Silicon-based and carbon-based composite particles

Abstract

The present invention relates to silicon-based and carbon-based composite particles, each of which consists of a bulk material in which multiple nanoscale silicon domains are embedded, and the bulk material has a total carbon content of 1 to 40% by weight, based on the total mass of the silicon-based composite particles, with the remainder being silicon and unintended impurities. The silicon-based and carbon-based composite particles have a volume-based median diameter D, which is determined by laser diffraction analysis according to ISO standard 13320:2020. 50 The diameter is in the range of 1 to 9 μm, and the volume-based diameter ratio D 90 / D 10 It is in the range of 1 to 6.

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 capability of intercalating lithium and forming an alloy of silicon and lithium. At room temperature, the most lithiated phase of silicon is Li3.75Si, which has a theoretical specific capacity of 3579 mAh / g, while the theoretical specific energy of graphite is 372 mAh / g. Accordingly, the battery industry has been seeking solutions that use silicon as a negative electrode active material for secondary LIBs for more than 10 years.

[0006] However, lithium intercalation causes significant volume fluctuation of silicon materials. In the most lithiated state, Li 3.75 3.75Si, the volume of the silicon material is as large as about 320% compared to its delithiated state. In addition, the electrolyte in contact with the surface of the active material usually reacts to form a lithium-containing solid phase known as a solid electrolyte interphase layer (SEI). This SEI layer represents irreversible loss of lithium in an electrochemical cell, with a corresponding decrease in the energy storage capacity of the cell. Since the formation of the SEI layer mainly occurs during the first charge-discharge cycle, the magnitude of irreversible lithium loss accompanying SEI layer formation is often represented by the first cycle efficiency (FCE) metric.

[0007] Furthermore, it has been shown that volume changes of silicon materials over lithiation and delithiation (charge-discharge) cycles cause serious problems relating to both structural degradation / collapse of the silicon material and instability of the SEI layer, leading to unacceptably low cycle performance and large capacity loss of LIBs. It has been proposed that this integrity problem of silicon materials is solved by using silicon in the form of nanoscale particles, usually less than 200 nm, preferably provided with a surface coating.

[0008] Sourice et al. (2016) (Non-Patent Document 1) disclose the production of amorphous silicon core particles with a diameter of 30 nm by laser-driven chemical vapor pyrolysis (LCVP) using silane gas diluted with helium. These particles are provided with a carbon coating having a thickness of 1 nm produced by a second-stage LCVP using ethylene gas. It is reported that these particles maintain a capacity of 1250 mAh·g⁻¹ at a C / 5 rate and 800 mAh·g⁻¹ at 2C after 500 charge-discharge cycles, and have an excellent Coulombic efficiency of 99.95%.

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

[0010] Orthner et al. (2021) (Non-Patent Literature 2) reported a study on the formation of amorphous silicon particles by flowing a mixture of silane and ethylene gas diluted with nitrogen into a tubular high-temperature wall reactor at 640, 690, and 1100°C under atmospheric pressure. The residence time was 1 to 5 seconds. The silane gas concentration in the mixed gas was 10 to 30 volume%, and the ethylene gas concentration was 0 to 11.3 volume%. The particles produced at 640°C and 690°C were found to be amorphous and homogeneous, and crystallization was absent or only partially present in these particles produced at 640°C and 690°C, respectively. The particle size varied in the range of 80 to 300 nm, with an average size of 200 nm. XRD analysis did not show the formation of SiC. XPS analysis showed that the carbon content in the amorphous particles decreased almost linearly from the particle surface towards the bulk interior of the particle. The initial capacity of the particles was 3070 mAh / g, which decreased to 2200 mAh / g after the second cycle, but the Coulomb efficiency remained stable at over 99.5%. The high Coulomb efficiency was attributed to the low formation of the SEI layer due to the relatively large amount of carbon present on the particle surface. However, the particles produced at 1100°C were found to consist of a mixture of crystalline Si (approximately 15 wt%), amorphous Si (approximately 14 wt%), and amorphous SiC (approximately 71 wt%). The crystallite size of Si was 70 nm. Non-patent document 2 further reports that the formation of SiC was deemed unfavorable, as the particles exhibited significantly lower initial cycle efficiency and specific capacity (917 mAh / g) compared to pure Si.

[0011] Patent Document 2 discloses that relatively high temperatures and long heat treatment can convert an amorphous structure to a crystalline structure. This document discloses forming silicon alloy particles by thermal decomposition of a precursor gas mixture, as described in Patent Document 1, and then heat-treating them at 800-900°C for 10-240 minutes. The heat-treated particles are 25-180 m 2It is disclosed that the material has a BET of approximately 15-110 nm in diameter per g, a total content of 0.05-20 atomic percent of C and / or N, and contains nano-sized crystallites with a diameter of 1-15 nm embedded therein.

[0012] It is further known that calcining nanoscale silicon particles in a carbon matrix can provide stable particles and reduce the formation of SEI layers. Wang et al. (2013) (Non-Patent Literature 3) disclose composite particles prepared by thermally decomposing a mixture of 50-100 nm nanoscale silicon particles and coal tar pitch, and then pulverizing the decomposed mixture to form a composite of Si particles embedded in an amorphous carbon matrix (Si / αC). A composite containing 20 wt% Si was found to exhibit stable lithium storage capacity for long-term cycling. The 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 was explained by the fact that in the (Si / αC) composite, the silicon nanoparticles are encapsulated in amorphous SiOx and amorphous carbon, which provides sufficient conductivity and tough elasticity, suppressing stress caused by the reaction of Si and Li during the charge-discharge process.

[0013] Zhu et al. (2018) (Non-Patent Literature 4) reported a study investigating the correlation between the main physical parameters and electrochemical properties of silicon particles when used in the anode of a LIB. This study examined parameters 41.4, 36.11, and 7.33m, respectively. 2 The sample contained three crystalline silicon particle samples, denoted as S1, S2, and S3, each having a BET specific surface area of ​​approximately 50, 100, and 150 nm. These correspond 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 binders, and then coated onto a copper conductor to form three anode samples, each containing particles S1, S2, and S3. The active material packing amount in each anode sample was approximately 0.5 mg / cm³. 2The 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 are prone to shattering and cracking during repeated charge-discharge cycles, particularly when the particle size is larger than 150 nm, as reported in the literature.

[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, as schematically shown in Figure 1 of Non-Patent Literature 6 (reproduced here as Figure 1), suggest that carbon atoms released by the simultaneous decomposition of silane and ethylene function as an inhibitor of silicon atom crystal growth by forming intercalated layers of SiC and C between silicon crystallites. This calculation 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 were in the size range of 40 nm or larger, 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. The film, 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), was found to exhibit cycle stability comparable to that of graphite, and therefore the best cycle stability acceptable for commercial use, with 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 capacity and FCE of the synthesized film decreased significantly with increasing carbon content in the film. However, the capacity 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 lithium secondary 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.

[0017] It is well known that by grinding crystalline silicon, the particles can be refined, resulting in a relatively narrow particle size distribution when measured as D90 / D10 (see, for example, Nilsen and Kleiv (2020) (Non-Patent Literature 8)). However, as shown in Figure 16, such particles have significantly different and unattractive shapes. In the crystalline silicon grinding process described in Non-Patent Literature 8, a D90 / D10 of 5 was achieved with a material having a D50 of 1 micron, but the BET specific surface area was high at 32.6 square meters / gram, a parameter that results in extremely low (and inappropriate) first-cycle efficiency in lithium anodes. [Prior art documents] [Patent Documents]

[0018] [Patent Document 1] International Publication No. 2021 / 160824 [License 2] International Publication No. 2022 / 200606 [License 3] China Patent Publication No. 115881931 [License 4] European Patent Application No. 22158616.7 [Patent Document 5] U.S. Patent and Trademark Office Publication No. 2014 / 225030 [Non-licensed literature]

[0019] [Non-licensed 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-licensed 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-licensed 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] Lee et al. (2016), "Insights from Studying the Origins of Reversible and Irreversible Capacities on Silicon Electrodes", Journal of The Electrochemical Society, 164 (1) A6206-A6212 [Non-Patent Document 8] Nilsen, BE and Kleiv, RA, "Silicon Powder Properties Produced in a Planetary Ball Mill as a Function of Grinding Time, Grinding Bead Size and Rotational Speed", Silicon, October 2020, Volume 12, Issue 10, pp 2413 - 2423. [Overview of the project] [Problems that the invention aims to solve]

[0020] The main objective of the present invention is to provide a particulate silicon-based and carbon-based composite material having a relatively narrow particle size distribution and a relatively small specific surface area, which, when used as a negative electrode active material for a rechargeable lithium-ion battery, has good charge / discharge capacity and initial lithiumization efficiency.

[0021] A further object of the present invention is to provide a method for producing the secondary composite particles. [Brief explanation of the drawing]

[0022] [Figure 1] This figure shows the XRD analysis of 1.7 nm silicon nanoparticles (sample S1 or S2) embedded in a carbon-rich matrix after heat treatment, according to Patent Document 4. [Figure 2] This figure shows the XRD analysis of 3.4 nm silicon nanoparticles (sample S3) embedded in a carbon-rich matrix after heat treatment, according to Patent Document 4. [Figure 3] This is a TEM image showing crystalline silicon nanodomains in silicon-based composite particles (sample S1) according to Patent Document 4 after heat treatment. [Figure 4] This is a series of TEM images showing secondary composite particles according to Patent Document 4. [Figure 5] This is a TEM image showing pure silicon nanoparticles with the same outer diameter as those in Figure 4, and which have not undergone heat treatment. [Figure 6] This figure shows the XRD analysis of particles produced by the present invention. [Figure 7] a) is a TEM image showing one embodiment of the present invention. b) is a diagram showing EELS elemental analysis across the particles. [Figure 8] a) is a TEM image of one embodiment of the present invention. b) is a diagram showing EELS elemental analysis across the particles. [Figure 9] This figure shows a Fourier transform using a bandpass mask centered at 0.314 nm to highlight the crystalline silicon in the example shown in the TEM image of Figure 7a). [Figure 10] This figure shows a Fourier transform using a bandpass mask centered at 0.252 nm to highlight the silicon carbide in the example shown in the TEM image of Figure 7a). [Figure 11]a) is a figure showing the particle size distribution of two powders (S4 and S5) prepared using similar temperatures and gas mixtures, and represents the volume-based distribution. b) is a figure showing the particle size distribution of two powders (S4 and S5) prepared using similar temperatures and gas mixtures, and represents the area-based distribution. [Figure 12] This figure shows the cycle data for powder S6 produced by the method described herein, followed by heat treatment, PAN coating, and polymer crosslinking. [Figure 13] This figure shows the cycle data for powder S5 produced by the method described herein, followed by bitumen coating and heat treatment. [Figure 14] This figure shows the cycle data for powder S4 in three versions (no heat treatment, with heat treatment, and heat treatment after sugar coating). [Figure 15] a) is a SEM image of the particulate material according to the present invention before a gentle grinding process. b) is a SEM image of the particulate material according to the present invention after a gentle grinding process. [Figure 16] This figure shows SEM images of various metallurgical-grade crystalline silicon particles (Non-Patent Literature 8) that were ground according to different grinding conditions. [Figure 17] Figure 15b) shows a subdivision of the SEM image, and is an example of an outer circumference that is an arc. [Modes for carrying out the invention]

[0023] This invention can be considered an improvement on the secondary particles described in concurrently pending European Patent Application No. 22158616.7 (European Patent Application Publication No. 4234489) (Patent Document 4).

[0024] The particles described in Patent Document 4 are produced by injecting a homogeneous gas mixture consisting of a first silicon-containing precursor gas and a second carbon-containing precursor gas, with an atomic ratio of Si:C in the range of approximately 0 to 10, into a reactor space maintained at a reaction temperature of 500 to 1200°C, most preferably 700 to 900°C. The precursor gas mixture may be preheated to a temperature in the range of less than 300°C to 500°C. XRD analysis revealed that the resulting particles are composites in which amorphous silicon nanoscale domains are embedded in an amorphous silicon and carbon matrix. The particle size is described as being in the range of 10 nm to 1 μm, and the Si:C ratio of the particles is in the range of [0.2,7], most preferably [1,4]. This corresponds to a total carbon content in the particles being in the range of 12.5 to 83.3 atomic percent (5.8 to 68.1 wt%).

[0025] In one embodiment described in Patent Document 4, the precursor gas was silane and ethene with a Si:C molar ratio of 1:1, preheated to approximately 400°C. This gas mixture was injected into a reactor space containing nitrogen gas heated to a temperature of 810°C, such that the temperature of the gas mixture obtained inside the reactor was 810°C. The residence time was less than 0.5 seconds. The resulting particles were described as composites consisting of an amorphous silicon and carbon matrix with particle sizes ranging from 10 nm to 1 μm, and embedded with multiple nano-sized domains consisting of amorphous silicon with an average crystallite size of 1.7 nm. The total carbon content of the particles was 35 atomic percent.

[0026] Table 1 of Patent Document 4 lists the initial cycle capacity and cycle characteristics measured for particle samples with total carbon content in the range of 14 to 35 atomic percent. This table shows that the particle with the highest carbon content (35 atomic percent) showed the best cycle characteristics, with 621 cycles until the capacity decreased by 20%, but the lowest initial cycle capacity of 1000 mAh / g. On the other hand, the particle with the lowest carbon content (14 atomic percent) showed the worst cycle characteristics, with only 36 cycles, but the highest initial cycle capacity of 2200 mAh / g.

[0027] [Notes on Terminology] Patent Document 4 uses three adjectives, "primary," "secondary," and "tertiary," when referring to particles. These adjectives refer to the aggregate level of particles and do not indicate the number of elements that make up the particle. Primary particles are particles that do not contain any other particles, although they may later be embedded in secondary particles. Secondary particles are particles composed of multiple primary particles. Tertiary particles are particles composed of multiple secondary particles.

[0028] Since this application focuses solely on "secondary" level aggregates, for clarity, it is preferable to use the term "nanoscale domain" instead of "primary particle" and the term "silicon-based composite particle" instead of "secondary particle." Accordingly, the term "nanoscale domain" in this application corresponds to "primary particle" in Patent Document 4, and the term "silicon-based composite particle" in this application corresponds to "secondary particle" in Patent Document 4.

[0029] However, this does not necessarily mean that the nanoscale domains of the present application are identical to the primary particles of the prior art, nor does it mean that the silicon-based composite particles of the present application are identical to the secondary particles of the prior art. In some embodiments of the particles of the present application, there may be differences in chemical composition and / or structure compared to the primary and secondary particles of Patent Document 4.

[0030] [Silicon-based composite particles] A first aspect of the present invention relates to silicon-based composite particles, wherein each of the silicon-based composite particles is - Composed of a bulk material containing silicon and carbon, -Having multiple nanoscale silicon domains embedded within the bulk material, The total chemical composition of the silicon-based composite particles is: -Based on the total mass of the silicon-based composite particles, 2.3 to 60.9 atomic percent (approximately 1 to 40 weight percent) of carbon and -Containing silicon and the remainder which is an unintended impurity, The silicon-based composite particles are, - Volume-based median diameter D50 is in the range of 1 to 9 μm, and - volume-based diameter ratio D 90 / D 10 is in the range of 1 to 9, and - volume-based particle diameter D 10 , D 50 , D 90 are determined by laser diffraction analysis in accordance with ISO 13320:2020.

[0031] As used herein, the terms "total chemical composition containing an element" and / or "total amount of an element" encompass the total content of the element in all constituent components and all parts from the core center to the surface of the present silicon-based composite particles, but do not include the final surface coating formed on the particles. The final content of the element in the surface coating formed on the particles is excluded from the total content of the particles.

[0032] In view of the prior secondary particles of Patent Document 4, the technical feature common to all embodiments of the silicon-based composite particles of the present application is that through improved control of temperature and flow conditions during nucleation and growth of the particles, the particles have a relatively narrow size distribution while being increased in size. This is defined as: volume-based median diameter D 50 is in the range of 1 to 9 μm, and the D 90 / D 10 ratio is specified to be in the range of 1 to 9. The BET specific surface area of the particles, determined according to ISO 9277:2010, is in the range of 0.4 to 5 m 2 / g.

[0033] In one embodiment, the silicon-based composite particles of the present invention advantageously have a volume-based median diameter D determined by laser diffraction analysis in accordance with ISO 13320:2020 50 of 1.1 to 8 μm, more preferably 1.2 to 7 μm, still more preferably 1.6 to 6 μm, and most preferably 2.0 to 5 μm.

[0034] As used herein, the phrase "comprising silicon and carbon"

[0035] Laser diffraction analysis in accordance with ISO standard 13320:2020 is used to determine the volume-based particle size distribution D of silicon-based composite particles. 10 and D 90 It can also be used to provide D 90 / D 10 It is used to determine ratios.

[0036] In one embodiment, the silicon-based composite particles of the present invention are advantageously determined by ISO standard 13320:2020. 90 / D 10 The ratio is in the range of 1.5 to 8, preferably 2 to 7, more preferably 2 to 6, and most preferably 3 to 5.

[0037] In one embodiment, the total chemical composition of the silicon-based composite particles is advantageously 2.3 to 50.1 atomic% (about 1 to 30 wt%) of carbon in total amount, preferably 4.5 to 47 atomic% (about 2 to 27.5 wt%), more preferably 6.7 to 43.8 atomic% (about 3 to 25 wt%), more preferably 11 to 36.9 atomic% (about 5 to 20 wt%), more preferably 15 to 33.9 atomic% (about 7 to 18 wt%), and most preferably 18.8 to 29.2 atomic% (about 9 to 15 wt%), with the remainder being silicon and unintended impurities.

[0038] A higher carbon content results in greater stability, which is advantageous for some particle applications, while a lower carbon content leads to higher capacity, which is preferable for other applications.

[0039] The relatively large particle size of the silicon-based composite particles in this invention is advantageous in that it improves the efficiency of the first cycle. After manufacturing and assembly, lithium-ion secondary batteries must undergo an initial charge-discharge cycle (often called a chemical formation cycle). In chemical formation, lithium ions released by the positive electrode active material during the charging phase move through the electrolyte and are absorbed by the negative electrode active material. Subsequently, the reverse phenomenon occurs during the discharge phase. However, it has been found that the amount of lithium ions returning to the positive electrode during the discharge phase is less than the amount of lithium ions released from the positive electrode during the charging phase. This loss of (available) lithium in the battery during the first cycle is known to increase linearly with the total surface area of ​​the active material, and depending on the type of electrode used, it usually reduces the battery's energy storage capacity by 2-20%. Reference 7 states that this loss of lithium due to the formation of a solid electrolyte interface layer during the first cycle is approximately 10 mAh / m² per surface area. 2 This is an estimate.

[0040] The relatively narrow particle size distribution in the silicon-based composite particles of this application is particularly D 50 When the diameter is relatively large, there is an advantage in that there are relatively few "too large" particles, that is, the D of the particles. 99 This offers the advantage that fractionation does not become so large as to significantly reduce the material's capacity and cycle characteristics. As particles become larger, the diffusion distance of lithium atoms moving in and out of the particle increases, increasing the current density on the surface and thereby increasing charge transfer resistance. Both of these mechanisms increase the risk of lithium being diffusely trapped inside the particle. Therefore, particles that are too large become partially inactive as active material. The largest particles also risk having too much absolute expansion, which can cause cell delamination and other damage. Furthermore, a narrow particle size distribution means that there are few very small particles, i.e., particles with a very large surface area per unit weight, which therefore contribute to lithium loss during the conversion cycle.

[0041] Therefore, the silicon-based particles of the present invention have a relatively low D 90 / D 10 Ratio and a relatively large D 50By combining particle sizes, a combined effect is obtained that provides an active material with relatively few minimum size fractions that result in relatively high FCE loss, and also with relatively few maximum size fractions that are partially "dead" as active material. This makes it possible to use particles with a relatively large average diameter that provide good first-cycle efficiency without impairing charge / discharge speed or stability.

[0042] The silicon-based composite particles of this application are considered to be composite particles having a "raisin-filled dough" structure, similar to the preceding secondary particles of Patent Document 4, in which multiple minute nanoscale silicon domains ("raisins") are embedded in a bulk material ("dough") composed of silicon and carbon. The term "composite particle" used here refers to multiple nanoscale silicon domains, each constituting a first chemical phase, dispersed in the bulk material composed of silicon and carbon, and constituting at least one second chemical phase of the particle. The local distribution of silicon and carbon within the matrix may vary depending on the manufacturing history and subsequent heat treatment, but the nanoscale silicon domains are expected to be the main contributor to lithium storage capacity.

[0043] Experimental experience and tests on particle formation have shown that reaction temperature can alter the reaction kinetics and mechanism during the growth of silicon-based composite particles. This is supported, for example, by the temperature dependence of silanes and hydrocarbons, more precisely by the fact that the Si-H bond vibrations of silanes are activated at lower temperatures than the CH bond vibrations of hydrocarbons.

[0044] While not bound by theory, in the initial stages of homogeneous nucleation where nanoscale silicon domains are formed, liquid or semi-solid droplets with some fluidity at the reaction temperature are formed. Once the carbon-containing precursor gas becomes energetically available for the reaction, it is assumed that a layer of amorphous SiC and / or C forms around these droplets, thereby inhibiting the bonding of silicon nanoscale domains and / or their growth into larger silicon domains. As shown in Non-Patent Literature 6, the silicon domains are maintained in a nanoscale state by the carbon layer.

[0045] A droplet of liquid or semi-liquid silicon with a carbon layer subsequently undergoes two competing processes: droplet aggregation (driven by Brownian motion) and solidification (stepwise removal of hydrogen from Si or C precursor molecules). Droplets that come into contact before solidification (at least one droplet) aggregate to form nearly spherical silicon-based composite particles. The aggregation process is weakly dependent on temperature, while the processes of droplet formation, gas consumption, and solidification (hydrogen removal) are all exponential with temperature.

[0046] Therefore, at relatively high reaction temperatures exceeding 700-750°C, the initially formed droplets solidify into nanoscale silicon domains and rapidly release hydrogen, resulting in a limited aggregation time before the fluidity of the aggregate decreases and particle growth is restricted. Furthermore, at high temperatures, a large number of particles are generated, leaving little gas around the particles to sustain particle growth after initial droplet formation. Additionally, at high temperatures, CVD growth of carbon and silicon on already formed droplets occurs very rapidly. This explains why particles generated at high temperatures (at least 700-750°C) under otherwise identical conditions tend to be very small (with diameters of a few tenths of a nanometer) and exhibit a higher carbon content compared to particles formed at decomposition temperatures below 700°C using the same gas mixture. In this case, the (high-temperature) "dough" is composed of a silicon-carbon alloy.

[0047] Below 700°C, down to approximately 450°C, the solidification of droplets is delayed due to the decrease in temperature. Therefore, the reaction time increases, and more nanoscale domains gather to form relatively large, nearly spherical aggregates. Simultaneously, the gas consumption rate also decreases, requiring longer residence times to obtain a commercially viable precursor conversion rate. If both the reaction temperature and time can be controlled, it becomes possible to grow relatively large particles and control the particle size. In this case, the silicon-based composite particles are thought to consist mainly of densely packed nanoscale silicon domain "raisins," with amorphous SiC and / or C layers along the boundaries between the "raisins." The "basis" (bulk material) in this case is amorphous SiC present at the boundaries between the densely packed nanoscale silicon domain aggregates. x It is composed of a layer and / or an amorphous carbon layer several atomically thick. This results in a relatively high volume silicon density within the particle in the form of multiple relatively large nanoscale silicon domains. This structure is considered to be somewhat similar to the structure described by the silicon-carbon-containing thin film disclosed in Non-Patent Literature 6, which is formed on micron-sized carbon particles, but the essential difference is that in the particles of this application, this composition is present throughout the entire particle, from the core to the outer surface.

[0048] Therefore, in one embodiment, the bulk material consisting of silicon and carbon is amorphous SiC surrounding nanoscale silicon domains. x It is thought to be a network of amorphous SiC. x This may include Si atoms covalently bonded to both C atoms and Si atoms, as well as C atoms bonded to both C atoms and Si atoms. It is expected that the majority of carbon atoms in the bulk material will be bonded to at least one silicon atom. This clearly distinguishes the products of this application from conventional powders produced by depositing silicon particles into a porous carbon matrix. In another embodiment, the amorphous SiC x In addition to nanoscale silicon domains, nanoscale SiC xIt is partially crystallized in domains. Therefore, the term “silicon and carbon bulk material” used here means that the bulk material is C, Si, and / or SiC x This means it may include phases / domains.

[0049] In one embodiment, the bulk material of silicon-based composite particles according to the first aspect of the present invention is C and Si and / or SiC x It is composed of silicon and carbon existing in the form of phases / domains.

[0050] Particles that come into contact after solidification remain as separated particles. Particles that come into contact at an intermediate stage between the "fluid" and solid states may aggregate to form large clusters of minute particles. In this case, laser diffraction and DLS may show large values, while BET shows much smaller particle sizes.

[0051] Furthermore, when producing particles by the decomposition of silicon-containing gas and carbon-containing gas, followed by seed formation and aggregation and / or particle growth by chemical vapor deposition, relatively large particle size and a narrow particle size distribution of the composite particles of this application can be obtained by promoting rapid heating to a (relatively low) target process temperature to initiate condensation, applying a sufficiently long residence time to reduce turbulence in the gas phase, and controlling the flow conditions in the reactor so that at least the majority of the particles achieve the same or nearly the same residence time.

[0052] 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 (such as nitrogen and argon), and only trace amounts of oxygen (residue of air).

[0053] 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 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 may contain as much as 30 atomic percent of hydrogen in one embodiment, but preferably less than 1 atomic percent. In one embodiment, the unintended impurity 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.

[0054] 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.

[0055] Therefore, in one embodiment, the generated particles may mainly contain silicon and carbon, as well as unintended impurities including oxygen and / or hydrogen, small amounts of hydrogen, and final traces of unavoidable impurities and 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.

[0056] In a particularly preferred embodiment, the total chemical composition of the silicon-based composite particles is: -Based on the total mass of silicon-based composite particles, the composition contains 2.3 to 50.1 atomic% (approximately 1 to 30 wt%) of carbon, preferably 6.7 to 43.8 atomic% (approximately 3 to 25 wt%) of carbon, more preferably 11 to 36.9 atomic% (approximately 5 to 20 wt%) of carbon, more preferably 15 to 33.9 atomic% (approximately 7 to 18 wt%) of carbon, and most preferably 18.8 to 29.2 atomic% (approximately 9 to 15 wt%) of carbon, -0.1 to 4 atomic percent of oxygen, preferably 0.2 to 3 atomic percent of oxygen, more preferably 0.3 to 2 atomic percent of oxygen, more preferably 0.4 to 1 atomic percent of oxygen, most preferably 0.5 to 1 atomic percent of oxygen, - Less than 30 atomic percent of hydrogen, preferably less than 20 atomic percent of hydrogen, more preferably less than 15 atomic percent of hydrogen, more preferably less than 10 atomic percent of hydrogen, more preferably less than 5 atomic percent of hydrogen, most preferably less than 1 atomic percent of hydrogen, -Si and the remainder which are unintended impurities This includes.

[0057] The total content of silicon, and / or carbon, and / or hydrogen, and / or oxygen in silicon-based composite particles can be determined, for example, by atomic absorption spectrometry (AA), inductively coupled plasma mass spectrometry (ICP-MS), ICP-OES, or X-ray fluorescence spectrometry (XRF). 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.

[0058] Silicon-based composite particles can be used directly in the anode. In a preferred embodiment, the silicon-based composite particles further include an outer coating to protect them from oxidation in air and reaction with electrolytes, and can be used directly in the anode. In a preferred embodiment, the anode further includes battery-grade graphite or other carbon allotropes, so that both the silicon-based composite material and graphite / carbon of the present invention contribute to lithium storage. Battery-grade graphite is commercially available from many manufacturers using various manufacturing methods.

[0059] In one embodiment, silicon-based composite particles may further include an outer coating. The outer coating may be intended, for example, to improve stability against oxidation, improve electronic conductivity, provide good and strong chemical bonding between the matrix and particles, or improve dispersion properties. The outer coating may further be optimized to facilitate electron transport, lithium transport, and / or charge transfer reactions. The outer coating may further be optimized to obtain a thin and stable SEI layer. The outer coating may be carbon, organometallic structures, organic molecules, Li x Siy O, Ti x O, Al x The coating may include oxides such as 0, or organometallic structures, or any combination thereof. 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. The coating can be applied using wet chemical processes, CVD, ALD, or other techniques.

[0060] In a preferred embodiment, the particles according to the present invention further include a surface coating of an amorphous or crystalline carbon layer having a thickness in the range of 0.5 to 10 nm, preferably 1 to 5 nm, and most preferably 2 to 3 nm, as determined by Auger spectroscopy.

[0061] 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.

[0062] In one embodiment, the coating applied to silicon-based composite particles is formed by exposing the silicon-based composite particles to a carbon-containing gas and heating the gas to a coating temperature at which it reacts with the silicon-based composite particles. In one embodiment, the coating temperature is 30°C to 1200°C, preferably 300°C to 1000°C, and most preferably 600°C to 900°C.

[0063] The silicon-based composite particles described above are typically spherical or nearly spherical in shape. However, the particles may aggregate into single-branched or multi-directional particle chains. Such chains can be broken by a gentle grinding process, i.e., a grinding process using sufficient force (supply pressure and grinding pressure) to break the chains. This results in a more uniform particle size distribution, but without the resulting size being so large that a large portion of the particle surface is altered by the grinding process.

[0064] Therefore, in one embodiment, the silicon-based composite particles according to the first aspect of the present invention undergo a gentle grinding process that maintains the substantially spherical shape of the particles.

[0065] The term "nearly spherical" used here means that the particles are formed such that their shape meets the following criteria. -Of all the segments of the outer circumference of particles appearing in the SEM image of the material, at least 50%, preferably at least 60%, more preferably at least 70%, more preferably at least 80%, more preferably at least 90%, and most preferably at least 95%, are circular arcs having arc length s, where s is determined by the relationship s = r × π / 180 × θ, where r is the radius of the circle whose curvature is the same as that of the circular arc, π is a mathematical constant equal to the ratio of the circumference of the circle to its diameter, and θ is the angle in degrees that the circular arc makes at the center of the circle. - The angle θ is in the range of 10° to 360°.

[0066] In one embodiment, the silicon-based composite particles have a BET specific surface area of ​​0.2 to 10 m² as determined by ISO standard 9277:2010. 2 / g, preferably 0.3-8m 2 / g, more preferably 0.4~6m 2 / g, most preferably 0.5~4m 2 It is / g.

[0067] [Nanoscale domain] A further difference from the secondary particles described in Patent Document 4 is that the nanoscale silicon domains (referred to as primary particles in Patent Document 4) of the silicon-based composite particles of this application are substantially pure silicon. While the presence of carbon in the precursor gas mixture may allow some carbon to enter these nanoscale silicon domains, it is likely only in trace amounts. Determination of the crystal lattice constant by XRD analysis (e.g., after rapid crystallization at 900°C for 30 minutes) is consistent with that of pure silicon.

[0068] Furthermore, based on experience with carbon gettering in silicon for solar cells, for example, the inventors are unaware of reports indicating high carbon mobility at such temperatures. This suggests that even if carbon is present within nanoscale domains, its content is extremely low. While XRD analysis of pre-crystallization particles is in good agreement with that of amorphous silicon, electron energy loss spectroscopy (EELS), averaging over a somewhat broader region encompassing both nanoscale domains and the binding matrix, demonstrates the presence of carbon. This may indicate the presence of some carbon within nanoscale domains. Depth-direction variations in the C:Si ratio within a volume contributing to a single data point also contribute to some uncertainty in the EELS data. Moreover, if the silicon originates from SiH4 or other hydrogen-containing precursor gases, residual fractions of H may also be present within the nanoscale silicon domains.

[0069] Therefore, the term "nanoscale silicon domain" used herein refers to nanoscale silicon particles that may contain trace amounts of carbon and / or hydrogen and / or oxygen. The silicon content is at least 90 atomic percent, and may be as high as 98-100 atomic percent, based on the mass of the nanoscale silicon domain.

[0070] The average diameter of nanoscale silicon domains is typically in the range of 0.5 to 10 nm. In one embodiment, the average diameter of the nanodomains, which are mainly silicon and constitute the nanosize domains, is 1 to 8 nm, more preferably 2 to 7 nm, more preferably 3 to 6 nm, and most preferably 4 to 5 nm. This average diameter is determined by lead belt refinement of X-ray powder diffraction (XPD) data after heat treatment of silicon-based composite particles to crystallize the nanosize silicon domains therein, as required.

[0071] An advantage of the secondary particles according to the present invention is that they can be manufactured at a temperature at which the nanodomains, primarily silicon, constituting the primary particles become amorphous. Lithium batteries manufactured from amorphous silicon have improved tolerance to volume changes associated with lithiumization cycles compared to those made from crystalline silicon. However, the nanodomains, primarily silicon, constituting the primary particles may be crystalline, or a mixture of amorphous and crystalline nanodomains.

[0072] The advantage of nanoscale silicon domains is that, when used as an active material in lithium-ion secondary batteries, they are expected to increase lithiation capacity without impairing cycle characteristics. Lithiation capacity is increased because silicon domains provide a large storage volume for lithium atoms, and cycle characteristics are improved because nanoscale silicon is more robust and can withstand 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, the fact that CC bonds remain intact and the particle structure is maintained even in the lithified state is also considered very attractive.

[0073] X-ray diffraction (XRD) (also referred to as powder X-ray diffraction (PXD) or X-ray powder diffraction (XPD) in the literature when applied to particulate matter) yields different diffraction patterns for crystalline and amorphous materials. Crystalline materials, due to their high order and symmetry in atomic structure, tend to exhibit sharp peaks, or Bragg peaks, in XRD measurements. In the case of crystalline silicon materials, XRD analysis typically shows sharp peaks at 28.4°, 47.4°, and 56.1° in the measured diffraction pattern. In contrast, amorphous materials, which lack the long-range ordering properties of crystalline atomic structure, typically show significantly broader, "smeared-out" peaks in the measured diffraction pattern. Amorphous silicon typically shows rounded peaks at 28° and 52°. These rounded peaks can be fitted using Gaussian fitting to reduce noise and obtain clearly defined values ​​for the maximum peak value and width. This type of fitting can be performed by any skilled XRD operator.

[0074] Furthermore, the "sharpness" of the peak can be used to distinguish between crystalline and amorphous materials. When non-monochromatic CuKα emission is applied and measured with a Gaussian-fitted diffractometer, the typical full width at half maximum (FWHM) of the XRD peak of crystalline silicon is usually less than 2° to 4°, while the FWHM of amorphous silicon is usually greater than 4°. The FWHM is the width of the peak curve measured between two points on the y-axis that are half the maximum amplitude of the peak curve (after subtracting the background signal and / or the signal from the sample holder). In samples containing both amorphous and crystalline silicon, XRD analysis yields diffraction patterns that show both a sharp Bragg peak typical of the crystalline phase and a broader, more Gaussian peak typical of the amorphous phase. Using the diffraction pattern, the crystalline fraction of the sample can be estimated from the ratio of the area below the Bragg peak above the amorphous broad peak to the combined area of ​​the broad peak and the Bragg peak. Prior to calculation, the linear background must be subtracted from the calculation.

[0075] The angles and angular tolerances used in this XRD analysis refer to the use of a diffractometer employing non-monochromatic CuKα radiation. This is because this radiation has high intensity and a wavelength of 1.5406 angstroms, which corresponds well to the interatomic distances of crystalline solids, enabling analysis sensitive to the presence of crystalline phases in silicon particles. XRD analysis using a diffractometer employing CuKα radiation is a natural choice for similar reasons, and is therefore the most widely used technique in XRD analysis, well known and mastered by those skilled in the art. Other diffractometers employing radiation of other wavelengths may yield different angles and angular tolerances. However, those skilled in the art know how to convert these values ​​from one radiation source to another.

[0076] Furthermore, silicon crystalline nanodomains (less than several hundred nanometers) result in a characteristic peak expansion of the Bragg peak obtained by X-ray powder diffraction (XPD). This peak expansion can be used, for example, to determine the average diameter of nano-sized domains (embedded within silicon-based composite particles) by Rietveld refinement of XPD data obtained from XPD analysis of silicon-based composite particles in unimodal or multimodal distributions.

[0077] If some or all of the nanodomains constituting the nanosize domain are amorphous, particle size measurement should include an initial heat treatment to crystallize the nanodomains constituting the nanosize domain, for example, heat treatment at 900°C for at least 30 minutes.

[0078] Rietveld analysis of XPD data for determining average particle size is well known and mastered by those skilled in the art. An example of such analysis is the so-called Rietveld refinement, which involves fitting XPD data calculated from a crystalline Si model to experimental data obtained from XPD measurements of silicon-based composite particle samples using the least squares method. Rietveld refinement can be performed using freely available software such as GSAS-II (Non-Patent Literature 5) or commercially available software such as Topas (Non-Patent Literature 6). The instrumental contribution to the Bragg peak width is calculated from the instrument's geometric shape ("Fundamental Parameter Method" (Non-Patent Literature 7)) or described by the Thomson-Cox-Hastings pseudo-Voigt function (Non-Patent Literature 8) experimentally determined from highly crystalline standard materials such as NIST SRM 640f silicon. The instrumental contribution to the Bragg peak remains fixed during Rietveld refinement. Any additional broadening of the observed Bragg peak is assumed to be due to minute crystallite sizes and to have a Lorentz shape. This crystallite size broadening is modeled by refining the additional contribution β to the calculated Bragg peak width, which changes depending on the scattering angle as shown below.

number

[0079] [Product by Process] A second aspect of the present invention relates to particles produced by a method according to a third aspect of the present invention.

[0080] [Manufacturing method] A second aspect of the present invention relates to a method for producing silicon-based composite particles according to the first aspect of the present invention, the method being: - Initial pressure is 5 × 10 3 ~6×10 5 A step using a reactor having a decomposition compartment containing a first reactor gas, where the temperature is in the range of Pa and the first reactor temperature is in the range of 450 to 650°C, - 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. - The step of injecting the precursor gas mixture into the decomposition compartment and mixing it with the first reactor gas to form a second reactor gas mixture, The above method further, - A step of maintaining the temperature of the second reactor gas mixture within ±20°C, preferably within ±10°C, more preferably within ±5°C, and most preferably within ±1°C, of ​​the first reactor temperature while holding the second reactor gas mixture in the decomposition compartment for a residence time in the range of 10 to 300 seconds. - Includes the step of extracting the particles from the decomposition compartment. It is characterized by the following:

[0081] The essential characteristic of the particles in this application is that the particles are relatively large D particles of 1-9 μm. 50 And, D 90 / D 10 The particle size distribution has a relatively narrow ratio in the range of 1 to 9. This is achieved by controlling the flow conditions so that the majority, preferably all, of the particles in the gas phase within the reactor are exposed to virtually identical average temperature conditions and durations (residence times) before being extracted and cooled.

[0082] In typical continuous flow reactors, thermal convection becomes dominant when reaction times exceed a few seconds, making it difficult to achieve laminar flow. The residence time of a single atom or particle within the reactor can vary significantly depending on its path. This means that more precursor gas may be discharged from the reactor unconsumed, and many particles may exit the reactor while remaining very small. At the same time, some particles may circulate within the reactor for extended periods, so there is no clear upper limit to particle size.

[0083] Therefore, the reactor is a tubular high-temperature wall reactor, and the preheated precursor gas mixture and the preheated first gas are injected simultaneously from one end. The flow conditions in the reactor are laminar to ensure a predictable migration time until the generated particles are extracted from the opposite end.

[0084] Another method to ensure nearly identical processing conditions involves injecting a mixture of preheated precursor gases into a closed-type high-temperature wall reactor and extracting the entire batch by flushing or vacuum suction once the intended residence time is reached, or by allowing the particles to grow heavy enough to settle from the gas phase, and then recovering and extracting them. In particular, rapid acceleration at corners can cause the settling of heavy particles, as in cyclone particle separators.

[0085] The latter solution, which involves allowing the particles to grow until they fall from the gas phase, can result in a significant sorting effect on the resulting particles. This sorting effect is strong enough to include smaller size fractions of particles that remain entrained in the gas phase and are discharged from the reactor along with the gas entraining the particles during particle recovery, thus achieving the intended D 90 / D 10 A narrow particle size distribution with a specific ratio can be obtained.

[0086] 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.

[0087] Similarly, the term “second precursor gas of carbon-containing compound” as used herein refers to 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), ethyne (C2H2), cyclohexane, cyclohexene, toluene, benzene, or mixtures thereof. This gas phase may also contain small or large amounts of hydrogen.

[0088] 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), butane (C4H 10 ), etene (C2H4), ethyne (C2H2), propene (C3H6), butene (C4H8), pentene (C5H 10 ), a mixture of hydrocarbon gases selected from cyclohexane, cyclohexene, toluene, benzene, and mixtures thereof. 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.

[0089] The production yield in a gas-phase reaction process, defined as the ratio of the mass of generated particles to the mass of the precursor gas supplied to the reactor, has been shown to depend on process parameters such as the concentration of the precursor gas in the reaction region, the reaction temperature, and / or the residence time of the precursor gas in the reaction region. Generally, higher reaction temperatures lead to a higher degree of dissociation of the precursor gas, and consequently, a higher production yield. Furthermore, residence time can also have a significant impact on the production yield. Generally, longer residence times allow more of the injected gas to react and form particles. Therefore, the characteristic of obtaining large particles using relatively long residence times is advantageous from the standpoint of production yield. This method has the advantage of achieving a high production yield, which gives it a significant economic advantage given that silicon hydride gases such as silane and disilane are relatively expensive.

[0090] In one embodiment, the method of the present invention, -A reactor is used that has a tubular high-temperature wall-decomposition compartment having a first end and a second end, and -A constant volume flow of a preheated precursor gas mixture and a constant volume flow of a preheated first reactor gas are injected into the first end to form a constant volume flow of a second reactor gas mixture within the tubular high-temperature wall decomposition compartment, and - The second reactor gas mixture is passed through the tubular high-temperature wall decomposition compartment from the first end to the second end under laminar flow conditions with a Reynolds number of less than 2000, and -By extracting the second reactor gas mixture containing the formed particles at the second end, or -A reactor equipped with a closed-type high-temperature wall-breaking compartment containing a first reactor gas, and - A preheated precursor gas mixture is injected into the high-temperature wall decomposition compartment at a first time point to form a second reactor gas mixture, and -When the residence time is reached, calculated from the first time point, both the second reactor gas mixture and the formed particles are extracted from the high-temperature wall decomposition compartment by vacuum suction or flushing. or -A reactor is used that comprises a closed-type high-temperature wall decomposition compartment containing a first reactor gas and a cooling recovery chamber provided at the bottom of the decomposition compartment, and - A preheated precursor gas mixture is injected into the high-temperature wall decomposition compartment to form a second reactor gas mixture, and -By retaining the second reactor gas mixture in the decomposition compartment until the formed particles grow to a size that allows them to settle from the second reactor gas mixture and fall into the recovery chamber by gravity, This allows for advantageous maintenance of the temperature of the second reactor gas mixture within the decomposition compartment.

[0091] The relatively large defined residence time range reflects the relatively large decomposition temperature range of 450-650°C and the particle size range of 1-9 μm applicable to particle formation in this invention. Table 2 below shows the results for D with a residence time of 45 seconds and reaction temperatures of 570°C and 620°C. 50 Two examples are shown in which particles of 3.8 and 3.9 μm were obtained. Those skilled in the art can determine the residence time and temperature to be used to produce particles of these sizes based on this disclosure and general knowledge, and can obtain the intended narrow particle size distribution by controlling the gas flow rate and temperature in the reactor as necessary through simple trial and error.

[0092] In embodiments of the present invention, the first reactor temperature is in the range of 475 to 630°C, preferably 500 to 620°C, more preferably 525 to 600°C, and most preferably 550 to 580°C.

[0093] In embodiments of the present invention, the residence time is advantageously in the range of 12.5 to 250 seconds, preferably 15 to 200 seconds, more preferably 17.5 to 150 seconds, more preferably 20 to 100 seconds, more preferably 25 to 75 seconds, and most preferably 30 to 50 seconds.

[0094] 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 reactor gas, 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.

[0095] In embodiments of the present invention, the atomic ratio 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.

[0096] In embodiments of the present invention, the precursor gas mixture can be preheated to a temperature in the range of 250 to 450°C, preferably 300 to 390°C, more preferably 325 to 380°C, and most preferably 350 to 370°C, before injecting a homogeneous gas mixture into the reactor space.

[0097] The term “reactor gas” as used herein encompasses the exhaust gas generated from the previous production of silicon-based composite 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.

[0098] By heat-treating the particles before and after surface coating, good transport and adhesion properties can be obtained, and cycle stability can be improved. The following options are available: - Crosslinking / cyclization only; significant hydrogen remains in 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 rate, risk of excessive SiC formation at the Si-C interface, risk of capacity reduction, however, coating quality may be further improved) (above 1000℃)

[0099] In one embodiment, the method according to the present invention involves depositing an amorphous or crystalline carbon layer on the outer surface of particles by chemical vapor deposition of a carbon-containing precursor gas, preferably an alkene gas, at a temperature in the range of 650 to 750°C. This amorphous or crystalline carbon layer is advantageously in the range of 0.5 to 20 nm, preferably 1 to 10 nm, most preferably 2 to 7 nm (determined by Auger spectroscopy), in order to improve surface properties and electronic conductivity, reduce the risk of fire, and promote the formation of a stable solid electrolyte interface (SEI). The present invention is not limited to specific coating materials or particle coating methods, and any coating and coating methods known to those skilled in the art for coating silicon particles can be used.

[0100] [List of drawings] Figure 1 shows the XRD analysis of 1.7 nm silicon nanoparticles (sample S1 or S2) embedded in a carbon-rich matrix according to Patent Document 4, after heat treatment at 900°C for 30 minutes. The average atomic content of the composite material is 35% carbon and 65% silicon.

[0101] Figure 2 shows the XRD analysis of 3.4 nm silicon nanoparticles (sample S3) embedded in a carbon-rich matrix according to Patent Document 4 after heat treatment at 900°C for 30 minutes, using a unimodal crystallite size distribution. The average atomic content of the composite material is 16% carbon and 84% silicon.

[0102] Figure 3 is a TEM image showing crystalline silicon nanodomains of silicon-based composite particles (sample S1) according to Patent Document 4 after heat treatment at 900°C for 30 minutes.

[0103] Figure 4 is a series of TEM images showing secondary composite particles according to Patent Document 4.

[0104] Figure 5 is a TEM image showing pure silicon nanoparticles with the same outer diameter as those in Figure 4, but without heat treatment.

[0105] Figure 6 shows the XRD analysis of particles produced according to the present invention. These particles have a total carbon content of 14% by weight.

[0106] Figure 7a) is a TEM image showing one embodiment of the present invention, and Figure 7b) is a diagram showing EELS elemental analysis across a particle.

[0107] Figure 8a) shows a TEM image of one embodiment of the present invention, and Figure 8b) shows the EELS elemental analysis across the particles.

[0108] Figures 9 and 10 show Fourier transforms using bandpass masks centered at 0.314 nm and 0.252 nm, respectively, to highlight crystalline silicon and silicon carbide in the example shown in the TEM image of Figure 7a).

[0109] Figures 11a) and 11b) show the size distributions of two powders prepared using similar temperatures and gas mixtures. In the S4 powder (gray line), the residence time and temperature in the reactor were non-uniform. In the S5 powder (black line), the residence time and temperature were as per the present invention. Both particle size distributions were measured immediately after silicon particle production and before coating. Figure 11a) shows the volume-based distribution, and Figure 11b) shows the area-weighted distribution. The volume-based figure shows that the fine particles in the left tail contribute little to the cell capacity. The area-weighted figure shows that this same tail significantly contributes to SEI formation and, consequently, to FCE reduction.

[0110] Figure 12 shows cycle data for S6 powder manufactured by the method described herein, followed by 650°C heat treatment, PAN coating, and polymer crosslinking at 500°C. The reference is a pure graphite electrode, and the upper line indicates a cell containing 10 wt% silicon in 90 wt% graphite. 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 the repetition of the 2×C / 10+20×C / 2 set. Capacity and FCE were measured in a separate cell without graphite to reduce uncertainty, as graphite helps prevent electrode delamination, allowing for accurate measurement of silicon degradation.

[0111] Figure 13 shows the cycle data for S5 powder manufactured by the method described herein, followed by 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 in 85 wt% graphite. 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 the repetition of the 2×C / 10+20×C / 2 set. Here again, FCE and capacitance were measured in a separate cell without graphite.

[0112] Figure 14 shows the cycle data for S4 powder in three versions. S4-1: No heat treatment S4-2: Heat treatment at 820°C for 2 hours S4-3: After sugar coating, heat treatment at 820°C for 2 hours. In all cases, the powder was mixed with graphite in a 50 / 50 ratio. Chemical conversion rate test (3 cycles each for C / 10, C / 5, C / 3, C / 2, C, and 2C) S4-2 additional test: 20 × (C / 20 + 10 × C / 3), after approximately 250 cycles: new rate test, then return to 25 × (C / 10 + 10 × 1 C / 3). For S4-3, after approximately 250 cycles (C / 10 + 20xC / 2) The highest point of the low-speed cycle was used as the "maximum capacity" for S4-3.

[0113] Figures 15a) and 15b) show SEM images of the particulate material according to the present invention before (Figure 15a)) and after (Figure 15b)) a gentle grinding process. In the unground material, the outer circumference of all particles can be seen as an aggregate with a nearly circular outer circumference, whereas in the gently ground material, as indicated by the white arrows, the outer circumference of some particles is not circular.

[0114] Figure 16 shows SEM images of various metallurgical-grade crystalline silicon particles (Non-Patent Literature 8) obtained under different grinding conditions. Because silicon is a brittle material, the surface edges are initially very sharp, but after more extensive grinding, the particles gradually aggregate with each other and tend to become more irregular in shape.

[0115] Figure 17 shows a portion of the SEM image from Figure 15b), illustrating an example where the outer perimeter is an arc. This is a result of fracture during the grinding process, and the portion of the outer perimeter that does not form an arc / circle is shown as a dotted line.

[0116] [Verification of the invention] The present invention will be described in more detail by reference to examples.

[0117] [Comparative experiment] This chapter compares the particle size and particle size distribution obtained by the present invention with the particle size distribution and particle size of a sample prepared by the method described in Patent Document 4, and further compares it with the prior art silicon particles disclosed in Patent Document 5.

[0118] All silicon-based composite particle samples used in this comparison were prepared by condensation and chemical vapor deposition of a mixture of silicon-containing precursor gas and carbon-containing precursor gas under a protective atmosphere in a decomposition reactor (except for Patent Document 5, which used only silicon-containing precursor gas).

[0119] The following is a typical manufacturing process for producing the C1, C2, and C3 particles shown below. A homogeneous first mixture of silane and ethene gases in a specific molar ratio was heated to a specific preheating temperature and then introduced into a reaction chamber. In the reaction chamber, the homogeneous precursor gas mixture was rapidly heated to a specific reaction temperature by further mixing with approximately 10 times the amount of preheated inert gas (nitrogen) to form a second gas mixture. The second gas mixture passed through the reactor for a controlled residence time, after which it was discharged and cooled to halt the gas condensation / chemical vapor deposition reaction. The non-uniformity of how rapidly the various gas fractions were diluted / heated resulted in differences in particle size distribution.

[0120] S4 powder was produced in reactors with slightly different thermal histories for various gas fractionations, resulting in smaller reactor sizes for high-temperature fractionations and larger reactor sizes for low-temperature fractionations.

[0121] A typical manufacturing process for producing the particles in the present invention (including powders S6, S5, S7, and S8 described later) is as follows: A homogeneous first mixture of silane gas and ethene gas in a specific molar ratio is heated to a predetermined preheating temperature and then introduced into a reactor chamber, where the homogeneous precursor gas mixture is supplied to a sealed chamber containing some preheated gas (residual from the previous manufacturing batch) to form a second gas mixture. The low reaction temperature ensures that variations in dilution / heating are not very important for particle formation. The second gas mixture is maintained for a predetermined residence time, during which the reactants are consumed by the chemical reaction and the particle size increases. Finally, the gas is discharged from the chamber to stop the reaction. This ensures a very similar history for all particles and a very homogeneous particle size distribution, while maintaining a good yield of silane and carbon precursors.

[0122] The applied molar ratio of silane and ethene precursor gases, preheating temperature (of the precursor gas mixture), reaction temperature (of the second gas mixture), and residence time are shown in Table 1 or Table 2 below. Table 1 shows the manufacturing parameters used for the “old” secondary particles based on the disclosure in Patent Document 4, and Table 2 shows the manufacturing parameters used for the particles according to the present invention. Furthermore, these tables show the BET and D of the recovered particles after annealing and CVD-based coating processes to make the particles resistant to air. 90 / D 10 The ratio is shown. Samples C2 and C3 have high D 90 / D 10 This can probably be explained by a completely heterogeneous gas mixture due to turbulence that results in short residence times and variations in residence times.

[0123] The recovered particles include both the heavier, settled fraction (recovered from the bottom of the reactor) and the minute entrained particles recovered by downstream filtration of the gas flow leaving the reactor. BET was measured in accordance with ISO 9277:2010. See Table 1 for details. 90 / D 10The ratio was determined by laser diffraction (using a Malvern Mastersizer 3000 instrument) in accordance with ISO 13320:2020. A low BET specific surface area of ​​the particles is crucial for achieving high first-cycle efficiency (FCE) in the conversion cycle of lithium batteries. High FCE is important for reducing the manufacturing cost of lithium-ion batteries (LIBs).

[0124] Table 1 shows the process parameters used for comparative silicon-based composite particles and the resulting properties. [Table 1] 1) Prior art examples in Patent Document 5

[0125] Table 2 shows the process parameters used for the silicon-based composite particle sample according to the present invention and the properties obtained. [Table 2]

[0126] [Examples] A mixture of silane and ethene gases was mixed and preheated to 350°C, then supplied to a sealed reactor containing the first gas, which maintained a pressure of approximately 200 kPa and a temperature of 560°C. The reactor was supplied with silane gas at a flow rate of 8.8 slm (equivalent to standard liters per minute - 0.00073386 mol / second) and ethene gas at 3.2 slm for approximately 1 minute. The pressure inside the reactor then rose to approximately 0.9 kPa. These gases were held in the reactor for a further 45 seconds, after which the reactor was opened, the particles were flushed out, recovered, and coated for stabilization in the atmosphere.

[0127] Next, the particles were analyzed by XRD and found to be completely amorphous, as shown in the XRD diagram in Figure 6. A later derivative product D, which is nearly identical to this product, was also analyzed. 10 , D 50 , D 90 These values ​​were measured as 3.0, 6.9, and 14.3, respectively.

[0128] Subsequently, the particles were heat-treated at 900°C for 2 hours to crystallize their domains, and the domain sizes were determined by XRD analysis and Rietveld refinement. The obtained Si crystallites were estimated to be 1.9 nm, and the SiC crystallites were estimated to be 1.5 nm.

[0129] Figures 7a) and 8a) are TEM images of two particles with particle sizes of approximately 3 μm and 0.8 μm, respectively. These images show that the particles are extremely dense, lack any discernible porosity, and do not contain any discernible phases. This characteristic was confirmed by elemental composition analysis based on electron energy loss spectroscopy (EELS) performed across the particles along the cross-sections indicated by the two white lines in Figures 7a) and 8a), respectively.

[0130] The nanoscale crystalline domains of Si and SiC expected to be found in the heat-treated particles are too small to be directly observed in these TEM images. The crystalline phase can be visualized by Fourier transform using bandpass masks centered at 0.314 nm and 0.252 nm, corresponding to the maximum interplanar spacings in crystalline silicon and silicon carbide, respectively.

[0131] Figure 9 shows the results of a transformation using a bandpass mask centered at 0.314 nm for the sample shown in the TEM image of Figure 7a). This transformation was performed on a cross-section of the particle containing the graphite substrate on which the particle sample was fixed during analysis. This graphite is barely visible as a somewhat dark region occupying about 10% of the area at the bottom of the image. Above this relatively dark region are numerous bright dots indicating the presence of crystalline silicon. Note the relatively uniform and homogeneous distribution. This indicates that nanoscale domains of silicon are uniformly distributed throughout the particle. A similar impression can be seen in Figure 10, showing the transformation results using a bandpass mask centered at 0.258 nm in the same part of the particle, indicating the presence of nanoscale domains of crystalline silicon carbide.

[0132] These photographs were superimposed on each other, with the crystalline phase shown in one color and the crystalline silicon carbide phase in a contrasting color. This result is not included in this application because it is impossible to distinguish each phase in a black and white reproduction. However, the superimposed photographs showed that the silicon crystals and silicon carbide crystals were intertwined while being spatially separated. This was predicted by a composite structure consisting of densely packed aggregates of silicon domains having layers of amorphous carbon and / or amorphous silicon carbide at the particle boundaries, which crystallized upon heat treatment and accumulated in the crystalline silicon carbide regions between the crystalline silicon domains.

[0133] Therefore, these results are considered to confirm that the particles of this embodiment, manufactured at a relatively low temperature of 560°C and a pressure of less than 1 atmosphere, have a composite structure similar to the film described in Non-Patent Literature 6, provided that this composition is uniform throughout the particle, from the core to the outer surface. The homogeneity of these nanoscale silicon domains, the relatively large particle size, and the relatively narrow particle size distribution make these particles particularly suitable as a negative electrode active material for secondary LIBs. This is because they have a size that provides high initial cycle efficiency, a uniform distribution of carbon phases that provide excellent electrical conductivity and silicon phases that provide excellent lithium diffusivity (conductivity), and at the same time, a relatively high silicon content that provides high volumetric lithium storage capacity due to numerous fine nanoscale domains with excellent cycle characteristics.

[0134] The assertion that a narrow particle size distribution is advantageous has a solid theoretical basis, and experimental evidence from cell data supports this assertion. Because various powders included for reference were not available for rigorous testing, some quantities were estimated from available data, while others were measured directly. All cell data below is from coin-cell batteries. A standard CMC binder with pH-controlled aqueous buffer and a standard carbonate electrolyte containing 2% fluoroethylene carbonate as the sole additive were used. This tends to underestimate FCE due to the presence of many other surfaces that introduce losses. Therefore, the good FCE results shown herein are expected to be further improved in optimized commercial batteries.

[0135] To improve the electron transport properties of the materials, the samples were coated with trace amounts of conductive carbon. In both cases, the materials were coated by wet chemical coating using a solvent and polymer. Subsequently, the polymer was crosslinked or carbonized to form a conductive carbon network around the particles. For the S6 and S5 samples, the amount of carbon was selected so that the added carbon accounted for 2% by weight of the total sample weight after heat treatment. S6 was degassed at 650°C, coated with polyacrylonitrile, and crosslinked at 500°C. S5, on the other hand, was coated with bitumen and thermally decomposed at 900°C. For reference, data from smaller and more diverse S4 powders coated with sugar and thermally decomposed at 820°C for 2 hours were used. Several different types of PAN and bitumen precursors were tested, but the results were substantially similar to those shown here.

[0136] For powders S6 and S5, 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.

[0137] For S4 powder, only cells containing a 50 / 50 mixture of the powder and flake graphite are available. To evaluate the capacity and FCE of these cells, the lithiumization / delithiation capacity of the graphite fraction in the first cycle was evaluated using a graphite reference cell. Next, these values ​​were used to calculate the capacity and FCE that silicon should possess to obtain the measured total amount. The results of the S4 calculations are shown in the table below. Furthermore, since the sample is expected to require several cycles to fully activate all the powder, the FCE was recalculated based on the measured maximum capacity, assuming that all FCE loss occurred in the first cycle. Therefore, the reference FCE is clearly overestimated, but this optimal value will be used in subsequent comparisons. [Table 3]

[0138] This allows us to compare the FCE of powders with a narrow size distribution with the results of reference S4, which was produced using the same binder system and the same electrolyte. [Table 4]

[0139] As can be understood, the powder produced by the method disclosed herein exhibits remarkably high FCE values, especially considering that they are measured in coin-cell batteries. At the same time, long-term cycling demonstrates that the same powder can provide high capacity over many cycles when incorporated into appropriate electrodes.

[0140] Using a similar method to that used for sample S5, but manufactured in a chamber with more uniform temperature control, slightly smaller particles were obtained. These particles were then subjected to relatively gentle jet milling using a Schedio SSM100 spiral jet mill.

[0141] An example of the obtained particles is shown in Figure 15. While most of the surface remains completely untouched, the longest particle chains are broken down into smaller, more uniformly sized fragments. Using a feed rate of 1.9 kg / hr, a grinding pressure of 3.5 bar, and a feed pressure of 6 bar, the D90 / D10 ratio decreased from 4.5 to 2.6, but the BET specific surface area remained at 2 m². 2 It was / grams.

[0142] This improvement is likely beneficial because it allows for more uniform dispersion of the silicon composite material within the anode when mixed with graphite (the largest coarse particles disappear). Furthermore, although the material is easily recognizable as it is primarily composed of spherical particles, some of the surface consists of fragments where chains or spheres have been broken.

[0143] Figure 17, a magnified view of several particles from the SEM image in Figure 15b), shows that the majority of the particle's outer circumference is an arc. The outer circumference that does not form part of the arc / circle, which is a result of damage during the grinding process, is shown as a dotted line in Figure 17.

Claims

1. Silicon-based composite particles, each of the silicon-based composite particles is - Made of bulk material containing silicon and carbon, - Having a plurality of nanoscale silicon domains embedded within the bulk material, The silicon-based composite particles are, - Based on the total mass of the silicon-based composite particles, carbon is present in an amount of 2.3 to 60.9 atomic percent (approximately 1 to 40% by weight), and - The total chemical composition consists of silicon and unintended impurities. The silicon-based composite particles are, - Volume-based median diameter D ５０ It is in the range of 1 to 9 μm. - Volume-based diameter ratio D ９０ / D １０ The range is from 1 to 9. - Volume-based particle size D １０ , D ５０ , D ９０ These are silicon-based composite particles determined by laser diffraction analysis in accordance with ISO standard 13320:2020.

2. The silicon-based composite particles have a volume-based median diameter D determined by laser diffraction analysis in accordance with ISO standard 13320:2020. ５０ The silicon-based composite particles according to claim 1, wherein the particle size is 1.1 to 8 μm, more preferably 1.2 to 7 μm, more preferably 1.6 to 6 μm, and most preferably 2.0 to 5 μm.

3. The silicon-based composite particles have a volume-based diameter ratio D determined in accordance with ISO 13320:2020 ９０ / D １０ is in the range of 1.5 to 8, preferably 2 to 7, more preferably 2 to 6, and most preferably 3 to 5. The silicon-based composite particle according to claim 1 or 2.

4. A silicon-based composite particle according to any one of claims 1 to 3, wherein the average diameter of nano-sized domains 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, and optionally includes subjecting the silicon-based composite particle to heat treatment to crystallize the nano-sized domains inside it before the Rietveld refinement of the X-ray powder diffraction (XPD) data.

5. The total chemical composition of the silicon-based composite particles is - Contains carbon in a total amount of 2.3 to 50.1 atomic% (about 1 to 30 wt%), preferably 4.5 to 47 atomic% (about 2 to 27.5 wt%), more preferably 6.7 to 43.8 atomic% (about 3 to 25 wt%), more preferably 11 to 36.9 atomic% (about 5 to 20 wt%), more preferably 15 to 33.9 atomic% (about 7 to 18 wt%), and most preferably 18.8 to 29.2 atomic% (about 9 to 15 wt%). - The remainder is silicon and unintended impurities, as described in any one of claims 1 to 4.

6. The total chemical composition of the silicon-based composite particles is further defined as follows: -Based on the total mass of the silicon-based composite particles, the total amount of oxygen is less than 1.5% by weight, preferably less than 1.25% by weight, more preferably less than 1% by weight, more preferably less than 0.75% by weight, and most preferably less than 0.5% by weight. - The silicon-based composite particle according to claim 5, comprising hydrogen in a total amount of less than 1.5% by weight, preferably less than 1.25% by weight, more preferably less than 1% by weight, more preferably less than 0.75% by weight, and most preferably less than 0.5% by weight, based on the total mass of the silicon-based composite particle.

7. The particles further have an outer coating on their outer surface, and the coating is - Amorphous or crystalline carbon allotropes, Li ｘ Si ｙ O, Ti ｘ O, or Al ｘ An oxide or organometallic structure selected from O, and Having a thickness 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, - A particle according to any one of claims 1 to 6, which is an amorphous or crystalline carbon layer having a thickness determined by Auger spectroscopy in the range of 0.5 to 20 nm, preferably 1 to 10 nm, and most preferably 2 to 7 nm.

8. Silicon-based composite particles according to any one of claims 1 to 7, wherein the bulk material comprises an alloy of silicon and carbon.

9. Silicon-based composite particles according to any one of claims 1 to 7, wherein the bulk material includes an amorphous SiC layer and / or an amorphous C layer present at the boundaries between densely packed aggregates of nanoscale silicon domains.

10. Silicon-based composite particles according to any one of claims 1 to 9, wherein the particles are subjected to a grinding process.

11. The aforementioned particles meet the following criteria: - Of all the segments of the outer circumference of particles appearing in the SEM image of the material, at least 50%, preferably at least 60%, more preferably at least 70%, more preferably at least 80%, more preferably at least 90%, and most preferably at least 95%, are arcs having arc length s, where s is determined by the relationship s = r × π / 180 × θ, where r is the radius of the circle whose curvature is the same as that of the arc, π is a mathematical constant equal to the ratio of the circumference of the circle to its diameter, and θ is the angle in degrees that the arc makes at the center of the circle, and - The angle θ is in the range of 10° to 360°. A silicon-based composite particle according to any one of claims 1 to 10, which is substantially spherical as determined by [the relevant method].

12. The BET specific surface area, as determined by ISO standard 9277:2010, is between 0.2 and 10 m². ２ / g, preferably 0.3 to 8m ２ / g, more preferably 0.4 to 6m ２ / g, more preferably 0.5 to 4m ２ Silicon-based composite particles according to any one of claims 1 to 11, wherein the particle size is / g.

13. A method for producing silicon-based composite particles according to any one of claims 1 to 12, wherein the method is: - Initial pressure is 5 × 10 ３ ~6 x 10 ５ A step of using a reactor having a decomposition compartment containing a first reactor gas, which is in the range of Pa and whose first reactor temperature is in the range of 450 to 650°C, - 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, - The process includes the step of injecting the precursor gas mixture into the decomposition compartment and mixing it with the first reactor gas to form a second reactor gas mixture, The above method further, - A step of maintaining the second reactor gas mixture in the decomposition compartment for a residence time in the range of 10 to 300 seconds, during which time the temperature of the second reactor gas mixture is maintained within ±20°C, preferably within ±10°C, more preferably within ±5°C, and most preferably within ±1°C from the first reactor temperature. A method comprising the step of extracting the particles from the decomposition compartment.

14. The method according to claim 13, wherein the residence time is in the range of 12.5 to 250 seconds, preferably 15 to 200 seconds, more preferably 17.5 to 150 seconds, more preferably 20 to 100 seconds, more preferably 25 to 75 seconds, and most preferably 30 to 50 seconds.

15. The method according to claim 13 or 14, wherein the precursor gas mixture is preheated to a temperature in the range of 250 to 450°C, preferably 300 to 390°C, more preferably 325 to 380°C, and most preferably 350 to 370°C, before the homogeneous gas mixture is injected into the reactor space.

16. - The first precursor gas is silane (SiH ４ ), disilane (Si ２ H ６ ), trichlorosilane (HCl ３ It is either Si, an organosilane, or a mixture thereof. - The second precursor gas is either an organosilane or a hydrocarbon, preferably methane (CH4). ４ ), ethane (C ２ H ６ ), propane (C ３ H ８ ), butane (C ４ H １０ ), Eten (C ２ H ４ ), etyne (C ２ H ２ ), propene (C ３ H ６ ), butene (C ４ H ８ ), Penten (C ５ H １０ The method according to any one of claims 13 to 15, wherein the cyclohexane, cyclohexene, toluene, benzene, or a mixture thereof.

17. The method according to any one of claims 13 to 16, wherein the first reactor temperature is in the range of 475 to 630°C, preferably 500 to 620°C, more preferably 525 to 600°C, and most preferably 550 to 580°C.

18. The method according to any one of claims 13 to 17, wherein the atomic ratio of silicon to carbon 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.

19. - Using a reactor equipped with a tubular high-temperature wall-decomposition compartment having a first end and a second end, - A constant volume flow of preheated precursor gas mixture and a constant volume flow of preheated first reactor gas are injected into the first end to form a low volume flow of the second reactor gas mixture within the tubular high-temperature wall decomposition compartment, and - The second reactor gas mixture is passed through the tubular high-temperature wall decomposition compartment from the first end to the second end under laminar flow conditions with a Reynolds number of less than 2000, and - By extracting the second reactor gas mixture containing the formed particles at the second end, or - Using a reactor equipped with a closed-type high-temperature wall-decomposition compartment containing the first reactor gas, - A preheated precursor gas mixture is injected into the high-temperature wall decomposition compartment at a first time to form a second reactor gas mixture, and - When the residence time is reached, calculated from the first time point, both the second reactor gas mixture and the formed particles are extracted from the high-temperature wall decomposition compartment by vacuum suction or flushing. or - Using a reactor equipped with a closed-type high-temperature wall decomposition compartment containing a first reactor gas and a cooling recovery chamber provided at the bottom of the decomposition compartment, - A preheated precursor gas mixture is injected into the high-temperature wall decomposition compartment to form a second reactor gas mixture, and - By holding the second reactor gas mixture in the high-temperature wall decomposition compartment until the formed particles grow to a size that allows them to settle from the second reactor gas mixture and fall into the recovery chamber by gravity, The method according to any one of claims 13 to 18, wherein the temperature of the second reactor gas mixture is obtained.

20. The method according to any one of claims 13 to 19, further comprising depositing an amorphous or crystalline carbon layer on the outer surface of the particles by chemical vapor deposition of a carbon-containing precursor gas, preferably an alkene gas, at a temperature in the range of 650 to 750°C.

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