阅读说明：本技术 负极活性物质、混合负极活性物质材料、以及负极活性物质颗粒的制造方法 (Negative electrode active material, mixed negative electrode active material, and method for producing negative electrode active material particles ) 是由 广濑贵一 松野拓史 酒井玲子 高桥广太 粟野英和 于 2018-05-18 设计创作，主要内容包括：本发明是一种负极活性物质,其包含负极活性物质颗粒,所述负极活性物质的特征在于,负极活性物质颗粒含有硅化合物颗粒,该硅化合物颗粒包含含氧的硅化合物,硅化合物颗粒含有锂化合物,构成硅化合物颗粒的Si的至少一部分以不含Li的Si<Sup>2+</Sup>～Si<Sup>3+</Sup>的氧化物、以及含有Li与Si<Sup>2+</Sup>～Si<Sup>3+</Sup>的化合物中的至少一种形态存在。由此,提供一种负极活性物质、及含有该负极活性物质的混合负极活性物质材料、以及可制造上述负极活性物质所包含的负极活性物质颗粒的负极活性物质颗粒的制造方法,将所述负极活性物质用作二次电池的负极活性物质时,可增加电池容量,可提升循环特性及初始充放电特性。(The present invention is an anode active material comprising anode active material particles, wherein the anode active material particles contain silicon compound particles containing a silicon compound containing oxygen, the silicon compound particles contain a lithium compound, and at least a part of Si constituting the silicon compound particles is Si containing no Li 2+ ～Si 3+ Oxide of (a), andcontaining Li and Si 2+ ～Si 3+ At least one form of the compound of (1). Thus, a negative electrode active material, a mixed negative electrode active material containing the negative electrode active material, and a method for producing negative electrode active material particles capable of producing negative electrode active material particles contained in the negative electrode active material are provided, in which when the negative electrode active material is used as a negative electrode active material for a secondary battery, the battery capacity can be increased, and the cycle characteristics and initial charge/discharge characteristics can be improved.)

1. An anode active material comprising anode active material particles, the anode active material being characterized in that,

the negative electrode active material particles contain silicon compound particles containing a silicon compound containing oxygen,

the silicon compound particles contain a lithium compound and,

at least a part of Si constituting the silicon compound particles is Si containing no Li²⁺～Si³⁺Oxide of (5), and Li and Si²⁺～Si³⁺At least one form of the compound of (1).

2. The negative electrode active material according to claim 1, wherein the silicon compound particles have a peak or a shoulder in the XANES region at the Si K-edge of an X-ray absorption spectrum obtained when X-ray absorption fine structure analysis is performed, in the energy range of 1844eV to 1846.5 eV.

3. The negative electrode active material according to claim 2, wherein the intensity of a peak or shoulder occurring in the energy 1844eV to 1846.5eV in the XANES region of the Si K-edge of the silicon compound particle becomes stronger as the amount of charge increases during charging.

4. The negative electrode active material according to any one of claims 1 to 3, wherein the silicon compound particles have a peak at a position having an energy of 534eV or more and less than 535eV in an XANES region at an O K-edge of an X-ray absorption spectrum obtained when an X-ray absorption fine structure analysis is performed.

5. The negative electrode active material according to any one of claims 1 to 4, wherein the silicon compound particles contain Li₂SiO₃And Li₂Si₂O₅At least one kind of the above-mentioned lithium compounds.

6. The negative electrode active material according to any one of claims 1 to 5, wherein the silicon compound has a silicon to oxygen ratio of SiO_x: x is more than or equal to 0.5 and less than or equal to 1.6.

7. The negative electrode active material according to any one of claims 1 to 6, wherein the silicon compound particles have a half-width (2 θ) of a diffraction peak derived from a Si (111) crystal plane obtained by X-ray diffraction using Cu-Ka rays of 1.2 ° or more, and a crystallite size corresponding to the crystal plane of 7.5nm or less.

8. The negative electrode active material according to any one of claims 1 to 7, wherein the negative electrode active material particles have a median particle diameter of 1.0 μm or more and 15 μm or less.

9. The negative electrode active material according to any one of claims 1 to 8, wherein the negative electrode active material particles contain a carbon material in a surface layer portion.

10. The negative electrode active material according to claim 9, wherein the carbon material has an average thickness of 5nm to 5000 nm.

11. A mixed anode active material comprising the anode active material according to any one of claims 1 to 10 and a carbon-based active material.

12. A method for producing negative electrode active material particles containing silicon compound particles, characterized by producing negative electrode active material particles by the following steps:

a step of producing silicon compound particles containing a silicon compound containing oxygen;

a step of allowing the silicon compound particles to absorb Li; and

heat treatment is performed while stirring the Li-absorbed silicon compound particles in a furnace, thereby making at least a part of Si constituting the silicon compound particles to be Li-free Si²⁺～Si³⁺Oxide of (5), and Li and Si²⁺～Si³⁺The step (2) wherein at least one of the compounds (a) and (b) is present.

Technical Field

The present invention relates to a negative electrode active material, a mixed negative electrode active material, and a method for producing negative electrode active material particles.

Background

In recent years, small electronic devices such as mobile terminals have been widely spread, and further reduction in size, weight, and life are strongly demanded. In response to such market demands, development of a secondary battery which is particularly small and lightweight and can achieve high energy density has been advanced. The application of the secondary battery is not limited to small-sized electronic devices, and its application to large-sized electronic devices such as automobiles and power storage systems such as houses is also being studied.

Among them, lithium ion secondary batteries are expected to be small and easy to have a high capacity, and to be capable of obtaining a higher energy density than lead batteries and nickel-cadmium batteries.

The lithium ion secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, and the negative electrode contains a negative electrode active material involved in charge and discharge reactions.

As the negative electrode active material, a carbon-based active material is widely used, but further improvement in battery capacity is demanded in accordance with recent market demand. In order to increase the battery capacity, the use of silicon as a negative electrode active material is being studied. This is because the theoretical capacity of silicon (4199mAh/g) is 10 times or more greater than the theoretical capacity of graphite (372mAh/g), and therefore a significant increase in battery capacity can be expected. Development of a silicon material as a negative electrode active material has been studied not only for a simple substance of silicon but also for compounds represented by alloys and oxides. In addition, as for the shape of the active material, studies have been made on the carbon-based active material from a standard coating type to a one-piece type deposited directly on the current collector.

However, when silicon is used as a main material for the negative electrode active material, the negative electrode active material expands and contracts during charge and discharge, and therefore, the negative electrode active material is easily broken mainly in the vicinity of the surface layer of the negative electrode active material. Further, an ionic material is generated inside the active material, and the negative electrode active material becomes a material which is easily broken. If the surface layer of the negative electrode active material is broken, a new surface is generated, and the reaction area of the active material increases. In this case, the decomposition reaction of the electrolyte occurs on the fresh surface, and a coating film, which is a decomposition product of the electrolyte, is formed on the fresh surface, so that the electrolyte is consumed. Therefore, the cycle characteristics of the battery may become easily degraded.

Heretofore, various studies have been made on negative electrode materials and electrode structures for lithium ion secondary batteries, which have silicon materials as main materials, in order to improve the initial efficiency and cycle characteristics of the batteries.

Specifically, silicon and amorphous silica are simultaneously deposited by a vapor phase method for the purpose of obtaining good cycle characteristics and high safety (for example, see patent document 1). In addition, in order to obtain high battery capacity and safety, a carbon material (conductive material) is provided on the surface layer of the silicon oxide particles (for example, refer to patent document 2). Further, in order to improve cycle characteristics and obtain high input/output characteristics, an active material containing silicon and oxygen is prepared, 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). In order to improve cycle characteristics, the silicon active material is formed so as to contain oxygen and have an average oxygen content of 40 at% or less and a large oxygen content near the current collector (see, for example, patent document 4).

In addition, in order to improve the first charge-discharge efficiency, the composition contains Si phase and SiO₂、M_yA nanocomposite of an O metal oxide (for example, see patent document 5). Further, in order to improve cycle characteristics, SiO is added_x(0.8. ltoreq. x.ltoreq.1.5, particle size range of 1 to 50 μm) is mixed with a carbon material and calcined at high temperature (for example, see 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 active material is controlled so that the difference between the maximum value and the minimum value of the molar ratio in the vicinity of the interface between the active material and the current collector is 0.4 or less (see, for example, patent document 7). In addition, in order to improve the load characteristics of the battery, a metal oxide containing lithium is used (for example, see patent document 8). In addition, in order to improve cycle characteristics, a hydrophobic layer such as a silane compound is formed on a surface layer of a silicon material (for example, see patent document 9). In addition, in order to improve cycle characteristics, conductivity is imparted by using silicon oxide and forming a graphite coating on the surface layer thereof (for example, see patent document 10). In patent document 10, the displacement value obtained from the RAMAN spectrum relating to the graphite coating is 1330cm^-1And 1580cm^-1Show a broad peak and their intensity ratio I₁₃₃₀/I₁₅₈₀1.5 < I₁₃₃₀/I₁₅₈₀Is less than 3. Further, particles having a silicon microcrystalline phase dispersed in silica are used for the purpose of increasing the battery capacity and improving the cycle characteristics (for example, see patent document 11). In order to improve overcharge and overdischarge characteristics, a silicon oxide in which the atomic ratio of silicon to oxygen is controlled to 1: y (0 < y < 2) is used (for example, see patent document 12).

Disclosure of Invention

Technical problem to be solved by the invention

As described above, in recent years, high performance and multi-functionalization of small electronic devices such as mobile terminals have been progressing, and an increase in battery capacity of a lithium ion secondary battery as a main power source thereof has been demanded. As one approach to solve this problem, development of a lithium ion secondary battery including a negative electrode using a silicon material as a main material is desired. Further, it is desired that the initial charge-discharge characteristics and cycle characteristics of the lithium ion secondary battery using the silicon material are as similar as those of the lithium ion secondary battery using the carbon-based active material. The cycle characteristics of the battery can be greatly improved by using a silicon oxide material. In addition, as a method of improving the initial efficiency of the battery, a method of doping Li in a silicon oxide material can be used. However, although the characteristics of the negative electrode active material using the silicon material can be greatly improved in this way, the cycle characteristics of the silicon material are still low as compared with the carbon material, and a silicon material having cycle characteristics equivalent to those of the carbon material has not been proposed.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a negative electrode active material capable of increasing the battery capacity and improving the cycle characteristics and initial charge and discharge characteristics when used as a negative electrode active material for a secondary battery, and a mixed negative electrode active material containing the negative electrode active material. Another object of the present invention is to provide a method for producing negative electrode active material particles, which can produce negative electrode active material particles contained in the negative electrode active material.

Means for solving the problems

In order to achieve the above object, the present invention provides an anode active material comprising anode active material particles, wherein the anode active material particles contain silicon compound particles containing a silicon compound containing oxygen, the silicon compound particles contain a lithium compound, and at least a part of Si constituting the silicon compound particles is Si containing no Li²⁺～Si³⁺Oxide of (5), and Li and Si²⁺～Si³⁺At least one form of the compound of (1).

Since the negative electrode active material (hereinafter, also referred to as a silicon-based negative electrode active material) of the present invention contains the negative electrode active material particles containing the silicon compound particles (hereinafter, also referred to as silicon-based negative electrode active material particles), the battery capacity can be improved. Further, by including the lithium compound in the silicon compound particles, irreversible capacity generated at the time of charging can be reduced. In addition, at least a part of Si of the anode active material particles constituting the anode active material of the present invention is Si containing no Li²⁺～Si³⁺Oxide of (5), and Li and Si²⁺～Si³⁺At least one of the compounds (c) is present, and therefore, the cycle characteristics of the battery can be improved.

In this case, it is preferable that: the silicon compound particles have a peak or a shoulder (shoulderpeak) in an X-ray absorption near edge structure (XANES) region of an Si K-edge of an X-ray absorption spectrum obtained when X-ray absorption fine structure analysis (XAFS) is performed in a range of energy 1844eV to 1846.5 eV.

In this case, Si is present as the silicon element²⁺～Si³⁺Therefore, the cycle characteristics of the battery can be improved.

Further, in this case, it is preferable that: during charging, the intensity of a peak or shoulder occurring in the range of energy 1844eV to 1846.5eV in the XANES region of the SiK-edge of the silicon compound particles becomes stronger as the amount of charge increases.

When such a peak is present, the cycle characteristics of the battery using the negative electrode active material of the present invention can be further improved.

Further, it is preferable that: the silicon compound particles have a peak at a position having an energy of 534eV or more and less than 535eV in an XANES region at an O K-edge of an X-ray absorption spectrum obtained when X-ray absorption fine structure analysis is performed.

In the XANES region at the O K-edge, the peak appearing at an energy 534eV originates from the Li-O bond, and further, the peak appearing at 535eV originates from the Si-O bond. Having a peak at a position close to 534eV means that a part of Si-O bonds have changed to stable Li-O bonds. In this manner, the change in the bulk phase (bulk phase) structure associated with charge and discharge can be stabilized.

Further, it is preferable that the silicon compound particles contain Li₂SiO₃And Li₂Si₂O₅At least one kind of the above-mentioned lithium compounds.

When the silicon compound particles contain the lithium silicate as a lithium compound, which is relatively stable, the initial charge-discharge characteristics and the cycle characteristics of the negative electrode active material can be improved, and the stability of the slurry in the production of the electrode can be further improved.

Further, it is preferable that the silicon compound is composed of silicon and oxygen in a ratio of SiO_x: x is more than or equal to 0.5 and less than or equal to 1.6.

If containing such a silicon compound, i.e. SiO_x(0.5. ltoreq. x. ltoreq.1.6) or a negative electrode active material of silicon oxideThe negative electrode active material has better cycle characteristics.

Further, it is preferable that: the silicon compound particles have a half-width (2 theta) of a diffraction peak derived from a Si (111) crystal plane, which is obtained by X-ray diffraction using Cu-Kalpha rays, of 1.2 DEG or more, and have a crystallite size corresponding to the crystal plane of 7.5nm or less.

When the negative electrode active material in which the silicon compound particles have the silicon crystallinity is used as a negative electrode active material for a lithium ion secondary battery, more favorable cycle characteristics and initial charge-discharge characteristics can be obtained.

Further, the negative electrode active material particles preferably have a median particle diameter of 1.0 μm or more and 15 μm or less.

When the median diameter is 1.0 μm or more, the irreversible capacity of the battery can be suppressed from increasing due to an increase in the surface area per unit mass. On the other hand, by setting the median diameter to 15 μm or less, the particles are less likely to be broken, and therefore, the new surface is less likely to appear.

Preferably, the negative electrode active material particles include a carbon material in a surface layer portion.

Since the improvement in conductivity can be achieved by including the negative electrode active material particles with the carbon material in the surface layer portion thereof in this manner, when the negative electrode active material containing such negative electrode active material particles is used as a negative electrode active material for a secondary battery, battery characteristics can be improved.

The carbon material preferably has an average thickness of 5nm to 5000 nm.

When the average thickness of the carbon material is 5nm or more, the conductivity can be improved. When the average thickness of the coated carbon material is 5000nm or less, a sufficient amount of silicon compound particles can be secured by using the negative electrode active material containing the negative electrode active material particles in a lithium ion secondary battery, and thus, a decrease in battery capacity can be suppressed.

In order to achieve the above object, the present invention provides a mixed negative electrode active material comprising the negative electrode active material of the present invention and a carbon-based active material.

In this way, by including the silicon-based negative electrode active material of the present invention and including the carbon-based active material as a material for forming the negative electrode active material layer, the electrical conductivity of the negative electrode active material layer can be improved, and the expansion stress associated with charging can be relaxed. Further, by mixing a silicon-based negative electrode active material with a carbon-based active material, the battery capacity can be increased.

Further, in order to achieve the above object, the present invention provides a method for producing negative electrode active material particles containing silicon compound particles, the method comprising the steps of: a step of producing silicon compound particles containing a silicon compound containing oxygen; a step of allowing the silicon compound particles to absorb Li; and heat-treating the silicon compound particles into which Li has been absorbed while stirring the silicon compound particles in a furnace, thereby converting at least a part of Si constituting the silicon compound particles into Si containing no Li²⁺～Si³⁺Oxide of (5), and Li and Si²⁺～Si³⁺The step (2) wherein at least one of the compounds (a) and (b) is present.

By this manufacturing method, it is possible to manufacture negative electrode active material particles which can increase the battery capacity and improve the cycle characteristics and initial charge-discharge characteristics when used as a negative electrode active material for a secondary battery.

Effects of the invention

The negative electrode active material of the present invention has a high capacity when used as a negative electrode active material for a secondary battery, and can obtain good cycle characteristics and initial charge-discharge characteristics. In addition, the same effect can be obtained also in a mixed negative electrode active material containing the negative electrode active material.

In addition, according to the method for producing the negative electrode active material particles of the present invention, it is possible to produce negative electrode active material particles which have a high capacity and good cycle characteristics and initial charge and discharge characteristics when used as a negative electrode active material for a secondary battery.

Drawings

Fig. 1 is a sectional view showing an example of the structure of a negative electrode for a nonaqueous electrolyte secondary battery containing the negative electrode active material of the present invention.

Fig. 2 is a schematic view showing an example of a modification device that can be used for electrochemical lithium doping in the method for producing negative electrode active material particles according to the present invention.

FIG. 3 shows Si K-edge spectra measured in example 1-1 and comparative example 1-1.

FIG. 4 is an O K-edge spectrum measured in example 1-2 and comparative example 1-1.

Fig. 5 is an exploded view showing an example of the structure (laminate film type) of a lithium ion secondary battery including the negative electrode active material of the present invention.

FIG. 6 shows the measured Si K-edge spectrum of example 1-2 during charging.

FIG. 7 shows the measured Si K-edge spectrum of comparative example 1-1 during charging.

Detailed Description

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

As described above, as one of the methods for increasing the battery capacity of a lithium ion secondary battery, studies are being made on using a negative electrode using a silicon material as a main material as a negative electrode of the lithium ion secondary battery. It is expected that the initial charge-discharge characteristics and cycle characteristics of the lithium ion secondary battery using the silicon material are as similar as those of the lithium ion secondary battery using the carbon-based active material. However, conventionally, there has been no proposal for a negative electrode active material that exhibits initial charge-discharge characteristics and cycle characteristics equivalent to those of a carbon-based active material when used as a negative electrode active material for a lithium ion secondary battery.

Accordingly, the present inventors have made extensive studies to obtain a negative electrode active material that can increase the battery capacity and improve the cycle characteristics and initial charge and discharge characteristics when used as a negative electrode active material for a secondary battery, and have completed the present invention. As a result, they have found that a high battery capacity and good cycle characteristics can be obtained when a negative electrode active material is used, and the present invention has been completed based on the finding that a negative electrode active material containing negative electrode active material particles,the negative electrode active material is characterized in that the negative electrode active material particles contain silicon compound particles containing a silicon compound containing oxygen, the silicon compound particles contain a lithium compound, and at least a part of Si constituting the silicon compound particles is Si containing no Li²⁺～Si³⁺Oxide of (5), and Li and Si²⁺～Si³⁺At least one form of the compound of (1).

< negative electrode >

First, a negative electrode (negative electrode for nonaqueous electrolyte secondary batteries) will be described. Fig. 1 is a sectional view showing an example of the structure of a negative electrode of the present invention.

[ Structure of negative electrode ]

As shown in fig. 1, the negative electrode 10 has a structure in which a negative electrode active material layer 12 is provided on a negative electrode current collector 11. The negative electrode active material layer 12 may be provided on both surfaces of the negative electrode current collector 11 or only on one surface of the negative electrode current collector 11. Further, the negative electrode using the negative electrode active material of the present invention may not include the negative electrode current collector 11.

[ negative electrode Current collector ]

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

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

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

[ negative electrode active material layer ]

The negative electrode active material layer 12 in fig. 1 contains the negative electrode active material of the present invention that can store and release lithium ions, and may further contain other materials such as a negative electrode binder (binder) and a conductive assistant, from the viewpoint of battery design. The anode active material of the present invention contains anode active material particles containing silicon compound particles containing a silicon compound containing an oxygen-containing silicon compound.

It is preferable that the silicon compound is composed of silicon and oxygen in a ratio of SiO_x: x is more than or equal to 0.5 and less than or equal to 1.6. When x is 0.5 or more, the ratio of oxygen is higher than that of the simple substance silicon, and thus the cycle characteristics are good. When x is 1.6 or less, the resistance of silicon oxide does not become too high, which is preferable. Among them, SiO is preferable_xX in the composition (1) is close to 1. This is because high cycle characteristics can be obtained. The composition of the silicon compound in the present invention does not necessarily mean the purity of 100%, and a trace amount of impurity elements may be contained in the composition. As described above, since the negative electrode active material of the present invention contains the negative electrode active material particles containing a silicon compound, the battery capacity can be increased.

In the anode active material of the present invention, the silicon compound particles contain a lithium compound. More specifically, the silicon compound particles preferably contain Li₂SiO₃And Li₂Si₂O₅At least one of them. The particles of the silicon compound destabilize SiO contained in the silicon compound during the absorption or desorption of lithium during the charge and discharge of the battery₂Since the component is partially modified with lithium silicate, irreversible capacity generated during charging can be reduced. Further, when the lithium silicate is contained as a lithium compound, stability to the slurry in the production of the electrode can be further improved.

Furthermore, although by using Li₂SiO₃、Li₂Si₂O₅At least one kind of the lithium compound (b) is present in the bulk of the silicon compound particles, and the battery characteristics are improved. In such a lithium compound, the valence number of the silicon element is +4 (Si)⁴⁺). In addition, these lithium silicates can be quantified by NMR (Nuclear Magnetic Resonance) or XPS (X-ray photoelectron spectroscopy). The XPS and NMR measurements can be performed under the following conditions, for example.

XPS

"device: x-ray photoelectron spectrometer

"X-ray source: monochromatized Al Ka ray

"X-ray spot (spot) diameter: 100 μm

Argon (Ar) ion gun sputtering conditions: 0.5kV/2mm

²⁹Si-MAS-NMR (magic angle rotating nuclear magnetic resonance)

"device: 700NMR spectrometer manufactured by Bruker

"Probe: 50 μ L of 4mm HR-MAS rotor (rotor)

"sample rotation speed: 10kHz

"determination of ambient temperature: 25 deg.C

Further, at least a part of Si of the silicon compound particles constituting the negative electrode active material of the present invention is Si containing no Li²⁺～Si³⁺Oxide of (5), and Li and Si²⁺～Si³⁺At least one form of the compound of (1). This means that Si is contained in at least one of the form of an oxide not containing Li and the form of a compound containing Li²⁺And Si³⁺Either or both. In addition, contains Li and Si²⁺～Si³⁺The compound of (A) is Si²⁺～Si³⁺Since the oxide of (a) absorbs Li, it is difficult to describe the oxide by a molecular formula or a composition formula.

General silicon oxide materials undergo a silicidation (silicidation) reaction in which Si reacts with Li by charging, and SiO₂The silication (silication) of lithium reacting with Li, whereby silicon alone has capacity. That is, Si alone functions as an active material for storing and desorbing Li. Here, SiO with 4-valent Si₂Li formed by the silication of lithium during charging, which reacts with Li₄SiO₄Lithium silicate has 4-valent Si, which is a stable lithium compound and is not easy to desorb Li. Therefore, the lithium silicate does not function as an active material and can have an irreversible capacity. On the other hand, with Si²⁺～Si³⁺Si in the form of (1) acts as an active material, and the charge-discharge cycle is operated with the intermediate valence Si having an Si-O bond. Therefore, the anode active material of the present invention can pass through Si²⁺～Si³⁺The presence of morphological Si promotes cyclability. Especially Si in the intermediate valence state (other than Si)⁰Or Si⁴⁺Is instead of Si⁺、Si²⁺、Si³⁺) In the above, the larger the valence, the more improved the cycle characteristics. That is, when Si having valence numbers 2 and 3 is present as in the present invention, cycle characteristics are further improved as compared with Si having valence number 1.

Further, in the present invention, it is preferable that: the silicon compound particles have a peak or shoulder in the XANES region of the Si K-edge of the X-ray absorption spectrum obtained when X-ray absorption fine structure analysis is performed, in the range of energy 1844eV to 1846.5 eV. The peak or shoulder appearing in this range is derived from Si²⁺And Si³⁺. Therefore, when such a peak or a shoulder appears, the battery has a stable phase structure, and thus the battery cycle performance can be greatly improved. In addition, waveform separation simulation was performed to confirm that there was a peak or a shoulder in the above range.

Further, in the present invention, it is preferable that: during charging, the intensity of a peak or shoulder appearing in the range of energy 1844eV to 1846.5eV in the XANES region of the SiK-edge of the silicon compound particles becomes stronger as the amount of charge increases. In this case, it is considered that the silicon element having the valence contributes to charging, and the cyclability can be improved by forming a stable phase structure.

Further, in the present invention, it is preferable that: the silicon compound particles have a peak at a position having an energy of 534eV or more and less than 535eV in an XANES region at the O K-edge of an X-ray absorption spectrum obtained when an X-ray absorption fine structure analysis is performed. The peak appearing at the energy 534eV originates from the Li-O bond, and further, the peak appearing at 535eV originates from the Si-O bond. Having a peak at a position close to 534eV means that a part of Si-O bonds have changed to stable Li-O bonds. In this manner, the change in the bulk phase structure accompanying charge and discharge can be stabilized. In addition, waveform separation simulation was performed to confirm that there was a peak or a shoulder in the above range.

Further, it is preferable that: the silicon compound particles have a half-width (2 theta) of a diffraction peak derived from the Si (111) crystal plane, which is obtained by X-ray diffraction using Cu-Kalpha rays, of 1.2 DEG or more, and a crystallite size corresponding to the crystal plane of 7.5nm or less. In addition, it is particularly preferable that the crystallites have a small size and are substantially amorphous. This peak appears at around 28.4 ± 0.5 ° when the crystallinity is high (when the half width is narrow). The lower the silicon crystallinity of the silicon compound in the silicon compound particles, the better, and particularly if the amount of the silicon crystal present is small, the battery characteristics can be improved, and further, a stable lithium compound can be produced.

In the negative electrode active material of the present invention, the negative electrode active material particles preferably contain a carbon material in a surface layer portion. Since the improvement in conductivity can be obtained by including the negative electrode active material particles with the carbon material in the surface layer portion thereof, when the negative electrode active material containing such negative electrode active material particles is used as a negative electrode active material for a secondary battery, battery characteristics can be improved.

In this case, the average thickness of the carbon material in the surface layer portion of the negative electrode active material particles is preferably 5nm to 5000 nm. When the average thickness of the carbon material is 5nm or more, the conductivity can be improved. When the average thickness of the coated carbon material is 5000nm or less, when the negative electrode active material containing the negative electrode active material particles is used as a negative electrode active material for a lithium ion secondary battery, a decrease in battery capacity can be suppressed.

The average thickness of the carbon material can be calculated, for example, by the following procedure. First, the anode active material particles were observed at an arbitrary magnification using a TEM (transmission electron microscope). The ratio is preferably a ratio at which the thickness can be measured and the thickness of the carbon material can be visually confirmed. Next, the thickness of the carbon material was measured at arbitrary 15 points. In this case, it is preferable to set the measurement position widely and randomly without concentrating on a specific position as much as possible. Finally, the average thickness of the carbon material at the 15 points was calculated.

The coverage of the carbon material is not particularly limited, but is desirably as high as possible. If the coverage is 30% or more, the conductivity is further improved, which is preferable. The method of coating the carbon material is not particularly limited, but a sugar carbonization method or a thermal decomposition method of a hydrocarbon gas is preferable. This is because the coverage can be improved.

Further, the median particle diameter (D) of the anode active material particles is preferable₅₀: particle diameter at 50% cumulative volume) of 1.0 to 15 μm. The reason for this is that if the median diameter is within the above range, lithium ions are easily stored and released during charge and discharge, and the negative electrode active material particles are less likely to be broken. When the median diameter is 1.0 μm or more, the surface area per unit mass of the negative electrode active material particles can be reduced, and an increase in irreversible capacity of the battery can be suppressed. On the other hand, by setting the median diameter to 15 μm or less, the particles are less likely to be broken, and therefore, the new surface is less likely to appear.

In addition, the anode active material layer 12 may contain a mixed anode active material containing the anode active material (silicon-based anode active material) of the present invention described above and a carbon-based active material. This reduces the resistance of the negative electrode active material layer, and at the same time, relieves the expansion stress associated with charging. Examples of the carbon-based active material include pyrolytic carbons (pyrolyticcarbon), cokes (coke), glassy carbon fibers, calcined organic polymer compounds, and carbon blacks.

In addition, the ratio of the mass of the silicon-based negative electrode active material to the total mass of the silicon-based negative electrode active material and the carbon-based active material of the present invention is preferably 6 mass% or more. When the ratio of the mass of the silicon-based negative electrode active material to the total mass of the silicon-based negative electrode active material and the carbon-based active material is 6 mass% or more, the battery capacity can be reliably increased.

As the negative electrode binder included in the negative electrode active material layer, for example, any one or more of a polymer material, a synthetic rubber, and the like can be used. Examples of the polymer material include polyvinylidene fluoride, polyimide, polyamide-imide, aramid, polyacrylic acid, lithium polyacrylate, and carboxymethyl cellulose. Examples of the synthetic rubber include styrene-butadiene rubber, fluorine rubber, ethylene-propylene-diene rubber, and the like.

As the negative electrode conductive auxiliary agent, for example, any one or more carbon materials such as carbon black, acetylene black, graphite, ketjen black, carbon nanotubes, and carbon nanofibers can be used.

The negative electrode active material layer is formed by, for example, a coating method. The coating method is a method of mixing a silicon-based negative electrode active material with the binder and the like, mixing a conductive auxiliary agent and a carbon-based active material as needed, and then dispersing the mixture in an organic solvent, water or the like to perform coating.

[ method for producing negative electrode ]

The negative electrode 10 can be manufactured, for example, by the following steps. First, a method for producing negative electrode active material particles contained in a negative electrode active material will be described. Initially, particles of a silicon compound containing a silicon compound, the silicon compound containing oxygen, are produced. Then, the silicon compound particles are caused to absorb lithium. Subsequently, the silicon compound particles having absorbed Li are subjected to a heat treatment while being stirred in a furnace, whereby at least a part of Si constituting the silicon compound particles is converted into Si containing no Li²⁺～Si³⁺Oxide of (5), and Li and Si²⁺～Si³⁺At least one form of the compound of (1). In this manner, negative electrode active material particles were produced. In this case, during the heat treatment, the silicon compound particles are stirred, whereby Si can be stably produced²⁺～Si³⁺. If stirring is not performed during the heat treatment, Si cannot be stably produced²⁺～Si³⁺。

The negative electrode active material produced by the production method can form a silicon compound having a specific valence, and can produce a negative electrode active material which has a high capacity and has good cycle characteristics and initial charge/discharge characteristics when used as a negative electrode active material for a secondary battery.

Next, the method for producing the negative electrode active material of the present invention will be described more specifically.

First, silicon compound particles containing a silicon compound containing oxygen are produced. To the following, SiO_xThe case where silicon oxide represented by (0.5. ltoreq. x.ltoreq.1.6) is used as the silicon compound containing oxygen will be described. First, a raw material for generating a silicon oxide gas is heated at a temperature in the range of 900 to 1600 ℃ in the presence of an inert gas under reduced pressure to generate a silicon oxide gas. In this case, a mixture of metal silicon powder and silicon dioxide powder can be used as the raw material. Considering the presence of oxygen on the surface of the metal silicon powder and a trace amount of oxygen in the reaction furnace, the mixing molar ratio is desirably in the range of 0.8 < metal silicon powder/silicon dioxide powder < 1.3.

The generated silicon oxide gas is solidified and deposited on the adsorption plate. Next, the deposit of silicon oxide is taken out in a state where the temperature in the reaction furnace is reduced to 100 ℃ or lower, and is pulverized and powdered by using a ball mill, jet mill, or the like. The silicon compound particles can be produced in the above manner. The silicon crystallites in the silicon compound particles can be controlled by changing the vaporization temperature of the raw material for generating the silicon oxide gas or by heat treatment after the silicon compound particles are generated.

Here, a carbon material layer may be generated on the surface layer of the silicon compound particles. As a method of generating the carbon material layer, a pyrolytic CVD method is desirable. An example of a method for forming a carbon material layer by the thermal decomposition CVD method will be described below.

First, silicon compound particles are set in a furnace. Subsequently, a hydrocarbon gas is introduced into the furnace, and the temperature in the furnace is raised. The decomposition temperature is not particularly limited, but is preferably 1200 ℃ or lower, more preferably 950 ℃ or lower. By setting the decomposition temperature to 1200 ℃ or lower, unexpected disproportionation of the active material particles can be suppressed. Raise the temperature in the furnaceAfter the temperature reaches a predetermined temperature, a carbon layer is formed on the surface of the silicon compound particles. The hydrocarbon gas as the raw material of the carbon material is not particularly limited, but is desirably C_nH_mIn the composition, n is less than or equal to 3. If n is less than or equal to 3, the production cost can be reduced and the physical properties of the decomposition product can be improved.

Next, the silicon compound particles produced in the above manner were made to absorb Li. In this way, negative electrode active material particles containing lithium-absorbed silicon compound particles were produced. That is, the silicon compound particles are thereby modified, and Li is generated inside the silicon compound particles₂SiO₃And Li₂Si₂O₅And the like. By performing the heat treatment while stirring the Li-absorbed silicon compound particles in the furnace (also referred to as a thermal stirring method), at least a part of Si constituting the silicon compound particles can be converted into Si containing no Li²⁺～Si^{3 +}Oxide of (5), and Li and Si²⁺～Si³⁺At least one form of the compound of (1).

More specifically, Li can be doped by immersing the silicon compound particles in a lithium-containing solution. For example, lithium can be absorbed by immersing silicon compound particles in a solution a prepared by dissolving lithium in an ether solvent. It is also possible to make the solution A further contain a polycyclic aromatic compound or a linear polyphenylene (polyphenylene) compound. After the absorption of lithium, active lithium can be desorbed from the silicon compound particles by immersing the silicon compound particles in the solution B containing the polycyclic aromatic compound or its derivative. As the solvent of the solution B, for example, an ether solvent, a ketone solvent, an ester solvent, an alcohol solvent, an amine solvent, or a mixed solvent thereof can be used. Alternatively, after immersion in the solution a, the obtained silicon active material particles may be heat-treated while being stirred under an inert gas. The lithium compound can be stabilized by performing the heat treatment while stirring. Then, the washing may be performed by a method of washing with alcohol, alkaline water in which lithium carbonate is dissolved, weak acid, pure water, or the like.

As the ether solvent used in the solution a, diethyl ether, methyl tert-butyl ether, tetrahydrofuran, dioxane, 1, 2-dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or a mixed solvent thereof can be used. Among them, tetrahydrofuran, dioxane, and 1, 2-dimethoxyethane are particularly preferably used. These solvents are preferably dehydrated and preferably deoxygenated.

Further, as the polycyclic aromatic compound contained in the solution a, naphthalene, anthracene, phenanthrene, tetracene, pentacene, pyrene, picene, triphenylene, coronene, or the like can be used,

And one or more derivatives thereof, and as the linear polyphenylene compound, one or more of biphenyl, terphenyl, and derivatives thereof can be used.

As the polycyclic aromatic compound contained in solution B, naphthalene, anthracene, phenanthrene, tetracene, pentacene, pyrene, picene, triphenylene, coronene, or the like can be used,

And derivatives thereof.

As the ether solvent of the solution B, diethyl ether, methyl tert-butyl ether, tetrahydrofuran, dioxane, 1, 2-dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and the like can be used.

As the ketone solvent, acetone, acetophenone, or the like can be used.

As the ester solvent, methyl formate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, and the like can be used.

As the alcohol solvent, methanol, ethanol, propanol, isopropanol, or the like can be used.

As the amine solvent, methylamine, ethylamine, ethylenediamine, and the like can be used.

In addition, modification can be performed by an electrochemical doping method. In this case, the substance generated in the bulk can be controlled by adjusting the suction potential and the desorption potential or by changing the current density, the bath temperature, and the number of times of suction and desorption.

In the modification by the electrochemical doping method, for example, Li doping can be performed using the modification apparatus 20 shown in fig. 2. The apparatus structure is not particularly limited to the structure of the reforming apparatus 20. The reforming apparatus 20 shown in fig. 2 includes: a bath 27 filled with the electrolyte 23; a counter electrode 21 disposed in the bath 27 and connected to one side of the power source 26; a powder container 25 disposed in the bath 27 and connected to the other side of the power supply 26; and a separator 24 provided between the counter electrode 21 and the powder container 25. The silicon compound particles 22 are contained in the powder containing container 25. Lithium salt is dissolved in the electrolytic solution 23 or a lithium-containing compound is combined with the counter electrode 21, and a voltage is applied between the powder container 25 and the counter electrode 21 by the power supply 26 to pass a current, whereby lithium can be taken in into the silicon compound particles.

As the lithium source used in the electrochemical doping method, at least one of metal lithium, lithium transition metal phosphate, lithium oxide of nickel, lithium oxide of cobalt, lithium oxide of manganese, lithium nitrate, and lithium halide can be used. The form of the lithium salt is not particularly required. That is, a lithium salt may be used as the counter electrode 21, and a lithium salt may also be used as the electrolyte of the electrolytic solution 23.

In this case, as a solvent of the electrolyte 23, dimethyl carbonate, ethylene carbonate (ethylene carbonate), propylene carbonate (propylene carbonate), diethyl carbonate, dioxane, diglyme, triglyme, tetraglyme, a mixture thereof, or the like can be used. Further, as the electrolyte of the electrolytic solution 23, lithium tetrafluoroborate (LiBF) can also be used₄) Lithium hexafluorophosphate (LiPF)₆) Lithium perchlorate (LiClO)₄) And their derivatives, and particularly lithium nitrate (LiNO) can be used as an electrolyte also serving as a Li source₃) Lithium chloride (LiCl), and the like. Further, in the electrochemical doping method, after Li is taken in, a process of desorbing Li from the silicon compound particles may be included. Thereby, the amount of Li taken into the silicon compound particles can be adjusted.

After electrochemical uptake of Li, thermal agitation is used to change the valence state of silicon. The thermal agitation can be achieved by a heating device having an agitation mechanism for agitating the powder. Specifically, the heating can be performed by a fluidized bed heating apparatus or a rotary kiln (rotary kiln) as a heating apparatus provided with a rotary cylindrical furnace, and a rotary kiln is preferable from the viewpoint of productivity.

The negative electrode active material prepared in the above manner is mixed with other materials such as a negative electrode binder, a conductive assistant, and the like to prepare a negative electrode mixture, and then an organic solvent or water, and the like are added to prepare a slurry. Subsequently, the above slurry is applied on the surface of the anode current collector and dried, thereby forming an anode active material layer. In this case, hot pressing or the like may be performed as necessary. The negative electrode can be produced in the above manner.

< lithium ion Secondary Battery >

Next, a lithium ion secondary battery containing the negative electrode active material of the present invention will be described. Here, a laminated film type lithium ion secondary battery is exemplified as a specific example.

[ Structure of laminated film type lithium ion Secondary Battery ]

The laminated film type lithium ion secondary battery 30 shown in fig. 5 mainly contains a wound electrode assembly 31 inside a sheet-shaped exterior member 35. The wound electrode body is wound with a separator between a positive electrode and a negative electrode. Further, a laminate may be housed with a separator between the positive electrode and the negative electrode. In any of the electrode bodies, a positive electrode lead 32 is attached to the positive electrode and a negative electrode lead 33 is attached to the negative electrode. The outermost peripheral portion 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, for example. The positive electrode lead 32 is made of a conductive material such as aluminum, for example, and the negative electrode lead 33 is made of a conductive material such as nickel or copper, for example.

The exterior member 35 is, for example, a laminated film in which a fusion-bonded layer, a metal layer, and a surface protective layer are laminated in this order, and outer peripheral edge portions of the fusion-bonded layers of the two films are fusion-bonded to each other or bonded to each other with an adhesive or the like so that the fusion-bonded layer faces the wound electrode body 31. The fusion-bonded layer portion is a film of polyethylene, polypropylene, or the like, for example, and the metal layer portion is an aluminum foil or the like. The protective layer is, for example, nylon or the like.

An adhesion film 34 for preventing intrusion of external air is inserted between the exterior member 35 and the positive and negative electrode leads. The material is, for example, polyethylene, polypropylene, polyolefin resin.

[ Positive electrode ]

The positive electrode has a positive electrode active material layer on both surfaces or one surface of a positive electrode current collector, for example, as in the negative electrode 10 of fig. 1.

The positive electrode current collector is formed of a conductive material such as aluminum.

The positive electrode active material layer contains one or more of positive electrode materials capable of storing and releasing lithium ions, and may contain other materials such as a binder, a conductive aid, and a dispersant according to design. In this case, the binder and the conductive aid may be the same as the negative electrode binder and the negative electrode conductive aid described above, for example.

As the positive electrode material, a lithium-containing compound is desirable. Examples of the lithium-containing compound include a complex oxide composed of lithium and a transition metal element, and a phosphoric acid compound having lithium and a transition metal element. Among these positive electrode materials, a compound containing at least one of nickel, iron, manganese, and cobalt is preferable. The chemical formula of these positive electrode materials is, for example, Li_xM1O₂Or Li_yM2PO₄And (4) showing. Wherein M1 and M2 represent at least one transition metal element. The values of x and y are different depending on the charge/discharge state of the battery, but are usually 0.05. ltoreq. x.ltoreq.1.10 and 0.05. ltoreq. y.ltoreq.1.10.

Examples of the composite oxide having lithium and a transition metal element include lithium cobalt composite oxide (Li)_xCoO₂) Lithium nickel composite oxide (Li)_xNiO₂) And the like. Examples of the phosphate compound having lithium and a transition metal element include a lithium iron phosphate compound (LiFePO)₄) Or lithium iron manganese phosphate compounds (LiFe)_1-uMn_uPO₄(0 < u < 1)), and the like. When these positive electrode materials are used, a high battery capacity can be obtained and excellent cycle characteristics can be obtained.

[ negative electrode ]

The negative electrode has the same structure as the negative electrode 10 for the nonaqueous electrolyte secondary battery shown in fig. 1, and has, for example, negative electrode active material layers 12 on both sides of the current collector 11. The negative electrode preferably has a negative electrode charge capacity larger than the electric capacity (as the charge capacity of the battery) obtained by the positive electrode active material. This is because deposition 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. At this time, for example, the following regions are provided: the negative electrode active material layer provided on the negative electrode current collector has no region of the positive electrode active material layer opposed thereto. This is for stable cell design.

The non-opposing region, i.e., the region where the negative electrode active material layer and the positive electrode active material layer do not face each other, is hardly affected by charge and discharge. Therefore, the negative electrode active material layer can maintain the state immediately after formation. This makes it possible to accurately investigate the composition of the negative electrode active material and other components with good reproducibility, regardless of the presence or absence of charge and discharge.

[ separator ]

The separator separates the positive electrode from the negative electrode, prevents short-circuiting of current accompanying contact of the two electrodes, and allows lithium ions to pass therethrough. The separator may be formed of a porous film made of, for example, a synthetic resin or ceramic, or may have a laminated structure in which two or more porous films are laminated. Examples of the synthetic resin include polytetrafluoroethylene, polypropylene, and polyethylene.

[ electrolyte ]

A liquid electrolyte (electrolytic solution) is impregnated into at least a part of the active material layer or the separator. The electrolyte solution contains an electrolyte salt dissolved in a solvent, and may further contain other materials such as additives.

The solvent can be, for example, a nonaqueous solvent. Examples of the nonaqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, 1, 2-dimethoxyethane, tetrahydrofuran, and the like. Among them, it is desirable to use at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. This is because more favorable characteristics can be obtained. In addition, in this case, by combining a high-viscosity solvent such as ethylene carbonate or propylene carbonate with a low-viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate, more excellent characteristics can be obtained. This is because the dissociation property and ion mobility of the electrolyte salt are improved.

When an alloy-based negative electrode is used, it is particularly desirable that the solvent contains at least one of a halogenated chain carbonate and a halogenated cyclic carbonate. This forms a stable film on the surface of the negative electrode active material during charge and discharge, particularly during charge. Here, the halogenated chain carbonate means a chain carbonate having a halogen as a constituent element (at least one hydrogen is substituted by a halogen). Further, the halogenated cyclic carbonate means a cyclic carbonate having halogen as a constituent element (i.e., at least one hydrogen is substituted by halogen).

The type of halogen is not particularly limited, but fluorine is preferable. This is because fluorine forms a film of better quality than other halogens. Further, the larger the amount of halogen, the better. This is because the obtained coating film is more stable and the decomposition reaction of the electrolyte solution can be 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-dioxolan-2-one and 4, 5-difluoro-1, 3-dioxolan-2-one.

The solvent additive is preferably a cyclic carbonate containing an unsaturated carbon bond. This is because a stable film is formed on the surface of the negative electrode during charge and discharge, and the decomposition reaction of the electrolyte can be suppressed. Examples of the unsaturated carbon-bonded cyclic carbonate include vinylene carbonate and vinylethylene carbonate.

The solvent additive preferably contains sultone (cyclic sulfonate). The reason for this is that the chemical stability of the battery may be improved. Examples of the sultone include propane sultone and propylene sultone.

Further, the solvent preferably contains an acid anhydride. The reason for this is that the chemical stability of the electrolyte solution is improved. Examples of the acid anhydride include propane disulfonic acid anhydride (propane disulfonic acid anhydride).

The electrolyte salt may contain any one or more of light metal salts such as lithium salts. The lithium salt includes, for example, lithium hexafluorophosphate (LiPF)₆) Lithium tetrafluoroborate (LiBF)₄) And the like.

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

[ method for producing laminated film type Secondary Battery ]

In the present invention, a negative electrode can be 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 can be produced using the produced negative electrode.

First, a positive electrode was produced using the above-described positive electrode material. First, a positive electrode active material is mixed with a binder, a conductive additive, and the like as needed to prepare a positive electrode mixture, and then the mixture is dispersed in an organic solvent to prepare a positive electrode mixture slurry. Next, the mixture slurry is applied to the positive electrode current collector by a coating apparatus such as a die coater having a knife roll (knife roll) or a die head (die head), and the positive electrode active material layer is obtained by hot air drying the mixture slurry. Finally, the positive electrode active material layer is compression-molded by a roll press or the like. At this time, heating may be performed, or heating or compression may be repeated several times.

Next, a negative electrode is produced by forming a negative electrode active material layer on a negative electrode current collector by the same operation procedure as that for producing the negative electrode 10 for a nonaqueous electrolyte secondary battery.

When manufacturing the positive electrode and the negative electrode, active material layers are formed on both surfaces of the positive electrode current collector and the negative electrode current collector, respectively. In this case, the active material application length may be different in both surfaces of any one of the electrodes (see fig. 1).

Next, an electrolytic solution was prepared. Next, as shown in fig. 5, the cathode lead 32 is attached to the cathode current collector by ultrasonic welding, and the anode lead 33 is attached to the anode current collector at the same time. Next, the positive electrode and the negative electrode are laminated or wound with a separator interposed therebetween to produce a wound electrode assembly 31, and a protective tape is bonded to the outermost portion of the wound electrode assembly. Next, the wound electrode body is molded to have a flat shape. Next, the wound electrode assembly is sandwiched between the folded film-shaped exterior members 35, and then the insulating portions of the exterior members are bonded to each other by a heat welding method, and the wound electrode assembly is sealed in a state of being opened only in one direction. A sealing film is inserted between the positive electrode lead and the negative electrode lead and the exterior member. A predetermined amount of the electrolyte solution prepared above was added through the opening, and then vacuum impregnation was performed. After impregnation, the openings were bonded by vacuum heat fusion. In this way, the lithium-ion secondary battery 30 of the laminate film type can be manufactured.