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

Abstract

A composite particle containing carbon and silicon, and having a crystalline metal oxide particle whose end is present inward of the surface of the composite particle, and a hole is present on the surface of the composite particle. According to the present invention, a composite particle can be provided in which silicon is attached within the fine pores of a carbon material having prescribed fine pores, and a crystalline metal oxide particle is contained, whose end is present inward of the surface of the composite particle, and a hole is present on the surface of the composite particle. By using this composite particle, a lithium ion secondary battery having excellent rate characteristics and cycle characteristics can be provided.

Description

Technical Field

[0001] This invention relates to composite particles, negative electrode active materials, and negative electrode composite layers for lithium-ion secondary batteries containing the same, as well as lithium-ion secondary batteries. Background Technology

[0002] In secondary batteries used in IT devices such as smartphones and tablets, as well as dust collectors, power tools, electric bicycles, drones, and automobiles, there is a need for negative electrode active materials that combine high capacity and high output. As a negative electrode active material, silicon (theoretical specific capacity: 4200 mAh / g), which has a higher theoretical specific capacity than currently used graphite (theoretical specific capacity: 372 mAh / g), has attracted attention.

[0003] However, with the electrochemical insertion and extraction of lithium, silicon (Si) undergoes a maximum volume expansion and contraction of approximately 3 to 4 times. It is known that this causes silicon particles to self-destruct or peel off from the electrode, resulting in significantly lower cycle characteristics in lithium-ion secondary batteries using silicon. Furthermore, due to its slower reaction with Li compared to graphite, there is a problem of reduced capacity that can be effectively utilized during rapid charge and discharge. Therefore, current research focuses on reducing the degree of expansion and contraction as a whole as the negative electrode material and performing surface treatments to lower resistivity, rather than simply replacing graphite with silicon.

[0004] As a negative electrode material for lithium-ion secondary batteries with surface treatment, Japanese Patent Application Publication No. 2002-141069 (Patent Document 1) discloses a structure in which metal oxide particles are dispersed on the surface of a carbon material or in an amorphous carbon coating.

[0005] In addition, Japanese Patent Publication No. 2014-514683 (Patent Document 2) discloses a structure in which metal oxide particles are dispersed on the surface of a silicon core material or in an amorphous carbon coating.

[0006] Prior art literature

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2002-141069

[0009] Patent Document 2: Japanese Patent Publication No. 2014-514683 Summary of the Invention

[0010] However, the negative electrode materials for lithium-ion secondary batteries in Patent Documents 1 and 2 do not possess sufficient rate capability and cycle performance.

[0011] Furthermore, although the composite particles described in Patent Document 1 have a structure in which metal oxides are dispersed around the carbon material and the carbon material and metal oxides are covered with an amorphous carbon film, there are no oxides inside the core material and the structure is not a structure in which pores are connected to oxide particles from the surface.

[0012] Although the composite particles described in Patent Document 2 contain metal oxide particles dispersed on the surface of the silicon core or in the amorphous carbon coating, there are no oxides inside the core, and the structure is not one where pores connect to oxide particles from the surface.

[0013] The object of this invention is to provide a lithium-ion secondary battery with excellent rate performance and cycle performance, and to provide composite particles that can be used in the lithium-ion secondary battery.

[0014] The present invention is structured as follows.

[0015] [1] A composite particle, which is a composite particle containing carbon and silicon.

[0016] The composite particles contain metal oxide particles.

[0017] The ends of the metal oxide particles are located inside the surface of the composite particles, and pores are present on the surface of the composite particles.

[0018] When the average distance from the outermost surface of the composite particle to the end of the metal oxide particle is denoted as (L1), and the average depth of the holes with a diameter of 10 nm or more in the hole, measured from the outermost surface, is denoted as (L2), (L1) / (L2) is 0.5 or more.

[0019] [2] According to the composite particles described in [1], the metal oxide particles exhibit crystallinity.

[0020] [3] According to the composite particle described in [1] or [2], the average distance (L1) from the outermost surface position of the composite particle to the end of the metal oxide particle is 10 to 1000 nm.

[0021] [4] The average diameter D of the composite particles according to any one of [1] to [3] is... S50 The wavelength range is 10–200 nm.

[0022] [5] The composite particles according to any one of [1] to [4] have a crystallite size of 5 to 200 nm as determined by powder X-ray diffraction (powder XRD).

[0023] [6] The composite particles according to any one of [1] to [5], wherein the metal oxide particles comprise at least one selected from Al, Ti, V, Y, Zr, Nb, Mo, W, La, Hf, Ta, Ce, and comprise one selected from Li, Na, K, Mg, Ca, Ba, B, N, P, S, F, Cl as an arbitrary component, and exist in the form of a compound or in the form of their respective oxides.

[0024] [7] According to the composite particles described in [6], the total content of Al, Ti, V, Y, Zr, Nb, Mo, W, La, Hf, Ta, and Ce as elements is 0.006 to 8.00% by mass, and the total content of Li, Na, K, Mg, Ca, Ba, B, N, P, S, F, and Cl as elements is 0.00 to 5.00% by mass.

[0025] [8] The average area D of the diameter of the opening of the pores formed on the surface of the composite particle according to any one of [1] to [6]. A,S The wavelength range is 10–200 nm.

[0026] [9] The composite particle according to any one of [1] to [7] has an average ratio of the area of ​​the opening of the pore formed on the surface of the composite particle to the area of ​​the outermost surface of 5 to 65%.

[0027]

[10] The composite particle according to any one of [1] to [8], wherein the average depth (L2) of the pores with a diameter of 10 nm or more in the pores is 10 to 1000 nm from the outermost position.

[0028]

[11] The cumulative pore volume V for pores smaller than 200 nm, calculated using the BJH method for the composite particles described in any of [1] to [9]. 200 The value is 0.003–0.15 cm. 3 / g.

[0029]

[12] The cumulative pore volume V for pores with a diameter of 3 nm or more and 200 nm or less, obtained by BJH method for the composite particles according to any one of [1] to

[10] , is calculated using the composite particle composition according to any one of [1] to

[10] . 3-200 It is 0.003cm 3 / g or more.

[0030]

[13] The cumulative pore volume V for pores with a diameter of 3 nm or more and 200 nm or less, obtained by BJH method for the composite particles according to any one of [1] to

[11] . 3-200Compared to the cumulative pore volume V calculated using the BJH method for pores with a diameter of less than 200 nm, 200 The ratio is over 55%.

[0031]

[14] The 50% particle size D in the cumulative particle size distribution based on volume of the composite particles according to any one of [1] to

[12] V50 The particle size is greater than 1.0 μm and less than 20.0 μm, and 90% of the particle size D in this cumulative particle size distribution is... V90 It is below 30.0μm.

[0032]

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

[13] has a BET specific surface area of ​​2.0 m². 2 / g or more and 20.0m 2 / g or less.

[0033]

[16] The composite particle according to any one of [1] to

[14] , in the Raman spectrum of the composite particle, in the range of 450 to 495 cm⁻¹ -1 A peak exists within the range of [a certain value], and the intensity of this peak is denoted as I. Si The strength of the G-band (1600cm) -1 The peak intensity near the target is denoted as I. G The strength of the D-band (1360cm) -1 The peak intensity near the target is denoted as I. D hour,

[0034] I Si / I G Values ​​between 0.10 and 1.30

[0035] R value (I) D / I G The value is above 1.00 and below 1.30.

[0036]

[17] The composite particle according to any one of [1] to

[15] has a half-width of 3.0 degrees or more in the XRD spectrum of the composite particle using Cu-Kα rays.

[0037]

[18] The composite particles according to any one of [1] to

[16] have an oxygen content of 0.3 to 10% by mass.

[0038]

[19] The composite particles according to any one of [1] to

[17] do not contain SiC.

[0039]

[20] The composite particles according to any one of [1] to

[18] contain 20 to 85% Si by mass.

[0040]

[21] The carbon in the composite particles according to any one of [1] to

[19] is amorphous.

[0041]

[22] According to any one of [1] to

[20] , when the atomic ratios of Si, O and C obtained by narrow spectrum determination of Si, O and C using X-ray photoelectron spectroscopy are respectively denoted as A Si A O and A C The ratios of SiO2 and SiO among the Si ratios obtained through Si2p spectral state analysis are denoted as B. SiO2 B SiO At that time, A Si It is above 0.05, and A C / (A C +A Si ×(B SiO2 +B SiO The density is above 0.55, and the true density, determined by dry density measurement of helium, is 1.80 g / cm³. 3 Above and 2.30 g / cm 3 the following.

[0042]

[23] A method for manufacturing composite particles includes the following steps (1), (2) and (3),

[0043] Step (1) is a process of coating raw carbon or a resin that can be transformed into raw carbon by heating in an inactive atmosphere in step (2) described later with metal oxides or metal oxide precursors.

[0044] Step (2) is to heat the material coated with metal oxide or metal oxide precursor obtained in step (1) in an inactive atmosphere and then activate it to obtain a carbon material with pores formed by the action of metal oxide and fine pores formed by activation.

[0045] Step (3) involves applying a Si-containing gas to the heated carbon material to cause Si-containing compounds to precipitate from the surface and pores of the carbon material, thereby obtaining composite particles containing porous carbon and silicon.

[0046]

[24] A negative electrode active material comprising the composite particles described in any one of [1] to

[22] .

[0047]

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

[24] .

[0048]

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

[25] .

[0049] By using the composite particles of the present invention, lithium-ion secondary batteries with excellent rate performance and cycle performance can be provided. Attached Figure Description

[0050] Figure 1 This is a cross-sectional SEM image of a portion of the composite particles of the present invention.

[0051] Figure 2 It is Figure 1 The image is obtained by binarizing the cross-sectional SEM image.

[0052] Figure 3 It is used according to the Figure 2 The area of ​​the empty metal oxide particle is obtained from the image, and the curve of the circle-to-diameter conversion at a cumulative frequency of 50% is obtained.

[0053] Figure 4 It is an SEM image of the surface of the composite particles.

[0054] Figure 5 It is Figure 4 The image is obtained by binarizing the SEM image. Detailed Implementation

[0055] The embodiments of the present invention will be described below.

[0056] [1] Composite particles

[0057] One embodiment of the present invention relates to a composite particle comprising silicon and carbon. Preferably, the carbon comprises amorphous porous carbon. By comprising amorphous porous carbon, it is possible to absorb volume changes caused by the expansion and contraction of silicon associated with lithiation and delithiation. Furthermore, the composite particle contains metal oxide particles, the ends of which are located further inward than the surface of the composite particle, and pores are present on the surface of the composite particle.

[0058] Preferably, the metal oxide particles exhibit crystallinity, which can be confirmed by methods such as transmission electron microscopy (TEM), TEM-based electron diffraction, and powder X-ray diffraction (powder XRD).

[0059] The hole is a narrow-diameter cavity with an opening on the surface of the composite particle and extending into the surface layer from the opening, with its tip (point) not reaching the other surface of the composite particle, thus forming a dead end.

[0060] The term "surface portion" refers to a layer of thickness within 50% of the particle diameter of the composite particle, measured from the surface of the composite particle.

[0061] Here, the term "pore" as used later refers to the entirety of tiny voids existing within the composite particles, the diameter and volume of which are determined in this specification through nitrogen adsorption experiments. The concept of pores is inclusive of the aforementioned pores.

[0062] In this specification, the term "surface" means external surface. Therefore, the interior of a pore or the interior of a micropore does not correspond to the surface of a composite particle.

[0063] One embodiment of the present invention relates to composite particles that are measured using devices such as surface and cross-sectional SEM, STEM, and EDS, which are capable of clearly distinguishing core material and oxide particles and clearly identifying pores. Next, an example of a cross-sectional SEM measurement method will be described.

[0064] First, cross-sectional SEM observation is performed on the composite particle group obtained from a homogeneous sample. For example, one could scoop a spoonful from a large amount of well-mixed composite particle powder using a microspatula and place it on a carbon ribbon, then use a cross-section polisher to reveal the cross-section; or embed the well-mixed powder in resin and grind it to generate a cross-section.

[0065] Even when the composite particles contain other particles with significantly different shapes and / or compositions, these can be distinguished from the composite particles using SEM and EDS (SEM-EDS). Therefore, even if the composite particles exist in the form of an electrode composite layer in a lithium-ion secondary battery, their characteristics can be determined through SEM-EDS of their cross-sections. However, particles that break during electrode pressing are removed from the measurement. Whether breakage occurred during electrode pressing can be easily determined from the shape of adjacent composite particles.

[0066] Regarding the composite particles used for cross-sectional SEM measurements, for example, 100 fields of view are arbitrarily selected. However, the same particle is measured in one field of view. The magnification is set from 1 to 100,000 times, and is set to a magnification that allows for clear identification of the target object.

[0067] To determine the distance, depth, diameter, and scale of a target from the obtained image, image analysis software such as ImageJ can be used.

[0068] The distance and depth of the target can be obtained by preparing images of 100 fields of view, finding the maximum value among the measured values ​​for each field of view, and averaging it over the 100 fields of view.

[0069] The diameter of the target can be calculated by preparing images of 100 fields of view and binarizing them to obtain the diameter of the circle based on the area at 50% cumulative area frequency.

[0070] The proportion of the target can be obtained from the binary image of 100 fields of view.

[0071] Figure 1 The image shows a cross-sectional SEM image of composite particle 1, which is a specific example of the composite particle of the present invention. Figure 1 It is a cross-sectional SEM image of a portion of the composite particle 1, including the surface layer.

[0072] The composite particle 1 has multiple pores, including pores 2a, 2b, 2c, 2d, and 2e, in its surface layer. Figure 1 In the image, pore 2d does not have an opening on the surface of composite particle 1, but other cross-sectional SEM images of composite particle 1 confirm that an opening exists on its surface. Metal oxide particles 3a, 3b, 3c, and 3d are present at the deepest parts of pores 2a, 2b, 2c, and 2d, respectively. Figure 1 In the study, it could not be confirmed that metal oxide particles 3c were present at the deepest part of pore 2c, but it was confirmed that metal oxide particles 3d were present at the deepest part of pore 2d through other cross-sectional SEM images of composite particles 1.

[0073] In one embodiment of the present invention, the composite particle preferably has an average distance (L1) from the outermost surface position of the composite particle to the end of the metal oxide particle of 10 nm or more and 1000 nm or less.

[0074] Here, "the tip of the metal oxide particle" refers to the point on the line representing the outline of the metal oxide particle in the cross-sectional SEM image of the composite particle that is closest to the tip (point) of the deepest part of the hole.

[0075] use Figure 1 The cross-sectional SEM image shown illustrates how the mean value (L1) is calculated. The metal oxide particles appearing in the cross-sectional SEM image are assumed to be ellipsoids. Consider the tangent to the composite particle and, among two tangents of the parallel metal oxide particle, the tangent furthest from the tangent to the composite particle. Choose the combination of tangents to the composite particle and the metal oxide particle whose distance between the two tangents is the smallest. Figure 1In this context, the combination selected for metal oxide particle 3a is the tangent TL1 of composite particle 1 and the tangent TL2 of metal oxide particle 2a. The distance L between tangents TL1 and TL2 is measured, and the largest distance L among the distances measured for each metal oxide particle is taken as the distance L1 with respect to that field of view. The average of L1 for 100 fields of view is the average value (L1).

[0076] L1 is the distance from the outermost surface position of the composite particle to the end of the metal oxide particle.

[0077] When the average value (L1) is 10 nm or more, the pores formed inside the composite particles become deeper, thus increasing the surface area of ​​the composite particles that can react with lithium ions, thereby reducing resistance and improving rate performance. From the same point of view, the average value (L1) is more preferably 15 nm or more, and even more preferably 20 nm or more.

[0078] When the average value (L1) is below 1000 nm, the pores formed inside the composite particles become shallower, which reduces side reactions and thus suppresses the decrease in cycling characteristics. From the same point of view, the distance is more preferably below 900 nm, and even more preferably below 800 nm.

[0079] One embodiment of the present invention relates to composite particles, preferably the metal oxide particles having an average diameter D. S50 It is between 10nm and 200nm.

[0080] The D S50 The cross-sectional SEM image of the composite particle with 100 fields of view can be used to determine the diameter of the target using the method described above.

[0081] When the D S50 When the diameter is above 10 nm, pores with a diameter of 10 nm or more can be formed on the surface of the composite particles, improving the rate capability. From the same perspective, the D... S50 More preferably, it is 15nm or more, and even more preferably 20nm or more.

[0082] When the D S50 When the diameter is below 200 nm, the diameter of the pores on the surface of the composite particles can be suppressed to below 200 nm, thus suppressing the decrease in energy density. From the same perspective, the D... S50 More preferably, it is below 150nm, and even more preferably below 100nm.

[0083] In one embodiment of the present invention, the composite particles preferably have a crystallite size of 5 nm or more and 200 nm or less, as determined by powder X-ray diffraction (Powder XRD).

[0084] When the crystallite size is 5 nm or larger, pores can be formed on the surface of the composite particles, improving the magnification characteristics. From the same perspective, the crystallite size is more preferably 10 nm or larger, and even more preferably 15 nm or larger. Furthermore, radiation light can also be used as the light source for powder XRD.

[0085] When the crystallite size is below 200 nm, the diameter of the metal oxide particles can be below 200 nm, which allows the D-type pores on the surface of the composite particles to be reduced. S50 The crystallite size is suppressed to below 200 nm, thus suppressing the decrease in energy density. From the same point of view, the crystallite size is more preferably below 150 nm, and even more preferably below 100 nm.

[0086] These crystallite sizes can be calculated from the half-width of the peaks of crystals, for example, using the Scherrer formula.

[0087] D=Kλ / (Bcosθ) (1)

[0088] Here,

[0089] D: Crystal size (nm)

[0090] K: Scherrer constant (=0.85)

[0091] λ: Wavelength of X-rays (nm)

[0092] B: Broadening of diffraction lines (rad)

[0093] θ: Bragg angle (rad)

[0094] Unless there are special circumstances, the peak of the crystal used should be set as the strongest peak. If it is impossible to accurately measure it under any circumstances, the second strongest peak should be used in turn.

[0095] In one embodiment of the present invention, the composite particles contain at least one selected from Al, Ti, V, Y, Zr, Nb, Mo, W, La, Hf, Ta, and Ce, and may also contain at least one selected from Li, Na, K, Mg, Ca, Ba, B, N, P, S, F, and Cl. Furthermore, they may exist as compounds or as their respective oxides.

[0096] When the metal oxide particles contain Al, Ti, V, Y, Zr, Nb, Mo, W, La, Hf, Ta, or Ce, pores can be formed on the surface of the composite particles. Furthermore, considering the ease of adjusting the pore diameter and the pore formation rate, the metal oxide particles more preferably contain Ti, V, Y, or Nb. Li, Na, K, Mg, Ca, Ba, B, N, P, S, F, and Cl are used to accelerate pore formation during the manufacture of the composite particles of the present invention.

[0097] The presence of these elements can be confirmed by elemental analysis, such as inductively coupled plasma atomic emission spectrometry (ICP-AES), and by the identification of crystal peaks by XRD.

[0098] In one embodiment of the present invention, the composite particles preferably contain a total content of Al, Ti, V, Y, Zr, Nb, Mo, W, La, Hf, Ta, and Ce of 0.006% by mass or more and 8.0% by mass or less.

[0099] When the total content is 0.006% by mass or more, numerous pores can be formed on the surface of the composite particles, improving the rate capability. From the same viewpoint, the total content is more preferably 0.01% by mass or more, and even more preferably 0.03% by mass or more.

[0100] When the total content is 8.00% by mass or less, excessive pore formation on the surface of the composite particles can be suppressed, and the reduction in the cycling characteristics of the composite particles can be suppressed. Furthermore, the reduction in energy density can be suppressed. From the same viewpoint, the total content is more preferably 7.00% by mass or less, and even more preferably 6.00% by mass or less.

[0101] The total content of the elements Li, Na, K, Mg, Ca, Ba, B, N, P, S, F, and Cl is preferably 0.00% by mass or more and 5.00% by mass or less. When the total content exceeds 5.00% by mass, there is a tendency for the energy density to decrease.

[0102] Their content is determined by elemental analysis, such as ICP-AES.

[0103] In one embodiment of the present invention, the composite particle preferably has an average area D of the diameter of the openings of the pores formed on the surface of the composite particle. A,S It is between 10nm and 200nm.

[0104] The D A,S The diameter of the target can be determined using the SEM image of the composite particles with 100 fields of view, following the method described above.

[0105] When the D A,S When the nanometer size is above 10 nm, the area of ​​the composite particles that can effectively react with lithium ions increases, thus improving the rate capability. From the same perspective, the D... A,S More preferably, it is 15nm or more, and even more preferably 20nm or more.

[0106] When the D A,S When the wavelength is below 200 nm, the decrease in energy density caused by the increase in voids within the particle can be suppressed. From the same perspective, the D... A,S More preferably, it is below 150nm, and even more preferably below 100nm.

[0107] In one embodiment of the present invention, the composite particle preferably has an average ratio of the area of ​​the openings of the pores formed on the surface of the composite particle to the maximum surface area of ​​5% or more and 65% or less. The term "maximum surface area" refers to the surface area of ​​the composite particle assuming there are no openings of pores on its surface.

[0108] The ratio can be obtained by binarizing the SEM image of the composite particles, for example... Figure 5 After creating a pattern of such a hole shape, the area of ​​the field of view is calculated by dividing the sum of the areas of each pattern by the sum of the areas of each pattern and the area of ​​the remaining portion. The average of this ratio can be obtained by calculating the ratio for all 100 fields of view and averaging the results.

[0109] When the average value of the stated proportion is 5% or more, the surface area of ​​the composite particles capable of reacting with lithium ions increases, and the rate capability is improved. From the same viewpoint, the average value of the stated proportion is more preferably 7% or more, and even more preferably 10% or more.

[0110] When the average value of the stated ratio is 65% or less, the decrease in energy density caused by the increase in voids within the particles can be suppressed. From the same point of view, the average value of the stated ratio is more preferably 60% or less, and even more preferably 55% or less.

[0111] In one embodiment of the present invention, the composite particle preferably has an average depth (L2) of pores with a diameter of 10 nm or more, measured from the surface, of 10 nm or more and less than 1000 nm.

[0112] Here, "aperture" refers to the size of the opening of the pore on the surface of the composite particle in the cross-sectional SEM image.

[0113] use Figure 1The cross-sectional SEM image shown illustrates the method for calculating the average value (L²). For pores with a diameter greater than 10 nm containing metal oxide particles at their deepest point, the value of L is determined. For pores where no metal oxide particles are present at their deepest point, L is selected as the combination of the tangent to the composite particle and the tangent parallel to it at the deepest point of the pore, where the distance between the two tangents is minimized. d The distances L and L' measured for each pore with a diameter of 10 nm or larger will be... d The largest value among them is taken as the distance L2 with respect to that field of view, and the average of L2 for 100 fields of view is the average value (L2). L2 is the distance from the outermost surface position of the composite particle to the end of the metal oxide particle.

[0114] When the average value (L2) is 10 nm or more, the area capable of reacting with Li ions increases, resulting in lower resistance and improved rate performance. From the same perspective, the average value (L2) is more preferably 15 nm or more, and even more preferably 20 nm or more.

[0115] When the average value (L2) is below 1000 nm, side reactions can be reduced, thus suppressing the decrease in cycle characteristics. From the same point of view, the average value (L2) is more preferably below 900 nm, and even more preferably below 800 nm.

[0116] In one embodiment of the present invention, the composite particles require that the ratio of the average value (L1) to the average value (L2) (L1) / (L2) is 0.5 or more.

[0117] When the ratio is 0.5 or higher, the probability that pores formed by the metal oxide particles are continuously formed from the surface of the composite particles to the ends of the metal oxide particles increases, thus increasing the area of ​​the composite particles that can react with lithium ions, thereby reducing resistance and improving rate performance. From the same point of view, the ratio is more preferably 0.6 or higher, and even more preferably 0.8 or higher.

[0118] The composite particles according to one embodiment of the present invention preferably utilize the cumulative pore volume V for pores with a diameter of less than 200 nm, calculated using the BJH method based on nitrogen adsorption experiments. 200 It is 0.003cm 3 / g or more and 0.150cm 3 / g or less.

[0119] Through the V 200 It is 0.003cm 3 With a surface area of ​​ / g or more, the composite particles have increased surface area that can react with lithium ions, thereby reducing resistance and improving rate performance. From the same perspective, the V...200 More preferably, it is 0.004 cm. 3 / g or more, further preferably 0.005cm 3 / g or more.

[0120] Through the V 200 It is 0.150cm 3 Below / g, side reactions can be reduced, thus suppressing the decrease in cycle characteristics. From the same perspective, the V... 200 More preferably 0.140cm 3 Below / g, more preferably 0.135cm 3 / g or less.

[0121] Here, the cumulative pore volume V 200 It is the cumulative pore volume when the relative pressure is 0.99 in the nitrogen adsorption test.

[0122] The cumulative pore volume V 200 It was obtained by analyzing the adsorption isotherm obtained from nitrogen adsorption experiments using a known method. Details will be described later.

[0123] In one embodiment of the present invention, the composite particles preferably utilize the cumulative pore volume V calculated using the BJH method for pores with a diameter of 3 nm or more and 200 nm or less. 3-200 It is 0.003cm 2 / g or more.

[0124] Through the V 3-200 It is 0.003cm 3 / g or higher, which facilitates the reaction with the core material (lithium diffusion) and improves rate performance. Here, "core material" refers to the portion of the composite particles other than the crystalline metal oxide particles, and is composed of silicon, carbon, and fine pores including the aforementioned pores. From the same perspective, the V... 3-200 More preferably, it is 0.005cm 3 / g or more, further preferably 0.020cm 3 / g or more.

[0125] In one embodiment of the present invention, the composite particles preferably utilize the cumulative pore volume V calculated using the BJH method for pores with a diameter of 3 nm to 200 nm. 3-200 Compared to the cumulative pore volume V calculated using the BJH method for pores with a diameter of less than 200 nm, 200 The ratio V 3-200 / V 200 It is over 55%.

[0126] With a ratio of 55% or higher, the effective surface area of ​​the composite particles capable of reacting with lithium ions increases, thereby reducing resistance and improving rate performance. Furthermore, pores smaller than 3 nm are less conducive to lithium-ion reaction and increase side reactions, leading to a decrease in initial efficiency and cycling characteristics. From the same viewpoint, the ratio is more preferably 65% ​​or higher, and even more preferably 75% or higher.

[0127] One embodiment of the present invention relates to composite particles, preferably comprising 50% of the particle size D in the cumulative particle size distribution based on volume. V50 It is between 1.0μm and 20μm.

[0128] The reason is, through D V50 With a particle size of 1.0 μm or larger, it can reduce side reactions with the electrolyte. Furthermore, the powder exhibits excellent workability, making it easy to prepare slurries with suitable viscosity and density for coating; additionally, its density can be easily increased when used as an electrode. From the same perspective, D... V50 More preferably, it is 2.0 μm or more, and even more preferably, it is 3.0 μm or more.

[0129] On the other hand, when D V50 When the particle size is below 20 μm, the surface area of ​​the composite particles that can react with lithium ions increases, resulting in lower resistance and improved rate performance. Furthermore, the expansion and contraction of lithium-ion secondary batteries during charge and discharge are suppressed, improving cycle performance. From the same perspective, D... V50 More preferably, it is 15.0 μm or less, and even more preferably, it is 10.0 μm or less.

[0130] One embodiment of the present invention relates to composite particles, preferably in which 90% of the particle size D in the cumulative particle size distribution based on volume is... V90 It is below 30μm.

[0131] Through D V90 With a particle size below 30 μm, the expansion and contraction of lithium-ion secondary batteries during charge and discharge are suppressed, improving cycle characteristics. Furthermore, when the composite particles are coated onto the current collector in slurry form, it becomes less likely to cause striations and abnormal unevenness. From the same perspective, D... V90 More preferably, it is 25 μm or less, and even more preferably, it is 20 μm or less.

[0132] The cumulative particle size distribution of these volumetric benchmarks is determined using, for example, a laser diffraction particle size analyzer, SEM, or cross-sectional SEM.

[0133] One embodiment of the present invention relates to a composite particle, preferably with a BET specific surface area of ​​2.0 m². 2 / g or more and 20.0m 2 / g or less. The specific surface area via BET is 2.0m².2 With a surface area of ​​2.5 m² / g or more, the area of ​​the composite particles that can react with lithium ions increases, thereby reducing resistivity and improving rate performance. From the same perspective, a BET specific surface area of ​​2.5 m² is more preferable. 2 / g or more, further preferably 3.0m 2 / g or more. The specific surface area via BET is 20.0 m². 2 Below a certain value (g), side reactions between the composite particles and the electrolyte are reduced. From the same perspective, a BET specific surface area of ​​18.0 m² is more preferable. 2 / g or less, more preferably 15.0m 2 / g or less.

[0134] BET specific surface area is typically measured using specialized measuring apparatus known in the art. Nitrogen is usually used as the adsorbent gas, but carbon dioxide, argon, etc., are sometimes also used.

[0135] One embodiment of the present invention relates to composite particles that preferably exhibit a Raman spectrum in the range of 450–495 cm⁻¹. -1 Peaks exist within the range of 520 cm⁻¹. Typically, crystalline silicon has a peak at 520 cm⁻¹. -1 A peak appears nearby. Since amorphous silicon exhibits a peak at a lower Raman shift, the peak appears in the range of 450–495 cm⁻¹. -1 The presence of peaks indicates that the composite particles have amorphous silicon. When silicon is amorphous, the expansion and contraction during charging and discharging are relatively isotropic, thus improving cycle performance.

[0136] One embodiment of the present invention relates to composite particles, when 450-495 cm -1 The intensity of the peak is denoted as I. Si The strength of the G-band (1600cm) -1 The peak intensity near the target is denoted as I. G The strength of the D-band (1360cm) -1 The peak intensity near the target is denoted as I. D When, I is preferred Si / I G It is above 0.10 and below 1.30.

[0137] When I Si / I G When the value is less than 0.10, there is a tendency for the energy density to decrease. From the same perspective, I... Si / I G More preferably, it is 0.20 or higher, and even more preferably, it is 0.25 or higher. When I Si / I GWhen the value is greater than 1.30, silicon is more concentrated in the surface layer of the composite particles, which may lead to poorer cycle performance. From the same perspective, I... Si / I G More preferably, it is 0.80 or less; even more preferably, it is 0.75 or less; and still more preferably, it is 0.70 or less.

[0138] The intensity I of the D band obtained by Raman spectroscopy D and the intensity I of the G-band G The ratio is the R value (I). D / I G The preferred value is 1.00 or higher and 1.30 or lower.

[0139] When the R value is 1.00 or higher, the reaction resistance between the composite particles and lithium ions decreases, and the rate capability improves. From the same point of view, the R value is more preferably 1.03 or higher, and even more preferably 1.05 or higher.

[0140] When the R value is 1.30 or less, the carbon defects in the composite particles are fewer, which suppresses side reactions with the electrolyte and inhibits the decrease in cycling characteristics. From the same point of view, the R value is more preferably 1.29 or less, and even more preferably 1.28 or less.

[0141] The G band in the Raman spectrum is obtained at 1600 cm⁻¹ when measuring carbon materials. -1 The nearby peak, band D, is obtained at 1350 cm⁻¹ when the same measurements were performed on carbon materials. -1 Nearby peaks. "Peak Intensity" is set to the height from the baseline to the peak apex after adjusting for the baseline.

[0142] In one embodiment of the present invention, the composite particles exhibit a half-width at half-maximum (WWHM) of 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 WWHM of the Si (111) surface peak is 3.0 degrees or more, the crystallites are small, thus suppressing breakage associated with charge and discharge. This leads to improvements in the initial coulombic efficiency and coulombic efficiency of the lithium-ion secondary battery. From the same viewpoint, the WWHM is preferably 3.5 degrees or more, more preferably 4.0 degrees or more. Furthermore, the WWHM is preferably 10.0 degrees or less, more preferably 8.0 degrees or less, and even more preferably 6.0 degrees or less.

[0143] In one embodiment of the present invention, the composite particles preferably do not contain SiC. When SiC is present in the composite particles, the capacity and energy density are significantly reduced.

[0144] In one embodiment of the present invention, the composite particles preferably have a ratio of (peak intensity of the SiC(111) surface) / (peak intensity of the Si(111) surface) of 0.01 or less in the XRD pattern obtained by powder XRD using Cu-Kα rays. Therefore, the composite particles contain no SiC (silicon carbide) or have an extremely low SiC content, thus improving the utilization rate of silicon as a battery active material and increasing the initial discharge capacity. Furthermore, the ratio of (peak intensity of the SiC(111) surface) / (peak intensity of the Si(111) surface) is also expressed as I. SiC(111) / I Si(111) More preferably I SiC(111) / I Si(111) The lower limit is 0, meaning no peak intensity was observed on the SiC(111) surface. Furthermore, a peak on the SiC(111) surface means a peak originating from SiC, appearing around 35 degrees (deg) in 2θ terms. Additionally, a peak on the Si(111) surface means a peak originating from Si, appearing around 28 degrees in 2θ terms.

[0145] Here, "peak intensity" is set to the height from the baseline to the peak after the baseline is corrected.

[0146] The composite particles according to one embodiment of the present invention preferably have an oxygen content of 0.3% by mass or more and 10.0% by mass or less.

[0147] Since pure Si has high reactivity, its reactivity can be reduced by partially oxidizing it, thus suppressing the rapid deterioration of the composite particles. Furthermore, since the composite particles contain metal oxides, the oxygen content is preferably 0.3% by mass or more. From the same viewpoint, 0.4% by mass or more is more preferred, 0.5% by mass or more is even more preferred, 0.6% by mass or more is particularly preferred, and 0.9% by mass or more is most preferred.

[0148] When the oxygen content is 10.0% by mass or less, silicon oxidation can be moderately suppressed, thereby reducing the irreversible capacity when used as a negative electrode material. From the same point of view, 7.0% by mass or less is more preferred, and 5.0% by mass or less is even more preferred.

[0149] The oxygen content is determined using, for example, a simultaneous oxygen and nitrogen analyzer.

[0150] In one embodiment of the present invention, the composite particles preferably contain 20% or more but less than 85% silicon (Si) by mass.

[0151] When the silicon content is 20% by mass or more, the amount of silicon in the composite particles is sufficient, which can improve the discharge capacity. From the same point of view, the silicon content is more preferably 30% by mass or more, and even more preferably 40% by mass or more.

[0152] When the silicon content is 85% by mass or less, the silicon content is not excessive, thus allowing the carbon, acting as a carrier, to absorb volume changes caused by its expansion and contraction. From the same point of view, the silicon content is more preferably 80% by mass or less, and even more preferably 75% by mass or less.

[0153] The silicon content in the composite particles can be obtained by ICP-AES, which will be described later.

[0154] One embodiment of the present invention relates to composite particles that further have a carbon-containing coating on part or all of their surface and the inner wall surfaces of pores not in contact with metal oxides or the inner wall surfaces of fine pores not filled with silicon. Such coated composite particles, i.e., particles composed of composite particles and coatings, are referred to below as "coated composite particles." The structure of this coated composite particle has the following characteristics.

[0155] When the atomic ratios of Si, O, and C obtained from the narrow spectrum of Si, O, and C in the coated composite particles using X-ray photoelectron spectroscopy (XPS) are denoted as A... Si A O And A C The ratios of SiO2 and SiO among the Si ratios obtained through Si2p spectral state analysis are denoted as B. SiO2 B SiO When, A is preferred. Si It is above 0.05 and A C / (A C +A Si ×(B SiO2 +B SiO The value is above 0.55. Furthermore, A... Si +A O +A C =1.00.

[0156] As is well known, XPS is a method for obtaining knowledge and insights about the types, quantities, and chemical bonding states of elements present on the surface of a material and at depths of several nm.

[0157] <1>A Si / (A Si +A O +A C )

[0158] When A Si / (A Si +A O +A C When the value is less than 0.05, the coating is too thick, and the resistance increases.Si / (A Si +A O +A C The preferred value is 0.15 or higher, and more preferably 0.25 or higher. Since the analysis depth of XPS is only a few nm, which is very shallow, the ability to observe Si to some extent means that the coating is an extremely thin layer.

[0159] Because the coating contains carbon and oxygen, it has lower electronic conductivity compared to carbon-coated layers. When the coating is too thick, the resistance increases, therefore a thin layer is required.

[0160] <2>A C / (A C +A Si ×(B SiO2 +B SiO ))

[0161] A C / (A C +A Si ×(B SiO2 +B SiO The value of is an indicator of the carbon concentration on the surface of the coated composite particles and at a depth of several nm (the spatial resolution depth in XPS). This is because the Si present on the surface of the coated composite particles and at a depth of several nm is considered to exist in the form of oxides such as SiO2 and SiO. However, due to the presence of Si in A C The information also includes information about the carbon in the carrier, so this indicator does not reflect only the carbon concentration of the coating.

[0162] When A C / (A C +A Si ×(B SiO2 +B SiO When the value of is less than 0.5, the carbon concentration on the surface of the composite particles and at a depth of several nm becomes low, resulting in a lower oxidation suppression ability. Therefore, the value is preferably 0.5 or higher. The value is more preferably 0.75 or higher. The value is even more preferably 0.85 or higher. Furthermore, the value is preferably 0.98 or lower. When it exceeds 0.98, the silicon oxide concentration on the surface and at a depth of several nm becomes too low, thus reducing the oxidation suppression ability. Although the structure of the coating cannot be determined, the inventors presume it to be a thin film layer composed of carbon and silicon oxide.

[0163] A C / (A C +A Si ×(B SiO2 +B SiOThe value of ) can be changed, for example, by adjusting the reaction temperature, reaction time, reaction pressure, or the type or concentration of unsaturated hydrocarbons in the preparation method of coated composite particles.

[0164] The carbon in the coating preferably comprises compounds derived from hydrocarbons. This can be determined by measuring the pyrolysis GC-MC of the coated composite particles, and finding that the gas produced from the coated composite particles between 200°C and 600°C contains compounds derived from hydrocarbons.

[0165] The coating can be manufactured by applying a carbon source with unsaturated bonds to a carrier at low temperature, followed by oxidation of the resulting material. Details are described later.

[0166] One embodiment of the present invention relates to coated composite particles, preferably with a coating thickness so thin that it is substantially unmeasurable in cross-sectional observation using an electron microscope. When the coating thickness is as thin as described above, the resistivity of the coated composite particles is low. Scanning electron microscopes (SEMs) lack the resolution to distinguish thicknesses of several nanometers, and therefore cannot measure coatings thinner than that. Transmission electron microscopes (TEMs) have sufficient resolution to observe even coatings several nanometers thick, but in practice, when preparing TEM observation samples containing coated thin films from coated composite particles, the coating of the coated composite particles is damaged during processing, resulting in destruction, and therefore cannot be observed. The phrase "substantially unmeasurable" refers to this state. However, even thin films that are substantially unmeasurable in cross-sectional observation using an electron microscope can have their presence of a coating determined by XPS and the hydrophobicity test described later.

[0167] The true density of the coated composite particles involved in this invention is 1.80 g / cm³. 3 The above value was calculated using a dry density measurement of helium.

[0168] True density less than 1.80 g / cm³ 3 This means that the amount of silicon filling the pores of carbon in the coated composite particles is small, and the coating is a thick layer of low-density organic matter such as tar components and polymers.

[0169] When the true density is 1.80 g / cm³ 3 The above indicates that the silicon content in the pores of the carbon in the coated composite particles is sufficient and the coating is thin, which can improve the specific capacitance and reduce the resistivity of the coated composite particles. From the same point of view, the true density is preferably 1.85 g / cm³. 3 The above, more preferably 1.88 g / cm³ 3 above.

[0170] The true density of the coated composite particles involved in this invention is 2.30 g / cm³. 3 The following applies when the true density is 2.30 g / cm³. 3 In the following case, the carbon in the coated composite particles is amorphous, and the carbon structure is more isotropic. Since its density is lower than that of carbon and silicon according to literature values, it can be assumed that there are pores in the coated composite particles that prevent helium from penetrating from the outside of the particles, thus improving cycle performance. Furthermore, since the amount of silicon carbide in the coated composite particles is low, the reduction in silicon utilization can be suppressed. Silicon carbide has a higher density than carbon and Si, therefore, when it is present in the coated composite particles, the true density increases. From this point of view, the true density is preferably 1.99 g / cm³. 3 The preferred value is 1.97 g / cm³. 3 the following.

[0171] True density, obtained through dry density measurement, can be determined using the gas-phase displacement method. The gas-phase displacement method involves placing a sample and helium gas into a container whose volume has been pre-determined using helium gas in an environment maintained at a constant temperature. The true density is calculated based on the volume of helium gas displaced by the sample and the mass of the sample. For example, the AccuPyc II 1340 gas hydrometer manufactured by Micromeritics can be used for the gas-phase displacement method.

[0172] The coating can be formed by oxidizing the composite particles after applying unsaturated hydrocarbons at a low temperature below 400°C (i.e., hydrosilylation reaction).

[0173] As the unsaturated hydrocarbon, any hydrocarbon having double and / or triple bonds can be used. If the hydrocarbon is a compound with low vapor pressure and does not vaporize at atmospheric pressure, it can be used at a pressure below atmospheric pressure. Examples of hydrocarbons that are gases at atmospheric pressure include acetylene, ethylene, propylene, and 1,3-butadiene, with acetylene and ethylene being more preferred. In this case, multiple types of hydrocarbons can be used. Alternatively, it can be used in combination with inert gases such as helium or argon, or reducing gases such as hydrogen.

[0174] In one embodiment of the present invention, the coated composite particles are preferably hydrophobic. When hydrophobic, the water-protective effect is improved. Furthermore, the negative electrode binder layer contains a polymer that acts as a binder. Since the polymer has good affinity for the hydrophobic particles, it can be more uniformly dispersed when preparing the slurry for negative electrode coating.

[0175] As a method for determining hydrophobicity, observing the seepage behavior of powder into water is simple and easy to determine. This determination can be performed, for example, using the method described in the examples.

[0176] [2] Raw material carbon

[0177] The carbon material used as the raw material for the composite particles involved in one embodiment of the present invention, i.e., "raw material carbon", is not particularly limited as long as it is not graphite, but is preferably amorphous carbon.

[0178] Furthermore, preferably, the raw material carbon is activated to become porous carbon. Porous carbon refers to carbon with a total micropore volume of 0.20 cm³. 3 / g or BET specific surface area is 200m² 2 Carbon content of 1 g or more. Since porous carbon is considered to have a high adsorption rate for silanes, fine silicon can be precipitated within the pores, for example, when manufacturing composite particles using CVD with silane gas. As for shape, particle-like or fibrous forms are possible, with particle-like forms being preferred. This is because when in particle form, the pores are formed isotropically, thus the composite particles expand and contract isotropically during lithiation and delithiation, resulting in excellent cycling characteristics. For isotropic expansion and contraction, a small aspect ratio of the particles is preferred, and spherical (with a circular cross-section) is more preferable. Examples of porous carbon include activated carbon. Furthermore, activated carbon is typically amorphous carbon.

[0179] One embodiment of the present invention relates to composite particles, preferably in which the raw material carbon is activated to achieve a cumulative pore volume V corresponding to a pore diameter of 200 nm or less, calculated by the BJH method. 200 Become 0.30cm 3 / g or more. Through the aforementioned V 200 0.30cm 3 A concentration of V / g or higher can increase the internal silicon content, thus improving the specific capacity of the composite particles. From this perspective, the raw material carbon possesses the aforementioned V... 200 More preferably 0.50cm 3 / g or more, further preferably 0.60cm 3 / g or more. Additionally, at this point, the cumulative pore volume V, calculated using the BJH method, corresponds to a pore diameter of 3nm or more and 200nm or less. 3-200 The ratio V to the cumulative pore volume V200 corresponding to pore diameters below 200 nm, calculated using the BJH method. 3-200 / V 200 V is preferred 3-200 / V 200 <0.3. Since silicon precipitates more in micropores smaller than 3 nm, therefore, when the ratio of V... 3-200 / V200 When the concentration is less than 0.3, the formation of crystalline lithium silicide can be suppressed during battery charging and discharging, resulting in a significant improvement in cycle performance.

[0180] One embodiment of the present invention relates to composite particles, preferably in which the raw material carbon is activated to achieve a BET specific surface area of ​​200 m². 2 / g or more. Passing through 200m 2 A surface area of ​​800 m² / g or higher can increase the internal silicon content, thus improving the specific capacity of the composite particles. From this perspective, a BET specific surface area of ​​800 m² / g is more preferable. 2 / g or more, further preferably 1500m 2 / g or more.

[0181] The raw material carbon is preferably obtained by carbonizing phenolic resin and / or a copolymer resin of resorcinol and formaldehyde. Alternatively, the resin can be heat-treated at 150°C to 300°C for 1 to 6 hours to cure it before carbonization. Alternatively, the resin can be broken down after curing to obtain particle sizes of approximately 0.5 to 5.0 mm. Preferably, it is manufactured by carbonizing the resin at a temperature of 400°C to 1100°C in an inert gas atmosphere for 1 to 20 hours.

[0182] One embodiment of the present invention relates to composite particles, preferably comprising 50% of the particle size D in the cumulative particle size distribution of the raw material carbon on a volume basis. V50 It is between 1.0μm and 20μm.

[0183] Through D V50 With a particle size of 1.0 μm or larger, side reactions between the composite particles and the electrolyte are reduced. Furthermore, the powder exhibits excellent workability, making it easy to prepare slurries with suitable viscosity and density for coating. Additionally, it is easy to increase the density when used as an electrode.

[0184] Starting from the same point of view, D V50 More preferably, it is 2.0 μm or more, and even more preferably 3.0 μm or more. (Through D...) V50 With a particle size below 20.0 μm, the expansion and contraction of the battery during charging and discharging are suppressed, improving cycle characteristics. Furthermore, the smaller the particle size of the composite material, the greater the surface area available for reaction with lithium ions, resulting in lower resistivity and improved rate performance. From the same perspective, D... V50 More preferably, it is 15.0 μm or less, and even more preferably, it is 10.0 μm or less.

[0185] If the raw carbon is not subjected to intensive crushing and grading processes, then neither the activated carbon material nor the composite particles after silicon precipitation will produce D V10 DV50 D V90 Almost nothing has changed.

[0186] Even after obtaining the composite particles, appropriate processing can be performed to dissolve silicon and obtain activated carbon materials. Therefore, even starting from the state of the composite particles, the physical properties of the activated carbon materials can be examined. For example, the properties of the D... V50 Cumulative pore volume V 200 and V 3-200 BET specific surface area.

[0187] [3] Methods for manufacturing composite particles

[0188] The composite particles according to one embodiment of the present invention can be manufactured, for example, by the following processes (1), (2), (3), but are not limited thereto.

[0189] Step (1): A step of coating raw carbon or a resin that can be transformed into raw carbon by heating in an inactive atmosphere in step (2) described later with metal oxides or metal oxide precursors.

[0190] Step (2): The material coated with metal oxide or metal oxide precursor obtained in step (1) is heated in an inactive atmosphere and then activated to obtain a carbon material having pores formed by the action of metal oxide and fine pores formed by activation.

[0191] In the nitrogen adsorption test, the cumulative pore volume of the carbon material, calculated using the BJH method, for pores with a diameter of less than 200 nm, is denoted as V. 200 The cumulative pore volume for pores with a diameter of 3 nm or more but less than 200 nm, obtained by conversion using the BJH method, is denoted as V. 3-200 When the value is less than V, the preferred value is: 0.02 < V. 3-200 / V 200 <0.40, and the specific surface area of ​​BET is 800m². 2 / g or more.

[0192] Through V 3-200 / V 200 A value <0.40 can reduce excess voids in the composite particles obtained in subsequent processes, thereby increasing energy density. From the same perspective, V is more preferred. 3-200 / V 200 <0.35, further optimization of V 3-200 / V 200 <0.30. Passing through 0.02 < V 3-200 / V 200In subsequent processes, the proportion of fine pores larger than 3 nm in the resulting composite particles increases. From the same perspective, 0.03 < V is more preferable. 3-200 / V 200 Further optimization is to select 0.05 < V 3-200 / V 200 .

[0193] Step (3): A process in which Si-containing gas is applied to the heated carbon material to cause Si-containing compounds to precipitate on the surface and in the pores of the carbon material, thereby obtaining composite particles containing porous carbon and silicon.

[0194] (Process (1))

[0195] Step (1) is a step of coating raw carbon or a resin that can be transformed into raw carbon by heating in an inert atmosphere in step (2) described later with a metal oxide or a metal oxide precursor. The coating layer formed using the metal oxide or metal oxide precursor can be an island structure dispersed in an island shape on the surface of the raw carbon, or it can uniformly cover the surface. Step (1) can include: a step of preparing a solution containing at least one metal oxide precursor selected from metal alkoxides and metal complexes (including chelate complexes) and a solvent; and a step of spraying the solution in a mist onto the raw carbon that has become fluid or the resin that can be transformed into raw carbon by heating in an inert atmosphere in step (2) described later. At this time, if the coverage rate of the coating layer is 10% or more, the proportion of the pore area on the surface of the composite particles described later is 5% or more, which is therefore preferred. From the same point of view, the coverage rate of the coating layer is more preferably 15% or more, and even more preferably 20% or more.

[0196] Phenolic resins and copolymers of resorcinol and formaldehyde are preferred as the resins.

[0197] The metal oxide precursor is selected from at least one of metal alkoxides and metal complexes (including chelate complexes), preferably a substance that is stably soluble in a solvent. Specifically, examples include titanium tetraisopropoxide (IV), niobium pentaethanol (V), vanadium triisopropoxide (V), aluminum triisopropoxide (III), yttrium triisopropoxide (III), cerium triisopropoxide (III), and lithium ethoxide.

[0198] The solvent is selected from water and organic solvents. There are no particular limitations as long as the solvent can dissolve the metal oxide precursor without reacting with it, but solvents with a boiling point of about 100°C, such as ethanol, isopropanol, butanol, hexane, and toluene, are preferred.

[0199] The concentration of the metal oxide precursor in the precursor solution is preferably 3% by mass or more. By maintaining a precursor concentration of 3% by mass or more, productivity is improved. From the same viewpoint, the precursor concentration is more preferably 5% by mass or more, and even more preferably 10% by mass or more. The precursor concentration is preferably 50% by mass or less. When the concentration is too high, the coating rate decreases. From the same viewpoint, the precursor concentration is more preferably 40% by mass or less, and even more preferably 35% by mass or less.

[0200] There is no particular limitation on the method for making the raw material carbon or the resin that is transformed into raw material carbon in the later step (2) into a fluid state, but examples include using a rolling fluidized bed and a rotating fluidized bed, with the use of a rolling fluidized bed being preferred. As a rolling fluidized bed device, examples include the MP series manufactured by Powertech Co., Ltd.

[0201] When using a rolling fluidized bed, it is preferable to operate the system with the gas supply temperature at or above the boiling point of the organic solvent by 10°C. By setting the temperature within this range, it is easy to maintain fluidity.

[0202] When using a rotating fluidized bed, it is preferable to carry out the operation in a low-humidity atmosphere. Examples of low-humidity atmospheres include nitrogen atmosphere, argon atmosphere, or atmospheric atmosphere with a humidity of 25% or less.

[0203] There is no limitation on the air supply volume of the rolling fluidized bed, but it is preferable that the raw material carbon or the resin that can be transformed into raw material carbon in the later step (2) flows completely.

[0204] There are no particular limitations on the method of spraying the precursor solution onto the raw material carbon, but examples include the use of tube pumps and spray nozzles.

[0205] By heat-treating the coated raw carbon or the resin that can be transformed into raw carbon in the following step (2), or by subjecting it to a sol-gel reaction, the coated metal oxide precursor layer can be formed into a metal oxide layer. However, since it becomes crystalline metal oxide particles in the next step, the heat treatment or sol-gel reaction may or may not be carried out.

[0206] (Process (2))

[0207] Step (2) is to heat the material coated with metal oxide or metal oxide precursor obtained in step (1) in an inactive atmosphere and then activate it to obtain a carbon material having pores formed by the action of metal oxide and fine pores formed by activation.

[0208] Step (2) can include: heating the material coated with metal oxide or metal oxide precursor obtained in step (1) to 700°C to 1100°C under an inactive atmosphere; and then switching to an activating gas (activating gas) such as CO2 gas or water vapor gas, and maintaining the temperature for 1 to 20 hours. During this time, the coated metal oxide precursor layer becomes crystalline metal oxide particles, which react with the raw material carbon while eroding into the raw material carbon. At this time, a structure is formed where continuous pores of approximately the same diameter as the metal oxide particles are formed from the surface of the raw material carbon toward the interior, and crystalline metal oxide particles are present at the deepest part of the pores. By having crystalline metal oxide particles at the deepest part of the pores, current concentration at the deepest part of the pores can be suppressed, and degradation starting from the deepest part of the pores can be suppressed. Furthermore, by making the metal oxide crystalline, lithium-ion conductivity can be improved, and reaction with lithium ions can occur even at the locations where metal oxides are present, thus improving rate performance. In addition, through activation, fine pores with a diameter of less than 3 nm are developed in the raw carbon, and porous carbon materials with different pore diameters can be obtained.

[0209] The diameter of the crystalline metal oxide particles varies depending on the type of oxide, the type of precursor, the coating state, the surface state of the raw carbon, the heating temperature, etc., but the type of oxide has a significant impact. In order to obtain a composite material with a target pore size, it is necessary to appropriately select the type of oxide.

[0210] The erosion rate of the crystalline metal oxide particles into the raw carbon varies depending on the type of oxide, activation temperature, and raw carbon. Furthermore, the depth of the formed pores is proportional to the activation time. On the other hand, to obtain composite particles with the target silicon content, a sufficient amount of fine pores with a diameter less than 3 nm needs to be formed in the raw carbon. Therefore, it is necessary to preferentially determine the activation conditions of the raw carbon and then appropriately select the type of oxide that forms the target pore depth under those conditions.

[0211] (Process (3))

[0212] Step (3) involves applying a Si-containing gas to the heated carbon material to precipitate Si-containing compounds on the surface and within the pores of the carbon material, thereby obtaining composite particles containing porous carbon and silicon. Step (3) may include the following steps: by applying a Si-containing gas, preferably a silane gas, to the heated carbon material, thermal decomposition of the Si-containing gas occurs within the pores of the carbon material, thereby precipitating Si-containing compounds within the pores and on the surface of the carbon material, resulting in composite particles.

[0213] For example, if the carbon material is placed in the chamber of a CVD apparatus and silane gas is applied to the carbon material while it is heated, the silane enters into the fine pores of the carbon material and undergoes thermal decomposition, thereby allowing silicon to precipitate within the fine pores of the carbon material. As a method for this purpose, the apparatus and method shown, for example, in U.S. Patent 10,424,786 can be used.

[0214] When silicon is present within the pores of the carbon material, the durability against stress within the composite particles associated with the expansion and contraction of silicon during battery charging and discharging is increased, which is therefore preferable. Furthermore, the diameter of the pores where silicon is deposited is preferably less than 3 nm. Silicon deposited in pores with a diameter less than 3 nm suppresses the formation of crystalline lithium silicides during charging and discharging, resulting in a significant improvement in cycle performance. From this viewpoint, the carbon material is preferably a porous carbon material having a plurality of pores with a diameter less than 3 nm.

[0215] Besides silane (SiH4), other Si-containing gases used include disilane and trisilane. Additionally, other gases can be included in the Si-containing gas mixture, such as nitrogen, argon, helium, and hydrogen, which can be mixed as a carrier gas. Various CVD conditions, such as gas composition ratio, gas flow rate, temperature program, and the selection of fixed / fluidized bed, are adjusted appropriately while observing the properties of the products.

[0216] When silane gas is used, the processing temperature is 340°C to 450°C, more preferably 350°C to 420°C, and even more preferably 370°C to 400°C. By setting the temperature within this range, silicon can preferentially precipitate in the fine pores of the carbon material with a diameter of less than 3 nm, and composite particles that retain a state in which no silicon is precipitated in the pores formed by the action of crystalline metal oxide particles can be obtained.

[0217] When using silane gas, the furnace pressure during silicon precipitation is preferably 1500 Torr or less. With a furnace pressure of 1500 Torr or less, silicon can preferentially precipitate in pores with a diameter less than 3 nm, resulting in composite particles that retain the state where silicon has not precipitated in pores with a diameter greater than 3 nm formed by the action of crystalline metal oxide particles. From the same viewpoint, the furnace pressure is more preferably 1000 Torr or less, and even more preferably 900 Torr or less.

[0218] The processing time of step (3) is determined while analyzing the processed gas or the gas generated by the reaction in real time. Processing is stopped when the concentration of the processed gas rises sharply or the concentration of the gas generated by the reaction drops sharply. If processing continues, Si-containing compounds will begin to precipitate in pores with a diameter of 3 nm or more formed by the action of crystalline metal oxide particles, and eventually the pores will be filled with Si-containing compounds.

[0219] Alternatively, after obtaining composite particles by precipitating the Si-containing compound within the pores and on the surface of the carbon material, a portion of the Si-containing compound can be oxidized by contacting it with an oxygen-containing inert gas atmosphere. In particular, pure Si has high reactivity, so by partially oxidizing it, rapid deterioration of the composite particles can be suppressed.

[0220] [4] Negative electrode active material

[0221] One embodiment of the present invention relates to a negative electrode active material comprising composite particles. Regarding the composite particles, two or more types may be mixed. Other components may be further included. Examples of these other components include those commonly used as negative electrode active materials in lithium-ion secondary batteries. Examples include graphite, hard carbon, soft carbon, and lithium titanate (Li4Ti5O). 12 This includes alloys of active materials such as silicon and tin, as well as their composites. These components are typically used in particulate form. One or more components other than particles can be used in composites. Graphite particles and hard carbon are particularly preferred.

[0222] When other components are included to form the negative electrode active material, adjustments are made so that the composite particles constitute 1 to 50% by mass in the negative electrode active material. Preferably, the proportion is 2 to 25% by mass. By mixing with other carbon materials and / or conductive additives, a negative electrode active material can be produced that maintains the excellent properties of the composite particles while also possessing the excellent properties of the other carbon materials. When multiple types of materials are used as the negative electrode active material, they can be pre-mixed before use, or they can be added sequentially when preparing the slurry for forming the negative electrode mixture (described later).

[0223] Commercially available mixers and agitators can be used as devices for mixing composite particles and other materials. Specific examples include mortars, spiral ribbon mixers, V-type mixers, W-type mixers, single-blade mixers, Nauta mixers, and the like.

[0224] [5] Negative electrode mixture layer

[0225] One embodiment of the present invention relates to a negative electrode compound layer comprising the negative electrode active material described above [4]. The negative electrode compound layer of the present invention can be used as a negative electrode compound layer for lithium-ion secondary batteries. The negative electrode compound layer is generally composed of a negative electrode active material, a binder, and a conductive additive as an arbitrary component.

[0226] The manufacturing method of the negative electrode binder layer can employ known methods, such as those described below. A slurry for forming the negative electrode binder is prepared using a negative electrode active material, a binder, a conductive additive as an arbitrary component, and a solvent. The slurry is applied to a current collector such as copper foil and dried. It is then further vacuum dried to remove the solvent. The resulting object is sometimes referred to as a negative electrode sheet. The negative electrode sheet consists of a negative electrode binder layer and a current collector. After the negative electrode sheet is cut or punched into the desired shape and size, it is pressed to increase the density of the electrode binder layer (sometimes called electrode density). When the electrode density is increased, the energy density of the battery increases. The pressing method is not particularly limited as long as it can be processed to achieve the desired electrode density, but examples include uniaxial pressing, rolling, etc. In the embodiments described later, a process of pressing after shaping is illustrated, but shaping can also be performed after pressing. In this invention, the object with the desired shape and electrode density is referred to as a negative electrode. The negative electrode also includes a negative electrode in which current collector tabs are further mounted on the current collector as needed.

[0227] As a binder, any binder commonly used in the negative electrode binder layer of lithium-ion secondary batteries can be freely selected. Examples include polyethylene, polypropylene, ethylene-propylene terpolymer, butadiene rubber, styrene-butadiene rubber (SBR), butyl rubber, acrylic rubber, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyethylene oxide, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, carboxymethyl cellulose (CMC) and its salts, polyacrylic acid, and polyacrylamide. One or more binders 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.

[0228] There are no particular limitations on conductive additives, as long as they play a role in imparting electronic conductivity and dimensional stability to the electrode (to buffer the volume changes associated with lithium insertion and extraction). Examples include carbon nanotubes, carbon nanofibers, fumed carbon fibers (e.g., "VGCF-H" manufactured by Showa Denko Co., Ltd.), conductive carbon black (e.g., "Denka Black" 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., "SFG6L" manufactured by Imerys Graffito & Carbon Co., Ltd.). Multiple types of these can also be used.

[0229] The conductive additive preferably comprises carbon nanotubes, carbon nanofibers, or vapor-phase carbon fibers, wherein the fiber length of these conductive additives is preferably the D of the composite particles. V50 More than half of the fiber length. If the fiber length is within this range, these conductive additives bridge the negative electrode active material containing composite particles, thereby improving cycle characteristics. Furthermore, if single-walled and / or multi-walled carbon nanotubes with a fiber diameter of 15 nm or less are used, the number of bridges increases with the same amount of addition compared to using carbon nanotubes with a thicker fiber diameter, making them more preferable. Additionally, their greater flexibility makes them even more preferable from the viewpoint of increasing electrode density.

[0230] The amount of conductive additive used in preparing the slurry for electrode coating is preferably 1 to 30 parts by mass relative to 100 parts by mass of the negative electrode material.

[0231] There are no particular limitations on the solvents used in preparing the electrode coating paste, and examples include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), isopropanol, tetrahydrofuran (THF), and water. When using water as a solvent for the binder, a thickener is also preferred. The amount of solvent can be adjusted to achieve a viscosity that facilitates coating the current collector.

[0232] [6] Lithium-ion secondary batteries

[0233] The lithium-ion secondary battery of the present invention includes the aforementioned negative electrode compound layer. The lithium-ion secondary battery typically includes a negative electrode composed of the negative electrode compound layer and a current collector, a positive electrode composed of a positive electrode compound layer and a current collector, at least one of a non-aqueous electrolyte and a non-aqueous polymer electrolyte present therebetween, a separator, and a battery casing housing them. The lithium-ion secondary battery, as long as it includes the negative electrode compound layer, can employ other components without particular limitation, including conventionally known configurations.

[0234] The positive electrode layer typically consists of positive electrode material, conductive additives, and binders. The positive electrode in the lithium-ion secondary battery can adopt the general configuration of a typical lithium-ion secondary battery.

[0235] As a cathode material, there are no particular limitations as long as it is capable of reversible electrochemical lithium insertion and extraction, and the standard redox potentials of these reactions are sufficiently high compared to the standard redox potentials of the anode reactions. For example, LiCoO2, LiNiO2, LiMn2O4, and LiCo... 1 / 3 Mn 1 / 3 Ni 1 / 3 O2, LiCo 0.6 Mn 0.2 Ni 0.2 O2, LiCo 0.8 Mn 0.1 Ni 0.1 O2, carbon-coated LiFePO4, or mixtures thereof.

[0236] As a conductive additive, adhesive, or solvent for slurry preparation, the substances listed in the negative electrode section can be used. Aluminum foil is preferably used as a current collector.

[0237] Non-aqueous electrolytes and non-aqueous polymer electrolytes used in lithium-ion batteries can utilize substances known as electrolytes for lithium-ion secondary batteries. For example, substances obtained by dissolving lithium salts such as LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3, and CH3SO3Li in the following solvents and polymers can be used. Examples of solvents include 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; gel polymers containing polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, and polymethyl methacrylate; and polymers having ethylene oxide bonds.

[0238] Alternatively, a small amount of additives commonly used in lithium-ion battery electrolytes may be added to the non-aqueous electrolyte. Examples of such substances include vinylene carbonate (VC), biphenyl, propanesultone (PS), fluoroethylene carbonate (FEC), and ethylene sultone (ES). VC and FEC are preferred examples. The amount added is preferably 0.01 to 20% by mass relative to 100% by mass of the non-aqueous electrolyte.

[0239] As a separator, it is possible to freely choose from separators that can be used in general lithium-ion secondary batteries, including combinations thereof, such as microporous membranes made of polyethylene or polypropylene. Alternatively, separators obtained by mixing particles such as SiO2 and Al2O3 as fillers into such separators and attaching them to the surface can also be used.

[0240] As for battery casings, there are no particular restrictions as long as they can accommodate the positive electrode, negative electrode, separator, and electrolyte. In addition to the battery casings that are standardized in the industry, such as those for commercially available battery packs, 18650 cylindrical batteries, and coin-shaped batteries, battery casings in shapes encapsulated in aluminum packaging materials can be freely designed and used.

[0241] Each electrode can be encapsulated after stacking for use. Additionally, individual cells can be connected in series to be used as a battery pack or module.

[0242] The lithium-ion secondary battery involved in this invention can be used as a power source for electronic devices such as smartphones, tablets, and mobile information terminals; a power source for motors in power tools, dust collectors, electric bicycles, drones, and electric vehicles; and for storing electricity obtained through fuel cells, solar power generation, wind power generation, etc.

[0243] Example

[0244] The present invention is illustrated below with examples and comparative examples, but the present invention is not limited to these examples. The determination of material properties and the evaluation of battery characteristics are carried out as follows.

[0245] [1] Evaluation of material properties

[0246] [1-1]D V10 D V50 D V90 (Particle size distribution determination)

[0247] One spoonful of sample (using a very small spatula) and two drops of a 100-fold dilution of a nonionic surfactant (SARAYA Co., Ltd., coconut oil high-performance detergent) stock solution (32% by mass) were added to 15 mL of water and ultrasonically dispersed for 3 minutes. The dispersion was then placed in a laser diffraction particle size distribution analyzer (LMS-2000e) manufactured by Seishin Enterprises Co., Ltd., and the volumetric cumulative particle size distribution was measured to determine the 10% particle size D. V10 50% particle size D V50 90% particle size D V90 .

[0248] [1-2] BET specific surface area, pore volume (nitrogen adsorption test)

[0249] As the measuring apparatus, a NOVA (registered trademark) 4200e manufactured by Quantachrome was used. The sample was placed in the sample chamber (9mm × 135mm) so that the total surface area of ​​the sample was 2 to 60 m². 2 The sample was dried at 300℃ under vacuum for 1 hour, and then its weight was measured. Nitrogen gas was used in the measurement.

[0250] The minimum relative pressure set during measurement was 0.005, and the maximum relative pressure set was 0.995. The BET specific surface area of ​​the carbon material and composite particles was calculated using the BET multi-point method based on adsorption isotherm data from relative pressures around 0.005 to less than 0.08. The BET specific surface area of ​​the composite particles was calculated using the BET multi-point method based on adsorption isotherm data from three points around relative pressures of 0.1, 0.2, and 0.3. The total cumulative micropore volume V... 200 Based on the adsorption isotherm data at two points before and after a relative pressure of 0.99, the adsorption amount at a relative pressure of 0.99 (pore diameter of 200 nm in the BJH method) was calculated using a linear approximation. Furthermore, the cumulative pore volume calculated using the BJH method for pores with diameters greater than 3 nm and less than 200 nm was used as V. 3-200 At this point, the density of the liquid nitrogen is set to 0.808 g / cm³. 3 The volume of 1 mol of nitrogen under standard conditions was set to 22.4133 L, and the atomic weight of nitrogen was set to 14.0067.

[0251] In addition, V was calculated. 3-200 Compared to V 200 The ratio V 3-200 / V200 .

[0252] [1-3] Oxygen content

[0253] 20 mg of sample was weighed into a nickel capsule, and the oxygen content in the composite particles was calculated in mass percent using an EMGA (registered trademark)-920 oxygen and nitrogen analyzer (manufactured by Horiba Manufacturing Co., Ltd.).

[0254] [1-4] Elemental content of silicon and metals, etc. (ICP-AES analysis)

[0255] 10 mg of sample was weighed into a platinum crucible, and potassium sodium carbonate and boric acid were added. After melting using a gas burner, the sample was leached in ultrapure water by heating. After cooling, 30% (w / w) hydrogen peroxide aqueous solution, citric acid aqueous solution, and sulfuric acid were added to completely dissolve the melt. The solution was washed into a PTFE volumetric flask, and Yb, Cd, and Ga standard solutions were added to bring the volume to 250 mL. The diluted solution was quantitatively analyzed using an Agilent 5110 ICP-AES (Agilent Technology). Determinations were performed with n=2, and the average value was used.

[0256] [1-5] Identification of metal oxides (powder X-ray diffraction (powder XRD))

[0257] The sample was filled into a glass specimen plate (window length × width: 18 mm × 20 mm, depth: 0.2 mm), and the following method was used for determination.

[0258] XRD device: SmartLab manufactured by Rigaku Co., Ltd. (registered trademark)

[0259] X-ray source: Cu-Kα rays

[0260] Kβ ray removal method: Ni filter

[0261] X-ray output: 45kV, 200mA

[0262] Measurement range: 10.0°~80.0°.

[0263] Scanning speed: 10.0° / min

[0264] For the obtained XRD patterns, background removal and Kα2 component removal were performed using analytical software (PDXL2, manufactured by Rigaku Co., Ltd.). After smoothing, profile fitting was performed to identify the metal oxides and determine the peak positions, intensities, and half-widths. Furthermore, the (111) plane of Si has diffraction peaks near 2θ = 28°, and the (111) plane of SiC has diffraction peaks near 2θ = 35°.

[0265] [1-6] Image analysis using SEM

[0266] Samples were taken from the powder of well-mixed composite particles using a small spatula, loaded onto a carbon ribbon, and observed as is, while observing the individual particles. For cross-section observation, the sample was embedded in resin, ground, and cross-sectioned using a cross-sectioning tool manufactured by Nippon Electronics Co., Ltd. (registered trademark). The resulting samples were then observed. The following methods were used for observation, measurement, and analysis.

[0267] SEM: Scanning electron microscope device: Regulus (registered trademark) 8220 (manufactured by Hitachi Hitek Co., Ltd.)

[0268] Accelerating voltage: 1~3kV

[0269] Focal length: 1.5~3.0mm

[0270] Observation modes: SE+BSE(U) (surface observation), LA100(U) (section observation)

[0271] Observation magnification: 10,000 to 100,000 times (the magnification of the target object can be clearly identified).

[0272] (The average distance from the outermost position of the composite particle to the end of the metal oxide particle (L1))

[0273] like Figure 1 As shown, using the method described above, the distance between the tangent of the composite particle and the tangent parallel to it and tangent to the end of the metal oxide particle (the whiter part) existing inside the composite particle is measured, and the minimum value of this distance is taken as L. The measured value is calculated according to the scale bar reduction. The average value of 100 randomly selected fields of view of the observed metal oxide particles is taken as the average distance (L1) from the outermost surface position of the composite particle to the end of the metal oxide particle. However, if multiple metal oxide particles are observed in one field of view, the largest value is taken as L1 for that field of view. In addition, the same particle is assumed to be measured within one field of view. Moreover, if the metal oxide particle exists within a distance of 5% of the equivalent diameter of the circle from the centroid of the observed composite particle cross-section, the above distance is defined as half the diameter of the particle cross-section. Here, the "cross-sectional diameter" in the cross-sectional SEM image of the composite particle refers to the diameter of the cross-section of an individual particle obtained by observing the cross-section of the composite particle through a cross-sectional SEM, for example, the equivalent circle diameter calculated based on the cross-sectional area of ​​the particle using image analysis software such as ImageJ.

[0274] (Diameter D of metal oxide particles) S50 )

[0275] like Figure 2As shown, the obtained cross-sectional SEM image is binarized in a way that extracts only metal oxide particles as white, and the area S of each continuous individual white region within the field of view is calculated separately. The same operation is performed for any selected 100 fields of view where metal oxide particles can be observed, as shown... Figure 3 Calculate the cumulative frequency of each area as shown, and then determine the equivalent diameter of the circle at 50% of the cumulative frequency (S / π). 1 / 2 ).

[0276] The specific method is as follows: Open the acquired SEM image in Photoshop (Adobe), select "Image / Mode / Resolution," select "Set Measurement Scale / Custom" in the Measurement Log, and enter the scale value of the SEM image and the current pixel length. Next, select the area outside the banded portion of the SEM image and apply "Image / Crop." Then, select "Filter / Blur / Blur (Gaussian)," and set the radius (R) to 1.0 pixel. Next, select "Image / Tone Correction / Digrayscale," and adjust the threshold so that only metal oxides are extracted as white. When using the SEM's automatic contrast for shooting, use approximately 170 as the standard. Next, select the "Auto Selection Tool," set the tolerance to 1, and disable anti-aliasing and adjacent checks. In this state, click on a white area, and all consecutive individual areas will be automatically selected. In this state, select "Record Measurement Value" in the Measurement Log, calculate the area of ​​all white areas within the field of view, and output the results.

[0277] However, the diameter can also be calculated using other software based on the binarization of the SEM image, or it can be obtained from compositional analysis images, etc.

[0278] (Average diameter of the hole D) A,S )

[0279] like Figure 5 As shown, only the holes are extracted in black. Figure 4 The SEM image of the composite particle surface shown is binarized, and the area S of each individual black, continuous region within the field of view is calculated. The same operation is performed for any 100 selected fields of view from which the metal oxide particles can be observed, such as... Figure 3 Calculate the cumulative frequency of each area as shown, and then determine the equivalent diameter of the circle at 50% of the cumulative frequency (S / π). 1 / 2The specific method is the same as the method for calculating the diameter of metal oxides, but the binarization threshold is set to around 90 when using the automatic contrast function of SEM for imaging. The average diameter of the metal oxide particles and the average diameter of the pores are similar, but they are not entirely consistent because the average diameter of the metal oxide particles is calculated from cross-sectional SEM images. Furthermore, pores are sometimes connected or become smaller during silicon precipitation, so the average diameter is not always consistent with the average diameter of the pores observed from the SEM images. Also, because the pore diameter obtained by the BJH method in the nitrogen adsorption isotherm is smaller than the actual pore diameter, the average pore diameter observed from the SEM images may not be consistent with the pore diameter obtained from the nitrogen adsorption isotherm.

[0280] (Average ratio of the area of ​​holes on the surface)

[0281] The average area ratio of the holes on the surface is calculated by taking the ratio of the area of ​​the black region to the area of ​​the observation region from the binarized image of the SEM taken when determining the diameter of the holes. The magnification is adjusted so that only particles are in the field of view, and the same operation is performed for arbitrarily selected 100 fields of view to calculate the average value.

[0282] (The average depth (L2) of pores with a diameter of 10 nm or more, measured from the outermost surface position)

[0283] Similar to determining the distance from the outermost surface of the composite particle to the tip of the metal oxide particle, the minimum value L is determined by measuring the distance between the tangent of the composite particle and a line parallel to it and tangent to the tip (point) of a hole with a diameter of 10 nm or more. The measured value is calculated using a scaled-down approach. The average value of 100 fields of view, arbitrarily selected, is used, allowing observation of fine holes with a diameter of 10 nm or more. However, if multiple holes with a diameter of 10 nm or more are observed in a single field of view, the largest value is used as the representative value for that field of view. Furthermore, the same particle is assumed to be measured in a single field of view. Here, the aperture is the largest value among the opening sizes of consecutive holes. Additionally, if a metal oxide particle is present at the deepest part of the hole, the depth is defined as the distance from the outermost surface of the composite particle to the tip of the metal oxide particle. The depth and the distance from the outermost surface of the particle to the end of the metal oxide particle are, in principle, approximately equal. When the average distance from the outermost surface of the particle to the end of the metal oxide particle is denoted as (L1), and the average distance from the outermost surface of the particle to the deepest part of the pore with a diameter of 10 nm or more is denoted as (L2), (L1) / (L2) takes a value close to 1. However, in cases where the carbon material inherently contains voids, (L1) / (L2) becomes smaller. Furthermore, the smaller this value, the more pores with a diameter of 10 nm or more exist beyond the effect of the metal oxide particles (i.e., where no metal oxide exists at the deepest part of the pore), leading to a decrease in cycling characteristics.

[0284] [1-7] Raman I Si / I G R value (I) D / I G )

[0285] The determination was performed under the following conditions.

[0286] Micro Raman Spectroscopy Apparatus: Horiba Corporation LabRAM (registered trademark) HR Evolution

[0287] Excitation wavelength: 532nm

[0288] Exposure time: 10 seconds

[0289] Total number of times: 2

[0290] Diffraction grating: 300 lines / mm (600nm)

[0291] Sample testing: Use a spatula to place the composite particles on a glass slide to homogenize the powder. This will allow for a wider testing range than described below.

[0292] Measurement range: 80μm long × 100μm wide, the measurement range is filled only with composite particles.

[0293] Point count: 100 points were measured at a longitudinal feed of 17.8 μm and a transverse feed of 22.2 μm. The averaged spectra were obtained and analyzed as follows.

[0294] Observe the 450–495 cm⁻¹ in the Raman spectrum -1 The peak. The intensity of this peak is denoted as I. Si Compare it with 1580cm -1 Nearby peak intensity (I) G The ratio of ) is denoted as (I) Si / I G ). 1350 cm⁻¹ in the Raman spectrum -1 Nearby peak intensity (I) D ) and 1580cm -1 Nearby peak intensity (I) G The ratio of ) to R value (I) D / I G The intensity will be calculated from the height of the baseline to the peak.

[0295] [1-8] X-ray photoelectron spectroscopy (XPS)

[0296] Using a small spatula, place the sample on the adhesive surface of the double-sided tape attached to the Si substrate, spreading it evenly so that the double-sided tape on the substrate is not exposed. Gently press with the spatula to flatten the measurement surface to some extent. Spread the sample over a wider area than the measurement area (approximately 100 μm Φ). This is to ensure that only composite particles are distributed within the measurement area. The sample is then measured using the following method.

[0297] [Measuring Apparatus]

[0298] Device: PHIQuanteraII (manufactured by Alibaba Co., Ltd.)

[0299] X-ray source: Al monochromatic (25W, 15kV)

[0300] Analysis range: Φ100μm

[0301] Electron / ion neutralization gun: ON

[0302] Photoelectronic detection angle: 45 degrees

[0303] Narrow scan

[0304] Pass Energy: 55 eV; Step: 0.2 eV; Dwell Time: 20 ms

[0305] Sweep count: O (25 sweeps); C, Si (50 sweeps)

[0306] [Analysis Method]

[0307] [Energy Correction]

[0308] The narrow spectrum was corrected so that the 1s peak of carbon was 284.6 eV.

[0309] [C, O, Si atomic ratio A] C A O A Si ]

[0310] Calculate the area ratio of the narrow spectrum of C, O, and Si as the atomic number ratio. The atomic number ratio A of C, O, and Si. C A O A Si The total is set to 1.00.

[0311] [Si state ratio B] SiO2 B SiO B Si ]

[0312] For the 2p narrow spectrum of Si, the following method is used for peak fitting to calculate the state ratio B of Si. SiO2 B SiO B Si .

[0313] (Chemical shift) Si 0 valence = 99 eV, Si 2 valence = 101 eV, Si 4 valence = 103 eV

[0314] (Peak Fitting Method) The analytical software automatically adjusts the half-value width and peak apex to minimize the residual between the peak fitting result and the measurement result. Furthermore, regarding the peak apex adjustment, the width of all three components is adjusted in increments of ±0.5 eV. The analytical software used is the software provided with the aforementioned measurement device.

[0315] Background subtraction method: Shirley method

[0316] • Function: Gauss-Lorentz

[0317] Si 0% valence means so-called elemental Si. Si 2% valence means SiO. Si 4% valence means SiO2. Si 1% and 3% valences have low intensity, thus reducing the accuracy of peak fitting, and are therefore excluded. Although Si 2% valence generally includes silicon carbide, when observing the peak shape of the narrow C1s spectrum, no perturbation (shoulders, tails, etc.) of the peak shape involved in the 282.5–283.0 eV chemical shift originating from silicon carbide is observed, therefore the presence of silicon carbide is considered to be below the detection limit. Therefore, the Si 2% valence peak is considered to represent only SiO.

[0318] [1-9] Hydrophobicity

[0319] Immerse a 20 mL glass sample vial (bottle diameter × height: Φ28 mm × 61 mm) in room temperature pure water until it reaches a depth of approximately 1 cm. Measure 0.05 g of the complex particles on a piece of packaging paper and slowly add the particles into the sample vial. The addition height of the complex particles should be 0.5–3.0 cm from the water surface. After addition, allow the sample vial to stand and observe the penetration behavior of the complex particles into the water. Visually confirm the behavior; complex particles that do not reach the bottom of the vial even after 5 minutes of standing are considered hydrophobic. Complex particles that reach the bottom of the vial within 5 minutes under the same conditions are considered hydrophilic.

[0320] [2] Evaluation of capacity and initial coulombic efficiency

[0321] [2-1] Fabrication of the negative electrode

[0322] Styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) are used as adhesives.

[0323] Specifically, an SBR aqueous dispersion containing 40% by mass of SBR solids and a CMC aqueous solution containing 2% by mass of CMC powder were obtained.

[0324] As a mixed conductive additive, a substance was prepared by mixing carbon black (SUPER C 45 (registered trademark), manufactured by Imelis Graffiti & Carbon Co., Ltd.) and single-walled carbon nanotubes (WPB-030, manufactured by OCSiAl Co., Ltd.) in a mass ratio of 5:1.

[0325] A CMC aqueous solution and an SBR aqueous dispersion were mixed to form 96.4 parts by mass of composite particles, 0.6 parts by mass of a mixed conductive additive, and 1.5 parts by mass of CMC solid components, so that the SBR solid component was 1.5 parts by mass. An appropriate amount of water was added to adjust the viscosity, and the mixture was kneaded using a rotation-revolution mixer (Sinkee Co., Ltd.) to obtain a slurry for forming the negative electrode composite layer. The slurry concentration was 45–55% by mass.

[0326] The slurry for forming the negative electrode mixture layer was uniformly coated onto a 20 μm thick copper foil (serving as the current collector foil) using a doctor blade with a gap of 75 μm. After drying on a hot plate, it was vacuum dried at 70°C for 12 hours, thereby forming the negative electrode mixture layer on the current collector foil. This is referred to as a negative electrode sheet (a sheet composed of the negative electrode mixture layer and the current collector foil). The mass per unit area is approximately 3 mg / cm³. 2 .

[0327] The negative electrode sheet is punched into a 16mmΦ shape and then pressed using a uniaxial press to adjust the density of the negative electrode binder layer to 1.2g / cm³. 3 , thus obtaining the negative electrode.

[0328] The electrode density (negative electrode density) of the negative electrode is calculated as follows. The mass and thickness of the negative electrode obtained using the above method are measured, and the mass and thickness of the current collector foil with a pre-measured punch size of 16 mmΦ are subtracted from these to determine the mass and thickness of the negative electrode binder layer. The electrode density (negative electrode density) is then calculated based on these values.

[0329] [2-2] Making a coin cell (lithium counter battery)

[0330] Within a polypropylene insulating gasket (approximately 18 mm inner diameter), the aforementioned negative electrode and a 1.7 mm thick lithium metal foil (cut to 17.5 mm Φ) are stacked, sandwiching a separator (polypropylene microporous membrane) impregnated with electrolyte. At this point, the negative electrode's anode layer is positioned so that it faces the lithium metal foil through the separator. This is then placed in a 2320 coin-shaped chamber and sealed using a caulking machine to serve as a test battery (lithium-ion counter electrode battery).

[0331] The electrolyte in the lithium counter electrode battery uses a liquid obtained by dissolving 1 part by mass of vinylene carbonate (VC) in 100 parts by mass of a solvent, thereby dissolving the electrolyte lithium hexafluorophosphate (LiPF6) in the solvent at a concentration of 1.2 mol / L. The solvent is obtained by mixing ethylene carbonate, ethyl methyl carbonate and diethyl carbonate in a volume ratio of 3:5:2.

[0332] [2-3] Initial charge specific capacity, initial discharge specific capacity

[0333] The experiment was conducted using a lithium-ion battery. Constant current (CC) charging was performed from OCV (Open Circuit Voltage) at a current equivalent to 0.01C until 0.005V was reached. At the 0.005V mark, constant voltage (CV) charging was switched to. The cutoff condition was set at the point where the current decayed to the equivalent of 0.005C. The specific capacity at this point was taken as the initial charge specific capacity. Next, with the upper voltage set at 1.5V, constant current discharging was performed at a current equivalent to 0.01C. The specific capacity at this point was taken as the initial discharge specific capacity.

[0334] The experiment was conducted in a constant temperature bath set at 25°C. At this temperature, the specific capacity was obtained by dividing the capacity by the mass of the negative electrode active material. Furthermore, in this experiment, the "current equivalent to 1C" refers to the current required to discharge the negative electrode in one hour, based on the mass of Si and amorphous carbon in the negative electrode active material, and the theoretical specific capacities (4200 mAh / g and 200 mAh / g, respectively).

[0335] [2-4] Si conversion of initial discharge specific capacity

[0336] When the total percentage (wt%) of oxygen, silicon, and metal elements contained in the composite particles is denoted as W, O W Si W a When Si is converted to the initial discharge specific capacity, it is calculated using the following formula (2).

[0337] Si conversion of initial discharge specific capacity = 100 × {initial discharge specific capacity - (100 - W)} o -W Si -W a )×2} / W Si (2)

[0338] (100-W o -W Si -W a The specific capacity is the carbon content in the composite particles. The discharge specific capacity of this carbon is set to 200 mAh / g. The specific capacity obtained by subtracting it from the initial discharge specific capacity of the composite particles is divided by the silicon content.

[0339] [2-5] Initial Coulomb efficiency

[0340] The value obtained by dividing the initial discharge specific capacity by the initial charge specific capacity, expressed as a percentage, i.e., (initial discharge specific capacity) / (initial charge specific capacity) × 100, is taken as the initial coulombic efficiency (%).

[0341] [3] Capacity retention rate after 100 cycles, capacity retention rate at 1C rate discharge

[0342] [3-1] Battery Making

[0343] [3-1-1] Negative electrode fabrication

[0344] The sheet consisting of the negative electrode mixture layer and the current collector foil obtained in [2-1] was adjusted using a roller press to achieve a negative electrode mixture layer density of 1.2–1.3 g / cm³. 3 This ensures that the area of ​​the coating layer is 21.84 cm². 2 (4.2cm × 5.2cm), the uncoated portion of the mixture layer (=the tab area) is 1.5cm. 2 The negative electrode is obtained by punching in the manner of (1.0cm×1.5cm).

[0345] [3-1-2] Positive electrode production

[0346] Add 95g of LiNi 3 / 5 Mn 1 / 5 Co 1 / 5 O2(D V50 A slurry-like dispersion was prepared by mixing 11 μm of carbon black (manufactured by Imelice Graffit & Carbon Co., Ltd., SUPER-C65) as a conductive additive, 3 g of polyvinylidene fluoride (PVdF) as a binder, and an appropriate amount of N-methylpyrrolidone.

[0347] The dispersion was applied to a 20 μm thick aluminum foil using a roller coater to achieve a uniform thickness. After drying, it was rolled to ensure that the coated area of ​​the mixture layer was 20.00 cm². 2 (4.0cm × 5.0cm), the uncoated portion of the mixture layer (=the tab portion) is 1.5cm. 2 The positive electrode is obtained by punching in the manner of (1.0cm×1.5cm).

[0348] [3-1-3] Construction of a Diode Battery

[0349] For the negative and positive electrodes, Al tabs are installed on Al foil and Ni tabs are installed on Cu foil, respectively. They are stacked facing each other with a polypropylene thin film microporous membrane in between, and encapsulated using an aluminum lamination. After injecting the electrolyte described in [2-2], the openings are sealed by thermal fusion, thereby producing a battery.

[0350] [3-2] Determination of reference capacity

[0351] In a constant temperature bath at 25°C, the battery was set to an upper limit voltage of 4.2V and a cutoff current of 2.5mA, and charged at 0.1C using CC and CV modes, and discharged at 0.1C using CC mode with a lower limit voltage of 2.7V. This operation was repeated a total of 4 times, and the discharge capacity of the 4th discharge was taken as the reference capacity (a) of the diode battery.

[0352] [3-3] Capacity maintenance rate after 100 cycles

[0353] The experiment was conducted using a diode battery whose baseline capacity was determined in [3-2]. Regarding charging, the upper voltage was set to 4.2V, and after CC mode charging at 0.2C from OCV, charging was performed in CV mode with a cutoff value set to 0.05C.

[0354] Regarding discharge, set the lower limit voltage to 2.8V and perform a 0.2C discharge in CC mode.

[0355] This charge-discharge operation is considered as one cycle. The charge-discharge cycle is repeated 100 times in a constant temperature bath at 25°C. The discharge capacity of the 500th cycle is taken as the cycle discharge capacity (b). The value of the cycle discharge capacity (b) / the reference capacity (a) of the diode measured under the above conditions, expressed as a percentage, i.e., 100 × (b) / (a), is taken as the cycle capacity retention rate.

[0356] [3-4] Capacity maintenance rate at 1C rate

[0357] The experiment was conducted using a diode battery whose baseline capacity was determined in [3-2]. Regarding charging, the upper voltage was set to 4.2V, and after CC mode charging at 0.2C from OCV, charging was performed in CV mode with a cutoff value set to 0.05C.

[0358] Regarding discharge, the lower limit voltage is set to 2.8V, and a 1.0C discharge is performed in CC mode. The discharge capacity at this time is taken as the 1C rate discharge capacity (c).

[0359] The 1C rate discharge capacity (c) / the reference capacity (a) of the diode battery, measured under the above conditions, is expressed as a percentage, i.e., 100 × (c) / (a), and is taken as the 1C rate discharge capacity maintenance rate.

[0360] [Examples 1-24, Comparative Examples 1-6]

[0361] The composite particles were manufactured using the manufacturing methods described in the above [3] manufacturing method of composite particles, including steps (1), (2), and (3).

[0362] The BET specific surface area and particle size distribution (D) of spherical phenolic resin carbides or graphite used as raw material carbon were compared. v10 D v50 D v90 The coating conditions for the metal oxide precursor are shown in Table 1, the activation conditions and the properties after activation are shown in Tables 2-1 to 2-3 (hereinafter collectively referred to as "Table 2"), the silicon precipitation conditions and the properties of the composite particles are shown in Tables 3-1 to 3-3 (hereinafter collectively referred to as "Table 3"), and the battery evaluation results are shown in Table 4.

[0363] A solution containing a metal oxide precursor is added to a rolling flow coating device (MP-01_mini, manufactured by Parrec Co., Ltd.), and dry mixing is performed until the solution is completely sprayed.

[0364] (Operating conditions of the rolling flow coating device)

[0365] Rotor: Standard

[0366] • Filter: FPM

[0367] • Network: 800M

[0368] Nozzle type: NPX-II

[0369] • Nozzle diameter: 1.2mm

[0370] • Nozzle position: Tangential

[0371] • Number of nozzles: 1

[0372] Rotor rotation speed: 400 rpm

[0373] • Spray pressure: 0.17 (MPa)

[0374] • Cleaning pressure: 0.2 (MPa)

[0375] • Filter cleaning time / interval: 4.0 / 0.3 (s / s)

[0376] • Air supply volume: 0.2m³ 3 / min

[0377] • Gas supply temperature: recorded in Table 1

[0378] Atmosphere: N2

[0379] • Spray rate: 2.0 g / min

[0380] Activation conditions

[0381] Temperature rise:

[0382] Atmosphere: N2

[0383] Speed: 150℃ / hour

[0384] activation:

[0385] Atmosphere: CO2

[0386] • Temperature: Recorded in Table 2

[0387] • Holding time: recorded in Table 2. Cooling:

[0388] Atmosphere: N2

[0389] Speed: 150℃ / hour

[0390] Silicon precipitation conditions

[0391] Pre-drying:

[0392] Atmosphere: Vacuum

[0393] Temperature: 110℃

[0394] • Duration: 3 hours

[0395] Temperature rise:

[0396] Atmosphere: Ar

[0397] Speed: 150℃ / hour

[0398] Silicon precipitation conditions

[0399] • Atmosphere: SiH4 (100% concentration) • Temperature: 400℃

[0400] • Pressure: 760 torrents

[0401] • Processing time: Recorded in Table 3. Cooling:

[0402] Atmosphere: Ar

[0403] Speed: 150℃ / hour

[0404] Surface oxidation

[0405] • Atmosphere: Ar / O2 (95 / 5 vol%) • Temperature: 30℃

[0406] • Time: 1 hour

[0407]

[0408]

[0409]

[0410]

[0411]

[0412]

[0413]

[0414] Table 4

[0415]

[0416] The evaluation results for the batteries were determined as follows: the cycle characteristics of the diode battery were above 70%, and the rate characteristic was above 70%, while the coin cell battery exhibited good characteristics. Furthermore, since this was based on the use of high-capacity silicon as the negative electrode active material, an initial discharge specific capacity of 3000 mAh / g or higher (Si equivalent) was also used as a criterion for judging good characteristics.

[0417] Comparative Example 1 was not coated with a metal oxide precursor, but the test was conducted under the same conditions as in Example 1. However, in contrast, in Example 1, it was confirmed that the rate performance and cycling performance were improved.

[0418] Comparative Example 2 was performed in the same manner as Example 13 until activation, followed by removal of Y₂O₃ with a 1.0 mol / L aqueous nitric acid solution for silicon precipitation. Although pore formation based on the effect of metal oxide particles was achieved, the cycling characteristics were significantly reduced. This is presumably because the current concentrates at the deepest part of the pore, accelerating degradation from there. Therefore, it is believed that the presence of metal oxide particles at the ends of the pores can prevent current concentration and result in improved rate performance due to the increased reaction area with lithium.

[0419] Comparative Example 4 uses the raw material carbon obtained in Example 5 based on Japanese Patent Application Publication No. 2014-122158. In Comparative Example 4, magnesium acetate tetrahydrate (manufactured by Kishida Chemical Co., Ltd.), hydroxypropyl cellulose (HPC) powder, and water were mixed in a mass ratio of 5:5:1. The resulting mixed powder was dried and placed in an alumina sintering vessel. The mixture was heated to 900°C in an electric furnace under an argon atmosphere and held for 1 hour. Then, it was cooled to room temperature, and 100 times the volume of a 1 mol / L sulfuric acid aqueous solution was added to the powder. After stirring at room temperature, the mixture was filtered and washed with water to prepare the raw material carbon, which was then activated and silicon precipitated. Although pores larger than 10 nm were identified, it was also found that the metal oxide particles did not reach the particle interior, and many pores without metal oxides were present at the deepest part. As with Comparative Example 2, the cycling characteristics were significantly reduced.

[0420] Examples 2, 3, 4, 5, and 6 differed from Example 1 in the particle size of the raw carbon and consequently the composite particles, but still exhibited good cycle and rate performance. When comparing only these examples, as the particle size of the raw carbon increased, the expansion and contraction associated with the charging and discharging of the composite particles increased, thus reducing both cycle and rate performance. If D V50 Exceeding 20.0 μm or D V90 The tendency becomes significant when the particle size exceeds 30.0 μm. Conversely, if the particle size decreases, there is a tendency for improved rate performance and cycle characteristics, but with the increase of specific surface area, side reactions increase. Therefore, when D... V50 When the diameter is less than 1.0 μm, the cycling performance is significantly reduced.

[0421] Examples 7, 8, 12-23, and Comparative Example 3 used the same raw carbon as in Example 1, but differed in the type of metal oxide precursor, the amount of coating on the raw carbon, and the activation conditions. In Comparative Example 3, the metal oxide particles were amorphous, but no pores were formed, resulting in deteriorated rate performance. In Examples 1-25, both rate performance and cycling performance were excellent, but the degree of pore formation derived from the oxide varied depending on the type of oxide. To obtain the target structure, the activation conditions needed to be adjusted. In all examples, (L1) / (L2) was greater than 0.5, and the average diameter of the metal oxide particles and the average diameter of the pores were similar. Therefore, it was concluded that the pores larger than 10 nm inside the composite particles were generated by the action of the metal oxide particles. It was speculated that metal oxide particles existed at the deepest part of these pores.

[0422] If the orifice depth is greater, the rate capability improves, but at the same time, side reactions increase and the circulation performance decreases. In particular, if the orifice depth exceeds 1000 μm, the circulation performance decreases significantly.

[0423] Larger pore diameters result in more voids unrelated to lithium reactions, thus reducing the rate performance improvement. This tendency is particularly pronounced above 200 nm. Conversely, smaller pore diameters lead to greater rate performance improvement, but the effect diminishes below 10 nm. Conversely, the decrease in cycle performance due to increased side reactions associated with increased specific surface area becomes significant.

[0424] The larger the proportion of the orifice opening area, the greater the improvement in rate performance. However, if it exceeds 65%, the decrease in cycle performance due to the increased side reactions accompanying the increase in specific surface area becomes greater. Below 5%, the high resistivity caused by the presence of metal oxide particles becomes more significant than the improvement in rate performance, and the rate performance actually decreases.

[0425] The larger the specific surface area and the cumulative pore volume V200 (based on the BJH method) for pore diameters below 200 nm, the greater the improvement in rate capability. However, if these values ​​exceed 20 nm, the improvement is more significant. 2 / g, 0.15cm 3 / g, then the decrease in cycle characteristics caused by the increase in side reactions accompanying the increase in specific surface area becomes greater. Conversely, when it is 2m 2 / g, 0.004cm 3 At / g, compared to the improvement in rate performance, the high resistivity caused by the presence of metal oxide particles becomes significant, and the rate performance actually decreases.

[0426] If the cumulative pore volume V for diameters greater than 3nm and less than 200nm is calculated based on the BJH method... 3-200 and V 3-200Relative to the V 200 The ratios were 0.003cm. 3 When the content is above 75% per gram, the improvement in rate capability becomes significant.

[0427] When the combined elemental content of Al, Ti, V, Y, Zr, Nb, Mo, W, La, Hf, Ta, and Ce exceeds 8.00% by mass, the energy density and initial efficiency decrease. When it is less than 0.08% by mass, no improvement in rate performance or cycling performance is observed. When the combined elemental content of Li, Na, K, Mg, Ca, Ba, B, N, P, S, F, and Cl exceeds 5.00% by mass, relatively large pores tend to form in fine pore diameters less than 3 nm determined using the BJH method, leading to a tendency for reduced cycling performance. These elements can be used to adjust all characteristics related to pore formation, such as pore formation rate, pore diameter, depth, their distribution, and pore uniformity. They can be included or excluded, and can form compounds with Al, Ti, V, Y, Zr, Nb, W, La, Hf, Ta, and Ce, or can be their respective oxides.

[0428] When the crystallite size based on powder XRD is greater than 5 nm, pores are easily formed; if it is less than 5 nm or amorphous, pores are difficult to form. Furthermore, the reduced conductivity of lithium ions results in high resistance and decreased rate capability. When the crystallite size based on powder XRD is greater than 200 nm, there is an average diameter D of the metal oxide particles obtained by cross-sectional SEM. S50 A tendency to exceed 200nm.

[0429] Furthermore, Figures 1-5 This is the result of Example 20.

[0430] Examples 9, 10, and Comparative Example 5 illustrate that the crystallinity of the raw carbon differs from that of Example 1. The raw carbon in Example 9 exhibits higher amorphousness compared to that in Example 1, while the raw carbon in Example 10 shows slightly lower amorphousness. The degree of amorphousness can be determined based on the half-width at half-maximum (WHM) of the XRD pattern. High amorphousness improves rate performance but increases the likelihood of side reactions and reduces cycle performance. Low amorphousness exhibits the opposite tendency. Therefore, an R value of 1.00 or higher and 1.30 or lower is preferred. When graphite is used as the raw carbon, no fine pores are formed, and almost no silicon is precipitated. Therefore, although the rate performance and cycle performance are good, the initial charge specific capacity and initial discharge specific capacity of the composite particles are significantly inferior compared to other materials.

[0431] Example 11 differs from Example 1 in activation conditions and silicon precipitation conditions, but both rate performance and cycling characteristics remain good. Activation increases the cumulative pore volume (less than 3 nm in diameter), as determined by the BJH method, and improves silicon content, thereby suppressing the decline in cycling characteristics. However, extending the silicon precipitation time without changing the cumulative pore volume results in silicon precipitation on the surface of the carbon feedstock. Furthermore, pores formed by the action of metal oxide particles are filled with silicon, leading to a significant decrease in cycling characteristics. Conversely, shortening the silicon precipitation time leaves many pores with diameters less than 3 nm, increasing side reactions and causing a further decrease in cycling characteristics.

[0432] In Example 24, after silicon precipitation, the silicon was treated with acetylene / Ar (20 / 80 vol%) gas at 400°C and 760 Torr for 1.3 hours. Otherwise, the test was conducted under the same conditions as in Example 1, but with an improved initial coulombic efficiency. This suggests that a thin coating on the surface can prevent irreversible capacity increases compared to deactivation (inactivation) through surface oxidation. The composite at this time showed an A calculated by XPS. Si A is 0.45. C / (A C +A Si ×(B SiO2 +B SiO The value of )) is 0.94, and the true density is 1.97 g / cm³. 3 In addition, the resulting composite exhibits hydrophobicity.

[0433] Comparative Example 6 uses the composite material prepared in Comparative Example 1 as the core material, and after coating as described in Table 1, it is fired at 950°C for 6.5 hours in a nitrogen atmosphere. Cycling characteristics and rate performance are significantly reduced. This is due to the formation of SiC.

[0434] Explanation of reference numerals in the attached figures

[0435] 1: Composite particles

[0436] 2a, 2b, 2c, 2d, 2e: Holes

[0437] 3a, 3b, 3c, 3d: Metal oxide particles

[0438] TL1, TL2: Tangents

[0439] L: Distance

Claims

1. A composite particle comprising carbon and silicon. The composite particles contain metal oxide particles. The ends of the metal oxide particles are located inside the surface of the composite particles, and pores exist on the surface of the composite particles, with crystalline metal oxide particles at the deepest part of the pores. The composite particles have silicon precipitated in pores with a diameter of less than 3 nm. When the average distance from the outermost surface of the composite particle to the end of the metal oxide particle is denoted as (L1), and the average depth of the holes with a diameter of 10 nm or more in the hole, measured from the outermost surface, is denoted as (L2), (L1) / (L2) is 0.5 or more.

2. The composite particles according to claim 1, wherein the metal oxide particles exhibit crystallinity.

3. The composite particle according to claim 1, wherein the average distance (L1) from the outermost surface position of the composite particle to the end of the metal oxide particle is 10 to 1000 nm.

4. The composite particles according to claim 1, wherein the average diameter D of the metal oxide particles is... S50 The wavelength range is 10–200 nm.

5. The composite particles according to claim 1, wherein the crystallite size of the metal oxide particles, determined by powder X-ray diffraction (powder XRD), is 5–200 nm.

6. The composite particles according to claim 1, wherein the metal oxide particles comprise at least one selected from Al, Ti, V, Y, Zr, Nb, Mo, W, La, Hf, Ta, Ce, and comprise one selected from Li, Na, K, Mg, Ca, Ba, B, N, P, S, F, Cl as an arbitrary component, and exist in the form of a compound or in the form of their respective oxides.

7. The composite particles according to claim 6, wherein the total content of Al, Ti, V, Y, Zr, Nb, Mo, W, La, Hf, Ta, and Ce as elements is 0.006 to 8.00% by mass, and the total content of Li, Na, K, Mg, Ca, Ba, B, N, P, S, F, and Cl as elements is greater than 0.00% by mass and less than 5.00% by mass.

8. The composite particle according to claim 1, wherein the average area D of the diameter of the opening of the pores formed on the surface of the composite particle is... A,S The wavelength range is 10–200 nm.

9. The composite particle according to claim 1, wherein the average ratio of the area of ​​the opening of the pores formed on the surface of the composite particle to the area of ​​the outermost surface is 5 to 65%.

10. The composite particle according to claim 1, wherein the average depth (L2) of the pores with a diameter of 10 nm or more in the pores is 10 to 1000 nm from the outermost surface position.

11. The composite particles according to claim 1, wherein the cumulative pore volume V for pores with a diameter of less than 200 nm, calculated using the BJH method. 200 The value is 0.003–0.15 cm. 3 / g.

12. The composite particles according to claim 1, wherein the cumulative pore volume V for pores with a diameter of 3 nm or more and less than 200 nm, calculated using the BJH method. 3-200 It is 0.003cm 3 / g or more.

13. The composite particles according to claim 1, wherein the cumulative pore volume V for pores with a diameter of 3 nm or more and less than 200 nm, calculated using the BJH method. 3-200 Compared to the cumulative pore volume V calculated using the BJH method for pores with a diameter of less than 200 nm, 200 The ratio is over 55%.

14. The composite particles according to claim 1, wherein 50% of the particle size D in the cumulative particle size distribution based on volume is... V50 The particle size is greater than 1.0 μm and less than 20.0 μm, and 90% of the particle size D in this cumulative particle size distribution is... V90 It is below 30.0μm.

15. The composite particle according to claim 1, having a BET specific surface area of ​​2.0 m². 2 / g or more and 20.0m 2 / g or less.

16. The composite particle according to claim 1, wherein the Raman spectrum of the composite particle is in the range of 450–495 cm⁻¹ -1 A peak exists within the range of [a certain value], and the intensity of this peak is denoted as I. Si The strength of the G-band is 1600cm. -1 The peak intensity near the target is denoted as I. G The strength of the D-band is 1360cm. -1 The peak intensity near the target is denoted as I. D hour, I Si / I G Values ​​between 0.10 and 1.30 R value is I D / I G It is between 1.00 and 1.

30.

17. The composite particle according to claim 1, wherein in the X-ray diffraction pattern of the composite particle using Cu-Kα rays, the half-width of the peak of the (111) plane of Si is 3.0 degrees or more.

18. The composite particles according to claim 1, wherein the oxygen content is 0.3 to 10% by mass.

19. The composite particles according to claim 1 do not contain SiC.

20. The composite particles according to claim 1, wherein the Si content is 20-85% by mass.

21. The composite particle according to claim 1, wherein the carbon is amorphous.

22. The composite particle according to claim 1, wherein the atomic ratios of Si, O, and C obtained by narrow-spectrum X-ray photoelectron spectroscopy of Si, O, and C are respectively denoted as A. Si A O and A C The ratios of SiO2 and SiO among the Si ratios obtained through Si2p spectral state analysis are denoted as B. SiO2 B SiO At that time, A Si It is above 0.05, and A C / (A C +A Si ×(B SiO2 +B SiO The true density, determined by dry density measurement of helium gas, is 1.80 g / cm³, and is above 0.

55. 3 Above and 2.30 g / cm 3 the following.

23. A method for manufacturing composite particles, comprising the following steps (1), (2) and (3). Step (1) is a process of coating raw carbon or a resin that can be transformed into raw carbon by heating in an inactive atmosphere in step (2) described later with metal oxides or metal oxide precursors, wherein the raw carbon has fine pores of less than 3 nanometers. Step (2) involves heating the material coated with metal oxide or metal oxide precursor obtained in step (1) in an inactive atmosphere and then activating it to obtain a carbon material having pores formed by the action of metal oxide and fine pores formed by activation. Step (3) is to apply Si-containing gas to the heated carbon material to precipitate Si-containing compounds on the surface and in the pores of the carbon material, thereby obtaining composite particles containing porous carbon and silicon. The Si-containing gas contains silane. In step (3), the processing temperature is 340~450°C and the pressure is below 1500 Torr.

24. A negative electrode active material comprising the composite particles described in any one of claims 1 to 22.

25. A negative electrode mixture layer comprising the negative electrode active material as described in claim 24.

26. A lithium-ion secondary battery comprising the negative electrode binder layer as described in claim 25.

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