JP2017188319A - Negative electrode active substance, mixed negative electrode active substance material, and method for manufacturing negative electrode active substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode active substance which can enhance initial charge and discharge characteristics and cycle characteristics when used as a negative electrode active substance of a secondary battery.SOLUTION: A negative electrode active substance comprises negative electrode active substance particles. The negative electrode active substance particles include silicon compound particles including a silicon compound (SiO: 0.5≤x≤1.6). The silicon compound particles include at least one of LiSiOand LiSiO. The negative electrode active substance particles are 1.0 to 15 μm in median diameter. When a particle size distribution of the negative electrode active substance particles is represented by the formula 1 of Rosin-Rammler's distribution below, the value of a distribution constant n is 5.0 or less. R=100exp(-ad) Formula 1, (In the formula 1, R represents a plus sieve (mass%) of a distribution amount cumulative value, d represents a particle diameter (μm) of the negative electrode active substance particles, a is a constant, and n represents a distribution constant).SELECTED DRAWING: Figure 1

Description

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

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

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

  Said lithium ion secondary battery is equipped with the electrolyte solution with the positive electrode, the negative electrode, and the separator, and the negative electrode contains the negative electrode active material in connection with charging / discharging reaction.

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

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

  To date, various studies have been made on negative electrode materials and electrode configurations for lithium ion secondary batteries mainly composed of a siliceous material in order to improve battery initial efficiency and cycle characteristics.

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

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

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

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

  The present invention has been made in view of the above-described problems. When used as a negative electrode active material for a secondary battery, the present invention provides a negative electrode active material capable of improving initial charge / discharge characteristics and cycle characteristics, and the negative electrode active material. It is an object to provide a mixed negative electrode active material containing a material, 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. . It is another object of the present invention to provide a method for producing the negative electrode active material of the present invention capable of improving the initial charge / discharge characteristics and cycle characteristics.

In order to achieve the above object, the present invention provides a negative electrode active material including negative electrode active material particles, wherein the negative electrode active material particles include a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6). Containing silicon compound particles, wherein 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 have a median diameter of 1.0 μm or more and 15 μm or less. When the particle size distribution of the negative electrode active material particles is expressed by the following formula 1 of the Rosin-Ramler's distribution, the value of the distribution constant n is 5.0 or less. Provide active material.
R = 100exp (−ad ⁿ ) Equation 1
(However, R in Formula 1 is on the sieve of the cumulative amount of distribution (% by mass), d is the particle size (μm) of the negative electrode active material particles, a is a constant, and n is a distribution constant.)

  Thus, if the median diameter of the negative electrode active material particles is 1.0 μm or more, it is possible to suppress an increase in battery irreversible capacity due to an increase in surface area per mass. On the other hand, when the median diameter is set to 15 μm or less, the particles are difficult to break and a new surface is difficult to appear. In addition, if the negative electrode active material particles have a distribution constant n of 5.0 or less in the Rosin-Lambler distribution, the sizes of the particles are appropriately aligned and Li dissolution from the negative electrode active material particles In addition, since the particle size distribution of the negative electrode active material particles is spread within an appropriate range, fine particles having a particularly small particle size become contact points between the negative electrode active material particles among the negative electrode active material particles. The detachability of the is improved. As a result, the negative electrode active material of the present invention can improve initial efficiency and cycle characteristics when used in a non-aqueous electrolyte secondary battery.

  At this time, when the particle size distribution of the negative electrode active material particles is expressed by Formula 1 of the Rosin-Rammler distribution, the value of the distribution constant n is preferably 3.0 or less.

  If negative electrode active material particles having a distribution constant n in Formula 1 of 3.0 or less are included, the negative electrode active material can be further improved in initial efficiency and cycle characteristics.

  Further, the negative electrode active material of the present invention is a mixed solution in which a mixture of 10% by mass of the negative electrode active material particles and 90% by mass of the carbon active material and pure water is mixed at a mass ratio of 1:10. It is preferable that the pH after 1 hour has passed is 13.0 or less.

  If pH measured on the said conditions is 13.0 or less, since the binding property in the aqueous | water-based slurry in which the negative electrode active material produced at the time of electrode preparation was disperse | distributed improves more, cycling characteristics can be improved more.

The negative electrode active material particles have a pore distribution based on a BJH (Barrett-Joyner-Halenda) method and have a peak at a pore diameter of 1 to 100 nm and a total pore volume of 0.005 cm ³ / g or more. It is preferable that

Since such a negative electrode active material has a pore diameter adjusted to an appropriate range, moisture desorption is smooth, and moisture that is chemically bonded at a high temperature is easily desorbed. . In addition, when the total pore volume is 0.005 cm ³ / g or more, the impregnation with the electrolytic solution becomes smooth. Therefore, cycle characteristics are further improved.

Further, the negative active material particles are preferably a true density is of 2.20 g / cm ³ or more 2.50 g / cm ³ or less.

  When the true density is in the above range, the reaction rate of the silicon compound particles and Li is within a desired range, and the anode active material particles are appropriately inserted with Li into the silicon compound particles. Therefore, cycle characteristics are further improved.

The negative electrode active material particles include Li ₂ CO ₃ and LiOH on the surface, and the content of the Li ₂ CO ₃ is 0.01% by mass or more and 5.00% by mass with respect to the mass of the negative electrode active material particles. It is preferable that the LiOH content is 0.01% by mass or more and 5.00% by mass or less with respect to the mass of the negative electrode active material particles.

If the content of Li ₂ CO ₃ and LiOH on the surface of the negative electrode active material particles is 0.01% by mass or more with respect to the mass of the negative electrode active material, respectively, the amount of Li used as a medium when Li diffuses is Since it exists sufficiently, the electron conductivity is further improved. Further, if each less 5.00 wt% the content of Li ₂ CO ₃ and LiOH, since the amount of these Li compounds are suitable amount, it is reliably obtained effect of improving electron conductivity. Such a negative electrode active material of the present invention can further improve cycle characteristics.

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

  If the negative electrode active material in which the silicon compound particles have the above-described 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.

Moreover, the negative electrode active material of the present invention is the above-mentioned silicon compound particles, wherein the maximum peak intensity value A in the Si and Li silicate regions given by the chemical shift value of −60 to −95 ppm obtained from the ²⁹ Si-MAS-NMR spectrum And, it is preferable that the peak intensity value B of the SiO ₂ region given by −96 to −150 ppm as the chemical shift value satisfies the relationship of A> B.

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

  In addition, a test cell comprising a negative electrode containing a mixture of the negative electrode active material and the carbon-based active material and counter lithium is prepared, and in the test cell, charging is performed such that current is inserted so that lithium is inserted into the negative electrode active material. 30 times of charge / discharge consisting of discharge through which current flows so as to desorb lithium from the negative electrode active material, and the discharge capacity Q in each charge / discharge is differentiated by the potential V of the negative electrode with respect to the counter lithium. When the graph showing the relationship between the differentiated differential value dQ / dV and the potential V is drawn, the potential V of the negative electrode during the Xth and subsequent discharges (1 ≦ X ≦ 30) is 0.40 V to. It is preferable to have a peak in the range of 55V.

  The above peak in the V-dQ / dV curve is similar to the peak of the siliceous material, and the discharge curve on the higher potential side rises sharply, so that the capacity is easily developed when designing the battery. Moreover, if the said peak expresses by charge / discharge within 30 times, it will become a negative electrode active material in which a stable bulk is formed.

  Moreover, it is preferable that the negative electrode active material particles include a carbon material in a surface layer portion.

  Thus, electroconductivity improvement is acquired because the negative electrode active material particle contains a carbon material in the surface layer part.

  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, conductivity can be improved. Moreover, 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 a negative electrode active material including such negative electrode active material particles in a lithium ion secondary battery. , Battery capacity reduction can be suppressed.

  Provided is a mixed negative electrode active material comprising the negative electrode active material and a carbon-based active material.

  Thus, as a material for forming the negative electrode active material layer, the conductivity of the negative electrode active material layer can be improved by including the carbon-based active material together with the negative electrode active material (silicon-based negative electrode active material) of the present invention. At the same time, the expansion stress associated with charging can be relaxed. Further, the battery capacity can be increased by mixing the silicon-based negative electrode active material with the carbon-based active material.

  In order to achieve the above object, the present invention includes the above 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 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 further increased. It becomes possible to improve.

  In order to achieve the above object, the present invention includes a negative electrode active material layer formed of the above mixed negative electrode active material and a negative electrode current collector, and the negative electrode active material layer includes the negative electrode current collector. Provided is 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 ppm by mass or less.

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

  Moreover, in order to achieve the said objective, this invention provides the lithium ion secondary battery which uses the negative electrode containing said negative electrode active material.

  If it is a lithium ion secondary battery using the negative electrode containing such a negative electrode active material, while being high capacity | capacitance, favorable cycling characteristics and initial stage charge / discharge characteristics will be obtained.

In order to achieve the above object, the present invention provides a method for producing a negative electrode active material including negative electrode active material particles containing silicon compound particles, wherein the 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 of Li ₂ SiO ₃ and Li ₄ SiO _4. When the median diameter is 1.0 μm or more and 15 μm or less from the negative electrode active material particles, and the particle size distribution of the negative electrode active material particles is expressed by the following Rosin-Rammler distribution formula 1, the value of the distribution constant n is A method of producing a negative electrode active material, comprising producing a negative electrode active material using the selected negative electrode active material particles.
R = 100exp (−ad ⁿ ) Equation 1
(However, R in Formula 1 is on the sieve of the cumulative amount of distribution (% by mass), d is the particle size (μm) of the negative electrode active material particles, a is a constant, and n is a distribution constant.)

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

  In order to achieve the above object, the present invention produces a negative electrode using the negative electrode active material produced by the method for producing a negative electrode active material, and produces a lithium ion secondary battery using the produced negative electrode. A method for manufacturing a lithium ion secondary battery is provided.

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

  When the negative electrode active material of the present invention is used as a negative electrode active material for a secondary battery, high capacity and good cycle characteristics and initial charge / discharge characteristics can be obtained. Moreover, the same effect is acquired also in the mixed negative electrode active material material containing this negative electrode active material, a negative electrode, and a lithium ion secondary battery. Moreover, if it is a manufacturing method of the negative electrode active material of this invention, when it uses as a negative electrode active material of a secondary battery, the negative electrode active material which has a favorable cycling characteristic and an initial stage charge / discharge characteristic can be manufactured.

It is sectional drawing which shows the structure of the negative electrode for nonaqueous electrolyte secondary batteries of this invention. It is the schematic which shows an example of the reformer in a bulk which can be used for an electrochemical dope method. It is an example of the ²⁹ Si-MAS-NMR spectrum measured from silicon compound particle | grains when modification | reformation is performed by the electrochemical doping method. It is an example of ^{29 Si-MAS-NMR} spectra measured from the silicon compound particles in the case of performing the reforming by thermal doping. It is a figure showing the structural example (laminate film type) of the lithium secondary battery of this invention. It is a graph showing the relationship between the ratio of the silicon type active material particle with respect to the total amount of a negative electrode active material, and the increase rate of the battery capacity of a secondary battery.

  Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to this.

  As described above, as one method for increasing the battery capacity of a lithium ion secondary battery, the use of a negative electrode using a silicon material as a main material as a negative electrode of a lithium ion secondary battery has been studied. The lithium ion secondary battery using this siliceous material is desired to have initial charge / discharge characteristics and cycle characteristics similar to those of a lithium ion secondary battery using a carbon-based active material, but the carbon-based active material is used. A negative electrode active material having initial charge / discharge characteristics and cycle characteristics equivalent to those of a lithium ion secondary battery has not been proposed.

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

The negative electrode active material of the present invention includes negative electrode active material particles. Then, the anode active material particles, silicon compound: containing a silicon compound particles containing _{(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 . The negative electrode active material particles have a median diameter of 1.0 μm or more and 15 μm or less. Furthermore, the negative electrode active material particles have a distribution constant n of 5.0 or less when the particle size distribution is expressed by the following Rosin-Rammler distribution formula 1.
R = 100exp (−ad ⁿ ) Equation 1
(However, R in Formula 1 is on the sieve of the cumulative amount of distribution (% by mass), d is the particle size (μm) of the negative electrode active material particles, a is a constant, and n is a distribution constant.)

Since such a negative electrode active material includes negative electrode active material particles (also referred to as silicon-based active material particles) containing silicon compound particles, the battery capacity can be improved. In addition, the SiO ₂ component, which is destabilized during the insertion and removal of lithium during battery charging / discharging in the silicon compound, has been modified to lithium silicate in advance, reducing the irreversible capacity generated during charging. can do. Furthermore, if the median diameter of the negative electrode active material particles is 1.0 μm or more, an increase in battery irreversible capacity due to an increase in surface area per mass can be suppressed. On the other hand, when the median diameter is set to 15 μm or less, the particles are difficult to break and a new surface is difficult to appear. In addition, it is said that the rosin Ramler distribution expression represented by Expression 1 well represents the particle size distribution generated by crushing and pulverization. This Rosin-Rammler distribution equation indicates that the larger the value of n, the narrower the particle size range and the relatively uniform particle size. If the negative electrode active material particles have a distribution constant n value of 5.0 or less in the rosin Ramler distribution, the sizes of the particles are moderately aligned and Li dissolution from the negative electrode active material particles can be suppressed. In addition, since the particle size distribution of the negative electrode active material particles is spread within an appropriate range, among the negative electrode active material particles, fine particles having a particularly small particle diameter serve as contact points between the negative electrode active material particles, and conductivity and Li desorption properties are improved. improves. As a result, the negative electrode active material of the present invention can improve the initial efficiency and cycle characteristics when used in a non-aqueous electrolyte secondary battery.

  In particular, when the particle size distribution of the negative electrode active material particles is expressed by Formula 1 of the rosin Ramler distribution, the value of the distribution constant n is preferably 3.0 or less. With such a configuration, it is possible to further improve the initial efficiency and cycle characteristics.

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

[Configuration of negative electrode]
As shown in FIG. 1, the negative electrode 10 is configured to have a negative electrode active material layer 12 on a negative electrode current collector 11. The negative electrode active material layer 12 may be provided on both surfaces or only one surface of the negative electrode current collector 11. Furthermore, the negative electrode current collector 11 may be omitted as long as the negative electrode active material of the present invention is used.

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

  The negative electrode current collector 11 preferably contains carbon (C) or sulfur (S) in addition to the main element. This is because the physical strength of the negative electrode current collector is improved. In particular, in the case of having an active material layer that expands during charging, if the current collector contains the above-described element, there is an effect of suppressing electrode deformation including the current collector. Although content of said content element is not specifically limited, Especially, it is preferable that it is 100 mass ppm or less, respectively. This is because a higher deformation suppressing effect can be obtained. Such a deformation suppressing effect can further improve the cycle characteristics.

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

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

  The negative electrode active material layer 12 may include a mixed negative electrode active 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 reduced. Examples of the carbon-based active material include pyrolytic carbons, cokes, glassy carbon fibers, organic polymer compound fired bodies, carbon blacks, and the like.

  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) of the present invention and the carbon-based active material is 6% by mass. The above is preferable. If 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 contains silicon compound particles, and the silicon compound particles are a silicon oxide material containing a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6). The composition is preferably such that x is close to 1. This is because high cycle characteristics can be obtained. Note that the composition of the silicon compound in the present invention does not necessarily mean a purity of 100%, and may contain a trace amount of impurity elements.

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 . When at least one of Li ₄ SiO ₄ and Li ₂ SiO ₃ is present in the bulk of the silicon compound particles, the battery characteristics are improved. However, when the two types of lithium silicate are present together, the battery characteristics are further improved. Note that these lithium silicates can be quantified by NMR (Nuclear Magnetic Resonance) or XPS (X-ray photoelectron spectroscopy: X-ray photoelectron spectroscopy). The XPS and NMR measurements can be performed, for example, under the following conditions.

XPS
・ Device: 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 × 2 mm.
²⁹ Si MAS NMR (magic angle rotating nuclear magnetic resonance)
Apparatus: 700 NMR spectrometer manufactured by Bruker,
Probe: 4 mm HR-MAS rotor 50 μL,
Sample rotation speed: 10 kHz,
-Measurement environment temperature: 25 ° C.

  In addition, the silicon compound particles have a half-value 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 preferable that it is 7.5 nm or less. The silicon crystallinity of the silicon compound in the silicon compound particles is preferably as low as possible. In particular, if the amount of Si crystal is small, battery characteristics can be improved, and a stable Li compound can be generated.

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

  In the negative electrode active material of the present invention, the negative electrode active material particles preferably include a carbon material in the surface layer portion. When the negative electrode active material particles include 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 a secondary battery. Battery characteristics can be improved.

  Moreover, it is preferable that the average thickness of the carbon material of the surface layer part of negative electrode active material particles is 10 nm or more and 5000 nm or less. If the average thickness of the carbon material is 10 nm or more, conductivity can be 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 converted into lithium ion When used as a negative electrode active material for a secondary battery, a decrease in battery capacity can be suppressed.

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

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

  The negative electrode active material of the present invention is a mixture in which a mixture of 10% by mass of negative electrode active material particles (silicon-based active material particles) and 90% by mass of carbon active material and pure water is mixed at a mass ratio of 1:10. The liquid preferably has a pH of 13.0 or less after one hour has elapsed since the liquid mixture was prepared. If pH measured on the said conditions is 13.0 or less, since the binding property in the aqueous | water-based slurry in which the negative electrode active material produced at the time of electrode preparation was disperse | distributed improves more, cycling characteristics can be improved more.

  Further, in a mixed solution in which negative electrode active material particles (silicon-based active material particles) and pure water are mixed at a mass ratio of 1: 4, the pH after 1 hour has elapsed since the preparation of the mixed solution is 13.0. The following is preferable. Even if it is such, since the binding property in the aqueous slurry in which the negative electrode active material produced at the time of electrode production is dispersed is further improved, the cycle characteristics can be further improved.

The negative electrode active material particles preferably have a peak in the pore diameter of 1 to 100 nm and the total pore volume of 0.005 cm ³ / g or more in the pore distribution based on the BJH method. Since such a negative electrode active material has a pore diameter adjusted to an appropriate range, moisture desorption is smooth, and moisture that is chemically bonded at a high temperature is easily desorbed. . In addition, when the total pore volume is 0.005 cm ³ / g or more, the impregnation with the electrolytic solution becomes smooth. Therefore, cycle characteristics are further improved.

Further, the anode active material particles are preferably a true density is of 2.20 g / cm ³ or more 2.50 g / cm ³ less. When the true density is in the above range, the reaction rate of the silicon compound particles and Li is within a desired range, and the anode active material particles are appropriately inserted with Li into the silicon compound particles. Therefore, cycle characteristics are further improved.

The negative electrode active material particles include LiOH and Li ₂ CO ₃ on the surface, the LiOH content is 0.01% by mass or more and 5.00% by mass or less with respect to the mass of the negative electrode active material particles, and It is preferable that the content of Li ₂ CO ₃ satisfies 0.01% by mass or more and 5.00% by mass or less with respect to the mass of the negative electrode active material particles. When the negative electrode active material particles include Li ₂ CO ₃ and LiOH on the surface with such a content, the electron conductivity is further improved. As a result, the cycle characteristics of the secondary battery can be further improved.

  Moreover, the negative electrode active material (silicon-based active material) of the present invention is a test cell comprising a negative electrode containing a mixture of the silicon-based active material and a carbon-based active material and counter electrode lithium, and in the test cell, Charging / discharging consisting of charging in which current is inserted to insert lithium into the silicon-based active material and discharging in which current is discharged to detach lithium from the silicon-based active material is performed 30 times, and the discharge capacity Q in each charging / discharging is determined. When a graph showing the relationship between the differential value dQ / dV differentiated by the potential V of the negative electrode with respect to the counter electrode lithium and the potential V is drawn, the negative electrode during the Xth and subsequent discharges (1 ≦ X ≦ 30) The electrode potential V preferably has a peak in the range of 0.40V to 0.55V. The above peak in the V-dQ / dV curve is similar to the peak of the siliceous material, and the discharge curve on the higher potential side rises sharply, so that the capacity is easily developed when designing the battery. Moreover, if it is a negative electrode active material which the said peak expresses by charge / discharge within 30 times, it can be judged that the stable bulk is formed.

  Moreover, as a negative electrode binder contained in a negative electrode active material layer, any one or more types, such as a polymeric material and a synthetic rubber, can be used, for example. Examples of the polymer material include polyvinylidene fluoride, polyimide, polyamideimide, aramid, polyacrylic acid, lithium polyacrylate, and carboxymethylcellulose. Examples of the synthetic rubber include styrene butadiene rubber, fluorine rubber, and ethylene propylene diene.

  As a negative electrode conductive support agent, any 1 or more types of carbon materials, such as carbon black, acetylene black, graphite, ketjen black, a carbon nanotube, carbon nanofiber, can be used, for example.

  The negative electrode active material layer is formed by, for example, a coating method. The coating method is a method in which negative electrode active material particles and the above-mentioned binder, and the like, and a conductive additive and a carbon material are mixed as necessary, and then dispersed and applied in an organic solvent or water.

[Production method of negative electrode]
The negative electrode can be produced, for example, by the following procedure. First, the manufacturing method of the negative electrode active material used for a negative electrode is demonstrated. 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 . Thereby, negative electrode active material particles are produced. Alternatively, lithium may be inserted into the silicon compound particles after the silicon compound particles are coated with a carbon material.

  Next, when the median diameter is 1.0 μm or more and 15 μm or less from the negative electrode active material particles, and the particle size distribution of the negative electrode active material particles is expressed by the following formula 1 of Rosin-Rammler distribution, the value of the distribution constant n is 5.0. Select the following: And the negative electrode active material is manufactured using the selected negative electrode active material particles.

  More specifically, the negative electrode active material can be produced as follows. First, a raw material that generates silicon oxide gas is heated in a temperature range of 900 ° C. to 1600 ° C. under reduced pressure in the presence of an inert gas to generate silicon oxide gas. Considering the surface oxygen of the metal silicon powder and the presence of a trace amount of oxygen in the reaction furnace, the mixing molar ratio is preferably in the range of 0.8 <metal silicon powder / silicon dioxide powder <1.3.

  The generated silicon oxide gas is solidified and deposited on the adsorption plate. Next, a silicon oxide deposit is taken out in a state where the temperature in the reactor is lowered to 100 ° C. or lower, and pulverized and powdered using a ball mill, a jet mill or the like. As described above, silicon compound particles can be produced. Note that the Si crystallites in the silicon compound particles can be controlled by changing the vaporization temperature or by heat treatment after generation.

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

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

Next, Li is inserted into the negative electrode active material particles including the silicon active material particles produced as described above, and at least one of Li ₂ SiO ₃ and Li ₄ SiO ₄ is contained. Li is preferably inserted by a thermal doping method.

In the modification by the thermal doping method, for example, the modification can be performed by mixing silicon compound particles 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, LiH powder and silicon oxide powder are sufficiently mixed in an Ar or N ₂ atmosphere, sealed, and homogenized by stirring the sealed container. Thereafter, heating and baking are performed in the range of 700 ° C. to 800 ° C. to perform modification. When the modification is performed in an N ₂ atmosphere, the surface of the obtained negative electrode active material particles contains Li ₃ N. Thereafter, if the negative electrode active material particles are washed with pure water or the like, Li ₂ CO ₃ and LiOH can be generated on the surface. The amount of pure water can be, for example, 4 times equivalent to the powder. The cleaning time can be adjusted according to the powder. Thereafter, by drying, silicon compound particles having an appropriate amount of ions can be obtained.

  Further, the modification may be performed by an electrochemical doping method. At this time, the substance generated in the bulk can be controlled by adjusting the insertion potential and the desorption potential, changing the current density, the bath temperature, and the number of times of insertion and desorption. For example, in-bulk reforming can be performed using the in-bulk reforming apparatus 20 shown in FIG. The device structure is not particularly limited to the structure of the in-bulk reforming device 20.

  The in-bulk reforming apparatus 20 shown in FIG. 2 is disposed in the bathtub 27 filled with the electrolytic solution 23, the counter electrode 21 disposed in the bathtub 27 and connected to one side of the power supply 26, and disposed in the bathtub 27. 26, and a separator 24 provided between the counter electrode 21 and the powder storage container 25. Silicon compound particles 22 are stored in the powder storage container 25.

  In the modification by the electrochemical doping method, for example, a lithium salt is dissolved in the electrolytic solution 23 or a compound containing Li is assembled in the counter electrode 21, and a voltage is applied between the powder container 25 and the counter electrode 21 by the power source 26. The lithium can be inserted into the silicon compound particles by applying an electric current.

  By inserting Li electrochemically, Li is inserted at a site different from Li inserted by a thermal method. Therefore, for example, if the electrochemical doping is further performed after the thermal doping, the initial efficiency can be further improved and the growth of silicon crystallites by the thermal method can be reduced.

  The lithium source used in the electrochemical doping method includes at least one of metal lithium, transition metal lithium phosphate, lithium oxide of Ni, lithium oxide of Co, lithium oxide of Mn, lithium nitrate, and lithium halide. One can be used. The form of the lithium salt is not limited. That is, a lithium salt may be used as the counter electrode 21 or may be used as an electrolyte of the electrolytic solution 23.

At this time, as a solvent of the electrolytic solution 23, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, dioxane, diglyme, triglyme, tetraglyme, and a mixture thereof can be used. Further, LiBF ₄ , LiPF ₆ , LiClO ₄ and derivatives thereof can also be used as the electrolyte of the electrolytic solution 23. In particular, LiNO ₃ , LiCl, and the like can also be used as the electrolyte that also serves as the Li source. Further, in the electrochemical doping method, after the insertion of Li, a desorption process of Li from the silicon compound particles may be included. This makes it possible to adjust the amount of Li inserted into the silicon compound particles.

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 the case where the electrochemical doping method is used. FIG. 3 shows an example of a ²⁹ Si-MAS-NMR spectrum measured from silicon compound particles when the modification is performed only by the electrochemical doping method. In FIG. 3, the peak given in the vicinity of −75 ppm is a peak derived from Li ₂ SiO _3, and the peak given from −80 to −100 ppm is a peak derived from Si. Note that over the -80 to-100 _ppm, in some cases having a peak of _{Li 2 SiO 3, Li 4 SiO} 4 other Li silicate.

FIG. 4 shows an example of a ²⁹ Si-MAS-NMR spectrum measured from silicon compound particles when modification is performed by a thermal doping method. In FIG. 4, the peak given in the vicinity of −75 ppm is a peak derived from Li ₂ SiO _3, and the peak given from −80 to −100 ppm is a peak derived from Si. Note that over the -80 to-100 _ppm, in some cases having a peak of _{Li 2 SiO 3, Li 4 SiO} 4 other Li silicate. Note that the peak of Li ₄ SiO ₄ can be confirmed from the XPS spectrum.

  Next, when the median diameter is 1.0 μm or more and 15 μm or less from the negative electrode active material particles, and the particle size distribution of the negative electrode active material particles is expressed by the following formula 1 of Rosin-Rammler distribution, the value of the distribution constant n is 5.0. Select the following: The median diameter and particle size distribution can be measured by, for example, a laser diffraction method.

  The selection of the negative electrode active material particles is not necessarily performed every time the negative electrode active material is produced. The median diameter is 1.0 μm or more and 15 μm or less, and the particle size distribution of the negative electrode active material particles is expressed by the following rosin Ramler distribution formula 1. If the production conditions for obtaining negative electrode active material particles satisfying a distribution constant n value of 5.0 or less are found and selected, then the negative electrode active material is produced under the same conditions as the selected conditions. can do.

  The negative electrode active material produced as described above is mixed with other materials such as a negative electrode binder and a conductive additive to form a negative electrode mixture, and then an organic solvent or water is added to obtain 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, you may perform a heat press etc. as needed. A negative electrode can be produced as described above.

<Lithium ion secondary battery>
Next, the lithium ion secondary battery of the present invention will be described. The lithium ion secondary battery of the present invention uses 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 is taken as an example.

[Configuration of laminated film type lithium ion secondary battery]
A laminated film type lithium ion secondary battery 30 shown in FIG. 5 is one in which a wound electrode body 31 is accommodated mainly in a sheet-like exterior member 35. This wound body has a separator between a positive electrode and a negative electrode and is wound. There is also a case where a separator is provided between the positive electrode and the negative electrode and a laminate is accommodated. In both electrode bodies, the positive electrode lead 32 is attached to the positive electrode, and the negative electrode lead 33 is attached to the negative electrode. The outermost peripheral part of the electrode body is protected by a protective tape.

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

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

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

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

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

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

As the positive electrode material, a lithium-containing compound is desirable. Examples of the lithium-containing compound include a composite oxide composed of lithium and a transition metal element, or a phosphate compound having lithium and a transition metal element. Among these described positive electrode materials, compounds having at least one of nickel, iron, manganese, and cobalt are 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 or more transition metal elements. The values of x and y vary depending on the battery charge / discharge state, but are generally expressed as 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 phosphate compound having lithium and a transition metal element include a lithium iron phosphate compound (LiFePO ₄ ) or a lithium iron manganese phosphate compound (LiFe _1-u Mn _u PO ₄ (0 <u <1)). Is mentioned. This is because, when these positive electrode materials are used, a high battery capacity can be obtained and excellent cycle characteristics can be obtained.

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

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

  In the non-opposing region, that is, the region where the negative electrode active material layer and the positive electrode active material layer are not opposed to each other, there is almost no influence of charge / discharge. Therefore, the state of the negative electrode active material layer is maintained as it is immediately after formation. This makes it possible to accurately examine the composition with good reproducibility without depending on the presence or absence of charge / discharge, such as the composition of the negative electrode active material.

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

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

  For example, a non-aqueous solvent can be used as the solvent. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, 1,2-dimethoxyethane, 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. In this case, more advantageous characteristics can be obtained by combining a high viscosity solvent such as ethylene carbonate or propylene carbonate and a low viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate or diethyl carbonate. This is because the dissociation property and ion mobility of the electrolyte salt are improved.

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

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

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

  The solvent additive preferably contains an unsaturated carbon bond cyclic carbonate. 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 the unsaturated carbon bond cyclic ester carbonate include vinylene carbonate and vinyl ethylene carbonate.

  The solvent additive preferably contains sultone (cyclic sulfonic acid ester). This is because the chemical stability of the battery is improved. Examples of sultone include propane sultone and propene sultone.

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

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

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

[Production method of laminated film type secondary battery]
In this invention, a negative electrode is produced using the negative electrode active material manufactured with the manufacturing method of said negative electrode active material of this invention, and a lithium ion secondary battery is manufactured using this produced negative electrode.

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

  Next, a negative electrode is produced by forming a negative electrode active material layer on the negative electrode current collector, using the same operation procedure as the production of the negative electrode 10 for a lithium ion secondary battery described above.

  When producing the positive electrode and the negative electrode, respective active material layers are formed on both surfaces of the positive electrode and the negative electrode current collector. At this time, the active material application length of both surface portions may be shifted in either electrode (see FIG. 1).

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

  EXAMPLES Hereinafter, the present invention will be described more specifically 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 laminate film type lithium ion secondary battery 30 shown in FIG. 5 was produced by the following procedure.

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

Next, a negative electrode was produced. First, a negative electrode active material was produced as follows. A raw material in which metallic silicon and silicon dioxide are mixed is introduced into a reaction furnace, and vaporized in a vacuum atmosphere of 10 Pa is deposited on an adsorption plate. After sufficiently cooling, the deposit is taken out and pulverized by a ball mill. . The value 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, the carbon material was coat | covered on the surface of silicon compound particle | grains by performing pyrolysis CVD.

Subsequently, lithium was inserted into the silicon compound particles by a thermal doping method and modified. First, the silicon compound particles coated with the carbon material were sufficiently mixed with LiH powder in an N ₂ atmosphere, sealed, and stirred together to homogenize the sealed container. Then, it heated and baked in the range of 700 to 800 degreeC. Through the above treatment, lithium was inserted into the silicon compound particles. In this way, negative electrode active material particles were produced. 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 4 times equivalent of pure water with respect to the negative electrode active material particles. By this cleaning, LiOH and Li ₂ CO ₃ were generated on the surface of the negative electrode active material particles. Thereafter, the negative electrode active material particles were dried.

  The median diameter of the negative electrode active material particles was 4.0 μm, and the distribution constant n of Formula 1 of the rosin Ramler distribution was 3.2.

  Next, the negative electrode active material particles (silicon-based 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 and artificial graphite coated with a pitch layer 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 additive 1 (carbon nanotube, CNT), conductive additive 2 (carbon fine particles having a median diameter of about 50 nm), styrene butadiene rubber (styrene butadiene copolymer, hereinafter referred to as SBR). And carboxymethylcellulose (hereinafter referred to as CMC) 92.5: 1: 1: 2.5: 3, and then mixed with a dry mass ratio, and diluted with pure water to obtain a negative electrode mixture slurry. In addition, said SBR and CMC are negative electrode binders (negative electrode binder).

As the negative electrode current collector, an electrolytic copper foil having a thickness of 15 μm was used. This electrolytic copper foil contained carbon and sulfur at a concentration of 70 mass ppm. 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. The amount of deposition (also referred to as area density) of the negative electrode active material layer per unit area on one side of the negative electrode after drying was 5 mg / cm ² .

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

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

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

  The cycle characteristics were examined as follows. First, in order to stabilize the battery, charge and discharge was performed for 2 cycles at 0.2 C in an atmosphere at 25 ° C., and the discharge capacity at the second cycle was measured. Subsequently, charge and discharge were performed until the total number of cycles reached 499 cycles, and the discharge capacity was measured each time. Finally, the discharge capacity at the 500th cycle obtained by 0.2 C charge / discharge was divided by the discharge capacity at the second cycle to calculate a capacity retention rate (hereinafter also simply referred to as a maintenance rate). In the normal cycle, that is, from the 3rd cycle to the 499th cycle, charging and discharging were performed with a charge of 0.7 C and a discharge of 0.5 C.

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

(Example 1-2 to Example 1-3, Comparative Example 1-1 to 1-2)
A secondary battery was manufactured in the same manner as 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 metal silicon and silicon dioxide in the raw material of the silicon compound and the heating temperature. The values of x of the silicon compounds 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 (silicon-based 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, and the distribution constant n of Formula 1 of the Rosin-Lambler distribution was 3.2. Li ₂ SiO ₃ and Li ₄ SiO ₄ were contained inside the silicon compound particles. Further, in a mixed solution in which a mixture of 10% by mass of negative electrode active material particles (silicon active material particles) and 90% by mass of the carbon active material and pure water was mixed at a mass ratio of 1:10, a mixed solution was prepared. 1 hour later, the pH was 10.8. The negative electrode active material particles had 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 was 0.045 cm ³ / g. Further, the true density of the negative electrode active material particles was 2.24 g / cm ³ . Further, the LiOH content was 0.65% by mass with respect to the mass of the negative electrode active material particles, and the Li ₂ CO ₃ content was 0.45% by mass with respect to the mass of the negative electrode active material particles. It was. Further, the silicon compound has a half-value width (2θ) of a diffraction peak due to the Si (111) crystal plane obtained by X-ray diffraction of 1.755 °, and a crystallite size due to the Si (111) crystal plane. Was 4.86 nm.

Moreover, in all the above Examples and Comparative Examples, peaks of Si and Li silicate regions given by −60 to −95 ppm as chemical shift values obtained from ²⁹ Si-MAS-NMR spectra were developed. In all of the above Examples and Comparative Examples, the maximum peak intensity values A in the Si and Li silicate regions given by −60 to −95 ppm as chemical shift values obtained from ²⁹ Si-MAS-NMR spectra, and −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 cell type test cell was prepared from the negative electrode and the counter electrode lithium prepared as described above, and the discharge behavior was evaluated. More specifically, first, constant current and constant voltage charging was performed up to 0 V with the counter electrode Li, and the charging was terminated when the current density reached 0.05 mA / cm ² . Then, constant current discharge was performed to 1.2V. The current density at this time was 0.2 mA / cm ² . This charge / discharge was repeated 30 times, and from the data obtained in each charge / discharge, a graph was drawn with the vertical axis representing the rate of change in capacity (dQ / dV) and the horizontal axis representing the voltage (V), where V was 0.4-0. It was confirmed whether a peak was obtained in the range of .55 (V). As a result, in Example 1-1 and Comparative Example 1-1 in which x of SiOx was 0.5 or less, the peak was not obtained. In the other Examples and Comparative Examples, the peak was obtained in charge / discharge within 30 times, and the peak was obtained in all charge / discharge from the charge / discharge where the peak first appeared until the 30th charge / discharge.

  As shown in Table 1, in the silicon compound represented by SiOx, when the value of x was outside the range of 0.5 ≦ x ≦ 1.6, the battery characteristics deteriorated. For example, as shown in Comparative Example 1-1, when there is not enough oxygen (x = 0.3), 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 silicon oxide capacity was not substantially exhibited, 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 in the silicon compound particles was changed as shown in Table 2, and cycle characteristics and initial efficiency were evaluated.

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

Since the silicon compound contains stable lithium silicate such as Li ₂ SiO ₃ and Li ₄ SiO ₄ , the capacity retention ratio and the initial efficiency were improved. In particular, when both Li ₂ SiO ₃ and Li ₄ SiO ₄ lithium silicates were included, the capacity retention ratio and the initial efficiency were further improved. On the other hand, the capacity retention ratio and the initial efficiency were lowered in Comparative Example 2-1, which was not modified and lithium was not included in the silicon compound.

(Example 3-1 to Example 3-4)
A secondary battery was fabricated under the same conditions as in Example 1-2 except that the median diameter of the negative electrode active material particles and the value of the distribution constant n of Formula 1 of the Rosin Ramler distribution were changed to the values shown in Table 3, and the cycle characteristics and initial Efficiency was evaluated. The value of the distribution constant n can be adjusted by changing the grinding time and classification time of the silicon compound particles.

(Example 3-5 to Example 3-6)
Example 1 except that the modification method of the silicon compound particles was changed to the electrochemical doping method, and the median diameter of the negative electrode active material particles and the value of the distribution constant n in the formula 1 of the rosin Ramler distribution were changed to the values shown in Table 3. A secondary battery was produced under the same conditions as -2, and cycle characteristics and initial efficiency were evaluated. In the electrochemical doping method, the in-bulk reformer shown in FIG. 2 was used.

(Comparative Example 3-1)
Example 1 except that the modification method of the silicon compound particles was changed to the electrochemical doping method, and the median diameter of the negative electrode active material particles and the value of the distribution constant n in the formula 1 of the rosin Ramler distribution were changed to the values shown in Table 3. A secondary battery was produced under the same conditions as -2, and cycle characteristics and initial efficiency were evaluated. In the electrochemical doping method, the in-bulk reformer shown in FIG. 2 was used.

(Comparative Example 3-2 to Comparative Example 3-4)
A secondary battery was fabricated under the same conditions as in Example 1-2 except that the median diameter of the negative electrode active material particles and the value of the distribution constant n of Formula 1 of the Rosin Ramler distribution were changed to the values shown in Table 3, and the cycle characteristics and initial Efficiency was evaluated.

  As can be seen from Table 3, in the examples where the median diameter satisfies 1.0 μm or more and 15 μm or less and the distribution constant n satisfies 5.0 or less, the capacity retention ratio and the initial efficiency are improved. In particular, in Examples 3-1 and 3-4 in which the dispersion constant n was 3.0 or less, the capacity retention ratio and the initial efficiency were further improved. On the other hand, in Comparative Example 3-3 in which the median diameter is less than 1.0 μm and in Example 3-4 in which the median diameter is greater than 15 μm, the capacity retention ratio and the initial efficiency are lowered. Moreover, also in Comparative Examples 3-1 and 3-2 in which the dispersion constant n is larger than 5.0, the capacity retention ratio and the initial efficiency were lowered.

(Example 4-1 to Example 4-2)
After preparing a liquid mixture of a mixed liquid in which a mixture of 10% by mass of negative electrode active material particles (silicon-based active material particles) and 90% by mass of carbon active material and pure water was mixed at a mass ratio of 1:10. A secondary battery was fabricated under the same conditions as in Example 1-2 except that the pH after one hour had elapsed was changed as shown in Table 4, and the cycle characteristics and initial efficiency were evaluated.

  As can be seen from Table 4, the capacity retention rate was improved when the pH was 13.0 or less.

(Example 5-1 to Example 5-4)
A secondary battery was fabricated under the same conditions as in Example 1-2 except that the true density of the negative electrode active material particles and the pore distribution based on the BJH method were changed as shown in Table 5, and the cycle characteristics and initial efficiency were evaluated. did. The true density and pore distribution of the negative electrode active material particles were adjusted by changing the heating temperature at the time of preparing the silicon compound particles.

As can be seen from Table 5, the 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, Examples 1-2 and 5-2 that satisfy all the conditions that the total pore volume is 0.005 cm ³ / g or more are Examples 5-1, 5-2, and 5-5 that do not satisfy at least one of the above conditions. The capacity retention rate was higher than 4.

(Example 6-1 to Example 6-6)
A secondary battery was fabricated under the same conditions as in Example 1-2 except that the contents of LiOH and Li ₂ CO _{3 on} the surface of the negative electrode active material particles were changed as shown in Table 6, and cycle characteristics and initial efficiency were evaluated. did.

As shown in Table 6, Example 6 where the content of Li ₂ CO _{3 and} the content of LiOH both satisfy the condition of 0.01% by mass or more and 5.00% by mass or less with respect to the mass of the negative electrode active material particles. In the case of −2 to 6-5, the capacity retention rate was improved as compared with Examples 6-1 and 6-6 that did not satisfy this condition.

(Examples 7-1 to 7-6)
A secondary battery was fabricated 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 in the silicon compound particles can be controlled by changing the vaporization temperature of the raw material, or by heat treatment after the formation of the silicon compound particles.

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

(Example 8-1)
The silicon compound was prepared under the same conditions as in Example 1-2 except that the relationship between the maximum peak intensity value A in the Si and Li silicate regions and the peak intensity value B derived from the SiO ₂ region was A <B. A secondary 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 8, the battery characteristics improved when the peak intensity relationship was A> B.

(Example 9-1)
In the V-dQ / dV curve obtained by charging and discharging 30 times in the test cell, a negative electrode active material in which no peak was obtained in the range of 0.40 V to 0.55 V in any charging / discharging was used. A secondary battery was manufactured under the same conditions as in Example 1-2, and the cycle characteristics and initial efficiency were evaluated.

  In order for the discharge curve shape to rise more sharply, the silicon compound (SiOx) needs to exhibit a discharge behavior similar to that of silicon (Si). Since the silicon compound that does not exhibit a peak in the above-described range after 30 charge / discharge cycles has a relatively gentle discharge curve, the initial efficiency is slightly lowered when a secondary battery is obtained. If the peak appears within 30 charge / discharge cycles, a stable bulk was formed, and the capacity retention rate and initial efficiency were improved.

(Examples 10-1 to 10-5)
A secondary battery was produced 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 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 10, since the conductivity is particularly improved when the thickness of the carbon layer is 10 nm or more, the capacity retention ratio and the initial efficiency can be improved. On the other hand, if the film thickness of the carbon layer is 5000 nm or less, the amount of silicon compound particles can be sufficiently secured in battery design, and the battery capacity does not decrease.

(Example 11-1)
A secondary battery was produced under the same conditions as in Example 1-2 except that the mass ratio 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. 6 is a graph showing the relationship between the ratio of the silicon-based active material particles to the total amount of the negative electrode active material and the increase rate of the battery capacity of the secondary battery. The graph indicated by A in FIG. 6 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 indicated by B in FIG. 6 shows the increase rate of the battery capacity when the ratio of the silicon compound particles not doped with Li is increased. As can be seen from FIG. 6, when the ratio of the silicon compound is 6% by mass or more, the increase rate of the battery capacity is increased as compared with the conventional case, and the volume energy density is particularly remarkably increased.

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

10 ... negative electrode, 11 ... negative electrode current collector, 12 ... negative electrode active material layer,
20 ... reformer in bulk, 21 ... counter electrode,
22 ... Silicon oxide particles, 23 ... Electrolyte, 24 ... Separator,
25 ... Powder storage container, 26 ... Power supply, 27 ... Bathtub,
30 ... lithium secondary battery (laminated film type), 31 ... wound electrode body,
32 ... Positive electrode lead, 33 ... Negative electrode lead, 34 ... Adhesion film,
35 ... exterior member.

Claims (13)

A negative electrode active material comprising 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 of Li ₂ SiO ₃ and Li ₄ SiO ₄ ,
The negative electrode active material particles have a median diameter of 1.0 μm or more and 15 μm or less,
A negative electrode active material having a distribution constant n of 5.0 or less when the particle size distribution of the negative electrode active material particles is expressed by the following formula 1 of rosin Ramler distribution.
R = 100exp (−ad ⁿ ) Equation 1
(However, R in Formula 1 is on the sieve of the cumulative amount of distribution (% by mass), d is the particle size (μm) of the negative electrode active material particles, a is a constant, and n is a distribution constant.)   2. The negative electrode active material according to claim 1, wherein when the particle size distribution of the negative electrode active material particles is expressed by Formula 1 of the Rosin-Lambler distribution, the value of the distribution constant n is 3.0 or less.   In a mixed solution obtained by mixing a mixture of 10% by mass of the negative electrode active material particles and 90% by mass of the carbon active material and pure water at a mass ratio of 1:10, after one hour has elapsed since the mixed solution was prepared. The negative electrode active material according to claim 1, wherein the pH of the negative electrode is 13.0 or less. The negative electrode active material particles have a peak in a pore diameter of 1 to 100 nm in a pore distribution based on a BJH method, and have a total pore volume of 0.005 cm ³ / g or more. The negative electrode active material according to any one of claims 1 to 3. The negative active material particles, the negative electrode active according to any one of claims 1 to 4, wherein the true density is of 2.20 g / cm ³ or more 2.50 g / cm ³ or less material. The negative electrode active material particles include Li ₂ CO ₃ and LiOH on the surface,
The content of Li ₂ CO ₃ is 0.01% by mass or more and 5.00% by mass or less with respect to the mass of the negative electrode active material particles, and the content of LiOH is that of the negative electrode active material particles. The negative electrode active material according to claim 1, wherein the negative electrode active material is 0.01% by mass or more and 5.00% by mass or less with respect to the mass.   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 7 The negative electrode active material according to claim 1, wherein the negative electrode active material is 5 nm or less. In the silicon compound particles, the maximum peak intensity value A in the Si and Li silicate regions given by the chemical shift value of −60 to −95 ppm obtained from the ²⁹ Si-MAS-NMR spectrum, and the chemical shift value of −96 to − 8. The negative electrode active material according to claim 1, wherein a peak intensity value B of the SiO ₂ region given at 150 ppm satisfies a relationship of A> B. 9.   A negative electrode containing a mixture of the negative electrode active material and the carbon-based active material, and a test cell comprising a counter lithium, and charging the current to insert lithium into the negative electrode active material in the test cell; A charge / discharge process comprising 30 discharges through which a current is passed so as to desorb lithium from the negative electrode active material, and the discharge capacity Q in each charge / discharge is differentiated by the potential V of the negative electrode with respect to the counter 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 is 0.40 V to 0.55 V at the time of discharge after the Xth (1 ≦ X ≦ 30). The negative electrode active material according to claim 1, wherein the negative electrode active material has a peak in the range.   The negative electrode active material according to any one of claims 1 to 9, wherein the negative electrode active material particles include a carbon material in a surface layer portion.   The negative active material according to claim 10, wherein an average thickness of the carbon material is 10 nm or more and 5000 nm or less.   A mixed negative electrode active material comprising the negative electrode active material according to claim 1 and a carbon-based active material. A method for producing a negative electrode active material comprising negative electrode active material particles containing silicon compound particles,
Producing silicon compound particles containing a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6);
Inserting lithium into the silicon compound particles and containing at least one of Li ₂ SiO ₃ and Li ₄ SiO ₄ ;
To produce negative electrode active material particles,
From the negative electrode active material particles, the median diameter is 1.0 μm or more and 15 μm or less,
A step of selecting particles having a distribution constant n of 5.0 or less when the particle size distribution of the negative electrode active material particles is expressed by the following formula 1 of the rosin Ramler distribution:
A method for producing a negative electrode active material, wherein a negative electrode active material is produced using the selected negative electrode active material particles.
R = 100exp (−ad ⁿ ) Equation 1
(However, R in Formula 1 is on the sieve of the cumulative amount of distribution (% by mass), d is the particle size (μm) of the negative electrode active material particles, a is a constant, and n is a distribution constant.)

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