Therefore, the negative electrode active material from which this peak is obtained becomes a stable battery material and can improve cycle characteristics.

The number of times of X in the 0V-1.2V cycle is not particularly limited. For example, the upper limit of X can be 99. That is, the range of X can be 0 ≦ X ≦ 99. The range of X is more preferably 0 ≦ X ≦ 49, further preferably 0 ≦ X ≦ 9, and particularly preferably X = 0.

When the upper limit of X is 99, after the 0V-1.2V cycle is performed 0 times or more and 99 times or less and then charged for 60 hours, the negative electrode active material after charge termination is ⁷ Li-MAS-NMR spectrum. As long as it has a chemical shift value in the range of 25 to 55 ppm and a peak in the range of 0 to 3 ppm. In this case, for example, after performing the 0V-1.2V cycle 19 times, these peaks may appear during the 60-hour charge of the 20th cycle, or after performing the 0V-1.2V cycle 49 times, These peaks may appear during 60 hours of charge at the 50th cycle.

In the present invention, a peak in the range of 0 to 3 ppm may appear first, and then a peak in the range of 25 to 55 ppm may appear in addition to this peak. For example, a peak in the range of 0 to 3 ppm appears when charging for 60 hours in the first cycle (ie, X = 0), and a range of 0 to 3 ppm when charging for 60 hours in the 10th cycle (ie, X = 9). A peak in the range of 25 to 55 ppm may be expressed together with the above peak.

In the present invention, it is particularly preferable that two types of peaks appear within the following number of times.

First, it is preferable that the peak in the range of 25 to 55 ppm is expressed within 49 times of X.

With such a negative electrode active material, when this negative electrode active material is used as the negative electrode active material of a lithium ion secondary battery, the time (number of cycles) until the secondary battery is stabilized should be reduced. Can do. Thereby, the cycle deterioration rate at the initial stage of the charge / discharge cycle is further reduced, and the cycle characteristics are further improved. A secondary battery having such a negative electrode active material has stable cycle characteristics.

In addition, it is preferable that the peak in the range of 0 to 3 ppm appears within 9 times of X.

With such a negative electrode active material, when this negative electrode active material is used as the negative electrode active material of a lithium ion secondary battery, the time until the stable Li compound is generated inside the negative electrode active material particles (number of cycles) ) Can be reduced. Thereby, Li diffusion in the bulk of the silicon oxide can be made easier.

In addition, it is preferable that X in the peak in the range of 25 to 55 ppm and the peak in the range of 0 to 3 ppm appears when X is 0 times.

In addition, it is preferable that the peak in the range of 25 to 55 ppm decreases while repeating the cycle of 0 V constant current constant voltage charging and 1.2 V constant current discharge within 49 times. That is, in the negative electrode active material of the present invention, it is preferable that a peak in the range of 25 to 55 ppm appears and decreases while the 0V-1.2V cycle is repeated within 49 times. In particular, a peak in the range of 25 to 55 ppm is preferably expressed and disappeared. As a specific example of this aspect, a peak in the range of 25 to 55 ppm appears when charging for 60 hours in the first cycle (ie, X = 0), and when charging for 60 hours in the 10th cycle (ie, X = 9). An embodiment in which the peak in the range of 25 to 55 ppm is reduced.

Such a negative electrode active material stabilizes the bulk state of silicon oxide by repeating Li insertion and desorption. That is, by repeating Li insertion and desorption, the state of the active material becomes a state suitable for charging and discharging.

Particularly, in the negative electrode active material of the present invention, in the repetition of 0V-1.2V cycle, not only the peak in the range of 25 to 55 ppm appears and decreases (especially disappears), but this peak also shows 0V-1.2V cycle. It is preferable to gradually shift in the direction close to 0 ppm while repeating the above. Such a negative electrode active material can create a more stable bulk state by repeating Li insertion and desorption.

Although the reason why the negative electrode active material exhibiting a peak in the range of 25 to 55 ppm as described above improves the cycle characteristics has not been completely elucidated, the battery was charged at least under the above charging condition A. It is clear that the active material in which the above two types of peaks are obtained improves the cycle characteristics in some cases.

Moreover, the negative electrode active material has a half-width (2θ) of a diffraction peak due to the Si (111) crystal plane obtained by X-ray diffraction of 1.2 ° or more, and a crystallite size corresponding to the crystal plane is It is preferable that it is 7.5 nm or less.

The lower the silicon crystallinity of the silicon oxide, the better, and the Si crystallite in the silicon oxide has the above-mentioned crystallinity, so that the negative electrode active material containing such silicon oxide can be used as a negative electrode active material for a lithium ion secondary battery. When used as a substance, better cycle characteristics and initial charge / discharge characteristics can be obtained.

Median size of the anode active material particles (D _50: particle diameter when the cumulative volume is 50%) is not particularly limited, it is preferably 0.5μm or more 20μm or less. This is because, if the median diameter is in the above range, lithium ions are easily occluded and released during charging and discharging, and the particles are difficult to break. If the median diameter is 0.5 μm or more, the surface area per mass can be reduced, and an increase in battery irreversible capacity can be suppressed. On the other hand, when the median diameter is 20 μm or less, the particles are difficult to break, so that a new surface is difficult to appear.

Moreover, the average thickness of the carbon material is preferably 1 nm or more and 5000 nm or less.

The average thickness of the carbon material can be calculated by the following procedure, for example. First, the negative electrode active material is observed with a TEM (transmission electron microscope) at an arbitrary magnification. This magnification is preferably a magnification capable of visually confirming the thickness of the carbon material so that the thickness can be measured. Subsequently, the thickness of the carbon material is measured at any 15 points. In this case, it is preferable to set the measurement position widely and randomly without concentrating on a specific place as much as possible. Finally, the average value of the thicknesses of the 15 carbon materials is calculated.

¡The coverage of the carbon material is not particularly limited, but is preferably as high as possible. A coverage of 30% or more is preferable because electric conductivity is further improved. The method for coating the carbon material is not particularly limited, but a sugar carbonization method and a pyrolysis method of hydrocarbon gas are preferable. This is because the coverage can be improved.

Further, as the negative electrode binder contained in the negative electrode active material layer 12, for example, one or more of polymer materials, synthetic rubbers, and the like can be used. Examples of the polymer material include polyvinylidene fluoride, polyimide, polyamideimide, aramid, polyacrylic acid, lithium polyacrylate, and carboxymethylcellulose. Examples of the synthetic rubber include styrene butadiene rubber, fluorine rubber, and ethylene propylene diene.

As the negative electrode conductive additive, for example, one or more carbon materials such as carbon black, acetylene black, graphite, ketjen black, carbon nanotube, and carbon nanofiber can be used.

The negative electrode active material layer 12 may contain a carbon-based active material in addition to the negative electrode active material (silicon-based active material) of the present invention. As a result, the electrical resistance of the negative electrode active material layer 12 can be reduced and the expansion stress associated with charging can be reduced. Examples of the carbon-based active material include pyrolytic carbons, cokes, glassy carbon fibers, organic polymer compound fired bodies, carbon blacks, and the like.

The negative electrode active material layer 12 is formed by, for example, a coating method. The coating method is a method in which a silicon-based active material and the above-described binder, etc., and a conductive assistant and a carbon-based active material are mixed as necessary, and then dispersed in an organic solvent or water and applied.

[Production method of negative electrode]
The negative electrode 10 can be manufactured, for example, by the following procedure. First, the manufacturing method of the negative electrode active material used for a negative electrode is demonstrated. First, negative electrode active material particles containing a silicon compound represented by the general formula SiO _x (0.5 ≦ x ≦ 1.6) are prepared. Next, a secondary battery having a negative electrode including a negative electrode active material including the negative electrode active material particles and a counter electrode made of metallic lithium is manufactured. Next, after repeating the cycle of 0 V constant current constant voltage charging and 1.2 V constant current discharging of the secondary battery thus manufactured X times (X ≧ 0), the secondary battery was further subjected to 0 V constant current. Constant voltage charging (however, charging is terminated 60 hours after reaching 0V) is performed. Next, the negative electrode active material is measured by ⁷ Li-MAS-NMR in a state where charging is terminated. Next, a negative electrode active material having peaks in the range of 25 to 55 ppm and in the range of 0 to 3 ppm as chemical shift values obtained from the spectrum of ⁷ Li-MAS-NMR is selected.

The negative electrode active material particles containing silicon oxide (SiO _x : 0.5 ≦ x ≦ 1.6) can be produced by the following method, for example. First, a raw material for generating silicon oxide gas is heated in a temperature range of 900 ° C. to 1600 ° C. under reduced pressure in the presence of an inert gas to generate silicon oxide gas. At this time, the raw material can be a mixture of metal silicon powder and silicon dioxide powder. Considering the surface oxygen of the metal silicon powder and the presence of a trace amount of oxygen in the reaction furnace, the mixing molar ratio is preferably in the range of 0.8 <metal silicon powder / silicon dioxide powder <1.3.

Next, the generated silicon oxide gas is solidified and deposited on the adsorption plate (deposition plate). Next, a silicon oxide deposit is taken out in a state where the temperature in the reactor is lowered to 100 ° C. or lower, and pulverized and powdered using a ball mill, a jet mill or the like. As described above, negative electrode active material particles can be produced.

Note that the Si crystallites in the negative electrode active material particles are obtained by changing the vaporization temperature of the raw material that generates the silicon oxide gas, the deposition plate temperature, the injection amount of the gas (inert gas, reducing gas) with respect to the deposition flow of the silicon oxide gas, or It can be controlled by the type, the heat treatment after the production of the negative electrode active material particles, or the temperature or time when depositing the carbon material described later.

Note that the number of cycles in which the peak in the range of 25 to 55 ppm and the peak in the range of 0 to 3 ppm appear is the temperature of the deposition plate at the time of silicon oxide deposition, the heating temperature or time at which the carbon material is deposited by CVD described later, or It can be controlled by pulverization conditions of silicon oxide deposits. For example, when the temperature of the deposition plate during silicon oxide deposition is increased, these peaks (particularly, peaks in the range of 25 to 55 ppm) can be easily obtained. However, if this temperature is too high, the onset of these peaks may be delayed.

Next, a carbon material is formed on the surface layer of the prepared negative electrode active material particles. However, this step is not essential. As a method for generating the carbon material layer, a thermal decomposition CVD method is desirable. An example of a method for generating a carbon material layer by pyrolytic CVD will be described below.

First, negative electrode active material particles are set in a furnace. Next, hydrocarbon gas is introduced into the furnace to raise the temperature in the furnace. The decomposition temperature is not particularly limited, but is preferably 1200 ° C. or lower, and more preferably 950 ° C. or lower. By setting the decomposition temperature to 1200 ° C. or lower, unintended disproportionation of the negative electrode active material particles can be suppressed. After raising the furnace temperature to a predetermined temperature, a carbon material is generated in the surface layer portion of the negative electrode active material particles. The hydrocarbon gas used as the raw material for the carbon material is not particularly limited, but it is desirable that n ≦ 3 in the C _n H _m composition. If n ≦ 3, the production cost can be reduced, and the physical properties of the decomposition product can be improved.

Thus, by covering the anode active material particles with the carbon material, the compound state inside the bulk can be made more uniform, the stability as the active material can be improved, and a higher effect can be obtained.

Next, a secondary battery having a negative electrode including a negative electrode active material including the negative electrode active material particles and a counter electrode made of metallic lithium is prepared. Here, as a specific example of the secondary battery for testing, a 2032 type coin battery is taken as an example.

First, a negative electrode used for a 2032 type coin battery is prepared. This negative electrode should just contain the negative electrode active material of this invention. For example, the negative electrode shown in FIG. The method for producing the negative electrode can be the same as the method for producing the negative electrode of the present invention. Also, a counter electrode made of metallic lithium is prepared. A specific example is a metal lithium foil having a thickness of 0.5 mm. Next, an electrolytic solution and a separator are prepared. Specific examples thereof are the same as those used for the secondary battery of the present invention described later.

Subsequently, the bottom pig of the 2032 type coin battery, the lithium foil, and the separator are stacked, and the electrolytic solution is injected, then the negative electrode and the spacer (for example, thickness 1.0 mm) are stacked, and the electrolytic solution is injected. Then, a 2032 type coin battery can be manufactured by lifting up the spring and the upper part of the coin battery in this order and caulking with an automatic coin cell caulking machine.

Next, after repeating the cycle of 0 V constant current constant voltage charging and 1.2 V constant current discharging of the secondary battery thus manufactured X times (X ≧ 0), the secondary battery was further subjected to 0 V constant current. Constant voltage charging (however, charging is terminated 60 hours after reaching 0V) is performed. The details of the charging condition A are as described above. The upper limit of X can be appropriately set according to the quality of the negative electrode active material to be produced (for example, 99), but is preferably as small as possible as described above.

Next, the negative electrode active material is measured by ⁷ Li-MAS-NMR in a state where charging is terminated. The negative electrode active material is measured by solid ⁷ Li-MAS-NMR. In this case, the apparatus to be used is not particularly limited, and examples thereof include a Bruker 700 NMR spectrometer. At this time, a 2.5 mm diameter rotor is used as the probe, the sample rotation speed is 16 kHz, and the measurement environment temperature is 25 ° C.

⁷ Li-MAS-NMR measurement procedure, taking as an example the case where a peak in the range of 0 to 3 ppm and a peak in the range of 25 to 55 ppm appear during 60 hours of charge in the first cycle (ie, X = 0) Will be explained.

In order to measure NMR of the negative electrode active material, usually about 20 coin batteries are required for each cycle. This is to ensure a sufficient amount of the negative electrode active material packed in the NMR rotor. Therefore, in the case of the above example, 20 coin batteries may be prepared. First, 20 negative electrodes including a negative electrode active material manufactured under the same manufacturing conditions are prepared. Next, 20 2032 type coin batteries having the negative electrode are produced, and charging of these coin batteries is performed under charging condition A (X = 0). Next, 20 coin batteries in a state where charging is terminated are disassembled in a glove box, and the negative electrode active material is peeled off from the negative electrode and packed in one NMR rotor. Next, the NMR measurement of the negative electrode active material thus packed in the NMR rotor is performed. By this measurement, it was confirmed that a peak in the range of 0 to 3 ppm and a peak in the range of 25 to 55 ppm were expressed, and the test was terminated. In addition, when two types of peaks appear in the second cycle, a total of 40 coin batteries are produced. With such a measurement method, it is possible to reliably determine at which cycle two types of peaks appear.

Next, a negative electrode active material having peaks in the range of 25 to 55 ppm and in the range of 0 to 3 ppm as chemical shift values obtained from the spectrum of ⁷ Li-MAS-NMR is selected. For example, when a negative electrode active material is produced under certain production conditions, NMR measurement of this negative electrode active material is performed, and it is confirmed that two types of peaks are obtained within 9 times, the negative electrode active material produced under the same production conditions. The negative electrode active material can be selected on the assumption that all two types of peaks are those in which two types of peaks are expressed within 9 times. In addition, by changing the conditions for producing the negative electrode active material or the carbon coating conditions and measuring each time with ⁷ Li-MAS-NMR, how long it takes to obtain two types of peaks in each production condition ( It can also be determined whether the number of cycles) is required.

In the negative electrode active material manufactured by such a manufacturing method, the silicon dioxide component present in the bulk of the silicon oxide changes into a stable Li compound upon reaction with Li, and the silicon-lithium bond state is a secondary battery. It will be induced to a state suitable for.

After mixing the negative electrode active material manufactured (selected) as described above with other materials such as a negative electrode binder and a conductive additive to form a negative electrode mixture, an organic solvent or water is added. Use slurry. Next, the negative electrode mixture slurry is applied to the surface of the negative electrode current collector 11 and dried to form the negative electrode active material layer 12. At this time, you may perform a heat press etc. as needed. A negative electrode can be produced as described above.

<Lithium ion secondary battery>
Next, the lithium ion secondary battery of the present invention will be described. The lithium ion secondary battery of the present invention uses the negative electrode of the present invention as a negative electrode. Here, as a specific example, a laminated film type lithium ion secondary battery is taken as an example.

[Configuration of laminated film type secondary battery]
A laminated film type lithium ion secondary battery 30 shown in FIG. 3 is one in which a wound electrode body 31 is accommodated mainly in a sheet-like exterior member 35. This wound body has a separator between a positive electrode and a negative electrode and is wound. There is also a case where a separator is provided between the positive electrode and the negative electrode and a laminate is accommodated. In both electrode bodies, the positive electrode lead 32 is attached to the positive electrode, and the negative electrode lead 33 is attached to the negative electrode. The outermost peripheral part of the electrode body is protected by a protective tape.

The positive and negative electrode leads are led out in one direction from the inside of the exterior member 35 to the outside, for example. The positive electrode lead 32 is formed of a conductive material such as aluminum, and the negative electrode lead 33 is formed of a conductive material such as nickel or copper.

The exterior member 35 is, for example, a laminate film in which a fusion layer, a metal layer, and a surface protective layer are laminated in this order. The laminate film is formed of two sheets so that the fusion layer faces the wound electrode body 31. The outer peripheral edges of the fusion layer of the film are bonded together with an adhesive or the like. The fused part is, for example, a film such as polyethylene or polypropylene, and the metal part is aluminum foil or the like. The protective layer is, for example, nylon.

An adhesion film 34 is inserted between the exterior member 35 and the positive and negative electrode leads to prevent intrusion of outside air. This material is, for example, polyethylene, polypropylene, or polyolefin resin.

[Positive electrode]
The positive electrode has, for example, a positive electrode active material layer on both surfaces or one surface of the positive electrode current collector, similarly to the negative electrode 10 of FIG.

The positive electrode current collector is made of, for example, a conductive material such as aluminum.

The positive electrode active material layer includes one or more positive electrode materials capable of occluding and releasing lithium ions, and includes other materials such as a binder, a conductive additive, and a dispersant depending on the design. You may go out. In this case, the details regarding the binder and the conductive additive can be the same as, for example, the negative electrode binder and the negative electrode conductive additive already described.

As the positive electrode material, a lithium-containing compound is desirable. Examples of the lithium-containing compound include a composite oxide composed of lithium and a transition metal element, or a phosphate compound having lithium and a transition metal element. Among these positive electrode materials, compounds having at least one of nickel, iron, manganese, and cobalt are preferable. The chemical formulas of these positive electrode materials are represented by, for example, Li _x M1O ₂ or Li _y M2PO ₄ . In the above chemical formula, M1 and M2 represent at least one or more transition metal elements, and the values of x and y vary depending on the battery charge / discharge state, but generally 0.05 ≦ x ≦ 1 .10, 0.05 ≦ y ≦ 1.10.

Examples of the composite oxide having lithium and a transition metal element include lithium cobalt composite oxide (Li _x CoO ₂ ) and lithium nickel composite oxide (Li _x NiO ₂ ). Examples of the phosphoric acid compound having a lithium iron phosphate compound (LiFePO ₄ ) and a lithium iron manganese phosphate compound (LiFe _1-u Mn _u PO ₄ (0 <u <1)). This is because if the above positive electrode material is used, a high battery capacity can be obtained and excellent cycle characteristics can be obtained.

[Negative electrode]
The negative electrode has the same configuration as the negative electrode 10 of FIG. 2 described above, and has, for example, negative electrode active material layers on both sides of the current collector. This negative electrode preferably has a negative electrode charge capacity larger than the electric capacity (charge capacity as a battery) obtained from the positive electrode active material agent. Thereby, precipitation of lithium metal on the negative electrode can be suppressed.

The positive electrode active material layer is provided on a part of both surfaces of the positive electrode current collector, and the negative electrode active material layer is also provided on a part of both surfaces of the negative electrode current collector. In this case, for example, the negative electrode active material layer provided on the negative electrode current collector is provided with a region where there is no opposing positive electrode active material layer. This is to perform a stable battery design.

In the region where the negative electrode active material layer and the positive electrode active material layer do not face each other, there is almost no influence of charge / discharge. Therefore, the state of the negative electrode active material layer is maintained as it is, so that the composition and the like of the negative electrode active material can be accurately examined with good reproducibility without depending on the presence or absence of charge / discharge.

[Separator]
The separator separates the positive electrode and the negative electrode, and allows lithium ions to pass through while preventing current short-circuiting due to bipolar contact. This separator is formed of, for example, a porous film made of synthetic resin or ceramic, and may have a laminated structure in which two or more kinds of porous films are laminated. Examples of the synthetic resin include polytetrafluoroethylene, polypropylene, and polyethylene.

[Electrolyte]
At least a part of the active material layer or the separator is impregnated with a liquid electrolyte (electrolytic solution). This electrolytic solution has an electrolyte salt dissolved in a solvent, and may contain other materials such as additives.

As the solvent, for example, a non-aqueous solvent can be used. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran and the like. Among these, it is desirable to use at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. This is because better characteristics can be obtained. In this case, the dissociation property and ion mobility of the electrolyte salt are improved by using a combination of a high viscosity solvent such as ethylene carbonate and propylene carbonate and a low viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. be able to.

In the case of using an alloy-based negative electrode, it is desirable to contain at least one of a halogenated chain carbonate or a halogenated cyclic carbonate as a solvent. Thereby, a stable film is formed on the surface of the negative electrode active material during charging and discharging, particularly during charging. Here, the halogenated chain carbonate ester is a chain carbonate ester having halogen as a constituent element (at least one hydrogen is replaced by halogen). The halogenated cyclic carbonate is a cyclic carbonate having halogen as a constituent element (that is, at least one hydrogen is replaced by a halogen).

The type of halogen is not particularly limited, but fluorine is preferred. This is because a film having a better quality than other halogens is formed. Further, the larger the number of halogens, the better. This is because the resulting coating is more stable and the decomposition reaction of the electrolyte is reduced.

Examples of the halogenated chain carbonate include fluoromethyl methyl carbonate and difluoromethyl methyl carbonate. Examples of the halogenated cyclic carbonate include 4-fluoro-1,3-dioxolane-2-one, 4,5-difluoro-1,3-dioxolane-2-one, and the like.

It is preferable that the solvent additive contains an unsaturated carbon bond cyclic carbonate. This is because a stable film is formed on the negative electrode surface during charging and discharging, and the decomposition reaction of the electrolytic solution can be suppressed. Examples of the unsaturated carbon-bonded cyclic ester carbonate include vinylene carbonate and vinyl ethylene carbonate.

It is also preferable that sultone (cyclic sulfonic acid ester) is included as a solvent additive. This is because the chemical stability of the battery is improved. Examples of sultone include propane sultone and propene sultone.

Furthermore, the solvent preferably contains an acid anhydride. This is because the chemical stability of the electrolytic solution is improved. Examples of the acid anhydride include propanedisulfonic acid anhydride.

The electrolyte salt can contain, for example, any one or more of light metal salts such as lithium salts. Examples of the lithium salt include lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ).

The content of the electrolyte salt is preferably 0.5 mol / kg or more and 2.5 mol / kg or less with respect to the solvent. This is because high ion conductivity is obtained.

[Production method of laminated film type lithium ion secondary battery]
First, a positive electrode is manufactured using the positive electrode material described above. First, a positive electrode active material and, if necessary, a binder, a conductive additive and the like are mixed to form a positive electrode mixture, and then dispersed in an organic solvent to form a positive electrode mixture slurry. Subsequently, the mixture slurry is applied to the positive electrode current collector with a coating apparatus such as a die coater having a knife roll or a die head, and dried with hot air to obtain a positive electrode active material layer. Finally, the positive electrode active material layer is compression molded with a roll press or the like. At this time, heating may be performed, or heating or compression may be repeated a plurality of times.

Next, a negative electrode is produced by forming a negative electrode active material layer on the negative electrode current collector, using the same operation procedure as that for producing the negative electrode 10 described above.

When producing the positive electrode and the negative electrode, respective active material layers are formed on both surfaces of the positive electrode and the negative electrode current collector. At this time, the active material application length of both surface portions may be shifted in either electrode (see FIG. 2).

Subsequently, an electrolyte solution is prepared. Subsequently, the positive electrode lead 32 is attached to the positive electrode current collector and the negative electrode lead 33 is attached to the negative electrode current collector by ultrasonic welding or the like. Subsequently, the positive electrode and the negative electrode are laminated or wound via a separator to produce a wound electrode body 31, and a protective tape is bonded to the outermost periphery. Next, the wound body is molded so as to have a flat shape. Subsequently, after sandwiching the wound electrode body between the folded film-shaped exterior members, the insulating portions of the exterior member 35 are bonded to each other by a thermal fusion method, and the wound electrode body is released in only one direction. Enclose. An adhesion film is inserted between the positive electrode lead and the negative electrode lead and the exterior member. A predetermined amount of the prepared electrolytic solution is introduced from the release section, and vacuum impregnation is performed. After impregnation, the release part is bonded by a vacuum heat fusion method. As described above, the laminated film type lithium ion secondary battery 30 can be manufactured.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples.

Example 1-1
The laminate film type lithium ion secondary battery 30 shown in FIG. 3 was produced by the following procedure.

First, a positive electrode was produced. The positive electrode active material is 95% by mass of LiNi _0.7 Co _0.25 Al _0.05 O (lithium nickel cobalt aluminum complex oxide: NCA), which is a lithium nickel cobalt composite oxide, and 2.5% of the positive electrode conductive auxiliary agent. % And 2.5% by mass of a positive electrode binder (polyvinylidene fluoride: PVDF) were mixed to obtain a positive electrode mixture. Subsequently, the positive electrode mixture was dispersed in an organic solvent (N-methyl-2-pyrrolidone: NMP) to obtain a paste slurry. Subsequently, the slurry was applied to both surfaces of the positive electrode current collector with a coating apparatus having a die head, and dried with a hot air drying apparatus. At this time, a positive electrode current collector having a thickness of 15 μm was used. Finally, compression molding was performed with a roll press.

Next, a negative electrode was produced. As the negative electrode active material, a raw material mixed with metallic silicon and silicon dioxide is introduced into a reaction furnace, vaporized in a vacuum atmosphere of 10 Pa is deposited on an adsorption plate, sufficiently cooled, and then the deposit is taken out. It grind | pulverized with the ball mill. After adjusting the particle size, pyrolytic CVD was performed to form a carbon material on the surface layer of the negative electrode active material particles. Subsequently, the negative active material particles, the precursor of the negative electrode binder (polyamic acid), the conductive auxiliary agent 1 (flaky graphite) and the conductive auxiliary agent 2 (acetylene black) are dried at a mass of 80: 8: 10: 2. After mixing at a ratio, it was diluted with NMP to obtain a paste-like negative electrode mixture slurry. In this case, NMP was used as a solvent for the polyamic acid. Subsequently, the negative electrode mixture slurry was applied to both surfaces of the negative electrode current collector with a coating apparatus and then dried. As this negative electrode current collector, an electrolytic copper foil (thickness = 15 μm) was used. Finally, baking was performed at 400 ° C. for 1 hour in a vacuum atmosphere. Thereby, the negative electrode binder (polyimide) was formed. Thereby, a negative electrode active material layer was formed on both surfaces of the negative electrode current collector. At this time, the negative electrode current collector contained carbon and sulfur, and their contents were all 100 ppm by mass or less.

Next, after mixing a solvent (4-fluoro-1,3-dioxolan-2-one (FEC), ethylene carbonate (EC) and dimethyl carbonate (DMC)), an electrolyte salt (lithium hexafluorophosphate: LiPF) ₆ ) was dissolved to prepare an electrolytic solution. In this case, the composition of the solvent was FEC: EC: DMC = 10: 20: 70 by volume ratio, and the content of the electrolyte salt was 1.0 mol / kg with respect to the solvent.

Next, a secondary battery was assembled as follows. First, an aluminum lead was ultrasonically welded to one end of the positive electrode current collector, and a nickel lead was welded to one end of the negative electrode current collector. Subsequently, a positive electrode, a separator, a negative electrode, and a separator were laminated in this order and wound in the longitudinal direction to obtain a wound electrode body. The end portion was fixed with a PET protective tape. As the separator, a laminated film (thickness: 12 μm) sandwiched between a film mainly composed of porous polyethylene and a film mainly composed of porous polypropylene was used. Subsequently, after sandwiching the electrode body between the exterior members, the outer peripheral edges excluding one side were heat-sealed, and the electrode body was housed inside. As the exterior member, a nylon film, an aluminum foil, and an aluminum laminate film in which a polypropylene film was laminated were used. Subsequently, an electrolytic solution prepared from the opening was injected, impregnated in a vacuum atmosphere, heat-sealed, and sealed.

The cycle characteristics and initial charge / discharge characteristics of the secondary battery produced as described above were evaluated.

The cycle characteristics were examined as follows. First, in order to stabilize the battery, charge and discharge was performed for 2 cycles in an atmosphere at 25 ° C., and the discharge capacity at the second cycle was measured. Subsequently, charge and discharge were performed until the total number of cycles reached 100, and the discharge capacity was measured each time. Finally, the discharge capacity at the 100th cycle was divided by the discharge capacity at the second cycle, and the capacity retention rate was calculated. As cycling conditions, a constant current density until reaching 4.2V, 2.5 mA / cm was charged with ^2, the current density at 4.2V constant voltage at the stage of reaching the voltage 4.2V 0.25 mA / cm ² The battery was charged until During discharging, discharging was performed at a constant current density of 2.5 mA / cm ² until the voltage reached 2.5V.

For the initial charge / discharge characteristics, the initial efficiency (initial efficiency) (%) = (initial discharge capacity / initial charge capacity) × 100 was calculated. The atmosphere and temperature were the same as when the cycle characteristics were examined, and the charge / discharge conditions were 0.2 times that when the cycle characteristics were examined.

Next, a 2032 type coin battery was assembled as a secondary battery for the ⁷ Li-MAS-NMR measurement test. For each cycle, 20 coin batteries having a negative electrode including a negative electrode active material manufactured under the same manufacturing conditions were prepared.

As the negative electrode, a negative electrode produced in the same procedure as the negative electrode of the laminate film type lithium ion secondary battery 30 in Example 1-1 was used. The deposition amount (also referred to as area density) of the negative electrode active material layer per unit area on one side of the negative electrode was 2.5 mg / cm ² .

As the electrolytic solution, an electrolytic solution prepared in the same procedure as the electrolytic solution of the laminate film type lithium ion secondary battery 30 in Example 1-1 was used.

As the counter electrode, a metal lithium foil having a thickness of 0.5 mm was used. Further, polyethylene having a thickness of 20 μm was used as a separator.

Subsequently, the bottom pig of the 2032 type coin battery, the lithium foil, and the separator are stacked, and 150 mL of the electrolytic solution is injected, and subsequently, the negative electrode and the spacer (thickness: 1.0 mm) are stacked, and 150 mL of the electrolytic solution is injected. Then, a 2032 type coin battery was manufactured by lifting up the spring and the upper lid of the coin battery in this order and caulking with an automatic coin cell caulking machine.

The measurement conditions for ⁷ Li-MAS-NMR were the same as the charging conditions A described above. That is, a predetermined number of 0V-1.2V cycles were performed, and then charging was performed for 60 hours. Thereby, the measurement result of NMR in each cycle was obtained. In addition, the NMR measurement of the negative electrode active material was performed by disassembling a coin battery containing the negative electrode active material in a glove box, peeling the negative electrode active material from the negative electrode, and filling the NMR rotor. In this example, the upper limit of X in the 0V-1.2V cycle was 99. For example, a negative electrode active material that did not exhibit a peak in the range of 25 to 55 ppm by the time of 60-hour charging at the 100th cycle is regarded as a negative electrode active material from which this peak is not obtained, and “25 to 55 ppm in the table” "" None ".

(Example 1-2 to Example 1-10, Comparative Example 1-1 to 1-4)
Oxygen in bulk of silicon oxide, half-value width (half-value width) of diffraction peak due to Si (111) crystal plane obtained by X-ray diffraction (this is also the crystallite size calculated from this half-value width) Reflected), presence / absence of peak in the range of 25-55 ppm, presence / absence of peak in the range of 0-3 ppm, presence / absence of “expression and decrease within 50 times” (ie, repeating 0V-1.2V cycle within 49 times) Except that the peak in the range of 25 to 55 ppm is expressed and decreased) and the cycle number at the time of peak expression in the range of 25 to 55 ppm (indicated by Cy) is changed as in Example 1-1. A secondary battery was manufactured. Table 1 shows the results of Examples 1-1 to 1-10 and Comparative Examples 1-1 to 1-4.

The negative electrode active materials of Examples 1-1 to 1-10 and Comparative Examples 1-1 to 1-4 had the following properties. The median diameter of the negative electrode active material particles was 4 μm. The negative electrode active material particles included a carbon material having an average thickness of 100 nm in the surface layer portion. In particular, in all of the negative electrode active materials of Example 1-1 to Example 1-10, a peak in the range of 0 to 3 ppm appears upon charging for 60 hours in the first cycle, and once in the range of 0 to 3 ppm There was no decrease during repeated 0V-1.2V cycles. As will be described later, the peak in the range of 25 to 55 ppm at the beginning of the charge / discharge cycle may shift toward 0 ppm by repeating the charge / discharge cycle. At this time, since the peak shift value of the shifted peak is larger than the peak shift value of the peak in the range of 0 to 3 ppm, the peak in the range of 0 to 3 ppm may be buried in the shifted peak.

As shown in Table 1, in the silicon oxide represented by SiOx, when the value of x was outside the range of 0.5 ≦ x ≦ 1.6, the battery characteristics deteriorated. For example, as shown in Comparative Example 1-1, when there is not enough oxygen (x = 0.3), a peak in the range of 25 to 55 ppm does not appear, and a stable Li silicate peak (range of 0 to 3 ppm) ) Was not obtained. Therefore, the capacity maintenance rate of the secondary battery was significantly deteriorated. In addition, although the initial efficiency of the secondary battery was a high value, since the cycle characteristics were greatly deteriorated, it was judged comprehensively and concluded that the battery characteristics were poor. On the other hand, as shown in Comparative Example 1-3, when the amount of oxygen increased (x = 1.8), the electron resistance and the ion diffusion resistance increased, the battery evaluation was difficult, and the battery initial efficiency was greatly reduced. Therefore, the evaluation of cycle characteristics was stopped. In Comparative Example 1-2, x of SiOx was 0.5, but two types of peaks did not appear, so the results of cycle characteristics and initial efficiency were poor.

On the other hand, the secondary batteries (Example 1-1 to Example 1-10) using the negative electrode active material of the present invention had good cycle characteristics. FIG. 1 is a ⁷ Li-MAS-NMR spectrum measured in Example 1-3 of the present invention. The peak in the range of 25 to 55 ppm in FIG. 1 is presumed to indicate the presence of Li—Si bonds.

On the other hand, FIG. 4 is a ⁷ Li-MAS-NMR spectrum measured using a general silicon simple substance negative electrode containing silicon simple substance as a negative electrode active material. This spectrum was also obtained under the same conditions as in Example 1-3. That is, this spectrum shows that a 2032 type coin battery was produced in the same manner as in Example 1-3, and only the 60-hour charge was performed without performing the 0V-1.2V cycle, and the negative electrode after the 60-hour charge was applied to the NMR rotor. It was obtained by packing and performing NMR measurement.

As shown in FIG. 4, the peak value obtained from ⁷ Li-MAS-NMR when a general silicon simple substance negative electrode is used appears around 10 ppm. On the other hand, as shown in FIG. 1, when a negative electrode containing silicon oxide is measured, the peak value is greatly shifted to the plus side according to the bulk state of silicon oxide. This is presumed to be due to the large distance between silicon atoms. After obtaining this peak value, a stable bulk situation can be created by gradually shifting this peak toward 0 ppm while repeating Li insertion and desorption (repeat 0V-1.2V cycle). it can.

The peak in the range of 0 to 3 ppm shown in FIG. 1 indicates the reaction between the oxygen side of the silicon oxide and Li, and is presumed to indicate the presence of the Li silicate layer. The negative electrode active material from which this peak is obtained is likely to generate a stable Li compound inside the negative electrode active material particles by charging and discharging. Therefore, in the negative electrode active material from which this peak is obtained, Li easily diffuses in the bulk of the silicon oxide. Therefore, the negative electrode active material from which this peak is obtained becomes a stable battery material and can improve cycle characteristics. A sharp peak near 0 ppm in FIG. 1 represents the presence of LiPF ₆ and is not essential. On the other hand, as shown in Comparative Example 1-4, a negative electrode active material in which a peak in the range of 0 to 3 ppm is not obtained is a material in which a sufficient silicate layer cannot be obtained even when Li insertion and removal are repeated. Such a negative electrode active material is considered to have enlarged SiO ₂ in the bulk and difficult to occlude Li. Therefore, when this negative electrode active material is used as the negative electrode active material of a lithium ion secondary battery, the cycle characteristics are degraded.

Further, as in Example 1-1 to Example 1-6 and Example 1-8 to Example 1-10, it is preferable that X in the range of 25 to 55 ppm appears within 49 times. With such a negative electrode active material, when this negative electrode active material is used as the negative electrode active material of a lithium ion secondary battery, the time (number of cycles) until the secondary battery is stabilized should be reduced. Can do. Thereby, the cycle deterioration rate at the initial stage of the charge / discharge cycle is further reduced, and the cycle characteristics are further improved. A secondary battery having such a negative electrode active material has stable cycle characteristics.

In addition, as described above, charging and discharging are repeated for a state in which the peak considered to indicate a Li—Si bond is largely shifted to the positive side, and this peak is closer to 0, thereby stabilizing the bulk of the silicon oxide. Li-Si once expressed in repeating the 0V-1.2V cycle within 49 times as in Example 1-1 to Example 1-6, Example 1-8, and Example 1-9 It is desirable to reduce the peaks indicating binding (peaks in the range of 25 to 55 ppm). In particular, it is preferable that this peak disappears (disappears). As described above, by “expressing and decreasing within 50 times”, the bulk of the silicon oxide is stabilized at an earlier stage of the charge / discharge cycle.

For example, when Example 1-5 and Example 1-10 in which the peak has the same expression cycle (40th cycle) are compared, after the peak appears within 50 times, more than 50 cycles (specifically In particular, Example 1-5, which “appears and decreases within 50 times”, suppresses a decrease in the battery retention rate at the beginning of the cycle, and the cycle characteristics are lower than Example 1-10 that decreases at 70 times). More improved. Therefore, when judged comprehensively, it is desirable to use a material in which the above-mentioned peak appears and decreases as early as possible.

(Example 2-1 to Example 2-6)
A secondary battery was fabricated under the same conditions as in Example 1-3 except that the median diameter of the negative electrode active material particles was changed, and the cycle characteristics and initial efficiency were evaluated. The results are shown in Table 2. In Tables 2 to 4 below, the results of Example 1-3 are also shown.

As shown in Table 2, when the particle size of the negative electrode active material particles is 0.5 μm or more, an increase in surface area can be suppressed, and therefore both the battery maintenance ratio and the initial efficiency tend to be better. Moreover, since it became difficult for a negative electrode active material to expand | swell at the time of charge as a particle size is 20 micrometers or less, and a negative electrode active material becomes difficult to break, it turned out that a battery characteristic can be improved.

Example 3-1
A secondary battery was fabricated under the same conditions as in Example 1-3 except that the negative electrode current collector did not contain carbon and sulfur, and the cycle characteristics and initial efficiency were evaluated. The results are shown in Table 3.

As shown in Table 3, it is possible to suppress deformation of the negative electrode during charging by adding carbon and sulfur to each 100 ppm by mass or less in the negative electrode current collector. As a result, it was found that the battery maintenance rate was improved.

(Example 4-1 to Example 4-7)
A secondary battery was fabricated under the same conditions as in Example 1-3 except that the thickness of the carbon material was changed, and the cycle characteristics and the initial efficiency were evaluated. The results are shown in Table 4.

As a result of changing the thickness of the carbon material and evaluating the battery characteristics, when the carbon material was not deposited, both the initial efficiency and the maintenance rate of the battery were lowered. It is presumed that the carbon material has an effect of suppressing the decomposition of the electrolytic solution. Increasing the thickness of the carbon material stabilizes the battery characteristics, but as the carbon material becomes thicker, it is difficult to improve the battery capacity. Even with a thickness of about 5 μm (5000 nm), the battery capacity is difficult to improve. Further, in the experiment in which the thickness of the carbon material was about 7 μm, the capacity was not expressed more. Judging comprehensively from these results, it is considered that the thickness of the carbon material is preferably 5 μm or less.

Note that the present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

Claims

A negative electrode active material comprising negative electrode active material particles, wherein the negative electrode active material particles contain a silicon compound represented by SiO x (0.5 ≦ x ≦ 1.6),
The negative electrode active material containing the negative electrode active material particles is used for a negative electrode of a secondary battery having metallic lithium as a counter electrode, and a cycle of 0 V constant current constant voltage charging and 1.2 V constant current discharge of the secondary battery is performed X times ( After repeating X ≧ 0), in the state where the secondary battery was further charged with 0V constant current and constant voltage (however, after 60 hours from 0V, the charge was stopped), the negative electrode active material after the end of charge was 7 A negative electrode active material characterized by having a peak in a range of 25 to 55 ppm and a range of 0 to 3 ppm as a chemical shift value obtained from a Li-MAS-NMR spectrum.
The negative electrode active material according to claim 1, wherein the peak in the range of 25 to 55 ppm appears within 49 times of the X.
3. The negative electrode active material according to claim 1 or 2, wherein the peak in the range of 0 to 3 ppm appears within 9 times of the X.
The negative electrode active material according to any one of claims 1 to 3, wherein the peak in the range of 25 to 55 ppm and the peak in the range of 0 to 3 ppm are expressed when the X is 0 times. .
5. The peak in the range of 25 to 55 ppm decreases while repeating the cycle of 0V constant current constant voltage charging and 1.2V constant current discharge within 49 times. 2. The negative electrode active material according to item 1.
The negative electrode active material has a full width at half maximum (2θ) of a diffraction peak due to the Si (111) crystal plane obtained by X-ray diffraction of 1.2 ° or more, and a crystallite size corresponding to the crystal plane is 7 The negative electrode active material according to claim 1, wherein the negative electrode active material is 5 nm or less.
7. The negative electrode active material according to claim 1, wherein a median diameter of the negative electrode active material particles is 0.5 μm or more and 20 μm or less.
The negative electrode active material according to any one of claims 1 to 7, wherein the negative electrode active material particles include a carbon material in a surface layer portion.
9. The negative electrode active material according to claim 8, wherein an average thickness of the carbon material is 1 nm or more and 5000 nm or less.
A negative electrode comprising the negative electrode active material according to any one of claims 1 to 9.
The negative electrode includes a negative electrode active material layer containing the negative electrode active material,
A negative electrode current collector,
The negative electrode active material layer is formed on the negative electrode current collector,
11. The negative electrode according to claim 10, wherein the negative electrode current collector contains carbon and sulfur, and the content thereof is 100 ppm by mass or less.
A lithium ion secondary battery using the negative electrode according to claim 10 or 11 as a negative electrode.
A method for producing a negative electrode active material containing negative electrode active material particles,
Preparing negative electrode active material particles containing a silicon compound represented by the general formula SiO x (0.5 ≦ x ≦ 1.6);
Producing a secondary battery having a negative electrode containing a negative electrode active material containing the negative electrode active material particles and a counter electrode made of metallic lithium;
After repeating the cycle of 0V constant current and constant voltage charge and 1.2V constant current discharge of the secondary battery X times (X ≧ 0), the secondary battery is further charged with 0V constant current and constant voltage (however, it becomes 0V). A process of stopping charging after 60 hours),
Measuring the negative electrode active material by 7 Li-MAS-NMR in the state of charge termination;
And a step of selecting a negative electrode active material obtained from the 7 Li-MAS-NMR spectrum, having a chemical shift value in the range of 25 to 55 ppm and a peak in the range of 0 to 3 ppm. Manufacturing method.
A negative electrode is produced using the negative electrode active material produced by the method for producing a negative electrode active material according to claim 13, and a lithium ion secondary battery is produced using the produced negative electrode. Battery manufacturing method.