JP6862091B2 - Method for manufacturing negative electrode active material, mixed negative electrode active material, negative electrode for non-aqueous electrolyte secondary battery, lithium ion secondary battery, and negative electrode active material - Google Patents

Description

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

In recent years, small electronic devices such as mobile terminals have become widespread, and further miniaturization, weight reduction, and long life are strongly required. In response to such market demands, the development of a secondary battery that is particularly compact, lightweight, and capable of obtaining a high energy density is being promoted. This secondary battery is being considered for application not only to small electronic devices but also to large electronic devices such as automobiles and electric power storage systems such as houses.

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

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

While carbon-based active materials are widely used as the negative electrode active material, further improvement in battery capacity is required due to recent market demands. In order to improve the battery capacity, it is being studied to use silicon as a negative electrode active material. This is because the theoretical capacity of silicon (4199 mAh / g) is more than 10 times larger than the theoretical capacity of graphite (372 mAh / g), so that a significant improvement in battery capacity can be expected. The development of Kay material as a negative electrode active material is being studied not only for silicon alone, but also for compounds typified by alloys and oxides. In addition, the shape of the active material has been studied from the standard coating type for carbon-based active materials to the integrated type that deposits directly on the current collector.

However, when silicon is used as the main raw material as the negative electrode active material, the negative electrode active material expands and contracts during charging and discharging, so that it is easily cracked mainly in the vicinity of the surface layer of the negative electrode active material. In addition, an ionic substance is generated inside the active material, and the negative electrode active material becomes a fragile substance. When the surface layer of the negative electrode active material is cracked, a new surface is created, which increases the reaction area of the active material. At this time, the decomposition reaction of the electrolytic solution occurs on the new surface, and the electrolytic solution is consumed because a film which is a decomposition product of the electrolytic solution is formed on the new surface. Therefore, the cycle characteristics tend to deteriorate.

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

Specifically, silicon and amorphous silicon dioxide are simultaneously deposited using the vapor phase method for the purpose of obtaining good cycle characteristics and high safety (see, for example, Patent Document 1). Further, in order to obtain 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). Further, in order to improve the 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 is formed in the vicinity of the current collector (). For example, see Patent Document 3). Further, in order to improve the cycle characteristics, oxygen is contained in the silicon active material, and the average oxygen content is 40 at% or less, and the oxygen content is increased in a place close to the current collector. (See, for example, 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. Further, in order to improve the 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). Further, in order to improve the 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 near the interface between the active material and the current collector is set. The active material is controlled within a range of 0.4 or less (see, for example, Patent Document 7). Further, in order to improve the battery load characteristics, a metal oxide containing lithium is used (see, for example, Patent Document 8). Further, in order to improve the cycle characteristics, a hydrophobic layer such as a silane compound is formed on the surface layer of the Kay material (see, for example, Patent Document 9). Further, in order to improve the cycle characteristics, silicon oxide is used and a graphite film is formed on the surface layer thereof to impart conductivity (see, for example, Patent Document 10). In Patent Document 10, with respect to the shift value obtained from the Raman spectra 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} <3. Further, in order to improve the high battery capacity and cycle characteristics, particles having a silicon microcrystalline phase dispersed in silicon dioxide are used (see, for example, Patent Document 11). Further, in order to improve the overcharge and overdischarge characteristics, a silicon oxide in which the atomic number ratio of silicon and oxygen is controlled to 1: y (0 <y <2) is used (see, for example, Patent Document 12).

Japanese Unexamined Patent Publication No. 2001-185127 JP-A-2002-042806 Japanese Unexamined Patent Publication No. 2006-164954 Japanese Unexamined Patent Publication No. 2006-114454 Japanese Unexamined Patent Publication No. 2009-070825 Japanese Unexamined Patent Publication No. 2008-282819 Japanese Unexamined Patent Publication No. 2008-251369 Japanese Unexamined Patent Publication No. 2008-177346 JP-A-2007-234255 Japanese Unexamined Patent Publication No. 2009-21204 Japanese Unexamined Patent Publication No. 2009-205950 Japanese Patent No. 2997741

As mentioned above, in recent years, small mobile devices such as electronic devices have been promoted to have higher performance and higher functionality, and the lithium ion secondary battery, which is the main power source of the device, is required to have an increased battery capacity. There is. As one method for solving this problem, it is desired to develop a lithium ion secondary battery composed of a negative electrode using a Kay material as a main material. Further, a lithium ion secondary battery using a Kay material is desired to have initial efficiency and cycle characteristics close to those of a lithium ion secondary battery using a carbon-based active material. However, it has not been possible to propose a negative electrode active material that exhibits the same initial efficiency and cycle stability as a lithium ion secondary battery using a carbon-based active material.

The present invention has been made in view of the above-mentioned problems, and is a negative electrode active material capable of improving initial charge / discharge characteristics and cycle characteristics when used as a negative electrode active material of a secondary battery. An object of the present invention is to provide a mixed negative electrode active material containing a substance, a negative electrode having a negative electrode active material layer formed of the negative electrode active material, and a lithium ion secondary battery using the negative electrode active material of the present invention. .. Another object of the present invention is to provide a method for producing a negative electrode active material of the present invention capable of improving initial charge / discharge characteristics and cycle characteristics.

In order to achieve the above object, the present invention is a negative electrode active material containing negative electrode active material particles, and the negative electrode active material particles contain a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6). The silicon compound particles are contained, the silicon compound particles _{contain at least one of Li 2} SiO ₃ and Li ₄ SiO ₄ , and the negative electrode active material particles are under the conditions of a temperature of 20 ° C. and a relative humidity of 30%. The amount of water measured by the water vaporization method in which the negative electrode active material particles are heated from 20 ° C. to 120 ° C. in the Karl Fisher titration method after holding for 24 hours is 5000 with respect to the mass of the negative electrode active material particles. and the mass ppm or less, and, true density is at 2.20 g / cm ³ or more 2.50 g / cm ³ or less, and, in a pore distribution based on the BJH method has a peak in the pore diameter of 1~100nm Provided is a negative electrode active material having a total pore capacity of 0.005 cm ^{3 / g or more.}

Since the negative electrode active material of the present invention contains negative electrode active material particles (also referred to as silicon-based active material particles) containing silicon compound particles, the battery capacity can be improved. _{Further, since the SiO 2} component portion of the silicon compound, which is destabilized when the battery is charged and discharged during charging and discharging, is modified to lithium silicate in advance, the irreversible capacity generated during charging is reduced. can do. Further, in such a negative electrode active material, the amount of water contained in the negative electrode active material particles is small, and the pore diameter is adjusted to an appropriate range, so that water desorption is smooth and the water content is removed. Moisture that is chemically bonded at high temperature can be easily desorbed. Therefore, since the Li-doped SiO having good performance is contained in the negative electrode active material, it is possible to improve the initial charge / discharge characteristics and the cycle characteristics when used in a secondary battery.

At this time, the amount of water measured by the water vaporization method in which the negative electrode active material particles are heated from 20 ° C. to 120 ° C. in the Karl Fischer titration method is 1000 mass ppm or less with respect to the mass of the negative electrode active material particles. Is preferable.

As described above, when the water content of the negative electrode active material particles is smaller, the initial charge / discharge characteristics and the cycle characteristics of the secondary battery can be further improved.

Further, in the Karl Fischer titration method, the amount of water measured by the water vaporization method in which the negative electrode active material particles are heated from 120 ° C. to 300 ° C. is 500 mass ppm or less with respect to the mass of the negative electrode active material particles. It is preferable to have.

As described above, when the content of water desorbed at 120 ° C. to 300 ° C. is 500 mass ppm or less with respect to the mass of the negative electrode active material particles, the cycle characteristics of the secondary battery can be further improved.

Further, in the Karl Fischer titration method, the amount of water measured by the water vaporization method in which the negative electrode active material particles are heated from 300 ° C. to 500 ° C. is 200% by mass or less with respect to the mass of the negative electrode active material particles. Is preferable.

As described above, when the content of water desorbed at 300 ° C. to 500 ° C. is 200 mass ppm or less with respect to the mass of the negative electrode active material particles, the cycle characteristics of the secondary battery can be further improved.

Further, it is preferable that at least a part of the surface of the negative electrode active material particles is _{coated with Li 2} CO _{3 and Li OH.}

If the negative electrode active material particles contain Li ₂ CO ₃ and Li OH on the surface in this way, the electron conductivity is further improved. As a result, the initial charge / discharge characteristics and cycle characteristics of the secondary battery can be further improved.

Further, the silicon compound particles have 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 preferably 7.5 nm or less.

If the negative electrode active material in which the silicon compound particles have the above-mentioned silicon crystallinity is used as the negative electrode active material of the lithium ion secondary battery, better cycle characteristics and initial charge / discharge characteristics can be obtained.

Further, the negative electrode active material of the present invention has the maximum peak intensity value A of the Si and Li silicate regions given at -60 to -95 ppm as a chemical shift value obtained from the ^{29 Si-MAS-NMR spectrum in the silicon compound particles.} It is preferable that the peak intensity value B _{in the SiO 2} region given at -96 to -150 ppm as the chemical shift value satisfies the relationship of A> B.

If the amount of Si and Li ₂ SiO _{3 in} the silicon compound particles is larger than that of the SiO ₂ component, the negative electrode active material can sufficiently obtain the effect of improving the battery characteristics by inserting Li.

Further, a test cell composed of a negative electrode containing a mixture of the negative electrode active material and a carbon-based active material and counter electrode lithium is prepared, and in the test cell, a current is passed so as to insert lithium into the negative electrode active material. , A charge / discharge consisting of a discharge in which a current is passed so as to desorb lithium from the negative electrode active material is carried out 30 times, and the discharge capacity Q in each charge / discharge is differentiated by the potential V of the negative electrode electrode based on the counter electrode lithium. When a graph showing the relationship between the differential value dQ / dV and the potential V is drawn, the potential V of the negative electrode at the time of discharging after the Xth time (1 ≦ X ≦ 30) is 0.40 V to 0. It is preferable that the peak is in the range of 55V.

The above-mentioned peak in the V-dQ / dV curve is similar to the peak of the Kay material, and the discharge curve on the higher potential side rises sharply, so that the capacity is easily expressed when designing the battery. Further, if the peak is expressed by charging / discharging within 30 times, it becomes a negative electrode active material in which a stable bulk is formed.

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

When the median diameter is 1.0 μm or more, it is possible to suppress an increase in the irreversible capacity of the battery due to an increase in the surface area per mass. On the other hand, when the median diameter is set to 15 μm or less, the particles are less likely to crack and a new surface is less likely to appear.

Further, the negative electrode active material particles preferably contain a carbon material in the surface layer portion.

As described above, when the negative electrode active material particles contain the carbon material in the surface layer portion thereof, the conductivity can be improved.

The average thickness of the carbon material is preferably 10 nm or more and 5000 nm or less.

If the average thickness of the carbon material is 10 nm or more, the conductivity can be improved. Further, if the average thickness of the carbon material to be coated is 5000 nm or less, a sufficient amount of silicon compound particles can be secured by using the negative electrode active material containing such negative electrode active material particles in the lithium ion secondary battery. , It is possible to suppress a decrease in battery capacity.

Provided is a mixed negative electrode active material material characterized by containing the above negative electrode active material and a carbon-based active material.

As described above, by including the carbon-based active material together with the negative electrode active material (silicon-based negative electrode active material) of the present invention as the material for forming the negative electrode active material layer, the conductivity of the negative electrode active material layer can be improved. At the same time, it becomes possible to relax the expansion stress associated with charging. Further, the battery capacity can be increased by mixing the silicon negative electrode active material with the carbon active material.

Further, in order to achieve the above object, the present invention includes the above-mentioned mixed negative electrode active material, and the ratio of the mass of the negative electrode active material to the total mass of the negative electrode active material and the carbon-based active material is 6. Provided is a negative electrode for a non-aqueous electrolyte secondary battery, which is characterized by having a mass% or more.

If the ratio of the mass of the negative electrode active material (silicon-based negative electrode active material) to the total mass of the negative electrode active material (silicon-based negative electrode active material) and the carbon-based active material is 6% by mass or more, the battery capacity is increased. It is possible to improve.

Further, in order to achieve the above object, the present invention has a negative electrode active material layer formed of the mixed negative electrode active material and a negative electrode current collector, and the negative electrode active material layer is the negative electrode current collector. Provided is a negative electrode for a non-aqueous electrolyte secondary battery, which is formed on a body, and the negative electrode current collector contains carbon and sulfur, and the content thereof is 100% by mass or less. ..

As described above, when the negative electrode current collector constituting the negative electrode contains carbon and sulfur in the above amounts, the deformation of the negative electrode during charging can be suppressed.

Further, in order to achieve the above object, the present invention provides a lithium ion secondary battery characterized in that a negative electrode containing the above negative electrode active material is used.

A lithium ion secondary battery using a negative electrode containing such a negative electrode active material can obtain high capacity, good cycle characteristics, and initial charge / discharge characteristics.

Further, in order to achieve the above object, the present invention is a method for producing a negative electrode active material containing negative electrode active material particles containing silicon compound particles, wherein the silicon compound (SiO _x : 0.5 ≦ x ≦ 1). Negative electrode active material particles by a step of producing silicon compound particles containing .6) and a step of inserting lithium into the silicon compound particles _{to contain at least one of Li 2} SiO ₃ and Li ₄ SiO _4. The negative electrode active material particles are heated from 20 ° C. to 120 ° C. in the Karl Fisher titration method after being held for 24 hours under the conditions of a temperature of 20 ° C. and a relative humidity of 30%. water measured amount of moisture vaporization method that is said is 5000 mass ppm or less based on the mass of the negative electrode active material particles, and the true density is at 2.20 g / cm ³ or more 2.50 g / cm ³ or less, In addition, the selected negative electrode includes a step of selecting particles having a peak in a pore diameter of 1 to 100 nm and a total pore volume of 0.005 cm ^{3 / g or more in the pore distribution based on the BJH method.} Provided is a method for producing a negative electrode active material, which comprises producing a negative electrode active material using active material particles.

By selecting silicon-based active material particles in this way to produce a negative electrode active material, it has a high capacity when used as a negative electrode active material for a lithium ion secondary battery, and has good cycle characteristics and initial charge / discharge characteristics. The negative electrode active material having the above can be produced.

Further, in order to achieve the above object, the present invention manufactures a negative electrode using the negative electrode active material manufactured by the above method for manufacturing a negative electrode active material, and manufactures a lithium ion secondary battery using the manufactured negative electrode. Provided is a method for manufacturing a lithium ion secondary battery.

By using the negative electrode active material produced as described above, it is possible to produce a lithium ion secondary battery having a high capacity and good cycle characteristics and initial charge / discharge characteristics.

When the negative electrode active material of the present invention is used as the negative electrode active material of a secondary battery, it has a high capacity and good cycle characteristics and initial charge / discharge characteristics can be obtained. Further, the same effect can be obtained in the mixed negative electrode active material containing the negative electrode active material, the negative electrode, and the lithium ion secondary battery. Further, according to the method for producing a negative electrode active material of the present invention, a negative electrode active material having good cycle characteristics and initial charge / discharge characteristics can be produced when used as a negative electrode active material of a secondary battery.

It is sectional drawing which shows the structure of the negative electrode for a non-aqueous electrolyte secondary battery of this invention. ^{This is an example of a 29} Si-MAS-NMR spectrum measured from silicon compound particles when modified by a redox method. ^{This is an example of a 29} Si-MAS-NMR spectrum measured from silicon compound particles when modified by a thermal doping method. It is a figure which shows the structural example (laminate film type) of the lithium secondary battery of this invention. It is a graph which shows the relationship between the ratio of the silicon-based active material particle with respect to the total amount of the negative electrode active material, and the increase rate of the battery capacity of a secondary battery.

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 Kay material as a main material as a negative electrode of a lithium ion secondary battery. A lithium ion secondary battery using this Kay material is desired to have initial charge / discharge characteristics and cycle characteristics close to those of a lithium ion secondary battery using a carbon-based active material, but a carbon-based active material is used. It has not been possible to propose a negative electrode active material having initial charge / discharge characteristics and cycle characteristics equivalent to those of a lithium ion secondary battery.

Therefore, the present inventors have made diligent studies in order to obtain a negative electrode active material having a high battery capacity and good cycle characteristics and initial efficiency when used in a secondary battery, and have reached the present invention.

The negative electrode active material of the present invention contains negative electrode active material particles. The negative electrode active material particles _{contain silicon compound particles containing a silicon compound (SiO x} : 0.5 ≦ x ≦ 1.6). The silicon compound particles contain at least one lithium silicate of _{Li 2} SiO ₃ and Li ₄ SiO _4. As for the negative electrode active material particles, the amount of water measured by the water vaporization method in which the negative electrode active material particles are heated from 20 ° C. to 120 ° C. in the Karl Fischer titration method is 5000 mass ppm or less with respect to the mass of the negative electrode active material particles. Is. Further, the anode active material particles, a true density of 2.20 g / cm ³ or more 2.50 g / cm ³ or less. Further, the negative electrode active material particles have a peak in the pore diameter of 1 to 100 nm in the pore distribution based on the BJH method, and the total pore volume is 0.005 cm ³ / g or more.

Since such a negative electrode active material contains negative electrode active material particles (also referred to as silicon-based active material particles) containing silicon compound particles, the battery capacity can be improved. _{Further, since the SiO 2} component portion of the silicon compound, which is destabilized when the battery is charged and discharged during charging and discharging, is modified to lithium silicate in advance, the irreversible capacity generated during charging is reduced. can do. Further, in such a negative electrode active material, the amount of water contained in the negative electrode active material particles is small, and the pore diameter is adjusted to an appropriate range, so that water desorption is smooth and the water content is removed. Moisture that is chemically bonded at high temperature can be easily desorbed. Therefore, since the Li-doped SiO having good performance is contained in the negative electrode active material, it is possible to improve the initial charge / discharge characteristics and the cycle characteristics when used in a secondary battery.

Negative electrode If the true density of the active material particles and the peak position of the pore diameter and the total pore capacity in the pore distribution based on the BJH method are within the above ranges, the negative electrode holding the pores in which the contained water can easily escape. It can be said that it is an active material particle.

<Negative electrode for non-aqueous electrolyte secondary battery>
First, the negative electrode for a non-aqueous electrolyte secondary battery will be described. FIG. 1 shows a cross-sectional configuration of a negative electrode for a non-aqueous electrolyte secondary battery (hereinafter, also referred to as “negative electrode”) according to an embodiment of the present invention.

[Construction of negative electrode]
As shown in FIG. 1, the negative electrode 10 has a negative electrode active material layer 12 on the negative electrode current collector 11. The negative electrode active material layer 12 may be provided on both sides or only one side of the negative electrode current collector 11. Further, the negative electrode current collector 11 may not be provided 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 made of an excellent conductive material and 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) and sulfur (S) in addition to the main element. This is because the physical strength of the negative electrode current collector is improved. In particular, when the current collector has an active material layer that expands during charging, if the current collector contains the above elements, there is an effect of suppressing deformation of the electrodes including the current collector. The content of the above-mentioned contained elements is not particularly limited, but is preferably 100 mass ppm or less. This is because a higher deformation suppressing effect can be obtained. The cycle characteristics can be further improved by such a deformation suppressing effect.

Further, the surface of the negative electrode current collector 11 may or may not be roughened. The roughened negative electrode current collector is, for example, a metal foil that has been electrolyzed, embossed, or chemically etched. The unroughened 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 materials such as a negative electrode binder (binder) and a conductive auxiliary agent. May include. The negative electrode active material contains negative electrode active material particles, and the negative electrode active material particles include silicon compound particles _{containing a silicon compound (SiO x} : 0.5 ≦ x ≦ 1.6).

Further, the negative electrode active material layer 12 may contain a mixed negative electrode active material material containing the negative electrode active material (silicon-based negative electrode active material) of the present invention and a carbon-based active material. As a result, the electrical resistance of the negative electrode active material layer is reduced, and the expansion stress associated with charging can be relaxed. As the carbon-based active material, for example, pyrolytic carbons, cokes, glassy carbon fibers, calcined organic polymer compounds, carbon blacks and the like can be used.

Further, in the negative electrode of the present invention, the ratio of the mass of the negative electrode active material (silicon-based negative electrode active material) to the total mass of the negative electrode active material (silicon-based negative electrode active material) and the carbon-based active material of the present invention is 6% by mass. The above is preferable. When the ratio of the mass of the negative electrode active material of the present invention to the total mass of the negative electrode active material and the carbon-based active material of the present invention is 6% by mass or more, the battery capacity can be reliably improved.

Further, as described above, the negative electrode active material of the present invention is a silicon oxide material containing silicon compound particles, and the silicon compound particles contain a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6). The composition preferably has x 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 100% purity, and may contain a trace amount of impurity elements.

Further, in the negative electrode active material of the present invention, the silicon compound particles contain at least one of _{Li 2} SiO ₃ and Li ₄ SiO _{4. The battery characteristics are improved by the presence of at least one type of Li 4} SiO ₄ and Li ₂ SiO ₃ inside the bulk of the silicon compound particles, but the battery characteristics are further improved when the above two types of lithium silicates coexist. These lithium silicates can be quantified by NMR (Nuclear Magnetic Resonance) or XPS (X-ray photoelectron spectroscopy). XPS and NMR measurements can be performed, for example, under the following conditions.

XPS
・ Equipment: X-ray photoelectron spectrometer,
・ X-ray source: Monochromatic Al Kα ray,
・ X-ray spot diameter: 100 μm,
-Ar ion gun sputtering conditions: 0.5 kV / 2 mm x 2 mm.
²⁹ Si MAS NMR (Magic Angle Spinning Nuclear Magnetic Resonance)
-Equipment: Bruker 700 NMR spectrometer,
-Probe: 4 mm HR-MAS rotor 50 μL,
-Sample rotation speed: 10 kHz,
-Measurement environment temperature: 25 ° C.

Further, the silicon compound particles have 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 the crystallite size corresponding to the crystal plane is It is preferably 7.5 nm or less. The lower the silicon crystallinity of the silicon compound in the silicon compound particles, the better. In particular, when the abundance of Si crystals is small, the battery characteristics can be improved and a stable Li compound can be produced.

Further, the negative electrode active material of the present invention has the maximum peak intensity value A of the Si and Li silicate regions given at -60 to -95 ppm as a chemical shift value obtained from the ^{29 Si-MAS-NMR spectrum in the silicon compound particles.} It is preferable that the peak intensity value B _{in the SiO 2} region given at -96 to -150 ppm as the chemical shift value satisfies the relationship of A> B. If the amount of the silicon component or Li ₂ SiO ₃ is relatively large in the silicon compound particles based on the SiO ₂ component, the effect of improving the battery characteristics by inserting Li can be sufficiently obtained. ^{The measurement conditions for 29} Si-MAS-NMR may be the same as described above.

Further, in the negative electrode active material of the present invention, the negative electrode active material particles preferably contain a carbon material in the surface layer portion. Since the negative electrode active material particles contain a carbon material in the surface layer portion, the conductivity can be improved. Therefore, when the negative electrode active material containing such negative electrode active material particles is used as the negative electrode active material of the secondary battery, , Battery characteristics can be improved.

The average thickness of the carbon material on the surface layer of the negative electrode active material particles is preferably 10 nm or more and 5000 nm or less. If the average thickness of the carbon material is 10 nm or more, the conductivity is improved, and 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 ion. When used as the negative electrode active material of the next battery, the decrease in battery capacity can be suppressed.

The average thickness of this carbon material can be calculated, for example, by the following procedure. First, the negative electrode active material particles are observed at an arbitrary magnification by a TEM (transmission electron microscope). As for this magnification, it is preferable that the thickness of the carbon material can be visually confirmed 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 above 15 carbon materials is calculated.

The coverage of the carbon material is not particularly limited, but it is desirable that the coverage is as high as possible. When the coverage is 30% or more, the electrical conductivity is further improved, which is preferable. The method for coating the carbon material is not particularly limited, but the sugar carbonization method and the thermal decomposition method for hydrocarbon gas are preferable. This is because the coverage can be improved.

The negative electrode active material particles of the present invention have a moisture measurement amount of 1000 mass ppm with respect to the mass of the negative electrode active material particles in the Karl Fischer titration method in the water vaporization method in which the negative electrode active material particles are heated from 20 ° C. to 120 ° C. It is preferably as follows. As described above, if the amount of water measured when the negative electrode active material particles are heated at a temperature of 20 ° C. to 120 ° C. is smaller, the initial charge / discharge characteristics and cycle characteristics of the secondary battery can be further improved. ..

Further, in the negative electrode active material particles of the present invention, the amount of water measured by the water vaporization method in which the negative electrode active material particles are heated from 120 ° C. to 300 ° C. in the Karl Fischer titration method is 500 with respect to the mass of the negative electrode active material particles. The mass is preferably ppm or less. As described above, if the content of water that is desorbed at 120 ° C. to 300 ° C. and is chemically bonded at a higher temperature is 500 mass ppm or less with respect to the mass of the negative electrode active material particles, the secondary battery is used. Since the amount of water that gradually flows out through the charge / discharge cycle is small, the cycle characteristics of the secondary battery can be further improved.

In addition, the amount of water measured by the water vaporization method in which the negative electrode active material particles are heated from 300 ° C. to 500 ° C. in the Karl Fischer titration method is 200 mass ppm or less with respect to the mass of the negative electrode active material particles. Is preferable. In such a case, since the amount of water that gradually flows out through the charge / discharge cycle when the secondary battery is used is particularly small, the cycle characteristics of the secondary battery can be further improved.

Usually, the water that escapes at a high temperature such as 120 ° C. to 300 ° C. or 300 ° C. to 500 ° C. is the water that is strongly bonded to the surface and is difficult to escape when the electrode is dried at about 100 ° C. That is, this is water that is strongly bound like water of crystallization. Therefore, if the content of water that is difficult to remove when the electrode is dried is small, the cycle characteristics of the secondary battery can be further improved.

Further, it is preferable that at least a part of the surface of the negative electrode active material particles is _{coated with Li 2} CO _{3 and Li OH.} If the negative electrode active material particles contain Li ₂ CO ₃ and Li OH on the surface in this way, the electron conductivity is further improved. As a result, the initial charge / discharge characteristics and cycle characteristics of the secondary battery can be further improved.

_{Further, it is preferable that the median diameter (D 50} : particle diameter when the cumulative volume is 50%) of the negative electrode active material particles is 1.0 μm or more and 15 μm 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 less likely to crack. When the median diameter is 1.0 μm or more, the surface area per mass can be reduced and the increase in the irreversible capacity of the battery can be suppressed. On the other hand, when the median diameter is 15 μm or less, the particles are less likely to crack and a new surface is less likely to appear.

Further, for the negative electrode active material (silicon-based active material) of the present invention, a test cell composed of a negative electrode electrode containing a mixture of the silicon-based active material and a carbon-based active material and counter electrode lithium is prepared, and in the test cell, a test cell is prepared. Charging / discharging consisting of charging in which a current is passed so as to insert lithium into the silicon-based active material and discharging in which a current is passed so as to desorb lithium from the silicon-based active material is carried out 30 times, and the discharge capacity Q in each charge / discharge is determined. When a graph showing the relationship between the potential V and the differential value dQ / dV differentiated by the potential V of the negative electrode electrode with reference to the counter electrode lithium is drawn, the negative electrode at the time of discharge after the Xth time (1 ≦ X ≦ 30). It is preferable that the potential V of the electrode has a peak in the range of 0.40V to 0.55V. The above-mentioned peak in the V-dQ / dV curve is similar to the peak of the Kay material, and the discharge curve on the higher potential side rises sharply, so that the capacity is easily expressed when designing the battery. Further, it can be determined that a stable bulk is formed if the negative electrode active material develops the peak after charging and discharging within 30 times.

Further, as the negative electrode binder contained in the negative electrode active material layer, for example, any one or more of a polymer material, synthetic rubber and the like can be used. The polymer material is, for example, polyvinylidene fluoride, polyimide, polyamideimide, aramid, polyacrylic acid, lithium polyacrylate, carboxymethyl cellulose and the like. The synthetic rubber is, for example, styrene-butadiene rubber, fluorine-based rubber, ethylene propylene diene, or the like.

As the negative electrode conductive auxiliary agent, for example, any one or more of carbon materials such as carbon black, acetylene black, graphite, kechen 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 in which the negative electrode active material particles are mixed with the above-mentioned binder, and if necessary, a conductive auxiliary agent and a carbon material are mixed, and then dispersed in an organic solvent, water, or the like for coating.

[Manufacturing method of negative electrode]
The negative electrode can be manufactured, for example, by the following procedure. First, a method for producing a negative electrode active material used for a negative electrode will be described. First, silicon compound _{particles containing a silicon compound (SiO x} : 0.5 ≦ x ≦ 1.6) are prepared. Next, lithium is inserted into the silicon compound particles to contain at least one of _{Li 2} SiO ₃ and Li ₄ SiO _4. As a result, negative electrode active material particles are produced. Further, the silicon compound particles may be coated with a carbon material, and then lithium may be inserted into the silicon compound particles.

Next, the negative electrode active material particles are held at a temperature of 20 ° C. and a relative humidity of 30% for 24 hours, and then the negative electrode active material particles are heated from 20 ° C. to 120 ° C. in the Karl Fischer titration method. water measured amount of at law, the negative active or less material 5000 mass ppm relative to the mass of the particle, and a true density of not more than 2.20 g / cm ³ or more 2.50 g / cm ^3, and, BJH In the pore distribution based on the method, those having a peak in the pore diameter of 1 to 100 nm and having a total pore volume of 0.005 cm ³ / g or more are selected. Then, the negative electrode active material is produced by using the selected negative electrode active material particles.

More specifically, the negative electrode active material can be produced as follows. First, the raw material that generates silicon oxide gas is heated in the temperature range of 900 ° C. to 1600 ° C. under reduced pressure in the presence of an inert gas to generate silicon oxide gas. Considering the presence of surface oxygen of the metallic silicon powder and trace oxygen in the reaction furnace, it is desirable that the mixed molar ratio is in the range of 0.8 <metallic 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 lowered to 100 ° C. or lower, and pulverized and pulverized by using a ball mill, a jet mill or the like. As described above, silicon compound particles can be produced. The Si crystals in the silicon compound particles can be controlled by changing the vaporization temperature or by heat treatment after formation.

Here, a layer of carbon material may be formed on the surface layer of the silicon compound particles. A pyrolysis CVD method is desirable as a method for forming a layer of carbon material. A method of forming a carbon material layer by a thermal decomposition CVD method will be described.

First, the silicon compound particles are set in the furnace. Next, a hydrocarbon gas is introduced into the furnace to raise the temperature inside 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, unintentional disproportionation of the active material particles can be suppressed. After raising the temperature in the furnace to a predetermined temperature, a carbon layer is formed on the surface of the silicon compound particles. The hydrocarbon gas used as a raw material for the carbon material is not particularly limited, but it is desirable that n ≦ 3 in _{the C n} H _{m composition.} When n ≦ 3, the manufacturing cost can be lowered and the physical properties of the decomposition product can be improved.

Next, Li is inserted into the negative electrode active material particles containing the silicon active material particles prepared as described above, and at least one of _{Li 2} SiO ₃ and Li ₄ SiO _{4 is contained.} Li is preferably inserted by the heat doping method.

In the modification by the heat doping method, for example, the silicon compound particles can be modified by mixing with LiH and heating in an inert atmosphere. As the inert atmosphere, for example, an Ar atmosphere, an N ₂ atmosphere, or a mixed atmosphere of _{Ar and N 2 can be used.} More specifically, first, thoroughly mixed and LiH powder and silicon oxide powder under Ar or N ₂ atmosphere, a sealing and homogenized by stirring each sealed container. Then, it is reformed by heating and firing in the range of 700 ° C. to 800 ° C. When the _{modification is performed in an N 2} atmosphere, the surface of the obtained negative electrode active material particles contains _{Li 3 N.} After that, if the negative electrode active material particles are washed with pure water or the like, Li ₂ CO ₃ and Li OH can be generated on the surface. The cleaning time can be adjusted according to the powder. After that, if drying is performed, negative electrode active material particles having a reduced amount of water on the surface can be synthesized.

Further, the modification may be carried out by a redox method. In the modification by the redox method, for example, lithium can be inserted by first immersing the silicon compound particles in a solution in which lithium is dissolved in an ether solvent. The solution may further contain a polycyclic aromatic compound or a linear polyphenylene compound. _{Further, if N 2} is bubbled in this solution _{, Li 3} N can be produced at the same time as lithium is inserted. Then, the active lithium may be desorbed from the silicon compound particles by immersing the silicon compound particles in a solution containing an alcohol solvent, a carboxylic acid solvent, water, or a mixed solvent thereof. The solution used for desorption of active lithium contains a compound having a quinoid structure in the molecule as a solute, and a solution containing an ether solvent, a ketone solvent, an ester solvent, or a mixed solvent thereof is used as a solvent. You may. In this way, if the active lithium is desorbed after the lithium is inserted, a negative electrode active material having higher water resistance can be obtained. Then, it may be washed by a method of washing with alkaline water in which alcohol or lithium carbonate is dissolved, weak acid, pure water or the like.

When the modification is performed by the thermal doping method, the ²⁹ Si-MAS-NMR spectrum obtained from the silicon compound particles is different from that when the redox method is used. ^{FIG. 2 shows an example of the 29} Si-MAS-NMR spectrum measured from the silicon compound particles when modified by the redox method. In FIG. 2, the peak given in the vicinity of _{−75 ppm is the peak derived from Li 2} SiO _3, and the peak given in the vicinity of −80 to −100 ppm is the peak derived from Si. In addition, it may have a peak of Li silicate other than _{Li 2} SiO ₃ and Li ₄ SiO ₄ from -80 to -100 ppm.

^{Further, FIG. 3 shows an example of the 29} Si-MAS-NMR spectrum measured from the silicon compound particles when modified by the thermal doping method. In FIG. 3, the peak given in the vicinity of _{−75 ppm is the peak derived from Li 2} SiO _3, and the peak given in the vicinity of −80 to −100 ppm is the peak derived from Si. In addition, it may have a peak of Li silicate other than _{Li 2} SiO ₃ and Li ₄ SiO ₄ from -80 to -100 ppm. From the XPS spectrum, _{the peak of Li 4} SiO ₄ can be confirmed.

Next, the negative electrode active material particles after modification were held at a temperature of 20 ° C. and a relative humidity of 30% for 24 hours, and then the negative electrode active material particles in the Karl Fischer titration method were changed from 20 ° C. to 120 ° C. water measured amount of moisture vaporization method for heating, and 5000 ppm by mass or less relative to the weight of the anode active material particles, and the true density is at 2.20 g / cm ³ or more 2.50 g / cm ³ or less, In addition, in the pore distribution based on the BJH method, those having a peak in the pore diameter of 1 to 100 nm and having a total pore volume of 0.005 cm ³ / g or more are selected.

It should be noted that the selection of the negative electrode active material particles does not necessarily have to be performed each time the negative electrode active material is produced, and the above measurement is performed and the negative electrode active material particles are heated from 20 ° C. to 120 ° C. in the Karl Fischer titration method. If the production conditions in which the water content measured by the method, the true density, the peak position of the pore diameter in the pore distribution based on the BJH method, and the total pore volume all satisfy the above ranges are found and selected, then The negative electrode active material can be produced under the same conditions as the selected conditions.

Further, the water content measurement by the Karl Fischer titration method, the water vaporization method, the true density measurement, and the pore distribution measurement by the BJH method may be performed by ordinary methods.

The negative electrode active material prepared as described above is mixed with other materials such as a negative electrode binder and a conductive auxiliary agent to form a negative electrode mixture, and then an organic solvent or water is added to prepare a slurry. Next, the above slurry is applied to the surface of the negative electrode current collector and dried to form a negative electrode active material layer. At this time, a heating press or the like may be performed if necessary. As described above, the negative electrode can be manufactured.

<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 a negative electrode containing the negative electrode active material of the present invention. Here, as a specific example, a laminated film type lithium ion secondary battery will be taken as an example.

[Structure of laminated film type lithium ion secondary battery]
The laminated film type lithium ion secondary battery 20 shown in FIG. 4 has a wound electrode body 21 housed mainly inside a sheet-shaped exterior member 25. This wound body has a separator between the positive electrode and the negative electrode and is wound. There is also a case where a separator is provided between the positive electrode and the negative electrode to store the laminate. In both electrode bodies, the positive electrode lead 22 is attached to the positive electrode, and the negative electrode lead 23 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 25 toward the outside, for example. The positive electrode lead 22 is formed of a conductive material such as aluminum, and the negative electrode lead 23 is formed of a conductive material such as nickel or copper.

The exterior member 25 is, for example, a laminated film in which a fused layer, a metal layer, and a surface protective layer are laminated in this order. The laminated film is made of two films so that the fused layer faces the electrode body 21. The outer peripheral edges of the fusion layer are fused or bonded with an adhesive or the like. The fused portion is a film such as polyethylene or polypropylene, and the metal portion is an aluminum foil or the like. The protective layer is, for example, nylon.

An adhesive film 24 is inserted between the exterior member 25 and the positive and negative electrode leads to prevent outside air from entering. This material is, for example, polyethylene, polypropylene, polyolefin resin.

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

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

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

A lithium-containing compound is desirable as the positive electrode material. Examples of the lithium-containing compound include a composite oxide composed of lithium and a transition metal element, and a phosphoric acid compound having lithium and a transition metal element. Among these described positive electrode materials, a compound having at least one of nickel, iron, manganese, and cobalt is preferable. These chemical formulas are represented by, for example, Li _x M1O ₂ or Li _y M2PO _4. In the formula, M1 and M2 represent at least one transition metal element. The values of x and y show different values depending on the battery charge / discharge state, but are generally shown by 0.05 ≦ x ≦ 1.10 and 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 lithium and a transition metal element include a lithium iron phosphoric acid compound (LiFePO ₄ ) and a lithium iron manganese phosphoric acid compound (LiFe _1-u Mn _u PO ₄ (0 <u <1)). Can be mentioned. This is because when these positive electrode materials are used, a high battery capacity can be obtained and also excellent cycle characteristics can be obtained.

[Negative electrode]
The negative electrode has the same configuration as the negative electrode 10 for a lithium ion secondary battery of FIG. 1 described above, and has, for example, negative electrode active material layers 12 on both sides of the current collector 11. It is preferable that the negative electrode has a larger negative electrode charge capacity than the electric capacity (charge capacity as a battery) obtained from the positive electrode active material. This is because the precipitation of lithium metal on the negative electrode can be suppressed.

The positive electrode active material layer is provided on a part of both sides of the positive electrode current collector, and the negative electrode active material layer is also provided on a part of both sides 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 in which the opposite positive electrode active material layer does not exist. This is for stable battery design.

In the non-opposing region, that is, the region where the negative electrode active material layer and the positive electrode active material layer do not face each other, the influence of charging and discharging is hardly affected. Therefore, the state of the negative electrode active material layer is maintained as it is immediately after formation. As a result, the composition of the negative electrode active material can be accurately investigated with good reproducibility regardless of 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 a current short circuit due to contact between the two electrodes. 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, polyethylene and the like.

[Electrolytic solution]
At least a part of the active material layer or the separator is impregnated with a liquid electrolyte (electrolyte 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, ethylmethyl carbonate, methylpropyl carbonate, 1,2-dimethoxyethane, and tetrahydrofuran. 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. Further, in this case, more superior characteristics can be obtained 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. This is because the dissociability 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 or a halogenated cyclic carbonate. As a result, a stable film is formed on the surface of the negative electrode active material during charging / discharging, particularly during charging. Here, the halogenated chain-chain carbonic acid ester is a chain-chain carbonic acid ester having halogen as a constituent element (at least one hydrogen is substituted with halogen). The halogenated cyclic carbonate is a cyclic carbonate having halogen as a constituent element (that is, at least one hydrogen is substituted with halogen).

The type of halogen is not particularly limited, but fluorine is preferable. This is because it forms a film of better quality than other halogens. Further, the larger the number of halogens, the more desirable. 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 fluoromethylmethyl carbonate and difluoromethylmethyl carbonate. Examples of the halogenated cyclic carbonate include 4-fluoro-1,3-dioxolan-2-one and 4,5-difluoro-1,3-dioxolan-2-one.

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

Further, it is preferable to contain sultone (cyclic sulfonic acid ester) as a solvent additive. This is because the chemical stability of the battery is improved. Examples of the sultone include propane sultone and propene sultone.

Further, 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 anhydride.

The electrolyte salt can include, 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 ionic conductivity can be obtained.

[Manufacturing method of laminated film type secondary battery]
In the present invention, a negative electrode is produced using the negative electrode active material produced by the above-mentioned 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.

First, a positive electrode is prepared using the above-mentioned positive electrode material. First, the positive electrode active material is mixed with a binder, a conductive auxiliary agent, etc., if necessary, to form a positive electrode mixture, and then dispersed in an organic solvent to prepare a positive electrode mixture slurry. Subsequently, the mixture slurry is applied to the positive electrode current collector with a coating device such as a knife roll or a die coater having 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, the negative electrode active material layer is formed on the negative electrode current collector to prepare the negative electrode by using the same work procedure as the production of the negative electrode 10 for the lithium ion secondary battery described above.

When the positive electrode and the negative electrode are manufactured, the active material layers are formed on both sides of the positive electrode and the negative electrode current collector. At this time, the active material coating lengths on both sides of both electrodes may be different (see FIG. 1).

Then, the electrolytic solution is adjusted. Subsequently, the positive electrode lead 22 is attached to the positive electrode current collector by ultrasonic welding or the like, and the negative electrode lead 23 is attached to the negative electrode current collector. Subsequently, the positive electrode and the negative electrode are laminated or wound via a separator to prepare a wound electrode body 21, and a protective tape is adhered to the outermost peripheral portion thereof. 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 25, the insulating portions of the exterior members are adhered to each other by a heat fusion method, and the wound electrode body is released in only one direction. Is enclosed. An adhesive film is inserted between the positive electrode lead and the negative electrode lead and the exterior member. A predetermined amount of the above-adjusted electrolytic solution is charged from the release portion, and vacuum impregnation is performed. After impregnation, the release portion is adhered by a vacuum heat fusion method. As described above, the laminated film type lithium ion secondary battery 20 can be manufactured.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited to these Examples.

(Example 1-1)
The laminated film type lithium ion secondary battery 20 shown in FIG. 4 was produced by the following procedure.

First, a positive electrode was prepared. The positive electrode active material is LiNi _0.7 Co _0.25 Al _0.05 O, which is a lithium nickel cobalt composite oxide, 95% by mass, a positive electrode conductive auxiliary agent 2.5% by mass, and a positive electrode binder (polyvinylidene fluoride). : PVDF) 2.5% by mass was mixed to prepare a positive electrode mixture. Subsequently, the positive electrode mixture was dispersed in an organic solvent (N-methyl-2-pyrrolidone: NMP) to prepare a paste-like slurry. Subsequently, the slurry was applied to both sides of the positive electrode current collector with a coating device having a die head, and dried with a hot air drying device. 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 prepared. First, the negative electrode active material was prepared as follows. A raw material in which metallic silicon and silicon dioxide were mixed was introduced into a reactor, vaporized in an atmosphere of 10 Pa of vacuum, deposited on an adsorption plate, cooled sufficiently, and then the deposit was taken out and pulverized with a ball mill. .. The value of x of _{SiO x} of the silicon compound particles thus obtained was 0.5. Subsequently, the particle size of the silicon compound particles was adjusted by classification. Then, by performing thermal decomposition CVD, the surface of the silicon compound particles was coated with a carbon material.

Subsequently, lithium was inserted into the silicon compound particles by a heat doping method to modify the particles. First, a silicon compound particles after the coating of carbon material, thoroughly mixed with LiH powder and the anode active material particles under N _2, a sealing, was homogenized by stirring each sealed container. Then, it was heated and fired in the range of 700 ° C. to 800 ° C. Through the above treatment, lithium was inserted into the negative electrode active material particles. Further, during this thermal doping, lithium nitride was generated on the surface of the negative electrode active material particles. Next, the negative electrode active material particles were washed with pure water equivalent to 4 times the negative electrode active material particles. Then, the negative electrode active material particles were dried.

A part of the negative electrode active material particles produced here was taken out, and the water content was measured by the water vaporization method in the Karl Fischer titration method. As a result, the water content measured by the moisture vaporization method in which the negative electrode active material particles held for 24 hours under the conditions of a temperature of 20 ° C. and a relative humidity of 30% were heated from 20 ° C. to 120 ° C. became the mass of the negative electrode active material particles. On the other hand, the moisture measurement value by the moisture vaporization method heated from 550 mass ppm and 120 ° C. to 300 ° C. is 120 mass ppm with respect to the mass of the negative electrode active material particles by the moisture vaporization method heated from 300 ° C. to 500 ° C. The measured water content was 60 mass ppm with respect to the mass of the negative electrode active material particles.

The true density of the produced negative electrode active material particles was 2.29 g / cm ³ .

Moreover, when the pore distribution was measured based on the BJH method, the pore distribution had a peak in the pore diameter of 1 to 100 nm, and the total pore volume was 0.025 cm ³ / g.

Next, the negative electrode active material particles and the carbon-based active material were blended at a mass ratio of 1: 9 to prepare a mixed negative electrode active material. Here, as the carbon-based active material, a mixture of natural graphite coated with a pitch layer and artificial graphite at a mass ratio of 5: 5 was used. The median diameter of the carbon-based active material was 20 μm.

Next, the prepared mixed negative electrode active material, conductive auxiliary agent 1 (carbon nanotube, CNT), conductive auxiliary agent 2 (carbon fine particles having a median diameter of about 50 nm), styrene butadiene rubber (styrene butadiene copolymer, hereinafter referred to as SBR). , Carboxymethyl cellulose (hereinafter referred to as CMC) at a dry mass ratio of 92.5: 1: 1: 2.5: 3, and then diluted with pure water to prepare a negative electrode mixture slurry. The above SBR and CMC are negative electrode binders (negative electrode binders).

Further, as the negative electrode current collector, an electrolytic copper foil having a thickness of 15 μm was used. The electrolytic copper foil contained carbon and sulfur at concentrations of 70 mass ppm each. Finally, the negative electrode mixture slurry was applied to the negative electrode current collector and dried in a vacuum atmosphere at 100 ° C. for 1 hour. After drying, the amount of the negative electrode active material layer deposited per unit area on one side of the negative electrode (also referred to as area density) was 5 mg / cm ² .

Next, after mixing the solvent (4-fluoro-1,3-dioxolane-2-one (FEC), ethylene carbonate (EC) and dimethyl carbonate (DMC)), the electrolyte salt (lithium hexafluorophosphate: LiPF). ₆ ) was dissolved to prepare an electrolytic solution. In this case, the composition of the solvent was set to FEC: EC: DMC = 10: 20: 70 in the deposition ratio, and the content of the electrolyte salt was set to 1.2 mol / kg with respect to the solvent.

Next, the secondary battery was assembled as follows. First, an aluminum reed was ultrasonically welded to one end of the positive electrode current collector, and a nickel reed was welded to one end of the negative electrode current collector. Subsequently, the positive electrode, the separator, the negative electrode, and the separator were laminated in this order and rotated in the longitudinal direction to obtain a rotating electrode body. The winding end portion was fixed with PET protective tape. As the separator, a laminated film (thickness 12 μm) sandwiched between a film containing porous polypropylene as a main component and a film containing porous polyethylene as a main component was used. Subsequently, after sandwiching the electrode body between the exterior members, the outer peripheral edges excluding one side were heat-sealed to each other, and the electrode body was housed inside. As the exterior member, a nylon film, an aluminum foil, and an aluminum laminated film in which a polypropylene film was laminated were used. Subsequently, the prepared electrolytic solution was injected through the opening, 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 investigated as follows. First, in order to stabilize the battery, charging and discharging were performed for two cycles at 0.2 C in an atmosphere of 25 ° C., and the discharge capacity of the second cycle was measured. Subsequently, charging and discharging were performed until the total number of cycles reached 499 cycles, and the discharge capacity was measured each time. Finally, the discharge capacity of the 500th cycle obtained by charging and discharging 0.2C was divided by the discharge capacity of the second cycle to calculate the capacity retention rate (hereinafter, also simply referred to as the maintenance rate). From the normal cycle, that is, from the 3rd cycle to the 499th cycle, charging and discharging were performed with 0.7C for charging and 0.5C for discharging.

When investigating the initial charge / discharge characteristics, the initial efficiency (hereinafter sometimes referred to as the initial efficiency) was calculated. The initial efficiency was calculated from the formula represented by the initial efficiency (%) = (initial discharge capacity / initial charge capacity) × 100. The ambient temperature was the same as when the cycle characteristics were examined.

(Examples 1-2 to Examples 1-3, Comparative Examples 1-1 to 1-2)
A secondary battery was manufactured in the same manner as in Example 1-1, except that the amount of oxygen in the bulk of the silicon compound was adjusted. In this case, the amount of oxygen was adjusted by changing the ratio of metallic silicon and silicon dioxide in the raw material of the silicon compound and the heating temperature. The values of x of the silicon compound represented by _{SiO x} in Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2 are shown in Table 1.

At this time, the negative electrode active material particles of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2 had the following properties. The median diameter of the negative electrode active material particles was 4 μm. _{Li 2} SiO ₃ and Li ₄ SiO ₄ were contained inside the silicon compound particles. Further, the silicon compound has a half width (2θ) of the diffraction peak due to the Si (111) crystal plane obtained by X-ray diffraction at 1.755 °, and the crystallite size due to the Si (111) crystal plane. Was 4.86 nm.

Further, in all the above Examples and Comparative Examples, peaks in the Si and Li silicate regions given at -60 to -95 ppm as chemical shift values obtained from the ^{29 Si-MAS-NMR spectrum were expressed.} Further, in all the above Examples and Comparative Examples, the maximum peak intensity values A of the Si and Li silicate regions given at -60 to -95 ppm as the chemical shift values obtained from the ^{29 Si-MAS-NMR spectrum and -96 to -96 to} The relationship with the peak intensity value B _{in the SiO 2} region given at −150 ppm was A> B.

The average thickness of the carbon material contained in the negative electrode active material particles was 100 nm.

Further, a 2032 size coin battery type test cell was prepared from the negative electrode and the counter electrode lithium prepared as described above, and the discharge behavior thereof was evaluated. More specifically, first, constant current and constant voltage charging was performed with the counter electrode Li up to 0 V, and charging was terminated when the ^{current density reached 0.05 mA / cm 2.} Then, constant current discharge was performed up to 1.2V. The current density at this time was 0.2 mA / cm ² . This charging / discharging is repeated 30 times, and from the data obtained in each charging / discharging, a graph is drawn with the vertical axis representing the rate of change in capacitance (dQ / dV) and the horizontal axis representing the voltage (V), with V being 0.4 to 0. It was confirmed whether a peak could be obtained in the range of .55 (V). As a result, the above peak was not obtained in Example 1-1 and Comparative Example 1-1 in which x of SiOx was 0.5 or less. In the other examples and comparative examples, the peak was obtained within 30 times of charging and discharging, and the above peak was obtained in all charging and discharging from the first charging and discharging to the 30th charging and discharging.

Table 1 shows the evaluation results of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2.

As shown in Table 1, in the silicon compound represented by SiOx, when the value of x was out of 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), the initial efficiency is improved, but the capacity retention rate is significantly deteriorated. On the other hand, as shown in Comparative Example 1-2, when the amount of oxygen was large (x = 1.8), the conductivity was lowered and the capacity of the silicon oxide was substantially not developed, so the evaluation was stopped.

(Example 2-1 and Example 2-2)
A secondary battery was produced under the same conditions as in Example 1-2 except that the type of lithium silicate contained inside the silicon compound particles was changed as shown in Table 2, and the cycle characteristics and initial efficiency were evaluated .

(Comparative Example 2-1)
A secondary battery was prepared under the same conditions as in Example 1-2 except that lithium was not inserted into the silicon compound particles, and the cycle characteristics and initial efficiency were evaluated.

The results of Example 2-1 and Example 2-2 and Comparative Example 2-1 are shown in Table 2.

Since the silicon compound contains _{a stable lithium silicate such as Li 2} SiO ₃ and Li ₄ SiO ₄ , the capacity retention rate and the initial efficiency are improved. In particular, when both Li ₂ SiO ₃ and Li ₄ SiO ₄ lithium silicates are contained, the capacity retention rate and the initial efficiency are further improved. On the other hand, in Comparative Example 2-1 in which the silicon compound was not contained with lithium without modification, the capacity retention rate and the initial efficiency were lowered.

(Examples 3-1 to 3-3)
A secondary battery was prepared under the same conditions as in Example 1-2 except that the measured water content, true density, and pore distribution of the negative electrode active material particles were changed as shown in Table 3, and the cycle characteristics and initial efficiency were adjusted. evaluated. The amount of water contained in the negative electrode active material particles measured by the Karl Fischer titration method was adjusted by changing the heating time in the heat doping and the cleaning time with pure water after the heat doping. The true density and pore distribution of the negative electrode active material particles were adjusted by changing the heating temperature at the time of producing the silicon compound particles.

(Examples 3-4 to 3-6)
A secondary battery under the same conditions as in Example 1-2 except that the method for modifying silicon compound particles was a redox method and the measured water content, true density, and pore distribution were changed as shown in Table 3. Was prepared and the cycle characteristics and initial efficiency were evaluated.

(Comparative Examples 3-1 to 3-4)
A secondary battery was prepared under the same conditions as in Example 3-1 except that the measured water content, true density, and pore distribution of the negative electrode active material particles were changed as shown in Table 3. The efficiency was evaluated.

(Comparative Example 3-5)
A secondary battery was prepared under the same conditions as in Example 3-4 except that the measured water content, true density, and pore distribution of the negative electrode active material particles were changed as shown in Table 3, and the cycle characteristics and the first time were obtained. The efficiency was evaluated.

As shown in Table 3, the amount of water measured by the water vaporization method in which the negative electrode active material particles are heated from 20 ° C. to 120 ° C. in the Karl Fischer titration method is 5000 mass ppm or less with respect to the mass of the negative electrode active material particles. There, and true density is at 2.20 g / cm ³ or more 2.50 g / cm ³ or less, and, in a pore distribution based on the BJH method has a peak in the pore diameter of 1 to 100 nm, the total pore Examples 3-1 to 3-6 and 1-2 which satisfy all the conditions that the capacity is 0.005 cm ³ / g or more are Comparative Examples 3-1 to 3-5 and 2 which do not satisfy at least one of the above conditions. The capacity retention rate and initial efficiency were higher than -1. Further, when the amount of water measured by the water vaporization method from 20 ° C. to 120 ° C. was 1000 mass ppm or less with respect to the mass of the negative electrode active material particles, the capacity retention rate and the initial efficiency were particularly improved.

Further, the amount of water measured by the water vaporization method from 120 ° C. to 300 ° C. is 500 mass ppm or less with respect to the mass of the negative electrode active material particles, and the amount of water measured by the water vaporization method from 300 ° C. to 500 ° C. However, in Examples 3-1 and 1-2 in which the mass of the negative electrode active material particles was 200 mass ppm or less, the capacity retention rate was improved as compared with Examples 3-2 and 3-3.

(Example 4-1)
The atmosphere in the thermal dope _{was changed from the N 2} atmosphere to the Ar atmosphere, Li ₃ N was not generated, and then Li ₂ CO ₃ and Li OH were not generated, but under the same conditions as in Example 1-2. The next battery was prepared and the cycle characteristics and initial efficiency were evaluated.

_{The presence of Li 2} CO ₃ and Li OH on the surface of the negative electrode active material particles improved the capacity retention rate and the initial efficiency.

(Examples 5-1 to 5-6)
A secondary battery was prepared under the same conditions as in Example 1-2 except that the crystallinity of the silicon compound particles was changed as shown in Table 5, and the cycle characteristics and initial efficiency were evaluated. The crystallinity of the silicon compound particles can be controlled by changing the vaporization temperature of the raw material and heat treatment after the silicon compound particles are formed.

In particular, a high capacity retention rate was obtained with a low crystallinity material having a half width of 1.2 ° or more and a crystallinity size of 7.5 nm or less due to the Si (111) plane.

(Example 6-1)
Under the same conditions as in Example 1-2, except that the relationship between the maximum peak intensity value A of the Si and Li silicate regions and _{the peak intensity value B derived from the SiO 2 region of the silicon compound is A <B.} The next battery was prepared and the cycle characteristics and initial efficiency were evaluated. In this case, by reducing the amount of insertion of lithium during reforming _to reduce the amount of Li 2 SiO _3, it has a small intensity A of a peak derived from the Li 2 SiO _3.

As can be seen from Table 6, the battery characteristics were improved when the relationship of peak intensities was A> B.

(Example 7-1)
In the V-dQ / dV curve obtained by charging and discharging 30 times in the above test cell, a negative electrode active material in which V did not peak in the range of 0.40V to 0.55V was used in any charging and discharging. A secondary battery was produced under the same conditions as in Example 1-2 except for the above, and the cycle characteristics and initial efficiency were evaluated.

In order for the discharge curve shape to rise sharper, it is necessary for the silicon compound (SiOx) to exhibit the same discharge behavior as silicon (Si). Since the silicon compound has a relatively gentle discharge curve in which a peak does not appear in the above range after 30 times of charging and discharging, the initial efficiency is slightly lowered when the secondary battery is used. If the peak is expressed by charging / discharging within 30 times, a stable bulk is formed, and the capacity retention rate and the initial efficiency are improved.

(Examples 8-1 to 8-6)
A secondary battery was prepared under the same conditions as in Example 1-2 except that the median diameter of the silicon compound was changed as shown in Table 8, and the cycle characteristics and initial efficiency were evaluated.

When the median diameter of the silicon compound was 1.0 μm or more, the maintenance rate was improved. It is considered that this is because the surface area per mass of the silicon compound was not too large and the area where the side reaction occurred could be reduced. On the other hand, when the median diameter is 15 μm or less, the particles are hard to break during charging, and SEI (solid electrolyte interface) due to the new surface is hard to be generated during charging and discharging, so that the loss of reversible Li can be suppressed. Further, when the median diameter of the silicon-based active material particles is 15 μm or less, the expansion amount of the silicon compound particles during charging does not increase, so that physical and electrical destruction of the negative electrode active material layer due to expansion can be prevented.

(Examples 9-1 to 9-5)
A secondary battery was prepared under the same conditions as in Example 1-2 except that the average thickness of the carbon material coated on the surface of the silicon-based active material particles was changed, and the cycle characteristics and the initial efficiency were evaluated. The average thickness of the carbon material can be adjusted by changing the CVD conditions.

As can be seen from Table 9, when the film thickness of the carbon layer is 10 nm or more, the conductivity is particularly improved, so that the capacity retention rate and the initial efficiency can be improved. On the other hand, when the film thickness of the carbon layer is 5000 nm or less, the amount of silicon compound particles can be sufficiently secured in the battery design, so that the battery capacity does not decrease.

(Example 10-1)
A secondary battery was produced under the same conditions as in Example 1-2 except that the ratio of the mass of the silicon-based active material particles in the negative electrode active material was changed, and the rate of increase in battery capacity was evaluated.

FIG. 5 shows a graph showing the relationship between the ratio of silicon-based active material particles to the total amount of negative electrode active material and the rate of increase in battery capacity of the secondary battery. The graph shown by A in FIG. 5 shows the rate of increase in battery capacity when the proportion of silicon compound particles is increased in the negative electrode active material of the negative electrode of the present invention. On the other hand, the graph shown by B in FIG. 5 shows the rate of increase in battery capacity when the proportion of silicon compound particles not doped with Li is increased. As can be seen from FIG. 5, when the proportion of the silicon compound is 6% by mass or more, the rate of increase in battery capacity is larger than in the conventional case, and the volumetric energy density is particularly significantly increased.

The present invention is not limited to the above embodiment. The above-described embodiment is an example, and any object having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect and effect is the present invention. Is included in the technical scope of.

10 ... Negative electrode, 11 ... Negative electrode current collector, 12 ... Negative electrode active material layer,
20 ... Lithium secondary battery (laminated film type), 21 ... Winding electrode body,
22 ... Positive electrode lead, 23 ... Negative electrode lead, 24 ... Adhesive film,
25 ... Exterior member.

Claims (15)

Negative electrode active material A negative electrode active material containing particles.
The negative electrode active material particles contain silicon compound particles containing a silicon compound _{(SiO x: 0.5 ≦ x ≦ 1.6).}
The silicon compound particles contain at least one or more of _{Li 2} SiO ₃ and Li ₄ SiO _4.
The negative electrode active material particles are held for 24 hours under the conditions of a temperature of 20 ° C. and a relative humidity of 30%, and then a moisture vaporization method for heating the negative electrode active material particles from 20 ° C. to 120 ° C. in the Carl Fisher titration method. The amount of water measured in the above is 5000 mass ppm or less with respect to the mass of the negative electrode active material particles, and the amount of water measured by the water vaporization method in which the negative electrode active material particles are heated from 120 ° C. to 300 ° C. is the negative value. It is 500 mass ppm or less with respect to the mass of the active material particles, and the amount of water measured by the moisture vaporization method in which the negative electrode active material particles are heated from 300 ° C. to 500 ° C. is 200 with respect to the mass of the negative electrode active material particles. and the mass ppm or less, and, true density is at 2.20 g / cm ³ or more 2.50 g / cm ³ or less, and, in a pore distribution based on the BJH method has a peak in the pore diameter of 1~100nm , A negative electrode active material having a total pore capacity of 0.005 cm ^{3 / g or more.} The amount of water measured by the water vaporization method in which the negative electrode active material particles are heated from 20 ° C. to 120 ° C. in the Karl Fischer titration method is 1000 mass ppm or less with respect to the mass of the negative electrode active material particles. The negative electrode active material according to claim 1. The negative electrode active material according to claim 1 or 2 , wherein at least a part of the surface of the negative electrode active material particles is _{coated with Li 2} CO _{3 and LiOH.} The silicon compound particles have a half-value width (2θ) of 1.2 ° or more of the diffraction peak due to the Si (111) crystal plane obtained by X-ray diffraction, and the crystallite size corresponding to the crystal plane is 7. The negative electrode active material according to any one of claims 1 to 3 , which is characterized by having a thickness of .5 nm or less. In the silicon compound particles, the maximum peak intensity value A of the Si and Li silicate region given at -60 to -95 ppm as the chemical shift value obtained from the ^{29 Si-MAS-NMR spectrum and the chemical shift value of -96 to--} The negative electrode active material according to any one of claims 1 to 4 _{, wherein the peak intensity value B in the SiO 2} region given at 150 ppm satisfies the relationship A> B. A test cell composed of a negative electrode electrode containing a mixture of the negative electrode active material and a carbon-based active material and counter electrode lithium is prepared, and in the test cell, charging is performed by passing a current so as to insert lithium into the negative electrode active material. Charging and discharging consisting of a discharge in which a current is passed so as to desorb lithium from the negative electrode active material is carried out 30 times, and the discharge capacity Q in each charging and discharging is differentiated by the potential V of the negative electrode electrode with respect to the counter electrode lithium. When a graph showing the relationship between the value dQ / dV and the potential V is drawn, the potential V of the negative electrode at the time of discharging after the Xth time (1 ≦ X ≦ 30) is 0.40V to 0.55V. The negative electrode active material according to any one of claims 1 to 5 , wherein the negative electrode has a peak in the range. The negative electrode active material according to any one of claims 1 to 6 , wherein the negative electrode active material particles have a median diameter of 1.0 μm or more and 15 μm or less. The negative electrode active material according to any one of claims 1 to 7 , wherein the negative electrode active material particles contain a carbon material in the surface layer portion. The negative electrode active material according to claim 8 , wherein the average thickness of the carbon material is 10 nm or more and 5000 nm or less. A mixed negative electrode active material material comprising the negative electrode active material according to any one of claims 1 to 9 and a carbon-based active material. The mixed negative electrode active material according to claim 10 is included, and the ratio of the mass of the negative electrode active material to the total mass of the negative electrode active material and the carbon-based active material is 6% by mass or more. Negative electrode for non-aqueous electrolyte secondary batteries. A negative electrode active material layer formed of the mixed negative electrode active material according to claim 10 and a negative electrode active material layer.
It has a negative electrode current collector and
The negative electrode active material layer is formed on the negative electrode current collector, and the negative electrode active material layer is formed on the negative electrode current collector.
A negative electrode for a non-aqueous electrolyte secondary battery, wherein the negative electrode current collector contains carbon and sulfur, and the content thereof is 100 mass ppm or less. A lithium ion secondary battery characterized in that a negative electrode containing the negative electrode active material according to any one of claims 1 to 9 is used as the negative electrode. Negative electrode active material containing silicon compound particles A method for producing a negative electrode active material containing particles.
A step of producing silicon compound particles containing a silicon compound (SiO _{x: 0.5 ≦ x ≦ 1.6) and}
A step of inserting lithium into the silicon compound particles to contain at least one or more of _{Li 2} SiO ₃ and Li ₄ SiO _4.
To prepare negative electrode active material particles by
A moisture vaporization method for heating the negative electrode active material particles from 20 ° C. to 120 ° C. in the Karl Fischer titration method after holding the negative electrode active material particles at a temperature of 20 ° C. and a relative humidity of 30% for 24 hours. Moisture measurement amount in the water vaporization method for heating the negative electrode active material particles from 120 ° C. to 300 ° C., and water content measurement by the water vaporization method for heating the negative electrode active material particles from 300 ° C. to 500 ° C. A step of measuring the amount , the true density, the pore distribution based on the BJH method, and the total pore volume,
Moisture vaporization method in which the negative electrode active material particles are heated from 20 ° C. to 120 ° C. in the Carl Fisher titration method after holding the negative negative material active material particles at a temperature of 20 ° C. and a relative humidity of 30% for 24 hours. The amount of water measured in the above is 5000 mass ppm or less with respect to the mass of the negative electrode active material particles, and the amount of water measured by the water vaporization method in which the negative electrode active material particles are heated from 120 ° C. to 300 ° C. is the negative value. It is 500 mass ppm or less with respect to the mass of the active material particles, and the amount of water measured by the moisture vaporization method in which the negative electrode active material particles are heated from 300 ° C. to 500 ° C. is 200 with respect to the mass of the negative electrode active material particles. and the mass ppm or less, and, true density is at 2.20 g / cm ³ or more 2.50 g / cm ³ or less, and, in a pore distribution based on the BJH method has a peak in the pore diameter of 1~100nm , Including the step of selecting those having a total pore volume of 0.005 cm ^{3 / g or more.}
A method for producing a negative electrode active material, which comprises producing a negative electrode active material using the selected negative electrode active material particles. A negative electrode active material is produced by the method for producing a negative electrode active material according to claim 14 , a negative electrode is produced using the produced negative electrode active material, and a lithium ion secondary battery is produced using the produced negative electrode. A method for manufacturing a lithium ion secondary battery.

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