Composite particles, method for their manufacture and use thereof

Abstract

The objective of this invention is to provide carbon-coated Si-C composite particles that can simultaneously maintain high Si utilization in lithium-ion secondary batteries and suppress initial coulombic efficiency degradation caused by oxidation over time. The carbon-coated Si-C composite particles of this invention have a carbonaceous layer on the surface of the Si-C composite particles containing carbon materials and silicon, with a carbon coating rate of over 70% and a BET specific surface area of ​​200 m². 2 Below / g, in the Raman spectrum of the carbon-coated Si-C composite particles, the R value (I D / I G The Si-induced peak is located between 0.30 and 1.10, and the Si-induced peak is present in the range of 450–495 cm⁻¹. ‑1 The intensity of this peak is expressed as I. Si At that time, I Si / I G The carbon-coated Si-C composite particles, in the XRD spectrum measured using Cu-Kα powder XRD, have a full width at half maximum (FWHM) of 3.00 degrees or more on the Si111 surface, and the ratio of (peak intensity of SiC111 surface) to (peak intensity of Si111 surface) is less than 0.01.

Description

Technical Field

[0001] This invention relates to composite particles, their manufacturing methods, and their uses. Background Technology

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

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

[0004] As a high-capacity and long-life anode material, for example, Patent Document 1 discloses a silicon-carbon composite material (Si-C composite material), which is obtained by generating silicon within the pores of porous carbon through contacting porous carbon particles with silane gas at high temperature. Patent Document 1 also discloses a material obtained by further coating the Si-C composite material with a carbonaceous layer using chemical vapor deposition (CVD).

[0005] Existing technical documents

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

[0007] According to the inventors' research, when the Si-C composite material disclosed in Patent Document 1, which is coated with a carbon layer, is used as a negative electrode active material, the carbon coating rate of the Si-C composite material is low when the carbon layer is coated with the Si-C composite material at low temperature, which cannot suppress the exposure of Si on the surface. The Si-C composite material oxidizes over time, resulting in a decrease in initial efficiency. In addition, when the Si-C composite material is coated with a carbon layer at high temperature, silicon carbide (Si-C) is generated on the high-temperature side, which reduces the Si utilization rate of the lithium-ion secondary battery.

[0008] The objective of this invention is to provide a carbon-coated Si-C composite particle that can achieve both high Si utilization in lithium-ion secondary batteries and suppress the degradation of initial coulombic efficiency caused by oxidation over time.

[0009] Patent Document 1 does not discuss the carbonaceous material of the carbon coating. While Patent Document 1 describes experimental examples at low temperatures, it does not describe the effects, leaving the details unclear. To form a high-quality carbonaceous layer, carbon CVD is generally required at high temperatures.

[0010] On the other hand, it is believed that silicon carbide (SiC) is generated when carbon and silicon are exposed to high temperatures in a state of contact. Since silicon carbide does not undergo lithium insertion / extraction reactions, increasing the proportion of silicon carbide in the negative electrode active material leads to a decrease in the specific capacity of the negative electrode active material.

[0011] To suppress SiC formation and obtain a high-quality carbonaceous layer, the inventors investigated the temperature and carbon source during carbon CVD. As a result, they discovered the conditions for a carbon CVD method that resulted in a high initial coulombic efficiency of the lithium-ion secondary battery even after storing the carbon-coated Si-C composite particles for two months, and also revealed a novel carbon-coated Si-C composite particle, thus completing this invention.

[0012] That is, the present invention includes, for example, the following solutions. [1]

[0014] A carbon-coated Si-C composite particle, wherein a carbonaceous layer exists on the surface of the Si-C composite particle containing carbon material and silicon.

[0015] The carbon layer coverage (carbon coverage) on the surface of the Si-C composite particles is above 70%.

[0016] BET has a specific surface area of ​​200 m². 2 / g or less

[0017] In the Raman spectrum of the carbon-coated Si-C composite particles,

[0018] R value (I) D / I G () is above 0.30 and below 1.10,

[0019] The peak caused by Si exists in the range of 450–495 cm⁻¹ -1 The intensity of this peak is expressed as I. Si hour,

[0020] I Si / I G Below 0.15

[0021] The XRD patterns of the carbon-coated Si-C composite particles, as determined by powder XRD using Cu-Kα rays, are shown in the image.

[0022] The full width at half maximum (FWHM) of the Si111 surface is greater than 3.00 degrees.

[0023] The ratio of (peak intensity of SiC111 surface) to (peak intensity of Si111 surface) is less than 0.01. [2]

[0025] According to [1], the true density of carbon-coated Si-C composite particles obtained by a He hydrometer is 2.00–2.20 g / cm³. 3 . [3]

[0027] According to the carbon-coated Si-C composite particles described in [1] or [2], the 50% particle size D in the cumulative particle size distribution based on volume is... V50 The range is 2.0–30.0 μm. [4]

[0029] According to any one of [1] to [3], the carbon-coated Si-C composite particles contain 20 to 70% by mass of silicon. [5]

[0031] According to any one of [1] to [4], the oxygen content of the carbon-coated Si-C composite particles is less than 10.0% by mass. [6]

[0033] According to any one of [1] to [5], the oxygen content of the carbon-coated Si-C composite particles is less than 4.0% by mass. [7]

[0035] According to any one of [1] to [6], the carbon-coated Si-C composite particles have an average thickness of 5 to 100 nm. [8]

[0037] According to any one of [1] to [7], the carbon-coated Si-C composite particles, the R value (I D / I G The value is greater than 0.30 and less than 1.00. [9]

[0039] According to any one of [1] to [8], the BET specific surface area of ​​carbon-coated Si-C composite particles is 6.0 m². 2 / g or less.

[10]

[0041] According to any one of [1] to [8], the BET specific surface area of ​​carbon-coated Si-C composite particles is 5.0 to 200.0 m². 2 / g.

[11]

[0043] A polymer-coated carbon-coated Si-C composite particle, wherein at least a portion of the surface of the carbon-coated Si-C composite particle described in any one of [1] to

[10] has a polymer coating layer.

[0044] The polymer coating contains inorganic particles and polymers selected from graphite and carbon black, and the polymer content is 0.1 to 10.0% by mass.

[12]

[0046] A method for manufacturing carbon-coated Si-C composite particles, comprising step (A) and step (B),

[0047] Process (A): Silicon-containing gas is applied to porous carbon, causing silicon to deposit within the pores and on the surface of the porous carbon, resulting in Si-C composite particles.

[0048] Step (B): Using at least one of acetylene and ethylene as a carbon source, a carbonaceous layer is formed on the surface of the Si-C composite particles at 600–750°C using chemical vapor deposition (CVD).

[13]

[0050] According to the method for manufacturing carbon-coated Si-C composite particles described in

[12] , the steps (A) and (B) are performed consecutively.

[14]

[0052] According to the manufacturing method of carbon-coated Si-C composite particles described in

[12] or

[13] , carbon-coated Si-C composite particles as described in any one of [1] to

[10] are manufactured.

[15]

[0054] A negative electrode composite layer comprising carbon-coated Si-C composite particles described in any one of [1] to

[10] .

[16]

[0056] A negative electrode layer comprising polymer-coated carbon-coated Si-C composite particles as described in

[11] .

[17]

[0058] A lithium-ion secondary battery comprising the negative electrode compound layer described in

[15] or

[16] .

[0059] The carbon-coated Si-C composite particles of the present invention provide a lithium-ion secondary battery with high Si utilization and high initial coulombic efficiency even after being stored in air for two months. Furthermore, since the Si-C composite particles are coated with carbon, silicon oxidation can be prevented, thereby providing a negative electrode material for lithium-ion secondary batteries with excellent oxidation resistance. Attached Figure Description

[0060] Figure 1 (a) is a Raman spectrum of the carbon-coated Si-C composite particles of Example 1. Figure 1 (b) is a diagram showing the Raman spectrum of the uncoated Si-C composite particles of Comparative Example 2.

[0061] Figure 2 (a) is an XRD pattern representing the carbon-coated Si-C composite particles of Example 1. Figure 2 (b) is an XRD pattern representing the carbon-coated Si-C composite particles of Example 4. Figure 2 (c) is the XRD spectrum of the carbon-coated Si-C composite particles of Comparative Example 3.

[0062] Figure 3 This is a cross-sectional SEM image of the carbon-coated SiC composite particles from Example 1.

[0063] Figure 4 This is a cross-sectional SEM image of the carbon-coated SiC composite particles from Example 1. Detailed Implementation

[0064] Next, the present invention will be described in detail. Furthermore, in the present invention, "peak intensity" refers to "peak height".

[0065] [1] Carbon-coated Si-C composite particles

[0066] In the carbon-coated Si-C composite particles of the present invention, a carbonaceous layer exists on at least a portion of the surface of the Si-C composite particles containing carbon materials and silicon.

[0067] Si-C composite particles are composite particles containing carbon materials and silicon, typically composite particles in which silicon (Si) has been precipitated on the surface and within the pores of carbon materials. Generally, Si-C composite particles can be obtained, for example, by chemical vapor deposition (CVD) using silicon sources such as silanes (SiH4) to precipitate amorphous silicon onto porous carbon.

[0068] The carbon-coated Si-C composite particles of the present invention have a structure in which at least a portion of the surface of the Si-C composite particles is covered with a carbonaceous layer. The carbon-coated Si-C composite particles can be obtained, for example, from Si-C composite particles using a chemical vapor deposition (CVD) method (C-CVD) with a carbon source described later. The carbon-coated Si-C composite particles of the present invention can be substantially without voids (pores), or they can be with voids (pores). Here, as an example of substantially without voids (pores), examples include a method where the pores of the Si-C composite particles are substantially completely filled with a carbon source. Conversely, as an example of having voids (pores), examples include a method where, even if a carbon coating layer is formed on the surface of the pores of the Si-C composite particles using a C-CVD method, the total volume of the pores is not filled with carbon, or a method where there are pores that are not coated with carbon. In any case, the carbon-coated Si-C composite particles of the present invention suppress silicon oxidation by using carbon-coated Si-C composite particles, making them suitable for applications such as anode materials.

[0069] In the carbon-coated Si-C composite particles, the D band intensity (1360 cm⁻¹) obtained by Raman spectroscopy -1 Nearby peak intensity) I D With G-band strength (1600cm) -1 Nearby peak intensity) I G The ratio is the R value (I). D / I G The R value is 0.30 or higher and 1.10 or lower. When the R value is 0.30 or higher, the reaction resistance is sufficiently low, thus improving the rate characteristics of the battery. On the other hand, an R value of 1.10 or lower indicates fewer defects in the carbonaceous layer. With an R value of 1.10 or lower, side reactions are reduced, thus improving the coulombic efficiency. From the same point of view, an R value of 0.50 or higher is preferred, and more preferably 0.70 or higher.

[0070] Furthermore, in one embodiment of the carbon-coated Si-C composite particles of the present invention, the R value is preferably less than 1.00, more preferably 0.98 or less, and even more preferably 0.95 or less. This R value is particularly desirable when the carbon-coated Si-C composite particles are substantially free of voids (pores).

[0071] The carbon-coated Si-C composite particles exhibit Raman spectra ranging from 450 to 495 cm⁻¹. -1 There are peaks originating from Si (silicon). Furthermore, peaks originating from silicon appear in the 450–495 cm⁻¹ range. -1 The peak intensity is denoted as I. Si Typically, crystalline Si (silicon) is found at 520 cm⁻¹. -1A peak appears near the amorphous silicon, while a peak appears at a lower Raman shift. That is, the carbon-coated Si-C composite particles possess amorphous silicon. When silicon has high amorphousness, the expansion / contraction during charging and discharging is relatively isotropic, thus improving cycle characteristics. As the wavenumber increases, amorphousness decreases and crystallinity increases, thus worsening cycle characteristics.

[0072] In the carbon-coated Si-C composite particles, the Raman spectroscopy results in a peak intensity I due to silicon. Si With the strength I of the G band G The ratio of I Si / I G The value should be below 0.15. The presence of a silicon peak in the Raman spectrum indicates that silicon is deposited near the surface of the carbon-coated Si-C composite particles. If this value is within the aforementioned range, it indicates less silicon precipitated on the porous carbon surface and / or less silicon within the carbon pores near the surface of the carbon-coated SiC composite particles. This results in improved cycle performance due to a reduced proportion of silicon in direct contact with the electrolyte. Si / I G Preferably, it is 0.12 or less, more preferably 0.10 or less. Additionally, as I... Si / I G There is no particular restriction on the lower limit, which is usually 0, and preferably 0.001.

[0073] In the carbon-coated Si-C composite particles, the full width at half maximum (FWHM) of the Si 111 plane is 3.00 degrees or more in the XRD spectrum obtained using Cu-Kα powder XRD. A FWHM of 3.00 degrees or more on the Si 111 plane results in smaller crystallite size, suppressing damage to the silicon region associated with charging and discharging. From the same viewpoint, a FWHM of 3.10 degrees or more is preferred, more preferably 3.20 degrees or more, and even more preferably 4.50 degrees or more. Furthermore, a FWHM of 10.00 degrees or less is preferred, more preferably 7.00 degrees or less, and even more preferably 5.85 degrees or less.

[0074] In the XRD pattern obtained by powder XRD using Cu-Kα rays, the ratio of (peak intensity of SiC at the 111 facet) to (peak intensity of Si at the 111 facet) of the carbon-coated Si-C composite particles is less than 0.01. This ratio of less than 0.01 indicates that the carbon-coated Si-C composite particles contain no SiC (silicon carbide) or have extremely low SiC content, thus improving the utilization rate of silicon as a battery active material. Furthermore, the ratio of (peak intensity of SiC at the 111 facet) to (peak intensity of Si at the 111 facet) is also denoted as I. SiC111 / I Si111 As I SiC111 / I Si111The lower limit is 0. That is, it is preferable that no peak intensity of SiC is observed. Furthermore, the peak intensity of SiC refers to the peak from SiC where 2θ appears near 35°. In addition, the peak intensity of Si refers to the peak from Si where 2θ appears near 28°.

[0075] The true density of the carbon-coated Si-C composite particles, as measured by a He hydrometer, is preferably 2.00–2.20 g / cm³. 3 More preferably, it is 2.03–2.18 g / cm³. 3 When the true density is within the aforementioned range, using carbon-coated Si-C composite particles in negative electrode materials such as negative electrode flux layers for lithium-ion batteries can suppress the problem of a sharp decrease in capacity that can be charged with high current, and is therefore preferred.

[0076] True density can be determined using the gas-phase displacement method. This method calculates true density based on the volume of helium gas occupying a given solvent in an environment maintained at a constant temperature. An example apparatus for this method is the AccuPycII 1340 gas pycnometer manufactured by Micromeritics.

[0077] In the carbon-coated Si-C composite particles, 50% of the particle size D in the cumulative particle size distribution based on volume is... V50 Preferably, it is 2.0–30.0 μm. D V50 The D-value of the composite particles can be determined using laser diffraction. V50 If the particle size is above 2.0 μm, the carbon-coated Si-C composite particle powder exhibits excellent processability, making it easy to formulate slurries with suitable viscosity and density for coating, and the density during electrode formation is easily increased. From this perspective, D V50 More preferably, it is 3.0 μm or more, and even more preferably, it is 4.0 μm or more.

[0078] The carbon-coated Si-C composite particles D V50 If the particle size is below 30.0 μm, the diffusion length of lithium within individual particles becomes shorter, resulting in excellent rate characteristics for lithium-ion batteries. Furthermore, when coated onto the current collector in slurry form, it does not produce streaks or abnormal unevenness. From this perspective, D V50 More preferably, it is 25.0 μm or less, and even more preferably, it is 20.0 μm or less.

[0079] In the carbon-coated Si-C composite particles, the silicon (Si element) content is preferably 20-70% by mass. With a silicon content of 20% by mass or more, a specific capacity of 840 mAh / g or higher, significantly exceeding the theoretical specific capacity of graphite, can theoretically be obtained. From this perspective, the content is more preferably 30% by mass or more, and even more preferably 40% by mass or more.

[0080] In the carbon-coated Si-C composite particles, with a silicon content of 70% by mass or less, the volume change caused by the expansion / contraction of the carbon material acting as a carrier, preferably a carbon material derived from porous carbon, can be absorbed. From this viewpoint, the silicon content is more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less.

[0081] The silicon content in the carbon-coated Si-C composite particles can be determined by fluorescence X-ray analysis of the composite particles using methods such as the basic parameter method (FP method). Alternatively, the carbon components in the carbon-coated Si-C composite particles can be removed by combustion, and the remaining ash components can be completely dissolved in acid or alkali, followed by quantification using methods such as inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0082] The oxygen content in the carbon-coated Si-C composite particles is preferably 10.0% by mass or less. If the oxygen content of the composite particles is 10.0% by mass or less, the irreversible capacity of the negative electrode material for lithium-ion secondary batteries can be reduced. From the same viewpoint, the oxygen content is preferably 9.0% by mass or less, more preferably 8.0% by mass or less. There is no particular limitation on the lower limit of the oxygen content, but it is preferably 0.0% by mass, more preferably 0.5% by mass. Since the Si in the carbon-coated Si-C composite particles is coated with carbon, it is less prone to oxidation over time, and the oxygen content can be maintained at a low level.

[0083] Furthermore, in one embodiment of the carbon-coated Si-C composite particles of the present invention, the oxygen content is preferably 4.0% by mass or less, more preferably 3.8% by mass or less. This oxygen content is particularly desirable when the carbon-coated Si-C composite particles have porous (microporous) portions. In the present invention, unless otherwise specified, the oxygen content of the carbon-coated Si-C composite particles refers to the oxygen content of the carbon-coated Si-C composite particles stored within two days after manufacturing or in a non-oxidizing atmosphere. If it is impossible to measure within two days after manufacturing due to process reasons, etc., the value can be the same as that within two days after manufacturing if stored in an inert atmosphere such as argon, even if measured later. This is because oxidation is not promoted when stored in an inert atmosphere.

[0084] The oxygen content in the carbon-coated Si-C composite particles can be measured, for example, by a simultaneous oxygen and nitrogen measuring device.

[0085] In the carbon-coated Si-C composite particles, the carbon layer coverage (carbon coverage rate) on the surface of the Si-C composite particles is 70% or more. Because most of the surface of the Si-C composite particles is covered by carbon, silicon oxidation can be prevented. Therefore, the carbon-coated Si-C composite particles can be used as a negative electrode material for lithium-ion secondary batteries with excellent oxidation resistance. The carbon coverage rate is preferably 80% or more. An upper limit for the carbon coverage rate is 100%.

[0086] The carbon coverage rate can be determined based on cross-sectional SEM or TEM images of the carbon-coated Si-C composite particles. Specifically, for example, the perimeter of the Si-C composite particle and the length of the carbonaceous layer covering the Si-C composite particle can be calculated from the cross-sectional SEM or TEM images, and the carbon coverage rate can be determined based on their ratio. Alternatively, the carbon coverage rate can be obtained by using the proportion of areas on the surface of the carbon-coated Si-C composite particle with a higher carbon concentration than the interior. For example, in a cross-sectional SEM-EDS of the particle, 10 points on the outer perimeter after dividing the cross-section into ten equal parts are taken as measurement points on the particle surface. The carbon concentration at the center point and the measurement points on the particle surface is measured. If at least 7 of the measurement points on the particle surface have a higher carbon concentration than the center point, the carbon coverage rate can be confirmed to be 70% or higher. This analysis is not limited to cross-sectional SEM but can also be performed using cross-sectional TEM, and is effective when the carbon-coated Si-C composite particles have fine structures such as pores, making it difficult to determine the length from cross-sectional SEM images.

[0087] In one embodiment of the carbon-coated Si-C composite particles of the present invention, the average thickness of the carbonaceous layer is 5 to 100 nm. This average thickness is particularly desirable when the carbon-coated Si-C composite particles are substantially free of voids (pores) and when the carbon coating rate of the carbon-coated Si-C composite particles is 70% or more.

[0088] When the average thickness of the carbonaceous layer is 5 nm or more, the aforementioned Si-C composite particles can be completely coated, thus resulting in a battery with high initial coulombic efficiency. On the other hand, when the average thickness of the carbonaceous layer is 100 nm or less, the lithium diffusion distance is small, thus resulting in a battery with good rate characteristics. From the same viewpoint, the average thickness of the carbonaceous layer is preferably 7 nm or more, more preferably 10 nm or more, and even more preferably 15 nm or more. Furthermore, the average thickness of the carbonaceous layer is preferably 90 nm or less, more preferably 80 nm or less.

[0089] The average thickness of the carbonaceous layer of the carbon-coated Si-C composite particles can be determined from cross-sectional SEM images of the carbon-coated Si-C composite particles.

[0090] In one embodiment of the carbon-coated Si-C composite particles of the present invention, the average thickness of the carbonaceous layer is 5 to 100 nm, and the coverage rate (carbon coverage rate) of the carbonaceous layer on the surface of the Si-C composite particles is preferably 70% or more. Since such carbon-coated Si-C composite particles have a sufficiently thick carbonaceous layer on most of the particle surface, the exposure of surface Si is highly suppressed, and the contact between silicon (Si) and the outside environment is particularly minimal, thus suppressing oxidation over time. Therefore, when such carbon-coated Si-C composite particles are used in anode active materials, etc., the degradation of initial coulombic efficiency can be particularly effectively suppressed.

[0091] The carbon-coated Si-C composite particles of this invention have a BET specific surface area of ​​200 m². 2 / g or less. When carbon-coated Si-C composite particles have a sufficient carbonaceous layer on their surface, the BET specific surface area is typically 200 m². 2 / g or less.

[0092] In one embodiment of the carbon-coated Si-C composite particles of the present invention, the BET specific surface area is preferably 6.0 m². 2 / g or less. Especially when the carbon-coated Si-C composite particles are substantially free of voids (pores), such a BET specific surface area is preferred. A BET specific surface area of ​​6.0 m² is preferable. 2 Below a certain value, the decomposition reaction of the electrolyte as a side reaction is less likely to occur, which is therefore preferred. From this point of view, the BET specific surface area of ​​the carbon-coated Si-C composite particles is more preferably 5.5 m². 2 / g or less, more preferably 5.0m 2 / g or less. Nitrogen gas was used as the adsorbed gas when determining the BET specific surface area. The lower limit of the BET specific surface area of ​​the carbon-coated Si-C composite particles is typically 0.5m². 2 / g, preferably 1.0m 2 / g.

[0093] Furthermore, in one embodiment of the carbon-coated Si-C composite particles of the present invention, the BET specific surface area is preferably 5.0 to 200.0 m². 2 / g. Especially when the carbon-coated Si-C composite particles are in a porous (microporous) configuration, a BET specific surface area of ​​this size is preferred. In this case, the BET specific surface area of ​​the carbon-coated Si-C composite particles is more preferably 6.5 m². 2 / g or more, further preferably 8m 2 / g or more, and more preferably 180.0m 2 / g or more, further preferably 170.0m 2 / g or less. Even with such a BET specific surface area, the carbon-coated Si-C composite particles of this invention, by having a porous (microporous) portion, can prevent silicon oxidation by having a carbonaceous layer on the surface, such as inside the micropores. Furthermore, by having a small amount of Si exposed on the surface and coating the Si with carbonaceous material, reactions caused by direct contact between Si and the electrolyte can be suppressed, making it suitable for use as a negative electrode material, etc. Additionally, when the carbon-coated Si-C composite particles of this invention have porous (microporous) portions, the expansion of the Si-C composite particles can be suppressed.

[0094] [2] Polymer-coated carbon-coated Si-C composite particles

[0095] The composite particles of the present invention can also be polymer-coated carbon-coated Si-C composite particles having a polymer coating layer on at least a portion of the surface of the carbon-coated Si-C composite particles described above [1]. The polymer-coated carbon-coated Si-C composite particles of the present invention are composite particles having a polymer coating layer on at least a portion of the surface of the carbon-coated Si-C composite particles, that is, composite particles having a polymer coating layer on the carbonaceous layer of the carbon-coated Si-C composite particles.

[0096] The polymer coating contains one or more inorganic particles selected from graphite and carbon black, as well as a polymer, with a polymer content of 0.1 to 10.0% by mass.

[0097] The polymer coating layer contains inorganic particles that act as conductive additives, enabling the composite particle surface to acquire conductive protrusions. Therefore, when the polymer-coated carbon-coated Si-C composite particles of the present invention are used in the negative electrode additive layer, adjacent negative electrode materials can easily conduct to each other even when the composite particles expand and contract. Furthermore, the overall resistivity of the negative electrode material can be reduced.

[0098] (Inorganic particles)

[0099] The inorganic particles contained in the polymer coating include one or more of graphite and carbon black, and are typically conductive particles.

[0100] From the viewpoint of improving cycle characteristics, the content of inorganic particles is preferably 1.0 to 10.0% by mass in polymer-coated carbon-coated Si-C composite particles, more preferably 2.0 to 9.0% by mass, and even more preferably 3.0 to 8.0% by mass.

[0101] The particle size of the inorganic particles is preferably less than 1 / 2 that of the polymer-coated carbon-coated Si-C composite particles. This is to make it easier for the inorganic particles to exist on the surface of the carbon-coated Si-C composite particles.

[0102] The particle size of the inorganic particles can be determined by observing the polymer-coated carbon-coated Si-C composite particles using a scanning electron microscope (SEM).

[0103] As inorganic particles, at least one of granular graphite and carbon black is preferred, with granular graphite being preferred from the viewpoint of improving cycle characteristics. Examples of granular graphite include particles of artificial graphite, natural graphite, and MC (mesophase carbon). Examples of carbon black include acetylene black, Ketjen black, thermal cracking carbon black, and furnace black, with acetylene black being preferred from the viewpoint of electrical conductivity.

[0104] From the perspective of simultaneously improving battery capacity and charge / discharge efficiency, the crystallinity of granular graphite is preferably higher than that of carbon present on the surface of carbon-coated Si-C composite particles. Specifically, the average interplanar spacing (d) of granular graphite is determined based on the vibrational method. 002 The value of the interplanar spacing is preferably 0.335 nm to 0.347 nm, more preferably 0.335 nm to 0.345 nm, even more preferably 0.335 nm to 0.340 nm, and particularly preferably 0.335 nm to 0.337 nm. When the average interplanar spacing of granular graphite is less than 0.347 nm, the granular graphite has high crystallinity, and there is a tendency to improve both battery capacity and charge / discharge efficiency simultaneously. On the other hand, the theoretical value of graphite crystal is 0.335 nm, so when the average interplanar spacing of granular graphite is close to this value, there is a tendency to improve both battery capacity and charge / discharge efficiency simultaneously.

[0105] The shape of granular graphite is not particularly limited; it can be flat or spherical. From the perspective of improving cycle performance, flat graphite is preferred.

[0106] In this disclosure, flat graphite refers to graphite with an average aspect ratio of not 1, that is, graphite having a minor axis and a major axis. Examples of flat graphite include graphite with scaly, flake, or blocky shapes.

[0107] There is no particular limitation on the average aspect ratio of the inorganic particles. From the viewpoint of easily ensuring the conduction between inorganic particles and improving the circulation characteristics, the average aspect ratio is preferably 0.3 or less, more preferably 0.2 or less. The average aspect ratio of the inorganic particles is preferably 0.001 or more, more preferably 0.01 or more.

[0108] The aspect ratio of inorganic particles is determined through SEM observation. Specifically, for 100 inorganic particles randomly selected from an SEM image, the length along the major axis is set as A, and the length along the minor axis (or the thickness direction in the case of flat graphite) is set as B. The value is calculated in the form of B / A. The average aspect ratio is the arithmetic mean of the aspect ratios of the 100 inorganic particles.

[0109] Inorganic particles can be primary particles (single particles) or secondary particles (granulated particles) formed from multiple primary particles. In addition, flat graphite can be porous graphite particles.

[0110] (polymer)

[0111] The polymer-coated carbon-coated Si-C composite particles comprise a polymer coating layer present on at least a portion of the surface of the carbon-coated Si-C composite particles, the polymer coating layer containing a polymer.

[0112] The polymer content in the polymer-coated carbon-coated Si-C composite particles is 0.1% by mass or more. A polymer content of 0.1% by mass or more improves the cycle durability of the battery. From this viewpoint, the polymer content is preferably 0.2% by mass or more, and more preferably 0.3% by mass or more.

[0113] Furthermore, the polymer content in the polymer-coated carbon Si-C composite particles is 10.0% by mass or less. When it is 10.0% by mass or less, the conductivity of the polymer-coated carbon Si-C composite particles decreases less, which can improve the rate characteristics of the battery. From this point of view, the polymer content in the polymer-coated carbon Si-C composite particles is preferably 7.0% by mass or less, more preferably 5.0% by mass or less.

[0114] The polymer content of polymer-coated carbon-coated Si-C composites can be determined, for example, by heating the fully dried polymer-coated carbon-coated Si-C composite to a temperature above the polymer decomposition temperature but below the decomposition temperature of the carbon-coated Si-C composite particles and inorganic particles (e.g., 300°C), and then measuring the mass of the polymer-coated carbon-coated Si-C composite after polymer decomposition. Specifically, when the mass of the polymer-coated carbon-coated Si-C composite before heating is denoted as Ag, and the mass of the polymer-coated carbon-coated Si-C composite after heating is denoted as Bg, (AB) represents the polymer content. Therefore, the polymer content can be calculated using [(AB) / A} × 100.

[0115] The determination of the polymer content mentioned above can also be performed using thermogravimetric analysis (TG). This method is preferred because it requires a small sample volume and allows for high-precision determination.

[0116] There are no particular restrictions on the type of polymer. For example, at least one of polysaccharides, cellulose derivatives, animal-derived water-soluble polymers, lignin derivatives, and water-soluble synthetic polymers can be selected.

[0117] Specifically, examples of polysaccharides include starch derivatives such as acetic acid starch, phosphate starch, carboxymethyl starch, and hydroxyethyl starch, as well as dextrin, dextrin derivatives, cyclodextrin, alginic acid, arginine derivatives, sodium alginate, agarose, carrageenan, xyloglucan, glycogen, tamarind gum, pullulan, and pectin.

[0118] Examples of cellulose derivatives include carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose.

[0119] Examples of animal-derived water-soluble polymers include casein and gelatin.

[0120] Examples of water-soluble synthetic polymers include water-soluble acrylic polymers, water-soluble epoxy polymers, water-soluble polyesters, water-soluble polyamides, and water-soluble polyethers. More specifically, examples include polyvinyl alcohol, polyacrylic acid, polyacrylate, polyvinylsulfonic acid, polyvinylsulfonate, poly4-vinylphenol, poly4-vinylphenol salt, polystyrene sulfonic acid, polystyrene sulfonate, polyaniline sulfonic acid, polyacrylamide, polyvinylpyrrolidone, and polyethylene glycol. These polymers can be used in metal salt, alkylene glycol ester, or other forms.

[0121] The polymer preferably comprises, as a first component, one or more selected from polysaccharides, cellulose derivatives, gelatin, casein, and water-soluble polyethers, and as a second component, one or more selected from monosaccharides, disaccharides, oligosaccharides, amino acids, gallic acid, tannins, saccharin, salts of saccharin, and butanediol. In this embodiment, a polysaccharide refers to a compound having a structure composed of 10 or more monosaccharide molecules, and an oligosaccharide refers to a compound having a structure composed of 3 to 10 monosaccharide molecules. Furthermore, in this invention, these second components are also treated as polymers.

[0122] Specifically, the aforementioned polysaccharides can be cited as examples of polysaccharides.

[0123] Specifically, the aforementioned cellulose derivatives can be cited as examples of cellulose derivatives.

[0124] Specifically, examples of water-soluble polyethers include polyalkylene glycols such as polyethylene glycol.

[0125] Specifically, examples of monosaccharides include arabinose, glucose, mannose, and galactose.

[0126] Specifically, examples of disaccharides include sucrose, maltose, lactose, cellobiose, and trehalose.

[0127] Specifically, examples of oligosaccharides include raffinose, stachyose, and maltotriose.

[0128] Specifically, examples of amino acids include glycine, alanine, valine, leucine, isoleucine, serine, threonine, cysteine, cystine, methionine, aspartic acid, glutamic acid, lysine, arginine, phenylalanine, tyrosine, histidine, tryptophan, proline, hydroxyproline, and glycylglycine.

[0129] Specifically, examples of tannins include tea catechins and persimmon catechins.

[0130] The first component preferably contains at least one polysaccharide, and more preferably at least one selected from starch, dextrin, and pullulan. It is believed that the first component, by being present in a manner that covers at least a portion of the surface of the polymer-coated carbon-coated Si-C composite material, can inhibit the reaction between the polymer-coated carbon-coated Si-C composite material and the electrolyte in the battery, thereby improving cycle performance.

[0131] The second component preferably contains at least one selected from disaccharides and monosaccharides, and more preferably contains at least one selected from maltose, lactose, trehalose, and glucose. It is believed that the second component, when incorporated into the first component, inhibits the solubility of the precipitated film formed by the first component in water or electrolyte. By using both the first and second components, it is possible to firmly coat the surface of the carbon-coated Si-C composite material and improve the binding force of inorganic particles. Therefore, the cycle performance of the battery can be improved.

[0132] Based on the above viewpoint, when the polymer contains a first component and a second component, its mass ratio (first component: second component) is preferably 1:1 to 25:1, more preferably 3:1 to 20:1, and even more preferably 5:1 to 15:1.

[0133] (Manufacturing method)

[0134] There are no particular limitations on the method of having the polymer present on at least a portion of the surface of the carbon-coated Si-C composite particles. For example, the polymer can be attached to the carbon-coated Si-C composite particles by adding them to a liquid in which the polymer is dissolved or dispersed and stirring as needed. The polymer-coated Si-C composite particles are then removed from the liquid and dried as needed, thereby obtaining carbon-coated Si-C composite particles with polymer adhering to their surface.

[0135] The temperature of the solution or dispersion (hereinafter collectively referred to as solution) during stirring is not particularly limited, and can be selected from 5 to 95°C. When the solution is heated, the solvent or dispersion medium used in the solution (hereinafter collectively referred to as solvent) is distilled, which may cause changes in the solution concentration. To avoid this, the solution needs to be prepared in a closed system or the solvent needs to be refluxed. If the polymer can be uniformly distributed on at least a portion of the surface of the carbon-coated Si-C composite particles, the process can be carried out simultaneously with the distillation of the solvent. The stirring atmosphere is not particularly limited as long as it does not impair the performance of the polymer-coated carbon-coated Si-C composite particles.

[0136] There are no particular restrictions on the drying temperature, as long as it does not cause the polymer to decompose and distill off; for example, it can be selected from 50 to 200°C. Drying can be carried out under an inert atmosphere or under vacuum.

[0137] There are no particular restrictions on the polymer content in the solution; for example, it can be selected from 0.1% to 20% by mass.

[0138] There are no particular restrictions on the solvent used in the solution, as long as it can dissolve and disperse the polymer and polymer precursor. For example, water, acetonitrile, methanol, ethanol, 2-propanol, ketones such as acetone and methyl ethyl ketone, and esters such as ethyl acetate and n-butyl acetate can be used as solvents, or two or more of them can be mixed. Additionally, an acid or base can be added to adjust the pH of the solution as needed. Well-known products can be used as acids and bases.

[0139] [3] Method for manufacturing carbon-coated Si-C composite particles

[0140] The method for manufacturing carbon-coated Si-C composite particles of the present invention includes the following steps (A) and (B). By the method for manufacturing carbon-coated Si-C composite particles of the present invention, the carbon-coated Si-C composite particles of the present invention described above, namely the carbon-coated Si-C composite particles described above [1], can be obtained.

[0141] Process (A): A process in which silicon-containing gas is applied to porous carbon, causing silicon to be deposited in the pores and on the surface of the porous carbon, thereby obtaining Si-C composite particles.

[0142] Process (B): A process of forming a carbonaceous layer on the surface of the Si-C composite particles at 600–750°C using chemical vapor deposition (CVD) with at least one carbon source selected from acetylene and ethylene as the carbon source.

[0143] By means of the method for manufacturing carbon-coated Si-C composite particles, the carbon-coated Si-C composite particles of the present invention, namely the carbon-coated Si-C composite particles described above [1], can be obtained.

[0144] Furthermore, the method for obtaining porous carbon in the manufacturing method of the carbon-coated Si-C composite particles is not particularly limited. For example, porous carbon can be obtained by the following step (α) of preparing porous carbon.

[0145] (Process (α))

[0146] The process (α) for preparing porous carbon is not particularly limited as long as porous carbon can be obtained. As for porous carbon, as long as fine silicon can be precipitated inside its pores, even if the silicon expands and contracts with lithium insertion / extraction, stress will be generated to maintain the pore structure, and there will be unoccupied spaces. These spaces can be flattened to reduce the overall expansion and contraction of the anode material. There are no particular limitations. Specific examples of porous carbon include carbon obtained by thermal decomposition of activated carbon, resin, and organic matter, molecular sieve carbon, activated carbon fibers, condensates of vapor-grown carbon fibers, condensates of CNTs (carbon nanotubes), and inorganic template carbon.

[0147] In this specification, porous carbon is defined as having a BET specific surface area of ​​200 m². 2 Carbonaceous materials with a surface area of ​​800 m² or more are preferred. The porous carbon used as the raw material for the carbon-coated Si-C composite particles of this invention preferably has a BET specific surface area of ​​800 m². 2 / g or more, more preferably 1000m 2 Carbonaceous materials of / g or higher. The upper limit of the BET specific surface area of ​​the porous carbon used as the raw material for carbon-coated Si-C composite particles in this invention is not particularly limited, for example, it is 4000 m². 2 / g or less, preferably 3800m 2 / g or less.

[0148] To investigate the pore distribution of porous carbon, known methods are employed, for example, to analyze adsorption-desorption isotherms based on gas adsorption. The adsorbed gas is not particularly limited; nitrogen, carbon dioxide, and argon are commonly used. In this invention, nitrogen is used as the adsorbed gas.

[0149] Porous carbon can be commercially available products with a specific pore distribution, but it can also be manufactured by adjusting the conditions for thermal decomposition of the resin while investigating changes in the pore distribution using the methods described above.

[0150] (Process (A))

[0151] Step (A) is a process in which silicon-containing gas, preferably silane gas, is applied to porous carbon to deposit silicon inside and on the surface of the porous carbon, thereby obtaining Si-C composite particles.

[0152] In step (A), for example, granular porous carbon is placed in the chamber of a CVD apparatus, and a silicon-containing gas (preferably a silane gas) is applied to the porous carbon material under heating. By exposing the porous carbon particles to the silicon-containing gas at high temperature, silicon can be precipitated (deposited) on the surface and within the pores of the porous carbon. The silicon-containing gas enters into the pores of the porous carbon, thereby enabling at least a portion of the silicon to be precipitated within the pores. As a method for achieving this objective, for example, the apparatus and method shown in Patent Document 1 can be used.

[0153] (Process (B))

[0154] Step (B) is a step of forming a carbonaceous layer on the surface of the Si-C composite particles using chemical vapor deposition (CVD) at 600–750°C, with at least one selected from acetylene and ethylene as the carbon source.

[0155] In step (B), for example, the Si-C composite particles obtained in step (A) are placed in the chamber of a CVD apparatus, and at least one selected from acetylene and ethylene is introduced as a carbon source under heating. Carbon is generated through the thermal decomposition reaction of acetylene or ethylene, allowing carbon to precipitate on the surface of the Si-C composite particles. More preferably, only acetylene is used as the carbon source. As the reactor, a fixed bed or a fluidized bed can be used. In addition to the reaction gas, hydrogen, nitrogen, argon, and helium can be used as the carrier gas.

[0156] In this invention, the formation of silicon carbide (SiC) is suppressed by performing carbon CVD (hereinafter sometimes referred to as C-CVD) on the carbon source at a relatively low temperature. Furthermore, by thermally decomposing the carbon source at a relatively high temperature within the range that suppresses SiC formation, a high-quality carbonaceous layer can be precipitated. Specifically, the temperature is 600–750°C. For the same reason, the temperature is more preferably 650–700°C.

[0157] In the manufacturing method of the present invention, it is preferable to perform the steps (A) and (B) consecutively, and it is also preferable to supply the Si-C composite particles obtained in step (A) to step (B) after purging with an inert gas. Here, the inert gas refers to a non-oxidizing gas, which may contain hydrogen or the like. In addition, the purging with the inert gas may be accompanied by heating.

[0158] It is preferable to perform the process (A) and the process (B) consecutively, or to supply the Si-C composite particles obtained in the process (A) to the process (B) after replacing them with an inert gas, so that the Si-C composite particles obtained in the process (A) are supplied to the process (B) without being oxidized.

[0159] In this invention, "performing the process (A) and the process (B) consecutively" means performing the process (B) without removing the furnace after the process (A). That is, it includes a method that includes the gas replacement process as described above.

[0160] [4] Negative electrode mixture layer

[0161] The negative electrode mixture layer of the present invention contains the carbon-coated Si-C composite particles. The carbon-coated Si-C composite particles contained in the negative electrode mixture layer are the carbon-coated Si-C composite particles of the present invention, that is, the carbon-coated Si-C composite particles described above [1]. Alternatively, the negative electrode mixture layer may also contain polymer-coated carbon-coated Si-C composite particles described above [2] instead of carbon-coated Si-C composite particles.

[0162] In the negative electrode compound layer, the carbon-coated Si-C composite particles or polymer-coated carbon-coated Si-C composite particles function as the negative electrode material. 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 generally comprises a negative electrode material, a binder, and conductive additives as optional components. Here, in the present invention, the negative electrode material refers to the negative electrode active material and composites of the negative electrode active material with other materials.

[0163] The negative electrode binder layer can be manufactured using, for example, a known method as shown below. A slurry for forming the negative electrode binder layer is prepared using a negative electrode material, a binder, a conductive additive (optional), and a solvent. The slurry is coated onto a current collector such as copper foil and dried. After further vacuum drying, it is rolled and then cut or stamped into the necessary shapes and sizes. The rolling pressure is typically 100–500 MPa. The resulting product is sometimes referred to as a negative electrode sheet. The negative electrode sheet is obtained by pressing and consists of a negative electrode binder layer and a current collector. The electrode density (negative electrode binder layer density) is not particularly limited, but is preferably 0.7 g / cm³. 3 The above, and preferably 1.9 g / cm³ 3 the following.

[0164] As a negative electrode material, the carbon-coated Si-C composite particles or polymer-coated carbon-coated Si-C composite particles of the present invention can be used alone or in combination with other negative electrode materials. As other negative electrode materials, active materials commonly used as negative electrode active materials in lithium-ion secondary batteries can be used. When using other negative electrode materials, the carbon-coated Si-C composite particles or polymer-coated carbon-coated Si-C composite particles are typically used in combination with other negative electrode materials.

[0165] Other anode materials that can be cited include graphite, hard carbon, and lithium titanate (Li4Ti5O). 12This includes alloy-based active materials such as silicon and tin, as well as their composite materials. These anode materials are typically granular. As anode materials other than carbon-coated Si-C composite particles, one or more types can be used. Graphite (graphite particles) and hard carbon are particularly preferred. One preferred form of the anode material of the present invention is a form comprising carbon-coated Si-C composite particles and graphite particles.

[0166] When the anode material is formed from carbon-coated Si-C composite particles and other anode materials, the carbon-coated Si-C composite particles preferably contain 2 to 99% by mass relative to 100% by mass of the anode material, more preferably 4 to 70% by mass.

[0167] The same applies when the carbon-coated Si-C composite particles are partially or completely replaced with polymer-coated carbon-coated Si-C composite particles, as described above.

[0168] As a binder, any binder commonly used in the negative electrode binder layer of a lithium-ion secondary battery can be freely selected. Examples include polyethylene, polypropylene, ethylene-propylene terpolymer, butadiene rubber, styrene-butadiene rubber, butyl rubber, acrylic rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene oxide, polychlorohydrin, polyphosphazene, polyacrylonitrile, carboxymethyl cellulose and its salts, polyacrylic acid, and polyacrylamide. One binder can be used alone, or two or more can be used. The amount of binder is preferably 0.5 to 30 parts by weight relative to 100 parts by weight of the negative electrode material.

[0169] There are no particular limitations on conductive additives as long as they can impart conductivity and dimensional stability (absorb volume changes during lithium insertion / extraction) to the electrode. Examples include carbon nanotubes, carbon nanofibers, fumed carbon fibers (e.g., "VGCF-H" manufactured by Showa Denko Co., Ltd.), conductive carbon black (e.g., "Denka Black" manufactured by Denka Co., Ltd., "SUPER C65" manufactured by Imelis Graffito & Carbon Co., Ltd., "SUPER C45" manufactured by Imelis Graffito & Carbon Co., Ltd.), and conductive graphite (e.g., "KS6L" manufactured by Imelis Graffito & Carbon Co., Ltd., "SFG6L" manufactured by Imelis Graffito & Carbon Co., Ltd.). In addition, two or more of the aforementioned conductive additives may be used. The amount of conductive additive is preferably 1 to 30 parts by mass relative to 100 parts by mass of the negative electrode material.

[0170] The conductive additives preferably include carbon nanotubes, carbon nanofibers, and vapor-phase carbon fibers, and the fiber length of these conductive additives is preferably the D of the composite particles. v50The length should be at least half that of the composite carbon particles. If this length is achieved, these conductive additives crosslink between the negative electrode active material containing the composite carbon particles, improving cycle performance. Single-walled and multi-walled carbon nanotubes and carbon nanofibers with a fiber diameter of 15 nm or less are preferred because they can increase the number of crosslinks with the same amount of addition compared to coarser fibrous carbon. Furthermore, their greater flexibility makes them even more preferable from the viewpoint of increasing electrode density.

[0171] The amount of conductive additive is preferably 1 to 30 parts by mass relative to 100 parts by mass of carbon-coated Si-C composite particles and / or polymer-coated carbon-coated Si-C composite particles.

[0172] There are no particular limitations on the solvents used to prepare the electrode coating paste, and examples include N-methyl-2-pyrrolidone, dimethylformamide, isopropanol, and water. When using water as a solvent for the binder, a thickener is preferred. The amount of solvent is adjusted to achieve a viscosity that facilitates application to the current collector.

[0173] [5] Lithium-ion secondary batteries

[0174] 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 aforementioned 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; and a separator; and further includes a battery casing housing them. The lithium-ion secondary battery may include the aforementioned negative electrode compound layer, but other structures, including those previously known, may be used without particular limitation.

[0175] The positive electrode layer typically consists of a positive electrode material, conductive additives, and a binder. The positive electrode in the lithium-ion secondary battery can utilize the general structure found in typical lithium-ion secondary batteries.

[0176] As a cathode material, there are no particular limitations as long as it can reversibly perform electrochemical insertion and extraction of lithium, and these reactions are sufficiently high compared to the standard redox potential of the anode reaction. For example, LiCoO2, LiNiO2, LiMn2O4, and LiCo are preferred materials. 1 / 3 Mn 1 / 3 Ni 1 / 3 O2, carbon-coated LiFePO4, or mixtures thereof.

[0177] Materials mentioned above can be used as conductive additives, adhesives, and solvents for slurry preparation. Aluminum foil is preferably used as a current collector.

[0178] There are no particular limitations on the non-aqueous electrolytes and non-aqueous polymer electrolytes used in lithium-ion batteries. Examples of non-aqueous electrolytes include organic electrolytes obtained by dissolving lithium salts such as LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3, and CH3SO3Li in non-aqueous solvents such as ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, butyl carbonate, acetonitrile, propionitrile, dimethoxyethane, tetrahydrofuran, and γ-butyrolactone.

[0179] Examples of non-aqueous polymer electrolytes include gel-like polymer electrolytes containing polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, and polymethyl methacrylate; and solid polymer electrolytes containing polymers with ethylene oxide bonds.

[0180] Additionally, a small amount of additives used in lithium-ion battery electrolytes can be added to the non-aqueous electrolyte. Examples of such substances include vinylene carbonate (VC), biphenyl, propanesulfonate lactone (PS), fluoroethylene carbonate (FEC), and vinyl sulfate (ES). VC and FEC are preferred. The amount added is preferably 0.01 to 20% by mass relative to 100% by mass of the non-aqueous electrolyte.

[0181] As the separator, any combination of separators suitable for general lithium-ion secondary batteries can be freely selected, such as microporous membranes made of polyethylene or polypropylene. Alternatively, separators containing particles such as SiO2 and / or Al2O3 as fillers, as well as separators attached to their surfaces, can also be used.

[0182] As for battery casings, there are no particular restrictions as long as they can accommodate the positive and negative electrodes, as well as the separator and electrolyte. In addition to industry-standard products such as commercially available battery packs, 18650 cylindrical single cells, and coin-sized single cells, battery casings in the form of aluminum packaging materials can be freely designed and used.

[0183] Each electrode can be used as a component after being stacked. Alternatively, individual cells can be connected in series to be used as a battery pack or module.

[0184] The lithium-ion secondary battery of the present invention can be used as a power source for electronic devices such as smartphones, tablets, and mobile information terminals; as a power source for motors in power tools, vacuum cleaners, electric bicycles, drones, and electric vehicles; and for storing electricity obtained from fuel cells, solar power generation, wind power generation, etc.

[0185] Example

[0186] The present invention will now be specifically described with reference to examples and comparative examples, but the present invention is not limited to these examples. The determination of physical properties and battery evaluation were performed as follows.

[0187] [Raman spectroscopy determination]

[0188] Raman spectroscopy determination of the particles obtained in the Examples and Comparative Examples was performed under the following conditions.

[0189] Micro Raman Spectroscopy Apparatus: LabRAM HR Evolution manufactured by Horiba Co., Ltd.

[0190] Excitation wavelength: 532nm

[0191] Exposure time: 5 seconds

[0192] Total number of times: 2

[0193] Diffraction grating: 300 lines / mm (600nm)

[0194] Measurement range: 80 μm (length) × 100 μm (width)

[0195] Point count: 100 points were evaluated with a vertical feed of 17.8 μm and a horizontal feed of 22.2 μm.

[0196] For peak intensity, the height from the baseline to the peak is taken as the intensity. 1360 cm⁻¹ is calculated from the measured spectrum. -1 Nearby peak intensity I D (From amorphous components) and 1600cm -1 Nearby peak intensity I G (from graphite composition) ratio (I) D / I G Two measurements were taken, and the average value was used as the R value, which served as an evaluation index for the carbonaceous content of the carbonaceous layer.

[0197] Additionally, it was calculated that the height range is 450-495cm. -1 Peak intensity I from amorphous silicon Si With the I G The ratio (I) Si / I G ). Measured at 2 locations and used the average value as I. Si / I G This is used as an indicator of the coating of carbonaceous materials.

[0198] The Raman spectra of Example 1 and Comparative Example 2 are shown below. Figure 1 .

[0199] [Powder XRD Determination]

[0200] The particles obtained in the examples and comparative examples were filled into a glass sample plate (window length × width: 18 × 20 mm, depth: 0.2 mm) and measured under the following conditions.

[0201] XRD device: SmartLab manufactured by Rigaku Co., Ltd. (registered trademark)

[0202] Types of X-rays: Cu-Kα rays

[0203] Kβ ray removal method: Ni filter

[0204] X-ray output: 45kV, 200mA

[0205] Measurement range: 10.0~80.0°

[0206] Scanning speed: 10.0° / minute

[0207] For the obtained XRD spectra, background removal and Kα2 component removal were performed using analysis software (PDXL2, manufactured by Rigaku Co., Ltd.). After smoothing, peak fitting was performed to determine the peak positions and intensities. Additionally, the full width at half maximum (FWHM) of the Si 111 plane and the ratio of (peak intensity of the SiC 111 plane) to (peak intensity of the Si 111 plane) were calculated. Regarding peak intensity, the height from the baseline to the peak apex was taken as the peak intensity.

[0208] [True density determination]

[0209] After vacuum drying the sample at 180℃ for 12 hours, fill the measuring cell to 40-60% capacity in a glove box under a dry argon atmosphere. Tap the measuring cell more than 100 times, and then measure the sample weight. Afterward, remove the sample and expose it to the atmosphere, and measure the true density under the following conditions.

[0210] • Apparatus: Micromeriticssha AccuPycII 1340 gas hydrometer

[0211] • Measuring cell: aluminum, depth 39.3 mm, inner diameter 18 mm

[0212] Carrier gas: Helium

[0213] • Atmospheric pressure: 21.5 psig (148.2 kPag)

[0214] • Number of purging cycles during measurement: 200

[0215] Temperature: 25℃±1℃

[0216] [Acquisition of cross-sectional SEM-EDS images and carbon concentration analysis using cross-sectional SEM-EDS]

[0217] The cross-sectional SEM images of the particles obtained in the examples and comparative examples, as well as the carbon concentration obtained using cross-sectional SEM-EDS, were obtained under the following conditions. Furthermore, SEM refers to Scanning Electron Microscope, and EDS refers to Energy Dispersive X-ray Spectroscopy.

[0218] The sample was mounted on a carbon ribbon, and the particles were observed as before. The cross-section was machined using a cross-section polishing machine manufactured by Nippon Electronics Co., Ltd. Observations and measurements were performed using the following apparatus and under the following conditions.

[0219] • SEM: Scanning electron microscope setup: Regulus 8220 (manufactured by Hitachi Hitek Co., Ltd.)

[0220] • EDS: XFlash (registered trademark) 5060 FlatQUAD (made by Blu-ray Co., Ltd.)

[0221] Accelerating voltage: 1~20kV

[0222] • Magnification: 500–5,000x (select appropriately based on particle size)

[0223] The average thickness of the carbonaceous layer (carbon layer) is the average of the thickness of the carbon coating at three locations on a single particle, obtained by measuring the thickness of six randomly selected particles.

[0224] Regarding the carbon coverage rate, in Examples 1-5 and Comparative Examples 1-4, the outer perimeter length of the Si-C composite particles was calculated based on cross-sectional SEM images of six randomly selected particles, and the length of the carbonaceous layer (carbon layer) covering the Si-C composite particles was calculated as the ratio (length of the carbonaceous layer (carbon layer) covering the Si-C composite particles / outer perimeter length of the Si-C composite particles × 100). In Examples 6-13 and Comparative Examples 5-8, in cross-sectional SEM-EDS of six randomly selected particles, ten points on the outer perimeter of the cross-section, divided into ten equal parts, were used as measurement points on the particle surface. The carbon concentration at the center point and the measurement points on the particle surface was measured, and the proportion of measurement points on the particle surface with a carbon concentration higher than that at the center point was determined.

[0225] Cross-sectional SEM images of the carbon-coated Si-C composite particles from Example 1 are shown below. Figure 3 and Figure 4 .exist Figure 3 and Figure 4 In the diagram, 1 represents the carbonaceous layer and 2 represents the Si-C composite particles.

[0226] [BET specific surface area measurement, pore volume measurement]

[0227] Place the sample into the sample cell (9mm × 135mm) to achieve a total sample surface area of ​​2–60 m². 2 The sample was dried under vacuum at 300°C for 1 hour, and then the weight of the sample was determined according to the following method.

[0228] • Device: NOVA4200e (registered trademark) manufactured by Quantachrome Instruments.

[0229] • Gas to be measured: Nitrogen

[0230] • Relative pressure setpoint for the measurement range: 0.005~0.995

[0231] (Calculation method)

[0232] (BET specific surface area calculation method)

[0233] The BET specific surface area of ​​porous carbon materials was calculated using the BET multi-point method based on adsorption isotherm data with relative pressures around 0.005 to less than 0.08.

[0234] The BET specific surface area of ​​the composite particles was calculated using the BET multi-point method based on adsorption isotherm data at three points with relative pressures of approximately 0.1, 0.2, and 0.3.

[0235] (Method for calculating the volume of fine pores)

[0236] The pore volume was calculated using the adsorption isotherm data at two points near a relative pressure of 0.99, and the adsorption amount at a relative pressure of 0.99 was determined by a linear approximation. At this point, the density of the nitrogen solution was 0.808 g / cc, the volume of 1 mol of nitrogen under standard conditions was 22.4133 L, and the atomic weight of nitrogen was calculated as 14.0067.

[0237] [Particle size distribution determination]

[0238] One scoop of the particles obtained in the examples and comparative examples, along with two drops of a 100-fold dilution of the nonionic surfactant (SIRAYA coconut oil high-performance detergent) stock solution (32% by mass), was added to 15 mL of water and ultrasonically dispersed for 3 minutes. The dispersion was then placed in a laser diffraction particle size analyzer (LMS-2000e) manufactured by Seishin Enterprises Co., Ltd., and the cumulative particle size distribution based on volume was measured to determine the 50% particle size D. V50 .

[0239] [Oxygen Content Measurement]

[0240] The oxygen content of the particles obtained in the Examples and Comparative Examples was determined under the following conditions.

[0241] • Oxygen / Nitrogen / Hydrogen Analyzer: EMGA-920 manufactured by Horiba Manufacturing Co., Ltd.

[0242] Carrier gas: Argon

[0243] Approximately 20 mg of the particles obtained in the examples and comparative examples were weighed into a nickel bag and measured using a simultaneous oxygen and nitrogen analysis device (melting in an inert gas → infrared absorption method).

[0244] Furthermore, the oxygen content was measured within 2 days after the carbon-coated Si-C composite particles were manufactured using C-CVD (for Comparative Examples 2, 5, 6, and 7, it was within 2 days after the Si-C composite particles were manufactured) and after storage for 2 months. The 2-month storage conditions involved placing the carbon-coated Si-C composite particles (for Comparative Examples 2, 5, 6, and 7, they were Si-C composite particles) in a 0.04 mm thick polyethylene bag with a clamp (manufactured by Unipac Co., Ltd., Japan) and storing them in a constant temperature chamber (temperature 23°C, humidity 50%). The oxygen content within 2 days of manufacture was also recorded as "oxygen content after CVD treatment," and the oxygen content after 2 months of storage was also recorded as "oxygen content after 2 months."

[0245] [Si (Silicon) Content Measurement]

[0246] The silicon content of the particles obtained in the Examples and Comparative Examples was determined under the following conditions.

[0247] [Si content (mass%) in samples analyzed by fluorescence X-ray diffraction]

[0248] The sample was filled into a sample cup and the Si content was determined by the basic parameter method (FP method) in mass % using the following method.

[0249] Fluorescent X-ray device: NEX CG manufactured by Rigaku

[0250] Tube voltage: 50kV

[0251] Tube current: 1.00mA

[0252] Sample cup: φ32 12mL CH1530

[0253] Sample weight: 2-4g

[0254] Sample height: 5–18 mm

[0255] Furthermore, the FP method is implemented using the analysis software provided with the device.

[0256] [TG (Polymer Content Analysis)]

[0257] The polymer content was determined using the following apparatus and under the following conditions.

[0258] • Measuring apparatus: TG-DTA2000SE (manufactured by NETZSCH Japan Co., Ltd.)

[0259] • Measurement temperature: room temperature to 1000℃

[0260] • Sample size: 13–15 mg

[0261] • Heating rate: 10℃ / minute

[0262] • Atmospheric gas: Ar

[0263] • Flow rate: 100ml / minute

[0264] The weight loss caused by thermal decomposition at 200℃~350℃ is taken as the polymer content, and the polymer content rate is calculated.

[0265] [The production of negative electrode plates]

[0266] Styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) are used as adhesives.

[0267] Specifically, an SBR aqueous dispersion containing 40% by mass of SBR solids and an aqueous solution of CMC powder containing 2% by mass of CMC were used.

[0268] As a mixed conductive additive, a mixture was prepared by mixing carbon black (SUPER C 45, manufactured by Imelis Graffiti & Carbon Co., Ltd.) and vapor-grown carbon fiber (VGCF-H, manufactured by Showa Denko Co., Ltd.) in a mass ratio of 3:2.

[0269] The negative electrode material, mixed conductive additive, 2% CMC aqueous solution, and 40% SBR aqueous dispersion were mixed to produce a negative electrode material of 90 parts by mass, a mixed conductive additive of 5 parts by mass, a CMC solid component of 2.5 parts by mass, and an SBR solid component of 2.5 parts by mass. An appropriate amount of water for adjusting viscosity was added, and the mixture was kneaded using a rotation / revolution mixer (Sinkee Co., Ltd.) to obtain a slurry for forming a negative electrode mixture layer.

[0270] The negative electrode slurry for forming the negative electrode mixture was uniformly coated to a thickness of 150 μm onto a 20 μm thick copper foil using a scraper. After drying with a hot plate, it was then vacuum dried to obtain the negative electrode sheet. The dried negative electrode sheet was pressed at a pressure of 300 MPa using a uniaxial press to obtain a negative electrode sheet for battery evaluation. The thickness of the obtained negative electrode sheet, including the copper foil thickness, was 62 μm.

[0271] [Determination of Electrode Density]

[0272] The pressed negative electrode sheet (current collector + negative electrode flux layer) is punched into a circle with a diameter of 16 mm, and its mass and thickness are measured. The mass and thickness of the current collector (circle with a diameter of 16 mm) are subtracted from these values ​​to obtain the mass and thickness of the negative electrode flux layer. Based on the mass, thickness, and diameter (16 mm) of the negative electrode flux layer, the coating weight (obtained by dividing the aforementioned mass of the negative electrode flux layer by the electrode area) and the electrode density (density of the negative electrode flux layer) are calculated.

[0273] [Making a coin cell (lithium-ion single cell with counter electrode)]

[0274] The negative electrode sheet is punched to 16mmφ and formed by pressing with a uniaxial press. The density of the negative electrode mixture layer is adjusted to 1.4g / cc to obtain the negative electrode.

[0275] A separator (polypropylene microporous membrane) impregnated with electrolyte is stacked within a polypropylene insulating gasket (approximately 18 mm inner diameter), sandwiched between the aforementioned negative electrode and a 1.7 mm thick lithium foil punched to a diameter of 17.5 mm. The negative electrode's negative electrode layer is stacked with the lithium foil facing away from the separator. This is configured as a 2320 coin-shaped single cell and sealed with a caulking machine to form a test single cell (lithium counter electrode single cell).

[0276] Furthermore, the electrolyte in the lithium counter electrode single cell is a liquid obtained as follows: 1 part by mass of vinylene carbonate (VC) and 10 parts by mass of fluoroethylene carbonate (FEC) are mixed in 100 parts by mass of a solvent obtained by mixing ethylene carbonate, methyl ethyl carbonate and diethyl carbonate in a volume ratio of 3:5:2, and then electrolyte LiPF6 is dissolved in it to achieve a concentration of 1 mol / L.

[0277] [Determination of initial embedding specific capacity and initial coulombic efficiency]

[0278] Experiments were conducted using a single-cell lithium-ion battery with a lithium counter electrode. First, a constant current (CC) discharge was performed at a current equivalent to 0.1C until 0.005V. Next, at 0.005V, the discharge mode was switched to constant voltage (CV) discharge, with a cutoff current of 0.005C. The specific capacity at this point was taken as the initial insertion / extraction specific capacity. Then, the upper limit voltage was set to 1.5V, and the battery was charged in CC mode at a current equivalent to 0.1C. The specific capacity at this point was taken as the initial extraction / extraction specific capacity.

[0279] The experiment was conducted in a constant temperature bath set at 25°C. At this temperature, the specific capacity was the value obtained by dividing the capacity by the mass of the negative electrode material. Furthermore, in this experiment, the "current value equivalent to 1C" was estimated based on the mass of Si and carbon (including graphite) in the negative electrode active material, and the theoretical specific capacities (4200 mAh / g and 372 mAh / g, respectively), representing the current required to discharge the negative electrode to its full capacity in one hour.

[0280] The initial coulombic efficiency is the result of the initial de-entrapment ratio / initial insertion ratio expressed as a percentage.

[0281] Furthermore, the initial coulombic efficiency was determined by fabricating a negative electrode within two days of the carbon-coated Si-C composite particles being manufactured using C-CVD (for Comparative Examples 2, 5, 6, and 7, this was within two days of Si-C composite particle manufacturing), followed by coin cell fabrication and initial coulombic efficiency measurement within one week. Regarding the products stored for two months in a 0.04 mm thick polyethylene bag with a clamp (manufactured by Unipac Co., Ltd., Japan), containing carbon-coated Si-C composite particles (for Comparative Examples 2, 5, 6, and 7, Si-C composite particles), and then in a constant temperature chamber (temperature 23°C, humidity 50%), the negative electrode was fabricated within two days after two months, followed by coin cell fabrication and initial coulombic efficiency measurement within one week. Furthermore, the initial coulombic efficiency within two days of manufacturing is simply referred to as "initial coulombic efficiency," and the initial coulombic efficiency after two months of storage is also recorded as "initial coulombic efficiency after two months of storage."

[0282] In addition, the ratio of the initial coulombic efficiency to the initial coulombic efficiency after 2 months of storage is used as the retention rate (%) of the initial coulombic efficiency after 2 months.

[0283] [Calculation of Si utilization rate]

[0284] The initial intercalation specific capacity of the carbon-coated Si-C composite particles, calculated based on the initial intercalation specific capacity of the lithium counter electrode single cell and the capacity of graphite, is taken as the initial intercalation specific capacity of the carbon-coated Si-C. That is, the initial intercalation specific capacity of the carbon-coated Si-C is calculated by the following formula.

[0285] (Initial intercalation specific capacity of carbon-coated Si-C) = {(Initial intercalation specific capacity) - (Initial intercalation specific capacity of graphite × Graphite mass ratio)} / (Mass ratio of carbon-coated Si-C)

[0286] Here, the initial graphite intercalation specific capacity is calculated using the theoretical specific capacity of carbon, which is 372 mAh / g.

[0287] Furthermore, here, the graphite mass ratio refers to the mass ratio of graphite in the overall negative electrode material. The carbon-coated Si-C mass ratio refers to the mass ratio of carbon-coated Si-C composite particles in the overall negative electrode material. In this embodiment and the comparative example, their sum is 1.

[0288] The initial Si intercalation specific capacity is calculated by subtracting the initial carbon intercalation specific capacity of the carbon-coated Si-C composite particles from the initial intercalation specific capacity of the carbon-coated Si-C, and then dividing by the silicon content in the sample. That is, the initial Si intercalation specific capacity is calculated using the following formula.

[0289] (Initial Si intercalation specific capacity) = {(Initial intercalation specific capacity of carbon-coated Si-C) - (Initial intercalation specific capacity of carbon in carbon-coated Si-C composite particles)} / Si content

[0290] Furthermore, the Si utilization rate (%) is obtained by dividing the initial Si intercalation specific capacity by the theoretical value of the silicon intercalation specific capacity (4200 mAh / g) and multiplying by 100. That is, the Si utilization rate is calculated by the following formula.

[0291] (Si utilization rate) = 100 × (initial Si embedding capacity) / 4200 (%)

[0292] Furthermore, the initial carbon intercalation specific capacity in carbon-coated Si-C composite particles is obtained by setting the theoretical capacity of carbon to 372 mAh / g, multiplying it by the carbon content (100 - Si content - oxygen content), and then dividing by 100.

[0293] The following describes the modulation methods, sources, and physical properties of the raw materials for anode materials (porous carbon, Si-C composite particles, carbon-coated Si-C composite particles, and graphite particles).

[0294] Porous carbon

[0295] As a porous carbon (1), using BET with a specific surface area of ​​1700 m² 2 / g and particle size D V50 Commercially available activated carbon with a diameter of 9.2 μm.

[0296] As porous carbon (2), using BET with a specific surface area of ​​1700 m² 2 / g and particle size D V50 Commercially available activated carbon with a diameter of 7.0 μm.

[0297] [Si-C composite particles]

[0298] (Si-C composite particles(1))

[0299] The specific surface area of ​​the BET is 1700 m². 2 / g and particle size D V50Porous carbon (1) with a diameter of 9.2 μm was treated in a tube furnace with a 1.3 vol% silane gas flow mixed with nitrogen at a set temperature of 450 °C, a pressure of 760 Torr, and a flow rate of 100 sccm for 8 hours, causing silicon to precipitate on the surface and inside of the resulting porous carbon, thus obtaining Si-C composite particles (1). The D of the Si-C composite particles (1) V50 Its thickness is 9.2 μm and its BET specific surface area is 3.2 m². 2 / g and the silicon content is 48% by mass.

[0300] (Si-C composite particles(2))

[0301] The specific surface area of ​​the BET is 1700 m². 2 / g and particle size D V50 Porous carbon (2) with a diameter of 7.0 μm was treated in a tube furnace with a 1.3 vol% silane gas flow mixed with nitrogen at a set temperature of 450 °C, a pressure of 760 Torr, and a flow rate of 100 sccm for 7.5 hours, causing silicon to precipitate on the surface and inside of the obtained porous carbon, resulting in Si-C composite particles (2). The D of the Si-C composite particles (2) V50 It has a thickness of 7.0 μm and a BET specific surface area of ​​14.2 m². 2 / g and the silicon content is 46% by mass.

[0302] [Modulation method of carbon-coated Si-C composite particles]

[0303] The obtained Si-C composite particles were placed in the chamber of a horizontal tubular furnace CVD device. After vacuum Ar replacement, the tubular furnace was heated to the target temperature in 25 minutes. Acetylene, ethylene or methane gas was introduced as a carbon source under heating. Carbon was coated onto the Si-C composite particles through thermal decomposition reaction.

[0304] Furthermore, the carbon source, temperature, and other conditions are shown in the various embodiments and comparative examples.

[0305] [Graphite particles]

[0306] Using BET specific surface area = 2.7m² 2 / g, Particle size D V10 =7μm, particle size D V50 =14μm, particle size D V90 Commercially available synthetic graphite with a diameter of 27 μm and a tap density of 0.98 g / cc.

[0307] [Anode Material]

[0308] By mixing the carbon-coated Si-C composite particles of the present invention (in Comparative Examples 2, 5, 6, and 7, Si-C composite particles) with graphite particles, a hybrid anode material for battery evaluation was prepared. In this case, the graphite particles were mixed such that the silicon content in the hybrid anode material was 4.9 to 5.7% by mass.

[0309] [Example 1]

[0310] The Si-C composite particles (1) obtained by the aforementioned method were subjected to C-CVD at 650 °C for 120 minutes using acetylene gas as the carbon source to modulate carbon-coated Si-C composite particles. Their physical properties are shown in Table 1.

[0311] The obtained carbon-coated Si-C composite particles are a novel type of carbon-coated Si-C composite particles, capable of simultaneously achieving an R value of 0.78 in Raman spectroscopy while being 100% coated with high-quality carbon, and an I value in XRD spectrum. SiC111 / I Si111 The result is 0.00, therefore there is no SiC result.

[0312] The carbon-coated Si-C composite particles and graphite particles were mixed to obtain a hybrid anode material. The mass ratios of these particles in the overall hybrid anode material were 0.114 and 0.886, respectively. The battery characteristics are shown in Table 2. It can be seen that this anode material has higher silicon utilization and higher initial coulombic efficiency compared to previous technologies.

[0313] [Example 2]

[0314] For the Si-C composite particles (1) obtained by the aforementioned method, carbon-coated Si-C composite particles were modulated by C-CVD at 650°C for 60 minutes using acetylene gas as the carbon source. Their physical properties are shown in Table 1.

[0315] Similar to Example 1, it simultaneously achieved an R value of less than 1.00 in the Raman spectrum and an I value in the XRD. SiC111 / I Si111 The result is 0.00.

[0316] The carbonaceous layer has a thin average thickness of 17.2 nm. This carbon-coated Si-C composite particles and graphite particles were mixed to obtain a hybrid anode material. The mass ratios of these particles in the overall hybrid anode material were 0.108 and 0.892, respectively. Its battery characteristics are shown in Table 2. It can be seen that it exhibits good battery performance.

[0317] [Example 3]

[0318] For the Si-C composite particles (1) obtained by the aforementioned method, carbon-coated Si-C composite particles were modulated by C-CVD under conditions of 650°C and 120 minutes using acetylene gas as the carbon source. Their physical properties are shown in Table 1.

[0319] In Raman spectroscopy I Si / I G With a small value of 0.01, it is possible to simultaneously achieve an R value of less than 1.00 for Raman spectroscopy and an I value of less than 1.00 for XRD. SiC111 / I Si111 The value of 0.00 is the same as in Example 1. Regarding the BET specific surface area after carbon coating, the BET specific surface area before carbon coating in Example 3 is greater than that in Example 1, so the result is that the BET specific surface area after carbon coating is also greater than that in Example 1.

[0320] The carbon-coated Si-C composite particles and graphite particles were mixed to obtain a hybrid anode material. The mass ratios of these particles in the overall hybrid anode material were 0.119 and 0.881, respectively. Its battery characteristics are shown in Table 2. It can be seen that the battery performance is good.

[0321] [Example 4]

[0322] For the Si-C composite particles (1) obtained by the aforementioned method, carbon-coated Si-C composite particles were modulated by C-CVD at 700°C for 16 minutes using acetylene as the carbon source. Their physical properties are shown in Table 1.

[0323] Compared to Example 1, the R value of the Raman spectrum is 0.84, and the I value of the XRD is... SiC111 / I Si111 The value is 0.00, which is the same as in Example 1.

[0324] The full width at half maximum (FWHM) of the Si111 plane in XRD was 3.36 degrees, which is slightly smaller than 5.02 degrees in Example 1, suggesting that the amorphousness of Si is slightly lower than that in Example 1.

[0325] The carbon-coated Si-C composite particles and graphite particles were mixed to obtain a hybrid anode material. The mass ratios of these particles in the overall hybrid anode material were 0.114 and 0.886, respectively. Its battery characteristics are shown in Table 2. It can be seen that it exhibits good battery characteristics.

[0326] [Example 5]

[0327] For the Si-C composite particles (2) obtained by the aforementioned method, carbon-coated Si-C composite particles were modulated by C-CVD under conditions of 700°C and 16 minutes, with acetylene as the carbon source.

[0328] Its physical properties are shown in Table 1. Compared with Example 1, the R value of the Raman spectrum is 0.83, and the I value of the XRD is... SiC111 / I Si111 The value is 0.00, which is the same as in Example 1.

[0329] The half-width at half maximum (WHM) of the Si111 plane in XRD was 4.73 degrees, which is slightly smaller than the 5.02 degrees in Example 1, suggesting that the amorphousness of Si is slightly lower than that in Example 1.

[0330] The carbon-coated Si-C composite particles and graphite particles were mixed to obtain a hybrid anode material. The mass ratios of these particles in the overall hybrid anode material were 0.119 and 0.881, respectively. Its battery characteristics are shown in Table 2. It can be seen that the battery performance is good.

[0331] [Comparative Example 1]

[0332] For the Si-C composite particles (1) obtained by the aforementioned method, carbon-coated Si-C composite particles were modulated by C-CVD at 550 °C for 60 minutes using acetylene as the carbon source. Their physical properties are shown in Table 1.

[0333] The carbon coverage rate is 9%, which is a significant decrease compared to the example.

[0334] The carbon-coated Si-C composite particles and graphite particles were mixed to obtain a hybrid anode material. The mass ratios of these particles in the overall hybrid anode material were 0.108 and 0.892, respectively. The battery characteristics are shown in Table 2. It can be seen that the Si utilization rate and initial coulombic efficiency are low, and the initial coulombic efficiency decreases after two months of storage, indicating poor battery characteristics.

[0335] [Comparative Example 2]

[0336] The Si-C composite particles (1) obtained by the aforementioned method were not subjected to C-CVD. Instead, the Si-C composite particles (1) and graphite particles were mixed to obtain a hybrid anode material. The mass ratios of the Si-C composite particles and graphite particles in the overall hybrid anode material were 0.118 and 0.882, respectively. The physical properties of the Si-C composite particles are shown in Table 1, and the battery characteristics of the anode material are shown in Table 2.

[0337] Compared to Example 1, since there is no carbonaceous layer, there is no inhibition of oxidation over time, and the initial coulombic efficiency is low after 2 months of storage.

[0338] [Comparative Example 3]

[0339] For the Si-C composite particles (1) obtained by the aforementioned method, carbon-coated Si-C composite particles were modulated by C-CVD at 800°C for 15 minutes using ethylene as a carbon source. Their physical properties are shown in Table 1.

[0340] Compared to Example 1, the R value of the Raman spectrum is 1.06, indicating that the carbonaceous layer was obtained from inferior carbon. Additionally, I Si The peak moved to 518cm -1 This indicates that it is crystalline Si rather than amorphous Si. Additionally, the I₂ in the XRD... SiC111 / I Si111 The value of 0.19 indicates the formation of SiC. Furthermore, it is believed that the sample underwent heat treatment at 800℃, resulting in larger crystallites and a low half-width of 2.20 degrees for the Si111 surface in XRD.

[0341] The carbon-coated Si-C composite particles and graphite particles were mixed to obtain a hybrid anode material. The mass ratios of these particles in the overall hybrid anode material were 0.108 and 0.892, respectively. The battery characteristics are shown in Table 2. It can be seen that the initial intercalation specific capacity, Si utilization rate, and initial coulombic efficiency are poor.

[0342] [Comparative Example 4]

[0343] For the Si-C composite particles (1) obtained by the aforementioned method, carbon-coated Si-C composite particles were modulated by C-CVD at 900 °C for 15 minutes using methane as the carbon source. Their physical properties are shown in Table 1.

[0344] The Si111 plane of the XRD has a small full width at half maximum (FWHM), which is 0.50 degrees. SiC111 / I Si111 The value of 1.50 indicates the increase in crystallite diameter and the formation of SiC.

[0345] The carbon-coated Si-C composite particles and graphite particles were mixed to obtain a hybrid anode material. The mass ratios of these particles in the overall hybrid anode material were 0.108 and 0.892, respectively. The battery characteristics are shown in Table 2. It can be seen that the initial intercalation specific capacity and Si utilization are poor.

[0346]

[0347]

[0348] As shown in Table 2, the battery having a negative electrode flux layer containing carbon-coated Si-C composite particles according to an embodiment of the present invention has a high Si utilization rate of over 80.0% and a high initial coulombic efficiency retention rate of around 100.0%.

[0349] [Example 6]

[0350] [Modulation of carbon-coated Si-C composite particles]

[0351] In a horizontal tubular furnace (manufactured by Koyo Heat Treatment Equipment Co., Ltd.) with an inner diameter of 7 cm, the BET specific surface area was 1850 m². 2 / g and particle size D V50 Porous carbon with a diameter of 9.9 μm was treated with 100% silane gas at a set temperature of 400 °C, a pressure of 760 Torr, and a flow rate of 65 sccm for 1.13 hours to precipitate silicon on the surface and inside the porous carbon, yielding Si-C composite particles. Next, the silane gas was removed with Ar gas to replace it with an inert atmosphere. Then, while heating at a rate of 25 °C / min, an acetylene / Ar dilution gas with a concentration of 20% by volume was introduced at a flow rate of 100 sccm until the temperature reached 650 °C. This temperature was then maintained at 650 °C for 0.5 hours for acetylene treatment (C-CVD). Finally, the temperature was lowered to room temperature while flowing Ar gas to obtain carbon-coated Si-C composites. The physical properties of the obtained carbon-coated Si-C composite particles are shown in Table 4.

[0352] [Evaluation of Battery Characteristics]

[0353] The obtained carbon-coated Si-C composite particles and graphite particles were mixed to obtain a hybrid anode material. The mass ratio of carbon-coated Si-C composite particles and graphite particles in the overall hybrid anode material and their battery characteristics are shown in Table 5.

[0354] [Examples 7-10, Comparative Example 8]

[0355] The porous carbon used as raw material in Example 6 was adjusted to have the BET specific surface area and particle size D as shown in Table 3. V50 Porous carbon was used as a raw material, and the silane and acetylene treatment conditions were set as described in Table 3. Otherwise, carbon-coated Si-C composite particles were obtained in the same manner as in Example 6. The physical properties of the obtained carbon-coated Si-C composite particles are shown in Table 4.

[0356] The obtained carbon-coated Si-C composite particles and graphite particles were mixed to obtain a hybrid anode material. The mass ratio of carbon-coated Si-C composite particles and graphite particles in the overall hybrid anode material and their battery characteristics are shown in Table 5.

[0357] [Example 11]

[0358] Using the porous carbon used as raw material in Example 6, the silane treatment conditions and acetylene treatment conditions were all the same as in Example 6, to obtain carbon-coated Si-C composite particles.

[0359] Add 150g of flake graphite (KS-6, Timcal), 40g of acetylene black (HS-100, Denki Kagaku Kogyo Co., Ltd.), and 10g of carboxymethyl cellulose to 800g of water, disperse and mix using a bead mill to obtain a dispersion of inorganic particles (solid content 25% by mass).

[0360] Using a micropipette, 0.500 g of pure water and 1.067 g of an aqueous solution of 4.5% pullulan were added to a sealed wide-mouth polyethylene bottle TB-1 (capacity: 105 mL, inner diameter of mouth × outer diameter of cap × total height (mm): φ57 × φ67 × 60). The mixture was then stirred for 2 minutes at 1000 rpm using a spin / revolution mixer (Sinkee Co., Ltd.). Next, 2.668 g of carbon-coated Si-C composite particles were added, and the mixture was again stirred for 2 minutes at 1000 rpm using a spin / revolution mixer. Then, 1.380 g of the above-mentioned conductive material dispersion (11% by weight solids) was added, and the mixture was again stirred for 2 minutes at 1000 rpm using a spin / revolution mixer. Add 0.111 g of a 4.8% by mass aqueous solution of trehalose to the obtained slurry using a micropipette, and mix again for 2 minutes at 1000 rpm using a rotation / revolution mixer. Spread Teflon (registered trademark) sheets and dry the resulting slurry on a hot plate at 110°C for 5 hours. Recover the dried solids and crush them in a mortar to obtain polymer-coated carbon-coated Si-C composites. The polymer content is 2.0% by mass. The physical properties of the obtained polymer-coated carbon-coated Si-C composite particles are shown in Table 4.

[0361] The obtained polymer-coated carbon Si-C composite particles and graphite particles were mixed to obtain a hybrid anode material. The mass ratio of polymer-coated carbon Si-C composite particles and graphite particles in the overall hybrid anode material and their battery characteristics are shown in Table 5.

[0362] [Example 12]

[0363] Using the porous carbon used as raw material in Example 6, the silane treatment conditions and acetylene treatment conditions were all the same as in Example 6, to obtain carbon-coated Si-C composite particles.

[0364] Add 150g of flake graphite (KS-6, Timcal), 40g of acetylene black (HS100, Denki Kagaku Kogyo Co., Ltd.), and 10g of carboxymethyl cellulose to 800g of water, disperse and mix using a bead mill to obtain a dispersion of inorganic particles (solid content 25% by mass).

[0365] Using a micropipette, 0.500 g of pure water and 1.068 g of an aqueous solution of 4.5% tamarind gum were added to a sealed wide-mouth polyethylene bottle TB-1 (capacity: 105 mL, inner diameter of mouth × outer diameter of cap × total height (mm): φ57 × φ67 × 60). The mixture was then stirred for 2 minutes at 1000 rpm using a spin / revolution mixer (Sinkee Co., Ltd.). Next, 2.667 g of carbon-coated Si-C composite particles were added, and the mixture was again stirred for 2 minutes at 1000 rpm using a spin / revolution mixer. Then, 1.382 g of a dispersion of the above inorganic particles (11% solids) was added, and the mixture was again stirred for 2 minutes at 1000 rpm using a spin / revolution mixer. 0.113 g of a 4.8% (w / w) aqueous solution of sorbitol was added to the obtained slurry using a micropipette, and the mixture was mixed again at 1000 rpm for 2 minutes using a spin / revolution mixer. The resulting slurry and Teflon (registered trademark) sheets were spread and dried on a hot plate at 110°C for 5 hours. The dried solids were recovered and crushed in a mortar to obtain polymer-coated carbon-coated Si-C composites. The polymer content was 2.1% (w / w). The properties of the obtained polymer-coated carbon-coated Si-C composite particles are shown in Table 4.

[0366] The obtained polymer-coated carbon Si-C composite particles and graphite particles were mixed to obtain a hybrid anode material. The mass ratio of polymer-coated carbon Si-C composite particles and graphite particles in the overall hybrid anode material and their battery characteristics are shown in Table 5.

[0367] [Example 13]

[0368] Using the porous carbon used as raw material in Example 6, the silane treatment conditions and acetylene treatment conditions were all the same as in Example 6, to obtain carbon-coated Si-C composite particles.

[0369] Add 150g of flake graphite (KS-6, Timcal), 40g of acetylene black (HS100, Denki Kagaku Kogyo Co., Ltd.), and 10g of carboxymethyl cellulose to 800g of water, disperse and mix using a bead mill to obtain a dispersion of inorganic particles (solid content 25% by mass).

[0370] Using a micropipette, 0.500 g of pure water and 1.065 g of an aqueous solution of 4.5% pectin were added to a sealed wide-mouth polyethylene bottle TB-1 (capacity: 105 mL, inner diameter of mouth × outer diameter of cap × total height (mm): φ57 × φ67 × 60). The mixture was then stirred for 2 minutes at 1000 rpm using a spin / revolution mixer (Sinkee Co., Ltd.). Next, 2.662 g of carbon-coated Si-C composite particles were added, and the mixture was again stirred for 2 minutes at 1000 rpm using a spin / revolution mixer. Finally, 1.378 g of the above inorganic particle dispersion (11% solids) was added, and the mixture was stirred again for 2 minutes at 1000 rpm using a spin / revolution mixer. 0.108 g of a 4.8% (w / w) aqueous solution of sorbitol was added to the obtained slurry using a micropipette, and the mixture was again mixed for 2 minutes at 1000 rpm using a rotation / revolution mixer. Teflon (registered trademark) sheets were spread, and the resulting slurry was dried for 5 hours on a hot plate at 110°C. The dried solids were recovered and crushed in a mortar to obtain polymer-coated carbon-coated Si-C composites. The polymer content was 1.9% (w / w). The properties of the obtained polymer-coated carbon-coated Si-C composite particles are shown in Table 4.

[0371] The obtained polymer-coated carbon Si-C composite particles and graphite particles were mixed to obtain a hybrid anode material. The mass ratio of polymer-coated carbon Si-C composite particles and graphite particles in the overall hybrid anode material and their battery characteristics are shown in Table 5.

[0372] [Comparative Examples 5-7]

[0373] For the BET specific surface area and particle size D shown in Table 3 V50 Porous carbon was subjected to silane treatment under the conditions shown in Table 3, causing silicon to precipitate on the surface and inside of the porous carbon, resulting in Si-C composite particles. The physical properties of the obtained Si-C composite particles are shown in Table 4.

[0374] The obtained Si-C composite particles and graphite particles were mixed to obtain a hybrid anode material. The mass ratio of Si-C composite particles to graphite particles in the overall hybrid anode material and their battery characteristics are shown in Table 5.

[0375]

[0376]

[0377]

[0378] The results above show that the oxygen content of the composite particles in Examples 6 to 13 did not increase significantly after 2 months, thus inhibiting oxidation. Furthermore, the battery characteristics also show high Si utilization, with a sufficient initial coulombic efficiency of over 86%, and the same initial coulombic efficiency is maintained after 2 months of storage.

[0379] On the other hand, in Comparative Examples 5-7, oxidation occurred over time, and the initial coulombic efficiency deteriorated after two months of storage. Furthermore, in Comparative Example 8, the BET specific surface area of ​​the carbon-coated Si-C composite particles was too high, resulting in insufficient initial coulombic efficiency.

[0380] Industrial availability

[0381] The carbon-coated Si-C composite particles of the present invention can be suitably used as negative electrode active materials constituting the negative electrode binder layer in lithium-ion secondary batteries, for example. The lithium-ion secondary battery of the present invention is suitable for use in IT devices such as smartphones and tablets, vacuum cleaners, power tools, electric bicycles, drones, car anti-theft systems, and applications requiring high capacity and high output.

Claims

1. A carbon-coated Si-C composite particle, wherein a carbonaceous layer exists on the surface of the Si-C composite particle containing carbon material and silicon. The carbon coverage rate of the carbonaceous layer on the surface of the Si-C composite particles is 70% or more. The carbon coverage rate is calculated as follows: based on cross-sectional SEM or TEM images, the outer perimeter of the Si-C composite particles and the length of the carbonaceous layer covering the Si-C composite particles are calculated, and the carbon coverage rate is calculated based on the ratio of the two. The BET specific surface area of ​​carbon-coated Si-C composite particles is 200 m². 2 / g or less In the Raman spectrum of the carbon-coated Si-C composite particles, R value is I D / I G For values ​​between 0.30 and 1.10, I D The strength of the D-band is 1360cm. -1 Nearby peak intensity, I G The strength of the G-belt is 1600 cm. -1 Nearby peak intensity, The peak caused by Si exists in the range of 450~495 cm⁻¹ -1 The intensity of this peak is expressed as I. Si hour, I Si / I G Below 0.15 The XRD patterns of the carbon-coated Si-C composite particles, as determined by powder XRD using Cu-Kα rays, are shown in the image. The full width at half maximum (FWHM) of the Si111 surface is greater than 3.00 degrees. The ratio of (peak intensity of SiC111 surface) to (peak intensity of Si111 surface) is less than 0.

01.

2. The carbon-coated Si-C composite particles according to claim 1, The true density obtained from the He hydrometer is 2.00~2.20 g / cm³. 3 .

3. The carbon-coated Si-C composite particles according to claim 1, 50% of the particle size D in the cumulative particle size distribution based on volume V50 The range is 2.0~30.0μm.

4. The carbon-coated Si-C composite particles according to claim 1, The silicon content is 20-70% of the mass of the carbon-coated Si-C composite particles.

5. The carbon-coated Si-C composite particles according to claim 1, The oxygen content is less than 10.0% by mass of the carbon-coated Si-C composite particles.

6. The carbon-coated Si-C composite particles according to claim 1, The oxygen content is less than 4.0% by mass of the carbon-coated Si-C composite particles.

7. The carbon-coated Si-C composite particles according to claim 1, The average thickness of the carbonaceous layer is 5~100 nm.

8. The carbon-coated Si-C composite particles according to claim 1, The R value is I D / I G It is greater than 0.30 and less than 1.

00.

9. The carbon-coated Si-C composite particles according to claim 1, The BET specific surface area of ​​carbon-coated Si-C composite particles is 6.0 m². 2 / g or less.

10. The carbon-coated Si-C composite particles according to claim 1, The BET specific surface area of ​​carbon-coated Si-C composite particles is 5.0~200.0 m². 2 / g.

11. A polymer-coated carbon-coated Si-C composite particle, wherein at least a portion of the surface of the carbon-coated Si-C composite particle according to any one of claims 1 to 10 has a polymer coating layer. The polymer coating contains inorganic particles and polymers selected from graphite and carbon black, and the polymer content is 0.1 to 10.0% by mass of the carbon-coated Si-C composite particles.

12. A negative electrode additive layer comprising carbon-coated Si-C composite particles as described in any one of claims 1 to 10.

13. A negative electrode composite layer comprising the polymer-coated carbon-coated Si-C composite particles of claim 11.

14. A lithium-ion secondary battery comprising the negative electrode binder layer as described in claim 12.

15. A lithium-ion secondary battery comprising the negative electrode binder layer as described in claim 13.

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