KR102335474B1 - Negative electrode active material, mixed negative electrode active material material, and manufacturing method of negative electrode active material - Google Patents

Abstract

The present invention is a negative electrode active material comprising negative electrode active material particles, wherein the negative electrode active material particles _{contain a silicon compound particle containing a silicon compound (SiO x} : 0.5≤x≤1.6), the silicon compound particle contains a Li compound, It is a negative electrode active material characterized by containing Al element and Na element as a constituent element of a negative electrode active material particle, and the mass ratio M _Na /M _Al of Al element and Na element satisfy|fills following formula (1). Thereby, the slurry produced at the time of preparation of the negative electrode of a secondary battery can be stabilized, and when used as a negative electrode active material of a secondary battery, the negative electrode active material which can improve initial stage charging/discharging characteristic and cycling characteristics is provided. <Formula 1> 0.022≤M _Na /M _Al ≤61

Description

Negative electrode active material, mixed negative electrode active material material, and manufacturing method of negative electrode active material

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

BACKGROUND ART In recent years, small electronic devices typified by mobile terminals and the like have been widely used, and further miniaturization, weight reduction and longer lifespan are strongly demanded. In response to such a market demand, development of a secondary battery that is particularly small, lightweight, and capable of obtaining a high energy density is in progress. This secondary battery is not limited to small electronic devices, and application to large electronic devices typified by automobiles and power storage systems typified by houses and the like is also being studied.

Especially, since a lithium ion secondary battery is small and it is easy to perform high capacity|capacitance, and also higher energy density than a lead battery and a nickel-cadmium battery is obtained, it is highly anticipated.

The said lithium ion secondary battery is equipped with electrolyte solution with a positive electrode, a negative electrode, and a separator, The negative electrode contains the negative electrode active material concerning charge/discharge reaction.

As this negative electrode active material, while a carbon-based active material is widely used, the further improvement of battery capacity is calculated|required from the recent market demand. The use of silicon as a negative electrode active material for improving battery capacity has been studied. This is because, since the theoretical capacity of silicon (4199 mAh/g) is 10 times or more larger than that of graphite (372 mAh/g), a significant improvement in battery capacity can be expected. The development of a silicon material as a negative electrode active material has been studied not only for a single silicon but also for an alloy, a compound represented by an oxide, and the like. In addition, the shape of the active material is studied from a standard coating type to an integrated type directly deposited on the current collector for a carbon-based active material.

However, when silicon is used as the main raw material as the negative electrode active material, the negative electrode active material expands and contracts during charging and discharging, so that it becomes brittle mainly in the vicinity of the surface layer of the negative electrode active material. In addition, an ionic material is generated inside the active material, and the negative electrode active material becomes a fragile material. When the surface layer of the negative electrode active material is broken, a new surface is formed thereby, and the reaction area of the active material is increased. At this time, since a decomposition reaction of the electrolyte occurs on the new surface and a film that is a decomposition product of the electrolyte is formed on the new surface, the electrolyte is consumed. For this reason, cycling characteristics fall easily.

Until now, in order to improve battery initial stage efficiency and cycle characteristics, various examinations are made about the negative electrode material for lithium ion secondary batteries which mainly made a silicon material, and electrode structure.

Specifically, silicon and amorphous silicon dioxide are simultaneously deposited using a vapor phase method for the purpose of obtaining good cycle characteristics and high safety (for example, refer to Patent Document 1). Moreover, in order to acquire high battery capacity and safety|security, the carbon material (electron conductive material) is provided in the surface layer of a silicon oxide particle (refer patent document 2, for example). In addition, in order to improve cycle characteristics and obtain high input/output characteristics, an active material containing silicon and oxygen is prepared, and an active material layer having a high oxygen ratio in the vicinity of the current collector is formed (for example, Patent Document 3) Reference). Moreover, in order to improve cycling characteristics, oxygen is made to contain in a silicon active material, and it forms so that an average oxygen content may be 40 at% or less, and the oxygen content may increase in a place close to an electrical power collector (for example, refer patent document 4).

Further, the first time and using the Si phase, the nanocomposite containing SiO _2, M _y O metal oxide in order to improve the charge-discharge efficiency (see, for example Patent Document 5). Further, in order to improve cycle characteristics, SiO _x (0.8≤x≤1.5, particle size range = 1 µm to 50 µm) and carbon material are mixed and fired at a high temperature (see, for example, Patent Document 6). In order to improve cycle characteristics, the molar ratio of oxygen to silicon in the negative electrode active material is 0.1 to 1.2, and the difference between the maximum and minimum molar ratios in the vicinity of the interface between the active material and the current collector is 0.4 or less. is controlled (see, for example, Patent Document 7). Moreover, in order to improve battery load characteristics, the metal oxide containing lithium is used (for example, refer patent document 8). Moreover, in order to improve cycling characteristics, hydrophobic layers, such as a silane compound, are formed in the silicon material surface layer (for example, refer patent document 9). Moreover, for the improvement of cycling characteristics, electroconductivity is provided by using silicon oxide and forming a graphite film in the surface layer (for example, refer patent document 10). In the Patent Document 10, with respect to the shift value obtained from the RAMAN spectrum of the graphite film, and 1330㎝ ^{-1 -1} 1580㎝ with a broad peak is indicated on, and their intensity ratio _{I 1330 / I 1580 1.5 <I} 1330 /I ₁₅₈₀ <3. Moreover, for the improvement of high battery capacity and cycling characteristics, the particle|grains which have the silicon microcrystal phase disperse|distributed in silicon dioxide are used (for example, refer patent document 11). Moreover, in order to improve overcharge and overdischarge characteristics, the silicon oxide which controlled the atomic ratio of silicon and oxygen to 1:y (0<y<2) is used (refer patent document 12, for example).

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

As described above, in recent years, small-sized electronic devices, such as mobile terminals, have progressed in performance and multifunctionality, and lithium ion secondary batteries, which are main power sources thereof, are required to increase battery capacity. As one method of solving this problem, development of a lithium ion secondary battery including a negative electrode using a silicon material as a main material is desired. In addition, when a silicon material is used, high initial efficiency and capacity retention can be obtained by using a silicon material doped with Li. On the other hand, on the other hand, the silicon material doped with Li has low stability to an aqueous solvent, and when manufacturing a negative electrode Since the stability of the aqueous negative electrode slurry mixed with the silicon material to be produced will fall, it is industrially unsuitable.

The present invention has been made in view of the above problems, it is possible to stabilize the slurry produced during the production of the negative electrode of the secondary battery, and when used as the negative electrode active material of the secondary battery, improving the initial charge/discharge characteristics and cycle characteristics It aims to provide a possible negative electrode active material, and a mixed negative electrode active material material containing this negative electrode active material. Another object of the present invention is to provide a method for producing a negative electrode active material capable of stabilizing the slurry produced during negative electrode production and improving initial charge/discharge characteristics and cycle characteristics.

In order to achieve the above object, the present invention is a negative electrode active material comprising negative electrode active material particles, wherein the negative electrode active material particles contain a silicon compound particle including a silicon compound _{(SiO x: 0.5≤x≤1.6), the silicon} The compound particles contain a Li compound, and contain an Al element and an Na element as constituent elements of the negative electrode active material particle, and the mass ratio M _Na /M _Al of the Al element and the Na element is expressed by the following formula 1 It provides a negative electrode active material, characterized in that it is satisfied.

<Formula 1> 0.022≤M _Na /M _Al ≤61

Since the negative electrode active material of the present invention contains negative electrode active material particles (also referred to as silicon-based active material particles) containing silicon compound particles, battery capacity can be improved. In addition, when the silicon compound particles contain the Li compound, the irreversible capacity generated during charging can be reduced. Thereby, the initial efficiency and cycle characteristics of a battery can be improved. In addition, in the preparation of a slurry (aqueous negative electrode slurry) in which a negative electrode active material or the like is dispersed in an aqueous solvent by including an Al element and a Na element in the same balance as _{the mass ratio M Na} /M _{Al of Formula 1, Li in the negative electrode active material particles} The elution of Li ions from the compound is suppressed, and the stability of the aqueous negative electrode slurry is improved.

At this time, in the negative electrode active material of the present invention _{, it is preferable that the mass ratio M Na} /M _Al further satisfies the following formula (2).

<Formula 2> 0.36≤M _Na /M _Al ≤3.3

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

Moreover, in this case, it is preferable that the said Al element is contained in the range of 0.02 mass % or more and 1.1 mass % or less with respect to the said silicon compound particle in the negative electrode active material of this invention.

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

Moreover, in the negative electrode active material of this invention, it is preferable that Na element is contained in the range of 0.024 mass % or more and 1.22 mass % or less with respect to a silicon compound particle.

Stability of the aqueous negative electrode slurry can be further improved as Na element is contained in 0.024 mass % or more. If the Na element is contained in the range of 1.22 mass % or less, the fall of battery capacity can be prevented.

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

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

Moreover, it is preferable that the molecular weight of the said polyacrylic acid Na is the range of 250,000 or more and 1 million or less.

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

Moreover, when the said polyacrylic acid Na is made into 1% aqueous solution, it is preferable to set it as what becomes the range whose pH is 6 or more and 10 or less.

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

In addition, it is preferable that the negative electrode active material particles 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.}

By including the lithium silicate as described above as the lithium compound, the irreversible capacity generated during charging can be reduced, and the initial efficiency and cycle characteristics of the battery can be improved.

The silicon compound particles have a half width (2θ) of a peak attributable to a Si(111) crystal plane in an X-ray diffraction spectrum using Cu-Kα ray of 1.2° or more, and a crystallite size corresponding to the crystal plane. is preferably 7.5 nm or less.

When a silicon compound particle uses the negative electrode active material which has said silicon crystallinity as a negative electrode active material of a lithium ion secondary battery, more favorable cycling characteristics and initial stage charge/discharge characteristic will be acquired.

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

In the silicon compound particles, based on the SiO ₂ ingredient and as long as more than the amount of Si and Li ₂ SiO _3, the negative electrode active material is the effect of improving the battery characteristics is sufficiently obtained by insertion of Li.

In addition, the negative electrode active material particles preferably have a median diameter of 3 µm or more and 15 µm or less.

When the median diameter of the negative electrode active material particles is 3 µm or more, it is possible to suppress an increase in the battery irreversible capacity due to an increase in the surface area per mass. On the other hand, when the median diameter is 15 µm or less, since the particles are less likely to be broken, it is difficult to form a new surface.

Moreover, it is preferable that the said negative electrode active material particle contains a carbon material in a surface layer part.

In this way, when the negative electrode active material particles contain a carbon material in the surface layer portion, an improvement in conductivity is obtained.

Moreover, it is preferable that the average thickness of the said carbon material is 5 nm or more and 5000 nm or less.

If the average thickness of a carbon material is 5 nm or more, an electroconductive improvement will be acquired. In addition, if the average thickness of the carbon material to be coated is 5000 nm or less, by using the negative electrode active material containing such negative electrode active material particles in a lithium ion secondary battery, a sufficient amount of silicon compound particles can be secured, so that a decrease in battery capacity is suppressed can do.

In addition, in order to achieve the above object, the present invention provides a mixed negative electrode active material comprising the negative electrode active material and the carbon-based active material.

As described above, by including the carbon-based active material together with the negative electrode active material (silicon-based negative electrode active material) of the present invention as a material for forming the negative electrode active material layer, the conductivity of the negative electrode active material layer can be improved and swelling accompanying charging It becomes possible to relieve stress. In addition, the battery capacity can be increased by mixing the silicon-based negative electrode active material with the carbon-based active material.

In addition, in order to achieve the above object, the present invention is a method for producing a negative electrode active material including negative electrode active material particles containing silicon compound particles, silicon compound particles containing a silicon compound (SiO _x : 0.5≤x≤1.6) A negative electrode active material particle is produced by a step of preparing the silicon compound particles and a step of inserting Li into the silicon compound particles to contain the Li compound, and Al and Na elements are added to the negative electrode active material particles, and the mass ratio of the Al element and the Na element A method for producing a negative electrode active material, comprising the step of including M _Na /M _{Al so} that it satisfies the following formula (1), and manufacturing the negative electrode active material using the negative electrode active material particles including the Al element and the Na element provides

<Formula 1> 0.022≤M _Na /M _Al ≤61

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

The negative electrode active material of the present invention can particularly stabilize the aqueous negative electrode slurry produced during negative electrode production, and when used as a negative electrode active material for a secondary battery, good cycle characteristics and initial charge/discharge characteristics can be obtained with a high capacity. Moreover, the same effect is acquired also in the mixed negative electrode active material material containing this negative electrode active material. In addition, according to the method for producing a negative electrode active material of the present invention, the aqueous slurry produced during negative electrode production can be stabilized, and when used as a negative electrode active material for a lithium ion secondary battery, a negative electrode having good cycle characteristics and initial charge/discharge characteristics An active material can be prepared.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows an example of the structure of the negative electrode for nonaqueous electrolyte secondary batteries containing the negative electrode active material of this invention.
^{Fig. 2 is an example of a 29} Si-MAS-NMR spectrum measured from silicon compound particles when reforming is performed by a redox method.
^{Fig. 3 is an example of a 29} Si-MAS-NMR spectrum measured from silicon compound particles when 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 silicon-based active material particles to the total amount of the negative electrode active material and the increase rate of the battery capacity of the secondary battery.

EMBODIMENT OF THE INVENTION Hereinafter, although embodiment is described about this invention, this invention is not limited to this.

As mentioned above, as one method of increasing the battery capacity of a lithium ion secondary battery, the use of the negative electrode which used the silicon material as a main material as a negative electrode of a lithium ion secondary battery is examined. In particular, the silicon material doped with Li has good initial charge/discharge characteristics and cycle characteristics, but there is a problem that the stability of an aqueous negative electrode slurry containing such a silicon material decreases, and lithium ion secondary batteries using a carbon-based active material and It has not been possible to propose a negative electrode active material having equivalent slurry stability, initial charge/discharge characteristics, and cycle characteristics.

Then, the present inventors repeated earnest examination in order to obtain the negative electrode active material which becomes high battery capacity, and slurry stability, cycling characteristics, and the first-time efficiency becomes favorable, when used for a secondary battery, and led to this invention.

The negative electrode active material of the present invention contains negative electrode active material particles. Moreover, this negative electrode active material particle _{contains the silicon compound particle containing a silicon compound (SiOx: 0.5<=x<} =1.6), and this silicon compound particle contains the Li compound. Further, the negative electrode active material of the present invention contains an Al element and a Na element as constituent elements of the negative electrode active material particles, and the mass ratio M _Na /M _Al of the Al element and the Na element satisfies the following formula (1).

<Formula 1> 0.022≤M _Na /M _Al ≤61

Since such a negative electrode active material contains negative electrode active material particles containing silicon compound particles, battery capacity can be improved. In addition, when the silicon compound particles contain the Li compound as described above, the irreversible capacity generated during charging can be reduced. In addition, in the preparation of a slurry (aqueous negative electrode slurry) in which a negative electrode active material or the like is dispersed in an aqueous solvent by including an Al element and a Na element in the same balance as _{the mass ratio M Na} /M _{Al of Formula 1, Li in the negative electrode active material particles} The elution of Li ions from the compound is suppressed, and the stability of the aqueous negative electrode slurry is improved. Moreover, the effect of suppressing the elution of Li ions and improving the stability with respect to an aqueous solvent is low only by including either Al element or Na element.

_{Moreover, it is especially preferable that the said mass ratio M Na} /M _Al in negative electrode active material particle|grains satisfy|fills following formula (2).

<Formula 2> 0.36≤M _Na /M _Al ≤3.3

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

In addition, each mass of Al element and Na element in a negative electrode active material particle can be measured by the measuring method by ICP (Inductively Coupled Plasma).

<Negative electrode for non-aqueous electrolyte secondary battery>

Next, the negative electrode for nonaqueous electrolyte secondary batteries containing the negative electrode active material of this invention is demonstrated. BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows an example of the structure of the negative electrode for nonaqueous electrolyte secondary batteries (henceforth "negative electrode" is also called).

[Configuration of negative electrode]

As shown in FIG. 1 , the negative electrode 10 has a structure including the negative electrode active material layer 12 on the negative electrode current collector 11 . This negative electrode active material layer 12 may be provided only on both surfaces or one surface of the negative electrode current collector 11 . In addition, as long as the negative electrode active material of this invention is used, the negative electrode collector 11 may not be needed.

[Negative electrode current collector]

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

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

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

[Negative electrode active material layer]

The negative electrode active material layer 12 contains the negative electrode active material of the present invention capable of occluding and releasing lithium ions, and may further contain other materials such as a negative electrode binder (binder) and a conductive aid from the viewpoint of battery design. The negative electrode active material includes negative electrode active material particles, and the negative electrode active material particles include silicon compound particles containing a silicon compound _{(SiO x: 0.5≦x≦1.6).}

Moreover, the negative electrode active material layer 12 may contain the mixed negative electrode active material material containing the negative electrode active material of this invention, and a carbon-type active material. Thereby, while the electrical resistance of a negative electrode active material layer falls, it becomes possible to relieve|moderate the expansion stress accompanying charging. As the carbon-based active material, for example, thermally decomposed carbons, cokes, glassy carbon fibers, organic high molecular compound sintered bodies, carbon blacks and the like can be used.

In addition, in the mixed negative electrode active material, it is preferable that the 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) and the carbon-based active material of the present invention is 6% by mass or more. When the mass ratio of the silicon-based negative electrode active material to the total mass of the silicon-based negative electrode active material and the carbon-based active material is 6% by 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 contains silicon compound particles, and the silicon compound particles are a silicon _{oxide material containing a silicon compound (SiO x} : 0.5≤x≤1.6), but the composition thereof is that x is 1 It is preferable to be closer to This is because high cycle characteristics are obtained. In addition, the composition of the silicon compound in this invention does not necessarily mean 100% of purity, and may contain a trace amount of impurity elements.

Further, in the negative electrode active material of the present invention, the silicon compound particles preferably 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 this case, since the SiO 2} component in the silicon compound, which is destabilized during insertion and desorption of lithium during charging and discharging of the battery, was previously modified with a separate lithium silicate, the irreversible capacity generated during charging could be reduced.

_{In addition, the presence of at least one 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 battery characteristics, but coexisting two or more Li compounds results in better battery characteristics. is improved In addition, these lithium silicates can be quantified by NMR (Nuclear Magnetic Resonance) or XPS (X-ray photoelectron spectroscopy: X-ray photoelectron spectroscopy). The measurement of XPS and NMR can be performed under the following conditions, for example.

XPS

Apparatus: X-ray photoelectron spectroscopy device,

·X-ray source: monochromatic Al Kα rays,

·X-ray spot diameter: 100㎛,

·Ar ion total sputtering condition: 0.5kV/2mm×2mm.

²⁹ Si MAS NMR (Magic Angle Rotation Nuclear Magnetic Resonance)

Apparatus: 700 NMR spectrometer manufactured by Bruker,

·Probe: 4mmHR-MAS rotor 50μL,

·Sample rotation speed: 10 kHz,

·Measured environment temperature: 25℃.

In addition, as described above, the negative electrode active material of the present invention contains, as constituent elements of the negative electrode active material particles, the Al element and the Na element so as to satisfy the relationship of formula (1). At this time, it is preferable that Al element is contained in the range of 0.02 mass % or more and 1.1 mass % or less with respect to a silicon compound particle. When the Al element is contained in 0.02 mass % or more with respect to the silicon compound particles, more sufficient slurry stability is obtained, and when the Al element is contained in the range of 1.1 mass % or less with respect to the silicon compound particles, the battery capacity is deterioration can be prevented.

Moreover, it is preferable that Na element is contained in the range of 0.024 mass % or more and 1.22 mass % or less with respect to a silicon compound particle. Moreover, when element Na is contained in 0.024 mass % or more with respect to a silicon compound particle, more sufficient slurry stability is obtained, When element Na is contained in the range of 1.22 mass % or less with respect to a silicon compound particle, battery capacity deterioration can be prevented.

Moreover, it is preferable that the negative electrode active material particle|grains contain polyacrylic acid Na. In this case, since the elution of Li ions from the Li compound in the negative electrode active material particles is more suppressed, the stability of the aqueous negative electrode slurry is further improved.

Moreover, it is preferable that the molecular weight of this polyacrylic acid Na is the range of 250,000 or more and 1 million or less. When the molecular weight includes polyacrylic acid Na in the above range, the stability of the aqueous negative electrode slurry is further improved.

Moreover, when this polyacrylic acid Na is made into 1% aqueous solution, it is preferable to set it as what becomes the range whose pH is 6 or more and 10 or less. When such polyacrylic acid Na is included, the elution of Li ions from the Li compound in the negative electrode active material particles is more suppressed, so that the stability of the aqueous negative electrode slurry is further improved. Moreover, when polyacrylic acid Na is made into 1% aqueous solution, it is especially preferable to set it as the range whose pH is 7 or more and 9 or less. In the case of such weakly alkaline polyacrylic acid Na, it is particularly difficult to elute Li from Li silicate.

In addition, silicon compound particles have a half width (2θ) of a diffraction peak attributable to the Si(111) crystal plane obtained by X-ray diffraction using Cu-Kα rays of 1.2° or more, and the crystallite size corresponding to the crystal plane is It is preferable that it is 7.5 nm or less. This peak appears in the vicinity of 2θ=28.4±0.5° when the crystallinity is high (when the half width is narrow). The lower the silicon crystallinity of the silicon compound in the silicon compound particle, the better. In particular, when there is little Si crystal, the battery characteristics can be improved, and further, a stable Li compound can be produced.

Further, in the negative electrode active material of the present invention, in the silicon compound particles, the maximum peak intensity value A in the Si and Li silicate region provided at -60 to -95 ppm as a chemical shift value obtained from ^{29 Si-MAS-NMR spectrum,} as a chemical shift values -96 to the peak intensity value of the SiO ₂ region B are given in -150ppm, it is preferable to satisfy the relation that a> B. In the silicon compound particle, SiO _{2 If the amount of the silicon component or Li 2} SiO ₃ is relatively large in the case of the component as a reference, the effect of improving the battery characteristics by the insertion of Li is sufficiently obtained. In addition, ^{the measurement conditions of 29} Si-MAS-NMR should just be the same as the above.

In addition, the median diameter of the negative electrode active material particles is preferably (D ₅₀ particle size at which the cumulative volume is 50%) or less than the 15㎛ 3㎛. This is because, while the median diameter is within the above range, lithium ions are easily occluded and released at the time of charging and discharging, and particles are less likely to be broken. When the median diameter is 3 µm or more, the surface area per mass can be made small, and an increase in the battery irreversible capacity can be suppressed. On the other hand, when the median diameter is 15 µm or less, the particles are less likely to be broken, so that a new surface is less likely to come out.

Moreover, in the negative electrode active material of this invention, it is preferable that the negative electrode active material particle|grains contain a carbon material in a surface layer part. When the negative electrode active material particles contain a carbon material in their surface layer portion, since an improvement in conductivity is obtained, when a negative electrode active material containing such negative electrode active material particles is used as a negative electrode active material of a secondary battery, battery characteristics can be improved.

Moreover, it is preferable that the average thickness of the carbon material of the surface layer part of negative electrode active material particle|grains are 5 nm or more and 5000 nm or less. When the average thickness of the carbon material is 5 nm or more, conductivity improvement is obtained, and when the average thickness of the carbon material to be coated is 5000 nm or less, a negative electrode active material containing such negative electrode active material particles is used as a negative electrode active material of a lithium ion secondary battery , a decrease in battery capacity can be suppressed.

The average thickness of this carbon material is computable with the following procedure, for example. First, the negative electrode active material particles are observed at an arbitrary magnification with a TEM (transmission electron microscope). As for this magnification, the magnification which can confirm the thickness of a carbon material visually is preferable so that thickness can be measured. Then, 15 arbitrary points WHEREIN: The thickness of a carbon material is measured. In this case, it is preferable to set the measurement positions at random widely, without concentrating on a specific place as much as possible. Finally, the thickness average value of the 15 points|pieces of the carbon material is computed.

Although the coverage of a carbon material is not specifically limited, The one as high as possible is preferable. If the coverage is 30% or more, it is preferable because the electrical conductivity further improves. Although the coating method of a carbon material is not specifically limited, The sugar carbonization method and the thermal decomposition method of hydrocarbon gas are preferable. This is because the coverage can be improved.

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

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

The negative electrode active material layer is formed, for example, by a coating method. The coating method is a method of dispersing the negative electrode active material particles, the binder, and the like, and, if necessary, a conductive auxiliary agent and a carbon material, and then dispersing them in an organic solvent, water, or the like.

[Method for manufacturing negative electrode]

A negative electrode can be manufactured by the following procedure, for example. First, the manufacturing method of the negative electrode active material used for a negative electrode is demonstrated. First, silicon compound _{particles containing a silicon compound (SiO x} : 0.5≤x≤1.6) are prepared. Next, Li is inserted into the silicon compound particles to contain the Li compound. In this way, negative electrode active material particles are produced. Next, an Al element and an Na element are included in the prepared negative electrode active material particles so that a mass ratio M _Na /M _Al of the Al element and the Na element satisfies the following formula (1). And the negative electrode active material is manufactured using the negative electrode active material particle containing Al element and Na element.

<Formula 1> 0.022≤M _Na /M _Al ≤61

More specifically, the negative electrode active material can be manufactured as follows. First, a raw material for generating silicon oxide gas is heated in a temperature range of 900°C to 1600°C under reduced pressure in the presence of an inert gas to generate silicon oxide gas. Considering the surface oxygen of the metallic silicon powder and the presence of trace oxygen in the reaction furnace, it is preferable that the mixing molar ratio be 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 suction plate. Next, the silicon oxide deposit is taken out in the state which lowered|reduced the internal temperature of a reaction furnace to 100 degrees C or less, and it grind|pulverizes using a ball mill, a jet mill, etc., and performs pulverization. You may classify the powder obtained in this way. In the present invention, the particle size distribution of the silicon compound particles can be adjusted at the time of the pulverization step and the classification step. As described above, silicon compound particles can be produced. In addition, Si crystallites in the silicon compound particles can be controlled by changing the vaporization temperature or heat treatment after generation.

Here, you may produce|generate the layer of a carbon material in the surface layer of a silicon compound particle. As a method of producing the carbon material layer, the thermal decomposition CVD method is preferable. A method for producing a carbon material layer by thermal decomposition CVD method will be described.

First, silicon compound particles are set in a furnace. Next, hydrocarbon gas is introduced into the furnace, and the temperature inside the furnace is raised. Although the decomposition temperature is not specifically limited, 1200 degrees C or less is preferable, More preferably, it is 950 degrees C or less. By setting the decomposition temperature to 1200°C or less, unintended disproportionation of the active material particles can be suppressed. After raising the furnace temperature to a predetermined temperature, a carbon layer is formed on the surface of the silicon compound particles. In addition, although the hydrocarbon gas used as a raw material of a carbon material is although it does not specifically limit, It is preferable that _n < _{=3 in C n H m composition.} If n≤3, the manufacturing cost can be lowered and the physical properties of the decomposition product can be improved.

Next, Li is inserted into the silicon active material particles prepared as described above to contain a Li compound. At this time, it is preferable to contain at least 1 or more types of _{Li 2} Si ₂ O ₅ , Li ₂ SiO ₃ , and Li ₄ SiO _{4 as the Li compound.} In order to obtain such Li silicates, the insertion of Li is preferably performed by a redox method.

In the modification by the redox method, lithium can be inserted, for example, by first immersing the silicon active material particles in a solution A in which lithium is dissolved in an ether solvent. The solution A may further contain a polycyclic aromatic compound or a linear polyphenylene compound. After the insertion of lithium, active lithium can be desorbed from the silicon active material particles by immersing the silicon active material particles in a solution B containing a polycyclic aromatic compound or a derivative thereof. As the solvent of the solution B, for example, an ether-based solvent, a ketone-based solvent, an ester-based solvent, an alcohol-based solvent, an amine-based solvent, or a mixed solvent thereof can be used. Alternatively, after being immersed in the solution A, the obtained silicon active material particles may be heat-treated under an inert gas at 400 to 800°C. The Li compound can be stabilized by heat treatment. Then, you may wash|clean by the method of washing|cleaning with alcohol, alkaline water in which lithium carbonate was melt|dissolved, weak acid, pure water, etc.

Examples of the ether solvent used in the solution A include diethyl ether, tert-butylmethyl ether, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol. Dimethyl ether or a mixed solvent thereof may be used. Among these, it is particularly preferable to use tetrahydrofuran, dioxane and 1,2-dimethoxyethane. It is preferable that these solvents are dehydrated, and it is preferable that it is deoxygenated.

In addition, as the polycyclic aromatic compound contained in the solution A, one or more of naphthalene, anthracene, phenanthrene, naphthacene, pentacene, pyrene, picene, triphenylene, coronene, chrysene and derivatives thereof can be used. , As the straight-chain polyphenylene compound, at least one of biphenyl, terphenyl and derivatives thereof can be used.

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

Further, examples of the ether solvent for solution B include diethyl ether, tert-butylmethyl 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 a ketone solvent, acetone, acetophenone, etc. can be used.

As an ester solvent, methyl formate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, etc. can be used.

As an alcohol solvent, methanol, ethanol, propanol, isopropyl alcohol, etc. can be used.

As an amine solvent, methylamine, ethylamine, ethylenediamine, etc. can be used.

In addition, you may insert Li into the silicon active material particle by the thermal doping method. In the modification by the thermal doping method, for example, the silicon active material particles are mixed with LiH powder or Li powder, and the modification is possible by heating in a non-oxidizing atmosphere. As the non-oxidizing atmosphere, for example, an Ar atmosphere or the like can be used. More specifically, first, LiH powder or Li powder and silicon oxide powder are sufficiently mixed in an Ar atmosphere, sealed, and homogenized by stirring for each sealed container. Then, it reforms by heating in the range of 700 degreeC - 750 degreeC. 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.

In addition, when reforming is performed by the thermal doping method, the ²⁹ Si-MAS-NMR spectrum obtained from the silicon compound particles is different from the case where the redox method is used. ^{An example of the 29} Si-MAS-NMR spectrum measured from the silicon compound particle when reforming by the redox method in FIG. 2 is shown. In FIG. 2, a peak given near -75 ppm is _{a peak derived from Li 2} SiO ₃ , and a peak given at -80 to -100 ppm is a peak derived from Si. Moreover, it may have a peak of Li silicates other than _{Li 2} SiO ₃ and Li ₄ SiO ₄ over -80 to -100 ppm.

^{In addition, an example of the 29} Si-MAS-NMR spectrum measured from silicon compound particle|grains when modifying by the thermal dope method is shown in FIG. In FIG. 3 , a peak given near -75 ppm is _{a peak derived from Li 2} SiO ₃ , and a peak given at -80 to -100 ppm is a peak derived from Si. Moreover, it may have a peak of Li silicates other than _{Li 2} SiO ₃ and Li ₄ SiO ₄ over -80 to -100 ppm. In addition, the peak of _{Li 4} SiO ₄ can be confirmed from the XPS spectrum.

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

More specifically, by dispersing aluminum phosphate in an aqueous solution of Na polyacrylate, and spraying and coating the dispersion on the surface of the negative electrode active material particles, it is possible to make the negative electrode active material particles contain Al element and Na element. Moreover, since the mass of the Na element which exists in polyacrylic acid Na powder per unit mass is determined, content of Na element can be adjusted by adjusting the amount of polyacrylic acid Na powder dissolved in aqueous solution. Since the mass of the Al element present in the aluminum phosphate per unit mass is also determined, the content of the Al element can be adjusted by the amount of the aluminum phosphate as described above. That is, the mass ratio M _Na /M _Al can be set as the range of Formula 1 by adjusting the addition amount of polyacrylic acid Na and aluminum phosphate.

For example, when it is desired to put 0.12 mass % of Na element with respect to a silicon compound particle, a silicon compound particle is prepared first. At this time, the mass of the prepared silicon compound particles is measured. Next, when preparing an aqueous polyacrylic acid Na aqueous solution, polyacrylic acid so that the concentration of polyacrylic acid Na is 0.12 mass % with respect to the mass of the silicon compound particles in terms of Na (0.5 mass % with respect to the silicon compound particles in terms of polyacrylic acid Na) Na is dissolved. Next, a predetermined amount of aluminum phosphate is added to the polyacrylic acid Na aqueous solution so that the mass ratio M _Na /M _{Al satisfies Formula 1 to prepare a dispersion.} What is necessary is just to spray the silicon compound particle which prepared all the dispersion liquids produced in this way.

After mixing the negative electrode active material produced as mentioned above with other materials, such as a negative electrode binder and a conductive support agent, and setting it as a negative electrode mixture, an organic solvent, water, etc. are added and it is set as a slurry. Next, on the surface of the negative electrode current collector, the slurry is applied and dried to form a negative electrode active material layer. At this time, you may perform hot press etc. as needed. As described above, a negative electrode can be produced.

<Lithium Ion Secondary Battery>

Next, the lithium ion secondary battery containing the negative electrode active material of this invention is demonstrated. Here, as a specific example, the lithium ion secondary battery of a laminated film type is mentioned as an example.

[Configuration of Laminate Film Type Lithium Ion Secondary Battery]

In the laminate film-type lithium ion secondary battery 20 shown in FIG. 4 , the wound electrode body 21 is mainly housed inside the sheet-shaped exterior member 25 . This wound body is wound with a separator between the positive electrode and the negative electrode. Moreover, there exists a case where a laminated body is accommodated with a separator between a positive electrode and a negative electrode. In any electrode body, the positive electrode lead 22 is attached to the positive electrode, and the negative electrode lead 23 is attached to the negative electrode. The outermost periphery of the electrode body is protected by a protective tape.

The positive and negative electrode leads are led out in one direction from the inside of the exterior member 25 toward the outside, for example. The positive electrode lead 22 is formed of, for example, a conductive material such as aluminum, and the negative electrode lead 23 is formed of, for example, a conductive material such as nickel and copper.

The exterior member 25 is, for example, a laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order. The outer periphery portions in the layers are butted against each other by fusion bonding or an adhesive or the like. The fusion-bonded portion is, for example, a film such as polyethylene or polypropylene, and the metal portion is aluminum foil or the like. The protective layer is, for example, nylon or the like.

An adhesive film 24 is inserted between the exterior member 25 and the positive and negative electrode leads to prevent intrusion of external air. The material is, for example, polyethylene, polypropylene or polyolefin resin.

[Positive pole]

The positive electrode has, for example, a positive electrode active material layer on both surfaces or one side of the positive electrode current collector, similarly to the negative electrode 10 of FIG. 1 .

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

The positive electrode active material layer contains any one or two or more types of positive electrode materials capable of intercalating and releasing lithium ions, and may contain other materials such as a binder, a conductive aid, and a dispersant according to design. In this case, the detail regarding a binder and a conductive support agent is the same as that of the negative electrode binder and negative electrode conductive support agent which were already described, for example.

As the positive electrode material, a lithium-containing compound is preferable. Examples of the lithium-containing compound include a composite oxide containing lithium and a transition metal element, or a phosphoric acid compound containing lithium and a transition metal element. Among these described positive electrode materials, compounds having at least one or more of nickel, iron, manganese and cobalt are preferable. As their chemical formula, for example, Li _x M1O ₂ or Li _y M2PO ₄ . In the formula, M1 and M2 represent at least one or more transition metal elements. The values of x and y show different values depending on the battery charge/discharge state, but are generally expressed as 0.05≤x≤1.10 and 0.05≤y≤1.10.

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

[Negative pole]

The negative electrode has a structure similar to that of the negative electrode 10 for a lithium ion secondary battery of FIG. 1 , and includes, for example, negative electrode active material layers 12 on both surfaces of the current collector 11 . It is preferable that this negative electrode has a large negative electrode charging capacity with respect to the electric capacity (charging capacity as a battery) 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, in the negative electrode active material layer provided on the negative electrode current collector, a region in which the opposite positive electrode active material layer does not exist is provided. This is for performing stable battery design.

In a non-opposite region, that is, in a region where the negative electrode active material layer and the positive electrode active material layer do not face each other, it is hardly affected by charging and discharging. Therefore, the state of the negative electrode active material layer is maintained immediately after formation. Thereby, the composition etc. can be accurately investigated with good reproducibility, irrespective of the presence or absence of charging/discharging, such as a composition of a negative electrode active material.

[Separator]

A separator separates a positive electrode and a negative electrode, and allows lithium ions to pass while preventing the electric current short circuit accompanying positive electrode contact. This separator is formed of, for example, a porous film containing a synthetic resin or ceramic, and may have a laminated structure in which two or more types of porous films are laminated. As a synthetic resin, polytetrafluoroethylene, polypropylene, polyethylene, etc. are mentioned, for example.

[electrolyte]

At least a part of the active material layer or the separator is impregnated with a liquid electrolyte (electrolyte solution). In this electrolyte solution, the electrolyte salt is melt|dissolved in the solvent, and it may contain other materials, such as an additive.

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

In the case of using an alloy-based negative electrode, it is particularly preferable to include, as a solvent, at least one of a halogenated chain carbonate and a halogenated cyclic carbonate. Thereby, a stable film is formed on the surface of the negative electrode active material during charging and discharging, particularly during charging. Here, the halogenated chain carbonate ester is a chain carbonate ester having a halogen as a constituent element (at least one hydrogen is substituted with a halogen). In addition, halogenated cyclic carbonate ester is cyclic carbonate ester which has halogen as a structural element (that is, at least 1 hydrogen was substituted by halogen).

Although the kind of halogen is not specifically limited, Fluorine is preferable. This is because a film of better quality than other halogens is formed. Moreover, it is so preferable that there are many halogen numbers. This is because the film obtained is more stable, and the decomposition reaction of electrolyte solution is reduced.

Examples of the halogenated chain carbonate ester include fluoromethylmethyl carbonate and difluoromethylmethyl carbonate. Examples of the halogenated cyclic carbonate include 4-fluoro-1,3-dioxolan-2-one and 4,5-difluoro-1,3-dioxolan-2-one.

As a solvent additive, it is preferable to contain the unsaturated carbon-bonded cyclic carbonate ester. This is because a stable film is formed on the surface of the negative electrode during charging and discharging, and the decomposition reaction of the electrolyte can be suppressed. As unsaturated carbon-bonded cyclic carbonate ester, vinylene carbonate, vinylethylene carbonate, etc. are mentioned, for example.

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

Moreover, it is preferable that the solvent contains the acid anhydride. This is because the chemical stability of the electrolyte is improved. As an acid anhydride, propanedisulfonic acid anhydride is mentioned, for example.

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

It is preferable that content of electrolyte salt is 0.5 mol/kg or more and 2.5 mol/kg or less with respect to a solvent. This is because high ionic conductivity is obtained.

[Manufacturing method of laminated film type secondary battery]

In the present invention, a negative electrode can be produced using the negative electrode active material produced by the method for producing the negative electrode active material of the present invention described above, and a lithium ion secondary battery can be manufactured using the produced 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, etc. are mixed to make a positive mixture, and then dispersed in an organic solvent to obtain a positive electrode mixture slurry. Then, the mixture slurry is apply|coated to a positive electrode collector with coating apparatus, such as a die coater which has a knife roll or a die head, and it is made to dry with hot air, and a positive electrode active material layer is obtained. Finally, the positive electrode active material layer is compression-molded with a roll press machine or the like. At this time, you may heat and you may repeat heating or compression in multiple times.

Next, a negative electrode active material layer is formed on the negative electrode current collector and a negative electrode is produced using the same operation procedure as in the production of the negative electrode 10 for lithium ion secondary batteries.

When producing the positive electrode and the negative electrode, respective active material layers are formed on both surfaces of the positive electrode and the negative electrode current collector. At this time, also in any electrode, the active material application|coating length of both surfaces may shift|deviate (refer FIG. 1).

Then, the electrolyte is adjusted. Subsequently, the positive electrode lead 22 is attached to the positive electrode current collector and the negative electrode lead 23 is attached to the negative electrode current collector by ultrasonic welding or the like. Then, the positive electrode and the negative electrode are laminated or wound through a separator to produce the wound electrode body 21, and a protective tape is adhered to the outermost periphery thereof. Next, the wound body is molded so as to have a flat shape. Subsequently, after sandwiching the wound electrode body between the folded film-shaped exterior members 25, the insulating parts of the exterior member are adhered to each other by a heat fusion method, and the wound electrode body is sealed in a state of being released in only one direction. An adhesive film is inserted between the positive electrode lead and the negative electrode lead and the exterior member. A predetermined amount of the adjusted electrolytic solution is injected from the release unit, and vacuum impregnation is performed. After impregnation, the release portion is adhered by vacuum heat sealing method. As mentioned above, the lithium ion secondary battery 20 of a laminate film type 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)

With the following procedure, the lithium ion secondary battery 20 of the laminate film type shown in FIG. 4 was produced.

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

Next, a negative electrode was produced. First, the negative electrode active material was produced as follows. A raw material in which metallic silicon and silicon dioxide were mixed was introduced into a reaction furnace, and the vaporized material was deposited on a suction plate in an atmosphere of a vacuum degree of 10 Pa. After cooling sufficiently, the deposit was taken out and pulverized with a ball mill. As such a silicon compound SiO _x value of x of the particles obtained was 0.5. Then, the particle size of the silicon compound particle was adjusted by classification. Then, the carbon material was coat|covered on the surface of the silicon compound particle by performing thermal decomposition CVD.

Subsequently, the silicon compound particles (negative electrode active material particles) coated with the carbon film were reformed by inserting lithium by the oxidation-reduction method. First, the negative electrode active material particles were immersed in a solution (solution C) in which lithium pieces and naphthalene, which is 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 piece for a mass of 10% by mass to the mixed solution of THF and naphthalene. In addition, the solution temperature at the time of immersing negative electrode active material particle|grains was 20 degreeC, and immersion time was 20 hours. Thereafter, the negative electrode active material particles were taken out by filtration. Lithium was inserted into the negative electrode active material particles by the above treatment.

Then, the obtained negative electrode active material particle|grains were heat-processed at 600 degreeC in argon atmosphere for 24 hours, and Li compound was stabilized.

Next, the negative electrode active material particles were washed, and the washed negative electrode active material particles were dried under reduced pressure. In this way, the negative electrode active material particles were modified. By the above process, negative electrode active material particle|grains were produced.

Next, the polyacrylic acid Na aqueous solution which disperse|distributed aluminum phosphate was sprayed to the negative electrode active material particle|grains, and 0.44 mass % of Al elements and 0.49 mass % of Na elements were made to contain. That is, mass ratio M _Na /M _Al was 1.1, and was satisfy|filling Formula 1 and Formula 2. In addition, the molecular weight of polyacrylic acid Na used here was 600, and pH when it was set as 1% aqueous solution was 8.8.

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

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

Here, in order to evaluate the stability of the aqueous slurry containing negative electrode active material particles, 30 g of a part of the prepared negative electrode mixture slurry is taken out separately from that for secondary battery production, stored at 20° C., and gas from after negative electrode mixture slurry production The time to occurrence was measured.

In addition, as the negative electrode current collector, an electrolytic copper foil having a thickness of 15 µm was used. In this electrolytic copper foil, carbon and sulfur were each contained in the density|concentration of 70 mass ppm. Finally, the negative electrode mixture slurry was applied to the negative electrode current collector and dried at 100°C for 1 hour in a vacuum atmosphere. 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 after drying was 5 mg/cm 2 .

Then, after mixing the solvent (4-fluoro-1,3-dioxolan-2-one (FEC), ethylene carbonate (EC) and dimethyl carbonate (DMC)), an electrolyte salt (hexafluorophosphoric acid) Lithium: LiPF ₆ ) was dissolved to prepare an electrolyte solution. In this case, the composition of the solvent was set to FEC:EC:DMC=10:20:70 by volume ratio, and the content of the electrolyte salt was 1.2 mol/kg with respect to the solvent.

Next, the secondary battery was assembled as follows. First, an aluminum lead was ultrasonically welded to one end of the positive electrode current collector, and a nickel lead was welded to one end of the negative electrode current collector. Then, the positive electrode, the separator, the negative electrode, and the separator were laminated in this order and wound in the longitudinal direction to obtain a wound electrode body. The winding end part was fixed with PET masking tape. For the separator, a laminated film (thickness of 12 mu m) sandwiched by a film containing porous polyethylene as a main component with a film containing porous polypropylene as a main component was used. Then, after sandwiching the electrode body between the exterior members, the outer peripheral portions except for one side were thermally fused to each other, and the electrode body was housed therein. As the exterior member, an aluminum laminate film in which a nylon film, an aluminum foil and a polypropylene film were laminated was used. Then, the prepared electrolyte solution was poured from the opening part, and after impregnating in a vacuum atmosphere, it heat-sealed and sealed.

The cycle characteristics and first time charge/discharge characteristics of the secondary battery produced as mentioned above were evaluated.

Cycle characteristics were investigated as follows. First, 2 cycles of charging and discharging were performed at 0.2C in an atmosphere of 25 degreeC for battery stabilization, and the discharge capacity of the 2nd cycle was measured. Then, charging and discharging were performed until the total number of cycles became 499 cycles, and the discharge capacity was measured each time. Finally, the discharge capacity at the 500th cycle obtained by 0.2C charging and discharging was divided by the discharge capacity at the second cycle to calculate the capacity retention ratio (hereinafter, simply referred to as retention ratio). In the normal cycle, that is, from the 3rd cycle to the 499th cycle, charging and discharging were performed at 0.7C of charge and 0.5C of discharge.

When examining the first time charging/discharging characteristics, the first time efficiency (it may be called initial stage efficiency below) was computed. First time efficiency was computed from the formula represented by first time efficiency (%) = (first time discharge capacity/first time charge capacity) *100. Atmospheric temperature was made similar to the case where cycling characteristics were investigated.

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

A secondary battery was manufactured in the same manner as in Example 1-1 except that the amount of oxygen in the bulk of the silicon compound was adjusted. In this case, the oxygen amount was adjusted by changing the ratio and heating temperature of the metallic silicon and silicon dioxide in the raw material of a silicon compound. Embodiments shown in the Examples 1-1 to 1-3, Comparative Examples 1-1, the x value of the silicon compound represented by a, a SiO _x in Table 1. 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 µm. _{Li 2} Si ₂ O ₅ and Li ₂ SiO ₃ were contained inside the silicon compound particles. Further, in the silicon compound, the half width (2θ) of the diffraction peak resulting from the Si(111) crystal plane obtained by X-ray diffraction was 2.257°, and the crystallite size resulting from the Si(111) crystal plane was 3.77 nm. In addition, the average thickness of the carbon material coat|covered on the surface was 50 nm.

Moreover, in all the said Examples and comparative examples, the peak of Si and Li silicate area|region given at -60 to -95 ppm as a chemical shift value obtained from ^{29 Si-MAS-NMR spectrum expressed.} In addition, in all 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 a chemical shift value obtained from ^{29 Si-MAS-NMR spectrum, and -96 to -150 ppm} The relationship with the peak intensity value B of the SiO _{2 region given in was A>B.}

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

As shown in Table 1, _{in the silicon compound represented by SiO x} , when the value of x was outside the range of 0.5≤x≤1.6, the battery characteristics deteriorated. For example, as shown in Comparative Example 1-1, when oxygen is insufficient (x=0.3), the initial efficiency is improved, but the capacity retention rate is remarkably deteriorated. On the other hand, as shown in Comparative Example 1-2, when there is a large amount of oxygen (x=1.8), since the electroconductivity fall and the capacity|capacitance of a silicon oxide did not express substantially, evaluation was stopped. In addition, in Examples 1-1 to 1-3, the time until gas generation was 3 days or more, and it was found that the aqueous negative electrode slurry stability was improved as compared to Comparative Example 1-1. In addition, in Comparative Example 1-2, the measurement of the time until gas generation was not performed.

(Examples 2-1 to 2-2)

In addition to changing the type of lithium silicate included in the silicon compound particles as shown in Table 2, a secondary battery was manufactured under the same conditions as in Example 1-2, and cycle characteristics, initial efficiency, and stability of aqueous negative electrode slurry were evaluated. did.

(Comparative Example 2-1)

A secondary battery was produced under the same conditions as in Example 1-2 except that Li was not inserted into the silicon compound particles, and cycle characteristics, initial efficiency, and 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.

Since the silicon compound particles _{contain stable lithium silicate such as Li 2} SiO ₃ and Li ₄ SiO ₄ , capacity retention rate and initial efficiency are improved. In particular, in the case of including two types of lithium silicate, the capacity retention rate and initial efficiency were further improved. Moreover, the time until gas generation became 2 days or more, and sufficient stability of the aqueous|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 the Li compound, there was no gas generation, but the initial efficiency was remarkably reduced.

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

By changing the mass concentrations of the Al element and the Na element contained in the silicon compound particles, in addition to changing _{the value of the mass ratio M Na} /M _Al as shown in Table 3, a secondary battery was prepared under the same conditions as in Example 1-2, , cycle characteristics, initial efficiency, and stability of the aqueous negative electrode slurry were evaluated.

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

As can be seen from Table 3, when the value of the mass ratio M _Na / M satisfying the formula _Al 1 0.022≤M _Na / _Al ≤61 M, compared to the time of gas generation does not satisfy the formula (1) Example 3 It became longer than 4 to 3-8. Further, in Comparative Examples 3-1 to 3-3 in which at least one of the Al element and the Na element was not included, the time until gas generation was further shortened. Therefore, as in the present invention, when the negative electrode active material particles contain Al and Na elements as constituent elements, and the mass ratio M _Na /M _Al of these elements satisfies Formula 1, the stability of the aqueous negative electrode slurry This improvement was confirmed.

(Examples 4-1 to 4-5)

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

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

As Table 4 shows, the time until gas generation changes according to the molecular weight of polyacrylic acid Na. Among these, as in Examples 1-2 and 4-2 to 4-4, when the molecular weight of Na polyacrylate is 250,000 or more and 1 million or less, the time to gas generation becomes longer, and the stability of the aqueous negative electrode slurry is further improved. improvement was found.

(Examples 5-1 to 5-4)

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

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

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

(Examples 6-1 to 6-9)

In addition to changing the crystallinity of the silicon compound particles as shown in Table 6, a secondary battery was produced under the same conditions as in Example 1-2, and cycle characteristics, initial efficiency, and stability of the aqueous negative electrode slurry were evaluated. In addition, the crystallinity in a silicon compound particle can be controlled by changing the vaporization temperature of a raw material, or heat processing after generation|generation of a silicon compound particle. In addition, in Example 6-9, although the half value width was computed as 20 degrees or more, it is a result of fitting using analysis software, and a peak is not obtained substantially. Therefore, it can be said that the silicon compound of Example 6-9 is substantially amorphous.

In particular, a high capacity retention rate was obtained in a low-crystalline material having a half width of not less than 1.2 DEG , and also having a crystallite size of 7.5 nm or less due to the Si(111) plane thereon.

(Example 7-1)

A secondary battery was manufactured under the same conditions as in Example 1-2, except that the relationship between the maximum peak intensity value A of the Si and Li silicate regions and the _{peak intensity value B derived from the SiO 2 region was A<B for the silicon compound.} Then, cycle characteristics, initial efficiency, and stability of the aqueous negative electrode slurry were evaluated. In this case, by reducing the amount of insertion of the lithium at the time of modification, by reducing the amount of Li ₂ SiO _3, it was reduced the intensity A of a peak derived from the Li ₂ SiO _3.

As can be seen from Table 7, the case where the relationship between the peak intensities was A>B improved the battery characteristics.

(Examples 8-1 to 8-6)

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

When the median diameter of the silicon compound was 3 µm or more, the retention rate and initial efficiency were further improved. This is considered to be because the surface area per mass of the silicon compound was not too large and the area in which a side reaction occurred was able to be made small. On the other hand, if the median diameter is 15 µm or less, the particles are less likely to break during charging, and SEI (solid electrolyte interface) due to the new surface is unlikely to be generated during charging and discharging, so that the loss of reversible Li can be suppressed. In addition, if the median diameter of the silicon-based active material particles is 15 µm or less, the amount of expansion of the silicon compound particles during charging does not increase, so that physical and electrical destruction of the negative electrode active material layer due to expansion can be prevented.

(Examples 9-1 to 9-4)

In addition to changing the average thickness of the carbon material coated on the surface of the silicon-based active material particles, a secondary battery was prepared under the same conditions as in Example 1-2, and cycle characteristics, initial efficiency, and stability of the aqueous negative electrode slurry were evaluated. The average thickness of the carbon material can be adjusted by changing the CVD conditions.

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

(Example 10-1)

A secondary battery was produced under the same conditions as in Example 1-2, except that the mass ratio of the silicon-based active material particles in the negative electrode active material was changed, and the increase rate 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 increase rate of the battery capacity of the secondary battery. The graph indicated by A in FIG. 5 shows the increase rate of the battery capacity when the ratio of the silicon compound particles is increased in the negative electrode active material of the negative electrode of the present invention. On the other hand, the graph shown by B in FIG. 5 has shown the increase rate of the battery capacity at the time of increasing the ratio of the silicon compound particle which is not doped with Li. When the ratio of the silicon compound becomes 6 mass % or more so that FIG. 5 may show, the increase rate of a battery capacity becomes large compared with the past, and a volume energy density increases especially remarkably.

In addition, this invention is not limited to the said embodiment. The above-mentioned embodiment is an illustration, and any thing which has substantially the same structure as the technical idea described in the claim of this invention, and exhibits the same effect is included in the technical scope of this invention.

Claims (15)

A negative electrode active material comprising negative electrode active material particles, comprising:
The negative electrode active material particles contain silicon compound particles containing a silicon compound (SiOx: 0.5≤x≤1.6),
The silicon compound particles contain a Li compound,
As constituent elements on the surface of the negative electrode active material particle, the Al element and Na element are included, and the mass ratio M _Na /M _Al of the Al element and the Na element on the surface of the negative electrode active material particle is the following formula 1, the negative electrode active material characterized in that it satisfies.
<Formula 1> 0.022≤M _Na /M _Al ≤61 The negative electrode active material according to claim 1, wherein the mass ratio M _Na /M _Al satisfies Equation 2 below.
<Formula 2> 0.36≤M _Na /M _Al ≤3.3 The negative electrode active material according to claim 1, wherein the Al element is contained in an amount of 0.02 mass% or more and 1.1 mass% or less with respect to the silicon compound particles. The negative electrode active material according to claim 1, wherein the Na element is contained in a range of 0.024 mass% or more and 1.22 mass% or less with respect to the silicon compound particles. The negative electrode active material according to claim 1, wherein the negative electrode active material particles contain polyacrylic acid Na. The negative electrode active material according to claim 5, wherein the molecular weight of the polyacrylic acid Na is in the range of 250,000 or more and 1,000,000 or less. The negative electrode active material according to claim 5, wherein the pH is in the range of 6 or more and 10 or less when the polyacrylic acid Na is used as a 1% aqueous solution. The negative electrode active material according to claim 1, 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.} The silicon compound particle according to claim 1, wherein the half width (2θ) of the diffraction peak resulting from the Si(111) crystal plane obtained by X-ray diffraction using Cu-Kα ray is 1.2° or more, and The corresponding crystallite size is 7.5 nm or less. The silicon compound particle according to claim 1, ^{obtained from 29} Si-MAS-NMR spectrum, the maximum peak intensity value A of Si and Li silicate region given at -60 to -95 ppm as a chemical shift value, and the chemical shift A negative electrode active material characterized in that the peak intensity value B of _{the SiO 2} region given at -96 to -150 ppm as a value satisfies the relationship A>B. The negative electrode active material according to claim 1, wherein the negative electrode active material particles have a median diameter of 3 µm or more and 15 µm or less. The negative electrode active material according to claim 1, wherein the negative electrode active material particles include a carbon material in the surface layer portion. The negative electrode active material according to claim 12, wherein the carbon material has an average thickness of 5 nm or more and 5000 nm or less. A mixed negative electrode active material comprising the negative electrode active material according to any one of claims 1 to 13 and a carbon-based active material. A method for producing a negative electrode active material comprising negative electrode active material particles containing silicon compound particles, the method comprising:
A step of producing silicon compound particles containing a silicon compound (SiO _{x: 0.5≤x≤1.6);}
A step of inserting Li into the silicon compound particles to contain the Li compound
to produce negative electrode active material particles by
A liquid containing an Al element and a Na element is sprayed on the surface of the negative electrode active material particle, and the Al element and the Na element are mixed with the Al element and the Na element in a mass ratio M _Na / Including the step of including M _{Al so} that it satisfies the following formula 1,
A method for producing a negative electrode active material, characterized in that the negative electrode active material is manufactured by using the negative electrode active material particles containing the Al element and the Na element.
<Formula 1> 0.022≤M _Na /M _Al ≤61

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