KR20190049683A - A negative electrode active material, a mixed negative electrode active material, and a method for manufacturing a negative electrode active material - Google Patents

Abstract

The present invention is a negative electrode active material comprising negative electrode active material particles, wherein the negative electrode active material particle contains silicon compound particles containing silicon compounds (SiO _x : 0.5? _X? 1.6), the silicon compound particles containing Li compounds, Wherein the negative electrode active material particle includes Al and Na elements as constituent elements of the negative electrode active material particle and a mass ratio M _Na / M _Al of the Al element and the Na element satisfies the following formula 1: Thereby, a negative electrode active material capable of stabilizing a slurry produced at the time of manufacturing the negative electrode of the secondary battery and improving initial charge / discharge characteristics and cycle characteristics at the time of use as the negative electrode active material of the secondary battery is provided. <Formula 1> 0.022? M _Na / M _Al? 61

Description

A negative electrode active material, a mixed negative electrode active material, and a method for manufacturing a negative electrode active material

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

2. Description of the Related Art In recent years, small-sized electronic devices represented by mobile terminals and the like have become widespread, and further downsizing, weight reduction, and long life are strongly demanded. In response to such market demand, development of a secondary battery capable of achieving a particularly compact, lightweight and high energy density is underway. The secondary battery is not limited to a small electronic apparatus, but is also being studied for application to a power storage system represented by a large electronic apparatus represented by an automobile or a house.

Among them, lithium ion secondary batteries are expected to be small in size and high in capacity, and are expected to have higher energy densities than lead batteries and nickel-cadmium batteries.

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

As the negative electrode active material, a carbon-based active material is widely used, and further improvement of battery capacity is demanded from recent market demands. It has been studied to use silicon as a negative electrode active material for improving battery capacity. This is because the theoretical capacity of silicon (4199 mAh / g) is 10 times larger than the theoretical capacity of graphite (372 mAh / g), so that a significant improvement in the capacity of the battery can be expected. The development of a cast steel as a negative electrode active material has been studied not only for a silicon single substance but also for a compound represented by an alloy or an oxide. In addition, the active material form has been examined in a carbon-based active material from a standard coating type to an integral type which is directly deposited on the current collector.

However, when silicon is used as the main raw material as the negative electrode active material, the negative electrode active material expands and shrinks during charging and discharging, and therefore, the negative electrode active material tends to be easily broken near the surface layer of the negative electrode active material. Also, an ionic material is generated inside the active material, and the negative electrode active material becomes a fragile material. When the surface of the negative electrode active material is broken, a new surface is formed thereby increasing the reaction area of the active material. At this time, a decomposition reaction of the electrolytic solution occurs on the new surface, and a coating film which is a decomposition product of the electrolytic solution is formed on the new surface, so that the electrolytic solution is consumed. As a result, the cycle characteristics tend to decrease.

Up to now, in order to improve the initial efficiency and cycle characteristics of a battery, various studies have been made on a negative electrode material and an electrode configuration for a lithium ion secondary battery based on a cast material.

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

In order to improve the charge / discharge efficiency at _first , a nanocomposite containing a Si phase, SiO ₂ , or M _y O metal oxide is used (see, for example, Patent Document 5). In order to improve cycle characteristics, SiOx (0.8? _X ? 1.5, particle diameter = 1 to 50 占 퐉) and carbon materials are mixed and baked at a high temperature (see, for example, Patent Document 6). In order to improve the cycle characteristics, the ratio of oxygen to silicon in the negative electrode active material is 0.1 to 1.2, and the difference between the maximum value and the minimum value of the molar ratio in the vicinity of the interface between the active material and the collector is 0.4 or less. (See, for example, Patent Document 7). Further, in order to improve battery load characteristics, a metal oxide containing lithium is used (for example, see Patent Document 8). Further, in order to improve the cycle characteristics, a hydrophobic layer such as a silane compound is formed on the surface layer of the silk material (see, for example, Patent Document 9). In order to improve cycle characteristics, silicon oxide is used, and a graphite film is formed on the surface layer thereof to impart conductivity (see, for example, Patent Document 10). In Patent Document 10, broad peaks at ₁₃₃₀ cm ^-1 and 1580 cm ^-1 are shown with respect to the shift value obtained from the RAMAN spectrum concerning the graphite coating, and their intensity ratio I ₁₃₃₀ / I ₁₅₈₀ is 1.5 <I ₁₃₃₀ / I ₁₅₈₀ < 3. In order to improve the high battery capacity and cycle characteristics, particles having a purity of silicon suspended in silicon dioxide are used (see, for example, Patent Document 11). In addition, in order to improve the overcharging and overdischarging characteristics, a silicon oxide whose atomic ratio of silicon and oxygen is controlled to be 1: y (0 <y <2) is used (see, for example, Patent Document 12).

Japanese Patent Application Laid-Open No. 2001-185127 Japanese Patent Application Laid-Open No. 2002-042806 Japanese Patent Application Laid-Open No. 2006-164954 Japanese Patent Application Laid-Open No. 2006-114454 Japanese Patent Application Laid-Open No. 2009-070825 Japanese Patent Application Laid-Open No. 2008-282819 Japanese Patent Application Laid-Open No. 2008-251369 Japanese Patent Application Laid-Open No. 2008-177346 Japanese Patent Application Laid-Open No. 2007-234255 Japanese Patent Application Laid-Open No. 2009-212074 Japanese Patent Application Laid-Open No. 2009-205950 Japanese Patent No. 2997741 Specification

As described above, in recent years, small-sized electronic apparatuses such as mobile terminals are becoming more sophisticated and multifunctional, and lithium ion secondary batteries, which are the main power source thereof, are required to have increased battery capacity. As a method for solving this problem, development of a lithium ion secondary battery including a negative electrode using a cast material as a main material has been desired. On the other hand, when a cast steel material doped with Li is used, a high initial efficiency and a capacity retention rate can be obtained. On the other hand, a cast steel material doped with Li has low stability to an aqueous solvent, The stability of the water-based negative electrode slurry mixed with the gypsum material is lowered, and thus it is industrially unsuitable.

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a secondary battery which can stabilize a slurry produced at the time of manufacturing negative electrode of a secondary battery and improve initial charge / discharge characteristics and cycle characteristics It is an object of the present invention to provide a mixed negative-electrode active material including a negative active material that can be used and a negative active material. It is also an object of the present invention to provide a method for producing a negative electrode active material which can stabilize a slurry to be produced at the time of producing the negative electrode and improve initial charge / discharge characteristics and cycle characteristics.

In order to achieve the above object, the present invention is a negative electrode active material comprising negative electrode active material particles, wherein the negative electrode active material particles contain silicon compound particles containing a silicon compound (SiO _x : 0.5? _X? 1.6) Wherein the compound particle contains a Li compound and contains Al element and Na element as constituent elements of the negative electrode active material particle and a mass ratio M _Na / M _Al of the Al element and Na element satisfies the following formula 1 The negative electrode active material according to any one of claims 1 to 3,

<Formula 1> 0.022? M _Na / M _Al? 61

Since the negative electrode active material of the present invention includes negative electrode active material particles (also referred to as silicon-based active material particles) containing silicon compound particles, the battery capacity can be improved. Further, the irreversible capacity generated at the time of filling can be reduced by containing the Li compound in the silicon compound particles. As a result, the efficiency and cycle characteristics of the battery can be improved at the first time. In the production of the slurry (aqueous negative electrode slurry) in which the negative electrode active material and the like are dispersed in the aqueous solvent by including the Al element and the Na element in the same balance as the mass ratio M _Na / M _{Al in} the formula 1, Li The elution of Li ions from the compound is suppressed, and the stability of the aqueous negative electrode slurry is improved.

At this time, in the negative electrode active material of the present invention, it is preferable that the mass ratio M _Na / M _Al satisfies the following formula 2 additionally.

& Quot _; (2) & quot _; 0.36 & lt _; / = M _Na / M _Al &

The stability of the aqueous negative electrode slurry is further improved by including the Al element and the Na element in the mass ratio M _Na / M _Al .

In this case, it is preferable that the negative electrode active material of the present invention contains the Al element in an amount of 0.02 mass% or more and 1.1 mass% or less with respect to the silicon compound particle.

If the Al element is contained in an amount of 0.02 mass% or more, the stability of the aqueous negative electrode slurry can be further improved. If the Al element is included in the range of 1.1 mass% or less, the deterioration of the battery capacity can be prevented.

It is preferable that the negative electrode active material of the present invention contains the Na element in an amount of 0.024 mass% or more and 1.22 mass% or less with respect to the silicon compound particle.

If the Na element is contained in an amount of 0.024 mass% or more, the stability of the aqueous negative electrode slurry can be further improved. If the Na element is contained in the range of 1.22 mass% or less, the battery capacity can be prevented from lowering.

Further, it is preferable that the negative electrode active material particle contains polyacrylic acid Na.

If this is the case, the elution of Li ions from the Li compound in the negative electrode active material particles is further suppressed, so that the stability of the aqueous negative electrode slurry is further improved.

It is also preferable that the molecular weight of the polyacrylic acid Na is in the range of 250,000 or more and 1,000,000 or less.

The stability of the aqueous negative electrode slurry is further improved if the molecular weight includes polyacrylic acid Na in the above range.

When the polyacrylic acid Na is a 1% aqueous solution, it is preferable that the pH is in the range of 6 or more and 10 or less.

If such polyacrylic acid Na is contained, the elution of Li ions from the Li compound in the negative electrode active material particles is further suppressed, so that the stability of the aqueous negative electrode slurry is further improved.

Further, it is preferable that the negative electrode active material particle contains at least one of Li ₂ Si ₂ O ₅ , Li ₂ SiO ₃ , and Li ₄ SiO ₄ as a Li compound.

By including lithium silicate as the lithium compound, the irreversible capacity generated at the time of charging can be reduced, and the efficiency and cycle characteristics of the battery can be improved at the first time.

In addition, the silicon compound particles preferably have a half-width (2?) Of a peak attributable to a Si (111) crystal plane in an X-ray diffraction spectrum using a Cu-K? Line of 1.2 占 or more and a crystallite size Is preferably 7.5 nm or less.

When the negative electrode active material having the silicon crystallinity of the silicon compound particles is used as the negative electrode active material of the lithium ion secondary battery, better cycle characteristics and initial charge / discharge characteristics can be obtained.

The negative electrode active material of the present invention has the maximum peak strength value A of the Si and Li silicate regions, which is obtained from the ²⁹ Si-MAS-NMR spectrum and is given at -60 to -95 ppm as the chemical shift value, , And the peak intensity value B of the SiO ₂ region given at -96 to -150 ppm as the chemical shift value satisfies the relation A> B.

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

It is preferable that the negative electrode active material particles have a median diameter of 3 탆 or more and 15 탆 or less.

When the median diameter of the negative electrode active material particles is 3 mu m or more, increase in cell irreversible capacity due to increase in surface area per mass can be suppressed. On the other hand, when the median diameter is 15 占 퐉 or less, the particles are less likely to be broken, and new surfaces are less likely to occur.

It is preferable that the negative electrode active material particle contains a carbon material in the surface layer portion.

As described above, the negative electrode active material particles contain a carbon material in the surface layer portion, thereby improving the conductivity.

The average thickness of the carbonaceous material is preferably 5 nm or more and 5000 nm or less.

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

In order to achieve the above object, the present invention provides a mixed negative electrode active material characterized by comprising the negative electrode active material and the carbonaceous active material.

As described above, by including the carbon-based active material together with the negative electrode active material (silicon-based negative electrode active material) of the present invention as a material for forming the negative-electrode active material layer, it is possible to improve the conductivity of the negative electrode active material layer, It becomes possible to relax the stress. Further, the capacity of the battery can be increased by mixing the silicon-based negative electrode active material with the carbon-based active material.

In order to accomplish the above object, the present invention provides a method for producing a negative electrode active material comprising negative electrode active material particles containing silicon compound particles, comprising the steps of: preparing a silicon compound particle containing a silicon compound (SiO _x : 0.5? _X? 1.6) And a step of inserting Li into the silicon compound particles to prepare a negative electrode active material particle by a step of containing a Li compound, and mixing the Al element and the Na element in the negative electrode active material particle with the mass ratio of the Al element and the Na element M _Na / M _Al to satisfy the following formula (1), wherein the negative electrode active material is produced by using the negative electrode active material particles containing the Al element and the Na element .

<Formula 1> 0.022? M _Na / M _Al? 61

The aqueous negative electrode slurry to be produced at the time of producing the negative electrode can be particularly stabilized by incorporating the Al element and the Na element into the negative electrode active material particles in the mass ratio described above and by producing the negative electrode active material, and when the negative electrode active material is used as the negative electrode active material of the lithium ion secondary battery It is possible to produce a negative electrode active material having good cycle characteristics and initial charge / discharge characteristics as well as a high capacity.

The negative electrode active material of the present invention can stabilize the aqueous negative electrode slurry to be produced at the time of producing the negative electrode, and when used as a negative electrode active material of a secondary battery, good cycle characteristics and initial charge / discharge characteristics can be obtained at a high capacity. The same effect can be obtained also in the mixed negative-electrode active material including the negative-electrode active material. In addition, according to the method for producing the negative electrode active material of the present invention, it is possible to stabilize the aqueous slurry to be produced at the time of manufacturing the negative electrode, and when used as the negative electrode active material of the lithium ion secondary battery, An active material can be produced.

1 is a cross-sectional view showing an example of the configuration of a negative electrode for a nonaqueous electrolyte secondary battery including a negative electrode active material of the present invention.
2 is an example of a ²⁹ Si-MAS-NMR spectrum measured from silicon compound particles when the modification is carried out by an oxidation-reduction method.
3 is an example of a ²⁹ Si-MAS-NMR spectrum measured from silicon compound particles when the modification is performed by the thermal doping method.
4 is a view showing a configuration example (laminate film type) of a lithium secondary battery including the negative electrode active material of the present invention.
5 is a graph showing the relationship between the ratio of the silicon-based active material particles to the total amount of the negative electrode active material and the rate of increase of the battery capacity of the secondary battery.

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

As described above, as one method for increasing the battery capacity of a lithium ion secondary battery, it has been studied to use a negative electrode using a roughened material as a main material as a negative electrode of a lithium ion secondary battery. In particular, although the Si-based material doped with Li has good initial charge / discharge characteristics and cycle characteristics, there is a problem that the stability of the aqueous negative electrode slurry containing such a Si-based material is deteriorated. It has not been possible to propose a negative electrode active material having equivalent slurry stability, initial charge / discharge characteristics and cycle characteristics.

Thus, the inventors of the present invention have made intensive investigations to obtain a negative electrode active material having a high battery capacity and good slurry stability, cycle characteristics, and initial efficiency when used in a secondary battery, leading to the present invention.

The negative electrode active material of the present invention includes negative electrode active material particles. Further, the negative electrode active material particles contain silicon compound particles containing a silicon compound (SiO _x : 0.5? _X? 1.6), and the silicon compound particles contain a Li compound. Further, the negative electrode active material of the present invention contains Al and Na as constituent elements of the negative electrode active material particle, and the mass ratio M _Na / M _Al of the Al element and Na element satisfies the following formula (1).

<Formula 1> 0.022? M _Na / M _Al? 61

Since the negative electrode active material includes the negative electrode active material particles including the silicon compound particles, the battery capacity can be improved. Further, when the silicon compound particles include the Li compound as described above, the irreversible capacity generated at the time of charging can be reduced. In the production of the slurry (aqueous negative electrode slurry) in which the negative electrode active material and the like are dispersed in the water-based solvent by including the Al element and the Na element in the same balance as the mass ratio M _Na / M _Al of the formula 1, Li The elution of Li ions from the compound is suppressed, and the stability of the aqueous negative electrode slurry is improved. In addition, the effect of suppressing the elution of Li ions and improving the stability to an aqueous solvent is low only by containing any one of the Al element and the Na element.

It is particularly preferable that the mass ratio M _Na / M _Al in the negative electrode active material particle satisfies the following formula (2).

& Quot _; (2) & quot _; 0.36 & lt _; / = M _Na / M _Al &

When the mass ratio M _Na / M _Al satisfies the formula 2, the elution of Li ions from the silicon compound particles can be further suppressed, and the stability against an aqueous solvent is particularly improved.

The mass of each of the Al element and the Na element in the negative electrode active material particles can be measured by an ICP (Inductively Coupled Plasma) measurement method.

&Lt; Negative electrode for non-aqueous electrolyte secondary battery &

Next, a negative electrode for a nonaqueous electrolyte secondary battery including the negative electrode active material of the present invention will be described. 1 is a cross-sectional view showing an example of the configuration of a negative electrode for a nonaqueous electrolyte secondary battery (hereinafter also referred to as &quot; negative electrode &quot;).

[Configuration of negative electrode]

As shown in Fig. 1, the negative electrode 10 is configured to have the negative electrode active material layer 12 on the negative electrode collector 11. The negative electrode active material layer 12 may be provided on both sides or only one side of the negative electrode collector 11. Further, if the negative electrode active material of the present invention is used, the negative electrode collector 11 may be omitted.

[Negative collector]

The negative electrode collector 11 is made of a material having excellent electrical conductivity and excellent mechanical strength. Examples of the conductive material usable for the negative electrode collector 11 include copper (Cu) and nickel (Ni). The conductive material is preferably a material that does not form an intermetallic compound with lithium (Li).

The negative electrode 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 collector is improved. Particularly, when the current collector has an active material layer that expands at the time of charging, if the current collector contains the element, deformation of the electrode including the current collector is suppressed. The content of the contained element is not particularly limited, but is preferably 100 mass ppm or less in each case. And a higher strain inhibiting effect can be obtained. The cycle characteristics can be further improved by such strain suppressing effect.

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

[Negative electrode active material layer]

The negative electrode active material layer 12 includes the negative electrode active material of the present invention capable of intercalating and deintercalating lithium ions and may further contain other materials such as a negative electrode binder (binder) and a conductive auxiliary agent from the viewpoint of battery design. The negative electrode active material includes negative electrode active material particles, and the negative electrode active material particles include silicon compound particles containing a silicon compound (SiO _x : 0.5? _X? 1.6).

The negative electrode active material layer 12 may include a mixed negative electrode active material including the negative electrode active material and the carbonaceous active material of the present invention. Thereby, the electrical resistance of the negative electrode active material layer is lowered, and the expansion stress accompanying charging can be relaxed. As the carbon-based active material, for example, pyrolytic carbon, cokes, glassy carbon fiber, sintered organic polymer compound, carbon black and the like can be used.

The mixed negative electrode active material preferably has a mass ratio of the silicon-based negative electrode active material to the total mass of the negative electrode active material (silicon-based negative electrode active material) of the present invention and the carbon-based active material of 6 mass% or more. When the mass ratio of the silicon-based negative electrode active material to the total mass of the silicon-based negative-electrode active material and the carbon-based active material is 6 mass% or more, it is possible to reliably improve the battery capacity.

Further, as described above, the negative electrode active material of the present invention includes silicon compound particles, and the silicon compound particles are silicon oxide compounds containing silicon compounds (SiO _x : 0.5? _X? 1.6) Is preferable. This is because a high cycle characteristic is obtained. In addition, the composition of the silicon compound in the present invention does not necessarily mean a purity of 100%, but may contain a trace amount of an impurity element.

In the negative electrode active material of the present invention, it is preferable that the silicon compound particle contains at least one or more of Li ₂ Si ₂ O ₅ , Li ₂ SiO ₃ , and Li ₄ SiO ₄ as the Li compound. This is because the irreversible capacity generated at the time of charging can be reduced because the SiO ₂ component portion of the silicon compound which is destabilized at the time of inserting and removing lithium at the time of charge and discharge of the battery is previously modified with another lithium silicate.

Further, the battery characteristics are improved by the presence of at least one or more of Li ₂ Si ₂ O ₅ , Li ₂ SiO _3, and Li ₄ SiO ₄ in the bulk of the silicon compound particles. However, when two or more Li compounds are coexisted, . In addition, these lithium silicates can be quantified by NMR (Nuclear Magnetic Resonance) or X-ray photoelectron spectroscopy (XPS). Measurement of XPS and NMR can be performed, for example, under the following conditions.

XPS

· Apparatus: X-ray photoelectron spectrometer,

· X-ray source: monochromatic Al Kα line,

X-ray spot diameter: 100 占 퐉,

Ar ion total sputter condition: 0.5 kV / 2 mm x 2 mm.

²⁹ Si MAS NMR (magic spinning nuclear magnetic resonance)

Device: 700NMR spectrometer manufactured by Bruker,

Probe: 50 [mu] L of 4 mm HR-MAS rotor,

Sample rotation speed: 10 kHz,

· Measuring environment Temperature: 25 ℃.

Further, as described above, the negative electrode active material of the present invention contains Al and Na elements as constituent elements of the negative electrode active material particles so as to satisfy the relationship of the formula (1). At this time, it is preferable that the Al element is contained in the range of 0.02 mass% or more and 1.1 mass% or less with respect to the silicon compound particle. When the Al element is contained in an amount of not less than 1.1% by mass with respect to the silicon compound particle, a sufficient slurry stability is obtained when the Al element is contained in an amount of not less than 0.02% by mass based on the silicon compound particle, It is possible to prevent degradation.

It is preferable that the Na element is contained in an amount of 0.024 mass% or more and 1.22 mass% or less with respect to the silicon compound particle. Further, when the Na element is contained in an amount of 0.024 mass% or more with respect to the silicon compound particle, more sufficient slurry stability is obtained, and when the Na element is contained in the amount of 1.22 mass% or less with respect to the silicon compound particle, Can be prevented.

It is also preferable that the negative electrode active material particles contain polyacrylic acid Na. If this is the case, the elution of Li ions from the Li compound in the negative electrode active material particles is further suppressed, so that the stability of the aqueous negative electrode slurry is further improved.

It is also preferable that the molecular weight of the polyacrylic acid Na is in the range of 250,000 or more and 1,000,000 or less. The stability of the aqueous negative electrode slurry is further improved if the molecular weight includes polyacrylic acid Na in the above range.

When the polyacrylic acid Na is a 1% aqueous solution, it is preferable that the pH is in the range of 6 or more and 10 or less. If such polyacrylic acid Na is contained, the elution of Li ions from the Li compound in the negative electrode active material particles is further suppressed, so that the stability of the aqueous negative electrode slurry is further improved. When the polyacrylic acid Na is a 1% aqueous solution, it is particularly preferable that the pH is in the range of 7 to 9 inclusive. When such weakly alkaline polyacrylic acid Na is used, Li is hardly eluted from Li silicate.

Further, the silicon compound particles have a half-width (2?) Of a diffraction peak attributable to a Si (111) crystal plane obtained by X-ray diffraction using a Cu-K? Ray of 1.2 or more and a crystallite size corresponding to the crystal plane is And is preferably 7.5 nm or less. This peak appears near 2θ = 28.4 ± 0.5 ° when the crystallinity is high (when the half band width is narrow). The lower the silicon crystallinity of the silicon compound in the silicon compound particles is, the better the lower the degree of silicon crystallinity. Particularly, when the amount of Si crystals present is small, the battery characteristics can be improved and a stable Li compound can be produced.

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

It is also preferable that the median diameter (D ₅₀ : particle diameter when the cumulative volume is 50%) of the negative electrode active material particles is 3 탆 or more and 15 탆 or less. When the median diameter is within the above range, lithium ions are likely to occlude and release lithium ions during charging and discharging, and particles are less likely to break. When the median diameter is 3 占 퐉 or more, the surface area per mass can be reduced and the increase in the battery irreversible capacity can be suppressed. On the other hand, when the median diameter is 15 占 퐉 or less, it is difficult for the particles to break, and therefore, a new surface is difficult to come out.

In the negative electrode active material of the present invention, it is preferable that the negative electrode active material particle contains a carbon material in the surface layer portion. Since the negative electrode active material particles contain a carbon material in the surface layer portion, the improvement in conductivity can be obtained. Therefore, when the negative electrode active material containing such negative electrode active material particles is used as the negative electrode active material of the secondary battery, battery characteristics can be improved.

The average thickness of the carbonaceous material in the surface layer portion of the negative electrode active material particles is preferably 5 nm or more and 5000 nm or less. When the average thickness of the carbonaceous material is 5 nm or more, the conductivity is improved and the average thickness of the coated carbonaceous material is 5000 nm or less. When the negative electrode active material containing such negative electrode active material particles is used as the negative electrode active material of the lithium ion secondary battery , And the deterioration of the battery capacity can be suppressed.

The average thickness of the carbon material can be calculated, for example, by the following procedure. First, the negative electrode active material particles are observed at a certain magnification by a TEM (transmission electron microscope). The magnification is preferably a magnification capable of confirming the thickness of the material that is shot by the eyes so that the thickness can be measured. Subsequently, the thickness of the carbon material is measured at an arbitrary 15 point. In this case, it is preferable to set the measurement position at random at a wide range without focusing on a specific place as much as possible. Finally, the average thickness value of the carbon material of 15 points is calculated.

The covering ratio of the carbonaceous material is not particularly limited, but is preferably as high as possible. When the covering ratio is 30% or more, it is preferable because the electric conductivity is further improved. The method of coating the carbonaceous material is not particularly limited, but the sugar carbonization method and the thermal decomposition method of the hydrocarbon gas are preferable. This is because the covering ratio can be improved.

As the negative electrode binder contained in the negative electrode active material layer, any one or more of, for example, a polymer material and a synthetic rubber may be used. The polymer material is, for example, polyvinylidene fluoride, polyimide, polyamideimide, aramid, polyacrylic acid, lithium polyacrylate, carboxymethylcellulose and the like. The synthetic rubber is, for example, a styrene butadiene rubber, a fluorine rubber, or an ethylene propylene diene.

As the negative electrode conductive auxiliary, at least one of carbon materials such as carbon black, acetylene black, graphite, Ketjen black, carbon nanotubes, and carbon nanofibers can be used.

The negative electrode active material layer is formed by, for example, a coating method. The coating method is a method in which the negative electrode active material particles and the binder, and if necessary, the conductive auxiliary agent and the carbon material are mixed and dispersed in an organic solvent or water.

[Manufacturing method of negative electrode]

The negative electrode can be produced, for example, by the following procedure. First, a method of manufacturing the negative electrode active material used for the negative electrode will be described. First, silicon compound particles containing a silicon compound (SiO _x : 0.5? _X? 1.6) are prepared. Next, Li is inserted into the silicon compound particles to contain a Li compound. Thus, negative electrode active material particles are produced. Next, Al element and Na element are included in the negative electrode active material particle so that the mass ratio M _Na / M _Al of Al element and Na element satisfies the following formula (1). Then, the negative electrode active material is produced using the negative electrode active material particles containing the Al element and the Na element.

<Formula 1> 0.022? M _Na / M _Al? 61

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

The generated silicon oxide gas is solidified and deposited on the adsorption plate. Next, the silicon oxide deposit is taken out from the reactor while the internal temperature of the reactor is lowered to 100 DEG C or lower, and pulverized using a ball mill, a jet mill or the like, and pulverized. The powder thus obtained may be classified. In the present invention, the particle size distribution of the silicon compound particles can be adjusted during the pulverizing step and the classifying step. Thus, silicon compound particles can be prepared. Further, the Si crystallite in the silicon compound particles can be controlled by changing the vaporization temperature or by heat treatment after the generation.

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

First, the silicon compound particles are set in a furnace. Next, a hydrocarbon gas is introduced into the furnace, and the furnace temperature is raised. The decomposition temperature is not particularly limited, but is preferably 1,200 占 폚 or lower, more preferably 950 占 폚 or lower. By setting the decomposition temperature to 1200 占 폚 or less, unintended disproportionation of the active material particles can be suppressed. After raising the internal temperature to a predetermined temperature, a carbon layer is formed on the surface of the silicon compound particles. The hydrocarbon gas used as the raw material of the carbonaceous material is not particularly limited, but it is preferable that _{n? 3 in the} C _n H _m composition. If n &lt; = 3, the production cost can be lowered, and the physical properties of the decomposition product can be improved.

Next, Li is inserted into the silicon active material particles prepared as described above to contain a Li compound. At this time, it is preferable to contain at least one or more of Li ₂ Si ₂ O ₅ , Li ₂ SiO ₃ and Li ₄ SiO ₄ as the Li compound. In order to obtain Li silicates such as these, the Li insertion is preferably carried out by the redox method.

In the modification by the oxidation-reduction method, lithium can be inserted, for example, by first immersing the silicon active material particle in a solution A in which lithium is dissolved in an ether solvent. A polycyclic aromatic compound or a straight-chain polyphenylene compound may be further contained in this solution A. After inserting lithium, active lithium may be desorbed from the silicon active material particle by immersing the silicon active material particle in the solution B containing the polycyclic aromatic compound or its derivative. The solvent of the solution B may be, for example, an ether solvent, a ketone solvent, an ester solvent, an alcohol solvent, an amine solvent, or a mixed solvent thereof. Or after immersing in the solution A, the obtained silicon active material particles may be subjected to heat treatment under an inert gas at 400 to 800 ° C. The Li compound can be stabilized by heat treatment. Thereafter, it may be cleaned by a method of washing with alcohol, weak alkali, or pure water in which lithium carbonate is dissolved.

Examples of the ether solvent used in the solution A include diethyl ether, tert-butyl methyl ether, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol Dimethyl ether, a mixed solvent thereof, and the like can be used. Among these, tetrahydrofuran, dioxane and 1,2-dimethoxyethane are particularly preferably used. These solvents are preferably dehydrated and deoxygenated.

As the polycyclic aromatic compound contained in the solution A, at least one of naphthalene, anthracene, phenanthrene, naphthacene, pentacene, pyrene, picene, triphenylene, coronene, chrysene and derivatives thereof can be used As the linear polyphenylene compound, at least one of biphenyl, terphenyl and derivatives thereof can be used.

As the polycyclic aromatic compound contained in the solution B, at least one of naphthalene, anthracene, phenanthrene, naphthacene, pentacene, pyrene, picene, triphenylene, coronene, chrysene and derivatives thereof may be used.

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

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

As the ester-based solvent, methyl formate, methyl acetate, ethyl acetate, propyl acetate and isopropyl acetate may be used.

As the alcoholic solvent, methanol, ethanol, propanol, isopropyl alcohol and the like can be used.

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

In addition, Li may be inserted into the silicon active material particle by the thermal doping method. In the modification by the heat-doping method, for example, the silicon active material particles can be modified by mixing them with LiH powder or Li powder and heating in a non-oxidizing atmosphere. As the non-oxidizing atmosphere, for example, an Ar atmosphere or the like can be used. More specifically, LiH powder or Li powder and silicon oxide powder are thoroughly mixed in an Ar atmosphere and sealed, followed by stirring for each sealed container to make it uniform. Thereafter, the reforming is performed by heating in the range of 700 to 750 ° C. In this case, in order to desorb Li from the silicon compound, the powder after heating may be sufficiently cooled and then washed with alcohol, alkaline water, weak acid or pure water.

Further, when the modification is carried out by the thermal doping method, the ²⁹ Si-MAS-NMR spectrum obtained from the silicon compound particles is different from the case where the redox method is used. Fig. 2 shows an example of a ²⁹ Si-MAS-NMR spectrum measured from the silicon compound particles when the modification is carried out by the oxidation-reduction method. In Fig. 2, the peak imparted at around -75 ppm is a peak derived from Li ₂ SiO ₃ , and the peak imparted at -80 to -100 ppm is a peak derived from Si. In addition, there are cases where Li silicate peaks other than Li ₂ SiO ₃ and Li ₄ SiO ₄ are present over -80 to -100 ppm.

3 shows an example of a ²⁹ Si-MAS-NMR spectrum measured from the silicon compound particles when the modification is carried out by the thermal doping method. In Fig. 3, the peak imparted to the vicinity of -75 ppm is a peak derived from Li ₂ SiO ₃ , and the peak imparted to -80 to -100 ppm is a peak derived from Si. In addition, there are cases where Li silicate peaks other than Li ₂ SiO ₃ and Li ₄ SiO ₄ are present over -80 to -100 ppm. From the XPS spectrum, a peak of Li ₄ SiO ₄ can be confirmed.

Next, Al element and Na element are included in the negative electrode active material particle so that the mass ratio M _Na / M _Al of the Al element and Na element satisfies the above-mentioned formula (1).

More specifically, the aluminum element and the Na element can be contained in the negative electrode active material particles by dispersing aluminum phosphate in an aqueous solution of polyacrylic acid Na and spraying the dispersion onto the surface of the negative electrode active material particles. Further, since the mass of the Na element present in the polyacrylic acid Na powder per unit mass is determined, the content of the Na element can be adjusted by adjusting the amount of the polyacrylic acid Na powder dissolved in the aqueous solution. Since the mass of Al element present in aluminum phosphate per unit mass is also determined, the content of Al element can be adjusted by the amount of aluminum phosphate in the same manner as described above. That is, the mass ratio M _Na / M _Al can be set within the range of Formula 1 by adjusting the amounts of the polyacrylic acid Na and aluminum phosphate added.

For example, when it is desired to add 0.12 mass% of Na element to silicon compound particles, first, silicon compound particles are prepared. The mass of the silicon compound particles prepared at this time is measured. Next, when the aqueous solution of polyacrylic acid Na is prepared, the concentration of polyacrylic acid Na is adjusted to 0.12 mass% (0.5 mass% relative to the silicon compound particles in terms of sodium polyacrylate) based on the mass of the silicon compound particles in terms of Na Na is dissolved. Next, a predetermined amount of aluminum phosphate is added to the aqueous solution of polyacrylic acid Na so that the mass ratio M _Na / M _Al satisfies the formula (1). All of the dispersion thus prepared may be sprayed with the silicon compound particles.

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

&Lt; Lithium ion secondary battery >

Next, a lithium ion secondary battery including the negative electrode active material of the present invention will be described. Here, as a specific example, a laminate film type lithium ion secondary battery is taken as an example.

[Configuration of Laminate Film Type Lithium Ion Secondary Battery]

The laminate film type lithium ion secondary cell 20 shown in Fig. 4 is one in which the wound electrode body 21 is housed in a sheet-like casing member 25 mainly. This winding is wound with a separator between the positive electrode and the negative electrode. There is also a case where the laminate is housed with the separator between the positive electrode and the negative electrode. In any of the electrode bodies, the positive electrode lead 22 is attached to the positive electrode, and the negative electrode lead 23 is attached to the negative electrode. The outermost peripheral portion of the electrode body is protected by a protective tape.

The control electrode leads extend in one direction from the inside of the sheathing member 25 to the outside, for example. The positive electrode lead 22 is made of a conductive material such as aluminum and the negative electrode lead 23 is made of a conductive material such as nickel or copper.

The exterior member 25 is, for example, a laminate film in which a fusing layer, a metal layer, and a surface protection layer are laminated in this order, and the lamination film is a laminate film in which the fusing layer faces the electrode body 21, And the outer peripheral edges of the layer are mutually fused or adhered with an adhesive or the like. The fused portion is, for example, a film such as polyethylene or polypropylene, and the metal portion is an aluminum foil or the like. The protective layer is, for example, nylon or the like.

An adhesive film 24 is inserted between the sheathing member 25 and the lead of the positive electrode for preventing entry of outside air. This material is, for example, polyethylene, polypropylene or polyolefin resin.

[Positive]

Like the negative electrode 10 of Fig. 1, for example, the positive electrode has a positive electrode active material layer on both sides or one side of the positive electrode collector.

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

The positive electrode active material layer contains any one or more kinds of positive electrode materials capable of lithium ion intercalation and deintercalation, and may contain other materials such as a binder, a conductive auxiliary agent, and a dispersant depending on the design. In this case, the details of the binder and the conductive auxiliary agent are the same as those described above for the negative electrode binder and the negative electrode conductive auxiliary agent, for example.

As the positive electrode material, a lithium-containing compound is preferable. The lithium-containing compound includes, for example, a composite oxide containing lithium and a transition metal element, or a phosphoric acid compound having lithium and a transition metal element. Of the positive electrode materials described above, a compound having at least one of nickel, iron, manganese, and cobalt is preferable. As their formulas, for example, Li_xM1O₂ Or Li_yM2PO₄. In the formulas, M1 and M2 represent at least one kind of transition metal element. The values of x and y are different from each other depending on the state of charge / discharge of the battery, but generally, 0.05? x? 1.10 and 0.05? y?

Examples of the composite oxide having lithium and a transition metal element include a lithium cobalt complex oxide (Li _x CoO ₂ ) and a lithium nickel composite oxide (Li _x NiO ₂ ). Examples of the phosphoric acid compound having lithium and a transition metal element include a lithium iron phosphate compound (LiFePO ₄ ) or a lithium iron manganese phosphate compound (LiFe _{1 - u} Mn _u PO ₄ (0 <u <1) . When these positive electrode materials are used, a high battery capacity can be obtained and excellent cycle characteristics can be obtained.

[Negative pole]

The negative electrode has the same structure as that of the negative electrode 10 for lithium ion secondary battery shown in Fig. 1, and has negative electrode active material layers 12 on both surfaces of the current collector 11, for example. The negative electrode preferably has a larger negative electrode charging capacity than the electric capacity (charging capacity as a cell) obtained from the positive electrode active material. This is because precipitation of lithium metal on the negative electrode can be suppressed.

The positive electrode active material layer is provided on a part of both surfaces of the positive electrode current collector, and the negative electrode active material layer is also provided on a part of both surfaces of the negative electrode current collector. In this case, for example, the negative electrode active material layer provided on the negative electrode collector is provided with a region in which the opposite positive electrode active material layer does not exist. This is to perform a stable battery design.

In a region where 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, is hardly affected by charge and discharge. Therefore, the state of the negative electrode active material layer is maintained immediately after formation. As a result, it is possible to accurately examine the composition and the like with good reproducibility without depending on the presence or absence of charge and discharge, such as the composition of the negative electrode active material.

[Separator]

The separator isolates the positive electrode and the negative electrode to allow lithium ions to pass therethrough while preventing a short circuit of current accompanying the contact between the electrodes. The separator may be formed of, for example, a synthetic resin or a porous film containing ceramics, and may have a laminated structure in which two or more porous films are laminated. Examples of the synthetic resin include polytetrafluoroethylene, polypropylene, polyethylene, and the like.

[Electrolytic solution]

At least a part of the active material layer or the separator is impregnated with a liquid electrolyte (electrolytic solution). The electrolytic solution contains an electrolytic salt dissolved in a solvent and may contain other materials such as an additive.

As the solvent, for example, a non-aqueous solvent may be used. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl carbonate, 1,2-dimethoxyethane and tetrahydrofuran. Among them, it is preferable to use at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate. And better characteristics can be obtained. In this case, superior characteristics can be obtained by combining a high viscosity solvent such as ethylene carbonate and propylene carbonate with a low viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate or diethyl carbonate. This is because the dissociability and ion mobility of the electrolyte salt are improved.

In the case of using the alloy-based negative electrode, it is particularly preferable that at least one of the halogenated chain carbonate ester and the halogenated cyclic carbonate ester is contained as the solvent. As a result, a stable film is formed on the surface of the negative electrode active material during charging / discharging, particularly charging. Here, the halogenated chain carbonate ester is a chain carbonate ester (in which at least one hydrogen is substituted by halogen) having a halogen as a constituent element. Further, the halogenated cyclic carbonic ester is a cyclic carbonic ester having a halogen as a constituent element (that is, at least one hydrogen is substituted by halogen).

The kind of the halogen is not particularly limited, but fluorine is preferable. This is because it forms a coating film superior to other halogens. Also, the larger the number of halogen atoms, the better. This is because the obtained film is more stable and the decomposition reaction of the electrolytic solution is reduced.

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

As the solvent additive, it is preferable to contain an unsaturated carbon-bonded cyclic carbonate ester. This is because a stable film is formed on the surface of the negative electrode at the time of charging and discharging, and the decomposition reaction of the electrolytic solution can be suppressed. As the unsaturated carbon-bonded cyclic carbonic ester, for example, vinylene carbonate, vinyl ethylene carbonate and the like can be given.

As the solvent addition, it is preferable to contain sultone (cyclic sulfonic acid ester). This is because the chemical stability of the battery improves. Examples of the sultone include propanesultone and propensultone.

Further, the solvent preferably contains an acid anhydride. This is because the chemical stability of the electrolytic solution is improved. As the acid anhydride, for example, propane disulfonic anhydride can be mentioned.

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

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

[Method of producing laminate film type secondary battery]

In the present invention, the negative electrode can be manufactured using the negative electrode active material produced by the method of manufacturing the negative electrode active material of the present invention, and the lithium ion secondary battery can be manufactured using the prepared negative electrode.

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

Subsequently, a negative electrode active material layer is formed on the negative electrode current collector by using the same working procedure as that for the above-described negative electrode for lithium ion secondary battery 10, and a negative electrode is prepared.

When producing the positive electrode and the negative electrode, the respective active material layers are formed on both surfaces of the positive electrode and the negative electrode current collector. At this time, the coating length of the active material on both sides may be deviated from any electrode (see Fig. 1).

Subsequently, the electrolyte is adjusted. Subsequently, the positive electrode lead 22 is attached to the positive electrode current collector by ultrasonic welding or the like, and the negative electrode lead 23 is attached to the negative electrode current collector. Subsequently, the positive electrode and the negative electrode are laminated or wound by way of a separator to prepare the wound electrode body 21, and a protective tape is bonded to the outermost periphery thereof. Then, the winding body is formed to have a flat shape. Subsequently, after the wound electrode body is sandwiched between the sheathing members 25 on the folded film, the insulating members of the sheathing member are adhered to each other by the heat welding method, and the wound electrode body is sealed in a state in which only one direction is released. A positive film lead is inserted between the negative electrode lead and the exterior member. A predetermined amount of the adjusted electrolytic solution is charged from the liberating portion, and vacuum impregnation is performed. After the impregnation, the release part is bonded by the vacuum heat sealing method. In this way, a laminate film type lithium ion secondary battery 20 can be manufactured.

Example

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

(Example 1-1)

A laminate film type lithium ion secondary cell 20 shown in Fig. 4 was produced by the following procedures.

The positive electrode was first fabricated. The positive electrode active material was prepared by mixing 95 mass% of LiNi _0.7 Co _0.25 Al _0.05 O, a lithium nickel cobalt composite oxide, 2.5 mass% of a positive electrode active material, and 2.5 mass% of a positive electrode binder (polyvinylidene fluoride: PVDF) . Subsequently, the positive electrode mixture was dispersed in an organic solvent (N-methyl-2-pyrrolidone: NMP) to obtain a paste-like 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 type drying apparatus. At this time, the positive electrode current collector having a thickness of 15 mu m was used. Finally, compression molding was performed using a roll press.

Next, a negative electrode was produced. First, a negative electrode active material was prepared as follows. A raw material obtained by mixing metallic silicon and silicon dioxide was introduced into a reaction furnace and vaporized in an atmosphere of a degree of vacuum of 10 Pa was deposited on an adsorption plate and sufficiently cooled, and then the deposit was taken out and crushed by a ball mill. The x value of SiO _x of the silicon compound particles thus obtained was 0.5. Subsequently, the particle size of the silicon compound particles was adjusted by classification. Thereafter, thermal decomposition CVD was performed to cover the surface of the silicon compound particles with a carbon material.

Subsequently, lithium was inserted into the silicon compound particles coated with the carbon coating (negative electrode active material particles) by an oxidation reduction method to carry out the modification. First, the negative electrode active material particles were immersed in a solution (solution C) in which a lithium piece and an aromatic compound naphthalene were dissolved in tetrahydrofuran (hereinafter referred to as THF). This solution C was prepared by dissolving naphthalene in a THF solvent at a concentration of 0.2 mol / L and then adding a lithium component in an amount of 10 mass% to the mixed solution of THF and naphthalene. The solution temperature at the time of immersing the negative electrode active material particles was 20 占 폚 and the immersion time was 20 hours. Thereafter, the negative electrode active material particles were taken out by filtration. Through the above process, lithium was inserted into the negative electrode active material particles.

Subsequently, the obtained negative electrode active material particles were subjected to heat treatment at 600 캜 for 24 hours in an argon atmosphere to stabilize the Li compound.

Next, the negative electrode active material particles were washed, and the negative electrode active material particles after the washing treatment were dried under a reduced pressure. Thus, the negative electrode active material particles were modified. By the above treatment, the negative electrode active material particles were produced.

Next, an aqueous solution of sodium polyacrylate in which aluminum phosphate was dispersed was sprayed on the negative electrode active material particles to contain 0.44 mass% of Al element and 0.49 mass% of Na element. That is, the mass ratio M _Na / M _Al was 1.1, which satisfied Equation 1 and Equation 2. The molecular weight of the polyacrylic acid Na used herein was 600,000, and the pH when the aqueous solution was 1% aqueous solution was 8.8.

Next, the negative electrode active material particles (silicon-based negative electrode active material) for forming the negative electrode and the carbon-based active material were mixed in a mass ratio of 2: 8 to prepare a negative electrode active material. Here, as the carbonaceous active material, natural graphite coated with a pitch layer and artificial graphite mixed in a mass ratio of 5: 5 were used. The median diameter of the carbon-based active material was 20 占 퐉.

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

Here, in order to evaluate the stability of the aqueous slurry containing the negative electrode active material particles, 30 g of the prepared negative electrode material mixture slurry was taken out separately from those for the production of the secondary battery and stored at 20 占 폚, The time to occurrence was measured.

As the negative electrode current collector, an electrolytic copper foil having a thickness of 15 mu m was used. The electrolytic copper foil contained carbon and sulfur in a concentration of 70 mass ppm respectively. Finally, the negative electrode mixture slurry was applied to the negative electrode current collector and dried in a vacuum atmosphere at 100 占 폚 for 1 hour. After drying, the deposition amount (also referred to as an areal density) of the negative electrode active material layer per unit area on one side of the negative electrode was 5 mg / cm 2.

Subsequently, the mixture was mixed with a solvent (4-fluoro-1,3-dioxolan-2-one (FEC), ethylene carbonate (EC) and dimethyl carbonate (DMC) Lithium: 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.

Subsequently, the secondary battery was assembled as follows. First, an aluminum lead was ultrasonically welded to one end of the positive electrode current collector, and 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. And the end of the sounding was fixed with a PET protective tape. As the separator, a laminated film (thickness: 12 mu m) was used which was sandwiched by a film mainly composed of porous polyethylene by a film mainly composed of porous polypropylene. Subsequently, after the electrode bodies were sandwiched between the outer sheath members, the outer circumferential edge portions except for one side were thermally fused, and the electrode bodies were housed inside. An aluminum laminated film laminated with a nylon film, an aluminum foil and a polypropylene film was used as the exterior member. Subsequently, the electrolyte prepared from the openings was injected, impregnated in a vacuum atmosphere, thermally fused, and sealed.

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

 Cycle characteristics were examined as follows. For the first time, the battery was charged and discharged at 0.2 C for 2 cycles under an atmosphere of 25 캜 for battery stabilization, and the discharge capacity at the second cycle was measured. Subsequently, charging and discharging were carried out until the total cycle number became 499 cycles, and the discharge capacity was measured every time. Finally, the discharge capacity at the 500th cycle obtained by 0.2C charge / discharge was divided by the discharge capacity at the second cycle, and the capacity retention rate (hereinafter simply referred to as retention rate) was calculated. Charge and discharge were performed at a normal cycle, that is, from the 3rd cycle to the 499th cycle at a charge of 0.7C and a discharge of 0.5C.

In the case where the charge / discharge characteristics were investigated for the first time, the efficiency (hereinafter, also referred to as initial efficiency) was calculated first. The first efficiency was calculated from the equation represented by the first efficiency (%) = (first discharge capacity / first charge capacity) × 100. The atmospheric temperature was the same as in the case where the cycle characteristics were examined.

(Examples 1-2 to 1-3, Comparative Examples 1-1 and 1-2)

A secondary battery was produced in the same manner as in Example 1-1 except that the amount of oxygen in the bulk of the silicon compound was adjusted. In this case, the oxygen content was adjusted by changing the ratio of the silicon metal and silicon dioxide in the raw material of the silicon compound and the heating temperature. Table 1 shows the values of x of the silicon compounds represented by SiO _x in Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2.

At this time, the silicon-based active material particles of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2 had the following properties. The median diameter of the silicon-based active material particles in the negative electrode active material particles was 8 占 퐉. The inside of the silicon compound particles contained Li ₂ Si ₂ O ₅ and Li ₂ SiO ₃ . The silicon compound had a half width (2?) Of 2.257 占 of the diffraction peak due to the Si (111) crystal face obtained by X-ray diffraction and a crystallite size attributable to the Si (111) crystal face of 3.77 nm. The average thickness of the carbon material coated on the surface was 50 nm.

In all of the above Examples and Comparative Examples, peaks of Si and Li silicate regions imparted at -60 to -95 ppm as a chemical shift value obtained from the ²⁹ Si-MAS-NMR spectrum were expressed. In all of the above Examples and Comparative Examples, the maximum peak intensity value A of the Si and Li silicate regions given at -60 to -95 ppm as the chemical shift value obtained from the ²⁹ Si-MAS-NMR spectrum and the maximum peak intensity value A of -96 to -150 ppm And the peak intensity value B of the SiO ₂ region imparted by the above-mentioned method was A > B.

The evaluation results of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2 are shown in Table 1.

As shown in Table 1, when the value of x in the silicon compound represented by SiO _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 the amount of oxygen is insufficient (x = 0.3), the efficiency is improved for the first time, but the capacity retention rate remarkably deteriorates. On the other hand, as shown in Comparative Example 1-2, when the amount of oxygen was large (x = 1.8), the conductivity was deteriorated and the silicon oxide capacity was not substantially developed. Further, in Examples 1-1 to 1-3, it was found that the time until the generation of the gas was 3 days or more, and the stability of the aqueous negative electrode slurry was improved as compared with Comparative Example 1-1. In Comparative Example 1-2, time measurement until gas generation was not performed.

(Examples 2-1 to 2-2)

Secondary batteries were produced under the same conditions as in Example 1-2 except that the kinds of lithium silicate contained in the silicon compound particles were changed as shown in Table 2, and the cycle characteristics, the initial efficiency and the stability of the aqueous negative electrode slurry were evaluated did.

(Comparative Example 2-1)

A secondary battery was produced under the same conditions as in Example 1-2 except that Li was not inserted into the silicon compound particles, and the cycle characteristics, the initial efficiency, and the stability of the aqueous negative electrode slurry were evaluated.

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

When the silicon compound particles contain stable lithium silicate such as Li ₂ SiO ₃ and Li ₄ SiO ₄ , the capacity retention rate and initial efficiency were improved. In particular, when two types of lithium silicate were included, the capacity retention rate and the initial efficiency were further improved. Further, the time until the generation of the gas was two days or more, and the stability of the water-based negative electrode slurry was obtained. On the other hand, when the silicon compound particles did not contain a Li compound as in Comparative Example 2-1, no gas was generated, but the initial efficiency remarkably decreased.

(Examples 3-1 to 3-35, Comparative Examples 3-1 to 3-8)

By changing the mass concentration of Al element and Na element contained in the silicon compound particles, in addition to the mass ratio it was changed as the value of M _Na / M _Al in Table 3, Examples 1-2 and to prepare a secondary battery under the same conditions , Cycle characteristics, initial efficiency and stability of the water-based negative electrode slurry.

Table 3 shows the results of Examples 3-1 to 3-35 and Comparative Examples 3-1 to 3-8.

As can be seen from Table 3, when the value of the mass ratio M _Na / M _Al satisfies the formula 1 0.022 M _Na / M _Al ≤ 61, the time until the gas generation is shorter than that of Comparative Example 3- 4 to 3-8. Further, in Comparative Examples 3-1 to 3-3 not including at least one of the Al element and the Na element, the time until the generation of the gas was further shortened. Therefore, as in the present invention, when the negative electrode active material particle contains Al and Na elements as its constituent elements and the mass ratio M _Na / M _Al of these elements satisfies the formula 1, the stability of the aqueous negative electrode slurry Was improved.

(Examples 4-1 to 4-5)

A secondary battery was produced under the same conditions as in Example 1-2 except that the molecular weight of the polyacrylic acid Na was changed as shown in Table 4, and the cycle characteristics, the initial efficiency and the stability of the aqueous negative electrode slurry were evaluated.

Table 4 shows the results of Examples 4-1 to 4-5.

As can be seen from Table 4, the time until the generation of the gas varies depending on the molecular weight of the polyacrylic acid Na. In particular, as in Examples 1-2 and 4-2 to 4-4, when the molecular weight of the polyacrylic acid Na is 250,000 or more and 1,000,000 or less, the time until the generation of the gas becomes longer and the stability of the aqueous negative electrode slurry is further improved And improved.

(Examples 5-1 to 5-4)

A secondary battery was produced under the same conditions as in Example 1-2 except that polyacrylic acid Na in which pH was as shown in Table 5 was used as a 1% aqueous solution to evaluate the cycle characteristics, the initial efficiency and the stability of the aqueous negative electrode slurry .

The results of Examples 5-1 to 5-4 are shown in Table 5.

As can be seen from Table 5, when the pH was 6 to 10, it was found that the time until gas generation was long and the stability of the aqueous negative electrode slurry was high. In particular, when the pH is 7 to 9, the stability of the aqueous negative electrode slurry is higher.

(Examples 6-1 to 6-9)

A secondary battery was produced under the same conditions as in Example 1-2 except that the crystallinity of the silicon compound particles was changed as shown in Table 6, and the cycle characteristics, the initial efficiency and the stability of the aqueous negative electrode slurry were evaluated. The crystallinity in the silicon compound particles can be controlled by changing the vaporization temperature of the raw material or by heat treatment after the generation of the silicon compound particles. In Example 6-9, the full width at half maximum is calculated to be 20 degrees or more, but the result is obtained by fitting using analysis software, and substantially no peak is obtained. Therefore, the silicon compound of Example 6-9 can be said to be substantially amorphous.

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

(Example 7-1)

A secondary battery was manufactured under the same conditions as in Example 1-2 except that the relation between the maximum peak intensity value A of the Si and Li silicate regions and the peak intensity value B derived from the SiO ₂ region was A & And the cycle characteristics, the initial efficiency, and the stability of the water-based negative electrode slurry were evaluated. In this case, by reducing the insertion amount of lithium at the time of modification, the amount of Li ₂ SiO ₃ is reduced to reduce the intensity A of the peak derived from Li ₂ SiO ₃ .

As can be seen from Table 7, the battery characteristics were improved when the relationship of the peak intensity was A> B.

(Examples 8-1 to 8-6)

A secondary battery was produced under the same conditions as in Example 1-2 except that the median diameter of the silicon compound particles was changed as shown in Table 8, and the cycle characteristics, the initial efficiency and the stability of the aqueous negative electrode slurry were evaluated.

When the median diameter of the silicon compound was 3 m or more, the retention and initial efficiency were further improved. This is considered to be because the surface area per mass of the silicon compound is not excessively large and the area where side reactions occur can be reduced. On the other hand, when the median diameter is 15 μm or less, the particles are hardly broken at the time of charging, and SEI (solid electrolyte interface) due to the new surface is not generated at the time of charging and discharging, so that loss of reversible Li can be suppressed. If the median diameter of the silicon-based active material particles is 15 μm or less, the expansion amount of the silicon compound particles at the time of filling does not increase, so physical and electrical breakdown of the negative electrode active material layer due to expansion can be prevented.

(Examples 9-1 to 9-4)

A secondary battery was manufactured under the same conditions as in Example 1-2 except that the average thickness of the carbonaceous material coated on the surface of the silicon-based active material was changed, and the cycle characteristics, the first efficiency and the stability of the aqueous negative electrode slurry were evaluated. The average thickness of the carbonaceous material can be adjusted by changing the CVD condition.

As can be seen from Table 9, since the film thickness of the carbon layer is 5 nm or more, the conductivity is improved, and the capacity retention rate and initial efficiency can be improved. On the other hand, if the thickness of the carbon layer is 5000 nm or less, the amount of the silicon compound particles can be sufficiently secured in the battery design, so that the battery capacity does not decrease.

(Example 10-1)

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

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

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

Claims (15)

1. A negative electrode active material comprising negative electrode active material particles,
Wherein the negative electrode active material particles contain silicon compound particles containing a silicon compound (SiOx: 0.5? X? 1.6)
The silicon compound particle contains a Li compound,
Wherein the negative electrode active material particle includes an Al element and an Na element as constituent elements, and a mass ratio M _Na / M _Al of the Al element and the Na element satisfies the following formula (1).
<Formula 1> 0.022? M _Na / M _Al? 61 The negative electrode active material according to claim 1, wherein the mass ratio M _Na / M _Al satisfies the following formula (2).
& Quot _; (2) & quot _; 0.36 & lt _; / = M _Na / M _Al & The negative electrode active material according to claim 1 or 2, wherein the Al element is contained in an amount of 0.02 mass% or more and 1.1 mass% or less based on the silicon compound particle. The negative electrode active material according to any one of claims 1 to 3, wherein the Na element is contained in an amount of 0.024 mass% to 1.22 mass% with respect to the silicon compound particle. The negative electrode active material according to any one of claims 1 to 4, wherein the negative electrode active material particles comprise polyacrylic acid Na. The negative electrode active material according to claim 5, wherein the polyacrylic acid Na has a molecular weight of 250,000 or more and 1,000,000 or less. The negative electrode active material according to claim 5 or 6, wherein the pH is in the range of 6 to 10 when the polyacrylic acid Na is a 1% aqueous solution. The lithium _secondary battery according to any one of claims 1 to 7, wherein the negative electrode active material particles include at least one of Li ₂ Si ₂ O ₅ , Li ₂ SiO ₃ , and Li ₄ SiO ₄ as a Li compound Negative active material. 9. The silicon compound particle according to any one of claims 1 to 8, wherein the silicon compound particle has a half-width (2?) Of a diffraction peak attributed to a Si (111) crystal plane obtained by X-ray diffraction using a Cu- Deg.] Or more and a crystallite size corresponding to the crystal plane is 7.5 nm or less. 10. The method according to any one of claims 1 to 9, wherein in the silicon compound particles, a maximum of Si and Li silicate regions, which are obtained from the ²⁹ Si-MAS-NMR spectrum and are given at -60 to -95 ppm as chemical shift values Wherein the peak intensity value A and the peak intensity value B of the SiO ₂ region given at -96 to -150 ppm as the chemical shift value satisfy the relation A> B. 11. The negative electrode active material according to any one of claims 1 to 10, wherein the negative electrode active material particles have a median diameter of 3 mu m or more and 15 mu m or less. 12. The negative electrode active material according to any one of claims 1 to 11, wherein the negative electrode active material particles contain a carbon material in a surface layer portion. 13. The negative electrode active material according to claim 12, wherein the carbonaceous material has an average thickness of 5 nm or more and 5000 nm or less. A mixed negative electrode active material material comprising the negative electrode active material according to any one of claims 1 to 13 and a carbonaceous active material. A method for producing a negative electrode active material comprising negative electrode active material particles containing silicon compound particles,
A step of producing a silicon compound particle containing a silicon compound (SiO _x : 0.5? _X? 1.6)
A step of inserting Li into the silicon compound particle to contain a Li compound
The negative electrode active material particles were produced by the above-
And a step of including the Al element and the Na element in the negative electrode active material particle so that the mass ratio M _Na / M _Al of the Al element and the Na element satisfy the following formula 1,
Wherein the negative electrode active material is produced by using the negative electrode active material particles containing the Al element and the Na element.
<Formula 1> 0.022? M _Na / M _Al? 61

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