JP6448525B2 - Non-aqueous electrolyte secondary battery negative electrode active material, non-aqueous electrolyte secondary battery negative electrode, non-aqueous electrolyte secondary battery, and method for producing non-aqueous electrolyte secondary battery negative electrode material - Google Patents

Description

  The present invention relates to a negative electrode active material for a non-aqueous electrolyte secondary battery, a negative electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery including the same, and a method for producing a negative electrode material for a non-aqueous electrolyte secondary battery.

  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 easy to miniaturize and increase capacity, and can obtain higher energy density than lead batteries and nickel cadmium batteries.

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

  As a negative electrode active material, while carbon materials are widely used, further improvement in battery capacity is required due to recent market demand. As an element for improving battery capacity, the 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. The shape of the active material is studied from a standard coating type of carbon 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 silicon-based active material particles expand and contract during charge / discharge, and therefore, the silicon-based active material particles tend to break mainly in the vicinity of the surface layer. Further, an ionic material is generated inside the active material, and the silicon-based active material particles are easily broken. When the negative electrode active material surface layer is cracked, a new surface is generated and the reaction area of the active material is increased. At this time, a decomposition reaction of the electrolytic solution occurs on the new surface, and a coating film 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 the cycle characteristics, oxygen is contained in the silicon active material, the average oxygen content is 40 at% or less, and the oxygen content is increased at a location close to the current collector. (For example, see 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 the initial charge / discharge efficiency, a Li-containing material is added to the negative electrode, and pre-doping is performed to decompose Li and return Li to the positive electrode when the negative electrode potential is high (see, for example, Patent Document 6).

  Further, in order to improve cycle characteristics, SiOx (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 (for example, see Patent Document 7). Further, in order to improve cycle characteristics, the molar ratio of oxygen to silicon in the negative electrode active material is 0.1 to 1.2, and the molar ratio of oxygen amount to silicon amount in the vicinity of the interface between the active material and the current collector The active material is controlled in a range where the difference between the maximum value and the minimum value is 0.4 or less (see, for example, Patent Document 8). Further, in order to improve battery load characteristics, a metal oxide containing lithium is used (see, for example, Patent Document 9). In addition, in order to improve cycle characteristics, a hydrophobic layer such as a silane compound is formed on the surface of the siliceous material (see, for example, Patent Document 10).

In order to improve cycle characteristics, silicon oxide is used and conductivity is imparted by forming a graphite film on the surface layer (see, for example, Patent Document 11). In this case, in Patent Document 11, 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.

  Moreover, in order to improve high battery capacity and cycle characteristics, particles having a silicon microcrystalline phase dispersed in silicon dioxide are used (see, for example, Patent Document 12). 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 (for example, see Patent Document 13). .

JP 2001-185127 A JP 2002-042806 A JP 2006-164955 A JP 2006-114454 A JP 2009-070825 A Special table 2013-513206 gazette 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. 2999741

  As described above, in recent years, small electronic devices typified by mobile terminals and the like have been promoted to have high performance and multiple functions, and non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, which are the main power sources thereof. Is required to increase battery capacity. As one method for solving this problem, development of a non-aqueous electrolyte secondary battery including a negative electrode using a siliceous material as a main material is desired. In addition, non-aqueous electrolyte secondary batteries using a siliceous material are desired to have cycle characteristics close to those of a non-aqueous electrolyte secondary battery using a carbon material.

  The present invention has been made in view of the above problems, and provides a negative electrode active material for a non-aqueous electrolyte secondary battery capable of increasing battery capacity and improving cycle characteristics and battery initial efficiency. With the goal. Another object of the present invention is to provide a nonaqueous electrolyte secondary battery using the negative electrode active material. Another object of the present invention is to provide a method for producing a negative electrode material for a non-aqueous electrolyte secondary battery that increases battery capacity and is excellent in cycle characteristics and battery initial efficiency.

In order to achieve the above object, the present invention provides a non-aqueous solution having negative electrode active material particles, the negative electrode active material particles containing a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6). A negative electrode active material for an electrolyte secondary battery, wherein the negative electrode active material particles have a carbon coating on at least a part of a surface thereof, and the carbon coating was measured by isolating the carbon coating from the negative electrode active material particles. The specific surface area by the multipoint BET method is 5 m ² / g or more and 1000 m ² / g or less, and the carbon coating film has a compression resistivity of 1. which is measured by isolating the carbon coating film from the negative electrode active material particles. Provided is a negative electrode active material for a non-aqueous electrolyte secondary battery that is 1.0 × 10 ⁻³ Ω · cm to 1.0 Ω · cm when compressed to a density of 0 g / cm ³ .

  Since the negative electrode active material of the present invention has negative electrode active material particles containing a silicon compound, the battery capacity is much larger than when the carbon-based active material particles are mainly used, and the negative electrode active material particles containing a silicon compound By having at least a part of the surface covered with the carbon film, the film has excellent conductivity. Furthermore, when the specific surface area of the carbon coating isolated from the negative electrode active material particles is in the above range, the impregnation property of the battery electrolyte is good. Moreover, if the specific surface area of the isolated carbon film is in the above range, the amount of the binder adsorbed on the surface of the negative electrode active material particles becomes appropriate, and the binding property is improved. Further, if the compression resistivity of the isolated carbon coating is as described above, the surface conductivity of the negative electrode active material particles is sufficient, and Li precipitation due to power concentration on the surface hardly occurs. Further, by measuring the specific surface area and compression resistivity of the isolated carbon film, it is possible to remove the influence of the silicon compound and the like and measure the characteristics of the pure carbon film. Such a negative electrode active material has a high capacity when used as a negative electrode, and further exhibits an excellent capacity retention ratio and initial efficiency. Hereinafter, the negative electrode active material particles made of a silicon compound coated with a carbon coating in the present invention are also referred to as “silicon-based active material particles”.

At this time, the true density of the carbon coating is preferably in the range of 1.2 g / cm ³ or more and 1.9 g / cm ³ or less.

If the true density of the carbon coating is 1.9 g / cm ³ or less, the carbon coating on the surface of the silicon compound will not be too dense, so that the internal silicon compound can be easily impregnated with the electrolyte, and cycle characteristics and initial charge can be improved. Battery characteristics such as discharge characteristics are further improved. Further, when the true density is 1.2 g / cm ³ or more, the specific surface area of the negative electrode active material particles containing the silicon compound becomes an appropriate value, and an appropriate amount of the binder is adsorbed when the negative electrode is manufactured. Thus, the effect of the binder is improved, and the battery characteristics are further improved.

At this time, the carbon coating was prepared by isolating the carbon coating from the negative electrode active material particles, and charging the isolated carbon coating into a measurement container so that the mass per unit area was 0.15 g / cm ² . Later, it is preferable that the compression density when compressed by pressing at 50 MPa is 1.0 g / cm ³ or more and 1.8 g / cm ³ or less.

  The negative electrode active material in which the carbon coating isolated from the silicon-based active material particles satisfies the above-described compression density has excellent conductivity inside the electrode because the conductive auxiliary agent tends to cling to the silicon-based active material particles at the time of preparing the negative electrode. Can be.

  At this time, it is preferable that the content rate of the said carbon film is 0.1 to 25 mass% with respect to the said negative electrode active material particle.

  If it has a carbon film in such a ratio, the negative electrode active material particle containing a high capacity | capacitance silicon compound can be included in a suitable ratio, and sufficient battery capacity can be ensured.

  Further, at this time, the carbon coating is characterized by the type II or type III in the IUPAC classification of the adsorption / desorption isotherm in the adsorption / desorption isotherm by nitrogen gas measured by isolating the carbon coating from the negative electrode active material particles. It is preferable to have.

  When the adsorption / desorption isotherm measured from the carbon coating isolated from the silicon-based active material particles is type II or type III, it can be said that the surface of the carbon coating is nonporous. Binder consumption can be minimized, and since the binder is not excessively adsorbed, it has an excellent effect on binding of silicon-based active material particles containing a silicon compound having a large expansion / contraction amount. be able to.

  At this time, the carbon coating can be isolated by removing the silicon compound from the negative electrode active material particles by reacting the negative electrode active material particles with a solution containing hydrofluoric acid and nitric acid. .

  Specifically, the carbon film can be isolated by such a method.

At this time, the carbon film is in the Raman spectrum obtained by Raman spectrum analysis, have a scattering peak at 1330 cm ^-1 and 1580 cm ^-1, a ratio of the intensity of their scattering peak _I 1330 _{/ I 1580} is 0. It is preferable that 7 <I ₁₃₃₀ / I ₁₅₈₀ <2.0 is satisfied.

  As long as the carbon coating of the silicon-based active material particles satisfies the above peak intensity ratio, the ratio of the carbon material having a diamond structure and the carbon material having a graphite structure contained in the carbon coating can be optimized.

In this case, the carbon film is, the TOF-SIMS (time-of-flight secondary ion mass _{spectrometry),} fragments of C y _{H z} type compounds are detected, as a fragment of the _C y _{H z} type compounds, 6 ≧ y It is preferable that at least a part satisfying the range of ≧ 2, 2y + 2 ≧ z ≧ 2y−2 is detected.

By TOF-SIMS, as long as the surface condition of Compound fragments such as C _y H _z type fragment is detected, the better the compatibility with the anode binder such as CMC (carboxymethyl cellulose), polyimide, more battery characteristics improves.

At this time, the fragment of the C _y H _z compound detected by the carbon coating has a C ₄ H ₉ detection intensity D and a C ₃ H ₅ detection intensity E of 2.5 ≧ D / E in TOF-SIMS. It is preferable that the relationship of ≧ 0.3 is satisfied.

If the ratio of the detected intensities of C ₄ H ₉ and C ₃ H ₅ satisfies the above range, the conductivity improving effect by the carbon coating can be made more effective.

  At this time, the average thickness of the carbon coating is preferably 5 nm or more and 5000 nm or less.

  If the carbon film satisfies such an average thickness, sufficient conductivity can be imparted and the ratio of the silicon compound can be increased.

  At this time, the average coverage of the carbon coating is preferably 30% or more.

  By using the above average coverage, the carbon component works particularly effectively for improving the conductivity when the negative electrode active material containing such silicon-based active material particles is used as the negative electrode active material of the lithium ion secondary battery. .

  At this time, it is preferable that the carbon film is obtained by pyrolyzing a compound containing carbon.

  The carbon film obtained by such a method has a high average coverage on the surface of the silicon-based active material particles.

At this time, in the silicon compound, as the chemical shift value obtained from the ²⁹ Si-MAS-NMR spectrum, the peak area A of the amorphous silicon region given by −20 to −74 ppm and the crystallinity given by −75 to −94 ppm It is preferable that the peak area B of the silicon region and the Li silicate region and the peak area C of the silica region given to −95 to −150 ppm satisfy the formula (1).
Formula (1): 5.0 ≧ A / B ≧ 0.01, 6.0 ≧ (A + B) /C≧0.02

If the silicon compound contained in the silicon-based active material particles has a peak area ratio satisfying the above formula (1) in the ²⁹ Si-MAS-NMR spectrum, the expansion of the amorphous silicon that suppresses the expansion due to the insertion of Li can be reduced. Since the ratio is high, expansion of the negative electrode is suppressed, and better cycle characteristics can be obtained. Moreover, if it is such, since the ratio of a silica component with respect to a silicon component and a Li silicate component is small, the fall of the electronic conductivity in a silicon compound can be suppressed.

  At this time, the negative electrode active material particles have a half-value width (2θ) of a diffraction peak attributed to the Si (111) crystal plane obtained by X-ray diffraction of 1.2 ° or more and a crystal attributed to the crystal plane. The child size is preferably 7.5 nm or less.

  Since the silicon compound having such a half width and crystallite size has low crystallinity and a small amount of Si crystals, the battery characteristics can be improved. In addition, the presence of such a low-crystallinity silicon compound makes it possible to generate a stable Li compound.

  Moreover, it is preferable at this time that the median diameter of the said negative electrode active material particle is 0.5 micrometer or more and 20 micrometers or less.

  If the negative electrode active material includes silicon-based active material particles having such a median diameter, lithium ion is easily occluded and released during charge and discharge, and the silicon-based active material particles are difficult to break. As a result, the capacity maintenance rate can be improved.

  At this time, it is preferable that at least a part of the negative electrode active material particles contain Li.

  The initial efficiency is improved by including the Li compound in the silicon-based active material particles contained in the negative electrode. In addition, since the initial efficiency of the negative electrode in the case of a nonaqueous electrolyte secondary battery is increased, a deviation in the balance between the positive electrode and the negative electrode during the cycle test is suppressed, and the maintenance ratio is improved.

The negative electrode active material particle of the present invention, at least a portion of the anode active material particles _preferably contains at least one or more of Li 2 SiO ₃ and _Li 4 SiO _4.

  If the silicon-based active material particles contain the above-described Li silicate that is relatively stable as a Li compound, the stability with respect to the slurry during electrode production is further improved.

Moreover, the negative electrode active material particles of the present invention are the negative electrode active material particles of the crystalline silicon region and Li silicate region, which are obtained from the ²⁹ Si-MAS-NMR spectrum and given as a chemical shift value of −75 to −94 ppm. It is preferable that the maximum peak intensity value H and the peak intensity value I of the silica region given by -95 to -150 ppm as the chemical shift value satisfy the relationship of H> I.

If the silicon-based active material particles have a larger amount of crystalline silicon and Li silicate such as Li ₂ SiO ₃ based on the silica (SiO ₂ ) component, the effect of improving battery characteristics due to insertion of Li will be sufficient. It becomes the negative electrode active material obtained.

  Further, a test cell comprising a negative electrode containing a mixture of the negative electrode active material for a non-aqueous electrolyte secondary battery and a carbon-based active material and counter electrode lithium is prepared, and the test cell is used for the non-aqueous electrolyte secondary battery. Charging / discharging consisting of charging for flowing current to insert lithium into the negative electrode active material and discharging for flowing current to desorb lithium from the negative electrode active material for non-aqueous electrolyte secondary battery was performed 30 times. When a graph showing the relationship between the differential value dQ / dV obtained by differentiating the discharge capacity Q in the discharge with respect to the potential V of the negative electrode with respect to the counter lithium as a reference and the potential V is drawn from the Xth time (1 ≦ X It is preferable that the potential V of the negative electrode has a peak in the range of 0.40 V to 0.55 V during the discharge of ≦ 30.

  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.

  At this time, the negative electrode active material of the present invention preferably further contains carbon-based active material particles.

  In the present invention, if carbon-based active material particles are further contained in addition to silicon-based active material particles, better cycle characteristics and initial charge / discharge characteristics can be obtained while increasing the capacity of the negative electrode.

  At this time, the ratio of the mass of the negative electrode active material particles to the total mass of the negative electrode active material particles and the carbon-based active material particles is preferably 5% by mass or more.

  If the ratio of the negative electrode active material particles containing a silicon compound is as described above, the battery capacity can be further increased.

  At this time, it is preferable that the average particle size F of the negative electrode active material particles satisfies the relationship of 25 ≧ G / F ≧ 0.5 with respect to the average particle size G of the carbon-based active material particles.

  When the average particle diameter G of the carbon-based active material particles and the average particle diameter F of the negative electrode active material particles containing the silicon compound satisfy the relationship as described above, the destruction of the composite material layer can be prevented. Further, when the carbon-based active material particles are larger than the negative electrode active material particles containing a silicon compound, the negative electrode volume density and initial efficiency during charging are improved, and the battery energy density is improved.

  At this time, the carbon-based active material particles are preferably a graphite material.

  The graphite material is preferable because it can exhibit better initial efficiency and capacity retention than other carbon-based active materials.

  In order to achieve the above object, the present invention includes a negative electrode active material layer containing the negative electrode active material for a non-aqueous electrolyte secondary battery, and a negative electrode current collector, A negative electrode for a non-aqueous electrolyte secondary battery, wherein the negative electrode current collector is formed on a negative electrode current collector, and the negative electrode current collector contains carbon and sulfur, both of which are 100 ppm by mass or less. I will provide a.

  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 nonaqueous electrolyte secondary battery characterized by including said negative electrode active material for nonaqueous electrolyte secondary batteries.

  The nonaqueous electrolyte secondary battery using the negative electrode active material of the present invention has a high capacity and good cycle characteristics and initial charge / discharge characteristics.

In order to achieve the above object, the present invention provides a method for producing a negative electrode material for a non-aqueous electrolyte secondary battery including negative electrode active material particles, wherein SiO _x (0.5 ≦ x ≦ 1.6) The step of producing particles of the silicon compound represented, the step of coating at least a part of the surface of the particles of the silicon compound with a carbon coating, and the particles of the silicon compound coated with the carbon coating, The carbon film was isolated and measured from silicon compound particles having a specific surface area of 5 m ² / g or more and 1000 m ² / g or less as measured by the multi-point BET method, which was isolated and measured. The silicon compound particles coated with the carbon coating having a compression resistivity of 1.0 × 10 ⁻³ Ω · cm to 1.0 Ω · cm when compressed to a density of 1.0 g / cm ³ are selected. And having a process A negative electrode material for a non-aqueous electrolyte secondary battery is manufactured using the silicon compound particles coated with the carbon coating as negative electrode active material particles. .

  With such a manufacturing method, by using the silicon compound particles coated with the carbon coating selected as described above as the negative electrode active material particles, a high capacity and an excellent capacity retention rate and initial efficiency are obtained. A negative electrode material for a non-aqueous electrolyte secondary battery can be produced.

  When the negative electrode active material of the present invention is used as a negative electrode active material for a non-aqueous electrolyte secondary battery, a high capacity and good cycle characteristics and initial charge / discharge characteristics can be obtained. Moreover, the same characteristic can be acquired also in the secondary battery containing the negative electrode active material for nonaqueous electrolyte secondary batteries of this invention. Moreover, the same effect can be acquired also in the electronic device, electric tool, electric vehicle, electric power storage system, etc. which used the secondary battery of this invention.

  Moreover, if it is the manufacturing method of the negative electrode material of this invention, the negative electrode material for nonaqueous electrolyte secondary batteries which has a high capacity | capacitance and favorable cycling characteristics and initial stage charge / discharge characteristics can be manufactured.

It is a schematic sectional drawing of the negative electrode using the negative electrode active material for nonaqueous electrolyte secondary batteries of this invention. It is a plot figure for calculating | requiring the density of the carbon film of the negative electrode active material particle in this invention. It is an exploded view which shows an example of a structure of the nonaqueous electrolyte secondary battery (laminated film type lithium ion secondary battery) of this invention.

  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 non-aqueous electrolyte secondary battery, it has been studied to use a negative electrode using a siliceous material as a main material as a negative electrode of a non-aqueous electrolyte secondary battery.

  The non-aqueous electrolyte secondary battery using this siliceous material is expected to have cycle characteristics similar to those of the non-aqueous electrolyte secondary battery using the carbon material, but the non-aqueous electrolyte secondary battery using the carbon material is desired. No negative electrode material having a cycle stability equivalent to that of the above has been proposed. In particular, the silicon compound containing oxygen has a lower initial efficiency than the carbon material, so that the battery capacity has been limited to that extent.

  Accordingly, the present inventors have conducted intensive studies on a negative electrode active material that can provide good cycle characteristics and initial efficiency when used in a negative electrode of a non-aqueous electrolyte secondary battery, leading to the present invention.

The negative electrode active material for a nonaqueous electrolyte secondary battery of the present invention includes negative electrode active material particles. The negative electrode active material particles are silicon-based active material particles containing a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6). The silicon-based active material particles have a carbon coating on at least a part of the surface. Further, the carbon coating has a specific surface area of 5 m ² / g or more and 1000 m ² / g or less by a multi-point BET method measured by isolation from the silicon active material particles, and is isolated from the silicon active material particles and measured. The compressed resistivity is 1.0 × 10 ⁻³ Ω · cm to 1.0 Ω · cm when compressed to a density of 1.0 g / cm ³ .

  Since the negative electrode active material of the present invention has silicon-based active material particles, the battery capacity is large, and at least a part of the surface of the silicon-based active material particles is coated with a carbon film, thereby having excellent conductivity. It will be a thing.

Moreover, when the specific surface area by the multipoint BET method measured by isolating the carbon film from the silicon-based active material particles is less than 5 m ² / g, the impregnation property of the electrolytic solution is poor, and cycle characteristics, initial charge / discharge characteristics, etc. The battery characteristics deteriorate. Moreover, when the specific surface area of the carbon film isolated from the silicon-based active material particles exceeds 1000 m ² / g, the coatability when the negative electrode active material is made into a slurry is deteriorated. Further, when the compression resistivity measured when the carbon coating isolated from the silicon-based active material particles is compressed to a density of 1.0 g / cm ³ exceeds 1.0 Ω · cm, the surface of the silicon-based active material particles Conductivity is insufficient, and battery characteristics such as cycle characteristics and initial charge / discharge characteristics are deteriorated. Further, when the compression resistivity is less than 1.0 × 10 ⁻³ Ω · cm, current concentration is likely to occur on the surface of the silicon-based active material particles, and Li precipitation occurs during charging / discharging of the battery. Characteristics deteriorate.

On the other hand, the negative electrode active material of the present invention has a specific surface area of 5 m ² / g or more and 1000 m ² / g or less according to the multipoint BET method measured by isolating the carbon film from the silicon-based active material particles, and the carbon film Since the compression resistivity measured by isolating from the silicon-based active material particles is 1.0 × 10 ⁻³ Ω · cm to 1.0 Ω · cm when compressed to a density of 1.0 g / cm ³ , When used in a secondary battery, the above-described deterioration of battery characteristics is unlikely to occur, and high battery capacity, good cycle characteristics, and initial charge / discharge characteristics can be obtained.

<1. Negative electrode for non-aqueous electrolyte secondary battery>
The negative electrode for nonaqueous electrolyte secondary batteries using the negative electrode material for nonaqueous electrolyte secondary batteries of the present invention will be described. FIG. 1 shows a cross-sectional configuration of a negative electrode for a nonaqueous electrolyte secondary battery (hereinafter sometimes simply 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 carbon and sulfur 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.

  The surface of the negative electrode current collector 11 may be roughened or not roughened. The roughened negative electrode current collector is, for example, a metal foil subjected to electrolytic treatment, embossing treatment, or chemical etching. 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 includes the negative electrode active material of the present invention, and may further include other materials such as a negative electrode binder and a negative electrode conductive additive in battery design. As the negative electrode active material, in addition to the negative electrode active material particles (silicon-based active material particles) containing a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6), a carbon-based active material or the like may also be included. The negative electrode active material for a nonaqueous electrolyte secondary battery of the present invention is a material constituting the negative electrode active material layer 12.

  The silicon-based active material particles contained in the negative electrode active material of the present invention contain a silicon compound that can occlude and release lithium ions.

As described above, the silicon-based active material particles contained in the negative electrode active material of the present invention contain a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6). As the composition of the silicon compound, x is preferably close to 1. This is because high cycle characteristics can be obtained. Moreover, the siliceous material composition in the present invention does not necessarily mean 100% purity, and may contain a trace amount of impurity elements.

In addition, as described above, at least a part of the surface of the silicon-based active material particles contained in the negative electrode active material of the present invention is covered with the carbon film. As described above, the carbon coating has a specific surface area of 5 m ² / g or more and 1000 m ² / g or less according to the multipoint BET method measured by isolating the carbon coating from the silicon-based active material particles and measuring the carbon coating. The compression resistivity measured by isolation from the silicon-based active material particles is 1.0 × 10 ⁻³ Ω · cm or more and 1.0 Ω · cm or less when compressed to a density of 1.0 g / cm ³ .

At this time, the carbon coating was isolated from the silicon-based active material particles, and after the charged carbon coating was charged in a measurement container so that the mass per unit area was 0.15 g / cm ² , the carbon coating was 50 MPa. The compression density when compressed by pressing is preferably 1.0 g / cm ³ or more and 1.8 g / cm ³ or less. When the carbon coating isolated from the silicon-based active material particles satisfies the above-mentioned compression density, the conductive auxiliary agent tends to cling to the silicon-based active material particles at the time of preparing the negative electrode, and the amount of binder adsorbed becomes an appropriate amount. The electrical conductivity inside the electrode can be made excellent.

  Moreover, it is preferable that the carbon coating has the characteristics of type II or type III in the IUPAC classification of the adsorption / desorption isotherm in the adsorption / desorption isotherm by nitrogen gas measured by isolating the carbon coating from the silicon-based active material particles. If the adsorption / desorption isotherm measured by isolating the carbon coating is type II or type III, the surface of the carbon coating is non-porous. Therefore, when the negative electrode is produced using the negative electrode active material of the present invention, , Binder consumption can be minimized. Furthermore, since the binder is not excessively adsorbed on the surface of the negative electrode active material, the negative electrode active material containing silicon-based active material particles having a large expansion / contraction amount can be appropriately bound.

  As a method for isolating the carbon film from the silicon-based active material particles, for example, the following isolation method can be used. First, silicon-based active material particles having a carbon coating are added to a Teflon (registered trademark) beaker, ion-exchanged water and ethanol are further added, and the mixture is thoroughly stirred with a Teflon (registered trademark) stirring rod. Thereafter, hydrofluoric acid is added and stirred, nitric acid is added, ion-exchanged water is added as appropriate, nitric acid is further added, and the mixture is allowed to stand for 3 hours. Then, the isolated carbon film is filtered by filtering the obtained black solution. Thereafter, the isolated carbon film is washed with water, further washed with ethanol, and then vacuum-dried at 200 ° C. for 10 hours. Various analyzes such as X-ray diffraction and Raman spectroscopy can be performed on the isolated carbon film thus obtained as a measurement target. And by performing various analyzes with respect to the isolated carbon film, it becomes possible to remove the influence of the silicon compound etc. of a core material, and to measure the characteristic of a pure carbon film.

  The specific surface area of the carbon film isolated from the silicon-based active material particles can be obtained by extrapolation of four or more points where the correlation coefficient R> 0.99 of the adsorption isotherm using the multipoint BET method.

The compression resistivity of the carbon film isolated from the silicon-based active material particles can be measured, for example, under the following conditions.
・ Equipment: Powder resistance measurement system MCP-PD manufactured by Mitsubishi Chemical Analytech ・ 4-probe method ・ Preparation: 0.30 g
And pressure Measurement: 20 N up to pressure, measured powder resistance per 5N, extrapolating measurements obtained, calculated compression resistance of at 1.0 g / cm ^3.

The adsorption / desorption isotherm can be measured by adsorbing / desorbing nitrogen as an adsorbed molecule on an adsorbent (here, silicon-based active material particles). As a measuring device, BELSORP-mini manufactured by Nippon Bell Co., Ltd. can be used. When there is a history (hysteresis) of nitrogen adsorption / desorption, nitrogen adsorption when the maximum history difference ΔV of nitrogen adsorption amount at the same pressure during adsorption / desorption is p / p ⁰ = 0.9. If ΔV / V ≦ 0.05 compared with the amount V, the history is due to measurement error, and the adsorption / desorption isotherm can be classified as type II or type III, assuming that there is substantially no history. . Here, p / p ⁰ is the relative pressure, which is the equilibrium pressure divided by the saturated vapor pressure.

  As a method for separating silicon-based active material particles having different classifications into adsorption isotherms, for example, when separating silicon-based active material particles having types II and IV, first, powder of silicon-based active material particles is used. Leave in an 80% humidity environment for 10 hours (stir 3 or more times in the middle). Next, the powder is filled in the cylindrical container so that the bulk density is 5% with respect to the space in the cylindrical container, and after stirring the cylindrical container for 2 hours, the cylindrical container is set up and allowed to stand. The operation of allowing to stand until deposition is repeated twice. In the obtained powder, 20% (type II) deposited on the top and 20% (type IV) deposited on the bottom can be separated, respectively, to separate type II and type IV. it can.

In the present invention, the true density of the carbon coating on the surface of the silicon-based active material particles is preferably in the range of 1.2 g / cm ³ or more and 1.9 g / cm ³ or less. If the true density of the carbon coating is 1.9 g / cm ³ or less, the carbon coating on the surface of the silicon-based active material particles does not become too dense, so that the electrolyte is contained in the silicon compound contained in the silicon-based active material particles. Impregnation is easy and battery characteristics such as cycle characteristics and initial charge / discharge characteristics are improved. In addition, when the true density is 1.2 g / cm ³ or more, the specific surface area of the silicon-based active material particles becomes an appropriate value, and the binder is adsorbed by an appropriate amount when the negative electrode is produced. This improves the battery characteristics.

  Here, the true density of the carbon film formed on the surface of the silicon-based active material particles is, for example, a plot of the carbon film content (% by mass) and the density of the silicon-based active material particles as shown in FIG. Can be obtained by calculating the true density of only the carbon film by performing extrapolation at a point where the content of the carbon film is 100% by mass by linear approximation. That is, the true density of the carbon film measured here is not measured by isolation.

Further, in the present invention, the silicon-based active material carbon coating formed on the surface of the particles, in the Raman spectrum obtained by Raman spectrum analysis, have a scattering peak at 1330 cm ^-1 and 1580 cm ^-1, their scattering peaks It is preferable that the intensity ratio I ₁₃₃₀ / I ₁₅₈₀ satisfies 0.7 <I ₁₃₃₀ / I ₁₅₈₀ <2.0. Thereby, the ratio of the carbon material having a diamond structure and the carbon material having a graphite structure contained in the carbon film can be optimized. As a result, when the negative electrode active material including the silicon-based active material particles having the carbon coating is used as the negative electrode of the nonaqueous electrolyte secondary battery, a nonaqueous electrolyte secondary battery having good battery characteristics can be obtained.

Further, the Raman spectrum can be obtained by microscopic Raman analysis (that is, Raman spectrum analysis), and the ratio of the carbon component having a diamond structure and the carbon component having a graphite structure can be obtained from the obtained Raman spectrum. That is, diamond shows a sharp peak with a Raman shift of 1330 cm ⁻¹ and graphite with a Raman shift of 1580 cm ⁻¹ , and the ratio of the carbon component having a diamond structure and the carbon component having a graphite structure is simply determined from the intensity ratio. Can do. Diamond has high strength, high density, and high insulation, and graphite has excellent electrical conductivity. Therefore, the carbon film satisfying the above peak intensity ratio is optimized for each of the above characteristics, and as a result, it is possible to prevent electrode destruction due to expansion / contraction of the electrode material during charge / discharge and to have a negative electrode active material having a conductive network It becomes.

  Moreover, it is preferable that the content rate of a carbon film is 0.1 to 25 mass% with respect to silicon type active material particle. The carbon film content is more preferably 4% by mass or more and 20% by mass or less.

  If this content is 0.1% by mass or more, it is possible to reliably improve the electrical conductivity of the silicon-based active material particles. On the other hand, when the content is 25% by mass or less, the battery characteristics are improved and the battery capacity is increased. The coating method of the carbon-based compound is not particularly limited, but a sugar carbonization method and a hydrocarbon gas pyrolysis method are preferable. In this case, the carbon coating is obtained by thermally decomposing a compound containing carbon. A carbon film containing a carbon material such as graphite can be formed by such a method. Moreover, with these methods, the coverage of the carbon coating on the surface of the silicon-based active material particles can be improved.

  Moreover, in this invention, it is preferable that the average thickness of the carbon film in the surface of a silicon type active material particle is 5 nm or more and 5000 nm or less. In particular, the average thickness of the carbon coating is more preferably 5 nm or more and 500 nm or less. If average thickness is 5 nm or more, sufficient electroconductivity will be acquired and a battery characteristic will improve with an electroconductive improvement. In addition, if the average thickness is 5000 nm or less, the thickness of the carbon coating does not become too large with respect to the particle size of the silicon-based active material particles, and the ratio of the silicon compound in the negative electrode active material can be maintained high. The energy density in the case of an electrolyte secondary battery is improved. Furthermore, if the average thickness is 500 nm or less, the ratio of the silicon compound in the negative electrode active material can be kept higher. Note that the average thickness of the carbon coating in the silicon-based active material particles can be determined by cross-sectional observation using FIB-TEM (Focused Ion Beam-Transmission Electron Microscope).

  In the present invention, the average coverage of the carbon coating on the surface of the silicon-based active material particles is preferably 30% or more. When the average coverage is 30% or more, the carbon component works particularly effectively for improving the conductivity, and the battery characteristics are improved. The average coverage was defined as surface (carbon detection intensity) / (silicon detection intensity) by local composition analysis using SEM-EDX (Scanning Electron Microscope-Energy Dispersive X-ray Spectroscope).

Further, in the present invention, the carbon coating on the surface of the silicon-based active material particles by _TOF-SIMS, fragment C y _{H z} type compounds are detected, as a fragment of the _C y _{H z} type compounds, 6 ≧ y ≧ Preferably, those satisfying the range of 2, 2y + 2 ≧ z ≧ 2y−2 are at least partially detected. If the surface state is such that a compound fragment such as a C _y H _z- based fragment is detected, compatibility with a negative electrode binder such as CMC or polyimide is improved, and battery characteristics are improved.

In this case, in particular, the fragment of the C _y H _z compound detected by the carbon coating has a detection intensity D of C ₄ H _{9 and} a detection intensity E of C ₃ H ₅ of 2.5 ≧ D / E in TOF-SIMS. It is preferable that the relationship of ≧ 0.3 is satisfied. If the ratio D / E of the detected intensity is 2.5 or less, the electrical resistance of the surface is small, so that the conductivity is improved and the battery characteristics are improved. Further, if the ratio D / E of the detected intensity is 0.3 or more, the carbon coating on the surface is sufficiently formed, so that the conductivity is improved by the carbon coating on the entire surface, and the battery characteristics are improved. improves. In addition, the type and amount of the C _y H _z -based compound fragment to be detected can be adjusted by changing the CVD conditions (gas, temperature) and subsequent processing conditions. As post-processing here, the baking processing etc. which are performed in a vacuum or argon atmosphere after CVD processing at 950-1200 degreeC, etc. are mentioned, for example.

TOF-SIMS can be measured, for example, under the following conditions.
PHI TRIFT 2 made by ULVAC-PHI
・ Primary ion source: Ga
-Sample temperature: 25 ° C
・ Acceleration voltage: 5 kV
・ Spot size: 100μm × 100μm
Sputtering: Ga, 100 μm × 100 μm, 10 s
・ Anion mass spectrum ・ Sample ： Powder pellet

Further, in the silicon compound contained in the silicon-based active material particles, the peak area A of the amorphous silicon region given by −20 to −74 ppm and −75 to −94 ppm as the chemical shift value obtained from the ²⁹ Si-MAS-NMR spectrum. It is preferable that the peak area B of the crystalline silicon region and the Li silicate region given by the formula (1) and the peak area C of the silica region given to -95 to -150 ppm satisfy the formula (1). The chemical shift is based on tetramethylsilane.
Formula (1): 5.0 ≧ A / B ≧ 0.01, 6.0 ≧ (A + B) /C≧0.02

The higher the proportion of amorphous silicon that can suppress the expansion associated with the insertion of Li, the lower the expansion of the negative electrode when the battery is made, and the cycle characteristics are improved. In addition, since the ratio of the silica component to the silicon component such as amorphous silicon and crystalline silicon and the Li silicate component such as Li ₂ SiO ₃ is small as long as the range of the above formula (1) is satisfied, Therefore, the battery characteristics can be improved.

Further, the negative electrode active material of the present invention is the maximum peak of the crystalline silicon region and the Li silicate region, which are obtained from the ²⁹ Si-MAS-NMR spectrum and given as a chemical shift value of −75 to −94 ppm in the negative electrode active material particles. It is preferable that the intensity value H and the peak intensity value I of the silica region given as −95 to −150 ppm as the chemical shift value satisfy the relationship of H> I. If the silicon compound particles have a relatively large amount of silicon silicate component or Li silicate component such as Li ₂ SiO ₃ when the SiO ₂ component is used as a reference, the effect of improving battery characteristics by inserting Li can be sufficiently obtained. It is done.

^{The 29} Si-MAS-NMR spectrum can be measured, for example, under the following conditions.
²⁹ Si MAS NMR (magic angle rotating nuclear magnetic resonance)
Apparatus: 700 NMR spectrometer manufactured by Bruker, Inc. Probe: 4 mm HR-MAS rotor 50 μL
・ Sample rotation speed: 10 kHz
・ Measurement environment temperature: 25 ℃

  The median diameter of the silicon-based active material particles is not particularly limited, but is preferably 0.5 μm or more and 20 μm or less. This is because, within this range, lithium ions are easily occluded and released during charging and discharging, and the particles are difficult to break. If this median diameter is 0.5 μm or more, the surface area will not increase, and the battery irreversible capacity can be reduced. On the other hand, if the median diameter is 20 μm or less, it is preferable because the particles are difficult to break and a new surface is hardly produced.

  In the present invention, the half width (2θ) of the diffraction peak derived from the (111) crystal plane obtained by X-ray diffraction of the silicon compound contained in the silicon-based active material particles is preferably 1.2 ° or more. Moreover, it is preferable that the crystallite size resulting from the crystal plane is 7.5 nm or less. A silicon compound having such a half width and crystallite size has low crystallinity. By using a silicon compound having low crystallinity and a small amount of Si crystals, battery characteristics can be improved. In addition, the presence of such a low-crystallinity silicon compound makes it possible to generate a stable Li compound.

  In the present invention, it is preferable that at least a part of the silicon-based active material particles contains Li. In order to contain Li in silicon-based active material particles, Li may be doped into a silicon compound. Examples of a method for doping Li into a silicon compound include a thermal doping method in which silicon-based active material particles and metallic lithium are mixed and heated, and an electrochemical method. By including the Li compound in the silicon compound, the initial efficiency is improved. In addition, since the initial efficiency of the negative electrode in the case of a nonaqueous electrolyte secondary battery is increased, a deviation in the balance between the positive electrode and the negative electrode during the cycle test is suppressed, and the maintenance ratio is improved.

In addition, when the silicon-based active material particles contain Li, it is preferable that at least a part of the silicon-based active material particles contains at least one of Li ₂ SiO ₃ and Li ₄ SiO ₄ . If the silicon-based active material particles contain the above-described Li silicate that is relatively stable as a Li compound, the stability with respect to the slurry during electrode production is further improved.

  Further, as a method for doping Li into a silicon compound, an oxidation-reduction method can also be used. In the modification by the redox method, for example, lithium can be inserted by first immersing silicon compound particles in a solution A in which lithium is dissolved in an ether solvent. The solution A may further contain a polycyclic aromatic compound or a linear polyphenylene compound. After insertion of lithium, active lithium can be desorbed from the silicon compound particles by immersing the silicon compound particles in a solution B containing a polycyclic aromatic compound or a derivative thereof. As the solvent of the solution B, for example, an ether solvent, a ketone solvent, an ester solvent, an alcohol solvent, an amine solvent, or a mixed solvent thereof can be used. Furthermore, after immersing in the solution B, the active lithium is removed from the silicon compound particles by immersing the silicon compound particles in a solution C containing an alcohol solvent, a carboxylic acid solvent, water, or a mixed solvent thereof. Can be separated. Instead of the solution C, a solution C ′ containing a compound having a quinoid structure in the molecule as a solute and containing an ether solvent, a ketone solvent, an ester solvent, or a mixed solvent thereof as a solvent may be used. . Further, the immersion of the silicon compound particles in the solutions B, C, and C ′ may be repeated. Thus, if active lithium is desorbed after insertion of lithium, a negative electrode active material with higher water resistance is obtained. Then, you may wash | clean with the alkaline water, weak acid, or pure water which melt | dissolved alcohol and lithium carbonate.

  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.

  Examples of the negative electrode conductive aid include one or more of carbon materials such as carbon black, acetylene black, and graphite such as flaky graphite, and carbon materials (carbon-based materials) such as ketjen black, carbon nanotubes, and carbon nanofibers. . These conductive assistants are preferably in the form of particles having a median diameter smaller than that of the silicon compound.

  In the present invention, the negative electrode active material layer 12 of FIG. 1 may further contain carbon-based active material particles in addition to the negative electrode active material of the present invention. As a result, it is possible to reduce the electrical resistance of the negative electrode active material layer 12 containing the negative electrode active material of the present invention and to relieve the expansion stress associated with charging. Examples of the carbon-based active material include pyrolytic carbons, cokes, glassy carbon fibers, organic polymer compound fired bodies, and carbon blacks. Among these, the carbon-based active material particles are preferably a graphite material. The graphite material can exhibit better initial efficiency and capacity retention than other carbon-based active material particles.

  In the present invention, the ratio of the mass of the silicon-based active material particles to the total mass of the silicon-based active material particles and the carbon-based active material particles is preferably 5% by mass or more. Further, the ratio of the mass of the silicon-based active material particles is more preferably less than 90% by mass. If it is a negative electrode active material containing silicon-based active material particles at such a ratio, good initial efficiency and capacity retention can be obtained when used for the negative electrode of a non-aqueous electrolyte secondary battery. Of course, even if the mass ratio of the silicon-based active material particles is 90% by mass or more and 100% by mass or less, if the negative electrode active material of the present invention is used, high battery capacity, good cycle characteristics, and good initial charge are obtained. Discharge characteristics can be obtained.

  The average particle size F of the silicon-based active material particles preferably satisfies the relationship of 25 ≧ G / F ≧ 0.5 with respect to the average particle size G of the carbon-based active material particles. That is, it is desirable that the average particle diameter of the carbon-based active material particles is approximately equal to or greater than the average particle diameter of the silicon-based active material particles. This prevents the destruction of the composite layer when the silicon-based active material particles that expand and contract with Li insertion / extraction during battery charging / discharging are the same or smaller than the carbon-based active material particles. Because it can be done. Thus, when the carbon-based active material particles are larger than the silicon-based active material particles, the negative electrode volume density and initial efficiency during charging are improved, and the battery energy density is improved.

  The negative electrode active material layer 12 in FIG. 1 is formed by, for example, a coating method. The coating method is a method in which silicon-based active material particles and the above-mentioned binder, etc., and a conductive additive and carbon-based active material particles are mixed as necessary, and then dispersed in an organic solvent or water for coating.

[Production method of negative electrode]
A method for producing the negative electrode of the present invention will be described.

Initially, the manufacturing method of the negative electrode material contained in a negative electrode is demonstrated. First, a silicon compound represented by SiO _x (0.5 ≦ x ≦ 1.6) is produced. Next, the surface of the silicon compound is coated with a carbon film. Here, by inserting Li into the silicon compound, the silicon compound may be modified by generating the Li compound on the surface, inside, or both of the silicon compound.

Thereafter, a part of the silicon compound particles coated with the carbon coating is taken out, the carbon coating is isolated from the taken out silicon compound particles, and the specific surface area and compression resistivity are measured. And the specific surface area by the multipoint BET method measured by isolating the carbon film is 5 m ² / g or more and 1000 m ² / g or less, and the compression resistivity measured by isolating the carbon film is 1.0 g / Particles of a silicon compound coated with an original carbon film taken out satisfying the condition of 1.0 × 10 ⁻³ Ω · cm to 1.0 Ω · cm when compressed to a density of cm ³ are used as negative electrode actives. Sort as material particles.

  More specifically, the negative electrode material can be manufactured, for example, by the following procedure.

  First, a raw material (vaporization starting material) that generates silicon oxide gas is heated in the temperature range of 900 ° C. to 1600 ° C. in the presence of an inert gas or under reduced pressure to generate silicon oxide gas. In this case, the raw material is a mixture of metal silicon powder and silicon dioxide powder, and considering the surface oxygen of the metal silicon powder and the presence of trace amounts of oxygen in the reactor, the mixing molar ratio is 0.8 <metal silicon powder / It is desirable that the silicon dioxide powder is in the range of <1.3. The Si crystallites in the particles are controlled by changing the preparation range and vaporization temperature, and by heat treatment after generation. The generated gas is deposited on the adsorption plate. The deposit is taken out with the temperature in the reactor lowered to 100 ° C. or lower, and pulverized and powdered using a ball mill, a jet mill or the like.

  Next, a carbon film is coated on the surface of the obtained powder material. Thermal CVD is desirable as a method for generating a carbon film on the surface of the obtained powder material. In thermal CVD, a powder material is set in a furnace, and a hydrocarbon gas is filled to raise the temperature in the furnace. The decomposition temperature is not particularly limited, but is particularly preferably 1200 ° C. or lower. More desirably, the temperature is 950 ° C. or lower, and unintended disproportionation of the silicon compound particles can be suppressed.

When a carbon film is formed by thermal CVD, the specific surface area and compression resistivity when the carbon film is isolated from the silicon compound particles are the CVD temperature, time, and degree of stirring of the powder material (silicon compound powder) during CVD. It can be controlled by adjusting. In addition, the amount of carbon coating, thickness, coverage, and adsorption / desorption isotherm classification when the carbon coating is isolated from silicon compound particles are also included in the CVD temperature, time, and CVD powder material (silicon compound powder). It can be controlled by adjusting the degree of stirring. In addition, the peak intensity ratio I ₁₃₃₀ / I ₁₅₈₀ in the Raman spectrum can be adjusted by adjusting the temperature in the furnace. The density of the carbon coating and the compression density when the carbon coating is isolated from the silicon compound particles can be controlled by adjusting the gas flow rate during CVD.

Subsequently, a part of the silicon compound particles coated with the carbon film is taken out, for example, using the above-described carbon film isolation method, specific surface area and compression resistivity measurement method, the silicon compound particles taken out. The carbon film is isolated from the glass and the specific surface area and compression resistivity are measured. And the specific surface area by the multipoint BET method measured by isolating the carbon film is 5 m ² / g or more and 1000 m ² / g or less, and the compression resistivity measured by isolating the carbon film is 1.0 g / When compressed to a density of cm ³ , when the condition of 1.0 × 10 ⁻³ Ω · cm to 1.0 Ω · cm is satisfied, the extracted silicon compound particles coated with the original carbon coating are used as the negative electrode active material. Sort as material particles.

The selection of the silicon compound particles is not necessarily performed every time the negative electrode material is produced, and the specific surface area according to the multipoint BET method once measured by isolating the carbon coating is 5 m ² / g or more and 1000 m ² / g. And the compression resistivity measured by isolating the carbon film is 1.0 × 10 ⁻³ Ω · cm to 1.0 Ω · cm when compressed to a density of 1.0 g / cm ^3. If manufacturing conditions for obtaining a carbon coating that satisfies the conditions are found and selected, then the negative electrode material can be manufactured under the same conditions as the selected conditions.

  A negative electrode material for a non-aqueous electrolyte secondary battery is prepared using the silicon compound particles having the carbon coating thus selected as negative electrode active material particles.

  Subsequently, the negative electrode active material particles, the negative electrode binder, and other materials such as a conductive additive are mixed to form a negative electrode mixture, and then an organic solvent or water is added to obtain a slurry.

  Next, a negative electrode mixture slurry is applied to the surface of the negative electrode current collector and dried to form the negative electrode active material layer 12 shown in FIG. At this time, a heating press or the like may be performed as necessary. Thus, a negative electrode can be manufactured.

  Further, when a carbon-based material having a median diameter smaller than that of the silicon-based active material particles is added as a conductive additive, for example, acetylene black can be selected and added.

Hydrocarbon gas is not particularly limited, 3 ≧ n of C _n H _m composition it is desirable. This is because the manufacturing cost can be lowered and the physical properties of the decomposition product are good.

<2. Lithium ion secondary battery>
Next, a lithium ion secondary battery containing the negative electrode active material of the present invention will be described.

[Configuration of laminated film type lithium ion secondary battery]
A laminated film type secondary battery 20 shown in FIG. 3 is one in which a wound electrode body 21 is accommodated mainly in a sheet-like exterior member 25. 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 22 is attached to the positive electrode, and the negative electrode lead 23 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 25 to the outside, for example. The positive electrode lead 22 is formed of a conductive material such as aluminum, and the negative electrode lead 23 is formed of a conductive material such as nickel or copper.

  The exterior member 25 is, for example, a laminate film in which a fusion layer, a metal layer, and a surface protective layer are laminated in this order. The laminate film is formed by fusing two films so that the fusion layer faces the electrode body 21. The outer peripheral edge portions in the adhesion layer are bonded together with an adhesive or the like. The fused part is, for example, a film such as polyethylene or polypropylene, and the metal part is aluminum foil or the like. The protective layer is, for example, nylon.

  An adhesion film 24 is inserted between the exterior member 25 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 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 M ₁ O ₂ or Li _y M ₂ PO ₄ . In the formula, M ₁ and M ₂ represent at least one transition metal element. 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 ), lithium nickel composite oxide (Li _x NiO ₂ ), and phosphoric acid having lithium and a transition metal element. Examples of the compound include a lithium iron phosphate compound (LiFePO ₄ ) and a lithium iron manganese phosphate compound (LiFe _1-u Mn _u PO ₄ (u <1)). 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 negative electrode 10 for lithium ion secondary battery in FIG. 1 described above. For example, the negative electrode active material layer 12 containing the negative electrode active material of the present invention is provided on both surfaces of the current collector 11. Yes. This negative electrode preferably has a negative electrode charge capacity larger than the electric capacity (charge capacity as a battery) obtained from the positive electrode active material agent. 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 for 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 do not face each other, there is almost no influence of charge / discharge. Therefore, the state of the negative electrode active material layer is maintained as it is 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 nonaqueous solvent include the following materials. Ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, 1,2-dimethoxyethane, or tetrahydrofuran.

  Among these, at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate is desirable. 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.

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

  The positive electrode and the negative electrode are manufactured by the same manufacturing procedure as described above. In this case, each active material layer is 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 22 is attached to the positive electrode current collector and the negative electrode lead 23 is attached to the negative electrode current collector by ultrasonic welding or the like. Subsequently, a positive electrode and a negative electrode are laminated or wound via a separator to form a wound electrode body, and a protective tape is adhered to the outermost periphery (see FIG. 3). Next, the wound body is molded so as to have a flat shape. Subsequently, after the wound electrode body is sandwiched between the folded film-shaped exterior member 25, the insulating portions of the exterior member are bonded to each other by a heat fusion method, and the wound electrode body is released in only one direction. Enclose. The adhesion film 24 is inserted between the positive electrode lead 22 and the negative electrode lead 23 and the exterior member 25. 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.

  The laminated film type secondary battery 20 can be manufactured as described above.

  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 secondary battery 20 shown in FIG. 3 was produced by the following procedure.

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

  Next, a negative electrode was produced. In order to produce a negative electrode active material, first, a raw material in which metallic silicon and silicon dioxide were mixed was placed in a reaction furnace, deposited under a vacuum of 10 Pa, sufficiently cooled, and then the deposit was taken out and pulverized with a ball mill. After adjusting the particle size, a carbon film was obtained by performing thermal CVD. At this time, a rotary kiln type reactor was used for thermal CVD, methane gas as the carbon source, the temperature in the furnace was 1000 ° C., the pressure was 1 atm, and the CVD time was 6 hours.

The prepared powder was subjected to bulk modification using an electrochemical method in a 1: 1 mixed solvent of propylene carbonate and ethylene carbonate (containing 1.3 mol / kg of lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt). It was. The obtained material was dried under a carbon dioxide atmosphere.

Subsequently, a part of the powder obtained as described above was taken out, placed in a Teflon (registered trademark) beaker, further ion-exchanged water and ethanol were added, and the mixture was thoroughly stirred with a Teflon (registered trademark) stir bar. . Thereafter, hydrofluoric acid was added and stirred, nitric acid was added, ion-exchanged water was added as appropriate, nitric acid was further added, and the mixture was allowed to stand for 3 hours. Then, the isolated carbon film was filtered by filtering the obtained black solution. Subsequently, the isolated carbon film was washed with water, further washed with ethanol, and then vacuum-dried at 200 ° C. for 10 hours. The specific surface area by the multipoint BET method of the carbon coating thus isolated and the compression resistivity when compressed to a density of 1.0 g / cm ³ were measured.

In result, the compression resistance when the specific surface area by a multipoint BET method of the isolated carbon film compressed to a density of 180m ² /g,1.0g/cm ³ is 8.0 × ^{10 -3} Ω · cm there were.

  Subsequently, the negative active material, the precursor of the negative electrode binder (polyamic acid), the conductive additive 1 (flaky graphite), and the conductive additive 2 (acetylene black) are in a dry mass ratio of 80: 8: 10: 2. Then, the mixture was diluted with water to obtain a paste-like negative electrode mixture slurry. In this case, water was used as a solvent for polyacrylic acid. Subsequently, the negative electrode mixture slurry was applied to both surfaces of the negative electrode current collector with a coating apparatus and then dried. As this negative electrode current collector, an electrolytic copper foil (thickness = 15 μm) was used. Finally, it was dried in a vacuum atmosphere at 90 ° C. for 1 hour.

Next, after mixing a solvent (4-fluoro-1,3-dioxolan-2-one (FEC), ethylene carbonate (EC) and dimethyl carbonate (DMC)), an electrolyte salt (lithium hexafluorophosphate: LiPF) ₆ ) was dissolved to prepare an electrolytic solution. In this case, the composition of the solvent was FEC: EC: DMC = 10: 20: 70 by volume ratio, and the content of the electrolyte salt was 1.2 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 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 PET protective tape. As the separator, a laminated film of 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 except for one side were heat-sealed, and the electrode body was housed inside. As the exterior member, an aluminum laminated film in which a nylon film, an aluminum foil, and a polypropylene film were laminated was used. Subsequently, the prepared electrolyte was injected from the opening, impregnated in a vacuum atmosphere, and then heat-sealed and sealed.

(Example 1-2 to Example 1-5, Comparative Example 1-1 to Comparative Example 1-2)
A secondary battery was fabricated in the same manner as in Example 1-1 except that the amount of oxygen in the silicon compound represented by SiOx was adjusted.

The silicon-based active material particles in Example 1-1 to Example 1-5 and Comparative Example 1-1 to Comparative Example 1-2 all had the following physical properties. The peak area ratios of ²⁹ Si-MAS-NMR of the silicon compound contained in the silicon-based active material particles were A / B = 0.6 and (A + B) /C=0.32. Also, the median diameter _{D 50} of the silicon-based active material particle was 5.1 .mu.m. The full width at half maximum (2θ) of the diffraction peak attributable to the Si (111) crystal plane obtained by X-ray diffraction is 1.85 °, and the crystallite size attributable to the crystal plane Si (111) is 4.62 nm. It was.

In Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-2, the carbon coating content was 5%, the average thickness of the carbon coating was 110 nm, and the average coating of the carbon coating. The rate was 90%, and the true density of the carbon coating was 1.6 g / cm ³ . Further, the intensity ratio of Raman spectrum was I ₁₃₃₀ / I ₁₅₈₀ = 1.1. Further, the TOF-SIMS, y = 2,3,4, fragment _C y _{H z} compounds which are z = 2y-3,2y-1,2y + 1 is detected. Further, the intensity ratio D / E (Int (C ₄ H ₉ / C ₃ H ₅ )) of the detection intensity D of C ₄ H ₉ and the detection intensity E of C ₃ H ₅ by TOF-SIMS was 0.8. .

The compression resistance when compressed to a density of specific surface area by the multi-point BET method of the isolated carbon film 180m ² /g,1.0g/cm ³ is 8.0 × encountered ^{10 -3 Ω} · cm It was. Also, the adsorption and desorption isotherms of the isolated carbon coating had type II characteristics in the IUPAC classification. In addition, the compression density when the isolated carbon coating was charged in a measurement container so that the mass per unit area was 0.15 g / cm ² and compressed by pressing at 50 MPa was 1.1 g / cm ³ . .

  When the cycle characteristics (maintenance rate%) and the initial charge / discharge characteristics (initial efficiency%) of the secondary batteries of Example 1-1 to Example 1-5 and Comparative Example 1-1 to Comparative Example 1-2 were examined, The results shown in Table 1 were obtained.

The cycle characteristics were examined as follows. First, in order to stabilize the battery, charge / discharge was performed for 2 cycles in an atmosphere at 25 ° C., and the discharge capacity at the second cycle was measured. Subsequently, charge and discharge were performed until the total number of cycles reached 100, and the discharge capacity was measured each time. Finally, the discharge capacity at the 100th cycle was divided by the discharge capacity at the 2nd cycle (because it is expressed in% × 100), and the capacity maintenance rate was calculated. As cycling conditions, a constant current density until reaching 4.3V, and charged at 2.5 mA / cm ^2, the current density at 4.3V constant voltage at the stage of reaching the voltage charged to reach 0.25 mA / cm ² . During discharging, discharging was performed at a constant current density of ^2.5 mA / cm ² until the voltage reached 3.0V.

When examining the initial charge / discharge characteristics, the initial efficiency (%) = (initial discharge capacity / initial charge capacity) × 100 was calculated. The ambient temperature was the same as when the cycle characteristics were examined. The charge / discharge conditions were 0.2 times the cycle characteristics. That is, a constant current density until reaching 4.3V, and charged at 0.5 mA / cm ^2, at 4.3V constant voltage at the stage where the voltage reaches 4.3V until the current density reached 0.05 mA / cm ² The battery was charged and discharged at a constant current density of 0.5 mA / cm ² until the voltage reached 3.0V.

  The maintenance ratios and initial efficiency shown in Tables 1 to 9 below do not contain a carbon-based active material such as natural graphite (for example, a median diameter of 20 μm), and only a silicon compound having a carbon coating is used as the negative electrode active material. The maintenance rate and initial efficiency when used, that is, the maintenance rate and initial efficiency of the silicon compound are shown. As a result, it was possible to measure changes in retention rate and initial efficiency that depended solely on changes in silicon compounds (changes in oxygen content, crystallinity, median diameter, etc.) or changes in carbon coating (contents, composition, etc.). .

  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 decreased and both the maintenance rate and the initial efficiency decreased, and measurement was impossible.

(Example 2-1 to Example 2-3, Comparative Example 2-1 to Comparative Example 2-3)
The state of the carbon film coated on the surface of the silicon compound was changed, and the compression resistivity and the mass per unit area when the carbon film was isolated and measured to a density of 1.0 g / cm ³ were 0.15 g / A secondary battery was manufactured in the same manner as in Example 1-3, except that the compression density was changed after being charged into a measurement container so as to be cm ² and then pressurized and compressed at 50 MPa. In addition, the compression resistivity and compression density of the carbon coating when measured by isolating the carbon coating from the silicon compound are the CVD temperature, time, degree of stirring of the powder material (silicon compound powder) during CVD, and the CVD gas flow rate. Was done by adjusting.

  When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Examples 2-1 to 2-3 and Comparative examples 2-1 to 2-3 were examined, the results shown in Table 2 were obtained.

As shown in Table 2, when the compression resistivity when the density of the carbon coating is 1.0 g / cm ³ is 1.0 × 10 ⁻³ Ω · cm or more and 1.0 Ω · cm or less, at the time of charge / discharge Therefore, the deposition of Li or the like is unlikely to occur, and the conductivity of the negative electrode tends to be more uniform, so that the maintenance ratio and the initial efficiency are improved. Further, the compressed density of the carbon film is the case is less than 1.0 g / cm ³ or more 1.8 g / cm ^3, the binder is properly adsorbed at the surface silicon compound, thereby improving initial efficiency and capacity retention rate .

(Example 3-1 to Example 3-8, Comparative Example 3-1 to Comparative Example 3-2)
Content ratio of carbon coating to silicon-based active material particles, average thickness of carbon coating on silicon compound surface, average coverage of carbon coating on silicon compound surface, average true density on silicon compound surface, adsorption / desorption of isolated carbon coating A secondary battery was manufactured in the same manner as in Example 1-3 except that the IUPAC classification of the isotherm and the specific surface area of the isolated carbon film were changed. Content of carbon film, average thickness, average coverage, average true density, IUPAC classification of adsorption / desorption isotherm of isolated carbon film, change in specific surface area of isolated carbon film depends on CVD temperature, time and CVD It can be controlled by adjusting the degree of stirring of the silicon compound powder.

  When the cycle characteristics and initial charge / discharge characteristics of the secondary batteries of Example 3-1 to Example 3-8 and Comparative Example 3-1 to Comparative Example 3-2 were examined, the results shown in Table 6 were obtained. .

As can be seen from Table 3, in Example 3-1 to Example 3-8 in which the specific surface area of the isolated carbon coating is 5 m ² / g or more and 1000 m ² / g or less, Comparative Example 3-1 and Comparative Example Battery characteristics better than 3-2 are obtained. This is because when the specific surface area of the isolated carbon film is less than 5 m ² / g, the impregnating property of the electrolytic solution is lowered, and when the specific surface area of the isolated carbon film exceeds 1000 m ² / g, the binder is used. This is because, due to excessive adsorption, the binding property is lowered and the battery characteristics are deteriorated.

In the examples, the carbon film content is 0.1% to 25%, the carbon film thickness is 5 nm to 500 nm, the average coverage is 30%, and the true density of the carbon film is 1.2 g / cm ^3. Examples 1-3 and Examples 3-3 to ^{3 in which} 1.9 g / cm ³ or less of the above and the IUPAC adsorption / desorption isotherm classification of the isolated carbon coating satisfy all the conditions of type II or type III The best battery characteristic was obtained for -6. On the other hand, when one or more of these conditions were not satisfied, the battery characteristics were slightly worse than those of Examples 1-3 and Examples 3-3 to 3-6.

(Example 4-1 to Example 4-6)
A secondary battery was manufactured in the same manner as in Example 1-3, except that the ratio of Si component to SiO ₂ component in the silicon compound (ratio of Si to silica) and the degree of disproportionation were changed. The ratio of the Si component to the SiO ₂ component was changed in Examples 4-1 to 4-6 by changing the amounts of metal silicon and silica charged at the time of creating SiO. Further, in the silicon compound (SiO _x ), as the chemical shift value obtained from the ²⁹ Si-MAS-NMR spectrum, the peak area A of the amorphous silicon (a-Si) region given by −20 to −74 ppm and −75 to − The ratio A / B with the peak area B of the crystalline silicon (c-Si) region given at 94 ppm was adjusted by controlling the disproportionation degree by heat treatment.

  When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Example 4-1 to Example 4-6 were examined, the results shown in Table 4 were obtained.

As can be seen from Table 4, when 5.0 ≧ A / B ≧ 0.01, 6.0 ≧ (A + B) /C≧0.02 is satisfied (Examples 1-3, 4-3, 4- 4) Both maintenance rate and initial efficiency were good characteristics. When the a-Si component is increased, the initial efficiency is lowered, but the maintenance ratio is improved. This is because the balance is maintained in the range of 5.0 ≧ A / B ≧ 0.01. Further, if the ratio (A + B) / C of the Si component to the SiO ₂ component is 6 or less, expansion due to Li insertion can be suppressed to be small, so that the maintenance ratio is improved. Further, if (A + B) / C is 0.02 or more, the conductivity is improved, and both the maintenance ratio and the initial efficiency are improved. In the case where only 5.0 ≧ A / B ≧ 0.01 is satisfied (Examples 4-1 and 4-6), the maintenance ratio is compared to the case where both of the above ranges of A / B and (A + B) / C are satisfied. Decreases slightly. In the case where only 6.0 ≧ (A + B) /C≧0.02 is satisfied (Examples 2-2 and 2-5), compared to the case where both the above ranges of A / B and (A + B) / C are satisfied, The maintenance rate is slightly reduced.

(Example 5-1 to Example 5-5)
A secondary battery was manufactured in the same manner as in Example 1-3 except that the crystallinity of the silicon compound was changed. The change in crystallinity can be controlled by heat treatment in a non-atmospheric atmosphere. In Example 5-1, the crystallite size is calculated to be 1.542, but it is a result of fitting using analysis software, and a peak is not substantially obtained. Therefore, it can be said that the silicon compound of Example 5-1 is substantially amorphous.

  When the cycle characteristics and initial charge / discharge characteristics of the secondary batteries of Examples 5-1 to 5-5 were examined, the results shown in Table 5 were obtained.

  As can be seen from Table 5, when the crystallinity of the silicon compound was changed, the capacity retention ratio and the initial efficiency changed according to the crystallinity. In particular, a high retention rate is possible with a low crystalline material having a crystallite size of 7.5 nm or less due to the Si (111) plane. In particular, the best maintenance ratio can be obtained in the amorphous region. Further, the initial efficiency was slightly lowered as the crystallinity was lowered, but an initial efficiency of a level not causing a problem was obtained.

(Examples 6-1 to 6-3)
The state of the carbon coating on the surface of the silicon compound is varied, except that in the Raman spectrum analysis of carbon film, changing the intensity ratio _I 1330 _{/ I 1580} of the scattering peak of 1330 cm ^-1 and 1580 cm ^-1, Example 1 In the same manner as in Example 3, a secondary battery was manufactured. The scattering peak intensity ratio I ₁₃₃₀ / I ₁₅₈₀ was changed by changing the temperature and gas pressure during CVD.

  When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Example 6-1 to Example 6-3 were examined, the results shown in Table 6 were obtained.

As shown in Table 6, when the intensity ratio I ₁₃₃₀ / I ₁₅₈₀ of the scattering peak in the Raman spectrum is less than 2.0, the surface has few carbon components having a messy bonding mode derived from I ₁₃₃₀ , and the electron Since the conductivity is high, the maintenance rate and initial efficiency are improved. In addition, when I ₁₃₃₀ / I ₁₅₈₀ is larger than 0.7, there are few carbon components such as graphite derived from I ₁₅₈₀ on the surface, and ion conductivity and followability to expansion associated with insertion of Li in the silicon compound of the carbon coating. And the capacity maintenance rate is improved.

(Example 7-1 to Example 7-5, Comparative Example 7-1)
A secondary battery was produced in the same manner as in Example 1-3 except that the state of the carbon coating on the silicon compound surface was adjusted. That is, in Example 7-1 to Example 7-5, the C _y H _z fragment detected from the carbon film by TOF-SIMS, the detection intensity D of C ₄ H _{9 and} the detection of C ₃ H ₅ in TOF-SIMS The intensity ratio D / E of the intensity E was changed. In this case, the gas type, the CVD temperature, and the post-CVD temperature used for CVD of the silicon compound are adjusted. In Comparative Example 7-1, the carbon coating was not applied.

  When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Examples 7-1 to 7-5 and Comparative example 7-1 were examined, the results shown in Table 7 were obtained.

As shown in Table 7, when the fragment of the C _y H _z compound was detected and when the relationship of 2.5 ≧ D / E ≧ 0.3 was satisfied, the battery characteristics were improved. In addition, as in Comparative Example 7-1, when there is no carbon coating, the electrical conductivity at the negative electrode is deteriorated, so that the maintenance ratio and the initial efficiency are deteriorated. Moreover, when the fragment of the C _y H _z compound satisfying the range of 6 ≧ y ≧ 2, 2y + 2 ≧ z ≧ 2y−2 was detected, the battery characteristics were improved. In particular, when the value of y is small, that is, when only fragments of C _y H _z compounds with y = 2, 3, and 4 are detected, the battery characteristics are further improved.

(Examples 8-1 to 8-5)
A secondary battery was manufactured in the same manner as in Example 1-3 except that the median diameter of the silicon compound was adjusted. The median diameter was adjusted by changing the grinding time and classification conditions in the silicon compound production process. When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Examples 8-1 to 8-5 were examined, the results shown in Table 8 were obtained.

  As can be seen from Table 8, when the median diameter of the silicon compound was changed, the maintenance ratio and the initial efficiency changed accordingly. As shown in Examples 8-2 to 8-4, the capacity retention rate was higher when the median diameter of the silicon compound particles was 0.5 μm to 20 μm. In particular, when the median diameter was 0.5 μm or more and 12 μm or less, the maintenance ratio was improved.

(Examples 9-1 to 9-2)
A secondary battery was produced in the same manner as in Example 1-3, except that at least a part of the silicon-based active material particles contained Li by doping the silicon compound with Li. In Example 9-1, Li doping was performed using a thermal doping method, and in Example 9-2 using an electrochemical method.

  When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Examples 9-1 to 9-2 were examined, the results shown in Table 9 were obtained.

  As can be seen from Table 9, the retention rate was improved by adding Li to the silicon-based active material particles. In addition, as in Example 9-2, when Li was doped into silicon-based active material particles by an electrochemical modification method, the initial efficiency was improved. In addition, since the initial efficiency of the negative electrode in the case of a nonaqueous electrolyte secondary battery is increased, a deviation in the balance between the positive electrode and the negative electrode during the cycle test is suppressed, and the maintenance ratio is improved.

(Example 10-1 to Example 10-6)
In Example 10-1 to Example 10-6, a secondary battery was manufactured basically in the same manner as in Example 1-3. However, as a negative electrode active material, a carbon-based active material (artificial graphite and natural graphite was used). Graphite is mixed at a mass ratio of 1: 1), and the ratio of the content of the silicon compound and the carbon-based active material in the negative electrode (the ratio of the silicon compound (SiO material) to the entire active material) is changed. The binder was also changed according to the ratio. In Examples 10-1 to 10-3, a mixture of styrene butadiene rubber (indicated as SBR in Table 10) and CMC was used as the binder. In Examples 10-4 to 10-6, polyimide (indicated as PI in Table 10) was used as the binder.

(Comparative Example 10-1)
Other than using the negative electrode active material of the present invention, using only the carbon-based active material used in Example 10-1 to Example 10-6 as the negative electrode active material, and using lithium nickel cobalt aluminum composite oxide as the positive electrode material Produced a secondary battery in the same manner as in Example 1-3.

The cycle characteristics and initial charge / discharge characteristics of the secondary batteries of Examples 10-1 to 10-6 and Comparative Example 10-1 were examined. Moreover, the power capacity density (mAh / cm < ³ >) of the secondary battery of Examples 10-1 to 10-6 and Comparative Example 10-1 was measured, and the power capacity density of the secondary battery of Comparative Example 10-1 was used as a reference. The relative power capacity density was calculated in each case. These results are shown in Table 10.

  As can be seen from Table 10, when the ratio of the silicon-based active material particles is increased, the capacity of the negative electrode is increased, but the initial efficiency and the maintenance ratio are decreased. Moreover, the relative power capacity density shown in Table 10 is a combination of a silicon-based active material particle ratio of 0 and an NCA (lithium nickel cobalt aluminum composite oxide) positive electrode material as described above, and a discharge cutoff voltage in the battery. Is based on the power capacity density (Comparative Example 10-1). If the ratio of the silicon-based active material particles is reduced, the initial efficiency and the maintenance rate are improved, but the power capacity density is reduced. In particular, when only the carbon-based active material is used as the negative electrode active material as in Comparative Example 10-1, a lithium ion secondary battery having a high power capacity density cannot be obtained. In particular, when the ratio of the silicon-based active material particles is 5% by mass or more, a sufficient improvement in power capacity density is observed.

(Example 11-1 to Example 11-8)
The average particle diameter G of carbon-based active material in the negative electrode active material layer (median diameter D ₅₀ of carbon active material particles) and the average particle diameter F of silicon-based active material (median diameter D ₅₀ of silicon-based active material particles) are changed. Thus, a secondary battery was manufactured in the same manner as in Example 10-2 except that these ratios G / F were changed.

  When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Examples 11-1 to 11-8 were examined, the results shown in Table 11 were obtained.

  As can be seen from Table 11, it is desirable that the carbon-based active material particles in the negative electrode active material layer have a size equal to or greater than that of the silicon-based active material particles, that is, G / F ≧ 0.5. . When the silicon compound that expands and contracts is equal to or smaller than that of the carbon-based negative electrode material, the composite material layer can be prevented from being broken. When the carbon-based negative electrode material is larger than the silicon compound, the negative electrode volume density and initial efficiency during charging are improved, and the battery energy density is improved. In particular, by satisfying the range of 25 ≧ G / F ≧ 0.5, the initial efficiency and the maintenance rate are further improved.

(Example 12-1 to Example 12-4)
A secondary battery was manufactured in the same manner as in Example 10-2 except that the type of the carbon-based active material in the negative electrode was changed.

  When the cycle characteristics and initial charge / discharge characteristics of the secondary batteries of Examples 12-1 to 12-4 were examined, the results shown in Table 12 were obtained.

  As can be seen from Table 12, it is desirable that the carbon-based active material particles in the negative electrode active material layer include graphite-based materials such as artificial graphite and natural graphite. This is because the initial efficiency and maintenance rate of the graphite-based carbon material are high, and therefore, when the negative electrode is produced by mixing with the silicon-based active material particles, the battery characteristics are relatively improved.

(Example 13-1)
A laminate film type secondary battery as shown in FIG. 3 was produced by the following method.

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 mixed with metallic silicon and silicon dioxide was introduced into a reaction furnace, and vaporized in a 10 Pa vacuum atmosphere was deposited on an adsorption plate, cooled sufficiently, and then the deposit was taken out and pulverized with a ball mill. . The x value of SiO _x of the silicon compound particles thus obtained was 1.0. Subsequently, the particle size of the silicon compound particles was adjusted by classification. Then, the carbon film was coat | covered on the surface of the silicon compound particle | grain by performing pyrolysis CVD. At this time, a rotary kiln type reactor was used for thermal decomposition CVD, methane gas as a carbon source, the temperature in the furnace was 1000 ° C., the pressure was 1 atm, and the CVD time was 6 hours.

Subsequently, lithium was inserted into the silicon compound particles and modified by a redox method. First, the silicon compound particles were immersed in a solution (solution A ₁ ) in which lithium pieces and biphenyl, which is a linear polyphenylene compound, were dissolved in tetrahydrofuran (hereinafter also referred to as THF). The solution A ₁ was prepared by adding after the biphenyl in THF solvent dissolved at a concentration of 1 mol / L, the lithium pieces 10 mass% of the mass fraction with respect to a mixed solution of the THF and biphenyl. The temperature of the solution when dipping the silicon compound particles was 20 ° C., and the dipping time was 10 hours. Thereafter, silicon compound particles were collected by filtration. Through the above treatment, lithium was inserted into the silicon compound particles.

  Next, the silicon compound particles after lithium insertion were immersed in a solution (solution B) in which naphthalene was dissolved in THF. Solution B was prepared by dissolving naphthalene in a THF solvent at a concentration of 2 mol / L. The temperature of the solution when dipping the silicon compound particles was 20 ° C., and the dipping time was 20 hours. Thereafter, silicon compound particles were collected by filtration.

Next, the silicon compound particles after being brought into contact with the solution B were immersed in a solution (solution C) in which p-benzoquinone was dissolved in THF at a concentration of 1 mol / L. The immersion time was 2 hours. Thereafter, silicon compound particles were collected by filtration. Through the above treatment, Li ₂ SiO ₃ and Li ₄ SiO ₄ were generated inside the silicon compound particles.

  Next, the silicon compound particles were washed, and the silicon compound particles after the washing treatment were dried under reduced pressure. In this way, negative electrode active material particles were obtained.

Next, the specific surface area by the multipoint BET method of the isolated carbon film and the compression resistivity when compressed to a density of 1.0 g / cm ³ were measured by the same method as in Example 1-1.

In result, the compression resistance when the specific surface area by a multipoint BET method of the isolated carbon film compressed to a density of 180m ² /g,1.0g/cm ³ is 8.0 × ^{10 -3} Ω · cm there were.

  Next, the negative electrode active material particles and the carbon-based active material were blended at a mass ratio of 1: 9 to prepare a mixed negative electrode active material. Here, as the carbon-based active material, a mixture of natural graphite 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 by volume 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 PET protective tape. As the separator, a laminated film (thickness: 12 μm) sandwiched between a film mainly composed of porous polyethylene and a film mainly composed of porous polypropylene was used. Subsequently, after sandwiching the electrode body between the exterior members, the outer peripheral edges excluding one side were heat-sealed, and the electrode body was housed inside. As the exterior member, a nylon film, an aluminum foil, and an aluminum laminate film in which a polypropylene film was laminated were used. Subsequently, an electrolytic solution prepared from the opening was injected, impregnated in a vacuum atmosphere, heat-sealed, and sealed.

  The cycle characteristics and initial charge / discharge characteristics of the secondary battery produced as described above were evaluated by the same method as in Example 1-1.

(Example 13-2 to Example 13-5)
Secondary as in Example 13-1, except that the IUPAC classification of the adsorption / desorption isotherm of the isolated carbon coating and the compression density (at 50 MPa pressurization) of the isolated carbon coating were changed as shown in Table 13. The battery was manufactured, and cycle characteristics and initial charge / discharge characteristics were evaluated. The IUPAC classification of the adsorption and desorption isotherm of the isolated carbon film, the change in the compression density (at 50 MPa pressurization) of the isolated carbon film can be changed by adjusting the CVD temperature, time, and the degree of stirring of the silicon compound particles during the CVD. It can be controlled.

(Comparative Example 13-1 to Comparative Example 13-4)
Specific surface area of isolated carbon film, compression resistivity when compressed to a density of 1.0 g / cm ³ of isolated carbon film, average true density of carbon film on silicon compound surface, absorption of isolated carbon film A secondary battery was manufactured in the same manner as in Example 13-1, except that the IUPAC classification of the desorption isotherm was changed as shown in Table 13, and cycle characteristics and initial charge / discharge characteristics were evaluated. These parameters can also be controlled by adjusting the CVD temperature, time, and the degree of stirring of the silicon compound particles during CVD.

  At this time, the negative electrode active material particles of Examples 13-1 to 13-5 and Comparative Examples 13-1 to 13-4 had the following properties. The median diameter of the negative electrode active material particles was 4 μm. 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 2.257 °, and a crystallite size due to the Si (111) crystal plane. Was 3.77 nm.

In the negative electrode active material particles, the maximum peak intensity value H of the crystalline silicon region and the Li silicate region given by the chemical shift value of −75 to −94 ppm obtained from the ²⁹ Si-MAS-NMR spectrum, and the chemical shift value of − The relationship with the peak intensity value I in the silica region given at 95 to -150 ppm was H> I.

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 Examples and Comparative Examples, the peak was obtained in charge and discharge within 30 times, and the peak was obtained in all charge and discharge from the charge and discharge in which the peak first appeared until the 30th charge and discharge. .

  Table 13 shows the evaluation results of Examples 13-1 to 13-5 and Comparative Examples 13-1 to 13-4.

As can be seen from Table 13, in Examples 13-1 to 13-5 where the specific surface area of the isolated carbon coating is 5 m ² / g or more and 1000 m ² / g or less, the specific surface area is outside this range. Battery characteristics better than those of Comparative Example 13-3 and Comparative Example 13-4 are obtained. In addition, Example 13-1 to Example 13-5 in which the compressive resistivity when the density of the carbon film is 1.0 g / cm ³ is 1.0 × 10 ⁻³ Ω · cm or more and 1.0 Ω · cm or less. Thus, better battery characteristics can be obtained than Comparative Examples 13-3 and 13-4 whose compression resistivity is outside this range.

(Example 14-1)
Same as Example 13-1, except that the relationship between the maximum peak intensity value H of the crystalline silicon region and the Li silicate region and the peak intensity value I derived from the silicate region of the negative electrode active material particles was H <I Secondary batteries were manufactured under the conditions, and 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 H of a peak derived from the Li 2 SiO _3.

  As can be seen from Table 14, the battery characteristics improved when the peak intensity relationship was H> I.

(Example 15-1)
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 fabricated under the same conditions as in Example 13-1, 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.

(Example 16-1)
A secondary battery was produced under the same conditions as in Example 13-1, except that a copper foil containing no carbon and sulfur was used as the negative electrode current collector, and the cycle characteristics and initial efficiency were evaluated.

  When the current collector of the negative electrode contains 100 ppm by mass or less of carbon and sulfur, the strength of the current collector is improved. Therefore, when using a silicon-based negative electrode active material having a large expansion and contraction during charge / discharge of the secondary battery, it is possible to suppress the deformation and distortion of the current collector, and the battery characteristics, particularly as in Example 13-1. Cycle characteristics are improved.

(Comparative Example 17-1)
A secondary battery was produced in the same manner as in Example 13-1, except that lithium was not inserted into the silicon compound particles, and cycle characteristics and initial charge / discharge characteristics were evaluated.

  As can be seen from Table 17, Example 13-1, which was modified by inserting lithium into the silicon active material particles, had both initial efficiency and maintenance rate higher than those of Example 17-1, which was not modified. Improved.

  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 ... lithium secondary battery (laminated film type), 21 ... electrode body,
22 ... Positive electrode lead (positive electrode aluminum lead),
23 ... negative electrode lead (negative electrode nickel lead), 24 ... adhesion film,
25. Exterior member.

Claims (25)

A negative electrode active material for a non-aqueous electrolyte secondary battery having negative electrode active material particles, the negative electrode active material particles containing a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6),
The negative electrode active material particles have a carbon coating on at least a part of the surface,
The carbon coating has a specific surface area of 5 m ² / g or more and 1000 m ² / g or less by a multi-point BET method measured by isolating the carbon coating from the negative electrode active material particles, and
The carbon film has a compression resistivity of 1.0 × 10 ⁻³ Ω · cm or more when the carbon film is compressed to a density of 1.0 g / cm ^{3 when} the carbon film is isolated from the negative electrode active material particles. 0Ω · cm Ri der below,
True density of 1.2 g / cm ³ or more 1.9 g / cm ³ negative active material for a nonaqueous electrolyte secondary battery characterized by the following ranges der Rukoto of the carbon film. The carbon coating is prepared by isolating the carbon coating from the negative electrode active material particles, and charging the isolated carbon coating into a measurement container so that the mass per unit area is 0.15 g / cm ^2. 2. The negative electrode active material for a nonaqueous electrolyte secondary battery according to claim 1, wherein a compression density when compressed by pressing is 1.0 g / cm ³ or more and 1.8 g / cm ³ or less. The content of the carbon coating, the negative active for a non-aqueous electrolyte secondary battery negative electrode according to claim 1 or claim 2 with respect to material particles, characterized in that 25 wt% or less than 0.1 wt% Active material. The carbon coating has a characteristic of type II or type III in the IUPAC classification of the adsorption / desorption isotherm in an adsorption / desorption isotherm by nitrogen gas measured by isolating the carbon coating from the negative electrode active material particles. The negative electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3 . The carbon coating is isolated by reacting the negative electrode active material particles with a solution containing hydrofluoric acid and nitric acid to remove the silicon compound from the negative electrode active material particles. The negative electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4 . Wherein the carbon coating is in the Raman spectrum obtained by Raman spectrum analysis, it has a scattering peak at 1330 cm ^-1 and 1580 cm ^-1, a ratio of the intensity of their scattering peak _I 1330 _{/ I 1580} is _{0.7 <I 1330} / I ₁₅₈₀ negative active material for a nonaqueous electrolyte secondary battery as claimed in any one of claims 5, characterized in that satisfy _<2.0. In the carbon coating, a fragment of the C _y H _z compound is detected by TOF-SIMS, and the fragment of the C _y H _z compound satisfies the range of 6 ≧ y ≧ 2, 2y + 2 ≧ z ≧ 2y−2. 7. The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the substance is detected at least in part. The fragment of the C _y H _z compound detected by the carbon film has a detection intensity D of C ₄ H _{9 and} a detection intensity E of C ₃ H ₅ of 2.5 ≧ D / E ≧ 0.3 in TOF-SIMS. The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 7 , wherein the negative electrode active material satisfies the following relationship. Negative active material for a non-aqueous electrolyte secondary battery as claimed in any one of claims 8, wherein the average thickness of the carbon coating is of 5nm or 5000nm or less. Negative active material for a non-aqueous electrolyte secondary battery as claimed in any one of claims 9, wherein the average coverage of the carbon film is not less than 30%. Wherein the carbon coating is either negative active for a non-aqueous electrolyte secondary battery according to one of claims 10 to compounds containing carbon from claim 1, characterized in that is obtained by thermal decomposition material. In the silicon compound, as the chemical shift value obtained from the ²⁹ Si-MAS-NMR spectrum, the peak area A of the amorphous silicon region given by −20 to −74 ppm and the crystalline silicon region given by −75 to −94 ppm and Li The non-water according to any one of claims 1 to 11 , wherein the peak area B of the silicate region and the peak area C of the silica region given to -95 to -150 ppm satisfy the formula (1). Negative electrode active material for electrolyte secondary battery.
Formula (1): 5.0 ≧ A / B ≧ 0.01, 6.0 ≧ (A + B) /C≧0.02 The negative electrode active material particles have a full width at half maximum (2θ) of a diffraction peak attributed to the Si (111) crystal plane obtained by X-ray diffraction of 1.2 ° or more and a crystallite size attributed to the crystal plane. negative active material for a non-aqueous electrolyte secondary battery as claimed in any one of claims 12, wherein the 7.5nm or less. The negative active material for a nonaqueous electrolyte secondary battery as claimed in any one of claims 13, wherein the median diameter of the negative electrode active material particles is 0.5μm or more 20μm or less. The negative electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 14 , wherein Li is contained in at least a part of the negative electrode active material particles. The negative electrode active material for a nonaqueous electrolyte secondary battery according to claim 15 , wherein at least a part of Li ₂ SiO ₃ and Li ₄ SiO ₄ is contained in at least a part of the negative electrode active material particles. . In the negative electrode active material particles, the maximum peak intensity value H of the crystalline silicon region and Li silicate region given by -75 to -94 ppm as the chemical shift value obtained from the ²⁹ Si-MAS-NMR spectrum, and the chemical shift value -95-150 ppm peak intensity value I is given silica region is, H> non-aqueous electrolyte secondary battery negative electrode according to claim 16 claims 1 to be characterized satisfies the relationship of I Active material. A test cell comprising a negative electrode containing a mixture of the negative electrode active material for a nonaqueous electrolyte secondary battery and a carbon-based active material and counter lithium is prepared, and in the test cell, the negative electrode active for the nonaqueous electrolyte secondary battery is prepared. Charging / discharging consisting of charging for flowing current to insert lithium into the substance and discharging for flowing current to desorb lithium from the negative electrode active material for non-aqueous electrolyte secondary battery was performed 30 times. When a graph showing the relationship between the differential value dQ / dV obtained by differentiating the discharge capacity Q with respect to the potential V of the negative electrode with respect to the counter electrode lithium and the potential V is drawn, the Xth and subsequent times (1 ≦ X ≦ 30 The non-reactive electrode according to any one of claims 1 to 17 , wherein the potential V of the negative electrode has a peak in the range of 0.40V to 0.55V during the discharge of (1). For water electrolyte secondary battery Electrode active material. The negative electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 18 , further comprising carbon-based active material particles. The nonaqueous electrolyte secondary according to claim 19 , wherein a ratio of the mass of the negative electrode active material particles to the total mass of the negative electrode active material particles and the carbon-based active material particles is 5% by mass or more. Negative electrode active material for batteries. The average particle diameter F of the negative electrode active material particles, to an average particle diameter G of the carbonaceous active material particles, according to claim 19 or claim characterized by satisfying the relationship of 25 ≧ G / F ≧ 0.5 20. A negative electrode active material for a nonaqueous electrolyte secondary battery according to 20 . The negative electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 19 to 21 , wherein the carbon-based active material particles are a graphite material. A negative electrode active material layer containing the negative electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 22 ,
A negative electrode current collector,
The negative electrode active material layer is formed on the negative electrode current collector,
The negative electrode current collector includes carbon and sulfur, and the content thereof is 100 ppm by mass or less, and the negative electrode for a non-aqueous electrolyte secondary battery. 23. A nonaqueous electrolyte secondary battery comprising the negative electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 22 . A method for producing a negative electrode material for a non-aqueous electrolyte secondary battery comprising negative electrode active material particles,
Producing a silicon compound particle represented by SiO _x (0.5 ≦ x ≦ 1.6);
Coating at least a part of the surface of the silicon compound particles with a carbon coating;
The specific surface area by the multipoint BET method measured by isolating the carbon coating from the silicon compound particles coated with the carbon coating is 5 m ² / g or more and 1000 m ² / g or less, and
The compression resistivity measured by isolating the carbon coating from the silicon compound particles coated with the carbon coating is 1.0 × 10 ⁻³ Ω · cm or more when compressed to a density of 1.0 g / cm ^3. 1.0Ω · cm Ri der below,
And a step of selecting particles true density of 1.2 g / cm ³ or more 1.9 g / cm ³ or less range der of Ru said silicon compound carbon film is coated in the carbon film,
A method for producing a negative electrode material for a non-aqueous electrolyte secondary battery, comprising producing a negative electrode material for a non-aqueous electrolyte secondary battery using the selected silicon compound particles coated with the carbon coating as negative electrode active material particles. .

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