KR20190059906A - A negative electrode active material, a mixed negative electrode active material and a negative electrode active material production method - Google Patents

Abstract

The present invention relates to 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), the silicon compound particles contain a Li compound, Characterized in that the negative electrode active material particles comprise a metal salt containing at least one salt selected from a salt of polyacrylic acid and a salt of carboxymethylcellulose and containing at least one metal selected from Mg and Al, to be. 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 when used as the negative electrode active material of the secondary battery is provided.

Description

A negative electrode active material, a mixed negative electrode active material and a negative electrode active material production method

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.

Background Art [0002] In recent years, small-sized electronic devices such as mobile terminals 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 obtaining a small, lightweight and high energy density is progressing. The secondary battery is not limited to a small electronic device 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, the lithium ion secondary battery is very small in size, easy to make high capacity, and has a much higher energy density than a lead battery and a nickel-cadmium battery.

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 related to charge / discharge reaction.

As the negative electrode active material, a carbon-based active material has been widely used, and further improvement of battery capacity is demanded from recent market demands. In order to improve battery capacity, it has been studied to use silicon as the negative electrode active material. 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 quartz as a negative electrode active material has been studied not only for a silicon group but also for a compound represented by an alloy or an oxide. In addition, the active material shape is studied from a standard coating type to a single type in which the carbon-based active material 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, it tends to break mainly in the vicinity of 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 negative electrode active material surface layer is broken, a new surface is generated thereby to increase the reaction area of the active material. At this time, a decomposition reaction of the electrolytic solution occurs on the new surface, and a film as a decomposed 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 cell initial efficiency and the cycle characteristics, various studies have been made on the negative electrode material and the 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). Further, in order to obtain a high battery capacity and safety, a carbon material (electron conduction material) is provided on the surface layer of the silicon oxide particles (see, for example, Patent Document 2). 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 the 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 the cycle characteristics, SiOx (0.8? _X ? 1.5, particle size range = 1 to 50 占 퐉) and carbon materials are mixed and baked at a high temperature (for example, see 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 near the interface of 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 (see, for example, Patent Document 8). Further, in order to improve the cycle characteristics, a hydrophobic layer such as a silane compound is formed on the surface layer of the 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 to impart conductivity (see, for example, Patent Document 10). In the Patent Document 10, with respect to the shift value obtained from the RAMAN spectrum of the graphite film, 1330cm ^-1 and 1580cm ^-1 of a broad peak with the indicated, their intensity ratio I ₁₃₃₀ / I ₁₅₈₀ is 1.5 <I ₁₃₃₀ / I ₁₅₈₀ < 3. In order to improve the high battery capacity and the cycle characteristics, particles having a purity of silicon suspended in silicon dioxide are used (see, for example, Patent Document 11). 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 devices represented by mobile terminals and the like are becoming more sophisticated and multifunctional, and lithium ion secondary batteries as their main power sources are required to increase their battery capacities. 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. In the case of using a roughened material, a high initial efficiency and a capacity retention rate can be obtained by using a roughened material doped with Li. On the other hand, a roughened material doped with Li has low stability against 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 And a mixed negative electrode active material including the negative electrode 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 provides 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 particle contains a Li compound and the negative electrode active material particle contains at least one salt selected from a salt of polyacrylic acid and a salt of carboxymethyl cellulose and contains at least one metal selected from Mg and Al And a negative electrode active material.

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, when the silicon compound particles contain a Li compound, the irreversible capacity generated upon charging can be reduced. As a result, the efficiency and cycle characteristics of the battery can be improved at the first time. Further, the negative electrode active material particles include a metal salt containing at least one salt selected from a salt of polyacrylic acid and a salt of carboxymethyl cellulose and at least one metal selected from Mg and Al, so that the negative electrode active material The elution of Li ions from the Li compound in the negative electrode active material particles is suppressed and the stability of the aqueous negative electrode slurry is improved.

At this time, it is preferable that the total amount of at least one salt selected from the salt of polyacrylic acid and the salt of carboxymethyl cellulose is in the range of 0.1 mass% to 5 mass% with respect to the total amount of the negative electrode active material particles.

When the total amount of at least one salt selected from a salt of polyacrylic acid and a salt of carboxymethyl cellulose is 0.1% by mass or more based on the total amount of the negative electrode active material particles, the elution of Li ions from the Li compound in the negative electrode active material particles is further suppressed , The stability of the aqueous negative electrode slurry is further improved. When the total amount of these salts is 5% by mass or less based on the total amount of the negative electrode active material particles, the battery capacity can be prevented from lowering.

At this time, it is preferable that at least one salt selected from the salt of polyacrylic acid and the salt of carboxymethyl cellulose is an ammonium salt.

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.

The total amount of the metal salt containing at least one metal selected from Mg and Al is preferably in the range of 0.1 mass% to 5 mass% with respect to the total amount of the negative electrode active material particles.

When the total amount of the metal salt is 0.1% by mass or more based on the total amount of the negative electrode active material particles, the elution of Li ions from the Li compound in the negative electrode active material particles is further suppressed, and the stability of the aqueous negative electrode slurry is further improved. When the total amount of the metal salt is 5% by mass or less based on the total amount of the negative electrode active material particles, the battery capacity can be prevented from lowering.

The metal salt containing at least one metal selected from the group consisting of Mg and Al is preferably a nitrate salt, a phosphate salt, a hydrochloride salt or a sulfate salt.

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.

The total content of the negative electrode active material particles based on the mass of the polyacrylic acid salt and at least one salt selected from the salt of carboxymethyl cellulose contained in the negative electrode active material particles is selected from among Mg and Al contained in the negative electrode active material particles Is smaller than the sum of the content based on the mass of the metal salt containing at least one kind of metal.

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.

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.

Further, the silicon compound particle has a half-width (2?) Of a peak attributed 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 are obtained.

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 are obtained from the ²⁹ Si-MAS-NMR spectrum in the silicon compound particles and are 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 As long as the on the basis of more than the amount of Si and Li ₂ SiO ₃ ingredient is a fully obtained the negative electrode active material to the effect of improving the cell characteristics due to insertion of Li.

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, it is difficult for the particles to break, and therefore, a new surface is difficult to come out.

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 carbon material to be coated is 5000 nm or less, by using a negative electrode active material containing such negative electrode active material particles in the lithium ion secondary battery, it is possible to secure a sufficient amount of the silicon compound particles, 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 achieve 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 negative electrode active material containing a silicon compound (SiOx: 0.5? _X? 1.6) A method for producing negative electrode active material particles, comprising the steps of: preparing particles; preparing negative electrode active material particles by a step of inserting Li into the silicon compound particles and containing a Li compound; and separating the negative electrode active material particles from a salt of polyacrylic acid and a salt of carboxymethylcellulose And at least one metal salt selected from the group consisting of a salt of polyacrylic acid and a salt of carboxymethyl cellulose, and a salt of at least one salt selected from salts of polyacrylic acid and carboxymethyl cellulose, , The negative electrode active material particles containing a metal salt containing at least one metal selected from Mg and Al W, provides a method for preparing a negative electrode active material, characterized in that for preparing the negative electrode active material.

By preparing the negative electrode active material by including the salt as described above in the negative electrode active material particles, it is possible to stabilize the aqueous negative electrode slurry produced at the time of manufacturing the negative electrode, and when used as the negative electrode active material of the lithium ion secondary battery, A negative electrode active material having good cycle characteristics and initial charge / discharge characteristics can be produced.

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 for a secondary battery, a high capacity, good cycle characteristics and initial charge / discharge characteristics are obtained. The same effect can be obtained also in the mixed negative-electrode active material including the negative-electrode active material. In addition, the method for producing the negative electrode active material of the present invention can stabilize the aqueous slurry produced at the time of manufacturing the negative electrode, and when used as the negative electrode active material of the lithium ion secondary battery, the negative electrode having good cycle characteristics and initial charge / 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. Particularly, although the Li-doped silicon carbide has good initial charging / discharging characteristics and cycle characteristics, there is a problem that the stability of the water-based negative electrode slurry containing such silicon carbide is deteriorated. Therefore, the lithium ion secondary battery using the carbon- , The initial charge / discharge characteristics and cycle characteristics of the negative electrode active material.

Therefore, 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, and have reached 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. In addition, the negative electrode active material particles include at least one salt selected from a salt of polyacrylic acid and a salt of carboxymethylcellulose. Further, the negative electrode active material particles include a metal salt containing at least one metal selected from Mg and Al.

Since the negative electrode active material includes negative electrode active material particles (also referred to as silicon-based active material particles) containing silicon compound particles, the battery capacity can be improved. Further, when the silicon compound particles contain a Li compound, the irreversible capacity generated upon charging can be reduced. As a result, the efficiency and cycle characteristics of the battery can be improved at the first time. Further, since the negative electrode active material particles include both the at least one salt selected from a salt of polyacrylic acid and a salt of carboxymethyl cellulose and the metal salt including at least one metal selected from Mg and Al, The elution of Li ions from the Li compound in the negative electrode active material particles is suppressed at the time of manufacturing the slurry in which the negative electrode active material or the like is dispersed (aqueous negative electrode slurry), and the stability of the aqueous negative electrode slurry is improved. The stability of the aqueous negative electrode slurry is not improved even when the negative electrode active material particles contain at least one salt selected from a salt of polyacrylic acid and a salt of carboxymethyl cellulose alone. Further, even if the negative electrode active material particles contain at least one kind of metal salt alone, the effect of improving the stability of the aqueous negative electrode slurry is small.

&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. In addition, 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 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 collector is improved. Particularly, in the case where the current collector has an active material layer that expands upon charging, if the current collector contains the element, deformation of the electrode including the current collector is suppressed. The content of the containing 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.

In addition, the surface of the negative electrode collector 11 may be roughened or not coarsened. The harmonized anode current collector is, for example, a metal foil subjected to an electrolytic treatment, an embossing treatment or a chemical etching treatment. The non-harmonized 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 absorbing and desorbing 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 designing . 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, glass-like 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 ratio of the mass of the silicon-based negative electrode active material to the total mass of the silicon-based negative electrode active material and the carbon-based active material is 6 mass% or more, it is possible to reliably improve the battery capacity.

In addition, as described above, the negative electrode active material of the present invention includes silicon compound particles, and the silicon compound particles are silicon oxide materials containing silicon compounds (SiO _x : 0.5? _X? 1.6) Is preferable. This is because a high cycle characteristic is obtained. The composition of the silicon compound in the present invention does not always mean a purity of 100% but may contain a trace amount of 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, among the silicon compounds, SiO ₂ which is destabilized by insertion and desorption of lithium at the time of charging / Since the component portion is previously modified with another lithium silicate, the irreversible capacity generated at the time of charging can be reduced.

Further, 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 improves the battery characteristics. 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 μL of 4 mm HR-MAS rotor,

· Sample rotation speed: 10 kHz,

· Measuring environment Temperature: 25 ℃.

As described above, the negative electrode active material of the present invention is characterized in that the negative electrode active material particle contains at least one salt selected from a salt of polyacrylic acid and a salt of carboxymethylcellulose, and further contains at least one kind selected from Mg and Al Of the metal salt. At this time, in the negative electrode active material of the present invention, the total amount of at least one salt selected from a salt of polyacrylic acid and a salt of carboxymethyl cellulose is in the range of 0.1 mass% to 5 mass% with respect to the total amount of negative electrode active material particles desirable. For example, when the negative electrode active material particles contain two or more kinds of salts selected from a salt of polyacrylic acid and a salt of carboxymethylcellulose, the total mass of the two or more kinds of salts is preferably 0.1 mass% Or more and 5 mass% or less. When the salt contains only one kind of salt, it is preferable that the mass of the salt is 0.1% by mass or more and 5% by mass or less with respect to the mass of the negative electrode active material particle. Thus, when the total amount of the salt is in the range of 0.1 mass% or more based on the total amount of the negative electrode active material particles, the elution of Li ions from the Li compound in the negative electrode active material particles is sufficiently suppressed, and the stability of the aqueous negative electrode slurry is further improved. If the total amount of the salt is 5% by mass or less based on the total amount of the negative electrode active material particles, the battery capacity is not lowered.

Further, in the negative electrode active material of the present invention, the total amount of the metal salt containing at least one metal selected from Mg and Al is contained in the range of 0.1 mass% to 5 mass% with respect to the total amount of the negative electrode active material particles desirable. When the negative electrode active material particles include two or more metal salts containing at least one metal selected from Mg and Al, the total mass of the two or more metal salts is preferably 0.1 By mass to 5% by mass or less. When only one kind of metal salt is contained, it is preferable that the mass of the metal salt is 0.1% by mass or more and 5% by mass or less with respect to the mass of the negative electrode active material particles. As described above, the total amount of the metal salt is in the range of 0.1 mass% or more based on the total amount of the negative electrode active material particles, whereby the elution of Li ions from the Li compound in the negative electrode active material particles is more sufficiently suppressed and the stability of the aqueous negative electrode slurry is further improved . If the total amount of the metal salt is in the range of 5 mass% or less based on the total amount of the negative electrode active material particles, the battery capacity is not lowered.

Particularly, in the present invention, the total content of at least one salt selected from salts of polyacrylic acid and salts of carboxymethyl cellulose contained in the negative electrode active material particles is selected from Mg and Al contained in the negative electrode active material particles Is preferably smaller than the sum of the content based on the mass of the metal salt containing at least one kind of metal. The stability of the aqueous negative electrode slurry is further improved by containing the metal salt more than the salt of polyacrylic acid or the like.

(CMC-NH ₄ ), a lithium salt of polyacrylic acid (PAA-Li) and an ammonium salt of polyacrylic acid (PAA-NH ₄ ) as a salt of polyacrylic acid or carboxymethylcellulose, And the like can be selected. Among them, it is particularly preferable that the salt of polyacrylic acid or the salt of carboxymethylcellulose is an ammonium salt. This is because the stability of the aqueous negative electrode slurry can be further improved.

In the present invention, the metal salt containing at least one kind of metal selected from Mg and Al is preferably a nitrate salt, a phosphate salt, a hydrochloride salt or a sulfate salt. This is because the stability of the water-based negative electrode slurry can be further improved by including such a component. More specifically, as the metal salt comprises a metal of at least one kind selected from Mg, _{Al, Mg (NO 3) 2} , MgCl 2, MgSO 4, Mg 3 (PO 4) 2, AlCl 3, Al (NO 3 ) ₃ , AlPO ₄ , and the like can be selected.

The salt of polyacrylic acid or salt of carboxymethyl cellulose and the metal salt containing at least one kind of metal selected from Mg and Al are preferably those which are weakly alkaline. When a weakly alkaline salt is used, Li is less liable to elute from Li silicate than when an acidic salt is used.

The silicon compound particle has a half-width (2?) Of a diffraction peak attributable to the Si (111) crystal plane obtained by X-ray diffraction using a Cu-K? Ray of 1.2 占 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, and in particular, when the amount of Si crystals present is small, the battery characteristics can be improved and a more stable Li compound can be produced.

In addition, the negative electrode active material of the present invention, the silicon compound particles in the ²⁹ Si-MAS-NMR spectrum obtained from a chemical shift value as a value A and a maximum peak intensity of Si and Li silicate area imparted from -60 to -95ppm, chemical It is preferable that the peak intensity value B of the SiO ₂ region given as the shift value at -96 to -150 ppm satisfies the relation A> B. If the amount of the silicon component or Li ₂ SiO ₃ is relatively large in the case of the silicon compound particle based on the SiO ₂ component, the effect of improving the battery characteristics by inserting Li can be 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 μm or more and 15 μm or less. When the median diameter is within the above range, the lithium ion is likely to be occluded and released during charging and discharging, and the particles are less likely to break. If the median diameter is 3 mu m 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 particles include 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 of 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 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, 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). This magnification is preferably a magnification capable of confirming the thickness of the carbon material by 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 a wide random range without focusing on a specific place as much as possible. Finally, the average value of the thicknesses of the carbon materials 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. Then, Li is inserted into the silicon compound particles to contain a Li compound. Thus, negative electrode active material particles are produced. Subsequently, the negative electrode active material particles thus prepared contain at least one salt selected from a salt of polyacrylic acid and a salt of carboxymethyl cellulose, and a metal salt containing at least one metal selected from Mg and Al. Then, the negative electrode active material is produced by using the negative electrode active material particles.

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. Subsequently, in a state where the temperature in the reaction furnace is lowered to 100 占 폚 or lower, sediments of silicon oxide are taken out 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. A pyrolytic CVD method is preferred as a method for producing a layer of carbon material. A method of producing a carbon material layer by thermal decomposition CVD will be described.

First, the silicon compound particles are set in a furnace. Subsequently, a hydrocarbon gas is introduced into the furnace, and the furnace temperature is raised. The decomposition temperature is not particularly limited, but is preferably 1200 ° C or lower, and more preferably 950 ° C or lower. When the decomposition temperature is 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 to be a 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.

Then, 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 insertion of Li is preferably carried out by the redox method.

In the modification by the oxidation-reduction method, lithium can be inserted, for example, by immersing the silicon active material particle in the solution A in which the lithium is dissolved in the 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 particles 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 desirably 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 may 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 or Li and heating them under a non-oxidizing atmosphere. As the non-oxidizing atmosphere, for example, an Ar atmosphere or the like can be used. More specifically, firstly, LiH powder or Li powder and silicon oxide powder are sufficiently mixed in an Ar atmosphere, followed by sealing, and stirring is performed for each sealed container. Thereafter, the reforming is performed by heating at a temperature in the range of 700 ° C 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 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, over -80 to -100 ppm of Li ₂ SiO ₃ , Li ₄ SiO ₄ In some cases, a peak of Li silicate is present.

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 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 some cases, Li silicate peaks other than Li ₂ SiO ₃ and Li ₄ SiO ₄ are present over -80 to -100 ppm. In addition, the peak of Li ₄ SiO ₄ can be confirmed from the XPS spectrum.

Subsequently, the negative electrode active material particles thus prepared contain at least one salt selected from a salt of polyacrylic acid and a salt of carboxymethyl cellulose, and a metal salt containing at least one metal selected from Mg and Al. In order to incorporate these salts in the negative electrode active material particles, the following method can be used.

For example, the following wet mixing method can be used. In the wet mixing method, a solution obtained by dispersing at least one salt selected from a salt of polyacrylic acid and a salt of carboxymethyl cellulose and a metal salt containing at least one metal selected from Mg and Al is dispersed on the surface of the negative electrode active material particle The salt may be included on the surface of the negative electrode active material particles by spraying and drying the negative electrode active material particles after spraying.

More specifically, for example, an aqueous solution in which a salt of polyacrylic acid and aluminum phosphate are dispersed in a water solvent may be sprayed onto the negative electrode active material particles to dry the negative electrode active material particles. The salt of the polyacrylic acid is dissolved in the water solvent, but since the aluminum phosphate is not dissolved, exchange of the cation or anion rarely occurs between these salts in the aqueous solvent. Therefore, when dispersed in a solvent, the concentration of each salt in the negative electrode active material particles can be adjusted by adjusting the mass of each salt according to the mass of the negative electrode active material particles. In addition, an organic solvent such as ethanol in which a salt of carboxymethyl cellulose and a metal salt are dispersed may be sprayed on the negative electrode active material particles to dry the negative electrode active material particles.

In addition to the above wet mixing method, a dry mixing method may also be used. In this case, by using a known treatment device (Hosokawa Micronobilta (R) NOB, Hosokawa Micron Nauta Mixer (R) DBX, etc.), at least an anode active material particle, a salt of polyacrylic acid and a salt of carboxymethylcellulose One kind of salt and a metal salt containing at least one metal selected from Mg and Al may be dry mixed to adhere each of the salts to the surface of the negative electrode active material 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 hot press or the like may be carried out 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 laminated film type lithium ion secondary cell 20 shown in Fig. 4 is one in which the wound electrode body 21 is housed in the sheet-like sheathing 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 provided on the positive electrode, and the negative electrode lead 23 is provided on the negative electrode. The outermost peripheral portion of the electrode body is protected by a protective tape.

For example, the government pole lead is led out from the inside of the exterior member 25 to the outside in one direction. 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 a laminate film in which, for example, a fusing layer, a metal layer, and a surface protective layer are laminated in this order. The laminate 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 of positive electrode materials capable of lithium ion storage and extraction, and may contain other materials such as a binder, a conductive auxiliary agent, and a dispersant depending on the design. In this case, details of the binder and the conductive auxiliary agent are the same as those of the negative electrode binder and the negative electrode conductive auxiliary agent described above.

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 these positive electrode materials, a compound having at least one of nickel, iron, manganese, and cobalt is preferable. These are represented by, for example, Li _x M ₁ O ₂ or Li _y M ₂ PO ₄ . In the formulas, M1 and M2 represent at least one kind of transition metal element. The values of x and y represent different values depending on the charge / discharge state of the battery, but generally 0.05? x? 1.10 and 0.05? y? 1.10.

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 the above-described negative electrode 10 for a lithium ion secondary battery of FIG. 1, and has, for example, a negative electrode active material layer 12 on both sides of the current collector 11. 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 where the opposite positive electrode active material layer does not exist. This is for carrying out a stable battery design.

In a non-opposing region, that is, a 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 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 investigate the composition and the like with high 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 separates the positive electrode and the negative electrode, and allows lithium ions to pass therethrough while preventing a current short circuit accompanying the positive electrode contact. 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. As the synthetic resin, for example, polytetrafluoroethylene, polypropylene, polyethylene and the like can be given.

[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 these, 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 and discharging, particularly charging. Here, the halogenated chain carbonic 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 a film of better quality than other halogens is formed. Also, the larger the number of halogen atoms, the better. This is because the obtained coating 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 electrolyte 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.

It is also preferable that the solvent 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 include 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 form 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 operation procedure as that for the above-mentioned negative electrode for lithium ion secondary battery 10, to produce a negative electrode.

When the positive electrode and the negative electrode are fabricated, 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 of the electrode may be deviated from any electrode (see Fig. 1).

Subsequently, the electrolyte is adjusted. Subsequently, the positive electrode lead 22 is provided on the positive electrode current collector by ultrasonic welding or the like, and the negative electrode lead 23 is provided on the negative electrode current collector. Subsequently, the positive electrode and the negative electrode are laminated or wound with a separator interposed therebetween to prepare the wound electrode body 21, and a protective tape is bonded to the outermost periphery thereof. Then, a winding 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 portions of the sheathing member are adhered to each other by the heat welding method, and only the one direction is released and the wound electrode body is sealed . An adhesive film is inserted between the positive electrode lead and the negative electrode lead and the sheathing 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 manner, the 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)

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

First, a positive electrode was prepared. 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) Respectively. Subsequently, the positive electrode mixture was dispersed in an organic solvent (N-methyl-2-pyrrolidone: NMP) to obtain a paste-like slurry. Subsequently, 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 prepared. 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 reactor and vaporized in an atmosphere of 10 Pa in a vacuum degree was deposited on the adsorption plate. After cooling sufficiently, the deposit was taken out and pulverized by a ball mill. The x value of SiO _x of the silicon compound particles thus obtained was 0.5. Subsequently, the particle diameter of the silicon compound particles was adjusted by classification. Thereafter, thermal decomposition CVD was carried out to cover the surface of the silicon compound particles with a carbon material.

Subsequently, lithium compounds were inserted into the silicon compound particles coated with the carbon coating (negative electrode active material particles) by the redox 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 naphthalene as an aromatic compound 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 fraction of 10 mass% to the mixture 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 filtered out. Through the above process, lithium was inserted into the negative electrode active material particles.

Subsequently, the obtained silicon compound particles were subjected to heat treatment at 600 캜 for 24 hours under an argon atmosphere to stabilize the Li compound.

Subsequently, the negative electrode active material particles were dried by spraying ethanol with carbon monoxide (CMC-NH ₄ ) and aluminum phosphate (AlPO ₄ ) dispersed in the negative electrode active material particles. The content of CMC-NH _{4 in} the negative electrode active material particles was 1% by mass and the content of AlPO ₄ was 2% by mass.

Subsequently, the negative electrode active material particles (silicon based negative electrode active material) for negative electrode and the carbonaceous active material were mixed at 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 at a mass ratio of 5: 5 were used. The median diameter of the carbon-based active material was 20 占 퐉.

Subsequently, 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), styrene butadiene rubber (styrene butadiene copolymer, hereinafter referred to as SBR) Cellulose (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 secondary battery production and stored at 20 占 폚 to generate gas Were 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, 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. The end of the wound 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 sheathing members, the outer circumferential edges excluding one side were thermally fused, and the electrode bodies were housed inside. An aluminum laminated film in which a nylon film, an aluminum foil and a polypropylene film were laminated was used as the exterior member. Subsequently, the electrolytic solution adjusted from the opening was injected, impregnated in a vacuum atmosphere, sealed by heat sealing.

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

Cycle characteristics were examined as follows. First, charging and discharging were carried out at 0.2 C under an atmosphere of 25 캜 for battery stabilization, and the discharge capacity at the second cycle was measured. Subsequently, charge and discharge 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. Charging and discharging were carried out at a normal cycle, that is, from the third 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 are investigated for the first time, the first efficiency (hereinafter also referred to as the initial efficiency) is calculated. 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 amount was adjusted by changing the ratio of the metal silicon 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 attributed 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 chemical shift values obtained from ²⁹ Si-MAS-NMR spectra 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 given by &quot; A &quot;

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 out of the range of 0.5? X? 1.6, the battery characteristics deteriorated. For example, as shown in Comparative Example 1-1, when oxygen is insufficient (x = 0.3), the efficiency is improved first, but the capacity retention rate is markedly deteriorated. On the other hand, as shown in Comparative Example 1-2, in the case where the amount of oxygen was large (x = 1.8), the conductivity was lowered and the silicon oxide capacity was not substantially developed. In Examples 1-1 to 1-3, the time until the generation of the gas was two days or more, and the stability of the aqueous negative electrode slurry was high. In Comparative Example 1-2, no measurement of the time until gas generation was performed.

(Examples 2-1 to 2-2)

A secondary battery was manufactured under the same conditions as in Example 1-2 except that the kind of lithium silicate contained in the silicon compound particles was changed as shown in Table 2, and the cycle characteristics, the initial efficiency and the stability of the aqueous negative electrode slurry were evaluated Respectively.

(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 first 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 ratio and the initial efficiency were improved to a high balance. In particular, when two types of lithium silicate are included, the capacity retention ratio and the initial efficiency are improved to a higher balance. Further, in Examples 1-2, 2-1, and 2-2, the time until the generation of the gas was one day or longer, and the stability of the water-based negative electrode slurry was obtained. On the other hand, as in Comparative Example 2-1, when the silicon compound particles did not contain a Li compound, no gas was generated, but the initial efficiency remarkably decreased.

(Examples 3-1 to 3-38)

A secondary battery was produced under the same conditions as in Example 1-2 except that the content of salt of carboxymethyl cellulose (CMC), the kind of the metal salt and the content of the metal salt were changed as shown in Table 3, and the cycle characteristics, The stability of the aqueous negative electrode slurry was evaluated.

Table 3 shows the results of Examples 3-1 to 3-38.

As can be seen from Table 3, when both the salt of carboxymethylcellulose and the metal salt containing Mg or Al are contained in the negative electrode active material particles, the time until the generation of gas becomes high, and the stability of the aqueous negative electrode slurry . Further, when the content of the salt of carboxymethylcellulose and the content of the metal salt containing Mg or Al were 0.1% by mass or more, the stability of the water-based negative electrode slurry was obtained. Further, as in Examples 3-10 to 3-14, in Examples 3-1 to 3-4, 3-15 to 3-26, and 3-3, as compared with the Examples in which the content of the salt of metal is lower than that of the salt of carboxymethylcellulose, 35 to 3-38, the time until the generation of the gas was further increased in the Examples in which the content of the metal salt was larger than the content of the salts of the carboxymethylcellulose.

(Examples 3-39 to 3-43)

A secondary battery was produced under the same conditions as in Example 1-2 except that carboxymethylcellulose was changed to a salt of polyacrylic acid (PAA), and the kind of the metal salt and the content of the metal salt were changed as shown in Table 4, , The initial efficiency and the stability of the aqueous negative electrode slurry were evaluated.

Table 4 shows the results of Examples 3-39 to 3-43. In the table, &quot; PAA-NH4 &quot; means an ammonium salt of polyacrylic acid.

As can be seen from Table 4, in the case where both the salt of polyacrylic acid and the metal salt containing Mg or Al are included in the negative electrode active material particles as in the case of using the salt of carboxymethyl cellulose, And the stability of the aqueous negative electrode slurry was improved.

(Comparative Example 3-1)

After modification of the negative electrode active material particles, the same operations as in Example 1-2 were carried out except that the salt of polyacrylic acid, the salt of carboxymethylcellulose, the metal salt containing Mg, and the metal salt containing Al were not contained in the negative electrode active material particles , And the cycle characteristics, the initial efficiency, and the stability of the aqueous negative electrode slurry were evaluated.

(Comparative Examples 3-2 to 3-7)

A secondary battery was fabricated under the same conditions as in Example 1-2 except that the negative electrode active material particles were not contained in the negative electrode active material particle only after the salt of polyacrylic acid or carboxymethylcellulose was modified after the modification of the negative electrode active material particles, , The initial efficiency and the stability of the aqueous negative electrode slurry were evaluated.

(Comparative Examples 3-8 to 3-14)

A secondary battery was fabricated under the same conditions as in Example 1-2 except that the salt of polyacrylic acid or the salt of carboxymethylcellulose was not contained in the negative electrode active material particles after the modification of the negative electrode active material particles and only the metal salt was contained, , The initial efficiency and the stability of the aqueous negative electrode slurry were evaluated.

The results of Comparative Examples 3-1 to 3-14 are shown in Table 5. In Table 5, &quot; PAA-Li &quot; means a lithium salt of polyacrylic acid.

As can be seen from Comparative Examples 3-2 to 3-7, when only the salt of polyacrylic acid or the salt of carboxymethylcellulose was contained in the negative electrode active material particles, the time until the generation of gas became the same as in Comparative Example 3-1 , The effect of improving the stability of the slurry was not obtained. Further, when only the metal salt is contained in the negative electrode active material particles, the time until the generation of the gas is increased as compared with Comparative Examples 3-1 to 3-7, but the results are shown in the examples shown in Tables 3 and 4.

(Example 4-1)

Except that a method of containing a salt of polyacrylic acid or a salt of carboxymethyl cellulose and a metal salt in the negative electrode active material particles was changed from a wet mixing method to a dry mixing method using Hosokawa Micronobiltar (R) NOB, -2, and the cycle characteristics, the initial efficiency, and the stability of the aqueous negative electrode slurry were evaluated. Concretely, 1 g of CMC-NH ₄ and 2 g of AlPO ₄ were added to 100 g of the negative electrode active material particles, and a treatment using a novilla rust was performed for 30 seconds.

(Example 4-2)

A negative electrode active material particle was prepared in the same manner as in Example 1 except that the method of containing a salt of polyacrylic acid or a salt of carboxymethylcellulose and a metal salt was changed from a wet mixing method to a dry mixing method using a Hosokawa Micron Nauta Mixer (R) -2, and the cycle characteristics, the initial efficiency, and the stability of the aqueous negative electrode slurry were evaluated. Concretely, 1 g of CMC-NH ₄ and 2 g of AlPO ₄ were added to 100 g of the negative electrode active material particles, and mixing was performed for 1 hour using a Nauta mixer.

The results of Examples 4-1 to 4-2 are shown in Table 6.

In the case of using the dry mixing method, the time until the generation of the gas was further increased as compared with the case of using the wet mixing method.

(Examples 5-1 to 5-9)

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 7, 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 5-9, the full width at half maximum was calculated to be 20 DEG or more, but the results were obtained by fitting using analysis software, and substantially no peak was obtained. Therefore, the silicon compounds of Examples 5-9 can be said to be substantially amorphous.

In particular, high initial efficiency and capacity retention rate were 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 a Si (111) face.

(Example 6-1)

The secondary battery was manufactured under the same conditions as in Example 1-2 except that the relationship between the maximum peak strength value A of the Si and Li silicate regions and the peak strength value B derived from the SiO ₂ region was A & And the cycle characteristics, the initial efficiency and the stability of the aqueous 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 was reduced, and the intensity A of the peak derived from Li ₂ SiO ₃ was reduced.

As can be seen from Table 8, the battery characteristics were improved when the relationship of peak intensity was A> B.

(Examples 7-1 to 7-6)

A secondary battery was manufactured 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 9, 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 made small. 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. When the median diameter of the silicon-based active material particle is 15 mu m or less, the amount of expansion of the silicon compound particles at the time of filling is not increased, so physical and electrical destruction of the negative electrode active material layer due to expansion can be prevented.

(Examples 8-1 to 8-4)

A secondary battery was fabricated 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 as shown in Table 10, and the cycle characteristics, the initial efficiency and the stability of the aqueous negative electrode slurry . The average thickness of the carbonaceous material can be adjusted by changing the CVD conditions.

As can be seen from Table 10, since the conductivity is improved when the thickness of the carbon layer is 5 nm or more, 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 is not lowered.

(Example 9-1)

A secondary battery was manufactured under the same conditions as in Example 1-2 except that the ratio of the mass of the silicon-based active material particles in the negative electrode active material was changed, and the rate of increase 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 in Fig. 5 shows the rate of increase of the battery capacity when the ratio of the silicon compound particles in the negative electrode active material of the present invention is increased. On the other hand, the graph shown by B in Fig. 5 shows the rate of increase of the battery capacity when the proportion of the silicon compound particles not doped with Li is increased. As can be seen from Fig. 5, when the proportion of the silicon compound is 6 mass% or more, the rate of increase of the battery capacity becomes larger than that of the prior art, and the volume energy density increases particularly remarkably.

The present invention is not limited to the above-described embodiments. The above embodiment is an example, and anything that has substantially the same structure as the technical idea described in the claims of the present invention and exhibits the same operational effects is included in the technical scope of the present invention.

Claims (14)

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 (SiO _x : 0.5? _X? 1.6)
Wherein the silicon compound particles contain a Li compound,
Characterized in that the negative electrode active material particles comprise at least one salt selected from a salt of polyacrylic acid and a salt of carboxymethylcellulose and a metal salt containing at least one metal selected from Mg and Al Active material. The positive electrode active material according to claim 1, wherein the total amount of at least one salt selected from the salt of polyacrylic acid and the salt of carboxymethyl cellulose is in a range of 0.1 mass% to 5 mass% with respect to the total amount of the negative electrode active material particles As a negative active material. The negative electrode active material according to claim 1 or 2, wherein the at least one salt selected from the salt of polyacrylic acid and the salt of carboxymethyl cellulose is an ammonium salt. The negative electrode active material according to any one of claims 1 to 3, wherein the total amount of the metal salt containing at least one metal selected from Mg and Al is 0.1% by mass or more and 5% by mass or less Lt; RTI ID = 0.0 &gt;%. &Lt; / RTI &gt; The negative electrode active material according to any one of claims 1 to 4, wherein the metal salt containing at least one metal selected from Mg and Al is at least one of nitrate, phosphate, hydrochloride and sulfate. The negative electrode active material composition according to any one of claims 1 to 5, wherein the sum of the content of at least one salt selected from the salt of polyacrylic acid and the salt of carboxymethyl cellulose contained in the negative electrode active material particle, Wherein the total amount of the negative electrode active material particles and the negative electrode active material particles is smaller than the total amount of the metal salt containing at least one metal selected from the group consisting of Mg and Al contained in the negative electrode active material on a mass basis. The lithium _secondary battery according to any one of claims 1 to 6, 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. The method according to any one of claims 1 to 7, wherein the silicon compound particle has a half-width (2?) Of a diffraction peak attributable 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. 9. The method according to any one of claims 1 to 8, wherein in the silicon compound particles, the maximum of the Si and Li silicate regions, which are obtained from the ²⁹ Si-MAS-NMR spectrum and are given at -60 to -95 ppm as the chemical shift value Wherein the peak intensity value A and the peak intensity value B of the SiO ₂ region imparted at -96 to -150 ppm as the chemical shift value satisfy a relation of A > B. 10. The negative electrode active material according to any one of claims 1 to 9, wherein the negative electrode active material particles have a median diameter of 3 mu m or more and 15 mu m or less. 11. The negative electrode active material according to any one of claims 1 to 10, wherein the negative electrode active material particle contains a carbon material in a surface layer portion. 12. The negative electrode active material according to claim 11, wherein the carbonaceous material has an average thickness of 5 nm or more and 5,000 nm or less. A mixed negative electrode active material material comprising the negative electrode active material according to any one of claims 1 to 12 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)
In the step of inserting Li into the silicon compound particles to contain a Li compound
The negative electrode active material particles were produced by the above-
And a step of incorporating into the negative electrode active material particles a metal salt containing at least one salt selected from a salt of polyacrylic acid and a salt of carboxymethyl cellulose and at least one metal selected from Mg and Al,
The negative electrode active material containing the metal salt containing at least one salt selected from the salt of polyacrylic acid and the salt of carboxymethyl cellulose and the metal salt containing at least one metal selected from Mg and Al, Wherein the negative electrode active material is produced by a method comprising the steps of:

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