Negative active material for nonaqueous electrolyte secondary battery, method for producing the same, and nonaqueous electrolyte secondary battery

Abstract

This invention provides a negative electrode active material for non-aqueous electrolyte secondary batteries containing negative electrode active material particles. These particles contain silicon compound particles containing Li2SiO3. When measured by X-ray diffraction, the half-width of the peak caused by the Li2SiO3 (020) surface is 1.1° to 1.5°. The peak intensity Ia caused by the Li2SiO3 (020) surface, the peak intensity Ib caused by the Li2SiO3 (111) surface, the intensity I(24.8°) at 2θ = 24.8°, and the intensity I(28.4°) at 2θ = 28.4° satisfy equations (1) to (3). This invention provides a negative electrode active material with high atmospheric stability that can improve the initial charge and discharge characteristics when used as a negative electrode active material for secondary batteries. 1.1≤Ib / Ia≤1.5···(1)I(24.8°) / Ia≤0.5···(2)I(28.4°) / Ia≤1.0···(3)

Description

Technical Field

[0001] This invention relates to negative electrode active materials for non-aqueous electrolyte secondary batteries and their preparation methods, as well as non-aqueous electrolyte secondary batteries. Background Technology

[0002] In recent years, small electronic devices, such as mobile terminals, have become widely used, creating a strong demand for further miniaturization, weight reduction, and extended lifespan. In response to this market demand, the development of a particularly small and lightweight rechargeable battery with high energy density has been promoted. The applications of this rechargeable battery are not limited to small electronic devices; its application in large electronic devices such as automobiles and in energy storage systems such as buildings is also under research.

[0003] Among them, lithium-ion secondary batteries are easy to miniaturize and increase capacity, and can achieve higher energy density than lead-acid and nickel-cadmium batteries, so they are highly anticipated.

[0004] The aforementioned lithium-ion secondary battery, in addition to having a positive electrode, a negative electrode, and a separator, also has an electrolyte, and the negative electrode contains negative electrode active materials related to the charge and discharge reaction.

[0005] Carbon-based active materials are widely used as anode active materials; however, recent market demands are driving a further increase in battery capacity. To improve battery capacity, research is underway to use silicon as anode active material. This is because silicon's theoretical capacity (4199 mAh / g) is more than 10 times greater than graphite's (372 mAh / g), thus promising a significant increase in battery capacity. The development of silicon materials as anode active materials involves research not only on elemental silicon but also on compounds such as alloys and oxides. Furthermore, regarding the shape of the active material, for carbon-based active materials, research is being conducted on everything from standard coating types to monolithic types directly deposited on the current collector.

[0006] However, when silicon is used as the main material for the negative electrode active material, it expands and contracts during charging and discharging, making it prone to breakage, primarily near the surface. Furthermore, ionic substances are generated within the active material, further increasing its fragility. If the surface of the negative electrode active material breaks down, new surfaces are created, increasing the reaction area. During this process, electrolyte decomposition occurs on these new surfaces, forming a film of electrolyte decomposition products, which consumes electrolyte. This leads to a decrease in the battery's cycle characteristics.

[0007] To date, various studies have been conducted on negative electrode active materials and electrode structures for lithium-ion secondary batteries that use silicon as the main material, in order to improve the initial efficiency and cycle characteristics of batteries.

[0008] Specifically, to achieve good cycle characteristics and high safety, silicon and amorphous silicon dioxide are simultaneously deposited using a vapor phase method (e.g., see Patent Document 1). Furthermore, to obtain high battery capacity and safety, a carbon material (conductive material) is disposed on the surface of the silicon oxide particles (e.g., see Patent Document 2). Further, to improve cycle characteristics and obtain high input / output characteristics, an active material containing silicon and oxygen is manufactured, and an active material layer with a high oxygen ratio near the current collector is formed (e.g., see Patent Document 3). Moreover, to enhance cycle characteristics, oxygen is contained in the silicon active material, and it is formed in a manner where the average oxygen content is 40 at% or less, and the oxygen content is higher near the current collector (e.g., see Patent Document 4).

[0009] In addition, to improve the initial charge and discharge efficiency, a phase containing Si, SiO2, and M is used. y Nanocomposites of O metal oxides (e.g., see Patent Document 5). Furthermore, to improve cycling characteristics, SiO₂ is used... x (0.8≤x≤1.5, particle size range = 1μm~50μm) is mixed with carbon material and calcined at high temperature (e.g., see Patent Document 6). Furthermore, to improve cycle characteristics, the molar ratio of oxygen to silicon in the negative electrode active material is set to 0.1~1.2, and the active material is controlled within a range where the difference between the maximum and minimum molar ratio near the interface between the active material and the current collector is less than 0.4 (e.g., see Patent Document 7). Furthermore, to improve the battery's load characteristics, a lithium-containing metal oxide is used (e.g., see Patent Document 8). Furthermore, to improve cycle characteristics, a hydrophobic layer such as a silane compound is formed on the surface of the silicon material (e.g., see Patent Document 9).

[0010] Furthermore, to improve cycling characteristics, silicon dioxide is used and a graphite coating is formed on its surface, thereby imparting conductivity (see, for example, Patent Document 10). In Patent Document 10, regarding the shift value obtained from the Raman spectrum associated with the graphite coating, at 1330 cm⁻¹... -1 and 1580cm -1 Broad peaks appear at I, and their intensity is greater than that of I. 1330 / I 1580 1.5 < I 1330 / I 1580<3. Furthermore, in order to obtain high battery capacity and improve cycle characteristics, a particle having a silicon microcrystalline phase dispersed in silicon dioxide is used (for example, see Patent Document 11). In addition, in order to improve overcharge and over-discharge characteristics, a silicon oxide with the atomic ratio of silicon to oxygen controlled at 1:y (0 < y < 2) is used (for example, see Patent Document 12). Existing technical documents Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2001-185127 Patent Document 2: Japanese Patent Application Publication No. 2002-042806 Patent Document 3: Japanese Patent Application Publication No. 2006-164954 Patent Document 4: Japanese Patent Application Publication No. 2006-114454 Patent Document 5: Japanese Patent Application Publication No. 2009-070825 Patent Document 6: Japanese Patent Application Publication No. 2008-282819 Patent Document 7: Japanese Patent Application Publication No. 2008-251369 Patent Document 8: Japanese Patent Application Publication No. 2008-177346 Patent Document 9: Japanese Patent Application Publication No. 2007-234255 Patent Document 10: Japanese Patent Application Publication No. 2009-212074 Patent Document 11: Japanese Patent Application Publication No. 2009-205950 Patent Document 12: Japanese Patent Application Publication No. 06-325765 Summary of the Invention The technical problem to be solved by the present invention

[0012] As mentioned above, in recent years, the increasing performance and multifunctionality of small electronic devices, such as mobile terminals, have necessitated greater capacity for lithium-ion secondary batteries, which serve as their primary power source. As one approach to addressing this issue, it is hoped that a lithium-ion secondary battery incorporating a negative electrode made primarily of silicon material is developed.

[0013] Furthermore, when using silicon materials, higher initial efficiency and capacity retention can be achieved by using Li-doped silicon. However, Li-doped silicon suffers from decreased stability in the atmosphere. In particular, the stability degradation is more significant for silicon materials with high Li doping ratios used to achieve higher initial efficiency. Such Li-doped silicon requires operation in low-humidity or inactive gas atmospheres, making it unsuitable for industrial applications.

[0014] This invention addresses the aforementioned problems and aims to provide a negative electrode active material that exhibits high atmospheric stability and improves initial charge-discharge characteristics when used as a negative electrode active material in a secondary battery, as well as a non-aqueous electrolyte secondary battery containing such a negative electrode active material. Furthermore, this invention also aims to provide a method for preparing a negative electrode active material that exhibits high atmospheric stability and improves initial charge-discharge characteristics. Technical means to solve technical problems

[0015] To address the aforementioned technical problems, the present invention provides a negative electrode active material for non-aqueous electrolyte secondary batteries, comprising negative electrode active material particles. The negative electrode active material for non-aqueous electrolyte secondary batteries is characterized in that the negative electrode active material particles contain silicon compound particles, which comprise silicon compounds (SiO₂). x : 0.8≤x≤1.2), the silicon compound particles contain Li2SiO3, and when the negative electrode active material particles are measured by X-ray diffraction using Cu-Kα rays, the half-width of the peak caused by the (020) plane of Li2SiO3 obtained by the X-ray diffraction is more than 1.1° and less than 1.5°. In the spectrum obtained by the X-ray diffraction, the intensity Ia of the peak caused by the (020) plane of Li2SiO3, the intensity Ib of the peak caused by the (111) plane of Li2SiO3, the intensity I(24.8°) at 2θ=24.8°, and the intensity I(28.4°) at 2θ=28.4° satisfy all of the following equations (1) to (3). 1.1≤Ib / Ia≤1.5···(1) I(24.8°) / Ia≤0.5···(2) I(28.4°) / Ia≤1.0···(3)

[0016] The negative electrode active material (also referred to as silicon-based active material) of the present invention, by including silicon-containing compound particles, can improve battery capacity. Furthermore, by including Li2SiO3 in the silicon compound particles, irreversible capacity generated during charging can be reduced. This improves initial efficiency. Moreover, regarding the spectrum obtained by X-ray diffraction, the half-width of the peak caused by the (020) plane of Li2SiO3 is 1.1° or more and 1.5° or less, and satisfies all of equations (1) to (3). Therefore, both improved initial efficiency and atmospheric stability can be achieved.

[0017] At this point, it is preferable that the spectrum obtained by X-ray diffraction does not have a peak near 2θ = 24.8° caused by Li2Si2O5.

[0018] Higher initial efficiency can be obtained by reducing the proportion of crystalline Li2Si2O5 in the negative electrode active material.

[0019] Furthermore, it is preferable that the spectrum obtained by X-ray diffraction does not have a peak near 2θ = 28.4° caused by the (111) plane of Si.

[0020] By reducing the proportion of crystalline Si in the negative electrode active material, the formation of lithium silicide during Li doping can be suppressed, thereby inhibiting lithium diffusion to the surface when stored in the atmosphere. Therefore, atmospheric stability can be further improved.

[0021] Furthermore, the spectrum obtained by X-ray diffraction preferably satisfies 1.2≤Ib / Ia≤1.3.

[0022] If the X-ray diffraction pattern obtained above falls within the aforementioned range, the amount of lithium contained in the silicon compound particles is appropriate, and Li₂SiO₃ exhibits appropriate crystallinity. Therefore, lithium diffusion to the surface can be suppressed when stored in the atmosphere, further enhancing its stability in the atmosphere.

[0023] Furthermore, it is preferable that the half-width of the peak caused by the (020) plane of the Li2SiO3 is 1.2° or more and 1.3° or less.

[0024] If the crystal size of Li2SiO3 is within the above range, then the crystallite size is within a suitable range, thus further improving its stability in the atmosphere.

[0025] Furthermore, preferably in the spectrum obtained by X-ray diffraction, the intensity I(29.9°) at 2θ=29.9° caused by LiOH·H2O satisfies I(29.9°) / Ia≤0.7.

[0026] If the concentration is within the aforementioned range, the absorption of moisture and carbonic acid from the atmosphere can be suppressed by keeping the amount of LiOH·H2O on the surface of the negative electrode active material particles within a suitable range. Therefore, its stability in the atmosphere can be further improved.

[0027] At this point, it is further preferred that the spectrum obtained by X-ray diffraction does not have a peak near 2θ = 29.9° caused by LiOH·H2O.

[0028] By eliminating LiOH·H2O from the negative electrode active material, the absorption of moisture and carbonic acid from the atmosphere can be suppressed, thereby further improving its stability in the atmosphere.

[0029] Furthermore, preferably in the spectrum obtained by X-ray diffraction, the intensity I(31.7°) at 2θ = 31.7° satisfies I(31.7°) / Ia ≤ 0.7.

[0030] If the concentration is within the aforementioned range, the amount of lithium carbonate contained on the surface of the negative electrode active material particles can be set to a suitable level. Therefore, it is possible to suppress the absorption of moisture from the atmosphere and further improve its stability in the atmosphere.

[0031] Furthermore, it is preferable that after dispersing the negative electrode active material particles in water at 25°C at a ratio of 10% by mass for 1 hour, the silicon content in the water is less than 50 ppm by mass.

[0032] If within the above-mentioned range, the leaching of adhesive silicon compounds from the atmosphere to the surface can be suppressed. Therefore, the aggregation of negative electrode active material particles can be suppressed.

[0033] Furthermore, the BET specific surface area of ​​the negative electrode active material particles is preferably 1 m². 2 / g or more and 3m 2 / g or less.

[0034] If it is within the above range, it can achieve a good balance between initial efficiency and atmospheric stability.

[0035] Furthermore, it is preferred that the median particle size (D50) of the negative electrode active material particles is 4.0 μm or more and 15 μm or less, and the ratio of the cumulative 90% particle size (D90) to the cumulative 10% particle size (D10) (D90 / D10) is 3 or less.

[0036] If the particle size is within the above range, the negative electrode active material particles have a suitable size, thus enabling uniform lithium doping. Therefore, a good balance can be achieved between primary efficiency and atmospheric stability.

[0037] Furthermore, it is preferable that the negative electrode active material particles contain carbon material in the surface layer, and the average thickness of the carbon material is more than 10 nm and less than 100 nm.

[0038] By incorporating carbon material into the surface layer of the negative electrode active material particles, electronic conductivity can be improved, thereby enhancing battery performance. Furthermore, by increasing the surface hydrophobicity, moisture absorption from the atmosphere can be suppressed. Moreover, if the average thickness of the carbon material is within the aforementioned range, electronic conductivity can be improved while maintaining lithium-ion conductivity. Therefore, a good balance can be achieved between initial efficiency and atmospheric stability.

[0039] Furthermore, the negative electrode active material particles preferably contain phosphate in the surface layer.

[0040] By including phosphate in the surface layer of the negative electrode active material particles, lithium diffused to the surface can be captured when stored in the atmosphere, inhibiting lithium dissolution from the active material particles. Therefore, its stability in the atmosphere can be further improved.

[0041] Furthermore, the present invention provides a non-aqueous electrolyte secondary battery, characterized in that it comprises the above-mentioned negative electrode active material for non-aqueous electrolyte secondary batteries.

[0042] For this type of non-aqueous electrolyte secondary battery, the negative electrode active material particles exhibit high stability in the atmosphere, thus offering greater flexibility in the manufacturing process and making it suitable for industrialization. Furthermore, by using the aforementioned negative electrode active material particles to manufacture the negative electrode, a secondary battery with high capacity and excellent initial charge-discharge characteristics can be produced.

[0043] Furthermore, this invention provides a method for preparing a negative electrode active material for a non-aqueous electrolyte secondary battery, which is a method for preparing a negative electrode active material for a non-aqueous electrolyte secondary battery containing silicon compound particles, characterized by manufacturing a silicon compound (SiO2)-containing negative electrode active material particles. x The method further comprises a step of screening negative electrode active material particles containing silicon compound particles with a content of 0.8 ≤ x ≤ 1.2, and a step of embedding Li into the silicon compound particles to make them contain Li2SiO3. The negative electrode active material particles are manufactured by means of X-ray diffraction of Cu-Kα rays. The negative electrode active material particles are measured by X-ray diffraction of Cu-Kα rays. The half-width of the peak caused by the (020) plane of Li2SiO3 obtained by X-ray diffraction is 1.1° or more and 1.5° or less. The negative electrode active material particles are all those whose intensity Ia of the peak caused by the (020) plane of Li2SiO3, intensity Ib of the peak caused by the (111) plane of Li2SiO3, intensity I (24.8°) at 2θ = 24.8°, and intensity I (28.4°) at 2θ = 28.4° satisfy the following formulas (1) to (3). The negative electrode active material particles selected are used to prepare a negative electrode active material for a non-aqueous electrolyte secondary battery. 1.1≤Ib / Ia≤1.5···(1) I(24.8°) / Ia≤0.5···(2) I(28.4°) / Ia≤1.0···(3)

[0044] Therefore, by preparing a negative electrode active material in such a way that the half-width of the peak caused by the (020) plane of Li2SiO3 in the spectrum obtained by X-ray diffraction of the negative electrode active material particles containing the above-mentioned Li-embedded silicon compound particles is 1.1° or more and 1.5° or less, and satisfies formulas (1) to (3), the stability of the negative electrode active material in the atmosphere can be improved, and a negative electrode active material with high capacity when used as a negative electrode active material for secondary batteries, and with good cycle characteristics and initial charge-discharge characteristics can be manufactured. Invention Effects

[0045] The non-aqueous electrolyte secondary battery negative electrode active material of the present invention exhibits high atmospheric stability and, when used as a negative electrode active material in a secondary battery, demonstrates high capacity and excellent initial charge-discharge characteristics. Furthermore, secondary batteries using the negative electrode active material of the present invention exhibit high capacity and excellent initial charge-discharge characteristics. Moreover, the preparation method of the non-aqueous electrolyte secondary battery negative electrode active material of the present invention improves the atmospheric stability of the negative electrode active material particles and enables the manufacture of a negative electrode active material with excellent initial charge-discharge characteristics when used as a negative electrode active material in a non-aqueous electrolyte secondary battery. Attached Figure Description

[0046] Figure 1 This is an example of an X-ray diffraction pattern of the negative electrode active material of the present invention using Cu-Kα rays. Figure 2 This is a cross-sectional view showing an example of the configuration of a negative electrode for a non-aqueous electrolyte secondary battery containing the negative electrode active material of the present invention. Figure 3 An exploded view showing a configuration example (laminated film type) of a lithium secondary battery containing the negative electrode active material of the present invention. Detailed Implementation

[0047] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

[0048] As mentioned above, one method for increasing the capacity of lithium-ion secondary batteries is the use of a negative electrode with silicon as the main material. To obtain initial charge-discharge and cycle characteristics approximately equivalent to those of lithium-ion secondary batteries using carbon-based active materials, it is necessary to improve the initial charge-discharge characteristics of the silicon material. However, when using silicon materials with improved initial charge-discharge characteristics through Li doping, there is a problem of decreased atmospheric stability, making it unsuitable for industrial applications. Therefore, to date, no negative electrode active material has been proposed that is industrially easy to operate and possesses initial charge-discharge characteristics equivalent to those of lithium-ion secondary batteries using carbon-based active materials.

[0049] In order to obtain a negative electrode active material that has high stability in the atmosphere and high battery capacity and good initial efficiency when used in secondary batteries, the inventors of this invention have conducted repeated and in-depth research and completed this invention.

[0050] [The negative electrode active material for non-aqueous electrolyte secondary batteries of the present invention] The negative electrode active material for a non-aqueous electrolyte secondary battery of the present invention comprises negative electrode active material particles. Furthermore, these negative electrode active material particles contain a silicon-containing compound (SiO₂). xThe silicon compound particles have a particle size of 0.8 ≤ x ≤ 1.2. These silicon compound particles contain Li₂SiO₃ as lithium silicate. Therefore, the negative electrode active material of the present invention, by including silicon compound particles, can improve battery capacity. Furthermore, since the silicon compound particles contain the aforementioned lithium silicate, irreversible capacity generated during charging can be reduced. As a result, the battery capacity, cycle characteristics, and initial charge / discharge efficiency of the secondary battery can be improved.

[0051] Furthermore, when the negative electrode active material of the non-aqueous electrolyte secondary battery of the present invention is measured by X-ray diffraction using Cu-Kα rays, the half-width of the peak caused by the (020) plane of Li2SiO3 obtained by the X-ray diffraction is 1.1° or more and 1.5° or less. Furthermore, in the spectrum obtained by the X-ray diffraction, the intensities Ia of the peak caused by the (020) plane of Li2SiO3, Ib of the peak caused by the (111) plane of Li2SiO3, I(24.8°) at 2θ = 24.8°, and I(28.4°) at 2θ = 28.4° satisfy all of the following equations (1) to (3). Therefore, it is possible to achieve both improved initial efficiency and stability in the atmosphere. 1.1≤Ib / Ia≤1.5···Equation (1) I(24.8°) / Ia≤0.5···Formula (2) I(28.4°) / Ia≤1.0···Formula (3)

[0052] Figure 1 An example of an X-ray diffraction pattern obtained by measuring the negative electrode active material of the non-aqueous electrolyte secondary battery of the present invention using Cu-Kα rays is shown. The peak caused by the (020) plane of Li2SiO3 usually appears around 2θ = 18.7°, and the peak caused by the (111) plane of Li2SiO3 usually appears around 2θ = 26.7°.

[0053] Specifically, the provisions of the negative electrode active material based on the X-ray diffraction pattern of the present invention have the following technical significance.

[0054] A half-width at half-maximum (WHM) of the peak caused by the (020) plane of Li₂SiO₃ is greater than 1.1° and less than 1.5°, indicating the formation of moderately crystalline lithium silicate within the silicon-based active material particles. When the WHM of the peak caused by the (020) plane of Li₂SiO₃ is less than 1.1°, excessive crystal growth occurs, resulting in decreased lithium diffusivity during battery charging and discharging, leading to a decrease in initial efficiency. When the WHM of the peak caused by the (020) plane of Li₂SiO₃ is greater than 1.5°, the crystallinity is low, making it prone to absorbing moisture and carbonic acid from the air. Consequently, its stability in the atmosphere deteriorates.

[0055] Satisfying equation (1) indicates that the lithium doping amount of the silicon-based active material particles is appropriate, and lithium silicate with moderate crystallinity is formed. Therefore, it is possible to balance the improvement of initial efficiency and the stability in the atmosphere. When Ib / Ia < 1.1, the lithium doping amount is excessive, and the lithium silicate crystal growth is excessive, so good stability in the atmosphere cannot be obtained. When 1.5 < Ib / Ia, the lithium doping amount of the silicon-based active material particles is small, so sufficient initial efficiency cannot be obtained.

[0056] Furthermore, as mentioned above, peak intensity Ia is obtained as the intensity of the peak caused by the (020) crystal plane of Li2SiO3. Peak intensity Ib, on the other hand, is obtained as the intensity of the peak caused by the SiO2 crystal plane. x The intensity is obtained by superimposing the broad peak of SiO₂ with the peak caused by the (111) crystal plane of Li₂SiO₃. Therefore, when the lithium doping content is large, SiO₂... x The peak intensity decreases, thus reducing the Ib / Ia ratio. Furthermore, during lithium silicate crystal growth, SiO... x The contribution of the broad peak to the Ib peak decreases, thus reducing the Ib / Ia ratio. Based on these relationships, the range of Ib / Ia can be defined as a parameter specifying an appropriate range for doping amount and crystallinity.

[0057] Satisfying equation (2) indicates that the type and ratio of lithium silicate in the silicon-based active material particles are suitable. The higher the ratio of Li2Si2O5, the higher the intensity at 2θ = 24.8°. Li2Si2O5 is a compound formed within a range where the lithium doping amount is relatively small for silicon-based active material particles. Therefore, when 0.5 < I(24.8°) / Ia, the overall or partial lithium content of the silicon-based active material particles is small, thus limiting the improvement effect on the initial efficiency. However, when equation (2) is satisfied, the improvement effect on the initial efficiency can be fully obtained.

[0058] Satisfying equation (3) indicates a lower proportion of crystalline Si. By reducing the proportion of crystalline Si, the formation of lithium silicide during Li doping can be suppressed. Lithium silicide dissolves in water more readily than lithium silicate and readily absorbs moisture from the air. Therefore, when the proportion of crystalline Si is high, lithium silicide will form during Li doping, absorbing moisture from the atmosphere and thus reducing its stability in the atmosphere. When equation (3) is satisfied, the proportion of crystalline Si is lower, thus enabling the fabrication of stable negative electrode active material particles in the atmosphere.

[0059] In addition, when comparing the intensity at each 2θ value of X-ray diffraction using Cu-Kα rays, values ​​that have undergone background correction are used. (1) The point with the lowest intensity within the range of 10°≤2θ≤15° is designated as point A. (2) The point with the lowest intensity within the range of 38°≤2θ≤45° is designated as point B. (3) At each 2θ value, the intensity of the line AB is subtracted from the intensity of the spectrum curve.

[0060] Furthermore, the aforementioned negative electrode active material preferably exhibits a spectrum obtained by X-ray diffraction that substantially lacks the peak near 2θ = 24.8° caused by Li₂Si₂O₅. When the peak caused by Li₂Si₂O₅ is absent, a sufficient amount of lithium is uniformly doped throughout the silicon-based active material particles. Therefore, a higher initial efficiency can be obtained.

[0061] The definition of whether or not the above peaks exist is as follows. (1) X-ray diffraction using Cu-Kα rays was performed at intervals of 2θ = 0.15° to obtain spectral data. When the angular intervals were reduced, the obtained data were averaged at intervals of 0.15°. (2) For the range of 10°≤2θ≤45°, perform the above background correction and prepare the spectrum after background correction. (3) Extract the minimum value (S) of the range 24.0°≤2θ≤25.0° from the second derivative obtained by taking the second derivative of the spectrum after background correction. (4) Calculate the standard deviation (σ) for the range of 10°≤2θ≤15°. (5) When S / σ < 5, it is determined to be without peaks; when 5 ≤ S / σ, it is determined to be with peaks.

[0062] Furthermore, the spectrum obtained by X-ray diffraction preferably does not have a peak near 2θ = 28.4° caused by the (111) plane of Si. By reducing the proportion of crystalline Si, the formation of lithium silicide can be suppressed when doped with Li, which can further improve the stability in the atmosphere.

[0063] The definition of whether or not the above peaks exist is as follows. (1) X-ray diffraction using Cu-Kα rays was performed at intervals of 2θ = 0.15° to obtain spectral data. When the angular intervals were reduced, the obtained data were averaged at intervals of 0.15°. (2) For the range of 10°≤2θ≤45°, perform the above background correction and prepare the spectrum after background correction. (3) Extract the minimum value (S) of the range 28.2°≤2θ≤28.6° from the second derivative obtained by taking the second derivative of the spectrum after background correction. (4) Calculate the standard deviation (σ) for the range of 10°≤2θ≤15°. (5) When S / σ < 5, it is determined to be without peaks; when 5 ≤ S / σ, it is determined to be with peaks.

[0064] Furthermore, the spectrum obtained by X-ray diffraction preferably satisfies 1.2 ≤ Ib / Ia ≤ 1.3. Within this range, a better balance can be struck between improved initial efficiency and atmospheric stability.

[0065] Furthermore, the half-width of the peak caused by the (020) plane of the Li2SiO3 is preferably 1.2° or more and 1.3° or less. If it is within the above range, it is possible to better balance the improvement of initial efficiency and the stability in the atmosphere.

[0066] Furthermore, preferably, in the spectrum obtained by X-ray diffraction, the intensity I(29.9°) at 2θ = 29.9° caused by LiOH·H₂O satisfies I(29.9°) / Ia ≤ 0.7. In the case of lithium-doped silicon-based active material particles, the higher intensity near 2θ = 29.9° indicates the presence of a large amount of LiOH·H₂O on the surface. Since LiOH·H₂O has the property of absorbing moisture and carbonic acid from the air, if I(29.9°) / Ia ≤ 0.7, it can be said that the amount of LiOH·H₂O present on the surface of the negative electrode active material particles is small, which can more effectively achieve good atmospheric stability.

[0067] Furthermore, it is even more preferable that the spectrum obtained by X-ray diffraction essentially does not contain the peak near 2θ = 29.9° caused by LiOH·H2O. When the particle surface does not contain LiOH·H2O, the absorption of moisture and carbonic acid from the air is further suppressed, thereby further improving its stability in the atmosphere.

[0068] The definition of whether or not the above peaks exist is as follows. (1) X-ray diffraction using Cu-Kα rays was performed at intervals of 2θ = 0.15° to obtain spectral data. When the angular intervals were reduced, the obtained data were averaged at intervals of 0.15°. (2) For the range of 10°≤2θ≤45°, perform the above background correction and prepare the spectrum after background correction. (3) Extract the minimum value (S) of the second derivative obtained by performing a second differentiation on the spectrum after background correction, within the range of 29.0°≤2θ≤30.0°. (4) Calculate the standard deviation (σ) for the range of 10°≤2θ≤15°. (5) When S / σ < 5, it is determined to be without peaks; when 5 ≤ S / σ, it is determined to be with peaks.

[0069] Furthermore, preferably, in the spectrum obtained by X-ray diffraction, the intensity I(31.7°) at 2θ = 31.7° satisfies I(31.7°) / Ia ≤ 0.7. If it is within the above range, the amount of lithium carbonate contained on the surface of the negative electrode active material particles can be set to a suitable amount. Therefore, the absorption of moisture from the atmosphere can be suppressed, and the stability in the atmosphere can be further improved.

[0070] Furthermore, it is preferable that after dispersing the negative electrode active material particles in water at 25°C at a ratio of 10% by mass for 1 hour, the silicon content in the water is less than 50 ppm by mass. When the amount of silicon dissolved in the water is low, silicon compounds are less likely to appear on the surface, even in air. When there are fewer silicon compounds appearing on the surface, the aggregation of negative electrode active material particles can be suppressed due to the reduced amount of hygroscopic and adhesive silicon compounds. When the silicon content in the water after dispersing in water at 25°C at a ratio of 10% by mass for 1 hour is less than 50 ppm by mass, the appearance of silicon compounds on the surface in air can be suppressed, and good atmospheric stability can be obtained.

[0071] Furthermore, the BET specific surface area of ​​the negative electrode active material particles is preferably 1 m². 2 / g or more and 3m 2 / g or less. If the specific surface area of ​​BET is 1m² 2 If the specific surface area is above 3 m² / g, lithium donation and acceptance can be fully realized on the surface of the negative electrode active material particles during battery manufacturing. Therefore, good initial efficiency can be achieved. 2 When the concentration is below a certain value, the surface area exposed to air can be reduced when stored in the atmosphere, thus achieving good atmospheric stability.

[0072] Furthermore, it is preferable that the median particle size (D50) of the negative electrode active material particles is 4.0 μm or more and 15 μm or less, and the ratio of the cumulative 90% particle size (D90) to the cumulative 10% particle size (D10) (D90 / D10) is 3 or less. When the negative electrode active material particles are small, the amount of lithium compounds on the particle surface increases. On the other hand, when the negative electrode active material particles are large, it is difficult for lithium to diffuse inside the particles, and the uniformity of lithium within the negative electrode active material particles decreases. If the median particle size is within the above range, lithium can be uniformly doped within the negative electrode active material particles. Therefore, the stability in the atmosphere can be further improved. In addition, if the D90 / D10 ratio is 3 or less, the proportion of small and large particles in the entire silicon-based negative electrode active material is small, so lithium can be uniformly doped without being affected by these particles. Therefore, the stability in the atmosphere can be further improved. In addition, the above particle size distribution is based on the volume-based particle size distribution measured using a laser scattering particle size distribution measuring device.

[0073] Furthermore, it is preferable that the negative electrode active material particles contain carbon material in the surface layer, and the average thickness of the carbon material is 10 nm or more and 100 nm or less. By including carbon material in the surface layer of the negative electrode active material particles, electronic conductivity can be improved, thereby enhancing battery characteristics. Furthermore, the increased hydrophobicity of the surface can suppress the absorption of moisture from the atmosphere. Moreover, if the average thickness of the carbon material is within the aforementioned range, electronic conductivity can be improved while maintaining lithium-ion conductivity. Therefore, a good balance can be achieved between initial efficiency and atmospheric stability.

[0074] The average thickness of the carbon material can be calculated, for example, according to the following steps. First, the negative electrode active material particles are observed using TEM (transmission electron microscopy) at any magnification. This magnification is preferably one that allows the thickness of the carbon material to be visually confirmed and thus measured. Then, the thickness of the carbon material is measured at any 15 points. Preferably, the measurement locations are set widely and randomly, avoiding concentration in specific areas. Finally, the average thickness of the carbon material at these 15 points is calculated.

[0075] There is no particular limitation on the carbon material coverage, but a high coverage is desirable. A coverage of 30% or higher further improves electronic conductivity and is therefore preferred. There is no particular limitation on the carbon material coverage method, but sugar carbonization and hydrocarbon pyrolysis are preferred because they can increase the coverage.

[0076] Furthermore, the negative electrode active material particles preferably contain phosphate in their surface layer. By including phosphate in the surface layer of the negative electrode active material particles, they can form a salt with lithium that diffuses to the surface when stored in the atmosphere, thereby capturing lithium and inhibiting lithium diffusion to the surface. Therefore, their stability in the atmosphere can be further improved.

[0077] The aforementioned phosphates are not particularly limited, but it is preferred to use any one or more of lithium phosphate, magnesium phosphate, and aluminum phosphate. Using these phosphates can suppress the absorption of moisture and carbonic acid from the atmosphere while also inhibiting lithium diffusion to the surface.

[0078] There are no particular limitations on the method used to coat the surface with the aforementioned phosphate. Dry mixing methods such as stirring, rotational mixing, and shear mixing can be used, or wet mixing methods such as spraying the negative electrode active material particles with phosphate that has been dispersed in the solution can be used. Shear mixing is preferred. Through shear mixing, the phosphate can be uniformly adhered to or covered on the surface.

[0079] <Negative electrode for non-aqueous electrolyte secondary batteries> Next, a negative electrode (hereinafter also referred to as "negative electrode") for a non-aqueous electrolyte secondary battery containing the negative electrode active material of the present invention will be described. Figure 2This is a cross-sectional view showing an example of the configuration of a negative electrode for a non-aqueous electrolyte secondary battery containing the negative electrode active material of the present invention.

[0080] [Composition of the negative electrode] like Figure 2 As shown, the negative electrode 10 has a negative electrode active material layer 12 on the negative electrode current collector 11. This negative electrode active material layer 12 can be disposed on both sides of the negative electrode current collector 11, or it can be disposed on only one side of the negative electrode current collector 11. Furthermore, if the negative electrode uses the negative electrode active material of the present invention, the negative electrode current collector 11 may be omitted.

[0081] [Negative current collector] The negative electrode current collector 11 is made of a material with excellent conductivity and excellent mechanical strength. Examples of conductive materials that can be used for the negative electrode current collector 11 include copper (Cu) and nickel (Ni). Preferably, this conductive material is one that does not form intermetallic compounds with lithium (Li).

[0082] The preferred negative electrode current collector 11 contains carbon (C) and sulfur (S) in addition to the main elements. This is because the physical strength of the negative electrode current collector is increased. In particular, when there is an active material layer that expands during charging, the presence of the aforementioned elements in the current collector helps to suppress deformation of the electrode containing the current collector. While the content of the aforementioned elements is not particularly limited, it is preferably 100 ppm by mass or less for each. This is because a higher degree of deformation suppression can be achieved. Through this deformation suppression effect, cycle characteristics can be further improved.

[0083] Furthermore, the surface of the negative current collector 11 may or may not be roughened. A roughened negative current collector may be, for example, a metal foil that has undergone electrolytic treatment, embossing, or chemical etching. An unroughened negative current collector may be, for example, a rolled metal foil.

[0084] [Negative electrode active material layer] The negative electrode active material layer 12 contains the negative electrode active material of the present invention. From the perspective of battery design, it may further contain other materials such as negative electrode binder (adhesive) or conductive additive.

[0085] Furthermore, the negative electrode active material layer 12 may contain a mixed negative electrode active material, which includes the negative electrode active material of the present invention and a carbon-based active material. By including a carbon-based active material, the resistance of the negative electrode active material layer decreases, and the expansion stress caused by charging can be alleviated. Examples of carbon-based active materials include pyrolytic carbon, coke, glassy carbon fibers, calcined organic polymer compounds, and carbon black.

[0086] Furthermore, in the mixed negative electrode active material, the mass ratio of silicon-based active material to the total mass of silicon-based negative electrode active material and carbon-based active material is preferably 6% by mass or more. If it is 6% by mass or more, the effect of increasing battery capacity by using silicon-based negative electrode active material can be reliably obtained.

[0087] Furthermore, as described above, the negative electrode active material of the present invention comprises silicon compound particles, wherein the silicon compound particles are silicon compound (SiO2)-containing particles. x The silicon oxide material has a composition of 0.8 ≤ x ≤ 1.2, with x preferably close to 1. This is because high cycling characteristics can be obtained. Furthermore, the composition of the silicon compound in this invention is not necessarily 100% pure and may contain trace amounts of impurity elements.

[0088] Furthermore, in the negative electrode active material of the present invention, the silicon compound particles contain Li2SiO3. These silicon compound particles, by pre-modifying the SiO2 component in the silicon compound that becomes unstable during lithium insertion or extraction during battery charging and discharging into other lithium silicates, can reduce irreversible capacity generated during charging.

[0089] Furthermore, the negative electrode binder included in the negative electrode active material layer can be any one or more of polymeric materials, synthetic rubbers, etc. Examples of polymeric materials include polyvinylidene fluoride, polyimide, polyamide-imide, aramid, polyacrylic acid, lithium polyacrylate, carboxymethyl cellulose, etc. Examples of synthetic rubbers include styrene-butadiene rubber, fluororubber, ethylene propylene diene, etc.

[0090] As a negative electrode conductive additive, one or more of the following carbon materials can be used: carbon black, acetylene black, graphite, Ketjen black, carbon nanotubes, and carbon nanofibers.

[0091] The negative electrode active material layer is formed, for example, by a coating method. The coating method refers to a method in which the negative electrode active material is dispersed in an organic solvent or water and coated onto a negative electrode current collector, etc., wherein the negative electrode active material is obtained by mixing negative electrode active material particles with the aforementioned binder, and, as needed, with conductive additives and carbon-based active material particles.

[0092] [Negative electrode active material and manufacturing method of negative electrode] The negative electrode active material and the negative electrode can be manufactured according to the following steps. First, the method for manufacturing the negative electrode active material used in the negative electrode will be described.

[0093] First, manufacture silicon compounds (SiO2) xSilicon compound particles with a density of 0.8 ≤ x ≤ 1.2 were then embedded with lithium to make them contain Li2SiO3. This produced negative electrode active material particles. Negative electrode active material particles that met the following conditions were selected from these particles. That is, the selection criteria were as follows: when the negative electrode active material particles were measured by X-ray diffraction using Cu-Kα rays, the half-width of the peak caused by the (020) plane of Li2SiO3 obtained by X-ray diffraction was 1.1° or more and 1.5° or less, and in the spectrum obtained by X-ray diffraction, the intensity Ia of the peak caused by the (020) plane of Li2SiO3, the intensity Ib of the peak caused by the (111) plane of Li2SiO3, the intensity I(24.8°) at 2θ = 24.8°, and the intensity I(28.4°) at 2θ = 28.4° satisfied the following formulas (1) to (3). Then, using the screened negative electrode active material particles, negative electrode active materials for non-aqueous electrolyte secondary batteries are prepared. 1.1≤Ib / Ia≤1.5···(1) I(24.8°) / Ia≤0.5···(2) I(28.4°) / Ia≤1.0···(3)

[0094] More specifically, the negative electrode active material can be prepared in the following manner. First, a raw material that produces silicon dioxide gas is heated under reduced pressure in the presence of an inactive gas within a temperature range of 900°C to 1600°C, causing it to produce silicon dioxide gas. Considering the presence of surface oxygen in the silicon metal powder and trace amounts of oxygen in the reactor, it is desirable that the mixing molar ratio be in the range of 0.8 < silicon metal powder / silicon dioxide powder < 1.3.

[0095] The generated silica gas solidifies and deposits on an adsorption plate. Then, with the furnace temperature lowered to below 100°C, the silica deposit is removed and pulverized using a ball mill, air jet mill, or similar method. The resulting powder can be graded. By pulverizing and grading, the particle size distribution and specific surface area of ​​the silicon compound particles can be adjusted. Silicon compound particles can be manufactured using this method. Furthermore, the Si crystallites within the silicon compound particles can be adjusted by changing the vaporization temperature or by post-processing heat treatment.

[0096] Here, a carbon material layer can be formed on the surface of silicon compound particles. Thermochemical vapor deposition (pyrolysis CVD) is a preferred method for forming the carbon material layer. The method for forming a carbon material layer using pyrolysis CVD will be described.

[0097] First, silicon compound particles are loaded into a furnace. Then, hydrocarbon gas is introduced into the furnace, and the furnace temperature is raised. The decomposition temperature is not particularly limited, but it is desirable to be below 1200°C, and more preferably below 850°C. By controlling the decomposition temperature, accidental disproportionation and crystal growth of the negative electrode active material particles can be suppressed. After the furnace temperature is raised to a specific level, a carbon layer forms on the surface of the silicon compound particles. Furthermore, the hydrocarbon gas used as a raw material for the carbon material is not particularly limited, but it is desirable to have a carbon content of [missing information]. n H m In this composition, n ≤ 4. If n ≤ 4, manufacturing costs can be reduced, and the physical properties of the decomposition products can be improved. By controlling the decomposition temperature and time, the thickness of the carbon material on the surface of the negative electrode active material particles can be adjusted.

[0098] Then, Li is inserted into the silicon compound particles manufactured as described above, so that they contain Li₂SiO₃. Lithium insertion is preferably carried out by a redox method.

[0099] In modifications performed via redox methods, for example, silicon compound particles are first immersed in a solution A containing lithium dissolved in an ether solvent, thereby enabling lithium intercalation. Solution A may further contain a polycyclic aromatic compound or a linear polyphenylene compound. After lithium intercalation, the silicon compound particles are immersed in a solution B containing a polycyclic aromatic compound or its derivatives, thereby extracting active lithium from the silicon compound particles. The solvent for solution B can be, for example, an ether-based solvent, a ketone-based solvent, an ester-based solvent, an alcohol-based solvent, an amine-based solvent, or a mixture of these solvents. Further, after immersion in solution B, the silicon compound particles are immersed in a solution C containing an alcohol-based solvent, a carboxylic acid-based solvent, water, or a mixture of these solvents, thereby extracting more active lithium from the silicon compound particles. Alternatively, a solution C' can be used instead of solution C, which contains a compound having a quinone-type structure as a solute and an ether-based solvent, a ketone-based solvent, an ester-based solvent, or a mixture of these solvents as a solvent. Furthermore, silicon compound particles can be repeatedly immersed in solutions B, C, and C'. If lithium is inserted and then extracted in the above manner, a negative electrode active material with higher water resistance can be obtained. Subsequently, it can be washed using methods such as alcohol, alkaline water containing dissolved lithium carbonate, weak acid, or pure water. The amount of lithium contained in the silicon active material particles can be adjusted by controlling the amount of lithium inserted and extracted.

[0100] As the ether-based solvent for solution A, diethyl ether, tert-butyl methyl ether, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or mixtures of these solvents can be used. Among these, tetrahydrofuran, dioxane, and 1,2-dimethoxyethane are particularly preferred. These solvents are preferably dehydrated and, more preferably, deoxygenated.

[0101] Furthermore, as polycyclic aromatic compounds contained in solution A, naphthalene, anthracene, phenanthrene, condensed tetraphenylene, condensed pentaphenylene, pyrene, fenestration, triphenylene, and guanine can be used. And one or more of these polycyclic aromatic compounds and their derivatives; as a linear polyphenylene compound, one or more of biphenyl, terphenyl and their derivatives can be used.

[0102] As polycyclic aromatic compounds contained in solution B, naphthalene, anthracene, phenanthrene, condensed tetraphenylene, condensed pentaphenylene, pyrene, fenestration, triphenylene, and guanine can be used. And one or more of these polycyclic aromatic compounds and their derivatives.

[0103] As an ether-based solvent for solution B, diethyl ether, tert-butyl methyl ether, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether can be used.

[0104] As a ketone solvent, acetone, acetophenone, etc. can be used.

[0105] As an ester solvent, methyl formate, methyl acetate, ethyl acetate, propyl acetate, and isopropyl acetate can be used.

[0106] As an alcohol solvent, it can use methanol, ethanol, propanol and isopropanol, etc.

[0107] As an amine solvent, methylamine, ethylamine, and ethylenediamine can be used.

[0108] When using solution C, the solvent can be mixed in multiple stages, for example, by mixing a ketone solvent with a silicon compound and stirring, and then adding an alcohol solvent.

[0109] As an alcohol-based solvent for solution C, methanol, ethanol, propanol, isopropanol, etc. can be used.

[0110] As a carboxylic acid solvent, it can use formic acid, acetic acid, oxalic acid, etc.

[0111] In addition, when water is used as the solvent, besides pure water, it can also be an aqueous solution containing solute, such as ammonia, lithium acetate, lithium carbonate, or lithium hydroxide.

[0112] Alternatively, a mixed solvent obtained by combining two or more of the above-mentioned alcohol solvents, carboxylic acid solvents, and water can be used.

[0113] After modification via oxidation-reduction, heat treatment can be performed. Heat treatment allows for the crystallization of lithium silicate within the lithium-doped silicon-based active material particles. The heat treatment machine is not particularly limited, but a rotary kiln is preferred. Using a rotary kiln ensures uniform heating. The heat treatment temperature is not particularly limited, but it is preferably performed at a temperature below 800°C, more preferably 650°C. The following applies. The heat treatment atmosphere is not particularly limited, but a non-reactive gas atmosphere such as argon or nitrogen is preferred. This helps suppress oxidation and carbon dioxide absorption during heat treatment. By controlling the heat treatment temperature, heat treatment time, and heat treatment atmosphere, the type and crystallinity of lithium silicate, the disproportionation degree and crystallinity of Si, and the presence of LiOH·H2O and lithium carbonate can be controlled. Although not particularly limited, a ventilated state is preferred over a sealed state. The oxidation-reduction process removes solvent or solute components remaining on the surface of silicon-based active material particles. By controlling the ventilation rate, the solvent or solute components remaining on the surface of silicon-based active material particles can react, thereby adhering to or covering the surface as carbon components. This allows adjustment of the surface area of ​​the silicon-based active material particles and the thickness of the carbon material in the surface layer.

[0114] Furthermore, Li can be embedded into silicon compound particles via thermal doping. For example, modification via thermal doping can be achieved by mixing silicon active material particles with LiH powder or Li powder and heating under a non-oxidizing atmosphere. An Ar atmosphere can be used as an example of a non-oxidizing atmosphere. More specifically, firstly, under an Ar atmosphere, LiH powder or Li powder is thoroughly mixed with silicon oxide powder and sealed, and the mixture is stirred along with the sealed container to homogenize it. Then, modification is performed by heating in the range of 700°C to 750°C. Furthermore, to remove some of the active Li from the silicon compound and to make the slurry more stable, the heated powder can be thoroughly cooled and washed with alcohol, alkaline water, weak acid, or pure water.

[0115] From the negative electrode active material particles (silicon compound particles) manufactured in the above manner, negative electrode active material particles that meet the above conditions when measured by X-ray diffraction using Cu-Kα rays are selected. The manufacturing conditions for negative electrode active material particles that meet each condition can be set experimentally.

[0116] <Composition of Aqueous Negative Electrode Slurry> By adding organic solvents or water to the negative electrode active material manufactured and screened in the above manner, an aqueous negative electrode slurry composition can be obtained. In this case, other materials such as negative electrode binders and conductive additives can be mixed into the negative electrode active material as needed before adding organic solvents or water.

[0117] Then, the above-mentioned aqueous negative electrode slurry composition is coated onto the surface of the negative electrode current collector and dried to form a negative electrode active material layer. At this time, hot pressing or other processes may also be performed as needed. The negative electrode can be manufactured using the above method.

[0118] <Lithium-ion secondary batteries> Next, a lithium-ion secondary battery incorporating the negative electrode active material of the present invention will be described. Here, as a specific example, a laminated film type lithium-ion secondary battery will be given.

[0119] [Structure of laminated film type lithium-ion secondary battery] Figure 3 The laminated lithium-ion secondary battery 20 shown primarily houses a wound electrode body 21 within a sheet-like outer component 25. This wound body has a separator between the positive and negative electrodes and is wound in place. Additionally, sometimes a separator is also present between the positive and negative electrodes, and a laminated body is also housed there. In any type of electrode body, a positive electrode lead 22 is attached to the positive electrode and a negative electrode lead 23 is attached to the negative electrode. The outermost periphery of the electrode body is protected by protective tape.

[0120] The positive and negative leads are led out in one direction from the inside of the outer component 25 toward the outside. The positive lead 22 is made of a conductive material such as aluminum, and the negative lead 23 is made of a conductive material such as nickel or copper.

[0121] The outer component 25 is, for example, a laminated film formed by sequentially stacking a welding layer, a metal layer, and a surface protective layer. In this laminated film, the outer peripheral portions of the welding layers of the two films are fused together with the welding layer facing the electrode body 21, or bonded together using an adhesive or the like. The welding portion is, for example, a film of polyethylene or polypropylene, and the metal portion is, for example, aluminum foil. The protective layer is, for example, nylon.

[0122] A sealing membrane 24 is inserted between the outer component 25 and the positive and negative leads to prevent the intrusion of external gases. The material is, for example, polyethylene, polypropylene, or polyolefin resin.

[0123] [positive electrode] Positive electrode, for example, with Figure 2 The negative electrode 10 is the same, and the positive electrode current collector has a layer of positive electrode active material on both sides or one side.

[0124] The positive current collector is formed, for example, from a conductive material such as aluminum.

[0125] The positive electrode active material layer includes any one or more positive electrode materials capable of absorbing and releasing lithium ions, and may also include other materials such as binders, conductive additives, and dispersants, depending on the design. In this case, the details of the binders and conductive additives are, for example, the same as those of the negative electrode binders and negative electrode conductive additives already described.

[0126] The cathode material is preferably a lithium-containing compound. Examples of such lithium-containing compounds include composite oxides composed of lithium and transition metal elements, or phosphate compounds containing lithium and transition metal elements. Among these described cathode materials, compounds containing at least one of nickel, iron, manganese, and cobalt are preferred. Chemical formulas for these cathode materials, for example, are derived from Li... x M1O2 or Li y M2PO4 is used as the denoting element. In the above formula, M1 and M2 represent at least one or more transition metal elements. The values ​​of x and y vary depending on the charge / discharge state of the battery, but are usually displayed as 0.05≤x≤1.10 and 0.05≤y≤1.10.

[0127] As a composite oxide containing lithium and a transition metal element, examples include lithium-cobalt composite oxide (Li₂O₃). x CoO2), lithium nickel composite oxide (Li x Examples of lithium-containing phosphoric acid compounds include lithium iron phosphate (LiFePO4) and lithium iron manganese phosphate (LiFe). 1-u Mn u PO4 (0 < u < 1), etc. This is because using these cathode materials can achieve high battery capacity and excellent cycle characteristics.

[0128] [negative electrode] The negative electrode has the same characteristics as the above. Figure 2 The lithium-ion secondary battery uses the same structure as the negative electrode 10, for example, having a negative electrode active material layer 12 on both sides of the current collector 11. Preferably, the negative electrode charging capacity of this negative electrode becomes larger than the capacity obtained from the positive electrode active material (as the battery charging capacity). This is because the deposition of lithium metal on the negative electrode can be suppressed.

[0129] The positive electrode active material layer is disposed on a portion of both sides of the positive electrode current collector, and the negative electrode active material layer is also disposed on a portion of both sides of the negative electrode current collector. In this case, for example, there are regions where the negative electrode active material layer disposed on the negative electrode current collector does not have an opposing positive electrode active material layer. This is for the purpose of a stable battery design.

[0130] In the non-opposite region, that is, in the region where the negative electrode active material layer and the positive electrode active material layer are not opposite each other, it is almost unaffected by charging and discharging. Therefore, the state of the negative electrode active material layer can be maintained after its formation, thereby enabling accurate and reproducible detection of the composition of the negative electrode active material, etc., regardless of whether charging and discharging occurs.

[0131] [Septum] The separator isolates the positive and negative electrodes, preventing short circuits caused by contact between the two electrodes and allowing lithium ions to pass through. This separator is formed, for example, from a porous membrane made of synthetic resin or ceramic, and may also have a laminated structure composed of two or more porous membranes. Examples of synthetic resins include polytetrafluoroethylene, polypropylene, and polyethylene.

[0132] Electrolyte At least a portion of the active material layer or in the membrane contains a liquid electrolyte (electrolyte). The electrolyte contains electrolyte salts dissolved in a solvent and may contain other materials such as additives.

[0133] Solvents can be, for example, non-aqueous solvents. Examples of non-aqueous solvents include ethylene carbonate, propylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, 1,2-dimethoxyethane, or tetrahydrofuran. Among these, it is desirable to use at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. This is because better properties can be obtained. Furthermore, by combining high-viscosity solvents such as ethylene carbonate and propylene carbonate with low-viscosity solvents such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate, even more advantageous properties can be obtained. This is because the dissociation and ion mobility of the electrolyte salt are increased.

[0134] When using alloy-based negative electrodes, it is desirable, in particular, that the solvent contains at least one of halochain carbonates or halocyclic carbonates. This allows a stable coating to form on the surface of the negative electrode active material during charging and discharging, especially during charging. Here, halochain carbonates refer to chain carbonates having a halogen as a constituent element (at least one hydrogen atom is replaced by a halogen). Furthermore, halocyclic carbonates refer to cyclic carbonates having a halogen as a constituent element (i.e., at least one hydrogen atom is replaced by a halogen).

[0135] There are no particular restrictions on the type of halogen, but fluorine is preferred. This is because it forms a superior coating compared to other halogens. Furthermore, a higher quantity of halogen is preferable, as it results in a more stable coating and reduces electrolyte decomposition reactions.

[0136] Examples of halogenated chain carbonates include fluoromethyl methyl carbonate and difluoromethyl methyl carbonate. Examples of halogenated cyclic carbonates include 4-fluoro-1,3-dioxolane-2-one and 4,5-difluoro-1,3-dioxolane-2-one.

[0137] As a solvent additive, unsaturated carbon-bonded cyclic carbonates are preferred. This is because they form a stable coating on the negative electrode surface during charging and discharging, which can suppress the decomposition reaction of the electrolyte. Examples of unsaturated carbon-bonded cyclic carbonates include vinylene carbonate or ethylene ethylene carbonate.

[0138] Furthermore, sulfonyl lactones (cyclic sulfonates) are preferably included as solvent additives. This is because they increase the chemical stability of the battery. Examples of sulfonyl lactones include propane sulfonyl lactone and propene sulfonyl lactone.

[0139] Furthermore, the solvent preferably includes an acid anhydride. This is because it increases the chemical stability of the electrolyte. Examples of acid anhydrides include, for instance, propane disulfonic acid anhydride.

[0140] The electrolyte salt can contain any one or more light metal salts, such as lithium salts. Examples of lithium salts include lithium hexafluorophosphate (LiPF6) and lithium tetrafluoroborate (LiBF4).

[0141] The content of the electrolyte salt relative to the solvent is preferably 0.5 mol / kg or more and 2.5 mol / kg or less. This is because it allows for high ionic conductivity.

[0142] [Manufacturing method of laminated film secondary battery] In this invention, a negative electrode can be manufactured using the negative electrode active material prepared by the method for preparing the negative electrode active material of this invention as described above, and the manufactured negative electrode can be used to manufacture a lithium-ion secondary battery.

[0143] The positive electrode is initially manufactured using the aforementioned positive electrode material. First, the positive electrode active material is mixed with binders, conductive additives, etc., as needed, to form a positive electrode mixture. This mixture is then dispersed in an organic solvent to form a positive electrode mixture slurry. Next, using a coating device such as a die coating machine equipped with a knife roll or die head, the mixture slurry is coated onto the positive electrode current collector and dried with hot air to obtain a positive electrode active material layer. Finally, the positive electrode active material layer is compressed and shaped using a roller press or similar device. Heating can be performed at this stage, and the heating or compression process can be repeated several times.

[0144] Subsequently, using the same operating steps as those used in manufacturing the negative electrode 10 for the aforementioned lithium-ion secondary battery, a layer of negative electrode active material is formed on the negative electrode current collector to manufacture the negative electrode.

[0145] During the manufacturing of the positive and negative electrodes, active material layers are formed on both sides of the positive and negative current collectors. At this time, the coating length of the active material on the two sides of any electrode may not be consistent (see reference). Figure 2 ).

[0146] Next, an electrolyte is prepared. Then, the positive electrode lead 22 is attached to the positive current collector using ultrasonic welding or the like, and simultaneously the negative electrode lead 23 is attached to the negative current collector. Next, the positive and negative electrodes are laminated or wound together with a separator in between to create a wound electrode body 21, and protective tape is adhered to its outermost periphery. Subsequently, the wound body is shaped into a flat form. Next, the wound electrode body is sandwiched between folded film-like outer components 25, and the insulating portions of the outer components are bonded together using a thermal fusion method, sealing the wound electrode body in a state open only in one direction. Next, a sealing film is inserted between the positive and negative electrode leads and the outer components. Next, a predetermined amount of the prepared electrolyte is added through the open portion, and vacuum impregnation is performed. After impregnation, the open portion is bonded using a vacuum thermal fusion method. This allows the manufacture of a laminated film type lithium-ion secondary battery 20. Example

[0147] The following examples and comparative examples of the present invention are shown to illustrate the present invention in more detail, but the present invention is not limited to these examples.

[0148] (Example 1-1) Follow these steps to manufacture Figure 3 The laminated film type lithium-ion secondary battery 20 is shown.

[0149] The positive electrode was initially manufactured. 95% by mass of the positive electrode active material, namely lithium nickel cobalt composite oxide (LiNi), was used. 0.7 Co 0.25 Al 0.05 A positive electrode binder (PVDF) and 2.5% by mass of positive electrode conductive additive and binder (polyvinylidene fluoride) are mixed to prepare a positive electrode mixture. Next, the positive electrode mixture is dispersed in an organic solvent (N-methyl-2-pyrrolidone: NMP) to form a paste. Then, the paste is coated onto both sides of the positive electrode current collector using a coating device with a die, and dried using a hot air drying device. At this point, a positive electrode current collector with a thickness of 15 μm is used. Finally, it is compressed and molded using a roller press.

[0150] Next, the negative electrode is manufactured. First, the negative electrode active material is manufactured as follows: A raw material consisting of a mixture of metallic silicon and silicon dioxide is introduced into a reactor, and the vaporized material is deposited onto an adsorption plate under a vacuum of 10 Pa. After sufficient cooling, the deposit is removed and pulverized using a ball mill. The resulting silicon compound particles are SiO₂. x The x-value is 0.8. Then, the particle size of the silicon compound particles is adjusted by gradation. Next, carbon material is coated onto the surface of the silicon compound particles by performing pyrolysis CVD using propylene gas. The Si crystallinity of the silicon compound particles is adjusted by pyrolysis CVD. Furthermore, the thickness of the carbon material is adjusted by the pyrolysis CVD temperature and time.

[0151] Then, lithium is inserted into silicon compound particles using a redox method to modify them. The amount of lithium contained in the silicon active material particles is adjusted by controlling the amount of lithium inserted and extracted.

[0152] Then, the modified silicon-based active material particles were subjected to heat treatment. A rotary kiln was used as the heat treatment machine, and heat treatment was carried out at a temperature below 800°C while argon gas was introduced. By controlling the heat treatment temperature, heat treatment time, and heat treatment atmosphere, the type and crystallinity of lithium silicate, the disproportionation degree and crystallinity of Si, and the presence of LiOH·H2O and lithium carbonate were adjusted.

[0153] Then, X-ray diffraction using Cu-Kα rays was performed, and background correction was performed according to the method described above to obtain a background-corrected spectrum. The values ​​Ia, Ib, I(24.8°), I(28.4°), I(29.9°), and I(31.7°) were read from the background-corrected spectrum. Based on these values, Ib / Ia, I(24.8°) / Ia, I(28.4°) / Ia, I(29.9°) / Ia, and I(31.7°) / Ia were calculated respectively. At this point, Ib / Ia = 1.3, I(24.8°) / Ia = 0.3, I(28.4°) / Ia = 0.8, I(29.9°) / Ia = 0.4, and I(31.7°) / Ia = 0.3. Furthermore, the half-width of the peak caused by the (020) plane of Li₂SiO₃ is 1.3°.

[0154] The amount of silicon in the water after dispersing the negative electrode active material particles at a ratio of 10% by mass in water at 25°C for 1 hour was determined using the following method. First, the negative electrode active material particles were dispersed at a ratio of 10% by mass in pure water at 25°C and stirred for 1 hour. Then, the dispersion was filtered, and the resulting filtrate was used to determine the amount of Si in the water using inductively coupled plasma optical emission spectrometry (ICP-OES). The result showed that the amount of Si was 10 ppm by mass.

[0155] In addition, the particle size distribution and BET specific surface area of ​​the silicon-based active material particles were determined. The median particle size was 7 μm, and D90 / D10 = 2. Furthermore, the BET specific surface area was 1 m². 2 / g.

[0156] Then, the negative electrode active material is incorporated into the carbon-based active material at a mass ratio of silicon-based active material particles to carbon-based active material particles of 2:8 to create a mixed negative electrode active material. Here, a material formed by mixing natural graphite and artificial graphite to be covered by the asphalt layer at a mass ratio of 5:5 is used as the carbon-based active material. Furthermore, the median particle size of the carbon-based active material is 20 μm.

[0157] Then, the above-mentioned mixed negative electrode active material, conductive additive 1 (carbon nanotubes, CNTs), conductive additive 2 (carbon microparticles with a median particle size of approximately 50 nm), styrene-butadiene rubber (styrene-butadiene copolymer, hereinafter referred to as SBR), and carboxymethyl cellulose (hereinafter referred to as CMC) are mixed at a dry mass ratio of 92.5:1:1:2.5:3, and then diluted with pure water to prepare an aqueous negative electrode slurry. In addition, the above-mentioned SBR and CMC are negative electrode binders (negative electrode adhesives).

[0158] Furthermore, an electrolytic copper foil with a thickness of 15 μm was used as the negative electrode current collector. This electrolytic copper foil contained carbon and sulfur, each at a concentration of 70 ppm by mass. Finally, a negative electrode slurry was coated onto the negative electrode current collector and dried at 100°C for 1 hour under a vacuum atmosphere. After drying, the deposition amount (also known as the areal density) of the negative electrode active material layer per unit area on one side of the negative electrode was 5 mg / cm³. 2 .

[0159] Then, the solvents (4-fluoro-1,3-dioxolane-2-one (FEC), ethylene carbonate (EC), and dimethyl carbonate (DMC)) were mixed to dissolve the electrolyte salt (lithium hexafluorophosphate: LiPF6) to prepare the electrolyte. At this point, the solvent composition was set to a volume ratio of FEC:EC:DMC = 10:20:70, and the electrolyte salt content was set to 1.2 mol / kg relative to the solvent.

[0160] The secondary battery is then assembled as follows: First, aluminum leads are ultrasonically welded to one end of the positive current collector, and nickel leads are welded to one end of the negative current collector. Next, the positive electrode, separator, negative electrode, and separator are sequentially stacked and wound along the long side to obtain a wound electrode body. The finished portion of the winding is secured with PET protective tape. A laminated film (12 μm thick) is used as the separator, which is formed by sandwiching a film of porous polyethylene as the main component between a film of porous polypropylene as the main component. Next, after the electrode body is sandwiched between the outer components, the outer peripheral portions except for one side are thermally fused together to house the electrode body inside. An aluminum laminated film consisting of a nylon film, aluminum foil, and a polypropylene film is used as the outer component. Next, the prepared electrolyte is injected through the opening, impregnated under a vacuum atmosphere, and then thermally fused to seal the battery.

[0161] The initial charge-discharge characteristics of the secondary battery manufactured in the above manner were evaluated.

[0162] When testing the initial charge and discharge characteristics, the initial efficiency (sometimes also called the initial capacity) is calculated. The initial efficiency is calculated using the formula: Initial efficiency (%) = (Initial discharge capacity / Initial charge capacity) × 100.

[0163] In addition, the atmospheric stability was evaluated using the following method: 10g of the manufactured negative electrode active material particles were placed in a constant temperature bath at 40°C and 75% RH and stored for 24 hours. After that, the initial efficiency, weight change, Li dissolution, and aggregation state were measured.

[0164] The amount of Li leaching was determined using the following steps. The amount of surface alkali stored before and after the thermostatic bath was measured separately. The amount of Li leaching was set as follows for the amount of surface alkali stored before the thermostatic bath (B1) and the amount of surface alkali stored after the thermostatic bath (B2). (Li dissolution amount) = B2 - B1

[0165] The surface alkalinity was determined using the following steps: First, 1 g of negative electrode active material particles were dispersed in 50 g of water at 25°C and stirred for 10 minutes. Then, the filtrate obtained by filtering the dispersion was neutralized and titrated. The weight of lithium ions in the filtrate was determined based on the titration amount required to reach pH 5. The surface alkalinity was calculated by dividing the obtained weight of lithium ions by the amount of lithium in the negative electrode active material.

[0166] The aggregation state was evaluated by comparing the weight on the sieve after suction sieving before and after storage in the constant temperature bath. Suction sieving was performed as follows: First, 100g of negative electrode active material particles were prepared and sieved for 2 minutes using a suction sieve with a pore size of 45μm. The suction pressure was set to 3kPa. After sieving, the weight on the sieve was measured. Then, the weight on the sieve before and after storage in the constant temperature bath was compared. A weight of 0.02g or more was considered agglomerated, and a weight of less than 0.02g was considered non-agglomerated.

[0167] (Examples 1-2 to 1-3, Comparative Examples 1-1 and 1-2) Except for adjusting the oxygen content within the bulk silicon compound, the secondary battery was manufactured in the same manner as in Example 1-1. This time, the oxygen content was adjusted by changing the ratio of metallic silicon to silicon dioxide in the silicon compound raw materials and the heating temperature. The silicon compounds used in Examples 1-1 to 1-3, and Comparative Examples 1-1 and 1-2, were modified to use SiO₂... x The x values ​​for the silicon compounds are shown in Table 1.

[0168] At this time, the silicon-based active material particles of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2 have the following properties. The silicon compound particles in the negative electrode active material particles contain Li₂SiO₃ internally. Furthermore, the half-width (2θ) of the diffraction peaks caused by the (020) crystal plane of Li₂SiO₃ obtained by X-ray diffraction of the silicon compound is 1.3°, Ib / Ia = 1.3, I(24.8°) / Ia = 0.3, I(28.4°) / Ia = 0.8, I(29.9°) / Ia = 0.4, and I(31.7°) / Ia = 0.3. Furthermore, peaks for Li₂Si₂O₅ and LiOH·H₂O were not detected. Furthermore, the average thickness of the carbon material covering the surface is 50 nm. Furthermore, the median particle size of the negative electrode active material particles is 7 μm. Furthermore, the BET specific surface area of ​​the negative electrode active material particles is 1 m². 2 / g.

[0169] The evaluation results of Examples 1-1 to 1-3 and Comparative Examples 1-1 and 1-2 are shown in Table 1.

[0170] [Table 1] SiO x Ratio: 20% by mass; Contains Li₂SiO₃; Li₂SiO₃ (0₂O) plane half-width: 1.3; Ib / Ia: 1.3 I(24.8°) / Ia: 0.3; Li2Si2O5 peak: none; I(28.4°) / Ia: 0.8; Si(111) surface peak: none I(29.9°) / Ia: 0.4; LiOH·H2O peak: none; I(31.7°) / Ia: 0.3; Silica leaching: 10 ppm by mass BET specific surface area: 1m 2 / g; D50 = 7μm; D90 / D10 = 2; Carbon material thickness: 50nm; Phosphate: None

[0171] As shown in Table 1, in the case of SiO x In the silicon compounds described, when the value of x is outside the range of 0.8 ≤ x ≤ 1.2, the battery characteristics or stability in the atmosphere deteriorates. For example, as shown in Comparative Example 1-1, when oxygen is insufficient (x = 0.7), the weight change and Li dissolution are large, and aggregation occurs. Furthermore, the initial efficiency decreases significantly before and after storage. On the other hand, as shown in Comparative Example 1-2, when the oxygen content is high (x = 1.3), the conductivity decreases, and the initial efficiency is low even before storage.

[0172] (Example 2-1, Example 2-2) Except for changing the half-width of Li2SiO3 contained within the silicon compound particles as shown in Table 2, secondary batteries were manufactured under the same conditions as in Examples 1-2, and the stability of the negative electrode active material in the atmosphere and the initial efficiency of the secondary battery were evaluated.

[0173] (Comparative Example 2-1) Except for not embedding lithium into silicon compound particles, secondary batteries were manufactured under the same conditions as in Examples 1-2, and the stability of the negative electrode active material in the atmosphere and the initial efficiency of the secondary battery were evaluated.

[0174] The results of Examples 2-1 to 2-4 and Comparative Examples 2-1 to 2-3 are shown in Table 2.

[0175] [Table 2] SiO x (x=0.9); SiO x Ratio: 20% by mass; Ib / Ia: 1.3 I(24.8°) / Ia: 0.3; Li2Si2O5 peak: none; I(28.4°) / Ia: 0.8; Si(111) surface peak: none I(29.9°) / Ia: 0.4; LiOH·H2O peak: none; I(31.7°) / Ia: 0.3; Silica leaching: 10 ppm by mass BET specific surface area: 1m 2 / g; D50 = 7μm; D90 / D10 = 2; Carbon material thickness: 50nm; Phosphate: None

[0176] By incorporating Li₂SiO₃ into the silicon compound, the initial efficiency was significantly improved. On the other hand, in Comparative Example 2-1, where no modification was performed and lithium was not incorporated into the silicon compound, the initial efficiency decreased. Furthermore, when the half-width at half-maximum (WHM) of Li₂SiO₃ was in the range of 1.1° to 1.5°, good initial efficiency and atmospheric stability were achieved. Conversely, in Comparative Example 2-2, where the WHM of Li₂SiO₃ was less than 1.1°, the initial efficiency before storage decreased. Moreover, in Comparative Example 2-3, where the WHM of Li₂SiO₃ was greater than 1.5°, a decrease in initial efficiency, weight increase, Li dissolution, and aggregation were observed after storage, indicating instability in the atmosphere.

[0177] (Examples 3-1 to 3-2, Comparative Examples 3-1 to 3-2) Except for adjusting Ib / Ia as shown in Table 3, secondary batteries were manufactured under the same conditions as in Examples 1-2, and the stability of the negative electrode active material in the atmosphere and the initial efficiency of the secondary battery were evaluated.

[0178] The results of Examples 3-1 to 3-2 and Comparative Examples 3-1 to 3-2 are shown in Table 3.

[0179] [Table 3] SiO x (x=0.9); SiO x Ratio: 20% by mass; Contains Li₂SiO₃; Half-width of Li₂SiO₃ (0₂O) plane: 1.3 I(24.8°) / Ia: 0.3; Li2Si2O5 peak: none; I(28.4°) / Ia: 0.8; Si(111) surface peak: none I(29.9°) / Ia: 0.4; LiOH·H2O peak: none; I(31.7°) / Ia: 0.3; Silica leaching: 10 ppm by mass BET specific surface area: 1m 2 / g; D50 = 7μm; D90 / D10 = 2; Carbon material thickness: 50nm; Phosphate: None

[0180] Table 3 shows that the initial efficiency and atmospheric stability are good when the ratio is within the range of 1.1 ≤ Ib / Ia ≤ 1.5. On the other hand, in Comparative Example 3-1 (Ib / Ia < 1.1), the weight increased after 24 hours of storage, Li dissolution was significant, and condensation was observed, indicating instability in the atmosphere. Furthermore, in Comparative Example 3-2 (1.5 < Ib / Ia), the initial efficiency before storage was low.

[0181] (Examples 4-1 to 4-2, Comparative Example 4-1) Except for changing the value of I(24.8°) / Ia and the presence or absence of the Li2Si2O5 peak as shown in Table 4, the secondary battery was manufactured under the same conditions as in Examples 1-2, and the stability of the negative electrode active material in the atmosphere and the initial efficiency of the secondary battery were evaluated.

[0182] [Table 4] SiO x (x=0.9); SiO x Ratio: 20% by mass; Contains Li₂SiO₃; Li₂SiO₃ (0₂O) plane half-width: 1.3; Ib / Ia: 1.3 I(28.4°) / Ia: 0.8; Si(111) surface peak: None I(29.9°) / Ia: 0.4; LiOH·H2O peak: none; I(31.7°) / Ia: 0.3; Silica leaching: 10 ppm by mass BET specific surface area: 1m 2 / g; D50 = 7μm; D90 / D10 = 2; Carbon material thickness: 50nm; Phosphate: None

[0183] As shown in Table 4, good initial efficiency was achieved when I(24.8°) / Ia ≤ 0.5. On the other hand, in Comparative Example 4-1, where 0.5 < I(24.8°) / Ia, the initial efficiency decreased significantly. Furthermore, the initial efficiency increased when there was no Li2Si2O5 peak compared to the case with the Li2Si2O5 peak.

[0184] (Examples 5-1 to 5-2, Comparative Example 5-1) Except for changing the value of I(28.4°) / Ia and the presence or absence of the Si peak as shown in Table 5, the secondary battery was manufactured under the same conditions as in Examples 1-2, and the stability of the negative electrode active material in the atmosphere and the initial efficiency of the secondary battery were evaluated.

[0185] [Table 5] SiO x (x=0.9); SiO x Ratio: 20% by mass; Contains Li₂SiO₃; Li₂SiO₃ (0₂O) half-width: 1.3; Ib / Ia: 13 I(24.8°) / Ia: 0.3; Li2Si2O5 peak: none I(29.9°) / Ia: 0.4; LiOH·H2O peak: none; I(31.7°) / Ia: 0.3; Silica leaching: 10 ppm by mass BET specific surface area: 1m 2 / g; D50 = 7μm; D90 / D10 = 2; Carbon material thickness: 50nm; Phosphate: None

[0186] As shown in Table 5, good atmospheric stability and initial efficiency were obtained when I(28.4°) / Ia ≤ 1.0. On the other hand, in Comparative Example 5-1, where 1.0 < I(28.4°) / Ia, a decrease in initial efficiency, an increase in weight, Li dissolution, and condensation were observed after 24 hours of storage, indicating instability in the atmosphere. Furthermore, even better characteristics were obtained when the peak of the Si(111) plane was not identified.

[0187] (Examples 6-1 to 6-3) Except for changing the value of I(29.9°) / Ia and the presence or absence of the LiOH·H2O peak as shown in Table 6, the secondary battery was manufactured under the same conditions as in Examples 1-2, and the stability of the negative electrode active material in the atmosphere and the initial efficiency of the secondary battery were evaluated.

[0188] [Table 6] SiO x (x=0.9); SiO x Ratio: 20% by mass; Contains Li₂SiO₃; Li₂SiO₃ (0₂O) plane half-width: 1.3; Ib / Ia: 1.3 I(24.8°) / Ia: 0.3; Li2Si2O5 peak: none; I(28.4°) / Ia: 0.8; Si(111) surface peak: none I(31.7°) / Ia: 0.3; Silica leaching: 10 ppm by mass BET specific surface area: 1m 2 / g; D50 = 7μm; D90 / D10 = 2; Carbon material thickness: 50nm; Phosphate: None

[0189] As shown in Table 6, when the ratio I(29.9°) / Ia ≤ 0.7, no condensation occurs even after 24 hours of storage, demonstrating particularly good atmospheric stability. Furthermore, when the LiOH·H₂O peak is not detected, no weight change is observed even after 24 hours of storage, and atmospheric stability remains good.

[0190] (Examples 7-1 to 7-2) Except for changing the value of I(31.7°) / Ia as shown in Table 7, the secondary battery was manufactured under the same conditions as in Examples 1-2, and the stability of the negative electrode active material in the atmosphere and the initial efficiency of the secondary battery were evaluated.

[0191] [Table 7] SiO x (x=0.9); SiO x Ratio: 20% by mass; Contains Li₂SiO₃; Li₂SiO₃ (0₂O) plane half-width: 1.3; Ib / Ia: 1.3 I(24.8°) / Ia: 0.3; Li2Si2O5 peak: none; I(28.4°) / Ia: 0.8; Si(111) surface peak: none I(29.9°) / Ia: 0.4; LiOH·H2O peak: none; Silica leaching: 10 ppm by mass BET specific surface area: 1m 2 / g; D50 = 7μm; D90 / D10 = 2; Carbon material thickness: 50nm; Phosphate: None

[0192] As shown in Table 7, when the value of I(31.7°) / Ia ≤ 0.7, no weight change was observed even after 24 hours of storage, indicating good stability in the atmosphere.

[0193] (Example 8-1, Example 8-2) Except for dispersing the negative electrode active material particles at a ratio of 10% by mass in water at 25°C for 1 hour, changing the amount of silicon in the water as shown in Table 8, the secondary battery was manufactured under the same conditions as in Examples 1-2, and the stability of the negative electrode active material in the atmosphere and the initial efficiency of the secondary battery were evaluated.

[0194] [Table 8] SiO x (x=0.9); SiO x Ratio: 20% by mass; Contains Li₂SiO₃; Li₂SiO₃ (0₂O) plane half-width: 1.3; Ib / Ia: 1.3 I(24.8°) / Ia: 0.3; Li2Si2O5 peak: none; I(28.4°) / Ia: 0.8; Si(111) surface peak: none I(29.9°) / Ia: 0.4; LiOH·H2O peak: none; I(31.7°) / Ia: 0.3 BET specific surface area: 1m 2 / g; D50 = 7μm; D90 / D10 = 2; Carbon material thickness: 50nm; Phosphate: None

[0195] As shown in Table 8, if the negative electrode active material particles are dispersed in water at 25°C at a ratio of 10% by mass for 1 hour, the silicon content in the water is less than 50 ppm. Even after storage for 24 hours, the weight does not change, indicating good stability in the atmosphere.

[0196] (Examples 9-1 to 9-3) Except for changing the BET specific surface area of ​​the silicon compound particles as shown in Table 9, the secondary batteries were manufactured under the same conditions as in Examples 1-2, and the stability of the negative electrode active material in the atmosphere and the initial efficiency of the secondary batteries were evaluated.

[0197] [Table 9] SiO x (x=0.9); SiO x Ratio: 20% by mass; Contains Li₂SiO₃; Li₂SiO₃ (0₂O) plane half-width: 1.3; Ib / Ia: 1.3 I(24.8°) / Ia: 0.3; Li2Si2O5 peak: none; I(28.4°) / Ia: 0.8; Si(111) surface peak: none I(29.9°) / Ia: 0.4; LiOH·H2O peak: none; I(31.7°) / Ia: 0.3; Silica leaching: 10 ppm by mass D50 = 7 μm; D90 / D10 = 2; Carbon material thickness: 50 nm; Phosphate: None

[0198] The BET specific surface area of ​​the negative electrode active material particles is 1m². 2 / g or more 3m 2 Good atmospheric stability and initial efficiency were achieved within the range of / g or less. In Example 9-1, where the BET specific surface area was less than 1, the initial efficiency decreased slightly. When the BET specific surface area was greater than 3m², the initial efficiency decreased slightly. 2 In Examples 9-3, where the weight was / g, an increase in weight was observed after 24 hours of storage.

[0199] (Examples 10-1 to 10-6) Except for adjusting the median particle size and D90 / D10 of the silicon-based active material particles, secondary batteries were manufactured under the same conditions as in Examples 1-2, and the stability of the negative electrode active material in the atmosphere and the initial efficiency of the secondary battery were evaluated.

[0200] [Table 10] SiO x (x=0.9); SiO x Ratio: 20% by mass; Contains Li₂SiO₃; Li₂SiO₃ (0₂O) plane half-width: 1.3; Ib / Ia: 1.3 I(24.8°) / Ia: 0.3; Li2Si2O5 peak: none; I(28.4°) / Ia: 0.8; Si(111) surface peak: none I(29.9°) / Ia: 0.4; LiOH·H2O peak: none; I(31.7°) / Ia: 0.3; Silica leaching: 10 ppm by mass BET specific surface area: 1m 2 / g; Carbon material thickness: 50nm; Phosphate: None

[0201] As shown in Table 10, good atmospheric stability and initial efficiency were obtained when the median particle size was 4.0 μm or larger and 15 μm or smaller, and the D90 / D10 ratio was 3 or smaller. In Example 10-1 (median particle size less than 4.0 μm) and Example 10-4 (median particle size greater than 15 μm), a slight decrease in initial efficiency was observed after 24 hours of storage. Furthermore, in Example 10-6 (D90 / D10 greater than 3), a slight decrease in initial efficiency was also observed after 24 hours of storage.

[0202] (Example 11-1) Except that no carbon material was coated on the surface of the silicon-based active material particles, secondary batteries were manufactured under the same conditions as in Examples 1-2, and the initial efficiency and slurry stability were evaluated.

[0203] (Examples 11-2 to 11-4) Except for changing the average thickness of the carbon material covering the surface of the silicon-based active material particles as shown in Table 11, secondary batteries were manufactured under the same conditions as in Examples 1-2, and the stability of the negative electrode active material in the atmosphere and the initial efficiency of the secondary battery were evaluated. The average thickness of the carbon material was adjusted by changing the CVD conditions.

[0204] [Table 11] SiO x (x=0.9); SiO x Ratio: 20% by mass; Contains Li₂SiO₃; Li₂SiO₃ (0₂O) plane half-width: 1.3; Ib / Ia: 1.3 I(24.8°) / Ia: 0.3; Li2Si2O5 peak: none; I(28.4°) / Ia: 0.8; Si(111) surface peak: none I(29.9°) / Ia: 0.4; LiOH·H2O peak: none; I(31.7°) / Ia: 0.3; Silica leaching: 10 ppm by mass BET specific surface area: 1m 2 / g; D50 = 7μm; D90 / D10 = 2; Phosphate: None

[0205] As shown in Table 11, good atmospheric stability and initial efficiency were achieved when the average thickness of the carbon material was 10 nm or more and less than 100 nm. In Example 11-1, where the surface did not contain carbon material, a slight decrease in initial efficiency was observed after 24 hours of storage. Furthermore, in Example 11-4, where the carbon material thickness was greater than 100 nm, the initial efficiency before storage was slightly lower.

[0206] (Examples 12-1 to 12-3) Except for including phosphate on the surface of the silicon-based active material particles, secondary batteries were manufactured under the same conditions as in Examples 1-2, and the stability of the negative electrode active material in the atmosphere and the initial efficiency of the secondary battery were evaluated. The phosphate was incorporated at a ratio of 1% by weight relative to the negative electrode active material particles and adhered to the surface of the particles by shear mixing.

[0207] [Table 12] SiO x (x=0.9); SiO x Ratio: 20% by mass; Contains Li₂SiO₃; Li₂SiO₃ (0₂O) plane half-width: 1.3; Ib / Ia: 1.3 I(24.8°) / Ia: 0.3; Li2Si2O5 peak: none; I(28.4°) / Ia: 0.8; Si(111) surface peak: none I(29.9°) / Ia: 0.4; LiOH·H2O peak: none; I(31.7°) / Ia: 0.3; Silica leaching: 10 ppm by mass BET specific surface area: 1m 2 / g; D50=7μm; D90 / D10=2; Carbon material thickness: 50nm;

[0208] As shown in Table 12, when the surface contains phosphate, the amount of Li leaching decreases after 24 hours of storage, thus improving the stability in the atmosphere.

[0209] Furthermore, this invention is not limited to the embodiments described above. The embodiments described above are illustrative examples; any technical solution that has substantially the same structure and performs the same effect as the technical concept described in the claims of this invention is included within the technical scope of this invention.

Claims

1. A negative electrode active material for a non-aqueous electrolyte secondary battery, comprising negative electrode active material particles, characterized in that... The negative electrode active material particles contain silicon compound particles, and the silicon compound particles contain silicon compound SiO. x Where 0.8 ≤ x ≤ 1.2, The silicon compound particles contain Li2SiO3. When the negative electrode active material particles were measured using Cu-Kα X-ray diffraction, The half-width of the peak caused by the (020) plane of Li2SiO3 obtained by this X-ray diffraction is greater than 1.1° and less than 1.5°. In the X-ray diffraction spectrum obtained by this method, the intensities Ia of the peak caused by the (020) plane of Li2SiO3, Ib of the peak caused by the (111) plane of Li2SiO3, I(24.8°) at 2θ=24.8°, and I(28.4°) at 2θ=28.4° satisfy all of the following equations (1) to (3): 1.1≤Ib / Ia≤1.5 ···(1); I(24.8°) / Ia≤0.5···(2); I(28.4°) / Ia≤1.0···(3).

2. The negative electrode active material for a nonaqueous electrolyte secondary cell according to claim 1, characterized by The spectrum obtained by X-ray diffraction does not have the peak near 2θ=24.8° caused by Li2Si2O5.

3. The negative electrode active material for a nonaqueous electrolyte secondary cell according to claim 1, characterized by The spectrum obtained by X-ray diffraction does not have a peak near 2θ=28.4° caused by the (111) plane of Si.

4. The negative electrode active material for a nonaqueous electrolyte secondary cell according to claim 1, characterized by The spectrum obtained by X-ray diffraction satisfies 1.2≤Ib / Ia≤1.

3.

5. The negative electrode active material for a nonaqueous electrolyte secondary cell according to claim 1, characterized by The half-width of the peak caused by the (020) plane of the Li2SiO3 is greater than 1.2° and less than 1.3°.

6. The negative electrode active material for a nonaqueous electrolyte secondary cell according to claim 1, characterized by In the spectrum obtained by X-ray diffraction, the intensity I(29.9°) at 2θ=29.9° caused by LiOH·H2O satisfies I(29.9°) / Ia≤0.

7.

7. The negative electrode active material for a nonaqueous electrolyte secondary cell according to claim 6, characterized by The spectrum obtained by X-ray diffraction does not have the peak near 2θ=29.9° caused by LiOH·H2O.

8. The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, characterized in that, In the spectrum obtained by X-ray diffraction, the intensity I(31.7°) at 2θ=31.7° satisfies I(31.7°) / Ia≤0.

7.

9. The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, characterized in that, After dispersing the negative electrode active material particles at a ratio of 10% by mass in water at 25°C for 1 hour, the silicon content in the water is less than 50 ppm by mass.

10. The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, characterized in that, The BET specific surface area of the negative electrode active material particles is 1 m 2 / g or more and 3 m 2 / g or less.

11. The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, characterized in that, The median particle size of the negative electrode active material particles is 4.0 μm or more and 15 μm or less, and the ratio of the cumulative 90% particle size D90 to the cumulative 10% particle size D10, D90 / D10, is 3 or less.

12. The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, characterized in that, The negative electrode active material particles contain carbon material in the surface layer, and the average thickness of the carbon material is more than 10 nm and less than 100 nm.

13. The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, characterized in that, The negative electrode active material particles contain phosphate in their surface layer.

14. A non-aqueous electrolyte secondary battery, characterized in that, The negative electrode active material for a non-aqueous electrolyte secondary battery as described in any one of claims 1 to 13.

15. A method for preparing a negative electrode active material for a non-aqueous electrolyte secondary battery, comprising a negative electrode active material containing silicon compound particles, characterized in that... By a process of producing silicon compound particles containing a silicon compound SiO x x, and a process of intercalating Li into the silicon compound particles to make them contain Li2SiO3, wherein 0.8≤x≤1.2, The preparation method further includes a step of screening the following negative electrode active material particles: When the negative electrode active material particles were measured by X-ray diffraction using Cu-Kα rays, the half-width of the peak caused by the (020) plane of Li2SiO3 obtained by X-ray diffraction was 1.1° or more and 1.5° or less. Furthermore, in the spectrum obtained by X-ray diffraction, all negative electrode active material particles whose intensities Ia of the peak caused by the (020) plane of Li2SiO3, Ib of the peak caused by the (111) plane of Li2SiO3, I(24.8°) at 2θ=24.8°, and I(28.4°) at 2θ=28.4° satisfy the following equations (1) to (3) are negative electrode active material particles. 1.1≤Ib / Ia≤1.5 ···(1) I(24.8°) / Ia≤0.5 ···(2) I(28.4°) / Ia≤1.0 ···(3) Using the screened negative electrode active material particles, a negative electrode active material for non-aqueous electrolyte secondary batteries was prepared.

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