Composite particles, negative electrode material, and lithium-ion secondary battery

Abstract

The present invention provides a composite particle capable of suppressing the oxidation over time of a Si-C composite material. The composite particle (B) of the present invention is a composite particle (B) comprising a composite particle (A) containing carbon and silicon, and an amorphous layer covering the surface thereof, wherein, in the Raman spectrum of the composite particle (B), a peak of silicon is present in the range of 450 to 495 cm ‑1 The intensity of this peak is represented by I Si The intensity of the G band (peak intensity in the vicinity of 1600 cm ‑1 ) is represented by I G The intensity of the D band (peak intensity in the vicinity of 1360 cm ‑1 ) is represented by I D When I Si / I G is 0.10 or greater and 0.65 or less, the R value (I D / I G ) is 1.00 or greater and 1.30 or less, and the half-peak width of the 111 plane of Si in the XRD spectrum using Cu-Kα rays is 3.0 degrees or greater.

Description

Technical Field

[0001] This invention relates to a method for manufacturing the particle, a negative electrode material, a negative electrode binder layer, and a lithium-ion secondary battery. Background Technology

[0002] As secondary batteries used in IT devices such as smartphones and tablets, vacuum cleaners, power tools, electric bicycles, drones, and automobiles, they require negative electrode active materials that combine high capacity and high output. Silicon (theoretical specific capacity: 4200 mAh / g), with a theoretical specific capacity higher than currently used graphite (theoretical specific capacity: 372 mAh / g), has attracted attention as a negative electrode active material.

[0003] However, with the electrochemical insertion and extraction of lithium, the volume of silicon (Si) expands and contracts by approximately 3 to 4 times. This causes silicon particles to self-destruct and / or peel off from the electrode, resulting in extremely low cycle characteristics in lithium-ion secondary batteries using silicon. Therefore, research is actively underway to develop structures that reduce the overall expansion and contraction as a negative electrode material, rather than simply replacing graphite with silicon. Many attempts have been made to combine this with carbon materials.

[0004] As a high-capacity and long-life anode material, the following silicon-carbon (Si-C) composite material is disclosed, which is obtained by generating silicon in the pores of porous carbon by exposing porous carbon particles to silane gas at high temperature (Japanese Patent Publication No. 2018-534720; Patent Document 1).

[0005] Existing technical documents

[0006] Patent Document 1: Japanese Patent Publication No. 2018-534720 Summary of the Invention

[0007] Patent Document 1 discloses a Si-C composite material coated with a carbonaceous layer. When used as an anode material, the inventors have found that at low temperatures, the carbon coverage of the Si-C composite material is low, and oxidation occurs over time, leading to a decrease in the specific capacity of the anode material. Furthermore, at high temperatures, the carbonaceous coating of the Si-C composite material results in the formation of silicon carbide (SiC), resulting in an anode material with low specific capacity. The objective of this invention is to provide composite particles capable of suppressing the time-dependent oxidation of Si-C composite materials coated at low temperatures.

[0008] In order to obtain a high-quality coating layer by suppressing the formation of SiC, the inventors studied the coating at low temperatures. The results showed that Si-C composite particles coated with a specific amorphous layer could suppress the oxidation of Si-C composite particles over time, and because no SiC was formed, the specific capacity of the material increased, thus completing this invention.

[0009] The solution of the present invention is as follows.

[0010] [1] A composite particle (B) comprising: a composite particle (A) containing carbon and silicon, and an amorphous layer covering the surface of the composite particle (A).

[0011] In the Raman spectrum of the composite particle (B),

[0012] The peak of silicon is located at 450–495 cm⁻¹. -1 The intensity of this peak is expressed as I. Si The strength of the G-band (1600cm) -1 The peak intensity near the target is represented by I. G And the strength of the D-band (1360cm) -1 The peak intensity near the target is represented by I. D hour,

[0013] I Si / I G Values ​​between 0.10 and 0.65 are considered high.

[0014] R value (I) D / I G () is above 1.00 and below 1.30

[0015] The composite particle (B) is shown in the XRD pattern using Cu-Kα rays.

[0016] The full width at half maximum (FWHM) of the 111 plane of Si is greater than 3.0 degrees.

[0017] [2] According to the composite particle (B) described in [1],

[0018] The composite particle (B) is shown in the XRD pattern using Cu-Kα rays.

[0019] The ratio of (peak intensity of SiC at the 111 plane) to (peak intensity of Si at the 111 plane) is less than 0.004.

[0020] [3] According to the composite particle (B) described in [1] or [2], the amorphous layer covering the surface of the composite particle (A) is a layer containing at least one of metal oxides and carbon.

[0021] [4] According to the composite particle (B) described in [3], the metal oxide in the amorphous layer covering the surface of the composite particle (A) contains at least one of oxides selected from Al, Ti, V, Cr, Hf, Fe, Co, Mn, Ni, Y, Zr, Mo, Nb, La, Ce, Ta or W and Li-containing oxides.

[0022] [5] According to the composite particle (B) described in [4], the content of metal elements is more than 0.1% by mass and less than 10.0% by mass.

[0023] [6] According to the composite particle (B) described in [3], the metal oxide in the amorphous layer covering the surface of the composite particle (A) is lithium titanate (Li4Ti5O). 12 The titanium content in the composite particles (B) is above 0.1% by mass and below 10.0% by mass.

[0024] [7] According to the composite particle (B) described in [3], the metal oxide in the amorphous layer covering the surface of the composite particle (A) is niobium pentoxide (Nb2O5) or oxygen-deficient niobium oxide (Nb2O) x And x = 4.5 to 4.9), the niobium content in the composite particles (B) is more than 0.1% by mass and less than 20.0% by mass.

[0025] [8] According to the composite particle (B) described in [3], the amorphous layer covering the surface of the composite particle (A) contains only carbon.

[0026] [9] The composite particle (B) according to any one of [1] to [8] has an amorphous layer covering the surface of the composite particle (A) with a thickness of 0.1 nm or more and 30 nm or less.

[0027]

[10] The composite particle (B) according to any one of [1] to [9] has an amorphous layer covering the surface of the composite particle (A) with a coverage rate of 50% or more.

[0028]

[11] The composite particle (B) according to any one of [1] to

[10] has an oxygen content of 10% by mass or less.

[0029]

[12] The composite particle (B) according to any one of [1] to

[11] has a silicon content of 20% by mass or more and 70% by mass or less.

[0030]

[13] The composite particle (B) according to any one of [1] to

[12] , the D of the composite particle (B) v50 With a micrometer diameter greater than 1.0 μm and less than 30.0 μm, the BET specific surface area is 0.3 m². 2 / g or more and 10.0m2 / g or less.

[0031]

[14] The composite particle (B) according to any one of [1] to

[13] satisfies at least one of the following in thermal analysis in air atmosphere: having two exothermic peaks at 400 to 800 °C and having no exothermic peak at 700 ± 10 °C.

[0032]

[15] The composite particle (B) according to any one of [1] to

[14] has metal oxide particles with an average particle size of less than 100 nm attached to its surface.

[0033]

[16] A method for manufacturing a composite particle (B) wherein, in manufacturing the composite particle (B) described in any one of [1] to

[15] , a physical vapor deposition (PVD) method is used to cover the surface of the composite particle (A) with an amorphous layer.

[0034]

[17] A method for manufacturing a composite particle (B), wherein when manufacturing the composite particle (B) according to any one of claims 1 to 15, an atomic layer deposition (ALD) method is used to cover the surface of the composite particle (A) with a metal oxide layer.

[0035]

[18] An anode material comprising the composite particles (B) described in any one of [1] to

[15] .

[0036]

[19] A negative electrode mixture layer comprising the negative electrode material described in

[18] .

[0037]

[20] A lithium-ion secondary battery comprising the negative electrode compound layer described in

[19] .

[0038] According to the composite particle (B) of the present invention, a negative electrode material for lithium-ion secondary batteries can be provided, which has high Si utilization, thus maintaining high specific capacity and excellent oxidation resistance. Attached Figure Description

[0039] Figure 1 TEM images showing the ends of the composite particles in Examples 1-5.

[0040] Figure 2 The Raman spectrum of the composite particles in Example 1-1 is shown.

[0041] Figure 3 The Raman spectra of the composite particles in Examples 1-8 are shown.

[0042] Figure 4 The Raman spectra of the composite particles in Comparative Examples 1-3 are shown.

[0043] Figure 5 The image shows the XRD pattern of the composite particles in Example 1-1.

[0044] Figure 6 The image shows the XRD patterns of the composite particles from Examples 1-2.

[0045] Figure 7 The image shows the XRD pattern of the composite particles in Comparative Example 1-1.

[0046] Figure 8 SEM images of the composite particles from Example 1-1.

[0047] Figure 9 SEM images of the composite particles in Comparative Example 1-1 are shown. Detailed Implementation

[0048] The embodiments of the present invention will be described below.

[0049] <1> Composite particles (B)

[0050] One embodiment of the composite particle (B) includes: a composite particle (A) containing carbon and silicon, and an amorphous layer covering the surface of the composite particle (A).

[0051] In the Raman spectrum of the composite particle (B),

[0052] The peak of silicon is located at 450–495 cm⁻¹. -1 The intensity of this peak is expressed as I. Si The strength of the G-band (1600cm) -1 The peak intensity near the target is represented by I. G And the strength of the D-band (1360cm) -1 The peak intensity near the target is represented by I. D hour,

[0053] I Si / I G Values ​​between 0.10 and 0.65 are considered high.

[0054] R value (I) D / I G () is above 1.00 and below 1.30

[0055] The composite particle (B) is shown in the XRD pattern using Cu-Kα rays.

[0056] The full width at half maximum (FWHM) of the 111 plane of Si is greater than 3.0 degrees.

[0057] One embodiment of the composite particle (B) has an amorphous layer on the surface of the composite particle (A) containing carbon material and silicon.

[0058] The composite particles (A) are preferably composite particles in which silicon (Si) has been precipitated on the surface and within the pores of a carbon material. The composite particles (A) are typically obtained by chemical vapor deposition (CVD) using a silicon source such as silane (SiH4) to precipitate amorphous silicon on porous carbon.

[0059] By forming an amorphous layer on the surface of the composite particle (A), the silicon in the composite particle (A) can be prevented from being oxidized by oxygen in the air.

[0060] The amorphous layer preferably contains at least one selected from metal oxides, carbon, phosphoric acid, polyphosphoric acid (with a degree of polymerization of 3 or more), and their salts. It can be a multilayer composed of these compounds, and two or more compounds can be mixed in one layer. More preferably, the amorphous layer contains at least one selected from metal oxides and carbon. As the metal oxide, it is desirable to contain at least one selected from oxides of Al, Ti, V, Cr, Hf, Fe, Co, Mn, Ni, Y, Zr, Mo, Nb, La, Ce, Ta, W, and Li-containing oxides, and particularly more preferably, it contains at least one selected from lithium titanate (Li4Ti5O). 12 The metal oxide layer is selected from at least one of niobium pentoxide (Nb₂O₅) and oxygen-deficient niobium oxide (Nb₂Ox, x = 4.5–4.9). The metal oxide layer is preferably amorphous. The presence of this material in the amorphous layer further prevents the silicon contained in the composite particles (B) from being oxidized by oxygen in the air. Furthermore, it has the effect of suppressing side reactions between Si and the electrolyte.

[0061] The composite particle (B) of one embodiment exhibits a Raman spectrum in the range of 450–495 cm⁻¹. -1 A peak caused by silicon (Si) is present. The presence of a silicon-induced peak in this range indicates that the composite particle (B) contains amorphous silicon. If the silicon is amorphous, the expansion / contraction during charging and discharging occurs isotropically, which can improve cycle characteristics.

[0062] In the composite particles (B) of one embodiment, the peak intensity I caused by the silicon is... Si With G-band strength (1600cm) -1 Nearby peak intensity) I G The ratio is I Si / I G It is above 0.10. The inventors believe that through I... Si / I G The concentration is above 0.10, indicating that silicon exists at a sufficient concentration near the surface within the composite particles (B). Therefore, lithium-ion secondary batteries using these composite particles (B) as anode materials exhibit excellent rate characteristics and initial coulombic efficiency. From this perspective, I... Si / I GPreferably, it is 0.11 or higher, more preferably 0.15 or higher, and even more preferably 0.30 or higher.

[0063] In the composite particle (B) of one embodiment, the I Si / I G It is below 0.65. The inventors believe that, through the aforementioned I... Si / I G With a silicon content below 0.65, silicon does not exist excessively near the surface of the composite particle (B). Therefore, the expansion / contraction stress during lithium insertion / extraction of the composite particle (B) does not concentrate near the surface of the composite particle (B). Lithium-ion secondary batteries using this composite particle (B) as the anode material exhibit excellent cycle characteristics. From this perspective, I Si / I G Preferably, it is 0.50 or less, and more preferably 0.33 or less.

[0064] In one embodiment of the composite particle (B), the D band intensity (1360 cm⁻¹) in its Raman spectrum is... -1 Nearby peak intensity) I D With G-band strength I G The ratio is the R value (I). D / I G The R value is 1.00 or higher. When the R value is 1.00 or higher, the crystal structure of the carbon material contained within the composite particle (B) contains a sufficient number of defects, thus enabling the formation of an amorphous material with tight adhesion to the composite particle (A) and a continuous amorphous layer without interruption by cracking in the middle. This improves the initial coulombic efficiency of the lithium-ion secondary battery. From this point of view, the R value is preferably 1.05 or higher, and more preferably 1.10 or higher.

[0065] In one embodiment of the composite particles (B), the R value is 1.30 or less. An R value less than 1.30 means that there are not many defects in the crystal structure of the carbon material. As a result, side reactions are reduced, thus the internal resistance of the battery is reduced and the rate characteristics are improved. From this point of view, the R value is preferably 1.25 or less, and more preferably 1.20 or less.

[0066] Here, peak intensity is the height from the baseline to the peak.

[0067] In the composite particles (B) of one embodiment, the half-width at half-maximum (WHM) of the Si 111 plane is 3.0 degrees or more in the XRD pattern (horizontal axis: 2θ, vertical axis: intensity) obtained by powder XRD using Cu-Kα rays. When the WHM of the Si 111 plane is 3.0 degrees or more, the crystallites are small, thus suppressing silicon cracking associated with charge and discharge. This improves the initial coulombic efficiency and coulombic efficiency of the lithium-ion secondary battery. From the same viewpoint, the WHM is preferably 3.5 degrees or more, more preferably 4.0 degrees or more. Furthermore, the WHM is preferably 10.0 degrees or less, more preferably 8.0 degrees or less, and even more preferably 6.0 degrees or less.

[0068] In one embodiment of the composite particle (B), the ratio of (peak intensity of the 111 facet of SiC) to (peak intensity of the 111 facet of Si) in the XRD pattern obtained by powder XRD using Cu-Kα rays is preferably 0.004 or less. With this ratio being 0.004 or less, the composite particle (B) contains no SiC (silicon carbide) or has an extremely low SiC content. This improves the utilization rate of silicon as a battery active material. Furthermore, the ratio of (peak intensity of the 111 facet of SiC) to (peak intensity of the 111 facet of Si) is also denoted as I. SiC111 / I Si111 .

[0069] I SiC111 / I Si111 The lower limit is 0.000. That is, it is more preferable that no peak of SiC is observed. Furthermore, the peak intensity of the 111 facet of SiC refers to the height from the baseline to the peak of the 2θ peak of the 111 facet of SiC, which appears near 35 degrees, in the XRD pattern. In addition, the peak intensity of the 111 facet of Si refers to the height from the baseline to the peak of the 2θ peak of the 111 facet of Si, which appears near 28 degrees.

[0070] When the amorphous layer is a metal oxide, the content of the metal element in the composite particle (B) is preferably 0.1% by mass or more. By being 0.1% by mass or more, oxidation caused by oxygen in the air can be sufficiently prevented. From this viewpoint, the content of the metal element is more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more.

[0071] The content of the metal element in the composite particle (B) is preferably 10.0% by mass or less. With a metal element content of 10.0% by mass or less, electron conduction on the surface of the composite particle (B) can proceed sufficiently rapidly. From this viewpoint, the metal element content is more preferably 9.0% by mass or less, and even more preferably 8.0% by mass or less.

[0072] Furthermore, the content of metal elements and silicon in the composite particles (B) of this specification can be determined by ICP-AES after these elements are dissolved from the composite particles (B).

[0073] The amorphous layer contains lithium titanate (Li4Ti5O) 12 In the case of composite particles (B), the content of titanium (converted to titanium) is preferably 0.1% by mass or more. By being 0.1% by mass or more, oxidation caused by oxygen in the air can be sufficiently prevented. From this viewpoint, the titanium content is more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more.

[0074] The titanium content in the composite particles (B) is preferably 10.0% by mass or less. At 10.0% by mass or less, electron conduction on the surface of the composite particles (B) can proceed sufficiently rapidly. From this viewpoint, the titanium content is more preferably 9.0% by mass or less, and even more preferably 8.0% by mass or less. The titanium content in the composite particles (B) can be determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) after the titanium has been dissolved from the composite particles (B).

[0075] The amorphous layer contains niobium pentoxide (Nb₂O₅) or oxygen-deficient niobium oxide (Nb₂O₅). x In the case of x = 4.5 to 4.9, the content of niobium (converted to niobium) in the composite particle (B) is preferably 0.1% by mass or more. By having a content of 0.1% by mass or more, oxidation caused by oxygen in the air can be sufficiently prevented. From this viewpoint, the niobium content is more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more.

[0076] Furthermore, the niobium content in the composite particle (B) is preferably 20.0% by mass or less. With a niobium content of 20.0% by mass or less, electron conduction on the surface of the composite particle (B) can proceed sufficiently rapidly. From this viewpoint, the niobium content is more preferably 15.0% by mass or less, and even more preferably 10.0% by mass or less.

[0077] Furthermore, the content of niobium and silicon in the composite particles (B) of this specification can be determined by ICP-AES, similar to that of titanium, after these elements have been dissolved from the composite particles (B).

[0078] In one embodiment, the carbon in the amorphous layer of the composite particle (B) is carbon that does not have a hexagonal network like graphite. This type of carbon can be obtained by physical vapor deposition, such as sputtering. However, it can also be carbon composed of very small graphite crystals with hexagonal network dimensions of about 0.3 to 0.4 nm. This type of carbon can be obtained, for example, by thermal decomposition of organic matter or CVD of hydrocarbon gases.

[0079] Amorphous materials can be composed of carbon alone. Here, "composed of carbon alone" means that the amorphous layer is composed of only carbon and does not contain other metal oxides, phosphoric acid, polyphosphoric acid (with a degree of polymerization of 3 or higher) and their salts.

[0080] By observing and analyzing the coating portion within the cross-section of the composite particle (B) using TEM-EDX, its lattice type and composition can be investigated, thus confirming that the coating is composed of amorphous carbon. Furthermore, the composite particle (A) and the coating within the cross-section of the composite particle (B) can be identified based on their different lattice types.

[0081] Phosphoric acid, polyphosphoric acid (with a degree of polymerization of 3 or higher), and their salts, such as anhydrous phosphoric acid (P₂O₅) and polyphosphoric acid (H₂O), are examples of these. (n+2) P n O (3n+1) Lanthanum phosphate (LaPO3), sodium tripolyphosphate (Na5P3O) 10 Lanthanum tripolyphosphate La5(P3O) 10 3. Sodium tetrapolyphosphate Na6P4O 13 Compounds such as these can be obtained by coating composite particles (A) with phosphoric acid (H3PO4) and heat-treating them, or by coating composite particles (A) with an aqueous solution of the aforementioned phosphate and drying them.

[0082] In one embodiment, the ratio of phosphorus content to silicon content in the composite particles (B), as determined by X-ray fluorescence analysis (XRF), is preferably 0.05 or higher and 1.00 or lower.

[0083] In one embodiment, the thickness of the amorphous layer in the composite particle (B) is preferably 0.1 nm or more. By having a thickness of 0.1 nm or more, oxidation caused by oxygen in the air can be sufficiently suppressed. From this viewpoint, the thickness of the amorphous layer is more preferably 0.3 nm or more, and even more preferably 0.4 nm or more.

[0084] In one embodiment, the thickness of the amorphous layer in the composite particle (B) is preferably 30.0 nm or less. With a thickness of 30.0 nm or less, electron conduction on the surface of the composite particle (B) can proceed sufficiently rapidly. From this viewpoint, the thickness of the amorphous layer is more preferably 20.0 nm or less, and even more preferably 10.0 nm or less.

[0085] The thickness of the amorphous layer in this specification can be determined based on TEM images of the cross-section or end of the composite particle (B). When the amorphous layer is composed of one or more selected from metal oxides, phosphoric acid, polyphosphoric acid (with a degree of polymerization of 3 or more), and their salts, it can be calculated based on the concentration and density of the amorphous layer in the composite particle (B) and the specific surface area of ​​the composite particle (B).

[0086] In one embodiment, the composite particles (B) preferably have a coating ratio of 50% or more of the composite particles (A) of the amorphous layer. With a coating ratio of 50% or more, oxidation caused by oxygen in the air can be sufficiently prevented. From this viewpoint, the coating ratio is more preferably 60% or more, and even more preferably 70% or more.

[0087] The coverage ratio of the amorphous layer to the composite particle (A) is determined by binarizing the image of the composite particle (B) from a scanning electron microscope (SEM) using image processing software to distinguish the coating layer and the composite particle (A) by color. The area of ​​the coating layer is then calculated using image processing, and its ratio to the total area of ​​the composite particle (B) is obtained. Photoshop (Adobe) can be used as an example of image processing software for binarizing SEM images, measuring area, and calculating coverage ratio, but it is not limited to any software capable of performing the same processing. Alternatively, compositional analysis images of the SEM can be obtained through image analysis.

[0088] In one embodiment, the oxygen content (converted to oxygen) in the composite particle (B) is preferably 20.0% by mass or less. By having an oxygen content of 20.0% by mass or less, the specific capacity of the composite particle (B) can be ensured to be sufficiently large. From this viewpoint, the oxygen content in the composite particle (B) is more preferably 10.0% by mass or less, and even more preferably 5.0% by mass or less.

[0089] The oxygen content can be determined, for example, by a device for simultaneous oxygen and nitrogen measurement.

[0090] The composite particles (B) of one embodiment preferably have a true density of 1.80 g / cm³. 3 The above. Therefore, a high energy density can be obtained. From this perspective, the true density of the composite particle (B) is preferably 1.90 g / cm³. 3 The above, more preferably 2.00 g / cm³ 3 That's all. True density can be determined using the hydrometer bottle method.

[0091] When the amorphous layer on the surface of the coated composite particle (A) is a metal oxide layer, its thickness is particularly preferably 4.0 nm or less. By being 4.0 nm or less, the surface of the composite particle (B) has sufficient electronic conductivity.

[0092] In one embodiment, when the amorphous layer of the composite particle (B) is a metal oxide layer, the coverage rate of the composite particle (A) is particularly preferably 95% or more, and most preferably 97% or more. With a coverage rate of 95% or more, oxidation caused by oxygen in the air can be sufficiently prevented, and side reactions with the electrolyte can be suppressed. The upper limit of the coverage rate is 100%.

[0093] To investigate the pore distribution of the composite particles (B), composite particles (A), and carbon materials, adsorption isotherms based on gas adsorption methods are analyzed, for example, using known methods. In one embodiment, nitrogen is used as the adsorbed gas.

[0094] Furthermore, in one embodiment, the composite particles (B) preferably have a silicon content of 20% by mass or more. With a silicon content of 20% by mass or more, calculations show that composite particles (B) with a specific capacity of 840 mA / g or more can be obtained. From this viewpoint, the silicon content is more preferably 30% by mass or more, and even more preferably 35% by mass or more.

[0095] In one embodiment, the composite particles (B) preferably have a silicon content of 70% by mass or less. With a silicon content of 70% by mass or less, the composite particles (B) contain sufficient portions capable of absorbing the expansion / contraction of silicon during charging and discharging. From this viewpoint, the silicon content is more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0096] The BET specific surface area of ​​the composite particle (B) according to one embodiment of the present invention is preferably 10.0 m². 2 / g or less. BET specific surface area is 10.0m². 2 When the surface area is below a certain value (e.g.), side reactions with the electrolyte are suppressed, and the initial coulombic efficiency increases. From the same perspective, a BET specific surface area of ​​7.0 m² is more preferable. 2 / g or less, more preferably 5.0m 2 / g or less.

[0097] The BET specific surface area of ​​the composite particle (B) according to one embodiment of the present invention is preferably 0.3 m². 2 / g or more. BET specific surface area is 0.3m². 2 When the surface area is above a certain value (e.g., g / g), the resistance during Li ion insertion / extraction decreases. From the same perspective, a BET specific surface area of ​​0.5 m² is more preferable. 2 / g or more, further preferably 1.0m 2 / g or more. The BET specific surface area can be determined by the BET specific surface area measuring device described later.

[0098] The 50% particle size D was obtained by measuring the volume-based cumulative particle size distribution of the composite particles (B) according to an embodiment of the present invention. v50Preferably, the particle size is 30.0 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less. When the particle size is 30.0 μm or less, the processability of the composite particles is improved, and when the composite particles are used as the negative electrode material of a lithium-ion secondary battery, the surface area of ​​the composite material can be maintained in a large state. When the composite material is used as the negative electrode material of a lithium-ion secondary battery, the resistance during Li ion intercalation / deintercalation is reduced, thus improving the input-output characteristics.

[0099] The 50% particle size D was obtained by measuring the volume-based cumulative particle size distribution of the composite particles (B) according to an embodiment of the present invention. v50 Preferably, the particle size is 1.0 μm or more, more preferably 4.0 μm or more, and even more preferably 7.0 μm or more. By making the D50 1.0 μm or more, the processability of the composite particles (B) is improved, and when the composite particles (B) are used as the negative electrode material of lithium-ion secondary batteries, the dispersion of the composite particle layer (B) in the negative electrode becomes higher, and the cycle characteristics become better.

[0100] D v50 It is the particle size that accounts for 50% of the cumulative particle size distribution based on volume, obtained by laser diffraction / scattering method.

[0101] In one embodiment of the present invention, when the amorphous layer is a metal oxide layer, the composite particle (B) preferably satisfies at least one of the following in thermal analysis (TG-DTA): under conditions of 100 ml / min of ambient air and a heating rate of 10°C / min, the number of exothermic peaks determined by DTA is two or less between 400 and 800°C; and there is no exothermic peak at 700°C ± 10°C. This indicates an inhibitory effect on oxidation caused by oxygen in the air. From the same viewpoint, satisfying both of these conditions is more preferable.

[0102] The coating amorphous layer can be either particles or a thin film. In the case of particles, it is desirable that the particles are not independent but connected to form a surface. By forming surfaces, the effect of preventing oxidation caused by oxygen in the air and suppressing side reactions with the electrolyte is improved.

[0103] In another embodiment of the present invention, the composite particles preferably consist of metal oxide particles with an average particle size of less than 100 nm attached to the surface of the amorphous layer. According to this structure, the presence of metal oxide particles with high affinity for the solid electrolyte on the surface of the composite material increases the contact area with the electrolyte, reduces resistance, and improves rate characteristics.

[0104] The structure can be confirmed by mapping images obtained through transmission electron microscopy (SEM) or Raman spectroscopy analysis.

[0105] <2> Method for manufacturing composite particles (B)

[0106] The composite particles (B) of one embodiment can be manufactured by the following steps (1) to (2).

[0107] Process (1): The process of manufacturing composite particles (A) containing carbon and silicon.

[0108] Process (2): The process of setting an amorphous layer on the surface of the composite particle (A).

[0109] Process (1)

[0110] Process (1) is the process of manufacturing composite particles (A) containing carbon and silicon.

[0111] Porous carbon is preferred as the carbon material used. In this specification, the term "porous carbon" refers to carbon with a BET specific surface area of ​​200 m². 2 Carbon of / g or more. As porous carbon, it is preferable to allow fine silicon to precipitate within the pores, where the stress maintaining the pore structure functions even as the silicon expands / contracts with lithium insertion / extraction, and / or where unoccupied spaces exist, which, when compressed, reduce the degree of expansion / contraction across the entire negative electrode material. Specific examples of porous carbon include activated carbon, carbon obtained through the thermal decomposition of resins and organic matter, carbon molecular sieves, activated carbon fibers, aggregates of fumed carbon fibers and carbon nanotubes, and inorganic template carbon.

[0112] To investigate the pore distribution of carbon materials, adsorption isotherms obtained by gas adsorption methods are analyzed, for example, using known methods. In one embodiment, nitrogen is used as the adsorbed gas.

[0113] As a carbon material, commercially available materials with a specific pore distribution can be used, but porous carbon with a desired pore distribution can also be manufactured, for example, by adjusting the conditions for synthesizing the resin and the conditions for thermally decomposing the resin while investigating changes in the pore distribution using the methods described above.

[0114] A silicon-containing gas, preferably a silane gas, can be applied to a carbon material to precipitate silicon within the pores and on the surface of the carbon material, resulting in composite particles (A). Specifically, amorphous silicon is typically precipitated on a carbon material using chemical vapor deposition (CVD) with a silicon source such as silane (SiH4).

[0115] Process (2)

[0116] Step (2) is a step in which an amorphous layer is formed on the surface of the composite particle (A) obtained in step (1) to obtain the composite particle (B). The method for forming the amorphous layer on the surface can be appropriately selected from known surface treatment methods. It can be a wet method in which the precursor of the amorphous layer is coated on the composite particle (A) by a wet method, and the solvent is removed and then heat-treated. It can also be a dry method such as physical vapor deposition (PVD) or atomic layer deposition (ALD) such as sputtering. Multiple methods can also be combined. The substrate temperature (processing temperature) is preferably 500°C or less, more preferably 200°C or less, and even more preferably 100°C or less. When the temperature is 500°C or less, the crystal structure and surface structure of the carbon and silicon contained in the composite particle (A) will not be modified, so it is preferred. In the case of a dry method such as physical vapor deposition (PVD) or atomic layer deposition (ALD) such as sputtering, the film formation processing time is preferably 3.00 nm / hour or less, more preferably 2.00 nm / hour or less. When the speed is below 3.00 nm / h, the film formation process is smooth and will not make the surface of the composite particles rough, thus obtaining composite particles (B) with high adhesion to the amorphous layer.

[0117] (Process (2) Method 1)

[0118] The first method is a process of forming an amorphous layer on the surface of composite particles (A) to obtain composite particles (B) by physical vapor deposition (PVD).

[0119] As a physical vapor deposition (PVD) method, sputtering is preferred. Known methods can be used for sputtering particles.

[0120] The amorphous layer formed on the surface of the composite particle (A) preferably contains at least one selected from metal oxides, carbon, phosphoric acid, polyphosphoric acid (with a degree of polymerization of 3 or more), and their salts. More preferably, it contains at least one selected from metal oxides and carbon. It is desirable that the metal oxide contains at least one selected from oxides of Al, Ti, V, Cr, Hf, Fe, Co, Mn, Ni, Y, Zr, Mo, Nb, La, Ce, Ta, W, and Li-containing oxides, and particularly more preferably, it contains at least one selected from lithium titanate (Li4Ti5O). 12 ), niobium pentoxide (Nb₂O₅) and oxygen-deficient niobium oxide (Nb₂O₅) x At least one of (x = 4.5 to 4.9), with carbon more preferably containing diamond-like carbon. They can be formed on the surface of the composite particles (A) by using a target that uses these materials in a sputtering process.

[0121] (Process (2) Method 2)

[0122] The second method involves forming an amorphous layer on the surface of composite particle (A) to obtain composite particle (B). Atomic layer deposition (ALD) is a method that utilizes the chemical adsorption and chemical reaction of various low-energy gases on the surface of a support. Known methods can be used for the ALD applied to composite particle (A).

[0123] The amorphous layer formed on the surface of the composite particle (A) is not particularly limited, but preferably contains at least one oxide selected from Al, Ti, V, Cr, Hf, Fe, Co, Mn, Ni, Y, Zr, Mo, Nb, La, Ce, Ta, W and Li-containing oxides, particularly niobium pentoxide (Nb2O5) and lithium titanate (Li4Ti5O) 12 One of the following. By using precursors of these materials in the ALD process, a metal oxide layer can be formed on the surface of the composite particle (A). Examples of precursors include compounds with niobium, titanium, or lithium as metal species and alcohols, diols, β-diketones, cyclopentadienes, organic amines, etc., as organic ligands.

[0124] (Process (2) Method 3)

[0125] The third method involves applying a coating liquid containing precursors or microparticles constituting an amorphous layer to the surface of composite particles (A) using a wet coating process to form an amorphous layer and obtain composite particles (B). There are no particular limitations on the coating method; examples include immersion coating and spray coating. For instance, composite particles (B) can be manufactured by spraying and mixing the coating liquid while the composite particles (A) are rotating, followed by heating the mixture.

[0126] <3> Anode material

[0127] The composite particles (B) of one embodiment can be used as negative electrode materials for non-aqueous secondary batteries, etc. They are suitable for use as negative electrode materials in lithium-ion secondary batteries. In one embodiment, "negative electrode material" refers to a negative electrode active material or a composite of a negative electrode active material and other materials.

[0128] As a negative electrode material, the composite particles (B) of one embodiment can be used alone, or they can be used together with other negative electrode materials. As other negative electrode materials, active materials commonly used as negative electrode active materials in lithium-ion secondary batteries can be used. When using other negative electrode materials, the composite particles (B) are usually mixed with other negative electrode materials.

[0129] Other anode materials that can be cited include graphite, hard carbon, and lithium titanate (Li4Ti5O). 12These negative electrode materials include alloy-based active materials such as silicon and tin, and their composite materials. These negative electrode materials are typically granular. One or more negative electrode materials other than composite particles (B) can be used. Graphite and hard carbon are particularly preferred. In the negative electrode mixture layer of one embodiment described later, one preferred method is to include composite particles (B) and graphite particles.

[0130] When the negative electrode material is formed from composite particles (B) and other negative electrode materials, the composite particles (B) preferably contain 2 to 99% by mass relative to 100% by mass of the negative electrode material, more preferably 10 to 90% by mass, even more preferably 20 to 80% by mass, and particularly preferably 30 to 70% by mass.

[0131] <4> Negative electrode mixture layer

[0132] One embodiment of the negative electrode binder layer contains the aforementioned negative electrode material. This negative electrode binder layer can be used as a negative electrode binder layer in non-aqueous secondary batteries, particularly lithium-ion secondary batteries. The negative electrode binder layer generally consists of a negative electrode material, a binder, and conductive additives as optional components.

[0133] The negative electrode binder layer can be manufactured using, for example, the following known methods.

[0134] (1) A slurry for forming a negative electrode binder layer is prepared using a negative electrode material, a binder, a conductive additive as an optional component, and a solvent.

[0135] (2) Apply the slurry to a current collector such as a copper foil and dry it.

[0136] (3) After further vacuum drying, roll pressing is performed, and then it is cut or punched into the required shape and size.

[0137] The pressure during rolling is typically 100–500 MPa. The resulting product can be called a negative electrode sheet. The negative electrode sheet is obtained through pressing and consists of a negative electrode flux layer and a current collector. The electrode density (negative electrode flux layer density) is not particularly limited, but is preferably 0.7 g / cm³. 3 The above, and preferably 1.8 g / cm³ 3 the following.

[0138] As a binder, any binder commonly used in the negative electrode binder layer of a lithium-ion secondary battery can be freely selected. Examples include polyethylene, polypropylene, ethylene-propylene terpolymer, butadiene rubber, styrene-butadiene rubber, butyl rubber, acrylic rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene oxide, polychlorohydrin, polyphosphazene, polyacrylonitrile, carboxymethyl cellulose and its salts, polyacrylic acid, and polyacrylamide. One binder can be used alone, or two or more can be used. The amount of binder is preferably 0.5 to 30 parts by weight relative to 100 parts by weight of the negative electrode material.

[0139] There are no particular limitations on conductive additives, as long as they can impart conductivity and dimensional stability (mitigation of volume changes during lithium insertion / extraction) to the electrode. Examples include carbon nanotubes, carbon nanofibers, fumed carbon fibers (e.g., "VGCF-H" manufactured by Showa Denko Co., Ltd.), conductive carbon black (e.g., "DenkaBlack" manufactured by Denka Co., Ltd., "SUPER C65" manufactured by Imerys Graffito & Carbon Co., Ltd., "SUPER C45" manufactured by Imerys Graffito & Carbon Co., Ltd.), and conductive graphite (e.g., "KS6L" manufactured by Imerys Graffito & Carbon Co., Ltd.). Furthermore, two or more of the aforementioned conductive additives may be used. The amount of conductive additive is preferably 1 to 30 parts by mass relative to 100 parts by mass of negative electrode material.

[0140] There are no particular limitations on the solvent used as a slurry for coating the modulating electrode. Examples include N-methyl-2-pyrrolidone, dimethylformamide, isopropanol, and water. When using water as a solvent for the binder, it is preferable to also use a thickener. The amount of solvent can be adjusted to achieve a viscosity that allows the slurry to be easily coated onto the current collector.

[0141] <5> Lithium-ion secondary batteries

[0142] One embodiment of the lithium-ion secondary battery includes the aforementioned negative electrode mixture layer. The lithium-ion secondary battery typically includes: a negative electrode composed of the negative electrode mixture layer and a current collector; a positive electrode composed of a positive electrode mixture layer and a current collector; at least one of a non-aqueous electrolyte and a non-aqueous polymer electrolyte present therebetween; and a separator; and further includes a battery casing housing them. The lithium-ion secondary battery may include the aforementioned negative electrode mixture layer, but other structures are not particularly limited and may include conventionally known structures.

[0143] The positive electrode layer typically consists of a positive electrode material, conductive additives, and a binder. The positive electrode in the lithium-ion secondary battery can utilize the general structure found in typical lithium-ion secondary batteries.

[0144] As a cathode material, there are no particular limitations as long as it can reversibly perform electrochemical lithium intercalation / deintercalation, and the redox potentials of these reactions are sufficiently high compared to the redox potentials of the anode reactions. For example, LiCoO2, LiNiO2, LiMn2O4, and LiCo are preferred materials. 1 / 3 Mn 1 / 3 Ni 1 / 3 O2, carbon-coated LiFePO4, or mixtures thereof.

[0145] Materials mentioned above can be used as conductive additives, adhesives, and solvents for slurry preparation. Aluminum foil is preferably used as a current collector.

[0146] There are no particular limitations on the non-aqueous electrolytes and non-aqueous polymer electrolytes used in lithium-ion secondary batteries. Examples of non-aqueous electrolytes include organic electrolytes obtained by dissolving lithium salts such as LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3, and CH3SO3Li in non-aqueous solvents such as ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, butyl carbonate, acetonitrile, propionitrile, dimethoxyethane, tetrahydrofuran, and γ-butyrolactone.

[0147] Examples of non-aqueous polymer electrolytes include gel-like polymer electrolytes containing polyethylene oxide, polyacrylonitrile, polyfluorobenzidine, and polymethyl methacrylate; and solid polymer electrolytes containing polymers with ethylene oxide bonds.

[0148] Additionally, a small amount of additives used in lithium-ion secondary battery electrolytes can be added to the non-aqueous electrolyte. Examples of such substances include vinylene carbonate (VC), biphenyl, propanesulfonate lactone (PS), fluoroethylene carbonate (FEC), and vinyl sulfate (ES). VC and FEC are preferred. The amount added is preferably 0.01 to 20% by mass relative to 100% by mass of the non-aqueous electrolyte.

[0149] As the separator, it is possible to freely select from separators that can be used in general lithium-ion secondary batteries, including combinations thereof, such as microporous membranes made of polyethylene or polypropylene. In addition, separators in which particles such as SiO2 or Al2O3 are mixed as fillers, as well as separators attached to their surfaces, can also be used.

[0150] As for battery casings, there are no particular restrictions as long as they can accommodate the positive and negative electrodes, as well as the separator and electrolyte. In addition to industry-standard products such as commercially available battery packs, 18650 cylindrical single cells, and button cells, battery casings in the form of aluminum packaging materials can be freely designed and used.

[0151] Each electrode can be used as a component after being stacked. Alternatively, individual cells can be connected in series to be used as a battery pack or module.

[0152] One embodiment of the lithium-ion secondary battery can be used as a power source for electronic devices such as smartphones, tablets, and mobile information terminals; as a power source for motors in power tools, vacuum cleaners, electric bicycles, drones, and electric vehicles; and for storing electricity obtained from fuel cells, solar power generation, wind power generation, etc.

[0153] Example

[0154] The present invention will be specifically described below with examples and comparative examples, but the present invention is not limited to these examples. The determination of physical properties and battery evaluation are described below.

[0155] Under the following conditions, the ratio of the contents of silicon, titanium, niobium, aluminum, yttrium, hafnium, cerium, vanadium, molybdenum, tungsten and carbon in the composite particles (B) obtained in the Examples and Comparative Examples were determined.

[0156] [Content of silicon, titanium, niobium, aluminum, yttrium, hafnium, cerium, vanadium, molybdenum, and tungsten]

[0157] The evaluation was performed by quantitative analysis using ICP-AES.

[0158] Device: Agilent 5110 (Agilent Technologies)

[0159] Weigh 10 mg of the sample into a platinum crucible, add 1 g of sodium potassium carbonate, and melt the mixture using a gas burner. Then, heat and impregnate the crucible with ultrapure water to dissolve it. After cooling, add 2 mL of 30% hydrogen peroxide solution, 5 mL of 10% ammonium tartrate aqueous solution, and 5 mL of (1+4) sulfuric acid to completely dissolve the melt. Pour the solution into a PTFE volumetric flask, add 1 mL of hydrogen peroxide solution, 2 mL of (1+4) sulfuric acid, Co standard solution, Ga standard solution, and Rb standard solution, and then dilute to 250 mL. Quantitatively analyze the diluted solution using ICP-AES. Determination is performed with n=2.

[0160] [Carbon content]

[0161] Measuring apparatus: HORIBA EMIA-920V

[0162] Weigh 10–13 mg of the sample in a ceramic crucible, add combustion aids (W powder, Sn granules), and determine the carbon and sulfur content using a carbon and sulfur analysis device (high-frequency heating infrared absorption method).

[0163] [Acquisition of TEM images]

[0164] TEM images of the composite particles (B) obtained in the Examples and Comparative Examples were obtained under the following conditions.

[0165] Sample processing

[0166] Processing was performed using an ion slicer with an accelerating voltage of 4.5 kV. Composite particles (B) were embedded in resin, clamped with Si auxiliary material, and processed into thin slices using an ion slicer.

[0167] TEM observation

[0168] Transmission electron microscope (TEM): Hitachi H9500, accelerating voltage 300kV

[0169] The average thickness of the amorphous layer of the composite particle (B) was determined using the following method.

[0170] (1) Randomly select one particle A1 from the composite particles (B) observed by TEM.

[0171] (2) Among the extracted particles A1, a portion with an amorphous layer is randomly selected, and the thickness t1 of the amorphous layer in the selected portion is measured. The thickness t1 is obtained by finding the intersection point x1 of the line perpendicular to the surface of the composite particle (A) and the composite particle (A), and the intersection point x2 of the line perpendicular to the outer periphery of the amorphous layer, and measuring the distance between the intersection points x1 and x2.

[0172] (3) Repeat steps (1) and (2) above 50 times. That is, measure the thickness t1 to t50 of the amorphous layer in 50 randomly extracted particles A1 to A50 from the composite particles (B) observed by TEM. Furthermore, the randomly extracted particles A1 to A50 do not overlap with each other.

[0173] (4) The arithmetic mean of the obtained values ​​t1 to t50 is taken as the average thickness t of the amorphous layer.

[0174] The average particle size of the metal oxide particles attached to the surface of the composite particle (B) was determined by the following method.

[0175] The cross-section of the composite particle (B) is exposed by FIB processing and mapped by STEM / EELS, thereby identifying the primary particles of the metal oxide within the composite particle.

[0176] (1) The field of view of a primary particle with more than one metal oxide observed randomly near the surface of a composite particle observed by STEM / EELS. Magnification is the magnification at which a primary particle can be clearly identified.

[0177] (2) Within the extracted field of view, using the STEM / EELS length measurement mode, six length measurements were performed on each primary particle at a 60° angle, ensuring that at least one point of intersection, to calculate the average particle size. The above measurements were performed on 50 randomly selected particles, and their average value was taken as the average particle size of the primary particles in the metal oxide particles. Calculations can be performed using other software, and can also be obtained from secondary electron images or transmission images, provided that the contrast of the primary particles can be clearly identified.

[0178] [Raman spectroscopy determination]

[0179] Raman spectroscopy determination of the composite particles (B) obtained in the Examples and Comparative Examples was performed under the following conditions.

[0180] Micro Raman Spectroscopy Apparatus: LabRAM HR Evolution manufactured by Horiba Co., Ltd.

[0181] Excitation wavelength: 532nm

[0182] Exposure time: 5 seconds

[0183] Total number of times: 2

[0184] Diffraction grating: 300 lines / mm (600nm)

[0185] Measurement range: 80 μm (length) × 100 μm (width)

[0186] Point count: 100 points were evaluated with a vertical feed of 17.8 μm and a horizontal feed of 22.2 μm.

[0187] For peak intensity, the height from the baseline to the peak is taken as the intensity. 1360 cm⁻¹ is calculated from the measured spectrum. -1 Nearby peak intensity I D (From amorphous components) and 1600cm -1 Nearby peak intensity I G (from graphite composition) ratio (I) D / I G This is used as the R-value, which serves as an indicator of the amount of defects contained in carbon materials.

[0188] Additionally, it was calculated that the height range is 450-495cm. -1 Peak intensity I from amorphous silicon Si With the I G The ratio (I) Si / I G ), which is used as an indicator of the inhomogeneity of the position near the surface within the silicon composite particle (B).

[0189] [Powder XRD Determination]

[0190] The particles obtained in the examples and comparative examples were filled into a glass sample plate (sample plate window 18×20mm, depth 0.2mm) and measured under the following conditions.

[0191] XRD device: SmartLab manufactured by Rigaku Co., Ltd. (registered trademark)

[0192] X-ray source: Cu-Kα rays

[0193] Kβ ray removal method: Ni filter

[0194] X-ray output: 45kV, 200mA

[0195] Measurement range: 10.0~80.0°

[0196] Scanning speed: 10.0° / minute

[0197] The obtained XRD pattern was analyzed using software (PDXL2, manufactured by Rigaku Co., Ltd.) to remove background and smooth the surface, followed by peak fitting to determine the peak positions and intensities. The full width at half maximum (FWHM) of the Si 111 plane and the ratio of (peak intensity of the Si 111 plane) / (peak intensity of the Si 111 plane) were calculated from the obtained XRD spectrum. SiC111 / I Si111 At this point, the height from the baseline to the peak is taken as the peak intensity.

[0198] [Determination of Oxygen Content]

[0199] The oxygen content of the particles obtained in the Examples and Comparative Examples was determined under the following conditions.

[0200] Oxygen / Nitrogen / Hydrogen Analyzer: EMGA-920 manufactured by Horiba Manufacturing Co., Ltd.

[0201] Carrier gas: Argon

[0202] Approximately 20 mg of the particles obtained in the examples and comparative examples were weighed into a nickel bag and measured using a simultaneous oxygen and nitrogen analysis device (melting in an inert gas → infrared absorption method).

[0203] Furthermore, the oxygen content was measured immediately after the composite particles (B) were manufactured and after two months of storage at room temperature and atmospheric conditions.

[0204] [Particle size distribution determination]

[0205] One scoop of the particles obtained in the examples and comparative examples, along with two drops of a 100-fold dilution of the nonionic surfactant (SIRAYA coconut oil high-performance detergent) stock solution (32% by mass), was added to 15 mL of water and ultrasonically dispersed for 3 minutes. The dispersion was then placed in a laser diffraction particle size analyzer (LMS-2000e) manufactured by Seishin Enterprises Co., Ltd., and the cumulative particle size distribution based on volume was measured to determine the 10% particle size D. V10 50% particle size D V50 and 90% particle size D V90 .

[0206] [True Density]

[0207] As the true density measuring apparatus, an Acupuncture II 1340 manufactured by Mycrometic was used. A 3g sample was added to a predetermined unit chamber, and the density was determined using the specific gravity bottle method. Helium was used as the gas for the true density measurement.

[0208] [coverage rate]

[0209] The coverage ratio was calculated based on the binarized image obtained from the SEM image. The white areas were adjusted to be an amorphous layer.

[0210] Coverage rate = Total area of ​​white regions / Total area of ​​particles × 100%

[0211] The specific method is as follows. An image is acquired by adjusting the image so that the entire particle is reflected in the SEM. Automatic contrast is used in this case. The acquired SEM image is opened in Photoshop (Adobe), and "Image / Mode / Grayscale" is selected. Next, "Image / Tone Correction / Averaging (Equalization)" is performed. Additionally, "Image / Tone Correction / Secondary Grayscale" is selected, the threshold is set to 110, and the process is executed. The "Quick Selection Tool" is selected, "Auto Adjust" is checked, "Hardness" is set to 100%, "Interval" is set to 25%, and "Diameter" is adjusted arbitrarily. The entire particle is selected, and "Image / Analysis / Record Measurements" is used to calculate the area. Then, the white area (identified as a domain) is selected and its area is measured in the same way. In cases where multiple regions exist, all regions are measured individually. The total area of ​​all white regions is calculated. Here, the lower limit for the size identified as a domain is 0.1 μm. That is, any dimension smaller than 0.1 μm in the vertical, horizontal, or diagonal dimensions is not considered a domain. This measurement was performed on any 50 particles obtained from the SEM image, and the average value was taken as the coverage rate.

[0212] Furthermore, before selecting the "Quick Selection Tool", select "Image / Analysis / Set Measurement Scale / Custom" to convert the scale value of the SEM image to pixels.

[0213] [Thermal Analysis (TG-DTA)]

[0214] Using a TG-DTA2000SE manufactured by Netch Corporation as a thermal analysis (TG-DTA) apparatus, 13 mg of sample was placed in an alumina sample dish, and the weight gain / loss and endothermic / exothermic behavior were measured at 25–800 °C with an air flow rate of 100 mL / min and a heating rate of 10 °C / min.

[0215] [BET specific surface area]

[0216] The NOVA2200e manufactured by Quantachrome was used as the BET surface area measuring apparatus. A 3g sample was placed in the sample chamber (9mm × 135mm) and dried at 300°C for 1 hour under vacuum before measurement. N2 was used as the gas for the BET surface area measurement.

[0217] [The production of negative electrode plates]

[0218] Styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) are used as adhesives.

[0219] Specifically, an SBR aqueous dispersion containing 40% by mass of SBR and a CMC aqueous solution containing dissolved CMC powder were obtained.

[0220] As a mixed conductive additive, a mixture is prepared by mixing carbon black (SUPER C 45 (registered trademark), manufactured by Imelice Graffit & Carbon Co., Ltd.) and vapor-grown carbon fiber (VGCF-H (registered trademark), manufactured by Showa Denko Co., Ltd.) in a mass ratio of 3:2.

[0221] 90 parts by mass of the negative electrode material obtained by mixing the composite particles (B) manufactured in the examples and comparative examples described later with graphite particles, 5 parts by mass of the mixed conductive additive, an aqueous solution of CMC with a solid content of 2.5 parts by mass, and an aqueous dispersion of SBR with a solid content of 2.5 parts by mass were mixed. An appropriate amount of water for adjusting viscosity was added to the mixture, and kneading was performed using a rotation / revolution mixer (Sinkee Co., Ltd.) to obtain a slurry for forming the negative electrode mixture layer.

[0222] [Anode Material]

[0223] The composite particles (B) obtained in the following examples were mixed with 11 parts by mass of the composite particles from the comparative example and 89 parts by mass of the graphite particles, thereby preparing a negative electrode material for battery evaluation.

[0224] The negative electrode slurry for forming the negative electrode mixture was uniformly coated to a thickness of 150 μm onto a 20 μm thick copper foil using a doctor blade. After drying with a hot plate, it was then vacuum dried to obtain the negative electrode sheet. The dried negative electrode sheet was pressed at a pressure of 300 MPa using a uniaxial press to obtain a negative electrode sheet for battery evaluation. The thickness of the obtained negative electrode sheet, including the copper foil thickness, was 62 μm.

[0225] [Determination of Electrode Density]

[0226] The pressed negative electrode sheet (current collector + negative electrode flux layer) is punched into a circle with a diameter of 16 mm, and its mass and thickness are measured. The mass and thickness of the current collector (circle with a diameter of 16 mm), which are measured separately, are subtracted from these values ​​to obtain the mass and thickness of the negative electrode flux layer. Based on the mass, thickness, and diameter (16 mm) of the negative electrode flux layer, the mass of the negative electrode flux per unit area and the electrode density (density of the negative electrode flux layer) are calculated. The electrode density is not particularly limited, but is preferably 0.7 g / cm³. 3 The above, and preferably 1.8 g / cm³ 3 the following.

[0227] In a polypropylene unit chamber (approximately 18 mm in inner diameter) with a screw-in cap, the aforementioned negative electrode and a 16 mm φ lithium metal foil are sandwiched and stacked using a separator (polypropylene microporous membrane (Celgard 2400)). Electrolyte is then added to form a test single cell (lithium counter electrode single cell). Here, in the lithium counter electrode single cell, the aforementioned negative electrode is referred to as the test electrode, and the lithium electrode is referred to as the counter electrode.

[0228] Furthermore, the electrolyte in a lithium counter electrode single cell is a liquid obtained by mixing 1% by mass of vinylene carbonate (VC) and 10% by mass of fluoroethylene carbonate (FEC) in a solvent composed of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate in a volume ratio of 3:5:2, and further dissolving the electrolyte LiPF6 therein to make the concentration 1 mol / L.

[0229] [Initial Li insertion / extraction specific capacity and initial coulombic efficiency determination experiments]

[0230] The experiment was conducted using a single-cell lithium counter electrode. Constant current (constant current: CC) discharge was performed from OCV to 0.005V at a current equivalent to 0.1C. Then, constant voltage (constant voltage: CV) discharge was initiated at 0.005V, with a cutoff current of 0.005C. The specific capacity at this point was taken as the initial Li insertion specific capacity. The cell was then charged in CC mode with an upper limit voltage of 1.5V at a current equivalent to 0.1C. The specific capacity at this point was taken as the initial Li extraction specific capacity.

[0231] The experiment was conducted in a constant temperature bath set at 25°C. At this temperature, the specific capacity was the value obtained by dividing the capacity by the mass of the negative electrode material. The initial coulombic efficiency was expressed as the percentage of the initial Li deintercalation / initial Li intercalation specific capacity.

[0232] [Calculation of the initial Li insertion / extraction specific capacity of composite particles (B)]

[0233] The initial Li deintercalation / intercalation capacity of the composite particles (B) is obtained by using the following formula, based on the initial Li deintercalation / intercalation capacity of the lithium-ion battery, the Li desorption capacity of the graphite particles, and the mass of the composite particles (B) used.

[0234] (Initial Li intercalation / deintercalation capacity of composite particles (B)) = (Initial Li intercalation / deintercalation capacity - Initial Li intercalation / deintercalation capacity of graphite) / (Mass of composite particles (B) in the sample electrode)

[0235] The initial Li intercalation / deintercalation specific capacity of the graphite particles was investigated by separately fabricating a lithium counter electrode with graphite particles as the sample electrode and measuring its charge and discharge.

[0236] Furthermore, the initial determination of the Li insertion / extraction capacity of the composite particles (B) was carried out immediately after the composite particles (B) were manufactured and after two months of storage at room temperature and atmospheric conditions.

[0237] [Calculation of Si utilization rate]

[0238] The Si utilization rate (%) is obtained by dividing the initial Li intercalation specific capacity of the lithium counter electrode single cell by the silicon content in the sample, dividing the result by the theoretical value of the Li intercalation specific capacity of silicon (4200 mAh / g), and then multiplying by 100. That is, as shown in the following formula.

[0239] (Si utilization) = 100 × {(initial embedding specific capacity) / (silicon content)} / 4200 (%)

[0240] The following describes the modulation method, source, and physical properties of the raw materials for the negative electrode material (carbon material, composite particles (A), composite particles (B), graphite particles).

[0241] [Carbon Materials]

[0242] As a carbon material, it uses BET with a specific surface area of ​​1700 m². 2 / g, and particle size D V50 Commercially available activated carbon with a diameter of 9.2 μm.

[0243] [Graphite particles]

[0244] Using BET specific surface area = 2.7m² 2 / g、D V10 =7μm, DV50 =14μm, D V90 Commercially available synthetic graphite particles with a diameter of 27 μm, tap density of 0.98 g / cc, specific capacity of 372 mAh / g, and initial coulombic efficiency of 92%.

[0245] [Composite Particle (A)]

[0246] For carbon materials, silicon was precipitated on the surface and inside the carbon material by treatment for 8 hours in a tube furnace with a 1.3 vol% silane gas stream mixed with nitrogen at a set temperature of 450 °C, a pressure of 760 Torr, and a flow rate of 100 sccm, to obtain composite particles (A). The D of this composite particle (A) V50 Its thickness is 9.2 μm and its BET specific surface area is 2.1 m². 2 / g and the silicon content is 43% by mass.

[0247] [Composite Particle (B)]

[0248] [Examples 1-1 to 1-22, Comparative Examples 1-3 and 1-5]

[0249] In each embodiment and comparative example, the compounds shown in Table 1-1 were used to prepare composite particles (A) in proportions shown in Table 1-1. The composite particles (A) were fed into a drum sputtering apparatus (PVD: manufactured by Toyoshima Corporation) or an atomic layer deposition fluidized bed (ALD: manufactured by Delphit IMP), and the materials were deposited on the surface of the composite particles (A) under the conditions shown in Table 1-1, thereby obtaining composite particles (B). The physical properties of the composite particles (B) and the results of battery evaluation are shown in Tables 1-1 to 1-3.

[0250] [Examples 1-23]

[0251] Composite particles (A) were fed into a drum sputtering apparatus (PVD: manufactured by Toyoshima Corporation). A film was formed on the surface of composite particles (A) using diamond-like carbon at 80°C under the conditions shown in Table 1, followed by a film formed using Nb2O5 at 380°C, thereby obtaining composite particles (B). The physical properties of composite particles (B) and the results of battery evaluation are shown in Tables 1-3.

[0252] [Examples 1-24]

[0253] 600g of composite particles (A) were added to a rolling coating apparatus (MP-01_mini, manufactured by Powerco Ltd.) and mixed while spraying the coating solution in a nitrogen atmosphere adjusted to 80°C and 1% by volume air. The resulting mixture was heat-treated in an electric tube furnace at 380°C under a nitrogen atmosphere under the following conditions to obtain composite particles (B). The physical properties of composite particles (B) and the results of battery evaluation are shown in Tables 1-1 to 1-3.

[0254] ·Coating solution

[0255] • Niobium pentaethoxy (prepared from high-purity chemicals) 13.5g

[0256] Anhydrous ethanol (Kanto Chemical) 76.5g

[0257] After being manufactured at a dew point of -60°C, the particles are left to stand for one month to pre-generate particles smaller than 100nm.

[0258] Operating conditions of the rolling flow coating unit

[0259] Rotor: Standard

[0260] • Filter: FPM

[0261] Mesh size: 800M

[0262] • Nozzle type: NPX-II

[0263] • Nozzle diameter: 1.2mm

[0264] • Nozzle position: Tangential

[0265] • Number of nozzles: 1

[0266] Rotor speed: 400 rpm

[0267] • Spray pressure: 0.17 (MPa)

[0268] • Drop pressure: 0.2 (MPa)

[0269] • Filter drop time / interval: 4.0 / 0.3 (seconds / second)

[0270] • Spray rate: 2g / cc

[0271] Heat treatment (electric tube furnace)

[0272] Maximum heat retention time: 1 hour

[0273] • Heating rate: 150℃ / hour

[0274] Cooling rate: 150℃ / hour.

[0275] [Comparative Example 1-1]

[0276] Composite particle (A) was used as is for composite particle (B). The physical properties and battery evaluation results are shown in Tables 1-1 to 1-3.

[0277] [Comparative Examples 1-2]

[0278] Chemical vapor deposition (CVD) was performed on composite particles (A) to form an amorphous layer on their surface. Propane was used as the feed gas and thermally decomposed at 1050 °C to obtain composite particles (B) with an amorphous carbon film formed on the surface of composite particles (A). The physical properties of composite particles (B) and the battery evaluation results are shown in Tables 1-1 to 1-3.

[0279] [Comparative Examples 1-4]

[0280] 100 parts by mass of composite particles (A) and 3 parts by mass of polyvinyl alcohol (PVA) were mixed and kneaded at 200°C for 30 minutes. Then, the mixture was heat-treated at 300°C for 10 minutes in a calcining furnace under a nitrogen atmosphere to obtain composite particles (B). The physical properties and battery evaluation results of composite particles (B) are shown in Tables 1-1 to 1-3.

[0281] The above conditions and results are summarized in Table 1.

[0282] In addition, TEM images of the ends of the composite particles (B) of Examples 1-5 are shown. Figure 1 .exist Figure 1 In the diagram, label A indicates an amorphous layer.

[0283] The Raman spectra of Example 1-1 are shown in... Figure 2 .

[0284] The Raman spectra of Examples 1-8 and Comparative Examples 1-3 are shown below. Figure 3 and Figure 4 The XRD patterns of Examples 1-1, 1-2 and Comparative Example 1-1 before analysis software processing are shown below. Figures 5-7 .

[0285] SEM images of Examples 1-1 and Comparative Examples 1-1 are shown below. Figure 8 and Figure 9 .

[0286] Table 1-1

[0287]

[0288] Table 1-2

[0289]

[0290] Table 1-3

[0291]

[0292] (The amorphous layer composition of Examples 1-3, Comparative Examples 1-2, and 1-4 is carbon. The content determination is no different from the weight of the composite particles (A), therefore no data is available.)

[0293] Based on Table 1, consider the following.

[0294] The results from the examples and comparative examples show that the R value and I of the Raman spectrum... Si / I G Composite particles (B) with values ​​within the predetermined range exhibit high initial coulombic efficiency both immediately after modulation and after two months of storage.

[0295] As can be seen from Examples 1-1 to 1-4, the material of the amorphous layer is Nb2O. x When LTO, C, and Nb2O5 are present, and the physical properties are as shown in Table 1, which meet the predetermined range of the present invention, the natural oxidation of the composite particles (B) can be prevented, and battery characteristics considered to be good can be obtained.

[0296] As can be seen from the results of Examples 1-5 to 1-8, the metal oxide layer of ALD can also prevent the oxidation of composite particles (B), and thus obtain what is considered to be good battery characteristics.

[0297] Furthermore, as shown in Examples 1-9 to 1-22, by using oxides of Al, V, Hf, Y, Mo, Ce, and W, as well as Li-containing oxides, as described in the specification, as metal oxides, it is possible to modulate the R value and I value of the Raman spectrum in the same way as in Examples 1-1 to 1-8. Si / I G Composite particles (B) with values ​​within a predetermined range can also prevent natural oxidation of composite particles (B), resulting in what is considered good battery characteristics.

[0298] The results from Examples 1-23 show that even when Nb2O is used together... x And carbon, can also modulate the R value and I value of the Raman spectrum in the same way as in Examples 1-1 to 1-8. Si / I G Composite particles (B) with values ​​within a predetermined range can also prevent natural oxidation of composite particles (B), resulting in battery characteristics considered good. Furthermore, as shown in the results of Examples 1-24, even wet-coated metal oxide layers can prevent oxidation of composite particles (B) in the same way as in Examples 1-1 to 1-23, resulting in battery characteristics considered good.

[0299] It can be seen that in Comparative Example 1-1, there is no amorphous layer, so oxidation cannot be prevented.

[0300] It can be seen that in Comparative Examples 1-2, the R value and I of the Raman spectra are... Si / I G The silicon density is small, resulting in a thicker carbon coating layer, which in turn reduces silicon utilization and capacity. Furthermore, since the full width at half maximum (FWHM) of the 111 plane of Si is also small, it can be inferred that the high-temperature heat treatment increases the crystallinity of silicon, leading to a decrease in the initial coulombic efficiency.

[0301] It can be seen that in Comparative Examples 1-3, the amorphous layer is thick and the R value and I value of the Raman spectrum are... Si / I G The small size of the silicon leads to decreased silicon utilization and reduced capacity. Furthermore, the high oxygen content facilitates silicon oxidation, resulting in a decrease in the initial coulombic efficiency (%) of batteries assembled after two months of storage.

[0302] It can be seen that in Comparative Examples 1-4, the solid-state method was used to coat the surface with PVA, but the amorphous layer was thick, resulting in I. Si / I G The smaller the silicon, the lower the silicon utilization rate and the lower the capacity.

[0303] It is believed that in Comparative Examples 1-5, the extended film formation time resulted in a higher R value and more defects in the carbon material, thus reducing the adhesion with the amorphous layer. As a result, the initial coulombic efficiency (%) of the assembled battery decreased after 2 months of storage.

Claims

1. A composite particle B, comprising: a composite particle A containing carbon and silicon, and an amorphous layer covering the surface of the composite particle A. In the Raman spectrum of the composite particle B, The peak of silicon is located at 450~495 cm⁻¹. -1 The intensity of this peak is expressed as I. Si The strength of the G-band is 1600cm. -1 The peak intensity in the vicinity is represented by I. G And the strength of the D-band is 1360cm. -1 The peak intensity in the vicinity is represented by I. D hour, I Si / I G Values ​​between 0.10 and 0.65 are considered high. R value is I D / I G A score between 1.00 and 1.

30. The composite particle B is shown in the XRD pattern using Cu-Kα rays. The full width at half maximum (FWHM) of the 111 plane of Si is greater than 3.0 degrees.

2. The composite particle B according to claim 1, The composite particle B is shown in the XRD pattern using Cu-Kα rays. The ratio of (peak intensity of SiC at the 111 plane) to (peak intensity of Si at the 111 plane) is less than 0.

004.

3. The composite particle B according to claim 1 or 2, The amorphous layer covering the surface of composite particle A is a layer containing at least one of metal oxides and carbon.

4. The composite particle B according to claim 3, The metal oxide in the amorphous layer covering the surface of composite particle A contains at least one of oxides selected from Al, Ti, V, Cr, Hf, Fe, Co, Mn, Ni, Y, Zr, Mo, Nb, La, Ce, Ta, or W and Li-containing oxides.

5. The composite particle B according to claim 3, The metal oxide in the amorphous layer covering the surface of composite particle A is lithium titanate, i.e., Li4Ti5O. 12 The titanium content in composite particles B is above 0.1% by mass and below 10.0% by mass.

6. The composite particle B according to claim 3, The metal oxide in the amorphous layer covering the surface of composite particle A is niobium pentoxide (Nb₂O₅) or oxygen-deficient niobium oxide (Nb₂O₃). x Furthermore, x = 4.5~4.9, and the niobium content in composite particle B is above 0.1% by mass and below 20.0% by mass.

7. The composite particle B according to claim 3, The amorphous layer covering the surface of composite particle A contains only carbon.

8. The composite particle B according to claim 1, The thickness of the amorphous layer covering the surface of the composite particle A is greater than 0.1 nm and less than 30 nm.

9. The composite particle B according to claim 1, The coverage rate of the amorphous layer covering the surface of composite particle A is over 50%.

10. The composite particle B according to claim 1, The oxygen content of composite particle B is less than 10% by mass.

11. The composite particle B according to claim 1, The silicon content of composite particle B is above 20% by mass and below 70% by mass.

12. The composite particle B according to claim 1, D of composite particle B v50 With a micrometer diameter greater than 1.0 μm and less than 30.0 μm, the BET specific surface area is 0.3 m². 2 / g or more and 10.0m 2 / g or less.

13. The composite particle B according to claim 1, The composite particle B satisfies at least one of the following in the thermal analysis under air atmosphere: it has two exothermic peaks at 400~800℃ and no exothermic peak at 700±10℃.

14. The composite particle B according to claim 1, Metal oxide particles with an average particle size of less than 100 nm are attached to the surface of composite particle B.

15. A method for manufacturing composite particle B, wherein when manufacturing composite particle B according to any one of claims 1 to 14, a physical vapor deposition (PVD) method is used to cover the surface of the composite particle A with an amorphous layer.

16. A method for manufacturing composite particle B, wherein when manufacturing composite particle B according to any one of claims 1 to 6, 8 to 14, an atomic layer deposition method, i.e., the ALD method, is used to cover the surface of the composite particle A with an amorphous layer, wherein the amorphous layer is a metal oxide layer.

17. A negative electrode material comprising composite particles B as described in any one of claims 1 to 14.

18. A negative electrode mixture layer comprising the negative electrode material of claim 17.

19. A lithium-ion secondary battery comprising the negative electrode binder layer as described in claim 18.

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