Silicon-based composite particles with a growth ring structure

Abstract

This invention relates to particulate silicon-carbon composite particles and a method for producing these particles, wherein the particles have a volume-based median diameter (D 50 The material consists of a bulk body with a diameter of 0.05 to 10 μm, a total Si content of 60 to 95 atomic percent, and a total C content of 5 to 40 atomic percent. The bulk body further has one or more internal shell-like spatial regions with increased carbon content, and the peak of the carbon-to-silicon elemental ratio is in the range of 1 to 15 atomic percentage points higher than the average elemental ratio of the bulk material.

Description

[Technical Field]

[0001] The present invention relates to a particulate silicon-carbon composite material that exhibits high charge / discharge capacity and first-cycle efficiency when used as a negative electrode active material for lithium-ion secondary batteries, and to a method for producing the same. [Background technology]

[0002] Carbon-containing fossil fuels currently account for approximately 80% of the world's energy demand. The majority of fossil fuels are burned after varying degrees of purification of the resulting exhaust / combustion gases before they are released into the atmosphere. These emissions cause serious pollution, global warming, and ocean acidification problems. Therefore, there is a growing societal demand for and concern for the development and implementation of climate-neutral and non-polluting alternatives.

[0003] Electricity is a versatile form of energy that produces little pollution when used for heating, driving electric engines, and operating electronic equipment. Furthermore, in certain sectors of society, portable storage of electrical energy is required to enable power supply. Lithium-ion batteries (LIBs) are currently the best commercially available battery type for applications requiring high volumetric and gravimetric energy storage density and high-efficiency delivery performance. However, to fully utilize power supply options, batteries with higher storage densities than currently available LIBs are needed.

[0004] The main energy storage constraint in current lithium-ion batteries (LIBs) is their graphite-based anodes, as graphite has a relatively limited capacity to store lithium. Therefore, in the battery field, there is a desire to find other materials more suitable than graphite as anode active materials for LIBs.

[0005] Silicon is known to have a relatively high ability to incorporate lithium and form silicon-lithium alloys. At room temperature, the most lithified phase of silicon is Li 3.75This phase is silicon, and while graphite has a theoretical specific energy of 372 mAh / g, this phase has a theoretical specific capacity of 3579 mAh / g. Therefore, the battery industry has been exploring solutions using silicon as the negative electrode active material for secondary lithium-ion batteries for over a decade.

[0006] However, lithium incorporation causes significant volume changes in silicon materials. Li is the most lithium-filled state. 3.75 In silicon (Si), the volume of the silicon material is approximately 320% larger compared to its non-lithified state. Furthermore, the electrolyte in contact with the active material surface typically reacts to form a lithium-containing solid phase known as the solid electrolyte interface layer (SEI). This SEI layer represents the irreversible loss of lithium in the electrochemical cell, and consequently, its energy storage capacity decreases. Since SEI layer formation mainly occurs during the initial charge-discharge cycle, the magnitude of the irreversible lithium loss associated with SEI layer formation is often expressed by the first-cycle efficiency (FCE) metric.

[0007] Furthermore, volume changes in silicon materials during lithium-ion and delithiation (charge-discharge) cycles have been shown to cause serious problems related to both structural degradation / collapse of the silicon material and instability of the SEI layer, resulting in unacceptably low cycle performance and large capacity losses in LIBs. It has been proposed that this integrity problem of silicon materials can be solved by using silicon in the form of nanoscale particles, usually less than 200 nm, preferably with a surface coating.

[0008] Sourice et al. (2016) (Non-Patent Literature 1) disclose the production of amorphous silicon core particles with a diameter of 30 nm by laser-driven chemical vapor deposition (LCVP) using helium-diluted silane gas. These particles are coated with a 1 nm thick carbon coating fabricated by a second-stage LCVP using ethylene gas. These particles are reported to maintain capacities of 1250 mAh.g⁻¹ at a C / 5 rate and 800 mAh.g⁻¹ at 2C after 500 charge-discharge cycles, exhibiting an excellent Coulomb efficiency of 99.95%.

[0009] Furthermore, it is known that nanoscale silicon-based particles containing other elements can be manufactured on an industrial scale by thermally induced decomposition of a mixture of precursor gases. An example of this is known from Patent Document 1, which discloses the production of amorphous particles with a diameter of 10 to 200 nm of silicon alloyed with 0.05 to 2 atomic percent of C and / or N by the simultaneous thermally induced decomposition of silicon and carbon-containing gases. In one embodiment, Si 0.98 C 0.02 The particles are disclosed to be produced by passing a homogeneous gas mixture of silane and ethene preheated to 400°C through the mixture, then passing this mixture through a reactor where it is mixed with nitrogen gas heated to a temperature of 810°C. The relative amounts of gases in the final gas mixture in the reactor were approximately 28 mol% silane, 1.5 mol% ethene, and the remainder (less than 70 mol%) nitrogen. The residence time was approximately 1 second. These particles are described to have a homogeneous structure.

[0010] Orthner et al. (2021) (Non-Patent Document 2) reported a study on the formation of amorphous silicon-based particles by flowing a mixture of silane diluted with nitrogen and ethylene gas through a tubular high-temperature wall reactor at 640, 690, and 1100 °C under atmospheric pressure. The residence time was 1 - 5 seconds. The silane gas concentration in the mixed gas was 10 - 30 vol%, and the ethylene gas was 0 - 11.3 vol%. The particles prepared at 640 °C and 690 °C were found to be amorphous and homogeneous, and in these particles prepared at 640 °C and 690 °C respectively, crystallization was either absent or only slight partial crystallization. The particle size varied in the range of 80 - 300 nm, and the average size was 200 nm. In the XRD analysis, the formation of SiC was not shown. In the XPS analysis, it was shown that the carbon content in the amorphous particles decreased almost linearly from the particle surface towards the bulk interior of the particles. The initial capacity of the particles was 3070 mAh / g, and after the second cycle, it decreased to 2200 mAh / g, but it was shown that the Coulomb efficiency stabilized above 99.5%. The high Coulomb efficiency was due to the low formation of the SEI layer due to the relatively large amount of carbon present on the particle surface. However, the particles prepared at 1100 °C were found to consist of a mixture of crystalline Si (about 15 wt%), amorphous Si (about 14 wt%) and amorphous SiC (about 71 wt%). The crystallite size of Si was 70 nm. Non-Patent Document 2 further reported that the formation of SiC was considered disadvantageous because the particles showed significantly lower first-cycle efficiency and specific capacity (917 mAh / g) compared to pure Si.

[0011] Patent Document 2 discloses that relatively high temperature and long-time heat treatment can convert an amorphous structure into a crystalline structure. This document discloses forming carbon-alloyed silicon particles by thermal-induced decomposition of a mixture of precursor gases as in Patent Document 1 above, and then heat-treating them at 800 - 900 °C for 10 - 240 minutes. The heat-treated particles were 25 - 180 m 2It is disclosed to have a BET of / g (diameter about 15 to 110 nm), contain C and / or N with a total content of 0.05 to 20 atomic %, and include nanosized crystallites with a diameter of 1 to 15 nm embedded therein.

[0012] It is further known that firing nanoscale silicon particles in a carbon matrix can provide stable particles and reduce the formation of the SEI layer. Wang et al. (2013) (Non-Patent Document 3) disclosed composite particles prepared by pyrolyzing a mixture of nanoscale silicon particles of 50 to 100 nm and coal tar pitch and then grinding the pyrolyzed mixture to form a composite of Si particles embedded in an amorphous carbon matrix (Si / αC). It was found that the composite containing 20 wt% Si exhibits stable lithium storage capacity for long-term cycling. This composite anode showed a capacity of 400.3 mAh / g and maintained a high capacity retention rate of 71.3% even after 1000 cycles. This is because in the (Si / αC) composite, silicon nanoparticles are encapsulated by amorphous SiOx and amorphous carbon, which provides sufficient conductivity and strong elasticity and can suppress the stress caused by the reaction between Si and Li during the charge-discharge process.

[0013] Zhu et al. (2018) (Non-Patent Document 4) reported a study investigating the correlation between the main physical parameters and electrochemical properties of silicon particles when used in the anode of LIBs. This investigation included three samples of crystalline silicon particles shown as S1, S2, and S3 having BET specific surface areas of 41.4, 36.11, and 7.33 m 2 / g, respectively. This corresponds to particle sizes of approximately 50, 100, and 150 nm for the spherical or pseudo-spherical components that are usually connected as a group to form each particle of the three samples. This corresponds to D50 particle sizes of approximately 50, 100, and 150 nm. Each of the three particle samples was mixed with conductive carbon and sodium alginate binder and then coated on a copper conductor to form three anode samples having particles of S1, S2, and S3, respectively. In each anode sample, the active material filling amount was about 0.5 mg / cm2 The anode samples were assembled into CR2032 type coin half-cells with identical electrolytes and cathodes to investigate the effect of silicon particle size on the electrochemical properties of the cells. This investigation showed that all three cells, S1, S2, and S3 respectively, had a reversible capacity of approximately 2500 mAh / g, while the first-cycle Coulomb efficiencies (FCE) obtained for S1, S2, and S3 were 78.51%, 83.12%, and 89.26%, respectively. The strong positive correlation between particle size and first-cycle efficiency is attributable to the difference in specific surface area. The increased specific surface area of ​​smaller particle size Si anodes inevitably increases the SEI formation reaction at the electrode-electrolyte interface, resulting in a higher irreversible SEI formation capability. However, it was found that reducing the particle size increases the rate capability of the Si anode. This is due to the shorter Li diffusion distance of smaller particle size Si anodes. At a rate of 20C, the supply capacities of S1, S2, and S3 were found to be 992.23, 323.17, and 233.43 mAh / g, respectively. Furthermore, the cycle performance of Si anodes with different particle sizes was found to be superior with smaller particle sizes, demonstrating excellent cycle stability. After 300 cycles, the capacity retention rates of S1, S2, and S3 were 96.12%, 93.98%, and 76.73%, respectively. This result was attributed to the fact that larger Si particles were more prone to shattering and cracking during repeated charge-discharge cycles, particularly when the particle size of the spherical "constituent blocks" was greater than 150 nm.

[0014] Another factor that favors the use of small silicon particles, as reported by Rhenlund et al. (2017) (Non-Patent Literature 5), is the controlled diffusion trapping of lithium within the electrode. Their investigation shows that during the cycle, small amounts of elemental lithium are trapped within the electrode active material by bidirectional diffusion, which moves lithium into the bulk of the active material, thereby significantly delaying the lithium extraction process. This Li-trapping mechanism was demonstrated using silicon particles with a D50 of 50 nm.

[0015] Sung et al. (2021) (Non-Patent Literature 6) reported on the nucleation and growth mechanisms of silicon and carbon-containing films on carbon substrates. This study included computer simulations based on density functional theory (DFT) and film synthesis by thermal decomposition of silane and ethylene gas mixtures at various silane-to-ethylene ratios, from silane alone to a ratio of 10:7, at 475°C. The synthesized films were grown on planar amorphous carbon nanoparticle substrates or on spherical graphite particles, then coated with 5 wt% pitch-based carbon and annealed at 900°C. These films were fabricated to thicknesses of 20–25 nm or 60–70 nm, requiring approximately 45 minutes or 78 minutes for growth, respectively. The particle size of the graphite particles on which the films were deposited is not explicitly stated in this document, but from Figure 3 of Non-Patent Literature 6, the graphite particles appear to be substantially spherical with a diameter of approximately 10 μm. DFT calculations suggested that, as schematically shown in Figure 1 of Non-Patent Literature 6, the formation of intercalated layers of SiC and C between silicon crystallites, by which carbon atoms released by the simultaneous decomposition of silane and ethylene function as an inhibitor of silicon atom crystal growth. The calculations further showed that the lower the silane-to-ethylene ratio, the smaller the silicon crystallites in the film. This result was confirmed by analysis of the synthesized films, which found that in pure Si films, the silicon crystallites in the film ranged in size from 40 nm upwards, while in silicon and carbon films, the film with the lowest carbon content had silicon crystallites of 3.8 nm, and the film with the highest carbon content had silicon crystallites of 0.85 nm. When the film was synthesized with a silane-to-ethylene ratio of 10:5 and composed of silicon and 36.8 atomic%C (corresponding to 20.1 wt%C), it was found to exhibit cycle stability comparable to graphite, and therefore the best cycle stability acceptable for commercial use, and to exhibit a specific capacity of 1974.3 mAh / g. The silicon crystallites in this film had an average grain size of 0.97 nm. The literature further reports, as expected, that the specific volume and FCE of the synthesized film decreased significantly with increasing carbon content. However, the volume did not decrease with increasing film thickness, as might have been expected.This result, as described in Non-Patent Document 6, demonstrates that it is possible to increase the Si content without any side effects of Si size growth, which was a serious constraint on high specific capacity by chemical vapor deposition processes.

[0016] Patent Document 3 discloses a composite material for secondary lithium batteries, as well as a method for producing and utilizing this new composite material. This new composite material contains nanosilicon and carbon atoms, with carbon atoms uniformly distributed within the nanosilicon at the atomic level. The carbon atoms and silicon atoms combine to form amorphous Si-C bonds, and no SiC crystallization peaks are observed in X-ray diffraction (XRD) spectroscopy. The solid-state nuclear magnetic resonance (NMR) detection 29Si NMR spectrum of the new composite material shows that when the silicon peak is located between -70 ppm and -130 ppm, the Si-C resonance peak is located between 20 ppm and -20 ppm, and the area ratio of the Si-C resonance peak to the silicon peak is (0.1, 5.0). The average particle size D of the new composite material is... 50 The particle size is disclosed to be between 1 nm and 50 μm, and the mass of carbon atoms accounts for 0.5 to 50% of the mass of the new composite material. [Prior art documents] [Patent Documents]

[0017] [Patent Document 1] International Publication No. 2021 / 160824 [Patent Document 2] International Publication No. 2022 / 200606 [Patent Document 3] Chinese Patent Application Publication No. 115881931 [Non-patent literature]

[0018] [Non-Patent Document 1] Sourice et al. (2016), "Core-shell amorphous silicon-carbon nanoparticles for high performance anodes in lithium-ion batteries", Journal of Power Sources, vol. 328, pp. 527-535 Non-Patent Document 2 Orthner et al. (2021), "Direct gas phase synthesis of amorphous Si / C nanoparticles as anode material for lithium ion battery", Journal of Alloys and Compounds, 870 (2021), 159315, https: / / doi.Org / 10.1016 / j.jallcom.2021.159315 Non-Patent Document 3 Wang Y.K., Chou S. L., Kim J. H., Liu H. K. and Dou S. X., "Nano-composites of silicon and carbon derived from coal tar pitch: Cheap anode materials for lithium-ion batteries with long cycle life and enhanced capacity" Electrochim. Acta, 2013, 93, 213-221 Non-Patent Document 4 Zhu et al. (2018), "Correlation between the physical parameters and the electrochemical performance of a silicon anode in lithium-ion batteries", Journal of Materiomics, 5, (2019), pp. 164-175,https: / / doi.org / 10.1016 / j.jmat.2019.03.005 [Non-Patent Document 5] Rhenlund et al. (2017), "Lithium trapping in alloy forming electrodes and current collectors for lithium based batteries", Energy Environ. Sci., 10, pp. 1350-1357, DOI: 10.1039 / c7ee00244k [Non-Patent Document 6] Sung et al. (2021), "Subnano-sized silicon anode via crystal growth inhibition mechanism and its application in a prototype battery pack", Nature energy, VOL 6, DECEMBER 2021, pp. 1164-1175, https: / / doi.org / 10.1038 / s41560-021-00945-z [Non-Patent Document 7] BH Toby, RB Von Dreele, GSAS-II: the genesis of a modern open-source all purpose crystallography software package, Journal of Applied Crystallography, 46 (2013) 544-549 [Non-Patent Document 8] AA Coelho, TOPAS and TOPAS-Academic: an optimization program integrating computer algebra and crystallographic objects written in C plus, Journal of Applied Crystallography, 51 (2018) 210-218 [Non-Patent Document 9] RW Cheary, AA Coelho, JP Cline, Fundamental parameters line profile fitting in laboratory diffractometers, Journal of Research of the National Institute of Standards and Technology, 109 (2004) 1-25 [Non-Patent Document 10] P. Thompson, ED Cox, JB Hastings, Rietveld Refinement of Debye- Scherrer Synchrotron X-ray Data from Al2O3, Journal of Applied Crystallography, 20 (1987) 79-83 [Overview of the project] [Problems that the invention aims to solve]

[0019] The main objective of the present invention is to provide a particulate silicon-carbon composite material that has high cycle capability when used as an active material for a rechargeable lithium-ion battery.

[0020] A further object of the present invention is to provide a method for producing the above-mentioned composite material. [Brief explanation of the drawing]

[0021] [Figure 1] This figure shows a high-angle annular dark-field scanning transmission electron microscope (TEM) image of an exemplary embodiment (S1) of multilayer particles according to the present invention. [Figure 2] This figure shows the carbon and silicon content determined by EELS along a line crossing the particles of sample S1 according to the present invention, and a TEM image of the same portion of the particles used for EELS analysis. [Figure 3] This is a high-resolution TEM image of the particles of sample S2 according to the present invention, which was heat-treated at 900°C for 2 hours. [Figure 4] This is a TEM image of a particle in embodiment (S4) of the present invention. [Figure 5] This is a TEM image of another particle in embodiment (S4) of the present invention. [Figure 6] This is a high-angle annular dark-field scanning transmission electron microscope image showing crystalline silicon nanodomains in secondary composite particles (sample S4) after heat treatment at 900°C for 30 minutes. [Figure 7] This figure shows the cycle data of a powder sample (sample S5) according to the present invention, which was produced by the method of the present invention and subsequently underwent heat treatment, PAN coating, and polymer crosslinking. [Figure 8] This figure shows the cycle data of a powder sample (sample S6) according to the present invention, which was manufactured by the method of the present invention and subsequently subjected to bitumen coating and heat treatment. [Figure 9] This is a post-cycle SEM image of bitumen-coated SiC composite particles (sample S6) after a long cycle. [Modes for carrying out the invention]

[0022] This invention is based on the observation that when silicon-carbon particles are used as a negative electrode active material in lithium-ion secondary batteries (LIBs), improved cycle stability is achieved when the carbon content is unevenly distributed in the silicon material and one or more relatively carbon-rich shell-like layers are formed within the bulk phase of the particles.

[0023] Each of these one or more relatively carbon-rich embedded shell-like layers is often visible as a ring surrounding the particle core in a transmission electron microscope (TEM) image of the particle's cross-section, similar to how annual rings are visible in a cross-section of a tree trunk. Figure 1 shows a TEM image of a multilayer particle (referred to here as sample S1), which is an embodiment of the particles according to the present invention, reference numeral 1. This image shows multiple rings with increased carbon content within a silicon-based matrix material, reference numeral 2. These rings do not need to be circular and may have an irregular shape, as shown in the image.

[0024] Although not bound by theory, the reason for the observed improvement in the cyclicity of such multilayer particles is thought to be that since the flow of electrons in the anode passes through only the solid phase, lithium ions capture electrons and initiate diffusion into the silicon-based particles mainly at some positions (at the contact points) on the particle surface and leave at the same positions. When this occurs, the flow of lithium ions moves in the same direction and may draw silicon atoms from the silicon-based particles, causing silicon leakage into the electrolyte. However, the presence of high-carbon regions inside the bulk of the silicon-based particles is thought to function as a partial barrier to this flow, thereby expanding lithium diffusion to a wider area inside the silicon-based particles. Also, the carbon-rich phase / region within the silicon-based particles is thought to make it more difficult for silicon to pass through, and thus the silicon-based particles are more stable with respect to charge-discharge cycles. One or more embedded shell-like layers that are relatively carbon-rich can be regarded as "armouring" the silicon-based bulk material. On the other hand, if these carbon-rich rings are overly carbon-rich, the lithium diffusion barrier becomes too high, and a decrease in the practically usable charge capacity at a specific charge-discharge rate may be measured.

[0025] [Particles] A first aspect of the present invention is a silicon-based particle made from a bulk material containing silicon and carbon, - The silicon-based particle has a volume-based median diameter D 50 determined by laser diffraction analysis conforming to ISO 13320:2020 of 0.05 to 10 μm, - The silicon-based particle - has a total carbon content C total of 5 to 40 atomic % based on the total mass of the silicon-based composite particle, - with the remainder being silicon and unintentional impurities, has a chemical composition, - The particle includes one or more internal shell-like space regions with an increased carbon content within the bulk material of the particle, and a peak C of elemental carbon content peakHowever, the average carbon content C average 1 to 15 atomic percentage points higher, - The peak C of the elemental carbon content in each of the one or more internal shell-like spatial regions within the bulk material. peak and the average carbon content C average The present invention relates to silicon-based particles, characterized in that the elemental properties are determined by elemental analysis by electron energy loss spectroscopy performed along a straight line extending at least from the core of the particle to the particle surface, but excluding the particle surface, and variations on a length scale of less than 5 nm, preferably less than 2 nm, and most preferably less than 1 nm, are smoothed out.

[0026] The term "core" used here refers to the volume center region of a particle, while the term "outer surface region" refers to the particle body adjacent to that outer surface, i.e., the particle body 1 to 10 nm below the particle surface. However, this term strictly refers to the bulk particle body in the surface region, excluding the surface coating (if present).

[0027] The term “internal shell-like spatial region within bulk material” as used herein refers to a localized spatial increase in carbon content within the particle body, formed as an internal layer encompassing the particle core. If two or more such internal shell-like spatial regions / layers exist, they should preferably be spaced apart from each other within the bulk material. The internal shell-like layers are typically substantially concentric, achieving a Russian-shaped structure as shown in the TEM photograph in Figure 1, which shows several shell-like layers within a particle of sample S1, labeled with reference number 2. Between the shell-like layers 2, the bulk material of the particle is labeled with reference number 3 in the figure.

[0028] These one or more relatively carbon-rich layers have a three-dimensional shape similar to a shell / coating deposited on the outer surface of a particle, except that these layers are located within the particle body and not on its outer surface. A mapping of the elemental balance of the cross-section of particle S1, shown in Figure 1, obtained along a straight line from the particle core to its outer surface, shows that the C content is substantially horizontal within the region representing bulk material, as shown in the elemental analysis diagram in Figure 2. average This generates a graph in which each of the shell-like layers rises as a local maximum value in terms of C content.

[0029] Electron energy loss spectroscopy (EELS) was performed on a straight line passing across the particle core of the particles having these internal shell-like layers. The elemental balance mapping typically displays a figure as shown in Figure 2. In this embodiment, the particles are approximately 800 nm in diameter and contain four shell-like layers, labeled reference numeral 2 in the figure. As shown in the figure, the total Si and C content within the particles is substantially uniform in the sense that the curves for Si and C content are horizontal. Thus, the (average) elemental ratio Si:C in the particle core is substantially equal to the (average) elemental ratio Si:C in the outer region of the particle, near its surface. The EELS figure of the particles from sample S1, shown in Figure 2, includes a sharp increase at the surface. This is because the sample of these particles is coated with an amorphous carbon surface.

[0030] Each of the internal shell-like layers 2 is represented in the EELS diagram shown in Figure 2 by a vertical dotted line located on a descending peak in Si content and a corresponding ascending peak in carbon content. This figure also shows a cross-section of a TEM image of the same portion of the particle used for EELS analysis, showing that the inverted peaks in Si and C content along the lines on the Si and C content curves are attributable to the internal shell-like layers 2.

[0031] The graph for carbon content shows peaks indicating increased carbon content at distances of approximately 250, 380, 300, and 650 nm on both sides of the particle center, while the graph for silicon content shows corresponding (but opposite) peaks indicating decreased silicon content at the same locations from the particle center. The superimposed vertical lines in Figure 2 indicate that each of the corresponding peaks for increased carbon content and decreased silicon content at these locations from the particle center coincides with the annular ring shown in the TEM image. These are each of the corresponding pairs of peaks for increased C and decreased Si on the graphs for carbon and silicon content. Therefore, C peak C average A value at least one atomic percentage point higher is an indicator of the presence of a relatively carbon-rich embedded shell-like layer according to the present invention.

[0032] In one embodiment, C peak Determining the content may advantageously involve smoothing out variations on small length scales, such as less than 2 nm, most preferably less than 1 nm, by digital filtering of signal noise.

[0033] Digital filtering of signal noise in measurements is a standard procedure in most experimental procedures and is therefore well known to those skilled in the art. One way to do this is to recalculate each data point as the average of several neighboring data points from the original dataset. In a Gaussian filter, the contribution of neighboring data points is weighted based on the distance from the data point, which is calculated according to a Gaussian distribution function. Thus, in one embodiment, smoothing of the measurements can be achieved using a Gaussian digital filter or by averaging measurements obtained over multiple neighboring spatial measurement regions. The width of the digital filter should be less than 5 nm, preferably less than 2 nm, and most preferably less than 1 nm, in order to avoid the removal of information regarding actual concentration variations.

[0034] In one embodiment, elemental analysis by electron energy loss spectroscopy reveals the carbon content of at least one relatively carbon-rich shell-like layer. peak The decision and C average The decision was, -A cross-sectional slice less than 70 nm thick, including the particle center, is prepared using a focused ion beam (FIB). - EELS elemental analysis is performed along a straight line passing through the cross-section from the center of the slice to the outer surface, and then, -Optionally, the measured values ​​are smoothed by using a Gaussian digital filter or by averaging the measured values ​​obtained for multiple adjacent spatial measurement regions. - Using the local maximum value of the carbon content of the first peak along the straight line, located away from the particle center, the C of the first peak peak Furthermore, if present, a similar C for each of the other corresponding pairs of peaks on the aforementioned straight line where the carbon content increases and the silicon content decreases. peak The decision was made, -By averaging the determined C content of all measurement points along the aforementioned straight line, C average to decide It is obtained by doing so.

[0035] Observations of one or more shell-like layers within particles according to the present invention indicate that there may be an upper limit to the carbon concentration. While not bound by theory, this is thought to be because an increase in carbon concentration in the shell-like layers contributes to both stabilization and a decrease in lithium mobility. At relatively low increases in carbon concentration, the stabilization effect is observed to be dominant, while at higher carbon content, the effect of decreased lithium mobility becomes more pronounced than the increase in stability. Empirical observations made by the inventors indicate that the local increase in carbon in one or more shell-like layers is advantageously less than 15 atomic percent points. That is, if the total carbon content of the particles is 20 atomic percent, the (local) carbon content at the peaks of one or more shell-like layers should preferably be 35 atomic percent or less.

[0036] In one embodiment, at least one relatively carbon-rich shell-like layer C peak C is the average carbon content. average Advantageously, the range is 1 to 12 atomic percent points higher, preferably 1 to 10 atomic percent points, more preferably 2 to 8 atomic percent points, more preferably 3 to 6 atomic percent points, and most preferably 4 to 5 atomic percent points higher.

[0037] The terms "total carbon content" or "total silicon content" used herein refer to the total carbon or silicon content in the bulk material and are measures of the average carbon or silicon content in the bulk material. For example, if the total carbon content in the bulk material is 5 atomic percent (sometimes expressed as at%), then on average there are 5 carbon atoms for every 100 atoms in the bulk material. Similarly, the term "total chemical composition of particles" used herein refers to the total content of elements present throughout the particle. However, it does not include the material / elements of any coating on the particle surface. Total content refers only to the material of particles without any surface coating. The determination of the total content of elements in the bulk material, such as silicon, carbon, hydrogen, and / or oxygen, can be obtained, for example, by atomic absorption spectrometry (AA), inductively coupled plasma mass spectrometry (ICP-MS), ICP-OES, or X-ray fluorescence spectrometry (XRF). These are well-known techniques mastered by those skilled in the art. The total carbon content of particles may also be determined by burning a sample of the particles and measuring / determining the amount of carbon dioxide produced. The total carbon content of secondary particles may also be determined by burning a sample of the particles and measuring / determining the amount of carbon dioxide produced. For coated particles, the elemental composition of particles inside the coating can be determined by using focused ion beam scanning electron microscopy or tunneling electron microscopy (FIB-SEM or FIB / TEM) cross-sections combined with elemental analysis techniques by electron dispersion spectroscopy (EDS) and / or electron energy loss spectroscopy (EELS). These are also well-known techniques mastered by those skilled in the art. The hydrogen content can be estimated by thermally decomposing the sample in an inert atmosphere and measuring the released hydrogen gas with a mass spectrometer. These are also well-known techniques mastered by those skilled in the art.

[0038] The term “bulk” as used herein is used to mean “the majority of something.” That is, the “bulk material” of the particles according to the claims is the main component of the particle body. Although not bound by theory, the bulk material of the particles according to the first aspect of the present invention is considered to be a silicon-based chemical phase, where carbon atoms are thought to substitute for silicon atoms in the molecular structure (which may be single-crystal or polycrystalline and / or amorphous) of the silicon-based chemical phase having spatial variations in the elemental balance of Si and C that form the inner shell / layer. In any case, whether or not this assumption is correct, the inventors have not known any observation or empirical evidence to indicate or suggest that the inner shell / layer in the bulk material of the particles according to the present invention is a separate chemical phase, thereby causing the particles to become composite particles. On the contrary, all evidence suggests that these inner shell / layer is a spatial variation in the elemental balance of the molecular structure of the silicon-based chemical phase constituting the bulk material of the particles, and therefore an integral part of the bulk material, as would be expected if the particles were grown by CVD with a temporary change in reaction kinetics to make them more carbon-rich.

[0039] C peak to C average Limiting the carbon content to 1-15 atomic percentage points higher is introduced to avoid detecting signal noise and / or final arbitrary elemental ratio variations as a relatively carbon-rich embedding layer. Furthermore, such an increase in carbon content in the layer is thought to make the particles more robust to volume changes during lithium-ion secondary battery active materials. Since the diffusion rates of lithium and silicon are strong functions of the local Si:C ratio, even small changes in carbon content are expected to have a beneficial effect on particle stability by making expansion more homogeneous.

[0040] The determination of elemental ratios in different parts of a particle is obtained by elemental analysis using electron energy loss spectroscopy (EELS). EELS involves passing an electron beam through a thin sample of the specimen (typically less than 70 nm thick) and analyzing the content of the sample using electron scattering. EELS instruments are usually integrated into transmission electron microscopes (TEM) and / or scanning transmission electron microscopes (STEM). STEM-based EELS has theoretical spatial resolution down to the atomic scale (0.1–1 nm) for samples with clear boundaries, but has somewhat coarser resolution for samples with depth variations, such as the particle sample in this invention. In any case, STEM-based EELS can detect changes in the elemental content of a sample down to a resolution of a few nanometers. Therefore, by using EELS to scan and determine the elemental composition of a sliced ​​sample of the particle according to the present invention along a straight line intersecting the cross-section of the particle containing the center point of the sliced ​​sample, each of at least one relatively carbon-rich shell-like layers appears as a peak with a local maximum value in the curve representing the carbon content of the bulk material (which has elemental ratios close to the average ratio determined by the total carbon content). Similarly, each of the at least one relatively carbon-rich shell-like layers appears as an opposite peak (compared to the carbon curve) with a local minimum in the curve representing the silicon content of the bulk material. An example of this is shown in Figure 2.

[0041] EELS elemental analysis has been used for several decades and is therefore well known to those skilled in the art. It is known that EELS elemental analysis is sensitive to the instruments and sample preparation methods used, which can affect the determination of the absolute atomic composition of the sample. Performing an analysis that provides a robust and accurate answer regarding the elemental balance in the sample is within the ordinary skill of those skilled in the art. This is especially true when the measurement aims to find relative changes in the content of elements (C and Si), as is the case with these particles. Therefore, EELS elemental analysis is particularly robust and reliable, and the use of EELS analysis is important for C average C for peakIt is known to be very suitable for determining content. Therefore, it is unnecessary to further describe how the carbon content of at least one relatively carbon-rich embedded shell-like layer is determined by elemental analysis by electron energy loss spectroscopy. Those skilled in the art can reliably determine whether a sample of such particles has one or more embedded layers with a relatively increased carbon content, as described above.

[0042] However, the EELS elemental analysis described herein is performed as follows: The EELS sample powder was dispersed on a clean, mirror-polished Si wafer. Transmission electron microscope (TEM) samples were prepared by focused ion beam (FIB) treatment using a Thermo Fisher Scientific Helios G4 UX dual-beam system. In FIB, particles selected for TEM were first coated with a carbon or platinum protective layer. The first part of the protective layer was Ga in the outer part of the particle. + To avoid ion beam damage, the layers were formed by electron beam-assisted deposition. The upper and main portions of the protective layer were formed by ion beam-assisted deposition. After protective coating, the coated particles were cut out and transferred to a dedicated Cu TEM half-grid using a tungsten "EasyLift" micromanipulator following a standard lift-out procedure. All roughening was performed using Ga + The ion acceleration voltage was 30kV. For the final thinning, to minimize surface damage, the TEM sample and thin film were thinned at 5kV, followed by 2kV. The final thickness of the TEM sample ranged from 30 to 60 nm.

[0043] TEM was performed using a double spherical aberration-corrected cold cathode field emission gun JEOL ARM 200FC, operated at 200kV. This apparatus included a Quantum ER spectrometer for electron energy loss spectroscopy (EELS) and a 100mm solid angle covering 0.98 sr for energy dispersive X-ray spectroscopy (EDS). 2The system is equipped with a Gatan Image Filter (GIF) featuring a Centurio silicon drift detector. All spectroscopic measurements were performed in scanning transmission electron microscopy (STEM) mode by simultaneously executing both EDS and dual EELS, meaning that an EDS spectrum and two EEL spectra were acquired for each pixel in the mapping region. For EELS, a low-loss spectrum covering the zero-loss peak and a high-loss spectrum covering the K peaks of carbon, oxygen, and silicon were acquired with a dispersion of 1 eV / channel on a 2048 × 2048 pixel CCD camera installed at the end of the GIF. All quantification of chemical composition was based on EELS data. For each pixel, the low-loss spectrum was used for both energy calibration and deconvolution of multiple scattering in the high-loss spectrum. EELS data was quantified using GMS3, version 3.4, to obtain the chemical composition within the mapping region. The corresponding EDS data was primarily used to confirm the presence of elements other than silicon, carbon, and oxygen within the particles. The graph showing the line profile of chemical composition as a function of distance in the FIB creation cross-section is based on a rectangular map passing through the center of the mapped particle. The width of these maps was typically in the range of 10–40 nm. To obtain better statistics in the shown line profiles, all pixels perpendicular to the line profile direction were summed and averaged.

[0044] Alternatively, in one embodiment, elemental analysis by electron energy loss spectroscopy reveals at least one relatively carbon-rich shell-like layer of C peak The determination is obtained by the same procedure as above, except that it is performed over the entire cross-section of the particle sample. This latter alternative method has the advantage of more robustly identifying the presence of a relatively carbon-rich shell-like layer within the bulk material of the particle. This is because, as shown in Figure 2, the peaks on the carbon curve and similarly on the silicon curve are nearly identical and are distributed symmetrically around the particle center. Such a form of change in carbon content along a straight line (and the corresponding reverse change in silicon content) is a strong indicator of an embedded shell-like layer.

[0045] Due to transient changes in reaction kinetics during CVD growth, one or more relatively carbon-rich embedded shell-like layers are formed. As a result, changes in the elemental composition of the bulk material associated with such shell-like layers are formed as peaks / local maximums on a graph showing the elemental composition of the bulk material as a function of the distance from the particle center to its outer surface, as shown in Figure 2. Therefore, the "peak of carbon content" used here refers to the C peak The term "cosmetic layer" refers to the local maximum value of carbon content associated with relatively carbon-rich shell-like layers.

[0046] In one embodiment, particles according to the first aspect of the present invention may, in some embodiments, further include an outer shell / layer / coating deposited on their outer surface. This outer shell / layer / coating may be formed of any material known to those skilled in the art as suitable for silicon particles used as a negative electrode active material in lithium-ion batteries. An example of a suitable outer shell / layer / coating is amorphous carbon.

[0047] In one embodiment, the total chemical composition of the particles is: -Total content of carbon is 10-37 atomic%, preferably 15-33 atomic%, more preferably 20-30 atomic%, and most preferably 23-26 atomic%, -Silicon and the remainder which are unintended impurities This includes.

[0048] The bulk material of particles according to the present invention is such that the total content of Si and C in the bulk material is within the above range, i.e., C tot In addition to carbon and silicon, any other elements may be included, as long as silicon makes up the remainder of the chemical composition, with a minimum of 5 atomic percent and a maximum of 40 atomic percent.

[0049] The advantage of applying condensation and chemical vapor deposition of a mixture of silicon-containing and carbon-containing precursor gases under a protective atmosphere is that this method provides excellent control over which elements are introduced into the reactor and, consequently, which elements are present in the resulting particles. For example, if the silicon-containing precursor gas is silane and the carbon-containing precursor gas is hydrocarbon, the reactor will mainly contain elements such as hydrogen, carbon, and silicon, along with typically inert gas elements (nitrogen, argon, etc.) and trace amounts of oxygen (residue of air). Therefore, the resulting particles will mainly contain silicon and carbon, as well as small amounts of hydrogen, and unavoidable impurities and final traces of oxygen. However, when measuring the actual product, 0.3-4% by weight of oxygen is often detected, which is due to exposure to air that occurs after the manufacturing process is complete, for example, during the preparation of characterization samples.

[0050] Ideally, oxygen should not be present within the particles. This is because the presence of oxygen causes the loss of irreversible bonds between lithium atoms, reducing the first-cycle efficiency of LIBs using these particles as negative electrode active material. However, in practice, it is difficult to protect the particles from contact with surrounding oxygen, so the term "unintended impurity" used here may include as much as 4 atomic percent of oxygen in some embodiments, but is preferably less than 0.5 atomic percent. Therefore, in one embodiment, the total oxygen content of the particles according to the present invention is less than 4 atomic percent, preferably less than 3 atomic percent, more preferably less than 2 atomic percent, more preferably less than 1 atomic percent, and most preferably less than 0.5 atomic percent.

[0051] Furthermore, since the particles according to the present invention in one embodiment are produced by condensation of a hydrogen-containing precursor gas and chemical vapor deposition, the resulting particles may still contain residual / trace amounts of hydrogen in the final product. Theoretically, when the hydrogen content is reduced to less than one atom per silicon or carbon atom, the particles are expected to solidify. Since hydrogen bonded to silicon is more likely to detach at lower temperatures than hydrogen bonded to carbon, a hydrogen content of less than one atom per carbon atom is easily achievable. Ideally, hydrogen should be removed because it can contribute to HF formation when interacting with LiPF6 salts in the electrolyte of a Li-ion battery. Therefore, the term "unintended impurity" as used herein can, in one embodiment, contain as much as 30 atomic percent of hydrogen, but preferably less than 1 atomic percent, depending on the temperature and residence time applied to particle formation. Thus, in one embodiment, the particles may contain less than 30 atomic percent of H, preferably less than 20 atomic percent of H, more preferably less than 15 atomic percent, more preferably less than 10 atomic percent, more preferably less than 5 atomic percent, and most preferably less than 1 atomic percent.

[0052] In a particularly preferred embodiment, the elemental composition of the particles according to the present invention is advantageously as follows: -Total carbon content C total The amount is 5-30 atomic%, preferably 6-25 atomic%, preferably 7-20 atomic%, more preferably 8-15 atomic%, more preferably 9-14 atomic%, and most preferably 10-12 atomic%, - The total amount of oxygen in the particles is 0.1 to 4 atomic%, preferably 0.2 to 3 atomic%, more preferably 0.3 to 2 atomic%, more preferably 0.4 to 1 atomic%, and most preferably 0.5 to 1 atomic%. - The total amount of hydrogen in the particles is less than 5 atomic percent, preferably less than 1 atomic percent, and furthermore, - The remainder consists of Si and unintended impurities.

[0053] In one embodiment, the particles according to the present invention are advantageously characterized by having a relatively large particle median diameter D 50This is because it is known that the first cycle loss of lithium due to the formation of a solid electrolyte interface increases with increasing (total) particle surface area of ​​the active material. Furthermore, especially D 50 When the diameter is relatively large, a relatively narrow particle size distribution is beneficial. This is because there are fewer particles that are "too big" and / or too small. As particles get larger, the diffusion distance of lithium atoms moving in and out of the particle increases, and the risk of lithium being diffusely trapped within the particle increases. Therefore, particles that are too big are more or less "dead" as active material. On the other hand, if strict requirements are set for the maximum size of the largest particles, a narrow distribution will result in fewer small particles. Particles that are too small have a large surface area, leading to lower first-cycle efficiency.

[0054] Therefore, in one embodiment, the particles according to the present invention further have a volume-based median diameter D determined by laser diffraction analysis in accordance with the ISO 13320:2020 standard. 50 However, the particle size is 1 to 9 μm, preferably 1.1 to 8 μm, more preferably 1.2 to 7 μm, more preferably 1.6 to 6 μm, and most preferably 2 to 5 μm.

[0055] In one embodiment, the plurality of particles according to the present invention are determined by laser diffraction analysis in accordance with the ISO 13320:2020 standard. 90 / D 10 The ratio is in the range of 1 to 10, preferably 2 to 8, and most preferably 3 to 6.

[0056] In one embodiment, the particles according to the present invention may further include a plurality of nanoscale silicon domains embedded in a bulk material. The advantage of this embodiment of the particles is that the primary nanodomains are thought to increase the lithiation capacity without impairing the cycle characteristics when used as an active material in lithium-ion secondary batteries. The lithiation capacity is increased because the silicon domains provide a high-capacity storage volume for lithium atoms, and the cycle characteristics are improved because nanoscale silicon is more robust and withstands volume fluctuations associated with lithiation / delithiation cycles much better than larger silicon domains. Furthermore, since lithiation of silicon domains involves significant cleavage / breaking of Si-Si bonds, it is also considered very attractive that the CC bonds remain intact and the particle structure is maintained even in the lithified state.

[0057] In one embodiment, the average diameter of nanoscale silicon domains, as determined by Rietveld refinement of X-ray powder diffraction (XPD) data, is typically in the range of 0.5 to 10 nm, preferably 1 to 8 nm, more preferably 2 to 7 nm, more preferably 3 to 6 nm, and most preferably 4 to 5 nm. Optionally, the particles may be heat-treated to crystallize potentially amorphous nanoscale silicon domains embedded within the particles before the average particle size of the primary particles is determined by the Rietveld method. The heat treatment is carried out at 900°C or higher for at least 30 minutes, preferably at a heating rate of 1°C per minute above 600°C.

[0058] The average particle size of nanoscale silicon domains can be determined by Rietveld analysis of XPD data, which is well known and mastered by those skilled in the art. Since Rietveld analysis detects the crystalline phase, determining the primary particle size may, advantageously, include a pre-heat treatment at approximately 900°C for 30 minutes to ensure that the final amorphous nanoscale silicon domains present in the bulk material of the particles crystallize before determination. An example of such analysis is so-called Rietveld refinement, which involves fitting XPD data calculated from a crystalline Si model to experimental data obtained by XPD measurement of secondary particle samples using the least squares method. Rietveld refinement can be performed using freely available software such as GSAS-II (Non-Patent Literature 7) or commercially available software such as Topas (Non-Patent Literature 8). The instrumental contribution to the width of the Bragg peak is calculated from the geometric shape of the instrument ("fundamental parameter method" (Non-Patent Literature 9)) or described by the Thomson-Cox-Hastings pseudo-Voigt function experimentally determined from highly crystalline standards such as NIST SRM 640f silicon (Non-Patent Literature 10). The instrumental contribution to the Bragg peak remains fixed during Rietveld refinement. All observed additional broadening of the Bragg peak is assumed to be due to minute crystallite size and to have a Lorentz shape. This crystallite size broadening is modeled by refining the calculated additional contribution β to the Bragg peak width, which changes with the scattering angle as follows.

[0059]

number

[0060] Furthermore, the particles according to the present invention are advantageously further provided with a coating on their outer surface to protect the particle surface from oxidation when in contact with air and from reaction with electrolytes that form the SEI layer. Examples of outer coatings include amorphous or crystalline carbon allotropes, polymers, resins, crosslinked or pyrolytic polymers or resins, Li x Si y O, Ti x O, Al x Examples include oxides such as 0, or any combination thereof. In one embodiment, the coating thickness is in the range of 1 to 100 nm, preferably 2 to 60 nm, more preferably 3 to 20 nm, and most preferably 3 to 10 nm, in order to improve surface properties, reduce fire risk, and promote the formation of a stable solid electrolyte interface (SEI). The coating can be applied using wet chemical methods, CVD, ALD, or other techniques.

[0061] The present invention is not limited to a specific coating material or a specific particle coating method, and any coating and coating method known to those skilled in the art for coating silicon particles can be used.

[0062] When applying a carbon surface coating to particles, it is advantageous to heat-treat the carbon using methods such as the following, in order to obtain good transport and adhesion properties later. - Crosslinking / cyclization only; significant amount of hydrogen remains in the particles and coating; more elastic carbon phase (~300°C); low bulk power stability; low / medium capacity. - Low-temperature annealing and CVD coating (amorphous silicon remains, resulting in faster initial cycle charging) (600~800℃) - Medium-temperature annealing and CVD coating (improved lithium conductivity, improved CE, high capacity, however, some or all of the Si nanodomains crystallize) (800~1000℃) - High-temperature carbonization (high carbon diffusion, risk of excessive SiC formation at the Si-C interface, risk of capacity reduction, however, coating quality may be further improved) (above 1000°C).

[0063] In a preferred embodiment, the particles according to the present invention further include a surface coating of amorphous or crystalline carbon having a thickness of 0.5 to 10 nm, preferably 2 to 5 nm, as determined by Auger spectroscopy.

[0064] In particular, carbon coatings in the 1–10 nm range can be characterized with considerable accuracy using Auger spectroscopy. Furthermore, FIB-TEM cross-sectional images clearly distinguish the carbon coating from the particles, using a clear contrast between heavy silicon atoms and light carbon atoms. This characterization can be performed by those skilled in the art. Similarly, any oxide coating can be clearly separated from the silicon-based bulk by the same method.

[0065] In one embodiment, a first aspect of the present invention relates to silicon-based particles made from a bulk material containing silicon and carbon, - The silicon-based particles have a volume-based median diameter D determined by laser diffraction analysis in accordance with ISO 13320:2020. 50 The size is 0.05 to 10 μm. -The silicon-based particles are, -Total carbon content C total However, it is 5-40 atomic percent based on the total mass of silicon-based composite particles. -The remainder is silicon and unintended impurities. Having a chemical composition, - The particles include one or more internal shell-like spatial regions within the bulk material of the particles, with an increased carbon content, and the peak C of the elemental carbon content peak C is the average carbon content. average 1 to 15 atomic percentage points higher than - The peak C of the elemental carbon content in each of the one or more internal shell-like spatial regions within the bulk material. peak and the average carbon content C averageThe elemental properties are determined by elemental analysis using electron energy loss spectroscopy performed along a straight line extending at least from the particle core to the particle surface, but excluding the particle surface, and variations on a length scale of less than 5 nm, preferably less than 2 nm, and most preferably less than 1 nm are smoothed out.

[0066] [Method for manufacturing particles] The silicon-based and carbon-based composite particles according to the present invention are preferably produced by condensing a mixture of silicon-containing precursor gas and carbon-containing precursor gas and performing chemical vapor deposition (CVD) in a protective atmosphere (i.e., an atmosphere that contains no oxygen or only trace amounts of oxygen).

[0067] A second aspect of the present invention relates to a method for producing silicon-based particles according to the first aspect of the present invention, wherein this method is - A step of forming a precursor gas mixture comprising a first precursor gas of a silicon-containing compound and a second precursor gas of a carbon-containing compound, wherein the atomic ratio of silicon to carbon (Si:C) in the precursor gas mixture is in the range of 0.2 to 50. - A step of preheating the precursor gas mixture to a temperature of 300-350°C, -A step using a reactor having a decomposition chamber heated to a first reaction temperature at which the precursor gas mixture condenses to form particle seeds, wherein the particle seeds are then grown by chemical vapor decomposition (CVD), - The step of injecting the precursor gas mixture into the decomposition chamber, The above method further, - A step of maintaining the injected precursor gas mixture in the chamber for a residence time in the range of 1 to 300 seconds, and during the residence time, subjecting the injected precursor gas mixture to at least one temperature change, from the first reaction temperature to the second reaction temperature, and then back to the first reaction temperature. -The step of extracting the particles from the decomposition chamber, - The absolute temperature difference between the first reaction temperature and the second reaction temperature is in the range of 1 to 100°C, preferably 3 to 75°C, more preferably 5 to 50°C, more preferably 10 to 35°C, and most preferably 20 to 25°C.

[0068] The term "absolute temperature change of X°C" used here means that the temperature difference between the first reaction temperature and the second reaction temperature is either X°C lower than the first reaction temperature, or X°C higher than the first reaction temperature.

[0069] In one embodiment, the first reaction temperature is in the range of 450 to 900°C, preferably 500 to 800°C, more preferably 550 to 700°C, and most preferably 600 to 650°C.

[0070] In one embodiment, the residence time is advantageously in the range of 2 to 250 seconds, preferably 3 to 200 seconds, more preferably 5 to 150 seconds, more preferably 10 to 120 seconds, more preferably 15 to 90 seconds, and most preferably 20 to 60 seconds.

[0071] In one embodiment, the atomic ratio of silicon to carbon (Si:C) in the precursor gas mixture is advantageously in the range of 0.3 to 45, preferably 0.4 to 40, more preferably 0.5 to 30, more preferably 0.6 to 25, more preferably 0.8 to 15, more preferably 1.0 to 8, more preferably 1.2 to 5, and most preferably 1.5 to 2.0.

[0072] While not bound by theory, it is thought that periodic temperature fluctuations during particle growth alter the relative reaction kinetics of the CVD growth process. Lower reaction temperatures result in relatively high concentrations of silicon deposited in the sediment, leading to a correspondingly lower carbon concentration, while higher reaction temperatures increase the carbon concentration in the sediment. Therefore, by undergoing several consecutive periodic temperature fluctuations spaced apart during particle CVD growth, the particles form a series of carbon-rich shell-like layers separated by an intermediate bulk layer having a relatively high silicon content and a correspondingly low carbon content.

[0073] In one embodiment, the method according to the present invention further involves a first reaction temperature of 5 × 10 3 ~6×10 5 The process may include pre-filling the decomposition chamber with a first reactor gas having an initial pressure in the range of Pa. This feature has the effect of rapidly heating the injected precursor gas mixture to the first reaction temperature by mixing it with a first reaction gas phase preheated in the decomposition chamber to form a second reactor gas mixture. The first reactor gas phase may be a completely inert gas such as Ar, or a gas inert at the relevant temperature such as N2, or exhaust gas from a previous manufacturing process (including unreacted species) containing hydrogen and some residual silicon or carbon precursor species at concentrations too low to form particles at the relevant temperature.

[0074] While not bound by theory, this feature is thought to enable the formation of particle embodiments containing multiple nanoscale silicon domains embedded in the bulk material described above. The mechanism is thought to be that when producing particles by condensation and chemical vapor deposition of a mixture of silicon-containing precursor gas and carbon-containing precursor gas in a protective atmosphere, the silicon-containing precursor gas begins to decompose and condense depending on the ratio of precursor gases and the applied reaction conditions, forming a vast number of minute nanodomains consisting of mostly pure silicon. Subsequently, the carbon-containing precursor gas begins to decompose and condense together with the remaining silicon-containing precursor gas, and the bulk phase of silicon and carbon grows on the already formed minute nanodomains of mostly pure silicon via chemical vapor deposition. The domain size is determined by both the utilization of the different precursor gases and the rate at which these particles are formed and come into contact. Since the chemical reaction in this initial formation stage is strongly temperature-dependent, the domain size is also expected to be strongly dependent on the heating rate and temperature.

[0075] Furthermore, if the silicon precursor gas is SiH4, the initial reaction is assumed to begin with H2 detaching from SiH4, forming a highly reactive SiH2 molecule. SiH2 then reacts with another SiH4 to form Si2H6, or with a carbon precursor gas molecule, such as C2H4, to form SiC2H6, or with C2H2 to form SiC2H4. The ratio of Si2H6 to SiC2H4 or SiC2H6, and the reactivity of the carbon-containing gas with the silicon nanodomains, are strongly temperature-dependent. Therefore, even small changes in temperature can affect the relative incorporation probabilities of Si and C in the final product.

[0076] Both of these explanations (and under various conditions, both may be true) lead to the conclusion that small changes in temperature result in significant variations in the relative consumption rates of the Si and C precursor gases. In at least some gas mixtures, an increase in reactor temperature leads to an increase in the relative consumption of C, and a decrease in temperature leads to an increase in the relative consumption of Si.

[0077] In one embodiment of the present invention, temperature fluctuations are achieved by transporting gas between different zones of the decomposition chamber, heated to a first reaction temperature and a second reaction temperature, respectively, by thermal convection. Particles carried by the gas flow can exchange energy with the chamber walls by convection and / or radiation, meaning that the temperature controlling particle growth varies depending on the location within the decomposition chamber.

[0078] In one embodiment of the present invention, the temperature change is due to turbulence generated when the gas enters the high-temperature wall decomposition chamber. When the particles are near the nozzle supplying the gas, the temperature drops to a second reaction temperature, but when the particles are on the reactor wall far from the nozzle, the temperature reaches the first reaction temperature.

[0079] In another embodiment of the present invention, the gas is transported by laminar flow or near plug-flow through a tubular high-temperature wall decomposition chamber having alternating temperature zones heated to first and second reaction temperatures, respectively, which also results in variations in the decomposition temperature.

[0080] In one embodiment, the at least one temperature change from the first reaction temperature to the second reaction temperature is -A reactor having a high-temperature wall-decomposition chamber including at least one first zone and at least one second zone, wherein the wall temperature of the at least one first zone is equal to the first reaction temperature and the wall temperature of the at least one second zone is equal to the second reaction temperature, and - Transporting the precursor gas mixture in the high-temperature wall decomposition chamber by thermal convection between the at least one first zone and the at least one second zone, or, - Using a reactor having a high-temperature wall decomposition chamber that includes an injection zone and a first decomposition zone having walls whose wall temperature is equal to the first reaction temperature, and - To create turbulence in the injected precursor gas mixture within the decomposition chamber, and to transport the second reactor gas mixture between the injection zone and the first decomposition zone of the high-temperature wall decomposition chamber, or, -A reactor having a tubular high-temperature wall-decomposition chamber in which a plurality of first zones and a plurality of second zones are arranged alternately, wherein the wall temperature of the first zones is equal to the first reaction temperature, and the wall temperature of the second zones is equal to the second reaction temperature, and - The precursor gas mixture, which is optionally mixed with the first reactor gas to form the second reactor gas, is injected into the first end of the tubular high-temperature wall-decomposition chamber, and the precursor gas mixture, or optionally the second reactor gas mixture, is passed through the tubular high-temperature wall-decomposition chamber under laminar flow conditions with a Reynolds number of less than 2000. It is obtained by one of the following means.

[0081] Particle size also depends on temperature. Smaller particles are formed at higher temperatures and shorter residence times. Larger particles are formed at lower temperatures and longer residence times. Furthermore, even smaller particles can be obtained by diluting silane or a silane / hydrocarbon mixture with, for example, H2, argon, or N2. Moreover, this process can be carried out at low pressures of less than 100 mbar, atmospheric pressure, or higher pressures. Alternatively, the pressure can be varied during particle growth. After the particles have grown over a selected residence time, in one embodiment, the particles can be extracted by flushing or vacuum.

[0082] To prevent excessive SiC formation with an average particle size exceeding 500 nm, the reaction temperature can be relatively low (below 640°C) and the residence time can be long (more than 10 seconds). In many types of reactors (fluidized bed reactors or flow-through reactors), controlling the reaction time is very difficult because some gases find a short path through the decomposition chamber, while others find a long path. This broad distribution leads to the generation of small particles and reduced utilization of the reactant species in gases that travel the short path, and excessive particle growth and aggregation in gases that travel the long path. Therefore, in one embodiment, it is advantageous to control the residence time to obtain both particle size control and good utilization of the reactant gas. A long residence time means that it becomes more difficult to realize a laminar flow field or a nearly plugged flow reactor because the gas density changes as the precursor gas decomposes to produce light hydrogen gas.

[0083] One way to achieve fairly uniform residence times is to fill a sealed decomposition chamber so that the pressure increases. Once the pressure rises to a point where the reaction rate becomes significant, the reaction accelerates simultaneously throughout the entire chamber, resulting in fairly uniform growth conditions. Uniformity of growth conditions can also be improved by a moderate packing density. Furthermore, if the chamber has walls with temperature differences, the gases can be mixed by thermal convection, potentially providing the desired temperature fluctuations for forming a ring structure. The reaction can be stopped by pumping or flushing the gas out of the decomposition chamber and moving the particles and gas to a low-temperature zone where the reaction stops.

[0084] Since silane is consumed faster than most hydrocarbon precursors, a gradient of increasing carbon content is created towards the particle surface, causing greater expansion in the particle core than at the periphery, and increasing the likelihood of particle cracking during the cycle. By continuously supplying gas to the chamber after the reaction has started, similar conditions can be maintained in the early and later stages of particle formation, and the carbon content is controlled primarily by temperature rather than by the gas mixture. In addition, the presence of a small amount of carbon precursor gas at the start of silane filling can reduce the difference between the particle core and the outer layer.

[0085] Continuous filling of a fixed volume also contributes to turbulent gas mixing, resulting in a more uniform gas concentration and enabling the temperature changes necessary to form one or more shell-like layers within the bulk material of the particles.

[0086] The advantage of applying condensation and chemical vapor deposition of a mixture of silicon-containing and carbon-containing precursor gases under a protective atmosphere is that this method provides excellent control over which elements are introduced into the reactor and, consequently, which elements are present in the resulting particles. For example, if the silicon-containing precursor gas is silane and the carbon-containing precursor gas is hydrocarbon, the reactor will mainly contain elements such as hydrogen, carbon, and silicon, along with typically inert gas elements (nitrogen, argon, etc.) and trace amounts of oxygen (residue of air). Therefore, the resulting particles will mainly contain silicon and carbon, possibly small amounts of hydrogen and oxygen, and inevitably, final traces of impurities.

[0087] The term "first precursor gas of a silicon-containing compound" as used herein refers to any silicon-containing compound that exists in a gaseous state and reacts at the intended reaction temperature to form Si particles. Suitable examples of first precursor gases include, but are not limited to, silane (SiH4), disilane (Si2H6), trichlorosilane (HCl3Si), or mixtures thereof.

[0088] Similarly, the term “second precursor gas of carbon-containing compound” as used herein means any carbon-containing compound that incorporates C atoms into the matrix surrounding the Si particles formed when heated to the intended reaction temperature. Suitable examples of second precursor gases of carbon-containing compound include, but are not limited to, alkanes, alkenes, alkynes, aromatic compounds, and mixtures thereof. In exemplary embodiments, the second precursor gas of carbon-containing compound is at least an organosilane or hydrocarbon, preferably methane (CH4), ethane (C2H6), propane (C3H8), ethene (C2H4), propene (C3H6), butene (C4H8), pentene (C5H 10 ), etyn (C2H2), cyclohexane, cyclohexene, toluene, benzene, or mixtures thereof.

[0089] A particularly preferred exemplary embodiment of the precursor gas, i.e., a homogeneous gas mixture of a gaseous silicon-hydrogen compound and a gaseous substitution element C-hydrogen compound, is silane (SiH4) or disilane (Si2H6), methane (CH4), ethane (C2H6), propane (C3H8), ethene (C2H4), propene (C3H6), butene (C4H8), pentene (C5H 10 ), Hexene (C6H 12 ), ethyne (C2H2), cyclohexane, cyclohexene, toluene, benzene, and a mixture of these hydrocarbon gases are used. It is considered preferable to partially use a larger, more stable ring structure, as this is likely to increase the ratio of CC bonds to Si-C bonds in the first matrix.

[0090] It is clear that one or more precursor gases containing both C and Si, such as SiC2H8, can also be used, as long as the gas mixture contains at least two different gases having different Si:C ratios and different conversion temperature dependencies.

[0091] A second aspect of the present invention provides a manufacturing method that, as seen in the TEM image of the particles of sample S1 in Figure 1, produces high-density particles with no or very limited measurable porosity after hydrogen has been removed by heat treatment. This is further confirmed by FIB-SEM or FIB-TEM cross-sections of several exemplary embodiments of the particles. No signs of porosity are observed in the individual particles.

[0092] The reaction kinetics in a gas reaction that forms particles from a precursor gas can vary significantly depending on which gases are used as the first and / or second precursor gases, and the reaction temperature at which the particles are formed. Therefore, the atomic ratio C:Si in the precursor gas can deviate significantly from the overall (average) atomic ratio C:Si in the resulting particles. Thus, the phrase "the relative amounts of the first and second precursor gases are adjusted so that the particles formed achieve an atomic ratio C:Si within the range of..." means that the relative amounts of the first and second precursor gases, which are mixed and homogenized, are adjusted so that when the precursor gas mixture is heated to the intended reaction temperature and reacts to form particles, the resulting particles obtain the intended atomic ratio.

[0093] The term “reactor gas” as used herein encompasses the exhaust gas generated by the previous production of secondary particles and / or gases that are inert at the reaction temperature used. In this context, inert means chemically inert to condensed particles. Examples of suitable inert gases include hydrogen, nitrogen, noble gases such as helium, neon, and argon, and other gases that do not chemically react with the precursor gas at the reaction temperature.

[0094] [List of drawings] Figure 1 is a high-angle annular dark-field scanning transmission electron microscope image of an exemplary embodiment (indicated here as S1) of the multilayer particles according to the present invention, which have multiple relatively carbon-rich shell-like layers embedded in a bulk material.

[0095] Figure 2 shows a diagram of the carbon and silicon content of the particles of sample S1 according to the present invention, determined by EELS along a line crossing the particle, and a TEM image of the same portion of the particle used for EELS analysis. As can be seen, the EELS mean is lower than the total carbon measurement, but the variation is still systematic and significant.

[0096] Figure 3 is a high-resolution TEM image of the particles of the sample indicated as S2 according to the present invention, after heat treatment at 900°C for 2 hours. Individual atoms are recognizable in this image. The image was further processed with a circular bandpass filter to highlight regions where the lattice constant matches that of crystalline silicon (0.314 nm), and the brightest spots are atoms incorporated into silicon nanocrystals. The bottom of the image is a graphite sample holder. The interlayer spacing of the graphite is similar to the filter value. This may explain the slightly lower intensity spots in the dark areas, which the bandpass filter attenuates but does not completely remove. The inset shows that the ring structure of these particles is maintained on a long length scale even after heat treatment, while domains smaller than 2 nm are significantly rearranged. Since the manufacturing parameters of this powder are very similar to those of HM47B and HM52, the ring structure image is expected to represent these samples as well.

[0097] Figures 4 and 5 show two TEM images of different particles in an embodiment of the particle according to the present invention, indicated as S4. The two figures show that the average carbon content and characteristic peak height are very similar in the two particles, despite some variability in each batch, and although the rings indicate that the particles have been exposed to different temperature ranges and different time periods.

[0098] Figure 6 is a high-angle annular dark-field scanning transmission electron microscope image showing crystalline silicon nanodomains in secondary composite particles (sample S4) after heat treatment at 900°C for 30 minutes.

[0099] Figure 7 shows the cycle data for a powder sample according to the present invention (indicated here as S5), which was produced by the method according to the present invention, including further heat treatment at 650°C, PAN coating, and polymer crosslinking at 500°C. The reference is a pure graphite electrode, and the upper line shows a cell containing 10 wt% silicon-based powder in 90 wt% graphite, both of which are full cells equipped with LFP counter electrodes. The cycle program was 4×C / 20-3×C / 10-3×C / 5-3×C / 3-3×C / 2-3×1C-3×2C-1×C / 20, followed by repeated sets of 2×C / 10+20×C / 2. Volume and FCE were obtained from a separate cell containing only graphite, S6, to avoid numerical uncertainty. This cell maintains a volume that remains virtually unchanged even after more than 100 cycles.

[0100] Figure 8 shows the cycle data for a powder sample according to the present invention (indicated here as S6), manufactured by the method according to the present invention, including subsequent bitumen coating and heat treatment at 900°C. The reference is a pure graphite electrode, and the upper line shows a cell containing 15 wt% silicon-based powder in 85 wt% graphite, both of which are full cells equipped with LFP counter electrodes. The cycle program was 4×C / 20-3×C / 10-3×C / 5-3×C / 3-3×C / 2-3×1C-3×2C-1×C / 20, followed by repeated sets of 2×C / 10+20×C / 2. To avoid numerical uncertainty, the volume and FCE were obtained from a separate cell containing only graphite-free S6. This cell maintains a much higher volume than the reference even after more than 150 cycles.

[0101] Figure 9 shows a post-cycle SEM image of bitumen-coated SiC composite particles (sample S6) after a long cycle. The bright areas indicate silicon. Some degradation is observed in the outer regions, which is likely due to co-diffusion of Si with Li to the outside of the particles, where it interacted with the electrolyte and formed the SiO phase. The presence of the SiC internal boundary suppresses large shape changes, so the particle shape is generally maintained.

[0102] [Verification of the present invention] The present invention will be described in more detail by reference to examples.

[0103] The following reactor concept was used to produce the particles used in the examples.

[0104] Half of a roughly cylindrical steel chamber, approximately 30 liters in size, is heated to the maximum reaction temperature. On the opposite side, the tank is connected to a supply nozzle and valve, which then passes through a filter and connects to a vacuum pump. The temperature of the chamber wall adjacent to the nozzle and valve is kept low, although the temperatures shown here are estimates, and the high temperatures are measured precisely, while the inner wall temperatures, in particular, are not measured precisely and include a strong gradient. It is assumed that no growth occurs in the coldest part of the chamber. Optimization of the minimum temperature can be done by adding sensors and varying the adiabatic level of the low-temperature wall, as those skilled in the art would know.

[0105] The chamber was closed and filled with a gas mixture to a low pressure limit of 20 kPa. A mixture of silane and ethylene was supplied into the chamber through a nozzle. The nozzle was slightly heated by the chamber walls and the gas inside the chamber, making it difficult to determine the exact nozzle temperature. The filling time was varied by changing the filling rate. Filling continued until a "high pressure limit" of 90 kPa was reached.

[0106] After filling was complete, the gas mixture was retained in the reactor for a "holding time." During the "holding time," the pressure increased slightly further. The gas was pumped out of the chamber. Powder samples were collected from both the chamber wall and the filter. The parameters used for sample preparation are summarized in the table below.

[0107] [Table 1]

[0108] The ring structure according to the present invention was found in all samples prepared by the above method, and this was investigated using the EELS method. Experiments with samples S4 and S3 show that although details within the reactor may affect the total carbon consumption, the desired C content can be achieved through experimental adjustments by changing the flow rate. In HD39, the position of the high-temperature section is arranged to reduce convection, which likely results in longer residence times in each temperature zone, and therefore a stronger ring. In S3, the reactor wall was slightly thicker, which affected the heat distribution within the chamber, and this also affected the average value, but the features described in the present invention were maintained.

[0109] Furthermore, sample S2 was heat-treated at 900°C for 2 hours, resulting in localized reorganization of atoms. Figure 3 shows that this reorganization did not reach the length scale of the ring structure. The rings remained clearly visible even after heat treatment. To confirm that the generated particles exhibited good cycleability, the powder produced by the above method was post-treated to remove excess hydrogen, coated with a carbon precursor, and then thermally decomposed to enhance the conductivity of the carbon coating and improve the localized ordering of Si-C atoms. In this process, carbon and silicon atoms are not expected to migrate to a degree that would affect the observed ring structure (migration exceeding 5 nm), but crystallization or reordering on a scale of less than 1 nm is anticipated. No systematic differences in the ring structure were observed in the cross-sectional images of the heat-treated and untreated samples.

[0110] For samples S5 and S6, the amount of carbon was selected so that the added carbon constituted 2% by weight of the total sample weight after heat treatment. S5 was degassed at 650°C, then coated with polyacrylonitrile and crosslinked at 500°C, while S6 was coated with bitumen and thermally decomposed at 900°C. Several different types of PAN and bitumen precursors were tested, but the results were not substantially different from those shown here.

[0111] For powders S5 and S6, two types of cells were fabricated. First, electrodes using only silicon-based active material were cycled as the anode of a full cell to test the powder's capacity and initial cycle efficiency. Next, similar cells were fabricated, but here, to ensure that electrode delamination or poor contact would not affect the results, the electrodes contained a mixture of silicon-based material and flaky graphite. These cells were used for rate testing and long-term cycle stability testing. The FCE of these cells is dominated by high-BET flaky graphite. The motivation for this type of testing was to obtain reliable data without rigorous optimization of the electrode processing recipe, which would require a very large test batch size. It is expected that any commercial battery manufacturer will be able to combine this material with commercial-grade graphite and, through normal optimization efforts, combine demonstrated cycleability with demonstrated FCE and capacity.

Claims

1. Silicon-based particles made from a bulk material containing silicon and carbon, - The silicon-based particles have a median volume-weighted diameter (D) determined by laser diffraction analysis in accordance with ISO 13320:2020. ５０ The size is 0.05 to 10 μm. - The silicon-based particles are, - Total carbon content C ｔｏｔａｌ However, it is 5 to 40 atomic percent based on the total mass of silicon-based composite particles. - The remainder consists of silicon and unintended impurities. Having a chemical composition, - The particles include one or more internal shell-like spatial regions within the bulk material of the particles, with an increased carbon content, and the peak C of the elemental carbon content ｐｅａｋ However, the average carbon content C ａｖｅｒａｇｅ It is 1 to 15 atomic percentage points higher than - The peak C of the elemental carbon content in each of the one or more internal shell-like spatial regions within the bulk material. ｐｅａｋ and the average carbon content C ａｖｅｒａｇｅ Silicon-based particles, characterized in that the elemental properties are determined by elemental analysis by electron energy loss spectroscopy performed along a straight line extending from the particle core to the particle surface, but excluding the particle surface, and variations on a length scale of less than 5 nm, preferably less than 2 nm, and most preferably less than 1 nm, are smoothed out.

2. Said C ｐｅａｋ The average carbon content C ａｖｅｒａｇｅ The particles according to claim 1, which are in the range of 1 to 12 atomic percent points higher, preferably 1 to 10 atomic percent points higher, more preferably 2 to 8 atomic percent points higher, more preferably 3 to 6 atomic percent points higher, and most preferably 4 to 5 atomic percent points higher.

3. The total chemical composition of the aforementioned particles is - A total content of 10 to 37 atomic percent, preferably 15 to 33 atomic percent, more preferably 20 to 30 atomic percent, and most preferably 23 to 26 atomic percent of carbon, - The particle according to claim 1 or 2, comprising silicon and the remainder being unintended impurities.

4. The particles according to any one of claims 1 to 3, wherein the total oxygen content of the particles is less than 4 atomic percent, preferably less than 3 atomic percent, more preferably less than 2 atomic percent, more preferably less than 1 atomic percent, and most preferably less than 0.5 atomic percent.

5. The particles according to any one of claims 1 to 4, wherein the total hydrogen content of the particles is less than 30 atomic%, preferably less than 20 atomic%, more preferably less than 15 atomic%, more preferably less than 10 atomic%, more preferably less than 5 atomic%, and most preferably less than 1 atomic%.

6. In the total chemical composition of the particles, - The total amount of carbon C in the particles ｔｏｔａｌ is 5 to 30 atomic%, preferably 6 to 25 atomic%, preferably 7 to 20 atomic%, more preferably 8 to 15 atomic%, more preferably 9 to 14 atomic%, or most preferably 10 to 12 atomic%, and - The total amount of oxygen in the particles is 0.1 to 4 atomic%, preferably 0.2 to 3 atomic%, more preferably 0.3 to 2 atomic%, more preferably 0.4 to 1 atomic%, or most preferably 0.5 to 1 atomic%, - The total amount of hydrogen in the particles is less than 5 atomic percent, preferably less than 1 atomic percent, and further, - The particles according to claim 1 or 2, wherein the remainder is Si and unintended impurities.

7. The multiple particles have a volume-based median diameter D measured by laser diffraction analysis in accordance with ISO 13320:2020. ５０ The particles according to any one of claims 1 to 6, wherein the particle size is 1 to 9 μm, preferably 1.1 to 8 μm, more preferably 1.2 to 7 μm, more preferably 1.6 to 6 μm, and most preferably 2 to 5 μm.

8. The plurality of particles according to the present invention are measured by laser diffraction analysis in accordance with the ISO 13320:2020 standard. ９０ / D １０ The particles according to any one of claims 1 to 7, wherein the ratio is in the range of 1 to 10, preferably 2 to 8, and most preferably 3 to 6.

9. The particles according to any one of claims 1 to 8, wherein the particles further comprise a plurality of nanoscale silicon domains embedded in the bulk material, and after optionally heat treatment at 900°C or above for at least 30 minutes, the average diameter of the nanoscale silicon domains, as determined by Rietveld refinement of X-ray powder diffraction (XPD) data, is in the range of 0.5 to 10 nm, preferably 1 to 8 nm, more preferably 2 to 7 nm, more preferably 3 to 6 nm, and most preferably 4 to 5 nm.

10. The particle has an outer coating on its outer surface, and the coating is - Amorphous or crystalline carbon allotropes, Li ｘ Si ｙ O, Ti ｘ O, or Al ｘ It is one or more oxides selected from O, and - The thickness is in the range of 1 to 100 nm, preferably 2 to 60 nm, more preferably 3 to 20 nm, and most preferably 3 to 10 nm. or, - An amorphous or crystalline carbon layer having a thickness of 0.5 to 10 nm, preferably 2 to 5 nm, as determined by Auger spectroscopy. A particle according to any one of claims 1 to 9, which is any of the above.

11. Elemental analysis by electron energy loss spectroscopy revealed the C content of at least one relatively carbon-rich shell-like layer. ｐｅａｋ The decision was - A cross-sectional slice less than 70 nm thick, including the particle center of the particle, is prepared using a focused ion beam (FIB). - Perform EELS elemental analysis along a straight line passing through the cross-section from the center of the slice to the outer surface, and then, - The measured values ​​are smoothed by optionally using a Gaussian digital filter, or by averaging the measured values ​​obtained for multiple adjacent spatial measurement regions. - Using the local maximum value of the carbon content of the first peak along the straight line, located away from the particle center, the C of the first peak ｐｅａｋ Furthermore, if present, the same C for each of the other corresponding pairs of peaks on the aforementioned straight line where the carbon content increases and the silicon content decreases. ｐｅａｋ The decision was made, - By averaging the determined C content at all measurement points along the straight line, excluding the outer surface region, the C ａｖｅｒａｇｅ A particle according to any one of claims 1 to 10, obtained by determining the following.

12. The smoothing of the variations in elemental analysis by the aforementioned electron energy loss spectroscopy is A Gaussian digital filter having a width of less than -5 nm, preferably less than 2 nm, most preferably less than 1 nm, is used, or - A particle according to any one of claims 1 to 11, obtained by averaging the measured values ​​obtained for a plurality of adjacent spatial measurement regions.

13. A method for producing silicon-based particles, - A step of forming a precursor gas mixture comprising a first precursor gas of a silicon-containing compound and a second precursor gas of a carbon-containing compound, wherein the atomic ratio of silicon to carbon (Si:C) in the precursor gas mixture is in the range of 0.2 to 50, - A step of preheating the precursor gas mixture to a temperature of 300 to 350°C, - A step of using a reactor having a decomposition chamber heated to a first reaction temperature in which the precursor gas mixture condenses to form particle seeds, wherein the particle seeds are then grown by chemical vapor decomposition (CVD), - The step of injecting the precursor gas mixture into the decomposition chamber, The above method further, - A step of maintaining the injected precursor gas mixture in the decomposition chamber for a residence time in the range of 1 to 300 seconds, and during the residence time, subjecting the injected precursor gas mixture to at least one temperature change, from the first reaction temperature to the second reaction temperature, and then back to the first reaction temperature. - The process includes the step of extracting the particles from the decomposition chamber, A method for producing silicon-based particles, wherein the absolute temperature difference between the first reaction temperature and the second reaction temperature is in the range of 1 to 100°C, preferably 3 to 75°C, more preferably 5 to 50°C, more preferably 10 to 35°C, and most preferably 20 to 25°C.

14. The method according to claim 13, wherein the first reaction temperature is in the range of 450 to 900°C, preferably 500 to 800°C, more preferably 550 to 700°C, and most preferably 600 to 650°C.

15. The method according to claim 13 or 14, wherein the residence time is in the range of 2 to 250 seconds, preferably 3 to 200 seconds, more preferably 5 to 150 seconds, more preferably 10 to 120 seconds, more preferably 15 to 90 seconds, and most preferably 20 to 60 seconds.

16. The method according to any one of claims 13 to 15, wherein the atomic ratio of silicon to carbon (Si:C) in the precursor gas mixture is in the range of 0.3 to 45, preferably 0.4 to 40, more preferably 0.5 to 30, more preferably 0.6 to 25, more preferably 0.8 to 15, more preferably 1.0 to 8, more preferably 1.2 to 5, and most preferably 1.5 to 2.

0.

17. - The first precursor gas is silane (SiH ４ ) and disilane (Si ２ H ６ ) one or more of the following, - The second precursor gas is methane (CH4). ４ ), ethane (C ２ H ６ ), propane (C ３ H ８ ), Eten (C ２ H ４ ), hexene (C ６ H １２ ), etyne (C ２ H ２ The method according to any one of claims 13 to 16, wherein the first is one or more of cyclohexane, cyclohexene, toluene, and benzene.

18. - The above method further involves 5 × 10 at the first reaction temperature. ３ ~6 x 10 ５ This includes pre-filling the decomposition chamber with a first reactor gas having an initial pressure in the range of Pa, The method according to any one of claims 13 to 17, wherein the first reactor gas is one or more of argon, nitrogen, or exhaust gas from the previous particle production.

19. - Using a sealed decomposition chamber pre-filled with the first reactor gas, The method according to claim 18, wherein the precursor gas mixture is gradually injected over a period of at least 50% to 100% of the residence time, and when the residence time is reached, the decomposition chamber is opened and flushed with an inert gas to extract the formed particles.

20. The at least one temperature change from the first reaction temperature to the second reaction temperature is, - Using a reactor having a high-temperature wall-decomposition chamber including at least one first zone and at least one second zone, wherein the wall temperature of the at least one first zone is equal to the first reaction temperature and the wall temperature of the at least one second zone is equal to the second reaction temperature, and - Transporting the precursor gas mixture in the high-temperature wall decomposition chamber by thermal convection between the at least one first zone and the at least one second zone, or, - Using a reactor having a high-temperature wall decomposition chamber that includes an injection zone and a first decomposition zone having walls whose wall temperature is equal to the first reaction temperature, and - To create turbulence in the precursor gas mixture injected in the decomposition chamber, and to transport the second reactor gas mixture between the injection zone and the first decomposition zone of the high-temperature wall decomposition chamber, or, - Using a reactor having a tubular high-temperature wall-decomposition chamber in which multiple first zones and second zones are arranged alternately, wherein the wall temperature of the first zone is equal to the first reaction temperature, and the wall temperature of the second zone is equal to the second reaction temperature, and - The precursor gas mixture, which is optionally mixed with the first reactor gas to form the second reactor gas, is injected into the first end of the tubular high-temperature wall decomposition chamber, and the precursor gas mixture or optionally the second reactor gas mixture is passed through the tubular high-temperature wall decomposition chamber under laminar flow conditions with a Reynolds number of less than 2000. The method according to any one of claims 13 to 18, obtained by any one of the following means.

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